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Selenium (Se) is an integral component of glutathione peroxidase and is able to detoxify peroxides that can affect arachidonic acid (AA) metabolism, thereby influencing eicosanoid biosynthesis. This study investigated the effects of oxidant stress, a consequence of Se deficiency, on eicosanoid formation and important key enzyme expression in bovine aortic endothelial cells (BAEC). Bovine aortic endothelial cells cultured in Se-deficient media and stimulated with tumor necrosis factor α or H
2O
2 produced significantly less prostacyclin (PGI
2) and more 15-hydroxyeicosatetraenoic acid, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), and thromboxane than Se-supplemented BAEC. Additionally, reverse transcription polymerase chain reaction and immunoblotting determined that the mRNA and protein levels of the eicosanoid forming enzymes cyclooxygenase-1 (COX1), cyclooxygenase-2 (COX2), and PGI synthase were not significantly changed. The addition of 15-HPETE to Se-supplemented BAEC inhibited the production of PGI
2 suggesting that the accumulation of lipid hydroperoxides during Se-deficiency may be the underlying factor in the altered eicosanoid production during Se deficiency. Furthermore, inhibition of COX and addition of PGH
2 to Se-deficient or Se-supplemented BAEC still resulted in lower PGI
2 formation by Se-deficient cells. Together, these results suggest that Se deficiency modifies eicosanoid production by affecting the activity of key enzymes, particularly PGI synthase, rather than their transcription or translation.