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Immunotoxicity

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Description of key information

28-Day Rat Diet NOAEL (systemic toxicity): 500 ppm, NOAEL (humoral immune response): 6000 ppm; no humoral immune response. EPA OPPTS 870.7800; Reliability = 1

Key value for chemical safety assessment

Effect on immunotoxicity: via oral route

Link to relevant study records
Reference
Endpoint:
immunotoxicity: 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:
EPA OPPTS 870.7800
Deviations:
no
GLP compliance:
yes
Species:
rat
Strain:
other: Crl:CD(SD)
Sex:
female
Route of administration:
oral: feed
Vehicle:
other: LLC Certified Rodent LabDiet® 5002
Analytical verification of doses or concentrations:
yes
Duration of treatment / exposure:
At least 28 days
Dose / conc.:
100 ppm
Remarks:
(8.8 mg/kg bw/d)
Dose / conc.:
500 ppm
Remarks:
(41 mg/kg bw/d)
Dose / conc.:
2 000 ppm
Remarks:
(166 mg/kg bw/d)
Dose / conc.:
6 000 ppm
Remarks:
(474 mg/kg bw/d)
No. of animals per sex per dose:
10 female animals/dose
Control animals:
yes, concurrent vehicle
Positive control:
cyclophosphamide monohydrate
Clinical signs:
no effects observed
Mortality:
no mortality observed
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
- Adverse, test substance-related effects were observed on body weight and body weight gains in female rats fed ≥2000 ppm.
- The overall body weight gain (test Day 1-29), when compared to the control group for female rats fed 2000, and 6000 ppm, was 73 and 69% of the control, respectively. The reduction in overall body weight gain for the 2000 and 6000 ppm groups corresponded to a 91 and 88% reduction in mean body weight. These effects in body weight and body weight gain were considered test substance-related and adverse due to the magnitude of change.
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
- Adverse, test substance-related effects on food consumption were observed in female rats fed ≥2000 ppm. Statistically significant decreases were observed in rats fed 2000 ppm during interval Days 15-22 and 22-29 and 6000 ppm throughout the study (all statistically significant).
- Mean overall daily food consumption (test Day 1-29) in 2000 and 6000 ppm was 92% and 85% of the control, respectively.
Food efficiency:
effects observed, treatment-related
Description (incidence and severity):
- Adverse effects on food efficiency was observed in female rats fed 2000 and 6000 ppm of test substance. Mean overall daily food efficiency (test Day 1-29) in 2000 and 6000 ppm groups was 79% and 81% of the control, respectively.
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Immunological findings:
no effects observed
Organ weight findings including organ / body weight ratios:
no effects observed
Gross pathological findings:
no effects observed
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
not examined
Humoral immunity examinations:
no effects observed
Key result
Dose descriptor:
NOAEL
Remarks:
Humoral Immune response
Effect level:
6 000 ppm
Sex:
female
Basis for effect level:
other: Based on the lack of test substance-related effects on humoral immune function in female rats at any dietary concentration tested
Remarks on result:
other: 6000 ppm is equivalent to 474 mg/kg bw/day in female rats
Key result
Dose descriptor:
NOAEL
Remarks:
systemic toxicity
Effect level:
500 ppm
Sex:
female
Basis for effect level:
body weight and weight gain
food consumption and compound intake
food efficiency
Remarks on result:
other: 500 ppm is equivalent to 41 mg/kg bw/d in female rats
Conclusions:
Test substance is not considered to be an immunotoxicant.
Executive summary:

The study was conducted according to guideline U.S. EPA OPPTS 870.7800 to evaluate the potential of test substance to suppress the primary humoral immune response to sheep red blood cells (sRBC) when incorporated into nutritionally adequate diet and fed to female rats for at least 28 days. The dietary route of administration was selected because it is a potential route of human exposure. Groups of 10 female rats were administered the test substance at dietary levels of 0, 100, 500, 2000, or 6000 ppm. Body weights, food consumption measurements, and clinical observations were recorded during the in-life period. Prior to sacrifice, the immune system was stimulated by injecting sRBC on test Day 24 and blood samples were collected from each rat on test Day 29. The serum samples were assayed for their concentrations of sRBC-specific IgM antibodies to provide a quantitative assessment of humoral immune response. Serum from animals challenged with a positive control immunosuppressive agent was analyzed concurrently to provide confirmation that the assay performance was acceptable for detection of immunosuppression. At sacrifice, each animal was examined grossly and selected organs were weighed (brain, spleen, and thymus).

Samples of the test diets were analyzed, and the results indicated that the test substance was at the targeted concentrations, homogeneously mixed, and stable under the conditions of the study. The overall mean daily intake of test substance was calculated to be 0, 8.8, 41, 166, and 474 mg/kg body weight (bw)/day for the 0, 100, 500, 2000, and 6000 ppm concentrations, respectively.

Adverse effects on body weight, body weight gain and nutritional parameters were observed in female rats fed 2000 and 6000 ppm. No clinical signs of systemic toxicity were observed. No test substance-related effects were observed on gross pathology, absolute and relative brain, spleen, and thymus weights and humoral immune response.

The no-observed-adverse-effect level (NOAEL) for test substance humoral immune response was 6000 ppm, the highest dietary concentration tested. This concentration is equivalent to 474 mg/kg bw/day in female rats. This NOAEL was based on the lack of test substance-related effects on humoral immune function in female rats at any dietary concentration tested.

The NOAEL for test substance systemic toxicity was 500 ppm. This NOAEL was based on reductions in body weight, body weight gains and nutritional parameters in female rats fed ≥2000 ppm test substance.

Under the conditions of this study, test substance is not considered to be an immunotoxicant.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed

Effect on immunotoxicity: via inhalation route

Endpoint conclusion
Endpoint conclusion:
no study available

Effect on immunotoxicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

A 28-day immunotoxicity study was conducted with the test substance in female rats up to and including a maximum dietary concentration of 6000 ppm (equivalent to 474 mg/kg bw/day). Selection of the species, sex, and maximum exposure concentration were based on inputs from the U.S. EPA (U.S. EPA Memorandum June 10, 2014, DPX-RAB55: Report of the Dose Adequacy Review Team (DART) – Dose Selection for Immunotoxicity Study, PC Code 129210, DP Barcode 419857, Decision No. 490530). Dietary exposure to the test substance produced no treatment-related effects on thymus or spleen weight or on the antibody response to sheep red blood cells. Test substance related reductions in body weight, mean body weight gain and food efficiency were observed over the 28-day interval at 2000 and 6000 ppm. Based on these results, there is no evidence that the test substance induces toxicity to the immune system.

Justification for classification or non-classification

The test substance did not produce a humoral response in rats or mice in immunotoxicity studies. Therefore, the substance does not need to be classified for immunotoxicity according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.