Objectives: The objective was to study potential regulation of insulin-like growth factor I (IGF I), its binding proteins, and the IGF I receptor by reactive oxygen species in vascular smooth muscle cells.
Methods: We used cultured rat aortic smooth muscle cells exposed to xanthine (100 microM) and xanthine oxidase (5 microU/ml) or H2O2 (200 microM) and measured IGF I mRNA levels by solution hybridization/RNase protection assays, IGF I protein levels by radioimmunoassay, and IGF binding proteins by Western ligand blotting. Additionally, we measured the effect of anti-IGF I antiserum on xanthine/xanthine oxidase- and H2O2-stimulated [3H]thymidine incorporation.
Results: Xanthine/xanthine oxidase and H2O2 stimulated increases in IGF I mRNA and protein levels and reduced IGF binding protein-4 levels in conditioned medium. The effect of xanthine/xanthine oxidase was inhibited by the scavengers superoxide dismutase and catalase. Xanthine/xanthine oxidase- and H2O2-stimulated DNA synthesis was completely inhibited by a neutralizing anti-IGF I antiserum.
Conclusion: Reactive oxygen species increased vascular smooth muscle cell synthesis of IGF I and reduced levels of the inhibitory IGF binding protein-4. Furthermore, reactive oxygen species-induced DNA synthesis was inhibited by an anti-IGF I antiserum. These findings suggest that the autocrine IGF I system plays an important role in vascular smooth muscle cell growth responses to reactive oxygen species. Furthermore, the findings have important implications for understanding biological responses to changes in redox state.