The antiplatelet mechanism of aspirin is to make arachidonic acid lose its ability to transform into prostaglandin endoperoxide
and hindering the formation of prostaglandin E2 and thromboxane A2 through inhibiting the activity of cyclooxygenase in platelets.17 However, a study shows that aspirin resistance exists in a few patients although aspirin has a good therapeutic effect in the treatment of acute myocardial infarction,18 that is, acute thrombosis may occur even after taking aspirin, and the incidence of adverse reactions increases with the increase of dosage.
The key regulatory step in PG biosynthesis is the enzymatic conversion of the fatty acid precursor by PG endoperoxide
synthase, PTGS1 and PTGS2, into PGG.
Ergosterol derivatives like ergosterol endoperoxide
isolated from P.
These ethnopharmacological applications led to the isolation of the sesquiterpene lactone endoperoxide
artemisinin present in the aerial parts of the plant [3,4].
Iso also made the mRNA of prostaglandin endoperoxide
synthase 2 (Ptgs2, also known as Cox2, an important regulation factor of bone metabolism) express rhythmically.
Furthermore, at 100-500 [micro]M, Ir-6 exhibited relatively weak activity against platelet aggregation induced by 0.01 U/mL thrombin or 1 [micro]M U46619, a prostaglandin endoperoxide
analogue; this result indicated that Ir-6 had more potent activity against collagen-induced aggregation than t that induced by other agonists AA, thrombin, and U46619 (Figure 1(c)).
[H.sub.2][O.sub.2] induced spawning in staghorn corals (Hayashibara et al., 2004) and red abalone (Morse et al., 1977),with the latter through the activation of enzyme-catalyzed synthesis of prostaglandin endoperoxide
. It has been suggested that ROS induction of apoptosis is involved in tail regression during amphibian metamorphosis (Inoue et al., 2004).
(20) (A) The thiolate of GSH could be stabilized by [Arg.sup.126] and could attack on the endoperoxide
oxygen atom at the C-9 carbon of [PGH.sub.2] to produce an unstable reaction intermediate.
In gravid adult abalone, [H.sub.2][O.sub.2] causes activation of prostaglandin endoperoxide
synthetase, which then uses polyunsaturated fatty acids and molecular oxygen to produce prostaglandin endoperoxide
, a short-lived, reactive prostaglandin precursor [for review see Morse et al.
DMA exhibits high reactivity towards singlet oxygen forming a stable endoperoxide
derivative (DMA-[O.sub.2]) via a Diels-Alder cycloaddition across its middle ring.
Isoprostanes are very readily formed in biological fluids  from oxidized arachidonic acid and through endoperoxide
Kraemer et al., "The aspirin and heme-binding sites of ovine and murine prostaglandin endoperoxide
synthases," The Journal of Biological Chemistry, vol.