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

The effect of CoCl2 on the cytotoxic activity of various antioxidants again st human or al tumor cell lines (HSC-2, HSG) and normal human gingival fibr oblasts (HGF) was investigated. Noncytotoxic concentrations of CoCl2 signif icantly reduced the cytotoxic activity of sodium ascorbate, gallic acid, ep igallocatechin gallate (EGCG), curcumin and dopamine, but not that of sodiu m 5, 6-benzylidene-L-ascorbate (SBA) and benzaldehyde. Among these compound s, benzaldehyde showed the most prominent tumor specific cytotoxic action. ESR spectroscopy showed that these antioxidants produced radicals under alk aline condition and that their radical intensity was transiently enhanced a nd finally disappeared by addition of CoCl2. Antioxidants which are sensiti ve to CoCl2 generally had higher cytotoxic activity and oxidation potential (measured by NO monitor) and addition of CoCl2 significantly reduced their oxidation potential. The present study suggests that cobalt ion stimulates the oxidation of antioxidants to their inactive products.