Evaluation for adverse reaction of drugs using metabolic parameters

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Nitroglycerin (GTN) has been used as the drug of choice in the treatment of angina pectoris. It has been shown that some glutathione S-transferases (GSTs) catalyze the metabolic conversion from GTN to glyceryl dinitrates (GDNs). In this study, we examined the substrate specificity of GSTs for GTN.Alpha and mu GSTs were isolated from the liver and mucosa from pig, human and Caco-2 cells. Mu GSTs degraded GTN time-dependently and formed 1,3-GDN in preference to 1,2-GDN at ratio (1,2-GDN/1,3GDN) of 0.61, whereas alpha GSTs formed twice as much as different hydrolyzing portions of the nitrogroups.We found an enzyme involved in the hydrolysis of amide-linkage of indomethacin and partially characterized it as well as its substrate specificity. The purified enzyme effectively hydrolyzed the amide linkage in indomethacin but not those in a-naphthylacetate and p-nitrophenylacetate which are typical substrate for carboxylestrase. The Michaelis constant and maximum velocity values for indomethacin were 67 mM and 9 nmol/mg protein/min, respectively. This enzyme designated as ES-male. The activity of indomethacin hydrolysis was relatively high in the pig, rabbit and human liver, but not in those form rat and mouse. Two carboxylesteases with pl 6.0 and 6.2 derived from rat liver microsomes were purified. The two isozymes were remarkably different in substrate specificity. Carboxylesterases pl 6.0 and 6.2 are identical to the enzymes referred to as hydrolase A and B,respectively, from the results of amino acid sequence analyzes. Pranlukast was effectively hydrolyzed by caroxylesterase pl 6.2 but not by the pl 6.0 enzyme and the difference in the pranlukast metabolism between the human and the rat could be explained by the substrate specificity of carboxylesteases.