Endothelium-dependent flow-mediated vasodilation in the postprandial state in type 2 diabetes mellitus

A single, high-fat meal adversely affects postprandial endothelial function: a systematic review and meta-analysis

BACKGROUND

Endothelial dysfunction is a predictive risk factor for the development of atherosclerosis and is assessed by flow-mediated dilation (FMD). Although it is known that NO-dependent endothelial dysfunction occurs after consuming a high-fat meal, the magnitude of the effect and the factors that affect the response are unquantified.

OBJECTIVES

We conducted a systematic review and meta-analysis exploring the quantitative effects of a single high-fat meal on endothelial function and determined the factors that modify the FMD response.

METHODS

Six databases were systematically searched for original research published up to January 2022. Eligible studies measured fasting and postprandial FMD following consumption of a high-fat meal. Meta-regression was used to analyze the effect of moderator variables.

RESULTS

There were 131 studies included, of which 90 were suitable for quantitative meta-analysis. A high-fat meal challenge transiently caused endothelial dysfunction, decreasing postprandial FMD at 2 hours [-1.02 percentage points (pp); 95% CI: -1.34 to -0.70 pp; P < 0.01; I2 = 93.3%], 3 hours [-1.04 pp; 95% CI: -1.48 to -0.59 pp; P < 0.001; I2 = 84.5%], and 4 hours [-1.19 pp; 95% CI: -1.53 to -0.84 pp; P < 0.01; I2 = 94.6%]. Younger, healthy-weight participants exhibited a greater postprandial reduction in the FMD percentage change than older, heavier, at-risk groups after a high-fat meal ( P < 0.05). The percentage of fat in the meals was inversely associated with the magnitude of postprandial changes in FMD at 3 hours (P < 0.01).

CONCLUSIONS

A single, high-fat meal adversely impacts endothelial function, with the magnitude of the impact on postprandial FMD moderated by the fasting FMD, participant age, BMI, and fat content of the meal. Recommendations are made to standardize the design of future postprandial FMD studies and optimize interpretation of results, as high-fat meals are commonly used in clinical studies as a challenge to assess endothelial function and therapeutics. This trial was registered at PROSPERO as CRD42020187244.

Role of Fluid Milk in Attenuating Postprandial Hyperglycemia and Hypertriglyceridemia

Postprandial plasma glucose and triglyceride concentrations are predictive of relative cardiovascular disease (CVD) risk, and the pathogenesis of both insulin resistance and atherosclerosis has been attributed to acute states of hyperglycemia and hypertriglyceridemia. Postprandial lipemia and hyperglycemia suppress vascular reactivity and induce endothelial dysfunction. Epidemiological studies suggest that chronically-high consumption of milk and milk products is associated with a reduced risk of type 2 diabetes, metabolic syndrome, and CVD. The addition of dairy products to meals high in carbohydrates and fat may lessen these risks through reductions in postprandial glucose and triglyceride responses. Purported mechanisms include dairy proteins and bioactive compounds, which may explain the inverse relationship between dairy consumption and cardiometabolic diseases. The current review evaluates the available literature describing the relationships between metabolic dysfunction, postprandial metabolism, and vascular dysfunction and discusses the potential role of milk and dairy products in attenuating these impairments.

Effects of Acute Cocoa Supplementation on Postprandial Apolipoproteins, Lipoprotein Subclasses, and Inflammatory Biomarkers in Adults with Type 2 Diabetes after a High-Fat Meal

Dyslipidemia and inflammation exacerbate postprandial metabolic stress in people with diabetes. Acute dietary supplementation with polyphenols shows promise in improving postprandial metabolic stress in type 2 diabetes (T2D). Cocoa is a rich source of dietary polyphenols with demonstrated cardioprotective effects in adults without diabetes. To date, the acute effects of cocoa on postprandial lipids and inflammation have received little attention in the presence of T2D. This report expands on our earlier observation that polyphenol-rich cocoa, given as a beverage with a fast-food-style, high-fat breakfast, increased postprandial high-density lipoprotein-cholesterol (HDL-C) in adults with T2D. We now test whether polyphenol-rich cocoa modulated postprandial apolipoproteins (Apo-A1, B), non-esterified fatty acids, nuclear magnetic resonance (NMR)-derived lipoprotein subclass profiles, and select biomarkers of inflammation following the same dietary challenge. We found that cocoa decreased NMR-derived concentrations of total very low-density lipoprotein and chylomicron particles and increased the concentration of total HDL particles over the 6-hour postprandial phase. Serum interleukin-18 was decreased by cocoa vs. placebo. Thus, polyphenol-rich cocoa may alleviate postprandial dyslipidemia and inflammation following a high-fat dietary challenge in adults with T2D. The study was registered at clinicaltrials.gov as NCT01886989.

The VLDL receptor plays a key role in the metabolism of postprandial remnant lipoproteins

A new concept to account for the process of postprandial remnant lipoprotein metabolism is proposed based on the characteristics of lipoprotein particles and their receptors. The characteristics of remnant lipoprotein (RLP) were investigated using an immuno-separation method. The majority of the postprandial lipoproteins increased after fat intake was shown to be VLDL remnants, not chylomicron (CM) remnants, based on the significantly high ratio of apoB100/apoB48 in the RLP and the high degree of similarity in the particle size of the apoB48 and apoB100 carrying lipoproteins, which fluctuate in parallel during a 6 h period after fat intake. The VLDL receptor was discovered as a receptor for TG-rich lipoprotein metabolism and is located in peripheral tissues such as skeletal muscle, adipose tissue, etc., but not in the liver. Postprandial VLDL particles are strongly bound and internalized into cells expressing the VLDL receptor. Ligands that bind to VLDL receptor, such as LPL and Lp(a), present in RLP. The presence of various specific ligands in VLDL remnants may enhance the capacity for binding to the VLDL receptor, which play the role primarily for energy delivery to the peripheral tissues, but is also a causal factor in atherogenic diseases when excessively and/or continuously remained in plasma.

High glucose causes vascular dysfunction through Akt/eNOS pathway: reciprocal modulation by juglone and resveratrol

Transient elevations in blood glucose level may lead to changes in vascular function. Herein, we investigated the effects of high-glucose or high-fructose challenge, as well as potential influence of juglone or resveratrol on vascular reactivity, Akt/eNOS, and insulin signaling effectors in rat aorta. Aortic segments of rats were incubated with high glucose (30 mmol/L) or high fructose (2 mmol/L) in the absence and presence of juglone (5 μmol/L) or resveratrol (10 μmol/L). Acute high-glucose incubation markedly decreased acetylcholine-induced relaxation, which is further inhibited by juglone, but ameliorated by resveratrol. Incubation with high glucose caused significant reduction in pAkt/total Akt and peNOS/total eNOS ratios, as well as in the expression of some genes involved in insulin signaling. Juglone produced a further impairment, whereas resveratrol resulted in an improvement on the expression profiles of these proteins and genes. Acute exposure of aortic segments to high glucose causes a reduction in acetylcholine-induced relaxation in association with suppression of Akt/eNOS pathway, as well as several genes in insulin signaling pathway. Juglone and resveratrol have opposite actions on vascular relaxation and the above signaling targets. These findings could be relevant for the treatment of hyperglycemia-induced vascular complications.

A review of glucagon-like peptide-1 receptor agonists and their effects on lowering postprandial plasma glucose and cardiovascular outcomes in the treatment of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is an independent risk factor for cardiovascular (CV) comorbidities, with CV disease being the most common cause of death in adults with T2DM. Although glucocentric therapies may improve glycaemic control (as determined by glycated haemoglobin levels), evidence suggests that this approach alone has limited beneficial effects on CV outcomes relative to improvements in lipid and blood pressure control. This may be explained in part by the fact that current antidiabetic treatment regimens primarily address overall glycaemia and/or fasting plasma glucose, but not the postprandial plasma glucose (PPG) excursions that have a fundamental causative role in increasing CV risk. This literature review evaluates the relationship between PPG and the risk of CV disease, discusses the treatment of T2DM with glucagon-like peptide-1 receptor agonists (GLP-1 RAs) and examines the associated CV outcomes. The literature analysis suggests that exaggerated PPG excursions are a risk factor for CV disease because of their adverse pathophysiologic effects on the vasculature, resulting in increased all-cause and CV-related mortality. Although GLP-1 RAs are well established in the current T2DM treatment paradigm, a subgroup of these compounds has a particularly pronounced, persistent and short-lived effect on gastric emptying and, hence, lower PPG substantially. However, current long-term data on CV outcomes with GLP-1 RAs are contradictory, with both beneficial and adverse effects having been reported. This review explores the opportunity to direct treatment towards controlling PPG excursions, thereby improving not only overall glycaemic control but also CV outcomes.

Summation of blood glucose and TAG to characterise the ‘metabolic load index’

Research points to postprandial glucose and TAG measures as preferable assessments of cardiovascular risk as compared with fasting values. Although elevated postprandial glycaemic and lipaemic responses are thought to substantially increase chronic disease risk, postprandial glycaemia and lipaemia have historically only been considered separately. However, carbohydrates and fats can generally ‘compete’ for clearance from the stomach, small intestine, bloodstream and within the peripheral cell. Further, there are previous data demonstrating that the addition of carbohydrate to a high-fat meal blunts the postprandial lipaemic response, and the addition of fat to a high-carbohydrate meal blunts the postprandial glycaemic response. Thus, postprandial glycaemia and lipaemia are interrelated. The purpose of this brief review is 2-fold: first, to review the current evidence implicating postprandial glycaemia and lipaemia in chronic disease risk, and, second, to examine the possible utility of a single postprandial glycaemic and lipaemic summative value, which will be referred to as the metabolic load index. The potential benefits of the metabolic load index extend to the clinician, patient and researcher.

Acute Cocoa Supplementation Increases Postprandial HDL Cholesterol and Insulin in Obese Adults with Type 2 Diabetes after Consumption of a High-Fat Breakfast

BACKGROUND

Dietary cocoa is an important source of flavonoids and is associated with favorable cardiovascular disease effects, such as improvements in vascular function and lipid profiles, in nondiabetic adults. Type 2 diabetes (T2D) is associated with adverse effects on postprandial serum glucose, lipids, inflammation, and vascular function.

OBJECTIVE

We examined the hypothesis that cocoa reduces metabolic stress in obese T2D adults after a high-fat fast-food-style meal.

METHODS

Adults with T2D [n = 18; age (mean ± SE): 56 ± 3 y; BMI (in kg/m(2)): 35.3 ± 2.0; 14 women; 4 men] were randomly assigned to receive cocoa beverage (960 mg total polyphenols; 480 mg flavanols) or flavanol-free placebo (110 mg total polyphenols; <0.1 mg flavanols) with a high-fat fast-food-style breakfast [766 kcal, 50 g fat (59% energy)] in a crossover trial. After an overnight fast (10-12 h), participants consumed the breakfast with cocoa or placebo, and blood sample collection [glucose, insulin, lipids, and high-sensitivity C-reactive protein (hsCRP)] and vascular measurements were conducted at 0.5, 1, 2, 4, and 6 h postprandially on each study day. Insulin resistance was evaluated by homeostasis model assessment.

RESULTS

Over the 6-h study, and specifically at 1 and 4 h, cocoa increased HDL cholesterol vs. placebo (overall Δ: 1.5 ± 0.8 mg/dL; P ≤ 0.01) but had no effect on total and LDL cholesterol, triglycerides, glucose, and hsCRP. Cocoa increased serum insulin concentrations overall (Δ: 5.2 ± 3.2 mU/L; P < 0.05) and specifically at 4 h but had no overall effects on insulin resistance (except at 4 h, P < 0.05), systolic or diastolic blood pressure, or small artery elasticity. However, large artery elasticity was overall lower after cocoa vs. placebo (Δ: -1.6 ± 0.7 mL/mm Hg; P < 0.05), with the difference significant only at 2 h.

CONCLUSION

Acute cocoa supplementation showed no clear overall benefit in T2D patients after a high-fat fast-food-style meal challenge. Although HDL cholesterol and insulin remained higher throughout the 6-h postprandial period, an overall decrease in large artery elasticity was found after cocoa consumption. This trial was registered at clinicaltrials.gov as NCT01886989.

Acute Hyperglycemia Impairs Vascular Function in Healthy and Cardiometabolic Diseased Subjects

Objectives—

Controversy exists over the effect of acute hyperglycemia on vascular function. In this systematic review, we compared the effect of acute hyperglycemia on endothelial and vascular smooth muscle functions across healthy and cardiometabolic diseased subjects.

Approach and Results—

A systematic search of MEDLINE, EMBASE, and Web of Science from inception until July 2014 identified articles evaluating endothelial or vascular smooth muscle function during acute hyperglycemia and normoglycemia. Meta-analyses compared the standardized mean difference (SMD) in endothelial and vascular smooth muscle functions between acute hyperglycemia and normoglycemia. Subgroup analyses and metaregression identified sources of heterogeneity. Thirty-nine articles (525 healthy and 540 cardiometabolic subjects) were analyzed. Endothelial function was decreased (39 studies; n=1065; SMD, −1.25; 95% confidence interval, −1.52 to −0.98; P <0.01), whereas vascular smooth muscle function was preserved (6 studies; n=144; SMD, −0.07; 95% confidence interval, −0.30 to 0.16; P =0.55) during acute hyperglycemia compared with normoglycemia. Significant heterogeneity was detected among endothelial function studies ( P <0.01). A subgroup analysis revealed that endothelial function was decreased in the macrocirculation (30 studies; n=884; SMD, −1.40; 95% confidence interval, −1.68 to −1.12; P <0.01) but not in the microcirculation (9 studies; n=181; SMD, −0.63; 95% confidence interval, −1.36 to 0.11; P =0.09). Similar results were observed according to health status. Macrovascular endothelial function was inversely associated with age, blood pressure, and low-density lipoprotein cholesterol and was positively associated with the postocclusion interval of vascular assessment.

Conclusions—

To our knowledge, this is the first systematic review and meta-analysis of its kind. In healthy and diseased subjects, we found evidence for macrovascular but not microvascular endothelial dysfunction during acute hyperglycemia.

Glucagon-like peptide-1 protects against ischemic left ventricular dysfunction during hyperglycemia in patients with coronary artery disease and type 2 diabetes mellitus

Background

Enhancement of myocardial glucose uptake may reduce fatty acid oxidation and improve tolerance to ischemia. Hyperglycemia, in association with hyperinsulinemia, stimulates this metabolic change but may have deleterious effects on left ventricular (LV) function. The incretin hormone, glucagon-like peptide-1 (GLP-1), also has favorable cardiovascular effects, and has emerged as an alternative method of altering myocardial substrate utilization. In patients with coronary artery disease (CAD), we investigated: (1) the effect of a hyperinsulinemic hyperglycemic clamp (HHC) on myocardial performance during dobutamine stress echocardiography (DSE), and (2) whether an infusion of GLP-1(7-36) at the time of HHC protects against ischemic LV dysfunction during DSE in patients with type 2 diabetes mellitus (T2DM).

Methods

In study 1, twelve patients underwent two DSEs with tissue Doppler imaging (TDI)—one during the steady-state phase of a HHC. In study 2, ten patients with T2DM underwent two DSEs with TDI during the steady-state phase of a HHC. GLP-1(7-36) was infused intravenously at 1.2 pmol/kg/min during one of the scans. In both studies, global LV function was assessed by ejection fraction and mitral annular systolic velocity, and regional wall LV function was assessed using peak systolic velocity, strain and strain rate from 12 paired non-apical segments.

Results

In study 1, the HHC (compared with control) increased glucose (13.0 ± 1.9 versus 4.8 ± 0.5 mmol/l, p < 0.0001) and insulin (1,212 ± 514 versus 114 ± 47 pmol/l, p = 0.01) concentrations, and reduced FFA levels (249 ± 175 versus 1,001 ± 333 μmol/l, p < 0.0001), but had no net effect on either global or regional LV function. In study 2, GLP-1 enhanced both global (ejection fraction, 77.5 ± 5.0 versus 71.3 ± 4.3%, p = 0.004) and regional (peak systolic strain −18.1 ± 6.6 versus −15.5 ± 5.4%, p < 0.0001) myocardial performance at peak stress and at 30 min recovery. These effects were predominantly driven by a reduction in contractile dysfunction in regions subject to demand ischemia.

Conclusions

In patients with CAD, hyperinsulinemic hyperglycemia has a neutral effect on LV function during DSE. However, GLP-1 at the time of hyperglycemia improves myocardial tolerance to demand ischemia in patients with T2DM.

Trial Registration: http://www.isrctn.org. Unique identifier ISRCTN69686930

A single dose of sodium nitrate does not improve oral glucose tolerance in patients with type 2 diabetes mellitus

Dietary nitrate (NO3(-)) supplementation has been proposed as an emerging treatment strategy for type 2 diabetes. We hypothesized that ingestion of a single bolus of dietary NO3(-) ingestion improves oral glucose tolerance in patients with type 2 diabetes. Seventeen men with type 2 diabetes (glycated hemoglobin, 7.3% ± 0.2%) participated in a randomized crossover experiment. The subjects ingested a glucose beverage 2.5 hours after consumption of either sodium NO3(-) (0.15 mmol NaNO3(-) · kg(-1)) or a placebo solution. Venous blood samples were collected before ingestion of the glucose beverage and every 30 minutes thereafter during a 2-hour period to assess postprandial plasma glucose and insulin concentrations. The results show that plasma NO3(-) and nitrite levels were increased after NaNO3(-) as opposed to placebo ingestion (treatment-effect, P = .001). Despite the elevated plasma NO3(-) and nitrite levels, ingestion of NaNO3(-) did not attenuate the postprandial rise in plasma glucose and insulin concentrations (time × treatment interaction, P = .41 for glucose, P = .93 for insulin). Despite the lack of effect on oral glucose tolerance, basal plasma glucose concentrations measured 2.5 hours after NaNO3(-) ingestion were lower when compared with the placebo treatment (7.5 ± 0.4 vs 8.3 ± 0.4 mmol/L, respectively; P = .04). We conclude that ingestion of a single dose of dietary NO3(-) does not improve subsequent oral glucose tolerance in patients with type 2 diabetes.

Changes in meal composition and duration affect postprandial endothelial function in healthy humans

Endothelial function, measured by flow-mediated dilatation (FMD), predicts cardiovascular events and is impaired postprandially. The objective of this study was to evaluate the effects of changes in composition or duration of ingestion of a meal, which slows gastric emptying and/or small intestinal nutrient exposure, on postprandial endothelial function. Twelve healthy subjects (6 male, 6 female; 33 ± 6 yr) were each studied on three occasions, in a randomized crossover design. After an overnight fast, subjects consumed a [(13)C]octanoic acid-labeled mashed potato meal ("meal 1"), or meal 1 mixed with 9 g guar ("meal 2") within 10 min, or meal 1 divided into 12 equal portions over 60 min ("meal 3"). Brachial artery FMD was measured every 30 min for 120 min. Blood glucose, serum insulin, and gastric emptying (breath test) were evaluated for 240 min. Data are means ± SE. Compared with meal 1, meal 2 was associated with slower gastric emptying (half-emptying time 285 ± 27 vs. 208 ± 15 min, P < 0.05), lower postprandial blood glucose and insulin (P < 0.001 for both), and a delayed, but more sustained, suppression of FMD (P < 0.001). After meal 3, both glycemic increment and reduction in FMD were less than after meal 2 (P < 0.05 for both). The decrement in FMD was directly related to the increment in blood glucose (r = 0.46, P = 0.02). We conclude that, in health, postprandial FMD is influenced by perturbation of gastric emptying and the duration of meal consumption, which also impact on glycemia.

Endothelial dysfunction in diabetes: pathogenesis, significance, and treatment

Type 2 diabetes (T2D) markedly increases the risk of cardiovascular disease. Endothelial dysfunction (ED), an early indicator of diabetic vascular disease, is common in T2D and independently predicts cardiovascular risk. Although the precise pathogenic mechanisms for ED in T2D remain unclear, at inception they probably involve uncoupling of both endothelial nitric oxide synthase activity and mitochondrial oxidative phosphorylation, as well as the activation of vascular nicotinamide adenine dinucleotide phosphate oxidase. The major contributing factors include dyslipoproteinemia, oxidative stress, and inflammation. Therapeutic interventions are designed to target these pathophysiological factors that underlie ED. Therapeutic interventions, including lifestyle changes, antiglycemic agents and lipid-regulating therapies, aim to correct hyperglycemia and atherogenic dyslipidemia and to improve ED. However, high residual cardiovascular risk is seen in both research and clinical practice settings. Well-designed studies of endothelial function in appropriately selected volunteers afford a good opportunity to test new therapeutic interventions, paving the way for clinical trials and utilization in the care of the diabetic patient. However, based on the results from a recent clinical trial, niacin should not be added to a statin in individuals with low high-density lipoprotein cholesterol and very well controlled low-density lipoprotein cholesterol.

Ascorbic acid prevents vascular dysfunction induced by oral glucose load in healthy subjects

OBJECTIVES

To examine the effects of oral glucose load on forearm circulatory regulation before and after ascorbic acid administration in healthy subjects.

DESIGN

Microcirculation study with laser Doppler was performed at the hand in basal conditions, after ischemia and after acetylcholine and nitroprusside; strain gauge plethysmography was performed at basal and after ischemia. The tests were repeated in the same sequence 2 hour after oral administration of glucose (75 g). The subjects were randomised for administration of ascorbic acid (1 g bid) or placebo (sodium bicarbonate 1 g bid) for 10 days. After that, the tests were repeated before and after a new oral glucose load. Blood pressure and heart rate were monitored.

RESULTS

Macrocirculatory flux, pressure values and heart rate were unvaried throughout the study. The glucose load caused a reduction in the hyperemic peak flow with laser Doppler and plethysmography; it reduced flux recovery time and hyperemic curve area after ischemia; acetylcholine elicited a minor increase in flux with laser Doppler. The response to nitroprusside was unvaried after glucose load as compared to basal conditions. Treatment with ascorbic acid prevented the decrease in hyperemia after glucose, detected with laser Doppler and plethysmography. Ascorbic acid prevented the decreased response to acetylcholine after glucose, the response to nitroprusside was unaffected by ascorbic acid. Results after placebo were unvaried.

CONCLUSIONS

Oral glucose load impairs endothelium dependent dilation and hyperaemia at microcirculation, probably via oxidative stress; ascorbic acid can prevent it.

Impact of glycemic and blood pressure variability on surrogate measures of cardiovascular outcomes in type 2 diabetic patients

OBJECTIVE

The effect of glycemic variability (GV) on cardiovascular risk has not been fully clarified in type 2 diabetes. We evaluated the effect of GV, blood pressure (BP), and oxidative stress on intima-media thickness (IMT), left ventricular mass index (LVMI), flow-mediated dilation (FMD), and sympathovagal balance (low frequency [LF]/high frequency [HF] ratio) in 26 type 2 diabetic patients (diabetes duration 4.41±4.81 years; HbA1c 6.70±1.25%) receiving diet and/or metformin treatment, with no hypotensive treatment or complications.

RESEARCH DESIGN AND METHODS

Continuous glucose monitoring (CGM) data were used to calculate mean amplitude of glycemic excursion (MAGE), continuous overall net glycemic action (CONGA)-2, mean blood glucose (MBG), mean postprandial glucose excursion (MPPGE), and incremental area under the curve (IAUC). Blood pressure (BP), circadian rhythm, and urinary 15-F2t-isoprostane (8-iso-prostaglandin F2α [PGF2α]) were also evaluated. Subjects were divided into dipper (D) and nondipper (ND) groups according to ΔBP.

RESULTS

IMT and LVMI were increased in ND versus D (0.77±0.08 vs. 0.68±0.13 [P=0.04] and 67±14 vs. 55±11 [P=0.03], respectively). MBG, MAGE, and IAUC were significantly associated with LF/HF ratio at night (r=0.50, P=0.01; r=0.40, P=0.04; r=0.41, P=0.04, respectively), MPPGE was negatively associated with FMD (r=-0.45, P=0.02), and CONGA-2 was positively associated with LVMI (r=0.55, P=0.006). The Δsystolic BP was negatively associated with IMT (r=-0.43, P=0.03) and with LVMI (r=-0.52, P=0.01). Urinary 8-iso-PGF2α was positively associated with LVMI (r=0.68 P<0.001).

CONCLUSIONS

An impaired GV and BP variability is associated with endothelial and cardiovascular damage in short-term diabetic patients with optimal metabolic control. Oxidative stress is the only independent predictor of increased LV mass and correlates with glucose and BP variability.

Coronary microvascular dysfunction in diabetes mellitus: A review

The exploration of coronary microcirculatory dysfunction in diabetes has accelerated in recent years. Cardiac function is compromised in diabetes. Diabetic patients manifest accelerated atherosclerosis in coronary arteries. These data are confirmed in diabetic animal models, where lesions of small coronary arteries have been described. These concepts are epitomized in the classic microvascular complications of diabetes, i.e. blindness, kidney failure and distal dry gangrene. Most importantly, accumulating data indicate that insights gained from the link between inflammation and diabetes can yield predictive and prognostic information of considerable clinical utility. This review summarizes the evidence for the predisposing factors and the mechanisms involved in diabetes, and assesses the current state of knowledge regarding the triggers for inflammation in this disease. We evaluate the roles of hyperglycemia, oxidative stress, polyol pathway, protein kinase C, advanced glycation end products, insulin resistance, peroxisome proliferator-activated receptor-γ, inflammation, and diabetic cardiomyopathy as a "stem cell disease". Furthermore, we discuss the mechanisms responsible for impaired coronary arteriole function. Finally, we consider how new insights in diabetes may provide innovative therapeutic strategies.

Glucose control is associated with patient survival in diabetic patients after renal transplantation

INTRODUCTION

The efficacy of tight glycemic control for the prevention of death and renal failure in the general diabetic population is well established. However, in diabetic renal-allograft recipients, the effect of different treatment strategies on outcomes is undetermined.

METHODS

We conducted a cohort study of 798 diabetic, renal-allograft recipients transplanted at the Medical University of Vienna between 1990 and 2004. We studied the influence of glucose parameters and diabetes treatment on mortality and graft loss. Marginal-structural models and multivariable Cox regression analysis were used to control for confounding.

RESULTS

Maximal glucose levels but not HbA1c were independently associated with mortality. Being in the highest quartile of maximal glucose increased the adjusted risk of death by a factor of 2.2 (P value for trend 0.009). Furthermore, in patients receiving insulin, the risk of death was increased 1.7-fold (95% confidence interval 0.9-3.1) compared with diet and 2.0-fold (95% confidence interval 1.1-3.7) compared with oral medication. Maximal glucose, HbA1c, or diabetes treatment did not influence death-censored functional graft survival.

DISCUSSION

In conclusion, maximal glucose levels and insulin treatment were independently associated with higher rates of mortality in our cohort of diabetic, renal-allograft recipients. However, graft survival was unaffected.

Postprandial endothelial dysfunction in subjects with new-onset type 2 diabetes: an acarbose and nateglinide comparative study

BACKGROUND

Postprandial hyperglycemia is believed to affect vascular endothelial function. The aim of our study was to compare the effects of acarbose and nateglinide on postprandial endothelial dysfunction.

METHODS

We recruited a total of 30 patients with newly diagnosed type 2 diabetes (19 men and 11 women, age 67.8 +/- 7.3 years). Patients were randomly assigned to 3 groups receiving either 300 mg/day acarbose, 270 mg/day nateglinide, or no medication. A cookie test (consisting of 75 g carbohydrate, 25 g butter fat, and 7 g protein for a total of 553 kcal) was performed as dietary tolerance testing. During the cookie test, glucose and insulin levels were determined at 0, 30, 60, and 120 min after load. In addition, endothelial function was assessed by % flow-mediated dilation (FMD) of the brachial artery at 0 and 120 min after cookie load.

RESULTS

Postprandial glucose and insulin levels were similar in the 3 groups. Postprandial endothelial dysfunction was similar in the 3 groups before treatment. After 12 weeks of intervention, postprandial FMD was significantly improved in the acarbose group compared with the control group (6.8 +/- 1.3% vs 5.2 +/- 1.1%, p = 0.0022). Area under the curve (AUC) for insulin response was significantly increased in the nateglinide and control groups; however, no significant change was observed in the acarbose group.

CONCLUSIONS

Our results suggest that acarbose improves postprandial endothelial function by improvement of postprandial hyperglycemia, independent of postprandial hyperinsulinemia. Acarbose may thus have more beneficial effects on postprandial endothelial function in patients with type 2 diabetes than nateglinide.

Postprandial hyperglycemia as an etiological factor in vascular failure

Postprandial hyperglycemia is characterized by hyperglycemic spikes that induce endothelial dysfunction, inflammatory reactions and oxidative stress, which may lead to progression of atherosclerosis and occurrence of cardiovascular events. Emerging data indicate that postprandial hyperglycemia or even impaired glucose tolerance may predispose to progression of atherosclerosis and cardiovascular events. There is evidence that postprandial hyperglycemia, but not fasting hyperglycemia, independently predicts the occurrence of cardiovascular events. We proposed a concept of 'vascular failure' as a comprehensive syndrome of vascular dysfunction extending from risk factors to advanced atherosclerotic disease. Postprandial hyperglycemia is therefore one of the very important pathophysiological states contributing to vascular failure. Accordingly, controlling postprandial hyperglycemia should be the focus of future clinical investigation as a potential target for preventing vascular failure.

Location of arterial stiffening differs in those with impaired fasting glucose versus diabetes: implications for left ventricular hypertrophy from the Multi-Ethnic Study of Atherosclerosis

OBJECTIVE

To determine whether middle-aged and older individuals with impaired fasting glucose (IFG), but no clinical evidence of cardiovascular disease, exhibit abnormal changes in proximal thoracic aortic stiffness or left ventricular (LV) mass when compared with healthy counterparts.

RESEARCH DESIGN AND METHODS

From the Multi-Ethnic Study of Atherosclerosis, 2,240 subjects with normal fasting glucose (NFG), 845 with IFG, and 414 with diabetes, all aged 45 to 85 years and without preexisting coronary artery disease, underwent MRI determinations of total arterial and proximal thoracic aortic stiffness and LV mass. The presence or absence of other factors known to influence arterial stiffness was assessed.

RESULTS

After adjustment for clinical factors known to modify arterial stiffness, proximal thoracic aortic stiffness was not increased in those with IFG compared with those with NFG (1.90 +/- 0.05 versus 1.91 +/- 0.04 10(-3) mmHg(-1), respectively, P = 0.83). After accounting for clinical factors known to influence LV mass, LV mass was increased in those with diabetes relative to those with NFG (150.6 +/- 1.4 versus 145.8 +/- 0.81 g, P < 0.0009) but not in those with IFG in comparison with NFG (145.2 +/- 1.03 versus 145.8 +/- 0.81 g, P = 0.56).

CONCLUSIONS

Middle-aged and older individuals with the pre-diabetes state of IFG do not exhibit abnormal proximal thoracic distensibility or LV hypertrophy relative to individuals with NFG. For this reason, an opportunity may exist in those with IFG to prevent LV hypertrophy and abnormal aortic stiffness that is observed in middle-aged and older individuals with diabetes.

Impairment of endothelium-dependent ACh-induced relaxation in aorta of diabetic db/db mice--possible dysfunction of receptor and/or receptor-G protein coupling

Diabetes is a risk factor of ischemic heart disease, cerebral ischemia, and atherosclerosis, in which endothelial dysfunction plays a role in the pathogenesis. We examined vascular responses in the aorta of pre-diabetic db/db mice with normoglycemia, hyperlipidemia, and hyperinsulinemia (6 weeks old), and diabetic db/db mice with hyperglycemia, hyperlipidemia, and hyperinsulinemia (11 weeks old) in comparison with age-matched non-diabetic db/+ mice. Prostaglandin F2alpha (PGF2alpha)-induced contraction was significantly enhanced in the aorta of diabetic but not pre-diabetic db/db mice compared to age-matched non-diabetic db/+ mice. Acetylcholine (ACh), adenosine-5'-diphosphate (ADP), NaF, a G protein activator and A-23187, a Ca-ionophore, caused endothelium-dependent and nitric oxide (NO)-mediated relaxation, and sodium nitroprusside (SNP), an NO donor, caused endothelium-independent relaxation in the pre-contracted aorta of db/db mice. Maximal endothelium-dependent ACh-induced relaxation was reduced in diabetic but not pre-diabetic db/db mice compared to age-matched db/+ mice, while maximal SNP-induced relaxation was not different between diabetic and non-diabetic mice. ACh-induced relaxation in diabetic db/db mice was not affected by ozagrel, a thromboxane A2 (TXA2) synthetase inhibitor, or acetylsalicylic acid (aspirin), a cyclooxygenase inhibitor, suggesting no involvement of endogenous TXA2 or prostanoids in the reduction of relaxation. Maximal endothelium-dependent ADP-, A-23187-, and NaF-induced relaxation was not reduced in diabetic db/db mice. EC50 values for ACh- and SNP-induced relaxation were increased in diabetic but not pre-diabetic db/db mice, suggesting decreases in sensitivity to NO in diabetic mice. Two-week treatment with KV-5070, a PPARgamma agonist, lowered plasma glucose, triglyceride (TG), and insulin but not cholesterol, and reversed the reduced ACh-induced relaxation. In conclusion, ACh-induced endothelium-dependent relaxation is impaired in diabetic db/db mice, probably due to the dysfunction of ACh receptors and/or receptor-G protein coupling. Endothelial dysfunction was not genetic and was considered to be initiated primarily by hyperglycemia, and was improved by anti-diabetic treatment with a PPARgamma agonist.

Therapeutic regulation of endothelial dysfunction in type 2 diabetes mellitus

Endothelial dysfunction is universal in diabetes, being intimately involved with the development of cardiovascular disease. The pathogenesis of endothelial dysfunction in diabetes is complex. It is initially related to the effects of fatty acids and insulin resistance on 'uncoupling' of both endothelial nitric oxide synthase activity and mitochondrial function. Oxidative stress activates protein kinase C (PKC), polyol, hexosamine and nuclear factor kappa B pathways, thereby aggravating endothelial dysfunction. Improvements in endothelial function in the peripheral circulation in diabetes have been demonstrated with monotherapies, including statins, fibrates, angiotensin-converting enzyme (ACE) inhibitors, metformin and fish oils. These observations are supported by large clinical end point trials. Other studies show benefits with certain antioxidants, L-arginine, folate, PKC-inhibitors, peroxisome proliferator activated receptor (PPAR)-alpha and -gamma agonists and phosphodiesterase (PDE-5) inhibitors. However, the benefits of these agents remain to be shown in clinical end point trials. Combination treatments, for example, statins plus ACE inhibitors and statins plus fibrates, have also been demonstrated to have additive benefits on endothelial function in diabetes, but there are no clinical outcome data to date. Measurement of endothelial dysfunction in cardiovascular research can provide fresh opportunities for exploring the mechanism of benefit of new therapeutic regimens and for planning and designing large clinical trials.

Effects of low- and high-advanced glycation endproduct meals on macro- and microvascular endothelial function and oxidative stress in patients with type 2 diabetes mellitus

BACKGROUND

An advanced glycation endproducts (AGEs)-rich diet induces significant increases in inflammatory and endothelial dysfunction markers in type 2 diabetes mellitus (T2DM).

OBJECTIVE

The aim was to investigate the acute effects of dietary AGEs on vascular function in T2DM patients.

DESIGN

Twenty inpatients with T2DM [x (+/-SEM) age: 55.4 +/- 2.2 y; glycated hemoglobin: 8.8 +/- 0.5%] were investigated. In a randomized crossover design, the effects of a low-AGE (LAGE) and high-AGE (HAGE) meal on macrovascular [by flow-mediated dilatation (FMD)] and microvascular (by Laser-Doppler flowmetry) function, serum markers of endothelial dysfunction (E-selectin, intracellular adhesion molecule 1, and vascular cell adhesion molecule 1), oxidative stress, and serum AGE were assessed. The meals had identical ingredients but different AGE amounts (15.100 compared with 2.750 kU AGE for the HAGE and LAGE meals, respectively), which were obtained by varying the cooking temperature and time. The measurements were performed at baseline and 2, 4, and 6 h after each meal.

RESULTS

After the HAGE meal, FMD decreased by 36.2%, from 5.77 +/- 0.65% (baseline) to 3.93 +/- 0.48 (2 h), 3.70 +/- 0.42 (4 h), and 4.42 +/- 0.54% (6 h) (P<0.01 for all compared with baseline). After the LAGE meal, FMD decreased by 20.9%, from 6.04 +/- 0.68% (baseline) to 4.75 +/- 0.48% (2 h), 4.69 +/- 0.51% (4 h), and 5.62 +/- 0.63% (6 h), respectively (P<0.01 for all compared with baseline; P<0.001 for all compared with the HAGE meal). This impairment of macrovascular function after the HAGE meal was paralleled by an impairment of microvascular function (-67.2%) and increased concentrations of serum AGE and markers of endothelial dysfunction and oxidative stress.

CONCLUSIONS

In patients with T2DM, a HAGE meal induces a more pronounced acute impairment of vascular function than does an otherwise identical LAGE meal. Therefore, chemical modifications of food by means of cooking play a major role in influencing the extent of postprandial vascular dysfunction.

The deleterious effects of hyperglycemia on platelet function in diabetic patients with acute coronary syndromes mediation by superoxide production, resolution with intensive insulin administration

OBJECTIVES

This study sought to assess the determinants of platelet nitric oxide (NO) responsiveness in diabetic patients admitted with acute coronary syndromes (ACS) and the short-term effects of aggressive glycemic control on these factors.

BACKGROUND

Hyperglycemia is an independent risk factor for mortality in both diabetic patients and nondiabetic patients with ACS. The mechanism(s) underlying this observation and potential benefit from its correction remain uncertain. Although a reduction in NO bioavailability has been proposed, this remains untested in the ACS setting.

METHODS

A total of 76 diabetic patients with ACS were studied. Putative correlations between admission blood sugar level (BSL), inhibition of platelet aggregation by the NO donor sodium nitroprusside (SNP), and superoxide (O2-) were assessed. Hyperglycemic patients (n = 60) were randomized to acute glycemic control with intravenous versus subcutaneous insulin, and changes in the aforementioned parameters were compared. Plasma levels of the endogenous inhibitor of NO synthase asymmetric dimethylarginine (ADMA) were also monitored.

RESULTS

There was an inverse correlation between admission BSL and both platelet SNP response (p = 0.007) and ADMA levels (p = 0.045), and a positive correlation with O2- generation (p < 0.001). Intravenous insulin infusion resulted in a greater reduction (p < 0.001) in BSL, differentially improved platelet responsiveness to SNP (p = 0.049), and decreased O2- (p < 0.001) and ADMA levels (p = 0.049).

CONCLUSIONS

A component of platelet dysfunction in diabetic patients with ACS is impaired responsiveness to the anti-aggregatory effects of NO, probably reflecting increased NO clearance by O2-. This phenomenon is reversed by acute aggressive glycemic control. These findings provide a further rationale for use of insulin therapy in acute myocardial infarction and suggest its extension to ACS patients.

Targeting postprandial hyperglycemia

In healthy individuals, blood glucose levels in the fasting state are maintained by the continuous basal-level insulin secretion. After a meal, the rise in postprandial glucose (PPG) is controlled by the rapid pancreatic release of insulin, stimulated by both glucose and the intestinal production of the incretins glucose-dependent insulinotropic polypeptide and glucagon-like peptide 1. In diabetic individuals, postprandial insulin secretion is insufficient to suppress an excessive rise in PPG. There is increasing evidence that elevated PPG exerts a more deleterious effect on the vascular system than elevation of fasting plasma glucose. In particular, individuals with normal fasting plasma glucose but impaired glucose tolerance have significantly increased risk of cardiovascular events. With the recognition of the importance of PPG and the availability of new pharmacologic options, management of diabetes will shift to greater attention to PPG levels. The prototype for such an approach is in the treatment of gestational diabetes and diabetic pregnancies where PPG is the primary target of efforts at glycemic control. These efforts have been extremely successful in improving the outlook for diabetic pregnant women. There are many approaches to reduction of PPG; dietary management and promotion of exercise are very effective. Sulfonylureas, meglitinides, metformin, thiazolidinediones, and disaccharidase inhibitors all counteract PPG elevation. The development of glucagon-like peptide 1 agonists such as exendin and dipeptidyl peptidase IV inhibitors such as vildagliptin offers a new approach to suppression of PPG elevation. New semisynthetic insulin analogues permit a more aggressive response to postprandial glucose elevation, with lower risk of hypoglycemia, than with regular insulin. Inhaled insulin also has a rapid onset of action and offers benefits in PPG control. It is proposed that an aggressive treatment approach focusing on PPG, similar to the current standards for diabetic pregancies, be directed at individuals with diabetes and impaired glucose tolerance.

Prevalence and correlates of post-prandial hyperglycaemia in a large sample of patients with type 2 diabetes mellitus

AIMS/HYPOTHESIS

Post-prandial glucose may be a risk factor for cardiovascular disease and chronic diabetic complications. We tested the hypothesis that post-prandial hyperglycaemia is common in type 2 diabetes, even among patients in apparently good glycaemic control, and that simple clinical characteristics identify subsets of diabetic patients with frequent post-prandial hyperglycaemia.

SUBJECTS AND METHODS

Three self-assessed daily blood glucose profiles over a 1-week period, including 18 glucose readings before and 2 h after meals, were obtained from 3,284 unselected outpatients (men 51%; age 63+/-10 years) with non-insulin-treated type 2 diabetes mellitus attending 500 different diabetes clinics operating throughout Italy.

RESULTS

A post-prandial blood glucose value >8.89 mmol/l (160 mg/dl) was recorded at least once in 84% of patients, and 81% of patients had at least one Delta glucose > or =2.22 mmol/l (40 mg/dl). Among patients with apparently good metabolic control, 38% had >40% of post-prandial blood glucose readings >8.89 mmol/l (> or =4 of 9 meals in total), and 36% had >40% Delta glucose > or =2.22 mmol/l. In multivariate analysis adjusted for pre-prandial glucose levels, older age, longer duration of diabetes, absence of obesity, hyperlipidaemia and hypertension, as well as treatment with sulfonylureas, were significantly associated with greater glucose excursions after meals.

CONCLUSIONS/INTERPRETATION

These results indicate that post-prandial hyperglycaemia is a very frequent phenomenon in patients with type 2 diabetes mellitus on active treatment; can occur even when metabolic control is apparently good; and can be predicted by simple clinical features.

Haemoglobin and flow-mediated vasodilation

A low [Hb] (Hb concentration) is out-balanced by peripheral vasodilation via mechanisms that are incompletely understood. Peripheral vasodilation is influenced by NO (nitric oxide) released from vascular endothelium in response to increased vessel wall shear stress, and absorption by Hb is the main mechanism by which the bioactivity of NO is disarmed. Thus we propose that graded NO absorption is the mechanism through which a low [Hb] is related to peripheral vasodilation. In the present study, we examined the relationship between [Hb] and FMD (flow-mediated vasodilation; 5 min of cuff ischaemia) of the radial and brachial arteries in 33 normal subjects and in 13 patients with Type II diabetes, known to have impaired NO-mediated vasodilation. The smaller radial artery provided the more sensitive test, as it had a 2-fold larger FMD than the brachial artery (22±18% compared with 9±18% respectively, in normal subjects; means±S.D., P<0.05). FMD of the radial artery had a negative correlation with [Hb] (r2=−0.66, P<0.05; n=27). In subjects with [Hb] below and above the median of 14.1 g/dl, the radial artery FMD was 30±22% compared with 13±12% respectively (P<0.05). In diabetic patients, FMD was lower and a co-variation with [Hb] could not be established. Thus, in normal subjects, NO-mediated endothelium-related vasodilation at least partly out-balanced the ‘added burden’ of a low [Hb] during post-ischaemic reperfusion.

Prolonged deterioration of endothelial dysfunction in response to postprandial lipaemia is attenuated by vitamin C in Type 2 diabetes

BACKGROUND

Endothelial dysfunction (ED) has been described in Type 2 diabetes (T2DM). We have described previously a diminution of flow-mediated arterial dilatation and, by implication, further ED in T2DM in response to postprandial lipaemia (PPL) at 4 h. This is possibly mediated by oxidative stress/alteration of the nitric oxide (NO) pathway. T2DM subjects tend to exhibit both exaggerated and prolonged PPL. We therefore studied the relationship of PPL to the duration of ED in T2DM subjects and oxidative stress with or without the antioxidant, vitamin C.

METHODS

Twenty subjects with T2DM with moderate glycaemic control (mean HbA1c 8.4%) were studied. After an overnight fast, all subjects consumed a standard fat meal. Endothelial function (EF), lipid profiles, and venous free radicals were measured in the fasting, peak lipaemic phase (4 h) and postprandially to 8 h. The study was repeated in a double-blinded manner with placebo, vitamin C (1 g) therapy for 2 days prior to re-testing and with the fat meal. Oxidative stress was assessed by lipid-derived free radicals in plasma, ex vivo by electron paramagnetic resonance spectroscopy (EPR) and by markers of lipid peroxidation (TBARS). Endothelial function was assessed by flow-mediated vasodilatation (FMD) of the brachial artery.

RESULTS

There was a significant decrease in endothelial function in response to PPL from baseline (B) 1.3 +/- 1.3% to 4 h 0.22 +/- 1.1% (P < 0.05) and 8 h 0.7 +/- 0.9% (P < 0.05) (mean +/- sem). The endothelial dysfunction seen was attenuated at each time point with vitamin C. Baseline EF with vitamin C changed from (fasting) 3.8 +/- 0.9-2.8 +/- 0.8 (at 4 h) and 2.9 +/- 1.3 (at 8 h) in response to PPL. Vitamin C attenuated postprandial (PP) oxidative stress significantly only at the 4-h time point [301.1 +/- 118 (B) to 224.7 +/- 72 P < 0.05] and not at 8 h 301.1 +/- 118 (B) to 260 +/- 183 (P = NS). There were no changes with placebo treatment in any variable. PPL was associated with a PP rise in TG levels (in mmol/l) from (B) 1.8 +/- 1 to 2.7 +/- 1 at 4 h and 1.95 +/- 1.2 at 8 h (P = 0.0002 and 0.33, respectively).

CONCLUSION

PPL is associated with prolonged endothelial dysfunction for at least 8 h after a fatty meal. Vitamin C treatment improves endothelial dysfunction at all time points and attenuates PPL-induced oxidative stress. This highlights the importance of low-fat meals in T2DM and suggests a role for vitamin C therapy to improve endothelial function during meal ingestion.

Temporary hyperglycaemia provokes monocyte adhesion to endothelial cells in rat thoracic aorta

AIMS/HYPOTHESIS

Several epidemiological data suggest that patients with postprandial hyperglycaemia are at high risk of cardiovascular disease. The aim of this study was to elucidate the effect of a glucose 'spike' on monocyte adhesion to rat aortic endothelial cells.

MATERIALS AND METHODS

Monocyte adhesion to endothelial cells in vivo was quantitated using an en face method for observation of endothelial surface after immunohistochemical staining for CD68 in the thoracic aortas of Sprague-Dawley rats after several kinds of blood glucose rises.

RESULTS

The number of monocytes adhering to endothelial cells increased at 30 min after injection of glucose in 8-week-old Sprague-Dawley rats. The increased adhesion returned to the basal level at 120 min after glucose injection, concomitantly with the return of blood glucose levels to normal. The infusion of octreotide to inhibit endogenous insulin secretion did not prevent the glucose-induced increase in monocyte adhesion to endothelial cells. On the other hand, the number of monocytes adhering to endothelial cells did not increase in rats with streptozotocin-induced diabetes and sustained hyperglycaemia.

CONCLUSIONS/INTERPRETATION

Our data demonstrate that a temporary rise in blood glucose levels can in itself promote a reversible increase in monocyte adhesion to arterial endothelial cells.

Postprandial Myocardial Perfusion in Healthy Subjects and in Type 2 Diabetic Patients

Background— In diabetic patients, postprandial hyperglycemia is a more powerful risk factor for cardiovascular disease than fasting hyperglycemia itself. A negative influence of acute hyperglycemia on systemic endothelial function (brachial artery) has been shown. However, myocardial perfusion during postprandial hyperglycemia has not been investigated.

Methods and Results— We evaluated the effects of a standardized mixed meal on myocardial perfusion in 20 healthy subjects and 20 consecutive patients with type 2 diabetes mellitus without macrovascular or microvascular complications. Myocardial perfusion was assessed in fasting and postprandial states by myocardial contrast echocardiography. Fasting myocardial flow velocity (β, 0.65±0.27 versus 0.67±0.24; P =NS), myocardial blood volume (MBV; 8.3±1.2 versus 8.4±2; P =NS), and myocardial blood flow (5.4±1.5 versus 5.6±2; P =NS) did not differ between control subjects and diabetic patients. In the postprandial state, β (0.67±0.24 versus 0.92±0.35; P <0.01), MBV (8.4±2 versus 10.9±2.7; P <0.01), and myocardial blood flow (5.6±2 versus 9.9±2.8; P <0.01) increased significantly in control subjects. In diabetic patients, β increased (0.65±0.27 versus 0.8±0.24; P <0.01) but MBV (8.3±1.2 versus 4.3±1.3; P <0.01) and myocardial blood flow (5.4±1.5 versus 3.4±0.9; P <0.01) decreased significantly. Changes in MBV (expressed as [(MBV postprandial −MBV fasting )/MBV fasting ]×100) were significantly correlated with postprandial glycemia levels in diabetic patients.

Conclusions— Postprandial hyperglycemia determines myocardial perfusion defects in type 2 diabetic patients. They are secondary to deterioration in microvascular function causing a decrease in MBV. In diabetic patients without microvascular or macrovascular complications, postprandial myocardial perfusion defects may represent an early marker of the atherogenic process in the coronary circulation; hence, its reversal constitutes a potential goal of treatment.

The beneficial effect of a diet with low glycaemic index on 24 h glucose profiles in healthy young people as assessed by continuous glucose monitoring

Elevated postprandial glycaemia has been linked to CVD in a number of different epidemiological studies involving predominantly non-diabetic volunteers. The MiniMed continuous glucose monitor, which measures blood glucose every 5 min, over a 24 h period, was used to investigate changes in blood glucose readings before and after instigating a diet with low glycaemic index (GI) for 1 week in free-living healthy individuals. Nine healthy people (age 27 (SEM 1.3) years, BMI 23.7 (SEM 0.7) kg/m2, one male, eight females) completed the study. A reduction in GI (59.7 (SEM 2) v. 52.1 (SEM 2), P<0.01) occurred in all nine subjects while energy and other macronutrients remained constant. A significant reduction was also observed in fasting glucose at 06.00 hours (5.4 (SEM 0.2) v. 4.4 (SEM 0.3) mmol/l, P<0.001), mean glucose (5.6 (SEM 0.2) v. 5.1 (SEM 0.2) mmol/l, P=0.004), area under the 24 h glucose curve (8102 (SEM 243) v. 750 (SEM 235) mmol/l per min, P=0.004) and area under the overnight, 8 h glucose curve (2677 (SEM 92) v. 2223 (SEM 121) mmol/l per min, P=0.01). The present study provides important data on how a simple adjustment to the diet can improve glucose profiles that, if sustained in the long term, would be predicted from epidemiological studies to have a favourable influence on CVD.

Mechanisms, Significance and Treatment of Vascular Dysfunction in Type 2 Diabetes Mellitus

Endothelial dysfunction and increased arterial stiffness occur early in the pathogenesis of diabetic vasculopathy. They are both powerful independent predictors of cardiovascular risk. Advances in non-invasive methodologies have led to widespread clinical investigation of these abnormalities in diabetes mellitus, generating a wealth of new knowledge concerning the mechanisms of vascular dysfunction, risk factor associations and potential treatment targets. Endothelial dysfunction primarily reflects decreased availability of nitric oxide (NO), a critical endothelium-derived vasoactive factor with vasodilatory and anti-atherosclerotic properties. Techniques for assessing endothelial dysfunction include ultrasonographic measurement of flow-mediated vasodilatation of the brachial artery and plethysmography measurement of forearm blood flow responses to vasoactive agents. Arterial stiffness may be assessed using pulse wave analysis to generate measures of pulse wave velocity, arterial compliance and wave reflection. The pathogenesis of endothelial dysfunction in type 2 diabetes is multifactorial, with principal contributors being oxidative stress, dyslipidaemia and hyperglycaemia. Elevated blood glucose levels drive production of reactive oxidant species (ROS) via multiple pathways, resulting in uncoupling of mitochondrial oxidative phosphorylation and endothelial NO synthase (eNOS) activity, reducing NO availability and generating further ROS. Hyperglycaemia also contributes to accelerated arterial stiffening by increasing formation of advanced glycation end-products (AGEs), which alter vessel wall structure and function. Diabetic dyslipidaemia is characterised by accumulation of triglyceride-rich lipoproteins, small dense low-density lipoprotein (LDL) particles, reduced high-density lipoprotein (HDL)-cholesterol and increased postprandial free fatty acid flux. These lipid abnormalities contribute to increasing oxidative stress and may directly inhibit eNOS activity. Although lipid-regulating agents such as HMG-CoA reductase inhibitors (statins), fibric acid derivatives (fibrates) and fish oils are used to treat diabetic dyslipidaemia, their impact on vascular function is less clear. Studies in type 2 diabetes have yielded inconsistent results, but this may reflect sampling variation and the potential over-riding influence of oxidative stress, dysglycaemia and insulin resistance on endothelial dysfunction. Results of positive intervention trials suggest that improvement in vascular function is mediated by both lipid and non-lipid mechanisms, including anti-inflammatory, anti-oxidative and direct effects on the arterial wall. Other treatments, such as renin-angiotensin-aldosterone system antagonists, insulin sensitisers and lifestyle-based interventions, have shown beneficial effects on vascular function in type 2 diabetes. Novel approaches, targeting eNOS and AGEs, are under development, as are new lipid-regulating therapies that more effectively lower LDL-cholesterol and raise HDL-cholesterol. Combination therapy may potentially increase therapeutic efficacy and permit use of lower doses, thereby reducing the risk of adverse drug effects and interactions. Concomitant treatments that specifically target oxidative stress may also improve endothelial dysfunction in diabetes. Vascular function studies can be used to explore the therapeutic potential and mechanisms of action of new and established interventions, and provide useful surrogate measures for cardiovascular endpoints in clinical trials.

Postprandial hyperglycemia and diabetes complications: is it time to treat?

Increasing evidence suggests that the postprandial state is a contributing factor to the development of atherosclerosis. In diabetes, the postprandial phase is characterized by a rapid and large increase in blood glucose levels, and the possibility that the postprandial "hyperglycemic spikes" may be relevant to the onset of cardiovascular complications has recently received much attention. Epidemiological studies and preliminary intervention studies have shown that postprandial hyperglycemia is a direct and independent risk factor for cardiovascular disease (CVD). Most of the cardiovascular risk factors are modified in the postprandial phase in diabetic subjects and directly affected by an acute increase of glycemia. The mechanisms through which acute hyperglycemia exerts its effects may be identified in the production of free radicals. This alarmingly suggestive body of evidence for a harmful effect of postprandial hyperglycemia on diabetes complications has been sufficient to influence guidelines from key professional scientific societies. Correcting the postprandial hyperglycemia may form part of the strategy for the prevention and management of CVDs in diabetes.

Assessment of flow-mediated vasodilatation (FMD) of the brachial artery: effects of technical aspects of the FMD measurement on the FMD response

AIMS

The ability to assess endothelial function non-invasively with B-mode ultrasound has lead to its widespread application in a variety of studies. However, the absolute values obtained using this approach vary considerably across studies. We studied whether technical aspects of the methodology can explain the wide variety in absolute values across studies.

METHODS AND RESULTS

A literature search was performed to identify published reports on flow-mediated vasodilatation (FMD) of the brachial artery published between 1992 and 2001. Information on type of equipment (wall track/B-mode), location of the measurement (antecubital fossa/upper arm), occlusion site (lower/upper arm), occlusion duration (min), and occlusion pressure was extracted. Patient characteristics were also extracted. For the healthy populations, mean FMD varied from 0.20 to 19.2%; for the coronary heart disease (CHD) patients FMD varied from -1.3 to 14%; for subjects with diabetes mellitus FMD varied from 0.75 to 12%. Compared with occlusion at the upper arm, lower arm occlusion was related to decreased FMD (mean difference in FMD -2.47%; 95% CI 0.55-4.39). An occlusion duration of > or =4.5 min was related to an increased FMD compared with an occlusion time of < or =4 min (mean difference 1.30%; 95% CI 0.35-2.46). These findings were adjusted for other technical aspects of the methodology and for differences in risk factors between populations.

CONCLUSION

Mean FMD differs widely between studies. There is a great overlap between populations (healthy, CHD, diabetics). Our findings suggest that the technical aspects of the measurements, the location, and the duration of the occlusion may explain some of these differences, whereas type of equipment, location of the measurement, and occlusion pressure do not.

The postprandial state does not impair endothelial function in women with type 2 diabetes irrespective of glycaemic control

AIMS/HYPOTHESIS

The postprandial state has been shown to be associated with endothelial dysfunction, a predictor of cardiovascular morbidity. In type 2 diabetes, postprandial metabolic excursions are prolonged and exaggerated, but less pronounced if glycaemic control is optimised. We investigated the impact of improved glycaemic control on endothelial function in the postprandial state.

METHODS

We studied 19 postmenopausal women with type 2 diabetes and ten non-diabetic subjects. Participants with diabetes were re-studied 3 months after intensive glucose regulation. We measured forearm blood flow by strain gauge plethysmography during rest, during acetylcholine infusion and post ischaemia in the fasting state, and again 3 hours after a mixed meal (660 kcal, 55% fat).

RESULTS

Endothelium-dependent vasodilation was impaired in the diabetic group (p<0.005) and improved following an HbA1c reduction of 0.96% (p<0.05 for high-dose acetylcholine infusion). Postprandial metabolic excursions were higher in the diabetic group (p<0.001, p<0.01 and p<0.05 for glucose, insulin and triglycerides respectively). Resting forearm blood flow increased in all groups after the meal (p<0.005). There was no difference in fasting and postprandial endothelium-dependent vasodilation before and after improved glucose regulation in either group.

CONCLUSIONS/INTERPRETATION

The postprandial state does not impair endothelial function in non-diabetic women and does not make pre-existing endothelial dysfunction worse in women with type 2 diabetes, irrespective of glycaemic control.

Endothelial function and postprandial lipemia

It is widely recognised that post-prandial lipoproteins play a role in the development of atherosclerosis, but the mechanisms underlying this role are unclear. An attractive working hypothesis is that the pathogenetic link is endothelial dysfunction. The available data seem to corroborate this theory and recognise triggering by oxidative stress, but some of the evidence is still contradictory.

Nontraditional risk factors for cardiovascular disease in diabetes

People with type 2 diabetes are disproportionately affected by cardiovascular disease (CVD), compared with those without diabetes. Traditional risk factors do not fully explain this excess risk, and other "nontraditional" risk factors may be important. This review will highlight the importance of nontraditional risk factors for CVD in the setting of type 2 diabetes and discuss their role in the pathogenesis of the excess CVD morbidity and mortality in these patients. We will also discuss the impact of various therapies used in patients with diabetes on nontraditional risk factors.

The Role of Exercise in the Treatment of Cardiovascular Disease Associated with Type 2 Diabetes Mellitus

The role of exercise training in the prevention and treatment of type 2 diabetes mellitus has been studied extensively over the past two decades. Although the primary treatment aim for patients with type 2 diabetes is metabolic control, the morbidity and mortality associated with the disease is more a function of cardiovascular disease. As exercise is associated with favourable reductions in the risk for cardiovascular disease in other high-risk populations, here we explore the role of exercise in the treatment of cardiovascular maladaptations associated with type 2 diabetes. The cardiovascular adaptation to type 2 diabetes is characterised by hypertrophy, stiffening and loss of functional reserve. Clinically, the cardiovascular adaptations to the diabetic state are associated with an increased risk for cardiovascular disease. Functionally, these adaptations have been shown to contribute to a reduced exercise capacity, which may explain the reduced cardiovascular fitness observed in this population. Exercise training is associated with improved exercise capacity in various populations, including type 2 diabetes. Several structural and functional adaptations within the cardiovascular system following exercise training could explain these findings, such as reductions in ventricular and vascular structural hypertrophy and compliance coupled with increased functional reserve. Although these cardiovascular adaptations to aerobic exercise training have been well documented in older populations with similar decrements in cardiovascular fitness and function, they have yet to be examined in patients with type 2 diabetes. For this reason, we contend that exercise training may be an excellent therapeutic adjunct in the treatment of diabetic cardiovascular disease.

Acute hyperglycemia causes intracellular formation of CML and activation of ras, p42/44 MAPK, and nuclear factor kappaB in PBMCs

Twenty-three nondiabetic volunteers were divided into three groups. In group A (n = 9), the glucose infusion was adjusted to maintain blood glucose at 5 mmol/l (euglycemic clamp). In group B (n = 9), the glucose infusion was adjusted to maintain blood glucose at 10 mmol/l (hyperglycemic clamp) over 2 h. Group C consisted of five volunteers who were studied as the control group. Peripheral blood mononuclear cells (PBMCs) were isolated before and at the end of a 2-h clamp. In group C, PBMCs were isolated before and after 2 h without performing a clamp. The euglycemic clamp as well as "no clamp" had no effects on all parameters studied. In contrast, a significant increase in carboxymethyllysine (CML) content and p21(ras) and p42/44 mitogen-activated protein kinase (MAPK) phosphorylation was observed at the end of a 2-h hyperglycemic clamp. The nuclear factor (NF)-kappaB (but not Oct-1) binding activity increased significantly in the hyperglycemic clamp. Western blots confirmed NF-kappaB-p65-antigen translocation into the nucleus. IkappaBalpha did not change significantly in both groups. Hyperglycemia-mediated NF-kappaB activation and increase of CML content, p21(ras), and p42/44 MAPK phosphorylation was also seen in ex vivo-isolated PBMCs stimulated with 5 or 10 mmol/l glucose. Addition of insulin did not influence the results. Inhibition of activation of ras, MAPK, or protein kinase C blocked hyperglycemia-mediated NF-kappaB activation in ex vivo-isolated PBMCs stimulated with 10 mmol/l glucose. Similar data were obtained using an NF-kappaB-luciferase reporter plasmid. Therefore, we can conclude that an acute hyperglycemia-mediated mononuclear cell activation is dependent on activation of ras, p42/p44 MAPK phosphorylation, and subsequent NF-kappaB activation and results in transcriptional activity in PBMCs.

Inflammatory mediators are induced by dietary glycotoxins, a major risk factor for diabetic angiopathy

Diet is a major environmental source of proinflammatory AGEs (heat-generated advanced glycation end products); its impact in humans remains unclear. We explored the effects of two equivalent diets, one regular (high AGE, H-AGE) and the other with 5-fold lower AGE (L-AGE) content on inflammatory mediators of 24 diabetic subjects: 11 in a 2-week crossover and 13 in a 6-week study. After 2 weeks on H-AGE, serum AGEs increased by 64.5% (P = 0.02) and on L-AGE decreased by 30% (P = 0.02). The mononuclear cell tumor necrosis factor-alphabeta-actin mRNA ratio was 1.4 +/- 0.5 on H-AGE and 0.9 +/- 0.5 on L-AGE (P = 0.05), whereas serum vascular adhesion molecule-1 was 1,108 +/- 429 and 698 +/- 347 ngml (P = 0.01) on L- and H-AGE, respectively. After 6 weeks, peripheral blood mononuclear cell tumor necrosis factor-alpha rose by 86.3% (P = 0.006) and declined by 20% (P, not significant) on H- or L-AGE diet, respectively; C-reactive protein increased by 35% on H-AGE and decreased by 20% on L-AGE (P = 0.014), and vascular adhesion molecule-1 declined by 20% on L-AGE (P < 0.01) and increased by 4% on H-AGE. Serum AGEs were increased by 28.2% on H-AGE (P = 0.06) and reduced by 40% on L-AGE (P = 0.02), whereas AGE low density lipoprotein was increased by 32% on H-AGE and reduced by 33% on L-AGE diet (P < 0.05). Thus in diabetes, environmental (dietary) AGEs promote inflammatory mediators, leading to tissue injury. Restriction of dietary AGEs suppresses these effects.

Temporal heterogeneity of endothelium-dependent and -independent dilatation of brachial artery in patients with coronary artery disease

BACKGROUND

Endothelial function is routinely assessed with high frequency ultrasound of the brachial artery. Fixed time points (1' post-occlusion and 3' post-nitrate) are commonly used to assess dynamic changes in brachial artery diameter. The underlying assumption is the lack of variability in temporal response to both endothelium-dependent and -independent stimuli.

OBJECTIVE

To evaluate the temporal course of endothelium-dependent (flow-mediated) and endothelium-independent (nitrate-induced) vasodilation of the brachial artery in patients with coronary artery disease (CAD) using high resolution (10 MHz) ultrasound.

METHODS

Thirty-seven patients with angiographically assessed CAD were prospectively enrolled in the study. End-diastolic, two-dimensional, long axis ultrasonographic images of the brachial artery were digitally stored on-line every 10 s, from baseline up to 4' during flow-mediated and up to 7' during 300 micrograms sublingual nitrate-induced vasodilation of the brachial artery.

RESULTS

The mean percent endothelium-dependent flow-mediated maximal dilation (FMD) measured at 60 s was lower than the mean peak FMD (4.8 +/- 4.1 vs. 6.6 +/- 5.2%; p < 0.01). By 60 s only eight patients (35%) reached their maximum FMD response. The mean time to reach peak FMD was 87 +/- 33 s. The mean time for the peak nitrate dilation was 291 +/- 73 s. The peak nitrate-induced percent dilation was higher than that measured at 3 min (12.2 +/- 6.7 vs. 5.4 +/- 4.5%; p < 0.001). By 190 s, only four patients (11%) reached their maximum nitrate response.

CONCLUSION

The routinely used measurement time points for evaluation of FMD and endothelium-independent vasodilation may not be adequate to detect the peak responses of individual patients with CAD.

Reversible hypertension following coeliac disease treatment: the role of moderate hyperhomocysteinaemia and vascular endothelial dysfunction

The vascular endothelium maintains a relatively vasodilated state via the release of nitric oxide (NO), a process that could be disrupted by hyperhomocysteinaemia. Since endothelial dysfunction is associated with increased systemic vascular resistance that is the hallmark of sustained arterial hypertension, we hypothesised that in patients with both hypertension and coeliac disease with hyperhomocysteinaemia (via malabsorption of essential cofactors), treatment of the latter disease could improve blood pressure (BP) control. A single patient with proven sustained hypertension and newly-diagnosed coeliac disease had baseline and post-treatment BP and endothelial function assessed by ambulatory BP monitoring (ABPM) and brachial artery forearm occlusion plethysmography respectively. This 49 year-old woman had uncomplicated sustained hypertension proven on repeated ABPM carried out 6 weeks apart (daytime mean 151/92 mm Hg and 155/95 mm Hg), and sub-clinical coeliac disease (gluten-sensitive enteropathy). Initial assessments revealed raised homocysteine levels with low normal vitamin B(12) level. It was likely that she had impaired absorption of essential cofactors for normal homocysteine metabolism. She adhered to a gluten-free diet and was give oral iron, folate and B(6) supplementations as well as B(12) injections for 3 months. Her BP had improved by 6 months and normalised by 15 months (daytime ABPM mean 128/80 mm Hg). There was parallel restoration of normal endothelial function with normalisation of her homocysteine levels. These observations suggest that sub-clinical coeliac disease related hyperhomocysteinaemia might cause endothelial dysfunction, potentially giving rise to a reversible form of hypertension. In addition, this case study supports the notion that irrespective of aetiology, endothelial dysfunction may be the precursor of hypertension. This highlights the need to resolve co-existing vascular risk factors in patients with hypertension.

Endothelial function in the post-prandial state

In recent years the endothelium has emerged as an important protective barrier against the development of atherosclerosis. Endothelial dysfunction, often characterised by impaired endothelium-dependent vasodilation, is generally considered to be an early marker of cardiovascular disease. Recently, it has been noted that the post-prandial state is associated with impaired endothelium-dependent vasodilation. Since man lives in a post-prandial state most of the day, prolonged exposure to dietary factors which impair endothelial function or delayed post-prandial recovery of the endothelium could negatively affect the cardiovascular risk profile. This review will focus on post-prandial endothelial function characterised by endothelium-dependent changes in vasomotion.

Ferric saccharate induces oxygen radical stress and endothelial dysfunction in vivo

BACKGROUND

Intravenous iron supplementation is used widely in haemodialysis patients. However, nontransferrin-bound iron (NTBI), which increases after intravenous supplementation of ferric saccharate, has been suggested to act as a catalytic agent in oxygen radical formation in vitro and may thus contribute to endothelial impairment in vivo.

MATERIALS AND METHODS

In 20 healthy volunteers the effect of 100 mg ferric saccharate infusion was investigated. Vascular ultrasound was used to assess endothelium-dependent vasodilatation at baseline, and 10 and 240 min after ferric saccharate infusion. Whole blood was collected to measure NTBI and in vivo radical formation was assessed by electron spin resonance. A time-control study was performed using saline infusion.

RESULTS

Infusion of ferric saccharate induces a greater than fourfold increase in NTBI, as well as a transient, significant (P < 0.01) reduction of flow-mediated dilatation 10 min after infusion of ferric saccharate, when compared with saline. The generation of superoxide in whole blood increased significantly 10 and 240 min after infusion of ferric saccharate by, respectively, 70 and 53%.

CONCLUSIONS

Iron infusion at a currently used therapeutic dose for intravenous iron supplementation leads to increased oxygen radical stress and acute endothelial dysfunction.

Effect of insulin therapy on endothelium-dependent dilation in type 2 diabetes mellitus

Endothelial dysfunction is an early marker of atherosclerosis occurring in patients with type 2 diabetes mellitus. Endothelium-dependent dilation (EDD) has been shown to improve by combined therapy of insulin and metformin. Studies on endothelium-independent vasodilatory capacity, however, have had controversial results. We sought to investigate the vascular reactivity--EDD and endothelium-independent dilation--and their changes induced by the addition of insulin therapy to patients with type 2 diabetes mellitus pretreated with diet and oral hypoglycemic drugs. We therefore performed vascular studies in 21 poorly controlled type 2 diabetic patients and 11 nondiabetic control subjects by using high resolution ultrasound of the brachial artery. After 3 months of additional insulin therapy, vascular and laboratory measurements including C-reactive protein and parameters of glucose and lipoprotein metabolism were repeated. At baseline, EDD was significantly impaired in diabetic patients compared with controls (2.7 +/- 2.2% vs 7.0 +/- 1.8%, p <0.001), whereas endothelium-independent dilation was normal in both groups. After insulin therapy, EDD increased from 2.7 +/- 2.2% to 5.0 +/- 2.8% (p <0.001) in diabetic patients. All other vascular parameters did not change over the treatment period. The absolute change in EDD showed a significant negative correlation with the change in hemoglobin A(1c) (r = -0.67, p <0.001) and with fasting blood glucose (r = -0.84, p <0.001) levels. In contrast, there was no correlation between EDD and the observed changes in lipid and C-reactive protein levels. Our findings demonstrate that insulin therapy has beneficial effects on vascular function, resulting in enhanced EDD, most probably due to an improved glycemic control as the underlying mechanism.

Effect of diet on vascular reactivity: an emerging marker for vascular risk

New technology for studying vascular activity in vivo has shown that the endothelium plays a critical role in the development of atherosclerosis. The healthy endothelium is a metabolically active tissue that exquisitely regulates vascular tone via release of the powerful vasodilator, nitric oxide. Endothelial integrity reduces cell adhesion, lipid deposition, and other early steps in atherogenesis. There is compelling evidence that endothelial function can be altered within hours of eating certain foods, further affirming the role of dietary factors in the prevention and progression of cardiovascular disease. This article reviews recent work on dietary factors (fatty acids, L-arginine, antioxidants, polyphenols, and folic acid) that alter vascular tone, and critically evaluates two noninvasive measures (flow-mediated dilation and total peripheral resistance) for use in dietary intervention trials.