Geniposide Enhances Melanogenesis by Stem Cell Factor/c‐Kit Signalling in Norepinephrine‐Exposed Normal Human Epidermal Melanocyte

Abstract:  Geniposide is an iridoid glycoside isolated from the fruit of Gardenia jasminoides Ellis used as a Chinese traditional medicine for treatment of generalized vitiligo. Stem cell factor from keratinocyte recognizes and activates its receptor c‐kit carried by melanocyte to potent enhance melanocytic melanogenesis that can be suppressed by norepinephrine. This study addresses the action and mechanism of geniposide enhancing melanogenesis in norepinephrine‐exposed normal human epidermal melanocyte. Flow cytometry results from this study exhibited the augmentation effect of geniposide on production of c‐kit receptor by norepinephrine‐exposed normal human epidermal melanocyte. However, geniposide did not affect the production of stem cell factor by norepinephrine‐exposed normal human epidermal keratinocyte assessed by cellular enzyme‐linked immunosorbent assay (ELISA). ELISA indicated that at the presence of stem cell factor, geniposide was capable of elevating the level of extracellular signal‐regulated kinase 1/2 phosphorylation within norepinephrine‐exposed normal human epidermal melanocyte, which is known to be involved in stem cell factor/c‐kit downstream signalling. And inhibition of c‐kit with inhibitory antibody K44.2 completely blocked the increase in geniposide‐stimulated extracellular signal‐regulated kinase 1/2 phosphorylation. In addition, spectrophotometry demonstrated the enhancement effect of geniposide on melanogenesis (tyrosinase activity and melanin production) in norepinephrine‐exposed normal human epidermal melanocyte at the presence of stem cell factor, which was blocked by c‐kit inhibitory antibody K44.2. Data from this study suggest that geniposide can enhance melanogenesis by stem cell factor/c‐kit signalling in which the expression of c‐kit receptor is augmented in norepinephrine‐exposed normal human epidermal melanocyte.