Registration Dossier

Administrative data

Endpoint:
basic toxicokinetics, other
Remarks:
Expert statement
Type of information:
other: Expert statement
Adequacy of study:
supporting study
Study period:
November 2014
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference
Reference Type:
other: Expert statement
Title:
Unnamed
Year:
2014
Report Date:
2014

Materials and methods

Objective of study:
toxicokinetics
Test guideline
Qualifier:
no guideline required
Principles of method if other than guideline:
No ADME studies are available for FAT 40075 D. Therefore, the toxicokinetic assessment of FAT 40075 D is predicted based on its physico-chemical properties and available toxicological study data. The OECD QSAR application toolbox v3.2 was also utilized to make a qualitative prediction of metabolites formed in the liver and skin.
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
other: Solid

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:
Oral route:
There is no repeated dose toxicity study available. There is an acute oral toxicity study, in which no clinical symptoms were observed during a 14-day post-dose period. A high dose of 5000 mg/kg bw was administered as a single dose in water.
However, the absence of any clinical symptoms does not mean that no oral absorption occurred, since this is also a function of the toxicity of the substance. Very low toxicity would disguise any absorption. It is also possible that the single large dose may not absorb as efficiently as smaller repeat doses, due to absorption mechanisms being saturated. The OECD QSAR application toolbox was used to apply Lipinski's Rule of Five. FAT 40075/D was predicted to be not orally bioavailable based on these rules. The toolbox is also designed to predict possible metabolites that can be produced by phase 1 (e.g. oxidation/reduction) and phase 2 (e.g. conjugation) biotransformations in the liver, based on the structure of the parent molecule. This biotransformation can occur during the first pass effect, but can also occur if the unmetabolised molecule passes into the systemic circulation and returns through the liver. In the absence of any evidence for absorption based on the available acute toxicity study, use of physico-chemical data are used to make an assessment. The log Pow of 3.46 indicates that oral absorption is favoured. The substance is very water soluble, so will easily dissolve in GI fluids. The molecular weight between 500-1000 indicates absorption cannot be excluded. In conclusion, FAT 40075/D has the potential for oral absorption based on its physico-chemical properties.

Inhalation route:
There is no information available regarding the absorption or toxicity of FAT 40075/D via inhalation. The vapour pressure of FAT 40075/D is predicted to be low indicating that inhalation exposure from volatilisation is unlikely to be a potential route of exposure. The particle size distribution (L50D = 5.77 µm, L10D = 1.9 µm) of the test material indicates the presence of inhalable and respirable particles. REACH endpoint specific guidance (R.7c) states that respirable particles are <15 µm. However, according to other REACH guidance (chapter R.14) respirable particles are regarded as being <10 µm. According to the particle size distribution study, 50 % of particles are <5.77 µm. Therefore, there is high potential for deposition in the alveoli, where dissolution in the alveolar fluid could occur followed by absorption. Inhalable particles are likely to be cleared from the lungs by the mucociliary escalator, but then swallowed making them potentially available for absorption via the GI tract. In conclusion, uptake via the inhalation route is expected to be potentially high based on the particle size distribution and high water solubility allowing quick dissolution in alveolar fluid followed by absorption.

Dermal route:
There is no information available regarding the absorption or toxicity of FAT 40075/D following dermal exposure. Dermal absorption is influenced inter alia by water solubility, log Pow and molecular weight. REACH endpoint specific guidance (R.7c) indicates that a log Pow of 3.46 favours dermal absorption particularly if water solubility is high, as is the case here. The molecular weight above 500 reduces the likelihood but on balance the molecular weight is not considered high enough to prevent this molecule from crossing the dermal barrier. In conclusion, FAT 40075/D has a low to moderate potential for dermal absorption.
Details on distribution in tissues:
The acute oral toxicity study indicated no change in organs or tissues. However, an orange dye could be indiscernible from the tissue and organ colour. FAT 40075/D has the potential for absorption via all routes and therefore also the potential for distribution. For the oral route, distribution of the parent would be dependent on the amount of metabolism in the liver and on any excretion via the biliary duct. The OECD toolbox predicts it will not be bioavailable, and also predicts a moderate number of potential metabolites. It is therefore possible that some of the metabolites may distribute rather than the parent, although this cannot be excluded, despite the toolbox prediction. In conclusion, FAT 40075/D and/or its metabolites have the potential for distribution.
Details on excretion:
There is no repeated dose study to assess the presence of the parent in either faeces of urine. No information was present in the acute oral toxicity study. Therefore, assessment of excretion can only be based on the physico-chemical nature of the parent. The parent has a molecular weight >300 and therefore any non-metabolised substance is likely to be excreted via the bile duct. Predicted metabolites with molecular weights of approximately 300 or less are very likely to be excreted via urine. Predicted metabolites with similar structures to the parent are likely to follow the same excretion path via the bile duct. In conclusion, excretion of FAT 40075/D is likely via biliary excretion rather than urine. Metabolites would be expected to be excreted via urine (if molecular weight <300) and via bile (if molecular weight >300), although it is conceivable that both routes could be used.

Metabolite characterisation studies

Details on metabolites:
Potential metabolites of FAT 40075/D in the liver and skin have been predicted using OECD Toolbox. Eleven metabolites were predicted for liver metabolism (all are bioavailable) and seven metabolites for skin metabolism (2 are bioavailable and 5 are not bioavailable). One metabolite was common in both liver and skin.

The OECD Toolbox has predicted that FAT 40075/D will undergo phase I transformations (reductions, hydroxylations, oxidations). Some of these transformations, such as reductions, may also occur in the intestine due to action by microflora.

Metabolites M2, M3, M6, were identified by the websites PubChem and ChemSpider.

Toxicologically relevant metabolites:

2, 5-Dimethyl-1, 4-benzenediamine:
A search of CCRIS database indicated negative Ames results in TA1535, TA 1537, TA 1538, TA100 (with and without activation) and negative in TA98 (no activation) but positive in TA98 (with activation). Since aromatic amino compounds have been associated with carcinogenicity, there is some potential for toxicity from this metabolite.

Metabolites containing amino, hydrazino and azo-groups:
It is known that certain aromatic amines are associated with human carcinogenicity and rat carcinogenicity. Similarly, metabolites with the azo-functional group can be reduced to an amine either by phase I transformation in the liver or by the action of microflora in the intestine followed by absorption, resulting in potential carcinogens. Molecules with an aromatic hydrazine group may also produce enhanced toxicity. This does not mean that either of these specific metabolites are carcinogens, but the potential is considered to exist.

Metabolites with phenolic groups:
Metabolites which have phenolic groups present should also be considered potentially more toxic than the parent, due to the oxidation of phenols which is known to produce quinones/semiquinones which can become involved in binding to the –SH or –NH2 groups in proteins leading to inactivation of the protein. They are also associated with superoxide anion production ultimately leading to formation of hydroxyl radicals which can cause cell damage.

In addition to the prediction from the toolbox, a visual assessment of the structure of the parent indicates there is the possibility of one of the metabolites being a triazine derivative, specifically 2-chloro-4, 6-diamino-S-triazine could form due to reduction processes either in the liver (Phase I) or via microflora in the intestine which are known to reduce nitro and azo groups. A quick search of TOXNET indicated three Ames tests (on TA100, 97 and 98 strains) all with negative results. No other data was indicated.

Applicant's summary and conclusion

Conclusions:
The absorption, distribution, metabolism and excretion of FAT 40075 D have been predicted in the absence of toxicokinetic studies. FAT 40075/D has the potential for oral absorption based on its physico-chemical properties. FAT 40075/D uptake via the inhalation route is expected to be potentially high. FAT 40075/D is expected to have a low to moderate potential for dermal absorption. FAT 40075/D and/or its metabolites have the potential for distribution. The OECD toolbox predicts that FAT 40075/D will undergo typical phase I biotransformations. Excretion of FAT 40075/D is expected to be mainly via bile and the GI tract, but not via urine. Metabolites would be expected to be excreted via urine (if molecular weight < 300) and via bile (if molecular weight >300), although it is conceivable that both routes could be used.