Prostaglandins, Leukotrienesand Essential Fatfy Acids (1998) 58(6), 421424 © HarcourtBrace& Co. Ltd 1998 Effects of lysine clonixinate on cyclooxygenase I and II in rat lung and stomach preparations A. M. Franchi, G. Di Girolamo, A. R. de los Santos, M. L. Marti, M. A. F. Gimeno Centro de Estudios Farmacologicos y Botanicos (CEFYBO), Consejo Nacional de Investigaciones Cientfficas y Tecnicas (CONICET), Serrano 669, (1414) Buenos Aires, Argentina Summary Lysine clonixinate (LC) is a drug of antiinflammatory antipyretic and analgesic activity that produces minor digestive side-effects. This fact induced us to think that LC is possibly a weak COX-1 inhibitor. In order to investigate our hypothesis we inhibited cyclooxygenase activity with LC or indomethacin (INDO) in rat lung and stomach obtained from rats treated with lipopolysacharide (LPS) and control rats. Rat lung preparations incubated with 14C-arachidonic acid synthesise mainly PGE2. LC at 2.5 and 4.1 x 104 M does not modify the basal production of PGE 2 (probably COX-l) but at 6.8 x 10-2 M significantly inhibited PGE2 production (approximately 48.5% inhibition, P < 0.001). On the other hand, INDO at 104 inhibited the basal production of PGE 2 by around 73%. In LPS-treated rats, the production of PGE2 was significantly higher than in the lungs of control rats, probably due to the induction of COX-2. The addition of LC at 2.7 and 4.1 x 10-2 M recovered the control values of PGE2 inhibiting, probably only from COX-2 activity. LC at higher concentrations (6.8 x 10-2 M) and INDO 104 M inhibited PGE2 formed by COX-2 and also partly by COX-1 activity. INTRODUCTION The PGH2 synthase is a rate-limiting enzyme in prosta- glandin and thromboxane synthesis, it possesses two enzymatic activities, a cyclooxygenase which catalyses the oxygenation of arachidonic acid to PGG2 and per- oxidase which reduces PGG2 to PGH2.~ Until recently, a single cyclooxygenase (COX) was recognized as the enzyme responsible for the generation of the prosta- glandins. However, a second form of the enzyme has now been identified, which is induced by proinflammatory cytokines, growth factor hormones and oncogenes. This cyclooxygenase (COX-2) is specifically associated with cells and tissues involved in inflammation.2-4 Actually, cyclooxygenase has been found in two forms, namely the constitutive, widely occurring enzyme (COX-l) and the inducible isoform (COX-2), which is expressed after stim- ulation with endotoxin lipopolysacharide (LPS) or some cytokines? The LPS of gram-negative bacteria elicit a wide range of effects in biological systems in vivo and in vitro. Received 8 November 1996 Accepted 26 May 1998 Correspondence to: A. M. Franchi Several cell types and tissues, such as lung challenged with LPS, produce increased amounts of both nitric oxide 5 and prostaglandins. 6 Systemic administration of LPS resulted in induction of COX-2 mRNA within 1 h and inducible nitric oxide synthase (iNOS) in lung, without affecting levels of COX-1. 7 Previous studies in vitro sug- gested that side-effects of non-steroidal antfinflammatory drugs (NSMDS) correlate with their ability to inhibit COX- 1, while the antiinflammatory effects are due to their ability to inhibit COX-2. On the other hand, the anti- inflammatory steroid dexamethasone completely inhibited the expression of COX-2, whereas COX-1 was unaffected in macrophages stimulated with LPSfi The unique involvement of the isoform COX-2 in inflammatory disorders has provided an exciting opportu- nity for developing pharmacologic agents that selectively inhibit COX-2. Most of the currently available NSMDs are generally one or two orders of magnitude more potent in bloclrang COX-1.9 Lysine clonixinate (LC) is a drug of anti- inflammatory, antipyretic and analgesic activity which has proven to be rapid and effective in clinical uses. ~°-12 It has been reported that LC produces minor digestive side- effects. ~3 This fact induces us to think that this drug is possibly a weak COX-1 inhibitor; in the rat lung a high 421