Thrombosis Research 95 (1999) 335–339 BRIEF COMMUNICATION Orally Administered Acetylsalicylic Acid Decreases Protein Incorporation into the Cytoskeleton of Thrombin-Stimulated Platelets Nair Yukie Maeda 1 , Sergio P. Bydlowski 1 , Antonio Augusto B. Lopes 2 1 Fundac ¸a ˜o Pro ´ -Sangue Hemocentro de Sa ˜ o Paulo, Brazil; 2 Heart Institute, University of Sa ˜ o Paulo, School of Medicine, Sa ˜ o Paulo, Brazil. (Received 25 May 1998 by J.C. Prieto; revised/accepted 25 January 1999) Key Words: Blood platelets; Acetylsalicylic acid; Platelet and stimulated platelets can be analyzed in Triton cytoskeleton X-100-insoluble platelet fractions. Triton X-100 is a detergent that solubilizes most of the platelet proteins but not actin filaments and some of the P latelet cytoskeletal core is made up of long proteins that are associated with them in intact cytoplasmic actin filaments, a microtubule cells [8]. coil at platelet periphery and a membrane During platelet activation, the amount of actin skeleton at the inner side of the lipid bilayer. In polymerized onto filaments rapidly increases from recent years, advances in the understanding of the 30 to 40% to 60 to 70% of total platelet actin [9]. structure and function of the platelet cytoskeleton Actin polymerization is largely related to agonist- have provided considerable evidence that the cyto- induced inositol phospholipid hydrolysis [10] that skeleton has functions other than contractile ones [1–3]. Several regulatory proteins including tyro- can be observed early during shape change, a few sine kinases have been recovered with the mem- seconds after addition of the stimulus but is quanti- brane skeleton, suggesting that the cytoskeletal tatively more pronounced during secretion. At high elements may play a role in localizing signaling concentrations, strong agonists such as thrombin molecules [4–7]. Platelet activation is followed by are able to induce inositol phospholipid hydrolysis dramatic changes in the cytoskeletal organization. and secretion in a cyclooxygenase-independent These include cross-linking of preexisting actin fila- manner. However, at lower agonist concentrations, ments, increased polymerization of actin mono- phosphoinositide metabolism occurs during secre- mers onto filaments at platelet periphery and de- tion and may be entirely dependent on the forma- veloping filopodia, and binding of filament network tion of endoperoxides and thromboxane A 2 [11]. to myosin, a tension generating interaction re- Consequently, inhibitors of cyclooxygenase might quired for the retraction process. alter the pattern of cytoskeletal organization under The cytoskeletal organization in unstimulated some conditions of platelet stimulation. Acetylsalicylic acid (ASA) has been widely shown to be effective as an antithrombotic agent. The Abbreviations: ASA, acetylsalicylic acid; EDTA, edetic acid; rationale for its use in cardiovascular disorders is EGTA, egtazic acid; BSA, bovine serum albumin; PMSF, phenyl- that the compound inhibits the synthesis of throm- methylsulphonyl fluoride. Corresponding author: N.Y. Maeda, Laborato ´ rio de Biotecno- boxane A 2 by irreversibly blocking platelet cyclo- logia, Fundac ¸a ˜o Pro ´ -Sangue Hemocentro de Sa ˜o Paulo, Av. Dr. oxygenase [12]. This study was planned to investi- Ene ´as C. Aguiar, 155, PAMB – 1 ° andar 05403-000, Sa ˜ o Paulo, SP, Brazil. Tel/Fax: +55 (11) 282 2398. gate possible effects of cyclooxygenase blockade 0049-3848/99 $–see front matter  1999 Elsevier Science Ltd. All rights reserved. PII S0049-3848(99)00053-5