MTBA

Repeated dose toxicity: oral

Administrative data

Endpoint:

repeated dose toxicity: oral

Adequacy of study:

other information

Data source

Reference

Reference Type:

other: Body responsible for the test

Title:

Unnamed

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: 92/69/EEC, B.7

GLP compliance:

yes

Limit test:

no

Test animals

Species:

other: rat, Wistar Hsd Cpb:WU

Administration / exposure

Route of administration:

oral: unspecified

Vehicle:

other: 2% aqueous Cremophor EL

Details on oral exposure:

Method of administration:
gavage

Duration of treatment / exposure:

Test duration: 28 days

Frequency of treatment:

Dosing regime: 7 days/week

No. of animals per sex per dose:

Male: 5 animals at 0 mg/kg bw/day
Male: 5 animals at 10 mg/kg bw/day
Male: 5 animals at 100 mg/kg bw/day
Male: 5 animals at 1000 mg/kg bw/day
Female: 5 animals at 0 mg/kg bw/day
Female: 5 animals at 10 mg/kg bw/day
Female: 5 animals at 100 mg/kg bw/day
Female: 5 animals at 1000 mg/kg bw/day

Results and discussion

Results of examinations

Details on results:

Clinical observations:
Mortality

No animal died during the study. Therefore, survival was not
affected by the treatment with the test substance.


Clinical Observations

No clinical signs were observed in males up to 1000 mg/kg
and in females up to 100 mg/kg. At 1000 mg/kg 3 out of 5
females showed hair loss on day 9 or starting on day 25.
Piloerection was seen in one female at this dose level on
day 17. Since this finding was isolated the occurrence is
considered to be incidental. No other clinical signs were
observed in any animal.


Functional Observational Battery (FOB)

Reddened oral cavity was observed in 3 out of 5 females at
1000 mg/kg. Additionally, alopecia was observed in 3 females
at this dosage. Open field observations revealed a
reduction of the mean number of rearings in 100 and 1000
mg/kg females; the numbers were as following with increasing
dosages: 16.6 - 16.0 - 11.0 - 10.0.

A slightly reduced tail pinch response, which was observed
in males at 100 mg/kg is assumed to be of no toxicological
relevance, since dose dependency was absent.


Motor Activity (MA)

The activity determination over the entire 60 minute
observation period as well as the results of the 10-minute
intervals did not reveal any relevant effect on motor (MA)
and locomotor activity (LMA) in males up to 1000 mg/kg and
in females up to 100 mg/kg. In particular, up to these
dosages, there were no remarkable differences in the first
10-minute intervals, which are regarded as best indicator
for an increase or decrease in activity before the animals
habituate to a minimal level of activity.

In 1000 mg/kg females both MA and LMA were slightly
decreased compared to control (during 60 minute observation
period: 27% MA, 32% LMA; during the first 10-minute
interval: 18% MA, 23% LMA).


Body Weights

The mean body weights of treated males and females did not
differ relevantly from controls up to 100 mg/kg.

At 1000 mg/kg body weight gain was reduced in both sexes. In
males this effect was obvious in week 4, in females after 2
weeks of treatment; at these time points about 10% less in
both sexes compared to controls. At the end of treatment the
difference to control was still 10% in males and in females
decreased up to 17%.

The transient decrease in body weights in male and female
groups from day 23 to day 24 and from day 27 to 28 were
caused by the urinary collection and blood sampling periods.

Laboratory findings:
Hematology

Hematological investigation revealed the following
treatment-related slight changes on parameters on red and
white blood and on blood coagulation at 1000 mg/kg (partly
p>0.05):

Mean corpuscular hemoglobin concentration was increased in
males and reticulocyte count was decreased in both sexes.
Furthermore, the count of monocytes was slightly increased
in both sexes and of leucocytes, neutrophils, lymphocytes
and atypical leucocytes in males. Thromboplastin time
(HQuick) was increased in males and females.

Slightly decreased hematocrit value in males at 1000 mg/kg,
which was statistically significantly different from control
value, is considered to be of no toxicological relevance,
since the difference from control was low and all individual
values were within the 2s range of historical data.


Clinical Chemistry

Determination of enzyme activities in peripheral blood
revealed slightly increased values for aspartate
aminotransferase, alanine aminotransferase, and alkaline
phosphatase in both sexes at 1000 mg/kg (APh: p<=0.01).

Determination of substrates in blood samples showed
increased urea concentrations in males and total bilirubin
concentrations in both sexes at 1000 mg/kg. At this dosage
concentrations of triglycerides, protein, and albumin were
decreased in both sexes and of glucose in females (mostly
p<=0.01).

The determination of blood electrolytes did not evidence any
toxicologically relevant differences to control.


Urinalysis

Urinalysis revealed increased urine volume in males at 1000
mg/kg. Density and protein excretion (both p>0.05) as well
as protein creatinine ratio and pH were slightly lower in
this group compared to control.

The semi-quantitatively determined blood, bilirubin,
glucose, urobilinogen and ketone body concentrations were
unremarkable in all groups. The sediments showed no
abnormalities in males or females.

Effects in organs:
Ophthalmological Investigation

Ophthalmological investigation was performed on all animals
before the start of the study and on control and high dose
animals at the end of the treatment period. These
examinations at termination gave no evidence for treatment-
related effects.


Necropsy


Gross pathology revealed the following findings at 1000
mg/kg:

In almost all animals at this dosage an enlarged liver was
observed.

Two rats of each sex showed a size diminished thymus.

Prostate and seminal vesicles of two rats and uterus of one
rat were also diminished in size.

Three females were hairless in the abdominal region.

The spleen of all males and one female was reduced in size.

There were a few other findings recorded during necropsy.
However, they were evenly distributed amongst the groups
and, thus, are considered as spontaneous.


Organ Weights

In both sexes absolute and relative thymus (up to 51%) and
spleen (up to 31%) weights were reduced at 1000 mg/kg
(thymus weights in males: p>0.05).

Furthermore, absolute and relative liver weights were
statistically significantly increased in males and females
at 1000 mg/kg (up to 59%).

The determination of the weights of the other organs gave no
evidence for treatment-related effects.


Histopathology

The histopathological examination revealed the following
test substance-induced findings:

In the liver of all 1000 mg/kg rats a slight to moderate
cytoplasmic change of the perivascular hepatocytes was
noticed. This finding was characterized by a condensed
eosinophilic cytoplasm of the affected cells, which gave the
liver a coarse cobblestone pattern. Two males and females
each of this dose showed additionally a minimal to slight
hypertrophy of the interlobular hepatocytes. One 1000 mg/kg
animal of each sex had an increased number of single cell
necrosis. In almost all rats treated at 1000 mg/kg a minimal
to slight fat accumulation was noticed in the centrilobular
area.

In all males and three females dosed at 1000 mg/kg a slight
to marked atrophy of the thymus was noticed.

In the sternum and femur of almost all 1000 mg/kg animals an
increased grade of fatty replacement of the bone marrow was
seen.

In the male genital system, the testes of all 1000 mg/kg
males showed a minimal to moderate spermatide degeneration
in the seminiferous tubules. This was accompanied by
cellular debris in the epididymides of all males at this
dose and by an oligospermia in three of these males.
Furthermore, three of the affected males showed atrophy of
the prostate, the seminal vesicles and the coagulating
glands.

Two females at 1000 mg/kg showed a moderate atrophy of the
uterus. With respect to the ovaries of these rats, no
alteration was observed.

The submandibular glands of four rats of each sex treated at
1000 mg/kg showed a minimal to moderate atrophy of the
ducts.

Two 1000 mg/kg females showed a minimal to slight
hypertrophy of the follicular epithelium of the thyroid
gland.

In three females at 1000 mg/kg a minimal to moderate hair
growth arrest was noticed in the skin of the abdominal
region. In one animal this was accompanied by a slight focal
dermatitis.

All other findings were evenly distributed throughout the
dose groups and/or are known from control rats of that age
and strain and thus are considered to be incidental.

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

> 10 mg/kg bw/day (nominal)

Basis for effect level:

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

2

Dose descriptor:

NOEL

Effect level:

10 mg/kg bw/day (nominal)

Basis for effect level:

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

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Classified as: Not classified