Tribuloside acts on the PDE/cAMP/PKA pathway to enhance melanogenesis, melanocyte dendricity and melanosome transport

Ethnopharmacological relevance: Tribuloside, a natural flavonoid extracted from Chinese medicine Tribulus terrestrisL., has shown potent efficacy in treating various diseases. In China, the fruits of Tribulus terrestrisL. have long been utilized for relieving headache, dizziness, itchiness, and vitiligo. Water-based extract derived from Tribulus terrestrisL. can enhance melanogenesis in mouse hair follicle melanocytes by elevating the expression of α-melanocyte stimulating hormone (α-MSH) and melanocortin-1 recepter (MC-1R). Nevertheless, there is a lack of information regarding the impact of tribuloside on pigmentation in both laboratory settings and living organisms.

Aim of the study: The present research aimed to examine the impact of tribuloside on pigmentation, and delve into the underlying mechanism.

Materials and methods: Following the administration of tribuloside in human epidermal melanocytes (HEMCs), we utilized microplate reader, Masson-Fontana ammoniacal silver stain, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to measure melanin contents, dendrite lengths, melanosome counts; L-DOPA oxidation assay to indicate Tyrosinase activity, Western blotting to evaluate the expression of melanogenic and associated phosphodiesterase (PDE)/cyclic adenosine monophosphate (cAMP)/cyclic-AMP dependent protein kinase A (PKA) pathway proteins. A PDE-Glo assay to verify the inhibitory effect of tribuloside on PDE was also conducted. Additionally, we examined the impact of tribuloside on the pigmentation in both zebrafish model and human skin samples.

Results: Tribuloside had a notable impact on the production of melanin in melanocytes, zebrafish, and human skin samples. These functions might be attributed to the inhibitory effect of tribuloside on PDE, which could increase the intracellular level of cAMP to stimulate the phosphorylation of cAMP-response element binding (CREB). Once activated, it induced microphthalmia-associated transcription factor (MITF) expression and increased the expression of Tyrosinase, Rab27a and cell division cycle protein 42 (Cdc42), ultimately facilitating melanogenesis, melanocyte dendricity, and melanin transport.

Conclusion: Tribuloside acts on the PDE/cAMP/PKA pathway to enhance melanogenesis, melanocyte dendricity, and melanosome transport; meanwhile, tribuloside does not have any toxic effects on cells and may be introduced into clinical prescriptions to promote pigmentation.

MITF; Melanocyte; Melanogenesis; Melanosome transport; PDE/cAMP/PKA; Tribuloside.