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Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
1979
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Old study without much details, but reasonable description.

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
1979

Materials and methods

Objective of study:
absorption
excretion
metabolism
Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
L-aspartate was dosed by the oral and the ip route to 15-days-old mice and also to adult mice. Plasma levels and excreted CO2 were followed over the time after dosing.
GLP compliance:
not specified

Test material

Constituent 1
Chemical structure
Reference substance name:
Aspartic acid
EC Number:
200-291-6
EC Name:
Aspartic acid
Cas Number:
56-84-8
Molecular formula:
C4H7NO4
IUPAC Name:
aspartic acid
Details on test material:
L-aspartic acid was supplied by Aldrich Chemical Co., Milwaukee, Wis.
L-[U-14C]-aspartic acid was obtained from Amersham/Searle Corp. (Arlington Heights, Ill.) with a specific activity of 10 mCi/mmol and with a radioactive purity of 98 percent. Radiochemical purity was determined in three thin-layer chromatography solvent systems.
Radiolabelling:
yes

Test animals

Species:
mouse
Strain:
CD-1
Sex:
not specified
Details on test animals or test system and environmental conditions:
Charles River, CD-1 mice, weighing between 6-9 g (15-day-old) and 35-40 g (90-day-old, adult) were used in this study.

Administration / exposure

Route of administration:
other: oral by gavage and also intraperitoneal.
Vehicle:
not specified
Details on exposure:
Attempts to dissolve L-aspartic acid in distilled water at the required concentrations were unsuccessful. For this reason, monosodium L-aspartate was prepared by the equimolar addition of L-aspartic acid and sodium hydroxide.

Oral drug administration was accomplished by intubation with an 18 gauge, curved intubation needle, for adult mice, or Tygon tubing (0.64 mm, i.d. x 1.02 mm o.d.) for 15-day-old mice. Intraperitoneal (ip) administration was by means of a 26-gauge needle.
The volume of the injected amino acid solution was between 0.15 and 0.40 ml in all studies.
Nursing pups were removed from their mother 3 h prior to aspartate administration. Adult mice were fasted overnight.
Duration and frequency of treatment / exposure:
One application.
Doses / concentrations
Remarks:
Doses / Concentrations:
Solutions were prepared in distilled water having final aspartic acid concentrations of: 1 - 100 mg/ml (adults); or 0.3 - 33 mg/ml (15-day-old mice).
Radioactive dosing solutions were prepared as above and contained approximately 3 µCi/ml.
No. of animals per sex per dose / concentration:
5 mice for obtaining plasma from adult mice for each time point.
10 - 12 mice for obtaining plasma from 15-d-old mice for each time point.
3 mice for obtaining exhaled CO2.
Control animals:
other: saline was used as a negative control.
Positive control reference chemical:
No.
Details on dosing and sampling:
Blood Sampling: Adult Mice
Adult mice were sacrificed by decapitation and blood was collected from the wound into glass tubes containing heparin. Plasma was obtained by centrifugation and equal quantities of plasma from five mice were pooled at each time point. Plasma samples were stored frozen at -20 °C until subsequent analysis.

Blood Sampling: 15-Day-Old Mice
At each time point 10-12 15-day-old mice were anesthetized by ethyl ether inhalation; each animal was placed on its back and pinned to a cork board. A small pocket of skin was formed in each animal by making a right angle incision in the skin between the head and left foreleg. The subclavian vein was cut and blood was collected from the pocket into a plastic syringe (1 ml capacity) containing heparin. The hub of the syringe was sealed by heat, and plasma was obtained by centrifugation. The pooled plasma samples were stored frozen at -20 °C until subsequent analysis.

14CO2 Excretion
Immediately after [14C]-aspartate administration three mice were placed in a cylindrical glass metabolism cage, and 1.5 L/min of room air was drawn in series through the metabolism cage and through three gas washers, each of which contained 20 ml ethanolamine : methyl cellosolve (1 : 2, v/v). The washers were changed at 30 min intervals; their contents were pooled, and aliquots of the pooled samples were assayed for radioactivity.

Results and discussion

Main ADME resultsopen allclose all
Type:
absorption
Results:
15-d-old mice: Elevated plasma levels were only detected after 1000 mg/kg. Maximum plasma levels were found at 30 min p.a., for oral and i.p.. A rapid decline of the plasma level followed with a half-life of 0.21 h for i.p. and 0.15 h for oral.
Type:
absorption
Results:
Adult mice: Elevated plasma levels were only detected after 1000 mg/kg. Maximum plasma levels were found at 30 min p.a., for oral and i.p.. A rapid decline of the plasma level followed with a half-life of 0.19 h for i.p. and 0.26 h for oral.
Type:
excretion
Results:
Young mice: 65 - 85 % of the administered 14C was exhaled within 5 h p.a., for both routes and for the 3 doses. A reduced metabolisation was observed in the first 30 min p.a. in the high dose group.
Type:
excretion
Results:
Adult mice: 59 - 75 % of the administered 14C was exhaled within 5 h p.a., for both routes and for the 3 doses. A reduced metabolisation was observed in the first 30 min p.a. in the high dose group.

Toxicokinetic / pharmacokinetic studies

Details on absorption:
Plasma Concentrations of Aspartic Acid: 15-Day-Old Mice
An elevation in the plasma concentrations was present at 30 min and 60 min after the 1000 mg/kg dose. However, after a dose of 100 mg/kg only a minimal increase in the plasma concentration was observed. At the 10 mg/kg, the plasma concentrations at all times were similar to control values.
A similar plasma profile was observed after the ip administration of various doses of aspartate to 15-day-old mice. The plasma concentrations of aspartic acid 30 min after the 1000 mg/kg dose were 180 times greater than the plasma aspartic acid concentrations in mice given saline. It was again significant to note that plasma concentrations were only moderately increased at the dose of 100 mg/kg and not altered at all at a dose of 10 mg/kg.
Peak plasma concentrations of aspartic acid after the 1000 mg/kg dose were slightly greater after ip administration (718 µg/ml) than after oral administration (554 µg/ml). However, the areas under the oral and ip plasma concentration-time curves were 667 µg/ml/h and 628 µg/ml/h, respectively. The similarity in these values suggested that the bioavailability of L-aspartate was similar after both oral and ip administration to 15-day-old mice.
The plasma concentrations of aspartic acid in 15-day-old mice given aspartate ip (1000 mg/kg) declined with a half-life of 0.21 h, and this half-life after oral administration of the compound was 0.15 h.
These rapid disappearance rates reflected the rapid systemic metabolism of aspartic acid and partially accounted for the nearly constant plasma concentrations observed after lower doses of aspartic acid.

Plasma Concentrations of Aspartic Acid: Adult Mice
Dose-dependent increases in plasma concentrations of aspartic acid were not observed after either oral or ip administration of 10 or 100 mg/kg L-aspartate. However, after both oral and ip doses of 1000 mg/kg L-aspartate, elevated plasma concentrations of aspartic acid occurred.
After 1000 mg/kg L-aspartate, plasma concentrations of aspartic acid declined with half-lives of 0.19 h (ip) and 0.26 h (oral). These rates of disappearance of aspartate approximated decline observed after ip administration of 1000 mg/kg aspartate to 15-day-old mice (0.21hr).
The areas under the aspartic acid plasma concentration curves after oral and ip administration of 1000 mg/kg L-aspartate were 122 µg/mg/h and 891 µg/ml/h, respectively. These results suggested that the systemic availability of aspartic acid in adult mice was much less after oral administration than after ip administration. Therefore, this differed from that observed in 15-day-old mice in which the apparent systemic availability of aspartate after either oral or ip administration was similar.

See also the attachment.
Details on excretion:
14CO2 Excretion
15-day-old mice: Ca. 65 to 85 % of the administered 14C was exhaled as 14CO2 within 5 h p.a for both administration routes. Only minor differences in the rates of 14CO2 excretion were observed in the 10 and 100 mg/kg treatment groups. However, at the 1000 mg/kg dose, the rate of 14CO2 excretion was greatly reduced during the initial 30-min interval after both oral and ip aspartate administration. These results suggested that the animal's ability to oxidize the exogenous aspartate to CO2 was exceeded in the group of 15-day-old mice given 1000 mg/kg.
After 1 h the rates of conversion of aspartate to 14CO2 were not appreciably different among the three treatment groups. The decrease in the rate of 14CO2 production after a dose of 1000 mg/kg [14C]-L-aspartate corresponded to the time interval during which greatly elevated plasma concentrations of aspartic acid were observed.

Adult mice: Ca. 59 to 75 % of the administered 14C was exhaled as 14CO2 within 5 h p.a for both administration routes. A pronounced decrease in the rate of 14CO2 excretion occurred during the 0-30 min interval after 1000 mg/kg [ 14C]-L-aspartate as compared to the rates after 10 and 100 mg/kg, similarily as was observed in young mice.This decrease in the metabolism rate may have been partially responsible for the elevated plasma concentrations which also occurred at those times.

See also the attachment.
Toxicokinetic parametersopen allclose all
Toxicokinetic parameters:
Tmax: 30 min
Toxicokinetic parameters:
half-life 1st: 0.15 - 0.26 h
Toxicokinetic parameters:
other: excretion as CO2 within 5 h p.a.: 59 - 85 % of administered 14C.

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
CO2.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): no bioaccumulation potential based on study results
Executive summary:

Plasma concentrations of aspartic acid were determined after the oral or intraperitoneal (ip) administration of 0, 10, 100 and 1000 mg/kg L-aspartate to 15-day-old and adult mice.

Plasma levels before dosing were 3.5 - 5µg/mL in young mice and 3 to 7 µg/mL in adult mice.

Plasma concentrations of aspartic acid were elevated 30 min after 1000 mg/kg L­aspartate (oral or ip) to 15-day-old and adult mice. Thereafter, plasma concentrations rapidly declined exponentially (log concentration versus time) with a half-life of approximately 0.2 h in both age groups. Aspartic acid plasma concentrations were not appreciably altered after the oral or ip administration of 10 and 100 mg/kg L-aspartate.

 

After oral administration of 1000 mg/kg L-aspartate, the area under the plasma aspartic acid concentration curve was much greater for 15-day-old mice than that for adult mice. Since plasma concentrations of aspartic acid in both age groups declined with similar rates after ip administration of L-aspartate, this difference cannot be accounted for by differences in the systemic metabolism of aspartate. However the systematic availability of orally aspartic acid may differ with age because of differences in the rates of metabolism of aspartic acid in the gut.

 

The rates of 14CO2 excretion were also determined after the oral or ip administration of [14C]-L-aspartate to 15-day-old and adult mice. After the oral or ip administration of 10 and 100 mg/kg [14C]-L-aspartate, these rates were similar in both 15-day-old and adult mice. However at 1000 mg/kg, the rates of 14CO2 excretion, as percent of dose, were depressed during the first 30 min after both oral and ip administration of the compound to both age groups. This inability to metabolize high doses of aspartate at the same rates as lower doses, may contribute to the elevated plasma concentrations of aspartic acid in animals given 1000 mg/kg.