Coencapsulation of hepatocytes and bone marrow stem cells: in vitro conversion of ammonia and in vivo lowering of bilirubin in hyperbilirubemia Gunn rats

A comprehensive review of advances in hepatocyte microencapsulation: selecting materials and preserving cell viability

Liver failure represents a critical medical condition with a traditionally grim prognosis, where treatment options have been notably limited. Historically, liver transplantation has stood as the sole definitive cure, yet the stark disparity between the limited availability of liver donations and the high demand for such organs has significantly hampered its feasibility. This discrepancy has necessitated the exploration of hepatocyte transplantation as a temporary, supportive intervention. In light of this, our review delves into the burgeoning field of hepatocyte transplantation, with a focus on the latest advancements in maintaining hepatocyte function, co-microencapsulation techniques, xenogeneic hepatocyte transplantation, and the selection of materials for microencapsulation. Our examination of hepatocyte microencapsulation research highlights that, to date, most studies have been conducted in vitro or using liver failure mouse models, with a notable paucity of experiments on larger mammals. The functionality of microencapsulated hepatocytes is primarily inferred through indirect measures such as urea and albumin production and the rate of ammonia clearance. Furthermore, research on the mechanisms underlying hepatocyte co-microencapsulation remains limited, and the practicality of xenogeneic hepatocyte transplantation requires further validation. The potential of hepatocyte microencapsulation extends beyond the current scope of application, suggesting a promising horizon for liver failure treatment modalities. Innovations in encapsulation materials and techniques aim to enhance cell viability and function, indicating a need for comprehensive studies that bridge the gap between small-scale laboratory success and clinical applicability. Moreover, the integration of bioengineering and regenerative medicine offers novel pathways to refine hepatocyte transplantation, potentially overcoming the challenges of immune rejection and ensuring the long-term functionality of transplanted cells. In conclusion, while hepatocyte microencapsulation and transplantation herald a new era in liver failure therapy, significant strides must be made to translate these experimental approaches into viable clinical solutions. Future research should aim to expand the experimental models to include larger mammals, thereby providing a clearer understanding of the clinical potential of these therapies. Additionally, a deeper exploration into the mechanisms of cell survival and function within microcapsules, alongside the development of innovative encapsulation materials, will be critical in advancing the field and offering new hope to patients with liver failure.

Stem Cell-Based Strategies: The Future Direction of Bioartificial Liver Development

Acute liver failure (ALF) results from severe liver damage or end-stage liver disease. It is extremely fatal and causes serious health and economic burdens worldwide. Once ALF occurs, liver transplantation (LT) is the only definitive and recommended treatment; however, LT is limited by the scarcity of liver grafts. Consequently, the clinical use of bioartificial liver (BAL) has been proposed as a treatment strategy for ALF. Human primary hepatocytes are an ideal cell source for these methods. However, their high demand and superior viability prevent their widespread use. Hence, finding alternatives that meet the seed cell quality and quantity requirements is imperative. Stem cells with self-renewing, immunogenic, and differentiative capacities are potential cell sources. MSCs and its secretomes encompass a spectrum of beneficial properties, such as anti-inflammatory, immunomodulatory, anti-ROS (reactive oxygen species), anti-apoptotic, pro-metabolomic, anti-fibrogenesis, and pro-regenerative attributes. This review focused on the recent status and future directions of stem cell-based strategies in BAL for ALF. Additionally, we discussed the opportunities and challenges associated with promoting such strategies for clinical applications.

Beneficial Effects of Human Mesenchymal Stromal Cells on Porcine Hepatocyte Viability and Albumin Secretion

Porcine hepatocytes transplanted during acute liver failure might support metabolic functions until the diseased liver recovers its function. Here, we isolated high numbers of viable pig hepatocytes and evaluated hepatocyte functionality after encapsulation. We further investigated whether coculture and coencapsulation of hepatocytes with human multipotent mesenchymal stromal cells (MSC) are beneficial on hepatocyte function. Livers from 10 kg pigs (n = 9) were harvested, and hepatocytes were isolated from liver suspensions for microencapsulation using alginate and poly(ethylene-glycol)- (PEG-) grafted alginate hydrogels, either alone or in combination with MSC. Viability, albumin secretion, and diazepam catabolism of hepatocytes were measured for one week. 9.2 ± 3.6 × 10⁹ hepatocytes with 95.2 ± 3.1% viability were obtained after isolation. At day 3, free hepatocytes displayed 99% viability, whereas microencapsulation in alginate and PEG-grafted alginate decreased viability to 62% and 48%, respectively. Albumin secretion and diazepam catabolism occurred in free and microencapsulated hepatocytes. Coencapsulation of hepatocytes with MSC significantly improved viability and albumin secretion at days 4 and 8 (p < 0.05). Coculture with MSC significantly increased and prolonged albumin secretion. In conclusion, we established a protocol for isolation and microencapsulation of high numbers of viable pig hepatocytes and demonstrated that the presence of MSC is beneficial for the viability and function of porcine hepatocytes.

Advances in cell encapsulation technology and its application in drug delivery

INTRODUCTION

Cell encapsulation technology has improved enormously since it was proposed 50 years ago. The advantages offered over other alternative systems, such as the prevention of repetitive drug administration, have triggered the use of this technology in multiple therapeutic applications.

AREAS COVERED

In this article, improvements in cell encapsulation technology and strategies to overcome the drawbacks that prevent its use in the clinic have been summarized and discussed. Different studies and clinical trials that have been performed in several therapeutic applications have also been described.

EXPERT OPINION

The authors believe that the future translation of this technology from bench to bedside requires the optimization of diverse aspects: i) biosafety, controlling and monitoring cell viability; ii) biocompatibility, reducing pericapsular fibrotic growth and hypoxia suffered by the graft; iii) control over drug delivery; iv) and the final scale up. On the other hand, an area that deserves more attention is the cryopreservation of encapsulated cells as this will facilitate the arrival of these biosystems to the clinic.

Migration of human umbilical cord blood cells into rat liver

BACKGROUND AND OBJECTIVES

Cell therapy provides an effective strategy for the treatment of an impaired liver. Human umbilical cord blood progenitor cells have the potential to differentiate into hepatocytes. Progenitor cells transplanted into the spleen could migrate directly into the liver through portal circulation. To track migration of human umbilical cord blood progenitor cells in cirrhotic rat liver after intrasplenic transplantation and to prove the possibility similar behavior of human umbilical cord blood nucleated cells in humans.

METHODS AND RESULTS

Umbilical cord blood samples from full-term deliveries will be collected after obtaining an informed consent from the mother. The collection procedure will be conducted after completion of delivery and will not interfere with the normal obstetric procedures. Adult male Sprague Dawley rats were subjected to liver cirrhosis by intraperitoneal injection of thioacetamide. Cirrhotic rats were treated with human umbilical cord blood nucleated cells by intra-splenic transplantation. Migration of intrasplenic transplanted human umbilical cord blood cells to the liver was successfully documented with Immunohistochemistry. The liver and spleen from recipient animals were removed. Histopathological and immunohistochemical analysis were performed 20 weeks after intrasplenic injection of the cells. Intrasplenically injected cells migrate to the liver of recipient animals.

CONCLUSIONS

Human cord blood nucleated cells have the potential to differentiate into hepatocytes and substantially improve the histology and function of the cirrhotic liver in rats. Relocation into liver after intrasplenic transplantation could be detected by immunohistochemistry. Transdifferentiated cells could be efficiently stained with antihuman hepatocytes.

Coculture with mesenchymal stem cells results in improved viability and function of human hepatocytes

Hepatocyte transplantation is becoming an accepted therapy for acute liver failure, either as a bridge to liver regeneration or to organ transplantation. Hepatocytes provide liver function in place of the failing organ. The maintenance of sufficient viability and function of the transplanted hepatocytes is a concern. There is a lot of recent interest in mesenchymal stem cells (MSCs) for the provision of structural and trophic support to hepatocytes, but few studies currently use primary human hepatocytes. The aim of this study was to investigate if coculture of human MSCs with cryopreserved human hepatocytes may improve their function and viability, thus with potential for cellular therapy of liver disease. MSCs were isolated from human umbilical cord or adipose tissue. Hepatocytes were isolated from donor organs unsuitable for transplantation. MSCs and hepatocytes were cocultured in both direct and indirect contact. Conditioned medium (CM) from cocultured MSCs and hepatocytes was also used on hepatocytes. Viability and liver-specific function were compared between test and controls. Human hepatocytes that were cocultured directly with MSCs demonstrated improved production of albumin from day 5 to day 25 of culture. This effect was most prominent at day 15. Likewise, urea production was improved in coculture from day 5 to 25. Indirect coculture demonstrated improved albumin production by day 4 (1,107 ng/ml) versus hepatocyte monoculture (940 ng/ml). Hepatocytes in CM demonstrated a nonsignificant improvement in function. The viability of cocultured hepatocytes was superior to that of monocultured cells with up to a 16% improvement. Thus, coculture of human hepatocytes with MSCs demonstrates both improved function and viability. The effect is seen mainly with direct coculture but can also be seen in indirect culture and with CM. Such coculture conditions may convey major advantages in hepatocyte survival and function for cell transplantation.

Transplantation of Co-Microencapsulated Hepatocytes and HUVECs for Treatment of Fulminant Hepatic Failure

Purpose:

Microencapsulated hepatocytes might solve immunological rejection, broadening a new perspective for the treatment of fulminant hepatic failure (FHF). However, the transplantation of microcapsulated hepatocytes is limited by low cell viability Nevertheless, the co-microencapsulation of hepatocytes and human umbilical vein endothelial cells (HUVECs) may make the treatment of FHF more promising.

Methods:

We prepared the microcapsules using the high-voltage electrostatic droplet spray method, transplanted the empty microcapsules, isolated hepatocytes, microcapsulated hepatocytes, and co-microencapsulated hepatocytes and HUVEC intraperitoneally into rat models of FHF induced by D-aminogalactose (D-gal). After 1, 3, and 7 days, and 2, 3, and 4 weeks posttransplantation, we calculated the mortality and assessed alanine aminotransferase (ALT), aspartate aminotransferase (AST), and albumin (ALB) levels in the serum of the model; evaluated the integrality and recovery of microcapsules; and stained with hematoxylin and eosin (H&E) the recovered microcapsules as well as the liver of the FHF rats.

Results:

Hepatocyte-specific functions, including the levels of ALT, AST, and ALB in the serum of the co-microencapsulation group, were significantly better than those in the other groups (p<0.05) from 2 to 4 weeks after transplantation. Moreover, cotransplantation of the microencapsulated hepatocytes and HUVECs decreased the mortality rate of the FHF rats. The recovered microcapsules were intact, and recovery was up to 90%. H&E staining showed that the microencapsulated cells were still alive, and the liver tissues had started to recover after 4 weeks posttransplantation.

Conclusion:

The microcapsules have good biocompatibility and immunoprotection to protect the hepatocytes from immunological rejection. Cotransplantation of the microencapsulated hepatocytes and HUVECs could decrease mortality rates and improve liver function in FHF.

Microencapsulating and Banking Living Cells for Cell-Based Medicine

A major challenge to the eventual success of the emerging cell-based medicine such as tissue engineering, regenerative medicine, and cell transplantation is the limited availability of the desired cell sources. This challenge can be addressed by cell microencapsulation to overcome the undesired immune response (i.e., to achieve immunoisolation) so that non-autologous cells can be used to treat human diseases, and by cell/tissue preservation to bank living cells for wide distribution to end users so that they are readily available when needed in the future. This review summarizes the status quo of research in both cell microencapsulation and banking the microencapsulated cells. It is concluded with a brief outlook of future research directions in this important field.

Artificial cell microencapsulated stem cells in regenerative medicine, tissue engineering and cell therapy

Adult stem cells, especially isolated from bone marrow, have been extensively investigated in recent years. Studies focus on their multiple plasticity oftransdifferentiating into various cell lineages and on their potential in cellular therapy in regenerative medicine. In many cases, there is the need for tissue engineering manipulation. Among the different approaches of stem cells tissue engineering, microencapsulation can immobilize stem cells to provide a favorable microenvironment for stem cells survival and functioning. Furthermore, microencapsulated stem cells are immunoisolated after transplantation. We show that one intraperitoneal injection of microencapsulated bone marrow stem cells can prolong the survival of liver failure rat models with 90% of the liver removed surgically. In addition to transdifferentiation, bone marrow stem cells can act as feeder cells. For example, when coencapsulated with hepatocytes, stem cells can increase the viability and function of the hepatocytes in vitro and in vivo.

Microencapsulated stem cells for tissue repairing: implications in cell-based myocardial therapy

Stem cells have the unique properties of self-renewal, pluripotency and a high proliferative capability, which contributes to a large biomass potential. Hence, these cells act as a useful source for acquiring renewable adult cell lines. This, in turn, acts as a potent therapeutic tool to treat various diseases related to the heart, liver and kidney, as well as neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease. However, a major problem that must be overcome before it can be effectively implemented into the clinical setting is a suitable delivery system that can retain an optimal quantity of the cells at the targeted site for a maximal clinical benefit; a system that will give a mechanical as well as an immune protection to the foreign cells, while at the same time enhancing the yields of differentiated cells, maintaining cell microenvironments and sustaining the differentiated cell functions. To address this issue we opted for a novel delivery system, termed the ‘artificial cells’, which are semipermeable microcapsules with strong and thin multilayer membrane components with specific mass transport properties. Here, we briefly introduce the concept of artificial cells for encapsulation of stem cells and investigate the application of microencapsulation technology as an ideal tool for all stem transplantations and relate their role to the emerging field of cellular cardiomyoplasty.

Design and Evaluation of a Cell Microencapsulating Device for Cell Assembly Technology

A cell encapsulation device based on the principle of high-voltage dispersion technology was designed and constructed. The parameters that influenced the formation of cell microcapsules, such as; voltage, push speed, electrode distance, and syringe size were analyzed and optimized. Unlike the traditional cell microencapsulating devices, both of the electrodes were separated from the CaCl2 solution in this device, which simplified the procedure of keeping the operation within a sanitary environment. Integrated adipose derived stem cell (ADSC) microcapsules with smooth surface and consistent diameter distribution were prepared. After 1-week in culture as a microcapsule and 3 days assembled in a construct, the ADSCs maintained a high viability and significant proliferation that established a favorable basis for the controlled assembly of cell microcapsules.

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.

Liver cell transplantation for Crigler-Najjar syndrome type I: Update and perspectives

Liver cell transplantation is an attractive technique to treat liver-based inborn errors of metabolism. The feasibility and efficacy of the procedure has been demonstrated, leading to medium term partial metabolic control of various diseases. Crigler-Najjar is the paradigm of such diseases in that the host liver is lacking one function with an otherwise normal parenchyma. The patient is at permanent risk for irreversible brain damage. The goal of liver cell transplantation is to reduce serum bilirubin levels within safe limits and to alleviate phototherapy requirements to improve quality of life. Preliminary data on Gunn rats, the rodent model of the disease, were encouraging and have led to successful clinical trials. Herein we report on two additional patients and describe the current limits of the technique in terms of durability of the response as compared to alternative therapeutic procedures. We discuss the future developments of the technique and new emerging perspectives.

Differentiation of rat bone marrow stem cells in liver after partial hepatectomy

AIM: To investigate the differentiation of rat bone marrow stem cells in liver after partial hepatectomy.

METHODS: Bone marrow cells were collected from the tibia of rat with partial hepatectomy, the medial and left hepatic lobes were excised. The bone marrow stem cells (Thy⁺CD3^-CD45RA^- cells) were enriched from the bone marrow cells by depleting red cells and fluorescence-activated cell sorting. The sorted bone marrow stem cells were labeled by PKH26-GL in vitro and autotransplanted by portal vein injection. After 2 wk, the transplanted bone marrow stem cells in liver were examined by the immunohistochemistry of albumin (hepatocyte-specific marker).

RESULTS: The bone marrow stem cells (Thy⁺CD3^-CD45RA^- cells) accounted for 2.8% of bone marrow cells without red cells. The labeling rate of 10 μM PKH26-GL on sorted bone marrow stem cells was about 95%. There were sporadic PKH26-GL-labeled cells among hepatocytes in liver tissue section, and some of the cells expressed albumin.

CONCLUSION: Rat bone marrow stem cells can differentiate into hepatocytes in regenerative environment and may participate in liver regeneration after partial hepatectomy.

Transdifferentiation of bioencapsulated bone marrow cells into hepatocyte-like cells in the 90% hepatectomized rat model

Under specific conditions, bone marrow cells can transdifferentiate into a variety of cell types including hepatocytes. In this study, bioencapsulated bone marrow cells were transplanted intraperitoneally into 90% hepatectomized rats. We then followed the transdifferentiation of the bone marrow cells and the effect of this on liver regeneration in this liver failure model. Bone marrow cells isolated from Wistar rats were bioencapsulated using alginate-polylysine-alginate method. These bioencapsulated bone marrow cells were transplanted intraperitoneally into 90% hepatectomized Wistar rats. Blood chemistry, HGF, liver weight, and survival of the recipient rats were evaluated. Histology and immunocytochemistry were used to analyze the bioencapsulated cells before and 14 days after transplantation. Unlike free bone marrow cells, transplantation of bioencapsulated bone marrow cells improved the survival of 90% hepatectomized rats and improved the blood chemistry with an efficacy similar to that of bioencapsulated hepatocytes or free hepatocytes transplantation. Some bioencapsulated bone marrow cells expressed hepatocytes markers of cytokeratins 8, cytokeratins 18, albumin, and AFP after 2 weeks of transplantation. These results suggest that syngeneic bioencapsulated bone marrow cells can transdifferentiate into hepatocyte-like cells in the peritoneal cavity of 90% hepatectomized rats and increased the survival rates of these rats. In conclusion, these findings suggest the potential for a new alternative to hepatocyte transplantation for cellular therapy of acute liver failure.

Coencapsulation of hepatocytes and bone marrow cells: In vitro and in vivo studies

Bioencapsulation of cells is one of the many areas of artificial cells being extensively investigated by centers around the world. This includes the bioencapsulation of hepatocytes. A number of methods have been developed to maintain the specific function and phenotype of the bioencapsulated hepatocytes for in vitro and in vivo applications. These include supplementation of factors in the culture medium; use of appropriate substrates and the co-cultivation of hepatocytes with other type of cells, the so called "feeder cells". These feeder cells can be of liver origin or non-liver origin. We have recently studied the role of bone marrow cells in the maintenance of hepatocytes viability and phenotype by using the coculture of hepatocytes with bone marrow cells (nucleated cells including stem cells), and the coencapsulation of hepatocytes with bone marrow stem cells. This way, the hepatocytes viability and specific function can be maintained significantly longer. In vivo studies of both syngeneic and xenogeneic transplantation show that the hepatocytes viability can be maintained longer when coencapsulated with bone marrow cells. Transplantation of coencapsulated hepatocytes and bone marrow cells enhances the ability of the hepatocytes in correcting congenital hyperbilirubinmia in Gunn rats. Both in vitro and in vivo studies show that bone marrow cells can enhance the viability and phenotype maintenance of hepatocytes. Thus, bone marrow cells play an important role as a new type of feeder cells for bioencapsulated hepatocytes for the cellular therapy of liver diseases.

Transplantation of bioencapsulated bone marrow stem cells improves hepatic regeneration and survival of 90% hepatectomized rats: a preliminary report

We transplanted bioencapsulated bone marrow stem cells intraperitoneally into 90% hepatectomized rats and found that this increases both the rates of hepatic regeneration and survival of the animals. Bone marrow cells isolated from Wistar rats were bioencapsulated using alginate-polylysine-alginate method. These bioencapsulated bone marrow cells were transplanted intraperitoneally into 90% hepatectomized syngeneic wistar rats. Control groups included 90% hepatectomized group receiving intraperitoneal injection of either empty microcapsules or free bone marrow cells. Unlike the control groups, transplantation of bioencapsulated bone marrow cells improved the survival of 90% hepatectomized rats, with an efficacy similar to that of bioencapsulated hepatocytes or free hepatocytes. These results suggest that syngeneic bioencapsulated bone marrow stem cells can increase the survival rates of 90% hepatectomized rats. We also discuss the potential for a new alternative to hepatocyte transplantation for cellular therapy of acute liver failure. In particular, bone marrow stem cells can be obtained from the same patient with no immunorejection, whereas in hepatocyte transplant, immunosuppressant will be needed to prevent immunorejection of the donor hepatocytes.

Scalable encapsulation of hepatocytes by electrostatic spraying

Encapsulating cells by polyelectrolyte complex coacervation can be accomplished at physiological temperature and buffer conditions. One of the oppositely charged polyelectrolytes in the microcapsule core can be collagen or any other natural extra-cellular matrices suitable for cellular support while the other polyelectrolyte forms the ultra-thin shell to ensure efficient mass transfer. These microcapsules with ultra-thin shell are difficult to produce in large quantities due to their fragility. In this study, electrostatic spraying technique was used to achieve a scalable production of one such type of microcapsules formed by complex coacervation between the cationic methylated collagen and anionic terpolymer of hydroxylethyl methacrylate, methyl methacrylate and methylacrylic acid (HEMA-MMA-MAA). It was found that the microcapsule sizes were dependent on several important operational parameters, such as the diameter of the spraying needle, the flow rate of the hepatocytes-collagen mixture and the voltage of the electrical field. The microcapsules with diameters of 200-800 microm and a narrow size distribution (standard deviation of 5-28%) were successfully produced. The above parameters also influenced the hepatocyte viability and functions. With a practical encapsulation rate of up to 55 ml/h per orifice required in bio-artificial liver-assisted device applications, we have produced large quantities of microcapsules maintaining comparable cell viability (>87%), mechanical stability and bio-functions to the manually extruded microcapsules.

Therapeutic applications of polymeric artificial cells

Polymeric artificial cells have the potential to be used for a wide variety of therapeutic applications, such as the encapsulation of transplanted islet cells to treat diabetic patients. Recent advances in biotechnology, molecular biology, nanotechnology and polymer chemistry are now opening up further exciting possibilities in this field. However, it is also recognized that there are several key obstacles to overcome in bringing such approaches into routine clinical use. This review describes the historical development and principles behind polymeric artificial cells, the present state of the art in their therapeutic application, and the promises and challenges for the future.

Effects of amino acid additions on ammonium stressed CHO cells

Ammonium is a toxic and inhibitory byproduct of mammalian cell metabolism. At the end of a typical recombinant protein production campaign, the ammonium concentration can be as high as 10 mM, mainly due to glutamine metabolism. Intracellular pH (pH(i)) levels are sensitive to ammonium, which negatively impacts both cell growth and recombinant protein productivity. Ammonium also negatively affects the recombinant protein glycosylation profile, thus altering quality. Many strategies have been adopted to reduce ammonium accumulation, with limited results. This study investigated the addition of amino acids to the growth media for Chinese hamster ovary (CHO) cell cultures as a means of mitigating the negative effects of ammonium. Threonine, proline, and glycine additions improved CHO cell growth and recombinant protein levels. Further, the threonine, proline, and glycine additions positively impacted important metabolic parameters, including glucose consumption, lactate production, glutamine utilization, and final ammonium levels. Additionally, threonine, proline, and glycine increased the level of alpha(2,3)-linked sialic acid, galactose-beta(1,4)-N-acetylglucosamine, and alpha(2,6)-linked sialic acid residues on the recombinant tissue plasminogen activator (t-PA). Thus, threonine, proline, and glycine can be used to mitigate some of the toxic effects of ammonium on cell growth, recombinant protein productivity, and protein quality.

Hepatocytes cultured in alginate microspheres: an optimized technique to study enzyme induction

An important application of hepatocyte cultures is identification of drugs acting as inducers of biotransformation enzymes that alter metabolic clearance of other therapeutic agents. In the present study we optimized an in vitro system with hepatocytes cultured in alginate microspheres that allow studies of enzyme induction with excellent sensitivity. Induction factors obtained with standard inducers, such as 3-methylcholanthrene or phenobarbital, were higher compared to those with conventional hepatocyte co-cultures on collagen coated dishes. This is illustrated by activities of 7-ethoxyresorufin-O-deethylase (EROD) after incubation with 5 microM 3-methylcholanthrene (3-MC), a standard inducer for cytochrome P4501A1 and 1A2. Mean activities for solvent controls and 3-MC exposed cells were 2.99 and 449 pmol/min/mg protein (induction factor: 150) for hepatocytes cultured in microspheres compared to 2.72 and 80.6 pmol/min/mg (induction factor: 29.6) for hepatocytes on collagen coated dishes. To compare these in vitro data to the in vivo situation male Sprague Dawley rats, the same strain that was used also for the in vitro studies, were exposed to 3-MC in vivo using a protocol that guarantees maximal induction. Activities were 29.2 and 1656 pmol/min/mg in liver homogenate of solvent and 3-MC treated animals (induction factor: 56.7). Thus, the absolute activities of 3-MC exposed hepatocytes in microspheres are lower compared to the in vivo situation. However, the induction factor in vitro was even higher compared to the in vivo situation (150-fold versus 56.7-fold). A similar scenario was observed using phenobarbital (0.75 mM) for induction of CYP2B and 3A isoenzymes: induction factors for testosterone hydroxylation in position 16beta were 127.5- and 50.4-fold for hepatocytes in microspheres and conventionally cultured hepatocytes, respectively. The new in vitro system with hepatocytes embedded in solid alginate microspheres offers several technical advantages: (i) the solid alginate microspheres can be liquefied within 60s, allowing a fast and complete harvest of hepatocytes; (ii) alginate capsules are stable allowing transport and mechanical stress; (iii) high numbers of hepatocytes can be encapsulated in short periods; (iv) defined cell numbers between 600 hepatocytes, the approximate number of cells in one capsule, and 18 x 10(6) hepatocytes, the number of hepatocytes in 6 ml alginate, can be transferred to a culture dish or flask. Thus, encapsulated hepatocytes allow a flexible organization of experiments with respect to cell number. In conclusion, we optimized a technique for encapsulation of hepatocytes in alginate microspheres that allows identification of enzyme induction with an improved sensitivity compared to existing systems.

CellMAC: a novel technology for encapsulation of mammalian cells in cellulose sulfate/pDADMAC capsules assembled on a transient alginate/Ca2+ scaffold

Microencapsulation of desired mammalian cell phenotypes in biocompatible polymer matrices represents a powerful technology for cell-based therapies and biopharmaceutical manufacturing of protein therapeutics. We have pioneered a novel jet break-up-compatible process for encapsulation of mammalian cells in cellulose sulfate (CS)/poly-diallyl-dimethyl-ammoniumchloride (pDADMAC) (CellMAC) capsules. CS and pDADMAC polymerize on a transient ad hoc co-assembled Ca2+/alginate scaffold and form homogenous capsules following dissolution of the alginate core by Ca2+ chelating agents. CellMAC capsules exhibited excellent mechanical properties and showed a molecular weight cut-off between 43 and 77kDa. Chinese hamster ovary cells engineered for constitutive production of the glycohormone erythropoietin reached high viable cell densities when grown inside CellMAC capsules, while specific erythropoietin (EPO) productivities matched those of conventional non-encapsulated control cultures. CellMAC-encapsulated EPO-production cell lines induced increased EPO serum levels when implanted intraperitoneally into mice and provided robust glycoprotein production during standard stirred-tank bioreactor operation. We expect the CellMAC technology to foster advances in therapeutic encapsulation of engineered cell lines as well as manufacturing of protein pharmaceuticals.

Artificial cell bioencapsulation in macro, micro, nano, and molecular dimensions: keynote lecture

Artificial cells now ranges from macro-dimensions, to micron-dimensions, to nano-dimensions, and to molecular dimensions. Those in the macro-dimensions are suitable for use in the bioencapsulation of cells, tissues, microorganisms, and bioreactants. Those in the micron-dimensions are suitable for the bioencapsulation of enzymes, microorganisms, peptides, drugs, vaccine, and other materials. Those in the nano-dimension are being used for blood substitutes and carriers for enzymes, peptides, drugs, etc. Those in the molecular-dimensions are used as blood substitutes, crosslinked enzymes etc.

Artificial Cells for Cell and Organ Replacements

The artificial cell is a Canadian invention (Chang, Science, 1964). This principle is being actively investigated for use in cell and organ replacements. The earliest routine clinical use of artificial cells is in the form of coated activated charcoal for hemoperfusion for use in the removal of drugs, and toxins and waste in uremia and liver failure. Encapsulated cells are being studied for the treatment of diabetes, liver failure, and kidney failure, and the use of encapsulated genetically-engineered cells is being investigated for gene therapy. Blood substitutes based on modified hemoglobin are already in Phase III clinical trials in patients, with as much as 20 units being infused into each patient during trauma surgery. Artificial cells containing enzymes are being developed for clinical trial in hereditary enzyme deficiency diseases and other diseases. The artificial cell is also being investigated for drug delivery and for other uses in biotechnology, chemical engineering, and medicine.