Azide

The SOS Chromotest, a colorimetric bacterial assay for genotoxins: validation study with 83 compounds

The SOS Chromotest is a simple bacterial colorimetric assay for genotoxicity. It is based on the measure of the induction of sfiA, a gene controlled by the general repressor of the SOS system in E. coli. Expression of sfiA is monitored by means of a gene fusion with lacZ, the structural gene for beta-galactosidase. We have examined 83 compounds of various chemical classes with the SOS Chromotest using a standard procedure. Comparison of the results with those obtained in the Mutatest (the Ames test) showed that most (90%) of the mutagenic compounds were also SOS inducers. For these compounds a quantitative correlation was observed between the mutagenic potency and the SOS-inducing potency (SOSIP). The case of the 10% remaining compounds giving conflicting results in the two tests is discussed. Sensitivity, specificity and accuracy for carcinogenicity prediction have been evaluated for the SOS Chromotest and the Mutatest using 73 chemicals for which carcinogenicity data were available. In spite of some differences, similar results were obtained in the two tests. The present data indicate that the SOS Chromotest has many practical advantages and may be used as a primary screening tool or as part of a battery of short-term tests for carcinogens.

A mutagenic metabolite synthesized by Salmonella typhimurium grown in the presence of azide is azidoalanine

A mutagenic azide metabolite was purified from the medium in which Salmonella typhimurium cells were grown in the presence of azide. This metabolite was identified to be azidoalanine based on infrared and mass spectroscopy and elemental analysis. This compound appeared to be identical to the mutagenic compound synthesized in vitro from azide and O-acetylserine by partially purified O-acetylserine sulfhydrylase. The metabolite (azidoalanine) mutagenic efficiency and spectrum in S. typhimurium was similar to that of inorganic azide. The compounds 2-azidoethylamine, 2-bromoethylamine, 3-bromopropionic acid and N-(azidomethyl) phthalimide were also mutagenic with a similar spectrum to azide and azidoalanine, but with lower efficiency. The compounds 3-azidopropylamine, 4-azidobutylamine, 3-chloroalanine and ethylamine were only weakly or nonmutagenic. Numerous other chloro, bromo and azido phthalimide derivatives tested were nonmutagenic. It is suggested that the lack of azide mutagenicity (and perhaps carcinogenicity) in mammalian cells may be due to their inability to convert azide to azidoalanine.

In vitro production of azide mutagenic metabolite in Arabidopsis, Drosophila and Neurospora

The ability of Arabidopsis, Drosophila and Neurospora to convert azide to its mutagenic metabolite was investigated. Cultures of these organisms all contained significant levels of O-acetylserine sulfhydrylase activity. Extracts from each organism produced a product from O-acetylserine and azide in vitro which was mutagenic in Salmonella typhimurium TA1530.

Lack of induction of single-strand breaks in mammalian cells by sodium azide and its proximal mutagen

The mutagenicity of sodium azide in both higher plants and bacteria is well documented. However, in mammalian cells, research on the effects of azide on gene mutations has produced conflicting results. Furthermore, no research has been conducted on the effects of azide and its proximal mutagen (mutagenic metabolite) on DNA single-strand breaks. Experiments were designed to overcome this lack of information on azide mutagenicity and to evaluate the potential hazard of azide exposure to man. Chinese hamster V79 cells were treated with either azide or its proximal mutagen(s) for 2 or 6 h, respectively, and analyzed by alkaline elution for single-strand breaks. The data showed that neither azide nor the proximal mutagen(s) induced single-strand DNA breaks or DNA-protein cross-links. Therefore it appears that neither azide nor its proximal mutagen(s) interact directly with DNA and this suggests that azide may be an indirect-acting mutagen. Furthermore, this lack of interaction with DNA may account for azide's lack of carcinogenicity.

Evaluation of mutagenicity and other adverse effects of occupational exposure to sodium azide

The ubiquitous use of sodium azide has resulted in widespread occupational exposure to it in both laboratory and industrial settings, despite a lack of knowledge of the risks which may be involved. Explosive, toxic, and mutagenic hazards have been shown at even low-dose exposures. These effects occur in many species, from cellular damage through pathology of whole systems, and human fatalities have been reported. The advantages to its availability for applicable uses precludes reaching a "no exposure" level, but efforts to decrease unnecessary exposure can reduce its risk; therefore a quantitative procedure for determining human exposure is necessary. However, for various reasons present methods for this type of evaluation of azide are unsatisfactory, and minimizing hazard is dependent upon good laboratory hygiene and motivated personnel. The increasing use of azide and proportionally increasing occupational and accidental exposure in the future warrants the undertaking of chronic exposure studies, which hopefully will result in more explicit guidelines for human protection.

Comparative evaluation of different pairs of DNA repair-deficient and DNA repair-proficient bacterial tester strains for rapid detection of chemical mutagens and carcinogens

The aim of the present study was to evaluate the usefulness of different pairs of DNA repair-deficient and DNA repair-proficient bacterial tester strains in a mutagenicity/carcinogenicity screen, possibly as complements to the Ames test. 70 carcinogenic and non-carcinogenic compounds, representing a variety of chemical structures, were tested for their DNA-damaging effects, using 6 different DNA-repair-deficient bacterial strains. 2 Bacillus subtilis systems, H17/M45 and HLL3g/HJ-15, were used. The susceptibility of Escherichia coli AB1157 was compared with the susceptibility of 4 recombination-deficient mutants, JC5547, JC2921, JC2926 and JC5519. The test compounds were applied onto paper disks (spot test, ST), or incorporated into a top agar layer (agar-incorporation test, AT). The 2 B. subtilis systems were generally found to be more sensitive and reliable than the assays using E coli. The incorporation of the test compounds in the agar increased the sensitivity of the test for polycyclic aromatic hydrocarbons and other poorly water-soluble compounds. Hydrazines and several other highly polar chemicals could be tested more efficiently when applied onto paper disks. About 30% of the test compounds did not induce any growth inhibition and so could not be tested properly. In order to evaluate the ability of these DNA-repair tests to complement the Ames Salmonella mutagenicity test in a genetic toxicology screening program, results from this study were compared with published data both on mutagenicity in the Ames test and on carcinogenicity. 8 carcinogens generally found to be non-mutagenic for Salmonella were tested: 2 showed DNA-damaging properties (mitomycin C, 1,2-dimethylhydrazine), 5 failed to do so (actinomycin D, griseofulvin, thioacetamide, diethylstilbestrol, safrole), and one (thiourea) was not toxic, so that no classification was possible. 2 non-carcinogenic bacterial mutagens were examined; one, sodium azide, was equitoxic for repair-proficient and -deficient strains, while the other, nitrofurantoin, primarily inhibited repair-deficient strains. The DNA-repair tests failed to indicate the mutagenic and carcinogenic properties of acridine orange. Nalidixic acid, a non-mutagenic DNA synthesis inhibitor, damaged bacterial DNA. Apart from the differences summarized above, carcinogenicity was indicated correctly by the Salmonella S9 assay and most sets of DNA-repair-deficient and DNA-repair-proficient tester strains evaluated in this study. Thus, several more carcinogens could be detected by performing the Ames test and the bacterial DNA-repair tests in tandem than by using either test alone. Nevertheless, the use of both bacterial in vitro systems in a battery of short-term tests for mutagenicity/carcinogenicity evaluation is not considered to be ideal, since the Ames test and the pairs of DNA-repair-deficient and DNA-repair-proficient tester strains used had several shortcomings in common under the conditions of this study.

Isolation of an azide mutagenic metabolite in Salmonella typhimurium

A scheme that employs a cation-exchange column and high-pressure liquid chromatography (HPLC) is devised to isolate and process large quantities of azide metabolite produced by S. typhimurium TA1530 strain. The mutagenic metabolite adheres strongly to the cation-exchange column, thus providing a convenient way to separate the metabolite from unreacted azide (N3-). The metabolite is very polar and only sparingly soluble in most organic solvents. Recrystallization in a methanol-carbon tetrachloride solvent system gave rise to microcrystalline material that decomposes with charring and gas evolution at 173-176 degrees C. The infrared spectrum indicates the presence of a covalently bound azide moiety.

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.

Effects of L-cysteine and O-acetyl-L-serine in the synthesis and mutagenicity of azide metabolite

The ability of L-cysteine to inhibit azide-metabolite synthesis and mutagenicity is investigated in Salmonella typhimurium TA1530 and cys E6 strains. L-cysteine specifically inhibits the synthesis of the mutagenic azide metabolite as other compounds containing SH group did not affect the production of this metabolite. Azide mutagenicity is completely inhibited by L-cysteine at a concentration (5 mumoles/plate) where the metabolite mutagenicity was not affected. O-Acetyl-L-serine can reverse the L-cysteine mediated inhibition of the metabolite synthesis and thus mutagenicity in the same strains. These results suggest that O-acetyl-L-serine may be required to synthesize the azide metabolite or its precursor.

Genetic and biochemical characterization of waxy mutants in cereals

During fine structure analyses of artificially induced waxy mutants in maize by use of Nelson's pollen analysis methods, it was noticed that some mutants showed a phenotype intermediate between waxy and normal nonwaxy. Such intermediate or leaky waxy mutants were frequent among mutants induced by a chemical mutagen, EMS. They seemed to be located evenly within the waxy locus. This would suggest that they might have been missense mutations, which would produce full-sized but partially inactivated enzymes, rather than deletions or frameshift mutations. To confirm the intermediate phenotype, a rapid measuring system was developed to measure waxiness of endosperm quantitatively. It was based on the blue value method and is applicable to a single grain of rice. Among the 27 waxy mutant lines of maize, including 11 EMS-induced, two of the EMS-induced mutants were clearly intermediate. Eighteen EMS induced wx mutants of rice were also examined, and nine were intermediate.

Effects of pH on the mutagenicity of sodium azide in Neurospora crassa and Salmonella typhimurium

Sodium azide at various pH values did not cause a significant increase in the frequency of forward mutation above the control frequency at the adenine-3 (ad-3) region in resting conidia and in conidia from growing cultures of heterokaryons 12 and 59 of Neurospora crassa. Conidia from ad-3 mutants were plated with sodium azide at various pH values, and no obvious increase in reverse mutation above the controls was observed. Data are presented showing that sodium azide at pH 3 is inactivating conidia by interacting with the cytoplasma rather than the nucleus, and this may be the primary reasons that no mutation at the ad-3 region was detected. The dependence of sodium azide mutagenicity on pH was investigated in histidine-requiring mutants of Salmonella typhimurium using a suspension test. There were no significant differences in the reversion frequencies among the pH values (3-8) tested. Thus, no pH dependence is associated with sodium azide mutagenicity, nor are growth and/or DNA replication required for mutagenicity by sodium azide, in S. typhimurium.