The effect of vitamin E on endothelial function of micro- and macrocirculation and left ventricular function in type 1 and type 2 diabetic patients

Effect of vitamin E intake on glycemic control and insulin resistance in diabetic patients: an updated systematic review and meta-analysis of randomized controlled trials

Since a 2014 meta-analysis, several randomized controlled trials (RCTs) evaluating the effect of vitamin E intake on glycemic indices and insulin resistance in adults with diabetes have reached inconsistent conclusions. Therefore, we updated the previous meta-analysis to summarize the current evidence in this regard. Online databases including PubMed, Scopus, ISI Web of Science, and Google Scholar were searched to identify relevant studies published up to September 30, 2021, using relevant keywords. Random-effects models were used to obtain overall mean difference (MD) comparing vitamin E intake with a control group. In total, 38 RCTs with a total sample size of 2171 diabetic patients (1110 in vitamin E groups and 1061 in control groups) were included. Combining the results from 28 RCTs on fasting blood glucose, 32 RCTs on HbA1c, 13 RCTs on fasting insulin, and 9 studies on homeostatic model assessment for insulin resistance (HOMA-IR) showed a summary MD of -3.35 mg/dL (95% CI: -8.10 to 1.40, P = 0.16), -0.21% (95% CI: -0.33 to -0.09, P = 0.001), -1.05 µIU/mL (95% CI: -1.53 to -0.58, P < 0.001), and -0.44 (95% CI: -0.82 to -0.05, P = 0.02), respectively. This indicates a significant lowering effect of vitamin E on HbA1c, fasting insulin and HOMA-IR, while no significant effect on fasting blood glucose in diabetic patients. However, in subgroup analyses, we found that vitamin E intake significantly reduced fasting blood glucose in studies with an intervention duration of < 10 weeks. In conclusion, vitamin E intake has a beneficial role in improving HbA1c and insulin resistance in a population with diabetes. Moreover, short-term interventions with vitamin E have resulted in lower fasting blood glucose in these patients. This meta-analysis was registered in PROSPERO with code CRD42022343118.

Endothelial dysfunction: developmental mechanisms and therapeutic strategies

Introduction: Every year the importance of the normal functioning of the endothelial layer of the vascular wall in maintaining the health of the body becomes more and more obvious.

The physiological role of the endothelium: The endothelium is a metabolically active organ actively involved in the regulation of hemostasis, modulation of inflammation, maintenance of hemovascular homeostasis, regulation of angiogenesis, vascular tone, and permeability.

Risk factors for the development of endothelial dysfunction: Currently, insufficient bioavailability of nitric oxide is considered the most significant risk factor for endothelial dysfunction.

Mechanisms of development of endothelial dysfunction: The genesis of endothelial dysfunction is a multifactorial process. Among various complex mechanisms, this review examines oxidative stress, inflammation, hyperglycemia, vitamin D deficiency, dyslipidemia, excess visceral fat, hyperhomocysteinemia, hyperuricemia, as well as primary genetic defect of endotheliocytes, as the most common causes in the population underlying the development of endothelial dysfunction.

Markers of endothelial dysfunction in various diseases: This article discusses the main biomarkers of endothelial dysfunction currently used, as well as promising biomarkers in the future for laboratory diagnosis of this pathology.

Therapeutic strategies: Therapeutic approaches to the endothelium in order to prevent or reduce a degree of damage to the vascular wall are briefly described.

Conclusion: Endothelial dysfunction is a typical pathological process involved in the pathogenesis of many diseases. Thus, pharmacological agents with endothelioprotective properties can provide more therapeutic benefits than a drug without such an effect.

Could nutrient supplements provide additional glycemic control in diabetes management? A systematic review and meta-analysis of randomized controlled trials of as an add-on nutritional supplementation therapy

This systematic review and meta-analysis assessed the antidiabetic effect of pharmaconutrients as an add-on in type 2 diabetes mellitus patients by pooling data from currently available randomized controlled trials (RCTs). Data sources included the PubMed and EMBASE, Cochrane Central Register of Controlled Trials. RCTs reporting changes in glycosylated hemoglobin (HbA1c), fasting blood glucose (FBG), or homeostasis model assessment of insulin resistance (HOMA-IR) levels following add-on pharmaconutritional therapies for T2DM patients consuming antidiabetic drugs were targeted. Using random-effects meta-analyses, we identified pharmaconutrients with effects on glycemic outcomes. Heterogeneity among studies was presented using I² values. Among 9537 articles, 119 RCTs with nine pharmaconutrients (chromium; coenzyme Q10; omega-3 fatty acids; vitamins C, D, and E; alpha-lipoic acid; selenium; and zinc) were included. Chromium (HbA1c, FBG, and HOMA-IR), coenzyme Q10 (HbA1c and FBG), vitamin C (HbA1c and FBG), and vitamin E (HbA1c and HOMA-IR) significantly improved glycemic control. Baseline HbA1c level and study duration influenced the effects of chromium and vitamin E on HbA1c level. Sensitivity analyses did not modify the pooled effects of pharmaconutrients on glycemic control. Administration of chromium, coenzyme Q10, and vitamins C and E for T2DM significantly improved glycemic control. This study has been registered in PROSPERO (CRD42018115229).

The effects of sesame oil on metabolic biomarkers: a systematic review and meta-analysis of clinical trials

Background

Clinical evidences showing the effects of sesame oil on metabolic biomarkers led to inconsistent results.

Propose

This meta-analysis was designed to examine the effects of sesame oil on metabolic biomarkers in adults, including the maximum number of clinical trials.

Methods

Google Scholar, PubMed, Web of Science, and Scopus were systematically searched to date up to July 2021 to identify eligible clinical trial studies. We obtained the pooled estimates of weighted mean differences (WMDs) with their 95% confidence intervals (CIs) using random-effects meta-analysis.

Result

Meta-analysis showed that sesame oil consumption significantly lowered the levels of fasting blood glucose (FBG) (WMD: -3.268 mg/dl; 95% CI: -4.677, -1.86; P < 0.001), and malondialdehyde (MDA) (WMD: -4.847 nmol/dL; 95% CI: -7.051, -2.698; P < 0.001) between the intervention and control groups. Also, this study showed sesame oil consumption significantly decreased HbA1C (WMD: -2.057%; 95% CI: -3.467, -0.646; P = 0.004), systolic blood pressure (SBP) (WMD: -2.679 mmHg; 95% CI: -5.257, -0.101; P < 0.001), diastolic blood pressure (DBP) (WMD: -1.981 mmHg; 95% CI: -3.916, -0.046; P = 0.045), body weight (WMD: -0.346 kg; 95% CI: -0.641, -0.051; P = 0.021), and body mass index (BMI) (WMD: -0.385 kg/m2; 95% CI:-0.721, -0.049; P = 0.025) after intervention. No significant effect was seen in serum insulin levels (p > .05).

Conclusions

The current study provided some evidence regarding the beneficial effects of sesame oil on metabolic biomarkers. Further studies are still required to confirm our results.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-022-00997-2.

Therapeutic potential of targeting oxidative stress in diabetic cardiomyopathy

Even in the absence of coronary artery disease and hypertension, diabetes mellitus (DM) may increase the risk for heart failure development. This risk evolves from functional and structural alterations induced by diabetes in the heart, a cardiac entity termed diabetic cardiomyopathy (DbCM). Oxidative stress, defined as the imbalance of reactive oxygen species (ROS) has been increasingly proposed to contribute to the development of DbCM. There are several sources of ROS production including the mitochondria, NAD(P)H oxidase, xanthine oxidase, and uncoupled nitric oxide synthase. Overproduction of ROS in DbCM is thought to be counterbalanced by elevated antioxidant defense enzymes such as catalase and superoxide dismutase. Excess ROS in the cardiomyocyte results in further ROS production, mitochondrial DNA damage, lipid peroxidation, post-translational modifications of proteins and ultimately cell death and cardiac dysfunction. Furthermore, ROS modulates transcription factors responsible for expression of antioxidant enzymes. Lastly, evidence exists that several pharmacological agents may convey cardiovascular benefit by antioxidant mechanisms. As such, increasing our understanding of the pathways that lead to increased ROS production and impaired antioxidant defense may enable the development of therapeutic strategies against the progression of DbCM. Herein, we review the current knowledge about causes and consequences of ROS in DbCM, as well as the therapeutic potential and strategies of targeting oxidative stress in the diabetic heart.

Combined effect of high-dose vitamin A, vitamin E supplementation, and zinc on adult patients with diabetes: A randomized trial

In type 2 diabetes mellitus (T2DM), hyperglycemia leads to oxidative insult. Vitamins A and E have antioxidant potentials and may help in managing diabetes. The combined effect of high-dose vitamin A plus E supplementation with and without zinc on T2DM, has never been examined. Thus, this study aimed to evaluate and compare the effect of high-dose vitamin A plus E supplementation (AE) versus high-dose vitamin A plus E with zinc (AEZ), on different diabetic parameters. Ninety-eight patients with T2DM were randomized to receive either: 50,000 IU vitamin A and 100 mg vitamin E (AE group, N = 36), an equivalent dose of vitamin A and E combined with 25 mg zinc (AEZ group, N = 35), or no supplements (control group, N = 27) for three months. Compared to control, AEZ group showed significant reductions in fasting blood glucose, 2 h postprandial blood glucose, and glycated hemoglobin (HbA1c) with significant increases in homeostasis model assessment of beta-cell function and difference value of fasting insulin. Two hair loss cases were recorded in both treated groups. Although vitamin A needs dose moderation, these results suggest that, high-dose vitamin A plus E supplementation combined with zinc may improve glycemic control, β-cell function, and insulin secretion in adults with T2DM.

Impact of Vitamin E supplementation on vascular function in haptoglobin genotype stratified diabetes patients (EVAS Trial): a randomised controlled trial

AIMS

Vitamin E (Vit-E) may preferentially improve cardiovascular risk in haptoglobin 2-2 (Hp2-2) genotype diabetes individuals. We studied the impact of Vit-E supplementation on vascular function in diabetes individuals stratified by haptoglobin genotype in Singapore.

METHODS

In this 24-week, double blind, placebo-controlled RCT, we recruited 187 subjects (101 Hp2-2, 86 non-Hp2-2).

INTERVENTION

alpha-tocopherol-400 IU.

PRIMARY OUTCOME

Change in EndoPAT-derived reactive-hyperaemia index (RHI) and augmentation index (AIx); Secondary Outcomes: Pulse-Wave velocity (Sphygmocor-PWV), carotid intima media thickness (CIMT), inflammation (hsCRP), derivatives of reactive-oxygen metabolites (dROMs), biological antioxidant-potential (BAPs), HbA1c, LDL-C, HDL-C and oxidised LDL-C (ox-LDL).

RESULTS

Overall, with Vit-E supplementation no significant change in RHI, PWV, CIMT, hsCRP, dROMS, BAPs, HDL-C and HbA1c was observed (p > 0.05); an increase in LDL-C with concomitant decrease in ox-LDL, and incidentally increase in eGFR was observed (p < 0.05). No interaction effect with haptoglobin genotype was seen for all outcomes (p > 0.05). Subgroup analysis: In the non-Hp-2-2 group, Vit-E supplementation led to a higher EndoPAT-derived AIx, accompanied by higher LDL and ox-LDL concentrations (p < 0.05); Hp2-2 group: Vit-E supplementation led to higher eGFR when compared to the non-Hp2-2 group (exploratory) (p < 0.05). We observed an interaction effect for baseline haptoglobin concentration (threshold > 119 mg/dl) with intervention in terms of increased EndoPAT-derived AIx in the Hp > 119 mg/dl group whereas no change in the group with Hp ≤ 119 mg/dl.

CONCLUSION

Vit-E supplementation did not show any preferential benefit or deleterious effect on vascular function in Hp2-2 diabetes subjects in Singapore. A possible deleterious effect of an increase in arterial stiffness in individuals with Hp > 119 mg/dl was observed. Future studies should consider personalisation based on baseline Hp concentrations in patients with T2DM rather than just Hp2-2 genotype to evaluate impact on the detailed lipid pathways, cardiac and renal physiology. The impact of ethnic differences needs to be explored in greater details.

Targeting vascular (endothelial) dysfunction

Cardiovascular diseases are major contributors to global deaths and disability-adjusted life years, with hypertension a significant risk factor for all causes of death. The endothelium that lines the inner wall of the vasculature regulates essential haemostatic functions, such as vascular tone, circulation of blood cells, inflammation and platelet activity. Endothelial dysfunction is an early predictor of atherosclerosis and future cardiovascular events. We review the prognostic value of obtaining measurements of endothelial function, the clinical techniques for its determination, the mechanisms leading to endothelial dysfunction and the therapeutic treatment of endothelial dysfunction. Since vascular oxidative stress and inflammation are major determinants of endothelial function, we have also addressed current antioxidant and anti-inflammatory therapies. In the light of recent data that dispute the prognostic value of endothelial function in healthy human cohorts, we also discuss alternative diagnostic parameters such as vascular stiffness index and intima/media thickness ratio. We also suggest that assessing vascular function, including that of smooth muscle and even perivascular adipose tissue, may be an appropriate parameter for clinical investigations.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Microvascular Changes in the Diabetic Foot

Impairment of the microcirculation of diabetic patients may contribute to secondary complications in the lower extremity, such as foot infections and ulcerations. These microcirculatory changes, which are mainly functional rather than structural, are responsible for the impaired ability of the microvasculature to vasodilate in response to injury. Dysfunction of vascular endothelial cells and vascular smooth muscle cells both contribute to the reduction in vasodilation that is observed in diabetic patients. Nerve-axon reflex related microvascular vasodilation is also impaired in the diabetic population, and there is a growing belief that both the failure of the vessels to dilate and the impairment of the nerve axon reflex are major causes for impaired wound healing in diabetic patients. Further studies are necessary to clarify the precise etiology of endothelial and smooth muscle dysfunction in diabetic patients so that potential therapeutic interventions may be identified.

Reversibility of endothelial dysfunction in diabetes: role of polyphenols

The endothelium, a thin single sheet of endothelial cells, is a metabolically active layer that coats the inner surface of blood vessels and acts as an interface between the circulating blood and the vessel wall. The endothelium through the secretion of vasodilators and vasoconstrictors serves as a critical mediator of vascular homeostasis. During the development of the vascular system, it regulates cellular adhesion and vessel wall inflammation in addition to maintaining vasculogenesis and angiogenesis. A shift in the functions of the endothelium towards vasoconstriction, proinflammatory and prothrombic states characterise improper functioning of these cells, leading to endothelial dysfunction (ED), implicated in the pathogenesis of many diseases including diabetes. Major mechanisms of ED include the down-regulation of endothelial nitric oxide synthase levels, differential expression of vascular endothelial growth factor, endoplasmic reticulum stress, inflammatory pathways and oxidative stress. ED tends to be the initial event in macrovascular complications such as coronary artery disease, peripheral arterial disease, stroke and microvascular complications such as nephropathy, neuropathy and retinopathy. Numerous strategies have been developed to protect endothelial cells against various stimuli, of which the role of polyphenolic compounds in modulating the differentially regulated pathways and thus maintaining vascular homeostasis has been proven to be beneficial. This review addresses the factors stimulating ED in diabetes and the molecular mechanisms of natural polyphenol antioxidants in maintaining vascular homeostasis.

Vascular endothelial dysfunction and pharmacological treatment

The endothelium exerts multiple actions involving regulation of vascular permeability and tone, coagulation and fibrinolysis, inflammatory and immunological reactions and cell growth. Alterations of one or more such actions may cause vascular endothelial dysfunction. Different risk factors such as hypercholesterolemia, homocystinemia, hyperglycemia, hypertension, smoking, inflammation, and aging contribute to the development of endothelial dysfunction. Mechanisms underlying endothelial dysfunction are multiple, including impaired endothelium-derived vasodilators, enhanced endothelium-derived vasoconstrictors, over production of reactive oxygen species and reactive nitrogen species, activation of inflammatory and immune reactions, and imbalance of coagulation and fibrinolysis. Endothelial dysfunction occurs in many cardiovascular diseases, which involves different mechanisms, depending on specific risk factors affecting the disease. Among these mechanisms, a reduction in nitric oxide (NO) bioavailability plays a central role in the development of endothelial dysfunction because NO exerts diverse physiological actions, including vasodilation, anti-inflammation, antiplatelet, antiproliferation and antimigration. Experimental and clinical studies have demonstrated that a variety of currently used or investigational drugs, such as angiotensin-converting enzyme inhibitors, angiotensin AT1 receptors blockers, angiotensin-(1-7), antioxidants, beta-blockers, calcium channel blockers, endothelial NO synthase enhancers, phosphodiesterase 5 inhibitors, sphingosine-1-phosphate and statins, exert endothelial protective effects. Due to the difference in mechanisms of action, these drugs need to be used according to specific mechanisms underlying endothelial dysfunction of the disease.

The Role of Organelle Stresses in Diabetes Mellitus and Obesity: Implication for Treatment

The type 2 diabetes pandemic in recent decades is a huge global health threat. This pandemic is primarily attributed to the surplus of nutrients and the increased prevalence of obesity worldwide. In contrast, calorie restriction and weight reduction can drastically prevent type 2 diabetes, indicating a central role of nutrient excess in the development of diabetes. Recently, the molecular links between excessive nutrients, organelle stress, and development of metabolic disease have been extensively studied. Specifically, excessive nutrients trigger endoplasmic reticulum stress and increase the production of mitochondrial reactive oxygen species, leading to activation of stress signaling pathway, inflammatory response, lipogenesis, and pancreatic beta-cell death. Autophagy is required for clearance of hepatic lipid clearance, alleviation of pancreatic beta-cell stress, and white adipocyte differentiation. ROS scavengers, chemical chaperones, and autophagy activators have demonstrated promising effects for the treatment of insulin resistance and diabetes in preclinical models. Further results from clinical trials are eagerly awaited.

α-Tocopherol Improves Microcirculatory Dysfunction on Fructose Fed Hamsters

Fructose, an everyday component of western diet associated to chronic hyperglycemia and enhanced free radical production, impairs endothelial function and supplementation with antioxidants might improve it. In this study we investigated if vitamin E could reverse the microvascular damage elicited by fructose. Male Syrian golden hamsters drank either 10% fructose solution (F) or filtered water (C), combined with three concentrations of vitamin E in their chows [zero, normal (VE) or 5X (5XVE)] during 60 days. Microvascular reactivity in response to topical application of acetylcholine (Ach; endothelium-dependent vasodilator) or sodium nitroprusside (SNP; endothelium-independent vasodilator) and macromolecular permeability increase induced by either 30 min ischemia followed by reperfusion (I/R) or topical application of histamine (5 μM) were assessed using the cheek pouch preparation. Compared to controls (drinking filtered water), fructose-drinking animals showed decreased vasodilatation to acetylcholine in all concentrations tested (-56.2% for 10^-9M, -53.9% for 10^-7M and -43.7% for 10^-5M). On the other hand, vitamin E supplementation resulted in increased responses for both water and fructose drinking groups (177.4% for F vs. F/5XVE and 241.6% for C vs. C/5XVE for 10^-5M Ach). Endothelial-independent vasodilatation explored by topical application of SNP was restored and even enhanced with the supplementation of 5X vitamin E in both groups (80.1% for F vs. F/5XVE; 144.2% for C vs. C/5XVE; 3.4% of difference for C/5XVE vs. F/5XVE on 10^-5M SNP). The number of leaky sites after I/R and histamine stimuli in vitamin E supplemented animals decreased (-25.1% and -15.3% for F vs. F/5XVE; and -21.7% and -16% of leaky sites comparing C vs. C/5XVE, respectively for I/R and histamine stimuli) pointing to tightening of the endothelial barrier for macromolecular permeability. Our results strongly suggest that vitamin E could improve the endothelial function and permeability barrier and also reverse impairments elicited by sugar overload.

Effects of supplementation with the fat-soluble vitamins E and D on fasting flow-mediated vasodilation in adults: a meta-analysis of randomized controlled trials

The effects of fat-soluble vitamin supplementation on cardiovascular disease (CVD) risk are not clear. Therefore, we performed a meta-analysis to quantify effects of fat-soluble vitamin supplements on fasting flow-mediated vasodilation (FMD) of the brachial artery, a validated marker to assess CVD risk. Randomized placebo-controlled trials (RCTs) were identified by a systematic search till July 2014. Seven RCTs studying the effects of vitamin E supplements (range: 300 to 1800 IU per day) and nine RCTs examining the effects of vitamin D supplements, that involved, respectively, 303 and 658 adults, were included. No studies with carotenoid or vitamin K supplements were found. Vitamin E supplementation increased FMD vs. control by 2.42% (95% CI: 0.46% to 4.37%; p = 0.015). No effects of vitamin D supplementation were found (0.15%; 95% CI: −0.21% to 0.51%; p = 0.41). These effects did not depend on subject characteristics, treatment characteristics or technical aspects of the FMD measurement. However, no dose-response relationship was evident for vitamin E, statistical significance depended on one study, while the levels of supplement were far above recommended intakes. The current meta-analysis, therefore, does not provide unambiguous evidence to support the use of fat-soluble vitamin supplements to improve fasting FMD in adults.

The role of prostaglandin and antioxidant availability in recovery from forearm ischemia-reperfusion injury in humans

BACKGROUND

Endothelial dysfunction, manifesting as attenuated flow-mediated dilation (FMD), is clinically important. Antioxidants may prevent this dysfunction; however, the acute effects of oral administration in humans are unknown. Low flow-mediated constriction (L-FMC), a further parameter of endothelial health, is largely unstudied and the mechanisms for this response unclear.

METHODS

Twelve healthy participants (five women and seven men) completed three test conditions: control; antioxidant cocktail (α-lipoic acid, vitamins C and E); and prostaglandin inhibitor ingestion (ibuprofen). Ultrasound measurements of brachial artery responses were assessed throughout 5 min of forearm ischemia and 3 min after. Subsequently, an ischemia-reperfusion injury was induced by a 20-min upper arm occlusion. Further, vascular function protocols were completed at 15, 30, and 45 min of recovery.

RESULTS

Endothelial dysfunction was evident in all conditions. FMD was attenuated at 15 min after ischemia-reperfusion injury (Pre: 6.24 ± 0.58%; Post15: 0.24 ± 0.75%; mean ± SD, P < 0.05), but recovered by 45 min. Antioxidant administration did not preserve FMD compared with control (P > 0.05). The magnitude of L-FMC was augmented at 15 min (Pre: 1.44 ± 0.27%; Post15: 3.75 ± 1.73%; P < 0.05) and recovered by 45 min. Ibuprofen administration produced the largest constrictive response (Pre: -1.13 ± 1.71%; Post15: -5.57 ± 3.82%; time × condition interaction: P < 0.05).

CONCLUSION

Results demonstrate ischemia-reperfusion injury causes endothelial dysfunction and acute oral antioxidant supplementation fails to reduce its magnitude. Our results also suggest that a lack of shear stress during occlusion combined with suppression of prostaglandin synthesis magnifies L-FMC, possibly due to augmented endothelin-1 expression.

Influence of vitamin E supplementation on glycaemic control: a meta-analysis of randomised controlled trials

Observational studies have revealed that higher serum vitamin E concentrations and increased vitamin E intake and vitamin E supplementation are associated with beneficial effects on glycaemic control in type 2 diabetes mellitus (T2DM). However, whether vitamin E supplementation exerts a definitive effect on glycaemic control remains unclear. This article involves a meta-analysis of randomised controlled trials of vitamin E to better characterise its impact on HbA1c, fasting glucose and fasting insulin. PubMed, EMBASE and the Cochrane Library were electronically searched from the earliest possible date through April 2013 for all relevant studies. Weighted mean difference (WMD) was calculated for net changes using fixed-effects or random-effects models. Standard methods for assessing statistical heterogeneity and publication bias were used. Fourteen randomised controlled trials involving individual data on 714 subjects were collected in this meta-analysis. Increased vitamin E supplementation did not result in significant benefits in glycaemic control as measured by reductions in HbA1c, fasting glucose and fasting insulin. Subgroup analyses revealed a significant reduction in HbA1c (-0.58%, 95% CI -0.83 to -0.34) and fasting insulin (-9.0 pmol/l, 95% CI -15.90 to -2.10) compared with controls in patients with low baseline vitamin E status. Subgroup analyses also demonstrated that the outcomes may have been influenced by the vitamin E dosage, study duration, ethnic group, serum HbA1c concentration, and fasting glucose control status. In conclusion, there is currently insufficient evidence to support a potential beneficial effect of vitamin E supplementation on improvements of HbA1c and fasting glucose and insulin concentrations in subjects with T2DM.

Brachial artery responses to ambient pollution, temperature, and humidity in people with type 2 diabetes: a repeated-measures study

BACKGROUND

Extreme weather and air pollution are associated with increased cardiovascular risk in people with diabetes.

OBJECTIVES

In a population with diabetes, we conducted a novel assessment of vascular brachial artery responses both to ambient pollution and to weather (temperature and water vapor pressure, a measure of humidity).

METHODS

Sixty-four 49- to 85-year-old Boston residents with type 2 diabetes completed up to five study visits (279 repeated measures). Brachial artery diameter (BAD) was measured by ultrasound before and after brachial artery occlusion [i.e., flow-mediated dilation (FMD)] and before and after nitroglycerin-mediated dilation (NMD). Ambient concentrations of fine particulate mass (PM2.5), black carbon (BC), organic carbon (OC), elemental carbon, particle number, and sulfate were measured at our monitoring site; ambient concentrations of carbon monoxide, nitrogen dioxide, and ozone were obtained from state monitors. Particle exposure in the home and during each trip to the clinic (home/trip exposure) was measured continuously and as a 5-day integrated sample. We used linear models with fixed effects for participants, adjusting for date, season, temperature, and water vapor pressure on the day of each visit, to estimate associations between our outcomes and interquartile range increases in exposure.

RESULTS

Baseline BAD was negatively associated with particle pollution, including home/trip-integrated BC (-0.02 mm; 95% CI: -0.04, -0.003, for a 0.28 μg/m3 increase in BC), OC (-0.08 mm; 95% CI: -0.14, -0.03, for a 1.61 μg/m3 increase) as well as PM2.5, 5-day average ambient PM2.5, and BC. BAD was positively associated with ambient temperature and water vapor pressure. However, exposures were not consistently associated with FMD or NMD.

CONCLUSION

Brachial artery diameter, a predictor of cardiovascular risk, decreased in association with particle pollution and increased in association with ambient temperature in our study population of adults with type 2 diabetes.

CITATION

Zanobetti A, Luttmann-Gibson H, Horton ES, Cohen A, Coull BA, Hoffmann B, Schwartz JD, Mittleman MA, Li Y, Stone PH, de Souza C, Lamparello B, Koutrakis P, Gold DR. 2014. Brachial artery responses to ambient pollution, temperature, and humidity in people with type 2 diabetes: a repeated-measures study. Environ Health Perspect 122:242-248; http://dx.doi.org/10.1289/ehp.1206136.

Effect of antioxidant vitamin supplementation on endothelial function in type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials

Controversy exists among trials assessing whether prolonged antioxidant vitamin supplementation improves endothelial function in type 2 diabetes mellitus (T2DM) subjects. The aim of this study was to systematically review and quantify the effect of antioxidant vitamin supplementation on endothelial function in T2DM subjects. MEDLINE, Cochrane, Scopus and Web of Science were searched up to February 2013 for randomized controlled trials assessing the effect of antioxidant vitamin E and/or C supplementation on endothelial function in T2DM subjects. Ten randomized controlled trials comparing antioxidant vitamin-supplemented and control groups (overall n = 296) met the inclusion criteria. Post-intervention standardized mean difference (SMD) in endothelial function did not reach statistical significance between groups (0.35; 95% confidence interval = -0.17, 0.88; P = 0.18). In subgroup analysis, post-intervention endothelial function was significantly improved by antioxidant vitamin supplementation in T2DM subgroups with body mass index (BMI) ≤ 29.45 kg m(-2) (SMD = 1.02; P < 0.05), but not in T2DM subgroups with BMI > 29.45 kg m(-2) (SMD = -0.07; P = 0.70). In meta-regression, an inverse association was found between BMI and post-intervention SMD in endothelial function (B = -0.024, P = 0.02). Prolonged antioxidant vitamin E and/or C supplementation could be effective to improve endothelial function in non-obese T2DM subjects.

Metformin improves endothelial function in type 1 diabetic subjects: a pilot, placebo-controlled randomized study

AIMS

Several studies have investigated the effects of metformin treatment in patients with type 1 diabetes mellitus (T1DM). No study has hitherto examined its effects on endothelial function in these patients. In this study we sought to evaluate the effect of metformin on endothelial function in type 1 diabetic patients.

METHODS

Forty-two uncomplicated T1DM patients were randomized in a placebo-controlled, double-blind, 6-month trial to treatment with either metformin or placebo. Glycometabolic and clinical parameters as well as flow-mediated dilation (FMD) and nitrate-mediated dilation (NMD) of the right brachial artery were measured at baseline and at the end of the study. Glycaemic variability (GV, calculated from continuous glucose monitoring data) and a biomarker of oxidative stress [urinary 8-iso-prostaglandin F2α (PGF2α)] were also assessed.

RESULTS

Baseline data were similar in the two groups. Compared with placebo, metformin significantly reduced body weight [-2.27 kg (95% confidence interval: -3.99; -0.54); p = 0.012] whilst improved FMD [1.32% (0.30; 2.43); p = 0.013] and increased PGF2α [149 pg/mg creatinine (50; 248); p = 0.004]. Notably, the improvement of FMD did not correlate with the decrease of body weight (r(2)  < 1%). NMD, haemoglobin A1c, GV, daily insulin dose and other parameters did not significantly change after the treatment comparing the two groups.

CONCLUSIONS

Our pilot trial showed that, in uncomplicated type 1 diabetic subjects, metformin improved FMD and increased PGF2α, a marker of oxidative stress, irrespective of its effects on glycaemic control and body weight. Randomized, blinded clinical trials are needed to evaluate the benefits and risks of metformin added to insulin in type 1 diabetes.

Atorvastatin improves erectile dysfunction in patients initially irresponsive to Sildenafil by the activation of endothelial nitric oxide synthase

This study aimed at comparing the effects of atorvastatin and vitamin E on erectile dysfunction in patients initially irresponsive to sildenafil, with investigation into the underlying possible mechanisms. Sixty patients were randomly divided into three groups: the atorvastatin group received 80 mg daily, the vitamin E group received 400 IU daily and the control group received placebo capsules. Patients were examined both before and after 6 weeks of treatment for biochemical tests; Superoxide dismutase (SOD), glutathione peroxidase (GPO), C-reactive protein (CRP), interleukin-6 (IL-6), nitric oxide (NO) and endothelial nitric oxide synthase (eNOS) and for erectile function tests; International index of erectile function (IIEF-5) scores and Rigiscan. Both atorvastatin and vitamin E showed a statistically significant GPO increase (P<0.05) and a statistically significant IL-6 decrease (P<0.05). Only atorvastatin showed a statistically significant increase in NO (15.19%, P<0.05), eNOS (20.58%, P<0.01), IIEF-5 score (53.1%, P<0.001) and Rigiscan rigidity parameters (P<0.01), in addition to a statistically significant decrease in CRP (57.9%, P<0.01). However, SOD showed a statistically significant increase only after vitamin E intake (23.1%, P<0.05). Both atorvatstain and vitamin E had antioxidant and anti-inflammatory activities. Although activating eNOS by atorvastatin was the real difference, and expected to be the main mechanism for NO increase and for improving erectile dysfunction. Atorvastatin, but not vitamin E, is a promising drug for sildenafil nonresponders.

Correlations between Endothelial Functions and ROS Detection in Diabetic Microvascular Wall: Early and Late Ascorbic Acid Supplementation

The correlation between endothelial function and reactive oxygen species detecting from diabetic microvascular wall and the antioxidant effect of ascorbic acid (AA) during early and late phases of diabetic induction were determined. Male Spraque-Dawley rats were divided into four groups: control, diabetes rats (DM, using iv.injection of 55 mg/kg BW streptozotocin, (STZ)), and two groups of DM rats treated with AA (1 g/L, (STZ)) starting on day 2 (DM + AAday2) and week 6th (DM + AA6wk). On 12th week after STZ injection, the findings showed that in DM group, Ach (10(-5) M)-induced vasodilatation was decreased, while the number of leukocyte adhesion was increased significantly (P < 0.01). Interestingly, these abnormalities induced by DM could be protected or improved in both AA-treated groups, DM + AAday2 and DM + AA6wk. By using dihydrorhodamine 123, our findings also indicated that the existing of ROS productions on diabetic arteriolar and venular walls were different significantly (ROS(arteriole) = 165.89 ± 24.59 and ROS(venule) = 172.26 ± 34.70) (P < 0.05). Moreover by using BH4 inhibitor to induce increase in arteriolar ROS, the results also confirmed that AA could improve endothelial function with closed correlation to its potential to reduce vascular ROS content.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Our systematic review has demonstrated that antioxidant supplements may increase mortality. We have now updated this review.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements for prevention of mortality in adults.

SEARCH METHODS

We searched The Cochrane Library, MEDLINE, EMBASE, LILACS, the Science Citation Index Expanded, and Conference Proceedings Citation Index-Science to February 2011. We scanned bibliographies of relevant publications and asked pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention.

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Random-effects and fixed-effect model meta-analyses were conducted. Risk of bias was considered in order to minimise the risk of systematic errors. Trial sequential analyses were conducted to minimise the risk of random errors. Random-effects model meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Seventy-eight randomised trials with 296,707 participants were included. Fifty-six trials including 244,056 participants had low risk of bias. Twenty-six trials included 215,900 healthy participants. Fifty-two trials included 80,807 participants with various diseases in a stable phase. The mean age was 63 years (range 18 to 103 years). The mean proportion of women was 46%. Of the 78 trials, 46 used the parallel-group design, 30 the factorial design, and 2 the cross-over design. All antioxidants were administered orally, either alone or in combination with vitamins, minerals, or other interventions. The duration of supplementation varied from 28 days to 12 years (mean duration 3 years; median duration 2 years). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects model meta-analysis (21,484 dead/183,749 (11.7%) versus 11,479 dead/112,958 (10.2%); 78 trials, relative risk (RR) 1.02, 95% confidence interval (CI) 0.98 to 1.05) but significantly increased mortality in a fixed-effect model (RR 1.03, 95% CI 1.01 to 1.05). Heterogeneity was low with an I(2)- of 12%. In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. Meta-regression analysis did not find a significant difference in the estimated intervention effect in the primary prevention and the secondary prevention trials. In the 56 trials with a low risk of bias, the antioxidant supplements significantly increased mortality (18,833 dead/146,320 (12.9%) versus 10,320 dead/97,736 (10.6%); RR 1.04, 95% CI 1.01 to 1.07). This effect was confirmed by trial sequential analysis. Excluding factorial trials with potential confounding showed that 38 trials with low risk of bias demonstrated a significant increase in mortality (2822 dead/26,903 (10.5%) versus 2473 dead/26,052 (9.5%); RR 1.10, 95% CI 1.05 to 1.15). In trials with low risk of bias, beta-carotene (13,202 dead/96,003 (13.8%) versus 8556 dead/77,003 (11.1%); 26 trials, RR 1.05, 95% CI 1.01 to 1.09) and vitamin E (11,689 dead/97,523 (12.0%) versus 7561 dead/73,721 (10.3%); 46 trials, RR 1.03, 95% CI 1.00 to 1.05) significantly increased mortality, whereas vitamin A (3444 dead/24,596 (14.0%) versus 2249 dead/16,548 (13.6%); 12 trials, RR 1.07, 95% CI 0.97 to 1.18), vitamin C (3637 dead/36,659 (9.9%) versus 2717 dead/29,283 (9.3%); 29 trials, RR 1.02, 95% CI 0.98 to 1.07), and selenium (2670 dead/39,779 (6.7%) versus 1468 dead/22,961 (6.4%); 17 trials, RR 0.97, 95% CI 0.91 to 1.03) did not significantly affect mortality. In univariate meta-regression analysis, the dose of vitamin A was significantly associated with increased mortality (RR 1.0006, 95% CI 1.0002 to 1.001, P = 0.002).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.

Effects of N-acetyl-cysteine on endothelial function and inflammation in patients with type 2 diabetes mellitus

Endothelial dysfunction has been associated with premature vascular disease. There is increasing data that N-acetyl-cysteine (NAC) may prevent or improve endothelial dysfunction. The aim of this study was to assess the effects of NAC on endothelial function in patients with type 2 diabetes mellitus, a population at high risk for endothelial dysfunction. Twenty-four patients with diabetes mellitus were assigned randomly to initial therapy with either 900 mg NAC or placebo twice daily in a double-blind, cross-over study design. Flowmediated vasodilation (FMD) of the brachial artery was assessed at baseline, after four weeks of therapy, after a four-week wash-out period, and after another four weeks on the opposite treatment. Plasma and red blood cell glutathione levels and high-sensitivity C-reactive protein (CRP) were measured at all four visits. At baseline, FMD was moderately impaired (3.7±2.9%). There was no significant change in FMD after four weeks of NAC therapy as compared to placebo (0.1±3.6% vs. 1.2±4.2%). Similarly, there was no significant change in glutathione levels. However, median CRP decreased from 2.35 to 2.14 mg/L during NAC therapy (p=0.04), while it increased from 2.24 to 2.65 mg/L with placebo. No side effects were noted during the treatment period. In this double-blind, randomized cross-over study, four weeks of oral NAC therapy failed to improve endothelial dysfunction in patients with diabetes mellitus. However, NAC therapy decreased CRP levels, suggesting that this compound may have some efficacy in reducing systemic inflammation.

Antihypertensive and antioxidant effects of dietary black sesame meal in pre-hypertensive humans

BACKGROUND

It has been known that hypertension is an independent risk factor for cardiovascular disease (CVD). CVD is the major cause of morbidity and mortality in developed and developing countries. Elevation of blood pressure (BP) increases the adverse effect for cardiovascular outcomes. Prevention of increased BP plays a crucial role in a reduction of those outcomes, leading to a decrease in mortality. Therefore, the purpose of this study was to investigate the effects of dietary black sesame meal on BP and oxidative stress in individuals with prehypertension.

METHODS

Twenty-two women and eight men (aged 49.8 ± 6.6 years) with prehypertension were randomly divided into two groups, 15 subjects per group. They ingested 2.52 g black sesame meal capsules or placebo capsules each day for 4 weeks. Blood samples were obtained after overnight fasting for measurement of plasma lipid, malondialdehyde (MDA) and vitamin E levels. Anthropometry, body composition and BP were measured before and after 4-week administration of black sesame meal or a placebo.

RESULTS

The results showed that 4-week administration of black sesame meal significantly decreased systolic BP (129.3 ± 6.8 vs. 121.0 ± 9.0 mmHg, P < 0.05) and MDA level (1.8 ± 0.6 vs. 1.2 ± 0.6 μmol/L, P < 0.05), and increased vitamin E level (29.4 ± 6.0 vs. 38.2 ± 7.8 μmol/L, P < 0.01). In the black sesame meal group, the change in SBP tended to be positively related to the change in MDA (R = 0.50, P = 0.05), while the change in DBP was negatively related to the change in vitamin E (R = -0.55, P < 0.05). There were no correlations between changes in BP and oxidative stress in the control group.

CONCLUSIONS

These results suggest the possible antihypertensive effects of black sesame meal on improving antioxidant status and decreasing oxidant stress. These data may imply a beneficial effect of black sesame meal on prevention of CVD.

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.

Oxidative stress and endothelial dysfunction: therapeutic implications

In a previous issue of Annals of Medicine, we presented evidence in support of the concept that an abnormally increased production of reactive oxygen species plays a central role in the genesis and progression of cardiovascular disease. While a number of preclinical lines of evidence support this concept, and despite the results of many studies suggesting a beneficial impact of antioxidant drugs on endothelial function, large clinical trials have failed to demonstrate a benefit of antioxidants on cardiovascular outcomes. Studies exploring the possibility that classical antioxidants such as vitamin C, vitamin E, selenium, or folic acid may improve the prognosis of patients with cardiac disease have substantially reported neutral-and occasionally negative-results. In contrast, medications such as statins, ACE inhibitors, certain β-blockers, or angiotensin I receptor blockers, which possess indirect 'ancillary' antioxidant properties, have been associated with beneficial effects in both preclinical studies and large clinical trials. The reasons for the failure of the 'direct' approach to antioxidant therapy, and for the success of the therapy with these drugs, are discussed in the present review.

Dietary antioxidant interventions in type 2 diabetes patients: a meta-analysis

An imbalance between reactive oxygen species (ROS) production and antioxidant scavenging has been implicated in type 2 diabetes. ROS are a byproduct in type 2 diabetes, generated during protein glycation and as a consequence of advanced glycation end-products-receptor binding; they impair insulin signalling pathways and induce cytotoxicity in pancreatic beta cells. Neutralisation of oxidants by increased antioxidant availability may mitigate these effects. Several human intervention studies have been undertaken to determine whether dietary antioxidants exert beneficial effects for type 2 diabetes patients. This paper describes a systematic review and meta-analysis of the effects of dietary supplementation with antioxidant vitamins C or E on (1) plasma glucose and insulin concentrations, as an indicator of the capacity for antioxidant to interfere with disease process and (2) on glycated haemoglobin A1C as a measure of antioxidant effects on posttranslational protein modification implicated in disease complications. Combined analysis of 14 studies that met inclusion criteria revealed that dietary antioxidant supplementation did not affect plasma glucose or insulin levels, suggesting that they could not interfere with the pathogenesis of insulin resistance. However, HbA1C levels were significantly reduced by antioxidant supplementation, suggesting that antioxidants may have some benefit in protecting against the complications of type 2 diabetes.

Vitamin E supplementation and hepatic drug metabolism in humans

Meta-analyses studies suggest that high-dose vitamin E may be associated with increased mortality in some populations. Vitamin E may increase the production of CYP3A4 in the liver, and this could lead to an increase in drug metabolism, potentially lowering the efficacy of therapeutic drugs. We hypothesized that upregulation of CYP3A4 by alpha-tocopherol (alpha-TOH) would decrease the plasma concentration of the CYP3A4 substrate midazolam. Baseline metabolism of midazolam (1 mg intravenously) was determined in 12 healthy subjects before randomization into 2 groups of 6 to receive either RRR-alpha-TOH (750 IU/d) or placebo for 3 weeks. At completion, subjects were given an additional 1 mg intravenous bolus of midazolam. Plasma midazolam, 1-hydroxy-midazolam, and urinary alpha-TOH metabolite excretion were measured using gas chromatography mass spectrometry. Serum alpha-TOH was measured using high performance liquid chromatography with electrochemical detection. Serum alpha-TOH increased by 100% (P = 0.002) and urinary alpha-TOH metabolite excretion increased 20-fold in the treatment group versus placebo (P = 0.001). There was no effect on the area under time curve of midazolam in subjects taking alpha-TOH compared with placebo. These findings do not support the hypothesis that alpha-TOH supplementation interferes with hepatic CYP3A4-mediated drug metabolism.

Mitochondrial dysfunction in diabetes: from molecular mechanisms to functional significance and therapeutic opportunities

Given their essential function in aerobic metabolism, mitochondria are intuitively of interest in regard to the pathophysiology of diabetes. Qualitative, quantitative, and functional perturbations in mitochondria have been identified and affect the cause and complications of diabetes. Moreover, as a consequence of fuel oxidation, mitochondria generate considerable reactive oxygen species (ROS). Evidence is accumulating that these radicals per se are important in the pathophysiology of diabetes and its complications. In this review, we first present basic concepts underlying mitochondrial physiology. We then address mitochondrial function and ROS as related to diabetes. We consider different forms of diabetes and address both insulin secretion and insulin sensitivity. We also address the role of mitochondrial uncoupling and coenzyme Q. Finally, we address the potential for targeting mitochondria in the therapy of diabetes.

Role of protein kinase C in diabetic complications

Hyperglycemia is an important factor in the development of macrovascular and microvascular complications in all diabetic patients. Several hypotheses have been postulated to explain the adverse effect of hyperglycemia on the vasculature; and one of these hypotheses is the activation of specific isoforms of protein kinase C (PKC) by diabetes. In this review, we summarize the molecular mechanisms of PKC activation and its relationship to diabetic complications. PKC activity regulates vascular permeability, contractility, extracellular matrix synthesis, hormone receptor turnover and proliferation, cell growth, angiogenesis, cytokine activation and leukocyte adhesion. All of these properties are abnormal in diabetes and are correlated with increased diacylglycerol-PKC pathway and PKCα, β1/2 and δ isoforms activation in the retina, aorta, heart and renal glomeruli.

NO/peroxynitrite dynamics of high glucose-exposed HUVECs: chemiluminescent measurement and computational model

Pathogenesis of many of diabetes-related vascular complications is associated with endothelial cell (EC) dysfunction, which is reduced bioavailability of EC-released nitric oxide (NO). Interaction dynamics of NO, superoxide (O(2)(-)) and peroxynitrite (ONOO(-)) are dependent on both their productions and consumptions through various pathways. Quantitative knowledge of these interaction dynamics in high glucose-induced EC dysfunction remains poorly understood. We developed an integrated experimental and computational approach to gain a quantitative understanding of the interactions of NO, O(2)(-) and ONOO(-) in high glucose-exposed ECs. End-products, nitrite and nitrate, were measured using a chemiluminescence analyzer. A computational biochemical reaction network model was developed to predict the effect of high glucose on ECs NO, O(2)(-) and ONOO(-). ECs NO and O(2)(-) productions increased in high glucose as evidenced by increased total NOx concentration, primarily increasing nitrate concentration. The model predicted an increase in O(2)(-) and ONOO(-) concentrations and a decrease in NO concentration in high glucose conditions. Administration of superoxide dismutase (SOD) decreased O(2)(-) concentration and increased NO concentration, thus SOD improved high glucose-induced changes in these interactions. An important finding of this study was that the NO bioavailability decreased in high glucose conditions even though NO production of EC increased. The integrated approach provides a framework to predict NO, O(2)(-) and ONOO(-) concentrations and productions that are difficult to measure in one experiment and will be useful in further EC dysfunction studies.

[Endothelial dysfunction in type 1 diabetes]

Vascular complications are the main cause of mortality and morbidity in diabetes. Mechanisms involved in the development of micro and macrovascular disease are complex and partially understood, but invariably begin as a dysfunctional endothelium. Nitric oxide is an important regulator of endothelial function and the impairment of its activity is determinant of the endothelial dysfunction. In type 1 diabetes, many factors like acute, chronic and post-prandial hyperglycemia, as well as the duration of diabetes or autonomic neuropathy and microalbuminuria are associated to endothelial dysfunction. Oxidative stress, polyol pathway activation, protein kinase C activation and the presence of advanced glycation end-products are potential mechanisms involved in the development of endothelial dysfunction. Early detection of endothelial dysfunction has prognostic value for the development of vascular complications and may be important in strategies for primary prevention of cardiovascular endpoints in type 1 diabetes.

Therapeutic interventions and oxidative stress in diabetes

Many therapeutic agents that are used in patients with diabetes mitigate oxidative stress. These agents are of particular interest because oxidative stress is elevated in diabetes and is thought to contribute to vascular dysfunction. Agents that merely quench already formed reactive oxygen species have demonstrated limited success in improving cardiovascular outcomes. Thus, although vitamin E, C, and alpha lipoic acid appeared promising in animal models and initial human studies, subsequent larger trials have failed to demonstrate improvement in cardiovascular outcomes. Drugs that limit the production of oxidative stress are more successful in improving vascular outcomes in patients with diabetes. Thus, although statins, ACE inhibitors, ARBs and thiazolinediones are used for varied clinical purposes, their increased efficacy in improving cardiovascular outcomes is likely related to their success in reducing the production of reactive oxygen species at an earlier part of the cascade, thereby more effectively decreasing the oxidative stress burden. In particular, statins and ACE inhibitors/ ARBs appear the most successful at reducing oxidative stress and vascular disease and have potential for synergistic effects.

Oxidative stress as a common mediator for apoptosis induced-cardiac damage in diabetic rats

AIM

To investigate the possible role of oxidative stress as a common mediator of apoptosis and cardiac damage in diabetes.

MATERIALS AND METHODS

This experimental work was conducted on 5 groups of Wistar rats. Group I was the control group. Diabetes type 1 was induced in other groups (by streptozotocin) and animals received insulin or vitamin E (300 mg /kg body weight), both insulin and vitamin E, or no treatment for 4 weeks according to their group. At the end of the study, serum and cardiac tissues were examined for biochemical parameters of cardiac function, oxidative stress and apoptosis. Electron microscopy pictures of cardiac tissue were also evaluated for signs of cardiac damage

RESULTS

Markers of oxidative stress, apoptosis, inflammation as well as manifestations of cardiac damage as assessed by electron microscopy were significantly decreased in rats treated with both insulin and vitamin E when compared with untreated diabetic rats or rats treated with either insulin or vitamin E alone

CONCLUSION

Administration of both vitamin E and insulin was effective in reducing markers of oxidative stress and apoptosis and improving parameters of cardiac function in experiments animals. Antioxidants might prove beneficial as an adjuvant treatment in addition to insulin in type 1 diabetes associated with manifestations of cardiac complications.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Animal and physiological research as well as observational studies suggest that antioxidant supplements may improve survival.

OBJECTIVES

To assess the effect of antioxidant supplements on mortality in primary or secondary prevention randomised clinical trials.

SEARCH STRATEGY

We searched The Cochrane Library (Issue 3, 2005), MEDLINE (1966 to October 2005), EMBASE (1985 to October 2005), and the Science Citation Index Expanded (1945 to October 2005). We scanned bibliographies of relevant publications and wrote to pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention. Included participants were either healthy (primary prevention trials) or had any disease (secondary prevention trials).

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Trials with adequate randomisation, blinding, and follow-up were classified as having a low risk of bias. Random-effects and fixed-effect meta-analyses were performed. Random-effects meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Sixty-seven randomised trials with 232,550 participants were included. Forty-seven trials including 180,938 participants had low risk of bias. Twenty-one trials included 164,439 healthy participants. Forty-six trials included 68111 participants with various diseases (gastrointestinal, cardiovascular, neurological, ocular, dermatological, rheumatoid, renal, endocrinological, or unspecified). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects meta-analysis (relative risk [RR] 1.02, 95% confidence interval [CI] 0.99 to 1.06), but significantly increased mortality in a fixed-effect model (RR 1.04, 95% CI 1.02 to 1.06). In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. In the trials with a low risk of bias, the antioxidant supplements significantly increased mortality (RR 1.05, 95% CI 1.02 to 1.08). When the different antioxidants were assessed separately, analyses including trials with a low risk of bias and excluding selenium trials found significantly increased mortality by vitamin A (RR 1.16, 95% CI 1.10 to 1.24), beta-carotene (RR 1.07, 95% CI 1.02 to 1.11), and vitamin E (RR 1.04, 95% CI 1.01 to 1.07), but no significant detrimental effect of vitamin C (RR 1.06, 95% CI 0.94 to 1.20). Low-bias risk trials on selenium found no significant effect on mortality (RR 0.91, 95% CI 0.76 to 1.09).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Vitamin A, beta-carotene, and vitamin E may increase mortality. Future randomised trials could evaluate the potential effects of vitamin C and selenium for primary and secondary prevention. Such trials should be closely monitored for potential harmful effects. Antioxidant supplements need to be considered medicinal products and should undergo sufficient evaluation before marketing.

Role of nitrosative stress in early neuropathy and vascular dysfunction in streptozotocin-diabetic rats

Evidence for important roles of the highly reactive oxidant peroxynitrite in diabetic complications is emerging. We evaluated the role of peroxynitrite in early peripheral neuropathy and vascular dysfunction in STZ-diabetic rats. In the first dose-finding study, control and STZ-diabetic rats were maintained with or without the potent peroxynitrite decomposition catalyst Fe(III)tetrakis-2-(N-triethylene glycol monomethyl ether) pyridyl porphyrin (FP15) at 3, 5, or 10 mg.kg(-1).day(-1) in the drinking water for 4 wk after an initial 2 wk without treatment for assessment of early neuropathy. In the second study with similar experimental design, control and STZ-diabetic rats were maintained with or without FP15, 5 mg.kg(-1).day(-1), for vascular studies. Rats with 6-wk duration of diabetes developed motor and sensory nerve conduction velocity deficits, mechanical hyperalgesia, and tactile allodynia in the absence of small sensory nerve fiber degeneration. They also had increased nitrotyrosine and poly(ADP-ribose) immunofluorescence in the sciatic nerve and dorsal root ganglia. All these variables were dose-dependently corrected by FP15, with minimal differences between the 5 and 10 mg.kg(-1).day(-1) doses. FP15, 5 mg.kg(-1).day(-1), also corrected endoneurial nutritive blood flow and nitrotyrosine, but not superoxide, fluorescence in aorta and epineurial arterioles. Diabetes-induced decreases in acetylcholine-mediated relaxation by epineurial arterioles and coronary and mesenteric arteries, as well as bradykinin-induced relaxation by coronary and mesenteric arteries, were alleviated by FP15 treatment. The findings reveal the important role of nitrosative stress in early neuropathy and vasculopathy and provide the rationale for further studies of peroxynitrite decomposition catalysts in long-term diabetic models.

The effect of vitamin E on blood pressure in individuals with type 2 diabetes: a randomized, double-blind, placebo-controlled trial

OBJECTIVE

Oxidative stress has been suggested to play a role in the development of diabetes, hypertension and vascular dysfunction. Vitamin E, a major lipid-soluble dietary antioxidant, has two major dietary forms, alpha-tocopherol and gamma-tocopherol. The potential importance of gamma-tocopherol has largely been overlooked. Our aim was to investigate the effect of alpha-tocopherol and gamma-tocopherol supplementation on 24-h ambulatory blood pressure (BP) and heart rate, vascular function and oxidative stress in individuals with type 2 diabetes.

METHOD

Fifty-eight individuals with type 2 diabetes were randomized in a double-blind, placebo-controlled trial. Participants were randomized to a daily dose of 500 mg/day RRR-alpha-tocopherol, 500 mg/day mixed tocopherols (60% gamma-tocopherol) or placebo for 6 weeks. Primary endpoints were 24-h ambulatory BP and heart rate, endothelium-dependent and independent vasodilation and plasma and urinary F2-isoprostanes.

RESULTS

Treatment with alpha-tocopherol significantly increased systolic BP [7.0 (5.2, 8.8) mmHg, P < 0.0001], diastolic BP [5.3 (4.0, 6.5) mmHg, P < 0.0001], pulse pressure [1.8 (0.6, 3.0) mmHg, P < 0.005] and heart rate [2.0 (0.6, 3.3) bpm, P < 0.005] versus placebo. Treatment with mixed tocopherols significantly increased systolic BP [6.8 (4.9, 8.6) mmHg, P < 0.0001], diastolic BP [3.6 (2.3, 4.9) mmHg, P < 0.0001], pulse pressure [3.2 (2.0, 4.4) mmHg, P < 0.0001] and heart rate [1.8 (0.5, 3.2) bpm, P < 0.01] versus placebo. Treatment with alpha-tocopherol or mixed tocopherols significantly reduced plasma F2-isoprostanes versus placebo, but had no effect on urinary F2-isoprostanes. Endothelium-dependent and independent vasodilation was not affected by either treatment.

CONCLUSION

In contrast to our initial hypothesis, treatment with either alpha- or mixed tocopherols significantly increased BP, pulse pressure and heart rate in individuals with type 2 diabetes.

Antioxidants and CVD in diabetes: where do we stand now

Diabetes is an oxidative stress disorder as a result of both hyperglycemia and increased levels of free fatty acids. Oxidative stress has been implicated in the pathogenesis of diabetes-related complications, and treatment with antioxidants seemed to be a promising therapeutic option. Although animal studies and preliminary human studies were initially encouraging, subsequent human studies have failed to show a clear benefit of antioxidants, whereas some studies have even suggested that they can be potentially harmful. Therefore, treatment with antioxidants cannot be currently recommended as a therapeutic option.

Algorithm for Complementary and Alternative Medicine Practice and Research in Type 2 Diabetes

OBJECTIVE

To develop a model to direct the prescription of nutritional and botanical medicines in the treatment of type 2 diabetes for both clinical and research purposes.

METHODS

Available literature on nutritional and botanical medicines was reviewed and categorized as follows: antioxidant/anti-inflammatory; insulin sensitizer; and beta-cell protectant/insulin secretagogue. Literature describing laboratory assessment for glycemic control, insulin resistance, and beta-cell reserve was also reviewed and a clinical decision tree was developed.

RESULTS

Clinical algorithms were created to guide the use of nutritional and botanic medicines using validated laboratory measures of glycemic control, insulin sensitivity, and beta-cell reserve. Nutrient and botanic medicines with clinical trial research support include coenzyme Q10, carnitine, alpha-lipoic acid, N-acetylcysteine, vitamin D, vitamin C, vitamin E, chromium, vanadium, omega-3 fatty acids, cinnamon (Cinnamomum cassia), fenugreek (Trigonella foenum-graecum), and gymnema (Gymnema sylvestre).

CONCLUSIONS

Clinical algorithms can direct supplementation in clinical practice and provide research models for clinical investigation. Algorithms also provide a framework for integration of future evidence as it becomes available. Research funding to investigate potentially beneficial practices in complementary medicine is critically important for optimal patient care and safety.

Air pollution and inflammation in type 2 diabetes: a mechanism for susceptibility

BACKGROUND

Particulate air pollution has been associated with several adverse cardiovascular health outcomes, and people with diabetes may be especially vulnerable. One potential pathway is inflammation and endothelial dysfunction-processes in which cell adhesion molecules and inflammatory markers play important roles.

AIM

To examine whether plasma levels of soluble intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and von Willebrand factor (vWF) were associated with particle exposure in 92 Boston area residents with type 2 diabetes.

METHODS

Daily average ambient levels of air pollution (fine particles (PM2.5), black carbon (BC) and sulphates) were measured approximately 500 m from the patient examination site and evaluated for associations with ICAM-1, VCAM-1 and vWF. Linear regressions were fit to plasma levels of ICAM-1, VCAM-1 and vWF, with the particulate pollutant index, apparent temperature, season, age, race, sex, glycosylated haemoglobin, cholesterol, smoking history and body mass index as predictors.

RESULTS

Air pollutant exposure measures showed consistently positive point estimates of association with the inflammatory markers. Among participants not taking statins and those with a history of smoking, associations between PM(2.5), BC and VCAM-1 were particularly strong.

CONCLUSIONS

These results corroborate evidence suggesting that inflammatory mechanisms may explain the increased risk of air pollution-associated cardiovascular events among those with diabetes.

Evidence-Based Protocol for Diabetic Foot Ulcers

BACKGROUND

Diabetic foot ulcers are the single biggest risk factor for nontraumatic foot amputations in persons with diabetes. Foot ulcers occur in 12 to 25 percent of persons with diabetes and precede 84 percent of all nontraumatic amputations in this growing population. Because of the high incidence of foot ulcers, amputations remain a source of morbidity and mortality in persons with diabetes. Strict adherence to evidence-based protocols as described herein will prevent the majority of these amputations.

METHODS

The collective experience of treating patients with neuropathic diabetic foot ulcers in four major diabetic foot programs in the United States and Europe was analyzed.

RESULTS

The following protocol was developed for patients with diabetic foot ulcers: (1) establishment of good communication among the patient, the wound healing team, and the primary medical doctor; (2) comprehensive, protocol-driven care of the entire patient, including hemoglobin A1c, microalbuminuria, and cholesterol as well as early treatment of retinopathy, nephropathy, and cardiac disease; (3) weekly objective measurement of the wound with digital photography, planimetry, and documentation of the wound-healing process using the Wound Electronic Medical Record, if available; (4) objective evaluation of blood flow in the lower extremities (e.g., noninvasive flow studies); (5) débridement of hyperkeratotic, infected, and nonviable tissue; (6) use of systemic antibiotics for deep infection, drainage, and cellulitis; (7) off-loading; (8) maintenance of a moist wound bed; (9) use of growth factor and/or cellular therapy if the wound is not healing after 3 weeks with this protocol; and (10) consideration of the use of vacuum-assisted therapy in complex wounds.

CONCLUSIONS

In diabetic foot ulcers, availability of the above modalities, in combination with early recognition and comprehensive treatment, ensures rapid healing, minimizes morbidity and mortality rates, and eliminates toe and limb amputations in the absence of ischemia and osteomyelitis.

Valsartan improves resting skin blood flow in type 2 diabetic patients and reduces poly(adenosine diphosphate-ribose) polymerase activation

OBJECTIVE

To examine the effect of a 12-week daily treatment with 160 mg of valsartan, an angiotensin II receptor blocker, on the microcirculation and macrocirculation of type 2 diabetic patients (T2DM) and healthy subjects.

METHODS

This was a prospective, randomized, double-blind, placebo-controlled crossover study. Thirteen T2DM with no severe complications and 13 healthy subjects completed the trial.

RESULTS

Treatment with valsartan in T2DM improved the resting forearm skin blood flow and increased the resting brachial artery diameter but had no effects on arterial blood pressure, large vessel vascular reactivity, or carotid intima-media thickness. Resting skin blood flow increased by 60% (2%-90%; median and 25th-75th percentiles) during valsartan treatment and by only 2% (-22% to 27%) during placebo treatment (P < .05). No changes were observed in the nondiabetic subjects. Immunostaining studies of forearm skin biopsy samples from T2DM and healthy subjects showed that valsartan reduced poly(adenosine diphosphate-ribose) polymerase (PARP) activity in 50% (6/12) of the subjects. PARP activity remained unchanged in placebo-treated subjects (P < .02). In addition, valsartan treatment increased CD31 staining in 33% (4/12) of the subjects, whereas no change was noted in sequential skin biopsy samples of placebo-treated subjects (P = .057). Valsartan had no effect on the biochemical markers of endothelial cell activation and other cytokines, including CAMs, interleukin 6, tumor necrosis factor alpha, C-reactive protein, adiponectin, and plasma activator inhibitor 1.

CONCLUSIONS

Valsartan increases the resting skin blood flow in T2DM, likely through reduction of PARP activity.

Investigational agents that protect pancreatic islet β-cells from failure

Type 2 diabetes is associated with insulin resistance and reduced insulin secretion, which results in hyperglycaemia. This can then lead to diabetic complications such as retinopathy, neuropathy, nephropathy and cardiovascular disease. Although insulin resistance may be present earlier in the progression of the disease, it is now generally accepted that it is the deterioration in insulin-secretory function that leads to hyperglycaemia. This reduction in insulin secretion in Type 2 diabetes is due to both islet beta-cell dysfunction and death. Therefore, interventions that maintain the normal function and protect the pancreatic islet beta-cells from death are crucial in the treatment of Type 2 diabetes so that plasma glucose levels may be maintained within the normal range. Recently, a number of compounds have been shown to protect beta-cells from failure. This review examines the evidence that the existing therapies for Type 2 diabetes that were developed to lower plasma glucose (metformin) or improve insulin sensitivity (thiazolidinediones) may also have islet-protective function. Newer emerging therapeutic agents that are designed to increase the levels of glucagon-like peptide-1 not only stimulate insulin secretion but also appear to increase islet beta-cell mass. Evidence will also be presented that the future of drug therapy designed to prevent beta-cell failure should target the formation of advanced glycation end products and alleviate oxidative and endoplasmic reticulum stress.

Vascular complications in diabetes mellitus: the role of endothelial dysfunction

The endothelium is a complex organ with a multitude of properties essential for control of vascular functions. Dysfunction of the vascular endothelium is regarded as an important factor in the pathogenesis of diabetic micro- and macro-angiopathy. Endothelial dysfunction in Type I and II diabetes complicated by micro- or macro-albuminuria is generalized in that it affects many aspects of endothelial function and occurs not only in the kidney. The close linkage between microalbuminuria and endothelial dysfunction in diabetes is an attractive explanation for the fact that microalbuminuria is a risk marker for atherothrombosis. In Type I diabetes, endothelial dysfunction precedes and may cause diabetic microangiopathy, but it is not clear whether endothelial dysfunction is a feature of the diabetic state itself. In Type II diabetes, endothelial function is impaired from the onset of the disease and is strongly related to adverse outcomes. It is not clear whether impaired endothelial function is caused by hyperglycaemia or by other factors. Impaired endothelial function is closely associated with and may contribute to insulin resistance regardless of the presence of diabetes. Endothelial dysfunction in diabetes originates from three main sources. Hyperglycaemia and its immediate biochemical sequelae directly alter endothelial function or influence endothelial cell functioning indirectly by the synthesis of growth factors, cytokines and vasoactive agents in other cells. Finally, the components of the metabolic syndrome can impair endothelial function.