OXIDIZED LOW-DENSITY-LIPOPROTEIN ACTS ON ENDOTHELIAL-CELLS IN CULTURETO ENHANCE ENDOTHELIN SECRETION AND MONOCYTE MIGRATION

Monocyte deposition on the endothelium is the initial step in atheroge nesis. Oxidized low density lipoprotein (Ox-LDL) is involved in the de velopment of the fatty streak which progresses to the atherosclerotic lesion. Our interest focussed on the question, does the endothelium re act to Ox-LDL to produce humoral substances that might influence the m igration of human blood monocytes? Chemotaxis of monocytes was assesse d by the modified membrane-filter technique based on the Boyden chambe r principle. Exposure of porcine aorta endothelial cells (ECs) to Ox-L DL (100 mu g/ml) increased the directional migration of monocytes by 2 5% (p < 0.01) over that of ECs in the absence of Ox-LDL. Radioimmunoas say of the EC culture media revealed the presence of immunoreactive en dothelin-1 (ir-ET-1). The endothelin converting enzyme inhibitor; phos phoramidone (10 mu M), when incubated together with ECs and Ox-LDL, su ppressed the synthesis of ir-ET-1 by 53% (p < 0.05) and the migration decreased by 12% (p < 0.05). Preincubation of monocytes with the ETA r eceptor-selective antagonist, BQ-123 (1 mu M), followed by exposure to ECs plus Ox-LDL, lead to a decrease in their migration by 12% (p < 0. 05) compared to monocytes not treated with BQ-123. These results show that Ox-LDL acts on ECs to enhance the synthesis of ir-ET-1 which in t urn increases the directional migration of monocytes. Phosphoramidone decreased the synthesis of ir-ET-1 but migration was affected only mod estly; monocyte ETA receptor blockade by BQ-123 also suppressed migrat ion toward EC chemoattactants to a small extent. Both results suggest that in addition to ir-ET-1 other chemotactic factors are being releas ed by the ECs; Ox-LDL appears to enhance their release or synthesis.