Effect of cyclooxygenase blockade on different platelet functions activated by tumor cells

Vol. 70, Suppl. 1

ABSTRACTS

OF 12TH NATIONAL

Sll

CONGRESS

c 005 BLOCKADE ON DIFFERENT PLATELET EFFECT OF CYCLOOXYGENASE ACTIVATED BY TUMOR CELLS. I . Pacchiarini, M. Zucchella, F. FUNCTIONS Tacconi, A. Saporiti, A. Brocchieri and G. Grignani. Department of Internal Medicine, Section of Medical Pathology, University of Pavia, IRCCS Policlinico S. Matteo, Pavia, Italy. We studied the effect on platelets of cells isolated from 26 human tumor tissues (11 colon carcinomas, 11 breast carcinomas, 2 pancreatic carcinomas, 1 gastric carcinoma and 1 esophageal carcinoma). Tumor cells (105/ml) significantly increased platelet adhesion to glass beads (Hellem’s metod); they were also found to possess a potent, dose-dependent platelet aggregating activity (1 05-4x105/ml) and aggregation was accompanied by significant release of ATP and PDGF and by production of TxB,. Preincubation of platelets with a low concentration (1 pM) of indobufen, a cyclooxygenase

inhibitor,

significantly

reduced

only tumor cell induced

TxB,

production

and ATP release, while the other platelet functions were not modified. Higher concentrations of the drug (10 or 100 p.M) were able to inhibit also tumor cell induced platelet aggregation and PDGF release, while platelet adhesion to glass beads was unchanged even at these doses. Finally, preincubation of neoplastic cells with indobufen (400 pM) had no effect on their ability to induce platelet aggregation and TxB, production. These data demonstrate that cyclooxygenase blockade in platelets has different effects on several platelet functions activated by tumor cells, while cyclooxygenase blockade in tumor cells does not modify their ability to activate platelet function ‘in vitro’.

c 006 ROLE OF P-SELECTIN AND CATHEPSIN G IN ARACHIDONIC ACID (AA) TRANSCELLULAR METABOLISM DURING PLATELET-PMN INTERACTION. N.Maueeri, V. Evangelista, P. Piccardoni, A. Celardo, G. Dell’Elba, G. de Gaetano and C. Cerletti. Consorzio Mario Negri Sud, 66030 Santa Maria Imbaro. PMN and platelets stirred and stimulated by fMLP formed a mixed cell aggregate as a consequence of PM&induced platelet activation via cathepsin G. In these conditions cathepsin G activated-platelets utilize AA and LTM from fMLP stimulated PMN to form TxB2 and LTCa. In the present report we analyzed the role of P-selectin-mediated platelet-PMN contact on transcellular metabolization of AA. Mixed cell populations (107PMN/108platelets/ml) stimulated with 1pM fMLP produced 30&6 ng/ml of TxB2 and 2.0+0.0lpg/ml of LTC4 measured by specific RIAs (mean&EM; n=7). Radioactive TxB2 and peptidoleukotrienes identified by HPLC were produced only when suspensions of 3H-AA-labeled PMN/unlabeled platelets were stimulated together. In samples treated with eglin C (1 mg/ml), in which platelet activation induced by cathepsin G was blocked, formation of TxB2 and LTGl was completely abolished. F(ab) anti P-selectin (GE-12, kind gift of B. Furie) almost completely prevented platelet production of 3H-TxB2 and reduced overall TxB2 and LTC4 synthesis by 53+8 and 88+10% of control, respectively. GE-12 did not affect platelet activation as measured by 3H-5HT release neither when platelets were activated by PMN in mixed cell suspension nor when platelets were activated by PMN-derived supematant or purified cathepsin G. Our results indicate that transcellular metabolism of AA between PMN and platelets requires P-selectin-mediated cellcell contact and platelet activation by cathepsin G.