Diammonium 2,2'-dithiodiacetate

Endpoint summary

Description of key information

Based on read-across form the source substance NaTG, the targes substance DADTDG shows an oral NOAEL of 38 mg/kg bw/day, while the dermal LOAEL for local effects in rats is determinde to be 21 mg/kg bw/day and the dermal NOAEL for systemic effects is determined to be >=341 mg/kg bw/day.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Justification for type of information:

This scenario covers the analogue approach for which the read-across hypothesis is based on the assumption, that source and target substance form common metabolites. This approach serves to use existing data on repeated-dose toxicity and reproductive toxicity endpoints of the source substance to predict the property that would be observed in a study with the target substance if it were to be conducted.

It is very likely, that the main metabolite of the source substance sodium thioglycolate is the oxidized form which is structural and chemical similar to the anion of the target substance DADTDG. 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.

Differences regarding molecular weight of source and target substance will most likely lead to lower resorption and distribution of the target substance compared to the source. Therefore, corrections for molecular weight are applied.

For detailed information see section 13.2.

Reason / purpose for cross-reference:

read-across: supporting information

Reason / purpose for cross-reference:

read-across source

Dose descriptor:

NOEL

Effect level:

13 mg/kg bw/day (actual dose received)

Based on:

act. ingr.

Sex:

male/female

Basis for effect level:

other:

Dose descriptor:

NOAEL

Effect level:

38 mg/kg bw/day (actual dose received)

Based on:

act. ingr.

Sex:

male/female

Basis for effect level:

clinical biochemistry

Remarks on result:

other: corrected for molecular weight differences

Dose descriptor:

LOAEL

Effect level:

114 mg/kg bw/day (actual dose received)

Based on:

act. ingr.

Sex:

male/female

Basis for effect level:

clinical biochemistry

histopathology: non-neoplastic

mortality

Remarks on result:

other: corrected for molecular weight differences

Conclusions:

Based on the read across hypothesis, DADTDG is expected to show clinical biochemical effects as well as microscopic changes in the liver at dose levels of 114 mg/kg bw/ day or higher (LOAEL). The NOAEL was determined to be 38 mg/kg bw/day, while the NOEL is determined to be 13 mg/kg bw/day. All these values were corrected for molecular weight differences to the source substance.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

38 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: dermal

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Justification for type of information:

This scenario covers the analogue approach for which the read-across hypothesis is based on the assumption, that source and target substance form common metabolites. This approach serves to use existing data on repeated-dose toxicity and reproductive toxicity endpoints of the source substance to predict the property that would be observed in a study with the target substance if it were to be conducted.

It is very likely, that the main metabolite of the source substance sodium thioglycolate is the oxidized form which is structural and chemical similar to the anion of the target substance DADTDG. 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.

Differences regarding molecular weight of source and target substance will most likely lead to lower resorption and distribution of the target substance compared to the source. Therefore, corrections for molecular weight are applied.

For detailed information see section 13.2.

Reason / purpose for cross-reference:

read-across: supporting information

Reason / purpose for cross-reference:

read-across source

Dose descriptor:

LOAEL

Remarks:

local effects

Effect level:

21 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

Remarks on result:

other: corrected for molecular weight differences

Dose descriptor:

NOAEL

Remarks:

systemic effects

Effect level:

>= 341 mg/kg bw/day

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

Remarks on result:

other: corrected for molecular weight differencea

Conclusions:

Based on the read-across hypothethis, effects of repeated dose application of the test substance via dermal route should be comparable to the effects observed with the source substance. After correction for molecular weight differences, the NOAEL for systemic effects of the target substance was determined to be higher or equal to 341 mg/kg bw/day. The determined LOAEL for local effects is 21 mg/kg bw/day.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

341 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Additional information

The subchronic toxicity of sodium thioglycolate (NaTG) was evaluated by oral and dermal administrations. In this context the main metabolite of these studies, the anion of DADTDG, can be considered as co-tested in all described studies here.

The potential toxicity of NaTG was evaluated following repeated oral administration for 13 weeks, according to OECD Guideline 408. The test item was administered daily by gavage to Sprague-Dawley rats (10 Males and 10 Females), at the dose-levels of 0, 7, 20, 60 mg/kg/d during 90 days. An additional group of 6 male and 6 female rats was concurrently treated with the vehicle and high dose level; this group was retained following the final exposure for a further 4 weeks to assess the reversibility of any adverse findings.

Body weights were recorded pre-test, weekly and at death or prior to necropsy. Animals were observed twice daily for mortality ant clinical signs. Detailed clinical observations were made once before the beginning of the treatment period, and then once a week until the end of the study. During week 11, this examination was included in the detailed clinical observation of the Functional Observation Battery for all animals except recovery animals. Whole blood, serum and plasma were sampled just prior to necropsy and analysed for related haematological and clinical chemistry parameters. All animals were examined for gross pathology, and organs were weighed and submitted to histopathology.

At 60 mg/kg/day, one female was prematurely sacrificed on day 14 due to humane reasons, and one male was found dead on day 90. Death was attributed to the test item treatment. At 60 mg/kg/day, changes were observed; they were also noted in the animals sacrificed on schedule. These changes were found in the heart of the dead male, the kidneys of the female sacrificed for humane reasons, and the liver and thymus of both animals. Hypersalivation, piloerection, abnormal growth of teeth, alopecia and/or areas of thinned hair were transiently observed in some of the surviving animals. At laboratory investigations, marked panleucopenia was noted (all the white blood cell subtypes were affected), with high mean red blood cell count, hemoglobin concentration, packed cell volume and mean prothrombin time for males and females. Hypoglycemia was noted in males and females, associated with high urea (males and females) and creatinine (males only) levels and low chloride levels (only female). Other blood perturbation were observed (High fat acid level -in males and females- high aspartate aminotransferase -males only- and high ALAT -males and females). Thioglycolate-related changes were also noted in the liver of males and females, the heart of males and the kidneys of females. Considering the treatment-related effects observed at 60 mg/kg bw/d -mortality, microscopic changes in the heart of males, kidney of females, and liver of males, and the changes in some haematological and blood chemistry parameters - this dose level is regarded as clearly toxic dose level.

At 20 mg/kg/day, in the absence of treatment related histopathological changes, the reversible modifications of some biochemical parameters observed in the females are not considered to be adverse. At 7 mg/kg/day, the test item did not elicit any signs of toxicity. Consequently, under the experimental conditions, the No-Observed-Adverse-Effect-Level (NOAEL) is 20 mg/kg/day (Rousseau, 2008).

NaTG (99% pure) was administered dermally to F344/N rats andB₆C₃F₁mice (10/sex/dose level) following a protocol comparable to the OECD guideline 411. Rats and mice were given NaTG in a vehicle of 95% ethanol:deionized water (1:1) by dermal application 5 days per week, for 13 weeks. Doses were appliedin a fixed dose volume of 0.5 ml/kg bw to rats or 0.2 ml/kg bw to mice. Rats were administered 0, 11.25, 22.5, 45, 90, or 180 mg NaTG/kg bw/d and mice 0, 22.5, 45, 90, 180 or 360 mg NaTG/kg bw/d. In addition, 2 groups of 10 rats per sex/group were dosed with 0 or 180 mg/kgbw/d for 21 days and used for clinical chemistry and hematology estimations on day 4 and day 21 and then disposed of without further examination. Throughout the study, the animals were checked twice a day for mortality and clinical signs. Formal clinical observations were performed and recorded weekly. Body weight and food consumption were recorded weekly. Clinical chemistry and hematology was performed on the main groups of rats at termination, and hematology on the mice at termination. Heart, kidney, liver, lung, spleen, tests, thymus and thyroid/parathyroid weights were measured at termination, with a complete histopathologic examination inclusive of gross lesions of the high dose and control groups. Food consumption and clinical chemistry parameters including 3-hydroxybutyrate, free fatty acids and total cholesterol were also measured.

In the rats, all animals survived the 13-week administration. A slight decrease of the mean body weight gain was observed in males treated with 90 and 180 mg/kg bw/d, respectively. The mean food consumption was not affected by the treatment. Significant clinical observations noted in both sexes were limited to dermal irritation, thickened skin and ulcerations at the site of application. In males and females, the incidence of dermal irritation at the site of application was 10/10 for all five-treatment groups. Thickening of the skin at the site of application was observed in 1 and 2 males from the 90 and 180 mg/kgbw/d dose groups and in 3, 10 and 10 females from the 45, 90 and 180mg/kgbw/d dose groups, respectively. Ulceration at the site of application was observed in 1, 1, 5 and 8 male rats from the 11.25, 22.5, 90 and 180 mg/kgbw/d dose groups and 10 females from each of the 90 and 180 mg/kgbw/d dose groups, respectively. All other clinical observations noted during the study were not considered to be biologically significant.

There were slight, but statistically significant, changes in the relative kidneys weight in males at 90 and 180 mg/kg bw/d and in females at 180 mg/kg bw/d, in the absolute and relative liver weights in males at 45 mg/kgbw/d, in the relative spleen weight in males at 90 mg/kg bw/d, in the relative testes weight at 90 and 180 mg/kg bw/d and in the thyroid/parathyroid relative weight in females at 22.5 mg/kg bw/d, but these effects were not dose responsive or considered to be biologically significant.

There were limited statistically significant differences at termination in some blood chemistry and hematology results when compared to the control group, but these effects were not dose responsive nor considered to be biologically significant.

The only treatment related gross and microscopic lesions were at site of application with epidermal and sebaceous gland hyperplasia, and hyperkeratosis with severity comparable between all treated groups. There were no other treatment related microscopic lesions. Thus, no target organ for toxicity was identified (other than skin at site of application).

The Lowest-Observed-Effect-Level (LOEL) at the application site was 11.25 mg/kg bw/d based on histopathologic examination. There was no No-Observed-Effect-Level (NOEL) at the application site. The NOAEL for systemic toxicity can be estimated to be higher than 180 mg/kg bw/d.

In the mice, all animals survived the 13 weeks administration. Body weights and food consumption were not affected by the treatment in either sex during the course of the study. The only clinical observation related to treatment was skin irritation at site of application in 6/10 males at 360 mg/kg bw/day but not in females.

There was a slight increase of the absolute and relative heart weight at 180 and 360 mg/kg bw/d male and female, of the absolute kidney weight in females at 180 and 360 mg/kg bw/d, and of the absolute and relative liver weight in males at 180 and 360 mg/kg bw/d and in females at all doses from 45 mg/kg bw/d upwards.

Haematology showed no biologically significant changes in males, but in females there was some small decrease, in red blood cells at 22.5, 45, 180 and 360 mg/kg bw/d and hemoglobin levels at 22.5, 45, and 360 mg/kg bw/d.

There were no significant gross lesions. On microscopic histopathology, skin lesions were observed at the site of application in males and females at all dose levels, with the exception of the 22.5 mg/kgbw/ddose group males with minimal to moderate hyperplasia of the epidermis accompanied, in some animals, by sebaceous gland hyperplasia, hyperkeratosis, dermal inflammation and/or parakeratosis. The severity of the changes was comparable between all treatment groups in both the male and female mice. Thus, no target organ for toxicity was identified (other than skin at the site of application).

The Lowest-Observed-Effect-Level (LOEL) at the application site was 45 mg/kg bw/d based on histopathologic examination. The No-Observed-Effect-Level (NOEL) at the application site was 22.5 mg/kg bw/d. The NOAEL for systemic toxicity can be estimated to higher than 360 mg/kg bw/d.

There is no information available on inhalation toxicity after repeated exposure to thioglycolic acid or its salts.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
Read-across to thioglycolate anion studies which can be served as a surrogate for DADTDG. A lot of repeat-dose and toxicity to reproduction GLP and OECD TG studies are available for thioglycolic acid and its salts. The main metabolite of the thioglycolate is the oxidized form which is structural and chemical similar to the anion of DADTDG. Therefore, DADTDG can be considered as co-tested in all mentioned studies under section 7.5 and 7.8. Due to the metabolism of thioglycolate and its salts, repeat-dose toxicity as well as toxicity to reproduction for DADTDG does not need to be conducted.

Justification for selection of repeated dose toxicity dermal - systemic effects endpoint:
NTP study comparable to OECD TG study: Read-across to thioglycolate anion studies which can be served as a surrogate for DADTDG. A lot of repeat-dose and toxicity to reproduction GLP and OECD TG studies are available for thioglycolic acid and its salts. The main metabolite of the thioglycolate is the oxidized form which is structural and chemical similar to the anion of DADTDG. Therefore, DADTDG can be considered as co-tested in all mentioned studies under section 7.5 and 7.8. Due to the metabolism of thioglycolate and its salts, repeat-dose toxicity as well as toxicity to reproduction for DADTDG does not need to be conducted.

Repeated dose toxicity: via oral route - systemic effects (target organ) cardiovascular / hematological: hematopoiesis; digestive: liver

Repeated dose toxicity: dermal - systemic effects (target organ) other: skin

Justification for classification or non-classification

The substance is not classified for STOT since the mortality observed at 60 mg/kg bw/day is already covered by the classification for acute oral toxicity. Sub-lethal effects that would warrant a STOT classification were not found.

Therefore, also the main metabolite, the dithiodiglycolic anion, co-tested in all studies, is not considered to cause STOTs and based on this data, no classification for DADTDG is needed in this context.