1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole

Neurotoxicity

Description of key information

- Oral: NOAEL for neurotoxicity was 100 mg/kg bw, male/female, rats, acute, OECD TG 424, Milburn 2005

Key value for chemical safety assessment

Effect on neurotoxicity: via oral route

Link to relevant study records

Reference

Endpoint:

neurotoxicity: acute oral

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

15 Sep 2004 to 02 Feb 2005

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.6200 (Neurotoxicity Screening Battery)

Version / remarks:

1998

Qualifier:

according to guideline

Guideline:

OECD Guideline 424 (Neurotoxicity Study in Rodents)

Version / remarks:

1997

GLP compliance:

yes (incl. QA statement)

Species:

rat

Strain:

other: Alpk:APfSD (Wistar)

Sex:

male/female

Route of administration:

oral: gavage

Vehicle:

corn oil

Duration of treatment / exposure:

Single dose on Day 1

Dose / conc.:

30 mg/kg bw (total dose)

Dose / conc.:

100 mg/kg bw (total dose)

Dose / conc.:

300 mg/kg bw (total dose)

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Dose descriptor:

NOAEL

Remarks:

Neurotoxicity

Effect level:

100 mg/kg bw (total dose)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

behaviour (functional findings)

clinical signs

Critical effects observed:

no

TEST SUBSTANCE ANALYSIS

The mean concentrations for the batch of dosing preparations analysed were within 5% of the nominal concentration. 

The reanalysis of the test substance in dosing preparations at concentrations of 3 mg/mL and 100 mg/mL when stored at room temperature was shown to be satisfactory for 8 days.

 

CLINICAL SIGNS

There were multiple clinical effects in both sexes at 300 mg/kg that were evident on day 1. The severity of the effects was such that 2 females were killed for humane reasons. The majority of clinical observations were recorded at the time of peak effect (5-6 hours after dosing).

 

BODY WEIGHT

There were no treatment-related effects on body weights. Adjusted body weight in 300 mg/kg males was statistically signicantly lower than controls on day 1, but in the absence of effects at later times, this was considered not to be related to treatment.

 

FOOD CONSUMPTION

Males at all dose levels had lower food consumption in week 2. There was no evidence of a similar finding in the week following dose administration, no differences in females, no evidence of a dose-response and therefore, these small differences are considered to be incidental to treatment.

 

FUNCTIONAL OBSERVATION BATTERY

- Clinical observations:

There were a number of clinical observations recorded at the time of peak effect on day 1 in rats dosed with 300 mg/kg, and females were more affected than males. Two females were killed due to the severity of the clinical observations. In total, 5 males and 8 females showed clinical signs of toxicity on day 1 at 300 mg/kg. The clinical signs were no longer present the following day.

A small number of animals in the 100 mg/kg groups showed a limited number of treatment related clinical signs (tip-toe gait in 3 females, signs of diarrhoea in 1 female, piloerection in 1 male) at the time of peak effect but the majority were unaffected. Although a finding of reduced splay reflex was recorded in 1 male and 3 females in this group, this finding was observed to a similar extent in control animals at different time points (day 8 and 15) and was not correlated with any effect on quantitative measurement of landing foot splay. Therefore, it was considered incidental and not treatment-related. The clinical observations were no longer evident on day 2.

The only clinical observation in the 30 mg/kg group was reduced splay reflex in 1 male and 1 female on day 1. However, this finding was observed to a similar extent in control animals at different time points (day 8 and 15), was not correlated with any effect on quantitative measurement of landing foot splay and was considered to be incidental to treatment.

- Landing foot splay measurements:

There were no treatment-related effects on landing foot splay.

- Time to tail-flick:

Females dosed with 300 mg/kg had an increased time to tail flick on day 1. There were no other treatment related effects. 

- Fore- and hind-limb grip strength measurements:

There were no treatment-related effects on fore or hind-limb grip strength. In 100 mg/kg males, hind-limb grip strength was higher at day 8 and lower at day 15 than in controls. The lack of a consistent effect and absence of a dose-response indicates that these were not related to treatment.

- Motor activity measurements:

On day 1 females dosed with 300 mg/kg had reduced activity at each time interval and overall. Males dosed with 300 mg/kg also had slightly reduced activity, with statistically signicant reductions in minutes 11-15 and overall. There were no effects on motor activity in the 30 and 100 mg/kg dose groups on day 1. There were no treatment-related effects on motor activity on day 8 or 15. Instances of statistically signicant differences from control were observed for certain isolated time intervals in particular groups and days, but these were not part of a pattern of effect and were incidental to treatment.

 

BRAIN WEIGHTS

There were no differences in brain weight that were considered to be related to treatment. Males dosed with 300 mg/kg had slightly higher brain weight than controls. However, control group mean brain weight (1.94 g) was relatively low compared to the historical control range (1.90 - 2.11 g), and the group mean brain weight values for all treated groups were similar and were within the range of historical control values. Therefore, this small difference is considered to represent normal variation and to be incidental to treatment. There were no differences from control in females or in males in the lower dose groups.

 

MACROSCOPIC FINDINGS

There were no treatment-related macroscopic findings.

 

MICROSCOPIC FINDINGS

There were no treatment-related microscopic findings in this study. There was a minor increase (2 versus 1 in control group) in the finding of minimal distal tibial nerve demyelination in females at 300 mg/kg. As this value fell within the historical control incidence for this age and strain of rat, it was considered not to be treatment-related. 

Conclusions:

Single oral administration of 300 mg/kg produced multiple clinical signs of toxicity in females, and 2 of 10 females were killed for humane reasons. Females in this group also had reduced motor activity and increased time to tail flick on day 1. Males dosed with 300 mg/kg had multiple clinical signs and slightly reduced motor activity on day 1. These effects were rapidly reversible, and no treatment-related effects were observed after day 1. There were no treatment related effects on brain weight or micropathology of the nervous system at any dose level. The only treatment related effects at 100 mg/kg were a limited number of transient clinical signs in 1 male and 3 females at the time of peak effect on day 1. These are considered to represent general systemic toxicity rather than a direct neurotoxic effect. There were no effects at 30 mg/kg. The no effect level for neuropathology was 300 mg/kg, the highest dose tested, based on absence of any effects on brain weights or micropathology. The dose level of 100 mg/kg represented a clear NOAEL for neurotoxicity.

Executive summary:

Groups of ten male and ten female (Wistar-derived) rats were administered single oral doses of 0 (control), 30, 100 or 300 mg/kg bw in corn oil and were observed for the following 14 days. This study was conducted according to OECD TG 424 and following GLP. All animals were observed prior to the study start and daily throughout the study for any changes in clinical condition. In addition, a Functional Observation Battery (FOB), including quantitative assessments of landing foot splay, sensory perception and muscle weakness, were performed in week -1, and on days 1, 8 and 15. Locomotor activity was also monitored in week -1, and on days 1, 8 and 15. Body weights and food consumption were measured weekly throughout the study. At the end of the scheduled period, 5 rats/sex/group were perfused in situ. Selected nervous system tissues were removed, processed and examined microscopically.

There were multiple clinical signs recorded in both sexes receiving 300 mg/kg at the time of peak effect on day 1. These included abnormal gait, decreased or increased activity, cold, pale, hunched, breathing rate increased/irregular, piloerection, signs of diarrhoea, reduced splay reex, tip toe gait, stains around the nose, stained with urine (wet) and/or subdued behaviour. Females were more affected than males, and two females were killed due to the severity of the clinical signs. The clinical observations Were no longer evident on day 2. A small number of animals in the 100 mg/kg group showed only limited, transient clinical signs (piloerection, tip-toe gait, signs ofdiarrhoea) at the time of peak effect on day 1, but the majority were unaffected. Due to the low incidence, rapid reversibility (day 2), and the absence of any corresponding ndings in quantitative measurements of the FOB or histopathology, these are considered to represent general systemic toxicity rather than a specic neurotoxic effect. At 30 mg/kg, there were no treatment-related clinical signs. There were no effects on body weights. There were no treatment-related effects on food consumption. On day 1 both sexes dosed with 300 mg/kg had reduced motor activity and females had an increased time to tail ick. There were no treatment-related effects on fore or hind limb grip strength, brain weight or neuropathology.

Single oral administration of 300 mg/kg produced multiple clinical signs of toxicity in females, and 2 of 10 females were killed for humane reasons. Females in this group also had reduced motor activity and increased time to tail flick on day 1. Males dosed with 300 mg/kg had multiple clinical signs and slightly reduced motor activity on day 1. These effects were rapidly reversible, and no treatment-related effects were observed after day 1. There were no treatment related effects on brain weight or micropathology of the nervous system at any dose level. The only treatment related effects at 100 mg/kg were a limited number of transient clinical signs in 1 male and 3 females at the time of peak effect on day 1. These are considered to represent general systemic toxicity rather than a direct neurotoxic effect. There were no effects at 30 mg/kg. The no effect level for neuropathology was 300 mg/kg, the highest dose tested, based on absence of any effects on brain weights or micropathology. The dose level of 100 mg/kg represented a clear NOAEL for neurotoxicity.

Effect on neurotoxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Neurotoxicity: acute oral 

A supporting study is avaialbe for this endpoint (Milburn 2005) whereby groups of ten male and ten female (Wistar-derived) rats were administered single oral doses of 0 (control), 30, 100 or 300 mg/kg bw in corn oil and were observed for the following 14 days. This study was conducted according to OECD TG 424 and following GLP. Single oral administration of 300 mg/kg produced multiple clinical signs of toxicity in females, and 2 of 10 females were killed for humane reasons. Females in this group also had reduced motor activity and increased time to tail flick on day 1. Males dosed with 300 mg/kg had multiple clinical signs and slightly reduced motor activity on day 1. These effects were rapidly reversible, and no treatment-related effects were observed after day 1. There were no treatment related effects on brain weight or micropathology of the nervous system at any dose level. The only treatment related effects at 100 mg/kg were a limited number of transient clinical signs in 1 male and 3 females at the time of peak effect on day 1. These are considered to represent general systemic toxicity rather than a direct neurotoxic effect. There were no effects at 30 mg/kg. The no effect level for neuropathology was 300 mg/kg, the highest dose tested, based on absence of any effects on brain weights or micropathology. The dose level of 100 mg/kg represented a clear NOAEL for neurotoxicity.