Apoptosis in atherosclerosis. Does it contribute to plaque instability?

Role of Matrix Gla Protein in the Complex Network of Coronary Artery Disease: A Comprehensive Review

Coronary artery disease (CAD) is widely recognized as one of the most important clinical entities. In recent years, a large body of accumulated data suggest that coronary artery calcification, a process highly prevalent in patients with CAD, occurs via well-organized biologic processes, rather than passively, as previously regarded. Matrix Gla protein (MGP), a vitamin K-dependent protein, emerged as an important inhibitor of both intimal and medial vascular calcification. The functionality of MGP hinges on two post-translational modifications: phosphorylation and carboxylation. Depending on the above-noted modifications, various species of MGP may exist in circulation, each with their respective level of functionality. Emerging data suggest that dysfunctional species of MGP, markedly, dephosphorylated-uncarboxylated MGP, might find its application as biomarkers of microvascular health, and assist in clinical decision making with regard to initiation of vitamin K supplementation. Hence, in this review we summarized the current knowledge with respect to the role of MGP in the complex network of vascular calcification with concurrent inferences to CAD. In addition, we discussed the effects of warfarin use on MGP functionality, with concomitant implications to coronary plaque stability.

Interleukin-6 is an independent predictor of progressive atherosclerosis in the carotid artery: The Tromsø Study

BACKGROUND AND AIMS

Novel biomarkers are linked to cardiovascular disease (CVD). The aim of the present study was to investigate the association between 28 blood biomarkers and the formation and progression of carotid plaque.

METHODS

In a nested case control study with 703 participants from the population based Tromsø Study, a large biomarker panel was measured in blood obtained at baseline. Carotid ultrasound was assessed both at baseline and at 6 years of follow-up. Four groups were defined: Group 1: no plaque at baseline or at follow-up (reference group); Group 2: novel plaque at follow-up; Group 3: stable plaque at follow-up; Group 4: progression of plaque at follow-up. By multinomial logistic regression analyses, we assessed the risk of being in the different plaque groups with regard to traditional cardiovascular risk factors and levels of biomarkers at baseline.

RESULTS

Adjusted for traditional risk factors, interleukin-6 (IL-6) was an independent predictor of plaque progression (OR 1.44, 95% CI 1.12-1.85 per SD increase in IL-6 level). This result remained significant after inclusion of other novel biomarkers to the model, and when subjects with former CVD were excluded. Neopterin was protective of novel plaque formation (OR 0.73, 95% CI 0.57-0.93). Myeloperoxidase and Caspase-1 were independent predictors of plaque progression, but this effect disappeared when excluding subjects with former CVD.

CONCLUSIONS

IL-6 is an independent predictor of plaque progression, suggesting that it may be a marker of progressive atherosclerosis in the general population and that its central role in CVD may be related to promotion of plaque growth.

Expression of a metalloproteinase family of ADAMTS in human vulnerable carotid lesions

AIMS

ADAMTS family of metalloproteases (a disintegrin and metalloprotease with thrombospondin motifs) possesses high proteolytic activity especially regarding proteoglycans. Their expression pattern in carotid plaques is as-yet unknown. The aim of the study was therefore the analysis of expression of ADAMTS1, 4, 5, and 13 and their inhibitors TIMP-1 and TIMP-3 in stable and unstable carotid plaques.

METHODS

Atherosclerotic plaques were collected from 40 patients (29 men, 11 women, mean age 70 years) undergoing carotid endarterectomy. The specimens were categorized into two groups (stable/unstable) according to Redgrave und Rothwell (The Oxford Plaque Study, 2008). SYBR Green-based real-time PCR, histology, and immunohistochemistry were performed.

RESULTS

All ADAMTS tested in our study were expressed in both stable and unstable plaques, especially in smooth muscle cells (SMCs) and macrophages. Analysis of the expression pattern on mRNA level showed significant higher expression of ADAMTS1 in unstable plaques compared with stable plaques (1.7-fold, P = 0.049). The expression of ADAMTS4 and 5 was also increased in unstable lesions; however, these changes were not statistically significant (1.2-fold, P = 0.667 and 1.6-fold, P = 0.077). Expression of TIMP-1 was significantly reduced in unstable plaques compared with stable ones (1.9-fold, P = 0.014).

CONCLUSION

SMCs seem to be an important source of ADAMTS analyzed in our study. Furthermore, expression of ADAMTS1 was found to be increased in unstable carotid lesions and might potentially contribute to plaque vulnerability.

Mouse models of atherosclerosis: a historical perspective and recent advances

Atherosclerosis represents a significant cause of morbidity and mortality in both the developed and developing countries. Animal models of atherosclerosis have served as valuable tools for providing insights on its aetiology, pathophysiology and complications. They can be used for invasive interrogation of physiological function and provide a platform for testing the efficacy and safety of different pharmacological therapies. Compared to studies using human subjects, animal models have the advantages of being easier to manage, with controllable diet and environmental risk factors. Moreover, pathophysiological changes can be induced either genetically or pharmacologically to study the harmful effects of these interventions. There is no single ideal animal model, as different systems are suitable for different research objectives. A good understanding of the similarities and differences to humans enables effective extrapolation of data for translational application. In this article, we will examine the different mouse models for the study and elucidation of the pathophysiological mechanisms underlying atherosclerosis. We also review recent advances in the field, such as the role of oxidative stress in promoting endoplasmic reticulum stress, mitochondrial dysfunction and mitochondrial DNA damage, which can result in vascular inflammation and atherosclerosis. Finally, novel therapeutic approaches to reduce vascular damage caused by chronic inflammation using microRNA and nano-medicine technology, are discussed.

Human cells involved in atherosclerosis have a sex

The influence of sex has been largely described in cardiovascular diseases. Atherosclerosis is a complex process that involves many cell types such as vessel cells, immune cells and endothelial progenitor cells; however, many, if not all, studies do not report the sex of the cells. This review focuses on sex differences in human cells involved in the atherosclerotic process, emphasizing the role of sex hormones. Furthermore, we report sex differences and issues related to the processes that determine the fate of the cells such as apoptotic and autophagic mechanisms. The analysis of the data reveals that there are still many gaps in our knowledge regarding sex influences in atherosclerosis, largely for the cell types that have not been well studied, stressing the urgent need for a clear definition of experimental conditions and the inclusion of both sexes in preclinical studies.

Relationship between thyroid function and carotid artery plaque ulceration

Carotid artery plaque ulceration (PU) is known to be associated with cerebrovascular events (CVE). Even within euthyroid ranges, thyroid function has been reported to be associated with carotid atherosclerosis. However, the relationship between thyroid function and carotid PU remains unclear. Our aim was to determine the relationship between thyroid function and PU in patients with internal carotid artery stenosis (ICS). Records of patients with CVE were retrospectively reviewed. A total of 250 consecutive patients with ICS who had computed tomography angiography (CTA) of the carotid arteries following hospitalization were included in the study. CTA was used for the evaluation of carotid artery plaque morphology and ulceration. Plaque morphology was classified as fatty, mixed or calcified. Patients were divided into two groups according to the presence or absence of PU. Subclinical hypothyroidism (SCH) and hypothyroidism were significantly more common in patients with PU (p < 0.001 and p = 0.003, respectively). Patients with PU had higher incidence of low-normal FT4 levels (p = 0.02). Compared with patients who had no PU, patients with PU had decreased FT4 levels and elevated TSH levels (p = 0.001 and p = 0.001, respectively). TSH level (OR 1.33, p = 0.001), SCH (OR 4.2, p = 0.001), hypothyroidism (OR 3.15, p = 0.037), fatty plaque (OR 2.16, p = 0.01) and calcified plaque (OR 0.19, p < 0.001) were independently associated with PU. Our results suggest that SCH and hypothyroidism could be a risk factor for PU and subsequent CVE. Thyroid functions may be useful for risk stratification of patients with ICS.

Adhesion molecule CD146 and its soluble form correlate well with carotid atherosclerosis and plaque instability

AIMS

Intraplaque neovascularization and foam cell infiltration contribute to the development of unstable plaque, leading to thromboembolism and stroke. Cell adhesion molecules (CAMs) have been reported to be involved in the progression of atherosclerosis and plaque vulnerability. The aim of this study was to assess the association of adhesion molecule CD146 with carotid plaque instability.

METHODS

We collected forty atherosclerotic plaques from 40 patients undergoing carotid endarterectomy. The clinical information of each patient was obtained, and the plaque morphology and characteristics were examined by the ultrasound. The CD146 expressions of the plaques were graded by using semiquantitative scales. The serum level of soluble form of CD146 was detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

CD146 expression was mainly on the intraplaque blood vessels and infiltrated macrophages. The CD146 expression was strongly correlated with the matrix metalloproteinase-9(MMP-9)expressions (P < 0.001) in the plaques. Soluble CD146 (sCD146) was also elevated in patients with atherosclerotic plaques. There was significant correlation between the increased CD146 expression and sCD146 level (P = 0.0057). sCD146 correlated well with serum MMP-9 (P < 0.0044), IL-6 (P = 0.0044) and high sensitivity C-reactive protein (hsCRP) (P = 0.005).

CONCLUSIONS

Adhesion molecules CD146 and its soluble form strongly correlated with the development of inflammation of atherosclerosis and plaque instability. CD146 may be a promising biomarker for monitoring the development and instability of atherosclerotic plaque in patients with carotid diseases.

Th17 cells and IL-17 are involved in the disruption of vulnerable plaques triggered by short-term combination stimulation in apolipoprotein E-knockout mice

Considerable evidence indicates that type 1 T helper (Th1)- and Th17-mediated immune responses promote the formation of atherosclerotic plaques while that CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) have a protective effect. However, the functions of diverse CD4(+) lymphocyte subsets in plaque rupture remain poorly understood because of a shortage of satisfactory plaque rupture models. Here, we established a murine model of atherosclerotic plaque rupture using a high-fat diet and collar placement on the carotid artery, and triggered plaque rupture by short-term stimulation with a combination of lipopolysaccharide, phenylephrine injection and cold in apolipoprotein E-knockout (ApoE(-/-)) mice. We investigated the associations between Th1 cells, Th17 cells and Tregs and plaque rupture by PCR, flow cytometry, ELISA and immunohistochemistry. In total, 75% (18/24) of vulnerable plaques, but no stable plaques, showed rupture characteristics. The proportion of Th17 cells was increased among splenocytes after treatment, but the changes in the levels of Th1 cells and Tregs were not related to rupture. Furthermore, the treatment resulted in high levels of interleukin-17 (IL-17) in the serum and in the region of plaque rupture. In vitro, IL-17 increased the level of apoptosis, a major factor associated with plaque rupture, in cultured murine vascular smooth muscle cells. Th17 cells and IL-17 may be involved in the disruption of vulnerable plaques triggered by short-term stimulation with lipopolysaccharide, phenylephrine injection and cold in ApoE(-/-)mice.

Molecular imaging to identify the vulnerable plaque--from basic research to clinical practice

Cardiovascular disease (CVD) is still the leading cause of death in the Western World. Adverse outcomes of CVD include stroke, myocardial infarction, and heart failure. Atherosclerosis is considered to be the major cause of CVD and is estimated to cause half of all deaths in developed countries. Atherosclerotic lesions of the vessel wall may obstruct blood flow mechanically through stenosis, but rupture of atherosclerotic plaques causing formation of occlusive thrombi is far more prevalent. Unfortunately, conventional diagnostic tools fail to assess whether a plaque is vulnerable to rupture. Research over the past decade identified the biological processes that are implicated in the course towards plaque rupture, like cell death and inflammation. Knowledge about plaque biology propelled the development of imaging techniques that target biologic processes in order to predict the vulnerable plaque. This paper discusses novel and existing molecular imaging targets and addresses advantages and disadvantages of these targets and respective imaging techniques in respect of clinical application and socio-economic impact.

Vitamin K-antagonists accelerate atherosclerotic calcification and induce a vulnerable plaque phenotype

BACKGROUND

Vitamin K-antagonists (VKA) are treatment of choice and standard care for patients with venous thrombosis and thromboembolic risk. In experimental animal models as well as humans, VKA have been shown to promote medial elastocalcinosis. As vascular calcification is considered an independent risk factor for plaque instability, we here investigated the effect of VKA on coronary calcification in patients and on calcification of atherosclerotic plaques in the ApoE(-/-) model of atherosclerosis.

METHODOLOGY/PRINCIPAL FINDINGS

A total of 266 patients (133 VKA users and 133 gender and Framingham Risk Score matched non-VKA users) underwent 64-slice MDCT to assess the degree of coronary artery disease (CAD). VKA-users developed significantly more calcified coronary plaques as compared to non-VKA users. ApoE(-/-) mice (10 weeks) received a Western type diet (WTD) for 12 weeks, after which mice were fed a WTD supplemented with vitamin K(1) (VK(1), 1.5 mg/g) or vitamin K(1) and warfarin (VK(1)&W; 1.5 mg/g & 3.0 mg/g) for 1 or 4 weeks, after which mice were sacrificed. Warfarin significantly increased frequency and extent of vascular calcification. Also, plaque calcification comprised microcalcification of the intimal layer. Furthermore, warfarin treatment decreased plaque expression of calcification regulatory protein carboxylated matrix Gla-protein, increased apoptosis and, surprisingly outward plaque remodeling, without affecting overall plaque burden.

CONCLUSIONS/SIGNIFICANCE

VKA use is associated with coronary artery plaque calcification in patients with suspected CAD and causes changes in plaque morphology with features of plaque vulnerability in ApoE(-/-) mice. Our findings underscore the need for alternative anticoagulants that do not interfere with the vitamin K cycle.

Transforming growth factor-β and atherosclerosis: interwoven atherogenic and atheroprotective aspects

Age-related progression of cardiovascular disease is by far the largest health problem in the US and involves vascular damage, progressive vascular fibrosis and the accumulation of lipid-rich atherosclerotic lesions. Advanced lesions can restrict flow to key organs and can trigger occlusive thrombosis resulting in a stroke or myocardial infarction. Transforming growth factor-beta (TGF-β) is a major orchestrator of the fibroproliferative response to tissue damage. In the early stages of repair, TGF-β is released from platelets and activated from matrix reservoirs; it then stimulates the chemotaxis of repair cells, modulates immunity and inflammation and induces matrix production. At later stages, it negatively regulates fibrosis through its strong antiproliferative and apoptotic effects on fibrotic cells. In advanced lesions, TGF-β might be important in arterial calcification, commonly referred to as "hardening of the arteries". Because TGF-β can signal through multiple pathways, namely the SMADs, a MAPK pathway and the Rho/ROCK pathways, selective defects in TGF-β signaling can disrupt otherwise coordinated pathways of tissue regeneration. TGF-β is known to control cell proliferation, cell migration, matrix synthesis, wound contraction, calcification and the immune response, all being major components of the atherosclerotic process. However, many of the effects of TGF-β are essential to normal tissue repair and thus, TGF-β is often thought to be "atheroprotective". The present review attempts to parse systematically the known effects of TGF-β on both the major risk factors for atherosclerosis and to isolate the role of TGF-β in the many component pathways involved in atherogenesis.

The prognostic impact of soluble apoptosis-stimulating fragment on mortality in patients with carotid atherosclerosis

BACKGROUND AND PURPOSE

Markers of apoptosis are associated with cardiovascular disease. The soluble apoptosis-stimulating fragment (sFAS) was found to be a predictor for outcome in patients with heart failure, but its importance in patients with atherosclerotic disease has not been fully understood as yet. The aim of the present study was to investigate the impact of sFAS on all-cause and cardiovascular mortality in patients with atherosclerosis in the carotid arteries.

METHODS

We studied 981 of 1286 consecutive patients with neurological asymptomatic carotid atherosclerosis as evaluated by duplex Doppler sonography. Patients were prospectively followed for long-term all-cause and cardiovascular mortality.

RESULTS

During a median follow-up of 6.2 years (interquartile range, 5.9 to 6.6 years), a total of 250 deaths (25.5%), including 165 (66%) cardiovascular deaths, were recorded. The risk for all-cause and for cardiovascular mortality, respectively, increased significantly with sFAS concentrations (P<0.001). The hazard ratio for all-cause death was elevated by 2.3-fold (P<0.001) and for cardiovascular death by 2.4-fold (P<0.001) in patients within the highest quintile of sFAS compared with patients within the lowest quintile, respectively. Results remained significant after adjustment for potential confounders and established cardiovascular risk factors, including high-sensitivity C-reactive protein. Patients with high sFAS but low high-sensitivity C-reactive protein had a comparable survival rate with those with elevated high-sensitivity C-reactive protein only (P=0.50).

CONCLUSIONS

Markers of apoptosis, as measured by sFAS, were found to be independent risk predictors for death in patients with atherosclerotic disease in the carotid arteries.

Plaque rupture is a determinant of vascular events in carotid artery atherosclerotic disease: involvement of matrix metalloproteinases 2 and 9

BACKGROUND AND PURPOSE

Unstable carotid atherosclerotic plaques are characterized by cap rupture, leading to thromboembolism and stroke. Matrix metalloproteinases (MMPs) have been implicated in the progression of atherosclerosis and plaque rupture. The aim of this study was to assess the relationship between the expressions of MMP-2 and MMP-9 and carotid plaque instability.

METHODS

Eighty atherosclerotic plaques were collected from 74 patients undergoing carotid endarterectomy. Clinical information was obtained from each patient, and plaque morphology was examined at the macroscopic and microscopic levels. The immunohistochemical expressions of MMPs were graded using semiquantitative scales.

RESULTS

Macroscopic ulceration (84.6% versus 63.4%, p=0.042) and microscopic cap rupture (79.5% versus 51.2%, p=0.010) were more common in symptomatic than in asymptomatic patients. Immunoreactivities of MMP-2 and MMP-9 were increased in 40 and 36 atheromatous plaques, respectively. Macroscopic ulceration was strongly correlated with the expressions of MMP-2 (p<0.001) and MMP-9 (p=0.001). There were significant correlations between increased MMP-2 expression and cap rupture (p=0.002), intraplaque hemorrhage (p=0.039), and a thin fibrous cap (p=0.002), and between increased MMP-9 expression and cap rupture (p=0.010) and a large lipid core (p=0.013).

CONCLUSIONS

Plaque rupture was significantly associated with the development of vascular events in carotid atherosclerotic disease. MMP-2 and MMP-9 are strongly correlated with plaque instability.

Apolipoprotein L6, induced in atherosclerotic lesions, promotes apoptosis and blocks Beclin 1-dependent autophagy in atherosclerotic cells

Inflammatory cytokine-regulated apoptosis and autophagy play pivotal roles in plaque rupture and thrombosis of atherosclerotic lesions. However, the molecular interplay between apoptosis and autophagy in vascular cells has not been investigated. Our prior study showed that human apolipoprotein L6 (ApoL6), a pro-apoptotic BH3-only member of the Bcl-2 family, was one of the downstream targets of interferon-γ (INFγ), which sensitizes atherosclerotic lesion-derived cells (LDCs) to Fas-induced apoptosis. To investigate whether ApoL6 plays a causal role in atherosclerotic apoptosis and autophagy, in this study, we demonstrate that IFNγ treatment itself strongly induces ApoL6, and ApoL6 is highly expressed and partially co-localized with activated caspase 3 in activated smooth muscle cells in atherosclerotic lesions. In addition, overexpression of ApoL6 promotes reactive oxygen species (ROS) generation, caspase activation, and subsequent apoptosis, which can be blocked by pan caspase inhibitor and ROS scavenger. Knockdown of ApoL6 expression by siApoL6 suppresses INFγ- and Fas-mediated apoptosis. Further, ApoL6 binds Bcl-X(L), one of the most abundant anti-death proteins in LDCs. Interestingly, forced ApoL6 expression in LDCs induces degradation of Beclin 1, accumulation of p62, and subsequent attenuation of LC3-II formation and translocation and thus autophagy, whereas siApoL6 treatment reverts the phenotype. Taken together, our results suggest that ApoL6 regulates both apoptosis and autophagy in SMCs. IFNγ-initiated, ApoL6-induced apoptosis in vascular cells may be an important factor causing plaque instability and a potential therapeutic target for treating atherosclerosis and cardiovascular disease.

Atherosclerosis and sex hormones: current concepts

CVD (cardiovascular disease) is the leading cause of death for women. Considerable progress has been made in both our understanding of the complexities governing menopausal hormone therapy and our understanding of the cellular and molecular mechanisms underlying hormone and hormone receptor function. Understanding the interplay of atherosclerosis and sex steroid hormones and their cognate receptors at the level of the vessel wall has important ramifications for clinical practice. In the present review, we discuss the epidemiology of CVD in men and women, the clinical impact of sex hormones on CVD, and summarize our current understanding of the pathogenesis of atherosclerosis with a focus on gender differences in CVD, its clinical presentation and course, and pathobiology. The critical animal and human data that pertain to the role of oestrogens, androgens and progestins on the vessel wall is also reviewed, with particular attention to the actions of sex hormones on each of the three key cell types involved in atherogenesis: the endothelium, smooth muscle cells and macrophages. Where relevant, the systemic (metabolic) effects of sex hormones that influence atherogenesis, such as those involving vascular reactivity, inflammation and lipoprotein metabolism, are discussed. In addition, four key current concepts in the field are explored: (i) total hormone exposure time and coronary heart disease risk; (ii) the importance of tissue specificity of sex steroid hormones, critical timing and the stage of atherosclerosis in hormone action; (iii) biomarkers for atherosclerosis with regard to hormone therapy; and (iv) the complex role of sex steroids in inflammation. Future studies in this field will contribute to guiding clinical treatment recommendations for women and help define research priorities.

Molecular imaging of atherosclerotic plaques targeted to oxidized LDL receptor LOX-1 by SPECT/CT and magnetic resonance

BACKGROUND

The oxidized low-density lipoprotein receptor (LDLR) LOX-1 plays a crucial role in atherosclerosis. We sought to detect and assess atherosclerotic plaque in vivo by using single-photon emission computed tomography/computed tomography and magnetic resonance imaging and a molecular probe targeted at LOX-1.

METHODS AND RESULTS

Apolipoprotein E(-/-) mice fed a Western diet and LDLR(-/-) and LDLR(-/-)/LOX-1(-/-) mice fed an atherogenic diet were used. Imaging probes consisted of liposomes decorated with anti-LOX-1 antibodies or nonspecific immunoglobulin G, (111)indium or gadolinium, and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine fluorescence markers. In vivo imaging was performed 24 hours after intravenous injection (150 microL) of LOX-1 or nonspecific immunoglobulin G probes labeled with either (111)indium (600 muCi) or gadolinium (0.075 mmol/kg), followed by aortic excision for phosphor imaging and Sudan IV staining, or fluorescence imaging and hematoxylin/eosin staining. The LOX-1 probe also colocalized with specific cell types, apoptosis, and matrix metalloproteinase-9 expression in frozen aortic sections. Single-photon emission computed tomography/computed tomography imaging of the LOX-1 probe showed aortic arch "hot spots" in apolipoprotein E(-/-) mice (n=8), confirmed by phosphor imaging. Magnetic resonance imaging showed significant Gd enhancement in atherosclerotic plaques in LDLR(-/-) mice with the LOX-1 (n=7) but not with the nonspecific immunoglobulin G (n=5) probe. No signal enhancement was observed in LDLR(-/-)/LOX-1(-/-) mice injected with the LOX-1 probe (n=5). These results were confirmed by ex vivo fluorescence imaging. The LOX-1 probe bound preferentially to the plaque shoulder, a region with vulnerable plaque features, including extensive LOX-1 expression, macrophage accumulation, apoptosis, and matrix metalloproteinase-9 expression.

CONCLUSIONS

LOX-1 can be used as a target for molecular imaging of atherosclerotic plaque in vivo. Furthermore, the LOX-1 imaging signal is associated with markers of rupture-prone atherosclerotic plaque.

Cardiovascular inflammation and lesion cell apoptosis: a novel connection via the interferon-inducible immunoproteasome

OBJECTIVE

Increasing evidence suggests that chronic inflammation contributes to atherogenesis, and that acute inflammatory events cause plaque rupture, thrombosis, and myocardial infarction. The present studies examined how inflammatory factors, such as interferon-gamma (IFNgamma), cause increased sensitivity to apoptosis in vascular lesion cells.

METHODS AND RESULTS

Cells from the fibrous cap of human atherosclerotic lesions were sensitized by interferon-gamma (IFNgamma) to Fas-induced apoptosis, in a Bcl-X(L) reversible manner. Microarray profiling identified 72 INFgamma-induced transcripts with potential relevance to apoptosis. Half could be excluded because they were induced by IRF-1 overexpression, which did not sensitize to apoptosis. IFNgamma treatment strongly reduced Mcl-1, phospho-Bcl-2 (ser70), and phospho-Bcl-X(L) (ser62) protein levels. Candidate transcripts were modulated by siRNA, overexpression, or inhibitors to assess the effect on IFNgamma-induced Fas sensitivity. Surprisingly, siRNA knockdown of PSMB8 (LMP7), an "immunoproteasome" component, reversed IFNgamma-induced sensitivity to Fas ligation and prevented Fas/IFNgamma-induced degradation of Mcl-1, but did not protect p-Bcl-2 or p-Bcl-X(L). Proteasome inhibition markedly increased Mcl-1, p-Bcl-2, and p-Bcl-X(L) levels after IFNgamma treatment.

CONCLUSIONS

Although critical for antigen presentation, the immunoproteasome appears to be a key link between inflammatory factors and the control of vascular cell apoptosis and may thus be an important factor in plaque rupture and myocardial infarction.

Contributions of hyperhomocysteinemia to atherosclerosis: Causal relationship and potential mechanisms

Hyperhomocysteinemia (HHcy) is considered an independent risk factor for cardiovascular disease, including ischemic heart disease, stroke, and peripheral vascular disease. Mutations in the enzymes and/or nutritional deficiencies in B vitamins required for homocysteine metabolism can induce HHcy. Studies using genetic- or diet-induced animal models of HHcy have demonstrated a causal relationship between HHcy and accelerated atherosclerosis. Oxidative stress and activation of proinflammatory factors have been proposed to explain the atherogenic effects of HHcy. Recently, HHcy-induced endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) have been found to play a role in HHcy-induced atherogenesis. This review will focus on the cellular mechanisms of HHcy in atherosclerosis from both in vivo and in vitro studies. The contributions of ER stress and the UPR in atherogenesis will be emphasized. Results from recent clinical trials assessing the cardiovascular risk of lowering total plasma homocysteine levels and new findings examining the atherogenic role of HHcy in wild-type C57BL/6J mice will also be discussed. (c) 2009 International Union of Biochemistry and Molecular Biology, Inc.

Role of microparticles in atherothrombosis

Cell activation or apoptosis leads to plasma membrane blebbing and microparticle (MP) release in the extracellular space. MPs are submicron membrane vesicles which express a panel of phospholipids and proteins specific of the cells they are derived from. Exposure of negatively charged phospholipids and tissue factor confers a procoagulant potential to MPs. MPs accumulate in the lipid core of the atherosclertotic plaque and is a major determinant of its thrombogenecity. Elevation of plasma MPs levels, particularly those of endothelial origin, reflects cellular injury and is considered now as a surrogate marker of vascular dysfunction. Thus, MPs can be seen as triggers of a vicious circle for they promote prothrombogenic and pro-inflammatory responses as well as cellular dysfunction within the vascular compartment. A better knowledge of MP composition and biological effects as well as the mechanisms leading to their clearance will probably open new therapeutic approaches in the treatment of atherothrombosis.

Clinical relevance of advanced glycation endproducts for vascular surgery

Atherosclerosis is the main contributor to cardiovascular disease and leads to intimal plaque formation, which may progress to plaque rupture with subsequent thromboembolic events and/or occlusion of the arterial lumen. There is increasing evidence that the development or progression of atherosclerosis is associated with advanced glycation endproducts (AGEs). AGEs are a heterogeneous group of compounds formed by the non-enzymatic reaction of reducing sugars with proteins, lipids, and nucleic acids. An increased understanding of the mechanisms of formation and interaction of AGEs has allowed the development of several potential anti-AGE strategies. This review summarizes AGE formation and biochemistry, the pathogeneic role of AGEs in cardiovascular disease, anti-AGE therapies and clinical relevance to vascular surgery.

Matrix vesicles in the fibrous cap of atherosclerotic plaque: possible contribution to plaque rupture

Plaque rupture is the most common type of plaque complication and leads to acute ischaemic events such as myocardial infarction and stroke. Calcification has been suggested as a possible indicator of plaque instability. Although the role of matrix vesicles in the initial stages of arterial calcification has been recognized, no studies have yet been carried out to examine a possible role of matrix vesicles in plaque destabilization. Tissue specimens selected for the present study represented carotid specimens obtained from patients undergoing carotid endarterectomy. Serial frozen cross-sections of the tissue specimens were cut and mounted on glass slides. The thickness of the fibrous cap (FCT) in each advanced atherosclerotic lesion, containing a well developed lipid/necrotic core, was measured at its narrowest sites in sets of serial sections. According to established criteria, atherosclerotic plaque specimens were histologically subdivided into two groups: vulnerable plaques with thin fibrous caps (FCT <100 μm) and presumably stable plaques, in which fibrous caps were thicker than 100 μm. Twenty-four carotid plaques (12 vulnerable and 12 presumably stable plaques) were collected for the present analysis of matrix vesicles in fibrous caps. In order to provide a sufficient number of representative areas from each plaque, laser capture microdissection (LCM) was carried out. The quantification of matrix vesicles in ultrathin sections of vulnerable and stable plaques revealed that the numbers of matrix vesicles were significantly higher in fibrous caps of vulnerable plaques than those in stable plaques (8.908±0.544 versus 6.208±0.467 matrix vesicles per 1.92 μm² standard area; P= 0.0002). Electron microscopy combined with X-ray elemental microanalysis showed that some matrix vesicles in atherosclerotic plaques were undergoing calcification and were characterized by a high content of calcium and phosphorus. The percentage of calcified matrix vesicles/microcalcifications was significantly higher in fibrous caps in vulnerable plaques compared with that in stable plaques (6.705±0.436 versus 5.322±0A94; P= 0.0474). The findings reinforce a view that the texture of the extracellular matrix in the thinning fibrous cap of atherosclerotic plaque is altered and this might contribute to plaque destabilization.

Broad and specific caspase inhibitor-induced acute repression of apoptosis in atherosclerotic lesions evaluated by radiolabeled annexin A5 imaging

OBJECTIVES

The purpose of this study was to evaluate the role of caspase inhibitors on acute resolution of apoptosis in atherosclerotic lesions as evaluated by imaging with annexin A5.

BACKGROUND

Extensive apoptosis of macrophages has been reported at the site of plaque rupture in patients dying of acute coronary syndrome.

METHODS

Of 31 New Zealand White atherosclerotic rabbits, 6 received broad caspase, 3 received caspase-1, 3 received caspase-3, 3 received caspase-8, and 4 received caspase-9 inhibitors; 12 animals did not receive any caspase inhibitors (treatment control group). Six unmanipulated rabbits were used for comparison (disease control group). Technetium-99m-labeled annexin A5 was used for imaging atherosclerotic lesions; 6 of the 12 uninhibited atherosclerotic rabbits received (99m)Tc-labeled mutant annexin A5 (radiotracer control group). Gamma images were obtained, and quantitative radiotracer uptake was compared with pathologic findings.

RESULTS

Atherosclerotic lesions were best visible in untreated atherosclerotic rabbits. Quantitative annexin uptake, defined as the percent of injected dose per g of abdominal aorta tissue, was significantly higher in untreated atherosclerotic animals (mean +/- SD = 0.0515 +/- 0.0099) compared with the normal rabbits (0.0065 +/- 0.0008; p < 0.0001) or atherosclerotic rabbits receiving mutant annexin (0.014 +/- 0.0024; p < 0.0001). Among all caspase inhibitor-treated rabbits, uptake was 39% lower (0.0314 +/- 0.0151) than in untreated atherosclerotic animals (p < 0.01). Uptake was also significantly lower in rabbits receiving broad caspase (0.0206 +/- 0.0058; p < 0.0001) or caspase-1, -3, or -9 (0.0272 +/- 0.0088, p < 0.01; 0.0286 +/- 0.0095, p < 0.01; 0.0300 +/- 0.0021, p < 0.01, respectively) inhibitors. Caspase-8 inhibitor did not affect apoptosis (0.0618 +/- 0.0047; p = NS). Upon histologic characterization, a substantial decrease in macrophage apoptosis was observed in caspase-inhibited animals.

CONCLUSIONS

Molecular imaging, using radiolabeled annexin A5, allows the detection of acute resolution of apoptosis as a result of caspase inhibition in experimental atherosclerosis. If proven clinically, this may allow development of novel intervention strategies in acute vascular events.

Anti-apoptotic effects of probucol are associated with downregulation of Daxx expression in THP-1 macrophage

AIM

To study the relationship between Daxx expression and the antiapoptotic effects of probucol in THP-1 macrophage.

MATERIALS AND METHODS

Apoptosis of THP-1 derived macrophages was induced by exposure to oxidized low density lipoprotein (oxLDL). The development of apoptosis was determined by flow cytometry analysis and nucleic acid-binding dye acridin orange. Reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and indirect immunofluorescence were used to evaluate the expression of Daxx and caspase-3 at both mRNA and protein level.

RESULTS

As expected, THP-1 macrophages exposed to 100 mg/l oxLDL for 48 h exhibited typical morphologic changes of apoptosis, including condensed chromatin and shrunken nucleus. oxLDL treatment markedly increased Daxx expression in a time- and dose-dependent manner, and facilitated Daxx translocation from cytoplasm to nucleus. The percentage of cells with Daxx in nuclei was significantly increased from 8 to 59%. Treatment with probucol (50 micromol/l) for 4 h prior to exposure to oxLDL significantly inhibited Daxx expression and THP-1 macrophage apoptosis by 61.3%. Furthermore, oxLDL enhanced caspase-3 expression with increased mRNA and protein levels, but without obvious change in translocation of caspase-3 (the cells with nuclear Daxx: 14 vs 8%). In contrast, probucol attenuated oxLDL-stimulated caspase-3 expression in THP-1 macrophages.

CONCLUSION

OxLDL-induced apoptosis of THP-1 macrophage is associated with Daxx up-regulation; while inhibition of apoptosis by probucol is related to decreased Daxx expression and nuclear translocation.

Effects of 4-hydroxy-2-nonenal on cultured human aortic endothelial cells and myocardial cell

To study the effects of 4-hydroxy-2-nonenal (HNE) on cultured human aortic endothelial cells and myocardial cells so as to explore the mechanism of the pathogenesis of atherosclerosis. In situ cell death technique, quantitative DNA damage detection and immunohistochemistry were used to identify the cell apoptosis and DNA damage in cultured human aortic endothelial cells and myocardial cells. Tail moment was 32.80+/-1.12, 44.30+/-0.99 and 74.6+/-0.97 when HAOEC were treated with 5 muM, 10muM and 15 muM of HNE for 10 hours, which were of statistical significance when compared with the normal group (6.0+/-0.67, P < 0.001 respectively), But when HAOEC was treated with 1 muM of HNE, the tail moment was 11.3+/-0.9, which was of no statistical difference compared with the untreated group(P>0.05). When human aortic endothelial cells (HAOEC) were treated with 5 muM, 10muM and 15 muM of HNE for 10 hours, the percent of nonviable cells were 5.70+/-0.55, 25.96+/-2.02 and 50.80+/-3.40 (P<0.001 respectively when compared with the normal group with the percent of 0.27+/-0.13). But when HAOEC was treated with 1 muM of HNE for 10 hours, the percent of nonviable cells was 2.5+/-0.22, and no difference was observed when compared with the untreated group (P>0.05). When cultured human myocardial cells were treated with 5 muM of HNE for 10 hours, TUNEL staining showed a greater number of apoptotic cells in HNE-treated human myocardial cells. No TUNEL-positive cells were observed in untreated group. When HAOEC was treated with 5 muM of HNE for 10 hours, immunocytochemical labeling with polyclonal antibody to HNE-modified proteins revealed specific cytoplasmic staining in cells incubated with HNE, whereas staining was absent in control cells incubated with vehicle. But 1 muM of HNE treatment didn't present positive stainings. Higher concentrations of HNE (10 muM and 15 muM) showed much stronger positive stainings. HNE induces DNA damage and cell apoptosis of cultured aortic endothelial cells and myocardial cells. The DNA damage and apoptosis levels are proportional to the HNE concentrations.

Cellular origins and thrombogenic activity of microparticles isolated from human atherosclerotic plaques

OBJECTIVES

In this study, we evaluated the cellular origins and thrombogenic potential of microparticles.

BACKGROUND

Human atherosclerotic plaques contain submicron vesicles (microparticles) released during cell activation or apoptosis.

METHODS

Microparticles were purified from plaques and platelet-free plasma from 26 patients undergoing carotid endarterectomy. Flow cytometry analysis revealed the presence of large amounts of microparticles in plaques but not in healthy vessels.

RESULTS

Most plaque microparticles originated from leukocytes, of which 29 +/- 5% were macrophages, 15 +/- 3% lymphocytes, and 8 +/- 1% granulocytes. Plaques microparticles also derived from erythrocytes (27 +/- 4%), smooth muscle (13 +/- 4%) and endothelial cells (8 +/- 2%), but not from platelets. Plaques from asymptomatic and symptomatic patients showed no differences in microparticle origins. Microparticles were at least 200-fold more concentrated in plaque than in plasma. Plasma microparticles were primarily platelet-derived in contrast with those of plaque and showed no smooth muscle cell origin. Both plaque and plasma microparticles exposed tissue factor and generated thrombin, but this activity was twice as high in microparticles isolated from plaques, reflecting the thrombogenic contribution of the individual classes of microparticles.

CONCLUSIONS

These results demonstrate that microparticles are more abundant and more thrombogenic in human atherosclerotic plaques than in plasma. The different cellular origins of plaque and plasma microparticles might explain the increased thrombogenic activity of plaque microparticles.

Soluble Fas, a mediator of apoptosis, C-reactive protein, and coronary and extracoronary atherosclerosis

RATIONALE

Findings from laboratory studies strongly suggest a role for apoptosis, the process of programmed cell death, in cardiovascular disease. No population-based study has yet investigated whether serum levels of soluble forms of Fas, a receptor capable of inducing the apoptosis cascade, are associated with coronary and extracoronary atherosclerosis.

METHODS

Within the Rotterdam Coronary Calcification Study, a population-based cohort study, we measured coronary calcification using electron-beam computed tomography, abdominal aortic calcification by abdominal X-ray, carotid plaques and common carotid intima-media thickness (IMT) by ultrasonography, and lower extremity atherosclerosis by computation of the ankle-arm index. Levels of sFas and of the inflammatory mediator C-reactive protein (CRP) were measured in 1036 participants.

RESULTS

Levels of sFas were not related to coronary or extracoronary atherosclerosis. CRP showed strong associations with measures of atherosclerosis, including coronary atherosclerosis, which largely remained after adjustment for traditional cardiovascular risk factors.

CONCLUSION

The results of this study do not support a role for sFas in the identification of subjects with atherosclerosis.

A hypothesis for vulnerable plaque rupture due to stress-induced debonding around cellular microcalcifications in thin fibrous caps

In this article, we advance a hypothesis for the rupture of thin fibrous cap atheroma, namely that minute (10-mum-diameter) cellular-level microcalcifications in the cap, which heretofore have gone undetected because they lie below the visibility of current in vivo imaging techniques, cause local stress concentrations that lead to interfacial debonding. New theoretical solutions are presented for the local stress concentration around these minute spherical inclusions that predict a nearly 2-fold increase in interfacial stress that is relatively insensitive to the location of the hypothesized microinclusions in the cap. To experimentally confirm the existence of the hypothesized cellular-level microcalcifications, we examined autopsy specimens of coronary atheromatous lesions using in vitro imaging techniques whose resolution far exceeds conventional magnetic resonance imaging, intravascular ultrasound, and optical coherence tomography approaches. These high-resolution imaging modalities, which include confocal microscopy with calcium-specific staining and micro-computed tomography imaging, provide images of cellular-level calcifications within the cap proper. As anticipated, the minute inclusions in the cap are very rare compared with the numerous calcified macrophages observed in the necrotic core. Our mathematical model predicts that inclusions located in an area of high circumferential stress (>300 kPa) in the cap can intensify this stress to nearly 600 kPa when the cap thickness is <65 microm. The most likely candidates for the inclusions are either calcified macrophages or smooth muscle cells that have undergone apoptosis.

Lesional Overexpression of Matrix Metalloproteinase-9 Promotes Intraplaque Hemorrhage in Advanced Lesions But Not at Earlier Stages of Atherogenesis

Background— Matrix metalloproteinase-9 (MMP-9) is involved in atherosclerosis and elevated MMP-9 activity has been found in unstable plaques, suggesting a crucial role in plaque rupture. This study aims to assess the effect of MMP-9 on plaque stability in apolipoprotein E-deficient mice at different stages of plaque progression.

Methods and Results— Atherosclerotic lesions were elicited in carotid arteries by perivascular collar placement. MMP-9 overexpression in intermediate or advanced plaques was effected by intraluminal incubation with an adenovirus (Ad.MMP-9). A subset was coincubated with Ad.TIMP-1. Mock virus served as a control. Plaques were analyzed histologically. In intermediate lesions, MMP-9 overexpression induced outward remodeling, as shown by a 30% increase in media size ( p =0.03). In both intermediate and advanced lesions, prevalence of vulnerable plaque morphology tended to be increased. Half of MMP-9–treated lesions displayed intraplaque hemorrhage, whereas in controls and the Ad.MMP-9/Ad.TIMP-1 group this was 8% and 16%, respectively ( p =0.007). Colocalization with neovessels may point to neo-angiogenesis as a source for intraplaque hemorrhage.

Conclusion— These data show a differential effect of MMP-9 at various stages of plaque progression and suggest that lesion-targeted MMP-9 inhibition might be a valuable therapeutic modality in stabilizing advanced plaques, but not at earlier stages of lesion progression.

?2-glycoprotein I protects J774A.1 macrophages and human coronary artery smooth muscle cells against apoptosis

beta(2)-Glycoprotein I (beta(2)-GPI) is a plasma glycoprotein with multifactorial relevance to clinical consequences. It was previously indicated that beta(2)-GPI can selectively bind to apoptotic cells. This study was designed to determine the role of beta(2)-GPI in apoptosis. Using an immunohistochemical study, we observed that beta(2)-GPI was co-localized with the apoptotic macrophages and smooth muscle cells (SMCs) of human coronary arteries. The contribution of beta(2)-GPI to apoptotic death was then investigated in vascular cells. Two nitric oxide (NO) donors, S-nitrosoglutathione (GSNO) and S-nitroso-N-acetyl penicillamine (SNAP) were used in this study to trigger apoptosis in J774A.1 macrophages and human coronary artery smooth muscle cells (HCASMC). Cell viability was significantly improved in beta(2)-GPI-treated cells. It was also possible to detect a remarkable inhibitory effect by beta(2)-GPI on the NO-induced apoptosis by preventing nuclear shrinkage. Furthermore, the NO-induced apoptosis was associated with increase in caspase-3 activity and in the protein levels of caspase-3, c-Fos, and c-Jun. However, all these apoptosis-related events were inhibited in vascular cells treated with 200 microg/ml beta(2)-GPI. This is the first study to show that beta(2)-GPI may be important in the prevention of apoptosis in vascular cells.

Development of radiocontrast agents for vascular imaging: progress to date

The revolution in molecular imaging techniques is profoundly changing the understanding of the pathophysiology and treatment of atherosclerosis. With these rapid changes there is an increasing demand for development of sensitive and well tolerated novel imaging agents that can be rapidly translated from small animal models into patients with atherosclerosis. Nuclear medicine and positron emission tomography techniques have the ability to detect and serially monitor a variety of biologic and pathophysiologic processes usually with tracer quantities of radiolabeled peptides, drugs, and other molecules at dosages free of pharmacologic adverse effects unlike the current generation of intravenous agents required for magnetic resonance imaging (MRI) and computed axial tomography (CT) scanning. A representative sampling of the wide array of radiopharmaceuticals developed specifically for radionuclide imaging of atherosclerosis, that have been approved for clinical use and those in pre-clinical trials, have been reviewed in this article. The presence of an inflammatory stimulus increases expression of CC (cysteine-cysteine motif) chemokine receptor (CCR)-2 on monocytes and macrophages, and somatostatin receptors on T lymphocytes. Radiolabeled monocyte chemoattractant protein (MCP)-1 binds with high affinity to CCR-2 and can be used to detect subacute and chronic inflammatory lesions. Similarly, radiolabeled octreotide or depreotide can be used to detect activated T lymphocytes which may identify the vulnerable plaque. Animal models indicate that (99m)Tc-annexin V, (125)I-MCP-1 and [(18)F]-fluoro-2-deoxyglucose are effective in identifying apoptotic cell death, macrophage infiltration and metabolic activity in atheromatous lesions, respectively. Expression of alpha(v)beta(3) integrin is increased in activated endothelial cells and vascular smooth muscle cells after vascular injury, and alpha(v)beta(3) integrin is minimally expressed on smooth muscle cells and is not expressed on quiescent epithelial cells. Radiolabeled high-affinity peptides can be used to target the alpha(v)beta(3) integrin and visualize areas of vascular damage. Advances in technology such as the micro-single photon emission computed tomography (microSPECT) have the potential to overcome the drawbacks of older CT and MRI methodologies, such as lack of biologically relevant ligands and compatible blood pool contrast agents for imaging. Despite these advances in imaging technology, the small size of atheromatous lesions makes it difficult to detect using external imaging techniques. Therefore, recently there has been renewed interest in the use of intravascular catheter-based radiation detectors.

Insulin-like growth factor-1 receptor activation inhibits oxidized LDL-induced cytochrome C release and apoptosis via the phosphatidylinositol 3 kinase/Akt signaling pathway

OBJECTIVE

We have shown previously that oxidized LDL decreases insulin-like growth factor-1 (IGF-1) and IGF-1 receptor expression in vascular smooth muscle cells and that IGF-1 and IGF-1 receptor expression are reduced in the deep intima of early atherosclerotic lesions. Because oxidized LDL is potentially important for the depletion of vascular smooth muscle cells contributing to plaque destabilization, we studied the role of IGF-1 in oxidized LDL-induced apoptosis.

METHODS AND RESULTS

We provide evidence that oxidized LDL-induced apoptosis is caused by decreased mitochondrial membrane potential and increased cytochrome C release in human aortic vascular smooth muscle cells. Overexpression of the IGF-1 receptor by using an adenovirus completely abrogated these effects. The antiapoptotic function of the IGF-1 receptor was associated with increased Akt kinase activity and increased expression of phosphorylated Bad. Moreover, a dominant-negative p85 phosphatidylinositol 3-kinase adenovirus blocked the capacity of the IGF-1 receptor to prevent oxidized LDL-induced apoptosis.

CONCLUSIONS

Our data demonstrate that IGF-1 receptor activation inhibits oxidized LDL-induced cytochrome C release and apoptosis through the phosphatidylinositol 3-kinase/Akt signaling pathway and suggest that genetic or pharmacological activation of the IGF-1 receptor may be a useful strategy to stabilize atherosclerotic plaques.

All hydrophobic HMG-CoA reductase inhibitors induce apoptotic death in rat pulmonary vein endothelial cells

3-Hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase inhibitors (statins) are effective in patients with hypercholesterolemia to reduce risk of cardiovascular diseases, because of not only their lowering cholesterol effects but also their pleiotropic effects, such as improvement of endothelial cell dysfunction. On the other hand, statins prevent cell proliferation of various cells, including endothelial cells. We examined effects of all statins available at present on the viability of cultured rat pulmonary vein endothelial cells. Lovastatin, simvastatin, atorvastatin, fluvastatin and cerivastatin, which are hydrophobic statins, markedly reduced cell viability associated with DNA fragmentation, DNA laddering and activation of caspase-3, suggesting apoptotic cell death. Pravastatin, which is a hydrophilic statin, however, did not induce cell apoptosis. Apoptosis induced by hydrophobic statins was associated with activation of apoptosis-related intracellular signal transduction systems; attenuation of localization of RhoA to the membrane, induction of Rac1, and increase in phosphorylation of c-Jun N-terminal kinase and c-Jun. Endothelial cell apoptosis is underlying the improvement of the endothelial dysfunction with hydrophobic statins.

Coronary atherosclerosis and somatic mutations: an overview of the contributive factors for oxidative DNA damage

Coronary artery disease (CAD) is a multifactorial process that appears to be caused by the interaction of environmental risk factors with multiple predisposing genes. Genetic research on CAD has traditionally focused on investigation aimed at identifying disease-susceptibility genes. Recent evidence suggests that somatically acquired DNA mutations may also contribute significantly to the pathogenesis of the disease, underlining the similarity between atherosclerotic and carcinogenic processes. The generation of oxidative stress has been emphasized as an important cause of DNA damage in atherosclerosis. This review highlights some of the major atherogenic risk factors as likely mediators in the oxidative modification of DNA. It also examines the hypothesis that an increase in oxidative stress may derive from "oxidatively" damaged mitochondria. Accordingly, further research in this field should be given high priority, since increased somatic DNA damage could be an important pathogenic factor and an additional prognostic predictor, as well as a potential target for therapeutic strategies in coronary artery disease.

Genes potentially involved in plaque rupture

PURPOSE OF REVIEW

Rupture of an atherosclerotic plaque is the predominant underlying event in the pathogenesis of acute coronary syndromes and stroke. While ruptured plaques are morphologically well described, the precise molecular mechanisms involved in plaque rupture are still incompletely understood. Over the last few years, techniques like microarray, suppression subtractive hybridization and differential display enabled us to study complex gene expression profiles that occur during the process of atherogenesis. In this review we focus on recent large-scale gene expression profiles performed on whole mount vascular specimens.

RECENT FINDINGS

The gene expression profiles on whole mount vascular tissue confirmed that at least three mechanisms are involved in plaque rupture: (1) a disturbed balance in extracellular matrix turnover, (2) disturbed regulation of cell turnover and (3) processes involved in lipid metabolism. Animal models exhibiting features of plaque rupture reflect the involvement of these three mechanisms. The most dramatic mouse phenotypes were observed after interventions in at least two of these mechanisms.

SUMMARY

The observation of plaque rupture in recent mice models is indicative of the multifactorial process of plaque rupture. This multifactorial character of plaque rupture suggests that interventions may be most effective when they influence more than one mechanisms at a time.

Arachidonic acid release by cPLA2 may be causally related to NO-induced apoptosis in vascular smooth muscle cells

Apoptosis has been shown to occur in vascular smooth muscle cells during the development of atherosclerosis. In order to investigate the possible role of arachidonic acid during apoptosis in vascular smooth muscle, we induced apoptosis in cultured rat aortal smooth muscle cells (SMCs) by treatment with either UV (ultraviolet) radiation, tumor necrosis factor-alpha (TNF-alpha) or NO donor drugs (sodium nitroprusside, or S-nitroso-N-acetyl-D-penicillamine, SNAP). Apoptosis was detected by either DNA fragmentation analysis or by TUNEL analysis. UV radiation, TNF-alpha and NO were observed to stimulate apoptosis in the cells as well as to stimulate arachidonate release from the cells. NO also increased levels of cPLA2 in the cells, which is an enzyme that is frequently activated in cells that release arachidonate. These agents stimulated arachidonate release somewhat earlier than they stimulated apoptosis in the cells. The inhibition of cPLA2 by arachidonyl trifluoromethyl ketone (AACOCF3) also led to the inhibition of arachidonate release from the cells as well as the inhibition of nitroprusside stimulated apoptosis. Arachidonic acid itself could induce apoptosis in the cultured cells. These observations provide evidence that arachidonate may be involved in apoptosis in vascular smooth muscle.