Reaction Process: Reactome:R-GGA-211979

Prostaglandin H2

C20H32O5 (352.225)

Prostaglandin H2 (PGH2) is the first intermediate in the biosynthesis of all prostaglandins. Prostaglandins are synthesized from arachidonic acid by the enzyme COX-1 and COX-2, which are also called PGH synthase 1 and 2. These enzymes generate a reactive intermediate PGH2 which has a reasonably long half-life (90-100 s) but is highly lipophilic. PGH2 is converted into the biologically active prostaglandins by prostaglandin isomerases, yielding PGE2, PGD2, and PGF2, or by thromboxane synthase to make TXA2 or by prostacyclin synthase to make PGI2. Most nonsteroidal anti-inflammatory drugs such as aspirin and indomethacin inhibit both PGH synthase 1 and 2. A key feature for eicosanoid transcellular biosynthesis is the export of PGH2 or LTA4 from the donor cell as well as the uptake of these reactive intermediates by the acceptor cell. Very little is known about either process despite the demonstrated importance of both events. In cells, PGH2 rearranges nonenzymatically to LGs even in the presence of enzymes that use PGH2 as a substrate. When platelets form thromboxane A2 (TXA2) from endogenous arachidonic acid (AA), PGH2 reaches concentrations very similar to those of TXA2 and high enough to produce strong platelet activation. Therefore, platelet activation by TXA2 appears to go along with an activation by PGH2. The agonism of PGH2 is limited by the formation of inhibitory prostaglandins, especially PGD2 at higher concentrations. That is why thromboxane synthase inhibitors in PRP and at a physiological HSA concentration do not augment platelet activation (PMID: 2798452, 15650407, 16968946). Prostaglandins are eicosanoids. The eicosanoids consist of the prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs), and lipoxins (LXs). The PGs and TXs are collectively identified as prostanoids. Prostaglandins were originally shown to be synthesized in the prostate gland, thromboxanes from platelets (thrombocytes), and leukotrienes from leukocytes, hence the derivation of their names. All mammalian cells except erythrocytes synthesize eicosanoids. These molecules are extremely potent and are able to cause profound physiological effects at very dilute concentrations. All eicosanoids function locally at the site of synthesis through receptor-mediated G-protein linked signalling pathways. Prostaglandin h2, also known as pgh2 or 9s,11r-epidioxy-15s-hydroxy-5z,13e-prostadienoate, is a member of the class of compounds known as prostaglandins and related compounds. Prostaglandins and related compounds are unsaturated carboxylic acids consisting of a 20 carbon skeleton that also contains a five member ring, and are based upon the fatty acid arachidonic acid. Thus, prostaglandin h2 is considered to be an eicosanoid lipid molecule. Prostaglandin h2 is practically insoluble (in water) and a weakly acidic compound (based on its pKa). Prostaglandin h2 can be found in a number of food items such as gooseberry, evergreen huckleberry, quince, and capers, which makes prostaglandin h2 a potential biomarker for the consumption of these food products. Prostaglandin h2 can be found primarily in human platelet tissue. In humans, prostaglandin h2 is involved in several metabolic pathways, some of which include magnesium salicylate action pathway, ketorolac action pathway, trisalicylate-choline action pathway, and salicylate-sodium action pathway. Prostaglandin h2 is also involved in a couple of metabolic disorders, which include leukotriene C4 synthesis deficiency and tiaprofenic acid action pathway. Prostaglandin h2 is acted upon by: Prostacyclin synthase to create prostacyclin Thromboxane-A synthase to create thromboxane A2 and 12-(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid (HHT) (see 12-Hydroxyheptadecatrienoic acid) Prostaglandin D2 synthase to create prostaglandin D2 Prostaglandin E synthase to create prostaglandin E2 Prostaglandin h2 rearranges non-enzymatically to: A mixture of 12-(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid (HHT) and 12-(S)-hydroxy-5Z,8Z,10E-heptadecatrienoic acid (see 12-Hydroxyheptadecatrienoic acid) Use of Prostaglandin H2: regulating the constriction and dilation of blood vessels stimulating platelet aggregation Effects of Aspirin on Prostaglandin H2: Aspirin has been hypothesized to block the conversion of arachidonic acid to Prostaglandin . D009676 - Noxae > D016877 - Oxidants > D010545 - Peroxides

Thromboxane A2

C20H32O5 (352.225)

A thromboxane which is produced by activated platelets and has prothrombotic properties: it stimulates activation of new platelets as well as increases platelet aggregation.