Smart drug delivery systems are very popular drug delivery systems for treatment to common disease such as gene therapy, heart disease, cancer therapy, and neuropathy. Neuropathy is the most common chronic complication of diabetes that is associated with especially loss of peripheral nerve fibers. Hyperglycemia, insulin deficiency and dyslipidemia largely affect the development and progression of diabetic neuropathy. Several metabolic disruptions including altered protein kinase C, elevated polyol pathway activity, oxidative stress, the formation of advanced glycation and lipoxidation end products, and various pro-inflammatory changes directly affect neural tissue and cause neurodegenerative changes in diabetes. The therapeutic interventions of these metabolic pathways have a limited success to relieve the symptoms of diabetic neuropathy. This review emphasizes on the pathogenesis of neurovascular changes, presently available therapeutic approaches future directions for the management of diabetic neuropathy and related new drug delivery systems.
- Diabetic neuropathy
Diabetes mellitus (DM) is the most common disease, causing neuropathy worldwide. In the last century, although we have more information about clinical forms of diabetic neuropathy, sufficient knowledge about the pathophysiology of neuropathy could not be reached.
Diabetic neuropathy is defined as a peripheral neuropathy that may occur in clinical and subclinical levels and develops in the DM ground in the absence of other peripheral neuropathy factors.
While neuropathy is present at the time of diagnosis in 10% of diabetic patients, this rate reaches to 50% at the end of 20 years. There are studies, which demonstrate that neuropathy starts within 9 years after the diagnosis of Type 2 diabetes. It may include manifestations associated with somatic and/or autonomic parts of peripheral nervous system.
The relationship between DM and neuropathy is known for over 100 years. The classification was first suggested by Leyden in 1893 with hyperesthetic (painful), paralytic (motor), and ataxic forms. Large sensory, small sensory, autonomic, and motor fibers may be affected by neuropathy. The findings may be symmetrical or asymmetrical. The most common form of neuropathy is distal sensorimotor polyneuropathy. The most common mononeuropathy is carpal tunnel syndrome (CTS). However, the recognition of some rare types such as diabetic lumbosacral radiculoplexus neuropathy that may cause pain and weakness is important for the reduction of morbidity.
The annual incidence of neuropathy is closely associated with the known duration of diabetes. Height, maximum body mass index, smoking, systolic and diastolic blood pressures, estradiol level, and cholesterol level were not found different in those with neuropathy and without neuropathy.
Given that diabetes is estimated to affect about 246 million people worldwide, it may be calculated that there are 20–30 million people suffering from symptomatic diabetic neuropathy. This number is thought to double by 2030 .
The contribution of neuropathy to mortality is very low. Disability was reported to be in 44% of the patients with Type 1 DM and definite neuropathy, and partial restriction was reported to be in activity in 74% of those with Type 2 DM and sensory neuropathy [2,3]. Hypertension, independent of duration of diabetes, has been shown to be the most important factor in the development of neuropathy in a study of Pittsburg Epidemiology of Diabetes Complications (EDC) about the effects of hypertension, height, and smoking on the incidence of distal symmetric polyneuropathy in long-lasting and poorly controlled diabetic patients .
Diabetic cardiac autonomic neuropathy is a serious complication seen in one fourth of Types 1 and 2 diabetic patients. It results in high mortality and silent myocardial ischemia. Autonomic dysfunction has been shown as the reason for having the risk of cardiovascular disease and sudden death in patients with Type 2 diabetes. The activation of cytokines is the indicator of the inflammation in patients with diabetes. These changes have been associated with the sympathetic–vagal balance disorders. Patients have complaints of orthostatic hypotension, exercise intolerance, lack of enhanced stability during surgery, silent myocardial infarction, and ischemia. The use of heart rate change (HRV) and Valsalva maneuver has been reported in the diagnosis of cardiac autonomic neuropathy . An over activation of the sympathetic system and the activation of inflammatory cascade were observed with hyperleptinemia and lack of adiponectin in case of sleep apnea that is common in diabetes and metabolic syndrome. Ultimately, negative effects seen in the autonomic nervous system as a result of cardiovascular function impairment give rise to higher morbidity and mortality in diabetic patients .
2. Pathogenesis of diabetic neuropathy
Diabetic neuropathy develops as a result of involvement of different nerves in varying degrees in different individuals. The actual lesions were observed to be in peripheral nerve axons in histopathological studies conducted in patients with diabetic neuropathy.
There is a close relationship between the degree and duration of hyperglycemia and the development of diabetic neuropathy. Development of neuropathy can be delayed or prevented through good metabolic control. The development of clinical diabetic neuropathy was observed to be decreased by 69% in the primary prevention group and 57% in the secondary intervention group after 5 years of intensive diabetes treatment in those with Type 1 diabetes in a study. Six separate factors associated with each other are thought to have an important role in the pathogenesis of DM.
Several mechanisms have been suggested in the pathogenesis of diabetic neuropathy. These are metabolic processes which involve direct nerve damage, endoneurial microvascular damage, autoimmune inflammation, and reduced neurotrophic support.
Epidemiological studies showed that the duration and severity of hyperglycemia are major risks in the development of neuropathy in patients with Types 1 and 2 DM . Common opinion on the development of DSP (diabetic symmetric polyneuropathy) is that starting of the early nerve damage from the short, thin, myelinated A-delta fibers and unmyelinated C type of nerve fibers. The gold standard to assess the morphological changes in the short nerve fibers is a skin biopsy. However, not providing information about the nerve function, cost, and superficiality and being of no use in all patients with Type 1 diabetes limit this technique. The presence of a valid clinical practice, which identifies early short fiber disorder by using imaging techniques, was reported recently .
2.1. Metabolic factors
2.1.1. Increased glycosylation end products
The glycosylation of the plasma and tissue proteins plays a major role in diabetic microvascular complications by causing the formation of advanced glycation end products (AGEs). Excess glucose combines with amino acids on circulating and tissue proteins in the presence of chronic hyperglycemia. This non-enzymatic process initially leads to the formation of reversible early glycosylation end products and, later, to irreversible advanced glycosylation end products. Advanced glycosylation products change their function by modifying intracellular proteins and extracellular matrix proteins that interact with extracellular integrins. AGE precursors modify plasma proteins by binding IGU receptors RAGE (receptor of advanced glycation end products) in mesangial endothelial cells, microglia, and macrophages. Thus, they initiate the production of reactive oxygen species (ROS). The activation of NF-κB initiates proinflammatory gene expression. Cytokines and growth factors are expressed by macrophages and mesangial cells . Significantly increased serum concentrations of AGEs have been reported to lead to the development of diabetic complications by their proinflammatory effect in diabetic patients. The other effects of AGEs are increasing in vascular permeability, procoagulant activity, adhesion molecule expression, and monocyte invasion .
2.2. Oxidative stress
As mentioned above, hyperglycemia causes accumulation of ROS and oxidative stress eventually by interacting with many different ways. The free radical is a chemical species usually having very reactive unpaired electron in the molecular or atomic orbit. Although free radical reactions are necessary for defense mechanisms of immune system cells including neutrophils and macrophage, the overproduction of free radicals results in tissue injury and cell death. Free radicals affect all essential components of cells such as lipids, proteins, DNA, and carbohydrates and lead to the deterioration of their structure. The formation and elimination rates of free radicals are in balance in the organism, which are known as oxidative balance. The organism is not affected by free radicals as long as oxidative stability is provided. Studies in which the relationship between diabetes and diabetes complications and the ROS are shown, it is highlighted that tissue injury due to non-enzymatic glycation, metabolic stress caused by changes in energy metabolism, sorbitol path activity, hypoxia, and ischemia–reperfusion, increases the production of free radical and alters the antioxidant defense system. There are studies, which support that the formation of free radical is a direct result of hyperglycemia, as well as experimental trials that show that the formation of free radical starts when the endothelial and smooth muscle cells were incubated in the medium containing high concentrations of glucose. Hyperglycemia-mediated ROS production occurs via three mechanisms. The first mechanism is the auto-oxidation of glucose and superoxide production. Glucose is converted to reactive keto aldehydes and superoxide anion in the presence of a transition element. The chain of reactions results in the transformation of superoxide radical into extremely reactive hydroxyl radical via hydrogen peroxide. The intracellular glucose oxidation leads to the release of NADH. NADH is used for providing needed energy for ATP production by the oxidative phosphorylation way in the respiratory chain. Superoxide radical is released during this reaction in the respiratory chain. The production of superoxide radicals increases in this way in the presence of high glucose concentration. Mitochondrial respiratory chain is the main intracellular source of ROS production. It is considered that superoxide radical occurs continuously during normal respiration chain of events. Recent studies showed that much pathology in diabetes was associated with increased mitochondrial ROS production. The second mechanism in the hyperglycemia-mediated ROS production is the glycation of proteins and the formation of AGE products. When the proteins exposed to high glucose concentrations, glucose leads to uncontrolled glycation reactions by binding to protein without requiring the mediation of an enzyme. The glycated protein causes the formation of ROS by donating an electron to molecular oxygen. AGE products are formed after this non-enzymatic reaction. Advanced glycosylation products lead to endothelial damage by increasing vasoconstriction via endothelin-1 and have the capacity to generate free radicals through complex biochemical mechanisms. Toxic effects of AGEs also include being able to change the structure and function of proteins and to induce oxidative stress with its receptors. The third mechanism of ROS production is polyol pathway. High glucose concentration causes the sorbitol production by polyol pathway. As NADH is used for the activity of enzyme aldose reductase in this pathway, intracellular NADH is consumed. NADH is required for converting oxidized glutathione to reduced form and nitric oxide (NO) synthesis. Therefore, being active of the sorbitol way and the absence of NADPH ultimately mean a limitation of cell’s antioxidant capacity. The decrease in reduced glutathione and NO synthesis that has a function in vasodilatation leads to the reduction of endoneurial blood flow, consequently endoneurial hypoxia or ischemia. Due to this event, the damage occurs in neuronal cells, Schwann cells.
2.3. Vascular hypotheses
Swellings of the capillary vascular endothelial cells, thickening of the blood vessel wall, and undergoing aggregation or fibrin and occlusion with platelets of capillary lumen were shown in various studies. The sudden onset of clinical signs of focal neuropathies in diabetes supports the vascular cause. Decrease in NO production, abnormalities in eicosanoid production, and an increase in oxidative pathway lead to vasoconstriction in endoneurial microvascularization and nerve hypoxia.
2.4. Immunological mechanisms
Autoantibodies against the sympathetic ganglia develop in patients with insulin-dependent diabetes. Endoneurial or epineural lymphocytic infiltration has been displayed in the sural nerve biopsy of diabetic patients. Coexistence of diabetic neuropathy and chronic inflammatory demyelinating polyneuropathy is also a suggestive finding of immune or cytotoxic factors .
2.5. Neurotrophic factors
Neurotrophins are proteins that ensure the growth, permanence, survival, and differentiation into different specific populations of the neurons. There are studies, which show that impaired neurotrophic support is involved in the pathogenesis of diabetic polyneuropathy. Since nerve growth factor (NGF), a typical growth factor for the nerve, is needed for the survival and the continuity of sympathetic and thin sensory nerve fibers, it was examined particularly well. NGF also regulates the expression of the neuropeptides including calcium gene-related peptide and substance P in sympathetic nerves and sensory neurons of dorsal root ganglion. Retrograde axonal transport from target tissue to neuronal cell body is impaired in diabetes. There is evidence, which shows that NGF expression is decreased in the skin, submandibular glands, and the sympathetic ganglia in experimental diabetic neuropathy. NGF, when administered to rats with streptozotocin-induced diabetes, prevented the protection of the response to thermal painful stimuli (tail flick threshold) and the decrease in levels of neuropeptides including calcitonin gene-related peptide and substance P measured in the cervical dorsal root ganglia. In diabetic autonomic neuropathy model, dystrophic changes in sympathetic ganglia following the administration of NGF indicate that there may be a different dosing effect. Neurotrophin-3 (NT-3) supports the differentiation and survival of sensory neurons. Decreased messenger RNA (mRNA) was shown in the leg muscle of NT-3 diabetic mice. Due to their neurotrophic effect in the treatment of diabetic neuropathy in recent years, glucagon-like peptide-1 (GLP-1) analogues (exendin-4) and peptides such as ghrelin were also found to give successful results in animal models .
Symptoms and physical examination findings should be evaluated together for an accurate diagnosis of diabetic peripheral neuropathy (DPN). Standardization and easy application of diagnostic methods are of great importance in terms of widespread availability. There is no gold standard in the detection of presence of diabetic neuropathy. The San Antonio consensus panel recommends performing at least one measurement in five different diagnostic categories. These are symptom scoring, physical examination scoring, QST, cAFT, and EDS. The neurological examinations of the patients often reveal gloves socks style sensory deficit, hyporeflexia or areflexia, increase in vibration sense perception threshold, and moderate atrophy and weakness particularly in intrinsic foot muscles.
Neuropathic pain is one of the most common symptoms that are ignored by both the patient and the physician. Of the patients, 12.5% with painful DPN stated that they had never mentioned the pain to the physicians before and 40% expressed that they had received no treatment for pain. There are several questioning methods to query pain due to diabetic polyneuropathy, but none of these methods have been accepted as the gold standard.
Visual Analog Scale (VAS) is an easy method applied by grading the pain on a scale of 1–10 by the patient. Another method of pain assessment is “The Leeds Assessment of Neuropathic Symptoms and Signs” (LANSS) pain inquiry. Having a LANSS score of 12 or more is diagnostic for neuropathic pain. The Michigan Neuropathy Screening Instrument is one of the other commonly used interrogation methods, which is used in the diagnosis of neuropathic pain. Neuropathy Disability Score (NDS), which was first developed by Dick for the standardization of examination findings and correct interpretation of the findings and was simplified and modified in the following years, is regarded as a reliable and easy method that does not require experience in neurology. NDS = 0 is considered normal, NDS = 10 indicates maximum deficits, and NDS = 6 or more indicates the risk of developing diabetic foot ulcers. Touch pressure, vibration, hot–cold sensation, thermal pain, cold pain, and mechanical pain detection thresholds are tested in quantitative sensory testing.
The tests related to the vasomotor control, baroreceptor reflex, sudomotor function, pupil, bladder, and bowel innervation are used in autonomic function tests. Electrodiagnostic studies are one of the most common and objective methods used in the diagnosis of DPN. Weakness of electrodiagnostic studies is not showing the early stages of thin fiber damage. Unmyelinated C fiber injury, the most common cause of painful DPN, does not provide any electrophysiological findings, but thick myelinated Aα and Aβ fiber involvements have EDS findings.
Staining of a 3-mm skin sample using protein gene product-9.5 allows the assessment of intraepidermal thin fibers and early diagnosis of neuropathic damage. Although its sensitivity is high, its use is limited because it is an invasive procedure .
4. Treatment in diabetic neuropathy
The prevention of occurrence of diabetic polyneuropathy or its definitive treatment is impossible.However, some measures that slow down the development of neuropathy, reduce the severity of symptoms, and prevent the complications of neuropathy may be taken. Normal or nearly normal blood glucose control of the patients should be provided. Keeping HGBA1C below 7, cholesterol control, smoking cessation, alcohol reduction, avoiding obesity, and having foot care delay the progression of neuropathy. When the structural link between membrane ion channel dysfunction and axonal loss is assessed, neuropathy can be diagnosed at an early stage with the detection of clinical biomarkers (biomarkers) that may identify the presence of early changes in ion channel. Therefore, the opportunity arises to start treatment without irreversible nerve damage .
4.1. Metabolic control
The most important treatment for the prevention of diabetic PNP (peripheral neuropathy) is to control blood glucose. According to Diabetes Control and Complications Center (DCTT) data, the reduction of neuropathy by 57% has been shown in Type 1 DM after 5 years of tight blood glucose control.
The addition of myoinositol to the diet was shown to improve nerve Na–K ATPase activity and nerve conduction values in laboratory studies; however, no improvement was found in electrophysiological parameters in humans. Their potential benefits are being able to inhibit nerve damage. Thus, its administration is recommended at an early stage.
4.3. Vitamin addition
Vitamin treatment is often a non-specific therapy in neuropathy. Controlled studies show that receiving thiamine, vitamin B12, pyridoxine, or pantothenic acid in diabetic neuropathy is of no use [2,15].
4.4. ROS inhibitors
5. Current therapeutic strategies in diabetic neuropathy
DPN is one of the most common symptoms of chronic neuropathic pain in clinical practice. Various treatment methods are tried in patients with diabetic neuropathy. Tramadol, an opioid, is a weak opioid analgesic used for reducing severe pain. It was reported that randomized controlled trials for a period of 6 weeks were better than the placebo and symptomatic relief continued for at least 6 months. The likelihood of side effects, as other opioid-like drugs, is common. However, the development of drug tolerance and the development of addiction with long-term therapy with tramadol are not common. NMDA receptors play a key role in the sensitization of the neuropathic pain, but the use of these drugs is not widespread because of their dose-limiting side effects . NMDA receptor antagonists are used for modulation of excitatory transmission in the primary afferent spinothalamic neuron synapses in recent years. The pain ceases with the blockade of excitatory glutamatergic NMDA receptors in the spinal cord. Dextromethorphan is one example of such painkiller medications. NMDA receptor antagonists have been shown to be as effective as opioid analgesics for chronic pain conditions. The diagnosis of diabetic neuropathy was made by a clinical evaluation (medical history, motor, sensory, and reflex examination) and electrophysiological tests for 24 patients with Type 2 diabetes and diabetic neuropathy. Pain complaints of the patients were assessed with a VAS before and after the treatment. While a significant improvement in VAS scores was observed in both treatment groups compared to the control group, the difference between treatment groups was found to be significant. In conclusion, Memantine (NMDA receptor antagonist) treatment provides an improvement in the treatment of neuropathic pain in diabetic polyneuropathy .
Flavonoids, which many positive effects on human health were determined, have antioxidant, anti-inflammatory, cholesterol lowering, antibacterial, antihyperglycemic, and antiallergic features. It may be called P factor or P vitamin considering its capillary circulation regulating blood pressure lowering effects. The main one of these flavonoids is proantocianidin found in grape seeds. The grape seed extract was given at the dose of 25 mg/kg and 50 mg/kg by oral gavage for 6 weeks in a study in which diabetes was induced in BALB/C mice. The pain threshold was measured using the Hot Plate Test, a thermal pain model, in these animals at the end of second and sixth weeks. When the sciatic nerve and abdominal aorta tissue from animals were examined histologically at the end of the study, hot plate measurements of the groups received grape seed extract and the measurements between other groups were considered significant. UCE (was seen to decrease damage in diabetes-induced micro and macrovascular complications in histological evaluations .
5.1. DPP-4 inhibitors
Dipeptidyl peptidase-4 incretin hormones are secreted from intestinal endocrine cells. It plays a key role in regulating blood glucose levels by stimulating glucose-dependent insulin secretion, decreasing glucagon secretion, and slowing gastric emptying. DPP-4 inactivates GLP-1 and glucose-dependent insulin tropical polypeptides (GIP) in vivo by destroying them. These peptides are short lived in the circulation because they are destroyed by DPP-4. Alogliptin is a DPP-4 inhibitor. The effects of this medication on vascular and neural complications were evaluated in male Sprague–Dawley rats with STZ-induced diabetes. Alogliptin was observed to regulate MNCV and thermal response latency after a 12-week treatment. No improvement in the decrease in intraepidermal nerve fiber density was detected while SNCVs of the mice were regulating. PKF 275-055, new analog of Vildagliptin, was given to STZ-induced diabetic rats in the study of Bianchi et al., and it was found that it displays an anabolic effect by preventing changes in nociceptive threshold, Na–K ATPase, and NCP. DPP-4 inhibitors were stated to prevent some neural and vascular complications associated with diabetes in the studies conducted [9,31,32,33].
5.2. Cannabinoid CB1 receptor antagonists
Nabilone is a CB1 predominant receptor agonist. It was used in neuropathic pain based on the anecdotal evidence and uncontrolled case series . Pain reduction has been reported to occur in 30% of the patients in a single center, randomized, double-blind, placebo-controlled, flexible 5-week study conducted by administering a dose ranges from 1 to 4 mg per day or placebo. DPN symptoms disappeared, and their impaired sleep and standard of living were improved in those received flexible dose. Nabilone is a well tolerated and successful adjuvant in patients with DPN. Rimonabant is a CB1 receptor antagonist; it accelerates skin blood flow and decreases TNF-α level in diabetic rats. It was stated that Rimonabant may be beneficial in the treatment of DPN due to its micro and macro blood vessel protection and inflammatory effects [9,34,35].
5.3. Natural products
Satılmış, I. Diyabetes Mellitusda İnsülin Tedavisinin Periferik Sinir Sistemine Etkileri: Klinik ve Elektrofozyolojik Değerlendirme, Sağlık Bakanlığı Şişli Etfal Eğitim ve Araştırma Hastanesi 2. Nöroloji Kliniği, Uzmanlık Tezi, İstanbul, 2007.
Terzi M, Cengiz N, Onar MK. Diyabetik Nöropati. OMÜ Tıp Dergisi. 2004;21(1):39–49.
Jennifer AT, James BD. The Spectrum of Diabetic Neuropathies. Phys Med Rehabil Clin N Am. 2008;19(1):1–26.
Habib AA, Brannapan 3 TH. Therapeutic Strategies for Diabetic Neuropathy, Springer Science + Business media, LLC, 2010.
Vinik AI, Erbas T, Casellini CM, Diabetic Cardiac Autonomic Neuropathy, İnflammation and Cardiovascular Disease, J Diabet. 2013;4(1):4-18.
Vinik AI, Maser RE, Ziegler D. Autonomic İmbalance; Prophet of Doom or Scope for Hope? Diabet Med. 2011;28:643–651.
Şahin C. Diyabetik Sıçanlarda Meydana Gelen Sinir Yaralanmaları Onarımında Perinörotomi Uygulamasının Etkisi, Genelkurmay Başkanlığı Gata Haydarpaşa Eğitim Hastanesi Plastik VE Rekonstrüktif Cerrahi Servis Şefliği, Tıpta Uzmanlık Tezi, 2011.
Nouri MN, Ahmed A, Bril V, Orszag A, Ng E, Nwe P, Perkins BA. Diabetic Neuropathy and Axon Reflex Mediated Neurogenic Vasodilatation in Type 1 Diabetes. PLoS ONE 2012;7(4):e34807. doi:10.371/journal.Done.0034807
Sing R, Kishore L, Kaur N. Diabetic Peripheral Neuropathy: Current Perspective and Future Directions. Pharmacolog Res. 2014;80:21–35.
Singh R, Barden A, Mori T, Beilin L. Advanced Glycation End-Products: A Review. Diabetologia. 2001;44(2):129–146.
Kılıç E, Fisetin ve Alfa Lipoik Asidin Ağrılı Diyabetik Nöropati Üzerine Etkilerinin İncelenmesi: Fare Modelinde İn Vivo Davranışsal Çalışma, Ondokuz Mayıs Üniversitesi Tıp Fakültesi İç Hastalıkları Anabilim Dalı Endokrinoloji Bilim Dalı, Uzmanlık Tezi, Samsun, 2013.
Erbaş O. Diyabetik Nöropatili Sıçanlarda Oksitosin,Mesna ve Glutamin’ in, Nöropati Üzerine Etkilerinin Elektrofizyolojik (EMG) ve Histolojik Yöntemlerle Araştırılması, Ege Üniversitesi Tıp Fakültesi Fizyoloji Anabilim Dalı Tıpta Uzmanlık Tezi, İzmir, 2012.
Cengizhan E. Diyabetik Hastalarda Mıchıgan Nöropati Tarama Enstrümanı Bulgularının Elektrofizyolojik Bulgularla Bağıntısı, Süleyman Demirel Üniversitesi Tıp Fakültesi Nöroloji Anabilim Dalı Tıpta Uzmanlık Tezi, Isparta, 2010.
Kiernan MC.Emergence of a Predicitive Clinical Biomarker for Diabetic Neuropathy. Diabetes 2012;61:1346-1347.
Ağırman M. Diyabetik Hastalarda Polinöropati ve Karpal Tünel Sendromu Tanısında Ultrasonun Elektrofizyolojiye Göre Tanıdaki Yerinin Araştırılması, Marmara Üniversitesi Tıp Fakültesi Fiziksel Tıp ve Rehabilitasyon Anabilim Dalı, Uzmanlık Tezi, İstanbul, 2012.
Dam PSV, Cotter MA, Bravenboer B, Cameron NE. Pathogenesis of Diabetic Neuropathy: Focus on Neurovascular Mechanisms. Eur J Pharmacol. 2013;719:180–186.
Sharma SS, Kumar A, Arora M, Kaundal RK. Neuroprotective Potential of Combination of Resveratrol and 4-Amino 1,8 Naphthalimide in Experimental Diabetic Neuropathy: Focus on Functional, Sensorimotor and Biochemical Changes. Free Radic Res. 2009;43:400–408.
Li F, Obrosova IG, Abatan O, Tian D, Larkin D, Stuenkel EL, et al. Taurine Replacement Attenuates Hyperalgesia and Abnormal Calcium Signaling in Sensoryneurons of STZ-D Rats. Am J Physiol Endocrinol Metab 2005;288:E29–E36.
Hotta N, Toyota T, Matsuoka K, Shigeta Y, Kikkawa R, Kaneko T, et al. Clin-ical efficacy of fidarestat, a novel aldose reductase inhibitor, for diabeticperipheral neuropathy: a 52-week multicenter placebo-controlled double-blind parallel group study. Diabet Care 2001;24:1776–82.
Hotta N, Akanuma Y, Kawamori R, Matsuoka K, Oka Y, Shichiri M, et al. Long-Term Clinical Effects of Epalrestat, an Aldose Reductase İnhibitor, on Diabetic Peripheral Neuropathy: The 3-Year, Multicenter, Comparativealdose Reductase İnhibitor-Diabetes Complications Trial. Diabet Care. 2006;29:1538–1544.
Said G. Focal and Multifocal Diabetic Neuropathies. Arq Neuropsiquiatr. 2007;65(4):1272–1278.
Tahrani AA, Aswith T, Stevens MJ. Emerging Drugs for Diabetic Neuropathy. Expert Opin Emerg Drugs 2010;15(4):661–683.
Rowbotham MC, Goli V, Kunz NR, Lei D. Venlafaxine Extended Release in the Treatment of Painful Diabetic Neuropathy: A Double-Blind, Placebo-Controlled Study. Pain 2004;110:697–706.
Sultan A, Gaskell H, Derry S, Moore RA. Duloxetine for Painful Diabetic Neuropathy and Fibromyalgia Pain: Systematic Review of Randomised Trials. BMC Neurol. 2008;8:29.
Vinik AI, Nevoret ML, Casellini C, Parson H. Diabetic Neuropathy. Endocrinal Metab Clin N Am 2013;42:747–787.
Raskin P, Donofrio PD, Rosenthal NR, et al. Topiramate vs Placebo in Painful Diabetic Neuropathy: Analgesic and Metabolic Effects. Neurol. 2004;63:865–873.
Mason L, Moore RA, Derry S, et al. Systematic Review of Topical Capsaicin for the Treatment of Chronic Pain. BMJ 2004;328:991.
Bennett GJ, Doyle T, Salvemini D. Mitotoxicity in Distal Symmetrical Sensory Peripheral Neuropathies. Nat Rev Neurol. 2014;10:326–336.
Gökçe F. Diyabetik Polinöropatik Hastalarda Memantinin Ağrı Üzerine Etkinliği. Orijinal Araştırma 2014;36:474–478.
Yurt A. Streptozosinle Diyabet Oluşturulan Farelerde Üzüm Çekġrdeği Ektresinin Nöropatik Ağrı Üzerine Etkiler, İnönü Üniversitesi Sağlık Bilimleri Enstitüsü Yüksek Lisans Tezi, Malatya, 2015.
Neumiller JJ, Wood L, Campbell RK. Dipeptidyl Peptidase-4 İnhibitors for the Treatment of Type 2 Diabetes Mellitus. Pharmacother. 2010;30:463–484.
Lam S, Saad M. Saxagliptin: A New Dipeptidyl Peptidase-4 İnhibitor for Type 2 diabetes. Cardiol Rev. 2010;18:213–217.
Davidson EP, Coppey LJ, Dake B, Yorek MA. Treatment of Streptozotocin-İnduced Diabetic Rats with Alogliptin: Effect on Vascular and Neuralcomplications. Exp Diabet Res. 2011:8104–8169.
Toth C, Mawani S, Brady S, Chan C, Liu C, Mehina E, et al. Anenriched-Enrolment, Randomized Withdrawal, Flexible-Dose, Double-Blindplacebo-Controlled, Parallel Assignment Efficacy Study of Nabilone As Adjuvant in the Treatment of Diabetic Peripheral Neuropathic Pain. Pain. 2012;153:2073–2082.
Liu WJ, Jin HY, Park JH, Baek HS, Park TS. Effect of Rimonabant, the Cannabinoid CB1 Receptor Antagonist, on Peripheral Nerve in Streptozotocin-İnduced Diabetic Rat. Eur J Pharmacol. 2010;637:70–76.