Ex vivo demonstration of a synergistic effect of Adapalene and benzoyl peroxide on inflammatory acne lesions

Acne is a chronic inflammatory disease of the pilosebaceous follicle. Thanks to its ability to reduce both comedones and inflammatory lesions, the association of a retinoid and benzoyl peroxide (BPO) is now recommended for the treatment of acne. However, the mechanisms of action of this combined therapy on inflammatory acne lesions are not well understood. In an ex vivo immunohistochemistry study, we investigated the potential synergistic modulator effect of Adapalene associated with BPO on keratinocytes proliferation/differentiation and innate immunity in inflammatory acne lesions. We demonstrated that proliferation (Ki-67), adhesion/differentiation (integrin alpha(2), alpha(3) and alpha(6)) and innate immunity (TLR-2, beta-defensin 4, IL-8) markers are overexpressed in inflammatory acne skin compared with uninvolved acne skin. Association of Adapalene and BPO significantly decreased expression of Ki67, alpha(2) and alpha(6) integrins, TLR-2, beta-defensin 4 and IL-8 in inflammatory acne skin, whereas single treatments with Adapalene or BPO alone were less effective. These results contribute to explain the comedolytic and anti-inflammatory activities of this combined therapy observed in recent clinical trials.