Comparison of comedolytic effect of benzoyl peroxide and adapalene in rhino mice

Background and objective: 2.5% benzoyl peroxide (BPO) gel and 0.1% adapalene gel have a comedolytic effect, and are widely used as therapeutic agents for acne vulgaris. In this study, to clarify the comedolytic mechanisms of BPO and adapalene, we compared the comedolytic effects of both agents using rhino mice, a spontaneous comedogenic model. Method: Rhino mice received daily topical treatment with BPO gel or placebo (up to 9 weeks) and adapalene gel (up to 3 weeks) on dorsal skin, respectively. The dorsal skin was excised from rhino mice after 5-, 7- and 9-week treatment with BPO gel and 3-week treatment with adapalene gel, and the epidermal sheet and the vertical sections of the skin stained with hematoxylin and eosin were prepared to measure the comedo size, the comedo number and the thickness of epidermis, respectively. In addition, mRNA expression levels of keratinization factors and cell adhesion molecules were measured by RT-PCR. Result: BPO gel decreased the size of comedo after 7- and 9- week treatment, but did not change the number of comedo. A slight increase in the thickness of epidermis was observed after 5-, 7- and 9-week treatment. On the other hand, adapalene gel decreased the size and the number of comedo, and remarkably increased the thickness of epidermis after 3-week treatment. In the BPO gel treatment group, obvious change in mRNA expression was not observed. On the other hand, adapalene gel downregulated the mRNA expression of differentiation factors (filaggrin and loricrin) and cell adhesion molecules (desmoglein-1 and corneodesmosin), and upregulated the mRNA expression of inflammatory keratin (K6). Conclusion: This study suggests that BPO gel and adapalene gel showed comedolytic effects on rhino mice via a different mechanism each other.