Isocycloseram

Neurotoxicity

Administrative data

Endpoint:

neurotoxicity: sub-chronic oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Experimental start: 24 January 2018, Experimental end: 20 July 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

This neurotoxicity study was generated to meet the data requirements of regulations not related to REACH in non-EEA countries.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2019

Report date:

2019

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 424 (Neurotoxicity Study in Rodents)

Version / remarks:

1997

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

4-(5-(3,5-dichloro-4-fluorophenyl)-5-(trifluoromethyl)-4,5-dihydro-1,2-oxazol-3-yl)-N-(2-ethyl-3-oxo-1,2-oxazolidin-4-yl)-2-methylbenzamide

Cas Number:

2061933-85-3

Molecular formula:

C23H19Cl2F4N3O4

IUPAC Name:

4-(5-(3,5-dichloro-4-fluorophenyl)-5-(trifluoromethyl)-4,5-dihydro-1,2-oxazol-3-yl)-N-(2-ethyl-3-oxo-1,2-oxazolidin-4-yl)-2-methylbenzamide

Test material form:

solid: particulate/powder

Test animals

Species:

rat

Strain:

Wistar

Remarks:

RccHan Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

Source: Envigo RMS Limited
Age at start of treatment: 45 to 47 days
Weight: 154 to 194 g (males), 124 to 159 g (females)
Acclimatisation period: 13 days
Housing: animals were housed three to four in polycarbonate cages with stainless steel mesh lid, separated by sex, with wood based bedding. Aspen chew blocks were provided to each cage, as well as plastic shelter. Animals were separated into single housing overnight prior to functional observations battery testing.
Feed: Rat and Mouse No. 1 Maintenance Diet, ad libitum
Water: Public supply water, ad libitum
Air supply: filtered fresh air was passed to atmosphere and not recirculated (air exchange rate not reported)
Temperature: 20 to 24 °C (a temperature of 19 °C was recorded on one occasion)
Humidity: 40 to 70%
Lighting: artificial lighting on a 12 hours light to 12 hours darkness cycle

Administration / exposure

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Remarks:

The substance was incorporated into the diet

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The treated diet was analysed with a suitable ultra pressure liquid chromatography method to confirm the concentrations of the test substance in the food. All samples analysed had mean concentrations within or equal to the acceptance criteria of ± 10% of their nominal concentrations. For homogeneity, the RSD of concentrations for all samples in each group was within the acceptance criteria of ≤10%.

Duration of treatment / exposure:

13 weeks

Frequency of treatment:

Daily, dietary exposure

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

50 ppm

Doses / concentrations 2

Dose / conc.:

150 ppm

Doses / concentrations 3

Dose / conc.:

300 ppm

No. of animals per sex per dose:

Ten females, ten males per dose group

Control animals:

yes, plain diet

Details on study design:

Randomly allocated on arrival. Using the sequence of cages in the battery, one animal at a time was placed in each cage with the procedure being repeated until each cage held the appropriate number of animals. Each sex was allocated separately. On Day 1 (before feeding of the treated diets) variations in body weight of the animals were checked to ensure that they did not exceed ± 20% of the mean for the appropriate sex. Two females were replaced with spare animals of suitable weight from the same batch due to body weight range extremes.

Examinations

Observations and clinical examinations performed and frequency:

Animals were inspected visually at least twice daily for evidence of ill-health or reaction to treatment. Cages were inspected daily for evidence of animal ill-health amongst the occupants. A detailed weekly physical examination was performed on each animal to monitor general health. The body weight of each animal was recorded one week before start of exposure, on the day of commencement of treatment and weekly throughout the study. The weight of food supplied to each cage, that remaining and an estimate of any spilled was recorded for the week before treatment started and for each week throughout the study. Ophthalmic examinations including examination of the eyes of each animal were done by means of a binocular during the acclimatisation period and in week 12 of the treatment period. Blood samples were collected from each animal at necropsy.

Neurobehavioural examinations performed and frequency:

A functional observational battery (FOB) was performed on all animals before commencement of treatment and during Weeks 2, 4, 8 and 13 of treatment. Animals were tested by an observer who was unaware of the treatment group to which each animal belonged. Animals were caged individually the day before observations took place and the labels on these cages showed only the study, animal and cage numbers. Labels on cages of other animals of the same sex as those being tested were also changed such that they showed no group information. Animals were not necessarily all tested on the same day, but the numbers of animals and the times of testing were balanced across the groups on each day of testing. Investigations included in cage observations, in hand observations, observations in the arena with a two minute recording period, reactivity investigations and motor activity measurements.

Sacrifice and (histo)pathology:

All study animals were subject to a detailed necropsy. After a review of the history of each animal, a full macroscopic examination of the tissues was performed. All external features and orifices were examined visually. Any abnormality in the appearance or size of any organ and tissue (external and cut surface) was recorded and the required tissue samples preserved in appropriate fixative. Various organs were weighed, and pathology investigations were performed on the adrenals, epididymides, duodenum, jejunum, liver, testes and any tissues with recorded abnormalities.

Positive control:

Not applicable

Statistics:

See information in "Any other information"

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, non-treatment-related

Description (incidence and severity):

Overall (Week 0 to 13) body weight gain was high, when compared with controls, for males receiving 50, 150 or 300 ppm (+16, +14 and +16% of control, respectively) with no relationship to increasing dietary concentration. There was a similar finding in the females, where body weight gain was slightly high at 150 and 300 ppm (+10 and +11% of control, for females receiving 150 or 300 ppm, respectively). These findings were considered non-adverse.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

Group mean food intake was marginally high, when compared with controls, for males receiving 50, 150 or 300 ppm, but the differences from control were slight and there was no trend with increasing dietary concentration. There was no similar finding in the females.

Ophthalmological findings:

no effects observed

Behaviour (functional findings):

effects observed, non-treatment-related

Description (incidence and severity):

No treatment-related findings were recorded for the in cage observations, in hand observations and observations in the arena. At the investigations in Weeks 8 and 13 there was an increase in urination frequency, when compared with controls, in males receiving 50, 150 or 300 ppm. There was, however, no dose response and examination of the individual data revealed the findings to be transient in nature with the same animals not consistently affected (with the exception of Animal Nos. 40 (150 ppm) and 18 (300 ppm) that also had increased urination noted at the pretreatment investigation). There were a few incidences of isolated abnormal motor movements, but these were considered transient findings that were attributed to normal biological variation. Reactivity responses and grip strength were unaffected by the treatment with the substance. There were a few isolated statistically significant differences from control with regard to grip strength, but these were inconsistent between investigations and on each occasion, the extent of the difference from controls was minimal. Body temperature was statistically significantly low in Week 13 the males receiving 300 ppm, but the extent of the difference from control was also minimal and all individual values were within the historical control range (36.9 to 38.2 °C; n=30). There was no treatment-related effect on the motor activity. The investigations in Week 8 and 13 revealed, when compared to controls, a statistically significant decrease of low (cage-floor activity) beam breaks at the 6- and 12-minute intervals in males given 150 or 300 ppm, resulting in statistically significantly low total beam breaks in Week 8. These variations were, however, reflecting trends that were present at the pre-treatment investigation. In addition, the mean values were consistent with the background control data whilst the mean values for the controls were above the background range. In addition, rearing (high beam) scores, a more sensitive marker for any decrease of activity, were clearly similar to controls. Consequently, the statistically significant differences were not attributable to treatment.

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Neuropathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Effect levels

Key result

Dose descriptor:

NOAEL

Effect level:

300 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

behaviour (functional findings)

neuropathology

Remarks on result:

other: Equivalent to 24.8 and 32.7 mg/kg bw/day in male and female rats.

Target system / organ toxicity

Key result

Critical effects observed:

no

Applicant's summary and conclusion

Conclusions:

The NOAEL for neurotoxicity resulting from dietary exposure to the substance over a period of 13 weeks was 300 ppm in female and male Han Wistar rats.

Executive summary:

The neurotoxicity of the substance when administered via the diet to female and male Han Wistar rats over a period of 13 weeks was studied under GLP to OECD TG 424. Ten female and ten male rats per dose group were exposed to plain diet (negative control) or standard rodent diet treated with the substance at nominal levels of 50, 150 or 300 ppm. The analysis of the food by a suitable ultra pressure liquid chromatography method confirmed mean concentrations within or equal to the acceptance criteria of ± 10% of their nominal concentrations. For homogeneity, the RSD of concentrations for all samples in each group was within the acceptance criteria of ≤10%. The mean achieved dosages during the 13 weeks of treatment were 3.92, 13.2 and 24.8 mg/kg/day in males and 5.49, 15.6 and 32.7 mg/kg/day in females at dietary concentrations of 50, 150 and 300 ppm, respectively. There were no signs that were attributable to treatment with SYN547407 and no animals died during the treatment period. There were no in-cage, in-hand or arena observations that were attributable to treatment and reactivity, grip strength and motor activity were also unaffected by treatment. There were no treatment-related ophthalmic findings. Body weight gain slightly was high at 50 ppm in males and at 150, 500 ppm in both sexes but there was no relationship to increasing dietary concentration, and there was no corresponding effect upon food consumption. There was no effect of treatment on brain weight and there were no treatment-related macroscopic or neurohistopathological findings.