Acetaldehyde oxime

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vivo

Link to relevant study records

Reference

Endpoint:

in vivo mammalian germ cell study: gene mutation

Remarks:

Type of genotoxicity: gene mutation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1981

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well documented study.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 477 (Genetic Toxicology: Sex-linked Recessive Lethal Test in Drosophila melanogaster)

GLP compliance:

not specified

Type of assay:

Drosophila SLRL assay

Species:

Drosophila melanogaster

Strain:

other: Canton-S

Sex:

male

Route of administration:

oral: feed

Details on exposure:

Young adult Canton-S males (post-meiotic germ cell stages) and young adult Canton-S males of 1-2 days old (pre-meiotic germ cell stages) were exposed to 2000 ppm AAO by feeding on glass fiber filter paper that had been inundated with either the exposure or control solution. This method also results in contact exposure and inhalation of any fumes that are present. The solvent used is a 5% sucrose solution kept at a pH of 6.8 by a phosphate buffer (1:1 ratio of 4.539 g KH2PO4 per L and 5.938g Na2HPO4.2H2O per L).

Duration of treatment / exposure:

3 days

Remarks:

Doses / Concentrations:
2000 ppm
Basis:
nominal conc.

Control animals:

yes, concurrent vehicle

Positive control(s):

ethyl methane sulfonate: post-meiotic germ cell stages
dimethylnitrosamine: pre-meiotic germ cell stages

Sex:

male

Genotoxicity:

negative

Vehicle controls validity:

valid

Positive controls validity:

valid

Conclusions:

Interpretation of results (migrated information): negative
Genetic testing of acetaldehyde oxime in the Drosophila melanogaster sex-linked recessive lethal test indicates that it is not mutagenic in this organism. There is evidence, however, that AAO may have induced a significant level of sterility in the treated males.

Executive summary:

In the original study on post-meiotic germ cells a cluster of 8 mutants was recovered in the acetyldehyde oxime (AAO) series. In general terms, a cluster constitutes more than one lethal mutation recovered from an individual treated male. In instances where the overall mutation frequency is low, as in the present study, it is not clear that such clusters represent independent mutational events or that they result from a clone of germ cells carrying a prior formed spontaneous mutation. In the former case the mutations would be dispersed over the length of the X chromosome whereas in the latter case they would all occur at the same genetic locus. Unfortunately, the SRLR test does not possess the capability to detect which of these two alternatives is the true situation. When the cluster of 8 was considered as 8 independent events the frequency of mutations in the AAO treated series was significantly elevated above the control frequency. On the other hand, when the cluster was treated as a single prior event the effect of AAO was not significant. The equivocal nature of these data necessitated repeating the experiment. When the data of the second experiment are pooled with those of the first experiment a statistical analysis indicates that AAO did not induce a significant number of mutations. This is true whether the cluster is treated as 8 independent events or a single prior event.

In order to further substantiate that AAO is not mutagenic in higher eukaryotes it was decided to ascertain what effect, if any, it had on spermatogonial cells. These cells are considered to be at highest risk in males because they can accumulate genetic damage over the life time of the organism. Furthermore, they are physiologically different from the post meiotic germ cells in that they are continuously undergoing cell proliferation.

The data clearly show AAO to be non-mutagenic in Drosophila spermatogonial cells. An additional observation that deserves mention, however, is the fact that approximately 23% of the males on test with AAO exhibited complete sterility. This compares to a frequency of 6% in the negative control and is significant.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

Additional information from genetic toxicity in vivo:

Genetic toxicity was evaluated in ten in vitro tests and in four in vivo tests. The in vitro tests comprise four bacterial reverse mutation tests (Simmon 1975; Rogers-Back et al. 1988; 1979; Wudl 1980), three in vitro mammalian cell gene mutation tests (Allied Chemical 1979; Stetka 1981; Rogers-Back et al. 1988), an unscheduled DNA synthesis (UDS) test (Williams 1985), asister chromatic exchange (SCE) test (Stetka 1981) and an alkaline elution test (Williams 1980). The four in vivo study reports comprise a sex-linked recessive lethal test (Brewen 1981), an in vivo SCE (Stetka 1981), an in vivo cytogenetic test (Brewen 1981) and a mouse dominant lethal test (Wudl 1980).

Four bacterial reverse mutation tests were conducted (Wudl 1980; Rogers-Back et al. 1988; Simmon 1975; Allied Chemical 1979). The results are summarized in the table below.

 

	TA98		TA100		TA1535		TA1537		TA1538
	- S9	+S9	-S9	+S9	-S9	+S9	-S9	+S9	-S9	+S9
Simmon 1975	-	-	-	-	-	-	-	-	-	-
Allied Chemical 1979	-	-	-	-	+	+	-	-	-	-
Wudl 1980	nc		-	-	+	+	nc		nc
Rogers-Back et al. 1988	-	-	-	-	-	-	-	-	-	-

nc: not conducte

In two tests (Simmon 1975; Rogers-Back et al. 1988) all tested Salmonella typhimurium strains (TA98, TA100, TA1535, TA1538) scored negative with and without metabolic activation. In the two other tests (Allied Chemical 1979; Wudl 1980), one strain, TA1535, scored positive. S. typhimurium TA1535 has a GC base pair at the primary reversion site and is able to detect base-pair substitutions. A bacterial strain (e.g. TA102) that detects cross-linking agents was not included in the tests.

 

Three in vitro mammalian gene mutation studies were performed. Two studies (1979; Stetka 1981) used Chinese Hamster Ovary (CHO) cells to check the ability of AAO to induce mutations in the HPRT1 gene. A third study (Rogers-Back et al. 1988) used lymphoma cells to evaluate the mutation rate in the tk gene.

In the most recent HPRT study (Stetka 1981), the test compound was applied only without metabolic activation. It was concluded that AAO does not cause mutations at the HPRT locus in CHO cells under the conditions of this assay while the positive control generated a clear positive dose response. In the other HPRT study (1979), sporadic non-reproducible positive responses were observed at various dose levels of AAO. There was no clear demonstration of a dose-response.

In the mouse lymphoma L5178Y TK+/- assay (Rogers-Back et al. 1988), AAO was mutagenic in the absence and presence of metabolic activation.

 

An unscheduled DNA synthesis (UDS) test was performed with GM38 fibroblast and primary Syrian hamster embryo (SHE) cells (Williams 1985). The UDS test measures the DNA repair synthesis after excision and removal of a stretch of DNA containing the region of damage induced by chemical or physical agents. AAO did not reproducibly induce UDS in these mammalian cells in the dose range 0.01-10 mg/mL.

 

A sister chromatic exchange (SCE) test was conducted to detect reciprocal exchanges of DNA between two sister chromatids of a duplicating chromosome. Analysis of the results of this assay indicates that AAO induces SCEs both with and without metabolic activation (Stetka 1981). AAO is, however, a very weak SCE-inducer, as not even a doubling of the background SCE frequency was observed.

An alkaline elution test with and without the use of cytosine-1-β-D-arabinofuranoside (ara-C)was performed (Williams 1980). AAO alone did not reproducibly produce atypical alkaline elution patterns (a measure of DNA damage). DNA strand breakage was detected when AAO was incubated in the presence of ara-C to prevent resealing of strand breaks produced during DNA repair. A dose-response occurred under these conditions corresponding to a frequency of about 4-40 x 10^-8 breaks per nucleotide or 400-4000 breaks per cell during 4 h incubation.

 

Overall, these in vitro results show no or a low level of DNA damage, which is repairable as judged by the alkaline elution experiments.

 

AAO tested negative in all four conducted in vivo tests, comprising two somatic (SCE (Stetka 1981) and cytogenetic test (Brewen 1981)) and two heritable germ cell mutagenicity tests (sex-linked recessive lethal (Brewen 1981) and mouse dominant lethal test (Wudl 1980)).

The rapid metabolisation and elimination observed in the toxicokinetic study and the low mutagenic potential of AAO observed in some of the in vitro tests provide an explanation for the non mutagenicity of AAO in all the conducted in vivo tests.

Since AAO tested negative in all four in vivo mutagenicity tests, including two somatic and two heritable germ cell mutagenicity tests, AAO is not classified as a germ cell mutagen.

Justification for selection of genetic toxicity endpoint
SLRD-1981 is selected as the key study regarding gene mutation.
For chromosome aberrations; cytogenetics mouse_1981 is the key study.

Justification for classification or non-classification

Since AAO tested negative in all four in vivo mutagenicity tests, including two somatic and two heritable germ cell mutagenicity tests, classification as a germ cell mutagen is not required.