Abstract

Melanogenesis is regulated primarily by tyrosinase (TYR) and microphthalmia-associated transcription factor (MITF), making safe natural melanogenic stimulators desirable for cosmetic applications targeting hypopigmentation and hair graying. Rice bran contains bioactive compounds and minerals with potential biological activity; however, the melanogenic effects of Thai rice bran extracts (TRBE) remain poorly understood. This study evaluated the melanogenic potential of TRBE from four Thai rice cultivars using B16F10 melanoma cells. Cells were treated with TRBE (20–160 µg/mL) for 72 h, with α-melanocyte-stimulating hormone (α-MSH, 10 nM) used as a positive control. Melanin content, intracellular TYR activity, cytotoxicity (SRB assay), L-DOPA staining, and protein expression (MITF, TYR, PMEL) were assessed. Mineral composition was analyzed using ICP-OES. All TRBE exhibited no cytotoxic effects. Among them, Jasmine TRBE showed the strongest dose-dependent increase in melanin production and TYR activity. L-DOPA staining confirmed enhanced enzymatic activity. Western blot analysis demonstrated upregulation of MITF, TYR, and PMEL, indicating activation of melanogenic signaling and melanosome maturation. ICP-OES analysis revealed the presence of silicon and minerals including phosphorus, potassium, and magnesium. These findings suggest that TRBE, particularly the Jasmine cultivar, enhances melanogenesis via MITF-mediated pathways and may serve as promising natural candidates for pigmentation-related cosmetic applications.

Key words: B16F10 melanoma cells, Mineral extract, Melanogenesis, Pigmentation, Thai rice bran