Registration Dossier

Administrative data

Endpoint:
basic toxicokinetics
Type of information:
other: Expert statement
Adequacy of study:
key study
Study period:
2013-02-15
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Expert statement, no study available

Data source

Reference
Reference Type:
other: Expert statement
Title:
Unnamed
Year:
2016
Report Date:
2016

Materials and methods

Test guideline
Qualifier:
no guideline followed
Guideline:
other: Expert statement
Principles of method if other than guideline:
Expert statement
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
other: Colourless liquid

Test animals

Details on test animals and environmental conditions:
not applicable

Administration / exposure

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:
not applicable
Positive control:
not applicable
Details on study design:
not applicable
Details on dosing and sampling:
not applicable
Statistics:
not applicable

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:
Generally, oral absorption is favoured for molecular weights below 500 g/mol. Since dissolution of cyclohexylidenebis[tert-butyl] peroxide in the gastro-intestinal fluids is limited by its lipophilic properties (log Pow > 4 and water solubility 1mg/L) absorption through the mucosal surface is estimated to be slow. Administered without a vehicle in an acute oral toxicity study performed on rats, cyclohexylidenebis[tert-butyl] peroxide (65 % solution) lead to a LD50 of 16653 mg/kg bw/day. Furthermore, long-term administration of cyclohexylidenebis[tert-butyl] peroxide in a combined repeated dose toxicity study with the reproduction/developmental toxicity screening study (OECD guideline 422) indicate that the compound, and to a lower amount, its hydrolysis products became bioavailable. This is supported by the result of the developmental toxicity study (OECD guideline 414) and the subchronic repeated dose toxicity study (OECD guideline 408). Changes in organ weight (kidney and liver) were observed in both studies. Dose related elevation of the protein, ketone and leucocytes content of the urine observed in the 90 day study substantiate the fact that the substance influence the activity of the kidneys and therefore becomes bioavailable.
As indicated by the half-life values from the hydrolysis test, a certain proportion of cyclohexylidenebis[tert-butyl] peroxide will hydrolyze to tert-butyl hydroperoxide and cyclohexanone following oral administration which is indicated by the half-live in an aqueous solution at acidic to neutral conditions. The results of the hydrolysis tests at a pH range of 4 to 9 are somewhat representative for the conditions found in the GIT with the stomach having an acidic milieu (~ pH 1.4 to 4.5) and the intestine a slightly acidic to slightly alkaline milieu
(~ pH 5 to 8). Due to the lower log Pow values of the hydrolysis products, readily absorption through the GIT epithelium is assumed. Furthermore, molecular weights of the hydrolysis products combined with their relatively high water solubility (> 10 g/L) may allow the direct uptake into the systemic circulation through aqueous pores or via carriage of the molecules across the membrane with the bulk passage of water.
Based on the vapour pressure of 12.3 Pa at 25 °C cyclohexylidenebis[tert-butyl] peroxide might become available for inhalation only to a lower extend. If the substance would reach the lungs in its vapour or gaseous state, slow absorption directly across the respiratory tract epithelium by passive diffusion is likely to occur due to its log Pow value and water solubility. Since specific effects of systemic toxicity were observed after oral administration systemic availability is expected also after inhalation exposure.
Cyclohexylidenebis[tert-butyl] peroxide is unlikely to penetrate through the skin as the log Pow value and water solubility limit dermal penetration. It is general accepted that if a compound’s water solubility is low (1 mg/L), absorption can be anticipated to be low. Moreover, for substances with a log Pow above 4, both penetration into stratum corneum and partition into the epidermis are unlikely to occur. These assumptions based on the physico-chemical properties of cyclohexylidenebis[tert-butyl] peroxide are further supported by the results achieved from an acute dermal toxicity study performed on rabbits. During this study no test item related mortality and no specific effects of systemic toxicity were observed. The LD50 was > 2000 mg/kg bw. However, cyclohexylidenebis[tert-butyl] peroxide caused slight skin irritation which in turn may favour direct absorption into the systemic circulation.
Taken together, physico-chemical properties and experimental data indicate bioavailability of cyclohexylidenebis[tert-butyl] peroxide via oral and to a lesser extend also via inhalation and dermal route.
Details on distribution in tissues:
Assuming that cyclohexylidenebis[tert-butyl] peroxide 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. However, slow hydrolysis of cyclohexylidenebis[tert-butyl] peroxide into tert-butyl hydroperoxide and cycohexanone is likely to occur. As mentioned above, the physico-chemical properties, especially the lower molecular weight and relatively high water solubility of the hydrolysis products favour systemic absorption. Direct transport through aqueous pores is likely to be an entry route to the systemic circulation. The results from the combined repeated dose toxicity study with the reproduction/developmental toxicity screening test indicate that, following absorption, the liver and the kidney are the primary target organs affected by the chemical. Elevated liver weight at 1000, 300, and 100 mg/kg bw/day and kidney weights at 1000 mg/kg bw/day compared to control group were observed. Similar results were observed in the read across study (OECD guideline 414) determining the developmental toxicity over a period of 20 days. Females had an enlarged liver at necropsy at doses of 1000, 300 and 100 mg/kg bw/day. Also minimal to moderate centribular hypertrophy of hepatocytes was evident in females from all treatment groups. Further evidence can be found in the 90 days repeated dose toxicity study, showing changes in some urine parameters, in male animals and in organ weights (kidney and liver weights – male and female). Also occurance of hyaline-like droplets in the epithel cells of proximal convoluted tubules of males was observed.
Details on excretion:
As discussed above, cyclohexylidenebis[tert-butyl] peroxide will be hydrolysed both after being in contact with an aqueous solution or enzymatically and will probably not be excreted in its unhydrolysed form. The degradation products tert-butyl hydroperoxide and cyclohexanone have a low molecular weight (90.12 g/mol and 98.15 g/mol, respectively), are miscible in water and thus may directly be excreted by urine. Cyclohexanone was shown to be converted to 1,2- and 1,4-cyclohexanol and excreted via urine in its unconjugated or conjugated form (Mraz et al., 1994).

Metabolite characterisation studies

Details on metabolites:
Based on the structure of the molecule, cyclohexylidenebis[tert-butyl] peroxide may be hydrolysed after being in contact with an aqueous solution as well as enzymatically. The first degradation product tert-butyl hydroperoxide may be converted by glutathione peroxidase into tert-butanol which in turn could be conjugated with glucuronic acid or sulfate to increase the compound’s hydrophilicity (Chance, B. et al. 1979). Oxidation of tert-butanol by alcohol dehydrogenases (ADH) and aldehyde dehydrogenases (AlDH) is an alternative metabolic pathway resulting in 2,2-dimethyl-propionic acid (pivalic acid). Pivalic acid is estimated to be conjugated with glucuronic acid or amino-acids like glutamine in order to ultimately facilitate excretion. The second degradation product, cyclohexanone, was shown to be reduced to cyclohexanol and subsequently converted to 1,2- and 1,4-cyclohexanol (Mraz et al., 1994). Thus, metabolites are not assumed to be more toxic than the parent compound which is further supported by the results obtained in the in vitro mutation and cytogenetic assays in the presence of a metabolic activation system.

Bioaccessibility

Bioaccessibility testing results:
Physico-chemical properties, particularly water solubility and octanol-water partition coefficient and experimental data indicate bioavailability of cyclohexylidenebis[tert-butyl] peroxide via oral and inhalation and to a lesser extend also via dermal route.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): no bioaccumulation potential based on study results
Physico-chemical properties,particularly water solubility and octanol-water partition coefficient and experimental data indicate bioavailability of cyclohexylidenebis[tert-butyl] peroxide via oral and to a lesser extend also via inhalation and dermal route. Intracellular concentration is likely to be higher than extracellular due to the lipophilicity of cyclohexylidenebis[tert-butyl] peroxide. Hydrolytic and metabolic conversion into tert-butyl hydroperoxide and cyclohexanone is expected and hydroxylation/conjugation of Phase I-metabolites may further increase hydrophilicity. Metabolites of cyclohexylidenebis[tert-butyl] peroxide are not considered to be more toxic than cyclohexylidenebis[tert-butyl] peroxide itself. Excretion via urine is assumed to be the main excretion pathway of metabolites formed due to their molecular weight ( 300 g/mol in rat) and water solubility. Bioaccumulation of cyclohexylidenebis[tert-butyl] peroxide itself and its hydrolysis products is not likely to occur due to hydrolytic degradation and the physico-chemical properties of the hydrolysis products.