AhR and PPARα:: antagonistic effects on CYP2B and CYP3A, and additive inhibitory effects on CYP2C11

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates a spectrum of toxic and biological effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin ( TCDD) and related compounds. The peroxisome proliferator-activated receptor alpha (PPAR alpha) is a member of the nuclear receptor super-family of ligand-activated transcription factors and it functions as an obligate heterodimer with retinoid X-receptor alpha RXR alpha. The aim was to investigate whether the negative cross-talk recently proposed by the present authors between AhR and PPAR alpha on CYP4A and CYP1A has any impact on other cytochrome P450 enzymes. Treatment of male Wistar rats with a PPAR alpha ligand clofibric acid (CA) induced CYP2B1/2 and CYP3A proteins, activities, and the mRNA expression of CYP2B1, CYP2B2, CYP3A1 and CYP3A2, and suppressed CYP2C11 protein, activities and mRNA expression. AhR ligand Sudan III (S.III) treatment decreased basal and CA-induced CYP2B, CYP3A and CYP2C11 protein, activities and mRNA expression. To the best of the authors' knowledge, this is the first study showing the presence of mutual effects of AhR and PPAR alpha on CYP2B and CYP3A and an additive inhibitory effect on CYP2C11 in the livers of male rats.