inducing acne inflammation in rat skin with oleic acid and cutibacterium acnes

Establishing a Compound Acne Model in Rats Using Oleic Acid and C. acnes

Acne vulgaris is a common chronic skin disease characterized by the presence of comedones, papules, and pustules on the face, neck, and chest, which, in severe cases, may progress to nodules, cysts, and permanent scars1. Epidemiological studies report that acne impacts 9.4% of the global population while its resulting symptoms pose severe physical and psychosocial challenges2,3.
The pathogenesis of acne is multifactorial, including four critical processes: excess sebum production, comedone formation, follicular colonization by skin microbiota, and the release of inflammatory mediators around the pilosebaceous unit4,5. Increased sebum secretion, resulting in the accumulation of excess unsaturated free fatty acids (UFFAs), contributes to the abnormal reproduction of skin microbiota, one of which is Cutibacterium acnes, as shown in genomic studies6. Meanwhile, skin microbiota decomposes the sebum and increases the concentration of UFFAs, leading to a vicious circle7. In addition, excess UFFAs cause hyperkeratinization in hair follicles, which in turn triggers acne8. Skin microbiota and increased sebum both activate Toll-like receptors (TLRs) to produce multiple proinflammatory cytokines such as interleukin (IL)-1 and TNF-&#945;9,10. This cascade of inflammation, coupled with increased sebum and microbial overgrowth, culminates in pronounced hyperkeratosis of the hair follicle and the onset of acne11.
The rapid development in the field of acne research and related clinical requirements has driven the creation of a series of animal models of acne inflammation on the rat ear, the backs of rats or mice, and rabbit ear12,13,14,15. The methods include intradermal injection of C. acnes,&#160;the application of oils on the skin to simulate the abnormal secretion of the sebaceous glands and hyperkeratinization, or a combination of both to accelerate the skin inflammation to form acne16,17,18,19. However, the usage and dosage of chemical agents and biological agents vary among previous studies, which may confuse researchers intending to establish an appropriate acne model. This study aimed to establish an easy-to-operate and effective method to form a compound acne rodent model and provide a model reference for researchers studying acne vulgaris.

Author Spotlight: Development and Evaluation of a Compound Acne Rodent Model Using C. acnes and Oleic Acid

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.

Inducing Acne Inflammation in Rat Skin with Oleic Acid and Cutibacterium acnes

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 two thirds and one half 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 off 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.

inducing-acne-inflammation-rat-skin-with-oleic-acid-cutibacterium

Research

JoVE Journal

Medicine

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).&#160;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)-&#945; 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.

This protocol outlines the procedure for inducing acne inflammation in rat skin with oleic acid and Cutibacterium acnes.

Acne vulgaris is a prevalent chronic skin condition characterized by the presence of comedones, papules, and pustules on the face, neck, and chest. To ...