Disodium disulphite

Neurotoxicity

Administrative data

Endpoint:

neurotoxicity: sub-chronic oral

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well-documented study of metabisulphite effects on cognitive function.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

publication

Title:

Effect of sulfite on cognitive function in normal and sulfite oxidase deficient rats.

Author:

Kücükatay, V.; et al.

Year:

2005

Bibliographic source:

Neurotox. Teratol. 27, 47-54

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Metabisulfite effects on cognitive function were studied in adult male albino rats and sulfite oxidase-deficient rats. Groups of adult male albino rats were treated as follows: drinking water with Na2S2O5 (25 mg/kg), vitamin E, and Na2S2O5 plus vitamin E. These treatments were for 6 weeks. A 4th group served as control. The same set of experiments was performed on sulphite oxidase-deficient (SOXD) rats. Active avoidance behaviour was studied. Prior to this, motor function of the rats was tested using the Hanging Wire Test. At the end, blood was collected for determination of plasma S-sulphonate levels. After exsanguination brain and liver tissues were removed immediately for measuring hippocampus TBARS levels and assay of SOX activity, respectively.

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Disodium disulphite

EC Number:

231-673-0

EC Name:

Disodium disulphite

Cas Number:

7681-57-4

Molecular formula:

Na2S2O5

IUPAC Name:

disodium disulphite

Details on test material:

- Name of test material (as cited in study report): sodium metabisulfite
- Molecular formula (if other than submission substance):Na2S2O5
- Molecular weight (if other than submission substance): 190.1 g/mol
- Substance type: technical product
- Physical state: solid, white powder
No further details are given.

Test animals

Species:

rat

Strain:

not specified

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: breeding colony of the tet laboratory
- Age at study initiation: adult
- Weight at study initiation: 180-200 g
- Housing: four to five per cage
- Diet (ad libitum): standard rat chow for normal rast and Low-Mo-diet for SOX-deficient rats
- Water (ad libitum): tap water

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 - 25 °C
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: drinking water

Vehicle:

water

Remarks:

and olive oil administered to the groups not receiving vitamin E

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
- group 1: drinking water with Na2S2O5 (25 mg/kg*d)
- group 2: vitamin E (50 mg/kg*d dissolved in olive oil given via gastric gavage)
- group 3: drinking water with Na2S2O5 (25 mg/kg*d) plus vitamin E (50 mg/kg*d dissolved in olive oil given via gastric gavage)
- group 4: controls

The same set of experiments was performed on sulphite oxidase-deficient (SOXD) rats. The SOX deficiency was produced by a low molybdenum diet and concurrent addition of 200 ppm sodium tungstate to their drinking water starting 3 weeks before sulphite and vitamin E dosing.

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

6 weeks

Doses / concentrations

Remarks:

Doses / Concentrations:
25 mg/kg*d Na2S2O5
Basis:
nominal in water

No. of animals per sex per dose:

10 animals each group (40 SOX-competent and 40 SOX-deficient, each divided into four subgroups)

Control animals:

yes

Details on study design:

- Rationale for animal assignment: randomly

Examinations

Observations and clinical examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: no data

DETAILED CLINICAL OBSERVATIONS: Yes / No / No data
- Time schedule:

BODY WEIGHT: Yes
- Time schedule for examinations: no data

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No data

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No data

OPHTHALMOSCOPIC EXAMINATION: No data

OTHER:
- At the end of the 6th week, blood was collected from the abdominal aorta under urethane anesthesia for determination of plasma S-sulphonate levels. Plasma S-sulphonate levels were measured as a biomarker for ingested sulfite according to the method of Gunnison et al (1987)

Neurobehavioural examinations performed and frequency:

MOTOR FUNCTION TESTING
- motor function of the rats was tested using the Hanging Wire Test before starting active avoidance responses measurements

ACTIVE AVOIDANCE RESPOSES AND THE ACTIVE LEVELS
- Active avoidance behaviour was studied in the middle of the 6th week.
- each rat was given 50 trials of the procedure daily for 5 days
- the results were expressed as the mean percent avoidance responses for each daily shuttle box session

Sacrifice and (histo)pathology:

- Time point of sacrifice: after 6 weeks of exposure, after blood collection
- Number of animals sacrificed: all animales
- Tissues evaluated:
After exsanguination brain and liver tissues were removed immediately for measuring hippocampus TBARS levels and assay of SOX activity in the livers, respectively. Hippocampus TBARS levels, an indicator of lipid peroxidation, were measured to determine if sulfite causes lipid peroxidation and in this manner induces neurotoxicity accordingt o the method of Winterbourn, et al (1985). Hepatic SOX activity was determined as an indicator of SOX status of the body according to the method of Cohen et al (1971).

Statistics:

Results were expressed as means +/- S.E. Statistical comparison for repeated measurements between groups were made by repeated measures ANOVA for multiple comparisons, followed by TUKEY post hoc test. Differences between mean values in study groups were evaluated by a one-way ANOVA followed by TUKEY post hoc test. P values <0.05 were accepted as statistically significant.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

not specified

Clinical biochemistry findings:

not specified

Behaviour (functional findings):

effects observed, treatment-related

Description (incidence and severity):

only in sulphite oxidase-deficient rats

Gross pathological findings:

not specified

Neuropathological findings:

not specified

Details on results:

CLINICAL SIGNS AND MORTALITY
- There were no signs of toxicity in any of the experimental groups.
- Treatment groups in both series exhibited similar survival.

BODY WEIGHT AND WEIGHT GAIN
- Treatment groups in both series exhibited similar weight gain.

NEUROBEHAVIOUR
- Rats of all groups did not have any motor coordination and balance abnormalities.
- Na2S2O5 induced impairment of active avoidance learning in sulphite oxidase-deficient rats but not in normal rats.
- Vitamin E did not reverse the acvtive avoiding learning in the sulphite oxidase-deficient rats

OTHER FINDINGS
- plasma S-sulphonate level was found to be increased significantly in all sulfite exposed groups by adding sulfite to the drinking water; vitamin E had no effect on this parameter [F(3,19) = 9,23, p<0.001]
- Metabisulphite had no effect on hippocampus TBARS levels in normal rats.
- However, the TBARS levels were significantly increased by metabisulphite in the enzyme-deficient rats.
- Vitamin E reversed the observed detrimental neurotoxic effects of metabisulphite in the sulphite oxidase-deficient rats on their hippocampal TBARS

Effect levels

Dose descriptor:

NOAEL

Remarks on result:

not determinable

Remarks:

no NOAEL identified

Applicant's summary and conclusion

Conclusions:

In conclusion, the studied sodium metabisulphite exposure has neurotoxic effects in sulphite oxidase-deficient rats, but not in normal rats. This effect may not depend on oxidative stress.