The biological activity of hydrogen peroxide. IV. Enhancement of its clastogenic actions by coadministration of L-histidine

An enhancing effect of L-histidine (L-His) was detected on the induction by hydrogen peroxide (H2O2) of chromosomal aberrations of both the chromosome type and the chromatid type, in human embryonic fibroblasts. The maximum efficiency of induction was about 8-fold higher in the presence of L-His than in the presence of H2O2 alone, at a concentration of L-His of 50 microM. D-His and DL-His showed lower enhancing effects than L-His, with approximately 2-fold and 5-fold enhancement of induction of chromosomal aberrations, respectively. L-Histidinol and L-His-methyl ester, among various derivatives of L-His tested, also enhanced this process. However, the effects of these derivatives were smaller than those of L-His in a range of concentrations equivalent to that of the most effective dose of L-His (50 microM), while they produced greater enhancement than L-His at concentrations higher than 200 microM. Other derivatives of L-His, such as L-carnosine, urocanic acid, imidazolepyruvic acid, 1-methyl-L-His, imidazolelactic acid, imidazoleacetic acid and histamine and imidazole itself did not enhance the frequency of chromosomal aberrations induced by H2O2. These results indicate that at least both the imidazole ring and the amino group are essential components of the chemical structure of L-His required for the enhancing effect. Moreover, in order to cause such an enhancing effect, L-His had to be applied together with H2O2 to cells, because the enhancing effect of L-His was not observed with cells which were washed after pretreatment with L-His. The preliminary study suggested that this enhancing effect depends on the His-peroxide adduct derived from L-His and H2O2. None of the amino acids tested other than His produced any enhancing effect on the induction of chromosomal aberrations by H2O2.