Carcinogenesis, Vol 18, 1045-1048, Copyright © 1997 by Oxford University Press
DJ Kelman, D Christodoulou, DA Wink, LK Keefer, A Srinivasan and A Dipple
Gaseous nitric oxide (NO), an environmental pollutant found in cigarette
smoke and diesel exhaust, has been shown to generate mutations in aerobic
in vitro assays. The objective of this study was to identify which oxides
of nitrogen, formed in the gaseous phase from NO, possess mutagenic
activity. Samples of the plasmid pSP189, in 1 M HEPES buffer, pH 7.4, were
exposed to preparations of nitrogen dioxide (NO2), dinitrogen trioxide
(N2O3) or an air control. The gas mixtures were formed in a gas-tight
syringe and were then introduced into 1 l flasks. The plasmid solution was
introduced immediately afterwards. Transformation of Escherichia coli
strain MBM7070 with the treated plasmids allowed analysis of mutation
frequencies and the types of mutations induced in the target supF gene. The
mutation frequency resulting from NO2 exposure was not different from that
of the control. However, N2O3 produced a substantial number of mutations.
The mutation frequency and the types of mutations were found to depend on
the length of time that the gases were allowed to incubate in the syringe
prior to introduction into the 1 l flasks (mutation frequency was maximal
at approximately 2 min). The most prevalent mutations were AT-->GC
transitions (68%), followed by GC-->AT transitions (30%), similar to
previous findings when pure NO was bubbled through pSP189 solutions. These
results suggest that it is N2O3, rather than NO2, that is the most likely
source of mutagenic potential from gaseous nitrogen oxides.
ARTICLES
Relative mutagenicities of gaseous nitrogen oxides in the supF gene of pSP189
Chemistry of Carcinogenesis Laboratory, ABL-Basic Research Program, NCI- Frederick Cancer Research and Development Center, MD 21702, USA.
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