Acetone oxime

Endpoint summary

Description of key information

The NOEL in a 90 day sub-chronic oral study in the rat was 10 mg/kg.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Route of administration:

oral: gavage

Vehicle:

water

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Weekly analyses of dosing mixtures confirmed that the appropriate concentration had been achieved. Values for individual samples ranged from 94 to 108% of desired (nominal) concentration, while the average value for the entire study was 100 +/- 2.97% of the nominal concentration.

Duration of treatment / exposure:

90 days, followed by a 30 day recovery period

Frequency of treatment:

Single daily gavage dose

Remarks:

Doses / Concentrations:
10 mg/kg
Basis:

Remarks:

Doses / Concentrations:
50 mg/kg
Basis:

Remarks:

Doses / Concentrations:
250 mg/kg
Basis:

No. of animals per sex per dose:

25 per sex per dose. Five animals per sex per group were sacrificed after 45 days, ten animals per sex per group were sacrificed after 90 days and the remaining animals were sacrificed after a one month treatment-free recovery period.

Control animals:

yes, concurrent vehicle

Positive control:

None

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily, once in the morning and once in the afternoon.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Pretest and weekly thereafter preceding dosing on the day performed

BODY WEIGHT: Yes
- Time schedule for examinations: Twice pretest, weekly during treatment and terminally (afterfasting)

FOOD CONSUMPTION: Yes
- Time schedule for examinations: One week prior to treatment and during the fourth, eighth and twelfth weeks of the study.

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: Pre-test, at 90 days and then one month later (recovery group)

HAEMATOLOGY: Yes
- Time schedule for collection of blood: 45, 90 days and one month later (recovery group)
- Animals fasted: Yes
- Parameters examined: Methemoglobin concentration, hemoglobin concentration, hematocrit, erythrocyte count, reticulocyte count, platelet count, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular haemoglobin concentration, prothrombin time, activated partial thromboplastin time, total and differential leukocyte counts, erythrocyte morphology

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: 45, 90 days and one month later (recovery group)
- Animals fasted: Yes
- Parameters examined: Serum glutamic oxaloacetic transaminase, serum glutamic pyruvic transaminase, alkaline phosphatase, blood urea nitrogen, fasting glucose, cholesterol, total protein, albumin, albumin/globulin ratio (calculated), creatinine, total bilirubin, direct bilirubin, sodium, potassium, chloride, calcium, inorganic phosphorus

Sacrifice and pathology:

ORGAN WEIGHTS: Yes - adrenals, brain, heart, kidneys, liver, lungs, spleen, testes with epididymides, ovaries
GROSS PATHOLOGY: Yes -complete gross postmortem examinations were performed on all animals.
HISTOPATHOLOGY: Yes
All animals: bone marrow (sternum), kidneys (2), liver (2 lobes), spleen, testes with epididymides (2)
High-dose and control animals: adrenals (2), aorta (thoracic), bone (femur with marrow and sternum), brain (3 sections), oesophagus, heart, intestine, cecum, colon, duodenum, ileum, jejunum, rectum, lungs (with mainstem bronchi - 2), lymph nodes (mesenteric, mediastinal), mammary gland (right inguinal with skin), nerve (right sciatic w/Biceps femoris), ovaries (2), pancreas, pituitary, salivary gland (mandibular), skeletal muscle (right biceps femoris), spinal cord (thoracic), stomach (glandular, nonglandular), thymus, thyroid/parathyroids (2), trachea, urinary bladder, uterus (corpus and cervix uteri), gross lesions (including a section of apparently normal contiguous tissue)

Statistics:

Body weight, body weight gain, food consumption, hematology and clinical chemistry parameters, organ weights and organ/body and organ/brain weight ratios were analyzed. Mean values of all dose groups were compared to control at each time interval.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Details on results:

BODY WEIGHT AND WEIGHT GAIN: Mean body weights and weight gains in high-dose males (250 mg/kg/day) were slightly (6.4%) lower than mean control values at termination of dosing.

HAEMATOLOGY: Dose-related, statistically significant methemoglobinemia, anemia, reticulocytosis and erythrocyte morphology changes
in mid- and high-dose males and females at both 45 and 90 days and slight anemia in low-dose females at 45 days only. Effects in mid- and high-dose animals did not increase in severity over time and were reversible after cessation of treatment. The magnitude of differences from control values was similar for methemoglobin, hemoglobin, hematocrit and total erythrocyte (RBC) values at 45 and 90 days, and reticulocyte counts were less elevated at 90 days than at 45 days. Methemoglobin values and erythrocyte morphology were comparable for all groups at termination of the recovery period, while hemoglobin, hematocrit and RBC values for mid- and high-dose animals were comparable to or higher than control values and reticulocyte counts for treated groups were comparable to or lower than control values. Elevations in mean corpuscular volume and mean corpuscular hemoglobin indices for mid- and high-dose animals were also seen at 45 and 90 days, but not at termination of the recovery period. Total leukocyte counts for high-dose animals were elevated at 45 and 90 days, but not at termination of the recovery period. Mean platelet counts for mid- and high-dose males, but not females, were higher than control values at 45 and 90 days, but not at termination of the recovery period. Although values were general ly within normal ranges, these a differences are suggestive of an effect of test substance administration and may represent a compensatory response by the bone marrow to the methemoglobinemia and anemia seen in these animals. Total bilirubin values for high-dose males and females were higher than control values at both 45 and 90 days. This is consistent with the hematologic effects (apparent accelerated erythrocyte destruction) seen in this group and was reversible after cessation of treatment.

CLINICAL CHEMISTRY: Effects on clinical chemistry parameters which were seen exclusively or primarily in males included reversible decreases in cholesterol, total protein and serum albumin levels and a slight increase in serum alkaline phosphatase levels in the mid- and/or high-dose
groups. Cholesterol values for mid- and high-dose males were approximately 30% (27 to 36%) lower than control values at both 45 and 90 days. Decreases in total serum protein and serum albumin levels, relative to control values, with corresponding increases in the albumin/globulin (A/G) ratio, were seen for high dose males at both 45 and 90 days. Differences in high-dose females were limited to a slight (non-statistical ly significant) decrease in total protein at Day 45 only and statistically significant increases in A/G ratio at both 45 and 90 days. Values for all of these parameters were comparable for control and treated groups at termination of the recovery period. The mean serum alkaline phosphatase value for high-dose males was statistically significantly higher than the control mean at 90 days, but not at 45 days or at termination of the recovery period. Although the difference seen was slight, it is considered suggestive of a reversible effect of test substance administration in high-dose males.

ORGAN WEIGHTS:
Organ weight effects included elevated liver weights in high-dose animals and elevated spleen weights in mid-and high-dose animals.
Mean liver weights, liver/body weight ratios and liver/brain weight ratios were higher than control values for high-dose males and females at both 45 and 90 days. Differences at 45 days were more pronounced in males than in females, while differences at 90 days were comparable for the two sexes. Recovery was apparent in females after one month without test substance administration, but mean liver weights for high-dose males remained elevated (12%), relative to control values.
Mean spleen weights, both absolute and relative to body and brain weights, for mid- and high-dose males and females were markedly higher than mean control values at both 45 and 90 days. Spleen weights for mid-dose animals were approximately twice those of control animals, while weights for high-dose animals were approximately 3 to 4 times control weights. Differences were more pronounced at 45 than at 90 days and reversibility of this effect was evident after cessation of treatment. At termination of the recovery period, spleen weight indices for mid-dose animals were comparable to control values and indices for high-dose animals remained slightly (30 to 50%) higher than control values.

GROSS PATHOLOGY: Enlarged spleens in mid- and high-dose animals.

HISTOPATHOLOGY:
In the liver, treatment-related alterations consisted of pigmentation of phagocytic cells and an increase in the severity of extramedullary hematopoiesis in both sexes. Specific evidence of hepatotoxicity was observed only in treated male rats. Treatment-related hepatic lesions observed in the top dose male rats included minimal bile duct proliferation, cytoplasmic vacuolization and foci of cellular alteration.
Splenic changes included increases in extramedullary hematopoiesis, pigmentation and congestion of the red pulp.

The treatment-related changes were increased in a dose-related manner, increased in incidence and severity with time, and were not resolved following a 30-day recovery period. Hepatocellular changes were more severe in treated male rats than in female rats.

Dose descriptor:

NOEL

Effect level:

10 mg/kg bw/day (nominal)

Based on:

act. ingr.

Sex:

male/female

Critical effects observed:

not specified

Conclusions:

The 90 day NOEL in the rat is 10 mg/kg/day

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

10 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

Sufficient to meet data requirements. The study is Klimisch 2.

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Following dosing of rats for 90 days at 10, 50 and 250 mg/kg, dose-related, statistically significant methaemoglobinemia, anemia, reticulocytosis and erythrocyte morphology changes were observed in mid- and high-dose animals. Treatment-related changes were also observed in the liver and spleen. The histopathological changes in the liver and spleen were increased in a dose-related manner, increased in incidence and severity with time, and were not resolved following the 30-day recovery period. Hepatocellular changes were more severe in treated male rats than in female rats and specific evidence of hepatotoxicity was observed only in treated males. The hepatic and splenic changes are suggestive of a haemolytic process affecting the erythrocytes with splenic congestion, splenic and hepatic haemosiderin pigment accumulation and extramedullary haematopoiesis in response to the loss of erythrocytes.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
Only one study available.

Repeated dose toxicity: via oral route - systemic effects (target organ) cardiovascular / hematological: hematopoiesis; cardiovascular / hematological: spleen; digestive: liver

Justification for classification or non-classification

The findings from the 90 day study at the relevant dose levels were not of sufficient severity to warrant classification.