Registration Dossier

Administrative data

Endpoint:
immunotoxicity: short-term oral
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2011-10-21 to 2011-11-21
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2012
Report Date:
2012

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
EPA OPPTS 870.7800
Deviations:
no
GLP compliance:
yes
Remarks:
US EPA Standards (40 CFR Part 160).
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
other: solution
Details on test material:
- Name of test material (as cited in study report): boric acid
- Substance type: inorganic acid
- Physical state: white, odorless, crystalline solid
- Analytical purity: 99% (56.37% B203; boron oxide)
- Purity test date: 2011-08-24
- Lot/batch No.: 8C20
- Stability under test conditions: stable

Test animals

Species:
mouse
Strain:
B6C3F1
Sex:
female

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
CMC (carboxymethyl cellulose)
Remarks:
1 % (w/v)
Details on exposure:
The test substance was administered daily to four groups of 10 female B6C3F 1 mice by oral gavage, at dose levels of 250, 500, 750 and 1000 mglkg for 28 consecutive days. A vehicle control group of 10 animals received only the vehicle (1% carboxymethylcellulose). Four days prior to sacrifice, all animals were given an intravenous injection (IV) of approximately 3 x 10E8 SRBCs. The positive control group of 10 animals (which also received the IV injection of approximately 3 x 10E8 SRBCs 4 days prior to splenocyte harvest) was given an intraperitoneal dose of cyclophosphamide (80 mg/kg bw) approximately 24 hours prior to sacrifice. Endpoints monitored in the study, in addition to hemolytic plaque formation, consisted of clinical observations, body weight, food consumption, and spleen and thymus weight.
Analytical verification of doses or concentrations:
yes
Duration of treatment / exposure:
28 days
Frequency of treatment:
once daily
Doses / concentrations
Remarks:
Doses / Concentrations:
250, 500, 750 and 1000 mg/kg bw
Basis:
actual ingested
No. of animals per sex per dose:
10
Control animals:
yes, concurrent vehicle
other: cyclophosphamide (positive control)

Results and discussion

Effect levels

Dose descriptor:
other: Immunotoxicity
Sex:
female
Basis for effect level:
other: see 'Remark'
Remarks on result:
not measured/tested
Remarks:
Effect level not specified (migrated information)

Applicant's summary and conclusion

Conclusions:
Boric acid was not immunotoxic in the sheep red blood cell (SRBC) hemolytic plaque assay.
Executive summary:

Boric acid was tested in the sheep red blood cell (SRBC) hemolytic plaque assay to determine if it had the capacity to cause adverse effects on the functional responsiveness of major components of the immune system. The hemolytic plaque assay, used in the current study design, determines the functionality of the T-cell dependent antibody response (TDAR). In this study SRBCs were used to induce IgM antibody-forming B-lymphocytes in vivo in rodent splenocytes. The extent of induction of splenic lymphocytes was quantitated by assessing splenocytes for their ability to lyse SRBCs in the presence of guinea pig complement. The test substance was administered daily to four groups of 10 female B6C3F1 mice by oral gavage, at dose levels of 250, 500, 750 and 1000 mg/kg for 28 consecutive days. A vehicle control group of 10 animals received only the vehicle (1 % carboxymethylcellulose). Four days prior to sacrifice, all animals were given an intravenous injection (IV) of approximately 3 x 10E8 SRBCs. The positive control group of 10 animals (which also received the IV injection of approximately 3 x 10E8 SRBCs 4 days prior to splenocyte harvest) was given an intraperitoneal dose of cyclophosphamide (80 mg/kg bw) approximately 24 hours prior to sacrifice. Endpoints monitored in the study, in addition to hemolytic plaque formation, consisted of clinical observations, body weight, food consumption, and spleen and thymus weight. After the spleens were collected and weighed, single cell suspensions of splenocytes were prepared in complete RPMI-1640 medium for each separate spleen. Two tubes for each spleen containing different dilutions of splenocytes plus SRBCs and an excess of guinea pig complement were prepared. Duplicate Cunningham chambers, one for each tube, were filled with an aliquot of the contents of the appropriate tube and incubated at 37 °C for at least one hour. Areas of SRBC lysis formed holes or plaques in the thin layer or lawn of the SRBCs and were indicative of immune cell secretion of antibodies. One of the two chamber slides (per animal spleen) was selected for analysis based on a visual impression that there were sufficient numbers of plaques. The plaques were then counted using a low power microscope. A statistically significant, dose-dependent reduction of plaques in the boric acid-treated animals compared to the vehicle control animals was considered indication of an adverse effect of the test substance on the immune system. There were no deaths and no adverse clinical observations due to test substance treatment. Body weight, body weight changes and food consumption were normal. There were no statistically significant reductions in absolute spleen or thymus weights in the boric acid-treated group relative to the vehicle control animals. There was a statistically significant reduction in plaque-forming cells in the positive control (cyclophosphamide) animals compared to the vehicle control animals. There was a reduction in plaque formation in all boric acid-treated groups compared to the vehicle control animals. The reductions in plaque formation appeared to be dose-dependent, at least up to the second highest dose level. However, none of the reductions in plaque formation were statistically significant, and therefore it is concluded that boric acid was not immunotoxic under the conditions of exposure described in this report.