Development of islet-like cell clusters after pancreas transplantation in the spontaneously diabetic Torri rat

A Comprehensive Review on Preclinical Diabetic Models

BACKGROUND

Preclinical experimental models historically play a critical role in the exploration and characterization of disease pathophysiology. Further, these in-vivo and in-vitro preclinical experiments help in target identification, evaluation of novel therapeutic agents and validation of treatments.

INTRODUCTION

Diabetes mellitus (DM) is a multifaceted metabolic disorder of multidimensional aetiologies with the cardinal feature of chronic hyperglycemia. To avoid or minimize late complications of diabetes and related costs, primary prevention and early treatment are therefore necessary. Due to its chronic manifestations, new treatment strategies need to be developed, because of the limited effectiveness of the current therapies.

METHODS

The study included electronic databases such as Pubmed, Web of Science and Scopus. The datasets were searched for entries of studies up to June, 2018.

RESULTS

A large number of in-vivo and in-vitro models have been presented for evaluating the mechanism of anti-hyperglycaemic effect of drugs in hormone-, chemically-, pathogen-induced animal models of diabetes mellitus. The advantages and limitations of each model have also been addressed in this review.

CONCLUSION

This review encompasses the wide pathophysiological and molecular mechanisms associated with diabetes, particularly focusing on the challenges associated with the evaluation and predictive validation of these models as ideal animal models for preclinical assessments and discovering new drugs and therapeutic agents for translational application in humans. This review may further contribute to discover a novel drug to treat diabetes more efficaciously with minimum or no side effects. Furthermore, it also highlights ongoing research and considers the future perspectives in the field of diabetes.

Phenotypic characterization of a novel type 2 diabetes animal model in a SHANXI MU colony of Chinese hamsters

PURPOSE

Developing animal models for human diseases is critical for studying complex diseases such as type 2 diabetes mellitus (T2DM). Since inbred colonies of Chinese hamsters tend toward spontaneous development of diabetes, we investigated them as a possible model.

METHODS

We regarded individuals with fasting blood glucose (FBG) higher than 6.0 mmol/L and post-prandial blood glucose (PBG) higher than 7.0 mmol/L as diabetic based on the mean and 95% frequency distribution values of FBG and PBG. Diabetic hamsters were characterized based on metabolic profiles, histopathological features, and changes in the expression of genes involved in glucose and lipid metabolism.

RESULTS

Metabolic analyses showed that diabetic hamsters exhibited mild hyperglycemia, hypertriglyceridemia, glucose intolerance, and insulin resistance. Histopathological analysis revealed that cell nuclei migrated inward in skeletal muscle and obvious partial liver lipid deposition and focal necrosis was found. We additionally observed mild injury, atrophy, and occasional vacuolization in islet cells. Changes in the expression of several genes related to glucose and lipid metabolism were observed. Decreased expression of adiponectin and GLUT4 and increased expression of PPARγ, Akt, and leptin was observed in skeletal muscle. Decreased expression of adiponectin with increased expression of PPARγ and leptin was observed in the liver.

CONCLUSIONS

These results indicate that we have established a spontaneous diabetic hamster line that closely mimics human T2DM, which may hold potential for further research on the pathogenesis and treatment of this disease.

Experimental diabetes induced by alloxan and streptozotocin: The current state of the art

Diabetes mellitus is a chronic metabolic disorder with a high prevalence worldwide. Animal models of diabetes represent an important tool in diabetes investigation that helps us to avoid unnecessary and ethically challenging studies in human subjects, as well as to obtain a comprehensive scientific viewpoint of this disease. Although there are several methods through which diabetes can be induced, chemical methods of alloxan- and streptozotocin-induced diabetes represent the most important and highly preferable experimental models for this pathological condition. Therefore, the aim of this article was to review the current knowledge related to quoted models of diabetes, including to this point available information about mechanism of action, particular time- and dose-dependent protocols, frequent problems, as well as major limitations linked to laboratory application of alloxan and sterptozotocin in inducing diabetes. Given that diabetes is known to be closely associated with serious health consequences it is of fundamental importance that current animal models for induction of diabetes should be continuously upgraded in order to improve overall prevention, diagnosis and treatment of this pathological condition.

Basement membrane extract preserves islet viability and activity in vitro by up-regulating α3 integrin and its signal

OBJECTIVE

Survival of transplanted islets is limited partly because of the disruption of the islet basement membrane (BM) occurring during isolation. We hypothesized that the embedment of BM extract (BME) could induce a viable cell mass and prolong islet functionality before transplantation.

METHODS

A special reconstituted BME that solidifies into a gel at 37°C was used to embed isolated islets in this study. The strategy was used to re-establish the interaction between the islets and peri-islet BM.

RESULTS

Islets embedded in BME showed lower caspase-3 levels and higher Akt activity than those in suspension. Moreover, we found for the first time that the expression of α3 integrin and focal adhesion kinase (FAK) and FAK activity was up-regulated in islets after BME embedment. The reverse effect was observed on islet apoptosis when islets rescued from a 24-hour suspension culture were embedded in BME for the next 24 hours. In addition, expression of pancreatic duodenal homeobox factor-1 and phospho-extracellular signal-regulated kinase 1/2 was partially preserved, suggesting the positive effect of BME on islet development.

CONCLUSIONS

These results indicate that BME embedment of islets can up-regulate the expression of α3 integrin and its signal transduction, which may improve islet viability.

Spontaneous type 2 diabetic rodent models

Diabetes mellitus, especially type 2 diabetes (T2DM), is one of the most common chronic diseases and continues to increase in numbers with large proportion of health care budget being used. Many animal models have been established in order to investigate the mechanisms and pathophysiologic progress of T2DM and find effective treatments for its complications. On the basis of their strains, features, advantages, and disadvantages, various types of animal models of T2DM can be divided into spontaneously diabetic models, artificially induced diabetic models, and transgenic/knockout diabetic models. Among these models, the spontaneous rodent models are used more frequently because many of them can closely describe the characteristic features of T2DM, especially obesity and insulin resistance. In this paper, we aim to investigate the current available spontaneous rodent models for T2DM with regard to their characteristic features, advantages, and disadvantages, and especially to describe appropriate selection and usefulness of different spontaneous rodent models in testing of various new antidiabetic drugs for the treatment of type 2 diabetes.

Preservation of islet survival by upregulating α3 integrin signaling: the importance of 3-dimensional islet culture in basement membrane extract

AIM

Islet transplantation is a promising treatment to cure diabetes, but is associated with a high rate of early graft failure. The isolation process leads to the loss of the surrounding extracellular matrix, resulting in eventual islet disintegration and apoptosis. The purpose of this study was to determine the effects on the viability of isolated islets of embedding islets in reconstituted basement membrane extract (BME), which is similar to the normal peri-islet BM composition in vivo.

METHODS

Isolated mouse islets were embedded in BME gel for 24 or 48 hours. Expression of caspase-3, α3, and α5, focal adhesion kinase (FAK), phosphor-FAK, and pancreatic duodenal homeobox factor (PDX)-1 were detected with Western immunoblotting.

RESULTS

Impaired aggregation of single islet cells could only be observed in non-BME medium. Islets embedded in BME gel were partially protected from anoikis showed decreased caspase-3 compared with non-BME islets. We also observed an increase of α3 integrin, FAK protein level, and FAK activity. Furthermore, expression of PDX-1 was preserved at 48 hours, suggesting a positive contribution of BME to β-cell activity.

CONCLUSION

These results indicated that embedding islets in BME can upregulate α3 integrin, which may result in preservation of viability and function of isolated islets.

Oxygenation of the portal vein by intraperitoneal administration of oxygenated perfluorochemical improves the engraftment and function of intraportally transplanted islets

OBJECTIVES

One of the major obstacles for successful intraportal islet transplantation (IPIT) is early graft loss due to hypoxia. We therefore examined the effect of intraperitoneal oxygenated perfluorochemical (PFC) on oxygenation of the portal vein with respect to islet engraftment and function after IPIT in a rat model.

METHODS

First, we measured the oxygen tension and saturation in the portal vein of Lewis rats before and after intraperitoneal injection of oxygenated PFC. Second, blood glucose levels, glucose tolerance, and the number of surviving islets were measured after IPIT with oxygenated PFC (group 1), with PFC saturated by nitrogen (group 2), and without any PFC (control).

RESULTS

Both oxygen tension and saturation in the portal vein significantly increased after injection of oxygenated PFC. In IPIT, the functional success rate in group 1 was 83.3%, compared with 16.7% in group 2 and 16.7% in the control. On the 28th posttransplantation day, the number of engrafted islets in the liver in group 1 (12.8 [SD, 3.3]) was significantly higher than that in group 2 (4.7 [SD, 3.0]) and in the control group (6.5 [SD, 3.3]).

CONCLUSIONS

We clearly demonstrated the effect of intraperitoneal oxygenated PFC on oxygenation of the portal vein, resulting in better IPIT outcomes.

Type 2 diabetes mellitus in a non-obese mouse model induced by Meg1/Grb10 overexpression

We assessed the possibility of C57BL/6-Tg (Meg1/Grb10)isn(Meg1 Tg) mice as a non-obese type 2 diabetes (2DM) animal model. Meg1 Tg mice were born normal, but their weight did not increase as much as normal after weaning and showed about 85% of normal size at 20 weeks of age. Body mass index of Meg1 Tg mice was also smaller than that of control mice. The glucose tolerance test and insulin tolerance test showed that Meg1 Tg mice had reduced ability to normalize the blood glucose level. Blood urea nitrogen (BUN) in Meg1 Tg mice (19.6 +/- 1.2 mg/dl) was significantly lower than in controls (22.0 +/- 0.8 mg/dl), while plasma triglyceride, insulin, adiponectin, and resistin levels were significantly higher (202.0 +/- 23.4 mg/dl vs 146.3 +/- 23.4 mg/dl, 152.4 +/- 16.3 pg/ml vs 88.1 +/- 16.9 pg/ml, 74.4 +/- 10.9 microg/ml vs 48.3 +/- 7.0 microg/ml, and 4.0 +/- 0.2 ng/ml vs 3.6 +/- 0.2 ng/ml, respectively). Body, visceral fat weight and liver weights were significantly lower (19.6 +/- 0.4 g vs 24.3 +/- 0.3 g, 376.7 +/- 29.6 mg to 507.5 +/- 23.0 mg, and 906.0 +/- 41.8 mg to 1,001.0 +/- 15.1 mg, respectively). Thus, hyperinsulinemia observed in Meg1 Tg mice indicates that their insulin signaling pathway is somehow inhibited. With high fat diet, the diabetes onset rate of Meg1 Tg mice increased up to 60%. These results suggest that Meg1 Tg mice resemble human 2DM.

Development of β-Cells in the Native Pancreas After Pancreas Allo-Transplantation in the Spontaneously Diabetic Torii Rat

BACKGROUND

We previously demonstrated the development of beta-cells in the native pancreas after syngeneic pancreas transplantation (PTx) in a model of type 2 diabetes, namely the Spontaneously Diabetic Torii (SDT; RT1 a) rat. In this study, we evaluated the effect of fully allogeneic PTx (allo-PTx) under immunosuppression on the native pancreases in the recipients.

MATERIALS AND METHODS

Diabetic 25-week-old SDT rats were divided into two groups: untreated controls and PTx-treated recipients. Dark Agouti (RT1 a) pancreases were then transplanted into the SDT rats. FK506 was administered daily postoperatively. Each group was examined for 15 weeks.

RESULTS

Control SDT rats showed a disappearance of the pancreatic and duodenal homeobox-1 (PDX-1) expression of the pancreases with the development of diabetes. In addition, the islets were gradually replaced by fibrosis, thus resulting in a marked decrease in the beta-cell mass at 40 weeks of age. On the other hand, in PTx recipients, islet-like cell clusters were found in the native pancreases. The beta-cell mass significantly increased in the native pancreases in the recipients at 10 and 15 weeks posttransplantation in comparison to the age-matched controls. Moreover, we observed the re-expression of PDX-1 in the islet-like cell clusters. Interestingly, insulin and glucagon double-positive stained cells in the mesenchyme and insulin single-positive cells in the ductal epithelium were also observed.

CONCLUSIONS

Our results indicated that the benefits of avoiding glucose toxicity by allo-PTx under immunosuppression could therefore induce the PDX-1 expression in the native pancreases, thus potentially resulting in the development of beta-cells in type 2 diabetic recipients.

Pancreas transplantation using type I and type II spontaneously diabetic rats--our experimental experience

Pancreas transplantation (PTx) is the only therapy that can cure type 1 diabetes mellitus. With the recent advance of surgical procedures and immunosuppression, the outcome of PTx has become better than it used to be before, but some problems still remain. It is rather difficult to induce tolerance and to reverse rejection once it occurred because pancreas graft itself has a strong immunogenicity. Another important issue is regarding the recurrence of autoimmune disease in the pancreatic graft, therefore, some animal models are necessary to delineate and regulate those immune responses specific for PTx. Recently, PTx is also clinically applicable for type 2 diabetic patients with end-stage renal disease. It has been shown that insulin resistance was improved by PTx in type 2 diabetic recipients. In the current study, we have introduced some useful type 1 and type 2 diabetic models mainly based on our experimental experiences.

Dynamic production of hypoxia-inducible factor-1alpha in early transplanted islets

More than half of transplanted beta-cells undergo apoptotic cell death triggered by nonimmunological factors within a few days after transplantation. To investigate the dynamic hypoxic responses in early transplanted islets, syngeneic islets were transplanted under the kidney capsule of balb/c mice. Hypoxia-inducible factor-1alpha (HIF-1alpha) was strongly expressed at post-transplant day (POD) 1, increased on POD 3, and gradually diminished on POD 14. Insulin secretion decreased on POD 3 in association with a significant increase of HIF-1alpha-related beta-cell death, which can be suppressed by short-term hyperbaric oxygen therapy. On POD 7, apoptosis was not further activated by continually produced HIF-1alpha. In contrast, improvement of nerve growth factor and duodenal homeobox factor-1 (PDx-1) production resulted in islet graft recovery and remodeling. In addition, significant activation of vascular endothelial growth factor in islet grafts on POD 7 correlated with development of massive newly formed microvessels, whose maturation is advanced on POD 14 with gradual diminution of HIF-1alpha. We conclude that (1) transplanted islets strongly express HIF-1alpha in association with beta-cell death and decreased insulin production until adequate revascularization is established and (2) early suppression of HIF-1alpha results in less beta-cell death thereby minimizing early graft failure.

In vitro and in vivo improvement of islet survival following treatment with nerve growth factor

BACKGROUND

Nerve growth factor (NGF) has been reported to play an important regulatory role in pancreatic beta-cell function. However, the usefulness of NGF in a transplantation setting is unknown.

METHODS

A marginal number of islet cells (260 islet equivalents/recipient) cultured for 24 hr with NGF (500 ng/ml) was syngeneically transplanted under the kidney capsule of streptozotocin-induced diabetic Balb/c mice. Fluorescence microscopy was used to evaluate islet viability. Islet function was evaluated in vitro and in vivo by static assay and glucose tolerance test, respectively.

RESULTS

In vitro, improved viability and survival were found in murine islets cultured in serum-free medium for 96 hr with 500 ng/ml NGF (P<0.05). NGF-treated islets had more insulin secretion than islets cultured without NGF in response to 2.8 mmol/L glucose (P<0.05), and 20 mmol/L glucose conditions. In vivo, 67% of recipients with a submarginal number of islets cultured in NGF attained normoglycemia for more than 120 days, whereas transplanted islets without NGF treatment survived a maximum of 13 days in control mice. At posttransplant day 4, recipients of NGF-cultured islets showed significant improvement of glucose tolerance. On immunohistochemistry, the kidney capsules containing NGF-cultured islets displayed higher insulin content, and more dilated neoplastic microvessels than control renal capsules. The number of apoptotic cells using TUNEL staining decreased by nearly 50% in NGF-cultured islet grafts in comparison to control islet grafts.

CONCLUSIONS

The above data suggest potential advantages of NGF for islet survival following transplantation. This neurotrophic approach may prove beneficial in human islet transplantation.