MAST-CELL DEGRANULATION INDUCED BY 2 PHOSPHOLIPASE A(2) HOMOLOGS - DISSOCIATION BETWEEN ENZYMATIC AND BIOLOGICAL-ACTIVITIES

Bothropstoxin-I and bothropstoxin-II are phospholipase A(2) homologues isolated from Bothrops jararacussu snake venom. The former is devoid of phospholipase A(2) activity whereas the latter has very low enzymat ic activity. In this study, we have investigated the in vivo (rat paw and skin oedema) and in vitro (mast cell degranulation) inflammatory e ffects caused by bothropstoxin-I and bothropstoxin-II. Bothropstoxin-I (25-100 mu g/paw) and bothropstoxin-II (12.5-50 mu g/paw) caused dose -dependent rat paw oedema. The intradermal injection of bothropstoxin- I (0.125-5 mu g/site) and bothropstoxin-II (0.125-5 mu g/site) into ra t skin also resulted in dose-dependent oedema formation. These oedemat ogenic activities were largely reduced in animals pretreated with the histamine/5-hydroxytryptamine (5-HT) receptor antagonist cyproheptadin e (2 mg/kg, i.p. 0.5 h before). Similarly, p-bromophenacyl bromide, a compound known to inhibit phospholipase A(2) activity, significantly i nhibited rat paw and skin oedema induced by both phospholipase A(2) ho mologues. The polyanion heparin (5 IU/site) significantly reduced the rat skin oedema induced by either bothropstoxin-I or bothropstoxin-II as well as the paw oedema (50 IU/site) induced by the former. When ass ayed in the rat peritoneal mast cells in vitro, both bothropstoxin-I ( 10 and 100 mu g/ml) and bothropstoxin-II (3 and 10 mu g/ml) significan tly caused [C-14]5-HT release. The [C-14]5-HT release caused by these phospholipase A(2) homologues were reduced by p-bromophenacyl bromide and heparin (50 IU/ml). Our results indicate that oedema formation ind uced by bothropstoxin-I and bothropstoxin-II is mostly dependent on in vivo mast cell degranulation. Since heparin greatly reduced the oedem atogenic activity of these phospholipase A(2) homologues, it is likely that the cationic charge of these substances plays a major role in th e mast cell activation. Our results also indicate that p-bromophenacyl bromide may not be a suitable pharmacological tool to investigate the correlation between enzymatic activity and the inflammatory effects o f phospholipases A(2). (C) 1998 Elsevier Science B.V.