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Cyclooxygenases have two main isoforms that are called COX-1 and COX-2 (as well as a COX-3). COX-1 is responsible for the synthesis of prostaglandin and thromboxane in many types of cells, including the gastro-intestinal tract and blood platelets. COX-2 plays a major role in prostaglandin biosynthesis in inflammatory cells and in the central ...
These alternate metabolites of COX-1 may contribute to its activities. COX-1 promotes the production of the natural mucus lining that protects the inner stomach and contributes to reduced acid secretion and reduced pepsin content. [18] [19] COX-1 is normally present in a variety of areas of the body, including not only the stomach but any site ...
COX is a common target for anti-inflammatory drugs. The most significant difference between the isoenzymes, which allows for selective inhibition, is the substitution of isoleucine at position 523 in COX-1 with valine in COX-2. The smaller Val 523 residue in COX-2 allows access to a hydrophobic side-pocket in the enzyme (which Ile 523 ...
Aspirin is ≈170-fold more potent in inhibiting COX-1 than COX-2. [40] Studies of meloxicam 7.5 mg per day for 23 days find a level of gastric injury similar to that of a placebo , and for meloxicam 15 mg per day a level of injury lower than that of other NSAIDs; however, in clinical practice meloxicam can still cause some ulcer complications.
Structure of COX-2 inactivated by Aspirin. In the active site of each of the two enzymes, Serine 516 has been acetylated. Also visible is the salicylic acid which has transferred the acetyl group, and the heme cofactor. There are at least two different cyclooxygenase isozymes: COX-1 (PTGS1) and COX-2 (PTGS2).
Rofecoxib is a selective COX-2 inhibitor, or "coxib". Though the class of coxibs includes several agents, degrees of COX-2 selectivity vary among them, with celecoxib (Celebrex) being the least COX-2 selective, and rofecoxib (Vioxx), valdecoxib (Bextra), and etoricoxib (Arcoxia), being highly COX-2 selective. [10]
Ketorolac is a non-selective COX inhibitor. [26] It is considered a first-generation NSAID, [ 15 ] : 279 a group of drugs that non-selectively inhibit both COX-1 and COX-2 enzymes, which can lead to gastrointestinal side effects. [ 27 ]
COX-3 is the third and most recently discovered cyclooxygenase (COX3050) isozyme, while the first two to be discovered were COX-1 and COX-2. The COX-3 isozyme is encoded by the same gene as COX-1, with the difference that COX-3 retains an intron that is not retained in COX-1. [1] [2]