Effects of trivalent chromium on hepatic CYP-linked monooxygenases in laying hens.

Chromium is an essential nutrient required for the metabolism of carbohydrates and lipids in humans and many animal species. We evaluated whether feeding laying hens with high levels of different chemical forms of trivalent chromium may affect hepatic metabolizing cytochrome P-450 (CYP)-linked enzymes. Modulation of CYP-dependent monooxygenases (which play a pivotal role in the endogenous metabolism) by Cr(III) was tested using either specific substrates as probes of different CYPs or testosterone as a multi-bioprobe. The CYP-supported oxidases were studied in liver microsomes from laying hens fed with diet supplemented with either 25 or 50 ppm chromium chloride as a yeast or as aminoniacinate. Although at 25 ppm no appreciable effects were observed, at 50 ppm a general inactivation of the recorded monooxygenases (ranging from 34% loss for ethoxycoumarin O-deethylase with chromium chloride to 85% loss for O-deethylation of ethoxyresorufin with either chromium yeast or aminoniacinate) were achieved in the supplemented groups vs controls. The only exception was the O-dealkylation of pentoxyresorufin, which was significantly boosted by both chromium yeast (up to 65% increase) and chromium aminoniacinate (up to 141%). Measurements of the regio- and stereoselective hydroxylation of testosterone used as a multi-bioprobe corroborated the inactivating properties of Cr(III) at the higher dose. Taken as a whole, these findings seem to indicate that high levels of Cr(III) supplementation can substantially impair CYP-catalysed drug metabolism in laying hens.

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

Effects of beta-carotene (betaCT) on microsomal CYP-linked monooxygenases were investigated using both the regio- and stereo-selective hydroxylation of testosterone (as multibiomarker) 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 betaCT (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 betaCT 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 betaCT accumulated in the various tissues, the liver being the most affected organ. These findings are consistent with the concept that betaCT is a pro-oxidant and potentially co-carcinogenic pro-vitamin, and may help explain why, in large quantities, it can have harmful effects in humans.