Sodium methanolate

Repeated dose toxicity: oral

Administrative data

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Methyl alcohol poisoning. II. Development of a model for ocular toxicity in methyl alcohol poisoning using the Rhesus monkey.

Author:

Martin-Amat, G., Tephly, T.R., McMartin, K.E., Makar, A.B., Hayreh, M.S., Hayreh, S.S., Baumbach, G., Cancilla, P.

Year:

1977

Bibliographic source:

Arch Ophthalmol 95: 1847-1850

Reference 2

Reference Type:

publication

Title:

Methanol poisoning: Ocular toxicity produced by formate.

Author:

Martin-Amat, G. et al.

Year:

1978

Bibliographic source:

Toxicol Appl Pharmacol 45: 201-208

Reference 3

Reference Type:

publication

Title:

Methyl alcohol poisoning IV. Alterations of the morphological findings of the retina and optic nerve.

Author:

Baumbach, G.L. et al.

Year:

1977

Bibliographic source:

Arch Ophthalmol 95: 1859-1865

Reference 4

Reference Type:

publication

Title:

Methyl alcohol poisoning.

Author:

Hayreh, M.S. et al.

Year:

1977

Bibliographic source:

Arch Ophthalmol 95: 1851-1858

Reference 5

Reference Type:

publication

Title:

No information

Author:

Martin-Amat, G. et al.

Year:

1977

Bibliographic source:

Metab Syst 2: 419-428 (cited in DGMK 1982)

Reference 6

Reference Type:

publication

Title:

Methanol poisoning I. The role of formic acid in the development of metabolic acidosis in the monkey and the reversal by 4-methylpyrazol.

Author:

McMartin, K.E. et al.

Year:

1975

Bibliographic source:

Biochem Med 13: 319-333

Materials and methods

Principles of method if other than guideline:

Test model in monkeys for methanol-induced occular toxicity after short-term exposure to characterize the toxicity syndrome and histological manifestations.

GLP compliance:

no

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Methanol

EC Number:

200-659-6

EC Name:

Methanol

Cas Number:

67-56-1

Molecular formula:

CH4O

IUPAC Name:

Methyl alcohol

Test animals

Species:

monkey

Strain:

other: Macaca mulatta

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: 2.6-4.4 kg

Administration / exposure

Route of administration:

other: nasogastric tube

Vehicle:

water

Details on oral exposure:

VEHICLE
- Concentration in vehicle: 20% (w/v)
- Amount of vehicle (if gavage): 10 mL/kg

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

approx. 1.5 to 6 days

Frequency of treatment:

variable

Doses / concentrations

Dose / conc.:

2 000 mg/kg bw/day (nominal)

Remarks:

initially 2000 mg/kg, thereafter 500 mg/kg at variable frequencies and time points (exception: one animal 1000 mg/kg at 44 and 72 h and 2000 mg/kg at 144 h)

No. of animals per sex per dose:

6 males in total

Control animals:

other: internal/same animal prior to treatment

Details on study design:

- Dose selection rationale: A high initial dose (2000 mg/kg) was followed by lower doses depending on the animal´s acidotic response in blood. Experience had told (McMartin et al., 1975) that after a single dose of 3000 mg/kg bw, in general, the animals died within 20 to 30 h without demonstrating ocular abnormalities. (Martin-Amat et al., 1977).

Positive control:

not applicable

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes (McMartin 1975, 3000 mg/kg)
- Time schedule: Continuously from application until death (approx. 33 h after application)
- Cage side observations included: clinical signs, mortality


DETAILED CLINICAL OBSERVATIONS: Yes: cerebrospinal fluid pressure in cerebellomedullary cistern by cisternal puncture (2 animals)
- Time schedule: not specified


OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: one week before and during the course of intoxication, not further specified
- Dose groups that were examined: all animals: stereoscopic color fundus photography, fluorescein fundus angiography, pupillary light reflex,


HAEMATOLOGY: No


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: prior to treatment and throughout the course of the study
- Animals fasted: No data
- How many animals: all
- Parameters examined: blood pH, bicarbonate levels, methyl alcohol, blood formate (cerebrospinal fluid: 2 animals), pO2, pCO2


URINALYSIS: No

Sacrifice and pathology:

GROSS PATHOLOGY: No
HISTOPATHOLOGY: Yes (light and electron microscopic studies of neuronal tissues and nerve fibres associated with the eyes: retina, optic nerve heads, optic nerves of 2 control and 3 treated animals)

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Under methanol treatment acc. to this test design, formate levels were between min. 7.2 and max. 14.4 mEq/L in blood and 7.9 to 13.9 mEq/L in cerebrospinal fluid, blood bicarbonate min. 4.0 and max. 10.2 mEq/L, and blood pH min. 7.13 and max. 7.28. Methanol levels ranged from 1540 to 2840 mg/L (Martin-Amat et al., 1977).

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

effects observed, treatment-related

Description (incidence and severity):

The only detectable ocular change was optic disc edema (of the optic papilla). The primary sites of ocular injury were the optic nerve heads and the anterior segment of the optic nerve rather than the retinal ganglion cells themselves. In all eyes with optic disc changes, pupils were dilated and reacted poorly to light.

Haematological findings:

not examined

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Neuropathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

All six animals developed fundus changes at the head of the optic nerve (optic disc) within 43 to 171 h after methanol ingestion, expressed as intraaxonal swellings (Hayreh et al, 1977). Electronmicroscopic studies revealed swelling of the nerve fibers with an accumulation/clustering of swollen mitochondria in the optic nerve head being maximally in the lamina cribrosa region. Furthermore, in the retrolaminar and intraorbital optic nerve, swelling of astrocytes was prominent as well as swelling of the cytoplasm of the oligodendroglial cytoplasm in contact with the axons (Baumbach et al., 1977). Alterations were not observed in the retina itself: the ganglion cells of the retina were intact with only minimal swellings of the mitochondria and loss of cristae. But these findings were also present in the control tissue (Baumbach et al., 1977).

Histopathological findings: neoplastic:

not examined

Effect levels

Key result

Dose descriptor:

NOAEL

Remarks on result:

not determinable

Remarks:

no NOAEL identified

Target system / organ toxicity

Key result

Critical effects observed:

yes

Lowest effective dose / conc.:

2 000 mg/kg bw/day (nominal)

System:

eye

Organ:

other: optic nerve

Treatment related:

yes

Applicant's summary and conclusion

Conclusions:

While acute methanol toxicity in monkeys (after a single dose) does not yield ocular signs, repeated dosing succeeded in producing ocular lesions (Martin-Amat et al, 1977). The only detectable ocular change was optic disc edema (of the optic papilla) which was similar to that seen in raised intracranial pressure in humans, but without this pressure after methanol (Hayreh et al, 1977). The primary sites of ocular injury were the optic nerve heads and the anterior segment of the optic nerve rather than the retinal ganglion cells themselves. It appears that interference with oxidative phosphorylation causes mitochondrial damage, thus disruption of active axoplasmic flow in the retrolaminar optic nerve (Baumbach et al., 1977; Hayreh et al., 1977). [note: In humans it has been hypothesized that optic atrophy, which often follows acute methanol intoxication, is secondary to injury of the retinal ganglion cells.]. Mechanistically, there is a close causal relationship between the prolonged increase in formic acid from methanol and the development of optic edema. Similar effects can be produced by intravenous administration of formate without acidosis (Martin-Amat et al., 1978).