OBJECTIVES: Of several enzymes metabolizing xenobiotics, cytochrome P450 (CYP) and peroxidase enzymes seem to be most important. One of the major challenges in studies investigating metabolism of xenobiotics is to resolve which of these two groups of enzymes is predominant to metabolize individual xenobiotic compounds. Utilization of selective inhibitors of CYP and peroxidase enzymes might be a useful tool to identify the contribution of these enzymes to metabolism of xenobiotics in samples, where both types of enzymes are present. The aim of this study was to investigate specificities of several known CYP inhibitors to these enzymes; whether they inhibit only the CYP enzymes and do not inhibit peroxidases. METHODS: Since the oxidation of o-anisidine catalyzed by a model peroxidase used, horseradish peroxidase (HRP), is a two-substrate reaction, the inhibition potential of tested chemicals was studied with respect to both peroxidase substrates, o-anisidine and hydrogen peroxide. Initial velocities of o-anisidine oxidation by HRP under various conditions were determined spectrophotometrically. RESULTS: The CYP inhibitors metyrapone, troleandomycine, disulfiram, sulfaphenazole, quinidine and 1-aminobenzotriazole do not inhibit o-anisidine oxidation catalyzed by HRP. In contrast, ketoconazole, diethyldithiocarbamate, ellipticine, α-naphtoflavone, proadifen SKF525A, piperonylbutoxide, were found to inhibit not only the CYPs, but also the HRP-mediated oxidation of o-anisidine. Interestingly, α-naphtoflavone inhibits oxidation of o-anisidine by HRP with respect to H2O2, but not with respect to o-anisidine. Diethyldithiocarbamate is the most potent peroxidase inhibitor of o-anisidine oxidation with Ki with respect to o-anisidine of 10 μM and Ki with respect to H2O2 of 60 μM, being even the better peroxidase inhibitor than the classical "peroxidase inhibitor" - propyl gallate (Ki with respect to o-anisidine of 60 μM and Ki with respect to H2O2 of 750 μM). CONCLUSIONS: The results of the present study demonstrate that 1-aminobenzotriazole, a potent inhibitor of various CYP enzymes, seems to be the best candidate suitable for utilization in studies evaluating participation of CYP enzymes in metabolism of xenobiotics in various complex biological materials containing both CYP and peroxidase enzymes. Moreover, precaution to prevent misinterpretation of results is necessary in cases when proadifen SKF525A, piperonylbutoxide, diethyldithiocarbamate, ketoconazole, α-naphtoflavone and ellipticine are used in similar studies (as CYP inhibitors in various complex biological materials containing both CYP and peroxidase enzymes), since these chemicals can except of CYP enzymes inhibit also peroxidase-mediated reactions.

• MeSH
• aktivace enzymů účinky léků   MeSH
• benzoflavony chemie   farmakologie   MeSH
• chinidin chemie   farmakologie   MeSH
• disulfiram chemie   farmakologie   MeSH
• dithiokarb chemie   farmakologie   MeSH
• elipticiny chemie   farmakologie   MeSH
• inhibitory cytochromu P450 MeSH
• inhibitory enzymů chemie   farmakologie   MeSH
• ketokonazol chemie   farmakologie   MeSH
• křenová peroxidasa antagonisté a inhibitory   metabolismus   MeSH
• lidé MeSH
• metyrapon chemie   farmakologie   MeSH
• piperonylbutoxid chemie   farmakologie   MeSH
• proadifen chemie   farmakologie   MeSH
• substrátová specifita účinky léků   MeSH
• sulfafenazol chemie   farmakologie   MeSH
• systém (enzymů) cytochromů P-450 MeSH
• triazoly chemie   farmakologie   MeSH
• troleandomycin chemie   farmakologie   MeSH
• vztahy mezi strukturou a aktivitou MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• srovnávací studie MeSH

OBJECTIVES: The aim of this study was to assess the effect of various flavonoids on the NADPH:cytochrome P450 oxidoreductase (CYPOR) activity in respect of the reduction of different electron acceptors as well as to study an impact of flavonoids on monooxygenation of a model substrate of cytochrome P450 (CYP). DESIGN: The modulation of CYPOR activity was determined spectrophotometrically based on the time course of the reduction of different electron acceptors. The CYP reduction was monitored via its complex formation with CO, having pronounced the absorption maximum at 450 nm. Finally, effect of CYPOR stimulation by 7,8benzoflavone (ANF) on 7pentoxyresorufin Odepentylation was assayed in the microsomal monooxygenation system using the fluorimetric detection of formed resorufin. RESULTS: The stimulation of CYPOR activity via ANF was found to be associated with following electron acceptors: cytochrome c, potassium ferricyanide, cytochrome b5, but not with CYP. Surprisingly, 5,6benzoflavone, a position isomer of ANF, was ineffective in the CYPOR stimulation as well as the other flavonoids tested. In microsomal preparations, ANF did not markedly enhance the reaction rate of monooxygenation of CYP2B4 model substrate. CONCLUSION: Our results document that among all of the tested flavonoids only ANF is able to stimulate CYPOR activity, however, the ANF-mediated stimulation of CYPOR has no impact on the oxidative metabolism catalyzed by CYP system.

• MeSH
• antioxidancia farmakologie   MeSH
• benzoflavony chemie   metabolismus   MeSH
• beta-naftoflavon chemie   metabolismus   MeSH
• časové faktory MeSH
• cytochromy b5 metabolismus   MeSH
• cytochromy c metabolismus   MeSH
• ferrikyanidy metabolismus   MeSH
• flavonoidy chemie   farmakologie   MeSH
• fluorometrie MeSH
• králíci MeSH
• kyselina lipoová farmakologie   MeSH
• mikrozomy účinky léků   enzymologie   metabolismus   MeSH
• NADPH-cytochrom c-reduktasa metabolismus   MeSH
• oxaziny metabolismus   MeSH
• oxid uhelnatý metabolismus   MeSH
• oxidace-redukce účinky léků   MeSH
• spektrofotometrie MeSH
• systém (enzymů) cytochromů P-450 metabolismus   MeSH
• zvířata MeSH
• Check Tag
• králíci MeSH
• mužské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH