Inflammatory Serum Amyloid A and Its Impact on Vascular and Renal Function

Abstract

Introduction: Serum Amyloid A (SAA) increases its concentration up to 1000-fold in an acute inflammation and can continue the high concentration to chronic stage of diseases, including diabetes, rheumatic diseases, vascular atherosclerosis and renal failure. HDL is believed to be a protective element in the process of atherosclerosis. Our hypothesis is to investigate the function of SAA in stimulating endothelial cells migration and proliferation. We also aim to certify that supplemental HDL has the ability to mask the inflammation and pre-atherosclerotic process induced by SAA. In addition, we are to explore that purified HDL may be the potential therapy to weaken the process of chronic pathology caused by increasing SAA. Methods: HCtAE cells were stimulated via different concentration of SAA for 6 hours and the migration, proliferation were assessed after the stimulation. The gene expression of TNF, TF, NFκB, VEGF, etc was examined. In Western blotting the expression of p-P65 and NFκB was assessed. Apoe gene knockout (ApoE-/-) C57 mice were randomly allocated to four groups that received saline as a vehicle control, lipopolysaccharide (LPS 10 μg/mL, the same time as SAA) as a parallel (second) control, recombinant SAA group and pre-treated with HDL before SAA group. The amount of LPS administered according to the contamination levels in the SAAtreatment group to eliminate the effect from this low level of LPS contained in the recombinant SAA used here. The samples were collected in early stage as young group and late stage as old group. The samples included urine, plasma, heart tissue, aorta, kidneys and other vital organs for further biochemical and molecular analysis. Results: SAA induced the expression of TNF, pro-coagulative tissue factor (F3), NFκB and P65. SAA also increased HCtEC expression of VEGF, migration and proliferation, which was inhibited by multi-angiokinase receptor inhibitor BIBF1120. In animal work conducted in this study, administration of SAA induced the inflammatory factors TNF, TF, NFκB, and this expression was evident early 2 weeks after cessation of SAA treatment (young group) and at 16 weeks after cessation of SAA treatment (old group), which were partially reversed by co-supplementation with human HDL. In addition, the contaminated LPS did not elicit these effects caused by SAA. In aorta histochemistry staining, the lesion size in HDL group was not eliminated, however, the ! IV! size was significantly decreased compared to the SAA group. The biochemical and biological assessment of renal function, HDL/SAA group was not as severe as the SAA group. Conclusions: Outcomes from an experimental cell model of inflammation collectively indicate that SAA induces inflammatory pathways, cellular migration and proliferation, while multi-angiokinase receptor inhibitor BIBF1120 inhibits the proangiogenic activity of SAA on vascular endothelial cells. In the ApoE-/- mouse model of atherosclerosis, supplemented HDL has ability to reverse the inflammatory and proatherosclerotic effects induced by SAA in both acute and chronic stages. The NFκB plays a crucial role in the pathway of SAA induction.