Heme Oxygenase Attenuates Angiotensin II-Mediated Increase in Cyclooxygenase-2 Activity in Human Femoral Endothelial Cells

Abstract

Abstract-Heme oxygenase (HO) regulates cellular heme levels and catalyzes the formation of bilirubin and carbon monoxide. We hypothesize that the status of the endothelial HO system influences the angiotensin (Ang) II-induced increase in the endothelial production of prostaglandin I 2 (PGI 2 ) (measured as 6-keto-PGF 1␣ ) and prostaglandin E 2 (PGE 2 ), eicosanoids that modulate the vascular actions of Ang II. In the present study, we determined the effect of interventions that suppress HO activity or induce HO-1 gene expression on Ang II-mediated increase in 6-keto-PGF 1␣ and PGE 2 in cultures of human femoral artery endothelial cells. Incubation of endothelial cells with Ang II (100 ng/mL) for 24 hours increased the levels of both 6-keto-PGF 1␣ and PGE 2 in the culture media. Key Words: heme oxygenase Ⅲ cyclooxygenase activity Ⅲ prostaglandins Ⅲ angiotensin II Ⅲ endothelial cell Ⅲ gene transfer T he vascular endothelium manufactures prostaglandin E 2 (PGE 2 ) and/or I 2 (PGI 2 ) via a pathway that involves oxygenation of arachidonic acid by cyclooxygenase (COX)-1 and -2. 1-3 Angiotensin (Ang) II acutely stimulates prostaglandin synthesis in endothelial cells by promoting phospholipase-catalyzed deacylation of arachidonic acid, and thus increasing the amount of arachidonic acid available to COX, and also may induce COX-2 expression. 4 As prostaglandins produced by the vascular endothelium subserve mechanisms that counteract the actions of Ang II on the vasculature, 5 the interplay between endothelium-derived prostaglandins and Ang II has great functional relevance.COX-1 and COX-2 are heme proteins, 6 and it is well documented that the heme prosthetic group of both COX isoforms is essential for the expression of catalytic activity. 6 According to a recent study, prostaglandin synthesis in rabbit coronary and human endothelial cells decreases in response to interventions that upregulate the expression of heme oxygenase (HO)-1. 7,8 HO isoforms -1 and -2 catalyze the metabolisms of heme to biliverdin and carbon monoxide (CO), respectively, an antioxidant and a vasoactive mediator. 9,10 HO isoforms, particularly HO-1, play a critical role in the regulation of cellular heme levels, 11 which in turn may impact on the expression of catalytically active COX isoforms. 7,8 Previous studies have documented induction of vascular and renal HO-1 in response to Ang II in vivo. 12,13 It is conceivable, then, that Ang II-mediated upregulation of HO-1 creates a setting that does not favor Ang II-induced stimulation of prostaglandin synthesis. We tested this hypothesis by examining the effect of interventions that suppress HO activity, or induce HO-1 gene expression, on Ang II-induced prostaglandin synthesis in cultures of human femoral endothelial cells. Methods Cell Culture ConditionsHuman femoral artery endothelial cells were obtained from ATCC (Manassas, VA) and were grown in MCDB131 medium (GIBCO-BRL; passages 12 to 25) supplemented with 10% fetal bovine serum, 10 ng/mL endothelial growth factor (Sigma), and 1 g/mL hydrocorti...

The blockade of cyclooxygenases-1 and -2 reduces the effects of hypoxia on endothelial cells

“…Indeed, Ejima and Perrella (27) demonstrated that in the absence of COX-2 there is no up-regulation of HO-1 following LPS treatment in mice, demonstrating that COX is actually the stimulus for HO-1 expression. In contrast, but in agreement with these data, prior induction of HO-1 by gene therapy or by chemical products, such as cobalt protoporphyrin, abrogates COX-2 expression in various inflammatory models (28)(29)(30). Similarly, treatment with a COX-2 inhibitor is associated with HO-1 up-regulation (31).…”

Heme Oxygenase-2 Deficiency Contributes to Diabetes-Mediated Increase in Superoxide Anion and Renal Dysfunction

“…Upregulation of HO-1 inhibits the inflammatory response, presumably by a decrease in cellular heme-mediated oxidative stress (50) and vasoconstrictors (46,(51)(52)(53)(54)(55). Consistent with these observations, mice and humans who are deficient in HO-1 experience progressive chronic inflammation and are sensitive to stressful injury, presumably as a result of elevated cellular heme and iron (56,57).…”

Cyclooxygenase-2 and hypoxia-regulated proteins are modulated by basic fibroblast growth factor in acute renal failure

“…Additionally, recent publications have shown a direct association between COX-2 and FGF-2 (Baguma-Nibasheka et al, 2007), and COX-2 mRNA has been shown to increase in response to FGF-2 administration in retinal epithelial cells, (Ershov and Basan, 1999). A decrease in COX-2 and an increase in HO-1 activity have also been observed in endothelial cells (Morimoto et al, 2001;Li et al, 2003), suggesting that the heme-hemoxygenase system could be a negative regulator for COX-2 expression. In summary, it is obvious that this study has some limitations due to two facts, namely that it is an in vivo study and, as such, it is hard to isolate one single effect, and that most of the experiments are not quantitative, so they only refl ect a relationship between the compared proteins.…”