Induction of cytochrome P450 enzymes and over-generation of oxygen radicals in beta-carotene supplemented rats

Effects of beta-carotene (OCT) on microsomal CYP-linked monooxygenases were investigated using both the regio- and stereo-selective hydroxylation of testosterone (as multi-biomarker) and highly specific substrates as probes of various isoenzymes. CYP-catalyzed reactions were studied in the liver, kidney, lung and intestine of Sprague-Dawley rats of both sexes supplemented with 250 or 500 mg/kg body wt OCT (per os) in a single or repeated (daily for 5 days) fashion. Generalized boosting effects (2-15-fold increases) were observed in the various tissues for carcinogen metabolizing enzymes associated with CYP1A1/2, CYP3A1/2, CYP2E1, CYP2B1/2 and CYP2C11. Induction of the most affected CYPs was corroborated by western blot linked to densitometric analyses. Measurement of reactive oxygen species (ROS) produced by subcellular preparations from either control or OCT supplemented rats was performed by EPR detection of the nitroxide radical yielded by the reaction with ROS of the hydroxylamine spin probe bis(1-hydroxy-2,2,6,6-tetramethyl-4-piperidinyl)decandioate. Marked ROS over-generation associated with CYP induction (up to 33-fold increase in the liver) was recorded in the various organs (liver > lung > intestine > kidney). CYP and ROS induction are substantially in keeping with the concentration of OCT accumulated in the various tissues, the liver being the most affected organ. These findings are consistent with the concept that OCT is a pro-oxidant and potentially cocarcinogenic pro-vitamin, and may help explain why, in large quantities, it can have harmful effects in humans.