Isovaleric acid

Endpoint summary

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well-documented publication which meets basic scientific principles. Screening test method, accepted scientific standards, sufficiently documented, acceptable for assessment.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Method: other: see Method

GLP compliance:

no

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source:
- Age at study initiation: 4 weeks
- Weight at study initiation: 90 g
- Housing: in groups of 5 or 6
- Diet: ad libitum (30% dextrose, 20% cormmeal; 20% soybeanmeal, 10% casein, 9% corn starch, 5% corn oil, 4% salt mixture, 2% mixture of vitamins in dextrose)

Route of administration:

oral: feed

Vehicle:

other: diet

Details on oral exposure:

DIET PREPARATION
no data

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

14 d (pilot study) and 90 d (main study)

Frequency of treatment:

continuous

Remarks:

Doses / Concentrations:
5 % [= 50000 ppm)
Basis:
nominal in diet

Remarks:

Doses / Concentrations:
approx. 5000 mg/kg bw/day
Basis:
actual ingested

No. of animals per sex per dose:

5 to 6 males

Control animals:

yes, concurrent no treatment

Details on study design:

Post-exposure period: no

Clinical signs:

not specified

Mortality:

not specified

Body weight and weight changes:

no effects observed

Description (incidence and severity):

weight gain 6.2g/day; identical to controls

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

14g/day

Haematological findings:

no effects observed

Urinalysis findings:

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

no findings; 35 organs examined

Histopathological findings: neoplastic:

no effects observed

Description (incidence and severity):

no findings; 35 organs examined

Dose descriptor:

NOAEL

Effect level:

ca. 50 000 ppm

Based on:

test mat.

Sex:

male

Basis for effect level:

other: 5% in feed = 50,000 ppm in feed

Dose descriptor:

NOAEL

Effect level:

5 other: %

Dose descriptor:

NOAEL

Effect level:

5 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Calculated, assuming a food uptake of 100g/kg bw and day

Critical effects observed:

not specified

Range-finding study:

At 10-% TS, food consumption was markedly reduced, associated with substantial weight loss. 

Definitive study:
At 5 % [approx. 5000 mg/(kg bw and day)], no adverse effects were noted with respect to body weight development and organ weights, histology, and blood parameters. No local effects (irritation) were observed at that dose level.

The mean urinary pH value was 8.4 in animals ingesting isovaleric acid salt, compared with 7.2 for the control animals (Amoore et al, 1978). 

 

Conclusions:

Despite the low number of animals it can be concluded that in light of the high dose applied the prolonged uptake of the TS is not associated with toxic effects in rats.

Executive summary:

In a rat feeding study, neutralised isovaleric acid was fed to a group of 5 to 6 male SD rats for 90 days at 5% (50,000 ppm) in the diet. In a pilot study with 10%, the food intake was significantly reduced, rats lost significantly weight, and one rat dies. No effects were seen in the main study In the main study, the parameters examined (food consumption, bodyweight development, organ weights, haematology, blood chemistry, urinalysis, and histopathology of 35 organs) did not significantly differ from controls with the exception of a more basic urine in treated rats compared to controls (pH 8.4 versus 7.2). Based on the above the authors concluded that the NOAEL was 5% in diet or 5000 mg/kg bw/day in this study (Amoore et al, 1978). 

 

The protocol of this pre-guideline, pre-GLP study is not fully comparable to current guideline studies since the animal number was low, only male rats were used, and because the documentation is brief. On the other hand side the study clearly showed that ingestion of even large amounts of isovaleric acid with the feed over a 3-months period did not cause local or systemic adverse effects. The study is therefore considered to be valid and suitable for assessment.

 

NOAEL of 5000 mg/kg for sodium isovalerate corresponds to an NOAEL of 4100 mg/kg for the free isovaleric acid.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

4 100 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

sufficient

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

In a rat feeding study, neutralised isovaleric acid was fed to a group of 5 to 6 male SD rats for 90 days at 5% (50,000 ppm) in the diet. In a pilot study with 10%, the food intake was significantly reduced, rats lost significantly weight, and one rat dies. No effects were seen in the main study In the main study, the parameters examined (food consumption, bodyweight development, organ weights, haematology, blood chemistry, urinalysis, and histopathology of 35 organs) did not significantly differ from controls with the exception of a more basic urine in treated rats compared to controls (pH 8.4 versus 7.2). Based on the above the authors concluded that the NOAEL was 5% in diet or 5000 mg/kg bw/day in this study (Amoore et al, 1978).

The protocol of this pre-guideline, pre-GLP study is not fully comparable to current guideline studies since the animal number was low, only male rats were used, and because the documentation is brief. On the other hand side the study clearly showed that ingestion of even large amounts of isovaleric acid with the feed over a 3-months period did not cause local or systemic adverse effects. The study is therefore considered to be valid and suitable for assessment.

 

3-methylbutanol can be used for Read Across to isovaleric acid for the following reason: 3-methylbutanol was shown to be rapidly oxidised to isovaleric acid via isovaleric aldehyde and only minor quantities were excreted unchanged with the breath and urine. 9% of the dose was found in the urine as the glucuronide of tri-acetyl-isoamylmethylester at 24 hours post dose, hence conversion of the alcohol to isovaleric acid was approx. 90% (BG Chemie, 1997). Thus isovaleric acid is rapidly, but not exclusively, formed following dosing with 3-methylbutanol.

With the alcohol no systemic effects (e.g. neurological effects), that would not be expected for the acid were reported. Also the local effects of the acid, i.e. irritation, are not relevant for the repeated dose toxicity endpoint.

The repeated dose toxicity of the supporting substance, 3-methylbutanol, was determined in a subchronic drinking water study using rats (Wistar, 10 animals per dose and sex) according to OECD 408 and under GLP conditions. The administration of 3-Methylbutanol to male and female Wistar rats via the drinking water at dose levels of 0, 1000, 4000, and 16000 ppm over 3 months did not cause clear signs of toxicity at any dose level. In top dose males, statistically significant changes in red blood cell count, volume, and haemoglobin content was noted, but these changes were not considered to be of toxicological relevance, or adverse. Concentrations higher than 16000 ppm could not be administered. Hence, the NOAEL was 16000 ppm in drinking water, i.e. 1068 mg/kg bw and day in males and 1431 mg/kg bw and day in females (BASF; 1990).

Overall, the BASF study supports the findings made by Amoore et al. (1978) with isovalerate itself because no adverse effect was noted up to and including the top dose of 16,000 ppm of 3-methylbutanol in drinking water. Higher concentrations were not tolerated by the animals, a higher NOAEL was therefore not achievable with the supporting substance. Therefore the NOAEL of 5000 mg isovaleric acid/kg bw and day obtained by Amoore is considered to be suitable for any further considerations.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
Subchronic high dose study using isovaleric acid salt (sodium isovalerate). The NOAEL is calculated for the free acid.

Justification for classification or non-classification

No adverse effects observed