Inhibition of Drug Metabolizing Enzymes (Cytochrome P450) in Vitro as Well as in Vivo by Phyllanthus amarus SCHUM & THONN

Abstract

An alcoholic extract of Phyllanthus amarus (P. amarus) was found to inhibit cytochrome P450 (P450) enzymes both in vivo as well as in vitro. This was studied using specific resorufin derivatives, as substrate for isoenzymes in the P450 super family. Concentration needed for 50% inhibition of 7-ethoxyresorufin-O-deethylase (EROD), CYP1A1 was 4.6 μg/ml while concentration needed for 7-methoxyresorufin-O-demethylase (MROD) CYP1A2 was 7.725 μg/ml and 7-pentoxyresorufin-O-depentylase (PROD), CYP2B1/2 was found to be 4.18 μg/ml indicating that the extract inhibited the P450 enzymes at very low concentration. Extract also inhibited the activity of aniline hydroxylase (an indicator of CYP 2E1 activity, IC₅₀ 50 μg/ml) and aminopyrine demethylase (an indicator of CYP 1A, 2A 2B, 2D and 3A activity, IC₅₀ >1000 μg/ml). Oral administration of the extract was also found to reduce the elevated P450 enzyme activities produced by phenobarbitone by 50% at 250 mg/kg body weight. The implication of these results on the inhibition of carcinogenesis produced by the extract is discussed.