反式曲马朵在大鼠肝微粒体O-去甲基代谢中的立体选择性

STEREOSELECTIVITY IN O-DEMETHYLATION OF TRANS TRAMADOL IN RAT LIVER MICROSOMES IN VITRO

目的 研究反式曲马朵O 去甲基代谢的立体选择性。方法 高效毛细管电泳法测定大鼠肝微粒体孵育液中反式曲马朵和O 去甲基曲马朵对映体的浓度 ,酶促动力学方法研究O 去甲基曲马朵对映体的生成。结果(- ) O 去甲基曲马朵生成有较大的Vmax;反式曲马朵两对映体间存在相互作用 ,使 (+) O 去甲基曲马朵生成的Vmax明显减慢 ;奎宁及奎尼丁对 (+) O 去甲基曲马朵生成的抑制作用较强。结论 反式曲马朵O 去甲基代谢有立体选择性 ,对映体间的相互作用及酶抑制剂使其立体选择性程度加强。

AIM To study the stereoselectivity in O -demethylation of trans tramadol. METHODS With or without quinine and quinidine as inhibitors, rat liver microsomes were incubated in vitro with the enantiomers or the racemate of trans tramadol. The concentrations of the enantiomers of trans tramadol and O -demethyltramadol in the incubates were determined by high performance capillary electrophoresis. The O -demethylation processes were assayed by using the enzyme kinetic analysis method. RESULTS After incubation, the concentrations of (-)- O -demethyltramadol were higher than those of (+)-enantiomer in all rat liver microsomal incubates. Enzyme kinetic analysis showed that the K m of the formation of the enantiomers of O -demethyltramadol were similar; The V max and Cl int of the formation of (-)- O -demethyltramadol were significantly higher than those of the formation of (+)-enantiomer. When the racemate of trans tramadol was used as the substrate, there was interaction between the two enantiomers. The K m of the formation of the enantiomers of O -demethyltramadol increased, the V max of the formation of (+)- O -demethyltramadol decreased, the V max of the formation of (-)- O -demethyltramadol increased slightly. The O -demethylation of the enantiomers of trans tramadol was shown to be inhibited competitively by quinine and quinidine. The K i of quinine and quinidine were 1 6 and 10 8 μmol·L -1 to the formation of (-)- O -demethyltramadol, 0 8 and 3 4 μmol·L -1 to the formation of (+)- O -demethyltramadol, respectively. Furthermore, quinine and quinidine were found to have stereoselective inhibition on the formation of O -demethyltramadol, both mainly inhibited the formation of (+)- O -demethyltramadol. CONCLUSION The O -demethylation of trans tramadol was found to be stereoselective in rat liver microsomes in vitro , preferentially metabolized (-)-enantiomer. The stereoselectivity could be influenced by the interaction between the two enantiomers and the enzyme selective inhibitors.