Simplified test for determination of drug-oxidizing capacity in rats with chemical-induced liver injury using caffeine and trimethadione as model drugs

Measurements of caffeine and plasma metabolite/caffeine ratios as a test for hepatic drug-oxidizing capacity in goats

The aim of this investigation was to determine the pharmacokinetics and demethylation of caffeine (CF) and the metabolite/CF ratios that correlated best with CF clearance, which were used to evaluate hepatic drug-oxidizing capacity of CF after a single intravenous dose (5 mg/kg) in hair goats (n = 9). Pharmacokinetic parameters of CF and its metabolites, theobromine (TB), paraxanthine (PX) and theophylline (TP), were calculated. The plasma metabolic ratios TB/CF, PX/CF, TP/CF and TB+PX+TP/CF were determined at 6, 8 and 10 h after CF administration to evaluate their hepatic drug-oxidizing capacity. The plasma concentration-time data of CF were fit to a two-compartment model in all animals. The clearance of CF was 0.08 ± 0.02 L/h/kg, and the volume of distribution was 0.91 ± 0.16 L/kg. The demethylation fractions of CF to TB, PX and TP were 0.24, 0.37 and 0.39, respectively. Correlations between the metabolic ratios and CF clearance were quite high, except for the PX/CF ratio, particularly at 6 h (r = 0.650-0.750, P < 0.01, 0.05) and 10 h (r = 0.650-0.767, P < 0.01, 0.05). Plasma metabolite/CF ratios, except for the PX/CF ratio, may be useful as an alternative to measurements of CF clearance for the determination of the hepatic drug-oxidizing capacity in goats.

Effect of berberine on hepatocyte proliferation, inducible nitric oxide synthase expression, cytochrome P450 2E1 and 1A2 activities in diethylnitrosamine- and phenobarbital-treated rats

This study investigated the effect of berberine on the early phase of hepatocarcinogenesis stimulated by diethylnitrosamine (DEN, 150 mg/kg, 4 weeks) plus phenobarbital (PB, 75 mg/kg, 7 days) in rats. The expressions of proliferating cell nuclear antigen (PCNA) and inducible nitric oxide synthase (iNOS) were evaluated by immunohistochemistry. The activities of CYP isoenzymes were analyzed using different probe drugs including chlorzoxazone (CYP2E1) and phenacetin (CYP1A2) by high-performance liquid chromatography (HPLC) in vivo or in vitro. Results showed that the expressions of PCNA and iNOS were induced by DEN plus PB in liver tissues. Oral administration of berberine (50mg/kg) inhibited the hepatocyte proliferation and iNOS expression, decreased cytochrome P450 content, inhibited activities of CYP2E1 and CYP1A2 in DEN-plus-PB-treated rats in vivo. Moreover, berberine (10, 50 and 100 microM) inhibited the activities of CYP2E1 and CYP1A2 in microsomes isolated from DEN-plus-PB-treated rats in vitro, suggesting that anti-hepatocarcinogenetic potential of berberine might be due to inhibiting oxidative metabolic activities of CYP 2E1 and CYP1A2, and decreasing NO production in rats.

Effect of toluidines and dinitrotoluenes on caffeine metabolic ratio in rat

Caffeine (1,3,7-trimethylxanthine, CA) is metabolised by N-demethylation to three primary metabolites: theophylline (TP), paraxanthine (PX) and theobromine (TB). This process is mediated in 95% by CYP1A2. Thus the measurement of CA demethylated metabolites can be used as a marker of CYP1A2 activity in vivo. In the present study, caffeine and its primary metabolites were determined simultaneously in plasma of rats pretreated with three isomers of toluidine at doses: 1, 10, 60 mg/kg b.w., p.o. and four isomers of dinitrotoluene (DNT) at doses: 100 and 200 mg/kg b.w., p.o. Caffeine metabolite ratios in plasma: TB/CA, PX/CA, TP/CA, TB + PX + TP/CA were calculated and compared to those of control rats. Administration of toluidines resulted in a 2-20 fold increase of the concentration ratios of metabolites to caffeine. All toluidines seem to be inducers of CYP1A2. To the best of our knowledge this is the first information concerning the effect of toluidines on caffeine metabolism. Two out of the four tested dinitrotoluenes slightly affected CYP1A2 activity; 2,3- and 3,4-DNT increased estimated parameters 2-6 fold. Two others, 2,4- and 2,6-DNT can be considered as moderate hepatotoxic agents decreasing CA metabolic ratios to 4-70% of the control values.

Changes in caffeine, lidocaine and trimethadione metabolism in carbon tetrachloride-intoxicated rats as assessed by a "cocktail" study

We investigated the possibility of predicting liver damage from changes in the serum concentrations of caffeine (10 mg/kg), lidocaine (4 mg/kg) and trimethadione (4 mg/kg), which are metabolized catalysed by different cytochrome P450 (P450) and/or are dependent on blood flow, in rats with carbon tetrachloride (CCl4: 0.25 ml/kg)-induced liver injury using a strategy referred to as a "cocktail" study. These 3 probe drugs were simultaneously administered intravenously. The half-lives (t1/2) of caffeine, lidocaine and trimethadione were significantly longer in the CCl4-treated group than in oil-treated controls, but no significant differences were observed in mean apparent volumes of distribution (Vd). Serum total body clearance (CL) values of all three drugs were markedly reduced in CCl4-treated animals. In rats with liver damage, the production of 3 metabolites (theobromine, paraxanthine and theophylline) of caffeine in addition to the only metabolite (dimethadione) of trimethadione after intravenous administration of probe drugs were significantly reduced compared to those of controls. These findings suggest that each probe drug, metabolized by different or partially overlapping P450, is useful in evaluating drug-oxidizing capacity in liver disease.