There is an important link between platelets and inflammation, thrombosis, and vascular and tissue repair mechanisms. Proliferative, mitogenic and inflammatory substances are released by activated platelets into the local microenvironment of vascular lesions.1 Thus, vascular and tissue repair mechanisms are affected and even controlled by activated platelets.

The epidermal growth factor (EGF) superfamily is a group of growth factors, cytokine-like mediators, and extracellular matrix proteins. A new gene for an EGF-related protein was isolated in 2002 in developing mice.2 This new mammalian gene encodes a protein with a signal peptide at the amino-terminus followed by several EGF (epidermal growth factor)-like repeats and one CUB (complement C1r/C1s) domain at the carboxyl terminus. This gene family was termed SCUBE, standing for signal-peptide-CUB-EGF-like domain-containing proteins. Expression of SCUBE1 (signal peptide-CUB-EGF-like domain-containing protein 1) has been detected in platelet-rich thrombi and in human atherosclerotic lesions. Tu et al.3 described experiments revealing that recombinant fragments of SCUBE enhanced platelet aggregation and adhesion. Activated and adherent platelets release SCUBE1, which adheres to the subendothelial matrix.4 Thus, SCUBE1 plays pathological roles in atherothrombosis by functioning as a novel platelet-endothelial adhesion molecule.5–7 Platelet activation is the most important step in arterial thrombosis, and is accordingly responsible for ischemic complications of acute coronary syndromes (ACS).8–10

Coronary stents are the mainstay of percutaneous coronary revascularization procedures, and their use has significantly decreased the rates of acute vessel closure and restenosis. Stent thrombosis (ST) after percutaneous coronary intervention (PCI) is an uncommon and potentially catastrophic event that can manifest as myocardial infarction and sudden death. Platelets play a pivotal role in thrombus formation, including ST, and thus optimal antiplatelet therapy is of critical importance in the prevention of ST.7 If the coronary stent is obstructed 30 days or more after implantation, it is termed late ST. Both bare-metal stents (BMS) and drug-eluting stents (DES) induce platelet activation, platelet adhesion and thrombus formation; therefore, effective antiplatelet therapy is mandatory for some time after stent implantation. Stents gradually become covered with endothelial cells that do not induce thrombus formation, and the need for platelet inhibition decreases. Cytotoxic drugs are used in patients with DES in order to reduce smooth muscle cell growth after PCI and to inhibit endothelialization.8 However, the underlying mechanism of late ST has not yet been fully elucidated.

High platelet reactivity is a risk factor for thrombotic events. For this reason, in this study, we examined the role of SCUBE1 in the development of late coronary ST.

This study was approved by the institutional review boards of our hospitals, and written informed consent was obtained from the participants. The investigation conformed to the principles outlined in the Declaration of Helsinki.9

The baseline characteristics and laboratory parameters of patients and control subjects are shown in Table 1. There were no significant differences between groups in terms of age, gender, hypertension, diabetes, smoking, serum creatinine level or platelet count. There was no clopidogrel use in the control group or the STEMI without ST group. The number of patients who used clopidogrel in the STEMI with late ST group was 28, in whom the mean elapsed time from the deployment of the initial stent that became occluded was 84 days. The other 12 patients in the STEMI with late ST group received clopidogrel treatment for one month after discharge only. The Gensini score of the STEMI without ST group was 34±8.8, and that of the STEMI with late ST group was 36±10.2. The severity of coronary atherosclerosis did not differ between the STEMI groups (p=0.42). Thrombolysis in Myocardial Infarction (TIMI)-3 flow was measured in 32 patients after primary PCI in the STEMI with late ST group. TIMI-1 flow was observed in the other eight patients in this group. TIMI-3 flow was observed in all patients in the STEMI without ST group. The mean stent length in the STEMI with late ST group was 38±6.2 mm, and that in the STEMI without ST group was 34±3.2 (p=0.34). Bifurcation stents were not used in any group. Glycoprotein IIb/IIIa inhibitors were administered to 28 subjects in the STEMI with late ST group after revascularization because of high thrombus burden.

The mean SCUBE1 level was 30±7.4 ng/ml among the control subjects, 48.2±8.9 ng/ml in the STEMI without ST group and 67.6±6.9 ng/ml at admission and 50±7.6 ng/ml at hospital discharge in the STEMI with late ST group (Figure 1).

Figure 1.

Comparison of SCUBE1 levels between the groups. ST: stent thrombosis; STEMI: ST-elevation myocardial infarction.

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The mean SCUBE1 levels in the STEMI with late ST group at admission and in the STEMI without ST group were significantly higher than in the control group (p<0.01). The mean SCUBE1 level in the STEMI with late ST group was significantly higher than that of the STEMI without ST group (p=0.03). The mean SCUBE1 level in the STEMI with late ST group at discharge was significantly lower than that of the STEMI with late ST group at admission (p=0.04). The mean SCUBE-1 level of patients who had TIMI-1 flow after primary PCI was higher than that of patients who had TIMI-3 flow after primary PCI at discharge from the hospital in the STEMI with late ST group (66.1±4.4 ng/ml, 46±3.9 ng/ml, p=0.02) (Table 2).

Univariate regression analysis showed that age and hemoglobin, platelet count, high-sensitivity C-reactive protein and SCUBE1 levels were possible confounding factors for the presence of late ST. In multivariate regression analysis, serum SCUBE1 (odds ratio [OR]: 1.022; 95% confidence interval [CI]: 1.011-1.033, p<0.001) remained an independent predictor for the presence of late ST (Table 3). In addition, ROC curve analysis was used to determine the optimal SCUBE1 cut-off value for predicting late ST. The area under the curve was calculated as 0.972 (95% CI 0.95-0.98). The optimal SCUBE1 cut-off value was 59.2 ng/ml, with a sensitivity of 95.4% and specificity of 82.9% (Figure 2).

Figure 2.

Receiver operating characteristic (ROC) curve of SCUBE1 and late ST. CI: confidence interval.

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The major findings of our study are as follows: (i) to the best of our knowledge, the present work is the first clinical study to show a graded relationship between late ST development and serum SCUBE1 level; (ii) for the first time, SCUBE1 was found to be an independent predictor for the presence of late ST.

SCUBE1 plays important roles in cardiovascular biology by activating platelets.4 SCUBE1 deposition has been immunohistochemically determined in the subendothelial matrix of advanced atherosclerotic lesions in humans. EGF-like repeats are responsible for adhesion.4 Platelet activation and aggregation are well recognized as primary reactions in arterial thrombosis and are thus involved in the ischemic complications of ACS.6,7 ACS are initiated by plaque rupture or erosion, with subsequent platelet activation and thrombus formation. The role of platelet activation in the pathogenesis of this atherothrombotic complication is shown by the importance of antiplatelet drugs in the management of ACS.9,10

Coronary stents are the mainstay of percutaneous coronary revascularization procedures, and their use has significantly decreased the rates of acute vessel closure and restenosis. ST after PCI is an uncommon and potentially catastrophic event that can manifest as myocardial infarction and sudden death. The optimization of stent implantation and dual antiplatelet therapy have markedly reduced the occurrence of this complication.11 DES were introduced into clinical practice to reduce the rates of restenosis that were observed with the use of BMS for the treatment of coronary artery disease.12

However, despite the promising results, concerns have been raised regarding the potentially increased risk of late ST, which is thought to be a consequence of delayed endothelialization.13 A number of studies have assessed the incidence of ST, most reporting a figure of 0.5-2%. Although a quantitatively minor problem, ST has a major clinical impact due to the high risk of myocardial infarction and death. The case fatality rate of ST has been reported to be as high as 45%.13 Delayed endothelial coverage, persistent fibrin deposition and ongoing vessel inflammation are associated with ST >30 days after stent implantation. Re-endothelialization after stent implantation is significantly delayed in patients with DES compared with BMS and is likely responsible for the higher rates of late ST associated with first-generation DES.14 Stent malapposition is defined as a lack of contact between the stent struts and the underlying arterial wall intima (despite full stent expansion at its nominal diameter). Late stent malapposition is typically the result of positive vessel wall remodeling (i.e., outward arterial wall expansion away from the stent struts that were well apposed at the time of implantation); this occurs more often in patients with DES than in those with BMS and has been associated with late ST.

Finally, neoatherosclerotic plaques can develop in the neointima within previously stented areas; these plaques may rupture and lead to ST.14 Neoatherosclerotic plaques have been observed in patients with BMS and DES. However, pathological evidence suggests that neoatherosclerosis may develop earlier in DES.15 Its development appears to be similar in patients with first- and second-generation DES.16

A study of 985 patients who underwent primary angioplasty for STEMI, including 102 patients with confirmed ST, demonstrated a higher occurrence of in-hospital death or recurrent myocardial infarction in patients who presented with ST compared with those presenting with STEMI secondary to a de novo lesion.17 Additionally, in patients with STEMI and ST, there was a higher thrombus burden, more frequent distal embolization and fewer successful results from PCI.18

Platelets play a pivotal role in thrombus formation, including ST, and so optimal antiplatelet therapy is of critical importance in the prevention of ST.7 High platelet reactivity is a risk factor for thrombotic events. Dai et al.19 demonstrated the role of SCUBE1 in patients with ACS and acute ischemic stroke. According to Wu et al.,20 plasma SCUBE1 appears to be redundant for baseline hemostasis but constitutes an important platelet adhesive system in pathological thrombosis. In their study, genetic loss or inhibition of plasma SCUBE1 protected mice against fatal thromboembolism and had a modest effect on bleeding. Hence, targeting plasma SCUBE1 could be a novel therapeutic strategy to prevent thrombosis.

Similarly, we found that SCUBE1 levels were very high in the study population at admission compared with control subjects (p<0.01). We also found that the mean SCUBE1 level in STEMI patients with late ST was significantly higher than in those with STEMI without ST (p=0.03). After coronary stent implantation and antiplatelet therapy, SCUBE1 levels decreased significantly (p=0.04). Mean SCUBE1 levels were high at hospital discharge because of eight patients in the STEMI with ST group who had TIMI1 flow on the coronary angiogram after primary PCI.

Our study results are consistent with findings from previous studies. We demonstrated for the first time a graded relationship between serum SCUBE1 level and late ST development. In multivariate regression analysis, serum SCUBE1 level was found to be a significant and independent predictor for the presence of late coronary ST.

First, our study population was small, and there is thus a need for future studies with larger sample sizes. Second, we had insufficient data regarding the types of stents that were completely occluded in the STEMI with late ST group.

The authors have no conflicts of interest to declare.