Reduced von Willebrand factor-cleaving protease (ADAMTS13) activity in acute myocardial infarction.

Abstract

Von Willebrand factor (VWF) is a glycoprotein that plays an important role in the primary hemostatic process by inducing platelet adhesion and aggregation at sites of vascular injury under conditions of high shear stress [1]. The hemostatic activity of VWF is strongly dependent on its multimeric structure, with the highest activity in unusually large VWF multimers (UL-VWF) secreted from the Weibel–Palade bodies of endothelial cells and α-granules of platelets. Risk factor analysis in patients with angina pectoris or myocardial infarction (MI) has found that high plasma levels of VWF are associated with an increased risk of subsequent MI [2, 3]. Recent studies have shown that UL-VWF is regulated by a plasma VWF-cleaving protease, named ADAMTS13 [4-6]. Studies using recombinant ADAMTS13 demonstrated that it directly cleaved the Tyr842–Met843 peptide bond within the VWF A2 domain [7]. On the other hand, intracoronary thrombus formation plays an important role in the onset of acute myocardial infarction (AMI) [8]. The initial stimulus is thought to be an interaction between flowing platelets and the exposed subendothelial matrix subsequent to the coronary plaque disruption [9]. Based on these observations, we hypothesized that ADAMTS13 might contribute to the regulation of platelet thrombus formation at the sites of plaque disruption in AMI. In the present study, we measured the plasma VWF and ADAMTS13 levels in patients with AMI, stable exertional angina (SEA), and chest pain syndrome (CPS), and examined the relationship between these levels and clinical findings. We also investigated immunohistochemical localization of VWF and ADAMTS13 antigen in coronary thrombi obtained from patients with AMI. Our subjects comprised 104 patients (63 men and 41 women; mean age, 68 ± 1 years; range, 45–90) who underwent diagnostic cardiac catheterization. Forty-one consecutive patients with AMI (29 men and 12 women) who were admitted within 72 h of the onset of symptoms were included in this study. The SEA group consisted of 33 patients who had typical exertional angina and 90% narrowing of a major coronary artery. The most recent attack in each patient in this group occurred at least 4 weeks before entry into the study. The CPS group consisted of 30 patients who had no significant coronary arterial stenosis (≤ 25% of luminal diameter), and no coronary spasm upon intracoronary injection of acetylcholine. Venous blood samples were obtained from patients with AMI after admission to our hospital before starting heparin or other drugs at the time of coronary angiography. The blood samples taken from patients with SEA and CPS post-admission were also obtained at the time of coronary angiography. The study protocol was approved by the ethics committee at our institution, and written informed consent was obtained from each patient and his or her family. Data are expressed as the mean ± SEM. Comparisons between multiple groups were performed by one-way anova followed by Fisher's protected least significant difference test. Results with P < 0.05 were considered statistically significant. VWF antigen level in plasma (mU mL−1), measured by a sandwich ELISA kit (Roche, Tokyo, Japan), increased significantly in patients with AMI compared with SEA and CPS (2151 ± 97, 1445 ± 93 and 1425 ± 76, respectively; P < 0.0001 in AMI vs. SEA and CPS). The ADAMTS13 antigen level (mU mL−1) was measured by sandwich ELISA using polyclonal antibody (PoAb) against ADAMTS13 as previously reported [10]. The plasma ADAMTS13 antigen levels were significantly lower in patients with AMI than in those with SEA and CPS on admission (799 ± 29, 996 ± 31 and 967 ± 31, respectively; P < 0.0001 in AMI vs. SEA, and P = 0.0002 in AMI vs. CPS). The plasma ADAMTS13 enzymatic activity (mU mL−1), measured using fluorescence-quenching substrate for ADAMTS13, FRETS-VWF73 (Peptide Institute, Osaka, Japan) [11], also significantly decreased in patients with AMI compared to the SEA and CPS groups on admission (768 ± 27, 893 ± 27 and 936 ± 29, respectively; P = 0.0014 in AMI vs. SEA, and P < 0.0001 in AMI vs. CPS). The linear regression analysis showed that there was a significant positive correlation between ADAMTS13 antigen and activity levels (r = 0.840, P < 0.0001). Furthermore, there were significant inverse correlations between VWF antigen and ADAMTS13 antigen or activity levels (r =−0.447, P < 0.0001; r = −0.412, P < 0.0001; respectively). Several studies demonstrated the decreased plasma ADAMTS13 levels in various thrombocytopenic disorders [12-14], indicating that ADAMTS13 might regulate physiologic and pathologic platelet thrombus formation. Recently, Reiter et al. [15] showed that infusion of the vasopressin analog, desmopressin, induced an increase in the plasma concentration of VWF and a lower activity of ADAMTS13 during acute phase reactions, indicating that plasma ADAMTS13 might be consumed in order to eliminate the more platelet-adhesive and agglutinating forms of VWF. Our data suggest that the decrease of plasma ADAMTS13 in AMI might involve its rapid response to increased VWF activity. The ratio of VWF antigen levels to ADAMTS13 antigen levels was calculated to define the tendency toward platelet thrombus formation in patients with AMI. As shown in Fig. 1A, the ratio of VWF antigen/ADAMTS13 antigen was significantly higher in patients with AMI compared to the SEA and CPS groups (2.9 ± 0.2, 1.5 ± 0.1 and 1.5 ± 0.1, respectively; P < 0.0001 in AMI vs. SEA and CPS). Furthermore, we analyzed the relationship between the ratio of VWF antigen/ADAMTS13 antigen levels and in-hospital cardiovascular events in AMI patients. Nine patients in the AMI group had cardiovascular events during the in-hospital stay (cardiovascular death in one patient, non-fatal MI in two patients, refractory angina in one patient, emergent coronary revascularization in one patient, and heart failure with NYHA Class IV in four patients). As shown in Fig. 1B, the ratio of VWF antigen/ADAMTS13 antigen was significantly higher in the AMI patients with in-hospital cardiovascular events than in those without (3.9 ± 0.3 vs. 2.7 ± 0.2, P = 0.0046 by Mann–Whitney U-test). Table 1 shows the results of univariate Cox hazards analysis of risk factors for in-hospital cardiovascular events in patients with AMI. The low ADAMTS13 antigen and high VWF/ADAMTS13 ratio on admission were significant predictors for in-hospital cardiovascular events after AMI [odds ratio (OR) 0.006, 95% confidence interval (95% CI) 5.9 × 10−4–0.591; P = 0.029 in plasma ADAMTS13 antigen levels, OR 1.90, 95% CI 1.11–3.25; P = 0.019 in VWF/ADAMTS13 ratio, respectively]. Ratio of plasma von Willebrand factor (VWF) antigen/ADAMTS13 antigen levels in all patients on admission (A), and ratio of plasma VWF antigen/ADAMTS13 antigen in all acute myocardial infarction (AMI) patients on admission with and without cardiovascular events (B). Representative photomicrographs of hematoxylin–eosin (HE) stain and immunohistochemistry for VWF, ADAMTS13, glycoprotein IIb/IIIa on platelets, fibrin, monocytes/macrophages, granulocytes, and negative control in a coronary thrombus obtained from a patient with AMI (C). Bars indicate 100 μm. In the present study, we examined the immunohistochemical localization of ADAMTS13, using anti-ADAMTS13 monoclonal antibody WHS29–1A, and the localization of VWF, platelets, fibrin and inflammatory cells in samples obtained from coronary thrombectomy in 15 out of 41 AMI patients. The coronary thrombi were composed mainly of platelets, fibrin, and inflammatory cells including neutrophils and macrophages. Immunohistochemical staining revealed the prominent presence of VWF at the sites of platelet accumulation and fibrin deposition. ADAMTS13 antigen was positive in all coronary thrombi obtained from the AMI patients. The distribution pattern of ADAMTS13 antigen was similar to the distribution of VWF in the serial sections, but not to the distribution of the inflammatory cells in the coronary thrombi (Fig. 1C). The corollary of these findings is that ADAMTS13 might bind to the VWF in the lesion responsible for coronary thrombus formation and form a tight enzyme–substrate complex with VWF by interaction with the whole molecule. This might result in ADAMTS13 consumption and/or its incorporation into the coronary thrombi together with VWF. In conclusion, we studied changes in VWF and ADAMTS13 levels in AMI patients. The increase in the ratio of VWF/ADAMTS13 was associated with the occurrence of in-hospital cardiovascular events after AMI, although a small number of AMI patients were examined in the present study. A large-scale clinical trial might be needed in the future. However, our data suggests that the VWF/ADAMTS13 ratio might be a useful predictor for monitoring adverse cardiovascular events during follow-up in AMI patients. The treatments that lower the VWF/ADAMTS13 ratio might contribute to the prevention for future cardiac events after AMI. We gratefully acknowledge the cooperation of the interventional cardiologists at the Departments of Cardiovascular Medicine, Graduate School of Medical Sciences, Kumamoto University (Drs T. Kudo, H. Maruyoshi, S. Kojima, T. Hayasaki, K. Tsujita, S. Sugiyama, M. Yoshimura), the Department of Cardiology, Fukuoka Tokushukai Medical Center (Dr H. Shimomura) and the Division of Cardiology, Kumamoto Red-Cross Hospital (Drs S. Koide, H. Sumida, and Y. Ogata), for this study. This study was supported in part by Grants-in-Aid for Scientific Research B17390232 and C17590752 from the Ministry of Education, Culture, Sports, Science and Technology, Tokyo, Japan. The authors state that they have no conflict of interest.