Aspirin (acetylsalicylic acid, ASA) is effective in the primary and secondary prevention of vascular events. This effect is mediated in large part by platelet inhibition; however, non-platelet-mediated effects may also be relevant in the overall efficacy of ASA. We determined the effect of ASA on the synthesis of DNA and total proteins in cultured human coronary endothelial cells (HCAECs). Fourth generation HCAECs were cultured and treated with ASA and rate of synthesis of DNA and total proteins was determined by incorporation of [H-3]thymidine and [H-3]proline, respectively. ASA inhibited DNA synthesis by 50% at a concentration of 1 mM and protein synthesis by 50% at a concentration of 2 mM. The inhibitory effect of ASA was observed as early as 2 h after treatment of HCAECs. The inhibition of DNA and protein synthesis could be reversed within 24 h after removal of the drug from I he culture medium. Indomethacin also inhibited DNA and protein synthesis. Western blot analysis revealed that the expression of p53 protein was increased after treatment of the cells with ASA. These observations indicate that ASA decreases endothelial cell proliferation through cell cycle arrest mediated by enhanced p53 expression. Arrest of endothelial proliferation and activation may be an important mechanism of thes beneficial effect of ASA in acute coronary syndromes. (C) 2002 Elsevier Science (USA). All rights reserved.