Registration Dossier

Administrative data

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 meets 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

Reference
Name:
Unnamed
Type:
Constituent
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-monomethylethanolamine (PMME), phosphatidylcholine (PC), sphingomyelin, lysophosphatidylcholine, CDP-MME and phosphoryl-MME (Ph-MME) 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]MME incorporation into phospholipids and water-soluble products.

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

a) The principal labeled phospholipid was phosphatidylmonomethylethanolamine (PMME) which contained more than 80% of the total lipid bound radioactivity. Little label was associated with either phosphatidyldimethylethanolamine (PDME) or phosphatidylcholine (PC).

b) The magnitude of radioactivity present in the total water-solubles was considerably greater than that present in lipids and a plateau was reached by 24 hours. The majority of the radioactivity was present in a material chromatogramming like phosphorylmonomethylethanolamine (Ph- MME). There was less radioactivity associated with MME and the presumed CDP-monomethylethanolamine (CDP-MME).

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]MME was estimated after an 8 hour incubation. The amount of radioactivity present in PMME and Ph-MME continued to increase up to 4 mM [3H]MME, the highest concentration employed. The quantity of radioactivity in PDME and PC (Figure 3A) was slight at 4 mM MME suggesting that N-methyltransferase activity is relatively inactive under these conditions. There was a slight increase of the labeling of MME and CDP-MME with increasing base content in the medium.

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

Growth media:

a) Control = cells grown and incubated in DMEM (Dulbecco's Modified Eagle Medium).

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.

After labeling with [3H]MME for 24 hours, 25% of the isotope was recovered in lipids (Table I) and most was present in PMME. In cells grown in medium devoid of choline, the labeling of lipids and PMME was 145% and 150% respectively as compared to control values. There was no significant differences in labeling in cells grown in medium devoid methionine as compared to controls. The conversion of PMME to PDME or PDME to PC was very low in the three growth medium. The radioactivity associated with MME and Ph- MME was reduced in cells grown in the absence of methionine, after 1 day the radioactive medium was removed and replaced by DMEM medium containing non-radioactive MME and this resulted in a rapid decline in the radioactivity present in MME and Ph-MME by 2 days. The decrease was less pronounced with the phospholipids and at 2 days, PMME was still the major product.

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.