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Basic toxicokinetics

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Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
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:
Is 2-Dimethylaminoethanol (Deanol) Indeed A Precursor Of Brain Acetylcholine ? A Gas Chromatographic Evaluation
Author:
Zahniser, N.R., D. Chou and I. Hanin
Year:
1977
Bibliographic source:
The Journal Of Pharmacology And Experimental Therapeutics Vol. 200, No. 3

Materials and methods

Objective of study:
distribution
Principles of method if other than guideline:
DMAE - more precisely that p-acetamidobenzoate salt of deanol - was administered i.p. to rats or mice and the Acetylcholine (ACh) levels in the brain or different brain sections were determined via a gaschromatigraphic method.
GLP compliance:
not specified

Test material

Constituent 1
Reference substance name:
p-acetamidobenzoate salt of deanol
IUPAC Name:
p-acetamidobenzoate salt of deanol
Details on test material:
In the following studies deanol was administered as its p-acetamidobenzoate salt (Deaner; deanol) which is marketed by Riker Laboratories, Northridge, Calif.; and, thus, all doses refer to the salt form of the drug.

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals or test system and environmental conditions:
Sprague-Dawley rats (male, 180-200 g) were obtained from Zivic-Miller Laboratories (Allison Park, Pa.).
Either Swiss-Webster mice from Hilltop Lab Animals, Inc. (Scottdale, Pa.) or Charles River mice from Charles River Laboratories, Inc. (Wilmington, Mass.) were used (either sex, 25-30 g) as specified in the text.

Administration / exposure

Route of administration:
intraperitoneal
Vehicle:
not specified
Details on exposure:
Route: injection
Duration and frequency of treatment / exposure:
one pretreatment via i.p. injection
Doses / concentrationsopen allclose all
Dose / conc.:
33.3 mg/kg bw/day
Remarks:
rats
Dose / conc.:
100 mg/kg bw/day
Remarks:
rats
Dose / conc.:
300 mg/kg bw/day
Remarks:
rats / mice
Dose / conc.:
900 mg/kg bw/day
Remarks:
rats / mice
Dose / conc.:
3 000 mg/kg bw/day
Remarks:
mice
No. of animals per sex per dose / concentration:
5 - 10 depending on the experiments
Control animals:
yes
Positive control reference chemical:
no data
Details on study design:
The concentrations of deanol, ACh and Ch were determined in mice or rats treated acutely with deanol (i.p.) or saline (an equivalent volume on a per weight basis; i.p.)
Brain dose-concentration studies. Whole brain levels of deanol, ACh and Ch were determined in female Swiss-Webster mice after pretreatment 30 minutes earlier with 33.3, 100, 300 or 900 mg/kg of deanol. A similar study was conducted using male Swiss-Webster mice pretreated 30 minutes earlier with 300, 900 or 3000 mg/kg of deanol.
Regional brain studies.
1) Male Swiss-Webster mice were pretreated with either 300 or 900 mg/kg of deanol 30 minutes prior to killing. Deanol and ACh concentrations were determined in whole brains from half of the treated group and in both striate from mice in the other half of the treated group.
2) Male rats were pretreated with 550 mg/kg of deanol and killed 15 minutes later. Concentrations of deanol and ACh were measured in whole brain as well as in the cortex, striatum and hippocampus from rats receiving identical treatment.
Brain time-course study. Swiss-Webster mice (either sex) were pretreated with 300 mg/kg of deanol 1, 2, 6, 8, 12 or 30 minutes before sacrifice with microwave irradiation. Control mice were sacrificed at identical intervals after receiving saline injections and also included a noninjected group reported as zero minutes. Whole brain levels of deanol, ACh and Ch were determined.
Plasma time-course study. Swiss-Webster or Charles River male mice were pretreated with 300 mg/kg of deanol 1, 2, 6, 8, 12, 15, 20 or 32 minutes before decapitation. A group of noninjected mice were included in the control group and, thus, constituted a zero minute pretreatment group. Only deanol levels were determined in the plasma of the treated and control mice.
Details on dosing and sampling:
The brain was removed from the skull, dissected when necessary at room temperature, weighed and immediately homogenized in ice-cold 0.4 N perchloric acid for 20 seconds.
In order to assay for deanol, ACh and Ch in the same tissue, each resulting supernatant was split into two separate samples. One sample (0.8 mL) was assayed for deanol, whereas the other sample (2.0 mL) was assayed for ACh and Ch plus deanol
Pooled brain supernatant (pH 4.2-4.4) from noninjected animals was used for the external standard samples to which known concentrations of deanol and preanol or ACh, Ch and PCh were added.
Buffer blank samples containing 2.5 mL ofpH 4 ammonium acetate buffer, instead of tissue supernatant, were also routinely included.

Brains from mice and rats killed by microwave irradiation were assayed for free deanol concentration. Also brains and plasma from mice killed by decapitation were analyzed for basal deanol levels. Peripheral tissues-liver, lung and heart-were taken from rats which had been killed by microwave irradiation; however, the peripheral tissues were not irradiated in these animals. These tissues were also assayed for deanol content.
1 mL heparinized blood was taken from the rats
Statistics:
two-tailed Student’s t test

Results and discussion

Preliminary studies:
no data

Toxicokinetic / pharmacokinetic studies

Details on absorption:
rapid distribution after i.p. administration
Details on distribution in tissues:
With increasing concentration of deanol administered, the percentage of the total amount of the drug recovered in the brain increased but never exceeded 0.2 % of the total administered dose. Even at the highest injected concentration, 3000 mg/kg, which approximated the LD50 in the mice, less than 0.2 % of the administered dose was found in the brain after the 30-minute pretreatment period. No sex difference in the response to deanol was observed.
The whole brain ACh levels of the animals treated with deanol over the entire dosage range did not differ significantly from control levels. The female mice did have a lower basal whole brain ACh level than that of the male mice.
Ch levels were also not significantly different from control levels in either group for any of the doses of deanol checked.

The regional distribution study in rats: whole brain, cortex, striatum and hippocampus
The deanol level in whole brain appears to reach a peak between 16 to 20 minutes after intraperitoneal injection of deanol.
From the plasma level curve for deanol, it is evident that deanol rapidly entered the systemic circulation after i.p. injection.
Details on excretion:
Assuming plasma deanol levels decay exponentially, an estimation of the plasma half-life for deanol from this study in the mouse is 15 minutes. There may be, however, a two-phase decline in plasma deanol levels with an early phase having a half-life <10 minutes and a later phase >15 minutes.

Metabolite characterisation studies

Metabolites identified:
not specified
Details on metabolites:
no data

Any other information on results incl. tables

Only the cation exchange resins Amberlite CG-120 (Stavinoha and Weintraub, 1974) and Dowex 50W-X8 consistently extracted greater than 80% of all three labeled tracers from the tissue samples. The two liquid extraction procedures extracted only 20% of the deanol, whereas the precipitation procedure extracted 50%. Consequently it was decided to use Dowex 50W-X8 resin in subsequent experiments.

The limit of sensitivity of this deanol assay was determined to be 300 pmol (picomol).

Applicant's summary and conclusion

Conclusions:
Interpretation of results: no bioaccumulation potential based on study results
No free endogenous deanol was detected in either whole brains or brain areas (cortex, striatum and hippocampus) from microwaved mice or rats. Whole brains removed from decapitated mice also contained no free deanol greater than 300 pmol (= 0.3 nmol). Even when the tissue extract assayed was made 3 times more concentrated than usual, no free deanol was found. Also, no endogenous deanol was detectable in the peripheral tissues analyzed. Plasma taken from untreated mice did not contain any free deanol.
Executive summary:

Zahniser and colleagues investigated in 1977, the role of DMEA as a possible precursor of acetylcholine. In their test, they could not prove that free deanol exists in the tissues examined in the unbound form or its concentration is below the sensitivity of the gas chromatographic assay used. Endogenous level of free deanol in the whole brain less than 1 nmol/g of tissue (wet weight). No significant elevation in mouse whole brain ACh levels after i.p. administration of DMAE could be found. Additionally there was no postmortem rise in the concentration of free deanol in the whole mouse brain. In other words, no deanol could be detected in any of the samples. On the other hand, free Ch levels rose and levels of ACh dropped significantly from control levels in brains left for 5 or 15 minutes at room temperature. Deanol, therefore, seems to be relatively nontoxic because of its high incorporation into endogenous lipid-forming pathways and its poor penetration into the central nervous system.

The primary source for de novo synthesis of Ch in the mammal is, in fact, the liver where phosphatidyldimethylaminoethanol has been shown to be the immediate precursor of phosphatidylcholine. Furthermore, evidence exists that exogenously administered deanol can also serve as a precursor of phosphoryl and phosphatidylcholine in the liver.

In conclusion, DMAE ist not likely to be a direct precursor of brain ACh in rodents. The only increase in ACh levels detected after acute deanol administration occurred selectively in mouse striatum following the massive dose of 900 mg/kg of this agent.

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