GROUP-I, GROUP-II AND GROUP-III EXTRACELLULAR PHOSPHOLIPASES A(2) - SELECTIVE-INHIBITION OF GROUP-II ENZYMES BY INDOMETHACIN BUT NOT OTHER NSAIDS

The three types (groups I, II and III) of stable extracellular 14 kDa phospholipase A(2) enzymes differ in their primary amino acid sequence s and their properties. It may thus be possible to design low-molecula r weight inhibitors targeted to the secretory form of mammalian PLA(2) . This enzyme has been implicated in inflammatory disorders. We have s tudied the inhibition of four distinct PLA(2) enzymes by a range of NS AIDs, using H-3-oleate release from prelabelled membranes of E. coli f or assay. The enzymes used were cobra venom PLA, (Naja naja, a group I enzyme), bee venom PLA(2) (Apis mellifera, group III), recombinant hu man synovial PLA(2) (group II) and rat peritoneal PLA(2) (group II). U nder the conditions of the H-3-oleate E. coli assay, 1 mM concentratio ns of aspirin, sodium salicylate, paracetamol (acetaminophen), oxphenb utazone, ibuprofen, flurbiprofen and nabumetone failed to inhibit sign ificantly any of the four enzymes. However, indomethacin inhibited all four enzymes, although effects were greatest on the two group II enzy mes (rat peritoneal and human synovial PLA(2)). Approximate IC50 value s were 28 and 35 mu M, respectively. Inhibition by indomethacin was no t time dependent and was greater at micromolar rather than millimolar levels of calcium. We conclude that indomethacin but not the other tes ted classes of NSAID inhibits the group II PLA(2) enzyme in a selectiv e manner and suggest that this may be relevant both to its clinical sp ectrum and to the design of novel pharmaceutical leads.