Interactions of Endosulfan and Methoxychlor Involving CYP3A4 and CYP2B6 in Human HepaRG Cells

Abstract

Humans are usually exposed to several pesticides simultaneously; consequently, combined actions between pesticides themselves or between pesticides and other chemicals need to be addressed in the risk assessment. Many pesticides are efficient activators of pregnane X receptor (PXR) and/or constitutive androstane receptor (CAR), two major nuclear receptors that are also activated by other substrates. In the present work, we searched for interactions between endosulfan and methoxychlor, two organochlorine pesticides whose major routes of metabolism involve CAR-and PXR-regulated CYP3A4 and CYP2B6, and whose mechanisms of action in humans remain poorly understood. For this purpose, HepaRG cells were treated with both pesticides separately or in mixture for 24 hours or 2 weeks at concentrations relevant to human exposure levels. In combination they exerted synergistic cytotoxic effects. Whatever the duration of treatment, both compounds increased CYP3A4 and CYP2B6 mRNA levels while differently affecting their corresponding activities. Endosulfan exerted a direct reversible inhibition of CYP3A4 activity that was confirmed in human liver microsomes. By contrast, methoxychlor induced this activity. The effects of the mixture on CYP3A4 activity were equal to the sum of those of each individual compound, suggesting an additive effect of each pesticide. Despite CYP2B6 activity being unchanged and increased with endosulfan and methoxychlor, respectively, no change was observed with their mixture, supporting an antagonistic effect. Altogether, our data suggest that CAR and PXR activators endosulfan and methoxychlor can interact together and with other exogenous substrates in human hepatocytes. Their effects on CYP3A4 and CYP2B6 activities could have important consequences if extrapolated to the in vivo situation.

A cellular model to study drug-induced liver injury in nonalcoholic fatty liver disease: Application to acetaminophen

“…Thus, relevant experimental models are needed to determine which compounds can pose a specific risk in NAFLD and to understand why they are more hepatotoxic in this dysmetabolic context. Since the HepaRG cell line has been shown to be a valuable model to study hepatotoxicity induced by drugs and toxins (Anthérieu et al, 2011; McGill et al, 2011; Savary et al, 2014; Sharanek et al, 2014; Tobwala et al, 2015), a first goal of our study was to determine whether this cell line could also be used as a pertinent model of human NALFD. To this end, HepaRG cells were incubated for one week in different conditions of incubation with stearic acid, oleic acid and insulin.…”

“…In the past few years, the metabolically competent human hepatoma HepaRG cell line has been shown to be a valuable model to study the mechanism of hepatotoxicity induced by drugs and toxicants (Anthérieu et al, 2011; McGill et al, 2011; Savary et al, 2014; Sharanek et al, 2014; Tobwala et al, 2015). Indeed, HepaRG cells express most of the enzymes and transcription factors involved in xenobiotic biotransformation and transport (Andersson et al, 2012; Aninat et al, 2006; Anthérieu et al, 2012).…”

Food safety in Thailand 1: it is safe to eat watermelon and durian in Thailand

“…For example, DDT and fenvalerate are known to induce several human CYP enzymes [50]. An endocrine disrupter pesticide endosulfan has been shown to reversibly inhibit human CYP3A4 enzyme [56]. Dimethoate pretreatment in rats caused an increase in the activities of glutathione peroxidase and glutathione reductase, as compared to the control animals [57].…”

Nuclear receptors and nonalcoholic fatty liver disease

“…The well characterized endogenous ligands of CAR include bilirubin, bile acids, and androstanes [129–132]. Exogenous CAR activators include medications (such as phenobarbital), environmental pollutants (PCBs) and pesticides/pesticide metabolites (methoxychlor, dichlorodiphenyldichloroethylene — DDE), and pyrene [84,133–135]. CAR ligands are species-specific which can be attributed to limited conservation of CAR’s ligand binding domain.…”