Metabolism of kurarinone by human liver microsomes and its effect on cytotoxicity

Abstract

Context: Kurarinone, the most abundant prenylated flavonoid in Sophora flavescens Aiton (Leguminosae), is a promising antitumor therapeutic. However, it shows significant hepatotoxicity. Furthermore, how kurarinone is metabolized in humans remains unclear. Objective: The objective of this study is to investigate kurarinone metabolism in human liver microsomes (HLMs) and the role of metabolism in kurarinone-induced cytotoxicity. Materials and methods: The UDP-glucuronosyltransferase isoforms (UGTs) involved in kurarinone glucuronidation were identified using chemical inhibitors (100-1000 μM phenylbutazone; 10-100 μM β-estradiol; 10-100 μM 1-naphthol; 10-500 μM propofol; and 100-1000 μM fluconazole) and recombinant human UGTs. Kurarinone (2-500 μM) was incubated with HLMs and UGTs (0.5 mg/mL) for 15 min to determine enzyme kinetic parameters. The IC50 value of kurarinone (10-200 μM) was evaluated in a HLMs/3T3 cell co-culture system. Results: Kurarinone is extensively converted to two glucuronides (M3 and M4) in HLMs. M3 formation was catalyzed by multiple UGT1As, with UGT1A3 showing the highest intrinsic clearance (120.60 mL/min/mg). M4 formation was catalyzed by UGT1A1, UGT2B4, and UGT2B7. UGT1A1 showed the highest intrinsic clearance (60.61 mL/min/mg). The kinetic profiles of the five main UGTs and HLMs fit substrate inhibition kinetics, with Km values ranging from 5.20 to 46.52 μM, Vmax values ranging from 0.20 to 3.06 μmol/min/mg, and Ksi values ranging from 25.58 to 230.30 μM. The kurarinone IC50 value was 93 M in the control group, 102 M in HLMs with NADPH, and 160 M in HLMs with UDPGA. Discussion and conclusion: Kurarinone glucuronidation is a detoxification pathway. This information may help to elucidate the risk factors regulating kurarinone toxicity.