Hexanedioic acid, di-C16-18 (even numbered) alkyl esters

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Basic data given.

Data source

Reference

Reference Type:

publication

Title:

ELIMINATION, DISTRIBUTION AND METABOLISM OF DI- (2-ETHYLHEXYL)ADIPATE (DEHA) IN RATS

Author:

Takahashi et al.

Year:

1981

Bibliographic source:

Toxicology, 22, 223-233.

Materials and methods

Objective of study:

distribution

excretion

metabolism

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Principles of method if other than guideline:

The excretion, retention, distribution and metabolism of di-(2-ethylhexyl) adipate (DEHA) have been studied in the rat.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Bis(2-ethylhexyl) adipate

EC Number:

203-090-1

EC Name:

Bis(2-ethylhexyl) adipate

Cas Number:

103-23-1

Molecular formula:

C22H42O4

IUPAC Name:

bis(2-ethylhexyl) adipate

Details on test material:

Non-radioactive test material:
- Name of test material (as cited in study report): Di-(2-ethylhexyl)adipate (DEHA)
- Source: Tokyo Kasei Co., Japan
- Analytical purity: highest purity commercially available.

Radioactive test material:
- Name of test material (as cited in study report): [I4C] 1,6-DEHA
- Radiochemical purity (if radiolabelling): 99% pure
- Specific activity (if radiolabelling): 1.01 mCi/mmol

MEHA and mono-(2-ethylhexyl)succinate (MEHS) were synthesized by conventional methods and the identities were confirmed by mass spectrometry
and elementary analysis. Mono-(2-ethylhexyl)phthalate (MEHP) was prepared according to a procedure described previously.

Radiolabelling:

yes

Remarks:

[14C]DEHA

Test animals

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source:
- Age at study initiation: no data
- Weight at study initiation: 150 - 270 g
- Fasting period before study: overnight
- Housing: After dosing, each rat was kept in a metabolic chamber and allowed free access to food and water.

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

DMSO

Details on exposure:

VEHICLE
- Justification for use and choice of vehicle (if other than water): test substance was given as a saturated solution in dimethyl sulfoxide (DMSO) - because of its poor solubility in water.

Duration and frequency of treatment / exposure:

Elimination study: 2 days
Distribution study: up to 96 hours
Metabolite study: up to 6 hours

Doses / concentrations

Remarks:

Doses / Concentrations:
Elimination and Distribution studies: 500 mg/kg of [14C]DEHA as a saturated solution in dimethyl sulfoxide (DMSO)
Metabolite study: 100 mg of non-labelled DEHA as a 5% solution in DMSO

No. of animals per sex per dose / concentration:

Elimination study: 2 rats
Distribution study: 3 rats per group
Metabolite study: 5 rats

Control animals:

yes

Positive control reference chemical:

No

Details on dosing and sampling:

ELIMINATION STUDY
Rats were given (by stomach tube) a dose of 500 mg/kg of [14C]DEHA (1.26 µCi/rat) as a saturated solution in dimethyl sulfoxide (DMSO) because of its poor solubility in water. After dosing, each rat was kept in a metabolic chamber and allowed free access to food and water. Respiratory carbon dioxide, urine and faeces were collected over 2 days. Respiratory carbon dioxide was trapped in ethanolamine and a portion of the trap was mixed with a toluene based scintillator. An aliquot of the urine was dissolved in a dioxane-scintillator. The faeces were pulverized and samples were combusted to 14CO2 which was trapped in an ethanolamine-scintillator.

DISTRIBUTION STUDY
Three rats in each group were given a single oral dose of [14C]DEHA under the same conditions as above. The animals were sacrificed at various time intervals after dosing. Blood samples were taken by heart puncture from anaesthetized animals and aliquots were oxidized to 14CO2 for measuring radioactivity. Organs and tissues were removed, dried in air and pulverized. Samples were oxidized to 14CO2 for measuring radioactivity. Only the intestine was digested in an 0.5 N NaOH solution under reflux and an aliquot was transferred to a dioxane-scintillator. The scintillators used were the same as previously reported. Radioactivity measurement was made with an LSC-651 scintillation counter (Aloka).

METABOLITE CHARACTERISATION STUDIES
The rats were given 100 mg of non-labelled DEHA as a 5% solution in DMSO which was warmed to about 40°C to assist solution. A control group of rats received an equal volume of DMSO in place of DEHA. At 1, 3 and 6 h after dosing, the rats were killed. Collected urine and blood were diluted with water and the latter was further sonicated. After decapitation of rats, liver, pancreas, stomach and small intestine were removed and frozen immediately. Cold organs were chopped finely and homogenized in about 10 vols. of cold saline solution with a Waring blender. These samples were extracted twice with diethyl ether after acidification to about pH 1.5 with HCl saturated with NaCl. After evaporating to a small volume with caution, the ether extracts were methylated with diazomethane or trimethylsilylated with TMS-HT and the metabolites were determined by gas-liquid chromatography (GLC), using acenaphthene, trans-stilbene and n-octadecane as internal standards. A Shimadzu GC-4CM gas chromatograph equipped with hydrogen flame ionization detector was used and the conditions used were: glass column (3 mm I.D. × 2 m) packed with (a) 5% DEGS on 60--80 mesh Chromosorb W, (b) 3% OV-275, (c) 3% E-301; flow rate of nitrogen gas, 40 mL/min; injection port temperature, 190°C; column temperature, 180°C.

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on distribution in tissues:

Of all the tissues examined, relatively high levels of activity appeared in the liver, kidney, blood, muscle and adipose tissue apart from the stomach
and intestine. All other tissues contained very little residual radioactivity. In liver, kidney, testicle and muscle, the amount of residual radioactivity
reached a maximum in the first 6 - 12 h and reduced to less than 50% at 24 h. In other tissues the radioactivity declined with time after 6 h. The
liver showed a greater amount of activity than the kidney, but had the same order of values as the kidney when compared in terms of specific
activity. The blood contained about 1% of the radioactivity after 6-12 h and then decreased to undetectable levels by the end of 2 days.
It is also evident that total radioactivity in the tissues examined was about 10% after 24 h of dosing and it decreased to about 2% and 0.5% after 48 h and 96 h, respectively. From these results, it can be concluded that the elimination of radioactivity from tissues and organs is very rapid and there is no specific organ affinity under our experimental conditions.

Details on excretion:

Excretion within 24 h amounted to 86% of the administered dose and almost all the dose was excreted in 48 h. The greater part of the excretion was recovered in breath and urine; excretion in faeces was small. Although variation between 2 animals was great, the appearance of 14CO2 in breath reached a maximum within 24 h, suggesting that metabolic change of DEHA began soon after the administration of the labelled compound.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

In urine, adipic acid (AA) appeared in a short time and its excretion reached 20-30% of the administered dose within 6 h and neither mono-(2-ethylhexyl)adipate (MEHA) nor DEHA was detected. Also in blood, only AA appeared and the level was less than 1% at any time interval.
In the stomach when DEHA given by tube, AA and MEHA were found along with DEHA. The concentration of DEHA declined very rapidly with time accompanied by appearance of MEHA and AA with a peak value at 3 h.
In the intestine, the amount of AA increased with time, but MEHA was not found.
In liver, only AA was found and it increased to a range of 2-3% with time.
From these results, it is clear that orally ingested DEHA is rapidly hydrolyzed to MEHA and AA which is the main intermediate metabolite.
Mono-(2-ethylhexyl)succinate (MEHS), an expected metabolite, was not found in any sample of tissue and urine.

Any other information on results incl. tables

In vitro hydrolysis experiments:

In vitro hydrolysis of DEHA and MEHA was investigated using 3 kinds of tissue preparations from liver, pancreas and small intestine. DEHA was readily hydrolyzed to MEHA or AA by each of these preparations. The rate of formation of AA from DEHA was approximately the same for all tissue, whereas the appearance of MEHA was rapid only with pancreatic tissue, and for intestine it was negligible. The rate of hydrolysis from MEHA to AA was higher than that from DEHA, and the highest activity was found in the intestinal preparation.

Summary:

The excretion, retention, distribution and metabolism of di-(2-ethylhexyl) adipate (DEHA) have been studied in the rat. After oral administration of [14C]DEHA, almost all the dose was excreted within 48 h, predominantly in the urine and as respiratory carbon dioxide. The faecal excretion was low. There was no evidence of the accumulation of radioactivity in any organs or tissues. Adipic acid (AA) was found to be the main urinary metabolite; it was also detected in the digestive tract, blood and liver. In vitro, DEHA was hydrolyzed at a significant rate by tissue preparations prepared from liver, pancreas and small intestine of the rat. These results suggest that orally administered DEHA is rapidly hydrolyzed in the body to form AA without any accumulation of mono-(2- ethylhexyl)adipate (MEHA).

Table 1: APPEARANCE OF AA AND MEHA AFTER THE ORAL ADMINISTRATION OF DEHA TO RATS

Rat	Time (h)	% of administered dose
		Urine AA	Blood AA	Stomach			Intestine AA	Liver AA
				AA	MEHA	DEHA
1	1	5.7		3.9	8.7	57.4	2.0	0.2
2	3	5.6	0.5	8.9	6.3	43.2	4.4	1.7
3	3	1.5	0.5	9.8	11.6	45.6	13.8	0.5
4	6	23.0	0.7	3.3	4.5	5.6	19.7	2.1
5	6	29.5	0.6	3.6	1.0	2.9	19.1	3.3

 

Applicant's summary and conclusion

Conclusions:

Interpretation of results: no bioaccumulation potential based on study results