Kazushige Tanaka

Antiinflammatory action of thielocin A1β, a group II phospholipase A2 specific inhibitor, in rat carrageenan-induced pleurisy

Extracellular phospholipase A2 (PLA2) activity was detected in exudate from rat carrageenan-induced pleurisy using [3H]oleic acid-labeledEscherichia coli as substrate. Both exudate volume and PLA2 activity increased up to 24 h after carrageenin injection. Specific absorption of this activity by anti-group II PLA2 (PLA2-II) antibody indicated that the PLA2 activity in the pleural exudate was PLA2-II. Thielocin Alβ, a novel type of PLA2 inhibitor from fungi, inhibited this PLA2-II activity in a dose-dependent manner (IC50=0.32μM). Thielocin A1β correspondingly reduced both exudate volume and PLA2-II activity in the exudate in a dose-dependent manner when coinjected with carrageenan. The exudate volume was also significantly decreased when indomethacin, a cyclooxygenase inhibitor, or dexamethasone, a steroidal antiinflammatory drug, was coinjected with carrageenan. However, neither indomethacin nor dexamethasone could significantly attenuate the PLA2-II activity in exudate In addition, indomethacin and dexamethasone significantly reduced the levels of PGE2 in the exudate. However, thielocin A1β had no effect on the PGE2 content in the exudate. These results suggest that thielocin A1β shows antiinflammatory activity due to inhibition of PLA2-II and offer evidence for the significance of PLA21I in the propagation of inflammatory processes.

Effect of thielocin A1β on bee venom phospholipase A2-induced edema in mouse paw

Several investigators have reported that inactivation of secretory phospholipase A2 purified from bee venom with p-bromophenacyl bromide, an irreversible inhibitor, before injection resulted in attenuation of the subsequent inflammatory reaction in the mouse paw edema model. Recently, thielocin A1 beta, a novel secretory phospholipase A2 inhibitor from fungi, was found to suppress histamine release from mast cells stimulated with secretory phospholipase A2. These observations led us to examine the effect of thielocin A1 beta against secretory phospholipase A2-induced paw edema. Thielocin A1 beta inhibited bee venom phospholipase A2 in a dose-dependent manner (IC50 = 1.4 microM). In addition, the inhibition of bee venom phospholipase A2 was noncompetitive (Ki = 0.57 microM) and reversible. Subplantar injection of bee venom phospholipase A2 produced a rapid but transient edematous response. Coinjection of thielocin A1 beta (1 microgram/paw) with bee venom phospholipase A2 resulted in a 44.7 +/- 4.6% reduction of edema formation. This anti-edema action was not enhanced by cyproheptadine (antihistamine/antiserotonin). These results suggest that thielocin A1 beta shows edema-reducing activity via inhibition of the phospholipase A2 activity which participates in histamine release by mast cells.