title: Metabolism of lidocaine by purified rat liver microsomal cytochrome P-450 isozymes.
abstract: The metabolism of lidocaine was studied using rat liver microsomes or a reconstituted lidocaine monooxygenase system with one of eight forms of cytochrome P-450 purified from liver microsomes from untreated- (P450 UT-2 and UT-5), phenobarbital- (P450 PB-1, PB-2, PB-4, and PB-5) or 3-methylcholanthrene- (P450 MC-1 and MC-5) treated rats. A reverse phase high-performance liquid chromatography system capable of simultaneously assaying four major lidocaine metabolites, namely, monoethylglycinexylidide (MEGX), 3-hydroxylidocaine (3-OH LID), methylhydroxylidocaine (Me-OH LID) and glycinexylidide (GX), was employed to determine the rate of formation of each metabolite. Untreated microsomes generated MEGX, Me-OH LID, and 3-OH LID, but the formation of GX was not detected. In male rat liver microsomes, MEGX was the major metabolite of lidocaine when a concentration of 1 mM was employed. The formation of MEGX and Me-OH LID was increased significantly (P less than 0.01) by microsomes from phenobarbital-treated rats, and the formation of 3-OH LID was increased with 3-methylcholanthrene. The study with the reconstituted system with purified cytochrome P-450 isozymes revealed that all eight forms of cytochrome P-450 used have an ability to N-deethylate lidocaine to form MEGX. Among these isozymes, cytochrome P450 PB-4 and P450 UT-2 showed a higher turnover number for the formation of MEGX. Me-OH LID was formed exclusively by P450 PB-5, and 3-OH LID exclusively by P450 MC-1. Selectivity of cytochrome P450 PB-5 for aromatic methyl hydroxylation of lidocaine was confirmed by an inhibition study; formation of Me-OH LID by microsomes of rats treated with phenobarbital was inhibited completely by antibody against P450 PB-5. It was concluded that different cytochrome P-450 isozymes metabolize lidocaine with a different rate and different position selectivities. Since a specific substrate of cytochrome P450 PB-5 (P-450e) is not known, lidocaine may be a useful substrate for the identification of P450 PB-5.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, Osaka City University Medical School, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Oda
authors.forename: S
authors.initials: S
authors.lastname: Imaoka
authors.forename: Y
authors.initials: Y
authors.lastname: Nakahira
authors.forename: A
authors.initials: A
authors.lastname: Asada
authors.forename: M
authors.initials: M
authors.lastname: Fujimori
authors.forename: S
authors.initials: S
authors.lastname: Fujita
authors.forename: Y
authors.initials: Y
authors.lastname: Funae
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D006900:Hydroxylation; D007527:Isoenzymes / Q000378:metabolism*; D008012:Lidocaine / Q000031:analogs & derivatives / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
chemical_list: D007527:Isoenzymes; D003577:Cytochrome P-450 Enzyme System; D008012:Lidocaine; C001173:monoethylglycinexylidide