Concentration-dependent effects of the nerve agents cyclosarin and VX on cytochrome P450 in a HepaRG cell-based liver...

The exposure to highly toxic organophosphorus (OP) compounds, including pesticides and nerve agents, is an ongoing medical challenge. OP can induce the uncontrolled overstimulation of the cholinergic system through inhibition of the enzyme acetylcholinesterase (AChE). The cytochrome P450 (CYP) enzymes in the liver play a predominant role in the metabolism of xenobiotics and are involved in the oxidative biotransformation of most clinical drugs. Previous research concerning the interactions between OP and CYP has usually focused on organothiophosphate pesticides that require CYP-mediated bioactivation to their active oxon metabolites to act as inhibitors of AChE. Since there has been little data available concerning the effect of nerve agents on CYP, we performed a study with cyclosarin (GF) and O-ethyl-S-[2-(diisopropylamino)-ethyl]-methylphosphonothioate (VX) by using a well-established, metabolically competent in vitro liver model (HepaRG cells). The inhibitory effect of the nerve agents GF and VX on the CYP3A4 enzyme was investigated showing a low CYP3A4 inhibitory potency. Changes on the transcription level of CYP and associated oxygenases were evaluated by quantitative reverse transcription polymerase chain reaction (qRT-PCR) using the two nerve agent concentrations 250 nM and 250 μM. In conclusion, the results demonstrated various effects on oxygenase-associated genes in dependence of the concentration and the structure of the nerve agent. Such information might be of relevance for potential interactions between nerve agents, antidotes or other clinically administered drugs, which are metabolized by the affected CYP, for example, for the therapy with benzodiazepines, that are used for the symptomatic treatment of OP poisoning and that require CYP-mediated biotransformation.