"Direct reacting
bilirubin" in serum of patients with cholestatic
liver disease and in serum of bile duct-ligated rats consists of a
complex mixture of
bilirubin metabolites. These metabolites were studied by means of high-pressure liquid chromatography.
Bilirubin glucuronides in normal bile are beta-glycosidic 1-O-acyl conjugates which are completely hydrolyzed on incubation with
beta-glucuronidase. Cholestatic serum contains
glucuronide and non-
glucuronide bilirubin metabolites. The
glucuronides were only partially hydrolyzable with
beta-glucuronidase. Compernolle et al. [11] showed that the 1-O-acyl bond of
bilirubin glucuronides is labile and prone to migrate from the C1 position at the glucuronosyl residue to positions C2, C3 and C4. The isomerisation products are non-beta-glycosidic,
beta-glucuronidase-resistant conjugates. The main
beta-glucuronidase-resistant conjugates in cholestatic serum were characterized as: non-beta-glycosidic
bilirubin monoglucuronide, non-beta-glycosidic diglucuronide and a diglucuronide isomer with beta-glycosidic and non-beta-glycosidic glucuronosyl groups. Moreover, a substantial amount of
bilirubin monoglucoside monoglucuronide was detected in cholestatic human serum.