Anti-Sulphaphenazole polyclonal antibody

1. Cytochrome P450 activities in vivo and in vitro and enzyme induction by phenobarbital, beta-naphthoflavone, isoniazid and triacetyloleandomycin were investigated in the female dwarf goat. In vivo kinetics of antipyrine, sulphadimidine and caffeine were studied separately and as a combination ('cocktail'). After establishing a lack of interaction between these compounds the effects of the inducing agents were investigated. lit vitro, hepatic microsomal enzyme activities and apoprotein levels were determined. 2. In the beta-naphthoflavone treated goat, the microsomal ethoxy-resorufin-O-deethylation rate was markedly increased. beta-naphthoflavone also induced caffeine plasma clearance but did not affect microsomal caffeine 1- and 3-demethylation rates. After phenobarbital treatment, caffeine plasma clearance was also increased. In contrast with beta-naphthoflavone treatment, phenobarbital treatment resulted in an increase of microsomal caffeine 1- and 3-demethylation rates. 3. Goat liver microsomes were able to hydroxylate tolbutamide, predominantly a CYP2C9 activity in man, and debrisoquine, a CYP2D activity in different species. These activities were not affected by either beta-naphthoflavone or phenobarbital. Sulphaphenazole was found to be a more potent inhibitor of tolbutamide hydroxylation than sulphadimethoxine. Quinine was a more potent inhibitor of debrisoquine hydroxylation than was quinidine. 4. As expected, the microsomal aniline-4-hydroxylation rate (CYP2E) was increased after isoniazid treatment. 5. The microsomal testosterone 6 beta-hydroxylation rate (CYP3A) was increased after phenobarbital and triacetyloleandomycin treatment. Antipyrine plasma clearance was also increased after phenobarbital treatment. 6. As cytochrome P450 activities and inducibility in the dwarf goat show many resemblances to those in man, they may be of value as a model for human biotransformation research.

Carboxychroman metabolites of the major dietary tocopherols are excreted in human urine, but the mechanism of their synthesis is unknown. We employed well-characterized inhibitors of specific cytochrome P-450 (CYP) enzymes to determine which form was likely involved in tocopherol side chain oxidation. Ketoconozole (1.0 muM), a potent and selective inhibitor of CYP3A, substantially inhibited metabolism of gamma- and cu-tocopherol in rat primary hepatocytes, and metabolism of gamma- and delta -tocopherol in HepG2/C3A cells. Sulphaphenazole and cyclosporin, inhibitors of CYP2C and CYP27, respectively, were without effect. Sesamin, a sesame lignan that causes elevation of tissue tocopherol concentration in rats, strongly inhibited tocopherol metabolism by HepG2/C3A cells at 1.0 muM These results support a CYP3A-dependent mechanism of side chain metabolism of tocopherols to water-soluble carboxychromans, and provide the first evidence of a specific enzyme involved in vitamin E metabolism. The data further suggest that sesamin increases tissue tocopherol concentration by inhibiting tocopherol catabolism. (C) 2000 Academic Press.