Bilirubin conjugates produced by human, dog, and rat hepatocytes transplanted into athymic Gunn rats

We developed a new hybrid mutant rat (athymic Gunn hybrid strain) that does not form and excrete conjugated bilirubin into bile and accepts xenografts because of T-lymphocyte deficiency. Cryopreserved isolated normal human, dog, or rat liver cells attached to collagen-coated microcarriers were transplanted into the athymic Gunn hybrid rats. Transplantation of human or rat liver cells resulted in biliary excretion of bilirubin conjugates predominantly as glucuronides, whereas isolated dog liver cells likewise transplanted resulted in the excretion of 40% to 50% of the conjugates as a glucoside-glucuronide diconjugate. The biliary bilirubin conjugates of the transplanted athymic Gunn hybrid rats paralleled those of the donor species. The data indicate that the types of bilirubin conjugates excreted by each species are determined by intrinsic properties of the respective hepatocytes rather than nutritional or other environmental factors. The findings also show that conjugation of bilirubin after liver cell transplantation results from functioning of the engrafted cells rather than activation of endogenous uridine diphosphatelucuronosyltransferase activity of the host.