Relationship between cardiovascular risk factors and atherosclerotic disease burden measured by intravascular ultrasound

OBJECTIVES

The goal of this study was to determine the relationship between established cardiovascular risk factors and the extent of coronary atherosclerotic plaque.

BACKGROUND

Few data exist correlating cardiovascular risk factors with volumetric measurements of coronary atheroma burden in patients with coronary artery disease.

METHODS

Clinical characteristics, quantitative coronary angiography, and intravascular ultrasound (IVUS) were evaluated in subjects enrolled in a study comparing atorvastatin and pravastatin. Plaque areas were measured at 1-mm intervals to compute atheroma volume. The percent of cross sections with an abnormal intimal thickness (>0.5 mm) was determined. Data on cardiovascular risk factors were collected.

RESULTS

In 654 subjects, atheroma volume averaged 174.5 mm3 and percent atheroma volume 38.9%. Atherosclerosis was present in 81.2% of 25,897 cross sections. In univariate analysis, there was a strong association between diabetes, male gender, and a history of either prior revascularization or stroke with percent atheroma volume. Hypertension or prior myocardial infarction was also predictive of more severe disease. Low-density lipoprotein and C-reactive protein were not significant predictors of greater disease burden. In multivariate analysis, diabetes, male gender, and a history of a prior interventional procedure remained strong predictors of increased atheroma volume. History of stroke, non-Caucasian race, and smoking status remained significant. Although multiple measures of IVUS disease burden were worse in subjects with diabetes, angiographic stenosis severity was not different.

CONCLUSIONS

Male gender, diabetes, and a history of prior revascularization are strong independent predictors of atherosclerotic burden in coronary disease patients. Many risk factors did not predict angiographic disease severity, suggesting different mechanisms drive stenosis development and atheroma accumulation.

Effect of very high-intensity statin therapy on regression of coronary atherosclerosis: the ASTEROID trial

CONTEXT

Prior intravascular ultrasound (IVUS) trials have demonstrated slowing or halting of atherosclerosis progression with statin therapy but have not shown convincing evidence of regression using percent atheroma volume (PAV), the most rigorous IVUS measure of disease progression and regression.

OBJECTIVE

To assess whether very intensive statin therapy could regress coronary atherosclerosis as determined by IVUS imaging.

DESIGN AND SETTING

Prospective, open-label blinded end-points trial (A Study to Evaluate the Effect of Rosuvastatin on Intravascular Ultrasound-Derived Coronary Atheroma Burden [ASTEROID]) was performed at 53 community and tertiary care centers in the United States, Canada, Europe, and Australia. A motorized IVUS pullback was used to assess coronary atheroma burden at baseline and after 24 months of treatment. Each pair of baseline and follow-up IVUS assessments was analyzed in a blinded fashion.

PATIENTS

Between November 2002 and October 2003, 507 patients had a baseline IVUS examination and received at least 1 dose of study drug. After 24 months, 349 patients had evaluable serial IVUS examinations.

INTERVENTION

All patients received intensive statin therapy with rosuvastatin, 40 mg/d.

MAIN OUTCOME MEASURES

Two primary efficacy parameters were prespecified: the change in PAV and the change in nominal atheroma volume in the 10-mm subsegment with the greatest disease severity at baseline. A secondary efficacy variable, change in normalized total atheroma volume for the entire artery, was also prespecified.

RESULTS

The mean (SD) baseline low-density lipoprotein cholesterol (LDL-C) level of 130.4 (34.3) mg/dL declined to 60.8 (20.0) mg/dL, a mean reduction of 53.2% (P<.001). Mean (SD) high-density lipoprotein cholesterol (HDL-C) level at baseline was 43.1 (11.1) mg/dL, increasing to 49.0 (12.6) mg/dL, an increase of 14.7% (P<.001). The mean (SD) change in PAV for the entire vessel was -0.98% (3.15%), with a median of -0.79% (97.5% CI, -1.21% to -0.53%) (P<.001 vs baseline). The mean (SD) change in atheroma volume in the most diseased 10-mm subsegment was -6.1 (10.1) mm3, with a median of -5.6 mm3 (97.5% CI, -6.8 to -4.0 mm3) (P<.001 vs baseline). Change in total atheroma volume showed a 6.8% median reduction; with a mean (SD) reduction of -14.7 (25.7) mm3, with a median of -12.5 mm3 (95% CI, -15.1 to -10.5 mm3) (P<.001 vs baseline). Adverse events were infrequent and similar to other statin trials.

CONCLUSIONS

Very high-intensity statin therapy using rosuvastatin 40 mg/d achieved an average LDL-C of 60.8 mg/dL and increased HDL-C by 14.7%, resulting in significant regression of atherosclerosis for all 3 prespecified IVUS measures of disease burden. Treatment to LDL-C levels below currently accepted guidelines, when accompanied by significant HDL-C increases, can regress atherosclerosis in coronary disease patients. Further studies are needed to determine the effect of the observed changes on clinical outcome.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00240318.

Effect of ACAT inhibition on the progression of coronary atherosclerosis

BACKGROUND

The enzyme acyl-coenzyme A:cholesterol acyltransferase (ACAT) esterifies cholesterol in a variety of tissues. In some animal models, ACAT inhibitors have antiatherosclerotic effects.

METHODS

We performed intravascular ultrasonography in 408 patients with angiographically documented coronary disease. All patients received usual care for secondary prevention, including statins, if indicated. Patients were randomly assigned to receive the ACAT inhibitor pactimibe (100 mg per day) or matching placebo. Ultrasonography was repeated after 18 months to measure the progression of atherosclerosis.

RESULTS

The primary efficacy variable analyzing the progression of atherosclerosis--the change in percent atheroma volume--was similar in the pactimibe and placebo groups (0.69 percent and 0.59 percent, respectively; P=0.77). However, both secondary efficacy variables assessed by means of intravascular ultrasonography showed unfavorable effects of pactimibe treatment. As compared with baseline values, the normalized total atheroma volume showed significant regression in the placebo group (-5.6 mm3, P=0.001) but not in the pactimibe group (-1.3 mm3, P=0.39; P=0.03 for the comparison between groups). The atheroma volume in the most diseased 10-mm subsegment regressed by 3.2 mm3 in the placebo group, as compared with a decrease of 1.3 mm3 in the pactimibe group (P=0.01). The combined incidence of adverse cardiovascular outcomes was similar in the two groups (P=0.53).

CONCLUSIONS

For patients with coronary disease, treatment with an ACAT inhibitor did not improve the primary efficacy variable (percent atheroma volume) and adversely affected two major secondary efficacy measures assessed by intravascular ultrasonography. ACAT inhibition is not an effective strategy for limiting atherosclerosis and may promote atherogenesis. (ClinicalTrials.gov number, NCT00268515.).

Relationship between atheroma regression and change in lumen size after infusion of apolipoprotein A-I Milano

OBJECTIVES

The aim of this study was to determine the relationship between atheroma regression and arterial wall remodeling.

BACKGROUND

Infusion of reconstituted high-density lipoprotein (rHDL) containing recombinant apolipoprotein A-I Milano (AIM) has been reported to promote rapid regression of coronary atherosclerosis. The current study analyzed intravascular ultrasound (IVUS) to define the changes that take place in the arterial wall that accompanied atheroma regression in this study.

METHODS

Forty-seven patients, ages 30 to 75 years, after an acute coronary syndrome were randomized to receive five weekly infusions of placebo or rHDL containing either low- or high-dose AIM. External elastic membrane (EEM) and lumen volumes were compared between coronary IVUS studies at baseline and follow-up.

RESULTS

In comparison with baseline, infusion of rHDL was associated with a 4.6% reduction in EEM volume. Lumen volume did not change. In 10-mm arterial subsegments with the greatest plaque burden at baseline, atheroma volume regressed by 10.9% with a similar reduction in EEM volume but with no change in lumen size. In contrast, EEM and atheroma volume did not change in the 10-mm segments containing the least plaque burden. The reduction in EEM in the most diseased segments was only apparent in subjects who underwent plaque regression. Reduction in EEM volume correlated with the decreased atheroma volume (r = 0.62), but there was no correlation between change in lumen size and change in plaque volume.

CONCLUSIONS

Remodeling of the arterial wall is a focal and heterogeneous process. After infusion of rHDL containing AIM, regression of coronary atherosclerosis is accompanied by reverse remodeling of the EEM, resulting in no change in luminal dimensions.

Compensatory enlargement of human coronary arteries during progression of atherosclerosis is unrelated to atheroma burden: serial intravascular ultrasound observations from the REVERSAL trial

AIMS

On the basis of the evidence from autopsy studies, it is accepted that compensatory enlargement (remodelling) of coronary arteries during progression of atherosclerosis diminishes once atheroma burden (cross-sectional area stenosis) reaches approximately 40%. Our aim was to evaluate whether atheroma burden is a limiting factor for coronary arterial remodelling using in vivo serial intravascular ultrasound (IVUS).

METHODS AND RESULTS

From the cohort of the Reversal of Atherosclerosis with Aggressive Lipid Lowering (REVERSAL) trial, we identified 210 focal coronary lesions at baseline IVUS. Of these, 128 lesions that had an increase in atheroma area at the 18-month follow-up IVUS were included in the analysis. Lesions were matched at baseline and follow-up. The increase in external elastic membrane (EEM) area for each mm(2) increase in atheroma area was not significantly different in lesions with <40 and >or=40% atheroma burden at baseline (1.62 vs. 1.28 mm(2), P=0.30). There were no correlations between atheroma burden at baseline and change in EEM (r=0.02, P=0.86) or change in lumen (r=0.04, P=0.64) areas.

CONCLUSION

Assessment of coronary arterial remodelling by serial IVUS revealed that compensatory remodelling is not limited by atheroma burden. Atheroma burden is not a determinant of arterial enlargement during the progression of atherosclerosis.

Quantification of 3-nitrotyrosine levels using a benchtop ion trap mass spectrometry method

Oxidative damage by reactive nitrogen species is linked to the pathogenesis of numerous inflammatory disorders, including atherosclerosis. 3-Nitrotyrosine (NO2Tyr), a posttranslational modification of proteins generated by reactive nitrogen species, serves as a "molecular fingerprint" for protein modification by nitric oxide (NO)-derived oxidants. Studies demonstrate that systemic levels of protein-bound NO2Tyr serve as an independent predictor of cardiovascular risks and are modulated by statin therapy. Measurement of NO2Tyr in biological matrices may thus serve both as a quantitative index of nitrative stress in vivo and an important new prognostic marker of clinical relevance. Analytical methods for the accurate detection and quantification of trace levels of NO2Tyr in biological tissues and fluids are, thus, of considerable interest. Here, we describe a rapid, sensitive, and specific method for the quantification of NO2Tyr in biological matrices using readily available benchtop ion-trap mass spectrometry instrumentation (e.g., LCQDeca) combined with high-performance liquid chromatography (HPLC) interface. Through judicious use of stable isotopically labeled precursors as synthetic internal standards, the tandem mass spectrometric method described simultaneously adjusts for potential intrapreparative sample losses and monitors potential artifactual generation of NO2Tyr during processing. The described method permits rapid and reproducible quantification of NO2Tyr in biological and clinical specimens at the 100 fmol on column detection limit and should prove useful for studies defining the impact of reactive nitrogen species in cardiovascular disease and other inflammatory disorders.

Recent trends in coronary intravascular ultrasound: Tracking atherosclerosis, pursuit of vulnerable plaques, and beyond

Within the past decade, intravascular ultrasound (IVUS) has proved to be a useful modality for guiding coronary interventions and assessment of cardiac allograft vasculopathy. During the last few years, IVUS has been used increasingly for the evaluation of the efficacy of various possible antiatherosclerotic therapies including high-dose statins, antihypertensives, and recombinant apolipoprotein A-I Milano. The recently introduced radiofrequency signal analysis is an advanced method for evaluation of IVUS signals to determine various histologic components of atherosclerotic plaques. Elastography is an allied technology for measuring the tissue strain that occurs in response to changes in intraluminal pressure. Whether radiofrequency signal analysis or elastography will become clinically useful tools for detecting vulnerable plaques remains an unanswered, burning question.

[Assessment of progression and regression of coronary atherosclerosis by intravascular ultrasound. A new paradigm shift?]

Intravascular ultrasound (IVUS) has emerged as a powerful imaging modality for the assessment of the arterial wall and it's response to the accumulation of atherosclerotic plaque. The ability to image the coronary arteries on a serial basis provides a unique opportunity for IVUS to monitor the impact that potential anti-atherosclerotic strategies exert on plaque burden. As a result, studies incorporating serial IVUS imaging as the primary endpoint have demonstrated that therapeutic strategies that modify LDL, HDL and blood pressure in patients with established coronary artery disease can have a profound impact on the progression of atherosclerotic plaque. This heralds a paradigm shift that emphasizes plaque regression as a potential target in the development of preventive strategies.

Effect of atorvastatin (80 mg/day) versus pravastatin (40 mg/day) on arterial remodeling at coronary branch points (from the REVERSAL study)

The effect of moderate and intensive lipid lowering on plaque progression and arterial remodeling at coronary branch points was investigated. Intensive (+1 +/- 19.6%), but not moderate (+4.1 +/- 15.1%), lipid lowering prevented an increase in the percent [corrected] plaque area at the branch points. The 2 strategies were associated with increased areas of the lumen (+7.6% to 9.4%) and external elastic membrane (+9.6% to 10.8%). In contrast, there was no significant change in plaque, lumen, and/or external elastic membrane areas at the nonbranch point site. These results suggest that intensive lipid lowering can have a dramatic effect on atheroma-prone regions and that remodeling in response to changes in plaque is a heterogenous process.

Impact of Short-Term Administration of High-Density Lipoproteins and Atorvastatin on Atherosclerosis in Rabbits

OBJECTIVE

This study investigates effects of short-term administration of high-density lipoproteins (HDL) and a statin on atherosclerosis in cholesterol-fed rabbits. Effects of HDL apolipoprotein and phospholipid composition have also been investigated.

METHODS AND RESULTS

Aortic atherosclerosis was established over 17 weeks in 46 rabbits by balloon denudation and cholesterol feeding. During the past 5 days of the cholesterol-feeding period, animals received: (1) no treatment; (2) oral atorvastatin 5 mg/kg on each of the 5 days; or (3) infusions of HDL (8 mg/kg apolipoprotein A-I) on days 1 and 3 of the treatment phase. After euthanization, lesion size and composition were assessed by histological and immunohistochemical analysis. HDL (but not atorvastatin) reduced lesion size by 36% (P<0.05). The ratio of smooth muscle cells to macrophages in the lesions increased 2.6-fold in animals infused with HDL (P<0.05) and 4-fold in those receiving atorvastatin (P<0.01). HDL and atorvastatin reduced matrix metalloproteinase (MMP)-9 expression by 42% (P<0.05) and 45% (P<0.03), respectively. HDL increased thrombomodulin expression 2-fold (P<0.03). The beneficial effects on lesion area and plaque cellular composition were influenced by HDL phospholipid and apolipoprotein composition.

CONCLUSIONS

Infusing small amounts of HDL rapidly reduces lesion size and is comparable to atorvastatin in promoting a stable plaque phenotype.

Formation of Dysfunctional High-Density Lipoprotein by Myeloperoxidase

Recent studies identify the presence of high-density lipoprotein (HDL) particles in patients with cardiovascular disease, which are "dysfunctional," lacking in typical atheroprotective properties, and promoting proinflammatory effects. The mechanisms for generating dysfunctional HDL have been unclear. New evidence points to a role for myeloperoxidase (MPO)-generated oxidants as participants in rendering HDL dysfunctional within human atherosclerotic plaque. Myeloperoxidase was recently shown to bind to HDL within human atherosclerotic lesions, and biophysical studies reveal MPO binding occurs via specific interactions with apolipoprotein (apo) A-I, the predominant protein of HDL. This likely facilitates the observed selective targeting of apoA-I for site-specific chlorination and nitration by MPO-generated reactive oxidants in vivo. One apparent consequence of MPO-catalyzed apoA-I oxidation includes the functional impairment of the ability of HDL to promote cellular cholesterol efflux via the adenosine triphosphate binding cassette-1 transport system. Myeloperoxidase-mediated loss of the atheroprotective functional properties of HDL may thus provide a novel mechanism linking inflammation and oxidative stress to the pathogenesis of atherosclerosis.

High-density lipoproteins as therapeutic targets

PURPOSE OF REVIEW

The concentration of cholesterol in HDL is an inverse predictor of future cardiovascular disease, with evidence mounting that therapies that increase HDL concentration are antiatherogenic. The best known antiatherogenic function of HDL particles relates to their ability to promote the efflux of cholesterol from cells. However, they also have antioxidant, antiinflammatory and antithrombotic properties.

RECENT FINDINGS

The past year has seen the publication of several papers that highlight a potential major protective role of HDL in states of acute inflammation. Papers showing extremely promising results using novel inhibitors of cholesteryl ester transfer protein as HDL-raising agents have also appeared. Finally, the discovery that ATP-binding cassette transporter G1 (ABCG1) transports cell cholesterol to large HDL particles in the extracellular space has largely reconciled apparent inconsistencies between basic research indicating that small, pre-beta-migrating HDL particles are the antiatherogenic components of HDL and epidemiological research that implicates larger HDL particles as the protective fraction.

SUMMARY

The finding that ABCG1 promotes the efflux of cholesterol from cells to large HDL particles also provides powerful circumstantial evidence that cholesteryl ester transfer protein inhibition (which increases HDL size) may enhance, rather than reduce, cholesterol efflux, and thus inhibit the development of atherosclerosis.

Myeloperoxidase and Cardiovascular Disease

Myeloperoxidase (MPO) is a leukocyte-derived enzyme that catalyzes the formation of a number of reactive oxidant species. In addition to being an integral component of the innate immune response, evidence has emerged that MPO-derived oxidants contribute to tissue damage during inflammation. MPO-catalyzed reactions have been attributed to potentially proatherogenic biological activities throughout the evolution of cardiovascular disease, including during initiation, propagation, and acute complication phases of the atherosclerotic process. As a result, MPO and its downstream inflammatory pathways represent attractive targets for both prognostication and therapeutic intervention in the prophylaxis of atherosclerotic cardiovascular disease.

Reconstituted high-density lipoproteins inhibit the acute pro-oxidant and proinflammatory vascular changes induced by a periarterial collar in normocholesterolemic rabbits

BACKGROUND

HDLs have antiinflammatory and antioxidant properties in vitro. This study investigates these properties in vivo.

METHODS AND RESULTS

Chow-fed, normocholesterolemic New Zealand White rabbits received a daily infusion of (1) saline, (2) reconstituted HDL (rHDL) containing 25 mg apolipoprotein (apo) A-I and 50 mg of either 1-palmitoyl-2-linoleoyl phosphatidylcholine (PLPC) or 1,2-dipalmitoyl phosphatidylcholine (DPPC), (3) 25 mg lipid-free apoA-I, or (4) 50 mg of either PLPC-small unilamellar vesicles (SUVs) or DPPC-SUVs on each of 3 consecutive days. Nonocclusive carotid periarterial collars were implanted after the second dose of treatment. Forty-eight hours after insertion of the collars, the arteries were removed and analyzed for the presence of reactive oxygen species, the infiltration of neutrophils, and the expression of adhesion proteins and chemokines. Insertion of the periarterial collar induced a 4.1-fold increase in presence of vascular wall reactive oxygen species. This effect was completely abolished in the animals infused with rHDL. The periarterial collar was associated with a dense infiltration of the arterial wall by polymorphonuclear leukocytes. This infiltration was inhibited by 73% to 94% in the animals infused with rHDL, by 75% in the animals infused with lipid-free apoA-I, and by 51% to 65% in animals infused with SUVs. There were no significant differences between the effects of PLPC and DPPC in either the rHDL or SUVs. Endothelial expression of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and monocyte chemoattractant protein-1 was also increased by the collar insertion and inhibited by rHDL, lipid-free apoA-I, and, to a lesser extent, also by the SUVs.

CONCLUSIONS

Infusion of rHDL, apoA-I, and phospholipid-SUVs inhibits the early pro-oxidant and proinflammatory changes induced by a periarterial collar in normocholesterolemic rabbits.

The role of myeloperoxidase in the pathogenesis of coronary artery disease

A growing body of evidence continues to emerge implicating the role of myeloperoxidase (MPO) and its oxidant products in the promotion of atherogenesis. A major mechanism by which MPO impacts the arterial wall is through its modification of net cellular cholesterol flux. MPO promotes lipid peroxidation and conversion of LDL to an atherogenic form, where it is taken up by macrophages, a critical step in foam cell formation. Emerging evidence suggests that HDL can also be modified by MPO derived oxidants, resulting in an impairment of cholesterol efflux. In addition, modified HDL appears to be a strong predictor of clinical risk. These features highlight MPO and its products as potential predictive markers and targets in atheroprotection.

Underuse of beta-blockers following myocardial infarction: a tale of two cities

AIMS

To measure factors associated with underuse of beta-blocker therapy after myocardial infarction (MI).

METHODS

The Newcastle and Perth collaborating centres of the World Health Organization (WHO) MONICA project (to MONItor trends and determinants of Cardiovascular disease) systematically evaluated all patients admitted to hospital in their respective regions with possible MI. A total of 1766 patients in Newcastle and 4,503 patients in Perth, discharged from hospital after confirmed MI from 1985 to 1993, were studied. Rates of beta-blocker use before and after hospital discharge were evaluated and correlates of beta-blocker use determined.

RESULTS

Beta-blocker use was similar in Newcastle and Perth before MI (21% of patients in each centre). During hospital admission, beta-blocker therapy was initiated nearly twice as frequently in Perth compared with Newcastle (66 vs 36%, respectively) and more patients were discharged from hospital on beta-blockers in Perth (68%) than in Newcastle (45%). The main factors associated with underuse of beta-blockers in multivariate analysis were geographical centre (odds ratio (OR) for Newcastle compared with Perth 0.3; 95% confidence interval (CI) 0.3-0.3), a history of previous MI (OR 0.6, 95% CI 0.5-0.7), admission to hospital in earlier years (OR 0.4, 95% CI 0.3-0.4 for years 1985-87 compared with years 1991-93), diabetes (OR 0.6, 95% CI 0.5-0.8) and the concomitant use of diuretics (OR 0.5, 95% CI 0.4-0.6) and calcium antagonists (OR 0.6, 95% CI 0.5-0.8).

CONCLUSIONS

Underuse of beta-blockers after MI was strongly related to hospital prescribing patterns and not to community use of beta-blockers. Underuse occurred in patients with diabetes and in patients with left ventricular dysfunction, patients who stand to benefit most from beta-blocker use following MI.

A flow cytometric method to assess antigen-specific proliferative responses of different subpopulations of fresh and cryopreserved human peripheral blood mononuclear cells

We have used PKH26 dye, which is incorporated stably into the membrane of cells, to determine, using flow cytometry, lymphocyte proliferative responses to the antigen tetanus toxoid in fresh and cryopreserved samples. Measuring cell proliferation with this dye has advantages over either 3H-thymidine or Bromodeoxyuridine (BrdU). Whereas the existing methods measure proliferation at a single time point, PKH26 gives a cumulative measure of cell proliferation. As PKH26 is incorporated into the cell membrane, cells do not have to be permeabilised to allow dye incorporation into a cytoplasmic compartment. Most importantly, PKH26 can be used in combination with monoclonal antibodies to surface markers on mixed populations of cells, to determine the proliferation of individual subpopulations, without the need for prior cell fractionation. We also show that PKH26 can be used with similar efficacy in both fresh and cryopreserved samples. In addition since PKH26 is a cumulative measure of proliferative responses we were able to show that restimulation of the dividing population in vitro with fresh antigen presenting cells (APC) and antigen permits characterisation of a further proliferating cell population. The use of PKH26 dye in combination with cell phenotyping and measurement of cytokine production at the single cell level will prove a powerful tool for multiparameter analyses of cellular responses to antigen.