Mitomycin C-induced acceleration of liver cell polyploidization in adult rat after partial hepatectomy

Mitomycin C, a DNA cross-linking agent, was administered for a week intraperitoneally to a normal 9-week-old rat in which hepatocyte proliferative activity had almost ceased. In the rat treated with mitomycin C, the number of polyploid cells with the DNA amounts more than 4C was not increased in comparison with that in the control rat without any treatment. However, the partial hepatectomy in the rat pretreated with mitomycin C provoked prominent hepatocyte polyploidization much greater in degree than that found in the hepatectomized rat without mitomycin C treatment. These results seem to indicate that the existence of cross-linking DNA damages is a latent factor necessary for the induction of abortive mitosis of a cell after completion of DNA synthesis, which results in the production of a mononuclear polyploid cell in one-step higher DNA class. Cross-linking DNA damages and DNA synthesis are the essential factors for the manifestation of polyploidization.     

Effect of the activation of macrophages on the course of regeneration of rat liver following partial hepatectomy

Stimulation of the Kupffer cells with E. coli endotoxin (the purified lipopolysaccharide) or with prodigiosan (a polysaccharide from Serratia marcescens) 24 h before partial hepatectomy (resection of 65-70% of the liver) stimulated and intensified the onset of liver regenerative activity (evaluated from changes in liver DNA synthesis, the H5 labelling index and the mitotic activity of the hepatocytes). Liver DNA synthesis increased together with the dose of endotoxin (i.v., from 25 to 1000 micrograms/kg body weight). If E. coli endotoxin was injected during or 3 h after partial hepatectomy, partial inhibition of liver DNA synthesis was observed. In mice stimulated with zymosan (a polysaccharide isolated from yeast), administered 5 days before performing partial hepatectomy, proliferation of the hepatocytes (evaluated from changes in the 3H labelling index and in the mitotic activity of the hepatocytes) was evaluated. The results confirm that proliferation is correlated to the state of reactivity of the Kupffer cells.     

Accumulation and release of triglycerides by rat liver following partial hepatectomy

Regenerating liver accumulates lipid for about 20 hr following partial hepatectomy. During this time incorporation of intravenously administered palmitate-9, 10-(3)H into beta-lipoprotein increased. 13 hr after partial hepatectomy, there was no change in the level of serum beta-lipoproteins, but the specific activities of the triglycerides in the liver and beta-lipoproteins were significantly diminished. Extension of these studies to the isolated perfused liver system demonstrated that 13 hr after partial hepatectomy the regenerating liver is capable of secreting greater quantities of the lipid, but not the protein, moiety of the beta-lipoproteins in comparison with liver taken immediately from a partially hepatectomized animal, although there was no difference between the weights of the livers. However following addition of palmitate-(3)H and (14)C-labeled amino acids to the perfusate, the specific activity of the hepatic and beta-lipoprotein triglycerides of the liver excised 13 hr after partial hepatectomy was diminished, but that of the protein was not affected. Prelabeling of the accumulated triglyceride with palmitate-1-(14)C in vivo revealed that the proportions of the accumulated triglyceride secreted as beta-lipoproteins by perfused livers excised immediately and 13 hr after partial hepatectomy were identical. It is concluded that regenerating liver rapidly acquires the ability to mobilize triglycerides at a rate equal to that of the much larger normal liver, so that it can handle all free fatty acids presented to it.     

Dynamics of Hlo content in rat liver after partial hepatectomy

• 1.1. The changes in the lysine-rich histone subfraction hl₀ have been quantitatively studied in rat liver during the regeneration period after partial hepatectomy.
• 2.2. A gradual decrease in this protein was found early after operation with a minimal value around the time of maximal mitotic activity.
• 3.3. The reduction in the hl₀ content paralleled well the increasing number 0f cells in the cell cycle.

     

In vitro stimulation of rat liver cells by homologous partial hepatectomy serum

Summary A low passage rat liver cell line demonstrated in vitro growth stimulation when cultured in the presence of serum of homologous, partially hepatectomized rats. After 4-day incubation a 3.25-fold increase in the cell population was observed in cultures supplemented with posthepatectomy serum at a dilution of 1∶10. No response was observed with sham-operated animal serum. Continous cultures of Chang human liver and Don hamster lung cells were not responsive to the posthepatectomy serum. The limitations of tetraphenylboron as a dispersing agent for primary rat liver cells are discussed. Supported by Grant 67-7 from the Illinois Division of the American Cancer Society.     

Folate metabolism in the rat liver during regeneration after partial hepatectomy

1. Folate metabolism was studied during the early phases of liver regeneration after partial hepatectomy in rats accustomed to eating during the first 8h of a daily 12h dark period. 2. The content of 5-CH(3)-H(4)folate was drastically decreased during the first hours of regeneration. 3. The total HCO-H(4)folate coenzymes showed a constant decrease during the first 3 days of regeneration, and a continuous interconversion between 5-HCO-H(4)folate and 10-HCO-H(4)folate. 4. 10-HCO-H(4)folate synthetase, serine hydroxymethyl-transferase and 5,10-CH(2)-H(4)folate dehydrogenase activities were relatively low during the first hours after the operation, and increased only several hours later. 5. The increase in enzyme activities showed a stepwise pattern, apparently due to an interaction between the regeneration process and the controlled feeding schedules.     

Thyroid status affects rat liver regeneration after partial hepatectomy by regulating cell cycle and apoptosis.

In rats, various growth factors and hormones, as well as partial hepatectomy (PH) are able to trigger the proliferative response of hepatocytes. Although recent evidence highlights the important role of thyroid hormones and thyroid status in regulating the growth of liver cells in vitro and in vivo models, the mechanism involved in the pro-proliferative effects of thyroid hormones is still unclear. Here we have investigated how in rats made hypo- and hyperthyroid after prolonged treatment respectively with propylthiouracil (PTU) and triiodothyronine (T3), the thyroid status affects liver regeneration after PH by regulating cell cycle and apoptosis proteins. Our results show that both in control and partially hepatectomized animals hyperthyroidism increases the cyclin D1, E and A levels and the activity of cyclin-cdk complexes, and decreases the levels of cdk inhibitors such as p16 and p27. On the contrary hypothyroidism induces a down-regulation of the activity of cyclin cdk complexes decreasing cyclin levels. Thyroid hormones control also p53 and p73, two proteins involved in apoptosis and growth arrest which are induced by PH. In particular, hypothyroidism increases and T3 treatment decreases p73 levels. The analysis of the phosphorylated forms of p42/44 and p38 MAPK revealed that they are induced during hepatic regeneration in euthyroid and hyperthyroid rats whereas they are negatively regulated in hypothyroid rats. In conclusion our data demonstrate that thyroid status can affects liver regeneration, altering the expression and the activity of the proteins involved in the control of cell cycle and growth arrest.     

Effect of rat liver chalones on liver cell proliferation at different times after partial hepatectomy]

The action of rat's liver ethanol extract (72--81 per cent saturation) on cell proliferation of this organ at various periods after a partial hepatectomy has been studied. The most sensitive periods of the action of G1- and G2-chalone were, resp., the time of cell transformation, and the middle of the premitotic period of cell cycle. The action of G2-chalone used is organ-specific, since the drug decreased the mitotic activity of both hepatocytes and stromal cells. At the same time, the proliferation of ear, tongue and small bowel epithelial cells remained unchanged.     

Specific gangliosides increase rapidly in rat liver following partial hepatectomy

Rat liver gangliosides (sialic acid containing glycosphingolipids) were analyzed by HPTLC and HPLC following either partial hepatectomy or sham operation. Analysis of whole liver gangliosides by HPTLC demonstrated that within 6 h after partial (68%) hepatectomy, there was a significant increase in GM1 compared to both sham and control animals. By 48 h, GM1 was further increased and the polysialylgangliosides GD1a, GD1b and GT1b had also risen significantly, whereas changes in GM3 were negligible. Gangliosides associated with the plasma membrane were increased up to 3.5-fold in regenerating liver compared to sham-hepatectomized controls as assessed by HPLC. Although elevations in membrane gangliosides were associated with hepatocyte proliferation, they did not closely follow the growth curve. The time course of changes in ganglioside biosynthesis suggests differential upregulation of GM3 synthase and GD3 synthase in regenerating livers.     

Oxygenation alters ganglioside expression in rat liver following partial hepatectomy

Gangliosides from livers of weanling rats were analyzed after 15% partial hepatectomy (PH) and different pre- and post-operative hyberbaric oxygenation (pre- and postHBO). Neu5Ac was the predominant ganglioside-derived sialic acid (>85%) compared to Neu5Gc. Almost identical low total sialic acid content (Neu5Ac+Neu5Gc) of the control and operated nonHBO animals opposed a 6.4- to 7.6-fold increase in pre- and postHBO animals (69.26 and 81.64pmol/mg wet weight, respectively). NanoESI-QTOF mass spectrometry combined with HPTLC immunostaining revealed GM3(Neu5Ac) and GM3(Neu5Gc) as major gangliosides, correlating with the respective sialic acid concentrations. Minor neolacto-series gangliosides were enhanced in preHBO and postHBO, but GM1-core gangliosides only in preHBO rats. GM2 and GalNAc-GM1b were clearly detectable in oxygenated rats compared to traces in the control and nonHBO animals. These results point at a functional role of gangliosides in liver growth regulation and reconstitution after PH combined with pre- and post-operative HBO treatment.     

Early changes in liver chromatin in response to partial hepatectomy]

Guinea-pig and mouse liver chromatin responds to the partial hepatectomy by an increase in binding of a basic dye acridine orange (AO) and by a decrease of its stability to heat in thermal denaturation test in situ. Degree of the changes in AO chromatin binding is identical in the cells of different ploidy and proportional to their DNA content. Treatment of the preparations by 0.6 M NaCl solutions under conditions bringing about the selective removal of histone H1 from the cells produces in vitro changes in DNA properties taking place in cells in vivo in the course of their activation. The treatment of cells with 0.35 M NaCl solution results in the disappearance of changes occurring in the chromatin of activated cells whereas the properties of control cells remain unchanged. The data obtained are interpreted as a result of the removal of some non-histone regulatory proteins from the chromatin of activated cells that is accompanied by changes in the character of DNA-histone interaction. At the time of maximum increase of AO binding a significant intensification of endogenous RNA polymerase activity was found, the incorporation of [3H] UTP in the nucleolus being higher than that in the extranucleolar part of the nucleus. High ionic strength in the incubation medium (0.4 M (NH4)2SO4) results in drastic increase of radioactive label in the nucleus and in the disappearance of differences between activated and non-activated chromatin. It is concluded that the intensification of RNA synthesis under the influence of proliferative stimulus is more likely dependent on the additional opening of DNA-matrix than on the direct activation of the enzyme.