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Skin sensitisation

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Administrative data

Endpoint:
skin sensitisation: in chemico
Type of information:
experimental study
Adequacy of study:
key study
Study period:
3 - 11 March 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2017
Report Date:
2017

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 442C (In Chemico Skin Sensitisation: Direct Peptide Reactivity Assay (DPRA))
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
insert date
Type of study:
direct peptide binding assay

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid

In chemico test system

Details on study design:
Skin sensitisation (In chemico test system) - Details on study design:
Synthetic peptide containing cysteine: Ac-RFAACAA-COOH, lot number 1556171, purity 95% (by HPLC), supplied by AnaSpec, stored frozen (-10°C to -30°C).
Synthetic peptide containing lysine: AC-RFAAKAA-COOH, lot number 1556172, purity 94% (by HPLC), suppoed by AnaSpec,stored frozen (-10°C to -30°C).

Positive control: cinnamic aldehyde, purity > 95%, was prepared at a concentration of 100 mM in acetonitrile

Preparation of peptide stock solutions:
Stock solutions of each peptide at concentrations of 0.667 mM were prepared by dissolution of pre-weighed aliquots of the appropriate peptide in ca 20 mL aliquots of the appropriate buffer solution (for cysteine, 100 mM phosphate buffer pH 7.5, for lysine 100 mM ammonium acetate buffer pH 10.2).

Preparation of peptide calibration standards:
Calibration standards of both peptides were prepared by diluting the requisite stock solution in the appropriate buffer and acetonitrile and contained each peptide at concentrations of 0.0167 mM, 0.0334 mM, 0.0667 mM, 0.133 mM, 0.267 mM and 0.534 mM. A buffer blank was also prepared.

Preparation of Reference (Stability) Controls and Precision Controls:
Reference (stability) controls and precision controls of both peptides were prepared at a concentration of 0.5 mM in acetonitrile. These were injected throughout the analytical run to confirm consistency of peptide response throughout each analytical run.

Preparation of Positive Control and Cysteine Peptide Depletion Samples and Co-elution Controls:
A 100 mM solution in acetonitrile of the test substance was prepared and further diluted in HPLC vials. Cysteine peptide depletion samples (in triplicate) were prepared by dilution of the 100 mM test substance solution in more acetonitrile and cysteine peptide stock solution. The final sample concentration was 5 mM of the test substance, 0.5 mM cysteine.
In place of the test substance, the positive control solution contained cinnamic aldehyde at a concentration of 5 mM with 0.5 mM cysteine.
The co-elution control sample contained 5 mM of the test substance in phosphate buffer solution. An additional control sample of 5 mM of Diola BHT in acetonitrile was also prepared so as to positively identify peak(s) of the test item in the co-elution control ensuring that the test item had not evaporated off during incubation and injection of the samples on the HPLC.

Preparation of Positive Control and Lysine Peptide Depletion Samples and Co-elution Controls:
A 100 mM solution in acetonitrile of the test substance was prepared and further diluted in HPLC vials. Lysine peptide depletion samples (in triplicate) were prepared by dilution of the 100 mM
test substance solution in lysine peptide stock solution. The final sample concentration was 25 mM of the test substance, 0.5 mM lysine.
In place of the test substance, the positive control solution contained cinnamic aldehyde at a concentration of 25 mM with 0.5 mM lysine. The co-elution control sample contained 25 mM of the test substance in ammonium acetate buffer solution. An additional control sample of 25 mM of Diola BHT in acetonitrile was also prepared so as to positively identify peak(s) of the test item in the co-elution control ensuring that the test item had not evaporated off during incubation and injection of the samples on the HPLC.

Incubation:
The appearance of the test substance, positive control samples and co-elution controls in the HPLC vials was documented following preparation with the vials then placed into the autosampler of the HPLC set at 25°C for a minimum of 22 hours incubation prior to initiation of the analysis run. Prior to initiation of the run the appearance of the samples in the vials was assessed and documented again.

Analysis:
The concentration of both the cysteine and lysine peptides in the presence of the test substance and the associated positive controls were quantified by HPLC using UV detection.
Equipment: HPLC Waters Alliance 2695 separation module an d2487 dual wavelength detector.
Column: Agilent Zorbax SB C18, 3.5 µm, 100 × 2.1 mm
Guard column: Phenomenex AJO4286
Column temperature: 30 °C
Sample temperature: 25 °C
Mobile phase A: 0.1% trifluoroacetic acid in water
Mobile phase B: 0.085% trifluoroacetic acid in acetonitrile
Flow rate: 0.35 mL/minute
Detector wavelength: UV, 220 nm
Injection volume: 2 μL
Run time: 30 minutes
Approximate retention time (cysteine): 11 minutes
Approximate retention time (lysine): 7 minutes

Calculations:
The peak area response for each peptide in each calibration chromatogram was measured. Calibration curves were constructed by linear regression of standard response versus standard concentration. The area responses of the peptide peak observed at the characteristic retention time of each peptide in each sample chromatogram was measured. Peptide depletion was determined using the following equation:

% peptide depletion = 100 - [(Peptide peak area in replicate depletion samples x 100) / (Mean peptide peak area of reference (stability) control samples)]


Results and discussion

Positive control results:
69.9% depletion (SD 0.21%, n = 3) and 57.9% depletion (SD 1.26%, n = 3) of cysteine and lysine, respectively, was observed with the positive control cinnamic aldehyde.

In vitro / in chemico

Resultsopen allclose all
Key result
Parameter:
other: cysteine depletion, %
Run / experiment:
1
Value:
-1.31
Vehicle controls validity:
valid
Remarks:
stability and precision controls
Negative controls validity:
not applicable
Positive controls validity:
valid
Remarks on result:
no indication of skin sensitisation
Key result
Parameter:
other: lysine depletion, %
Run / experiment:
1
Value:
-0.821
Vehicle controls validity:
valid
Remarks:
stability and precision controls
Negative controls validity:
not applicable
Positive controls validity:
valid
Remarks on result:
no indication of skin sensitisation
Other effects / acceptance of results:
ACCEPTANCE OF RESULTS:
- Acceptance criteria met for reference (stability) controls and precision controls of both peptides: yes, CV 0.97%, n = 6 and CV 0.26%, n = 6, for cysteine and lysine, respectively, at 0.50 and 0.51 mM).
- Acceptance criteria met for positive control: yes, 69.9% depletion (SD 0.21%, n=3) and 57.9% depletion (SD 1.26%, n=3) of cysteine and lysine, respectively, was observed with the positive control cinnamic aldehyde.
- Acceptance criteria met for variability between replicate measurements: yes, SD 0.81% (n=3) and SD 0.74% (n=3), respectively, for cysteine and lysine depletion by the test item.

TEST SUBSTANCE RESULTS:
Mean depletion of –1.31% and -0.821% was observed for the test substance with cysteine and lysine peptides, respectively. With the test substance not reacting with the cysteine nor lysine peptide it is classed as “no to minimal”, hence the DPRA prediction is negative.

Applicant's summary and conclusion

Interpretation of results:
other: DPRA was negative
Conclusions:
It can be concluded that this DPRA test is valid, and that the test substance was negative in the DPRA and is classified in the “no or minimal reactivity class” when using the Cysteine / Lysine prediction model.
Executive summary:

In a GLP-compliant OECD guideline 442C study, Direct Peptide Reactivity Assay (DPRA) was used to assess the reactivity of the substance by protein depletion being one part of its sensitisation mechanism. In the cysteine and lysine reactivity assay all analytical acceptance criteria of the test were met. The test substance caused -1.31% (SD 0.81%) and -0.821% (SD 0.74%) cysteine and lysine peptide depletion, respectively. These results are categorised as “no to minimal reactivity” based on the DPRA prediction model and is thus considered to be negative in the DPRA.