Abstract
3,6-Anhydro-l-galactose (AHG), a major monomeric constituent of red macroalgae (Rhodophyta), was recently reported to possess skin whitening activity. Moreover, AHG-containing oligosaccharides, such as agarooligosaccharides (AOSs) and neoagarooligosaccharides (NAOSs), have various physiological activities, including anti-inflammatory, antioxidant, and skin moisturizing effects. In this study, AHG and NAOSs were produced from agarose by enzymatic reactions catalyzed by an endo-type β-agarase, an exo-type β-agarase, and a neoagarobiose hydrolase. In a cell proliferation assay, AHG, AOSs, and NAOSs at 12.5, 25, and 50 μg/mL concentrations did not exhibit cytotoxicity toward murine B16 melanoma cells or human epidermal melanocytes. In an in vitro skin whitening activity assay of AHG, AOSs, and NAOSs at 50 μg/mL, AHG showed the highest skin whitening activity in both murine B16 melanoma cells and human epidermal melanocytes; this activity was mediated by the inhibition of melanogenesis. Neoagarotetraose and neoagarohexaose also exhibited in vitro skin whitening activity, whereas neoagarobiose and AOSs with degrees of polymerization of 3 (agarotriose), 5 (agaropentaose), and 7 (agaroheptaose) did not. Therefore, AHG is responsible for the skin whitening activity of agar-derived sugars, and the structural differences among the AHG-containing oligosaccharides may be responsible for their different skin whitening activities.
Highlights
Melanogenesis, the process by which melanin is produced, is primarily regulated by ultraviolet (UV) light [1]
Agarose the non-reducing end, or neoagarooligosaccharides (NAOSs), which have at the non-reducing depolymerized into agarooligosaccharides (AOSs), which have D-galactose (Gal) at the non-reducing end, by liquefaction via an acid or endo-type β-agarase, respectively (Figure 1B,C) [12,13]
NAOSs have different biosynthetic pathways: AOSs are produced mainly by the acid hydrolysis of agarose, whereas NAOSs are produced by the enzymatic hydrolysis of agarose or AOSs by β-agarases. We suggest that these structural differences may be responsible for the different anti-melanogenic activity of AOSs and NAOSs in murine melanoma cells and HEMs
Summary
Melanogenesis, the process by which melanin is produced, is primarily regulated by ultraviolet (UV) light [1]. 3,6-anhydro-L-galactose (AHG) (Figure 1A), the key monomeric sugar of red macroalgae, exerts a macroalgae, exerts a marked anti-melanogenic effect [12]. Agarose the non-reducing end, or neoagarooligosaccharides (NAOSs), which have at the non-reducing depolymerized into agarooligosaccharides (AOSs), which have D-galactose (Gal) at the non-reducing end, by liquefaction via an acid or endo-type β-agarase, respectively (Figure 1B,C) [12,13]. The AOSs end, or neoagarooligosaccharides (NAOSs), which have AHG at the non-reducing end, by liquefaction or NAOSs are enzymatically hydrolyzed into neoagarobiose (NeoDP2) by an exo-type via an acid or endo-type β-agarase, respectively (Figure 1B,C) [12,13]. AOSs has not AHG, together with Gal, as their major sugar units, the anti-melanogenic activity of AOSs been reported to date.
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