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Basic toxicokinetics

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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: see 'Remark'
Remarks:
The metabolism of succinonitrile was studied with radiolabelled 14C-succinonitrile. The radiolable was exclusively in both cyano-groups. The study provides information on the absorption, metabolism and excretion of succinonitrile and metabolites. The distribution in the body is not discussed, but this can be derived from the reported excretion time of the parent compound succinonitrile and from the physico-chemical properties.

Data source

Reference
Reference Type:
publication
Title:
Cumulative excretion of succinonitrile in mice
Author:
Curry SH
Year:
1975
Bibliographic source:
Biochemical Pharmacology 24, 351-354, 1975.

Materials and methods

Objective of study:
absorption
excretion
metabolism
toxicokinetics
Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 417 (Toxicokinetics)
Version / remarks:
OECD Guideline 417 was not adopted at the time of the study
Deviations:
yes
Remarks:
Distribution in the body has not been explicitly investigated. However, the kinetics of the excretion of the parent indicate, that the distribution volume is equal to that of the free body water.
Principles of method if other than guideline:
Mice were given [14C]succinonitrile intraperitoneally at a dose of 25 mg (50 µCi) per kg BW. Cumulative excretion of succinonitrile, cyanide andd thiocyanate was recorded.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
not specified
Details on test material:
The radiolabel [14C] was present in the 2 cyanogroups, so at the 1- and the 4-position.
Radiolabelling:
yes

Test animals

Species:
mouse
Strain:
not specified
Sex:
male
Details on test animals and environmental conditions:
Brown male mice had a mean body weight of 30 grams. The mice were given their normal diet throughout the experiment, which was conducted at room temperature (18-21 centigrade).

Administration / exposure

Route of administration:
intraperitoneal
Vehicle:
water
Details on exposure:
Single intraperitoneal dose with urine collection over 72 hours
Multiple dosing over 4 days with urine collection 24 hours after each intraperitoneal dose
Duration and frequency of treatment / exposure:
The injected mice were placed in groups of 6-8 in metabolic cages, designed to separate urine and faeces. The mice were given their normal diet throughout the experiment, which was conducted at room temperature (18-21 centigrades) for no longer than a week..
Doses / concentrations
Remarks:
Doses / Concentrations:
Single dose 25 mg/kg BW intraperitoneal (50 microCurie C14/kgBW)
Multiple dosing of 25 mg/kg BW/day each day over 4 days (50 microCurie C14/kgBW)
No. of animals per sex per dose:
The dose group was 6 to 8 mice in one metabolic cage.
Six groups of 6-8 mice were studied.
The urine and faeces of each group was analysed separately
Control animals:
no
Positive control:
Not applicable
Details on study design:
Single intraperitoneal dose with urine and faeces collection over 72 hours
Multiple dosing over 4 days with urine collection 24 hours after each intraperitoneal dose
Details on dosing and sampling:
The urine was collected in fractions over time from 0-2, 2-6, 6-24, 24-48 and 48-72 hours.
The faeces was collected from 0-24 and 48-72 hours.
The urine was acidified and extracted with 1. choroform and 2. isoamylalcohol 3. isoamylalcohol after adding ferrichloride and isothicyanate for extraction of radiolabelled metabolite thiocyanate.

Results and discussion

Main ADME resultsopen allclose all
Type:
absorption
Results:
In this study 83% of the applied radioactive dose of succinonitrile was recovered from the urine and 6.5% from the faeces after 72 hours. This means that succinonitrile is fully absorbed in the body after intraperitoneal application.
Type:
distribution
Results:
Because of a log(Kow) of -0.99 and a high water solubility is concluded, that succinonitrile is distributed in the free body water, that is 0.6-0.8 L/kg
Type:
metabolism
Results:
Succinonitrile is oxidised by P450 enzymes to hydroxysuccinonitrile, which immediately releases HCN and cyano-acetic acid. Cyanide is mainly metabolised to thiocyanate.
Type:
excretion
Results:
Succinonitrile and its metabolites cyanoacetic acid, cyanide, thiocyanate and other cyanide metabolites are all excreted in the urine.

Toxicokinetic / pharmacokinetic studies

Details on absorption:
The recovery of intraperitoneally applied radiolabelled succinonitrile was about 90% after 72 hours. This means that also 90% has been absorbed. Because of the large water solubility an a log(Kow) of -0.99 it is assumed that after intraperitoneal injection or ingestion the substance is absorbed within 1 to 3 hours.
Details on distribution in tissues:
The parent compound succinonitrile is excreted in the urine mainly in the first 6 hours after dosing. This supports the assumption, that the distribution volume of succinonitrile is the free body water (0.6-0.8 L/kg).
The partition coefficient between blood and organ tissue was estimated with a QSAR (DeJongh J, Verhaar HJ, Hermens JL, 1997. A quantitative property-property relationship (QPPR) approach to estimate in vitro tissue-blood partition coefficients of organic chemicals in rats and humans. Arch Toxicol.72(1):17-25). The partition coefficient was estimated to be between 0.6-0.8 L/L. This is more or less similar to the free body water volume. So it is concluded, that the distribution volume of succinonitrile is 0.6-0.8 L/kg.
Details on excretion:
The parent compound succinonitrile is excreted in the urine mainly in the first 6 hours after dosing. This supports the assumption, that the distribution volume of succinonitrile is the free body water (0.6-0.8 L/kg).
Cyanide and thiocyanate are excreted in the urine mainly in the first 24 hours after intraperitoneal injection.
Toxicokinetic parametersopen allclose all
Test no.:
#1
Toxicokinetic parameters:
half-life 1st: 1-2 hours for succinonitrile
Test no.:
#2
Toxicokinetic parameters:
half-life 1st: 1-2 hours for cyanide
Test no.:
#3
Toxicokinetic parameters:
half-life 1st: 4-8 hours for thiocyanate

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
The most toxic metabolite is cyanide. Cyanide is mainly metabolised to thiocyanate, but other metabolites are cyanate, 2-amino-thiazolodine-4-carboxylic acid, cysteine-(2-amino-thiazolodine-4-carboxylic acid), formic acid and C1 incorporation choline, methionine, allantoine (Baumeister RG, Schievelbein H, Zickgraf-Rüdel G, 1975. Toxicological and clinical aspects of cyanide metabolism. Arzneimittelforschung. 25(7):1056-64.).

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): no bioaccumulation potential based on study results
Succinonitrile is excreted within 6 hours after intraperitoneal injection. The main metabolite cyanide is also metabolised in a few hours to mainly thiocyanate, which is excreted within 24 hours after dosing. Other metabolites of cyanide are cyanate and formic acid, which may play a role in the C1 metabolic cycle. This explains the slow excretion rate of radioactive non-cyanide substances.
Executive summary:

Results from studies with radiolabelled succinonitrile in the carbon of both cyanide groups have shown, that:

·        Succinonitrile is fast absorbed via intraperitoneal injection.

·        Succinonitrile is distributed in the body water compartment

·        Only 50% of the cyanide in succinonitrile is converted into free HCN. 

·        Succinonitrile, the main metabolite HCN and its detoxified product thiocyanate are excreted in the urine within 24 hours.

 

 

Absorption

After intraperitoneal injection of radiolabelled succinonitrile about 90% of the applied radioactivity has been recovered. The absorption via the intraperitoneal and oral route is quite similar, but the absorption after ingestion is slower. So it is concluded that succinonitrile is also absorbed via ingestion. 

 

Distribution

Succinonitrile has a log[Kow] of -0.99 and a water solubility of 127.5 g/l. This means, that succinonitrile has a distribution phase similar to the body water. The volume of distribution is approximately 0.6–0.8 L/kg. Following intraperitoneal injection, succinonitrile has a mean distribution half-life of 8 -16 minutes. The rapid absorption and distribution results in peak concentrations within 30–60 minutes. The distribution in the body water compartment is supported by the findings of Curry (1975), who reported that succinonitrile was excreted in the urine unchanged during the first 2 hours after dosing. During that period metabolism reduces the concentration of succinonitrile in blood and urine too.

 

Metabolism

The major metabolic step is oxidation of succinonitrile into hydroxysuccinonitrile. Hydroxysuccinonitrile releases immediately hydrocyanic acid. The main metabolite of hydrocyanic acid is thiocyanate.

 

Excretion

An intraperitoneal dose of succinonitrile is excreted in the urine unchanged for about 10%. Its metabolites as thiocyanate, formic acid, cyanate and other cyanide metabolites are all excreted in the urine. Succinonitrile, HCN and thiocyanate metabolites are excreted for 50 to 60% in the first 24 hours after dosing. So bioaccumulation of succinonitrile does not occur in the body.