Enhancement of proliferation of intrasplenically transplanted hepatocytes in cirrhotic rats by hepatic stimulatory substance

Involvement of hepatic stimulator substance in experimentally induced fibrosis and cirrhosis in the rat

Liver fibrosis results from sustained wound healing response to chronic liver injury. Liver cirrhosis, the end stage of the fibrotic process, is characterized by disruption of the entire liver architecture and reduced hepatocyte regenerative ability. Hepatic stimulator substance (HSS) is a liver-specific growth factor triggering hepatocyte proliferation in vitro and in vivo. Previous studies have indicated the involvement of HSS in animal models of acute liver injury. The aim of the present study was to investigate the involvement of HSS in the process of fibrosis and cirrhosis induction. Liver fibrosis and cirrhosis were induced in rats by thioacetamide (TAA) administration (300 mg/l) in the drinking water for 3 months, and animals were killed at 0, 1, 2, and 3 months of treatment. TAA administration resulted in progressively increasing liver fibrosis, leading to the onset of cirrhosis at the end of the experimental time. HSS was continuously produced during the course of fibrosis and cirrhosis induction, peaking at the 2nd month of TAA treatment, coinciding with markers of hepatic proliferative capacity, as thymidine kinase activity and DNA biosynthesis. Significantly reduced HSS activity was noted in cirrhotic liver (3rd month). In this case, the exogenous HSS administration during the 3rd month of TAA treatment suppressed the onset of liver cirrhosis, stimulating the hepatic regenerative capacity. Our data indicate the active participation of HSS in the process of fibrosis and cirrhosis induction post-TAA treatment in rats, suggesting also the beneficial effect of HSS treatment against cirrhosis induction with future possible clinical implications.

Artificial liver support at present and in the future

Liver failure is a fatal disease. Liver transplantation is the only established treatment for liver failure; however, donor shortages remain problematic. In the United States and Europe, artificial livers as a bridge to liver transplantation are being considered. In Japan, we have taken a different approach to the treatment of end-stage liver diseases because of the characteristics of the health-care insurance system, regulated by the government. Furthermore, cadaveric liver transplantations are unsuited to the social mores of Japanese culture. Practically speaking, we believe that plasma exchange (PE) and continuous hemodiafiltration (CHDF) are the most effective therapies for the treatment of liver failure, although randomized controlled studies are needed to determine their effects. Overall, we believe that the first line of treatment for liver failure should be PE and CHDF, and the second line should be bioartificial liver support. In the near future, we hope that both gene therapy and regenerative medicine will contribute to the development of a functional artificial liver.

Insights on augmenter of liver regeneration cloning and function

Hepatic stimulator substance (HSS) has been referred to as a liver-specific but species non-specific growth factor. Gradient purification and sequence analysis of HSS protein indicated that it contained the augmenter of liver regeneration (ALR), also known as hepatopoietin (HPO). ALR, acting as a hepatotrophic growth factor, specifically stimulated proliferation of cultured hepatocytes as well as hepatoma cells in vitro, promoted liver regeneration and recovery of damaged hepatocytes and rescued acute hepatic failure in vivo. ALR belongs to the new Erv1/Alr protein family, members of which are found in lower and higher eukaryotes from yeast to man and even in some double-stranded DNA viruses. The present review article focuses on the molecular biology of ALR, examining the ALR gene and its expression from yeast to man and the biological function of ALR protein. ALR protein seems to be non-liver-specific as was previously believed, increasing the necessity to extend research on mammalian ALR protein in different tissues, organs and developmental stages in conditions of normal and abnormal cellular growth.

Transplantation of hepatocytes: Temporary elimination of scavenger cells prevents early loss of grafted cells

Transplants of isolated syngeneic and allogeneic hepatocytes are rapidly disintegrated, irrespective of the site of engraftment; be it spleen, liver, portal vein, peritoneum, or subcutaneous tissue. Host scavenger cells are responsible for this reaction. We designed a method overcoming early disintegration of the grafted hepatocytes. It consisted of administration of anti-asialoGM1 antiserum eliminating natural killer cells; sublethal whole body irradiation; and reconstitution with syngeneic bone marrow cells, ligation of host bile duct, intrasplenic hepatocyte transplantation, and three consecutive partial hepatectomies. Six months after transplantation a glycogen-rich, trabeculae-forming, dividing hepatocytes, situated along strands of newly-formed fibrous tissue and numerous dilated blind bile cannaliculae were observed. There was evidently more bile canaliculae in hosts with ligated bile duct than nonligated controls. This is the first study showing fibrous tissue formed at the site of hepatocyte implantation, and stellate cells are presumably involved in this process.

Viabilidade do fígado bioartificial utilizando hepatócitos humanos imunoprotegidos por macroencapsulação

OBJETIVO: O transplante de hepatócitos xenogênicos encapsulados pode ser utilizado no futuro em situações como a insuficiência hepática fulminante. Porém, observa-se perda precoce da expressão de genes hepatocitários específicos em hepatócitos humanos. O objetivo deste estudo é avaliar a influência da resposta imunológica na perda da expressão genética hepatocitária de hepatócitos humanos encapsulados e transplantados em ratos. MÉTODO: Hepatócitos humanos foram isolados de fragmentos hepáticos, encapsulados em fibras e transplantados em ratos. Nos dias 3, 7 e 14 após o transplante as fibras foram coletadas e avaliadas a morfologia por microscopia óptica e eletrônica, e a expressão dos genes por biologia molecular. O ARNm da albumina humana foi quantificado por RT-PCR e Northern blot. A resposta imunológica contra os hepatócitos foi avaliada através do ADN hepatocitário na busca de apoptose do núcleo celular e pelo aumento da expressão do CMH de classe I. RESULTADOS: Os aspectos morfológicos dos hepatócitos mantiveram-se normais até o sétimo dia após o transplante. Não se observaram células envolvidas com resposta imunológica do receptor nas fibras. Os transcritos da albumina foram detectados até D-14. Entre os dias 3 e 7 estavam em 30% em relação ao dia 0. A análise do ADN mostrou bandas preservadas sem a presença de fenômenos de apoptose nos diferentes dias. Não ocorreu aumento da expressão do CMH de classe I. CONCLUSÕES: Hepatócitos humanos encapsulados e transplantados em ratos permanecem viáveis apesar da diminuição da expressão de determinados genes. Este fenômeno, não se deve à resposta imunológica do receptor, mas ao próprio processo de isolamento celular.

Transplantation of hepatocytes: elimination of recipient natural killer cells with irradiation and bone marrow reconstitution prevent early graft dysfunction

Transplanted isolated syngeneic and allogeneic hepatocytes rapidly disintegrate, irrespective of the origin or the site of engraftment namely spleen, liver, portal vein, peritoneum, or subcutaneous tissues. Although various methods have been applied to attenuate this reaction, none have been found effective. We applied a combined protocol consisting of administration of anti-asialoGM1 antiserum (eliminating NK cells), sublethal whole-body irradiation, and reconstitution with syngeneic bone marrow cells to intrasplenic hepatocyte transplantation and 3 consecutive partial hepatectomies. This method overcame the early disintegration of grafted hepatocytes. Ninety days after transplantation numerous hepatocyte clusters and dilated bile canaliculae, occupying two thirds of the spleen, were observed, with some hepatocytes adhering to the bile ducts forming Hering's canals. Mitotic figures were noticed. There were no recipient mononuclear infiltrates around the hepatocyte clusters.

Hepatic stimulator substance administration ameliorates liver regeneration in an animal model of fulminant hepatic failure and encephalopathy

AIMS/BACKGROUND

Hepatic stimulator substance (HSS) is a liver-specific growth factor implicated in hepatocellular proliferation and hepatoprotection in models of acute liver injury. In the present study, we examined the effect of exogenous HSS administration on liver proliferating capacity and survival outcome in an experimental animal model of fulminant hepatic failure (FHF) and encephalopathy, induced by repeated injections of thioacetamide (TAA) in rats.

METHODS

Fulminant hepatic failure was induced in adult male Wistar rats by three consecutive intraperitoneal injections of TAA (400 mg/kg of body weight), at 24 h time intervals. The animals received intraperitoneally either a saline solution or HSS (50 mg protein/kg of body weight), 2 h after the second and third TAA injections. The animals were killed at 6, 12 and 18 h post the last injection of TAA.

RESULTS

Levels of liver enzymes and urea in serum, blood ammonia values, liver histology, stage of hepatic encephalopathy and survival were statistically significantly improved in TAA-intoxicated and HSS-treated rats compared to TAA-intoxicated and saline-treated ones. Furthermore, HSS ameliorated liver regenerative indices--DNA biosynthesis, thymidine kinase activity and hepatocyte mitotic activity--in a statistically significant manner.

CONCLUSIONS

Our data suggest the beneficial effect of HSS administration in this animal model of FHF and encephalopathy, supporting evidence for a possible use of HSS as supportive therapy, by increasing hepatocellular proliferation, in management of FHF.

Hepatic stimulator substance activity in the liver of thioacetamide-intoxicated rats

AIMS/BACKGROUND

Hepatic stimulator substance (HSS) is a known hepatic growth factor which appears to be organ-specific but species non-specific. We have recently shown that the administration of HSS enhanced hepatocyte proliferation occurring due to thioacetamide (TAA)-induced liver injury in rats (Theocharis SE, et al., Scand J Gastroenterol 1998; 33: 656-63). In the present study, we examined the activity of the endogenously produced HSS in the liver of TAA administered rats during injury and regeneration.

METHODS

TAA at a dose of 300 mg/kg of body weight was injected intraperitoneally in male Wistar rats. The animals were sacrificed at 0, 12, 24, 36, 48, 60 and 72 h after TAA administration. The rate of tritiated thymidine incorporation into hepatic DNA, the enzymatic activity of liver thymidine kinase and the assessment of mitotic index in hepatocytes were used to estimate liver regeneration. HSS extract was obtained from the livers of TAA-treated rats, sacrificed at the above mentioned time points. This HSS extract was injected in 34% partially hepatectomized rats, to assess its activity. The ability of the injected HSS extract to increase hepatocellular proliferation over that normally occurring 24 h following 34% partial hepatectomy was used to express the activity of HSS by determining the above mentioned indices of liver regeneration.

RESULTS

The administration of TAA caused severe hepatic injury recognized histopathologically as well as by the increased activities of serum hepatic enzymes aspartate and alanine aminotrasferases. The hepatic injury, which peaked at 24 and 36 h post-TAA treatment (p<0.001), was followed by hepatocyte proliferation, presenting peaks at 48 and 60 h (p<0.001). The activity of the endogenously produced HSS from livers of TAA-treated rats increased at 36 h after TAA administration as well as being highly expressed at 48 and 60 h thus coinciding with the peak of hepatocyte proliferation. At other time points, HSS activity was decreased.

CONCLUSIONS

The observed variations of HSS activity in rat liver suggest active participation of this growth factor in hepatocyte replication which follows toxin-induced liver injury as a repair mechanism process.