Induction of inducible nitric oxide synthase (iNOS) expression by oxLDL inhibits macrophage derived foam cell migration.

Deletion of inducible nitric oxide synthase (iNOS) in apolipoprotein E knockout mice was shown to mitigate the extent of arteriosclerosis. Oxidized low density lipoprotein (oxLDL) inhibits macrophage migration and traps foam cells, possibly through a mechanism involving oxidative stress. Here, we addressed whether a reduction of iNOS-mediated oxidative stress remobilizes macrophage-derived foam cells and may reverse plaque formation. Migration of RAW264.7 cells and bone marrow cells was quantified using a modified Boyden chamber. iNOS expression, phalloidin staining, focal adhesion kinase phosphorylation, lipid peroxides, nitric oxide (NO) and reactive oxygen species (ROS) production were assessed. oxLDL treatment significantly reduced cell migration compared to unstimulated cells (p < 0.05). This migratory arrest was reversed by co-incubation with a pharmacologic iNOS inhibitor 1400 W (p < 0.05) and iNOS-siRNA (p > 0.05). Furthermore, apoE/iNOS double knockout macrophages do not show migratory arrest in response to oxLDL uptake, compared to apoE knockout controls (p > 0.05). We documented significantly increased iNOS expression following oxLDL treatment and downregulation using 1400 W and small inhibitory RNA (siRNA). iNOS inhibition was associated with a reduction in NO and peroxynitrite (ONOO-)- and increased superoxide generation. Trolox treatment of RAW264.7 cells restored migration indicating that peroxynitrite mediated lipid peroxide formation is involved in the signaling pathway mediating cell arrest.. Here, we provide pharmacologic and genetic evidence that oxLDL induced iNOS expression inhibits macrophage-derived foam cell migration. Therefore, reduction of peroxynitrite and possibly lipid hydroperoxide levels in plaques represents a valuable therapeutic approach to reverse migratory arrest of macrophage-derived foam cells and to impair plaque formation.