Maugeri N, Evangelista V, Piccardoni P, Dell'Elba G, Celardo A, de Gaetano G, Cerletti C
Giulio Bizzozero Laboratory of Platelet and Leukocyte Pharmacology, Istituto di Richerche Farmacologiche Mario Negri, Consorzio Mario Negri Sud, Santa Maria Imbaro, Italy.
Blood. 1992 Jul 15;80(2):447-51.
Human polymorphonuclear leukocytes (PMN) activated by n-formyl-methionyl-leucyl-phenylalanine (fMLP), in the presence of cytochalasin B, are able to induce activation of coincubated autologous platelets "via" cathepsin G released from the azurophilic granules. However, thromboxane (Tx) B2 production in this system cannot be completely explained by cathepsin G-stimulated platelet arachidonate metabolism. Indeed, the amount of TxB2 found in supernatants of platelet/PMN suspensions challenged with 1 mumol/L fMLP was twofold to fourfold higher than that measured when platelets were stimulated by supernatants from fMLP-activated PMN. In the present report, we analyzed the possibility that PMN-induced TxB2 production in this system is the result of transcellular metabolism of arachidonic acid (AA) between fMLP-activated PMN and cathepsin G-stimulated platelets. 3H-AA-labeled PMN were used to test if a transfer of AA or metabolite(s) occur from PMN to platelets. Our results showed that: (1) 3H-TxB2 and 3H-12-HHT are synthesized when 3H-AA-labeled PMN are activated mixed to unlabeled platelets; (2) total radioactivity released by fMLP-stimulated PMN is increased in the presence of platelets, whereas the membrane content of unesterified 3H-AA is reduced; (3) platelet cyclooxygenase inhibition completely prevents 3H-TxB2 synthesis; and (4) inhibition of cathepsin G-induced platelet activation with the antiprotease eglin C blocks the formation of 3H-TxB2. These data show that in the experimental system used, platelets use PMN-derived unmetabolized AA to synthesize TxB2.
在细胞松弛素B存在的情况下，被N-甲酰甲硫氨酰-亮氨酰-苯丙氨酸（fMLP）激活的人多形核白细胞（PMN）能够通过从嗜天青颗粒释放的组织蛋白酶G诱导共孵育的自体血小板活化。然而，该系统中血栓素（Tx）B2的产生不能完全用组织蛋白酶G刺激的血小板花生四烯酸代谢来解释。事实上，用1μmol/L fMLP刺激的血小板/PMN悬浮液上清液中发现的TxB2量比用fMLP激活的PMN上清液刺激血小板时测得的量高两倍至四倍。在本报告中，我们分析了在该系统中PMN诱导的TxB2产生是fMLP激活的PMN和组织蛋白酶G刺激的血小板之间花生四烯酸（AA）跨细胞代谢结果的可能性。用3H-AA标记的PMN来测试是否发生了AA或代谢物从PMN向血小板的转移。我们的结果表明：（1）当3H-AA标记的PMN与未标记的血小板混合激活时，会合成3H-TxB2和3H-12-HHT；（2）在血小板存在的情况下，fMLP刺激的PMN释放的总放射性增加，而未酯化的3H-AA的膜含量降低；（3）血小板环氧化酶抑制完全阻止3H-TxB2的合成；（4）用抗蛋白酶埃格林C抑制组织蛋白酶G诱导的血小板活化可阻断3H-TxB2的形成。这些数据表明，在所使用的实验系统中，血小板利用PMN来源的未代谢AA合成TxB2。
