Takahashi Makoto, Takara Kensaku, Toyozato Tomonao, Wada Koji
Department of Bioscience and Biotechnology, Faculty of Agriculture, University of the Ryukyus, Nishiro-cho, Okinawa, Japan.
J Oleo Sci. 2012;61(10):585-92. doi: 10.5650/jos.61.585.
The methanol extract of Morus australis (shimaguwa) acts as a whitening agent due to the inhibition of tyrosinase activity. In order to explore the mechanism(s) of the whitening action, constituents of the 95% methanol extract from the dried stems of shimaguwa were isolated and their skin-whitening capacity was examined. Bioassay-guided fractionation of the methanol soluble extract of shimaguwa led to the isolation of 2, 4, 2', 4'-hydroxycalcone (chalcone 1) and three analogues of chalcone 1 with 3'-substituted resorcinol moieties (chalcones 2-4). Chalcone derivative 4 proved to be a novel compound and was fully characterized. Chalcones 1-4 were evaluated for inhibition activity on mushroom tyrosinase using L-tyrosine as the substrate. The parent chalcone 1 was a highly effective inhibitor of tyrosinase activity (IC₅₀ = 0.21 μM) compared to arbutin (IC₅₀ = 164 μM). Compared to chalcone 1, chalcones 2 and 3, which possess 3'-substituted isoprenyl or bulky 2-benzoylbiphenyl, showed significantly decreased tyrosinase activity, while chalcone 4, possessing 3'-substituted 2-hydroxy-1-pentene group, showed slightly increased activity.The effects of chalcones 1-4 on melanin synthesis, without affecting cell growth, were assayed in melanin-producing B16 murine melanoma cells. Chalcone 3 significantly reduced cell viability before reaching the IC₅₀ value for melanin synthesis. In contrast, the inhibitory effects of chalcones 1, 2 and 4 were more than 100-fold greater than that of arbutin, with little or no cytotoxicity. More significantly, chalcone 2, which exhibited less tyrosinase inhibitory activity compared to the parent chalcone 1, showed the highest inhibition of melanin synthesis in B16 cells among the chalcones tested. Accordingly, chalcones 1 and 2, and the novel chalcone 4 might be the active components responsible for the whitening ability of shimaguwa. Moreover, whitening ability was not exclusively due to tyrosinase inhibition.
澳洲桑（shimaguwa）的甲醇提取物由于抑制酪氨酸酶活性而具有美白作用。为了探究其美白作用的机制，对shimaguwa干燥茎干的95%甲醇提取物的成分进行了分离，并检测了它们的皮肤美白能力。通过生物活性导向的分离方法，从shimaguwa的甲醇可溶提取物中分离出了2, 4, 2', 4'-羟基查耳酮（查耳酮1）以及三种带有3'-取代间苯二酚部分的查耳酮1类似物（查耳酮2 - 4）。查耳酮衍生物4被证明是一种新化合物，并对其进行了全面表征。以L - 酪氨酸为底物，评估了查耳酮1 - 4对蘑菇酪氨酸酶的抑制活性。与熊果苷（IC₅₀ = 164 μM）相比，母体查耳酮1是酪氨酸酶活性的高效抑制剂（IC₅₀ = 0.21 μM）。与查耳酮1相比，具有3'-取代异戊烯基或庞大的2 - 苯甲酰基联苯的查耳酮2和3显示出酪氨酸酶活性显著降低，而具有3'-取代2 - 羟基 - 1 - 戊烯基的查耳酮4显示出活性略有增加。在产生黑色素的B16小鼠黑色素瘤细胞中检测了查耳酮1 - 4对黑色素合成的影响，且不影响细胞生长。在达到黑色素合成的IC₅₀值之前，查耳酮3显著降低了细胞活力。相比之下，查耳酮1、2和4的抑制作用比熊果苷大100倍以上，且几乎没有细胞毒性。更显著的是，与母体查耳酮1相比，酪氨酸酶抑制活性较低的查耳酮2在测试的查耳酮中对B16细胞的黑色素合成显示出最高的抑制作用。因此，查耳酮1和2以及新的查耳酮4可能是shimaguwa美白能力的活性成分。此外，美白能力并非仅仅归因于酪氨酸酶抑制。
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