Reactive oxygen species produced by macrophage-derived foam cells regulate the activity of vascular matrix metalloproteinases in vitro. Implications for atherosclerotic plaque stability.

TLDR

Vulnerable atherosclerotic plaques are enriched in lipid‑laden macrophages that exhibit matrix metalloproteinase activity. The study tested whether reactive oxygen species released by macrophage‑derived foam cells activate latent pro‑MMPs in the vascular matrix. In vitro, the authors exposed MMPs secreted by cultured human vascular smooth muscle cells to superoxide, nitric oxide, hydrogen peroxide, and peroxynitrite, assessing activation by zymography, Western blotting, and enzymatic assays. They found that superoxide and peroxynitrite activate gelatinases, peroxynitrite nitrates MMP‑2 to confer collagenolytic activity, and hydrogen peroxide shows a biphasic effect, indicating ROS can modulate matrix degradation and potentially destabilize plaques.

Abstract

Vulnerable areas of atherosclerotic plaques often contain lipid-laden macrophages and display matrix metalloproteinase activity. We hypothesized that reactive oxygen species released by macrophage-derived foam cells could trigger activation of latent proforms of metalloproteinases in the vascular interstitium. We showed that in vivo generated macrophage foam cells produce superoxide, nitric oxide, and hydrogen peroxide after isolation from hypercholesterolemic rabbits. Effects of these reactive oxygens and that of peroxynitrite, likely to result from simultaneous production of nitric oxide and superoxide, were tested in vitro using metalloproteinases secreted by cultured human vascular smooth muscle cells. Enzymes in culture media or affinity-purified (pro-MMP-2 and MMP-9) were examined by SDS-PAGE zymography, Western blotting, and enzymatic assays. Under the conditions used, incubation with xanthine/xanthine oxidase increased the amount of active gelatinases, while nitric oxide donors had no noticeable effect. Incubation with peroxynitrite resulted in nitration of MMP-2 and endowed it with collagenolytic activity. Hydrogen peroxide treatment showed a catalase-reversible biphasic effect (gelatinase activation at concentrations of 4 microM, inhibition at > or = 10-50 microM). Thus, reactive oxygen species can modulate matrix degradation in areas of high oxidant stress and could therefore contribute to instability of atherosclerotic plaques.