(+)-menthol

Repeated dose toxicity: oral

Administrative data

Endpoint:

chronic toxicity: oral

Remarks:

combined repeated dose and carcinogenicity

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Not GLP compliant study, no guideline specifically mentionned. However, the study is documented enough to be scientifically assessed and found reliable.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1979

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

DL Menthol

IUPAC Name:

DL Menthol

Constituent 2

Reference substance name:

Menthol

EC Number:

201-939-0

EC Name:

Menthol

Cas Number:

89-78-1

IUPAC Name:

2-isopropyl-5-methylcyclohexanol

Details on test material:

- Name of test material (as cited in study report): USP-grade DL-Menthol
- Lot/batch No.: 4-HTP-6 (for the first 3 weeks only) and N11-26-74-2054 (for the rest of the study)
- Storage condition of test material: The test material was stored at 1°C in their original containers
- Obtained from Glidden Organics International, Jacksonville, Florida (Lot No 4-HTP-6)
and from Norda, Inc., New York (Lot No N11-26-74-2054)

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Frederick Cancer Research Center, Frederick, Maryland
- Age at study initiation: 9 weeks
- Weight at study initiation: Not specified
- Diet (e.g. ad libitum): Wayne Lab Chow Meal and water available ad libitum
- Housing: Polycarbonate cages covered with stainless steel cage lids and non-woven fiber filter bonnets (Filtek, Appleton, Wis.).
Rats were housed 5 per cage until week 48, and then the males were divided into groups of 2 or 3 per cage.
- Diet : ad libitum
- Water : ad libitum
- Acclimation period: 4 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24 °C
- Humidity (%): 45-55%
- Air changes (per hr): 12 changes per hour
- Photoperiod : 12 hours dark/ 12 hours light

Administration / exposure

Route of administration:

oral: feed

Vehicle:

corn oil

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:

DIET PREPARATION
- Rate of preparation of diet (frequency): prepared each week and used within 1 week of preparation.
- Storage temperature of food: The containers were stored at room temperature.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Duplicate 10g dosed feed sample were extracted with 20ml of carbon disulfide, and aliquots of the extract analyzed by gas chromatography (thermal conductivity detector).
(see attached illustration for values)

Duration of treatment / exposure:

The compound was administered in the diet seven days a week for 103 weeks at the indicated level.
During the 2 weeks of observation, the animal were supplied with standard diet.

Frequency of treatment:

Feed hoppers were sanitized once a week at 81°C.

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0.375 %
Basis:
nominal in diet

Doses / concentrations 2

Remarks:

Doses / Concentrations:
0.75%
Basis:
nominal in diet

No. of animals per sex per dose:

50 animals per dose (sex ratio not mentionned)

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Based on the results of 13-week study (see cross reference studies).
- Rationale for animal assignment (if not random): Animals were segregated by body weight so that a homogeneous distribution of mean weight ranges was obtained between groups.

Examinations

Observations and examinations performed and frequency:

All animals were observed twice a day for signs of toxicity.
Clinical signs and the presence of palpable masses were recorded every week.
Mean body weights and food consumption were recorded every 2 weeks for the first 12 weeks and every month thereafter.

Sacrifice and pathology:

Animals that were moribund and those that survived to the termination of the study were killed by exsanguination under sodium pentobarbital anesthesia (Diabutal, Diamond Laboratories, Inc., Des Moines, Iowa).

The pathologic evaluation consisted of gross and microscopic examination of major tissues, major organs, and all gross lesions from killed animals and from animals found dead. The tissues were preserved in 10% buffered formalin, embedded in paraffin, sectioned, and stained with hematoxylin and eosin. The following tissues were examined microscopically: brain (frontal cortex and basal ganglia, parietal cortex and thalamus, and cerebellum and pons), pituitary, spinal cord (if neurologic signs were present), eyes (if grossly abnormal), esophagus, trachea, salivary gland, mandibular lymph node, thyroid, parathyroid, heart, thymus, lungs and mainstem bronchi, liver, gallbladder (mice), pancreas, spleen, kidney, adrenal, stomach, small intestine, colon, urinary bladder, prostate or uterus, testes or ovaries, sternebrae, femur, or vertebrae including marrow, mammary gland, tissue masses, and any macroscopic lesions.
A few tissues from some animals were not examined, particularly from those animals that died early. Also, some animals may have been missing, cannibalized, or judged to be in such an advanced state of autolysis as to preclude histopathologic evaluation. Thus, the number of animals from which particular organs or tissues were examined microscopically varies, and does not necessarily represent the number of animals that were placed on study in each group.

Statistics:

Pertinent data on this experiment have been recorded in an automatic data processing system, the Carcinogenesis Bioassay Data System (Linhart et al., 1974).
Probabilities of survival were estimated by the product-limit procedure of Kaplan and Meier (1958)
Statistical analyses for a possible dose-related effect on survival used the method of Cox (1972) for testing 2 groups for equality and Tarone's (1975) extensions of Cox's methods for testing dose related trend.
The one-tailed Fisher exact test (Cox, 1970) wa used to compare the tumor incidence of a control group with that of a group of dosed animals at each dose level.
The Cochran-Armitage test for linear trend in proportions, with continuity correction (Armitage, 1971) was also used.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Description (incidence and severity):

not significant in either sex

Mortality:

no mortality observed

Description (incidence):

not significant in either sex

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

mean body weight gains in dosed groups were slightly lower than in the control groups

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:

no effects observed

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

nephritis of questionable origin (see below "Details on results")

Histopathological findings: neoplastic:

no effects observed

Details on results:

A. Body Weights and Clinical Signs (Rats)
Mean body weights of the dosed male and female rats were slightly lower than those of the corresponding controls throughout the bioassay. No other clinical signs related to administration of the dl—menthol were noted. Clinical signs commonly observed among rats of this strain were noted at comparable rates in the control and dosed groups, particularly during the second year of the bioassay, and increased in incidence as the animals aged. These signs included eye changes (redness, paleness, cloudiness, lacrimination, a red discharge or bloody crust, and an enlarged or protruding eye), a hunched and/or thin appearance, urine stains on the abdominal fur, and occasionally, nasal discharge, sores on the body or the extremities, soft feces, and enlarged testes.
The incidence of palpable nodules and tissue masses in the dosed males was generally comparable to that in the control males, but was lower in the dosed females than in the control females.

B. Survival (Rats)
The Kaplan and Meier curves estimates the probabilities of survival for male and female rats administered dl—menthol in the diet at the doses of this bioassay, together with those of the matched controls. The results of the Tarone test for dose—related trend in mortality and the results of the Cox test comparing the survival of the control group with each dosed group are not significant in either sex.
In male rats, 34/50 (68%) of the high—dose group, 33/50 (66%) of the low—dose group, and 31/50 (62%) of the controls were alive at week 105. In females, 38/50 (76%) of the high—dose group, 35/50 (70%) of the low—dose group, and 36/50 (72%) of the controls were alive at week 105. Sufficient numbers of rats of each sex were at risk for the development of late—appearing tumors.

C. Pathology (Rats)
Each of the tumor types observed has been encountered previously as a spontaneous lesion, and occurred with no appreciable differences in frequency between control and dosed rats with a few exceptions. In female rats, chromophobe adenomas of the pituitary gland and fibroadenomas of the mammary gland were observed with greater frequency in female control rats. Chromophobe adenomas occurred in 28/48 controls, 25/47 low—dose, and 19/43 high—dose female rats. Mammary gland fibroadenomas were diagnosed in 20/50 female controls, 10/49 low—dose, and 7/49 high—dose rats. Mammary adenocarcinomas were seen in 1/50 controls, 3/49 low—dose, and 0/49 high—dose rats.
Chronic inflammation of the kidney was observed with greater frequency in the dosed males than in the control males (29/49 controls, 41/50 low—dose, 41/50 high—dose); however, this finding is of questionable importance, since such lesions are often found in aged male Fischer 344 rats.
All other inflammatory, degenerative, and hyperplastic lesions that occurred were similar in incidence and kind to those naturally occurring lesions found in aged Fischer 344 rats.

Effect levels

Dose descriptor:

NOAEL

Effect level:

7 500 ppm

Based on:

act. ingr.

Sex:

male/female

Basis for effect level:

other: overall effects

Remarks on result:

not determinable

Remarks:

no NOAEL identified

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Based on the histopathologic examination, DL-menthol was neither toxic nor carcinogenic to Fischer 344 rats under the conditions of this bioassay.

Executive summary:

Mean body weights of the dosed rats and mice were slightly lower than those of corresponding controls. No other clinical signs related to administration of DL-menthol were noted in any dosed groups of rats and mice. Survival at the end of the bioassay was at least 62% in all dosed and control groups of animals of each species, and sufficient numbers of animals were at risk for the development of late-appearing tumours.
In male rats, no tumours occurred at incidences which were considered to be associated with the administration of DL-menthol.
In female rats, no tumours occurred at higher incidences in dosed groups than in control groups. Fibro adenomas of the mammary gland occurred at lower incidences in the low-dose (10/49) and high-dose (7/49) groups than in the control group (20/50), and alveolar/bronchiolar adenomas or carcinomas of the lung occurred only in the controls (3/50).

The acute oral LD50 of menthol in Osborne-Mendel rats has been reported as 3,180 mg/kg body weight (Jenner et al., 1964) and as 2,900 mg/kg body weight (Herken, 1961).When administered in the diet to male and female rats for 5.5 weeks, D- or DL-menthol at 100 or 200 mg/kg body weight caused no adverse effects on gain in weight (Herken, 1961). No long-term studies have been reported previous to the present bioassay.
It is concluded that under the conditions of this bioassay, DL-menthol was not carcinogenic for either Fischer 344 rats or B6C3F1 mice.