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摘要
Dapsone is used in the treatment of Pneumocystis carinii pneumonia, an opportunistic infection that afflicts acquired immunodeficiency syndrome (AIDS) patients. Inhibition of N-acetyltransferase (NAT)-dependent acetylation of dapsone could increase peak plasma concentrations of dapsone and shift the biotransformation pathway to the P450-mediated formation of a toxic metabolite of dapsone, the hydroxylamine. Therefore, we have determined using human liver cytosol and bacterially expressed NATs, the NAT isoform responsible for acetylating dapsone and the potential for antiopportunistic infection drugs to inhibit this metabolic pathway, Formation of monoacetyldiaminodiphenylsulfone (MADDS) was quantitated by HPLC/UV detection at 270 nm after incubation of dapsone with 100 mu M acetyl coenzyme A regenerating system and human liver cytosol. The mean +/- SD apparent K-M for the formation of MADDS in three different human livers predicted to be fast acetylators based on genotyping was 98 +/- 17.6 mu M, and the V-max was 190 +/- 20 pmol/min/mg cytosol protein. Eadie-Hofstee transformation of the substrate velocity data was linear, indicating acetylation by a kinetically single enzyme. Sulfamethazine (250 mu M) inhibited dapsone acetylation by 100% and 80%, respectively, at dapsone concentrations of 3 and 100 mu M, in both fast- and slow-acetylating liver cytosol preparations, whereas para-aminobenzoic acid (100 mu M) did not inhibit MADDS formation at either of these dapsone concentrations Lineweaver-Burk plots of dapsone acetylation in the presence of 0, 25, and 50 mu M sulfamethazine showed an increase in the apparent K-M, with increase in sulfamethazine concentration with no change in the V-max, indicating competitive inhibition of dapsone acetylation by sulfamethazine. The apparent K-M of dapsone acetylation by bacterially expressed NAT1 and NAT2 enzymes was 687 and 136 mu M, respectively. Human liver cytosol preparations, predicted to be slow acetylators based on genotyping, acetylated dapsone at a significantly lower rate when compared with fast acetylator human liver cytosols. At clinically relevant concentrations, pyrimethamine, but not other antiopportunistic infection drugs (atovaquone, sulfadiazine, clarithromycin, trimethoprim, ketoconazole, and fluconazole), significantly but modestly (23%) inhibited MADDS formation in human liver cytosols. These data indicate that NAT2 is the predominant liver NAT isoform acetylating dapsone in vivo and that coadministration with antiopportunistic infection drugs should not significantly inhibit this acetylation pathway.
- 出版日期1995-4
