Liver regeneration in young and weaning animals: report of an experimental model, molecular and histopathological studies, and effect of immunosupressive drugs

Abstract

Liver regeneration is a complex physiological response that takes place after the loss of hepatocytes caused by liver injury, and in patients submitted to partial liver transplantation. It depends on hepatocyte and stem cells proliferation, the starting mechanisms (cell growth factors and cytokines) and hepatocyte apoptosis (programmed cell death). Among the experimental models for hepatic regeneration studies, there are no reports about experimental models of liver regeneration utilizing newborns or young weaning animals. In addition, the molecular mechanisms of cell proliferation and apoptosis, during the liver regenerating process were not adequately studied, as well as the effects of immunosuppressive drugs, administered in the postoperative period of liver transplantation. Purposes: 1. To standardize the experimental model of hepatic regeneration in suckling newborn animals. 2. To compare the features of the newborn rat liver regenerating process with the 21-day weaning rat; 3. To study the molecular phenomena involved in the liver regeneration, mainly those related to the genes of apoptosis and cellular proliferation; 4. To verify the effects of immunosuppressive drugs, Tacrolimus and corticosteroids on the hepatic regeneration. Material and methods: 1. Pilot plan: newborn suckling rats (age 4-7 days) will be submitted to 80% hepatectomy. The animals will be weighted and sacrificed 1, 2, 3, and 7 days after the surgery in order to harvest the remnant liver. Young weaning animals will be submitted to similar procedures. Histological analyses will be performed in the remnant livers and compared with control, non operated animals. Experimental groups: newborn rats (age 4-5 days) and young rats will be submitted to the surgical procedure and compared to non operated control animals. Tacrolimus and corticosteroids will be administered to similar groups of animals. The animals will be sacrificed in the 1st and 4th postoperative day, and the remnant liver will be harvested for histological, histomorphometric and molecular studies: to quantitate the expression levels of the cellular proliferation genes (interleukin 6) and of the apoptotic Bcl-2 gene family (Bcl-2, Bcl-xl, Bak e Bax). The present experimental work is planned to be the first one among a sequence of some experimental investigations that will be performed in the Pediatric Surgery Laboratory of University of São Paulo Medical School (LIM-30). The main purpose of these investigations is the study of the molecular mechanisms involved in the hepatic regeneration process. (AU)