Benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-, isotridecyl ester

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Type of information:

other: expert statement

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: No GLP-conform guideline study, but scientifically valid expert statement based i.a. on studies assessed with Klimisch 1 or 2

Data source

Reference

Reference Type:

other: Expert statement

Title:

Unnamed

Year:

2015

Report date:

2015

Materials and methods

Objective of study:

absorption

distribution

excretion

metabolism

toxicokinetics

Test guideline

Qualifier:

no guideline required

Principles of method if other than guideline:

An extensive assessment of the toxicokinetic behaviour of C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate was performed, taking into account the chemical structure, the available physico-chemical and toxicological data.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate

EC Number:

700-397-7

Cas Number:

847488-62-4

Molecular formula:

C30H52O3

IUPAC Name:

C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate

Test material form:

other: not applicable

Details on test material:

not applicable

Radiolabelling:

other: not applicable

Test animals

Species:

other: not applicable

Strain:

other: not applicable

Details on test animals or test system and environmental conditions:

not applicable

Administration / exposure

Route of administration:

other: All relevant routes of administration are discussed in the expert statement.

Vehicle:

other: not applicable

Details on exposure:

not applicable

Duration and frequency of treatment / exposure:

not applicable

Doses / concentrations

Remarks:

Doses / Concentrations:
not applicable

No. of animals per sex per dose / concentration:

not applicable

Control animals:

other: not applicable

Positive control reference chemical:

not applicable

Details on study design:

not applicable

Details on dosing and sampling:

not applicable

Statistics:

not applicable

Results and discussion

Main ADME results

Main ADME results 1

Type:

absorption

Results:

The relevant absorption rates were, also with regard to the possible hydrolysis products of the substance, estimated to: Oral absorption: approx. 50% Dermal absorption: approx. 50% Inhalative absorption: approx. 25%, provided that aerosols are formed

Main ADME results 2

Type:

distribution

Results:

The absolute systemic bioavailability of the substance is rather low and expected to be more extensive in fat tissues. The absorption is rather minor, no relevant peak exposure, AUC and prolonged bioavailability will occur.

Main ADME results 3

Type:

metabolism

Results:

It is most likely that the substance and its hydrolysis products (3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid, Isotridecanol) will be subject to metabolism by cytochrome P450 enzymes by mainly aliphatic hydroxylation and subsequent conjugation.

Main ADME results 4

Type:

excretion

Results:

A prolonged, extensive accumulation of the substance, hydrolysis products and their metabolites is not expected. The excretion of the metabolites, as such or after Phase 2 metabolism, will occur rather fast. No potential for bioaccumulation is given.

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Absorption from the gastrointestinal tract
In the small intestine absorption occurs mainly via passive diffusion or lipophilic compounds may form micelles and be taken into the lymphatic system. Additionally, metabolism can occur by gut microflora or by enzymes in the gastrointestinal mucosa. However, the absorption of highly lipophilic substances (Log Pow of 4 or above) may be limited by the inability of such substances to dissolve into gastrointestinal fluids and hence make contact with the mucosal surface. The absorption of such substances will be enhanced if they undergo micellular solubilisation by bile salts. Substances absorbed as micelles enter the circulation via the lymphatic system, bypassing the liver. Consequently, immediate Cytochrome P450 metabolism is less important here as for substances which directly enter the hepatic system via the portal vein.
According to ECHA’s guidance R.7c, it is stated that the smaller the molecule the more easily it may be taken up. Molecular weights below 500 are favourable for absorption. With a molecular weight of 460.7 g/mol, absorption in general can be considered as possible.
However, taking into account the Log Pow = 3.56 (at 25°C), which is only slightly below the above-mentioned boundary value, might indicate a beginning slightly hindered absorption e.g. by diffusion. Nevertheless, based on the Log Pow, absorption must be taken into account.
Only water-soluble substances will readily dissolve into the gastrointestinal fluids and hence be available for absorption. The water solubility was determined to be 0.33 mg/L (at 25°C) [Information from migrated NONS file]. Hence, only taking into account the slight solubility of the substance, absorption can be considered diminished.
The results of the available oral toxicity study (EC 413-750-2, EU method B.1, GLP) do indicate substance absorption. Piloerection was observed only two hours after test article administration in 2/5 male and 3/5 female rats. No other signs of toxicity were noted, gross pathology was negative and the LD50 was determined to be > 5000 mg/kg as no animal died upon single gavage of the test item at that dose. However, based on these results it cannot be definitively concluded to which extent absorption occurred and which species was absorbed; these minor reactions could be either due to the intrinsic non-toxicity of the test item or due to a rather poor absorption.
Similar information can be drawn from the subacute 28 day oral (gavage) study in rats. The NOAEL was determined to be 1000 mg/kg bw/day. EC 413-750-2, when daily administered to Sprague Dawley rats by oral route for 4 weeks, was on the whole well tolerated up to and including the highest dosage administered because no signs of toxicity were observed. However, at a dose of 100 mg/kg bw/day, some as non-adverse assessed effects were noted. E.g. in males, treatment induced hepatic centrilobular hypertrophy, which appeared generally diffuse in the 1000 mg group, and in the 100 mg group centrilobular hypertrophy was multifocal. The effects observed in the liver are also indicative that absorption occurred and, due to the reversibility of the effect, that no accumulation of the substance is present to a certain extent.
Alkanes and phenols are in general resistant to hydrolysis, aliphatic alcohols however are common leaving groups, and aliphatic carboxylic acid esters are potentially susceptible for hydrolysis, in the acidic environment of the stomach, hydrolysis might be favoured additionally. In consequence, the absorption of the parent compound(s) is considered to be moderate, and additionally the absorption of the degradation products, which are most likely the phenolic acid (3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid, CAS 20170-32-5) and the aliphatic alcohol (isotridecanol, CAS 27458-92-0), which are smaller and expected to be more water soluble, needs to be considered, based on the available physico-chemical properties. Due to the partly lack of experimental data, some of the relevant properties were estimated using EpiSuite v4.10.
In general, the low molecular weight of the hydrolysis products makes them favourable for absorption. The uptake of the long-chain alcohols seems to be limited due to their low water solubility and high Log Pow at first glance. Also, since these alcohols are not toxicologically relevant, as they are non-toxic, their toxicokinetic and –dynamic fate can be neglected.
Similar considerations with regard to absorption apply to other hydrolysis product, 3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid, however, based on the available data, the toxicological relevance cannot be assessed in detail.
Also, the exact hydrolysis rate is unknown, and it cannot be stated in detail, to which extent the absorption of the hydrolysis products needs to be regarded. Taking into account only the absorption of the parent compound without hydrolysis, the oral absorption can be considered as limited, allowing an estimation of approx. 25%. Since hydrolysis is nevertheless a very likely scenario, the degradation products and their uptake should be considered, too. This leads to the estimation of a precautionary absorption rate of approx. 50% due to the similarly hindered absorption as the parent compound, probably overestimating the actual oral absorption.

Absorption from the respiratory tract
Concerning absorption in the respiratory tract, any gas, vapour or other substances inhaled as respirable dust (i.e. particle size ≤ 15µm) has to be sufficiently lipophilic to cross the alveolar and capillary membranes (moderate Log Pow values between 0-4 are favourable for absorption). The rate of systemic uptake of very hydrophilic gases or vapours may be limited by the rate at which they partition out of the aqueous fluids (mucus) lining the respiratory tract and into the blood. Such substances may be transported out of the lungs with the mucus and swallowed or pass across the respiratory epithelium via aqueous membrane pores. Lipophilic substances (Log Pow >0) have the potential to be absorbed directly across the respiratory tract epithelium. Any lipophilic compound may be taken up by micellular solubilisation but this mechanism may be of particular importance for highly lipophilic compounds (Log Pow >4), particularly those that are poorly soluble in water (1 mg/L or less) that would otherwise be poorly absorbed.
The substance (data from EC 413-750-2) has a rather low vapour pressure (166 Pa at 20°C, 430 Pa at 40°C, 2424 Pa at 80°C (calculation via linear regression)) and a boiling point of 220-245°C at 101.3 kPa, showing that the inhalative absorption as a gas does not have to be regarded. According to ECHA’s guidance, substances are not available for inhalation as a gas in a relevant manner with a vapour pressure less than 0.5 kPa (or a boiling point above 150°C).
In addition, it is liquid at room temperature, i.e. no particles of an inhalable size are present. Further, there is only a very limited potential for inhalation during use, e.g. the aerosol formation of solutions of the substance is very low. Nevertheless, in order to estimate the potential of the substance to be absorbed via the inhalatory route for this rare cases, its physico-chemical properties will be taken into account.
With a Log Pow = 3.56 (at 25°C; EC 413-750-2), even solved molecules of the substance have a diminished potential for absorption via respiratory tract epithelium by both passive diffusion and micellular solubilisation. The same applies for the possible hydrolysis products with a minor enlarged potential to be absorbed via micellular solubilisation. Also, without having concrete droplet sizes of potential aerosols, no statements regarding the deposition place and hence place-specific clearance mechanisms, e.g. ciliary movements, can be made. As a consequence, the absorption of the parent compound as well as possible hydrolysis products can be neglected and since the concrete hydrolysis rate is not available, a precautionary absorption rate of up to 25% can be estimated.

Absorption after dermal exposure
In order to cross the skin, a compound must first penetrate into the stratum corneum and may subsequently reach the epidermis, the dermis and the vascular network. The stratum corneum provides its greatest barrier function against hydrophilic compounds, whereas the epidermis is most resistant to penetration by highly lipophilic compounds. Substances with a molecular weight below 100 are favourable for penetration through the skin and substances above 500 are normally not able to penetrate. The substance must be sufficiently soluble in water to partition from the stratum corneum into the epidermis. Therefore, if the water solubility is below 1 mg/L, dermal uptake is likely to be low. Additionally, Log Pow values between 1 and 4 favour dermal absorption.
Above 4, the rate of penetration may be limited by the rate of transfer between the stratum corneum and the epidermis, but uptake into the stratum corneum will be high. Above 6, the rate of transfer between the stratum corneum and the epidermis will be slow and will limit absorption across the skin. Uptake into the stratum corneum itself may be slow. Moreover vapours of substances with vapour pressures below 100 Pa are likely to be well absorbed and the amount absorbed dermally is most likely more than 10% and less than 100 % of the amount that would be absorbed by inhalation. If the substance is a skin irritant or corrosive, damage to the skin surface may enhance penetration. During the whole absorption process into the skin, the compound can be subject to biotransformation.
In case of the substance, evaporation after skin contact does not need to be regarded due to the high boiling point and low vapour pressure, and hence it can be assumed that the substance will remain on the skin until mechanical removal. The substance was tested to be not irritating to the skin and eyes of rabbits. Hence, an enhanced dermal absorption due to irritating / corrosive properties does not need to be regarded.
With a molecular weight of 460.7 g/mol, a moderate to high absorption via the skin and hence a dermal absorption rate of 50-100% could be assumed. Taking into account a Log Pow = 3.56 (at 25°C; EC 413-750-2) and a water solubility 0.33 mg/L (at 25°C; EC 413-750-2), it can be concluded that the uptake into both the stratum corneum and epidermis does occur due to the Log Pow. The poor water solubility, i.e. < 1mg/L, however limits the uptake and partition from the stratum corneum into the epidermis and subsequent blood vessels. Hence, a rather low absorption rate can be expected.
Upon contact with the moisturised skin, solubilisation and subsequent hydrolysis should be considered, and hence the physico-chemical properties of the proposed hydrolysis products 3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid and Isotridecanol. Due to the low vapour pressure, a diminished contact time due to evaporisation does not need to be regarded. Although the molecular weight of 278.20 resp. 200.21 g/mol favours absorption, the high log Pow hinders the transfer from the stratum corneum into the epidermis. Hence, a similar absorption rate for the parent compound and potential hydrolysis products can be assumed. In consequence, a precautionary absorption rate of 50% should be taken into account.

Details on distribution in tissues:

Distribution
In general, it can be stated that the smaller the molecule, the wider is its distribution. A lipophilic molecule (Log Pow >0) is likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration particularly in fatty tissues. It is not possible to foresee protein binding, which can limit the amount of a substance available for distribution. Furthermore, if a substance undergoes extensive first-pass metabolism, predictions made on the basis of the physico-chemical characteristics of the parent substance may not be applicable.
In case of the substance, no quantitative data is available for distribution patterns. Taking into account its molecular weight of 460.7 g/mol, its rather lipophilic character and poor water solubility, the absolute systemic bioavailability is rather low and expected to be more extensive in fat tissues than in other tissues, especially when absorption occurred while bypassing the liver. Similar considerations apply to the potential hydrolysis products, although their bioavailability, if occurring, might be slightly enhanced compared to the parent compound. Unfortunately the actual hydrolysis rate is not available.
After oral exposure, the first target will be the gastrointestinal tract, where the parent compound, its hydrolysis products and possibly bacterial metabolites will be absorbed in small quantities and transferred via the blood stream to the liver. After first pass metabolism, the substances will be further distributed via the bloodstream. Here, especially the kidneys due to their filter function and the heart due to its enormous need for nutrients and consequently large blood flow through coronary arteries will be affected.
However, the estimated hydrolysis products and metabolites are smaller and more hydrophilic due to the hydroxyl groups, so that their distribution can be considered more facilitated than the parent compound. Since the solubility and hence absorption via the GI tract of the parent compound is rather limited, an excessive formation of its metabolites is unlikely and so is a peak exposure to the metabolites. Due to their tendency to be excreted rather fast compared to the parent compound, also a relevant AUC is not to be expected. After absorption of the parent compound via other routes, only a subsequent metabolism has to be taken into account, also leading to no relevant peak exposure.
Taking into account the results of the 28 day repeated dose toxicity study in rats, i.e. the fact that liver and kidneys (due to urine parameters) showed slight responses, a body-wide distribution is indicated, as this supports the assumption of a substance uptake via the portal vein and afterwards, most likely after first pass metabolism, a body-wide distribution via the blood stream and subsequent elimination through the kidneys.

Details on excretion:

Excretion
In general, the major routes of excretion for substances from the systemic circulation are the urine and/or the faeces (via bile and directly from the gastrointestinal mucosa). For non-polar volatile substances and metabolites exhaled air is an important route of excretion. Substances that are excreted favourable in the urine tend to be water-soluble and of low molecular weight (below 300 in the rat) and be ionised at the pH of urine. Most will have been filtered out of the blood by the kidneys though a small amount may enter the urine directly by passive diffusion and there is the potential for reabsorption into the systemic circulation across the tubular epithelium. Substances that are excreted in the bile tend to be amphipathic (containing both polar and nonpolar regions), hydrophobic/strongly polar and have higher molecular weights and pass through the intestines before they are excreted in the faeces and as a result may undergo enterohepatic recycling which will prolong their biological half-life. This is particularly a problem for conjugated molecules that are hydrolysed by gastrointestinal bacteria to form smaller more lipid soluble molecules that can then be reabsorbed from the GI tract. Those substances less likely to recirculate are substances having strong polarity and high molecular weight of their own accord. Other substances excreted in the faeces are those that have diffused out of the systemic circulation into the GIT directly, substances which have been removed from the gastrointestinal mucosa by efflux mechanisms and non-absorbed substances that have been ingested or inhaled and subsequently swallowed. Non-ionised and lipid soluble molecules may be excreted in the saliva (where they may be swallowed again) or in the sweat. Highly lipophilic substances that have penetrated the stratum corneum but not penetrated the viable epidermis may be sloughed off with or without metabolism with skin cells.
For the substance no data is available regarding its elimination. Concerning the above mentioned behaviour predicted for its metabolic fate, it is unlikely that the parent substance will be excreted unchanged. However, if unchanged excretion is assumed, based on the chemical structure of the substance, its molecular weight and its non-existent water solubility, it is unlikely to be excreted via the urine. The excretion, if any, of the parent compound will occur via the gastrointestinal tract (unabsorbed material) and the bile (small amounts of unchanged compound), and it could be subject to enterohepatic recycling. Also, assuming a Phase I/II metabolism for the substance, an excretion via the urine is less likely due to its rather high molecular weight, i.e. >300 g/mol.
Regarding the hydrolysis products of the substance and their metabolites, either a fast excretion for the unconjugated metabolites containing hydroxyl groups, or a fast elimination of the Phase 2 conjugated metabolites, can be expected, which applies mainly to the ketone, but also to the metabolites containing hydroxyl groups.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

For details, see attached file. Metabolites of the substance and possible hydrolysis products are estimated to be formed mainly via aliphatic hydroxylation or alcohol oxidation.

Any other information on results incl. tables

see attached expert statement

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): low bioaccumulation potential based on study results
The present expert statement covers all relevant toxicokinetic parameters to assess the behaviour of C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate in the body, the available information is sufficient to enable one to perform a proper risk assessment. Hence, no further information needs to be gathered and further studies can be omitted due to animal welfare. In conclusion, C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)pro¬pionate has no potential for bioaccumulation in its non-metabolized or metabolized form.

Executive summary:

In order to assess the toxicokinetic behaviour of C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, the available toxicological and physico-chemical data were evaluated.

C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is expected to be rather poorly absorbed via the oral route. With a molecular weight of 460.7 g/mol, absorption in general can be considered as possible. The Log Pow of 3.56 (at 25°C) might indicate a beginning slightly hindered absorption e.g. by diffusion, and low water solubility a low bioavailability. The presence of absorption is indicated by some effects observed in animal studies.

Based on the chemical structure C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, hydrolysis needs to be taken into account, which results most likely in 3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid and isotridecanol. The low molecular weight of the hydrolysis products make them favourable for absorption. The uptake of the long-chain alcohols seems to be limited due to their low water solubility and high Log Pow and is also not toxicologically relevant due to their non-toxicity. Similar considerations with regard to absorption apply to 3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid, however, without information on the toxicological relevance. As the oral absorption of C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate can be considered as limited, the oral absorption rate can be estimated to approx. 25%. Applying a similar estimation to the hydrolysis products, this leads to the estimation of a precautionary absorption rate of approx. 50%, probably overestimating the actual oral absorption.

The substance has a rather low vapour pressure, high boiling point and is liquid at room temperature, showing that the inhalative absorption as a gas or particles does not have to be regarded. Thinking of a possible, but very unlikely inhalation of an aerosol, and considering the available phys.-chem. data, the absorption of the parent compound as well as possible hydrolysis products can be neglected and since the concretehydrolysis rate is not available, a precautionary absorption rate of up to 25% can be estimated.

In case of C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, neither evaporation after skin contact nor very remarkable additional absorption-enhancing effects due to corrosivity need to be regarded. Taking into account the molecular weight, high Log Pow and low water solubility, a passage of the parent compound and similarly the possible hydrolysis products through the stratum corneum is unlikely, but cannot be completely excluded, and a precautionary absorption rate of 50% is assumed.

Taking into account the molecular weight of 460.7 g/mol, the rather lipophilic character and poor water solubility, the absolute systemic bioavailability of C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (and possible hydrolysis products) is rather low and expected to be more extensive in fat tissues than in other tissues. After first pass metabolism, more hydrophilic metabolites are expected to occur, and the absorption of the substance is rather minor, no relevant peak exposure, AUC and prolonged bioavailability will occur.

Since C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is not considered especially hydrolytically or metabolically stable, a prolonged, extensive accumulation is not expected. After metabolism, the excretion of the metabolites, either as such or after Phase 2 metabolism, will occur rather fast, as well as the unchanged hydrolysis products and their metabolites would; an accumulation is not very likely, too. It is most likely that the substance of interest and its hydrolysis products will be subject to metabolism by cytochrome P450 enzymes and subsequent conjugation.

In conclusion, C13-(branched)-alkyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate has a minor potential for bioaccumulation in its non-metabolised form, and will be excreted rapidly after hydrolysis and accompanying / subsequent metabolism. The relevant absorption rates were, also with regard to its possible hydrolysis products, estimated to:

Oral absorption: approx. 50%

Dermal absorption: approx. 50%

Inhalative absorption: approx. 25%, provided that aerosols are formed