Effect of ethanol feeding on hepatic microsomal UDP-glucuronyltransferase activity

Pharmacokinetic characterization of a human immunodeficiency virus protease inhibitor, saquinavir, during ethanol intake in rats

Throughout therapeutic drug monitoring of human immunodeficiency virus (HIV) protease inhibitors in HIV-infected patients, it was found that plasma concentrations of saquinavir (SQV) were reduced in patients who had a habit of alcohol intake during double protease therapy with SQV and ritonavir (RTV). This study confirmed the pharmacokinetic profiles of SQV during ethanol intake in rats. After oral administration of SQV alone (20 mg/kg) in rats prepared by free access to 15% ethanol solution for 14 days (day 14 rats), the area under the concentration vs time curves (AUC) showed a significant decrease (p<0.01) in comparison with control rats from 0.78+/-0.10 to 0.38+/-0.03 microg h/ml. For intravenous administration of SQV alone (5 mg/kg) to day 14 rats, the total body clearance increased significantly by 1.4-fold (p<0.05), whereas for intracolonic administration of SQV alone, no significant differences in the values of pharmacokinetic parameters were found between control and day 14 rats. With RTV, which has the strongest inhibitory effect on the CYP3A enzyme of the current HIV protease inhibitors, the AUC values of SQV at RTV doses of 2 and 20 mg/kg in day 14 rats also decreased significantly (p<0.01) from 1.30+/-0.06 to 0.57+/-0.05 microg h/ml and from 17.63+/-1.66 to 4.18+/-0.94 microg h/ml, respectively, indicating that the degree of the decrease of AUC values after oral administration with RTV after ethanol intake was larger than the mono-therapy with SQV. This study showed that ethanol-intake decreases the bioavailability of SQV after oral administration alone or with RTV. These observations provide useful information for the treatment of HIV-infected patients when they receive a combination therapy with SQV and RTV, and arouse attention for the effects of alcohol intake.

Effect of phenobarbital and p-hydroxyphenobarbital glucuronide on acetaminophen metabolites in isolated rat hepatocytes: use of a kinetic model to examine the rates of formation and egress

Conventional analysis of initial uptake and egress rates in isolated hepatocytes is limited in the ability to distinguish between rates of metabolite formation and egress, and to separate basolateral and canalicular transport processes. The present study examined the applicability of kinetic modeling in describing acetaminophen glucuronide (AG) and acetaminophen sulfate (AS) formation and egress in hepatocytes after acute exposure to phenobarbital or p-hydroxyphenobarbital glucuronide (p-OHPBG) in vitro, or in vivo phenobarbital pretreatment. A significant pretreatment effect on AG and AS disposition was seen based on initial rates of egress. In vivo phenobarbital pretreatment decreased the initial egress rate of AG compared to vehicle pretreatment, and the initial egress rate of AS compared to all other treatments. A pharmacokinetic model incorporating AG and AS formation in hepatocytes as well as egress processes (including diffusional and active transport components) was fit to the data. Parameter estimates derived from model fits to the data showed the expected increase in acetaminophen glucuronidation and decrease in sulfation after phenobarbital pretreatment; in addition, an increase in the AG diffusional rate constant and a decrease in the AS diffusional rate constant was apparent. The excretion Vmax for AG was decreased statistically after acute phenobarbital exposure in vitro, and in vivo phenobarbital pretreatment, with a concomitant statistical increase in the Km for AG excretion. In vitro acute p-OHPBG exposure also decreased significantly the excretion Vmax for AG. These data are consistent with the hypothesis that phenobarbital-impaired biliary excretion of AG is a function of impaired canalicular transport due to the presence of p-OHPBG. They further suggest that the mechanism may not be simple competitive inhibition. This work demonstrates the utility of a kinetic modeling approach to differentiate metabolic and transport processes when analyzing data from isolated hepatocyte studies. Additional information may be gained that would not be apparent by conventional methods of analysis.

Effect of xenobiotics on monooxygenase activities in cultured human hepatocytes

The activity of human cytochrome P450 monooxygenases, aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-deethylase can be increased by 3-methylcholanthrene, phenobarbital and ethanol in human hepatocytes maintained in primary culture. Total cytochrome P450 content increased two-fold after 48 hr of incubation with methylcholanthrene or phenobarbital and 1.5-fold after incubation with ethanol. The three chemicals elicited different effects on cytochrome P450 dependent activities. Addition of 3-methylcholanthrene caused a time- and concentration-dependent increase in both monooxygenase activities, aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-deethylase, while phenobarbital and ethanol increased 7-ethoxycoumarin O-deethylase activity but had no effect on aryl hydrocarbon hydroxylase. Dexamethasone per se had little or no effect on either monooxygenase activities, but potentiated the effect of the three chemicals on 7-ethoxycoumarin O-deethylase.