Assay for high glucose-mediated islet cell sensitization to apoptosis induced by streptozotocin and cytokines

Epigallocatechin gallate attenuated high glucose-induced pancreatic beta cell dysfunction by modulating DRP1-mediated mitochondrial apoptosis pathways

Long-term exposure to hyperglycemic conditions leads to β-cell dysfunction, particularly mitochondrial dysfunction, and inflammatory and oxidative stress responses, which are considered the primary causes of β-cell death and the hallmarks of diabetes. Plant-active ingredients may play a key role in glycemic control. Epigallocatechin gallate (EGCG) is a characteristic catechin derived from tea that possesses anti-diabetic properties. Nonetheless, its underlying mechanisms remain elusive. Herein, the protective role of EGCG on high glucose (33 mM)-induced pancreatic beta cell dysfunction and its possible molecular mechanisms were investigated. Briefly, MIN6 cells were treated with glucose and EGCG (10 µM, 20 µM, and 40 µM) for 48 h. Our results revealed that EGCG dose-dependently restored mitochondrial membrane potential and concomitantly alleviated cell apoptosis. Mechanistically, the expression level of apoptotic protein BAX and Dynamic related protein 1 (DRP1) was significantly downregulated following EGCG treatment, whereas that of the anti-apoptotic protein BCL-2 was significantly upregulated. Taken together, EGCG alleviated high glucose-induced pancreatic beta cell dysfunction by targeting the DRP1-related mitochondrial apoptosis pathway and thus can serve as a nutritional intervention for the preservation of beta cell dysfunction in patients with type 2 diabetes mellitus.

Nanoformulated natural therapeutics for management of streptozotocin-induced diabetes: potential use of curcumin nanoformulation

Aim: The goal of this study was to improve curcumin (CUR) aqueous solubility and bioavailability via nanoformulation, and then study its activity and mechanism of action as an antidiabetic agent. Methods: CUR-loaded pluronic nanomicelles (CURnp) were prepared and characterized. Biochemical assessments were performed as well as histological, confocal and RTPCR studies on pancreatic target tissues. Results: CURnp with a diameter of 333 ± 6 nm and ζ potential of -26.1 mv were obtained. Antidiabetic action of CURnp was attributed to significant upregulation of Pdx-1 and NKx6.1 gene expression and achievement of optimum redox balance, which led to alleviation of streptozotocin-induced β-cell damage via a significant upregulation in insulin gene expression proved by RTPCR studies and by the presence of 40% insulin positive cells through confocal microscope studies on pancreatic tissue.

A newly developed silymarin nanoformulation as a potential antidiabetic agent in experimental diabetes

Aim: This study aimed to develop a new stable nanoformulation of silymarin (SM) with optimum enhanced oral bioavailability and to evaluate its effect as well as mechanism of action as a superior antidiabetic agent over native SM using streptozotocin-induced diabetic rats. Materials and methods: SM-loaded pluronic nanomicelles (SMnp) were prepared and fully characterized. Biochemical parameters were performed as well as histological, confocal and reverse-transcription polymerase chain reaction studies on pancreatic target tissues. Results & conclusion: SMnp were found to improve significantly the antihyperglycemic, antioxidant and antihyperlipidemic properties as compared with native SM. In addition, SMnp was found to be a more efficient agent over SM in the management of diabetes and its associated complications due to its superior bioavailability in vivo, and the controlled release profile of SM.

[Formula: see text]

Toward closing the loop: an update on insulin pumps and continuous glucose monitoring systems

This article reviews current pump and continuous glucose monitoring therapy and what will be required to integrate these systems into closed-loop control. Issues with sensor accuracy, lag time, and calibration are discussed as well as issues with insulin pharmacodynamics, which result in a delayed onset of insulin action in a closed-loop system. A stepwise approach to closed-loop therapy is anticipated, where the first systems will suspend insulin delivery based on actual or predicted hypoglycemia. Subsequent systems may control to range, limiting the time spent in hyperglycemia by mitigating the effects of a missed food bolus or underestimate of consumed carbohydrates, while minimizing the risk of hypoglycemia.

Transfection of rat pancreatic islet tissue by polymeric gene vectors

BACKGROUND

In vitro genetic modification has been regarded as one option to improve the viability and functionality of pancreatic islets when used for transplantation in patients with diabetes, either as naked islets or in a type of bioartificial pancreas. In this approach, vector safety and poor transfection efficiency are major concerns.

METHODS

In this study, the influence of in vitro transfection conditions on polyplexes constructed of polyethyleneimine (PEI) and plasmid DNA (pDNA) on the transfection efficiency was investigated by varying the transfection medium, the pDNA dose, and the amines of polycation/phosphates of pDNA (N/P) ratio.

RESULTS

Ca2+-containing Krebs-Ringer-HEPES medium was more effective than RPMI 1640 medium by increasing transfection efficiency (2.5-fold). An increase in pDNA dose slightly reduced the transfection efficiency but had minimal influence on islet loss. However, the N/P ratio had a large effect on islet viability and transfection efficiency. For example, the PEI/pDNA ratio at N/P = 10 caused greater islet loss (56% vs. 28%) and 30-fold less transfection efficiency than at N/P = 5. Even under a set of best conditions selected from this study, mostly a fraction of cells located in the peripheral regions of an islet were transfected, and the viability and insulin secretion from the treated islets were not altered. However, it was found that the extent of apoptosis was noticeably higher (approximately 16%) than in untreated islets (approximately 2%).

CONCLUSIONS

These results suggest that the gene delivery efficacy to isolated islets can be improved by manipulating the transfection conditions. Polymeric vectors will broaden the options for islet transfection, which is currently limited to viral vectors.

Heat shock protein 27 overexpression mitigates cytokine-induced islet apoptosis and streptozotocin-induced diabetes

Beta-cell apoptosis occurs in diabetes mellitus (DM). Heat shock protein (HSP) 27 (human homolog of rodent HSP25) mitigates stress-induced apoptosis but has not been studied in beta-cells. We tested whether HSP27 overexpression attenuates streptozotocin (SZ)-induced DM in vivo and cytokine-induced islet apoptosis in vitro. DM was ascertained by ip glucose tolerance testing, and fasting serum insulin/glucose was measured. Pancreas was stained for insulin, HSP27, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling, and insulin content was measured. HSP25/27 was measured by immunoblotting, isoelectric focusing, and RT-PCR. Islet HSP25/27 oligomerization and inhibitory kappaB protein kinase gamma (nuclear factor kappaB essential modulator) binding were assessed by coimmunoprecipitation. HSP27 transgene (TG) in pancreas localized predominantly in beta-cells. Baseline pancreatic insulin levels in wild-type (WT) and HSP27TG mice were similar, but lower in WT than HSP27TG after SZ (P < 0.01). Intraperitoneal glucose tolerance testing confirmed protection from SZ-DM in HSP27TG. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and inducible nitric oxide synthase staining were increased in WT vs. HSP27TG islets (P < 0.05) after SZ. Caspase-3 activity was lower in islets from HSP27TG vs. WT mice after cytokine stress in vitro (P < 0.05). There was more HSP25 plus 27 protein from HSP27TG islets than HSP25 from WT (P < 0.01). HSP25 protein but not mRNA was increased in HSP27TG mice. Isoelectric focusing showed similar relative HSP phosphorylation in HSP27TG and WT (P > 0.05). HSP27 bound native HSP25 in TG islets; both bound to inhibitory kappaB protein kinase gamma (nuclear factor kappaB essential modulator). These data show islet protection by HSP27 by mitigation of apoptosis, possibly through nuclear factor kappaB regulation.