title: Metabolism of kurarinone by human liver microsomes and its effect on cytotoxicity.
abstract: BACKGROUND
  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.
  
  
  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 μM in the control group, 102 μM in HLMs with NADPH, and 160 μM in HLMs with UDPGA.
  
  
  CONCLUSIONS
  Kurarinone glucuronidation is a detoxification pathway. This information may help to elucidate the risk factors regulating kurarinone toxicity.
authors.affiliation: a Department of Pharmacology , School of Pharmacy, Fudan University , Shanghai , China.
authors.forename: Xiuwen
authors.initials: X
authors.lastname: Zhang
authors.affiliation: a Department of Pharmacology , School of Pharmacy, Fudan University , Shanghai , China.
authors.forename: Peng
authors.initials: P
authors.lastname: Jiang
authors.affiliation: a Department of Pharmacology , School of Pharmacy, Fudan University , Shanghai , China.
authors.forename: Ping
authors.initials: P
authors.lastname: Chen
authors.affiliation: a Department of Pharmacology , School of Pharmacy, Fudan University , Shanghai , China.
authors.forename: Nengneng
authors.initials: N
authors.lastname: Cheng
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D018920:Coculture Techniques; D003603:Cytotoxins / Q000378:metabolism* / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D005419:Flavonoids / Q000378:metabolism* / Q000633:toxicity; D020719:Glucuronides / Q000037:antagonists & inhibitors / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D051379:Mice; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*
chemical_list: D003603:Cytotoxins; D005419:Flavonoids; D020719:Glucuronides; C411319:kurarinone; D014453:Glucuronosyltransferase
keywords: Hepatotoxicity; Sophora flavescens Aiton; UDP-glucuronosyltransferase