Profiling of Urinary Glucuronidated Bile Acids across Age Groups.

We investigated the age-dependent changes in urinary excretion of glucuronidated bile acids at the C-3 position. Bile acid 3-glucuronides accounted for 0.5% of urinary bile acids in neonates, and the proportion of bile acid 3-glucuronides plateaued at 1-3 years of age. The 3-glucuronides of secondary bile acids were first secreted at 3 months of age, the same time as the establishment of the gut bacterial flora in infants. A considerable portion of bile acid 3-glucuronides were present as non-amidated forms. Our results indicate dynamic hepatic enzyme activity in which the levels of uridine 5'-diphospho-glucuronosyltransferases (UGTs) differ by age group, with higher glucuronidation activity of UGTs towards nonamidated bile acids than amidated bile acids.