Paraquat-dichloride

Immunotoxicity

Administrative data

Endpoint:

immunotoxicity: short-term oral

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2011

Report date:

2011

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.7800

Version / remarks:

(1998)

Deviations:

yes

GLP compliance:

yes

Limit test:

no

Test material

Test material information

1

Reference substance name:

Paraquat-dichloride

EC Number:

217-615-7

EC Name:

Paraquat-dichloride

Cas Number:

1910-42-5

Molecular formula:

C12H14N2.2Cl

IUPAC Name:

1,1’-dimethyl-4,4’-bipyridyldiylium dichloride

Results and discussion

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

>= 100 ppm

Based on:

test mat.

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Remarks:

original value (cation) presented in study.

2

Dose descriptor:

NOAEL

Effect level:

>= 138.1 ppm

Based on:

test mat.

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Remarks:

recalculated value, expressed as pure test substance, see ‘any other information on results incl. tables’ for respective calculation

Target system / organ toxicity

Critical effects observed:

no

Any other information on results incl. tables

Mean test substance consumption in the 0, 25, 75, and 100 ppm groups was 0, 6.9, 19.9, and 27.3 mg test substance/kg bw/day, respectively, over the entire 28-day study. All animals survived to the scheduled necropsy, except for a 75 ppm animal that escaped during the study which was euthanized and discarded. There were no treatment-related clinical observations or effects on body weights, food consumption, organ weights, or macroscopic findings for either the AFC or NKC assay animals. In the AFC assay, there were no effects attributed to the test substance on the specific activity or total activity of splenic IgM AFC to the T cell-dependent antigen sRBC. For the AFC positive control group (CPS), statistically significantly lower spleen weight, spleen cell numbers (63%), specific activity (100%), and total spleen activity (100%) of IgM antibody-forming cells were noted when compared to the vehicle control group. These effects on spleen weights, spleen cell numbers, and spleen activity (i.e., number of specific IgM antibody-forming cells directed towards the sRBC antigen) were consistent with the known immunosuppressant effects of CPS and validated the functionality of the AFC assay. In the NKC assay, there were no effects attributed to the test substance on NKC activity. For the NKC positive control group (anti asialo GM1), statistically significantly lower NKC activity at all effector:target ratios was noted when compared to the vehicle control group. This effect was consistent with the known effects of anti asialo GM1 on NKC activity, which validated the functionality of the NKC assay.

Applicant's summary and conclusion

Conclusions:

Based on the results of this study, treatment of female B6C3F1 mice with test substance on a continuous basis in the diet for a minimum of 28 consecutive days at 25, 75, and 100 ppm resulted in no suppression of the humoral (AFC) or innate (NKC) components of the immune system. The no-observed-effect level (NOEL) for both the AFC assay (humoral immunity) and the NKC assay (innate immunity) was 100 ppm (equivalent to approximately 27.3 mg test substance/kg body weight/day), the highest dose examined.

Executive summary:

The test substance was offered ad libitum in the diet for a minimum of 28 consecutive days to female B6C3F1 mice in Groups 2, 3, and 4 at dietary concentrations of 25, 75, and 100 ppm, respectively. Ten mice/group (Subset A) were used for the splenic Antibody-Forming Cell (AFC) assay and 10 mice/group (Subset B) were used for the Natural Killer Cell (NKC) assay. Mice in the AFC positive control group (Group 5A) were administered the positive control substance, cyclophosphamide (CPS) via intraperitoneal injection (50 mg/kg/day) once daily for 4 consecutive days (study days 24 through 27). All AFC group mice (Groups 1A-5A) were immunized with an intravenous or intraperitoneal injection of sheep red blood cells (sRBC) on study day 24, approximately 96 hours prior to the scheduled necropsy. Mice in the NKC positive control group (Group 6B) were administered the positive control substance (anti asialo GM1) via a single intravenous injection (0.2 mL/animal) on study day 27, approximately 24 hours prior to the scheduled necropsy. The concurrent control groups (Groups 1A and 1B) and the positive control groups (Groups 5A and 6B) were offered the basal diet on a regimen comparable to the test substance-treated groups. All animals were euthanized on study day 28. All animals were observed twice daily for mortality and morbidity. Clinical examinations were performed once daily for all animals. Detailed physical examinations were performed once weekly and on the day of the scheduled necropsy. Individual body weights were recorded twice weekly and food consumption was recorded approximately weekly. Complete necropsies were conducted on all animals at the scheduled necropsy. The kidney, lung, and spleen were weighed from all AFC- and NKC-designated animals at the scheduled necropsy. In addition, the thymus was weighed from all NKC-designated animals. Spleens were placed in Earle’s balanced salt solution/HEPES buffer and shipped to the immunological laboratory. After arrival at the immunological laboratory, spleen cell suspensions were prepared, spleen cell counts were performed, and the number of specific IgM antibody-forming cells directed towards the sRBC antigen were determined for the AFC-designated animals to measure the humoral immune response. In addition, immunological laboratory personnel prepared the spleens from the NKC-designated animals to measure innate immunity using the NKC assay.

Mean test substance consumption in the 0, 25, 75, and 100 ppm groups was 0, 6.9, 19.9, and 27.3 mg test substance/kg body weight/day, respectively, over the entire 28-day study. All animals survived to the scheduled necropsy, except for a 75 ppm animal that escaped during the study which was euthanized and discarded. There were no treatment-related clinical observations or effects on body weights, food consumption, organ weights, or macroscopic findings for either the AFC or NKC assay animals. In the AFC assay, there were no effects attributed to the test substance on the specific activity or total activity of splenic IgM AFC to the T cell-dependent antigen sRBC. For the AFC positive control group (CPS), statistically significantly lower spleen weight, spleen cell numbers (63%), specific activity (100%), and total spleen activity (100%) of IgM antibody-forming cells were noted when compared to the vehicle control group. These effects on spleen weights, spleen cell numbers, and spleen activity (i.e., number of specific IgM antibody-forming cells directed towards the sRBC antigen) were consistent with the known immunosuppressant effects of CPS and validated the functionality of the AFC assay. In the NKC assay, there were no effects attributed to the test substance on NKC activity. For the NKC positive control group (anti asialo GM1), statistically significantly lower NKC activity at all effector:target ratios was noted when compared to the vehicle control group. This effect was consistent with the known effects of anti asialo GM1 on NKC activity, which validated the functionality of the NKC assay.

In conclusion, the NOAEL for both the AFC assay (humoral immunity) and the NKC assay (innate immunity) was 100 ppm (equivalent to approximately 27.3 mg test substance/kg bw/day), the highest dose examined.