Differential effect of L-histidine in human lymphocytes damaged by different oxygen radical producing systems

The effect of histidine on damage induced by oxygen radicals was studied in peripheral blood lymphocytes treated with free oxygen radical-inducing agents: hydrogen peroxide, xanthine oxidase plus hypoxanthine, bleomycin and gamma-rays. L-Histidine, at a concentration of 1 mM, was found to potentiate both cell killing and inhibition of PHA-stimulated cell division brought about by hydrogen peroxide or xanthine oxidase plus hypoxanthine. In contrast, L-histidine did not affect gamma-ray- or bleomycin-induced cell killing and inhibition of PHA-stimulated cell division. We suggest that L-histidine potentiation of cell damage is mainly mediated by interaction of the amino acid with hydrogen peroxide and/or iron rather than with other reactive oxygen species. In addition, these results also indicate that hydrogen peroxide produced by gamma-radiation- or bleomycin-treated cells plays no role in the toxic effects elicited by these agents.