Effect of gemfibrozil +/- niacin +/- cholestyramine on endothelial function in patients with serum low-density lipoprotein cholesterol levels <160 mg/dl and high-density lipoprotein cholesterol levels <40 mg/dl

Quantitative and Dynamic MRI Measures of Peripheral Vascular Function

The endothelium regulates and mediates vascular homeostasis, allowing for dynamic changes of blood flow in response to mechanical and chemical stimuli. Endothelial dysfunction underlies many diseases and is purported to be the earliest pathologic change in the progression of atherosclerotic disease. Peripheral vascular function can be interrogated by measuring the response kinetics following induced ischemia or exercise. In the presence of endothelial dysfunction, there is a blunting and delay of the hyperemic response, which can be measured non-invasively using a variety of quantitative magnetic resonance imaging (MRI) methods. In this review, we summarize recent developments in non-contrast, proton MRI for dynamic quantification of blood flow and oxygenation. Methodologic description is provided for: blood oxygenation-level dependent (BOLD) signal that reflect combined effect of blood flow and capillary bed oxygen content; arterial spin labeling (ASL) for quantification of regional perfusion; phase contrast (PC) to quantify arterial flow waveforms and macrovascular blood flow velocity and rate; high-resolution MRI for luminal flow-mediated dilation; and dynamic MR oximetry to quantify oxygen saturation. Overall, results suggest that these dynamic and quantitative MRI methods can detect endothelial dysfunction both in the presence of overt cardiovascular disease (such as in patients with peripheral artery disease), as well as in sub-clinical settings (i.e., in chronic smokers, non-smokers exposed to e-cigarette aerosol, and as a function of age). Thus far, these tools have been relegated to the realm of research, used as biomarkers of disease progression and therapeutic response. With proper validation, MRI-measures of vascular function may ultimately be used to complement the standard clinical workup, providing additional insight into the optimal treatment strategy and evaluation of treatment efficacy.

Metabolic syndrome impairs reactivity and wall mechanics of cerebral resistance arteries in obese Zucker rats

The metabolic syndrome (MetS) is highly prevalent in the North American population and is associated with increased risk for development of cerebrovascular disease. This study determined the structural and functional changes in the middle cerebral arteries (MCA) during the progression of MetS and the effects of chronic pharmacological interventions on mitigating vascular alterations in obese Zucker rats (OZR), a translationally relevant model of MetS. The reactivity and wall mechanics of ex vivo pressurized MCA from lean Zucker rats (LZR) and OZR were determined at 7-8, 12-13, and 16-17 wk of age under control conditions and following chronic treatment with pharmacological agents targeting specific systemic pathologies. With increasing age, control OZR demonstrated reduced nitric oxide bioavailability, impaired dilator (acetylcholine) reactivity, elevated myogenic properties, structural narrowing, and wall stiffening compared with LZR. Antihypertensive therapy (e.g., captopril or hydralazine) starting at 7-8 wk of age blunted the progression of arterial stiffening compared with OZR controls, while treatments that reduced inflammation and oxidative stress (e.g., atorvastatin, rosiglitazone, and captopril) improved NO bioavailability and vascular reactivity compared with OZR controls and had mixed effects on structural remodeling. These data identify specific functional and structural cerebral adaptations that limit cerebrovascular blood flow in MetS patients, contributing to increased risk of cognitive decline, cerebral hypoperfusion, and ischemic stroke; however, these pathological adaptations could potentially be blunted if treated early in the progression of MetS.

Effect of niacin on endothelial function: a systematic review and meta-analysis of randomized controlled trials

Endothelial dysfunction is an independent predictor of incident atherosclerotic cardiovascular disease (ACVD). Niacin possesses high-density lipoprotein (HDL)-elevating, antioxidant and anti-inflammatory properties, all potentially contributing to the amelioration of endothelial function. However, controversies exist among trials reporting the effects of niacin on endothelium-dependent flow-mediated dilation (FMD) as a reliable surrogate of endothelial function. The objective of this study was to assess the effect of niacin on brachial artery FMD using a meta-analysis of available evidence. MEDLINE and Scopus databases were searched for randomized controlled trials investigating the impact of niacin therapy on brachial artery FMD. Meta-analysis of eligible studies was conducted using a random-effects model. Pooled effects were measured by weighted mean difference (WMD) and 95% confidence intervals (CIs). Quality assessment, and subgroup, meta-regression and sensitivity analyses were conducted using standard methods. Among 596 citations, 19 full-text articles were read and seven were found to be eligible for inclusion. Eligible studies involved 441 subjects comprising 228 in the niacin and 213 in the control groups. Niacin therapy significantly improved FMD (WMD: 1.98%; 95% CI: 0.91-3.05%; p = 0.0003) and this effect was robust in the sensitivity analysis. The effect size was greater in the subgroup of studies administering higher doses of niacin (≥ 2000 mg/day) as well as those studies administering niacin for primary prevention of ACVD. Meta-regression indicated no association between niacin-induced changes in FMD and changes in plasma HDL-cholesterol, low-density lipoprotein-cholesterol or triglycerides. None of the included studies could find any significant effect of niacin on nitroglycerin-mediated dilation. In conclusion, treatment with niacin improves endothelial function.

Effect of extended-release niacin on serum lipids and on endothelial function in adults with sickle cell anemia and low high-density lipoprotein cholesterol levels

Through bound apolipoprotein A-I (apoA-I), high-density lipoprotein cholesterol (HDL-C) activates endothelial nitric oxide synthase, inducing vasodilation. Because patients with sickle cell disease (SCD) have low apoA-I and endothelial dysfunction, we conducted a randomized, double-blinded, placebo-controlled trial to test whether extended-release niacin (niacin-ER) increases apoA-I-containing HDL-C and improves vascular function in SCD. Twenty-seven patients with SCD with levels of HDL-C <39 mg/dl or apoA-I <99 mg/dl were randomized to 12 weeks of niacin-ER, increased in 500-mg increments to a maximum of 1,500 mg/day, or placebo. The primary outcome was the absolute change in HDL-C level after 12 weeks, with endothelial function assessed before and at the end of treatment. Niacin-ER-treated patients trended to greater increase in HDL-C level compared with placebo treatment at 12 weeks (5.1 ± 7.7 vs 0.9 ± 3.8 mg/dl, 1-tailed p = 0.07), associated with significantly greater improvements in the ratios of low-density lipoprotein to HDL-C levels (1.24 vs 1.95, p = 0.003) and apolipoprotein B to apoA-I levels (0.46 vs 0.58, p = 0.03) compared with placebo-treated patients. No improvements were detected in 3 independent vascular physiology assays of endothelial function. Thus, the relatively small changes in HDL-C levels achieved by the dose of niacin-ER used in our study are not associated with improved vascular function in patients with SCD with initially low levels of apoA-I or HDL-C.

Blood pressure regulation VIII: resistance vessel tone and implications for a pro-atherogenic conduit artery endothelial cell phenotype

Dysfunction of the endothelium is proposed as the primary initiator of atherosclerotic peripheral artery disease, which occurs mainly in medium- to large-sized conduit arteries of the lower extremities (e.g., iliac, femoral, popliteal arteries). In this review article, we propose the novel concept that conduit artery endothelial cell phenotype is determined, in part, by microvascular tone in skeletal muscle resistance arteries through both changes in arterial blood pressure as well as upstream conduit artery shear stress patterns. First, we summarize the literature supporting the involvement of sympathetic nerve activity (SNA) and nitric oxide (NO) in the modulation of microvascular tone and arterial blood pressure. We then focus on the role of elevated blood pressure and shear stress profiles in modulating conduit artery endothelial cell phenotype. Last, we discuss findings from classic and emerging studies indicating that increased vascular resistance, as it occurs in the context of increased SNA and/or reduced NO bioavailability, is associated with greater oscillatory shear stress (e.g., increased retrograde shear) in upstream conduit arteries. The ideas put forth in this review set the stage for a new paradigm concerning the mechanistic link between increased microvascular tone and development of conduit artery endothelial dysfunction and thus increased risk for peripheral artery disease. Indeed, a vast amount of evidence supports the notion that excessive blood pressure and oscillatory shear stress are potent pro-atherogenic signals to the endothelium.

The vascular endothelium in diabetes--a therapeutic target?

Insulin resistance affects the vascular endothelium, and contributes to systemic insulin resistance by directly impairing the actions of insulin to redistribute blood flow as part of its normal actions driving muscle glucose uptake. Impaired vascular function is a component of the insulin resistance syndrome, and is a feature of type 2 diabetes. On this basis, the vascular endothelium has emerged as a therapeutic target where the intent is to improve systemic metabolic state by improving vascular function. We review the available literature presenting studies in humans, evaluating the effects of metabolically targeted and vascular targeted therapies on insulin action and systemic metabolism. Therapies that improve systemic insulin resistance exert strong concurrent effects to improve vascular function and vascular insulin action. RAS-acting agents and statins have widely recognized beneficial effects on vascular function but have not uniformly produced the hoped-for metabolic benefits. These observations support the notion that systemic metabolic benefits can arise from therapies targeted at the endothelium, but improving vascular insulin action does not result from all treatments that improve endothelium-dependent vasodilation. A better understanding of the mechanisms of insulin's actions in the vascular wall will advance our understanding of the specificity of these responses, and allow us to better target the vasculature for metabolic benefits.

Effects of high-dose modified-release nicotinic acid on atherosclerosis and vascular function: a randomized, placebo-controlled, magnetic resonance imaging study

OBJECTIVES

Our aim was to determine the effects of high-dose (2 g) nicotinic acid (NA) on progression of atherosclerosis and measures of vascular function.

BACKGROUND

NA raises high-density lipoprotein cholesterol (HDL-C) and reduces low-density lipoprotein cholesterol and is widely used as an adjunct to statin therapy in patients with coronary artery disease. Although changes in plasma lipoproteins suggest potential benefit, there is limited evidence of the effects of NA on disease progression when added to contemporary statin treatment.

METHODS

We performed a double-blind, randomized, placebo-controlled study of 2 g daily modified-release NA added to statin therapy in 71 patients with low HDL-C (<40 mg/dl) and either: 1) type 2 diabetes with coronary heart disease; or 2) carotid/peripheral atherosclerosis. The primary end point was the change in carotid artery wall area, quantified by magnetic resonance imaging, after 1 year.

RESULTS

NA increased HDL-C by 23% and decreased low-density lipoprotein cholesterol by 19%. At 12 months, NA significantly reduced carotid wall area compared with placebo (adjusted treatment difference: -1.64 mm(2) [95% confidence interval: -3.12 to -0.16]; p = 0.03). Mean change in carotid wall area was -1.1 +/- 2.6 mm(2) for NA versus +1.2 +/- 3.0 mm(2) for placebo. In both the treatment and placebo groups, larger plaques were more prone to changes in size (r = 0.4, p = 0.04 for placebo, and r = -0.5, p = 0.02 for NA).

CONCLUSIONS

In statin-treated patients with low HDL-C, high-dose modified-release NA, compared with placebo, significantly reduces carotid atherosclerosis within 12 months. (Oxford Niaspan Study: Effects of Niaspan on Atherosclerosis and Endothelial Function; NCT00232531).

PPAR activation: a new target for the treatment of hypertension

Hypertensive patients are at increased risk for cardiovascular complications. Inhibition of different pathophysiological mechanisms involved in hypertension and hypertension-related target organ damage may revert or prevent the progression of the pathological changes observed and reduce the occurrence of cardiovascular events. One of the new targets that may prevent or regress hypertensive vascular, renal, and perhaps brain changes in hypertension is the activation of nuclear receptors that have metabolic effects but also exert antiinflammatory action, the peroxisome proliferator activator receptor (PPAR) activators alpha and gamma. This review will discuss some of the evidence, both experimental and clinical, that suggests that activation of PPAR alpha and/or gamma in hypertension may exert beneficial cardiovascular protective effects.

Endothelial function, arterial stiffness and lipid lowering drugs

The endothelium is a dynamic organ that plays a pivotal role in cardiovascular homeostasis. Alteration in endothelial function precedes the development of atherosclerosis and contributes to its initiation, perpetuation and clinical manifestations. It has been suggested that the assessment of endothelial function could represent a barometer of vascular health that could be used to gauge cardiovascular risk. This review summarises the various methods used to assess endothelium-dependent vasodilatation and their potential prognostic implications. In addition, the techniques used to evaluate arterial stiffness are discussed. The latter is to some extent controlled by the endothelium and has been the subject of considerable research in recent years. This paper also discusses the effects of lipid lowering treatment on both endothelial function and arterial stiffness.

Elevated blood pressure in adolescent boys predicts endothelial dysfunction: the cardiovascular risk in young Finns study

Hypertension is a major risk factor for atherosclerosis. It may cause or be a consequence of endothelial dysfunction. We studied whether systolic blood pressure measured in childhood and adolescence predicts endothelial-dependent brachial flow-mediated dilation (FMD) in adulthood. Brachial FMD was measured in 2109 white adults, aged 24 to 39 years, in the 21-year follow-up of the Cardiovascular Risk in Young Finns Study. These subjects have risk factor data available dating back to their childhood (baseline in 1980, ages 3 to 18 years). In male subjects, the level of systolic blood pressure measured in adolescence (at ages 12 to 18 years at baseline) was inversely related to adulthood FMD (P=0.004). This association was independent of brachial diameter and other childhood (P=0.003) and adulthood risk factors, including blood pressure (P=0.03). Childhood (age 3 to 9 years at baseline) systolic blood pressure did not correlate with adult FMD in men or in women (P always >0.2). In male subjects, elevated systolic blood pressure in adolescence predicts impaired brachial endothelial function 21 years later in adulthood. This association is independent of other childhood and adulthood cardiovascular risk factors suggesting that blood pressure elevation in adolescence may have an influence on biological processes that regulate endothelium-dependent flow-mediated vasodilatation capacity.

Endothelial function and its assessment

Endothelial dysfunction is a characteristic aspect of most of the conditions associated with atherosclerosis and is commonly found as an early feature in atherothrombotic vascular disease. An appreciation of the underlying mechanisms of endothelial function, as well as dysfunction, is essential as this has critical influence on the different methods in the assessment of endothelial function and effects of various treatments on its quantification. Furthermore, endothelial dysfunction is recognised as a type of 'target organ damage' in common cardiovascular conditions (e.g., hypertension) and the area is of increasing interest for new drug development, as therapies that modulate the endothelium will have added advantages; thus, for the development of new/experimental drugs, an awareness of ways to assess the endothelium is necessary. In this review, an overview of different methods including biochemical markers, and invasive and non-invasive tools, to determine endothelial function is presented as well as their clinical relevance. Furthermore, the effects of various treatments on endothelial dysfunction and their underlying mechanisms are elucidated.

Beneficial vascular and metabolic effects of peroxisome proliferator-activated receptor-alpha activators

Fibric acid is a synthetic ligand of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)-alpha that is highly expressed in skeletal muscle and heart, where it promotes beta-oxidation of fatty acids to mediate hypolipidemic actions. PPAR-alpha regulates expression of key proteins involved in atherogenesis, vascular inflammation, plaque instability, and thrombosis. Thus, PPAR-alpha may exert direct antiatherogenic actions in the vascular wall. Endothelial dysfunction associated with the metabolic syndrome and other insulin-resistant states is characterized by impaired insulin-stimulated nitric oxide production from the endothelium and decreased blood flow to skeletal muscle. Thus, improvement in insulin sensitivity leads to improved endothelial function. This may be an additional mechanism whereby fibrates decrease the incidence of coronary heart disease. Adiponectin is a protein secreted specifically by adipose cells that may couple regulation of insulin sensitivity with energy metabolism and serve to link obesity with insulin resistance. In this review, we discuss the mechanisms underlying the vascular and metabolic effects of fibrates that may act synergistically to prevent or regress atherosclerosis and coronary heart disease.

Clinical impact of vasomotor function assessment and the role of ACE-inhibitors and statins

Impaired endothelial function is recognised as one of the earliest events of atherogenesis. Endothelium-dependent vasomotion has been the principal method to assess endothelial function. In this article, we will discuss the clinical value of the different techniques to evaluate endothelium-dependent vasomotion. To date, there seems not to be a simple and reliably endothelial function test to identify asymptomatic subjects at increased risk for cardiovascular disease in clinical practice. Recent studies indicate that pharmacological interventions, in particular with ACE-inhibitors and statins, might improve endothelial function. However, there is no solid evidence that improvement of endothelial function is a necessity for the observed reduction in cardiovascular events by these compounds. Overall, at this moment, there is no place in clinical practice for the use of endothelial function as a method for risk assessment or target of pharmacological interventions.

Evaluation of arterial endothelial function using transit times of artificially induced pulses

Impairment of arterial endothelial function is an early event in atherosclerosis and correlates with the major risk factors for cardiovascular disease. The most widely employed non-invasive measure of endothelial function involves brachial artery (BA) diameter measurement using ultrasound imaging before and after several minutes of blood flow occlusion. The change in arterial diameter is a measure of flow-mediated vasorelaxation (FMVR). The high between-laboratory variability of results and cost of instrumentation render this technique unsuitable for routine clinical use. We induce artificial pulses at the superficial radial artery using a linear actuator. An ultrasonic Doppler stethoscope detects these pulses 10-30 cm proximal to the point of pulse induction. The delay between pulse application and detection provides the pulse transit time (PTT). By measuring PTT before and after 5 min of BA occlusion and ensuing reactive hyperemia, FMVR may be measured based on the changes in PTT caused by changes in vessel caliber, smooth muscle tone and wall thickness. We (1) validate the sensitivity of this technique to arterial wall tone using sublingual nitroglycerin and (2) compare measurements of endothelial function to ultrasound BA diameter measurements in 12 human subjects. The PTT-based method is verified to measure arterial wall tone and is shown to provide 37% greater sensitivity (p < 0.05) to FMVR than BA diameter measurements. By measuring the change in pulse transit time before and after endothelial stimulus, a sensitive, reproducible and convenient measure of endothelial function may be obtained at a low cost.

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

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

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

AIMS

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

METHODS AND RESULTS

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

CONCLUSION

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

Comparative effects of statin and fibrate on nitric oxide bioactivity and matrix metalloproteinase in hyperlipidemia

OBJECTIVE

Because the lipoprotein effects of statin and fibric acid derivatives therapies differ, we studied the effects of these therapies in patients with hyperlipidemia on lipoproteins, vasomotor function, and plaque stability.

METHODS

We administered simvastatin, 20 mg daily, to 27 patients with hypercholesterolemia and coronary artery disease, or fenofibrate, 200 mg daily, to 27 patients with pure hypertriglyceridemia during 8 weeks.

RESULTS

As expected, simvastatin significantly lowered total cholesterol and low-density lipoprotein cholesterol (LDL-C) more, and fenofibrate decreased triglyceride and increased high-density lipoprotein cholesterol (HDL-C) more than either therapy. Simvastatin and fenofibrate significantly improved the percent flow-mediated dilator response to hyperemia by 183+/-41% and by 30+/-7%, respectively (each P<0.001); however, simvastatin significantly improved more (P<0.001). Simvastatin and fenofibrate significantly lowered plasma levels of tumor necrosis factor alpha (TNF-alpha) by 13+/-4% and by 10+/-4%, respectively (P=0.009 and P=0.006, respectively) with a similar degree (P=0.614). Simvastatin significantly reduced plasma levels of total MMP-9 and TIMP-1 more (P=0.005 and P=0.036, respectively), compared with fenofibrate showing no reduction. There were significant correlations between the degree of changes in TNF-alpha and the degree of changes in MMP-9 activity (r=0.376, P=0.053).

CONCLUSIONS

Simvastatin and fenofibrate demonstrated antiatherosclerotic effects via different mechanisms.

Effects of fenofibrate on lipoproteins, vasomotor function, and serological markers of inflammation, plaque stabilization, and hemostasis

We investigated the effects of fenofibrate, peroxisome proliferator-activated receptors (PPARs) agonist, on endothelial function in patients with hypertriglyceridemia. We administered placebo or fenofibrate 200 mg daily to 25 patients with hypertriglyceridemia for 8 weeks. This study was randomized, double-blind, placebo-controlled, crossover in design. Compared with placebo, fenofibrate significantly changed lipoprotein levels including non-HDL cholesterol and significantly improved the percent flow-mediated dilator response to hyperemia by 13 +/- 6% (P < 0.001) and lowered plasma levels of tumor necrosis factor-alpha by 13 +/- 3% (P < 0.001). Fenofibrate reduced fibrinogen and plasminogen activator inhibitor type 1 antigen levels by 17 +/- 3 and 10 +/- 3%, respectively (P < 0.001 and P = 0.014, respectively). However, fenofibrate did not significantly change plasma levels of nitrate, malondialdehyde, tissue factor activity, and serological markers of plaque stabilization. Fenofibrate significantly changed lipoprotein levels and improved the percent flow-mediated dilator response to hyperemia as well as lowered levels of tumor necrosis factor-alpha (TNF-alpha), fibrinogen, and plasminogen activator inhibitor type 1 antigen.

Clinical correlates and heritability of flow-mediated dilation in the community: the Framingham Heart Study

BACKGROUND

Studies in selected samples have linked impaired endothelial function with cardiovascular disease and its risk factors. The clinical correlates and heritability of endothelial function in the community have not been described.

METHODS AND RESULTS

We examined a measure of endothelial function, brachial artery flow-mediated dilation (FMD), expressed as both percent (FMD%) and actual dilation by ultrasound with the occlusion cuff below the elbow in 2883 Framingham Study participants (52.9% women; mean age, 61 years). A subset of 1096 participants performed a 6-minute walk test before FMD determination. Mean FMD% was 3.3+/-3.0% in women and 2.4+/-2.4% in men. In stepwise multivariable linear regression models, FMD% was inversely related to age, systolic blood pressure, body mass index (BMI), lipid-lowering medication, and smoking, whereas it was positively related to female gender, heart rate, and prior walk test. The estimated heritability of FMD% was 0.14. FMD actual dilation findings were similar, except that female sex and BMI were not significantly associated.

CONCLUSIONS

Increasing age, systolic blood pressure, BMI, and smoking were associated with lower FMD% in our community-based sample, whereas prior exercise and increasing heart rate were associated with higher FMD%. The estimated heritability of FMD was modest. Future research will permit more complete characterization of the genetic and environmental determinants of endothelial function and its prognostic value in the community.

Endothelium and the lipid metabolism: the current understanding

The endothelium is a dynamic organ and responds to various physical and humoral conditions. The endothelium secretes several biologically active substances, both vasoconstrictors and vasodilators, which control these processes. Endothelial function is most commonly assessed as the vasodilatory response to stimuli. Several endothelium-dependent agonists have been identified, each of which acts through a membrane receptor. Nitric oxide which is continuously synthesized by the endothelium has a wide range of biological properties that maintain vascular homeostasis. It is a potent vasodilator and inhibitor of platelet aggregation and thus has an important protective role. Endothelial dysfunction in hypercholesterolemic patients is in large part due to a reduced bioavailability of NO. Traditional coronary risk factors, especially hypercholesterolemia, produce endothelial dysfunction even in patients with normal blood vessels. The underlying mechanisms involve a local inflammatory response, release of cytokines and growth factors, activation of oxidation-sensitive mechanisms in the arterial wall, modulation of intracellular signaling pathways, increased oxidation of low-density lipoprotein cholesterol, and quenching of nitric oxide. Clinical studies have shown a significant improvement in endothelial dysfunction following lowering of serum cholesterol levels, infusion of nitric oxide donors like L-arginine and exercise training. Clinical trials are underway examining the role of endothelin-1 receptor antagonists like bosentan in the prevention of graft atherosclerosis.

Long-term treatment effect of atorvastatin on aortic stiffness in hypercholesterolaemic patients

AIM

To assess the effect of atorvastatin on aortic stiffness in hypercholesterolaemic patients free of arterial hypertension and diabetes mellitus.

METHODS AND RESULTS

The study included 36 patients (25 men and 11 women, mean age 56 +/- 12 years); 18 patients had stable coronary heart disease (CHD) and 18 were free of CHD at baseline. All patients received atorvastatin (20 mg/day) for a 2-year period. Aortic stiffness was assessed by transthoracic echocardiography at baseline and 2 years later. At baseline, total cholesterol, low density lipoprotein cholesterol (LDL-C) and LDL-C/high density lipoprotein cholesterol (HDL-C) ratio were positively related to aortic stiffness (p < 0.001 for all). The mean change in lipid parameters during treatment was: total cholesterol -38%, LDL-C -46%, triglycerides -29%, and HDL-C +6%, all significant (p = 0.029 to < 0.0001). After the 2-year treatment with atorvastatin, aortic stiffness was significantly reduced by 14% (p = 0.019). An improvement of left ventricular (LV) ejection fraction by 13% (p < 0.001) and a reduction of LV mass index by 9% (p = 0.008) were also recorded. The change in aortic stiffness was similar in patients with or without CHD.

CONCLUSION

Long-term treatment with atorvastatin improves aortic stiffness; this index is related to total and coronary mortality. Moreover, assessment of aortic stiffness may be useful in identifying which hypercholesterolaemic patients should be treated aggressively, regardless of CHD. The aortic stiffness effect may eventually become an index of the efficacy of lipid lowering treatment.

Improvement in endothelial dysfunction in patients with hypoalphalipoproteinemia and coronary artery disease treated with bezafibrate

Isolated low high-density lipoprotein cholesterol (HDLc) is a well-known risk factor for cardiovascular disease and is associated with arterial endothelium dysfunction. Several studies have shown that cholesterol lowering in patients with hypercholesterolemia improves endothelial function, but the effect of treating low HDLc levels remains unknown. We studied the effect of increasing HDLc on endothelial function in patients with coronary artery disease (CAD) and isolated low HDLc (HDLc) <0.91 mM, low-density lipoprotein cholesterol (LDLc) <4.1 mM, and triglycerides <2.8 mM. Flow-mediated endothelium-dependent dilatation (FMD) in response to reactive hyperemia was measured by brachial ultrasound, before and after bezafibrate treatment (400 mg daily for 6 months) in 16 patients with CAD and impaired FMD (<10%). After bezafibrate therapy, HDLc increased from 0.79-1.0 mM (p = 0.0008) at the expense of both HDL2 and HDL3 subfractions, apolipoprotein A-I increased from 1.04-1.19 g/l (p = 0.0012), and fibrinogen decreased from 4.45-3.39 g/l (p = 0.0007). The impaired FMD increased after bezafibrate treatment from a median of 2.5-12.3% (p = 0.0004). Endothelial function was normalized in eight patients (50%), improved in four (25%), and did not change in four (25%). These observations indicate that in patients with isolated low HDLc and CAD, bezafibrate treatment improves endothelial function of brachial arteries, increases HDLc and apolipoprotein A-I, and lowers fibrinogen concentrations.

Replacement of dietary saturated fatty acids by trans fatty acids lowers serum HDL cholesterol and impairs endothelial function in healthy men and women

We tested whether trans fatty acids and saturated fatty acids had different effects on flow-mediated vasodilation (FMD), a risk marker of coronary heart disease (CHD). Consumption of trans fatty acids is related to increased risk of CHD, probably through effects on lipoproteins. Trans fatty acids differ from most saturated fatty acids because they decrease serum high-density lipoprotein (HDL) cholesterol, and this may increase the risk of CHD. We fed 29 volunteers 2 controlled diets in a 2x4-week randomized crossover design. The "Trans-diet" contained 9.2 energy percent of trans fatty acids; these were replaced by saturated fatty acids in the "Sat-diet." Mean serum HDL cholesterol after the Trans-diet was 0.39 mmol/L (14.8 mg/dL), or 21% lower than after the Sat-diet (95% CI 0.28 to 0.50 mmol/L). Serum low density lipoprotein and triglyceride concentrations were stable. FMD+SD was 4.4+/-2.3% after the Trans-diet and 6.2+/-3.0% after the Sat-diet (difference -1.8%, 95% CI -3.2 to -0.4). Replacement of dietary saturated fatty acids by trans fatty acids impaired FMD of the brachial artery, which suggests increased risk of CHD. Further studies are needed to test whether the decrease in serum HDL cholesterol caused the impairment of FMD.

Effect of anti-oxidant treatment and cholesterol lowering on resting arterial tone, metabolic vasodilation and endothelial function in the human forearm: a randomized, placebo-controlled study

1. The aim of the present study was to determine whether anti-oxidant therapy with vitamin E and/or cholesterol-lowering therapy with simvastatin would augment resting forearm blood flow (FBF) and metabolic vasodilation in response to exercise and improve endothelial function in young patients with hypercholesterolaemia. 2. Endothelium-dependent and -independent, nitric oxide (NO)-mediated vasodilation have been shown to be impaired in young, otherwise healthy subjects with hypercholesterolaemia. Recent experimental and clinical studies suggest that vascular function may be improved with anti-oxidant or cholesterol- lowering therapy, although these treatments may be synergistic. 3. We compared FBF at rest, in response to isotonic exercise, the endothelium-dependent vasodilator acetylcholine (ACh), the endothelium-independent vasodilator sodium nitroprusside (SNP) and the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) in 26 young, otherwise healthy volunteers (mean (+/-SD) age 29+/-7 years; 14 female, 12 male) with hypercholesterolaemia, before and after 6 months treatment with vitamin E, simvastatin and/or placebo. Treatment was randomized, double-blinded in a 2 x 2 factorial design. Forearm blood flow was measured using venous occlusion plethysmography. 4. Vitamin E therapy increased plasma alpha-tocopherol from 39.5+/-9.6 to 75.7+/-33.8 micromol/L (P < 0.001). Simvastatin reduced total cholesterol from 6.9+/-1.7 to 4.9+/-0.8 mmol/L and low- density lipoprotein (LDL) from 4.8+/-1.7 to 3.0+/-0.7 mmol/L (both P < 0.001), although total and LDL-cholesterol also decreased slightly in the placebo group. Vitamin E increased resting FBF from 2.1+/-0.3 to 2.4+/-0.3 mL/100 mL per min (P = 0.04) and decreased resting forearm vascular resistance from 42.1+/-4.2 to 36.1+/-3.4 units (P = 0.01), but the reduction in resting FBF with L-NMMA was not affected. Vasodilation in response to isotonic exercise, ACh and SNP was similar before and after treatment in the placebo, vitamin E, simvastatin and in the combined vitamin E-simvastatin groups. NG-Monomethyl-L-arginine infusion reduced resting FBF and functional hyperaemia in response to exercise and these responses were not altered by treatment. 5. These data suggest that while vitamin E therapy augments resting FBF and reduces forearm vascular resistance in young hypercholesterolaemic subjects, these effects may not be via NO-dependent pathways. Metabolic vasodilation and responses to the NO-mediated vasodilators ACh and SNP were not favourably affected by anti-oxidant or cholesterol-lowering therapy, either alone or in combination.

Association between C-reactive protein, anti-Chlamydia pneumoniae antibodies, and vascular function in healthy adults

Abnormalities of vascular function occur in patients with risk factors for atherosclerosis before the development of obstructive disease. Our pilot data suggest that elevated serum markers of infection and/or inflammation are associated with functional abnormalities of the vasculature in subjects at otherwise low risk for atherosclerosis.

Effect of lipid reduction on the progression of renal disease: a meta-analysis

BACKGROUND

It has been proposed that hyperlipidemia contributes to the progression of renal disease. A large trial has not been performed; however, a number of small, controlled trials have been reported. We examined the effects of antilipemic agents on glomerular filtration rate and proteinuria or albuminuria in patients with renal disease.

METHODS

We used Medline, abstracts from scientific meetings, and bibliographies from recent reviews and scientific reports to locate pertinent studies. Thirteen prospective controlled trials examining the effects of antilipemic agents on renal function, proteinuria, or albuminuria were included. Studies were published as full reports or abstracts and were at least three months in duration. For five of the studies, individual patient data were obtained. Other summary data were independently extracted from the published reports by two investigators and included study quality, subject characteristics, cause of renal disease, change in serum cholesterol, blood pressure, glomerular filtration rate, proteinuria, and albuminuria.

RESULTS

There was a lower rate of decline in glomerular filtration rate with treatment compared with controls (treated controls, 0.156 mL/min/month; 95% CI, 0.026 to 0. 285 mL/min/month, P = 0.008). The study results were statistically homogeneous, and in a regression analysis, the effect of treatment on glomerular filtration rate did not correlate with study quality, the percentage change in cholesterol, the type of lipid-lowering agent, or the cause of renal disease. However, longer follow-up correlated with the amount of improvement in glomerular filtration rate from treatment (P = 0.007). There was a tendency for a favorable effect of treatment on protein or albumin excretion [Ln (treatment) - Ln (control) = -0.248, 95% CI, -0.562 to 0.064, P = 0. 077]. However, these results were statistically heterogeneous between studies (P < 0.001). No obvious explanation for this heterogeneity was apparent in a regression analysis examining potential reasons for differences in study results.

CONCLUSIONS

Lipid reduction may preserve glomerular filtration rate and may decrease proteinuria in patients with renal disease.

Flow-mediated dilatation

Arterial endothelial dysfunction is one of the key early events in atherogenesis, preceding structural atherosclerotic changes. It is also important in the late stages of obstructive atherosclerosis, predisposing to constriction and/or thrombosis. Endothelial function can be measured in coronary arteries and in the periphery by measuring vasomotor function after intra-arterial infusion of pharmacologic substances which enhance the release of endothelial nitric oxide. The disadvantage of these methods is their invasive nature, which generally makes them unsuitable for studies involving asymptomatic subjects. For this reason, noninvasive tests of endothelial function have been developed. In the most widely used of these, an ultrasound-based method, arterial diameter is measured in response to an increase in shear stress, which causes endothelium-dependent dilatation. Endothelial function assessed by this method correlates with invasive testing of coronary endothelial function, as well as with the severity and extent of coronary atherosclerosis. This noninvasive endothelial function testing has provided valuable insights into early atherogenesis, as well as into the potential reversibility of endothelial dysfunction by various strategies, including pharmacological agents (lipid lowering, ACE inhibition), L-arginine, antioxidants and hormones.

Fibrates, dyslipoproteinaemia and cardiovascular disease

Recent epidemiological data have reaffirmed that elevated plasma triglyceride and low HDL-cholesterol levels are important risk factors for atherosclerotic vascular disease. The rationale for the clinical use of fibric acid derivatives, which are designed to correct this metabolic nexus, is now on firmer ground. The mechanism of action of fibrates on lipoprotein metabolism has recently been elucidated at the molecular level and involves the activation of peroxisome proliferator-activated receptor-alpha 1 in the liver, with the net effect of improving the plasma transport rates of several lipoproteins. Other potential anti-atherothrombotic effects include the inhibition of coagulation and enhancement of fibrinolysis, as well as the inhibition of inflammatory mediators involved in atherogenesis. These consequences probably underpin the favourable effects of fibrates seen in recent angiographic and clinical trials. Two important clinical trials on the effect of gemfibrozil (Veterans Administration-HDL-Cholesterol Intervention Trial) and bezafibrate (Bezafibrate Infarction Prevention Study) have recently been completed in subjects with elevated triglyceride, low HDL and normal or near-normal LDL-cholesterol levels. The results testify to the efficacy of these agents in decreasing the incidence of cardiovascular events, particularly in patients with multiple risk factors and plasma triglyceride levels of over 2.2 mmol/l. The findings of these trials are compared with the statin-based Air Force/Texas Coronary Atherosclerosis Prevention Study, with a recommendation that future studies in appropriately selected patients should examine the synergistic effect of the fibrate/statin combination. The absolute risk reduction in the incidence of coronary events in the Veterans Administration-HDL-Cholesterol Intervention Trial compares favourably with the statin trials. The therapeutic aspects of the efficacy and safety of fibrates are reviewed. Besides primary mixed hyperlipidaemias, particular indications for the clinical use of fibrates include type 2 diabetes, the metabolic syndrome and renal insufficiency. The St Mary's, Ealing, Northwick Park Diabetes Cardiovascular Disease Prevention Study has suggested that fibrates may decrease the incidence of coronary events in type 2 diabetes, but this hypothesis will be more extensively tested in the Diabetes Atherosclerosis Intervention Study, Fenofibrate in Event Lowering in Diabetes Study and Lipids in Diabetes Study projects. Although significant new knowledge has accrued over the past few years concerning the fundamental and clinical aspects of fibrates, the success of these agents in clinical practice depends on the availability of methods for assessing cardiovascular risk as well as on treatment guidelines, which as presently designed and recommended may be inaccurate and suboptimal.

Cholesterol lowering and endothelial function

The pathophysiology of the association between cholesterol and atherosclerosis has been thought to involve the deposition, modification, and cellular uptake of cholesterol. We now believe that the process begins with vascular injury and involves inflammation and vessel remodeling. The vascular endothelium actively regulates vascular tone, lipid breakdown, thrombogenesis, inflammation, and vessel growth, all of which are important factors in the development of atherosclerosis. Endothelial dysfunction promotes atherosclerosis through vasoconstriction, monocyte and platelet adhesion, thrombogenesis, and cytokine and growth factor stimulation and release. An important component of endothelial dysfunction is reduced availability of nitric oxide, which is caused by low-density lipoproteins, especially if they are oxidized. This reduced availability appears to occur through a combination of decreased production, abnormal signaling, and increased destruction by oxygen-free radicals. Concurrently, endothelium-mediated vasoconstrictors, adhesion molecules, cytokines, growth factors, and thrombogenic factors, such as endothelin, are increased by oxidized low-density lipoprotein. Several studies have shown improvements in endothelial function with cholesterol lowering, which may explain the early and substantial reductions in major cardiovascular events associated with cholesterol lowering.

Acute effects of a high-fat meal with and without red wine on endothelial function in healthy subjects

It has been suggested that a high-fat meal may acutely impair endothelium-dependent vasodilation and that this impairment may be prevented by concomitant intake of antioxidants. Because red wine contains antioxidant polyphenols and may reduce cardiovascular disease, we examined the effect of red wine on postprandial endothelial function. Using a crossover design, 13 healthy volunteers consumed a high-fat meal (0.8 g fat/kg body weight) with red wine (3 ml/kg) or an isocaloric control beverage on 2 separate days, 1 week apart. Flow-mediated dilation of the brachial artery was examined by vascular ultrasound at baseline and at 2, 4, and 6 hours after the meal. At these times, flow-mediated dilation with the high-fat meal and control beverage was 9.5 +/- 5.0%, 7.9 +/- 5.1%, 6.8 +/- 3.6%, and 7.3 +/- 4.6%, respectively (nonsignificant trend). There was also a nonsignificant trend for flow-mediated dilation after the high-fat meal with wine: 8.0 +/- 4.1%, 5.7 +/- 4.7%, 6.4 +/- 3.1%, and 6.9 +/- 3.8%, respectively. There was no difference in the effects between wine and the control beverage (p = 0.77). Triglycerides increased 2- to 2.7-fold over baseline (p = 0.0001) with a peak occurring 5 hours after the high-fat meals. In contrast to previous studies, the present study did not demonstrate a significant effect of a high-fat meal on endothelial vasomotor function in healthy subjects. Under these conditions, we did not demonstrate a beneficial acute effect of red wine on endothelial function.

Effects of withdrawal of chronic estrogen therapy on brachial artery vasoreactivity in women with coronary artery disease

Withdrawal of oral estrogen therapy is associated with a deterioration in endothelial function in postmenopausal women with coronary artery disease. Our data also suggest that withdrawal of estrogen results in enhanced hyperemic flow, although this observation will require validation with further study.