Age-dependent reduction in GLUT-2 levels is correlated with the impairment of the insulin secretory response in isolated islets of Sprague-Dawley rats

Isolation of feline islets of Langerhans by selective osmotic shock produces glucose responsive islets

Introduction

Pancreatic islet isolation is essential for studying islet physiology, pathology, and transplantation, and feline islets could be an important model for human type II diabetes mellitus (T2D). Traditional isolation methods utilizing collagenases inflict damage and, in cats, may contribute to the difficulty in generating functional islets, as demonstrated by glucose-stimulated insulin secretion (GSIS). GLUT2 expression in β cells may allow for adaptation to hyperosmolar glucose solutions while exocrine tissue is selectively disrupted.

Methods

Here we developed a protocol for selective osmotic shock (SOS) for feline islet isolation and evaluated the effect of different hyperosmolar glucose concentrations (300 mmol/L and 600 mmol/L) and incubation times (20 min and 40 min) on purity, morphology, yield, and GSIS.

Results

Across protocol treatments, islet yield was moderate and morphology excellent. The treatment of 600 mmol/L glucose solution with 20 min incubation resulted in the highest stimulation index by GSIS.

Discussion

Glucose responsiveness was demonstrated, permitting future in vitro studies. This research opens avenues for understanding feline islet function and transplantation possibilities and enables an additional islet model for T2D.

IL-1beta promotes the age-associated decline of beta cell function

Aging is the prime risk factor for the development of type 2 diabetes. We investigated the role of the interleukin-1 (IL-1) system on insulin secretion in aged mice. During aging, expression of the protective IL-1 receptor antagonist decreased in islets, whereas IL-1beta gene expression increased specifically in the CD45 + islet immune cell fraction. One-year-old mice with a whole-body knockout of IL-1beta had higher insulin secretion in vivo and in isolated islets, along with enhanced proliferation marker Ki67 and elevated size and number of islets. Myeloid cell-specific IL-1beta knockout preserved glucose-stimulated insulin secretion during aging, whereas it declined in control mice. Isolated islets from aged myeloIL-1beta ko mice secreted more insulin along with increased expression of Ins2, Kir6.2, and of the cell-cycle gene E2f1. IL-1beta treatment of isolated islets reduced E2f1, Ins2, and Kir6.2 expression in beta cells. We conclude that IL-1beta contributes the age-associated decline of beta cell function.

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Islets from aged mice have increased IL-1beta and decreased IL-1Ra expression

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Islet immune cells are the source of increased IL-1beta expression during aging

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Myeloid-cell-specific IL-1beta knockout preserves insulin secretion in aged mice

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IL-1beta targets genes regulating insulin secretion and proliferation during aging

Increase of Calcium Sensing Receptor Expression Is Related to Compensatory Insulin Secretion during Aging in Mice

Type 2 diabetes is caused by both insulin resistance and relative insulin deficiency. To investigate age-related changes in glucose metabolism and development of type 2 diabetes, we compared glucose homeostasis in different groups of C57BL/6J mice ranging in age from 4 months to 20 months (4, 8, 12, 16 and 20 months). Interestingly, we observed that non-fasting glucose levels were not significantly changed, but glucose tolerance gradually increased by 20 months of age, whereas insulin sensitivity declined with age. We found that the size of islets and glucose-stimulated insulin secretion increased with aging. However, mRNA expression of pancreatic and duodenal homeobox 1 and granuphilin was decreased in islets of older mice compared with that of 4-month-old mice. Serum calcium (Ca²⁺) levels were significantly decreased at 12, 20 and 28 months of age compared with 4 months and calcium sensing receptor (CaSR) mRNA expression in the islets significantly increased with age. An extracellular calcium depletion agent upregulated CaSR mRNA expression and consequently enhanced insulin secretion in INS-1 cells and mouse islets. In conclusion, we suggest that decreased Ca²⁺ levels and increased CaSR expression might be involved in increased insulin secretion to compensate for insulin resistance in aged mice.

Age-related impairment of pancreatic Beta-cell function: pathophysiological and cellular mechanisms

The incidence of type 2 diabetes significantly increases with age. The relevance of this association is dramatically magnified by the concomitant global aging of the population, but the underlying mechanisms remain to be fully elucidated. Here, some recent advances in this field are reviewed at the level of both the pathophysiology of glucose homeostasis and the cellular senescence of pancreatic islets. Overall, recent results highlight the crucial role of beta-cell dysfunction in the age-related impairment of pancreatic endocrine function and delineate the possibility of new original therapeutic interventions.

Aging does not aggravate the pregnancy-induced adaptations in glucose tolerance in rats

Older age is an assumed risk factor for the development of gestational diabetes mellitus (GDM) in women. Here, we studied the effect of age and pregnancy on fat mass and glucose tolerance in rats. We performed intravenous glucose tolerance tests (IVGTTs) in 3- and 9-month-old rats, either nonpregnant or pregnant (day 20). In addition, we measured maternal fat mass, by dual-energy x-ray absorptiometry, and plasma leptin and lipid levels, as well as fetal parameters, on day 22. Nine-month-old rats had higher fat mass and plasma leptin, cholesterol, and triglyceride concentrations than 3-month-old rats. Glucose levels during the IVGTTs were elevated at several time points in 9-month-old rats, and the area under the curve (AUC) was increased. Pregnancy did not affect fat mass or the AUC for glucose during the IVGTT. The AUC for insulin during the IVGTTs was increased by age as well as pregnancy, but there was no interaction between the two by 2-factor analysis of variance. Reproductive performance was less optimal in 9-month-old rats, with a reduction of individual fetal and placental weight. In conclusion, 9-month-old rats exhibit a deterioration in glucose tolerance, possibly linked to the age-dependent increase in fat mass and leptin concentrations. Pregnancy also comprises certain adaptations in lipid and glucose metabolism, but because no interaction was found between both factors, the effect of pregnancy is not aggravated by aging. This may suggest than an increased gestational diabetes mellitus prevalence in older women can similarly be explained by age as such.

Comparative study on the preventing effects of oral vanadyl sulfate and dietary restriction on the age-related glucose intolerance in rats

BACKGROUND AND AIMS

Aging is associated with a progressive impairment of glucose tolerance. The aim of this study was to explore the protective effects of the chronic oral administration of the insulino-mimetic agent vanadyl sulfate (VOSO4) as compared with those exerted by a long-lasting dietary restriction.

METHODS

Male Sprague-Dawley rats, either fed ad libitum (AL) or subjected to 40% dietary restriction (DR), were used. VOSO4 (0.5 mg/mL drinking water) was administered to a subgroup of AL rats for two months, starting at 16 months of age. Rats were subjected to an intravenous glucose tolerance test (IVGTT) at 16 and 18 months of age. Finally, the beta-cell responsiveness to glucose was evaluated in vitro by the isolated perfused pancreas preparation.

RESULTS

The IVGTT performed in 16-month-old rats showed that DR prevented the development of the moderate glucose intolerance observed in AL rats. The IVGTT performed at 18 months of age confirmed the beneficial effect of DR and showed that VOSO4 was able to prevent the further age-related progression of glucose intolerance observed in AL rats. Pancreas perfusion studies showed that no increase in insulin secretion occurred in both VOSO4-treated and DR rats with respect to the age-matched AL controls, consistently with the in vivo observation of post-loading insulinaemic changes.

CONCLUSIONS

On the basis of these results, we conclude that the beneficial effect of both treatments is mostly related to an improvement of tissue sensitivity to insulin rather than to an insulinotropic effect.

Unique characteristics of the geriatric diabetic population and the role for therapeutic strategies that enhance glucagon-like peptide-1 activity

PURPOSE OF REVIEW

Care for elderly diabetic patients poses a unique clinical challenge. This review highlights distinct aspects of the pathophysiology and the risks for secondary complications in the geriatric diabetic population. Based on these considerations, we discuss emerging therapeutic options based on the actions of the incretin hormone glucagon-like peptide (GLP)-1, which may be ideal for achieving glycemic control in the elderly diabetic patient.

RECENT FINDINGS

Aging is associated with diminished capacity of pancreatic beta-cells to respond to glucose. This functional decline in beta-cell insulin secretion is a major contributor to the development of diabetes in the older patient. In addition, elderly diabetics suffer from a broader range of diabetic complications than do younger diabetics, warranting aggressive glycemic control. GLP-1 is known to improve beta-cell insulin secretion, increase beta-cell mass, and suppress glucagon secretion. Recent studies investigating improved GLP-1 activity have yielded promising results, with improved glycemic control in elderly patients with type 2 diabetes and without significant risk for hypoglycemia.

SUMMARY

Elderly diabetics are a growing subset of the type 2 diabetic population with unique pathophysiologic characteristics and diabetic risk profiles. Therapeutic strategies that incorporate enhancement of GLP-1 action on beta-cells to improve beta-cell insulin secretion and glycemic control may be ideal for this distinct population and should be validated with further long-term clinical studies.