Antioxidant alpha-tocopherol ameliorates glycemic control of GK rats, a model of type 2 diabetes

Reactive oxygen species, toxicity, oxidative stress, and antioxidants: chronic diseases and aging

A physiological level of oxygen/nitrogen free radicals and non-radical reactive species (collectively known as ROS/RNS) is termed oxidative eustress or "good stress" and is characterized by low to mild levels of oxidants involved in the regulation of various biochemical transformations such as carboxylation, hydroxylation, peroxidation, or modulation of signal transduction pathways such as Nuclear factor-κB (NF-κB), Mitogen-activated protein kinase (MAPK) cascade, phosphoinositide-3-kinase, nuclear factor erythroid 2-related factor 2 (Nrf2) and other processes. Increased levels of ROS/RNS, generated from both endogenous (mitochondria, NADPH oxidases) and/or exogenous sources (radiation, certain drugs, foods, cigarette smoking, pollution) result in a harmful condition termed oxidative stress ("bad stress"). Although it is widely accepted, that many chronic diseases are multifactorial in origin, they share oxidative stress as a common denominator. Here we review the importance of oxidative stress and the mechanisms through which oxidative stress contributes to the pathological states of an organism. Attention is focused on the chemistry of ROS and RNS (e.g. superoxide radical, hydrogen peroxide, hydroxyl radicals, peroxyl radicals, nitric oxide, peroxynitrite), and their role in oxidative damage of DNA, proteins, and membrane lipids. Quantitative and qualitative assessment of oxidative stress biomarkers is also discussed. Oxidative stress contributes to the pathology of cancer, cardiovascular diseases, diabetes, neurological disorders (Alzheimer's and Parkinson's diseases, Down syndrome), psychiatric diseases (depression, schizophrenia, bipolar disorder), renal disease, lung disease (chronic pulmonary obstruction, lung cancer), and aging. The concerted action of antioxidants to ameliorate the harmful effect of oxidative stress is achieved by antioxidant enzymes (Superoxide dismutases-SODs, catalase, glutathione peroxidase-GPx), and small molecular weight antioxidants (vitamins C and E, flavonoids, carotenoids, melatonin, ergothioneine, and others). Perhaps one of the most effective low molecular weight antioxidants is vitamin E, the first line of defense against the peroxidation of lipids. A promising approach appears to be the use of certain antioxidants (e.g. flavonoids), showing weak prooxidant properties that may boost cellular antioxidant systems and thus act as preventive anticancer agents. Redox metal-based enzyme mimetic compounds as potential pharmaceutical interventions and sirtuins as promising therapeutic targets for age-related diseases and anti-aging strategies are discussed.

Design and Investigation of New Water-Soluble Forms of α-Tocopherol with Antioxidant and Antiglycation Activity Using Amphiphilic Copolymers of N-Vinylpyrrolidone

Water-soluble forms of α-tocopherol (TP) as an effective antioxidant were obtained by encapsulating it into nanoparticles (NPs) of amphiphilic copolymers of N-vinylpyrrolidone with triethylene glycol dimethacrylate (CPL1-TP) and N-vinylpyrrolidone with hexyl methacrylate and triethylene glycol dimethacrylate (CPL2-TP) synthesized by radical copolymerization in toluene. The hydrodynamic radii of NPs loaded with TP (3.7 wt% per copolymers) were typically ca. 50 or 80 nm depending on copolymer composition, media, and temperature. Characterization of NPs was accomplished by transmission electron microscopy (TEM), IR-, and ¹H NMR spectroscopy. Quantum chemical modeling showed that TP molecules are capable to form hydrogen bonds with donor groups of the copolymer units. High antioxidant activity of both obtained forms of TP has been found by the thiobarbituric acid reactive species and chemiluminescence assays. CPL1-TP and CPL2-TP effectively inhibited the process of spontaneous lipid peroxidation as well as α-tocopherol itself. The IC₅₀ values of luminol chemiluminescence inhibition were determined. Antiglycation activity against vesperlysine and pentosidine-like AGEs of TP water-soluble forms was shown. The developed NPs of TP are promising as materials with antioxidant and antiglycation activity and can be used in various biomedical applications.

Redox Balance in Type 2 Diabetes: Therapeutic Potential and the Challenge of Antioxidant-Based Therapy

Oxidative stress is an important factor in the development of type 2 diabetes (T2D) and associated complications. Unfortunately, most clinical studies have failed to provide sufficient evidence regarding the benefits of antioxidants (AOXs) in treating this disease. Based on the known complexity of reactive oxygen species (ROS) functions in both the physiology and pathophysiology of glucose homeostasis, it is suggested that inappropriate dosing leads to the failure of AOXs in T2D treatment. To support this hypothesis, the role of oxidative stress in the pathophysiology of T2D is described, together with a summary of the evidence for the failure of AOXs in the management of diabetes. A comparison of preclinical and clinical studies indicates that suboptimal dosing of AOXs might explain the lack of benefits of AOXs. Conversely, the possibility that glycemic control might be adversely affected by excess AOXs is also considered, based on the role of ROS in insulin signaling. We suggest that AOX therapy should be given in a personalized manner according to the need, which is the presence and severity of oxidative stress. With the development of gold-standard biomarkers for oxidative stress, optimization of AOX therapy may be achieved to maximize the therapeutic potential of these agents.

Protective and therapeutic effects of natural products against diabetes mellitus via regenerating pancreatic β-cells and restoring their dysfunction

Diabetes mellitus is a growing public health concern and an increasing interest has been raised to search for new compounds with therapeutic effects on β-cells. There are chronic insulin resistance and loss of β-cell mass in the case of type-2 diabetes which covers about 90% of total diabetic patients. This work aims to critically review the protective and regenerative effects of various antidiabetic natural products on pancreatic β-cells. A thorough literature survey was conducted on the natural molecules and extracts having a protective, regenerative, and repairing effect on β-cells. The primary source of the literature was online scientific databases such as PubMed, Scopus, and Google Scholar. Besides, selected relevant textbooks were also consulted. Various natural molecules including berberine, curcumin, mangiferin, stevioside and capsaicin, and extracts obtained from the plants like Capsicum annum, Gymnema sylvestre, Stevia rebaudiana and Nymphaea stellate, were found to produce regenerative and anti-apoptosis effects on β-cells. These natural products were also found to increase insulin secretion by stimulating β-cells. The present review concluded that a large number of molecules and extracts, abundantly found in nature, possess antidiabetic effect via targeting β-cells. Further research is warranted to use these agents as a drug against diabetes.

Ascorbic Acid and Alpha-Tocopherol Contribute to the Therapy of Polycystic Ovarian Syndrome in Mouse Models

Polycystic ovary syndrome (PCOS) affects up to 10% of women within reproductive ages and has been a cause of infertility and poor quality of life. Alteration in the oxidant-antioxidant profile occurs in PCOS. This study, therefore, investigates the contribution of ascorbic acid (AA) and alpha-tocopherol(ATE) on different PCOS parameters. The mifepristone and letrozole models were used, and young mature female mice were randomly assigned to groups of six per group. On PCOS induction with either mifepristone or letrozole, mice were administered AA and ATE at doses ranging from 10-1000mg/kg to 0.1-1000 mg/kg in the respective models. Vaginal cytology, body weights, and temperature, as well as blood glucose, testosterone, and insulin levels, were measured. Total antioxidant capacity and malondialdehyde levels were analyzed. Determination of gene expression of some reactive oxygen species and histomorphological analysis on the ovaries and uteri were performed. At the end of the experiments, AA and ATE restored reproductive cycling, with AA being more effective. AA and ATE increased fasting blood glucose but had no significant effect on serum insulin levels. AA decreased testosterone levels, but ATE caused slight increases. AA and ATE both increased total antioxidant capacity and decreased malondialdehyde levels. AA and ATE also slightly upregulated the mRNA expressions of catalase, superoxide dismutase, and heme oxygenase 1 mainly. AA and ATE also decreased ovarian weight and mostly resolved cysts in the ovaries and congestion in the uterus. This study has shown that AA and ATE are beneficial in the therapy of PCOS.

Ameliorative impact of cold-pressed Rosmarinus officinalis oil against liver toxicity and genotoxic effects in streptozotocin-induced diabetic rats and their offspring

Diabetes mellitus (DM) is a chronic, lifelong condition threatening human health. Rosmarinus officinalis oil (RO) could have a future role in DM therapy. This study evaluated the composition and antioxidative potential of RO. Antidiabetic traits of RO in streptozotocin (STZ)-induced diabetic rats was also studied considering the ameliorative impact against embryogenesis defects using in vitro and in vivo biochemical, histological, and genetic assays. RO was investigated for fatty acids and bioactive compounds (tocols and total phenolic compounds), and antiradical potential against DPPH^• radicals. The genetic effects were investigated using comet assay and DNA fragmentation test. DM was induced to albino rats by injecting 60 mg/kg of STZ, while RO (100 mg/kg b.w.) was administered. The pregnant animals were divided into four groups; control (C), RO-treated (RO), diabetic (D), and combined diabetic with RO-treated (D-RO). The study was conducted for 180 days. In RO, the contents of polyunsaturated fatty acids, monounsaturated fatty acids, and saturated fatty acids were 42.3%, 41.7%, and 15.8%, respectively. The levels of α-, β-, γ-, and δ-tocopherols were 280, 20, 1,025, and 35 mg/100 g RO, respectively. RO contained 7.2 mg GAE/g of total phenolic compounds (TPC), while RO quenched 70% of DPPH^• radicals. While glucose levels reached the highest in DM rats, treating STZ-induced diabetic animals with RO-resoluted serum glucose levels. RO reduced the highest levels of serum chemistry parameters were recorded in DM animals. Histological photographs of maternal and fetus liver exhibited degenerated hepatic cells and congestion central vein. Comet cells and DNA fragments were significantly decreased in D-RO group comparing to the DM group. RO exhibited antidiabetic capabilities, and thus, it could be utilized as a functional ingredient in novel foods, nutraceuticals, and dietary supplements for diabetic patients. PRACTICAL APPLICATIONS: RO is rich in bioactive phytochemicals (tocols and phenolic compounds) with antiradical and antihyperglycemic capabilities. Tocols and phenolics are active in radical scavenging of reactive nitrogen species (i.e., peroxynitrite and nitrogen dioxide), and in the prevention of DNA bases nitration. Our results demonstrated that RO could improve the disturbed metabolism of carbohydrate in STZ-diabetic animals. The potential mode of action of bioactive compounds in RO most likely encompasses the intracellular pathway involved in glucose homeostasis or insulin signaling. In addition, the suppression of oxidative stress by phenolic compounds could provide to the antidiabetic impacts of RO. Our data supported that RO could be utilized to ameliorate DM. Protection with RO directed high protection of the maternal organs and offspring against the oxidative stress of diabetes due to the antihyperlipidemic effects and the antioxidant capabilities of RO.

Vitamin E supplementation and caloric restriction promotes regulation of insulin secretion and glycemic homeostasis by different mechanisms in rats

Vitamin E and caloric restriction have antioxidant effects in mammals. The aim of this study was to evaluate effects of vitamin E supplementation and caloric restriction upon insulin secretion and glucose homeostasis in rats. Male Wistar rats were distributed among the following groups: C, control group fed ad libitum; R, food quantity reduction of 40%; CV, control group supplemented with vitamin E [30 mg·kg^-1·day^-1]; and RV, food-restricted group supplemented with vitamin E. The experiments ran for 21 days. Glucose tolerance and insulin sensitivity was higher in the CV, R, and RV groups. Insulin secretion stimulated with different glucose concentrations was lower in the R and RV groups, compared with C and CV. In the presence of glucose and secretagogues, insulin secretion was higher in the CV group and was lower in the R and RV groups. An increase in insulin receptor occurred in the fat pad and muscle tissue of groups CV, R, and RV. Levels of hepatic insulin receptor and phospho-Akt protein were higher in groups R and RV, compared with C and CV, while muscle phospho-Akt was increased in the CV group. There was a reduction in hepatic RNA levels of the hepatocyte growth factor gene and insulin degrading enzyme in the R group, and increased levels of insulin degrading enzyme in the CV and RV groups. Thus, vitamin E supplementation and caloric restriction modulate insulin secretion by different mechanisms to maintain glucose homeostasis.

Pancreatic islet response to diabetes during pregnancy in rats

AIMS

The objective of this study was to assess the mechanisms underlying pancreatic islet adaptation in diabetic mothers and their pups. Additionally, the influence of pancreatic adaptations on maternal reproductive performance was also investigated.

MAIN METHODS

Wistar rats were injected with streptozotocin for diabetes induction. At adulthood (3 months), all animals underwent an oral glucose tolerance test (OGTT) for glucose assessment as an inclusion criterion. Following, the animals were mated. At day 18 of pregnancy, the mothers were killed for blood collect ion to determine fasting insulin and glucagon concentrations. The pancreas was removed and processed for the immunohistochemical analysis of insulin, glucagon, somatostatin, Ki-67 and PDX-1, superoxide dismutase 1 (SOD-1), glutathione peroxidase (GSH-Px) and malondialdehyde (MDA). The pregnant uterus was also collected for the evaluation of embryofetal loss.

KEY FINDINGS

The diabetic rats showed increased glucose, serum glucagon and insulin concentrations, and embryofetal loss rates. They also showed a reduction in pancreatic islets area and percentage of cells stained for insulin, increased the percentage of non-β cells (alpha e delta cells) stained for Ki-67, glucagon, and somatostatin. Moreover, the cells stained for somatostatin were spread across the islets and showed stronger staining for MDA and weaker staining for GSH-Px.

SIGNIFICANCE

Diabetes leads to adaptive responses from the endocrine pancreas in pregnancy that especially involves non-β cells, modifying the mantle-core structure. Nonetheless, these adaptations are not enough for glucose homeostasis and affect the maternal environment, which in turn impairs fetal development.

Addition of mushroom powder to pasta enhances the antioxidant content and modulates the predictive glycaemic response of pasta

This study reports the effects of addition of mushroom powder on the nutritional properties, predictive in vitro glycaemic response and antioxidant potential of durum wheat pasta. Addition of the mushroom powder enriched the pasta as a source of protein, and soluble and insoluble dietary fibre compared with durum wheat semolina. Incorporation of mushroom powder significantly decreased the extent of starch degradation and the area under the curve (AUC) of reducing sugars released during digestion, while the total phenolic content and antioxidant capacities of samples increased. A mutual inhibition system between the degree of starch gelatinisation and antioxidant capacity of the pasta samples was observed. These results suggest that mushroom powder could be incorporated into fresh semolina pasta, conferring healthier characteristics, namely lowering the potential glycaemic response and improving antioxidant capacity of the pasta.

Changes in glucose metabolism and mRNA expression of IRS-2 in rats exposed to phoxim and the protective effects of vitamin E

Research has shown that organophosphorus pesticides impair glucose homeostasis and cause insulin resistance and type 2 diabetes. The current study investigates the influence of phoxim on insulin signaling pathways and the protective effects of vitamin E. Phoxim (180 mg kg-1) and VE (200 mg kg-1) were administered orally to Sprague-Dawley rats over a period of 28 consecutive days. After exposure to phoxim, the animals showed glucose intolerance and hyperinsulinemia during glucose tolerance tests, and insulin tolerance tests demonstrated an impaired glucose-lowering effect of insulin. Phoxim increases the fasting glucose, insulin and cholesterol levels, as well as the liver hexokinase activity (HK) significantly while decreasing the high density lipoprotein (HDL) cholesterol, and glycogen content in the liver and skeletal muscles observably. Furthermore, we observed an increase of insulin resistance biomarkers and a decrease of insulin sensitivity indices. The insulin receptor substrate (IRS)-2 mRNA expressions of liver and skeletal muscles were down-regulated by phoxim, while the expression of IRS-1 showed no difference. There were no differences in triglycerides, LDL-cholesterol, and fasting glucose treated with phoxim. On the basis of biochemical and molecular findings, phoxim has been determined to impair glucose homeostasis through insulin resistance and insulin signaling pathway disruptions resulting in a reduced function of insulin in hepatocytes and muscles. VE supplementation reduced the fasting glucose, increased the glycogen content and HDL-cholesterol, but did not reduce the insulin resistance indices, when phoxim-treated rats were compared to VE supplemented rats. Overall, this study shows that vitamin E modifies the phoxim toxicity in rats only to a moderate degree.

Serum Lycopene Levels in Patients with Diabetic Retinopathy

Purpose.

Accumulating evidence indicates that oxidative stress may play an important role in the pathogenesis of type 2 diabetes and its complications. Lycopene, a very potent antioxidant of carotenoids, has received considerable scientific interest in recent years for its potential role in the prevention of oxidative stress-related chronic diseases. This study was undertaken to investigate whether the serum levels of lycopene are altered between type 2 diabetic patients with and without diabetic retinopathy.

Methods.

A total of 71 patients with type 2 diabetes were analyzed and compared with 23 nondiabetic healthy controls. Serum lycopene concentrations were assayed using high-performance liquid chromatography.

Results.

Lycopene level was found to be significantly lower in diabetic patients than in controls (p=0.021). In the diabetic group, subjects with proliferative diabetic retinopathy had significantly lower lycopene levels than subjects without diabetic retinopathy or with nonproliferative diabetic retinopathy. In the analysis of correlations, hemoglobin A1c were negatively correlated with lycopene (r=–0.345, p=0.007) after multivariate adjustment. A stepwise linear multiple regression model revealed that age and hemoglobin A1c were significant determinants of lycopene.

Conclusions.

Our findings show that measuring serum lycopene is a novel convenient method for evaluating oxidative damage. Diabetic patients, especially those with advanced diabetic retinopathy, had significantly lower serum lycopene levels; this suggests that lycopene may be helpful for the diagnosis, severity, and therapeutic evaluation of diabetic retinopathy.

Exploring the molecular mechanisms underlying α- and β-cell dysfunction in diabetes

Pancreatic islet dysfunction, including impaired insulin secretion in β cells and dysregulated glucagon secretion in α cells, is the chief pathology of diabetes. In β cells, oxidative stress, evoked by chronic hyperglycemia, was found to induce dysfunction of a critical transcription factor, PDX1, caused by its nucleocytoplasmic translocation via interactions with the insulin and JNK signaling pathways and another transcription factor, FOXO1. The significance of α-cell insulin signaling in the physiological and pathological regulation of α-cell biology was demonstrated in α-cell-specific insulin receptor knockout mice, which exhibited dysregulated glucagon secretion. Moreover, a high-glucose load directly induced excessive glucagon secretion in a glucagon-secreting cell line and isolated islets, together with impairment of insulin signaling. These findings indicate that disordered insulin signaling is central to the pathophysiology of islet dysfunction in both α and β cells. On the other hand, certain beneficial effects of GLP-1 on dysfunctional α and β cells indicate that it has therapeutic potential for diabetes patients who exhibit insulin resistance in islets. These studies, involving basic medical research approaches, have-at least in part-clarified the molecular mechanisms underlying α- and β-cell dysfunction in diabetes, and offer important clues that should aid the development of future therapeutic approaches to the disease.

Dietary regulation of adiponectin by direct and indirect lipid activators of nuclear hormone receptors

Adiponectin is an adipokine mainly secreted by adipocytes that presents antidiabetic, anti-inflammatory, and antiatherogenic functions. Therefore, modulation of adiponectin expression represents a promising target for prevention or treatment of several diseases including insulin resistance and type II diabetes. Pharmacological agents such as the nuclear hormone receptor synthetic agonists like peroxisome proliferator activated receptor γ agonists are of particular interest in therapeutic strategies due to their ability to increase the plasma adiponectin concentration. Nutritional approaches are also of particular interest, especially in primary prevention, since some active compounds of our diet (notably vitamins, carotenoids, or other essential nutrients) are direct or indirect lipid-activators of nuclear hormone receptors and are modifiers of adiponectin expression and secretion. The aim of the present review is to summarize current knowledge about the nutritional regulation of adiponectin by derivatives of active compounds naturally present in the diet acting as indirect or direct activators of nuclear hormone receptors.

Longitudinal associations of nutritional factors with glycated hemoglobin in youth with type 1 diabetes: the SEARCH Nutrition Ancillary Study

BACKGROUND

Improved glycated hemoglobin (Hb A1c) delays the progression of microvascular and macrovascular complications in individuals with type 1 diabetes (T1D). We previously showed that higher baseline intakes of n-3 (ω-3) fatty acids and leucine are associated with preserved β cell function 2 y later in youth with T1D.

OBJECTIVE

In the current study, we extend this work to explore the longitudinal associations of nutritional factors with Hb A1c in youth with T1D.

DESIGN

We included 908 T1D youth with baseline and follow-up Hb A1c measurements. Nutritional factors assessed at baseline were as follows: breastfeeding status and timing of complimentary food introduction; intakes of leucine, carbohydrates, protein, fat, and fiber estimated from a food-frequency questionnaire (FFQ); and plasma biomarkers for vitamins D and E, eicosapentaenoic acid (EPA), and docosahexaenoic acid. We fit linear regression models adjusted for baseline Hb A1c, sociodemographic variables, diabetes-related variables, time between baseline and follow-up visits, saturated fat, physical activity, and for FFQ-derived nutrients, total calories. The vitamin D model was further adjusted for season and body mass index z score.

RESULTS

The mean ± SD age and diabetes duration at baseline was 10.8 ± 3.9 y and 10.1 ± 5.8 mo, respectively. A total of 9.3% of participants had poor Hb A1c (value ≥9.5%) at baseline, which increased to 18.3% during follow-up (P < 0.0001). Intakes of EPA (β = -0.045, P = 0.046), leucine (β = -0.031, P = 0.0004), and protein (β = -0.003, P = 0.0002) were significantly negatively associated with follow-up Hb A1c after adjustment for confounders. Intake of carbohydrates was significantly positively (β = 0.001, P = 0.003) associated with follow-up Hb A1c after adjustment for confounders.

CONCLUSIONS

Several nutritional factors may be associated with Hb A1c during early stages of disease progression in youth recently diagnosed with T1D. In addition to the overall role of major macronutrients such as carbohydrates and protein, leucine and n-3 fatty acid intakes, such as of EPA, may be important for long-term glycemic control.

Serum magnesium, iron and ferritin levels in patients with diabetic retinopathy attending Makkah Eye Complex, Khartoum, Sudan

Diabetic retinopathy is the most common complications of diabetes mellitus that, in most occasions, lead to blindness. Multiple evidences linked the serum magnesium, iron and ferritin disturbance with diabetes and its complications. A case-control study was conducted at Makkah Eye Complex, Khartoum, Sudan, to compare the levels of serum magnesium, iron and ferritin in patients with diabetic retinopathy with diabetic patients without diabetic retinopathy (controls). Findings indicate that all patients had type 2 diabetes. The two groups (50 in each arm) were well matched in their basic characteristics. Median (25th-75th interquartile) of serum magnesium in patients with diabetic retinopathy were significantly lower than patients without diabetic retinopathy [1.48 (0.75-1.64) vs. 1.92 (1.4-2.3)mg/dl, P = 0.022]. The median of serum iron and ferritin were lower in cases than control group but did not reach a statistical significance [20.5 (17.2-48.0) vs. 27.0 (16.0-54.0) μg/dl, P = 0.568; 98.0 (45.0-134.75) vs. 101.0 (47.0-161.0) μg/l, P = 0.818]. The duration of diabetes [16.5 (9.3) vs. 11.2 (6.6) years; P = 0.014] and haemoglobin level [13.7 (0.9) vs. 12.5 (2.0) g/dl; P = 0.039] were significantly higher in cases group than control group. A significant inverse correlation was observed between serum magnesium and iron levels. Twenty (40 %) patients had severe non-proliferative diabetic retinopathy with mild macular edema, which is the most prevalent type among the cases group. Hypomagnesaemia among diabetic patients was associated with diabetic retinopathy, while serum iron and ferritin have no significant effect in this setting. Severe non-proliferative diabetic retinopathy with mild macular edema is the prevalent type in this study.

Effects of Fenugreek Seed Extract and Swimming Endurance Training on Plasma Glucose and Cardiac Antioxidant Enzymes Activity in Streptozotocin-induced Diabetic Rats

Objective

Diabetes mellitus is a group of metabolic diseases characterized by chronic hyperglycemia condition resulting from defective insulin secretion or resistance insulin action, or both. The purpose of this study was to evaluate the effect of 6 weeks swimming training and Trigonella foenum-graecum seed (fenugreek) extract, alone and in combination, on plasma glucose and cardiac antioxidant enzyme activity of streptozotocin-induced diabetic rats.

Methods

Fifty male Wistar rats were divided into five groups: diabetic control (DC, n = 8); healthy control (HC, n = 11); swimming training (S, n = 11); swimming training + fenugreek seed extract (1.74 g/kg body weight; SF1, n = 11); and swimming training + fenugreek seed extract (0.87 g/kg body weight; SF2, n = 9). Streptozotocin was used for the induction of diabetes. Results were analyzed using one-way analysis of variance followed by Tukey test.

Results

In comparison with the DC group, all groups exhibited a significant decrease in body weight (p < 0.05), except for the HC group. SF1 and HC groups showed significant decreases in plasma glucose levels compared with the DC group (p < 0.05). S, SF1, SF2, and HC groups showed significant elevations in cardiac antioxidant enzymes activity in comparison with the DC group.

Conclusion

The results indicated that the combination of endurance swimming training and fenugreek seed extract can significantly reduce the plasma glucose levels and increase cardiac antioxidant enzymes activity in diabetic rats. Our findings suggest that this combination could be useful for the treatment of hyperglycemia and cardiac oxidative stress induced by diabetes mellitus.

Effect of chronic administration of forskolin on glycemia and oxidative stress in rats with and without experimental diabetes

Forskolin is a diterpene derived from the plant Coleus forskohlii. Forskolin activates adenylate cyclase, which increases intracellular cAMP levels. The antioxidant and antiinflammatory action of forskolin is due to inhibition of macrophage activation with a subsequent reduction in thromboxane B2 and superoxide levels. These characteristics have made forskolin an effective medication for heart disease, hypertension, diabetes, and asthma. Here, we evaluated the effects of chronic forskolin administration on blood glucose and oxidative stress in 19 male Wistar rats with streptozotocin-induced diabetes compared to 8 healthy male Wistar rats. Rats were treated with forskolin, delivered daily for 8 weeks. Glucose was assessed by measuring fasting blood glucose in diabetic rats and with an oral glucose tolerance test (OGTT) in healthy rats. Oxidative stress was assessed by measuring 8-hydroxydeoxyguanosine (8‑OHdG) in 24-h urine samples. In diabetic rats, without forskolin, fasting blood glucose was significantly higher at the end than at the beginning of the experiment (8 weeks). In both healthy and diabetic rats, forskolin treatment lowered the fasting glucose at the end of the experiment but no effect was found on oral glucose tolerance. The 8-OHdG levels tended to be less elevated in forskolin-treated than in untreated group. Our results showed that chronic administration of forskolin decreased fasting blood glucose levels; however, the reductions of 8-OHdG were not statistically significant.

Antioxidant effect of mogrosides against oxidative stress induced by palmitic acid in mouse insulinoma NIT-1 cells

Excessive oxidative stress in pancreatic β cells, caused by glucose and fatty acids, is associated with the pathogenesis of type 2 diabetes. Mogrosides have shown antioxidant and antidiabetic activities in animal models of diabetes, but the underlying mechanisms remain unclear. This study evaluated the antioxidant effect of mogrosides on insulinoma cells under oxidative stress caused by palmitic acid, and investigated the underlying molecular mechanisms. Mouse insulinoma NIT-1 cells were cultured in medium containing 0.75 mM palmitic acid, mimicking oxidative stress. The effects of 1 mM mogrosides were determined with the dichlorodihydrofluorescein diacetate assay for intracellular reactive oxygen species (ROS) and FITC-Annexin V/PI assay for cell apoptosis. Expression of glucose transporter-2 (GLUT2) and pyruvate kinase was determined by semi-quantitative reverse-transcription polymerase chain reaction. Palmitic acid significantly increased intracellular ROS concentration 2-fold (P<0.05), and decreased expression of GLUT2 (by 60%, P<0.05) and pyruvate kinase (by 80%, P<0.05) mRNAs in NIT-1 cells. Compared with palmitic acid, co-treatment with 1 mM mogrosides for 48 h significantly reduced intracellular ROS concentration and restored mRNA expression levels of GLUT2 and pyruvate kinase. However, mogrosides did not reverse palmitic acid-induced apoptosis in NIT-1 cells. Our results indicate that mogrosides might exert their antioxidant effect by reducing intracellular ROS and regulating expression of genes involved in glucose metabolism. Further research is needed to achieve a better understanding of the signaling pathway involved in the antioxidant effect of mogrosides.

A comparative study of effects of omega-3 Fatty acids, alpha lipoic Acid and vitamin e in type 2 diabetes mellitus

BACKGROUND

Diabetes Mellitus is a metabolic disorder characterized by abnormal lipid and glucose metabolism. Various modes of adjuvant therapy have been advocated to ameliorate insulin resistance.

AIM

This study was intended to assess the effects of antioxidants; alpha lipoic acid (ALA), omega 3 fatty acid and vitamin E on parameters of insulin sensitivity (blood glucose and HbA1c) in patients of type 2 diabetes mellitus with documented insulin resistance.

SUBJECTS AND METHODS

It was a prospective, randomized, double blind, placebo controlled, single centered study. 104 patients with type 2 diabetes mellitus with insulin resistance were recruited. They were given ALA, omega 3 fatty acid, vitamin E or placebo. Fasting blood glucose and HbA1c were measured at first visit (V1) and after 90 days (V2). Statistical analysis was carried out by paired t-test by using SPSS software version 11 (SPSS, Chicago, USA).

RESULTS

Analysis of baseline (V1) vs. end of treatment period (V2) parameters, showed significant decrease in HbA1c in the three treatment group. We also observed decrease in fasting blood glucose in the three treatment group but it was not statistically significant (Gr. I = 0.51, Gr. II = 0.05, Gr. III = 0.22, Gr. IV = 0.88).

CONCLUSION

ALA, Omega 3 fatty acid and vitamin E can be used as add on therapy in patients with type 2 diabetes mellitus to improve insulin sensitivity and lipid metabolism.

Study of comparative effects of antioxidants on insulin sensitivity in type 2 diabetes mellitus

OBJECTIVES

This study intended to assess the effects of the antioxidants; Alpha Lipoic Acid (ALA), omega 3 fatty acids and vitamin E on the parameters of insulin sensitivity, oxidative stress, lipid metabolism and glycaemic control in patients of type 2 diabetes mellitus.

METHODS

This was a prospective, randomized, double blind, placebo controlled, single centred study. One hundred four patients with type 2 diabetes mellitus with insulin resistance were recruited for the study. They were given ALA, omega 3 fatty acids, vitamin E or placebo. Their weight, Body Mass Index (BMI) and Waist circumference were measured. The investigations which were fasting glucose and fasting total cholesterol. The insulin resistance was calculated on the basis of the BMI and the waist circumference.

RESULTS

In the intra group analysis at the baseline (V1) vs at the end of the treatment period (V5), we observed a significant decrease in the BMI, waist circumference and the total cholesterol in the three treatment groups. In the intergroup analysis at V5, ALA, omega 3 fatty acids and vitamin E showed a significant improvement in the total cholesterol as compared to the placebo and vitamin E showed the maximum improvement.

CONCLUSION

ALA, omega 3 fatty acids and vitamin E showed the improvement in insulin sensitivity. Since they differ in improving different parameters all of these three can be used as an add on therapy in patients with type 2 diabetes mellitus to improve their insulin sensitivity and lipid metabolism.

The molecular mechanisms of pancreatic β-cell glucotoxicity: recent findings and future research directions

It is well established that regular physiological stimulation by glucose plays a crucial role in the maintenance of the β-cell differentiated phenotype. In contrast, prolonged or repeated exposure to elevated glucose concentrations both in vitro and in vivo exerts deleterious or toxic effects on the β-cell phenotype, a concept termed as glucotoxicity. Evidence indicates that the latter may greatly contribute to the pathogenesis of type 2 diabetes. Through the activation of several mechanisms and signaling pathways, high glucose levels exert deleterious effects on β-cell function and survival and thereby, lead to the worsening of the disease over time. While the role of high glucose-induced β-cell overstimulation, oxidative stress, excessive Unfolded Protein Response (UPR) activation, and loss of differentiation in the alteration of the β-cell phenotype is well ascertained, at least in vitro and in animal models of type 2 diabetes, the role of other mechanisms such as inflammation, O-GlcNacylation, PKC activation, and amyloidogenesis requires further confirmation. On the other hand, protein glycation is an emerging mechanism that may play an important role in the glucotoxic deterioration of the β-cell phenotype. Finally, our recent evidence suggests that hypoxia may also be a new mechanism of β-cell glucotoxicity. Deciphering these molecular mechanisms of β-cell glucotoxicity is a mandatory first step toward the development of therapeutic strategies to protect β-cells and improve the functional β-cell mass in type 2 diabetes.

Honey--a novel antidiabetic agent

Diabetes mellitus remains a burden worldwide in spite of the availability of numerous antidiabetic drugs. Honey is a natural substance produced by bees from nectar. Several evidence-based health benefits have been ascribed to honey in the recent years. In this review article, we highlight findings which demonstrate the beneficial or potential effects of honey in the gastrointestinal tract (GIT), on the gut microbiota, in the liver, in the pancreas and how these effects could improve glycemic control and metabolic derangements. In healthy subjects or patients with impaired glucose tolerance or diabetes mellitus, various studies revealed that honey reduced blood glucose or was more tolerable than most common sugars or sweeteners. Pre-clinical studies provided more convincing evidence in support of honey as a potential antidiabetic agent than clinical studies did. The not-too-impressive clinical data could mainly be attributed to poor study designs or due to the fact that the clinical studies were preliminary. Based on the key constituents of honey, the possible mechanisms of action of antidiabetic effect of honey are proposed. The paper also highlights the potential impacts and future perspectives on the use of honey as an antidiabetic agent. It makes recommendations for further clinical studies on the potential antidiabetic effect of honey. This review provides insight on the potential use of honey, especially as a complementary agent, in the management of diabetes mellitus. Hence, it is very important to have well-designed, randomized controlled clinical trials that investigate the reproducibility (or otherwise) of these experimental data in diabetic human subjects.

Protective role of glibenclamide against nicotinamide-streptozotocin induced nuclear damage in diabetic Wistar rats

Objective:

To evaluate the protective effect of glibenclamide against the experimental diabetes-induced nuclear damage in Wistar rats.

Materials and Methods:

The anti-mutagenic effect of glibenclamide (0.5, 5 and 50 mg/kg, p.o daily for 4 weeks) was evaluated against the nicotinamide (NA)-streptozotocin (STZ) induced type-2 diabetes mellitus using bone marrow micronucleus and sperm abnormalities tests. The antioxidant status was tested by estimating the serum levels of lipid peroxidation (LPO), catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx).

Results:

The results indicated that glibenclamide at 50 mg/kg decreased the frequency of micronuclei in erythrocytes (P < 0.05) and sperm shape abnormality (P < 0.01) besides enhancing the antioxidant status (P < 0.05) in the diabetic rats. However, glibenclamide treatment did not enhance the polychromatic and normochromatic erythrocytes (P/N) ratio and sperm count in the diabetic condition.

Conclusion:

The observations indicate that the glibenclamide has anti-mutagenic potential which could be related to the antioxidant effect and might also possess anti-proliferative property.

Oxidative stress and diabetes mellitus

Increasing evidences have suggested that oxidative stress plays a major role in the pathogenesis of diabetes mellitus (DM). Oxidative stress also appears to be the pathogenic factor in underlying diabetic complications. Reactive oxygen species (ROS) are generated by environmental factors, such as ionizing radiation and chemical carcinogens, and also by endogenous processes, including energy metabolism in mitochondria. ROS produced either endogenously or exogenously can attack lipids, proteins and nucleic acids simultaneously in living cells. There are many potential mechanisms whereby excess glucose metabolites traveling along these pathways might promote the development of DM complication and cause pancreatic β cell damage. However, all these pathways have in common the formation of ROS, that, in excess and over time, causes chronic oxidative stress, which in turn causes defective insulin gene expression and insulin secretion as well as increased apoptosis. Various methods for determining biomarkers of cellular oxidative stress have been developed, and some have been proposed for sensitive assessment of antioxidant defense and oxidative damage in diabetes and its complications. However, their clinical utility is limited by less than optimal standardization techniques and the lack of sufficient large-sized, multi-marker prospective trials.

Ameliorative potential of resveratrol on proinflammatory cytokines, hyperglycemia mediated oxidative stress, and pancreatic beta-cell dysfunction in streptozotocin-nicotinamide-induced diabetic rats

Chronic exposure of pancreatic beta-cells to supraphysiologic glucose causes adverse beta-cell dysfunction. Thus, the present study was aimed to investigate the hypothesis that oral administration of resveratrol attenuates hyperglycemia, proinflammatory cytokines and antioxidant competence and protects beta-cell ultrastructure in streptozotocin-nicotinamide-induced diabetic rats. Oral administration of resveratrol (5 mg/kg body weight) to diabetic rats for 30 days showed a significant decline in the levels of blood glucose, glycosylated hemoglobin (HbA1c), TNF-alpha, IL-1beta, IL-6, NF-kappaB p65 unit and nitric oxide (NO) with concomitant elevation in plasma insulin. Further, resveratrol treated diabetic rats elicited a notable attenuation in the levels of lipid peroxides, hydroperoxides and protein carbonyls in both plasma and pancreatic tissues. The diminished activities of pancreatic superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) and glutathione-S-transferase (GST) as well as the decreased levels of plasma ceruloplasmin, vitamin C, vitamin E and reduced glutathione (GSH) in diabetic rats were reverted to near normalcy by resveratrol administration. Based on histological and ultrastructural observations, it is first-time reported that the oral administration of resveratrol may effectively rescue beta-cells from oxidative damage without affecting their function and structural integrity. The results of the present investigation demonstrated that resveratrol exhibits significant antidiabetic potential by attenuating hyperglycemia, enhancing insulin secretion and antioxidant competence in pancreatic beta-cells of diabetic rats.

Lipid peroxidation in relation to ageing and the role of endogenous aldehydes in diabetes and other age-related diseases

Lipid intermediates which are generated by ROS have drawn more attention after it was found that lipid peroxidation and lipid-radical cycles are two alternative processes. In biological membranes alpha-tocopherol and cytochrome b5, as known, act synergistically to overcome free radical injury and to form lipid-radical cycles. These cycles activate membrane proteins, protect membrane lipids from oxidation and prevent from formation of endogenous aldehydes. Experimental and clinical evidence accumulated for 5-6 years suggests that endogenous aldehydes, such as malonic dialdehyde (MDA) and methylglyoxal (MG), are the major initiators of the metabolic disorders. The age-related diseases emerge when cells cannot control formation of aldehydes and/or cannot abolish the negative effect of methylglyoxal on their metabolism. If the efficiency of the glyoxalase system is insufficient toxic aldehydes cause cumulative damage over a lifetime. In this paper, we provide evidence to consider ageing as a process in which lipid-radical cycles gradually substitute for lipid peroxidation. There are always two opposing tendencies or actions which counteract each other - actions of melatonin, lipid-radical cycles and the glyoxalase system (anti-ageing effect) and negative actions of the toxic aldehydes (pro-ageing effect). Life span is determined by the balance of two opposing processes.

Adiponectin expression is induced by vitamin E via a peroxisome proliferator-activated receptor gamma-dependent mechanism

Adiponectin is a well-known adipokine secreted by adipocytes that presents insulin-sensitizing properties. The regulation of expression of this adipokine by micronutrients is largely unknown. We demonstrate here that adiponectin expression is induced in adipocytes after exposure to tocopherols via the peroxisome proliferator-activated receptor gamma (PPARgamma) pathway. Vitamin E force feeding resulted in an induction of adiponectin in mice at both mRNA and protein levels. Adiponectin mRNA and protein secretion were also increased by vitamin E (alpha- and gamma-tocopherol) in 3T3-L1 cells, together with PPARgamma mRNA, independent of an antioxidant effect. In transient transfections, both alpha- and gamma-vitamers induced the luciferase gene reporter under the control of a human adiponectin promoter via a PPAR-responsive element. The induction of adiponectin by tocopherols seems to be PPARgamma dependent, because it was blocked by the specific antagonist GW9662. Finally, we showed that intracellular concentrations of a PPARgamma endogenous ligand, 15-deoxy-Delta12,14-prostaglandin J2, increased after treatment with tocopherols in 3T3-L1 cells. In summary, vitamin E up-regulates adiponectin expression via a mechanism that implicates PPARgamma together with its endogenous ligand 15-deoxy-Delta12,14-prostaglandin J2. The induction of adiponectin via an original molecular mechanism could be considered as the basis for the beneficial effect of vitamin E on insulin sensitivity.

Supplementation with magnesium and vitamin E were more effective than magnesium alone to decrease plasma lipids and blood viscosity in diabetic rats

Although magnesium and vitamin E (VE) have differing effects on diabetes, both are beneficial. We hypothesized that preventive supplementation of magnesium combined with VE could improve the metabolism of lipids and blood viscosity more effectively than the use of magnesium or VE alone. Our objective was to detect the effects of preventive supplementation of magnesium combined with VE on lipid peroxidation, lipid metabolic parameters, and blood viscosity in diabetic rats. Six dietary groups, all fed with high-energy diets, were formed and studied for 8 weeks: control group (C); VE group (E); middle-dose magnesium group (MM); high-dose magnesium group (HM); VE plus middle-dose magnesium group (EMM); and VE plus high-dose magnesium group (EHM). Compared with C group, malondialdehyde was inhibited in the E, EMM, and EHM groups (all P < .05); total cholesterol decreased in all 5 treated groups, and significant differences were found in groups E (P = .004), MM (P = .017), EMM (P = .016), and EHM (P = .020). Compared with the C group, high-density lipoprotein levels were elevated in the HM (P = .027) and EHM (P = .021) groups, and low-density lipoprotein levels were lower in the E (P = .010), EMM (P = .025), and EHM (P = .015) groups. Differences between middle and high shear rates of blood viscosity were significant in all treated groups compared with the C group (all P <or= .001). Statistical analysis showed that there was no interaction between magnesium and VE. We concluded that preventive supplementation of VE combined with magnesium was more beneficial to improve the plasma lipid parameters and blood viscosity in diabetic rats than magnesium alone.

Supplementation of hydrogen-rich water improves lipid and glucose metabolism in patients with type 2 diabetes or impaired glucose tolerance

Oxidative stress is recognized widely as being associated with various disorders including diabetes, hypertension, and atherosclerosis. It is well established that hydrogen has a reducing action. We therefore investigated the effects of hydrogen-rich water intake on lipid and glucose metabolism in patients with either type 2 diabetes mellitus (T2DM) or impaired glucose tolerance (IGT). We performed a randomized, double-blind, placebo-controlled, crossover study in 30 patients with T2DM controlled by diet and exercise therapy and 6 patients with IGT. The patients consumed either 900 mL/d of hydrogen-rich pure water or 900 mL of placebo pure water for 8 weeks, with a 12-week washout period. Several biomarkers of oxidative stress, insulin resistance, and glucose metabolism, assessed by an oral glucose tolerance test, were evaluated at baseline and at 8 weeks. Intake of hydrogen-rich water was associated with significant decreases in the levels of modified low-density lipoprotein (LDL) cholesterol (ie, modifications that increase the net negative charge of LDL), small dense LDL, and urinary 8-isoprostanes by 15.5% (P < .01), 5.7% (P < .05), and 6.6% (P < .05), respectively. Hydrogen-rich water intake was also associated with a trend of decreased serum concentrations of oxidized LDL and free fatty acids, and increased plasma levels of adiponectin and extracellular-superoxide dismutase. In 4 of 6 patients with IGT, intake of hydrogen-rich water normalized the oral glucose tolerance test. In conclusion, these results suggest that supplementation with hydrogen-rich water may have a beneficial role in prevention of T2DM and insulin resistance.

Supplementation of coenzyme Q10 and alpha-tocopherol lowers glycated hemoglobin level and lipid peroxidation in pancreas of diabetic rats

The importance of nutritional supplementation in diabetes remains an unresolved issue. The present study was undertaken to examine the effects of alpha-tocopherol and CoQ(10), powerful antioxidants, on metabolic control and on the pancreatic mitochondria of GK rats, a model of type 2 diabetes. We also evaluated the efficacy of these nutrients in preventing the diabetic pancreatic lesions observed in GK rats. Rats were divided into 4 groups, a control group of diabetic GK rats and 3 groups of GK rats administered with alpha-tocopherol and CoQ(10) alone or both in association, during 8 weeks. Fasting blood glucose levels were not significantly different between the groups, nor were blood glucose levels at 2 hours after a glucose load. HbA1c level was significantly reduced in the group supplemented with both antioxidants. Diabetes induced a decrease in coenzyme Q plasma levels that prevailed after treatment with antioxidants. In addition, the plasma alpha-tocopherol levels were higher after treatment with the antioxidants. An increment in some components of the antioxidant defense system was observed in pancreatic mitochondria of treated GK rats. Moreover, the antioxidants tested either alone or in association failed to prevent the pancreatic lesions in this animal model of type 2 diabetes. In conclusion, our results indicate that CoQ(10) and alpha-tocopherol decrease glycated HbA1c and pancreatic lipid peroxidation. These antioxidants increase some components of the antioxidant defense system but do not prevent pancreatic lesions. Thus, we cannot rule out the potential benefit of antioxidant treatments in type 2 diabetes in the prevention of their complications.

The effects of palm oil tocotrienol-rich fraction supplementation on biochemical parameters, oxidative stress and the vascular wall of streptozotocin-induced diabetic rats

OBJECTIVE

This study examined the effects of palm oil tocotrienol-rich fractions on streptozotocin-induced diabetic rats.

METHODS

Animals were divided into three groups: (i) normal non-diabetic (NDM), (ii) diabetic treated (tocotrienol-rich fractions - TRF) and (iii) diabetic untreated (non-TRF). The treatment group received oral administration of tocotrienol-rich fractions (200 mg/kg body weight) daily for eight weeks. The normal non-diabetic and the diabetic untreated groups were fed standard rat feed. Blood glucose and lipid profiles, oxidative stress markers and morphological changes of the thoracic aorta were evaluated.

RESULTS

Tocotrienol-rich fractions treatment reduced serum glucose and glycated hemoglobin concentrations. The tocotrienol-rich fractions group also showed significantly lower levels of plasma total cholesterol, low-density lipoprotein cholesterol, and triglyceride, as compared to the untreated group. The tocotrienol-rich fractions group had higher levels of high-density lipoprotein cholesterol, as compared to the untreated group. Superoxide dismutase activity and levels of vitamin C in plasma were increased in tocotrienol-rich fractions-treated rats. The levels of plasma and aorta malondealdehyde + 4-hydroxynonenal (MDA + 4-HNE) and oxidative DNA damage were significant following tocotrienol-rich fractions treatment. Electron microscopic examination showed that the normal morphology of the thoracic aorta was disrupted in STZ-diabetic rats. Tocotrienol-rich fractions supplementation resulted in a protective effect on the vessel wall.

CONCLUSION

These results show that tocotrienol-rich fractions lowers the blood glucose level and improves dyslipidemia. Levels of oxidative stress markers were also reduced by administration of tocotrienol-rich fractions. Vessel wall integrity was maintained due to the positive effects mediated by tocotrienol-rich fractions.

The role of CHOP messenger RNA expression in the link between oxidative stress and apoptosis

Low expression of antioxidant enzymes makes pancreatic beta-cells susceptible to cell damage by oxidative stress. Pancreatic beta-cell loss caused by endoplasmic reticulum stress is associated with the onset of diabetes mellitus. The present studies were undertaken to investigate a possible involvement of proapoptotic gene CHOP in pancreatic beta-cells damage by oxidative stress. The induction of CHOP messenger RNA and apoptosis were investigated in betaHC-9 cells after the oxidative stress by hydrogen peroxide and ribose. Latter was examined after the suppression of CHOP by small interfering RNA. For in vivo study, the pancreatic beta-cells were examined in CHOP-knockout (KO) mice after multiple low-dose streptozotocin (MLDS) administration. In betaHC-9 cells, both hydrogen peroxide and ribose obviously increased apoptotic cells, accompanied with enhanced CHOP messenger RNA expression. However, the number of apoptotic cells by those stimulations was significantly reduced by the addition of small interfering RNA against CHOP. In vivo study also showed that CHOP-KO mice were less susceptible to diabetes after MLDS administration. Although the oxidative stress marker level was similar to that of MLDS-treated wild type, the pancreatic beta-cell area was maintained in CHOP-KO mice. The present studies showed that CHOP should be important in pancreatic beta-cell injury by oxidative stress and indicate that CHOP may play a role in the development of pancreatic beta-cell damage on the onset of diabetes mellitus.

Regulation of the susceptibility to oxidative stress by cysteine availability in pancreatic beta-cells

Pancreatic beta-cells are susceptible to oxidative stress, which is related closely to the islet dysfunction. In the present study, using the pancreatic cell lines HIT-T15 and RINm5F as known in vitro models of impaired beta-cell function as well as primary rat islet beta-cells, we observed a relationship between intracellular glutathione levels and oxidative stress-mediated cell dysfunction. Hydrogen peroxide and 4-hydroxy-2-nonenal caused cell death in HIT-T15 and RINm5F cells at lower concentrations compared with non-beta-cells, such as HepG2 and NRK-49F cells. The extent of the cytotoxicity caused by the model oxidants was inversely correlated well with intracellular glutathione levels in the cell lines used. Treatment of HIT-T15 and RINm5F cells with l-cysteine or l-cystine significantly augmented the glutathione contents, surpassing the effect of N-acetylcysteine, and abrogated 4-hydroxy-2-nonenal-mediated cytotoxicity almost completely. l-Cysteine increased intracellular glutathione levels in primary beta-cells as well. Supplementation of l-cysteine to the RINm5F cell culture inhibited 4-hydroxy-2-nonenal-mediated cytosolic translocation of PDX-1, a key transcription factor for beta-cell function. Intrinsic transport activities (V(max)/K(m)) of the l-cystine/l-glutamate exchanger in HIT-T15 and RINm5F cells were considerably lower than that in NRK-49F cells, although gene expressions of the exchanger were similar in these cells. Results obtained from the present study suggest that the restricted activity of the l-cystine/l-glutamate exchanger controls the levels of intracellular glutathione, thereby making beta-cells become susceptible to oxidative stress.

Plasma and dietary vitamin E in relation to insulin secretion and sensitivity

AIM

In the Insulin Resistance and Atherosclerosis Study (IRAS), we have previously shown a protective effect of plasma alpha-tocopherol concentration against diabetes incidence among persons not taking vitamin E supplements. The biologic mechanism for such a protective effect could involve improvement in either insulin sensitivity (S(I)), insulin secretion or both. Thus, we examined vitamin E in relation to insulin secretion and S(I) among persons not taking vitamin E supplements.

METHODS

This analysis included 457 adults aged 40-69 years without a previous diabetes diagnosis or vitamin E supplement use at baseline and seen at the 5-year follow-up examination. Baseline nutrient intake was estimated from a validated 1-year food frequency questionnaire; plasma levels of alpha-tocopherol were also assessed. At follow up, a frequently sampled intravenous glucose tolerance test determined S(I), acute insulin response to glucose (AIR), and the disposition index (DI) was calculated as the sum of the log-transformed AIR and S(I) to reflect pancreatic compensation for insulin resistance.

RESULTS

In multivariable regression analyses, no relationship was observed for vitamin E intake and either S(I), AIR or DI. However, plasma alpha-tocopherol concentration was positively associated with log-transformed S(I) (beta= 0.27 +/- 0.09, p < 0.01) and DI (beta= 0.41 +/- 0.14, p < 0.01), but not with log-transformed AIR.

CONCLUSIONS

Plasma concentration of alpha-tocopherol may improve S(I) and pancreatic compensation for insulin resistance, although it does not seem to be related to acute insulin response.

The radical scavenger edaravone counteracts diabetes in multiple low-dose streptozotocin-treated mice

Edaravone is a potent scavenger of hydroxyl radicals and attenuates oxidative damage-related neurodegenerative diseases. Previous studies suggest that oxidative stress plays a key role in the pathogenesis of diabetes. The present study examined the effect of edaravone on diabetes in multiple low-dose streptozotocin-treated mice. Mice treated with low-doses of streptozotocin for five consecutive days showed progressive hyperglycemia and an increased incidence of diabetes. Daily treatment with edaravone during the streptozotocin injections counteracted the multiple low-dose streptozotocin-induced hyperglycemia in a dose-dependent manner. Edaravone protected against the multiple low-dose streptozotocin-induced reduction in pancreatic insulin. The suppressive effects of edaravone were also observed when it was administered after the last injection of streptozotocin. Histochemical examination showed that multiple low-dose streptozotocin treatment caused mononuclear cell infiltration in pancreatic islets, followed by hyperglycemia, and that edaravone significantly inhibited the multiple low-dose streptozotocin-induced insulitis. Multiple low-dose streptozotocin treatment also increased the lipid peroxidation product thiobarbituric acid reactive substance in pancreatic tissues of mice, and this effect was completely inhibited by edaravone. These findings suggest that edaravone, even after streptozotocin treatment, counteracts the development of multiple low-dose streptozotocin-induced diabetes by scavenging free radicals, which are possible mediators of the immune destruction of islet beta cells.

Evaluation of serum selenium levels in Turkish women with gestational diabetes mellitus, glucose intolerants, and normal controls

The aim of the study was to investigate the association between serum selenium levels in patients with gestational diabetes mellitus (GDM) and glucose intolerants and compare them with those of glucose-tolerant pregnant women. This cross-sectional study was prospectively performed in a total of 178 pregnant women undergoing a 50-g oral glucose tolerance test between 24 and 28 weeks of gestation who were grouped according to their status of glucose tolerance as with gestational diabetes (group A, abnormal 1- and 3-h glucose tolerance test; n = 30), glucose intolerant (group B, abnormal 1-h but normal 3-h glucose tolerance test; n = 47), or normal controls (group C, normal 1-h glucose test; n = 101). Serum selenium levels were measured with a graphite furnace atomic absorption spectrophotometer using a matrix modifier. Median maternal age and gestational age at the time of diagnosis in group A (gestational age = 24.8 [24-27]), group B (gestational age = 24.7 [24-27]), and group C (gestational age = 25 [24-28]) did not differ. Patients with gestational diabetes mellitus and those with glucose intolerants had lower selenium level than that of the normal pregnant women (P < 0.001). There was a significant inverse correlation between selenium and blood glucose level, and also selenium supplementation might prove beneficial on patients with GDM and prevent or retard them from secondary complications of diabetes.

Effect of antioxidants L-ascorbic acid and alpha-tocopherol supplementation in nickel exposed hyperglycemic rats

Nickel-induced hyperglycemia in rats under both acute and subchronic exposure conditions could be due to increased hepatic glycogenolysis, increased pancreatic release of glucagon, decreased peripheral utilization of glucose, or gluconeogenesis. We studied the effect of acute and subchronic nickel sulfate treatment on Wister strain male albino rats simultaneously treated with combined L-ascorbic acid and alpha-tocopherol. The simultaneous treatment with L-ascorbic acid or alpha-tocopherol appears to be beneficial for regulating glucose homeostasis in rats. A significant rise of blood glucose level was also observed with L-ascorbic acid supplementation alone, but not in the case of alpha-tocopherol supplementation alone.

Defective functional β-cell mass and Type 2 diabetes in the Goto-Kakizaki rat model

Increasing evidence indicates that decreased functional β-cell mass is the hallmark of Type 2 diabetes mellitus. Therefore, the debate focuses on the possible mechanisms responsible for abnormal islet microenvironment, decreased β-cell number, impaired β-cell function and their multifactorial etiologies. The information available on the Goto-Kakizaki/Par rat line, one of the best characterized animal models of spontaneous Type 2 diabetes mellitus, are reviewed in such a perspective. We propose that the defective β-cell mass and function in the Goto-Kakizaki/Par model reflect the complex interactions of multiple pathogenic players, including several independent loci containing genes responsible for some diabetic traits (but not decreased β-cell mass), gestational metabolic impairment inducing an epigenetic programming of the pancreas (decreased β-cell neogenesis), which is transmitted to the next generation, and loss of β-cell differentiation due to chronic exposure to hyperglycemia, inflammatory mediators, oxidative stress and perturbed islet microarchitecture.

Aldehydes and disturbance of carbohydrate metabolism: some consequences and possible approaches to its normalization

There are many well-documented errors of metabolism involving genetic defects that affect carbohydrate utilization. The array of disorders includes the defective utilization of glucose, as well as enzymatic deficiencies in glycolysis and gluconeogenesis, and the pentose phosphate pathway. Besides, there is considerable literature about metabolic syndrome and diabetes. However, the main problem of their origin remains obscure. Also, it is presently beyond doubt that there are various causes of insulin resistance. The development of insulin resistance may be associated not only with insulin production disorders or presence of insulin antagonists but also with modification of the number of receptors and sensitivity of peripheral tissues. The insulin resistance originates from insulin signal transmission defects at its initial stages. It is presently uncertain which mechanisms of adaptation regulation are activated or should be activated under hyperglycemia conditions. This is the main problem of the selection of strategy of hyperglycemia treatment but it is important that aldehydes - the secondary products of lipid peroxidation and protein glycation (malondialdehyde and methylglyoxal) - make a contribution to abnormal metabolism. As far as the role of methylglyoxal in inhibition of antioxidant enzymes is concerned, the involvement of the ketoaldehyde in such processes as oxidative stress, cell proliferation control, and carbohydrate metabolism disorders does not cast any doubt.

Antidiabetic effect of long-term supplementation with Siraitia grosvenori on the spontaneously diabetic Goto–Kakizaki rat

Siraitia grosvenori Swingle (SG) is a traditional Chinese fruit used as a folk medicine. Its extract (SG-ex) contains potent sweet elements with a sweetness several hundred times higher than table sugar. We investigated the antidiabetic effect of SG-ex in the type 2 diabetic Goto–Kakizaki (GK) rat. Diabetic 7-week-old GK rats were fed a diet supplemented with 0·4 % of the SG-ex for 13 weeks, and its antidiabetic effects were evaluated. SG-ex had no effect on food intake or body weight. In oral glucose tolerance tests (OGTT), SG-ex supplementation improved the insulin response at 15 min (control, 63 (sem 6) pm; SG-ex, 107 (sem 20) pm; P < 0·05) and reduced the plasma glucose level at 120 min after the glucose administration (control, 18·5 (sem 0·8) mm; SG-ex, 14·8 (sem 0·7) mm; P < 0·05). The total amount of insulin in whole pancreas taken from fasting rats was higher in the SG-ex-supplemented group, which may explain the greater capacity to secrete insulin during the OGTT. Thiobarbituric acid-reactive substances in both the liver and the plasma were lower in the SG-ex-supplemented group, suggesting that an absorbable component in SG-ex has an antioxidative effect on lipid peroxidation, thereby counteracting the oxidative stress caused by a diabetic state. Excreted urine volume and urinary albumin level for 24 h were both reduced in the SG-ex-supplemented group, suggesting the attenuation of kidney damage that is caused by diabetes. These data indicate that SG-ex supplementation may prevent complications and attenuate pathological conditions for type 2 diabetes, along with its sweet characteristics.