3,5,5-trimethylcyclohex-2-enone

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

distribution

Qualifier:

no guideline followed

Principles of method if other than guideline:

The distribution of isophorone in the organism was studied after ingestion.

GLP compliance:

not specified

Radiolabelling:

yes

Remarks:

14C

Species:

rabbit

Strain:

other: New Zealand

Sex:

female

Route of administration:

oral: gavage

Vehicle:

olive oil

Duration and frequency of treatment / exposure:

once

Dose / conc.:

4 000 other: mg/kg bw

No. of animals per sex per dose / concentration:

1

Control animals:

not specified

Details on study design:

Blood sample determination (0.5 hours after ingestion). Extraction of organs and GC analysis (identification of isophorone via Kovats index).

Type:

distribution

Results:

Distribution of isophorone in organs from high to low amounts: Stomach > ovaries > adrenal > spleen, liver > kidney, brain, heart > lung

MORTALITY
4000 mg/kg:
1/1 female rabbits: 1 hour after ingestion.

CONCLUSION
Rapid diffusion and distribution of isophorone through the body.
No bioaccumulation.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

distribution

Qualifier:

no guideline required

Principles of method if other than guideline:

The distribution of isophorone in organism was studied after inhalation 4 hours exposure

GLP compliance:

not specified

Radiolabelling:

not specified

Species:

rat

Strain:

Wistar

Sex:

male/female

Route of administration:

inhalation

Vehicle:

not specified

Duration and frequency of treatment / exposure:

4 hours

Dose / conc.:

2 000 other: mg/kg bw

Remarks:

corresponding to 400 ppm

No. of animals per sex per dose / concentration:

3

Control animals:

not specified

Type:

distribution

Results:

Distribution of isophorone in organs from high to low amounts: Kidney > Pancreas, adrenals, liver, brain

Details on distribution in tissues:

Rapid diffusion and distribution of isophorone through the body.
The total amount of isophorone measured in organs decreased with increasing post-exposure period.

MORTALITY

1/3 male and 1/3 female rats: immediately.

1/3 male and 1/3 female rats: 1.5 hour after ingestion.
1/3 male and 1/3 female rats: 3 hours after ingestion.

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

distribution

Qualifier:

no guideline followed

Principles of method if other than guideline:

The distribution of isophorone in the organism was studied after ingestion.

GLP compliance:

not specified

Species:

rat

Strain:

Wistar

Sex:

male/female

Route of administration:

oral: gavage

Vehicle:

other: olive oil

Duration and frequency of treatment / exposure:

once

Dose / conc.:

1 000 other: mg/kg bw

Dose / conc.:

4 000 other: mg/kg bw

No. of animals per sex per dose / concentration:

3

Control animals:

not specified

Details on study design:

Blood sample determination (0.5 hours after ingestion). Extraction of organs and GC analysis (identification of isophorone via Kovats index).

Type:

distribution

Results:

4000 mg/kg: Distribution of isophorone in organs (no differences between sex and time of death) from high to low amounts: Stomach > pancreas > adrenal > spleen > ovaries, tubes > brain, heart, lung, kidney > testes > liver.

Type:

distribution

Results:

1000 mg/kg: Traces of isophorone in the stomach (1-5 µg/g).

MORTALITY
4000 mg/kg:
3/3 male rats: 1 hour after ingestion.
3/3 female rats: 1, 3, 5 hours after ingestion.

1000 mg/kg:
6/6 rats 48 hours after ingestion

CONCLUSION
Rapid diffusion and distribution of isophorone through the body.
No bioaccumulation.

Reference 4

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

metabolism

Qualifier:

no guideline required

GLP compliance:

not specified

Species:

rabbit

Strain:

New Zealand White

Sex:

not specified

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: ca 2.5 kg

Route of administration:

oral: gavage

Vehicle:

other: pure substance followed by ca. 20 ml water

Duration and frequency of treatment / exposure:

single dose

Dose / conc.:

1 000 other: mg/kg bw

No. of animals per sex per dose / concentration:

not reported

Control animals:

not specified

Details on dosing and sampling:

Air sampling for 6 hours after dosing. Urine sampling 24 and 48 hours after dosing.
Exhaled air (only of a part of the animals, not of all): absorption on charcoal. Urine sampling for 48 hours.

ANALYSIS
Urine: enzymatic hydrolysis by beta-glucuronidase (buffered at pH 4.7, 37 ºC), extraction, gas chromatography, identification using Kovats index.
Charcoal: elution with dichloromethane, gas chromatography, identification using Kovats index.

Metabolites identified:

yes

Details on metabolites:

The following substances were identified in rabbit urine, however in varying ratios:
- Unreacted isophorone.
- 3,5,5-trimethylcyclohexan-1-one (dihydroisophorone).
- 3,5,5-trimethyl-2-cyclohexen-1-ol (isophorol - main metabolite in rabbits) eliminated as glucuronide.
- 3,5,5-trimethylcyclohexan-1-ol (CAS 116-02-9), cis (933-48-2) and trans (767-54-4) isomers.
These compounds were identified only via GC and correlation to Kovats indices.

Further compounds were seen, but could not be identified.

5,5-dimethyl-2-cyclohexen-1-one-3-carboxylic acid was extracted, isolated and identifled (GC, IR) in the urine of rabbits.

Substances found in the expired air of rabbits: Uunreacted isophorone

Conclusions:

The main metabolite of rabbits after isophorone administration was 5,5-dimethyl-2-cyclohexene-1-one-3-carboxylic acid found as glucuronide conjugate in the urine (after 48 hours).
Further detoxifications that occur in rabbits: hydrogenation of the 1-one-, the 2-ene- and both positions.
 
No distincion was made between alpha-isophorone, CAS-78-59-1, and beta-isophorone, CAS 471-01-2.

Reference 5

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

metabolism

Qualifier:

no guideline required

GLP compliance:

not specified

Species:

rat

Strain:

Wistar

Sex:

not specified

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: ca 250 g

Route of administration:

oral: gavage

Vehicle:

olive oil

Duration and frequency of treatment / exposure:

single dose

Dose / conc.:

1 000 other: mg/kg bw

No. of animals per sex per dose / concentration:

not reported

Control animals:

not specified

Details on dosing and sampling:

Air sampling for 6 hours after dosing. Urine sampling 24 and 48 hours after dosing.
Exhaled air (only of a part of the animals, not of all): absorption on charcoal. Urine sampling for 48 hours.

ANALYSIS
Urine: enzymatic hydrolysis by beta-glucuronidase (buffered at pH 4.7, 37 ºC), extraction, gas chromatography, identification using Kovats index.
Charcoal: elution with dichloromethane, gas chromatography, identification using Kovats index.

Metabolites identified:

yes

Details on metabolites:

The following substances were identified in rat urine, however, in varying ratios:
- Unreacted isophorone
- 3,5,5-trimethylcyclohexan-1-one (dihydroisophorone - main metabolite in rats)
- 3,5,5-trimethyl-2-cyclohexen-1-ol (isophorol) eliminated as glucuronide
- 3,5,5-trimethylcyclohexan-1-ol (CAS 116-02-9), cis- (933-48-2) and trans- (767-54-4) isomers
These compounds were identified only via GC and correlation to Kovats indices.

Further compounds were seen, but could not be identified.

Substances found in expired air of rats: Unreacted isophorone.

Conclusions:

The main metabolite in rats after isophorone administration is 3,5,5-trimethylcyclohexan-1-one (dihydroisophorone) in the urine (after 48 hours).
Further detoxifications that occur in rat: hydrogenation of the 1-one-position.
 
No distinction was made between alpha-isophorone, CAS-78-59-1, and beta-isophorone, CAS 471-01-2.

Reference 6

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

excretion

GLP compliance:

not specified

Species:

rat

Strain:

not specified

Sex:

male

Route of administration:

oral: gavage

Dose / conc.:

500 other: mg/kg bw

Details on study design:

500 mg/kg isophorone was administered in a single dose to male rats. Additionally, 500 mg/kg isophorone was administered to male rats for 8 consecutive days. Urine, feces and expired air were collected and the amount of radioactivity was determined.

Details on excretion:

80 % of radioactivity was excreted after 96 h. 50-65 % of radioactivity was excreted via urine (single-dose and repeated-dose). Slight difference between single-dose and repeated-dose administration: single-dose treated rats excrete a slightly higher amount of isophorone via feces compared to repeated-dose treated rats.

Conclusions:

Isophorone is rapidly excreted - mainly via glucuronidation. No evidence of bioaccumulation in rats.

Description of key information

Upon oral and inhalative administration, isophorone is well absorbed and rapidly distributed through the body of rats and rabbits. While part of the absorbed isophorone is excreted unchanged via urine and exhaled air, metabolites are mainly excreted as glucuronides. The tendency of isophorone to bioaccumulate is very low, since within 24 hours after administration more than 93% of orally administered isophorone was excreted by rats.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Absorption

Isophorone is well absorbed via the oral and inhalative route (Dutertre-Catella, 1976). Already 10 minutes after oral administration of 1 g 14C isophorone/kg to 2 rabbits, remarkable isophorone concentrations in the blood (0-102 μg/ml) were detected, which started to decrease from 75 – 141 μg/ml after 30 minutes and 88 - 94 μg/ml after 1 hour down to less than 0.5 μg/ml at 21 hours post treatment (Dutertre-Catella, 1976). Good dermal absorption can be concluded from the systemic effects in the acute toxicity studies.

 

Distribution

In male and female rats and rabbits isophorone is rapidly distributed. One hour after a single oral administration (4 g/kg) of 14C isophorone the highest concentrations were found in the stomach, pancreas, adrenals, spleen and liver of rats and rabbits. After inhalation (400 ppm) for 4 hours, the highest concentrations were obtained in the kidney, adrenals, liver, pancreas and brain of rats immediately after the termination of inhalation (Dutertre-Catella, 1976). 48 hours after oral administration of 1 g/kg isophorone to male and female rats, only traces of isophorone could be determined in the stomach and no isophorone was measured in the other organs (Dutertre-Catella, 1976).

 

Metabolism

After oral application of 1 g isophorone (3,5,5-trimethyl-2-cyclohexene-1-one)/kg bw, one main metabolite in rats and rabbits is 5,5-dimethyl-1-cyclohexene-3-one-1-carboxylic acid. This metabolite is formed by oxidation of the 3-methyl group of isophorone and then glucuronidated (Dutertre-Catella et al., 1978). Further metabolites may be formed through hydrogenation at the 1-one or/and 2-ene-position or after further oxidation processes. Dihydroisophorone (3,5,5-rimethylcyclohexanone), isophorol (3,5,5-trimethyl-2-cyclohexen-1-ol) and 3,5,5-trimethylcyclohexan-1-ol (cis- and trans-isomer), 6-Oxoisophorone (3,5,5-trimethyl-2-cyclohexen-1,6-dione), 4-Oxoisophorone (3,5,5-trimethyl-2-cyclohexen-1,4-dione), 4-hydroxyisophorone (4-hydroxy-3,5,5-trimethyl-2-cyclohexen-1-one) and 6-ydroxyisophorone (6-hydroxy-3,5,5-trimethyl-2-cyclohexen-1-one) were identified via GC/Kovats indices and GC/MS (Dutertre-Catella et al., 1978). Isophorol is eliminated as glucuronide (Dutertre-Catella et al., 1978). Dihydroisophorone is mainly found in the urine of rats, while rabbits produce primarily isophorol (Dutertre-Catella et al., 1978).

 

There are data to suggest that the glutathione system is also involved in the metabolism of isophorone. After i.p. administration of 500 mg isophorone/kg to sexually matured rats the glutathione depletion in liver, testes and epididymis was measured. In the liver 40 % reduction of the glutathione content was determined (maximum: 4 h after application), 82 % reduction was measured in testes (maximum: 4 h after application) and 72 % in the epididymis (maximum: 8 h after application) (Gandy et al., 1990).

 

Excretion

After administration of 400 ppm isophorone to rats (4 h), a part of the isophorone was expired unchanged (Dutertre-Catella, 1976). Also in the urine of orally treated rabbits and rats unreacted isophorone could be isolated (Dutertre-Catella et al., 1978).