Inhibition of platelet activation by 5‐aminosalicylic acid in inflammatory bowel disease

Background: Platelets play an important role in inflammation and are activated in inflammatory bowel disease. Micro‐vascular thrombosis in the gut wall leading to intestinal micro‐infarction may be a pathogenic feature of Crohn’s disease. 5‐Aminosalicylic acid is an effective treatment for patients with inflammatory bowel disease. Aims: To assess the effects of 5‐aminosalicylic acid on platelet activation, when taken orally and in vitro by patients with inflammatory bowel disease. Methods: Spontaneous and thrombin‐induced platelet activation were studied using fluorescent antibodies to the activated platelet surface glycoprotein P‐selectin and flow cytometry. Results: Baseline platelet activation in inflammatory bowel disease was significantly greater than that in controls ( P =0.0003). Independent of diagnosis or disease activity, spontaneous ex‐vivo platelet activation was 50% lower in patients with inflammatory bowel disease taking 5‐aminosalicylic acid orally than in those not on such treatment ( P < 0.05). In vitro , 5‐aminosalicylic acid significantly reduced both spontaneous ( P < 0.03 for ≥1 μ M 5‐aminosalicylic acid) and thrombin‐induced platelet activation ( P < 0.02 for ≥ 1 μ M 5‐aminosalicylic acid). Conclusions: 5‐Aminosalicylic acid given either orally or in vitro inhibits platelet activation. If this effect reflects an in vivo action in the gut, it could contribute to the beneficial actions of 5‐aminosalicylic acid in inflammatory bowel disease.