4-tert-butylpyrocatechol

Carcinogenicity

Description of key information

4-tert butylpyrocatechol may be considered as a weak nongenotoxic forestomach carcinogen with strong promoting activity when chronically administered by the oral route to the rat. The target organ and the administration route are irrelevant to the worker situation.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Test procedure and results described in sufficient details. However only one dose was tested, for 51 weeks, so that it is not sufficient to evaluate the carcinogenic potential of 4-tert-butylpyrocatechol as recommended by specific guidelines.

GLP compliance:

not specified

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS:
- Source: Charles River Japan, inc., Atsugi, Japan
- Age at study initiation: 6-week old
- Weight at study initiation: no data
- Housing: 4 to 5 to a plastic cage
- Food consumption: Oriental M basal diet ad libidum
- Water consumption: tap water ad libidum
- Acclimation period: one week

ENVIRONMENTAL CONDITIONS
- Temperature: 22-24°C
- Humidity (%): no data
- Air changes: conditioned air
- Photoperiod: 12-h light / 12-h dark cycle

In life dates: no data

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on exposure:

DIET PREPARATION
- Rate of preparation of diet: once a month
- Storage: in dark until use

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

51 weeks

Frequency of treatment:

daily

Remarks:

Doses / Concentrations:
0 and 1.5% (with or without MNNG pretreatment) (nominal), 1.5% = equivalent to approximately 700 mg/kg bw
Basis:

No. of animals per sex per dose:

10 in the basal diet control group; 15 in the TBC, and MNNG (basal diet) groups; 16 in the MNNG+TBC group

Control animals:

yes, plain diet

Details on study design:

At 6 weeks of age, one group was given 150 mg/kg bw of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in dimethylsulfoxide by stomach tube. Starting 1 week later, rats were given basal diet containing 1.5% TBC or basal diet alone for 51 weeks.
Further groups were administered the 1.5% TBC-supplemented diet or basal diet alone for 51 weeks without MNNG pretreatment.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: No data
DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: Yes
- Time schedule: once every 2 to 4 weeks

FOOD CONSUMPTION AND COMPOUND INTAKE:
- Time schedule: once every 2 to 4 weeks

FOOD EFFICIENCY: No data
OPHTHALMOSCOPIC EXAMINATION: No
HAEMATOLOGY: No
CLINICAL CHEMISTRY: No
URINALYSIS: No
NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

Stomach, esophagus, intestines, liver, and kidney were removed, the liver and and kidneys being weighed and fixed in 10% buffered formalin solution.The esophagus, stomach, and intestines were injected with formalin and later opened via an incision along the greater curvature. After fixation, 6 sections each were cut from the anterior and posterior walls of the forestomach and glandular stomach. Tissues were processed routinely for histopathological examination. Animals which survived until the end of experiment were included in the effective numbers.

Statistics:

Student's test and Fisher's exact test

Clinical signs:

not specified

Mortality:

not specified

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not specified

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not specified

Details on results:

BODY WEIGHT
At the end of the experiment, the body weights of animals given MNNG+TBC, or TBC without carcinogen pretreatment were 12 to 31.4% lower than those in the groups treated with MNNG and/or basal diet (BD) alone.

ORGAN WEIGHTS
The relative liver weights expressed as g/100 g body weight of animals treated with MNNG+TBC or with TBC without carcinogen pretreatment and the relative kidney weights of all treated animals were significantly higher than the respective control values.

GROSS PATHOLOGY
Grossly, only small tumours were observed in the forestomach epithelia in animals treated with MNNG alone. In the case of animals receiving MNNG+TBC, the forestomach were filled with tumour masses.
In the glandular stomach, some rats given MNNG+TBC had single polypoid lesions in the pyloric region, only one rat treated with MNNG alone having a polypoid lesion in the fundic region.

HISTOPATHOLOGY
Microscopically, the lesions in the forestomach could be classified into hyperplasia, papilloma, carcinoma in-situ, and squamous cell carcinoma. Hyperplasia was further classified into mild, moderate, severe, and marked (>1.0mm) depending on the thickness of the mucosa.

Hyperplasia was evident in all rats treated with MNNG. The incidence of papilloma and carcinoma in situ were not significantly different among the groups receiving MNNG treatment, whereas the incidences of squamous cell carcinomas were significantly higher in rats given MNNG+TBC (75%, P<0.01) than in the control group.
Hyperplasia was found in all rats given TBC alone. Lesions were distributed diffusely throughout the forestomach epithelium, and were characterised by upward hyperplasia.
Lesions in the glandular stomach were classified into adenomatous hyperplasia and adenocarcinoma categories. The lesions were mostly located in the pyloric region, where the incidence of adenomatous hyperplasias in rats treated with MNNG+TBC were significantly higher than in the control group (31.3%, P<0.05). The incidence of adenocarcinomas in rats treated with MNNG+TBC (18.8%) was higher than the control group value (0%), but the difference was not statistically significant.

Incidences of forestomach lesions

		Number (%) of rats with
Treatment	number of rats per group	Hyperplasia	Papilloma	Carcinoma in situ	Squamous cell carcinoma
MNNG + basal diet	15	15 (100)	11 (73.3)	3 (20)	3 (20)
MNNG + TBC	16	16 (100)	15 (93.8)	4 (25)	12 (75)p < 0.01
Basal diet	10	0 (0)	0 (0)	0 (0)	0 (0)
TBC	15	15 (100)p < 0.001	1 (6.7)	0 (0)	0 (0)

Incidences of glandular stomach lesions

		Number (%) of rats with
		Fundic region		Pyloric region
Treatment	number of rats per group	Adenomatous hyperplasia	Adenocarcinoma	Adenomatous hyperplasia	Adenocarcinoma
MNNG + basal diet	16	0 (0)	0 (0)	5 (31.3)p < 0.05	3 (18.8)
MNNG + TBC	16	1 (6.7)	0 (0)	0 (0)	0 (0)
Basal diet	10	0 (0)	0 (0)	0 (0)	0 (0)
TBC	15	0 (0)	0 (0)	0 (0)	0 (0)

Grade of forestomach hyperplasia

		Number (%) of rats with hyperplasia
Treatment	number of rats per group	Mild	Moderate	Severe	Marked
Basal diet	10	0 (0)	0 (0)	0 (0)	0 (0)
TBC	15	15 (100)p < 0.001	15 (100)p < 0.001	4 (26.7)	0 (0)

Conclusions:

TBC treatment significantly enhances forestomach and glandular stomach carcinogenesis in rats pretreated with MNNG.

It can not be ruled out that TBC may be a weak forestomach complete carcinogen, since it induced a small incidence (1/15 rats) of papillomas in forestomach epithelium without pretreatment with carcinogen. However, its hypothetical carcinogenic activity would appear less potent than its promoting activity.
TBC may be a nongenotoxic forestomach and /or glandular stomach weak carcinogens with a strong promoting activity.

Executive summary:

In a one-year tumour promotion study, 4 -tert-butylpyrocatechol (TBC) was administered to 15 to 16 Fischer 344 male rats in diet at dose levels of 0 or 1.5% (equivalent to ca. 700 mg/kg) for 51 weeks, with or without pretreatment with a single administration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), a rat forestomach carcinogen.

The body weight of treated animals was lower than that of the respective controls. The relative liver and kidney weights of all treated animals were significantly higher than the respective control values. In the case of animals receiving MNNG+TBC, the forestomachs were filled with tumour masses. In the glandular stomach, some rats given MNNG+TBC had single polypoid lesions in the pyloric region. The incidence of squamous cell carcinomas was significantly higher in rats given MNNG+TBC than in the control group (12/16 rats). Adenomatous hyperplasia was found in the

pyloric region of the glandular stomach of all rats given TBC alone (with no pre-treatment). Lesions were distributed diffusely throughout the forestomach epithelium, and were characterised by upward hyperplasia. The incidence of adenomatous hyperplasia in rats treated with MNNG+TBC was significantly higher than in the control group (5/16 rats).

Based on the results of this one-year tumour promotion study, TBC may be a weak nongenotoxic forestomach carcinogen with a strong promoting activity in the rat.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Justification for classification or non-classification

Based on the mode of action of tumour-promoting activity and on the lack of relevance of the target organ and the route of exposure potentially at risk in rats, 4-tert-butylpyrocatechol is not classified for carcinogenicity according to the criteria of UN/EU GHS.

Additional information

The carcinogenic potential of 4 -tert butylpyrocatechol (TBC) was indirectly studied in a one-year tumour promotion study in rats (Hirose et al., 1989), where TBC and other dihydroxybenzene derivatives were administered in the diet for 51 weeks (as potential promoting agents) following a single oral administration of a known forestomach and glandular stomach carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, as an initiating agent). Two distinct groups of rats, one with and one without pre-treatment by MNNG, were given TBC. Two distinct control groups receiving basal diet, one with and one without pre-treatment by MNNG, were included. This study was considered as a key study based on its validity 2 according to the Klimisch cotation criteria.

With pre-treatment by the carcinogen, the administration of TBC significantly increased the incidence of squamous cell carcinomas in the forestomach and the incidence of adenomatous hyperplasia in the pyloric region of the glandular stomach, compared to the respective controls. But without pre-treatment by the carcinogen, only one case of papilloma was observed in the forestomach, versus none in the respective control group, without reachinig statistical significance. Therefore, TBC significantly enhances the forestomach and glandular stomach carcinogenesis in the rat in case of co-administration with a recognized carcinogen.

It can not be ruled out that TBC be a weak forestomach carcinogen in the rat per se, based on the minimal incidence of benign tumours as papillomas seen in that species, but it should rather be considered as a weak nongenotoxic forestomach carcinogen with strong promoting activity resulting from its hyperplasiogenic effects when chronically administered by the oral route, as previously described for structurally-related antioxidants (1).

However, a functional human counterpart for the rodent forestomach does not exist. Histologically related organs in humans are oesophagus and stomach, but tissue dosimetry for these tissues is different from the rodent situation, where forestomach is a holding compartment, which allows the tissue considerably longer exposure to the chemical than oesophagus where transit time is rapid in case of oral administration (2). Furthermore, the oral route of administration is irrelevant to the worker situation.

Therefore, no classification is warranted for carcinogenicity.

(1) Ito N, Hirose M, Fukushima S, Tsuda H, Shirai T, Tatematsu M. Studies of antioxidants: their carcinogenic and modifying effects on chemical carcinogenesis. Food Chem Toxicol 24(10/11): 1071 - 82, 1986.

(2) Proctor DM, Gatto NM, Hong SJ & Allamneni KP. Mode-of-action framework for evaluating the relevance of rodent forestomach tumors in cancer risk assessment.Toxicol. Sci.98(2): 313 -26, 2007.