Trisiloxane, 3-ethyl-1,1,1,3,5,5,5-heptamethyl-

Endpoint summary

Description of key information

In a repeated dose toxicity study performed according to OECD 407 and GLP principles, a NOAEL of 50 mg/kg bw/day was determined for 3-ethylheptamethyltrisiloxane.

 

.

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:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

5 July 2005 to 13 December 2005

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 407 (Repeated Dose 28-Day Oral Toxicity Study in Rodents)

Version / remarks:

1995

Deviations:

yes

Remarks:

refer to "Overall Remarks" below

GLP compliance:

yes

Limit test:

no

Specific details on test material used for the study:

Storage: room temperature

Species:

rat

Strain:

Wistar

Details on species / strain selection:

Strain and species commonly used in repeatd dose toxicity studies

Sex:

male/female

Details on test animals or test system and environmental conditions:

Species: Rat
Strain: HsdBr1:WH: Wistar
Age: 7-9 weeks
Weight at dosing: M: 154-181g; F: 196-230g
Source: Harlan Winkelmann
Acclimation period: 7 days
Diet: Altromin 1324 maintenance diet for rats and mice, ad libitum
Water: Municpal drinking water ad libitum
Housing: Macrolon cages on Altromin saw fiber bedding. No. of animals house together not stated.

Environmental conditions -
Temperature: 19-25°C
Humidity: 45-65%
Air changes: 10 changes/hr
Photoperiod: 12 hr light/dark

Route of administration:

oral: gavage

Details on route of administration:

orally administered via gavage

Vehicle:

corn oil

Details on oral exposure:

Method of administration:
Gavage of a suspension, using a stomach tube

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The test item was dissolved in corn oil. The vehicle was chosen due to its non-toxic characteristics.
The single dosages (vigorously shaken) were prepared on every application day in the following ratios:
The test item was dissolved in corn oil at a ratio of 0.2 g to 20 mL.
Medium Dose (250 mg/kg bw): The test item was suspended in corn oil at a ratio of 1.0 g to 20 mL.
High Dose (1000 mg/kg bw): The test item was suspended in corn oil at a ratio of 4.0 g to 20 mL.

The homogeneity of the preparations was visually checked. During the application procedure no obvious separation was detected. Analysis of stability and homogeneity was performed and confirmed to be stable. Homogeneity analysis confirmed that mean recovery rates of 109 and 107% of nominal for the low and high dose groups respectively. Concentration analysis confirmed that mean recovery rates of 110, 108 and 106% of nominal for the low, mid and high dose groups respectively.

Duration of treatment / exposure:

Test duration: 28 days

Frequency of treatment:

once daily for 28 consecutive days

Dose / conc.:

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

Dose / conc.:

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

Dose / conc.:

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

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

No. of animals per sex per dose:

5 animals/sex/group

Control animals:

yes, concurrent vehicle

Details on study design:

Animals were randomly allocated to groups using a validated computer system. Each group consisted of 5 animals/sex. Y-14877 was dosed orally via gavage at 0, 50, 250 or 1000 mg/kg bw/d once daily for 28 days, employing a dose volume of 5 mL/kg bw. At necropsy selected organs were weighed and selected tissues were preserved for possible subsequent histological examination.

Positive control:

not applicable

Observations and examinations performed and frequency:

Observations: Animals were observed at least once a day for clinical observations and at least once daily for morbidity and mortality.

Body weight: Body weight was recorded individually for all rats prior to first application (day 0) and once a week thereafter (day 7, 14, 21, 27).

Food consumption: Calculated weekly (day 7, 14, 21, 27)

Behaviour/functional observation: Once before the first exposure and in the fourth exposure week sensory reactivity to stimuli of different types (e.g. auditory, visual and
proprioceptive stimuli, and motor activity assessment) was conducted.
- Home cage observation: parameters assessed - posture, palpebral closure, and the presence of convulsions or tremors. The rat's reactivity to removal from the cage and handling were then rated and the observer noted presence of salivation, lacrimation, and piloerection.
- Open field: each rat was placed on a table surrounded by a 10 cm cardboard rim for 3 minutes during which time the arousal level (alertness) and gait characteristics were recorded. The number of rears, supported (using the cardboard rim as support) and unsupported (unassisted), were counted separately. In addition, fecal boluses and pools of urine were counted. The presence of convulsions and tremors was again noted.
Reactions to the approach of a pencil, touch on the rump, and tail pinch using forceps were noted. The pupillary response was tested with the aid of a red light using a penlight stimulus.
Flexion reflex, equilibrium, grasping reflex (together with grip strength), righting reflexes and auditory startle were tested. Finally the rectal body temperature was taken

Ophthalmological examination: Not undertaken

Sacrifice and pathology:

All animals were euthanised by carbon dioxide asphyxiation and subjected to full gross necropsy.

Histopathology was conducted on control and high dose group animals. The following tissues were examined:
All gross lesions, brain (representative regions including cerebrum, cerebellum and pons), spinal cord, liver, kidneys, adrenals, stomach, intestine (small + large, including Peyer's patches, Lymph nodes acc. to application), thymus, thyroid, spleen, lung (+trachea), heart, gonads, accessory sex organs (e.g. uterus, prostate, seminal vesicles), urinary bladder, lymph nodes (Lymphocentrum mandibulare; Lnn axillares), peripheral nerve, bone marrow.

Additionally liver, stomach and thyroids were evaluated from all animals in the low and middle dose groups and kidneys from all male animals in the low and middle dose groups.

Organ weights: The adrenals, adrenals, brain, epididymides, heart, kidneys, liver, spleen, testes, thymus of each animal were weighed.

Other examinations:

Haematology and clinical chemistry: Blood was collected at necropsy via abdominal aorta puncture:
- Haematology: red blood cell parameters (haematocrit, haemoglobin concentration, erythrocyte count, platelet count), white blood cell parameters (total and differential (neutrophils, lymphocytes, eosinophils, basophils, monocytes, normoblasts) leukocyte count), clotting parameters (platelet count, prothrombin, activated partial thromboplastin time).
- Clinical chemistry: electrolytes (sodium, potassium, urea, creatinine), glucose, liver function tests (alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST)), lipid profile (cholesterol).

Urinalysis: The urine was collected into plain tubes by puncture of the urine bladder as a part of the necropsy the following parameters were examined:
The following urinary parameters were measured: specific gravity, pH, protein, glucose, ketones, bilirubin, urobilinogen, nitrite, leucocytes, erythrocytes

Statistics:

One-way analysis of variance (ANOVA) was carried out, followed by Student's t-test to reveal any differences between control and test groups

Clinical signs:

no effects observed

Description (incidence and severity):

Clinical signs of toxicity: No treatment related signs of clinical signs of toxicity were observed

Mortality:

no mortality observed

Description (incidence):

Mortality All animals survived up to the scheduled necropsy

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No relevant significant deviation in weight gain was found (on the 95% confidential level).

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

There were no treatment related effects on food consumption.

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Description (incidence and severity):

Ophthalmoscopic examination: Not applicable as no examinations were undertaken.

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

No test article related changes in haematological parameters were observed. With the exception of single borderline values (haematocrit, APTT, PTT), almost all individual and mean values were within the expected ranges. The single deviations were considered to be incidental and not toxicologically relevant.

Clinical biochemistry findings:

effects observed, non-treatment-related

Description (incidence and severity):

With the exception of the glucose values, all mean and most individual values were within the expected range. Statistically significant differences were found between some dose groups and the corresponding control groups both in male and female animals. As none of the mean and individual values showed marked pathological deviations, significant differences in general represent variation within a normal range and are of no toxicological relevance (refer to Table CA 7.5.1/01-2).

Urinalysis findings:

no effects observed

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

Functional and behavioural examination: No differences were observed prior to application and during the last week of dosing.
- Home cage observations: No abnormalities were recorded

Open field: No convulsions, tremors, stereotypy or bizarre behaviour were observed. Animals were used to handling during week 4 as it could be expected.
For supported and unassisted rears no abnormalities were detected.
Responses to reflex testing were normal in all groups.
On measures such as counts of urination and defecation differences could not be detected, since most of the rats displayed none of these activities even under baseline conditions.

Body temperatures were within normal ranges prior to dosing and during week 4.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Test article related effects (refer to Table CA 7.5.1/01-3):
- Liver: mean absolute and relative liver weight in all mid and high dose was increased compared to the weight in the corresponding control group, reaching statistical significance (p<0.05) for the absolute and relative values of the mid and high dose groups of both sexes and the absolute values of the male low dose group.
- Kidney: mean absolute and relative kidney weight in male mid and high dose was slightly increased compared to the weight in the corresponding control group, reaching statistical significance (p<0.05) for the absolute and relative values of the high dose group and the absolute value of the mid dose group. These effects correlated with hyaline droplet formation.
Calculated significant decrease was found for the absolute values of the female low dose group.

Non-test article related effects (these effects did not correlate with any associated histopathological findings in the representative tissues)
- Spleen: mean absolute and relative spleen weight in all dosed groups was slightly increased compared to the weight in the corresponding control group, reaching statistical significance (p<0.05) for the absolute value of the male low dose group.
- Adrenals: mean absolute adrenal weight in the male high dose group was slightly higher than the adrenal weight in the corresponding control group, reaching statistical significance (p<0.05).
- Thymus: mean absolute and relative thymus weight in the female high dose group was slightly decreased compared to the weight in the corresponding control group, reaching statistical significance (p<0.05). Calculated significant increase was found for the absolute values of the male low dose group.
Heart: mean relative heart weight in all dosed male groups, the absolute values in the female low dose and mid dose groups were slightly diminished compared to the heart weight in the corresponding control groups, reaching statistical significance (p<0.05).

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Marked hepatomegaly in all animals of both sexes in the high dose group and slight hepatomegaly in animals of both sexes in the mid-dose group.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Treatment related histopathological findings included (refer to Table CA 7.5.1/01-4):

- Liver: minimal to mild centrilobular hypertrophy was noted in all treated animals of each sex, being graded as minimal in all except 1/5 male and 1/5 given 1000 mg/kg bw/d where the change was mild. Minimal pigment plugs in the periportal bile ducts were noted in 1/5 males from each group given 250 or 1000 mg/kg bw/d. Staining for bile pigments was negative. These effects accounted for the hepatomegaly and higher organ weights which were noted principally at 250 and 1000 mg/kgbw/d. No liver enzyme increases or degenerative changes were associated with the hypertrophy, which is possibly due to P450 enzyme induction.

- Kidney: minimal to mild cortical tubular eosinophilic droplets were noted in nearly all treated males at 50, 250 and 1000 mg/kg bw/d with a dose related severity and incidence. These droplets stained positive for hyaline, being graded as moderate in all treated males.
In addition, minimal to moderate basophilic tubules in the kidneys were recorded at a higher severity and/or incidence in the treated groups than in the control groups (1/5, 3/5, 4/5 and 5/5 animals from groups receiving 0, 50, 250 and 1000 mg/kg bw/d, respectively). Granular casts at the corticomedullary junction were noted in 2/5 and 4/5 males given 250 and 1000 mg/kg bw/d, respectively. None of these findings were apparent in the females except for basophilic tubules, which were present at a similar incidence in the control and high dose groups.
Hyaline droplets are eosinophilic homogeneous cytoplasmic droplets that are normally present in the P2 segment of proximal tubule epithelia of young, mature male rats. The droplets represent alpha 2u-globulin sequestered in secondary lysosomes and and a normal occurrence in young male rats. Other changes concurrently seen in association with hyaline droplet accumulation include granular cast formation

- Thyroids: minimal follicular epithelial hypertrophy was noted in males at 50, 250 and 1000 mg/kg bw/d and in the females at 250 and 1000 mg/kg bw/d. Incidence was low but showed a dose relationship in both sexes. The thyroid effects were likely secondary to the liver effects observed, this however was not confirmed.

- Stomach: minimal or mild diffuse acanthosis in the forestomach was recorded in 1/5 males receiving 250 mg/kg bw/d and in 3/5 males and 4/5 females given 1000 mg/kg bw/d, with a dose-related increase in incidence and severity. In one female it was accompanied by mild hyperkeratosis. These effects are likely to be a local effect due to minimal irritant effect of the test article at the site of first contact.

Histopathological findings: neoplastic:

not examined

Other effects:

not examined

Details on results:

refer above

Dose descriptor:

NOAEL

Effect level:

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

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

organ weights and organ / body weight ratios

Dose descriptor:

NOEL

Effect level:

50 mg/kg bw/day (nominal)

Basis for effect level:

other: original NCD unit is mg/kg/day.

Critical effects observed:

yes

Lowest effective dose / conc.:

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

System:

hepatobiliary

Organ:

liver

thyroid gland

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

yes

Table CA 7.5.1/01-1:
Overview of 28 day toxicity in rats dosed orally (via gavage) with Y-14877: selected haematology parameters

Parameters	M (mg/kg bw/d)					F (mg/kg bw/d)
	0	50	250	1000		0	50	250	1000
Hb (g/dL)	15.34	16.24	17.30	15.40		16.78	15.04	14.88	15.58
HbCt (%)	48.78	50.30	52.37	51.40		51.65	46.27	43.54*	46.59
WBC (x10^3uL)	7.11	7.43	6.95	7.72		3.76	4.79	4.65	4.35
APTT (sec)	15.59	17.82	17.26	16.46		19.62	19.32	18.51	16.95*
PTT (sec)	34.52	40.13	34.73	34.50		42.87	38.12	38.19	30.49*
*: p=0.05
HbCt: haematocrit HbC: haemoglobin RBC red blood cell (erythrocyte) count					PT: prothrombin time APTT: activated partial thromboplastin time

Table CA 7.5.1/01-2:
Overview of 28 day toxicity in rats dosed orally (viagavage) with Y-14877: selected clinical chemistry parameters

Parameters	M (mg/kg bw/d)					F (mg/kg bw/d)
	0	50	250	1000		0	50	250	1000
ALT (U/I)	26.68	26.40	22.62	25.82		22.06	18.70*	23.22	24.22
Chol (mmol/L)	0.79	0.72	0.66	0.66		0.73	0.78	1.00*	1.27*
TP (g/L)	52.26	54.46	56.08	57.40*		56.68	57.82	61.76*	62.68*
Glucose (mmol/L)	14.54	12.63	12.22	16.09		9.49	11.97*	11.73*	13.37*
Na (mmol/L)	139.80	143.20	143.60*	143.00		136.80	139.80	138.80	137.40
K (mmol/L)	4.92	4.35	3.99*	4.78		3.85	3.89	3.70	3.63
*: p=0.05
ALT: alanine aminotransferase Chol: cholesterol TP: total protein					Na: sodium K: potassium

Table CA 7.5.1/01-3:
Overview of 28 day toxicity in rats dosed orally (viagavage) with Y-14877: selected organ weight data

Parameters	M (mg/kg bw/d)				F (mg/kg bw/d)
	0	50	250	1000	0	50	250	1000
Terminal b.w. g	298.60	321.80	320.60	307.60	208.80	203.60	206.80	205.00
Liver (abs) g	8.65	9.91*	12.09*	15.82*	6.64	6.95	9.18*	13.00*
Liver (rel)	3.13	3.19	3.91*	5.27*	3.26	3.53	4.49*	6.36*
Kidney (abs) g	1.99	2.22	2.42*	2.61*	1.53	1.37*	1.48	1.55
Kidney (rel)	0.70	0.72	0.78	0.87*	0.75	0.70	0.73	0.76
*: p=0.05 Abs: Absolute weight Rel: Organ weight relative to body weight (%)

Table CA 7.5.1/01-4:
Overview of 28 day toxicity in rats dosed orally (viagavage) with Y-14877: selected histopathology data

Parameters	M (mg/kg bw/d)				F(mg/kg bw/d)
	0	50	250	1000	0	50	250	1000
Liver [decedents, incidence/total number examined [minimal, mild, moderate, marked]]
Centrilobular hypertrophy	0,0/5 [0,0,0,0]	0,5/5 [5,0,0,0]	0,5/5 [5,0,0,0]	0,5/5 [1,4,0,0]	0,0/5 [0,0,0,0]	0,5/5 [5,0,0,0]	0,5/5 [5,0,0,0]	0,5/5 [4,1,0,0]
Focal mononuclear cell infiltrate	0,4/5 [0,4,0,0]	0,4/5 [0,4,0,0]	0,3/5 [0,3,0,0]	0,4/5 [0,4,0,0]	0,0/5 [0,0,0,0]	0,5/5 [0,5,0,0]	0,5/5 [0,5,0,0]	0,4/5 [0,4,0,0]
Kidney [decedents, incidence/total number examined [minimal, mild, moderate, marked]]
Basophilic tubules	0,1/5 [1,0,0,0]	0,3/5 [3,0,0,0]	0,4/5 [2,2,0,0]	0,5/5 [2,2,1,0]	0,1/5 [1,0,0,0]	-	-	0,2/5 [0,2,0,0]
Corticomedullary junction – granular casts	0,0/5 [0,0,0,0]	0,0/5 [0,0,0,0]	0,2/5 [0,1,1,0]	0,4/5 [0,1,3,0]	-	-	-	-
Cortical tubular eosinophilic droplets	0,0/5 [0,0,0,0]	0,5/5 [0,0,5,0]	0,5/5 [0,0,5,0]	0,5/5 [0,0,5,0]	-	-	-	-
Presence of a-2u globulin	0,0/5 [0,0,0,0]	0,5/5 [0,0,5,0]	0,5/5 [0,0,5,0]	0,4/5 [0,0,4,0]	-	-	-	-
Thyroid [decedents, surviving/total number [minimal, mild, moderate, marked]]
Follicular epithelial hypertrophy	0,0/5 [0,0,0,0]	0,1/5 [0,1,0,0]	0,2/5 [0,2,0,0]	0,3/5 [0,3,0,0]	0,0/5 [0,0,0,0]	0,0/5 [0,0,0,0]	0,1/5 [1,0,0,0]	0,2/5 [2,0,0,0]

Conclusions:

Based on the results of 28-day repeated dose toxicity study, performed according to OECD/EC guidelines and GLP principles, it is concluded that the NOAEL of Y-14877 is 50 mg/kg bw/d (based on increases in both kidney and liver weights, with associated histopathology and histopathological changes in the thyroid at 250 and 1000 mg/kg bw/day).

Executive summary:

The objective of this study was to evaluate the toxicity of Y-14877 when administered orally via gavage to Wistar rats for 28 days. Y-14877 was administered to groups of 5 male and 5 female rats at dose levels of 0, 50, 250 or 1000 mg/kg bw/d.

 

There were no unscheduled deaths or clinical signs of toxicity, with no significant deviation in weight gains observed. The functional observational battery confirmed no differences were observed prior to application and during the last week of dosing.

 

No test article related changes in haematological parameters were observed. With the exception of the glucose values in females, all mean and most individual values were within the expected range.

 

Test article related effects in organ weights included liver (mean absolute and relative liver weight in all mid and high dose was increased compared to the control group) and kidney (mean absolute and relative kidney weight in male mid and high dose was slightly increased compared to the weight in the corresponding control group, reaching statistical significance) these weight changes were accompanied by histopathological changes. In the liverminimal to mild centrilobular hypertrophy was noted in all treated animals of each sex, minimal pigment plugs in the periportal bile ducts were noted in 1/5 males from each group given 250 or 1000 mg/kg bw/d. Staining for bile pigments was negative. These effects accounted for the hepatomegaly and higher organ weights which were noted principally at 250 and 1000mg/kg bw/d. however, the assessment of P450 upregulation was limited to the blood liver enzyme (ALT, ALP, AST) analysis conducted at necropsy, rather than relevant cytochrome P450 activity associated with thyroid insufficiency (EROD, PROD, BROD, T₄-UDP-GT, T₃-UDP-GT, MUT-GT, HOBI-GT). In the kidney, minimal to mild cortical tubular eosinophilic droplets were noted in nearly all treated males at 50, 250 and 1000 mg/kg bw/d with a dose related severity and incidence. These droplets stained positive for hyaline, being graded as moderate in all treated males. In addition, minimal to moderate basophilic tubules in the kidneys were recorded at a higher severity and/or incidence in the treated groups than in the control groups. None of these findings were apparent in the females except for basophilic tubules, which were present at a similar incidence in the control and high dose groups. Hyaline droplets are eosinophilic homogeneous cytoplasmic droplets that are normally present in the P2 segment of proximal tubule epithelia of young, mature male rats. The droplets represent alpha 2u-globulin sequestered in secondary lysosomes and a normal occurrence in young male rats and are not deemed relevant for humans.

 

Other test article related histopathology findings were seen in the thyroid gland (minimal follicular epithelial hypertrophy was noted in males at 50, 250 and 1000 mg/kg bw/d and in the females at 250 and 1000 mg/kg bw/d. Incidence was low but showed a dose relationship in both sexes. The thyroid effects were likely secondary to the liver effects observed, this however was not confirmed), and stomach (minimal or mild diffuse acanthosis in the forestomach was recorded in 1/5 males receiving 250mg/kg bw/d and in 3/5 males and 4/5 females given 1000 mg/kg bw/d, with a dose-related increase in incidence and severity. In one female it was accompanied by mild hyperkeratosis. These effects are likely to be a local effect due to minimal irritant effect of the test article at the site of first contact.)

 

Based on the results obtained, it is concluded that Y-14877 produced toxicity at dose levels of 250 and 1000 mg/kg bw/d when administered orally via gavage for 28 consecutive days in Wistar rats under the conditions and procedures followed in the present study (based on increases in both kidney and liver weights, with associated histopathology and histopathological changes in the thyroid). There was no evidence of toxicity at 50 mg/kg bw/d and this is considered to be a NOAEL.

 

Thyroid changes observed (follicular epithelial hypertrophy) were attributed to a secondary effect of liver hypertrophy by the report authors. However, it was concluded that the observed liver hypertrophy was not attributable to liver enzyme induction. In the absence of mode of action work to confirm the biological relevance of the changes in thyroid histopathology observed, it cannot be concluded with certainty that these effects are not attributable to an endocrine mediation action.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

50 mg/kg bw/day

Study duration:

subacute

Species:

rat

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

Mode of Action Analysis / Human Relevance Framework

The objective of this study was to evaluate the toxicity of Y-14877 when administered orally via gavage to Wistar rats for 28 days. Y-14877 was administered to groups of 5 male and 5 female rats at dose levels of 0, 50, 250 or 1000 mg/kg bw/d.

 

There were no unscheduled deaths or clinical signs of toxicity, with no significant deviation in weight gains observed. The functional observational battery confirmed no differences were observed prior to application and during the last week of dosing.

 

No test article related changes in haematological parameters were observed. With the exception of the glucose values in females, all mean and most individual values were within the expected range.

 

Test article related effects in organ weights included liver (mean absolute and relative liver weight in all mid and high dose was increased compared to the control group) and kidney (mean absolute and relative kidney weight in male mid and high dose was slightly increased compared to the weight in the corresponding control group, reaching statistical significance) these weight changes were accompanied by histopathological changes. In the liverminimal to mild centrilobular hypertrophy was noted in all treated animals of each sex, minimal pigment plugs in the periportal bile ducts were noted in 1/5 males from each group given 250 or 1000 mg/kg bw/d. Staining for bile pigments was negative. These effects accounted for the hepatomegaly and higher organ weights which were noted principally at 250 and 1000mg/kg bw/d. however, the assessment of P450 upregulation was limited to the blood liver enzyme (ALT, ALP, AST) analysis conducted at necropsy, rather than relevant cytochrome P450 activity associated with thyroid insufficiency (EROD, PROD, BROD, T₄-UDP-GT, T₃-UDP-GT, MUT-GT, HOBI-GT). In the kidney, minimal to mild cortical tubular eosinophilic droplets were noted in nearly all treated males at 50, 250 and 1000 mg/kg bw/d with a dose related severity and incidence. These droplets stained positive for hyaline, being graded as moderate in all treated males. In addition, minimal to moderate basophilic tubules in the kidneys were recorded at a higher severity and/or incidence in the treated groups than in the control groups. None of these findings were apparent in the females except for basophilic tubules, which were present at a similar incidence in the control and high dose groups. Hyaline droplets are eosinophilic homogeneous cytoplasmic droplets that are normally present in the P2 segment of proximal tubule epithelia of young, mature male rats. The droplets represent alpha 2u-globulin sequestered in secondary lysosomes and a normal occurrence in young male rats and are not deemed relevant for humans.

 

Other test article related histopathology findings were seen in the thyroid gland (minimal follicular epithelial hypertrophy was noted in males at 50, 250 and 1000 mg/kg bw/d and in the females at 250 and 1000 mg/kg bw/d. Incidence was low but showed a dose relationship in both sexes. The thyroid effects were likely secondary to the liver effects observed, this however was not confirmed), and stomach (minimal or mild diffuse acanthosis in the forestomach was recorded in 1/5 males receiving 250mg/kg bw/d and in 3/5 males and 4/5 females given 1000 mg/kg bw/d, with a dose-related increase in incidence and severity. In one female it was accompanied by mild hyperkeratosis. These effects are likely to be a local effect due to minimal irritant effect of the test article at the site of first contact.)

 

Based on the results obtained, it is concluded that Y-14877 produced toxicity at dose levels of 250 and 1000 mg/kg bw/d when administered orally via gavage for 28 consecutive days in Wistar rats under the conditions and procedures followed in the present study (based on increases in both kidney and liver weights, with associated histopathology and histopathological changes in the thyroid). There was no evidence of toxicity at 50 mg/kg bw/d and this is considered to be a NOAEL.

 

Thyroid changes observed (follicular epithelial hypertrophy) were attributed to a secondary effect of liver hypertrophy by the report authors. However, it was concluded that the observed liver hypertrophy was not attributable to liver enzyme induction. In the absence of mode of action work to confirm the biological relevance of the changes in thyroid histopathology observed, it cannot be concluded with certainty that these effects are not attributable to an endocrine mediation action.

Justification for classification or non-classification

According to CLP (1272/2008/EC) classification criteria for repeated dose toxicity, no classification is required.