Atherosclerotic plaque rupture: emerging insights and opportunities

RNA interference-based therapies for atherosclerosis: Recent advances and future prospects

Atherosclerosis represents a pathological state that affects the arterial system of the organism. This chronic, progressive condition is typified by the accumulation of atheroma within arterial walls. Modulation of RNA molecules through RNA-based therapies has expanded the range of therapeutic options available for neurodegenerative diseases, infectious diseases, cancer, and, more recently, cardiovascular disease (CVD). Presently, microRNAs and small interfering RNAs (siRNAs) are the most widely employed therapeutic strategies for targeting RNA molecules, and for regulating gene expression and protein production. Nevertheless, for these agents to be developed into effective medications, various obstacles must be overcome, including inadequate binding affinity, instability, challenges of delivering to the tissues, immunogenicity, and off-target toxicity. In this comprehensive review, we discuss in detail the current state of RNA interference (RNAi)-based therapies.

Fibronectin-Integrin α5 Signaling in Vascular Complications of Type 1 Diabetes

Vascular complications are a major cause of illness and death in patients with type 1 diabetes (T1D). Diabetic vascular basement membranes are enriched in fibronectin (FN), an extracellular matrix protein that amplifies inflammatory signaling in endothelial cells through its main receptor, integrin α5β1. Binding of the integrin α5 cytoplasmic domain to phosphodiesterase 4D5 (PDE4D5), which increases phosphodiesterase catalytic activity and inhibits antiinflammatory cAMP signaling, was found to mediate these effects. Here, we examined mice in which the integrin α5 cytoplasmic domain is replaced by that of α2 (integrin α5/2) or the integrin α5 binding site in PDE4D is mutated (PDE4Dmut). T1D was induced via injection of streptozotocin and hyperlipidemia induced via injection of PCSK9 virus and provision of a high-fat diet. We found that in T1D and hyperlipidemia, the integrin α5/2 mutation reduced atherosclerosis plaque size by ∼50%, with reduced inflammatory cell invasion and metalloproteinase expression. Integrin α5/2 T1D mice also had improved blood-flow recovery from hindlimb ischemia and improved biomechanical properties of the carotid artery. By contrast, the PDE4Dmut had no beneficial effects in T1D. FN signaling through integrin α5 is thus a major contributor to diabetic vascular disease but not through its interaction with PDE4D.

Pathogenic role of microRNAs in atherosclerotic ischemic stroke: Implications for diagnosis and therapy

Ischemic stroke resulting from atherosclerosis (particularly in the carotid artery) is one of the major subtypes of stroke and has a high incidence of death. Disordered lipid homeostasis, lipid deposition, local macrophage infiltration, smooth muscle cell proliferation, and plaque rupture are the main pathological processes of atherosclerotic ischemic stroke. Hepatocytes, macrophages, endothelial cells and vascular smooth muscle cells are the main cell types participating in these processes. By inhibiting the expression of the target genes in these cells, microRNAs play a key role in regulating lipid disorders and atherosclerotic ischemic stroke. In this article, we listed the microRNAs implicated in the pathology of atherosclerotic ischemic stroke and aimed to explain their pro- or antiatherosclerotic roles. Our article provides an update on the potential diagnostic use of miRNAs for detecting growing plaques and impending clinical events. Finally, we provide a perspective on the therapeutic use of local microRNA delivery and discuss the challenges for this potential therapy.

New tendencies in non-surgical periodontal therapy

The aim of this review was to update the evidence of new approaches to non-surgical therapy (NSPT) in the treatment of periodontitis. Preclinical and clinical studies addressing the benefits of adjunctive antimicrobial photodynamic therapy, probiotics, prebiotics/synbiotics, statins, pro-resolving mediators, omega-6 and -3, ozone, and epigenetic therapy were scrutinized and discussed. Currently, the outcomes of these nine new approaches, when compared with subgingival debridement alone, did not demonstrate a significant added clinical benefit. However, some of these new alternative interventions may have the potential to improve the outcomes of NSPT alone. Future evidence based on randomized controlled clinical trials would help clinicians and patients in the selection of different adjunctive therapies.

Can N-3 polyunsaturated fatty acids be considered a potential adjuvant therapy for COVID-19-associated cardiovascular complications?

Coronavirus disease 2019 (COVID-19), caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), has currently led to a global pandemic with millions of confirmed and increasing cases around the world. The novel SARS-CoV-2 not only affects the lungs causing severe acute respiratory dysfunction but also leads to significant dysfunction in multiple organs and physiological systems including the cardiovascular system. A plethora of studies have shown the viral infection triggers an exaggerated immune response, hypercoagulation and oxidative stress, which contribute significantly to poor cardiovascular outcomes observed in COVID-19 patients. To date, there are no approved vaccines or therapies for COVID-19. Accordingly, cardiovascular protective and supportive therapies are urgent and necessary to the overall prognosis of COVID-19 patients. Accumulating literature has demonstrated the beneficial effects of n-3 polyunsaturated fatty acids (n-3 PUFA) toward the cardiovascular system, which include ameliorating uncontrolled inflammatory reactions, reduced oxidative stress and mitigating coagulopathy. Moreover, it has been demonstrated the n-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are precursors to a group of potent bioactive lipid mediators, generated endogenously, which mediate many of the beneficial effects attributed to their parent compounds. Considering the favorable safety profile for n-3 PUFAs and their metabolites, it is reasonable to consider n-3 PUFAs as potential adjuvant therapies for the clinical management of COVID-19 patients. In this article, we provide an overview of the pathogenesis of cardiovascular complications secondary to COVID-19 and focus on the mechanisms that may contribute to the likely benefits of n-3 PUFAs and their metabolites.

Leptin upregulates smooth muscle cell expression of MMP-9 to promote plaque destabilization by activating AP-1 via the leptin receptor/MAPK/ERK signaling pathways

Leptin has been reported to be expressed in carotid atherosclerotic plaques, where it can promote lesion instability. Matrix metalloproteinases (MMPs) produced by smooth muscle cells (SMCs) are known to contribute to the weakening of atherosclerotic plaques via the degradation of extracellular matrix (ECM) proteins. The present study investigated whether leptin promotes plaque rupture by increasing the expression of MMP in SMCs in vivo and in vitro. In vivo, the neointima/media ratio and expression of MMP in the carotid artery of ob/ob mice were measured following carotid ligation and systemic administration of leptin. In vitro, the effect of leptin treatment on the expression of MMP in isolated SMCs and the underlying signaling pathways were investigated by gelatin zymography and western blot analysis. The results demonstrated that leptin treatment significantly increased the neointima/media ratio and expression of MMP-9 in the carotid artery of mice following carotid ligation. In vitro, leptin also significantly increased the expression and activity of MMP-9 in cultured SMCs in a dose-dependent manner. Leptin also increased the production of MMP-9 by activating leptin receptor and mitogen-activated protein kinases, including extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), which in turn enhanced the binding of the transcription factor activator protein-1 (AP-1) to the MMP-9 promoter. The inhibition of leptin-activated phosphorylation of ERK and JNK suppressed the leptin-stimulated expression of AP-1 and MMP-9. Leptin treatment induced the expression of MMP-9 in SMCs, suggesting that leptin may have substantial involvement in plaque rupture by promoting the degradation of ECM.

Does Supplementation with Omega-3 PUFAs Add to the Prevention of Cardiovascular Disease?

PURPOSE OF REVIEW

Omega-3 fatty acids are increasingly used for the protection of cardiovascular disease. The main but not the sole mechanism of action is the reduction of triglyceride levels. In this review, we summarize the effect of omega-3 supplements on all-cause and cardiovascular mortality, myocardial infarction, and stroke from the relevant randomized controlled trials.

RECENT FINDINGS

Twenty-one randomized controlled trials assessed omega-3 supplementation on mortality and cardiovascular-related outcomes. From these studies, as well as from the relevant meta-analyses, we found that omega-3 supplements do not exert a consistent benefit for cardiovascular protection. There is uncertainty of a clear profit from omega-3 supplementation in cardiovascular disease.

Omega-3 fatty acids and inflammatory processes: from molecules to man

Inappropriate, excessive or uncontrolled inflammation contributes to a range of human diseases. Inflammation involves a multitude of cell types, chemical mediators and interactions. The present article will describe nutritional and metabolic aspects of omega-6 (n-6) and omega-3 (n-3) fatty acids and explain the roles of bioactive members of those fatty acid families in inflammatory processes. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are n-3 fatty acids found in oily fish and fish oil supplements. These fatty acids are capable of partly inhibiting many aspects of inflammation including leucocyte chemotaxis, adhesion molecule expression and leucocyte–endothelial adhesive interactions, production of eicosanoids like prostaglandins and leukotrienes from the n-6 fatty acid arachidonic acid and production of pro-inflammatory cytokines. In addition, EPA gives rise to eicosanoids that often have lower biological potency than those produced from arachidonic acid, and EPA and DHA give rise to anti-inflammatory and inflammation resolving mediators called resolvins, protectins and maresins. Mechanisms underlying the anti-inflammatory actions of EPA and DHA include altered cell membrane phospholipid fatty acid composition, disruption of lipid rafts, inhibition of activation of the pro-inflammatory transcription factor nuclear factor κB so reducing expression of inflammatory genes and activation of the anti-inflammatory transcription factor peroxisome proliferator-activated receptor γ. Animal experiments demonstrate benefit from EPA and DHA in a range of models of inflammatory conditions. Human trials demonstrate benefit of oral n-3 fatty acids in rheumatoid arthritis and in stabilizing advanced atherosclerotic plaques. Intravenous n-3 fatty acids may have benefits in critically ill patients through reduced inflammation. The anti-inflammatory and inflammation resolving actions of EPA, DHA and their derivatives are of clinical relevance.

Cardiovascular diseases, depression disorders and potential effects of omega-3 fatty acids

Cardiovascular disease (CVD) and depressive disorders (DD) are two of the most prevalent health problems in the world. Although CVD and depression have different origin, they share some common pathophysiological characteristics and risk factors, such as the increased production of proinflammatory cytokines, endothelial dysfunction, blood flow abnormalities, decreased glucose metabolism, elevated plasma homocysteine levels, oxidative stress and disorder in vitamin D metabolism. Current findings confirm the common underlying factors for both pathologies, which are related to dramatic dietary changes in the mid-19th century. By changing dietary ratio of omega-6 to omega-3 fatty acids from 1:1 to 15-20:1 some changes in metabolism were induced, such as increased pro-inflammatory mediators and modulations of different signaling pathways following pathophysiological response related to both, cardiovascular diseases and depressive disorders.

The Spatial Distribution of Plaque Vulnerabilities in Patients with Acute Myocardial Infarction

Objective

Although the plaque characteristics have been recognized in patients with acute myocardial infarction (AMI), the plaque spatial distribution is not well clarified. Using color-mapping intravascular ultrasound (iMAP-IVUS), we examined culprit lesions to clarify plaque morphology, composition and spatial distribution of the sites of potential vulnerability.

Methods

Sixty-eight culprit lesions in 64 consecutive AMI patients who underwent angiography and IVUS examinations before intervention were analyzed. Plaque morphology and composition were quantified with iMAP-IVUS. The spatial distribution of the sites of potential vulnerability was assessed with longitudinal reconstruction of the consecutive IVUS images. The plaque characteristics were also compared between ruptured and non-ruptured lesions, and between totally occlusive (TO) and non-TO lesions.

Results

The sites with maximum necrotic area (maxNA), maximum plaque burden (maxPB) and most severely narrowed (minimal luminal area, MLA) were recognized vulnerability. In the majority of cases, maxNA sites were proximal to the maxPB sites, and MLA sites were distal to the maxNA and maxPB sites. Ruptures usually occurred close to maxNA sites and proximal to maxPB and MLA sites. The average distance from the site of rupture to the maxNA site was 0.33 ± 4.04 mm. Ruptured lesions showed significant vessel remodeling, greater plaque volume, and greater lipidic volume compared to those of non-ruptured lesions. Both the length and plaque burden (PB) of TO lesions were greater than those of non-TO lesions.

Conclusions

Instead of overlapping on maxPB sites, most maxNA sites are proximal to the maxPB sites and are the sites most likely to rupture. Plaque morphology and composition play critical roles in plaque rupture and coronary occlusion.

Current evidence and future perspectives of omega-3 polyunsaturated fatty acids for the prevention of cardiovascular disease

Omega-3 fatty acids have been traditionally used for the prevention of major cardiovascular events in patients with or without a history of cardiovascular disease. Their main mechanism of action is to lower triglyceride levels, but they also exert anti-arrythmic and anti-inflammatory properties, they reduce blood pressure levels and stabilize the atherosclerotic plaques. There is a vast amount of evidence derived from randomized studies that seems to question their benefit for the prevention of major cardiovascular events. Upcoming trials will help to better clarify their use in certain indications.

Laser capture microdissection for analysis of macrophage gene expression from atherosclerotic lesions

Coronary artery disease, resulting from atherosclerosis, is the leading cause of death in the Western world. Most previous studies have subjected atherosclerotic arteries, a tissue of mixed cellular composition, to homogenization in order to identify the factors in plaque development, thereby obscuring information relevant to specific cell types. Because macrophage foam cells are critical mediators in atherosclerotic plaque advancement, we reasoned that performing gene analysis on those cells would provide specific insight in novel regulatory factors and potential therapeutic targets. We demonstrated for the first time in vascular biology that foam cell-specific RNA can be isolated by laser capture microdissection (LCM) of plaques. As expected, compared to whole tissue, a significant enrichment in foam cell-specific RNA transcripts was observed. Furthermore, because regression of atherosclerosis is a tantalizing clinical goal, we developed and reported a transplantation-based mouse model. This involved allowing plaques to form in apoE-/- mice and then changing the plaque's plasma environment from hyperlipidemia to normolipidemia. Under those conditions, rapid regression ensued in a process involving emigration of plaque foam cells to regional and systemic lymph nodes. Using LCM, we were able to show that under regression conditions, there was decreased expression in foam cells of inflammatory genes, but an up-regulation of cholesterol efflux genes. Interestingly, we also found that increased expression of chemokine receptor CCR7, a known factor in dendritic cell migration, was required for regression. In conclusion, the LCM methods described in this chapter, which have already lead to a number of striking findings, will likely further facilitate the study of cell type-specific gene expression in animal and human plaques during various stages of atherosclerosis, and after genetic, pharmacologic, and environmental perturbations.

The impact of long-chain n-3 polyunsaturated fatty acids on human health

A considerable literature has been published on the health benefits of fish, oil-rich fish and fish oils and their constituent long-chain (LC) n-3 PUFA. Evidence from epidemiological studies highlights the cardioprotective attributes of diets rich in fish, especially oil-rich fish. Data from intervention trials are consistent in suggesting that LC n-3 PUFA lower the risk of CVD, probably by the multiple mechanisms of lowering serum triacylglycerols, improving the LDL:HDL ratio, anti-arrhythmic effects on heart muscle, improved plaque stability, anti-thrombotic effects and reduced endothelial activation. Research indicates LC n-3 PUFA provision has an impact during development, and there is preliminary evidence that docosahexaenoic acid supplementation during pregnancy could optimise brain and retina development in the infant. LC n-3 PUFA are also postulated to ameliorate behavioural and mental health disturbances such as depression, schizophrenia, dementia and attention deficit hyperactivity disorder. However, despite some positive evidence in each of these areas, use of LC n-3 PUFA in these conditions remains at the experimental stage. In the case of immune function, there is little doubt that LC n-3 PUFA have a positive effect. Although intervention trials in rheumatoid arthritis show strong evidence of benefit, evidence for efficacy in other inflammatory conditions, including Crohn's disease, ulcerative colitis, psoriasis, lupus, multiple sclerosis, cystic fibrosis and asthma, is inconsistent or inadequate. More promising evidence in some conditions may come from studies which attempt to modify the fetal environment using LC n-3 PUFA supplementation during pregnancy.

Cardiovascular effects of marine omega-3 fatty acids

Much evidence shows that the marine omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid have beneficial effects in various cardiac disorders, and their use is recommended in guidelines for management of patients after myocardial infarction. However, questions have been raised about their usefulness alongside optimum medical therapies with agents proven to reduce risk of cardiac events in high-risk patients. Additionally, there is some evidence for a possible pro-arrhythmic effect in subsets of cardiac patients. Some uncertainly exists about the optimum dose needed to obtain beneficial effects and the relative merit of dietary intake of omega-3 polyunsaturated fatty acids versus supplements. We review evidence for the effects of omega-3 polyunsaturated fatty acids on various cardiac disorders and the risk factors for cardiac disease. We also assess areas of uncertainty needing further research.

Omega-3 fatty acids and inflammatory processes

Long chain fatty acids influence inflammation through a variety of mechanisms; many of these are mediated by, or at least associated with, changes in fatty acid composition of cell membranes. Changes in these compositions can modify membrane fluidity, cell signaling leading to altered gene expression, and the pattern of lipid mediator production. Cell involved in the inflammatory response are typically rich in the n-6 fatty acid arachidonic acid, but the contents of arachidonic acid and of the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can be altered through oral administration of EPA and DHA. Eicosanoids produced from arachidonic acid have roles in inflammation. EPA also gives rise to eicosanoids and these often have differing properties from those of arachidonic acid-derived eicosanoids. EPA and DHA give rise to newly discovered resolvins which are anti-inflammatory and inflammation resolving. Increased membrane content of EPA and DHA (and decreased arachidonic acid content) results in a changed pattern of production of eicosanoids and resolvins. Changing the fatty acid composition of cells involved in the inflammatory response also affects production of peptide mediators of inflammation (adhesion molecules, cytokines etc.). Thus, the fatty acid composition of cells involved in the inflammatory response influences their function; the contents of arachidonic acid, EPA and DHA appear to be especially important. The anti-inflammatory effects of marine n-3 PUFAs suggest that they may be useful as therapeutic agents in disorders with an inflammatory component.

Does smoking status affect the association between baseline white blood cell count and in-hospital mortality of patients presented with Acute Coronary Syndrome? The Greek study of Acute Coronary Syndromes (GREECS)

OBJECTIVES

In this work, we sought to investigate whether smoking status modifies the effect of white blood cell count (WBC) on in-hospital mortality of patients presented with acute coronary syndrome (ACS).

METHODS

A sample of 6 hospitals located in Greek urban and rural regions was selected. We recorded almost all consecutive patients due to ACS, from October 2003 to September 2004 (2172 patients).

RESULTS

The mean (standard deviation) WBC count was 9.14 (3.16) cells/dL. The in-hospital mortality rate was higher in patients of upper tertile compared to those of lower tertile of WBC (p<0.05). The interaction between smoking status and WBC count revealed that smoking status modifies the effect of WBC count on mortality (p for interaction=0.004). Thus, stratified analysis showed that the WBC count is an independent predictor of in-hospital mortality only among former and current smokers.

CONCLUSIONS

We demonstrated that the association between WBC count and mortality modified by smoking status and that WBC count is a predictor of mortality only among former and current smokers.

Intravascular detection of inflamed atherosclerotic plaques using a fluorescent photosensitizer targeted to the scavenger receptor

Inflammation plays an important role in the pathophysiology of atherosclerotic disease. We have previously shown that the targeted photosensitizer chlorin (e(6)) conjugated with maleylated albumin (MA-ce6) is taken up by macrophages via the scavenger receptor with high selectivity. In a rabbit model of inflamed plaque in New Zealand white rabbits via balloon injury of the aorto-iliac arteries and high cholesterol diet we showed that the targeted conjugate showed specificity towards plaques compared to free ce6. We now show that an intravascular fiber-based spectrofluorimeter advanced along the -iliac vessel through blood detects 24-fold higher fluorescence in atherosclerotic vessels compared to control rabbits (p < 0.001 ANOVA). Within the same animals, signal derived from the injured iliac artery was 16-fold higher than the contralateral uninjured iliac (p < 0.001). Arteries were removed and selective accumulation of MA-ce6 in plaques was confirmed using: (1) surface spectrofluorimetry, (2) fluorescence extraction of ce6 from aortic segments, and (3) confocal microscopy. Immunohistochemical analysis of the specimens showed a significant correlation between MA-ce6 uptake and RAM-11 macrophage staining (R = 0.83, p < 0.001) and an inverse correlation between MA-ce6 uptake and smooth muscle cell staining (R = -0.74, p < 0.001). MA-ce6 may function as a molecular imaging agent to detect and/or photodynamically treat inflamed plaques.

Aggregated low density lipoproteins decrease metalloproteinase-9 expression and activity in human coronary smooth muscle cells

Plaque stability largely depends on vascular smooth muscle cell (VSMC) function. VSMC secrete metalloproteinases (MMPs), matrix degrading endopeptidases, that regulate VSMC migration and function. Among them, gelatinase B or MMP-9 seems to have a protective effect by promoting a stable plaque phenotype. In macrophage foam cells oxidized LDL (oxLDL) uptake regulates MMP-9 expression. However, it is unknown whether VSMC-lipid loading by aggregated LDL (agLDL) internalization produces any effect on MMP-9 production by human resident vascular cells. In the present study, we analyzed the effect of lipid-internalization in MMP-9 and MMP-2 expression and activity and its consequences in VSMC migration. Our results show that agLDL-internalization down-regulates MMP-9 activity in a time-dependent manner up to 42% at 48h and in a dose-dependent manner up to 87% at 300 microg/mL. nLDL induced similar but not sustained decrease on MMP-9 activity. However, neither agLDL nor nLDL exerted any significant effect on MMP-2 and TIMP-1. VSMC regrowth after a scratch injury was significantly reduced by exposure to agLDL. We conclude that agLDL-lipid loading reduces MMP-9 activity and this effect is associated to inhibition of VSMC migration. Thus, agLDL internalization may have consequences on vascular remodeling after injury, and the stability of lipid-rich atherosclerotic plaques.

Photosensitizer delivery to vulnerable atherosclerotic plaque: comparison of macrophage-targeted conjugate versus free chlorin(e6)

We have previously shown that a conjugate (MA-ce6) between maleylated serum albumin and the photosensitizer chlorin(e6) (ce6) is targeted in vitro to macrophages via class A scavenger receptors. We now report on the ability of this conjugate to localize in macrophage-rich atherosclerotic plaques in vivo. Both the conjugate and the free photosensitizer ce6 are studied after injection into New Zealand White rabbits that are rendered atherosclerotic by a combination of aortic endothelial injury and cholesterol feeding into normal rabbits. Rabbits are sacrificed at 6 and 24 h after injection and intravascular fluorescence spectroscopy is carried out by fiber-based fluorimetry in intact blood-filled arteries. Surface spectrofluorimetry of numbered excised aortic segments together with injured and normal iliac arteries is carried out, and quantified ce6 content by subsequent extraction and quantitative fluorescence determination of the arterial segments and also of nontarget organs. There is good agreement between the various techniques for quantifying ce6 localization, and high contrast between arteries from atherosclerotic and normal rabbits is obtained. Fluorescence correlates with the highest burden of plaque in the aorta and the injured iliac artery. The highest accumulation in plaques is obtained using MA-ce6 at 24 h. Free ce6 gives better accumulation at 6 h compared to 24 h. The liver, spleen, lung, and gall bladder have the highest uptake in nontarget organs. Macrophage-targeted photosensitizer conjugates may have applications in both detecting and treating inflamed vulnerable plaque.

mRNA expression of genes involved in lipid efflux and matrix degradation in occlusive and ectatic atherosclerotic disease

BACKGROUND

Atherosclerotic plaque behaviour is influenced by intra-plaque inflammation, matrix turnover, and the lipid core volume. Peroxisome proliferator activated receptor gamma (PPARgamma) modulates atherosclerosis by its anti-inflammatory and anti-protease activity. PPARgamma promotes lipid efflux through the liver X receptor alpha (LXRalpha) and the ATP binding cassette transporter A1 (ABCA1). Matrix metalloproteinase 9 (MMP-9) and cyclooxygenase 2 (COX-2) are implicated in plaque instability.

AIMS

To assess the expression of these genes in occlusive and ectatic atherosclerotic disease to determine the relation between genes involved in lipid efflux and matrix degradation.

METHODS

Carotid endarterectomy specimens from 16 patients and aneurysm tissue from 16 patients undergoing abdominal aortic aneurysm repair were used. Inferior mesenteric arteries from colectomy specimens from 12 patients served as controls. Total RNA was extracted from pulverised tissue and reverse transcribed into cDNA. Quantitative real time polymerase chain reaction (PCR) was performed using fluorescently labelled probes for ABCA1, LXRalpha, PPARgamma, COX-2, and MMP-9.

RESULTS

PPARgamma expression was significantly lower in both occlusive and ecstatic atherosclerotic disease (p<0.001), whereas LXRalpha and ABCA1 expression was significantly increased (p<0.01). MMP-9 expression was significantly increased in diseased tissues (p<0.0001), and values were highest in occlusive disease (p<0.01). The increases in ABCA1 and MMP-9 mRNA were significantly correlated in diseased tissues (p<0.01, r=0.71 and r=0.78). COX-2 expression was increased in ectatic but low in occlusive disease (p<0.01).

CONCLUSION

This observational study suggests a role for therapeutic upregulation of PPARgamma, which could potentially upregulate lipid efflux through ABCA1 and inhibit matrix degradation through inhibition of MMP-9.

Peroxisome proliferator-activated receptor-gamma and its agonists in hypertension and atherosclerosis : mechanisms and clinical implications

Cardiovascular diseases are the leading cause of morbidity and mortality in the US. Proper management and/or prevention of atherosclerosis and hypertension, two complex and chronic disorders, would significantly reduce the risk for cardiovascular events such as myocardial infarction and stroke, but this requires an understanding of the mechanisms underlying their development and progression. Whereas a great deal has been learned and applied toward the management of these disorders, especially hypertension, morbidity and mortality remains unacceptably high, most likely because there are disease-causing mechanisms that have yet to be fully recognized. Understanding these disease mechanisms is necessary so that novel management strategies can be developed. One of these novel mechanisms centers on peroxisome proliferator-activated receptor (PPAR)-gamma. PPAR-gamma is a member of the nuclear receptor superfamily of ligand-activated transcription factors known to play a role in glucose homeostasis and adipocyte differentiation and, more recently, has been shown to have anti-inflammatory, antiatherogenic, and antihypertensive effects. Thiazolidinediones, a class of drugs used in the treatment of type 2 diabetes mellitus, are high-affinity ligands for PPAR-gamma. In this review, the anti-inflammatory, anti-atherosclerotic, and anti-hypertensive mechanisms by which PPAR-gamma and its agonists are thought to exert protective effects on the cardiovascular system are discussed. Ongoing clinical trials using PPAR-gamma activators for the management of cardiovascular diseases, especially in patients with type 2 diabetes mellitus, are summarized.

Monocyte recruitment and foam cell formation in atherosclerosis

Atherosclerosis is a chronic immune-inflammatory disease in which the interactions of monocytes with activated endothelium are crucial events leading to atherosclerotic alteration of the arterial intima. In early atherosclerosis, monocytes migrate into the subendothelial layer of the intima where they differentiate into macrophages or dendritic cells. In the subendothelial space enriched with atherogenic lipoproteins, most macrophages transform into foam cells. Foam cells aggregate to form the atheromatous core and as this process progresses, the atheromatous centres of plaques become necrotic, consisting of lipids, cholesterol crystals and cell debris. This review highlights some aspects of monocyte recruitment and foam cell formation in atherosclerosis.

Left ventricular systolic dysfunction, total mortality, and sudden death in patients with myocardial infarction treated with n-3 polyunsaturated fatty acids

BACKGROUND

Sudden death (SD) has a major impact on mortality (M) in patients with left ventricular systolic dysfunction (SyD). In GISSI-Prevenzione, treatment with n-3 polyunsaturated fatty acids (PUFA) reduced M and SD in post-MI patients, but their effect in patients with SyD is unknown.

METHODS

11,323 patients with prior MI and NYHA class < or = II were recruited. After excluding patients with no ejection fraction (EF) measurement (1684), and those with missing data (n=9), 9630 patients were available for analysis. Multivariate Cox regression adjusted models were fitted.

RESULTS

Compared to patients with EF > 50%, SyD patients had higher M (12.3% vs. 6.0%) and SD (3.4% vs. 1.4%) rates. PUFA reduced M similarly in patients with (RR 0.76 (0.60-0.96) P=0.02) and without SyD (RR 0.81 (0.59-1.10) P=0.17) (heterogeneity tests P=0.55). In contrast, the effect on SD was markedly asymmetrical: PUFA produced a marked reduction (RR 0.42 (0.26-0.67) P=0.0003) of risk in SyD patients whereas the effect was less evident (RR 0.89 (0.41-1.69) P=0.71) in patients with EF > 50% (heterogeneity tests P=0.07). There was a significant increase in SD with worsening EF (P test for trend=0.02), the benefit on SD in patients with EF < or = 40% being 4-fold higher than in those with EF > 50%.

CONCLUSIONS

Increasing SyD is associated with elevated risk of SD and with increasing benefit from PUFA. The effect of PUFA on SD reduction was greater in patients with SyD. Prospective trials testing the effect of PUFA in populations with SyD are required.

Relation of progression of coronary artery atherosclerosis to risk of cardiovascular events (from the Monitored Atherosclerosis Regression Study)

We investigated whether change in coronary artery atherosclerosis as measured by quantitative coronary angiography is related to cardiovascular event risk. Although many studies have demonstrated the effectiveness of statins in decreasing atherosclerotic progression and cardiovascular event risk, a relation between coronary atherosclerotic progression and event risk has not been documented in clinical trials that have evaluated statin therapy. The Monitored Atherosclerosis Regression Study (MARS) was a randomized, double-blind, placebo-controlled trial designed to test whether lovastatin would decrease coronary atherosclerotic progression as measured by quantitative coronary angiography. We followed 173 subjects in the MARS who had minimum luminal diameter and percent diameter stenosis measured at the beginning and end of a 2-year intervention. Postintervention follow-up events over a mean period of 9.4 years were reported by subjects and verified by medical records. Two-year percent stenosis and minimum luminal diameter changes were tested in relation to clinical event risk in multivariate Cox's regression models. Events ascertained were (1) coronary death and myocardial infarction, (2) coronary death, myocardial infarction, coronary artery bypass grafting, and percutaneous transluminal coronary angioplasty, and (3) any cardiovascular event. Increased percent stenosis was associated with significantly increased hazard ratios (HRs) in all event categories (category 1 HR 1.55 per SD percent stenosis, p <0.01; category 2 HR 1.58, p <0.01; category 3 HR 1.47, p = 0.01). Conversely, event risks were decreased for subjects who had increased minimum luminal diameter (category 1 HR 0.79, p = 0.04) and were not associated with category 2 (HR 0.79, p = 0.12) or category 3 (HR 0.81, p = 0.17). These results indicate that quantitative coronary angiographic changes are associated with cardiovascular events and support the long-term benefit of early intervention to decrease atherosclerosis.

Noninvasive in vivo measurement of vascular inflammation with F-18 fluorodeoxyglucose positron emission tomography

BACKGROUND

Fluorine 18 fluorodeoxyglucose (FDG) has been shown to accumulate in inflamed tissues. However, it is not known whether vascular inflammation can be measured noninvasively. The aim of this study was to test the hypothesis that vascular inflammation can be measured noninvasively by use of positron emission tomography (PET) with FDG.

METHODS AND RESULTS

Inflamed atherosclerotic lesions were induced in 9 male New Zealand white rabbits via balloon injury of the aortoiliac arterial segment and exposure to a high cholesterol diet. Ten rabbits fed standard chow served as controls. Three to six months after balloon injury, the rabbits were injected with FDG (1 mCi/kg), after which aortic uptake of FDG was assessed (3 hours after injection). Biodistribution of FDG activity within aortic segments was obtained by use of standard well gamma counting. FDG uptake was also determined noninvasively in a subset of 6 live atherosclerotic rabbits and 5 normal rabbits, via PET imaging and measurement of standardized uptake values over the abdominal aorta. Plaque macrophage density and smooth muscle cell density were determined by planimetric analysis of RAM-11 and smooth muscle actin staining, respectively. Biodistribution of FDG within nontarget organs was similar between atherosclerotic and control rabbits. However, well counter measurements of FDG uptake were significantly higher within atherosclerotic aortas compared with control aortas (P < .001). Within the upper abdominal aorta of the atherosclerotic group (area of greatest plaque formation), there was an approximately 19-fold increase in FDG uptake compared with controls (108.9 +/- 55.6 percent injected dose [%ID]/g x 10(3) vs 5.7 +/- 1.2 %ID/g x 10(3) [mean +/- SEM], P < .001). In parallel with these findings, FDG uptake, as determined by PET, was higher in atherosclerotic aortas (standardized uptake value for atherosclerotic aortas vs control aortas, 0.68 +/- 0.06 vs 0.13 +/- 0.01; P < .001). Moreover, macrophage density, assessed histologically, correlated with noninvasive (PET) measurements of FDG uptake (r = 0.93, P < .0001). In contrast to this finding, FDG uptake did not correlate with either aortic wall thickness or smooth muscle cell staining of the specimens.

CONCLUSION

These data show that FDG accumulates in macrophage-rich atherosclerotic plaques and demonstrate that vascular macrophage activity can be quantified noninvasively with FDG-PET. As such, measurement of vascular FDG uptake with PET holds promise for the noninvasive characterization of vascular inflammation.

Plasma cytokine response during the postprandial period: a potential causal process in vascular disease?

Chronic inflammation of the vascular endothelium produces endothelial dysfunction and ultimately atherogenesis. Postprandial hyperlipidaemia is an independent risk factor for cardiovascular disease. Recent studies show that the magnitude of postprandial lipaemia following a single fatty meal is negatively related to vascular function. This is associated with a transient increase in the concentrations of pro-inflammatory cytokines and soluble adhesion molecules and in pro-oxidant activity. One possible interpretation is that repeated exposure of the blood vessel wall to the activities of pro-inflammatory cytokines and pro-oxidants may damage the vascular endothelium and promote atherogenesis. Based on these results, we propose a model of a causal mechanism to explain how consumption of a fatty meal may impair vascular dysfunction.

Nuclear factor kappaB signaling in atherogenesis

Atherosclerosis is an inflammatory disease, characterized by the accumulation of macrophage-derived foam cells in the vessel wall and accompanied by the production of a wide range of chemokines, cytokines, and growth factors. These factors regulate the turnover and differentiation of immigrating and resident cells, eventually influencing plaque development. One of the key regulators of inflammation is the transcription factor nuclear factor kappaB (NF-kappaB), which, for a long time, has been regarded as a proatherogenic factor, mainly because of its regulation of many of the proinflammatory genes linked to atherosclerosis. NF-kappaB may play an important role in guarding the delicate balance of the atherosclerotic process as a direct regulator of proinflammatory and anti-inflammatory genes and as a regulator of cell survival and proliferation. Here we address recent literature on the function of NF-kappaB in inflammatory responses and its relation to atherosclerosis.

Macrophage-targeted photodynamic therapy

Photodynamic therapy (PDT) uses light activatable molecules that after illumination produce reactive oxygen species and unwanted tissue destruction. PDT has dual selectivity due to control of light delivery and to some extent selective photosensitizer (PS) accumulation in tumors or other diseased tissue, additional targeted selectivity of PS for disease is necessary. The delivery of drugs to selected lesions can be enhanced by the preparation of targeted macromolecular conjugates that employ cell type specific targeting by ligand-receptor recognition. Macrophages and monocytes express a scavenger-receptor that is a high-capacity route for delivering molecules into endocytic compartments in a cell-type specific manner. We have shown that by attaching PS to scavenger-receptor ligands it is possible to get three logs of selective cell killing in macrophages while leaving non-macrophage cells unharmed. The capability to selectively kill macrophages has applications in treating cancer and in the detection and therapy of vulnerable atherosclerotic plaque and possibly for autoimmune disease and some infections.

The effects of high glucose and atorvastatin on endothelial cell matrix production

BACKGROUND

Statins are known to enhance atherosclerotic plaque stability through influences on extracellular matrix homeostasis. Net matrix production reflects the relative balance of matrix production and degradation through enzymes such as matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitor of MMP (TIMPs). The effects of statins on endothelial cell production of these parameters following co-exposure with a proatherogenic stimulus such as high glucose are not known.

METHODS

Human endothelial cells were exposed for 72 h to 5 mm (control) or 25 mm (high) glucose +/- atorvastatin (1 micromol/l). Extracellular matrix homeostasis was assessed by measuring matrix metalloproteinase (MMP)-2 secretion, tissue inhibitor of MMP (TIMP)-1 and -2 secretion and net collagen IV production. Results were expressed as percentage +/- SEM of control values.

RESULTS

Exposure to high glucose increased cellular collagen IV expression to 190.1 +/- 11.7% (P < 0.0001) of control levels. No change in MMP-2 secretion (111.6 +/- 5.2%; P > 0.05) was observed but both TIMP-1 and TIMP-2 expression were increased to 136.3 +/- 6.4% and 144.0 +/- 27.5%, respectively (both P < 0.05). The presence of atorvastatin in high glucose conditions reduced collagen IV expression to 136.1 +/- 20.6%. This was paralleled by increased secretion of MMP-2 to 145.8 +/- 7.8% (P < 0.01), increased TIMP-2 expression to 208.0 +/- 21.3% (P < 0.005 compared with high glucose) but no change in TIMP-1 expression (155.1 +/- 14.6%) compared with high glucose alone. The presence of atorvastatin in control conditions did not affect levels of collagen IV expression (114.5 +/- 13.2%).

CONCLUSIONS

Endothelial cell exposure to high glucose was associated with a MMP/TIMP profile that increased extracellular matrix production which was attenuated by concurrent exposure to atorvastatin. Consequently, a mechanism by which the atherosclerotic plaque regression that is observed in patients taking these drugs has been demonstrated.

Fatty acids and the immune system: from basic science to clinical applications

Over the last 25 years, the effects of fatty acids on the immune system have been characterized using in vitro, animal and human studies. Advances in fatty acid biochemistry and molecular techniques have recently suggested new mechanisms by which fatty acids could potentially modify immune responses, including modification of the organization of cellular lipids and interaction with nuclear receptors. Possibilities for the clinical applications of n-3 PUFA are now developing. The present review focuses on the hypothesis that the anti-inflammatory properties of n-3 PUFA in the arterial wall may contribute to the protective effects of n-3 PUFA in CVD, as suggested by epidemiological and secondary prevention studies. Studies are just beginning to show that dietary n-3 PUFA can be incorporated into plaque lipid in human subjects, where they may influence the morphology and stability of the atherosclerotic lesion.

n–3 Fatty acids and cardiovascular disease: evidence explained and mechanisms explored

Long chain n–3 PUFAs (polyunsaturated fatty acids) are found in fatty fish and in fish oils. Substantial evidence from epidemiological and case-control studies indicates that consumption of fish, fatty fish and long-chain n–3 PUFAs reduces the risk of cardiovascular mortality. Secondary prevention studies using long-chain n–3 PUFAs in patients post-myocardial infarction have shown a reduction in total and cardiovascular mortality, with an especially potent effect on sudden death. Long-chain n–3 PUFAs have been shown to decrease blood triacylglycerol (triglyceride) concentrations, to decrease production of chemoattractants, growth factors, adhesion molecules, inflammatory eicosanoids and inflammatory cytokines, to lower blood pressure, to increase nitric oxide production, endothelial relaxation and vascular compliance, to decrease thrombosis and cardiac arrhythmias and to increase heart rate variability. These mechanisms most likely explain the primary and secondary cardiovascular protection afforded by long-chain n–3 PUFA consumption. A recent study suggests that long-chain n–3 PUFAs might also act to stabilize advanced atherosclerotic plaques, perhaps through their anti-inflammatory effects. As a result of the robust evidence in their favour, a number of recommendations to increase intake of long-chain n–3 PUFAs have been made.

Supplementary taurine may stabilize atheromatous plaque by antagonizing the activation of metalloproteinases by hypochlorous acid

The rupture of atherosclerotic plaque, responsible for triggering the majority of myocardial infarctions, presumably requires proteolysis of collagen fibers and other protein components of the intercellular matrix. This is achieved by activated matrix metalloproteases (MMPs) secreted by intimal macrophages and foam cells. MMPs are synthesized as inactive pro-enzymes in which coordinate binding of the thiol group of a key cysteine residue to the active-site zinc atom blocks proteolytic activity. Physiological activation of MMPs is mediated, in large measure, by phagocyte-derived hypochlorous acid (HOCL), which can oxidize the zinc-bound thiol to sulfinic acid, thus freeing the active-site zinc. HOCL also encourages proteolysis of ground substance by inactivating proteins such as TIMP-1 that are physiological inhibitors of MMPs. In vivo, the unrestrained oxidant activity of HOCL is opposed by taurine, which reacts spontaneously with HOCL to generate taurine chloramine, much more stable than HOCL. Taurine chloramine has less impact than HOCL on MMP activation, and does not impair the activity of TIMP-1. Since tissue levels of taurine can be boosted via supplementation, taurine may thus have potential for stabilizing plaque and thereby warding off infarction--an effect that should be reinforced by taurine's platelet-stabilizing activity. In light of recent epidemiological evidence that increased expression of myeloperoxidase - the enzyme which generates HOCL--is an important risk factor for coronary disease, supplemental taurine may indeed have broader utility for suppressing both the genesis and the rupture of atherosclerotic plaque.

The vascular biology of atherosclerosis

Despite many advances in cardiology, atherosclerosis remains a major medical problem. This is especially the case for individuals with insulin resistance and type 2 diabetes mellitus. Atherosclerotic lesions can develop as early as the second decade of life and progress into clinical disease over time. Atherosclerosis is a complex disorder, involving many cell types and circulating mediators and resulting in an inflammatory state. The control of transcription of inflammatory mediators via ligands for peroxisome proliferator-activated receptor-gamma, such as thiazolidinediones (TZDs), has been raised as a possible mechanism for improving atherosclerosis. Results of studies performed in vitro and in animal models suggest that TZDs may increase cholesterol efflux from macrophages, decrease cytokine expression, and limit chemokine levels. Such effects may underlie the decreases in atherosclerosis seen in mouse models of atherosclerosis after TZD treatment. The direct actions of the TZDs on atherosclerosis may couple with their effects on metabolic parameters through increased insulin sensitivity. Ongoing clinical trials evaluating cardiovascular end points with TZD therapy should provide insight into these possibilities.

The potential role of peroxisome proliferator-activated receptors on inflammation in type 2 diabetes mellitus and atherosclerosis

Increasing attention has focused on the role of inflammation in various chronic diseases, including atherosclerosis. Recent compelling data have begun to unite work from various arenas, such as epidemiology and vascular biology, and even clinical trials to provide evidence for inflammation as a mechanism underlying cardiovascular disease. Inflammation has been implicated in the pathogenesis, progression, and complications of both atherosclerosis and diabetes mellitus-2 complex disorders often found intertwined in patients. Although this story continues to evolve, peroxisome proliferator-activated receptors (PPARs) have been implicated as a molecular pathway involved in both these disease processes. In vitro data, animal work, and some human studies suggest that synthetic PPAR agonists in clinical use, such as thiazolidinediones, may not only regulate metabolic processes but may also limit inflammatory responses, including some involved in atherosclerosis.

Association of n-3 polyunsaturated fatty acids with stability of atherosclerotic plaques: a randomised controlled trial

BACKGROUND

N-3 polyunsaturated fatty acids (PUFAs) from oily fish protect against death from cardiovascular disease. We aimed to assess the hypothesis that incorporation of n-3 and n-6 PUFAs into advanced atherosclerotic plaques increases and decreases plaque stability, respectively.

METHODS

We did a randomised controlled trial of patients awaiting carotid endarterectomy. We randomly allocated patients control, sunflower oil (n-6), or fish-oil (n-3) capsules until surgery. Primary outcome was plaque morphology indicative of stability or instability, and outcome measures were concentrations of EPA, DHA, and linoleic acid in carotid plaques; plaque morphology; and presence of macrophages in plaques. Analysis was per protocol.

FINDINGS

188 patients were enrolled and randomised; 18 withdrew and eight were excluded. Duration of oil treatment was 7-189 days (median 42) and did not differ between groups. The proportions of EPA and DHA were higher in carotid plaque fractions in patients receiving fish oil compared with those receiving control (absolute difference 0.5 [95% CI 0.3-0.7], 0.4 [0.1-0.6], and 0.2 [0.1-0.4] g/100 g total fatty acids for EPA; and 0.3 [0.0-0.8], 0.4 [0.1-0.7], and 0.3 [0.1-0.6] g/100 g total fatty acids for DHA; in plaque phospholipids, cholesteryl esters, and triacylglycerols, respectively). Sunflower oil had little effect on the fatty acid composition of lipid fractions. Fewer plaques from patients being treated with fish oil had thin fibrous caps and signs of inflammation and more plaques had thick fibrous caps and no signs of inflammation, compared with plaques in patients in the control and sunflower oil groups (odds ratio 0.52 [95% CI 0.24-0.89] and 1.19 [1.02-1.57] vs control; 0.49 [0.23-0.90] and 1.16 [1.01-1.53] vs sunflower oil). The number of macrophages in plaques from patients receiving fish oil was lower than in the other two groups. Carotid plaque morphology and infiltration by macrophages did not differ between control and sunflower oil groups.

INTERPRETATION

Atherosclerotic plaques readily incorporate n-3 PUFAs from fish-oil supplementation, inducing changes that can enhance stability of atherosclerotic plaques. By contrast, increased consumption of n-6 PUFAs does not affect carotid plaque fatty-acid composition or stability over the time course studied here. Stability of plaques could explain reductions in non-fatal and fatal cardiovascular events associated with increased n-3 PUFA intake.

Insulin resistance, diabetes, and atherosclerosis: thiazolidinediones as therapeutic interventions

The insulin resistance syndrome, a cluster of metabolic abnormalities involving dyslipidemia, hypertension, diabetes, impaired glucose tolerance, and hypercoagulability, carries an increased risk of atherosclerosis. Although interventions targeting elements of this syndrome have dramatically reduced cardiovascular risk, the impact of glucose-lowering has been more disappointing. Thiazolidinediones (TZDs) are a new class of insulin-sensitizing agents that activate the nuclear receptor peroxisome proliferator-activated receptor-g. TZDs may improve not only glucose levels but also other metabolic parameters associated with insulin resistance. The TZD data are reviewed, with a focus on their potential cardiovascular effects.

Atherosclerosis in type 2 diabetes mellitus and insulin resistance: mechanistic links and therapeutic targets

The ongoing heavy burden of cardiovascular disease associated with diabetes mellitus highlights the failure of current treatment strategies to address effectively the cardiovascular risk profile in such patients. Insulin resistance is not only an underlying feature in most cases of type 2 diabetes, but is also associated, through the Insulin Resistance Syndrome, with cardiovascular risk factors that promote atherothrombosis through diverse mechanisms. Growing evidence suggests that treatment with anti-diabetic agents that improve insulin sensitivity, such as the thiazolidinediones, improve multiple components of the Insulin Resistance Syndrome, have beneficial effects on various atherothrombotic mechanisms, and reduce atherosclerosis in animal models and perhaps humans as well. Given data implicating chronic inflammation as a central feature of atherosclerosis, the anti-inflammatory activity of the thiazolidinediones may contribute to their potential anti-atherosclerotic effects. An improved understanding of the mechanisms linking diabetes, atherosclerosis, and cardiovascular disease is needed in order to understand how these and other current and emerging therapies might reduce diabetes-associated cardiovascular disease.

Vascular effects of GI262570X (PPAR-gamma agonist) in the brown adipose tissue of Han Wistar rats: a review of 1-month, 13-week, 27-week and 2-year oral toxicity studies

We describe and discuss microscopic findings in the brown adipose tissue (BAT) blood vessels of Han Wistar rats treated with GI262570X, a peroxisome proliferator-activated receptor-gamma agonist (PPAR-gamma agonist) by oral gavage for 28 days, 13 weeks, 27 weeks, and 2 years. Review of these studies revealed a consistent vascular change, consisting of multifocal fatty infiltration in the BAT of treated rats. A similar vascular change was not seen in other vessels or organs. Microscopically, fatty infiltration was characterized primarily by round, clear vacuoles within the tunica media and/or tunica adventitia of small and medium-sized arteries and arterioles. Occasionally, these vacuoles had peripherally located nuclei and morphologically resembled adipocytes, suggesting a well-characterized PPAR effect (ie, differentiation of stem cells or preadipocytes into mature adipocytes). However, administration of GI262570X up to 2 years failed to induce more severe or progressive lesions in the blood vessels of rat BAT and, in particular, did not result in induction of any atherosclerotic-like lesions or foam cell infiltration. At the longer exposure, there was an apparent reduction of severity and/or incidence, indicating a possible adaptive response. These results suggest that the possibility of generating atherosclerotic-like lesions through prolonged treatment of GI262570X (PPAR-gamma agonist) is highly unlikely in rats.