2-naphthol

Repeated dose toxicity: oral

Administrative data

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1989

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1989

Report date:

1989

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 407 (Repeated Dose 28-Day Oral Toxicity Study in Rodents)

Deviations:

yes

Remarks:

Functional observations were not conducted

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

2-naphthol

EC Number:

205-182-7

EC Name:

2-naphthol

Cas Number:

135-19-3

Molecular formula:

C10H8O

IUPAC Name:

2-naphthol

Test material form:

solid: particulate/powder

Test animals

Species:

rat

Strain:

Crj: CD(SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Italia S.P.A.
- Females (if applicable) nulliparous and non-pregnant: yes
- Age at study initiation: 27-29 days
- Weight at study initiation: Weight range of 10g for each sex
- Housing: five animals per polycarbonate cages
- Diet: Altromin AT rodent diet ad libitum
- Water: Tap water ad libitum
- Acclimation period: 14 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21°C +/- 2°C
- Humidity (%): 55% +/- 10%
- Air changes (per hr): ca. 20 per hr
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: Prepared daily by addition of the vehicle to the test compound.

VEHICLE
- Concentration in vehicle: 5 mg/mL, 15 mg/mL and 45 mg/mL
- Amount of vehicle (if gavage): 10 mL/kg bw

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples of the formulations prepared in week 1, 3 and 4 were analysed to check homogeneity and concentration of the preparation.

Duration of treatment / exposure:

4 weeks

Frequency of treatment:

Daily

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 mg/kg bw/day (nominal)

Doses / concentrations 2

Dose / conc.:

50 mg/kg bw/day (nominal)

Doses / concentrations 3

Dose / conc.:

150 mg/kg bw/day (nominal)

Doses / concentrations 4

Dose / conc.:

450 mg/kg bw/day (nominal)

No. of animals per sex per dose:

5 animals/sex/group + 5 animals/sex for control and high-dose groups (recovery animals)

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale:
- Fasting period before blood sampling for clinical biochemistry: Yes
- Post-exposure recovery period in satellite groups: 4 weeks

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Weekly

BODY WEIGHT: Yes
- Time schedule for examinations: Weekly

FOOD CONSUMPTION: Yes
- Food consumption: Recorded weekly by cage to calculate mean daily intake per rat.

WATER CONSUMPTION: YEs
- Time schedule for examinations: Daily

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: Prior to treatment, during week 4 of treatment and week 4 of recovery.
- Dose groups that were examined: all groups.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: During week 4 of treatment and recovery
- Anaesthetic used for blood collection: Yes (light ether)
- Animals fasted: Yes

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: During week 4 of treatment and recovery
- Animals fasted: Yes / No / Not specified

URINALYSIS: Yes
- Time schedule for collection of urine: During week 4 of treatment and recovery
- Metabolism cages used for collection of urine: Not specified
- Animals fasted: Yes

NEUROBEHAVIOURAL EXAMINATION: No

IMMUNOLOGY: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes

HISTOPATHOLOGY: Yes
The following tissues were investigated: abnormalities, adrenal glands, aorta, brain, caecum, cervix, colon, duodenum, eyes, harderian glands, head, heart, ileum, jejunum, kidneys, larynx and pharynx, liver, lungs, lymph nodes, mammary glands, oesophagus, ovaries, pancreas, pituitary gland, prostate gland, sciatic nerve, seminal vesicles, skeletal muscle, skin, spinal column, spleen, sternum, stifle joint, stomach, testes, thymus, thyroid, tongue, trachea, urinary bladder, uterus, vagina.

Statistics:

Standard deviations were calculated as considered appropriate. For continuous variables the significance of the differences between group means was assessed by analysis of variance, comparing the treated groups with controls and the intergroup variation. Differences between each treated group and the control group was assessed by Dunnett’s test using a pooled error variance.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

No relevant clinical signs were observed in male rats throughout the study. Amongst female animals, brown staining was apparent in 8/10 animals receiving 450 mg/kg bw/d of test substance. This discoloration usually affected the head, fore limbs and/or dorsal surface of the body, and was observed during the last week of the treatment until week 2 of the recovery period. This is not considered of toxicological significance.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

One animal dosed with 50 mg/kg bw/d died on Day 14, which was attributed to an intubation error during administration by the study director. No other animals died during the study.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No treatment-releated effects were reported.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

Food intake for the treated groups was similar to the control groups.

Food efficiency:

not examined

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

no effects observed

Description (incidence and severity):

There were no consistent intergroup differences in water consumption which could be attributed to treatment.

Ophthalmological findings:

no effects observed

Description (incidence and severity):

There were not ophthalmic lesions observed which could be related to treatment. The minor changes recorded during the study are consistent with those occurring frequently in this strain of rats and were without significance.

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Changes were recorded that could not be definitively considered related to treatment. At the end of recovery period, apparent variations were recorded in regards to packed cell volume, haemaglobin and red blood cells in male and female animals from the highest-dose group. Some of these variations were statistically significant but there toxicological significance could be confirmed.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

A significant increase in creatinine, sodium and calcium levels, and a decrease in potassium level were reported in male animals receiving 450 mg/kg bw/d at the end of the treatment period, however, the values were comparable to control animals at the end of the recovery period. Female animals from this same group had a significantly lower level of creatinine both at the end of treatment and recovery periods.
The variation in the level of creatinine would suggest that kidney was affected by the test substance, however, it did not reflected in other relevant clinical indices, during the urinalysis, nor during the histopahtological examination of kidney. Therefore, this change is not considered to be related to a nephrotoxic effect nor as toxicologically significant.

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

At the end of the treatment period, urine specific gravity and osmolarity readings for male animals were slightly increased in all treated groups (significant for mid- and high-dose groups) but decreased in female animals. Toxicological significance of the findings could not be definitively attributed to the test substance.

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, non-treatment-related

Description (incidence and severity):

All treated groups showed a slight and not dose-dependent increase in absolute and relative adrenal weights. These values were within Historical Control Data and not considered toxicologically significant.

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

Minimal changes were observed consistent with Historical Control Data for this strain of rats. Consequently, they were not considered relevant.

Histopathological findings: neoplastic:

no effects observed

Effect levels

Dose descriptor:

NOAEL

Effect level:

150 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

clinical signs

Target system / organ toxicity

Critical effects observed:

no

Applicant's summary and conclusion

Conclusions:

A short-term repeated-dose exposure to the test substance resulted in a NOAEL of 150 mg/kg bw/d.

Executive summary:

The toxicity of 2-naphthol following a short-term (4 weeks) repeated oral exposure was investigated using a method similar to the OECD Testing Guideline 407. The study was GLP-compliant.

Groups of five male and female SD rats were exposed to 0, 50, 150 or 450 mg/kg bw/d of test substance in CMC. In addition, two groups of five male and female SD rats received 0 or 450 mg/kg bw/d of test substance in CMC to be used as recovery groups.  The recovery period was 4 weeks.

Animals were observed twice daily for mortality and general clinical signs. More in-depth clinical observations were conducted weekly. Bodyweights were recorded weekly. Food and water consumptions were calculated on a weekly or daily basis, respectively.

During the last week of the treatment and recovery periods, blood and urine samples were collected to investigate haematology and clinical chemistry parameters, and to conduct urinalysis.

Ophthalmological examination was conducted on all groups prior to commencement, and during week 4 of treatment and recovery periods.

Animals were sacrificed at the end of the treatment or recovery period. Detailed post-mortem examinations were conducted. Absolute and relative weight of selected organs were determined. Histopathological examination of selected tissues was conducted.

The results of the study indicate that daily administration of the test substance was well-tolerated by animals exposed for 4 consecutive weeks. A slight increase in both absolute and relative adrenal weight was reported in all treated groups, but no relationship with dose levels was observed. Limited findings were concluded to be treatment-related, including brown staining of the coat in female animals receiving the highest-dose of test substance, as well as transient changes in the levels of creatinine, sodium and calcium in male animals at the same dose levels. While these changes in creatinine levels could potentially be indicative of a nephrotoxic effects, no supportive findings were identified during this study.

A NOAEL of 150 mg/kg bw/d can be derived from these results based on the brown staining observed in female animals, and changes in several clinical biochemistry parameters at 450 mg/kg bw/d.