Xylose

Endpoint summary

Description of key information

104 week feeding study; rat; NOAEL > 5% (highest dose tested; equivalent to 2214 and 2513 mg/kg in males and females, respectively); reliability = 2

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

chronic toxicity: oral

Remarks:

combined repeated dose and carcinogenicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: Ministry of Health, Labor and Welfare of Japan), 1996b. Guidelines for Designation of Food Additives, and for Revision of Standard for Use of Food Additives, Article No. 29 of the Life and Sanitation Bureau.

Deviations:

no

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Fischer 344/DuCrj

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 6-week-old
- Weight at study initiation: not reported
- Housing: plastic cages with woodchip bedding (three or four male rats/cage, five female rats/cage)
- Diet (e.g. ad libitum): basal diet (CRF-1) ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: one week

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 24 ± 1°C
- Humidity (%): 55 ± 5%
- Air changes (per hr): not reported
- Photoperiod (hrs dark / hrs light): 12-h light/dark cycle

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on oral exposure:

DIET PREPARATION: Diets were prepared once every three months by the forage supplier and preserved in the dark at 4°C prior to use.

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

104 weeks

Frequency of treatment:

Daily

Dose / conc.:

2.5 other: % (nominal in diet)

Remarks:

actual ingested: 1033 and 1203 mg/kg/day for males and females, respectively

Dose / conc.:

5 other: % (nominal in diet)

Remarks:

actual ingested: 2214 and 2513 mg/kg/day for males and females, respectively

No. of animals per sex per dose:

50/sex/dose

Control animals:

yes, plain diet

Details on study design:

- Dose selection rationale: The dietary dose levels were selected on the basis of the results of a previous 13-week subchronic toxicity study, performed with dietary doses of 0.2%, 0.6%, 1.7% and 5%. In the subchronic study, there were no deaths or any adverse clinical signs. Growth, food consumption, hematology, serum biochemistry and histopathology were unaffected by exposure to the test substance. A dietary dose of 5% or more was concluded as the maximum tolerated dose for both sexes in F344 rats, in line with Japanese government guidelines, and therefore was chosen as the highest dose for the present carcinogenicity study.

Positive control:

None

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily for mortality and moribundity

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Clinical examinations were performed daily.

BODY WEIGHT: Yes
- Time schedule for examinations: once a week for the first five weeks of the study and then once every five weeks

FOOD CONSUMPTION: Yes
- Time schedule for examinations: The amounts of food consumed for one week per cage were measured once every five weeks, and the daily consumptions of food per animal were calculated in order to determine the total intakes of test substance

FOOD EFFICIENCY: No data

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: Collected from abdominal aorta at necropsy
- Anaesthetic used for blood collection: No
- Animals fasted: Yes
- How many animals: All
- Parameters examined: white blood cells (WBC), red blood cells (RBC, hemoglobin concentration (Hb), hematocrit (Ht), and platelets (PLT)

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes

A complete necropsy was conducted on all animals. After careful gross examination, complete autopsies were performed on all animals. The brain, submaxillary gland, lungs, heart, liver, spleen, adrenal glands, kidneys and testes of each rat were weighed. Moribund or dead animals were also completely autopsied. Tumour masses, as well as all major organs and tissues, were fixed in 10% buffered formalin and paraffin sections were routinely prepared and stained with haematoxylin and eosin for histopathological analysis.

Statistics:

Data for body weights were analyzed by the Students t-test. Haematology, organ weight and final body weight data were analyzed for homogeneity of variance using the Bartletts test. Where the samples proved to be homogeneous, one-way analysis of variance was employed. If significant heterogeneity of variance (P < 0.01) was apparent, the equivalent non-parametric statistical method of Kruskal–Wallis was used. Where significant differences between the groups were detected, a multiple comparison test (Dunnetts test or Scheffes method) was applied. Final survival rates and the incidences of tumours were compared with the Fishers exact probability test.

Clinical signs:

no effects observed

Description (incidence and severity):

No treatment-related clinical signs were noted during the treatment period, except that soft faeces in the 5% males and females were found throughout the experimental period. Soft faeces observed in 5% males and females, possibly caused by the high concentration of the test substance excretion in the faeces, might be concerned in body weight suppression.

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Description (incidence and severity):

Although decreases in the final body weights were recorded in males and females receiving the 5% dose, the values during the experimental period were less than 10% lowered as compared with the control group. This weight suppression might be a result from the low calorific property of the test substance. However, the effect of the test substance on total calorie intake was considered to be a little, because the quantity of the test substance in the admixture was only 5% at the maximum, and food consumptions seem to have increased with the test substance concentrations in order to compensate low calorie.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

Daily food intake in the D-xylose-treated groups of both sexes was slightly increased with D-xylose concentration, but a good correlation between the dose of D-xylose and daily intake was observed.

Food efficiency:

not specified

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

In the organ weights, decrease in absolute and increase in relative brain weights were observed in males of the 5% group, and decrease of absolute kidney values was noted in females of the 5% group. However, there were no remarkable changes in these organs on histopathology. Increases in the absolute and relative testis weights were observed in males of the 5% group.

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Description (incidence and severity):

Increases in the absolute and relative testis weights were observed in males of the 5% group. In rats, spontaneous interstitial cell tumours in the testes occur at very high incidence, reaching 81–91% at 104 weeks of age. In the present study, the incidence of interstitial cell tumours in the control group was 92% (within the reference background range), whereas that in the 5% group was decreased to 72%. This low incidence was considered to reflect differences in testis weights between the control and 5% groups. Dietary restriction has been shown to reduce the incidences of a variety of rodent spontaneous tumours, including interstitial cell tumours in F344 rats. Additionally, the suppression of body weight is considered to be associated with low neoplasm incidences. In the present study, the suppression of body weight may have caused a low incidence of testis interstitial cell tumour. However, suppression of body weight gain is much weaker than those in dietary restriction experiments. Therefore, it is likely that unknown factors other than lower body weight might be also concerned. Histopathological assessment revealed pituitary adenomas and endometrial stromal polyps in the females, and thyroid adenomas in both sexes at relatively high incidences. However, the lack of significant differences between the control and treated groups suggests a spontaneous nature for these lesions. Large granular leukemia is well known to arise in aged F344 rats, and the incidence observed in the control group was within the range of reported values. The test substance-treated groups showed a tendency for decrease in the incidence of large granular leukemia, and again this might have been due to dietary restriction. Incidence in large granular leukemia might also be due to low body weight. Tumours were also detected in other organs or tissues, but their incidences were consistently very low. None of the treated groups showed significant increase in the incidence of any specific tumour over the control group level.

Dose descriptor:

NOAEL

Effect level:

> 5 other: % (equivalent to 2214 and 2513 mg/kg/day for males and females, respectively)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No test substance-related adverse effects observed at the highest dose tested.

Critical effects observed:

no

Conclusions:

NOAEL: 5% (equivalent to 2214 and 2513 mg/kg/day in males and females, respectively)

Executive summary:

Dietary administration of the test substance to F344 rats at dose levels of 2.5% or 5% (equivalent to overall achieved intakes of 1033 or 2214 mg/kg/day for males and 1203 or 2513 mg/kg/day for females, respectively) in the diet for 104 weeks exerted no effects on mortality, clinical signs or haematology data, except soft faeces in 5% males and females. Although decreases in the final body weights were recorded in males and females receiving the 5% dose, the values during the experimental period were less than 10% lowered as compared with the control group. This weight suppression might be a result from the low calorific property of the test substance. However, the effect of the test substance on total calorie intake was considered to be a little, because the quantity of the test substance in the admixture was only 5% at the maximum, and food consumptions seem to have increased with the test substance concentrations in order to compensate low calorie. Soft faeces observed in 5% males and females, possibly caused by the high concentration of the test substance excretion in the faeces, might be concerned in body weight suppression. In the organ weights, decrease in absolute and increase in relative brain weights were observed in males of the 5% group, and decrease of absolute kidney values was noted in females of the 5% group. However, here were no remarkable changes in these organs on histopathology. Increases in the absolute and relative testis weights were observed in males of the 5% group. In rats, spontaneous interstitial cell tumours in the testes occur at very high incidence, reaching 81–91% at 104 weeks of age. In the present study, the incidence of interstitial cell tumours in the control group was 92% (within the reference background range), whereas that in the 5% group was decreased to 72%. This low incidence was considered to reflect differences in testis weights between the control and 5% groups. Dietary restriction has been shown to reduce the incidences of a variety of rodent spontaneous tumours, including interstitial cell tumours in F344 rats. Additionally, the suppression of body weight is considered to be associated with low neoplasm incidences. In the present study, the suppression of body weight may have caused a low incidence of testis interstitial cell tumour. However, suppression of body weight gain is much weaker than those in dietary restriction experiments. Therefore, it is likely that unknown factors other than lower body weight might be also concerned. Histopathological assessment revealed pituitary adenomas and endometrial stromal polyps in the females, and thyroid adenomas in both sexes at relatively high incidences. However, the lack of significant differences between the control and treated groups suggests a spontaneous nature for these lesions. Large granular leukaemia is well known to arise in aged F344 rats, and the incidence observed in our control group was within the range of reported values. The test substance-treated groups showed a tendency for decrease in the incidence of large granular leukaemia, and again this might have been due to dietary restriction. Incidence in large granular leukaemia might also be due to low body weight. Tumours were also detected in other organs or tissues, but their incidences were consistently very low. None of the treated groups showed significant increase in the incidence of any specific tumour over the control group level. In conclusion, the present results demonstrate that the test substance dose not exert any carcinogenic potential in male and female F344 rats fed for two years. The NOAEL for this study was 5% (equivalent to 2214 and 2513 mg/kg/day in males and females, respectively).

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

2 513 mg/kg bw/day

Study duration:

chronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

The test substance was fed to groups of 50 male and 50 female F344 rats at dietary doses of 0% (control), 2.5% (equivalent to 1033 and 1203 mg/kg for males and females, respectively) and 5% (equivalent to 2214 and 2513 mg/kg for males and females, respectively) for 104 weeks. Growth suppression and soft faeces were observed in male and female rats of the 5% group. However, no significant differences from the controls were noted with regard to clinical signs, mortality and haematological findings. Decrease in absolute weight and increase in relative weight of the brain in males and decrease of absolute kidney weight in females were observed in the 5% group, but there were no remarkable histopathological changes. A variety of tumours developed in all groups, including the controls, but all were histologically similar to those known to occur spontaneously in F344 rats, and no statistically significant increase in the incidence of any type of neoplastic lesion was found for either sex in the treated groups. A NOAEL of >5% (highest dose tested) was determined. Thus, it was concluded that, under the experimental conditions, D-xylose is not carcinogenic to F344 rats.

Justification for classification or non-classification

Based on no adverse test substance-related effects at 5% (highest dose tested) in a 104-week rat feeding study, no classification is required for repeat toxicity according to EU Classification and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.