2-methylaminoethanol

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

no information given

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 Type:

publication

Title:

Unnamed

Year:

1984

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The chemical N-Methylethanolamine was vaporized and administered to approximately 15 pregnant rats in one to three concentrations for 7 hr/day on gestation days 7 to 15, and dams were sacrificed on day 20. Fetuses were individually weighed, and two-thirds of them were fixed in Bouin's solution and examined for soft-tissue anomalies. The other one-third were fixed in alcohol, stained with Alizarin Red and examined for skeletal defects.

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

2-methylaminoethanol

EC Number:

203-710-0

EC Name:

2-methylaminoethanol

Cas Number:

109-83-1

Molecular formula:

C3H9NO

IUPAC Name:

2-(methylamino)ethan-1-ol

Test animals

Species:

rat

Strain:

Sprague-Dawley

Remarks:

Virgin female and male Sprague-Dawley rats specified to be free of mycoplasma and Sendai virus and of internal and external parasites

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Wilmington, MA
- Weight at study initiation: males: > 300 g, females: 200 to 300 g
- Housing: Females were placed alone in 38 x 33 x 17-cm polycarbonate cages with filter tops. Bedding consisted of cleaned, heat-treated sawdust from a local supplier (Absorb-Dri, Tasty Foods, Cincinnati, OH)
- Diet (e.g. ad libitum): Purina Lab Chow was available ad libitum except when pregnant animals were in exposure chambers
- Water (e.g. ad libitum): Tap water was available ad libitum except when pregnant animals were in exposure chambers
- Acclimation period: Acclimatisation to a 12-hr light-dark cycle (lights on at 6 am) and to a temperature of 24 + 2°C for 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 24 + 2°C
- Humidity (%): not controlled, typically was in the range of 40 + 20%
- Air changes: Air flow through the chambers provided approximately four air changes per minute.
- Photoperiod (hrs dark / hrs light): 2-hr light-dark cycle (lights on at 6 am)

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposures were conducted sequentially in one or two chambers, with a third chamber for sham exposure of control subjects.
- Pregnant females were transported from the animal quarters to the inhalation chambers in their home cages with filter tops (Hazleton Systems, Aberdeen, MD). They were placed individually in 13 x 25 x 189-cm stainless steel wire mesh cages within exposure chambers.
- Control animals were placed in similar chambers for the same hours as the exposed animals; a pooled group of controls (N = 34) served as the comparison group for the first three chemicals examined. Another group of 15 controls served as the comparison group for the last two chemicals examined, as these groups were exposed at a later time (approximately 6 months later) than the first three.
- Air flow through the chambers provided approximately four air changes per minute.
- Exposures, as outlined above, were conducted 7 hr/day, and the animals were left in the chamber for at least one additional hour blow-off time after vapor generation terminated.
- Vaporization was achieved by bubbling air through the test item which was heated to approximately 40°C (for the higher concentrations). This vapor was then mixed with filtered room air to obtain the desired concentration and introduced into 0.5 m3 exposure chambers (Charles Spengler and Associates, Cincinnati, OH).

TEST ATMOSPHERE
- The concentration was continually monitored by a Miran I infrared spectrophotometer (Foxboro Analytical, South Norwalk, CT) with the concentration recorded hourly.
- Typically, two or three charcoal tube samples (silica gel tubes for 2- methylaminoethanol) were taken weekly from the chamber air for independent verification of the concentration by gas chromatograph.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentrations within the exposure chambers as measured by the infrared analyser were relatively close to those obtained from gas chromatography (please refer to corresponding table).

Details on mating procedure:

Males weighing over 300 g were placed individually into a cage with three females weighing 200 to 300 g. Vaginal smears were taken each morning, and the presence of sperm marked day zero of gestation.

Duration of treatment / exposure:

7 hours (animals were left in the chamber for at least one additional hour blow-off time after vapour generation terminated)

Frequency of treatment:

Exposures, as outlined above, were conducted 7 hr/day, and the animals were left in the chamber for at least one additional hour blow-off time after vapour generation terminated. They were then returned in their individual housing cages to the animal quarters, where water bottles were replaced. Exposures were conducted on gestation days 7-15.

Duration of test:

Exposures were conducted on gestation days 7-15.
15 days of gestation.
On day 20 of gestation, dams were sacrificed.

Doses / concentrations

Dose / conc.:

150 ppm

Remarks:

Doses / Concentrations: 150.0 +/- 15.2 ppm
Basis: other: vapour generated, by gas chromatography

No. of animals per sex per dose:

approximately 15 pregnant rats

Control animals:

yes

Details on study design:

Controls: three solvents were compared with a pooled group (N = 34) of sham-exposed controls, and the remaining two were compared with a group of 15 controls.

Examinations

Maternal examinations:

BODY WEIGHT: Yes
- Time schedule for examinations: weekly (i.e., on days 7, 14, and 21)

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes
- Time schedule for examinations: weekly (i.e., on days 7, 14, and 21)

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Time schedule for examinations: weekly (i.e., on days 7, 14, and 21)

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20


OTHER: any other signs of maternal toxicity were noted daily.

Ovaries and uterine content:

The entire uterus was removed and numbers of resorption sites (classified as early, middle or late) and live fetuses were determined.

Blood sampling:

Not examined

Fetal examinations:

Fetuses were serially removed, blotted of excess fluids, weighed, examined for external malformations and external sex determined.
One third of the fetuses were randomly selected and placed in 95% ethanol, and the remaining fetuses were placed in Bouin's solution. After being in the Bouin's solution for at least 1 week, these fetuses were examined for visceral abnormalities using Wilson's razor blade sectioning technique. The viscera were examined with the aid of a dissecting microscope. A representative sample of sections with malformations was identified by dam number and saved in 70% alcohol.

Fetuses were examined for skeletal defects by using a modified Staples technique. They were fixed in 95% alcohol, eviscerated and macerated in 2% KOH/Alizarin Red S solution. The fetuses were further macerated and cleared in the appropriate solutions of 2% KOH/glycerin (60:40, 40:60, 20:80) and stored in 100% glycerin. A crystal of thymol was added to each storage vial to retard fungal growth. Storage vials were individually identified by dam number.

Statistics:

Numbers of implants and proportions of resorptions were independently analysed by using a Kruskal-Wallis test corrected for ties, with subsequent multiple comparisons to determine where the differences occurred. Analysis of pup weights involved a mixed model analysis of covariance (with the number of live pups in the litter as the covariate) using maximum likelihood estimation. The model was mixed, since there was both within-litter and between-litter variation. Subsequently, pairwise comparisons between the pooled control group and each treatment group were performed. Incidence of total defects and of total variants were compared using a Kruskal-Wallis test with multiple comparisons with the litter as the experimental unit and the level of significance at p< 0.05.

Indices:

no information given

Historical control data:

no information given

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

not specified

Dermal irritation (if dermal study):

not examined

Mortality:

not specified

Body weight and weight changes:

not specified

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not examined

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

not specified

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Endocrine findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

not examined

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Other effects:

no effects observed

Description (incidence and severity):

see attachment

Details on results:

At 150 ppm N-Methylethanolamine (mean concentration from 28 silica gel tubes, one per day, analyzed in duplicate = 150.0 ppm), no maternal toxicity was observed.

Maternal developmental toxicity

Number of abortions:

not examined

Pre- and post-implantation loss:

not examined

Total litter losses by resorption:

not specified

Early or late resorptions:

no effects observed

Description (incidence and severity):

Litters with resorptions (%): 10(56)
Resorptions/litter: 0.7

Dead fetuses:

no effects observed

Description (incidence and severity):

Total live fetuses: 212
Live fetuses/litter: 11.8

Changes in pregnancy duration:

not examined

Changes in number of pregnant:

not examined

Other effects:

no effects observed

Description (incidence and severity):

Number pregnant/number mated: 18/24
Implants/dam: 11.9
Number (%) of litters with abnormal fetuses (Litter with at least one fetus having either skeletal or visceral anomalies): 7(39)

Details on maternal toxic effects:

At 150 ppm N-Methylethanolamine (mean concentration from 28 silica gel tubes, one per day, analyzed in duplicate = 150.0 ppm), no maternal toxicity was observed.

Effect levels (maternal animals)

Dose descriptor:

NOAEC

Effect level:

>= 150 ppm (nominal)

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

Remarks on result:

other: no adverse effects observed

Results (fetuses)

Fetal body weight changes:

no effects observed

Description (incidence and severity):

(see attachment)

Reduction in number of live offspring:

not specified

Changes in sex ratio:

not specified

Changes in litter size and weights:

not specified

Anogenital distance of all rodent fetuses:

not examined

Changes in postnatal survival:

not examined

External malformations:

no effects observed

Skeletal malformations:

no effects observed

Description (incidence and severity):

(see attachment)

Visceral malformations:

no effects observed

Description (incidence and severity):

(see attachment)

Other effects:

no effects observed

Description (incidence and severity):

(see attachment)

Details on embryotoxic / teratogenic effects:

At 150 ppm N-Methylethanolamine (mean concentration from 28 silica gel tubes, one per day, analyzed in duplicate = 150.0 ppm), no fetal toxicity was observed.

Effect levels (fetuses)

Dose descriptor:

NOAEC

Effect level:

>= 150 ppm (nominal)

Based on:

test mat.

Basis for effect level:

other: fetotoxicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Low vapor pressure also prevented our generating high concentrations of 2-MAE. At 150 ppm 2-MAE (mean concentration from 28 silica gel tubes, one per day, analyzed in duplicate = 150.0 ppm), no maternal or fetal toxicity was observed (see attachment).

Finally, the lack of teratogenic response of 2-methylaminoethanol was interesting and from a mechanistic or theoretical point of view, would merit follow up using a different route of exposure. At first glance, one might expect that its biotransformation would be similar to that of 2-ME. However, our results of no maternal or fetal toxicity at 150 ppm 2-MAE suggest that this may not be the case; since the amine is likely more lipidsoluble and less water-soluble than the methoxy portion, the absorption and excretion of the 2-MAE is likely quite different from that of 2-ME. Thus it would be of interest to see if a higher dose of 2-MAE would be teratogenic, though a route other than inhalation would be required, since the vapor concentration we used was near the saturation point.' This lack of teratogenicity at three times the concentration of a teratogenic level of its structurally similar glycol ether, points to a relatively strict structural requirement to produce teratogenic effects.

We observed that embryotoxicity decreases as alkyl chain length increases, similar to observations with testicular atrophy.

Applicant's summary and conclusion

Conclusions:

In this study N-Methylethanolamine showed neither maternal nor fetal toxicity effects.

Executive summary:

MMEA was vaporized and administered (near the saturation point) to 18 pregnant rats in one to three concentrations for 7 h/day on gestation days 7 to 15. The dams were sacrificed on day 20 of gestation. Fetuses were individually weighed, and two-thirds of them were fixed in Bouin's solution and examined for soft-tissue anomalies. The other one-third were fixed in alcohol, stained with Alizarin Red and examined for skeletal defects. As overall result for the substance MMEA, neither maternal nor fetal toxicity effects were found. No teratogenicity was observed. The NOAECs were ≥ 460 mg/m³, the highest dose tested for both, dams and fetuses.