calcimycin and 13-hydroperoxy-9-11-octadecadienoic-acid

Noncyclooxygenase metabolites of arachidonic acid (AA) have been proposed to mediate endothelium-dependent vasodilation in the coronary microcirculation. Therefore, we examined the formation and bioactivity of AA metabolites in porcine coronary (PC) microvascular endothelial cells and microvessels, respectively. The major noncyclooxygenase metabolite produced by microvascular endothelial cells was 12(S)-hydroxyeicosatetraenoic acid (HETE), a lipoxygenase product. 12(S)-HETE release was markedly increased by pretreatment with 13(S)-hydroperoxyoctadecadienoic acid but not by the reduced congener 13(S)-hydroxyoctadecadienoic acid, suggesting oxidative upregulation of 12(S)-HETE output. 12(S)-HETE produced potent relaxation and hyperpolarization of PC microvessels (EC(50), expressed as -log[M] = 13.5 +/- 0.5). Moreover, 12(S)-HETE potently activated large-conductance Ca(2+)-activated K(+) currents in PC microvascular smooth muscle cells. In contrast, 12(S)-HETE was not a major product of conduit PC endothelial AA metabolism and did not exhibit potent bioactivity in conduit PC arteries. We suggest that, in the coronary microcirculation, 12(S)-HETE can function as a potent hyperpolarizing vasodilator that may contribute to endothelium-dependent relaxation, particularly in the setting of oxidative stress.

Topics: 12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; Animals; Arachidonate 12-Lipoxygenase; Arachidonic Acid; Caffeic Acids; Calcimycin; Cells, Cultured; Coronary Circulation; Endothelium, Vascular; Ionophores; Large-Conductance Calcium-Activated Potassium Channels; Leukotrienes; Linoleic Acids; Lipid Peroxides; Lipoxygenase Inhibitors; Membrane Potentials; Microcirculation; Muscle, Smooth, Vascular; Oxidative Stress; Potassium Channels; Potassium Channels, Calcium-Activated; Swine; Tritium; Vasoconstrictor Agents; Vasodilation

Human platelets are devoid of 5-lipoxygenase activity but convert exogenous leukotriene A4 (LTA4) either by a specific LTC4 synthase to leukotriene C4 or via a 12-lipoxygenase mediated reaction to lipoxins. Unstimulated platelets mainly produced LTC4, whereas only minor amounts of lipoxins were formed. Platelet activation with thrombin, collagen or ionophore A23187 increased the conversion of LTA4 to lipoxins and decreased the leukotriene production. Maximal effects were observed after incubation with ionophore A23187, which induced synthesis of comparable amounts of lipoxins and cysteinyl leukotrienes (LTC4, LTD4 and LTE4). Chelation of intra- and extracellular calcium with quin-2 and EDTA reversed the ionophore A23187-induced stimulation of lipoxin synthesis from LTA4 and inhibited the formation of 12-hydroxyeicosatetraenoic acid (12-HETE) from endogenous substrate. However, calcium did not affect the 12-lipoxygenase activity in the 100,000 x g supernatant of sonicated platelet suspensions. Furthermore, the stimulatory effect on lipoxin formation induced by platelet agonists could be mimicked in intact platelets by the addition of low concentrations of arachidonic acid, 12-hydroperoxyeicosatetraenoic acid (12-HPETE) or 13-hydroperoxyoctadecadienoic acid (13-HPODE). The results indicate that the elevated lipoxin synthesis during platelet activation is due to stimulated 12-lipoxygenase activity induced by endogenously formed 12-HPETE.

Topics: 12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; Aminoquinolines; Arachidonate 12-Lipoxygenase; Arachidonic Acid; Blood Platelets; Calcimycin; Edetic Acid; Humans; Hydroxyeicosatetraenoic Acids; Leukotriene A4; Leukotrienes; Linoleic Acids; Lipid Peroxides; Lipoxins; Platelet Activation