ABSTRACT
The effect of human serum albumin (HSA), alpha1-acid glycoprotein (alpha1-AGP), and alpha- and gamma-globulins on the in vitro metabolism of debrisoquine in human, hamster and rat liver microsomes was studied. Interaction of albumin with cytochrome P450 mediated phenytoin metabolism has been reported. Since plasma protein binding of phenytoin is high, in the present study a weakly protein bound drug, debrisoquine, was studied. Debrisoquine is a substrate of CYP2D6. The debrisoquine 4-hydroxylation was measured using a radio-TLC method. Among the four plasma proteins, alpha-globulins had the strongest inhibitory effect on the debrisoquine 4-hydroxylase activity. The inhibition with 2% alpha-globulins was 42+/-18% for human and higher for hamster and rat liver microsomes (65-71%). HSA had less effect than alpha-globulins. In the presence of HSA, the decrease in activity was between 18 and 35% for all liver microsomes studied. The debrisoquine 4-hydroxylase activity was not significantly changed by alpha1-AGP or gamma-globulins. Using an ultra-filtration method, the protein binding of debrisoquine to 4% HSA, 0.5% alpha1-AGP, 2% alpha-globulins and 2% gamma-globulins was found to be 22, 20, 22 and 5%, respectively. Since the observed inhibition is inconsistent with level of protein binding, it appears, particularly in the case of alpha-globulins, that the plasma proteins interact with CYP2D directly.
Subject(s)
Adrenergic Agents/metabolism , Alpha-Globulins/pharmacology , Cytochrome P-450 CYP2D6/metabolism , Debrisoquin/metabolism , Microsomes, Liver/metabolism , Serum Albumin/pharmacology , Alpha-Globulins/metabolism , Animals , Cricetinae , Humans , Male , Protein Binding , Rats , Rats, Sprague-Dawley , Serum Albumin/metabolism , Species SpecificityABSTRACT
1. Caucasian liver samples were used in this study. N-demethylation of trimethadione (TMO) to dimethadione (DMO) was monitored in the presence of chemical inhibitors of CYPs, such as fluconazole, quinidine, dimethyl-nitrosamine, acetaminophen, phenacetin, chlorzoxazone and mephenytoin. Trimethadione N-demethylation was selectively inhibited by dimethylnitrosamine and chlorzoxazone (> 50%) and weakly inhibited by tolbutamide (12%) and fluconazole (22%), whereas other inhibitors showed no effect. This result suggested that TMO metabolism to DMO is mainly mediated by CYP2E1 and marginally by CYP2C and CYP3A4. 2. Fifteen human livers were screened and interindividual variability of TMO N-demethylation activity was 3-fold. Chlorzoxazone 6-hydroxylation activity was also measured and both activities were significantly correlated (r=0.735, p < 0.01). 3. DMO production by human cDNA expressed CYP enzymes was observed mainly for CYP2E1 (10.8 nmol/tube), marginally for CYP2C8 (0.22 nmol/tube) and not detectable for other CYP enzymes. 4. These results indicate that TMO metabolism is primarily catalysed by CYP2E1 and that trimethadione would be a suitable selective probe drug for the estimation of human CYP2E1 activity in vivo.
Subject(s)
Anticonvulsants/metabolism , Cytochrome P-450 CYP2E1/metabolism , Cytochrome P-450 Enzyme System/metabolism , Liver/enzymology , Trimethadione/metabolism , Chlorzoxazone/metabolism , Cytochrome P-450 CYP2E1/genetics , Cytochrome P-450 CYP2E1 Inhibitors , Cytochrome P-450 Enzyme Inhibitors , Cytochrome P-450 Enzyme System/genetics , Enzyme Inhibitors/pharmacology , Humans , In Vitro Techniques , Inactivation, Metabolic , Isoenzymes , Methylation/drug effects , Microsomes, Liver/metabolismABSTRACT
The protease inhibitors, ritonavir, indinavir and saquinavir, the most potent anti-HIV drugs developed to date, interact with many drugs by competing for CYP3A4, an enzyme central to the metabolism of a wide variety of compounds. Human liver microsomes were used to compare inhibition by these three protease inhibitors. The inhibition was the greatest with ritonavir and indinavir and less potent with saquinavir.
Subject(s)
Cytochrome P-450 Enzyme System/drug effects , HIV Protease Inhibitors/pharmacology , Indinavir/pharmacology , Mixed Function Oxygenases/drug effects , Ritonavir/pharmacology , Saquinavir/pharmacology , Antibiotics, Antitubercular/metabolism , Cytochrome P-450 CYP3A , Cytochrome P-450 Enzyme System/metabolism , Drug Interactions , Humans , In Vitro Techniques , Microsomes, Liver/drug effects , Microsomes, Liver/enzymology , Mixed Function Oxygenases/metabolism , Rifamycins/metabolism , Testosterone/metabolismABSTRACT
A gas chromatographic method was developed to determine metabolites of antipyrine, norantipyhis method requires no derivatization and has ample sensitivity to determine these metabolites in urine after ingestion of antipyrine, a compound widely used as a hepatic probe of drug oxidation.
