title: Decreased Expression of Multidrug Resistance-Associated Protein 4 (MRP4/ABCC4) Leads to Reduced Glucuronidation of Flavonoids in UGT1A1-Overexpressing HeLa Cells: The Role of Futile Recycling.
abstract: In this study, the role of futile recycling (or deglucuronidation) in the disposition of two flavonoids (i.e., genistein and apigenin) was explored using UGT1A1-overexpressing HeLa cells (or HeLa1A1 cells). Glucuronidation of the flavonoids by HeLa1A1 cell lysate followed the substrate inhibition kinetics (Vmax = 0.10 nmol/min/mg, Km = 0.54 μM, and Ksi = 2.0 μM for genistein; Vmax = 0.19 nmol/min/mg, Km = 0.56 μM, and Ksi = 3.7 μM for apigenin). Glucuronide was efficiently generated and excreted after incubation of the cells with the aglycone (at doses of 1.25-20 nmol). The excretion rates were 0.40-0.69 and 0.84-1.1 nmol/min/mg protein for genistein glucuronide (GG) and apigenin glucuronide (AG), respectively. Furthermore, glucuronide excretion and total glucuronidation were significantly reduced in MRP4 knocked-down as compared to control cells. The alterations were well characterized by a two-compartment pharmacokinetic model incorporating the process of futile recycling (defined by a first-order rate constant, Kde). The derived Kde values were 15 and 25 h(-1) for GG and AG, respectively. This was well consistent with the in vitro observation that AG was subjected to more efficient futile recycling compared to GG. In conclusion, futile recycling was involved in cellular glucuronidation, accounting for transporter-dependent glucuronidation of flavonoids.
authors.affiliation: Division of Pharmaceutics, College of Pharmacy, Jinan University, 601 Huangpu Avenue West, Guangzhou 510632, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Sun
authors.affiliation: Division of Pharmaceutics, College of Pharmacy, Jinan University, 601 Huangpu Avenue West, Guangzhou 510632, China.
authors.forename: Xiaotong
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Division of Pharmaceutics, College of Pharmacy, Jinan University, 601 Huangpu Avenue West, Guangzhou 510632, China.
authors.forename: Xingwang
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Division of Pharmaceutics, College of Pharmacy, Jinan University, 601 Huangpu Avenue West, Guangzhou 510632, China.
authors.forename: Baojian
authors.initials: B
authors.lastname: Wu
mesh_terms: D047310:Apigenin / Q000737:chemistry / Q000378:metabolism*; D019833:Genistein / Q000737:chemistry / Q000378:metabolism*; D020719:Glucuronides / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000099148:UGT1A1 Enzyme
chemical_list: D047310:Apigenin; D019833:Genistein; D020719:Glucuronides; D014453:Glucuronosyltransferase; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D000099148:UGT1A1 Enzyme; C073492:ABCC4 protein, human
keywords: HeLa cells; MRP4; UGT; efflux transporters; glucuronidation