Characterization of autoantibodies against uridine-diphosphate glucuronosyltransferase in patients with inflammatory liver diseases

Uridine diphosphate glucuronosyltransferase (UGT) was identified as an anti genic target in a subgroup of liver-kidney microsomal autoantibodies and wa s termed LKM-3. To evaluate the nature of LKM-3 antibodies, we screened ser a from 80 untreated patients with autoimmune hepatitis (AIH) type 1 and 2, primary biliary cirrhosis (PBC), AIH/PBC, hepatitis C virus (HCV) infection , and 12 healthy individuals (controls) against 7 recombinant human UGT iso enzymes (UGT1A1, UGT1A4, UGT1A6, UGT1A7, UGT1A9, UGT1A10, and UGT2B7). Auto antibodies reacting against various UGT isoenzymes were observed in sera fr om 3 of 18 AIH type 2 and I of 27 of the I-ICV patients. The anti-UGT-posit ive sera from AIH type 2 patients revealed the strongest immunoreactivity a gainst UGT1A1, the main UGT-isoform involved in the bilirubin glucuronidati on, Additionally, these sera were able to block UGT-mediated substrate gluc uronidation in vitro, The prevalence for UGT1A1 was shown by 2 independent techniques: (I) UGT1A1 was identified as the main antigen by Western blotti ng. Preabsorption of sera with UGT1A1 prevented reaction against all tested UGT-isoforms. (2) In vitro immunoinhibition experiments showed that glucur onidation of the anticancer drug flavopiridol by UGT1A1 was more strongly i nhibited than its UGT1A9-mediated biotransformation, In contrast, the serum from the HCV-patient reacted predominately with UGT1A6, and moreover, the immunoreactivity pattern was different from that of the AIH group. To summa rize, we show the subtype preference of antibodies against UGT1A1 in a subg roup of AIH type 2 patients. These autoantibodies inhibit UGT-mediated gluc uronidation in vitro, but it is unlikely that anti-UGT antibodies will have a marked effect on the patients capacity for drug biotransformation, as se rum bilirubin levels in patients remained within the normal range.