Identification of 92-kD gelatinase in human coronary atherosclerotic lesions. Association of active enzyme synthesis with unstable angina

Plaque disruption and thrombosis. Potential role of inflammation and infection

Considerable data from in vitro and in vivo studies of vascular biology, together with indirect evidence from clinical trials of lipid-lowering or modifying and lifestyle or risk factor modifying interventions, provide strong support for the concept that disruption of atherosclerotic plaque and subsequent thrombosis is a key precipitant of potentially lethal, acute coronary syndromes. Certain characteristics of plaques, including the size and composition of the lipid core, the structure and composition of the fibrous cap, and the presence of a local inflammatory process, predispose the plaque to disruption. Stresses resulting from biomechanical and hemodynamic forces acting on plaques may then trigger disruption, releasing the thrombogenic contents of the lipid core. Alterations in endothelial function may also contribute to vulnerability of plaque rupture and thrombosis. Therefore, interventions aimed at decreasing plaque vulnerability to disruption--all based on the concept of plaque stabilization--may reduce the risk of acute coronary syndromes. Although not yet rigorously validated in humans, plaque stabilization may prove to be an important clinical strategy for preventing the lethal consequences of coronary atherosclerosis.

Production and inhibition of the gelatinolytic matrix metalloproteinases in a human model of vein graft stenosis

OBJECTIVES

human vein graft stenoses are caused by intimal hyperplasia, a process which is characterised by extensive degradation and accumulation of extracellular matrix. This study investigated the role of the matrix metalloproteinases (MMPs) - the principal physiological mediators of extracellular matrix degradation - in the development of intimal hyperplasia in cultured human long saphenous vein.

DESIGN

experimental study.

MATERIALS AND METHODS

paired venous segments with the endothelium intact or denuded were cultured in standard conditions for 14 days. At the termination of culture, MMPs were extracted from one half of the tissue, whilst the remainder of the vein was prepared for histological examination.

RESULTS

stereologic analysis revealed that the endothelium intact veins developed a significantly thicker neointima when compared to the denuded venous segments (20 micron v. 0 micron, p=0.006). Quantification of MMPs by substrate gel enzymography demonstrated that the development of a neointima was associated with increased production of the gelatinolytic MMP-9 (p=0. 03) in intact veins. Immunocytochemistry showed that the MMP-9 localised to the internal elastic lumina, which suggested a role in facilitating smooth-muscle-cell migration into the intima. The role of MMPs-2 and -9 in intimal hyperplasia was further investigated by culturing intact venous segments with a therapeutic concentration of doxycycline--a potent MMP inhibitor. These experiments demonstrated that a therapeutic dose of doxycycline significantly reduced neointimal thickness (control 21 micron, doxycycline 10 mg/l-5.5 micron), in conjunction with a significant reduction in the production of MMP-9.

CONCLUSIONS

these data suggest that elevated levels of MMPs may play a significant role in the development of human intimal hyperplasia and that inhibition of these enzymes may offer a potential therapeutic strategy for the prevention of hyperplastic lesions.

Effect of the stromelysin-1 promoter on efficacy of pravastatin in coronary atherosclerosis and restenosis

It has proved difficult to identify high-risk patients for atherosclerosis and to determine how they might respond to medication. Recently, a common promoter variant of the human stromelysin-1 gene has been reported, which has been shown to affect the transcription. We investigated whether this polymorphism had any impact on the risk of events, especially restenosis and progression of coronary artery disease and whether the effect was modulated by treatment with pravastatin. The stromelysin-1 genotype was determined for 496 men with coronary artery disease and cholesterol levels between 4.0 and 8.0 mmol/L, participating in the Regression Growth Evaluation Statin Study (REGRESS) study, a clinical trial assessing the effect of the lipid-lowering drug pravastatin on the progression of atherosclerosis. Patients in the placebo group with 5A6A or 6A6A genotypes had more clinical events than patients with the 5A5A genotype (26% and 12%, respectively, p = 0.03). In the pravastatin group, the risk of clinical events in patients with 5A6A or 6A6A genotypes was lower, compared with placebo, whereas it was unchanged in those with a 5A5A genotype (p value for interaction: 0.038). Also, the incidence of repeat angioplasty in the placebo group was greater in patients with the 6A6A or 5A6A genotypes, compared with 5A homozygotes (38% and 40%, respectively, vs 11%, p = 0.09). Again, treatment substantially reduced the incidence in heterozygotes and 6A homozygotes (0% and 15%, respectively), whereas it was unchanged in 5A homozygotes (28%, p for interaction: 0.002). These effects were independent of the effects of pravastatin on the lipid levels. Thus, this study suggests that the stomelysin-1 promoter polymorphism confers a genotype-specific response to medication in determining clinical event-free survival and the risk for symptom-driven repeat angioplasty. This variant may therefore act as a predictor, not only of disease progression, but also of response to therapy and risk of restenosis.

Expression of stromelysin-3 in atherosclerotic lesions: regulation via CD40-CD40 ligand signaling in vitro and in vivo

Stromelysin-3 is an unusual matrix metalloproteinase, being released in the active rather than zymogen form and having a distinct substrate specificity, targeting serine proteinase inhibitors (serpins), which regulate cellular functions involved in atherosclerosis. We report here that human atherosclerotic plaques (n = 7) express stromelysin-3 in situ, whereas fatty streaks (n = 5) and normal arterial specimens (n = 5) contain little or no stromelysin-3. Stromelysin-3 mRNA and protein colocalized with endothelial cells, smooth muscle cells, and macrophages within the lesion. In vitro, usual inducers of matrix metalloproteinases such as interleukin-1, interferon-gamma, or tumor necrosis factor alpha did not augment stromelysin-3 in vascular wall cells. However, T cell-derived as well as recombinant CD40 ligand (CD40L, CD154), an inflammatory mediator recently localized in atheroma, induced de novo synthesis of stromelysin-3. In addition, stromelysin-3 mRNA and protein colocalized with CD40L and CD40 within atheroma. In accordance with the in situ and in vitro data obtained with human material, interruption of the CD40-CD40L signaling pathway in low density lipoprotein receptor-deficient hyperlipidemic mice substantially decreased expression of the enzyme within atherosclerotic plaques. These observations establish the expression of the unusual matrix metalloproteinase stromelysin-3 in human atherosclerotic lesions and implicate CD40-CD40L signaling in its regulation, thus providing a possible new pathway that triggers complications within atherosclerotic lesions.

Pharmacological effects of HMG CoA reductase inhibitors other than lipoprotein modulation

The HMG CoA reductase inhibitors reduce levels of low-density lipoproteins, raise high-density lipoproteins, and lower triglycerides. However, there are other pharmacological effects derived from HMG CoA reductase inhibitor therapy. Certain HMG CoA reductase inhibitors affect atherosclerotic plaque composition, endothelial function, platelet and clotting factors, and immune functioning. The unique extrahepatic pharmacological profile of agents in this class has not been fully characterized. All of the HMG CoA reductase inhibitors studied have improved endothelium-dependent vasodilatation. Vascular smooth muscle proliferation is not significantly affected by pravastatin but is by the other agents. Of all the HMG CoA reductase inhibitors, cerivastatin is the most potent inhibitor of vascular smooth muscle proliferation. Pravastatin is the only agent proven to significantly reduce platelet-thrombus formation and fibrinogen levels. Simvastatin has no effect on platelet-thrombus formation or fibrinogen levels, while atorvastatin and lovastatin have been shown to increase fibrinogen in some studies. Plasminogen activator inhibitor-1 levels are decreased by pravastatin, are not affected by atorvastatin, and are significantly increased by lovastatin and simvastatin. Pravastatin also has clinical benefits in transplant medicine as a result of inhibiting natural killer cell function, an effect that has not been explored with other HMG CoA reductase inhibitors.

Role of inflammation and metalloproteinases in plaque disruption and thrombosis

Numerous pathological, clinical, angiographic and angioscopic studies have demonstrated that acute coronary syndromes (unstable angina, acute myocardial infarction and ischemic sudden death) are most frequently the consequence of plaque disruption (plaque rupture or superficial plaque erosion) and consequent coronary thrombosis. Several serial angiographic studies have demonstrated that nearly 60-70% of acute coronary syndromes evolve from mildly to moderately obstructive atherosclerotic plaques. Coronary plaque disruption appears to be a function of both the composition of the plaque (plaque vulnerability ) as well as extrinsic triggers that may precipitate plaque disruption in a vulnerable plaque. Vulnerability for plaque disruption appears to be largely determined by the size of the lipid-rich atheromatous core, the thickness of the fibrous cap covering the core, and the presence of ongoing inflammation within and underneath the cap. Inflammatory cells may play a critical role in plaque disruption through the elaboration of matrix degrading metalloproteinases or MMPs (collagenases, gelatinases, stromelysins and matrilysin) and by inhibition of function and survival of matrix-synthesizing smooth muscle cells. Inflammatory cells may also play a critical role in triggering thrombosis following plaque disruption through the tissue factor pathway. In addition, stresses resulting from hemodynamic and mechanical forces may precipitate plaque disruption, particularly at points where the fibrous cap is weakest, such as at its shoulders. The degree of thrombosis following plaque disruption is determined by the thrombogenicity of the disrupted plaque, disturbed local rheology and systemic thrombotic-thrombolytic milieu. Surges in sympathetic activity provoked by sudden vigorous exercise, emotional stress -- including anger, or cold weather, may also trigger plaque disruption. These observations have led to the concept of plaque stabilization as a new clinical strategy for the prevention of acute coronary syndromes. Plaque stabilization can be achieved through pharmacologic and lifestyle-modifying interventions that reduce vulnerability to plaque disruption by altering plaque composition and/or inflammatory activity within the plaque.

Peroxisome proliferator-activated receptor gamma activators inhibit gene expression and migration in human vascular smooth muscle cells

Migration of vascular smooth muscle cells (VSMCs) plays an important role in atherogenesis and restenosis after arterial interventions. The expression of matrix metalloproteinases (MMPs), particularly MMP-9, contributes to VSMC migration. This process requires degradation of basal laminae and other components of the arterial extracellular matrix. Peroxisome proliferator-activated receptors (PPARs), members of the nuclear receptor family, regulate gene expression after activation by various ligands. Recent studies have suggested opposing effects of PPAR gamma (PPARgamma) activation on atherogenesis. The present study tested the hypotheses that human VSMCs express PPAR alpha (PPARalpha) and PPARgamma and that PPAR agonists in VSMCs modulate MMP-9 expression and activity, as well as VSMC migration. Human VSMCs expressed PPARalpha and PPARgamma mRNA and protein. Treatment of VSMCs with the PPARgamma ligands troglitazone and the naturally occurring 15-deoxy-Delta12, 14-prostaglandin J2 (15d-PGJ2) decreased phorbol 12-myristate 13-acetate-induced MMP-9 mRNA and protein levels, as well as MMP-9 gelatinolytic activity in the supernatants in a concentration-dependent manner. Six different PPARalpha activators lacked such effects. Addition of prostaglandin F2alpha, known to limit PPARgamma activity, diminished the MMP-9 inhibition seen with either troglitazone or 15d-PGJ2, further implicating PPARgamma in these effects. Finally, troglitazone and 15d-PGJ2 inhibited the platelet-derived growth factor-BB-induced migration of VSMCs in vitro in a concentration-dependent manner. PPARgamma activation may regulate VSMC migration and expression and activity of MMP-9. Thus, PPARgamma activation in VSMCs, via the antidiabetic agent troglitazone or naturally occurring ligands, may act to counterbalance other potentially proatherosclerotic PPARgamma effects.

Tissue inhibitors of metalloproteinases and metalloproteinases in atherosclerosis

The ability of the metalloproteinases to degrade extracellular matrix proteins is essential for the matrix remodelling that occurs during infiltration of inflammatory cells, intimal thickening, angiogenesis and plaque rupture which are a result of atherosclerosis. Increased metalloproteinase activity therefore requires stimulation of metalloproteinase expression by cytokines and growth factors, activation of metalloproteinases, and downregulation of tissue inhibitors of metalloproteinases. In addition, metalloproteinases may influence atherosclerosis by processing of proteins involved in inflammation and cell growth and death and the tissue inhibitors of metalloproteinases may also play a less inhibitory role by influencing cell growth and apoptosis.

Glycoprotein IIb/IIIa inhibitors in acute coronary syndromes: pathophysiologic foundation and clinical findings

The pathophysiologic basis for potent platelet inhibition in the acute coronary syndromes has been established. In the setting of PTCA for unstable angina and non-Q-wave myocardial infarction, there are clear data for a benefit of GP IIb/IIIa inhibition, whereas for primary PTCA in evolving myocardial infarction, preliminary data are very encouraging and a large-scale clinical trial is nearly completed. Glycoprotein IIb/IIIa inhibition as an adjunct to medical therapy for unstable angina is also the subject of encouraging preliminary data, and 3 large-scale clinical trials have just been completed. Preliminary data have also been accrued for GP IIb/IIIa inhibition as conjunctive therapy with thrombolytic agents, and large clinical trials are now commencing.

Marimastat inhibits neointimal thickening in a model of human vein graft stenosis

BACKGROUND

There is now accumulating evidence that matrix metalloproteinases (MMPs), the physiological mediators of matrix deposition and degradation, play an important role in the development of intimal hyperplasia following arterial bypass. This study investigated the effect of marimastat, an orally active specific MMP inhibitor, on neointima formation in cultured human saphenous vein.

METHODS

Segments of human saphenous vein obtained from ten patients undergoing arterial bypass surgery were cultured for 14 days in serum-supplemented RPMI medium (controls) or in control medium supplemented with marimastat at three different concentrations (treatment groups). Following culture, half of each segment was prepared for histological examination and MMPs were extracted from the other half for gelatin zymography.

RESULTS

Marimastat inhibited neointimal thickening in a concentration-dependent manner; inhibition was significant at 10(-5) and 10(-6) mol/l (P=0.006). This observation was paralleled by a significant reduction in the levels of MMP-2 and MMP-9 in the tissues.

CONCLUSION

Marimastat significantly reduced neointimal thickening in this laboratory model. MMP inhibitors may offer a potential therapeutic strategy in the prevention of intimal hyperplasia.

Mast cell infiltration in acute coronary syndromes: implications for plaque rupture

OBJECTIVES

To define the role of mast cells in plaque destabilization.

BACKGROUND

Inflammation is an essential feature of human coronary plaques. Macrophages and T lymphocytes are considered to contribute to destabilization of the plaques. The role of mast cells in this setting is less well studied. We therefore counted the mast cells in coronary atherectomy specimens from patients with chronic stable angina, unstable angina and severe unstable angina.

METHODS

Patients studied had chronic stable angina (group 1, n=11), "stabilized" unstable angina (group 2; Braunwald's class I and II, n=11) and "refractory" unstable angina (group 3; Braunwald's class III, n=7). Samples of culprit lesions (n=29) were obtained by directional atherectomy, snap-frozen and analyzed immunohistochemically. The numbers of mast cells and T lymphocytes per square millimeter squared were counted and the areas containing macrophages and smooth muscle cells were measured by computed planimetry.

RESULTS

We found that the numbers of mast cells and T lymphocytes increased from group 1 through groups 2 to 3. Specimens from group 3 also contained the largest numbers of tumor necrosis factor alpha (TNF-alpha)-positive mast cells and of matrix metalloproteinase (MMP)-9 (92 kD gelatinase)-positive macrophages.

CONCLUSIONS

Unstable coronary syndromes are associated with increased numbers of mast cells in culprit lesions. Activated mast cells secrete neutral proteases capable of degrading the extracellular matrix and TNF-alpha, capable of stimulating macrophages to synthesize MMP-9. Our observations suggest that mast cells, in addition to macrophages, contribute to matrix degradation and, hence, to progression of coronary syndromes.

Peripheral blood levels of matrix metalloproteases-2 and -9 are elevated in patients with acute coronary syndromes

OBJECTIVES

This study was sought to investigate whether peripheral blood levels of matrix metalloproteases (MMPs) are affected in patients with acute coronary syndromes (ACS).

BACKGROUND

Synthesis of MMPs has been reported in coronary atherosclerotic lesions in patients with unstable angina (UA), suggesting a pathogenic role of MMPs in the development of ACS.

METHODS

Using sandwich enzyme immunoassay, serum MMP-2 and plasma MMP-9 were measured in 33 patients with ACS (22 with acute myocardial infarction [AMI], 11 with UA), 17 with stable effort angina (EA) and 17 normal control subjects.

RESULTS

Serum MMP-2 in patients with UA and AMI on day 0 was two times greater than that in control subjects, and patients with EA showed higher MMP-2 levels than those in control subjects. Plasma MMP-9 in patients with UA and AMI on day 0 was elevated by threefold and twofold versus that in control subjects, respectively. In patients with UA and AMI who underwent medical treatment (n = 11 and 13, respectively), MMP-2 elevation was sustained until day 7. In patients with UA, MMP-9 elevation on day 0 was followed by a gradual decrease toward the control range up to day 7. Some patients with AMI showed a transient MMP-9 elevation with a peak on day 3, whereas in others, MMP-9 levels were significantly elevated on day 0 and remained higher than those in control subjects up to day 3.

CONCLUSIONS

Serial changes in serum MMP-2 and plasma MMP-9 were documented in patients with ACS. These findings provide an insight into the molecular mechanism of plaque destabilization.

The 5A/6A polymorphism in the promoter of the stromelysin-1 (MMP-3) gene predicts progression of angiographically determined coronary artery disease in men in the LOCAT gemfibrozil study. Lopid Coronary Angiography Trial

The relationship between the 5A/6A stromelysin-1 promoter polymorphism and progression of angiographically determined coronary artery disease (CAD) has been examined in men treated for 32 months with gemfibrozil or placebo in the Lopid Coronary Angiography Trial (LOCAT). The frequency of the 5A allele was 0.40 (95%, CI, 0.36-0.43), and in the sample as a whole 12% of the men were homozygous for the 5A allele. In the placebo group, diffuse progression of disease was, on average, completely prevented in men with the genotype 5A/5A as measured by a 0.30% increase in mean average diameter of the coronary artery segments (ADS), compared with a mean 1.79% decrease in the combined group with the genotype 5A6A or 6A6A (mean +/- S.E.M., +0.007 +/- 0.020 mm vs. -0.043 +/- 0.0.08 mm, P = 0.03). A similar relationship with genotype was seen for disease progression determined by the mean minimal luminal diameter (MLD); with the 5A5A group decreasing by an average of 1.72% compared with 5.54% in the 5A/6A plus 6A/6A group (-0.029 +/- 0.034 mm vs. -0.102 +/- 0.013 mm, P = 0.06). In the gemfibrozil-treated group, the effect on disease progression associated with the 5A/6A alleles was of a similar pattern as in the placebo group, but the effect was less marked and was not statistically significant. This study confirms the previously reported beneficial effect on disease progression associated with the 5A allele and raises the possibility that patients with CAD who are homozygous for the 6A allele, and who represent 25-30% of the population, may be at particular risk of rapid progression of disease and may require particularly aggressive lipid lowering therapy to prevent disease progression.

Binding of latent matrix metalloproteinase 9 to fibrin: activation via a plasmin-dependent pathway

The binding of two matrix metalloproteinases (MMP) to fibrin was evaluated. MMP-2 (72-kDa) and MMP-9 (92-, 130-, and 225-kDa) were selected since both contain a fibronectin-like region and fibronectin binds fibrin. Gelatin zymography indicated selective and dose dependent binding of MMP-9 to fibrin. No MMP-2 binding to fibrin occurred. Densitometry revealed that the 130- and 225-kDa forms demonstrated similar sigmoidal binding profiles whereas 92-kDa uptake was hyperbolic. Fibronectin and TIMP-1 competition studies indicated that the fibronectin and C-terminal MMP-9 domains, respectively, were not involved with fibrin binding. The MMP-9 collagen-like region may be of regulatory significance since type I and II fibrillar and type IV basement membrane collagens demonstrated fibrin binding. During fibrinolysis, latent fibrin-bound MMP-9 was processed to lower molecular weight forms consistent with proteolytic activation. This process was inhibited by epsilon-aminocaproic acid, indicating a plasmin-dependent pathway. The significance of these findings to procoagulant activity and MMP-mediated extracellular matrix destruction during inflammation and tumor invasion and metastasis is discussed.

Gelatinase B in proliferative vitreoretinal disorders

PURPOSE

To investigate whether gelatinases A and B are involved in the pathogenesis of proliferative vitreoretinal disorders.

METHODS

In a prospective study of 101 consecutive patients, vitreous and paired serum samples were obtained from 38 patients with rhegmatogenous retinal detachment complicated by proliferative vitreoretinopathy, 25 patients with rhegmatogenous retinal detachment with no proliferative vitreoretinopathy, and 38 patients with proliferative diabetic retinopathy. Gelatinase activities were determined by quantitative zymography.

RESULTS

All vitreous samples contained comparable levels of the constitutive gelatinase A. Inducible gelatinase B was detected in eight (32%) of 25 vitreous samples from patients with rhegmatogenous retinal detachment with no proliferative vitreoretinopathy (mean +/- SD, 319.5 +/- 521.0 scanning units), in 17 (44.7%) of 38 vitreous samples from patients with proliferative vitreoretinopathy (560.6 +/- 718.9 scanning units), and in 34 (89.5%) of 38 vitreous samples from patients with proliferative diabetic retinopathy (1,707.2 +/- 1,220.3 scanning units). The incidence of detection of gelatinase B in proliferative diabetic retinopathy cases was significantly higher than it was in rhegmatogenous retinal detachment with no proliferative vitreoretinopathy and proliferative vitreoretinopathy cases (P < .001). Gelatinase B levels in the vitreous samples of patients with proliferative diabetic retinopathy were higher than the levels found in patients with rhegmatogenous retinal detachment with no proliferative vitreoretinopathy and in patients with proliferative vitreoretinopathy (P = .0152). Gelatinase A was detected in all the tested sera, whereas none of the tested paired serum samples contained detectable gelatinase B activity.

CONCLUSIONS

Gelatinase B may play an important role in extracellular matrix degradation associated with neovascularization in proliferative diabetic retinopathy.

Matrix metalloproteinases and tissue inhibitors of metalloproteinases in giant cell arteritis: an immunocytochemical study

Giant cell arteritis (GCA) is a relatively common granulomatous arteritis of unknown etiology which mainly occurs in elderly people. Using histopathological findings from-seven biopsy cases of temporal artery and one autopsy case of GCA, and performing immunocytochemical staining for matrix metalloproteinase (MMP)-2 and -9 and tissue inhibitor of matrix metalloproteinase (TIMP)-1 and -2, we tested the hypothesis that an imbalance between MMPs and TIMPs may be a critical determinant in developing severe intimal hyperplasia and luminal stenosis. All biopsy cases revealed nearly complete luminal occlusion of the temporal artery with active lymphocytic infiltrate, fragmentation of internal lamina and median elastic fibers. Four of seven cases revealed typical GCA. The autopsy case was systematically sampled for histological examination, revealing GCA in the ascending aorta, main branches of aorta and coronary artery. Immunocytochemical staining revealed intense staining for MMP-2 and -9 in fragmented media of the aorta and artery, and less positive staining for TIMP-1 and -2 at the MMP-positive media. In situ hybridization revealed intense positive staining for TIMPs in GCA despite weak immunocytochemical staining for TIMPs. Control cases were negative for TIMPs by immunocytochemical staining whereas RNA message level was mildly positive at a lesser intensity than that of GCA. Granulomatous tissue of fibroblasts and giant cells were most intensely positive for MMPs. The presence of markedly increased MMPs and less increased TIMPs in GCA may implicate an MMPs-TIMPs imbalance in the pathogenesis of GCA.

Matrix metalloproteinases and coronary artery disease: a novel therapeutic target

Matrix metalloproteinases (MMP) are a family of enzymes that selectively digest individual components of the extracellular matrix. Their function has been studied in both normal physiologic processes and pathologic states. In the blood vessel, MMPs play an important role in maintaining the vessel's integrity by breaking down extracellular matrix while new matrix is being synthesized. This is necessary to avoid weakening from continuous mechanical stresses. However, in certain environments, these MMPs may contribute to cardiovascular pathologic processes. The purpose of this review is to first discuss the role of MMPs in coronary vascular disease. Evidence suggests that MMPs contribute to the development of de novo atherosclerotic plaques and postangioplasty restenotic plaques by allowing smooth muscle cells to migrate from the vascular media to the intima. Evidence also suggests that MMPs contribute to the rupture of these plaques by degrading the fibrous cap that surrounds them. With this increased molecular information that concerns the pathogenesis of coronary vascular disease, new molecular therapies aimed at altering these processes are being investigated. The rationale, mode of delivery, and prospects for success of these therapies will also be discussed here.

Localization of distinct F2-isoprostanes in human atherosclerotic lesions

F2-Isoprostanes are prostaglandin (PG) isomers formed in situ in cell membranes by peroxidation of arachidonic acid. 8-epi PGF2alpha and IPF2alpha-I are F2-isoprostanes produced in humans which circulate in plasma and are excreted in urine. Measurement of F2-isoprostanes may offer a sensitive, specific, and noninvasive method for measuring oxidant stress in clinical settings where reactive oxygen species are putatively involved. We determined whether isoprostanes were present in human atherosclerotic lesions, where lipid peroxidation is thought to occur in vivo. 8-epi PGF2alpha ranged from 1.310-3.450 pmol/micromol phospholipid in atherectomy specimens compared with 0.045-0.115 pmol/micromol phospholipid (P < 0.001) in vascular tissue devoid of atherosclerosis. Corresponding values of IPF2alpha-I were 5.6-13.8 vs. 0.16-0.44 pmol/micromol phospholipid (P < 0.001). Levels of the two isoprostanes in vascular tissue were highly correlated (r = 0.80, P < 0.0001). Immunohistochemical studies confirmed that foam cells adjacent to the lipid necrotic core of the plaque were markedly positive for 8-epi PGF2alpha. These cells were also reactive with anti-CD68, an epitope specific for human monocyte/macrophages. 8-epi PGF2alpha immunoreactivity was also detected in cells positive for anti-alpha-smooth muscle actin antibody, which specifically recognizes vascular smooth muscle cells. Our results indicate that 8-epi PGF2alpha and IPF2alpha-I, two distinct F2-isoprostanes and markers of oxidative stress in vivo, are present in human atherosclerotic plaque. Quantitation of these chemically stable products of lipid peroxidation in target tissues, as well as in biological fluids, may aid in the rational development of antioxidant drugs in humans.

The way ahead in the management of unstable coronary artery disease

Recent knowledge of the composition of coronary plaques is briefly reviewed, including factors that are considered to be responsible for the provocation of instability. Based on this information, possibilities for the early detection of threatening instability and measures to prevent destabilization of coronary plaques and to counteract thrombus formation are discussed.

Intravascular ultrasonic evidence for importance of plaque distribution (eccentric vs circumferential) in determining distensibility of the left anterior descending artery

Although previous studies have shown that coronary atherosclerosis is accompanied by impaired vessel wall compliance, few data exist regarding the regional vessel distensibility that may be important in order to gain an insight into the mechanism of atherosclerotic plaque rupture. Therefore, we analyzed 45 coronary sites of the proximal left anterior descending artery from 40 patients. Using intravascular ultrasound, luminal area in diastole (A) and in systole was measured at the diseased sites. With the ratio of luminal area changes (dA) to coronary pressure changes (dP) during a cardiac cycle, the total distensibility index was obtained by the formula: [(dA/A)/dP] x 10(3). At the sites with noncircumferential disease perimeters in diastole (L) and in systole were measured at the normal and narrowed portions. Using the changes in perimeters (dL) during a cardiac cycle, the regional distensibility index was obtained by the formula: [(dL/L)/dP] x 10(3). In 22 sites with circumferential disease, the total distensibility index was 1.03 +/- 0.61/mm Hg (mean +/- SD), and significantly lower than that from 23 sites with noncircumferential disease that showed 1.45 +/- 0.89/mm Hg (p <0.05). In noncircumferential disease, the regional distensibility index at narrowed portions was significantly lower, 0.33 +/- 0.47/mm Hg, than that at normal portion, 1.11 +/- 0.75/mm Hg (p <0.01), suggesting the heterogenous distribution of regional wall distensibility in noncircumferential lesions. These results indicate that the heterogeneous regional wall distensibility exists at the sites with noncircumferential disease where the total vessel distensibility is preserved by the presence of the compliant normal portion.

Differential expression of 92-kDa gelatinase in primary atherosclerotic versus restenotic coronary lesions

Rupture of atherosclerotic plaque resulting in intravascular thrombosis and myocardial infarction (MI), while a common sequelae of de novo atherosclerotic lesions, is an uncommon consequence of restenosis. We hypothesize that the rarity of MI associated with restenotic lesions is a result of cellular and biochemical modifications induced by the local response to mechanical injury rendering the site resistant to rupture. Clinical and angiographic features of patients presenting with symptomatic primary (n = 24) or restenotic coronary lesions (n = 12) who underwent directional atherectomy were compared. Histologic analysis and immunostaining for 92-kDa gelatinase were performed on each atherectomy specimen. There was no significant difference between the 2 groups regarding age, gender, incidence of diabetes, smoking, hypertension, hypercholesterolemia, or previous MI. Lesion length, extent, and distribution of disease and percent stenosis were not significantly different between groups. However, 8% of primary lesions were hypercellular compared with 75% of restenotic specimens (p = 0.0001). Hypercellularity in restenotic specimens was shown by adjacent section staining to be composed of smooth muscle cells. Ninety-two kDa gelatinase was expressed in 79% of primary lesions versus 0% of restenotic specimens (p = 0.0001). Thrombus was identified in 54% of primary lesions versus 22% of restenotic lesions (p <0.05). These findings suggest that, independent of clinical or angiographic influences, balloon injury induces increased lesion cellularity and reduced expression of 92-kDa gelatinase, possibly resulting in a reduced propensity for plaque rupture and thrombosis.

Medial elastic structure alterations in atherosclerotic arteries in minipigs: plaque proximity and arterial site specificity

Using a model of atherosclerosis in minipigs, we analyzed changes in elastic structure within the medial sections of the abdominal aorta and left interventricular coronary artery both in the vicinity of and distal to atheromatous plaques. Twenty-four animals, divided into three groups, were fed either a control diet or a hypercholesterolemic and hyperhomocysteinic atherogenic diet, alone or in association with an antihypertensor, namely isosorbide dinitrate (Risordan). The atherogenic diet, administered for a period of four months, induced in the minipig advanced noncalcified atherosclerotic lesions that were histologically similar to those found in humans. A morphodensitometric analysis of the medial elastic structures was carried out on images obtained from specifically stained transverse arterial sections examined under a light microscope. The volume density of the elastic structures was diminished in the arterial media of the atherosclerotic animals due to opening and widening of the fenestrae in the elastic laminate and increased communication between the interlamellar spaces. Whereas this elastolytic process was uniform and independent of the proximity of atheromatous plaques in the left interventricular coronary artery, it was intensified in the vicinity of the plaques in the abdominal aorta. Overall elastolytic activity was increased in the walls of atheromatous artery in both arterial sites, and metalloproteinases were implied in this increase of activity. We previously reported that treatment with isosorbide dinitrate significantly reduced the moderate systolic hypertension and the increase in transparietal stress observed in the abdominal aorta of atheromatous animals. We report here that isosorbide dinitrate prevented the atherogenic-diet-induced deterioration of the elastic structure in these arteries; complete inhibition of changes to the elastic laminae was evident in areas remote from plaque formation, but only partial inhibition in the vicinity of such plaques. It did not, however, prevent structural damage in the left interventricular coronary artery or modify the increase in parietal elastolytic activity in either of the two arteries. This suggests that damage to the elastic structure in atheromatous arteries is dependent not only on overall elastolytic activity but also on localized factors, possibly related to parietal stresses, affected by the presence of atheromatous plaques.

Reactive oxygen species produced by macrophage-derived foam cells regulate the activity of vascular matrix metalloproteinases in vitro. Implications for atherosclerotic plaque stability

Vulnerable areas of atherosclerotic plaques often contain lipid-laden macrophages and display matrix metalloproteinase activity. We hypothesized that reactive oxygen species released by macrophage-derived foam cells could trigger activation of latent proforms of metalloproteinases in the vascular interstitium. We showed that in vivo generated macrophage foam cells produce superoxide, nitric oxide, and hydrogen peroxide after isolation from hypercholesterolemic rabbits. Effects of these reactive oxygens and that of peroxynitrite, likely to result from simultaneous production of nitric oxide and superoxide, were tested in vitro using metalloproteinases secreted by cultured human vascular smooth muscle cells. Enzymes in culture media or affinity-purified (pro-MMP-2 and MMP-9) were examined by SDS-PAGE zymography, Western blotting, and enzymatic assays. Under the conditions used, incubation with xanthine/xanthine oxidase increased the amount of active gelatinases, while nitric oxide donors had no noticeable effect. Incubation with peroxynitrite resulted in nitration of MMP-2 and endowed it with collagenolytic activity. Hydrogen peroxide treatment showed a catalase-reversible biphasic effect (gelatinase activation at concentrations of 4 microM, inhibition at > or = 10-50 microM). Thus, reactive oxygen species can modulate matrix degradation in areas of high oxidant stress and could therefore contribute to instability of atherosclerotic plaques.

Elevated levels of 92-kd type IV collagenase (matrix metalloproteinase 9) in giant cell arteritis

OBJECTIVE

To determine if circulating gelatinase activity and matrix metalloproteinase 9 (MMP-9) (gelatinase B, or 92-kd type IV collagenase) antigenic levels are elevated in sera of patients with giant cell arteritis (GCA), and to ascertain if MMP-9 messenger RNA (mRNA) is deposited in situ at sites of disease involvement.

METHODS

Serum samples were collected from 12 patients with GCA and 12 healthy volunteers. Vascular tissue was obtained at the time of temporal artery biopsy. Type IV collagenase activity was determined by gelatin substrate zymography and the quantitative biotinylated gelatin substrate degradation assay. A double-sandwich immunoassay utilizing 2 different isotypes of monoclonal antibodies generated against MMP-9 was used for measuring serum MMP-9 antigenic levels. Finally, to localize sites of MMP-9 mRNA transcription in inflamed arteries, the method of reverse transcriptase in situ polymerase chain reaction (RTisPCR) was utilized.

RESULTS

Serum gelatinase activity and MMP-9 titers were significantly increased in patients with GCA (mean +/- SEM 198.9 +/- 36.9 micrograms gelatin/hour/ml serum, versus 21.2 +/- 4.0 in controls; P = 0.0006). The differences in antigenic MMP-9 levels were even more prominent (3005.4 +/- 900.6 ng/ml and 31.6 +/- 9.8 ng/ml in GCA and control sera, respectively; P = 0.007). By RTisPCR, MMP-9 mRNA was mainly detected in cytoplasm of cells resembling smooth muscle cells and fibroblasts in regions of fragmented elastic tissue in the lamina media.

CONCLUSION

Gelatinase activity, and specifically MMP-9 levels, are substantially elevated in sera of patients with GCA. Detection of MMP-9 mRNA in the lamina media of inflamed vasculature suggests that degradation of intercellular matrix, particularly elastic fibers, may play a key role in the pathogenesis of GCA. Further studies are needed to determine if the circulating MMP-9 level could be utilized as a clinical marker of disease activity.

Clinically stable angina pectoris is not necessarily associated with histologically stable atherosclerotic plaques

OBJECTIVE

To investigate the extent of plaque inflammation in culprit lesions of patients with chronic stable angina.

DESIGN

Retrospective study.

SETTING

Amsterdam reference centre.

SUBJECTS

89 consecutive patients who underwent directional coronary atherectomy, 58 of whom met the following inclusion criteria: chronic stable angina (Canadian Cardiovascular Society classification 1-3 (group 1, n = 28)); unstable angina (Braunwald class II (group 2, n = 18)); unstable angina (Braunwald class III (group 3, n = 12)).

INTERVENTIONS

Directional atherectomy in patients with angina pectoris.

MAIN OUTCOME MEASURES

Tissue areas of culprit lesions occupied by inflammatory cells and smooth muscle cells related to clinically defined ischaemic syndrome.

RESULTS

Areas (% of total surface area (mean (SEM)) rich in smooth muscle cells were larger in patients with chronic stable angina (group 1, 51.2 (20.9)) than in those with unstable angina (group 2, 42.1 (20.5); group 3, 29.5 (19.4)) (1 v 2 and 2 v 3, NS; 1 v 3, P < 0.004). Macrophage rich areas were significantly smaller in patients with stable angina (group 1, 21.8 (11.9)) than in those with unstable angina (group 2, 31.5 (14.6); group 3, 46.4 (16.7)) (1 v 2, P < 0.02; 2 v 3, P < 0.02; 1 v 3, P < 0.001). Mean numbers of T cells per mm2 were as follows: group 1, 17 (9.4); group 2, 25 (15.9); group 3, 41 (30.6) (1 v 2, P 0.04; 2 v 3, P 0.07; 1 v 3, P < 0.001). Areas with HLA-DR positive cells showed the same pattern as macrophages and T cells and were smaller in stable (29.9 (12.4)) than in unstable angina (group 2, 40.4 (17.6); group 3, 52.4 (12.0)) (1 v 2, P < 0.02; 2 v 3, P < 0.05; 1 v 3, P < 0.001).

CONCLUSION

The inverse relation between the extent of inflammatory activity in plaque tissues of culprit lesions and the clinical stability of the ischaemic syndrome supports the concept that reduction of inflammation favours plaque stabilisation. At the same time, the considerable overlap between groups indicates that patients with clinically stable angina do not all have histologically stable plaques.

Matrilysin is expressed by lipid-laden macrophages at sites of potential rupture in atherosclerotic lesions and localizes to areas of versican deposition, a proteoglycan substrate for the enzyme

Certain matrix metalloproteinases (MMP) are expressed within the fibrous areas surrounding acellular lipid cores of atherosclerotic plaques, suggesting that these proteinases degrade matrix proteins within these areas and weaken the structural integrity of the lesion. We report that matrilysin and macrophage metalloelastase, two broad-acting MMPs, were expressed in human atherosclerotic lesions in carotid endarterectomy samples (n = 18) but were not expressed in normal arteries (n = 7). In situ hybridization and immunohistochemistry revealed prominent expression of matrilysin in cells confined to the border between acellular lipid cores and overlying fibrous areas, a distribution distinct from other MMPs found in similar lesions. Metalloelastase was expressed in these same border areas. Matrilysin was present in lipid-laden macrophages, identified by staining with anti-CD-68 antibody. Furthermore, endarterectomy tissue in organ culture released matrilysin. Staining for versican demonstrated that this vascular proteoglycan was present at sites of matrilysin expression. Biochemical studies showed that matrilysin degraded versican much more efficiently than other MMPs present in atherosclerotic lesions. Our findings suggest that matrilysin, specifically expressed in atherosclerotic lesions, could cleave structural proteoglycans and other matrix components, potentially leading to separation of caps and shoulders from lipid cores.

Elafin, a serine elastase inhibitor, attenuates post-cardiac transplant coronary arteriopathy and reduces myocardial necrosis in rabbits afer heterotopic cardiac transplantation

We have related experimentally induced post-cardiac transplant coronary arteriopathy to increased elastolytic activity, IL-1beta, fibronectin-mediated inflammatory and smooth muscle cell (SMC) migration, and SMC proliferation. Since our in vitro studies show that a serine elastase releases SMC mitogens and facilitates IL-lbeta induction of fibronectin, we hypothesized that administration in vivo of the specific serine elastase inhibitor, elafin, would decrease the post-cardiac transplant coronary arteriopathy. Cholesterol-fed rabbits underwent a heterotopic cardiac transplant without immunosuppression and received elafin (1.79 mg/kg per d continuous infusion after a 9 mg bolus, n = 6) or vehicle (n = 6). 1 wk later, hearts were harvested for morphometric, immunohistochemical, and biochemical analyses. A > 70% decrease in the total number of coronary arteries with intimal thickening in elafin-treated compared to control donor hearts (P < 0.002) was associated with reduced vascular elastolytic activity judged by fewer breaks in the internal elastic lamina (P < 0.03), less accumulation of immunoreactive fibronectin (P < 0.02), and reduced cell proliferation quantified by proliferating cell nuclear antigen (P < 0.0001). Despite myocardial lymphocytic infiltration, wet weight of elafin-treated donor hearts was reduced by 50% compared to untreated controls (P < 0.002) and associated with relative preservation of myocyte integrity, instead of extensive myocardial necrosis (P < 0.004). This protective effect correlated with decreased myocardial elastolytic activity (P < 0.0001) and inflammatory cell proliferation (P < 0.0001) and with an elafin-inhibitable elastase in lymphocytes. Serine elastase activity thus appears an important therapeutic target for post-cardiac transplant coronary arteriopathy and myocardial necrosis induced by rejection.

Progression of coronary atherosclerosis is associated with a common genetic variant of the human stromelysin-1 promoter which results in reduced gene expression

There is a common polymorphism in the promoter sequence of the human stromelysin-1 gene, with one allele having a run of six adenosines (6A) and the other five adenosines (5A). We have previously reported, in a 3-year follow-up study of patients with coronary atherosclerosis, that those patients who are homozygous for the 6A allele show a more rapid progression of the disease. In this study, we have investigated whether the 5A/6A promoter polymorphism plays a role in the regulation of stromelysin-1 gene expression. In transient transfection experiments, a stromelysin-1 promoter construct with 6A at the polymorphic site was found to express less of the chloramphenicol acetyltransferase reporter gene than a construct containing 5A. Electrophoretic mobility shift assay and DNase I footprinting revealed the interaction of one or more nuclear protein(s) with the DNA sequence at the 5A/6A polymorphic site. The binding of one of the nucleoprotein factors was more readily detectable with an oligonucleotide probe corresponding to the 6A allele as compared with a probe corresponding to the 5A allele. Replacing the core binding sequence with a random DNA sequence abolished the interaction between the nuclear protein(s) and the probe and also increased reporter gene expression in transiently transfected cells. Thus, the common 5A/6A polymorphism of the human stromelysin-1 promoter appears to play an important role in regulating stromelysin-1 gene expression and may be involved in the progression of coronary heart disease.

Pathophysiology and inflammatory aspects of plaque rupture

Atherosclerotic plaque disruption with superimposed thrombosis is the main cause of acute coronary events. At present it is not known specifically how various risk factors influence the development and configuration of coronary plaques. The risk of plaque disruption depends more on plaque composition and vulnerability (plaque type) than on the degree of stenosis (plaque size). Lipid accumulation and chronic inflammation, particularly macrophage activities, seem to influence the development and the stability of a plaque and thus its propensity to rupture. Macrophages have the ability to secrete proteolytic enzymes and often infiltrate the region of imminent plaque rupture, and disruption may be associated with a generalized inflammatory reaction. Further, plaque disruption tends to occur at points where the plaque surface is weakest, corresponding to locations where mechanical and hemodynamic forces have their highest impact. The risk of plaque disruption is a function of both plaque vulnerability (intrinsic disease) and rupture triggers (extrinsic forces). The former predisposes the plaque to rupture; the latter may precipitate rupture. The danger of vulnerable plaques, however, is not related to disruption as such but to the resulting thrombosis. The magnitude of this thrombotic response and the ensuing flow obstruction depends on the contents and quantity of exposed thrombogenic plaque material, the degree of pre-existing stenosis, and the systemic thrombotic tendency. The thrombotic response is a dynamic process that is decisive for the clinical presentation and the outcome.

Gene therapy for the vulnerable plaque

Acute coronary events result from the rupture of an atherosclerotic plaque, leading to formation of an occlusive coronary thrombus. Recent developments in the field of gene transfer provide the opportunity to genetically modify cells involved in plaque rupture as well as thrombus formation and thus prevent acute coronary syndromes. A first approach consists of transferring genes, the product of which may stabilize the vulnerable plaque by reducing the plaque content in lipids and macrophages. Alternatively, the introduction into the atherosclerotic plaque of genes encoding for thrombolytic proteins or growth factors able to restore physiologic antithrombotic functions of endothelial cells may inhibit thrombus formation should the plaque rupture. The success of such strategies depends on the efficiency with which the transgene is introduced and expressed into the target cell, the duration of transgene expression and the ability of the transgene product to ultimately prevent plaque rupture or thrombus formation, or both.