Registration Dossier

Administrative data

Endpoint:
basic toxicokinetics, other
Type of information:
other: expert statement
Adequacy of study:
key study
Study period:
2018-03-07
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Expert Statement, no study available

Data source

Reference
Reference Type:
other: Expert Statement
Title:
Unnamed
Year:
2018
Report Date:
2018

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Expert Statement following recommendations of ECHA Guidance Document on Information Requirement and Chemical Safety Assessment Chapter R7c (2017).
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:
Bioavailability via oral route is strongly linked to physico-chemical properties of the substance (ECHA Guidance, 2017). Generally, absorption in the gastrointestinal tract (GIT) is favored for substances with a molecular weight below 500 g/mol and a logPow in the range of -1 to 4. The test substance itself having a molecular weight of 422.61 g/mol would therefore be on the edge of being favored for absorption. However, the test item is hydrolytically unstable and will degrade rapidly to its hydrolysis products within an aqueous environment such as body fluids. Therefore, molecular weights of hydrolysis products, i. e. 144.17 and 170.3 g/mol, have to be taken into account. Both indicate well absorption. In addition, logPow values of 1.36 (Aldehyde A) and 0.99 (IPDA) are also meeting the general criteria for becoming readily bioavailable.
The above considerations are supported by experimental toxicity data. Even though no signs of toxicity were observed in an acute oral toxicity study in rats with the test item, repeated administration revealed signs of systemic toxicity indicating that the substance or its hydrolysis products is readily absorbed via the GIT.
In the acute oral toxicity study with female rats, the test item did not induce any mortality, leading to an LD50 of > 2000 mg/kg bw. Diarrhoea was observed as clinical signs only. No pathological changes could be observed after the observation period of 14 days.
Repeated administration of the test item to rats revealed signs of systemic toxicity at 1000 mg/kg bw. These findings indicate that the compound or its hydrolysis products becomes bioavailable and are of low toxicity.
No data on repeated dose toxicity are available for Aldehyde A. Based on an acute oral toxicity study Aldehyde A did not induce any signs of toxicity or mortality following administration of the limit dose of 2000 mg/kg bw indicating its rather non-toxic nature when absorbed.
IPDA is classified for acute oral and dermal toxicity, giving indication that it is readily absorbed via both routes. Further, a 13-week oral toxicity study with IPDA according to OECD TG 408 revealed no treatment-related clinical signs, symptoms or mortality. However, food and water consumption and body weight gain were significantly reduced in high dose animals. Further, morphological alterations in the kidneys were recorded supporting the fact that the substance becomes bioavailable via the oral route.

Due to its low vapour pressure (<0.01 Pa at 20 °C) and high boiling point (> 150 °C) it is unlikely that the test item will be available as a vapour. However, if it was the case absorption via inhalation route is considered possible due to the rapid hydrolysis upon contact with mucosal membranes of the respiratory tract. This would enable uptake of hydrolysis products which are smaller in molecular size and of better water solubility facilitating absorption across the respiratory tract epithelium by passive diffusion.

Similarly, based on physicochemical properties of the test item penetration through the skin is assumed to be low. It is generally accepted that if a compound’s water solubility falls between 1-100 mg/L, absorption can be anticipated to be low to moderate. This assumption based on the physicochemical properties of the test item is further supported by the results achieved from the LLNA showing skin sensitising properties. Thus, a small amount of the compound or its hydrolysis products might penetrate the skin. The test item is not skin or eye irritating, thus penetration by dermal damage may be excluded. However, since IPDA one of the hydrolysis products is classified for acute dermal toxicity, the absence of pronounced clinical signs indicate low amount of hydrolysis when administered on the bare skin. Further, no skin or eye irritation properties were obtained for the test item. In contrast to its hydrolysis products IPDA, being both skin and eye corrosive and Aldehyde A being eye irritating. Therefore, it is anticipated that hydrolysis of the test item on the skin does not take place in a significant amount, since effects as expected from its hydrolysis products were not observed. This further supports the assumption that the test item itself will not be readily absorbed via the skin. However, the test item was found to be a skin sensitizer indicating that at least to some little extent the test item itself or its hydrolysis product was absorbed.

Taken together, physicochemical properties and experimental data indicate bioavailability of the test item or rather its hydrolysis products via oral and dermal route albeit to a small amount.
Details on distribution in tissues:
Assuming that the test item or its hydrolysis products become bioavailable to the organism following oral, dermal or inhalation intake, they may be distributed into the body fluids due to moderate to high hydrophilicity and low logPow values of both hydrolysis products. In turn the extracellular concentration may be higher than intercellular concentration. As outlined before, it is expected that the test item itself does not reach the blood system before being hydrolysed to a significant extend. The physicochemical properties of the hydrolysis products favour systemic distribution. The results from the repeated dose toxicity study indicate that the kidneys are the primary target organs affected by IPDA. Due to the rapid hydrolysis reaction in the body, it is unlikely that the test item can bioaccumulate. Moreover, both hydrolysis products are highly water soluble and have a low log Pow value and are thus also of no concern for bioaccumulation.
Details on excretion:
As discussed above, the test item will hydrolyse rapidly in an aqueous environment and will probably not be excreted as such. Due to their small molecular weight and moderate to well water solubility both hydrolysis products are rather excreted via urine than faeces. Generally, in the rat renal excretion is facilitated for water-soluble molecules with a molecular weight below 300 g/mol.

Metabolite characterisation studies

Details on metabolites:
Based on the chemical structure of the test item and its hydrolysis products they may be metabolized by Phase I enzymes while undergoing functionalization reactions aiming to increase the compound’s hydrophilicity. Furthermore, Phase II conjugation reactions may covalently link an endogenous substrate to the parent compound or the Phase I metabolite in order to ultimately facilitate excretion.
Metabolism to more toxic metabolites is not expected, neither for the parent nor for the degradation products, based on the results obtained in the in vitro bacterial reverse mutation test (Ames test) as well as the HPRT and in the chromosome aberration test in the presence of a metabolic activation system.
The above considerations are supported by QSAR predictions. Both hydrolysis products were evaluated and possible metabolites (rat liver metabolism) were predicted. Aldehyde A is predicted to become hydroxylised, probably by Phase I CYP 450 enzymes, increasing its hydrophilicity. The same applies for IPDA, where hydroxylation is also followed by another oxidation and may take place at several C-atoms in the molecule. In addition, de-methylation of the terminal CH3- groups is predicted.

Applicant's summary and conclusion

Conclusions:
Based on its physicochemical characteristics, particularly water solubility and logPow absorption via oral, inhalation and dermal route is expected to be low for the test item itself. However, due to the rapid hydrolysis reaction in contact with aqueous solutions its hydrolysis products are considered to become bioavailable via the oral route and albeit to a less extend via the dermal route. Based on their physicochemical properties the test item itself as well as its hydrolysis products are unlikely to bioaccumulate. Hydrolytic and metabolic conversion is expected and conjugation of Phase I-metabolites may further increase hydrophilicity. Excretion via urine is assumed to be the main excretion pathway of degradation products and metabolites formed due to their expected lower molecular weight and higher water solubility.
Executive summary:

Toxicokinetics of Sika Hardener AI

Sika Hardener AI is an almost colourless liquid at ambient conditions with an ester-like odour. Its molecular weight is 422.61 g/mol. The substance hydrolyses rapidly (within minutes) upon contact with water. Therefore, water solubilities of the two hydrolysis products are the more reasonable parameter for further toxicokinetic considerations. A water solubility of 59.2 mg/L at 25 °C was determined for Aldehyde A and >492 g/L for Isophorone Diamine (IPDA). The logPow values were determined to be 1.36 and 0.99 for Aldehyde A and Isophorone Diamine, respectively. The vapour pressure of Sika Hardener AI is very low (0.00054 Pa at 20 °C).

Absorption

Bioavailability via oral route is strongly linked to physico-chemical properties of the substance (ECHA Guidance, 2017). Generally, absorption in the gastrointestinal tract (GIT) is favored for substances with a molecular weight below 500 g/mol and a logPow in the range of -1 to 4. The test substance itself having a molecular weight of 422.61 g/mol would therefore be on the edge of being favored for absorption. However, the test item is hydrolytically unstable and will degrade rapidly to its hydrolysis products within an aqueous environment such as body fluids. Therefore, molecular weights of hydrolysis products, i. e. 144.17 and 170.3 g/mol, have to be taken into account. Both indicate well absorption.In addition, logPow values of 1.36 (Aldehyde A) and 0.99 (IPDA) are also meeting the general criteria for becoming readily bioavailable.

The above considerations are supported by experimental toxicity data. Even though no signs of toxicity were observed in an acute oral toxicity study in rats with the test item, repeated administration revealed signs of systemic toxicity indicating that the substance or its hydrolysis products is readily absorbed via the GIT.

In the acute oral toxicity study with female rats, the test item did not induce any mortality, leading to an LD50 of > 2000 mg/kg bw. Diarrhoea was observed as clinical signs only. No pathological changes could be observed after the observation period of 14 days.

Repeated administration of the test item to rats revealed signs of systemic toxicity at 1000 mg/kg bw.These findings indicate that the compound or its hydrolysis products becomes bioavailable and are of low toxicity.

No data on repeated dose toxicity are available for Aldehyde A. Based on an acute oral toxicity study Aldehyde A did not induce any signs of toxicity or mortality following administration of the limit dose of 2000 mg/kg bw indicating its rather non-toxic nature when absorbed. IPDA is classified for acute oral and dermal toxicity, giving indication that it is readily absorbed via both routes. Further, a 13-week oral toxicity study with IPDA according to OECD TG 408 revealed no treatment-related clinical signs, symptoms or mortality. However, food and water consumption and body weight gain were significantly reduced in high dose animals. Further, morphological alterations in the kidneys were recorded supporting the fact that the substance becomes bioavailable via the oral route.

Due to its low vapour pressure(<0.01 Pa at 20 °C)and high boiling point (> 150 °C) it is unlikely that the test item will be available as a vapour. However, if it was the case absorption via inhalation route is considered possible due to the rapid hydrolysis upon contact with mucosal membranes of the respiratory tract. This would enable uptake of hydrolysis products which are smaller in molecular size and of better water solubility facilitating absorption across the respiratory tract epithelium by passive diffusion.

Similarly, based on physicochemical properties of the test itempenetration through the skin is assumed to be low.It is generally accepted that if a compound’s water solubility falls between 1-100 mg/L, absorption can be anticipated to be low to moderate. This assumption based on the physicochemical properties of the test item is further supported by the results achieved from the LLNA showing skin sensitising properties. Thus, a small amount of the compound or its hydrolysis products might penetrate the skin. The test item is not skin or eye irritating, thus penetration by dermal damage may be excluded. However, since IPDA one of the hydrolysis products is classified for acute dermal toxicity, the absence of pronounced clinical signs indicate low amount of hydrolysis when administered on the bare skin. Further, no skin or eye irritation properties were obtained for the test item. In contrast to its hydrolysis products IPDA, being both skin and eye corrosive and Aldehyde A being eye irritating. Therefore, it is anticipated that hydrolysis of the test item on the skin does not take place in a significant amount, since effects as expected from its hydrolysis products were not observed. This further supports the assumption that the test item itself will not be readily absorbed via the skin. However, the test item was found to be a skin sensitizer indicating that at least to some little extent the test item itself or its hydrolysis product was absorbed.

Taken together, physicochemical properties and experimental data indicate bioavailability of the test item or rather its hydrolysis products via oral and dermal route albeit to a small amount.

Distribution

Assuming that the test item or its hydrolysis products become bioavailable to the organism following oral, dermal or inhalation intake, they may be distributed into the body fluids due to moderate to high hydrophilicity and low logPow values of both hydrolysis products. In turn the extracellular concentration may be higher than intercellular concentration. As outlined before, it is expected that the test item itself does not reach the blood system before being hydrolysed to a significant extend. The physicochemical properties of the hydrolysis products favour systemic distribution. The results from the repeated dose toxicity study indicate that the kidneys are the primary target organs affected by IPDA. Due to the rapid hydrolysis reaction in the body, it is unlikely that the test item can bioaccumulate. Moreover, both hydrolysis products are highly water soluble and have a low log Pow value and are thus also of no concern for bioaccumulation.

Metabolism

Based on the chemical structure of the test item and its hydrolysis products they may be metabolized by Phase I enzymes while undergoing functionalization reactions aiming to increase the compound’s hydrophilicity. Furthermore, Phase II conjugation reactions may covalently link an endogenous substrate to the parent compound or the Phase I metabolite in order to ultimately facilitate excretion.

Metabolism to more toxic metabolites is not expected, neither for the parent nor for the degradation products, based on the results obtained in thein vitrobacterial reverse mutation test (Ames test) as well as the HPRT and in the chromosome aberration test in the presence of a metabolic activation system.

The above considerations are supported by QSAR predictions. Both hydrolysis products were evaluated and possible metabolites (rat liver metabolism) were predicted.

Aldehyde A is predicted to become hydroxylised, probably by Phase I CYP 450 enzymes, increasing its hydrophilicity.

The same applies for IPDA, where hydroxylation is also followed by another oxidation and may take place at several C-atoms in the molecule. In addition, de-methylation of the terminal CH3- groups is predicted.

Excretion

As discussed above, the test item will hydrolyse rapidly in an aqueous environment and will probably not be excreted as such. Due to their small molecular weight and moderate to well water solubility both hydrolysis products are rather excreted via urine than faeces. Generally, in the rat renal excretion is facilitated for water-soluble molecules with a molecular weight below 300 g/mol.

Summary

Based on its physicochemical characteristics, particularly water solubility and logPow absorption via oral, inhalation and dermal route is expected to be low for the test item itself. However, due to the rapid hydrolysis reaction in contact with aqueous solutions its hydrolysis products are considered to become bioavailable via the oral route and albeit to a less extend via the dermal route. Based on their physicochemical properties the test item itself as well as its hydrolysis products are unlikely to bioaccumulate.Hydrolytic and metabolic conversion is expected and conjugation of Phase I-metabolites may further increase hydrophilicity. Excretion via urine is assumed to be the main excretion pathway of degradation products and metabolites formed due to their expected lower molecular weight and higher water solubility.