Tinosporide promotes melanogenesis via activation of cAMP/PKA/CREB–MITF signaling in B16F10 and SK-MEL-2 cells

Abstract

Hypopigmentation disorders are characterized by impaired melanogenesis and remain challenging to manage due to limited efficacy of current interventions and insufficient mechanistic insights. Natural products represent a valuable source of bioactive phytoconstituents capable of regulating key pathways involved in melanin synthesis. Despite its extensive traditional use and diverse pharmacological activities, Tinospora cordifolia and its major bioactive constituent tinosporide remain unexplored for their role in melanogenesis. The present study aimed to evaluate the melanogenesis-promoting potential of bioactive phytoconstituents isolated from Tinospora cordifolia, and to elucidate their underlying molecular mechanisms. Four phytoconstituents–columbin, tinosporide, 8-hydroxy tinosporide and ecdysterone–were isolated and structurally characterized from T. cordifolia. Their melanogenic potential was evaluated in murine (B16F10) and human (SK-MEL-2) melanoma cells by assessing melanin content, tyrosinase activity, and expression of melanogenesis-associated genes. Intracellular cAMP levels and associated signalling pathways were further analysed to investigate the mechanism of action. Among the isolated compounds, tinosporide exhibited the most pronounced melanogenic activity, significantly increasing melanin synthesis and tyrosinase activity. Tinosporide promotes nuclear localization of the microphthalmia-associated transcription factor (MITF), leading to upregulation of MITF-target genes, including Trp1, Tyr, Dct, Pmel, and Mlana. Furthermore, mechanistic studies revealed that tinosporide elevated intracellular cAMP levels and induced the phosphorylation of PKA and CREB, thereby activating cAMP/PKA/CREB signalling pathway. Pharmacological inhibition of PKA and CREB markedly attenuated tinosporide-induced melanogenesis, confirming the essential role of the cAMP/PKA/CREB–MITF axis. Collectively, these findings identify tinosporide as a promising natural melanogenic agent derived from Tinospora cordifolia and highlight its potential relevance in the development of plant-based interventions for hypopigmentation disorders.

Graphical abstract

According to the Submission Guidelines, the graphics for chemical structure tinosporideshould be created using drawing programs such as ChemDraw (ChemBioDraw) with the ACS 1996 document settings.