2-nitrothiophene

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Fluctuation test, Klebsiella pneumoniae ur- pro-, lowest concentration that was mutagenic: 50 µmol/L

Plate-incorporation test, Salmonella typhimurium TA100 without metabolic activation, lowest concentration that was mutagenic: 2 µmol/L

Link to relevant study records

Reference

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Principles of method if other than guideline:

no guideline available

GLP compliance:

no

Type of assay:

other: Base-pair substitution, Fluctuation test and reverse mutation assay

Species / strain / cell type:

other: Klebsiella pneumoniae

Details on mammalian cell type (if applicable):

ur- pro-

Species / strain / cell type:

S. typhimurium TA 100

Metabolic activation:

without

Test concentrations with justification for top dose:

fluctuation test 0.02, 0.05, 0.1, 0.2, 0.5 mmol/L broth
plate-incorporation test 0, 0.001, 0.002, 0.005, 0.01, 0.02, 0.05, 0.1 mmol/L top agar

Details on test system and experimental conditions:

Fluctuation test:
Fluctuation tests (Luria and Delbrück, 1943) were carried out as described previously (Voogd et al., 1979, 1980). As test organisms, a Klebsiella pneumoniae mutant, requiring uracil and proline as growth factors was used. In this fluctuation test, nutrient broth containing the substance under investigation and seeded with 100 bacteria/mL was divided into 105 portions of equal volume in sterile culture tubes. With Klebsiella pneumoniae the volume of each portion was 2.5 ml. After incubation during 20 h at 37°C the total number of streptomycin-resistant (including streptomycin-dependent) bacteria was determined in 100 portions by the pour-plate technique. Nutrient agar (pH 7.5) supplemented with streptomycin (100 µg/mL) was used. These plates were incubated for 3 days at 37°C. The number of bacteria present in the 5 remaining tubes was determined by using nutrient agar without streptomycin.
If mutants were present in more than 90 cultures, the number of mutants in the median culture was used to estimate the mutation frequency according to Lea and Coulson (1949). In this case the formula M = m/(N x V) was used in which m = number of mutations in the median culture.

Plate-incorporation test:
Furthermore, the plate-incorporation test developed by Ames et al. (1975) was used with Salmonella lyphimurium TA100. The strains were kindly provided by Dr. B.N. Ames. No metabolic activation was applied. On each plate 3 ml of top agar, in which the compound under investigation was present, was added to 20 ml of the selection medium. The compounds were dissolved in dimethyl sulfoxide.
With Salmonella typhimurium TA100 the investigated compound was considered to be mutagenic if the number of revertants on the selection plates was at least 1.5 X the number of revertants on the controi plates. Furthermore, some dose-response relationship should be apparent. To each plate (containing 20 mL of agar) 3 mL of top agar were added,. The test was done in triplicate.

Species / strain:

S. typhimurium TA 100

Metabolic activation:

without

Genotoxicity:

positive

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

not specified

Untreated negative controls validity:

not specified

True negative controls validity:

not specified

Positive controls validity:

not specified

Species / strain:

other: Klebsiella pneumoniae

Metabolic activation:

without

Genotoxicity:

positive

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

not specified

Untreated negative controls validity:

not specified

True negative controls validity:

not specified

Positive controls validity:

not specified

Conclusions:

For 2 -nitrothiophene the lowest concentration that was mutagenic to Klebsiella pneumoniae in the fluctuation test was 0.05 mmole/L (50 µmol/L) broth and to Salmonella typhimurium TA100 in the plate-incorporation test it was 0.002 mmole/L (2 µmol/L) top agar, respectively.

Executive summary:

The mutagenic potential of the test item to induce base-pair substitution in bacteria was investigated in a fluctuation test with Klebsiella pneumonia ur- pro- and in a plate-incorporation test with Salmonella typhimurium TA100 without metabolic activation.

For 2 -nitrothiophene the lowest concentration that was mutagenic to Klebsiella pneumoniae in the fluctuation test was 0.05 mmole/L broth and to Salmonella typhimurium TA100 in the plate-incorporation test it was 0.002 mmole/L top agar, respectively.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (positive)

Genetic toxicity in vivo

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Genetic toxicity in vitro bacteria

The mutagenic potential of the test item to induce base-pair substitution in bacteria was investigated in a fluctuation test with Klebsiella pneumonia ur- pro- and in a plate-incorporation test with Salmonella typhimurium TA100 without metabolic activation.

For 2 -nitrothiophene the lowest concentration that was mutagenic t oKlebsiella pneumoniae in the fluctuation test was 0.05 mmole/L (50 µmol/L) broth and to Salmonella typhimurium TA100 in the plate-incorporation test it was 0.002 mmole/L (2 µmol/L) top agar, respectively.

Genetic toxicity in silico

Profiling

The registered substance was screened for mutagenicity with the OECD QSAR Toolbox v4.3.1. The following profilers were evaluated:

DNA alerts for AMES by OASIS v1.7 (LMC, Bulgaria)

DNA alerts for CA and MNT by OASIS v1.2 (LMC, Bulgaria)

DNA binding by OASIS v1.6 (LMC, Bulgaria)

in vitro mutagenicity (Ames test) alerts by ISS v2.4 (ISS, Italy)

in vivo mutagenicity (Micronucleus) alerts by ISS v2.4 (ISS, Italy)

DNA binding by OECD v2.3 (Liverpool John Moores University, UK)

The presented profilers revealed alerts for mutagenicity. As mechanisms for DNA binding the formation of electrophilic nitrenium ion which is capable of reacting with DNA via an SN1 mechanism and the formation of DNA reactive oxygen species were identified.

Prediction

Ames mutagenicity of the registered substance was predicted with the QSAR model SciQSAR v.3.1.00 implemented in the OECD QSAR Toolbox v4.3.1. The prediction is positive. It falls within the applicability of the model. This prediction is in accordance with alerts for DNA binding identified by the respective profilers in the OECD QSAR Toolbox v4.3.1.

Justification for classification or non-classification

As the test item showed mutagenic potential by inducing base-pair substitution in bacteria in an in vitro assay, the test substance is classified as H341 Cat. 2 ( Germ cell mutagenicity) for safety reasons in accordance with Regulation (EC) No 1272/2008. This result is supported by positive alerts for Ames mutagenicity and predicted DNA binding alerts in QSAR modeling.