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Endpoint:
additional toxicological information
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
1988
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well documented publication which meest basic scientific principles.

Data source

Reference
Reference Type:
publication
Title:
The Incorporation of Monomethylethanolamine and Dimethylethanolamine in Fetal Brain Aggregating Cell Culture
Author:
Dainous F. and Kanfer J.N.
Year:
1988
Bibliographic source:
Neurochemical Research, Vol. 13, No. i, 1988, pp. 1-8

Materials and methods

Type of study / information:
Metabolism
Test guideline
Qualifier:
no guideline followed
GLP compliance:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
2-dimethylaminoethanol
EC Number:
203-542-8
EC Name:
2-dimethylaminoethanol
Cas Number:
108-01-0
Molecular formula:
C4H11NO
IUPAC Name:
2-(dimethylamino)ethanol
Details on test material:
[3H] dimethylethanolamine (DME)(24.9 x 10^6 cpm/µmol) was obtained from Aldrich Chemical Co. (Milwaukee, Wisc.)
Phosphatidylethanolamine, phosphatidyl-N,N-dimethylethanolamine (PDME), phosphatidylcholine (PC), sphingomyelin, lysophosphatidylcholine, CDP-DME and phosphoryl-DME (Ph-DME) chemically synthesized were used as standards to visualize the exposure.

Results and discussion

Any other information on results incl. tables

1. Time-course of [3H]DME incorporation into phospholipids and water-soluble products.

Fetal rat brain aggregating cultures were grown in medium containing labeled DME for different time intervals and the radioactivity incorporated into the lipids plateaued at about 48 hours.

a) The appearance of radioactivity in lipids and phosphatidyldimethylethanolamine (PDME) following incubation with [3H]DME was lin ear up to 24 hours and a plateau was maintained for the next 48 hours. There was minimal labeling of phosphatidylcholine (PC).

b) The magnitude of radioactivity present in the total water-solubles was considerably greater than that present in lipids. Maximum labeling of the water solubles occurred by 24 hours and there was about a 50% decrease of the radioactivity by 72 hours. The same pattern was observed with presumed phosphoryldimethylethanolamine (Ph-DME). The amount of radioactivity present in both DME and CDP-dimethylethanolamine was low and nearly constant throughout the experiment.

2. Effect of Varying the Concentrations of [3H]DME on the Labeling of Water- Solubles and Phospholipids.

The amount of radioactivity present in products in the presence of varying concentrations of [3H]DME was estimated after an 8 hour incubation. The appearance of [3H]DME in DME, Ph-DME and CDP-DME (Figure 4B) was linear with respect to the concentration of [3H]DME employed from 0.050 to 1 mM and an apparent saturation for PDME was reached at 1 mM. The rate and amount of labeling of PC was slight with both labeled precursors. There was relatively low labeling of the presumed CDP-DME.

3. Effect of Various Growth Media on MME and DME Incorporation.

Growth media:

a) Control = cells grown and incubated in DMEM

b) Met = cells grown and incubated in DMEM in L-methionine free medium

c) Ch = cells grown and incubated in DMEM in choline free medium.

In cells labeled with [3H]DME for 24 hours there was no significant difference between the 3 media in the labeling of DME, Ph-DME and presumed CDP-DME of the water-solubles. In contrast, the labeling of lipids and PDME was greater in cells grown in the absence of methionine or choline as compared to control. There was very little labeling of PC suggesting that the methylation activity was relatively low. When these cells were transferred into non radioactive medium, there was a rapid decrease in the quantity of radioactivity in DME, Ph-DME and CDP-DME during the first 24 hours. The PDME radioactivity was decreased by one half in 24 hours.

Applicant's summary and conclusion

Conclusions:
Dimethylaminoethanol was rapidly phosphorilated after it entered the cell and served as a precursor of phosphatidyldimethylethanolamine. The rate of incorporation of DMAE into phospholipids was slower than the incorporation into water-soluble products.
Executive summary:

Fetal rat brain aggregating cell cultures were exposed to varying concentrations of [3H]monomethylethanolamine (MME) and [3H] dimethylethanolamine (DME). The rate of labeling of water-soluble comPOunds was more rapid and the amount of radioactivity present was greater than in the lipids. After a 72 hour incubation in the presence of millimolar concentrations of these nitrogenous bases, the major water-soluble products were the phosphorylated form of the bases. Little label was associated with the free bases or their cytidyl derivate. In the phospholipids, 97% of the radioactivity was recovered in phosphatidylmonomethylethanolamine (PMME) and 3% in phosphatidyldimethylethanolamine (PDME) or 95% in PDME and 5% in phosphatidylcholine (PC) after growth in presence of [3H]MME and [3H]DME respectively. The rate of formation of the radioactive products increased as function of the concentration of the nitrogenous base added up to 4 mM, the highest concentration employed. There was no significant difference in the pattern of labeling with cells grown in media devoid of methionine or choline. The turnover of the water-soluble metabolites was more rapid than in the phospholipids where an apparent half-life of 24 hours was calculated.


This in vitro experiment is considered to be of little significance because the conditions does not reflect the situation as it occurs in animals and humans to a limited extent. Therefore these results are judged only very careful. The actual animal GLP guideline studies are considered to be most reliable and provide valuable insights which allow judging the hazard profile of DMAE.

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