Impact of the herbal medicine Sophora flavescens on the oral pharmacokinetics of indinavir in rats: the involvement of CYP3A and P-glycoprotein

Abstract

Sophora flavescens is a Chinese medicinal herb used for the treatment of gastrointestinal hemorrhage, skin diseases, pyretic stranguria and viral hepatitis. In this study the herb-drug interactions between S. flavescens and indinavir, a protease inhibitor for HIV treatment, were evaluated in rats. Concomitant oral administration of Sophora extract (0.158 g/kg or 0.63 g/kg, p.o.) and indinavir (40 mg/kg, p.o.) in rats twice a day for 7 days resulted in a dose-dependent decrease of plasma indinavir concentrations, with 55%-83% decrease in AUC(0-∞) and 38%-78% reduction in C(max). The CL (Clearance)/F (fraction of dose available in the systemic circulation) increased up to 7.4-fold in Sophora-treated rats. Oxymatrine treatment (45 mg/kg, p.o.) also decreased indinavir concentrations, while the ethyl acetate fraction of Sophora extract had no effect. Urinary indinavir (24-h) was reduced, while the fraction of indinavir in faeces was increased after Sophora treatment. Compared to the controls, multiple dosing of Sophora extract elevated both mRNA and protein levels of P-gp in the small intestine and liver. In addition, Sophora treatment increased intestinal and hepatic mRNA expression of CYP3A1, but had less effect on CYP3A2 expression. Although protein levels of CYP3A1 and CYP3A2 were not altered by Sophora treatment, hepatic CYP3A activity increased in the Sophora-treated rats. All available data demonstrated that Sophora flavescens reduced plasma indinavir concentration after multiple concomitant doses, possibly through hepatic CYP3A activity and induction of intestinal and hepatic P-gp. The animal study would be useful for predicting potential interactions between natural products and oral pharmaceutics and understanding the mechanisms prior to human studies. Results in the current study suggest that patients using indinavir might be cautioned in the use of S. flavescens extract or Sophora-derived products.

Figure 1. Time course of the plasma concentration of indinavir.

Animals received oral administration of indinavir (40 mg/kg) together with (A) 1.5% Tween 80 (vehicle), 70% ethanol extract of Sophora flavescens (0.158 g/kg and 0.63 g/kg), (B) Oxymatrine capsule (45 mg/kg of oxymatrine equivalent), or ethyl acetate (EA) fraction of Sophora extract (0.082 g/kg), twice a day for 7 days, respectively. On the experimental day (day 8), animals were pretreated with corresponding vehicle or tested drugs at 1 h prior to the last dose of indinavir (40 mg/kg) given to all rats for pharmacokinetic study. Values are expressed as mean ± S.E.M. for each data point (n = 6–9).

Figure 2. Effect of Sophora extract on the output of urine and faeces, and on indinavir excreted via urine and faeces.

(A) Urine output, (B) Faeces output, (C) Indinavir excreted in urine, (D) Indinair excreted in faeces. The urine and faeces were collected from 8 p.m. on day 6 (after the second daily treatment) to 8 p.m. on day 7 (before the second daily treatment). Values are expressed as mean ± S.E.M. (n = 8–9).

Figure 3. Effect of Sophora extract on the intestinal and hepatic mRNA levels encoding CYP3A1, CYP3A2, mdr1a and mdr1b.

(A) CYP3A1, (B) CYP3A2, (C) mdr1a, (D) mdr1b. The mRNA contents were measured by real-time PCR and calculated as comparative levels over control using the 2^−ΔΔCT method (mean ± S.E.M., n = 7–9). Statistical significance is indicated as * P<0.05, ** P<0.01, compared to control.

Figure 4. Effect of Sophora extract on the expression of intestinal and hepatic CYP3A1 and CYP3A2.

(A) Statistical data analysis of Western blotting results, (B) image of Western blotting results. CYP3A1 and CYP3A2 levels were measured respectively using the specific anti-rat CYP3A1 and CYP3A2 antibodies. ERp29 was used as control for the normalization of CYP3A density. Bars represent mean ± S.E.M. of fold relative to the values in the control group (n = 7–8). No significant difference in the expression of either intestinal or hepatic CYP3A was observed.

Figure 5. Effect of Sophora extract on the expression of intestinal and hepatic P-gp.

(A) Statistical data analysis of Western blotting results, (B) image of Western blotting results. P-gp levels were measured using the anti-rat C219 antibody as described under Materials and Methods . ERp29 was used as control for the normalization of P-gp density. Bars represent mean ± S.E.M. of fold relative to the values in control group (n = 7–8). Statistical significance is indicated as * P<0.05, *** P<0.001, compared to control.

Figure 6. Effect of Sophora extract on the CYP3A activity in liver.

The CYP3A activity was measured using a luminescent assay (P450-Glo). Bars represent mean ± S.E.M. of fold relative to the values in the control group (n = 9). Statistical significance is indicated as * P<0.05, compared to control.