Endothelium-dependent vasodilatation, plasma markers of endothelial function, and adrenergic vasoconstrictor responses in type 1 diabetes under near-normoglycemic conditions

Vascular deficits contributing to skeletal fragility in type 1 diabetes

Over 1 million Americans are currently living with T1D and improvements in diabetes management have increased the number of adults with T1D living into later decades of life. This growing population of older adults with diabetes is more susceptible to aging comorbidities, including both vascular disease and osteoporosis. Indeed, adults with T1D have a 2- to 3- fold higher risk of any fracture and up to 7-fold higher risk of hip fracture compared to those without diabetes. Recently, diabetes-related vascular deficits have emerged as potential risks factors for impaired bone blood flow and poor bone health and it has been hypothesized that there is a direct pathophysiologic link between vascular disease and skeletal outcomes in T1D. Indeed, microvascular disease (MVD), one of the most serious consequences of diabetes, has been linked to worse bone microarchitecture in older adults with T1D compared to their counterparts without MVD. The association between the presence of microvascular complications and compromised bone microarchitecture indicates the potential direct deleterious effect of vascular compromise, leading to abnormal skeletal blood flow, altered bone remodeling, and deficits in bone structure. In addition, vascular diabetic complications are characterized by increased vascular calcification, decreased arterial distensibility, and vascular remodeling with increased arterial stiffness and thickness of the vessel walls. These extensive alterations in vascular structure lead to impaired myogenic control and reduced nitric-oxide mediated vasodilation, compromising regulation of blood flow across almost all vascular beds and significantly restricting skeletal muscle blood flow seen in those with T1D. Vascular deficits in T1D may very well extend to bone, compromising skeletal blood flow control, and resulting in reduced blood flow to bone, thus negatively impacting bone health. Indeed, several animal and ex vivo human studies report that diabetes induces microvascular damage within bone are strongly correlated with diabetes disease severity and duration. In this review article, we will discuss the contribution of diabetes-induced vascular deficits to bone density, bone microarchitecture, and bone blood flow regulation, and review the potential contribution of vascular disease to skeletal fragility in T1D.

Impact of gut-peripheral nervous system axis on the development of diabetic neuropathy

Diabetes is a chronic metabolic disease caused by a reduction in the production and/or action of insulin, with consequent development of hyperglycemia. Diabetic patients, especially those who develop neuropathy, presented dysbiosis, with an increase in the proportion of pathogenic bacteria and a decrease in the butyrate-producing bacteria. Due to this dysbiosis, diabetic patients presented a weakness of the intestinal permeability barrier and high bacterial product translocation to the bloodstream, in parallel to a high circulating levels of pro-inflammatory cytokines such as TNF-α. In this context, we propose here that dysbiosis-induced increased systemic levels of bacterial products, like lipopolysaccharide (LPS), leads to an increase in the production of pro-inflammatory cytokines, including TNF-α, by Schwann cells and spinal cord of diabetics, being crucial for the development of neuropathy.

Effects of "metabolic memory" on erectile function in diabetic men: A retrospective case-control study

OBJECTIVE

This study was performed to explore the effects of metabolic memory on diabetic erectile dysfunction (ED), especially the severity and response to treatment.

METHODS

Through medical records and follow-up by telephone, 67 patients meeting the criteria with a clinical diagnosis of ED and a diabetic history of more than 5 years were enrolled for erectile function analysis. They were divided into a glycemic control group, a glycemic non-control group and a metabolic memory group according to glycemic levels and treatments for diabetes in the past 5 years, and they were treated with phosphodiesterase type 5 (PDE5) inhibitors for 4 weeks. Erectile function and efficacy were assessed by the International Index for Erectile Function (IIEF), the Erection Hardness Score (EHS), and the Sexual Encounter Profile (SEP).

RESULTS

The patients in the glycemic control group performed better in erectile function than those in the other groups. The patients in the glycemic control group received a significantly greater score on both the EHS and the five domains of the IIEF than did the patients in the glycemic non-control group and the metabolic memory group (all P < .001). There were also statistically significant differences favoring the glycemic control group (P < .05) in SEP2 and SEP3 success rates. However, there were no significant differences between the metabolic memory group and the glycemic non-control group in these erectile function assessments (P > .05). Significant negative correlations were seen between HbA1c levels at the time of consultation and the scores on the IIEF-EF and the EHS (Pearson r-values of -0.338 with P = .005 and -0.273 with P = .025, respectively). HbA1c levels at the first diagnosis of diabetes mellitus (DM) were also significantly negatively correlated with scores on the IIEF-EF and the EHS with greater Pearson correlation coefficients (Pearson r-values of -0.478 with P < .001 and -0.392 with P = .001, respectively). Significant improvements on each of the erectile function assessments were observed among diabetic patients with ED, but no significant difference in efficacy was observed between each group.

CONCLUSIONS

The phenomenon of metabolic memory did have a significant influence on ED in men with diabetes, associated with the severity of ED but not the response to medical treatment. Early hyperglycemia exposure would have long-term disadvantageous effects on erectile function in diabetic patients with ED, which would be sustained even after the patients achieve better glycemic control.

PATIENTS SUMMARY

In this report, we looked at the erectile functions of 67 patients with a clinical diagnosis of ED and a diabetic history of more than 5 years. We found that early hyperglycemia exposure would have long-term disadvantageous effects on erectile function in diabetic patients with ED, which would be sustained even after the patients achieve better glycemic control. We further found that the effects were associated with the severity of ED but not the response to medical treatment in men with diabetes.

Clinical Research on the Aortic Elasticity in Patients with Type 1 Diabetes Mellitus Complicated with Hypertension

OBJECTIVE

To investigate the characteristics of aortic elasticity in type 1 diabetes mellitus (DM1) patients with hypertension using dual-source computed tomography (DSCT).

METHODS

Subjects were divided into four groups: 31 with hypertension (EH group), 28 with DM1 (DM1 group), 30 with hypertension and DM1 (DM1 + EH group), and 30 healthy volunteers (control group, CG). ECG-gated DSCT was used to measure the cross-sectional area of the aorta in diastole and systole and calculate the aortic elasticity (D). Analysis of variance and multiple linear regression were used for statistical analysis.

RESULTS

Compared with the CG, aortic elasticity (D) in the DM1 group patients was not significantly decreased. Compared with the EH group, the DM1 + EH group showed no significant change. The aortic elasticity (D) in the EH and DM1 + EH groups was significantly lower than that in the CG and DM1 group.

CONCLUSION

DM1 slightly affects the aortic elasticity of the descending aorta, whereas hypertension exerts the main effect.

Review: Endothelial dysfunction and pre-symptomatic atherosclerosis in type 1 diabetes — pathogenesis and identification

The vascular endothelium offers an attractive model for detecting functional abnormalities prior to structural changes in the vasculature. Demonstration of progression from endothelial dysfunction through to atherosclerosis is required. Measurements of forearm bloodflow, biochemical markers and biophysical assessments of the endothelium have been employed as research tools for investigating pre-symptomatic atherosclerosis.

However, studies examining endothelial function in type 1 diabetes have been sparse and conflicting. Differences in methodology and the study populations were potential confounding factors. Augmented vasodilatory prostanoids compensate for reduced nitric oxide bioavailability in determining endothelial function in type 1 diabetes. Hyperglycaemia appears to be the initiating event in type 1 diabetes which promotes a variety of biochemical events which are pathogenic to the endothelium.

Improved understanding of the endothelium may facilitate the development of novel diagnostic tools and interventions targeting the accelerated atherosclerosis associated with type 1 diabetes.

Clinical implications of oxidative stress and potential role of natural antioxidants in diabetic vascular complications

AIMS

The possible link between hyperglycaemia-induced oxidative stress (OxS) and diabetic complications is suggested by many in vitro studies. However, not much attention has been paid to the clinical evidence supporting this hypothesis, as well as to their possible therapeutic implications.

DATA SYNTHESIS

Some prospective studies show a direct correlation between an increase in OxS biomarkers and the appearance of diabetes complications. This is consistent with the evidence that any acute increase of glycaemia, particularly post-prandial, and hypoglycaemia causes endothelial dysfunction and inflammation, through the generation of an OxS. However, the detection of free radicals is difficult as they are highly reactive molecules with a short half-life. Instead, the metabolites of OxS are measured. Interventional trials with supplemented antioxidants have failed to show any beneficial effects. Conversely, natural foods show very promising results.

CONCLUSIONS

The "new antioxidant" approach includes the possibility of controlling free radical production and increasing intracellular antioxidant defence, a concept different from the old one, when antioxidant activities implied scavenging the free radicals already produced. A synergistic action in this respect could convincingly be obtained with a balanced 'Mediterranean Diet' (MedD) type. Early intensive glucose control is still the best strategy to avoid OxS and its associated diabetes complications.

The simultaneous control of hyperglycemia and GLP-1 infusion normalize endothelial function in type 1 diabetes

BACKGROUND

To test the effect of normoglycemia and glucagon-like peptide-1 (GLP-1), alone or in combination, on the possible normalization of endothelial function in type 1 diabetes.

METHODS

Fifteen people with type 1 diabetes participated in three experiments: reaching and maintaining normoglycemia for 4h; reaching and maintaining hyperglycemia plus GLP-1 infusion for 4h; and reaching and maintaining normoglycemia for 4h with simultaneous infusion of GLP-1.

RESULTS

Both normoglycemia and GLP-1 infusion restored endothelial function and decreased and plasma 8-iso prostaglandin F2α levels. However, only the combination of normoglycemia and GLP-1 was able to normalize endothelial function.

CONCLUSIONS

This study confirms that long-lasting hyperglycemia in type 1 diabetes induces a permanent alteration which contributes to maintaining endothelial dysfunction even when glycemia is normalized, and that in the presence of normoglycemia, GLP-1 can contribute to normalizing endothelial function.

Longitudinal Association Between Endothelial Dysfunction, Inflammation, and Clotting Biomarkers With Subclinical Atherosclerosis in Type 1 Diabetes: An Evaluation of the DCCT/EDIC Cohort

OBJECTIVE

There is considerable interest in identifying biomarkers that predict high risk for the development of macrovascular complications in patients with diabetes. Therefore, the longitudinal association between subclinical atherosclerosis as measured by internal carotid artery intima-media thickness (IMT) and acute-phase reactants, cytokines/adipokines, thrombosis, and adhesion molecules was examined.

RESEARCH DESIGN AND METHODS

Biomarkers were measured at four time points over 20 years in 886 DCCT/EDIC participants with type 1 diabetes. Four composite scores were created by combining z scores generated from within the data set of individual biomarkers: acute-phase reactants (fibrinogen, C-reactive protein), thrombosis (fibrinogen, active and total plasminogen activator inhibitor [PAI]-1), cytokines/adipokines (tumor necrosis factor receptor-1 and -2, active and total PAI-1, IL-6), and endothelial dysfunction (soluble intracellular adhesion molecule-1, soluble vascular cell adhesion molecule-1, and soluble E-selectin). Internal carotid IMT was measured at EDIC years 1, 6, and 12, with elevated IMT defined at each time point as being in the upper quintile of its distribution.

RESULTS

Logistic regression models indicate that while individual biomarkers were not predictive of or associated with subclinical atherosclerosis, composite scores of acute-phase reactants (odds ratio [OR] 2.78 [95% CI 1.42, 5.42]), thrombolytic factors (OR 2.83 [95% CI 1.45, 5.52]), and cytokines/adipokines (OR 2.83 [95% CI 1.48, 5.41]) measured at our final time point EDIC years 8-11 were associated with higher levels of atherosclerosis at EDIC year 12, but findings were not consistent at early time points. The endothelial dysfunction score was not appreciably predictive of or associated with subclinical atherosclerosis at any of the time points measured.

CONCLUSIONS

The pathophysiologic relationship between higher biomarker levels and progression of subclinical atherosclerosis remains unclear.

Decreased reactivity of skin microcirculation in response to L-arginine in later-onset type 1 diabetes

OBJECTIVE

The aim of our study was to evaluate the vasodilatory effect of l-arginine infusion on the skin microcirculation and to assess the relationship between this effect and the presence of microangiopathy in patients with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Capillaroscopy was performed before and after l-arginine infusion in 48 diabetic patients (26 women and 22 men; age, 39.8 ± 6.3 years) and 24 volunteers free of any chronic disease (13 women and 11 men; age, 38.0 ± 6.7 years). The skin microcirculation reactivity, as expressed by the percentage of area covered by capillaries (coverage) and the distance between capillaries (distance), and the relationship between microcirculation reactivity and the presence of microangiopathic complications were assessed.

RESULTS

The distance before l-arginine infusion was significantly lower in patients than in controls (221 [153-311] vs. 240 [185-356] µm; P = 0.02) and did not differ after l-arginine infusion (223.5 [127-318] vs. 242.5 [181-341] µm; P = 0.27). The difference between the coverage values obtained before and after l-arginine infusion (Δcoverage) was significantly different from zero in the control group but not in the diabetes group. Patients with later onset of diabetes were characterized by decreased skin microcirculation reactivity when compared with patients with earlier onset of diabetes (-1.18 [-5.07 to 11.60] vs. 1.36 [-6.00 to 8.06]; P = 0.02) despite the higher prevalence of retinopathy in patients with earlier onset of diabetes (64% vs. 26%; P = 0.02).

CONCLUSIONS

Skin microvascular reactivity is impaired in patients with later onset of type 1 diabetes. Capillaroscopy with l-arginine infusion is useful for the identification of skin microangiopathy in type 1 diabetes.

The emerging challenge in diabetes: the "metabolic memory"

Large randomized studies have established that early intensive glycemic control reduces the risk of diabetic complications, both micro and macrovascular. However, epidemiological and prospective data support a long-term influence of early metabolic control on clinical outcomes. This phenomenon has recently been defined as "metabolic memory." Potential mechanisms for propagating this "memory" may be the production of reactive species unrelated to the presence of hyperglycemia, depending on the previous production of AGEs which can maintain RAGE over-expression, on the level of glycation of mitochondrial proteins and on the amount of mtDNA produced, all conditions able to induce an altered gene expression which may be persistent even when glycemia is normalized. Clinically, the emergence of this "metabolic memory" suggests the need for a very early aggressive treatment aiming to "normalize" the metabolic control and the addition of agents which reduce cellular reactive species and glycation in addition to normalizing glucose levels in diabetic patients in order to minimize long-term diabetic complications.

Osteoprotegerin is associated with cardiovascular risk in hypertension and/or diabetes

BACKGROUND

Osteoprotegerin (OPG), a secreted member of the tumour necrosis factor receptor superfamily of cytokines, has been associated with endothelial dysfunction. We studied in type 2 diabetic and/or hypertensive patients the relationship between serum OPG and vascular alterations associated with these pathologies.

MATERIALS AND METHODS

We analysed 191 consecutive patients (52 with type 2 diabetes and 139 hypertensive nondiabetic patients) and 54 healthy controls. We assessed the relationship of OPG serum levels measured by ELISA with basal glycaemia, glycosylated haemoglobin, blood pressure, endothelial dysfunction (assessed by pulse wave velocity), retinopathy (by Keith-Wagener classification), left ventricular hypertrophy (by Cornell index), cardiovascular risk and target organs (heart, vascular, kidney) damage.

RESULTS

Serum OPG levels were higher in either hypertensive or diabetic patients and in patients with non-dipper and riser circadian blood pressure patterns. We found significant correlations between OPG levels and age, height, glycaemia, systolic, diastolic and pulse blood pressure, pulse wave velocity and left ventricular hypertrophy in both hypertensive and diabetic patients. OPG levels were also higher in hypertensive patients with retinopathy, patients with high probability of 10-year cardiovascular risk, patients with three or more damaged target organs (heart, vessels, kidneys) and patients with previous episodes of ischaemic cardiopathy or hypercholesterolaemia.

CONCLUSIONS

Osteoprotegerin is an indicator of diabetes- and hypertension-associated vascular pathologies as endothelial dysfunction and cardiovascular risk.

The role of glucosamine-induced ER stress in diabetic atherogenesis

Cardiovascular disease (CVD) is the major cause of mortality in individuals with diabetes mellitus. However the molecular and cellular mechanisms that predispose individuals with diabetes to the development and progression of atherosclerosis, the underlying cause of most CVD, are not understood. This paper summarizes the current state of our knowledge of pathways and mechanisms that may link diabetes and hyperglycemia to atherogenesis. We highlight recent work from our lab, and others', that supports a role for ER stress in these processes. The continued investigation of existing pathways, linking hyperglycemia and diabetes mellitus to atherosclerosis, and the identification of novel mechanisms and targets will be important to the development of new and effective antiatherosclerotic therapies tailored to individuals with diabetes.

Vascular dysfunction in diabetes: The endothelial progenitor cells as new therapeutic strategy

The vascular endothelium is a critical determinant of diabetes-associated vascular complications, and improving endothelial function is an important target for therapy. Diabetes mellitus contributes to endothelial cell injury and dysfunction. Endothelial progenitor cells (EPCs) play a critical role in maintaining endothelial function and might affect the progression of vascular disease. EPCs are essential to blood vessel formation, can differentiate into mature endothelial cells, and promote the repair of damaged endothelium. In diabetes, the circulating EPC count is low and their functionality is impaired. The mechanisms that underlie this reduced count and impaired functionality are poorly understood. Knowledge of the status of EPCs is critical for assessing the health of the vascular system, and interventions that increase the number of EPCs and restore their angiogenic activity in diabetes may prove to be particularly beneficial. The present review outlines current thinking on EPCs’ therapeutic potential in endothelial dysfunction in diabetes, as well as evidence-based perspectives regarding their use for vascular regenerative medicine.

Hyperglycaemia and the vessel wall: the pathophysiological aspects on the atherosclerotic burden in patients with diabetes

Large randomised studies have established that early intensive glycaemic control reduces the risk of diabetic complications, both microvascular and macrovascular. However, epidemiological and prospective data support a long-term influence of early metabolic control on clinical outcomes. This phenomenon has recently been defined as 'metabolic memory'. Furthermore, evidence suggests that 'glucose variability' may also be an independent risk factor for cardiovascular complications in diabetes. Studies suggest that all these different situations of hyperglycaemia share a common pathogenetic mechanism, increased oxidative stress, producing an endothelial dysfunction. The therapeutic challenge derived from these evidences is a need not only for an early tight glycaemic control, but also for maintaining glycaemia within a strict normal narrow range.

Effect of acute hyperglycaemia, long-term glycaemic control and insulin on endothelial dysfunction and inflammation in Type 1 diabetic patients with different characteristics

OBJECTIVE

To investigate the possibility of reversing endothelial dysfunction and inflammation by glucose normalization, antioxidants and insulin per se, in different subgroups of Type 1 diabetic patients.

METHODS

Three subgroups of Type 1 diabetic patients were studied: patients within 1 month of diagnosis (subgroup 1); patients with approximately 5 years' disease duration and with glycated haemoglobin (HbA(1c)) <or= 7.0% (subgroup 2) or > 7.0% since diagnosis (subgroup 3). Participants underwent four procedures: 2-h hyperglycaemic clamp followed by: (A) 12 h near-normalization of blood glucose, with the addition of vitamin C during the last 6 h; (B) 12-h vitamin C and near-normalization of blood glucose for the last 6 h; (C) both vitamin C and near-normalization of blood glucose for 12 h; (D) hyperglycaemic-hyperinsulinaemic clamp for 12 h, with the addition of vitamin C during the last 6 h.

RESULTS

After 2 h of hyperglycaemia, markers of endothelial dysfunction, nitrotyrosine, 8-iso prostaglandin F2alpha, soluble intercellular adhesion molecule-1, soluble vascular adhesion molecule-1, interleukin (IL)-6 and IL-18 were increased in all the subgroups. Levels were normalized, at all time points, by treatments A, B and C in the subgroups 1 and 2. In the third subgroup, levels were normalized only by the simultaneous normalization of blood glucose and vitamin C treatment. During treatment D, the levels were improved at 6 h in all the subgroups, but normalized at 12 h only after vitamin C in subgroups 1 and 2, but not in subgroup 3.

CONCLUSIONS

This study suggests that different subgroups of Type 1 diabetic patients react identically to acute hyperglycaemia and insulin, but differently to glucose normalization.

Diabetes impairs arteriogenesis in the peripheral circulation: review of molecular mechanisms

Patients suffering from both diabetes and PAD (peripheral arterial disease) are at risk of developing critical limb ischaemia and ulceration, and potentially requiring limb amputation. In addition, diabetes complicates surgical treatment of PAD and impairs arteriogenesis. Arteriogenesis is defined as the remodelling of pre-existing arterioles into conductance vessels to restore the perfusion distal to the occluded artery. Several strategies to promote arteriogenesis in the peripheral circulation have been devised, but the mechanisms through which diabetes impairs arteriogenesis are poorly understood. The present review provides an overview of the current literature on the deteriorating effects of diabetes on the key players in the arteriogenesis process. Diabetes affects arteriogenesis at a number of levels. First, it elevates vasomotor tone and attenuates sensing of shear stress and the response to vasodilatory stimuli, reducing the recruitment and dilatation of collateral arteries. Secondly, diabetes impairs the downstream signalling of monocytes, without decreasing monocyte attraction. In addition, EPC (endothelial progenitor cell) function is attenuated in diabetes. There is ample evidence that growth factor signalling is impaired in diabetic arteriogenesis. Although these defects could be restored in animal experiments, clinical results have been disappointing. Furthermore, the diabetes-induced impairment of eNOS (endothelial NO synthase) strongly affects outward remodelling, as NO signalling plays a key role in several remodelling processes. Finally, in the structural phase of arteriogenesis, diabetes impairs matrix turnover, smooth muscle cell proliferation and fibroblast migration. The review concludes with suggestions for new and more sophisticated therapeutic approaches for the diabetic population.

[Oxidative stress: a review on metabolic signaling in type 1 diabetes]

Diabetic complications appear to be multifactorial process. The biochemical and pathological mechanisms are associated with chronic hyperglycemia of diabetes and the increased oxidative stress which has been postulated to play a central role in these disorders. Accumulating evidence suggests that oxidative cell injury caused by free radicals contributes to the development of type 1 diabetes (DM1) complications and decreased efficiency of antioxidant defenses (both enzymatic and nonenzymatic) seems to correlate with the severity of pathological tissue changes in DM1. In this review, we report as oxidative stress may exert deleterious effects in diabetes, as well as address current strategies in study to down-regulating vascular injury.

Reactive oxygen-derived free radicals are key to the endothelial dysfunction of diabetes

Vascular complications are an important pathological issue in diabetes that lead to the further functional deterioration of several organs. The balance between endothelium-dependent relaxing factors and endothelium-dependent contracting factors (EDCFs) is crucial in controlling local vascular tone and function under normal conditions. Diabetic endothelial dysfunction is characterized by reduced endothelium-dependent relaxations and/or enhanced endothelium-dependent contractions. Elevated levels of oxygen-derived free radicals are the initial source of endothelial dysfunction in diabetes. Oxygen-derived free radicals not only reduce nitric oxide bioavailability, but also facilitate the production and/or action of EDCFs. Thus, the endothelial balance tips towards vasoconstrictor responses over the course of diabetes.

Endothelial dysfunction and cardiovascular risk factors

The endothelium plays an integral role in the regulation of vascular tone, platelet activity, leukocyte adhesion, and thrombosis and is intimately involved in the development of atherosclerosis. Endothelial dysfunction has been observed in patients with established coronary artery disease or coronary risk factors, both in the coronary and peripheral vasculature. Therapeutic interventions with lipid-lowering drugs, ACE inhibitors, physical activity, and antioxidant agents have been shown to improve endothelial function in coronary and peripheral vessels. This systemic manifestation and improvement of endothelial function suggests that a common mechanism may contribute to endothelial dysfunction in the coronary and peripheral circulation.

TARGET AUDIENCE

Internist, Cardiologists, Family physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to define the participation of cardiovascular risk factors in the various complications associated with endothelial dysfunction.

Risk factors related to inflammation and endothelial dysfunction in the DCCT/EDIC cohort and their relationship with nephropathy and macrovascular complications

OBJECTIVE

Because endothelial cell dysfunction and inflammation are key contributors to the development of complications in type 1 diabetes, we studied risk factors related to endothelial dysfunction and inflammation (C-reactive protein and fibrinogen, soluble vascular cell adhesion molecule-1, intracellular adhesion molecule-1, and E-selectin, and fibrinolytic markers) in a subgroup of patients from the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Intervention and Complications (EDIC) study cohort.

RESEARCH DESIGN AND METHODS

We determined which of these risk factors or clusters thereof are associated with the presence of and subsequent development of nephropathy and macrovascular complications (reflected by carotid intima-media thickness [IMT]).

RESULTS

After adjustment for conventional risk factors (age, sex, DCCT treatment group, diabetes duration, A1C, systolic blood pressure, waist-to-hip ratio, total and HDL cholesterol, and smoking status), fibrinogen remained strongly associated with progression of internal and common carotid IMT (P < 0.01) and soluble E-selectin had a strong association with nephropathy (P < 0.01).

CONCLUSIONS

The best predictor for IMT progression in the DCCT/EDIC cohort was plasma fibrinogen, and the levels of soluble E-selectin discriminate patients with albuminuria better than conventional risk factors.

Neurovascular control and neurogenic inflammation in diabetes

Loss of pain perception is currently seen as a key factor in the development of diabetic foot ulcers. However, recent studies suggest that nerves play a central role in tissue homeostasis and can orchestrate complex reparative as well as destructive processes in the feet. Evidence is presented that suggests that denervation can result in altered capillary blood flow (in patients with type 2 diabetes), oxygen delivery, fluid filtration, and inflammatory responses. These processes could render the feet of diabetic patients with neuropathy more susceptible to tissue damage, infection and perhaps, in a subset of patients, to the development of acute Charcot neuro-osteoarthropathy (CN).

Endothelial dysfunction in diabetes mellitus

Diabetes mellitus is associated with an increased risk of cardiovascular disease, even in the presence of intensive glycemic control. Substantial clinical and experimental evidence suggest that both diabetes and insulin resistance cause a combination of endothelial dysfunctions, which may diminish the anti-atherogenic role of the vascular endothelium. Both insulin resistance and endothelial dysfunction appear to precede the development of overt hyperglycemia in patients with type 2 diabetes. Therefore, in patients with diabetes or insulin resistance, endothelial dysfunction may be a critical early target for preventing atherosclerosis and cardiovascular disease. Microalbuminuria is now considered to be an atherosclerotic risk factor and predicts future cardiovascular disease risk in diabetic patients, in elderly patients, as well as in the general population. It has been implicated as an independent risk factor for cardiovascular disease and premature cardiovascular mortality for patients with type 1 and type 2 diabetes mellitus, as well as for patients with essential hypertension. A complete biochemical understanding of the mechanisms by which hyperglycemia causes vascular functional and structural changes associated with the diabetic milieu still eludes us. In recent years, the numerous biochemical and metabolic pathways postulated to have a causal role in the pathogenesis of diabetic vascular disease have been distilled into several unifying hypotheses. The role of chronic hyperglycemia in the development of diabetic microvascular complications and in neuropathy has been clearly established. However, the biochemical or cellular links between elevated blood glucose levels, and the vascular lesions remain incompletely understood. A number of trials have demonstrated that statins therapy as well as angiotensin converting enzyme inhibitors is associated with improvements in endothelial function in diabetes. Although antioxidants provide short-term improvement of endothelial function in humans, all studies of the effectiveness of preventive antioxidant therapy have been disappointing. Control of hyperglycemia thus remains the best way to improve endothelial function and to prevent atherosclerosis and other cardiovascular complications of diabetes. In the present review we provide the up to date details on this subject.

Multimarker approach to evaluate the incidence of the metabolic syndrome and longitudinal changes in metabolic risk factors: the Framingham Offspring Study

BACKGROUND

The metabolic syndrome (MetS) is associated with increased cardiovascular risk. We evaluated the relative contributions of circulating biomarkers representing distinct biological pathways to the incidence of MetS and to longitudinal changes of its constituent risk factors.

METHODS AND RESULTS

We measured 8 circulating biomarkers reflecting inflammation (C-reactive protein), hemostasis (plasminogen activator inhibitor-1, fibrinogen), neurohormonal activity (aldosterone, renin, B-type natriuretic peptide, N-terminal proatrial natriuretic peptide), and endothelial dysfunction (homocysteine) in 2292 Framingham Offspring Study participants (mean age, 57 years; 56% women). We related the biomarker panel to incidence of MetS on follow-up initially and then related biomarkers associated with incident MetS to longitudinal change in its components. On follow-up (mean, 2.9 years), 282 participants (of 1473 participants without prevalent MetS at baseline) developed MetS. After adjustment for clinical risk factors, the biomarker panel was associated with incident MetS (P=0.008). On backward elimination, plasminogen activator inhibitor-1 and aldosterone remained associated with incident MetS (multivariable-adjusted odds ratio per 1-SD increment log marker, 1.31 [P=0.004] and 1.21 [P=0.015], respectively). In multivariable analyses evaluating longitudinal change in MetS components (analyzed as continuous variables), plasminogen activator inhibitor-1 was significantly and positively associated with changes in fasting glucose, systolic blood pressure, and triglycerides (all P<0.05). Serum aldosterone was associated positively with change in systolic blood pressure (P=0.023) and inversely with change in high-density lipoprotein cholesterol (P=0.001).

CONCLUSIONS

Higher circulating plasminogen activator inhibitor-1 and aldosterone levels are associated with the development of MetS and with longitudinal change of its components, suggesting that these biomarkers and related pathways play a key role in mediating metabolic risk.

Telmisartan shows an equivalent effect of vitamin C in further improving endothelial dysfunction after glycemia normalization in type 1 diabetes

OBJECTIVE

Long-lasting hyperglycemia in type 1 diabetic patients induces permanent alterations of endothelial function by increased oxidative stress, even when glycemia is normalized.

RESEARCH DESIGN AND METHODS

In this study, 36 type 1 diabetic patients and 12 control subjects were enrolled. The diabetic patients were divided into three groups. The first group was treated for 24 h with insulin, achieving a near normalization of glycemia. After 12 h of this treatment, vitamin C was added for the remaining 12 h. The second group was treated for 24 h with vitamin C. After 12 h of this treatment, insulin was started, achieving a near normalization of glycemia for the remaining 12 h. The third group was treated for 24 h with both vitamin C and insulin, achieving near normalization of glycemia. The same protocols were performed after 1 month of telmisartan or placebo.

RESULTS

Neither normalization of glycemia nor vitamin C treatment alone was able to normalize endothelial dysfunction or oxidative stress. Combining insulin and vitamin C normalized endothelial dysfunction and decreased oxidative stress to normal levels. Telmisartan significantly improved basal endothelial function and decreased nitrotyrosine plasma levels. In patients treated with telmisartan, a near normalization of both flow-mediated vasodilation and oxidative stress was achieved when glycemia was normalized, whereas adding vitamin C infusion did not show further effect on endothelial function or nitrotyrosine plasma levels.

CONCLUSIONS

These data indicate that combining the normalization of glycemia with an antioxidant can normalize endothelial function in type 1 diabetic patients and that telmisartan works as an antioxidant like vitamin C.

Simultaneous control of hyperglycemia and oxidative stress normalizes endothelial function in type 1 diabetes

OBJECTIVE

Previous studies have shown that in type 1 diabetes endothelial dysfunction persists even when glycemia is normalized. Moreover, oxidative stress has recently been demonstrated to be the mediator of hyperglycemia-induced endothelial dysfunction.

RESEARCH DESIGN AND METHODS

Thirty-six type 1 diabetic patients and 12 control subjects were enrolled. The diabetic patients were divided into three groups. The first group was treated for 24 h with insulin, achieving a near-normalization of glycemia. After 12 h of this treatment, vitamin C was added for the remaining 12 h. The second group was treated for 24 h with vitamin C. After 12 h of this treatment, insulin was started, with achievement of near-normalization of glycemia for the remaining 12 h. The third group was treated for 24 h with both vitamin C and insulin, achieving near-normalization of glycemia.

RESULTS

Neither normalization of glycemia nor vitamin C treatment alone was able to normalize endothelial dysfunction or oxidative stress. However, a combination of insulin and vitamin C normalized endothelial dysfunction and decreased oxidative stress to normal levels.

CONCLUSIONS

This study suggests that long-lasting hyperglycemia in type 1 diabetic patients induces permanent alterations in endothelial cells, which may contribute to endothelial dysfunction by increased oxidative stress even when hyperglycemia is normalized.

Multiple biomarkers and the risk of incident hypertension

An understanding of mechanisms underlying the development of essential hypertension is critical for designing prevention and treatment strategies. Selected biomarkers may be elevated before the onset of hypertension, but previous studies are limited by cross-sectional designs or a focus on single biomarkers. We prospectively studied 1456 nonhypertensive individuals who had baseline measurement of 9 biomarkers: C-reactive protein (inflammation); fibrinogen (inflammation and thrombosis); plasminogen activator inhibitor-1 (fibrinolytic potential); aldosterone, renin, B-type natriuretic peptide, and N-terminal proatrial natriuretic peptide (neurohormonal activity); homocysteine (renal function and oxidant stress); and urinary albumin/creatinine ratio (glomerular endothelial function). Incident hypertension, defined as blood pressure > or =140/90 mm Hg or antihypertensive therapy, developed in 232 participants over a mean follow-up of 3 years. After adjustment for clinical risk factors, the biomarker panel was significantly associated with incident hypertension (P=0.002). Three (of 9) biomarkers were significantly related to incident hypertension on backward elimination (multivariable-adjusted odds ratios, per SD increment in biomarker): C-reactive protein (1.26; 95% CI: 1.05 to 1.51), plasminogen activator inhibitor-1 (1.28; 95% CI: 1.05 to 1.57), and urinary albumin/creatinine ratio (1.21; 95% CI: 1.02 to 1.43). The incidence of hypertension was 4.5, 6.4, and 9.9 per 100 person years for participants with 0, 1, and > or=2 elevated biomarkers, respectively (elevation defined as > or =1 SD above the mean). The threshold of > or =2 elevated biomarkers for predicting hypertension was associated with high specificity (0.92) but low sensitivity (0.15). Biomarkers of inflammation, reduced fibrinolytic potential, and low-grade albuminuria are jointly associated with the incidence of hypertension. These data support the premise that abnormalities in multiple biological pathways antedate the onset of overt hypertension.

Early diabetic neuropathy: Triggers and mechanisms

Peripheral neuropathy, and specifically distal peripheral neuropathy (DPN), is one of the most frequent and troublesome complications of diabetes mellitus. It is the major reason for morbidity and mortality among diabetic patients. It is also frequently associated with debilitating pain. Unfortunately, our knowledge of the natural history and pathogenesis of this disease remains limited. For a long time hyperglycemia was viewed as a major, if not the sole factor, responsible for all symptomatic presentations of DPN. Multiple clinical observations and animal studies supported this view. The control of blood glucose as an obligatory step of therapy to delay or reverse DPN is no longer an arguable issue. However, while supporting evidence for the glycemic hypothesis has accumulated, multiple controversies accumulated as well. It is obvious now that DPN cannot be fully understood without considering factors besides hyperglycemia. Some symptoms of DPN may develop with little, if any, correlation with the glycemic status of a patient. It is also clear that identification of these putative non-glycemic mechanisms of DPN is of utmost importance for our understanding of failures with existing treatments and for the development of new approaches for diagnosis and therapy of DPN. In this work we will review the strengths and weaknesses of the glycemic hypothesis, focusing on clinical and animal data and on the pathogenesis of early stages and triggers of DPN other than hyperglycemia.

Cross-sectional relations of serum aldosterone and urine sodium excretion to urinary albumin excretion in a community-based sample

Experimental models suggest that increased aldosterone and sodium intake are associated with renovascular damage and resultant proteinuria. We hypothesized that serum aldosterone and urinary sodium would be associated with urinary albumin excretion, an indicator of kidney damage. We evaluated 2700 participants (53% women, mean age 58 years) from the Framingham Offspring Study who attended a routine examination between 1995 and 1998, who were free of heart failure and renal failure, and underwent testing for serum aldosterone, spot urinary sodium, and urinary albumin excretion (urine albumin/creatinine ratio, UACR), the latter two indexed to urinary creatinine. Stepwise multivariable linear regression was used to evaluate the relations between UACR with urinary sodium index and serum aldosterone. In multivariable regression, log urinary sodium index was associated positively with log-UACR (P<0.0001). UACR levels in the fourth and fifth quintiles of urinary sodium index were 24% (95% confidence interval (CI) 3-49%), and twofold higher (95% CI 72-150%), respectively, relative to the lowest quintile (P-value for trend across quintiles <0.001). In multivariable models, log-transformed aldosterone was not related to log-UACR. The top quintile of serum aldosterone levels was associated with a 21% higher (95% 1-44%) UACR levels relative to the lowest quintile. Urinary albumin excretion was strongly and positively associated in a continuous fashion with urinary sodium excretion, whereas a weaker nonlinear positive relation with serum aldosterone was noted. Our cross-sectional observations raise the possibility that dietary salt intake may be associated with early renovascular damage.

Augmented Endothelium-Derived Hyperpolarizing Factor-Mediated Relaxations Attenuate Endothelial Dysfunction in Femoral and Mesenteric, but Not in Carotid Arteries from Type I Diabetic Rats

Individual vascular beds exhibit differences in vascular reactivity. The present study investigates the effects of streptozotocin-induced type I diabetes on endothelium-dependent responses of rat carotid, femoral, and mesenteric arteries. Rings with and without endothelium, suspended in organ chambers for isometric tension recording, were contracted with phenylephrine and exposed to increasing concentrations of acetylcholine. In carotid and femoral arteries, acetylcholine produced concentration- and endothelium-dependent relaxations that were abolished by Nomega-nitro-L-arginine methyl ester (L-NAME; specific nitric-oxide synthase inhibitor) and were impaired slightly in preparations from streptozotocin-treated rats (STZ-rats). This impairment could be prevented by L-arginine. In femoral arteries incubated with L-NAME, acetylcholine caused endothelium-dependent contractions that were abolished by 3-[(6-amino-(4-chlorobenzensulfonyl)-2-methyl-5,6,7,8-tetrahydronapht]-1-yl) propionic acid (S18886) (antagonist of thromboxane A2/prostaglandins H2-receptors) and reversed to relaxation by indomethacin (inhibitor of cyclooxygenase). The latter relaxation was inhibited by charybdotoxin plus apamin, suggesting a role of endothelium-dependent hyperpolarizing factor (EDHF). This EDHF-mediated component was augmented slightly in arteries from STZ-rats. In mesenteric arteries, relaxations to acetylcholine were only partially inhibited by L-NAME, and the L-NAME-resistant component was abolished by charybdotoxin plus apamin. In the mesenteric arteries from STZ-rats, L-NAME-sensitive relaxations to acetylcholine were reduced and the EDHF-component was augmented. These findings demonstrate a marked heterogeneity in endothelium-dependent responses in rat arteries and their differential adaptation in the course of type I diabetes. In particular, the EDHF-mediated component not only compensates for the reduced bioavailability of nitric oxide in the femoral and mesenteric artery but also counteracts the augmented endothelium-dependent contractions in the former.

Endothelial function and the prediction of CVD in diabetes

Endothelial dysfunction has received increasing attention as a potential contributor to the pathogenesis of vascular disease in diabetes mellitus. Technologies to detect endothelial dysfunction include assessment of endothelium-dependent vasodilatation and plasma levels of cell injury markers. Although clinical and epidemiologic studies show associations and potential links between endothelial dysfunction and outcome in diabetes, there is a substantial need for further work.

Alpha(2)-adrenergic receptor signalling in hypertension

Cardiovascular regulation by the sympathetic nervous system is mediated by activation of one or more of the nine known subtypes of the adrenergic receptor family; alpha(1A)-, alpha(1B)-, alpha(1D)-, alpha(2A)-, alpha(2B)-, alpha(2C)-, beta(1)-, beta(2)- and beta(3)-ARs (adrenoceptors). The role of the alpha(2)-AR family has long been known to include presynaptic inhibition of neurotransmitter release, diminished sympathetic efferent traffic, vasodilation and vasoconstriction. This complex response is mediated by one of three subtypes which all uniquely affect blood pressure and blood flow. All three subtypes are present in the brain, kidney, heart and vasculature. However, each differentially influences blood pressure and sympathetic transmission. Activation of alpha(2A)-ARs in cardiovascular control centres of the brain lowers blood pressure and decreases plasma noradrenaline (norepinephrine), activation of peripheral alpha(2B)-ARs causes sodium retention and vasoconstriction, whereas activation of peripheral alpha(2C)-ARs causes cold-induced vasoconstriction. In addition, non-selective agonists elicit endothelium-dependent vasodilation and presynaptic inhibition of noradrenaline release. The evidence that each of these receptor subtypes uniquely participates in cardiovascular control is discussed in this review.

Plasma Prekallikrein as a Risk Factor for Diabetic Retinopathy

BACKGROUND

The aim of the study was to verify the hypothesis that in diabetes there is an increased activation of coagulation system leading in consequence to diabetic retinopathy.

METHODS

Thirty three healthy subjects (controls, 16 males and 17 females) and 35 patients with diabetes type 1 (15 males and 20 females) were examined. We monitored plasma prekallikrein (PPK), glycemia, fructosamine, glycosylated hemoglobin, activated partial thromboplastin time (PTT), INR, fibrinolysis in euglobulins time (FET), level of antithrombin III (AT III), fibrinogen (Fb) and fibrinogen degradation products (FDP).

RESULTS

In diabetic patients without retinopathy, PKK concentration was 16% higher (p <0.005), in patients with background retinopathy 33% higher (p <0.001), and in patients with proliferative retinopathy PKK concentration was 50% higher (p <0.001) than in controls. In the subgroup of patients with proliferative retinopathy PTT was significantly shorter (p <0.001), and FET was significantly longer (p <0.001) than in control. In patients with diabetes higher FDP concentrations were found than in controls (p <0.05). Significant correlations were found between PPK and fructosamine levels in all diabetic patients (R(S)=+0.57 p <0.001), in diabetic patients without retinopathy (R(S)=+0.61, p <0.05), and in diabetic patients with retinopathy (R(S)=+0.62, p <0.005). We found negative correlation between PPK concentration and PTT (R(S)=-0.43, p <0.001) and positive correlation between PPK concentration and FET (R(S)=+0.59, p <0.00001) in the entire study group.

CONCLUSIONS

The occurrence of diabetic retinopathy is connected with higher levels of plasma prekallikrein.

Increased plasma markers of inflammation and endothelial dysfunction and their association with microvascular complications in Type 1 diabetic patients without clinically manifest macroangiopathy

AIMS

To evaluate whether plasma biomarkers of inflammation and endothelial dysfunction differed in Type 1 diabetic patients as compared with those in non-diabetic subjects, and to examine the association of these biomarkers with early stages of microvascular complications.

METHODS

Plasma biomarkers of inflammation [fibrinogen, hs-C-reactive protein (hs-CRP)] and endothelial dysfunction [von Willebrand factor (v-WF), intercellular adhesion molecule-1, plasminogen activator inhibitor-1 (PAI-1) activity] were measured in 88 non-smoking young patients with Type 1 diabetes without clinical macrovascular disease and in 40 healthy controls.

RESULTS

Plasma levels of hs-CRP, fibrinogen, v-WF, soluble intracellular adhesion molecule-1 (sICAM-1) and PAI-1 activity were markedly higher (P < 0.01 or less) in Type 1 diabetic patients than in healthy controls; these results were essentially unchanged when healthy controls were compared with patients without complications. After stratification by microvascular complication status, plasma biomarkers of inflammation and endothelial dysfunction were significantly increased in those with more advanced disease compared with those with early complications or without complications, respectively. However, while the significant differences in these biomarkers were little affected by adjustment for sex, age, BMI and blood pressure values, they were totally abolished after additional adjustment for diabetes duration and glycaemic control.

CONCLUSIONS

These results indicate that in Type 1 diabetes there is a subclinical, chronic inflammation which is, at least partly, independent of clinically manifest macro- and microvascular complications, smoking or other traditional cardiovascular risk factors; this subclinical inflammation is closely correlated to the magnitude and duration of hyperglycaemia.

Vascular complications in diabetes mellitus: the role of endothelial dysfunction

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

Pharmacodynamics of L-NMMA in type 1 diabetes patients and control subjects

RATIONALE

L-NMMA is widely used in venous occlusion plethysmography studies to determine baseline NO production. Studies using L-NMMA indicate that endothelial dysfunction is present early in the course of diabetic microvascular complications. However, the optimal dose to maximally inhibit NO-production is unknown.

OBJECTIVE

To determine the L-NMMA-dose that maximally reduces basal forearm blood flow (FBF). To investigate whether there are any differences in the response to L-NMMA between non-complicated type 1 diabetes patients and control subjects.

METHODS

In eight non-complicated type 1 diabetes patients and nine healthy subjects FBF-responses to intra-arterial infusion of increasing doses of L-NMMA (0.01-1.6 mg/min/dL forearm volume [FAV]) were measured using the perfused forearm technique.

RESULTS

Infusion of 0.8 mg/min/dL maximally reduced FBF. The dose of 1.6 mg/min/dL did not additionally reduce FBF. No differences existed between non-complicated type 1 diabetes patients and controls with regard to EC50 (0.017 +/- 0.02 resp. 0.22 +/- 0.02 mg L-NMMA/min/dL) or maximal vasoconstrictive response (Delta FBF: 1.13 +/- 0.4 resp. 0.97 +/- 0.4 mL/min/dL). Throughout the study blood pressure increased significantly in both groups, possibly reflecting a systemic vasoconstrictive effect of L-NMMA.

CONCLUSIONS

The maximal vasoconstrictive dose was 0.8 mg/min/dL in type 1 diabetes patients as well as the control subjects. There were no significant differences between non-complicated type 1 diabetes subjects and controls with regard to the pharmacodynamics of L-NMMA. At high dosages of L-NMMA a systemic effect can not be ruled out.

Reduced forearm reactive hyperaemia in normoalbuminuric subjects with Type 1 diabetes and retinopathy

AIM

To determine whether the forearm vasodilatory response to reactive hyperaemia (RH) is reduced in normoalbuminuric subjects with Type 1 diabetes mellitus and retinopathy compared with subjects with no retinopathy.

METHODS

Forearm RH, an indicator of endothelial function, was measured, using strain-gauge plethysmography, in 39 normoalbuminuric subjects (22 with retinopathy) with long-standing Type 1 diabetes mellitus.

RESULTS

were evaluated in relation to conventional risk factors for atherosclerosis, and C-reactive protein (CRP), which we have recently determined to be an independent correlate of forearm RH.

RESULTS

Forearm RH was decreased in subjects with retinopathy compared with those with no retinopathy (219 +/- 182 vs. 473 +/- 355, P < 0.01). Both retinopathy and CRP proved to be independent and negative predictors, and explain 27% of the variance, in forearm RH.

CONCLUSION

Retinopathy in subjects with Type 1 diabetes mellitus may reflect a generalized process of endothelial dysfunction, even in the absence of microalbuminuria.

Insulin resistance and the endothelium

There is increasing evidence of a parallel progression between insulin resistance and endothelial dysfunction, suggesting a close association between insulin action and the endothelium. Numerous studies have demonstrated that endothelial dysfunction occurs early in the insulin-resistant state and is predictive of future cardiovascular events. Similarly, insulin resistance has been associated with the metabolic syndrome, which also increases the risk of adverse cardiovascular outcomes. Approaches that improve endothelial dysfunction, such as treatment with statins, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, or peroxisome proliferator-activated receptor gamma ligands, have been shown to prevent both diabetes and cardiovascular disease. This article reviews the relation between endothelial dysfunction and cardiovascular disease, assesses the endothelium in the spectrum of insulin resistance, and examines the effect of the thiazolidinediones on endothelial function.

Effect of Grape Seed Extract and Quercetin on Cardiovascular and Endothelial Parameters in High-Risk Subjects

Grape seed extract (GSE) has in vitro antioxidant activity but whether or not it works in vivo is not clear. In a fully randomised, crossover trial with 4-week treatment periods on 36 men and women with above-average vascular risk, we aimed to demonstrate that 2 g/day of GSE (1 g of polyphenols) alone, or with 1 g/day of added quercetin in yoghurt, favourably alters vascular function, endothelial function, and degree of oxidative damage in comparison to a control yoghurt. GSE alone improved flow-mediated dilatation determined ultrasonically by an absolute $1.1$ % compared with control. There was no effect of the combination of GSE with quercetin. No other blood or urine measure was altered. Thus sufficient polyphenols from GSE appear to be absorbed to influence endothelial nitric oxide production, and GSE has the potential to favourably influence vascular function.

Diabetes and Vascular Disease

The incidence of diabetes is on the rise; most of this increase is accounted for by type 2 diabetes and is secondary to the growing prevalence of obesity. Most of the late complications of both type 1 and type 2 diabetes are secondary to microvascular and macrovascular complications. Microvascular complications include retinopathy, neuropathy, and nephropathy. Nephropathy is strongly linked to the complications of macrovascular disease, which include cardiovascular, cerebrovascular, and peripheral vascular disease. Hence, once microalbuminuria (an early marker of nephropathy) is present, the patient is at a greater risk of cardiovascular disease and other microvascular complications, including retinopathy. A number of cellular mechanisms are altered secondary to hyperglycemia, and recently, a common pathway linking these mechanisms has been proposed, ultimately leading to oxidative damage and thus end-organ or tissue damage. Due to the increased risk of vascular complications, many diabetic patients undergo surgical procedures, including revascularization and bypass. Recent studies have highlighted the importance of strict glycemic control during the perioperative and postoperative period, even in the nondiabetic patient. The results of these studies have shown a decrease in morbidity, mortality, and hospital stay with strict glycemic control. Glycemic control has been directly linked to decreased microvascular complications. Macrovascular disease, however, has not been clearly linked to glucose levels alone, and although it certainly plays a role, other components of the metabolic syndrome, including blood pressure and lipid status, are equally important.

Insulin resistance and endothelial dysfunction

Insulin has multiple metabolic actions, including effects on blood vessels. Insulin normally increases blood flow by a mechanism which involves generation of nitric oxide (NO) via the arginine-NO pathway. Although insulin itself is a weak and physiologically unimportant vasodilatator, it appears to markedly potentiate endothelium-dependent vasodilatation. Therefore, anything that impairs insulin action in endothelial cells can be expected to be associated with endothelial dysfunction, i.e. loss of NO bioactivity in the vessel wall. Consistent with the idea that insulin resistance and endothelial dysfunction frequently coexist, all insulin-resistant conditions examined to date have been associated with endothelial dysfunction. However, the latter can also be caused by factors other than insulin resistance-such as a high concentration of low-density lipoprotein (LDL) cholesterol. Therapies which reverse insulin resistance-such as exercise, insulin and inhibitors of the renin-angiotensin-aldosterone (RAA) axis-also reverse endothelial dysfunction, which may thus be an inherent feature of insulin resistance.

The ocular hemodynamic response to nitric oxide synthase inhibition is unaltered in patients with early type I diabetes

BACKGROUND

An impaired ocular hemodynamic response to systemic nitric oxide synthesis inhibition has been demonstrated in patients with long-standing insulin-dependent diabetes mellitus. It is unclear whether this altered responsiveness is already detectable in early uncomplicated type I diabetes.

METHODS

The effect of the nitric oxide synthase inhibitor N(G)-monomethyl- l-arginine (L-NMMA) was studied in 10 male patients with early type I diabetes under euglycemic conditions and 10 healthy matched control subjects in a single (analyst) blinded cohort study design. Changes in ocular hemodynamics (fundus pulsation amplitude, mean flow velocity in the ophthalmic artery) and in pulse rate and mean blood pressure were measured in response to systemic intravenous doses of 1.5, 3, and 6 mg/kg L-NMMA.

RESULTS

L-NMMA dose-dependently and significantly decreased fundus pulsation amplitude (-21.0% vs -23.3% in diabetics and controls, respectively), mean flow velocity in the ophthalmic artery (-12.3% vs -10.8%) and pulse rate (-15.4% vs -16.6%) and increased mean arterial pressure (+19.5% vs +14.7%). The ocular and systemic hemodynamic effects of L-NMMA were not different between patients with diabetes and controls.

CONCLUSION

The responsiveness of the choroidal vasculature and the ophthalmic artery to L-NMMA is not altered in early type 1 diabetes. An impaired hemodynamic response to nitric oxide synthesis inhibition in diabetes is therefore not caused by a primary defect but rather due to altered vascular responsiveness secondary to long-standing disease.

von Willebrand factor and its propeptide in children with diabetes. Relation between endothelial dysfunction and microalbuminuria

It has been shown that patients with insulin-dependent diabetes mellitus have elevated von Willebrand factor (vWF) plasma concentrations. Plasma fibrinogen, vWF, and its propeptide concentrations have been evaluated in 102 children with insulin-dependent diabetes mellitus to determine whether an increase of vWF and its propeptide levels precedes and may predict the development of persistent microalbuminuria. The patients have been divided into two groups according to the presence or absence of microalbuminuria at the end of follow-up. They have been followed up for at least 8 y. Control group consisted of 80 age- and sex-matched healthy volunteers. At the beginning of the study there was no significant difference in fibrinogen, vWF, and its propeptide levels between patients and control subjects. During the follow-up, a significant increase of plasma vWF and its propeptide has been observed in the group of patients who later developed microalbuminuria but not in those who remained normoalbuminuric. This increase started 3 y and become statistically significant (p < 0.01) 2 y before the onset of microalbuminuria, persisting until the end of the study. During the entire follow-up plasma values of fibrinogen persisted in the normal range. In conclusion, an increase in plasma concentration of vWF and its propeptide precedes microalbuminuria and, therefore, can be useful to identify children with insulin-dependent diabetes mellitus at risk to develop incipient nephropathy later in life.

Tissue factor pathway inhibitor (TFPI) release after heparin stimulation is increased in Type 1 diabetic patients with albuminuria

AIMS

To study heparin-stimulated TFPI release in relation to complications in Type 1 diabetic patients.

SUBJECTS AND METHODS

Nineteen uncomplicated Type 1 diabetic patients (group I) were compared with 18 patients with retinopathy (group II), and nine patients with retinopathy and albuminuria (group III). Blood samples were taken before (basal) and till 30 min after 5000 IU of heparin i.v. (post-heparin). TFPI activity was measured chromogenically. Von Willebrand factor, tissue plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1) and thrombomodulin were also measured.

RESULTS

Basal TFPI activity was higher in group III (121 +/- 10%) compared with group II (111 +/- 8%) or group I (110 +/- 13%) (P < 0.05), and strongly correlated with albuminuria (r = 0.66, P < 0.05). At all time points after heparin administration, TFPI activity in group III was significantly higher than in group I. TFPI activity was also higher in group III than in group II 5-30 min post-heparin. The increase in post-heparin TFPI activity, measured as the incremental area under the curve, was higher in group III compared with group I (65 +/- 7 vs. 59 +/- 4; P < 0.05). Of the other parameters, only thrombomodulin was higher in group III (44 +/- 24 vs. 26 +/- 7 (group II) and 28 +/- 9 ng/ml (group I); P < 0.01).

CONCLUSIONS

We conclude that basal and post-heparin TFPI activity is increased in albuminuric patients. The increase in heparin-stimulated TFPI release in patients with albuminuria is higher than in patients with retinopathy or without complications. This could be the result of altered endothelial glycosaminoglycan characteristics.

Effects of chronic administration of L-arginine on vasoactive responses induced by endothelin-1 and its plasma level in streptozotocin-induced diabetic rats

To investigate the mechanism underlying increased endothelin-1 (ET-1) release in diabetic rats, we administered L-arginine chronically to streptozotocin (STZ)-induced diabetic rats. The plasma concentrations of glucose, ET-1 and NOx (NO2- + NO3-) were all significantly raised at 10 weeks after the STZ injection. Chronic administration of L-arginine resulted in a significantly higher plasma NOx concentration and a significantly lower plasma ET-1 level at 10 weeks compared with the untreated diabetic group. ET-1 induced a biphasic vasodilator/vasoconstrictor response in the perfused isolated mesenteric arterial beds from all groups. The vasodilatation was significantly greater in diabetic rats than in age-matched controls. Chronic oral L-arginine administration had no significant effect on the enhanced ET-1-induced vasodilatation seen in the untreated diabetic rats. The vasoconstrictions induced by ET-1 and methoxamine were significantly attenuated in STZ-diabetic rats. The attenuated vasoconstrictor response to ET-1, but not that to methoxamine, was further attenuated by chronic treatment with L-arginine. We conclude that since chronic L-arginine administration not only reduced the increase in plasma ET-1 levels but also further attenuated the ET-1-induced vasoconstriction without affecting the change in vasodilatation, chronic L-arginine administration could be valuable for the treatment of the symptoms of diabetic mellitus related to ET-1.

Type 1 and type 2 diabetic patients display different patterns of cellular microparticles

The development of vasculopathies in diabetes involves multifactorial processes including pathological activation of vascular cells. Release of microparticles by activated cells has been reported in diseases associated with thrombotic risk, but few data are available in diabetes. The aim of the present work was to explore the number and the procoagulant activity of cell-derived microparticles in type 1 and 2 diabetic patients. Compared with age-matched control subjects, type 1 diabetic patients presented significantly higher numbers of platelet and endothelial microparticles (PMP and EMP), total annexin V-positive blood cell microparticles (TMP), and increased levels of TMP-associated procoagulant activity. In type 2 diabetic patients, only TMP levels were significantly higher without concomitant increase of their procoagulant activity. Interestingly, in type 1 diabetic patients, TMP procoagulant activity was correlated with HbA(1c), suggesting that procoagulant activity is associated with glucose imbalance. These results showed that a wide vesiculation process, resulting from activation or apoptosis of several cell types, occurs in diabetes. However, diabetic patients differ by the procoagulant activity and the cellular origin of microparticles. In type 1 diabetic patients, TMP-procoagulant activity could be involved in vascular complications. Moreover, its correlation with HbA(1c) reinforces the importance of an optimal glycemic control in type 1 diabetes.

Vascular reactivity in diabetes mellitus

Cardiovascular disease is responsible for 70% of the deaths in diabetes mellitus. Endothelial dysfunction occurs early in atherosclerosis and can now be assessed accurately and reproducibly by noninvasive means. Hyperglycemia, insulin resistance, microvascular complications, and coexistent conditions have been shown to impair endothelial function in diabetes. Resistance to insulin's vasodilatory effect and increased free radical generation are probable mechanisms responsible for the endothelial dysfunction in this state. Improvement in glycemic control, insulin and insulin sensitizers, cholesterol lowering, hypolipidemic agents, angiotensin-converting enzyme inhibitors, and angiotensin II receptor blockers have improved clinical cardiovascular outcomes and have also been shown to improve endothelial function. Strategies designed to assess and improve endothelial function may be further beneficial in terms of cardiovascular outcomes in diabetes mellitus, and need to be tested in a clinical setting.