The Antimelanogenic Effect of Inularin Isolated from Flowers of Inula britannica on B16F10 Melanoma Cells and Zebrafish Embryos

Abstract

Melanogenesis is a complex process by which melanin is produced by melanocytes in melanosomes [1]. Melanin is responsible for skin, hair, and eye color and plays a critical role in protecting the skin against ultraviolet radiation [2]. However, excessive melanin synthesis and accumulation are associated with hyperpigmentation disorders including freckles, melasma, and senile lentigo [3]. Regulation of melanin production is therapeutically important when treating pigmentation-related disorders. Several synthetic antimelanogenic agents are known; however, only a few are used as skin-whitening agents because of various safety issues [4]. There is an increasing need for natural melanogenesis inhibitors with fewer side effects, for cosmetic and medicinal applications [5].Inula britannica Linnaeus (Asteraceae) is well known in China ("Xuan-Fu-Hua"), as its flowers are used in traditional Chinese medicine to treat digestive disorders, bronchitis, and inflammation [6]. In a preliminary screen using B16F10 melanoma cells, we found that a flower extract of I. britannica significantly reduced melanin production [7]. However, the active principle remained unclear. Further study of I. britannica flowers yielded a new sesquiterpene, inularin. Here, we describe its isolation and structural characterization, its antimelanogenic effect in B16F10 cells, and its effect on melanin production by embryonic zebrafish.An ethanol extract of I. britannica flowers was subjected to silica gel column chromatography and divided into four fractions (A-D) based on thin-layer chromatography (TLC) data. Fraction C, which significantly reduced melanin production (65% inhibition at 50 μg/ml) by B16F10 cells, was subjected to a further series of chromatographic separation steps guided by antimelanogenic activity, leading to isolation of inularin (Fig. 1A). The material was an amorphous white powder with a molecular ion peak at m/z 349.1626 [M + Na] + on highresolution electron ionization mass spectrometry (HRESIMS), corresponding to a molecular formula of C 17 H 26 O 6 . The 1 H-NMR spectrum displayed the characteristic signals of paired olefinic protons at δ H 6.28 (1H, s) and 5.68 (1H, s), two oxygenated methine protons at δ H 5.29 (1H, m) and 3.28 (1H, dd, J = 10.4, 4.8 Hz), two singlet methyls at δ H 1.17 (3H, s) and 1.03 (3H, s), and an acetoxymethyl at δ H 1.95 (3H, s) (Table 1). The 13 C-NMR spectrum (Table 1), combined with the distortionless enhancement by polarization transfer (DEPT) data, yielded 17 carbon signals consisting of three methyls, five methylenes, four methines, three quaternary carbons, and two carbonyl carbons; the signals at δ C 172.2 and 21.2 were assigned to an acetoxy group. These spectroscopic data suggest that inularin is a eudesmane-type sesquiterpene with an acetoxy moiety, as are its analogs [8]. A complete assignment of the chemical shifts of inularin and its substitution pattern was made using various 2D-NMR techniques. The 1 H-1 H correlation spectroscopy (COSY) correlations of inularin established two segments: ...

Anti-Melanogenesis Activity of 6-O-Isobutyrylbritannilactone from Inula britannica on B16F10 Melanocytes and In Vivo Zebrafish Models

“…In our previous study, silica gel chromatography was performed on an ethanol extract of I. britannica flowers, which resulted in four fractions (A–D) based on thin-layer chromatography (TLC) data. Fraction D, which markedly reduced melanin production in B16F10 cells, was subjected to further chromatography guided by its antimelanogenic effects, leading to the isolation of an active compound [ 22 ]. This compound was an amorphous white powder with a molecular ion peak at m / z 337 [M + H] + on electron ionization mass spectrometry (ESIMS), corresponding to a molecular formula of C 19 H 28 O 5 .…”

“…A previous study reported that a flower extract of I. britannica markedly reduced melanin production in B16F10 melanoma cells [ 21 ]. Through a further study, we discovered a new sesquiterpene called inularin structure and investigated its antimelanogenic activity [ 22 ]. The aim of this study was to discover safe and effective natural compounds for skin whitening and preventing abnormal hyperpigmentation.…”

The Challenging Melanoma Landscape: From Early Drug Discovery to Clinical Approval

“…Other tested compounds using zebrafish models were recently demonstrated to possess antimelanoma potential. Among them are diphlorethohydroxycarmalol [286], theaflavin [287], ellagic acid [288], inularin [289], and BEL β-trefoil [290].…”

Skin Barrier-enhancing, Antiwrinkle, and Antimelanogenic Effects of Probiotic Lysates Composed of Nucleotides

“…Melanogenesis is the process by which melanin is produced by melanocytes in melanosomes. Melanin, which is related to the color of the skin, hair, and eyes, protects the skin from UV radiation (Jang et al, 2020). However, oversynthesis and accumulation of melanin lead to the formation of melasma and freckles on the skin (Park et al, 2019).…”