A Rat Model of Compound Acne.

Acne vulgaris is a prevalent chronic skin condition characterized by the presence of comedones, papules, and pustules on the face, neck, and chest. To simulate the inflammation of acne vulgaris, this protocol details an approach to establish a compound acne rodent model by inducing acne inflammation in rat ears using oleic acid and Cutibacterium acnes (C. acnes). Rats were randomly divided into four groups: the normal control group (NC), ears treated with oleic acid group (OA), ears treated with C. acnes group (C. acnes), ears treated with oleic acid and C. acnes (OA + C. acnes). To mimic excessive sebum production, oleic acid was smeared on the ears of rats in OA and OA + C. acnes groups for 25 days. From days 21 to 25, C. acnes suspension was injected intradermally into the ears of rats in the C. acnes and OA + C. acnes groups to aggravate the acne inflammation. Ear thickness was measured weekly as a gauge of inflammation severity. Gross observation, hematoxylin and eosin staining, and immunohistochemistry (IHC) were conducted and the results showed that the ears of the OA group and the OA + C. acnes group were thickened and indurated, accompanied by erythema and the presence of comedones. Additionally, papules were observed in C. acnes and OA + C. acnes groups. The histopathology exhibited hyperkeratinization and expanded infundibulum of the hair follicles in OA and OA + C. acnes groups. Infiltration of inflammatory cells and abscesses were found in the dermis of C. acnes and OA + C. acnes groups. The IHC results confirmed increased levels of tumor necrosis factor (TNF)-α in the dermis of C. acnes and OA + C. acnes groups. All the above results collectively indicated the successful establishment of the compound acne rodent model.