Distribution of COX-1 and COX-2 in normal and inflamed tissues

Abstract

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used in the treatment of a number of inflammatory diseases and are believed to act via inhibition of the enzyme cyclooxygenase (COX). This enzyme catalyzes the conversion of arachidonic acid to the prostaglandins (PGs). Although commercially available NSAIDs are efficacious anti-inflammatory agents, significant side effects limit their use. Recently two forms of COX were identified - a constitutively expressed COX-1 and a cytokine-inducible COX-2. Potent anti-inflammatory agents like the glucocorticoids are known to inhibit specifically the expression of COX-2 while commercially available NSAIDs like indomethacin inhibit both COX-1 and COX-2. These findings have led to the hypothesis that toxicities associated with NSAID therapy are due to inhibition of the non-regulated or constitutive form of COX (COX-1), whereas therapeutic benefit derives from inhibition of the inducible enzyme, COX-2. We have examined the relative distribution of COX-1 and COX-2 in both normal and inflamed tissues and report that COX-1 expression dominates normal tissues while COX-2 mRNA is induced at the inflammatory site. Furthermore, compounds that selectively inhibit COX-2 are anti-inflammatory without gastric toxicity.