Open access peer-reviewed chapter

Animal Inhalation Models to Investigate Modulation of Inflammatory Bowel Diseases

Written By

Giuseppe Lo Sasso, Walter K. Schlage, Blaine Phillips, Manuel C. Peitsch and Julia Hoeng

Submitted: 22 November 2016 Reviewed: 04 May 2017 Published: 20 December 2017

DOI: 10.5772/intechopen.69569

From the Edited Volume

Experimental Animal Models of Human Diseases - An Effective Therapeutic Strategy

Edited by Ibeh Bartholomew

Chapter metrics overview

1,664 Chapter Downloads

View Full Metrics


Inflammatory bowel diseases (IBDs) comprise primarily two disease manifestations, ulcerative colitis (UC) and Crohn’s disease (CD), each with distinctive clinical and pathological features. Environmental and clinical factors strongly affect the development and clinical outcomes of IBDs. Among environmental factors, cigarette smoke (CS) is considered the most important risk factor for CD, while it attenuates the disease course of UC. Various animal models have been used to assess the impact of CS on intestinal pathophysiology. This chapter examines the suitability of animal inhalation/smoke exposure models for assessing the contrary effects of CS on UC and CD. It presents an updated literature review of IBD mouse models and a description of possible mechanisms relevant to relationships between IBD and smoking. In addition, it summarises various technical inhalation approaches, in the context of mouse disease models of IBD.


  • inhalation
  • inflammatory bowel disease
  • animal models
  • cigarette smoke
  • ulcerative colitis
  • Crohn’s disease

1. Introduction

Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the gastrointestinal tract encompassing two main disease manifestations, Crohn’s disease (CD) and ulcerative colitis (UC) [1].

CD and UC have many similarities in symptoms and disease phenotypes, making diagnosis challenging [2]. Currently, criteria for distinguishing these two manifestations are based exclusively on histopathological and endoscopic examinations [3]. Thus, UC is defined as a chronic, non-transmural inflammatory disease characterised by diffuse mucosal inflammation involving only the colon. Its primary clinical symptom is bloody diarrhoea [2, 4, 5, 6, 7]. As UC is an inflammatory disease, the state of the immune system is a fundamental aspect of the disorder, with an atypical T helper cell (Th)2 response, mediated by natural killer T cells that secrete interleukin (IL)-13 [1, 8, 9]. CD is a relapsing, transmural inflammatory disease that may affect the entire gastrointestinal tract. Its major clinical symptom is abdominal pain or nonspecific abdominal symptoms and bloody diarrhoea is rare. The T cell profile in CD is different from that of UC and, in fact, a Th1 cytokine profile is dominant in patients with CD [4, 7, 10, 11]. Notably, innate immune responses are similarly activated in both CD and UC [12]. Several studies suggested that IBD pathologies result from an inappropriate inflammatory response to intestinal microbes in a genetically susceptible host, with consequent alteration of the intestinal epithelium.

During IBD development, the paracellular space in the intestinal epithelium becomes more permeable, impacting defensive strategies naturally activated by specialized epithelial cells, including goblet and Paneth cells [13, 14, 15, 16]. This process primes a positive feedback loop, with increased exposure to the intestinal microbiota, leading to amplification of the inflammatory response. Observations in patients or animal models show that host-microbiome interactions and microbiome fluctuations play prominent roles in such inflammatory processes [17, 18]. However, whether these alterations contribute to the disease, or simply reflect secondary changes caused by the inflammation, is still under debate.

Indeed, the basic aetiology of IBD is still unclear and the potential factors contributing to the pathogenesis of the disease, such as dysbiosis, epithelial and/or immune system dysfunctions and oxidative stress, represent the major research topics in the IBD field. Moreover, new area of interest arose from the necessity of understanding the potential environmental causes behind the disease onset.

Among the environmental factors associated with IBDs, the most significant causes are cigarette smoke (CS) and nicotine, and these inversely affect the risk and course of UC and CD. The relationship between smoking and IBD has been known for many years, with the first report of a negative correlation between IBD and smoking, in a cohort of UC patients, published 40 years ago [19]. Since then, there have been numerous epidemiological, clinical and pre-clinical studies describing the dual effects of active smoking in the two forms of IBD [20, 21]. CS is associated with a higher risk for developing CD and a worse outcome in CD patients. In contrast, UC is considered a non-smokers’ disease, with a significantly lower risk of disease development in current smokers. Despite the considerable research on smoking and IBD, the molecular mechanisms for CS-induced impacts on IBD development, as well as the specific CS components responsible, are not well understood [22].

To better understand the different aetiological factors in the onset of IBD, a variety of disease models were developed. Human and in vitro studies have historical limitations because of design complexity, duration and cost or, for in vitro studies, the lack of translational applicability. Therefore, animal models are advantageous by allowing in vivo experiments to be conducted under more easily controlled conditions than those in human studies, while providing the organism complexity lacking in in vitro systems. Increased knowledge of mucosal immunity and host-microbiome interactions and dynamic, as well as the availability of new genetic engineering technologies, enabled the development of numerous murine models that, in turn, substantially increased the understanding of intestinal inflammatory processes [23, 24]. Arguably, none of these models can completely recapitulate the complexity of human IBD, but they can provide valuable information about major aspects of the disease, thereby enabling a common set of principles of human IBD pathogenesis to be established.

This book chapter reviews key studies conducted in animal inhalation/smoke exposure models aimed at evaluating the different modulation of UC and CD by CS. The application of inhalation technology to rodents, reproducing the clinical effects of smoking on colonic inflammation, will increase the chances of identifying new anti-inflammatory molecular mechanisms and possibly therapeutics, finally increasing the chances of IBDs defeat.


2. Technical aspects of inhalation

2.1. Methods of acute and chronic pulmonary delivery of aerosols to rodents

The technical means for pulmonary delivery of aerosols (either small molecules, proteins or mixtures) may employ either direct intratracheal administration or, alternatively, inhalation exposure, the latter often requiring restraint of animals.

For acute pulmonary delivery of an agent, intratracheal administration may be ideal. Its main advantages are that it requires little infrastructure or equipment and can be performed in a basic in vivo lab environment [25]. In addition, dose delivery can be accurately and reproducibly estimated [26]. However, this method also has several shortcomings, such as need for anaesthesia, inability to administer volatile agents or gases and unequal distribution in the lungs, resulting in minimal exposure to the alveoli. Overall, such concerns make intratracheal administration a less suitable method for subchronic or chronic pulmonary delivery.

For subchronic or chronic administration of aerosols to rodents, repeated inhalation exposure systems are preferred. Thus, animals are exposed to aerosols within a confined environment for a fixed daily duration. In the field of toxicology, testing guidelines for repeated dose exposure for toxicological assessments, such as the OECD TG413 guideline, recommend up to 6 h per day exposure for a 90 day exposure period. However, for therapeutic or disease modelling purposes, the exposure period must be determined empirically, based on the effective dose and the time needed for the target biological effect to occur. Importantly, exposure systems must enable consistent delivery of aerosols, at concentrations that are stable during the exposure period, and with appropriate aerosol properties to enable efficient inhalation and uptake [27].

Principally, two types of exposure chambers are routinely used to administer aerosols to rodents, whole body or nose-only exposure chambers, each with its own advantages and disadvantages [27]. Whole body exposure systems are restraint free, as the animals are placed into an exposure chamber, either in a cage or on a mesh or grid surface, depending on the specific system. Both chambers are technically simple, assuming sufficient infrastructure (aerosol generation and functional chambers). Both also enable exposure of large numbers of animals, for example, chambers of >700 L may each accommodate approximately 200 mice. The freedom of movement of animals during exposure results in minimal stress, although the animals require training to adjust to grid-caging systems and food is typically withdrawn to minimise oral uptake of aerosol constituents. One criticism of whole body exposures is that there is a high potential for compound uptake through non-inhalation routes because animals have surface contact with aerosol deposits on the cage surfaces and on their fur. In historical studies, up to 60% of aerosol constituents on the fur (pelt burden) were ingested following whole body exposures [28] and transdermal uptake may also be significant for some compounds. Because the skin is an effective barrier for drug transport, only potent drugs with appropriate physicochemical properties (low molecular weight and adequate solubility in aqueous and non-aqueous solvents) are suitable candidates for transdermal delivery [29, 30, 31]. Such mixed uptake mechanisms potentially occurring in whole body exposure systems complicate both dose estimations and require deconvolution of uptake amounts through oral/transdermal and inhaled routes.

Nose-only exposure chambers require restraint of the animals to permit only the head (nose) to be exposed to the test aerosol. This has the major advantage of decreasing deposition of aerosol constituents on the pelts, resulting in less oral uptake from grooming behaviour [32]. However, there are also disadvantages with this system, including technical asphyxiation (animal movements in the exposure tube may cut off their air supply); therefore, constant monitoring during the exposure period is required. In addition, because of stress associated with restraint in nose-only exposure systems, training is required to adapt animals to the technical procedures. Vehicle or fresh air exposures are also needed to help distinguish such stress-related effects from treatment effects [33]. The daily execution of nose-only exposures requires that animals be individually inserted into the exposure tubes, a technical aspect that may limit the numbers of animals that can be used in the experiments.

2.2. Dose translatability

Measurement of dosages in an in vivo inhalation experiment is dependent upon many parameters, including deposition of the agent to the lungs (which itself is dependent upon aerosol droplet size), respiratory minute volume and body weight of the animal. This relationship is generally described by the following formula [34]:


where DD is the delivered dose (mg/kg); C is the concentration of substance (mg/L); RMV is the respiratory minute volume (L/min) and IF is the inhalable fraction.

Among these parameters, the respiratory minute volume is important to determine the availability of compound for deposition and exchange in the lungs. This parameter may be calculated using allometric formulae relating body weights to minute volumes in laboratory animals [35, 36]. The alternative, direct measurement of the minute volume, as can be performed when nose-only exposure tubes are used (head-out plethysmography measurements), is preferable as it would enable the researcher to control any effects of test item on the minute volume, when calculating the estimated dosage.

Important for in vivo disease modelling is the translation of the animal models to human therapeutics or treatment regimen. This will require an estimation of human equivalent dose (HED), based on the animal data. The most commonly used method to convert to HED is with a body surface area conversion factor [37]. Alternatively, a mg/kg conversion factor may be applied, though this typically will result in a lower safety margin and higher HED values, compared with the body surface area conversion. HED is generally described by the following formula [37]:


where Km is the correction factor reflecting the relationship between body weight and body surface area (e.g. human Km = 37; mouse Km = 3; rat Km = 6 and dog Km = 20).


3. Overview of animal IBD models

The various types of animal models developed to study IBD may be divided into several categories depending on: the method of inducing the pathology (chemically induced, bacteria-induced or genetically engineered); the IBD subtype modelled in the animal (UC or CD); the site of inflammation (colon, ileum, both sites or systemic); and, in genetically engineered models, the gene modification strategy (conventional transgenic (Tg) or knockout (KO), cell-specific conditional Tg or KO, inducible KO, knock-in, innate, mutagen-induced or spontaneous models) [23, 38, 39]. The total number of IBD mouse models is growing, especially because of current genetic engineering approaches that accelerate development of new strains, so far, over 74 genetically engineered mouse models were reported to spontaneously develop intestinal inflammation [38]. The full description of all IBD models is beyond the scope of this chapter. However, Table 1 summarises the most significant IBD murine models, highlighting their methods of pathology induction, IBD subtypes, sites of inflammation and mechanism of action (Figure 1). More detailed reviews of the different mouse models of IBD are available (e.g. see Refs. [23, 40, 41]).

Figure 1.

Schematic view of major inflammatory and anti-inflammatory mechanisms implicated in inflammatory bowel diseases and the potential role of a nicotinic anti-inflammatory pathway. Top: altered microbiota in the colonic lumen and/or epithelial-damaging factors (e.g., DSS in experimentally induced colitis) lead to the disruption of the epithelial barrier function and the consequent infiltration of bacteria and other antigens. Middle: various inflammatory processes can be triggered in the lamina propria by the infiltrating bacteria (DSS-induced epithelial barrier; “Barrier dysfunction and epithelial permeability” and “Nicotinic anti-inflammatory pathway” sectors), haptens (oxazolone- and TNBS-induced inflammation, “Differential nicotine effects in UC-like (oxazolone) and CD-like (TNBS) colitis” sector) or by endogenous dysregulation of the balance between Th1/Th17-driven and Th2-driven immune activities, (genetically engineered mouse models; “Immune regulation” section). A hypothetical role of nicotinic receptor-mediated anti-inflammatory response is depicted in the “Nicotinic anti-inflammatory pathway” sector. Bottom: the colonic vasculature is symbolized as a tube running perpendicular to the cross section of the colon. The blood stream delivers leukocytes recruited by cytokine shedding from the local inflammatory sites and enables the perpetuation of the inflammation, e.g., via circulating T-cells. Systemically provided nicotine could increase the anti-inflammatory nicotinic signaling that is naturally transmitted by acetylcholine shed from the efferents of the vagus nerve that innervate the colonic wall. For details of these mechanisms, see Chapter 4.1 to 4.4. Modified from: De Jonge & Ulloah (2007), Ordas et al. (2012), Xu et al. (2014).

There is a close agreement in many pathological findings among experimental IBD models and human disease. These include the molecular pathways and histological features of tissue injury, dysfunction of the immune system (including impact of the microbiome), genetic heterogeneity and primary defects in mucosal barrier function. All pathologies have been well established in several experimental models of colitis; therefore, these models closely resemble aspects of the human diseases. These common features enable exploration of specific pathological mechanisms, facilitating development of new therapeutic approaches. However, none of these models fully reflects human IBD, with each representing rather a small tile of a mosaic. This hinders a generalised view of the systemic consequences of IBD, often masking possible extra-intestinal implications [42].

The presence of such a multitude of mouse models indicates that IBD is mediated by complicated, multifactorial mechanisms. As expected, this complexity is greater in human beings, where environmental and clinical factors, such as smoking, diet, drugs, ethnicity, geographical area, social status, gender, stress and appendectomy, further modulate onset of IBD pathologies [43, 44, 45, 46].

3.1. Inhalation studies investigating the effect of CS in rodent models of IBD

Clinical and pre-clinical findings suggested divergent effects of smoking or smoke constituents on the pathophysiology of the gut depending mainly on two conditions, the IBD subtype and the route of administration of the active substance (such as nicotine or CS). Active human smoking is difficult to mimic under laboratory conditions, while classical in vitro approaches have translational limitations. Thus, several animal models have been used to assess the impact of CS, nicotine or non-nicotine CS constituents on intestinal pathophysiology [47]. Both genetic- and chemically induced IBD models have been used and effects of various treatment regimens on gut inflammation in these systems are summarised in Table 2. There is a general consensus that CS and nicotine administration do not cause macroscopic or histological damage or inflammation in the healthy gut. However, differences in immune cell recruitment [48], cytokine secretion [49, 50, 51], mucosal barrier [52, 53] and oxidative stress were observed [54, 55], although without evident tissue damage.

IBD modelModel categoryIBD subtypeSite of inflammationMechanismReferences
DSSChemically inducedUCColonEpithelial cell damage[147, 148]
TNBSCD/UCColonHapten-dependent immunogenic response[149]
DNBSCD/UCColonHapten-dependent immunogenic response[150]
OxazoloneUCColonHapten-dependent immunogenic response[151]
Acetic acidUCColonEpithelial cell damage[152]
CarrageenanUCColonEpithelial cell damage[153]
IndomethacinCDSmall intestine
Epithelial cell damage[154]
IodoacetamideUCColonSulphydryl (SH) compound (e.g. glutathione) blocker[155]
DNCBUC/CDColonHapten-dependent immunogenic response[156]
Salmonella inducedBacterially inducedUCColonBacterial colonisation-induced inflammation[157]
Adherent invasive E. coliUCColon
Small intestine
Bacterial-dependent epithelial cell damage[158]
C3H/HejBirSpontaneousCDSmall intestine
Epithelial cell dysfunction[39]
SAMP1/4itCDSmall intestineEpithelial cell dysfunction[40]
IL-10−/−Genetically engineered/knockouts (KO)CDSmall intestine
Impaired Treg function[74]
TGF-β−/−UC/CDSystemicMacrophage hyperactivation and impaired Treg function[159]
IL-2−/−UCColon/systemic (no small intestine)Impaired T cell/Treg function[160]
NOD2−/−CDSmall intestine
NF-κB and TLR2 signalling dysregulation[161]
Small intestine
TNF-induced NF-κB signalling dysregulation[162]
MDR1A−/−UCColonAccumulation of bacterial products and increased T cell activation[163]
Gαi2−/−UCColonImpaired T/B cell function and epithelial cell damage[164]
TCRα−/−UCColonTh2-type inflammation[75]
IL-23−/−CDSmall intestine
Impaired Th17 cell function[165, 166]
XBP1−/−Genetically engineered, conditional KOCDSmall intestine
Loss of Paneth and goblet cells with impairment of mucosal defence[167]
NEMO−/−CDSmall intestine/colonNF-κB signalling dysregulation[168]
IL-7 Tg mice (IL-7 overexpression)Transgenic mouseUCColonCD4+ T cell infiltration-dependent inflammation[169]
STAT4 Tg mice (STAT4 overexpression)CDSmall intestine
Th1-type inflammation[170]
HLA-B27 Tg miceUC/CDSmall intestine
Bacterial sensitisation[171]
DNN-cadherin/keratin8−/−CDColonEpithelial cell dysfunction[172]
TNFΔAREMutation knock-inCDSmall intestineTNF-α overproduction[64]
CD45RB high-transferAdoptive transferCDSmall intestine
IL-12-driven Th1 hyper-response[173]

Table 1.

Classification of animal models of IBD. IBD subtype and site of inflammation predominantly addressed by the model, where applicable, are shown in bold font. DSS, dextran sulfate sodium; IBD, inflammatory bowel disease; DNBS, 2,4-dinitrobenzene sulfonic acid; TNBS, 2,4,6-trinitrobenzenesulfonic acid; UC, ulcerative colitis; CD, Crohn’s disease; DNCB, Dinitrochlorobenzene.

IBD modelIBD subtype—speciesTreatmentEndpoint observedEffects on intestinal inflammationReferences
TNBS colitisCD—ratCigarette smoke (inhalation)Mucosal damage: ↑
MPO activity: ↑
LTB4 level: ↑
GSH level: ↓
ROM generation: ↑
TNF-α protein: ↑
SOD activity: ↓
iNOS activity: ↑
COX2 protein: ↑
[54, 55, 56, 57]
Oral nicotineLTB4 level: ↓
PGE2 level: =
MPO activity: ↓
Histology score: ↓
iNOS protein: ↓
Serum IL-1: =
Low dose: ↓
High dose: ↑ or no effect
[78, 79]
CD—mouseSubcutaneous nicotineHistology score: ↑
DAI scoring: ↑
Treg/Th17 cell ratio: ↓
α7nAChR expression in T cells: no
Carbon monoxide (inhalation)Histology score: ↓
MPO activity: ↓
TNF-α protein and RNA: ↓
Oral TCDDHistology score: ↓
Colon cytokine proteins: ↓
Gene expression
Immune cells in MLN and colon
IodoacetamideCD—mouseOral nicotineMucosal damage: J↑; C↓
iNOS activity: J NA; C=
MPO activity: J=; C NA
PGE2 level: J↓; C↓
Histology score: J↑; C↓
Jejunitis: ↑
Colitis: ↓
IL-10−/− miceCD—mouseOral nicotineMucosal damage: J↑; C↓
Histology score: J↑; C↓
Gene expression
Jejunitis: ↑
Colitis: ↓
Carbon monoxide (inhalation)Histology score: ↓
Colon cytokine proteins: ↓
Gene expression
DNBS colitisUC—ratCigarette smoke (inhalation)Histology score: ↑
Mucosal damage: ↑
MPO activity: ↑
Subcutaneous nicotineMucosal damage: ↓
MPO activity: ↓
LTB4 level: ↓
ROM generation: ↓
Colon cytokine proteins: ↓
Cigarette smoke (inhalation)Mucosal damage: ↓
MPO activity: ↓
LTB4 level: ↓
ROM generation: ↓
Colon cytokine proteins: ↓
Cigarette smoke (inhalation)Histology score: ↓
Mucosal damage: ↓
MPO activity: ↓
iNOS activity: ↓
LTB4 level: ↓
Colon cytokine proteins: ↓
Oxazolone colitisUC—mouseSubcutaneous nicotineHistology score: ↓
DAI scoring: ↓
Treg/Th17 cell ratio: ↑
α7nAChR expression in T cells
DSS ColitisUC—mouseOral nicotineHistology score: ↓
DAI scoring: =
MPO activity: =
PGE2 level: ↓
Subcutaneous nicotineDAI scoring: ↓
Histology score: ↓
miRNA expression
Cigarette smoke (inhalation)Colon cytokine RNA: ↓
MPO activity: ↓
Infiltrating immune cells
DAI scoring: ↓
Cigarette smoke (inhalation)Mucosal damage: =
Colon cell proliferation: =
Colon cell apoptosis: =
Colon angiogenesis: ↑
Bcl2/VEGF protein: ↑
No effect[66]
Subcutaneous nicotineDAI scoring: ↓
Histology score: ↓
MPO activity: ↓
TNF-α and IL-6 mRNA: ↓
Oral nicotineDAI scoring: ↓
Histology score: ↓
Colon TNF-α protein: ↓
MPO activity: ↓
Colon cytokines mRNA: ↓
[81, 102]
Oral cotinineDAI scoring: =No effect[81]
Subcutaneous nicotineDAI scoring: =
Histology score: =
Colon TNF-α protein: =
No effect[81]
Intraperitoneal nicotineDAI scoring: =
Histology score: ↓
Colon TNF-α protein: ↑
No effect[81, 82]
Oral TCDDHistology score: ↓
Colon TNF-α RNA/protein: ↓
TCRα−/− miceUC—mouseCarbon monoxide (inhalation)Histology score: ↓
Colon cytokines RNA/protein: ↓
Clostridium difficile ToxAUC—mouseIntraluminal nicotineMPO activity: ↓
LTB4 level: ↓
Luminal fluid: ↓
Substance P release: ↓
↓ Colon;
No effect in ileum

Table 2.

Effects of cigarette smoke or related compounds in experimental models of IBD.

↑, potentiating effect; ↓, attenuating effect; =, no changes; TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; TCR, T cell receptor; NA, not applicable; ROM, reactive oxygen metabolites; DAI, disease activity index (for further details please see the reference), MPO, myeloperoxidase; LTB4, leukotriene B4; PGE2, prostaglandin E2; SOD, superoxide dismutase 2; COX, cyclooxygenase; iNOS, nitric oxide synthase.

Consistent with results of human epidemiological studies, CS had opposing effects on development of CD (negatively) and UC (positively) in several, but not all, of their respective IBD models. Only a few of these studies used inhalation exposure (Table 2) and most of their findings mimicked the effects of smoking in humans with IBD.

Thus, the dichotomous effects of CS inhalation, on development of CD versus UC, were perfectly reproduced using two different rat IBD models [54, 55, 56, 57, 58, 59, 60]. 2,4,6-trinitrobenzenesulphonic acid (TNBS) and 2,4-dinitrobenzene sulphonic acid (DNBS) were instilled into the rat colon to induce, respectively, CD- and UC-like symptoms. Indeed, pre-exposure of rats to CS increased acute (2–24 h post-induction) intestinal inflammation in the TNBS-induced colitis (CD-like) model [54, 55, 56, 57]. The authors used a ventilated smoking chamber filled with a fixed concentration of smoke, delivered by burning commercial cigarettes at a constant rate (2 or 4%, vol/vol, smoke/air) [61]. These results showed that promotion of neutrophil infiltration, as well as free radical production with the accumulation of reactive oxygen metabolites in the intestinal tissues, contributed significantly to the potentiating effects of CS on intestinal inflammation. In contrast, in DNBS-treated rats (UC-like model), CS inhalation improved macroscopic signs of colitis at the mucosal level and decreased the levels of colonic pro-inflammatory cytokines [59, 60]. In these latter papers, Ko et al. used a similar inhalation method to the aforementioned study [61], but with a different time of exposure and a few “homemade” modifications to the smoking chamber. One study, conducted in DNBS-treated rats exposed to CS for 15 days before and 2 days after DNBS instillation, showed increased macroscopic and histological damage in the CS-exposed rat colon [58]. Noteworthy, this study used a different inhalation method than did the others. Rats were exposed to a rhythmic inhalation of smoke, with only the nose exposed to the specialized chamber [62], and this chamber was filled with mainstream smoke from a high tar, unfiltered cigarette.

Furthermore, the effect of CS on the development of small intestinal inflammation (CD-like pathophysiology) was studied in a TNFΔARE mouse model [63]. In this mouse model, a knock-in mutation determines the deletion of the AU-region of the TNF-α mRNA, resulting in a systemic TNF-α overproduction and the consequent development of chronic Crohn’s-like ileitis and inflammatory arthritis [64]. The authors exposed the mice to CS 4 times a day with 30 min smoke-free intervals, 5 days per week for 2 or 4 weeks [65]. Contrarily to what obtain in human and rat CD, in this model CS did not modulate gut inflammation. Both molecular (e.g. inflammatory and autophagy gene expression) and histopathological endpoints were not affected by CS smoke compared to fresh air exposed mice.

In contrast to its effects in CD rodent models, CS exposure for 2 weeks decreased UC-like inflammation in an acute DSS-induced colitis model in mice [22]. Montbarbon et al. showed a significant decrease in macroscopic and histological colon damage, as well as in colonic pro-inflammatory cytokine expression, in DSS-exposed mice after CS inhalation. Interestingly, this study highlighted a pivotal role for a specific intestinal lymphocyte type, iNKT, in the CS-dependent protection of the colon. The authors used a ventilated smoking chamber of the InExpose® System and exposed the mice to the mainstream smoke of research cigarettes 5 days per week (5 cigarettes/day). However, a previous study, in a long-term mouse model of DSS-mediated chronic colitis, showed a CS-dependent increase in inflammation-associated colon adenoma/adenocarcinoma formation. Although specific inflammatory endpoints were not reported, the number of colon adenomas/adenocarcinomas was significantly increased in the CS-exposed mice [66]. This tumour formation was associated with inhibition of cellular apoptosis and supported by increased angiogenesis. As a possible explanation for this discrepancy, this study used Balb/c mice while the protective effects of CS [22] were observed in C57BL/6 mice. Opposite responses in Balb/c mice, compared with C57BL/6 and other mouse strains, were also reported for other chemical inducers of IBD [67]. Moreover, a different inhalation method was applied in the Balb/c mouse study. These mice were exposed to 2 or 4% CS in a ventilated smoking chamber for 1 h per day.

In the context of inhalation studies aimed to understand the major CS component responsible for the observed anti-inflammatory effects in the intestine, three studies on the anti-inflammatory properties of carbon monoxide (CO) in IBD models are notable. Indeed, CO, a prominent component of CS long considered as just being a toxic gas [68], was recently shown to exert potent cell protective effects because of its anti-inflammatory, anti-apoptotic and anti-oxidant capabilities [69, 70]. In three different studies, inhaled CO consistently decreased inflammation in chemically induced and genetic mouse models of UC and CD, respectively [71, 72, 73]. In particular, the same group of researchers [71, 72] exposed two different knockout mouse models, IL-10−/− [74] and TCRα−/− [75, 76], to CO at a concentration of 250 ppm (part per million) or compressed air (control), attempting to recapitulate, at least in part, CS effects on the development of CD and UC, respectively. IL-10−/− mice were generated by gene targeting in 1993 by Kuhn et al. [74], introducing two stop codons in exon 1 and 3 of the IL-10 gene in murine ES cells. These mice are characterised by extensive Th1-mediated enterocolitis originated by an antigen-driven uncontrolled immune response mainly resembling human CD condition. T cell receptor (TCR)α knockout mice were generated with a similar gene targeting approach [76], thus integrating a neomycin cassette in the first exon of the TCRα locus. In these mutant mice, the intestinal mucosal immunoregulatory mechanisms are negatively affected, triggering the development of UC-like symptoms [75]. Surprisingly, CO inhalation suppressed inflammation in both models, regardless of their IBD subtype, through a heme oxygenase (HO)-1 dependent pathway. The anti-inflammatory capabilities of CO were also confirmed in a TNBS-induced mouse model of CD. Mice were exposed to CO at 200 ppm, beginning after TNBS administration and throughout the remaining study period (3 days) [73]. Thus, the increased colonic damage induced by TNBS was significantly inhibited by the CO treatment, with a consistent suppression of inflammatory markers, such as TNF-α levels and myeloperoxidase (MPO) activity.

As highlighted in the aforementioned reports, although CS or CS component inhalation studies in mouse models seem to recapitulate most epidemiological observations in humans, differences in the inhalation methodologies are many and frequent, making impossible a clear and solid comparison between the studies.

The route of administration was relevant on the final effect also when single CS components, such as nicotine, were administered to IBD mouse models or patients [47]. Thus, in a TNBS mouse model of CD, the detrimental effects of subcutaneous nicotine administration [77] contrasted with the dose-dependent bivalent effect of nicotine administered in the drinking water, that is, positive at low and negative at high concentrations [78, 79]. Furthermore, subcutaneous or oral nicotine administration to rats treated with DNBS led to, respectively, decreased or increased colon inflammation [58, 59]. Finally, while oral or subcutaneous nicotine administration attenuated inflammation caused by DSS treatment in mice [50, 80], intraperitoneal nicotine injection had no effects [81, 82]. Inconsistencies related to different routes of administration of CS components were also observed in human studies [83, 84, 85, 86]. Overall, these observations suggested that the route of administration of a CS-related compound, such as nicotine, is important to consider in treating colitis. In animal models, it is clear that mimicking the nicotine intake profiles in smokers (inhalation) could result in increased treatment efficacy. This idea was supported in humans by the conflicting results obtained by local nicotine application (enemas) [87]. Therefore, although the colon may be an important site of action for CS components, the responsible molecule for the observed effects might act on many peripheral and central inflammatory pathways, such as vagus-related anti-inflammatory nicotinic signalling, or might require intermediate metabolic transformations.

3.2. Limits and pitfalls of studies using inhalation mouse models

Among the aforementioned studies, only a few used inhalation exposure (Table 2) models were observed, although many of the findings mimicked human smoking effects in IBD, the results were still variable. Such heterogeneity in observed CS effects on experimentally induced colitis is not unexpected, given variability in animal species and strains, IBD inducers, CS exposure schedules, endpoints and observation periods.

When comparing such quality-relevant exposure conditions, group sizes were usually sufficient, but most of the studies used only male mice or rats, instead of both genders as recommended by the Organisation for Economic Co-operation and Development (OECD) test guidelines. Only one rat study employed the preferable nose-only inhalation mode [58]. Many of the papers did not describe the exposure chambers sufficiently and explanations of exposure concentration parameters (such as number of puffs, flow rate and chamber volume) often did not enable derivation of the standard Total Particulate Matter (TPM) or smoke constituent concentration values, in a weight per volume unit (e.g. mg/L). The most evident heterogeneity among studies, however, was in exposure schedules and durations. The CS inhalation studies in IBD models typically used daily exposure durations no longer than one hour, with none using the recommended 6 h/day duration. Some studies pre-exposed the animals a few days before IBD induction and discontinued CS exposure after the induction treatment, while others continued exposure until the end of the study or began CS inhalation after IBD induction [59]. To explore more systematically the effects of inhaled CS or CS constituents on IBD in various models, there is a clear need to harmonise exposure conditions to be closer to minimal standards for inhalation toxicity studies. This is particularly true for exposure schedules and durations, as well as for documentation of meaningful concentration measurements in the exposure atmospheres (Table 3). Finally, to elucidate the molecular mechanisms of IBD-CS interactions, beyond the current knowledge, it will be necessary to combine robust IBD models (UC and CD), well-controlled, state-of-the-art inhalation exposure design and technology and disease-specific endpoints with systems-wide molecular profiling. We conducted systems toxicology-oriented inhalation studies using mouse models to investigate effects of CS and candidate modified risk tobacco products in chronic obstructive and cardiovascular diseases [33, 88, 89, 90, 91]. These studies demonstrated the feasibility and suitability of this approach for identifying the molecular basis of disease mechanisms and the biological impacts of CS. The study design and inhalation exposure technology were based on the OECD guidelines TG412 and TG413 for 28 and 90 days inhalation toxicity studies, respectively [92, 93]. Satellite groups were included to provide material for the additional molecular investigations and a similar study was conducted on rats exposed to nicotine aerosols [33]. A very detailed description of the study design and methodology was provided [94] and this might serve as a template for new IBD inhalation studies. Of course, adaptations will be necessary, based on specifications of the IBD models. For example, most chemically induced IBD models require acute, rather than subchronic or chronic, observation periods, while the genetically engineered IBD models develop the disease in a similar timeframe as the COPD and CVD models.

IBD model, inductionStudy designExposure durationInhalation technologyCS/inhalant characterisationReferences
(OECD TG 412 recommendation)At least 5 males and 5 females per group, 3 dose levels of test article, filtered air and/or vehicle control6 h/day; 5 (7) days/week; 28 daysNose-only preferred, whole body acceptable, detailed description of exposure chamber to be givenAnalytical characterisation; respirable particle size (1–3 μm MMAD), nominal and actual test article concentration (mass per volume) to be indicated, constant concentration during exposure period[92]
Rat (Sprague Dawley), TNBS enema8–10 rats/group (males only), 1 dose level, fresh air control1 h/day; 4 days pre-inductionWhole body, ventilated smoking chamber (20 L) with 5–6 rats, smoke generated with peristaltic pump“Camel” cigarettes, 4% v/v smoke, no characterisation[56]
Rat (Sprague Dawley), TNBS enema10–12 rats/group (males only), 2 dose levels, fresh air control1 h/day; 4 days pre-inductionWhole body, ventilated smoking chamber (20 L) with 5–6 rats, smoke generated with peristaltic pump“Camel” cigarettes, 2 and 4% v/v smoke, no characterisation[55]
Rat (Sprague Dawley), TNBS enema6–8 rats/group (males only), 1 dose level, fresh air control1 h/day; 4 days pre-inductionWhole body, ventilated smoking chamber (20 L) with 5–6 rats, smoke generated with peristaltic pump“Camel” cigarettes, 4% v/v smoke, no characterisation[54]
Rat (Sprague Dawley), TNBS enema10 rats/group (males only), 2 dose levels, fresh air control1 h/day; 8 days pre-inductionWhole body, ventilated smoking chamber (20 L) with 5–6 rats, smoke generated with peristaltic pump“Camel” cigarettes, 2 and 4% v/v smoke no characterisation[57]
Mouse (C57BL/6), DSS in drinking water6–10 mice/group (males only), 1 dose level, fresh air control2 week (5 days/week) pre-induction and 1 week post-inductionWhole body, InExpose chamber (Scireq) and rotary smoking machine3R4F reference cigarettes, mainstream smoke from 5 cigarettes (8 puffs per cigarette), no concentration/characterisation[22]
Rat (Sprague Dawley), DNBS enema6–8 rats/group, 3 dose levels, fresh air control (10 rats/group)5–40 min/day, 15 days pre-induction and 2 day post-inductionNose-only, puffwise smoke injection into chamber2R1 reference cigarette, 5, 20 or 40 puffs/day (undiluted), no concentration/characterisation[58]
Rat (Sprague Dawley), DNBS enema7 rats/group, 2 dose levels, fresh air control1 h/day; 3 days post-inductionWhole body, ventilated smoking chamber (20 L) with 5–6 rats, smoke generated with peristaltic pump smoke, no characterisation“Kings” cigarettes, 4% v/v; no concentration/characterisation[59]
Rat (Sprague Dawley), DNBS enema6–8 rats/group, 1 dose level, fresh air control1 h/day; 3 days pre-induction, 4 day post-inductionWhole body, ventilated smoking chamber (20 L) with 5–6 rats, smoke generated with peristaltic pump“Camel” cigarettes, 2 and 4% v/v smoke, no characterisation[60]
Mouse (Balb/c), DSS in drinking water5–12 mice/group (males only), 2 dose levels, fresh air control3 cycles of: 7 days DSS + CS (1 h/day) followed by 14 days recoveryWhole body, ventilated smoking chamber (20 L), smoke generated with peristaltic pump“Camel” cigarettes, 2 and 4% v/v smoke, no characterisation[66]
TCRα−/− mouse (C57BL/6)10 mice/group (5 males and 5 females), 1 dose level, fresh air control4 week (daily duration not indicated)Whole body, 3.70 ft2 plexiglass animal chamber, 12 L/min flow rateCO gas, 250 ppm in air, continuous measurement[72]
IL-10−/− mouse (C57BL/6)12 mice/group (males only), 1 dose level, fresh air control4 week (daily duration not indicated)Whole body, 3.70 ft2 plexiglass animal chamber, 12 L/min flow rateCO gas, 250 ppm in air, continuous measurement[71]
Mouse (C57BL/6), TNBS enema12 mice/group, 1 dose level, fresh air control3 day (permanent) post-inductionWhole body, acrylic chamberCO gas, 200 ppm in air, continuous measurement[73]

Table 3.

Comparison of exposure conditions in published inhalation studies using rodent IBD models.


4. Mechanisms of IBD pathogenesis with possible relationship to CS constituents

4.1. Nicotinic anti-inflammatory pathway

The vagus nerve transmits signals by releasing acetylcholine that, in turn, stimulates neuronal and immune cells via their nicotinic acetylcholine receptors (nAChR) [95, 96]. These are ligand-gated ion channels expressed not only in neuronal cells, but also in most mammalian non-neuronal cell types, though different cell type-specific downstream signalling functions [97]. In the nicotinic anti-inflammatory pathway, nAChR activation by acetylcholine or other ligands inhibits the downstream NF-κB pathway, attenuating production of TNF-α and other cytokines [98, 99]. This pathway was reported to be one of the most likely explanations for CS-associated anti-inflammatory responses in the gut. Mapping the relevant neuronal circuits revealed that efferent vagus nerve fibres innervated the small intestine and proximal colon [100]. Vagotomised mice were more susceptible than normal mice to developing colitis after exposure to DSS and had increased levels of NF-κB and cytokines, such as IL-1β, IL-6 and TNF-α [101, 102, 103]. Pretreatment with nicotine reversed these effects through activation of α7nAChR, identified as the major receptor involved in nicotinic anti-inflammatory pathways [99, 104]. Potential therapeutic applications of selective α7nAChR agonists, such as the partial α7 agonists 3-(2,4-dimethoxybenzylidene)-anabaseine (GTS-21) and anatabine citrate, and of α7nAChR-positive allosteric modulators, was explored in pre-clinical and clinical studies [105, 106, 107, 108, 109]. Moreover, additional nAChR subtypes, such as α4β2, α3β4, α3β2 and α6, were also proposed as targets for nicotine treatment [110, 111, 112], increasing the complexity, but also the therapeutic potential, of this approach. Although research on the mechanisms involved in nicotinic anti-inflammatory pathways has highlighted the pharmacological potential of nAChR agonists, studies showing contradictory results obtained with specific α7nAChR ligands [82] suggested that these compounds should be used with caution in patients with IBD.

4.2. Immune regulation

The immunosuppressive effects of cigarette smoking, on both cellular and humoral immunity, have long been recognised [113, 114, 115]. Studies exploring how nicotine or CS can suppress the immune system indicated that, in nicotine-treated animals, T cells did not enter the cell cycle and proliferate as expected. Similar effects were observed in smokers and in animals exposed to CS [116, 117, 118]. Several studies described the implications of CS for different immune cell types, as well as the diverse actions of nicotine or CS, depending on the pathological environment, for example, UC or CD, in which the immune cells originated [77, 99, 112, 119, 120, 121, 122]. For instance, when stimulated by lipopolysaccharide, peripheral blood mononuclear cells derived from smokers showed decreased IL-8 release only if subjects were also CD patients [122]. Similarly, the same investigators demonstrated that smokers with CD had significantly lower IL-10 (anti-inflammatory)/IL-12 (pro-inflammatory) ratios than non-smokers or smokers with UC. As suggested in some reports, the differential signalling of dendritic cells from CD (Th1-like) and UC patients exposed to cigarette smoke extract (CSE) in vitro could play a role in the opposing responses of cigarette smoke exposure, that is, a Th1-like response in CD, with increased Foxp3-positive CD4 T cells [121].

4.3. Barrier dysfunction and intestinal permeability

The intestinal mucosa is one of the most important physical barriers against external threats. Changes in intestinal permeability are crucial for the development of IBD [123] and several studies implicated CS in regulating barrier integrity. However, the effects of smoking on intestinal permeability are controversial. Several in vitro and in vivo observations, in studies using humans or rodents, suggested that decreased intestinal permeability in smokers might explain the protective effects of smoking in UC [53, 124, 125, 126, 127]. In contrast, a recent article reported that mice exposed to CS exhibited increased intestinal permeability and bacterial translocation, intestinal villi atrophy, damaged tight junctions and abnormal tight junction proteins [128]. However, no intestinal barrier changes were identified in the colons of control or CS-exposed mice, suggesting that there was CS-related organ specificity and, thus, possibly explaining the opposing effects of smoking on CD and UC.

4.4. Gut microbiota

Much evidence supports the strong impact of environmental factors on gut microbiota, and smoking has recently been investigated as a potential factor shaping the microbiota. This potential connection implied new possibilities regarding the role of smoking in IBD development. Thus, studies targeting selected bacterial groups reported that patients with active CD, who also smoked, had microbial profiles different from those of non-smoking patients with CD. Similar results were found in healthy smoking controls, suggesting that the association related not to intestinal inflammation but, instead, to a direct impacts of smoking on the microbiota [129, 130]. Differences between mice and humans at the level of the gut microbiota limit the usefulness of mouse models, relevant to CS, gut microbiota and IBD. However, a few studies using rats and mice were consistent with observations in humans, indicating CS-dependent shifts in gut microbiota compositions [131, 132, 133]. These observations supported a possible role for CS in shaping the gut microbiome, with potential, though still unknown, consequences for evolution of inflammation-related disorders, such as IBD.

4.5. Other potential mechanisms

Currently, the processes described in Sections 4.1–4.4 have been those most explored as potential links between CS and IBD development. However, there are several other possible mechanisms, indicative of how environmental factors might exponentially increase complexity of IBD pathology.

4.5.1. Colon motility

In UC, fasting colonic motility increased, whereas motor responses to food significantly decreased [134]. Observations in experimental animals and humans showed that nicotine promoted smooth muscle relaxation, reducing symptoms, such as diarrhoea and urgency without significantly influencing inflammation [135, 136, 137].

4.5.2. Eicosanoid-mediated inflammation

Smoking and nicotine may also affect UC by reducing eicosanoid-mediated inflammatory responses. Two studies independently demonstrated this specific effect in humans and rabbits [53, 138].

4.5.3. Rectal blood flow

Patients with UC have significantly higher rectal blood flow than normal controls, but smoking decreased rectal blood flow to within normal ranges [139, 140, 141]. However, changes in blood flow can affect intestinal inflammation in opposing ways. Decreasing blood flow can reduce levels of inflammatory mediators that reach the mucosal surface, while long-term impairment of rectal mucosal microvascular blood flow can result in a higher incidence of anastomotic breakdown in chronic smokers [140].

4.5.4. Non-nicotine-mediated effects

Although nicotine is considered to be the major mediator of CS effects on intestinal inflammation, there is a clear evidence for involvement of other smoke constituents in CS-dependent responses. Both UC and CD mouse models were affected by carbon monoxide (CO) inhalation [71, 72, 73, 142]. These studies suggested that the mechanism through which CO protected against intestinal inflammation involved promoting bactericidal activities of macrophages [142]. Nitric oxide (NO) was also suggested as contributing to beneficial CS effects, based on its relaxant effects on colonic smooth muscle from UC patients [143]. Moreover, physiological NO, derived from nicotine-stimulated intestinal neuronal cells, functioned as a mediator in smooth muscle relaxation in the colons of DSS-treated mice [137].


5. Conclusions

Smoking cigarettes is addictive and causes a number of serious diseases, including those of the respiratory and cardiovascular system [144], it also negatively impact on the gastrointestinal tract, such as CD [145]. Many of the adverse health effects of smoking are reversible and important health benefits are associated with smoking cessation [146]. With regard to the other major IBD form, a protective effect of cigarette smoking on the risk of UC development is well documented. However, whether CS constituents have beneficial effects on the course of the disease is less clear and the potential mechanisms are not understood.

CS inhalation studies in IBD mouse models would, ideally, reproduce the clinical effects of CS on colonic inflammation. This would facilitate identification of the mechanisms involved in the effects of CS on colitis and, eventually, lead to the characterisation of new anti-inflammatory processes involved in colon protection [22]. Nonetheless, so far, the results obtained using animal models of IBD following exposure to inhaled CS or to nicotine via non-inhalation routes, reflected the ambiguity of the clinical observations. These inconsistencies often reflect the high variability related to animal models (e.g. strains, IBD inducers, etc.) and inhalation methodologies. A more systematic and standardised approach is required to obtain consistent and reproducible data addressing the mechanisms by which CS interacts with the inflammatory processes in animal models of UC-like and CD-like colitis. Such systematic investigations could provide valuable insights into the possible anti-inflammatory effects of CS constituents in models related to UC. Corresponding studies in CD models would provide more mechanistic detail about how these compounds can enhance inflammation in CD.



We thank Edanz Group for editorial assistance and Stéphanie Boué for the artwork (Figure 1).


Conflict of interest

Authors are employees of Philip Morris International. Philip Morris International is the sole source of funding and sponsor of this project. W.K. Schlage is contracted and paid by Philip Morris International.


  1. 1. Abraham C, Cho JH. Inflammatory bowel disease. New England Journal of Medicine. 2009;361(21):2066-2078
  2. 2. Tontini GE, et al. Differential diagnosis in inflammatory bowel disease colitis: State of the art and future perspectives. World Journal of Gastroenterology. 2015;21(1):21-46
  3. 3. Annese V, et al. European evidence based consensus for endoscopy in inflammatory bowel disease. Journal of Crohn’s & Colitis. 2013;7(12):982-1018
  4. 4. Lennard-Jones J. Classification of inflammatory bowel disease. Scandinavian Journal of Gastroenterology. 1989;24(suppl 170):2-6
  5. 5. Baumgart DC, Sandborn WJ, Inflammatory bowel disease: Clinical aspects and established and evolving therapies. Lancet. 2007;369(9573):1641-1657
  6. 6. Hommes DW, van Deventer SJ. Endoscopy in inflammatory bowel diseases. Gastroenterology. 2004;126(6):1561-1573
  7. 7. Sartor RB. Mechanisms of disease: Pathogenesis of Crohn’s disease and ulcerative colitis. Nature Clinical Practice. Gastroenterology & Hepatology. 2006;3(7):390-407
  8. 8. Fuss IJ, et al. Nonclassical CD1d-restricted NK T cells that produce IL-13 characterize an atypical Th2 response in ulcerative colitis. Journal of Clinical Investigation. 2004;113(10):1490-1497
  9. 9. Fuss IJ, et al. Disparate CD4+ lamina propria (LP) lymphokine secretion profiles in inflammatory bowel disease. Crohn’s disease LP cells manifest increased secretion of IFN-gamma, whereas ulcerative colitis LP cells manifest increased secretion of IL-5. Journal of Immunology. 1996;157(3):1261-1270
  10. 10. Spencer DM, et al. Distinct inflammatory mechanisms mediate early versus late colitis in mice. Gastroenterology. 2002;122(1):94-105
  11. 11. Xu XR, et al. Dysregulation of mucosal immune response in pathogenesis of inflammatory bowel disease. World Journal of Gastroenterology. 2014;20(12):3255-3264
  12. 12. de Souza HS, Fiocchi C. Immunopathogenesis of IBD: Current state of the art. Nature Reviews Gastroenterology & Hepatology. 2016;13(1):13-27
  13. 13. Bruewer M, et al. Proinflammatory cytokines disrupt epithelial barrier function by apoptosis-independent mechanisms. Journal of Immunology. 2003;171(11):6164-6172
  14. 14. Simms LA, et al. Reduced alpha-defensin expression is associated with inflammation and not NOD2 mutation status in ileal Crohn’s disease. Gut. 2008;57(7):903-910
  15. 15. Turner JR. Molecular basis of epithelial barrier regulation: From basic mechanisms to clinical application. American Journal of Pathology. 2006;169(6):1901-1909
  16. 16. Wehkamp J, et al. Reduced Paneth cell alpha-defensins in ileal Crohn’s disease. Proceedings of the National Academy of Sciences of the United States of America. 2005;102(50):18129-18134
  17. 17. Carbonnel F, et al. Environmental risk factors in Crohn’s disease and ulcerative colitis: An update. Gastroentérologie Clinique et Biologique. 2009;33(Suppl 3):S145-S157
  18. 18. Round JL, Mazmanian SK. The gut microbiota shapes intestinal immune responses during health and disease. Nature Reviews Immunology. 2009;9(5):313-323
  19. 19. Samuelsson S. Ulceroscolitochproktit [dissertation]. Uppsala, Sweden: Department of Social Medicine, University of Uppsala; 1976
  20. 20. Mahid SS, et al. Smoking and inflammatory bowel disease: A meta-analysis. Mayo Clinic Proceedings. 2006;81(11):1462-1471
  21. 21. Parkes GC, Whelan K, Lindsay JO. Smoking in inflammatory bowel disease: Impact on disease course and insights into the aetiology of its effect. Journal of Crohn’s & Colitis. 2014:8(8):717-725
  22. 22. Montbarbon M, et al. Colonic inflammation in mice is improved by cigarette smoke through iNKT cells recruitment. PLoS One. 2013;8(4):e62208
  23. 23. Goyal N, et al. Animal models of inflammatory bowel disease: A review. Inflammopharmacology. 2014;22(4):219-233
  24. 24. Kiesler P, Fuss IJ, Strober W. Experimental models of inflammatory bowel diseases. CMGH Cellular and Molecular Gastroenterology and Hepatology. 2015;1(2):154-170
  25. 25. Driscoll KE, et al. Intratracheal instillation as an exposure technique for the evaluation of respiratory tract toxicity: Uses and limitations. Toxicological Sciences. 2000;55(1):24-35
  26. 26. Brain JD, et al. Pulmonary distribution of particles given by intratracheal instillation or by aerosol inhalation. Environmental Research. 1976;11(1):13-33
  27. 27. Phalen RF, Mendez LB, Oldham MJ. New developments in aerosol dosimetry. Inhalation Toxicology. 2010;22(Suppl 2):6-14
  28. 28. Wolff RK. Toxicology studies for inhaled and nasal delivery. Molecular Pharmaceutics. 2015;12(8):2688-2696
  29. 29. Margetts L, Sawyer R. Transdermal drug delivery: Principles and opioid therapy. Continuing Education in Anaesthesia, Critical Care & Pain. 2007;7(5):171-176
  30. 30. Mauderly JL, et al. Comparison of 3 methods of exposing rats to cigarette smoke. Experimental Pathology. 1989;37(1-4):194-197
  31. 31. Kanikkannan N, et al. Structure-activity relationship of chemical penetration enhancers in transdermal drug delivery. Current Medicinal Chemistry. 2000;7(6):593-608
  32. 32. Wong BA, Inhalation exposure systems: Design, methods and operation. Toxicologic Pathology. 2007;35(1):3-14
  33. 33. Phillips B, et al. Toxicity of aerosols of nicotine and pyruvic acid (separate and combined) in Sprague-Dawley rats in a 28-day OECD 412 inhalation study and assessment of systems toxicology. Inhalation Toxicology. 2015;27(9):405-431
  34. 34. Alexander DJ, et al. Association of Inhalation Toxicologists (AIT) working party recommendation for standard delivered dose calculation and expression in non-clinical aerosol inhalation toxicology studies with pharmaceuticals. Inhalation Toxicology. 2008;20(13):1179-1189
  35. 35. Bide RW, Armour SJ, Yee E. Allometric respiration/body mass data for animals to be used for estimates of inhalation toxicity to young adult humans. Journal of Applied Toxicology. 2000;20(4):273-290
  36. 36. Guyton AC. Measurement of the respiratory volumes of laboratory animals. American Journal of Physiology–Legacy Content. 1947;150(1):70-77
  37. 37. FDA, Guidance for Industry: Estimating the Maximum Safe Starting Dose in Initial Clinical Trials for Therapeutics in Adult Healthy Volunteers. Center for Drug Evaluation and Research (CDER), Silver Spring, Maryland, USA; 2005
  38. 38. Mizoguchi A, et al. Genetically engineered mouse models for studying inflammatory bowel disease. Journal of Pathology. 2016;238(2):205-219
  39. 39. Elson CO, Cong Y, and Sundberg J. The C3H/HeJBir mouse model: A high susceptibility phenotype for colitis. International Reviews of Immunology. 2000;19(1):63-75
  40. 40. Matsumoto S, et al. Inflammatory bowel disease-like enteritis and caecitis in a senescence accelerated mouse P1/Yit strain. Gut. 1998;43(1):71-78
  41. 41. Mizoguchi A. Animal models of inflammatory bowel disease. Progress in Molecular Biology and Translational Science. 2012;105:263-320
  42. 42. Brown SR, Coviello LC. Extraintestinal manifestations associated with inflammatory bowel disease. Surgical Clinics of North America. 2015;95(6):1245-1259, vii
  43. 43. Danese S, Sans M, Fiocchi C. Inflammatory bowel disease: The role of environmental factors. Autoimmunity Reviews. 2004;3(5):394-400
  44. 44. Baumgart DC. The diagnosis and treatment of Crohn’s disease and ulcerative colitis. Deutsches Ärzteblatt International. 2009;106(8):123-133
  45. 45. Ordas I, et al. Ulcerative colitis. Lancet. 2012;380(9853):1606-1619
  46. 46. Uhlig HH. Monogenic diseases associated with intestinal inflammation: Implications for the understanding of inflammatory bowel disease. Gut. 2013;62(12):1795-1805
  47. 47. Verschuere S, et al. The effect of smoking on intestinal inflammation: What can be learned from animal models? Journal of Crohn’s and Colitis. 2012;6(1):1-12
  48. 48. Verschuere S, et al. Cigarette smoking alters epithelial apoptosis and immune composition in murine GALT. Laboratory Investigation. 2011;91(7):1056-1067
  49. 49. Eliakim R, Karmeli F. Divergent effects of nicotine administration on cytokine levels in rat small bowel mucosa, colonic mucosa, and blood. IMAJ-RAMAT GAN. 2003;5(3):178-180
  50. 50. Qin Z, et al. Nicotine protects against DSS colitis through regulating microRNA-124 and STAT3. Journal of Molecular Medicine. 2016;95(2):221-233
  51. 51. Van Dijk JP, et al. Nicotine inhibits cytokine synthesis by mouse colonic mucosa. European Journal of Pharmacology. 1995;278(1):R11-R12
  52. 52. Eliakim R, Fan QX, Babyatsky MW. Chronic nicotine administration differentially alters jejunal and colonic inflammation in interleukin-10 deficient mice. European Journal of Gastroenterology and Hepatology. 2002;14(6):607-614
  53. 53. Zijlstra F, et al. Effect of nicotine on rectal mucus and mucosal eicosanoids. Gut. 1994;35(2):247-251
  54. 54. Guo X, et al. Protective role of cyclooxygenase inhibitors in the adverse action of passive cigarette smoking on the initiation of experimental colitis in rats. European Journal of Pharmacology. 2001;411(1):193-203
  55. 55. Guo X, et al. Involvement of neutrophils and free radicals in the potentiating effects of passive cigarette smoking on inflammatory bowel disease in rats. Gastroenterology. 1999;117(4):884-892
  56. 56. Guo X, et al. Aggravating effect of cigarette smoke exposure on experimental colitis is associated with leukotriene B4 and reactive oxygen metabolites. Digestion. 2001;63(3):180-187
  57. 57. Sun YP, et al. Effect of passive cigarette smoking on colonic α7-nicotinic acetylcholine receptors in TNBS-induced colitis in rats. Digestion. 2007;76(3-4):181-187
  58. 58. Galeazzi F, et al. Cigarette smoke aggravates experimental colitis in rats. Gastroenterology. 1999;117(4):877-883
  59. 59. Ko JK, Cho CH. The diverse actions of nicotine and different extracted fractions from tobacco smoke against hapten-induced colitis in rats. Toxicological Sciences. 2005;87(1):285-295
  60. 60. Ko JK, et al. Beneficial intervention of experimental colitis by passive cigarette smoking through the modulation of cytokines in rats. Journal of Investigative Medicine. 2001;49(1):21-29
  61. 61. Chow JY, Ma L, Cho CH. An experimental model for studying passive cigarette smoking effects on gastric ulceration. Life Sciences. 1996;58(26):2415-2422
  62. 62. Griffith RB, Standafer S. Simultaneous mainstream-sidestream smoke exposure systems II. The rat exposure system. Toxicology. 1985;35(1):13-24
  63. 63. Allais L, et al. The effect of cigarette smoke exposure on the development of inflammation in lungs, gut and joints of TNFΔARE mice. PLoS One. 2015;10(11):e0141570
  64. 64. Kontoyiannis D, et al. Genetic dissection of the cellular pathways and signaling mechanisms in modeled tumor necrosis factor-induced Crohn’s-like inflammatory bowel disease. Journal of Experimental Medicine. 2002;196(12):1563-1574
  65. 65. Bracke KR, et al. Cigarette smoke-induced pulmonary inflammation and emphysema are attenuated in CCR6-deficient mice. Journal of Immunology. 2006;177(7):4350-4359
  66. 66. Liu ES, et al. Cigarette smoke exposure increases ulcerative colitis-associated colonic adenoma formation in mice. Carcinogenesis. 2003;24(8):1407-1413
  67. 67. Low D, Nguyen DD, Mizoguchi E. Animal models of ulcerative colitis and their application in drug research. Drug Design, Development and Therapy. 2013;7:1341-1357
  68. 68. Smith CJ, et al. A repeatable method for determination of carboxyhemoglobin levels in smokers. Human and Experimental Toxicology. 1998;17(1):29-34
  69. 69. Ryter SW, Choi AM. Targeting heme oxygenase-1 and carbon monoxide for therapeutic modulation of inflammation. Translational Research. 2016;167(1):7-34
  70. 70. Takagi T, Uchiyama K, Naito Y. The therapeutic potential of carbon monoxide for inflammatory bowel disease. Digestion. 2015;91(1):13-18
  71. 71. Hegazi RA, et al. Carbon monoxide ameliorates chronic murine colitis through a heme oxygenase 1-dependent pathway. Journal of Experimental Medicine. 2005;202(12):1703-1713
  72. 72. Sheikh SZ, et al. An anti-inflammatory role for carbon monoxide and heme oxygenase-1 in chronic Th2-mediated murine colitis. Journal of Immunology. 2011;186(9):5506-5513
  73. 73. Takagi T, et al. Inhalation of carbon monoxide ameliorates TNBS-induced colitis in mice through the inhibition of TNF-α expression. Digestive Diseases and Sciences. 2010;55(10):2797-2804
  74. 74. Kuhn R, et al. Interleukin-10-deficient mice develop chronic enterocolitis. Cell. 1993;75(2):263-274
  75. 75. Mombaerts P, et al. Spontaneous development of inflammatory bowel disease in T cell receptor mutant mice. Cell. 1993;75(2):274-282
  76. 76. Mombaerts P, et al. Mutations in T-cell antigen receptor genes alpha and beta block thymocyte development at different stages. Nature. 1992;360(6401):225-231
  77. 77. Galitovskiy V, et al. Cytokine-induced alterations of α7 nicotinic receptor in colonic CD4 T cells mediate dichotomous response to nicotine in murine models of Th1/Th17-versus Th2-mediated colitis. Journal of Immunology. 2011;187(5):2677-2687
  78. 78. Eliakim R, et al. Effect of chronic nicotine administration on trinitrobenzene sulphonic acid-induced colitis. European Journal of Gastroenterology & Hepatology. 1998;10(12):1007-1020
  79. 79. Sykes A, et al. An investigation into the effect and mechanisms of action of nicotine in inflammatory bowel disease. Inflammation Research. 2000;49(7):311-319
  80. 80. Orr-Urtreger A, et al. Increased severity of experimental colitis in alpha5 nicotinic acetylcholine receptor subunit-deficient mice. Neuroreport. 2005;16(10):1123-1127
  81. 81. AlSharari SD, et al. Novel insights on the effect of nicotine in a murine colitis model. Journal of Pharmacol and Experimental Therapeutics. 2013;344(1):207-217
  82. 82. Snoek SA, et al. Selective α7 nicotinic acetylcholine receptor agonists worsen disease in experimental colitis. British Journal of Pharmacology. 2010;160(2):322-333
  83. 83. McGrath J, McDonald JWD, MacDonal d JK. Transdermal nicotine for induction of remission in ulcerative colitis. Cochrane Database of Systematic Reviews 2004, Issue 4. Art. No.: CD004722
  84. 84. Pullan RD, et al. Transdermal nicotine for active ulcerative colitis. New England Journal of Medicine. 1994;330(12):811-815
  85. 85. Sandborn W, et al. Nicotine tartrate liquid enemas for mildly to moderately active left‐sided ulcerative colitis unresponsive to first‐line therapy: A pilot study. Alimentary Pharmacology & Therapeutics. 1997;11(4):663-671
  86. 86. Ingram JR, et al. Preliminary observations of oral nicotine therapy for inflammatory bowel disease: An open-label phase I-II study of tolerance. Inflammatory Bowel Diseases. 2005;11(12):1092-1096
  87. 87. Ingram JR, et al. A randomized trial of nicotine enemas for active ulcerative colitis. Clinical Gastroenterology and Hepatology. 2005;3(11):1107-1114
  88. 88. Titz B, et al. Effects of cigarette smoke, cessation, and switching to two heat-not-burn tobacco products on lung lipid metabolism in C57BL/6 and Apoe−/− mice-an integrative systems toxicology analysis. Toxicological Sciences. 2016;149(2):441-457
  89. 89. Lo Sasso G, et al. Effects of cigarette smoke, cessation and switching to a candidate modified risk tobacco product on the liver in Apoe−/− mice—a systems toxicology analysis. Inhalation Toxicology. 2016;28(5):226-240
  90. 90. Phillips B, et al. A 7-month cigarette smoke inhalation study in C57BL/6 mice demonstrates reduced lung inflammation and emphysema following smoking cessation or aerosol exposure from a prototypic modified risk tobacco product. Food and Chemical Toxicology. 2015;80:328-345
  91. 91. Phillips B, et al. An 8-month systems toxicology inhalation/cessation study in Apoe−/− mice to investigate cardiovascular and respiratory exposure effects of a candidate modified risk tobacco product, THS 2.2, compared with conventional cigarettes. Toxicological Sciences. 2016;149(2):411-432
  92. 92. OECD, Test No. 412: Subacute Inhalation Toxicity: 28-Day Study. OECD Publishing, Paris Cedex, France; 2009
  93. 93. OECD, Test No. 413: Subchronic Inhalation Toxicity: 90-day Study. OECD Publishing, Paris Cedex, France; 2009
  94. 94. Ansari S, et al. Comprehensive systems biology analysis of a 7-month cigarette smoke inhalation study in C57BL/6 mice. Scientific Data. 2016;3:150077
  95. 95. de Jonge WJ, Ulloa L. The alpha7 nicotinic acetylcholine receptor as a pharmacological target for inflammation. British Journal of Pharmacology. 2007;151(7):915-929
  96. 96. Vidal C. Nicotinic receptors in the brain. Molecular biology, function, and therapeutics. Molecular and Chemical Neuropathology. 1996;28(1-3):3-11
  97. 97. Grando SA, et al. The non-neuronal cholinergic system: Basic science, therapeutic implications and new perspectives. Life Sciences. 2012;91(21-22):969-972
  98. 98. Matteoli G, Boeckxstaens GE. The vagal innervation of the gut and immune homeostasis. Gut. 2013;62(8):1214-1222
  99. 99. Wang H, et al. Nicotinic acetylcholine receptor alpha7 subunit is an essential regulator of inflammation. Nature. 2003;421(6921):384-388
  100. 100. Altschuler SM, et al. The central organization of the vagus nerve innervating the colon of the rat. Gastroenterology. 1993;104(2):502-509
  101. 101. Ghia JE, et al. Reactivation of inflammatory bowel disease in a mouse model of depression. Gastroenterology. 2009;136(7):2280-2288. e4
  102. 102. Ghia JE, et al. The vagus nerve: A tonic inhibitory influence associated with inflammatory bowel disease in a murine model. Gastroenterology. 2006;131(4):1122-1130
  103. 103. Sun P, et al. Involvement of MAPK/NF-kappaB signaling in the activation of the cholinergic anti-inflammatory pathway in experimental colitis by chronic vagus nerve stimulation. PLoS One. 2013;8(8):e69424
  104. 104. Wang H, et al. Cholinergic agonists inhibit HMGB1 release and improve survival in experimental sepsis. Nature Medicine. 2004;10(11):1216-1221
  105. 105. Freitas K, et al. Effects of alpha7 positive allosteric modulators in murine inflammatory and chronic neuropathic pain models. Neuropharmacology. 2013;65:156-164
  106. 106. Hashimoto K. Targeting of alpha7 nicotinic acetylcholine receptors in the treatment of schizophrenia and the use of auditory sensory gating as a translational biomarker. Current Pharmaceutical Design. 2015;21(26):3797-3806
  107. 107. Leonard S, et al. Smoking and schizophrenia: Abnormal nicotinic receptor expression. European Journal of Pharmacology. 2000;393(1-3):237-242
  108. 108. Meyer EM, et al. Analysis of 3-(4-hydroxy, 2-Methoxybenzylidene)anabaseine selectivity and activity at human and rat alpha-7 nicotinic receptors. Journal of Pharmacol and Experimental Therapeutics. 1998;287(3):918-925
  109. 109. Verma M, et al. Chronic anatabine treatment reduces alzheimer’s disease (ad)-like pathology and improves socio-behavioral deficits in a transgenic mouse model of AD. PLoS One. 2015;10(5):e0128224
  110. 110. Benhammou K, et al. [(3)H]Nicotine binding in peripheral blood cells of smokers is correlated with the number of cigarettes smoked per day. Neuropharmacology. 2000;39(13):2818-2829
  111. 111. Hosur V, Loring RH. alpha4beta2 nicotinic receptors partially mediate anti-inflammatory effects through Janus kinase 2-signal transducer and activator of transcription 3 but not calcium or cAMP signaling. Molecular Pharmacology. 2011;79(1):167-174
  112. 112. Safronova VG, et al. Nicotinic receptor involvement in regulation of functions of mouse neutrophils from inflammatory site. Immunobiology. 2016;221(7):761-772
  113. 113. Miller LG, et al. Reversible alterations in immunoregulatory T cells in smoking. Analysis by monoclonal antibodies and flow cytometry. CHEST Journal. 1982;82(5):526-529
  114. 114. Holt PG. Immune and inflammatory function in cigarette smokers. Thorax. 1987;42(4):241-249
  115. 115. Sopori M. Effects of cigarette smoke on the immune system. Nature Reviews Immunology. 2002;2(5):372-377
  116. 116. Geng Y, et al. Effects of nicotine on the immune response. I. Chronic exposure to nicotine impairs antigen receptor-mediated signal transduction in lymphocytes. Toxicology and Applied Pharmacology. 1995;135(2):268-278
  117. 117. Geng Y, et al. Effects of nicotine on the immune response. II. Chronic nicotine treatment induces T cell anergy. Journal of Immunology. 1996;156(7):2384-2390
  118. 118. Kalra R, et al. Effects of cigarette smoke on immune response: Chronic exposure to cigarette smoke impairs antigen-mediated signaling in T cells and depletes IP3-sensitive Ca(2+) stores. Journal of Pharmacol and Experimental Therapeutics. 2000;293(1):166-171
  119. 119. Borovikova LV, et al. Vagus nerve stimulation attenuates the systemic inflammatory response to endotoxin. Nature. 2000;405(6785):458-462
  120. 120. Hernandez CP, et al. Effects of cigarette smoke extract on primary activated T cells. Cellular Immunology. 2013;282(1):38-43
  121. 121. Ueno A, et al. Opposing effects of smoking in ulcerative colitis and Crohn’s disease may be explained by differential effects on dendritic cells. Inflammatory Bowel Diseases. 2014;20(5):800-810
  122. 122. Bergeron V, et al. Current smoking differentially affects blood mononuclear cells from patients with Crohn’s disease and ulcerative colitis: Relevance to its adverse role in the disease. Inflammatory Bowel Diseases. 2012;18(6):1101-1111
  123. 123. McGuckin MA, et al. Intestinal barrier dysfunction in inflammatory bowel diseases. Inflammatory Bowel Diseases. 2009;15(1):100-113
  124. 124. Prytz H, Benoni C, Tagesson C. Does smoking tighten the gut? Scandinavian Journal of Gastroenterology. 1989;24(9):1084-1088
  125. 125. McGilligan VE, et al. The effect of nicotine in vitro on the integrity of tight junctions in Caco-2 cell monolayers. Food and Chemical Toxicology. 2007;45(9):1593-1598
  126. 126. McGilligan VE, et al. Hypothesis about mechanisms through which nicotine might exert its effect on the interdependence of inflammation and gut barrier function in ulcerative colitis. Inflammatory Bowel Diseases. 2007;13(1):108-115
  127. 127. Suenaert P, et al. The effects of smoking and indomethacin on small intestinal permeability. Alimentary Pharmacology and Therapeutics. 2000;14(6):819-822
  128. 128. Zuo L, et al. Cigarette smoking is associated with intestinal barrier dysfunction in the small intestine but not in the large intestine of mice. Journal of Crohn’s and Colitis. 2014;8(12):1710-1722
  129. 129. Benjamin JL, et al. Smokers with active Crohn’s disease have a clinically relevant dysbiosis of the gastrointestinal microbiota. Inflammatory Bowel Diseases. 2012;18(6):1092-1100
  130. 130. Opstelten JL, et al. Gut microbial diversity is reduced in smokers with Crohn’s Disease. Inflammatory Bowel Diseases. 2016;22(9):2070-2077
  131. 131. Tomoda K, et al. Cigarette smoke decreases organic acids levels and population of bifidobacterium in the caecum of rats. Journal of Toxicological Sciences. 2011;36(3):261-266
  132. 132. Wang H, et al. Side-stream smoking reduces intestinal inflammation and increases expression of tight junction proteins. World Journal of Gastroenterology. 2012;18(18):2180-2187
  133. 133. Allais L, et al. Transient receptor potential channels in intestinal inflammation: What is the impact of cigarette smoking? Pathobiology. 2017;84(1):1-15
  134. 134. Collins SM. The immunomodulation of enteric neuromuscular function: Implications for motility and inflammatory disorders. Gastroenterology. 1996;111(6):1683-1699
  135. 135. Coulie B, et al. Colonic motility in chronic ulcerative proctosigmoiditis and the effects of nicotine on colonic motility in patients and healthy subjects. Alimentary Pharmacology and Therapeutics. 2001;15(5):653-663
  136. 136. Green JT, et al. Intra-luminal nicotine reduces smooth muscle tone and contractile activity in the distal large bowel. European Journal of Gastroenterology and Hepatology. 1999;11(11):1299-1304
  137. 137. Murakami I, et al. Nicotine-induced neurogenic relaxation in the mouse colon: Changes with dextran sodium sulfate-induced colitis. Journal of Pharmacological Sciences. 2009;109(1):128-138
  138. 138. Motley RJ, et al. Smoking, eicosanoids and ulcerative colitis. Journal of Pharmacy and Pharmacology. 1990;42(4):288-289
  139. 139. Srivastava ED, et al. Effect of ulcerative colitis and smoking on rectal blood flow. Gut. 1990;31(9):1021-1024
  140. 140. De Bruin AF, et al. The impact of chronic smoking on rectal mucosal blood flow. Techniques in Coloproctology. 2009;13(4):269-272
  141. 141. Zimmerman DD, et al. Smoking impairs rectal mucosal bloodflow—a pilot study: Possible implications for transanal advancement flap repair. Diseases of the Colon & Rectum. 2005;48(6):1228-1232
  142. 142. Onyiah JC, et al. Carbon monoxide and heme oxygenase-1 prevent intestinal inflammation in mice by promoting bacterial clearance. Gastroenterology. 2013;144(4):789-798
  143. 143. Green JT, et al. Nitric oxide mediates a therapeutic effect of nicotine in ulcerative colitis. Alimentary Pharmacology and Therapeutics. 2000;14(11):1429-1434
  144. 144. Centers for Disease Control and Prevention (US), National Center for Chronic Disease Prevention and Health Promotion, and O.o.S.a. Health, Publications and Reports of the Surgeon General, In: How Tobacco Smoke Causes Disease: The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General. Atlanta (GA): Centers for Disease Control and Prevention (US), National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health; 2010
  145. 145. Underner M, et al. Smoking, smoking cessation and Crohn’s disease. Presse Médicale. 2016;45(4 Pt 1):390-402
  146. 146. Fagerstrom K. The epidemiology of smoking: Health consequences and benefits of cessation. Drugs. 2002;62(Suppl 2):1-9
  147. 147. Cooper HS, et al. Clinicopathologic study of dextran sulfate sodium experimental murine colitis. Laboratory Investigation. 1993;69(2):238-249
  148. 148. Okayasu I, et al. A novel method in the induction of reliable experimental acute and chronic ulcerative colitis in mice. Gastroenterology. 1990;98(3):694-702
  149. 149. Grisham MB, et al. Metabolism of trinitrobenzene sulfonic acid by the rat colon produces reactive oxygen species. Gastroenterology. 1991;101(2):540-547
  150. 150. Hawkins JV, et al. Protease activity in a hapten-induced model of ulcerative colitis in rats. Digestive Diseases and Sciences. 1997;42(9):1969-1980
  151. 151. Boirivant M, et al. Oxazolone colitis: A murine model of T helper cell type 2 colitis treatable with antibodies to interleukin 4. Journal of Experimental Medicine. 1998;188(10):1929-1939
  152. 152. MacPherson BR, Pfeiffer CJ. Experimental production of diffuse colitis in rats. Digestion. 1978;17(2):135-150
  153. 153. Moyana TN, Lalonde JM. Carrageenan-induced intestinal injury in the rat—A model for inflammatory bowel disease. Annals of Clinical Laboratory Science. 1990;20(6):420-426
  154. 154. Banerjee AK, et al. Gut protein synthetic studies in a NSAID model of inflammatory bowel disease (IBD). Biochemical Society Transactions. 1991;19(2):186s
  155. 155. McKenzie SJ, et al. Evidence of oxidant-induced injury to epithelial cells during inflammatory bowel disease. Journal of Clinical Investigation. 1996;98(1):136-141
  156. 156. Meyers S, et al. Significance of anergy to dinitrochlorobenzene (DNCB) in inflammatory bowel disease: Family and postoperative studies. Gut. 1978;19(4):249-252
  157. 157. Bohnhoff M, Drake BL, Miller CP. Effect of streptomycin on susceptibility of intestinal tract to experimental Salmonella infection. Proceedings of the Society for Experimental Biology and Medicine. 1954;86(1):132-137
  158. 158. Mizoguchi E. Chitinase 3-like-1 exacerbates intestinal inflammation by enhancing bacterial adhesion and invasion in colonic epithelial cells. Gastroenterology. 2006;130(2):398-411
  159. 159. Shull MM, et al. Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease. Nature. 1992;359(6397):693-699
  160. 160. Sadlack B, et al. Ulcerative colitis-like disease in mice with a disrupted interleukin-2 gene. Cell. 1993;75(2):253-261
  161. 161. Kobayashi KS, et al. Nod2-dependent regulation of innate and adaptive immunity in the intestinal tract. Science. 2005;307(5710):731-734
  162. 162. Lee EG, et al. Failure to regulate TNF-induced NF-kappaB and cell death responses in A20-deficient mice. Science. 2000;289(5488):2350-2354
  163. 163. Panwala CM, Jones JC, Viney JL. A novel model of inflammatory bowel disease: Mice deficient for the multiple drug resistance gene, mdr1a, spontaneously develop colitis. Journal of Immunology. 1998;161(10):5733-5744
  164. 164. Rudolph U, et al. Ulcerative colitis and adenocarcinoma of the colon in G alpha i2-deficient mice. Nature Genetics. 1995;10(2):143-150
  165. 165. Eken A, Singh AK, Oukka M. Interleukin 23 in Crohn’s disease. Inflammatory Bowel Diseases. 2014;20(3):587-595
  166. 166. Neurath MF. IL-23: A master regulator in Crohn disease. Nature Medicine. 2007;13(1):26-28
  167. 167. Kaser A, et al. XBP1 links ER stress to intestinal inflammation and confers genetic risk for human inflammatory bowel disease. Cell. 2008;134(5):743-756
  168. 168. Nenci A, et al. Epithelial NEMO links innate immunity to chronic intestinal inflammation. Nature. 2007;446(7135):557-561
  169. 169. Watanabe M, et al. Interleukin 7 transgenic mice develop chronic colitis with decreased interleukin 7 protein accumulation in the colonic mucosa. Journal of Experimental Medicine. 1998;187(3):389-402
  170. 170. Wirtz S, et al. Cutting edge: Chronic intestinal inflammation in STAT-4 transgenic mice: Characterization of disease and adoptive transfer by TNF- plus IFN-gamma-producing CD4+ T cells that respond to bacterial antigens. Journal of Immunology. 1999;162(4):1884-1888
  171. 171. Rath HC, Wilson KH, Sartor RB. Differential induction of colitis and gastritis in HLA-B27 transgenic rats selectively colonized with Bacteroides vulgatus or Escherichia coli. Infection and Immunity. 1999;67(6):2969-2974
  172. 172. Hermiston ML, Gordon JI. Inflammatory bowel disease and adenomas in mice expressing a dominant negative N-cadherin. Science. 1995;270(5239):1203-1207
  173. 173. Leach MW, et al. Inflammatory bowel disease in C.B-17 scid mice reconstituted with the CD45RBhigh subset of CD4+ T cells. American Journal of Pathology. 1996;148(5):1503-1515
  174. 174. Benson JM, Shepherd DM. Aryl hydrocarbon receptor activation by TCDD reduces inflammation associated with Crohn’s disease. Toxicological Sciences. 2010;120(1):68-78. DOI: 10.1093/toxsci/kfq360
  175. 175. Eliakim R, et al. Dual effect of chronic nicotine administration: Augmentation of jejunitis and amelioration of colitis induced by iodoacetamide in rats. International Journal of Colorectal Disease. 2001;16(1):14-21
  176. 176. Hayashi S, et al. Nicotine suppresses acute colitis and colonic tumorigenesis associated with chronic colitis in mice. American Journal of Physiology-Gastrointestinal and Liver Physiology. 2014;307(10):G968-G978. DOI: 10.1152/ajpgi. 00346.2013
  177. 177. Takamura T, et al. Activation of the aryl hydrocarbon receptor pathway may ameliorate dextran sodium sulfate-induced colitis in mice. Immunology & Cell Biology. 2010;88(6):685-689
  178. 178. Vigna SR. Nicotine inhibits Clostridium difficile toxin A-induced colitis but not ileitis in rats. International Journal of Inflammation. 2016;2016:1-10

Written By

Giuseppe Lo Sasso, Walter K. Schlage, Blaine Phillips, Manuel C. Peitsch and Julia Hoeng

Submitted: 22 November 2016 Reviewed: 04 May 2017 Published: 20 December 2017