Fenofibrate induces plaque regression in hypercholesterolemic atherosclerotic rabbits: In vivo demonstration by high-resolution MRI

Pharmacological regression of atherosclerotic plaque in patients with type 2 diabetes

Atherosclerosis of the coronary arteries continues to be one of the major global health burdens and acute coronary syndrome is responsible annually for at least 30 % of all deaths globally. Acute coronary syndrome may be the consequence of thrombus formation after erosion or rupture of obstructive or non-obstructive atherosclerotic plaque. The rupture of plaques is mostly caused by mechanical stress usually called cap fatigue. Vulnerable plaques are characterized by a softer atheromatous core and a thinner fibrous cap, with inflammation and hypercholesterolemia playing a crucial role in the atherothrombotic process. Based on animal studies that extend back to the 1920s, regression of atherosclerotic plaques in humans has just started to be considered and pursued. The idea that the human atherosclerotic plaques could regress at all met an important resistance over the decades; indeed, advanced plaques contain components, such as necrosis, calcification and fibrosis, which are hard to be removed. However, new animal models and imaging technics allowed a more complete and accurate quantitative assessment of plaque volume and are shedding new light on atherosclerosis regression. In this review, we are revisiting the existence of atherosclerosis regression in preclinical and clinical studies, with a focus on the latest mechanistic insights and on the newest pharmacological agents, particularly in patients with diabetes. Interestingly, we suggested that based on literature insights and preclinical studies, a combination of drugs to target hyperglycemia, dyslipidemia and inflammation may be desirable for a fast-track Pharmacological regression of atherosclerotic plaque in patients with type 2 diabetes.

Spatial lipidomic profiles of atherosclerotic plaques: A mass spectrometry imaging study

Lipids contribute to atherosclerotic cardiovascular disease but their roles are not fully understood. Spatial lipid composition of atherosclerotic plaques was compared between species focusing on aortic plaques from New Zealand White rabbits and carotid plaques from humans (n = 3), using matrix-assisted laser desorption/ionization mass spectrometry imaging. Histologically discriminant lipids within plaque features (neointima and media in rabbits, and lipid-necrotic core and fibrous cap/tissue in humans) included sphingomyelins, phosphatidylcholines, and cholesteryl esters. There were 67 differential lipids between rabbit plaque features and 199 differential lipids in human, each with variable importance in projection score ≥1.0 and p < 0.05. The lipid profile of plaques in the rabbit model closely mimicked that of human plaques and two key pathways (impact value ≥ 0.1), sphingolipid and glycerophospholipid metabolism, were disrupted by atherosclerosis in both species. Thus, mass spectrometry imaging of spatial biomarkers offers valuable insights into atherosclerosis.

Two sides of the same coin: Non-alcoholic fatty liver disease and atherosclerosis

The prevalence of non-alcoholic fatty liver disease (NAFLD) and atherosclerosis remain high, which is primarily due to widespread adoption of a western diet and sedentary lifestyle. NAFLD, together with advanced forms of this disease such as non-alcoholic steatohepatitis (NASH) and cirrhosis, are closely associated with atherosclerotic-cardiovascular disease (ASCVD). In this review, we discussed the association between NAFLD and atherosclerosis and expounded on the common molecular biomarkers underpinning the pathogenesis of both NAFLD and atherosclerosis. Furthermore, we have summarized the mode of function and potential clinical utility of existing drugs in the context of these diseases.

Altered Peroxisome Proliferator-Activated Receptor Alpha Signaling in Variably Diseased Peripheral Arterial Segments

Objective

Peripheral atherosclerosis that accumulates in the extracranial carotid and lower extremity arteries can lead to significant morbidity and mortality. However, atherosclerotic disease progression is often not homogenous and is accelerated by diabetes. We previously observed increased phospholipid content in minimally (Min)-diseased arterial segments compared to maximally (Max)-diseased segments. Since Peroxisome Proliferator-Activated Receptor alpha (PPARα) is a key regulator of lipid metabolism, we hypothesized that it may have differential expression and signaling in Min vs. Max-diseased peripheral arterial segments.

Methods

Eighteen patients who underwent carotid endarterectomy (CEA), and 34 patients who underwent major lower extremity amputation were prospectively enrolled into a vascular tissue biobank. Min and Max-diseased segments were obtained in real-time from CEA plaque and amputated lower extremity arterial segments. mRNA and protein were isolated from specimens and the relative expression of ppara, and its downstream genes Acyl-CoA Oxidase 1 (acox1) and Carnitine Palmitoyltransferase 1A (cpt1a) were also evaluated. We evaluated gene expression and protein content relative to atherosclerotic disease severity and clinical diabetes status. Gene expression was also evaluated relative to Hemoglobin A1c and serum lipid profiles.

Results

In CEA segments of patients with diabetes, we observed significantly higher ppara and acox1 gene expression (p < 0.01 and p < 0.001 respectively), and higher PPARα protein content (p < 0.05). Hemoglobin A1c significantly correlated with expression of ppara (R² = 0.66, p < 0.001), acox1 (R² = 0.31, p < 0.05), and cpt1a (R² = 0.4, p < 0.05). There was no significant difference in gene expression between Min vs. Max-diseased CEA plaque segments. Conversely, in lower extremity arterial segments of patients with diabetes, we observed significantly lower ppara, acox1, and cpt1a expression (p < 0.05, p < 0.001, and p < 0.0001 respectively). Interestingly, CPT1A content was lower in arterial segments of patients with diabetes (p < 0.05). Hemoglobin A1c and HDL-cholesterol had negative correlations with ppara (R² = 0.44, p < 0.05; R² = 0.42, p < 0.05; respectively).

Conclusion

This study demonstrates the significant differential expression of ppara and its immediate downstream genes in human carotid and lower extremity arteries relative to disease severity and diabetes. These findings highlight that mechanisms that influence atheroprogression in the carotid and lower extremities peripheral arteries are not homogenous and can be impacted by patient diabetes status and serum cholesterol profiles. Further elucidating these differential molecular mechanisms can help improve targeted therapy of atherosclerosis in different peripheral arterial beds.

Highly Selective PPARα (Peroxisome Proliferator-Activated Receptor α) Agonist Pemafibrate Inhibits Stent Inflammation and Restenosis Assessed by Multimodality Molecular-Microstructural Imaging

BACKGROUND

New pharmacological approaches are needed to prevent stent restenosis. This study tested the hypothesis that pemafibrate, a novel clinical selective PPARα (peroxisome proliferator‐activated receptor α) agonist, suppresses coronary stent‐induced arterial inflammation and neointimal hyperplasia.

METHODS AND RESULTS

Yorkshire pigs randomly received either oral pemafibrate (30 mg/day; n=6) or control vehicle (n=7) for 7 days, followed by coronary arterial implantation of 3.5 × 12 mm bare metal stents (2–4 per animal; 44 stents total). On day 7, intracoronary molecular‐structural near‐infrared fluorescence and optical coherence tomography imaging was performed to assess the arterial inflammatory response, demonstrating that pemafibrate reduced stent‐induced inflammatory protease activity (near‐infrared fluorescence target‐to‐background ratio: pemafibrate, median [25th‐75th percentile]: 2.8 [2.5–3.3] versus control, 4.1 [3.3–4.3], P=0.02). At day 28, animals underwent repeat near‐infrared fluorescence–optical coherence tomography imaging and were euthanized, and coronary stent tissue molecular and histological analyses. Day 28 optical coherence tomography imaging showed that pemafibrate significantly reduced stent neointima volume (pemafibrate, 43.1 [33.7–54.1] mm³ versus control, 54.2 [41.2–81.1] mm³; P=0.03). In addition, pemafibrate suppressed day 28 stent‐induced cellular inflammation and neointima expression of the inflammatory mediators TNF‐α (tumor necrosis factor‐α) and MMP‐9 (matrix metalloproteinase 9) and enhanced the smooth muscle differentiation markers calponin and smoothelin. In vitro assays indicated that the STAT3 (signal transducer and activator of transcription 3)–myocardin axes mediated the inhibitory effects of pemafibrate on smooth muscle cell proliferation.

CONCLUSIONS

Pemafibrate reduces preclinical coronary stent inflammation and neointimal hyperplasia following bare metal stent deployment. These results motivate further trials evaluating pemafibrate as a new strategy to prevent clinical stent restenosis.

The Glitazars Paradox: Cardiotoxicity of the Metabolically Beneficial Dual PPARα and PPARγ Activation

The most common complications in patients with type-2 diabetes are hyperglycemia and hyperlipidemia that can lead to cardiovascular disease. Alleviation of these complications constitutes the major therapeutic approach for the treatment of diabetes mellitus. Agonists of peroxisome proliferator-activated receptor (PPAR) alpha and PPARγ are used for the treatment of hyperlipidemia and hyperglycemia, respectively. PPARs belong to the nuclear receptors superfamily and regulate fatty acid metabolism. PPARα ligands, such as fibrates, reduce circulating triglyceride levels, and PPARγ agonists, such as thiazolidinediones, improve insulin sensitivity. Dual-PPARα/γ agonists (glitazars) were developed to combine the beneficial effects of PPARα and PPARγ agonism. Although they improved metabolic parameters, they paradoxically aggravated congestive heart failure in patients with type-2 diabetes via mechanisms that remain elusive. Many of the glitazars, such as muraglitazar, tesaglitazar, and aleglitazar, were abandoned in phase-III clinical trials. The objective of this review article pertains to the understanding of how combined PPARα and PPARγ activation, which successfully targets the major complications of diabetes, causes cardiac dysfunction. Furthermore, it aims to suggest interventions that will maintain the beneficial effects of dual PPARα/γ agonism and alleviate adverse cardiac outcomes in diabetes.

Effect of fenofibrate on plasma apolipoprotein C-III levels: a systematic review and meta-analysis of randomised placebo-controlled trials

OBJECTIVES

This meta-analysis of randomised placebo-controlled clinical trials aimed to assess the effect of fenofibrate on apolipoprotein C-III (apo C-III), a key regulator of triglyceride metabolism.

MATERIALS AND METHODS

Randomised placebo-controlled trials investigating the impact of fenofibrate treatment on apo C-III levels were searched in PubMed-Medline, Scopus, Web of Science and Google Scholar databases from inception to 18 August 2017. Quantitative data synthesis was determined by a random-effects model and generic inverse variance method. Sensitivity analysis was conducted using the leave-one-out method. A weighted random-effects meta-regression was performed to evaluate glycaemic parameter confounders.

RESULTS

Meta-analysis of 10 clinical trials involving 477 subjects showed fenofibrate therapy decreased apo C-III levels (weighted mean difference (WMD) -4.78 mg/dL, 95% CI -6.95 to -2.61, p<0.001; I²66.87%). Subgroup analysis showed that fenofibrate reduced plasma apo C-III concentrations in subgroups of trials with treatment durations of either <12 weeks (WMD -4.50 mg/dL, p=0.001) or ≥12 weeks (WMD: -4.73 mg/dL, p=0.009) and doses of fenofibrate <200 mg/day (WMD -6.33 mg/dL, p<0.001) and >200 mg/day (p=0.006), with no significant difference between the subgroups.

CONCLUSION

This meta-analysis found that fenofibrate therapy significantly decreases apo C-III levels, an effect evident with both short-term treatment and doses less than 200 mg/day.

Fenofibrate effects on carotid artery intima-media thickness in adults with type 2 diabetes mellitus: A FIELD substudy

AIM

Dyslipidemia in type 2 diabetes contributes to an increased risk of cardiovascular disease. Fenofibrate, a lipid-regulating peroxisome proliferator-activated receptor-α (PPARα) agonist, has been shown to reduce vascular complications in adults with type 2 diabetes. The mechanisms for such benefit, however, are not yet well understood. We examined the effects of fenofibrate on carotid intima-media thickness (IMT), a marker of subclinical atherosclerosis, in adults with type 2 diabetes.

METHODS

In a prospectively designed substudy of the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study, we assessed carotid IMT in a subset of 422 representative adults. Traditional risk factors and IMT were assessed at 2 and 4 years after randomisation to fenofibrate (200 mg daily) or placebo. The prespecified primary study endpoint was the difference in IMT between treatment groups at 4 years. Post-hoc analyses were performed according to dyslipidemia and metabolic syndrome status.

RESULTS

There was no difference in carotid IMT comparing those assigned to fenofibrate or placebo at 2 or 4 years, despite statistically significant improvement in lipid and lipoprotein parameters at 2 and 4 years, including TC, LDL-C and TG, and HDL-C at 4 months and 2 years. Similarly, there was no difference in carotid IMT on fenofibrate compared with placebo in those with dyslipidemia or metabolic syndrome.

CONCLUSIONS

Fenofibrate was not associated with improved carotid IMT in adults with type 2 diabetes when compared with placebo, despite a statistically significant improvement in TC, LDL-C and TG at 2 and 4 years, and HDL-C at 4 months and 2 years.

Peroxisome Proliferator-Activated Receptor α in Lipid Metabolism and Atherosclerosis

Atherosclerosis is a chronic inflammatory disease with deposition of excessive cholesterol in the arterial intima. Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor that can activate or inhibit the expression of many target genes by forming a heterodimer complex with the retinoid X receptor. Activation of PPARα plays an important role in the metabolism of multiple lipids, including high-density lipoprotein, cholesterol, low-density lipoprotein, triglyceride, phospholipid, bile acids, and fatty acids. Increased PPARα activity also mitigates atherosclerosis by blocking macrophage foam cell formation, vascular inflammation, vascular smooth muscle cell proliferation and migration, plaque instability, and thrombogenicity. Clinical use of synthetic PPARα agonist fibrate improved dyslipidemia and attenuated atherosclerosis-related disease risk. This review summarizes PPARα in lipid and lipoprotein metabolism and atherosclerosis, and also highlights its potential therapeutic benefits.

Innovative pharmaceutical interventions in cardiovascular disease: Focusing on the contribution of non-HDL-C/LDL-C-lowering versus HDL-C-raising: A systematic review and meta-analysis of relevant preclinical studies and clinical trials

Non-HDL-cholesterol is well recognised as a primary causal risk factor in cardiovascular disease. However, despite consistent epidemiological evidence for an inverse association between HDL-C and coronary heart disease, clinical trials aimed at raising HDL-C (AIM-HIGH, HPS2-THRIVE, dal-OUTCOMES) failed to meet their primary goals. This systematic review and meta-analysis investigated the effects of established and novel treatment strategies, specifically targeting HDL, on inhibition of atherosclerosis in cholesteryl ester transfer protein-expressing animals, and the prevention of clinical events in randomised controlled trials. Linear regression analyses using data from preclinical studies revealed associations for TC and non-HDL-C and lesion area (R(2)=0.258, P=0.045; R(2)=0.760, P<0.001), but not for HDL-C (R(2)=0.030, P=0.556). In clinical trials, non-fatal myocardial infarction risk was significantly less in the treatment group with pooled odd ratios of 0.87 [0.81; 0.94] for all trials and 0.85 [0.78; 0.93] after excluding some trials due to off-target adverse events, whereas all-cause mortality was not affected (OR 1.05 [0.99-1.10]). Meta-regression analyses revealed a trend towards an association between between-group differences in absolute change from baseline in LDL-C and non-fatal myocardial infarction (P=0.066), whereas no correlation was found for HDL-C (P=0.955). We conclude that the protective role of lowering LDL-C and non-HDL-C is well-established. The contribution of raising HDL-C on inhibition of atherosclerosis and the prevention of cardiovascular disease remains undefined and may be dependent on the mode of action of HDL-C-modification. Nonetheless, treatment strategies aimed at improving HDL function and raising apolipoprotein A-I may be worth exploring.

Rabbit models for the study of human atherosclerosis: from pathophysiological mechanisms to translational medicine

Laboratory animal models play an important role in the study of human diseases. Using appropriate animals is critical not only for basic research but also for the development of therapeutics and diagnostic tools. Rabbits are widely used for the study of human atherosclerosis. Because rabbits have a unique feature of lipoprotein metabolism (like humans but unlike rodents) and are sensitive to a cholesterol diet, rabbit models have not only provided many insights into the pathogenesis and development of human atherosclerosis but also made a great contribution to translational research. In fact, rabbit was the first animal model used for studying human atherosclerosis, more than a century ago. Currently, three types of rabbit model are commonly used for the study of human atherosclerosis and lipid metabolism: (1) cholesterol-fed rabbits, (2) Watanabe heritable hyperlipidemic rabbits, analogous to human familial hypercholesterolemia due to genetic deficiency of LDL receptors, and (3) genetically modified (transgenic and knock-out) rabbits. Despite their importance, compared with the mouse, the most widely used laboratory animal model nowadays, the use of rabbit models is still limited. In this review, we focus on the features of rabbit lipoprotein metabolism and pathology of atherosclerotic lesions that make it the optimal model for human atherosclerotic disease, especially for the translational medicine. For the sake of clarity, the review is not an attempt to be completely inclusive, but instead attempts to summarize substantial information concisely and provide a guideline for experiments using rabbits.

Therapeutic strategies to deplete macrophages in atherosclerotic plaques

Macrophages can be found in all stages of atherosclerosis and are major contributors of atherosclerotic plaque development, progression and destabilization. Continuous recruitment of monocytes drives this chronic inflammatory disease, which can be intervened by several strategies: reducing the inflammatory stimulus by lowering circulating lipids and promoting cholesterol efflux from plaque, direct and indirect targeting of adhesion molecules and chemokines involved in monocyte adhesion and transmigration and inducing macrophage death in atherosclerotic plaques in combination with anti-inflammatory drugs. This review discusses the outlined strategies to deplete macrophages from atherosclerotic plaques to promote plaque stabilization.

Serum fibroblast growth factor 21 was elevated in subjects with type 2 diabetes mellitus and was associated with the presence of carotid artery plaques

AIMS

Fibroblast growth factor 21 (FGF21) is an important regulator of glucose/lipid metabolism. Although there are studies examining the relationship between serum FGF21 levels and glucose homeostasis, the role of FGF21 remains unclear. The objective of this study was to examine whether serum FGF21 levels are associated with metabolic parameters in subjects with varying degrees of obesity and glucose tolerance and with complications in subjects with type2 diabetes mellitus (T2DM).

METHODS

The study consisted of 213 subjects who were lean and had normal glucose tolerance (lean NGT), were overweight with NGT, had impaired glucose tolerance (IGT) or had T2DM. Serum FGF21 levels and their associations with the parameters of adiposity, glucose tolerance and the presence of diabetic complications were examined.

RESULTS

The serum FGF21 levels in T2DM were higher than in lean NGT. Serum FGF21 levels showed a positive correlation with the urine albumin-to-creatinine ratio (ACR) in all subjects except for the T2DM subjects, who showed a correlation after adjustment of age, gender and body mass index. Moreover, the subjects with carotid artery plaque showed higher serum FGF21 levels than those without complications.

CONCLUSION

Serum FGF21 levels were associated with the urine ACR and diabetic complications including carotid artery plaque.

Recombinant HDL(Milano) exerts greater anti-inflammatory and plaque stabilizing properties than HDL(wild-type)

OBJECTIVE

The aim of this study was to compare the effects of HDL(Milano) and HDL(wild-type), on regression and stabilization of atherosclerosis.

METHODS

Atherosclerotic New Zealand White rabbits received 2 infusions, 4 days apart, of HDL(Milano) (75mg/kg of apoA-I(Milano)), HDL(wild-type) (75mg/kg apoA-I(wild-type)) or placebo. Pre- and post-treatment plaque volume was assessed by MRI. Markers of plaque vulnerability and inflammation were evaluated. Liver and aortic cholesterol content, aortic ABCA-1 and liver SR-BI were quantified. The effect of apoA-I Milano and wild-type proteins on MCP-1 and COX-2 expression by macrophages was evaluated in vitro.

RESULTS

Both forms of HDL induced aortic plaque regression (-4.1% and -2.6% vs. pre-treatment in HDL(Milano) and HDL(wild-type) respectively, p<0.001 and p=0.009). A similar reduction in cholesterol content of aorta and liver was observed with both treatments vs. placebo. The expression of aortic ABCA-1 and hepatic SR-BI was significantly higher in both treated groups vs. placebo. A significantly reduced plaque macrophage density was observed in the HDL(Milano) vs. both HDL(wild-type) and placebo groups. Plaque levels of COX-2, MCP-1, Caspase-3 antigen and MMP-2 activity were significantly reduced in the HDL(Milano) vs. both HDL(wild-type) and placebo groups. In vitro studies showed that apoA-I(Milano) protein significantly reduced expression of COX-2 and MCP-1 in oxLDL loaded macrophages vs. apoA-I(wild-type).

CONCLUSIONS

Despite a similar effect on acute plaque regression, the infusion of HDL(Milano) exerts superior anti-inflammatory and plaque stabilizing effects than HDL(wild-type) in the short term.

Protective effects of dehydroepiandrosterone on atherosclerosis in ovariectomized rabbits via alleviating inflammatory injury in endothelial cells

OBJECTIVE

The risk for atherosclerosis is increased in postmenopausal women. Dehydroepiandrosterone (DHEA) is postulated to have anti-atherogenic properties, but the mechanism remains unclear. The aim of this study was to elucidate the protective effect of DHEA on atherosclerosis in ovariectomized rabbits.

METHODS

The lipid status and atherosclerotic lesions were examined in vivo in ovariectomized rabbits. The effects of DHEA on expression of inflammatory molecules were evaluated in vitro, such as nitric oxide (NO), malondialdehyde (MDA), monocyte chemoattractant protein-1 (MCP-1), adhesion molecules (ICAM-1, VCAM-1 and E-selectin) in the human umbilical vein endothelial cells (HUVECs) injured by oxidized low-density lipoproteins (ox-LDL). The adhesion of the monocytic U937 cells to HUVECs was treated with supernatants of ox-LDL treated HUVECs with or without DHEA, and then the expressions of CCR2, LFA-1, VLA-4 were analyzed in U937 cells. The HUVECs with or without LPS treatment were then treated with DHEA, and NF-κB activity was measured by luciferase activity.

RESULTS

DHEA administration alleviates efficiently the early pathologic damage of atherosclerosis, increases the serum NO level, and up-regulates the endothelial cell estrogen receptor (ER) expression of ovariectomized rabbits. DHEA in vitro significantly promotes NO synthesis, suppresses MDA and MCP-1 secretion of endothelial cells, and decreases ICAM-1, VCAM-1 and E-selectin expression in HUVECs; neither selective ERα antagonist (methyl-piperidino-pyrazole, MPP) nor ERβ antagonist (R,R-tetrahydrochrysene, R,RTHC) can abolish these effects. Furthermore, DHEA reduces CCR2, LFA-1 and VLA-4 expression in U937 cells, which in turn inhibits the adherence of monocytes to the injured endothelial cells. DHEA significantly decreased the LPS-induced NF-κB transcription.

CONCLUSIONS

Our findings suggest that DHEA can alleviate inflammation in endothelial cells. The effects of DHEA on endothelial cells are independent of ERα or ERβ pathway, but at least in part, through suppression of NF-κB activity, which protects from atherosclerosis triggered by monocyte adherence.

Future requirement for arterial wall imaging modalities in the evaluation of novel anti-atherosclerotic therapies

BACKGROUND

While arterial wall imaging has been used to characterize progression of atherosclerosis, there remain limitations to this approach.

SCOPE

A selective overview of emerging modalities to image the artery wall and highlight how they may be used to evaluate emerging anti-atherosclerotic agents.

FINDINGS

Ongoing developments appear to enable assessment of composition and molecular properties of plaque in addition to quantitation of burden. Non-invasiveness and correlation with clinical outcome remains a challenge.

CONCLUSION

New developments in imaging should enhance the ability to provide early characterization of the potential therapeutic efficacy of experimental agents.

Cholesterol diet and effect of long-term withdrawal on plaque development and composition in the thoracic aorta of New Zealand White rabbits

AIMS

Experimental study on plaque progression, regression and composition in atherosclerotic thoracic aorta of hypercholesterolemic rabbits after long-term withdrawal of cholesterol-enriched diet (CED).

METHODS

Rabbits were fed 2% cholesterol for 6 weeks followed by withdrawal periods for 15, 23, 34, 68, or 78 weeks. Cholesterol, triglyceride, and phospholipids levels in blood and cholesterol concentrations in aorta were quantified. Plaque size and cellularity, phenotype of macrophages and smooth muscle cells were (immuno)histomorphometrically analyzed in segments of the thoracic aorta.

RESULTS

After 6 weeks of CED, blood cholesterol levels were about 80-fold higher, whereas atherosclerosis and cholesterol content in the thoracic aorta were only minimally increased. However, the latter significantly increased within 15 weeks after cholesterol withdrawal, while serum cholesterol level was still 10-fold increased. Thereafter plaque area and cholesterol content remained almost unchanged until the end of the study despite a long-term normalization of serum cholesterol level after withdrawal of CED. Directly after 6 weeks of CED the densities of macrophages and apoptotic cells within plaques were highest, decreasing after cholesterol withdrawal, whereas, vice versa the density of smooth muscle cells (SMCs) significantly increased.

CONCLUSION

We suggest that atherosclerotic plaques respond to long-term withdrawal of CED by decrease in number and phenotype of macrophages and increase of SMCs without regression of the lesion size. The cellular changes are suggested to considerably contribute to higher plaque stability.

Fibrates in the prevention of cardiovascular disease in patients with type 2 diabetes mellitus--a pooled meta-analysis of randomized placebo-controlled clinical trials

OBJECTIVE

Fibrates are thought to be useful anti-dyslipidemic agents particularly in patients with diabetes mellitus and dyslipidemia characterized by high triglyceride (TG) and low high-density lipoprotein cholesterol (HDL-C) levels. We conducted a systematic review and meta-analysis of long-term randomized controlled trials to evaluate the role of fibrates in the prevention of cardiovascular events in patients with type 2 diabetes mellitus.

DATA SOURCES

English-language journals indexed in Index Medicus/MEDLINE and the Cochrane Collaboration databases (through December 2007), unpublished data from selected clinical trials.

DATA EXTRACTION AND ANALYSIS

A total of 11,590 patients from 6 published randomized placebo-controlled trials were analyzed using pooled meta-analysis techniques. Relative risks were computed for various cardiovascular outcomes and mortality, and statistical significance was tested using the z-test statistic (two-sided alpha error <0.05).

RESULTS

The use of fibrates did not significantly affect the risk of all-cause mortality or cardiac mortality, and also did not affect the risk of stroke, unstable angina, or invasive coronary revascularization. However, the relative risk of non-fatal myocardial infarction was significantly reduced by about 21% (pooled relative risk 0.79, p=0.006) with the use of fibrates.

CONCLUSIONS

Long-term use of fibrates in patients with type 2 diabetes mellitus significantly reduces the risk of non-fatal myocardial infarction, but has no significant effect on mortality or on other adverse cardiovascular outcomes.

A review of the current status of the management of mixed dyslipidemia associated with diabetes mellitus and metabolic syndrome

Current treatment guidelines recommend lowering elevated low-density lipoprotein (LDL) cholesterol levels with a statin as the primary lipid-modifying intervention to reduce cardiovascular risk in patients with type 2 diabetes mellitus or metabolic syndrome. However, even with high-dose statin therapy or the combination of statin plus ezetimibe, many patients remain at substantial risk of a cardiovascular event. Increasingly, there is recognition of the importance of treating all components of the atherogenic dyslipidemic profile associated with both conditions, specifically low high-density lipoprotein cholesterol and elevated triglyceride levels, in addition to lowering LDL cholesterol. Both niacin (nicotinic acid) and fibrates are recommended as options for combination with a statin in this setting. Data from ongoing prospective outcomes studies are needed to evaluate the efficacy and safety of these combinations.

Up-regulation of reverse cholesterol transport key players and rescue from global inflammation by ApoA-I(Milano)

Recombinant-ApoA-I_M (rApoA-I_M) administration has been shown to regress and stabilize atherosclerotic plaques. However, the mechanisms responsible for these beneficial effects are not fully understood. The aims of the present study were to define whether the benefits of rApoA-I_M treatment were mediated via an enhanced reverse cholesterol transport (RCT) and/or anti-inflammation-related mechanisms. Advanced aortic lesions were induced in New Zealand White rabbits (n= 16). Animals were randomized to placebo or rApoA-I_M (rApoA-I_M/phospholipids; ETC-216), two infusions 4 days apart. Four days after last dose, aortas and livers were processed for cholesterol content, expression of RCT-related receptors (ATP-binding cassette A-1 [ABCA-1] and scavenger receptor BI [SR-BI]), and inflammation-related markers (inducible nitric oxide synthase [iNOS] and capase-3). Oxidative stress was assessed in the vessel wall and in plasma. rApoA-I_M administration resulted in a significant reduction in the hepatic and aortic cholesterol content without differences in plasma levels. This effect was associated with an up-regulation of vessel wall ABCA-1, as well as a hepatic and arterial-wall SR-BI up-regulation. Systemic and atherosclerotic-plaque inflammation markers were significantly reduced by the rApoA-I_M administration, as demonstrated by a reduction in circulating oxidative stress markers and prostaglandin F1-α levels, and the down-regulation of the iNOS and caspase 3 in the aortic lesions. rApoA-IM up-regulated the ABCA-1 and SR-BI levels to a greater extent than the wild-type form of apoA-I in in vitro studies done with lipid-rich macrophages. Our data suggest that rApoA-I_M administration enhances RCT and induces a ‘rescue’ from the global inflammatory status associated with atherosclerotic disease. The Milano form of apoA-I seems to be more efficient in RCT than the apoA-I wild-type.

Ovariectomy increases vascular calcification via the OPG/RANKL cytokine signalling pathway

BACKGROUND

Observational studies suggest a strong relationship between menopause and vascular calcification. Receptor activator of nuclear factor-kappaBeta ligand (RANKL) and osteoprotegerin (OPG) are critical regulators of bone remodelling and modulate vascular calcification. We assessed the hypothesis that ovariectomy increases vascular calcification via the OPG/RANKL axis.

MATERIALS AND METHODS

Age-matched sexually mature rabbits were randomized to ovariectomy (OVX, n = 12) or sham procedure (SHAM, n = 12). One month post-procedure, atherosclerosis was induced by 15 months 0.2%-cholesterol diet and endothelial balloon denudations (at months 1 and 3). Aortic atherosclerosis was assessed in vivo by magnetic resonance imaging (MRI) at months 9 and 15. At sacrifice, aortas were harvested for ex vivo microcomputed tomography (microCT) and molecular analysis of the vascular tissue.

RESULTS

Vascular calcification density and calcific particle number were significantly greater in OVX than SHAM (8.4 +/- 2.8 vs. 1.9 +/- 0.6 mg cm(-3), P = 0.042, and 94 +/- 26 vs. 33 +/- 7 particles cm(-3), P = 0.046, respectively). Calcification morphology, as assessed by the arc angle subtended by the largest calcific particle, showed no difference between groups (OVX 33 +/- 7 degrees vs. SHAM 33 +/- 5 degrees , P = 0.99). By Western blot analysis, OVX increased the vascular OPG:RANKL ratio by 66%, P = 0.029, primarily by decreasing RANKL (P = 0.019). At month 9, MRI demonstrated no difference in atheroma volume between OVX and SHAM, and no significant change was seen by the end of the study.

CONCLUSIONS

In contrast to bone, vascular OPG:RANKL ratio increased in response to ovariectomy with a corresponding fourfold increase in arterial calcification. This diametrical organ-specific response may explain the comorbid association of osteoporosis with calcifying atherosclerosis in post-menopausal women.

Selective estrogen receptor modulation influences atherosclerotic plaque composition in a rabbit menopause model

OBJECTIVE

Osteoporosis trials suggest raloxifene decreased cardiovascular events in women with pre-existing atherosclerosis. We assessed the hypothesis that selective estrogen receptor modulation induces plaque stability in "menopausal" animals.

METHODS AND RESULTS

Atherosclerosis was induced in 42 ovariectomized New Zealand white rabbits by cholesterol feeding and mechanical injury. Animals were imaged by magnetic resonance imaging (MRI) for baseline atherosclerosis, and randomized to control (OVX (ovariectomized control group), n=12), raloxifene 35-60 mg/kg/day by diet admixture (RLX (raloxifene therapy group), n=24), or immediate sacrifice (n=6) for immunohistopathologic correlation of MRI. Six months later, rabbits underwent repeat MRI then sacrifice for micro-computed tomography (microCT) and molecular analysis. Unlike OVX, RLX reduced atheroma volume. Analysis for lesion inflammation revealed reductions in COX-2 (cyclooxygenase-2), MMP-1 (matrix metalloproteinase-1), MCP-1 (monocyte chemoattractant protein-1) expression and macrophage infiltration in RLX versus OVX with concomitant upregulation of estrogen receptor alpha (ERalpha). microCT showed similar total vascular calcification between groups, but calcifications in RLX were less nodular with better radial organization (mean calcific arc angle 63+/-7 degrees versus 33+/-6 degrees in OVX), the predicted result of a 53% increase in BMP-2 (bone-morphogenetic protein-2).

CONCLUSIONS

Raloxifene treatment results in reduced lesion volume, enhanced mechanical stability of vascular calcification, and less inflamed lesions characterized by less macrophage infiltration and reduced COX-2, MMP-1 and MCP-1 expression.

Aortic plaque imaging and monitoring atherosclerotic plaque interventions

The atherosclerotic process that results in coronary artery disease (CAD) is recognized to be a generalized process that may involve the entire vasculature. The association between CAD and atherosclerotic plaques in the thoracic aorta has often been reported using transesophageal echocardiography. An autopsy study showed plaques in the abdominal aorta, but not in the thoracic aorta, to be severe in patients with cardiac events. However, studies evaluating an association between abdominal aortic plaques and CAD are scarce. Recently, magnetic resonance imaging (MRI) has become a useful tool for the noninvasive evaluation of atherosclerotic plaques in both the thoracic and abdominal aortas. Plaques in the thoracic and abdominal aortas were found to be characteristically associated with hypercholesterolemia and smoking, respectively, suggesting different susceptibilities to risk factors. Because patients have various risk factors, it seems to be preferable to evaluate atherosclerosis in multiple vascular beds than in just 1 bed. Magnetic resonance imaging can evaluate atherosclerosis in multiple vascular beds in the same examination session. Complex aortic plaques, especially in the abdominal aorta, were found to be associated with myocardial infarction and complex coronary lesions, suggesting a link between aortic and coronary plaque instability. Aortic MRI may thus be useful for identifying vulnerable patients. Moreover, MRI is a powerful tool to serially evaluate plaque progression and regression. Intensive lipid-lowering therapy can regress aortic plaques, but the susceptibility to lipid lowering and the process of plaque regression may differ between the thoracic and abdominal aortic plaques.

Targeted contrast agent helps to monitor advanced plaque during progression: a magnetic resonance imaging study in rabbits

OBJECTIVE

Gadofluorine M has been reported to enhance early atherosclerotic plaque signals in magnetic resonance imaging (MRI). The aim of this study was to examine the use of Gadofluorine M to monitor the progression of advanced plaques in a rabbit model.

METHODS

Focal advanced atherosclerosis was induced in the right femoral arteries of 6 New Zealand white rabbits using a combination of cholesterol-enriched diet, and sequential air-desiccation, and balloon-overstretch injury. MRI with conventional 3 contrasts (T1, T2, and proton density [PD]) was performed to monitor the progression of the atherosclerotic plaques with 2 MRI scans separated by 4 to 8 weeks. Gadofluorine M was given intravenously to the rabbits 24 hours before the first MRI scans, and before (n = 3) or during (n = 3) the second MRI scan. The left femoral arteries were used as a control. Histopathologic images localized individual plaque components.

RESULTS

The advanced plaque displayed multilayered neointima that included foam cells, smooth muscle cells, and extracellular matrix. The separate image contrasts offered similar T1-weighted enhancement patterns, but the combination of all 3 contrasts helped to delineate plaque and lumen boundaries. Gadofluorine M strongly enhanced neointima areas with an image contrast (contrast-to-noise ratio [CNR]) of approximately 15, versus 2 in the control femoral arterial wall. With improved images, significant changes in neointima and total plaque volumes over the 4 to 8 weeks between scans could be identified. Gadofluorine M remained within the plaques with significant image enhancements (contrast-to-noise ratio = 5.8) for 2 months after a single injection.

CONCLUSION

This preliminary study in rabbits indicated that Gadofluorine M provides specific enhancements of components associated with advanced atherosclerotic plaques and may help to monitor the progression of the plaque in a rabbit model of atherogenesis.

PPARalpha ligands reduce PCB-induced endothelial activation: possible interactions in inflammation and atherosclerosis

Exposure to polychlorinated biphenyls (PCBs) can activate inflammatory responses in vascular endothelial cells. Activation of peroxisome proliferator-activated receptors (PPARs) by nutrients or synthetic agonists has been shown to block pro-inflammatory responses both in vitro and in vivo. Here we demonstrate that activation of PPARalpha by synthetic agonists can reduce 3,3'4,4'-tetrachlorobiphenyl (PCB77)-induced endothelial cell activation. Primary vascular endothelial cells were pretreated with the PPARalpha ligands fenofibrate or WY14643 followed by exposure to PCB77. PPARalpha activation protected endothelial cells against PCB77-induced expression of the pro-inflammatory proteins vascular cell adhesion molecule-1 (VCAM-1), cycloxygenase-2 (COX-2), and PCB77-induced expression and activity of the aryl hydrocarbon receptor (AHR) responsive cytochrome P450 1A1 (CYP1A1). Furthermore, basal AHR expression was downregulated by fenofibrate and WY14643. We also investigated the possible interactions between PCBs, and basal PPAR activity and protein expression. Treatment with PCB77 significantly reduced basal mRNA expression of PPARalpha and the PPAR responsive gene CYP4A1, as well as PPARalpha protein expression. Also, PCB77 exposure caused a significant decrease in basal PPAR-dependent reporter gene expression in MCF-7 cells. Overall, these findings suggest that PPARalpha agonists can reduce PCB77 induction of endothelial cell activation by inhibition of the AHR pathway, and that coplanar PCB induced pro-inflammatory effects could be mediated, in part, by inhibition of PPARalpha expression and function.

Plaque progression and regression in atherothrombosis

Atherosclerotic disease is a pathological process characterized by the deposition of lipid and other blood-borne material within the arterial wall. The deposition of these materials and the subsequent thickening of the wall may significantly compromise the vessel lumen. Atherosclerosis is a diffuse disease with focal clinical manifestations that are the consequence of thrombotic complications on disrupted atherosclerotic lesions. Until recently, atherosclerosis development was envisaged as an incessant progressing process; however, new evidence has shown that atherosclerotic plaque homeostasis is not necessarily a constantly progressing process. There are many data showing that atherosclerotic plaque formation can be slowed, stopped or even reversed. Comprehension of the underlying mechanisms involved in the homeostasis of atherosclerotic plaque (progression/regression) should allow the development of interventions enhancing the regression pathway. Novel imaging technology has allowed the accurate evaluation of plaque progression, vital in the assessment of the efficacy of interventions. In this review we discuss the processes involved in the formation and progression of atherosclerotic lesions, the triggers for plaque disruption, as well as new therapies. We also deal with the potential pathways of plaque regression, as well as tools for accurate serial atherosclerotic quantification.

Role of imaging end points in atherosclerosis trials: focus on intravascular ultrasound

Increasing attention has been focused on the appropriate role of surrogate markers in the development of novel anti-atherosclerotic therapies. Technological advances in imaging modalities allow for visualisation of the entire arterial wall. Intravascular ultrasound (IVUS) has been increasingly employed to precisely quantify the extent of coronary atherosclerosis. Use of IVUS has provided a number of important insights into the natural history of atherosclerosis and the remodelling changes of the arterial wall in response to plaque accumulation. More recently, clinical trials have employed serial evaluations of arterial segments by IVUS to assess the impact of medical therapies.

Gene therapy and stem cell therapy for cardiovascular diseases today: a model for translational research

Clinical trials looking at ways to promote myocardial regeneration have reported that the administered therapies have either neutral effects or modest benefits of questionable impact. These somewhat disappointing results should emphasize the need for translational research, with bidirectional feedback between the basic research laboratory and the clinical arena. Such a translational pathway is illustrated by the quest to find an effective therapy for restenosis, which culminated in the development of sirolimus. At this point a move away from the bedside and a return to the bench seems necessary to better understand the mechanisms of action of progenitor cells and stimulating factors. Without such basic knowledge research might be prematurely discouraged and the opportunity to fully understand the true potential of cardiovascular regenerative therapy might be missed.

Clinical significance of recent lipid trials on reducing risk in patients with type 2 diabetes mellitus

Type 2 diabetes mellitus is a significant risk factor for cardiovascular disease and is associated with significant cardiovascular morbidity and mortality. Current guidelines suggest lifestyle modification and at least a 30%-40% reduction of low-density lipoprotein (LDL) cholesterol with drug therapy, to a target level of <100 mg/dL. Additional secondary therapeutic targets include increasing high-density lipoprotein (HDL) cholesterol and lowering triglycerides. Although the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) remain first-line therapy, combination therapy with statins and fibrates or niacin is often needed to achieve target levels in patients with diabetes. Statins significantly lower LDL and decrease the relative risk for nonfatal myocardial infarction (MI) or coronary artery disease death. Clinical trials have demonstrated that in high-risk patients, such as those with diabetes, monotherapy with statins reduces overall cardiovascular events by 30%-40%. Fibrates have modest effects to lower LDL, but they significantly increase HDL and reduce triglycerides, they may improve glucose tolerance, and they have been shown to reduce nonfatal MI by 25%. Although data are limited, the combination of a statin and fenofibrate significantly reduced LDL, reduced triglycerides, and increased HDL compared with a statin alone. It is hoped that ongoing trials will demonstrate the clinical outcomes benefits of combination therapy in patients with diabetes.