Correction of congenital hyperbilirubinemia in homozygous Gunn rats by xenotransplantation of hamster livers

The homozygous Gunnj/jrat is an animal model for Crigler-Najjar syndrome in which the lack of the enzyme uridine diphosphoglucoronate-glucuronosyltransferase (UDP-GT) results in congenital unconjugated nonhemolytic hyperbilirubinemia. Because the binding of bilirubin to albumin in plasma varies from species to species, xenotransplantation (XTx) of liver afforded in this model the opportunity to study the interactions between xenoproteins of the donor and bilirubin of the recipient. For this purpose, orthotopic liver transplantation (OLTx) was performed from hamster to adult Gunnj/j rats. No immunosuppression (IS) was given to controls (Group I, n=5) and to OLTx recipients of syngeneic (Gunnj/j rat) grafts (Group II, n=5), whereas tacrolimus (1 mg/kg/day × 15 days, IM) and cyclophosphamide (8 mg/kg/day × 7 days, IP) were administered to animals receiving hamster xenografts (Group III, n=11). While untreated animals (Group I) died within 7 days (6.8±0.2 days) post-transplantation (Tx), the use however of IS resulted in prolonged (30.2±6.8 days) survival of xenogeneic recipients (Group III) who eventually succumbed to rejection. A precipitous decline in total serum bilirubin (TBili) from pre-operative levels of 5.3±1.0 mg/dL to 0.5±0.2 mg/dL was noted in both Group I and III animals, an observation that sustained itself only in the latter group during the course of their follow-up. The decrease in TBili was also associated with a contemporaneous increase in biliary concentration of conjugated bilirubin. No noticeable reversal of hyperbilirubinemia was however observed in OLTx recipients of syngeneic grafts (Group II). Taken together, these data suggest that hamster albumin and hepatocyte-associated xenoproteins and enzymes involved in the process of membrane transport and glucuronidation of bilirubin, functioned efficaciously after OLTx in Gunnj/jrats, resulting in the reversal of the inborn error of metabolism for the duration of follow-up. © Munksgaard, Copenhagen

Cellular and Molecular Bases of the Initiation of Fever

All phases of lipopolysaccharide (LPS)-induced fever are mediated by prostaglandin (PG) E(2). It is known that the second febrile phase (which starts at ~1.5 h post-LPS) and subsequent phases are mediated by PGE(2) that originated in endotheliocytes and perivascular cells of the brain. However, the location and phenotypes of the cells that produce PGE(2) triggering the first febrile phase (which starts at ~0.5 h) remain unknown. By studying PGE(2) synthesis at the enzymatic level, we found that it was activated in the lung and liver, but not in the brain, at the onset of the first phase of LPS fever in rats. This activation involved phosphorylation of cytosolic phospholipase A(2) (cPLA(2)) and transcriptional up-regulation of cyclooxygenase (COX)-2. The number of cells displaying COX-2 immunoreactivity surged in the lung and liver (but not in the brain) at the onset of fever, and the majority of these cells were identified as macrophages. When PGE(2) synthesis in the periphery was activated, the concentration of PGE(2) increased both in the venous blood (which collects PGE(2) from tissues) and arterial blood (which delivers PGE(2) to the brain). Most importantly, neutralization of circulating PGE(2) with an anti-PGE(2) antibody both delayed and attenuated LPS fever. It is concluded that fever is initiated by circulating PGE(2) synthesized by macrophages of the LPS-processing organs (lung and liver) via phosphorylation of cPLA(2) and transcriptional up-regulation of COX-2. Whether PGE(2) produced at the level of the blood–brain barrier also contributes to the development of the first phase remains to be clarified