Effect of the antiinflammatory prodrug, nabumetone and its principal active metabolite on rat gastric mucosal, aortic and platelet eicosanoid synthesis, in vitro and ex vivo

Abstract

Nabumetone is a novel non-steroidal antiinflammatory drug which although a weak cyclooxygenase inhibitor is converted by the liver to metabolites that are more potent inhibitors of cyclooxygenase. Nabumetone may thus avoid the occurrence of prostanoid-mediated gastropathy while maintaining its efficacy as an antiinflammatory agent. We compared the effect of nabumetone and 6-methoxy-2-naphthylacetic acid (6-MNA; the principal active metabolite of nabumetone) with that of naproxen and indomethacin on the synthesis of rat gastric prostaglandins I2 and E2, in vitro and ex vivo. Ex vivo platelet TXA2 and aortic PGI2 synthesis was also investigated in order to assess peripheral activity of nabumetone metabolites. In vitro, nabumetone was completely without effect on gastric mucosal prostanoid synthesis, whereas indomethacin, naproxen and 6-MNA (in this order of potency) inhibited prostanoid synthesis. Ex vivo, low dose naproxen and indomethacin (less than 5mg.kg-1) markedly inhibited gastric mucosal prostanoid synthesis at 30 min and 2 h post gavage, whereas nabumetone was without significant effect. Nabumetone administration also resulted in the inhibition of platelet TXA2 synthesis, whereas aortic PGI2 synthesis was unaltered. These data indicate that the administration of nabumetone may avoid NSAID gastropathy by leaving gastric mucosal prostanoid synthesis intact and also that the active metabolite(s) of nabumetone are effective inhibitors of cyclooxygenase in an NSAID-target tissue (platelet). The lack of effect of nabumetone administration on vascular PGI2 synthesis may confer an additional advantage over other NSAIDs, since the inhibition of peripheral PGI2 has been implicated in hypertensive and nephrotoxic side effects of NSAIDs.