AIM To study the influence of inducers BNFand PB on the stereoselective metabolism ofpropranolol in rat hepatic microsomes.METHODS Phase Ⅰ metabolism of propranololwas studied by using the microsomes induced byBNF an...AIM To study the influence of inducers BNFand PB on the stereoselective metabolism ofpropranolol in rat hepatic microsomes.METHODS Phase Ⅰ metabolism of propranololwas studied by using the microsomes induced byBNF and PB and the non-induced microsome asthe control.The enzymatic kinetic parameters ofpropranolol enantiomers were calculated byregression analysis of Lineweaver-Burk plots.Propranolol concentrations were assayed byHPLC.RESULTS A RP-HPLC method was developed todetermine propranolol concentration in rathepatic microsomes.The linearity equations forR（+）-propranolol and S（-）-propranolol wereA=705.7C+311.2C（R = 0.9987）and A= 697.2C+311.4C（R = 0.9970）respectively.Recoveriesof each enantiomer were 98.9%,99.5%,101.0%at 60 μmol/L,120 μmol/L,240 μmol/Lrespectively.At the concentration level of120 μmol/L,propranolol enantiomers weremetabolized at different rates in differentmicrosomes.The concentration ratio R（+）/S（-）of control and PB induced microsomesincreased with time,whereas that of microsomeinduced by BNF decreased.The assayed enzymeparameters were:1.Km.Control group:R（+）30+<sub>8</sub>,S（-）18+<sub>5</sub>;BNFgroup:R（+）34+3,S（-）39±7;PB group:R（+）38±17,S（-）36±10.2.Vmax.Control group:R（+）1.5+0.2,S（-）2.9±0.3;BNF group:R（+）3.8±0.3,S（-）3.3±0.5;PB group:R（+）0.07±0.03,S（-）1.94±0.07.3.Clint.Control group:R（+）60±3,S（-）170±30;BNF group:R（+）111.0±1,S（-）84± 5;PBgroup:R（+）2.0±2,S（-）56.0±1.Theenzyme.parameters compared with unpaired ttests showed that no stereoselectivity wasobserved in enzymatic affinity of threemicrosomes to enantiomers and their catalyticabilities were quite different and hadstereoselectivities.Compared with the control,microsome induced by BNF enhanced enzymeactivity to propranolol R（+）-enantiomer,andmicrosome induced by PB showed less enzymeactivity to propranolol S（-）-enantiomer whichremains the same stereoselectivities as that ofthe control.CONCLUSION Enzyme activity centers of themicrosome were changed in composition andregioselectivity after the induction of BNF andPB,and the stereoselectivities of propranololcytochrome P450 metabolism in rat hepaticmicrosomes were likely due to thestereoselectivities of the catalyzing function inenzyme.CYP1A subfamily induced by BNFexhibited pronounced contribution to propranololmetabolism with stereoselectivity to R（+）-enantiomer.CYP2B subfamily induced by PBexhibited moderate contribution to propranololmetabolism,but still had the stereoselectivity ofS（-）-enantiomer.展开更多
基金the National Natural Science Foundation of China,No.39370805.
文摘AIM To study the influence of inducers BNFand PB on the stereoselective metabolism ofpropranolol in rat hepatic microsomes.METHODS Phase Ⅰ metabolism of propranololwas studied by using the microsomes induced byBNF and PB and the non-induced microsome asthe control.The enzymatic kinetic parameters ofpropranolol enantiomers were calculated byregression analysis of Lineweaver-Burk plots.Propranolol concentrations were assayed byHPLC.RESULTS A RP-HPLC method was developed todetermine propranolol concentration in rathepatic microsomes.The linearity equations forR（+）-propranolol and S（-）-propranolol wereA=705.7C+311.2C（R = 0.9987）and A= 697.2C+311.4C（R = 0.9970）respectively.Recoveriesof each enantiomer were 98.9%,99.5%,101.0%at 60 μmol/L,120 μmol/L,240 μmol/Lrespectively.At the concentration level of120 μmol/L,propranolol enantiomers weremetabolized at different rates in differentmicrosomes.The concentration ratio R（+）/S（-）of control and PB induced microsomesincreased with time,whereas that of microsomeinduced by BNF decreased.The assayed enzymeparameters were:1.Km.Control group:R（+）30+<sub>8</sub>,S（-）18+<sub>5</sub>;BNFgroup:R（+）34+3,S（-）39±7;PB group:R（+）38±17,S（-）36±10.2.Vmax.Control group:R（+）1.5+0.2,S（-）2.9±0.3;BNF group:R（+）3.8±0.3,S（-）3.3±0.5;PB group:R（+）0.07±0.03,S（-）1.94±0.07.3.Clint.Control group:R（+）60±3,S（-）170±30;BNF group:R（+）111.0±1,S（-）84± 5;PBgroup:R（+）2.0±2,S（-）56.0±1.Theenzyme.parameters compared with unpaired ttests showed that no stereoselectivity wasobserved in enzymatic affinity of threemicrosomes to enantiomers and their catalyticabilities were quite different and hadstereoselectivities.Compared with the control,microsome induced by BNF enhanced enzymeactivity to propranolol R（+）-enantiomer,andmicrosome induced by PB showed less enzymeactivity to propranolol S（-）-enantiomer whichremains the same stereoselectivities as that ofthe control.CONCLUSION Enzyme activity centers of themicrosome were changed in composition andregioselectivity after the induction of BNF andPB,and the stereoselectivities of propranololcytochrome P450 metabolism in rat hepaticmicrosomes were likely due to thestereoselectivities of the catalyzing function inenzyme.CYP1A subfamily induced by BNFexhibited pronounced contribution to propranololmetabolism with stereoselectivity to R（+）-enantiomer.CYP2B subfamily induced by PBexhibited moderate contribution to propranololmetabolism,but still had the stereoselectivity ofS（-）-enantiomer.
