Lack of effect of serum amyloid A (SAA) on the ability of high-density lipoproteins to inhibit endothelial cell adhesion molecule expression

Abstract

Studies have been conducted to determine whether the ability of high density lipoproteins (HDL) to inhibit the cytokine-induced expression of vascular cell adhesion molecule-1 (VCAM-1) in endothelial cells is altered by the presence in HDL of the acute phase reactant, serum amyloid-A (SAA). Preparations of HDL₃ were isolated on two separate occasions from the plasma of each of 19 patients: the first was collected before and the second 3 days after undergoing coronary artery bypass graft surgery. Whereas the preoperative HDL₃ sample contained no SAA, in the postoperative sample SAA accounted for an average of 42% of the HDL₃ protein. The preoperative HDL₃ and postoperative, SAA-enriched HDL₃ were identical in terms of their ability to inhibit the tumour necrosis factor-α (TNF-α)-induced expression of VCAM-1 in human umbilical vein endothelial cells (HUVECs). To assess the effect of having an even greater SAA enrichment of HDL₃, samples of HDL₃ were incubated with purified SAA, which displaced almost all of the apoAI and about 40% of the apoAII from the HDL₃. This in vitro SAA-enriched HDL₃ inhibited the TNF-α induced expression of VCAM-1 in HUVECs in a concentration dependent manner, which was identical to that of the unmodified HDL₃. The presence of SAA did not alter the cell-surface binding of HDL₃ to endothelial cells. It has been concluded that the presence of SAA in HDL has no effect on the ability of these lipoproteins either to inhibit the expression of VCAM-1 in endothelial cells or to bind to proteins on the endothelial cell surface.