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 greater than or equal to 1 mu M 5-aminosalicylic acid) and thrombin-induced platelet activation (P < 0.02 for greater than or equal to 1 mu 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.