Oxidation decreases low density lipoprotein association with the subendothelium extracellular matrix

Vascular extracellular matrix in atherosclerosis

The extracellular matrix (ECM) is an essential component of the human body that is responsible for the proper function of various organs. Changes in the ECM have been implicated in the pathogenesis of several cardiovascular conditions including atherosclerosis, restenosis, and heart failure. Matrix components, such as collagens and noncollagenous proteins, influence the function and activity of vascular cells, particularly vascular smooth muscle cells and macrophages. Matrix proteins have been shown to be implicated in the development of atherosclerotic complications, such as plaque rupture, aneurysm formation, and calcification. ECM proteins control ECM remodeling through feedback signaling to matrix metalloproteinases (MMPs), which are the key players of ECM remodeling in both normal and pathological conditions. The production of MMPs is closely related to the development of an inflammatory response and is subjected to significant changes at different stages of atherosclerosis. Indeed, blood levels of circulating MMPs may be useful for the assessment of the inflammatory activity in atherosclerosis and the prediction of cardiovascular risk. The availability of a wide variety of low-molecular MMP inhibitors that can be conjugated with various labels provides a good perspective for specific targeting of MMPs and implementation of imaging techniques to visualize MMP activity in atherosclerotic plaques and, most interestingly, to monitor responses to antiatheroslerosis therapies. Finally, because of the crucial role of ECM in cardiovascular repair, the regenerative potential of ECM could be successfully used in constructing engineered scaffolds and vessels that mimic properties of the natural ECM and consist of the native ECM components or composite biomaterials. These scaffolds possess a great promise in vascular tissue engineering.

Nanoscale anionic macromolecules for selective retention of low-density lipoproteins

Synthetically designed anionic nanocarriers that mimic the charge properties of glycosaminoglycans can potentially sequester low-density lipoproteins (LDL) during the treatment of atherosclerosis. In this study, we explore the LDL retentivity of 15-20 nm anionic micelles formed from amphiphilic scorpion-like macromolecules (AScMs) as building blocks. The macromolecules comprise four aliphatic chains attached to mucic acid and a linear polyethylene glycol (PEG) segment to form micellar nanocarriers with a hydrophobic core and hydrophilic corona. Dynamic light scattering and transmission electron microscopy studies indicate that the carboxylate-terminated nanocarriers (20 nm) sequester LDL (22 nm), resulting in complexes with a diameter of 60-90 nm, but neutral ethoxy-terminated nanocarriers do not retain LDL. Further, carboxylate-terminated nanocarriers consistently bound to unoxidized LDL (Relative Electrophoretic Mobility, REM=1.0) and mildly oxidized LDL (REM=1.5), but not highly oxidized LDL (REM=3.6), whereas the neutral nanocarriers displayed no preference/affinity at all, indicating that the nanocarrier-LDL binding is charge-dependent. The binding affinity of unoxidized LDL for differentially charged nanocarriers, formed from varying ratios of carboxylate- and ethoxy-terminated macromolecules, was quantified. The 100% carboxylated nanocarriers elicited the highest binding affinity (K(d)=567 nm), whereas mixed micelles elicited significantly lower levels of binding affinity. Our results highlight the promise of synthetically designed nanomaterials in lipoprotein retention, a key step in managing the escalation of atherosclerosis.

Oxidative modifications of LDL increase its binding to extracellular matrix from human aortic intima: influence of lesion development, lipoprotein lipase and calcium

Retention of atherogenic lipoproteins in the arterial intima by extracellular matrix (ECM) is assumed to occur during early atherogenesis and its further development. Low density lipoprotein (LDL) trapped in the intima may undergo oxidative modifications, which initiate a chain reaction in atherogenesis. Lipoprotein lipase (LPL) has been found to mediate the binding of native and oxidized LDL to ECM produced by cultured cells and to contribute to foam cell formation by mildly oxidized LDL. In this study ECM, isolated from human aortic intima with different atherosclerotic lesions, was used for the first time to measure the binding to it in vitro of native and differently oxidized 125I-LDL. Oxidation of 125I-LDL increased its binding to the ECM, which was most prominent with the material isolated from intima at the early stage of atherogenesis. With the progression of atherosclerosis, the ability of the isolated intimal ECM to bind native and oxidized 125I-LDL decreased, and strongly oxidized 125I-LDL decreased more than native and moderately oxidized 125I-LDL. LPL increased the binding of moderately oxidized 125I-LDL to the ECM more than native 125I-LDL, while it had only a small effect on strongly oxidized 125I-LDL. LPL-mediated binding of native and oxidized 125I-LDL decreased with the development of atherosclerotic lesions. Calcium ions also increased the binding of LDL to the ECM. This enhanced binding increased with the extent of LDL oxidation, especially at the early stage of atherogenesis, and decreased with lesion progression. These data suggest that the ability of ECM to retain LDL in arterial intima depends on LDL oxidation status and changes with the progression of atherogenesis. In addition, LPL and calcium ions may participate in the retention of LDL in vivo.

Retention of oxidized LDL by extracellular matrix proteoglycans leads to its uptake by macrophages: an alternative approach to study lipoproteins cellular uptake

Interaction between arterial macrophages and oxidized LDL (Ox-LDL) leads to foam cell formation, a critical step during early atherogenesis. Until now, cellular uptake of lipoproteins was studied through incubation of the media-soluble lipoprotein with cultured macrophages. However, as lipoproteins in the arterial wall are bound to subendothelial matrix, we questioned whether the retention (binding) of Ox-LDL to a macrophage-derived extracellular matrix (ECM) could lead to enhanced uptake by macrophages. The uptake of ECM-bound Ox-LDL by activated macrophages (by phorbol myristate acetate) was lipoprotein dose dependent, time dependent and higher (by 1.5-fold) than the uptake of ECM-bound native LDL. Preincubation of the ECM with lipoprotein lipase before the addition of Ox-LDL was essential for the uptake of ECM-bound Ox-LDL by the macrophages. After radiolabeling of the ECM glycosaminoglycans (GAGs), we found that ECM-bound Ox-LDL is taken up by the macrophages together with the ECM-GAG. Finally, these results were further confirmed through the use of ECM obtained from mouse peritoneal macrophages (MPMs), derived from atherosclerotic, apoE-deficient mice. In 24-week-old mice with developed atherosclerosis, the GAG content of their MPM-derived ECM increased by 52%, the ability of their MPM-derived ECM to bind Ox-LDL increased by 57%, and macrophage uptake of Ox-LDL that was retained by the MPM-derived ECM increased by 86%. In conclusion, the present study demonstrated that ECM-bound Ox-LDL is taken up by activated macrophages. This may represent a physiopathological phenomenon that leads to cholesterol and oxysterol accumulation in arterial macrophages, the hallmark of early atherosclerosis.