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Neovascularization in atherectomy specimens from patients with unstable angina: Implications for pathogenesis of unstable angina
Neovascularization in atherectomy specimens from patients with unstable angina: Implications for pathogenesis of unstable angina Alan N. Tenaglia, MD,a Kevin G. Peters, MD,b Michael H. Sketch, Jr., MD,b and Brian H. Annex, MDb New Orleans, La., and Durham, N.C.
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 neovascularization may play a role in the pathogenesis of unstable angina. (Am Heart J 1998;135:10-4.)
Angiogenesis, the formation of new blood vessels, is a part of normal growth and development. However, angiogenesis is also important in several pathologic conditions such as rheumatoid arthritis, psoriasis, diabetic retinopathy, and tumor growth.1 The presence of neovascularization in atherosclerotic plaque was first noted by Koster2 more than 100 years ago. Barger also documented the existence of neovascularization in atherosclerosis by using cineangiography at autopsy.3 Neovascularization has been postulated to play a role in atherosclerosis by providing growth factors and cytokines to regions of plaque growth.4 The clinical significance of neovascularization in atherosclerosis is unknown. We hypothesized that neovascularization may play a role in the pathogenesis of acute ischemic syndromes such as unstable angina. Therefore the purpose of this study was to determine the frequency of neovascularization in a series of patients treated by directional coronary atherectomy for symptomatic coronary artery disease. The presence or absence of neovascularization in atherectomy samples was determined
From aTulane University Medical Center and bDuke University Medical Center. Guest editor for this manuscript was David R. Holmes, Jr., MD, Internal Medicine and Cardiovascular Diseases, Mayo Clinic, Rochester, Minn. Reprint requests: Alan N. Tenaglia, MD, Cardiology SL-48, Tulane University Medical Center, 1430 Tulane Ave., New Orleans, LA 70112. E-mail: [email protected] Copyright © 1998 by Mosby, Inc. 0002-8703/98/$5.00 + 0 4/1/82089
with immunohistochemical techniques and three different endothelial cell antibodies.
Methods Population Atherectomy tissue was examined from consecutive patients undergoing directional coronary atherectomy for the treatment of symptomatic coronary artery disease. Pertinent clinical data were prospectively collected and entered into a computerized database. Unstable coronary syndrome was defined as rest or postinfarct (<1 week) angina. Stable coronary syndromes included patients with stable, progressive, and new-onset (<6 weeks) angina without rest pain. A restenotic lesion was defined when an atherectomy was performed (>1 week, <6 months) after an interventional procedure at the same site. Percent diameter stenosis was graded semiquantitatively (100%, 95%, 75%, 50%, 25%, <25%, 0%) by experienced angiographers blinded to clinical data. All studies conformed to the guidelines of the institutional review committee.
Tissue preparation and analysis Atherectomy tissue was placed in ice-cold 4% paraformaldehyde (Fisher Scientific) for 2 hours followed by immersion in 30% sucrose/phosphate buffered saline. After embedding in OCT compound (Miles Scientific), tissue was frozen in liquid nitrogen and stored at –70o C. Frozen tissues were cryosectioned (7 µm slices) onto silanized slides, placed in cold acetone for 2 minutes, and stored at –70o C until analyzed. Immunohistochemistry was performed with methods similar to those previously described.5 In brief, blocking solution
Tenaglia et al.
American Heart Journal Volume 135, Number 1
Figure 1
Examples of immunohistochemistry with endothelial cell specific monoclonal antibody (CD-34) demonstrating several areas of neovascularization (red staining) within atherosclerotic plaque from two patients with unstable angina.
was applied for 30 minutes at room temperature. Endothelial cell–specific primary antibodies (BioGenex) were then applied for 30 minutes at room temperature in a humidified chamber. This application was followed by incubation with biotinylated antiimmunoglobulins and alkaline phosphatase conjugated streptavidin (Super Sensitive kit, BioGenex). Levamisole was added to block endogenous alkaline phosphatase activity, and immune complexes were localized with the chromogenic alkaline phosphatase substrate Vector Red (Vector Laboratories). Sections were counterstained with hematoxylin, dehydrated, and mounted with Permount (Fisher Scientific). All sections were stained with the endothelial cell–specific antibodies CD-34 and factor VIII–related antigen. A subset of specimens with sufficient tissue available was also stained with antibodies to a third
endothelial antigen, CD-31. In all experiments adjacent sections were stained with a nonsense murine immunoglobin G monoclonal antibody as a negative control, and sections of human placenta were used as a positive control. At least two sections were evaluated for each patient for the presence of neovascularization with a previously published definition: presence of one or more microvessels (three contiguous nonluminal endothelial cells) per high power (>200×) field.6 With previously described methods, slides were reviewed for the presence of neovascularization by consensus of two independent observers blinded to clinical data.7 In most cases demonstrating neovascularization, there were several areas of new vessels on each slide. All sections were scanned at low power (40×) to identify areas with the highest concentration of discrete microvessels staining with the endothelial–specific anti-
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Tenaglia et al.
American Heart Journal January 1998
Table I. Patient data
Age Male (%) Hypertension (%) Diabetes (%) Hypercholesterolemia (%) Tobacco use (%) Family history (%) Restenotic lesion (%) History of myocardial infarction (%) Diameter of stenosis before DCA Diameter of stenosis after DCA
Total (n = 28)
Unstable angina (n = 18)
Stable angina (n = 10)
58 ± 1 79 67 14 63 78 44 25 38 90 ± 13 12 ± 8
58 ± 12 83 71 11 53 76 47 22 44 92 ± 12 10 ± 8
57 ±16 70 60 20 80 80 40 30 30 87 ± 15 16 ± 8
p Value* 0.87 0.63 0.68 0.60 0.23 >0.99 >0.99 0.67 0.68 0.33 0.09
Data for age and diameter are presented as mean ± SD. DCA, Directional coronary atherectomy. *Unstable vs stable angina.
Table II. Number of microvessels per high-power field Specimen 1 2 3 4 5 6 7 8 9 10
CD-34
Factor VIII
Angina status
Lesion type
7 7 3 18 20 6 20 2 3 20
0 1 0 7 2 2 0 0 0 3
Stable Unstable Unstable Unstable Unstable Unstable Unstable Unstable Unstable Unstable
Restenosis Primary Primary Primary Restenosis Primary Restenosis Primary Restenosis Primary
bodies. The number of new vessels within the area of intimal plaque was then quantified by counting the highest number of individual microvessels on a 200× field.
Statistics Data are reported as mean + SD for continuous data and percentages for discrete data. Comparisons were made with student’s t test or Fisher’s exact test, as appropriate. A p value < 0.05 was considered statistically significant.
Results Twenty-eight patients were entered into the study. Table I lists clinical data. Overall, neovascularization was found in 10 (36%) of 28 specimens. Fig. 1 illustrates neovascularization in atherectomy tissue obtained from two patients with unstable angina. As shown in Table II, in all cases staining was more prominent with the CD-34 antibody than with the factor VIII–related antibody. In positive control placenta tissue, the CD-34 antibody staining was more prominent in the smaller, presumably newer vessels, whereas
the factor VIII antibody staining was more prominent in larger vessels. In a subset of 10 specimens, six with and four without neovascularization, the results for staining with the CD-31 antibody were identical to that with the CD-34 antibody. Neovascularization 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 a trend toward more neovascularization in restenosis lesions (57%) compared with primary lesions (29%, p = 0.21). Other clinical data, including age, sex, hypertension, diabetes, hypercholesterolemia, tobacco use, family history of coronary artery disease, history of myocardial infarction, preprocedure stenosis severity, and postprocedure residual stenosis were not associated with neovascularization.
Discussion Although the presence of angiogenesis in atherosclerosis has been recognized for more than 100 years, this
Tenaglia et al.
American Heart Journal Volume 135, Number 1
is the first study to demonstrate an association of neovascularization with the clinical presentation of an unstable coronary syndrome. Overall, we found neovascularization in 36% of plaques. This finding is similar to findings from the study of O’Brien et al.,6 which found neovascularization in 53% of atherectomy specimens. In addition, our study demonstrated that the frequency of neovascularization may be different depending on the endothelial marker used. Our results, showing better staining with the CD-34 and CD-31 antibodies, are consistent with results noted for tumor angiogenesis, in which the CD-31 antibody stained more blood vessels, especially smaller ones, than factor VIII antibody. 8 The only clinical variable statistically associated with the presence of neovascularization in atherectomy samples was unstable angina, thus implicating neovascularization in the pathogenesis of this disease process. Although it is possible that neovascularization may occur in response to an unstable plaque, there are several possible mechanisms whereby neovascularization may play a more causal role in acute ischemic coronary syndromes. First, accelerated cellular proliferation may occur because regions of plaque neovascularization are consistently associated with the highest number of proliferating cells (macrophages, smooth muscle cells, and endothelial cells).6,9 Second, neovascularization can result in plaque hemorrhage and thrombosis because new vessels are more friable and prone to hemorrhage,10 exposing potentially thrombogenic plaque contents to the vessel lumen. Third, neovascularization may result in increased local levels of leukocytes because of increased cell adhesion molecule expression. P-selectin expression is increased in unstable angina,11 and increased levels of E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 have been noted in areas of plaque neovascularization.12 These leukocytes may release proteases that weaken the plaque,13 resulting in plaque rupture and unstable angina. The finding of neovascularization in patients with restenosis lesions may provide insight into mechanisms for the pathogenesis of unstable angina in this population. Tissue factor protein has been found to be increased in plaque from patients with unstable versus stable angina,5 but restenotic lesions from patients with unstable angina did not contain tissue factor. Smooth muscle cell proliferation is considered the dominant mechanism in the pathogenesis of unstable angina in patients with restenotic lesions; these data suggest that neovascularization may play a role.
Neovascularization plays an important role in development and in other processes such as wound healing. Agents that can decrease neovascularization are being used with great promise as antineoplastic agents.14 The frequent finding of neovascularization in patients with symptomatic coronary artery disease raises the possibility that similar compounds might be useful in preventing or delaying the progression of coronary artery disease. Conversely, angiogenesis may be beneficial for patients with ischemic heart disease by promoting collateral blood flow. Therapeutic procedures designed to augment collateral growth by the administration of vascular endothelial growth factor DNA are currently being tested for treatment of patients with peripheral vascular disease.15 However, our study and the work of other investigators6,16 suggest that this approach will need to account for the possibility that neovascularization may cause unstable coronary syndromes.
Limitations This study is limited by the incomplete sampling of the atherosclerotic plaque obtained by atherectomy. However, use of this tissue avoids selection bias and processing artifacts that are inherent in the use of postmortem tissue. In addition, although the findings for unstable angina are statistically significant, the sample size is relatively small and other significant differences may have been missed (type 2 error).
Conclusions Neovascularization is seen more often in plaque from patients with unstable angina. Neovascularization may be important in the pathogenesis of unstable angina by increasing plaque concentrations of inflammatory cells or cytokines or by increasing the likelihood of plaque hemorrhage and thrombosis.
References 1. Eisenstein R. Angiogenesis in arteries: a review. Pharm Ther 1991;49:1-19. 2. Koster W. Endarteritis and arteritis. Berl Klin Wochenschr 1876;13:454-5. 3. Barger AC, Beeuwkes R III, Lainey LL, Silverman KJ. Hypothesis: vasa vasorum and neovascularization of human coronary arteries. A possible role in the pathophysiology of atherosclerosis. N Engl J Med 1984;310:175-7. 4. Kahlon R, Shapero J, Gotlieb AI. Angiogenesis in atherosclerosis. Can J Cardiol 1992;8:60-4. 5. Annex BH, Denning SM, Channon KM, Sketch MH, Stack RS, Morrissey JH, et al. Differential expression of tissue factor protein in directional atherectomy specimens from patients with stable and unstable coronary syndromes. Circulation 1995;91:619-22. 6. O’Brien ER, Garvin MR, Dev R, Stewart DK, Hinohara T, Simpson JB, et al. Angiogenesis in human coronary atherosclerotic plaques. Am J Pathol 1994;145:883-94.
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7. Wlinder N, Semple JP, Welch WR, Folkman J. Tumor angiogenesis and metastasis—correlation in invasive breast carcinoma. N Engl J Med 1991;324:1-8. 8. Gasparini G, Harris AL. Clinical importance of the determination of tumor angiogenesis in breast carcinoma: much more than a new prognostic tool. J Clin Oncol 1995;13:765-82. 9. O’Brien ER, Alpers CE, Stewart DK, Ferguson M, Tran N, Gordon, et al. Proliferation in primary and restenotic coronary atherectomy tissue. Circ Res 1993;73:223-31. 10. Gimbrone MA Jr, Gullino PM. Neovascularization induced by intraocular xenografts of normal, preneoplastic, and neoplastic mouse mammary tissue. J Nucl Card Imaging 1976;56:305-18. 11. Tenaglia AN, Buda AJ, Wilkins RG, Barron MK, Jeffords PR, Vo K, et al. Levels of expression of P-selectin, E-selectin, and intercellular adhesion molecule-1 in coronary atherectomy specimens from patients with stable and unstable angina pectoris. Am J Cardiol. 1997;79:742-7.
American Heart Journal January 1998
12. O’Brien KD, McDonald TO, Chait A, Allen MD, Alpers CE. Neovascular expression of E-selectin, intercellular adhesion molecule1, and vascular cell adhesion molecule-1 in human atherosclerosis and their relation to intimal leukocyte content. Circulation 1996;93:672-82. 13. Henney AM, Wakeley PR, Davies MJ, Foster K, Hembry R, Murphy G, et al. Localization of stromelysin gene expression in atherosclerotic plaques by in situ hybridization. Proc Natl Acad Sci USA 1991;88:8154-8. 14. Folkman J. Clinical applications of research on angiogenesis. N Engl J Med 1995;333:1757-63. 15. Isner JM, Walsh K, Symes J, Pieczek A, Takeshita S, Lowry J, et al. Arterial gene therapy for therapeutic angiogenesis in patients with peripheral artery disease. Circulation 1995;91:2687-92. 16. Engler DA. Use of vascular endothelial growth factor for therapeutic angiogenesis. Circulation 1996;94:1496-8.
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 neovascularization may play a role in the pathogenesis of unstable angina. (Am Heart J 1998;135:10-4.)
Angiogenesis, the formation of new blood vessels, is a part of normal growth and development. However, angiogenesis is also important in several pathologic conditions such as rheumatoid arthritis, psoriasis, diabetic retinopathy, and tumor growth.1 The presence of neovascularization in atherosclerotic plaque was first noted by Koster2 more than 100 years ago. Barger also documented the existence of neovascularization in atherosclerosis by using cineangiography at autopsy.3 Neovascularization has been postulated to play a role in atherosclerosis by providing growth factors and cytokines to regions of plaque growth.4 The clinical significance of neovascularization in atherosclerosis is unknown. We hypothesized that neovascularization may play a role in the pathogenesis of acute ischemic syndromes such as unstable angina. Therefore the purpose of this study was to determine the frequency of neovascularization in a series of patients treated by directional coronary atherectomy for symptomatic coronary artery disease. The presence or absence of neovascularization in atherectomy samples was determined
From aTulane University Medical Center and bDuke University Medical Center. Guest editor for this manuscript was David R. Holmes, Jr., MD, Internal Medicine and Cardiovascular Diseases, Mayo Clinic, Rochester, Minn. Reprint requests: Alan N. Tenaglia, MD, Cardiology SL-48, Tulane University Medical Center, 1430 Tulane Ave., New Orleans, LA 70112. E-mail: [email protected] Copyright © 1998 by Mosby, Inc. 0002-8703/98/$5.00 + 0 4/1/82089
with immunohistochemical techniques and three different endothelial cell antibodies.
Methods Population Atherectomy tissue was examined from consecutive patients undergoing directional coronary atherectomy for the treatment of symptomatic coronary artery disease. Pertinent clinical data were prospectively collected and entered into a computerized database. Unstable coronary syndrome was defined as rest or postinfarct (<1 week) angina. Stable coronary syndromes included patients with stable, progressive, and new-onset (<6 weeks) angina without rest pain. A restenotic lesion was defined when an atherectomy was performed (>1 week, <6 months) after an interventional procedure at the same site. Percent diameter stenosis was graded semiquantitatively (100%, 95%, 75%, 50%, 25%, <25%, 0%) by experienced angiographers blinded to clinical data. All studies conformed to the guidelines of the institutional review committee.
Tissue preparation and analysis Atherectomy tissue was placed in ice-cold 4% paraformaldehyde (Fisher Scientific) for 2 hours followed by immersion in 30% sucrose/phosphate buffered saline. After embedding in OCT compound (Miles Scientific), tissue was frozen in liquid nitrogen and stored at –70o C. Frozen tissues were cryosectioned (7 µm slices) onto silanized slides, placed in cold acetone for 2 minutes, and stored at –70o C until analyzed. Immunohistochemistry was performed with methods similar to those previously described.5 In brief, blocking solution
Tenaglia et al.
American Heart Journal Volume 135, Number 1
Figure 1
Examples of immunohistochemistry with endothelial cell specific monoclonal antibody (CD-34) demonstrating several areas of neovascularization (red staining) within atherosclerotic plaque from two patients with unstable angina.
was applied for 30 minutes at room temperature. Endothelial cell–specific primary antibodies (BioGenex) were then applied for 30 minutes at room temperature in a humidified chamber. This application was followed by incubation with biotinylated antiimmunoglobulins and alkaline phosphatase conjugated streptavidin (Super Sensitive kit, BioGenex). Levamisole was added to block endogenous alkaline phosphatase activity, and immune complexes were localized with the chromogenic alkaline phosphatase substrate Vector Red (Vector Laboratories). Sections were counterstained with hematoxylin, dehydrated, and mounted with Permount (Fisher Scientific). All sections were stained with the endothelial cell–specific antibodies CD-34 and factor VIII–related antigen. A subset of specimens with sufficient tissue available was also stained with antibodies to a third
endothelial antigen, CD-31. In all experiments adjacent sections were stained with a nonsense murine immunoglobin G monoclonal antibody as a negative control, and sections of human placenta were used as a positive control. At least two sections were evaluated for each patient for the presence of neovascularization with a previously published definition: presence of one or more microvessels (three contiguous nonluminal endothelial cells) per high power (>200×) field.6 With previously described methods, slides were reviewed for the presence of neovascularization by consensus of two independent observers blinded to clinical data.7 In most cases demonstrating neovascularization, there were several areas of new vessels on each slide. All sections were scanned at low power (40×) to identify areas with the highest concentration of discrete microvessels staining with the endothelial–specific anti-
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12
Tenaglia et al.
American Heart Journal January 1998
Table I. Patient data
Age Male (%) Hypertension (%) Diabetes (%) Hypercholesterolemia (%) Tobacco use (%) Family history (%) Restenotic lesion (%) History of myocardial infarction (%) Diameter of stenosis before DCA Diameter of stenosis after DCA
Total (n = 28)
Unstable angina (n = 18)
Stable angina (n = 10)
58 ± 1 79 67 14 63 78 44 25 38 90 ± 13 12 ± 8
58 ± 12 83 71 11 53 76 47 22 44 92 ± 12 10 ± 8
57 ±16 70 60 20 80 80 40 30 30 87 ± 15 16 ± 8
p Value* 0.87 0.63 0.68 0.60 0.23 >0.99 >0.99 0.67 0.68 0.33 0.09
Data for age and diameter are presented as mean ± SD. DCA, Directional coronary atherectomy. *Unstable vs stable angina.
Table II. Number of microvessels per high-power field Specimen 1 2 3 4 5 6 7 8 9 10
CD-34
Factor VIII
Angina status
Lesion type
7 7 3 18 20 6 20 2 3 20
0 1 0 7 2 2 0 0 0 3
Stable Unstable Unstable Unstable Unstable Unstable Unstable Unstable Unstable Unstable
Restenosis Primary Primary Primary Restenosis Primary Restenosis Primary Restenosis Primary
bodies. The number of new vessels within the area of intimal plaque was then quantified by counting the highest number of individual microvessels on a 200× field.
Statistics Data are reported as mean + SD for continuous data and percentages for discrete data. Comparisons were made with student’s t test or Fisher’s exact test, as appropriate. A p value < 0.05 was considered statistically significant.
Results Twenty-eight patients were entered into the study. Table I lists clinical data. Overall, neovascularization was found in 10 (36%) of 28 specimens. Fig. 1 illustrates neovascularization in atherectomy tissue obtained from two patients with unstable angina. As shown in Table II, in all cases staining was more prominent with the CD-34 antibody than with the factor VIII–related antibody. In positive control placenta tissue, the CD-34 antibody staining was more prominent in the smaller, presumably newer vessels, whereas
the factor VIII antibody staining was more prominent in larger vessels. In a subset of 10 specimens, six with and four without neovascularization, the results for staining with the CD-31 antibody were identical to that with the CD-34 antibody. Neovascularization 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 a trend toward more neovascularization in restenosis lesions (57%) compared with primary lesions (29%, p = 0.21). Other clinical data, including age, sex, hypertension, diabetes, hypercholesterolemia, tobacco use, family history of coronary artery disease, history of myocardial infarction, preprocedure stenosis severity, and postprocedure residual stenosis were not associated with neovascularization.
Discussion Although the presence of angiogenesis in atherosclerosis has been recognized for more than 100 years, this
Tenaglia et al.
American Heart Journal Volume 135, Number 1
is the first study to demonstrate an association of neovascularization with the clinical presentation of an unstable coronary syndrome. Overall, we found neovascularization in 36% of plaques. This finding is similar to findings from the study of O’Brien et al.,6 which found neovascularization in 53% of atherectomy specimens. In addition, our study demonstrated that the frequency of neovascularization may be different depending on the endothelial marker used. Our results, showing better staining with the CD-34 and CD-31 antibodies, are consistent with results noted for tumor angiogenesis, in which the CD-31 antibody stained more blood vessels, especially smaller ones, than factor VIII antibody. 8 The only clinical variable statistically associated with the presence of neovascularization in atherectomy samples was unstable angina, thus implicating neovascularization in the pathogenesis of this disease process. Although it is possible that neovascularization may occur in response to an unstable plaque, there are several possible mechanisms whereby neovascularization may play a more causal role in acute ischemic coronary syndromes. First, accelerated cellular proliferation may occur because regions of plaque neovascularization are consistently associated with the highest number of proliferating cells (macrophages, smooth muscle cells, and endothelial cells).6,9 Second, neovascularization can result in plaque hemorrhage and thrombosis because new vessels are more friable and prone to hemorrhage,10 exposing potentially thrombogenic plaque contents to the vessel lumen. Third, neovascularization may result in increased local levels of leukocytes because of increased cell adhesion molecule expression. P-selectin expression is increased in unstable angina,11 and increased levels of E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 have been noted in areas of plaque neovascularization.12 These leukocytes may release proteases that weaken the plaque,13 resulting in plaque rupture and unstable angina. The finding of neovascularization in patients with restenosis lesions may provide insight into mechanisms for the pathogenesis of unstable angina in this population. Tissue factor protein has been found to be increased in plaque from patients with unstable versus stable angina,5 but restenotic lesions from patients with unstable angina did not contain tissue factor. Smooth muscle cell proliferation is considered the dominant mechanism in the pathogenesis of unstable angina in patients with restenotic lesions; these data suggest that neovascularization may play a role.
Neovascularization plays an important role in development and in other processes such as wound healing. Agents that can decrease neovascularization are being used with great promise as antineoplastic agents.14 The frequent finding of neovascularization in patients with symptomatic coronary artery disease raises the possibility that similar compounds might be useful in preventing or delaying the progression of coronary artery disease. Conversely, angiogenesis may be beneficial for patients with ischemic heart disease by promoting collateral blood flow. Therapeutic procedures designed to augment collateral growth by the administration of vascular endothelial growth factor DNA are currently being tested for treatment of patients with peripheral vascular disease.15 However, our study and the work of other investigators6,16 suggest that this approach will need to account for the possibility that neovascularization may cause unstable coronary syndromes.
Limitations This study is limited by the incomplete sampling of the atherosclerotic plaque obtained by atherectomy. However, use of this tissue avoids selection bias and processing artifacts that are inherent in the use of postmortem tissue. In addition, although the findings for unstable angina are statistically significant, the sample size is relatively small and other significant differences may have been missed (type 2 error).
Conclusions Neovascularization is seen more often in plaque from patients with unstable angina. Neovascularization may be important in the pathogenesis of unstable angina by increasing plaque concentrations of inflammatory cells or cytokines or by increasing the likelihood of plaque hemorrhage and thrombosis.
References 1. Eisenstein R. Angiogenesis in arteries: a review. Pharm Ther 1991;49:1-19. 2. Koster W. Endarteritis and arteritis. Berl Klin Wochenschr 1876;13:454-5. 3. Barger AC, Beeuwkes R III, Lainey LL, Silverman KJ. Hypothesis: vasa vasorum and neovascularization of human coronary arteries. A possible role in the pathophysiology of atherosclerosis. N Engl J Med 1984;310:175-7. 4. Kahlon R, Shapero J, Gotlieb AI. Angiogenesis in atherosclerosis. Can J Cardiol 1992;8:60-4. 5. Annex BH, Denning SM, Channon KM, Sketch MH, Stack RS, Morrissey JH, et al. Differential expression of tissue factor protein in directional atherectomy specimens from patients with stable and unstable coronary syndromes. Circulation 1995;91:619-22. 6. O’Brien ER, Garvin MR, Dev R, Stewart DK, Hinohara T, Simpson JB, et al. Angiogenesis in human coronary atherosclerotic plaques. Am J Pathol 1994;145:883-94.
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7. Wlinder N, Semple JP, Welch WR, Folkman J. Tumor angiogenesis and metastasis—correlation in invasive breast carcinoma. N Engl J Med 1991;324:1-8. 8. Gasparini G, Harris AL. Clinical importance of the determination of tumor angiogenesis in breast carcinoma: much more than a new prognostic tool. J Clin Oncol 1995;13:765-82. 9. O’Brien ER, Alpers CE, Stewart DK, Ferguson M, Tran N, Gordon, et al. Proliferation in primary and restenotic coronary atherectomy tissue. Circ Res 1993;73:223-31. 10. Gimbrone MA Jr, Gullino PM. Neovascularization induced by intraocular xenografts of normal, preneoplastic, and neoplastic mouse mammary tissue. J Nucl Card Imaging 1976;56:305-18. 11. Tenaglia AN, Buda AJ, Wilkins RG, Barron MK, Jeffords PR, Vo K, et al. Levels of expression of P-selectin, E-selectin, and intercellular adhesion molecule-1 in coronary atherectomy specimens from patients with stable and unstable angina pectoris. Am J Cardiol. 1997;79:742-7.
American Heart Journal January 1998
12. O’Brien KD, McDonald TO, Chait A, Allen MD, Alpers CE. Neovascular expression of E-selectin, intercellular adhesion molecule1, and vascular cell adhesion molecule-1 in human atherosclerosis and their relation to intimal leukocyte content. Circulation 1996;93:672-82. 13. Henney AM, Wakeley PR, Davies MJ, Foster K, Hembry R, Murphy G, et al. Localization of stromelysin gene expression in atherosclerotic plaques by in situ hybridization. Proc Natl Acad Sci USA 1991;88:8154-8. 14. Folkman J. Clinical applications of research on angiogenesis. N Engl J Med 1995;333:1757-63. 15. Isner JM, Walsh K, Symes J, Pieczek A, Takeshita S, Lowry J, et al. Arterial gene therapy for therapeutic angiogenesis in patients with peripheral artery disease. Circulation 1995;91:2687-92. 16. Engler DA. Use of vascular endothelial growth factor for therapeutic angiogenesis. Circulation 1996;94:1496-8.