Vitamin E delays diabetes onset in the non-obese diabetic mouse

Aldehyde and xanthine oxidase activities in tissues of streptozotocin-induced diabetic rats: effects of vitamin E and selenium supplementation

Effects of vitamin E and selenium supplementation on aldehyde oxidase (AO) and xanthine oxidase (XO) activities and antioxidant status in liver, kidney, and heart of streptozotocin (STZ)-induced diabetic rats were examined. AO and XO activities increased significantly after induction of diabetes in rats. Following oral vitamin E (300 mg/kg) and sodium selenite (0.5 mg/kg) intake once a day for 4 weeks, XO activity decreased significantly. AO activity decreased significantly in liver, but remained unchanged in kidney and heart of vitamin E- and selenium-treated rats compared to the diabetic rats. Total antioxidants status, paraoxonase-1 (PON1) and erythrocyte superoxide dismutase activities significantly decreased in the diabetic rats compared to the controls, while a higher fasting plasma glucose level was observed in the diabetic animals. The glutathione peroxidase activity remained statistically unchanged. Malondialdehyde and oxidized low-density lipoprotein levels were higher in the diabetic animals; however, these values were significantly reduced following vitamin E and selenium supplementation. In summary, both AO and XO activities increase in STZ-induced diabetic rats, and vitamin E and selenium supplementation can reduce these activities. The results also indicate that administration of vitamin E and selenium has hypolipidemic, hypoglycemic, and antioxidative effects. It decreases tissue damages in diabetic rats, too.

Effects of vitamin E supplementation on glycaemic control in type 2 diabetes: systematic review of randomized controlled trials

WHAT IS KNOWN AND OBJECTIVE

Lowering haemoglobin A(₁c) (HbA(₁c)) has clearly been shown to reduce microvascular complications of diabetes and possibly macrovascular disease and vitamin E has been suggested as a possibly useful intervention. Our aim is to evaluate the effect of vitamin E supplementation on glycaemic control in type 2 diabetes.

METHODS

Clinical studies of vitamin E were identified from computerized searches of MEDLINE, EMBASE, EBM reviews and the Cochrane Library up until November 2008. Historical searches of reference lists of relevant articles were also undertaken. To be included in our review, a study had to be: (i) a randomized controlled trial comparing vitamin E monopreparation against placebo or no treatment in patients with type 2 diabetes, (ii) lasting at least 8 weeks, and (iii) reporting glycated haemoglobin or HbA(₁c). There was no language restriction. Study selection, data extraction and study quality assessment were performed by three reviewers with disagreement resolved by discussion. Treatment effect was estimated with the mean difference in the changes of HbA(₁c) from baseline to final assessment between the vitamin E and the control groups.

RESULTS

Nine trials involving 418 patients were included in this review. Vitamin E supplementation did not improve glycaemic control in the full set of type 2 diabetes patients. It was effective only in a subgroup of patients with inadequate glycaemic control at baseline (HbA(₁c) ≥ 8%) and in those whose baseline serum vitamin E levels were below normal ranges. The pooled mean difference in the changes of HbA(₁c) was -0.58% (95% CI -0.83% to -0.34%; P < 0.00001) which was the same for both subgroups of patients.

WHAT IS NEW AND CONCLUSIONS

The evidence suggests no beneficial effect of vitamin E supplementation in improving glycaemic control in unselected patients with type 2 diabetes. However, HbA(₁c) may decrease with vitamin E supplementation in patients with inadequate glycaemic control or low serum levels of vitamin E. This shows the importance of targeting therapy. Due to the limitations of the available evidence, further studies are warranted. Also, the safety and long-term benefit of such supplements remain to be determined before its clinical benefit can be established unequivocably.

Infant feeding and the risk of type 1 diabetes

Type 1 diabetes is generally considered to be a chronic, immune-mediated disease with a subclinical prodrome during which beta cell autoimmunity becomes overt disease at a variable rate in genetically susceptible individuals. Accumulated evidence supports a critical role of environmental factors in its development. Prospective birth cohort studies show that the first signs of beta cell autoimmunity may be initiated during the first year of life. This implies that risk factors for beta cell autoimmunity and type 1 diabetes must be operative in infancy. Early nutrition provides essential exogenous exposures in that period. This article discusses the role of factors related to infant nutrition in the development of beta cell autoimmunity and type 1 diabetes and the potential mechanistic pathways involved. So far, no specific dietary factor has been shown to be an unequivocal risk factor for beta cell autoimmunity or type 1 diabetes, and there are a number of contradictory observations with regard to the effect of various foods. This may reflect geographic and cultural differences in infant-feeding practices. Most studies suggest that the early introduction of complex foreign proteins may be a risk factor for beta cell autoimmunity, and a pilot intervention trial has implied that weaning to a highly hydrolyzed formula may decrease the risk of beta cell autoimmunity. Lack of vitamin D supplementation and accelerated growth might increase the risk of type 1 diabetes. Additional work, which includes the application of modern approaches such as metabolomics and epigenomics, is needed to discern the contribution of dietary factors in infancy to the diabetic disease process.

Intake of antioxidant vitamins and trace elements during pregnancy and risk of advanced beta cell autoimmunity in the child

BACKGROUND

Type 1 diabetes may have its origins in the fetal period of life. Free radicals were implicated in the cause of type 1 diabetes. It was hypothesized that antioxidant nutrients could protect against type 1 diabetes.

OBJECTIVE

We assessed whether high maternal intake of selected dietary antioxidants during pregnancy is associated with a reduced risk of advanced beta cell autoimmunity in the child, defined as repeated positivity for islet cell antibodies plus >/=1 other antibody, overt type 1 diabetes, or both.

DESIGN

The study was carried out as part of the population-based birth cohort of the Type 1 Diabetes Prediction and Prevention Project. The data comprised 4297 children with increased genetic susceptibility to type 1 diabetes, born at the University Hospital of Oulu or Tampere, Finland, between October 1997 and December 2002. The children were monitored for diabetes-associated autoantibodies from samples obtained at 3-12-mo intervals. Maternal antioxidant intake during pregnancy was assessed postnatally with a self-administered food-frequency questionnaire, which contained a question about consumption of dietary supplements.

RESULTS

Maternal intake of none of the studied antioxidant nutrients showed association with the risk of advanced beta cell autoimmunity in the child. The hazard ratios, indicating the change in risk per a 2-fold increase in the intake of each antioxidant, were nonsignificant and close to 1.

CONCLUSION

High maternal intake of retinol, beta-carotene, vitamin C, vitamin E, selenium, zinc, or manganese does not protect the child from development of advanced beta cell autoimmunity in early childhood.

Serum alpha- and gamma-tocopherol concentrations and risk of advanced beta cell autoimmunity in children with HLA-conferred susceptibility to type 1 diabetes mellitus

AIMS/HYPOTHESIS

The aim of our study was to assess the associations of serum alpha- and gamma-tocopherol concentrations with the risk of advanced beta cell autoimmunity in children with HLA-conferred genetic susceptibility to type 1 diabetes mellitus.

METHODS

A case-control study with 108 cases with advanced beta cell autoimmunity and 216 matched control participants nested within the birth cohort of the Type 1 Diabetes Prediction and Prevention Project. A serum sample for vitamin E analyses was collected from all the children in the cohort at the age of 1 year and thereafter at 12 month intervals. For each case-control group, all the repeated serum samples up to the age of seroconversion to autoantibody positivity in the case were analysed. A conditional logistic regression model was used to determine potential associations between seroconversion and serum tocopherol concentrations.

RESULTS

Serum alpha- or gamma-tocopherol concentrations were not significantly associated with the risk of advanced beta cell autoimmunity. The odds ratio (95% CI) for micromol/l increase in serum concentration of the first-year sample was 0.97 (0.92-1.03) for alpha-tocopherol and 1.10 (0.70-1.74) for gamma-tocopherol. However, there was an interaction between high values of gamma-tocopherol at the age of 1 year and the time of seroconversion (p = 0.024).

CONCLUSIONS/INTERPRETATION

It seems unlikely that high concentrations of alpha- or gamma-tocopherol protect against advanced beta cell autoimmunity in young children.

Vitamin E and risk of type 2 diabetes in the women's health study randomized controlled trial

We directly assessed the efficacy of vitamin E supplements for primary prevention of type 2 diabetes among apparently healthy women in the Women's Health Study randomized trial. Between 1992 and 2004, 38,716 apparently healthy U.S. women aged >or=45 years and free of diabetes, cancer, and cardiovascular disease were in two randomly assigned intervention groups and received 600 IU of vitamin E (alpha-tocopherol, n = 19,347) or placebo (n = 19,369) on alternate days. During a median 10-year follow-up, there were 827 cases of incident type 2 diabetes in the vitamin E group and 869 in the placebo group, a nonsignificant 5% risk reduction (relative risk [RR] 0.95 [95% CI 0.87-1.05], P = 0.31). There was no evidence that diabetes risk factors including age, BMI, postmenopausal hormone use, multivitamin use, physical activity, alcohol intake, and smoking status modified the effect of vitamin E on the risk of type 2 diabetes. In a sensitivity analysis taking compliance into account, women in the vitamin E group had an RR of 0.93 (95% CI 0.83-1.04) (P = 0.21) compared with those randomized to placebo. In this large trial with 10-year follow-up, alternate-day doses of 600 IU vitamin E provided no significant benefit for type 2 diabetes in initially healthy women.

Serum alpha-tocopherol concentrations and risk of type 1 diabetes mellitus: a cohort study in siblings of affected children

Animal models have indicated that alpha-tocopherol may protect against type 1 diabetes mellitus (DM1). Epidemiological data on the subject are scarce. The objective of this study was to evaluate the association of serum alpha-tocopherol concentration and risk of DM1 in a cohort of initially non-diabetic siblings of children affected by DM1 (n = 722). We used two study designs: 1) Siblings who progressed to DM1 were compared with control siblings who remained negative for DM1-associated autoantibodies in a nested case-control study design. 2) All siblings with DM1-associated autoantibodies were prospectively followed for DM1. In both designs, high concentrations of serum alpha-tocopherol tended to be associated with a lower risk of DM1 (p = 0.08 and 0.09, respectively). Although the results did not reach statistical significance, they support the hypothesis that high alpha-tocopherol levels may protect against DM1.

The metabolic syndrome and antioxidant concentrations: findings from the Third National Health and Nutrition Examination Survey

Oxidative stress may play a role in the pathophysiology of diabetes and cardiovascular disease, but little is known about antioxidant status among individuals with the metabolic syndrome who are at high risk for developing these conditions. Using data from the Third National Health and Nutrition Examination Survey (1988-1994), we compared circulating concentrations of vitamins A, C, and E; retinyl esters; five carotenoids; and selenium in 8,808 U.S. adults aged > or = 20 years with and without the metabolic syndrome. After adjusting for age, sex, race or ethnicity, education, smoking status, cotinine concentration, physical activity, fruit and vegetable intake, and vitamin or mineral use, participants with the metabolic syndrome had significantly lower concentrations of retinyl esters, vitamin C, and carotenoids, except lycopene. With additional adjustment for serum lipid concentrations, vitamin E concentrations were significantly lower in participants with the metabolic syndrome than those without the syndrome. Retinol concentrations were similar between the two groups. After excluding participants with diabetes, the results were very similar. Consumption of fruits and vegetables was also lower among people with the metabolic syndrome. Adults with the metabolic syndrome have suboptimal concentrations of several antioxidants, which may partially explain their increased risk for diabetes and cardiovascular disease.

Carbohydrate-energy restriction may protect the rat brain against oxidative damage and improve physical performance

Chronic energy restriction, alpha-tocopherol supplementation and their interaction with exhaustive exercise were investigated. Eleven-week-old male Wistar rats (n 6x 10) were fed either a control (C), a 30 % carbohydrate-energy-restricted control (R) or an alpha-tocopherol-supplemented (S) diet for 5 months. The animals in each diet were divided into exercised (E) and non-exercised (NE) groups. Before killing, the exercised rats were required to run to exhaustion (39 (se 6), 69 (se 11) and 18 (se 2) min for the C, R and S groups, respectively). Lipid peroxidation (thiobarbituric acid-reactive substances; TBARS), protein damage (reactive carbonyls) and alpha-tocopherol were determined in gastrocnemius, liver, brain and/or plasma. There was no difference in lipid peroxidation between the R and C groups, but in liver and muscle peroxidation appeared significantly lower in the S than the other two diets. TBARS in the brain were similar in all groups. On the other hand, reactive carbonyls showed that both the R and S diets reduced protein damage in the brain, while exhaustive exercise increased it. For liver and muscle, however, reactive carbonyl levels were similar in all groups. alpha-Tocopherol supplementation increased the vitamin concentrations in liver, muscle and plasma, but exercise decreased them in plasma and brain. Carbohydrate-energy restriction increased (P=0.0025) resistance to exhaustive exercise considerably without depleting stores of alpha-tocopherol or exacerbating oxidative damage in monitored tissues. It is concluded that while exhaustive exercise promotes a tissue-specific oxidative damage detectable only in brain proteins, both experimental diets tended to ameliorate this condition.

Thiazolidinediones for the prevention of diabetes in the non-obese diabetic (NOD) mouse: implications for human type 1 diabetes

BACKGROUND

Thiazolidinediones (TZDs) are a recently introduced generation of drugs acting as receptor agonists to reduce insulin resistance and used currently in combination with other hypoglycaemic agents for the treatment of type 2 diabetes. In addition, TZDs possess anti-inflammatory properties that make them of interest for reducing the T-cell inflammation occurring in the islets in type 1 diabetes.

METHODS

The action of TZD treatment on diabetes incidence in the non-obese diabetic (NOD) mouse was studied by investigating the effect of rosiglitazone (RGL) (400 mg/kg body weight by gavage) from 3 weeks of age (soon after weaning) onwards and comparing its effect to that of troglitazone (TGL) given by the same route.

RESULTS

We found that RGL and TGL both significantly reduced diabetes incidence by >50% in the NOD mouse compared to litter-matched control NOD mice (p<0.05 and p<0.01, respectively). However, the withdrawal of TGL from the market due to hepatotoxicity led us to re-analyse our data for toxic liver effects. We found that TGL was more toxic to mice than RGL (causing ten deaths as compared with one death).

CONCLUSION

RGL reduces diabetes incidence in the NOD mouse model of type 1 diabetes. This may be an effect resulting from its action as on inhibitor of pro-inflammatory genes such as cytokines and metabolic proteases. Its use may be considered for trials designed to protect beta-cell function in humans, especially in patients with latent autoimmune diabetes of adults (LADA) and also for disease prevention.

The role of oxidative stress in the onset and progression of diabetes and its complications: a summary of a Congress Series sponsored by UNESCO-MCBN, the American Diabetes Association and the German Diabetes Society

This review summarises the results and discussions of an UNESCO-MCBN supported symposium on oxidative stress and its role in the onset and progression of diabetes. There is convincing experimental and clinical evidence that the generation of reactive oxygen species (ROI) is increased in both types of diabetes and that the onset of diabetes is closely associated with oxidative stress. Nevertheless there is controversy about which markers of oxidative stress are most reliable and suitable for clinical practice. There are various mechanisms that contribute to the formation of ROI. It is generally accepted that vascular cells and especially the endothelium become one major source of ROI. An important role of oxidative stress for the development of vascular and neurological complications is suggested by experimental and clinical studies. The precise mechanisms by which oxidative stress may accelerate the development of complications in diabetes are only partly known. There is however evidence for a role of protein kinase C, advanced glycation end products (AGE) and activation of transcription factors such as NF kappa B, but the exact signalling pathways and the interactions with ROI remain a matter of discussion. Additionally, results of very recent studies suggest a role for ROI in the development of insulin resistance. ROI interfere with insulin signalling at various levels and are able to inhibit the translocation of GLUT4 in the plasma membrane. Evidence for a protective effect of antioxidants has been presented in experimental studies, but conclusive evidence from patient studies is missing. Large-scale clinical trials such as the DCCT Study or the UKPDS Study are needed to evaluate the long-term effects of antioxidants in diabetic patients and their potential to reduce the medical and socio-economic burden of diabetes and its complications.

Treatment with antioxidants at onset of type 1 diabetes in children: a randomized, double-blind placebo-controlled study

BACKGROUND

In recent years different types of immune interventions have been tried at the onset of type 1 diabetes. Although some have shown effects, none have proven to be sufficiently effective to justify the inherent risks and side effects. Antioxidants have no or minimal side effects. If they can protect the beta cells against free oxygen radicals during the inflammatory process this would be a safe and cheap intervention. To evaluate this hypothesis a combination of various antioxidative agents was employed in a double-blind randomized study.

METHODS

The study group comprised 46 children aged 1-17 years at diagnosis. They were followed for 3 years: 2 years whilst taking the tablets and 1 year of follow-up. Twenty-four children were randomly allocated to active treatment with high doses of antioxidants and 22 children to placebo tablets. The tablets were the same size and tasted identical.

RESULTS

Twenty patients had for more than 1 month an insulin dose <0.5 U/kg in parallel with a normal HbA(1c) value and stable blood glucose values, but with no difference observed between those with and without active treatment. Nor was any significant difference observed regarding C-peptide values, fasting as well as stimulated. Whilst the antioxidants demonstrated no positive effect, they also had no negative side effects.

CONCLUSION

At diagnosis of type 1 diabetes in children, high doses of antioxidative agents have no effect either on the preservation of beta cell function or on metabolic balance.

Dietary zinc supplementation inhibits NFkappaB activation and protects against chemically induced diabetes in CD1 mice

Zinc status in patients with Type I diabetes is significantly lower than healthy controls. Whether zinc supplementation can prevent the onset of Type I diabetes is unknown. Recent studies have suggested that the generation of reactive oxygen species (ROS) is a cause of beta cell death leading to Type I diabetes. In addition, we found that activation of NFkappaB (a ROS-sensitive transcription factor that regulates immune responses) may be the key cellular process that bridges oxidative stress and the death of beta cells. Zinc is a known antioxidant in the immune system. Therefore, this study is designed to test whether an increase in dietary zinc can prevent the onset of Type I diabetes by blocking NFkappaB activation in the pancreas. The results show that high zinc intake significantly reduced the severity of Type I diabetes (based on hyperglycemia, insulin level, and islet morphology) in alloxan and streptozotocin-induced diabetic models. Zinc supplementation also inhibited NFkappaB activation and decreased the expression of inducible NO synthase, a downstream target gene of NFkappaB. It is concluded that zinc supplementation can significantly inhibit the development of Type I diabetes. The ability of zinc to modulate NFkappaB activation in the diabetogenic pathway may be the key mechanism for zinc's protective effect. Inhibition of the NFkappaB pathway may prove to be an important criterion for choosing nutritional strategies for Type I diabetes prevention.

Troglitazone can prevent development of type 1 diabetes induced by multiple low-dose streptozotocin in mice

Recent investigations suggest that cytotoxic cytokines such as tumor necrosis factor (TNF)alpha and interleukin (IL)-1beta or free radicals play an essential role in destruction of pancreatic beta cells in Type 1 diabetes and that, therefore, anti-oxidant or anti-TNF alpha and IL-1beta therapy could prevent the development of Type I diabetes. Troglitazone belongs to a novel class of antidiabetic agent possessing the ability to enhance insulin action provably through activating PPAR gamma and to scavenge free radicals. In the present study, we examined whether troglitazone can prevent the development of Type 1 diabetes in multiple, low-dose streptozotocin (MLDSTZ)-injected mice. In addition, effects of troglitazone on cytokine-induced pancreatic beta cell damage were examined in vitro. Type 1 diabetes was induced by MLDSTZ injection to DBA/2 mice (40 mg/kg/day for 5 days). Troglitazone was administered as a 0.2% food admixture (240 mg/kg/day) for 4 weeks from the start of or immediately after STZ injection. MLDSTZ injection elevated plasma glucose to 615 +/- 8 mg/dl 4 weeks after final STZ injection and was accompanied by infiltration of leukocytes to pancreatic islets (insulitis). Troglitazone treatment with MLDSTZ injection prevented hyperglycemia (230 +/- 30 mg/dl) and, suppressed insulitis and TNF alpha production from intraperitoneal exudate cells. TNF alpha (10 pg/ml) and IL-1beta (1 pg/ml) addition to hamster insulinoma cell line HIT-T15 for 7 days in vitro decreased insulin secretion and cell viability. Simultaneous troglitazone addition (0.03 to approximately 3 microM) significantly improved cytokine-induced decrease in insulin secretion and in cell viability. These findings suggest that troglitazone prevents the development of Type 1 diabetes in the MLDSTZ model by suppressing insulitis associated with decreasing TNF alpha production from intraperitoneal exudate cells and the subsequent TNF alpha and IL-1beta-induced beta cell damage.

Low vitamin E status is a potential risk factor for insulin-dependent diabetes mellitus

OBJECTIVES

To study the association of vitamin E status with occurrence of insulin-dependent diabetes mellitus (IDDM).

DESIGN

A case-control study nested within a 21-year follow-up study.

SUBJECTS

Nineteen incident IDDM patients with an average age of 28 years and three individually matched controls per patient.

MAIN OUTCOME MEASURE

Serum concentrations of alpha-tocopherol.

RESULTS

Serum alpha-tocopherol concentration at the baseline examination was inversely associated with IDDM occurring 4-14 years later. The cholesterol-adjusted relative risk of IDDM between the highest and lowest thirds of the vitamin concentration was 0.12 (95% confidence interval = 0.02-0.85).

CONCLUSIONS

The finding corroborates the hypothesis of a protective effect of vitamin E against development of IDDM. Because of the relatively old age of the patients in the present population, further epidemiological studies on the topic are warranted.

Melatonin rhythms in mice: role in autoimmune and lymphoproliferative diseases

Production of melatonin (MLT) in the pineal gland (PG) of inbred mice such as C57BI/6J, BALB/c, and AKR strains is still a matter of debate. In a recent study we validated the presence of MLT in the PG of these inbred mice. We found a short-term MLT peak in the middle of the dark period with a pattern that mirrors that found previously in the serum. In another study, based on the known immunoregulatory role of MLT, we investigated the role of the PG and MLT in autoimmune diabetes mellitus type I using, as an experimental model, female nonobese diabetic (NOD) mice. Mice were pinealectomized or treated chronically with MLT (injected subcutaneously or administered via drinking water). We found that neonatal pinealectomy accelerates the development of disease in female NOD mice, whereas exogenous MLT protects animals. This is in spite of the fact that MLT increased the production of insulin autoantibodies (IAA). We conclude that PG and MLT influence the development of autoimmune diabetes, although the mechanism of action needs further investigation.

Serum concentrations of vitamins A and E in impaired glucose tolerance

Serum concentrations of vitamins A and E were measured in 32 subjects with impaired glucose tolerance (IGT) and 148 subjects with normal glucose tolerance using reversed-phase high-performance liquid chromatography. Fasting glucose, insulin and lipid concentrations were also measured. Serum vitamin A concentrations were higher in subjects with IGT 2.5 (1.1-3.4) vs. 2.1 (1.4-3.2) mumol/l [median (2.5-97.5 percentiles)] (P = 0.002), the difference remaining significant after adjustment for triglycerides (P = 0.028). There was a univariate association between vitamin A levels and insulin resistance (r = 0.164; P = 0.02) and in multivariate logistic regression analysis the relative risk of subjects with high vitamin A concentrations having IGT was 3.8 (P = 0.002). There were no differences in serum vitamin E concentrations between the groups. These data suggest that higher vitamin A concentrations found in non-insulin-dependent diabetes pre-date the onset of diabetes. Further studies are required to confirm this finding and to investigate the possibility of a role for vitamin A in the aetiology of diabetes and IGT.

Role of the pineal gland and melatonin in the development of autoimmune diabetes in non-obese diabetic mice

Earlier studies on the immunoregulatory role of the pineal gland and melatonin revealed that melatonin counteracts immunosuppression and thymus atrophy induced by stress or corticosteroid treatment. Moreover, melatonin protects mice injected with encephalitogenic viruses, synergizes with interleukin-2 (IL-2) in cancer immunotherapy and rescues hematopoiesis from cancer chemotherapy toxicity. In regard to the mechanism of action, melatonin seems to act directly on CD4+ lymphocytes which release opioid peptides with immunoenhancing properties along with other cytokines. Because of these findings, we investigated the role of the pineal gland and melatonin in autoimmune diabetes mellitus type I using, as an experimental model, female non-obese diabetic (NOD) mice. Mice were pinealectomized or treated chronically with melatonin (injected subcutaneously or administered via drinking water). This paper shows that neonatal pinealectomy accelerates the development of the disease in female NOD mice while exogenous melatonin protects the animals. This in spite of the fact that melatonin increased the production of insulin autoantibodies (IAA). We conclude that the pineal gland and melatonin influence the development of autoimmune diabetes although the mechanism of action that needs further investigation.