Dinitrogen oxide

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Link to relevant study records

Reference

Endpoint:

in vitro gene mutation study in bacteria

Remarks:

Type of genotoxicity: gene mutation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP, limited no. of strains used

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

yes

Remarks:

limited no. of strains used

GLP compliance:

no

Type of assay:

bacterial reverse mutation assay

Species / strain / cell type:

other: S. typhimurium TA 1535, TA 100

Additional strain / cell type characteristics:

not applicable

Metabolic activation:

with and without

Metabolic activation system:

Aroclor 1254

Test concentrations with justification for top dose:

0, 1, 3, 9, 27, 81%

Untreated negative controls:

yes

Positive controls:

yes

Positive control substance:

other: vinylidene chloride, 2-anthramine

Species / strain:

other: S. typhimurium TA 1535, TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

not applicable

Untreated negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

other: all strains/cell types tested

Remarks:

Migrated from field 'Test system'.

Conclusions:

Interpretation of results (migrated information):
negative

No increase in the number of revertant colonies were observed in strain TA100 or TA1535. At the maximum dose tested, 81%, no evidence of cytotoxicity was observed.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

Additional information from genetic toxicity in vitro:

Gene mutation (bacterial)

In the published literature N2O has been investigated using the Ames methodology (Baden et al., 1979; Baden & Monk, 1981) employing limitedSalmonella typhimurium (TA1535, TA98 and TA100) tester strains. These studies did not show evidence of increases in revertants. In the Badenet al(1979) study, no evidence of toxicity was observed when tested up to 1 atmosphere. In the Baden and Monk study however, toxicity was evident at 4 atmospheres and above.

 

Mammalian chromosome aberration (in vitro)

Data from a sister chromatid exchange (SCE) (Whiteet al., 1979) in Chinese hamster ovary cells did not show evidence of SCE following a 24h exposure to N2O

 

Mammalian gene mutation (in vitro)

In a mammalian gene mutation study, using Chinese hamster lung fibroblast involving mutation at thehprtlocus, using 8-azaguanine as the selective agent, N2O failed to induce an increase in mutant colonies following a 24 h exposure period. 

 

In vivobone marrow micronucleus

No data

 

QSAR data

QSAR data generated from Toxtree (v. 2.5.1) to partially address concerns over the genotoxicity of N2O returned negative results. Using the Benigni-Bossa rulebase¹for mutagenicity and carcinogenicity negative results were obtained for genotoxicity and non-genotoxic carcinogenicity predictions. Also, use of the ToxMIC-ISS plug-in²to allow identification of structural alerts for thein vivomicronucleus assay were analysed. Toxtree returned negative results for this endpoint as well.

 

Human data

Cohen et al (1980) related the incidence of cancer specifically to occupational exposure to N2O. The study population consisted of 30650 male dentists and 30547 chair side assistants (female) and was readily divided between those who did or did not give inhaled anaesthetics to their patients. Those that only used N2O accounted for 81.3% of the study population. No effect of anaesthetic exposure was seen in the dentists. The cancer rate among female assistants exposed to waste anaesthetics for more than 8 h/wk was 1.06±0.18% vs. 0.72±0.10% in those that were not exposed. The difference was not considered to be statistically significant. Among the various cancers types, only cancer of the cervix occurred more frequently in exposed assistants (0.29±0.10%) than in unexposed (0.12%±0.04%) assistants, however this increase was not statistically significant.

 

Genetic Toxicology Summary

The available experimental data on N2O do not satisfy the criteria required under the requirements of REACh to conclude that N2O lacks any genotoxic potential. When these results are considered in isolation and compared against the guideline requirements each test falls short of the minimum requirements. However, with this limited data along with negative QSAR data generated in-house, a negative carcinogenicity study (in mice) along with negative epidemiological data of cancer rates or deaths among dental / operating room personnel and the widespread use of N2O as both an analgesic and anaesthetic in humans there is little reason to believe that N2O is genotoxic in the absence of convincing evidence.

 

References:

Benigni, R., Bossa, C., Jeliazkova, N., Netzeva, T. and Worth. A. (2008). The Benigni / Bossa rulebase for mutagenicity and carcinogenicity - a module of Toxtree, by European Commission report EUR 23241 EN

Benigni, R., Bossa, C., Tcheremenskaia, O. and Worth, A. (2009). Development of structural alerts for the in vivo micronucleus assay in rodents", European Commission report EUR 23844

Cohen E.N., Brown B.W., Wu M.L., Whitcher C.E., Brodsky J.B., Gift H.C., Greenfield W., Jones T.W. & Driscoll E.J. (1980). Occupational disease in dentistry and chronic exposure to trace anaesthetic gases. J. Amer. Dent Ass. 101; pp 21-31

 

NOTES

1. Benigni-Bossa rulebase: The structural alerts (SAs) for carcinogenicity are molecular functional groups or substructures known to be linked to the carcinogenic activity of chemicals. As one or more SAs embedded in a molecular structure are recognised, the system flags the potential carcinogenicity of the chemical. The list of SAs in the Benigni-Bossa rulebase refers mainly to the knowledge on the action mechanisms of genotoxic carcinogenicity (thus they apply also to the mutagenic activity in bacteria), but includes also a number of SAs flagging potential non-genotoxic carcinogens.

 

Because of their nature, the SAs have the role of pointing to chemicals potentially toxic, whereas no conclusions or indications about nontoxic chemicals are possible (except by exclusion). Thus the SAs are not a discriminant model on the same ground

of the Quantitative Structure-Activity Relationships (QSAR) models that produce estimates for both positive and negative chemicals.

 

In addition to the SAs, this software includes QSAR models for: 1) the mutagenic activity of aromatic amines in the Salmonella typhimurium TA100 strain (Ames test); 2) the carcinogenic activity of the aromatic amines in rodents (summary activity from

rats and mice); 3) the mutagenic activity of unsaturated aldehydes in theSalmonella typhimuriumTA100 strain (Ames test).

 

2.ToxMIC-ISS: following identification of a structural alerts for thein vivomicronucleus assay, these structural alerts provide a coarse-grain filter for the preliminary screening of potentialin vivomutagens (Benigniet al., 2009)

Justification for selection of genetic toxicity endpoint
In order to address this endpoint a single study does not provide sufficient evidence to conclude this endpoint. Therefore, a weight of evidence approach has been used to address this endpoint principally from published data, QSAR data generated in house and history of use.

Justification for classification or non-classification

Dinitrogen oxide is considered to be devoid of genotoxic potential, classification therefore is not required.