Glycine

Endpoint summary

Description of key information

NOAEL (male, oral, glycine) ≥ 2000 mg/kg bw/d (28 days)

LOAEL (male/female, oral, glycine) = 1561 mg/kg bw/d (108 weeks)

NOAEL (male/female), oral, N-acetylglycine)  ≥ 1000 mg/kg bw/d (28 days)

LOAEL (male/female, subcutaneous, glycine) = 1500 mg/kg bw/d (108 weeks)

NOAEL (male, intraperitoneal, glycine) ≥ 600 mg/kg bw/d (26 weeks)

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study with restrictions (only two dose levels, limited documentation (clinical signs, gross pathology))

Reason / purpose for cross-reference:

reference to same study

Principles of method if other than guideline:

The carcinogenicity of glycine was assessed in rats by application in the drinking water.

GLP compliance:

no

Limit test:

no

Species:

rat

Strain:

Fischer 344/DuCrj

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Co. Japan, Inc. Atsugi
- Age at study initiation: 6 wks
- Housing: in plastic cages (3/sex/cage)
- Diet (ad libitum): pellet diet (CRF-1, Charles River, Japan)
- Water (ad libitum)

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 24 ± 2
- Humidity (%): 55 ± 5

Route of administration:

oral: drinking water

Vehicle:

unchanged (no vehicle)

Duration of treatment / exposure:

108 wks

Frequency of treatment:

continuously via drinking water

Dose / conc.:

2.5 other: %

Remarks:

nominal in water

Dose / conc.:

5 other: %

Remarks:

nominal in water

Dose / conc.:

1 534 mg/kg bw/day (actual dose received)

Remarks:

males

Dose / conc.:

3 280 mg/kg bw/day (actual dose received)

Remarks:

males

Dose / conc.:

1 587 mg/kg bw/day (actual dose received)

Remarks:

females

Dose / conc.:

3 082 mg/kg bw/day (actual dose received)

Remarks:

females

No. of animals per sex per dose:

50

Control animals:

other: drinking water without test substance

Details on study design:

- Dose selection rationale: on the basis of a preliminary subacute experiment (not further specified)

Observations and examinations performed and frequency:

BODY WEIGHT: Yes
- Time schedule for examinations: every one or two weeks

FOOD CONSUMPTION: Yes
- Time schedule for examinations: every four weeks

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Time schedule for examinations: daily

HAEMATOLOGY: Yes
- Time schedule for collection of blood: at week 108
- How many animals: all survivors
- Parameters checked: white/red blood cells, heamoglobin (Hb), haematocrit (Ht)

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at week 108
- How many animals: all survivors
- Parameters checked: glutamic oxalacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), lactate dehydrogenase (LDH), alkaline phosphatase (ALP), creatine phosphokinase (CPK), blood urea nitrogen (BUN), creatinine (CRE), Urea (UA), total protein (TP), albumin/globulin rate (A/G rate), blood glucose (BG), phospholipid (PL), total cholesterol (Tch), triglyceride (TG), natrium, potassium, calcium, chloride

URINALYSIS: Yes
- Parameters checked: leukocytes, nitrite, urobilinogen, protein, pH, ketone, glucose

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (all animals, including those that died or were sacrificed upon becoming moribund during the experiment)
HISTOPATHOLOGY: Yes (all organs were examined and samples were fixed in 10% buffered neutral formalin, embedded in paraffin, and routinely stained with hematoxylin and eosin; histological analysis of tumors in renal pelvis)

Statistics:

Wilcoxon t-test or chi-squared test

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

5% dose group: slightly increased mortality in females compared to controls

Mortality:

mortality observed, treatment-related

Description (incidence):

5% dose group: slightly increased mortality in females compared to controls

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

2.5 and 5% dose group: slight dose-dependent inhibition of mean body weight gain in both sexes

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not examined

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

no effects observed

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

5% dose group: significant changes of Hb and HT in males and females

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

2.5 and 5% dose group, males and females: significantly changes in CPK, BUN, TP, Tch and TG were observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

2.5 and 5% dose group: papillary necrosis and transitional hyperplasia was observed in male and female animals (no cases seen in the controls)

Histopathological findings: neoplastic:

effects observed, treatment-related

Description (incidence and severity):

2.5 and 5% dose group, females: kidney papillomas were seen, which were not observed in controls

Details on results:

CLINICAL SIGNS AND MORTALITY
Mortality of females of the high dose group was slightly increased when compared to controls (number of surviving females and males: 31, 46, 41 and 40, 45, 40 for the high, low, control group).

BODY WEIGHT AND WEIGHT GAIN
2.5 and 5% dose group, males and females: Mean body-weights were slightly but dose-dependently inhibited when compared to controls over the hole study period (only growth curves were given).

HAEMATOLOGY
5% dose group, males: A slight but not significant increase in white blood cells was observed. The Hb was significantly increased when compared to controls.
5% dose group, females: A slight but not significant increase in white blood cells and a slight but not significant decrease in red blood cells was observed. The Hb and HT were significantly decreased when compared to controls.
2.5% dose group, females: A slight but not significant increase in white blood cells and a slight but not significant decrease in red blood cells was observed.

CLINICAL CHEMISTRY
2.5 and 5% dose group, males and females: The CPK values were significantly decreased when compared to controls in both sexes and both dose groups. BUN was significantly increased in both sexes of the 5% dose group.
2.5 and 5% dose group, females: A significant and dose-dependent decrease of TP and Tch and a significant and dose-dependent increase in TG was observed.
Some sporadic effects on isolated parameters were observed which were considered as not treatement-related (see Table 1 "Any other information on results incl. tables").

URINALYSIS
No significant differences in urinalysis data between treated and control male and female animals were observed.

ORGAN WEIGHTS
No significant effects on the relative organ weights were observed in the treated groups when compared to controls.

HISTOPATHOLOGY: NON-NEOPLASTIC
The incidences of papillary necrosis in male rats fed 2.5 and 5% glycine were 4 and 7%, while the corresponding figures for females were 30 and 32%. Since necrosis of the renal papillae was limited to glycine-treated rats it was very likely linked to the induction of papillomas. Transitional hyperplasia in renal pelvis was observed in 2 female animals of the 2.5% dose group. Calcification indices in kidney were 39, 32 and 42% of the 0, 2.5 and 5% groups (see Table 2 "Any other information on results incl. tables").

HISTOPATHOLOGY: NEOPLASTIC (if applicable)
For the males, tumors were found in 90% of the high dose group, 97% of the low dose group and in 90% of the controls, while the corresponding figures for females were 59, 65 and 39%. These tumors were considered to be spontaneous in nature (see Table 3 "Any other information on results incl. tables").
One renal cell tumor was seen in one male of the high dose group. Kidney papillomas were found in 8% of the low dose group and in 6% of the high dose group females, but not in the controls. Since spontaneous tumors in this tissues are very rare, they were considered as treatment-related (see Table 3 "Any other information on results incl. tables").

Dose descriptor:

LOAEL

Effect level:

1 561 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: clinical chemistry; histopathology

Dose descriptor:

NOAEL

Effect level:

< 1 561 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

histopathology: neoplastic

histopathology: non-neoplastic

Critical effects observed:

not specified

Table 1: Clinical chemistry data for rats treated with the test substance (mean values± standard deviation)

	Males			Females
Group (%)	0	2.5	5	0	2.5	5
No. of rats	40	45	40	41	46	31
GOT (K-U)	122 ± 72	120 ± 57	114 ± 27	130 ± 53	117 ± 40	136 ± 68
GPT (K-U)	51 ± 34	55 ± 37	53 ± 12	59 ± 22	56 ± 12	66 ± 16
LDH (K-U)	2879 ± 772	2710 ± 972	2514 ± 819	2572 ± 1369	2666 ± 836	2556 ± 952
ALP (KA-U)	16 ± 6	15 ± 5	17 ± 5	19 ± 9	19 ± 5	25 ± 7*
CPK (IU/L)	754 ± 321	563 ± 217*	509 ± 197*	706 ± 392	545 ± 160*	446 ± 158*
BUN (mg/dL)	18 ± 3	17 ± 2	21 ± 3*	18 ± 2	17 ± 2	21 ± 3*
CRE (mg/dL)	0.6 ± 0.07	0.5 ± 0.10*	0.5 ± 0.11*	0.5 ± 0.06	0.5 ± 0.06	0.5 ± 0.07
UA (mg/dL)	2.3 ± 1.5	1.9 ± 0.6	2.5 ± 1.3	2.8 ± 1.8	2.0 ± 0.9*	2.5 ± 1.7
TP (g/dL)	6.9 ± 0.5	6.6 ± 0.3*	6.8 ± 0.4	7.5 ± 0.7	7.1 ± 0.5*	6.8 ± 0.7*
A/G (rate)	0.6 ± 0.09	0.7 ± 0.06*	0.7 ± 0.06*	0.8 ± 0.07	0.8 ± 0.06	0.8 ± 0.09
BG (mg/dL)	131 ± 46	127 ± 30	140 ± 51	136 ± 35	127 ± 15	125± 27
PL (mg/dL)	216 ± 62	205 ± 54	214 ± 61	211 ± 37	205 ± 36	202 ± 34
Tch (mg/dL)	150 ± 51	130 ± 39	129 ± 42	117 ± 22	104 ± 19*	98 ± 17*
TG (mg/dL)	175 ± 82	162 ± 59	198 ± 78	154 ± 73	209 ± 102*	226 ± 105*
Na (mEq/L)	144 ± 2	141 ± 2*	143 ± 2	141 ± 3	139 ± 1*	141 ± 4
K (mEq/L)	5.3 ± 0.7	4.6 ± 0.8*	5.3 ± 1.0	5.0 ± 0.9	4.4 ± 0.5*	4.7 ± 0.8
Ca (mg/dL)	11.1 ± 0.9	10.3 ± 0.5*	11.2 ± 1.1	11.2 ± 1.4	10.6 ± 0.6*	10.7 ± 1.1
Cl (mEq/L)	99 ± 1.9	101 ± 2.3*	99 ± 3.5	99 ± 2.0	98 ± 2.3	97± 4.3

*p<0.05, compared to control

Table 2: Histological findings for the urinary system for rats treated with the test substance

		No. of affected rats (%)
		Males			Females
Test substance concentration (%)		0	2.5	5	0	2.5	5
Effective No. of rats		40	45	40	41	46	31
Urinary system
Kidney	renal cell tumor	0	0	1(2)	0	0	0
	papillary necrosis	0	2(4)	3(7)	0	14(30)	10(32)
	calcification	0	0	0	16(39)	15(32)	13(42)
Pelvis	transitional hyperplasia	0	0	0	0	2(4)	0
	transitional cell tumor	1(2)	0	0	0	0	0
	papilloma	0	0	0	0	4(8)	2(6)

Table 3: Organ distribution and histological diagnosis for tumors in rats treated with the test substance

		No. of affected rats (%)
		Males			Females
Test substance concentration (%)		0	2.5	5	0	2.5	5
Effective No. of rats		40	45	40	41	46	31
Tumor development
Genital system
Testis	interstitial cell tumor	36(90)	44(97)	36(90)	27(59)	30(65)	12(39)
Prostate	adenoma	35(87)	44(97)	36(90)	-	-	-
	calcification	1(2)	2(4)	2(4)	-	-	-
Uterus	endometrial polyp	-	-	-	5(12)	18(39)	12(38)
	endometrial sarcoma	-	-	-	0	1(2)	0
	adenocarcinoma	-	-	-	1(2)	0	0
Mammary gland	firboma	0	0	0	1(2)	0	0
	adenoma	0	0	0	0	1(2)	1(3)
Endocrine system
Pituitary gland	adenoma	9(22)	6(13)	7(17)	13(31)	12(26)	9(29)
Thyroid gland	C-cell adenoma	4(10)	1(2)	3(7)	4(9)	3(6)	2(6)
	C-cell carcinoma	0	2(4)	1(2)	1(2)	1(2)	0
	papillary adenoma	1(2)	0	1(2)	0	2(4)	0
	papillary adenocarcinoma	0	1(2)	0	0	0	0
Adrenal gland	pheochromocytoma	5(13)	7(15)	5(13)	0	1(2)	0
Pancreas	islet cell tumor	6(15)	1(2)	2(4)	0	1(2)	0
Digestive system
Liver	neoplastic nodule	1(2)	0	0	0	0	1(3)
Respiratory system
Lung	adenoma	0	2(4)	0	0	1(2)	0
Urinary system
Kidney	renal cell tumor	0	0	1(2)	0	0	0
	transitional cell tumor	1(2)	0	0	0	0	0
	papilloma	0	0	0	0	4(8)	2(6)
Urinary bladder	papilloma	0	0	0	0	0	0
Body cavity
Peritoneum	mesothelioma	2(5)	2(4)	1(2)	0	0	0
Hematopoietic system
Leukemia		4(10)	6(13)	3(7)	6(14)	9(17)	3(9)
Integument, musculoskeletal system
Subcutis	fibroma	3(8)	0	0	4(10)	2(4)	0
	lipoma	0	1(2)	0	0	0	1(2)
	preputial/clitoral gland tumor	3(6)	2(4)	2(4)	0	0	1(2)
	fibrsarcoma	0	0	1(2)	0	0	0

Reference 2

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

refer to analogue justification provided in IUCLID section 13

Reason / purpose for cross-reference:

read-across source

Dose descriptor:

NOAEL

Effect level:

>= 1 000 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: NOAEL corresponding to the highest dose tested.

Dose descriptor:

NOAEL

Effect level:

>= 898.9 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: NOAEL corresponding to the highest dose tested.

Dose descriptor:

NOAEL

Effect level:

>= 989.9 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: NOAEL corresponding to the highest dose tested.

Critical effects observed:

not specified

Conclusions:

No adverse effects were observed in rats treated with the source substance for 28-days. A similar outcome is considered for the target substance.

Reference 3

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

13 Jul - 10 Aug 2005

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Test procedure according to national standards

Qualifier:

according to guideline

Guideline:

other: Guidelines for Toxicity Studies of Drugs (Japanese Ministry of Health, Labor, and Welfare, 1990)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Crj: CD(SD)

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories Japan, Inc., Yokohama, Japan
- Age at study initiation: 5 weeks
- Weight at study initiation: 193.9 - 215.1 g
- Fasting period before study: no
- Housing: metal blaket cage
- Diet (e.g. ad libitum): CRF-1 from Oriental Yeast Co., Ltd.
- Water (e.g. ad libitum): tap water
- Acclimation period: 6 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 26 °C
- Humidity (%): 30 - 70%
- Air changes (per hr): 10 - 15 times/h
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: gavage

Vehicle:

water

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: Test substance was prepared with water for injection purposes. Gavage solutions were prepared freshly every day.

VEHICLE
- Lot/batch no.: 5A88

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

28 days

Frequency of treatment:

once daily

Dose / conc.:

500 mg/kg bw/day (nominal)

Dose / conc.:

1 000 mg/kg bw/day (nominal)

Dose / conc.:

2 000 mg/kg bw/day (nominal)

No. of animals per sex per dose:

6

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: according to the recommended maximum dose in the Guidelines for Toxicity Studies of Drugs (Japanese Ministry of Health, Labor, and Welfare, 1990)

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
- Cage side observations: general condition and mortality

BODY WEIGHT: Yes
- Time schedule for examinations: Day 1, 3, 8, 15, 22, 28 and before sacrifice.

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

WATER CONSUMPTION: Yes
- Time schedule for examinations: Total water consumption for one day was measured between Day 2-3, 7-8, 14-15, 21-22 and 27- 28.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: One day after last administration
- Anaesthetic used for blood collection: Yes (ether)
- Animals fasted: Yes
- How many animals: all animals
- Parameters checked: RBC, MCV, platelet, HGB, hematocrit, MCH, MCHC, WBC, reticulocytes, PT, APTT, fibrinogen, neutrophil, lymphocytes, monocytes, eosinophils, basophils

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: One day after last administration
- Animals fasted: Yes
- How many animals: all animals
- Parameters checked: LDH, CPK, GOT, GPT, ALP, T-bilirubin, creatinine, urea nitrogen, triglyceride, total cholesterol, phospholipids, glucose, Na, K, Cl, Ca, inorganic-P, total protein, ALB, ALPHA1, ALPHA2, BETA, GAMMA

URINALYSIS: Yes
- Time schedule for collection of urine: During 18 hours after administration on Day 28.
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes
- Parameters checked: Urine volume, specific gravity, pH, glucose, protein, occult-blood, ketone, bilirubin, Na, K, Cl

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes: Adrenal gland, aorta, brain, cecum, coagulating gland, colon, duodenum, epididymis, esophagus, extraorbital lacrimal gland, eye, harderian gland, heart, ileum, jejunum, kidney, liver, lung, lymph node - cervical, lymph node - mecenteric, mammary gland, pancreas, parathyroid gland, pituitary gland, prostate, sciatic nerve, seminal vesicle, skeltal muscle, skin, spiral cord, spleen, sternum (bone marrow), stomach, sublingual gland, submandibular gland, testes, thymus, thyroid gland, tongue, trachea and urinary bladder

Statistics:

Barlett's test, Dunnett's test, Steel test

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):

no effects observed

Ophthalmological findings:

not specified

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
No mortality and no abnormalities were observed in all groups.

BODY WEIGHT AND WEIGHT GAIN
No differences were found between treatment group and control group.

FOOD CONSUMPTION
No differences were found between treatment group and control group.

WATER CONSUMPTION
No differences were found between treatment group and control group.

HAEMATOLOGY
No differences were found between treatment group and control group.

CLINICAL CHEMISTRY
Phospholipids were increased in treatment group at dosing of 2000 mg/kg in comparison with control group (p < 0.05). However, the change was small. This was not considered to be a substance-related toxicological effect.

URINALYSIS
Total urine volume and Cl was increased in treatment group at dosing of 2000 mg/kg in comparison with control group (p < 0.05). These changes were not regarded as toxicological effects by the test substance because no changes on kidney, other related organ for elimination of urine or other parameter of urinalysis was detected.

ORGAN WEIGHTS
No differences were found between treatment group and control group. With special regard to reproductive organs, there were no differences in absolute and relative testes weight in any treatment group when compared to controls.

GROSS PATHOLOGY
No differences were found between treatment group and control group.

HISTOPATHOLOGY: NON-NEOPLASTIC
No differences were found between treatment group and control group. In particular with regard to prostate, seminal vesicles and testes, no treatment-related effects were observed.

Dose descriptor:

NOAEL

Effect level:

>= 2 000 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: no effects observed at highest dose tested

Critical effects observed:

not specified

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

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

Oral Repeated Dose Toxicity

Oral repeated dose toxicity of glycine was investigated in a guideline study (Guidelines for toxicity studies of drugs) performed under GLP conditions (Taniguchi, 2006). 6 male Crj: CD(SD) rats were treated via gavage with the test substance dissolved in water at concentrations of 500, 1000, and 2000 mg/kg bw d for 28 days. Control animals received the vehicle.No unscheduled death, clinical signs, effects on body weight gain, food/water consumption and haematology were observed during the treatment time.Phospholipids were significantly increased in animals of the 2000 mg/kg bw/d dose group in comparison with controls. Urinalysis revealed an increase in total urine volume and chloride in animals of the 2000 mg/kg bw/d dose group in comparison with controls. Both effects were regarded as not treatment-related, since they occurred sporadically, without dose-relation and related effects on organ weights and histopathology. No effects were observed at gross- and histopathology and with regard on organ weights. In particular, no effects on testes, prostate, and seminal vesicles were observed. Therefore, a NOAEL ≥ 2000 mg/kg bw/d was determined for male rats.

Carcinogenicity of glycine after oral administration to male and female Fischer 344/DuCrj rats was investigated by Kitahori et al. (1994). The unchanged test substance was applied continuously via drinking water at 2.5 and 5% for 108 weeks to 50 animals per sex. The concentrations used correspond to 1534 and 3280 mg/kg bw/day for males and to 1587 and 3082 mg/kg bw/d for females, respectively, based on the body weights and water consumption data given in the publication. Control animals received drinking water without the test substance. Dose concentrations were chosen on the basis of a preliminary subacute experiment (unspecified). Observations and examinations comprised body weight development, food and water consumption, haematology, clinical chemistry, urinalysis, gross pathology and histopathology. Mortality of the high dose group females was slightly increased when compared to controls (31 vs. 41 surviving animals). Mean body weights of both sexes were slightly and dose-dependently inhibited over the whole study period when compared to controls. In the high dose group a slight, but not statistically significant increase in white blood cells was observed in both sexes when compared to controls. In addition, a slight decrease in red blood cells and a statistically significant decrease of the haemoglobin and haematocrit levels was observed in females. In the low dose group females a slight, but not statistically significant increase in white blood cells and decrease in red blood cells was observed when compared to controls. In both sexes of both dose groups, the creatine phosphokinase values were significantly lower when compared to controls. Blood urea nitrogen was significantly increased in both sexes of the high dose group. In females of both dose groups, a significant and dose-dependent decrease of total protein and total cholesterol and a significant and dose-dependent increase in triglycerides was observed. Some sporadic effects on isolated parameters were even more observed with regard to clinical chemistry which were considered as not treatment-related. The incidences of papillary necrosis in male rats fed 2.5 and 5% glycine were 4 and 7%, while the corresponding figures for females were 30 and 32%. Since necrosis of the renal papillae was limited to glycine-treated rats it was very likely linked to the induction of papillomas. Transitional hyperplasia in renal pelvis was observed in 2 female animals of the low dose group. Calcification indices in kidney were 39, 32 and 42% in females of the control, 2.5 and 5% groups, respectively. These effects were considered as non-neoplastic histopathology findings. Overall, tumors in males were found in 90% of the high dose group, 97% of the low dose group and in 90% of the controls, while the corresponding figures for females were 39, 65 and 59%. These tumors were considered to be spontaneous in nature. Based on the histological findings, a LOAEL of 1561 mg/kg bw/d was set for male and female rats.

In addition to the studies describe above, toxicity data of the read-across substance N-acteylglycine was also taken into consideration for assessment of effects after repeated oral administration. Enzymatic acetylation of proteins is a common posttranslational process. 80% of all soluble proteins are N-acetylated at the amino terminus with amino acids, glycine being the most frequent. N-acylpeptide hydrolases release acetylated amino acids which are then deacetylated by aminoacylases into constituent amino acids. N-acetylglycine was investigated in an OECD 407 guideline study under GLP conditions (Harper et al. 2010). 10 male and 10 female Sprague-Dawely rats per dose were administered N-acetylglycine via food at nominal concentrations of 100, 500 and 1000 mg/kg bw/d for 28 days. Control animals received either plain diet or glycine at 1000 mg/kg bw/d (nominal concentration). No animal died within the treatment period and no clinical signs were observed. Body weight gain and food consumption were unaffected. Ophthalmoscopic and neurobehavioural examinations revealed no treatment-related effects. At haematology, partial thromboplastin was significantly increased at 1000 mg/kg bw/d and activated partial prothrombin time was also significantly increased at 500 mg/kg bw/d in female animals. At 500 mg/kg bw/d, serum albumin was significantly decreased in male animals. No effects were observed at gross pathology. Relative organ weights, in particular of testes and ovaries, were unaffected as well. Histopathological investigations of tissues, including mammary and prostate gland, revealed no adverse findings. However, no results regarding organ weights and histopathology of the glycine-treated animals were given in the study report. Therefore, for N-acetylglycine a NOAEL of ≥ 1000 mg/kg bw/d was determined, corresponding to 898.9 and 989.9 mg/kg bw/d for male and female rats, respectively, based on weekly determined body weight and food consumption measurements.

 

Repeated Dose Toxicity: other routes

In addition to the oral studies, glycine was also investigated for adverse effects after subcutaneous injection to male and female Wistar rats for 30 days (Nemoto et al. 1977).10 animals per sex and group were treated with the test substance dissolved in physiological saline at doses of 100 and 1500 mg/kg bw/d. Control animals received the vehicle. No death were observed in any test group. At the beginning of the dosing period, spontaneous locomotion, respiratory depression and ptosis were observed in both sexes receiving 1500 mg glycine/kg bw/d from ca. 20 minutes after doing till 3 or 4 hours after. These signs almost disappeared 10 days after dosing. Hardening or necrosis was observed at the injection site of the test substance treated groups and progressed to marked necrosis by the end of the injection period. Food consumption in the males of the 1500 mg glycine/kg bw/d group was sometimes slightly less than in the control group. The number of white blood cells was significantly increased in both sexes of the 1500 mg/kg bw/d dose group. Differential count of neutrophils in females of the high dose group was significantly increased and lymphocytes were significantly decreased when compared to controls. In males of the 100 mg/kg bw/d dose group, differential count of neutrophils was significantly increased and lymphocytes were significantly decreased when compared to controls. No effects on body weight gain, clinical chemistry and urinalysis were observed. Determination of organ weights revealed significantly increased weights of spleen in both sexes in the 1500 mg/kg bw/d dose group. At histopathology, no treatment-related effects were observed. Based on the effects observed a LOAEL of 1500 mg/kg bw/d for male and female rats was set.

In the study of Nemoto et al. (1977), glycine was also administered via intraperitoneal injection to male Wistar rats for 26 weeks. 15 animals per group received the test substance dissolved in physiological saline at doses of 1.5, 30, and 600 mg/kg bw 6 days per week.One death occured incidentally in the glycine 1.5 mg/kg bw dose group. Writhing was observed immediately after i.p. injection of 600 mg glycine/kg bw. There was a slight increasing tendency in serum aspartate aminotransferase and alanine aminotransferase activities in higher dose groups (statistical significances were not known). No effects were observed regarding body weight gain, food consumption, haematology, urinalysis, gross pathology and organ weights. At histopathology, cell infiltration of myocardium, hyperplasia of the trachea epithelial cells, fibrosis of the liver and kidney were observed in several cases of treated groups. Other effects were found in the test substance treated groups and the control group with almost the same degree. Based on the effects observed, the NOAEL was set at 600 mg/kg bw/d for male rats.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:

Hazard assessment is based on the weight of evidence from all available studies on glycine and the read-across substance N-acetylglycine.

Justification for classification or non-classification

The available data on repeated dose toxicity of the test substance do not meet the criteria for classification according to Regulation (EC) 1272/2008 and Directive 67/548/EEC, and are therefore conclusive but not sufficient for classification.