1,1,3,3-tetramethylbutyl peroxyneodecanoate

Repeated dose toxicity: oral

Administrative data

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

The study was performed between 17 January 2012 (formulation chemistry) and 23 February 2013. The in-life phase of the study was conducted between 14 February 2012 (first day of treatment) and 13 March 2012 (final day of necropsy).

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

2013

Report date:

2013

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

2013

Report date:

2013

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 407 (Repeated Dose 28-Day Oral Toxicity Study in Rodents)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.7 (Repeated Dose (28 Days) Toxicity (Oral))

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

1,1,3,3-tetramethylbutyl peroxyneodecanoate

EC Number:

257-077-0

EC Name:

1,1,3,3-tetramethylbutyl peroxyneodecanoate

Cas Number:

51240-95-0

Molecular formula:

C18H36O3

IUPAC Name:

2,4,4-trimethylpentan-2-yl 2,2,3,5-tetramethylhexaneperoxoate; 2,4,4-trimethylpentan-2-yl 2,2-diethylhexaneperoxoate; 2,4,4-trimethylpentan-2-yl 2,2-dimethyloctaneperoxoate; 2,4,4-trimethylpentan-2-yl 2,4-dimethyl-2-(propan-2-yl)pentaneperoxoate; 2,4,4-trimethylpentan-2-yl 2-ethyl-2,5-dimethylhexaneperoxoate

Test material form:

other: Liquid

Details on test material:

- Name of test material (as cited in study report): 1,1,3,3-Tetramethylbutyl peroxyneodecanoate (CAS Number: 51240-95-0)
- Physical state: Clear colourless liquid
- Analytical purity: 93.2%
- Composition of test material, percentage of components: The test item is a 71.6% solution of 1,1,1,3-tetramethylbutyl peroxyneodecanoate (CAS Number: 51240-95-0) in isododecane and was tested as received.
- Lot/batch No.: 1110447097
- Expiration date of the lot/batch: 01 September 2012
- Storage condition of test material: Stored at approximately - 20ºC
- Other: Date received: 13 December 2011

Test animals

Species:

rat

Strain:

other: Wistar Han™:RccHan™:WIST

Sex:

male/female

Details on test animals or test system and environmental conditions:

Male and female rats were obtained from Harlan Laboratories U.K. Ltd. On receipt the animals were examined for signs of ill-health or injury. The animals were acclimatised for six days during which time their health status was assessed. A total of forty animals (twenty males and twenty females) were accepted into the study. At the start of treatment the males weighed 196 to 226 g, the females weighed 165 to 183 g, and were approximately six to eight weeks old.

The animals were housed in groups of five by sex in solid floor polypropylene cages with stainless steel mesh lids and softwood flake bedding. The animals were allowed free access to food and water. A pelleted diet was used. Mains drinking water was supplied from polycarbonate bottles attached to the cage. The diet and drinking water were considered not to contain any contaminant at a level that might have affected the purpose or integrity of the study. Environmental enrichment was provided in the form of wooden chew blocks and cardboard fun tunnels.

The animals were housed in a single air-conditioned room within the Harlan Laboratories Ltd. Barrier Maintained Rodent Facility. The rate of air exchange was at least fifteen air changes per hour and the low intensity fluorescent lighting was controlled to give twelve hours continuous light and twelve hours darkness. Environmental conditions were continuously monitored by a computerised system, and print-outs of hourly temperatures and humidities are included in the study records. The temperature and relative humidity controls were set to achieve Study Plan target values of 22 ± 3ºC and 50 ± 20% respectively, there were no deviations from these target ranges.

The animals were randomly allocated to treatment groups using a stratified body weight randomisation procedure and the group mean body weights were then determined to ensure similarity between the treatment groups. The cage distribution within the holding rack was also randomised. The animals were uniquely identified within the study by an ear punching system routinely used in these laboratories.

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

arachis oil

Details on oral exposure:

The test item was administered daily, for twenty-eight consecutive days, by gavage using a stainless steel cannula attached to a disposable plastic syringe. Control animals were treated in an identical manner with 4 ml/kg of Arachis oil BP.

The volume of test and control item administered to each animal was based on the most recent body weight and was adjusted at weekly intervals.

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

Twenty-eight consecutive days.

Frequency of treatment:

Daily.

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
30 mg/kg bw/day
Basis:
actual ingested

Doses / concentrations 2

Remarks:

Doses / Concentrations:
300 mg/kg bw/day
Basis:
actual ingested

Doses / concentrations 3

Remarks:

Doses / Concentrations:
1000 mg/kg bw/day
Basis:
actual ingested

No. of animals per sex per dose:

The test item was administered to three groups, each of five male and five female rats at dose levels of 30, 300 and 1000 mg/kg bw/day. A control group of five males and five females was dosed with vehicle alone (Arachis oil BP).

Control animals:

yes, concurrent vehicle

Details on study design:

The rat was selected for this study as it is a readily available rodent species historically used in safety evaluation studies and is acceptable to appropriate regulatory authorities.

The dose levels were chosen based on the results from previous toxicity work including a preliminary seven day range-finder investigation.

The oral route was selected as the most appropriate route of exposure, based on the physical properties of the test item, and the results of the study are believed to be of value in predicting the likely toxicity of the test item to man.

Positive control:

No data

Examinations

Observations and examinations performed and frequency:

Clinical Observations:
All animals were examined for overt signs of toxicity, ill-health or behavioural change immediately before dosing, up to thirty minutes post dosing and one and five hours after dosing during the working week. Animals were observed immediately before and after dosing and one hour after dosing at weekends. All observations were recorded.

Functional Observations:
Prior to the start of treatment (Day -1) and on Days 7, 14, 21 and 27, all animals were observed for signs of functional/behavioural toxicity. Functional performance tests were also performed on all animals during Week 4, together with an assessment of sensory reactivity to different stimuli. Observations were carried out from approximately two hours after dosing on each occasion.

Behavioural Assessments:
Detailed individual clinical observations were performed for each animal using a purpose built arena. The following parameters were observed:

Gait
Tremors
Twitches
Convulsions
Bizarre/Abnormal/Stereotypic behaviour
Salivation
Pilo-erection
Exophthalmia
Lachrymation
Hyper/Hypothermia
Skin colour
Respiration
Palpebral closure
Urination
Defecation
Transfer arousal
Tail elevation

This test was developed from the methods used by Irwin (1968) and Moser et al (1988). The scoring system used is outlined in The Key to Scoring System and Explanation for Behavioural Assessments and Sensory Reactivity Tests.

Functional Performance Tests:
Motor Activity - Twenty purpose built 44 infra-red beam automated activity monitors were used to assess motor activity. Animals of one sex were tested at each occasion and were randomly allocated to the activity monitors. The evaluation period was one hour for each animal. The time in seconds each animal was active and mobile was recorded for the overall one hour period and also during the final 20% of the period (considered to be the asymptotic period, Reiter and Macphail, 1979).

Forelimb/Hindlimb Grip Strength - An automated grip strength meter was used. Each animal was allowed to grip the proximal metal bar of the meter with its forepaws. The animal was pulled by the base of the tail until its grip was broken. The animal was drawn along the trough of the meter by the tail until its hind paws gripped the distal metal bar. The animal was pulled by the base of the tail until its grip was broken. A record of the force required to break the grip for each animal was made. Three consecutive trials were performed for each animal. The assessment was developed from the method employed by Meyer et al (1979).

Sensory Reactivity:
Each animal was individually assessed for sensory reactivity to auditory, visual and proprioceptive stimuli. This assessment was developed from the methods employed by Irwin (1968) and Moser et al (1988). The scoring system used is outlined in The Key to Scoring System and Explanation for Behavioural Assessments and Sensory Reactivity Tests.

The following parameters were observed:

Grasp response
Vocalisation
Toe pinch
Tail pinch
Finger approach
Touch escape
Pupil reflex
Blink reflex
Startle reflex

Body Weight:
Individual body weights were recorded on Day 1 and at weekly intervals thereafter. Body weights were also performed prior to terminal kill.

Food Consumption:
Food consumption was recorded for each cage group at weekly intervals throughout the study. Food conversion efficiency was calculated retrospectively.

Water Consumption:
As a possible increase in water consumption was observed in the preliminary study, formal gravimetric measurement of water intake was performed on a daily basis throughout the study.

Sacrifice and pathology:

On completion of the dosing period all animals were killed by intravenous overdose of sodium pentobarbitone followed by exsanguination.

All animals were subjected to a full external and internal examination, and any macroscopic abnormalities were recorded.

Thyroid Hormone Assessment:
At termination, blood samples were taken from the exsanguination procedure and the serum from each animal was stored frozen at approximately -20°C. No treatment-related effects on the pituitary-thyroid axis were identified, therefore these samples were not analysed and were discarded.

Organ Weights:
The following organs, removed from animals that were killed at the end of the study, were dissected free from fat and weighed before fixation:

Adrenals
Brain
Epididymides
Heart
Kidneys
Pituitary (post-fixation)
Prostate and Seminal Vesicles (with coagulating glands and fluids)
Liver
Ovaries
Spleen
Testes
Thymus
Thyroid/Parathyroid
Uterus with Cervix

Histopathology:
Samples of the following tissues were removed from all animals and preserved in buffered 10% formalin except where stated:

Adrenals ■
Aorta (thoracic)
Bone & bone marrow (femur including stifle joint)
Bone & bone marrow (sternum) ■
Brain (including cerebrum, cerebellum and pons) ■
Caecum ■
Colon ■
Duodenum ■
Epididymides ♦ ■
Eyes * ■
Gross lesions ■
Heart ■
Ileum ■
Jejunum ■
Kidneys ■
Liver ■
Lungs (with bronchi)# ■
Lymph nodes (mandibular and mesenteric) ■
Mammary gland ■
Muscle (skeletal) ■
Oesophagus ■
Ovaries ■
Pancreas
Pituitary ■
Prostate ■
Rectum ■
Salivary glands (submaxillary)
Sciatic nerve ■
Seminal vesicles (with coagulating glands and fluids) ■
Skin (hind limb)
Spinal cord (cervical, mid-thoracic and lumbar) ■
Spleen ■
Stomach ■
Testes ♦ ■
Thymus ■
Thyroid/Parathyroid ■
Trachea ■
Urinary bladder ■
Uterus & Cervix ■
Vagina ■

♦ = preserved in Bouin’s fluid then transferred to Industrial Methylated Spirits (IMS) approximately 48 hours later
* = eyes fixed in Davidson’s fluid
# = Lungs were inflated to approximately normal inspiratory volume with buffered 10% formalin before immersion in fixative

All tissues were despatched to the histology processing Test Site for processing. The tissues shown with the following symbol after their name ■ from all control and 1000 mg/kg bw/day dose group animals were prepared as paraffin blocks, sectioned at a nominal thickness of 5 µm and stained with Haematoxylin and Eosin for subsequent microscopic examination. In addition, sections of testes and epididymides were stained with Periodic Acid-Schiff (PAS) stain and examined. Any macroscopically observed lesions in all dosage groups were also similarly processed, together with the liver and spleen from all 30 and 300 mg/kg bw/day dose group animals.

Since there were indications of treatment-related changes, examination was subsequently extended to include similarly prepared sections of kidneys and thyroids from all animals from the 30 and 300 mg/kg bw/day groups.

Other examinations:

Laboratory Investigations:
Haematological and blood chemical investigations were performed on all animals from each test and control group at the end of the study (Day 28). Blood samples were obtained from the lateral tail vein. Where necessary repeat samples were obtained by cardiac puncture prior to necropsy on Day 29. Animals were not fasted prior to sampling.

Haematology:
The following parameters were measured on blood collected into tubes containing potassium EDTA anti-coagulant:

Haemoglobin (Hb)
Erythrocyte count (RBC)
Haematocrit (Hct)
Erythrocyte indices
- mean corpuscular haemoglobin (MCH)
- mean corpuscular volume (MCV)
- mean corpuscular haemoglobin concentration (MCHC)
Total leucocyte count (WBC)
Differential leucocyte count
- neutrophils (Neut)
- lymphocytes (Lymph)
- monocytes (Mono)
- eosinophils (Eos)
- basophils (Bas)
Platelet count (PLT)
Reticulocyte count (Retic)

Prothrombin time (CT) was assessed by ‘Innovin’ and Activated partial thromboplastin time (APTT) was assessed by ‘Actin FS’ using samples collected into sodium citrate solution (0.11 mol/l).

Blood Chemistry:
The following parameters were measured on plasma from blood collected into tubes containing lithium heparin anti-coagulant:

Urea
Glucose
Total protein (Tot.Prot.)
Albumin
Albumin/Globulin (A/G) ratio (by calculation)
Sodium (Na+)
Potassium (K+)
Chloride (Cl-)
Calcium (Ca++)
Inorganic phosphorus (P)
Aspartate aminotransferase (ASAT)
Alanine aminotransferase (ALAT)
Alkaline phosphatase (AP)
Creatinine (Creat)
Total cholesterol (Chol)
Total bilirubin (Bili)
Bile acids

Statistics:

Data were processed to give summary incidence or group mean and standard deviation values where appropriate. All data were summarised in tabular form.

Where considered appropriate, quantitative data was subjected to statistical analysis to detect the significance of intergroup differences from control; statistical significance was achieved at a level of p<0.05. Statistical analysis was performed on the following parameters:

Grip Strength, Motor Activity, Body Weight Change, Haematology, Blood Chemistry, Absolute Organ Weights, Body Weight-Relative Organ Weights

Data were analysed using the decision tree from the ProvantisTM Tables and Statistics Module as detailed below:

Where appropriate, data transformations were performed using the most suitable method. The homogeneity of variance from mean values was analysed using Bartlett’s test. Intergroup variance were assessed using suitable ANOVA, or if required, ANCOVA with appropriate covariates. Any transformed data were analysed to find the lowest treatment level that showed a significant effect, using the Williams Test for parametric data or the Shirley Test for non-parametric data. If no dose response was found, but the data shows non-homogeneity of means, the data were analysed by a stepwise Dunnett’s (parametric) or Steel (non-parametric) test to determine significant difference from the control group. Where the data were unsuitable for these analyses, pair-wise tests was performed using the Student t-test (parametric) or the Mann-Whitney U test (non-parametric).

Probability values (p) are presented as follows:

p<0.01 **
p<0.05 *
p>=0.05 (not significant)

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Clinical signs were restricted to post-dosing salivation for both sexes at 300 and 1000 mg/kg bw/day. A higher incidence of urination and defecation was noted for males at 1000 mg/kg bw/day during the last week of the study, although no similar findings were apparent for these animals during routine daily assessment of clinical signs, or for females at this dosage.

Mortality:

no mortality observed

Description (incidence):

There were no unscheduled deaths on the study.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

At 1000 mg/kg bw/day mean body weight gain of males tended to be slightly lower than control throughout the study, although differences only attained statistical significance during Week 3. By termination, overall body weight gain for the treatment period was only 81% of the concurrent control.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

At 1000 mg/kg bw/day food intake for males was slightly lower than control during Week 1 and Week 3. Although there was a suggestion of lower food intake during Week 1 for females at this dosage, the differences from control were slight and probably reflect normal biological variation. Subsequent food intake for the remainder of the study was essentially similar or slightly superior to control.

Food efficiency:

no effects observed

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

At 1000 mg/kg bw/day, water consumption for both sexes was notably higher than control throughout the study.
At 300 mg/kg bw/day water consumption of males tended to be higher than control during the first two weeks of treatment; thereafter water intake was generally similar to control. Water consumption of females at this dosage appeared unaffected by treatment.
At 30 mg/kg bw/day water consumption for both sexes was considered to have been unaffected by treatment. For females at this dosage, water consumption was noticeably higher than control on some occasions but in the absence of any similar increases for females at 300 mg/kg bw/day, these differences were considered to be incidental and unrelated to treatment.

Ophthalmological findings:

not specified

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

See below

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

See below

Urinalysis findings:

not examined

Behaviour (functional findings):

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

See below

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

At 1000 mg/kg bw/day, four males showed dark liver at necropsy, one of these males also showed pallor of the kidneys and a small prostate/seminal vesicles. At 300 mg/kg bw/day, one male showed pallor of the kidneys.

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

See below

Histopathological findings: neoplastic:

no effects observed

Details on results:

Assessment of the animals in a standard arena did not reveal any obvious neurological effects of treatment at 30, 300 or 1000 mg/kg bw/day.


The increased incidence of urination in males of the 1000 mg/kg bw/day group probably reflects the higher water consumption and, possibly also, the microscopic kidney changes observed for males at this dosage. In isolation, these findings were considered not to indicate any underlying behavioural or neurological effect of treatment.


Assessment of grip strength or motor activity did not reveal any consistent pattern of results that indicated an adverse effect of treatment at 30, 300 or 1000 mg/kg bw/day. For females at 1000 mg/kg bw/day lower hind limb grip strength during Test 2 attained statistical significance when compared with control. No statistically significant differences from control were apparent during the other assessment of grip strength at this dosage and, in isolation, this finding was considered incidental and unrelated to treatment. For females at 30 mg/kg bw/day lower fore limb grip strength during Test 1 attained statistical significance when compared to control. This isolated finding, in the absence of similar effects at higher dosages, was considered incidental and unrelated to treatment.


Sensory reactivity to different stimuli did not reveal any adverse effect of treatment at 30, 300 or 1000 mg/kg bw/day.


In males, at 300 and 1000 mg/kg bw/day lower haemoglobin, erythrocyte count and haematocrit values attained statistical significance compared with control. At 1000 mg/kg bw/day, mean values and the majority of individual values were also lower than the historical control range. At 300 mg/kg bw/day, while three of the five values for erythrocyte count were lower than the historical control range, the mean value was still within this control range and, for haemoglobin and haematocrit mean values and the majority of individual values were within the historical control range. Additionally at 1000 mg/kg bw/day, mean corpuscular haemoglobin was also statistically significantly lower than control. This seems to represent high values within the control rather than any adverse effect of treatment as all values at 1000 mg/kg bw/day were within the historical control range while three controls values exceeded this historical range. At 1000 mg/kg bw/day mean platelet count was higher than control, with differences attaining statistical significance. All individual values at this dosage exceeded the historical control range, but two of the five control values also exceeded this range. At all dosages mean corpuscular haemoglobin concentration was lower than control with differences attaining statistical significance. Once again this seems to represent high control values, with three controls exceeding the historical control range compared to none within the treatment groups. At all dosages, mean total leucocyte count was higher than concurrent control principally due to an increase in the mean number of neutrophils; these differences showed a dose-response relationship and attained statistical significance. With the exception of one male at 30 mg/kg bw/day, the individual neutrophil counts for treated males exceeded the historical control range and this range was also exceeded for total leucocyte count by the majority of males at 1000 mg/kg bw/day. At all dosages, mean prothrombin (CT) and activated partial thromboplastin (APTT) times were statistically significantly lower than control: individual and mean values were within the control range and no clear dosage relationship was apparent for prothrombin times.


In females at 1000 mg/kg bw/day, a lower mean haemoglobin value attained statistical significance when compared to control; values for four of the five females at this dosage were lower than the historical control range. Additionally at this dosage, lower mean corpuscular haemoglobin concentration also attained statistical significance when compared to control. However, as previously observed for males, this may represent high control values as values for all females at 1000 mg/kg bw/day were within historical control range while the control values exceeded this range. At 30 mg/kg bw/day, lower lymphocyte counts attained statistical significance when compared to control but the mean and all individual values were within the historical control range. In the absence of any similar decrease at higher dosages, this finding was considered fortuitous and unrelated to treatment. At all dosages higher neutrophil counts attained statistical significance when compared with control. The majority of individual values for treated animals exceeded the historical control range but for mean values no consistent dosage relationship was apparent.


In males, at 1000 mg/kg bw/day a higher mean albumin value attained statistical significance when compared to control; the majority of individual values and the group mean value at this dosage exceeded the historical control range. At all dosages, higher values for albumin/globulin ratio compared to control attained statistical significance and appeared to show a dose-response relationship. However, all individual and mean values for treated groups were within the historical control range, while the majority of individual control values and the control group mean were below this historical range. There were no corresponding findings noted for levels of total protein and only higher albumin levels for males at 1000 mg/kg bw/day attained statistical significance when compared to control. At all dosages, higher mean calcium levels showed a dose-response relationship and attained statistical significance; all group mean values and the majority of individual values were within the historical control range. At 1000 mg/kg bw/day higher mean sodium levels also attained statistical significance when compared with control, but all individual values at this high dosage were within the historical control range. At 300 and 1000 mg/kg bw/day, lower mean total cholesterol levels attained statistical significance compared with control. This may reflect high control levels as all control values and values at 30 mg/kg bw/day exceeded the historical control range, while only one value at 300 mg/kg bw/day and no values at 1000 mg/kg bw/day were outside the normal control range. At all dosages, mean values for total bilirubin were statistically significantly lower than control but differences showed no obvious dose-response relationship. Again this may reflect high control levels as only one value (occurring at 1000 mg/kg bw/day) marginally exceeded the historical control range for treated males compared to three out of five for the control group. At 1000 mg/kg bw/day, bile acid values were statistically significantly lower than control.


In females, at all dosages, higher levels of total protein and albumin attained statistical significance when compared to control; although the highest values occurred at the high dose of 1000 mg/kg bw/day, there was no dose-response relationship at lower doses. For total protein, mean values and the majority of individual values at 30 and 1000 mg/kg bw/day exceeded the historical control range, mean values and the majority of individual values for control and at 300 mg/kg bw/day were within this control range. For albumin, mean values and the majority of individual values at 1000 mg/kg bw/day exceeded the historical control range, but mean values and the majority of individual values at lower dosages were within this control range. At all dosages, higher calcium levels showed a dosage relationship and attained statistical significance when compared with control, however only one individual value at 1000 mg/kg bw/day exceeded the historical control range. At 300 and 1000 mg/kg bw/day, aspartate aminotransferase levels were statistically significantly lower than control but differences showed no dose-response relationship. This finding seems to reflect unusually high values within the control group as three of the five values exceeded the historical control range. A reduction in aspartate aminotransferase levels is unlikely to indicate an adverse effect of treatment.


At 1000 mg/kg bw/day, four males showed dark liver at necropsy, one of these males also showed pallor of the kidneys and a small prostate/seminal vesicles. At 300 mg/kg bw/day, one male showed pallor of the kidneys. No macroscopic findings were apparent at necropsy for both sexes at 30 mg/kg bw/day or females 300 and 1000 mg/kg bw/day.


Mean absolute and relative liver weights were higher in males at all doses and in females at 300 and 1000 mg/kg bw/day compared to control; with differences showing a dose-response relationship and attaining statistical significance. Mean absolute and relative kidney weights were higher in males at 300 and in both sexes at 1000 mg/kg bw/day compared to control; differences attaining statistical significance and for males showed a dose-response relationship. Mean absolute and relative spleen weights were higher in males at 300 and 1000 mg/kg bw/day compared to control; differences showing a dose-response relationship and attaining statistical significance. At 1000 mg/kg bw/day, both sexes showed statistically significantly higher mean absolute and relative adrenal and thyroid weights compared with control. Males at this dosage also showed statistically significant lower mean absolute and relative prostate/seminal vesicle weights compared with control. At 1000 mg/kg bw/day, females showed higher mean absolute and relative heart weight compared to control. However, all individual values at this dose were within the historical control range and, in the absence of any histopathological correlates, this finding was considered to be incidental and unrelated to treatment.


At all doses, both sexes showed centrilobular to diffuse hepatocellular hypertrophy of minimal to moderate severity in the liver. This finding was not paralleled by increased inflammatory and/or degenerative lesions and was, therefore, considered to represent an adaptive change due to increased metabolism of the xenobiotic. The finding is expected to be reversible upon cessation of treatment. Minimal degrees of bile concrements were found in four males receiving 1000 mg/kg bw/day but this was not paralleled by degenerative of proliferative changes of the bile ducts and was deemed to represent a secondary/metabolic change. At all doses, minimal/slight increased severity of extramedullary hemopoiesis was apparent in the spleen, in a dose dependent manner. This finding was considered to be an adaptive change due to increased demand. At all dosages, hyaline droplets nephropathy in the kidneys (consisting of increased severity of hyaline droplets, increased tubular degeneration/regeneration and granular casts) was observed for males. Additionally at 1000 mg/kg bw/day this nephropathy was often associated with interstitial inflammatory infiltrates. The occurrence of this nephropathy is deemed to be related to treatment. For males at 30 mg/kg bw/day and both sexes at 300 and 1000 mg/kg bw/day, thyroid follicular hypertrophy was observed at elevated incidence and severity when compared to controls. Follicular hypertrophy of the thyroids is deemed to be associated with the increased hepatic metabolization of thyroid hormones (T3/T4) due to the previously described hepatocellular hypertrophy and as such is considered to represent a secondary effect. The remainder of findings recorded were within the range of normal background lesions which may be recorded in animals of this strain and age.

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: The effects detected in females were considered to relate to adaptive microscopic liver, thyroid and spleen changes.

2

Dose descriptor:

NOAEL

Effect level:

300 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: see 'Remark'

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Treatment related findings were noted in both sexes at 30, 300 and 1000 mg/kg bw/day and it was not possible to identify a No Observed Effect Level (NOEL) for either sex. However, the effects detected in females were considered to relate to adaptive microscopic liver, thyroid and spleen changes and therefore 1000 mg/kg bw/day may be considered a No Observed Adverse Effect Level (NOAEL) for females. Similar microscopic liver, thyroid and spleen changes were apparent for males however microscopic kidney changes and a concomitant increase in neutrophils were also apparent at all dosages and a NOAEL for the male rat could not be established. Kidney changes were characterised by hyaline droplets, increased tubular degeneration/regeneration and granular casts and at 1000 mg/kg bw/day interstitial inflammatory infiltrates. The hyaline droplets were consistent with well documented changes that are peculiar to the male rat in response to treatment with some hydrocarbons. This effect is, therefore, not indicative of a hazard to human health. In the context of this study, the remaining kidney findings are more likely to be correlated to the same condition as the hyaline droplet accumulation and are therefore considered to represent limited relevance to humans. Excluding these kidney changes the No Observed Adverse Effect Level (NOAEL) for males was considered to be 300 mg/kg bw/day due to effects on haemoglobin, erythrocyte count and haematocrit values at 1000 mg/kg bw/day, the aetiology of which was uncertain.

Executive summary:

The oral administration of 1,1,3,3-Tetramethylbutyl peroxyneodecanoate (CAS Number: 51240-95-0) to rats for twenty-eight days at dose levels up to 1000 mg/kg bw/day resulted in treatment related findings for both sexes at 30, 300 and 1000 mg/kg bw/day and it was not possible to identify a No Observed Effect Level (NOEL) for either sex. The effects detected in females were considered to relate to adaptive microscopic liver, thyroid and spleen changes and therefore 1000 mg/kg bw/day may be considered a No Observed Adverse Effect Level (NOAEL) for females. Similar microscopic liver, thyroid and spleen changes were apparent for males however microscopic kidney changes and a concomitant increase in neutrophils were also apparent at all dosages and a NOAEL for the male rat could not be established. Kidney changes were characterised by hyaline droplets, increased tubular degeneration/regeneration and granular casts and at 1000 mg/kg bw/day interstitial inflammatory infiltrates. The hyaline droplets were consistent with well documented changes that are peculiar to the male rat in response to treatment with some hydrocarbons. This effect is, therefore, not indicative of a hazard to human health. In the context of this study, the remaining kidney findings are more likely to be correlated to the same condition as the hyaline droplet accumulation and are therefore considered to represent limited relevance to humans. Excluding these kidney changes the No Observed Adverse Effect Level (NOAEL) for males was considered to be 300 mg/kg bw/day due to effects on haemoglobin, erythrocyte count and haematocrit values at 1000 mg/kg bw/day, the aetiology of which was uncertain.