Serum hormone levels following partial hepatectomy in the rat.

Serum levels of insulin, glucagon, growth hormone (somatotrophin) and thyroxine (TT₄) were measured by radioimmunoassay following both sham operation and 70% partial hepatectomy in the rat to evaluate changes in hormone levels during liver regeneration. An eleven fold increase in glucagon was observed (from 112 ± 10 pg/ml to 1500 ± 200 pg/ml) 6 hours following partial hepatectomy but not sham operation. In contrast, insulin levels remained unchanged compared to sham controls for up to 72 hr while growth hormone fell to low levels, 6 to 48 hr after partial hepatectomy. Both total thyroxine and free thyroxine levels also fell 24–72 hours after hepatectomy. These studies suggest that growth hormone, thyroxine and insulin are not primary stimulants of hepatic regeneration although the data suggests that glucagon may modify this growth process.     

Impaired hepatic regeneration in metallothionein-I/II knockout mice after partial hepatectomy

Although the translocation of metallothionein (MT) from cytoplasm to nucleus has been demonstrated in liver during times of high requirement for zinc (fetal development and the neonatal period), the role of MT in cellular growth is not well understood. In this study, a potential role of MT in liver regeneration was investigated in wild type (WT) and MT-I and MT-II gene knockout (MT-null) mice after 35% partial hepatectomy (PH) or sham laparotomy. Hepatic MT levels and proliferation index were measured at 0, 5, 15, 24, 36, 48, and 60 hrs after PH and 48 hrs after sham laparotomy (control). MT levels were increased in WT mice (peak at 24 hrs after PH) and declined to normal levels by 60 hrs after PH. Immunohistochemical staining for MT in WT mice indicated the presence of MT in both nucleus and cytoplasm of hepatocytes at 24 hrs after PH, whereas MT was present mainly in the cytoplasm at 36-60 hrs after PH and 48 hrs after sham laparotomy. Hepatic proliferation index in both WT and MT-null mice, as determined by argyrophilic nucleolar organizing region staining and proliferating cell nuclear antigen immunohistochemical staining, reached a peak at 48 hrs and declined by 60 hrs after PH. Cell proliferation was significantly less in MT-null mice as compared to WT mice during liver regeneration after PH. These results suggest that MT may play a positive role in hepatic regeneration after PH.     

Endocrine changes following partial hepatectomy

Subtotal hepatectomy and all the paraoperative actions induce a condition of stress characterized by the intensification of catabolic processes and overproduction of hormones with glycogenolytic and lypolytic action: catecholamines, T3, T4, ensuring the conditions required by some energy-dependent processes (mitoses and proteosyntheses) assuring the regeneration of the operated liver. The latter presents a depletion of dehydrogenases, of PAS + materials and fatty loading of the liver cells. In the conditions of liver distress, the muscles are those which supply the glucose, ensuring an as rapid as possible return of glycemia to normal values.     

The nucleolar protein NML regulates hepatic ATP levels during liver regeneration after partial hepatectomy

We previously identified a novel protein complex, eNoSC, which senses intracellular energy status and epigenetically regulates the rDNA locus by changing the ratio between the numbers of active and silent gene clusters. eNoSC contains a novel nucleolar protein, Nucleomethylin (NML), which has a methyltransferase-like domain and binds to Lys9-dimethylated histone H3 at the rDNA locus, along with the NAD⁺-dependent deacetylase SIRT1 and the histone methyltransferase SUV39H. The aim of this study was to determine the role of NML in liver after partial hepatectomy (PHx). We assessed liver regeneration and lipid metabolism after PHx in wild-type (WT) and NML transgenic (NML-TG) mice. Survival rates of NML-TG mice were reduced after PHx. We found that hepatic triglyceride content in NML-TG mice remained elevated 48 h after PHx, but not delayed liver regeneration. Moreover, hepatic ATP levels in NML-TG mice were higher than that in WT 48 h after PHx. These observations suggest that NML may regulate consumption of hepatic triglyceride in liver regeneration after PHx due to storage of excess ATP. The delayed consumption of hepatic triglyceride may be the cause of reduced survival rate in NML-TG mice.     

PI3K/Akt activation is critical for early hepatic regeneration after partial hepatectomy

Hepatic resection is associated with rapid proliferation and regeneration of the remnant liver. Phosphatidylinositol 3-kinase (PI3K), composed of a p85alpha regulatory and a p110alpha catalytic subunit, participates in multiple cellular processes, including cell growth and survival; however, the role of PI3K in liver regeneration has not been clearly delineated. In this study, we used the potent PI3K inhibitor wortmannin and small interfering RNA (siRNA) targeting the p85alpha and p110alpha subunits to determine whether total or selective PI3K inhibition would abrogate the proliferative response of the liver after partial hepatectomy in mice. Hepatic resection is associated with an induction in PI3K activity; total PI3K blockade with wortmannin and selective inhibition of p85alpha or p110alpha with siRNA resulted in a significant decrease in hepatocyte proliferation, especially at the earliest time points. Fewer macrophages and Kupffer cells were present in the regenerating liver of mice treated with wortmannin or siRNA to p85alpha or p110alpha, as reflected by a paucity of F4/80-positive cells. Additionally, PI3K inhibition led to an aberrant architecture in the regenerating hepatocytes characterized by vacuolization, lipid deposition, and glycogen accumulation; these changes were not noted in the sham livers. Our data demonstrate that PI3K/Akt pathway activation plays a critical role in the early regenerative response of the liver after resection; inhibition of this pathway markedly abrogates the normal hepatic regenerative response, most likely by inhibiting macrophage infiltration and cytokine elaboration and thus hepatocyte priming for replication.     

Fas engagement accelerates liver regeneration after partial hepatectomy

Fas (CD95) is a receptor involved in induction of apoptotic cell death of Fas-bearing cells, including hepatocytes and T cells. Injection of Fas-specific antibodies into mice leads to fulminant hepatic failure and death. Fas also transduces growth-promoting signals in proliferating T cells, fibroblasts and some tumor cells. Here we show that partial hepatectomy, which triggers the immediate onset of liver regeneration, protected mice against the lethal effects of Fas-specific antibodies and prevented hepatocyte apoptosis in response to Fas engagement in vivo. Furthermore, Fas engagement accelerated liver regeneration after partial hepatectomy. Liver regeneration kinetics were delayed in mutant mice with decreased cell surface Fas expression (lpr mice). In contrast, regeneration was not delayed in lpr-cg mutant mice, which have a Fas mutation that prevents Fas-induced death but not Fas-dependent proliferative stimulation. Our results indicate that Fas engagement on cells in regenerating or healing tissues may promote cell growth.     

The degree of hepatic regeneration after partial hepatectomy in rats with peritonitis and the role of lipid peroxidation

Bile accumulation in the peritoneal cavity after partial hepatectomy reduces hepatic regeneration. In 70% of hepatectomized rats with bile peritonitis, hepatic DNA synthesis showed a delayed initiation and diminished peak level. Because intraperitoneal bile significantly accelerated lipid peroxidation and decreased energy metabolism in the liver remnant, all hepatectomized rats with bile peritonitis died within 7 days. Subcutaneous administration of exogenous combined antioxidants SOD and catalase dramatically reduced lipid peroxidation and improved the survival rate. Although the slightly elevated serum endotoxin level in rats with peritonitis may play a role in the inhibition of hepatic regeneration, the result suggest that intraperitoneal accumulation of bile components may also directly accelerate lipid peroxidation in the liver remnant, inhibiting the hepatic regeneration.     

Ultrastructural zonal heterogeneity of hepatocytes and mitochondria within the hepatic acinus during liver regeneration after partial hepatectomy

BACKGROUND INFORMATION: Partial hepatectomy (70%) induces cell proliferation until the original mass of the liver is restored. In the first 24 h after partial hepatectomy, drastic changes in the metabolism of the remaining liver have been shown to occur. To evaluate changes in hepatocyte ultrastructure within the hepatic acinus during the liver regenerative process, we investigated, by light and electron microscopy observations on specimens taken 0 h, 24 h and 96 h after partial hepatectomy, the hepatocyte structure and ultrastructure in the periportal and pericentral area of the hepatic acinus, with a particular emphasis on mitochondria ultrastructure. Moreover, some biochemical events that could affect the mitochondria ultrastructure and function were investigated. RESULTS: We found that, 24 h after partial hepatectomy, mitochondria with altered ultrastructure were preferentially localized in the periportal area. Periportal hepatocytes showed also an increase in the number of peroxisomes, free ribosomes, lysosomes and autophagosomes. Altered mitochondria showed swelling, an ultrastructural index of increased membrane permeability, a reduction in the number of cristae, and a rarefied, often vacuoled, matrix. Consistently, an increase in the mitochondrial oxidized/reduced glutathione ratio was found as well as calcium release from mitochondria in a manner inhibited by cyclosporin A. Interestingly, light and electron microscopy analysis showed that the hepatocytes in the periportal area were the cells with the major structural attributes to proliferate. At 96 h after partial hepatectomy, the preferential zonation of altered mitochondria was lost and the normal mitochondrial membrane permeability properties were restored. CONCLUSIONS: We suggest that 24 h after partial hepatectomy, a preferential zonation of altered mitochondria in the periportal hepatocytes could be involved in the changes of metabolic and functional heterogeneity of the hepatocytes within the hepatic acinus during the regenerative process.     

Effect of Kupffer cell blockade at different periods following partial hepatectomy on regeneration of hepatocytes

In male Wistar rats, weighing 140-160 g, the block of the liver mononuclear phagocyte system (MPS) was carried out by means of "carbonyl iron" (type R-100F, particle size 1-1.5 micron). It was induced 2 hours before or 3 and 18 hours after partial hepatectomy. Iron injection previously or at the early prereplicative regeneration period led to a significant delay of the hepatocyte nucleus labeling and mitotic indices peaks against the background of an overall depression of hepatocyte proliferation. The MPS block during the intensive DNA synthesis by regenerating liver hepatocytes was less effective. The facts testify to the importance of Kupffer's cells in the regulation of the reparative liver regeneration.     

Course of liver regeneration after partial hepatectomy in rats treated with dialysates obtained 17 hours after partial hepatectomy

Various theories have been put forward to explain the regenerative capacity of liver tissue induce by partial hepatectomy (PH). One of them presumes the existence of humoral factors stimulating proliferation of the liver tissue. We evaluated the course of liver regeneration after 65-70% PH as influenced by dialysates (DIA) of the organs of a rat killed 17 h after PH. In addition to kidney DIA, we were particularly interested in the effect of liver and spleen DIA. The experiments were carried out on rats weighting 310-370 g. Kidney, liver or spleen dialysate was administered subcutaneously and the rats were killed 12 or 24 h later by exsanguination from the abdominal aorta. In further rats, PH was performed 24 h after administering DIA and the rat were killed 18, 24, 30, 48 and 72 h after the operation. The initiation of liver regeneration was stimulated by all the given DIA, but especially by liver DIA. The faster onset of liver regeneration 18 h after PH in rats given spleen DIA is interesting. DIA did not greatly affect the hepatocytes of intact liver, but accelerated the initiation of liver regeneration after PH by synchronizing the cell cycle of proliferating hepatocytes. DIA obtained 17 h after PH contained substances which primarily stimulated liver DNA synthesis. From the changes in inhibition of the migration of spleen macrophages in the medium containing liver antigens, and from the circulating immunocomplex values, we conclude that DIA activation of the immune system, a well as the hepatic stimulator substance contained in the DIA, participates in acceleration of the liver regeneration process.     

Delayed liver regeneration after partial hepatectomy in adiponectin knockout mice

We previously demonstrated that adiponectin has anti-fibrogenic and anti-inflammatory effects in the liver of mouse models of various liver diseases. However, its role in liver regeneration remains unclear. The aim of this study was to determine the role of adiponectin in liver regeneration. We assessed liver regeneration after partial hepatectomy in wild-type (WT) and adiponectin knockout (KO) mice. We analyzed DNA replication and various signaling pathways involved in cell proliferation and metabolism. Adiponectin KO mice exhibited delayed DNA replication and increased lipid accumulation in the regenerating liver. The expression levels of peroxisome proliferator-activated receptor (PPAR) α and carnitine palmitoyltransferase-1 (CPT-1), a key enzyme in mitochondrial fatty acid oxidation, were decreased in adiponectin KO mice, suggesting possible contribution of altered fat metabolism to these phenomena. Collectively, the present results highlight a new role for adiponectin in the process of liver regeneration.