Intrasplenic hepatocyte transplantation in rats with experimental liver injury: morphological and morphometric studies

Allogeneic Hepatocyte Transplantation Using FK 506

Hepatocyte transplantation is an intriguing alternative to orthotopic liver transplantation. While engraftment of syngeneic hepatocytes can be achieved with relative ease, engraftment of allogeneic hepatocytes has been far more complicated. We used FK 506 (Tacrolimus), a novel and highly efficient immunosuppressant, which has been reported to augment liver regeneration in rats. Recipients of isolated syngeneic (LEW) and allogeneic (Wistar F.) rat hepatocytes (major histocompatibility barrier) recieved different immunosuppressive regiments with FK 506 or Cyclosporine A (CsA). Mature syngeneic hepatocytes could be retrieved up to post op day 300 with the lowest number of hepatocytes on post op day 20. Following allogeneic transplantation, no mature hepatocytes could be identified after post op day 10, though ductular like structures within the spleen were found in FK 506 but not CsA-treated animals. The epithelial cells of ductular like structures exhibit cytological features of CK-19 positive cells. Our results suggest that under CsA or FK 506 immunosuppression long-term survival of mature allogeneic hepatocytes within the spleen cannot be achieved across a major histocompatibility barrier though FK 506 allows engraftment of allogeneic donor type ductular cells. Copyright © 1997 Elsevier Science Inc.

Significant Improvement of Survival by Intrasplenic Hepatocyte Transplantation in Totally Hepatectomized Rats

The effect of intrasplenic hepatocyte transplantation (HTX) was studied in an experimental model of acute liver failure in rats with chronic liver atrophy. Rats underwent a portacaval shunt operation on Day -14 to induce liver atrophy, and underwent total hepatectomy on Day 0 as a start of acute liver failure. Intrasplenic hepatocyte or sham transplantation was performed on Day -7, -3, or -1 (n = 4 to 6 per group). During the period following hepatectomy, mean arterial blood pressure was maintained above 80 mm Hg and hypoglycaemia was prevented. Severity of hepatic encephalopathy was assessed by clinical grading and EEG spectral analysis, together with determination of blood ammonia and plasma amino acid concentrations, and “survival” time. Histological examination of the spleen and lungs was performed after sacrifice. Intrasplenic hepatocyte transplantation resulted in a significant improvement in clinical grading in all transplanted groups (p < 0.05), whereas a significant improvement in EEG left index was seen only in the group with transplantation on Day -1 (p < 0.05). In contrast to hepatocyte transplantation 1 day before total hepatectomy, rats with hepatocyte transplantation 3 and 7 days before total hepatectomy showed a significant 3- and 2-fold increase in “survival” time compared to sham transplanted controls: HTX at Day -1: 7.5 ± 0.3 h vs. 5.9 ± 0.6 h (p > 0.05), HTX at Day -3:19.7 ± 3.7 h vs. 6.5 ± 0.3 h (p < 0.05), and HTX at Day -7: 13.8 ± 3.2 h vs. 6.3 ± 0.3 h (p < 0.05). Furthermore, rats with hepatocyte transplantation on Day -3 and -7 showed significantly lower blood ammonia concentrations after total hepatectomy (p < 0.0001). Histological examination of the spleens after sacrifice showed clusters of hepatocytes in the red pulp. Hepatocytes present in the spleen for 3 and 7 days showed bile accumulation and spots of beginning necrosis. The present data show that in a hard model of complete liver failure in portacaval shunted rats, intrasplenic hepatocyte transplantation is able to prolong “survival” time significantly 2- to 3-fold. The relevance of this observation for human application is discussed.

Effect of Liver Cell Transplantation on Acute Hepatic Failure Induced by Massive Liver Resection in the Rat

Purpose

This study is designed to ascertain the most effective quantity and injection route of hepatocytes in an acute liver failure model induced by massive liver resection in rats.

Methods

Rats weighing 450 to 650 gm underwent partial hepatectomy that was 80% of their liver weight, resulting in acute liver failure. Hepatocytes were obtained by perfusing collagenase (Wako, Japan) solution through portal vein into liver of the allogenic rat. These hepatocytes were injected into different places with different dosage. The experimental groups were divided into the Control group, Splenic group I (2×10⁶ cells into splenic capsule), Splenic group II (2×10⁷ cells into splenic capsule), Portal vein group (2×10⁷ cells into portal vein), Subperitoneal group (2×10⁷ cells into subperitoneum). The experimental animals were observed carefully for 5 days for assessment of survival and regeneration of liver. Liver function tests including serum alanine aminotransferase (ALT), total bilirubin, gamma-glutamyl transferase (γ-GTP) on postoperative 1, 2, 3, 5th days and histologic examinations of specimens obtained from each respective groups on postoperative 5th day were performed.

Results

Serum ALT level on postoperative day 1 peaked and then gradually normalized showing statistical significance (p=0.035). Study groups showing statistically significant difference under repeated anova analysis were between the Splenic group II and Control (p=0.035), and between the Splenic group II and Portal vein group (p=0.001) with respect to serum ALT levels. Also, progression of each study group showed statistical significance. (p=0.02). Serum total bilirubin and r-GTP did not show any significant difference.

Conclusion

Hepatocyte transplantation of 2×10⁷ cells into spleen showed the best results in the acute hepatic failure rat.

Transdifferentiation into biliary ductular cells of hepatocytes transplanted into the spleen

AIMS

Transplantation of rat hepatocytes into the syngeneic rat spleen results in the appearance of cytokeratin (CK)7 and CK19 positive biliary cells that form ductules. We examined whether hepatocytes are the origin of these biliary ductular cells.

METHODS

We transplanted rat dipeptidyl peptidase IV (DPPIV) positive hepatocytes into the liver of retrorsine-treated and partially hepatectomised DPPIV negative rats, which resulted in proliferation of DPPIV positive hepatocytes in the liver. Two months later, hepatocytes were prepared from chimaeric livers of these rats and transplanted into the spleen of DPPIV negative rats. Four weeks later, the expression of DPPIV in CK7 positive ductules in the spleen was examined by immunofluorescent double-staining.

RESULTS

In the spleen of DPPIV negative rats transplanted with hepatocytes prepared from the chimaeric livers, DPPIV was found to be expressed in some CK7 positive biliary ductules where only a fraction of cells expressed DPPIV, whereas in the spleen of DPPIV negative rats transplanted with hepatocytes from livers of DPPIV positive rats, DPPIV was expressed in all CK7 positive biliary ductules.

CONCLUSION

The present study indicates that hepatocytes transplanted into the spleen could transdifferentiate into biliary cells that aggregate to form ductular structures.

Liver cancer stem cells

In an effort to review the evidence that liver cancer stem cells exist, two fundamental questions must be addressed. First, do hepatocellular carcinomas (HCC) arise from liver stem cells? Second, do HCCs contain cells that possess properties of cancer stem cells? For many years the finding of preneoplastic nodules in the liver during experimental induction of HCCs by chemicals was interpreted to support the hypothesis that HCC arose by dedifferentiation of mature liver cells. More recently, recognition of the role of small oval cells in the carcinogenic process led to a new hypothesis that HCC arises by maturation arrest of liver stem cells. Analysis of the cells in HCC supports the presence of cells with stem-cell properties (ie, immortality, transplantability, and resistance to therapy). However, definitive markers for these putative cancer stem cells have not yet been found and a liver cancer stem cell has not been isolated.

Hepatocyte differentiation from embryonic stem cells and umbilical cord blood cells

With the development of regeneration medicine, many researchers have attempted hepatic differentiation from nonhepatic-origin cell sources. The differentiation of embryonic stem (ES) cells into hepatocyte-like cells has been reported in several papers. Mouse ES cells have shown a potential to develop into hepatocyte-like cells in vitro on the basis of hepatic gene expression after adding several growth factors. We transplanted cultured embryoid body (EB) cells (male) into female mice. A liver specimen of the recipient was examined by immunohistochemical staining for albumin and fluorescence in situ hybridization for the Y chromosome after transplantation. Both Y chromosome- and albumin-positive cells were recognized in the recipient female liver, and were considered to be hepatocyte-like cells derived from ES cells containing the Y chromosome. Many groups, including ourselves, have studied hepatocyte-like cell differentiation from umbilical cord blood cells (UBCs). We cultured nucleated cells isolated from UBCs. Using immunostaining, ALB-positive and CK-19-positive cells were recognized in the culture. Dual staining of ALB and CK-19 demonstrated that ALB was coexpressed with CK-19, suggesting the existence of hepatic progenitors. In this review, we consider recent studies of the differentiation of hepatocytes from nonhepatic origins, especially ES cells and umbilical cord blood.

Transdifferentiation of mature rat hepatocytes into bile duct-like cells in vitro

We investigated the mechanism of phenotypic plasticity of hepatocytes in a three-dimensional organoid culture system, in which hepatocytic spheroids were embedded within a collagen gel matrix. Hepatocytes expressed several bile duct markers including cytokeratin (CK) 19 soon after culture and underwent branching morphogenesis within the matrix in the presence of insulin and epidermal growth factor. Cultured hepatocytes did not express Delta-like, a specific marker for oval cells and hepatoblasts. Furthermore, hepatocytes isolated from c-kit mutant rats (Ws/Ws), which are defective in proliferation of oval cells, showed essentially the same phenotypic changes as those isolated from control rats. The bile duct-like differentiation of hepatocytes was associated with increased expression of Jagged1, Jagged2, Notch1, and several Notch target genes. CK19 expression and branching morphogenesis were inhibited by dexamethasone, a mitogen-activated protein kinase kinase 1 (MEK1) inhibitor (PD98059), and a phosphatidyl inositol 3-kinase inhibitor (LY294002). After being cultured for more than 3 weeks within the gels, hepatocytes transformed into ductular structures surrounded by basement membranes. Our results suggest that hepatocytes might have the potential to transdifferentiate into bile duct-like cells without acquiring a stem-like phenotype and that this is mediated through specific protein tyrosine phosphorylation pathways.

Enrichment of hepatocytes differentiated from mouse embryonic stem cells as a transplantable source

BACKGROUND

We previously reported that hepatocytes can be differentiated from embryonic stem (ES) cells by way of embryoid body (EB) formation and are transplantable into the mouse liver. However, the transplantation of EB-derived cells frequently resulted in teratoma formation in the recipient liver. In the present study, we eliminated the tumorigenic cells from EB outgrowths and examined the effects of enriched ES-cell-derived hepatocyte transplantation into an injured liver.

METHODS

On day 15 in culture, the EBs were partially disaggregated and subcultured. Hepatocytes in the subcultured cells were examined by the expression of hepatocyte markers. Undifferentiated cells contaminating in the EB-derived cells were eliminated by Percoll discontinuous gradient centrifugation. Furthermore, undifferentiated cells, endothelial cells, and macrophages were eliminated by magnetic cell sorting using platelet/endothelial cell adhesion molecule (PECAM)-1 and Mac-1 antibodies. These enriched ES-cell-derived hepatocytes were then transplanted into the injured mouse liver.

RESULTS

Percoll centrifugation and PECAM-1 antibodies eliminated the undifferentiated cells expressing Oct-3/4 from the EB-derived cells. ES-cell-derived hepatocytes showed expression of liver-related genes, synthesis of urea and glycogen, and structural characteristics during subculture. A transplantation study showed that the enriched ES-cell-derived hepatocytes integrated into the injured mouse liver and produced no teratomas. When the ES-cell-derived hepatocytes were transplanted into a CCl4-injured liver, the liver function was subsequently improved.

CONCLUSIONS

Functional hepatocytes can be differentiated from mouse ES cells by way of EB formation. The elimination of undifferentiated cells from the EBs provides transplantable cells for liver failure without tumorigenicity.

Simultaneous segmental obstruction of bile duct and portal vein markedly changes a population of biliary and hepatic cells in human liver

BACKGROUND AND AIMS

No studies have investigated histologic changes caused by simultaneous segmental obstruction of the bile duct and portal vein in human liver.

PATIENTS/METHODS

Liver tissues with simultaneous obstruction of the segmental bile duct and portal vein (O(+/+) liver), with segmental bile duct obstruction alone (O(+/-) liver), and without obstruction (O(-/-) liver) were obtained from patients who underwent hepatectomy, and studied morphologically and immunohistochemically.

RESULTS

In O(+/+) liver, the proportional area consisting of hepatocytes was significantly less (31.0+/-25.8%) than in O(+/-) liver (78.4+/-18.9%) or O(-/-) liver (86.5+/-9.2%). In contrast, the proportional area consisting of biliary epithelial cells was significantly higher in O(+/+) liver (9.1+/-6.1%) than in O(+/-) liver (1.6+/-1.5%) or O(-/-) liver (0.7+/-0.6%). The proportional area consisting of fibrous tissue also was significantly higher in O(+/+) liver than in the other two groups. In O(+/+) liver, some cells located at the periphery of hepatocyte areas were immunoreactive for both hepatocyte and biliary epithelial cell markers.

CONCLUSION

Simultaneous segmental obstruction of the bile duct and portal vein induces a marked ductular increase, periportal fibrosis, and a reduction in the number of hepatocytes in human liver tissue.

Hepatic stem cells: a review

The existence of a liver stem cell population has only gained credence recently, following the results of animal experiments. These cells are thought to reside in the terminal bile ductules (canals of Hering). Hepatocyte division is responsible for liver regeneration after most causes of injury. However, stem cells may contribute to hepatocyte regeneration, or even take over this role if the liver injury is severe and associated with an impairment of hepatocyte proliferation as in cirrhosis or submassive/massive necrosis, due to drugs, toxins or viruses. "Oval" cells are the descendants of the stem cells and are found in the portal and periportal regions in experimental animals within days of the liver injury. These cells proliferate to form narrow ductules, which may stain positively for biliary cytokeratins CK 19, and radiate out into the damaged parenchyma. Both in vitro and in vivo animal studies now suggest that oval cells can differentiate into bile ductular cells or hepatocytes to allow repopulation of the injured liver. As the oval cells differentiate into hepatocytes they may show positive staining for pyruvate kinase isoenzyme L-PK, albumin and alpha-fetoprotein. There is also growing evidence that bone marrow stem cells may contribute to liver regeneration. The possible involvement of hepatic stem cells in the development of dysplastic nodules, hepatocellular carcinoma and cholangiocarcinoma has been suggested but remains highly controversial. Oval cell isolation and culture techniques, together with stem cell transplantation strategies, may in the future provide novel treatments for individuals with inherited and acquired hepatic disorders.

Allogeneic hepatocyte transplantation: Contribution of Fas-Fas ligand interaction to allogeneic hepatocyte rejection

Hepatocyte transplantation is a potential therapeutic modality for overcoming the shortage of liver donors, and the clinical application of allogeneic hepatocyte transplantation has been considered. However, there are two major problems with allogeneic hepatocyte transplantation: protection of transplanted hepatocytes from rejection and stimulation of the rapid proliferation of surviving cells. Without immunosuppression, allogeneic hepatocytes are rapidly rejected within a few days after transplantation, even though it is relatively easy to induce immunotolerance after allogeneic whole liver transplantation. Accordingly, different rejection mechanisms seem to operate after allogeneic hepatocyte transplantation and whole liver transplantation. To overcome the rejection of transplanted hepatocytes, induction of donor-specific unresponsiveness to graft without compromising the host immune system would be ideal. We previously reported that the Fas-Fas ligand system plays a critical role in the CD28-independent pathway of hepatocyte rejection. Therefore, blockade of rejection using CTLA4 immunoglobulin (CTLA4Ig) or anti-CD80/86 monoclonal antibodies and anti-FasL monoclonal antibody may prolong the survival of transplanted allogeneic hepatocytes. Furthermore, administration of hepatocyte growth factor (HGF) can promote the proliferation of allogeneic hepatocytes and this may lead to the development of a functioning liver substitute.

Comparison of liver progenitor cells in human atypical ductular reactions with those seen in experimental models of liver injury

The ultrastructural characteristics of liver progenitor cell types of human atypical ductular reactions seen in chronic cholestasis, in regenerating human liver after submassive necrosis, in alcoholic liver disease, and in focal nodular hyperplasia are compared with liver progenitor cell types seen during experimental cholangiocarcinogenesis in hamsters; during hepatocarcinogenesis in rats; and in response to periportal liver injury induced by allyl alcohol in rats. Three types of progenitor cells have been identified in human atypical ductular reactions: type I: primitive, has an oval shape, marginal chromatin, few cellular organelles, rare tonofilaments, and forms desmosomal junctions with adjacent liver cells; type II: bile duct-like, is located within ducts, has few organelles, and forms lateral membrane interdigitations with other duct-like cells; and type III: hepatocyte-like, is located in hepatic cords, forms a bile canaliculus, has tight junctions with other hepatocyte-like cells, prominent mitochondria and rough endoplasmic reticulum, and some have lysosomes and a poorly developed Golgi apparatus. Each type is seen during cholangiocarcinogenesis in hamsters, but the most prominent cell type is type II, duct-like. A more primitive cell type ("type 0 cell"), as well as type I cells, are seen in the intraportal zone of the liver within 1 to 2 days after carcinogen exposure or periportal injury in the rat, but both type II and type III are seen later as the progenitor cells expand into the liver lobule. After allyl alcohol injury, type 0 cells precede the appearance of type I and type III cells, but most of the cells that span the periportal necrotic zone are type III hepatocyte-like cells showing different degrees of hepatocytic differentiation. Some type II cells are also seen, but these are essentially limited to ducts. It is concluded that there is a primitive stem cell type in the liver (type 0) that may differentiate directly into type I and then into type II, duct-like or or type III hepatocyte-like cells. The terms oval cell, transitional hepatocyte, biliary hepatocyte, hepatocyte-like cell, atypical ductular cell, neocholangiole, etc., are used to describe these cells. Although these terms are useful as general descriptive terms for liver precursor cells at the light microscopic level, the cells included in these descriptive categories may be very different from one another biologically and ultrastructurally.

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

This study aimed at investigating the efficacy of hepatic stimulatory substance (HSS) on the proliferation of transplanted hepatocytes in the spleen of rats with carbon tetrachloride (CCl4)-induced liver cirrhosis. After hepatocyte transplantation (HTx; 1x10(7) cells/rat), the recipients received intravenous administration of HSS (3ml) of 2, 4, or 7 times/week to investigate the effect of the frequency of HSS treatment on the proliferation of intrasplenically transplanted hepatocytes. Next, to investigate the effect of the severity of liver cirrhosis on HSS-stimulated proliferation of transplanted hepatocytes, different doses (0.00, 0.08, 0.12, and 0.16 ml/week) of CCl4 were given to rats after HTx. The recipients were killed and the spleens were removed at 2 and 4 weeks after HTx and stained with bromodeoxyuridine (BrdU) and hematoxylin and eosin for determining the BrdU labeling index (L.I.) and the hepatocyte-occupied area ratio in the longitudinal cut surface of the spleen (H:S ratio), respectively. The H:S ratio was measured in the hematoxylin and eosin-stained splenic sections under a light microscope connected to an image processor. HSS-treated rats showed significantly higher BrdU L.I. and H:S ratios than the untreated control rats at 2 and 4 weeks after HTx. However, the difference in the BrdU L.I. and H:S ratio was not statistically significant among the HSS-treated rats. Without HSS treatment, the severity of liver cirrhosis did not affect the proliferation of intrasplenically transplanted hepatocytes. On the other hand, HSS-induced proliferation of transplanted hepatocytes was further enhanced in proportion to the severity of liver cirrhosis. The H:S ratio of the rats treated with 0.04, 0.08, and 0.16 ml/week of CCl4 after HTx was 1.27+/-0.5%, 4.32+/-0.65%, and 6.25+/-0.70%, respectively, at week 4. During the long-term observation of up to 12 weeks, a marked decrease in the H:S ratio was observed in HSS-untreated control rats at weeks 4-12 compared with week 2. While HSS-treated rats revealed gradual proliferation of intrasplenically transplanted hepatocytes, the difference in the H:S ratio between HSS-treated and -untreated rats became larger. These results indicate that HSS treatment of recipient rats stimulated the proliferation of intrasplenically transplanted hepatocytes in cirrhotic rats and that the severity of liver cirrhosis enhanced the stimulative effect of HSS on the proliferation of transplanted hepatocytes.

Membrane antigen expression of syngeneically but heterotopically transplanted hepatocytes in rats

The expression of membrane antigens on rat hepatocytes transplanted syngeneically and heterotopically was analyzed immunohistochemically using monoclonal antibodies against rat hepatocytes. Isolated adult and fetal hepatocytes were able to survive in the spleen, salivary gland, thymus, or subcapsular region of the kidney for various periods after transplantation. Fairly clear expression of HAM2, 4, and 8 antigens was observed on hepatocytes transplanted into syngeneic spleen, suggesting that the cells might be functionally equivalent to hepatocytes in situ. HAM4 antigen was localized specifically on the newly formed bile-canalicular faces of hepatocytes. The expression of HAM2 (MHC class I) antigen on the transplanted hepatocytes appeared much stronger on the side facing lymphoid tissues, than on the other faces, suggesting that some immunological reactions may take place between hepatocytes and lymphoid tissue. HAM8 antigen, which is localized on gap junctions between neighboring hepatocytes in rat liver, was also recognized between transplanted hepatocytes. In salivary glands where hepatocytes were transplanted, bile-canaliculus-like structures were observed not only between neighboring hepatocytes but also between hepatocytes and salivary acinar cells, suggesting good interaction between the two different epithelial cell types. Hepatocytes transplanted into thymus appeared viable, but most showed fatty degeneration. Some healthy hepatocytes survived in the interlobular connective tissue and the thymic cortical tissue. When fetal hepatocytes were transplanted heterotopically, they formed a mass consisting of hepatocytes and bile duct-like structures 7 wk after transplantation. The inoculated hepatocytes possessed HAM4 antigen, which was not recognized on fetal hepatocytes at day 14 of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)

The stem cells of the liver ? a selective review

The current status of the much-debated question of the still-hypothetical stem cells of the liver is reviewed, with an emphasis on their role in hepatocarcinogenesis. The widely held view of the primacy of the hepatocyte, notably of the mononuclear diploid type, in this process--the "hepatocytic theory"--has been compared with variants of the "stem cell hypothesis" based on the "non-parenchymal epithelial cells" of the liver--the "oval" or biliary ductular cells, the "nondescript periductular" cells and the "primitive" bipotential epithelial cells. An attempt has been made to concentrate mainly on the more recent publications, in an effort to balance the conflicting opinions expressed by comparing results obtained by the newer procedures currently in use. Despite some interesting and relevant findings it appears that the evidence in favour of the stem-cell hypothesis is still circumstantial and that the hepatocytic theory has not been invalidated. Presumably the question of the hepatic stem cells will be answered when the riddle of hepatocarcinogenesis has been solved.

Mouse hepatocytes migrate to liver parenchyma and function indefinitely after intrasplenic transplantation

One approach to gene therapy for hepatic diseases is to remove hepatocytes from an affected individual, genetically alter them in vitro, and reimplant them into a receptive locus. Although returning hepatocytes to the liver itself would be advantageous, the feasibility of this approach has never been evaluated due to the inability to distinguish donor from host hepatocytes. To unambiguously identify transplanted hepatocytes after transplantation, and to better quantitate their number and degree of liver function, two transgenic mouse lines were generated in a C57BL/6 background. The first expresses the Escherichia coli beta-galactosidase gene from the relatively liver-specific human alpha 1-antitrypsin (hAAT) promoter and allows transgenic hepatocytes to be readily identified after 5-bromo-4-chloro-3-indolyl beta-D-galactoside staining; the second produces the hAAT protein under control of the same promoter, which enables hepatocyte survival and maintenance of liver function to be quantitated by measuring the serum levels of hAAT. Hepatocytes isolated from transgenic donors were transplanted into nontransgenic C57BL/6 recipients by intrasplenic injection. Surprisingly, a large fraction of these cells were identified within the liver parenchyma but not the spleen at 2 months after transplantation. The high levels of serum hAAT detected in transplant recipients were stable for greater than 6 months, suggesting that established cells will survive indefinitely. These results have important implications for liver organogenesis and hepatic gene therapy.