OBJECTIVE Lithocholic acid,which is a secondary bile acid,has been reported to be hepatotoxic and carcinogenic.It is metabolized by human cytochrome P450 3A(CYP3A)to form 3-ketocholanoic acid.A previous study suggests...OBJECTIVE Lithocholic acid,which is a secondary bile acid,has been reported to be hepatotoxic and carcinogenic.It is metabolized by human cytochrome P450 3A(CYP3A)to form 3-ketocholanoic acid.A previous study suggests that vitamin E isomers(tocotrienols and tocopherols)are metabolized by CYP3 A.Given that substrates of an enzyme may competitively inhibit the enzyme,we determined whether alpha-tocotrienol,gamma-tocotrienol,delta-tocotrienol,tocotrienol-rich mixture(a mixture consisting of 25.7% d-α-tocotrienol,2.6% d-β-tocotrienol,28.6% d-γ-tocotrienol,8.4% d-δ-tocotrienol,25.6% d-α-tocopherol,and 4.3% d-α-tocomonoenol),and alpha-tocopherol inhibit human liver microsomal CYP3Aactivity,as assessed by the enzymatic conversion of lithocholic acid to 3-ketocholanoic acid and of testosterone to6β-hydroxytestosterone.METHODS Enzymatic formation of 3-ketocholanoic acid via lithocholic acid 3-oxidation was determined in pooled human liver microsomes and recombinant CYP3A4 and CYP3A5.Enzyme inhibition assay was conducted in a mixture containing potassium phosphate buffer(pH 7.4),human liver microsomes,NADPH,lithocholic acid,and various concentrations of a test chemical.The amount of 3-ketocholanoic acid formed was quantified by a novel,validated ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-MS-MS)method.RESULTS Lithocholic acid was metabolized to 3-ketocholanoic acid by human recombinant CYP3A4 and CYP3A5enzymes and human liver microsomes.Alpha-tocotrienol,gamma-tocotrienol,delta-tocotrienol,and tocotriernol-rich mixture,but not alpha-tocopherol,inhibited 3-ketocholanoic acid formation in human liver microsomes.Concentration-response experiments indicated that tocotrienol-rich mixture and delta-tocotrienol inhibited 3-ketocholanoic acid formation with IC50 values of 6.6±2.1μg·mL-1 and 19.0±1.0μmol·L-1,respectively.CONCLUSION Tocotrienols inhibited CYP3A-catalyzed lithocholic acid 3-oxidation but not CYP3A-catalyzed testosterone 6-beta-hydroxylation.This suggests that lithocholic acid and testosterone bind to different CYP3 Abinding sites and that tocotrienols preferentially inhibit the lithocholic acid binding site on CYP3 Aenzymes.展开更多
The cytochrome P450 superfamily,one of the most important drug-metabolizing enzyme systems in humans,is responsible for the metabolism of numerous xenobiotic substances as well as endogenous substrates.Induction or in...The cytochrome P450 superfamily,one of the most important drug-metabolizing enzyme systems in humans,is responsible for the metabolism of numerous xenobiotic substances as well as endogenous substrates.Induction or inhibition of the cytochrome P450 enzymes,after exposure to different drugs and chemicals,is directly linked to a number of drug-induced toxicity and drug interactions leading to treatment failure.As we know,the traditional Chinese medicine(TCM)has complicated components and is always coadministered with other drugs.Through searching and summing up the literatures about the effects of TCM on cytochrome P450 at home andabroad,the results show that the activity of cytochrome P450 was inhibited or induced by some single herbs,traditional Chinese prescriptions andthe active components of the TCM,such as the flavonoids,flavonoid derivatives,alkaloids,saponins,terpenoids,anthraquinones and lignans,and so on,which therefore might slow or speed metabolism of other drugs.The paper tips that much attention should be paid to the research fields of TCM on cytochrome P450,which is meaningful to clinical reasonable medicine treatment and new drug development.展开更多
基金The project supported by National University of Singapore Grant(R-148-000-185-133)
文摘OBJECTIVE Lithocholic acid,which is a secondary bile acid,has been reported to be hepatotoxic and carcinogenic.It is metabolized by human cytochrome P450 3A(CYP3A)to form 3-ketocholanoic acid.A previous study suggests that vitamin E isomers(tocotrienols and tocopherols)are metabolized by CYP3 A.Given that substrates of an enzyme may competitively inhibit the enzyme,we determined whether alpha-tocotrienol,gamma-tocotrienol,delta-tocotrienol,tocotrienol-rich mixture(a mixture consisting of 25.7% d-α-tocotrienol,2.6% d-β-tocotrienol,28.6% d-γ-tocotrienol,8.4% d-δ-tocotrienol,25.6% d-α-tocopherol,and 4.3% d-α-tocomonoenol),and alpha-tocopherol inhibit human liver microsomal CYP3Aactivity,as assessed by the enzymatic conversion of lithocholic acid to 3-ketocholanoic acid and of testosterone to6β-hydroxytestosterone.METHODS Enzymatic formation of 3-ketocholanoic acid via lithocholic acid 3-oxidation was determined in pooled human liver microsomes and recombinant CYP3A4 and CYP3A5.Enzyme inhibition assay was conducted in a mixture containing potassium phosphate buffer(pH 7.4),human liver microsomes,NADPH,lithocholic acid,and various concentrations of a test chemical.The amount of 3-ketocholanoic acid formed was quantified by a novel,validated ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-MS-MS)method.RESULTS Lithocholic acid was metabolized to 3-ketocholanoic acid by human recombinant CYP3A4 and CYP3A5enzymes and human liver microsomes.Alpha-tocotrienol,gamma-tocotrienol,delta-tocotrienol,and tocotriernol-rich mixture,but not alpha-tocopherol,inhibited 3-ketocholanoic acid formation in human liver microsomes.Concentration-response experiments indicated that tocotrienol-rich mixture and delta-tocotrienol inhibited 3-ketocholanoic acid formation with IC50 values of 6.6±2.1μg·mL-1 and 19.0±1.0μmol·L-1,respectively.CONCLUSION Tocotrienols inhibited CYP3A-catalyzed lithocholic acid 3-oxidation but not CYP3A-catalyzed testosterone 6-beta-hydroxylation.This suggests that lithocholic acid and testosterone bind to different CYP3 Abinding sites and that tocotrienols preferentially inhibit the lithocholic acid binding site on CYP3 Aenzymes.
文摘The cytochrome P450 superfamily,one of the most important drug-metabolizing enzyme systems in humans,is responsible for the metabolism of numerous xenobiotic substances as well as endogenous substrates.Induction or inhibition of the cytochrome P450 enzymes,after exposure to different drugs and chemicals,is directly linked to a number of drug-induced toxicity and drug interactions leading to treatment failure.As we know,the traditional Chinese medicine(TCM)has complicated components and is always coadministered with other drugs.Through searching and summing up the literatures about the effects of TCM on cytochrome P450 at home andabroad,the results show that the activity of cytochrome P450 was inhibited or induced by some single herbs,traditional Chinese prescriptions andthe active components of the TCM,such as the flavonoids,flavonoid derivatives,alkaloids,saponins,terpenoids,anthraquinones and lignans,and so on,which therefore might slow or speed metabolism of other drugs.The paper tips that much attention should be paid to the research fields of TCM on cytochrome P450,which is meaningful to clinical reasonable medicine treatment and new drug development.
