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J Am Coll Cardiol, 2004; 44:1408-1414, doi:10.1016/j.jacc.2004.06.066 © 2004 by the American College of Cardiology Foundation |
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* Department of Cardiovascular and Renal Medicine, Saga University Faculty of Medicine, Saga, Japan
Department of Cardiology, Koshigaya Hospital, Dokkyo University School of Medicine, Koshigaya, Japan
Yufu Itonaga Company, Tokyo, Japan
Department of Laboratory Medicine, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Tamaho, Japan
Manuscript received May 12, 2004; revised manuscript received June 23, 2004, accepted June 29, 2004.
* Reprint requests and correspondence: Dr. Teruo Inoue, Department of Cardiovascular and Renal Medicine, Saga University Faculty of Medicine, 5-1-1 Nabeshima, Saga 849-8501, Japan (Email: inouete{at}med.saga-uc.ac.jp).
| Abstract |
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BACKGROUND: The platelet phosphodiesterase III inhibitor called cilostazol also inhibits alpha-granule release of P-selectin in platelets. The P-selectinmediated platelet-leukocyte interaction promotes activation and upregulation of leukocyte Mac-1 after coronary stenting, which plays a key role on the mechanism of restenosis. Thus, cilostazol's potential inhibition of this process may lead to prevention of restenosis.
METHODS: Using flow cytometric analysis of whole blood obtained from the coronary sinus, the expression of platelet membrane glycoproteins and neutrophil adhesion molecules was observed in 70 consecutive patients undergoing coronary stenting. The patients were randomly assigned to either a cilostazol or ticlopidine group before stent placement.
RESULTS: The restenosis rate was lower (15% vs. 31%, p < 0.05) in the cilostazol group (n = 34) than in the ticlopidine group (n = 32). A stent-induced increase in platelet P-selectin (CD62P) expression and an increase in neutrophil Mac-1 (CD11b) expression were suppressed in the cilostazol group compared with the ticlopidine group. Angiographic late lumen loss was correlated with the relative changes in platelet P-selectin and neutrophil Mac-1 at 48 h after coronary stenting.
CONCLUSIONS: Cilostazol may have effects on suppression of P-selectinmediated platelet activation, platelet-leukocyte interaction, and subsequent Mac-1mediated leukocyte activation, which might lead to a reduced restenosis rate after coronary stent implantation.
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The activation of leukocytes, neutrophils, and monocytes, as well as their interaction with platelets mediated by cell adhesion molecules, are known to play an important causative role in the development of restenosis after percutaneous coronary intervention (PCI) (710). Among various adhesion molecules, leukocyte integrin, Mac-1 (CD11b/CD18), is considered to be one of the key proteins in the mechanism of restenosis. Clinical evidence indicates that PCI results in activation and upregulation of Mac-1 on the surface of neutrophils in association with restenosis (1015). In experimental models, Mac-1 blockade (16) or the absence of Mac-1 (17) suppressed neointimal thickening after PCI. There is increasing evidence that the interaction between platelets and leukocytes across an adherent layer of platelets precedes diapedesis and the infiltration of inflammatory cells into the PCI-induced injured vessel wall, which is denuded of vascular endothelial cells by balloon inflation (1820). Platelet surface P-selectin mediates the rolling attachment of leukocytes with the platelet layer (21,22). Furthermore, Mac-1 is of particular importance in the process of transplatelet migration and firm adhesion of leukocytes. In the process of the platelet-leukocyte interaction, an adhesion cascade appears to occur with considerable cross-talk between P-selectin and Mac-1 (20,21). Thus, we hypothesize that cilostazol's inhibitory effects on P-selectinmediated platelet-leukocyte interactions would also suppress leukocyte Mac-1 expression that leads to the prevention of neointimal thickening and restenosis.
To confirm this hypothesis clinically, we measured the in vivo expression of Mac-1 on the surface of neutrophils, as well as that of P-selectin on the surface of platelets in patients undergoing coronary stenting, and we compared two post-stent antiplatelet regimenscilostazol and ticlopidine. In addition, we also assessed cilostazol's direct action on neutrophil Mac-1 expression in an in vitro experiment.
| Methods |
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Expression of activation-dependent P-selectin on surface of platelets. Flow cytometric analysis of the internal alpha-granule membrane protein P-selectin expressed on the surface of activated platelets was performed using phycoerythrin-labeled anti-CD62P (Immunotech, Eugene, Oregon). Isotype-, fluorochrome-, and protein concentration-matched controls were run in parallel for phycoerythrin-labeled immunoglobulin G (IgG1) (Dako Cytomation, Glostrup, Denmark). Immunofluorescence staining was performed using minor modifications of previously published procedures. Briefly, 100 µl of whole blood was first fixed in 1 ml of 1% paraformaldehyde for 2 h at 4°C. After centrifugation at 10,000 rpm for 1 min, the supernatant was removed, and the pellets were washed twice with 1 ml of phosphate-buffered saline (PBS), followed by centrifugation at 10,000 rpm for 1 min. The pellets were then suspended in 1 ml of PBS with 0.1% bovine serum albumin and 20 µl of each monoclonal antibody was added. After incubation in the dark for 15 min at room temperature, the samples were washed once more and suspended in 1 ml of PBS. A FACSCalibur laser flow cytometry system (BD Bioscience, San Jose, California) was used for flow cytometry and calibrated daily with a mixture of monosized, fluorescent beads (CaliBRITE, BD Bioscience). We analyzed scatter signals and fluorescence intensity. The light-scattering properties projected on a scattergram identified the platelet cluster. Fluorescence intensity was expressed on individual cytohistograms, with the region of interest limited to the platelet cluster. The mean channel fluorescence intensity (MFI)was calculated as an index of the expression of P-selectin.
Expression of Mac-1 on surface of neutrophils in vivo. The expression of the adhesion molecule, Mac-1, on the surface of neutrophils was analyzed in the same manner as previously described. Briefly, whole blood was immediately collected into a tube containing acid citrate dextrose. Immunofluorescence staining was performed using fluorescein isothiocyanate (FITC)-labeled anti-CD16b (1D3; Beckman Coulter, Fullerton, California) and phycoerythrin-labeled anti-CD11b (Leu 15; Becton Dickinson). Isotype controls were run in parallel for FITC-labeled IgG1 (BD Bioscience) and phycoerythrin-labeled IgG2a (BD Bioscience). After completion of hemolysis by the lysing solution, the white blood cell sediment was fixed in a paraformaldehyde solution with PBS. Flow cytometric analysis was then performed using the FACSCalibur laser flow cytometer. We could detect neutrophils as CD16b-positive cells. Expression of CD11b (Mac-1 specific alpha subunit) on the surface of neutrophils was detected as MFI of phycoerythrin fluorescence.
In vitro assessment of cilostazol's direct action on neutrophil Mac-1. Blood was collected from seven healthy volunteers with sodium citrate. After completion of hemolysis, the white blood cells were sedimented, rinsed, and suspended. Cilostazol was dissolved in dimethyl sulfoxide (DMSO), and 3, 10, and 30 µmol/l doses of cilostazol were co-incubated with the white blood cell suspension and stimulated with 0.05 µmol/l of formyl-methyonyl leucyl phenylalanine (FMLP) for 24 h. Both FITC-labeled anti-CD16b and phycoerythrin-labeled anti-CD11b were added to the white blood cell suspension and incubated. Neutrophils were detected as CD16b-positive cells using the FACSCalibur flow cytometer. Expression of CD11b on the surface of neutrophils was detected as MFI of phycoerythrin fluorescence.
Statistical analysis. Data are expressed as the mean value ± SD. A comparison of clinical variables between the two groups was performed using the Mann-Whitney U test for continuous variables and the chi-square test for categorical variables. Serial changes in the in vivo variables were evaluated by repeated measures analysis of variance with Dunnett's post-hoc test for intra- and inter-group comparisons. In vitro tests were analyzed by the nonparametric Friedman test. Correlations between two parameters were evaluated by simple linear regression. The p values of <0.05 were considered significant.
| Results |
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Neointimal thickening and cell adhesion molecules. Angiographic late lumen loss was correlated with relative changes in platelet P-selectin (r = 0.27, p < 0.05) and neutrophil CD11b (r = 0.37, p < 0.01) at 48 h after coronary stenting (Fig. 2).
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| Discussion |
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Mechanisms of cilostazol's action. Cilostazol acts as a selective inhibitor of PDE type III, an enzyme that breaks down cyclic adenosine monophosphate (cAMP). A higher level of cAMP stimulates the production of cAMP-dependent protein kinase, resulting in a lower level of intracellular Ca++ within platelets, which, in turn, suppresses platelet activity (23). In addition to PDE III inhibition, we have observed a previous in vitro study that cilostazol inhibits an increase in P-selectin expression on the surface of adenosine diphosphate-stimulated platelets (2). Here we provide the first in vivo human data showing that cilostazol can inhibit stent-induced P-selectin expression on platelets, supporting the results of our previous in vitro experiments.
In the present study, we also demonstrated that cilostazol inhibited stent-induced Mac-1 upregulation on the surface of neutrophils. The activation of leukocytes, neutrophils, and monocytes is known to play an important causative role in the development of restenosis after PCI (710). Activated leukocytes transmigrate and infiltrate into the PCI-injured vessel wall and produce various cytokines, growth factors, free radicals, and proteolytic enzymes, leading to neointimal thickening and restenosis. At the PCI-injured vessel wall, which is denuded of vascular endothelial cells by the balloon inflation, platelets first adhere to the vessel surface and the platelet layer is formed. Leukocytes adhere to the platelet layer and then migrate into the vessel wallnamely, transplatelet leukocyte migration (1820). In the process of transplatelet leukocyte migration, platelet surface P-selectin binds to P-selectin glycoprotein ligand (PSGL)-1 on the surface of leukocytes and mediates the rolling attachment of leukocytes with the platelet layer (2122). In addition, subsequent firm adhesion of leukocytes is mediated by Mac-1, which is expressed on activated leukocytes and binds to ligands such as fibrinogen (20,21), platelet glycoprotein Ib alpha (24), intercellular adhesion molecule-2 (20), or junctional adhesion molecule-3 (25). Evangelista et al. (21,22) demonstrated in their in vitro experiment that the binding of P-selectin to PSGL-1 triggers tyrosine kinase-dependent signaling, which leads to functional upregulation or activation of Mac-1. Therefore, there is an important adhesion cascade between leukocytes and platelets, and cilostazol may block this cascade by acting on platelet P-selectin, as well as leukocyte Mac-1, to inhibit cross-talk between leukocytes and platelets. In this study, we focused on neutrophils but not monocytes based on our previous observations and the observations of others, that neutrophils are likely the first cells recruited to the injured vessel. Additionally, in the present study, we observed that cilostazol directly inhibited neutrophil surface Mac-1 upregulated in vitro by FMLP. The mechanism of cilostazol's direct inhibitory action for leukocyte Mac-1 is not well understood. Although cilostazol also has nonspecific inhibitory action for other PDEs in addition to PDE III, its inhibitory effect for PDE IV, which is known to be expressed in leukocytes, is very weak (26). Thus, we speculate that there are some unknown mechanisms independent of PDE inhibition. Our results suggest that cilostazol may inhibit Mac-1 both through a direct action as well as through inhibition of P-selectin and subsequent P-selectinPSGL-1 signaling.
There is much evidence that Mac-1 is one of the key proteins in the mechanism of restenosis. We have demonstrated clinically that PCI induced activation (15) and upregulation (1114) of Mac-1 on the surface of neutrophils and that Mac-1 kinetics were linked to angiographic late lumen lossnamely, neointimal thickening (13,14). Rogers et al. (16) demonstrated in the rabbit iliac artery model that Mac-1 blockade by a monoclonal antibody against CD11b suppressed neointimal thickening after balloon-induced or stent-induced vessel wall injury. Simon et al. (17) demonstrated that, in Mac-1deficient mice, neointimal thickening after balloon-induced carotid artery injury was suppressed compared with Wild-type mice. Therefore, chemical, biologic, or pharmacologic approaches targeting Mac-1 (i.e., Mac-1 blockade) are potentially powerful strategies for the prevention of restenosis.
Cilostazol also has direct inhibitory effects on smooth muscle cell growth and extracellular matrix synthesis through its PDE III-inhibiting action, which causes an increase of intracellular cAMP and a decrease of 3H-thymidine uptake (2,3). These effects possibly lead to direct inhibition of neointimal growth and a reduction in restenosis (4,2729). In addition to the direct inhibition of neointimal growth through the action of PDE III, the results of the present study suggest that cilostazol may act as a Mac-1 blocker, and that this may play a role in the reduction of restenosis.
Study limitations. The present study had several potential limitations. In this study, we investigated the quantity of Mac-1 on the cell surface (upregulation), rather than functional Mac-1 activity using a Mac-1 activation-dependent antibody. In our previous study, we assessed the serial process of activation and upregulation of Mac-1 after PCI. Although activation of Mac-1 occurred earlier than its upregulation (15), we confirmed that serial changes in activation and upregulation were parallel and that the clinical significance of both findings was similar. Thus, this study only focused on the simple quantitative assessment of Mac-1. Although we assessed separately platelet P-selectin and leukocyte Mac-1 in this study, quantifying the number of platelet-leukocyte conjugates or the Mac-1 expression on platelet-bound and nonplatelet-bound leukocytes might be of greater interest to further assess the adhesion cascade in the process of the platelet-leukocyte interaction with cross-talk between P-selectin and Mac-1 (30,31). This study compared cilostazol with ticlopidine, a therapeutic no longer in widespread use in the U.S. and European countries but a standard post-stent antiplatelet regimen in Japan. Recently, clopidogrel has replaced ticlopidine in Western countries (32,33). At present, however, clopidogrel is not available in Japan. The CREST (5) compared the cilostazol and placebo groups, both of which were under the baseline treatments with aspirin and clopidogrel and succeeded in the reduction of restenosis. Therefore, we can see that cilostazol prevents restenosis as an additional effect of clopidogrel.
Clinical implications. Although the biggest hurdle of PCIrestenosishas been markedly reduced since the introduction of coronary stents, bare-metal stents cannot reduce restenosis to <20%. On the other hand, recent advances in drug-eluting stents, such as the Sirolimus-coated stent, have further reduced restenosis to <10% (34). Even with the drug-eluting stents, however, small vessel lesions and the complication of diabetes are still weakness for conquest of restenosis (35). Therefore, the problem of restenosis remains unresolved, and we should continue trying to reduce the restenosis rate until it is nearly equal to zero. The CREST (5) demonstrated by subgroup analysis that cilostazol was associated with a significantly lower restenosis rate, even in patients with small vessel lesions and in patients with diabetes. Therefore, oral cilostazol would be a powerful strategy for a further reduction of restenosis in addition to drug-eluting stents.
Recent chemical, biologic, or pharmacologic approaches to prevent restenosis are "anti-proliferative" or "anti-inflammatory" strategies. Cilostazol may represent a hybrid drug for the prevention of restenosis having both antiproliferative (PDE-mediated inhibition of smooth muscle cell proliferation), as well as anti-inflammatory (inhibition of leukocyte integrin Mac-1) effects.
Conclusions. Cilostazol may have effects for inhibiting Mac-1mediated leukocyte activation directly or through P-selectinmediated platelet activation, which may lead to a reduction in the rate of restenosis after coronary stent implantation.
| Acknowledgments |
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| Footnotes |
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is a counterreceptor for the leukocyte integrin Mac-1 (CD11b/CD18) J Exp Med 2000;192:193-204.This article has been cited by other articles:
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