Hyperglycemia induces apoptosis of pancreatic islet endothelial cells via reactive nitrogen species-mediated Jun N-terminal kinase activation

Hyperglycemia significantly stimulates pancreatic islet endothelial cell apoptosis; however, the precise mechanisms are not fully understood. In the present study, treating pancreatic islet endothelial (MS-1) cells with high glucose (30 mmol/l) but not mannitol significantly increased the number of apoptotic cells as compared with a physiological glucose concentration (5.5 mmol/l). Hyperglycemia significantly stimulated the expression of inducible nitric oxide synthase (iNOS) and production of NO and peroxynitrite (ONOO⁻), relevant to MS-1 cell apoptosis. Moreover, induced reactive nitrogen species (RNS) significantly increased the expression of bax, cleaved caspase-3 and poly adenosine diphosphate (ADP)-ribose polymerase (PARP) via JNK activation, but the expression of bcl-2 was not altered. Furthermore, SP600125 (a specific inhibitor of JNK) and 1400W (a specific inhibitor of iNOS) significantly attenuated cell apoptosis induced by high glucose. Therefore, hyperglycemia triggers MS-1 cell apoptosis by activating an intrinsic-dependent apoptotic pathway via RNS-mediated JNK activation.     

Hyperglycemia promotes elevated generation of TXA2 in isolated rat uteri

The relationship between high glucose concentrations and arachidonic acid metabolism in uterine tissue from control and diabetic ovariectomized rats was evaluated. Uterine tissue from diabetic rats produced amounts of PGE₂ and PGF_2α similar to controls, while a lower production of 6-keto-PGF_1α (indicating the production of prostacyclin) and a higher production of TXB₂ (indicating the generation of TXA₂) was found in the diabetic group. A group of diabetic rats was treated with phlorizin to diminish plasma glucose levels. Phlorizin treatment did not alter production of PGE₂, PGF_2α, and 6-keto-PGF_1α in the diabetic group. A diminished production of TXB₂ was found in the treated diabetic uteri when compared to the non-treated diabetic group. Moreover, a positive correlation between plasma glucose levels and uterine TXB₂ generation was observed. When control uterine tissue was exposed in vitro to high concentrations of glucose (22 mM) and compared to control tissue incubated in the presence of glucose 11 mM alterations in the generation of PGE₂, PGF_2α, and 6-keto-PGF_1α were not found, but a higher production of TXB₂ was observed and values were similar to those obtained in the diabetic tissue. Alteration in the production of the prostanoids evaluated were not observed when diabetic tissue was incubated in the presence of high concentrations of glucose. These results provide evidence of a direct relationship between plasma glucose levels and uterine production of TXA₂.     

Regional Cerebral Glucose Utilization During Hyperglycemia

Previous data indicate that regional cerebral blood flow (rCBF) decreases during acute and chronic hyperglycemia. To test the hypothesis that the decrease in rCBF is secondary to a decrease in cerebral metabolic rate, the rate of regional cerebral glucose utilization (rCMRgl) was measured in awake-restrained rats during acute and chronic hyperglycemia. Acute hyperglycemia was produced by intraperitoneal injection of glucose, and chronic hyperglycemia was produced by treatment with streptozotocin. The rCMRgl was measured over a 10-min period using [6-14C]glucose. Glucose utilization was normal during acute hyperglycemia but decreased by 13% following 3 weeks of chronic hyperglycemia. The absence of a decrease in rCMRgl measured during acute hyperglycemia indicates that decreased rCBF cannot be explained by a change in the metabolic rate of the brain. The decrease in rCMRgl measured during chronic hyperglycemia does not necessarily indicate the presence of a drop in the metabolic rate of the brain because ketone bodies are available as an alternate fuel for oxidative metabolism. Therefore, it is unlikely that the decrease in rCMRgl measured during chronic hyperglycemia accounts for decreased rCBF.     

Elevation in plasma glucagon levels in response to stress in squirrel monkeys: comparisons of two subspecies (Saimiri sciureus boliviensis and Saimiri sciureus sciureus)

Bolivian (Bo) and Brazilian (Br) squirrel monkeys (SMs) were captured and restrained to determine patterns of glucagon and glucose response. In both subspecies, plasma glucagon and glucose levels rose rapidly in response to restraint procedures; glucagon levels in BrSMs and glucose levels in both subspecies returned to basal values in 15 minutes. The magnitude of the glucagon and glucose responses differed significantly between BoSMs and BrSMs.     

Effects of ketohexosemia on the ketohexose transport in the small intestine of rats

It was observed previously (Csáky, T.Z. and Fischer, E. (1981) Diabetes 30, 568–574), that sustained hyperglycemia enhances the intestinal transport of aldohexoses; on the other hand, hyperfructosemia affects primarily the transport of fructose. The present study examines in detail the hyperketosemia-induced intestinal ketose transport. Intravenously infused $\text{3-O-}\text{methylfructose}$ produces marked $\text{3-O-}\text{methylfructosemia}$ without concomitant hyperglycemia; in such animals the intestinal transport of both fructose and $\text{3-O-}\text{methylfructose}$ increased. The hyperketosemia-induced increased ketose transport was inhibited by phloretin but only if placed on the serosal compartment. Phlorizin affects neither the basal nor the induced intestinal ketohexose transport. The enhancement of the intestinal ketohexose transport is not sodium-dependent and is not inhibited by ouabain.     

The cardioprotective effect of an aqueous extract of fermented rooibos (Aspalathus linearis) on cultured cardiomyocytes derived from diabetic rats

Diabetic cardiomyopathy (DCM) is a disorder of the heart muscle that contributes to cardiovascular deaths in the diabetic population. Excessive generation of free radicals has been directly implicated in the pathogenesis of DCM. The use of antioxidants, through dietary supplementation, to combat increased cellular oxidative stress has gained popularity worldwide. Aspalathus linearis (rooibos) is a popular herbal tea that contains a novel antioxidant, aspalathin. Literature has reported on the antidiabetic, anti-inflammatory and free radical scavenging effects of rooibos. However, its protective effect against DCM has not been established. Therefore, this study investigated whether chronic exposure to an aqueous extract of fermented rooibos (FRE) has an ex vivo cardioprotective effect on hearts obtained from streptozotocin (STZ) induced diabetic rats. Adult Wistar rats were injected with 40 mg/kg of STZ. Two weeks after STZ injection, cardiomyocytes were isolated and cultured. Cultured cardiomyocytes were treated with FRE (1 and 10 μg/ml), vitamin E (50 μg/ml), and n-acetyl cysteine (1 mM) for 6 h, before exposure to either hydrogen peroxide (H₂O₂) or an ischemic solution. Cardiomyocytes exposed to H₂O₂ or an ischemic solution showed a decrease in metabolic activity and glutathione content with a concomitant increase in apoptosis and intracellular reactive oxygen species. Pretreatment with FRE was able to combat these effects and the observed amelioration was better than the known antioxidant vitamin E. This study provides evidence that an aqueous extract of fermented rooibos protects cardiomyocytes, derived from diabetic rats, against experimentally induced oxidative stress and ischemia.     

Haploinsufficiency in the PPARalpha and LDL receptor genes leads to gender- and age-specific obesity and hyperinsulinemia

When preparing peroxisome proliferator-activated receptor (PPAR)alpha:low-density lipoprotein receptor (LDLR) (-/-) double knockout mice, we unexpectedly found a unique gender- and age-specific obesity in the F1 generation, PPARalpha (+/-):LDLR (+/-), even in mice fed standard chow. Body weights of the male heterozygous mice increased up to about 60 g at 75 weeks of age, then decreased by about 30 g at 100 weeks of age. More than 95% of the heterozygous mice between 35- and 75-week-olds were overweight. Of interest, the obese heterozygous mice also exhibited hyperinsulinemia correlating with moderate insulin resistance. Hepatic gene expression of LDLR was lower than expected in the heterozygous mice, particularly at 50 and 75 weeks of age. In contrast, the hepatic expression of PPARalpha was higher than expected in obese heterozygous mice, but decreased in non-obese older heterozygous mice. Modulated expression of these genes may be partially associated with the onset of the hyperinsulinemia.     

Chronological characterization of diabetes development in male Spontaneously Diabetic Torii rats

To characterize the underlying mechanisms of diabetes development in males of the Spontaneously Diabetic Torii (SDT) rat, a novel spontaneous model for diabetes, we chronologically examined them, focusing on their diabetic features and the pathological changes in the pancreatic islets. Male SDT rats exhibited glucose intolerance with impaired insulin secretion after 14 weeks and developed diabetes with remarkable hyperglycemia and marked hypoinsulinemia after 20 weeks. At prediabetic stage (10-20 weeks), they were normoglycemic, but had significantly lower insulin levels of plasma and pancreas than the normal rats. Their beta-cell volume was already smaller significantly at 10 weeks than that of normal rats. The primary changes of the pancreatic islets were microvascular events such as congestion and hemorrhage at 8-10 weeks. Thereafter, the SDT rat islets were affected with inflammation and progressive fibrosis (at 10-20 weeks), and eventually atrophied with a loss of beta-cells (at 38 weeks). These results indicate that the male SDT rats develop spontaneous diabetes with an absolute decrease in the insulin secretory capacity of the islets.     

Silymarin induces recovery of pancreatic function after alloxan damage in rats

Alloxan has been widely used to produce experimental diabetes mellitus syndrome. This compound causes necrosis of pancreatic beta-cells and, as is well known, induces oxidant free radicals which play a relevant role in the etiology and pathogenesis of both experimental and human diabetes mellitus. Previously we have reported hypoglycemic and antilipoperoxidative actions of silymarin in serum and pancreatic tissue respectively. The aim of this study was to test whether silymarin could reduce the hyperglycemia and revert the pancreatic damage in alloxan treated rats, tested with silymarin in two protocols: using both compounds simultaneously for four or eight doses, or using the compound 20 days after alloxan administration for 9 weeks. Serum glucose and insulin were determined, and pancreatic fragments were used for histology and insulin immunohistochemistry. Pancreatic islets were isolated to assess insulin and Pdx1 mRNA expression by RT-PCR. Our results showed that 72 hours after alloxan administration, serum glucose increased and serum insulin decreased significantly, whereas pancreatic tissue presented morphological abnormalities such as islet shrinkage, necrotic areas, loss of cell organization, widespread lipoid deposits throughout the exocrine tissue, and loss of beta cells, but insulin and glucagon immunoreactivity was scattered if any. In contrast the pancreatic tissue and both insulin and glucose serum levels of rats treated with silymarin were similar to those of control animals. In addition, insulin and glucagon immunoreactive cells patterns in Langerhans islets were also normal, and normal insulin and Pdx1 mRNA expression patterns were detected during pancreatic recovery in Langerhans islets. The overall results suggest that silymarin induces pancreatic function recovery demonstrated by insulin and glucagon expression protein and normoglycemia after alloxan pancreatic damage in rats.