Fenofibrate inhibits angiogenesis in vitro and in vivo

Fenofibrate, a peroxisome proliferator-activated receptor (PPAR)-alpha activator, used as a normolipidemic agent, is thought to offer additional beneficial effects in atherosclerosis. Since angiogenesis is involved in plaque progression, hemorrhage, and instability, the main causes of ischemic events, this study was designed to evaluate the action of fenofibrate on angiogenesis. Our results show that fenofibrate (i) inhibits endothelial cell proliferation induced by angiogenic factors, followed at high concentrations by an increase in apoptosis, (ii) inhibits endothelial cell migration in a healing wound model, (iii) inhibits capillary tube formation in vitro, and (iv) inhibits angiogenesis in vivo. Concerning the mechanism of action, the inhibition of endothelial cell migration by fenofibrate can be explained by a disorganization of the actin cytoskeleton. At the molecular level, fenofibrate markedly decreased basic fibroblast growth factor-induced Akt activation and cyclooxygenase 2 gene expression. This inhibition of angiogenesis could participate in the beneficial effect of fenofibrate in atherosclerosis.     

Sphingosine 1-phosphate signal survival and mitogenesis are mediated by lipid-stereospecific binding of triacylglycerol-rich lipoproteins

Proof for the role of triacylglycerol-rich lipoproteins (TRLs) in the development of cardiovascular events is accumulating. We recently reported that postprandial TRLs bind to and internalize into human aortic vascular smooth muscle cells (HA-VSMCs) by a lipid-dependent mechanism. We now show that postprandial TRLs triggered hydrolysis of sphingomyelin and stimulation of the sphingosine kinase producing sphingosine 1-phosphate (S1P). In addition, postprandial TRLs exhibited survival and mitogenic effects. Interestingly, the signals were modulated by the nature of the fatty acids located at the sn-2 position in the triacylglycerol molecules of TRL. This lipid-stereospecific regulation of S1P cellular levels in HA-VSMCs provides a novel insight into the intrinsic role of dietary fatty acids and the mechanism mediated by triacylglycerol-containing postprandial lipoproteins in the pathogenesis of atherosclerosis.Received 14 August 2003; received after revision 8 October 2003; accepted 15 October 2003     

Inflammation and immune system interactions in atherosclerosis

Cardiovascular disease (CVD) is the leading cause of mortality worldwide, accounting for 16.7 million deaths each year. The underlying cause of the majority of CVD is atherosclerosis. In the past, atherosclerosis was considered to be the result of passive lipid accumulation in the vessel wall. Today’s picture is far more complex. Atherosclerosis is considered a chronic inflammatory disease that results in the formation of plaques in large and mid-sized arteries. Both cells of the innate and the adaptive immune system play a crucial role in its pathogenesis. By transforming immune cells into pro- and anti-inflammatory chemokine- and cytokine-producing units, and by guiding the interactions between the different immune cells, the immune system decisively influences the propensity of a given plaque to rupture and cause clinical symptoms like myocardial infarction and stroke. In this review, we give an overview on the newest insights in the role of different immune cells and subtypes in atherosclerosis.     

Flow signaling and atherosclerosis

Atherosclerosis rarely develops in the region of arteries exposed to undisturbed flow (u-flow, unidirectional flow). Instead, atherogenesis occurs in the area exposed to disturbed flow (d-flow, multidirectional flow). Based on these general pathohistological observations, u-flow is considered to be athero-protective, while d-flow is atherogenic. The fact that u-flow and d-flow induce such clearly different biological responses in the wall of large arteries indicates that these two types of flow activate each distinct intracellular signaling cascade in vascular endothelial cells (ECs), which are directly exposed to blood flow. The ability of ECs to differentially respond to the two types of flow provides an opportunity to identify molecular events that lead to endothelial dysfunction and atherosclerosis. In this review, we will focus on various molecular events, which are differentially regulated by these two flow types. We will discuss how various kinases, ER stress, inflammasome, SUMOylation, and DNA methylation play roles in the differential flow response, endothelial dysfunction, and atherosclerosis. We will also discuss the interplay among the molecular events and how they coordinately regulate flow-dependent signaling and cellular responses. It is hoped that clear understanding of the way how the two flow types beget each unique phenotype in ECs will lead us to possible points of intervention against endothelial dysfunction and cardiovascular diseases.     

Scavenger receptor family proteins: roles for atherosclerosis, host defence and disorders of the central nervous system

In this review, we summarize the structure and function of the scavenger receptor family of proteins including class A (type I and II macrophage scavenger receptors, MARCO), class B (CD36, scavenger receptor class BI), mucinlike (CD68/macrosialin, dSR-CI) and endothelial (LOX-1) receptors. Two motifs have been identified as ligand-binding domains a charged collagen structure of type I and II receptors, and an immunodominant domain of CD36. These structures can recognize a wide range of negatively charged macromolecules, including oxidized low-density lipoproteins, damaged or apoptotic cells, and pathogenic microorganisms. After binding, these ligands can be either internalized by endocytosis or phagocytosis, or remain at the cell surface and mediate adhesion or lipid transfer through caveolae. Under physiological conditions, scavenger receptors serve to scavenge or clean up cellular debris and other related materials, and they play a role in host defence. In pathological states, they mediate the recruitment, activation and transformation of macrophages and other cells which may be related to the development of atherosclerosis and to disorders caused by the accumulation of denatured materials, such as Alzheimer's disease. Received 17 September 1997; received after revision 16 March 1998; accepted 17 March 1998     

Statins: the new aspirin?

3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or statins, have been described as the principal and the most effective class of drug to reduce serum cholesterol levels. Statin therapies have been shown to reduce cardiovascular events, including myocardial infarction, stroke, and death, significantly, by altering vascular atherosclerosis development in patients with or without coronary artery disease symptoms. Extensive use of statins has led to the increase of some undesirable effects that are heavily counterbalanced by the benefits. Indeed, pleiotropic effects extend far beyond cholesterol reduction and involve non-lipid-related mechanisms that modify endothelial functions, immunoinflammatory responses, smooth muscle cell activation, proliferation and migration, atherosclerotic plaque stability, and thrombus formation. In this review, we describe in detail the targets and mechanisms of action of statins. Received 6 June 2002; received after revision 6 September 2002; accepted 6 September 2002 RID="*" ID="*"Corresponding author.     

Response of vascular mesenchymal stem/progenitor cells to hyperlipidemia

Hyperlipidemia is a risk factor for atherosclerosis that is characterized by lipid accumulation, inflammatory cell infiltration, and smooth muscle cell proliferation. It is well known that hyperlipidemia is a stimulator for endothelial dysfunction and smooth muscle cell migration during vascular disease development. Recently, it was found that vessel wall contains a variable number of mesenchymal stem cells (MSCs) that are quiescent in physiological conditions, but can be activated by a variety of stimuli, e.g., increased lipid level or hyperlipidemia. Vascular MSCs displayed characteristics of stem cells which can differentiate into several types of cells, e.g., smooth muscle cells, adipocytic, chondrocytic, and osteocytic lineages. In vitro, lipid loading can induce MSC migration and chemokines secretion. After MSC migration into the intima, they play an essential role in inflammatory response and cell accumulation during the initiation and progression of atherosclerosis. In addition, MSC transplantation has been explored as a therapeutic approach to treat atherosclerosis in animal models. In this review, we aim to summarize current progress in characterizing the identity of vascular MSCs and to discuss the mechanisms involved in the response of vascular stem/progenitor cells to lipid loading, as well as to explore therapeutic strategies for vascular diseases and shed new light on regenerative medicine.     

Integrin signaling in atherosclerosis

Atherosclerosis, a chronic lipid-driven inflammatory disease affecting large arteries, represents the primary cause of cardiovascular disease in the world. The local remodeling of the vessel intima during atherosclerosis involves the modulation of vascular cell phenotype, alteration of cell migration and proliferation, and propagation of local extracellular matrix remodeling. All of these responses represent targets of the integrin family of cell adhesion receptors. As such, alterations in integrin signaling affect multiple aspects of atherosclerosis, from the earliest induction of inflammation to the development of advanced fibrotic plaques. Integrin signaling has been shown to regulate endothelial phenotype, facilitate leukocyte homing, affect leukocyte function, and drive smooth muscle fibroproliferative remodeling. In addition, integrin signaling in platelets contributes to the thrombotic complications that typically drive the clinical manifestation of cardiovascular disease. In this review, we examine the current literature on integrin regulation of atherosclerotic plaque development and the suitability of integrins as potential therapeutic targets to limit cardiovascular disease and its complications.     

“Jnking” atherosclerosis

Numerous studies in animal models established a key role of the C-jun N-terminal kinase (JNK) family (JNK1, JNK2 and JNK3) in numerous pathological conditions, including cancer, cardiac hypertrophy and failure, neurodegenerative disorders, diabetes, arthritis and asthma. A possible function of JNK in atherosclerosis remained uncertain since conclusions have mainly been based on in vitro studies investigating endothelial cell activation, T-effector cell differentiation and proliferation of vascular smooth muscle cells, all of which represent crucial cellular processes involved in atherosclerosis. However, recent experiments demonstrated that macrophage-restricted deletion of JNK2 was sufficient to efficiently reduce atherosclerosis in mice. Furthermore, it has been shown that JNK2 specifically promotes scavenger receptor A-mediated foam cell formation, an essential step during early atherogenesis, which occurs when vascular macrophages internalize modified lipoproteins. Thus, specific inhibition of JNK2 activity may emerge as a novel and promising therapeutic approach to attenuate atheroma formation in the future. In this review, we discuss JNK-dependent cellular and molecular mechanisms underlying atherosclerosis. Received 9 June 2005; received after revision 18 July 2005; accepted 18 July 2005     

Updating the mechanisms of common fragile site instability: how to reconcile the different views?

Common fragile sites (CFSs) are large chromosomal regions long identified by conventional cytogenetics as sequences prone to breakage in cells subjected to replication stress. The interest in CFSs came from their key role in the formation of DNA damage, resulting in chromosomal rearrangements. The instability of CFSs was notably correlated with the appearance of genome instability in precancerous lesions and during tumor progression. Identification of the molecular mechanisms responsible for their instability therefore represents a major challenge. A number of data show that breaks result from mitotic entry before replication completion but the mechanisms responsible for such delayed replication of CFSs and relaxed checkpoint surveillance are still debated. In addition, clues to the molecular events leading to breakage just start to emerge. We present here the results of recent reports addressing these questions.     

Biomedicine and diseases: the Klippel-Trenaunay syndrome, vascular anomalies and vascular morphogenesis

Vascular morphogenesis is a vital process for embryonic development, normal physiologic conditions (e.g. wound healing) and pathological processes (e.g. atherosclerosis, cancer). Genetic studies of vascular anomalies have led to identification of critical genes involved in vascular morphogenesis. A susceptibility gene, VG5Q (formally named AGGF1), was cloned for Klippel-Trenaunay syndrome (KTS). AGGF1 encodes a potent angiogenic factor, and KTS-associated mutations enhance angiogenic activity of AGGF1, defining ‘increased angiogenesis’ as one molecular mechanism for the pathogenesis of KTS. Similar studies have identified other genes involved in vascular anomalies as important genes for vascular morphogenesis, including TIE2, VEGFR-3, RASA1, KRIT1, MGC4607, PDCD10, glomulin, FOXC2, NEMO, SOX18, ENG, ACVRLK1, MADH4, NDP, TIMP3, Notch3, COL3A1 and PTEN. Future studies of vascular anomaly genes will provide insights into the molecular mechanisms for vascular morphogenesis, and may lead to the development of therapeutic strategies for treating these and other angiogenesis-related diseases, including coronary artery disease and cancer.Received 24 November 2004; received after revision 21 January 2005; accepted 2 March 2005     

Polyisoprenyl phosphates: natural antiinflammatory lipid signals

Lipoxins (LX) and aspirin-triggered 15-epimer LX are leukocyte-derived eicosanoids generated during host defense that serve as down-regulatory signals. The specific intracellular events that govern cellular responses to inhibitory extracellular signals are of wide interest in order to understand pivotal intracellular events in diseases characterized by enhanced inflammatory responses, such as asthma, rheumatoid arthritis and atherosclerosis. We recently uncovered a novel role for polyisoprenyl phosphates, in particular presqualene diphosphate (PSDP), as natural down-regulatory signals in human neutrophils that directly inhibit phospholipase D and superoxide anion generation. Activation of LXA₄ receptors (ALXR) reverses proinflammatory receptor-initiated decrements in PSDP and inhibits cellular responses. These findings represent evidence for a novel paradigm for lipid-protein interactions in the control of cellular responses, namely receptor-initiated degradation of repressor lipids that is subject to regulation by aspirin treatment via the actions of aspirin-triggered 15-epimer LX at the ALXR, and identify new templates for antiinflammatory drugs by design.     

Characterization of apoptosis induced by marine natural products in non small cell lung cancer A549 cells

The effects of different marine derived agents were studied in A549 cell growth. These drugs induced cell cycle arrest at the G2-M phase associated with the up-regulation of GADD45alpha-gamma and down-regulation of c-Myc. In treated cells, GADD45alpha-gamma and c-Myc were up- and down-regulated, respectively. A cascade of events leading to apoptotic mitochondrial 'intrinsic' pathway was observed in treated cells: (1) dephosphorylation of BAD serine136; (2) BAD dissociation from 14-3-3 followed by its association with BCL-XL; (3) cytochrome c release; (4) caspase-3 activation, and (5) cleavage of vimentin. Caspase(s) inhibitor prevented the formation of cleavage products and, in turn, apoptosis was inhibited through a p53-independent mechanism. Moreover, these compounds did not activate NF-kappaB. Our findings may offer new insights into the mechanisms of action of these agents in A549 cells. The better understanding of their effects might be important to fully exploit the potential of these new drugs.     

The mutator phenotype theory of carcinogenesis and the complex histopathology of tumours: support for the theory from the independent occurrence of nuclear abnormality,loss of specialisation and invasiveness among occasional neoplastic lesions

The mutator phenotype theory of carcinogenesis suggests that genetic instability is an early and essential part of tumour development. This instability provides for substantially random cell-to-cell genomic variation (genomic heterogeneity) to arise among cells of individual tumours. Genetically unstable cells then produce 'successful' clones of cells with the necessary mutations for malignant behaviour. In a previous paper (Bignold L. P., Cell. Mol. Life Sci. 2002; 59: 950-958), it was pointed out that a population of cells which is heterogeneous for behaviour-related genes may well also be heterogeneous for morphology-related genes. This would result in cellular pleomorphism among cells of individual tumours, and so explain this almost universal characteristic of solid malignancies. paragraph sign If the concept of random genomic variability applies fully to the histopathology of tumours, then most tumours should show a mixture of neoplastic features, especially nuclear atypia, loss of specialised function (such as loss of production of mucus by glandular cells) and invasiveness. However, occasional lesions might be expected to occur which show these characteristics independently. That is, lesions should exist which exhibit one or two of the three characteristics of neoplasms without the other(s). paragraph sign This paper identifies, among human tumours, lesions which show independence of these characteristics. Two of the examples discussed are a Bowenoid solar keratosis that shows severe nuclear atypia, but no apparent loss of specialisation and no invasiveness. On the other hand, anaplastic small cell carcinoma of the lung often exhibits marked loss of differentiation, very aggressive invasion and metastasis, but little nuclear pleomorphism. paragraph sign These examples are considered to provide further support for the importance of the mutator phenotype to the pathogenesis of neoplasia.     

Initiation of genetic instability and tumour formation: a review and hypothesis of a nongenotoxic mechanism

Genetic instability in tumours results in cell-to-cell variability of genome which parallels the cell-to-cell variability of microscopic morphology and of behaviour (tumour cell heterogeneity) of these lesions. Genetic instability is therefore strongly supported as the fundamental process by which normal tissue cells become neoplastic. The commonest current suggestion for the mechanism of initiation of carcinogenesis is a 'direct hit' mutation of a 'cancer critical' gene in a somatic cell by carcinogenic agents. However, this mechanism does not account for the activity of carcinogens which are not mutagens, and does not explain why many mutagens are not carcinogens. This paper proposes a nonmutational (nongenotoxic) mechanism of initiation of genetic instability in previously normal cells as follows: 1) During S phase of local tissue stem cells, carcinogen binds to and disables the proofreading enzyme for a new DNA strand. 2) While it is disabled, the proofreading enzyme fails to correct illicit changes in the nucleotide sequence(s) for one or more genes for proofreading fidelity or repair of DNA in the new strand of DNA, which passes to one daughter cell. 3) When this daughter cell is a continuing stem cell, the resulting cell line remains immortal, and retains its prior differentiation commitment to produce daughter cells of a particular type. However, the acquired genetic instability in this cell line causes secondary mutations which lead to uncontrolled growth, and the heterogeneous morphologic and behavioural features of a tumour resembling the parent cell type.     

An eicosanoid-centric view of atherothrombotic risk factors

Cardiovascular disease is the foremost cause of morbidity and mortality in the Western world. Atherosclerosis followed by thrombosis (atherothrombosis) is the pathological process underlying most myocardial, cerebral, and peripheral vascular events. Atherothrombosis is a complex and heterogeneous inflammatory process that involves interactions between many cell types (including vascular smooth muscle cells, endothelial cells, macrophages, and platelets) and processes (including migration, proliferation, and activation). Despite a wealth of knowledge from many recent studies using knockout mouse and human genetic studies (GWAS and candidate approach) identifying genes and proteins directly involved in these processes, traditional cardiovascular risk factors (hyperlipidemia, hypertension, smoking, diabetes mellitus, sex, and age) remain the most useful predictor of disease. Eicosanoids (20 carbon polyunsaturated fatty acid derivatives of arachidonic acid and other essential fatty acids) are emerging as important regulators of cardiovascular disease processes. Drugs indirectly modulating these signals, including COX-1/COX-2 inhibitors, have proven to play major roles in the atherothrombotic process. However, the complexity of their roles and regulation by opposing eicosanoid signaling, have contributed to the lack of therapies directed at the eicosanoid receptors themselves. This is likely to change, as our understanding of the structure, signaling, and function of the eicosanoid receptors improves. Indeed, a major advance is emerging from the characterization of dysfunctional naturally occurring mutations of the eicosanoid receptors. In light of the proven and continuing importance of risk factors, we have elected to focus on the relationship between eicosanoids and cardiovascular risk factors.     

Cell surface heparan sulfate proteoglycans and lipoprotein metabolism

Cell surface heparan sulfate proteoglycans are involved in several aspects of the lipoprotein metabolism. Most of the biological activities of these proteoglycans are mediated via interactions of their heparan sulfate moieties with various protein ligands, including lipoproteins and lipases. The binding of lipoproteins to heparan sulfate is largely determined by their apoprotein composition, and apoproteins B and E display the highest affinity for heparan sulfate. Interactions of lipoproteins with heparan sulfate are important for the cellular uptake and turnover of lipoproteins, in part by enhancing the accessibility of lipoproteins to lipoprotein receptors and lipases. Apoprotein B may interact with receptors without involving heparan sulfate. Heparan sulfate has been further implicated in presentation and stabilization of lipoprotein lipase and hepatic lipase on cell surfaces and in the transport of lipoprotein lipase from extravascular cells to the luminal surface of the endothelia. In atherosclerosis, heparan sulfate is intimately involved in several events important to the pathophysiology of the disease. Heparan sulfate thus binds and regulates the activity of growth factors, cytokines, superoxide dismutase and antithrombin, which contribute to aberrant cell proliferation, migration and matrix production, scavenging of reactive oxygen radicals and thrombosis. In this review we discuss the various roles of heparan sulfate proteoglycans in vascular biology, with emphasis on interactions of heparan sulfate with lipoproteins and lipases and the molecular basis of such interactions.     

Clearance of cerebral Aβ in Alzheimer’s disease: reassessing the role of microglia and monocytes

Deficiency in cerebral amyloid β-protein (Aβ) clearance is implicated in the pathogenesis of the common late-onset forms of Alzheimer’s disease (AD). Accumulation of misfolded Aβ in the brain is believed to be a net result of imbalance between its production and removal. This in turn may trigger neuroinflammation, progressive synaptic loss, and ultimately cognitive decline. Clearance of cerebral Aβ is a complex process mediated by various systems and cell types, including vascular transport across the blood–brain barrier, glymphatic drainage, and engulfment and degradation by resident microglia and infiltrating innate immune cells. Recent studies have highlighted a new, unexpected role for peripheral monocytes and macrophages in restricting cerebral Aβ fibrils, and possibly soluble oligomers. In AD transgenic (ADtg) mice, monocyte ablation or inhibition of their migration into the brain exacerbated Aβ pathology, while blood enrichment with monocytes and their increased recruitment to plaque lesion sites greatly diminished Aβ burden. Profound neuroprotective effects in ADtg mice were further achieved through increased cerebral recruitment of myelomonocytes overexpressing Aβ-degrading enzymes. This review summarizes the literature on cellular and molecular mechanisms of cerebral Aβ clearance with an emphasis on the role of peripheral monocytes and macrophages in Aβ removal.