Barbital sodium

Repeated dose toxicity: oral

Administrative data

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1987

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: study meets generally accepted scientific principles, however focused on limited parameters, acceptable for assessment of hepatic and renal toxicity

Data source

Reference

Reference Type:

publication

Title:

The Chronic Hepatic or Renal Toxicity of Di(2-ethylhexyl) Phthalate, Acetaminophen, Sodium Barbital, and Phenobarbital in Male B6C3Fl Mice: Autoradiographic, Immunohistochemical, and Biochemical Evidence for Levels of DNA Synthesis Not Associated with...

Author:

WARD J. M., HAGIWARA A., ANDERSON L. M., LINDSEY K., DIWAN B. A.

Year:

1988

Bibliographic source:

Toxicology and Applied Pharmacology Vol.96, Pg.494, 1988

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The hypothesis that carcinogenesis or tumor promotion by xenobiotics may result at least in part from increased cell turnover elicited by the chronic cytotoxicity of the chemicals was tested.

- Principle of test:
384 mice were randomized into seven groups of 48 mice each (group 2-7) or 96 mice (group 1) with equal group mean body weights. Animals were maintained on diets containing DEHP at 12.000 or 6000 ppm, ACT at 10,000 or 5000 ppm, or BBS at 1000 ppm, water with PB at 500 ppm, or no test chemical for up to 40 weeks. Twelve mice from each group were killed at 2, 8, 24, and 40 weeks.

- Short description of test conditions:
Mice were housed five per polycarbonate cage in filtered racks, and fed Purina 50 10 autoclavable rodent meal and acidified water adlibitum. Mice were maintained at a temperature of 20 to 22°C and a relative humidity of 50 + 10% with 12 changes ofroom air per hour. Body weights were measured monthly or weekly.

- Parameters analysed / observed:
liver and kidney weights, Thymidine kinase levels in liver and kidneys, levels of hepatic and renal DNA synthesis (by tritiated thymidine autoradiography or BrdU immunohistochemistry) and histopathologic evaluation.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Barbital sodium

EC Number:

205-613-9

EC Name:

Barbital sodium

Cas Number:

144-02-5

Molecular formula:

C8H11N2O3.Na

IUPAC Name:

sodium 5,5-diethyl-4,6-dioxo-1,4,5,6-tetrahydropyrimidin-2-olate

Test material form:

not specified

Details on test material:

Sodium barbital purchased from Sigma Chemical Co., St. Louis, MO

Specific details on test material used for the study:

Sodium barbital (BBS) (Sigma Chemical Co., St. Louis, MO), Di(2-ethylhexyl) phthalate (DEHP) (Aldrich Chemical Co.. Inc.. Milwaukee, WI), and acetaminophen (ACT) (Aldrich Chemical Co.) were prepared at designated concentrations for dietary administration by mechanical mixing with feed. phenobarbital (PB)(Sigma Chemical Co.) was dissolved in drinking water for administration.

Test animals

Species:

mouse

Strain:

B6C3F1

Sex:

male

Details on test animals or test system and environmental conditions:

test animals:
Four hundred male B6C3Fl mice. 4 weeks of age, were obtained from the NC1 Animal Genetics and Production Branch, Frederick, Maryland.


environmental conditions:
Mice were housed five per polycarbonate cage in filtered racks, and fed Purina 50 10 autoclavable rodent meal and acidified water adlibitum. Mice were maintained at a temperature of 20 to 22°C and a relative humidity of 50 + 10% with 12 changes ofroom air per hour. Body weights were measured monthly or weekly.

Administration / exposure

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on oral exposure:

Test chemicals were prepared at designated concentrations for dietary administration by mechanical mixing with feed.

Analytical verification of doses or concentrations:

no

Duration of treatment / exposure:

2, 8, 24, and 40 weeks

Frequency of treatment:

daily

Doses / concentrations

Dose / conc.:

1 000 ppm

Remarks:

with diet

No. of animals per sex per dose:

12 male mice per duration of treatment (with diet containing 1000 ppm sodium barbital)

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale:
Doses were based on previous studies of carcinogenicity. tumor promotion, and toxicity (Ward et al., 1986: Hagiwara and Ward, 1986).

- Principle of test:
384 mice were randomized into seven groups of 48 mice each (group 2-7) or 96 mice (group 1) with equal group mean body weights. Animals were
maintained on diets containing DEHP at 12.000 or 6000 ppm, ACT at 10,000 or 5000 ppm, or BBS at 1000 ppm, water with PB at 500 ppm, or no test chemical for up to 40 weeks. Twelve mice from each group were killed at 2, 8, 24, and 40 weeks.

- Short description of test conditions:
Mice were housed five per polycarbonate cage in filtered racks, and fed Purina 50 10 autoclavable rodent meal and acidified water adlibitum. Mice were maintained at a temperature of 20 to 22°C and a relative humidity of 50 + 10% with 12 changes ofroom air per hour. Body weights were measured monthly or weekly.

- Parameters analysed / observed:
At each termination, six mice from each group were used for measuring liver and kidney weights, and for evaluation of Thymidine kinase levels in liver and kidneys. Another six mice were used for evaluation of levels of hepatic and renal DNA synthesis (by tritiated thymidine autoradiography or BrdU immunohistochemistry) and for histopathologic evaluation.

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Not specified

DETAILED CLINICAL OBSERVATIONS: Not specified

BODY WEIGHT: Yes
- Time schedule for examinations: monthly or weekly

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
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No

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

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

IMMUNOLOGY: No

OTHER:
Evaluation of liver and kidney weights, histopathology, and thymidine kinase (TK) activity in liver and kidney and levels of DNA synthesis, measured by tritiated thymidine ([3H]T) autoradiography or bromodeoxyuridine (BrdU) immunohistochemistry.

Sacrifice and pathology:

SACRIFICE: Not specified

HISTOPATHOLOGY: Yes
The liver, kidneys, and small intestine were fixed in 10% buffered formalin. Deparaffinized slides were coated with Kodak NTB-3 nuclear track emulsion (Eastman-Kodak Co.. Rochester, NY), exposed for 4 weeks in a light tight box with a drying agent at 4°C. and developed with Kodak D19. Slides were stained with hematoxylin and eosin. The number of labeled nuclei per thousand hepatocytes or renal tubular cells or number per unit area (mm*) were counted in random areas of each organ for each animal. Four to eight high-power (25 X) fields were generally evaluated per tissue. These slides were also examined histopathologically for lesions.

Results and discussion

Results of examinations

Clinical signs:

not specified

Mortality:

no mortality observed

Description (incidence):

Sodium barbital did not exhibited severe toxicity as measured by survival.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

Sodium barbital did not exhibited severe toxicity as measured by body weight maintenance.

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Cell turnover:
Sodium barbital caused both increased hepatocyte labeling indices and thymidine kinase activity in liver at 2 weeks, and elevated TK levels only in the kidney at this time.

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Sodium barbital caused significant increases in liver-to-body weight ratios (Histologically, centrilobular cytomegaly was noted). Kidney weights were not
changed.

Gross pathological findings:

not specified

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Centrilobular cytomegaly was noted after Sodium barbital treatment. Kidney weights were not changed.

Histopathological findings: neoplastic:

no effects observed

Effect levels

Dose descriptor:

LOEL

Effect level:

1 000 ppm

Based on:

test mat.

Sex:

male

Basis for effect level:

organ weights and organ / body weight ratios

Target system / organ toxicity

Critical effects observed:

yes

Lowest effective dose / conc.:

33 600 mg/kg bw (total dose)

System:

hepatobiliary

Organ:

liver

Treatment related:

yes

Dose response relationship:

not specified

Any other information on results incl. tables

Liver-to-body weight ratios (%) in male B6F3C1 mice fed sodium barbital for up to 40 weeks

Treatment (ppm)	experimental week 2	experimental week 8	experimental week 24	experimental week 40
Sodium barbital 1000	4.64 ± 0.18	4.98 ± 0.13	4.89 ± 0.09	4.97 ± 0.08
control	4.20 ± 0.04	3.97 ± 0.30	4.25 ± 0.06	3.71 ± 0.08

Renal weights (% of body) in male B6F3C1 mice fed sodium barbital for up to 40 weeks

Treatment (ppm)	experimental week 2	experimental week 8	experimental week 24	experimental week 40
Sodium barbital 1000	1.42 ± 0.02	1.39 ± 0.04	1.42 ± 0.04	1.39 ± 0.04
control	1.38 ± 0.02	1.47 ± 0.12	1.48 ± 0.04	1.45 ± 0.04

Applicant's summary and conclusion

Conclusions:

Sodium barbital did not exhibited severe toxicity as measured by survival or body weight maintenance, but caused significant increases in liver-to-body weight ratios in male mice. Histologically, centrilobular cytomegaly was noted after sodium barbital treatment. Kidney weights were not changed.

Executive summary:

The hypothesis that carcinogenesis or tumor promotion by xenobiotics may result at least in part from increased cell turnover elicited by the chronic cytotoxicity of the chemicals was tested. 384 male mice were randomized into seven groups of 48 mice each (group 2-7) or 96 mice (group 1) with equal group mean body weights. Animals were maintained on diets containing DEHP at 12.000 or 6000 ppm, ACT at 10,000 or 5000 ppm, or Sodium barbital at 1000 ppm, water with PB at 500 ppm, or no test chemical for up to 40 weeks. Twelve mice from each group were killed at 2, 8, 24, and 40 weeks. Body weights were measured monthly or weekly. At each termination, six mice from each group were used for measuring liver and kidney weights, and for evaluation of thymidine kinase (TK) levels in liver and kidneys. Another six mice were used for evaluation of levels of hepatic and renal DNA synthesis (by tritiated thymidine autoradiography or BrdU immunohistochemistry) and for histopathologic evaluation.

Sodium barbital did not exhibited severe toxicity as measured by survival or body weight maintenance, but caused significant increases in liver-to-body weight ratios in male mice. Histologically, centrilobular cytomegaly was noted after sodium barbital treatment. Sodium barbital caused both increased hepatocyte labeling indices and TK activity in liver at 2 weeks, and elevated TK levels only in the kidney at this time. Kidney weights were not changed. There were no other major effects on these measures of cell turnover.

The results of this study confirm that increased cell turnover is a clear and expected consequence of high toxicity, but provide no evidence that this phenomenon is a necessary mechanistic component of carcinogenesis or tumor promotion by nongenotoxic carcinogens.