A neutral-active, Ca2+-dependent
phospholipase A2 (PLA2) purified 11,000-fold from human synovial fluid (HSF) induced
edema when injected into the mouse foot pad. The
edema produced by HSF-PLA2 was dose-dependent and was positively correlated with the dose-dependent in vitro expression of PLA2 activity. Maximum
edema was achieved within 45 min after the injection and persisted for at least 6 h.
Aristolochic acid [8-methoxy-6-nitrophenanthro(3,4-d)-1,3-dioxole-5-
carboxylic acid], a major chemical component derived from various species of Aristolochia plant, produced a dose-dependent inhibition of in vitro
phospholipid hydrolysis by HSF-PLA2, porcine pancreatic PLA2,
snake venom (Naja naja) PLA2, and PLA2 isolated from human platelet. The sensitivity of these PLA2s to inhibition by
aristolochic acid varied markedly: HSF-PLA2 greater than N. naja PLA2 greater than human platelet PLA2 greater than porcine pancreatic PLA2. The inhibition of HSF-PLA2 by
aristolochic acid was independent of substrate concentration (18-144 microM) and Ca2+ concentration (0.1-4.0 mM). These observations indicate that inhibition of HSF-PLA2 by
aristolochic acid may result from direct interaction with the
enzyme. When
aristolochic acid was mixed with HSF-PLA2 and then injected into the mouse foot pad,
edema was inhibited in a dose-dependent manner and was positively correlated with in vitro inhibition of PLA2 activity. Alkylation of HSF-PLA2 with
p-bromophenacyl bromide concomitantly inhibited both
enzyme and
edema-inducing activity. These results clearly demonstrate that the neutral-active, Ca2+-dependent PLA2 isolated from human synovial fluid is proinflammatory and that catalytic activity is positively correlated with in vivo proinflammatory effects.