Inhibition of Tyrosinase and Melanogenesis by a White Mulberry Fruit Extract

Abstract

Ultraviolet B (UVB) radiation is a key factor in the overproduction of melanin in the skin. Melanocytes produce melanin through melanogenesis to protect the skin from UVB radiation-induced damage. However, excessive melanogenesis can lead to hyperpigmentation and increase the risk of malignant melanoma. Tyrosinase is the rate-limiting enzyme in melanogenesis; it catalyzes the oxidation of tyrosine to 3,4-dihydroxy-L-phenylalanine and subsequently to dopaquinone. Thus, inhibiting tyrosinase is a promising strategy for preventing melanogenesis and skin hyperpigmentation. White mulberry (Morus alba L.) is rich in antioxidants, and mulberry fruit extracts have been used as cosmetic skin-lightening agents. However, data on the capacity of mulberry fruit extracts to inhibit tyrosinase under UVB radiation-induced melanogenic conditions remain scarce, especially in an in vivo model. In this study, we evaluated the effects of a mulberry crude extract (MCE) on UVB radiation-induced melanogenesis in B16F10 melanoma cells and zebrafish embryos. The MCE significantly reduced tyrosinase activity and melanogenesis in a dose-dependent manner without inducing cytotoxicity. These effects are likely attributable to the antioxidant constituents of the extract. Our findings highlight the potential of this MCE as an effective tyrosinase inhibitor for the prevention of UVB radiation-induced skin hyperpigmentation.

Keywords: B16F10 cells; UVB radiation; melanogenesis; mulberry crude extract; tyrosinase inhibition; zebrafish embryo.

Figure 1

Comparison of MCE chromatogram with those of (A) rutin, (B) chlorogenic acid, and (C) mulberroside A, along with chemical structures of standard compounds. Chromatogram of MCE at 50 mg/mL is shown in red, chromatograms of standard compounds are shown in green, and chromatograms of MCE combined with each standard compound are shown in blue.

Figure 2

Effects of MCE and UVB radiation on B16F10 cell viability, tyrosinase activity, and melanin content. (A) Cytotoxic effect of MCE on B16F10 cells. (B) Effect of UVB radiation on B16F10 cell viability. (C) Effect of UVB radiation on cellular tyrosinase activity in B16F10 cells. (D) Impact of UVB radiation on melanin levels in B16F10 cells is presented as mean ± standard deviation. Statistical significance is indicated as * p < 0.05, ** p < 0.01, and **** p < 0.001, when compared to untreated group.

Figure 3

Inhibitory effect of MCE on UVB radiation-induced melanogenesis in B16F10 cells. B16F10 cells were exposed to UVB radiation (60 mJ/cm²) and treated with low-dose MCE (LMCE, 5 mg/mL) or high-dose MCE (HMCE, 10 mg/mL) for 24 h. (A) Cell viability, (B) tyrosinase activity, and (C) melanin content were assessed. (D) Representative images of pigmented cells scored from 1 (minimal pigmentation) to 4 (highly pigmented) (400× magnification). (E) Distribution of cells with different morphological features within and across treatment groups. Data are presented as mean ± standard deviation. * p < 0.05 and *** p < 0.01 indicate statistical significance between treatment groups. a and b indicate significant differences (p < 0.05) compared to UT and UVB radiation-only groups, respectively. UT represents untreated group.

Figure 4

Inhibitory effect of MCE on UVB radiation-induced melanogenesis in zebrafish embryos. (A) Effect of UVB radiation only, (B) effect of MCE only, (C) and effect of UVB radiation combined with the MCE on zebrafish embryo viability. (D) Eye color, characteristics, and migration of melanocytes in head region after various treatments, observed via stereomicroscopy at 200× magnification. (E) Semi-quantitative scoring of melanin distribution, categorized as 1, 2, or 3. Data are presented as mean ± standard deviation. * p < 0.05, ** p < 0.01, and *** p < 0.001 indicate statistical significance between treatment groups. UT represents untreated group.

Figure 5

Schematic diagram of preparing mulberry crude extract (MCE).