3-(methylthio)propionaldehyde

Endpoint summary

Description of key information

Skin sensitisation (in vivo, GPMT): sensitising

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Reference 1

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1979-10-9 to 1979-11-03

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

significant methodological deficiencies

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Principle of test: Skin sensitisation was investigated in male guinea pigs (10/group).
- Short description of test conditions: The animals were induced via inhalation exposure (first test group) and via intradermal injection (second test group), followed by a challenge treatment of intradermal injection.
- Parameters analysed / observed: clinical signs, skin reactions

GLP compliance:

no

Type of study:

other: please refer to "Principle of method if other than guideline"

Justification for non-LLNA method:

The test was performed in 1979 before the alternative OECD guidelines (LLNA and in vitro test methods) were available.

Species:

guinea pig

Strain:

not specified

Remarks:

albino SPF animals

Sex:

male

Route:

other: inhalation

Vehicle:

other: air

Remarks:

first group

Concentration / amount:

198.3 mg/m3 air corresponding to 46.1 ppm (nominal concentration: 200 mg/m3 air corresponding to 46.5 ppm)

Day(s)/duration:

2 weeks (exposure 6 h/day during 5 day/week)

Adequacy of induction:

other: induction via inhalation is not in line with current guidelines

Route:

intradermal

Vehicle:

water

Remarks:

second group

Concentration / amount:

intradermal injection on Day 1: 0.05 mL of a 0.1% aqueous dilution
intradermal injection on Day 2-10: 0.1 mL of a 0.1% aqueous dilution

Day(s)/duration:

2 weeks (5 injections/week for 2 weeks)

Adequacy of induction:

not specified

No.:

#1

Route:

intradermal

Vehicle:

water

Concentration / amount:

intradermal injection 0.05 mL of a 0.1% aqueous dilution two weeks after the last induction

Day(s)/duration:

24 h

Adequacy of challenge:

not specified

No. of animals per dose:

10

Challenge controls:

The control group is actually a challenge control.

Positive control substance(s):

no

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

induction via inhalation, 198.3 mg/m3 air (46.1 ppm), challenge via intradermal injection of 0.05 mL of an 0.1% aqueous solution

No. with + reactions:

6

Total no. in group:

10

Clinical observations:

6/10 moderate and 4/10 mild skin reactions, judged by diameter, colour and thickness of the test site / restlessness and wet nose during the first 30 minutes of exposure, kept eyes closed and nasal discharge during the remaining exposure period

Remarks on result:

positive indication of skin sensitisation

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

intradermal induction, 0.05 and 0.1 mL of an 0.1% aqueous solution, challenge via intradermal injection of 0.05 mL of an 0.1% aqueous solution

No. with + reactions:

1

Total no. in group:

10

Clinical observations:

1/10 moderate and 9/10 mild skin reactions, judged by diameter, colour and thickness of the test site

Remarks on result:

no indication of skin sensitisation

Reading:

1st reading

Hours after challenge:

24

Group:

negative control

Dose level:

no induction, challenge by intradermal injection of 0.05 mL of an 0.1% aqueous solution

No. with + reactions:

0

Total no. in group:

10

Clinical observations:

All control animals showed only mild skin reactions, judged by diameter, colour and thickness of the test site

Remarks on result:

no indication of skin sensitisation

During induction, the animals exposed via inhalation were restless and had a wet nose during the first 30 minutes of exposure. For the remaining part of the exposure period they kept their eyes closed and showed nasal discharge. Upon intradermal induction, all animals showed mild to moderate reactions.

The challenge dose provoked 6/10 moderate and 4/10 mild reactions in animals which were induced via inhalation exposure and 1/10 moderate and 9/10 mild reactions in animals that were exposed intradermally. However, the reactions observed after challenge can not clearly be established to be skin sensitisation reactions.

Interpretation of results:

study cannot be used for classification

Reference 2

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1979-04 to 1979-05

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Remarks:

no negative control group; instead positive control group (20 animals tested positive with 50.000 IU/100 g of Penicillin-G-Na); maximum non-irritating concentrations used for induction instead of highest to cause mild-to-moderate skin irritation; no details on animals and environmental conditions, no details on erythema and edema of individual animals

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 406 (Skin Sensitisation)

Version / remarks:

adopted 17 Jul 1992

Deviations:

yes

Remarks:

no negative control group but positive control group (50.000 IU/100 g of Penicillin-G-Na); maximum non-irritating concentrations used for induction instead of highest to cause mild-to-moderate skin irritation; topical induction for 24 h instead of 48 h

GLP compliance:

no

Type of study:

guinea pig maximisation test

Justification for non-LLNA method:

The test was performed in 1979 before the alternative OECD guidelines (LLNA and in vitro test methods) were available.

Species:

guinea pig

Strain:

Pirbright-Hartley

Sex:

male

Details on test animals and environmental conditions:

- Source: Tierzüchterei Willy Krispien, Ahrensburg, Germany
- Animal body weight at study initiation: 300 - 320 g
- no data on housing, diet, water supply and environmental conditions

Route:

intradermal and epicutaneous

Vehicle:

physiological saline

Concentration / amount:

intradermal induction on Day 1: 1%
epicutaneous induction on Day 7: 5%

Day(s)/duration:

intradermal induction: single treatment; epicutaneous induction: 24 h

Adequacy of induction:

other: Selection of concentration based on the results of the pre-test (determination of maximum non-irritating concentrations)

No.:

#1

Route:

epicutaneous, occlusive

Vehicle:

unchanged (no vehicle)

Concentration / amount:

5% in physiological saline

Day(s)/duration:

24 h

Adequacy of challenge:

highest non-irritant concentration

No. of animals per dose:

20

Details on study design:

RANGE FINDING TESTS:
The primary irritation by the test substance upon intracutaneous and epicutaneous exposure was tested in a pre-experiment. Graded dilutions of the test substance in physiological saline (2-fold dilution steps) were applied. The animals were induced with 0.1 mL test substance intradermally, followed by epicutaneous induction of 1 mL test substance one week later under occlusive conditions. Intracutaneous doses were tested in 5 animals each; each animal received up to 5 different concentrations. Epicutaneous doses were tested in 5 animals, each; but only one concentration per animal. Skin reactions were evaluated 24 h post application. Concentrations for the main experiment were chosen to be the highest non-irritating concentration.

MAIN STUDY
A. INDUCTION EXPOSURE
- No. of exposures: 2 (intradermal and epicutaneous, respectively)
- Exposure period: single injection (intradermal) and 48 h (epicutaneous)
- Test groups:
Intradermal (3 pairs of injections):
Injection 1: 1:1 (v/v) mixture complete Freund's adjuvant (FCA) and distilled water
Injection 2: 1% test substance in phosphate buffered saline (PBS)
Injection 3: 1% test substance in a 1:1 mixture of complete Freund's adjuvant (FCA) and PBS
Epicutaneous: One week after the injections, a 2 x 4 cm patch of gauze was soaked with 5% test item formulated in PBS and applied to the test site. The treated areas were covered with alufoil and fixed with an elastic bandage for 24 h.
- Control group: Not included in the study.

B. CHALLENGE EXPOSURE
- No. of exposures: 1
- Day of challenge: 2 weeks after epidermal induction (Day 20)
- Exposure period: 24 h
- Test groups: test substance
- Concentrations: 5% formulation in PBS
- Evaluation (hr after challenge): 48 h

Challenge controls:

Not included in the study.

Positive control substance(s):

yes

Remarks:

Penicillin-G-Na

Positive control results:

All animals induced intracutaneously, epicutaneously and challenged with 50.000 IU / 100 g of Penicillin-G-Na tested positive in this study.

Key result

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

induction: 1% intradermal, 5% epicutaneous; challenge 5%

No. with + reactions:

20

Total no. in group:

20

Clinical observations:

no

Key result

Reading:

2nd reading

Hours after challenge:

48

Group:

positive control

Dose level:

induction: 50.000 IU / 100 g intradermal, 50.000 IU / 100 g epicutaneous; challenge 550.000 IU / 100 g

No. with + reactions:

20

Total no. in group:

20

Clinical observations:

no

Reading:

2nd reading

Group:

negative control

Remarks on result:

other: No negative control included in this study.

No mortality or adverse clinical observations were reported in this study. In addition, the result of the first reading time point after challenge were not reported.

Interpretation of results:

Category 1A (indication of significant skin sensitising potential) based on GHS criteria

Conclusions:

CLP: Skin sens. 1, H317 according to Regulation (EC) No. 1272/2008

Reference 3

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 406 (Skin Sensitisation)

Version / remarks:

adopted 17 Jul 1992

Deviations:

yes

Remarks:

no challenge control, limited information on materials and methods

GLP compliance:

yes

Type of study:

guinea pig maximisation test

Species:

guinea pig

Strain:

Dunkin-Hartley

Sex:

male/female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Covance, Inc., Denver, Pennsylvania, USA
- Age at study initiation: 5-7 weeks
- Housing: individually in suspended, stainless steel cages with wire mesh bottoms
- Diet: Certified Guinea Pig Diet No. 5026 (PMI Nutrition International, St. Louis, Missouri), ad libitum
- Water: tap water, ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 16-25
- Humidity (%): 20-62
- Photoperiod (hrs dark / hrs light): 12/12

Route:

intradermal and epicutaneous

Vehicle:

propylene glycol

Concentration / amount:

intradermal induction on Day 1: 5% in propylene glycol
epicutaneous induction on Day 7: 0.2 mL unchanged

Day(s)/duration:

intradermal induction: single treatment on Day 0; epicutaneous induction: 24 h exposure on Day 6

Adequacy of induction:

other: concentration chosen based on the results of a preliminary range-finding study in which 100% produced a score of 0.5 in 2/6 animals

No.:

#1

Route:

epicutaneous, occlusive

Vehicle:

unchanged (no vehicle)

Concentration / amount:

0.1 mL

Day(s)/duration:

Day 21, 48 h

Adequacy of challenge:

other: concentration chosen based on the results of a preliminary range-finding study in which 100% produced a score of 0.5 in 2/6 animals

No.:

#2

Route:

epicutaneous, occlusive

Vehicle:

propylene glycol

Concentration / amount:

25%

Day(s)/duration:

Day 21, 48 h

Adequacy of challenge:

other: The concentration was chosen due to excess irritation in the control group after the first challenge.

No. of animals per dose:

20 (10 male and 10 female)

Details on study design:

RANGE FINDING TESTS:
Induction and maximum non irritant concentration for challenge was determined in a pre-test: 5% MTPA in propylene glycol administered intradermally produced local necrosis. 25% topical application produced no irritation, and up to 100% only produced a score of 0.5 in 2 of 6 animals.

MAIN STUDY
A. INDUCTION EXPOSURE
- No. of exposures: 2 (intradermal and epicutaneous, respectively)
- Exposure period: single injection (intradermal) and 24 h (epicutaneous)
Intradermal (3 pairs of injections):
Injection 1: 50% complete Freund's adjuvant (FCA) in distilled water
Injection 2: 5% test substance in propylene glycol
Injection 3: 5% test substance in 50% aqueous FCA
Epicutaneous: 7 days after the injections, 0.2 mL of undiluted test substance were applied on a 2 x 4 inch patch of filter paper and applied to the reclipped areas which had received the intradermal injections. The patches were covered by impermable plastic and secured with an elastic adhesive bandage wound around the animals torso. After 48 h occluded contact the skin was wiped free of excess test material with gauze soaked in 0.9% saline.
- Control group: Not included in the study.


B. CHALLENGE EXPOSURE
- No. of exposures: 2
- Day of challenge: 2 weeks after epidermal induction (Day 20)
- Exposure period: 24 h
- Test groups: test substance
- Control group: Not included in the study.
- Concentrations: 0.1 mL undiluted test item
- Evaluation (hr after challenge): 24 and 48 h

Challenge controls:

No challenge control group was included.

Positive control substance(s):

yes

Remarks:

a-hexylcinnamaldehyde

Positive control results:

Two positive control groups were included. Both groups were induced intradermally with 50% FCA in distilled water, 30% a-hexylcinnamaldehyde (HCA) in propylene glycol, and 30% HCA in 50% aqueous FCA. Epicutaneous induction was with a 48 h occluded contact with undiluted HCA. Animals were challenged with both 50% HCA in propylene glycol and undiluted HCA. Challenge with undiluted HCA induced a skin sensitisation of a score of 1 or greater in 40% of the animals. The severity indices were 0.6 (24 h) and 0.35 (48 h). Challenge with 50% HCA induced a positive response in 90% of the animals with severity indices of 1.1 (24 h) and 0.9 (48 h).

Key result

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

induction: 5% intradermal and 0.2 mL unchanged epicutaneous induction, challenge with 100% epicutaneous induction

No. with + reactions:

3

Total no. in group:

19

Remarks on result:

other: 1/10 females died on Day 10

Key result

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

induction: 5% intradermal and 0.2 mL unchanged epicutaneous induction, challenge with 100% epicutaneous induction

No. with + reactions:

5

Total no. in group:

19

Remarks on result:

other: 1/10 females died on Day 10

Reading:

2nd reading

Hours after challenge:

48

Group:

negative control

Dose level:

induction with vehicle, untreated during challenge

No. with + reactions:

0

Total no. in group:

10

Remarks on result:

other: 4/10 animals gave a result of score 1. In view of this, a score of 2 or greater was used as basis for a positive response.

Reading:

1st reading

Hours after challenge:

24

Group:

positive control

Dose level:

induction: 30% intradermal and 0.2 mL unchanged epicutaneous induction, challenge with 100% epicutaneous induction

No. with + reactions:

1

Total no. in group:

10

Reading:

2nd reading

Hours after challenge:

48

Group:

positive control

Dose level:

induction: 30% intradermal and 0.2 mL unchanged epicutaneous induction, challenge with 100% epicutaneous induction

No. with + reactions:

0

Total no. in group:

10

Key result

Reading:

1st reading

Hours after challenge:

24

Group:

test chemical

Dose level:

induction: 5% intradermal and 0.2 mL unchanged epicutaneous induction, challenge with 25% epicutaneous induction

No. with + reactions:

2

Total no. in group:

19

Remarks on result:

other: re-challenge, 1st reading

Key result

Reading:

2nd reading

Hours after challenge:

48

Group:

test chemical

Dose level:

induction: 5% intradermal and 0.2 mL unchanged epicutaneous induction, challenge with 25% epicutaneous induction

No. with + reactions:

4

Total no. in group:

19

Remarks on result:

other: re-challenge, 2nd reading

Reading:

1st reading

Hours after challenge:

24

Group:

positive control

Dose level:

induction: 30% intradermal and 0.2 mL unchanged epicutaneous induction, challenge with 50% epicutaneous induction

No. with + reactions:

2

Total no. in group:

10

Reading:

2nd reading

Hours after challenge:

48

Group:

positive control

Dose level:

induction: 30% intradermal and 0.2 mL unchanged epicutaneous induction, challenge with 50% epicutaneous induction

No. with + reactions:

0

Total no. in group:

10

Results of pilot study:
Intradermal injections of 5% MTPA produced local
necrosis and the concentration was considered adequate for
the main study. Topical application of 25% produced no
local irritation and 50, 70, 100% produced a score of
0.5 in 2 or 3 of 6 animals. Therefore undiluted MTPA was used for the
main study epicutaneous induction and challenge.

Table 1: Results of main study - Incidences of skin responses at challenge and in irritation control animals

Compound	Group	No. of animals	Time	Erythema Score					Edema	Necrosis
				0	0.5	1	2	3
Test item, 100%	Challenge	19	24	14	1	1	0	3	5	3
		19	48	8	5	1	0	5	11	4
Test item, 25%	Re-challenge	19	24	12	4	0	0	2	3	0
		19	48	3	8	3	0	4	13	2
Test item, 100%	Irritation	10	24	8	0	0	0	2	2	2
		10	48	6	2	0	0	0	4	1
Test item, 25%	Irritation	10	24	5	5	0	0	0	3	0
		10	48	1	5	4	0	0	6	0
HCA, 100%	Challenge	10	24	2	4	3	1	0	2	0
		10	48	5	3	2	0	0	0	0
HCA, 100%	Irritation	10	24	8	2	0	0	0	0	0
		10	48	10	0	0	0	0	0	0
HCA, 50%	Challenge	10	24	0	2	6	2	0	1	0
		10	48	0	2	8	0	0	0	0
HCA, 50%	Irritation	10	24	4	5	1	0	0	0	0
		10	48	6	4	0	0	0	0	0

HCA: a-hexylcinnamaldehyde
One female of the MTPA sensitization group died on day 10 of the study.
The irritation reaction was unexpectedly high compared to the  pre-study.

In summary, based on the scores of 2 or greater with epicutaneous challenge at 25% the test item  produced sensitization in 22% of the guinea pigs; therefore,this material was classified as a "mild sensitizer" based on the Magnusson and 

Kligman allergenicity rating criteria.

Interpretation of results:

study cannot be used for classification

Conclusions:

Based on the experimental findings, the test item causes erythema, edema and necrosis to the skin. However, due to the highly skin irritating properties, a distinct conclusion on skin sensitising effects cannot be drawn. Therefore the skin sensitisation study test result is considered to be inconclusive due to irritating effects of the test item to the skin.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

Three studies are available to assess the skin sensitising properties of the test item.

In a key study (non-GLP, pre-OECD guideline), a Guinea Pig Maximisation Test (GPMT) was performed using a protocol similar to OECD guideline 406 (79-0020-DKT). Twenty male Pirbright-Hartley guinea pigs were induced intradermally with 1% test substance formulated in phosphate buffered saline (PBS) with or without an adjuvant (FCA) on Day 1 and induced epicutaneously with 5% test substance formulated in PBS on Day 7. The concentrations were selected as the highest non-irritating concentrations, based on the results of a preliminary range-finding test, in which the maximum non-irritating concentration was identified. The epicutaneous induction was performed for 24 h under occlusive conditions; after which the patch was removed. Two weeks after epicutaenous induction, a challenge was performed. All the guinea pigs were treated epicutaneously with 5% test item for 24 h under occlusive conditions.

A group of 20 guinea pigs served as positive control group and was treated (induced and challenged) with penicillin-G-sodium (50.000 IU/ 100 g). No negative/vehicle control group was included in the study. The skin reactions were assessed 48 h after patch removal based on the occurrence of skin reactions (grade 0 to 5) in the sensitised animals.

48 h after challenge, all test item treated animals (20/20) showed severe skin sensitising reactions. The same observation was made for all animals of the positive control group, thus demonstrating the sensitivity of the test.

Under the conditions of the test and based on the experimental findings, the test item is considered to be sensitising to the skin.

The results of the key study were confirmed in two supporting studies, in which the test substance was applied at doses causing mild skin irritation. Skin reactions consistent with skin sensitisation were observed in all animals.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

Respiratory sensitisation:

According to the OECD SIDS Initial Assessment Report (SIAM 17; Arona Nov. 2003; 3-(Methylthio) propionaldehyde) the mode of action is in particular characterized by the local irritation potential of the test item to skin and mucous membranes. With regard to respiratory irritation, it is unclear from the existing studies whether the observed local effects in inhalation studies are attributable to the test item or to acrolein, an impurity which is enriched in the vapor phase under the test conditions. However, at up to 50 ppm (216 mg/m3), the highest concentration tested, no respiratory irritation was detected in a 9 day study with repeated exposure with acrolein-free 3-(methylthio) propionaldehyde. Furthermore, no evidence for respiratory sensitization has been reported.

Justification for classification or non-classification

The available data on skin sensitisation meet the criteria for classification as Skin Sens. 1A (H317) according to Regulation (EC) No. 1272/2008 (CLP) and according to the criteria of the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) of the United Nations.