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Aberrant regulation of protease activity, mainly from imbalance between protease and protease inhibitor activities in skin, is known to be involved various inflammatory skin diseases, including atopic dermatitis and psoriasis. Impairment of acid mantle in the stratum corneum, which maintains the pH within normal acidic range, triggers and/or exacerbates the inflammatory responses in skin. Previous studies reported that maintenance of skin surface pH by topical application of acidic formulation alleviates and prevents atopic dermatitis (AD)-like symptoms in various AD models. Protease-activated receptor (PAR)-2 is an important mediator between pH and inflammation and we have previously reported the therapeutic effects of topical PAR-2 antagonist in atopic dermatitis. Recently, we also reported that topical PAR-2 antagonist can improve the psoriasis symptoms in imiquimod-induced animal model. Based on those results, in this study, we tried to evaluate the effects of topical acidic formulation on psoriasis, using imiquimod-induced animal models. Acidic formulation (ph 3.5) was topically applied on imiquimod-applied site in hairless mouse for 7 days. Thickness of the skin, erythema and trans-epidermal water loss (TEWL) as a representation of epidermal permeability barrier function, were measured during the application period. After the application, skin biopsy was taken for further histological assessments. As a result, significant prevention of skin thickening and TEWL increase were observed in acidic formulation applied site. Histological observation also confirmed the anti-inflammatory effects of acidic formulation. While further investigation needs to be performed to clarify the therapeutic potential of acidic formulation for psoriasis treatment, these results suggest that maintaining skin surface pH within its normal range is important for inflammatory skin diseases, including psoriasis.
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