Continuous HGF supply from HGF-expressing fibroblasts transplanted into spleen prevents CCl4-induced acute liver injury in rats

Notch inhibition promotes fetal liver stem/progenitor cells differentiation into hepatocytes via the inhibition of HNF-1β

In a previous study, the Notch pathway inhibited with N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (also called DAPT) was shown to promote the differentiation of fetal liver stem/progenitor cells (FLSPCs) into hepatocytes and to impair cholangiocyte differentiation. The precise mechanism for this, however, was not elucidated. Two mechanisms are possible: Notch inhibition might directly up-regulate hepatocyte differentiation via HGF (hepatocyte growth factor) and HNF (hepatocyte nuclear factor)-4α or might impair cholangiocyte differentiation thereby indirectly rendering hepatocyte differentiation as the dominant state. In this study, HGF and HNF expression was detected after the Notch pathway was inhibited. Although our initial investigation indicated that the inhibition of Notch induced hepatocyte differentiation with an efficiency similar to the induction via HGF, the results of this study demonstrate that Notch inhibition does not induce significant up-regulation of HGF or HNF-4α in FLSPCs. This suggests that Notch inhibition induces hepatocyte differentiation without the influence of HGF or HNF-4α. Moreover, significant down-regulation of HNF-1β was observed, presumably dependent on an impairment of cholangiocyte differentiation. To confirm this presumption, HNF-1β was blocked in FLSPCs and was followed by hepatocyte differentiation. The expression of markers of mature cholangiocyte was impaired and hepatocyte markers were elevated significantly. The data thus demonstrate that the inhibition of cholangiocyte differentiation spontaneously induces hepatocyte differentiation and further suggest that hepatocyte differentiation from FLSPCs occurs at the expense of the impairment of cholangiocyte differentiation, probably being enhanced partially via HNF-1β down-regulation or Notch inhibition.

Intrasplenic transplantation of bioencapsulated mesenchymal stem cells improves the recovery rates of 90% partial hepatectomized rats

Mesenchymal stem cells (MSCs) derived from bone marrow can secrete cytokines and growth factors and can transdifferentiate into liver cells. We transplanted polymeric membrane bioencapsulated MSCs into the spleens of 90% partial hepatectomized rats. This resulted in 91.6% recovery rates. This is compared to a recovery rate of 21.4% in the 90% hepatectomized rats and 25% in the 90% hepatectomized rats receiving intrasplenic transplantation of free MSCs. After 14 days, the remnant livers in the bioencapsulated MSCs group are not significantly different in weight when compared to the sham control group. From day 1 to day 3 after surgery, in the bioencapsulated MSCs group, the plasma HGF and IL-6 were significantly higher than those in the free MSCs group and control group (P < 0.01); plasma TNF-α was significantly lower (P < 0.001). We concluded that the intrasplenic transplantation of bioencapsulated MSCs significantly increases the recovery rates of 90% hepatectomized rats. It is likely that the initial effect is from proliver regeneration factors followed later by the transdifferentiated hepatocyte-like cells. However, histopathological analysis and hepatocyte proliferation study will be needed to better understand the regenerative mechanisms of this result. This study has implications in improving the survival and recovery of patients with very severe liver failure due to hepatitis, trauma, or extensive surgical resection.

A novel solid-phase site-specific PEGylation enhances the in vitro and in vivo biostabilty of recombinant human keratinocyte growth factor 1

Keratinocyte growth factor 1 (KGF-1) has proven useful in the treatment of pathologies associated with dermal adnexae, liver, lung, and the gastrointestinal tract diseases. However, poor stability and short plasma half-life of the protein have restricted its therapeutic applications. While it is possible to improve the stability and extend the circulating half-life of recombinant human KGF-1 (rhKGF-1) using solution-phase PEGylation, such preparations have heterogeneous structures and often low specific activities due to multiple and/or uncontrolled PEGylation. In the present study, a novel solid-phase PEGylation strategy was employed to produce homogenous mono-PEGylated rhKGF-1. RhKGF-1 protein was immobilized on a Heparin-Sepharose column and then a site-selective PEGylation reaction was carried out by a reductive alkylation at the N-terminal amino acid of the protein. The mono-PEGylated rhKGF-1, which accounted for over 40% of the total rhKGF-1 used in the PEGylation reaction, was purified to homogeneity by SP Sepharose ion-exchange chromatography. Our biophysical and biochemical studies demonstrated that the solid-phase PEGylation significantly enhanced the in vitro and in vivo biostability without affecting the over all structure of the protein. Furthermore, pharmacokinetic analysis showed that modified rhKGF-1 had considerably longer plasma half-life than its intact counterpart. Our cell-based analysis showed that, similar to rhKGF-1, PEGylated rhKGF-1 induced proliferation in NIH 3T3 cells through the activation of MAPK/Erk pathway. Notably, PEGylated rhKGF-1 exhibited a greater hepatoprotection against CCl(4)-induced injury in rats compared to rhKGF-1.

Human amniotic fluid-derived stem cells can differentiate into hepatocyte-like cells in vitro and in vivo

Although human amniotic fluid is an attractive source of multipotent stem cells, the potential of amniotic fluid stem cells (AFSCs) to differentiate into hepatic cells has not been extensively evaluated. In this study, we examined whether human AFSCs can differentiate into a hepatic cell lineage in vitro and in vivo. After being treated with cytokines (fibroblast growth factor 4, basic fibroblast growth factor, hepatocyte growth factor, and oncostatin), AFSCs developed a morphology similar to that of hepatocytes. RT-PCR and immunofluorescence analysis showed that the treated AFSCs expressed the hepatocyte-specific markers albumin, cytokeratin 18, and alpha-fetoprotein. The differentiated cells also developed hepatocyte-specific functions, i.e., they secreted albumin, absorbed indocyanine green, and stored glycogen. When transplanted into CCl(4)-injured immunodeficient mice, undifferentiated AFSCs were integrated into the liver tissue, and they expressed markers characteristic of mature human hepatocytes. Although integration of AFSCs into the liver was limited (0.1-0.3% of hepatocytes), histological analysis showed that the recipient mice recovered more rapidly from CCl(4) injury than CCl(4)-injured mice that did not receive AFSCs. AFSCs can differentiate into hepatocyte-like cells in vitro and in vivo and can represent an easily accessible source of progenitor cells for hepatocyte regeneration and liver cell transplantation.

Plasmin-mediated proteolysis is required for hepatocyte growth factor activation during liver repair

The physiological relevance of the activation of hepatocyte growth factor (Hgf) by the plasminogen (Plg) system of proteases and its contribution to tissue repair are largely undefined. Here, we investigated whether the defective liver repair in mice lacking Plg is due to impaired activation of Hgf. Loss of Plg in vivo suppressed Hgf activation and signaling through its Met tyrosine kinase receptor. Without Plg, hepatocytes were unresponsive to Hgf-induced proliferation and migration, with a more pronounced impairment in hepatocyte movement within the hepatic environment. Most notably, circumventing the defect in proteolytic activation of Hgf by the downstream expression of an activated Met receptor corrected the functional deficits and improved liver repair in Plg-deficient mice. These findings support a fibrinolysis-unrelated role for Plg in modulating cell proliferation and migration by activation of Hgf.

CCl4-induced acute liver injury in mice is inhibited by hepatocyte growth factor overexpression but stimulated by NK2 overexpression

Hepatocyte growth factor (HGF) inhibits acute liver injury. NK2 acts as an antagonist to HGF in vitro, but its in vivo function has reached no consensus conclusions. We have investigated in vivo effects of HGF and NK2 on CCl4-induced acute liver injury. Elevation of the serum alanine aminotransferase level and extension of centrilobular necrosis were inhibited in HGF transgenic mice but were promoted in NK2 transgenic mice. Hepatocyte proliferation after liver injury was not inhibited in NK2 transgenic mice. Thus, this study indicates that HGF inhibits liver injury, and NK2 antagonizes HGF on liver injury, however, NK2 may not antagonize HGF on hepatocyte proliferation.

Increased carbon tetrachloride-induced liver injury and fibrosis in FGFR4-deficient mice

Carbon tetrachloride (CCl(4)) intoxification in rodents is a commonly used model of both acute and chronic liver injury. Recently, we showed that mice in which FGFR4 was ablated from the germline exhibited elevated cholesterol metabolism and bile acid synthesis coincident with unrepressed levels of cytochrome P450 7A (CYP7A), the rate-limiting enzyme in cholesterol disposal. Of the four fibroblast growth factor (FGF) receptor genes expressed in adult liver, FGFR4 is expressed specifically in mature hepatocytes. To determine whether FGFR4 plays a broader role in liver-specific metabolic functions, we examined the impact of both acute and chronic exposure to CCl(4) in FGFR4-deficient mice. Following acute CCl(4) exposure, the FGFR4-deficient mice exhibited accelerated liver injury, a significant increase in liver mass and delayed hepatolobular repair. Chronic CCl(4) exposure resulted in severe fibrosis in livers of FGFR4-deficient mice compared to normal mice. Analysis at both mRNA and protein levels indicated an 8-hour delay in FGFR4-deficient mice in the down-regulation of cytochrome P450 2E1 (CYP2E1) protein, the major enzyme whose products underlie CCl(4)-induced injury. These results show that hepatocyte FGFR4 protects against acute and chronic insult to the liver and prevents accompanying fibrosis. The results show that FGFR4 acts by promotion of processes that restore hepatolobular architecture rather than cellularity while limiting damage due to prolonged CYP2E1 activity.

Delayed liver regeneration with negative regulation of hepatocyte growth factor and positive regulation of transforming growth factor-beta1 mRNA after portal branch ligation in biliary obstructed rats

BACKGROUND

The influence of obstructive jaundice on liver regeneration is still controversial. The aim of this study was to investigate liver regeneration after portal branch ligation (PBL) in the jaundiced rat, focusing on hepatocyte growth factor (HGF) and transforming growth factor-beta1 (TGF-beta 1).

METHODS

Male Wistar rats underwent PBL or a sham operation 7 days after a common bile duct ligation. Liver wet weight, proliferating cell nuclear antigen labeling, HGF and TGF-beta 1 mRNA expression, and immunohistochemical staining with alpha-smooth muscle actin antibody were studied.

RESULTS

The rate of liver regeneration in jaundiced liver was decreased as compared to a non-jaundiced liver. DNA synthesis in the jaundiced non-ligated lobe was significantly lower than in the non-jaundiced liver as was the peak level of HGF mRNA expression after PBL. In contrast, the level of TGF-beta 1 mRNA expression was higher in the jaundiced liver, and alpha-smooth muscle actin staining showed that hepatic stellate cells were gradually activated into myofibroblast-like cells.

CONCLUSIONS

Obstructive jaundice decreased the expression of HGF mRNA and increased the expression of TGF-beta 1 mRNA, resulting in delayed liver regeneration after PBL. We suggest that hepatic stellate cells activated in obstructive jaundice may affect the expression of these growth factors.

Restitutive response of Mini rat liver to injury induced by a single oral administration of thioacetamide

Mini rats are a transgenic rat strain carrying antisense gene for rat growth hormone (GH), resulting in retarded growth and a lower blood GH level (136 +/- 42.0 ng/mL) compared with that of age-matched parental strain Wistar rats (329 +/- 337 ng/mL). Mini rats have been used by several investigators as a GH deficiency model. In this work, we gave a single oral administration of thioacetamide (TAA), a hepatotoxicant, to both Mini rats and Wistar rats to ascertain the influence of GH deficiency on liver response to chemically induced injury and subsequent regeneration. TAA administration caused liver injury in both strains, with a greater extent of injury in Mini rats. Proliferation of bile epithelial cells and so-called oval cells was prominent at Day 3 in Mini rats only, and this change correlated well with serum total bilirubin concentrations. Antibody against Ki-67 antigen revealed that cellular proliferation after TAA-induced liver injury was suppressed but prolonged in the Mini rat liver. Although hepatic stellate cells and Kupffer cells/macrophages were more abundant in the livers of TAA-treated Mini rats, the hepatic expression patterns of hepatocyte growth factor and transforming growth factor beta 1 were comparable to those of Wistar rats. Insulin-like growth factor-I gene expression was significantly reduced in the Mini rat liver. Our results imply that a lower GH level may exacerbate chemically induced liver injury, enhance infiltration/proliferation of non-parenchymal cells, suppress regeneration of hepatocytes, and induce proliferation of bile epithelial cells and oval cells when the liver is injured by TAA.

Increased c-met expression during ductal beta cell neogenesis in experimental autoimmune diabetes

C-met immunoreactivity and its co-expression with duct-associated insulin were evaluated in pancreata of non-obese diabetic (NOD) and low-dose streptozotocin (Id-STZ) mice. Diabetic NOD and non-diabetic NOD at the age of 4-8, 15-22 and 30-41 weeks and Balb/c mice at the same age intervals were studied. Ld-STZ mice were studied at day 12 and 24 after STZ administration. A stronger ductal c-met immunoreactivity and a significantly higher number of c-met positive ducts were found in diabetic NOD vs both non-diabetic NOD and Balb/c mice of comparable age. In non-diabetic NOD, the ductal c-met immunoreactivity progressively increased with age and was significantly higher than controls. In 1d-STZ mice a significantly increased ductal c-met immunoreactivity was detected both at day 12 and 24 vs untreated mice. C-met positive ductal cells were also positive for insulin although insulin positive c-met negative ducts were present. This study showed an increased c-met expression and the co-expression of c-met and duct-associated insulin, in both NOD and 1d-STZ mice.

Acute liver failure: targeted artificial and hepatocyte-based support of liver regeneration and reversal of multiorgan failure

Acute liver failure (ALF) still represents a major therapeutic challenge for hepatologists due to its high mortality rate as a result of multiorgan failure. Although emergency orthotopic liver transplantation represents a major advance in the management of selected patients, it is not applicable to all candidates due to limited organ availability. Therefore, new therapeutic options should be developed to bridge selected patients to transplantation or to treat patients not candidates for liver transplantation. Although new techniques for cell culture and perfusion have resulted in a number of promising devices for the provision of temporary liver support in acute liver failure, their clinical efficacy is as yet uncertain. Controlled trials on a multi-centre basis in well-defined patient groups and with standardised outcome measures, including the extent to which treatment influences cell damage and regeneration and prevents or reverses multiorgan failure, will be essential to properly evaluate the clinical value of current and evolving artificial and bioartificial devices. The same considerations must also apply to the assessment of therapeutic efficacy of hepatocyte transplantation. A better understanding of mechanisms responsible for the development of liver cell death, along with cellular and molecular mechanisms allowing surviving cells to proliferate in a hostile environment, will be required if a more targeted therapeutic approach to decreasing hepatocellular injury and enhancing liver regeneration is to be achieved. Whether extracorporeal devices or the transplantation of primary hepatocytes, stem cells or cells genetically engineered to over-express key metabolic functions, a proliferative phenotype and/or cytoprotective pathways will be best suited to meeting these demanding challenges remains to be determined.

Hepatocyte growth factor is essential for amelioration of hyperglycemia in streptozotocin-induced diabetic mice receiving a marginal mass of intrahepatic islet grafts

BACKGROUND

It is crucial for clinical islet transplantation to find a procedure to improve the success rate of insulin independence after islet transplantation. In the present study, we determined whether hepatocyte growth factor (HGF) has a favorable effect on amelioration of hyperglycemia in streptozotocin (STZ, 200 mg/kg)-induced diabetic mice (C57BL/6) receiving a marginal mass of intrahepatic islet isografts.

METHODS

Isolated syngeneic islets were transplanted into the liver of recipients. HGF with dextran sulfate (DS) was administered intraperitoneally once a day at day 0, 2, 4, 6, and 8 relative to islet transplantation. DS has been known to enhance the effect of HGF.

RESULTS

It was found that the number of 250 islets was a marginal mass as donor islets in this model, in which 2 out of 14 diabetic mice receiving 250 islets became normoglycemic by 90 days after transplantation. The treatment with HGF (100 microg) in conjunction with DS (200 microg) produced normoglycemia in all mice (n = 5). Morphological study as well as intraperitoneal glucose tolerance test revealed the beneficial effects of HGF. To our surprise, six out of nine mice receiving 250 islets and treated with DS alone became normoglycemic. Additional anti-HGF antibody treatment (100 microg, day -1, 0, 2, 4, 6, and 8) abolished the effects of DS, indicating that the effect by DS is mediated via the endogenous HGF. The effects of DS were not observed when the renal subcapsular space was the site of islet transplantation. There was a significant increase in plasma HGF levels in mice after the intrahepatic grafts but not the renal subcapsular one.

CONCLUSIONS

These findings demonstrate that HGF is essential for amelioration of hyperglycemia in STZ-induced diabetic mice when a marginal mass of islets was grafted into the liver. As the liver is the site of clinical islet transplantation and the inability to achieve insulin independence after transplantation is a major obstacle for successful transplantation, HGF may facilitate to overcome such an important issue for clinical islet transplantation.

Hepatocyte growth factor supply accelerates compensatory hypertrophy caused by portal branch ligation in normal and jaundiced rats

BACKGROUND

Hepatocyte growth factor (HGF), first identified as the most potent mitogen for hepatocytes, significantly stimulates liver regeneration after hepatectomy. In this report, we examined whether HGF is also useful in accelerating compensatory hypertrophy caused by portal branch ligation in normal and jaundiced rats.

MATERIALS AND METHODS

Normal and reversible obstructive jaundiced rats underwent portal ligation of the left lateral and median branches, which supply approximately 70% of the total volume of the liver. Simultaneously, the animals were continuously treated with either recombinant human HGF (rhHGF) or vehicle alone via an intraperitoneally implanted osmotic pump. Two and four days after portal ligation, the degree of compensatory hypertrophy in unoccluded lobes was examined by measuring the wet weight ratios of the unoccluded lobes to the whole liver and the 5-bromo-2'-deoxyuridine labeling index of hepatocytes in each group.

RESULTS

The HGF treatment significantly increased the wet weight ratios and the DNA synthesis in nonoccluded lobes 2 and 4 days after portal ligation in both normal and jaundiced rats. Moreover, rhHGF supply promptly decreased serum total bilirubin level in jaundiced rats.

CONCLUSIONS

Continuous rhHGF administration not only accelerates compensatory hypertrophy in normal and jaundiced rats but also ameliorates hyperbilirubinemia in jaundiced rats.

Hepatocyte growth factor prevents lipopolysaccharide-induced hepatic sinusoidal endothelial cell injury and intrasinusoidal fibrin deposition in rats

BACKGROUND

Acute endotoxemia is known to cause activation of Kupffer cells as well as serious injury in parenchymal and nonparenchymal cells in the liver. We have recently shown that a continuous recombinant hepatocyte growth factor (rHGF) supply prevents lipopolysaccharide (LPS)-induced liver injury in rats. As an attempt to elucidate the mechanism, here we investigate the cytoprotective effect of rHGF on sinusoidal endothelial cells (SECs) in LPS-induced liver injury in rats.

MATERIALS AND METHODS

In order to supply rHGF continuously to the liver, syngenic rat fibroblasts genetically modified to secret rat rHGF were implanted in the spleen. Fourteen days after cell implantation, we injected LPS intravenously and evaluated SEC damage histologically and blood chemically.

RESULTS

Phosphotungstic acid-hematoxylin staining revealed that rHGF treatment greatly attenuated intrasinusoidal LPS-induced fibrin deposition. The ultrastructural changes in SECs caused by LPS administration in control rats were barely detectable in rHGF-treated rats. Blood chemical analyses showed that rHGF potently suppressed the LPS-induced increase in serum hyaluronic acid and transaminase levels.

CONCLUSIONS

Our results indicate an important role for HGF in SEC protection in vivo and would suggest a novel therapeutic strategy for liver diseases with SEC injury.

Interactions between scatter factors and their receptors: hints for therapeutic applications

The scatter factors, which include hepatocyte growth factor and macrophage stimulating protein, stand out from other cytokines because of their uncommon biological properties. In addition to promoting cell growth and protection from apoptosis, they are involved in the control of cell dissociation, migration into extracellular matrices, and a unique process of differentiation called 'branching morphogenesis'. Through the concerted regulation of these complex phenomena, scatter factors promote development, regeneration, and reconstruction of normal organ architecture. In transformed epithelia, scatter factors can mediate tumor invasive growth, a harmful feature of neoplastic progression in which cancer cells invade surrounding tissues, penetrate across the vascular walls, and eventually disseminate throughout the body, giving rise to systemic metastases. A much-debated issue in basic biology, which has strong implications for experimental medicine, is how to dissociate the favorable effects of growth factors from their adverse ones. Accordingly, to find agonists or antagonists with potential therapeutic applications is a crucial undertaking for current research. Domain-mapping analyses of growth factor molecules can help to isolate specific structural requirements for the induction of selective biological effects. Based on the observation that certain growth factors must undergo posttranslational modifications to exert a full response, it is possible to interfere with their activation mechanisms to modulate their functions. Finally, the identification of cell type-specific coreceptors able to potentiate their activity allows drawing of a functional body map, where some organs or tissues may be more responsive than others to growth factors. This review is focused on how, and to what extent, scatter factors can behave 'well' or 'badly' according to their molecular structure, the way they are activated, and the way they interact with cell surface receptors and coreceptors.

Portal branch ligation with a continuous hepatocyte growth factor supply makes extensive hepatectomy possible in cirrhotic rats

In a cirrhotic liver, the regenerative ability and specific functions are so impaired that excessive resection easily complicates postoperative liver dysfunction, which frequently leads to life-threatening multiple-organ failure. Hepatocyte growth factor (HGF), first identified as the most potent stimulator of DNA synthesis in primary hepatocytes, not only stimulates liver regeneration, but also accelerates hepatic function, improves fibrosis, and protects liver cells against injury. Therefore, we investigated the efficacy of preoperative portal branch ligation (PBL) (which can induce compensatory hypertrophy of the unaffected lobes) combined with a continuous HGF supply in the performance of extensive hepatectomy in cirrhotic rats. Cirrhosis was induced by intraperitoneal injections of dimethylnitrosamine (DMN) three times per week for 3 weeks. Five days after the last injection, when 70% hepatectomy is lethal, the rats underwent portal ligation of the left lateral and median branches (corresponding to approximately 70% of the total volume of the liver). Simultaneously, they were continuously treated with either recombinant human HGF (rhHGF) or vehicle from an intraperitoneally implanted osmotic pump. Four days after the portal ligation, the occluded lobes were resected. The HGF treatment rapidly increased both the wet weight of the unoccluded lobes and the hepatocellular DNA synthesis. The blood chemical analysis indicated that HGF significantly suppressed the posthepatectomy liver dysfunction. Most importantly, the HGF treatment markedly improved the survival rate of the rats at 48 hours after the major hepatectomy. In conclusion, PBL combined with a continuous HGF supply makes extensive hepatectomy possible in cirrhotic rats, mainly by promoting the hypertrophy of the unaffected lobes.

Hepatocyte growth factor promotes liver regeneration with prompt improvement of hyperbilirubinemia in hepatectomized cholestatic rats

BACKGROUND

In hepatectomy for patients with liver cirrhosis or cholestasis, prolonged postoperative hyperbilirubinemia is a troublesome complication and, if uncontrolled, often leads to life-threatening hepatic failure. Hepatocyte growth factor (HGF), first identified as the most potent mitogen for primary hepatocytes, has been shown to have multiple biological properties on liver, including mitogenic, antifibrotic, and cytoprotective activities. This study investigated the beneficial effects of a perioperative HGF supply to jaundiced liver after hepatectomy in rats.

MATERIALS AND METHODS

As a model of jaundiced liver, we used an alpha-naphtylisocyocyanate (ANIT)-induced intrahepatic cholestasis model. Forty-eight hours after intraperitoneal injection of ANIT (75 mg/kg), when the total serum bilirubin level was moderately increased, a 70 % hepatectomy was performed. Human recombinant HGF (250 microgram/kg) (n = 15) or vehicle alone (n = 15) was intermittently administered to the rats 12 h before surgery and every 12 h after that until sacrifice.

RESULTS

Perioperative HGF treatment effectively accelerated hepatocellular DNA synthesis of cholestatic liver followed by increase in the regenerated liver weight. Moreover, HGF supply promptly improved hyperbilirubinemia within 24 h after surgery. Histological examination revealed that HGF administration attenuated periportal inflammation and formation of bile duct obstructions. Postoperative serum concentrations of tumor necrosis factor-alpha, a representative inflammatory cytokine, were not altered by HGF treatment.

CONCLUSIONS

Perioperative HGF supply not only promotes liver regeneration but also ameliorates hyperbilirubinemia in hepatectomized cholestatic rats. This mode of HGF treatment may be clinically useful for hepatectomy in patients with cholestasis.

Anti-hepatocyte growth factor antibody inhibits hepatocyte proliferation during liver regeneration

In vitro studies have shown hepatocyte growth factor (HGF) to be a potent mitogen for hepatocytes. Direct evidence of a mitogenic role in vivo was sought by inhibiting HGF activity, using continuous administration of neutralizing antibody to rats which had a stimulus for liver regeneration. Alzet osmotic mini-pumps, administering a constant supply of anti-HGF monoclonal antibody (clone D9), were inserted intraperitoneally into male Wistar rats; an irrelevant isotypical antibody was administered to controls. Forty-five animals received an intragastric bolus of 40 per cent carbon tetrachloride (CCl4) and groups of three test and control animals were killed at 24 h intervals for 7 days. Treatment with anti-HGF monoclonal antibody significantly inhibited the levels of immunodetectable HGF in the sera of rats following CCl4 administration. In comparison with controls, hepatocyte proliferation as assessed by bromodeoxyuridine labelling in anti-HGF-treated animals was significantly inhibited at 24 h (P < 0.001), 48 h (P < 0.001), and 96 h (P < 0.05) post-CCl4 administration. In contrast, sinusoidal cell proliferation was not significantly different from controls at any time point. Inhibition of the parenchymal proliferative response to acute CCl4-induced liver injury by the in vivo neutralization of HGF provides direct evidence that this growth factor plays an important role in liver regeneration following necrosis.

HGF: its organotrophic role and therapeutic potential

Hepatocyte growth factor (HGF), originally implicated as a long-sought after hepatotrophic factor, supports epithelial branching duct formation in the developing lung as, a mesenchymal-derived morphogen. HGF elicits a potent organotrophic function for regeneration of organs including the liver, kidney and lung, through epithelial-stromal interactions. It prevents the onset or progress of hepatic fibrosis/cirrhosis, as well as the accompanying severe hepatic failure, and may become an effective drug for the treatment of fatty liver. HGF prevents the onset of acute and chronic renal failure, acts as pulmotrophic factor which enhances lung regeneration, and suppresses the onset of lung fibrosis. HGF may also be effective for treatment of vascular diseases, gastric ulcers, diabetes mellitus and neuronal diseases. Our results provide a new therapeutic strategy for treating such diseases.

Mitogenic-factor-dependent regulation of lipopolysaccharide and cytokine mixture-mediated hepatocyte nitric oxide synthesis in vitro

Hepatocellular mitogen (HGF and EGF) inhibited lipopolysaccharide and cytokine mixture (referred as LPS/CM)-induced NO synthesis and cellular injury in hepatocytes. Mitogenic inhibitors such as hydroxyurea and Wortmannin could not reverse EGF or HGF-inhibited NO production, whereas both of them showed some inhibitory effect on hepatocyte NO synthesis. Although activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) had no effect on hepatocyte NO synthesis, deletion of PKC activity by long-term treatment of hepatocytes with PMA abolished LPS/CM-induced NO production. In addition, pretreatment of hepatocytes with HGF and EGF also blocked LPS/CM-induced NO synthesis in the hepatocyte. These results suggest that proliferating signal is not directly involved in mitogen-inhibited NO synthesis in the hepatocyte, and LPS/CM-mediated NO synthesis is associated with the metabolic/redox state of hepatocytes.

Perioperative continuous hepatocyte growth factor supply prevents postoperative liver failure in rats with liver cirrhosis

Insufficient regeneration and dysfunction of cirrhotic liver following partial hepatectomy often make the resection extremely vulnerable to postoperative liver failure, which frequently leads to multiple organ failure. Hepatocyte growth factor (HGF), first identified as the most potent mitogen for primary hepatocytes, not only stimulates hepatic regeneration but also accelerates liver function, improves fibrosis, and protects liver cells against injury. Therefore, we investigated the ability of a continuous supply of HGF to cirrhotic livers to prevent postoperative liver failure in rats. After liver cirrhosis was induced in 40 rats by the intraperitoneal injection of dimethylnitrosamine (DMN) for 4 weeks, fibroblasts genetically modified to secret rat HGF or control fibroblasts were implanted in the spleens of 20 syngenic rats per group to supply HGF continuously and directly to the cirrhotic livers. Two weeks after the implantation, all rats underwent a 30% hepatectomy. The HGF administration significantly improved liver fibrosis at the time of operation, attenuated the postoperative hepatic damage on histological examination, markedly accelerated the liver regeneration at 24 h after the hepatectomy. The blood chemical analysis indicated that HGF significantly suppressed postoperative liver failure. Most importantly, the HGF treatment significantly improved the survival rate of the rats at 48 h after the hepatectomy. The perioperative continuous supply of HGF from the spleen effectively prevented liver failure following resection of cirrhotic livers in rats.

Continuous hepatocyte growth factor supply prevents lipopolysaccharide-induced liver injury in rats

We present a rat model in which continuous supply of hepatocyte growth factor (HGF) prevents liver injury induced by carbon tetrachloride (CCl4) and E. coli 011:B4 lipopolysaccharide (LPS). Rat fibroblasts genetically modified to secrete rat HGF were implanted in syngenic rat spleen 7 days before administration of the hepatotoxins. Rats with HGF-secreting fibroblasts in the spleen showed a dramatic resistance to CCl4- and LPS-induced liver injury. In the LPS-induced liver injury model, blood chemical analysis revealed that the increase in serum glutamic oxalacetic transaminase level and the decrease in blood sugar level were remarkably suppressed in rats with HGF-secreting cells in the spleen. Most importantly, their survival rate was greatly improved compared to other control groups of rats. Thus our results indicate a new role of HGF in liver protection during endotoxemia and convey important clinical implications for developing new therapeutic modalities in the treatment of liver failure caused by endotoxemia.

Control of invasive growth by hepatocyte growth factor (HGF) and related scatter factors

Hepatocyte growth factor (HGF) is the prototype of a family of structurally related soluble molecules, named scatter factors (SFs). These control a complex genetic programme leading to cell-dissociation, migration in the extracellular matrix, growth, acquisition of polarity and tubule formation. This programme is pivotal during the embryonic development of epithelial and some mesodermal-derived tissues. In the adult HGF sustains cell survival and regeneration. A structurally related molecule, originally identified as macrophage stimulating protein (MSP), triggers the same complex genetic programme in epithelial and neural cells. The receptors for HGF and MSP are the tyrosine kinases encoded by the homologous genes MET and RON. As a distinctive feature, these receptors act via a two-phosphotyrosine docking site, capable of concomitant activation of multiple intracellular transducers and signalling pathways. In a number of malignant tumours, MET and RON constitutively sustain the genetic programme of scattering, leading to invasive growth and metastatic phenotype. Four MET-related receptors have been recently identified (the SEX protein family). These molecules are predominantly expressed during development and are likely to mediate repelling cues between cells of different type.