non-steroidal anti-inflammatory drug (NSAID)s are thought to work via inhibition of the enzyme, cyclo-oxygenase (COX), also known as prostaglandin synthetase
NSAIDs are a heterogeneous class including aspirin and various other nonselective and selective inhibitors of cyclooxygenase (COX). Aspirin is the only NSAID used for prevention and treatment of coronary heart disease (CHD)
cyclo-oxygenase is present in different forms - the two isoforms are encoded by different genes and have unique patterns of expression:
cyclo-oxygenase 1 (COX1)
COX-1 isozyme is essential for the maintenance of normal physiologic states in many tissues including the kidney, gastrointestinal tract, and platelets - for example, COX-1 activation in the gastric mucosa leads to prostaglandin PGI2 (prostacyclin) production, which is cytoprotective
thromboxane A2, which is primarily synthesized in platelets through COX-1 activity, causes platelet aggregation, vasoconstriction, and smooth muscle proliferation
cyclo-oxygenase 2 (COX2) is less widely expressed, but is readily induced by pro-inflammatory stimuli, and catalyses production of prostaglandins that mediate inflammation
inhibition of COX-1 is thought to be the main way in which NSAIDs cause gastrointestinal damage
anti-inflammatory efficacy is believed to result from inhibition of COX-2
at therapeutic doses, COX-2 inhibitors inhibit COX-2 but not COX-1, so it was postulated that they should relieve inflammation with less gastrointestinal toxicity than conventional NSAIDs
it now is apparent that selective inhibition of COX-2 appears more complex than first suggested, as COX-2 has many other functions besides its role in inflammation
in vascular endothelium, it mediates production of prostaglandin PGI2 (prostacyclin), a vasodilator and inhibitor of both platelet aggregation and proliferation of vascular smooth muscle cells
therefore in consideration that COX-1 mediates synthesis of thromboxane A2 (vasoconstrictor and stimulator of both platelet aggregation and vascular proliferation) both isoforms are probably important in vascular homeostasis and regulation of platelet function
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