Exogenous Histidine as a Co-factor which Exacerbates the Toxicity of Hydrogen Peroxide in Cultured Mammalian and Bacterial Cells

The killing of Escherichia coli cells by H₂O₂ is higher when exposure to the oxidant is performed in a complete culture medium, as compared to saline. Whereas MgSO_4, CaCl₂, thiamine or glucose, added separately or in combination with the saline, had no effect on the cytotoxic response to H₂O₂, the cytotoxicity appeared highly dependent upon the presence of the casamino acids in the incubation medium. One of these amino acids, histidine, was found to greatly augment the toxicity of H₂O₂ in E. coli. This effect of histidine was also observed in mammalian cells. In fact, both the cytoxicity and the DNA damage produced by H₂O₂ in Chinese hamster ovary (CHO) cells were significantly increased by this amino acid.