Inhibition of TNF-α induced ICAM-1, VCAM-1 and E-selectin expression by selenium

Abstract

The initiation of an atherosclerotic lesion involves an endothelial cell pro-inflammatory state that recruits leukocytes and promotes their movement across the endothelium. These processes require endothelial expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and endothelial-leukocyte adhesion molecule-1 (E-selectin). Tumor necrosis factor-α (TNF-α) is a powerful inducer of these adhesion molecules. Selenium status is known to affect the rate of atherosclerosis. These experiments tested whether selenium alters cytokine-induced expression of these adhesion molecules. Human umbilical vein endothelial cells (HUVECs) were pretreated for 24 h with sodium selenite (0–2 μM) and then treated with 0 or 50 U/ml TNF-α in the presence of 0–2 μM selenite. ICAM-1, VCAM-1 and E-selectin were detected by ELISA and their mRNAs were evaluated by Northern blots. Selenite significantly inhibited TNF-α-induced expression of each adhesion molecule in a dose-dependent manner and reduced the level of the respective mRNAs. Nuclear factor-κB (NF-κB) is required for transcription of these adhesion molecule genes. Western blot analysis revealed that selenite did not inhibit the translocation of the p65 subunit of NF-κB to the nucleus. In conclusion, these data indicate selenium can modulate cytokine-induced expression of ICAM-1, VCAM-1 and E-selectin in HUVECs without interfering with translocation of NF-κB.

Introduction

One function of the vascular endothelial cell is to recruit leukocytes into underlying tissue during inflammation. The transmigration of leukocytes across the endothelial lining of the blood vessel is regulated in part by specific endothelial–leukocyte adhesion molecules [1]. The leukocyte transmigration process is basic to both acute and chronic inflammatory states [1], [2], [3]. A major event in the development of the pro-inflammatory state is the expression of endothelial cell adhesion molecules for the recruitment of leukocytes to the site of injury. The regulation of NF-κB activation is one key step in controlling inflammatory processes. Suppression of the pro-inflammatory endothelial cell state will limit the atherosclerotic process.

The induced expression of ICAM-1, VCAM-1 and E-selectin requires the activation of NF-κB. NF-κB is an inducible transcriptional factor, which exists in the cytoplasm in its inactive form as the protein heterodimer, p50/p65, associated with an inhibitor protein, IκB. Extracellular inducers attach to specific cell surface receptors that recruit binding proteins. These proteins initiate a cascade of kinases that result in the activation of IκB kinases. Phosphorylation of IκB releases it from the p50/p65 heterodimer and marks it for proteosomal degradation. Activated NF-κB translocates to the nucleus and binds DNA at specific κB sites in promotor regions [4], [5].

Selenium is a micronutrient whose antioxidant functions are mediated through selenoproteins such as the glutathione peroxidases and thioredoxin reductases [6]. Selenium deficiency decreases protection from oxidative stress, decreases glutathione peroxidase activity, increases lipid peroxidation (including LDL oxidation) and increases the risk of atherosclerosis. Conversely, supplementation with selenium activates the glutathione system, protects against peroxidation of LDL and other lipids and slows the atherosclerotic process [7], [8], [9]. Selenium deficiency also enhances neutrophil adhesion to endothelial cells [10].

This study tested whether physiological levels of selenium would alter the expression of TNF-α-induced expression of ICAM-1, VCAM-1 and E-selectin in HUVECs. Follow-up studies determined the effects of selenium on the activation of NF-κB caused by TNF-α treatment.