Mechanism of action of aspirin

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Tridimensional model of the chemical structure of aspirin. Aspirin-3D-balls.png
Tridimensional model of the chemical structure 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. [1] This makes aspirin different from other NSAIDs (such as diclofenac and ibuprofen), which are reversible inhibitors; aspirin creates an allosteric change in the structure of the COX enzyme. [2] However, other effects of aspirin, such as uncoupling oxidative phosphorylation in mitochondria, [3] and the modulation of signaling through NF-κB, are also being investigated. Some of its effects are like those of salicylic acid, which is not an acetylating agent.

Contents

Effects on cyclooxygenase

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. COX-2 inhibited by Aspirin.png
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). Aspirin is non-selective and irreversibly inhibits both forms [4] (but is weakly more selective for COX-1 [5] ). It does so by acetylating the hydroxyl of a serine residue at the 530 amino acid position. [6] Normally COX produces prostaglandins, most of which are pro-inflammatory, and thromboxanes, which promote clotting. Aspirin-modified COX-2 produces 15-epi-lipoxins, which act to resolve inflammatory responses similar to other lipoxins. [7]

Newer NSAID drugs called COX-2 selective inhibitors have been developed that inhibit only COX-2, with the hope for reduction of gastrointestinal side-effects. [8] However, several COX-2 selective inhibitors have subsequently been withdrawn after evidence emerged that COX-2 inhibitors increase the risk of heart attack. [9] The underlying mechanism for the deleterious effect proposes that endothelial cells lining the microvasculature in the body express COX-2, whose selective inhibition results in levels of prostaglandin I2 (PGI2, prostacyclin) down-regulated relative to thromboxane (since COX-1 in platelets is unaffected).[ citation needed ] Thus, the protective anti-coagulative effect of PGI2 is decreased, increasing the risk of thrombus and associated heart attacks and other circulatory problems.[ citation needed ] As platelets have only mitochondria DNA (mtDNA), they are unable to synthesize new COX once aspirin has irreversibly inhibited the enzyme, an important difference between aspirin and the reversible inhibitors. [10]

Effects on prostaglandins and thromboxanes

Prostaglandins are local chemical messengers that exert multiple effects including but not limited to the transmission of pain information to the brain, modulation of the hypothalamic thermostat, and inflammation. They are produced in response to the stimulation of phospholipids within the plasma membrane of cells resulting in the release of arachidonic acid (prostaglandin precursor). [11] Thromboxanes are responsible for the aggregation of platelets that form blood clots. [12]

Low-dose, long-term aspirin use irreversibly blocks the formation of thromboxane A2 in platelets, producing an inhibitory effect on platelet aggregation. [13] This effect is mediated by the irreversible blockage of COX-1 in platelets, since mature platelets don't express COX-2. [14]

This antiplatelet property makes aspirin useful for reducing the incidence of heart attacks; [13] heart attacks are primarily caused by blood clots, and their reduction with the introduction of small amounts of aspirin has been seen to be an effective medical intervention.[ citation needed ] A dose of 40 mg of aspirin a day is able to inhibit a large proportion of maximum thromboxane A2 release provoked acutely, with the prostaglandin I2 synthesis being little affected; however, higher doses of aspirin are required to attain further inhibition. [15]

A side-effect of aspirin mechanism is that the ability of the blood in general to clot is reduced, and excessive bleeding may result from the use of aspirin. [16]

Other methods of action

Aspirin has been shown to have three additional modes of action. It uncouples oxidative phosphorylation in cartilaginous (and hepatic) mitochondria, by diffusing from the intermembrane space as a proton carrier back into the mitochondrial matrix, where it ionizes once again to release protons. [17] In short, aspirin buffers and transports the protons, acting as a competitor to ATP synthase. When high doses of aspirin are given, aspirin may actually cause hyperthermia due to the heat released from the electron transport chain, as opposed to the antipyretic action of aspirin seen with lower doses.

Additionally, aspirin induces the formation of NO-radicals in the body, which have been shown in mice to have an independent mechanism of reducing inflammation. This reduces leukocyte adhesion, which is an important step in immune response to infection. There is currently insufficient evidence to show that aspirin helps to fight infection. [18]

More recent data also suggests that salicylic acid and its derivatives modulate signaling through NF-κB. [19] NF-κB is a transcription factor complex that plays a central role in many biological processes, including inflammation.

Reye's syndrome

Reye's syndrome is a potentially fatal disease that causes numerous detrimental effects to many organs, especially the brain and liver, as well as causing hypoglycemia. [20] The exact cause is unknown, and while it has been associated with aspirin consumption by children with viral illness, it also occurs in the absence of aspirin use.

The disease causes fatty liver with minimal inflammation and severe encephalopathy (with swelling of the brain). The liver may become slightly enlarged and firm, and there is a change in the appearance of the kidneys. Jaundice is not usually present. [21]

Early diagnosis is vital; while most children recover with supportive therapy, severe brain injury or death are potential complications.

See also

Related Research Articles

<span class="mw-page-title-main">Aspirin</span> Medication

Aspirin, also known as acetylsalicylic acid (ASA), is a nonsteroidal anti-inflammatory drug (NSAID) used to reduce pain, fever, and inflammation, and as an antithrombotic. Specific inflammatory conditions that aspirin is used to treat include Kawasaki disease, pericarditis, and rheumatic fever.

<span class="mw-page-title-main">Nonsteroidal anti-inflammatory drug</span> Class of therapeutic drug for relieving pain and inflammation

Non-steroidal anti-inflammatory drugs (NSAID) are members of a therapeutic drug class which reduces pain, decreases inflammation, decreases fever, and prevents blood clots. Side effects depend on the specific drug, its dose and duration of use, but largely include an increased risk of gastrointestinal ulcers and bleeds, heart attack, and kidney disease.

<span class="mw-page-title-main">Prostaglandin</span> Group of physiologically active lipid compounds

Prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids that have diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are derived enzymatically from the fatty acid arachidonic acid. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring. They are a subclass of eicosanoids and of the prostanoid class of fatty acid derivatives.

<span class="mw-page-title-main">Arachidonic acid</span> Fatty acid used metabolically in many organisms

Arachidonic acid is a polyunsaturated omega−6 fatty acid 20:4(ω−6), or 20:4(5,8,11,14). If its precursors or diet contains linoleic acid it is formed by biosynthesis and can be deposited in animal fats. It is a precursor in the formation of leukotrienes, prostaglandins, and thromboxanes.

<span class="mw-page-title-main">Cyclooxygenase</span> Class of enzymes

Cyclooxygenase (COX), officially known as prostaglandin-endoperoxide synthase (PTGS), is an enzyme that is responsible for biosynthesis of prostanoids, including thromboxane and prostaglandins such as prostacyclin, from arachidonic acid. A member of the animal-type heme peroxidase family, it is also known as prostaglandin G/H synthase. The specific reaction catalyzed is the conversion from arachidonic acid to prostaglandin H2 via a short-living prostaglandin G2 intermediate.

Cyclooxygenase-2 inhibitors, also known as coxibs, are a type of nonsteroidal anti-inflammatory drug (NSAID) that directly target cyclooxygenase-2 (COX-2), an enzyme responsible for inflammation and pain. Targeting selectivity for COX-2 reduces the risk of peptic ulceration and is the main feature of celecoxib, rofecoxib, and other members of this drug class.

<span class="mw-page-title-main">Prostacyclin</span> Chemical compound

Prostacyclin (also called prostaglandin I2 or PGI2) is a prostaglandin member of the eicosanoid family of lipid molecules. It inhibits platelet activation and is also an effective vasodilator.

<span class="mw-page-title-main">Thromboxane</span> Group of lipids

Thromboxane is a member of the family of lipids known as eicosanoids. The two major thromboxanes are thromboxane A2 and thromboxane B2. The distinguishing feature of thromboxanes is a 6-membered ether-containing ring.

<span class="mw-page-title-main">Indometacin</span> Anti-inflammatory drug

Indometacin, also known as indomethacin, is a nonsteroidal anti-inflammatory drug (NSAID) commonly used as a prescription medication to reduce fever, pain, stiffness, and swelling from inflammation. It works by inhibiting the production of prostaglandins, endogenous signaling molecules known to cause these symptoms. It does this by inhibiting cyclooxygenase, an enzyme that catalyzes the production of prostaglandins.

<span class="mw-page-title-main">Thromboxane receptor</span> Mammalian protein found in Homo sapiens

The thromboxane receptor (TP) also known as the prostanoid TP receptor is a protein that in humans is encoded by the TBXA2R gene, The thromboxane receptor is one among the five classes of prostanoid receptors and was the first eicosanoid receptor cloned. The TP receptor derives its name from its preferred endogenous ligand thromboxane A2.

A prostaglandin antagonist is a hormone antagonist acting upon one or more prostaglandins, a subclass of eicosanoid compounds which function as signaling molecules in numerous types of animal tissues.

Thromboxane A<sub>2</sub> Chemical compound

Thromboxane A2 (TXA2) is a type of thromboxane that is produced by activated platelets during hemostasis and has prothrombotic properties: it stimulates activation of new platelets as well as increases platelet aggregation. This is achieved by activating the thromboxane receptor, which results in platelet-shape change, inside-out activation of integrins, and degranulation. Circulating fibrinogen binds these receptors on adjacent platelets, further strengthening the clot. TXA2 is also a known vasoconstrictor and is especially important during tissue injury and inflammation. It is also regarded as responsible for Prinzmetal's angina.

Prostaglandin H<sub>2</sub> Chemical compound

Prostaglandin H2 (PGH2), or prostaglandin H2 (PGH2), is a type of prostaglandin and a precursor for many other biologically significant molecules. It is synthesized from arachidonic acid in a reaction catalyzed by a cyclooxygenase enzyme. The conversion from arachidonic acid to prostaglandin H2 is a two-step process. First, COX-1 catalyzes the addition of two free oxygens to form the 1,2-dioxane bridge and a peroxide functional group to form prostaglandin G2 (PGG2). Second, COX-2 reduces the peroxide functional group to a secondary alcohol, forming prostaglandin H2. Other peroxidases like hydroquinone have been observed to reduce PGG2 to PGH2. PGH2 is unstable at room temperature, with a half life of 90–100 seconds, so it is often converted into a different prostaglandin.

<span class="mw-page-title-main">Cyclooxygenase-2</span> Human enzyme involved in inflammation

Cyclooxygenase-2 (COX-2), also known as prostaglandin-endoperoxide synthase 2 (HUGO PTGS2), is an enzyme that in humans is encoded by the PTGS2 gene. In humans it is one of three cyclooxygenases. It is involved in the conversion of arachidonic acid to prostaglandin H2, an important precursor of prostacyclin, which is expressed in inflammation.

<span class="mw-page-title-main">Cyclooxygenase-1</span> Enzyme

Cyclooxygenase 1 (COX-1), also known as prostaglandin-endoperoxide synthase 1, is an enzyme that in humans is encoded by the PTGS1 gene. In humans it is one of two cyclooxygenases.

Cyclooxygenases are enzymes that take part in a complex biosynthetic cascade that results in the conversion of polyunsaturated fatty acids to prostaglandins and thromboxane(s). Their main role is to catalyze the transformation of arachidonic acid into the intermediate prostaglandin H2, which is the precursor of a variety of prostanoids with diverse and potent biological actions. Cyclooxygenases have two main isoforms that are called COX-1 and COX-2. 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 nervous system. Prostaglandin synthesis in these sites is a key factor in the development of inflammation and hyperalgesia. COX-2 inhibitors have analgesic and anti-inflammatory activity by blocking the transformation of arachidonic acid into prostaglandin H2 selectively.

Thromboregulation is the series of mechanisms in how a primary clot is regulated. These mechanisms include, competitive inhibition or negative feedback. It includes primary hemostasis, which is the process of how blood platelets adhere to the endothelium of an injured blood vessel. Platelet aggregation is fundamental to repair vascular damage and the initiation of the blood thrombus formation. The elimination of clots is also part of thromboregulation. Failure in platelet clot regulation may cause hemorrhage or thrombosis. Substances called thromboregulators control every part of these events.

<span class="mw-page-title-main">12-Hydroxyheptadecatrienoic acid</span> Chemical compound

12-Hydroxyheptadecatrienoic acid (also termed 12-HHT, 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid, or 12(S)-HHTrE) is a 17 carbon metabolite of the 20 carbon polyunsaturated fatty acid, arachidonic acid. 12-HHT is less ambiguously termed 12-(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid to indicate the S stereoisomerism of its 12-hydroxyl residue and the Z, E, and E cis–trans isomerism of its three double bonds. 12-HHT was discovered and structurally defined in 1973 by Paulina Wlodawer, Bengt Samuelsson, and Mats Hamberg. It was identified as a product of arachidonic acid metabolism made by microsomes isolated from sheep seminal vesicle glands and by intact human platelets. 12-HHT was for many years thought to be merely a biologically inactive byproduct of prostaglandin synthesis. More recent studies, however, have attached potentially important activity to it.

Prostaglandin inhibitors are drugs that inhibit the synthesis of prostaglandin in human body. There are various types of prostaglandins responsible for different physiological reactions such as maintaining the blood flow in stomach and kidney, regulating the contraction of involuntary muscles and blood vessels, and act as a mediator of inflammation and pain. Cyclooxygenase (COX) and Phospholipase A2 are the major enzymes involved in prostaglandin production, and they are the drug targets for prostaglandin inhibitors. There are mainly 2 classes of prostaglandin inhibitors, namely non- steroidal anti- inflammatory drugs (NSAIDs) and glucocorticoids. In the following sections, the medical uses, side effects, contraindications, toxicity and the pharmacology of these prostaglandin inhibitors will be discussed.

<span class="mw-page-title-main">Lysine acetylsalicylate</span> Chemical compound

Lysine acetylsalicylate, also known as aspirin DL-lysine or lysine aspirin, is a more soluble form of acetylsalicylic acid (aspirin). As with aspirin itself, it is a nonsteroidal anti-inflammatory drug (NSAID) with analgesic, anti-inflammatory, antithrombotic and antipyretic properties. It is composed of the ammonium form of the amino acid lysine paired with the conjugate base of aspirin.

References

  1. ↑ Tóth L, Muszbek L, Komáromi I (March 2013). "Mechanism of the irreversible inhibition of human cyclooxygenase-1 by aspirin as predicted by QM/MM calculations". Journal of Molecular Graphics & Modelling. 40: 99–109. doi:10.1016/j.jmgm.2012.12.013. PMID   23384979.
  2. ↑ Giménez-Bastida JA, Boeglin WE, Boutaud O, Malkowski MG, Schneider C (January 2019). "Residual cyclooxygenase activity of aspirin-acetylated COX-2 forms 15 R-prostaglandins that inhibit platelet aggregation". FASEB Journal. 33 (1): 1033–1041. doi: 10.1096/fj.201801018R . PMC   6355089 . PMID   30096040.
  3. ↑ Jörgensen TG, Weis-Fogh US, Nielsen HH, Olesen HP (November 1976). "Salicylate- and aspirin-induced uncoupling of oxidative phosphorylation in mitochondria isolated from the mucosal membrane of the stomach". Scandinavian Journal of Clinical and Laboratory Investigation. 36 (7): 649–654. doi:10.1080/00365517609054490. PMID   1019575.
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  5. ↑ Kerola M, Vuolteenaho K, Kosonen O, Kankaanranta H, Sarna S, Moilanen E (January 2009). "Effects of nimesulide, acetylsalicylic acid, ibuprofen and nabumetone on cyclooxygenase-1- and cyclooxygenase-2-mediated prostanoid production in healthy volunteers ex vivo". Basic & Clinical Pharmacology & Toxicology. 104 (1): 17–21. doi: 10.1111/j.1742-7843.2008.00332.x . PMID   19152549.
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  7. ↑ Chandrasekharan JA, Sharma-Walia N (September 2015). "Lipoxins: nature's way to resolve inflammation". Journal of Inflammation Research. 8: 181–192. doi: 10.2147/JIR.S90380 . PMC   4598198 . PMID   26457057.
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  9. ↑ Varga Z, Sabzwari SR, Vargova V (April 2017). "Cardiovascular Risk of Nonsteroidal Anti-Inflammatory Drugs: An Under-Recognized Public Health Issue". Cureus. 9 (4): e1144. doi: 10.7759/cureus.1144 . PMC   5422108 . PMID   28491485.
  10. ↑ Peng N, Guo L, Wei Z, Wang X, Zhao L, Kang L, et al. (November 2023). "Platelet mitochondrial DNA methylation: A novel biomarker for myocardial infarction - A preliminary study". International Journal of Cardiology. 398: 131606. doi:10.1016/j.ijcard.2023.131606. PMID   37996014. S2CID   265395351.
  11. ↑ Sherwood L (2013). Human Physiology: from Cells to Systems. Belmont, CA: Brooks/Cole, Cengage Learning. p. 758.
  12. ↑ Szczuko M, Kozioł I, Kotlęga D, Brodowski J, Drozd A (October 2021). "The Role of Thromboxane in the Course and Treatment of Ischemic Stroke: Review". International Journal of Molecular Sciences. 22 (21): 11644. doi: 10.3390/ijms222111644 . PMC   8584264 . PMID   34769074.
  13. 1 2 "Aspirin in Heart Attack and Stroke Prevention". American Heart Association. Archived from the original on 1 November 2004. The American Heart Association recommends aspirin use for patients who've had a myocardial infarction (heart attack), unstable angina, ischemic stroke (caused by blood clot) or transient ischemic attacks (TIAs or "little strokes"), if not contraindicated. This recommendation is based on sound evidence from clinical trials showing that aspirin helps prevent the recurrence of such events as heart attack, hospitalization for recurrent angina, second strokes, etc. (secondary prevention). Studies show aspirin also helps prevent these events from occurring in people at high risk (primary prevention).
  14. ↑ Smith, William L.; Langenbach, Robert (2001-06-15). "Why there are two cyclooxygenase isozymes". The Journal of Clinical Investigation. 107 (12): 1491–1495. doi:10.1172/JCI13271. ISSN   0021-9738. PMC   200199 . PMID   11413152.
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  18. ↑ Paul-Clark MJ, Van Cao T, Moradi-Bidhendi N, Cooper D, Gilroy DW (July 2004). "15-epi-lipoxin A4-mediated induction of nitric oxide explains how aspirin inhibits acute inflammation". The Journal of Experimental Medicine. 200 (1): 69–78. doi:10.1084/jem.20040566. PMC   2213311 . PMID   15238606.
  19. ↑ McCarty MF, Block KI (September 2006). "Preadministration of high-dose salicylates, suppressors of NF-kappaB activation, may increase the chemosensitivity of many cancers: an example of proapoptotic signal modulation therapy". Integrative Cancer Therapies. 5 (3): 252–268. doi: 10.1177/1534735406291499 . PMID   16880431.
  20. ↑ "Reye syndrome" at Dorland's Medical Dictionary
  21. ↑ Suchy FJ, Sokol RJ, Balistreri WF (2007). Liver Disease in Children. Cambridge: Cambridge University Press. ISBN   978-0-521-85657-7.
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