Cyclooxygenase isoenzymes and newer therapeutic potential for selective COX-2 inhibitors.

Cyclooxygenase (COX), also known as prostaglandin G/H synthase, is a membrane-bound enzyme responsible for the oxidation of arachidonic acid to prostaglandins that was first identified over 20 years ago. In the past decade, however, more progress has been made in understanding the role of cyclooxygenase enzymes in various pathophysiological conditions. Two cyclooxygenase isoforms have been identified and are referred to as COX-1 and COX-2. COX-1 enzyme is constitutively expressed and regulates a number of housekeeping functions such as vascular hemostasis and gastroprotection, whereas COX-2 is inducible (i.e., sites of inflammation) by number of mediators such as growth factors, cytokines and endotoxins. Nonsteroidal antiinflammatory drugs (NSAIDs) produce their therapeutic effects through inhibition of COX, the enzyme that makes prostaglandins. Nonselective inhibition of COX isoenzyme leads to not only beneficial therapeutic effects but also a number of detrimental effects. Beneficial effects are due to inhibition of COX-2 and detrimental effects are due to inhibition of physiological COX-1. The present review discusses the biology as well as the role of these COX isoenzymes in various pathophysiological conditions.