Regulation of paraoxonase 1 (PON1) in PCB 126-exposed male Sprague Dawley rats
Highlights
► PCB126 is a potent AhR agonist and reported to increase oxidative stress. ► PON1 is an important serum antioxidant, produced in the liver and attached to HDL. ► In rats PCB126 increased hepatic PON1 mRNA and hepatic and serum PON1 activity. ► No changes in lipid peroxides (TBARS) or total serum antioxidant capacity were seen. ► Increased PON1 activity may ameliorate oxidative stress produced by PCB126.
Introduction
Polychlorinated biphenyls (PCBs) are persistent organic pollutants and ubiquitous in the environment even though their commercial production has been banned for decades. Most of the 209 individual PCB congeners are highly resistant to biotransformation and bioaccumulate. Certain congeners with non-ortho or mono-ortho chlorine substitution are called “dioxin-like PCBs” because their binding to the arylhydrocarbon receptor (AhR) and biochemical and toxic activities are similar to those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (Bandiera et al., 1982, Hestermann et al., 2000). PCB 126 is the most potent AhR agonist among all PCB congeners tested (Bandiera et al., 1982) and has a toxic equivalency factor (TEF) of 0.1 compared to TCDD, which qualifies it as the most toxic PCB in this family (Van den Berg et al., 2006). Like TCDD, PCB 126 significantly alters the expression of numerous genes and increases enzyme activities, particularly CYP 1A1/2 (Kopec et al., 2010). PCBs also increase intracellular oxidative stress which has been associated with a variety of disease processes, including carcinogenesis and cardiovascular damage (Hennig et al., 2002, Hennig et al., 2005, Ludewig et al., 2008). Several studies have shown that the dioxin-like PCBs (e.g., PCB77 and PCB 126) induce ROS and cause lipid oxidation in endothelial cells which is associated with atherosclerosis (Hassoun et al., 2002, Choi et al., 2010).
Paraoxonase 1 (PON1), a member of a three gene family which includes PON2 and PON3, is a calcium-dependent hydrolase with substrate specificity towards esters, phosphotriester lactones, carbonates and other compounds (Costa et al., 2005a, Costa et al., 2005b). PON1 is primarily synthesized in the liver and secreted into the blood as a major high density lipoprotein (HDL)-associated enzyme (La Du et al., 1999). Besides chemoprotection through detoxification of organophosphorus (OP) pesticides, it displays preventive properties against cardiovascular disease, mainly through removal of oxidized lipids in low density lipoproteins and cell membranes (Furlong et al., 2005, Furlong et al., 2010).
Recently, XRE (xenobiotic response element)-like sequences were described in the promoter region of PON1 and these sequences were identified as possible binding sites for the activated AhR (Gouedard et al., 2004). In this publication dietary polyphenols and 3-methylcholanthrene (3-MC) were shown to induce PON1 through the AhR-dependent pathway. We therefore hypothesized that PCB 126, as an AhR agonist, may influence PON1 expression and thereby hepatic and serum PON1 activities, a possible protective mechanism against PCB-induced ROS. Here we show that PCB 126 increased hepatic PON1 expression and liver and serum PON1 activity as well as serum HDL levels and hepatic CYP1A1 and AhR transcription in male Sprague Dawley rats in vivo, while no consistent change in lipid peroxides (TBARS) and serum total antioxidant activity was observed.
Section snippets
Chemicals and reagents
PCB 126 was synthesized and purified using a modified Suzuki-coupling method of 3,4,5-trichlorobromobenzene with 3,4-dichlorophenyl boronic acid utilizing a palladium-catalyzed cross coupling reaction as previously reported (Luthe et al., 2009). All reagents were obtained from Fisher Scientific (Pittsburgh, PA) and were the highest purity available, if not stated otherwise.
Animals and treatment protocol
Male Sprague-Dawley rats (75–100 g) from Harlan Laboratories Inc. (Indianapolis, IN) were housed in a controlled environment
Biometrical parameters
In the dose–response study (Table 1, upper half) the growth of rats treated with the high dose (5 μmol/kg) of PCB 126 was significantly decreased (P < 0.05) and the final body weights were decreased by 31% (P < 0.05). Liver weights were significantly increased by the lower dose of 1 μmol/kg PCB 126 (46%, P < 0.05), and both doses significantly increased the relative liver weight (51% and 54%, respectively). In the time–response study (Table 1, lower half) weight gain of PCB 126-treated rats was
Discussion
Recently, researchers reported that PCB 126, the most potent dioxin-like PCB congener and a conventional food chain persistent organic pollutant, was found in Chicago air (Zhao et al., 2010). This suggests a new exposure source besides the food chain. PCB 126 was shown to induce oxidative stress and cause lipid peroxidation (Hassoun et al., 2002). PON1 is believed to protect against lipid peroxidation and to lower the risk of developing coronary artery disease and atherosclerosis (Shih et al.,
Funding
This study is supported by NIEHS P42 ES013661 and DOD DAMD17-02-1-0241.
Conflicts of interest
The authors declare that there are no conflicts of interest.
Acknowledgement
The authors would like to thank the members of the Robertson and Ludewig laboratories for help with animal treatments and necropsy.
References (46)
- et al.
Binding of polychlorinated biphenyls classified as either phenobarbitone-, 3-methylcholanthrene- or mixed-type inducers to cytosolic Ah receptor
Chem. Biol. Interact.
(1982) - et al.
Differential effect of antioxidant treatment on plasma and tissue paraoxonase activity in hyperleptinemic rats
Pharmacol. Res.
(2005) - et al.
The ferric reducing ability of plasma (FRAP) as a measure of antioxidant power: the FRAP assay
Anal. Biochem.
(1996) - et al.
Quercetin blocks caveolae-dependent pro-inflammatory responses induced by co-planar PCBs
Environ. Int.
(2010) - et al.
Modulation of paraoxonase (PON1) activity
Biochem. Pharmacol.
(2005) - et al.
Serum paraoxonase undergoes inhibition and proteolysis during experimental acute pancreatitis
J. Gastrointest. Surg.
(2008) - et al.
Role of paraoxonase (PON1) status in pesticide sensitivity: genetic and temporal determinants
Neurotoxicology
(2005) - et al.
Human PON1 a biomarker of risk of disease and exposure
Chem. Biol. Interact.
(2010) - et al.
Proinflammatory properties of coplanar PCBs: in vitro and in vivo evidence
Toxicol. Appl. Pharmacol.
(2002) - et al.
Relative contributions of affinity and intrinsic efficacy to aryl hydrocarbon receptor ligand potency
Toxicol. Appl. Pharmacol.
(2000)
Induction of paraoxonase 1 and apolipoprotein A-I gene expression by aspirin
J. Lipid Res.
On the physiological role(s) of the paraoxonases
Chem. Biol. Interact.
Acute toxicity of 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126) in male Sprague-Dawley rats: effects on hepatic oxidative stress, glutathione and metals status
Environ. Int.
Metabolic activation of PCBs to carcinogens in vivo – a review
Environ. Toxicol. Pharmacol.
Monofluorinated analogues of polychlorinated biphenyls (F-PCBs): synthesis using the Suzuki-coupling, characterization, specific properties and intended use
Chemosphere
Estrogenic effect of dioxin-like aryl hydrocarbon receptor (AhR) agonist (PCB congener 126) in salmon hepatocytes
Mar. Environ. Res.
Apolipoprotein A-I gene expression is upregulated by polychlorinated biphenyls in rat liver
J. Nutr. Biochem.
Assay for lipid peroxides in animal tissues by thiobarbituric acid reaction
Anal. Biochem.
Effect of dietary fiber on hypercholesterolemia induced by dietary PCB or cholesterol in rats
J. Nutr.
Immunohistochemical evidence for the expression and induction of paraoxonase in rat liver, kidney, lung and brain tissue. Implications for its physiological role
Chem. Biol. Interact.
Aryl hydrocarbon receptor-independent activation of estrogen receptor-dependent transcription by 3-methylcholanthrene
Toxicol. Appl. Pharmacol.
7H-Dibenzo[c,g]carbazole and 5,9-dimethyldibenzo[c,g]carbazole exert multiple toxic events contributing to tumor promotion in rat liver epithelial ‘stem-like’ cells
Mutat. Res.
Development of a synthetic PCB mixture resembling the average polychlorinated biphenyl profile in Chicago air
Environ. Int.
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2017, Chemico-Biological InteractionsCitation Excerpt :The polychlorinated biphenol 126 (PCB 126), the most potent dioxin-like PCB congener and an AhR ligand, increases levels of PON1 mRNA in the liver and serum of Sprague- Dawley rats [46–48], an effect which is modulated by hepatic selenium (Se), selenium-dependent glutathione peroxidase and glutathione (GSH). To evaluate possible interactions with PON1, Shen et al. [46–48] analyzed the influence of varying levels of dietary selenium (Se) and N-acetylcysteine (NAC), a scavenger of reactive oxygen species (ROS) and precursor for GSH synthesis, in the absence and presence of PCB 126 in male Sprague- Dawley rats. These modulators significantly increased liver PON1 mRNA and protein levels, along with activity in serum after exposure to PCB 126 and 3-methylcholanthrene (3-MC) [46–48].
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