Human skin comprises the epidermis and dermis, which perform interactive functional activities with each other in order to maintain the skin’s tensile strength. In particular, the dermal layer is crucial for skin protection. However, skin aging destroys collagen and elastin fibers, causing wrinkles, pigments, and sagging. Skin aging-related factors, such as tumor necrosis factor-α (TNF-α), promote the generation of intercellular reactive oxygen species (ROS). These are known to stimulate the hypersecretion of matrix metalloproteinase-1 (MMP-1), which degrades collagen and inhibits collagen synthesis. In this study, as part of our ongoing discovery of natural products, we investigated potential natural products derived from ginkgo fruit (Ginkgo biloba fruit) with protective effects against TNF-α-induced skin aging. Phytochemical investigation of the MeOH extract of G. biloba fruits, aided by liquid chromatography–mass spectrometry, led to the isolation of 14 compounds (1–14) from the n-butanol-soluble fraction. These were structurally determined to be: (E)-coniferin (1), syringin (2), 4-hydroxybenzoic acid 4-O-β-D-glucopyranoside (3), vanillic acid 4-O-β-D-glucopyranoside (4), glucosyringic acid (5), (E)-ferulic acid 4-O-β-D-glucoside (6), (E)-sinapic acid 4-O-β-D-glucopyranoside (7), ginkgotoxin-5-glucoside (8), ginkgopanoside (9), (Z)-4-coumaric acid 4-O-β-D-glucopyranoside (10), (1′R,2′S,5′R,8′S,2′Z,4′E)-dihydrophaseic acid 3’-O-β-D-glucopyranoside (11), eucomic acid (12), rutin (13), and laricitrin 3-rutinoside (L3R) (14). Biological evaluation of the isolated compounds for their effects on intracellular ROS generation showed that, of these 14 compounds, L3R (14) inhibited TNF-α-stimulated ROS generation (p < 0.001 at 100 μM). Inhibition of ROS generation by L3R led to the suppression of MMP-1 secretion and protection against collagen degradation. The inhibitory effect of L3R was mediated by the inhibition of extracellular signal regulated kinase (ERK) phosphorylation. Furthermore, L3R diminished the secretion of pro-inflammatory cytokines interleukin 6 (IL-6) and interleukin 8 (IL-8). Based on these experimental results, L3R is a potential bioactive natural product that can be used to protect against skin damage, including aging, in cosmetics and pharmaceuticals.
Yakuchinone A (1) is a bioactive diarylheptanoid isolated from the dried fruits of Alpinia oxyphylla. Microbial transformation has been recognized as an efficient method to produce new biologically active derivatives from natural products. In the present study, microbial transformation of yakuchinone A was performed with the fungus Mucor hiemalis KCTC 26779, which led to the isolation of nine new metabolites (2, 3a, 3b, and 4–9). Their structures were elucidated as (3S)-oxyphyllacinol (2), (3S,7R)- and (3S,7S)-7-hydroxyoxyphyllacinol (3a and 3b), (3S)-oxyphyllacinol-4′-O-β-d-glucopyranoside (4), (3S)-4″-hydroxyoxyphyllacinol (5), (3S)-3″-hydroxyoxyphyllacinol (6), (3S)-2″-hydroxyoxyphyllacinol (7), (3S)-2″-hydroxyoxyphyllacinol-2″-O-β-d-glucopyranoside (8), and (3S)-oxyphyllacinol-3-O-β-d-glucopyranoside (9) based on the comprehensive spectroscopic analyses and the application of modified Mosher’s method. All compounds were evaluated for their cytotoxic activities against melanoma, as well as breast, lung, and colorectal cancer cell lines. Compound 9, which was O-glucosylated on the diarylheptanoid alkyl chain, exhibited the most selective cytotoxic activities against melanoma cell lines with the IC50 values ranging from 6.09 to 9.74 μM, indicating that it might be considered as a possible anti-cancer lead compound.
Kaempferia parviflora Wall. ex Baker (Zingiberaceae), commonly known as Thai ginseng or black ginger, is a tropical medicinal plant in many regions. It has been traditionally used to treat various ailments, including ulcers, dysentery, gout, allergies, abscesses, and osteoarthritis. As part of our ongoing phytochemical study aimed at discovering bioactive natural products, we investigated potential bioactive methoxyflavones from K. parviflora rhizomes. Phytochemical analysis aided by liquid chromatography–mass spectrometry (LC-MS) led to the isolation of six methoxyflavones (1–6) from the n-hexane fraction of the methanolic extract of K. parviflora rhizomes. The isolated compounds were structurally determined to be 3,7-dimethoxy-5-hydroxyflavone (1), 5-hydroxy-7-methoxyflavone (2), 7,4′-dimethylapigenin (3), 3,5,7-trimethoxyflavone (4), 3,7,4′-trimethylkaempferol (5), and 5-hydroxy-3,7,3′,4′-tetramethoxyflavone (6), based on NMR data and LC-MS analysis. All of the isolated compounds were evaluated for their anti-melanogenic activities. In the activity assay, 7,4′-dimethylapigenin (3) and 3,5,7-trimethoxyflavone (4) significantly inhibited tyrosinase activity and melanin content in IBMX-stimulated B16F10 cells. In addition, structure–activity relationship analysis revealed that the methoxy group at C-5 in methoxyflavones is key to their anti-melanogenic activity. This study experimentally demonstrated that K. parviflora rhizomes are rich in methoxyflavones and can be a valuable natural resource for anti-melanogenic compounds.
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