Impaired liver regeneration after partial hepatectomy in db/db mice

Fatty liver is the most common hepatic disorder in humans and supposed to be a cause of poor prognosis after liver transplantation and hepatic resection which could be resulted from impaired liver regeneration. This study was carried out to analyze the process of liver regeneration in db/db mice which show severe steatosis because of abnormal leptin receptor. We performed 70% partial hepatectomy (PH) on db/db mice and normal +m/+m mice, and then sacrificed the animals 1, 2, 3, 5, 7 and 10 days later. The liver samples were weighed and examined histologically or immunohistochemically. As a result, the liver mass restitution was significantly inhibited in db/db mice compared with +m/+m mice. The BrdU labelling index peaked at 2 days after PH in both strains, although the value was lower in db/db mice. After that, interestingly, it decreased to the control level at 5 days in +m/+m mice while the recovery was delayed in db/db mice. Similar sequence was also observed in the PCNA labelling index. In addition, the peak time of the mitosis index was 2 days and 5 days after PH in +m/+m mice and in db/db mice, respectively. Thus, although not significant, the proliferative response of hepatocytes to PH occurred somewhat more transient and sharply in +m/+m mice while it lasted somewhat longer in db/db mice. This suggests that db/db mice may be valuable as one of the animal models for the investigation of the effects of steatosis on the liver regeneration.     

Dynamic change in expression of LECT2 during liver regeneration after partial hepatectomy in mice

Leukocyte-cell-derived chemotaxin 2 (LECT2) was first isolated from the culture fluid of phytohemagglutinin-activated human T-cell leukemia SKW-3 cells and was found to be expressed in the human, bovine and murine livers. To further analyze the role of LECT2 in the liver, we investigated the expression of mouse LECT2 (mLECT2) during liver regeneration after partial hepatectomy (PHx) using immunohistochemical and in situ hybridization techniques. Mouse LECT2 protein and mRNA were detected in most hepatocytes in normal mouse; however, at 30 min after PHx, they were not detected in liver tissue. At 2 h after PHx, expression of mLECT2 protein was seen in hepatocytes surrounding the central vein, although mRNA expression levels were still low. At 6 h after PHx, a marked number of hepatocytes expressing mLECT2 protein and mRNA were seen throughout the liver, and at 12 h after PHx, hepatocytes expressing mLECT2 protein and mRNA further increased in number. However, expression levels of mLECT2 protein and mRNA at 24 h after PHx were significantly lower when compared with levels after 12 h. These results indicate that LECT2 triggers the early events of regeneration with concomitant suppression of hepatocyte proliferation.     

Enhanced liver regeneration in IL-10-deficient mice after partial hepatectomy via stimulating inflammatory response and activating hepatocyte STAT3

Emerging evidence suggests that proinflammatory cytokines, including tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), play a critical role in the initiation and progression of liver regeneration; however, relatively little is known about the role of anti-inflammatory cytokine IL-10 in liver regeneration after partial hepatectomy (PHx). Here, we examined the role of IL-10 in liver regeneration using a model of PHx in several strains of genetically modified mice. After PHx, expression of IL-10 mRNA in the liver and spleen was significantly elevated. Such elevation was diminished in TLR4 mutant mice. Compared with wild-type mice, IL-10(-/-) mice had higher levels of expression of proinflammatory cytokines (IL-6, TNF-α, and IFN-γ) and inflammatory markers (CCR2 and F4/80) in the liver, as well as higher serum levels of proinflammatory cytokines after PHx. The number of neutrophils and macrophages was also higher in the livers of IL-10(-/-) mice than in wild-type mice after PHx. Liver regeneration as determined by BrdU incorporation after PHx was higher in IL-10(-/-) mice than in wild-type mice, which was associated with higher levels of activation of IL-6 downstream signal STAT3 in the liver. An additional deletion of STAT3 in hepatocytes significantly reduced liver regeneration in IL-10(-/-) mice after PHx. Collectively, IL-10 plays an important role in negatively regulating liver regeneration via limiting inflammatory response and subsequently tempering hepatic STAT3 activation.     

Portal vein arterialization promotes liver regeneration after extended partial hepatectomy in a rat model

In the current study, we sought to establish a novel rat model of portal vein arterialization (PVA) and evaluate its impact on liver regeneration after extended partial hepatectomy (PH). A total of 105 Sprague-Dawley rats were randomly assigned to three groups: 68% hepatectomy (the PH group), portal arterialization after 68% hepatectomy (the PVA group), and right nephrectomy only (the control group). Liver regeneration rate (LRR), 5-bromo-2-deoxyuridine (BrdU) labeling index, and liver functions were assessed on postoperative day 2, 7, 14 and 28. The 28-day survival rates were compared among the three groups. The 28-day survival rates were similar in all groups (P  =  0.331), and the anastomotic patency was 100%. The LRR in the PVA group was significantly higher than that of the PH group within postoperative 14 days (P < 0.05). The PVA and PH group had increased serum alanine aminotransferase levels (232 ± 61 U/L and 212 ± 53 U/L, respectively) compared with the control group (101 ± 13 U/L) on postoperative day 2, whereas from postoperative day 7 to day 28 there were no differences among the three groups. Serum albumin values were higher after the PVA procedure within postoperative day 14, which gradually became comparable on postoperative day 28 among the three groups. The peaks of BrdU labeling index appeared on postoperative day 2 in all rats, and the PVA procedure was associated with increased BrdU labeling index from postoperative day 7 to 28. The 28-day survival of the PVA rats was comparable. Our findings demonstrate that the PVA procedure utilizing portal vein trunk-renal artery microvascular reconstruction promotes remnant liver regeneration and confers beneficial effects on maintaining and even optimizing liver function after extended partial hepatectomy in rats.     

Liver regeneration and immune system--morphological and cytochemical studies of activated spleen cells during the liver regeneration after partial hepatectomy

Morphological and cytochemical changes were investigated in spleen cells after 70% hepatectomy in mice. During liver regeneration after the hepatectomy, the spleen weight gradually rose to a peak at 6 day. In the spleen, the number of POD-positive myelocytic cells and NCAE-positive granulocytic cells also reached a peak 4 days after the operation and then decreased. On the other hand, ANBE-positive monocytic cells gradually increased up to 9 day and didn't decrease for this period. On day 9 of the culture, the boundary between the red and the white pulps of the spleen became unclear. In this spleen, the clusters of blast cells were sporadically observed. Splenic T cells cocultured with nonparenchymal adherent normal liver cell or nonparenchymal adherent normal liver cell supernatant developed into granulocyte colonies in earlier periods and monocyte colonies in later periods. These findings suggest that the factors released from liver cells may regulate strictly spleen cell activation. Blast cell formation in the culture with nonparenchymal adherent normal liver cell supernatant was amplified by anti interferon (alpha + beta) antibody. These facts indicate that the functional network of cytokines is formed by the interaction of various cytokines (IL-1, IL-6, CSF, IFN, etc.) in nonparenchymal adherent normal liver cell supernatant.     

Effects of partial hepatectomy on the immune responses in mice

Experiments were performed to investigate the immune responses occurring as a result of partial hepatectomy (HEP) in mice. On Day 12 mice subjected to HEP showed a twofold rise in serum levels of IgG when compared with sham-operated (ShO) controls. The effects of HEP on specific antibody production following a single immunization with sheep red blood cells (SRBCs) were investigated. An early appearance of direct (IgM) splenic plaque-forming cells (PFCs) and significantly elevated indirect (IgG) PFCs were found in HEP mice. Elevated, early-appearing mercaptoethanol-resistant (IgG) hemagglutinating antibodies were also demonstrated in the sera of HEP mice. In addition to these findings our study showed that humoral and cell-mediated responses are affected by HEP in opposing fashion. Partial hepatectomy performed immediately after skin grafting suppressed a first set allograft rejection in mice. Furthermore, inhibited delayed-type hypersensitivity (DTH) response against SRBCs, as evaluated by a footpad weight assay, was demonstrated in HEP mice compared with the ShO controls. When SRBC-primed mice were partially hepatectomized 15 days later, they responded in a manner typical of the secondary immune response, showing an increased production of indirect (IgG) splenic PFCs. A similar anamnestic response was observed in mice sensitized with leptospiral antigen 50 days prior to HEP or exposed to carbon tetrachloride (CCl4) hepatotoxin. The mice responded by elevated serum IgG-specific antibodies as measured by solid-phase enzyme-linked immunosorbent assay (ELISA). Since HEP induced in mice immunological disturbances similar to those associated with liver disease, it is suggested that partial hepatectomy creating liver deficiency followed by regeneration may be a useful experimental model to study the immune status of various forms of hepatic damage.     

Activation of extrathymic T cells in the liver during liver regeneration following partial hepatectomy.

Partial hepatectomy was performed in C57BL/6 mice to investigate whether extrathymic T cells in the liver are activated during liver regeneration. This study is based on the finding that in mice with malignant tumours, extrathymic T cells in the liver are activated and yet the intrathymic pathway is suppressed (i.e. thymic atrophy). Attention was therefore focused on whether a similar phenomenon is induced during benign cell regeneration. Extrathymic T cells were identified using the two-colour immunofluorescence test for CD3 and interleukin-2 receptor beta-chain (IL-2R beta) [or lymphocyte function-associated antigen-1 (LFA-1)] antigens. They were estimated to be intermediate CD3+ [or T-cell receptor (TcR)] cells with high expressions of IL-2R beta and LFA-1. It was demonstrated that the proportion and number of intermediate CD3+ cells increased in the early phase (days 2-4 after partial hepatectomy), and that the thymus was inversely atrophic at the same time. This raised the possibility that extrathymic T cells may also be responsible for regulation of normal cell regeneration.     

Facilitation of liver regeneration after partial hepatectomy by ventromedial hypothalamic lesions in rats

Whether or not the hypothalamus is involved in initiating hepatic DNA synthesis after partial hepatectomy is unclear. To determine the role of the ventromedial hypothalamic nuclei in liver regeneration after partial hepatectomy, we studied hepatic DNA synthesis during liver regeneration in rats with bilateral lesions of these nuclei. Lesions of the ventromedial hypothalamus accelerated the increase in hepatic DNA synthesis and raised the peak level of thymidine incorporation after partial hepatectomy. These effects of hypothalamic lesions were completely inhibited by hepatic vagotomy. Thus, lesions of the ventromedial hypothalamus appear to promote hepatic regeneration by increasing vagal stimulation of the liver.     

大鼠肝大部切除后肝再生过程中肝小叶结构的重建

目的:观察正常大鼠肝大部切除后肝再生过程中肝小叶大小的动态变化,有助于探明大鼠肝再生过程中肝小叶结构的重建过程,并提供组织学依据.方法:正常雄性Wistar大鼠随机分为正常对照组、假手术组和部分肝切除组.采用Higgins和Anderson方法行大鼠70％肝切除,术中即刻称取切除肝叶的湿重.分别于术后12 h、24h、72 h、120 h、1周、2周处死大鼠,留取全部肝组织称湿重,统一留取肝右叶肝组织中性甲醛固定,石蜡包埋连续切片进行H-E染色,显微镜下观察再生肝肝小叶大小变化.结果:正常大鼠部分肝切除后,12h可观察到肝小叶面积开始增大,120 h达高峰,从1周开始可见汇管区门静脉终末支的增大并与邻近中央静脉相联系,肝小叶结构逐步重建,2周时肝小叶面积接近正常,小叶数目增加.正常对照组和假手术组大鼠未见上述动态变化.结论:正常大鼠部分肝切除后,肝再生通过早期肝小叶面积增大,后期肝小叶数目增多而恢复.     

Influence of the stress induced by partial hepatectomy in the circadian liver regeneration

Regeneration induced by partial hepetectomy is synchronized by the circadian variation of corticosterone that inhibits periodically the DNA synthesis. But, the amplitude and the postoperative delay of the first regenerating wave vary according to the nycthemeral time of the surgery that induces a powerful stress corticosterone release. Partial hepatectomy performed in the morning inhibits the subsequent corticosterone wave and the first DNA synthesis wave occurs early with a low amplitude. The same operation performed in the evening does not change the subsequent corticosterone wave and the first DNA synthesis wave is delayed but amplified. These results disprove the methodology used by many investigators: they sacrifice all the animals at the same nycthemeral time and perform operations at various delays before sacrifices in order to avoid the circadian synchronization.     

Catalase-negative peroxisomes: transient appearance in rat hepatocytes during liver regeneration after partial hepatectomy.

Using light microscopy enzyme cytochemistry to localize catalase activity in peroxisomes, a population of peroxisome-negative hepatocytes was detected in livers of rats during liver regeneration induced by two-thirds partial hepatectomy. However, examination by electron microscopy revealed that this population of hepatocytes contained peroxisomes with a delimiting membrane and a nucleoid, but no cytochemically demonstrable catalase activity within their matrix. Regenerating livers 6, 18, 24, 36, 48 and 72 hours, and 1 week after partial hepatectomy showed hepatocytes without catalase activity. However, their numbers varied, with the most numerous appearing at 24 hours after partial hepatectomy. Mitosis of catalase-negative hepatocytes were seen along with mitosis of hepatocytes containing the normal complement of catalase-positive peroxisomes. The catalase-negative hepatocytes did not show evidence of apoptosis or necrotic cell death. Lysosomal acid phosphatase activity and bile canalicular ATPase activity were present in hepatocytes with catalase-negative peroxisomes. Another population of hepatocytes with a small number of catalase-positive peroxisomes appeared and were more numerous at 36 hours after partial hepatectomy; ultrastructurally, these hepatocytes contained both catalase-negative peroxisomes, which appeared to undergo dissolution, and catalase-positive peroxisomes, which were smaller in size. After complete restoration of the liver, all hepatocytes displayed essentially uniform numbers of catalase-positive peroxisomes. These studies indicated that during liver regeneration there is a transient loss of catalase in peroxisomes of some hepatocytes. These cells proliferate and with time acquire new catalase-positive peroxisomes. The observations are discussed in relation to peroxisome biogenesis, hepatocellular carcinogenesis, and oxidative stress during liver regeneration.     

Hepatic glucose-6-phosphate dehydrogenase, cholesterogenesis, and serum lipoproteins in liver regeneration after partial hepatectomy

Liver regeneration after partial hepatectomy was used as an experimental model for studying mammalian cell division and replication. The rate of cell proliferation in this hyperplastic model was correlated with hepatic de novo synthesis of cholesterol, with the hexose monophosphate shunt pathway of glucose metabolism, and with serum lipoproteins. An increase of hepatic cholesterol esters and of incorporation of tritiated water in cholesterol esters was observed at 24 hr after partial hepatectomy. Partial hepatectomy also resulted in an increase of hepatic glucose-6-phosphate dehydrogenase and in alteration of serum lipoproteins, primarily due to a selective decline in high density lipoprotein fraction.     

Expression of NCAM in activated portal fibroblasts during regeneration of the rat liver after partial hepatectomy

In the portal tract of the regenerating liver after partial hepatectomy, vascular and bile ductular remodeling takes place in response to the portal hyperdynamic state and parenchymal hyperplasia. In order to reveal phenotypical changes in the portal fibroblasts, we immunohistochemically investigated neural cell adhesion molecules (NCAM) and alpha smooth muscle actin (alphaSMA) expression and the ultrastructural changes in them during liver regeneration. In the control rat liver, portal fibroblasts were negative for both NCAM and alphaSMA. They became positive for both markers two days after partial hepatectomy, increased in staining intensity, reached a maximum at three to four days, then decreased, being still clearly positive at 14 days. Under an electron microscope, portal fibroblasts from the regenerating liver had larger amounts of cytoplasm and rough endoplasmic reticulum than those from the control liver; thus they might be activated. Additionally, periportal hepatic stellate cells in the regenerating liver were activated with alphaSMA, but without NCAM. The present study has demonstrated that portal fibroblasts express NCAM and alphaSMA in the regenerating liver after partial hepatectomy via transformation into myofibroblasts following reconstruction of the portal tracts.     

Expression of epidermal growth factor receptor protein in the liver of db/db mice after partial hepatectomy

Liver regeneration was impaired after partial hepatectomy (PH) in leptin receptor-deficient db/db mice with severe liver steatosis. In the present study, we analyzed the mode of epidermal growth factor receptor (EGFR) protein expression in the liver of 5- and 10-week-old db/db and age-matched control mice. In 5-week-old db/db mice, neither the expression of EGFR protein in the intact liver nor the rate of liver regeneration after PH was significantly different from that in age-matched control mice. However, in 10-week-old db/db mice, the level of EGFR protein expression was very low and liver regeneration was prominently suppressed. Histopathologically, much severer fatty change was observed in the liver of 10-week-old db/db mice than 5-week-old db/db mice. These results suggest that the down-regulation of EGFR protein expression is associated with an impairment of liver regeneration in db/db mice and that the severity of hepatic steatosis plays an indirect role in the impairment of liver regeneration by modifying EGFR expression.     

Inhibitory effect of vitamin e administration on the progression of liver regeneration induced by partial hepatectomy in rats

We have proposed that controlled peroxidative modifications of membranes could be playing a role in the early steps of liver regeneration. Hence, lipid peroxidation (LP) was modified in vivo by treatment with vitamin E in rats subjected to partial hepatectomy (PH), and its influence on liver regeneration was evaluated. Our results, using several methods to monitor LP, indicate that vitamin E administration promoted a decreased LP rate in liver subcellular membranes. Vitamin E drastically diminished cytosolic LP, shifting earlier increased LP in plasma membranes, and promoted a higher increase of nuclear LP in animals subjected to PH. Pretreatment with vitamin E induced a striking reduction of liver mass recovery and nuclear bromodeoxyuridine labeling (clearly shown at 24 hours after surgery), as well as promoted a decreased expression of cyclin D1 and of the proliferating cell nuclear antigen after PH. These effects seem to lead to a decreased mitotic index at 48 hours after PH. Vitamin E pretreatment also diminished PH-induced hypoglycemia but elevated serum bilirubin level, which was not observed in PH animals without vitamin treatment. In conclusion, an enhanced but controlled LP seems to play a critical role during the early phases of liver regeneration. Decreasing magnitude or time course of the PH-promoted enhanced LP (at early post-PH stages) by in vivo treatment with vitamin E could promote an early termination of preparative cell events, which lead to the replicative phase, during PH-promoted liver proliferation. The latter could have a significant implication in the antitumorigenic effect ascribed to the treatment with vitamin E.