Survival of conditionally immortalized hepatocytes in the spleen of syngeneic rats

Strategies for immortalization of primary hepatocytes

The liver has the unique capacity to regenerate in response to a damaging event. Liver regeneration is hereby largely driven by hepatocyte proliferation, which in turn relies on cell cycling. The hepatocyte cell cycle is a complex process that is tightly regulated by several well-established mechanisms. In vitro, isolated hepatocytes do not longer retain this proliferative capacity. However, in vitro cell growth can be boosted by immortalization of hepatocytes. Well-defined immortalization genes can be artificially overexpressed in hepatocytes or the cells can be conditionally immortalized leading to controlled cell proliferation. This paper discusses the current immortalization techniques and provides a state-of-the-art overview of the actually available immortalized hepatocyte-derived cell lines and their applications.

Establishment of Highly Differentiated Immortalized Human Hepatocyte Line With Simian Virus 40 Large Tumor Antigen for Liver Based Cell Therapy

Acute liver failure and metabolic liver disorder animal models have demonstrated that hepatocytes transplanted into the liver or spleen survive and participate in the liver repopulation process, and recent studies have documented the usefulness of hepatocyte transplantation in humans. However, despite the promising cell therapy, there are still many restrictions, such as the shortage of donor human livers and the limited lifespan and the functional insufficiency of primary cultured hepatocytes. The immortalized and highly differentiated human hepatocyte could provide an unlimited supply of transplantable cells. In this study, we established an efficient and highly differentiated immortalized human hepatocyte line for bioartificial liver and hepatocyte transplantation research. Hepatocytes isolated from the liver of a 25 year old, brain dead male were transfected with pcDNA3.1 (-) recombinant plasmid containing the genes encoding simian virus 40 (SV40) large tumor antigen. One of the hepatocyte clones, HepLL, displayed highly differentiated liver functions with immortalized characteristics and was selected with a 700-300 microg/ml of G418 technique in 42 days. To characterize this immortalized cell line for cell therapy in the near future, HepLL cells were studied with immunohistochemistry, reverse transcription-polymerase chain reactions, immunoblotting, and tumorigenicity tests. The results revealed that HepLL cells displayed morphologic characteristics of liver parenchymal cells, secreted albumin, synthesized urea and glycogen, and expressed liver enriched functional markers, but there were no tumorigenic qualities after transplantation into severe combined immunodeficiency mice. Thus this immortalized human hepatocyte line is expected to be a useful tool for studying the functions of differentiated human hepatocyte and a promising strategy to resolve the shortages of donor organs and the limits of primary human hepatocyte for transplantation and bioartificial liver support systems.

Rodent nutritional model of non-alcoholic steatohepatitis: species, strain and sex difference studies

BACKGROUND AND AIM

The methionine choline-deficient (MCD) diet leads to steatohepatitis in rodents. The aim of the present study was to investigate species, strain and sex differences in this nutritional model of non-alcoholic steatohepatitis (NASH).

METHODS

Male and female Wistar, Long-Evans and Sprague-Dawley rats, and C57/BL6 mice (n = 6 per group) were fed a MCD diet for 4 weeks. Control groups received an identical diet supplemented with choline bitartrate (0.2% w/w) and methionine (0.3% w/w). Liver pathology (steatosis and inflammation) and ultrastructure, liver lipid profile (total lipids, triglycerides, lipid peroxidation products), liver : body mass ratios and serum alanine aminotransferase (ALT) levels were compared between these groups.

RESULTS

The MCD diet-fed male rats developed greater steatosis (P < 0.001), had higher liver lipid content (P < 0.05) and had higher serum ALT levels (P < 0.005) than did female rats. Wistar rats (both sexes) had higher liver lipid levels (P < 0.05), serum ALT levels (P < 0.05), and liver mass : body mass ratios (P < 0.025) than did Long-Evans and Sprague-Dawley rats. In female groups, Wistar rats showed greater fatty change than did the other two strains (P < 0.05). All rats fed the MCD diet developed hepatic steatosis, but necrosis and inflammation were minor features and fibrosis was absent. Compared with Wistar rats, male C57/BL6 mice showed a marked increase in inflammatory foci (P < 0.001), end products of lipid peroxidation (free thiobarbituric acid reactive substances) (P < 0.005), and mitochondrial injury, while showing less steatosis (P < 0.005), lower hepatic triglyceride levels, (P < 0.005) and lower early lipid peroxidation products (conjugated dienes and lipid hydroperoxides; P < 0.005 and P < 0.01, respectively).

CONCLUSIONS

The Wistar strain and the male sex are associated with the greatest degree of steatosis in rats subjected to the MCD diet. Of the groups studied, male C57/BL6 mice develop the most inflammation and necrosis, lipid peroxidation, and ultrastructural injury, and best approximate the histological features of NASH.

Temporary amelioration of bilirubin conjugation defect in Gunn rats by transplanting conditionally immortalized hepatocytes

BACKGROUND

Conditionally immortalized hepatocytes (CIH) have been used in hepatocyte transplantation as an alternative to primary hepatocytes to cope with the shortage of donor organs. However, CIH are known to undergo apoptosis at body temperature and survive in vivo for a short period. In the present study, we investigated whether CIH function or not and how long their function is maintained in vivo.

METHODS

Various CIH cell lines that were established with temperature-sensitive Simian virus 40 large T antigen were transplanted into the spleen of Gunn rats, which are defective in bilirubin uridine diphosphate glucuronoside transferase (BUGT). Then, we measured biological changes over 3 months.

RESULTS

Serum bilirubin of the syngeneic CIH recipients decreased by 30%, which was maintained for 8 weeks. Thereafter, it began to rise to basal levels. The recipients of allogeneic CIH showed a minor reduction of bilirubin, although this was not statistically significant. However, there was no significant change in the bilirubin level in recipients of BUGT-defective congeneic CIH throughout the study period. Bilirubin monoglucuronides in the bile were not detected in the recipients of BUGT-defective CIH. However, they appeared in recipients of non-defective CIH and made up approximately 41% of total bile pigments.

CONCLUSIONS

Conditionally immortalized hepatocytes expressed hepatocyte function in vivo as well as in vitro, but the function lasted for a couple of months. According to our previous study, the limited functional duration may be related to the inevitable occurrence of apoptosis of these cells at body temperature. These data suggest that CIH can be used in hepatocyte transplantation only for temporary hepatic support.