Identification of the human liver UDP-glucuronosyltransferase involved in the metabolism of p-ethoxyphenylurea (dulcin).
Dulcin (DL), now banned, was once a widely used artificial sweetener. DL possesses an ureido group that is metabolized by direct glucuronidation in rabbit liver microsomes. Dulcin N-glucuronide (DNG) is the only type of ureido N-glucuronide known to date; ureido glucuronidation in humans has not been previously reported. Accordingly, the glucuronidation of DL was studied using human liver microsomes (HLM) and expressed human UDP-glucuronosyltransferase (UGT) enzymes. The average K (m) and V (max) values from nine HLM samples were 2.10 mM and 0.156 nmol/mg/min, respectively. Of the six human UGT isoforms screened for their ability to glucuronidate DL, only UGT1A1 and UGT1A9 showed activity. The apparent K (m) values using UGT1A1 and UGT1A9 were 5.06 and 6.99 mM, and the apparent V (max) values were 0.0461 and 0.106 nmol/min/mg, respectively. Phenolphthalein, a substrate for UGT1A9, inhibited DL glucuronidation in HLM competitively (K (i) = 0.356 mM), but bilirubin, a substrate for UGT1A1, did not. These results suggest that UGT1A9 is a key enzyme catalyzing the glucuronidation of DL.
Uesawa
Yoshihiro
Y
Department of Pharmaceutics, Clinical Pharmaceutics Laboratory, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo, 204-8588, Japan. uesawa@my-pharm.ac.jp
Staines
Adam G
AG
Lockley
David
D
Mohri
Kiminori
K
Burchell
Brian
B
D001663:Bilirubin / Q000494:pharmacology; D020719:Glucuronides / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000502:physiology*; D006801:Humans; D007527:Isoenzymes / Q000502:physiology; D008099:Liver / Q000201:enzymology*; D020113:Phenolphthalein / Q000494:pharmacology; D010671:Phenylurea Compounds / Q000378:metabolism*
D020719:Glucuronides; D007527:Isoenzymes; D010671:Phenylurea Compounds; D020113:Phenolphthalein; C004352:dulcin; D014453:Glucuronosyltransferase; D001663:Bilirubin