Effect of the colloidal silver on the intracellular and extracellular antioxidants. MCF-7 breast cancer cells and PBMC were treated with colloidal silver for 5 h and the antioxidants production were measured as described in methods, using colorimetric assay kits. a) Gpx activity, b) Catalase activity, c) Total antioxidant production. The experiments were performed in triplicates; data shown represent mean + SD of three independent experiments. *P < 0.05 as compared with untreated cells.