Inflammatory oedema induced by the Lys-49 phospholipase A(2) homologue piratoxin-I in the rat and rabbit - Effect of polyanions and p-bromophenacyl bromide

Piratoxin-I (PrTX-I) is a Lys-49 phospholipase (PLA(2)) homologue, isolated from Bothrops pirajai snake venom, that has no phospholipase activity. In this study, we investigated the in vivo oedematogenic activity of PrTX-I in both the rat and the rabbit as well as the ability of PrTX-I to activate r at mast cells in vitro. In the rat paw and skin, PrTX-I (3-100 mu g/paw) in duced a dose-dependent oedema chat was associated with extensive mast cell degranulation. The involvement of mast cells in PrTX-I-mediated oedema form ation in the rat was further confirmed by the findings that this protein si gnificantly activated rat peritoneal mast cells in vitro, causing the relea se of [C-14]5-hydroxytryptamine ([C-14]5-HT; 51 +/- 1%). In the rabbit, PrT X-I (10-100 mu g/site) also induced dose-dependent skin oedema formation th at was not affected by either mepyramine (a histamine H-1 receptor antagoni st) or cyproheptadine (1.0 mu g/site), indicating that mast cells do not pl ay a role in this animal species. The bradykinin B-2 receptor antagonist Ho e 140 (0.5 mu g/site) and the platelet-activating factor (PAF) receptor ant agonist WEB 2086 (200 mu g/site) also failed to affect the PrTX-I-induced r abbit skin oedema, ruling out the involvement of kinins and PAF. The PLA, i nhibitor p-bromophenacyl bromide greatly reduced the PrTX-I-induced oedema in both the rat and the rabbit, and also inhibited the rat in vine mast cel l activation induced by this PLA(2) homologue. The polyanions heparin and d ermatan sulphate efficiently prevented oedema formation in both species, an d heparin inhibited PrTX-I-induced rat mast cell degranulation. Our results are consistent with the suggestion that the cationic charge of PrTX-I play s a major role in the inflammatory responses induced by this PLA, homologue . (C) 2000 Elsevier Science Inc.