Pro-apoptotic proteins and proliferation process: role of nitric oxide increased in partial hepatectomized rats

RONCO, M.T; ALVAREZ, M.L; MONTI, J.; CARRILLO, M.C; CARNOVALE C.E

Salvador, Brasil

Congreso; Biennial Scientific Meeting of the International Association for the Study of the Liver; 2004

International Association for the Study of the Liver

In the immediate hours following a partial hepatectomy (PH) exist an induction of inducible nitric oxide synthase (iNOS) and subsequent release of nitric oxide (NO). In a previous work we found a marked increase in the peak of DNA synthesis in hepatectomized animals when the NO production was diminished by two NOS inhibitors (aminoguanidine or N6-monomethyl L-arginine). In order to investigate the precise role of NO in liver regeneration, we study the effect of NO increase on the expression of pro-apoptotic proteins (Bax, p53) and antiapoptotic protein (Bcl-xL), as well as proliferation process. Two-thirds partial hepatectomy male Wistar rats were randomized in three experimental groups: control (PH-C), treated with iNOS inductor, LPS (2 mg/kg body weight, i.p.: PH-LPS) and treated with a NO donor, sodiumnitropruside (2.5 mg/kg body  weight i.v. at a rate of 1mL/h: PH-SNP). Animals were killed at 5 and 24 h after surgery. At 5 h post-PH, hepatic cytosolic iNOS showed an increase of 30% in PH-LPS animals with respect to PH-C, analyzed by immunoblotting. Cytosolic nitrate (expressed as nitrates nmol/100 mg protein) were higher in treated groups with respect  to PH-C at 5h post-PH (PH-C: 8.9±1.2; PH-LPS: 16.1±1.9*; PH-SNP: 20.5±2.6*). At 5 h post-surgery, the expression of liver mitochondrial Bax protein in PH-LPS and PH-SNP showed an increase of 56 and 45% with respect to PH-C, respectively. Levels of antiapoptotic protein Bcl-xL did not show difference between the groups studied. In liver total lysates, the expression of p53 protein showed an increase of 40% at 5 h post-PH in treated animals with respect to PH-C. No differences between PH-LPS, PH-SNP and PD-C were observed in proliferation process, evaluated by both estimation of DNA synthesis, [3H]thymidine incorporation and PCNA-immunohistochemical staining at 24 h after surgery. These results indicate that do not exist an increase of proliferation in resting liver after NO augmentation. On the other hand, the increase of NO result in cell death by apoptosis via the pro-apoptotic proteins Bax and p53. Our results suggest that NO can contribute in the tightly regulation of the growth process in liver regeneration.