Acetaldehyde oxime

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1982

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The study is well documented. No data about GLP compliance.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1982

Report date:

1982

Materials and methods

Objective of study:

distribution

excretion

toxicokinetics

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Acetaldehyde oxime

EC Number:

203-479-6

EC Name:

Acetaldehyde oxime

Cas Number:

107-29-9

Molecular formula:

C2H5NO

IUPAC Name:

acetaldehyde oxime

Details on test material:

Acetalydehyde oxime (AAO)

Radiolabeled AAO:
- test material: AAO-(1,2-14C)
- specific activity: 101.6 μCi/mmol
- source: synthesized by Dr. William Boyle (Corporate R&D) from acetaldehyde(1,2-14C), supplied by New England Nuclear, and hydroxylamine
- radiochemical purity: > 98% (determined by HPLC)

Unlabeled AAO:
- test material AAO
- source: Sigma Chemical Company
- purity: > 99%

Radiolabelling:

yes

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Wilmington, MA, USA
- Mean weight of the groups: 200-273 g
- Individual metabolism cages: yes (Roth-type, Bellacour Company, Laurelton, NY, USA)
- Diet: ad libitum
- Water: ad libitum

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Remarks:

distilled water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Dosing solutions were prepared by diluting labeled AAO with unlabeled AAO, to yield a mixture containing the appropriate concentration and specific activity. The specific activity of the dosing solutions was verified by liquid scintillation spectroscopy.

Duration and frequency of treatment / exposure:

1 treatment

Doses / concentrations

Remarks:

Doses / Concentrations:
7.5, 75, 375 and 750 mg AAO/kg bw

No. of animals per sex per dose / concentration:

3

Control animals:

no

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, faeces, liver, kidney, testes, muscle, spleen, fat, blood
- collected and removed for analysis at:
urine: 4, 8, 24, 48, 72 and 96 h
feces: 24, 48, 72 and 96 h
- Other: air, collected at 0.5, 1, 2, 3, 4, 6, 8, 24, 48, 72 and 96 h

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on distribution in tissues:

At all dose levels, the highest concentrations of radioactivity were found in the liver and kidney. The concentration of radioactivity in the muscle and blood were generally similar to one another but lower than kidney and liver at all dose levels. The concentration of radioactivity in the fat, testes and spleen at the two lowest dose levels were also similar to concentrations in the muscle and blood. With higher exposure, however, the concentration of radioactivity in the spleen and testes was greater than the muscle and blood and the concentration of radioactivity in the fat was lower than in the muscle and blood. The relationship between exposure level and concentration of radioactivity (in all tissues except fat) was linear.

Details on excretion:

No clear-cut pattern or dose-related differences were apparent in the proportion of administered radioactivity excreted in the urine. However, in the feces, with increasing dose, the percent of administered radioactivity excreted appeared to decrease. This decrease between low and high exposure animals was significant to the 0.05 level (Student's t-test).
Urinary excretion accounted for 12-16% of the radioactivity given to the animals. HPLC analysis of the 4 h urine of animals given 375 mg/kg of 14C-AAO indicated the presence of both cis and trans isomers of the parent compound as well as 4 metabolites.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

HPLC analysis of the 4 h urine of animals given 375 mg/kg of 14C-AAO indicated the presence of both cis and trans isomers of the parent compound as well as 4 metabolites. About 31% of the radioactivity in the 4 h sample was found to be associated with the parent compound. By 16 h of dosing, however, no parent compound was found in the urine. Most of the radioactivity eluted from the column in fractions 8-10. Because of the nature of the reversed-phase column used in these studies, water-soluble compounds elute first followed in order by more hydrophobic components. The major peak detected in fractions 8-10 of the 16 h urine sample is therefore much more water-soluble than the parent compound and the other metabolites. This observation is in keeping with the normal pattern of metabolism, in which a xenobiotic is progressively biotransformed to more readily excretable water-soluble derivatives.

Any other information on results incl. tables

Elimination of radioactivity in the expired air

Regardless of the dose, 63 -68% of the total quantity of radioactivity administered was excreted as 14CO2 by 96 h. However, with increasing dose, at early times after exposure, a lesser percentage was excreted as 14CO2. For example, by 8 h after dosing, animals given 7.5 mg/kg had excreted 58% of the administered radioactivity as 14CO2, but animals given 750 mg/kg had excreted only about 20% as 14CO2. This delayed excretion effect might be the result of several factors, such as saturation of absorption from the gastrointestinal tract, saturation of transport systems or more likely, in view of biochemical evidence presented later, a saturation of the biotransformation process responsible for the production of CO2 from AAO.

The maximum rates of excretion of 14CO2 at all dose levels occurred during the initial 8 h after administration of 14CO2 -AAO and in all cases, except the lowest dose level, decreased monoexponentially thereafter. At the lowest dose level, the decrease in the rate of 14CO2 excretion was biphasic. When the maximum rates of 14CO2 excretion are plotted versus the quantity of 14C-AAO administered, a non-linear relationship is observed. The shape of the resulting curve verifies the earlier observation that at higher levels of administration, saturable processes are overwhelmed. This saturation phenomenon is a distinctive characteristic of enzyme-catalyzed reactions.

Effects of disulfiram pretreatment on the excretion of radioactivity in the expired air

Pretreatment with disulfiram resulted in significantly less (p<0.1, Student's t-test) excretion of 14CO2 during the initial 4 h after administration of 14C-AAO. At 6 h and after, however, no significant difference in the amount of radioactivity excreted as 14CO2 was observed. Since disulfiram is known to inhibit the enzyme aldehyde dehydrogenase, the decrease in the initial rate of 14CO2 excretion after disulfiram treatment is a strong indication that the two-carbon metabolism of AAO is via acetaldehyde and the tricarboxylic acid (TCA) cycle. The fate of the hydroxylamine portion of the AAO molecule is unclear at this time.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): low bioaccumulation potential based on study results Probably very low: That some of the administered radioactivity remained in the tissues (12-24%) is not suprising given the widespread incorporation of TCA products into normal biological constituents.
1. Acetaldehyde oxime (AAO) when administered to the whole animal, is rapidly hydrolyzed and the carbon portion of the molecule undergoes further oxidation in the tricarboxylic acid (TCA) cycle. The priarmy product of this aerobic metabolic pathway is carbon dioxide. Other products generated in this pathway are used widely in the synthesis of biological compounds ranging from sugars and amino acids to more specialized molecules such as cytochromes and hemoglobin. Products of the carbon metabolism of AAO can therefore be considered to be harmless, and would be handled no differently than compounds produced endogenously.

2. Elimination of carbon derived from AAO is primarily as exhaled carbon dioxide and proceeds very rapidly after adminitstration of the compound. The initial rate of excretion , however, is apparently dose-dependent and can be decreased significantly by administration of high levels of AAO.

3. Altough elimination was not complete, a relatively large portion of the administered radioactivity was excreted during the 96 h period of the studies reported here. That some of the administered radioactivity remained in the tissues (12-24%) is not suprising given the widespread incorporation of TCA products into normal biological constituents.

Executive summary:

Elimination of radioactivity from animals given ¹⁴C-acetaldehyde oxime (¹⁴C-AAO) was very rapid. The major route of elimination of radioactivity was as ¹⁴CO₂ in the expired air of the animals, accounting for 63 -68% of the radioactivity administered. Urinary excretion accounted for 11-16% of the radioactivity administered, and excretion in the feces was minimal (1 -3%). Elimination of radioactivity via the expired air and the urine was essentially complete by 24 h except for the animals given the highest dose of acetaldehyde oxime (AAO).

Elimination by all routes accounted for 76 -88% of the radioactivity given to the animals during the 4 -day study period. The highest tissue concentrations of radioactivity were found in the liver and kidney. The relationship between exposure level and concentration of radioactivity in all tissues studied, except fat, was linear. The concentration of radioactivity in the fat of animals given 750 mg/kg was not significantly higher than in animals given 375 mg/kg.

The total amount of radioactivity excreted by 96 h in the expired air, urine and feces was directly proportional to dose. However, a dose-related effect was noted in the initial rate of excretion of exhaled ¹⁴CO₂. With

increased dose, a decreased initial rate of excretion of ¹⁴CO₂ was observed. Since 63 -68% of the carbon-14 given to the animals as ¹⁴C-AAO was eliminated as ¹⁴CO₂, and since the initial excretion rate of exhaled ¹⁴CO₂ was affected by exposure level, it was reasoned that enzymes of the tricarboxylic acid (TCA) cycle are probably involved in the metabolism of this compound. To test this hypothesis, an experiment was performed in which animals were first pretreated with Disulfiram, which is an inhibitor of mammalian aldehyde dehydrogenase, and then given 0.75 mg/kg of ¹⁴C-AAO. Disulfiram pretreatment did result in a significantly reduced initial rate of excretion of ¹⁴CO₂, compared to unpretreated control animals.

This observation supports the hypothesis of TCA cycle involvement, since the aldehyde dehydrogenase is responsible for the oxidation of acetaldehyde to acetic acid which is subsequently oxidized to CO₂ via the TCA cycle.