Mechanism of action of aspirin

Aspirin causes several different effects in the body, mainly the reduction of inflammation, analgesia (relief of pain), the prevention of clotting, and the reduction of fever. Much of this is believed to be due to decreased production of prostaglandins and TXA2. Aspirin's ability to suppress the production of prostaglandins and thromboxanes is due to its irreversible inactivation of the cyclooxygenase (COX) enzyme. Cyclooxygenase is required for prostaglandin and thromboxane synthesis. Aspirin acts as an acetylating agent where an acetyl group is covalently attached to a serine residue in the active site of the COX enzyme. This makes aspirin different from other NSAIDs (such as diclofenac and ibuprofen), which are reversible inhibitors. However, other effects of aspirin, such as uncoupling oxidative phosphorylation in , and the modulation of signaling through NF-κB, are also being investigated.

The mechanism of aspirin's analgesic, anti-inflammatory and antipyretic properties was unknown through the drug's heyday in the early- to mid-twentieth century; Heinrich Dreser's explanation, widely accepted since the drug was first brought to market, was that aspirin relieved pain by acting on the central nervous system. In 1958 Harry Collier, a biochemist in the London laboratory of pharmaceutical company Parke Davis, began investigating the relationship between kinins and the effects of aspirin. In tests on guinea pigs, Collier found that aspirin, if given beforehand, inhibited the bronchoconstriction effects of bradykinin. He found that cutting the guinea pigs' vagus nerve did not affect the action of bradykinin or the inhibitory effect of aspirin—evidence that aspirin worked locally to combat pain and inflammation, rather than on the central nervous system. In 1963, Collier began working with University of London pharmacology graduate student Priscilla Piper to determine the precise mechanism of aspirin's effects. However, it was difficult to pin down the precise biochemical goings-on in live research animals, and in vitro tests on removed animal tissues did not behave like in vivo tests.

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