CONSTITUTIVE ANDROSTANE RECEPTOR DEPENDENT AND INDEPENDENT MODULATION OF CYP3A2, CYP1A2 BY PHENOBARBITAL AND FIBRATE IN RATS’ LIVER

Cytochrome P450 enzymes, CYP3A and CYP1A are major drug metabolizing enzymes in the liver. CYP3A enzymes have a major role in the metabolism of 30-40% of all used drugs. CYP1A2 is a key enzyme having an important role in the metabolic clearance of 5% of currently marketed drugs. CYP1A2 participates in the metabolic activation of chemical mutagens in cooked food, therefore its activity is suspected to be on e of the possible risk factors determining the carcinoge nicity of heterocyclic amines in human beings. In a previous report, we have reported the induction of CYP3A2 and the inhibition of CYP1A2 by Fibrate (CFA) and proved CYP1A2 inhibition to be PPAR α-dependent. CYP3A2 and CYP1A2 have been reported to be induced in the liver by Phenobarbital (PB) wh ile Fibrates was reported to induce CYP3A2. However the exact mechanism of the induction of CYP3A2 by CFA and PB and induction of CYP1A2 by PB has not been clarified yet whether it is through Constituti ve Androstane Receptor (CAR) or other receptor as PPAR α or Pregnane X Receptor (PXR). We treated Wistar female rats (with normal expression of CAR protein) and Wistar femal Kyoto rats (with low expr ession of CAR protein) with PB and Clofibric Acid (CFA). PB caused a high CYP3A2 induction in Wistar female rats and a low induction in (WKY) indicating that PB induced CYP3A2 in a CAR-dependent manner. Interestingly, PB treatment induced CYP1A2 in Wistar female rats and failed to induce it in (WKY) indicating that the induction of CYP1A2 by PB to b e CAR-dependent. Moreover CFA induced CYP3A2 protein similarly in both rat strains indicating that CYP3A2 induction by Fibrates is CAR-independent and most probably to be PXR or PPAR α-dependent. For the best of our knowledge this is the first rep ort that shows a clear evidence of the CAR-dependent induction of CYP1A2 and CYP3A2 by PB and the CAR-independent induction of CYP3A2 by fibrates.