Steatosis is not sufficient to cause an impaired regenerative response after partial hepatectomy in rats

BACKGROUND/AIMS: Fatty liver is known to be associated with increased mortality and morbidity after liver resection. The ability of fatty liver to regenerate after two-thirds partial hepatectomy was studied in three different models of steatosis in rats: obese Zucker rats, orotic acid-fed Wistar rats and Wistar rats fed a methionine-low, choline-deficient diet. METHODS: Liver regeneration was assessed 24 h after partial hepatectomy by bromodeoxyuridine incorporation (immunohistochemistry), proliferating cell nuclear antigen, cyclin E and cyclin-dependent kinase 2 protein expression (Western blot analysis) and cyclin-dependent kinase 2 activity (kinase assays using histone H1 as a substrate). RESULTS: No significant difference of proliferative response was found between orotic acid or methionine-low, choline-deficient diet-fed and control Wistar rats 24 h after partial hepatectomy. In contrast, hepatocyte proliferation in obese Zucker rats after partial hepatectomy was significantly reduced when compared with their lean controls. CONCLUSIONS: Steatosis per se does not impair liver regeneration. The reduced liver regeneration observed in obese Zucker rats may not be due to fatty infiltration itself but to other factors such as leptin receptor dysfunction.     

Growth hormone promotes early initiation of hepatocyte growth factor gene expression in the liver of hypophysectomized rats after partial hepatectomy.

GH accelerates hepatic regeneration in the rat. Hepatocyte growth factor (HGF), a potent hepatocyte mitogen in vitro, is considered to be a major regulator of hepatic regeneration. In the present study, the effects of GH and insulin-like growth factor-I (IGF-I) on HGF gene expression in regenerating rat liver was investigated. In hypophysectomized rats treated with GH, hepatic HGF mRNA levels were increased 3 h after partial hepatectomy and reached peak levels after 5 h. In rats with intact pituitaries and in hypophysectomized rats not given GH treatment, HGF mRNA levels in liver were unchanged during the first 5 h following hepatectomy and reached peak levels after 10-18 h. DNA synthesis in the liver of GH-treated rats increased from low levels 10 h after hepatectomy to peak levels after 18 h. In rats without GH treatment the synthesis of DNA was still low 18 h after hepatectomy and was increased after 26 h. Treatment of hypophysectomized rats with IGF-I promoted increases in hepatic HGF mRNA levels and DNA synthesis 3.5 h and 15 h after hepatectomy respectively. HGF mRNA levels were constantly lower after sham-hepatectomy than after partial hepatectomy. In summary, in hypophysectomized rats the responses of hepatic HGF gene expression and DNA synthesis to partial hepatectomy were both accelerated by treatment with GH or IGF-I.     

大鼠部分肝切除后肝细胞生长因子激活因子抑制因子1,2的表达

目的探讨肝细胞生长因子激活因子抑制因子(hepatocyte growth factor activator inhibitor,HAI)1、HAI-2在部分肝切除后的表达特点,分析HAI-1和HAI-2在肝再生中的作用。方法随机将健康雄性SD大鼠分成对照组和肝切除组,各30只。在肝切除手术前和手术后3 h、12 h、24 h以及48 h时,对比2组HAI-1和HAI-2 mRNA和蛋白的表达变化。结果手术前2组HAI-1、HAI-2的mRNA及蛋白均呈显著低表达,组间无明显差异(P0.05);与手术前相比,术后对照组HAI-1、HAI-2的mRNA及蛋白均无明显变化(P0.05);而肝切除组HAI-1 mRNA和蛋白表达水平先显著升高再逐渐下降,同时间点与对照组比较,差异均有统计学意义(P0.05);HAI-2 mRNA和蛋白则无明显变化(P0.05)。结论 HAI-1在部分肝切除肝细胞再生过程中呈持续高表达,其可能参与了肝细胞再生过程,而HAI-2对肝再生过程无明显影响。     

Fas (APO-1/CD95) mRNA is down-regulated in liver regeneration after hepatectomy in rats

The interaction of Fas (APO-1/CD95) and the Fas ligand system induces apoptosis. However, the role of the Fas/Fas ligand system in normal physiological liver cell death remains to be determined. Using northern blotting analysis, we investigated the role of Fas and Fas ligand mRNA expression in liver regeneration in rats until 14 days after partial hepatectomy. Partial hepatectomy led to a significant decrease in Fas mRNA levels at 2 h, with a further gradual reduction until 18 h. The minimum Fas mRNA levels persisted until 5 days after the surgery. Fas mRNA levels then increased markedly at 6 days, and gradually increased to the initial levels by 14 days after the surgery. However, partial hepatectomy did not affect the expression of Fas ligand mRNA levels. These findings suggest that Fas mRNA is down-regulated in liver regeneration after partial hepatectomy, and that when the original liver mass is gradually regenerating, Fas mRNA is again up-regulated to the initial levels. Received: March 4, 1999 / Accepted: July 23, 1999     

Liver regeneration is impaired in lipodystrophic fatty liver dystrophy mice

We previously reported that mice subjected to partial hepatectomy exhibit rapid development of hypoglycemia followed by transient accumulation of fat in the early regenerating liver. We also showed that disrupting these metabolic alterations results in impaired liver regeneration. The studies reported here were undertaken to further characterize and investigate the functional importance of changes in systemic adipose metabolism during normal liver regeneration. The results showed that a systemic catabolic response is induced in each of two distinct, commonly used experimental models of liver regeneration (partial hepatectomy and carbon tetrachloride treatment), and that this response occurs in proportion to the degree of induced hepatic insufficiency. Together, these observations suggest that catabolism of systemic adipose stores may be essential for normal liver regeneration. To test this possibility, we investigated the hepatic regenerative response in fatty liver dystrophy (fld) mice, which exhibit partial lipodystrophy and have diminished peripheral adipose stores. The results showed that the development of hypoglycemia and hepatic accumulation of fat was attenuated and liver regeneration was impaired following partial hepatectomy in these animals. The fld mice also exhibited increased hepatic p21 expression and diminished plasma levels of the adipose-derived hormones adiponectin and leptin, which have each been implicated as regulators of liver regeneration. Conclusion: These data suggest that the hypoglycemia that develops after partial hepatectomy induces systemic lipolysis followed by accumulation of fat derived from peripheral stores in the early regenerating liver, and that these events may be essential for initiation of normal liver regeneration.     

Hyperbaric oxygenation promotes regeneration of biliary cells and improves cholestasis in rats

AIM:To investigate the effects of hyperbaric oxygenation(HBO) on regeneration of the biliary ductal system and postoperative cholestasis in hepatectomized rats.METHODS:HBO was performed in Wistar rats daily starting 12 h after a 70% partial hepatectomy.Regenerated liver weight,serum parameters and the proliferating cell nuclear antigen labeling index of hepatocytes and biliary ductal cells were measured.Hepatocyte growth factor(HGF),c-Met and transforming growth factor(TGF) β-1 mRNA expression levels were a...     

PPAR alpha is necessary for the lipopenic action of hyperleptinemia on white adipose and liver tissue

Adenovirus-induced hyperleptinemia causes rapid disappearance of body fat in normal rats, presumably by up-regulating fatty acid oxidation within white adipocytes. To determine the role of peroxisomal proliferation-activated receptor (PPAR)alpha expression, which was increased during the rapid loss of fat, we infused adenovirus-leptin into PPAR alpha(-/-) and PPAR alpha(+/+) mice. Despite similar degrees of hyperleptinemia and reduction in food intake, epididymal fat pad weight declined 55% in wild-type but only 6% in PPAR alpha(-/-) mice; liver triacylglycerol fell 39% in the wild-type group but was unchanged in PPAR(-/-) mice. Carnitine palmitoyl transferase-1 mRNA rose 52% in the wild-type mice but did not increase in PPAR alpha(-/-) mice. PPAR gamma coactivator-1 alpha rose 3-fold in the fat and 46% in the liver of wild-type mice but was unchanged in PPAR alpha(-/-) mice. Although AMP-activated protein kinase could not be implicated in the lipopenic actions of hyperleptinemia, acetyl CoA carboxylase protein was reduced in the liver of wild-type but not in PPAR alpha(-/-) mice. Thus, in PPAR alpha(-/-) mice, up-regulation of carnitine palmitoyl transferase-1 mRNA in fat, down-regulation of acetyl CoA carboxylase in liver, and up-regulation of PPAR gamma coactivator-1 alpha mRNA in both tissues are abolished, as is the reduction in their triacylglycerol content.     

Sex difference in hepatic peroxisome proliferator-activated receptor alpha expression: influence of pituitary and gonadal hormones

Peroxisome proliferator-activated receptor (PPAR) alpha is a nuclear receptor that is mainly expressed in tissues with a high degree of fatty acid oxidation such as liver, heart, and skeletal muscle. Unsaturated fatty acids, their derivatives, and fibrates activate PPARalpha. Male rats are more responsive to fibrates than female rats. We therefore wanted to investigate if there is a sex difference in PPARalpha expression. Male rats had higher levels of hepatic PPARalpha mRNA and protein than female rats. Fasting increased hepatic PPARalpha mRNA levels to a similar degree in both sexes. Gonadectomy of male rats decreased PPARalpha mRNA expression to similar levels as in intact and gonadectomized female rats. Hypophysectomy increased hepatic PPARalpha mRNA and protein levels. The increase in PPARalpha mRNA after hypophysectomy was more pronounced in females than in males. GH treatment decreased PPARalpha mRNA and protein levels, but the sex-differentiated secretory pattern of GH does not determine the sex-differentiated expression of PPARalpha. The expression of PPARalpha mRNA in heart or soleus muscle was not influenced by gender, gonadectomy, hypophysectomy, or GH treatment. In summary, pituitary-dependent hormones specifically regulate hepatic PPARalpha expression. Sex hormones regulate the sex difference in hepatic PPARalpha levels, but not via the sexually dimorphic GH secretory pattern.     

Regulatory effects of corticosterone on ornithine decarboxylase activity during liver regeneration in rats

AIMS: The regulation of ornithine decarboxylase (ODC) gene expression and enzyme activity by corticosterone during rat liver regeneration induced by partial hepatectomy (PH) was evaluated. METHODS: Bilateral adrenalectomies were performed on ether-anesthetized rats 3 days before PH. Corticosterone in sesame oil was injected subcutaneously to adrenalectomized rats. ODC mRNA, ODC protein and enzyme activity were detected by in situ hybridization, Western blot and high performance liquid chromatography (HPLC), respectively. RESULTS: The ODC mRNA levels, protein accumulation and enzyme activity were lower in the intact liver compared to the regenerating liver. After PH, mRNA levels were remarkably enhanced in all groups and peaked at 5 h post-PH, and presented a persistent increase only in adrenalectomy rats during the regeneration process. Corticosterone treatment resulted in a dose-dependent decrease in ODC mRNA content after 5 h post-PH. ODC protein accumulation in adrenalectomy rats was higher than that in sham-adrenalectomy rats, but it decreased in corticosterone-treated (10 mg/kg) rats until 24 h post-PH, with a strong decline seen in 40 mg/kg corticosterone-treated rats. ODC activity was rapidly promoted, and the highest levels were observed at 6 h after PH in all groups. After corticosterone treatment, the activities declined significantly at 6 h post-PH, with the lowest value found in the 40 mg/kg group. CONCLUSIONS: Corticosterone treatment results in dose-dependent decreases in ODC mRNA and enzyme protein both in the intact liver and the regenerating liver. The change in ODC activity is partially related to alterations of ODC mRNA and protein accumulation.     

Differential expression of basolateral and canalicular organic anion transporters during regeneration of rat liver

BACKGROUND & AIMS: Liver regeneration in response to various forms of injury or surgical resection is a complex process resulting in restoration of the original liver mass and maintenance of liver-specific functions such as bile formation. However, liver regeneration is frequently associated with cholestasis, whose molecular pathogenesis remains unknown. METHODS: To study the molecular mechanisms leading to cholestasis, expression of all major hepatic organic anion transporters contributing to bile formation was determined for up to 2 weeks in rats after 70% partial hepatectomy. RESULTS: Inversely related to serum bile acid levels, basolateral transporters including the sodium-taurocholate cotransporter (Ntcp) and the organic anion transporting polypeptides Oatp1 and Oatp2 were markedly down-regulated at both protein and steady-state mRNA levels by 50%-60% of controls (P < 0.05) during early replicative stages of regeneration (12 hours to 2 days) with a slightly delayed time course for Oatp2. Expression of all basolateral transporters returned to control values between 4 and 4 days after partial hepatectomy. In contrast, protein and mRNA expression of both the canalicular ATP-dependent bile salt export pump (Bsep) and the multiorganic anion transporter Mrp2 remained unchanged or were slightly increased during liver regeneration, but also returned to control values 7-14 days after partial hepatectomy. CONCLUSIONS: The data suggest a differential regulation of basolateral and canalicular organic anion transporters in the regenerating liver. Unaltered expression of Bsep and Mrp2 provides a potential molecular mechanism for regenerating liver cells to maintain or even increase bile secretion expressed per weight of remaining liver. However, down-regulation of basolateral organic anion transporters might protect replicating liver cells by diminishing uptake of potentially hepatotoxic bile salts, because the remaining liver initially cannot cope with the original bile acid pool size.     

Effect of serotonin receptor 2 blockage on liver regeneration after partial hepatectomy in the rat liver.

The effect of serotonin receptor 2 blockade (5-HT(2)) on liver regeneration after 30-34% and 60-70% partial hepatectomy in the rat liver was investigated. Materials and methods: Male Wistar rats were subjected to 60-70% (group I) and 30-34% (group II) partial hepatectomy. Serotonin receptor 2 blockade was exerted by intraperitoneal administration of ketanserin at different doses and time points after partial hepatectomy. The rats of all groups were killed at different time points until 96 h after partial hepatectomy. The rate of liver regeneration was evaluated by the mitotic index in hematoxylin and eosin sections, the immunochemical detection of Ki67 and proliferating cell nuclear antigens, the rate of [(3)H]-thymidine incorporation into hepatic DNA and liver thymidine kinase enzymatic activity. Results: Liver regeneration peaked at 24 and 32 h after partial hepatectomy in 60-70% hepatectomized rats. In 30-34% hepatectomized rats liver regeneration peaked at 60 h, whereas low rates of regenerative activity were observed between 24 and 72 h after partial hepatectomy. Ketanserin administration arrested liver regeneration only when administered at 16 h after 60-70% partial hepatectomy. Ketanserin also abrogated the observed peak of regenerative activity at 60 h in 30-34% hepatectomized rats when administered at 52 h after partial hepatectomy. All indices of liver regeneration were affected by ketanserin administration. Conclusions: Serotonin receptor 2 blockade can arrest liver regeneration only when administered close to G1/S transition point, and that while serotonin may be a cofactor for DNA synthesis, it does not play a role in initiation of liver regeneration.