Tumor Necrosis Factor-α–Induced Iron Sequestration and Oxidative Stress in Human Endothelial Cells

Abstract

Objective-Tumor necrosis factor (TNF)-␣-induced endothelial injury, which is associated with atherosclerosis, is mediated by intracellular reactive oxygen species. Iron is essential for the amplification of oxidative stress. We tested whether TNF-␣ accelerated iron accumulation in vascular endothelium, favoring synthesis of hydroxyl radical. Methods and Results-Diverse iron transporters, including iron import proteins (transferrin receptor [TfR] and divalent metal transporter 1 [DMT1]) and an iron export protein (ferroportin 1 [FP1]) coexist in human umbilical endothelial cells (HUVECs). TNF-␣ caused upregulation of TfR and DMT1 and downregulation of FP1, which were demonstrated in mRNA as well as protein levels. These changes in iron transporters were accompanied by accumulation of iron that was both transferrin-dependent and transferrin-independent. Modifications of these mRNAs were regulated posttranscriptionally, and were coordinated with activation of binding activity of iron regulatory protein 1 to the iron responsive element on transporter mRNAs. Using a salicylate trap method, we observed that only simultaneous exposure of endothelial cells to iron and TNF-␣ accelerated hydroxyl radical production. Conclusions-TNF-␣ could cause intracellular iron sequestration, which may participate importantly in the pathophysiology of atherosclerosis and cardiovascular disease. Key Words: cytokines Ⅲ endothelium Ⅲ free radicals Ⅲ inflammation Ⅲ iron A therosclerosis now is generally recognized as a chronic inflammatory condition, and inflammatory cytokines such as tumor necrosis factor (TNF)-␣ have been associated with the development of atherosclerotic lesions and consequent cardiovascular events. 1,2 Dysfunction and loss of vascular endothelial cells, which provide a nonthrombogenic surface and a permeability barrier, occur early in atherosclerosis. 3 Several lines of evidence has suggested that TNF-␣-induced cell injury is mediated through its ability to promote intracellular reactive oxygen species (ROS) formation. 4,5 Among these species, superoxide anion (O 2 Ϫ ) and hydrogen peroxide (H 2 O 2 ) are not very reactive, and usually are neutralized by an elaborate antioxidant defense system. However, transition metal-catalyzed Haber-Weiss reaction can transform O 2 Ϫ and H 2 O 2 to hydroxyl radical, which are extremely powerful oxidizing species. 6,7 Iron is an essential element required for biochemical reactions subserving a wide variety of functions in cells and organisms. 8 However, free iron, possibly the most important transition metal in biologic systems, can act as an electron donor. 6,9 Excessive intracellular accumulation of iron therefore could amplify the damaging effect of oxidative stress in inflammatory conditions, leading to cell injury.The recent identification of iron transport proteins has rapidly expanded our knowledge of molecular aspects of iron processing, especially in the reticuloendothelial system and small intestine. 10,11 Such proteins include transferrin receptor (TfR), divalent metal tr...

Reduced sensitivity of the ferroportin Q248H mutant to physiological concentrations of hepcidin

“…36,55,56 Ferroportin is expressed in vascular endothelial cells, 5,57,58 and exposure of human umbilical vein endothelial cells to tumor necrosis factor-α leads to decreased ferroportin expression and an increase in iron-mediated hydroxyl radical formation. 57 Therefore, any effect that the Q248H mutation might have in enhancing ferroportin expression in pulmonary vascular endothelial cells 58 and reducing cellular iron in the setting of sickle cell anemia might be expected to provide protection from oxidant damage to the endothelium. Tricuspid regurgitation values determined by echocardiography, which reflect systolic pulmonary artery pressure, 29 were significantly lower in ferroportin Q248H heterozygotes than in subjects with both wild-type alleles.…”

“…Pulmonary hypertension, as documented by right heart catheterization, is present in 6-11% of adults with sickle cell anemia. 36,55,56 Ferroportin is expressed in vascular endothelial cells, 5,57,58 and exposure of human umbilical vein endothelial cells to tumor necrosis factor-α leads to decreased ferroportin expression and an increase in iron-mediated hydroxyl radical formation.…”

A role for activated endothelial cells in red blood cell clearance: implications for vasopathology

“…As for erythrophagocytosis by macrophages, endothelial cells have also been shown to be capable of recycleing iron upon activation by increasing the expression of key enzymes in this pathway, such as heme oxygenase-1 (HO-1), ferroportin and ferritin. [39][40][41][42] The characteristics of RBC which may affect the fate and rate of processing could include cellular features such as membrane integrity, rigidity and viscosity.…”

Correlation of tumor necrosis factor alpha and interleukin 6 with hypertensive renal damage

“…27 Furthermore, IL-6 and TNF-a can also induce the contraction and proliferation of mesangial cells, [28][29][30] deposit of matrix, acceleration of glomerulosclerosis, and stimulate the proliferation of the fibroblast, whereby to produce collagen fibers which can finally lead to renal fibrosis.…”