ACTIVITY OF NIMESULIDE ON CONSTITUTE AND INDUCIBLE CYCLOOXYGENASES

Prostaglandins are pro-inflammatory but are gastroprotective. The gast ric mucosa synthesizes prostaglandins mainly via constitutive cyclooxy genase (COX-1), whereas leucocytes have inducible enzyme (COX-2). Nime sulide (GAS 51803-78-2) differentially inhibited prostanoid synthesis in these human tissues as well as with in vitro enzyme assays, and was less potent than indometacin (GAS 53-86-1) on COX-1. Fresh human gast ric mucosa was cut finely, washed and pre-incubated (100 mg in I ml ph osphate buffered saline PH 7.4) with ol without nimesulide ol indometa cin (0.1-100 mu g/ml; 0 degrees C, 30 min). The fluid was replaced wit h fresh Identical solution, incubated (37 degrees C; 30 min) and the,s olution assayed.Isolated leucocytes front human peripheral blood were incubated (1-1.5 x 10(6), 2 ml Krebs solution) with or without nimesul ide ol indometacin (0.1-100 mu g/ml, 37 degrees C, 1 h), stimulated wi th lipopolysaccharide (5 mu g/ml), further incubated for 24 h at. 37 d egrees C and the medium assayed for the prostanoids PGE, TXB(2), 6-ket o-PGF(Ia) and the leukotriene LTB(4) by radioimmunoassay (RIA). In vit ro assays with COX-I from ram seminal vesicles, or COX-2 from sheep pl acenta, were preformed by preincubating the enzymes with vehicle alone (controls) or with drug for 5 min at 37 degrees C. Arachidonate (10 m u mol/l was added and further incubated for 2 min at 37 degrees C. Rea ctions were terminated and PGE determined by RTA. Both drugs caused co ncentration-related inhibitions of prostanoid accumulation ill incubat es of both tissues. Nimesulide reduced PGE accumulation more potently in incubates of stimulated leucocytes than of gastric mucosa. With gas tric tissue, nimesulide was less potent than indometacin by approximat ely 6-22 fold (IC50 for PGE, TXB(2), 6-keto-PGF(Ia), respectively; 14. 8 vs 2.5; 12.8 vs 1.0, 31.1 vs 1.4 mu mol/l; p < 0.05 to 0.02). With t he leucocytes, the concentrations of both drugs, particularly indometa cin were not low enough to calculate the IC50 With the in vitro assay, nimesulide (0.01 to 100 mu mol/l did not inhibit PGE formation by COX -I but caused a concentration-related inhibition df PGE formation by C OX-2 (4-60%). These results are consistent with the effective analgesi c/anti-inflammatory activity of nimesulide coupled with better gastric tolerance compared to indometacin.