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

Abstract

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.

Targeting xenobiotic receptors PXR and CAR in human diseases

“…Recent studies showed that treatment of rifampicin causes toxicity and liver injury [20]. Several PXR antagonists, such as ET-743, ketoconazole, FLB-12, sulforaphane, A-792611, polychlorinated biphenyls, coumestrol, aryl sulfonamides and allyl isothiocyanate, have been reported [21–29]. CAR antagonists or inverse agonists such as meclizine, clotrimazole and PK11195 have also been discovered [30,31].…”

Small-molecule modulators of the constitutive androstane receptor

“…In these reports, the main focus was the inhibition of PXR, and that of CAR was studied only for comparison purposes. These reported compounds include the quinoline alkaloid camptothecin [38], the antihyperglycemic agent metformin [39], the natural compound allyl isothiocyanate [40], and the antifungal ketoconazole [41]. We note that most known inhibitors of hCAR are also PXR activators, confounding the use of these molecules in instances of both receptors being present and functional.…”

Utilizing Mechanistic Biomarkers in Treating Paracetamol Hepatotoxicity

“…The enzymes that convert PCM to NAPQI are controlled by hepatic nuclear receptors such as the constitutive androstane receptor (CAR) and the pregnane X receptor (PXR). In vitro studies have demonstrated that blocking CAR/PXR activity renders hepatocytes more resilient to otherwise toxic PCM levels . Risks of this approach are the concurrent shutdown glutathione synthesis from NAC.…”