N-[3-({[2,2-dimethyl-3-(morpholin-4-yl)propylidene]amino}methyl)-3,5,5-trimethylcyclohexyl]-2,2-dimethyl-3-(morpholin-4-yl)propan-1-imine

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics

Type of information:

other: Expert statement

Adequacy of study:

key study

Study period:

2014-05-06

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Expert statement, no study available

Qualifier:

according to guideline

Guideline:

other: Expert statement

Principles of method if other than guideline:

Expert statement

GLP compliance:

yes

Details on test animals or test system and environmental conditions:

not applicable

Details on exposure:

not applicable

Duration and frequency of treatment / exposure:

not applicable

Remarks:

Doses / Concentrations:
not applicable

No. of animals per sex per dose / concentration:

not applicable

Positive control reference chemical:

not applicable

Details on study design:

not applicable

Details on dosing and sampling:

not applicable

Statistics:

not applicable

Preliminary studies:

not applicable

Details on absorption:

Generally, oral absorption is facilitated for molecular weights below 500 g/mol. The relatively low water solubility may limit oral absorption by the inability of the substance to dissolve in the gastro-intestinal fluids, which in turn hinders contact with the mucosal surface. However, Sika Hardener MI will be hydrolysed after being in contact with an aqueous solution and the degradation products have physicochemical properties (higher water solubility) facilitating oral absorption. Administered without a vehicle in an acute oral toxicity study performed on rats, Sika Hardener MI lead to a LD50 of > 2000 mg/kg bw. Neither clinical signs during the entire study period nor pathological changes could be observed after the observation period of 14 days. Additionally, no adverse effects were observed in the sub-acute repeated dose toxicity study after oral administration. These findings indicate that the compound or its hydrolysis products do not become bioavailable or, in case of absorption, are of low toxicity.
Based on the low vapour pressure of 0.00533 Pa at 20 °C, exposure to Sika Hardener MI via inhalation is expected to be unlikely.
The assumptions concerning absorption of Sika Hardener MI and its hydrolysis products based on the physicochemical properties are 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. Since Sika Hardener MI induces dermal irritation increased penetration after long term application cannot be excluded.

Details on distribution in tissues:

Assuming that Sika Hardener MI is absorbed into the body following oral intake, it may be distributed into the interior part of cells due to its lipophilic properties and in turn the intracellular concentration may be higher than extracellular concentration particularly in adipose tissues. In contrast distribution via the blood stream is expected for the hydrolysis products due to their higher water solubility. Although the estimated BCF value of Sika Hardener MI is above 2000 L/kg wet-wt. no bioaccumulation potential is expected since the compound is hydrolysed very fast and both degradation products are highly water soluble and have low log Pow values.

Details on excretion:

As discussed above, Sika Hardener MI will be hydrolysed after being in contact with an aqueous solution and will probably not be excreted in its unhydrolysed form. Based on the low molecular weights and the high water solubility, the hydrolysis products are assumed to be excreted via urine. Generally, in the rat renal excretion is facilitated for water-soluble molecules with a molecular weight below 300 g/mol.

Details on metabolites:

Based on the structure of the molecule, Sika Hardener MI and its hydrolysis products 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 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.

Bioaccessibility (or Bioavailability) testing results:

Taken together, physicochemical properties and experimental data indicate bioavailability of Sika Hardener MI via oral and dermal route albeit to a small amount.

Conclusions:

No bioaccumulation potential is expected based on study results.

Executive summary:

Based on physicochemical characteristics, particularly water solubility absorption via oral and dermal route is expected to be low. If absorbed, intracellular concentration is likely to be higher than extracellular due to the lipophilicity of SIKA Hardener MI. 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. Based on hydrolytical degradation bioaccumulation of SIKA Hardener MI is considered unlikely based on the physicochemical properties of the hydrolysis products.

Description of key information

Based on physicochemical characteristics, particularly water solubility absorption via oral and dermal route is expected to be low. If absorbed, intracellular concentration is likely to be higher than extracellular due to the lipophilicity of Sika Hardener MI. 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. Based on hydrolytical degradation bioaccumulation of Sika Hardener MI is considered unlikely based on the physicochemical properties of the hydrolysis products.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Toxicokinetic Assessment of N-[3-({[2,2-dimethyl-3-(morpholin-4-yl)propylidene]amino}methyl)-3,5,5-trimethylcyclohexyl]-2,2-dimethyl-3-(morpholin-4-yl)propan-1-imine (Sika Hardener MI)

 

Toxicological profile of Sika Hardener MI

An acute oral toxicity study conducted with Sika Hardener MI using rats revealed a LD50 value of > 2000 mg/kg bw. In an acute dermal toxicity study the LD50 value was also determined to be greater than 2000 mg/kg bw. No acute inhalation toxicity study was conducted with Sika Hardener MI since the vapour pressure of the substance is low and inhalation exposure is considered unlikely. In an in vitro skin irritation study conducted with Sika Hardener MI a skin irritating effect was observed when applied on a human skin model. A BCOP test revealed that Sika Hardener MI does not induce severe eye damage. An in vivo test on eye irritation is currently conducted. In a LLNA test a skin sensitising potential of Sika Hardener MI was observed when applied on the ear of mice. Sika Hardener MI did not induce reverse mutations in a bacterial reverse mutation test (Ames test) with five Salmonella typhimurium strains in the absence and presence of a metabolic activation system. An in vitro gene mutation assay and an in vitro cytogenetic assay on mammalian cells have been conducted to further assess genetic toxicity. Sika Hardener MI did not induce gene mutation or chromosome aberrations in these tests. Furthermore, a combined repeated dose toxicity study with the reproduction/developmental toxicity screening test was performed revealing no adverse effects up to a limit concentration of 1000 mg/kg bw/day.

 

Toxicokinetics of Sika Hardener MI

Sika Hardener MI is a colourless liquid at room temperature and has a molecular weight of 476.74 g/mol. Since Sika Hardener MI has two stereogenic carbon atoms the substance is an unspecific mixture of cis and trans diastereomers, with each of the stereoisomers assumed to be present as a mixture of E/Z isomers (E,E; E,Z; Z,Z). Water solubility of ca. 1 g/L at 25 °C and a log Pow value of 2.1 at 25 °C were determined. The BCF value was estimated to be 2721 L/kg wet-wt. The vapour pressure of Sika Hardener MI is 0.00533 Pa at 20 °C. In an aqueous solution, Sika Hardener MI is degraded quickly hydrolytically into 2,2-dimethyl-3-(morpholin-4-yl)propanal (Aldehyde M) and 3-Aminomethyl-3,5,5-trimethylcyclohexylamine (Isophorone diamine). Both substances have a higher water solubility (≥ 500 g/L) and a lower log Pow value (1.7 and 0.99, respectively) than Sika Hardener MI itself.

 

Absorption

Generally, oral absorption is facilitated for molecular weights below 500 g/mol. The relatively low water solubility may limit oral absorption by the inability of the substance to dissolve in the gastro-intestinal fluids, which in turn hinders contact with the mucosal surface. However, Sika Hardener MI will be hydrolysed after being in contact with an aqueous solution and degradation products have physicochemical properties (higher water solubility) facilitating oral absorption. Administered without a vehicle in an acute oral toxicity study performed on rats, Sika Hardener MI lead to a LD50 of > 2000 mg/kg bw. Neither clinical signs during the entire study period nor pathological changes could be observed after the observation period of 14 days. Additionally, no adverse effects were observed in the sub-acute repeated dose toxicity study after oral administration. These findings indicate that the compound or its hydrolysis products do not become bioavailable or, in case of absorption, are of low toxicity.

Based on the low vapour pressure of 0.00533 Pa at 20 °C exposure to Sika Hardener MI via inhalation is expected to be unlikely.

Dermal absorption of Sika Hardener MI is expected to occur based on physicochemical properties. This assumption is 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. Since Sika Hardener MI induces dermal irritation increased penetration after long term application cannot be excluded.

 

Taken together, physicochemical properties and experimental data indicate bioavailability of Sika Hardener MI via oral and dermal route albeit to a small amount.

 

Distribution

Assuming that Sika Hardener MI is absorbed into the body following oral intake, it may be distributed into the interior part of cells due to its lipophilic properties and in turn the intracellular concentration may be higher than extracellular concentration particularly in adipose tissues. In contrast distribution via the blood stream is expected for the hydrolysis products due to their higher water solubility. Although the estimated BCF value of Sika Hardener MI is above 2000 L/kg wet-wt. no bioaccumulation potential is expected since the compound is hydrolysed very fast and both degradation products are highly water soluble and have low log Pow values.

 

Metabolism

Based on the structure of the molecule, Sika Hardener MI and its hydrolysis products 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 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.

 

Excretion

As discussed above, Sika Hardener MI will be hydrolysed after being in contact with an aqueous solution and will probably not be excreted in its unhydrolysed form. Based on the low molecular weights and the high water solubility hydrolysis products are assumed to be excreted via urine. Generally, in the rat renal excretion is facilitated for water-soluble molecules with a molecular weight below 300 g/mol.

 

Summary

Based on physicochemical characteristics, particularly water solubility and log Pow absorption via oral and dermal route is expected to be moderate to high. If absorbed, intracellular concentration is likely to be higher than extracellular due to the lipophilicity of Sika Hardener MI. 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. Based on hydrolytical degradation bioaccumulation of Sika Hardener MI is considered unlikely based on the physicochemical properties of the hydrolysis products.

 

References

ECHA (2012), Guidance on information requirements and chemical safety assessment, Chapter R.7c: Endpoint specific guidance.

Marquardt H., Schäfer S. (2004). Toxicology. Academic Press, San Diego, USA, 2nd Edition 688-689.