Evidence that temporary complete occlusion of splenic vessels prevents massive embolization and sudden death associated with intrasplenic hepatocellular transplantation

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.

Exploiting the unique regenerative capacity of the liver to underpin cell and gene therapy strategies for genetic and acquired liver disease

The number of genetic or acquired diseases of the liver treatable by organ transplantation is ever-increasing as transplantation techniques improve placing additional demands on an already limited organ supply. While cell and gene therapies are distinctly different modalities, they offer a synergistic alternative to organ transplant due to distinct architectural and physiological properties of the liver. The hepatic blood supply and fenestrated endothelial system affords relatively facile accessibility for cell and/or gene delivery. More importantly, however, the remarkable capacity of hepatocytes to proliferate and repopulate the liver creates opportunities for new treatments based on emerging technologies. This review will summarise current understanding of liver regeneration, describe clinical and experimental cell and gene therapeutic modalities and discuss critical challenges to translate these new technologies to wider clinical utility. This article is part of a Directed Issue entitled: "Regenerative Medicine: the challenge of translation".

Development of hepatic tissue engineering

Liver transplantation is still the only treatment for end-staged liver diseases in children. However, donor organ shortage and immunosuppression are major limitations. Thus, approaches of hepatocyte transplantation are under investigation. Using cells might permit mass expansion, cryopreservation, and the ex vivo genetic modification of cells. For the development of cell-transplantation techniques, the use of three-dimensional scaffolds as carrier was shown to be advantageous. Polymeric matrices permit the formation of a neo-tissue and stimulation by the modification of the matrix surface. Another important issue is to define the right cell type for transplantation. Adult hepatocytes have a limited growth and differentiation potential. In contrast, fetal liver cells (FLC) possess an enormous growth and a bipotential differentiation potential. Thus, these cells may be very attractive as a cell resource for developing cell-based liver replacement. A third major issue in this approach is the neo-vascularization. Therefore, the transplantation in a recently developed model using a microsurgically created arterioveno-venous (AV) loop as a central vessel for the neo-tissue was used for transplantation of FLC in a fibrin-matrix. Initial results indicated that the transplantation of FLC using the AV-loop transplantation model may be promising for the development of highly vascularized in vivo tissue-engineered liver support systems.

Therapeutic potential of adult bone marrow stem cells in liver disease and delivery approaches

Hematopoietic stem cells (HSCs) and mesenchymal stem cell (MSCs) are two main subtypes of bone marrow stem cells. Extensive studies have been carried out to investigate the therapeutic potential of BMSCs in liver disease. A number of animal and human studies demonstrated that either HSCs or MSCs could be applied to therapeutic purposes in certain liver diseases. The diseased liver may recruit migratory stem cells, particularly from the bone marrow, to generate hepatocyte-like cells either by transdifferentiation or cell fusion. Transplantation of BMSCs has therapeutic effects of restoration of liver mass and function, alleviation of fibrosis and correction of inherited liver diseases. There are still controversial results over the potential effects of BMSCs on liver diseases, and some of the discrepancies are thought to be lied in the differences of experimental protocols, differences in individual research laboratory, and the uncertainties of the techniques employed. Several potential approaches for BMSCs delivery in liver diseases have been proposed in animal studies and human trials. BMSCs can be delivered via intraportal vein, systemic infusion, intraperitoneal, intrahepatic, intrasplenic. The optimal stem cells delivery should be easy to perform, less invasive and traumatic, minimum side effects, and with high cells survival rate. In this review, we focus on the up-to-date evidence of therapeutic effects of BMSCs on liver disease, the characteristics of various delivery approaches, and the considerations for future studies.

Hepatic tissue engineering: from transplantation to customized cell-based liver directed therapies from the laboratory

Today, liver transplantation is still the only curative treatment for liver failure due to end-stages liver diseases. Donor organ shortage, high cost and the need of immunosuppressive medications are still the major limitations in the field of liver transplantation. Thus, alternative innovative cell-based liver directed therapies, e.g. liver tissue engineering, are under investigation with the aim, that in future an artificial liver tissue could be created and be used for the replacement of the liver function in patients. Using cells instead of organs in this setting should permit (i) expansion of cells in an in vitro phase, (ii) genetic or immunological manipulation of cells for transplantation, (iii) tissue typing and cryopreservation in a cell bank, and (iv) the ex vivo genetic modification of patient's own cells prior re-implantation. Function and differentiation of liver cells are influenced by the three-dimensional organ architecture. The use of polymeric matrices permits the three dimensional formation of a neo-tissue and specific stimulation by adequate modification of the matrix-surface which might be essential for appropriate differentiation of transplanted cells. Additionally, culturing hepatocytes on three dimensional matrices permits culture in a flow bioreactor system with increased function and survival of the cultured cells. Based on bioreactor technology, bioartificial liver devices (BAL) are developed for extracorporeal liver support. Although BALs improved clinical and metabolic conditions, increased patient survival rates have not been proven yet. For intra-corporeal liver replacement, a concept which combines Tissue Engineering using three-dimensional, highly porous matrices with cell transplantation could be useful. In such a concept, whole liver mass transplantation, long term engraftment and function as well as correction of a metabolic defect in animal models could be achieved with a principally reversible procedure. Future studies have to investigate, which environmental conditions and transplantation system would be most suitable for the development of artificial functional liver tissue including blood supply for a potential use in a clinical setting.

Hepatic tissue engineering: from transplantation to customized cell-based liver directed therapies from the laboratory

Today, liver transplantation is still the only curative treatment for liver failure due to end-stages liver diseases. Donor organ shortage, high cost and the need of immunosuppressive medications are still the major limitations in the field of liver transplantation. Thus, alternative innovative cell-based liver directed therapies, e.g. liver tissue engineering, are under investigation with the aim, that in future an artificial liver tissue could be created and be used for the replacement of the liver function in patients. Using cells instead of organs in this setting should permit (i) expansion of cells in an in vitro phase, (ii) genetic or immunological manipulation of cells for transplantation, (iii) tissue typing and cryopreservation in a cell bank, and (iv) the ex vivo genetic modification of patient's own cells prior re-implantation. Function and differentiation of liver cells are influenced by the three-dimensional organ architecture. The use of polymeric matrices permits the three dimensional formation of a neo-tissue and specific stimulation by adequate modification of the matrix-surface which might be essential for appropriate differentiation of transplanted cells. Additionally, culturing hepatocytes on three dimensional matrices permits culture in a flow bioreactor system with increased function and survival of the cultured cells. Based on bioreactor technology, bioartificial liver devices (BAL) are developed for extracorporeal liver support. Although BALs improved clinical and metabolic conditions, increased patient survival rates have not been proven yet. For intra-corporeal liver replacement, a concept which combines Tissue Engineering using three-dimensional, highly porous matrices with cell transplantation could be useful. In such a concept, whole liver mass transplantation, long term engraftment and function as well as correction of a metabolic defect in animal models could be achieved with a principally reversible procedure. Future studies have to investigate, which environmental conditions and transplantation system would be most suitable for the development of artificial functional liver tissue including blood supply for a potential use in a clinical setting.

Growth and Metabolism of Human Hepatocytes on Biomodified Collagen Poly(lactic-co-glycolic acid) Three-Dimensional Scaffold

Hepatic tissue engineering offers a promising approach toward alleviating the need for donor liver, yet many challenges must be overcome including choice of scaffold, cell source, and immunologic barriers. Poly(lactic-co-glycolic acid) (PLGA) polymers are innovative biodegradable materials that have been shown to be useful as scaffolds for seeding and culturing various types of cells. In this study, a porous sponge scaffold of modified PLGA polymer with collagen was investigated for its ability to improve the growth and metabolism of human hepatocytes. We evaluated the biocompatibility of collagen-modified PLGA (C-PLGA) scaffolds with hepatocytes isolated from human liver. Cell adhesion and function (cell density, culture lifespan, albumin synthesis, urea synthesis, and ammonia elimination and diazepam clearance) were assessed during different culture periods. The number of hepatocytes cultured in C-PLGA scaffolds was higher compared with those cultured in PLGA scaffolds without collagen modification, and the lifespan of hepatocytes cultured in C-PLGA scaffolds was longer than that of cells cultured in PLGA scaffolds. Albumin and urea synthesis and ammonia elimination from attached hepatocytes were greater in C-PLGA than in PLGA scaffolds, with the exception of diazepam clearance. Collagen-modified PLGA scaffold is a promising biomaterial for hepatic tissue engineering.

Injectable Liver: A Novel Approach Using Fibrin Gel as a Matrix for Culture and Intrahepatic Transplantation of Hepatocytes

Cell transplantation and tissue engineering with liver cells are currently under investigation as experimental therapies for certain liver diseases. In this study we evaluated a fibrin-based gel matrix as carrier for hepatocytes in culture. Furthermore, a novel technique for direct intrahepatic injection of fibrin gel-immobilized hepatocytes was developed and evaluated in a rat model. Hepatocytes were harvested from rats. Fibrin matrix was generated with modified fibrin sealant. Cells, in medium containing epidermal growth factor and insulin, were seeded in a drop of fibrin matrix onto plastic culture dishes. Cell numbers were assessed by DNA content. Hepatocyte differentiation was evaluated by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistology (IH) for cytokeratin (CK)-18 and albumin. PKH26-labeled fibrin gel-immobilized hepatocytes were transplanted into liver by direct injection underneath the capsule. Fluorescence microscopy of explanted liver was performed to identify PKH26+ donor cells. Neotissue was characterized by IH for the markers CK-18, ED1, and desmin. Culture in a fibrin matrix allowed stable cell numbers and three-dimensional neotissue formation. RT-PCR and IH showed preservation of liver-specific markers CK-18 and albumin in vitro. Transplanted cells were identified by fluorescence microscopy after 2 and 7 days. CK-18 and desmin staining showed integration of hepatocytes and hepatic stellate cells into the host liver. Fibrin matrix is an appropriate environment for hepatocytes in culture. Direct intrahepatic injection of fibrin gel-immobilized hepatocytes is technically feasible. We conclude that fibrin gel immobilization is an attractive tool for the development of tissue engineering-based liver support systems.

Multiple intrasplenic hepatocyte transplantations in the dalmatian dog

BACKGROUND

Hepatocyte transplantation is an attractive potential treatment for liver-based inborn errors of metabolism and for fulminant hepatic failure. Dalmatian dogs have a metabolic error that results in hyperuricosuria. This report focuses on the effect of multiple, sequential intrasplenic transplants of fresh and cryopreserved hepatocytes in dalmatians.

METHODS

Dalmatians underwent intrasplenic hepatocyte transplantation with hepatocytes taken from healthy mongrels. Dalmatian urinary uric acid excretion was measured preoperatively, and this served as the control value. Three hepatocyte transplantations were performed at 30-day intervals--the first with freshly isolated cells, and both the second and the third with cryopreserved hepatocytes from the same donor. Urinary uric acid excretion was measured postoperatively twice per week.

RESULTS

The urinary uric acid excretion decreased an average of 54% after the first hepatocyte transplantation. The effect was transient and lasted an average of 22 days (range, 19-50 days). Subsequent intrasplenic hepatocyte transplantation with cryopreserved hepatocytes resulted in similar decreases in urinary uric acid excretion. Each transplant resulted in a significant decrease in urinary uric acid excretion when compared with baseline values (P = < .001).

CONCLUSIONS

Sequential intrasplenic hepatocyte transplantation is feasible in this model. This method provided a significant, but transient, correction in urinary uric acid excretion that was similar with either fresh or cryopreserved hepatocytes. A substantial biologic effect provided by cryopreserved hepatocytes has important implications in clinical hepatocyte transplantation.

The risks of total pancreatectomy and splenic islet autotransplantation

The intraportal site is the most common site for islet transplantation. Many other sites have been tried experimentally, including the spleen, which has successfully lead to insulin independence in a number of animal models. Nevertheless, there are no detailed reports of total pancreatectomy and splenic islet autotransplantation in humans. Five patients underwent total pancreatectomy and splenic islet autotransplantation for chronic pancreatitis. Four patients had a pylorus-preserving total pancreatectomy and one patient a duodenal-preserving pancreatectomy. In three cases islets were embolized into both the portal vein and spleen. Two patients received splenic islet transplants alone. Islets were transplanted by retrograde venous infusion via the short gastric veins (n = 3), splenic vein stump (n = 1), and the left gastroepiploic vein (n = 1). The total volumes of transplanted pancreatic digest in those receiving combined intraportal and splenic autografts (n = 3) were 15.8, 13.0, and 13.5 ml. The volumes in those receiving a splenic-alone autograft (n = 2) were 12.0 and 5 ml. The mean rise in portal pressure was 18 cm of water. Complications related to the splenic autograft included a wedge splenic infarct, an emergency splenectomy, and a portal vein thrombosis in one patient having a combined intraportal and splenic autograft. Two patients developed insulin independence. two patients were still insulin independent at 1-year follow-up, and all had normal HbA1c levels (mean 5.6, range 5.2-6.3). Splenic islet autotransplantation, after total pancreatectomy, does lead to insulin independence. However, in our experience the combined procedure has a high morbidity because of splenic infarction and venous thrombosis.

Long-term differentiated function of heterotopically transplanted hepatocytes on three-dimensional polymer matrices

Hepatocyte transplantation using porous matrices is under investigation as an alternative therapy for certain liver diseases. For this purpose, long-term function of transplanted hepatocytes is mandatory. This problem has not been sufficiently investigated yet. In this study Lewis rats were used as donors and recipients. Stimulated (group A, portocaval shunt) or unstimulated (group B) hepatocytes were transplanted into prevascularized polyvinyl-alcohol matrices. Cell-free matrices served as controls (group C). Matrices were harvested between 1 h and 1 year after implantation and analyzed by morphometry; albumin RNA in situ hybridization; and cytokeratin-, actin-, desmin-, and macrophage-specific antigen immunohistology. The hepatocyte number significantly decreased within the first week following implantation. Between 1 month and 1 year after transplantation a significant increase in hepatocyte number was noted in groups A and B. Albumin transcripts of transplanted hepatocytes were at normal levels at all times except for group B after 1 year. The immunohistology suggested engraftment of nonparenchymal liver cells. We conclude that 3-dimensional matrices provide a sufficient environment for long-term engraftment of transplanted liver cells. The hepatocytes are able, despite suboptimal initial engraftment, to repopulate the scaffold for at least half of the recipient's life span and maintain cell-specific function after sufficient stimulation.

The subcutaneous spleen: a new model for percutaneous access to the portal venous system

Correction of hepatic failure or metabolic disease by hepatocellular transplantation may require replacement of up to 10% of enzyme function with normal or genetically corrected cells. Although single injections of hepatocytes have not been able to consistently achieve this level of functional replacement in experimental models, multiple injections should theoretically be able to approach this goal. Delivery of multiple doses of hepatocytes to the spleen in experimental animals is complicated by the need to perform multiple laparotomies. By relocating the spleen to a subcutaneous position, the authors have designed an animal model to facilitate multiple splenic injections without the need for repeated celiotomies. Because it is in the prefascial plane, multiple hepatocyte injections can be delivered to the spleen percutaneously using only minimal sedation. Bleeding secondary to needle puncture is contained by a pseudocapsule which develops around the spleen. No statistical difference in the degree of hepatocyte migration to the liver has been demonstrated in animals transplanted via the subcutaneous spleen compared with animals transplanted by laparotomy (0.51% vs. 0.56%, p = .785).

Pharmacokinetic parameters of antipyrine in dog after hepatectomy

Pharmacokinetic studies with antipyrine were carried out on beagle dogs to determine the consequence of hepatectomy on hepatic drug metabolizing capacity, the rate of hepatic regeneration, and the possible beneficial effect of hepatocellular transplantation. The drug (250 mg) was administered by short IV infusion in three groups of dogs (first group, 65% hepatectomy; second group, 65% hepatectomy with hepatocyte transplantation; third group 80% hepatectomy). Pharmacokinetic parameters of antipyrine were evaluated before surgery and within 10 d after surgery. Blood samples were taken at frequent intervals after drug administration and antipyrine was assayed in plasma by a specific HPLC method with UV detection. Before surgery, the mean elimination half-life was about 1.1 h and total clearance averaged 6 L h-1. In dogs with 65% hepatectomy, no statistical differences in pharmacokinetic parameters of antipyrine appeared before or after surgery. When 65% hepatectomy was associated with hepatocyte transplantation, a significant increase in elimination half-life and a significant decrease in total clearance were observed. The same statistical differences in the pharmacokinetic parameters were observed in the group with 80% hepatectomy. Transplantation of isolated hepatocytes into the spleen did not correct hepatocellular insufficiency. In this study, numerous laboratory tests were performed. A significant correlation was found between serum albumin, cholesterol, factor V, ALAT, total bilirubin, and ratio of amino acids and the pharmacokinetic parameters of antipyrine.

111Indium labeling of hepatocytes for analysis of short-term biodistribution of transplanted cells

Hepatocyte transplantation is useful for ex vivo gene therapy and liver repopulation. Methods for hepatic reconstitution have recently been developed but optimization of hepatocyte transplantation systems is necessary. To develop systems for noninvasive assessment of the biodistribution of transplanted cells, we labeled hepatocytes with 111indium-oxine. Our initial studies showed that hepatocytes incorporated 111indium-oxine with an efficiency of approximately 20%. After labeling, cell viability was unchanged and 111indium was present in hepatocytes after overnight culture, as well as after intrasplenic transplantation. Transplanted cells were successfully localized by means of scintigraphic imaging. The scintigraphic patterns of cell distribution were different when hepatocytes were transplanted by means of either spleen or internal jugular vein, which deposit cells into separate vascular beds. Quantitative analysis of the biodistribution of 111indium-labeled hepatocytes indicated that within 2 hr of intrasplenic transplantation, cells were predominantly localized in liver and spleen, and occasionally in lungs. To determine whether the rate of intrasplenic cell injection influenced translocation of hepatocytes, we transplanted cells in normal rats. Despite intrasplenic cell injection at a variety of rates, organ-specific distribution of 111indium-labeled hepatocytes remained unchanged. Labeling with 111indium did not affect long-term survival of transplanted hepatocytes. These results indicate that 111indium-labeling of hepatocytes should greatly assist noninvasive analysis in the short-term of the biodistribution of transplanted hepatocytes.