Treatment of carbon tetrachloride and phenobarbital-induced chronic liver failure with intrasplenic hepatocyte transplantation

Prolonged engraftment of transplanted hepatocytes in the liver by transient pro-survival factor supplementation using ex vivo mRNA transfection

Cell transplantation therapy needs engraftment efficiency improvement of transplanted cells to the host tissues. Ex vivo transfection of a pro-survival gene to transplanted cells is a possible solution; however prolonged expression and/or genomic integration of the gene can be cancer promoting. To supply pro-survival protein only when it is needed, we used mRNA transfection, which exhibits transient protein expression profiles without the risk of genomic integration. Ex vivo transfection of mRNA encoding Bcl-2, a pro-survival factor, led to enhanced hepatocyte engraftment in both of normal and diseased mouse liver, effectively supporting liver function in a model of chronic hepatitis. The transplanted hepatocytes maintained their viability and function in the liver for at least one month, though Bcl-2 expression from mRNA was sustained for just a few days. Mechanism analyses suggest that Bcl-2 inhibits Kupffer cell-mediated hepatocyte clearance, which occurs within 2 days after transplantation. Within 2 days, hepatocytes migrated to the liver parenchyma, presumably a suitable place for the hepatocytes to survive without Bcl-2 expression. Thus, the duration of Bcl-2 expression from mRNA was sufficient to achieve prolonged engraftment. Ex vivo mRNA transfection allows supply of pro-survival factors to transplanted cells with minimal safety concerns accompanying prolonged expression, providing an effective platform to improve engraftment efficiency in cell transplantation therapy.

Engraftment and Function of Intrasplenically Transplanted Cold Stored Rat Hepatocytes

Hepatocellular transplant may potentially be efficacious for the treatment of selected liver metabolic disorders and acute hepatic failure. On the other hand, the use of hepatocyte cold preservation techniques in these transplantation protocols would allow to have available cells at the right time and place and, consequently, make an optimal use of scarce human hepatocytes. In our experiments we evaluated the biodistribution and functionality of cold preserved hepatocytes transplanted in the spleen of syngeneic rats. Isolated hepatocytes were labeled with the fluorescent dye 5(6)-carboxyfluorescein diacetate succinimidyl-ester, cold-preserved in modified University of Wisconsin (UW) solution for 48 or 96 h, and then transplanted into the spleen. Recipient animals were euthanized at 0 and 3 h, and at 1, 2, 3, 5, 10, and 14 days after transplantation for tissue analysis. Labeled hepatocytes were clearly identifiable in the recipient tissues up to 14 days later. Fluorescence microscopy also showed no significant differences in biodistribution when either cold stored or freshly isolated hepatocytes were transplanted. In addition, functional activity of transplanted cells was demonstrated by immunohistochemical detection of albumin at levels comparable to those found in normal hepatocytes. Our findings establish that cold preserved hepatocytes appear morphologically and biochemically normal after intrasplenic transplantation. Consequently, it indicates that modified UW solution makes it possible to safety preserve hepatocytes for up to 96 h before transplantation, perhaps providing sufficient time for hepatocyte allocation and potential recipient preparation, if applicable clinically.

Role of Intrasplenic Hepatocyte Transplantation in Improving Survival and Liver Regeneration after Hepatic Resection in Cirrhotic Rats

We studied the effect of preoperative hepatocyte transplantation on the prevention of liver failure in cirrhotic rats after hepatic resection. Two groups of Lewis rats were rendered cirrhotic by IP injection of 1% dimethylnitrosamine and were subjected to 33% hepatectomy. Two days before the resection, 36 rats in group I received intrasplenic hepatocyte transplantation, and 25 rats in group II were given intrasplenic injection of normal saline as a control. By the end of the third postoperative day, the rats in group I had better survival and a better biochemical profile than those in group II. The liver growth rate and the labeling index of proliferating cell nuclear antigen (PCNA-LI) showed a steady rise in group I. Compared with group II, group I had a significantly lower transforming growth factor (TGF-β1) level (p < 0.05). We conclude that preoperative intrasplenic hepatocyte transplantation improves survival and facilitates regeneration in cirrhotic rats after hepatic resection.

A Simple and Effective Method to Improve Intrasplenic Rat Hepatocyte Transplantation

Transplanted hepatocytes integrate, survive, and express their specific functions in the liver parenchyma. The aim of this study was to determine whether a large number of hepatocytes could move from the spleen to the liver when the cells are injected together with sodium nitroprusside, and if the improved hepatocyte migration may be related with portal vein dilatation. Wistar rats were transplanted in the spleen with fluorescent-labeled hepatocytes alone or together with sodium nitroprusside. At 1, 3, 6, and 24 h after the transplant, the liver from recipient animals was removed and morphometric analyses were performed. Portal and arterial pressures were also measured immediately after intrasplenic injection of a solution of sodium nitroprusside, hepatocytes alone, or hepatocytes plus sodium nitroprusside. Intrasplenically injected sodium nitroprusside produced a transient drop in arterial pressure and a sustained reduction in portal pressure. During hepatocyte transplantation it increased the number of transplanted cells migrating to the liver after 3 h. Sodium nitroprusside simultaneously injected with hepatocytes in the spleen allowed more cells to migrate into the liver of the host animal without risk in animal survival.

The history and use of human hepatocytes for the treatment of liver diseases: the first 100 patients

Orthotopic liver transplantation remains the only curative treatment for many end-stage liver diseases, yet the number of patients receiving liver transplants remains limited by the number of organs available for transplant. There is a need for alternative therapies for liver diseases. The transplantation of isolated hepatocytes (liver cells) has been used as an experimental therapy for liver disease in a limited number of cases. Recently, the 100th case of hepatocyte transplantation was reported. This review discusses the history of the hepatocyte transplant field, the major discoveries that supported and enabled the first hepatocyte transplants, and reviews the cases and outcomes of the first 100 clinical transplants. Some of the problems that limit the application or efficacy of hepatocyte transplantation are discussed, as are possible solutions to these problems. In conclusion, hepatocyte transplants have proven effective particularly in cases of metabolic liver disease where reversal or amelioration of the characteristic symptoms of the disease is easily quantified. However, no patients have been completely corrected of a metabolic liver disease for a significant amount of time by hepatocyte transplantation alone. It is likely that future developments in new sources of cells for transplantation will be required before this cellular therapy can be fully implemented and available for large numbers of patients.

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.

Clinical uses of liver stem cells

Liver transplantation offers a definitive cure for many liver and metabolic diseases. However, the complex invasive procedure and paucity of donor liver graft organs limit its clinical applicability. Liver stem cells provide a potentially limitless source of cells that would be useful for a variety of clinical applications. These stem cells or hepatocytes generated from them can be used in cellular transplantation, bioartificial liver devices and drug testing in the development of new drugs. In this chapter, we review the technical aspects of clinical applications of liver stem cells and the progress made to date in the clinical setting. The difficulties and challenges of realizing the potential of these cells are discussed.

Cell therapeutic options in liver diseases: cell types, medical devices and regulatory issues

Although significant progress has been made in the field of orthotopic liver transplantation, cell-based therapies seem to be a promising alternative to whole-organ transplantation. The reasons are manifold but organ shortage is the main cause for this approach. However, many problems such as the question which cell type should be used or which application site is best for transplantation have been raised. In addition, some clinicians have had success by cultivating liver cells in bioreactors for temporary life support. Besides answering the question which cell type, which injection site or even which culture form should be used for liver support recent international harmonization of legal requirements is needed to be addressed by clinicians, scientists and companies dealing with cellular therapies. We here briefly summarize the possible cell types used to partially or temporarily correct liver diseases, the most recent development of bioreactor technology and important regulatory issues.

Primary human hepatocytes on biodegradable poly(l-lactic acid) matrices: a promising model for improving transplantation efficiency with tissue engineering

Liver transplantation is an established treatment for acute and chronic liver disease. However, because of the shortage of donor organs, it does not fulfill the needs of all patients. Hepatocyte transplantation is promising as an alternative method for the treatment of end-stage liver disease and as bridging therapy until liver transplantation. Our group has been working on the optimization of matrix-based hepatocyte transplantation. In order to increase cell survival after transplantation, freshly isolated human hepatocytes were seeded onto biodegradable poly(l-lactic acid) (PLLA) polymer scaffolds and were cultured in a flow bioreactor. PLLA discs were seeded with human hepatocytes and exposed to a recirculated medium flow for 6 days. Human hepatocytes formed spheroidal aggregates with a liver-like morphology and active metabolic function. Phase contrast microscopy showed increasing numbers of spheroids of increasing diameter during the culture period. Hematoxylin and eosin histology showed viable and intact hepatocytes inside the spheroids. Immunohistochemistry confirmed sustained hepatocyte function and a preserved hepatocyte-specific cytoskeleton. Albumin, alpha-1-antitrypsin, and urea assays showed continued production during the culture period. Northern blot analysis demonstrated increasing albumin signals. Scanning electron micrographs showed hepatocyte spheroids with relatively smooth undulating surfaces and numerous microvilli. Transmission electron micrographs revealed intact hepatocytes and junctional complexes with coated pits and vesicles inside the spheroids. Therefore, we conclude that primary human hepatocytes, precultured in a flow bioreactor on a PLLA scaffold, reorganize to form morphologically intact liver neotissue, and this might offer an optimized method for hepatocyte transplantation because of the expected reduction of the initial cell loss, the high regenerative potential in vivo, and the preformed functional integrity.

An overview of animal models for investigating the pathogenesis and therapeutic strategies in acute hepatic failure

Acute hepatic failure (AHF) is a severe liver injury accompanied by hepatic encephalopathy which causes multiorgan failure with an extremely high mortality rate, even if intensive care is provided. Management of severe AHF continues to be one of the most challenging problems in clinical medicine. Liver transplantation has been shown to be the most effective therapy, but the procedure is limited by shortage of donor organs. Although a number of clinical trials testing different liver assist devices are under way, these systems alone have no significant effect on patient survival and are only regarded as a useful approach to bridge patients with AHF to liver transplantation. As a result, reproducible experimental animal models resembling the clinical conditions are still needed. The three main approaches used to create an animal model for AHF are: surgical procedures, toxic liver injury and infective procedures. Most common models are based on surgical techniques (total/partial hepatectomy, complete/transient devascularization) or the use of hepatotoxic drugs (acetaminophen, galactosamine, thioacetamide, and others), and very few satisfactory viral models are available. We have recently developed a viral model of AHF by means of the inoculation of rabbits with the virus of rabbit hemorrhagic disease. This model displays biochemical and histological characteristics, and clinical features that resemble those in human AHF. In the present article an overview is given of the most widely used animal models of AHF, and their main advantages and disadvantages are reviewed.

The use of stem cells in liver disease

PURPOSE OF REVIEW

Cell transplantation to restore liver function as an alternative to whole liver transplantation has thus far not been successful in humans.

RECENT FINDINGS

Adult mature hepatocytes and various populations of liver progenitors and stem cells are being studied for their regenerative capabilities. Hepatocyte transplantation to treat metabolic deficiencies has shown promising early improvement in liver function; however, long-term success has not been achieved. Liver progenitor cells can now be identified and were shown to be capable to differentiate into a hepatocyte-like phenotype. Despite evidence of mesenchymal stem cell fusion in animal models of liver regeneration, encouraging results were seen in a small group of patients receiving autologous transplantation of CD133 mesenchymal stem cells to repopulate the liver after extensive hepatectomy for liver masses. Ethical issues, availability, potential rejection and limited understanding of the totipotent capabilities of embryonic stem cells are the limitations that prevent their use for restoration of liver function. The effectiveness of embryonic stem cells to support liver function has been proven with their application in the bioartificial liver model in rodents.

SUMMARY

There is ongoing research to restore liver function in cell biology, animal models and clinical trials using mature hepatocytes, liver progenitor cells, mesenchymal stem cells and embryonic stem cells.

Review of hepatocyte transplantation

BACKGROUND

Hepatocyte transplantation is a promising treatment for several liver diseases and can also be used as a "bridge" to liver transplantation in cases of liver failure. Although the first animal experiments with this technique began in 1967, it was first applied in humans only in 1992. Unfortunately, unequivocal evidence of transplanted human hepatocyte function has been obtained in only one patient with Crigler-Najjar syndrome type I and, even then, the amount of bilirubin-UDP-glucuronosyltransferase enzyme activity derived from the transplanted cells was not sufficient to eliminate the patient's eventual need for organ transplantation.

METHODS

A literature review was carried out using MEDLINE and library searches.

RESULTS

This review considers the following: (1) alternatives or bridges to orthotopic liver transplantation (OLT); (2) solutions to the shortage of organs-the shortage of organ donors has impeded the development of human hepatocyte transplantation, and immortalized hepatocytes in particular could provide an unlimited supply of transplantable cells in a nearly future; (3) future directions. We review these efforts along with hepatocyte transplantation over the last 13 years.

Restrictive model of compensated carbon tetrachloride-induced cirrhosis in rats

AIM: To develop a simplified and quick protocol to induce cirrhosis and standardize models of partial liver resection in rats.

METHODS: In Fischer F344 rats two modified protocols of phenobarbital-carbon tetrachloride (CCl₄) (dilution 50%) gavage to induce cirrhosis (frequency adjusted according to weight, but each subsequent dose was systematically administered) were tested, i.e. the rapid and slow protocols. Prothrombin time (PT) and total bilirubin (TB) were also evaluated. Animals from the rapid group underwent 15% hepatectomy and animals from the slow group underwent 70% hepatectomy.

RESULTS: Rapid protocol: This corresponded to 1 gavage/4 d over 6 wk (mortality 30%). Mean PT was 35.2 ± 2.8 s (normal: 14.5 s), and mean TB was 1.8 ± 0.2 mg/dL (normal: 0.1 mg/dL). Slow protocol: This corresponded to 1 gavage/6 d over 9 wk (mortality 10%). Mean PT was 11.8 ± 0.2 s (normal: 14.5 s), and mean TB was 0.4 ± 0.04 mg/dL (normal: 0.1 mg/dL). Pathological analyses were performed in both protocols which showed persistent cirrhosis at 3 mo. Rat mortality in the rapid gavage group who underwent 15% hepatectomy and in the slow gavage group who underwent 70% hepatectomy was 50% and 70%, respectively.

CONCLUSION: Our modified model is a simplified method to induce cirrhosis which is rapid (6 to 9 wk), efficient and stable up to 3 mo. Using this method, “Child Pugh A” or “Child Pugh BC” cirrhotic rats were obtained. Our models of cirrhosis and hepatectomy can be used in various situations focusing on postoperative survival.

Bioartificial liver systems: why, what, whither?

Acute liver disease is a life-threatening condition for which liver transplantation is the only recognized effective therapy. While etiology varies considerably, the clinical course of acute liver failure is common among the etiologies: encephalopathy progressing toward coma and multiple organ failure. Detoxification processes, such as molecular adsorbent recirculating system (MARS®) and Prometheus, have had limited success in altering blood chemistries positively in clinical evaluations, but have not been shown to be clinically effective with regard to patient survival or other clinical outcomes in any Phase III prospective, randomized trial. Bioartificial liver systems, which use liver cells (hepatocytes) to provide metabolic support as well as detoxification, have shown promising results in early clinical evaluations, but again have not demonstrated clinical significance in any Phase III prospective, randomized trial. Cell transplantation therapy has had limited success but is not practicable for wide use owing to a lack of cells (whole-organ transplantation has priority). New approaches in regenerative medicine for treatment of liver disease need to be directed toward providing a functional cell source, expandable in large quantities, for use in various applications. To this end, a novel bioreactor design is described that closely mimics the native liver cell environment and is easily scaled from microscopic (<1 ml cells) to clinical (∼600 ml cells) size, while maintaining the same local cell environment throughout the bioreactor. The bioreactor is used for study of primary liver cell isolates, liver-derived cell lines and stem/progenitor cells.

Characteristics of rat bone marrow cells differentiated into a liver cell lineage and dynamics of the transplanted cells in the injured liver

BACKGROUND

Bone marrow cells (BMCs) have been shown to differentiate into a liver cell lineage, but little is known about their dynamics following transplantation. BMCs were cultured to investigate the expression of liver-specific genes in vitro and transplanted into in vivo liver-injury models to elucidate their dynamics in the liver.

METHODS

The mRNA expression of various liver-specific genes in BMCs cocultured with hepatocytes was analyzed using reverse transcription-polymerase chain reaction. BMCs from transgenic rats expressing green fiuorescent protein were transplanted into the spleen of rat liver-injury models induced with 2-acetylaminofiuorene (2-AAF) or carbon tetrachloride (CCl4). BMCs were also transplanted directly into livers treated with CCl4 to determine which route is better for transplantation.

RESULTS

BMCs differentiated into a liver cell lineage in vitro and expressed mRNAs consistent with mature hepatocytes, including albumin. The transplanted BMCs were found in the liver in the CCl4-induced injury model, but not in the 2-AAF-induced model. The hepatocyte growth factor and fibroblast growth factor mRNA levels in the liver were significantly higher in the CCl4-induced model than in the 2-AAF-induced model. Migration of BMCs to the liver was more effective following injection into the liver, rather than into the spleen.

CONCLUSIONS

Cultured BMCs differentiated into a liver cell lineage are a potential source for cell transplantation. Transplantation is successful in the severely injured liver with a high level of expression of mRNAs for growth factors. Injection of BMCs directly into the liver is the preferred route of administration.

Experimental models of acute and chronic liver failure in nude mice to study hepatocyte transplantation

Although hepatocyte transplantation is a promising therapy for acute liver failure in human, there is still a lack of animal models suffering from hepatic injury in which the benefits of hepatocyte transplantation could be evaluated solely, without the bias caused by immunosuppression. As a consequence, the aim of the study was first to develop reproducible models of partial hepatectomy and of thioacetamide (TA)- or Jo2-induced acute liver failure in nude mice. Chronic liver disease was also investigated by repeated injections of sublethal doses of thioacetamide. Survival rates, routine histologic observations, alanin aminotransferase sera content, Ki67, and caspase 3 immunodetection were investigated both after 40% partial hepatectomy and after toxic-induced damages. Liver injuries were more severe and/or precocious in nude mice than in Balb/c mice for a given treatment with a maximum of acute injury obtained 24 h after single toxic injection, and were found to be transitory and reversible within 10 days. Toxics induced apoptosis followed by necrosis, confirming recent published data. Onset of fibrosis leading to reproducible chronic cirrhosis in nude mice correlated with increasing number of Ki67-positive cells, indicating that high levels of cell proliferation occurred. Chronic cirrhosis progressively reversed to fibrosis when the treatment ceased. Preliminary results demonstrated that engrafted xenogeneic hepatocytes could be detected in the host liver by anti-MHC class I immunohistochemistry. Fractions enriched in 2n or 4n hepatocytes by cell sorting using a flow cytometer were equivalent to the unpurified fraction in terms of engraftment in control nude mice or in nude mice subjected to PH. However, in mice suffering from liver injury 24 h after Jo2 or TA treatment, the engraftment of 2n hepatocytes was about twice that of an unpurified hepatocyte population or of a population enriched in 4n hepatocytes.

Hepatocyte transplantation

Isolated hepatocyte transplantation has long been recognized as a potential treatment for life-threatening liver disease. The basis for proceeding with clinical trials has been established by the extensive laboratory work in animal models. Human hepatocyte transplantation has been applied in individual cases and very small, uncontrolled series. Data, although sparse, demonstrate the safety and feasibility of this approach and are supportive, if less than conclusive, of effectiveness. The experience of hepatocyte transplantation in the laboratory and clinical arenas is reviewed and discussion will examine what is believed to be the primary cause for the slow growth of this technology in the clinical setting, namely a severe shortage of usable primary human hepatocytes. The potential of isolated hepatocyte transplantation remains largely untapped and awaits alternate sources of cells for transplantation other than those from discarded human cadaveric livers.

Developmental changes in glutathione S-transferase isoforms expression and activity in intrasplenic fetal liver tissue transplants in rats

The aim of the present study was to characterise developmental changes in glutathione S-transferase (GST) isoforms expression and in glutathione conjugation capacity in intrasplenic liver tissue transplants. For this purpose, syngenic fetal liver tissue suspensions were transplanted into the spleens of adult male Fischer 344 rats. Three days, 1, 2, 4 weeks, 2, 4, 6 months and 1 year later, transplant-recipients and control animals were sacrificed and class alpha, mu and pi GST isoforms expression and GST activities using the substrates o-dinitrobenzene and 1-chloro-2,4-dinitrobenzene were assessed in livers and spleens. In the hepatocytes of the adult livers no class pi, but a distinct class alpha and mu GST expression was seen. The bile duct epithelia were class pi GST positive. Fetal livers displayed almost no class alpha and mu, but a slight class pi GST expression. The same pattern was seen in 3-day-old intrasplenic liver tissue transplants. Up to 2 weeks after surgery the class alpha and mu GST expression increased in the hepatocytes of the transplants, whereas the immunostaining for class pi GST disappeared. No remarkable changes were seen thereafter. Normal conjugation capacities were observed with the livers of both groups of rats. Control spleens displayed only low GST activities. From 2 months after transplantation on activities were significantly higher in transplant-containing spleens than in respective control organs with a further increase up to one year after grafting. These results show that intrasplenically transplanted fetal liver cells proliferate and differentiate into mature cells displaying a GST expression pattern with respective enzyme activities similar to adult liver.

Evaluation of 2-year-old intrasplenic fetal liver tissue transplants in rats

Liver cell transplantation into host organs like the spleen may possibly provide a temporary relief after extensive liver resection or severe liver disease or may enable treatment of an enzyme deficiency. With time, however, dedifferentiation or malignant transformation of the ectopically transplanted cells may be possible. Thus, in the present study syngenic fetal liver tissue suspensions were transplanted into the spleen of adult male rats and evaluated 2 years thereafter in comparison to orthotopic livers for histopathological changes and (as markers for preneoplastic transformation) for cytochrome P450 (P450) and glutathione S-transferase (GST) isoform expression. Because inducibility of P450 and GST isoforms may be changed in preneoplastic foci, prior to sacrifice animals were additionally treated either with beta-naphthoflavone, phenobarbital, dexamethasone, or the respective solvent. In the 2-year-old grafts more than 70% of the spleen mass was occupied by the transplant. The transplanted hepatocytes were arranged in cord-like structures. Also few bile ducts were present. Morphologically, no signs of malignancy were visible. With all rats, transplant recipients as well as controls, however, discrete nodular structures were seen in the livers. Due to age, both livers and transplants displayed only a low P450 2B1 and 3A2 and GST class alpha and mu isoform expression. No immunostaining for P450 1A1 was visible. At both sites, beta-naphthoflavone, phenobarbital, or dexamethasone treatment enhanced P450 1A1, P450 2B1 and 3A2, or P450 3A2 expression, respectively. No immunostaining for GST class pi isoforms was seen in the transplants. The livers of both transplant recipients and control rats, however, displayed GST pi-positive foci, corresponding to the nodular structures seen histomorphologically. Compared to the surrounding tissue, these foci also exhibited a more pronounced staining for GST class alpha and mu isoforms and a stronger inducibility of the P450 1A1 expression due to beta-naphthoflavone. In conclusion, in contrast to the livers, no preneoplastic foci seem to appear in the intrasplenic transplants even 2 years after transplantation. This may be due either to the protection of these transplants by the orthotopic livers or to the different humoral and nerval influences at the ectopic site.

Influence of recipient gender on cytochrome P450 isoforms expression in intrasplenic fetal liver tissue transplants in rats

Rat livers display a sex-specific cytochrome P450 (P450) isoforms expression pattern which is regulated by a differential profile of growth hormone (GH) secretion. The aim of the present study was to elucidate whether liver cell transplants at an ectopic site are also subject to this influence. Fetal liver tissue suspensions of mixed gender were transplanted into the spleen of adult male or female syngenic recipients. Four months after grafting transplant recipients and age-matched controls were treated with beta-naphthoflavone (BNF), phenobarbital (PB), dexamethasone (DEX) or the solvents and sacrificed 24 or 48 h thereafter. Livers and intrasplenic transplants were evaluated for the expression of the P450 subtypes 1A1, 2B1, 2E1, 3A2 and 4A1 by means of immunohistochemistry. The livers of both male and female rats displayed nearly no P450 1A1, but a distinct P450 2B1, 2E1, 3A2 and 4A1 expression. Whereas no sex differences were seen in the P450 1A1 expression, the immunostaining for P450 2B1, 3A2 and 4A1 was stronger in males and that for P450 2E1 in females. Similarly, in the intrasplenic liver cell transplants almost no P450 1A1, but a noticeable P450 2B1, 2E1, 3A2 and 4A1 expression was observed. Like in the respective livers, the immunostaining for P450 2B1, 3A2 and 4A1 was stronger in the transplants hosted by male than by female rats, whereas the opposite was the case for the P450 2E1 expression. Both in livers and transplants with some sex-specific differences P450 1A1 and 2E1 expression was induced by BNF, that of P450 2B1 by BNF and PB, and that of P450 3A2 by PB and DEX. These results indicate that the P450 system of ectopically transplanted liver cells is influenced by the gender of the recipient organism like that of the orthotopic livers.

Effects of different mitogens on intrasplenic liver tissue transplants in comparison to orthotopic liver

Ectopic liver cell transplants, when compared to orthotopic liver, can serve as a tool to study topic influences on liver cell differentiation, multiplication, function and responsiveness to xenobiotics. The aim of the present study was to evaluate, if characteristic effects of mitogens are exerted in both liver and intrasplenic liver cell transplants in a similar manner. Fetal liver tissue suspensions were transplanted into the spleens of adult male syngenic rats. Four months later, transplant recipients and controls were treated with fluorene (FEN), fluorenone (FON), 2-acetylaminofluorene (AAF), N-nitrosodibenzylamine (NDBA) or the solvent 48 hours before sacrifice. The following parameters were assessed within livers and spleens: mitotic activity of hepatocytes, glycogen content, cytochrome P450 (P450) isoforms expression, P450 mediated monooxygenase functions, tissue content of lipid peroxides (LPO) and of reduced and oxidized glutathione (GSH; GSSG). In both orthotopic livers and intrasplenic transplants FEN, FON or NDBA administration increased the mitotic activity of the hepatocytes. Treatment with the mitogens caused a distinct and characteristic induction of the P450 isoforms expression and of the respective monooxygenase functions in the livers and (with certain differences) also in the transplants. FEN and FON slightly increased, AAF and NDBA reduced liver glycogen content. The latter effect was also seen in the transplants. NDBA administration caused a slight increase in tissue LPO content in livers, but not in spleens. Additionally, AAF or NDBA treatment led to an elevation of liver (but not of spleen) GSH and GSSG concentrations. The results of the present investigation show that characteristic effects of mitogens on orthotopic liver occur with certain differences also in ectopic liver cell transplants.