PX-52, a Novel Inhibitor of 14 kDa Secretory and 85 kDa Cytosolic Phospholipases A₂

Abstract

Previously we reported that PGBx, a prostaglandin oligomer with anti-inflammatory activity, inhibited 14 kDa phospholipase A₂ (PLA₂) activity and blocked arachidonic acid mobilization in prelabeled human neutrophils (Biochim. Biophys. Acta 1006:272-277, 278–286, 1989) This study describes a new inhibitor of phospholipase A₂, PX-52, that also blocks agonist induced arachidonic acid mobilization in prelabeled cells. PX-52, a fatty acid polymer, inhibited hydrolysis of ¹⁴C-oleate labeled E.coli by a variety of 14 kDa PLA₂S including human PMN, sperm, synovial fluid and disc, as well as porcine pancreas, N. naja, and bee venom in a dose-dependent manner with IC₅₀S ranging from 1.0–3.7 uM. Inhibition of activity was comparable at different Ca²⁺ concentrations, but was relieved by increasing substrate concentration or by methylation of PX-52. Hydrolysis of [¹⁴C]-arachidonyl phosphatidylcholine by 85 kDa, cytosolic PLA2 from U937 cells was similarly inhibited by PX-52, the IC₅₀ = 5 uM. Arachidonic acid mobilization induced by A23187 in prelabeled human PMNs was blocked by PX-52; IC₅₀ = 10–15 uM while concentrations of up to 80 uM oleate had no effect. These results demonstrate that PX-52 inhibits the in vitro activity of secretory and cytosolic PLA₂s and agonist-induced arachidonic acid release from human cells. Given its ability to block the arachidonic acid cascade, PX-52 may be useful in the control of inflammation.