Effect of an imidazolineoxyl nitric oxide on prostaglandin synthesis in experimental shock: possible role of nitrogen dioxide in prostacyclin synthase inactivation.

The effect of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a nitric oxide (NO) scavenger that yields nitrogen dioxide (NO(2)) in a rat endotoxemia model was investigated. Endotoxin (lipopolysaccharide [LPS]) increased NO synthase (NOS) activity and inducible NOS expression measured in lung and plasma levels of nitrite/nitrate, 6-oxo-prostaglandin (PG) F(1alpha), thromboxane B(2), and PGF(2alpha). Infusion of cPTIO significantly reduced LPS-induced mean arterial blood pressure decline and mortality and selectively reduced LPS-induced 6-oxo-PGF(1alpha) plasma levels and prostacyclin synthase (PGIS) activity measured in the lung and aorta.

Transcellular formation of thromboxane A(2) in mixed incubations of endothelial cells and aspirin-treated platelets strongly depends on the prostaglandin I-synthase activity.

Despite an almost total suppression of platelet cyclooxygenase (COX) by aspirin, as monitored ex vivo, incomplete suppression of thromboxane (Tx)A(2) metabolite excretion has been detected in some patients with unstable angina treated with low doses of aspirin. A plausible explanation for this finding is the transcellular formation of TxA(2) by platelets from prostaglandin H(2) released by endothelial cells. We recently reported that probably only COX and PGI-synthase (PGIS) are involved in the biosynthesis of prostanoids in endothelial cells.

Rate of vasoconstrictor prostanoids released by endothelial cells depends on cyclooxygenase-2 expression and prostaglandin I synthase activity.

This study was undertaken to investigate the enzymatic regulation of the biosynthesis of vasoconstrictor prostanoids by resting and interleukin (IL)-1(beta)stimulated human umbilical vein endothelial cells (HUVECs). Biosynthesis of eicosanoids in response to IL-1beta, exogenous labeled arachidonic acid (AA), or histamine, as well as their spontaneous release, was evaluated by means of HPLC and RIA. HUVECs exposed to IL-1beta produced prostaglandin (PG) I2 for no longer than 30 seconds after the substrate was added irrespective of the cyclooxygenase (COX) activity, whereas the time course of PGE2 and PGD2 formation was parallel to the COX activity.

Interleukin-1 enhances the ability of cultured human umbilical vein endothelial cells to oxidize linoleic acid.

Human umbilical vein endothelial cells (HUVEC) were treated with recombinant interleukin (IL)-1 beta, and the metabolism of exogenous linoleic acid was studied. High performance liquid chromatography, gas chromatography-mass spectrometry, and chiral analysis revealed that HUVEC enzymatically convert linoleic acid mainly into 13-(S)hydroxy-9(Z),11(E)-octadecadienoic (13-HODE) and 9-(R)hydroxy-10(E),12(Z)-octadecadienoic acids, which may isomerize toward all-trans compounds. IL-1 beta increased the formation of all octadecanoids in a time- and dose-dependent manner with similar EC50 (approximately 1 unit/ml).

Characterization of arachidonic acid metabolites through the 12-lipoxygenase pathway in human epidermis by high-performance liquid chromatography and gas chromatography/mass spectrometry.

Fragments of human epidermis were incubated in the presence of exogenous arachidonic acid. The incubates were subjected to reversed-phase and straight-phase high-performance liquid chromatography and finally the identity of the arachidonic acid metabolites of the 12-lipoxygenase pathway was determined by means of gas chromatography/mass spectrometry. It was found that human epidermis produces 8-hydroxy-11,12-epoxy- and 10-hydroxy-11,12-epoxyeicosatrienoic acid, 8,9,12-, 8,11,12- and 10,11,12-trihydroxyeicosatrienoic acid, 12-keto-eicosatetraenoic acid and 12-hydroxy-eicosatetraenoic acid derived from arachidonic acid via the 12-lipoxygenase pathway.