Self-assembling peptide nanofiber as a novel culture system for isolated porcine hepatocytes

Three-dimensional hydrogel culture conditions promote the differentiation of human induced pluripotent stem cells into hepatocytes

BACKGROUND AIMS

Human induced pluripotent stem cells (hiPSCs) are becoming increasingly popular in research endeavors due to their potential for clinical application; however, such application is challenging due to limitations such as inferior function and low induction efficiency. In this study, we aimed to establish a three-dimensional (3D) culture condition to mimic the environment in which hepatogenesis occurs in vivo to enhance the differentiation of hiPSCs for large-scale culture and high throughput BAL application.

METHODS

We used hydrogel to create hepatocyte-like cell (HLC) spheroids in a 3D culture condition and analyzed the cell-behavior and differentiation properties of hiPSCs in a synthetic nanofiber scaffold.

RESULTS

We found that treating cells with Y-27632 promoted the formation of spheroids, and the cells aggregated more rapidly in a 3D culture condition. The ALB secretion, urea production and glycogen synthesis by HLCs in 3D were significantly higher than those grown in a 2-dimensional culture condition. In addition, the metabolic activities of the CYP450 enzymes were also higher in cells differentiated in the 3D culture condition.

CONCLUSIONS

3D hydrogel culture condition can promote differentiation of hiPSCs into hepatocytes. The 3D culture approach could be applied to the differentiation of hiPSCs into hepatocytes for bioartificial liver.

Biomaterials and Culture Technologies for Regenerative Therapy of Liver Tissue

Regenerative approach has emerged to substitute the current extracorporeal technologies for the treatment of diseased and damaged liver tissue. This is based on the use of biomaterials that modulate the responses of hepatic cells through the unique matrix properties tuned to recapitulate regenerative functions. Cells in liver preserve their phenotype or differentiate through the interactions with extracellular matrix molecules. Therefore, the intrinsic properties of the engineered biomaterials, such as stiffness and surface topography, need to be tailored to induce appropriate cellular functions. The matrix physical stimuli can be combined with biochemical cues, such as immobilized functional groups or the delivered actions of signaling molecules. Furthermore, the external modulation of cells, through cocultures with nonparenchymal cells (e.g., endothelial cells) that can signal bioactive molecules, is another promising avenue to regenerate liver tissue. This review disseminates the recent approaches of regenerating liver tissue, with a focus on the development of biomaterials and the related culture technologies.

Optimization of Three Dimensional Culturing of the HepG2 Cell Line in Fibrin Scaffold

BACKGROUND

A potential treatment for healing hepatic tissue is delivering isolated hepatic cells to the site of injury to promote hepatic cells formation. In this technology, providing an appropriate injectable system for delivery of hepatic cells is an important issue. In this regard, fibrin scaffolds were designed with many advantages over other scaffolds like cell delivery vehicles for biodegradation, biocompatibility and hemostasis.

OBJECTIVES

The aim of this study was to determine suitable cell culture circumstances for HepG2 cell proliferation and differentiation in 3D fibrin scaffolds by evaluating Ca(2+) concentrations, cell numbers, various ratios of plasma/RPMI 1640 and thickness of fibrin scaffold.

MATERIALS AND METHODS

In a one-stage experimental design, Box-Behnken design strategy was performed by Minitab 15 software (version 15, Minitab. State College, PA) with three factors at three levels (low, medium and high) and 27 runs for identification of the effects of ratio of plasma/RPMI 1640, Ca(2+) concentration and thickness on the formation of fibrin gel scaffold and 3D HepG2 culture.

RESULTS

The optimal concentrations for fibrin scaffold fabrication were achieved by adding 0.15 mol CaCl2 (50 µL) and 1 × 10(5) cells to 1:4 of plasma/RPMI 1640 ratio (500 µL with 2.3 mm thickness per well).

CONCLUSIONS

Our approach provided easy handle method using inexpensive materials like human plasma instead of purified fibrinogen to fabricate fibrin scaffold.

Cells and materials for liver tissue engineering

Liver transplantation is currently the most efficacious treatment for end-stage liver diseases. However, one main problem with liver transplantation is the limited number of donor organs that are available. Therefore, liver tissue engineering based on cell transplantation that combines materials to mimic the liver is under investigation with the goal of restoring normal liver functions. Tissue engineering aims to mimic the interactions among cells with a scaffold. Particular materials or a matrix serve as a scaffold and provide a three-dimensional environment for cell proliferation and interaction. Moreover, the scaffold plays a role in regulating cell maturation and function via these interactions. In cultures of hepatic lineage cells, regulation of cell proliferation and specific function using biocompatible synthetic, biodegradable bioderived matrices, protein-coated materials, surface-modified nanofibers, and decellularized biomatrix has been demonstrated. Furthermore, beneficial effects of addition of growth factor cocktails to a flow bioreactor or coculture system on cell viability and function have been observed. In addition, a system for growing stem cells, liver progenitor cells, and primary hepatocytes for transplantation into animal models was developed, which produces hepatic lineage cells that are functional and that show long-term proliferation following transplantation. The major limitation of cells proliferated with matrix-based transplantation systems is the high initial cell loss and dysfunction, which may be due to the absence of blood flow and the changes in nutrients. Thus, the development of vascular-like scaffold structures, the formation of functional bile ducts, and the maintenance of complex metabolic functions remain as major problems in hepatic tissue engineering and will need to be addressed to enable further advances toward clinical applications.

Novel infectious agent-free hemostatic material (TDM-621) in cardiovascular surgery

SUBJECTS

Currently, hemostatic materials made from human blood components and animal-derived collagen is used for controlling operative hemorrhage in the cardiovascular surgery field. In this study, we focused on an entirely synthetic self-assembling peptide (development code: TDM-621) that gels when in contact with blood or other bodily fluids and stops bleeding upon contact with a wound site. We investigated its usefulness as a hemostatic material in animal and clinical studies.

METHODS

Before we began the clinical study, we demonstrated the hemostasis efficacy and safety of TDM-621 in animal experimental models. Twenty-five patients (22 men, 3 women) were enrolled in the clinical study, and the following procedures were performed: 1) coronary artery bypass graft (CABG) (n = 9), 2) abdominal aortic graft replacement (n = 4), and 3) peripheral artery bypass (n = 12). The TDM-621 material was applied to a total of 33 vascular anastomotic graft sites (some patients received material at more than one site). Both hemostatic efficacy and safety were examined.

RESULTS

A total of 33 anastomotic graft sites in 25 patients were evaluated, and the averaged primary and secondary efficacy rate was 94.5%. No postoperative bleeding or adverse events (including serious adverse events) with a causal relationship to treatment were observed.

CONCLUSION

This study indicated that TDM-621 is a more effective and reliable hemostat than commonly-used general hemostatic agents and, therefore, will be very useful in several cardiovascular surgery applications.

Regenerative Cells for Transplantation in Hepatic Failure

Human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells have an enormous potential; however, their potential clinical application is being arrested due to various limitations such as teratoma formation followed by tumorigenesis, emergent usage, and the quality control of cells, as well as safety issues regarding long-term culture are also delaying their clinical application. In addition, human ES cells have two crucial issues: immunogenicity and ethical issues associated with their clinical application. The efficient generation of human iPS cells requires gene transfer, yet the mechanism underlying pluripotent stem cell induction has not yet been fully elucidated. Otherwise, although human adult regenerative cells including mesenchymal stem cells have a limited capacity for differentiation, they are nevertheless promising candidates for tissue regeneration in a clinical setting. This review highlights the use of regenerative cells for transplantation in hepatic failure.

Transplant of Primary Human Hepatocytes Cocultured With Bone Marrow Stromal Cells to SCID Alb-uPA Mice

Hepatocytes are vulnerable to loss of function and viability in culture. Modified culture methods have been applied to maintain their functional status. Heterotypic interactions between hepatocytes and nonparenchymal neighbors in liver milieu are thought to modulate cell differentiation. Cocultivation of hepatocyte with various cell types has been applied to mimic the hepatic environment. Bone marrow stromal cells (BMSC) are plastic cell lines capable of transforming to other cell types. In this study hepatocyte coculture with BMSCs achieved long-term function of human hepatocytes in culture for 4 weeks. In vitro functional status of human hepatocytes in BMSC coculture was compared with fibroblast coculture and collagen culture by measuring albumin, human-α-1-antitrypsin (hAAT), urea secretion, CYP450 activity, and staining for intracellular albumin and glycogen. After 2 weeks in culture hepatocytes were retrieved and transplanted to severe combined immunodeficiency/albumin linked-urokinase type plasminogen activator (SCID Alb-uPA) mice and engraft-ment capacity was analyzed by human hepatic-specific function measured by hAAT levels in mouse serum, and Alu staining of mouse liver for human hepatocytes. Hepatocytes from BMSC coculture had significantly higher albumin, hAAT secretion, urea production, and cytochrome P450 (CYP450) activity than other culture groups. Staining confirmed the higher functional status in BMSC coculture. Transplantation of hepatocytes detached from BMSC cocultures showed significantly higher engraftment function than hepatocytes from other culture groups measured by hAAT levels in mouse serum. In conclusion, BMSC coculture has excellent potential for hepatocyte function preservation in vitro and in vivo after transplant. It is possible to use BMSC hepatocyte coculture as a supply of cell therapy in liver disease.

Polymer nanofibrous structures: Fabrication, biofunctionalization, and cell interactions

Extracellular matrix fibers (ECM) such as collagen, elastin, and keratin provide biological and physical support for cell attachment, proliferation, migration, differentiation and ultimately cell fate. Therefore, ECM fibers are an important component in tissue and organ development and regeneration. Meanwhile, polymer nanofibers could play the same critical role in tissue regeneration process. Fibrous structures can be fabricated from a variety of materials and methods with diameters ranging throughout the size scale where cells can sense individual fibers (several nanometers to several microns). Polymer nanofiber scaffolds can be designed in a way that predictably modulates a variety of important cell behaviors towards a desired overall function. The nanofibrous topography itself, independent of the fiber material, has demonstrated the potential to modulate cell behaviors desirable in tissue engineering such as: unidirectional alignment; increased viability, attachment, and ECM production; guided migration; and controlled differentiation. The versatility of polymer nanofibers for functionalization with biomolecules opens the door to vast opportunities for the design of tissue engineering scaffolds with even greater control over cell incorporation and function. Despite the promise of polymer nanofibers as tissue engineering scaffolds there have been few clinically relevant successes because no single fabrication technique currently combines control over structural arrangement, material composition, and biofunctionalization, while maintaining reasonable cost and yield. Promising strategies are currently being investigated to allow for the fabrication of optimal polymer nanofiber tissue engineering scaffolds with the goal of treating damaged and degenerated tissues in a clinical setting.

Treatment of acute liver failure in mice by hepatocyte xenotransplantation

Liver diseases still have a high mortality even though liver transplantation has become a standard treatment. Currently, hepatocyte transplantation has been proposed as another promising strategy. One limitation is the availability of human livers as a source of hepatocytes. Because of an unlimited supply, the use of porcine hepatocytes might address this problem. Regardless of the source, once isolated hepatocytes lose specific functionality due to the loss of the natural microenvironment. For this reason, we tested the ability of a self-assembling peptide nanofiber (SAPNF) to provide a provisional three-dimensional (3D) support to interact with cells to control their function in vivo. Isolated porcine hepatocytes were embedded in SAPNF, or collagen type I and transplanted by direct injection into the splenic pulp of SCID mice suffering from acute liver failure (ALF) by 90% hepatectomy. SAPNF porcine hepatocyte transplantation produced engraftment that was far superior to that obtained using collagen and prolonged the survival of mice with ALF, in contrast with controls. An ultrastructural evaluation using transmission electron microscopy indicated extensive cell-cell communication and preservation of hepatocyte architecture. The transplanted SAPNF hepatocytes showed higher expression of albumin and PAS and lower apoptotic events assessed by TUNEL staining. Hepatocytes culture in a truly 3D network allows in vivo maintaining of differentiated functions, and once transplanted between widely divergent species can function to correct acute liver failure in mice and prolong their survival.

Cell delivery: from cell transplantation to organ engineering

Cell populations derived from adult tissue and stem cells possess a great expectation for the treatment of several diseases. Great efforts have been made to generate cells with therapeutic impact from stem cells. However, it is clear that the development of systems to deliver such cells to induce efficient engraftment, growth, and function is a real necessity. Biologic and artificial scaffolds have received significant attention for their potential therapeutic application when use to form tissues in vitro and facilitate engraftment in vivo. Ultimately more sophisticated methods for decellularization of organs have been successfully used in tissue engineering and regenerative medicine applications. These decellularized tissues and organs appear to provide bioactive molecules and bioinductive properties to induce homing, differentiation, and proliferation of cells. The combination of decellularized organs and stem cells may dramatically improve the survival, engraftment, and fate control of transplanted stem cells and their ultimate clinical utility, opening the doors to a new era of organ engineering.

Intramuscular transplantation of engineered hepatic tissue constructs corrects acute and chronic liver failure in mice

BACKGROUND & AIMS

Transplantation of isolated hepatocytes holds great promise as an alternative to whole organ liver transplantation. For treatment of liver failure, access to the portal circulation has significant risks and intrahepatic hepatocyte engraftment is poor. In advanced cirrhosis, transplantation into an extrahepatic site is necessary and intrasplenic engraftment is short-lived. Strategies that allow repeated extrahepatic infusion of hepatocytes could improve the efficacy and safety of hepatocyte transplantation for the treatment of liver failure.

METHODS

A non-immunogenic self-assembling peptide nanofiber (SAPNF) was developed as a three-dimensional scaffold and combined with growth factors derived from a conditionally immortalized human hepatocyte cell line to engineer a hepatic tissue graft that would allow hepatocyte engraftment outside the liver.

RESULTS

The hepatic tissue constructs maintained hepatocyte-specific gene expression and functionality in vitro. When transplanted into skeletal muscle as an extrahepatic site for engraftment, the engineered hepatic grafts provided life-saving support in models of acute, fulminant, and chronic liver failure that recapitulates these clinical diseases.

CONCLUSIONS

SAPNF-engineered hepatic constructs engrafted and functioned as hepatic tissues within the muscle to provide life-sustaining liver support. These engineered tissue constructs contained no animal products that would limit their development as a therapeutic approach.

Hepatic stem cells and liver development

The liver consists of many cell types with specialized functions. Hepatocytes are one of the main players in the organ and therefore are the most vulnerable cells to damage. Since they are not everlasting cells, they need to be replenished throughout life. Although the capacity of hepatocytes to contribute to their own maintenance has long been recognized, recent studies have indicated the presence of both intrahepatic and extrahepatic stem/progenitor cell populations that serve to maintain the normal organ and to regenerate damaged parenchyma in response to a variety of insults.The intrahepatic compartment most likely derives primarily from the biliary tree, particularly the most proximal branches, i.e. the canals of Hering and smallest ductules. The extrahepatic compartment is at least in part derived from diverse populations of cells from the bone marrow. Embryonic stem cells (ES's) are considered as a part of the extrahepatic compartment. Due to their pluripotent capabilities, ES cell-derived cells form a potential future source of hepatocytes, to replace or restore hepatic tissues that have been damaged by disease or injury. Progressing knowledge about stem cells in the liver would allow a better understanding of the mechanisms of hepatic homeostasis and regeneration. Although a human stem cell-derived cell type equivalent to primary hepatocytes does not yet exist, the promising results obtained with extrahepatic stem cells would open the way to cell-based therapy for liver diseases.

The 3-D Culture andIn VivoGrowth of the Human Hepatocellular Carcinoma Cell Line HepG2 in a Self-Assembling Peptide Nanofiber Scaffold

We report the use of the RADA16-I scaffold to mimic the ECM microenvironment and support tumor cell adherence and survival. Cellular morphology, proliferation, adhesion ability, andin vivotumor formation were studied in the human hepatocellular carcinoma cell line HepG2 in the 3-D RADA16-I scaffold. No significant differences in HepG2 cell proliferation, adhesion, and albumin secretion were observed in the peptide scaffold compared to collagen I. Furthermore, the HepG2 cells precultured in the peptide scaffold showed a higher proliferation rate and formed significantly bigger tumors when compared to cells grown on a traditional 2D monolayer, suggesting that the 3-D RADA16-I scaffold can mimic the tumor microenvironment and promote a malignant phenotype in HepG2 cells. Our results indicate that the RADA16-I scaffold can serve as an ideal model for tumorigenesis, growth, local invasion, and metastasis.

Establishment of a three-dimensional co-culture system by porcine hepatocytes and bone marrow mesenchymal stem cells in vitro

AIM

The application of porcine hepatocytes in liver support systems has been hampered by the short-term survival. Co-cultivation of hepatocytes with non-parenchymal cells may be beneficial for optimizing cell functions via heterotypic interactions. In this study, we present a new cultivation system of porcine hepatocytes and mesenchymal stem cells (MSCs) in a randomly distributed co-culture manner.

METHODS

Mononuclear cells were isolated from bone marrow aspirate of swines (n = 3) by density gradient centrifugation. MSCs were characterized by flow cytometry with CD29, CD44, CD45 and CD90, respectively. Then freshly isolated hepatocytes were simultaneously inoculated with MSCs in a hepatocyte dominant manner. The morphological and functional changes of heterotypic interactions were characterized.

RESULTS

Ninety percent MSCs of passage 3 were positive for CD29, CD44 and CD90, but negative for CD45. A rapid attachment and self-organization of three-dimensional hepatocyte aggregates were encouraged. The cell ultrastructure indicating heterotypic junctions remained similar to that of hepatocytes in vivo. Fluorescence microscopy further verified that MSCs served as a feeder layer for hepatocyte aggregates. Hepatocyte performance levels such as albumin secretion, urea synthesis and CYP3A1 induction were all significantly enhanced in co-culture group compared with hepatocyte homo-culture (P < 0.05). The best hepatic function levels were achieved on day 2 and moderately decreased in the following co-culture days. Moreover, the cell cycle of hepatocytes manifested the same trend in parallel to the enhancement of hepatocyte functionality.

CONCLUSIONS

A three-dimensional co-culture system by porcine hepatocytes and bone marrow MSCs was for the first time established in vitro. Enhanced liver-specific functions make such a co-culture system a promising tool for tissue engineering, cell biology, and bioartificial liver devices.

Reestablishment of microenvironment is necessary to maintain in vitro and in vivo human islet function

Islet transplantation is associated with an elevated rate of early graft failure. The isolation process leads to structural and functional abnormalities. The reestablishment of the cell-matrix relationship is important to modulate the survival and function of islets. Thus, we evaluated the effect of human fibronectin (hFN) and self-assembling peptide nanofiber (SAPNF) in the ability to support islet function in vitro and after transplantation into streptozotocin (STZ)-induced diabetic severe combined immunodeficiency (SCID) mice. Human isolated islets were cultured with hFN or SAPNF for 7 days. Their ability to maintain insulin production/glucose responsiveness over time was evaluated. Islets embedded in hFN, SAPNF, or alone were transplanted into STZ-induced diabetic SCID mice. Islet grafts were removed after 14 days to evaluate insulin content, insulin expression, and apoptosis. SAPNF-entrapped islets maintained satisfactory morphology/viability and capability of glucose-dependent insulin secretion for over 7 days, whereas islets cultured in hFN underwent widespread deterioration. In vivo grafts containing human islets in SAPNF showed remarkably higher insulin content and expression when compared with human islets in hFn or alone. RT-PCR revealed lower caspase-3 expression in SAPNF islets grafts. These studies indicate that the reestablishment of the cell-matrix interactions by a synthetic matrix in the immediate postisolation period is a useful tool to maintain islet functions in vitro and in vivo.