Nα-acetyl-DL-tryptophan

Endpoint summary

Description of key information

Oral, rat: NOAEL = 2500 mg/kg bw/day

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

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

Principles of method if other than guideline:

- Short description of test conditions: The teratogenic effects of N-acetyl-L-tryptophan was investigated in JCL-ICR mouse.
The test substance was orally administered to pregnant mice at doses of 2.5 and 5 g/kg bw/day from GD 6 to 15. All F0-dams were autopsied to assess foetal parameters on GD 18.

GLP compliance:

no

Limit test:

no

Species:

mouse

Strain:

ICR

Remarks:

JCR-ICR

Details on species / strain selection:

TEST ANIMALS
- Source: CLEA Japan, Meguro, Japan
- Age at study initiation: 12 - 13 weeks
- Diet: MF except for gestation and lactation period and NMF for gestation and lactation period, purchased by Oriental Yeast Co., Ltd, Japan, were given ad libitum
- Water: tap water, ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2
- Humidity (%): 55 ± 5

Sex:

female

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Details on oral exposure:

VEHICLE
- Justification for use and choice of vehicle (if other than water): Due to the low water solubility, CMC was used as vehicle for oral application.
- Concentration in vehicle: 1%

Analytical verification of doses or concentrations:

no

Duration of treatment / exposure:

females: 10 days (from Day 6 to 15 of gestation (GD))

Frequency of treatment:

once a day

Dose / conc.:

5 000 mg/kg bw/day (nominal)

Dose / conc.:

2 500 mg/kg bw/day (nominal)

No. of animals per sex per dose:

20 females (control)
23 females (2500 mg/kg bw/day)
20 females (5000 mg/kg bw/day)

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale: Doses were selected based on range-finding tests.
gavage: Based on a LD50 of 12500 mg/kg bw, a dose of 5000 mg/kg bw/day was selected as highest applied dose.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: every other day

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
- Time schedule for examinations: every other day

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No

Sacrifice and pathology:

GROSS PATHOLOGY and ORGAN WEIGHT: Yes. The animals were sacrificed on GD 18.
- Organs examined: brain, pituitary, thymus, heart, lungs, liver, kidneys, spleen, adrenals, ovaries

HISTOPATHOLOGY: No

Statistics:

Wilcoxon test: fetal mortality, number of fetus with external abnormalities, number of fetus with skeletal abnormalities except for ossification, number of fetus with visceral abnormallities, number of offspring with malformation and variation, number of live offspring, and postnatal differentiation
Chi-squared test: sex ratio, copulation ratio, pregnancy rate, delivering rate, and mortality
t test: other items

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

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

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Other effects:

not examined

Key result

Dose descriptor:

NOAEL

Effect level:

5 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: no adverse effects observed up to and including the highest dose level

Key result

Critical effects observed:

no

Reference 2

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

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

Principles of method if other than guideline:

- Short description of test conditions: The teratological study of N-acetyl-L-tryptophan was conducted in Wistar rats. N-acetyl-L-tryptophan was administered per oral at doses of 2.5 and 5.0 g/kg bw/day from gestation day (GD) 7 to 17. All dams were autopsied for the assessment of fetal developmental parameters on GD 20.

GLP compliance:

no

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: KITAYAMA LABES CO.,LTD., Ina-city, Japan
- Age at study initiation: 11 weeks
- Diet: MF except for gestation and lactation period and NMF for gestation and lactation period, purchased by Oriental Yeast Co., Ltd, Japan, were given ad libitum
- Water: tap water, ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2
- Humidity (%): 55 ± 5

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
VEHICLE
- Justification for use and choice of vehicle (if other than water): due to the low water solubility, CMC was used as vehicle
- Concentration in vehicle: 1%

Analytical verification of doses or concentrations:

no

Duration of treatment / exposure:

females: 11 days; (from Day 7 to 17 of gestation (GD))

Frequency of treatment:

once a day

Dose / conc.:

2 500 mg/kg bw/day (nominal)

Dose / conc.:

5 000 mg/kg bw/day (nominal)

No. of animals per sex per dose:

21 females (control)
22 females (2500 mg/kg bw/day)
20 females (5000 mg/kg bw/day)

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Since the LD50 value was 15000 mg/kg bw for oral administration, 5000 mg/kg bw/day was applied as the highest dose.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: every second day

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
- Time schedule for examinations: every second day

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: on Day 20 of gestation
- Anaesthetic used for blood collection: Yes, chloroform
- How many animals: 21 in control, 22 in 2500 mg/kg bw/day and 20 in 5000 mg/kg bw/day
- Parameters checked: erythrocytes, leucocytes, hemoglobin, hematocrit, platelets

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: on Day 20 of gestation
- How many animals: 21 in control, 22 in 2500 mg/kg bw/day and 20 in 5000 mg/kg bw/day
- Parameters checked: total protein, urea N, glucose, GOT (glutamate oxaloacetate transaminase), GPT (glutamate pyruvate transaminase)

Sacrifice and pathology:

GROSS PATHOLOGY: Yes. All the dams were sacrificed on GD 20.
- Organs examined: brain, pituitary, thymus, heart, lungs, liver, kidneys, spleen, adrenals, ovaries

HISTOPATHOLOGY: No

Other examinations:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of implantations: Yes

Fetal examinations
- External examinations: Yes: all per litter
- Skeletal examinations: Yes: all per litter

Statistics:

Wilcoxon test for % of fetal death, the number of abnormal fetus, the number of live offsprings, % of malformation, % of anomaly, effects on development of offspring, and the number of variation and ossification except for ossified calnei and ossified tail. Chi-squared test for copulation index, fertility index, delivery index, rearing index, sex ratio of fetus and offspring. t test for the rest items

Clinical signs:

no effects observed

Mortality:

mortality observed, non-treatment-related

Description (incidence):

One dam of the 5000 mg/kg bw/day dose group died caused by pneumonia.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

The body weight gain was significantly reduced (35%) in the 5000 mg/kg bw/day group compared to the control group.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Food consumption was significantly decreased in the 2500 and 5000 mg/kg bw/day dose groups (9 and 15%, respectively).

Food efficiency:

not examined

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

effects observed, treatment-related

Description (incidence and severity):

Water consumption was significantly increased in the 5000 mg/kg bw/day group.

Ophthalmological findings:

not examined

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

The level of leucocytes was significantly increased in the 5000 mg/kg bw/day group. As no other haematological effects were found in any group, this effect is not considered as treatment-related.

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

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):

The absolute weight of thymus was significantly decreased in the 5000 mg/kg bw/day group. As no relevant effects were observed on the relative organ weight or during gross pathology examination, this is not considered to be a treatment-related effect.

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Other effects:

no effects observed

Key result

Dose descriptor:

NOAEL

Effect level:

2 500 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

body weight and weight gain

Dose descriptor:

LOAEL

Effect level:

5 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

body weight and weight gain

Key result

Critical effects observed:

no

Table 1. Effect of N-acetyl-L-Tryptophan on pregnant females treated orally on days 7 to 17 of gestation

	Control	N-acetyl-L-tryptophan (g/kg)
		2.5	5.0
No. of pregnant females	21	22	20
Maternal death	0	0	1
Body weight gain during gestation (g ± S.D.)	124 ± 24	114 ± 14	79 ± 36**
Food consumption during gestation (g/100g ± S.D.)	145 ± 11	133 ± 9**	124 ± 12**
Organ weight Thymus  (g ± S.D.)	0.26 ± 0.07	0.20 ± 0.07	0.18 ± 0.08**
Hematological findings Erythrocytes (10000/mm3 ± S.D.)	96 ± 23	103 ± 29	115 ± 32*

*:        significantly different from control at P≤0.05

**:      significantly different from control at P≤0.01

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

2 500 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The available information comprises adequate and reliable studies from a reference substance with similar structure and intrinsic properties. Read-across is justified based on stereoisomerism. Source and target substance differ only in the three-dimensional orientations of their atoms in space (please refer to the analogue justification). The selected studies are thus sufficient to fulfil the standard information requirements set out in Annex VIII-IX, 8.6, in accordance with Annex XI, 1.5, of Regulation (EC) No 1907/2006.

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

Justification for read-across

There are no available data assessing the repeated dose toxicity potential of N-acetyl-DL-tryptophan (CAS 87-32-1). The assessment of repeated dose toxicity was therefore based on studies conducted with a source substance (N-acetyl-L-tryptophan (CAS 1218-34-4)) as part of a read across approach, which is in accordance with Regulation (EC) No 1907/2006, Annex XI, 1.5. in order to fulfil the standard data requirements defined in Regulation (EC) No 1907/2006, Annex VIII, 8.6. Structural similarities and comparable toxicokinetic properties of the source and target substance are the basis of read-across. A detailed justification for the analogue read-across approach is provided in the technical dossier (see IUCLID Section 13).

Repeated dose toxicity: oral

CAS 1218 -34 -4

In a non-guideline study of the systemic and developmental/teratogenic effects of N-acetyl-L-tryptophan, the test substance was orally administered to pregnant Wistar rats at the doses of 2500 and 5000 mg/kg bw/day from day 7 to 17 of gestation (Kadota et al., 1980). There were 21, 22 and 20 females in the control, 2500 and 5000 mg/kg bw/day groups, respectively. All dams were sacrificed on gestation day (GD) 20. In the dams, the mortality, clinical signs, body weight and food consumption were recorded. At sacrifice, haematological and clinical chemistry parameters were examined, and a gross pathology examination was performed. The body weight gain was significantly reduced (35%) in the 5000 mg/kg bw/day group compared with the control group. The food consumption was significantly decreased in the 2500 and 5000 mg/kg bw/day dose groups (by 9 and 15%, respectively) when compared with the control group. A significant increase in water consumption was also observed at the highest dose level, compared with the control group. At 5000 mg/kg bw/day, the level of leucocytes was significantly increased and the absolute thymus weight was significantly decreased. As no other haematological effects were found in any group and no relevant effects were observed on the relative thymus weight or during gross pathology examination, these effects are not considered as treatment-related. Based on the reduction in body weight gain and food consumption at the highest dose level, the NOAEL for systemic toxicity was considered to be 2500 mg/kg bw/day in female rats.

The systemic and developmental/teratogenic effects of N-acetyl-L-tryptophan were assessed in a non-guideline study performed in JCL-ICR mice (Ueshima et al., 1980a). The test substance was orally administered to pregnant mice at doses of 2500 and 5000 mg/kg bw/day from Day 6 to Day 15 of gestation. There were 20, 23 and 20 females in the control, 2500 and 5000 mg/kg b/day groups, respectively. All dams (F0) were sacrificed on Day 18 of gestation. The following maternal parameters for systemic toxicity were evaluated: mortality, clinical signs, body weight, food consumption and gross pathology. No maternal toxicity was observed for any of the assessed parameters in any treatment group, when compared with the control group. The gross pathology examination did not show treatment-related abnormalities. Based on the results of this study, the NOAEL systemic was ≥ 5000 mg/kg bw/day in female mice.

 

Repeated dose toxicity: intraperitoneal

CAS 1218-34-4

In the study performed by Ueshima et al. (1980a), the potential systemic and developmental effects of N-acetyl-L-tryptophan were also assessed via the intraperitoneal route. The test substance was intraperitoneally (i.p.) administered to the mice at doses of 100, 300 and 900 mg/kg bw/day from Day 6 to Day 15 of gestation. In group 1, there were 20, 22, 23, and 22 animals in control, 100, 300 and 900 mg/kg bw/day, respectively, sacrificed on GD 18. In group 2, there were 13, 11, 12 and 12 animals in control, 100, 300 and 900 mg/kg bw/day, respectively, sacrificed on Day 21 postpartum. The following maternal (F0) parameters for systemic toxicity were evaluated: mortality, clinical signs, body weight, haematology and clinical chemistry. At sacrifice, a gross pathology examination was performed. No treatment-related adverse effects were observed in the dams and the macroscopic examination showed no treatment-related abnormalities. The NOAEL for systemic toxicity was considered to be ≥ 900 mg/kg bw/day.

In the study performed by Kadota et al. (1980), the potential systemic and developmental effects of N-acetyl-L-tryptophan via the intraperitoneal route were evaluated in Wistar rats (Kadota et al., 1980). N-acetyl-L-tryptophan was intraperitoneally (i.p.) administered to pregnant dams (F0) at doses of 150, 300 and 600 mg/kg bw/day from GD 7 to 17. Two thirds of the dams were sacrificed on day 20 of gestation, while the remaining dams were allowed to litter and sacrificed on postpartum day 21-28. There were a total of 33, 33, 33, and 34 animals in control, 150, 300 and 600 mg/kg bw/day, respectively. The following maternal (F0) parameters for systemic toxicity were evaluated: mortality, clinical signs, body weight, haematology and clinical chemistry. At sacrifice, a gross pathology examination was performed. In the dams, no treatment-related and toxicologically relevant effects were observed. Based on these results, the NOAEL for systemic toxicity was ≥ 600 mg/kg bw/day in dams.

 

Repeated dose toxicity: intravenous

The systemic and developmental/teratogenic effects of N-acetyl-L-tryptophan were assessed in a non-guideline study performed in rabbits (Ueshima et al., 1980b). The test substance was intravenously administered to pregnant rabbits from GD 6 - 18 at doses of 125, 250, 500 and 1000 mg/kg bw/day. There were 13, 12, 12, 12 and 11 dams in the control, 125, 250, 500 and 1000 mg/kg bw/day group, respectively. Dams were sacrificed on GD 29. The mortality and clinical signs, and body weight was recorded in the dams. Haematological and clinical chemistry parameters were assessed, and gross pathology examination was performed at sacrifice. Significantly decreased levels of RBC (red blood cell count), haemoglobin and haematocrit were observed in the 1000 mg/kg bw/day group in comparison to the control group. No other treatment-related adverse effects were observed in dams. Based on these results, the NOAEL for systemic toxicity was considered to be 500 mg/kg bw/day for dams.

Overall conclusion

Following the oral administration of the source substance (N-acetyl-L-tryptophan) for 10 consecutive days a NOAEL systemic of 2500 mg/kg bw/day in female rats was determined, based on a reduced body weight gain and decreased food consumption in the 5000 mg/kg bw/day group. In mice, no treatment-related or toxicologically relevant effects were observed after oral administration of the source substance for 10 consecutive days, leading to a NOAEL systemic ≥ 5000 mg/kg bw/day. Due to the absence of treatment-related and toxicologically relevant effects after intraperitoneal administration of the test substance the NOAEL systemic was considered to be ≥ 900 mg/kg bw/day in mice and to be ≥ 600 mg/kg bw/day in rats, respectively. In rabbits, significantly decreased levels of RBC (red blood cell count), haemoglobin and haematocrit were observed after intravenous administration of 1000 mg/kg bw/day, resulting in a NOAEL systemic of 500 mg/kg bw/day.

The doses administered via the oral exposure route in the rat and the mouse are substantially higher than the limit dose of 1000 mg/kg bw/day recommended in the current OECD guideline 407. No target organ toxicity was observed at any dose level. Moreover, data on systemic toxicity following repeated exposure after intraperitoneal and intravenous administration did not indicate any treatment-related adverse effects of the source substance. Exposure via these routes can be regarded as a worst case situation, as the substance is directly and entirely systemically available.

Overall, the available data consistently shows a very low systemic toxicity in several species via several routes of exposure. Therefore the available data are considered to be sufficient to meet the data requirements and to be suitable to read across to the target substance N-acetyl-DL-tryptophan. The lowest NOAEL after oral administration is considered to be 2500 mg/kg bw/day in rats.

Justification for classification or non-classification

According to Article 13 of Regulation (EC) No. 1907/2006 "General Requirements for Generation of Information on Intrinsic Properties of substances", information on intrinsic properties of substances may be generated by means other than tests e.g. from information from structurally related substances (grouping or read-across), provided that conditions set out in Annex XI are met. Annex XI, "General rules for adaptation of this standard testing regime set out in Annexes VII to X” states that “substances whose physicochemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity may be considered as a group, or ‘category’ of substances. This avoids the need to test every substance for every endpoint". Since the analogue concept is applied to N-acetyl-DL-tryptophan, data will be generated from information on reference source substance(s) to avoid unnecessary animal testing. Additionally, once the analogue read-across concept is applied, substances will be classified and labelled on this basis.

Therefore the available source and target substance data on repeated dose toxicity do not meet the classification criteria according to Regulation (EC) 1272/2008, and are therefore conclusive but not sufficient for classification.