Modulation of TRPV1 function by Citrus reticulata (tangerine) fruit extract for the treatment of sensitive skin

Sensitive skin (SS) is a clinical syndrome defined by the occurrence of unpleasant sensations (such as stinging, burning, pain, pruritus, and tingling) in response to stimuli that normally should not provoke them. According to growing evidence, transient receptor potential vanilloid subtype 1 (TRPV1) has elevated expression in individuals with SS and is linked with the severity of SS symptoms. However, its pathogenesis is still unknown.Herein, Citrus reticulata (Tangerine) fruit extract (CR) was obtained and examined for its effect on SS with a focus on TRPV1 stimulation and expression.A recombinant hTRPV1 over-expression cell line (HaCaT-TRPV1-OE cell) was constructed to screen substances and extracts from several plants. Intracellular calcium mobilization was monitored by Flexstation 3 and a fluorescence microscope using Fluo 8 AM fluorophore. Next, immunofluorescence was used to detect the TRPV1 expression under different stimulants treated for 24 h. To investigate the relief and increased tolerance of CR to lactic acid-induced skin discomfort, clinical tests were carried out on the nasolabial folds or cheek areas.According to the obtained results, compared to HaCaT cells, HaCaT-TRPV1-OE cells showed a higher expression of TRPV1. Neuronal hyperresponsiveness in SS triggered by capsaicin (CAP), lactic acid, phenoxyethanol or nicotinamide may be through activation of TRPV1 and increased TRPV1 expression. CAP activates TRPV1 in HaCaT-TRPV1-OE cells, and more than 100 plants or chemicals were tested for their inhibitory effects before being screened for CR. CR (1%-4%) inhibited TRPV1 activation induced by CAP or phenoxyethanol or nicotinamide. Meanwhile, CR (0.25%) suppressed TRPV1 protein expression induced by phenoxyethanol or lactic acid. In vivo results showed that CR not only instantly relieved lactic acid-induced skin discomfort under 5 min but also enhanced skin tolerance to lactic acid after 7 days of continuous use.Topical application of CR showed an instant and long-lasting improvement in SS by modulating the activation and expression of TRPV1. Moreover, it has been suggested that CR might act as a TRPV1 inhibitor to reduce skin irritation or sensitivity.