Improvement in endothelial function by angiotensin-converting enzyme inhibition in non-insulin-dependent diabetes mellitus

Association between atherogenic risk-modulating proteins and endothelium-dependent flow-mediated dilation in coronary artery disease patients

PURPOSE

Endothelial dysfunction is an early and integral event in the development of atherosclerosis and coronary artery disease (CAD). Reduced NO bioavailability, oxidative stress, vasoconstriction, inflammation and senescence are all implicated in endothelial dysfunction. However, there are limited data examining associations between these pathways and direct in vivo bioassay measures of endothelial function in CAD patients. This study aimed to examine the relationships between in vivo measures of vascular function and the expression of atherogenic risk-modulating proteins in endothelial cells (ECs) isolated from the radial artery of CAD patients.

METHODS

Fifty-six patients with established CAD underwent trans-radial catheterization. Prior to catheterization, radial artery vascular function was assessed using a) flow-mediated dilation (FMD), and b) exercise-induced dilation in response to handgrip (HE%). Freshly isolated ECs were obtained from the radial artery during catheterization and protein content of eNOS, NAD(P)H oxidase subunit NOX2, NFκB, ET-1 and the senescence markers p53, p21 and p16 were evaluated alongside nitrotyrosine abundance and eNOS Ser¹¹⁷⁷ phosphorylation.

RESULTS

FMD was positively associated with eNOS Ser¹¹⁷⁷ phosphorylation (r = 0.290, P = 0.037), and protein content of p21 (r = 0.307, P = 0.027) and p16 (r = 0.426, P = 0.002). No associations were found between FMD and markers of oxidative stress, vasoconstriction or inflammation. In contrast to FMD, HE% was not associated with any of the EC proteins.

CONCLUSION

These data revealed a difference in the regulation of endothelium-dependent vasodilation measured in vivo between patients with CAD compared to previously reported data in subjects without a clinical diagnosis, suggesting that eNOS Ser¹¹⁷⁷ phosphorylation may be the key to maintain vasodilation in CAD patients.

Endothelium dysfunction in hind limb arteries of male Zucker Diabetic-Sprague Dawley rats

Endothelium dysfunction produces peripheral vascular disease comorbidities in type 2 diabetes, including hypertension, and critical limb ischemia. In this study we aimed to test endothelial dysfunction, the vasodilator effects of a proteinase-activated receptor 2 (PAR2) agonist (2fLIGRLO), and thromboxane A₂ synthase inhibitor (ozagrel) on PAR2 vasodilation in hind limb arteries ex vivo, using Zucker Diabetic-Sprague Dawley (ZDSD) rats, a model of type 2 diabetes. Male Sprague Dawley rats (SD) and ZDSD were fed a high-fat content 'Western diet' from 16 to 20 weeks of age (wks) then fed a standard laboratory diet. We identified diabetic ZDSD rats by two consecutive blood glucose measurements > 12.5 mM, based on weekly monitoring. We used acetylcholine, 2fLIGRLO, and nitroprusside with wire-myograph methods to compare relaxations of femoral, and saphenous arteries from diabetic ZDSD (21-23 wks) to age-matched normoglycemic SD. All arteries showed evidence of endothelium dysfunction using acetylcholine (reduced maximum relaxations, reduced sensitivity), and higher sensitivities to 2fLIGRLO, and nitroprusside in ZDSD vs SD. Ozagrel treatment of ZDSD distal segments, and end-branches of saphenous arteries decreased their sensitivities to 2fLIGRLO. We tested aortas for altered expression of endothelium-specific gene targets using PCR array and qPCR. PAR2, and placental growth factor gene transcripts were 1.5, and 4-times higher in ZDSD than SD aortas. Hind limb arteries of ZDSD exhibit endothelium dysfunction having less GPCR agonist induced vasodilation by endothelial NO-release. Different expression of several endothelial genes in ZDSD vs SD aortas, including PAR2, suggests altered inflammatory, and angiogenesis signaling pathways in the endothelium of ZDSD.

The Role of Endothelial Cells in the Onset, Development and Modulation of Vein Graft Disease

Endothelial cells comprise the intimal layer of the vasculature, playing a crucial role in facilitating and regulating aspects such nutrient transport, vascular homeostasis, and inflammatory response. Given the importance of these cells in maintaining a healthy haemodynamic environment, dysfunction of the endothelium is central to a host of vascular diseases and is a key predictor of cardiovascular risk. Of note, endothelial dysfunction is believed to be a key driver for vein graft disease-a pathology in which vein grafts utilised in coronary artery bypass graft surgery develop intimal hyperplasia and accelerated atherosclerosis, resulting in poor long-term patency rates. Activation and denudation of the endothelium following surgical trauma and implantation of the graft encourage a host of immune, inflammatory, and cellular differentiation responses that risk driving the graft to failure. This review aims to provide an overview of the current working knowledge regarding the role of endothelial cells in the onset, development, and modulation of vein graft disease, as well as addressing current surgical and medical management approaches which aim to beneficially modulate endothelial function and improve patient outcomes.

Plasma levels of Asymmetric Di Methyl Arginine and endothelial dysfunction in diabetic subjects with neuropathic foot ulcer

OBJECTIVE

Asymmetric dimethyl arginine (ADMA) is an amino acid that acts as an endogenous competitive inhibitor of Nitric oxide synthase, leading to endothelial dysfunction (ED). The aim of this study was to evaluate the relationship between plasma ADMA (p-ADMA) level and ED in diabetic subjects with neuropathic foot ulcer (NFU), and the possible predictors of p-ADMA level.

MATERIALS AND METHODS

80 diabetic subjects of matched age, sex and BMI were included; 40 with NFU (G1), 20 with peripheral nerve dysfunction (PND) (G2) and 20 without PND (G3), plus 20 matched healthy subjects (G4). Flow-mediated-dilatation (FMD) of brachial artery and Carotid-intima-media-thickness (CIMT) were measured to evaluate ED and subclinical atherosclerosis, respectively.

RESULTS

G1&2 had a significantly lower FMD than G3&4 [-5.09 (-22.5 to 22.92), 4.67 (-15 to 23.91) vs. 15.74 (8.33-36.59) and 20.1 (10.0-46.15)%, respectively] (p < 0.001), and higher CIMT [0.9 (0.6-1.5), 0.9 (0.6-1.3) vs. 0.6 (0.5-0.8) and 0.7 (0.5-0.9) cm, respectively] (p < 0.001, r = 0.237, p = 0.034, r = 0.330, p = 0.003, respectively), with no significant correlation with FMD (r = -0.176, p = 0.118). FMD was inversely and strongly related to CIMT (r = -0.520, p < 0.001). p-ADMA levels were significantly higher in uncontrolled hypertensive patients in comparison to controlled and normotensive subjects [717 (286-3611) vs. 648 (335-874) and 686 (526-857) ng/L, respectively] (p = 0.026). Metformin users and hypertensive subjects on ACEIs or ARBs had the lowest p-ADMA levels than the non-users (p < 0.001, p = 0.007, respectively).

CONCLUSION

The remarkable ED in diabetic subjects with NFU is unlikely to be due to alteration in p-ADMA. Further studies are needed in order to conclude a causal association between p-ADMA and ED in this group of patients.

Redox Signaling and Regional Heterogeneity of Endothelial Dysfunction in db/db Mice

The variable nature of vascular dysfunction in diabetes is not well understood. We explored the functional adaptation of different arteries in db/db mice in relation to increased severity and duration of diabetes. We compared endothelium-dependent and -independent vasodilation in the aortae, as well as the carotid and femoral arteries, of db/db mice at three ages in parallel with increased body weight, oxidative stress, and deterioration of glycemic control. Vascular responses to in vitro generation of reactive oxygen species (ROS) and expression of superoxide dismutase (SOD) isoforms were assessed. There was a progressive impairment of endothelium-dependent and -independent vasorelaxation in the aortae of db/db mice. The carotid artery was resistant to the effects of in vivo and in vitro induced oxidative stress, and it maintained unaltered vasodilatory responses, likely because the carotid artery relaxed in response to ROS. The femoral artery was more reliant on dilation mediated by endothelium-dependent hyperpolarizing factor(s), which was reduced in db/db mice at the earliest age examined and did not deteriorate with age. Substantial heterogeneity exists between the three arteries in signaling pathways and protein expression of SODs under physiological and diabetic conditions. A better understanding of vascular heterogeneity will help develop novel therapeutic approaches for targeted vascular treatments, including blood vessel replacement.

Assessment of resistance vessel function in human skeletal muscle: guidelines for experimental design, Doppler ultrasound, and pharmacology

The introduction of duplex Doppler ultrasound almost half a century ago signified a revolutionary advance in the ability to assess limb blood flow in humans. It is now widely used to assess blood flow under a variety of experimental conditions to study skeletal muscle resistance vessel function. Despite its pervasive adoption, there is substantial variability between studies in relation to experimental protocols, procedures for data analysis, and interpretation of findings. This guideline results from a collegial discussion among physiologists and pharmacologists, with the goal of providing general as well as specific recommendations regarding the conduct of human studies involving Doppler ultrasound-based measures of resistance vessel function in skeletal muscle. Indeed, the focus is on methods used to assess resistance vessel function and not upstream conduit artery function (i.e., macrovasculature), which has been expertly reviewed elsewhere. In particular, we address topics related to experimental design, data collection, and signal processing as well as review common procedures used to assess resistance vessel function, including postocclusive reactive hyperemia, passive limb movement, acute single limb exercise, and pharmacological interventions.

Angiotensin II-induced redox-sensitive SGLT1 and 2 expression promotes high glucose-induced endothelial cell senescence

High glucose (HG)-induced endothelial senescence and dysfunction contribute to the increased cardiovascular risk in diabetes. Empagliflozin, a selective sodium glucose co-transporter2 (SGLT2) inhibitor, reduced the risk of cardiovascular mortality in type 2 diabetic patients but the protective mechanism remains unclear. This study examines the role of SGLT2 in HG-induced endothelial senescence and dysfunction. Porcine coronary artery cultured endothelial cells (ECs) or segments were exposed to HG (25 mmol/L) before determination of senescence-associated beta-galactosidase activity, protein level by Western blot and immunofluorescence staining, mRNA by RT-PCR, nitric oxide (NO) by electron paramagnetic resonance, oxidative stress using dihydroethidium and glucose uptake using 2-NBD-glucose. HG increased ECs senescence markers and oxidative stress, down-regulated eNOS expression and NO formation, and induced the expression of VCAM-1, tissue factor, and the local angiotensin system, all these effects were prevented by empagliflozin. Empagliflozin and LX-4211 (dual SGLT1/2 inhibitor) reduced glucose uptake stimulated by HG and H₂ O₂ in ECs. HG increased SGLT1 and 2 protein levels in cultured ECs and native endothelium. Inhibition of the angiotensin system prevented HG-induced ECs senescence and SGLT1 and 2 expression. Thus, HG-induced ECs ageing is driven by the local angiotensin system via the redox-sensitive up-regulation of SGLT1 and 2, and, in turn, enhanced glucotoxicity.

Effects of Catheterization on Artery Function and Health: When Should Patients Start Exercising Following Their Coronary Intervention?

Coronary artery disease (CAD) is a leading cause of death worldwide, and percutaneous transluminal coronary angiography (PTCA) and/or percutaneous coronary intervention (PCI; angioplasty) are commonly used to diagnose and/or treat the obstructed coronaries. Exercise-based rehabilitation is recommended for all CAD patients; however, most guidelines do not specify when exercise training should commence following PTCA and/or PCI. Catheterization can result in arterial dysfunction and acute injury, and given the fact that exercise, particularly at higher intensities, is associated with elevated inflammatory and oxidative stress, endothelial dysfunction and a pro-thrombotic milieu, performing exercise post-PTCA/PCI may transiently elevate the risk of cardiac events. This review aims to summarize extant literature relating to the impacts of coronary interventions on arterial function, including the time-course of recovery and the potential deleterious and/or beneficial impacts of acute versus long-term exercise. The current literature suggests that arterial dysfunction induced by catheterization recovers 4-12 weeks following catheterization. This review proposes that a period of relative arterial vulnerability may exist and exercise during this period may contribute to elevated event susceptibility. We therefore suggest that CAD patients start an exercise training programme between 2 and 4 weeks post-PCI, recognizing that the literature suggest there is a 'grey area' for functional recovery between 2 and 12 weeks post-catheterization. The timing of exercise onset should take into consideration the individual characteristics of patients (age, severity of disease, comorbidities) and the intensity, frequency and duration of the exercise prescription.

Association of central blood pressure and cardiovascular diseases in diabetic patients with hypertension

To evaluate association of central blood pressure (BP) and cardiovascular disease (CVD) in diabetic patients with hypertension.This was a cross-section study and 360 participants were enrolled. Baseline characteristics were collected and indices of central BP including central systolic/diastolic BP (SBP/DBP), augmentation index adjusted for 75 beats per minute of heart rate (AIx@75) were measured. Participants were separated into with and without CVD groups and between-group differences were assessed. Linear regression analysis was used to evaluate potential risk factors for increased AIx@75. Logistic regression analysis was used to evaluate association between central SBP and AIx@75 with CVD.Mean age was 50.6 years and male participants accounted for 57.8%. Thirty-five and 43 participants had coronary heart disease and ischemic stroke. Compared with participants without CVD, those with CVD were more likely to be male and smokers and had higher glycated hemoglobin level. Additionally, participants with CVD had significantly higher central SBP and AIx@75 compared with those without CVD. Ageing, male gender, and presence of coronary heart disease and ischemic stroke were associated with increased AIx@75, whereas renin-angiotensin-axis inhibitor was associated with reduced AIx@75. After adjusted for traditional risk factors including brachial SBP, both central SBP, and AIx@75 remained significantly associated with CVD, with odds ratio and 95% confidence interval of 1.09 (1.08-1.31) and 1.20 (1.15-1.42), respectively.Diabetic patients with hypertension, ageing, male gender, and presence of CVD are independent risk factors of central BP increase; and increased central SBP and AIx@75 are significantly associated with CVD.

Review: Type 2 diabetes — implications for macrovascular mechanics and disease

Before macrovascular disease is established, type 2 diabetes is associated with structural and functional changes in large arteries that lead to increased stiffness, abnormal pulse wave travel and systolic hypertension. Structural changes result mainly from glycation of wall components. Functional changes originate in endothelial dysfunction. Increased arterial stiffness, or decreased arterial distensibility, increases pulse wave velocity and the amplitude of reflected waves, so that reflected waves arrive early and augment central systolic pressure. This promotes the development of left ventricular hypertrophy, an independent risk factor for cardiovascular mortality. One of the major mechanisms of arterial stiffening is endothelial dysfunction with reduced nitric oxide (NO)-mediated vasodilatation, the initial lesion in pre-atherosclerotic diabetes. To understand better the mechanisms of endothelial dysfunction will be vital if future therapeutic interventions are targeted to disease prevention. Protein glycation in poorly controlled diabetes is also damaging to blood vessels and must be limited by good diabetic control over the longer term.

Review: The pathogenesis of type 2 diabetes and cardiovascular disease

Type 2 diabetes mellitus is increasing in prevalence, and is a potent risk factor for the development of atherosclerotic vascular disease and increased risk of adverse cardiovascular events. Approximately 15—25% of patients presenting with ischaemic heart disease have a history of diabetes mellitus. This cohort of patients continues to be at heightened short and long-term risk. This review highlights the many proposed biological drivers that likely play a deterministic role in the cardiovascular outcome of patients with type 2 diabetes mellitus.

Endothelial dysfunction and coronary artery disease: a state of the art review. Cardiol Rev. 2015;23:119-129. [PMID: 25420051 DOI: 10.1097/crd.0000000000000047]

Atherosclerotic coronary artery disease (CAD) is a major cause of morbidity and mortality in the developed world. Endothelial dysfunction plays an important role in the development of atherosclerosis and predicts cardiovascular (CV) outcomes independent of conventional CV risk factors. In recent years, there have been tremendous improvements in the pharmacological prevention and management of CAD. In this review, the pathophysiology of endothelial dysfunction in relation to CAD is discussed and various techniques of invasive and noninvasive assessments of peripheral and coronary endothelial function described. In addition, evidence for the association of endothelial dysfunction and CV outcomes has been examined and finally the role of therapeutic interventions in endothelial dysfunction has been discussed.

Stability of murine bradykinin type 2 receptor despite treatment with NO, bradykinin, icatibant, or C1-INH

BACKGROUND

Little is known about factors which trigger and/or contribute to hereditary angioedema or ACE-inhibitor-mediated angioedema including variations in bradykinin type 2 receptor (B2R) expression and activity.

METHODS

Protein and mRNA expression of B2R and the increase of intracellular calcium (iCa) in response to bradykinin were monitored in porcine and murine endothelial cells in response to NO donors or bradykinin. B2R protein expression was evaluated in skin, heart, and lung of (i) mice with endothelial-specific overexpression of eNOS (eNOS(tg) ), (ii) in eNOS(-/-) mice and (iii) in C57BL/6 mice treated with the NO donor pentaerythritol tetranitrate (PETN), the NOS inhibitor l-nitroarginine (L-NA), plasma pool C1-INH, and the B2R antagonist icatibant. Aortic reactivity to bradykinin was investigated including eNOS(-/-) mice.

RESULTS

B2R protein and mRNA expression remained unchanged in cells subjected to L-NA, NO donors, and bradykinin in a time- and concentration-dependent manner. Likewise, increases of iCa in murine brain endothelial cells remained unchanged. B2R protein levels were similar in eNOS(tg) and eNOS(-/-) as compared to transgene-negative littermates. Likewise, treatment of C57BL/6 mice with PETN, L-NA, C1-INH or icatibant did not change B2R protein expression. In aortic rings of C57BL/6 mice, bradykinin induced B2R-dependent constrictions which were attenuated by endothelial NO and abolished by diclofenac indicating the functional importance of B2R-induced activation of endothelial NO synthase and cyclooxygenase.

CONCLUSION

These data suggest that alterations of B2R protein expression induced by NO, bradykinin, C1-INH, or icatibant unlikely contribute to bradykinin-induced angioedema. This finding does not rule out a role for NO in bradykinin-induced extravasation and/or angioedema.

Endothelial dysfunction in conduit arteries and in microcirculation. Novel therapeutic approaches

The vascular endothelium not only is a single monolayer of cells between the vessel lumen and the intimal wall, but also plays an important role by controlling vascular function and structure mainly via the production of nitric oxide (NO). The so called "cardiovascular risk factors" are associated with endothelial dysfunction, that reduces NO bioavailability, increases oxidative stress, and promotes inflammation contributing therefore to the development of atherosclerosis. The significant role of endothelial dysfunction in the development of atherosclerosis emphasizes the need for efficient therapeutic interventions. During the last years statins, angiotensin-converting enzyme inhibitors, angiotensin-receptor antagonists, antioxidants, beta-blockers and insulin sensitizers have been evaluated for their ability to restore endothelial function (Briasoulis et al., 2012). As there is not a straightforward relationship between therapeutic interventions and improvement of endothelial function but rather a complicated interrelationship between multiple cellular and sub-cellular targets, research has been focused on the understanding of the underlying mechanisms. Moreover, the development of novel diagnostic invasive and non-invasive methods has allowed the early detection of endothelial dysfunction expanding the role of therapeutic interventions and our knowledge. In the current review we present the available data concerning the contribution of endothelial dysfunction to atherogenesis and review the methods that assess endothelial function with a view to understand the multiple targets of therapeutic interventions. Finally we focus on the classic and novel therapeutic approaches aiming to improve endothelial dysfunction and the underlying mechanisms.

Effects of oral lycopene supplementation on vascular function in patients with cardiovascular disease and healthy volunteers: a randomised controlled trial

AIMS

The mechanisms by which a 'Mediterranean diet' reduces cardiovascular disease (CVD) burden remain poorly understood. Lycopene is a potent antioxidant found in such diets with evidence suggesting beneficial effects. We wished to investigate the effects of lycopene on the vasculature in CVD patients and separately, in healthy volunteers (HV).

METHODS AND RESULTS

We randomised 36 statin treated CVD patients and 36 healthy volunteers in a 2∶1 treatment allocation ratio to either 7 mg lycopene or placebo daily for 2 months in a double-blind trial. Forearm responses to intra-arterial infusions of acetylcholine (endothelium-dependent vasodilatation; EDV), sodium nitroprusside (endothelium-independent vasodilatation; EIDV), and NG-monomethyl-L-arginine (basal nitric oxide (NO) synthase activity) were measured using venous plethysmography. A range of vascular and biochemical secondary endpoints were also explored. EDV in CVD patients post-lycopene improved by 53% (95% CI: +9% to +93%, P = 0.03 vs. placebo) without changes to EIDV, or basal NO responses. HVs did not show changes in EDV after lycopene treatment. Blood pressure, arterial stiffness, lipids and hsCRP levels were unchanged for lycopene vs. placebo treatment groups in the CVD arm as well as the HV arm. At baseline, CVD patients had impaired EDV compared with HV (30% lower; 95% CI: -45% to -10%, P = 0.008), despite lower LDL cholesterol (1.2 mmol/L lower, 95% CI: -1.6 to -0.9 mmol/L, P<0.001). Post-therapy EDV responses for lycopene-treated CVD patients were similar to HVs at baseline (2% lower, 95% CI: -30% to +30%, P = 0.85), also suggesting lycopene improved endothelial function.

CONCLUSIONS

Lycopene supplementation improves endothelial function in CVD patients on optimal secondary prevention, but not in HVs.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01100385.

Cross-section imaging with M-mode as an alternative method for the measurement of brachial artery flow-mediated vasodilation

PURPOSE

Endothelial dysfunction is well known as a risk marker for initiation and progression of atherosclerosis. Flow-mediated vasodilation (FMD) of the brachial artery induced by postischemic forearm hyperemia is a widely used noninvasive method for evaluating endothelial function. M-mode ultrasonography offers high spatial and temporal resolution and is therefore suitable for diameter measurement of pulsatile vessels. We intended to compare FMD values obtained by M-mode on cross-section images and by the conventional method, ie, measurement with B-mode ultrasonography on longitudinal images.

METHODS

We recruited 37 subjects (19 women, mean age: 48.3 ± 15.2 years; range: 23-71 years) in whom we measured the brachial artery diameters at baseline and at maximum dilation after forearm ischemia. FMD was calculated as the percentage of postischemic dilation.

RESULTS

Baseline (3.92 ± 0.72 versus 3.91 ± 0.58 mm; p = 0.97) and maximal dilated diastolic diameter (4.26 ± 0.76 versus 4.23 ± 0.61 mm; p = 0.84), FMD (8.98 ± 3.84 versus 8.14 ± 1.99%; p = 0.84), and time to maximum dilation (48.7 ± 9.0 versus 49.3 ± 6.4 seconds, p = 0.64) were not different between the two methods.

CONCLUSIONS

M-mode brachial artery diastolic and systolic diameter measurement is feasible, suitable, and accurate for the assessment of FMD without the need for electrocardiography.

Flow-Mediated Vasodilatation and Intima-Media Thickness in Patients with Coexisting Heart Failure and Diabetes Receiving Medical Therapy

Objective

Intensive medical treatment of heart failure (HF) patients with diabetes may reduce the endothelial dysfunction and the accelerated atherosclerotic process seen in these patients. To study this, we investigated the endothelial function and the presence of atherosclerosis as measured by flow-mediated vasodilatation (FMD) and intima-media thickness (IMT) in intensively treated patients with coexisting HF and diabetes.

Research Design and Method

FMD of the brachial artery and IMT of the common carotid arteries were determined in 26 patients with systolic HF and diabetes who were in intensive medical therapy, as well as in 19 healthy controls. The two groups were matched according to age and sex. In all subjects left ventricular ejection fraction was measured by two-dimensional echocardiography. Biochemical parameters including serum cholesterol, HDL and LDL, triglyceride, glucose, hemoglobin/hemoglobin-A1C (HbA1C), brain natriuretic peptide (BNP) and N-terminal pro-BNP were also assessed.

Results

Mean FMD and IMT did not differ significantly between patients and controls. Left ventricular ejection fraction was lower in patients compared to controls (P < 0.001). The patients had a higher mean BNP, NT pro-BNP, triglyceride, HbA1C and glucose in comparison to controls. Cholesterol, HDL-cholesterol and LDL-cholesterol were lower in patients compared to controls.

Conclusions

Intensively treated patients with coexisting systolic HF and diabetes seem to have normal endothelial function as measured by FMD and they have no sign of accelerated atherosclerosis as measured by IMT. This suggests a positive effect of medication on the cardiovascular alterations in this group of patients.

Targeting endothelial dysfunction in vascular complications associated with diabetes

Cardiovascular complications associated with diabetes remain a significant health issue in westernized societies. Overwhelming evidence from clinical and laboratory investigations have demonstrated that these cardiovascular complications are initiated by a dysfunctional vascular endothelium. Indeed, endothelial dysfunction is one of the key events that occur during diabetes, leading to the acceleration of cardiovascular mortality and morbidity. In a diabetic milieu, endothelial dysfunction occurs as a result of attenuated production of endothelial derived nitric oxide (EDNO) and augmented levels of reactive oxygen species (ROS). Thus, in this review, we discuss novel therapeutic targets that either upregulate EDNO production or increase antioxidant enzyme capacity in an effort to limit oxidative stress and restore endothelial function. In particular, endogenous signaling molecules that positively modulate EDNO synthesis and mimetics of endogenous antioxidant enzymes will be highlighted. Consequently, manipulation of these unique targets, either alone or in combination, may represent a novel strategy to confer vascular protection, with the ultimate goal of improved outcomes for diabetes-associated vascular complications.

Angiotensin II type 1 receptor-dependent oxidative stress mediates endothelial dysfunction in type 2 diabetic mice

The mechanisms underlying the effect of the renin-angiotensin-aldosterone system (RAAS) inhibition on endothelial dysfunction in type 2 diabetes are incompletely understood. This study explored a causal relationship between RAAS activation and oxidative stress involved in diabetes-associated endothelial dysfunction. Daily oral administration of valsartan or enalapril at 10 mg/kg/day to db/db mice for 6 weeks reversed the blunted acetylcholine-induced endothelium-dependent dilatations, suppressed the upregulated expression of angiotensin II type 1 receptor (AT(1)R) and NAD(P)H oxidase subunits (p22(phox) and p47(phox)), and reduced reactive oxygen species (ROS) production. Acute exposure to AT(1)R blocker losartan restored the impaired endothelium-dependent dilatations in aortas of db/db mice and also in renal arteries of diabetic patients (fasting plasma glucose level > or =7.0 mmol/l). Similar observations were also made with apocynin, diphenyliodonium, or tempol treatment in db/db mouse aortas. DHE fluorescence revealed an overproduction of ROS in db/db aortas which was sensitive to inhibition by losartan or ROS scavengers. Losartan also prevented the impairment of endothelium-dependent dilatations under hyperglycemic conditions that were accompanied by high ROS production. The present study has identified an initiative role of AT(1)R activation in mediating endothelial dysfunction of arteries from db/db mice and diabetic patients.

Chronic cyanosis and vascular function: implications for patients with cyanotic congenital heart disease

In patients with cyanotic congenital heart disease, chronic hypoxaemia leads to important changes in blood vessel function and structure. Some of these alterations are maladaptive and probably contribute to impaired cardiopulmonary performance and an increased incidence of thrombotic and embolic events. Recent evidence suggests that deranged endothelial function, a sequel of chronic cyanosis, could be an important factor in the pathogenesis of cyanosis-associated cardiovascular risk. In this article, we discuss the physiological and mechanical consequences of compensatory erythrocytosis and possible pathophysiological mechanisms of vascular dysfunction in chronic cyanosis.

Review: Endothelial cell dysfunction, medial arterial calcification and osteoprotegerin in diabetes

Macrovascular complications such as cardiovascular disease and peripheral vascular disease are the leading cause of increased mortality and morbidity, respectively, in patients with diabetes mellitus. The aetiopathogenesis of macrovasculopathy in diabetes is multifactorial and differs in types 1 and 2 diabetes. Endothelial cell dysfunction is an early feature of diabetic vasculopathy and is associated with poor glycaemic control. Chronic hyperglycaemia may promote an adverse vascular milieu leading to early endothelial cell apoptosis, in the long run. The presence of apoptotic cells in the vascular lumen may trigger a cascade of reactions between the promoters and inhibitors of arterial calcification. Medial arterial calcification, a characteristic feature of diabetes, is an important predictor of cardiovascular disease and occurs independently of atherosclerosis. Medial arterial calcification may occur in the presence of normal serum calcium and phosphate levels. Osteoprotegerin is an important modulator of mineral metabolism and manifests its effects in the bone and arteries. It is hypothesised that osteoprotegerin is a key inhibitor of arterial calcification which is released by endothelial cells as a protective measure for survival in adverse conditions. It is a potential risk marker for early identification and monitoring of disturbed mineral metabolism and vasculopathy in diabetes.

Endothelial dysfunction in diabetes mellitus: molecular mechanisms and clinical implications

Cardiovascular disease is a major complication of diabetes mellitus, and improved strategies for prevention and treatment are needed. Endothelial dysfunction contributes to the pathogenesis and clinical expression of atherosclerosis in diabetes mellitus. This article reviews the evidence linking endothelial dysfunction to human diabetes mellitus and experimental studies that investigated the responsible mechanisms. We then discuss the implications of these studies for current management and for new approaches for the prevention and treatment of cardiovascular disease in patients with diabetes mellitus.

Higher arterial stiffness, greater peripheral vascular resistance and lower blood flow in lower-leg arteries are associated with long-term hyperglycaemia in type 2 diabetic patients with normal ankle-brachial index

BACKGROUND

Higher arterial stiffness and greater peripheral vascular resistance reduce blood flow in lower-leg arteries and contribute to the development of ischaemic limb in diabetic patients even without peripheral artery occlusive disease. The aim of this study was to clarify whether these vascular parameters are associated with long-term hyperglycaemia in diabetic patients.

METHODS

We examined 45 type 2 diabetic patients and 38 age-matched nondiabetic subjects without peripheral artery occlusive disease assessed by ankle-brachial index consecutively admitted to our hospital, and followed them over a 3-year period (3.7 +/- 0.7 years) with no vasodilative medication. Blood flow and resistive index, a measure of peripheral vascular resistance, at the popliteal artery were evaluated using gated two-dimensional cine-mode phase-contrast magnetic resonance imaging. Brachial-ankle pulse wave velocity was measured to assess arterial stiffness.

RESULTS

At baseline, consistent with our previous report, diabetic patients showed higher brachial-ankle pulse wave velocity (p < 0.0001) and resistive index (p < 0.0001) and lower flow volume (p = 0.0044) than those of nondiabetic subjects. Stepwise multiple regression analysis revealed that duration of diabetes, mean HbA(1c) during the study, use of renin-angiotensin system inhibitors and change per year in resistive index were identified as significant independent variables predicting change per year in blood flow (r(2) = 0.733, p < 0.0001) in diabetic patients. Mean HbA(1c) during the study was positively correlated with changes per year in brachial-ankle pulse wave velocity (p = 0.00007) and resistive index (p = 0.0014) and was negatively correlated with that in blood flow (p < 0.0001) in diabetic patients.

CONCLUSIONS

Long-term hyperglycaemia is a major cause of impaired peripheral circulation in lower-leg arteries in diabetic patients without peripheral artery occlusive disease.

Ramipril improves oxidative stress-related vascular endothelial dysfunction in db/db mice

Endothelial dysfunction often precedes Type 2 diabetes-associated cardiovascular complications. One important cause of endothelial dysfunction is oxidative stress, which can lead to reduced nitric oxide (NO) bioavailability. In this study, we examined the effects of ramipril (an angiotensin-converting enzyme inhibitor, ACEI) on reactive oxygen species (ROS) production and endothelium-dependent vasodilation using a Type 2 diabetic (db/db) murine model. Plasma concentration of 8-isoprostane ([8-isoP]) was measured and used as an indication of the amount of ROS production. Six weeks of ramipril (10 mg/kg/day) treatment significantly reduced [8-isoP] and improved acetylcholine(ACh)-induced vasodilation in db/db mice without altering responses in wild-type (WT) mice. Responsiveness of smooth muscle cells to NO, assessed by sodium nitroprusside-induced vasodilation, was not different between db/db and WT mice regardless of ramipril or vehicle treatment. Our results suggest that ramipril specifically improved endothelium-dependent vasodilation in Type 2 diabetic mice, possibly by reducing ROS levels.

Short-term oral treatment with the angiotensin II receptor antagonist losartan does not improve coronary vasomotor function in asymptomatic type 2 diabetes patients

BACKGROUND

We have previously found that acute intravenous infusion of an ACE inhibitor normalized the reduced coronary vasomotor function in type 2 diabetes. The aim of the present study was to extend this investigation to an angiotensin II receptor blocker (ARB) administered orally in normotensive, asymptomatic type 2 diabetes patients without albuminuria.

RESULTS

Fourteen type 2 diabetes patients were included. Each patient had myocardial perfusion measured by PET at three occasions: at baseline, following 3 weeks of treatment with 50mg/d and following another 3 weeks of treatment with 100mg/d of losartan. Baseline myocardial perfusion was similar at all three sessions (0.89+/-0.05, 0.90+/-0.08 and 0.84+/-0.05mL/(ming) tissue, respectively). Likewise, maximal hyperaemic perfusion after i.v. dipyridamole (0.56mg/kg bwt) was low but similar at the three sessions (2.01+/-0.14, 2.05+/-0.17 and 1.90+/-0.20mL/(ming) tissue, respectively). Myocardial perfusion reserve, i.e. maximal hyperaemic flow relative to baseline flow, was also low, but similar before and after treatment with losartan (2.36+/-0.24, 2.44+/-0.24 and 2.62+/-0.42mL/(ming) tissue, respectively).

CONCLUSIONS

Oral treatment with an ARB did not normalize coronary vasomotor function in type 2 diabetes patients without cardiovascular disease.

Long-term angiotensin II blockade may improve not only hyperglycemia but also age-associated cardiac fibrosis

In the present study, the effects of long-term angiotensin (Ang) II antagonism on the development of cardiac and endothelial disorders were examined in Spontaneously Diabetic Torii (SDT) rats. Blood glucose concentration started to increase markedly in the untreated SDT rats from 20 weeks of age, while the blood glucose concentrations of candesartan cilexetil-treated SDT rats were significantly lower until 30 weeks of age. Cardiac function deteriorated in SDT rats and was accompanied by severe cardiac fibrosis, cardiac hypertrophy, and microstructural pathologic change in cardiomyocytes. Cardiac function was very well preserved in the age-matched Sprague Dawley (SD) rats, but cardiac fibrosis developed with aging. Candesartan cilexetil treatment improved cardiac structural remodeling and cardiac function in SDT rats. Surprisingly, the degree of cardiac fibrosis in candesartan cilexetil-treated SDT rats was less than that of SD rats. Immunohistological staining confirmed that in addition to collagen deposition, fibroblasts and myofibroblasts were the main cellular components in the cardiac fibrotic areas. The diabetic hearts showed positive staining for ACE, Ang II, and AT(1) receptors. SDT rats also showed decreased endothelial function, which was improved with candesartan cilexetil treatment. These findings indicate that Ang II is involved in the development of cardiac dysfunction by accelerating cardiac remodeling and cardiomyocyte damage in the presence of hyperglycemia. On the other hand, although the mechanisms responsible for the cardiac fibrosis that occurs under normal conditions may differ greatly from those responsible for cardiac fibrosis with hyperglycemia, Ang II seems to play an important role in both.

Therapeutic interventions and oxidative stress in diabetes

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

Allopurinol and nitric oxide activity in the cerebral circulation of those with diabetes: a randomized trial

OBJECTIVE

Type 2 diabetes increases risk of stroke, perhaps because of impaired cerebrovascular basal nitric oxide (NO) activity. We investigated whether this activity is improved by a 2-week course of the xanthine oxidase inhibitor allopurinol.

RESEARCH DESIGN AND METHODS

We performed a randomized, double-blind, placebo-controlled crossover study. We measured the response to infusion of NG-monomethyl-L-arginine (l-NMMA) in males with type 2 diabetes before and after allopurinol or placebo. The primary end point was the change in internal carotid artery flow following L-NMMA infusion, expressed as the area under the flow-per-time curve.

RESULTS

We enrolled 14 participants. Allopurinol improved responses to L-NMMA when compared with responses associated with placebo (P = 0.032; median reduction in internal carotid artery flow following L-NMMA of 3,144 ml [95% CI 375-7,143]).

CONCLUSIONS

Xanthine oxidase inhibition with allopurinol appears to improve cerebral NO bioavailability, as evidenced by a greater response to infusion of L-NMMA.

Beta-blockers have a beneficial effect upon endothelial function and microalbuminuria in African-American subjects with diabetes and hypertension

BACKGROUND

Type 2 diabetes mellitus (T2DM) with microalbuminuria (MA) is associated with increased risk of cardiovascular events (CVE) that may be attenuated by angiotensin-converting enzyme inhibitors (ACEIs), unless microalbuminuria persists (PMA). African-Americans (AA) have a higher prevalence of nephropathy with suboptimal response to ACEIs. We studied the effects of beta-blockers addition and comparative effects of carvedilol with metoprolol on 24-h urinary-albumin excretion (UAE) and endothelial function (EF) in AA with PMA.

METHODS

Thirty-four AA 30-70 years of age with T2DM and PMA despite ACEI therapy were randomized to receive carvedilol or metoprolol in addition to ACEI and any other concurrent therapy. Carvedilol/metoprolol dose was titrated to achieve blood pressure (BP) <130/80 mm Hg. UAE and brachial-artery reactivity were studied at baseline and 12 weeks. We analyzed the effects of addition of beta-blockers and whether there was any difference in response between the two beta-blockers.

RESULTS

Thirty-three subjects completed the study; BP decreased to <135/80 mm Hg. After 12 weeks, beta-blocker treatment resulted in significant increase in flow-mediated dilatation (FMD) from 3.5+/-1% to 8.5+/-1% (P=.004) and significant reduction in mean log-transformed UAE from 2.655 g/g Cr+/-0.087 to 2.533 g/g Cr+/-0.093 (P=.028). FMD increased by 240% (P=.033) with carvedilol and by 110% (P=.096; NS) with metoprolol. UAE decreased with carvedilol by 0.35 g/g Cr (P=.023) and with metoprolol by 0.23 g/g Cr (P=.298; NS).

CONCLUSION

Our results clearly indicate that addition of beta-blockers to ACEI improves EF and reduces UAE in high-risk AA T2DM patients with PMA. Carvedilol but not metoprolol improves EF and reduces UAE in AA with identical BP control. Larger trials are needed to further elucidate the differential effects of carvedilol/metoprolol on EF and UAE and its impact on CVE in such patients.

An integrated view of insulin resistance and endothelial dysfunction

Endothelial dysfunction and insulin resistance are frequently comorbid states. Vasodilator actions of insulin are mediated by phosphatidylinositol 3-kinase (PI3K)-dependent signaling pathways that stimulate production of nitric oxide from vascular endothelium. This helps to couple metabolic and hemodynamic homeostasis under healthy conditions. In pathologic states, shared causal factors, including glucotoxicity, lipotoxicity, and inflammation selectively impair PI3K-dependent insulin signaling pathways that contribute to reciprocal relationships between insulin resistance and endothelial dysfunction. This article discusses the implications of pathway-selective insulin resistance in vascular endothelium, interactions between endothelial dysfunction and insulin resistance, and therapeutic interventions that may simultaneously improve both metabolic and cardiovascular physiology in insulin-resistant conditions.

Angiotensin-converting enzyme inhibition improves vascular function in rheumatoid arthritis

BACKGROUND

The excess in cardiovascular risk in patients with rheumatoid arthritis provides a strong rationale for early therapeutical interventions. In view of the similarities between atherosclerosis and rheumatoid arthritis and the proven benefit of angiotensin-converting enzyme inhibitors in atherosclerotic vascular disease, it was the aim of the present study to delineate the impact of ramipril on endothelial function as well as on markers of inflammation and oxidative stress in patients with rheumatoid arthritis.

METHODS AND RESULTS

Eleven patients with rheumatoid arthritis were included in this randomized, double-blind, crossover study to receive ramipril in an uptitration design (2.5 to 10 mg) for 8 weeks followed by placebo, or vice versa, on top of standard antiinflammatory therapy. Endothelial function assessed by flow-mediated dilation of the brachial artery, markers of inflammation and oxidative stress, and disease activity were investigated at baseline and after each treatment period. Endothelial function assessed by flow-mediated dilation increased from 2.85+/-1.49% to 4.00+/-1.81% (P=0.017) after 8 weeks of therapy with ramipril but did not change with placebo (from 2.85+/-1.49% to 2.84+/-2.47%; P=0.88). Although systolic blood pressure and heart rate remained unaltered, diastolic blood pressure decreased slightly from 78+/-7 to 74+/-6 mm Hg (P=0.03). Tumor necrosis factor-alpha showed a significant inverse correlation with flow-mediated dilation (r=-0.408, P=0.02), and CD40 significantly decreased after ramipril therapy (P=0.049).

CONCLUSIONS

Angiotensin-converting enzyme inhibition with 10 mg/d ramipril for 8 weeks on top of current antiinflammatory treatment markedly improved endothelial function in patients with rheumatoid arthritis. This finding suggests that angiotensin-converting enzyme inhibition may provide a novel strategy to prevent cardiovascular events in these patients.

Losartan improves impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in type 1 diabetic rats

We examined whether activation of angiotensin-1 receptors (AT1R) could account for impaired responses of cerebral arterioles during type 1 diabetes (T1D). First, we measured responses of cerebral arterioles in nondiabetic rats to eNOS-dependent (acetylcholine and adenosine diphosphate (ADP)) and -independent (nitroglycerin) agonists before and during application of angiotensin II. Next, we examined whether losartan could improve impaired responses of cerebral arterioles during T1D. In addition, we harvested cerebral microvessels for Western blot analysis of AT1R protein and measured production of superoxide anion by brain tissue under basal conditions and in response to angiotensin II in the absence or presence of losartan. We found that angiotensin II specifically impaired eNOS-dependent reactivity of cerebral arterioles. In addition, while losartan did not alter responses in nondiabetics, losartan restored impaired eNOS-dependent vasodilatation in diabetics. Further, AT1R protein was higher in diabetics compared to nondiabetics. Finally, superoxide production was higher in brain tissue from diabetics compared to nondiabetics under basal conditions, angiotensin II increased superoxide production in nondiabetics and diabetics, and losartan decreased basal (diabetics) and angiotensin II-induced production of superoxide (nondiabetics and diabetics). We suggest that activation of AT1R during T1D plays a critical role in impaired eNOS-dependent dilatation of cerebral arterioles.

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.

Improvement in endothelium dysfunction in diabetics treated with statins: a randomized comparison of atorvastatin 20 mg versus rosuvastatin 10 mg

AIM

To investigate the effect a 3-month treatment with atorvastatin 20 mg compared with rosuvastatin 10 mg on endothelium dysfunction in subjects with diabetes.

METHODS

A total of 22 consecutive subjects with diabetes who were not receiving statins were enrolled in the study. Endothelium function was assessed before treatment (T0), after 1 month (T1), and after 3 months of treatment (T2) with statins with brachial echo-Doppler test. Patients were randomized to receive atorvastatin 20 mg or rosuvastatin 10 mg. Blood samples were drawn in the meantime in order to evaluate C-reactive protein (CRP) plasmatic concentrations.

RESULTS

A total of 82% of patients enrolled showed endothelium dysfunction (hyperemic reserve <5%). Treatment with statins significantly improved endothelium function in diabetics. Subjects with endothelium dysfunction decreased from 82% (T0) to 44% (T2): mean hyperemic reserve values increased from 2.64% (T0) to 3.23% (T1) and 4% (T2) in patients treated with rosuvastatin (ANOVA P < 0.01), and from 2.74% (T0) to 2.75% (T1) and 4.40% (T2) in those treated with atorvastatin (ANOVA P < 0.01); differences were significant only comparing T2 with T0. Relative increase in endothelium reserve was 51.51% with rosuvastatin versus 60.58% with atorvastatin (P N.S.). Both statins significantly reduced plasmatic levels of CRP (3.18 +/- 2.43 mg/dL [T0] vs. 1.31 +/- 1.67 mg/dL [T2] with rosuvastatin [P < 0.01], 7.53 +/- 7.46 mg/dL [T0] vs. 2.92 +/- 2.06 mg/dL [T2] with atorvastatin [P < 0.01]). Relative reduction of CRP levels was -50.57% with rosuvastatin versus -36.28% with atorvastatin (P N.S.).

CONCLUSION

A 3-month treatment with either atorvastatin 20 mg or rosuvastatin 10 mg is effective in improving endothelium dysfunction in subjects with diabetes.

Dimethylarginine dimethylaminohydrolase (DDAH): expression, regulation, and function in the cardiovascular and renal systems

Asymmetric (N(G),N(G))-dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS). ADMA is a risk factor for endothelial dysfunction, cardiovascular mortality, and progression of chronic kidney disease. Two isoforms of dimethylarginine dimethylaminohydrolase (DDAH) metabolize ADMA. DDAH-1 is the predominant isoform in the proximal tubules of the kidney and in the liver. These organs extract ADMA from the circulation. DDAH-2 is the predominant isoform in the vasculature, where it is found in endothelial cells adjacent to the cell membrane and in intracellular vesicles and in vascular smooth muscle cells among the myofibrils and the nuclear envelope. In vivo gene silencing of DDAH-1 in the rat and DDAH +/- mice both have increased circulating ADMA, whereas gene silencing of DDAH-2 reduces vascular NO generation and endothelium-derived relaxation factor responses. DDAH-2 also is expressed in the kidney in the macula densa and distal nephron. Angiotensin type 1 receptor activation in kidneys reduces the expression of DDAH-1 but increases the expression of DDAH-2. This rapidly evolving evidence of isoform-specific distribution and regulation of DDAH expression in the kidney and blood vessels provides potential mechanisms for nephron site-specific regulation of NO production. In this review, the recent advances in the regulation and function of DDAH enzymes, their roles in the regulation of NO generation, and their possible contribution to endothelial dysfunction in patients with cardiovascular and kidney diseases are discussed.

Temporal effects of low-dose ACE inhibition on endothelial function in Type 1 diabetic patients

AIM

Increased asymmetrical dimethylarginine (ADMA) is known to disturb endothelial function. ACE inhibitors decrease plasma ADMA levels in diseases associated with endothelial dysfunction. The effects of ACE inhibition on endothelial function and plasma ADMA levels in Type 1 diabetic patients was evaluated in the study.

METHODS

Thirty Type 1 diabetic patients [29+/-6 yr; females (F)/males (M): 18/12] and 29 controls (30+/-6 yr; F/M: 16/13) were recruited. Flow-mediated dilatation (FMD), plasma ADMAand thiobarbituric acid reactive substances (TBARs) were determined at baseline, on day 15 and 90 of 0.5 mg qd trandolapril therapy.

RESULTS

Compared to controls, baseline FMD levels were lower (4.7+/-2.0% vs 11.2+/-3.9%) (p<0.001), plasma ADMA (271.1+/-48.1 nmol/l vs 237.5+/-25.1 nmol/l) (p<0.05) and TBARs levels [4517.1+/-2366.9 nmol/malondialdehyde (MDA) vs 1775.9+/-598.7 nmol/MDA] (p<0.001) were higher in diabetic patients. On day 90 of trandolapril treatment, FMD (8.6+/-4.1%) (p<0.01) increased, ADMA levels (229.6+/-42.9 nmol/l) (p<0.001) decreased and TBARs levels (1531.8+/-1036.0 nmol/MDA) (p<0.001) decreased significantly. FMD was negatively correlated with plasma ADMA (r=-0.228, p<0.01), and TBARs levels (r=-0.244, p=0.02), whereas ADMA and TBARs levels were correlated positively (r=0.399, p<0.0001).

CONCLUSIONS

In conclusion, endothelial dysfunction is associated with elevated plasma ADMA levels in Type 1 diabetic patients. Low-dose ACE inhibition improves endothelial dysfunction and reduces ADMA levels. The antioxidant action of ACE inhibitors may play role in this process.

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.

Aspects of nitric oxide in health and disease: a focus on hypertension and cardiovascular disease

Nitric oxide (nitrogen monoxide) (NO) plays an important role in a wide range of physiologic processes. A major mediator of endothelial function, NO regulates vasodilatory and antithrombotic actions in the vasculature and plays a role in reproductive functions, bronchodilation, bone formation, memory, insulin sensitivity, and gastrointestinal relaxation. NO is formed from NO synthase. Impaired NO bioactivity is strongly associated with endothelial dysfunction and cardiovascular disease, but is also implicated in a broad range of other disorders, including pulmonary hypertension, insulin resistance, erectile dysfunction, and preeclampsia. Numerous therapies designed to target NO are being investigated and developed, including NO donors and stimulants. The recent African-American Heart Failure Trial (A-HeFT) showed that the NO donor isosorbide dinitrate, combined with the vasodilator hydralazine, significantly reduced morbidity and mortality in black patients with moderate-to-severe heart failure. Antihypertensive drugs, including angiotensin-converting enzyme inhibitors, calcium channel blockers, and third-generation beta-blockers, are NO stimulants that have demonstrated significant improvement of endothelial function and NO bioactivity. Other cardiovascular therapies that may improve NO bioactivity include statins, l-arginine, and nonpharmacologic approaches such as exercise and dietary changes.

Multi-modal magnetic resonance imaging quantifies atherosclerosis and vascular dysfunction in patients with type 2 diabetes mellitus

Vascular magnetic resonance imaging (MRI) is emerging as a powerful research tool. We studied 18 patients with type 2 diabetes mellitus and 20 controls (all with coronary artery disease). MRI measured distensibility, pulse wave velocity (PWV) and atherosclerosis in the aorta, and brachial artery flow-mediated dilatation (FMD). Patients with diabetes showed lower aortic distensibility (2.1 x 10(-3) vs . 3.5 x 10(-3) mmHg-1, p<0.01), faster PWV (8.8 vs ., 6.2 m/s, p<0.01) and impaired FMD (8.5% vs . 13.8%, p<0.05). Diabetes was an independent negative predictor of distensibility. Aortic atherosclerosis was similar in the two groups. There was a negative correlation between aortic distensibility and atherosclerosis in control subjects only, suggesting that other factors such as protein cross-linking may explain lower aortic distensibility in diabetes. MRI provides comprehensive vascular phenotyping in patients with type 2 diabetes and is likely to be useful in studies of disease progression and drug therapy.

Attenuation of angiotensin II signaling recouples eNOS and inhibits nonendothelial NOX activity in diabetic mice

Angiotensin II (Ang II) levels are increased in patients with diabetes, but mechanisms underlying its contribution to diabetic vascular diseases are incompletely understood. We recently reported that in aortic endothelial cells, Ang II induces endothelial nitric oxide synthase (eNOS) uncoupling to produce superoxide (O(2)*(-)) rather than nitric oxide (NO*), upon loss of the tetrahydrobiopterin (H(4)B) salvage enzyme dihydrofolate reductase (DHFR). Here, we found that streptozotocin-induced diabetic mice had a marked increase in aortic O(2)*(-) production, which was inhibited by N-nitro-l-arginine methyl ester hydrochloride, indicating uncoupling of eNOS. Ang II receptor type 1 blocker candesartan or ACE inhibitor captopril markedly attenuated eNOS-derived O(2)*(-) and hydrogen peroxide production while augmenting NO* bioavailability in diabetic aortas, implicating recoupling of eNOS. O(2)*(-) and NO* production were characteristically and quantitatively measured by electron spin resonance. DHFR expression was decreased in diabetic aortas but significantly restored by candesartan or captopril. Either also improved vascular H(4)B content and endothelium-dependent vasorelaxation in diabetes. Rac1-dependent NAD(P)H oxidase (NOX) activity was more than doubled in the endothelium-denuded diabetic aortas but was attenuated by candesartan or captopril, indicating that NOX remains active in nonendothelial vascular tissues, although uncoupled eNOS is responsible for endothelial production of O(2)*(-). These data demonstrate a novel role of Ang II in diabetic uncoupling of eNOS and that Ang II-targeted therapy improves endothelial function via the novel mechanism of recoupling eNOS. Dual effectiveness on uncoupled eNOS and NOX may explain the high efficacy of Ang II antagonists in restoring endothelial function.

Inspection of skin hemodynamics with hyperspectral camera

Using hyperspectral imaging techniques, which enable us to simultaneously obtain spatial and wavelength information, we have improved upon the newly developed hyperspectral camera to develop a method of observing changes in skin melanin levels and hemodynamics over time. As an evaluation of this method, we measured the skin diffuse reflectance spectrum of the human middle finger in an experiment of blood flow blockage in the brachial region. The changes in skin hemodynamics observed through this method match the behavior expected based on clinical knowledge, and also show an extremely high correlation with results obtained by the Erythema Index, which is used to make similar calculations from a limited number of wavelengths.

The vascular endothelium in diabetes: a practical target for drug treatment?

Vascular disease remains a major cause of morbidity and mortality in diabetes mellitus, in spite of recent improvements in outcome, some of which may be modulated by improved endothelial function. Therapeutic strategies aimed directly at preventing, or minimising the extent of, these sequelae are required as an adjunct to treatments directed at normalising the metabolic milieu. The microvasculature, and the endothelium in particular, are early contributors to vascular dysfunction, thus raising the question as to how best to specifically target the endothelium. However, the expansive nature of the microvasculature, the varying demands that tissues have in terms of blood flow, and the heterogeneity that exists amongst cell types in different sites raises potential problems as to the practicality of such an approach. Further-more, temporal and genetic factors in the genesis of diabetic microvascular dysfunction may impact on therapeutic strategies. It is suggested that a systematic approach is required to understand the heterogeneity of the microvasculature, with particular emphasis on relating differences in gene and protein expression with functional properties. Such an approach may then provide the necessary information to allow exploitation of endothelial cell heterogeneity for unique targeted interventions, as well as providing the necessary rationale for pharmacological interventions (both prophylactic and corrective) aimed at the endothelium as a whole.

Impaired endothelium-dependent and -independent vasodilation in elderly patients with chronic heart failure

BACKGROUND

Impaired endothelium-dependent and independent vasodilator responses in chronic heart failure (CHF) have been well described. Previous studies involved younger patients and omitted medications prior to study.

AIMS

We explored if new therapeutic interventions would restore vasodilator responses in typical patients with chronic heart failure.

METHODS AND RESULTS

24 patients and 15 controls were recruited, patients were maintained on their usual medications. Forearm blood flow responses were measured by venous occlusion plethysmography in response to incremental doses of sodium nitroprusside (SNP) (6, 9 and 12 nmol/min), acetylcholine (ACH) (120, 180 and 240 nmol/min), angiotensin II (AII) (1, 10 and 100 nmol/min) and N(g)-Nitro-L-arginine methyl ester (L-NAME) (1, 2 and 4 nmol/min) infused into the non-dominant brachial artery. FBF responses to SNP were impaired in patients compared with controls (13.7(9.9,17.4) vs. 24.8(18.6,30.9)) arbitrary units, P<0.001). Similarly FBF responses to ACH were reduced in patients compared with controls (7.5(4.2,10.9) vs. 24.8(16.4,33.2)) arbitrary units, P<0.001. Decreased FBF was noted in response to AII and L-NAME but was significant only for AII and did not differ between groups.

CONCLUSIONS

In elderly patients with CHF, endothelium-dependent and independent vasodilator responses were blunted compared with controls. Defects in nitric oxide bioavailability and smooth muscle responsiveness are not reversed by modern medical management of the heart failure syndrome.

Divergent effects of angiotensin-converting enzyme inhibition on blood pressure and endothelial function in obese humans

Endothelial dysfunction is a pivotal early event in the development of atherosclerosis and a characteristic feature of obesity. This study was designed to investigate the effect of angiotensin-converting enzyme (ACE) inhibition on endothelial function in people who were obese but otherwise healthy. We performed a double-blind, randomised, placebo-controlled study examining the effect of the ACE inhibitor perindopril (4 mg per day) on flow-mediated vasodilatation (FMD) of the brachial artery, arterial blood pressure, glucose homeostasis and inflammatory cytokines. Eighteen obese subjects (all body mass index > 30 kg/m2) were randomised to receive perindopril or placebo for four weeks. Perindopril led to a fall in systolic blood pressure from 131 (standard error of mean [SEM] 3) to 117(5) mmHg and diastolic blood pressure from 74(4) mmHg to 68(4) mmHg, both p<0.001. Despite this fall in blood pressure, ACE inhibition had no effect on FMD, 8.2 (1.2)% versus 8.3 (1.5)%, p=0.9. ACE inhibition had no effect on insulin, lipids or circulating cytokines. In healthy obese humans, despite a significant reduction in blood pressure, ACE inhibition had no effect on FMD.