Paraoxonase 1 in Cattle Health and Disease

Abstract

Paraoxonase is a family of enzymes with diverse biological functions. This study investigates the role and effects of the paraoxonase enzyme, particularly in relation to cattle health and disease. The findings reveal that the paraoxonase enzyme mitigates oxidative stress, regulates the immune system, preserves liver function, and exerts other biological effects in cattle. Moreover, certain genetic variations associated with the paraoxonase enzyme may be linked to health issues, such as cattle diseases. Therefore, further research aimed at comprehending the relationship between the paraoxonase enzyme and cattle health may assist in the development of novel treatment and prevention strategies in future cattle breeding and veterinary applications.

1. Introduction

The Paraoxonase (PON) molecule comprises three distinct subtypes of enzymes: PON1, PON2, and PON3. PON1 is the most extensively studied subtype in humans and is typically the focus of research [1, 2]. The enzyme Paraoxonase 1 (PON1) was first discovered as an organophosphate pesticide-hydrolyzing enzyme in mammalian tissues by Mazur in the 1940s [3]. In 1953, Aldridge identified it as an α-esterase enzyme due to its ability to hydrolyze diethyl p-nitrophenyl phosphate [4]. Subsequently, PON1 was classified as an “aryl dialkyl phosphatase” by the International Union of Biochemistry and Molecular Biology Enzyme Commission owing to its ability to hydrolyze an aryl-dialkyl phosphate into a dialkyl phosphate and an aryl alcohol [5]. Further investigations have revealed that PON1 also functions as a lactonase and an arylesterase [6]. Moreover, PON1 has been shown to exhibit peroxidase-like activity by reducing H₂O₂ produced under oxidative stress conditions and converting lipid hydroperoxides in oxidized high-density lipoprotein (HDL) to hydroxides [7, 8].

PON1 is considered an antioxidant enzyme and is secreted by the liver. It is responsible for hydrolyzing organophosphate pesticides and neurotoxic compounds in the body [9, 10]. Additionally, PON1 has been reported to increase macrophages associated with cholesterol (CHOL) efflux, prevent protein modification by breaking down homocysteine thiolactone, and stabilize free radicals, thereby preserving membrane integrity [11].

PON1 exhibits genetic polymorphisms, with multiple alleles present in humans. As a result, individuals with different genetic variations may exhibit varying levels of activity. These variations play a significant role in many conditions believed to be associated with PON1 and disease risk [12].

Paraoxonase is also considered a negative acute phase reactant protein, which means its levels decrease during inflammation and may be a risk factor for inflammatory and infectious diseases [13, 14, 15, 16].

In cattle, we believe that research on paraoxonase enzyme activity is still insufficient. Therefore, the objective of this chapter is to provide an overview of the current research on paraoxonase enzyme in cattle health and disease.

2. General characteristics and structure of Paraoxonase 1

The PON1 protein consists of approximately 355 amino acids and is composed of two distinct regions: the N-terminal and the C-terminal. The N-terminal region of the protein binds a cofactor copper ion, which is essential for PON1’s catalytic activity. The C-terminal region, on the other hand, aids in substrate binding [17]. The N-terminal region also contains a hydrophobic signal sequence necessary for binding the enzyme with HDL [5]. The protein contains a central tunnel that houses two Ca⁺² ions, with one ion necessary for catalytic activity and the other for protein stability. This central tunnel forms the active site of the enzyme. The hydrophobic nature of PON1’s substrate is attributed to the hydrophobicity of the enzyme’s active site. Among the critical structural features of PON1 are active site amino acids, such as cysteine and histidine, that confer PON1 with the ability to hydrolyze toxic compounds, including organophosphates, which are responsible for PON1’s cellular anti-oxidative damage-reducing properties [8, 18].

3. Association of Paraoxonase 1 with oxidative stress

Oxidative stress arises from an imbalance between the generation of reactive oxygen species (ROS), including free radicals, and the body’s capacity to detoxify and neutralize them. ROS are highly reactive molecules that can harm cells, proteins, and DNA. Accumulation of ROS due to inefficient neutralization can lead to oxidative stress, resulting in cellular damage and contributing to the development of various diseases, such as cancer, cardiovascular disease, and neurodegenerative disorders. Factors contributing to oxidative stress include environmental pollutants, smoking, alcohol consumption, poor diet, and specific medications [19, 20, 21, 22, 23].

Antioxidants are molecules that can prevent or slow down oxidative damage to cells caused by free radicals. Free radicals are unstable molecules that can damage cells and contribute to the development of various diseases, including cancer, cardiovascular diseases, and neurodegenerative disorders. Antioxidants neutralize free radicals by donating an electron, thereby reducing their potential to cause harm. The consumption of antioxidant-rich foods and supplements has been associated with numerous health benefits. Antioxidants can help mitigate ROS and protect against oxidative stress [24, 25, 26, 27, 28].

The PON1 enzyme provides protective effects against cellular oxidative stress by reducing the damage induced by free radicals and other oxidant molecules. Specifically, PON1 hydrolyzes toxic compounds, such as organophosphates, thereby reducing oxidative stress and safeguarding cells [9, 29]. Moreover, PON1 is known to bind to high-density lipoprotein (HDL) in the bloodstream. This binding decreases the risk of atherosclerosis by preventing oxidation of low-density lipoprotein (LDL) or “bad” cholesterol. Decreased PON1 activity can lead to an increase in oxidative stress and an increased risk of atherosclerosis. The antioxidant activity of PON1 is derived from the free sulfhydryl group located on cysteine-284 [30]. It has been noted that the hydrolytic function of PON1 undergoes some degree of inactivation during the prevention of LDL oxidation [7].

PON1 also reduces cholesterol ester hydroperoxides associated with HDL more efficiently than those associated with LDL, likely due to the predominance of PON1 associated with HDL in the body. Thus, PON1 protects HDL against oxidative stress, rather than LDL [31]. The serum PON1 enzyme is found in association with HDL in plasma, and it prevents plasma lipoprotein oxidation [32]. PON1 enzyme is associated with apolipoprotein A1 and apolipoprotein J (clusterin) proteins of HDL [33]. PON1 binds to phospholipids and lipoproteins through the C-terminal hydrophobic termination region [34]. There is a close relationship between circulating PON1 and HDL, and PON1 can only interact with its endogenous substrate and exhibit its biological properties after being released by HDL. In return, PON1 protects HDL from oxidation [35].

PON1 is believed to play a significant role in protecting against oxidative stress by hydrolyzing both H₂O₂ and lipid peroxides, such as cholesteryl linoleate hydroperoxides [36]. As the O-P type ester bond found in paraoxon could also be present in lipoproteins associated with phospholipid peroxides and cholesteryl ester peroxides, the phosphotriesterase property of PON1 may contribute to the protection against oxidative stress [37]. In addition to its protective role against H₂O₂-induced lipid peroxidation, it has been found that PON1 also prevents the accumulation of peroxynitrite (ONOO^-) and oxidized phospholipids [38].

4. Paraoxonase-1 enzyme activity in some cattle diseases and metabolic conditions

Paraoxonase, an endogenous antioxidant produced by liver cells [39], plays a crucial role in protecting lipids, particularly HDL and LDL, from oxidative stress [37]. Paraoxonase is also considered a negative acute phase reactant protein [16]. In cattle with paratuberculosis, knowing the changes in acute-phase proteins will be beneficial for diagnosing and controlling the disease [40]. In a study by Akyüz et al. [41], a study was conducted on cows with paratuberculosis and found that PON1 activity was lower in the diseased animals compared to the control group, likely due to liver dysfunction and hepatocyte destruction. The authors suggested that PON1 activity could be used as a new biomarker for this infection. Similarly, in cows with clinical mastitis, Deveci et al. [42] observed a decrease in PON1 activity and HDL levels, and suggested that PON1 activity could be an antioxidant mediator in mastitis-induced inflammation. In addition, PON1 has been proposed as a potential marker for the detection of subclinical mastitis in dairy cows [43].

In lactating cows, PON1 activity has been found to be significantly higher in heifers during lactation compared to lactating cows [44]. However, the PON1 activity was found to be lower in postpartum and dry periods compared to lactating cows [45, 46], which was suggested to be related to changes in the lipid profile. Moreover, the observed low-serum PON1 activity at the end of pregnancy and early postpartum period in dairy cows was suggested to indicate an oxidative stress/antioxidant imbalance affected by reproductive stress and metabolic adaptation during the transition period [47]. PON1 activity was also found to increase toward the end of the colostrum period in transition period cattle [48].

PON1 activity has also been investigated in relation to fertility in dairy cows. In a study investigating the relationship between pregnancy rates and PON1 activity in dairy cows following synchronization using an intravaginal device protocol for progesterone secretion, the application of an intravaginal progesterone-releasing device was found to affect serum PON1 activity. The study showed a significant difference in PON activity at day 5 of progesterone releasing intravaginal device (PRID) application, which was suggested to be an indicator of fertility [49].

Researchers have also evaluated PON1 activity as a biomarker for fatty liver in dairy cows. They found that serum PON1 activity was lower in cows suffering from hepatic lipidosis and suggested that the addition of serum PON1 activity measurement to the biochemical profile could improve the diagnosis of fatty liver in dairy cows [50]. Future studies should focus on the diagnostic validation of serum PON1 testing for early prediction of fatty liver development and its correlation with hepatic triglyceride content in both healthy and diseased dairy cows. Additionally, the focus on the diagnostic validation of serum PON1 testing for early prediction of fatty liver development in dairy farms could lead to significant clinical impact and greater profitability in the dairy industry.

5. Conclusion

In conclusion, PON1 is an enzyme that plays a crucial role in reducing oxidative stress and safeguarding cells by hydrolyzing toxic compounds, such as organophosphates, in the body. PON1 is also known to bind with HDL, which reduces the risk of atherosclerosis by preventing the oxidation of LDL. Genetic variations in PON1 activity can affect an individual’s risk for various diseases, and decreased PON1 activity may increase oxidative stress and the risk of atherosclerosis. PON1 activity has been investigated in various contexts in cattle, including as a biomarker for infectious diseases and inflammation, fertility, and fatty liver. The findings suggest that PON1 activity could serve as a useful diagnostic tool for detecting and monitoring health issues in cattle. In cattle, the research on PON1 enzyme activity is limited, and further investigation is necessary to understand its role in cattle health and disease.