Diarsenic trioxide

Repeated dose toxicity: oral

Administrative data

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

publication

Title:

Results of a long-term carcinogenicity bioassay on Sprague-Dawley rats exposed to sodium arseniteadministered in drinking water

Author:

Soffritti M et al.

Year:

2006

Bibliographic source:

Ann. N.Y. Acad. Sci. 1076:578-591

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

A long-term carcinogenicity bioassay on sodium arsenite (NaAsO2) was performed. NaAsO2 was administrated with drinking water at concentrations of 200, 100, 50, or 0 mg/L, for 104 weeks to Sprague-Dawley rats (50/sex/group), 8 weeks old at the start of the study. The animals were monitored until spontaneous death at which time each animal underwent complete necropsy. Histopathological
evaluation of all pathological lesions and of all organs and tissues collected was routinely performed on each animal. Also, drinking water and feed consumption were monitored during the study as well
as body weight. Lastly, the animals were clinically examined during the study.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Sodium dioxoarsenate

EC Number:

232-070-5

EC Name:

Sodium dioxoarsenate

Cas Number:

7784-46-5

IUPAC Name:

sodium dioxoarsenate(1-)

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 8 weeks old
- Housing: animals were housed in groups of five in makrolon cages (41 cm X 25 cm X 15 cm) with
stainless-steel wire tops and a shallow layer of white wood-shavings as bedding.
- Diet: standard Corticella diet (Corticella S.p.A., Bologna, Italy)
- Water (ad libitum): tap water
ENVIRONMENTAL CONDITIONS
- Temperature: 21 ± 2°C
- Relative humidity: 50 - 60%
- Photoperiod (hrs dark / hrs light): 12/12 (natural and artificial light sources)
After weaning at 4 -5 weeks of age, the experimental animals were randomized in order to have no
more than one male and one female from each litter in the same group.

Administration / exposure

Route of administration:

oral: drinking water

Vehicle:

water

Details on oral exposure:

Each morning, leftover solution from the previous day was removed and glass drinking bottles were washed and refilled with fresh solution.

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

No data.

Duration of treatment / exposure:

104 weeks

Frequency of treatment:

ad libitum

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 mg/L drinking water

Doses / concentrations 2

Dose / conc.:

50 mg/L drinking water

Doses / concentrations 3

Dose / conc.:

100 mg/L drinking water

Doses / concentrations 4

Dose / conc.:

200 mg/L drinking water

Remarks:

Based on test substance

No. of animals per sex per dose:

20/sex/group

Control animals:

yes, concurrent no treatment

Details on study design:

NaAsO2 was administrated with drinking water at concentrations of 200, 100, 50, or 0 mg/L, for 104
weeks to Sprague-Dawley rats (50/sex/group), 8 weeks old at the start of the study. The animals
were monitored until spontaneous death at which time each animal underwent complete necropsy.
Histopathological evaluation of all pathological lesions and of all organs and tissues collected was
routinely performed on each animal. Also, drinking water and feed consumption were monitored duri
ng the study as well as body weight. Lastly, the animals were clinically examined during the study.

Positive control:

No data.

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: the animals were clinically examined for gross changes every 2 weeks for the durat
ion of the study.

DETAILED CLINICAL OBSERVATIONS: No data

DERMAL IRRITATION: No data

BODY WEIGHT: Yes
- Time schedule for examinations: body weight was measured individually once weekly for the first 13
weeks and then every 2 weeks until 111 weeks of age. Measurement of body weight contiuned every
8 weeks until the end of the experiment.

FOOD CONSUMPTION: Yes
- Time schedule for examinations: Mean daily feed consumption was measured once weekly per cage
for the first 13 weeks, and then every 2 weeks until 111 weeks of age.

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted a
verages from the consumption and body weight gain data: No data

WATER CONSUMPTION: Yes
- Time schedule for examinations: mean daily drinking water was measured once weekly per cage for
the first 13 weeks, and then every 2 weeks until 111 weeks of age.

OPHTHALMOSCOPIC EXAMINATION: No data

HAEMATOLOGY: No data

CLINICAL CHEMISTRY: No data

URINALYSIS: No data

NEUROBEHAVIOURAL EXAMINATION: No data
OTHER: extensive historical data are available on the tumor incidence among untreated rats.

Sacrifice and pathology:

The biophase ended at 159 weeks, with the death of the last animal at 167 weeks of age. Upon death, all animals underwent complete necropsy. Histopathology was routinely performed on the following organs and tissues of each animal from each group: skin and subcutaneous tissue, the brain (three sagittal sections), pituitary gland, Zymbal glands, salivary glands, Harderian glands, cranium
(five sections, with oral and nasal cavities and external and internal ear ducts), tongue, thyroid, parathyroid, pharynx, larynx, thymus and mediastinal lymph nodes, trachea, lung and mainstem bronchi,
heart, diaphragm, liver, spleen, pancreas, kidneys, adrenal glands, esophagus, stomach (fore and glandular), intestine (four levels), urinary bladder, prostate, gonads, interscapular brown fat pad,
subcutaneous and mesenteric lymph nodes, and other organs or tissues with pathological lesions.
All organs and tissues were preserved in 70% ethyl alcohol, except for bones, which were fixed in 10% formalinand the decalcified with 10% formaldehyde and 20% formic acid in water solution. The
normal specimens were trimmed, following SOP. Trimmed specimens were processed as paraffin blocks and 3 - 5 μm sections of every specimen were obtained. Sections were routinely stained with
Hematoxylin-Eosin.

Statistics:

Mutilple tumors of different types and sites, of different types in the same site, of the same types in bilateral organs, of the same types in the skin, subcutaneous tissue or mammary glands, or at distant sites of diffuse tissue (i.e., bones aand skeletal muscle) were plotted as single/independent tumors. Multiple tumors of the same type in the same tissue and organ, apart from those mentioned above, were plotted only once.
Three statistical tests were used to analyze neoplastic and non-neoplastic lesion incidence data. The Chi-square test and the Fisher's exact test (HAseman, 1978)* were used to evaluate differences in tumor incidence between treated and control groups. The Cochran-Armitage trend test (Armitage, 1971; Gart et al., 1979)** was used to test for linear trends in tumor incidence.

References
*, *** HASEMAN, J.K. 1978. Exact sample sizes with the Fisher-Irwin test for 2×2 tables. Biometrics 34:
106–109.
** ARMITAGE, P. 1971. Statistical Methods in Medical Research. JohnWiley & Sons. New York.
** GART, J.J., K.C. CHU & R.E. TARONE. 1979. Statistical issues in interpretation of chronic tests for
carcinogenicity. J. Natl. Cancer Inst. 62: 957–974.

Results and discussion

Results of examinations

Clinical signs:

not specified

Mortality:

mortality observed, treatment-related

Description (incidence):

Differences in survival rates were observed in both males and females; a slight decrease in the survival rate was observed in males treated at 200 and 100 mg/L, particularly from 40 weeks of age until
88 weeks of age, whereas in females, a decrease in survival rate was observed from 104 weeks of a ge until the end of the experiment.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

A dose related difference in mean body weight was observed in males. The difference was more evident in the males treated at 200 mg/L (circa 15% when compared with controls). Differences
in mean body weight were also observed in females of the groups treated at 200 and 100 mg/L. Mean body weight was about 20% less in females treated at 200 mg/L compared with control and
about 10% less in females treated at 100 mg/L. No treatment-related differences in body weight were observed in females treated at 50 mg/L.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

A dose-related lower intake of feed was also observed in both male and female rats. This difference was less marked between the group treated at 50 mg/L and the control in both males and females.

Food efficiency:

not specified

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

effects observed, treatment-related

Description (incidence and severity):

A dose-related lower intake of water containing various levels of NaAsO2 was observed in both male and female rats. In females, water consumption became similar between the group treated at 50 mg/L and the control after 88 weeks of age.

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Immunological findings:

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Neuropathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Long-term exposure of sodium arsenite administered in drinking water to Sprague-Dawley rats has been shown to induce toxic effects on the kidneys at concentrations as high as 200 mg/L and, to a
lesser extent 100 mg/L and 50 mg/L. Nephropathies were characterized by diffuse acute/chronic inflammation, tubular enlargement with deposits of ialin casts and marked fibrosis around glomeruli with distension of Bowman’s space.

Histopathological findings: neoplastic:

effects observed, treatment-related

Description (incidence and severity):

The main oncologic results of the experiment are attached below in the field "Attached background material" (Tables 1 and 2). Among males treated at 100 mg/L, a slightly increased incidence of animals bearing malignant tumors and a statistically significant increased number of total malignant tumors (P < 0.05) were observed when compared to controls. Sparse very infrequent benign and malignant tumors were observed in the treated groups, namely, one adenocarcinoma of the lung in a male treated at 200 mg/L; one carcinoma of the kidney and one papilloma of the pelvis in a male treated at 100 mg/L and two papillomas of the renal pelvis in another rat treated at the same dose. Renal pelvis papillomas were also observed in two males treated at 50 mg/L. Among females treated at 100 mg/L, a slightly increased incidence of animals bearing malignant tumors and an increase d number of total malignant tumors were observed when compare to controls. Among the females treated at 200 mg/L, one adenocarcinoma of the lung was observed. The same group also included two animals bearing kidney adenomas, two bearing kidney carcinomas, and one bearing a renal pelvis carcinoma. In the group treated at 100 mg/L, three animals were observed bearing kidney adenomas,
one bearing a kidney carcinoma and one bearing a renal pelvis papilloma. One animal bearing a bladder carcinoma was also observed among the females treated at 100 mg/L.

Other effects:

not specified

Details on results:

HISTORICAL CONTROL DATA
It must be noted that among the untreated Sprague-Dawley rats used in study experiment laboratories over the last 20 years (2265 males and 2274 females), the overall incidence of lung adenomas was 0.2% in males (range: 0–2.0%) and 0.1% in females (range: 0–1.0%), while the overall incidence of lung carcinomas was 0.1% in both males (range: 0–1.0%) and females (range: 0–1.3%). The overall incidence of the kidney adenomas was 0.1% in males (range: 0–1.3%) and 0.2% in females (range: 0–2.0%), while the overall incidence of kidney carcinomas was 0.2% in males (range: 0–0.3%) and 0.3% in females (range: 0–1.8%). With regard to historical data on the transitional cell epithelium of the renal pelvis and ureter, no papillomas were observed in either males or females, while only one
carcinoma was observed in a female (overall incidence: 0.04% and range: 0–1.0%). No carcinomas in the transitional cell epithelium of the bladder were observed in either males or females.

Effect levels

Key result

Dose descriptor:

LOEL

Effect level:

100 mg/L drinking water

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

food consumption and compound intake

water consumption and compound intake

Target system / organ toxicity

Critical effects observed:

no

Any other information on results incl. tables

NaAsO2 induces sparse benign and malignant tumors among treated rats  (not statistically significant).

Applicant's summary and conclusion

Executive summary:

A 2-year (104-week) carcinogenicity dose–response study was conducted with sodium arsenite (NaAsO2) administered via drinking water to Sprague-Dawley rats (50/sex/group, 8 weeks old at the start of the study) at concentration of 0, 50, 100 and 200 mg/L ad libitum. Mean daily drinking water and feed consumption were measured once weekly per cage for the first 13 weeks, then every 2 weeks until 111 weeks of age. Body weight was measured individually once weekly for the first 13 weeks, then every 2 weeks until 111 weeks of age (however, dose levels expressed in mg/kg bw/day are not provided in the publication). The rats were maintained until spontaneous death, at which time each animal underwent complete necropsy. Histopathological evaluation of all pathological lesions and of all organs and tissues collected was routinely performed.

A dose-related lower intake of water was observed in both male and female rats. In females, water consumption became similar between the group treated at 50 mg/L and the control after 88 weeks of age. A dose-related lower intake of feed was also noted in both male and female rats. This difference was less marked between the group treated at 50 mg/L and the control. A dose-related difference in mean body weight was observed in males. The difference was more evident at 200 mg/L (circa 15% when compared with controls). Mean body weight in females was about 20% less at 200 mg/L compared with control and about 10% less at 100 mg/L. No treatment-related differences in body weight were observed in females at 50 mg/L. A slight decrease in the survival rate was observed in males at 200 and 100 mg/L, particularly from 40 to 88 weeks of age, whereas in females, a decrease in survival rate was observed from 104 weeks of age until the end of the experiment.

Among males treated at 100 mg/L, a slightly increased incidence of animals bearing malignant tumors and a statistically significant increase in number of total malignant tumors (p<0.05) were observed when compared to controls. One adenocarcinoma of the lung was seen at 200 mg/L, one carcinoma of the kidney and one papilloma of the pelvis at 100 mg/L and two papillomas of the renal pelvis in another rat at the same dose. Renal pelvis papillomas were also observed in two males at 50 mg/L.

Among females treated at 100 mg/L, a slightly increased incidence of animals bearing malignant tumors and an increased number of total malignant tumors were observed when compared to controls. Three animals were found bearing kidney adenomas, one bearing a kidney carcinoma and one bearing a renal pelvis papilloma. One animal with a bladder carcinoma was also noted in this group. At 200 mg/L, one adenocarcinoma of the lung was observed. The same group also included two animals bearing kidney adenomas, two bearing kidney carcinomas and one bearing a renal pelvis carcinoma.

The authors concluded that, under the conditions of their study, sodium arsenite induced sparse benign and malignant tumours amongst treated rats. They noted that the types of tumours observed were infrequent in the strain of Sprague-Dawley rats of the colony used in their laboratory (Soffritti et al., 2006).