RESUMO
The metabolism of rofecoxib, a potent and selective inhibitor of cyclooxygenase-2, was examined in vitro using human liver subcellular fractions. The biotransformation of rofecoxib was highly dependent on the subcellular fraction and the redox system used. In liver microsomal incubations, NADPH-dependent oxidation of rofecoxib to 5-hydroxyrofecoxib predominated, whereas NADPH-dependent reduction of rofecoxib to the 3,4-dihydrohydroxy acid metabolites predominated in cytosolic incubations. In incubations with S9 fractions, metabolites resulting from both oxidative and reductive pathways were observed. In contrast to microsomes, the oxidation of rofecoxib to 5-hydroxyrofecoxib by S9 fractions followed two pathways, one NADPH-dependent and one NAD+-dependent (non-cytochrome P450), with the latter accounting for about 40% of total activity. The 5-hydroxyrofecoxib thus formed was found to undergo NADPH-dependent reduction ("back reduction") to rofecoxib in incubations with liver cytosolic fractions. In incubations with dialyzed liver cytosol, net hydration of rofecoxib to form 3,4-dihydro-5-hydroxyrofecoxib was observed, whereas the 3,4-dihydrohydroxy acid derivatives were formed when NADPH was present. Although 3,4-dihydro-5-hydroxyrofecoxib could be reduced to the 3,4-dihydrohydroxy acid by cytosol in the presence of NADPH, the former species does not appear to serve as an intermediate in the overall reductive pathway of rofecoxib metabolism. In incubations of greater than 2 h with S9 fractions, net reductive metabolism predominated over oxidative metabolism. These in vitro results are consistent with previous findings on the metabolism of rofecoxib in vivo in human and provide a valuable insight into mechanistic aspects of the complex metabolism of this drug.
Assuntos
Lactonas/metabolismo , Fígado/citologia , Fígado/metabolismo , Citosol/metabolismo , Relação Dose-Resposta a Droga , Humanos , Lactonas/química , Frações Subcelulares/metabolismo , SulfonasRESUMO
Compound A [(+)-(5S,6R,7R)-2-isopropylamino-7-[4-methoxy-2-((2R)-3-methoxy-2-methylpropyl)-5-(3,4-methylenedioxyphenyl) cyclopenteno [1,2-b] pyridine 6-carboxylic acid] is a new and selective endothelin ET(A) receptor antagonist. It underwent significant acyl glucuronidation and acyl glucosidation in human liver microsomes supplemented with UDP-glucuronic acid (UDPGA) and UDP-glucose (UDPG). These two conjugations were observed in a panel of human liver microsomal samples (n = 16) that gave rise to varying activities but with no significant correlation with each other in the native and activator-treated microsomal preparations (r(2)
Assuntos
Antagonistas dos Receptores de Endotelina , Glucosídeos/metabolismo , Glucuronídeos/metabolismo , Microssomos Hepáticos/metabolismo , Glucosídeos/química , Ácido Glucurônico/química , Ácido Glucurônico/metabolismo , Glucuronídeos/química , Humanos , Isoformas de Proteínas/química , Isoformas de Proteínas/metabolismo , Receptor de Endotelina A , Receptores de Endotelina/metabolismo , Uridina Difosfato Glucose/química , Uridina Difosfato Glucose/metabolismo , Uridina Difosfato Ácido Glucurônico/química , Uridina Difosfato Ácido Glucurônico/metabolismoRESUMO
The disposition and metabolism of rofecoxib, a selective cyclooxygenase-2 inhibitor, were examined in healthy human subjects and in cholecystectomy patients. After oral administration of [(14)C]rofecoxib (125 mg, 100 micro Ci) to healthy subjects, the mean concentrations of total radioactivity and rofecoxib in plasma as a function of time indicated that the t(max) was achieved at 9 h postdose. After t(max), levels of both radioactivity and rofecoxib decreased in a parallel, exponential fashion (effective t(1/2) approximately equal 17 h). A similar result was obtained after oral administration of [(14)C]rofecoxib (142 mg, 100 micro Ci) to cholecystectomy patients equipped with an L-tube. In healthy subjects, radioactivity was recovered predominantly from the urine (71.5% of dose), with a small amount excreted in feces (14.2%). In patients with an L-tube, half the radioactive dose was recovered in feces, with a lesser amount excreted in urine (28.8%) and a negligible fraction in bile (1.8%). Rofecoxib underwent extensive metabolism in humans, and very little parent drug was recovered unchanged in urine (<1%). Products resulting from both oxidative and reductive pathways were identified by a combination of (1)H NMR and liquid chromatography-tandem mass spectrometry analyses, and included rofecoxib-3',4'-trans-dihydrodiol, 4'-hydroxyrofecoxib-O-beta-D-glucuronide, diastereomeric 5-hydroxyrofecoxib-O-beta-D-glucuronide conjugates, 5-hydroxyrofecoxib, rofecoxib-erythro-3,4-dihydrohydroxy acid, and rofecoxib-threo-3,4-dihydrohydroxy acid. Interconversion of rofecoxib and 5-hydroxyrofecoxib appeared not to be a quantitatively important pathway of rofecoxib disposition in human subjects, in contrast to previous findings in rats.