5-HT及其受体在大鼠肝再生过程中的作用

目的分析5-羟色胺（5-HT）及其受体在大鼠肝脏再生过程中的作用。方法将50只雄性Wistar大鼠随机分成实验组和对照组。实验组大鼠于肝大部分切除术后24、36、48和72h处死,对照组行假手术。采用流式细胞技术检测大鼠肝脏增殖细胞核抗原（PCNA）表达、免疫组化法检测Ki67及5-HT表达、实时荧光定量PCR检测5-HT2A、2B受体亚型的表达。结果肝大部切除术后大鼠肝脏重量逐渐增加,PCNA和Ki67表达于术后24和36h达高峰;在肝切除术后各个时间点5-HT2A、2B受体在肝脏中的表达均显著升高,以术后36h最高;术后36h空肠嗜铬细胞5-HT含量高于24h,且都高于正常大鼠。结论肝脏再生过程中5-HT合成及其受体表达均显著上调,可能与肝脏的再生有关。     

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.     

Plasma-kallikrein clearance during liver regeneration after partial hepatectomy in the rat

Abstract: Aims/Background: The liver clears circulating plasma-kallikrein through a receptor-mediated endocytosis process: an initial fast phase is followed by a slow exponential phase. Methods: To determine whether the clearance rate of plasma-kallikrein is affected during liver regeneration, we perfused isolated rat livers with rat plasma-kallikrein (rPK) at 0, 1, 2, 3 and 7 days after partial hepatectomy or sham operation. Results: Liver regeneration was followed by the expression of the proliferating-cell nuclear antigen (PCNA) labeling index. The serum concentration of α₂-macroglobulin, an acute phase protein in rats, was measured. At day 1, the fast phase of rPK clearance rate increased in hepatectomized rats when compared with day 0 (4.9±0.4 and 3.7±0.4 mU/g liver · min, p<0.05). However, at day 2, the rPK fast phase clearance rate dropped significantly (2.6±0.2, p<0.05), when compared with day 1. No difference was found among the sham groups at different days of hepatectomy. These changes seem to be independent of the acute phase reaction. The regenerative liver weight increased continuously during the observation period. PCNA expression increased significantly after hepatectomy, with maximal PCNA-labeling indices at days 1 and 2, declining thereafter. Conclusion: The rPK fast phase clearance rate changes during liver regeneration, with a zenith occurring when PCNA labeling index is maximal (day 1) and a nadir occurring at the mitotic phase (day 2).     

The effect of extrahepatic cholestasis on liver regeneration after partial hepatectomy in the rat

Abstract: Liver regeneration after partial hepatectomy was studied in four groups of rats: control rats (n=12), rats with 1 week of common bile duct obstruction (n=11), rats with restoration of bile flow after 1 week of obstruction (n=9) and a sham-operated group (n=7). Parameters of DNA synthesis – thymidine kinase activity and in vivo bromodeoxyuridine incorporation – were measured at partial hepatectomy (T=0), and 24 and 48 h after partial hepatectomy. During common bile duct obstruction, DNA synthesis was already stimulated at T=0, but partial hepatectomy in common bile duct obstruction rats induced a delayed DNA synthesis. After 1 week of restoration of bile flow, normal DNA synthesis had returned at T=0, but DNA synthesis after partial hepatectomy was still delayed. The sham-operated rats showed a normal regeneration response after partial hepatectomy assessed by bromodeoxyuridine incorporation but delayed as assessed by thymidine kinase activity, partly due to the impaired physical condition of the animals. The present data support the hypothesis that during cholestasis, regeneration promoting, and inhibitory factors accumulate in the liver, their balance determining whether regeneration after partial hepatectomy will occur in a normal, enhanced or delayed way.     

Kinetic changes of liver regeneration and hepatocellular carcinoma cells after partial hepatectomy in rats

We investigated, using rats, the effect of partial hepatectomy (PH) on hepatocellular carcinoma (HCC, KDH-8 and AH-66) cells, and the effect of HCC cells on the regeneration of remaining hepatocytes after PH. Our results showed that PH significantly enhanced the growth of HCC cells in rats. Tumor volume increased more significantly in the partially hepatectomized group (H-group) than in the control group, and the tumor wet weights on the 14th postoperative day were significantly higher in the H-group than in the control group. Such an enhanced growth effect of PH on the injected (s.c) HCC cells was related to an abrupt increase of tumor volume within 24 hours after operation, which was supported by the mitotic indices (MI) of the KDH-8 cells. These phenomena of the enhanced growth of the HCC cells following PH were not observed at all in rats injected with estrogen receptor (ER)-negative mammary carcinoma (SST-2) or nonepithelial fibrosarcoma (KMT-75) cells. The MIs of the remaining hepatocytes after PH increased abruptly at the 30th postoperative hour and reached a maximum at the 36th postoperative hour, and the MIs were significantly higher in the H-group with the KDH-8 cells than in the H-group without them from the 42th to the 60th postoperative hour. In the control group, the MIs of hepatocytes were not regardless of the presence of KDH-8 cells. From these results, we speculate that some growth factor(s) induced by PH may act on injected (s.c.) HCC cells, and that the other growth factor(s) secreted by HCC cells may act on the regenerating hepatocytes after PH. This work was supported in part by a grant from the Japanese Ministry of Education. Science and Culture.     

Review: Regulation of liver regeneration by pro-inflammatory cytokines

The liver has tremendous regenerative capacity. This distinguishes it from other vital organs (e.g. the brain, heart and lungs) that cannot replace functional tissue once it has been destroyed. Although hepatocytes rarely proliferate in the healthy adult liver, virtually all surviving hepatocytes replicate at least once after 70% partial hepatectomy. Therefore, partial liver resection has been used to characterize mechanisms that regulate liver regeneration. Residual hepatocytes up-regulate both proliferative and liver-specific gene expression in order to preserve tissue specific function. In addition, hepatocyte proliferation is tightly co-ordinated to complement regenerative responses in hepatic nonparenchymal cells (e.g. endothelia, biliary epithelia, stellate and Kupffer cells), so that the entire organ can be reconstituted within days. Studies with neutralizing antibodies to tumour necrosis factor-α (TNF) clearly demonstrate that, after partial hepatectomy, TNF promotes liver cell proliferation. The present review focuses on the regulation of the hepatocyte proliferative response by pro-inflammatory cytokines.     

FK506 promotes liver regeneration by suppressing natural killer cell activity

We examined the mechanism of promotion of liver regeneration by tacrolimus hydrate (FK506), a potent immunosuppressant, after partial hepatectomy. The administration of FK506 significantly increased the bromodeoxyuridine (BrdU) labelling index at 36 and 48 h after 70% hepatectomy compared with the placebo group. Using the same model, we examined the effect of FK506 on the expression of hepatocyte growth factor (HGF) and transforming growth factor-β1 (TGF-β1) and found no changes in HGF and TGF-β1 mRNA expression in the liver or in the HGF protein concentration in plasma. We found that pretreatment with FK506 markedly reduced the activity and number of liver-resident natural killer (NK) cells at the time of partial hepatectomy. Our observations suggest that the promotion of liver regeneration by FK506 may be attributable to a reduction in the number of liver-resident NK cells and to inhibition of their activity.     

Lack of endothelial autophagy does not impair liver regeneration after partial hepatectomy in mice

Liver sinusoidal endothelial cells (LSEC) are key elements in regulating the liver response to injury and regeneration. While endothelial autophagy is essential to protect endothelial cells from injury-induced oxidative stress and fibrosis, its role in liver regeneration has not been elucidated. This study was intended to investigate the role of endothelial autophagy in liver regeneration in the context of partial hepatectomy (PHx). Analysis of autophagy levels in rat LSEC after PHx indicated a tendency to decrease activity the first 2 days after surgery. PHx performed in mice with impaired endothelial autophagy (Atg7^flox/flox;VE-Cadherin-Cre⁺) and their littermate controls showed no differences neither in liver-to-body weight ratio, histological analysis, hepatocyte proliferation nor vascular integrity during the first 7 days after PH and liver regeneration was completely achieved. Our results indicate that endothelial autophagy does not play an essential role in the coordination of the liver regeneration process after PHx.     

Relevance between lipid metabolism-associated genes and rat liver regeneration.

Aim: Lipids are important in constituting cell structure and participating in many biological processes, particularly in energy supplementation to cells. The aim of the present study is to elucidate the action of lipid metabolism-associated genes on rat liver regeneration (LR). Methods: Lipid metabolism-associated genes were obtained by collecting website data and retrieving related articles, and their expression changes in the regenerating rat liver were checked by the Rat Genome 230 2.0 array. Results: In total, 280 genes involved in lipid metabolism were proven to be LR-associated by comparing the gene expression discrepancy between the partial-hepatectomy and sham-operation groups. The initial and total expression numbers of these genes occurring in the initial phase, G(0)/G(1) transition, cell proliferation, cell differentiation, and structure-functional rebuilding of LR were 128, 33, 135, 6, and 267, 147, 1026, 306, respectively, illustrating that these genes were initially expressed mainly in the initiation stage and functioned in different phases. Upregulation (850 times) and downregulation (749 times), as well as 25 types of expression patterns, showed that the physiological and biochemical activities were diverse and complicated in LR. Conclusion: According to the results of the chip detection, it was presumed that fatty acid synthesis at 24-66 h, leukotriene and androgen synthesis at 16-168 h, prostaglandin synthesis at 2-96 h, triglyceride synthesis at 18-24 h, glycosphingolipid synthesis at 0.5-66 h, metabolism of phosphatidyl inositol and sphingomyelin at 2-16 h, and cholesterol catabolism at 30-168 h were enhanced. Throughout almost the whole LR, the genes participating in estrogen, glucocorticoid, and progesterone synthesis, and triglyceride catabolism were upregulated, while phospholipid and glycosphingolipid catabolism were downregulated.