Cyclopropanecarboxylic acid, 2-[1-(3,3-dimethylcyclohexyl)ethoxy]-2-methylpropyl ester

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics, other

Remarks:

An assessment of toxicokinetics, based on available data, in accordance with Annex VIII, Section 8.8.1 of Regulation (EC) No 1907/2006

Type of information:

other: Desk-based assessment

Adequacy of study:

key study

Study period:

Not applicable

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

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

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2020

Materials and methods

Objective of study:

toxicokinetics

Principles of method if other than guideline:

An assessment of toxicokinetics, based on available data, in accordance with Annex VIII, Section 8.8.1 of Regulation (EC) No 1907/2006

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

-

EC Number:

460-490-0

EC Name:

-

Cas Number:

477218-42-1

Molecular formula:

C18H32O3

IUPAC Name:

2-[(1S)-1-[(1R)-3,3-dimethylcyclohexyl]ethoxy]-2-methylpropyl cyclopropanecarboxylate; 2-[(1S)-1-[(1S)-3,3-dimethylcyclohexyl]ethoxy]-2-methylpropyl cyclopropanecarboxylate

Details on test material:

Detailed information on the 'test material identity' is provided in the attached document including information on individual constituents.

Test animals

Details on species / strain selection:

No animals were used in this desk-based assessment.

Details on test animals or test system and environmental conditions:

Not applicable

Administration / exposure

Details on exposure:

Desk-based assessment.

Duration and frequency of treatment / exposure:

Desk-based assessment.

No. of animals per sex per dose / concentration:

No animals were used in this desk-based assessment.

Positive control reference chemical:

Desk-based assessment.

Details on study design:

Not applicable

Details on dosing and sampling:

Not applicable

Statistics:

Not applicable

Results and discussion

Preliminary studies:

Desk-based assessment.

Toxicokinetic / pharmacokinetic studies

Details on absorption:

The physicochemical properties of the substance i.e. molecular weight of 296.451 g/mol, vapor pressure of 1.5 Pa at 20 °C, Log Pow of 5.5 to 5.6 at 35 °C, along with water solubility of 3.85 mg/L at 20 °C are indicative of potential absorption by oral route with uptake via intracellular pathway. Intake from the intracellular and active transport (influx) pathway exits through the basolateral membrane into the portal blood which results in first pass metabolism in the liver, this means that the concentration of the parent substance is reduced before reaching systemic circulation. Evidence of oral absorption is demonstrated by the clinical and macroscopic abnormalities observed following sub-acute oral exposure. Although similar absorption pattern is expected via inhalation, the substance is not highly volatile (vapor pressure of 1.5 Pa at 20 °C and high boiling point of 331 °C), this means bioavailability via this route is more limited. This is supported by the low acute inhalation toxicity observed in rat. In the absence of specific absorption data via this route, the conservative default route-to-route extrapolation can be applied with pulmonary absorption set at 100% for risk assessment purpose. Based on the high Log Pow of 5.5 to 5.6, the molecular weight above 100 g/mol, the low surface activity (surface tension 49.9 mN/m) and low water solubility, indicates dermal absorption may be more limited since the rate of penetration can be limited by the rate of transfer between the stratum corneum and the epidermis. Nevertheless, based on the indicated sensitisation potential of the test item, it shows some systemic uptake must occur although it may only be a small fraction of the applied dose. It can be considered the overall uptake via this route is very low demonstrated by the lack of toxicity observed following exposure during in vivo dermal studies. As a Tier I screen, in the absence of absorption data via this route, the conservative default value of 100% adsorption is used for risk assessments.

Details on distribution in tissues:

Based on the physicochemical properties and the observation of systemic toxicity following sub-acute exposure, a wide distribution of substance and/or its metabolite is expected. This is supported by observed histopathological changes in the heart, skeletal muscle, kidneys, Harderian gland, liver, and thyroid following sub-acute oral exposure at specified higher dose levels. Reduced mean grip strength and sedation are a demonstration of potential distribution to central nervous system (CNS). As the log Pow value is > 4 a longer biological half-life is expected resulting in a build-up of substance following continuous exposure at high concentration. This would result in toxicity as demonstrated in some of the histopathological changes observed after the two weeks recovery within the specified higher dose levels of the OECD 407 (2004) study within rats. Distribution of the substance into/past the stratum corneum is also expected based on log Pow of 5.6 as noted by the sensitisation observed in guinea pig and mice studies. However, based on the physicochemical properties of the substance systemic distribution via dermal exposure is more limited. Additionally, accumulation is more limited to the stratum corneum, and it is considered can be eventually be cleared as the stratum corneum is sloughed off.

Details on excretion:

The substance Log Pow is in the range of 5.5 to 5.6. The water solubility of 3.85 mg/L and the molecular weight of < 500 are indicative of longer biological half-life resulting in a build-up of the substance in vivo following absorption via the GI tract. However, uptake of the substance through intracellular and active transport (influx) pathway(s) and subsequent exit through the basolateral membrane into the portal blood would result in first pass metabolism in the liver. The metabolites are expected to be more polar derivatives, excreted via urine. Based on the molecular structure and solubility, they would be excreted into bile and urine as conjugated metabolites. Glucuronide conjugates are extensively excreted via bile, whereas sulphate conjugates are excreted via urine. This is supported by observed increased kidney weights with high incidences hyaline droplets and tubular basophilia following sub-acute exposure via oral route.

Metabolite characterisation studies

Metabolites identified:

not measured

Details on metabolites:

Metabolism is primarily through reductive and oxidative Phase I enzyme-catalyzed reactions in the liver and the GI track as demonstrated by the observed hepatocyte vacuolation which is considered an adaptive response to a xenobiotic. The main metabolic enzymes are non-P450 aldehyde reduction enzyme systems alcohol dehydrogenase (ADH), aldo-keto reductase (AKR) and short-chain dehydrogenase/reductase (SDR), and aldehyde oxidation enzyme systems xanthine oxidase (XO), aldehyde oxidase (AOX), aldehyde dehydrogenase (ALDH), esterase and hydrolases. Based on the structure of the substance: the metabolic pathway (hydrolysis) involving esterases and hydrolases are the most common and will result into production of: alcohol, aldehyde, carboxylic acid and ketone metabolite derivatives. The alcohol, aldehyde and ketone derivatives will be metabolised mainly by ADH, ALDH and to a lesser extend AKR, OX and AOX enzyme systems; producing carboxylic acid derivative(s). The carboxylic acidic derivatives will be further conjugated with glucuronides and sulphate via glucuronsyl transferase and sulphotransferase with subsequent elimination via urine. At low dose exposure, sulphation is expected to dominate, but as the doses increase glucuronidation becomes the major route of metabolism as glucuronsyl transferase has higher capacity than sulphotransferase. Observed metabolic turnover of the substance by Rainbow trout liver S9 fractions in vitro and observed increased metabolic enzyme activities such as aspartate aminotransferase and lactate dehydrogenase in rat in vivo studies are indicative of substance biotransformation. Histopathological changes in the liver in the form of increased incidence and mean grades of liver fatty change and increased incidence and mean grades of hepatocellular (centrilobular) hypertrophy, were observed within OECD 407 and OECD 422 studies and which are further indication of metabolism.

Applicant's summary and conclusion

Conclusions:

The substance possesses physicochemical properties which are favourable for ADME. The substance possesses physicochemical properties which are favourable for ADME. Available data demonstrate the potential for absorption as evidence by systemic toxicity under sub-acute oral exposure. The substance and its metabolites are widely distributed as demonstrated by observed effects in various organs including the Central Nervous System (CNS). Observations in liver and kidney demonstrate the biotransformation and elimination of the substance and its metabolites. There was no evidence of accumulation observed at the primary site of exposure (the gut) as demonstrated in the longer-term studies. In addition, the bioconcentration factor (BCF) within fish (corrected for mean lipid content 5%) was reported as 103 L/kg ww. The substance is not acutely toxic via all tested routes of exposure (oral, inhalation and dermal). Although no irritation is observed via local exposure, sensitisation was noted in vivo, this demonstrates potential protein binding, although the lack of observed systemic toxicity could be demonstration of reduced uptake from/through the stratum corneum. Specific target organ toxicities in the heart, lung, kidney and liver within sub-acute studies were reported. These consisted of minimal acinar degeneration, minimal to slight acinar hyperplasia, and increased porphyrin deposition in Harderian gland. In the heart, at higher administered dose levels: minimal to severe sarcoplasmic vacuolation, minimal to moderate single cell necrosis, increased incidence and mean grade of mononuclear foci, and minimal myocardial (interstitial) fibrosis were recorded in both sexes and multifocal progressive cardiomyopathy in observed females. In the kidney, increased incidence and mean grade of hyaline droplets and of tubular basophilia was recorded in the kidney of treated males; this was considered unrelated to treatment. Centrilobular hypertrophy was noted in the liver within 5/10 males and 5/10 females and haematopoiesis increased in females. Changes in the liver were considered an adaptive response since it was associated with hepatic enzyme induction i.e. increase aspartate aminotransferase activity (both sexes), elevated lactate dehydrogenase activity (females) and the elevated metabolite; ketone (both sexes). This toxicity is potentially driven by the log Pow which is within the range of 5.5 to 5.6 and the water solubility of 3.85 mg/L, which result in a longer biological half-life with potential accumulation of the substance following continuous exposure at high concentrations. However, the molecular weight is low with uptake via intracellular and active transport (influx) expected resulting in first pass metabolism with reduction in the concentration of the parent substance. Metabolism is influence by enzyme activity and continuous exposure especially at high concentration would result in enzymes saturation and reduced output. It is considered highly likely that this is the driving factor in the observed toxicity rather than tissue. It can be concluded that the bioaccumulation potential of the substance is low. However, it is noted that a prolonged half-life may result from metabolic output reduction which could result from enzyme saturation under continuous exposures at high concentrations.

Executive summary:

A desk-based assessment of the basic toxicokinetics of the substance, in accordance with Regulation (EC) 1907/2006: Annex VIII - Section 8.8.1. The substance possesses physicochemical properties which are favourable for ADME. Available data demonstrate the potential for absorption as evidence by systemic toxicity under sub-acute oral exposure. The substance and its metabolites are widely distributed as demonstrated by observed effects in various organs including the Central Nervous System (CNS). Observations in liver and kidney demonstrate the biotransformation and elimination of the substance and its metabolites. There was no evidence of accumulation observed at the primary site of exposure (the gut) as demonstrated in the longer-term studies such as the OECD, 407 and OECD 421. In addition, the bioconcentration factor (BCF) within fish (corrected for mean lipid content 5%) was reported as 103 L/kg ww, which is significantly lower than the cut of value of 2000 for substances that would be considered bioaccumulative. The substance is not acutely toxic via all tested routes of exposure (oral, inhalation and dermal). Although no irritation is observed via local exposure, sensitisation was noted in vivo in both guinea pig and mice studies, this demonstrates potential protein binding, although the lack of observed systemic toxicity could be demonstration of reduced uptake from/through the stratum corneum. Specific target organ toxicities in the heart, lung, kidney and liver within sub-acute studies were reported. These consisted of minimal acinar degeneration, minimal to slight acinar hyperplasia, and increased porphyrin deposition in Harderian gland. In the heart, at higher administered dose levels: minimal to severe sarcoplasmic vacuolation, minimal to moderate single cell necrosis, increased incidence and mean grade of mononuclear foci, and minimal myocardial (interstitial) fibrosis were recorded in both sexes and multifocal progressive cardiomyopathy in observed females. In the kidney, increased incidence and mean grade of hyaline droplets and of tubular basophilia was recorded in the kidney of treated males; this was considered unrelated to treatment. Centrilobular hypertrophy was noted in the liver within 5/10 males and 5/10 females and haematopoiesis increased in females. Changes in the liver were considered an adaptive response since it was associated with hepatic enzyme induction i.e. increase aspartate aminotransferase activity (both sexes), elevated lactate dehydrogenase activity (females) and the elevated metabolite; ketone (both sexes). This toxicity is potentially driven by the substance n-Octanol/Water partition coefficient (log Pow) which is within the range of 5.5 to 5.6 and the water solubility of 3.85 mg/L, which result in a longer biological half-life with potential accumulation of the substance following continuous exposure at high concentrations. However, the molecular weight is low with uptake via intracellular and active transport (influx) expected resulting in first pass metabolism with reduction in the concentration of the parent substance. Metabolism is influence by enzyme activity and continuous exposure especially at high concentration would result in enzymes saturation and reduced output. It is considered highly likely that this is the driving factor in the observed toxicity rather than tissue bioaccumulation especially since a reversal was observed as demonstrated by recovery and/or reduction in specific histopathological changes observed during the two weeks recovery period under the OECD 407 study in rats.It can be concluded that the bioaccumulation potential of the substance is low. However, it is noted that a prolonged half-life may result from metabolic output reduction which could result from enzyme saturation under continuous exposures at high concentrations. This was supported by the observations of reversal/reduction of effects at low administered concentrations during the recovery phase of the OECD 407 study.