Wide proinflammatory effect of electronegative low-density lipoprotein on human endothelial cells assayed by a protein array

Electronegative low-density lipoprotein (LDL(−)) is a modified subfraction of LDL present in plasma able to induce the release of interleukin 8 (IL-8) and monocyte chemotactic protein 1 (MCP-1) by human umbilical vein endothelial cells (HUVEC). To ascertain whether further inflammation mediator release could be induced by LDL(−), a protein array system was used to measure 42 cytokines and related compounds. Native LDL and LDL(−) isolated from normolipemic subjects were incubated for 24 h with HUVEC and culture supernatants were used to measure inflammation mediator release. The protein array revealed that IL-6, granulocyte/monocyte colony-stimulating factor (GM-CSF) and growth-related oncogene (GRO) release were increased by cultured HUVEC in response to LDL(−). LDL(−) enhanced production of IL-6 (4-fold vs. LDL(+)), GM-CSF (4-fold), GROβ (2-fold) and GROγ (7-fold) was confirmed by ELISA. Time-course experiments revealed that IL-6 was released earlier than the other inflammation mediators, suggesting a first-wave cytokine action. However, the addition of IL-6 alone did not stimulate the production of IL-8, MCP-1 or GM-CSF. Moreover, IL-8, MCP-1 or GM-CSF alone did not promote the release of the other inflammatory molecules. Modification of LDL(+) by phospholipase A2-mediated lipolysis or by loading with non-esterified fatty acids (NEFA) reproduced the action of LDL(−), thereby suggesting the involvement of NEFA and/or lysophosphatidylcholine in the release of these molecules. Our results indicate that LDL(−) promotes a proinflammatory phenotype in endothelial cells through the production of cytokines, chemokines and growth factors.