Effect of sodium azide on sister-chromatid exchanges in human lymphocytes and Chinese hamster cells

Previous reports from this laboratory and others indicate that sodium azide is a unique mutagen. It is highly mutagenic in S. typhimurium TA1530 as well as in barley, rice, peas, yeast and Chinese hamster V79 cells. However, azide apparently does not produce chromosome breaks in barley, Vicia or human lymphocytes. Therefore, a study of the effects of azide on sister-chromatid exchanges (SCE) appeared warranted. Human whole blood and Chinese hamster K1 cell line were exposed for 4 and 2 h resp. to various concentrations of sodium azide ranging from 10(-3) to 10(-7) M. Cells were harvested and chromosomes stained by the FPG technique. In human lymphocytes, concentrations above 10(-4) induced lethality whereas the K1 cell line was sensitive to concentrations above 10(-5) M. The lower concentrations of azide produced no significant increase in SCE frequency above controls. Concurrent mitomycin C treatments produced significant increases in SCE levels. This apparent lack of induction of SCEs above background combined with previous data demonstrating negative clastogenic but very positive mutagenic activity of azide confirms the uniqueness of this mutagen. It would appear that azide is one of the few known potent mutagens that does not increase SCEs and/or break chromosomes.