Marijn C. Meuwese

The endothelial glycocalyx: a potential barrier between health and vascular disease.

Purpose of review Although cardiovascular prevention has improved substantially, we still face the challenge of finding new targets to reduce the sequelae of atherosclerosis further. In this regard, optimizing the vasculoprotective effects of the vessel wall itself warrants intensive research. In particular, the endothelial glycocalyx, consisting of proteoglycans, glycoproteins and adsorbed plasma proteins, may play an essential role in protecting the vessel wall from atherosclerosis. Recent developments In this review, we will discuss the different vasculoprotective effects exerted by the endothelial glycocalyx, the factors that damage it, and the first preliminary data on the glycocalyx dimension in humans. Whereas most glycocalyx research has traditionally focused on the microvasculature, more recent data have underscored the importance of the glycocalyx in protecting the macrovasculature against pro-atherogenic insults. It has been shown that glycocalyx loss is accompanied by a wide array of unfavourable changes in both small and larger vessels. Pro-atherogenic stimuli increase the shedding of glycocalyx constituents into the circulation, contributing to the progressive loss of the vasculoprotective properties of the vessel wall. Novel techniques have facilitated reproducible measurements of systemic glycocalyx volume in humans. Consistent with experimental data, the volume of the human glycocalyx is also severely perturbed by exposure to atherogenic risk factors. Summary Cumulating evidence suggests that an intact glycocalyx protects the vessel wall, whereas disruption of the glycocalyx upon atherogenic stimuli increases vascular vulnerability for atherogenesis.

Measurement of carotid intima-media thickness to assess progression and regression of atherosclerosis.

Imaging modalities have been developed to assess atherosclerosis in vivo in the arterial wall because large clinical end-point studies are time-consuming and costly. Historically, in-hospital angiography and Doppler ultrasonography have been used to assess atherosclerosis development. Investigations of the arterial lumen are, however, increasingly being replaced by modalities that can measure changes in the arterial wall itself—intravascular ultrasonography, MRI and multislice CT. The fact that intravascular ultrasonography is invasive, CT involves substantial radiation exposure and requires contrast agents, and that MRI is time-consuming and technically challenging all limit the widespread use of these techniques. Moreover, all modalities have high associated costs. B-mode ultrasonographic imaging of the carotid arterial walls occupies a unique position in atherosclerosis research. This method enables sensitive, reproducible and noninvasive assessment of intima–media thickness (IMT) as a continuous variable. Epidemiological and clinical trial evidence as well as digitization and standardization have made carotid IMT a validated and accepted marker for generalized atherosclerosis burden and vascular disease risk. Here we describe the application of carotid IMT measurements as a tool in risk evaluation of individuals and in studies of atherosclerosis progression and regression.

ACAT Inhibition and Progression of Carotid Atherosclerosis in Patients With Familial Hypercholesterolemia: The CAPTIVATE Randomized Trial

CONTEXT Inhibition of acyl coenzyme A:cholesterol acyltransferase (ACAT), an intracellular enzyme involved in cholesterol accumulation, with pactimibe was developed to assist in the prevention of cardiovascular disease. OBJECTIVE To evaluate the efficacy and safety of pactimibe in inhibition of atherosclerosis. DESIGN, SETTING, AND PATIENTS A prospective, randomized, stratified, double-blind, placebo-controlled study (Carotid Atherosclerosis Progression Trial Investigating Vascular ACAT Inhibition Treatment Effects [CAPTIVATE]) of 892 patients heterozygous for familial hypercholesterolemia conducted at 40 lipid clinics in the United States, Canada, Europe, South Africa, and Israel between February 1, 2004, and December 31, 2005. Study was terminated on October 26, 2005. INTERVENTION Participants received either 100 mg/d of pactimibe (n = 443) or matching placebo (n = 438), in addition to standard lipid-lowering therapy. MAIN OUTCOME MEASURES Carotid atherosclerosis, assessed by ultrasound carotid intima-media thickness (CIMT), at baseline, 12, 18, and 24 months. Maximum CIMT was the primary end point and mean CIMT the secondary end point. RESULTS Because pactimibe failed to show efficacy in the intravascular coronary ultrasound ACTIVATE study, the CAPTIVATE study was terminated prematurely after a follow-up of 15 months. After 6 months of treatment with pactimibe, low-density lipoprotein cholesterol increased by 7.3% (SD, 23%) compared with 1.4% (SD, 28%) in the placebo group (P = .001). The carotid ultrasonographic scans of the 716 patients with at least 2 scans and obtained at least 40 weeks apart were analyzed. Maximum CIMT measurements did not show a pactimibe treatment effect (difference, 0.004 mm; 95% confidence interval [CI], -0.023 to 0.015 mm; P = .64); however, the less variable mean CIMT measurement revealed an increase of 0.014 mm (95% CI, -0.027 to 0.000 mm; P = .04) in patients administered pactimibe vs placebo. Major cardiovascular events (cardiovascular death, myocardial infarction, and stroke) occurred more often in patients administered pactimibe vs placebo (10/443 [2.3%] vs 1/438 [0.2%]; P = .01). CONCLUSIONS In patients with familial hypercholesterolemia, pactimibe had no effect on atherosclerosis as assessed by changes in maximum CIMT compared with placebo but was associated with an increase in mean CIMT as well as increased incidence of major cardiovascular events. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00151788.

Plasma concentrations of ascorbic acid and C-reactive protein, and risk of future coronary artery disease, in apparently healthy men and women: the EPIC-Norfolk prospective population study

High plasma concentrations of ascorbic acid, a marker of fruit and vegetable intake, are associated with low risk of coronary artery disease. Whether this relationship is explained by a reduction in systemic inflammation is unclear. We investigated the relationship between ascorbic acid plasma concentration and coronary artery disease risk, and in addition whether this relationship depended on classical risk factors and C-reactive protein (CRP) concentration. We used a prospective nested case-control design. The study consisted of 979 cases and 1794 controls (1767 men and 1006 women). Increasing ascorbic acid quartiles were associated with lower age, BMI, systolic and diastolic blood pressure, and CRP concentration, but with higher HDL-cholesterol concentration. No associations existed between ascorbic acid concentration and total cholesterol concentration or LDL-cholesterol concentration. When data from men and women were pooled, the risk estimates decreased with increasing ascorbic acid quartiles such that people in the highest ascorbic acid quartile had an odds ratio for future coronary artery disease of 0.67 (95 % CI 0.52, 0.87) compared with those in the lowest quartile (P for linearity=0.001). This relationship was independent of sex, age, diabetes, smoking, BMI, LDL-cholesterol, HDL-cholesterol, systolic blood pressure and CRP level. These data suggest that the risk reduction associated with higher ascorbic acid plasma concentrations, a marker of fruit and vegetable intake, is independent of classical risk factors and also independent of CRP concentration.

Serum Levels of Mannose-Binding Lectin and the Risk of Future Coronary Artery Disease in Apparently Healthy Men and Women

Objective—To determine the association between serum levels of mannose-binding lectin (MBL) and the risk of future coronary artery disease (CAD) in apparently healthy men and women. Methods and Results—We performed a prospective case-control study among apparently healthy men and women nested in the EPIC-Norfolk cohort. Baseline concentrations of MBL were measured in serum samples of 946 patients who experienced a myocardial infarction or died of CAD during follow-up, and 1799 matched controls who remained free of CAD. Among men, median MBL levels were 1.63 ng/mL (interquartile range [IQR]: 0.59 to 3.80) in cases and 1.20 ng/mL (IQR: 0.48 to 3.37) in controls. Among women, median MBL levels were 1.02 ng/mL (IQR: 0.43 to 2.95) in cases and 1.01 ng/mL (IQR: 0.43 to 2.94) in controls. After adjustment, the odds ratio in men for future CAD was 1.59 (95% confidence interval [CI]: 1.09 to 2.32; P for linearity=0.01) for those in the highest quartile compared with those in the lowest quartile. In women no such relation was observed. Conclusions—Elevated levels of MBL are associated with an increased risk of future CAD in apparently healthy men but not in women. The sex difference merits further exploration.

And then there were acyl coenzyme A:cholesterol acyl transferase inhibitors

Purpose of review The reputation of acyl coenzyme A:cholesterol acyltransferase (ACAT) inhibitors has changed profoundly from promising new drugs for cardiovascular prevention to drugs without clinical benefits or possibly even with adverse effects. Recent findings ACAT inhibitors decrease the intracellular conversion of free cholesterol into cholesteryl ester in a number of tissues, including intestine, liver and macrophages. In contrast to promising results in experimental animal models, all subsequent clinical studies in humans with ACAT inhibitors failed to show lipid profile changes as well as reductions in surrogate markers for coronary artery disease. In fact, there was even a tendency towards an increase in atheroma burden in the most recent and well executed clinical trials. In addition, the inhibition of this pivotal enzyme in cholesterol esterification may interfere with reverse cholesterol transport. Summary In our opinion, the consistent negative findings in recent clinical trials have virtually eliminated the chances for this class of drugs to be introduced for cardiovascular prevention. Possible strategies focused on selective ACAT 2 inhibition or the combination of ACAT inhibitors with compounds that stimulate reverse cholesterol transport may prove to have clinical benefit. This will have to await further clinical research in humans, however, as, obviously, rodent models cannot provide reliable data as to the efficacy of this class of drugs in humans.

Endothelial Surface Layer Degradation by Chronic Hyaluronidase Infusion Induces Proteinuria in Apolipoprotein E-Deficient Mice

Objective Functional studies show that disruption of endothelial surface layer (ESL) is accompanied by enhanced sensitivity of the vasculature towards atherogenic stimuli. However, relevance of ESL disruption as causal mechanism for vascular dysfunction remains to be demonstrated. We examined if loss of ESL through enzymatic degradation would affect vascular barrier properties in an atherogenic model. Methods Eight week old male apolipoprotein E deficient mice on Western-type diet for 10 weeks received continuous active or heat-inactivated hyaluronidase (10 U/hr, i.v.) through an osmotic minipump during 4 weeks. Blood chemistry and anatomic changes in both macrovasculature and kidneys were examined. Results Infusion with active hyaluronidase resulted in decreased ESL (0.32±0.22 mL) and plasma volume (1.03±0.18 mL) compared to inactivated hyaluronidase (0.52±0.29 mL and 1.28±0.08 mL, p<0.05 respectively).Active hyaluronidase increased proteinuria compared to inactive hyaluronidase (0.27±0.02 vs. 0.15±0.01 µg/µg protein/creatinin, p<0.05) without changes in glomerular morphology or development of tubulo-interstitial inflammation. Atherosclerotic lesions in the aortic branches showed increased matrix production (collagen, 32±5 vs. 18±3%; glycosaminoglycans, 11±5 vs. 0.1±0.01%, active vs. inactive hyaluronidase, p<0.05). Conclusion ESL degradation in apoE deficient mice contributes to reduced increased urinary protein excretion without significant changes in renal morphology. Second, the induction of compositional changes in atherogenic plaques by hyaluronidase point towards increased plaque vulnerability. These findings support further efforts to evaluate whether ESL restoration is a valuable target to prevent (micro) vascular disease progression.

Myeloperoxidase is not associated with scintigraphic myocardial perfusion abnormalities in type 2 diabetic patients with mild stable anginal complaints.

BACKGROUND MPO, an enzyme of the innate immune system, exhibits pro-atherogenic effects. These include oxidative damage to LDL- and HDL-cholesterol, and promotion of endothelial dysfunction. Recent studies revealed that MPO independently predicts adverse outcomes in patients with chest pain or suspected acute coronary syndrome. We evaluated whether plasma myeloperoxidase (MPO) levels are associated with scintigraphic myocardial perfusion abnormalities, in type 2 diabetic patients with mild anginal complaints. METHODS MPO was measured in plasma samples of 267 patients with diabetes mellitus type 2 and stable angina pectoris complaints (Canadian Cardiovascular Society class I-II/IV) prior to myocardial perfusion scintigraphy (MPS). RESULTS The median plasma level of MPO was 141 pmol/L (IQR 115-171 pmol/L). One-hundred-ninety patients (71%) had perfusion abnormalities on MPS and of these, 138 patients had myocardial ischemia. No relation was found between plasma MPO levels and the scintigraphic myocardial perfusion abnormalities. Even in combination with known other cardiovascular risk factors MPO failed to predict scintigraphic myocardial perfusion abnormalities. CONCLUSIONS MPO levels are not associated with scintigraphic myocardial perfusion abnormalities in type 2 diabetic patients with mild anginal complaints. Therefore, in type 2 diabetic patients MPO is not a useful biomarker to predict hemodynamically significant coronary artery disease.

Increases in myeloperoxidase levels after exercise in myocardial perfusion scintigraphy are not induced by myocardial ischemia

BACKGROUND Increased systemic levels of myeloperoxidase (MPO) have been reported in patients with acute myocardial ischemia. We studied the association between exercise-induced myocardial ischemia measured by myocardial perfusion scintigraphy (MPS) and the magnitude and time course of changes in MPO levels in humans. METHODS One hundred and twenty six patients underwent symptom limited exercise MPS. Myocardial ischemia was assessed semi-quantitatively. Plasma samples were taken before the start of exercise (baseline), at maximum exercise and every hour up to 6 h after maximum exercise. RESULTS Myocardial ischemia was present in 42 (33%) patients. MPO levels rapidly increased during exercise in patients with and without ischemia (to 131% (106-172%) and 145% (121-199%) of baseline, respectively). MPO levels and absolute changes in MPO did not differ between patients with and without ischemia at any time point. None of the patient characteristics, including presence of ischemia, was independently predictive of the absolute increase in MPO levels during exercise. CONCLUSIONS Exercise related immediate increases in MPO levels do not reflect myocardial ischemia.