2-2--azino-di-(3-ethylbenzothiazoline)-6-sulfonic-acid and glyceryl-2-arachidonate

The endocannabinoid, 2-arachidonoylglycerol (2-AG), is a selective substrate for the inducible isoform of prostaglandin H synthase (PGHS), PGHS-2. Its turnover leads to the formation of glyceryl esters of prostaglandins (PG-Gs), a subset of which elicits agonism at unique, as yet unidentified, receptors. The k(cat)/K(m) values for oxygenation of arachidonic acid (AA) and 2-AG by PGHS-2 are very similar, but the sensitivities of the two substrates to peroxide-dependent activation have not been compared. 15-Hydroperoxy derivatives of AA and 2-AG were found to be comparable in their ability to serve as substrates for the peroxidase activities of PGHS-2, PGHS-1, and glutathione peroxidase (GPx). They also were comparable in the activation of AA oxygenation by cyanide-inhibited PGHS-2. However, oxygenation of 2-AG was significantly suppressed relative to AA by the presence of GPx and GSH. Furthermore, 2-AG oxygenation by peroxidase-deficient H388YmPGHS-2 was much less efficient than AA oxygenation. Wild-type rates of 2-AG oxygenation were restored by treatment of H388YmPGHS-2 with hydroperoxide derivatives of AA or 2-AG. RNAi silencing of phospholipid hydroperoxide-specific GPx (GPx4) in NIH/3T3 cells led to increases in cellular peroxidation and in the levels of the isoprostane product, 8-epi-PGF(2α). GPx4 silencing led to 2-4-fold increases in PG-G formation but no change in PG formation. Thus, cellular peroxide tone may be an important determinant of the extent of endocannabinoid oxygenation by PGHS-2.

Topics: Amino Acid Substitution; Animals; Arachidonic Acid; Arachidonic Acids; Benzothiazoles; Biocatalysis; Cattle; Chromogenic Compounds; Cyclooxygenase 1; Cyclooxygenase 2; Endocannabinoids; Enzyme Activation; Gene Knockdown Techniques; Glutathione Peroxidase; Glutathione Peroxidase GPX1; Glycerides; Humans; Kinetics; Mice; NIH 3T3 Cells; Oxidation-Reduction; Oxidative Stress; Peroxides; Phospholipid Hydroperoxide Glutathione Peroxidase; Prostaglandins; RNA Interference; Sulfonic Acids