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Toxicological information

Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: acceptable publication which meets basic scientific principles

Data source

Reference
Reference Type:
publication
Title:
Kurze Wissenschaftliche Mitteilung zum Stoffwechsel von Triäthylcitrat und Acetyltriäthylcitrat
Author:
Bruns, F.H. and Werners, H.P.
Year:
1962
Bibliographic source:
Klinische Wochenschrift, Jg 40, Heft 22, 15.November 1962

Materials and methods

Objective of study:
metabolism
Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
It was investigated, whether triethyl citrate and triethyl-O-acetylcitrate are hydrolysed by a) liver homogenates and b) blood serum.
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Type:
Constituent
Test material form:
other: liquid
Details on test material:
- Name of test material (as cited in study report): triäthylcitrat, acetyltriäthylcitrat
- Substance type: organic / tricarbocylic ester
- Physical state: liquid
Radiolabelling:
no

Test animals

Species:
other: not applicable as in vitro test was performed - human serum and human, rat and mouse liver homogenates
Strain:
other: not applicable
Details on test animals and environmental conditions:
not applicable

Administration / exposure

Route of administration:
other:
Vehicle:
not specified
Details on exposure:
The enzymatic hydrolysis was measured as the enzymatic turnover of the reaction product of ethanol with alcohol dehydrogenase (ADH) and Diphosphopyridinnucleotid (DPN) photo-optically. In addition, the formation of acid valences was monitored by measuring the hydrogen ion concentration with the glass electrode. As enzyme solution, aqueous solutions of liver homogenates and blood serum were used.
Duration and frequency of treatment / exposure:
not applicable
Doses / concentrations
Remarks:
Doses / Concentrations:
not applicable
No. of animals per sex per dose:
not applicable
Control animals:
other: not applicable
Positive control:
not applicable
Details on study design:
not applicable
Details on dosing and sampling:
not applicable
Statistics:
no data

Results and discussion

Preliminary studies:
no data
Main ADME resultsopen allclose all
Type:
metabolism
Results:
The esters triethyl citrate and triethyl-O-acetyl-citrate are hydrolysed by liver homogenate of human, rat and mouse origin, and by blood serum.
Type:
metabolism
Results:
Per mole of triethyl citrate 1 mol of citric acid and 3 moles of ethanol are formed during complete hydrolysis.
Type:
metabolism
Results:
Per mole of triethyl-O-acetylcitrate 1 mol of citric acid, 3 moles of ethanol and 1 mol off acetic acid are formed during complete hydrolysis.

Toxicokinetic / pharmacokinetic studies

Details on absorption:
not applicable
Details on distribution in tissues:
not applicable
Details on excretion:
not applicable

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
Per mole of triethyl citrate 1 mol if citric acid and 3 moles of ethanol are formed during complete hydrolysis. In case of triethyl-O-acetylcitrate a further 1 mol of acetic acid is build. These three metabolites are known to appear in intermediary metabolism, where they are oxidised in well-defined paths in the organism to CO2 and H20.

Any other information on results incl. tables

It was noted that triethyl citrate is hydrolysed enzymatically by liver homogenate .The pH decreases during the reaction time of 45 minutes continuously. Ethanol appears simultaneously, as shown by the hydrogenation of DPN with ADH. Liver preparations from human, rat and mouse as well as blood sera of various origins catalyse the reaction. In mice and rats the specific activities of liver and blood serum homogenates were shown to be 20:1. The most used final concentration of 1 *10E-3 m for triethyl citrate did not saturate the esterase with substrate. By varying the substrate concentrations, we obtained the following hydrolysis velocities, where the turnover magnitude was set arbitrarily for the concentration of 3 *10E-2 = 1.00m.
triethyl citrate concentration relative activity - human Serum
3* 10E-2 1
2* 10E-2 0,66
1* 10E-2 0,5
5* 10E-3 0,38

The affinity of triethyl-O-acetyl to the enzyme is lower than that of triethyl citrate. The hydrolysis curve shows an exponential course and the reaction rate is accelerated by the extent that the acetyl group is cleaved.
The question which of the known esterases catalyses the enzymatic hydrolysis of triethyl citrate and triethyl-O-acetyl is not easy to answer. The liver esterase, which is also present in the blood serum, seems not to be responsible for this. The pH optimum of the hydrolysis is 9.0, a property that characterizes the pancreatic lipase. Also the fact that chinine inhibits the hydrolysis of triethyl citrate at a concentration of 1 *10E-3m to 15% and twice the concentration inhibits to 30%, while atoxyl is without influence, speaks for the preference of triethyl citrate and triethyl-O-acetyl to the lipase. A decision of this question is possible only on the basis of studies on homogeneous enzyme preparations.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): bioaccumulation potential cannot be judged based on study results
This publication on the hydrolysis potential of triethyl citrate and triethyl-O-acetylcitrate was conducted using an in in vitro approach with liver homogenates and blood serum. Therefore no guideline has to be / was followed. The validity of the experiments is judged to be given. The esters triethyl citrate and triethyl-O-acetyl-citrate, used as plasticizers, are hydrolysed by liver homogenate of human, rat and mouse origin, and by blood serum to citric acid and ethanol or acetic acid, citric acid and ethanol, respectively.
Executive summary:

The substance of interest triethyl citrate (TEC) and additionally triethyl-O-acetylcitrate (ATEC) were subject to an investigation of their potential to hydrolyse in vitro (Bruns and Werners, 1959). It was investigated, whether triethyl citrate and triethyl-O-acetylcitrate are hydrolysed by a) liver homogenates and b) blood serum. The esters triethyl citrate and triethyl-O-acetyl-citrate, used as plasticizers, are hydrolysed by liver homogenate of human, rat and mouse origin, and by blood serum to citric acid and ethanol or acetic acid, citric acid and ethanol, respectively. Per mole of triethyl citrate 1 mol if citric acid and 3 moles of ethanol are formed during complete hydrolysis. In case of triethyl-O-acetylcitrate a further 1 mol of acetic acid is build. These three metabolites are known to appear in intermediary metabolism, where they are oxidized in well-defined paths in the organism to CO2 and H20.