Triflumezopyrim

Immunotoxicity

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

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.