Inhibition of the Pro-Atherogenic Action of Serum Amyloid a (SAA) by Pharmacological Blockade of NFκB Pathway

The acute phase protein serum amyloid A (SAA) is a biomarker of inflammation. Elevated circulating SAA in chronic inflammatory disorders such as diabetes mellitus is associated with endothelial dysfunction and the earliest stages of atherosclerosis. Binding of SAA to cell receptors leads to increased production of mRNA encoding tumor necrosis factor (TNF), tissue factor (TF) and cytokines such as interleukin-6 (IL-6); the proteins produced by these genes display pro-inflammatory and pro-thrombotic activities that may be involved in promoting endothelial dysfunction. Activation of the transcription factor NFκB appears to be a central canonical pathway for SAA-mediated endothelial cell dysfunction. Targeting NFκB, using the specific inhibitor BAY11-7082, may be more effective at inhibiting SAA-mediated endothelial dysfunction than a pharmaceutical cocktail that targets its receptors. Human carotid artery endothelial (HCtAE) cells were cultured to confluence under normoglycaemic (5mM glucose) or hyperglycaemic conditions (25mM glucose) conditions and pre-incubated (1.5 h; 37°C) with 10µM BAY11-7082 or vehicle (control) followed by 10μg/mL SAA (4.5 h; 37°C). Notably, TF and TNF gene expression increased markedly in HCtAE cells after SAA stimulation whereas HCtAE cells pre-treated with BAY11-7082 (with SAA) showed TF and TNF mRNA levels similar to that determined in control cells (minus SAA). In the absence of BAY11-7082, both intracellular TNF and IL-6 protein increased following incubation with SAA as determined by immunofluorescence microscopy. This SAA activity was inhibited by BAY11-7082. ELISA analysis of HCtAE cell pellets and overlying supernatant confirmed the immunofluorescence data with SAA activity inhibited by BAY11-7082; IL-6 showed a greater sensitivity to the drug than TNF. In ex-vivo leukocyte adhesion studies of mice aorta, pre-treatment with BAY11-7082 showed a significant reduction in leukocyte adhesion compared with SAA-alone treated mice. Together these data suggest that inhibition of NFκB activation may protect the endothelium from the action of SAA by inhibiting pro-inflammatory and pro-thrombotic pathways.