(25S)-25-Cyclohexyl-5-O-demethyl-25-de(1-methylpropyl)-22,23-dihydroavermectin A1a

Endpoint summary

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

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

Adequacy of study:

key study

Study period:

From 29 Apr to 18 May 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study run to a method comparable with current guidelines and to GLP.

Qualifier:

according to guideline

Guideline:

OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)

Deviations:

no

GLP compliance:

yes

Type of study:

mouse local lymph node assay (LLNA)

Species:

mouse

Strain:

CBA

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Janvier, Le Genest-Saint-Isle, France
- Age at study initiation: Young adult animals (approx. 10 weeks old)
- Weight at study initiation: Body weight variation was within +/- 20% of the sex mean.
- Housing: Animals were group housed in labeled Makrolon cages containing sterilised sawdust as bedding material. Paper and shelters were supplied as cage-enrichment.
- Diet (e.g. ad libitum): Free access to pelleted rodent diet
- Water (e.g. ad libitum): Free access to tap water.
- Acclimation period: at least 5 days before the start of treatment

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18 to 24°C
- Humidity (%): 40 to 70%
- Air changes (per hr): at least 10 air changes/hour
- Photoperiod (hrs dark / hrs light): a 12-hour light/12-hour dark cycle

Vehicle:

dimethylformamide

Concentration:

1, 2 or 5% w/w

No. of animals per dose:

five female mice per dose

Details on study design:

RANGE FINDING TESTS:
- Irritation: No irritation was observed in any of the animals examined. White staining of test substance remnants on the dorsal surface of the ears of the animals treated at 10, 25 and 50% did not hamper scoring of erythema.
- Lymph node proliferation response: Variations in ear thickness during the observation period were less than 25% from Day 1 pre-dose values for all animals/all doses (where an assessment could be made).

MAIN STUDY
ANIMAL ASSIGNMENT AND TREATMENT
- Name of test method: Local Lymph Node Assay in the Mouse
- Criteria used to consider a positive response: If the results indicate a SI≥ 3, the test substance may be regarded as a skin sensitizer.

TREATMENT PREPARATION AND ADMINISTRATION
Three groups of five animals were treated with one test substance concentration per group. The highest test substance concentration was selected from the pre-screen test. One group of five animals was treated with vehicle.

Induction - Days 1, 2 and 3
The dorsal surface of both ears was topically treated (25 μL/ear) with the test substance, at approximately the same time on each day. The concentrations were stirred with a magnetic stirrer immediately prior to dosing. The control animals were treated in the same way as the experimental animals, except that the vehicle was administered instead of the test substance.

Excision of the nodes - Day 6
Each animal was injected via the tail vein with 0.25 mL of sterile phosphate buffered saline (PBS) containing 20 μCi of 3H-methyl thymidine. After five hours, all animals were killed by intraperitoneal injection (0.2 mL/animal) of Euthasol® 20%. The draining (auricular) lymph node of each ear was excised. The relative size of the nodes (as compared to normal) was estimated by visual examination and abnormalities of the nodes and surrounding area were recorded. The nodes were pooled for each animal in approximately 3 mL PBS.

Tissue processing for radioactivity - Day 6
Following excision of the nodes, a single cell suspension of lymph node cells (LNC) was prepared in PBS by gentle separation through stainless steel gauze (diameter 125 μm). LNC were washed twice with an excess of PBS by centrifugation at 200g for 10 minutes at 4ºC. To precipitate the DNA, the LNC were exposed to 5% trichloroacetic acid (TCA) and then stored in the refrigerator until the next day.

Radioactivity measurements - Day 7
Precipitates were recovered by centrifugation, resuspended in 1 mL TCA and transferred to 10 mL of Ultima Gold cocktail as the scintillation fluid. Radioactivity measurements were performed using a Packard scintillation counter. Counting time was to a statistical precision of ± 0.2% or a maximum of 5 minutes whichever came first. The scintillation counter was programmed to automatically subtract background and convert Counts Per Minute (CPM) to Disintegrations Per Minute (DPM).

OBSERVATIONS
- Mortality/Viability: Twice daily.
- Body weights: On Day 1 (pre-dose) and Day 6 (prior to necropsy).
- Clinical signs: Once daily on Days 1-6 (on Days 1-3 between 3 and 4 hours after dosing).
- Irritation: Once daily on Days 1-6 (on Days 1-3 within 1 hour after dosing) according to the following numerical scoring system. Furthermore, a description of all other (local) effects was recorded.

Parameter:

SI

Remarks on result:

other: The SI values calculated for the substance concentrations 1, 2 and 5% were 0.8, 0.7 and 0.6, respectively.

Parameter:

other: disintegrations per minute (DPM)

Remarks on result:

other: Mean DPM/animal values for the experimental groups treated with test substance concentrations 1, 2 and 5% were 639, 585 and 482 DPM, respectively. The mean DPM/animal value for the vehicle control group was 828 DPM.

Skin reactions / Irritation: No irritation of the ears was observed in any of the animals examined.

Systemic toxicity: No mortality occurred and no clinical signs of systemic toxicity were observed in the animals of the main study. Body weights and body weight gain of most experimental animals remained in the same range as controls over the study period. The body weight loss noted for the animals at 5% was considered not toxicologically significant since the changes were slight in nature.

Macroscopy of the auricular lymph nodes and surrounding area: All auricular lymph nodes of the animals of the experimental and control groups were considered normal in size. No macroscopic abnormalities of the surrounding area were noted for any of the animals.

Interpretation of results:

not sensitising

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

Since there was no indication that the test substance elicits a SI ≥ 3 when tested up to 5%, the test substance was not considered to be a skin sensitizer. It was established that the EC3 value (the estimated test substance concentration that will give a SI =3) (if any) exceeds 5%.
Based on these results, the test substance would not be regarded as a skin sensitizer according to the recommendations made in the test guidelines. The test substance does not have to be classified and has no obligatory labelling requirement for sensitization by skin contact according to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) of the United Nations (2011) (including all amendments) and the Regulation (EC) No 1272/2008 on classification, labelling and packaging of substances and mixtures (including all amendments).

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

One read-across LLNA study is available which was conducted according to OECD Guideline 429 under GLP (Latour, 2015).

Since there was no indication that the test substance elicits a SI ≥ 3 when tested up to 5%, the test substance was not considered to be a skin sensitizer. See read-across justification document attached in section 13.

Migrated from Short description of key information:

One read-across study (Latour, 2015) is available. Since there was no indication that the test substance elicits a SI ≥ 3 when tested up to 5%, the test substance was not considered to be a skin sensitizer.

Justification for selection of skin sensitisation endpoint:

Read-across study run to a method comparable with current guidelines and to GLP.

Justification for classification or non-classification

Skin sensitisation:

Animal test gave negative result (LLNA result SI < 3 (actual value 0.8)).

Therefore in accordance with Regulation (EC) No. 1272/2008 (as amended by Regulation (EC) No. 286/2011) Table 3.4.2, this substance should not be classified as skin sensitiser based on the test data.