Profound influence of LDL oxidative status and monocyte co-cultures on baboon endothelial activation

To investigate how increased LDL levels interact with endothelial cells by using well-defined LDL preparations to limit experimental biases caused by heterogeneity of LDL preparations.

We pooled LDL from multiple subjects and prepared several types of LDL from a single source. Then we observed their effects on cultured endothelial cells with and without monocyte co-culture.

Native and minimally oxidized LDL did not cause significant cell death under most circumstances, and did not up-regulate cellular adhesion molecule (CAM) expression. Native LDL did result in significant increases of MCP-1 release in five of eight subjects. However, extensively oxidized LDL caused a significant amount of cell death and dramatically decreased MCP-1 secretion. Minimally oxidized LDL elicited a mixed response pattern, with a great deal of variation among subjects. When endothelial cells were co-cultured with monocytes and treated with native LDL, significant up-regulation of CAMs was detected after 24 hours of exposure. Up-regulation was not seen in any treatment group that contained either native LDL or monocytes only, indicating a synergistic effect of LDL and monocytes on endothelial cells. Incubation of cultured monocytes with native LDL also resulted in TNF-α and IL-1β release in a dosage- and time-dependent manner. Neutralization of both TNF-α and IL-1β by 10 μg/mL polyclonal antibodies inhibited the up-regulation of CAMs.

Our results suggest that varying extents of oxidative modification of LDL lead to fundamentally different cytological effects and that native LDL exhibits greater endothelial activation capacity when it interactively cooperates with monocytes.