Nanoscale anionic macromolecules can inhibit cellular uptake of differentially oxidized LDL

Nanoscale particles could be synthetically designed to potentially intervene in lipoprotein matrix retention and lipoprotein uptake in cells, processes central to atherosclerosis. We recently reported on lipoprotein interactions of nanoscale micelles self-assembled from amphiphilic scorpion-like macromolecules based on a lauryl chloride-mucic acid hydrophobic backbone and poly(ethylene glycol) shell. These micelles can be engineered to present varying levels of anionic chemistry, a key mechanism to induce differential retentivity of low-density lipoproteins (LDL) (Chnari, E.; Lari, H. B.; Tian, L.; Uhrich, K. E.; Moghe, P. V. Biomaterials 2005, 26, 3749). In this study, we examined the cellular interactions and the ability of carboxylate-terminated nanoparticles to modulate cellular uptake of differentially oxidized LDL. The nanoparticles were found to be highly biocompatible with cultured IC21 macrophages at all concentrations examined. When the nanoparticles as well as LDL were incubated with the cells over 24 h, a marked reduction in cellular uptake of LDL was observed in a nanoparticle concentration-dependent manner. Intermediate concentrations of nanoparticles (10(-6) M) elicited the most charge-specific reduction in uptake, as indicated by the difference in uptake due to anionic and uncharged nanoparticles. At these concentrations, anionic nanoparticles reduced LDL uptake for all degrees of oxidation (no oxidation, mild, high) of LDL, albeit with qualitative differences in the effects. The anionic nanoparticles were particularly effective at reducing the very high levels of uptake of the most oxidized level of LDL. Since complexation of LDL with anionic nanoparticles is reduced at higher degrees of LDL oxidation, our results suggest that anionic nanoparticles interfere in highly oxidized (hox) LDL uptake, likely by targeting cellular/receptor uptake mechanism, but control unoxidized LDL uptake by mechanisms related to direct LDL-nanoparticle complexation. Thus, anionically functionalized nanoparticles can modulate the otherwise unregulated internalization of differentially oxidized LDL.