O-isopropyl ethylthiocarbamate

Repeated dose toxicity: oral

Administrative data

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016 - 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2017

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

O-isopropyl ethylthiocarbamate

EC Number:

205-517-7

EC Name:

O-isopropyl ethylthiocarbamate

Cas Number:

141-98-0

Molecular formula:

C6H13NOS

IUPAC Name:

N-ethyl(propan-2-yloxy)carbothioamide

Test animals

Species:

rat

Strain:

Wistar

Details on species / strain selection:

Wistar rats, Crl: WI(Han) (Full Barrier)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River, 97633 Sulzfeld, Germany
- Females (if applicable) nulliparous and non-pregnant: yes
- Age at study initiation:7-8 weeks
- Weight at study initiation:
males: 164 – 187 g(mean: 175.48 g, ± 20% = 140.38 – 210.57 g)
females: 124 – 138 g(mean: 129.70 g, ± 20% = 103.76 – 155.64 g)
- Fasting period before study:
- Housing:IVC cages (type IV, polysulphone cages) on Altromin saw fibre bedding
- Diet (e.g. ad libitum):Free access to Altromin 1324 maintenance diet for rats and mice
- Water (e.g. ad libitum):Free access to tap water, sulphur acidified to a pH of approximately 2.8 (drinking
water, municipal residue control, microbiological controls at regular intervals)
- Acclimation period:minimum 5 days

DETAILS OF FOOD AND WATER QUALITY:

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3 °C
- Humidity (%): 55 ± 10%
- Air changes (per hr): 10 x / hour
- Photoperiod (hrs dark / hrs light): 12 hours light, 12 hours dark

IN-LIFE DATES:
Acclimatisation Period: 22 December 2015 to 29 December 2015
Experimental Starting Date: 29 December 2015
Treatment Period: 05 January 2016 to 06 April 2016

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:

VEHICLE
- Concentration in vehicle: 0, 7.5, 25 and 75 mg/ml
- Amount of vehicle (if gavage): 4 ml/kg
- Lot/batch no. (if required): MKBV2080V

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

90 days

Frequency of treatment:

daily

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

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

Remarks:

Group name C

Doses / concentrations 2

Dose / conc.:

30 mg/kg bw/day (nominal)

Remarks:

Group name LD.

Purity level of 95,7 w/w % of test item solution taking into consideration , so dosage concentration is in mg AI/ kg bw /day

Doses / concentrations 3

Dose / conc.:

100 mg/kg bw/day (nominal)

Remarks:

Group name MD.

Purity level of 95,7 w/w % of test item solution taking into consideration , so dosage concentration is in mg AI/ kg bw /day

Doses / concentrations 4

Dose / conc.:

300 mg/kg bw/day (nominal)

Remarks:

Group name HD.

Purity level of 95,7 w/w % of test item solution taking into consideration , so dosage concentration is in mg AI/ kg bw /day

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily

BODY WEIGHT: Yes
- Time schedule for examinations: The body weight was recorded once before the assignment to the experimental groups,
on the first day of administration and weekly during the treatment period.

FOOD CONSUMPTION AND COMPOUND INTAKE (although this was not a feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes , Food consumption was measured cage wise weekly during the treatment period. For
calculation of the respective food consumption of individual animals the number of
animals per cage was taken into account.


FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: Yes

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


OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: Haematological parameters were examined at the end of the treatment prior to or as
part of the sacrifice of the animals
- Anaesthetic used for blood collection: Not specified
- Animals fasted: Yes
- How many animals: all
- Following Parameters were examined:
haematocrit value (Hct)
haemoglobin content (Hb)
red blood cell count (RBC)
mean corpuscular volume (MCV)
mean corpuscular haemoglobin (MCH)
mean corpuscular haemoglobin
concentration (MCHC)
reticulocytes (Re)
platelet count (PLT)
white blood cells (WBC)
neutrophils (Neu)
lymphocytes (Lym)
monocytes (Mono)
eosinophils (Eos)
basophils (Baso)
large unstained cells (Luc)



CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: Parameters of clinical biochemistry were examined at the end of the treatment prior to or
as part of the sacrifice of the animals
- Animals fasted: Yes
- How many animals: all
- Following Parameters were examined:
alanine aminotransferase (ALAT)
aspartate-aminotransferase (ASAT)
alkaline phosphatase (AP)
creatinine (Crea)
total protein (TP)
albumin (Alb)
urea mmol/L
total bilirubin (TBIL)
total bile acids (TBA)
total cholesterol (Chol)
glucose (Gluc)
sodium (Na)
potassium (K)

URINALYSIS: Yes
- Time schedule for collection of urine: A urinalysis was performed with samples collected from all animals prior to or as part of the sacrifice of the animals. Additionally, urine colour/ appearance were recorded.
- Metabolism cages used for collection of urine: Not specified
- Animals fasted: Yes
- Following Parameters were examined
specific gravity
nitrite
pH-value (pH)
protein
glucose
ketone bodies (Ket)
urobilinogen (UBG)
bilirubin (BIL)
erythroctes (Ery)
leukocytes (Leu)

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: Once before the first exposure and once in the last week of exposure multiple detailed behavioral observations were made outside the home cage using a functional
observational battery of tests
- Dose groups that were examined: all
- Battery of functions tested: sensory activity / grip strength / motor activity / other:

IMMUNOLOGY: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes

Organ Weight
The wet weight of the selected organs listed below of all sacrificed animals was recorded as soon as possible. Paired organs were weighed together. Organ weights of animals found dead or euthanized for animal welfare reasons were not taken.

liver
uterus with cervix
kidneys
thymus
adrenals
thyroid/ parathyroid glands
testes
spleen
epididymides
brain
prostate, seminal vesicles and coagulating glands
pituitary gland
ovaries
heart


HISTOPATHOLOGY: Yes:
The below listed organs were examined histopathologically after preparation of paraffin sections and haematoxylin-eosin staining. Histopathological evaluations were done for all animals of C and HD groups and on the animals found dead or euthanised prior to the planned day of sacrifice. For terminally sacrificed animals, examinations were extended to animals of the lower dose groups when treatment-related changes were observed in the high dose group. For LD and MD groups, only organs and tissues showing changes in the high dose group were examined. Any gross lesion macroscopically identified in any animal was examined microscopically. Discoloration possibly due to the test item was evaluated in the organs
of all dose groups.

adrenal glands
all gross lesions
aorta
brain (incl. medulla/pons, cerebellar and cerebral cortex)
caecum
colon
duodenum
epididymides
eyes with optic nerve and Harderian gland
femur with knee joint
heart
ileum (including Peyer´s patches)
jejunum
kidneys
liver
lungs
lymph nodes (mandibular)
lymph nodes (mesenteric and axillary)
mammary gland area (male and female)
oesophagus
ovaries
oviducts
pancreas
pituitary
prostate and seminal vesicles with coagulating glands as a whole
rectum
salivary glands (sublingual, submandibular)
sciatic nerve
skeletal muscle
skin
spinal cord (cervical, thoracic and lumbar segments)
spleen
sternum (with bone marrow)
stomach
testes
thymus
thyroid gland including parathyroid glands
tongue
trachea
ureters
urinary bladder
uterus with cervix and vagina

Results and discussion

Results of examinations

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

There were no treatment-related adverse observations in either sex.
The following clinical findings were recorded during the course of the study:
Salivation and moving the bedding were observed in MD und HD animals, immediately
after administration with a roughly similar incidence among those groups. These clinical
findings, closely related to the administration procedure, indicate a local effect of the test
item formulation and are not considered as signs of adverse systemic effects. These
findings were not observed in males and females of the LD and C groups.
In addition, ataxia was recorded which lasted for one day in each female HD animal
after dosing. As this effect was observed only on one single observation day per animal
it is considered not to be toxicologically relevant.
With the exception of the moribund condition of animal no 80 (female HD) no other clinical observations were recorded.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

There was no treatment-related mortality in either sex.
Animal no. 11 (male LD) was found dead on day 77 and animal no. 80 (female HD) was
euthanized for ethical reasons on day 39.
Based on the histopathological examination, the cause of death of animal no 11 was
considered to be related to an accidental event during the dosing procedure which
resulted in flow of test item/corn oil mixture into the blood vessels. Although the site of
tissue injury was not located other findings in histology support that conclusion.
Animal no 80 was euthanised after being found in a moribund condition. Prior to this
event no severe clinical findings had been observed in this animal. Moreover, no
histological observation or any other finding could explain the death of the animal.
Therefore, this was considered a random event or alternatively an event during the
dosing procedure may have been the reason for the death of this animal.
Besides that, no mortality occurred in the control or any of the dose groups during the
treatment period of this study.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

both males and females, the mean body weight increased with the progress of the
study in all groups.
In HD males the mean body weights were lower compared to controls throughout the
study with statistically significant differences from day 71. On day 90 the difference in
body weight of the HD males compared to controls reached 10.96 %. This body weight
reduction is considered to be a moderate toxicological effect. Moreover this effect might
show dose dependency as in MD males a very slight reduction in body weight was
observed (e.g. -2.69% of C on day 90).
In females the mean body weights were within the expected historical range of variation
(historical range: 262 g to 203 g at the end of the treatment) with no considerable or
statistically significant differences between dose groups and control group during the
treatment period.
In accordance with body weight development, in females the weight gain was within the
expected historical range of variation with no considerable or statistically significant
differences between dose groups and control group during the treatment period.
In HD males the body weight gains were reduced or statistically significantly reduced
throughout the study. The overall change in body weight from day 1 to 90 was
statistically significantly lower compared to the controls with a value of -26.02%
(deviation vs C).
Differences in body weight gain of other test item groups versus control were not
statistically significant and are considered not to be toxicologically relevant.
Therefore these finding in HD males but not females represent toxicological effects on
body weight which are considered to be test item dependent and moderate in the extent.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

There were no treatment-related observations in either sex.
No considerable effect of IPETC on food consumption was found in any of the groups
between dose groups and control group during the treatment period.

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

There were no treatment-related observations in either sex.
In female LD and MD animals, the content of EOS was increased with mean values of
1.47% in LD and 3.15% in MD compared to 1.17 % in control. The differences were not
statistically significant and were mainly derived either from 1/10 (MD, no. 63) or from
2/10 (LD, no. 52 and 58) animals. Moreover this effect was not observed in the HD
group. Therefore the higher content of EOS in LD and MD females is considered to
represent isolated incidental findings which are not toxicologically relevant.
All other hematology parameters in both sexes were within the normal range of variation
of the historical control data for this strain and statistically significant differences
between dose and control groups are not assumed to be biologically relevant.
Blood coagulation was not affected by IPETC treatment in either sex. The observed
values were within the normal range of variation of the historical control data and there
were no toxicologically relevant differences compared controls.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Several liver parameters in both genders of the HD group were statistically significantly
different to the corresponding control. In HD males ALAT (176% of C) and AP (181% of
C) activities and TBIL levels (213% of C) were statistically significantly higher compared
to the control. In HD females AP activity (200% of C) and Chol level (139% of C) were
statistically significantly higher, while ASAT activity (76% of C) was slightly but
statistically significantly lower compared to the control.
These moderate findings are considered to be test item related and correlate with
histopathology observations in liver and with liver weights.
All other parameters of clinical chemistry were within the normal range of variation of
historical control data for this strain and any differences are not assumed to be
toxicologically relevant.

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

In HD males higher levels of protein were found in the urine. In 1/8 animals the level of
protein was 500 mg/dL in 2/8 it was 100 mg/dL and in 5/8 the level was 30 mg/dL. In
contrast in the control only 4/8 animals showed a protein concentration of 30 mg/dL in
the urine, all others were negative. That observation in HD rat males correlates with
tubular hyaline droplet formation found in histopathology, which is accompanied by
degeneration/single cell necrosis and excess accumulation of the protein alpha-2u
globulin. Hyaline droplet formation is male rat specific and therefore also the higher
protein content in the urine of HD males is considered not to be relevant for humans.
Male no. 18 (LD) showed elevated levels of BIL (4 mg/dL) and male no 37 (HD) showed
increased levels of Leu (approx 500 cells/μL). As not found in other animals of either
sex, both findings are considered to be isolated events with no toxicological relevance.
All other parameters of urinalysis in test item treated males and females at the end of
the treatment period were not considerably different to the corresponding control and
were within the normal range of variation of historical data for this strain

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

In females of the MD and HD group, the FOB observations conducted prior to onset of
treatment found higher mean values for rearing supported, lower mean values for
rearing not supported and lower mean body temperatures, each of these differences
were statistically significant compared to the C group. As those animals were randomly
allocated to the groups and observed prior to treatment, those findings are considered to
be random and could represent a background for this species.
All other FOB parameters analysed prior to dosing, even though a statistically significant
difference could be observed, were not substantially different across groups and are
considered to represent normal behavior.
At the end of the study the following parameters of the FOB were found to be statistically
significantly different from control in both males and females: Higher incidence of slight
salivation in MD (males 5.8, females 5.6, control 4.0) and HD (males 6.6, females 6.0,
control 4.0), lower spontaneous activity in MD (males 3.0 females 3.1, control 4.0) and
HD (males 2.3, females 2.7, control 4.0). In addition in MD and HD females, statistically
significantly lower rearing supported values (MD 1.9, HD 1.3, C 4.2) were recorded.
During the constant observation time the animals tend to either rear supported at the
wall of the arena or not supported within the arena. As the sum of the overall rearing of
the MD and HD females is not considerably different to the C group the observed
differences in activity levels are considered not to be treatment-related or toxicologically
relevant. The observed signs of salivation are not considered toxicologically relevant.
All other FOB parameters were within the normal range of variation of historical control
data for this strain. Any statistically significant differences between dose and control
groups are not assumed to be biologically relevant.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

moderately higher mean absolute and/or relative weight of liver was recorded, compared
to the corresponding control (mean organ/body +25% in males and +29% in females). In
histology this effect is associated with centrilobular hepatocellular hyperthrophy in both
genders and with centrilobular vacuolation (fatty change) in males but not females.
Moreover this finding correlates with clinical chemistry parameters indicating
hepatotoxicity in both genders of the HD group. Therefore the observed liver weight
changes are considered to be toxicologically relevant and caused by the test item.
The absolute and/or relative weight of the thymus in both genders was statistically
significantly smaller in MD and HD dose groups compared to the controls, as well as in
LD females. The effect was dose dependent with mean organ/body values of -8% (LD
males), -27% (MD males), -45% (HD males), and -27% (LD females), -39% (MD
females) and -47% (HD females) of the corresponding control group, respectively. There
was no correlation to the hematology parameters. In histology this finding correlates with
increased incidence and severity of thymic athrophy/involution in the MD and HD groups
and was considered to be related to responses to stressful condition associated with
daily administration of the test item. Moreover the absolute weight of the thymus in all
groups is within the historical range of control data (0.5021 g to 0.1640 g in males,
0.4579 g to 0.1585 g in females). Therefore this effect is not considered to be test item
related.
In males of the HD group statistically significantly lower absolute and relative spleen
weights were recorded with mean organ/body value of 17% below C group. In HD
females a statistically not significant decrease in mean organ/body value of 15% below
the C group was recorded. In hematology of both genders this effect did not correlate
with changes in WBC numbers. Also in histology no correlating microscopic findings
were recorded. Therefore this observation is not considered to be toxicologically
relevant.
Statistically significantly lower relative weight of thyroid/parathyroid was recorded for MD
males with mean organ/body weight of 21% below the corresponding control. This effect
was not recorded for HD males. A similar, albeit not statistically significant, effect was
observed for the MD and HD females with values of mean organ/body weight of 19%
(MD) and 21% (HD) below the corresponding control. In MD males and HD males and
females this effect correlates in histology with diffuse thyroid follicular cell
hypertrophy/hyperplasia and is considered to be secondary to liver effects, i.e. an
adaptive effect and not adverse in nature.
The relative kidney weight of HD males but not females was statistically significantly
higher with mean organ/body weight value of 17% above the C group. There was no
difference in absolute kidney weight in either sex. In males, this finding correlates with
increased incidence and severity of hyaline droplet deposition and tubular degeneration
and/or regeneration in histology which is related to alpha-2u globulin and not considered
toxicologically relevant for humans (see also histopathology phase report).
Consequently, the increased relative kidney weight in HD males is not considered a
toxicologically relevant adverse effect.
In HD males a statistically significantly lower absolute weight of prostata with seminal
vesicles and coagulation glands (2.2 g in HD vs 2.9 g in C) as well as a slight, but
statistically significant decrease in absolute brain weight (2.0 g vs 2.2 g in C) was
recorded. The weight of both organs is only very slightly lower than control values and
the differences lose statistical significance when calculated relative to the body weight of
the animals. Therefore those observations are considered not to be biologically relevant
effects.
The relative, but not absolute, heart weight of HD males was statistically significantly
higher compared to the control. However, the absolute organ weight is within the
historical range of control data and with a mean organ/body deviation of +9 % compared
the C group, this effect is very mild. Therefore it is considered not to be biologically
relevant.
In HD males the absolute, but not relative, brain weight was statistically significantly
lower compared to the control. The absolute weight of brain is within the historical range
of control data (2.41 g to 1.77 g) and was only -6.3% of the control weight. Therefore it is
considered not to be toxicologically relevant background variation of this strain.
The weight of ovaries in HD females was statistically significantly higher with a deviation
of +27% in the absolute weight of the control animals. However no correlation was
recorded in histology therefore this effect is not considered to be toxicologically relevant.
Besides, all organ weights were within the normal range of variation of historical control
data for this strain and differences between dose and control groups, regardless of
statistical significance, are not assumed to be biologically relevant.

Gross pathological findings:

no effects observed

Description (incidence and severity):

There were no toxicologically relevant treatment-related macroscopic observations in
either sex.
A few pathological changes were observed in single animals. Abnormal dark color in
lung was observed in male no 11 (LD) which was found dead on day 77. This finding
correlates with congestion (grade 1)of the lungs noted during histology. The thymus
showed abnormal dark color in male no. 32 (HD), which based on histology was
concluded to be related to blood leakage. This finding is considered to have occurred
during sectioning of the animal, i.e. a technical artefact.
The kidneys of 7/10 males from the HD group were reported to be abnormal in color,
marbled and pale and showed an increased incidence of tubular degeneration and/or
regeneration. In histology these findings were found to correlate with hyaline droplet
deposition within the cytoplasm of the tubular cells. Tubular cell degeneration/single cell
necrosis caused by accumulation of alpha-2u globulin-containing hyaline droplets is a
male rat specific phenomen which does not occur in humans (see also histopathology
phase report). Therefore this finding is not considered toxicologically relevant.
Fluid filled uterus with cervix was recorded in 2/10 control females, and 1/10 females of
each dosing group. In histology, this finding correlated with female cyclic change and
represents a normal background finding for this strain.

Neuropathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Under the conditions of this study, treatment-related histomorphologic changes were
observed in the kidney of males and in the liver, thyroid glands, thymus and adrenal
glands of both sexes.
In the kidney, increased incidence and severity of hyaline droplet deposition in the
proximal tubules, along with increased incidence of tubular degeneration and/or
regeneration, were observed in males of the MD and the HD groups. These findings
were not observed in any females.
Hyaline droplets represent an accumulation of secondary lysosomes within the
cytoplasm containing alpha-2u globulin that reversibly bind to the inducing xenobiotics
and/or metabolites. Tubular cell degeneration/single cell necrosis followed by
regeneration can be elicited secondarily by excess accumulation of this protein.
However, this process is a male rat specific phenomenon, and deemed not to be
relevant to human.
In the liver, centrilobular hepatocellular hypertrophy was recorded in both sexes of the
MD and HD groups, and in some high dose males (4/10), hepatocellular vacuolation
(fatty change) in the centrilobular region was also observed. In addition, diffuse thyroid
follicular cell hypertrophy/hyperplasia was observed in 2/10 males of the MD group and
both sexes of the HD group (5/10 and 4/10 in males and females, respectively).
The observed hepatocellular hypertrophy was considered to be of metabolic nature and
of adaptive character like an enzyme induction. In addition a relationship between the
liver enzyme induction and thyroid follicular cell hypertrophy/hyperplasia was considered
biologically plausible, and therefore the observed thyroid follicular cell change was
concluded to be a secondary and/or adaptive consequence of liver enzyme induction
and not an adverse effect.
In some high dose male rats showing centrilobular hepatocellular hypertrophy fatty
change was also observed indicating functional alteration or disturbances. Although
there was no further indicator of cellular injuries, such as necrosis, apoptosis, and/or
induced inflammation, the fatty change is a potential indicator of cellular degeneration
processes and therefore, a dose level of 300 mg/kg bw/day was considered a lowestobserved-
adverse-effect-level for the liver of male rats under the condition of this study.Under the conditions of this study, treatment-related histomorphologic changes were
observed in the kidney of males and in the liver, thyroid glands, thymus and adrenal
glands of both sexes.
In the kidney, increased incidence and severity of hyaline droplet deposition in the
proximal tubules, along with increased incidence of tubular degeneration and/or
regeneration, were observed in males of the MD and the HD groups. These findings
were not observed in any females.
Hyaline droplets represent an accumulation of secondary lysosomes within the
cytoplasm containing alpha-2u globulin that reversibly bind to the inducing xenobiotics
and/or metabolites. Tubular cell degeneration/single cell necrosis followed by
regeneration can be elicited secondarily by excess accumulation of this protein.
However, this process is a male rat specific phenomenon, and deemed not to be
relevant to human.
In the liver, centrilobular hepatocellular hypertrophy was recorded in both sexes of the
MD and HD groups, and in some high dose males (4/10), hepatocellular vacuolation
(fatty change) in the centrilobular region was also observed. In addition, diffuse thyroid
follicular cell hypertrophy/hyperplasia was observed in 2/10 males of the MD group and
both sexes of the HD group (5/10 and 4/10 in males and females, respectively).
The observed hepatocellular hypertrophy was considered to be of metabolic nature and
of adaptive character like an enzyme induction. In addition a relationship between the
liver enzyme induction and thyroid follicular cell hypertrophy/hyperplasia was considered
biologically plausible, and therefore the observed thyroid follicular cell change was
concluded to be a secondary and/or adaptive consequence of liver enzyme induction
and not an adverse effect.
In some high dose male rats showing centrilobular hepatocellular hypertrophy fatty
change was also observed indicating functional alteration or disturbances. Although
there was no further indicator of cellular injuries, such as necrosis, apoptosis, and/or
induced inflammation, the fatty change is a potential indicator of cellular degeneration
processes and therefore, a dose level of 300 mg/kg bw/day was considered a lowestobserved-
adverse-effect-level for the liver of male rats under the condition of this study.
Accelerated thymic atrophy/involution was recorded in both sexes of the MD and HD
groups. In addition, increased incidence of diffuse adrenocortical hypertrophy was
recorded in male and female animals of the HD group. There were no atrophic changes
in other lymphoid tissues, such as spleen, Peyer’s patches, and axillary and mesenteric
lymph nodes, of survivors. From the histomorphologic viewpoint, accelerated thymic
atrophy/involution and adrenocortical diffuse hypertrophy were deemed not to be
adverse under the condition of this study, rather these were considered to be
histomorphologic changes as responses to a stressful condition associated with daily
administration of the test item.
In the present study, one male of the low dose group and one female of the high dose
group were found dead or euthanized for ethical reasons during the treatment period. It
was concluded that either animals’ deaths were due to technical failure/accidental event.
The remainder of findings recorded was within the range of normal background lesions
which may be recorded in animals of this strain and age, or was incidental lesions that
were not related to treatment with the test item.
From the result of histopathology, the histomorphological no-observed-adverse effect
level (NOAEL) was established at 300 mg/kg bw/day in female rats, whereas in male
rats, the NOAEL was deemed to be at 100 mg/kg bw/day because of the presence of
centrilobular hepatocellular vacuolation (fatty change) indicating functional alteration or
disturbances in the HD group.
Accelerated thymic atrophy and adrenocortical diffuse hypertrophy were considered to
be histologic changes as responses to a stressful condition, and deemed not to be
adverse under the condition of this study. Enhanced hyaline droplet deposition as well
as the associated increased tubular degeneration/regeneration are a male rat specific
event, and are of no human relevance.

Histopathological findings: neoplastic:

not specified

Effect levels

1

Key result

Dose descriptor:

NOAEL

Effect level:

100 mg/kg bw/day (nominal)

Based on:

act. ingr.

Sex:

male

Basis for effect level:

histopathology: non-neoplastic

2

Dose descriptor:

NOAEL

Effect level:

300 mg/kg bw/day (nominal)

Based on:

act. ingr.

Sex:

female

Basis for effect level:

histopathology: non-neoplastic

Target system / organ toxicity

Key result

Critical effects observed:

yes

Lowest effective dose / conc.:

300 mg/kg bw/day (nominal)

System:

hepatobiliary

Organ:

liver

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

no

Applicant's summary and conclusion

Conclusions:

The histomorphological no-observed-adverse effect level (NOAEL) was established at 300 mg/kg bw/day in female rats, whereas in male rats, the NOAEL was deemed to be at 100 mg/kg bw/day based on the presence of centrilobular hepatocellular vacuolation (fatty change) indicating functional alteration or disturbances. In support of histopathological findings indicating liver toxicity at the high dose, moderate changes in liver markers of clinical chemistry and increased liver weights were seen. Both effects were shown in males and females in similar extent. A moderate body
weight loss was recorded for male animals. Considering the range of affected liver parameters, the overall NOAEL of test item for systemic toxicity in this study is considered to be at 100 mg/kg bw/day.

Executive summary:

A repeated dose 90 day oral toxicity study was performed in rats, orally administered with 30, 100, 300 mg/kg bw/day of the test substance in corn oil according to OECD Guideline 408. Based on histomorphological findings a NOAEL value of 300 mg/kg bw/day was determined in female rats, whereas in male rats, the NOAEL obtained was 100 mg/kg bw/day based on the presence of centrilobular hepatocellular vacuolation. In support of histopathological findings indicating liver toxicity at the high dose, moderate changes in liver markers of clinical chemistry and increased liver weights were observed. Both effects were shown in males and females in similar extent. A moderate body weight loss was recorded for male animals. Considering the range of affected liver parameters the overall NOAEL of IPETC for systemic toxicity in the current study study is considered to be at 100 mg/kg bw/day.