Selective induction of human hepatic cytochromes P450 2B6 and 3A4 by metamizole.
ABSTRACT The pyrazolone drug metamizole is a widely used analgesic. Analysis of liver microsomes from patients treated with metamizole revealed selectively higher expression of cytochromes P450, CYP2B6 and CYP3A4 (3.8- and 2.8-fold, respectively), and 2.9-fold higher bupropion hydroxylase activity compared with untreated subjects. Further investigation of metamizole and various derivatives on different potential target genes in human primary hepatocytes demonstrated time- and concentration-dependent induction by metamizole of CYP2B6 (7.8- and 3.1-fold for mRNA and protein, respectively, at 100 muM) and CYP3A4 (2.4- and 2.9-fold, respectively), whereas other genes (CYP2C9, CYP2C19, CYP2D6, NADPH:cytochrome P450 reductase, ABCB1, constitutive androstane receptor (CAR), pregnane X receptor (PXR)) were not substantially altered. Using reporter gene assays, we show that metamizole is not acting as a direct ligand to either PXR or CAR, suggesting a phenobarbital-like mechanism of induction. These data warrant further studies to elucidate the drug-interaction potential of metamizole, especially in patients with long-term treatment.
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ABSTRACT: The aim of this study was to investigate the activity of the drug-metabolizing enzyme cytochrome P450 (CYP) 2B6 before and after in vivo induction by rifampin (INN, rifampicin) in white subjects and Chinese subjects by use of the probe drug bupropion (INN, amfebutamone). Healthy male white subjects (n = 9) and Chinese subjects (n = 9) (age range, 19-34 years) of known CYP2B6 genotype received orally administered bupropion (Zyban SR, 150 mg) alone and during daily treatment with rifampin (600 mg). Blood samples were taken for up to 72 hours after each bupropion dose, and plasma concentrations of bupropion and its active metabolites, hydroxybupropion, threohydrobupropion, and erythrohydrobupropion, were measured by HPLC. The subjects' CYP2B6 genotype was determined by use of a matrix-assisted laser desorption /ionization-time of flight (MALDI-TOF) mass spectrometry assay. Rifampin treatment increased the apparent clearance of bupropion in Chinese subjects and white subjects combined (n = 16) from 2.6 L x h(-1) x kg(-1) (95% confidence interval [CI], 2.3-3.0 L x h(-1) x kg(-1)) after bupropion alone to 7.9 L x h(-1) x kg(-1) (95% CI, 6.8-10.1 L x h(-1) x kg(-1)) during rifampin treatment. Rifampin treatment decreased the half-life of bupropion from 15.9 hours (95% CI, 13.5-20.4 hours) to 8.2 hours (95% CI, 6.7-12.4 hours). Rifampin treatment increased the hydroxybupropion maximum concentration from 395 ng/mL (95% CI, 341-497 ng/mL) to 548 ng/mL (95% CI, 490-638 ng/mL), decreased the area under the concentration-time curve extrapolated to infinity of hydroxybupropion from 14.7 microg x h/mL (95% CI, 12.7-18.4 microg x h/mL) to 8.4 microg x h/mL (95% CI, 7.4-10.2 microg x h/mL), and reduced the elimination half-life of hydroxybupropion from 21.9 hours (95% CI, 20.3-24.0 hours) to 10.7 hours (95% CI, 8.6-14.5 hours). There was no significant difference in the pharmacokinetics of bupropion or hydroxybupropion between white subjects and Chinese subjects before and after treatment with rifampin, once corrected for body weight. Rifampin significantly induces CYP2B6 activity in vivo, and the clinical consequences of potential interactions between rifampin and CYP2B6 substrates deserve further investigation. Rifampin appears to induce the elimination of hydroxybupropion. Differences in bupropion pharmacokinetics that were observed between white subjects and Chinese subjects can be attributed to differences in body weight, suggesting that, for a given subject weight, CYP2B6 activity is similar in white subjects and Chinese subjects.Clinical Pharmacology & Therapeutics 08/2006; 80(1):75-84. · 6.85 Impact Factor
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ABSTRACT: 1. Rat hepatic cytochrome P450s induced by dipyrone were studied enzymatically, immunochemically and immunohistochemically. 2. Dipyrone administered to male Wistar rats increased pentoxyresorufin O-depentylation (PROD), ethoxyresorufin O-deethylation (EROD) and 7-ethoxycoumarin O-deethylation (ECOD) activities up to 44-, 1.9-, and 2.6-fold, respectively. Aryl hydrocarbon hydroxylase (AHH) activity was not affected. 3. Immunoinhibition with the monoclonal antibody (Mab) 2-66-3 (to CYP2B1/2) markedly decreased PROD and EROD activities, but not AHH activity. The Mab 1-7-1 (to CYP1A1/2) was without effect. 4. Histochemically, the Mab 2-66-3 gave a strong and uniform staining in livers from dipyrone-treated rats, whereas the Mab 1-7-1 gave a positive reaction in a narrow perivenous strip. 5. The induction pattern as well as inhibition by the Mabs convincingly demonstrate the predominant production of CYP2B1/2 in the induction spectrum of dipyrone. The increase in enzyme activities other than PROD may be due to the overlapping substrate specificity of CYP2B1/2 enzymes. The immunohistochemical analysis also indicated the participation of CYP1A1/2.Human & Experimental Toxicology 02/1996; 15(1):45-50. · 1.45 Impact Factor
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ABSTRACT: We used human liver microsomes (HLMs) and recombinant cytochromes P450 (P450s) to identify the routes of efavirenz metabolism and the P450s involved. In HLMs, efavirenz undergoes primary oxidative hydroxylation to 8-hydroxyefavirenz (major) and 7-hydroxyefavirenz (minor) and secondary metabolism to 8,14-dihydroxyefavirenz. The formation of 8-hydroxyefavirenz in two HLMs showed sigmoidal kinetics (average apparent Km, 20.2 micro M; Vmax, 140 pmol/min/mg protein; and Hill coefficient, 1.5), whereas that of 7-hydroxyefavirenz formation was characterized by hyperbolic kinetics (Km, 40.1 micro M and Vmax, 20.5 pmol/min/mg protein). In a panel of 10 P450s, CYP2B6 formed 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz from efavirenz (10 micro M) at the highest rate. The Km value for the formation of 8-hydroxyefavirenz in CYP2B6 derived from hyperbolic Eq. 12.4 micro M) was close to that obtained in HLMs (Km, 20.2 micro M). None of the P450s tested showed activity toward 7-hydroxylation of efavirenz. When 8-hydroxyefavirenz (2.5 micro M) was used as a substrate, 8,14-dihydroxyefavirenz was formed by CYP2B6 at the highest rate, and its kinetics showed substrate inhibition (Ksi, approximately 94 micro M in HLMs and approximately 234 micro M in CYP2B6). In a panel of 11 HLMs, 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz formation rates from efavirenz (10 micro M) correlated significantly with the activity of CYP2B6 and CYP3A. N,N',N"-Triethylenethiophosphoramide (thioTEPA; 50 micro M) inhibited the formation rates of 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz from efavirenz (10 micro M) by > or = 60% in HLMs) and CYP2B6, with Ki values < 4 micro M. In conclusion, CYP2B6 is the principal catalyst of efavirenz sequential hydroxylation. Efavirenz systemic exposure is likely to be subject to interindividual variability in CYP2B6 activity and to drug interactions involving this isoform. Efavirenz may be a valuable phenotyping tool to study the role of CYP2B6 in human drug metabolism.Journal of Pharmacology and Experimental Therapeutics 07/2003; 306(1):287-300. · 3.89 Impact Factor