Vitamin C improves endothelium-dependent vasodilation in patients with insulin-dependent diabetes mellitus

Low Levels of Vitamin C during Pregnancy; a Risk Marker of Progression of Diabetic Retinopathy in Type 1 Diabetic Women?

Pregnancy is a risk factor for the development or aggravation of diabetic retinopathy. Here, we suggest a relationship between plasma vitamin C (vitC) status during pregnancy and into postpartum in type 1 diabetes and the possible progression of diabetic retinopathy based on data of 29 women. VitC was measured in first, second, and third trimesters and three months postpartum. The women had visual acuity testing and fundus photography performed at least twice during pregnancy and onto four months after birth. An overall retinopathy grade was assigned on a scale from 0 (no retinopathy) to four according to the International Clinical Diabetic Retinopathy scale. At baseline in 1st trimester, 12 women had no retinopathy; seventeen women had retinopathy in grade 1–3. The retinopathy grade increased in nine women; remained unchanged in 17 women, and improved in three women. No women had or developed proliferative retinopathy (grade 4). The level of vitC in 1st trimester predicted the possible progression of retinopathy—the lower the vitC, the more probable the progression (p = 0.03; OR 1.6 (95% CI:1.06–3.2); n = 29 (multiple logistic regression))—while the combined levels of 1st and 2nd trimesters and the mean vitC level of the whole pregnancy did not. The diabetes duration, retinopathy grade per se in 1st trimester, 24-h blood pressure measurements, kidney function, urinary protein, HbA1c, or lipid profile were not independent predictors of progression of retinopathy during pregnancy. Retrospectively, the women who experienced progression of their retinopathy during and into postpartum had significantly lower vitC levels in 1st trimester (p = 0.02; n = 9/20), combined level of vitC in 1st and 2nd trimester (p = 0.032; n = 7/18), and mean vitC level of the whole pregnancy (p = 0.036; n = 7/9), respectively. In conclusion, our results suggest that low vitC status in pregnancy could be associated with progression of diabetic retinopathy.

Early Detection Is the Best Prevention-Characterization of Oxidative Stress in Diabetes Mellitus and Its Consequences on the Cardiovascular System

Previous studies demonstrated an important role of oxidative stress in the pathogenesis of cardiovascular disease (CVD) in diabetic patients due to hyperglycemia. CVD remains the leading cause of premature death in the western world. Therefore, diabetes mellitus-associated oxidative stress and subsequent inflammation should be recognized at the earliest possible stage to start with the appropriate treatment before the onset of the cardiovascular sequelae such as arterial hypertension or coronary artery disease (CAD). The pathophysiology comprises increased reactive oxygen and nitrogen species (RONS) production by enzymatic and non-enzymatic sources, e.g., mitochondria, an uncoupled nitric oxide synthase, xanthine oxidase, and the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX). Considering that RONS originate from different cellular mechanisms in separate cellular compartments, adequate, sensitive, and compartment-specific methods for their quantification are crucial for early detection. In this review, we provide an overview of these methods with important information for early, appropriate, and effective treatment of these patients and their cardiovascular sequelae.

Vitamin C supplementation for diabetes management: A comprehensive narrative review

Growing evidence suggests that vitamin C supplementation may be an effective adjunct therapy in the management of people with diabetes. This paper critically reviews the current evidence on effects of vitamin C supplementation and its potential mechanisms in diabetes management. Evidence from meta-analyses of randomized controlled trials (RCTs) show favourable effects of vitamin C on glycaemic control and blood pressure that may be clinically meaningful, and mixed effects on blood lipids and endothelial function. However, evidence is mostly of low evidence certainty. Emerging evidence is promising for effects of vitamin C supplementation on some diabetes complications, particularly diabetic foot ulcers. However, there is a notable lack of robust and well-designed studies exploring effects of vitamin C as a single compound supplement on diabetes prevention and patient-important outcomes (i.e. prevention and amelioration of diabetes complications). RCTs are also required to investigate potential preventative or ameliorative effects of vitamin C on gestational diabetes outcomes. Oral vitamin C doses of 500-1000 mg per day are potentially effective, safe, and affordable for many individuals with diabetes. However, personalisation of supplementation regimens that consider factors such as vitamin C status, disease status, current glycaemic control, vitamin C intake, redox status, and genotype is important to optimize vitamin C's therapeutic effects safely. Finally, given a high prevalence of vitamin C deficiency in patients with complications, it is recommended that plasma vitamin C concentration be measured and monitored in the clinic setting.

Vitamin C and the management of diabetic foot ulcers: a literature review

OBJECTIVE

The lifetime risk of developing a diabetic foot ulcer (DFU) in people with diabetes is as high as 25%. A trio of factors constitute the diabetic foot syndrome that characterises DFUs, including neuropathy, vascular disease and infections. Vitamin C has important functions in the nervous, cardiovascular, and immune systems that are implicated in DFU development. Furthermore, vitamin C deficiency has been observed in individuals with DFUs, suggesting an important function of vitamin C in DFU management and treatment. Therefore, this literature review evaluates the role of vitamin C in the nervous, cardiovascular and immune systems in relation to wound healing and DFUs, as well as discussing vitamin C's lesser known role in depression, a condition that affects many individuals with a DFU.

METHOD

A literature search was done using PubMed, Cochrane Library, Embase, Ovid, Computer Retrieval of Information on Scientific Projects, and NIH Clinical Center. Search terms included 'diabetic foot ulcer,' 'diabetic foot,' 'vitamin C,' and 'ascorbic acid.'

RESULTS

Of the 71 studies initially identified, seven studies met the inclusion criteria, and only three were human clinical trials. Overall, the literature on this subject is limited, with mainly observational and animal studies, and few human clinical trials.

CONCLUSION

There is a need for additional human clinical trials on vitamin C supplementation in individuals with a DFU to fill the knowledge gap and guide clinical practice.

Pathophysiological Association between Diabetes Mellitus and Endothelial Dysfunction

Endothelial dysfunction plays a critical role in atherosclerosis progression, leading to cardiovascular complications. There are significant associations between diabetes mellitus, oxidative stress, and endothelial dysfunction. Oxidative stress is increased by chronic hyperglycemia and acute glucose fluctuations induced by postprandial hyperglycemia in patients with diabetes mellitus. In addition, selective insulin resistance in the phosphoinositide 3-kinase/Akt/endothelial nitric oxide (NO) synthase pathway in endothelial cells is involved in decreased NO production and increased endothelin-1 production from the endothelium, resulting in endothelial dysfunction. In a clinical setting, selecting an appropriate therapeutic intervention that improves or augments endothelial function is important for preventing diabetic vascular complications. Hypoglycemic drugs that reduce glucose fluctuations by decreasing the postprandial rise in blood glucose levels, such as glinides, α-glucosidase inhibitors and dipeptidyl peptidase 4 inhibitors, and hypoglycemic drugs that ameliorate insulin sensitivity, such as thiazolidinediones and metformin, are expected to improve or augment endothelial function in patients with diabetes. Glucagon-like peptide 1 receptor agonists, metformin, and sodium-glucose cotransporter 2 inhibitors may improve endothelial function through multiple mechanisms, some of which are independent of glucose control or insulin signaling. Oral administration of antioxidants is not recommended in patients with diabetes due to the lack of evidence for the efficacy against diabetic complications.

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.

C-Peptide as a Therapy for Type 1 Diabetes Mellitus

Diabetes mellitus (DM) is a complex metabolic disease affecting one-third of the United States population. It is characterized by hyperglycemia, where the hormone insulin is either not produced sufficiently or where there is a resistance to insulin. Patients with Type 1 DM (T1DM), in which the insulin-producing beta cells are destroyed by autoimmune mechanisms, have a significantly increased risk of developing life-threatening cardiovascular complications, even when exogenous insulin is administered. In fact, due to various factors such as limited blood glucose measurements and timing of insulin administration, only 37% of T1DM adults achieve normoglycemia. Furthermore, T1DM patients do not produce C-peptide, a cleavage product from insulin processing. C-peptide has potential therapeutic effects in vitro and in vivo on many complications of T1DM, such as peripheral neuropathy, atherosclerosis, and inflammation. Thus, delivery of C-peptide in conjunction with insulin through a pump, pancreatic islet transplantation, or genetically engineered Sertoli cells (an immune privileged cell type) may ameliorate many of the cardiovascular and vascular complications afflicting T1DM patients.

Ascorbic Acid Prevents Vascular Endothelial Dysfunction Induced by Electronic Hookah (Waterpipe) Vaping

Background Electronic hookah (e-hookah) vaping has increased in popularity among youth, who endorse unsubstantiated claims that flavored aerosol is detoxified as it passes through water. However, e-hookahs deliver nicotine by creating an aerosol of fine and ultrafine particles and other oxidants that may reduce the bioavailability of nitric oxide and impair endothelial function secondary to formation of oxygen-derived free radicals. Methods and Results We examined the acute effects of e-hookah vaping on endothelial function, and the extent to which increased oxidative stress contributes to the vaping-induced vascular impairment. Twenty-six healthy young adult habitual hookah smokers were invited to vape a 30-minute e-hookah session to evaluate the impact on endothelial function measured by brachial artery flow-mediated dilation (FMD). To test for oxidative stress mediation, plasma total antioxidant capacity levels were measured and the effect of e-hookah vaping on FMD was examined before and after intravenous infusion of the antioxidant ascorbic acid (n=11). Plasma nicotine and exhaled carbon monoxide levels were measured before and after the vaping session. Measurements were performed before and after sham-vaping control experiments (n=10). E-hookah vaping, which increased plasma nicotine (+4.93±0.92 ng/mL, P<0.001; mean±SE) with no changes in exhaled carbon monoxide (-0.15±0.17 ppm; P=0.479), increased mean arterial pressure (11±1 mm Hg, P<0.001) and acutely decreased FMD from 5.79±0.58% to 4.39±0.46% (P<0.001). Ascorbic acid infusion, which increased plasma total antioxidant capacity 5-fold, increased FMD at baseline (5.98±0.66% versus 9.46±0.87%, P<0.001), and prevented the acute FMD impairment by e-hookah vaping (9.46±0.87% versus 8.74±0.84%, P=0.002). All parameters were unchanged during sham studies. Conclusions E-hookah vaping has adverse effects on vascular function, likely mediated by oxidative stress, which overtime could accelerate development and progression of cardiovascular disease. Registration URL: https://ClinicalTrials.gov. Unique identifier: NCT03690427.

Vascular Dysfunction, Oxidative Stress, and Inflammation in Chronic Kidney Disease

Background

Increased arterial stiffness and vascular endothelial dysfunction are important nontraditional cardiovascular risk factors evident in patients with CKD. Vascular oxidative stress and inflammation may contribute to vascular dysfunction in CKD, but direct evidence is lacking.

Methods

We assessed carotid-femoral pulse-wave velocity (arterial stiffness) and brachial artery flow-mediated dilation (vascular endothelial function) in participants with moderate-to-severe CKD (eGFR 15-59 ml/min per 1.73 m²) and in healthy controls. Change in brachial artery flow-mediated dilation after an acute infusion of ascorbic acid to inhibit vascular oxidative stress (versus saline) was also measured. Protein expression of vascular endothelial cells collected from a peripheral vein and ELISAs to assess circulating markers were also performed.

Results

A total of 64 participants with CKD (mean±SD, 65±8 years) and 17 healthy controls (60±5 years) were included. Carotid-femoral pulse-wave velocity was greater in participants with CKD compared with healthy controls (1071±336 versus 732±128 cm/s; P<0.001). Brachial artery flow-mediated dilation was lower in participants with CKD compared with healthy controls (3.5%±2.8% versus 5.5%±3.2%; P=0.02). Circulating inflammation markers (C-reactive protein and IL-6) were elevated in the CKD group (P≤0.02). Endothelial cell protein expression of NADPH (intensity versus human umbilical vein endothelial cell control, 1.48±0.28 versus 1.25±0.31; P=0.05) was greater in participants with CKD. However, ascorbic acid significantly improved brachial artery flow-mediated dilation in control participants (saline, 5.5±3.2; ascorbic acid, 6.8±3.6); as compared with participants with CKD (saline, 3.5±2.8; ascorbic acid, 3.6±3.2) (group×condition interaction P=0.04), suggesting vascular oxidative stress could not be overcome with ascorbic acid in participants with CKD.

Conclusions

Vascular oxidative stress is present in CKD, which cannot be overcome with acute infusion of ascorbic acid.

Antioxidant supplements and endurance exercise: Current evidence and mechanistic insights

Antioxidant supplements are commonly consumed by endurance athletes to minimize exercise-induced oxidative stress, with the intention of enhancing recovery and improving performance. There are numerous commercially available nutritional supplements that are targeted to athletes and health enthusiasts that allegedly possess antioxidant properties. However, most of these compounds are poorly investigated with respect to their in vivo redox activity and efficacy in humans. Therefore, this review will firstly provide a background to endurance exercise-related redox signalling and the subsequent adaptations in skeletal muscle and vascular function. The review will then discuss commonly available compounds with purported antioxidant effects for use by athletes. N-acetyl cysteine may be of benefit over the days prior to an endurance event; while chronic intake of combined 1000 mg vitamin C + vitamin E is not recommended during periods of heavy training associated with adaptations in skeletal muscle. Melatonin, vitamin E and α-lipoic acid appear effective at decreasing markers of exercise-induced oxidative stress. However, evidence on their effects on endurance performance are either lacking or not supportive. Catechins, anthocyanins, coenzyme Q10 and vitamin C may improve vascular function, however, evidence is either limited to specific sub-populations and/or does not translate to improved performance. Finally, additional research should clarify the potential benefits of curcumin in improving muscle recovery post intensive exercise; and the potential hampering effects of astaxanthin, selenium and vitamin A on skeletal muscle adaptations to endurance training. Overall, we highlight the lack of supportive evidence for most antioxidant compounds to recommend to athletes.

Carpinus turczaninowii Extract May Alleviate High Glucose-Induced Arterial Damage and Inflammation

Hyperglycemia-induced oxidative stress triggers severe vascular damage and induces an inflammatory vascular state, and is, therefore, one of the main causes of atherosclerosis. Recently, interest in the natural compound Carpinus turczaninowii has increased because of its reported antioxidant and anti-inflammatory properties. We investigated whether a C. turczaninowii extract was capable of attenuating high glucose-induced inflammation and arterial damage using human aortic vascular smooth muscle cells (hASMCs). mRNA expression levels of proinflammatory response [interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α)], endoplasmic reticulum (ER) stress [CCAAT-enhancer-binding proteins (C/EBP) homologous protein (CHOP)], and adenosine monophosphate (AMP)-protein activated kinase α2 (AMPK α2)], and DNA damage [phosphorylated H2.AX (p-H2.AX)] were measured in hASMCs treated with the C. turczaninowii extracts (1 and 10 μg/mL) after being stimulated by high glucose (25 mM) or not. The C. turczaninowii extract attenuated the increased mRNA expression of IL-6, TNF-α, and CHOP in hASMCs under high glucose conditions. The expression levels of p-H2.AX and AMPK α2 induced by high glucose were also significantly decreased in response to treatment with the C. turczaninowii extract. In addition, 15 types of phenolic compounds including quercetin, myricitrin, and ellagic acid, which exhibit antioxidant and anti-inflammatory properties, were identified in the C. turczaninowii extract through ultra-performance liquid chromatography-quadrupole-time of flight (UPLC-Q-TOF) mass spectrometry. In conclusion, C. turczaninowii may alleviate high glucose-induced inflammation and arterial damage in hASMCs, and may have potential in the treatment of hyperglycemia-induced atherosclerosis.

Effects of Ginseng Supplementation and Endurance-Exercise in the Artery-Specific Vascular Responsiveness of Diabetic and Sedentary Rats

This study examined the effects of 12 weeks North-American ginseng supplementation, exercise training, and sedentary behavior on vascular responses in type I diabetic rats. The following hypotheses were tested: (1) ginseng supplementation would result in improved vascular responsiveness and sensitivity; (2) exercise training would result in further improvement in these vascular responses; (3) control rats with no access to exercise would show a depressed vascular response compared to control rats that were not exposed to a sedentary lifestyle. Groups: non-diabetic sedentary control (C_S), sedentary diabetic (D_S), sedentary diabetic with ginseng supplementation (D_S+GS), diabetic with ginseng supplementation and high-intensity endurance exercise (D+GS+EX), and control not exposed to sedentary behavior (C). Diabetes was induced by streptozotocin. Arteries were excised, cleaned, and mounted onto a myography system. Percent vasorelaxation to acetylcholine (ACh) (10^-8 M ACh to 10^-4 M ACh) of the carotid artery was similar in C_S (57 ± 31%), C (66 ± 35%), D_S (58 ± 36%), D+GS+Ex (71 ± 37%), and D_S+GS (64 ± 37%) (p > 0.05). Percent vasorelaxation of the aorta was smaller in C_S (23 ± 17%) compared to C (46 ± 35%), D_S (60 ± 40%), D+GS+Ex (64 ± 40%), and D_S+GS (56 ± 39%) (p < 0.05), and smaller in C compared to D+GS+Ex (p < 0.05). In the femoral, the percent vasorelaxation was reduced in D_S (18 ± 16%) compared to all the other conditions (C_S, 43 ± 22%; C, 79 ± 28%; D+GS+Ex, 55 ± 27%; D_S+GS, 45 ± 26%; p < 0.05), but larger in C compared to the other conditions (C_S, D_S, D+GS+Ex, D_S+GS; p < 0.05). Diabetes and sedentary lifestyle have detrimental effects on vascular responses that are evident in the femoral arteries of the diabetic rats. Ginseng supplementation restored the loss of sensitivity, with no added vascular protection of exercise training.

THE EFFECT OF DIABETES ON CARDIOVASCULAR SYSTEM

Diabetes mellitus (DM) is a critical and long-term disorder due to the insufficient production of insulin by the pancreas or ineffective use of insulin by the body. Importantly, cardiovascular disease (CVD) has long been thought to be linked with diabetes. Despite more diabetic individuals surviving from better medications and treatments, there has been significant rise in the morbidity and mortality from CVD. Indeed, the classification of DM based on the electrocardiogram signals of the heart will be an advantageous system. Further, computer-aided classification of DM with integrated algorithms may enhance the execution of the system. In this paper, we have reviewed various studies using heart rate variability signals for automated classification of diabetes. Furthermore, the different techniques used to extract the features and the efficiency of the classification systems are discussed.

Rationale and design of a multicenter placebo-controlled double-blind randomized trial to evaluate the effect of empagliflozin on endothelial function: the EMBLEM trial

BACKGROUND

Type 2 diabetes mellitus (T2DM) is characterized by systemic metabolic abnormalities and the development of micro- and macrovascular complications, resulting in a shortened life expectancy. A recent cardiovascular (CV) safety trial, the EMPA-REG OUTCOME trial, showed that empagliflozin, a sodium glucose cotransporter 2 (SGLT2) inhibitor, markedly reduced CV death and all-cause mortality and hospitalization for heart failure in patients with T2DM and established CV disease (CVD). SGLT2 inhibitors are known to not only decrease plasma glucose levels, but also favorably modulate a wide range of metabolic and hemodynamic disorders related to CV pathways. Although some experimental studies revealed a beneficial effect of SGLT2 inhibitors on atherosclerosis, there is a paucity of clinical data showing that they can slow the progression of atherosclerosis in patients with T2DM. Therefore, the EMBLEM trial was designed to investigate whether empagliflozin treatment can improve endothelial function, which plays a pivotal role in the pathogenesis of atherosclerosis, in patients with T2DM and established CVD.

METHODS

The EMBLEM trial is an ongoing, prospective, multicenter, placebo-controlled double-blind randomized, investigator-initiated clinical trial in Japan. A total of 110 participants with T2DM (HbA1c range 6.0-10.0%) and with established CVD will be randomized (1:1) to receive either empagliflozin 10 mg once daily or a placebo. The primary endpoint of the trial is change in the reactive hyperemia (RH)-peripheral arterial tonometry-derived RH index at 24 weeks from baseline. For comparison of treatment effects between the treatment groups, the baseline-adjusted means and their 95% confidence intervals will be estimated by analysis of covariance adjusted for the following allocation factors: HbA1c (<7.0 or ≥7.0%), age (<65 or ≥65 years), systolic blood pressure (<140 or ≥140 mmHg), and current smoking status (nonsmoker or smoker). Key secondary endpoints include the change from baseline for other vascular-related markers such as arterial stiffness, sympathetic nervous activity, and parameters of cardiac and renal function. Importantly, serious adverse effects independently on the causal relationship to the trial drugs and protocol will be also evaluated throughout the trial period.

DISCUSSION

EMBLEM is the first trial to assess the effect of empagliflozin on endothelial function in patients with T2DM and established CVD. Additionally, mechanisms associating empagliflozin-mediated actions with endothelial function and other CV markers will be evaluated. Thus, the trial is designed to elucidate potential mechanisms by which empagliflozin protects CV systems and improves CV outcomes. Trial registration Unique Trial Number, UMIN000024502 ( https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000028197 ).

Ebselen does not improve oxidative stress and vascular function in patients with diabetes: a randomized, crossover trial

Oxidative stress is a key driver of vascular dysfunction in diabetes mellitus. Ebselen is a glutathione peroxidase mimetic. A single-site, randomized, double-masked, placebo-controlled, crossover trial was carried out in 26 patients with type 1 or type 2 diabetes to evaluate effects of high-dose ebselen (150 mg po twice daily) administration on oxidative stress and endothelium-dependent vasodilation. Treatment periods were in random order of 4 wk duration, with a 4-wk washout between treatments. Measures of oxidative stress included nitrotyrosine, plasma 8-isoprostanes, and the ratio of reduced to oxidized glutathione. Vascular ultrasound of the brachial artery and plethysmographic measurement of blood flow were used to assess flow-mediated and methacholine-induced endothelium-dependent vasodilation of conduit and resistance vessels, respectively. Ebselen administration did not affect parameters of oxidative stress or conduit artery or forearm arteriolar vascular function compared with placebo treatment. There was no difference in outcome by diabetes type. Ebselen, at the dose and duration evaluated, does not improve the oxidative stress profile, nor does it affect endothelium-dependent vasodilation in patients with diabetes mellitus.

Vasodilator prostanoids compensate for attenuated nitric oxide mediated vasodilation in type 1 diabetes

Background Previous research examining endothelial function and the biochemical pathways mediating vasodilation in type 1 diabetes has been conflicting. Both impaired and preserved nitric oxide (NO) mediated vasodilation have been reported whilst some authors have suggested enhanced vasodilator prostanoid (P) activity. The aim of this study was to determine the relative contributions of NO and P to endothelial function in a homogenous group of type 1 diabetic patients free of other confounding factors that may influence vascular behaviour.^f ^

Methods and results Endothelial function was assessed using forearm venous plethysmography in 16 patients with uncomplicated type 1 (duration of diabetes 16.8±2.5 years (mean±SEM), HbA1C 7.53±0.21% ) and 15 non-diabetic age and sex matched healthy control subjects. Forearm responses to the endothelium-dependent vasodilator, acetylcholine (ACh) (7.5, 15 and 30 µg/min), were recorded at baseline and after intra-arterial infusion of L-NMMA (a NO synthase inhibitor). Responses to ACh were re-examined following co-infusion of L-NMMA and indomethacin (a cyclo-oxygenase inhibitor). Responses to ACh were calculated as areas under the curve (AUC). At baseline vasodilator responses to ACh were similar (p=0.3) in diabetic and non-diabetic subjects. However, L-NMMA reduced ACh mediated responses to a lesser extent in diabetic subjects than control subjects (3±6% versus 18±3%; p<0.03 respectively). Co-infusion with indomethacin further reduced blood flow, but the relative decrease in AUC was greater in the diabetic group (28±3% vs. 14±3%; p<0.001). The contribution of biochemical pathways other than NO and P were similar in both diabetic and control groups (69±7% vs. 68±4%; p=0.45).

Conclusions Vasodilator responses to ACh were unchanged in type 1 diabetes but this was reliant up on enhanced P mediated activity compensating for attenuated NO activity. Furthermore, vasoactive substances in addition to NO and P contribute significantly to vascular tone in both diabetic and non-diabetic subjects.

The Protective Effect of Antioxidants Consumption on Diabetes and Vascular Complications

Obesity and diabetes is generally accompanied by a chronic state of oxidative stress, disequilibrium in the redox balance, implicated in the development and progression of complications such as micro- and macro-angiopathies. Disorders in the inner layer of blood vessels, the endothelium, play an early and critical role in the development of these complications. Blunted endothelium-dependent relaxation and/or contractions are quietly associated to oxidative stress. Thus, preserving endothelial function and oxidative stress seems to be an optimization strategy in the prevention of vascular complications associated with diabetes. Diet is a major lifestyle factor that can greatly influence the incidence and the progression of type 2 diabetes and cardiovascular complications. The notion that foods not only provide basic nutrition but can also prevent diseases and ensure good health and longevity is now attained greater prominence. Some dietary and lifestyle modifications associated to antioxidative supply could be an effective prophylactic means to fight against oxidative stress in diabesity and complications. A significant benefit of phytochemicals (polyphenols in wine, grape, teas), vitamins (ascorbate, tocopherol), minerals (selenium, magnesium), and fruits and vegetables in foods is thought to be capable of scavenging free radicals, lowering the incidence of chronic diseases. In this review, we discuss the role of oxidative stress in diabetes and complications, highlight the endothelial dysfunction, and examine the impact of antioxidant foods, plants, fruits, and vegetables, currently used medication with antioxidant properties, in relation to the development and progression of diabetes and cardiovascular complications.

Quercetin inhibits LPS-induced adhesion molecule expression and oxidant production in human aortic endothelial cells by p38-mediated Nrf2 activation and antioxidant enzyme induction

Atherosclerosis, the underlying cause of ischemic heart disease and stroke, is an inflammatory disease of arteries in a hyperlipidemic milieu. Endothelial expression of cellular adhesion molecules, such as endothelial-leukocyte adhesion molecule-1 (E-selectin) and intercellular adhesion molecule-1 (ICAM-1), plays a critical role in the initiation and progression of atherosclerosis. The dietary flavonoid, quercetin, has been reported to inhibit expression of cellular adhesion molecules, but the underlying mechanisms are incompletely understood. In this study, we found that quercetin dose-dependently (5–20 µM) inhibits lipopolysaccharide (LPS)-induced mRNA and protein expression of E-selectin and ICAM-1 in human aortic endothelial cells (HAEC). Incubation of HAEC with quercetin also significantly reduced LPS-induced oxidant production, but did not inhibit activation of the nuclear factor-kappaB (NF-κB). Furthermore, quercetin induced activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) and subsequent mRNA and protein expression of the antioxidant enzymes, heme oxygenase-1 (HO-1), NAD(P)H dehydrogenase, quinone 1, and glutamate-cysteine ligase. The induction of Nrf2 and antioxidant enzymes was partly inhibited by the p38 mitogen-activated protein kinase (p38) inhibitor, SB203580. Our results suggest that quercetin suppresses LPS-induced oxidant production and adhesion molecule expression by inducing Nrf2 activation and antioxidant enzyme expression, which is partially mediated by p38; and the inhibitory effect of quercetin on adhesion molecule expression is not due to inhibition of NF-κB activation, but instead due to antioxidant-independent effects of HO-1.

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Quercetin inhibits LPS-induced oxidant production and adhesion molecule expression.

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Quercetin activates p38 MAP kinase and Nrf2, upregulating heme oxygenase-1 (HO-1).

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HO-1 rather than NF-κB may account for quercetin’s anti-inflammatory effects.

Ascorbic acid repletion: A possible therapy for diabetic macular edema?

Macular edema poses a significant risk for visual loss in persons with diabetic retinopathy. It occurs when plasma constituents and fluid leak out of damaged retinal microvasculature in the area of the macula, causing loss of central vision. Apoptotic loss of pericytes surrounding capillaries is perhaps the earliest feature of diabetic vascular damage in the macula, which is also associated with dysfunction of the endothelium and loss of the otherwise very tight endothelial permeability barrier. Increased oxidative stress is a key feature of damage to both cell types, mediated by excess superoxide from glucose-induced increases in mitochondrial metabolism, as well as by activation of the receptor for advanced glycation end products (RAGE). The latter in turn activates multiple pathways, some of which lead to increased oxidative stress, such as those involving NF-ĸB, NADPH oxidase, and endothelial nitric oxide synthase. Such cellular oxidative stress is associated with low cellular and plasma ascorbic acid levels in many subjects with diabetes in poor glycemic control. Whether repletion of low ascorbate in retinal endothelium and pericytes might help to prevent diabetic macular edema is unknown. However, cell culture studies show that the vitamin prevents high-glucose and RAGE-induced apoptosis in both cell types, that it preserves nitric oxide generated by endothelial cells, and that it tightens the leaky endothelial permeability barrier. Although these findings need to be confirmed in pre-clinical animal studies, it is worth considering clinical trials to determine whether adequate ascorbate repletion is possible and whether it might help to delay or even reverse early diabetic macular edema.

Effects of vitamin C treatment on collar-induced intimal thickening

Vitamin C has efficient antioxidant properties and is involved in important physiological processes such as collagen synthesis. As such, vitamin C deficiency leads to serious complications, including vascular diseases. The aim of this study was to investigate the effects of vitamin C treatment on collar-induced intimal thickening. Rabbits were fed a normocholesterolemic diet and a non-occlusive silicon collar was placed around the left carotid artery for 3, 7, and 14 days. The rabbits were treated with or without vitamin C (150 mg/kg/day). Collar-induced intimal thickening became apparent at day 7. The effect of the collar on intimal thickening was more prominent at day 14. Vitamin C treatment significantly inhibited collar-induced intimal thickening at day 14. The placement of the collar around the carotid artery decreased maximum contractile responses against contractile agents (KCl, phenylephrine, 5-hydroxytryptamine). The effect of the collar on contractile responses was enhanced as days elapsed. Decreased contractile responses of collared carotid arteries normalized at day 14 in the vitamin C treatment group. Vitamin C treatment also restored sensitivity to phenylephrine. The collar also significantly decreased acetylcholine-induced relaxations at day 3 and day 7. Acetylcholine-induced relaxations normalized in collared-arteries in the placebo group at day 14. Vitamin C treatment significantly increased acetylcholine-induced relaxations of both normal and collared carotid arteries at day 14. MMP-9 expression increased in collared arteries at day 3 and day 7 but did not change at day 14. MMP-2 expression increased in collared arteries at day 14. However, vitamin C treatment reduced collar-stimulated expression of MMP-2 at day 14. These findings indicate that vitamin C may have potentially beneficial effects on the early stages of atherosclerosis. Furthermore these results, for the first time, may indicate that vitamin C can also normalize decreased contractile response through perivascular collar placement.

Atazanavir improves cardiometabolic measures but not vascular function in patients with long-standing type 1 diabetes mellitus

AIMS

Vascular disease is the leading cause of morbidity and mortality in type 1 diabetes mellitus (T1DM). We previously demonstrated that patients with T1DM have impaired endothelial function, a forme fruste of atherosclerosis, as a result of increased oxidative stress. Bilirubin has emerged as a potent endogenous antioxidant with higher concentrations associated with lower rates of myocardial infarction and stroke.

METHODS

We tested the hypothesis that increasing endogenous bilirubin using atazanavir would improve cardiometabolic risk factors and vascular function in patients with T1DM to determine whether targeting bilirubin may be a novel therapeutic approach to reduce cardiovascular disease risk in this population. In this single-arm, open-label study, we evaluated blood pressure, lipid profile, and conduit artery function in fifteen subjects (mean age 45 ± 9 years) with T1DM following a 4-day treatment with atazanavir.

RESULTS

As anticipated, atazanavir significantly increased both serum total bilirubin levels (p < 0.0001) and plasma total antioxidant capacity (p < 0.0001). Reductions in total cholesterol (p = 0.04), LDL cholesterol (p = 0.04), and mean arterial pressure (p = 0.04) were also observed following atazanavir treatment. No changes were seen in either flow-mediated endothelium-dependent (p = 0.92) or nitroglycerine-mediated endothelium-independent (p = 0.68) vasodilation, measured by high-resolution B-mode ultrasonography at baseline and post-treatment.

CONCLUSION

Increasing serum bilirubin levels with atazanavir in subjects with T1DM over 4 days favorably reduces LDL and blood pressure but is not associated with improvements in endothelial function of conduit arteries.

Impact of vitamin D supplementation on arterial vasomotion, stiffness and endothelial biomarkers in chronic kidney disease patients

Background

Cardiovascular events are frequent and vascular endothelial function is abnormal in patients with chronic kidney disease (CKD). We demonstrated endothelial dysfunction with vitamin D deficiency in CKD patients; however the impact of cholecalciferol supplementation on vascular stiffness and vasomotor function, endothelial and bone biomarkers in CKD patients with low 25-hydroxy vitamin D [25(OH)D] is unknown, which this study investigated.

Methods

We assessed non-diabetic patients with CKD stage 3/4, age 17–80 years and serum 25(OH)D <75 nmol/L. Brachial artery Flow Mediated Dilation (FMD), Pulse Wave Velocity (PWV), Augmentation Index (AI) and circulating blood biomarkers were evaluated at baseline and at 16 weeks. Oral 300,000 units cholecalciferol was administered at baseline and 8-weeks.

Results

Clinical characteristics of 26 patients were: age 50±14 (mean±1SD) years, eGFR 41±11 ml/min/1.73 m², males 73%, dyslipidaemia 36%, smokers 23% and hypertensives 87%.

At 16-week serum 25(OH)D and calcium increased (43±16 to 84±29 nmol/L, p<0.001 and 2.37±0.09 to 2.42±0.09 mmol/L; p = 0.004, respectively) and parathyroid hormone decreased (10.8±8.6 to 7.4±4.4; p = 0.001). FMD improved from 3.1±3.3% to 6.1±3.7%, p = 0.001.

Endothelial biomarker concentrations decreased: E-Selectin from 5666±2123 to 5256±2058 pg/mL; p = 0.032, ICAM-1, 3.45±0.01 to 3.10±1.04 ng/mL; p = 0.038 and VCAM-1, 54±33 to 42±33 ng/mL; p = 0.006. eGFR, BP, PWV, AI, hsCRP, von Willebrand factor and Fibroblast Growth Factor-23, remained unchanged.

Conclusion

This study demonstrates for the first time improvement of endothelial vasomotor and secretory functions with vitamin D in CKD patients without significant adverse effects on arterial stiffness, serum calcium or FGF-23.

Trial Registration

ClinicalTrials.gov NCT02005718

Cardiovascular reactivity, stress, and physical activity

Psychological stress has been proposed as a major contributor to the progression of cardiovascular disease (CVD). Acute mental stress can activate the sympathetic-adrenal-medullary (SAM) axis, eliciting the release of catecholamines (NE and EPI) resulting in the elevation of heart rate (HR) and blood pressure (BP). Combined stress (psychological and physical) can exacerbate these cardiovascular responses, which may partially contribute to the elevated risk of CVD and increased proportionate mortality risks experienced by some occupations (e.g., firefighting and law enforcement). Studies have supported the benefits of physical activity on physiological and psychological health, including the cardiovascular response to acute stress. Aerobically trained individuals exhibit lower sympathetic nervous system (e.g., HR) reactivity and enhanced cardiovascular efficiency (e.g., lower vascular reactivity and decreased recovery time) in response to physical and/or psychological stress. In addition, resistance training has been demonstrated to attenuate cardiovascular responses and improve mental health. This review will examine stress-induced cardiovascular reactivity and plausible explanations for how exercise training and physical fitness (aerobic and resistance exercise) can attenuate cardiovascular responses to stress. This enhanced functionality may facilitate a reduction in the incidence of stroke and myocardial infarction. Finally, this review will also address the interaction of obesity and physical activity on cardiovascular reactivity and CVD.

Cellular and molecular mechanisms of endothelial dysfunction in diabetes

In healthy individuals, the vascular endothelium regulates an intricate balance of factors that maintain vascular homeostasis and normal arterial function. Functional disruption of the endothelium is known to be an early event that underlies the development of subsequent cardiovascular disease (CVD) including atherosclerosis and coronary heart disease. In addition, the rising global epidemic of type 2 diabetes is a significant problem conferring a significantly higher risk of CVD to individuals in whom endothelial dysfunction is also notable. This review first summarises the role of endothelium in health and explores and evaluates the impact of diabetes on endothelial function. The characteristic features of insulin resistance and other metabolic disturbances that may underlie long-term changes in vascular endothelial function (metabolic memory) are described along with proposed cellular, molecular and epigenetic mechanisms. Through understanding the underlying mechanisms, novel targets for future therapies to restore endothelial homeostasis and 'drive' a reparative cellular phenotype are explored.

High-intensity endurance training results in faster vessel-specific rate of vasorelaxation in type 1 diabetic rats

This study examined the effects of 6 weeks of moderate- (MD) and high-intensity endurance training (HD) and resistance training (RD) on the vasorelaxation responsiveness of the aorta, iliac, and femoral vessels in type 1 diabetic (D) rats. Vasorelaxation to acetylcholine was modeled as a mono-exponential function. A potential mediator of vasorelaxation, endothelial nitric oxide synthase (e-NOS) was determined by Western blots. Vessel lumen-to-wall ratios were calculated from H&E stains. The vasorelaxation time-constant (τ) (s) was smaller in control (C) (7.2±3.7) compared to D (9.1±4.4) and it was smaller in HD (5.4±1.5) compared to C, D, RD (8.3±3.7) and MD (8.7±3.8) (p<0.05). The rate of vasorelaxation (%·s⁻¹) was larger in HD (2.7±1.2) compared to C (2.0±1.2), D (2.0±1.5), RD (2.0±1.0), and MD (2.0±1.2) (p<0.05). τ vasorelaxation was smaller in the femoral (6.9±3.7) and iliac (6.9±4.7) than the aorta (9.0±5.0) (p<0.05). The rate of vasorelaxation was progressively larger from the femoral (3.1±1.4) to the iliac (2.0±0.9) and to the aorta (1.3±0.5) (p<0.05). e-NOS content (% of positive control) was greater in HD (104±90) compared to C (71±64), D (85±65), RD (69±43), and MD (76±44) (p<0.05). e-NOS normalized to lumen-to-wall ratio (%·mm⁻¹) was larger in the femoral (11.7±11.1) compared to the aorta (3.2±1.9) (p<0.05). Although vasorelaxation responses were vessel-specific, high-intensity endurance training was the most effective exercise modality in restoring the diabetes-related loss of vascular responsiveness. Changes in the vasoresponsiveness seem to be endothelium-dependent as evidenced by the greater e-NOS content in HD and the greater normalized e-NOS content in the smaller vessels.

Vessel-specific rate of vasorelaxation is slower in diabetic rats

The rate of adjustment of endothelium-dependent vasorelaxation was examined in the aorta, iliac and femoral arteries of eight control and eight diabetic rats with and without supplementation with vitamin C. Vessels were constricted using 10(-5) M phenylephrine (PE) and relaxed with 10(-4) M acetylcholine (ACh condition) or 10(-4) M ACh plus 10(-4) M vitamin C (ACh + vitamin C condition) in a myography system. Vasorelaxation was modelled as a mono-exponential function using a non-linear regression analysis. The adjustment (τ) of vasorelaxation was faster in control (6.6 ± 3.2 s) compared to diabetic rats (8.4 ± 3.4 s) (p < 0.05). The time-to-steady-state tended to be shorter in control (32.0 ± 13.9 s) compared to diabetic rats (38.0 ± 15.0 s) (p = 0.1). ACh + vitamin C did not speed the vasorelaxation response. The τ for vasorelaxation was shorter in the femoral (6.5 ± 2.7 s) and iliac (6.8 ± 2.5 s) compared to the aorta (9.2 ± 4.2 s) (p < 0.05). The rate of vasorelaxation was greater in the femoral (3.2 ± 1.4%·s(-1)) compared to the iliac (2.0 ± 1.0%·s(-1)) and aorta (1.1 ± 0.4%·s(-1)) in both groups and in the iliac compared to the aorta (p < 0.05) in the control group. In conclusion, the vasorelaxation response was vessel specific with a slower rate of adjustment in diabetic compared to control animals.

The distinctive nature of atherosclerotic vascular disease in diabetes: pathophysiological and morphological insights

As the incidence of diabetes mellitus continues to rise, parallel increases in the rates of diabetic atherosclerotic vascular disease are projected to impart major health and socioeconomic challenges for authorities worldwide. Diabetes results in a proatherogenic phenotype, manifesting in an accelerated, diffuse, polyvascular fashion. In this review, we highlight the pathophysiological and morphological hallmarks of diabetic atherosclerosis.

Ascorbate stimulates endothelial nitric oxide synthase enzyme activity by rapid modulation of its phosphorylation status

Long-term exposure to ascorbate is known to enhance endothelial nitric oxide synthase (eNOS) activity by stabilizing the eNOS cofactor tetrahydrobiopterin (BH4). We investigated acute effects of ascorbate on eNOS function in primary (HUVEC) and immortalized human endothelial cells (EA.hy926), aiming to provide a molecular explanation for the rapid vasodilatation seen in vivo upon administration of ascorbate. Enzymatic activity of eNOS and intracellular BH4 levels were assessed by means of an arginine-citrulline conversion assay and HPLC analysis, respectively. Over a period of 4h, ascorbate steadily increased eNOS activity, although endothelial BH4 levels remained unchanged compared to untreated control cells. Immunoblot analyses revealed that as early as 5 min after treatment ascorbate dose-dependently increased phosphorylation at eNOS-Ser1177 and concomitantly decreased phosphorylation at eNOS-Thr495, a phosphorylation pattern indicative of increased eNOS activity. By employing pharmacological inhibitors, siRNA-mediated knockdown approaches, and overexpression of the catalytic subunit of protein phosphatase 2A (PP2A), we show that this effect was at least partly owing to reduction of PP2A activity and subsequent activation of AMP-activated kinase. In this report, we unravel a novel mechanism for how ascorbate rapidly activates eNOS independent of its effects on BH4 stabilization.

Chronic hyperglycemia and subclinical myocardial injury

OBJECTIVES

The purpose of this study was to examine the association between hyperglycemia and subclinical myocardial injury in persons without clinically evident coronary heart disease (CHD).

BACKGROUND

Hyperglycemia is associated with an increased risk of cardiac events, but limited information is available on its relationship to subclinical myocardial damage. Elevated cardiac troponin T even below traditional detection levels can be detected by a novel high-sensitivity assay.

METHODS

We examined the association between baseline glycated hemoglobin (HbA1c) and high-sensitivity cardiac troponin T (hs-cTnT) in 9,661 participants free of CHD and heart failure in the ARIC (Atherosclerosis Risk in Communities) study. Multivariable logistic regression models characterized the association between clinical categories of HbA1c (<5.7%, 5.7% to 6.4%, and ≥6.5%) and our primary outcome of elevated hs-cTnT (≥14 ng/l).

RESULTS

Higher baseline values of HbA1c were associated in a graded fashion with elevated hs-cTnT (p for trend < 0.001). After adjusting for traditional risk factors, compared to persons with HbA1c <5.7%, the odds ratios of elevated hs-cTnT for persons with HbA1c 5.7% to 6.4% and ≥6.5% were 1.26 (95% confidence interval: 1.01 to 1.56) and 1.97 (95% confidence interval: 1.44 to 2.70), respectively.

CONCLUSIONS

Higher HbA1c is associated with elevated hs-cTnT among persons without clinically evident CHD, suggesting that hyperglycemia contributes to myocardial injury beyond its effects on development of clinical atherosclerotic coronary disease.

Endothelial dysfunction and diabetes: effects on angiogenesis, vascular remodeling, and wound healing

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by inappropriate hyperglycemia due to lack of or resistance to insulin. Patients with DM are frequently afflicted with ischemic vascular disease or wound healing defect. It is well known that type 2 DM causes amplification of the atherosclerotic process, endothelial cell dysfunction, glycosylation of extracellular matrix proteins, and vascular denervation. These complications ultimately lead to impairment of neovascularization and diabetic wound healing. Therapeutic angiogenesis remains an attractive treatment modality for chronic ischemic disorders including PAD and/or diabetic wound healing. Many experimental studies have identified better approaches for diabetic cardiovascular complications, however, successful clinical translation has been limited possibly due to the narrow therapeutic targets of these agents or the lack of rigorous evaluation of pathology and therapeutic mechanisms in experimental models of disease. This paper discusses the current body of evidence identifying endothelial dysfunction and impaired angiogenesis during diabetes.

Effects of glycemic regulation on chronic postischemia pain

BACKGROUND

Ischemia-reperfusion (I/R) injuries consist of enhanced oxidative and inflammatory responses along with microvascular dysfunction after prolonged ischemia and reperfusion. Because I/R injuries induce chronic postischemia pain (CPIP) in laboratory animals, it is possible that surgical procedures using prolonged ischemia may result in chronic postoperative pain. Glycemic modulation during ischemia and reperfusion could affect pain after I/R injury because glucose triggers oxidative, inflammatory, and thrombotic reactions, whereas insulin has antioxidative, antiinflammatory, and vasodilatory properties.

METHODS

One hundred ten rats underwent a 3-h period of ischemia followed by reperfusion to produce CPIP. Rats with CPIP had previously been divided into six groups with differing glycemic modulation paradigms: normal feeding; fasting; fasting with normal saline administration; fasting with dextrose administration; normal feeding with insulin administration; and normal feeding with insulin and dextrose administration. Blood glucose concentration was assessed during I/R in these separate groups of rats, and these rats were tested for mechanical and cold allodynia over the 21 days afterward (on days 2, 5, 7, 9, 12, and 21 after I/R injury).

RESULTS

I/R injury in rats with normoglycemia or relative hyperglycemia (normal feeding and fasting with dextrose administration groups) led to significant mechanical and cold allodynia; conversely, relative hypoglycemia associated with insulin treatment or fasting (fasting, fasting with normal saline administration, and normal feeding with insulin administration groups) reduced allodynia induced by I/R injury. Importantly, insulin treatment did not reduce allodynia when administered to fed rats given dextrose (normal feeding with dextrose and insulin administration group).

CONCLUSION

Study results suggest that glucose levels at the time of I/R injury significantly modulate postinjury pain thresholds in rats with CPIP. Strict glycemic control during I/R injury significantly reduces CPIP and, conversely, hyperglycemia significantly enhances it, which could have potential clinical applications especially in the surgical field.

Regulation of endothelial function by mitochondrial reactive oxygen species

Mitochondria are well known for their central roles in ATP production, calcium homeostasis, and heme and steroid biosynthesis. However, mitochondrial reactive oxygen species (ROS), including superoxide and hydrogen peroxide, once thought to be toxic byproducts of mitochondrial physiologic activities, have recently been recognized as important cell-signaling molecules in the vascular endothelium, where their production, conversion, and destruction are highly regulated. Mitochondrial reactive oxygen species appear to regulate important vascular homeostatic functions under basal conditions in a variety of vascular beds, where, in particular, they contribute to endothelium-dependent vasodilation. On exposure to cardiovascular risk factors, endothelial mitochondria produce excessive ROS in concert with other cellular ROS sources. Mitochondrial ROS, in this setting, act as important signaling molecules activating prothrombotic and proinflammatory pathways in the vascular endothelium, a process that initially manifests itself as endothelial dysfunction and, if persistent, may lead to the development of atherosclerotic plaques. This review concentrates on emerging appreciation of the importance of mitochondrial ROS as cell-signaling molecules in the vascular endothelium under both physiologic and pathophysiologic conditions. Future potential avenues of research in this field also are discussed.

Intravenous ascorbic acid to prevent and treat cancer-associated sepsis?

The history of ascorbic acid (AA) and cancer has been marked with controversy. Clinical studies evaluating AA in cancer outcome continue to the present day. However, the wealth of data suggesting that AA may be highly beneficial in addressing cancer-associated inflammation, particularly progression to systemic inflammatory response syndrome (SIRS) and multi organ failure (MOF), has been largely overlooked. Patients with advanced cancer are generally deficient in AA. Once these patients develop septic symptoms, a further decrease in ascorbic acid levels occurs. Given the known role of ascorbate in: a) maintaining endothelial and suppression of inflammatory markers; b) protection from sepsis in animal models; and c) direct antineoplastic effects, we propose the use of ascorbate as an adjuvant to existing modalities in the treatment and prevention of cancer-associated sepsis.

The Bilirubin-Increasing Drug Atazanavir Improves Endothelial Function in Patients With Type 2 Diabetes Mellitus

Objective—

In type 2 diabetes mellitus (T2DM), oxidative stress gives rise to endothelial dysfunction. Bilirubin, a powerful endogenous antioxidant, significantly attenuates endothelial dysfunction in preclinical experiments. The Gilbert syndrome is accompanied by a mild and lifelong hyperbilirubinemia and associated with only one third of the usual cardiovascular mortality risk. The hyperbilirubinemia caused by atazanavir treatment closely resembles the Gilbert syndrome. We thus hypothesized that treatment with atazanavir would ameliorate oxidative stress and vascular inflammation and improve endothelial function in T2DM.

Methods and Results—

In a double-blind, placebo-controlled crossover design, we induced a moderate hyperbilirubinemia by a 3-day atazanavir treatment in 16 subjects experiencing T2DM. On the fourth day, endothelial function was assessed by venous occlusion plethysmography. Endothelium-dependent and endothelium-independent vasodilation were assessed by intraarterial infusion of acetylcholine and nitroglycerin, respectively. Atazanavir treatment induced an increase in average bilirubin levels from 7 μmol/L (0.4 mg/dL) to 64 μmol/L (3.8 mg/dL). A significant improvement in plasma antioxidant capacity ( P <0.001) and endothelium-dependent vasodilation ( P =0.036) and a decrease in plasma von Willebrand factor ( P =0.052) were observed.

Conclusion—

Experimental hyperbilirubinemia is associated with a significant improvement of endothelial function in T2DM.

Organic nitrates and nitrate resistance in diabetes: the role of vascular dysfunction and oxidative stress with emphasis on antioxidant properties of pentaerithrityl tetranitrate

Organic nitrates represent a class of drugs which are clinically used for treatment of ischemic symptoms of angina as well as for congestive heart failure based on the idea to overcome the impaired NO bioavailability by “NO” replacement therapy. The present paper is focused on parallels between diabetes mellitus and nitrate tolerance, and aims to discuss the mechanisms underlying nitrate resistance in the setting of diabetes. Since oxidative stress was identified as an important factor in the development of tolerance to organic nitrates, but also represents a hallmark of diabetic complications, this may represent a common principle for both disorders where therapeutic intervention should start. This paper examines the evidence supporting the hypothesis that pentaerithrityl tetranitrate may represent a nitrate for treatment of ischemia in diabetic patients. This evidence is based on the considerations of parallels between diabetes mellitus and nitrate tolerance as well as on preliminary data from experimental diabetes studies.

Curcumin supplementation could improve diabetes-induced endothelial dysfunction associated with decreased vascular superoxide production and PKC inhibition

Background

Curcumin, an Asian spice and food-coloring agent, is known for its anti-oxidant properties. We propose that curcumin can improve diabetes-induced endothelial dysfunction through superoxide reduction.

Methods

Diabetes (DM) was induced in rats by streptozotocin (STZ). Daily curcumin oral feeding was started six weeks after the STZ injection. Twelve weeks after STZ injection, mesenteric arteriolar responses were recorded in real time using intravital fluorescence videomicroscopy. Superoxide and vascular protein kinase C (PKC-βII) were examined by hydroethidine and immunofluorescence, respectively.

Results

The dilatory response to acetylcholine (ACh) significantly decreased in DM arterioles as compared to control arterioles. There was no difference among groups when sodium nitroprusside (SNP) was used. ACh responses were significantly improved by both low and high doses (30 and 300 mg/kg, respectively) of curcumin supplementation. An oxygen radical-sensitive fluorescent probe, hydroethidine, was used to detect intracellular superoxide anion (O₂^●-) production. O₂^●- production was markedly increased in DM arterioles, but it was significantly reduced by supplementation of either low or high doses of curcumin. In addition, with a high dose of curcumin, diabetes-induced vascular PKC-βII expression was diminished.

Conclusion

Therefore, it is suggested that curcumin supplementation could improve diabetes-induced endothelial dysfunction significantly in relation to its potential to decrease superoxide production and PKC inhibition.

Effects of combined treatment with vitamins C and E on passive avoidance learning and memory in diabetic rats

Learning and memory deficits occur in diabetes mellitus. Although the pathogenesis of cognitive impairment in diabetes has not been fully elucidated, factors such as metabolic impairments, vascular complications and oxidative stress are thought to play possible roles. Here we investigated the effect of chronic treatment with vitamin C (50mg/kg, p.o), vitamin E (100mg/kg, p.o) and both together on passive avoidance learning (PAL) and memory in male Wistar control and diabetic rats. Treatments were begun at the onset of hyperglycemia. Passive avoidance learning was assessed 30 days later. Retention was tested 24h after training. At the end, animals were weighed and blood samples were drawn for plasma glucose measurement. Diabetes caused impairment in acquisition and retrieval processes of PAL and memory. The combination of vitamin C and E improved learning and memory in controls and reversed learning and memory deficits in diabetic rats. Combined treatment also affected the body weight and plasma glucose level of diabetic treated animals compared to untreated diabetic animals. Hypoglycemic effects and antioxidant properties of the vitamins may be involved in the nootropic effect of such treatment. These results show that combined treatment with vitamins C and E improved PAL and memory of control rats. In addition, combined vitamins administration to rats for 30 days from onset of diabetes alleviated the negative influence of diabetes on learning and memory. Therefore, combined vitamins treatment may provide a new potential alternative for prevention of impaired cognitive functions associated with diabetes and may warrant further clinical study.

Role of marginal vitamin C deficiency in atherogenesis: in vivo models and clinical studies

Vitamin C is a pivotal redox modulater in many biological reactions of which several remain poorly understood. Naturally, vitamin C has been the subject of many investigations over the past decades in relation to its possible beneficial effects on cardiovascular disease primarily based on its powerful yet general antioxidant properties. However, growing epidemiological, clinical and experimental evidence now suggests a more specific role of ascorbate in vasomotion and in the prevention of atherosclerosis. For example, in contrast to most other biological antioxidants, administration of vitamin C can apparently induce vasodilation. Millions of people worldwide can be diagnosed with vitamin C deficiency according to accepted definitions. In this perspective, the present review examines the evidence for a specific link between vitamin C deficiency and increased risk of atherosclerosis as well as the possible mechanisms by which vitamin C may exert its protective function.

Poor vitamin C status is associated with increased carotid intima-media thickness, decreased microvascular function, and delayed myocardial repolarization in young patients with type 1 diabetes

BACKGROUND

Vascular endothelial dysfunction, accelerated thickening of arterial intima, and changes in ventricular repolarization contribute to increased cardiovascular morbidity in type 1 diabetes (T1D). Although vitamin C has important antioxidant functions and increased oxidative stress is a central mechanism of cardiovascular dysfunction in T1D, the relation between vitamin C and the cardiovascular system in young diabetic patients has not been investigated.

OBJECTIVE

In a cohort of young patients with T1D, we investigated the relation of plasma concentrations of vitamin C with indexes of vascular function and structure and duration of the QT interval corrected for heart rate (QT(c)).

DESIGN

Carotid artery intima-media thickness, cutaneous microvascular function, and duration of the QT(c) interval were measured in 59 patients (mean age: 17 y; range: 10-22 y) with T1D (diabetes duration: 3-20 y). Plasma vitamin C was analyzed by HPLC with coulometric detection.

RESULTS

Carotid artery intima-media thickness and duration of the QT(c) interval were higher in patients in the lowest tertile of vitamin C than in those in the highest tertile (P < 0.05 for both). The cutaneous microvascular response to acetylcholine was lower (P = 0.003) in the lowest tertile group than in the highest tertile group, but the response to sodium nitroprusside was not significantly different between these 2 groups. All differences remained significant after adjustment for age, sex, diabetes duration, body mass index, and glycated hemoglobin.

CONCLUSIONS

In this relatively small-scale cross-sectional study of young patients with T1D, lower plasma concentrations of vitamin C seem to be associated with adverse changes in the microcirculation, peripheral arteries, and ventricular repolarization. Large-scale prospective studies are needed to confirm these results and to clarify the underlying mechanisms.

Elevated Glucose Attenuates Agonist- and Flow-Stimulated Endothelial Nitric Oxide Synthase Activity in Microvascular Retinal Endothelial Cells

Impaired vasoactive release of opposing vasodilator and vasoconstrictor mediators due to endothelial dysfunction is integral to the pathogenesis of diabetic retinopathy. The aim of this study was to determine the effect of hyperglycemia on the expression of endothelial nitric oxide synthase (eNOS) and the release of nitric oxide (NO) in bovine microvascular retinal endothelial cells (BRECs) under both static (basal and acetylcholine stimulated) and flow (laminar shear stress [10 dynes/cm2 and pulsatile flow 0.3 to 23 dynes/cm2) conditions using a laminar shear apparatus and an in vitro perfused transcapillary culture system. The activity and expression of eNOS, measured by nitrate levels and immunoblot, respectively, were determined following exposure of BRECs to varying concentrations of glucose and mannitol (0 to 25 mM). Under static conditions the expression of eNOS decreased significantly following exposure to increasing concentrations of glucose when compared to osmotic mannitol controls and was accompanied by a significant dose-dependent decrease in nitrate levels in conditioned medium. The acetylcholine stimulated increase in NO release (2.0 +/- 0.3-fold) was significantly reduced by 55% +/- 5% and 65% +/- 4.5% following exposure to 16 and 25 mM glucose, respectively, when compared to osmotic controls. In parallel studies, glucose significantly inhibited both laminar shear stress and pulsatile flow-induced activity when compared to mannitol. We conclude that hyperglycemia impairs agonist- and flow-dependent release of NO in retinal microvascular endothelial cells and may thus contribute to the vascular endothelial dysfunction and impaired autoregulation of diabetic retinopathy.

N-acetylcysteine improves microcirculatory flow during smoking: new effects of an old drug with possible benefits for smokers

BACKGROUND

Cigarette smoking provokes marked acute changes in the microcirculatory vasculature, including a reduced blood flow velocity. In accordance with the hypothesis that the reduced blood flow is due to an imbalance between pro-oxidants and oxidants, we recently showed that most of the reduction could be reversed by a high dose of vitamin C.

HYPOTHESIS

In the present work we tested the hypothesis that N-acetylcysteine, a mucolyticum and an antioxidant, may have an effect on the smoking-induced changes observed by vital capillary microscopy of the nailfold.

METHODS

In all, 37 healthy volunteers of both genders and with varied smoking habits were treated with N-acetylcysteine 200 mg t.i.d. for 2 weeks. In vivo investigation of the microcirculation by capillaroscopy was performed before and after treatment.

RESULTS

Treatment with N-acetylcysteine significantly reduced the smoking-induced relative decrease in capillary blood flow velocity in a group of volunteers with varied smoking habits (p = 0.0016). The preventive effect was clearly significant in smokers (p = 0.003).

CONCLUSION

Treatment with N-acetylcysteine has a positive impact on microcirculatory flow during smoking, particularly in habitual smokers.

Pharmacological and biological screening of ascorbigen: protection against glucose-induced endothelial cell toxicity

Cruciferous vegetables contain significant amounts of ascorbigen and related substances with known molecular structures. This study tested the hypothesis that ascorbigen demonstrates antioxidant properties and protects human umbilical cord endothelial cells against hyperglycemic toxicity in vitro. It was observed that ascorbigen, in micromolar concentrations, protected against endothelial cell death from glucose toxicity. Additionally, ascorbigen at 3.0 mm shifted the concentration response curve of l-phenylephrine to the right, with a reduction in the maximal contractile effects of the agonist. This action was not related to alpha-adrenoceptor blockade. Ascorbigen also relaxed the vascular tone induced by l-phenylephrine, which is not mediated by an endothelial cell nitric oxide-dependent mechanism. On the guinea-pig ileum, the spasmogenic effects of carbachol, histamine and serotonin were reduced in the presence of 3 mM ascorbigen. Spasm of the gut induced by the acetylcholinesterase inhibitor, physostigmine, was antagonized by ascorbigen with an IC50 of 286 microM. This natural product also has a weak antiparasitic activity. The cytoprotective effects of ascorbigen may be highly relevant in the optimum physiological regulation of the function and the therapeutic value of this substance in disease settings needs to be further investigated.

Quantitative regulation of intracellular endothelial nitric-oxide synthase (eNOS) coupling by both tetrahydrobiopterin-eNOS stoichiometry and biopterin redox status: insights from cells with tet-regulated GTP cyclohydrolase I expression

Tetrahydrobiopterin (BH4) is a critical determinant of endothelial nitric-oxide synthase (eNOS) activity. In the absence of BH4, eNOS becomes "uncoupled" and generates superoxide rather than NO. However, the stoichiometry of intracellular BH4/eNOS interactions is not well defined, and it is unclear whether intracellular BH4 deficiency alone is sufficient to induce eNOS uncoupling. To address these questions, we developed novel cell lines with tet-regulated expression of human GTP cyclohydrolase I (GTPCH), the rate-limiting enzyme in BH4 synthesis, to selectively induce intracellular BH4 deficiency by incubation with doxycycline. These cells were stably co-transfected to express a human eNOS-green fluorescent protein fusion protein, selecting clones expressing either low (GCH/eNOS-LOW) or high (GCH/eNOS-HIGH) levels. Doxycycline abolished GTPCH mRNA expression and GTPCH protein, leading to markedly diminished total biopterin levels and a decreased ratio of BH4 to oxidized biopterins in cells expressing eNOS. Intracellular BH4 deficiency induced superoxide generation from eNOS, as assessed by N-nitro-L-arginine methyl ester inhibitable 2-hydroxyethidium generation, and attenuated NO production. Quantitative analysis of cellular BH4 versus superoxide production between GCH/eNOS-LOW and GCH/eNOS-HIGH cells revealed a striking linear relationship between eNOS protein and cellular BH4 stoichiometry, with eNOS uncoupling at eNOS:BH4 molar ratio >1. Furthermore, increasing the intracellular BH2 concentration in the presence of a constant eNOS:BH4 ratio was sufficient to induce eNOS-dependent superoxide production. This specific, reductionist approach in a cell-based system reveals that eNOS:BH4 reaction stoichiometry together with the intracellular BH4:BH2 ratio, rather than absolute concentrations of BH4, are the key determinants of eNOS uncoupling, even in the absence of exogenous oxidative stress.

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.