Immunochemical identification of UGT isoforms in human small bowel and in Caco-2 cell monolayers

Previous work had suggested the presence of significant levels of UDP-glucu ronosyltransferase 1A1 (UGT1A1) catalytic activity in human small intestina l microsomes, with undetectable to low UGT1A6 and 2B7 activities. To confir m the presence of UGT1A6 isoform in human small bowel, to explore the possi ble absence of UGT1A6 and 2B7 in the organ, and to examine induced Caco-2 c ells as a potential model for human intestinal metabolism, Western blot ana lysis was performed using specific antibodies to the relevant UGT isoforms. Significant expression of UGT1A1 protein was observed in all samples of hu man small intestinal microsomes, while UGT1A6 expression was undetectable t o faint and UGT2B7 immunoreactivity was faint to detectable, Caco-2 cells t reated with typical enzyme-inducing agents resulted in low UGT2B7 expressio n but failed to mimic the UGT1A1 levels found in human small bowel. Further work needs to be performed to develop a comprehensive in vitro model for h uman small intestinal first-pass metabolism. (C) 2000 Academic Press.