Increased Inflammatory Markers in Patients with Reduced Antiplatelet Effect of Aspirin.

Inflammation may modify platelet function. This may lead to reduced antiplatelet drug efficacy in patients with coronary artery disease (CAD). The impact of low-grade inflammation on platelet aggregation in stable CAD patients receiving mono antiplatelet therapy with aspirin has not been investigated.

To investigate the association between platelet activation, platelet aggregation, and the inflammatory markers high-sensitive C-reactive protein (hs-CRP) and interleukin-6 (IL-6).

We performed a cross-sectional study on 524 stable high-risk CAD patients. Among these, 91% had a history of myocardial infarction, 23% had type 2 diabetes, and 13% had both. All patients received 75 mg aspirin daily as mono antiplatelet therapy, but no other antithrombotic treatment. Aspirin was ingested exactly one hour before blood sampling. Standardized blood sampling procedures included 30 minutes of rest in supine position before blood sampling, a large bore needle (19 G) and a minimum of stasis. Platelet aggregation was assessed by VerifyNow^® and multiple electrode aggregometry (Multiplate^®, MEA) using two agonists: arachidonic acid (AA, 1.0 mM) and collagen (1.0 μg/mL). Inflammation was evaluated by hs-CRP and IL-6. Platelet activation was assessed by soluble P-selectin (sP-selectin), and cyclooxygenase-1 inhibition was evaluated by measurement of serum thromboxane B₂.

Hs-CRP levels were significantly higher in upper aggregation tertile patients than in lower aggregation tertile patients. Similar results were obtained with IL-6, though not statististically significant (p≥0.15). Independent determinants of AA-induced MEA platelet aggregation were investigated using multiple regression analysis including hs-CRP, IL-6, prior myocardial infarction, diabetes, age, sex, and smoking. Hs-CRP (p=0.01) and smoking (p= 0.03) were significant determinants of AA-induced MEA platelet aggregation. Hs-CRP levels were elevated by 28–55% in upper aggregation tertile patients compared with lower aggregation tertile patients (p-values<0.05).

Platelet activation evaluated by sP-selectin was significantly higher in patients with MEA aggregation levels in the upper tertile than in the lower tertile (p=0.0001). Similar results were found with VerifyNow^®, though not statististically significant (p=0.26). No difference was found between hs-CRP or IL-6 levels in the upper and lower sP-selectin tertile (p-values≥0.84).

Optimal compliance in all patients was confirmed by serum thromboxane B₂ levels (median thromboxane B₂ ng/mL (IQR) 1.0 (0.5–1.8), range 0.02–26.4) below 30 ng/mL, corresponding to a more than 95% inhibition of cyclooxygenase-1 activity. However, patients with platelet aggregation in the upper aggregation tertile had higher serum thromboxane B₂ levels than patients in the lower aggregation tertile (median ng/mL: 3^rd tertile 1.2–1.7 vs. 1^st tertile 0.8–0.9). This difference was significant with MEA/AA (p=0.0002) and VerifyNow^® (p<0.0001), whereas only a trend was seen with MEA/collagen (p=0.06). No difference was found in hs-CRP or IL-6 levels in the upper and lower serum thromboxane B₂ tertile (p-values>0.17).

In stable high-risk CAD patients receiving mono antiplatelet therapy with aspirin, significantly increased hs-CRP levels were demonstrated in patients with augmented platelet aggregation. Our results indicate an association between chronic low-grade inflammation and reduced antiplatelet effect of aspirin, suggesting that patients with increased hs-CRP levels may have reduced cardiovascular protection from aspirin.

No relevant conflicts of interest to declare.