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

Glut-1 explains the evolutionary advantage of the loss of endogenous vitamin C-synthesis: The electron transfer hypothesis

Introduction

During evolution, some species including humans, monkeys and fruit bats lost the ability for ascorbic acid (AA) biosynthesis due to inactivation of the enzyme l-gulono-lactone oxidase (GLO) and subsequently became dependent on dietary vitamin C. There are four current hypotheses in relation to the benefit of vitamin C dependence in the context of adaptation and reproduction. Here we advance and test a new ‘electron transfer hypothesis’, which focusses on the role of the expression of glucose transporter 1 (Glut-1) in red blood cells (RBCs) in recycling vitamin C, thereby increasing the efficiency of micronutrient uptake.

Methods

To evaluate the benefit of Glut-1 expression, we determined vitamin C uptake into RBCs and potential release from two different species, humans with l-Gulono-lactone-oxidase (GLO-loss) and pigs with functional GLO.

Results

The oxidized form of vitamin C (dehydroascorbate, DHA) was transported into human RBCs via Glut-1. There was no transport of either the reduced (AA) or the oxidized vitamin in pig erythrocytes.

Conclusion

We propose that the transport of vitamin C increases an intracellular electron pool, which transfers electrons from intracellular ascorbate to extracellular substances like ascorbyl free radical or DHA, resulting in 100-fold smaller daily requirement of this essential redox sensitive micronutrient. This would be an advantage during seasonal changes of the availability from food and may be the key for the survival of individuals without vitamin C biosynthesis.

Lay Summary

40 million years ago some individuals lost the ability to synthesize vitamin C. Why did they survive such as humans until now? Individuals with a specific glucose transporter Glut-1 on their erythrocytes which transports vitamin C need less and are protected from scarcity due to seasons and food competitors.

The Pharmacokinetics of Vitamin C

The pharmacokinetics of vitamin C (vitC) is indeed complex. Regulated primarily by a family of saturable sodium dependent vitC transporters (SVCTs), the absorption and elimination are highly dose-dependent. Moreover, the tissue specific expression levels and subtypes of these SVCTs result in a compartmentalized distribution pattern with a diverse range of organ concentrations of vitC at homeostasis ranging from about 0.2 mM in the muscle and heart, and up to 10 mM in the brain and adrenal gland. The homeostasis of vitC is influenced by several factors, including genetic polymorphisms and environmental and lifestyle factors such as smoking and diet, as well as diseases. Going from physiological to pharmacological doses, vitC pharmacokinetics change from zero to first order, rendering the precise calculation of dosing regimens in, for example, cancer and sepsis treatment possible. Unfortunately, the complex pharmacokinetics of vitC has often been overlooked in the design of intervention studies, giving rise to misinterpretations and erroneous conclusions. The present review outlines the diverse aspects of vitC pharmacokinetics and examines how they affect vitC homeostasis under a variety of conditions.

Dietary Vitamin C in Human Health

Vitamin C is essential to prevent scurvy in humans and is implicated in the primary prevention of common and complex diseases such as coronary heart disease, stroke, and cancer. This chapter reviews the latest knowledge about dietary vitamin C in human health with an emphasis on studies of the molecular mechanisms of vitamin C maintenance as well as gene-nutrient interactions modifying these relationships. Epidemiological evidence indicates 5% prevalence for vitamin C deficiency and 13% prevalence for suboptimal status even in industrialized countries. The daily intake (dose) and the corresponding systemic concentrations (response) are related in a saturable relationship, and low systemic vitamin C concentrations in observational studies are associated with negative health outcomes. However, there is no evidence that vitamin C supplementation impacts the risks for all-cause mortality, impaired cognitive performance, reduced quality of life, the development of eye diseases, infections, cardiovascular disease, and cancers. This might be related to the fact that prevention would not be realized by supplementation in populations already adequately supplied through dietary sources. Recent genetic association studies indicate that the dietary intake might not be the sole determinant of systemic concentrations, since variations in genes participating in redox homeostasis and vitamin C transport had been associated with lowered plasma concentrations. However, impact sizes are generally low and these phenomena might only affect individual of suboptimal dietary supply.

Proanthocyanidins from Vitis vinifera inhibit oxidative stress-induced vascular impairment in pulmonary arteries from diabetic rats

BACKGROUND

Vitis vinifera L. (grape seed extract) is a natural source of proanthocyanidins with antioxidant and free radical-scavenging activities.

HYPOTHESIS

Grape seed extract supplementation may prevent vascular endothelium impairment associated with diabetes mellitus in rat pulmonary artery.

STUDY DESIGN

We evaluated endothelial function of rat pulmonary artery ex-vivo at the intermediate stage (4 weeks) of streptozotocin (STZ)-induced diabetes mellitus. We also evaluated the protective effect of grape seed extract administered daily, beginning the day after diabetes induction, or 15 days after diabetes induction, until the day of sacrifice. In addition, we compared the effect of grape seed extract supplementation with that of vitamin C.

METHODS

Rats were made diabetic with streptozotocin (STZ, 65mg/kg i.v.). Thirty days later rats were sacrificed and pulmonary vessels reactivity and endothelial function compared to that of age-matched healthy animals.

RESULTS

Concentration-response curves to ACh, NE, sodium nitroprusside (NO donor), but not to histamine and iloprost (prostacyclin analog), were significantly altered 4 weeks after STZ-injection. Antioxidant supplementation (3mg/kg/day) with either vitamin C or grape seed extract, starting the day after diabetes induction, significantly improved vasodilation to ACh and SNP. Norepinephrine-induced contractions were preserved by grape seed extract, but not vitamin C supplementation. Conversely, vitamin C but not grape seed extract showed beneficial effects contrasting the loss of body weight in diabetic animals. Abnormal vascular function was not reversed when antioxidant supplementations were postponed 15 days after the induction of diabetes.

CONCLUSIONS

This study provides scientific support for the therapeutic potential of an antioxidant therapy in endothelial impairment associated with diabetes. A daily supplementation of grape seed proanthocyanidins and/or vitamin C given at the earlier stage of disease may have a complementary role in the pharmacological therapy of diabetes and pulmonary vascular dysfunction.

Clinical and dietary predictors of common carotid artery intima media thickness in a population with type 1 and type 2 diabetes: A cross-sectional study

AIM

To determine the clinical and dietary predictors of common carotid artery intima media thickness (CCA IMT) in a cohort of subjects with type 1 and type 2 diabetes.

METHODS

Participants with type 1 (n = 23) and type 2 diabetes (n = 127) had mean and mean maximum CCA IMT measured using B mode ultrasound. Dietary intake was measured using a food frequency questionnaire. Clinical and dietary predictors of mean and mean maximum CCA IMT were determined using linear regression analysis adjusted for potential confounders.

RESULTS

The main predictors of mean and mean maximum CCA IMT were age and weight. After multivariate adjustment there were no dietary predictors of CCA IMT. However, in subjects that were not prescribed a lipid lowering medication alcohol consumption was positively associated with CCA IMT after multivariate adjustment. No difference existed in CCA IMT between subjects with type 1 or type 2 diabetes once age was adjusted for.

CONCLUSION

CCA IMT was predominantly predicted by age and weight in these subjects with diabetes. The finding that CCA IMT was not different between people with type 1 and type 2 diabetes warrants further investigation in a larger cohort.

Increased serum gamma-glutamyltransferase levels are associated with ventricular instability in type 2 diabetes

The purpose of our study is to examine the association between serum GGT levels and ventricular instability in Chinese patients with T2DM. We conducted a cross-sectional, community-based study in Nanjing, China from June to November 2011. Among 10,050 patients aged 40-79 years, we enrolled 2444 with pre-diabetes, 2496 with T2DM, and 4521 without diabetes (non-diabetes). Electrocardiograms were performed to measure the QT interval corrected for heart rate (QTc) and QT interval dispersion (QTd). Serum GGT levels, metabolic parameters, body mass index, and blood pressure were also measured. We found that there were no significant associations of increased QTc/QTd with serum GGT levels in participants with pre-existing T2DM and non-diabetes, after adjusting for age, duration of diabetes, and metabolic parameters. Even after adjustment, higher risks of QTc ≥ 440 ms/√s and QTd ≥ 58 ms were found in participants with serum GGT levels ≥49 U/L compared with those with <15 U/L in the pre-diabetes (QTc: OR 1.96, 95 % CI 1.23-2.47; QTd: OR 1.34, 95 % CI 1.07-1.94) and newly diagnosed T2DM (QTc: OR 2.01, 95 % CI 1.39-2.51; QTd: OR 1.53, 95 % CI 1.03-1.99) groups. We conclude that Increased serum GGT levels are associated with some markers of ventricular repolarization abnormalities in the early stage of T2DM.

Predictors of Increased Carotid Intima-Media Thickness in Youth With Type 1 Diabetes: The SEARCH CVD Study

OBJECTIVE

Youth with type 1 diabetes have worse cardiovascular (CV) risk factors and higher carotid intima-media thickness (IMT) than their peers without diabetes. Whether the burden of CV risk factors over time is associated with carotid IMT at follow-up in youth with type 1 diabetes is not known.

RESEARCH DESIGN AND METHODS

Two hundred ninety-eight youth with type 1 diabetes (mean age 13.3 ± 2.9 years, 87.6% non-Hispanic white, 53.7% male) had two study visits 5 years apart. CV risk factors, including BMI, lipids, blood pressure, hemoglobin A(1c), and smoking status, were assessed at both visits, and carotid IMT was measured at follow-up using B-mode ultrasonography. Linear regression models with an area under the curve measurement that incorporated the baseline and follow-up CV risk factors were used to evaluate the relationship with carotid IMT at follow-up.

RESULTS

All CV risk factors worsened significantly over time (except LDL cholesterol) (P < 0.05). From baseline to follow-up, the number of abnormal CV risk factors also increased (P < 0.05). Predictors of carotid IMT were older age, male sex, and higher BMI z score area under the curve (all P < 0.05).

CONCLUSIONS

The CV risk factor burden increases over time in youth with type 1 diabetes. BMI z score was the only modifiable CV risk factor that predicted carotid IMT. This study highlights the critical need to better understand the risk factors that influence carotid IMT early in the course of type 1 diabetes.

Effect of Vitamins C and E on Endothelial Function in Type 1 Diabetes Mellitus

BACKGROUND/OBJECTIVES

Endothelial dysfunction due to hyperglycemia-induced oxidative damage is an important predictor of future cardiovascular risk in patients with type 1 diabetes mellitus (T1DM) and is present in adolescent T1DM. We hypothesized that combined treatment with the antioxidant vitamins C and E might improve endothelial function (EF) and other biochemical risk factors in adolescents with T1DM.

SUBJECTS/METHODS

Open-label antioxidant supplementation was given for six weeks with endpoint measurements collected at baseline and study completion. Endpoints measured included EF and plasma measurements of biochemical endothelial risk.

RESULTS

Two males and 7 females were studied. Mean age was 12.9 ± 0.9 yrs; mean T1DM duration was 5.5 ± 2.5 yrs; mean BMI was 22.1 ± 3.8 kg/m(2); and mean hemoglobin A1c was 9.3 ± 1.1%. No differences were found for EF, high sensitivity CRP, total antioxidant capacity, adiponectin, or endothelial progenitor cells (EPCs) between before and after combined vitamin C and E therapy.

CONCLUSIONS

Our negative study results do not support previous findings of decreased oxidative damage, improved endothelial function, and increased vascular repair capacity with antioxidant therapy. Longer term studies may be needed to determine the effects, if any, of combined antioxidant therapy on EPCs, EF, and markers of micro- and macrovascular complications in T1DM.

Subclinical vascular endothelial dysfunctions and myocardial changes with type 1 diabetes mellitus in children and adolescents

Vascular endothelial dysfunction, accelerated thickening of arterial intima, and changes in ventricular functions contribute to increased cardiovascular morbidity in type 1 diabetes mellitus (T1DM). This study aimed to investigate the functional-structural changes in the arteries and myocardium together with affection of highly sensitive C-reactive protein (hsCRP), circulating endothelial cells (CECs), and vitamin C levels in children with T1DM. Also, to test the association with early atherosclerotic changes. The study included 30 children with a diagnosis of T1DM and 30 healthy subjects matched by sex, age, and body mass index. Serum lipids, HbA1c, hsCRP, vitamin C, and CECs were detected. Corrected QT interval (QTc), cardiac dimensions, and left ventricular (LV) functions were assessed using conventional echocardiography. Noninvasive ultrasound was used to measure brachial artery flow-mediated dilation (FMD) responses and carotid intima-media thickness (IMT). The QTc interval was significantly higher in the diabetic patients than in the control subjects (P < 0.001). The findings showed LV diastolic dysfunction as reflected by significantly lower early peak flow velocity, decreased E/A ratio, increased early filling deceleration time (DcT), and prolonged isovolumic relaxation time (IVRT) (P < 0.001 for each). The children with diabetes had a significantly lower FMD response, increased IMT, lower vitamin C level, higher hsCRP, and higher CEC compared with the control subjects (P < 0.001 for each). A positive correlation between CEC and HbA1c was found (P = 0.004). An alteration in myocardial function and endothelial dysfunction may begin early with the association of early atherosclerotic changes. These changes are accelerated when glycemic control is poor. The authors recommend early and close observation of children with diabetes for any alterations in cardiac and vascular endothelial function. Vitamin C supplementation may reduce the risk of complications.

Does vitamin C deficiency increase lifestyle-associated vascular disease progression? Evidence based on experimental and clinical studies

SIGNIFICANCE

Despite continuous advances in the prevention of cardiovascular disease (CVD), critical issues associated with an unhealthy lifestyle remain an increasing cause of morbidity and mortality in industrialized countries.

RECENT ADVANCES

A growing body of literature supports a specific role for vitamin C in a number of reactions that are associated with vascular function and control including, for example, nitric oxide bioavailability, lipid metabolism, and vascular integrity.

CRITICAL ISSUES

A large body of epidemiological evidence supports a relationship between poor vitamin C status and increased risk of developing CVD, and the prevalence of deficiency continues to be around 10%-20% of the general Western population although this problem could easily and cheaply be solved by supplementation. However, large intervention studies using vitamin C have not found a beneficial effect of supplementation. This review outlines the proposed mechanism by which vitamin C deficiency worsens CVD progression. In addition, it discusses problems with the currently available literature, including the discrepancies between the large intervention studies and the experimental and epidemiological literature.

FUTURE DIRECTIONS

Increased insights into vitamin C deficiency-mediated CVD progression will enable the design of future randomized controlled trials that are better suited to test the efficacy of vitamin C in disease prevention as well as the identification of high-risk individuals which could possibly benefit from supplementation.

Authors' perspective: What is the optimum intake of vitamin C in humans?

The recommended dietary allowance (RDA) of vitamin C has traditionally been based on the prevention of the vitamin C deficiency disease, scurvy. While higher intakes of vitamin C may exert additional health benefits, the limited Phase III randomized placebo-controlled trials (RCTs) of vitamin C supplementation have not found consistent benefit with respect to chronic disease prevention. To date, this has precluded upward adjustments of the current RDA. Here we argue that Phase III RCTs-designed principally to test the safety and efficacy of pharmaceutical drugs-are ill suited to assess the health benefits of essential nutrients; and the currently available scientific evidence is sufficient to determine the optimum intake of vitamin C in humans. This evidence establishes biological plausibility and mechanisms of action for vitamin C in the primary prevention of coronary heart disease, stroke, and cancer; and is buttressed by consistent data from prospective cohort studies based on blood analysis or dietary intake and well-designed Phase II RCTs. These RCTs show that vitamin C supplementation lowers hypertension, endothelial dysfunction, chronic inflammation, and Helicobacter pylori infection, which are independent risk factors of cardiovascular diseases and certain cancers. Furthermore, vitamin C acts as a biological antioxidant that can lower elevated levels of oxidative stress, which also may contribute to chronic disease prevention. Based on the combined evidence from human metabolic, pharmacokinetic, and observational studies and Phase II RCTs, we conclude that 200 mg per day is the optimum dietary intake of vitamin C for the majority of the adult population to maximize the vitamin's potential health benefits with the least risk of inadequacy or adverse health effects.

Altered oxido-reductive state in the diabetic heart: loss of cardioprotection due to protein disulfide isomerase

Diabetes is associated with an increased risk of heart failure, in part explained by endoplasmic reticulum stress and apoptosis. Protein disulfide isomerase (PDI) prevents stressed cardiomyocytes apoptosis. We hypothesized that diabetes impairs PDI function by an alteration in its oxido-reductive state. Myocardial biopsies harvested from the anterolateral left ventricular wall from diabetic (n = 7) and nondiabetic (n = 8) patients were used to assess PDI expression and cardiomyocyte death. A mouse model of diabetes (streptozotocin injection, 130 mg/mL) was used to study PDI expression and its redox state after ischemia/reperfusion injury induced by 30-min occlusion of the left anterior coronary artery followed by reperfusion. Transthoracic echocardiography was performed to assess cardiac remodeling after 1 wk. Western blot analysis was used to analyze PDI expression, and methoxy-polyethyleneglycol-maleimide was used to assess its redox state. Dehydroascorbate (DHA) administration was used to restore the PDI redox state. Diabetic patients had a greater number of transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells than nondiabetic patients despite a greater myocardial PDI expression suggesting altered PDI function. Diabetic mice had a worse postinfarction remodeling associated with an altered PDI redox state. DHA treatment restored functional PDI redox state and ameliorated post-myocardial infarction remodeling. An increase in PDI levels with a paradoxical decrease of its active form occurs in the diabetic heart after ischemia and may explain the lack of protective effects of PDI in diabetes. Restoration of PDI redox state prevents adverse remodeling. The potential significance of these findings deserves to be validated in a clinical setting.

High dietary fat and cholesterol exacerbates chronic vitamin C deficiency in guinea pigs

Vitamin C deficiency – or hypovitaminosis C defined as a plasma concentration below 23 μm – is estimated to affect hundreds of millions of people in the Western world, in particular subpopulations of low socio-economic status that tend to eat diets of poor nutritional value. Recent studies by us have shown that vitamin C deficiency may result in impaired brain development. Thus, the aim of the present study was to investigate if a poor diet high in fat and cholesterol affects the vitamin C status of guinea pigs kept on either sufficient or deficient levels of dietary ascorbate (Asc) for up to 6 months with particular emphasis on the brain. The present results show that a high-fat and cholesterol diet significantly decreased the vitamin C concentrations in the brain, irrespective of the vitamin C status of the animal (P < 0·001). The brain Asc oxidation ratio only depended on vitamin C status (P < 0·0001) and not on the dietary lipid content. In plasma, the levels of Asc significantly decreased when vitamin C in the diet was low or when the fat/cholesterol content was high (P < 0·0001 for both). The Asc oxidation ratio increased both with low vitamin C and with high fat and cholesterol content (P < 0·0001 for both). We show here for the first time that vitamin C homoeostasis of brain is affected by a diet rich in fat and cholesterol. The present findings suggest that this type of diet increases the turnover of Asc; hence, individuals consuming high-lipid diets may be at increased risk of vitamin C deficiency.