Abstract 447: Ac-SDKP Suppresses TNFα-induced ICAM-1 Expression In Endothelial Cells Via Inhibition Of IκB Kinase And NF-κB Activation

Abstract

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a naturally occurring tetrapeptide that prevents inflammation and fibrosis in hypertension and other cardiovascular diseases. We previously showed that Ac-SDKP decreased transcription factor NF-κB activation in angiotensin II-induced hypertension and also reduced intercellular adhesion molecule-1 (ICAM-1) expression in an experimental autoimmune myocarditis and hypertension animal model. However, the mechanisms by which Ac-SDKP down-regulated ICAM-1 expression are unclear. TNFα is a proinflammatory cytokine that induces ICAM-1 expression on different cell types. We hypothesized that Ac-SDKP suppresses TNFα-induced ICAM-1 via inhibition of IκB kinase (IKK) and subsequently by blockade of NF-κB activation. Human coronary artery endothelial cells were treated with Ac-SDKP or vehicle and then stimulated with TNFα (0.5 ng/ml). ICAM-1 protein expression and phosphorylation of IKK (p-IKK), inhibitory κB (p-IκB), p38 (p-p38) and ERK (p-ERK) were measured by Western Blot. Activation of NF-κB was determined by electrophoretic mobility shift assay (EMSA). ICAM-1 expression was virtually undetectable under basal conditions, but greatly increased by TNFα. Ac-SDKP dose-dependently suppressed TNFα-induced ICAM-1 expression (set at a value of 1.0 arbitrary units, AU) to 0.67±0.13 (p<0.05), 0.51±0.12 (p<0.01) and 0.39±0.09 AU (p<0.01) at 0.1 nM, 1 nM and 10 nM, respectively. In addition, Ac-SDKP (10 nM) inhibited TNFα-induced p-IKK from 1.0 to 0.71±0.02 AU (p<0.01). Ac-SDKP also inhibited TNFα-induced IKKβ expression from 1.0 to 0.64±0.12 AU (p<0.05), without affecting IKKα expression. Furthermore, Ac-SDKP inhibited TNFα-induced p-IκB from 1.0 to 0.54±0.03 AU (p<0.01). EMSA results showed that Ac-SDKP inhibited TNFα-mediated activation of NF-κB, which was 0.63±0.04-fold of TNFα-treated cells. However, Ac-SDKP had no effect on TNFα-induced p-p38 and p-ERK. Thus, we conclude that Ac-SDKP inhibits TNFα-induced IKK and subsequent degradation of IκB, thereby preventing NF-κB activation and ICAM-1 expression. These inhibitory effects are independent of p38 and ERK.