Oxidative stress is believed to play a key role in cardiovascular disorders. Thioredoxin (Trx) is an oxidative stress-limiting protein with anti-inflammatory and antiapoptotic properties. Here, we analyzed whether Trx-1 might exert atheroprotective effects by promoting macrophage differentiation into the M2 anti-inflammatory phenotype.

Trx-1 at 1 μg/mL induced downregulation of p16^INK4a and significantly promoted the polarization of anti-inflammatory M2 macrophages in macrophages exposed to interleukin (IL)-4 at 15 ng/mL or IL-4/IL-13 (10 ng/mL each) in vitro, as evidenced by the expression of the CD206 and IL-10 markers. In addition, Trx-1 induced downregulation of nuclear translocation of activator protein-1 and Ref-1, and significantly reduced the lipopolysaccharide-induced differentiation of inflammatory M1 macrophages, as indicated by the decreased expression of the M1 cytokines, tumor necrosis factor-α and monocyte chemoattractant protein-1. Consistently, Trx-1 administered to hyperlipoproteinemic ApoE2.Ki mice at 30 μg/30 g body weight challenged either with lipopolysaccharide at 30 μg/30 g body weight or with IL-4 at 500 ng/30 g body weight significantly induced the M2 phenotype while inhibiting differentiation of macrophages into the M1 phenotype in liver and thymus. ApoE2.Ki mice challenged once weekly with lipopolysaccharide for 5 weeks developed severe atherosclerotic lesions enriched with macrophages expressing predominantly M1 over M2 markers. In contrast, however, daily injections of Trx-1 shifted the phenotype pattern of lesional macrophages in these animals to predominantly M2 over M1, and the aortic lesion area was significantly reduced (from 100%±18% to 62.8%±9.8%; n=8; P<0.01). Consistently, Trx-1 colocalized with M2 but not with M1 macrophage markers in human atherosclerotic vessel specimens.

The ability of Trx-1 to promote differentiation of macrophages into an alternative, anti-inflammatory phenotype may explain its protective effects in cardiovascular diseases. These data provide novel insight into the link between oxidative stress and cardiovascular diseases.