Allyl isothiocyanate (AITC) inhibits pregnane X receptor (PXR) and constitutive androstane receptor (CAR) activation and protects against acetaminophen- and amiodarone-induced cytotoxicity.

Antagonizing the action of the pregnane X receptor (PXR) may have important clinical implications for preventing inducer-drug interactions and improving therapeutic efficacy. We identified a widely distributed isothiocyanate, allyl isothiocyanate (AITC), which acts as an effective antagonist of the nuclear receptor pregnane X receptor (PXR, NR1I2) and constitutive androstane receptor (CAR, NR1I3). HepG2 cells were used to assay reporter function, mRNA levels, and protein expression. Catalytic activities of the PXR and CAR target genes, CYP3A4 and CYP2B6, respectively, were also assessed in differentiated HepaRG cells. Protective effects of AITC on rifampin-induced cytotoxicity were observed, and transient transfection assays showed that AITC was able to effectively attenuate the agonist effects of rifampin and CITCO on human PXR and CAR activity, respectively. AITC-mediated reduction in the transcriptional activity of PXR and CAR correlated well with the suppression of CYP3A4 and CYP2B6 expression in HepG2 cells, which reflected the reduced catalytic activities of both of these genes following AITC treatment in differentiated HepaRG cells. Furthermore, AITC disrupts the co-regulations of PXR with several important co-regulators. Furthermore, the antagonist effect of AITC against PXR was found in HepaRG cells upon addition of acetaminophen (APAP) and amiodarone, indicating that AITC protects cells from drug-induced cytotoxicity. Taken together, our results show that AITC inhibits the transactivation effects of PXR and CAR and reduces the expression and function of CYP3A4 and CYP2B6. Additionally, AITC reversed the cytotoxic effects of APAP and amiodarone induced by PXR ligand. Results from this study suggest that AITC could be a powerful agent for reducing potentially dangerous interactions between transcriptional inducers of CYP enzymes and therapeutic drugs.

Inhibition of cytochrome P450 2C9 expression and activity in vitro by allyl isothiocyanate.

The growing interest in the use of natural herbal products and dietary supplements to treat and prevent diseases raises the question of medicinal drug safety. Allyl isothiocyanate, a hydrolysis product of a glucosinolate, sinigrin, has multiple beneficial properties, and based on this fact, allyl isothiocyanate-containing dietary supplements have been developed. To date, no studies of the effects of this compound on the cytochrome P450 2C9 have been reported. In this study, we found that allyl isothiocyanate reduced catalytic activity, messenger ribonucleic acid, and protein expression of cytochrome P450 2C9 in HepaRG cells. An investigation of the transcriptional activity of the pregnane X receptor and the constitutive androstane receptor revealed that allyl isothiocyanate disrupted the transcriptional coregulation effects of the pregnane X receptor/constitutive androstane receptor with several important coregulators and interfered with the assembly of transcriptional complexes of the cytochrome P450 2C9 pregnane X receptor/constitutive androstane receptor-response element. The decrease of cytochrome P450 2C9 expression and activity mediated by allyl isothiocyanate suggested that this agent could alter the metabolism of drugs metabolized by cytochrome P450 2C9. This may cause food/dietary supplement-drug interactions or alter the therapeutic effects, and even the toxicity of drugs coadministered with allyl isothiocyanate. Since the consumption of allyl isothiocyanate-containing food/dietary supplements continues to increase, it is important to predict and ultimately avoid interactions with concomitant drugs. It is required that these possible pharmacokinetic interactions be characterized and the recommendations available to patients and healthcare professionals be improved.