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Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

A study with the substance according to OECD 471 is planned to fil the identified data gap. Negative chromosomal abberation and gene mutation in mammalian cell studies are available for two and three category members respecitve. Based on the read-across hypothesis, BuMP is considered to be negative for chromosomal abberation as well as gene mutation in mammalian cells.

Link to relevant study records

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Endpoint:
in vitro gene mutation study in mammalian cells
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Justification for type of information:
There are no relevant variations in qualitative properties among source substances and the same potency is predicted for all target substances. This is Scenario 4 of the RAAF1. Substances MMP, BuMP, EHMP, iOMP, iC13MP, and ODMP are different alkyl esters of a common acid, 3-mercaptopropionic acid (3-MPA).
This scenario covers the category approach for which the read-across hypothesis is based on the assumption, that toxicity of compounds in this category are driven by a common toxophore. This approach serves to use existing data on genotoxicity, acute toxicity, repeated-dose toxicity and reproductive toxicity endpoints for substances in this category. For the REACH information requirement under consideration, the property investigated in studies conducted with different source substances is used to predict the property that would be observed in a study with the target substance if it were to be conducted. Similar properties are observed for the different source substances; this may include absence of effects for every member of the category.
There are differences in strength of the effects forming a regular pattern. This corresponds to Scenario 4 of the RAAF. The substances MMP, BuMP, EHMP, iOMP, iC13MP, and ODMP are esters of a common acid, 3-mercaptopropionic acid (3-MPA). All category members share the same mercaptopropionic acid moiety with one free SH group per MPA unit. The MPA unit with free SH is a prerequisite for this category.
The observed differences in effect levels (higher effect levels with increasing carbon chain length were observed in the available acute oral toxicity studies) are assumed to be mainly due to differences in molecular weight (corrections will be made for these differences) and decreasing bioavailability with increasing carbon chain length (no corrections are made for this effect; a worst-case approach is applied here, since based on the available data no exact quantification for bioavailability differences is possible at the moment).
It can be predicted with high confidence that the substances within this category will lead to the same type of effects. The main driver for toxicity is the free SH group of the MPA moiety.
Beside structural similarities and the common toxophore, the MPA moiety, category members are also likely to have similar metabolites. As explained in the Toxicokinetics section, substances are predicted to be rapidly hydrolysed into 3-MPA and the respective alcohol after absorption. According to low toxicity of the corresponding alcohols (Table 8), this would support the role of the MPA moiety as toxophore, as well as propose scenario 3 of the RAAF as applicable for this category approach. However, no experimental toxicokinetic data to support this hypothesis are available by now. To proof this hypothesis, simulated gastric acid hydrolysis studies, as well as in-vitro metabolism studies using liver microsomes will be conducted. Based on the results of these studies, scenario selection will be revaluated.

For detailed information refer to section 13.2.
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across: supporting information
Key result
Species / strain:
mouse lymphoma L5178Y cells
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
not examined
Positive controls validity:
valid
Key result
Species / strain:
mouse lymphoma L5178Y cells
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Positive controls validity:
other: The positive controls caused an increase in mutation frequency, but no clastogenic positive control (e.g., MMS) was used in the absence of S9.
Key result
Species / strain:
mouse lymphoma L5178Y cells
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Conclusions:
The category members 3-MPA, iOMP and MMP showed negative results in gene mutation assays in mammalian cells. Based on the category approach, BuMP is expected to show similar effects. Therefors, BuMP is considered not to induce gene mutation in mammalian cell.

As Toxikokinetic literature data indicate that after absorption rapid ester hydrolysis accurs to all category members, toxicokinetic in vitro studies are planned to gain better insight on toxicokinetic properties of the substances. Depending on the results of metabolism and simulated gastric acid hydrolysis studies, scenario selection will be revaluated.
Endpoint:
in vitro cytogenicity / chromosome aberration study in mammalian cells
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Justification for type of information:
There are no relevant variations in qualitative properties among source substances and the same potency is predicted for all target substances. This is Scenario 4 of the RAAF1. Substances MMP, BuMP, EHMP, iOMP, iC13MP, and ODMP are different alkyl esters of a common acid, 3-mercaptopropionic acid (3-MPA).
This scenario covers the category approach for which the read-across hypothesis is based on the assumption, that toxicity of compounds in this category are driven by a common toxophore. This approach serves to use existing data on genotoxicity, acute toxicity, repeated-dose toxicity and reproductive toxicity endpoints for substances in this category. For the REACH information requirement under consideration, the property investigated in studies conducted with different source substances is used to predict the property that would be observed in a study with the target substance if it were to be conducted. Similar properties are observed for the different source substances; this may include absence of effects for every member of the category.
There are differences in strength of the effects forming a regular pattern. This corresponds to Scenario 4 of the RAAF. The substances MMP, BuMP, EHMP, iOMP, iC13MP, and ODMP are esters of a common acid, 3-mercaptopropionic acid (3-MPA). All category members share the same mercaptopropionic acid moiety with one free SH group per MPA unit. The MPA unit with free SH is a prerequisite for this category.
The observed differences in effect levels (higher effect levels with increasing carbon chain length were observed in the available acute oral toxicity studies) are assumed to be mainly due to differences in molecular weight (corrections will be made for these differences) and decreasing bioavailability with increasing carbon chain length (no corrections are made for this effect; a worst-case approach is applied here, since based on the available data no exact quantification for bioavailability differences is possible at the moment).
It can be predicted with high confidence that the substances within this category will lead to the same type of effects. The main driver for toxicity is the free SH group of the MPA moiety.
Beside structural similarities and the common toxophore, the MPA moiety, category members are also likely to have similar metabolites. As explained in the Toxicokinetics section, substances are predicted to be rapidly hydrolysed into 3-MPA and the respective alcohol after absorption. According to low toxicity of the corresponding alcohols (Table 8), this would support the role of the MPA moiety as toxophore, as well as propose scenario 3 of the RAAF as applicable for this category approach. However, no experimental toxicokinetic data to support this hypothesis are available by now. To proof this hypothesis, simulated gastric acid hydrolysis studies, as well as in-vitro metabolism studies using liver microsomes will be conducted. Based on the results of these studies, scenario selection will be revaluated.

For detailed information refer to section 13.2.
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across: supporting information
Key result
Species / strain:
Chinese hamster lung fibroblasts (V79)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
xperiment I: > 1200 ug/ml (with and without S9 mix): Experiment II: > 1200 ug/ml with S9 mix; > 300 ug/ml without S9 mix
Key result
Species / strain:
lymphocytes: human
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Conclusions:
The category members 3-MAP and MMP showed negative results in in vitro chromosom abberation studies. Based on the category approach, BuMP is expected to show similar effects. Therefors, BuMP is considered not to induce chromosomal abbaration in mammalian cell.

As Toxikokinetic literature data indicate that after absorption rapid ester hydrolysis accurs to all category members, toxicokinetic in vitro studies are planned to gain better insight on toxicokinetic properties of the substances. Depending on the results of metabolism and simulated gastric acid hydrolysis studies, scenario selection will be revaluated.
Endpoint:
in vitro gene mutation study in bacteria
Data waiving:
other justification
Justification for data waiving:
other:
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Genetic toxicity in vivo

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

An Ames tests is planned for BuMP to fill the identified data gap.


Negative chromosomal aberration assays are available for MPA and MMP; An in-vitro chromosomal abberation assay is planned with EHMP to cover the range of alkyl chain length in this category and strengthen the hypothesis, that the esters do not lead to chromosomal aberration.
Negative mouse lymphoma assay are available for MPA, iOMP and MMP; No further studies on gene mutation in mammalian cells are planned.
The entirety of eventually available genotoxicity data in combination with the absence of structural alerts for genotoxicity in this category will be used to strengthen the weight of the evidence for non-genotoxicity.

Justification for classification or non-classification