Effects of low-dose aspirin on serum C-reactive protein and thromboxane B₂ concentrations: A placebo-controlled study using a highly sensitive C-reactive protein assay

OBJECTIVES: We performed a placebo-controlled study to evaluate the effect of low-dose aspirin on serum C-reactive protein (CRP) levels. BACKGROUND: Elevated circulating concentrations of CRP, an inflammatory marker, increase the risk of thrombotic cardiovascular diseases such as myocardial infarction (MI). Moreover, low-dose aspirin therapy has been reported to be more effective in preventing MI in men with higher CRP levels than it is in those with lower levels, raising the possibility that aspirin prevents thrombosis by reducing vascular inflammation. The effect of low-dose aspirin therapy on serum CRP levels in men has been addressed recently, but the results of the two studies conflict. METHODS: Effects of aspirin (81 mg every day or 325, 81 or 40 mg every-third-day given for 31 days) on serum CRP, using a highly-sensitive assay, and on serum platelet-cyclo-oxygenase (COX)-1-derived thromboxane (Tx) B₂ concentrations were studied simultaneously in 57 healthy volunteers (30 men and 27 women). RESULTS: Trough platelet COX-l-derived serum Tx B₂ concentrations decreased by 100% with daily aspirin and by 90%, 84% and 78% with 325, 81 and 40 mg aspirin every-third-day (p < 0.001). However, there were no significant changes in serum CRP levels from baseline with daily low-dose aspirin therapy, with any of the every-third-day aspirin regimens or with placebo treatment. CONCLUSIONS: Low doses of aspirin that markedly inhibit platelet COX-1 activity, as manifested by a profound decline in platelet-derived serum Tx B₂ concentrations, have no detectable effect on serum CRP levels in healthy men and women.