Microencapsulation and tissue engineering as an alternative treatment of diabetes

Stem cells differentiation into insulin-producing cells (IPCs): recent advances and current challenges

Type 1 diabetes mellitus (T1D) is a chronic disease characterized by an autoimmune destruction of insulin-producing β-pancreatic cells. Although many advances have been achieved in T1D treatment, current therapy strategies are often unable to maintain perfect control of glycemic levels. Several studies are searching for new and improved methodologies for expansion of β-cell cultures in vitro to increase the supply of these cells for pancreatic islets replacement therapy. A promising approach consists of differentiation of stem cells into insulin-producing cells (IPCs) in sufficient number and functional status to be transplanted. Differentiation protocols have been designed using consecutive cytokines or signaling modulator treatments, at specific dosages, to activate or inhibit the main signaling pathways that control the differentiation of induced pluripotent stem cells (iPSCs) into pancreatic β-cells. Here, we provide an overview of the current approaches and achievements in obtaining stem cell-derived β-cells and the numerous challenges, which still need to be overcome to achieve this goal. Clinical translation of stem cells-derived β-cells for efficient maintenance of long-term euglycemia remains a major issue. Therefore, research efforts have been directed to the final steps of in vitro differentiation, aiming at production of functional and mature β-cells and integration of interdisciplinary fields to generate efficient cell therapy strategies capable of reversing the clinical outcome of T1D.

Progress and challenges in macroencapsulation approaches for type 1 diabetes (T1D) treatment: Cells, biomaterials, and devices

Macroencapsulation technology has been an attractive topic in the field of treatment for Type 1 diabetes due to mechanical stability, versatility, and retrievability of the macro-capsule design. Macro-capsules can be categorized into extravascular and intravascular devices, in which solute transport relies either on diffusion or convection, respectively. Failure of macroencapsulation strategies can be due to limited regenerative capacity of the encased insulin-producing cells, sub-optimal performance of encapsulation biomaterials, insufficient immunoisolation, excessive blood thrombosis for vascular perfusion devices, and inadequate modes of mass transfer to support cell viability and function. However, significant technical advancements have been achieved in macroencapsulation technology, namely reducing diffusion distance for oxygen and nutrients, using pro-angiogenic factors to increase vascularization for islet engraftment, and optimizing membrane permeability and selectivity to prevent immune attacks from host's body. This review presents an overview of existing macroencapsulation devices and discusses the advances based on tissue-engineering approaches that will stimulate future research and development of macroencapsulation technology. Biotechnol. Bioeng. 2016;113: 1381-1402. © 2015 Wiley Periodicals, Inc.

Transplantation of microencapsulated cells expressing VEGF improves angiogenesis in implanted xenogeneic acellular dermis on wound

BACKGROUND

Cell-based gene therapy using cells that express angiogenic factors is an alternative technique for therapeutic angiogenesis in transplantation of xenogeneic acellular dermis matrix (ADM). However, immune rejection is a substantial obstacle to implantation of genetically engineered allogeneic or xenogeneic cells.

OBJECTIVE

To evaluate application of microencapsulated cells that express vascular endothelial growth factor (VEGF) in xenogeneic ADM transplants to improve wound angiogenesis and healing.

MATERIALS AND METHODS

NIH3T3 cells were genetically modified to secrete VEGF and enveloped in semipermeable microcapsules. Microencapsulated VEGF-NIH3T3 cells were implanted in defects on the dorsa of guinea pigs with xenogeneic ADM and autologous split-thickness skin grafts. Cell structure and microencapsulation were observed at microscopy, and expression of VEGF was detected using an enzyme-linked immunosorbent assay (ELISA) and immunochemistry. Extent of angiogenesis in the ADM and the survival rate of the composite skin were evaluated after 2 weeks. In addition, expression of human VEGF and CD31 in the implanted acellular dermis was assessed, and microvessel density was calculated.

RESULTS

Microencapsulated VEGF-expressing NIH3T3 cells were prepared successfully, and demonstrated proliferation and viability, and expressed VEGF both in vitro and in vivo. Extent of angiogenesis and survival rate of the composite skin containing the microencapsulated VEGF-expressing cells were significantly greater than in controls. Microencapsulated VEGF-expressing NIH3T3 cells augmented early angiogenesis in ADM implanted on wound and improved healing.

CONCLUSION

Microencapsulated xenogeneic cell-based gene therapy may be a novel approach to therapeutic angiogenesis in transplantation of xenogeneic ADM skin.

c-Kit and stem cell factor regulate PANC-1 cell differentiation into insulin- and glucagon-producing cells

Recent evidence has shown that stem cell factor (SCF) and its receptor, c-Kit, have an important role in pancreatic islet development by promoting islet cell differentiation and proliferation. In this study, we examined the role of c-Kit and SCF in the differentiation and proliferation of insulin- and glucagon-producing cells using a human pancreatic duct cell line (PANC-1). Our study showed that increased expression of endocrine cell markers (such as insulin and glucagon) and transcription factors (such as PDX-1 and PAX-6) coincided with a decrease in CK19(+) and c-Kit(+) cells (P<0.001) during PANC-1 cell differentiation, determined by immunofluorescence and qRT-PCR. Cells cultured with exogenous SCF showed an increase in insulin(+) (26%) and glucagon(+) (35%) cell differentiation (P<0.01), an increase in cell proliferation (P<0.05) and a decrease in cell apoptosis (P<0.01). siRNA knockdown of c-Kit resulted in a decrease in endocrine cell differentiation with a reduction in PDX-1 and insulin mRNA, as well as the number of cells immunostaining for PDX-1 and insulin. Taken together, these results show that c-Kit/SCF interactions are involved in mediating islet-like cluster formation and islet-like cell differentiation in a human pancreatic duct cell line.

Calcium phosphate cement chamber as an immunoisolative device for bioartificial pancreas: in vitro and preliminary in vivo study

OBJECTIVES

This study examined a calcium phosphate cement (CPC) chamber as an immunoisolative device to facilitate the use of xenogeneic cell sources without immunosuppression for the bioartificial pancreas (BAP).

METHODS

Mouse insulinoma cells were encapsulated in agarose gel and then enclosed in a CPC chamber to create a BAP. Bioartificial pancreas were evaluated by cell viability, live-dead cell ratio, and cytokine-mediated cytotoxicity assay and implanted into the peritoneal cavity of diabetic rats. Nonfasting blood glucose and serum insulin levels were analyzed perioperatively; BAPs were also retrieved for histological examination.

RESULTS

Insulinoma cells enclosed in the CPC chamber had normal viability, cell survival, and insulin secretion that was even cultured in media with cytokines. The nonfasting blood glucose level of rats was decreased from 460 +/- 50 to 132 +/- 43 mg/dL and maintained euglycemia for 22 days; serum insulin level was increased from 0.34 +/- 0.11 to 1.43 +/- 0.30 microg/dL after operation. Histological examination revealed the fibrous tissue envelopment, and immune-related cells that competed for oxygen resulting in hypoxia could be attributed to the dysfunction of BAPs.

CONCLUSIONS

This study proved the feasibility for using a CPC chamber as an immunoisolative device for the BAP. An alternative implanted site should be considered to extend the functional longevity of BAPs in further study.

Three-dimensional Cultures of Rat Pancreatic RIN-5F Cells in Porous PLGA-collagen Hybrid Scaffolds

Three-dimensional cultures of pancreatic islet cells in porous scaffolds or hydrogels have been constructed as a biohybrid artificial pancreas. A thin mesh of a PLGA-collagen hybrid was used to culture rat RIN-5F cells. The hybrid mesh was coated with laminin, fibronectin, vitronectin, type IV collagen, and poly(L-lysine) were evaluated and mesh without coating was used as a control. Cell adhered and proliferated on all of the coated and uncoated meshes. The cells formed spheroids in the uncoated, poly(L-lysine)-, fibronectin-, vitronectin-, and type IV collagen-coated hybrid meshes, while forming a layered structure in the laminin-coated hybrid mesh. Cell adhesion on the coated PLGA-collagen hybrid meshes was higher than that for the uncoated hybrid mesh. The laminin-coated hybrid mesh showed the greatest level of adhesion. The insulin secretion capacity of RIN-5F cells was at the same level for all coated and uncoated PLGA-collagen hybrid meshes and higher than that of cells cultured on cell culture plates. The 3D cultured PLGA-collagen hybrid meshes promoted insulin production capacity. Gene expression analysis showed that genes encoding insulin I, insulin II, and the pancreatic transcription factor PDX-1 (pancreas/duodenum homeobox 1) was expressed. These results indicate that the PLGA-collagen hybrid meshes support adhesion, proliferation, and differentiation of RIN-5F cells that allows culturing pancreatic islet cells on 3D constructs.

Pluronic F127 as a cell encapsulation material: utilization of membrane-stabilizing agents

Thermoreversible gelation of the copolymer Pluronic F127 (generic name, poloxamer 407) in water makes it a unique candidate for cell encapsulation applications, either alone or to promote cell seeding and attachment in tissue scaffolds. At concentrations of 15-20% (w/w), aqueous Pluronic F127 (F127) solutions gel at physiological temperatures. The effect of F127 on viability and proliferation of human liver carcinoma cells (HepG2) was determined for both liquid and gel formulations. Cell concentration and viability over a 5-day period were measured by the trypan blue assay via hemocytometry and results were confirmed in both the MTT and LDH assays. With 0.1-5% (w/w) F127 (liquid), cells proliferated and maintained high viability over 5 days. However, at 10% (w/w) F127 (liquid), there was a significant decrease in cell viability and no cell proliferation was evident. HepG2 cell encapsulation in F127 concentrations ranging from 15 to 20% (w/w) (gel) resulted in complete cell death by 5 days. This was also true for the HMEC-1 (endothelial) and L6 (muscle) cell lines evaluated. Cell-seeding density did not affect cell survival or proliferation. Membrane-stabilizing agents (hydrocortisone, glucose, and glycerol) were added to the F127 gel formulations to improve cell viability. The steroid hydrocortisone demonstrated the most significant improvement in viability, from <2% (in F127 alone) to >70% (with 60 nM hydrocortisone added). These results suggest that F127 formulations supplemented with membrane-stabilizing agents can serve as viable cell encapsulation materials. In addition, hydrocortisone may be generally useful in the promotion of cell viability for a wide range of encapsulation materials.

Survival and Function of Transplanted Islet Cells on an in Vivo, Vascularized Tissue Engineering Platform in the Rat: A Pilot Study 1

As in vivo tissue engineering of complex tissues and organs progresses, there is a need for an independently vascularized, alterable, and recoverable model. Current models of islet cell transplantation (release into the portal venous system, placement under the renal capsule, and microencapsulation) lack these qualities. We have developed a model of angiogenesis and spontaneous tissue generation in the rat that lends itself as a potential platform for tissue engineering. In this experiment, we examined the effectiveness of such a model in addressing some of the shortcomings of endocrine pancreatic transplantation. An arteriovenous loop was created in the groins of five adult inbred Sprague-Dawley rats, and placed within polycarbonate chambers. Isolated pancreatic islet cell clusters were placed within the chambers, suspended in a matrix of Matrigel®. The chambers were recovered at 3 weeks, and the newly generated tissue was processed for histologic and immunohistochemical analysis. By 3 weeks, spontaneous generation of angiogenesis and collagen matrix and deposition of a collagen matrix was observed. Surviving islet cells were identified by histology and their viability was confirmed via immunohistochemistry for insulin and glucagon. This study demonstrates the ability to maintain viability and functionality of transplanted islet cells on a tissue-engineered platform with an independent vascular supply. The model provides the ability to alter the graft environment via matrix substitution, cellular coculture, and administration of growth factors. The transplanted tissues are recoverable without animal sacrifice and are microsurgically transferable. This model may provide an in vivo culture platform for the study of islet transplantation.

Effect of rat-to-mouse bioartificial pancreas xenotransplantation on diabetic renal damage and survival

OBJECTIVE

Diabetic nephropathy is a life-threatening complication of diabetes mellitus. Bioartificial pancreas transplantation is becoming a therapeutic option for diabetes mellitus as it protects both allogeneic and xenogeneic islets from the host immune system. This study was undertaken to determine the effectiveness of bioartificial pancreas transplantation to improve or prevent diabetic renal damage.

METHODS

Approximately 800 rat islets were macroencapsulated in polyvinyl alcohol gel and then transplanted into the peritoneal cavity of diabetic mice (transplantation group [Tx group]). Diabetic mice transplanted with a capsule without islets served as a sham operation group. After transplantation, the following data were collected: survival, body weight, blood glucose, blood urea nitrogen, serum creatinine levels, urinalysis, water intake, and histological changes in the kidney.

RESULTS

There was a significant improvement in survival, blood glucose, blood urea nitrogen, and creatinine in the Tx group compared with the sham operation group. No remarkable changes were seen in urinary parameters between the 2 groups, and there was also no significant difference in water intake. Histological examination revealed that mesangial matrix expansion was decreased in the Tx group.

CONCLUSIONS

This study demonstrated that polyvinyl alcohol gel bioartificial pancreas transplantation can protect the kidney from diabetic damage.

From embryos to embryonic stem cells: biopolitics and therapeutic potential

The inner cell mass of the preimplantation blastocyst, from which all the cells of the body develop, is a source of embryonic stem cells. These cells can be maintained in their undifferentiated state over long periods in culture and yet retain their pluripotency. The generation of human stem cells capable of differentiating into all the cell types of the human body opens the way for the use of these cells in therapeutic transplantation for a myriad of diseases. However, as discussed here, there are a number of logistical, biological, and clinical hurdles that must be overcome prior to the use of these cells in routine clinical practice.

Engineering microenvironment for expansion of sensitive anchorage-dependent mammalian cells

Tissue engineering involves ex vivo seeding of anchorage-dependent mammalian cells onto scaffolds, or transplanting cells in vivo. The cell expansion currently requires repeated cell detachment from solid substrata by enzymatic, chemical or mechanical means. The report here presents a high yield three-dimensional culture and harvest system circumventing the conventional detachment requirements. Cells mixed with dilute cationic collagen were microencapsulated within an ultra-thin shell of synthetic polymers. The cationic collagen could rapidly form a conformal layer of collagen fibers around cells to support cell proliferation and functions. The collagen could be readily removed from cells with a buffer rinse after harvesting from the fragile microcapsules. The cells harvested from this system demonstrate improved attachment, morphology and functions over conventionally cultured cells, upon binding to ligand-conjugated polymer surfaces. The harvested cells can be re-encapsulated and allowed to proliferate again, or used immediately in applications.

Polímeros bioreabsorvíveis na engenharia de tecidos

A Engenharia de Tecidos consiste em um conjunto de conhecimentos e técnicas para a reconstrução de novos órgãos e tecidos. Baseada em conhecimentos das áreas de ciência e engenharia de materiais, biológica e médica, a técnica envolve a expansão in vitro de células viáveis do paciente doador sobre suportes de polímeros bioreabsorvíveis. O suporte degrada enquanto um novo órgão ou tecido é formado. Os poli(alfa-hidróxi ácidos) representam a principal classe de polímeros sintéticos bioreabsorvíveis e biodegradáveis utilizados na engenharia de tecidos. No desenvolvimento e na seleção desses materiais, o tempo de degradação é fundamental para o sucesso do implante. Os estudos e os desafios atuais são normalmente direcionados ao entendimento das relações entre composição química, cristalinidade, morfologia do suporte, e o processamento desses materiais. Este artigo faz uma revisão dos trabalhos recentes sobre a utilização dos polímeros sintéticos bioreabsorvíveis como suportes na engenharia de tecidos.

In Vivo Recognition by the Host Adaptive Immune System of Microencapsulated Xenogeneic Cells

BACKGROUND

Microencapsulation is under consideration as a means of enabling pancreatic islet transplantation. To understand better the ongoing destructive host response, we examined whether the adaptive immune system of the recipient recognized polymer-encapsulated xenogeneic cells implanted intraperitoneally.

METHODS

Balb/c mice were implanted with xenogeneic Chinese hamster ovary cells, inside and outside poly(hydroxyethyl methacrylate-methyl methacrylate) microcapsules, and responses were compared with xenografted Chinese hamster skin (positive control). Capsules were localized within an agarose rod. Splenocyte proliferation upon rechallenge in vitro, antibody titer in serum, and Th1/2 polarization (assessed by interleukin-4 and interferon-gamma in supernatants of antigen-challenged splenocytes and immunoglobulin [Ig]G1 and IgG2a antibody isotypes in serum) were measured.

RESULTS

Encapsulation did not prevent a strong recipient antibody response. Splenocyte proliferation in vitro did not differ after priming by implanted cells, inside or outside capsules. Thus, the capsule membrane did not prevent indirect recognition of shed antigens. However, after 10 days of implantation, proliferation was lower than that induced by skin grafts, although this difference disappeared by 2 months. This transient T-cell suppression was unexpected because encapsulated cell viability was already compromised by 10 days. The influence of Th1/2 bias did not explain the observed suppression. Cells inside capsules elicited a consistent Th2 response, whereas cells outside capsules elicited a mixed response, and skin xenografts showed an initial Th2 response that became mixed by 2 months.

CONCLUSIONS

Encapsulation does not prevent host immune responses, but the inflammatory response to the implanted biomaterials or xenogeneic cells may be responsible both for encapsulated cell death and transient T-cell suppression.

Immune tolerance in pancreatic islet xenotransplantation

AIM: To observe the effect of tail vein injection with donor hepatocytes and/or splenocytes on the islet xenotransplantation rejection.

METHODS: New-born male pigs and BALB/C mice were selected as donors and recipients respectively. Islet xenotransplantation was performed in recipients just after the third time of tail vein injection with donor hepatocytes and/or splenocytes. Macrophage phagocytosis, NK(natural killing cell) killing activity, T lymphocyte transforming function of spleen cells, antibody forming function of B lymphocytes, and T lymphocyte subsets were taken to monitor transplantation rejection. The effects of this kind of transplantation were indicated as variation of blood glucose and survival days of recipients.

RESULTS: The results showed that streptozotocin (STZ) could induce diabetes mellitus models of mice. The pre-injection of donor hepatocytes, splenocytes or their mixture by tail vein injection was effective in preventing donor islet transplantation from rejection, which was demonstrated by the above-mentioned immunological marks. Each group of transplantation could decrease blood glucose in recipients and increase survival days. Pre-injection of mixture of donor hepatocytes and splenocytes was more effective in preventing rejection as compared with that of donor hepatocyte or splenocyte pre-injection respectively.

CONCLUSION: Pre-injection of donor hepatocytes, splenocytes or their mixture before donor islet transplantation is a good way in preventing rejection.

Transplante de Pâncreas e de Ilhotas Pancreáticas: Visão de Nefrologista

Os autores, após dimensionarem o problema do diabetes mellitus e da nefropatia diabética no Brasil e no mundo, fazem uma revisão, sob a ótica do nefrologista, sobre transplante de pâncreas e de ilhotas pancreáticas, centrada nos riscos e benefícios do transplante combinado de pâncreas e rim (TCPR) para o diabético urêmico. No texto é ressaltada a importância da colaboração entre o endocrinologista e o nefrologista para melhorar a sobrevida dos diabéticos com nefropatia e para uma definição local sobre a viabilidade e validade do estabelecimento de um programa de TCPR.