Proliferation in primary and restenotic coronary atherectomy tissue. Implications for antiproliferative therapy

Molecular control of vascular smooth muscle cell differentiation

Changes in the differentiated state of the vascular smooth muscle cell (SMC) including enhanced growth responsiveness, altered lipid metabolism, and increased matrix production are known to play a key role in development of atherosclerotic disease. As such, there has been extensive interest in understanding the molecular mechanisms and factors that regulate differentiation of vascular SMC, and how this regulation might be disrupted in vascular disease. Key questions include determination of mechanisms that control the coordinate expression of genes required for the differentiated function of the smooth muscle cell, and determination as to how these regulatory processes are influenced by local environmental cues known to be important to control of smooth muscle differentiation. Of particular interest, a number of common cis regulatory elements including highly conserved CArG [CC(A/T)6GG] motifs or CArG-like motifs and a TGF beta control element have been identified in the promoters of virtually all smooth muscle differentiation marker genes characterized to date including smooth muscle alpha-actin, smooth muscle myosin heavy chain, telokin, and SM22 alpha and shown to be required for expression of these genes both in vivo and in vitro. In addition, studies have identified a number of trans factors that interact with these cis elements, and shown how the expression or activity of these factors is modified by local environmental cues such as contractile agonists that are known to influence differentiation of smooth muscle.

Serial volumetric (three-dimensional) intravascular ultrasound analysis of restenosis after directional coronary atherectomy

OBJECTIVES

We report the use of three-dimensional (volumetric) intravascular ultrasound (IVUS) analysis to assess serial changes after directional coronary atherectomy (DCA).

BACKGROUND

Recent serial planar IVUS studies have described a decrease in external elastic membrane (EEM) area following catheter-based intervention as an important mechanism of late lumen renarrowing.

METHODS

Thirty-one patients with de novo native coronary lesions treated with DCA in the Serial Ultrasound Restenosis (SURE) Trial and in Optimal Atherectomy Restenosis Study (OARS) were enrolled in this study. Serial IVUS was performed before and after intervention and at 6 months' follow-up. In a subgroup of 18 patients from the SURE trial, IVUS was also performed at 24 h and at 1 month postintervention. Segments, 20-mm-long (200 image slices), were analyzed using a previously validated three-dimensional, computerized, automated edge-detection algorithm. The EEM, lumen, and plaque+media (P+M = EEM-lumen) volumes were calculated.

RESULTS

At follow-up, lumen volume was smaller than at postintervention (159+/-69 mm3 vs. 179+/-49 mm3, p = 0.0003). From postintervention to follow-up, there was a decrease in EEM volume (377+/-107 to 352+/-125 mm3, p < 0.0001), but no change in P+M volume (p = 0.52). The delta lumen volume correlated strongly with deltaEEM volume (r = 0.842, p < 0.0001), but not with deltaP+M volume. In the 18 patients from the SURE Trial, the decrease in lumen and EEM volumes occurred late, between 1 month and 6 months of follow-up.

CONCLUSIONS

Volumetric IVUS analysis demonstrated that late lumen volume loss following DCA was a result of a decrease in EEM volume. This was a late event, occurring between 1 and 6 months' postintervention.

Mechanisms of vascular growth-promoting effects of neuropeptide Y: role of its inducible receptors

We have previously reported that neuropeptide Y (NPY), a sympathetic cotransmitter and vasoconstrictor, is mitogenic for vascular smooth muscle cells (VSMCs), and now report on the mechanisms mediating these effects. In rat aortic A10 cell line, NPY's potency was greater than that of norepinephrine, and efficacy similar to that of platelet-derived growth factor, but less than that of the full serum, in stimulating cell proliferation; this effect was optimal in cell 60-80% cell density. At lower cell density and serum content, NPY stimulated DNA fragmentation/apoptosis. In rat aortic primary VSMCs (RASMCs), mitogenic effect of NPY was bimodal with the first peak at 1 pM, a decline at 1 nM, and a second peak at 10-100 nM; peptide YY had similar but less efficacious effects. The first NPY's peak was mimicked by Y2 agonists, and blocked by Y2 antagonist (T4-[NPY(33-36]4), and the second mimicked by Y1 agonist and partially blocked by Y1 antagonist, BIBP3226, suggesting a multireceptor mode of action. In A10 and in RASMCs, the expression of NPY receptors, Y1, Y2 and Y5, using RT-PCR was undetectable in quiescent cells but detected after pre-treatment with NPY. The receptor induction was NPY dose-dependent and also affected by incubation time and presence of serum. The NPY mitogenic effects were attenuated by calcium channel blockers, particularly verapamil. In primary cultures of rat coronary endothelial cells (where NPY is also mitogenic), NPY stimulated mitogen-activated protein kinase (MAPK) activity. Thus, the growth-promoting effects of NPY in vascular cells occur at concentrations lower than vasoconstrictive, and appear to be mediated by inducible Y1, Y2, and Y5 receptors, calcium entry and possibly MAPK activation.

Picotamide, an antithromboxane agent, inhibits the migration and proliferation of arterial myocytes

Picotamide is an antiplatelet drug with a peculiar dual mechanism of action: it inhibits thromboxane A2 synthase and antagonizes the pharmacological responses mediated by thromboxane A2 receptor. We investigated the in vitro effect of picotamide on smooth muscle cell migration and proliferation. Picotamide (1-500 microM) decreased human and rat smooth muscle cell proliferation, evaluated as cell number, in a concentration-dependent and reversible manner. Picotamide inhibited DNA synthesis induced by fetal calf serum (10%), platelet-derived growth factor (PDGF-BB (20 ng/ml)), epidermal growth factor (EGF (1 nM)) and (15S)-hydroxy-11,9-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619 (10 microM, thromboxane A2 receptor agonist)). Co-incubation of U46619 together with EGF or PDGF-BB resulted in a marked amplification of [3H]thymidine incorporation that was completely reversed by picotamide. The drug also inhibited smooth muscle cell migration induced by fibrinogen (600 microg/ml) or PDGF-BB (20 ng/ml) in a concentration-dependent manner. The ability of picotamide to interfere with myocyte migration and proliferation confers, at least in vitro, a pharmacological interest on the compound in atherogenesis.

Remodeling after directional coronary atherectomy (with and without adjunct percutaneous transluminal coronary angioplasty): a serial angiographic and intravascular ultrasound analysis from the Optimal Atherectomy Restenosis Study

OBJECTIVES

The intravascular ultrasound (IVUS) substudy of OARS (Optimal Atherectomy Restenosis Study) was designed to assess the mechanisms of restenosis after directional coronary atherectomy (DCA).

BACKGROUND

Recent serial IVUS studies have indicated that late lumen loss after interventional procedures was determined primarily by the direction and magnitude of arterial remodeling, not by cellular proliferation.

METHODS

Complete quantitative coronary angiography (QCA) and IVUS were obtained in 104 patients before and after intervention and during follow-up. All studies were performed after administration of 200 microg of intracoronary nitroglycerin. Angiographic measurements included minimum lumen diameter (MLD), interpolated reference diameter and diameter stenosis (DS). Intravascular ultrasound measurements included lesion and reference external elastic membrane (EEM), lumen and plaque+media cross-sectional area (CSA). The axial location of the lesion site was at the smallest follow-up lumen CSA; the reference segment was the most normal-looking cross section within 10 mm proximal to the lesion but distal to any major side branch. Results are reported as mean +/- one standard deviation.

RESULTS

The QCA reference decreased from 3.51 +/- 0.46 mm to 3.22 +/- 0.44 mm; the MLD decreased from 3.22 +/- 0.47 mm to 2.03 +/- 0.72 mm; and the DS increased from 8 +/- 10% to 38 +/- 20%. On IVUS, the decrease in lumen CSA (from 8.8 +/- 2.5 mm2 to 5.5 +/- 4.0 mm2) was associated with a significant decrease in EEM (from 19.7 +/- 5.6 mm2 to 16.9 +/- 6.2 mm2); there was no significant increase in P+M (from 10.9 +/- 4.2 mm2 to 11.3 +/- 3.9 mm2). A change in lumen correlated with a change in EEM (r = 0.790, p < 0.0001), not with a change in P+M (r = 0.133, p = 0.2258). A decrease in reference EEM (from 19.1 +/- 7.7 mm2 to 17.6 +/- 8.0 mm2) also correlated with a decrease in lesion EEM (r = 0.665, p < 0.0001). Results in restenotic lesions were similar.

CONCLUSION

Restenosis after optimal DCA is caused primarily by a decrease in EEM CSA that extends into contiguous reference segments.

Cell proliferation in normal and atherosclerotic human aorta: proliferative splash in lipid-rich lesions

Local accumulation of cells (hypercellularity) in the intima of the arterial wall as a result of cell proliferation is recognized as one of the major manifestations of human atherosclerosis. In the present study we have used a monoclonal antibody against PCNA to identify the proliferative activity, in uninvolved intima of human aorta classified as diffuse intimal thickening, and in different types of atherosclerotic lesions: specifically, initial lesion, fatty streak, fibroatheroma and fibrous plaque. As compared with a diffuse intimal thickening, the cell number in the initial lesions, fatty streaks and in a fibrolipid plaque (fibroatheroma) was 1.5-3-fold higher, while the cellularity in a fibrous plaque (fibrotic lesion) was lower than in a fibroatheroma and comparable with the cell number in the initial lesions. Using monoclonal antibodies, inflammatory cells (T- and B-lymphocytes as well as monocytes-macrophages) have been revealed in the intima. However, most (84-93%) of the intimal cells were noninflammatory cells classified as resident cells possessing the antigens of smooth muscle cells and pericytes as well as a small number of cells unidentifiable with the antibodies used. The highest number of proliferating cells was found in a fibroatheroma (11-fold higher as compared with a diffuse intimal thickening). A significant, but lesser increase of PCNA-positive cells was revealed in other types of lesions, too. The proliferative 'splash' in lipid-rich lesions suggests a relationship between the lipid accumulation in atherosclerotic intima and the stimulation of proliferation. The highest proliferative index of resident cells (i.e. percentage of the PCNA-positive cells among the total number of resident cells) was revealed in fibrotic lesions. It was approximately eight-fold higher than in a diffuse intimal thickening. The proliferative index of inflammatory cells considerably exceeded that of resident cells. However, in all types of atherosclerotic lesions and in a diffuse intimal thickening it showed no significant differences and was similar to the proliferative index of inflammatory cells isolated from peripheral blood. This suggests that an increased number of resident cells in atherosclerotic lesions can be explained by stimulation of their proliferative activity, whereas an altered inflammatory cell number is rather a result of their penetration from the blood into the subendothelial intima with a constant proliferative index.

The extracellular matrix in balloon arterial injury: a novel target for restenosis prevention

The role of the extracellular matrix (ECM) in the pathobiology of restenosis has not been fully appreciated. Recent discoveries have shown the ECM to be a complex, heterogeneous structure whose components are dynamically altered in response to vascular injury. This report reviews the structure and function of vascular ECM and the importance of the matrix in modulating the vascular response to arterial injury such as balloon angioplasty and atherosclerosis.

Restenosis in human vein bypass grafts

The restenosis rate in vein bypass grafts is higher than in native coronary arteries, and both the cascade of regulatory factors and the vessel reaction may be altered. In this study, vein bypass atherectomy specimens were classified as primary (n = 10) or restenotic (n = 12). Immunohistochemistry with 11 primary antibodies showed low levels of proliferation in both tissues and similar amounts of extracellular matrix components in both primary and restenotic specimens at the time points at which tissue was removed for clinical reasons. Inflammation appeared increased in restenotic specimens. Using in situ hybridization, transforming growth factor-beta1 messenger RNA was detected in both primary and restenotic tissue, with a trend to higher expression in restenosis (8.4 +/- 5.3 vs. 9.4 +/- 7.4 grains/nucleus) and further increased expression in multiple compared with single restenoses (15.1 +/- 6.1 vs. 5.6 +/- 5.1 grains/nucleus, P < 0.05). Hence, there were no great differences in cell proliferation or extracellular matrix formation between primary and restenosis vein graft tissue, in contrast to previously described findings in arterial tissue. This suggests that primary vein graft tissue is already in a chronic 'restenosis-like' state and subsequent injury creates minimal additional upregulation.

IRT-1, a novel interferon-gamma-responsive transcript encoding a growth-suppressing basic leucine zipper protein

Interferon-gamma (IFN-gamma) inhibits proliferation of vascular smooth muscle cells (VSMCs) in culture and reduces arterial restenosis post-balloon angioplasty. The identification and characterization of IFN-gamma-specific transcripts in VSMCs are an important approach to discern the molecular mechanisms underlying vascular proliferative disease. In this report, we describe IRT-1, a novel mRNA transcript constitutively expressed in a number of human tissues, but expressed in human VSMCs only when they are stimulated with IFN-gamma. This mRNA expression is induced >200-fold 72 h after IFN-gamma treatment. IRT-1 mRNA is also acutely expressed in rat carotid arteries that are injured by balloon angioplasty. The IRT-1 cDNA transcript encodes a basic protein that contains a leucine zipper motif, a core nuclear localization sequence, and a single strongly hydrophobic region. Constitutive IRT-1 mRNA expression in human peripheral blood lymphocytes is reduced when these cells are stimulated to proliferate. Overexpression of IRT-1 protein in VSMCs alters their morphology and dramatically reduces their proliferative capacity. This study suggests that IRT-1 is an IFN-gamma-inducible factor that may regulate the progression of vascular proliferative diseases.

Direct effects of statins on the vascular wall

The beneficial effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) on coronary events have generally been attributed to their hypocholesterolemic properties. Mevalonate and other intermediates of cholesterol synthesis (isoprenoids) are necessary for cell proliferation and other important cell functions; thus effects other than cholesterol reduction may help to explain the antiatherosclerotic properties of statins. Recently we provided in vitro and in vivo evidence of decreased smooth-muscle cell (SMC) proliferation and migration by fluvastatin and simvastatin, but not by pravastatin, independent of plasma cholesterol reduction. The ability of fluvastatin to interfere with arterial SMC proliferation at therapeutic concentrations (0.1-1 microM) prompted us to investigate the pharmacologic activity of sera from 10 patients treated with fluvastatin, 40 mg once daily, on the proliferation of cultured human arterial myocytes. Pravastatin, 40 mg once daily, displays a lipid-lowering activity similar to that of fluvastatin without affecting SMC proliferation and was investigated as a control for assessing this non-lipid-related effect of fluvastatin. Fluvastatin and pravastatin, given for 6 days to patients with type IIa hypercholesterolemia, resulted in a similar decrease in low-density-lipoprotein (LDL) cholesterol. However, the addition of 15% whole-blood sera from patients treated with fluvastatin to the culture medium resulted in a 43% inhibition of cholesterol synthesis in SMCs (p < 0.01) that mirrored the pharmacokinetic profile of fluvastatin. When SMC proliferation was investigated, a significant inhibition of cell growth (-30%; p < 0.01) was detected with sera obtained 6 h after the last dose. No effect on SMC proliferation or cholesterol biosynthesis was observed when sera from patients treated with pravastatin were evaluated. These results suggest that statins exert a direct antiproliferative effect on the arterial wall, beyond their effects on plasma lipids, which could prevent significant cardiovascular disease.

Site-specific delivery of iloprost during experimental angioplasty suppresses smooth muscle cell proliferation

PURPOSE

The authors have previously reported that intramural delivery of iloprost during angioplasty suppresses local platelet aggregation at 1 hour in undiseased porcine arteries. In this study, the authors sought to quantify the effect of such treatment on medial vascular smooth muscle cell proliferation, an event implicated in the development of intimal hyperplasia.

MATERIALS AND METHODS

Three Yorkshire pigs underwent percutaneous transluminal angioplasty with hydrogel-coated balloons for a total of 10 iloprost-treated (experimental) and 10 saline-treated (control) arterial sites. The balloons were prepared with previously reported techniques and loaded with 2.25 microg of iloprost for the experimental sites. On the eighth day after angioplasty, these sites were harvested and prepared for immunohistochemical staining. Thin (4 microm) sections of the specimens were stained with use of monoclonal antibody to proliferating cell nuclear antigen (PCNA). Appropriate positive and negative controls were used. Approximately 350-500 vascular smooth muscle cells were randomly counted under high power (100x) by an experienced physician who was blinded to the origin of the specimen. A PCNA index (%) was calculated as follows: [(#PCNA [+] cells)/(#PCNA [+] cells + #PCNA [-] cells)]x 100. A paired t test was used for statistical comparison.

RESULTS

The PCNA indices for eight (n = 8) paired large vessels (iliac, carotid, subclavian) were 7.98 (+/- 1.8)%, for the iloprost-treated experimental sites, and 14.58 (+/- 3.8)% for the saline-treated control sites. This difference was statistically significant (P = .003). One large vessel pair was not available for analysis. When the pair of renal arteries of animal 3 were included (n = 9), the PCNA indices were 8.32 (+/- 2.3)% for the experimental sites, and 13.79 (+/- 4.2)% for the control sites. The differences were again significant (P = .01).

CONCLUSION

Intraarterial site-specific delivery of iloprost during angioplasty with drug-loaded, hydrogel-coated balloons significantly suppresses medial smooth muscle cells in swine at the expected peak period of proliferation of 7 days after angioplasty.

Conjugated equine estrogens inhibit progression of atherosclerosis but have no effect on intimal hyperplasia or arterial remodeling induced by balloon catheter injury in monkeys

OBJECTIVES

This study sought to determine the effects of estrogen treatment on atherosclerosis progression and the proliferative and structural responses of the atherosclerotic arteries to injury.

BACKGROUND

Estrogen treatment suppresses the intimal response to arterial injury in nonatherosclerotic rodents and rabbits and inhibits the in vitro proliferation of smooth muscle cells. However, the effect of estrogen on the response of atherosclerotic arteries to transmural injury, as occurs in balloon catheter angioplasty in humans, is unknown.

METHODS

Forty-six ovariectomized cynomolgus monkeys were fed an atherogenic diet for 30 months; 25 received 175 microg/day of conjugated equine estrogens, and 21 served as untreated control animals. All animals underwent balloon catheter injury of the left iliac artery. Subsets of animals underwent a necropsy study at 4, 7, 14 and 28 days after injury; injured and contralateral (uninjured) arteries were pressure-fixed and evaluated morphometrically.

RESULTS

Estrogen treatment resulted in a 37% decrease (p < 0.05) in atherosclerosis (plaque area) in the uninjured artery. In response to injury, arterial cell proliferation increased at days 4 and 7, and intimal area was increased two- to threefold at day 28 (p < 0.05). Although estrogen treatment resulted in a trend toward decreased arterial cell proliferation at day 4, there was evidence of increased cell proliferation in both media and intima at day 7 (p < 0.05). However, there was no effect of estrogen treatment on intimal area or indexes of arterial remodeling in the injured artery at day 28 (p > 0.4). CONCLUSIONS. In contrast to previous studies of nonatherosclerotic animals, the results indicate that in the circumstance of transmural injury to arteries of primates with preexisting atherosclerosis, estrogen does not suppress arterial neointimal or structural responses to injury.

Platelet-derived growth factor, intimal hyperplasia, and ischemic complications in giant cell arteritis

OBJECTIVE

To explore whether vasoocclusion in giant cell (temporal) arteritis (GCA) is related to intimal hyperplasia and in situ production of platelet-derived growth factor (PDGF).

METHODS

Temporal artery biopsy specimens from patients with GCA were analyzed for the presence of intimal hyperplasia. Expression of PDGF-A and PDGF-B was assessed by immunohistochemistry and digitized image analysis.

RESULTS

PDGF-A and PDGF-B were widely expressed in inflamed arteries. CD68+ macrophages, smooth muscle cells, and multinucleated giant cells produced PDGF, whereas hyperplastic intimal tissue did not. Arteries with marked luminal narrowing and those with no or minimal luminal narrowing differed in the extent and distribution of PDGF expression. Concentric intimal hyperplasia was associated with the accumulation of PDGF-A- and PDGF-B-producing CD68+ macrophages at the media-intima junction. PDGF+,CD68+ macrophages in close proximity to the internal elastic lamina frequently coproduced matrix metalloproteinase 2. Intimal hyperplasia of the temporal artery correlated with ischemic complications of GCA, such as ocular involvement, jaw claudication, and aortic arch syndrome.

CONCLUSION

Production of PDGF has a role in arterial occlusion in GCA. The excessive fibroproliferative response leading to luminal narrowing can be distinguished from the stenosing process in atherosclerosis and postangioplasty restenosis, suggesting that there are different response patterns to arterial injury. In GCA, macrophages at the media-intima border are the dominant source of PDGF. Since vasoocclusion is associated with a number of serious complications in GCA, inhibition of intimal proliferation should be a major goal of treatment.

Proliferation and the monoclonal origins of atherosclerotic lesions

Benditt's observation of the monoclonal origin of the atherosclerotic lesion has been controversial because it appeared to conflict with conventional wisdom. A new method based on a polymerase chain reaction amplification of the DNA of an X-inactivated gene from microdissected tissue confirms that Benditt was correct. However, this monoclonal expansion can also be found in nonatherosclerotic intima and media. These new data suggest that plaque clonality may represent expansion of preexisting patches of cells arising during development of the media. This developmental view does not conflict with other recent evidence that plaque expansion is associated with mutation or viral events. However, if plaques arise from patches, then early developmental mechanisms may be critical to the later evolution of the lesions.

Immunolocalization of thrombospondin-1 in human atherosclerotic and restenotic arteries

Experimental studies have implicated a functional role for the extracellular matrix glycoprotein thrombospondin-1 (TSP-1) in vascular smooth muscle cell proliferation and migration. We therefore sought to determine if TSP-1 might represent a specific component of the fibroproliferative tissue typically associated with restenosis lesions from human coronary and peripheral arteries. Positive immunostaining for TSP-1 was limited to hypocellular plaques typical of primary atherosclerosis; in contrast, such staining was nearly absent from the loose extracellular matrix of the fibroproliferative tissue typical of restenotic lesions. Only a small fraction of vascular smooth muscle cells in either primary or restenotic lesions demonstrated a cellular staining pattern for TSP-1, which was also observed in control studies performed in cell culture and in atherosclerotic rabbit arteries examined 3 days after experimental balloon angioplasty. Double-staining for TSP-1 and proliferating cell nuclear antigen in studies of human beings disclosed that only a small portion of proliferating cell nuclear antigen-positive cells also stained for TSP-1. The observations made in this series of specimens thus indicate that TSP-1 is not a major component of the extracellular matrix of human restenotic tissues, even when such specimens demonstrate evidence of hypercellularity or ongoing cellular proliferation. Because most restenosis specimens, however, were retrieved > or =1 month after the primary intervention, a functional role for TSP-1 in smooth muscle cell proliferation or migration at the early stages of lesion development is still possible.

Neovascularization in atherectomy specimens from patients with unstable angina: implications for pathogenesis of unstable angina

Although neovascularization has been noted in atherosclerotic plaque, the presence of neovascularization has not been correlated with clinical syndromes. This study examined the relation between neovascularization in atherosclerotic plaque removed during directional coronary atherectomy and clinical status in 28 patients. Neovascularization was determined by immunohistochemistry with endothelial cell-specific monoclonal antibodies and was found in nine (50%) of 18 specimens from patients with unstable angina and in only one (10%) of 10 specimens from patients with stable angina (p < 0.05). There was no significant relation between neovascularization and other clinical factors (age, sex, race, hypertension, diabetes, tobacco use, hypercholesterolemia, positive family history of coronary artery disease, history of myocardial infarction, or stenosis severity). These results suggest that neovoscularization may play a role in the pathogenesis of unstable angina.

The histologic characteristics of primary and restenotic carotid plaque

BACKGROUND

Although smooth muscle cell proliferation is a prominent feature of restenosis in experimental models, the role of cellular proliferation in the initiation and progression of carotid restenosis is not well documented.

METHODS

Between 1985 and 1995, 35 carotid endarterectomies (CEA) in 34 patients were performed for restenosis. Patient risk factors, cerebrovascular symptoms, and operative findings were recorded. Tissue specimens from 29 of these cases and 14 original specimens from the same patient were examined by light microscopy (H&E, trichrome, elastochrome, and Alcian blue) and immunohistochemistry (alpha actin, CD 68, vWF, and proliferating nuclear cell antigen (PCNA)) in order to determine the morphologic characteristics and cellular proliferative activity of the plaque.

RESULTS

Hemodynamically significant recurrent stenosis occurred in the 29 patients (69% symptomatic) between 2 months and 30 years after their initial CEAs. Eleven of 29 (38%) lesions were removed early (< 3 years). Recurrent lesions were characterized based on their components as neointimal thickening, 24% (7/29), neointimal thickening and atherosclerosis, 55% (16/29), or atherosclerotic, 21% (6/29). Nineteen of 29 (66%) plaques were complicated by mural thrombus or intraplaque hemorrhage. An inflammatory cell infiltrate consisting of macrophages and T lymphocytes was observed adjacent to areas of recurrent atherosclerosis and macrophages in regions of intimal thickening. Although infrequently present (generally 1-3% of cells) PCNA-positive cells were detected in 41% (12 of 29) of recurrent and 14% (2 of 14) of primary plaques. No PCNA-positive cells were detected in the remaining 67% (29 of 43) of specimens. There was no statistical difference in the number of PCNA-positive cells in early recurrent lesions compared to those recurring after 3 years (36% vs 44%). PCNA immunoreactivity when present was most commonly noted in macrophages associated with thrombus or atheroma rather than smooth muscle cells.

CONCLUSIONS

Although evidence of cellular proliferation was observed in 40% of recurrent carotid endarterectomy lesions, the proliferation rate was low (1-3%) and unrelated to the time interval of recurrence. Proliferative activity was most pronounced in macrophages associated with intraplaque hemorrhage or atheroma. The contribution of inflammatory cells to the biologic behavior of restenotic lesions requires further investigation.

Endothelin attenuates apoptosis in human smooth muscle cells

An imbalance between proliferation and apoptosis is an important causal factor for disorders involving abnormal cell accumulation. Endothelin (ET)-1, a 21-amino-acid peptide with mitogenic and vasoconstricting activities, not only acts as a mitogen, but also attenuates paclitaxel-induced apoptosis in smooth muscle cells. In both human pericardial and prostatic smooth muscle cells, addition of ET-1 reduced paclitaxel-induced DNA fragmentation and phosphatidylserine on the cell surface, two characteristics of apoptosis. By comparison, angiotensin II, another vasoactive peptide, did not have a significant effect on apoptosis. The effect of ET-1 was dose-dependent with an EC50 of 1 nM. These results suggest that ET is a potential survival factor for smooth muscle cells, and that altered activity of the ET system in disease states has potential to contribute to aberrant cell growth.

[Pathophysiology and therapeutic concepts in coronary restenosis]

Demonstration of a reduced restenosis rate after stent implantation (Benestent, STRESS) has initiated rapid increase in stent implantation rates with widening indications. At present, the majority of stents are implanted in "none-Benestent/STRESS-lesions" with the consequence of a higher restenosis rate as previously expected. Stent restenosis has therefore become a relevant problem in interventional cardiology. In contrast to balloon angioplasty, where acute and subacute recoil represents the major mechanism of restenosis, stent restenosis is exclusively attributed to neointima proliferation. Morphological studies have demonstrated that neointima is caused by early smooth muscle cell ingrowth with a maximum after 7 days which is then gradually replaced by extracellular matrix. Systematic clinical, angiographic and intravascular ultrasound studies have identified several risk factors for increased stent restenosis such as: diabetes mellitus, treatment of restenosis, serial stent implantation, small and calcified vessels, ostial lesions, venous bypass grafts and complex stenosis morphology. In addition, there is increasing evidence that aggressive implantation techniques with high pressures and oversized balloons may also induce higher restenosis rates. Optimal treatment of instent restenosis has not been determined so far. Balloon angioplasty is at present considered the therapeutic option of choice. Several small studies have shown, that in short, discrete lesions (< 10 mm) results of simple PTCA are acceptable with re-restenosis rates between 15 and 35%. The intervention is considered safe with low complication rates. In 10 to 15% additional stent implantation is necessary, usually due to dissections proximal or distal to the treated stent. In long, diffuse stent restenosis (> or = 10 mm), however, PTCA results in high re-restenosis rates up to > 80%. This is most likely due to insufficient early balloon angioplasty results with minimal luminal diameters (MLD) significantly below the previous stent diameter. Therefore, debulking techniques have been used to reduce neointima burden within the stent. At present 3 techniques are available: directional coronary atherectomy (DCA), Excimerlaser angioplasty (ELCA) or high frequency rotablation. All of these techniques achieve a significant reduction in plaque volume within the stent and in combination with balloon angioplasty allow larger MLDs than PTCA alone. Limited experiences with ELCA and rotablation have shown that the techniques are safe without major periinterventional complications. DCA, however, has been accompanied with stent destruction and therefore should be considered with large care, especially in stents with coil design. At present, no randomized controlled trials for the comparison of debulking techniques with or without balloon angioplasty versus balloon angioplasty alone are available. Three multicenter trials have been initiated (LARS, ARTIST and TWISTER) to compare debulking techniques versus balloon angioplasty in diffuse stent restenosis. Adjunct medical treatment after interventions for stent restenosis is usually limited to ASS alone, indications for additional application of Ticlopidine have not been verified so far. Positive results are expected for the use of local radiation therapy either by radioactive stent implantation or afterloading techniques. With increasing stent implantation rates and indications, about 400,000 stents will be implanted in 1997 worldwide. Considering a low restenosis rate of 20%, 80,000 stent restenosis will occur within one year. Final recommendations for optimal treatment of these patients are not yet available.

Edgar J. Poth Memorial/W.L. Gore and Associates, Inc. Lectureship. The clinical and pathological spectrum of recurrent carotid stenosis

BACKGROUND

Hemodynamically significant (> or =50%) carotid restenosis occurs in approximately 10% to 12% of individuals undergoing carotid endarterectomy. The underlying pathology is usually neointimal thickening within 3 years and recurrent atherosclerosis thereafter. Although a number of etiologic factors have been implicated in the development of restenosis, the etiology remains unclear and preventative measures relatively ineffective.

METHODS

A review of the English literature was undertaken to determine the incidence, clinical presentation, and pathologic features of carotid restenosis.

CONCLUSIONS

Carotid restenosis is the major factor limiting long-term patency after carotid endarterectomy. Although drug therapy has been shown to be effective in preventing restenosis in animal models, the results of clinical human trials have been disappointing. Delineation of the biochemical and molecular mechanisms contributing to the development of restenosis is essential if effective therapeutic interventions are to be developed.

Structural determinants of lumen narrowing after angioplasty in atherosclerotic nonhuman primates

PURPOSE

The relationship between lumen narrowing, intimal hyperplasia, and wall remodeling after angioplasty was explored in a nonhuman primate model of atherosclerosis.

METHODS

Cynomolgus monkeys (n = 37) used in long-term atherosclerosis studies underwent left iliac artery balloon injury. The uninjured right iliac artery served as a reference segment for intraanimal comparisons. One month later iliac arteries were fixed by perfusion (100 mm Hg) and removed for cross-sectional analysis to determine mean values for lumen area (LA), intimal area (IA), internal elastic lamina area (IELA), plaque burden (IA/IELA), and depth of wall injury. Values for each balloon-injured iliac artery were normalized to the contralateral uninjured iliac artery (percent of control), and linear regression analysis was performed comparing LA with IA, with IELA, and with depth of injury. Comparisons were also made between those arteries that remained dilated 1 month after balloon injury (LA > or = 140%; n = 13) and those that renarrowed (LA < or = 100%; n = 14).

RESULTS

For all 37 animals, LA 1 month after balloon injury correlated well with IELA (r = 0.72; p < 0.001) but not with IA (r = 0.10; p = 0.54), suggesting that changes in artery size rather than neointimal mass determined lumen caliber. When comparing arteries that remained dilated (n = 13) with those that renarrowed (n = 14), there were no differences in depth of wall injury (injury depth: 0, no injury; 1, intima; 2, IEL; 3, media; 4, EEL; 2.1 +/- 0.3 vs 1.6 +/- 0.3; p = 0.12), neointimal accumulation (IA, 507% +/- 118% vs. 421% +/- 81% of control; p = 0.55), or plaque burden (IA/IELA, 0.39 +/- 0.04 vs 0.37 +/- 0.06; p = 0.71), respectively. However, wall size defined as IELA was significantly smaller in arteries that renarrowed than in those that remained dilated (IELA, 115% +/- 14% vs 230% +/- 19% of control; p < 0.001).

CONCLUSIONS

Restenosis after angioplasty has been attributed to intimal hyperplasia, equating loss of lumen caliber with neointimal mass. The data presented herein suggest that lumen narrowing after arterial wall injury may have little to do with intimal mass per se, but rather that a change in wall caliber or wall narrowing is the cause of restenosis.

Arterial wall neovascularization--potential role in atherosclerosis and restenosis

Neointimal formation and arterial wall remodeling are pivotal causes of luminal narrowing in atherogenesis and restenosis. Arterial remodeling refers to a series of dynamic structural changes that arteries may undergo in response to various stimuli, including changes in blood flow and pressure, and acute injury. The biological mechanisms involved in arterial remodeling are poorly understood and are currently a main target for research. We have recently focused on the role of the arterial wall microcirculation (ie, vasa vasorum) in arterial remodeling after injury. In the past, a correlation between arterial wall neovascularization and the accumulation of arterial plaque has been documented; however, the dynamic role of these microvessels in arterial repair and luminal narrowing has not been examined. The type of arterial injury, the nature of the lesion that develops, and the arterial compartment in which angiogenesis occurs may determine the role of the vasa vasorum in arterial narrowing. In this review, we highlight the data that link arterial wall neovascularization with lesion formation and the process of arterial remodeling.

Intracoronary radiation decreases the second phase of intimal hyperplasia in a repeat balloon angioplasty model of restenosis

PURPOSE

Repeat balloon angioplasty is likely to induce intimal proliferation, which is associated with a higher restenosis rate. This study examined the effect of intracoronary ionizing radiation on restenotic lesions using repeat balloon injury in a normolipemic swine.

METHODS AND MATERIALS

Eight domestic normolipemic pigs underwent overstretch balloon angioplasty with a 3.5 mm balloon in the LAD and LCX, followed by repeat balloon injury at the same sites 4 weeks after the initial injury. At that time a high activity 192Iridium source was introduced immediately after the angioplasty by random assignment to deliver 14 Gy at 2 mm in eight of the injured coronary arteries (LAD and LCX). One month later the animals were killed and the coronary arteries pressure perfusion fixed. Serial sections were stained with H&E and VVG, then evaluated by histopathologic and morphometric techniques. Maximal intimal thickness (MIT), intimal area (IA), and intimal area corrected for the extent of injury (IA/FL) were measured in the irradiated and control arteries and were compared to control arteries with single injuries from previous studies.

RESULTS

Repeat balloon injury induced significant additional medial damage, which was associated with marked intimal hyperplasia in a concentric pattern. Intracoronary irradiation significantly decreased the total of neointima area formation (IA 93 + 0.35 mm2 compared to control 1.38 + 0.33 mm2 p < 0.01) and the MIT was also significantly reduced in the irradiated vessels (0.57 + 0.18 mm vs. 0.71 + 0.08 mm, p = 0.05).

CONCLUSIONS

Intracoronary irradiation immediately after the second balloon dilatation inhibits the intimal hyperplasia due to that injury. However, there was no effect on the existing neointima from the initial injury.

Restenosis or rapid progression in non-dilated sites are not predictors of late spontaneous coronary events

The present study was designed to assess the prognostic value of clinical and angiographic factors, and especially restenosis or rapid progression in non-dilated sites, on major spontaneous coronary events at long-term follow-up after a first successful coronary angioplasty performed for angina pectoris. A second aim was to assess the prognostic factors and especially restenosis in asymptomatic patients after angioplasty. The first 352 consecutive patients undergoing a successful coronary angioplasty were selected and followed-up. The following variables: age, sex, unstable angina, previous myocardial infarction, diabetes, hypercholesterolemia, tobacco consumption, hypertension, fibrinogen, coronary extent, single or multiple dilatation, restenosis, new progression, clinical deterioration of anginal status just before angiographic restudy or asymptomatic status were subjected to a stepwise regression analysis. Restenosis (a loss of 30% in diameter and/or a return to a >50% stenosis) and progression in non-dilated segments (a 20% reduction in diameter) were assessed by a computer-assisted method. Cardiac death, new myocardial infarction or new unstable angina, at long-term follow-up after angiographic restudy, were regarded as spontaneous coronary events and pooled in a single dependent variable. Thus 41 patients had a coronary event. In the overall population, clinical deterioration of anginal status (p<0.001, relative risk: 3.65) and fibrinogen (p<0.05, relative risk: 1.03) were independent predictors of spontaneous coronary events. Restenosis or new progression were not predictors. In asymptomatic patients (n=187), fibrinogen (p<0.01, relative risk=1.06) was the only predictor and restenosis was not an independent predictor of spontaneous coronary events. The best predictor of spontaneous coronary events at long-term follow-up after a first successful coronary angioplasty is clinical deterioration in anginal status in the months following the procedure. Restenosis does not appear as an independent predictor. Rapid progression observed in non-dilated sites is not an important prognostic factor.

Differential expression of nonmuscle myosin II isoforms in human atherosclerotic plaque

Intimal proliferation and functional changes involving vascular smooth muscle cells are key events in the development of atherosclerosis, including restenosis after percutaneous transluminal angioplasty. Nonmuscle myosin (NMM) is required for cytokinesis and has been shown in cultures of vascular smooth muscle cells to undergo changes of isoform expression depending on the stage of proliferation and differentiation. The purpose of this study was to examine the differential expression of the two most recently identified nonmuscle myosin heavy chain isoform II (NMMHC-II) isoforms A and B in atherosclerotic plaque. Primary atherosclerotic and restenotic atherectomy specimens and non-atherosclerotic controls, were analyzed by Western Blot analysis, immunohistochemistry and in situ hybridization. Nonmuscle myosin heavy chain isoform IIA (NMMHC-IIA) was equally expressed in all types of tissue specimens both at the protein and mRNA levels. In contrast, NMMHC-IIB protein was found in restenotic specimens and normal artery but was at very low levels in primary atherosclerotic plaque. By in situ hybridization NMMHC-IIB mRNA levels were significantly greater in restenotic versus primary atherosclerotic lesions. NMMHC-IIB expression is associated with vascular restenosis but is downregulated in stable atherosclerotic lesions, whereas NMMHC-IIA is expressed in both. These results indicate that these new myosin isoforms have different functions and should be regarded separately with respect to smooth muscle proliferation and restenosis. They should prove to be useful molecular markers for the study of atherosclerosis and restenosis.

The immediate early gene of human cytomegalovirus stimulates vascular smooth muscle cell proliferation in vitro and in vivo

Cytomegalovirus (CMV) infection has been carefully studied regarding the relationship with the vascular smooth muscle cell (VSMC) proliferation in either atherosclerosis or post-angioplasty restenosis, but its role in the vessel wall has yet to be elucidated. To clarify the pathogenic ability of CMV in the vessel wall, we transduced the immediate early (IE) gene of CMV into the VSMCs and endothelial cells (ECs) by hemagglutinating virus of Japan-liposome method. The in vitro IE gene transfer demonstrated that the conditioned medium of IE gene transferred ECs enhanced [3H]-thymidine uptake of VSMCs. The enhanced proliferation of the IE gene transferred VSMCs was observed after the stimulation by basic fibroblast growth factor. The in vivo IE gene transfer showed neointimal thickening while the control arteries did not. These findings thus suggest that the expression of CMV-IE gene in the vessel wall may play a role in the fibrocellular neointimal formation or progression of atherosclerosis in vivo.

Gene therapy and vascular disease: potential applications in vascular surgery

Advances in molecular biology have generated methods that are used to enhance diagnosis and treatment of a variety of human diseases. More recently modification of gene expression in cells by gene transfer has been introduced as a new therapeutic modality. The targeting of vascular cells with this method is appealing not only for anatomical reasons, but also because endovascular techniques provide access to the vasculature and makes site-specific delivery possible. Over the past few years, gene transfer has been widely used to explore the pathophysiology of vascular diseases in experimental models and available data suggests that this method may eventually become a therapeutic alternative for vascular disorders such as restenosis, graft failure, and critical ischaemia. In the following we discuss the methodology of gene transfer, its tentative use in vascular diseases related to vascular surgery, and the problems associated with this new technology.

Intravascular ultrasound insights into mechanisms of stenosis formation and restenosis

Using intravascular ultrasound (IVUS), stenosis formation and restenosis (or late lumen loss following coronary angioplasty procedures) can be subdivided into two distinct underlying components: tissue accumulation and arterial remodeling. Arterial remodeling is defined as a change in total arterial cross-sectional area over time; it can be adaptive (an increase in arterial cross-sectional area as a compensatory response to plaque accumulation) or pathologic (a decrease in arterial cross-sectional area or chronic arterial shrinkage). Adaptive arterial remodeling can delay the development of coronary artery stenoses and prevent restenosis; pathologic remodeling can contribute to de novo lesion formation and has been shown to be the dominant mechanism of restenosis following coronary intervention. Serial IVUS studies have also been used to study the natural history of the restenosis process; adaptive remodeling occurs early (within 1 month) and pathologic remodeling occurs late (between 1 and 6 months) after intervention. The residual plaque burden postintervention acts as an amplifier in this process.

Immunocytochemical determination of cell type and proliferation rate in human vein graft stenoses

PURPOSE

Vascular reconstructions are prone to fail as a result of the development of stenotic lesions, which have historically been attributed to myointimal hyperplasia. In animal models, these lesions are associated with marked proliferative smooth muscle cell (SMC) response to vascular injury. However, recent studies using sensitive immunocytochemical techniques in human lesions have generally failed to detect significant cellular proliferation. To clarify the role of cellular proliferation in humans, we characterized the cellular composition and proliferative index of 14 early infrainguinal vein graft stenoses.

METHODS

All infrainguinal vein grafts at our institution are prospectively enrolled in a duplex surveillance protocol, the details of which have been previously reported. Among 98 grafts placed within the last year, 11 patients were identified with 14 progressive, focal, high-grade lesions that met previously established threshold criteria for prophylactic revision to prevent graft thrombosis. Lesions were first detected from 1 week to 7 months after surgery and were removed and replaced with segmental interposition grafts (1.5 to 10 months). Freshly excised lesions were placed in Methyl Carnoy's fixative, paraffin embedded, and serially sectioned. The cellular composition of each lesion was determined with cell-specific immunochemical reagents: alpha SMC actin, von Willebrand factor (endothelial cell), CD 68 (macrophage), and CD 45RB (monocyte). Actively proliferating cells were identified using antibody to proliferating cell nuclear antigen (PCNA). The identity of PCNA-positive cells was determined by double-label immunocytochemical staining, and the proliferative index (PCNA-positive cells/total cells x 100) was calculated by computer-assisted counts of representative gridded cross-sections of each lesion.

RESULTS

All excised lesions demonstrated marked thickening with severe luminal encroachment and were highly cellular, with a predominance of alpha SMC actin+. Endothelial cells on the blood flow surface were present to a variable degree, and seven lesions exhibited striking numbers of macrophages and monocytes. The latter cell types were most abundant near microvessels in the deep neointima and adventitia. Active cellular proliferation was identified primarily in SMCs, with a mean PCNA index of 1.34%. However, significant PCNA reactivity was not limited to SMCs, but was also identified in macrophages and monocytes, particularly in lesions greater than 3 months old.

CONCLUSIONS

Previous immunocytochemical studies of human coronary restenosis atherectomy specimens have generally detected low rates of cellular proliferation (0.5%), but these lesions may not truly represent myointimal hyperplasia, rather a mixture of atherosclerosis, thrombosis, and "restenosis." In contrast, the present study of early human vein graft lesions detected by duplex surveillance indicates that significant cellular proliferation occurs, although rates are lower than those obtained in animals such as the rat carotid injury model. In addition, although SMCs are the predominant proliferating cell type in human vein grafts, our identification of proliferating monocytes and macrophages raises the question of the contribution of an inflammatory component to the development of human lesions. The present study represents the first report of PCNA determination in a series of human infrainguinal vein grafting procedures.

Restenosis: is there a pharmacologic fix in the pipeline?

One of the most frustrating aspects of restenosis is that it is the result of advances in medical care (there was no restenosis before the days of balloon angioplasty), yet it seems to be resistant to all that science has to offer. Still we believe there is reason to be optimistic. We are at last beginning to see some promise from clinical trials, and data being generated confirm some of the hypotheses previously generated from animal experiments. Thus the effects seen with the GP IIb/IIIa antibody 7E3 suggest that thrombosis may be as important in its long-term sequelae as it is for acute reocclusion. The jury is still out on whether antiproliferative approaches will be a therapeutic option, but local delivery paradigms using novel formulations delivered by catheter or impregnated in stents may allow the concept to be tested without the risk of systemic toxicity. Plans are also underway for gene therapy trials, although we may have to wait for better vector technology before taking these into the coronary bed. Perhaps we should move away from the "single pill" approach and accept that, like many infections, malignancies, or even heart failure, a multifaceted approach with combination therapy will provide the first glimmer of that brighter tomorrow.

Morphometric changes seen in balloon-injured porcine iliac arteries: the influence of sympathectomy on intimal hyperplasia and remodelling

OBJECTIVES

To assess the influence of lumbar sympathectomy on intimal thickening and arterial remodelling following balloon de-endothelialisation.

DESIGN

Experimental animal model with control and treated (sympathectomy) groups.

METHODS

Unilateral common iliac artery de-endothelialisation was performed in 36 male pigs using a 5F balloon catheter introduced via the profunda femoris artery. Bilateral lumbar sympathectomies were performed in 18 animals. Both iliac arteries were perfusion-fixed and harvested 4 weeks later. Arterial morphometry was assessed using computer image analysis.

RESULTS

Area measurements are expressed as median (interquartile range) in mm2. Balloon injury resulted in significant intimal thickening but no loss of lumen due to compensatory enlargement of the injured artery. Sympathectomy resulted in significant lumen enlargement (4.8 (2.6-6.3) vs. 1.9 (1.7-2.9)) in balloon-injured arteries. Although intimal thickening was reduced (0.9 (0.6-1.7) vs. 1.5 (0.9-2.0)), this was not statistically significant.

CONCLUSIONS

Sympathectomy increases lumen area 4 weeks after balloon injury to porcine iliac arteries. This effect is due to a combination of reduced arterial wall thickening and increased arterial size.

The role of the adventitia in the arterial response to angioplasty: the effect of intravascular radiation

PURPOSE

In the current series of experiments we have characterized cell proliferation leading to vascular lesion formation in a porcine model for post-angioplasty restenosis and examined the mechanism of action of intravascular beta irradiation in the prevention of lesion formation in this model.

METHODS AND MATERIALS

Juvenile male pigs were subjected to balloon overstretch injury of the left anterior descending and circumflex coronary arteries using clinical angioplasty catheters. Proliferating cells were labelled by injections of 50 mg/kg of bromo-deoxyuridine (BrDU) 24, 16 and 8 hrs prior to sacrifice and were detected by immunohistochemistry using a specific antibody to BrDU. In some cases, BrDU was given as a pulse 3 days after angioplasty and the animals sacrificed on day 14 to follow the migration of the cells which had proliferated earlier. Characterization of the proliferating cells was performed by immunohistochemistry using antibodies to specific cytoskeletal proteins specific for smooth muscle cells and myofibroblasts. Some vessels were treated at the time of angioplasty with 14 or 28 Gy (to a depth of 2 mm) intravascular irradiation using a flexible catheter with a pure beta emitter 90 SR/Y and the effect on cell proliferation and terminal transferase-mediated UTP nick-end labelling (TUNEL) examined 3 or 7 days later.

RESULTS

The first major site of cell proliferation between 2-3 days after angioplasty is the adventitia and not the medial wall. Seven days after angioplasty cell proliferation is predominant in the neointima and is reduced in the media and adventitia. Differential staining with antibodies directed against smooth muscle alpha actin and other cytoskeletal proteins indicates that the proliferating adventitial cells are myofibroblasts. Pulse label studies with BrDU indicates that the proliferating adventitial myofibroblasts migrate into the neointima and contribute to the mass of the restenosis lesion. Fourteen days after angioplasty the myofibroblasts in the neointima and the adventitia express alpha smooth muscle actin and form a fibrotic scar in the adventitia surrounding the injury site. Endovascular irradiation appears to inhibit development of the restenosis lesion by significantly reducing cell proliferation in the media and adventitia at early time points after injury. There were no significant differences in the percent of TUNEL labelled cells in the irradiated vessels compared to controls. Alpha actin staining of myofibroblasts in the adventitia was reduced in the irradiated vessels suggesting a positive effect of intravascular irradiation on vascular remodeling.

CONCLUSIONS

These studies have shown that adventitial myofibroblasts contribute to the problem of post-angioplasty restenosis by proliferating, forming a fibrotic scar surrounding the injury site, and migrating into the neointima. We hypothesize that the adventitial fibrosis which develops at the injury site contributes to negative vascular remodeling associated with clinical restenosis. Experiments in which vessels were exposed to intravascular irradiation at the time of angioplasty indicate that this treatment reduces post-angioplasty restenosis by inhibiting early cell proliferation in the media and adventitia and by preventing the fibrotic changes in the adventitia without a corresponding increase in cellular death or apoptosis in these tissues.

Deposition of PG-M/versican is a major cause of human coronary restenosis after percutaneous transluminal coronary angioplasty

To clarify the mechanisms of restenosis, restenotic human tissue specimens obtained by directional coronary atherectomy (DCA) in 43 patients were immunohistochemically analysed for cell proliferation and deposition of PG-M/versican, an important extracellular matrix proteoglycan of the vessel wall. The patients were classified into five groups according to the period after percutaneous transluminal coronary angioplasty (PTCA): 0-1 month (N = 6), 1-3 months (N = 12), 3-6 months (N = 11), more than 6 months (N = 6) and de novo lesions (N = 8). The tissue specimens were of 35 restenotic lesions following PTCA and eight primary stenotic lesions with no prior PTCA. Total cell numbers in the atherectomy specimens increased significantly up to 3 months after PTCA. Most cells were alpha-smooth muscle actin (alpha-SMA)-positive. To evaluate cell proliferation, the specimens were immunostained for Ki-67 antigen (clone MIB-1). A significant increase in the positive ratio was observed up to 1 month after PTCA, although the labelling index was less than 1 per cent at every stage. The deposition of PG-M/versican, as analysed by immunohistochemistry, was greatest during the period 1-3 months after primary angioplasty, when restenosis detected by angiography progresses most actively. These results suggest that the peak of cell proliferation in the neointima occurs earlier than angiographic restenosis and that the deposition of PG-M/versican may be a major factor in restenosis following angioplasty.

Effect of the new calcium antagonist lercanidipine and its enantiomers on the migration and proliferation of arterial myocytes

The in vitro effects were investigated of the new dihydropyridine calcium antagonist (CA) lercanidipine and its enantiomers on arterial myocyte (smooth muscle cell; SMC) migration and proliferation as related to L-type calcium channel inhibition. Lercanidipine and its enantiomers inhibited the replication and migration of arterial myocytes in concentration ranging from 10 to 50 microM. The antiproliferative effect of lercanidipine, evaluated as cell number, was dose dependent, with a potency similar to that of lacidipine and nifedipine, and was unrelated to the stereoselectivity of enantiomers to bind L-type calcium channels. The cell doubling time increased with drug concentration < or = 122 versus 38 h for controls. The cell growth inhibition induced by lercanidipine and its enantiomers was reversible. Lercanidipine dose dependently decreased [3H]thymidine incorporation into DNA; the (R)-enantiomer, displaying the lowest CA activity, was the most potent in this respect. The tested compounds were able to inhibit fibrinogen-induced myocyte migration in a dose-dependent manner, with the (R)-enantiomer showing the more pronounced effect. To directly rule out the role of calcium channels in the antiatherosclerotic properties of lercanidipine, we examined the effect of the compounds on serum-stimulated calcium influx in SMC. Fluorimetry of Fluo 3 was used to measure changes in free cytosolic Ca2+ concentration ([Ca2+]i) in SMC after long-term preincubation (24 h) with the tested CA. Lercanidipine and its enantiomers (25 microM) decreased the serum-induced elevation of [Ca2+]i in SMC with the (S)-enantiomer (69% inhibition) 2.4-fold more active than the counterpart and the racemate (29% inhibition). In conclusion, our in vitro results suggest that lercanidipine may directly interfere with events involved in atherogenesis. The studies performed with enantiomers of lercanidipine suggest that the observed effects are not related to the blockade of voltage-dependent Ca2+ channels and confirm at least in vitro a pharmacologic potential of the compound to negatively influence the process of atherogenesis.

Proliferative response of human and minipig smooth muscle cells after coronary angioplasty to growth factors and platelets

OBJECTIVES

Platelets aggregating at the site of angioplasty, shown to be a potent proliferative stimulus for cultured smooth muscle cells (SMC), could contribute to proliferation after angioplasty.

METHODS

SMC were cultivated from human aorta and restenosed coronary lesions as well as from minipig aorta and from normal and post angioplasty coronary artery segments (n = 6 per source). 3H-thymidine incorporation was used as a measure of proliferation.

RESULTS

3H-thymidine incorporation varied greatly after passage 7 in all cell lines, but was significantly higher in SMC from human coronary restenosed lesions compared to those from human aorta and minipig coronary post angioplasty segments in passage 2 (44 +/- 6.4 x 10(3) cpm/5000 SMC vs 20 +/- 3.9 and 12.1 +/- 2.1). However, all SMC exhibited a dramatic increase of 3H-incorporation after passage 7. Growth factors stimulated 3H-thymidine incorporation either dose dependently (PDGF-BB and bFGF) or only very modestly (PDGF-AA, EGF, IGF-1). The most potent stimulation was seen with PDGF-BB, 50 ng/ml, and was 17 +/- 6% (human restenosed) and 16 +/- 8% (minipig post angioplasty) of the values observed after stimulation with 10% fetal calf serum. The most effective combination of growth factors, PDGF-BB (50 ng/ml) + bFGF(20 ng/ml) + IGF-1 (50 ng/ml), produced a 3H-thymidine incorporation of 44 +/- 10% (human restenosed) and 42 +/- 11% (minipig post angioplasty) of FCS values. Stimulation by isolated platelets was dose dependent and significantly higher: 75 +/- 19% and 70 +/- 15% of FCS values for those SMC.

CONCLUSIONS

1) SMC from all sources studied exhibit significant changes of proliferation with increasing passages, excluding the comparability of data obtained with cells in different passages. 2) Data obtained with SMC from any source might not apply for SMC from human coronary restenosed lesions. 3) Currently tested growth factors do not fully account for the proliferative effect of platelets on cultured SMC.

Experimental models of accelerated atherosclerosis syndromes

The processes of angioplasty restenosis, vein graft failure, and transplant atherosclerosis, collectively termed 'syndromes of accelerated atherosclerosis', have been the focus of significant clinical and experimental research. Limitations of clinical studies have forced emphasis onto experimental animal models for the purpose of determining pathophysiology and evaluation of potential therapeutic strategies. However, the apparent failure of many in vivo animal models to predict interventional outcome in humans has raised doubt over their suitability as models of these pathophysiological states. Similar criticism has befallen the use of in vitro techniques for elucidating pathophysiology of the cellular elements. An awareness of the shortcomings of the various experimental models in use would therefore seem prerequisite both to a more critical evaluation of data generated from their use, and to the development of truly effective therapeutic strategies for humans.

Local catheter-based intracoronary radiation therapy for restenosis

Intracoronary radiation therapy was shown to be effective in limiting "restenosis-like" phenomena by inhibiting neointima formation after balloon angioplasty in porcine coronary arteries. Using the same treatment doses, both gamma and beta emitters demonstrated similar results, despite differences in isotope characteristics (e.g., penetration, activity, dose rate, and treatment time). In addition, intracoronary radiation delivered via a catheter-based system prior to coronary stenting reduced neointimal hyperplasia in the porcine model and may further reduce restenosis when coupled with stent implantation. Radioactive stents are of value, especially in large vessels, because of their low activity and proximity to the vessel wall. Adventitial labeling and immunostaining have suggested that the mechanisms by which radiation reduces restenosis are (1) inhibition of smooth muscle cell proliferation in the adventitia and (2) favorable effects on vessel remodeling. Technical radiation considerations are also discussed, including isotope selection, treatment dose, homogeneous dosimetry, treatment time, and total body dose to the patient and healthcare personnel. New catheter-based delivery systems for intracoronary use are currently being developed and are described. Preliminary clinical and angiographic studies using endovascular radiation after balloon angioplasty in both stented and nonstented peripheral and coronary arteries indicate favorable long-term results. In response to the growing enthusiasm for this approach, larger populations must be studied to determine whether this new therapy will influence the restenosis rate and clinical events after angioplasty and, in a broader sense, the field of interventional cardiology.

Potential role of the adventitia in arteritis and atherosclerosis

The role of the adventitia in vascular lesion formation has been largely ignored despite numerous studies which have suggested its potential importance. Adventitial reactions are common in atherosclerosis as well as arteritis. Experimental hypercholesterolemia in pigs and non-human primates stimulates the accumulation of inflammatory cells in the arterial adventitia. The extent of adventitial inflammation associated with human atherosclerotic plaques is correlated with the severity of intimal disease. Adventitial reactions also occur after balloon angioplasty. Our studies indicate that the major site of cell proliferation after angioplasty of porcine coronary arteries is the adventitia and not the medial wall. These cells have been identified as myofibroblasts on the basis of differential staining with smooth muscle specific antibodies and a role for these cells in arterial remodeling associated with angioplasty and late lumen loss is postulated. Evidence from pulse studies with bromodeoxyuridine suggests that adventitial myofibroblasts have the capacity to migrate into the forming intimal lesion after angioplasty and may be a major component of the neointima. Additional work will have to be directed at a more detailed examination of the response of adventitial cells to balloon injury and in the setting of atherosclerosis and arteritis to determine what role these cells might play vascular lesion development.

The arterial wall: a new pharmacological and therapeutic target

In recent years, two key concepts having numerous interrelationships were advanced for the understanding of various cardiovascular diseases: the "endothelial dysfunction" and the "arterial remodelling". Both endothelial dysfunction and arterial remodelling occur in various pathologies including essential hypertension, heart failure, atherosclerosis, restenosis after angioplasty, and pulmonary hypertension, and have modified the therapeutic approach by offering new pharmacological targets: specific receptors not only at the site of the vascular smooth muscle cells but also on the endothelial cells, growth factors that stimulate proliferation of smooth muscle, and receptors and enzymes of the extra-cellular matrix. Among the various substances under research, the present review will discuss angiotensin II receptor antagonists, endothelin receptor antagonists, nitrates-NO donors, potassium channel activators, and substances interfering with proteoglycans and other components of the extra-cellular matrix.

Restenosis--an open file

The main procedural drawback to percutaneous coronary angioplasty is restenosis of the treated site within 6 months. Despite advances in equipment, technique, and adjunctive therapies, restenosis has occurred in approximately one-third to one-half of all patients. The biology of restenosis can be divided into plaque persistence and recoil, thrombus formation and transformation, and cellular proliferation and vascular remodeling. Animal models of restenosis have helped to elucidate these mechanisms of restenosis and provide a means to test pharmacologic and mechanical strategies to reduce stenosis recurrence. While numerous agents have been tested in animal models, until recently none has translated into benefit in large-scale clinical trials. Two therapeutic "hopefuls" which have recently emerged in clinical practice are the potent platelet inhibitors, glycoprotein IIb/IIIa receptor antagonists, and intracoronary metallic stents. The IIb/IIIa receptor antagonists target thrombus formation at the angioplasty site, thereby minimizing abrupt vessel closure acutely and neointimal growth chronically, while intracoronary stents safely produce a large coronary arterial lumen acutely and prevent vessel recoil. Separately, these therapeutic strategies have been shown to reduce clinical restenosis 20-30% at 6-month follow-up. With these encouraging results, the future will certainly provide more pharmacologic and mechanical therapies targeting restenosis. With increased understanding of the restenotic process and continued refinement of effective treatments, it may be possible one day to prevent stenosis recurrence.