Tissue inhibitors of metalloproteinases and metalloproteinases in atherosclerosis

Immunological Aspects of Age-Related Macular Degeneration

Increasing evidence over the past two decades points to a pivotal role for immune mechanisms in age-related macular degeneration (AMD) pathobiology. In this chapter, we will explore immunological aspects of AMD, with a specific focus on how immune mechanisms modulate clinical phenotypes of disease and severity and how components of the immune system may serve as triggers for disease progression in both dry and neovascular AMD. We will briefly review the biology of the immune system, defining the role of immune mechanisms in chronic degenerative disease and differentiating from immune responses to acute injury or infection. We will explore current understanding of the roles of innate immunity (especially macrophages), antigen-specific immunity (T cells, B cells, and autoimmunity), immune amplifications systems, especially complement activity and the NLRP3 inflammasome, in the pathogenesis of both dry and neovascular AMD, reviewing data from pathology, experimental animal models, and clinical studies of AMD patients. We will also assess how interactions between the immune system and infectious pathogens could potentially modulate AMD pathobiology via alterations in in immune effector mechanisms. We will conclude by reviewing the paradigm of "response to injury," which provides a means to integrate various immunologic mechanisms along with nonimmune mechanisms of tissue injury and repair as a model to understand the pathobiology of AMD.

Matrix Metalloproteinases in Renal Diseases: A Critical Appraisal

Matrix metalloproteinases (MMPs) are endopeptidases within the metzincin protein family that not only cleave extracellular matrix (ECM) components, but also process the non-ECM molecules, including various growth factors and their binding proteins. MMPs participate in cell to ECM interactions, and MMPs are known to be involved in cell proliferation mechanisms and most probably apoptosis. These proteinases are grouped into six classes: collagenases, gelatinases, stromelysins, matrilysins, membrane type MMPs, and other MMPs. Various mechanisms regulate the activity of MMPs, inhibition by tissue inhibitors of metalloproteinases being the most important. In the kidney, intrinsic glomerular cells and tubular epithelial cells synthesize several MMPs. The measurement of circulating MMPs can provide valuable information in patients with kidney diseases. They play an important role in many renal diseases, both acute and chronic. This review attempts to summarize the current knowledge of MMPs in the kidney and discusses recent data from patient and animal studies with reference to specific diseases. A better understanding of the MMPs' role in renal remodeling may open the way to new interventions favoring deleterious renal changes in a number of kidney diseases.

Palmitate induces glycosylation of cyclooxygenase-2 in primary human vascular smooth muscle cells

Vascular basal cyclooxygenase-2 (COX-2) expression and activity can be induced by endotoxin, hypoxia, or ischemia. During vascular pathologies such as atherosclerosis, increases in COX-2 activity result in prostanoid production, a contributor to the development and progression of vascular inflammation leading to unstable atherosclerotic plaques and increased risk for thrombotic events. Recent studies demonstrate that select free fatty acids, such as palmitate, can act as proinflammatory mediators. However, the effect of palmitate on COX-2 expression and activity, and its impact on the development and progression of vascular inflammation, are not well elucidated. We investigated the effect of palmitate on COX-2 expression and function in human vascular smooth muscle cells. Cells were treated with palmitate, COX-2 protein levels were assessed using Western analysis, and activity was assessed via ELISA. We observed that palmitate dose-dependently increased COX-2 levels and specifically enhanced band intensity of the COX-2 74 kDa band (slowest migrating band). This response was attenuated by N-linked glycosylation inhibition, suggesting that palmitate impacts expression of the fully activated glycoform of COX-2. Palmitate-induced increases in COX-2 levels correlated with an increase in prostaglandin E₂ production that was also attenuated by a glycosylation inhibitor. Additionally, palmitate altered cell morphology and increased cell density which were reversed by selective COX-2 inhibition. Thus, we conclude that palmitate acts on COX-2 by two separate mechanisms of action in human vascular smooth muscle. It elicits dose-dependent increases in COX-2 protein expression and modulates regulation of COX-2 activity via modification of posttranslational glycosylation.

Oxidative theory of atherosclerosis and antioxidants

Atherosclerosis is a multifactorial process that begins early in infancy and affects all the humans. Early steps of atherogenesis and the evolution towards complex atherosclerotic plaques are briefly described. After a brief history of the 'Lipid theory of atherosclerosis', we report the most prominent discoveries on lipoproteins, their receptors and metabolism, and their role in atherogenesis. The main focus is the 'oxidative theory of atherosclerosis', with emphasis on free radicals and reactive oxygen species, lipid peroxidation and LDL oxidation, biological properties of oxidized LDL and their potential role in atherogenesis. Then, we report the properties of antioxidants and antioxidant systems and their effects in vitro, on cultured cells, in animal models and in humans. The surprising discrepancy between the efficacy of antioxidants in vitro and in animal models of atherosclerosis and the lack of protective effect against cardiovascular events and death in epidemiological study and clinical trials are discussed. In contrast, epidemiological studies seem to indicate that the Mediterranean diet may protect (in part) against atherosclerosis complications (myocardial infarction and cardiovascular death).

Neutrophil extracellular traps induce endothelial dysfunction in systemic lupus erythematosus through the activation of matrix metalloproteinase-2

RATIONALE

The structural and functional integrity of the endothelium is crucial in maintaining vascular homeostasis and preventing atherosclerosis. Patients with systemic lupus erythematosus (SLE) have an increased risk of developing endothelial dysfunction and premature cardiovascular disease. Neutrophil extracellular trap (NET) formation is increased in SLE and has been proposed to contribute to endothelial damage, but the mechanism remains unclear.

OBJECTIVE

To determine the mechanism by which enhanced NET formation by low-density granulocytes (LDGs) in SLE contributes to endothelial damage and disrupts the endothelium.

RESULTS

The putative role of NET-externalised matrix metalloproteinases (MMPs) in altering the functional integrity of the endothelium was examined. MMP-9 externalised by lupus LDGs during NET formation specifically impaired murine aortic endothelium-dependent vasorelaxation and induced endothelial cell apoptosis. Endothelial dysfunction correlated with the activation of endothelial MMP-2 by MMP-9 present in NETs, while inhibition of MMP-2 activation restored endothelium-dependent function and decreased NET-induced vascular cytotoxicity. Moreover, immunogenic complexes composed of MMP-9 and anti-MMP-9 were identified in SLE sera. These complexes, as well as anti-MMP-9 autoantibodies, induced NETosis and enhanced MMP-9 activity.

CONCLUSIONS

These observations implicate activation of endothelial MMP-2 by MMP-9 contained in NETs as an important player in endothelial dysfunction, and MMP-9 as a novel self-antigen in SLE. These results further support that aberrant NET formation plays pathogenic roles in SLE.

Age-related macular degeneration and changes in the extracellular matrix

Age-related macular degeneration (AMD) is the leading cause of permanent, irreversible, central blindness (scotoma in the central visual field that makes reading and writing impossible, stereoscopic vision, recognition of colors and details) in patients over the age of 50 years in European and North America countries, and an important role is attributed to disorders in the regulation of the extracellular matrix (ECM). The main aim of this article is to present the crucial processes that occur on the level of Bruch’s membrane, with special consideration of the metalloproteinase substrates, metalloproteinase, and tissue inhibitor of metalloproteinase (TIMP).

A comprehensive review of the literature was performed through MEDLINE and PubMed searches, covering the years 2005–2012, using the following keywords: AMD, extracellular matrix, metalloproteinases, tissue inhibitors of metalloproteinases, Bruch’s membrane, collagen, elastin.

In the pathogenesis of AMD, a significant role is played by collagen type I and type IV; elastin; fibulin-3, -5, and -6; matrix metalloproteinase (MMP)-2, MMP-9, MMP-14, and MMP-1; and TIMP-3. Other important mechanisms include: ARMS2 and HTR1 proteins, the complement system, the urokinase plasminogen activator system, and pro-renin receptor activation.

Continuous rebuilding of the extracellular matrix occurs in both early and advanced AMD, simultaneously with the dysfunction of retinal pigment epithelium (RPE) cells and endothelial cells. The pathological degradation or accumulation of ECM structural components are caused by impairment or hyperactivity of specific MMPs/TIMPs complexes, and is also endangered by the influence of other mechanisms connected with both genetic and environmental factors.

Dihydrotestosterone alters cyclooxygenase-2 levels in human coronary artery smooth muscle cells

Both protective and nonprotective effects of androgens on the cardiovascular system have been reported. Our previous studies show that the potent androgen receptor (AR) agonist dihydrotestosterone (DHT) increases levels of the vascular inflammatory mediator cyclooxygenase (COX)-2 in rodent cerebral arteries independent of an inflammatory stimulus. Little is known about the effects of androgens on inflammation in human vascular tissues. Therefore, we tested the hypothesis that DHT alters COX-2 levels in the absence and presence of induced inflammation in primary human coronary artery smooth muscle cells (HCASMC). Furthermore, we tested the ancillary hypothesis that DHT's effects on COX-2 levels are AR-dependent. Cells were treated with DHT (10 nM) or vehicle for 6 h in the presence or absence of LPS or IL-1beta. Similar to previous observations in rodent arteries, in HCASMC, DHT alone increased COX-2 levels compared with vehicle. This effect of DHT was attenuated in the presence of the AR antagonist bicalutamide. Conversely, in the presence of LPS or IL-1beta, increases in COX-2 were attenuated by cotreatment with DHT. Bicalutamide did not affect this response, suggesting that DHT-induced decreases in COX-2 levels occur independent of AR stimulation. Thus we conclude that DHT differentially influences COX-2 levels under physiological and pathophysiological conditions in HCASMC. This effect of DHT on COX-2 involves AR-dependent and- independent mechanisms, depending on the physiological state of the cell.

Atorvastatin Modulates Matrix Metalloproteinase Expression, Activity, and Signaling in Abdominal Aortic Aneurysms

Statins may reduce abdominal aortic aneurysm (AAA) progression. We sought to measure how atorvastatin (AT) treatment might modulate matrix metalloproteinase (MMP) expression and/or activity in human AAA. Tissue from human AAAs at surgical repair was obtained from patients who were either not on statins (NST, n = 19) or treated with AT (n = 19). Immunoblots measured expression and zymography measured activity. Expression of most proteins was greater in the central compared with distal AAA region. Matrix metalloproteinase 1, MMP2, MMP3, MMP9, Tissue Inhibitor of Metalloproteinase (TIMP2), TIMP3, TIMP4, or total Sma Mothers Against Decapentaplegia (SMAD2) expression did not differ with treatment. There was a trend toward reduced MMP8 and TIMP1 expression and MMP2 zymographic activity in the AT-treatment group. In contrast, AT-treated samples had significantly reduced MMP13 (P = .02), latent-transforming growth factor (TGF)-β (P = .02), and phospho-SMAD2 (P = .029) expression than NST-treated samples. We conclude that the AT-mediated decrease in MMP expression and activity reduces TGF-β signaling in the central region of human AAAs.

Periadventitial delivery of anti-EGF receptor antibody inhibits neointimal macrophage accumulation after angioplasty in a hypercholesterolaemic rabbit

Monocyte recruitment and their differentiation into macrophages are both early events in native and accelerated atherosclerosis that follows angioplasty. We have investigated the putative functional role of the epidermal growth factor receptor (EGFR) present on rabbit monocytes/macrophages. The impact of periadventitial delivery of an EGFR-specific, blocking monoclonal antibody (ICR62, which inhibits EGF-binding to its receptor) was investigated in a rabbit model of accelerated atherosclerosis induced by a combination of carotid injury and 4 weeks of a 2% cholesterol-diet. Two weeks after the initiation of the diet, a balloon-catheter angioplasty of the left common carotid artery was performed and a collar placed around the injured carotid artery immediately, for the delivery of ICR62 antibody, isotype-matched antibody or saline control. Monocyte/macrophage accumulation, cell proliferation and neointimal thickening were determined 2 weeks after the delivery of the antibodies. The function of the EGFR on rabbit monocytes was also investigated in vitro, using chemotaxis assays. Treatment with ICR62 was associated with a significant reduction in macrophage accumulation and neointimal thickening and a 76% reduction in neointimal area of the vessel wall compared with controls. In vitro ICR62 inhibited macrophage and smooth muscle cell migration towards EGFR ligands including EGF and HB-EGF. These findings suggest that EGFR ligation may be important in the development of early atherosclerotic lesions following balloon-catheter angioplasty, and periadventitial delivery may provide a feasible approach for administration of the inhibitors of EGFR-binding such as ICR62.

Inflammatory Disease Processes and Interactions with Nutrition

Inflammation is a stereotypical physiological response to infections and tissue injury; it initiates pathogen killing as well as tissue repair processes and helps to restore homeostasis at infected or damaged sites. Acute inflammatory reactions are usually self-limiting and resolve rapidly, due to the involvement of negative feedback mechanisms. Thus, regulated inflammatory responses are essential to remain healthy and maintain homeostasis. However, inflammatory responses that fail to regulate themselves can become chronic and contribute to the perpetuation and progression of disease. Characteristics typical of chronic inflammatory responses underlying the pathophysiology of several disorders include loss of barrier function, responsiveness to a normally benign stimulus, infiltration of inflammatory cells into compartments where they are not normally found in such high numbers, and overproduction of oxidants, cytokines, chemokines, eicosanoids and matrix metalloproteinases. The levels of these mediators amplify the inflammatory response, are destructive and contribute to the clinical symptoms. Various dietary components including long chain ω-3 fatty acids, antioxidant vitamins, plant flavonoids, prebiotics and probiotics have the potential to modulate predisposition to chronic inflammatory conditions and may have a role in their therapy. These components act through a variety of mechanisms including decreasing inflammatory mediator production through effects on cell signaling and gene expression (ω-3 fatty acids, vitamin E, plant flavonoids), reducing the production of damaging oxidants (vitamin E and other antioxidants), and promoting gut barrier function and anti-inflammatory responses (prebiotics and probiotics). However, in general really strong evidence of benefit to human health through anti-inflammatory actions is lacking for most of these dietary components. Thus, further studies addressing efficacy in humans linked to studies providing greater understanding of the mechanisms of action involved are required.

Serum Matrix Metalloproteinase-8 Concentrations Are Associated With Cardiovascular Outcome in Men

Objective— In culture studies matrix metalloproteinase (MMP)-8 thins the protecting fibrous cap of the atherosclerotic plaque thereby increasing its vulnerability. Results on the association of serum MMP-8 concentrations and cardiovascular diseases (CVD) are, however, scarce and contradictory.

Methods and Results— We analyzed the association between CVD or subclinical atherosclerosis and serum MMP-8 and tissue inhibitor of metalloproteinase-1 (TIMP-1) concentrations of 1018 men with the follow-up time of 10 years. MMP-8 concentrations or MMP-8/TIMP-1 ratios were higher in men with prevalent CVD or subclinical atherosclerosis at baseline than those without. In men free of CVD at baseline, MMP-8 concentrations associated with acute myocardial infarction, death from coronary heart disease (CHD), CVD, or from any cause with relative risks (RR) (95% CI) of 1.138 (1.009 to 1.284), 1.188 (1.034 to 1.365), 1.171 (1.026 to 1.338), and 1.136 (1.018 to 1.269), respectively, and MMP-8/TIMP-1 ratio with CHD death with an RR of 1.206 (1.028 to 1.414) per standard deviation (SD) increase. In men with no prevalent CVD but with subclinical atherosclerosis at baseline, elevated serum MMP-8 concentration predicted CVD death with an RR of 3.03 (1.09 to 8.44). TIMP-1 concentrations alone had no predictive value.

Conclusions— The results indicate that serum MMP-8 concentrations are elevated in prevalent or subclinical atherosclerosis and associate with the worst cardiovascular outcome.

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.

Impaired Inhibitory Effect of Interleukin-10 on the Balance Between Matrix Metalloproteinase-9 and Its Inhibitor in Mononuclear Cells From Hyperhomocysteinemic Subjects

BACKGROUND AND PURPOSE

Homocysteine has been linked to increased risk of ischemic stroke and other cardiovascular events, but the mechanism by which elevated plasma levels of homocysteine promotes atherogenesis remains unclear. Matrix degradation, partly regulated by the balance between matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs), plays an important role in atherogenesis and plaque destabilization, and we hypothesized an imbalance between MMPs and TIMPs in hyperhomocysteinemia.

METHODS

Serum MMP-9 and TIMP-1 was measured in 12 hyperhomocysteinemic and 12 control subjects. The release of MMP-9 and TIMP-1, with and without interleukin-10 (IL-10), and the effect of IL-10 on signal transducer and activator of transcription 3 (STAT3) phosphorylation were measured in peripheral blood mononuclear cells (PBMCs) from hyperhomocysteinemic and control subjects.

RESULTS

Our main findings were: (1) hyperhomocysteinemic subjects had raised serum levels of MMP-9 and MMP-9/TIMP-1 ratio comparing healthy controls; (2) although IL-10 markedly suppressed MMP-9 release from PBMCs in controls, no or only minor effect was seen in hyperhomocysteinemic subjects; (3) although IL-10 enhanced TIMP-1 levels in PBMCs from both hyperhomocysteinemic and control subjects, the increase was more prominent in controls, resulting in a marked difference in IL-10-induced changes in MMP-9/TIMP-1 ratio between these 2 groups; and (4) comparing PBMCs from controls, cells from hyperhomocysteinemic individuals had impaired IL-10-induced STAT3 phosphorylation.

CONCLUSIONS

Our findings suggest an attenuated inhibitory response to IL-10 on MMP-9 activity in hyperhomocysteinemic subjects, potentially promoting atherogenesis and plaque instability, representing a novel explanation for increased risk for atherosclerotic disease in these individuals.

Extracellular Superoxide Dismutase with Vaccinia Virus Anti-inflammatory Protein 35K or Tissue Inhibitor of Metalloproteinase-1: Combination Gene Therapy in the Treatment of Vein Graft Stenosis in Rabbits

Bypass graft surgery is limited by stenosis of vein grafts. Neointimal formation in vein graft stenosis is affected by oxidative stress, acute inflammatory response, and proliferation. Gene therapy offers a novel treatment strategy for vein graft stenosis because gene transfer can be done ex vivo during the graft operation. In this study we used adenovirus-mediated ex vivo gene transfer of extracellular superoxide dismutase (EC-SOD) alone or in combination with tissue inhibitor of metalloproteinase-1 (TIMP-1) or vaccinia virus antiinflammatory protein 35K to prevent vein graft stenosis in a jugular vein graft model in normocholesterolemic New Zealand White rabbits. Vein grafts were analyzed 14 and 28 days after the gene transfer, using histological methods. It was found that at the 2-week time point EC-SOD + 35K and EC-SOD + TIMP-1 combinations delivered by gene transfer were the most efficient treatments in decreasing neointimal formation. At the 4-week time point the effect was seen only in the EC-SOD + TIMP-1 combination group. The combination of antiinflammatory proteins (EC-SOD + 35K) was the most effective in reducing macrophage accumulation, which was still significant at the 4-week time point, but this did not prevent vein graft thickening. In conclusion, oxidative, inflammatory, and proliferative processes are important for neointimal formation in vein graft stenosis. In the rabbit model of vein graft disease, combination gene therapy with antioxidative, antiinflammatory, and antiproliferative genes was effective in decreasing neointimal formation. This may be because two different genes may more efficiently affect different pathogenetic pathways at the early stage of the disease process than gene transfer approaches based on single genes.

Myeloperoxidase and its contributory role in inflammatory vascular disease

Myeloperoxidase (MPO), a heme protein abundantly expressed in polymorphonuclear neutrophils (PMN), has long been viewed to function primarily as a bactericidal enzyme centrally linked to innate host defense. Recent observations now extend this perspective and suggest that MPO is profoundly involved in the regulation of cellular homeostasis and may play a central role in initiation and propagation of acute and chronic vascular inflammatory disease. For example, low levels of MPO-derived hypochlorous acid (HOCl) interfere with intracellular signaling events, MPO-dependent oxidation of lipoproteins modulates their affinity to macrophages and the vessel wall, MPO-mediated depletion of endothelial-derived nitric oxide (NO) impairs endothelium-dependent vasodilatation, and nitrotyrosine (NO(2)Tyr) formation by MPO sequestered into the vessel wall may affect matrix protein structure and function. Future studies are needed to further elucidate the significance of MPO in the development of acute and chronic vascular disease and to evaluate MPO as a potential target for treatment.

Bruch's membrane and the vascular intima: is there a common basis for age-related changes and disease?

Several clinical and epidemiological studies have concurrently illuminated established cardiovascular risk factors in age-related macular degeneration (AMD), raising the possibility that cardiovascular disease and AMD may share a similar pathogenic process. The vascular intima and the Bruch's membrane share several age-related changes and are the seat of many common molecules. Diseases of these structures may represent parallel responses to the tissue injury induced by multiple intercalated factors such as genetic variations, oxidative stress, inappropriately directed immune response or inflammatory disease complex. However, there are marked differences in the age-related changes in these two structures. The strategic location of the Bruch's membrane between the retinal pigment epithelium and the choriocapillaris can at least partially explain the differential susceptibility of AMD to cardiovascular risk factors. Unlike the vascular wall that is exposed to changes from the endothelium, the Bruch's membrane is subject to changes from both the endothelium (choriocapillaris) and epithelium (retinal pigment epithelium). Moreover, although both the vascular wall and Bruch's membrane become lipid laden with age, the lipid composition is characteristically different. This review examines the morphological and biochemical alterations in the senescent Bruch's membrane and its analogy to the vascular wall to evaluate the concurrence of atherosclerosis and AMD.

Tissue Inhibitor of Metalloproteinase 1 Adenoviral Gene Therapy Alone Is Equally Effective in Reducing Restenosis as Combination Gene Therapy in a Rabbit Restenosis Model

Neointimal formation is a common feature after angioplasty, bypass grafting and stenting. Angioplasty damages endothelium, causing pathological changes in arteries which lead to smooth muscle cell proliferation, synthesis of extracellular matrix components and eventually restenosis formation. Adenoviruses offer an efficient transgene expression in the vascular system. In this study, we compared the effects of different gene combinations. We wanted to find out whether adenoviral catheter-mediated delivery of an additive combination of the vascular endothelial growth factor (VEGF)-A with VEGF-C is more effective than the combination of tissue inhibitor of metalloproteinase 1 (TIMP-1) alone or with VEGF-C in a rabbit balloon denudation model. Additionally, we wanted to clarify whether the combination therapy prolongs the treatment effect. It was found that TIMP-1 alone prevents restenosis and that the combination of VEGF-A and VEGF-C has a similar effect at the 2-week time point. However, the combination of VEGF-A and VEGF-C lost the treatment effect at the 4-week time point due to the catch-up growth of neointima. On the other hand, TIMP-1 and the combination of TIMP-1 with VEGF-C still had an extended treatment effect at the 4-week time point. When considering the gene combination used in this study, it is concluded that gene therapy with adenoviral TIMP-1 alone is sufficient in reducing restenosis and that combination gene therapy does not bring any significant advantages.

The epidermal growth factor receptors and their family of ligands: their putative role in atherogenesis

The epidermal growth factor receptor is a member of type-I growth factor receptor family with tyrosine kinase activity that is activated following the binding of multiple cognate ligands. Several members of the EGF family of ligands are expressed by cells involved in atherogenesis. EGF receptor mediated processes have been well characterised within epithelial, smooth muscle and tumour cell lines in vitro, and the EGF receptor has been identified immunocytochemically on intimal smooth muscle cells within atherosclerotic plaques. There is also limited evidence for the expression of the EGF receptor family on leukocytes, although their function has yet to be clarified. In this review, we will discuss the biological functions of this receptor and its ligands and their potential to modulate the function of cells involved in the atherosclerotic process.

Synthesis and Structure−Activity Relationships of 4-alkynyloxy Phenyl Sulfanyl, Sulfinyl, and Sulfonyl Alkyl Hydroxamates as Tumor Necrosis Factor-α Converting Enzyme and Matrix Metalloproteinase Inhibitors

A series of 4-alkynyloxy phenyl sulfanyl, sulfinyl and sulfony alkyl and piperidine-4-carboxylic acid hydroxamides were synthesized. Their structure-activity relationships, against tumor necrosis factor-alpha (TACE) and matrix metalloproteinase (MMP) inhibitor activities, are presented by investigating the oxidation state on sulfur and altering the P1' substituent. The sulfonyl derivatives 20-24 carrying a 4-butynyloxy moiety were selective TACE inhibitors over the MMPs tested. The sulfinyl derivatives showed a preference for a specific oxidation on sulfur as in compounds 25-28. The selectivity over MMPs was also demonstrated in the sulfonyl series. The enhanced cellular activity was achieved upon incorporating a butynyloxy substituent in the piperidene series. Compounds 64 and 65 were potent inhibitors of TNF-alpha release in the mouse at 100 mg/kg po.

Loss of matrix metalloproteinase-9 or matrix metalloproteinase-12 protects apolipoprotein E-deficient mice against atherosclerotic media destruction but differentially affects plaque growth

BACKGROUND

Epidemiological and histological evidence implicates proteinases of the matrix metalloproteinase (MMP) family in atherosclerosis and aneurysm formation. We previously indicated a role for urokinase-type plasminogen activator in atherosclerotic media destruction by proteolytic activation of MMPs. However, the role of specific MMPs, such as MMP-9 and MMP-12, in atherosclerosis remains undefined.

METHODS AND RESULTS

MMP-9- or MMP-12-deficient mice were crossed in the atherosclerosis-prone apolipoprotein E-deficient background and fed a cholesterol-rich diet. Mice were killed at 15 or 25 weeks of diet to study intermediate and advanced lesions, respectively. Loss of MMP-9 reduced atherosclerotic burden throughout the aorta and impaired macrophage infiltration and collagen deposition, while MMP-12 deficiency did not affect lesion growth. MMP-9 or MMP-12 deficiency conferred significant protection against transmedial elastin degradation and ectasia in the atherosclerotic media.

CONCLUSIONS

This study is the first to provide direct genetic evidence for a significant involvement of MMP-9, but not of MMP-12, in atherosclerotic plaque growth. In addition, deficiency of MMP-9 or MMP-12 protected apolipoprotein E-deficient mice against atherosclerotic media destruction and ectasia, mechanisms that implicate the involvement of these MMPs in aneurysm formation.

Matrix metalloproteinases in renal development

Matrix metalloproteinases (MMPs) are enzymes with metal ion-dependent activity that degrade extracellular matrix (ECM) glycoproteins. MMPs play a vital role in various biological processes, such as embryogenesis, tissue remodeling, angiogenesis, and wound healing, and in certain disease processes, for example, metastasis of cancer cells. Following their activation, MMPs are believed to modulate both cell-cell and cell-matrix interactions, which in turn regulate cellular differentiation, migration, proliferation, and cell survival. Being involved in pericellular proteolysis, they maintain a gradient of ECM proteins by balancing ECM synthesis and degradation. Such a balance is critical for various mammalian developmental processes during embryonic life and also for the homeostasis of various organs and reparative processes in later life. During the past two decades the role of MMPs in the morphogenesis of various organs, including that of the metanephros, has been investigated extensively. Mammalian nephrogenesis comprises a series of intricate events characterized by a sustained remodeling and turnover of ECM, suggesting a potential role of MMPs in renal development. Conceivably, reciprocal inductive epithelial-mesenchymal interactions that take place at the very commencement of nephrogenesis are modulated by a number of ECM proteins. Their expression, especially at the epithelial-mesenchymal interface, are critical for metanephric development, and such a strategic expression is likely to be modified by a number of different macromolecules that exhibit spatiotemporal and stage-specific expression. Among them the most suitable candidate that could exert such a control would be MMPs. This review addresses the current status of our understanding of the functions and the role of MMPs in renal development.

Role of monocytes in atherogenesis

This review focuses on the role of monocytes in the early phase of atherogenesis, before foam cell formation. An emerging consensus underscores the importance of the cellular inflammatory system in atherogenesis. Initiation of the process apparently hinges on accumulating low-density lipoproteins (LDL) undergoing oxidation and glycation, providing stimuli for the release of monocyte attracting chemokines and for the upregulation of endothelial adhesive molecules. These conditions favor monocyte transmigration to the intima, where chemically modified, aggregated, or proteoglycan- or antibody-complexed LDL may be endocytotically internalized via scavenger receptors present on the emergent macrophage surface. The differentiating monocytes in concert with T lymphocytes exert a modulating effect on lipoproteins. These events propagate a series of reactions entailing generation of lipid peroxides and expression of chemokines, adhesion molecules, cytokines, and growth factors, thereby sustaining an ongoing inflammatory process leading ultimately to lesion formation. New data emerging from studies using transgenic animals, notably mice, have provided novel insights into many of the cellular interactions and signaling mechanisms involving monocytes/macrophages in the atherogenic processes. A number of these studies, focusing on mechanisms for monocyte activation and the roles of adhesive molecules, chemokines, cytokines and growth factors, are addressed in this review.

Temporal and spatial expression of tissue inhibitors of metalloproteinases 1 and 2 (TIMP-1 and -2) in the bovine corpus luteum

The matrix metalloproteinases (MMPs) and their endogenous inhibitors, tissue inhibitors of metalloproteinases (TIMPs), may mediate the dramatic structural and functional changes in the corpus luteum (CL) over the course of its life span. In addition to regulating MMP activity, TIMPs are also involved in a variety of cellular processes, including cell proliferation and steroidogenesis. In a series of initial studies, we determined that matrix metalloproteinase inhibitory activity was present in protein extracts from early (4 days old, estrus = day 0), mid (10-12 days old) and late (16 days old) CL (n = 3 for each stage). Reverse zymography revealed four metalloproteinase inhibitory protein bands with relative molecular masses that are consistent with those reported for TIMP-1 to -4. In order to gain a better understanding of TIMPs and their role in luteal function, we further characterized this inhibitory activity with a particular focus on the temporal and spatial expression of TIMP-1 and TIMP-2 in the bovine CL. Northern blotting revealed that the TIMP-1 transcript (0.9 kb) was expressed at a higher (p < 0.05) level in early and mid cycle CL than in the late stage. In contrast, two TIMP-2 mRNA species, one major 1 kb species and one minor 3.5 kb species, were significantly (p < 0.05) increased in the mid and late cycle CL than in the early. Western blotting analyses demonstrated no differences in TIMP-1 (29 kDa) protein levels between early and mid stages, while its levels decreased (p < 0.05) from the mid to late stage CL. Conversely, TIMP-2 (22 kDa) protein was detected at a low level in the early CL, but significantly (p < 0.05) increased in the mid and late stages. Immunohistochemistry revealed that both TIMP-1 and -2 were localized to large luteal cells from all three ages of CL. TIMP-1 was also localized in capillary smooth muscle cells, while TIMP-2 was restricted to the endothelial cells in the capillary compartment. In conclusion, the different temporal expression patterns of TIMP-1 and TIMP-2 suggest that TIMP-1 may be important for luteal formation and development, while TIMP-2 may play significant roles during luteal development and maintenance. Furthermore, the distinct localization of these two inhibitors in the vascular compartment indicates that they may serve diverse physiological functions during different stages of luteal angiogenesis.

Preventing saphenous vein graft failure: does gene therapy have a role?

Gene therapy potentially allows local delivery and expression of cytokines, growth factors, and other mediators. In spite of increasing knowledge of the human genome, applications in clinical practice are only just beginning. The main limitations of effective clinical gene therapy are safety and low transfection efficiency. Saphenous vein grafts permit the transfection of the conduit ex vivo. This allows a variety of transfection techniques to be used, enhancing the transfection efficiency while limiting the risk of systemic complications. This review examines the potential mechanisms of gene delivery and genetic targets that may be applied to saphenous vein graft failure.

Effect of revascularization on mortality associated with an elevated white blood cell count in acute coronary syndromes

Inflammation is increasingly recognized as having an important role in patients with acute coronary syndromes. We sought to determine whether an elevated white blood cell (WBC) count would predict subsequent mortality and whether revascularization would have a protective effect. We analyzed data from 10,480 patients with acute coronary syndromes enrolled in the PURSUIT trial who had a WBC count measured on admission. WBC count values were stratified by quartiles, and death rates at 6 months were examined in univariate and multivariate analyses. Propensity analysis was performed to assess the effect of revascularization on the relation between WBC count and mortality. In the lowest quartile of WBC count, mortality was 4.0%; it was 5.8% in the second quartile, 6.7% in the third quartile, and 8.0% in the fourth quartile (p <0.001). In a multivariable model incorporating baseline demographic and clinical variables, an increasing WBC count was a significant predictor of death, with a hazard ratio of 1.07 per 1,000/microl increment in WBC count (p <0.001). Furthermore, the interaction term between mortality due to an elevated WBC count and benefit of in-hospital revascularization was significant (hazard ratio 0.94, p = 0.032), suggesting that the excess risk due to an elevated WBC count was attenuated by revascularization. An elevated WBC count at hospital admission, although only a crude index of inflammation, nevertheless is an independent predictor of death at 6 months in patients with acute coronary syndromes. This finding supports a pivotal role for inflammation in acute coronary syndromes. Importantly, this study suggests that in-hospital revascularization may mitigate some of the excess risk due to inflammation.

Serum matrix metalloproteinase-3 and tissue inhibitor of metalloproteinases-1 as potential markers of carotid atherosclerosis in infraclinical hyperlipidemia

The proteolytic activity of proinflammatory matrix metalloproteinases (MMPs) is elevated in lipid-rich atherosclerotic plaques, thereby contributing to plaque fragility and rupture. We hypothesized that changes in circulating levels of MMPs and their specific inhibitors (TIMPs) could reflect the atherosclerotic process occurring within the arterial wall. We determined serum levels of MMP-3, MMP-9, TIMP-1 and TIMP-2 in dyslipidemic subjects and compared them to those of age- and sex-matched normolipidemic healthy controls. Serum levels of MMP-3, MMP-9 and TIMP-1 were significantly increased in hyperlipidemic subjects versus controls (+54, +29 and +15%, respectively; P<0.001). We also noted a trend to elevated serum MMP-3 levels in patients with atherosclerotic lesions when compared to patients free of atherosclerosis (P=0.07). Circulating levels of MMPs and TIMPs were associated neither with those of C-reactive protein, nor with those of alpha2-macroglobulin (a nonspecific MMP inhibitor), nor with intima-media thickness values. Nonetheless, when divided into tertiles, MMP-3 and TIMP-1 levels in the highest tertile were positively associated with the presence of carotid artery lesions (odds ratios=3.4 and 2.0, confidence intervals 1.7-13.9 and 1.3-7.9, respectively). Thus, serum levels of MMP-3, -9 and TIMP-1 are significantly elevated in asymptomatic hyperlipidemic subjects at high cardiovascular risk; however, MMP-3 and TIMP-1 levels are strongly positively associated with the presence of carotid lesions. Such elevations might reflect enhanced vascular matrix remodeling, a key feature of the progression of atherosclerotic disease.

Expression of matrix metalloproteinase-9 in mononuclear cells of hyperhomocysteinaemic subjects

Atherosclerotic plaque instability and rupture requires extracellular matrix modification, a complex process regulated by matrix metalloproteinases (MMPs). We hypothesized that homocysteine's atherogenic effects may involve MMP-mediated mechanisms. Our results showed the following: (i) Compared with healthy control subjects (n = 9), patients with hyperhomocysteinaemia (n = 9) had elevated mRNA levels of MMP-9 and tissue inhibitors of metalloproteinases-1 (TIMP-1) in freshly isolated peripheral blood mononuclear cells (PBMCs), which were positively correlated with homocysteine and negatively correlated with folate and vitamin B12 levels. (ii) Peripheral blood mononuclear cells obtained from these patients released markedly enhanced the amount of MMP-9 upon oxidized LDL (oxLDL) stimulation, whereas no such enhancing effect was seen in cells from healthy controls. (iii) During folic acid 6 weeks' treatment, normalization of homocysteine levels was accompanied by a significant reduction in mRNA levels of MMP-9 and TIMP-1 in PBMCs, as well as a marked reduction in oxLDL-stimulated release of MMP enzyme activity. These novel findings may suggest that homocysteine exerts its atherogenic effect in part by elevating levels and activity of MMPs, which in turn may enhance matrix degradation, potentially promoting atherogenesis and plaque instability. Moreover, our findings suggest that folic acid supplementation may down-regulate these inappropriate responses in these patients.

Regulation of matrix metalloproteinase (matrixin) genes in blood vessels: a multi-step recruitment model for pathological remodelling

Matrix metalloproteinases (MMPs; matrixins) are a family of structurally related enzymes that collectively promote turnover of all components of the extracellular matrix. Matrix turnover is required for vascular repair, but, if excessive, leads to pathologies that include aneurysm formation and atherosclerotic plaque instability. We review the positive and negative regulation of metalloproteinase gene induction. We propose that multiple steps of gene induction recruit a wider spectrum of MMPs, which may ultimately lead to a transition from matrix turnover to matrix destruction. Studying the detailed mechanisms involved may suggest possibilities for intervening selectively against pathological MMP induction.

Synthesis and structure-activity relationship of alpha-sulfonylhydroxamic acids as novel, orally active matrix metalloproteinase inhibitors for the treatment of osteoarthritis

The matrix metalloproteinases (MMPs) are a family of zinc-containing endopeptidases that play a key role in both physiological and pathological tissue degradation. These enzymes are strictly regulated by endogenous inhibitors such as tissue inhibitors of MMPs and alpha(2)-macroglobulins. Overexpression of these enzymes has been implicated in various pathological disorders such as arthritis, tumor metastasis, cardiovascular diseases, and multiple sclerosis. Developing effective small-molecule inhibitors to modulate MMP activity is one approach to treat these degenerative diseases. The present work focuses on the discovery and SAR of novel N-hydroxy-alpha-phenylsulfonylacetamide derivatives, which are potent, selective, and orally active MMP inhibitors.

Metalloproteinase inhibitors: biological actions and therapeutic opportunities

Tissue inhibitors of metalloproteinases (TIMPs) are the major cellular inhibitors of the matrix metalloproteinase (MMP) sub-family, exhibiting varying efficacy against different members, as well as different tissue expression patterns and modes of regulation. Other proteins have modest inhibitory activity against some of the MMPs, including domains of netrins, the procollagen C-terminal proteinase enhancer (PCPE), the reversion-inducing cysteine-rich protein with Kazal motifs (RECK), and tissue factor pathway inhibitor (TFPI-2), but their physiological significance is not at all clear. Alpha2-macroglobulin, thrombospondin-1 and thrombospondin-2 can bind to some MMPs and act as agents for their removal from the extracellular environment. In contrast, few effective inhibitors of other members of the metzincin family, the astacins or the distintegrin metalloproteinases, ADAMs have been identified. Many of these MMP inhibitors, including the TIMPs, possess other biological activities which may not be related to their inhibitory capacities. These need to be thoroughly characterized in order to allow informed development of MMP inhibitors as potential therapeutic agents. Over activity of MMPs has been implicated in many diseases, including those of the cardiovascular system, arthritis and cancer. The development of synthetic small molecule inhibitors has been actively pursued for some time, but the concept of the use of the natural inhibitors, such as the TIMPs, in gene based therapies is being assessed in animal models and should provide useful insights into the cell biology of degradative diseases.

Genes involved in atherosclerosis

Atherosclerosis is a multifactorial disease that involves several genes and proteins. The purpose of this article is to focus on the arterial wall and to review lipoprotein receptors, growth factors, cytokines, chemokines, matrix metalloproteinases, adhesion molecules, and apoptosis genes and their involvement in atherogenesis.

Peptide-retargeted adenovirus encoding a tissue inhibitor of metalloproteinase-1 decreases restenosis after intravascular gene transfer

In this study we have attached cyclic targeting peptides by way of a poly-lysine spacer on the surface of an adenovirus using a transglutaminase enzymatic reaction to enhance transduction efficiency and to modify tissue tropism in vivo. Nuclear targeted lacZ- and TIMP-1-encoding adenoviruses were coupled to a peptide-motif (HWGF) that can bind to matrix metalloproteinase (MMP)-2 and MMP-9. Modified viruses were used to evaluate gene transfer efficiency, biodistribution, and the effect on neointima formation following balloon denudation injury. In vitro, both rabbit aortic smooth muscle cells and human endothelial hybridoma cells demonstrated significantly increased reporter gene expression with HWGF-modified adenoviruses (AdlacZ(HWGF)) compared with control (AdlacZ) or mismatch peptide-modified (AdlacZ(MM)) adenoviruses. However, in human hepatocellular Hep-G2 cells, both AdlacZ(HWGF) and AdlacZ(MM) produced significantly lower transgene expression compared with the respective control viruses. In vivo, local intravascular catheter-mediated gene transfer of a HWGF-targeted TIMP-1-encoding adenovirus (AdTIMP-1(HWGF)) significantly reduced intimal thickening in a rabbit aortic balloon denudation model (P < 0.05) compared with the control adenovirus. X-Gal staining and biodistribution analyses with TaqMan RT-PCR revealed that the cyclic peptides altered vector tropism and, in particular, reduced transduction of the liver. We found that the HWGF peptide modification increased transduction efficiency of the adenovirus-mediated gene transfer in smooth muscle cells and endothelial cells in in vitro and enhanced gene transfer to the arterial wall in vivo; that peptide modification of adenoviruses beneficially modulated tissue tropism in vivo; and that efficient TIMP-1 gene transfer reduced intimal thickening in an established restenosis model in rabbits.

Microemulsion cyclosporin inhibits vascular remodelling and attenuates associated changes in profibrotic gene expression in an experimental model of allograft vasculopathy

BACKGROUND

Chronic allograft dysfunction (CAD), the leading cause of solid organ transplant failure, is characterized by histological evidence of extracellular matrix (ECM) accumulation (fibrosis). The aim of this study was to characterize the changes in fibrosis-associated gene expression in an experimental model of CAD and to measure the effect of the immunosuppressant cyclosporin on these changes.

METHODS

Lewis recipients of F344 rat thoracic to abdominal transplants were administered cyclosporin or no treatment. Vascular remodelling and ECM accumulation (picrosirius red) were measured using computerized histomorphometry. Fibrosis-associated gene expression was studied by semiquantitative reverse transcription-polymerase chain reaction.

RESULTS

Cyclosporin inhibited medial ECM accumulation and vascular remodelling in allografts. This was associated with an attenuation of the graft inflammatory infiltrate and a reduction in intragraft matrix metalloproteinase (MMP) 2 and MMP-9 messenger RNA (mRNA) levels. There was a significant negative correlation between neoadventitial ECM density and MMP-9 expression, as well as with vessel circumference. Neoadventitial ECM density was significantly higher in the cyclosporin-treated group than in animals with untreated allografts, as were mRNA levels of collagen 3 and tissue inhibitor of metalloproteinase 1.

CONCLUSION

The alloimmune injury itself may contribute directly to vascular remodelling and fibrosis in allograft vasculopathy. Cyclosporin attenuated this component of the pathophysiology of CAD effectively.

Enhanced invasive properties exhibited by smooth muscle cells are associated with elevated production of MMP-2 in patients with aortic aneurysms

BACKGROUND

abdominal aortic aneurysms (AAA) are associated with excessive vascular matrix remodelling. Recent findings suggest a systemic overproduction of matrix metalloproteinases-2 (MMP-2) by vascular smooth muscle cells (SMC) may be pivotal aetiologically. SMC migration is facilitated by MMP mediated proteolysis of the basement membrane and extracellular matrix. Our aim was to see if enhanced MMP-2 production by these SMC exhibit increased invasion, in an in vitro model of migration.

METHOD

SMC were derived from inferior mesenteric vein (IMV) harvested from patients undergoing aneurysm repair (n=6) or colectomy for diverticulosis (n=6, control). Using a modified Boyden chamber chemotaxis was measured towards platelet derived growth factor (PDGF) and foetal calf serum (FCS) and invasion through a Matrigel layer. MMP-2 production was quantified by ELISA and gelatin zymography.

RESULTS

chemoattractant studies demonstrated no difference in the effect of PDGF or FCS between the two populations of SMC. However, invasive studies demonstrated a significant increase in the number of migrating SMC isolated from IMV of AAA patients. Analysis of culture media extracts revealed that this difference was associated with a significant increase in production of MMP-2.

CONCLUSION

SMC derived from patients with AAA demonstrate increased invasive properties when compared to a control group. Increased migration appears to be due to overproduction of MMP-2. The enhanced migratory potential of these SMC may lead to extracellular matrix remodelling and subsequent medial disruption demonstrated in the aneurysmal aorta. These data further support evidence of the proteolytic role of MMP-2 in cell migration.

Expression of matrix metalloproteinase 3 in experimental atherosclerotic plaques

In atherosclerotic lesions, matrix metalloproteinases produced by foam cells (macrophages) are thought to increase plaque instability, promote plaque rupture, by degradating extracellular matrix. To investigate the relationship between the expression of these proteinases and the histologic appearance of atheromas, immunohistochemical analysis of matrix metalloproteinase 3 and cell-type markers was performed in atherosclerotic plaques induced in rabbit abdominal aortas by high-cholesterol diets and mechanical injury. In addition to an antibody against matrix metalloproteinase 3, RAM-11 and HHF-35 were used to detect macrophages and smooth muscle cells, respectively. Matrix metalloproteinase 3 was expressed diffusely within the plaques with a fibrofatty histologic pattern. In plaques with foam cell accumulation, matrix metalloproteinase 3 was seen in areas rich in foam cells and the smooth muscle cells near the lumen. In the plaques with fewer macrophages, the proteinase was expressed only in such smooth muscle cells. Matrix metalloproteinase 3 was expressed in the smooth muscle cells in plaques of all histologic types, and macrophages also expressed the metalloproteinase when present in significant numbers. These findings suggest that macrophage accumulation plays an important pathophysiologic role in causing the instability of atherosclerotic lesions by increasing the levels of matrix metalloproteinase 3.

Association of serum MMP-9 with autoantibodies against oxidized LDL

Monocyte-derived macrophages in atherosclerotic plaques secrete matrix metalloproteinases (MMPs), which may contribute to plaque rupture. There has been much speculation as to which factors precipitate in the arterial inflammation. Oxidized low density lipoprotein (oxLDL) has been suggested to have proinflammatory properties, and it has been shown to increase matrix metalloproteinase-9 (MMP-9) secretion by macrophages in vitro. We determined serum MMP-9 concentration and autoantibodies against oxLDL by ELISA in men with angina pectoris (n=243) and age-matched controls (n=238). The association between serum MMP-9 concentration and autoantibodies against oxLDL was evaluated. Autoantibody level against oxLDL, expressed in optical density units, was significantly higher in subjects with angina pectoris compared to controls (0.100+/-0.064 versus 0.088+/-0.051, respectively, P=0.030), but serum levels of MMP-9 did not differ significantly between these groups (54.2+/-29.9 versus 50.6+/-23.1 microg/l). However, autoantibodies against oxLDL correlated positively with serum MMP-9 (r=0.21, P<0.001). In a multiple regression model (including age, diastolic blood pressure, cholesterol, HDL cholesterol, triglycerides, BMI, smoking and MMP-9) serum MMP-9 (beta=0.200, P<0.001) and smoking (beta=0.179, P<0.001) were significantly associated with autoantibodies against oxLDL. In conclusion, autoantibodies against oxLDL were positively associated with angina pectoris and serum MMP-9. Since autoantibody level against oxLDL could be expected to reflect the degree of oxLDL in the vessel wall, our results suggest that oxLDL is associated with MMP-9 in vivo.

Hypochlorous acid oxygenates the cysteine switch domain of pro-matrilysin (MMP-7). A mechanism for matrix metalloproteinase activation and atherosclerotic plaque rupture by myeloperoxidase

Myeloperoxidase uses hydrogen peroxide (H2O2) to generate hypochlorous acid (HOCl), a potent cytotoxic oxidant. We demonstrate that HOCl regulates the activity of matrix metalloproteinase-7 (MMP-7, matrilysin) in vitro, suggesting that this oxidant activates MMPs in the artery wall. Indeed, both MMP-7 and myeloperoxidase were colocalized to lipid-laden macrophages in human atherosclerotic lesions. A highly conserved domain called the cysteine switch has been proposed to regulate MMP activity. When we exposed a synthetic peptide that mimicked the cysteine switch to HOCl, HPLC analysis showed that the thiol residue reacted rapidly, generating a near-quantitative yield of products. Tandem mass spectrometric analysis identified the products as sulfinic acid, sulfonic acid, and a dimer containing a disulfide bridge. In contrast, the peptide reacted slowly with H2O2, and the only product was the disulfide. Moreover, HOCl markedly activated pro-MMP-7, an MMP expressed at high levels in lipid-laden macrophages in vivo. Tandem mass spectrometric analysis of trypsin digests revealed that the thiol residue of the enzyme's cysteine switch domain had been converted to sulfinic acid. Thiol oxidation was associated with autolytic cleavage of pro-MMP-7, strongly suggesting that oxygenation activates the latent enzyme. In contrast, H2O2 failed to oxidize the thiol residue of the protein or activate the enzyme. Thus, HOCl activates pro-MMP-7 by converting the thiol residue of the cysteine switch to sulfinic acid. This activation mechanism is distinct from the well-studied proteolytic cleavage of MMP pro-enzymes. Our observations raise the possibility that HOCl generated by myeloperoxidase contributes to MMP activation, and therefore to plaque rupture, in the artery wall. HOCl and other oxidants might regulate MMP activity by the same mechanism in a variety of inflammatory conditions.

Oxidized LDL differentially regulates MMP-1 and TIMP-1 expression in vascular endothelial cells

We have reported recently that oxidized low-density lipoprotein (oxLDL) stimulates matrix metalloproteinase-1 (MMP-1) expression in human vascular endothelial cells. The present study was conducted to examine the effect of oxLDL on expression of Tissue inhibitor of metalloproteinase-1 (TIMP-1), an endogenous inhibitor of MMPs, in human vascular endothelial cells. Our enzyme-linked immunosorbent assay and Northern blot analysis showed that oxLDL inhibited TIMP-1 secretion and expression by human umbilical vein endothelial cells. In contrast, PMA stimulated TIMP-1 expression and secretion. Both oxLDL and PMA increased MMP-1 expression and secretion significantly as previously reported. Inhibition by oxLDL of TIMP-1 expression was also observed in human aortic endothelial cells. Collagenase activity as detected by an enzymatic activity assay demonstrated, as expected, an increase in collagenase activity in the culture medium from oxLDL-treated cells as compared with that from untreated cells. The presented data indicates that oxLDL differentially regulates TIMP-1 and MMP-1 expression, whereas PMA coordinately regulates TIMP-1 and MMP-1 in vascular endothelial cells. The lack of coordination in the secretion of MMP-1 and TIMP-1 induced by oxLDL leads to an increased collagen-degrading activity that may contribute to destabilization of atherosclerotic plaques.

Local gene transfer of tissue inhibitor of metalloproteinase-2 influences vein graft remodeling in a mouse model

Recently, we established a new mouse model of vein graft arteriosclerosis by grafting vena cava to carotid arteries. In many respects, the morphological features of this murine vascular graft model resemble those of human venous bypass graft disease. Using this model, we studied the effects of local gene transfer of tissue inhibitor of metalloproteinase-2 (TIMP-2) on vein graft remodeling. Mouse isogeneic vessels of the vena caval veins were grafted end to end into carotid arteries, then enveloped with the replication-defective recombinant adenoviruses overexpressing human TIMP-2 (RAdTIMP-2) or beta-galactosidase (RAdLacZ) at 1x10(10) plaque-forming units/mL in a total volume of 50 microL, and incubated at room temperature for 20 minutes. In the untreated group, vessel wall thickening was observed as early as 1 week after surgery and progressed to 4- to 10-fold the original thickness in grafted veins at 4 and 8 weeks, respectively. RAdLacZ vector treatment significantly enhanced neointimal lesions at 8 weeks, which was completely blocked by RAdTIMP-2 gene overexpression. Interestingly, RAdTIMP-2 gene transfer resulted in a reduction in vessel diameter of grafted veins compared with ungrafted veins (819+/-96 versus 624+/-67 microm, respectively; P<0.05). Maximal beta-galactosidase activity was found at 2 weeks and was detectable until 4 weeks after gene transfer. Double immunofluorescence studies demonstrated that cells overexpressing TIMP-2 were mostly localized in the adventitia and were MAC-1-positive monocytes/macrophages but not smooth muscle cells. Furthermore, the activity of matrix metalloproteinases was markedly decreased in the vessel walls treated with RAdTIMP-2 compared with that in the untreated control group and the RAdLacZ-treated group. Thus, this mouse model has been proven to be useful in gene transfer studies. Our findings demonstrate that local TIMP-2 gene transfer significantly reduces vein graft diameter, ie, remodeling to an artery-like vessel via inhibition of matrix metalloproteinase activity.

Interleukin-15 expression in atherosclerotic plaques: an alternative pathway for T-cell activation in atherosclerosis?

T-cell activation in atherosclerotic plaques is thought to be initiated by plaque-derived antigens, such as oxidized LDL (oxLDL). An alternative pathway of T-cell activation independent of antigen stimulation, mediated by the cytokine interleukin (IL)-15, was recently described. We investigated IL-15 expression in atherosclerotic plaques in relation to plaque morphology, inflammatory cells, T-cell activation, and oxidation-specific epitopes by use of immunohistochemistry. In situ hybridization was used to evaluate IL-15 mRNA expression. We also studied the proliferative response of plaque-derived T-cell lines to IL-15 in vitro using [(3)H]thymidine incorporation. Fresh-frozen specimens were classified as fibrous (n=9), fibrolipid (n=8), and lipid-rich (n=14) plaques; normal vessels (n=4) served as reference. Expression of IL-15 mRNA and protein was found almost solely in fibrolipid and lipid-rich plaques, associated with oxLDL-positive macrophages. Sequential immunostains revealed colocalization between IL-15- and CD40L-positive T cells. Moreover, plaque-derived T-cell lines were highly responsive to IL-15. Hence, IL-15 could provide a pathway for antigen-independent T-cell activation.

Quercetin inhibits matrix metalloproteinase-1 expression in human vascular endothelial cells through extracellular signal-regulated kinase

Studies have shown that intake of quercetin was inversely associated with mortality from coronary heart disease. Since recent studies documented that disruption of atherosclerotic plaques is the key event triggering acute myocardial infarction, and vascular endothelium-derived matrix metalloproteinase-1 (MMP-1) contributes to plaque destabilization, we examined the effect of quercetin on MMP-1 expression in human vascular endothelial cells. Our results showed that quercetin significantly inhibited basal and oxidized LDL (oxLDL)-stimulated MMP-1 expression. Our data also indicated that extracellular signal-regulated kinase (ERK) mediated the basal and oxLDL-stimulated expression of MMP-1, and quercetin is a potent inhibitor of ERK, suggesting that quercetin may inhibit MMP-1 expression by blocking the ERK pathway. Finally, we showed that quercetin stimulated tissue inhibitor of metalloproteinase-1 expression in oxLDL- and PMA-treated cells. In conclusion, the present study demonstrated for the first time that quercetin inhibited MMP-1 expression in vascular endothelial cells, suggesting that quercetin might contribute to plaque stabilization.

Chlamydia pneumoniae proteins induce secretion of the 92-kDa gelatinase by human monocyte- derived macrophages

Chlamydia pneumoniae, an intracellular Gram-negative respiratory bacterium, and macrophages are present in inflammatory tissue sites such as atherosclerotic lesions, where abnormal degradation of the extracellular matrix takes place. To evaluate the potential of C pneumoniae for participation in matrix destruction, we studied the effect of this bacterium on the production of 3 matrix-degrading metalloproteinases, 92-kDa gelatinase, interstitial collagenase-1, and stromelysin-1, and their natural inhibitor TIMP-1 (tissue inhibitor of metalloproteinases-1) by human monocyte-derived macrophages differentiated in vitro. Spontaneous production of collagenase and stromelysin by these cells was minimal and was not influenced by C pneumoniae. In contrast, the cells secreted substantial basal quantities of 92-kDa gelatinase, the secretion of which was stimulated (on average, 2.5-fold) by C pneumoniae. C pneumoniae regulated the expression of 92-kDa gelatinase by macrophages at the pretranslational level. Macrophages secreted only small quantities of TIMP-1. The chlamydial proteins Omp2, MOMP, and HSP60 were also found to participate in the induction of 92-kDa gelatinase by C pneumoniae. Denaturation of chlamydial proteins by boiling reduced 92-kDa gelatinase secretion only partially (by 35%), suggesting that the heat-stabile lipopolysaccharide molecules also stimulate secretion of the enzyme. The results show that production of 92-kDa gelatinase by human macrophages is selectively upregulated by C pneumoniae, which suggests that these bacteria, when present in a macrophage-containing inflammatory environment, actively participate in the destruction of the extracellular matrix.