Novel experimental strategies to prevent the development of type 1 diabetes mellitus

Polysaccharide from Hovenia dulcis (Guaizao) improves pancreatic injury and regulates liver glycometabolism to alleviate STZ-induced type 1 diabetes mellitus in rats

Hovenia dulcis is a traditional medicinal and edible plant and has a major geographical presence in China. In this study, a polysaccharide purified from H. dulcis (HDPs-2A) was found to ameliorate type 1 diabetes mellitus (T1DM) in streptozotocin-induced diabetic rat. HDPs-2A treatment resulted in significantly lower fasting blood glucose levels, but higher body weight, plasma insulin, and liver glycogen levels. Moreover, HDPs-2A improved dyslipidemia, pancreatic oxidative stress, and reduced serum pro-inflammatory factors. In addition, HDPs-2A up-regulated PDX-1, activated and up-regulated IRS2 expression, and regulated apoptosis and regeneration of islet β cells to recover islet β-cell function injury in TIDM rats. HDPs-2A also up-regulated the expression of pancreatic GK and GLUT2 to improve insulin secretion ability of islet β-cells, ultimately improving the glucose metabolism disorder of T1DM rats. Moreover, HDPs-2A significantly up-regulated the expression of GK and down-regulated the expression of G6Pase in liver to improve liver glycogen synthesis, inhibit liver gluconiogenesis, and improve liver glucose metabolism disorder of T1DM rats. In summary, the hypoglycemic mechanisms of HDPs-2A may include regulating the regeneration and apoptosis of islet β-cells and activating liver glycometabolism-related signaling pathways in T1DM rats.

Designing an Engineered Construct Gene Sensitive to Carbohydrate In-vitro and Candidate for Human Insulin Gene Therapy In-vivo

Diabetes is a common disorder worldwide, and exhaustive efforts have been made to cure this disease. Gene therapy has been considered as a potential curative method that has had more stability in comparison with other pharmaceutical methods. However, the application of gene therapy as a definitive treatment demands further investigation. This study is aimed to prepare a suitable high- performance vector for gene therapy in diabetes mellitus. The designed vector has had prominent characteristics, such as directed replacement, which makes it a suitable method for treating or preventing other genetic disorders. The whole rDNA sequence of the human genome was scanned. The 800 bp two homology arms were digested by EcoRI, synthesized and cloned into the pGEM-B1 plasmid (prokaryotic moiety). The carbohydrate sensitive promoter, L-pyruvate kinase, and insulin gene were sub-cloned between homologous arms (eukaryotic moiety). The PGEM-B1 plasmid was digested by EcoRI, and the eukaryotic fragments were purified and transfected into Hela cell and then cultured. Afterward, the 300 µg/mL of glucose were added to the culture medium. Insulin expression in the transfected cells with 200 and 400 ng of the construct in comparison with negative control was detected using western blot and ELISA methods. Results have shown insulin expression in different glucose concentrates.

Babul (Acacia nilotica)

Purpose

– The prevalence of diabetes has increased manifold and now become a public health problem from being mild disorder. There is a need to discover more effective and safer antidiabetic agents by utilizing the rich heritage of medicinal plants. Tannins are polyphenols that are obtained from various parts of different plants belonging to multiple species and considered as potential drugs for the treatment of non-insulin-dependent diabetes mellitus. The paper aims to discuss these issues.

Design/methodology/approach

– The study was conducted in three phases: incorporation of Babul powder in biscuits: assessment of Glycemic Index (GI): suitability of Babul powder on diabetic subjects statistical analysis: area under curve (AUC) for increase in blood glucose was calculated by trapezoidal rule and means were tested for significance by paired t-test. Mean glucose levels of all subjects were calculated for each time point. p<0.05 was considered statistically significant.

Findings

– Tannins are polyphenols that are obtained from various parts of different plants belonging to multiple species. As an indigenous plant of Rajasthan, Babul contains high amount of tannin levels ranging from 18 to 27 percent in deseeded pods from ssp. indica, whereas ssp. nilotica reached up to 50 percent. Hence, Babul was selected as the source of tannin and subjected to diabetics for its suitability. The study concluded that Babul powder is effective in management of blood glucose levels even the simple sugars also and can be considered as suitable for diabetics. The active component for the purpose may be the presence of tannin in the Babul.

Research limitations/implications

– The study was conducted on limited number of subjects. A confirmation study is suggested on the diabetic population.

Originality/value

– The prevalence of diabetes is rapidly rising all over the globe at an alarming rate. Over few decades, the status of diabetes has changed from being considered as a mild disorder of the elderly to one of the major causes of morbidity and mortality affecting the youth and middle-aged people. Therefore, the present study focused on the development of tannin-based nutraceutical for incorporation in common foods and its health-promoting effect on diabetes.

Macrophage migration inhibitory factor deficiency protects pancreatic islets from cytokine-induced apoptosis in vitro

During pathogenesis of diabetes, pancreatic islets are exposed to high levels of cytokines and other inflammatory mediators that induce deterioration of insulin-producing beta cells. Macrophage migration inhibitory factor (MIF) plays a key role in the onset and development of several immunoinflammatory diseases and also controls apoptotic cell death. Because the occurrence of apoptosis plays a pathogenetic role in beta cell death during type 1 diabetes development and MIF is expressed in beta cells, we explored the influence of MIF deficiency on cytokine-induced apoptosis in pancreatic islets. The results indicated clearly that elevated MIF secretion preceded C57BL/6 pancreatic islets death induced by interferon (IFN)-γ + tumour necrosis factor (TNF)-α + interleukin (IL)-1β. Consequently, MIF-deficient [MIF-knock-out (KO)] pancreatic islets or islet cells showed significant resistance to cytokine-induced death than those isolated from C57BL/6 mice. Furthermore, upon exposure to cytokines pancreatic islets from MIF-KO mice maintained normal insulin expression and produced less cyclooxygenase-2 (COX-2) than those from wild-type C57BL6 mice. The final outcome of cytokine-induced islet apoptosis in islets from wild-type mice was the activation of mitochondrial membrane pore-forming protein Bcl-2-associated X protein and effector caspase 3. In contrast, these apoptotic mediators remained at normal levels in islets from MIF-KO mice suggesting that MIF absence prevented initiation of the mitochondrial apoptotic pathway. Additionally, the protection from apoptosis was also mediated by up-regulation of prosurvival kinase extracellular-regulated kinase 1/2 in MIF-KO islets. These data indicate that MIF is involved in the propagation of pancreatic islets apoptosis probably via nuclear factor-κB and mitochondria-related proteins.

Altered redox homeostasis in human diabetes saliva

BACKGROUND

Oxidative stress has been implicated in the pathogenesis of diabetes mellitus (DM). Levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), 8-epi-prostaglandin-F(2α) (8-epi-PGF2α), and total protein carbonyls were measured to assess whether DM is associated with altered salivary redox homeostasis.

METHODS

A total of 215 patients with diabetes and 481 healthy controls were recruited from the Department of Endocrinology at the Jewish General Hospital in Montreal. Levels of oxidative biomarkers were assayed using enzyme-linked immunosorbent assay (ELISA) in whole unstimulated saliva. Associations of the redox data with exposure to insulin, metformin and dietary control were assessed by logistic regression analyses.

RESULTS

We observed (i) significantly higher mean levels of 8-OHdG and protein carbonyls in whole unstimulated saliva of patients with diabetes compared to controls, (ii) higher mean levels of protein carbonyls in type 1 diabetes as well as higher mean levels of 8-OHdG and protein carbonyls in type 2 diabetes compared to controls, (iii) elevated levels of protein carbonyls in diet-controlled patients and in patients with diabetes on insulin and metformin, (iv) elevated levels of 8-OHdG in patients on metformin, and (v) significant associations between subjects with DM and salivary 8-OHdG and protein carbonyls.

CONCLUSION

DM is associated with increased oxidative modification of salivary DNA and proteins. Salivary redox homeostasis is perturbed in DM and may inform on the presence of the disease and efficacy of therapeutic interventions.

PK11195, a specific ligand of the peripheral benzodiazepine receptor, may protect pancreatic beta-cells from cytokine-induced cell death

We cultured isolated islets from human or porcine origin in the presence or absence of IL1 and TNFα and studied cytoprotective effects of two structurally different PBR ligands. Storage of pig or human islets in the presence of cytokines significantly lowered the fraction of vital beta-cells. Compared with cytokine incubations PK11195 alone or in combination with cytokines was effective to prevent cytokine induced cell death. The data indicate that cold storage in the presence of PK11195 may further protect beta-cells from cytokine induced cell death. This ligand may be helpful to preserve beta-cell survival before transplantation.

The protective effect of simvastatin against low dose streptozotocin induced type 1 diabetes in mice is independent of inhibition of HMG-CoA reductase

Besides a cholesterol-lowering effect, simvastatin possesses anti-inflammatory properties attributed to inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and/or direct binding to, and inhibition of, the integrin lymphocyte function associated antigen-1 (LFA-1). We have shown that simvastatin protects against multiple low dose streptozotocin (MLDS) induced type 1 diabetes in mice. Presently, we examined if this effect could be abolished by co-administration of mevalonic acid, thus determining if the protective effect is dependent or independent of inhibition of HMG-CoA reductase. Mevalonic acid did not affect the protective effect of simvastatin against MLDS diabetes. Moreover, spleens from these mice did not show any signs of toxic side-effects, thus excluding the possibility that the protective effect is secondary to a general inflammatory response. We suggest that simvastatin's protective effect mainly is independent of HMG-CoA reductase inhibition. This implies that inhibition of LFA-1 activation is important for the protective effect exerted by simvastatin.

Mouse models and the genetics of diabetes: is there evidence for genetic overlap between type 1 and type 2 diabetes?

In humans, both type 1 and type 2 diabetes exemplify genetically heterogeneous complex diseases in which epigenetic factors contribute to underlying genetic susceptibility. Extended human pedigrees often show inheritance of both diabetes types. A common pathophysiological denominator in both disease forms is pancreatic beta-cell exposure to proinflammatory cytokines. Hence, it is intuitive that systemically expressed genes regulating beta-cell ability to withstand chronic diabetogenic stress may represent a component of shared susceptibility to both major disease forms. In this review, the authors assemble evidence from genetic experiments using animal models developing clearly distinct diabetes syndromes to inquire whether some degree of overlap in genes contributing susceptibility can be demonstrated. The conclusion is that although overlap exists in the pathophysiological insults leading to beta-cell destruction in the currently studied rodent models, the genetic bases seem quite distinct.

Susceptibility to streptozotocin-induced diabetes is mapped to mouse chromosome 11

To study the contribution of beta-cell vulnerability to susceptibility to diabetes, we studied beta-cell vulnerability to a single high dose of streptozotocin (STZ) in an animal model of type 2 diabetes, the NSY mouse, a sister strain of the STZ-sensitive NOD mouse, in comparison with the STZ-resistant C3H mouse. NSY mice were found to be extremely sensitive to STZ. Introgression of a single Chr 11, where STZ-sensitivity was mapped in the NOD mouse, from NSY mice converted STZ-resistant C3H mice to STZ-sensitive. Two nucleotide substitutions were identified in the nucleoredoxin gene, a positional and functional candidate gene for STZ-induced diabetes on Chr 11. These data, together with the co-localization of type 1 (Idd4) and type 2 (Nidd1n) susceptibility genes on Chr 11, suggest that the intrinsic vulnerability of pancreatic beta cells is determined by a gene or genes on Chr 11, which may also contribute to susceptibility to spontaneous diabetes.

Diabetes, oxidative stress, and antioxidants: a review

Increasing evidence in both experimental and clinical studies suggests that oxidative stress plays a major role in the pathogenesis of both types of diabetes mellitus. Free radicals are formed disproportionately in diabetes by glucose oxidation, nonenzymatic glycation of proteins, and the subsequent oxidative degradation of glycated proteins. Abnormally high levels of free radicals and the simultaneous decline of antioxidant defense mechanisms can lead to damage of cellular organelles and enzymes, increased lipid peroxidation, and development of insulin resistance. These consequences of oxidative stress can promote the development of complications of diabetes mellitus. Changes in oxidative stress biomarkers, including superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase, glutathione levels, vitamins, lipid peroxidation, nitrite concentration, nonenzymatic glycosylated proteins, and hyperglycemia in diabetes, and their consequences, are discussed in this review. In vivo studies of the effects of various conventional and alternative drugs on these biomarkers are surveyed. There is a need to continue to explore the relationship between free radicals, diabetes, and its complications, and to elucidate the mechanisms by which increased oxidative stress accelerates the development of diabetic complications, in an effort to expand treatment options.

Interleukin-1beta swiftly down-regulates UCP-2 mRNA in beta-cells by mechanisms not directly coupled to toxicity

Regulation of uncoupling protein-2 (UCP-2) in beta-cells is presently unclear but may involve oxidative stress. We tested for regulation by beta-cell toxic cytokines. Exposure to interleukin-1beta (IL-1beta, 10 ng/ml) for 6 h down-regulated UCP-2 mRNA in clonal INS-1 cells, by 37 +/- 7%, and in rat pancreatic islets, by 55 +/- 8%. In contrast, a 6 h exposure to IL-1beta did not affect viability as assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, or mitochondrial membrane potential, or ATP cellular contents. Continued exposure to IL-1beta was accompanied by decreased viability and persisting down-regulation of UCP-2 mRNA. Exposure to a combination of IL-1beta and tumor necrosis factor (TNF)-alpha for 48 h additively decreased cell viability and UCP-2 mRNA. The constitutive nitric oxide (NO) synthase inhibitor N-omega-nitro-L-arginine methyl ester (L-NAME, 1 mM) partially protected against toxicity but failed to significantly affect UCP-2 mRNA expression. The inducible NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 1 mM) protected completely against cytokine-induced toxicity. L-NMMA per se down-regulated UCP-2 mRNA (by 64 +/- 7%). Transfection with a UCP-2-antisense nucleotide failed to affect IL-1beta induced toxicity. In conclusion, down-regulation of UCP-2 mRNA by IL-1beta is an early event of cytokine interaction with beta-cells which is not directly coupled to toxicity.

Hepatocyte growth factor preserves beta cell mass and mitigates hyperglycemia in streptozotocin-induced diabetic mice

Type I diabetes is an autoimmune disease that results in destructive depletion of the insulin-producing beta cells in the islets of Langerhans in pancreas. With the knowledge that hepatocyte growth factor (HGF) is a potent survival factor for a wide variety of cells, we hypothesized that supplementation of HGF may provide a novel strategy for protecting pancreatic beta cells from destructive death and for preserving insulin production. In this study, we demonstrate that expression of the exogenous HGF gene preserved insulin excretion and mitigated hyperglycemia of diabetic mice induced by streptozotocin. Blood glucose levels were significantly reduced in mice receiving a single intravenous injection of naked HGF gene at various time points after streptozotocin administration. Consistently, HGF concomitantly increased serum insulin levels in diabetic mice. Immunohistochemical staining revealed a marked preservation of insulin-producing beta cells by HGF in the pancreatic islets of the diabetic mice. This beneficial effect of HGF was apparently mediated by both protection of beta cells from death and promotion of their proliferation. Delivery of HGF gene in vivo induced pro-survival Akt kinase activation and Bcl-xL expression in the pancreatic islets of diabetic mice. These findings suggest that supplementation of HGF to prevent beta cells from destructive depletion and to promote their proliferation might be an effective strategy for ameliorating type I diabetes.