Exo-1,7,7-trimethylbicyclo[2.2.1]hept-2-yl methacrylate

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Objective of study:

toxicokinetics

Qualifier:

no guideline followed

Principles of method if other than guideline:

Three male rats per compound were intravenously administered IBOMA at target concentration 8.0 mg/kg (36 µmol/kg), using Intralipid 20% as the dose vehicle. After dose administration, blood samples (~200 μL) were collected at 5, 10, 30, 60, and 180 minutes into individual pre-weighed glass vials containing ethyl acetate (600 μL) acidified with 10% trifluoroacetic acid (TFA). After vortexing and subsequent centrifugation, the blood extracts underwent quantitative analysis for IBOMA by gas chromatography tandem mass spectrometry (GC/MS-MS).

GLP compliance:

no

Specific details on test material used for the study:

TEST MATERIAL:
- Name of test material: Isoborny methacrylate

Radiolabelling:

no

Species:

rat

Strain:

Fischer 344/DuCrj

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (Kingston, New York)
- Age at study initiation: 9-12 weeks
- Weight at study initiation: 183-196 g
- Housing: singly in glass Roth-type metabolism cages
- Diet (e.g. ad libitum): LabDiet Certified Rodent Diet #5002 (PMI Nutrition International, St. Louis, Missouri) in pelleted form, ad libitum
- Water (e.g. ad libitum): Municipal water, ad libitum
- Acclimation period: 7d

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22°C with a range of 20°C-26°C
- Humidity (%): 50% with a range of 30-70%
- Photoperiod (hrs dark / hrs light): 12-hour light/dark (on at 6:00 a.m. and off at 6:00 p.m.)

Route of administration:

intravenous

Vehicle:

other: Intralipid 20%

Details on exposure:

Appropriate amounts of the test substance were added to sterile pharmaceutical grade Intralipid 20% using aseptic technique to obtain the appropriate concentration. The amount of dose solution administered was targeted at 2.5 mL/kg bw and injected over ~1minute to correspond to an injection rate of ~0.5 mL/min. The dose was stored at ambient temperature (19-25°C) and used within 24 hours of preparation.

Duration and frequency of treatment / exposure:

single iv treatment

Dose / conc.:

8 mg/kg bw/day (nominal)

Remarks:

corresponds to 36 µmol/kg

No. of animals per sex per dose / concentration:

3 males

Control animals:

yes, concurrent vehicle

other: another isobornyl ester (isobornyl acetate, IBOAC) was tested for its toxikokinetic properties for comparison reasons (rad-across background)

Positive control reference chemical:

no

Details on study design:

- Dose selection rationale: previous studies of this type have used similar equimolar ratios

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY
- Tissues and body fluids sampled: blood
- Time and frequency of sampling: 5, 10, 30, 60 and 180 minutes post-dosing

Statistics:

Descriptive statistics were used, i.e., mean ± standard deviation, where applicable. All descriptive statistic calculations were conducted using Microsoft Excel (Microsoft Corporation, Redmond, Washington) spreadsheets in full precision mode (15 digits of accuracy). Pharmacokinetic parameters that were calculated for blood used the pharmacokinetic computer modeling program PK Plus (v. 9.6, Simulation Plus, Inc., Lancaster, California, United States of America).

Preliminary studies:

The solubility of both IBOAC and IBOA was tested up to 10 mg/mL in saline and Intralipid 20%. Both test materials were insoluble at this concentration in saline but were soluble in Intralipid 20%; thus they were prepared using the latter vehicle .

Key result

Test no.:

#1

Toxicokinetic parameters:

half-life 1st: 1.27 min-1

Remarks:

relevant for the vast majority of applied test substance

Key result

Test no.:

#1

Toxicokinetic parameters:

other: <1.0% of the corresponding administered dose remains in the blood 10 minutes post-intravenous administration

Test no.:

#1

Toxicokinetic parameters:

AUC: 397 µg-min/g

Metabolites identified:

not measured

The resulting blood time course showed that the substance was quickly hydrolyzed with less than 1.0% of the corresponding administered dose remaining in the blood 10 minutes post-intravenous administration and around 0.1% remaining 180 minutes post-intravenous administration. Further pharmacokinetic analysis of the blood concentrations of the substance showed that both compounds were biphasic (alpha [α] and beta [β] phases; i.e. a two-compartment model) in which there is a dominant initial distribution and hydrolysis step (i.e. t_½α) with a subsequent phase of further hydrolysis and elimination (i.e. t_½β). The initial distribution and hydrolysis step had an average calculated t_½αvalue of 1.27 min^-1and accounts for metabolic fate of the vast majority of applied test substance quantities. The secondary hydrolysis and elimination phase (t_½β) had an average value of 61.1 min^-. The cause of the beta-phase associated with the minor portion of the test substance's kinetics is currently unclear and may be of limited relevance to normal physiology. The average area under the curve (AUC_0-t) value was 397 µg-min/g, respectively.

Conclusions:

Overall, the analysis of the blood pharmacokinetics indicated that the parent test material is rapidly removed from blood circulation (i.e. blood compartment)in vivo in a very similar manner. Hence, these data support a pharmacokinetics-based Read-Across for IBOAC and IBOMA.

Executive summary:

This non-GLP pharmacokinetic study of isobornyl acetate (IBOAC) and isobornyl methacrylate (IBOMA) in rats via intravenous administration evaluated the hydrolysis and pharmacokinetic characteristics as measured by the rate of parent (IBOAC or IBOMA) disappearance. The purpose of this study was to evaluate whether these data can be used in a pharmacokinetics-based Read-Across approach similar to several other well-studied (meth)acrylates.

Three male rats per compound were intravenously administered either IBOAC or IBOMA at target concentrations 7.0 mg/kg (36 µmol/kg) or 8.0 mg/kg (36 µmol/kg), respectively, using Intralipid 20% as the dose vehicle. After dose administration, blood samples (~200 μL) were collected at 5, 10, 30, 60, and 180 minutes into individual pre-weighed glass vials containing ethyl acetate (600 μL) acidified with 10% trifluoroacetic acid (TFA). After vortexing and subsequent centrifugation, the blood extracts underwent quantitative analysis for either IBOAC or IBOMA by gas chromatography tandem mass spectrometry (GC/MS-MS).

The resulting blood time course showed that both substances were quickly hydrolyzed with less than 1.0% of the corresponding administered dose remaining in the blood 10 minutes post-intravenous administration and around 0.1% remaining 180 minutes post-intravenous administration. Further pharmacokinetic analysis of the blood concentrations of both IBOAC and IBOMA showed that both compounds were biphasic (alpha [α] and beta [β] phases; i.e. a two-compartment model) in which there is a dominant initial distribution and hydrolysis step (i.e. t_½α) with a subsequent phase of further hydrolysis and elimination (i.e. t_½β). The initial distribution and hydrolysis step had average calculated t_½αvalues of 0.866 and 1.27 min^-1for IBOAC and IBOMA, respectively, and accounts for metabolic fate of the vast majority of applied test substance quantities. The secondary hydrolysis and elimination phase (t_½β) had average values of 55.1 and 61.1 min^-1for IBOAC and IBOMA, respectively. The cause of the beta-phase associated with the minor portion of IBOAC and IBOMA kinetics is currently unclear and may be of limited relevance to normal physiology. The average area under the curve (AUC_0-t) values for IBOAC and IBOMA were 363 and 397 µg-min/g, respectively.

NOTE: Any of data in this dataset are disseminated by the European Union on a right-to-know basis and this is not a publication in the same sense as a book or an article in a journal. The right of ownership in any part of this information is reserved by the data owner(s). The use of this information for any other, e.g. commercial purpose is strictly reserved to the data owners and those persons or legal entities having paid the respective access fee for the intended purpose.

Reference 2

Endpoint:

basic toxicokinetics, other

Remarks:

(Q)SAR

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Justification for type of information:

see Read Across Justification

Principles of method if other than guideline:

Protein/GSH reactivity modelling with OECD Toolbox

GLP compliance:

no

The algorithm of the OECD toolbox has been used to predict GSH/protein reactiviry.

Test Chemical / Compound Identity	Acronym	SMILES	Molecular Weight	Protein Binding Potency
Methacrylic acid	MAA	CC(=C)C(=O)O	100.12	No alert found
Methyl methacrylate	MMA	CC(=C)C(=O)OC	100.12	Slightly reactive (GSH) >> Methacrylates (MA)
Isobornyl methacrylate	IBOMA	CC(=C)C(=O)OC1CC2CCC1(C2(C)C)C	222.32	Slightly reactive (GSH) >> Methacrylates (MA)

Conclusions:

Slight reactivity expected for IBOMA and MMA which is used as further methycrylate ester in this read across approach. No reactivity with GSH expected for MAA which is used as methycrylic metabolite in this read across approach.

A dataset with methacrylic acid derivatives has been assessed using the reactivity profiler in the OECD QSAR Toolbox. This profiler contains structural alerts derived from an analysis of experimental reactivity data as measured using glutathione (the Schultz assay). The profiler assigns chemicals to one of five potency classes (non-reactive, slightly reactive, moderately reactive, highly reactive and extremely reactive) based on the experimental results.

For Methacrylic acid, no alert was found, while the majority of the methacrylate esters are slightly reactive. For methacrylate esters it is well known that the addition of an alkyl group on the alpha-carbon significantly reduces reactivity in the Michael addition reaction.

Also for read across purposes according to ECHA's RAAF (2017), this study is applicable with a high level of confidence.

Executive summary:

A dataset with methacrylic acid derivatives has been assessed using the reactivity profiler in the OECD QSAR Toolbox. This profiler contains structural alerts derived from an analysis of experimental reactivity data as measured using glutathione (the Schultz assay). The profiler assigns chemicals to one of five potency classes (non-reactive, slightly reactive, moderately reactive, highly reactive and extremely reactive) based on the experimental results.

 

For Methacrylic acid, no alert was found, while the majority of the methacrylate esters are slightly reactive. For methacrylate esters it is well known that the addition of an alkyl group on the alpha-carbon significantly reduces reactivity in the Michael addition reaction.

 

There are also a group of vinyl carboxamides (methacrylamide derivatives) that have been flagged as being moderately reactive. It should be noted, however, that in the underlying QSAR data in the TB there is no information regarding the effect of an alpha substituent for this class of chemical. In reality this means that no chemicals were tested with glutathione that contained an alpha alkyl substituent thus the prediction is being made based on the un-substituted parent (acrylamide; thus the over-cautious prediction). The investigator indicated that they are likely to be pretty unreactive in reality.

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

GLP compliance:

not specified

Radiolabelling:

yes

Remarks:

Tritium-labelled test substance

Species:

mouse

Strain:

other: dd

Sex:

male

Route of administration:

dermal

Vehicle:

water

Dose / conc.:

3.18 other: µg/mL bath water

Remarks:

almost complete body exposed

Control animals:

no

Conclusions:

Interpretation of results: no bioaccumulation potential based on study results Isobornyl acetate is rapidly absorbed through the skin and undergoes rapid metabolism.

Executive summary:

The dermal resorption of Isobornyl acetate was tested in male dd-mice. The Tritium-marked substance was added to a foam bath fluid (3.18 µg/ml bath water) in order to reflect realistic conditions of taking a bath. The substance was applied to a surface of 3 cm² of the shaved and depilated skin with a fitted cylinder. After 5, 10, 20, 30 and 40 minutes, 0.1 ml blood was tapped from the tail vein, respectively. The maximum concentration of 60 ng Isobornyl acetate/ml was detected after 10 min. Thereafter, a rapid degradation occurred, resulting in 15 ng/ml after 40 min.

Description of key information

The physico-chemical properties (low vapour pressure, low water solubility, high partition coefficient of approx. 5; see respective chapters) indicate a relative low absorption potential of IBOMA via all routes (with reference to ECHA guidance R.7c, 2017).

Experimentally proven rapid hydrolysis of IBOMA by unspecific carboxylesterases to the methacryic metabolite methacylic acid/MAA and alcohol metabolite isoborneol/ IBO so that systemic effects of IBOMA can be assessed with the help of these metabolites and the respective metabolite donor substances (methyl methacrylate/MMA and isobornyl acetate/ IBOAC). Also, there is no bioaccumulation potential of IBOMA.

MAA is further metabolised in the Citric Acid Cycle (valine pathway), finally down to to respirable CO2. IBO is further metabolised to Camphor/CAM which is further oxidized, conjugated and eliminated in the urine.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Absorption

The physico-chemical properties (low vapour pressure, low water solubility, high partition coefficient of approx. 5; see respective chapters) indicate a relative low absorption of IBOMA via all routes (with reference to ECHA guidance R.7c, 2017).

 

Metabolism & Excretion

Ester hydrolysis by carboxylesterases has been established as the primary step in the metabolism of esters of simple carboxyl acids like methacrylic acid (MAA). 

For IBOMA, this hydrolytic step leads to the rapid formation of MAA and IBO. Thus, systemic effects of IBOA can also be assessed by read acoss to these metabolites and their respective donor substances (i.e. substances, which were rapidly metabolised to these metabolites) with a high level of confidence and according to ECHA's RAAF guidance (2017). This read across is justified in detail in the attached read across justification.

 

Primary metabolism of Isobornyl Methacrylate

A comparative, non-GLP toxicokinetic study of both IBOAc (as metabolite donor substance for IBO) and IBOMA in rats via intravenous administration is available which evaluated the hydrolysis rate of both IBOAc and IBOMA in vivo (DOW, 2019).

Three male rats per compound were intravenously administered either IBOAc or IBOMA at 7.0 mg/kg (36 µmol/kg) or 8.0 mg/kg (36 µmol/kg), respectively, using Intralipid 20% as the dose vehicle. After dose administration, blood samples (~200 μL) were collected at 5, 10, 30, 60, and 180 minutes into individual pre-weighed glass vials containing ethyl acetate (600 μL) acidified with 10% trifluoroacetic acid. After vortexing and subsequent centrifugation, the blood extracts underwent quantitative analysis for either IBOAc or IBOMA by gas chromatography with tandem mass spectrometry (GC/MS-MS).

The resulting blood time course showed that both substances were quickly hydrolyzed with less than 1.0% of the corresponding administered dose remaining in the blood 10 minutes post-intravenous administration and less than 0.1% remaining 180 minutes post-intravenous administration. Further pharmacokinetic analysis of the blood concentrations of both IBOAc and IBOMA showed that both compounds were biphasic (alpha [α] and beta [β] phases; i.e., a two-compartment model) in which there is a dominant initial distribution and hydrolysis step (i.e. t½α) with a subsequent phase of further hydrolysis and elimination (i.e. t½β). The initial distribution and hydrolysis step had average calculated half-life (t½α) values of 0.866 and 1.27 min-1 for IBOAc and IBOMA, respectively, and accounts for metabolic fate of the vast majority of the applied test substance quantities (i.e. administered dose). The secondary hydrolysis and elimination phase (t½β) had values of 55.1 and 61.1 min-1 for IBOAc and IBOMA, respectively. The cause of the t½β phase associated with the minor portion of IBOAc and IBOMA kinetics is currently unclear and may be of limited relevance to normal human physiology for occupational and consumer exposures. The average area under the curve (AUC0-t) values for IBOAc and IBOMA were 363 and 397 µg-min/g, respectively. 

Overall, the analysis of the blood pharmacokinetics indicated that both parent test materials are rapidly removed from blood circulation (i.e. blood compartment) in vivo in a very similar manner. Hence, these data support the hypothesis that IBOAc can serve as donor substance for the alcohol metabolite IBO with a high level of confidence.

 

Subsequent metabolism of Methacrylic Acid and Isoborneol within the body

Methacrylic Acid (MAA)

As taken from the OECD SIAR: “Methacrylic acid and the corresponding alcohol are subsequently cleared predominantly via the liver (valine pathway and the TCA (TriCarboxylic Acid) cycle, respectively).”

Methyl methacrylate (MMA) is rapidly degraded in the body to MAA, it can thus be understood as metabolite donor for MAA:

Taken from the OECD SIAR (2001): “Other short chain alkyl-methacrylate esters, like MMA, are initially hydrolyzed by non-specific carboxylesterases to methacrylic acid and the structurally corresponding alcohol in several tissues (ECETOC 1995, 1996b).

Moreover, studies on a number of lower alkyl-methacrylate esters completed after the year 2000 confirmed consistently their rapid hydrolysis by ubiquitous carboxylesterases (see details in the Read Across Justification). First pass (local) hydrolysis of the parent ester has been shown to be significant for all routes of exposure. Parent ester will also be effectively hydrolysed within the G.I. tract and within the tissues of the upper respiratory tract (particularly the olfactory tissue). Systemically absorbed parent ester will be effectively removed during the first pass through the liver (%LBF) resulting in their relatively rapid elimination from the body (T_50%).

A more recent study, designed to extend an earlier work on lower alkyl methacrylates (Jones 2002) to higher and more complex methacrylate esters, studied the in vitro metabolism of those esters in rat blood and liver microsomes (DOW, 2013). This study included as well MMA and confirmed earlier findings on its rapid hydrolysis (see details in the Read Across Justification).

 

Isoborneol (IBO)

In a pharmacokinetic study with 6 Wistar rats, orally administered IBO in a dose of 90 mg/kg bw was absorbed rapidly (tmax0.27 h after dosing; t1/21.33 h). In accordance to the results of other mentioned studies in the respective publication, CAM was identified as main metabolite and showed very similar kinetic properties (tmax0.28 h after dosing; t1/2 1.01 h; Sun et al. 2014).

Orientating information on the further metabolism of CAM as metabolite of IBO is available: CAM is rapidly oxidized and then conjugated in the liver to the glucuronide form. Campherol conjugated to glucuronic acid is then eliminated mainly in the urine as an inactive compound (U.S. EPA, 2006).