Carnosic acid ameliorates postinflammatory hyperpigmentation by inhibiting inflammatory reaction and melanin deposition.

The potential therapeutic effects of carnosic acid (CA) on postinflammatory hyperpigmentation (PIH) were evaluated, including its effects on melanin deposition in zebrafish, melanogenesis and melanosome transfer in skin cells and skin wound healing in mice. Our results demonstrated that CA dose-dependently decreased melanin deposition in the skin of juvenile zebrafishes. It also inhibited melanogenesis in melanoma cells and melanosome transfer to keratinocytes. Next, CA was loaded in a liposome-hydrogel system (LP-GEL) to treat skin wounds in mice. The results showed that CA-LP-GEL, as well as LP-GEL, could accelerate skin wound healing and repair the structure of healing skins in mice. Comparatively, the levels of inflammatory factors (IL-1β and TNF-a) in healing skins were significantly increased by LP-GEL, but reduced by CA-LP-GEL. In addition, Fontana-Masson staining analysis of healing skin showed that the melanoma cells were restored by the treatment of LP-GEL and CA-LP-GEL, while the melanin content was significantly increased only by LP-GEL. Real-time PCR data showed that CA decreased the gene expression related with melanogenesis (MITF, TYR and TRP-1), melanosome transfer (MLPH, Myova and Rab27a) and inflammatory cytokines (IL-1β and TNF-α) in vitro and in vivo. In conclusion, CA could reduce melanin deposition in the skin by inhibiting melanogenesis and melanosome transfer. CA-LP-GEL was found to accelerate skin wound healing and suppress inflammation and hyperpigmentation in mice. These results suggest that CA has a big developing potentiality for PIH treatment.