Effect of cobalt ion on radical intensity and cytotoxic activity of antioxidants.

The effect of CoCl 2 on the cytotoxic activity of various antioxidants against human oral tumor cell lines (HSC-2, HSG) and normal human gingival fibroblasts (HGF) was investigated. Noncytotoxic concentrations of CoCl 2 significantly reduced the cytotoxic activity of sodium ascorbate, gallic acid, epigallocatechin gallate (EGCG), curcumin and dopamine, but not that of sodium 5,6-benzylidene-L-ascorbate (SBA) and benzaldehyde. Among these compounds, benzaldehyde showed the most prominent tumor-specific cytotoxic action. ESR spectroscopy showed that these antioxidants produced radicals under alkaline condition and that their radical intensity was transiently enhanced and finally disappeared by addition of CoCl 2 . Antioxidants which are sensitive to CoCl 2 generally had higher cytotoxic activity and oxidation potential (measured by NO monitor) and addition of CoCl 2 significantly reduced their oxidation potential. The present study suggests that cobalt ion stimulates the oxidation of antioxidants to their inactive products.