Effects of two cannabinoids on hepatic microsomal cytochrome P-450.

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Abstract
The effects of cannabidiol (CBD) and .DELTA.9-tetrahydrocannabinol (.DELTA.9-THC) on the synthesis and degradation of hepatic microsomal cytochrome P-450 were studied in mice. Cannabinoids used (10, 50 and 100 mg/kg, i.p.) did not affect .delta.-aminolevulinic acid synthetase activity in the liver. .DELTA.9-THC-treatment (10, 50 and 100 mg/kg, i.p.) markedly stimulated heme oxygenase activity in hepatic 18,000 .times. g supernatant fractions in a dose-dependent manner, whereas CBD-treatment was without effect. In vitro experiments, CBD and .DELTA.9-THC (40 to 160 .mu.M) markedly inhibited nicotinamide adenine dinucleotide phosphate (NADPH)-induced lipid peroxidation in hepatic microsomes. When CBD was incubated with the hepatic microsomes in the prsence of an NADPH-generating system, cytochrome P-450 content decreased significantly. However, .DELTA.9-THC showed no effects in similar experiments. The rate of decrease in the cytochrome P-450 content using CBD (160 .mu.M) was 0.212 nmol/mg protein/20 min in microsomes from control mice. This value increased significantly in microsomes from phenobarbital-treated mice (0.792 nmol/mg protein/20 min) but not in those from 3-methylcholanthrene-treated mice (0.190 nmol/mg protein/20 min). The metabolic rate (per nmol cytochrome P-450) of CBD was also increased significantly by phenobarbital-treatment but not by 3-methylcholanthrene-treatment. These results suggest that CBD metabolites rather than CBD itself, play some role in the decreasing effect on cytochrome P-450 content in the hepatic microsomes in vitro, and that the microsomal formation of reactive metabolite of CBD is increased by phenobarbital treatment.