Acnegenicity testing in rabbits. An objective quantification method.

Area of Science:

• Dermatology
• Toxicology
• Biometry

Background:

• The rabbit ear assay is a standard method for evaluating acnegenicity.
• Current methods for quantifying follicular hyperkeratosis in this assay rely on subjective visual scoring, which can lead to inter-observer variability.
• There is a need for a more objective and reproducible method for assessing acnegenicity in preclinical studies.

Purpose of the Study:

• To develop and validate an objective method for quantifying follicular hyperkeratosis in the rabbit ear assay.
• To assess the reliability and reproducibility of the proposed quantification method.
• To establish preliminary area percentage thresholds corresponding to established visual scoring grades.

Main Methods:

• Follicular hyperkeratosis was quantified using the area percentage (area%) of hyperkeratinized follicles visible in stereomicroscopic images of rabbit epidermis.
• Two independent observers quantified the response using the proposed area% method across six different formulations.
• Inter-observer variability was statistically evaluated to assess the uniformity of the quantification.

Main Results:

• The area% quantification method demonstrated suitability as an objective alternative to visual scoring.
• The median relative difference between the two observers' area% quantification was 26%.
• No statistically significant difference was found between the two observers' quantification results (p > 0.10), indicating good uniformity.

Conclusions:

• The proposed area% quantification method provides an objective and reproducible approach for assessing follicular hyperkeratosis in the rabbit ear assay.
• Preliminary area% values of 2%, 7%, and 15% are suggested as equivalents to visual scores of 1, 2, and 3, respectively.
• This objective method enhances the reliability of acnegenicity testing in dermatological research.