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Circulating Endothelial Progenitor Cells and In-Stent Restenosis: Friend, Foe, or None of the Above?
Canadian Journal of Cardiology 30 (2014) 6e7
Editorial
Circulating Endothelial Progenitor Cells and In-Stent Restenosis: Friend, Foe, or None of the Above? Benjamin Hibbert, MD,a and Edward R. O’Brien, MDb a b
Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario, Canada
Division of Cardiology, Libin Cardiovascular Institute of Alberta, Calgary, Alberta, Canada
See article by Haine et al., pages 102-108 of this issue.
Percutaneous coronary intervention with implantation of a metallic or bioresorbable stent remains the cornerstone of modern coronary revascularization.1 Because of the regularity with which percutaneous coronary intervention is performed, in-stent restenosis (ISR) continues to be a frequent clinical entity despite remarkable advancements in stent technology, including cytostatic drug elution, improved polymer technology, and optimized stent architecture. Remarkably, the precise mechanism of ISR remains incompletely understood and predictive models, including the identification of novel biomarkers, to permit identification of patients who will develop vessel renarrowing is needed. Endothelial progenitor cells (EPCs) were first described by Asahara et al.2 in 1997 and subsequently this term has been used to describe cells derived from culture-based assays and circulating cells enumerated using flow cytometry.3 The term, circulating progenitor cells (CPCs), or circulating endothelial progenitors, has typically been reserved to describe cells expressing CD34 with a combination of vascular endothelial growth factor receptor-2 (VEGFR-2 or KDR), and/or CD133. In contrast, culture-based assays that yield angiogenic outgrowth cells have also been used to enumerate “EPCs” with early outgrowth of nonproliferative populations, termed cultured angiogenic cells or CACs.4 CPCs and CACs have been studied extensively for their role in vascular repair and their association with clinical outcomes. Indeed, the first evidence that highlighted progenitors might be important to artery homeostasis came from rodent models of vascular injury that demonstrated mobilization and homing to the injured vessel wall, improving re-endothelialization and reducing neointima formation.5,6 As
Received for publication November 12, 2013. Accepted November 12, 2013. Corresponding author: Dr Edward R. O’Brien, Division of Cardiology, Libin Cardiovascular Institute of Alberta, Foothills Medical Centre, Room C823, 1403-29th St NW, Calgary, Alberta T2N 2T9, Canada. Tel.: þ1-403944-5918; fax: þ1-403-944-2906. E-mail: [email protected] See page 7 for disclosure information.
well, CACs7 and CPCs8 are predictive of cardiovascular events thereby leading to the exciting possibility that vascular progenitor populations might play roles as a biomarker and a novel therapeutic target. Hence, a number of groups have tried to develop innovative strategies to leverage our understanding of progenitor cell biology to improve stent performance. The Genous CD34 antibody-coated stent attempted to improve EPC adherence to improve re-endothelialization after stent implantation but has met with mixed clinical performance.9 In contrast, our group has sought to improve EPC paracrine function by eluting inhibitors of glycogen synthase kinase 3b or heat shock protein 27 with reliable improvements in re-endothelialization observed in preclinical stent models.10-12 However, development of an intima within the stented vessel is only in part regulated by progenitor cell biology, and clinical application of these technologies is likely to be used as a complement to existing platforms rather than as a stand-alone therapy for prevention of ISR. Another application that has been the subject of numerous studies is the performance of CAC and CPC number and/or function as a predictor of developing ISR. CAC number and adhesive properties have been reported to be predictive of developing binary ISR.13,14 CPC performance as a biomarker has yielded mixed results with some groups reporting higher15 and some studies lower numbers16 of cells as predictive of binary restenosis or the need for target lesion revascularization. However, the divergent results might, at least in part, be explained by differences in the definition of CPC used, the population studied, and in the concomitant medical therapy17dall factors known to confound CPC levels. In this issue of the Canadian Journal of Cardiology, Haine et al.18 report on the relationship between CPC levels and 6month late lumen loss (LLL) quantified using quantitative coronary angiography in 98 patients receiving bare metal stents. In this large prospective cohort, CPCsddefined as CD34þ/KDRþdfailed to demonstrate any relationship with LLL or percentage of intimal hyperplasia on intravascular ultrasound. This study stands as an important negative result and the authors are to be congratulated for their thoughtful
0828-282X/$ - see front matter Ó 2014 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.cjca.2013.11.010
Hibbert and O’Brien Circulating EPCs and In-Stent Restenosis
design of the study to exclude confounding variables. Moreover, the size of the cohort and the use of LLL as an end point allowed them to adjust for numerous variablesdincluding the use of statin medication.19 As a result, the potential value of this subset of progenitor cells as a biomarker for patients undergoing bare metal stent implantation can be conclusively discounted. However, a number of important questions regarding the role of EPCs in the prediction of ISR remain. Perhaps most evident is the potential role of other subsets of progenitor cellsdin particular, the performance of cells quantified using a modified International Society of Hematotherapy and Graft Engineering (ISHAGE) protocol20,21 to quantify CD45dim/ CD34þ/KDRþ, with the inclusion of additional markers (ie, CD117 or CD133), and/or of CACs. Second, although the current article questions the use of CD34/KDR cells as a biomarker in the population studieddas recognized by the authorsdthe performance of these cells in other patient cohorts remains to be validated or refuted. Nonetheless, this study serves as a model for the design and undertaking of future studies of CPCs and ISR and reminds us of the significant contribution negative results make to understanding biology and clinical phenomena. Disclosures The authors have no conflicts of interest to disclose. References 1. Ouzounian M, Ghali W, Yip AM, et al. Determinants of percutaneous coronary intervention vs coronary artery bypass grafting: an interprovincial comparison. Can J Cardiol 2013;29:1454-61.
7
8. Werner N, Kosiol S, Schiegl T, et al. Circulating endothelial progenitor cells and cardiovascular outcomes. N Engl J Med 2005;353:999-1007. 9. Beijk MA, Klomp M, Verouden NJ, et al. Genous endothelial progenitor cell capturing stent vs. the Taxus Liberte stent in patients with de novo coronary lesions with a high-risk of coronary restenosis: a randomized, single-centre, pilot study. Eur Heart J 2010;31:1055-64. 10. Hibbert B, Ma X, Pourdjabbar A, et al. Inhibition of endothelial progenitor cell glycogen synthase kinase-3beta results in attenuated neointima formation and enhanced re-endothelialization after arterial injury. Cardiovasc Res 2009;83:16-23. 11. Ma X, Hibbert B, Dhaliwal B, et al. Delayed re-endothelialization with rapamycin-coated stents is rescued by the addition of a glycogen synthase kinase-3beta inhibitor. Cardiovasc Res 2010;86:338-45. 12. Ma X, Hibbert B, McNulty M, et al. Heat shock protein 27 attenuates neointima formation and accelerates reendothelialization after arterial injury and stent implantation: importance of vascular endothelial growth factor up-regulation. FASEB 2013. [Epub ahead of print] 13. Hibbert B, Chen YX, O’Brien ER. c-kit-immunopositive vascular progenitor cells populate human coronary in-stent restenosis but not primary atherosclerotic lesions. Am J Physiol Heart Circ Physiol 2004;287:H518-24. 14. George J, Herz I, Goldstein E, et al. Number and adhesive properties of circulating endothelial progenitor cells in patients with in-stent restenosis. Arterioscler Thromb Vasc Biol 2003;23:e57-60. 15. Bonello L, Harhouri K, Baumstarck K, et al. Mobilization of CD34þ KDRþ endothelial progenitor cells predicts target lesion revascularization. J Thromb Haemost 2012;10:1906-13.
2. Asahara T, Murohara T, Sullivan A, et al. Isolation of putative progenitor endothelial cells for angiogenesis. Science 1997;275:964-7.
16. Pelliccia F, Cianfrocca C, Rosano G, et al. Role of endothelial progenitor cells in restenosis and progression of coronary atherosclerosis after percutaneous coronary intervention: a prospective study. JACC Cardiovasc Interv 2010;3:78-86.
3. Costiniuk CT, Hibbert BM, Simard T, et al. Circulating endothelial progenitor cells in HIV infection: a systematic review. Trends Cardiovasc Med 2013;23:192-200.
17. Hibbert B, Ma X, Pourdjabbar A, et al. Pre-procedural atorvastatin mobilizes endothelial progenitor cells: clues to the salutary effects of statins on healing of stented human arteries. PLoS One 2011;6:e16413.
4. Hirschi KK, Ingram DA, Yoder MC. Assessing identity, phenotype, and fate of endothelial progenitor cells. Arterioscler Thromb Vasc Biol 2008;28:1584-95.
18. Haine SE, Van Craenenbroeck EM, Hoymans VY, et al. Levels of circulating CD34þ/KDRþ cells do not predict coronary in-stent restenosis. Can J Cardiol 2014;30:102-8.
5. Werner N, Priller J, Laufs U, et al. Bone marrow-derived progenitor cells modulate vascular reendothelialization and neointimal formation: effect of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibition. Arterioscler Thromb Vasc Biol 2002;22:1567-72.
19. Hibbert B, Simard T, Ramirez FD, et al. The effect of statins on circulating endothelial progenitor cells in humans: a systematic review. J Cardiovasc Pharmacol 2013;62:491-6.
6. Werner N, Junk S, Laufs U, et al. Intravenous transfusion of endothelial progenitor cells reduces neointima formation after vascular injury. Circ Res 2003;93:e17-24.
20. Schmidt-Lucke C, Fichtlscherer S, Aicher A, et al. Quantification of circulating endothelial progenitor cells using the modified ISHAGE protocol. PLoS One 2010;5:e13790.
7. Hill JM, Zalos G, Halcox JP, et al. Circulating endothelial progenitor cells, vascular function, and cardiovascular risk. N Engl J Med 2003;348: 593-600.
21. Costiniuk CT, Hibbert BM, Filion LG, et al. Circulating endothelial progenitor cell levels are not reduced in HIV-infected men. J Infect Dis 2012;205:713-7.
Editorial
Circulating Endothelial Progenitor Cells and In-Stent Restenosis: Friend, Foe, or None of the Above? Benjamin Hibbert, MD,a and Edward R. O’Brien, MDb a b
Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario, Canada
Division of Cardiology, Libin Cardiovascular Institute of Alberta, Calgary, Alberta, Canada
See article by Haine et al., pages 102-108 of this issue.
Percutaneous coronary intervention with implantation of a metallic or bioresorbable stent remains the cornerstone of modern coronary revascularization.1 Because of the regularity with which percutaneous coronary intervention is performed, in-stent restenosis (ISR) continues to be a frequent clinical entity despite remarkable advancements in stent technology, including cytostatic drug elution, improved polymer technology, and optimized stent architecture. Remarkably, the precise mechanism of ISR remains incompletely understood and predictive models, including the identification of novel biomarkers, to permit identification of patients who will develop vessel renarrowing is needed. Endothelial progenitor cells (EPCs) were first described by Asahara et al.2 in 1997 and subsequently this term has been used to describe cells derived from culture-based assays and circulating cells enumerated using flow cytometry.3 The term, circulating progenitor cells (CPCs), or circulating endothelial progenitors, has typically been reserved to describe cells expressing CD34 with a combination of vascular endothelial growth factor receptor-2 (VEGFR-2 or KDR), and/or CD133. In contrast, culture-based assays that yield angiogenic outgrowth cells have also been used to enumerate “EPCs” with early outgrowth of nonproliferative populations, termed cultured angiogenic cells or CACs.4 CPCs and CACs have been studied extensively for their role in vascular repair and their association with clinical outcomes. Indeed, the first evidence that highlighted progenitors might be important to artery homeostasis came from rodent models of vascular injury that demonstrated mobilization and homing to the injured vessel wall, improving re-endothelialization and reducing neointima formation.5,6 As
Received for publication November 12, 2013. Accepted November 12, 2013. Corresponding author: Dr Edward R. O’Brien, Division of Cardiology, Libin Cardiovascular Institute of Alberta, Foothills Medical Centre, Room C823, 1403-29th St NW, Calgary, Alberta T2N 2T9, Canada. Tel.: þ1-403944-5918; fax: þ1-403-944-2906. E-mail: [email protected] See page 7 for disclosure information.
well, CACs7 and CPCs8 are predictive of cardiovascular events thereby leading to the exciting possibility that vascular progenitor populations might play roles as a biomarker and a novel therapeutic target. Hence, a number of groups have tried to develop innovative strategies to leverage our understanding of progenitor cell biology to improve stent performance. The Genous CD34 antibody-coated stent attempted to improve EPC adherence to improve re-endothelialization after stent implantation but has met with mixed clinical performance.9 In contrast, our group has sought to improve EPC paracrine function by eluting inhibitors of glycogen synthase kinase 3b or heat shock protein 27 with reliable improvements in re-endothelialization observed in preclinical stent models.10-12 However, development of an intima within the stented vessel is only in part regulated by progenitor cell biology, and clinical application of these technologies is likely to be used as a complement to existing platforms rather than as a stand-alone therapy for prevention of ISR. Another application that has been the subject of numerous studies is the performance of CAC and CPC number and/or function as a predictor of developing ISR. CAC number and adhesive properties have been reported to be predictive of developing binary ISR.13,14 CPC performance as a biomarker has yielded mixed results with some groups reporting higher15 and some studies lower numbers16 of cells as predictive of binary restenosis or the need for target lesion revascularization. However, the divergent results might, at least in part, be explained by differences in the definition of CPC used, the population studied, and in the concomitant medical therapy17dall factors known to confound CPC levels. In this issue of the Canadian Journal of Cardiology, Haine et al.18 report on the relationship between CPC levels and 6month late lumen loss (LLL) quantified using quantitative coronary angiography in 98 patients receiving bare metal stents. In this large prospective cohort, CPCsddefined as CD34þ/KDRþdfailed to demonstrate any relationship with LLL or percentage of intimal hyperplasia on intravascular ultrasound. This study stands as an important negative result and the authors are to be congratulated for their thoughtful
0828-282X/$ - see front matter Ó 2014 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.cjca.2013.11.010
Hibbert and O’Brien Circulating EPCs and In-Stent Restenosis
design of the study to exclude confounding variables. Moreover, the size of the cohort and the use of LLL as an end point allowed them to adjust for numerous variablesdincluding the use of statin medication.19 As a result, the potential value of this subset of progenitor cells as a biomarker for patients undergoing bare metal stent implantation can be conclusively discounted. However, a number of important questions regarding the role of EPCs in the prediction of ISR remain. Perhaps most evident is the potential role of other subsets of progenitor cellsdin particular, the performance of cells quantified using a modified International Society of Hematotherapy and Graft Engineering (ISHAGE) protocol20,21 to quantify CD45dim/ CD34þ/KDRþ, with the inclusion of additional markers (ie, CD117 or CD133), and/or of CACs. Second, although the current article questions the use of CD34/KDR cells as a biomarker in the population studieddas recognized by the authorsdthe performance of these cells in other patient cohorts remains to be validated or refuted. Nonetheless, this study serves as a model for the design and undertaking of future studies of CPCs and ISR and reminds us of the significant contribution negative results make to understanding biology and clinical phenomena. Disclosures The authors have no conflicts of interest to disclose. References 1. Ouzounian M, Ghali W, Yip AM, et al. Determinants of percutaneous coronary intervention vs coronary artery bypass grafting: an interprovincial comparison. Can J Cardiol 2013;29:1454-61.
7
8. Werner N, Kosiol S, Schiegl T, et al. Circulating endothelial progenitor cells and cardiovascular outcomes. N Engl J Med 2005;353:999-1007. 9. Beijk MA, Klomp M, Verouden NJ, et al. Genous endothelial progenitor cell capturing stent vs. the Taxus Liberte stent in patients with de novo coronary lesions with a high-risk of coronary restenosis: a randomized, single-centre, pilot study. Eur Heart J 2010;31:1055-64. 10. Hibbert B, Ma X, Pourdjabbar A, et al. Inhibition of endothelial progenitor cell glycogen synthase kinase-3beta results in attenuated neointima formation and enhanced re-endothelialization after arterial injury. Cardiovasc Res 2009;83:16-23. 11. Ma X, Hibbert B, Dhaliwal B, et al. Delayed re-endothelialization with rapamycin-coated stents is rescued by the addition of a glycogen synthase kinase-3beta inhibitor. Cardiovasc Res 2010;86:338-45. 12. Ma X, Hibbert B, McNulty M, et al. Heat shock protein 27 attenuates neointima formation and accelerates reendothelialization after arterial injury and stent implantation: importance of vascular endothelial growth factor up-regulation. FASEB 2013. [Epub ahead of print] 13. Hibbert B, Chen YX, O’Brien ER. c-kit-immunopositive vascular progenitor cells populate human coronary in-stent restenosis but not primary atherosclerotic lesions. Am J Physiol Heart Circ Physiol 2004;287:H518-24. 14. George J, Herz I, Goldstein E, et al. Number and adhesive properties of circulating endothelial progenitor cells in patients with in-stent restenosis. Arterioscler Thromb Vasc Biol 2003;23:e57-60. 15. Bonello L, Harhouri K, Baumstarck K, et al. Mobilization of CD34þ KDRþ endothelial progenitor cells predicts target lesion revascularization. J Thromb Haemost 2012;10:1906-13.
2. Asahara T, Murohara T, Sullivan A, et al. Isolation of putative progenitor endothelial cells for angiogenesis. Science 1997;275:964-7.
16. Pelliccia F, Cianfrocca C, Rosano G, et al. Role of endothelial progenitor cells in restenosis and progression of coronary atherosclerosis after percutaneous coronary intervention: a prospective study. JACC Cardiovasc Interv 2010;3:78-86.
3. Costiniuk CT, Hibbert BM, Simard T, et al. Circulating endothelial progenitor cells in HIV infection: a systematic review. Trends Cardiovasc Med 2013;23:192-200.
17. Hibbert B, Ma X, Pourdjabbar A, et al. Pre-procedural atorvastatin mobilizes endothelial progenitor cells: clues to the salutary effects of statins on healing of stented human arteries. PLoS One 2011;6:e16413.
4. Hirschi KK, Ingram DA, Yoder MC. Assessing identity, phenotype, and fate of endothelial progenitor cells. Arterioscler Thromb Vasc Biol 2008;28:1584-95.
18. Haine SE, Van Craenenbroeck EM, Hoymans VY, et al. Levels of circulating CD34þ/KDRþ cells do not predict coronary in-stent restenosis. Can J Cardiol 2014;30:102-8.
5. Werner N, Priller J, Laufs U, et al. Bone marrow-derived progenitor cells modulate vascular reendothelialization and neointimal formation: effect of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibition. Arterioscler Thromb Vasc Biol 2002;22:1567-72.
19. Hibbert B, Simard T, Ramirez FD, et al. The effect of statins on circulating endothelial progenitor cells in humans: a systematic review. J Cardiovasc Pharmacol 2013;62:491-6.
6. Werner N, Junk S, Laufs U, et al. Intravenous transfusion of endothelial progenitor cells reduces neointima formation after vascular injury. Circ Res 2003;93:e17-24.
20. Schmidt-Lucke C, Fichtlscherer S, Aicher A, et al. Quantification of circulating endothelial progenitor cells using the modified ISHAGE protocol. PLoS One 2010;5:e13790.
7. Hill JM, Zalos G, Halcox JP, et al. Circulating endothelial progenitor cells, vascular function, and cardiovascular risk. N Engl J Med 2003;348: 593-600.
21. Costiniuk CT, Hibbert BM, Filion LG, et al. Circulating endothelial progenitor cell levels are not reduced in HIV-infected men. J Infect Dis 2012;205:713-7.