The metabolism in vitro and hepatic microsomal interactions of some enantiomeric drug substrates

1. The metabolism in vitro and microsomal interactions of (+)-amphetamine, (-)-amphetamine, (+)-benzphetamine and (-)-benzphetamine were studied with hepatic microsomes from phenobarbitone-pretreated male rabbits. 2. (+)-Benzphetamine was N-demethylated 30-35% faster than (-)-benzphetamine, but the apparent Michaelis constants for the two enantiomers were similar. 3. (-)-Amphetamine was deaminated about 200% faster than (+)-amphetamine. 4. The benzphetamine enantiomers gave qualitatively and quantitatively identical type I microsomal difference spectra (peak, 390nm; trough, 425nm) indicating identical apparent binding affinities for microsomes and identical spectral changes at maxima (DeltaE(max.) values). 5. The amphetamine enantiomers gave qualitatively identical type II microsomal difference spectra (peak, 433nm; trough, 395nm). However, the type II spectral data indicated that (+)-amphetamine had a markedly higher apparent binding affinity than (-)-amphetamine for microsomes. The amphetamine enantiomers gave identical DeltaE(max.) values. 6. The benzphetamine enantiomers (0.5mm) enhanced the rate of microsomal cytochrome P-450 reduction by NADPH by 400-500%, (+)-benzphetamine enhancing the rate 20-25% more than (-)-benzphetamine. 7. The amphetamine enantiomers decreased the rate of microsomal cytochrome P-450 reduction by NADPH. At a concentration of 2mm, (+)-amphetamine decreased the rate more than (-)-amphetamine. 7. All four enantiomers enhanced microsomal NADPH oxidation.

The effects of unsaturated fatty acids on hepatic microsomal drug metabolism and cytochrome P-450

1. The effects of unsaturated fatty acids on drug-metabolizing enzymes in vitro were measured by using rat and rabbit hepatic 9000g supernatant fractions. 2. Unsaturated fatty acids inhibited the hepatic microsomal metabolism of ;type I' drugs with inhibition increasing with unsaturation: arachidonic acid>linolenic acid>linoleic acid>oleic acid. Inhibition was independent of lipid peroxidation. Linoleic acid competitively inhibited the microsomal O-demethylation of p-nitroanisole and the N-demethylation of (+)-benzphetamine. 3. The hepatic microsomal metabolism of ;type II' substrates, aniline and (-)-amphetamine, was not affected by unsaturated fatty acids. 4. The rate of reduction of p-nitrobenzoic acid and Neoprontosil was accelerated by unsaturated fatty acids. 5. Linoleic acid up to 3.5mm did not decelerate the generation of NADPH by rat liver soluble fraction, nor the activity of NADPH-cytochrome c reductase of rat liver microsomes. Hepatic microsomal NADPH oxidase activity was slightly enhanced by added linoleic acid. 6. No measurable disappearance of exogenously added linoleic acid occurred when this fatty acid was incubated with rat liver microsomes and an NADPH source. 7. The unsaturated fatty acids used in this study produced type I spectra when added to rat liver microsomes, and affected several microsomal enzyme activities in a manner characteristic of type I ligands.