Author + information
- Received February 15, 2017
- Revision received April 5, 2017
- Accepted May 4, 2017
- Published online August 21, 2017.
- Han Saem Jeong, MD,
- Soon Jun Hong, MD, PhD∗ (, )
- Sang-A Cho, MS,
- Jong-Ho Kim, PhD,
- Jae Young Cho, MD,
- Seung Hun Lee, MD,
- Hyung Joon Joo, MD, PhD,
- Jae Hyoung Park, MD, PhD,
- Cheol Woong Yu, MD, PhD and
- Do-Sun Lim, MD, PhD
- Department of Cardiology, Cardiovascular Center, Korea University Anam Hospital, Seoul, Republic of Korea
- ↵∗Address for correspondence:
Dr. Soon Jun Hong, Department of Cardiology, Cardiovascular Center, Korea University Anam Hospital, 126-1, 5-ka, Anam-dong, Sungbuk-ku, Seoul 136-705, Republic of Korea.
Objectives This study compared adenosine-associated pleiotropic effects of the 2 P2Y12 receptor antagonists on vascular function, systemic inflammation, and circulating endothelial progenitor cells (EPCs).
Background Both ticagrelor and prasugrel have potent antiplatelet effects. However, only ticagrelor inhibits cellular uptake of adenosine.
Methods Using a randomized, crossover design with 10-week follow-up ticagrelor or prasugrel was administered to type 2 diabetic patients with non–ST-segment elevation acute coronary syndrome requiring stent implantation. A total of 62 patients underwent randomization in a 1:1 ratio to receive ticagrelor or prasugrel for 5 weeks followed by a direct cross over to the alternative treatment for 5 additional weeks. Brachial artery flow-mediated dilation, inflammatory markers, and number of circulating EPCs were compared.
Results Improvement in brachial artery flow-mediated dilation was greater in the ticagrelor group (0.15 ± 0.19 mm vs. −0.03 ± 0.18 mm; p < 0.001). Moreover, ticagrelor compared with prasugrel decreased interleukin 6 (−0.58 ± 0.43 pg/ml vs. −0.05 ± 0.24 pg/ml; p < 0.001), tumor necrosis factor alpha (−5.62 ± 4.40 pg/ml vs. −0.42 ± 2.64 pg/ml; p < 0.001), and increased adiponectin (2.31 ± 2.00 μg/ml vs. 0.08 ± 1.50 μg/ml; p < 0.001) during 10-week follow-up. Other inflammatory cytokines like high-sensitivity C-reactive protein and soluble vascular cell adhesion molecule-1 were decreased in both groups. Ticagrelor compared with prasugrel significantly increased absolute numbers of circulating EPCs CD34+/KDR+ (42.5 ± 37.8 per μl vs. −28.2 ± 23.7 per μl; p < 0.001), CD34+/CD117+ (51.9 ± 77.2 per μl vs. −66.3 ± 45.2 per μl; p < 0.001), and CD34+/CD133+ (55.2 ± 69.2 per μl vs. −28.0 ± 34.1 per μl; p < 0.001).
Conclusions Compared with prasugrel, ticagrelor significantly decreased inflammatory cytokines such as interleukin 6 and tumor necrosis factor alpha and increased circulating EPCs, contributing to improved arterial endothelial function in diabetic non–ST-segment elevation acute coronary syndrome patients. Thus, data support that pleiotropic effects of ticagrelor beyond its potent antiplatelet effects could contribute to additional clinical benefits. (Comparison of Ticagrelor vs. Prasugrel on Inflammation, Arterial Stiffness, Endothelial Function, and Circulating Endothelial Progenitor Cells in Diabetic Patients With Non-ST Elevation Acute Coronary Syndrome [NSTE-ACS] Requiring Coronary Stenting; NCT02487732)
The 2014 American Heart Association/American College of Cardiology guidelines for managing patients with non–ST-segment elevation acute coronary syndrome (NSTE-ACS) recommend ticagrelor or prasugrel over clopidogrel for P2Y12 receptor antagonists after coronary stenting (1). Ticagrelor is a direct acting, reversibly binding P2Y12 receptor antagonist. In the PLATO (Platelet Inhibition and Patient Outcomes) trial, administration of ticagrelor showed better benefits of cardiovascular death, myocardial infarction, stroke, and all-cause mortality compared with clopidogrel (2). Prasugrel, similar to clopidogrel, is a prodrug requiring hepatic metabolism to generate an active metabolite that acts as an irreversibly binding P2Y12 antagonist. Unlike ticagrelor, administration of prasugrel did not improve cardiovascular mortality in TRITON-TIMI 38 (Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition with Prasugrel-Thrombolysis In Myocardial Infarction 38) (3).
In addition to its P2Y12 antagonism, ticagrelor has been shown to inhibit adenosine uptake via equilibrative nucleoside transporter 1, thereby protecting extracellular adenosine from its intracellular metabolism (4). As a consequence, elevated plasma adenosine levels have been documented in patients treated with ticagrelor, and this unique mechanism has been proposed to contribute to the cardiovascular mortality benefit in ticagrelor (5). Moreover, a previous study demonstrated that administration of ticagrelor showed a mortality benefit from sepsis, suggesting the immune-modulating function of ticagrelor (6). We hypothesized that administration of ticagrelor, with increases in circulating adenosine levels, would modulate circulating endothelial progenitor cell (EPC) levels and decrease inflammatory cytokines, thereby improving vascular endothelial function. The proinflammatory status and increased platelet reactivity in diabetic patients could intensify the benefits from ticagrelor (7). Therefore, we performed a prospective, randomized, crossover design, open-label study to investigate the pleiotropic and antiplatelet effects of ticagrelor versus prasugrel in type 2 diabetic patients with NSTE-ACS.
Patients 35 to 74 years of age were eligible if they were: 1) newly diagnosed with type 2 diabetes or had type 2 diabetes and were taking hypoglycemic agents; and 2) were also diagnosed with NSTE-ACS with successful coronary stent implantation, with Thrombolysis In Myocardial Infarction flow grade 3 after the procedure. A total of 411 patients were screened for inclusion at Korea University Anam Hospital Cardiovascular Center from July 2015 to April 2016 (Figure 1). Exclusion criteria were: 1) history of stroke or transient ischemic attack; 2) body weight <60 kg; 3) prior use of either ticagrelor or prasugrel within a month prior to randomization; 4) hypersensitivity to ticagrelor, prasugrel, or any of the excipients; 5) pre-load of ticagrelor or prasugrel; 6) current use of clopidogrel; 7) hemoglobin A1c >9%; 8) type 1 diabetes; 9) decreased serum platelet level <100,000/μl; 10) need for chronic oral anticoagulant therapy or chronic low-molecular-weight heparin; 11) gastrointestinal bleeding within the past 6 months; 12) major surgery within 30 days; 13) left ventricular ejection fraction <40%; 14) hepatic dysfunction (aspartate aminotransferase or alanine aminotransferase greater than twice the upper limit); 15) gastrointestinal disorder such as Crohn’s disease; 16) alcohol abuse; 17) steroid or hormone replacement therapy; 18) serum creatinine >2.0 mg/dl; 19) prior history of percutaneous coronary intervention or coronary bypass surgery; 20) history of intracranial bleeding at any time; 21) life expectancy <1 year; or 22) known pregnancy, breast-feeding, or intention to become pregnant during the study period.
This study was a prospective, open-label, randomized, crossover trial. A total of 62 patients underwent randomization in a 1:1 ratio to receive ticagrelor (180 mg loading dose, 90 mg twice daily) or prasugrel (60 mg loading dose, 10 mg once daily) for 5 weeks followed by a direct crossover to the alternative treatment for 5 additional weeks (Figure 1). The total duration for receiving drugs was 10 weeks with no washout period at the time of crossover as dual antiplatelet therapy should be continued for at least 12 months for ACS patients after stenting (1). Patients received randomization numbers sequentially from a computer-generated randomization list in blocks of 2 by individuals who had no contact with the people who assigned patients to study groups and performed no assessments on patients. The investigator who performed brachial artery flow-mediated dilatation (baFMD) was unaware of the randomization assignments until the final data were obtained. The study was approved by the Korea University Hospital Institute Review Board, and written informed consent was obtained from all participants or their legal guardians. All clinical investigations were conducted according to the principles of the Declaration of Helsinki.
The primary endpoint was a comparison of changes in vascular function, and secondary endpoints compared changes in proinflammatory cytokines and circulating EPCs at 5- and 10-week follow-up. Vascular function was evaluated by baFMD, brachial-ankle pulse wave velocity (baPWV), and augmentation index. Inflammatory cytokines such as interleukin (IL)-6 and tumor necrosis factor (TNF)-α, high-sensitivity C-reactive protein (hsCRP), soluble vascular cell adhesion molecule (SlVCAM)-1, soluble intercellular adhesion molecule (slICAM)-1, and adiponectin were compared. Height, weight, waist circumference, blood pressure, inhibition of platelet aggregation, homeostasis model assessment, plasma glucose, hemoglobin A1c, lipid profiles, adverse reactions, and concomitant drugs were evaluated at each follow-up visit. Major adverse cardiovascular events were recorded for all-cause death, cardiac death, myocardial infarction, and target vessel revascularization.
Blood samples for adenosine measurements
Blood samples (2 ml) for measuring plasma adenosine levels were collected into heparinized tubes (367874, BD Biosciences, San Jose, California) containing the ice-cold stop solution (3 ml). The stop solution consisted of 4.2 mmol/l ethylenediaminetetraacetic acid disodium (1.08454.0250, Merck Millipore, Billerica, Massachusetts), 0.2 mmol/l dipyridamole (D9766), 5 mmol/l erythro-9-(2-hydroxy-3-nonyl)-adenine (E114), 79 mmol/l α,β-methyleneadenosine-5′-diphosphate (M8386), and 1 μg/ml deoxycoformycin (SML0508) (all from Sigma, St. Louis, Missouri) in 0.9% sodium chloride solution (21618, USB Corporation, Cleveland, Ohio). The samples were centrifuged at 2,500 g for 10 min at 4°C. The supernatant was deproteinized by adding 2 ml of 70% perchloric acid (311421, Sigma) before the second centrifugation. Samples were analyzed by high-performance liquid chromatography. The high-performance liquid chromatography system consisted of a binary pump, diode array detector, and autosampler (Agilent, Santa Clara, California) at the Korea Basic Science Institute (Seoul, Republic of Korea). Samples were separated on a reverse-phase column (2.0 mm × 150 mm, 5 μm) (Unison US-C18, Imtakt, Portland, Oregon) at 30°C. The 0.1% phosphoric acid and acetonitrile were used as mobile phases A and B, respectively. The linear gradient conditions were follows: 0% (B) for 5 min, 0% to 50% (B) for 5 min, 50% (B) for 2 min, and 0% (B) for 8 min. The flow rate was 0.2 ml/min and the injection volume was 10 μl. The standards and samples were detected at a wavelength of 257 nm.
Serum adenosine deaminase measurements
Fresh serum was isolated after centrifugation of whole blood. The adenosine deaminase activity was measured by the ammonium formed (Beckman DX, Pasadena, California) after incubation (40 min at 37°C) of 125 μl serum with 750 μl adenosine (28 mmol/l).
Baseline blood samples were drawn after loading of ticagrelor or prasugrel in fasting status. Inflammatory markers such as hsCRP, IL-6, TNF-α, slVCAM-1, and slICAM-1 were measured at the beginning of the study and at the 5- and 10-week follow-up visits. Blood samples were centrifuged to obtain plasma, which was stored at −80°C. TNF-α was measured using a sandwich enzyme-linked immunosorbent assay with a lower limit of quantification of 0.5 pg/ml (ALPCO Diagnostics, Salem, New Hampshire). Undetectable TNF-α values were recorded as 0.4 pg/ml. High-sensitivity IL-6 was measured by sandwich enzyme-linked immunosorbent assays with a lower limit of quantification of 0.16 pg/ml (ALPCO Diagnostics), and hsCRP concentration was quantified using a latex nephelometer II (Dade Behring Inc., Newark, Delaware). slICAM-1, slVCAM-1, and adiponectin were measured using enzyme-linked immunosorbent assays according to the manufacturer’s instructions (R&D Systems, Minneapolis, Minnesota).
Artery diameter was measured using a high-frequency ultrasound machine (Vivid 7, GE Vingmed Ultrasound, Horten, Norway) with 10-MHz linear-array transducer. Electrocardiography-gated, vessel end-diastole B-mode images were analyzed. Two independent experienced physicians examined and measured for all participants using the same investigation protocol and techniques. After a satisfactory transducer position was found, the antecubital fossa was marked, with the arm in the same position throughout the examination. After a 10-min resting period in the supine position, the left brachial artery was identified longitudinally. After recording the resting brachial artery diameter, a cuff was placed around the forearm distal to the target artery and inflated to 250 mm Hg. Inflation was maintained for 5 min. Endothelium-dependent vasodilation was assessed as change in the diameter of the brachial artery 60 s of reactive hyperemia relative to the baseline measurements after deflation of the cuff around the forearm. After baseline conditions were reestablished 15 min later, brachial artery measurements were repeated, followed by nitroglycerin at a dose of 0.4 mg administered by spray under the tongue to assess endothelium-independent vasodilation. These measurements were averaged. All images were coded and recorded in a portable hard disc drive for subsequent blinded analysis. Arterial diameter was measured in millimeters as the distance between the anterior wall media-adventitial interface and the posterior wall intima-lumen interface at end diastole, coincident with the R-wave on the electrocardiogram at 2 sites along the artery and for 3 cardiac cycles, with these 6 measurements averaged. The interobserver variability were 0.03 ± 0.02 mm by 2 physicians in 20 independent studies and the intraclass correlation coefficient for maximum diameter was 0.96 and for percent dilation was 0.81. The intraobserver variability was 0.02 ± 0.01 mm and the intraclass correlation coefficient for maximum diameter was 0.94 and for percent dilation was 0.82.
Pulse wave velocity, central blood pressure, and augmentation index
All patients were evaluated for baPWV at baseline and at 5- and 10-week follow-up. After resting in a supine position for 5 min, baPWV was measured using a volume-plethysmographic apparatus (model BP-203RPE II, Colin, Komaki, Japan). The instrument simultaneously recorded baPWV and brachial and ankle blood pressures on the left and right sides.
Central pressure recordings were obtained using an Omron HEM-9000AI (cSBP-Omron) (Omron Healthcare, Kyoto, Japan) according to the manufacturer’s instructions. Blood pressure measurement used the digital oscillometric method using a blood pressure cuff. Accompanying augmentation index calculation was based on pressure waveforms calibrated using brachial systolic and diastolic blood pressure. Augmentation index was determined as change in pressure between the first and second peaks divided by pulse pressure (augmentation index = ΔP / PP). The first peak was obtained when blood ejected from the aorta. The second pressure peak occurred when blood reflected at the aortic bifurcation. Pulse pressure was overall peak pressure. All data were stored for subsequent blinded analysis.
Peripheral blood samples (4 ml) were drawn into heparinized tubes after fasting overnight. Peripheral blood mononuclear cells were isolated within 1 h by density gradient centrifugation using Ficoll-Paque Plus (17-1440-03, Amersham Biosciences, Piscataway, New Jersey) and stored at 4°C. For flow cytometric analysis, cells were washed with phosphate-buffered saline containing 2% fetal bovine serum, and were double-stained with anti-CD34-FITC (348053, BD Pharmingen, San Diego, California) and anti-KDR-PE (FAB357P, R&D Systems), anti-CD34-FITC and anti-CD117-PE (555714, BD Pharmingen), or anti-CD34-FITC and anti-CD133-PE (130-080-801, Miltenyi Biotec, Bergisch Gladbach, Germany) monoclonal antibodies diluted 1:100 in phosphate-buffered saline containing 2% fetal bovine serum for 20 min at 4°C. The negative control was stained with fluorescein isothiocyanate mouse IgG1 isotype control (555909, BD Pharmingen) and phycoerythrin mouse IgG1 isotype control (349043, BD Pharmingen) antibodies. After washing with phosphate-buffered saline containing 2% fetal bovine serum, cells were resuspended and analyzed by flow cytometry. For double-staining experiments, interference of 2 fluorescence channels was adjusted by compensation. Each sample of 3,000 cells was analyzed on a FACSVantage SE flow sorter (BD Biosciences). Dead cells and debris were gated out using scatter properties. Data were analyzed using CellQuest Pro software (BD Biosciences). CD34+/KDR+ or CD34+/CD117+ or CD34+/CD133+ double-positive cells were defined as circulating EPCs after gating on the lymphocyte population. The number of positive cells was calculated as absolute leukocyte count by percentage (%) of positive cells and expressed as absolute number of cells per 1 ml whole blood.
Sample size calculation and statistical analysis
Data were expressed as mean ± SD or median (interquartile range [IQR]) for continuous variables. Data for categorical variables were expressed as number and percentage of patients. Chi-square or Fisher exact tests were used for categorical variables; Student t tests for normal distribution and Kruskal-Wallis tests for non-normal distribution were used for continuous variables. Change from baseline was calculated as the value at the end of treatment (over the 10-week period) subtracted from the value at the beginning. Results were compared between groups by analysis of variance with adjusted sequence effect and period effect test to adjust for carryover effects. Comparisons before and after treatment were analyzed by paired Student t test. Carryover effects were compared by unpaired Student t test. This study used per-protocol analysis. Using a 2-sided test for differences in independent binomial proportions with alpha level 0.05, we calculated that 48 patients (24 patients/group) in a crossover design would need to be randomized for the study to have 80% power for detecting an absolute increase of 1.5% or greater in baFMD between the 2 groups (8,9). Therefore, we enrolled 31 patients/group to account for 20% loss over the 10 weeks of follow-up. A p value <0.05 was considered statistically significant. SAS software version 9.3 (SAS Institute, Cary, North Carolina) was used for analyses.
Baseline patient characteristics (n = 62) of mean age, body mass index, and lipid profile were similar between the groups (Table 1). Baseline values for inflammatory cytokines, circulating EPCs and vascular function were similar between the groups (Online Table 1).
Effects of ticagrelor and prasugrel on vascular function
Improvement in baFMD was significantly greater in the ticagrelor group (0.15 ± 0.19 mm vs. −0.03 ± 0.18 mm; p < 0.001) (Table 2, Figure 2A). Improvement in baFMD was significantly greater in the ticagrelor group (4.2 ± 0.6 mm vs. 4.1 ± 0.6 mm; p < 0.001) compared with the prasugrel group after 10-week follow-up (Figure 2B). Ticagrelor significantly increased baFMD (4.3 ± 0.6 mm vs. 3.9 ± 0.5 mm; p = 0.037) compared with the prasugrel group from baseline to 5-week follow-up before crossover (Figure 2C). Measurement of brachial artery dilation after nitroglycerine did not show significant differences between groups. No significant differences were detected in pulse wave velocity, ankle-brachial index, central blood pressure, or augmentation index.
Effects of ticagrelor and prasugrel on plasma adenosine concentration
Plasma adenosine concentration after ticagrelor and prasugrel loading dose was 1.7-fold higher in ticagrelor group (1.22 μM [IQR: 1.10 to 1.30 μM] vs. 0.73 μM [IQR: 0.60 to 0.77 μM]; p < 0.001) (Online Figure 1A). Adenosine deaminase activity did not differ between the 2 groups at 5-week follow-up (13.0 IU [IQR: 12.0 to 17.0 IU] vs. 10.0 IU [IQR: 8.0 to 13.5 IU]; p = 0.43) (Online Figure 1B).
Effects of ticagrelor and prasugrel on inflammatory cytokines, platelet function, and laboratory data
Ticagrelor significantly decreased IL-6 (−0.58 ± 0.43 pg/ml vs. −0.05 ± 0.24 pg/ml; p < 0.001), TNF-α (−5.62 ± 4.40 pg/ml vs. −0.42 ± 2.64 pg/ml; p < 0.001), and increased adiponectin (2.31 ± 2.00 μg/ml vs. 0.08 ± 1.50 μg/ml; p < 0.001) compared with prasugrel (Table 3). Figures 3A to 3F showed that ticagrelor significantly decreased IL-6, TNF-α, and increased adiponectin compared with prasugrel after 10-week follow-up. Inhibition of platelet function was higher in the ticagrelor group than the prasugrel group (−90 ± 84.7 platelet reactivity units vs. −81.9 ± 99.3 platelet reactivity units) but the differences were not statistically significant. In the ticagrelor group, significant elevations of uric acid and creatinine level were observed compared with the prasugrel group (0.42 ± 0.37 mg/dl vs. −0.24 ± 0.34 mg/dl, p < 0.001 for uric acid; 0.07 ± 0.07 mg/dl vs. −0.08 ± 0.11 mg/dl, p < 0.001 for creatinine) (Table 3).
Effects of ticagrelor and prasugrel in circulating EPCs
The ticagrelor group resulted in significant increases in absolute numbers of circulating EPCs: CD34+/KDR+ (42.5 ± 37.8 per μl vs. −28.2 ± 23.7 per μl; p < 0.001), CD34+/CD117+ (51.9 ± 77.2 per μl vs. −66.3 ± 45.2 per μl; p < 0.001), and CD34+/CD133+ (55.2 ± 69.2 per μl vs. −28.0 ± 34.1 per μl; p < 0.001) compared with the prasugrel group (Table 4). Figures 4A to 4F showed that ticagrelor significantly increased CD34+/KDR+, CD34+/CD117+, and CD34+/CD133+ cells compared with prasugrel after 10-week follow-up.
This prospective, randomized, crossover study compared the effects of ticagrelor and prasugrel on vascular function, inflammatory cytokines, and circulating endothelial progenitor cells over a 10-week follow-up period. Administration of ticagrelor significantly improved arterial endothelial function evaluated as baFMD. Moreover, ticagrelor significantly decreased proinflammatory cytokines such as IL-6 and TNF-α, and increased adiponectin during the follow-up. Ticagrelor significantly increased absolute numbers of circulating endothelial progenitor cells defined as CD34+/KDR+, CD34+/CD117+, and CD34+/CD133+ cells. The significant decreases in proinflammatory cytokines and increases in circulating EPCs in the ticagrelor group are likely P2Y12-independent as compared with the alternative P2Y12 antagonist prasugrel. These pleiotropic effects may contribute to the observed improvement of arterial endothelial function.
In this study, ticagrelor but not prasugrel inhibited inflammatory cytokines such as IL-6 and TNF-α, but not hsCRP and increased the adiponectin concentration. One of the possible explanations can be anti-inflammatory properties from a reduction in platelet P2Y12-mediated platelet–leukocyte interactions (10). However, in our study, ticagrelor resulted in significant improvement in inflammatory cytokines compared with prasugrel. Inhibition of inflammation during the periods of administering ticagrelor suggested that ticagrelor had pleiotropic effects beyond P2Y12 inhibition. A recent study showed that ticagrelor had effects going beyond platelet activity compared with prasugrel (11). It had been highlighted that administration of ticagrelor improved inflammatory cytokines by increasing serum adenosine levels. Ticagrelor increases level of plasma adenosine in patients with ACS (12). Adenosine acts on 4 different receptors, A1, A2A, A2B, and A3, which have different actions (13). At higher concentrations of ticagrelor, adenosine mainly acts on the A2A and A2B receptors. These receptors down-regulate proinflammatory cytokines such as IL-6 and TNF-α (14,15). The A2A receptor is crucial for coronary vasodilation and the A2B receptor also induces coronary vasodilation (16). Administration of ticagrelor has been shown to augment adenosine-induced increases in coronary vasodilation in healthy subjects and in ACS patients (17,18). Furthermore, the A2A receptor mediates endothelial progenitor cell migration (19). In this study, improvement of proinflammatory cytokines such as IL-6 and TNF-α in ticagrelor would be characteristic. Although some previous studies have reported insignificant anti-inflammatory effects of ticagrelor, inclusion and exclusion criteria are quite different from our study population, and the discrepancy in the included patients could lead to different results from our study (20,21). We only enrolled diabetic patients with NSTE-ACS who were considered to be extremely high-risk patients with proinflammatory status, and inflammatory condition of our included patients could intensify the benefits of ticagrelor. Insignificant anti-inflammatory effects observed in DISPERSE 2 (Dose Confirmation Study Assessing Anti-Platelet Effects of AZD6140 vs Clopidogrel in NSTEMI 2) trial might be from relatively low proportion of diabetic patients or patients with NSTE-ACS (21). Also, concomitant medications such as statins after coronary stent implantation could have influenced in decreasing inflammatory cytokines in both ticagrelor and prasugrel groups with more prominent decreases in IL-6 and TNF-α in the ticagrelor group. Elevation of creatinine in the ticagrelor group may be another sign of elevated plasma adenosine (Table 3). Adenosine mediates afferent arteriolar vasoconstriction through the A1 receptor and is related to elevation of creatinine (22). Ticagrelor enhances activation of the adenosine monophosphate activated protein kinase signaling pathway and consequently up-regulates endothelial nitric oxide synthase and cardiac cyclooxygenase-2 (23). Accordingly, improvement in inflammatory cytokines might have contributed to mobilization of EPCs and restoration of vascular function in this study.
Elevation of adiponectin could be also related to pleiotropic effects of ticagrelor. Adiponectin has been known for its anti-inflammatory and cardioprotective effects (24). Interestingly, adenosine plays an important role in the action of adiponectin. Adenosine monophosphate activated protein kinase, activating endothelial nitric oxide synthase, is a key in adiponectin-mediated metabolic modulation and cardiovascular protection (25). It is not clear how ticagrelor elevates the adiponectin level, and whether elevated level of adenosine stimulates adiponectin. Nevertheless, the increase in adiponectin levels could be a unique process in ticagrelor, ultimately contributing to cardioprotection.
Ticagrelor also showed increased levels of circulating EPCs from baseline. Prasugrel showed decreased levels of circulating EPCs that were below baseline (Table 4). In 1 study, ticagrelor increased EPCs in ACS patients, similar to our findings (26). Improvements were seen in circulating EPCs only in periods of ticagrelor administration and not when prasugrel was administered (Figure 4). At baseline after NSTE-ACS, the level of circulating EPCs is thought to be elevated to repair damaged vascular endothelium (27,28). Under circumstances of vascular injury or after statin therapy (27), EPCs are mobilized into peripheral circulation and incorporate at sites of injury (29). Circulating EPCs are important in vascular homeostasis and endothelial repair processes (30). Increased levels of circulating EPCs with ticagrelor might have resulted from increased plasma adenosine mediating endothelial progenitor cell migration. Adenosine promotes circulating EPCs through the A2A and A3 receptors, but proangiogenic molecules stimulated by adenosine could also contribute to an increase in circulating EPCs (31,32). Patients with increased levels of circulating EPCs have better vascular function, regardless of risk factors (30). Increases in circulating EPCs during the 10-week follow-up in this study suggested that rapid restoration of the damaged endothelium contributed to improved arterial endothelial function.
Improvement of baFMD suggested that ticagrelor improved nitric oxide–dependent endothelial dysfunction. In a previous study, ticagrelor increased phospholipase A2, cyclooxygenase-2 expression, and endothelial nitric oxide synthase activation (33). Adenosine up-regulated these downstream molecules and stimulated nitric oxide (34). As a consequence, adenosine might have directly contributed to improvements in baFMD. Finally, decreased inflammatory cytokines together with increased numbers of circulating EPCs after ticagrelor administration might have contributed significantly in the improvement of arterial endothelial function in type 2 diabetic patients with ACS in this study. As shown in the PLATO trial, ticagrelor, unlike other P2Y12 antagonists, has revealed cardiovascular mortality benefit during the 12-month follow-up (2). Pleiotropic effects of ticagrelor such as decreasing systemic inflammation and increasing circulating endothelial progenitor cells led to the improvement in arterial endothelial function, ultimately reducing hard cardiovascular endpoints.
This crossover design had no washout period at the time of crossover because dual antiplatelet therapy should be continued 12 months after coronary stenting in patients with ACS (Online Table 2). We used analysis of variance to adjust sequence effects and period effect tests to adjust carryover effects, and showed serial changes in primary endpoints in Figures 2, 3, and 4. The total number of study participants was relatively small, and the study duration was short for evaluating cardiovascular events. Prolonged follow-up might be needed to evaluate effects on pulse wave velocity, ankle-brachial index, central blood pressure, and augmentation index.
In comparison with prasugrel, ticagrelor significantly decreased proinflammatory cytokines and increased circulating endothelial progenitor cells. These effects contributed to improvement in arterial endothelial function in diabetic NSTE-ACS patients. Our findings with ticagrelor in comparison with the alternative P2Y12 antagonist prasugrel, despite similar platelet inhibition level, support that ticagrelor has effects beyond its potent antiplatelet effects that can contribute to its favorable clinical outcomes.
WHAT IS KNOWN? Both ticagrelor and prasugrel have potent antiplatelet effects and have been administrated in patients with ACS. However, only ticagrelor inhibits cellular uptake of adenosine.
WHAT IS NEW? In the present study, administration of ticagrelor significantly improved arterial endothelial function evaluated as baFMD. Ticagrelor also meaningfully decreased circulating proinflammatory cytokines such as IL-6 and TNF-α, and increased adiponectin levels during the follow-up. Moreover, ticagrelor significantly increased absolute numbers of circulating endothelial progenitor cells.
WHAT IS NEXT? Future studies are needed to examine who can show more beneficial effects with ticagrelor than prasugrel.
The authors would like to express their sincere appreciation to the study participants and would like to thank I-Rang Lim, Seung Cheol Choi, Chi-Yeon Park, and Ji-Hyun Choi for their excellent assistance. Joo Hee Chung (Seoul Center, Korea Basic Science Institute) performed the high-performance liquid chromatography data analysis.
For a supplemental table and figures, please see the online version of this article.
This research was supported by an unconditional grant from AstraZeneca, a grant from the Korea Health Technology R&D Project through the Korea Health Industry Development Institute, funding from the Ministry of Health & Welfare (grant no. HI14C0209), and a grant from the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning, Republic of Korea (no. NRF-2014R1A2A1A11051998). The authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Abbreviations and Acronyms
- acute coronary syndrome
- brachial artery flow-mediated dilation
- brachial-ankle pulse wave velocity
- endothelial progenitor cell
- high-sensitivity C-reactive protein
- interquartile range
- international units
- non–ST-segment elevation
- soluble intercellular adhesion molecule
- soluble vascular cell adhesion molecule
- tumor necrosis factor
- Received February 15, 2017.
- Revision received April 5, 2017.
- Accepted May 4, 2017.
- 2017 American College of Cardiology Foundation
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