Effects of beta-carotene on oxidative stress in normal and diabetic rats

Increasing interest in the role of oxidative stress and beta-carotene in disease and prevention led us to examine the results of beta-carotene's administration in diabetic rats, a model for high-oxidative stress. In this experiment, amounts of lipid peroxidation, glutathione, and glutathione disulfide, and activity levels of catalase, glutathione peroxidase, glutathione reductase, superoxide dismutase, and gamma-glutamyl transpeptidase were measured in the liver, kidney, and heart of Sprague-Dawley rats with streptozotocin-induced diabetes, and after treatment with 10 mg/kg/day of beta-carotene for 14 days. Beta-carotene treatment resulted in the reversal of the diabetes-induced increase in hepatic and cardiac catalase activity, the decreased levels of glutathione disulfide in the heart, and the increased cardiac and renal levels of lipid peroxidation. Treatment with beta-carotene exacerbated the increased glutathione peroxidase activity in the heart and the decreased catalase activity in the kidneys. In contrast to reduced hepatic glutathione levels in untreated diabetic rats, beta-carotene treatment increased glutathione levels in diabetic rats. Increased hepatic gamma-glutamyl transpeptidase activity in diabetic rats was not reduced by treatment. Thus, beta-carotene therapy for 14 days prevented/reversed some, but not all, diabetes-induced changes in oxidative stress parameters.     

Diabetic changes in the redox status of the microsomal protein folding machinery

Changes in assisted protein folding are largely unexplored in diabetes. In the present studies, we have identified a reductive shift in the redox status of rat liver microsomes after 4 weeks of streptozotocin-induced diabetes. This change was reflected by a significant increase in the total- and protein-sulfhydryl content, as well as in the free sulfhydryl groups of the major protein disulfide isomerases (PDIs), the 58 kDa PDI and the 57 kDa ERp57 but not other chaperones. A parallel decrease of the protein-disulfide oxidoreductase activity was detected in the microsomal fraction of diabetic livers. The oxidant of PDI, Ero1-Lalpha showed a more oxidized status in diabetic rats. Our results reveal major changes in the redox status of the endoplasmic reticulum and its redox chaperones in diabetic rats, which may contribute to the defective protein secretion of the diabetic liver.     

Effect of Eugenia Jambolana seed kernel on antioxidant defense system in streptozotocin-induced diabetes in rats

Increased oxidative stress has been suggested to be involved in the pathogenesis and progression of diabetic tissue damage. The aim of this study was to investigate the effect of ethanolic extract of Eugenia jambolana seed kernel on antioxidant defense systems of plasma and pancreas in streptozotocin-induced diabetes in rats. The levels of glucose, vitamin-C, vitamin-E, ceruloplasmin, reduced glutathione and lipidperoxides were estimated in plasma of control and experimental groups of rats. The levels of lipidperoxides, reduced glutathione and activities of superoxide dismutase, catalase and glutathione peroxidase were assayed in pancreatic tissue of control and experimental groups of rats. A significant increase in the levels of plasma glucose, vitamin-E, ceruloplasmin, lipid peroxides and a concomitant decrease in the levels of vitamin-C, reduced glutathione were observed in diabetic rats. The activities of pancreatic antioxidant enzymes were altered in diabetic rats. These alterations were reverted back to near normal level after the treatment with Eugenia jambolana seed kernel and glibenclamide. Histopathological studies also revealed that the protective effect of Eugenia jambolana seed kernel on pancreatic beta-cells. The present study shows that Eugenia jambolana seed kernel decreased oxidative stress in diabetic rats, which inturn may be due to its hypoglycemic property.     

Antihyperglycemic effect of fraxetin on hepatic key enzymes of carbohydrate metabolism in streptozotocin-induced diabetic rats

Epidemiological studies have demonstrated that the diabetes mellitus is a serious health burden for both governments and healthcare providers. The present study was hypothesized to evaluate the antihyperglycemic potential of fraxetin by determining the activities of key enzymes of carbohydrate metabolism in streptozotocin (STZ) – induced diabetic rats. Diabetes was induced in male albino Wistar rats by intraperitoneal administration of STZ (40 mg/kg b.w). Fraxetin was administered to diabetic rats intra gastrically at 20, 40, 80 mg/kg b.w for 30 days. The dose 80 mg/kg b.w, significantly reduced the levels of blood glucose and glycosylated hemoglobin (HbA1c) and increased plasma insulin level. The altered activities of the key enzymes of carbohydrate metabolism such as glucokinase, glucose-6-phosphate dehydrogenase, glucose-6-phosphatase, fructose-1,6-bisphosphatase and hepatic enzymes (aspartate transaminase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP)) in the liver tissues of diabetic rats were significantly reverted to near normal levels by the administration of fraxetin. Further, fraxetin administration to diabetic rats improved body weight and hepatic glycogen content demonstrated its antihyperglycemic potential. The present findings suggest that fraxetin may be useful in the treatment of diabetes even though clinical studies to evaluate this possibility may be warranted.     

Phlorizin Pretreatment Reduces Acute Renal Toxicity in a Mouse Model for Diabetic Nephropathy

Streptozotocin (STZ) is widely used as diabetogenic agent in animal models for diabetic nephropathy (DN). However, it is also directly cytotoxic to kidneys, making it difficult to distinguish between DN-related and STZ-induced nephropathy. Therefore, an improved protocol to generate mice for DN studies, with a quick and robust achievement of the diabetic state, without direct kidney toxicity is required. To investigate the mechanism leading to STZ-induced nephropathy, kidney damage was induced with a high dose of STZ. This resulted in delayed gastric emptying, at least partially caused by impaired desacyl ghrelin clearance. STZ uptake in the kidneys is to a large extent mediated by the sodium/glucose cotransporters (Sglts) because the Sglt inhibitor phlorizin could reduce STZ uptake in the kidneys. Consequently, the direct toxic effects in the kidney and the gastric dilatation were resolved without interfering with the β-cell toxicity. Furthermore, pancreatic STZ uptake was increased, hereby decreasing the threshold for β-cell toxicity, allowing for single low non-nephrotoxic STZ doses (70 mg/kg). In conclusion, this study provides novel insights into the mechanism of STZ toxicity in kidneys and suggests a more efficient regime to induce DN with little or no toxic side effects.     

Transplanting fragments of diabetic pancreas into activated omentum gives rise to new insulin producing cells

To determine if pancreatic progenitor cells can be induced to form insulin producing cells in vivo, we auto-transplanted fragments of streptozotocin-induced diabetic pancreas into omentum pre-injected with a foreign material. As shown previously, omentum pre-activated in this manner becomes rich in growth factors and progenitor cells. After auto-transplanting diabetic pancreas in the activated omentum, new insulin secreting cells appeared in the omentum in niches surrounding the foreign particles--a site previously shown to harbor progenitor cells. Extracts of these omenta contained measurable insulin. Four of eight diabetic animals treated in this manner became normoglycemic. This shows that new insulin producing cells can be regenerated from diabetic pancreas by auto-transplanting pancreatic fragments into the activated omentum, an environment rich in growth factors and progenitor cells.     

Reduced Brain Antioxidant Capacity in Rat Models of Betacytotoxic-Induced Experimental Sporadic Alzheimer’s Disease and Diabetes Mellitus

It is believed that oxidative stress (OS) plays a central role in the pathogenesis of metabolic diseases like diabetes mellitus (DM) and its complications (like peripheral neuropathy) as well as in neurodegenerative disorders like sporadic Alzheimer’s disease (sAD). Representative experimental models of these diseases are streptozotocin (STZ)-induced diabetic rats and STZ-intracerebroventricularly (STZ-icv) treated rats, in which antioxidant capacity (AC) against peroxyl (ORAC_-ROO ^•) and hydroxyl (ORAC_-OH ^•) free radicals (FR) was measured in three different brain regions: the hippocampus (HPC), the cerebellum (CB), and the brain stem (BS) by means of oxygen radical absorbance capacity (ORAC) assay. In the brain of both STZ-induced diabetic and STZ-icv treated rats decreased AC has been found demonstrating regionally specific distribution. In the diabetic rats these abnormalities were not associated with the development of peripheral diabetic neuropathy (PDN). Also, these abnormalities were not prevented by the intracerebroventricularly (icv) pretreatment of glucose transport inhibitor 5–thio-d-glucose (TG) in the STZ-icv treated rats, suggesting different mechanism of STZ-induced central effects from those at the periphery. Similarities of the OS alterations in the brain of STZ-icv rats and humans with sAD could be useful in the search for the new drugs in the treatment of sAD that have antioxidant activity. In the STZ-induced diabetic animals the existence of PDN was tested by the paw pressure test, 3 weeks following the diabetes induction. Mechanical nociceptive thresholds were measured three times at 10–min intervals by applying increased pressure to the hind paw until the paw-withdrawal or overt struggling was elicited. Only those diabetic animals which demonstrated decreased withdrawal threshold values in comparison with the control non-diabetic animals (C) were considered to have developed the PDN. Special issue dedicated to Dr. Moussa Youdim.     

Glucosamine-induced increase in Akt phosphorylation corresponds to increased endoplasmic reticulum stress in astroglial cells

Increased glucose flux through the hexosamine biosynthetic pathway (HBP) is known to affect the activity of a number of signal transduction pathways and lead to insulin resistance. Although widely studied in insulin responsive tissues, the effect of increased HBP activity on largely insulin unresponsive tissues, such as the brain, remains relatively unknown. Herein, we investigate the effects of increased HBP flux on Akt activation in a human astroglial cells line using glucosamine, a compound commonly used to mimic hyperglycemic conditions by increasing HBP flux. Cellular treatment with 8 mM glucosamine resulted in a 96.8% ± 24.6 increase in Akt phosphorylation after 5 h of treatment that remained elevated throughout the 9-h time course. Glucosamine treatment also resulted in modest increases in global levels of the O-GlcNAc protein modification. Increasing O-GlcNAc levels using the O-GlcNAcase inhibitor streptozotocin (STZ) also increased Akt phosphorylation by 96.8% ± 11.0 after only 3 h although for a shorter duration than glucosamine; however, the more potent O-GlcNAcase inhibitors O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc) and 1,2-dideoxy-2′-propyl-α-d-glucopyranoso-[2,1-d]-Δ2′-thiazoline (NAGBT) failed to mimic the increases in phospho-Akt indicating that the Akt phosphorylation is not a result of increased O-GlcNAc protein modification. Further analysis indicated that this increased phosphorylation was also not due to increased osmotic stress and was not attenuated by N-acetylcysteine eliminating the potential role of oxidative stress in the observed phospho-Akt increases. Glucosamine treatment, but not STZ treatment, did correlate with a large increase in the expression of the endoplasmic reticulum (ER) stress marker GRP 78. Altogether, these results indicate that increased HBP flux in human astroglial cells results in a rapid, short-term phosphorylation of Akt that is likely a result of increased ER stress. The mechanism by which STZ increases Akt phosphorylation, however, remains unknown.     

一次性静脉注射高剂量链脲佐菌素建立1型糖尿病小型猪模型

目的：探讨通过一次性注射高剂量链脲佐菌素（ streptozotocin,STZ）方法建立1型糖尿病小型猪模型的可行性。方法中华实验小型猪耳缘静脉一次性注射链脲佐菌素溶液150 mg/kg,分别在给药前和给药后10 min、30 min、90 min、第1天、第2天、第3天和第7天空腹采集静脉血,动态监测空腹血糖,并利用静脉糖耐量实验和C肽释放实验对模型进行鉴定。结果给药后第1天开始,模型组空腹血糖明显升高并始终维持在16.7～20.6 mmol/L的浓度范围,达到糖尿病标准;静脉葡萄糖耐量试验和C肽释放实验结果表明,静脉注射体积分数50％的葡萄糖1 h后模型猪血糖浓度高于11.1 mmol/L,2 h后未能恢复至空腹血糖水平;而胰岛素和C肽在注入葡萄糖后基本未发生任何反应,始终保持痕量水平。结论一次性静脉注射大剂量链脲佐菌素的方法能够成功建立1型糖尿病小型猪模型。     

Illuminating the molecular basis of diabetic arteriopathy: A proteomic comparison of aortic tissue from diabetic and healthy rats

Arterial disease is a major diabetic complication, yet the component molecular mechanisms of diabetic arteriopathy remain poorly understood. In order to identify major proteins/pathways implicated in diabetic arteriopathy, we studied the effect of 16‐wk untreated streptozotocin‐induced diabetes on the rat aortic proteome. Specific protein levels in isolated aortas were compared in six discrete, pair‐wise (streptozotocin‐diabetic and non‐diabetic age‐matched controls) experiments in which individual proteins were identified and quantified by iTRAQ combined with LC‐MS/MS. A total of 398 unique non‐redundant proteins were identified in at least one experiment and 208 were detected in three or more. Between‐group comparisons revealed significant changes or trends towards changes in relative abundance of 51 proteins (25 increased, 26 decreased). Differences in levels of selected proteins were supported by Western blotting and/or enzyme assays. The most prominent diabetes‐associated changes were in groups of proteins linked to oxidative stress responses and the structure/function of myofibrils and microfilaments. Indexes of mitochondrial content were measurably lower in aortic tissue from diabetic animals. Functional cluster analysis also showed decreased levels of glycolytic enzymes and mitochondrial electron transport system‐complex components. These findings newly implicate several proteins/functional pathways in the pathogenesis of arteriosclerosis/diabetic arteriopathy.