Dibenzylbenzene, ar-methyl derivative

Endpoint summary

Description of key information

A GLP OECD 408 repeated toxicity study (Sanofi, 1992) was performed on the registered substance.

In this 4-month oral toxicity study, the NOAEL was found to be 50 mg/kg bw/day, based on a LOAEL estimated at 500 mg/kg bw/day (effects on liver in both sexes).
When dibenzyltoluene (trade name: JARYLEC DBT) is administered at 50 mg/kg bw/day, slight hypertrophy of centrilobular hepatocytes was seen in few animals (2/20) without any other changes. Thus, this dose level was considered as the NOAEL.

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 02 August 1989 to 13 December 1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

Version / remarks:

Study conducted prior to the adoption of the most recent version of this guideline.

Deviations:

yes

Remarks:

The animals were treated for at least 120 days instead of 90; the neurobiological examination was not performed; it is not reported whether opthalmoscopic examination was conducted before the beginning of the treatment period.

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River, France
- Age at study initiation: approximately 7 weeks old
- Weight at study initiation:
Mean initial bodyweight for males was 185 g
Mean initial bodyweight for females was 160 g
- Diet (e.g. ad libitum): a complete commercial diet ad libitum
- Water (e.g. ad libitum): tap-water through automatic waterers ad libitum
- Acclimation period: at least 1 week before beginning treatment


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 2
- Humidity (%): 60 +/- 10
- Air changes (per hr): 12
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 02 August To: 13 December 1989

Route of administration:

oral: gavage

Vehicle:

other: 10% gum arabic solution

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
The compound was prepared extemporaneously as a suspension in a 10% aqueous gum arabic solution

VEHICLE
- Justification for use and choice of vehicle (if other than water): no
- Concentration in vehicle: 10 %
- Amount of vehicle (if gavage): 5 mL/kg bw

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analyses were carried out during the study to control the concentration of suspensions at approximately 3 months, 4 months and 4 months and 2 weeks after the beginning of the treatment period.

Duration of treatment / exposure:

At least 120 days (between 133 and 142)

Frequency of treatment:

daily

Dose / conc.:

0 mg/kg bw/day (nominal)

Dose / conc.:

5 mg/kg bw/day (nominal)

Dose / conc.:

50 mg/kg bw/day (nominal)

Dose / conc.:

500 mg/kg bw/day (nominal)

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Details on study design:

post-exposure period : no

Positive control:

No

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: No data

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: The animals were observed at least twice daily (at least once on Saturdays, Sundays and public holidays) throughout the study for clinical signs (for which date of onset and progression were recorded) and for mortality.


BODY WEIGHT: Yes
- Time schedule for examinations: animals were weighed before the beginning of the treatment period, then weekly throughout the study.


FOOD CONSUMPTION : Yes
- Time schedule: individual food intake was measured weekly from which mean individual daily values were calculated on a weekly basis.

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: day 126
- Dose groups that were examined: all animals


HAEMATOLOGY: Yes
- Time schedule for collection of blood: on days 128 and 129
- Anaesthetic used for blood collection: No
- Animals fasted: Yes
- How many animals: 80
- Parameters checked in table [1] were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: days 132 and 133
- Animals fasted: Yes
- How many animals: 80
- Parameters checked in table [2] were examined.


URINALYSIS: Yes
- Time schedule for collection of urine: days 121 to 125
- Metabolism cages used for collection of urine: No data
- Animals fasted: No
- How many animals: 40
- Parameters checked in table [3] were examined.


NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

Necropsy was performed from day 134 to day 143.

GROSS PATHOLOGY: Yes (see table 4 for tissues examined and table 5 for organ weights )
HISTOPATHOLOGY: Yes (see table 6)

Other examinations:

Not reported; no treatment-free period performed.

Statistics:

1. Parametric methods
Parametric, statistical tests are used when the theoretical distribution of the data is normal.
Step 1 consists of the Levene test for the equality of variances.
. If the Levene test cannot be performed or is not significant (equal variances), step 2 consists of testing for a treatment (group) effect using one-way analysis of variance (1-ANOVA).
- If 1-ANOVA is not significant, no further analysis is performed, the means being considered not different.
- If 1-ANOVA is significant (rejection of null hypothesis that population means are equal), step 3 consists of intergroup comparisons by the Student t test taking 1-ANOVA residual variance as a pooled estimate of the variability.

. If the Levene test is significant (unequal variances), step 2 consists of pairwise comparisons of variances (with the reference group) using the Snedecor F statistic.
- If a pairwise comparison is not significant (equal variances), step 3 consists of intergroup comparison by the classical Student t test.
- If a pairwise comparison is significant (unequal variances), step 3 consists of intergroup comparisons by the approximate Student t test using Welch's method.

To take into account multiple comparisons, p values are calculated according to Bonferroni's method (<= 6 comparisons) or Scheffé's method (> 6 comparisons).

2. Non-parametric methods
Non-parametric methods are routinely used when the theoretical distribution of the data is not normal.
Overall equality of the group means is tested by the Kruskall Wallis test. If the test is significant (unequal means), then intergroup comparisons are carried out pairwise by the same method. If the test is not significant, the means are considered to be not different.

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

Soiled urogenital area, blood on the muzzle and thinness were noted in one female given 50 mg/kg bw/day from day 100. Soiled urogenital area or blood on the muzzle was also noted, respectively, in one female or one male given 5 mg/kg bw/day. Hair loss was noted in one female given 50 mg/kg bw/day. These signs were not considered as related to the treatment with the compound.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

One male given 5 mg/kg bw/day and one male given 500 mg/kg bw/day were found dead on days 61 and 60, respectively. Death was attributed to probable inhalation pneumonia following oesophageal occlusion as shown by the microscopic examination.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No treatment-related variations were noted in the body weight gain.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

A slight increase (sometimes statistically significant compared to controls) was noted in the animals given 500 mg/kg bw/day throughout the study.

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

no effects observed

Description (incidence and severity):

No treatment-related lesions were observed at the end of the treatment period.

Haematological findings:

no effects observed

Description (incidence and severity):

There were no relevant variations that can be related to the treatment with the test substance.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

An increase in total cholesterol level (+69% compared to the controls) was noted in males given 500 mg/kg bw/day. A slight decrease in creatininemia was noted in the test substance-treated groups without dose relationship. This change has no toxicological significance.

Endocrine findings:

not examined

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

An increase in the absolute and relative kidney weight (approximately + 20%) was noted in the males given 500 mg/kg/day. As this was not associated with histological or biological modifications, this increase was considered to be of no toxicological significance.
A slight increase in the relative liver weight (with increase absolute values which however, were not statistically significant) was noted in the males and females given 500 mg/kg bw/day.

Gross pathological findings:

no effects observed

Description (incidence and severity):

The post-mortem examinations performed on all animals did no show any treatment-related lesions

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

A slight hypertrophy of centrilobular hepatocytes was noted in 2/10 males given 50 mg/kg/day and 10/10 males given 500 mg/kg bw/day. In 4/10 males of the high dose group, this was accompanied with a slight hypertrophy of the mediolobular hepatocytes. These changes were more or less associated with a decrease in the incidence of hepatocytes cytoplasmiques margination.

Histopathology of the decedent animals:
Moderate or marked acute pulmonary edema (congestion and alveolar edema) was seen in the two decedent animals, with perivascular edema and intra-alveolar hemorrhage in animal given 5 mg/kg bw/day and serosity in laryngeal and tracheal lumen in animal given 500 mg/kg/bw/day.
Moderate and marked distension of the oesophageal lumen by vegetal particles was noted and found also, mixed with serosity, in the tracheal and pharyngeal lumen in animal given 5 mg/kg bw/day.
Slight vacuolation of centrilobular hepatocytes was seen in animal given 5 mg/kg bw/day as well as moderate adrenocortical hyperplasia and various congestion changes in animal given 500 mg/kg/day. These changes are of little significance.

Histopathological findings: neoplastic:

not examined

Key result

Dose descriptor:

NOAEL

Effect level:

50 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

Dose descriptor:

LOAEL

Effect level:

500 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

histopathology: non-neoplastic

organ weights and organ / body weight ratios

Critical effects observed:

yes

Lowest effective dose / conc.:

500 mg/kg bw/day (actual dose received)

System:

hepatobiliary

Organ:

liver

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

not specified

Table 7 Clinical chemistry - relevant/statistical changes

Exposure Group	Control	5 mg/kg/d	50 mg/kg/d	500 mg/kg/d
Males
Clinical Chemistry
Total cholesterol nM	1.67 +/- 0.076	1.95 +/- 0.163	2.07 +/- 0.102	2.82 +/- 0.130*

* Statistically significant difference from the control group

Conclusions:

In this 4-month oral toxicity study, the NOAEL was found to be 50 mg/kg bw/day, based on a LOAEL estimated at 500 mg/kg bw/day (effects on liver in both sexes).
When dibenzyltoluene (trade name: JARYLEC DBT) is administered at 50 mg/kg bw/day, slight hypertrophy of centrilobular hepatocytes was seen in few animals (2/20) without any other changes. Thus, this dose level was considered as the NOAEL.

Executive summary:

The aim of the present study was to assess the oral toxicity of dibenzytoluene (trade name: JARYLEC DBT) to Sprague Dawley rats. The compound was administered once a day by gavage for at least 120 days at the dose levels of 0, 5, 50 and 500 mg/kg bw/day. Each group was composed of 10 males and 10 females. The control group received the vehicle only (l0 % gum arabic solution). The clinical signs were observed twice a day, the body-weight and the food consumption were recorded once a week. For all animals, ophthalmology, clinical pathology, hematology investigations and urine analysis were performed after at least 120 days of treatment. After at least 120 days of treatment, the rats were sacrificed and a full macroscopic examination was performed, selected organs weighted, and certain organs submitted to histological examination.

No treatment-related mortality or clinical signs were noted and the growth rate of animals was unmodified. Ophthalmoscopic and hematological examinations, urinalysis and macroscopic examinations did not show any treatment-related lesions. At 500 mg/kg bw/day, the compound induced changes suggesting an enzyme induction: hypertrophy of centrilobular (and sometimes mediolobular) hepatocytes in most animals associated with a slight increase in cholesterol levels in males, a slight increase in food intake and in the relative liver weight in both sexes. A slight increase in kidney weight was noted in high-dose males, but it was considered without toxicological relevance since it was not associated with histological or biological modifications. At 50 mg/kg bw/day, only two males showed a slight hypertrophy of centrilobular hepatocytes without any other changes; Thus, this dose level was considered as a non-toxic dose. Consequently, under the experimental conditions of this 4-month oral toxicity study, the NOAEL was found to be 50 mg/kg bw/day, based on a LOAEL estimated at 500 mg/kg bw/day (effects on liver in both sexes).

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

50 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Organ:

liver

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

90-day repeated toxicity study (OECD 408)

The aim of the present study was to assess the oral toxicity of dibenzytoluene (trade name: JARYLEC DBT) to Sprague Dawley rats. The compound was administered once a day by gavage for at least 120 days at the dose levels of 0, 5, 50 and 500 mg/kg bw/day. Each group was composed of 10 males and 10 females. The control group received the vehicle only (l0 % gum arabic solution). The clinical signs were observed twice a day, the body-weight and the food consumption were recorded once a week. For all animals, ophthalmology, clinical pathology, hematology investigations and urine analysis were performed after at least 120 days of treatment. After at least 120 days of treatment, the rats were sacrificed and a full macroscopic examination was performed, selected organs weighted, and certain organs submitted to histological examination.

No treatment-related mortality or clinical signs were noted and the growth rate of animals was unmodified. Ophthalmoscopic and hematological examinations, urinalysis and macroscopic examinations did not show any treatment-related lesions. At 500 mg/kg bw/day, the compound induced changes suggesting an enzyme induction: hypertrophy of centrilobular (and sometimes mediolobular) hepatocytes in most animals associated with a slight increase in cholesterol levels in males, a slight increase in food intake and in the relative liver weight in both sexes. A slight increase in kidney weight was noted in high-dose males, but it was considered without toxicological relevance since it was not associated with histological or biological modifications. At 50 mg/kg bw/day, only two males showed a slight hypertrophy of centrilobular hepatocytes without any other changes; Thus, this dose level was considered as a non-toxic dose. Consequently, under the experimental conditions of this 4-month oral toxicity study, the NOAEL was found to be 50 mg/kg bw/day, based on a LOAEL estimated at 500 mg/kg bw/day (effects on liver in both sexes).

 

MTD study in rabbits (2019)

The objective of this non-GLP preliminary study was to evaluate the potential toxic effects of the test item following daily oral administration (gavage) in non-pregnant female rabbits, and to establish a Maximum Tolerated Dose (MTD), in order to assist the selection of dose levels for a further preliminary embryo-fetal development study to be performed in this species.

Three non-pregnant female New Zealand White rabbits received the test item, by daily oral gavage for 14 days. The test item was administered at 300 mg/kg/day for 7 days (Day 1 to Day 7), and then at 1000 mg/kg/day for another 7-day period (Day 8 to Day 14). The test item was formulated as an emulsion in the vehicle (0.5% carboxymethylcellulose/0.5% Tween 80 in drinking water treated by reverse osmosis) and was administered under a constant dosage volume of 5 mL/kg/day. The animals were observed daily for mortality and clinical signs. Body weight and food consumption were regularly recorded. The surviving animals were euthanized on completion of the treatment period. A post-mortem macroscopic examination of the principal thoracic and abdominal organs was performed on both terminated as scheduled and prematurely euthanized animals.

One female was prematurely sacrificed on Day 10 due to signs of poor clinical condition (thin appearance from Day 8 and hypoactivity, abdominal breathing and absence of feces on the day of sacrifice) associated with body weight loss and reduced food consumption from Day 1. Necropsy findings were gastric red and black discolorations. A relationship to the test item treatment cannot be excluded.

No clinical signs were reported in the two surviving females.

Body weight and food consumption were unaffected at 300 mg/kg/day in the two surviving females while at 1000 mg/kg/day, a body weight loss was recorded in one female (around -14% vs. Day 1) associated with reduced food consumption in the two females (between -95% and -30% vs. the Day 1-8 period).

No necropsy findings were observed at final sacrifice.

 

Conclusion

The potential toxicity of the test item was evaluated following daily oral administration (gavage) in the non-pregnant female rabbit at 300 mg/kg/day from Day 1 to Day 7 and 1000 mg/kg/day from Day 8 to Day 14.

Based on the results of this study, the Maximum Tolerated Dose (MTD) was considered to be lower than 1000 mg/kg/day.

Justification for classification or non-classification

No classification for repeated dose effects or target organ toxicity is indicated according to the classification, labeling and packaging (CLP) regulation (EC 1272/2008).