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Neurotoxicity

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Description of key information

Acute Rat Gavage NOAEL: 100 mg/kg; not neurotoxic. OECD 424; Reliability = 1

90-Day Rat Diet NOAEL (subchronic toxicity): 1500 ppm, NOAEL (neurotoxicity): 6000 ppm; not neurotoxic. OECD 408; Reliability = 1

Key value for chemical safety assessment

Effect on neurotoxicity: via oral route

Link to relevant study records

Referenceopen allclose all

Endpoint:
neurotoxicity: sub-chronic oral
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity in Rodents)
Deviations:
yes
Qualifier:
according to
Guideline:
EPA OPPTS 870.6200 (Neurotoxicity Screening Battery)
Deviations:
yes
Qualifier:
according to
Guideline:
EU Method B.26 (Sub-Chronic Oral Toxicity Test: Repeated Dose 90-Day Oral Toxicity Study in Rodents)
Deviations:
yes
Qualifier:
according to
Guideline:
other: MAFF Japan, 2-1-9 Notification 12 Nousan 8147, Agricultural Chemicals Regulation Laws (2000)
Deviations:
yes
GLP compliance:
yes
Limit test:
no
Species:
rat
Strain:
other: CD® [Crl:CD(SD)]
Sex:
male/female
Route of administration:
oral: feed
Vehicle:
other: Meal Lab Diet
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
The analytical results show that the test article was homogeneously mixed in the diet and present at the targeted concentrations. Test article was not detected in control samples. The stability of test substance in rodent diet for the concentration range used in this study was well characterized during method validation, which established 17-day room temperature stability for the test diet.
Duration of treatment / exposure:
At least 13 weeks
Frequency of treatment:
The test subsatnce was available in the diet ad libitum
Dose / conc.:
100 ppm
Remarks:
(Male: 4.5 mg/kg bw/d; Female: 6 mg/kg bw/d)
Dose / conc.:
400 ppm
Remarks:
(Male: 18 mg/kg bw/d; Female: 23 mg/kg bw/d)
Dose / conc.:
1 500 ppm
Remarks:
(Male: 70 mg/kg bw/d; Female: 83 mg/kg bw/d)
Dose / conc.:
6 000 ppm
Remarks:
(Male: 274 mg/kg bw/d; Female: 316 mg/kg bw/d)
No. of animals per sex per dose:
16
Control animals:
yes, concurrent vehicle
Clinical signs:
effects observed, non-treatment-related
Mortality:
mortality observed, non-treatment-related
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
- Adverse, test substance-related decreases (compared to control) in body weight parameters were observed in male and female rats at 6000 ppm. Overall (Weeks 1-13) mean body weight change at 6000 ppm for males and females was 21% (statistically significant) and 6% (not statistically significant), respectively lower than control.
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
- Adverse, test substane-related decreases (compared to controls) in food intake parameters were observed in male and female rats at 6000 ppm, and correlated with the body weight effects. Statistically significant decreases in weekly mean food consumption were noted for all 13 weeks in males at 6000 ppm and for 11 of the 13 weeks in females at 6000 ppm (Week 6 and 12 values did not reach statistical significance).
- Statistically significant decreases in mean food consumption were noted for all 3 monthly intervals in males and females at 6000 ppm and the overall (Weeks 1-13) mean food consumption of males and females at 6000 ppm was statistically significantly lower (11% and 16%, respectively) compared to control.
Food efficiency:
effects observed, treatment-related
Description (incidence and severity):
- During the first week of the study, feed efficiency values were statistically significantly decreased at 6000 ppm for both sexes when compared to control. A statistically significant decrease (21%) in the mean food efficiency for Month 2 was noted in males at 6000 ppm.
- Overall (Weeks 1-13) food efficiency of males and females at 6000 ppm were lower than controls for males (11% which is not statistically significant) and higher than controls for females (12% which is not statistically significant).
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
no effects observed
Haematological findings:
effects observed, non-treatment-related
Clinical biochemistry findings:
effects observed, non-treatment-related
Urinalysis findings:
effects observed, non-treatment-related
Behaviour (functional findings):
effects observed, non-treatment-related
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
Test substance related organ weight changes were limited to increased absolute and relative liver weights of males and females at 6000 ppm. Increased absolute liver, relative liver to body weight percentage and relative liver to brain weight ratios were observed in males by 5%, 19% (statistically significant) and 3%, and in females by 11%, 17% (statistically significant) and 9%, respectively. The increased liver weights correlated with minimal microscopic centrilobular hepatocellular hypertrophy in males at 6000 ppm and were considered most likely adaptive and non-adverse.
Gross pathological findings:
no effects observed
Neuropathological findings:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Test substance related microscopic changes were limited to the livers of males at 6000 ppm. Minimal centrilobular hepatocellular hypertrophy was observed in 4 of 10 males at 6000 ppm. The centrilobular hypertrophy was characterized by minimal enlargement of the hepatocytes surrounding the central vein. The hepatocellular hypertrophy was considered non-adverse and consistent with an adaptive increase in liver enzyme content.
Histopathological findings: neoplastic:
not examined
Key result
Dose descriptor:
NOAEL
Effect level:
1 500 ppm
Sex:
male/female
Basis for effect level:
body weight and weight gain
food consumption and compound intake
food efficiency
Remarks on result:
other: based on adverse effects on body weight and nutritional parameters in male and female rats at 6000 ppm
Remarks:
1500 ppm is equivalent to 70 and 83 mg/kg body weight/day for males and females, respectively
Conclusions:
No test substance related microscopic findings consistent with neurotoxicity.
Executive summary:

The study was conducted according to guidelines, U.S. EPA OPPTS 870.3100, 870.6200 and OECD Guideline 408 to evaluate the subchronic toxicity of test substance when administered in the diet to rats for 13 weeks. Four treatment groups of 16 male and 16 female rats were administered test substance at respective dietary concentrations of 100, 400, 1500, and 6000 ppm. One additional group of 16 animals/sex served as the control and received untreated rodent diet. The untreated or treated rodent diet was available to all groups ad libitum for 13 weeks.

Observations for morbidity, mortality, injury, and the availability of food and water were conducted twice daily for all animals. Additional cageside observations were conducted once daily, except on the days of the weekly detailed clinical observation. Body weights were measured and recorded prior to randomization, predose on Day 1, and weekly thereafter. Food consumption was measured and recorded weekly.

Food efficiency and compound consumption were calculated weekly. Ophthalmoscopic examinations were conducted on all animals pretest and on all surviving animals prior to the terminal necropsy. Functional Observational Battery (FOB) and Motor Activity (MA) tests were conducted on designated animals (10/sex/group) pretest and during Weeks 4, 8, and 13. Blood samples for clinical pathology evaluations were collected from designated animals at the terminal necropsy. Urine samples for clinical pathology evaluations were collected from designated animals prior to the terminal necropsy. Blood samples for possible determination of the plasma concentrations of the test subsatnce and/or metabolites were collected from designated animals on Day 60. During Week 14, the last six animals/sex/group were necropsied for neuropathology evaluations. At study termination for non-neuropathology animals, necropsy examinations were performed, organ weights were recorded, and tissues were microscopically examined. A full complement of tissues was microscopically examined for animals at 0 and 6000 ppm, with gross lesions and a potential target organ (liver) examined at 100, 400, and 1500 ppm.

The overall mean compound consumption of test substance in the 100, 400, 1500, and 6000 ppm groups was 4.5, 18, 70, and 274 mg/kg body weight (bw)/day, respectively, for male rats and 6.0, 23, 83, and 316 mg/kg bw/day, respectively, for female rats.

No test substance-related effects were noted on the following parameters: survival, clinical findings, functional observational battery, locomotor activity, ophthalmoscopic evaluations, hematology, coagulation, clinical chemistry, urine/urine chemistry, or macroscopic evaluations. There was one unscheduled death in the 100 ppm (female) group on test Day 88; the cause of death was undetermined but was not attributed to the test article.

Adverse, test substance-related decreases (compared to control) in body weight parameters were observed in male and female rats at 6000 ppm. Weekly mean body weight changes were also generally lower compared to controls in males and females at 6000 ppm, but with only occasional statistical significance. Overall (Weeks 1-13) mean body weight change at 6000 ppm for males and females was 21 (statistically significant) and 6% (not statistically significant), respectively, lower than control.

Adverse, test substance-related decreases (compared to controls) in food intake parameters were observed in male and female rats at 6000 ppm, and correlated with the body weight effects. Overall (Weeks 1-13) mean food consumption of males and females at 6000 ppm was statistically significantly lower (11% and 16%, respectively) compared to control. Weekly food efficiency values were generally similar to control except for Week 1, when food efficiency was statistically significantly decreased in males and females at 6000 ppm compared to control.

Test substance related organ weight changes were limited to increased absolute and relative liver weights of males and females at 6000 ppm. The increased liver weights correlated with minimal centrilobular hepatocellular hypertrophy observed in 4 of 10 males at 6000 ppm. The hepatocellular hypertrophy was considered non-adverse and likely adaptive (i.e. enzymatic induction). There was no test substance related microscopic findings consistent with neurotoxicity.

Under the conditions of this study, the no-observed-adverse-effect level (NOAEL) of test substance was considered to be 1500 ppm (70 and 83 mg/kg body weight/day for males and females, respectively). The NOAEL was based on adverse effects on body weight and nutritional parameters in male and female rats at 6000 ppm.

Endpoint:
neurotoxicity: acute oral
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 424 (Neurotoxicity Study in Rodents)
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 870.6200 (Neurotoxicity Screening Battery)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method B.43 (Neurotoxicity Study in Rodents)
Deviations:
no
Qualifier:
according to
Guideline:
other: MAFF Japan Testing Guidelines for Toxicity Studies 12 Nousan 8147, Section 2-1-7 (2000)
Deviations:
no
GLP compliance:
yes
Species:
rat
Strain:
other: Crl:CD(SD)
Sex:
male/female
Route of administration:
oral: gavage
Vehicle:
other: 0.1% Tween-80 in 0.5% methylcellulose
Analytical verification of doses or concentrations:
yes
Frequency of treatment:
single dose
Dose / conc.:
100 mg/kg bw (total dose)
Dose / conc.:
500 mg/kg bw (total dose)
Dose / conc.:
2 000 mg/kg bw (total dose)
No. of animals per sex per dose:
12
Control animals:
yes, concurrent vehicle
Clinical signs:
no effects observed
Mortality:
no mortality observed
Body weight and weight changes:
effects observed, non-treatment-related
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
- Adverse, test substance-related reductions compared to controls were observed on mean food consumption in males and females administered 500 and 2000 mg/kg. Statistically significant reductions in mean food consumption occurred during the interval test Days 0-1 in males and females adminstered 500 and 2000 mg/kg. These reductions in food consumption correlated with the reductions in mean body weight gains during those intervals.
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
effects observed, treatment-related
Description (incidence and severity):
- A statistically significant increase compared to control in forelimb grip strength observed on test Day 0 (approximately 2 hours after test substance administration) in females administered 2000 mg/kg.
- Statistically significant reductions compared to controls in body temperature were observed on test Day 0 (approximately 2 hours after test substance administration) in males and females administered 500 and 2000 mg/kg.
- A statistically significant reduction compared to control in the mean number of rearing movements observed in 2000 mg/kg females on test Day 0.
- Males and females in the 2000 mg/kg group had a statistically significant higher incidence compared to control of high posture (7/12 and 4/12, respectively) on test Day 0 while in the open field.
- Adverse, test substance-related reductions compared to controls in motor activity were observed on test day 0 in 500 and 2000 mg/kg males and females.
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
not examined
Neuropathological findings:
effects observed, non-treatment-related
Histopathological findings: non-neoplastic:
not examined
Histopathological findings: neoplastic:
not examined
Key result
Dose descriptor:
NOAEL
Effect level:
100 mg/kg bw (total dose)
Sex:
male/female
Basis for effect level:
body weight and weight gain
food consumption and compound intake
behaviour (functional findings)
Remarks on result:
other: based on effects on body weight gains, food consumption, body temperature, and motor activity at 500 mg/kg and above
Conclusions:
NOAEL (males/females): 100 mg/kg bw (Body weight gains, food consumption, body temperature, and motor activity)
Executive summary:

The study was conducted according to guidelines, OECD guideline 424 and EPA OPPTS 870.6200 to assess the potential neurotoxicity of test substance in rats after acute exposure. Young adult male and female rats (12 rats /sex/dose) were administered a single oral dose by gavage of 0, 100, 500, or 2000 mg/kg body weight test substance in 0.1% Tween-80 in 0.5% methylcellulose. Samples of the dosing preparation were analyzed to verify the homogeneity, concentration, and stability of test substance in the vehicle. The rats were weighed on test days 0, 1, 7, and 14. Food consumption was determined for the intervals of test Days 0-1, 0-7, 7-14, and 0-14. Clinical signs of toxicity were assessed daily from test Day 0 through the day of sacrifice (except on the day of the Day 7 and Day 14 neurobehavioral evaluation).

A neurobehavioral test battery, consisting of motor activity and functional observational battery assessments, was conducted on all study rats prior to test substance administration in order to obtain baseline measurements. This neurobehavioral test battery was conducted again on test Day 0 approximately 2 hours after administration of the test substance. The neurobehavioral test battery was repeated again on test Days 7 and 14. On test Day 16, six rats per sex per group were anesthetized and underwent whole-body in situ perfusion. Tissues from the control and 2000 mg/kg groups and gross lesions were processed for histopathology and examined. No deaths occurred during the study.

No test substance-related or statistically significant effects occurred on mean body weights in males or females. Transient, test substance-related reductions were observed on mean body weight gains in males and females administered 500 and 2000 mg/kg. Adverse, test substance-related reductions were observed on mean food consumption in males and females administered 500 and 2000 mg/kg. No adverse clinical signs of toxicity were observed in males or females.

A test substance-related increase in forelimb grip strength was observed on test Day 0 in females administered 2000 mg/kg. Test substance-related reductions in body temperature were observed on test Day 0 in males and females administered 500 and 2000 mg/kg. A test substance-related reduction in the mean number of rearing movements was observed in 2000 mg/kg females on test Day 0. Males and females in the 2000 mg/kg group had a statistically significant higher incidence compared to control of high posture (7/12 and 4/12, respectively) on test Day 0 while in the open field. Adverse, test substance-related reductions compared to controls in motor activity were observed on test Day 0 in 500 and 2000 mg/kg males and females.

There were no test substance-related gross or microscopic anatomic pathology effects observed in this study.

Under the conditions of this study, the no-observed-adverse effect level (NOAEL) in males and females was considered to be 100 mg/kg body weight, based on effects on body weight gains, food consumption, body temperature, and motor activity at 500 mg/kg and above test substance.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed

Effect on neurotoxicity: via inhalation route

Endpoint conclusion
Endpoint conclusion:
no study available

Effect on neurotoxicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

No evidence of a primary effect on the nervous system was observed in toxicity studies conducted with the test substance. 

 

The NOAEL in an acute neurotoxicity study was 100 mg/kg bw based on body weight gain reductions or body weight loss that occurred between the day of dosing and the day following at dose levels of 500 and 2000 mg/kg bw. Accompanying changes in neurobehavioral parameters and motor activity on the day of dosing occurred at the same dose levels. There was no evidence of any histopathological changes in nervous system tissues.

 

The 90-day oral feeding study in rats conducted with the test substance included endpoints required for the subchronic neurotoxicity study in rats. The NOAEL for subchronic toxicity was 1500 ppm (70 and 83 mg/kg bw/day, respectively) based on adverse effects on body weight and nutritional parameters in male and female rats at 6000 ppm. The NOAEL for neurotoxicity and neuropathology was 6000 ppm (274 and 316 mg/kg bw/day, males and females respectively), the highest concentration tested, based on a lack of adverse, test substance-related effects on neurobehavioral and neuropathology parameters at this concentration.

 

No treatment related clinical signs indicative of potential neurotoxicity were observed in short-term and long- term exposure studies in rats, mice, or dogs.

Justification for classification or non-classification

The test substance was negative for neurotoxicity in an acute and a 90-day rat neurotoxicity study. Therefore, the substance does not need to be classified for neurotoxicity according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.