Glucuronidation of 1'-hydroxyestragole (1'-HE) by human UDP-glucuronosyltransferases UGT2B7 and UGT1A9.
Estragole (4-allyl-1-methoxybenzene) is a naturally occurring food flavoring agent found in basil, fennel, bay leaves, and other spices. Estragole and its metabolite, 1'-hydroxyestragole (1'-HE), are hepatocarcinogens in rodent models. Recent studies from our laboratory have shown that glucuronidation of 1'-HE is a major detoxification pathway for estragole and 1'-HE, accounting for as much as 30% of urinary metabolites of estragole in rodents. Therefore, this study was designed to investigate the glucuronidation of 1'-HE in human liver microsomes in vitro and identify the specific uridine diphosphate glucuronosyltransferase (UGT) isoforms responsible for 1'-HE glucuronidation. The formation of the glucuronide of 1'-HE (1'-HEG) followed atypical kinetics, and the data best fit to a Hill equation, resulting in apparent kinetic parameters of Km = 1.45 mM, Vmax = 164.5 pmoles/min/mg protein, and n = 1.4. There was a significant intersubject variation in 1'-HE glucuronidation in 27 human liver samples, with a CV of 42%. A screen of cDNA expressed UGT isoforms indicated that UGT2B7 (83.94 +/- 0.188 pmols/min/mg), UGT1A9 (51.36 +/- 0.72 pmoles/min/mg), and UGT2B15 (8.18 +/- 0.037 pmoles/min/mg) were responsible for 1'-HEG formation. Glucuronidation of 1'-HE was not detected in cells expressing UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A7, UGT1A8, and UGT1A10. 1'-HE glucuronidation in 27 individual human liver samples significantly (p < 0.05) correlated with the glucuronidation of other UGT2B7 substrates (morphine and ibuprofen). These results imply that concomitant chronic intake of therapeutic drugs and dietary components that are UGT2B7 and/or UGT1A9 substrates may interfere with estragole metabolism. Our results also have toxicogenetic significance, as UGT2B7 is polymorphic and could potentially result in genetic differences in glucuronidation of 1'-HE and, hence, toxicity of estragole.
Iyer
Lalitha V
LV
Biopharmaceutical Division, SRI International, 333 Ravenswood Avenue, Menlo Park, California 94025, USA. lalitha.iyer@sri.com
Ho
Mark N
MN
Shinn
Walter M
WM
Bradford
Wallace W
WW
Tanga
Mary J
MJ
Nath
Shirley S
SS
Green
Carol E
CE
D000701:Analgesics, Opioid / Q000493:pharmacokinetics; D000840:Anisoles / Q000493:pharmacokinetics*; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000493:pharmacokinetics; D002273:Carcinogens / Q000493:pharmacokinetics*; D020719:Glucuronides / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007052:Ibuprofen / Q000493:pharmacokinetics; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008862:Microsomes, Liver / Q000378:metabolism; D009020:Morphine / Q000493:pharmacokinetics; D009596:Nitrophenols / Q000493:pharmacokinetics
D000701:Analgesics, Opioid; D000840:Anisoles; D000894:Anti-Inflammatory Agents, Non-Steroidal; D002273:Carcinogens; D020719:Glucuronides; D007527:Isoenzymes; D009596:Nitrophenols; C014037:1'-hydroxyestragole; D009020:Morphine; D014453:Glucuronosyltransferase; D007052:Ibuprofen; C024836:4-nitrophenol