Harnessing the gut to treat diabetes

Garlic (Allium sativum L.) in diabetes and its complications: Recent advances in mechanisms of action

Diabetes mellitus (DM) is a metabolic disease characterized by chronic hyperglycemia and impaired islet secretion that places a heavy burden on the global health care system due to its high incidence rate, long disease course and many complications. Fortunately, garlic (Allium sativum L.), a well-known medicinal plant and functional food without the toxicity and side effects of conventional drugs, has shown positive effects in the treatment of diabetes and its complications. With interdisciplinary development and in-depth exploration, we offer a clear and comprehensive summary of the research from the past ten years, focusing on the mechanisms and development processes of garlic in the treatment of diabetes and its complications, aiming to provide a new perspective for the treatment of diabetes and promote the efficient development of this field.

Low Molecular Weight Barley β-Glucan Affects Glucose and Lipid Metabolism by Prebiotic Effects

We investigated the effect of low molecular weight barley β-glucan (LMW-BG) on cecal fermentation, glucose, and lipid metabolism through comparisons to high molecular weight β-glucan (HMW-BG). C57BL/6J male mice were fed a moderate-fat diet for 61 days. LMW-BG or HMW-BG was added to the diet corresponding to 4% β-glucan. We measured the apparent absorption of fat, serum biomarkers, the expression levels of genes involved in glucose and lipid metabolism in the liver and ileum, and bacterial counts of the major microbiota groups using real time PCR. The concentration of short-chain fatty acids (SCFAs) in the cecum was analyzed by GC/MS. Significant reductions in serum leptin, total- and LDL-cholesterol concentrations, and mRNA expression levels of sterol regulatory element-binding protein-1c (SREBP-1c) were observed in both BG groups. HMW-BG specific effects were observed in inhibiting fat absorption and reducing abdominal deposit fat, whereas LMW-BG specific effects were observed in increasing bacterial counts of Bifidobacterium and Bacteroides and cecal total SCFAs, acetate, and propionate. mRNA expression of neurogenin 3 was increased in the LMW-BG group. We report that LMW-BG affects glucose and lipid metabolism via a prebiotic effect, whereas the high viscosity of HMW-BG in the digestive tract is responsible for its specific effects.

Generation of Insulin-Expressing Cells in Mouse Small Intestine by Pdx1, MafA, and BETA2/NeuroD

BACKGROUND

To develop surrogate insulin-producing cells for diabetes therapy, adult stem cells have been identified in various tissues and studied for their conversion into β-cells. Pancreatic progenitor cells are derived from the endodermal epithelium and formed in a manner similar to gut progenitor cells. Here, we generated insulin-producing cells from the intestinal epithelial cells that induced many of the specific pancreatic transcription factors using adenoviral vectors carrying three genes: PMB (pancreatic and duodenal homeobox 1 [Pdx1], V-maf musculoaponeurotic fibrosarcoma oncogene homolog A [MafA], and BETA2/NeuroD).

METHODS

By direct injection into the intestine through the cranial mesenteric artery, adenoviruses (Ad) were successfully delivered to the entire intestine. After virus injection, we could confirm that the small intestine of the mouse was appropriately infected with the Ad-Pdx1 and triple Ad-PMB.

RESULTS

Four weeks after the injection, insulin mRNA was expressed in the small intestine, and the insulin gene expression was induced in Ad-Pdx1 and Ad-PMB compared to control Ad-green fluorescent protein. In addition, the conversion of intestinal cells into insulin-expressing cells was detected in parts of the crypts and villi located in the small intestine.

CONCLUSION

These data indicated that PMB facilitate the differentiation of mouse intestinal cells into insulin-expressing cells. In conclusion, the small intestine is an accessible and abundant source of surrogate insulin-producing cells.

Regenerative medicine and cell-based approaches to restore pancreatic function

The pancreas is a complex organ with exocrine and endocrine components. Many pathologies impair exocrine function, including chronic pancreatitis, cystic fibrosis and pancreatic ductal adenocarcinoma. Conversely, when the endocrine pancreas fails to secrete sufficient insulin, patients develop diabetes mellitus. Pathology in either the endocrine or exocrine pancreas results in devastating economic and personal consequences. The current standard therapy for treating patients with type 1 diabetes mellitus is daily exogenous insulin injections, but cell sources of insulin provide superior glycaemic regulation and research is now focused on the goal of regenerating or replacing β cells. Stem-cell-based models might be useful to study exocrine pancreatic disorders, and mesenchymal stem cells or secreted factors might delay disease progression. Although the standards that bioengineered cells must meet before being considered as a viable therapy are not yet established, any potential therapy must be acceptably safe and functionally superior to current therapies. Here, we describe progress and challenges in cell-based methods to restore pancreatic function, with a focus on optimizing the site for cell delivery and decreasing requirements for immunosuppression through encapsulation. We also discuss the tools and strategies being used to generate exocrine pancreas and insulin-producing β-cell surrogates in situ and highlight obstacles to clinical application.

Membranes to achieve immunoprotection of transplanted islets

Transplantation of islet or beta cells is seen as the cure for type 1 diabetes since it allows physiological regulation of blood glucose levels without requiring any compliance from the patients. In order to circumvent the use of immunosuppressive drugs (and their side effects), semipermeable membranes have been developed to encapsulate and immunoprotect transplanted cells. This review presents the historical developments of immunoisolation and provides an update on the current research in this field. A particular emphasis is laid on the fabrication, characterization and performance of membranes developed for immunoisolation applications.

Reprogramming of enteroendocrine K cells to pancreatic β-cells through the combined expression of Nkx6.1 and Neurogenin3, and reaggregation in suspension culture

Recent studies have demonstrated that adult cells such as pancreatic exocrine cells can be converted to pancreatic β-cells in a process called cell reprogramming. Enteroendocrine cells and β-cells share similar pathways of differentiation during embryonic development. Notably, enteroendocrine K cells express many of the key proteins found in β-cells. Thus, K cells could be reprogrammed to β-cells under certain conditions. However, there is no clear evidence on whether these cells convert to β-cells. K cells were selected from STC-1 cells, an enteroendocrine cell line expressing multiple hormones. K cells were found to express many genes of transcription factors crucial for islet development and differentiation except for Nkx6.1 and Neurogenin3. A K cell clone stably expressing Nkx6.1 (Nkx6.1(+)-K cells) was established. Induction of Neurogenin3 expression in Nkx6.1(+)-K cells, by either treatment with a γ-secretase inhibitor or infection with a recombinant adenovirus expressing Neurogenin3, led to a significant increase in Insulin1 mRNA expression. After infection with the adenovirus expressing Neurogenin3 and reaggregation in suspension culture, about 50% of Nkx6.1(+)-K cells expressed insulin as determined by immunostaining. The intracellular insulin content was increased markedly. Electron microscopy revealed the presence of insulin granules. However, glucose-stimulated insulin secretion was defective, and there was no glucose lowering effect after transplantation of these cells in diabetic mice. In conclusion, we demonstrated that K cells could be reprogrammed partially to β-cells through the combined expression of Nkx6.1 and Neurogenin3, and reaggregation in suspension culture.

Restoring insulin production for type 1 diabetes

Current therapies for the treatment of type 1 diabetes include daily administration of exogenous insulin and, less frequently, whole-pancreas or islet transplantation. Insulin injections often result in inaccurate insulin doses, exposing the patient to hypo- and/or hyperglycemic episodes that lead to long-term complications. Islet transplantation is also limited by lack of high-quality islet donors, early graft failure, and chronic post-transplant immunosuppressive treatment. These barriers could be circumvented by designing a safe and efficient strategy to restore insulin production within the patient's body. Porcine islets have been considered as a possible alternative source of transplantable insulin-producing cells to replace human cadaveric islets. More recently, embryonic or induced pluripotent stem cells have also been examined for their ability to differentiate in vitro into pancreatic endocrine cells. Alternatively, it may be feasible to generate new β-cells by ectopic expression of key transcription factors in endogenous non-β-cells. Finally, engineering surrogate β-cells by in vivo delivery of the insulin gene to specific tissues is also being studied as a possible therapy for type 1 diabetes. In the present review, we discuss these different approaches to restore insulin production.

[Stem cell properties of therapeutic potential]

Stem cell research is a innovative technology that focuses on using undifferentiated cells able to self-renew through the asymmetrical or symmetrical divisions. Three types of stem cells have been studied in laboratory including embryonic stem cell, adult stem cells and induced pluripotent stem cells. Embryonic stem cells are pluripotent stem cells derived from the inner cell mass and it can give rise to any fetal or adult cell type. Adult stem cells are multipotent, have the ability to differentiate into a limited number of specialized cell types, and have been obtained from the bone marrow, umbilical cord blood, placenta and adipose tissue. Stem cell therapy is the most promising therapy for several degenerative and devastating diseases including digestive tract disease such as liver failure, inflammatory bowel disease, Celiac sprue, and pancreatitis. Further understanding of biological properties of stem cells will lead to safe and successful stem cell therapies. (Korean J Gastroenterol 2011;58: 125-132).

Reprogramming gut and pancreas endocrine cells to treat diabetes

Multiple approaches have been investigated with the ultimate goal of providing insulin independence to patients with either type 1 or type 2 diabetes. Approaches to produce insulin-secreting cells in culture, convert non-β-cells into functional β-cells or engineer autologous cells to express and secrete insulin in a meal-responsive manner have all been described. This research has been facilitated by significant improvements in both viral and non-viral gene delivery approaches that have enabled new experimental strategies. Many studies have examined possible avenues to confer islet cytoprotection against immune rejection, inflammation and apoptosis by genetic manipulation of islet cells prior to islet transplantation. Here we review several reports based on the reprogramming of pancreas and gut endocrine cells to treat diabetes.

K-cells and glucose-dependent insulinotropic polypeptide in health and disease

In the 1970s, glucose-dependent insulinotropic polypeptide (GIP, formerly gastric inhibitory polypeptide), a 42-amino acid peptide hormone, was discovered through a search for enterogastrones and subsequently identified as an incretin, or an insulinotropic hormone secreted in response to intraluminal nutrients. Independent of the discovery of GIP, the K-cell was identified in small intestine by characteristic ultrastructural features. Subsequently, it was realized that K-cells are the predominant source of circulating GIP. The density of K-cells may increase under conditions including high-fat diet and obesity, and generally correlates with plasma GIP levels. In addition to GIP, K-cells secrete xenin, a peptide with as of yet poorly understood physiological functions, and GIP is often colocalized with the other incretin hormone glucagon-like peptide-1 (GLP-1). Differential posttranslational processing of proGIP produces 30 and 42 amino acid versions of GIP. Its secretion is elicited by intraluminal nutrients, especially carbohydrate and fat, through the action of SGLT1, GPR40, GPR120, and GPR119. There is also evidence of regulation of GIP secretion via neural pathways and somatostatin. Intracellular signaling mechanisms of GIP secretion are still elusive but include activation of adenylyl cyclase, protein kinase A (PKA), and protein kinase C (PKC). GIP has extrapancreatic actions on adipogenesis, neural progenitor cell proliferation, and bone metabolism. However, the clinical or physiological relevance of these extrapancreatic actions remain to be defined in humans. The application of GIP as a glucose-lowering drug is limited due to reduced efficacy in humans with type 2 diabetes and its potential obesogenic effects demonstrated by rodent studies. There is some evidence to suggest that a reduction in GIP production or action may be a strategy to reduce obesity. The meal-dependent nature of GIP release makes K-cells a potential target for genetically engineered production of satiety factors or glucose-lowering agents, for example, insulin. Transgenic mice engineered to produce insulin from intestinal K-cells are resistant to diabetes induced by a beta-cell toxin. Collectively, K-cells and GIP play important roles in health and disease, and both may be targets for novel therapies.

Treatment of diabetes with glucagon-like peptide-1 gene therapy

IMPORTANCE OF THE FIELD

Glucagon-like peptide (GLP)-1 receptor agonists are in widespread clinical use for the treatment of diabetes. While effective, these peptides require frequent injections to maintain efficacy. Therefore, alternative delivery methods including gene therapy are currently being evaluated.

AREAS COVERED IN THIS REVIEW

Here, we review the biology of GLP-1, evidence supporting the clinical use of the native peptide as well as synthetic GLP-1 receptor agonists, and the rationale for their delivery by gene therapy. We then review progress made in the field of GLP-1 gene therapy for both type 1 and type 2 diabetes.

WHAT THE READER WILL GAIN

Efforts to improve the biological half-life of GLP-1 receptor agonists are discussed. We focus on the development of both viral and non-viral gene delivery methods, highlighting vector designs and the strengths and weaknesses of these approaches. We also discuss the utility of targeting regulated GLP-1 production to tissues including the liver, muscle, islet and gut.

TAKE HOME MESSAGE

GLP-1 is a natural peptide possessing several actions that effectively combat diabetes. Current delivery methods for GLP-1-based drugs are cumbersome and do not recapitulate the normal secretion pattern of the native hormone. Gene therapy offers a useful method for directing long-term production and secretion of the native peptide. Targeted production of GLP-1 using tissue-specific promoters and delivery methods may improve therapeutic efficacy, while also eliminating the burden of frequent injections.

APC and its modifiers in colon cancer

Colon cancer closely follows the paradigm of a single "gatekeeper gene." Mutations inactivating the APC (adenomatous polyposis coli) gene are found in approximately 80% of all human colon tumors and heterozygosity for such mutations produces an autosomal dominant colon cancer predisposition in humans and in murine models. However, this tight association between a single genotype and phenotype belies a complex association of genetic and epigenetic factors that together generate the broad phenotypic spectrum ofboth familial and sporadic colon cancers. In this Chapter, we give a general overview of the structure, function and outstanding issues concerning the role of Apc in human and experimental colon cancer. The availability of increasingly close models for human colon cancer in genetically tractable animal species enables the discovery and eventual molecular identification of genetic modifiers of the Apc-mutant phenotypes, connecting the central role of Apc in colon carcinogenesis to the myriad factors that ultimately determine the course of the disease.

Incretin release from gut is acutely enhanced by sugar but not by sweeteners in vivo

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are released during meals from endocrine cells located in the gut mucosa and stimulate insulin secretion from pancreatic beta-cells in a glucose-dependent manner. Although the gut epithelium senses luminal sugars, the mechanism of sugar sensing and its downstream events coupled to the release of the incretin hormones are not clearly elucidated. Recently, it was reported that sucralose, a sweetener that activates the sweet receptors of taste buds, triggers incretin release from a murine enteroendocrine cell line in vitro. We confirmed that immunoreactivity of alpha-gustducin, a key G-coupled protein involved in taste sensing, is sometimes colocalized with GIP in rat duodenum. We investigated whether secretion of incretins in response to carbohydrates is mediated via taste receptors by feeding rats the sweet-tasting compounds saccharin, acesulfame potassium, d-tryptophan, sucralose, or stevia. Oral gavage of these sweeteners did not reduce the blood glucose excursion to a subsequent intraperitoneal glucose tolerance test. Neither oral sucralose nor oral stevia reduced blood glucose levels in Zucker diabetic fatty rats. Finally, whereas oral glucose increased plasma GIP levels approximately 4-fold and GLP-1 levels approximately 2.5-fold postadministration, none of the sweeteners tested significantly increased levels of these incretins. Collectively, our findings do not support the concept that release of incretins from enteroendocrine cells is triggered by carbohydrates via a pathway identical to the sensation of "sweet taste" in the tongue.

Diabetes mellitus: an opportunity for therapy with stem cells?

In both Type 1 and 2 diabetes, insufficient numbers of insulin-producing beta-cells are a major cause of defective control of blood glucose and its complications. Restoration of damaged beta-cells by endocrine pancreas regeneration would be an ideal therapeutic option. The possibility of generating insulin-secreting cells with adult pancreatic stem or progenitor cells has been investigated extensively. The conversion of differentiated cells such as hepatocytes into beta-cells is being attempted using molecular insights into the transcriptional make-up of beta-cells. Additionally, the enhanced proliferation of beta-cells in vivo or in vitro is being pursued as a strategy for regenerative medicine for diabetes. Advances have also been made in directing the differentiation of embryonic stem cells into beta-cells. Although progress is encouraging, major gaps in our understanding of developmental biology of the pancreas and adult beta-cell dynamics remain to be bridged before a therapeutic application is made possible.

Stem cells, a two-edged sword: Risks and potentials of regenerative medicine

The recent advancements in stem cell (SC) biology have led to the concept of regenerative medicine, which is based on the potential of SC for therapies aimed to facilitate the repair of degenerating or injured tissues. Nonetheless, prior to large scale clinical applications, critical aspects need to be further addressed, including the long-term safety, tolerability, and efficacy of SC-based treatments. Most problematic among the risks of SC-based therapies, in addition to the possible rejection or loss of function of the infused cells, is their potential neoplastic transformation. Indeed, SCs may be used to cure devastating diseases, but their specific properties of self-renewal and clonogenicity may render them prone to generate cancers. In this respect, ‘Stemness’ might be seen as a two-edged sword, its bright side being represented by normal SCs, its dark side by cancer SCs. A better understanding of SC biology will help fulfill the promise of regenerative medicine aimed at curing human pathologies and fighting cancer from its roots.

Stem cell-based therapy in gastroenterology and hepatology

Protagonists of a new scientific era, stem cells are promising tools on which regenerative medicine relies for the treatment of human pathologies. Stem cells can be obtained from various sources, including embryos, fetal tissues, umbilical cord blood, and also terminally differentiated organs. Once forced to expand and differentiate into functional progenies, stem cells may become suitable for cell replacement and tissue engineering. The manipulation and/or stimulation of adult stem cells seems to be particularly promising, as it could improve the endogenous regenerative potential without risks of rejection and overcome the ethical and political issues related to embryonic stem cell research. Stem cells are already leaving the bench and reaching the bedside, despite an incomplete knowledge of the genetic control program driving their fate and plasticity. In gastroenterology and hepatology, the first attempts to translate stem cell basic research into novel therapeutic strategies have been made for the treatment of several disorders, such as inflammatory bowel diseases, diabetes mellitus, celiachy and acute or chronic hepatopaties. Nonetheless, critical aspects need to be further addressed, including the long-term safety, tolerability and efficacy of cell-based treatments, as well as their carcinogenic potential. Aim of this review is to summarize the state-of-the-arts on gastrointestinal and hepatic stem cells and on stem cell-based therapies in gastroenterology and hepatology, highlighting both the benefits and the potential risks of these new tools for the treatment and prevention of human diseases.

Treatment of obesity and diabetes in mice by transplant of gut cells engineered to produce leptin

Leptin injections evoke weight loss by causing a reduction in food consumption and an increase in energy expenditure. Also, the administration of leptin lowers blood glucose levels in some rodent models of diabetes and in humans with lipodystrophy. We explored the therapeutic potential of delivering leptin to obese, diabetic ob/ob mice and to mice fed on a high-fat diet (HFD), by transplanting gut-derived cells engineered to produce leptin, under the regulation of an inducing agent, mifepristone. These cells expressed and released leptin in a mifepristone dose-dependent and time-dependent manner. The engineered cells were either transplanted into the mice under the kidney capsule or were encapsulated in alginate and injected into the intraperitoneal cavity, while mifepristone was delivered by implanting 14-day release pellets. In ob/ob mice, leptin delivery by this method caused a significant reduction in food intake and profound weight loss, which was controllable by adjusting the dose of mifepristone. These transplants also achieved rapid and persistent amelioration of diabetes. However, mice fed on a HFD were resistant to the leptin therapy. These results indicate that gut cells can be modified to express leptin in an inducible manner and that the transplantation of these cells has a therapeutic effect in leptin-deficient mice, but not in mice fed on a HFD.

Modulation of glucagon-like peptide 1 and energy metabolism by inulin and oligofructose: experimental data

Inulin-type fructans have been tested for their capacity to modulate lipid and glucose metabolism in several animal models. Oligofructose (OFS) decreases food intake, fat mass development, and hepatic steatosis in normal and in obese rats; moreover, it exerts an antidiabetic effect in streptozotocin-treated rats and high-fat-fed mice. In most cases, the beneficial effects of OFS are linked to an increase of glucagon-like peptide-1 (GLP-1) level in the portal vein and of GLP-1 and proglucagon mRNA, its precursor, in the proximal colon. In this organ, OFS increases the number of GLP-1-positive L cells by promoting factors (Neurogenin 3 and NeuroD) involved in the differentiation of stem cells into L cells. The chronic administration of GLP-1 receptor antagonist exendin 9-39 totally prevents the beneficial effects of OFS (improved glucose tolerance, fasting blood glucose, glucose-stimulated insulin secretion, insulin-sensitive hepatic glucose production, and reduced body weight gain). Furthermore GLP-1 receptor knockout mice are completely insensitive to the antidiabetic actions of OFS. These findings highlight the potential interest of enhancing endogenous GLP-1 secretion by inulin-type fructans for the prevention/treatment of obesity and type 2 diabetes. Moreover, OFS is also able to modulate other gastrointestinal peptides (such as PYY and ghrelin) that could be involved in the control of food intake. Several studies in humans already support interest in OFS in the control of satiety, triglyceridemia, or steatohepatitis. The link with gut peptides production in humans remains to be proven.

Reversal of streptozotocin-induced diabetes in rats by gene therapy with betacellulin and pancreatic duodenal homeobox-1

Ultrasound-targeted microbubble destruction (UTMD) was used to direct betacellulin (BTC) and pancreatic duodenal homeobox-1 (PDX1) to rat pancreas 48 h after islet destruction by streptozotocin (STZ). Sprague-Dawley rats were rendered diabetic by STZ injection. Controls included normal rats, STZ only without UTMD, and UTMD with DsRed reporter gene. Blood glucose increased dramatically in all rats 48 h after STZ, and continued to rise after UTMD with BTC alone. Blood glucose declined from day 3 to day 10 after UTMD with PDX1, but remained elevated (261+/-8 mg/dl). However, in rats treated with both BTC and PDX1, blood glucose remained below 200 mg/dl throughout day 10. This was accompanied by normalization of blood insulin and C-peptide. Histology demonstrated islet-like clusters of glucagon-staining cells in the rats treated with BTC and PDX1, but these clusters disappeared by 30 days after UTMD treatment. Although regeneration of insulin-producing islets was not seen, diabetes was reversed for up to 15 days after a single UTMD treatment by ectopic insulin production by pancreatic acinar cells. These cells co-expressed amylase and insulin and demonstrated several beta-cell markers by reverse transcription-PCR. Gene therapy by UTMD can reverse diabetes in vivo in adult rats by restoring pancreatic insulin production.

Dietary non-digestible carbohydrates promote L-cell differentiation in the proximal colon of rats

One of the challenges in type 2 diabetes treatment is to ensure pancreas functionality with gut peptides such as glucagon-like peptide-1 (GLP-1). We have recently shown that the endogenous GLP-1 production is promoted by dietary non-digestible carbohydrates (oligofructose), the higher GLP-1 secretion could participate in the control of obesity and associated disorders. This experimental study was designed to highlight the mechanisms of endogenous increase of GLP-1 following non-digestible carbohydrate feeding. Male Wistar rats were fed a standard diet (70.4 g/100 g total carbohydrates; controls) or the same diet supplemented with oligofructose (10 g/100 g diet) for 4 weeks. GLP-1-producing L-cells of the colon were quantified by immunohistochemistry. GLP-1 was quantified by ELISA, and proglucagon, neurogenin 3 and NeuroD mRNA were measured in the colon by quantitative RT-PCR. The number of GLP-1-expressing cells was doubled in the proximal colon of oligofructose-treated rats, a phenomenon correlated with the increase in proglucagon mRNA and peptide content in the tissue. Moreover, oligofructose increased the number of enteroendocrine L-cells in the proximal colon by a mechanism involving up-regulation of two differentiation factors: neurogenin 3 and NeuroD. It is the first demonstration that nutrients fermented in the gut may promote L-cell differentiation in the proximal colon, a phenomenon contributing to a higher endogenous GLP-1 production. These results suggest a new mechanism by which dietary fibres may lower food intake and fat mass development.

Towards stem-cell therapy in the endocrine pancreas

Many approaches of stem-cell therapy for the treatment of diabetes have been described. One is the application of stem cells for replacement of nonfunctional islet cells in the native endogenous pancreas; another one is the use of stem cells as an inexhaustible source for islet-cell transplantation. During recent years three types of stem cells have been investigated: embryonic stem cells, bone-marrow-derived stem cells and organ-bound stem cells. We discuss the advantages and limitations of these different cell types. The applicability for the treatment of dysfunction of beta cells in the pancreas has been demonstrated for all three cell types, but more-detailed understanding of the sequence of events during differentiation is required to produce fully functional insulin-producing cells.

The bioartificial pancreas: progress and challenges

Diabetes remains a devastating disease, with tremendous cost in terms of human suffering and healthcare expenditures. A bioartificial pancreas has the potential as a promising approach to preventing or reversing complications associated with this disease. Bioartificial pancreatic constructs are based on encapsulation of islet cells with a semipermeable membrane so that cells can be protected from the host's immune system. Encapsulation of islet cells eliminates the requirement of immunosuppressive drugs, and offers a possible solution to the shortage of donors as it may allow the use of animal islets or insulin-producing cells engineered from stem cells. During the past 2 decades, several major approaches for immunoprotection of islets have been studied. The microencapsulation approach is quite promising because of its improved diffusion capacity, and technical ease of transplantation. It has the potential for providing an effective long-term treatment or cure of Type 1 diabetes.

Approaches towards endogenous pancreatic regeneration

The phenomenon of pancreatic regeneration in mammals has been well documented. It has been shown that pancreatic tissue is able to regenerate in several species of mammal after surgical insult. This tissue is also known to have the potential to maintain or increase its beta-cell mass in response to metabolic demands during pregnancy and obesity. Since deficiency in beta-cell mass is the hallmark of most forms of diabetes, it is worthwhile understanding pancreatic regeneration in the context of this disease. With this view in mind, this article aims to discuss the potential use in clinical strategies of knowledge that we obtained from studies carried out in animal models of diabetes. Approaches to achieve this goal involve the use of biomolecules, adult stem cells and gene therapy. Various molecules, such as glucagon-like peptide-1, beta-cellulin, nicotinamide, gastrin, epidermal growth factor-1 and thyroid hormone, play major roles in the initiation of endogenous islet regeneration in diabetes. The most accepted hypothesis is that these molecules stimulate islet precursor cells to undergo neogenesis or to induce replication of existing beta-cells, emphasizing the importance of pancreas-resident stem/progenitor cells in islet regeneration. Moreover, the potential of adult stem cell population from bone marrow, umbilical cord blood, liver, spleen, or amniotic membrane, is also discussed with regard to their potential to induce pancreatic regeneration.

New sources of pancreatic beta-cells

Two major initiatives are under way to correct the beta-cell deficit of diabetes: one would generate beta-cells ex vivo that are suitable for transplantation, and the second would stimulate regeneration of beta-cells in the pancreas. Studies of ex vivo expansion suggest that beta-cells have a potential for dedifferentiation, expansion, and redifferentiation. Work with mouse and human embryonic stem (ES) cells has not yet produced cells with the phenotype of true beta-cells, but there has been recent progress in directing ES cells to endoderm. Putative islet stem/progenitor cells have been identified in mouse pancreas, and formation of new beta-cells from duct, acinar and liver cells is an active area of investigation. Peptides, including glucagon-like peptide-1/exendin-4 and the combination of epidermal growth factor and gastrin, can stimulate regeneration of beta-cells in vivo. Recent progress in the search for new sources of beta-cells has opened promising new opportunities and spawned clinical trials.