5-(dithiolan-3-yl)valeric acid

Endpoint summary

Description of key information

Two in vitro tests were perfomred to assess the skin irritation / corrosion potential of alpha-Lipoic acid.

The Bovine Cornea Opacity and Permeability assay was perfomred to assess the eye irritation / corrosion potential of alpha-Lipoic acid.

On Reconstructed Human Epidermis (RHE, EpiDerm) the test item showed no corrosive but irritating effects.

With the the BCOP-assay no predictiction can be made about effects of the test item on the eyes.

Key value for chemical safety assessment

Skin irritation / corrosion

Link to relevant study records

Reference

Reference 1

Endpoint:

skin corrosion: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017-01-04 - 2017-02-23

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 431 (In Vitro Skin Corrosion: Reconstructed Human Epidermis (RHE) Test Method)

Version / remarks:

2016-07-29

GLP compliance:

yes (incl. QA statement)

Test system:

human skin model

Source species:

human

Cell type:

other: NHEC: normal human-derived epidermal keratinocytes

Justification for test system used:

The EpiDerm(TM) Skin Model is a well established organotypic, three-dimensional model of the human epidermis and is used for in vitro experiments many years. It is known for its similaryty to huaman skin.

Vehicle:

water

Details on test system:

The test was carried out with the reconstituted three-dimensional human skin model EpiDerm(TM) (MatTek). This skin model consists of normal human epidermal keratinocytes (NHEK) which have been cultured to form a multilayered, highly differentiated model of the human epidermis. The NHEK are cultured on chemically modified, collagen-coated cell culture inserts (Millicell(R)). The EpiDerm(TM) epidermis model exhibits in vivo-like morphological and growth characteristics which are uniform and highly reproducible. It consists of organised basal, spinous and granular layers and a multi-layered stratum corneum analogous to patterns found in vivo.

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

Negative control: 50 µL distilled Water
Positive control: 50 µL 8 N KOH
Test Item: 25 mg + 25 µL H2O

Duration of treatment / exposure:

3 min; 60 min

Number of replicates:

4 per dose group
2 repliocates for each treatment period

Irritation / corrosion parameter:

% tissue viability

Run / experiment:

3 min

Value:

ca. 97.5

Vehicle controls validity:

not examined

Negative controls validity:

valid

Positive controls validity:

valid

Irritation / corrosion parameter:

% tissue viability

Run / experiment:

60 min

Value:

ca. 77.5

Vehicle controls validity:

not examined

Negative controls validity:

valid

Positive controls validity:

valid

Interpretation of results:

other: not corrosive

Conclusions:

In the study under the given conditions the test item showed no corrosive effects. The test item is classified as "non-corrosive".

Executive summary:

In the present study the skin corrosivity of Thioctic Acid was analysed. Since corrosive chemicals are cytotoxic after a short tim exposure to the stratum corneum of the epidermis the cytotoxic effects of the test item on EpiDerm(TM), a reconstituted three-dimensional human epidermis model, were determined. Hereby, the test item was applied topically. Cytotoxicity is expressed as the reduction of mitochondrial dehydrogensase activity measured by formazan production from MTT after a 3 min and 60 min exposure period and compared to those of the concurrent negative controls.

Reference 2

Endpoint:

skin irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017-03-17 - 2017-05-26

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 439 (In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method)

Version / remarks:

2015-07-06

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.46 (In Vitro Skin Irritation: Reconstructed Human Epidermis Model Test)

Version / remarks:

2012-07-06

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test system:

human skin model

Source species:

human

Cell type:

other: NHEC: normal human-derived epidermal keratinocytes

Justification for test system used:

This test uses the EpiDerm™ reconstructed human epidermis model (MatTek) which consists of normal human epidermal keratinocytes (NHEK) and therefore represents in vitro the target organ of the species of interest and closely mimics the biochemical and physiological properties of the upper parts of the human, i.e. the epidermis.

Vehicle:

physiological saline

Remarks:

DPBS: Dulbecco’s phosphate buffered saline

Details on test system:

The test was carried out with the reconstituted three-dimensional human skin model EpiDerm(TM) (MatTek). This skin model consists of normal human epidermal keratinocytes (NHEK) which have been cultured to form a multilayered, highly differentiated model of the human epidermis. The NHEK are cultured on chemically modified, collagen-coated cell culture inserts (Millicell(R)). The EpiDerm(TM) epidermis model exhibits in vivo-like morphological and growth characteristics which are uniform and highly reproducible. It consists of organised basal, spinous and granular layers and a multi-layered stratum corneum analogous to patterns found in vivo.

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

Negative control: 30 µL DPBS
Positive Control: 30 µL 5% SDS solution
Test Item: 25 mg + 25 µL DPBS

Duration of treatment / exposure:

60 min (35 min in the incubator -> 37 °C, 5 % CO2; 25 min under sterile flow)

Duration of post-treatment incubation (if applicable):

42 h (24 h in the incubator -> 37 °C, 5 % CO2, 95 % humidity; 18 h under same conditions, but in new wells with fresh assay medium)

Number of replicates:

3

Irritation / corrosion parameter:

% tissue viability

Value:

ca. 22

Vehicle controls validity:

not examined

Negative controls validity:

valid

Positive controls validity:

valid

Interpretation of results:

Category 2 (irritant) based on GHS criteria

Conclusions:

In this study under the given conditions the test item showed irritant effects. The relative mean tissue viability after 60 min of exposure and 42 h post-incubation was ≤ 50%. The test item is therefore classified as “irritant” in accordance with UN GHS “Category 2”.

Executive summary:

In the present study the skin irritant potential of Thioctic Acid was analysed. The EpiDerm™-Standard Model (EPI-200™), a reconstituted three-dimensional human epidermis model, was used as a replacement for the Draize Skin Irritation Test (OECD TG 404, [7]) to distinguish between UN GHS “Category 2” skin irritating test substances and not categorized test substances (“No Category”) which may be considered as non-irritant. Hereby, the test item was applied topically. Cytotoxicity is expressed as the reduction of mitochondrial dehydrogenase activity measured by formazan production from MTT after a 60 min exposure and 42 h post-incubation period and compared to those of the concurrent negative controls.

The test item showed irritant effects. The mean relative tissue viability (% negative control) was ≤ 50% (22%) after 60 min treatment and 42 h post-incubation.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Eye irritation

Link to relevant study records

Reference

Endpoint:

eye irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017-01-20 - 2017-03-15

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 437 (Bovine Corneal Opacity and Permeability Test Method for Identifying i) Chemicals Inducing Serious Eye Damage and ii) Chemicals Not Requiring Classification for Eye Irritation or Serious Eye Damage)

Deviations:

yes

Remarks:

Phenol red free RPMI 1640 medium instead of phenol red free EMEM

GLP compliance:

yes (incl. QA statement)

Species:

cattle

Strain:

not specified

Details on test animals or tissues and environmental conditions:

The Assay uses isolated corneas obtained as a by-product from animals freshly slaughtered.

Vehicle:

physiological saline

Controls:

yes, concurrent positive control

yes, concurrent negative control

Amount / concentration applied:

Negative control: physiological saline 0.9 % NaCl
Positive control: Imidazole 20 % in physiological saline 0.9 % NaCl
Test item: 20 % suspended in physiological saline 0.9 % NaCl

Duration of treatment / exposure:

4 h

Number of animals or in vitro replicates:

3 corneas in each group

Irritation parameter:

in vitro irritation score

Value:

ca. 36.57

Vehicle controls validity:

not examined

Negative controls validity:

valid

Remarks:

IVIS: 1.63

Positive controls validity:

valid

Remarks:

IVIS: 122.97

Irritation parameter:

cornea opacity score

Value:

ca. 36.54

Vehicle controls validity:

not examined

Remarks:

Corrected opacity: 0

Negative controls validity:

valid

Remarks:

Corrected opacity: 101

Positive controls validity:

valid

Irritation parameter:

fluorescein leakage

Remarks:

Corrected OD490

Value:

ca. 0.002

Negative controls validity:

valid

Positive controls validity:

valid

Remarks:

1.462

Interpretation of results:

GHS criteria not met

Conclusions:

No prediction can be made regarding the classification of the test substance Thioctic Acid to the evaluation criteria. Further testing in another suitable method is to be done with tonnage band increase.

Executive summary:

The eye irritancy potencial of Thioctic Acid was investigated in the bovine corneal opacity and permeability assay.

The test item was suspended with physiologicalsaline 0.9 % to give a 20 % concentration.

Mean in vitro irritation score: 36.57

Classification: No prediction can be made

The in vitro irritation score obtained with the positive control fell witin the two standard deviations of the current historical mean and therefore this assay is concidered to be valid.

The negative control responses should result in opacity and permeability values that are less the establisched upper limits for background bovine corneas treated with the respective negative control.

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

The relative mean tissue viability after 60 min of exposure and 42 h post-incubation was ≤ 50%. According to the CLP regulation the test item is therefore classified as “skin irritant" (UN GHS “Category 2”).

The IVIS obtained by the PCOP assay is 36.57. An IVIS between 3 and 55 can't be used for classification.

As alpha-Lipoic acid is classified as "skin irritant" (UN GHS "Category 2") it can be concluded it also may cause serious eye irritations (UN GHS "Category 2").