Multiple circulating alkaloids and saponins from intravenous Kang-Ai injection inhibit human cytochromes P450 and UDP-glucuronosyltransferase isozymes: potential drug-drug interactions

Abstract Background Kang-Ai injection is widely used as an adjuvant therapy drug for many cancers, leukopenia and chronic hepatitis B. Circulating alkaloids and saponins are believed to be responsible for therapeutic effects. However, their pharmacokinetics and excretion in vivo and the risk of drug-drug interactions (DDI) through inhibiting human cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes remain unclear. Methods Pharmacokinetics and excretion of circulating compounds were investigated in rats using a validated ultra high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS) method. Further, the inhibitory effects of nine major compounds against eleven CYP and UGT isozymes were assayed using well-accepted specific substrate for each enzyme. Results After dosing, 9 alkaloids were found with Cmax and t1/2 values of 0.17–422.70 µmol/L and 1.78–4.33 h, respectively. Additionally, 28 saponins exhibited considerable systemic exposure with t1/2 values of 0.63–7.22 h, whereas other trace saponins could be negligible or undetected. Besides, over 90% of alkaloids were excreted through hepatobiliary and renal excretion. Likewise, astragalosides and PPT-type ginsenosides also involved in hepatobiliary and/or renal excretion. PPD-type ginsenosides were mainly excreted to urine. Furthermore, PPD-type ginsenosides were extensively bound (fu−plasma approximately 1%), whereas astragalosides and PPT-type ginsenosides displayed fu−plasma values of 12.35% and 60.23–87.36%, respectively. Moreover, matrine and oxymatrine both exhibited weak inhibition against CYP3A4 with IC50 values of 387.40 and 604.60 µM. Similar results were observed for astragaloside IV towards CYP2C9, ginsenoside Rg1 against UGT1A1, ginsenoside Re against CYP2C8, ginsenoside Rd against CYP2B6and CYP3A4, and ginsenoside Rc against UGT1A9 with IC50 values between 20.19 and 92.21 µM. Ginsenoside Rb1 showed moderate inhibitory effect against CYP2C9 (IC50 = 8.81 µM). Through kinetic modeling, their inhibition mechanisms towards those CYP and UGT isozymes were explored with obtained Ki values. In vitro-in vivo extrapolation ([I]/Ki = 1.15 for oxymatrine) showed the inhibition of systemic clearance for CYP3A4 substrates seemed more possible, while other major circulating compounds displayed negligible DDI risk due to [I]/Ki no more than 0.1. Conclusions These facts lead to better understanding of chemical basis responsible for therapeutic action of Kang-Ai injection, and facilitate to pay more attention on the DDI for informing its rational clinical use.