EFFECTS OF IBUPROFEN ENANTIOMERS AND ITS COENZYME-A THIOESTERS ON HUMAN PROSTAGLANDIN ENDOPEROXIDE SYNTHASES

1 Ibuprofen enantiomers and their respective coenzyme A thioesters wer e tested in human platelets and blood monocytes to determine their sel ectivity and potency as inhibitors of cyclo-oxygenase activity of pros taglandin endoperoxide synthase-1 (PGHS-1) and PGHS-2. 2 Human blood f rom volunteers was drawn and allowed to clot at 37 degrees C for 1 h i n the presence of increasing concentrations of the test compounds (R-i buprofen, S-ibuprofen, R-ibuprofenoyl-CoA, S-ibuprofenoyl-CoA, NS-398) . Immunoreactive (ir) thromboxane B-2 (TXB2) concentrations in serum w ere determined by a specific EIA assay as an index of the cyclo-oxygen ase activity of platelet PGHS-1. 3 Heparin-treated blood from the same donors was incubated at 37 degrees C for 24 h with the same concentra tions of the test compounds in the presence of lipopolysaccharide (LPS , 10 mu g ml(-1)). The contribution of PGHS-1 was suppressed by pretre atment of the volunteers with aspirin (500 mg; 48 h before venepunctur e). As a measure of LPS induced PGHS-2 activity immunoreactive prostag landin E-2 (irPGE(2)) plasma concentrations were determined by a speci fic EIA assay. 4 S-ibuprofen inhibited the activity of PGHS-1 (IC50 2. 1 mu M) and PGHS-2 (IC50 1.6 mu M) equally. R-ibuprofen inhibited PGHS -1 (IC50 34.9) less potently than S-ibuprofen and showed no inhibition of PGHS-2 up to 250 mu M. By contrast R-ibuprofenoyl-CoA thioester in hibited PGE(2) production from LPS-stimulated monocytes almost two ord ers of magnitude more potently than the generation of TXB2 (IC50 5.6 v s 219 mu M). 5 Western blotting of PGHS-2 after LPS induction of blood monocytes showed a concentration-dependent inhibition of PGHS-2 prote in expression by ibuprofenoyl-CoA thioesters. 6 These data confirm tha t S-ibuprofen represents the active entity in the racemate with respec t to cyclooxygenase activity. More importantly the data suggest a cont ribution of the R-enantiomer to therapeutic effects not only by chiral inversion to S-ibuprofen but also via inhibition of induction of PGHS -2 mediated by R-ibuprofenoyl-CoA thioester. 7 The data may explain wh y racemic ibuprofen is ranked as one of the safest non-steroidal antii nflammatory drugs (NSAIDs) so far determined in epidemiological studie s.