BILIRUBIN GLUCURONIDATION BY INTACT GUNN RAT FIBROBLASTS EXPRESSING BILIRUBIN UDP-GLUCURONOSYLTRANSFERASE

Crigler-Najjar (CN) disease is an inherited disorder of bilirubin meta bolism. The disease is caused by a deficiency of the hepatic enzyme bi lirubin UDP-glucuronosyltransferase (B-UGT). Patients with CN disease have high serum levels of the toxic compound, unconjugated bilirubin. The only defect in bilirubin metabolism of CN patients is the absence of B-UGT activity. The transplantation of cells able to glucuronidate bilirubin should therefore lower serum bilirubin levels. The Gunn rat is the animal model of CN disease. Primary Gunn rat fibroblasts (GURF) were transduced with a recombinant retrovirus, capable of transferrin g B-UGT cDNA. A cell line was obtained expressing B-UGT at a level com parable to hepatocytes. Bilirubin added to the culture medium of these cells was glucuronidated and excreted. The B-UGT activities of transd uced GURF and freshly isolated Wistar hepatocytes were compared at dif ferent bilirubin concentrations. The specific B-UGT activities of thes e two cell types were comparable when physiological bilirubin concentr ations (5-10 mu M) were present in the culture media. At higher biliru bin concentrations (20-80 mu M) the hepatocytes were more active than the transduced GURF. We conclude that with the addition of only one en zyme (B-UGT) fibroblasts can perform the complete set of reactions nec essary for bilirubin glucuronidation. The difference in B-UGT activity between transduced GURF and hepatocytes at 20-80 mu M bilirubin can b e explained by lower UDP-glucuronic acid and glutathione S-transferase levels in GURF. Our findings also indicate that these cells could be used to develop extrahepatic gene therapy for CN disease.