Inhibition of hepatic microsomal drug-metabolizing enzymes by habu snake ( trimeresurus flavoviridis) venom fractions

Abstract

An inhibitor of hepatic microsomal drug-metabolizing enzyme activity was isolated from the venom of the Habu snake ( Trimeresurus flavoviridis) by gel filtration through Sephadex G-100 and Amberlite CG-50 column chromatography. The inhibitor, designated R-CG-50-2, gave one band on sodium dodecylsulfate (SDS) polyacrylamide gel electrophoresis and caused high hemorrhagic activity when administered i.c. to rabbits. R-CG-50-2 inhibited the drug-metabolizing enzyme system even after being heated at 70° for 5 min, in spite of a complete loss of hemorrhagic activity. Cytochrome P-450 content and NADPH-cytochrome c reductase activity of rat hepatic microsomes were decreased by administration in vivo either R-CG-50-2 or heated R-CG-50-2. The extent of the decrease was greater with unheated R-CG-50-2 than with heated R-CG-50-2. In both cases, cytochrome P-420, the inactive form of cytochrome P-450, was not detected. Lipid peroxidation in hepatic microsomes was also decreased by administration of unheated R-CG-50-2 but the decrease was not significant. In an in vitro experiment, both heated and unheated R-CG-50-2 decreased the cytochrome P-450 content and the NADPH-cytochrome c reductase activity of microsomes, but, unlike the results in vivo, cytochrome P-450 was converted to cytochrome P-420. Microsomal lipid peroxidation was greatly inhibited by either heated or unheated R-CG-50-2 in vitro. It was concluded that the inhibition of the hepatic microsomal drug-metabolizing enzyme system by either heated or unheated R-CG-50-2 may have been due to the decrease in the cytochrome P-450 content and the NADPH-cytochrome c reductase activity, and that lipid peroxidation may not have had an effect on the inhibition.