Matrix metalloproteinases and atherosclerotic plaque instability

Heregulin, cysteine rich-61 and matrix metalloproteinase 9 expression in human carotid atherosclerotic plaques: relationship with clinical data

OBJECTIVES

Heregulins (HRGs) are known to induce expression of angiogenic factors such as cysteine rich-61 (CYR61) and collectively to promote neoangiogenesis. Along with extracellular matrix remodelling, mediated by matrix metalloproteinases (MMPs), these factors are important in atherogenesis. The aim of the present study was to investigate HRG, CYR61 and MMP-9 expression and their relationship with clinical and histopathological findings in carotid occlusive disease.

MATERIALS AND METHODS

Specimens of human carotid atherosclerotic plaque (n=90) were obtained by endarterectomy. Expression of HRG, CYR61 and MMP-9 was assessed by immunohistochemical and Western blot analysis. Associations between protein expression and degree of carotid stenosis, presence of symptoms, presence of an infarct in CT scan and carotid plaque histopathology were investigated.

RESULTS

An increase in HRG, CYR61 and MMP-9 expression was found, particularly in neovascularized regions of the plaques. High HRG expression was associated with the degree of carotid stenosis (p=0.028) and plaque histopathology (p=0.002). More than half of specimens from plaques with >90% stenosis had intense expression of CYR61 (p=0.047). Increased expression of MMP-9 was associated with degree of stenosis and presence of cerebral infarct on CT scan (p=0.05).

CONCLUSION

HRG, CYR61 and MMP-9 are highly expressed in human atherosclerotic carotid plaques. The association with the degree of stenosis and/or plaque histopathology implies an involvement in lesion progression.

Pregnancy-Associated Plasma Protein-A Is Markedly Expressed by Monocyte-Macrophage Cells in Vulnerable and Ruptured Carotid Atherosclerotic Plaques

OBJECTIVES

The study aim was to evaluate serologic expression of pregnancy-associated protein-A (PAPP-A) in patients affected by cerebrovascular accidents and to correlate it with histopathologic carotid plaque complexity.

BACKGROUND

Little is known about PAPP-A expression in carotid atherosclerotic disease and whether this protein represents a marker of plaque vulnerability also in carotid district.

METHODS

Seventy-two carotid plaques from patients submitted to surgical endarterectomy (19 who suffered a major stroke, 24 transient ischemic attack, and 29 asymptomatic) were evaluated. Serologic PAPP-A levels were determined by enzyme-linked immunoadsorbent assay. Plaques were divided in three groups based on histology: 1) stable (n = 38); 2) vulnerable (n = 13); 3) ruptured with thrombus (n = 14). Immunohistochemical staining for PAPP-A, smooth muscle cells, macrophages, and T-lymphocytes was performed in all cases. Real-time polymerase chain reaction assessed local PAPP-A production, and double immunofluorescence confocal microscopy (ICM) characterized cell type expressing PAPP-A.

RESULTS

Pregnancy-associated protein-A (serologic values were 4.02 +/- 0.18 mIU/l in Group 1, 7.43 +/- 0.97 mIU/l in Group 2, and 6.97 +/- 0.75 mIU/l in Group 3 [1 vs. 3, p = 0.01; 1 vs. 2, p = 0.004; 2 vs. 3, p = 0.71, respectively]). Pregnancy-associated protein-A (expression showed a mean score value of 0.62 +/- 0.06 for stable plaques, 2.54 +/- 0.14 for vulnerable plaques, and 2.71 +/- 0.12 for ruptured plaques [1 vs. 2, p = 0.001; 1 vs. 3, p = 0.001; 2 vs. 3, p = 0.37, respectively]). Real-time polymerase chain reaction demonstrated local messenger ribonucleic acid PAPP-A production, and double ICM confirmed monocyte/macrophage expression of PAPP-A in Groups 2 and 3 but not Group 1.

CONCLUSIONS

This study suggests that PAPP-A is a marker of carotid plaque destabilization and rupture. Further studies are necessary to determine if PAPP-A can represents a new target for stratifying the risk of cerebrovascular events.

Inflammation and atherosclerosis: novel insights into plaque formation and destabilization

BACKGROUND AND PURPOSE

The simplistic view of atherosclerosis as a disorder of pathological lipid deposition has been redefined by the more complex concept of an ongoing inflammatory response.

SUMMARY OF REVIEW

Apolipoprotein E and low-density lipoprotein (LDL)-receptor-deficient mice develop accelerated atherosclerosis allowing in-depth pathophysiological investigations. Atherosclerotic plaques in these mice contain large numbers of T cells and macrophages. Crossbreeding apolipoprotein E-deficient mice with T-cell-deficient mice and mice with impaired macrophage function (osteopetrotic op/op mice) disclosed the important impact of immune cells on atherosclerotic lesion development. In contrast to the detrimental role of T cells and macrophages, B cells appear to be atheroprotective. These basic experimental findings have partly been confirmed in studies of the human carotid artery system. Inflammation is not only instrumental in the development of human atheromatous plaques, but, importantly, plays a crucial role in the destabilization of internal carotid artery plaques, thus converting chronic atherosclerosis into an acute thrombo-embolic disorder. Humoral factors involved in internal carotid artery destabilization include cytokines, cyclooxygenase-2, matrix metalloproteinases, and tissue factor. Antibodies to oxidized LDL can reflect disease activity on one hand, but can also confer atheroprotection. Novel MRI techniques may aid in the in vivo assessment of acute plaque inflammation in humans.

CONCLUSIONS

The impact of inflammation on the development of atherosclerotic plaques and their destabilization opens new avenues for treatment. The effects of statins, acetylsalicyclic acid and angiotensin-converting enzyme inhibitors on stroke prevention may partly be attributable to their profound anti-inflammatory actions. Vaccination against modified LDL and heat shock proteins halt plaque progression in experimental atherosclerosis. Their potential for prevention of human atherosclerosis is currently under investigation.

Role of annexin II in estrogen-induced macrophage matrix metalloproteinase-9 activity: the modulating effect of statins

Annexin II (ANXII) is a receptor for tissue plasminogen activator and plasminogen for the conversion to plasmin, which, in turn, induces metalloproteinase-9 (MMP-9). 17beta-Estradiol (E(2)) is reported to decrease plasminogen activity inhibitor-1 and increase plasmin and matrix metalloproteinase activity. However, the combined effects of estrogen and statins on macrophage MMP-9 activity and ANXII expression remain unclear. Treatment of J774A.1 macrophages with 1.0-100 nM of E(2) for 24h increased both MMP-9 activity and ANXII expression in a dose-dependent manner (p<0.05). Preincubation with EGTA (10mM) released ANXII from the cell membrane and inhibited the E(2)-mediated MMP-9 activity as did incubation of macrophages with anti-annexin IgG. In the presence or absence of E(2) (5 nM), simvastatin treatment in the range of 0.1-5.0 microM significantly reduced macrophage MMP-9 enzymatic activity (p<0.005) in a dose-dependent manner. In the presence or absence of E(2), simvastatin also decreased ANXII expression (p<0.05). These findings indicate that ANXII plays a central role in modulating the enzymatic activity of MMP-9 in response to E(2) and that E(2)-mediated ANXII expression and MMP-9 activity can be prevented by simvastatin. Prevention of E(2)-mediated activation of MMP-9 by simvastatin suggests that concurrent statin use may account for early event risk of myocardial infarction seen with hormone therapy in recent clinical trials.

Gelatinases [matrix metalloproteinase-2 (MMP-2) and MMP-9] induce carotid plaque instability but their systemic levels are not predictive of local events

Matrix metalloproteinases (MMPs) appear to play a central role in atherosclerotic plaque remodeling; however, the relationship of increased MMP levels in inducing carotid plaque instability remains controversial. We investigated whether gelatinases (MMP-2 and MMP-9) are implicated in carotid intraplaque hemorrhage and whether their serum levels may predict local carotid events. Nineteen carotid specimens obtained by endarterectomy of 18 patients were studied. The presence of gross intraplaque hemorrhage was recorded before plaque removal and quantification of MMP-2, MMP-9, and tissue inhibitor of metalloproteinase-1 (TIMP-1) in extracts from (1) the more stenotic area of the plaque, (2) the periphery of the plaque, and (3) serum was performed by enzyme-linked immunosorbent assay. MMP-9 levels measured in extracts from the most stenotic area were significantly higher in patients with intraplaque hemorrhage (p = 0.007); however, serum levels showed no difference, while those taken from the periphery of the lesion were also increased but did not reach a statistically significant level (p = 0.06). An increase in MMP-2 values was observed in the periphery of the lesion (p = 0.04) in patients with intraplaque hemorrhage. TIMP-1 levels showed no difference between the two groups regardless of the presence or absence of intraplaque hemorrhage. No significant differences in MMP levels were observed between symptomatic and asymptomatic patients. Increased levels of MMPs, particularly MMP-9, have been implicated in carotid intraplaque hemorrhage without their serum levels being predictive of local events.

Matrix metalloproteinases and diabetic vascular complications

Diabetes mellitus (DM) is associated with an increased incidence of cardiovascular events and microvascular complications. These complications contribute to the morbidity and mortality associated with DM. There is increasing evidence supporting a role for matrix metalloproteinases (MMPs) and their inhibitors (tissue inhibitors of matrix metalloproteinases - TIMPs) in the atherosclerotic process. However, the relationship between MMPs/TIMPs and diabetic angiopathy is less well defined. Hyperglycemia directly or indirectly (eg, via oxidative stress or advanced glycation products) increases MMP expression and activity. These changes are associated with histologic alterations in large vessels. On the other hand, low proteolytic activity of MMPs contributes to diabetic nephropathy. Within atherosclerotic plaques an imbalance between MMPs and TIMPs may induce matrix degradation, resulting in an increased risk of plaque rupture. Furthermore, because MMPs enhance blood coagulability, MMPs and TIMPs may play a role in acute thrombotic occlusion of vessels and consequent cardiovascular events. Some drugs can inhibit MMP activity. However, the precise mechanisms involved are still not defined. Further research is required to demonstrate the causative relationship between MMPs/TIMPs and diabetic atherosclerosis. It also remains to be established if the long-term administration of MMP inhibitors can prevent acute cardiovascular events.

Macrophage migration inhibitory factor induces MMP-9 expression: implications for destabilization of human atherosclerotic plaques

Macrophage migration inhibitory factor (MIF) has been shown to participate in both experimental and human atherogenesis. Expression of MMP-9 has been shown to play a role in the instability of atherosclerotic plaque. Thus, we hypothesize that MIF may participate in the destabilization of atherosclerotic plaques by stimulating MMP-9 expression. This hypothesis was investigated by examining the expression of MIF and MMP-9 in human atherosclerotic plaques using two-color immunostaining and by determining the potential role of MIF in the induction of MMP-9 expression in vascular smooth muscle cells (VSMC) and macrophages in vitro. Two-color immunohistochemistry demonstrated that MIF was strongly upregulated by macrophages and VSMCs. This was associated with marked increase in MMP-9 expression in vulnerable atheromatous plaques, but not in the fibrous lesions. Upregulation of MIF and MMP-9 in vulnerable atheromatous plaques was associated with the weakening of fibrous caps. The role of MIF in MMP-9 expression was demonstrated by the ability of MIF to directly induce MMP-9 mRNA and protein expression in macrophages and in VSMCs in a dose and time-dependent manner, which was blocked by a neutralizing MIF antibody. In conclusion, MIF and MMP-9 are markedly upregulated in vulnerable atheromatous plaques. The ability of MIF to induce MMP-9 expression in VSMCs and macrophages suggests that MIF may play a role in the destabilization of human atherosclerotic plaques.

The Relationship Between Plasma MMP-1, -7, -8 and -13 Levels and Embolic Potential During Carotid Endoluminal Intervention

BACKGROUND

Patients undergoing carotid endoluminal intervention are at risk of embolic stroke even with the use of distal protection devices. Matrix metalloproteinases (MMPs) have been implicated as a causal factor in plaque instability leading to spontaneous embolisation. We investigated whether plasma MMP levels correlated with the embolisation during carotid endoluminal intervention.

METHODS

Thirty circumferentially intact carotid endarterectomy specimens were subjected to a standardised angioplasty procedure in a pulsatile ex vivo model. Emboli collected in a series of distal filters were counted and sized. Plasma samples were collected pre-operatively and analysed for MMP-7 and MMP-8 levels using Western immunoblotting. MMP-1 and MMP-13 levels were determined using ELISA. Emboli number and maximum size were correlated with plasma levels of the MMPs using Spearmans rank.

RESULTS

Total MMP-8 levels were related to maximum embolus size (r=0.442, p=0.005) but not emboli number (r=0.342, p=0.052). MMP-1, -7 and -13 were not correlated with either emboli number or with maximum embolus size.

CONCLUSION

Pre-operative plasma MMP-8 levels are related to the size of emboli from plaques during carotid endovascular intervention. Further in vivo studies need to be performed to assess the importance of this finding. There is potential for development of plasma markers to identify those patients at greater risk of embolic stroke during carotid endoluminal intervention.

Matrix metalloproteinases and atherosclerosis

Atherosclerosis is a major cause of coronary heart disease, and matrix metalloproteinases (MMPs) play an important role in atherosclerosis by degrading the extracellular matrix, which results in cardiovascular remodeling. Recent studies have identified enhanced expression of MMPs in the atherosclerotic lesion and their contribution to weakening of the vascular wall by degrading the extracellular matrix. The transcription, enzyme processing, and specific inhibition of MMPs by tissue inhibitors of matrix metalloproteinase (TIMPs) regulate these effects. These processes are also modified by inflammatory cytokines and cell-cell contact signaling. Both animal experiments and clinical sample analysis have shown that balance in expression and activation of MMPs and inhibition by TIMPs is critical for the development of stenotic and aneurysmal change. Polymorphism in the MMP gene promoter contributes to inter-individual differences in susceptibility to coronary heart disease. The development of therapeutic drugs specifically targeting MMPs may thus be useful for the prevention of atherosclerotic lesion progression, plaque rupture, and restenosis.

Overexpression of IL-18 decreases intimal collagen content and promotes a vulnerable plaque phenotype in apolipoprotein-E-deficient mice

OBJECTIVE

Although IL-18 has been implicated in atherosclerotic lesion development, little is known about its role in advanced atherosclerotic plaques. This study aims to assess the effect of IL-18 overexpression on the stability of preexisting plaques.

METHODS AND RESULTS

Atherosclerotic lesions were elicited in carotid arteries of apolipoprotein E (apoE)-deficient mice (n=32) by placement of a perivascular collar. Overexpression of IL-18 was effected by intravenous injection of an adenoviral vector 5 weeks after surgery. Two weeks after transduction, lesions were analyzed histologically with regard to plaque morphology and composition or by real-time polymerase chain reaction. No difference in plaque size was detected between groups. In the Ad.IL-18-treated group, 62% of lesions displayed a vulnerable morphology or even intraplaque hemorrhage as compared with only 24% in the controls (P=0.037). In agreement, IL-18 overexpression reduced intimal collagen by 44% (P<0.003) and cap-to-core ratio by 41% (P<0.002). Although IL-18 did not affect the expression of collagen synthesis-related genes, it was found to enhance the collagenolytic activity of vascular smooth muscle cells in vitro, suggesting that the low collagen content is attributable to matrix degradation rather than to decreased synthesis.

CONCLUSIONS

Systemic IL-18 overexpression markedly decreases intimal collagen content and cap thickness, leading to a vulnerable plaque morphology.

Decreased plasminogen activator inhibitor-1 levels in coronary artery aneurysmatic patients

BACKGROUND

Matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of arterial aneurysms through increased proteolysis of extracellular matrix proteins. Increased proteolysis due to elevated matrix degrading enzyme activity in the arterial wall may act as a susceptibility factor for the development of coronary aneurysms. Plasmin strongly stimulates pro-MMP enzyme conversion to the active form. Plasmin hyperactivity due to decreased plasminogen activator inhibitor-1 (PAI-1) may cause MMP over activity and coronary aneurysms. The aim of this study was to investigate the association between PAI-1 and presence of coronary aneurysms.

METHODS

Twenty-three patients with aneurysmal coronary artery disease and stable angina were enrolled into study (Group 1). Twenty-two patients without coronary aneurysm were selected as a control group (Group 2). PAI-1 was measured in peripheral venous blood.

RESULTS

The plasma PAI-1 level was lower in the coronary artery aneurysmatic patients compared to the control group (8.41 +/- 4.28 vs. 13.32 +/- 10.05 ng/ml, p = 0.037). Serum C-reactive protein (CRP) values were not significantly different between groups (3.83 +/- 1.08 vs. 4.01 +/- 1.35 mg/l, p >0.05).

CONCLUSION

Increased matrix degrading enzyme activity can cause arterial wall destruction through increased proteolysis of extracellular matrix proteins. Unregulated plasmin hyperactivity due to decreased inhibition by PAI-1 may play an important role in coronary aneurysm formation.

Elastinolytic matrix metalloproteinases and their inhibitors as therapeutic targets in atherosclerotic plaque instability

Atherosclerosis is a dynamic pathologic process involving interactions between many cell types and chemical mediators. There is increased evidence in the literature that matrix metalloproteinases, especially those with elastolytic activity, are associated with atherosclerotic plaque instability. Results of recent studies also suggest that the balance between matrix metalloproteinases and their inhibitors contributes to the extracellular matrix integrity, and an imbalance could be a predeterminate of both cerebral and cardiac ischemic events. Significant evidence demonstrates that the balance between elastolytic matrix metalloproteinases and their inhibitors are involved in the atherosclerotic process. Studies investigating pharmacologic therapies that inhibit matrix metalloproteinases or increase their natural inhibitor levels suggest an antiatherosclerotic and potential plaque-stabilizing benefit. Carefully designed clinical trials must be completed to better understand the functions and interactions of these enzymes with the goal of developing selective therapies to prevent the progression and complications of atherosclerosis.

Unstable Carotid Plaques Exhibit Raised Matrix Metalloproteinase-8 Activity

BACKGROUND

The fibrous cap of atherosclerotic plaques is composed predominantly of type I and III collagen. Unstable carotid plaques are characterized by rupture of their cap, leading to thromboembolism and stroke. The proteolytic mechanisms causing plaque disruption are undefined, but the collagenolytic matrix metalloproteinase (MMP) -1, -8, and -13 may be implicated. The aim of this study was to quantify the concentrations of these collagenases in carotid plaques and to determine their relationship to markers of plaque instability.

METHODS AND RESULTS

Atherosclerotic plaques were collected from 159 patients undergoing carotid endarterectomy. The presence and timing of carotid territory symptoms were ascertained. Preoperative embolization was recorded by transcranial Doppler. Each plaque was assessed for histological features of instability. Plaque MMP concentrations were quantified with ELISA. Significantly higher concentrations of active MMP-8 were observed in the plaques of symptomatic patients (20.5 versus 11.4 ng/g; P=0.0002), in plaques of emboli-positive patients (22.7 versus 13.5 ng/g; P=0.0037), and in those plaques showing histological evidence of rupture (20.8 versus 14.7 ng/g; P=0.0036). No differences were seen in the levels of MMP-1 and MMP-13. Immunohistochemistry, in situ hybridization, and colocalization studies confirmed the presence of MMP-8 protein and mRNA within the plaque, which colocalized with macrophages.

CONCLUSIONS

These data suggest that the active form of MMP-8 may be partly responsible for degradation of the collagen cap of atherosclerotic plaques. This enzyme represents an attractive target for drug therapy aimed at stabilizing vulnerable plaques.

Elevation in Plasma MMP-9 Following Carotid Endarterectomy is Associated with Particulate Cerebral Embolisation

OBJECTIVES

To study plasma MMP-9 levels before and after carotid endarterectomy (CEA).

DESIGN

Observational study.

METHODS

Pre-operative (morning of surgery) and post-operative (48 h) plasma samples were obtained from 75 consecutive patients undergoing CEA. MMP-9 concentrations were quantified using ELISA. Transcranial Doppler monitoring was performed on each patient to detect particulate embolisation during the dissection phase of the CEA, until the application of carotid clamps.

RESULTS

The median post-operative plasma MMP-9 level of emboli-positive patients was significantly higher than their median pre-operative value (14.9 ng/ml vs. 8.8 ng/ml; p=0.038). However, no significant difference was seen in the plasma MMP-9 level of emboli-negative patients (7.7 ng/ml vs. 7.1 ng/ml; p=0.364). A greater rise was seen in the median plasma MMP-9 levels of those patients suffering >2 emboli (from 3.4 to 19.3 ng/ml; p=0.041) than those patients suffering 1 or 2 emboli (from 10.1 to 12.8 ng/ml; p=0.340).

CONCLUSIONS

Plasma MMP-9 only rises after CEA in patients with evidence of embolisation. This increase is more pronounced in those with high numbers of emboli. These data suggest that the increase in MMP-9 is due to cerebral damage caused by embolisation.

Matrix metalloproteinases: contribution to pathogenesis, diagnosis, surveillance and treatment of abdominal aortic aneurysms

BACKGROUND

Aortic abdominal aneurysm (AAA) represents a common chronic degenerative disease of the aortic wall. Chronic inflammation and enzymatic degradation of elastic lamellae and extracellular matrix (ECM) proteins constitute the most prominent characteristics of AAAs. There is mounting evidence that matrix metalloproteinases (MMPs) are the predominant proteinases in the AAA wall. These enzymes represent a potential target for therapeutic intervention to modify vascular pathology. This paper is an overview of matrix metalloproteinases and their role in the pathophysiology, diagnosis and treatment of AAA.

LITERATURE SEARCH

Comprehensive search of the MEDLINE, EMBASE and HEAL-Link databases from 1980 to 2003.

FINDINGS

Increased levels of MMPs expression and activity have been demonstrated within the aortic wall of AAA, associating with histological alterations. An imbalance between MMPs and their inhibitors (Tissue Inhibitors of Matrix Metalloproteinases - TIMPs), may tip the equilibrium towards matrix degradation. MMPs as systemic biochemical markers of AAAs may contribute to diagnosis of unsuspected AAAs or to the surveillance of patients with small AAAs. Evidence of variations in MMPs, TIMPs and their mediator genes promoting the increased inheritance susceptibility of AAAs is less well documented. However,a broad spectrum of pharmaceutical agents (e.g. doxycycline, statins etc.) is known to inhibit MMP activity and attenuate medial destruction.

CONCLUSION

Randomized clinical studies in patients in the early stages of AAA or in healthy individuals with great propensity to AAA development are required to demonstrate the causative relationship between MMPs and AAA. It still remains obscure whether long-term administration of MMP inhibitors can decelerate or even prevent the need for surgical repair.

The role of statins in vascular disease

BACKGROUND

Recent publications have highlighted the benefits of statins in non-cardiac occlusive disease but also the failure of vascular surgeons to recognise and treat the risk factors for atherosclerosis, in particular hypercholesterolaemia. The aim of this review is to clarify the current experimental and clinical evidence for the use of statins in vascular disease.

METHODS

Literature compiled from an extensive search of Medline and the Cochrane database has been used for the basis of this review.

RESULTS

Experimental and clinical evidence consistently reports that statins improve endothelial dysfunction, are anti-inflammatory, anti-proliferative, anti-thrombogenic and anti-proteolytic. These effects are known to inhibit atherogenesis and improve plaque stability. Independent groups support the use of statins in the prevention of both primary and secondary cardiac events. The National Stroke association recommends their use to reduce strokes following myocardial infarction and the Heart Protection Study reports benefits in patients with non-cardiac occlusive disease.

CONCLUSIONS

There is substantial evidence advocating the use of statins in patients with clinically significant vascular disease. In the future this may evolve to include those patients at risk from neointimal hyperplasia, aneurysmal disease and ischaemia reperfusion injury.

MT1-MMP-dependent, apoptotic remodeling of unmineralized cartilage: a critical process in skeletal growth

Skeletal tissues develop either by intramembranous ossification, where bone is formed within a soft connective tissue, or by endochondral ossification. The latter proceeds via cartilage anlagen, which through hypertrophy, mineralization, and partial resorption ultimately provides scaffolding for bone formation. Here, we describe a novel and essential mechanism governing remodeling of unmineralized cartilage anlagen into membranous bone, as well as tendons and ligaments. Membrane-type 1 matrix metalloproteinase (MT1-MMP)–dependent dissolution of unmineralized cartilages, coupled with apoptosis of nonhypertrophic chondrocytes, mediates remodeling of these cartilages into other tissues. The MT1-MMP deficiency disrupts this process and uncouples apoptotic demise of chondrocytes and cartilage degradation, resulting in the persistence of “ghost” cartilages with adverse effects on skeletal integrity. Some cells entrapped in these ghost cartilages escape apoptosis, maintain DNA synthesis, and assume phenotypes normally found in the tissues replacing unmineralized cartilages. The coordinated apoptosis and matrix metalloproteinase-directed cartilage dissolution is akin to metamorphosis and may thus represent its evolutionary legacy in mammals.

Different expression of MMPs/TIMP-1 in human atherosclerotic lesions. Relation to plaque features and vascular bed

BACKGROUND

Proteolytic imbalance might determine arterial remodeling and plaque destabilization in atherosclerotic vessels. The aim of this study was to examine differences in the patterns of metalloproteinases (MMPs) and MMP inhibitor (TIMP-1) expression in advanced human atheromas, both in relation to the plaque features and the vascular bed involved.

METHODS AND RESULTS

Immunohistochemistry for MMP-1, -3, -9 and TIMP-1 as well as the collagen content were measured in vascular sections from patients undergoing peripheral revascularization (carotid n=11, femoral n=23) and aorto-coronary bypass surgery (mammary arteries n=20, as controls). Increased expression of all MMPs was detected in atherosclerotic as compared with control sections (P<0.01). Aneurysmal plaques showed a significant increase of MMP-1 and-3 and a reduction in total collagen (P<0.05) in relation to occlusive lesions. Calcification areas in atherosclerotic plaques were consistently associated with increased TIMP-1 expression (P<0.01). Finally, MMP-9 expression was higher in occlusive lesions from carotid than femoral arteries (P<0.01).

CONCLUSIONS

Aneurysm lesions expressed higher MMP-1 and-3 expression than occlusive plaques, and MMP-9 was mainly detected in carotid as compared with femoral arteries. TIMP-1 was associated with arterial calcification. These differences in the MMPs/TIMP-1 expression might determine the evolution of advanced atherosclerotic plaques and contribute to its vulnerability.

Serum plasma pregnancy-associated protein A: a potential marker of echogenic carotid atherosclerotic plaques in asymptomatic hyperlipidemic subjects at high cardiovascular risk

OBJECTIVE

The proteolytic activity of metalloproteinases, proinflammatory enzymes that degrade extracellular matrix, is elevated in lipid-rich atherosclerotic plaques, thereby contributing to plaque fragility and rupture. Pregnancy-associated plasma protein (PAPP-A) is a metalloproteinase, expressed in unstable atherosclerotic plaques, whose circulating levels are elevated in acute coronary syndromes. We evaluated serum PAPP-A levels as a marker of the premature development of atherosclerosis in hyperlipidemic subjects at elevated cardiovascular risk.

METHODS AND RESULTS

Serum PAPP-A levels were determined in asymptomatic hyperlipidemic male subjects (n=64; mean+/-SD age, 51+/-7 years) in whom intima-media thickness (IMT) and lesion status in the carotid artery were evaluated by noninvasive ultrasonography and compared with those of a normolipidemic control group (n=25). No difference was observed in circulating PAPP-A levels between hyperlipidemic subjects and controls (8.99+/-2.93 and 8.03+/-2.75 mIU/L, respectively; mean+/-SD) nor between hyperlipidemic subjects who presented with a luminal obstruction of the carotid artery (9.26+/-2.53 mIU/L) and those who did not (8.85+/-3.29 mIU/L). By contrast, in patients with atheromatous carotid plaques, a positive association between serum levels of PAPP-A and C-reactive protein was observed (P<0.05); moreover, subjects exhibiting hyperechoic or isoechoic, echogenic lesions had significantly higher PAPP-A levels compared with those with hypoechoic lesions (10.32+/-2.72 vs 8.27+/-2.18 mIU/L, P<0.05) and with normolipidemic controls (P<0.05).

CONCLUSIONS

Elevated serum PAPP-A levels represent a potential marker of the degree of echogenicity of carotid atherosclerotic plaques in asymptomatic hyperlipidemic patients at high cardiovascular risk and equally of an enhanced local inflammatory state involving remodeling of subendothelial extracellular matrix.

Prospective, randomized, double-blind trial investigating the effect of doxycycline on matrix metalloproteinase expression within atherosclerotic carotid plaques

BACKGROUND AND PURPOSE

Elevated levels of matrix metalloproteinases (MMPs), particularly MMP-1 and MMP-9, have been implicated in plaque rupture. It has been suggested that inhibition of MMPs may stabilize vulnerable atherosclerotic plaques and improve clinical outcome. The aim of the study was to investigate the ability of doxycycline, a nonspecific MMP inhibitor, to reduce MMP concentration in carotid atheroma.

METHODS

The study design was a prospective, double-blind randomized trial. One hundred patients requiring carotid endarterectomy were randomized to receive 200 mg/d doxycycline or placebo for 2 to 8 weeks before surgery. During endarterectomy, carotid plaques were retrieved. The concentrations of MMPs and doxycycline were determined in the atherosclerotic tissue by enzyme-linked immunosorbent assay and high-performance liquid chromatography, respectively. Clinical events were recorded, as was the rate of preoperative embolization (transcranial Doppler).

RESULTS

Analysis of endarterectomized specimens demonstrated a mean doxycycline concentration of 6.0 micro g/g wet weight in treated patients. Administration of doxycycline significantly reduced the concentration of MMP-1 in carotid plaques from a mean of 14.8 to 10.3 ng/100g wet weight (P=0.038). This difference was due to decreased MMP-1 transcript (P<0.001). There was no difference in any other MMP (MMP-2, -3, or -9) or tissue inhibitor of matrix metalloproteinases-1 or -2.

CONCLUSIONS

Doxycycline penetrated atherosclerotic plaques with acceptable tissue levels. This resulted in a reduction in MMP-1 concentration because of decreased expression.