Enzymatically Modified Nonoxidized Low-Density Lipoprotein Induces Interleukin-8 in Human Endothelial Cells

Abstract

Background-Treatment of low-density lipoprotein (LDL) with a protease and cholesterolesterase transforms the lipoprotein to an entity that resembles lipoprotein particles in atherosclerotic lesions, which have a high content of free cholesterol, reflecting extensive de-esterification in the intima. Because de-esterification would occur beneath the endothelium, we examined the effects of enzymatically modified LDL (E-LDL) on cultured endothelial cells. Methods and Results-Incubation of endothelial cells with E-LDL provoked selective accumulation of interleukin (IL)-8 mRNA and production of the cytokine. Chemical analyses and depletion experiments indicated that the effect was caused by the presence of free fatty acids in the altered lipoprotein. Reconstitution studies demonstrated that the oleic and linoleic acids associated with E-LDL are particularly effective IL-8 inducers. The effects of E-LDL on endothelial cells could be abrogated with albumin. Conclusion-IL-8 is required for rolling monocytes to adhere firmly to the endothelium; thus, the findings reveal a link between subendothelial entrapment of LDL, cleavage of cholesterol esters, and monocyte recruitment into the lesion.

Enzymatically Modified Low‐Density Lipoprotein Is Present in All Stages of Aortic Valve Sclerosis: Implications for Pathogenesis of the Disease

“…The analysis of the lipid composition of early valvular cusp lesions (grade 1) compared with internal control tissues by mass spectrometry detecting both unesterified cholesterol and linoleic acid corroborated our immunohistochemical findings. While it is known that free cholesterol has an intrinsic complement‐activating capacity (see later),28 free fatty acids contained in the eLDL particle not only bind and activate C129 but also play multifaceted roles through their dual capacity to exert stimulatory and cytotoxic effects on neighboring cells 14, 15…”

“…If the capacity of the system is overburdened (eg, hypercholesterolemia), accumulation of eLDL is the consequence with subsequent generation of potentially harmful C5b‐9 complexes by both the classic and the alternative pathway 12, 13. Further, free fatty acids contained in the eLDL particle play multifaceted roles through their dual capacity to exert stimulatory and cytotoxic effects on neighboring cells 14, 15. These findings suggest a crucial role for inflammation in the initiation of atherosclerosis, with emphasis on eLDL as one important causative component.…”

Low-Density Lipoprotein Modified by Macrophage-Derived Lysosomal Hydrolases Induces Expression and Secretion of IL-8 Via p38 MAPK and NF-κB by Human Monocyte-Derived Macrophages

“…19 Similarly, H-LDL induced substantial expression of IL-1␤ mRNA in macrophages, but the mature translational product was barely detectable in the cell culture media after 24 hours of incubation, suggesting that IL-1␤ was subjected to posttranscriptional regulation. However, in sharp contrast to E-LDL that has been shown to induce secretion of IL-8 by endothelial cells, 7 but not by macrophages, 19 H-LDL induced substantial secretion of IL-8 by human monocyte-derived macrophages. Interestingly, even native LDL has been shown to induce secretion of IL-8 by smooth muscle cells.…”

“…25 Moreover, cholesterol has been shown to be the main component of lipoproteins to activate p38 MAPK 26 and to induce secretion of IL-8. 27 H-LDL is also enriched with free fatty acids that have previously been shown to be critical in expression of IL-8 7,28 and activation of the p38 MAPK 29 and NF-B 28 in endothelial cells. The effects of free fatty acids are likely to be mediated by PPAR␣, which is abundantly expressed in endothelial cells and drives the expression of IL-8 in these cells.…”

“…In addition, there is evidence for enzymatic modification of LDL in the arterial intima, 6 leading to the generation of morphologically modified unesterified cholesterol-rich particles with proinflammatory properties, such as secretion of IL-8 from endothelial cells. 7 Isolated LDL particles treated with trypsin and cholesteryl esterase, ie, enzymatically-modified LDL (E-LDL) have served as an in vitro model for this type of modification. Stimulated by these findings, we recently hypothesized that lysosomal proteases and lipases derived from arterial cells would modify LDL in atherosclerotic lesions.…”