Background-Cytotoxic oxidized LDL (oxLDL) has been shown to promote apoptosis in cultured vascular smooth muscle cells (VSMCs). We investigated the localization of oxLDL and its association with apoptosis and the expression of apoptosis-related proteins in early and advanced atherosclerotic lesions. Methods and Results-Atherosclerotic plaques (nϭ23) from patients undergoing aortic, carotid, or femoral arterial surgery were studied. In early lesions, oxLDL was located predominantly in the superficial intima and in the media just beneath the internal elastic lamina. Medial VSMCs staining positive for oxLDL showed expression of BAX, a proapoptotic protein of the BCL-2 family. Apoptosis, as detected by DNA in situ terminal deoxynucleotidyl transferase end-labeling (TUNEL), was not present in these early lesions. In advanced plaques, areas of the intima positive for oxLDL showed lower ␣-smooth muscle actin immunoreactivity (PϽ0.01) and higher BAX immunoreactivity (PϽ0.05). Furthermore, these areas showed an increased number of apoptotic VSMCs (PϽ0.01). Western blot analysis revealed that oxLDL increases BAX expression in cultured human coronary VSMCs. Conclusions-We conclude that in early atherosclerotic lesions, oxLDL-positive VSMCs express BAX, which increases the susceptibility of these cells to undergo apoptosis. This could be important in our understanding of the transition of early lesions into advanced atherosclerotic plaques, which are characterized by regions of cell death. In advanced plaques, oxLDL-positive areas of the intima show higher BAX immunoreactivity and TUNEL-positive VSMCs, and this may contribute to plaque instability and rupture.

In summary, these data suggest that Ang II increases macrophage LO activity via AT 1 receptor-mediated mechanisms and this further increases the ability of the cells to generate minimally oxidized LDL. These studies provide a link between hypertension and the associated increased atherosclerosis observed in hypertensive patients.

Background — Inflammatory mediators such as tumor necrosis factor-α (TNF-α), interleukin 1β (IL-1β), IL-6, and interferon γ (IFN-γ) may change coronary plaque integrity by altering vascular smooth muscle cell (VSMC) survival and modifying the extracellular matrix. Insulin-like growth factor-1 (IGF-1) prevents apoptosis, promotes matrix formation, and can decrease TNF-α or IL-1β–induced proteoglycan degradation. Methods and Results — To determine the effects of cytokines on the IGF-1 system, rat aortic VSMCs were exposed to TNF-α (10 to 500 ng/mL), IL-1β (20 pg to 10 ng/mL), IL-6 (100 pg to 15 ng/mL), or IFN-γ (10 to 600 U/mL). IL-1β, IL-6, and IFN-γ did not regulate IGF-1, IGF-1 receptor (R), or IGF binding proteins (IGFBPs). However, TNF-α markedly decreased IGF-1 mRNA (85% reduction at 24 hours) and increased IGFBP-3 mRNA and protein (300% increase at 24 hours). These changes were blocked by actinomycin D, consistent with a transcriptional mechanism. Experiments using TNF binding protein-1 indicated that these effects were not attributable to secretion of an autocrine factor. Anti–IGFBP-3 antibodies increased VSMC DNA synthesis 3-fold. In addition, apoptosis induced by TNF-α, IFN-γ, and Fas ligand was markedly reduced by desamino-(1-3)-IGF-1. Conclusions — TNF-α, a cytokine that is upregulated in atherosclerotic plaques, reduces IGF-1 and increases IGFBP-3 in VSMCs, likely leading to a reduction in bioactive IGF-1. Because IGF-1 is important for growth and survival of VSMCs, its downregulation by TNF-α possibly plays a crucial role in acute and chronic coronary syndromes by decreasing VSMC viability and promoting plaque instability.