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Toxicological information

Repeated dose toxicity: oral

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Administrative data

Endpoint:
sub-chronic toxicity: oral
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1988
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Test procedure in accordance with national standard methods with acceptable restrictions

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
1988
Report Date:
1988

Materials and methods

Test guideline
Qualifier:
no guideline followed
GLP compliance:
not specified
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
not specified
Details on test material:
no data

Test animals

Species:
monkey
Strain:
other: Macaca nemestrina
Sex:
female
Details on test animals and environmental conditions:
Subjects were five wild-born, adult, female
Macaca nemestrina obtained from Primate Imports
(Port Washington, NY). The monkeys were individually
housed in cages in rooms with 12-hr alternating on-off
light cycles. Their diet consisted of Purina Monkey Chow
in biscuit form, ad libitum, supplemented with fresh fruit
weekly and a highly caloric liquid diet during the most
severe stage of intoxication. Water availability was restricted
for approximately 20 hr prior to each testing session.
Monkey 022 was approximately three diopters myopic
and was corrected during testing with spectacle
lenses.

Administration / exposure

Route of administration:
other: oral in fruit juice or by intubation
Vehicle:
other:
Details on oral exposure:
Four of the monkeys were dosed orally 5 days per week (after daily vision testing) with 0.64 mM/kg of 2,5-hexanedione (Eastman-Kodak Co.) either in fruit juice or by intubation (and then supplemented with the same volume of fruit juice). Monkey 022 was dosed for 15 weeks, while monkeys 472, 468, and 564 were dosed for 17 weeks. A fifth monkey, 469, served as a control and was sham dosed with fruit juice for 17 weeks. Monkey 564 was terminated 3 weeks after the end of dosing, while the others were terminated at least 20 weeks after the end of dosing.
Analytical verification of doses or concentrations:
not specified
Details on analytical verification of doses or concentrations:
no data
Duration of treatment / exposure:
our of the monkeys were dosed orally 5 days per week (after daily vision testing) with 0.64 mM/kg of 2,5-hexanedione (Eastman-Kodak Co.) either in fruit juice or by intubation (and then supplemented with the same volume of fruit juice). Monkey 022 was dosed for 15 weeks, while monkeys 472, 468, and 564 were dosed for 17 weeks. A fifth monkey, 469, served as a control and was sham dosed with fruit juice for 17 weeks. Monkey 564 was terminated 3 weeks after the end of dosing, while the others were terminated at least 20 weeks after the end of dosing.
Frequency of treatment:
5 days per week
No. of animals per sex per dose:
our of the monkeys were dosed orally 5 days per week (after daily vision testing) with 0.64 mM/kg of 2,5-hexanedione (Eastman-Kodak Co.) either in fruit juice or by intubation (and then supplemented with the same volume of fruit juice). Monkey 022 was dosed for 15 weeks, while monkeys 472, 468, and 564 were dosed for 17 weeks. A fifth monkey, 469, served as a control and was sham dosed with fruit juice for 17 weeks. Monkey 564 was terminated 3 weeks after the end of dosing, while the others were terminated at least 20 weeks after the end of dosing.
Control animals:
yes, concurrent vehicle
Details on study design:
Visual testing, visuomotor testing and neurological changes, tissue pathology
Positive control:
no

Examinations

Observations and examinations performed and frequency:
Visual testing, visuomotor testing and neurological changes, tissue pathology
Sacrifice and pathology:
tissue pathology
Other examinations:
Visual testing, visuomotor testing and neurological changes
Statistics:
FData points obtained from behavioral
testing were considered statistically different from
controls if they were reduced 2 standard deviations below
the mean of the baseline data.

Results and discussion

Results of examinations

Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
no mortality
Mortality:
mortality observed, treatment-related
Description (incidence):
no mortality
Body weight and weight changes:
not specified
Food consumption and compound intake (if feeding study):
not specified
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
effects observed, treatment-related
Haematological findings:
not specified
Clinical biochemistry findings:
not specified
Urinalysis findings:
not specified
Behaviour (functional findings):
effects observed, treatment-related
Organ weight findings including organ / body weight ratios:
not specified
Gross pathological findings:
not specified
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
visual system
Histopathological findings: neoplastic:
not specified
Details on results:
Macaques exposed to 2,5-HD developed
axonal swellings in fiber tracts throughout the
nervous system, including prominent swellings
in distal optic tracts. This finding is characteristic
of the effects on macaques of other
axonotoxic chemicals such as acrylamide and
carbon disulfide. Unlike these other chemicals,
however, 2,5-HD produced no permanent
degeneration in the visual system. Measures
of visual function were consistent with
these morphological observations. Although
during 2,5-HD exposure, and for several
weeks after exposure, some monkeys showed
slight to moderate decreases in visual contrast
sensitivity, this deficit recovered completely
shortly after the end of dosing.
All 2,5-HD-exposed monkeys exhibited a
progressive motor dysfunction which began
about 3 months after the start of dosing, continued
to advance for 5 to 7 weeks after dosing
had been stopped, and then showed signs
of partial recovery. Peripheral nerve and spinal
cord of a monkey terminated shortly after
the end of dosing (No. 564) contained axonal
swellings and early degeneration in long
tracts, while those of monkeys terminated
months later were profoundly degenerated.
This pattern of neuronal susceptibility to
2,5-HD is similar to that reported in man.
Yamamura (1969), Korobkin et al. (1975)
and Rizzuto et al. (1980) have described motor
deficits lasting for months to years, but
only infrequent (usually transient) cases of visual
dysfunction, in humans exposed to 2,5-
HD precursors.

Effect levels

open allclose all
Dose descriptor:
other: motor dysfunction
Effect level:
ca. 0.64 mg/kg bw/day (nominal)
Based on:
test mat.
Sex:
female
Dose descriptor:
other: visual loss
Effect level:
ca. 0.64 mg/kg bw/day (nominal)
Based on:
test mat.
Sex:
female

Target system / organ toxicity

Critical effects observed:
not specified

Applicant's summary and conclusion

Conclusions:
Following a 20-week recovery period, we
found no permanent changes in contrast sensitivity
or degeneration in the visual system.

Dosing with 2,5-HD caused severe and
progressive degeneration in peripheral nerves
and long tracts of spinal cord. Motor changes,
including tremor and weakness of the limbs,
ataxia, and severe postural weakness, were
prominent. Limb weakness progressed from
distal to proximal muscle groups. Although
onset of motor changes was slightly earlier in
the upper limbs than in the lower limbs (possibly
due to more precise testing of the upper
limbs), the latter were eventually more severely
affected and never fully recovered
function even 5 months after dosing was
stopped. When cutaneous sensitivity was assessed
20 weeks after the end of dosing in one
monkey, it was also reduced, especially distally.
Executive summary:

Visual sensitivity and neurological status were monitored

in four female macaque monkeys dosed orally with 2,5-hexanedione (0.64 mM/kg, 5 days

per week) for 15 or 17 weeks. The first sign of toxicity was intention tremor seen after 3 months

of dosing. This was followed, a week later, by a moderate decrease in visual contrast sensitivity,

which returned to baseline 6 to 11 weeks after the end of dosing. Acuity and flicker resolution

were not disrupted. A progressive general weakness ensued for 5 to 7 weeks after dosing had

ended. Some slow recovery was seen, although the animals remained severely disabled 20 weeks

after dosing was discontinued. Pathologic changes were examined 3 weeks (one monkey) and

20 weeks (three monkeys) after dosing. Soon after the end of dosing, axonal swellings were

present throughout the distal optic tracts, peripheral nerves, and long tracts of the spinal cord.

Twenty weeks after dosing, there was no indication of degeneration in the retinocortical pathway.

Peripheral nerves showed widespread axonal loss, residual ongoing degeneration, and only

slight regeneration. Axon loss and gliosis were evident in distal dorsal columns, and to a lesser

extent, dorsal spinocerebellar and corticospinal tracts. These effects of 2,5-hexanedione on the

macaque differ from those found previously for two other axonotoxic compounds, acrylamide

monomer and carbon disultide, which caused marked permanent degeneration that was most

prominent in the visual system.