In vitro inhibition of cytochrome P-450 reductases from pig liver microsomes by garlic extracts.

The activity of microsomal NADPH-cytochrome-P-450-reductase and NADH-cytochrome-b5-reductase are inhibited after the addition of an aqueous extract of a pharmaceutical preparation of garlic (Allium sativum, L.) to buffer-suspended microsomes. Incubation of garlic extract with isolated pig liver microsomes also decreases the activity of cytochrome P-450-dependent ethoxycoumarin deethylation. As measured by malondialdehyde release, the effects on the enzyme system are evidently not due to lipid peroxidation. No loss of cytochrome P-450 pigment is observed. Moreover, it could be shown that addition of garlic extract displays no protective effect on microsomal lipids when oxidation occurs spontaneously or is enforced by short-wave UV-irradiation. The above findings were reproduced after applying a HPLC-purified preparation of alliin to the incubation mixtures, suggesting that alliin is the active principle for the inhibitory effects observed in vitro.