A Rat Model of Compound Acne

This study aims to establish an easy-to-operate and effective method to form a compound acne rodent model. We confirm that this compound acne rodent model is better than the models only induced by Cutibacterium acnes or oleic acids. Some researchers only adopted a single methodology to cause acne inflammation, such as applying oils or injecting microbes.

However, studies show that interplay between both exacerbates acne inflammation. This protocol aims to provide a method and evaluation criteria for an acne model that combines C.acnes with oleic acids. Our findings show that the compound model induced by oils and C.acnes may be more consistent with the clinical lesion of acne compared to smearing oleic acid alone or injecting C.acnes alone.

Furthermore, we try to establish criteria for evaluating acne inflammation. To begin, take an electronic vernier caliper. Position its outer jaw at the midpoint of the ear's outer edge and extend it into the ear canal.

Measure and record the thickness at 2/3 and 1/2 points along the line. Then, tilt the rat's head to one side, orienting the ear upwards. Apply 50 microliters of oleic acid evenly to both the ventral and dorsal sides of the ear once daily for 25 days.

Using a one milliliter syringe equipped with a 34 or 36 gauge needle, inject 50 microliters of Cutibacterium acnes suspension intradermally into the ventral surface of the ear. On day 25, measure and record the thickness of the ears. After cutting the ears of the euthanized rat, drill fixed size holes in the ears using an eight millimeter ring drill.

After preparing and staining the ear sections, observe them under a light microscope. Record the pathological changes for follow-up evaluation by a pathologist and assign scores to these changes according to the table shown here. The ears in the oleic acid and oleic acid with Cutibacterium acnes groups showed thickening, induration, erythema, scales, and comedones with occasional bleeding due to scratching.

Histopathological analysis revealed parakeratosis, hyperkeratosis, and hypertrophy in the oleic acid and oleic acid with Cutibacterium acnes groups. Pathological scoring indicated increased severity in these groups compared to the control group. Immunohistochemistry showed higher expression of TNF-alpha in the dermis of the Cutibacterium acnes and oleic acid with Cutibacterium acnes groups.