Folic acid inhibits homocysteine-induced superoxide anion production and nuclear factor kappa B activation in macrophagesThis paper is one of a selection of papers published in this Special Issue, entitled Young Investigator's Forum.

Folic acid supplementation is a promising approach for patients with cardiovascular diseases associated with hyperhomocysteinemia. We have demonstrated that homocysteine (Hcy) activates nuclear factor-κB (NF-κB), a transcription factor that plays an important role in inflammatory responses. The aim of the present study was to investigate the effect of folic acid on Hcy-induced NF-κB activation in macrophages. Hcy treatment (100 μmol/L) resulted in NF-κB activation and increased monocyte chemoattractant protein-1 (MCP-1) expression in THP-1 derived macrophages. Hcy-induced NF-κB activation was associated with a significant increase in the intracellular superoxide anion levels. There was a significant increase in phosphorylation and membrane translocation of NADPH oxidase p47phox subunit in Hcy-treated cells. Addition of folic acid (200 ng/mL) to the culture medium abolished NADPH oxidase-dependent superoxide anion generation in macrophages by preventing phosphorylation of p47phox subunit. Consequently, Hcy-induced NF-κB activation and MCP-1 expression was inhibited. Such an inhibitory effect of folic acid was independent of its Hcy-lowering ability. Taken together, these results suggest that folic acid treatment can effectively inhibit Hcy-induced oxidative stress and inflammatory responses in macrophages. This may represent one of the mechanisms by which folic acid supplementation exerts a protective effect in cardiovascular disorders.