Flavonoids, taxifolin and luteolin attenuate cellular melanogenesis despite increasing tyrosinase protein levels

Constituents of Cryptotaenia japonica Inhibit Melanogenesis via CREB- and MAPK-Associated Signaling Pathways in Murine B16 Melanoma Cells

Melanin plays an important role in protecting the skin against ultraviolet light and is responsible for skin color. However, overproduction of melanin is related to several skin disorders, such as age spots, freckles, café au lait spots, Becker’s nevus and other hyperpigmentation syndromes. The aim of this study was to identify the effects of kaempferol-7-O-β-d-glucuronide (K7G) and tilianin, isolated from Cryptotaenia japonica, on melanogenesis and their mechanisms of action in murine B16 melanoma cells. The α-melanocyte-stimulating hormone (α-MSH)-induced melanin production was significantly inhibited by K7G and tilianin in a dose-dependent manner. The effects of these compounds on the signaling pathway of melanogenesis were examined. K7G and tilianin downregulated the expression of microphthalmia-associated transcription factor (MITF) and melanocyte-specific enzymes, i.e., tyrosinase and TRP1. These compounds also inhibited the phosphorylation of cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB) in a dose-dependent manner. In addition, these compounds increased the phosphorylation of extracellular signal-regulated kinase (ERK) but decreased the phosphorylation of c-Jun N-terminal kinase (JNK) in B16 cells. Based on the above results, the anti-melanogenic effects of these compounds are caused by suppression of the MAPK signaling pathway through the down-regulation of α-MSH-induced CREB accumulation. This finding suggests that K7G and tilianin may be good candidates for further research to develop therapeutic agents for hyperpigmentation diseases.

Antimelanogenic effects of luteolin 7-sulfate isolated from Phyllospadix iwatensis Makino

BACKGROUND

Abnormal deposition of melanin may cause an aesthetic skin problem; therefore, the control of unwanted excessive melanin synthesis is the major goal of cosmetic research.

OBJECTIVES

To identify novel tyrosinase (TYR) inhibitors from marine plants and examine their cellular antimelanogenic effects.

METHODS

The extracts of 50 marine plants endemic to Korea were screened against human TYR. Active constituents were then isolated from the selected plant extracts that showed potential and their chemical structures elucidated. Furthermore, their antimelanogenic effects were examined using murine melanoma B16/F10 cells and human epidermal melanocytes (HEM).

RESULTS

Among the tested extracts, that of Phyllospadix iwatensis Makino exhibited the strongest human TYR inhibitory activity. The active constituents were purified from the butanol fraction of the P. iwatensis extract and identified as hispidulin 7-sulfate and luteolin 7-sulfate. Luteolin 7-sulfate inhibited human TYR more strongly than hispidulin 7-sulfate, luteolin, hispidulin and arbutin. Furthermore, luteolin 7-sulfate showed lower cytotoxicity than luteolin in both B16/F10 cells and HEM. Luteolin 7-sulfate attenuated cellular melanin synthesis more effectively in B16/F10 cells and HEM stimulated by α-melanocyte-stimulating hormone and l-tyrosine than arbutin.

CONCLUSIONS

This study demonstrates that luteolin 7-sulfate isolated from P. iwatensis is a human TYR inhibitor with advantageous antimelanogenic properties, and would be useful for development as a therapeutic agent for the control of unwanted skin pigmentation.

Molecular mechanisms of flavonoids in melanin synthesis and the potential for the prevention and treatment of melanoma

Flavonoids are becoming popular nutraceuticals. Different flavonoids show similar or distinct biological effects on different tissues or cell types, which may limit or define their usefulness in cancer prevention and/or treatment application. This review focuses on a few selected flavonoids and discusses their functions in normal and transformed pigment cells, including cyanidin, apigenin, genistein, fisetin, EGCG, luteolin, baicalein, quercetin and kaempferol. Flavonoids exhibit melanogenic or anti-melanogenic effects mainly via transcriptional factor MiTF and/or the melanogenesis enzymes tyrosinase, DCT or TYRP-1. To identify a direct target has been a challenge as most studies were not able to discriminate whether the effect(s) of the flavonoid were from direct targeting or represented indirect effects. Flavonoids exhibit an anti-melanoma effect via inhibiting cell proliferation and invasion and inducing apoptosis. The mechanisms are also multi-fold, via ROS-scavenging, immune-modulation, cell cycle regulation and epigenetic modification including DNA methylation and histone deacetylation. In summary, although many flavonoid compounds are extremely promising nutraceuticals, their detailed molecular mechanism and their multi-target (simultaneously targeting multiple molecules) nature warrant further investigation before advancement to translational studies or clinical trials.

Antimicrobial, Anthelmintic Activities and Characterisation of Functional Phenolic Acids of Achyranthes aspera Linn.: A Medicinal Plant Used for the Treatment of Wounds and Ringworm in East Africa

Achyranthes aspera Linn. (Amaranthaceae) commonly known as Prickly Chaff flower (English) is traditionally used for treating a number of ailments. Different parts of the plant are used in treating wounds and ringworm in East Africa and elsewhere for a number of ailments. In this study, leaf extracts of A. aspera collected from two different geographical locations (Ciaat, Eritrea and Ukulinga, South Africa) were evaluated for antibacterial, antifungal, anthelmintic activities and the plant characterized for functional phenolic acids as well as protein binding capacity. The pathogens used in the tests were, two Gram-negative (Escherichia coli and Klebsiella pneumoniae), two Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus), a filamentus yeast-like fungus (Candida albicans) and a free-living nematode (Caenorhabditis elegans). The water and acetone extracts of the samples collected from Ciaat exhibited good antibacterial, antifungal and anthelmintic activity (MIC < 1 mg/ml) except the water extract against E. coli which showed moderate activity. In contrast, the extracts collected from Ukulinga exhibited moderate to weak activities except for the acetone (aq.) extracts which had good activity against some of the tested organisms. UHPLC-MS/MS revealed variation in the levels of some functional phenolic compounds, with rutin, chlorogenic acid and genistein not being detected in the extracts from Ukulinga. The variation was also observed in the protein binding capacity, which could offer a predictive wound healing model. All extracts from plant samples collected at Ciaat expressed significant dominant potency compared to similar extracts from Ukulinga.

Inhibitory Effect of Dried Pomegranate Concentration Powder on Melanogenesis in B16F10 Melanoma Cells; Involvement of p38 and PKA Signaling Pathways

Plants rich in antioxidant substances may be useful for preventing skin aging. Pomegranates, containing flavonoids and other polyphenolic compounds, are widely consumed due to their beneficial properties. We examined the underlying mechanisms of dried pomegranate concentrate powder (PCP) on melanin synthesis in B16F10 melanoma cells. The antioxidant effects of PCP were determined by measuring free radical scavenging capacity and transcript levels of antioxidant enzymes. To explore the inhibitory effects of PCP on melanin synthesis, we measured tyrosinase activity and melanin content in α-melanocyte stimulating hormone (α-MSH)-stimulated B16F10 cells. In addition, the levels of tyrosinase-related protein-1 (TRP-1), TRP-2, tyrosinase, and microphthalmia-associated transcription factor (MITF) expression were determined by Western blotting. Changes in the phosphorylation status of protein kinase A (PKA), cAMP response element-binding protein (CREB), mitogen-activated protein kinases (MAPKs), phosphatidylinositol 3-kinase (PI3K), serine/threonine kinase Akt, and glycogen kinase 3β (GSK3β) were also examined. The free radical scavenging activity of PCP increased in a dose-dependent manner. In PCP-treated B16F10 cells, transcript levels of glutathione peroxidase-1 (GPx-1) were increased compared with α-MSH-stimulated cells. In addition, PCP led to the down-regulation of phospho-p38, phospho-PKA, phospho-CREB, phospho-GSK3β, MITF, and TRP-1 compared with α-MSH-stimulated B16F10 cells. We believe this effect may be associated with PCP activity, which leads to the inhibition of melanin production and tyrosinase activity. These results suggest that PCP decreases tyrosinase activity and melanin production via inactivation of the p38 and PKA signaling pathways, and subsequently decreases phosphorylation of CREB, MITF, and melanogenic enzymes. These observations provided new insights on the molecular mechanisms of the skin-whitening property of PCP.

Oral Polypodium leucomotos increases the anti-inflammatory and melanogenic responses of the skin to different modalities of sun exposures: a pilot study

BACKGROUND

The effects on the inflammatory and tanning responses of sunlight/UVR of several oral antioxidants are still unknown.

OBJECTIVE

Assess intensity, time course of the inflammatory, and tanning responses to increasing dosages of solar-simulated radiation (SSR) at baseline and after oral supplementation of an extract of Polypodium leucotomos (PLE).

METHODS

Ten healthy subjects underwent phototesting with SSR with a visual and spectrophotometrical assessment of the responses with or without daily oral supplementation of two tablets containing 240 mg of PLE for a total of 15 days.

RESULTS

Polypodium leucotomos supplementation induced a significant increase of the minimal erythema dose (MED), a faster recovery of the inflammation following the delivery of super-erythemal doses, and no significant changes of the minimal melanogenic dose (MMD). Spectrophotometric assessment of the Δa* in test areas exposed to equally doses of SSR did not show differences.

CONCLUSIONS

Polypodium leucotomos supplementation increased the MED and induced a faster recovery of the inflammation and a stronger tanning response with no changes in the melanogenic threshold.

A study of the human skin-whitening effects of resveratryl triacetate

Resveratrol has a variety of bioactivities that include its anti-melanogenic effects, but its use in cosmetics has been challenging partly because of its chemical instability. Resveratryl triacetate (RTA) is a prodrug that can enhance stability. The purpose of this study was to examine the skin safety and whitening effects of RTA in human subjects. The primary skin irritation potentials of RTA and resveratrol were tested at 0.1 and 0.5 % on human subjects. Resveratrol at a concentration of 0.5 % induced weak skin irritation, whereas RTA did not induce any skin responses. The skin-whitening efficacy of a cosmetic formulation containing 0.4 % RTA was evaluated in two different test models. In the artificial tanning model, the test product and the control product were applied twice daily to the skin of the forearms of 22 human subjects after pigmentation induction by ultraviolet irradiation. Applying the test and the control products to the artificial tanning model for 8 weeks increased the individual topology angles (ITA°) by 17.06 and 13.81 %, respectively, a difference that was statistically significant (p < 0.05). In the hyperpigmentation model, the test product and the control product were applied twice daily to the faces of 21 human subjects. The averaged intensity of the hyperpigmented spots decreased by 2.67 % in the test group and 1.46 % in the control group, a difference that was statistically significant (p < 0.05). Therefore, RTA incorporated into cosmetic formulations can whiten human skin without inducing skin irritation.

Ultrasound-assisted extraction of arabinogalactan and dihydroquercetin simultaneously from Larix gmelinii as a pretreatment for pulping and papermaking

An ultrasound-assisted extraction (UAE) method using ethanol was applied for extracting arabinogalactan (AG) and dihydroquercetin (DHQ) simultaneously from larch wood, as a pretreatment for pulping and papermaking. The extraction parameters were optimized by a Box-Behnken experimental design with the yields of AG and DHQ as the response values. Under optimum conditions (three extractions, each using 40% ethanol, for 50 min, 200 W ultrasound power and 1∶18 solid-liquid ratio), the yields of AG and DHQ were 183.4 and 36.76 mg/g, respectively. After UAE pretreated, the wood chips were used for Kraft pulping (KP) and high boiling solvent pulping (HBSP). The pulping yield after pretreatment was higher than that of untreated (the pulping yields of untreated HBSP and KP were 42.37% and 39.60%, and the pulping yields of HBSP and KP after UAE-pretreated were 44.23% and 41.50% respectively), as indicated by a lower kappa number (77.91 and 27.30 for untreated HBSP and KP; 77.01 and 26.83 for UAE-pretreated HBSP and KP). Furthermore, the characteristics of paper produced from pretreated wood chips were superior to those from the untreated chips: the basis weight was lower (85.67 and 82.48 g·cm(-2) for paper from untreated KP and HBSP; 79.94 and 80.25 g·cm(-2) for paper from UAE-pretreated KP and HBSP), and the tensile strengths, tearing strengths, bursting strengths, and folding strengths were higher than these of paper after UAE-pretreated, respectively.

Development of an ionic liquid-based microwave-assisted method for the extraction and determination of taxifolin in different parts of Larix gmelinii

An ionic liquid-based microwave-assisted extraction method (ILMAE) was successfully applied for the extraction of taxifolin from Larix gmelinii. Different kinds of 1-alkyl-3-methylimidazolium ionic liquids with different kinds of cations and anions were studied and 1-butyl-3-methylimidazolium bromide was chosen as the optimal solvent for taxifolin extraction. The optimal conditions of ILMAE were determined by single factor experiments and Box-Behnken design as follows: [C₄mim]Br concentration of 1.00 M, soaking time of 2 h, liquid-solid ratio of 15:1 mL/g, microwave irradiation power of 406 W, microwave irradiation time of 14 min. No degradation of taxifolin had been observed under the optimum conditions as evidenced from the stability studies performed with standard taxifolin. Compared with traditional solvent and methods, ILMAE provided higher extraction yield, lower energy and time consumption. The distribution of taxifolin in different parts of larch and the influences of age, orientation, and season on the accumulation of taxifolin were analyzed for the sufficient utilization of L. gmelinii.

Screening for potential co-products in a Miscanthus sinensis mapping family by liquid chromatography with mass spectrometry detection

Society is demanding more green chemicals from sustainable sources. Miscanthus is a potential source of platform chemicals and bioethanol through fermentation. Miscanthus sinensis (M. sinensis) has been found to contain particularly high levels of soluble phenols (hydroxycinnamates and flavonoids) which may have application in the nutraceutical, cosmetic and pharmaceutical industries. Here, we describe the first study on the identification and quantification of phenols from the leaf tissue of a bi-parental M. sinensis mapping family. Parents and progeny showed complex profiles of phenols with highly related structures which complicated characterisation of individual phenotypes. Separation of semi-purified extracts by reverse-phase liquid chromatography, coupled with detection by diode array and ESI-MS/MS, enabled distinction of different profiles of phenols. Ten hydroxycinnamates (O-cinnamoylquinic acids) and several flavones (one mono-O-glycosyl flavone, eight mono-C-glycosyl flavones, two di-C-glycosyl flavones, five O-glycosyl-C-glycosyl flavones and nine 2″-O-glycosyl-C-glycosyl flavones) were identified and quantified in leaf tissue of two hundred progeny and maternal and paternal plants during the seedling stage. Progeny exhibiting high, moderate and low amounts of hydroxycinnamates and flavonoids and both parents were selected and screened at seven months' growth to determine the abundance of these phenols at their highest biomass and compared with seedlings. Concentrations of phenols generally decreased as leaves matured. Several flavone-glycosides were identified. This technique can be used for rapid screening of plants in a mapping family to identify genotypes with high phenol content to add value in the biorefinery chain. This comparative study provides information on the content of potentially valuable compounds from readily renewable resources and possible biomarkers for identification in breeding programmes.

Inhibitory and Acceleratory Effects of Inonotus obliquus on Tyrosinase Activity and Melanin Formation in B16 Melanoma Cells

The aim of the present study is to preliminarily investigate the antimelanogenesis effect of Inonotus obliquus extracts by cell-free mushroom tyrosinase assay. It was found that petroleum ether and n-butanol extracts might contain unknown potential tyrosinase inhibitors, while its ethyl acetate extract might contain some unknown accelerators. Six compounds were isolated and their structures were identified by interpretation of NMR data and nicotinic acid was first discovered in Inonotus obliquus. In cells testing, betulin and trametenolic acid decreased tyrosinase activity and melanin content, while inotodiol and lanosterol significantly increased tyrosinase activity and melanin content, showing an AC⁡₅₀ of 9.74 and 8.43 μM, respectively. Nicotinie acid, 3β,22,25-trihydroxy-lanosta-8-ene, had a little or no effect on tyrosinase. Betulin exhibited a mode of noncompetitive inhibition with a K_I = K_IS of 0.4 μM on tyrosinase activity showing an IC₅₀ of 5.13 μM and being more effective than kojic acid (6.43 μM), and trametenolic acid exhibited a mode of mixed inhibition with a K_I of 0.9 μM, K_IS of 0.5 μM, and an IC₅₀ of 7.25 μM. We proposed betulin and trametenolic acid as a new candidate of potent tyrosinase inhibitors and inotodiol and lanosterol as accelerators that could be used as therapeutic agent.

Effects of resveratrol, oxyresveratrol, and their acetylated derivatives on cellular melanogenesis

Resveratrol and oxyresveratrol are naturally occurring phenolic compounds with various bioactivities, but their uses in cosmetics have been partly limited by their chemical instabilities. This study was performed to examine the anti-melanogenic effects of the acetylated derivatives from resveratrol and oxyresveratrol. Resveratrol and oxyresveratrol were chemically modified to triacetyl resveratrol and tetraacetyl oxyresveratrol, respectively. The acetylated compounds were less susceptible than the parent compounds to oxidative discoloration. The acetylated compounds inhibited the activities of tyrosinases less than parent compounds in vitro, but they were as effective at cellular melanogenesis inhibition, indicating bioconversion to parent compounds inside cells. Supporting this notion, the parent compounds were regenerated when the acetylated compounds were digested with cell lysates. Although resveratrol and triacetyl resveratrol inhibited tyrosinase activity less effectively than oxyresveratrol and tetraacetyl oxyresveratrol in vitro, they inhibited cellular melanogenesis more effectively. This discrepancy was explained by strong inhibition of tyrosinase expression by resveratrol and triacetyl resveratrol. Experiments using a reconstituted skin model indicated that resveratrol derivatives can affect melanin synthesis and cell viability to different extents. Collectively, this study suggests that acetylated derivatives of resveratrol have great potential as anti-melanogenic agents for cosmetic use in terms of efficacy, safety, and stability.

Chemical profiling and in vitro biological effects of Cardiospermum halicacabum L. (Sapindaceae) aerial parts and seeds for applications in neurodegenerative disorders

Cardiospermum halicacabum is widely used in traditional medicine. Previous studies have focused on the aerial parts, while the seeds have been poorly investigated. This work aimed to analyse the chemical composition of extracts from aerial parts and seeds obtained using Naviglio and Soxhlet (PN, PS, and SN, SS, respectively), the inhibitory properties against tyrosinase, acetylcholinesterase (AChE), and butyrylcholinesterase (BChE) and the antioxidant effects. PN total extract showed significant anti-tyrosinase activity (IC50 value of 10.8 µg/mL). After partitioning with n-hexane, an HPLC method for analysing chemical constituents was established. Apigenin, luteolin, and apigenin-7-O-glucoside are the predominant constituents. SN n-hexane fraction was the most active inhibitor of BChE (IC50 of 57.9 µg/mL). Gas chromatography-mass spectrometry analysis revealed fatty acids, including eicosanoic acid, methyl 11-eicosenoate and oleic acid, as the major constituents. These findings suggest the potentiality of both seeds and aerial parts of C. halicacabum in the treatment of neurological disorders.

Inhibitory effects of salidroside and paeonol on tyrosinase activity and melanin synthesis in mouse B16F10 melanoma cells and ultraviolet B-induced pigmentation in guinea pig skin

Salidroside, the major active component of Rhodiola rosea, a herb with antioxidant, free radical scavenging and tyrosinase inhibitory effects, has been recently reported in protecting the kerationcytes from the UV radiation, suggesting the potential of this component in depigmentation. Paeonol is isolated from Moutan Cortex Radicis with anti-inflammation/microbial activities, was reported to induce the down-regulation of microphthalmia-associated transcription factor and subsequently tyrosinase. To testify the potential of these compounds as melanin formation inhibitors for hyperpigmentation therapy, the influence of salidroside and paeonol on pigmentation was investigated. With arbutin as a positive control, salidroside and paeonol were evaluated for their inhibitory effect on the cell viability, tyrosinase activity and melanin synthesis in B16F10 melanoma cells, as well as their effects in UVB-induced hyperpigmentation in brown guinea pig skins. It was demonstrated that the significant inhibition of salidroside (33.0%) and paeonol (22.2-30.9%) on the tyrosinase activity is slightly lower than that of arbutin (18.4-44.7%). However, salidroside exhibited the dose-dependent inhibition (30.6-42.0%) in melanin synthesis at a low concentration of 100 μM, paeonol and arbutin expressed inhibition rates of 27.4-37.2% and 25.8-45.6% within 500-1000 μM. The in vivo topical application of these compounds was demonstrated to obviously decrease the hyperpigmentation on UVB stimulated guinea pig skin. This study provided the original evidence for the salidroside and paeonol as therapeutic agents for pigmentation disorder and skin lightening, with further clinical investigation of these compounds in the field of depigmentation was suggested.

Inhibition of c-Kit signaling by diosmetin isolated from Chrysanthemum morifolium

The interaction of stem cell factor (SCF) with its cognate receptor c-Kit is closely associated with the survival and maturation of melanocytes. To investigate novel depigmentation agents, we screened 2,000 plant extracts for c-Kit inhibitors to identify active small molecules by using time-resolved fluorescence enzyme assays. For the active extracts identified as inhibitors of c-Kit enzyme, we evaluated the effects of the active extracts and isolated flavonoids on c-Kit phosphorylation in MO7e/melanocytes. Anti-melanogenic activity was also examined in melanocytes and melanoderm model. The flavonoids such as diosmetin, apigenin, acacetin and luteolin isolated from Chrysanthemum morifolium were found to be active in inhibiting c-Kit both at enzyme and cellular levels. In addition, these flavonoids attenuated SCF-induced proliferation of human primary melanocytes without toxicity and suppressed ultraviolet (UV) B irradiation-mediated melanin synthesis significantly. Among the active flavonoids, diosmetin was found to inhibit SCF-induced melanogenesis in a human melanoderm model. These results strongly suggest that C. morifolium extract and diosmetin have potential to suppress SCF-/UVB-induced melanogenesis, and could be developed as anti-pigmentation agents.

Isolation of resveratrol from vitis viniferae caulis and its potent inhibition of human tyrosinase

Tyrosinase (TYR) catalyzes rate-limiting reactions of cellular melanin synthesis, and its inhibitors are of commercial interest as potential skin whitening agents. However, the limited availability of human TYR makes the screening of TYR inhibitors difficult. To overcome this hurdle, we transformed nonmelanocytic human embryonic kidney (HEK) 293 cells to express human TYR constitutively. Using these cells as a source of human TYR, the ethanolic extracts of 52 medicinal plants grown in Korea were tested for human TYR activity, and the extract of Vitis Viniferae Caulis (dried stems of the grape tree, Vitis vinifera L.) was found to inhibit human TYR activity potently. An active compound was isolated from this extract by solvent fractionation followed by liquid column chromatography and identified as resveratrol by spectroscopic and chromatographic analyses. Resveratrol was determined to be a highly potent inhibitor of human TYR (IC50 = 0.39 μg mL⁻¹) as compared with p-coumaric acid (IC50 = 0.66 μg mL⁻¹) and arbutin (IC50 > 100 μg mL⁻¹) and inhibited melanin synthesis by human epidermal melanocytes at subtoxic concentrations. This study suggests that resveratrol and resveratrol-containing extracts of Vitis Viniferae Caulis have a potential use as skin whitening agents.

Cyclohexanediol bis-ethylhexanoate inhibits melanogenesis of murine B16 melanoma and UV-induced pigmentation in human skin

The role of cyclohexane diester analogues in the formation of melanin has been recently reported. In the present study, we investigated the inhibitory effect of cyclohexanediol bis-ethylhexanoate (CHEH) on melanogenesis in B16 melanoma cells and on UV-B-induced pigmentation in human skin. CHEH significantly reduced the melanin content in a dose-dependent manner, without cytotoxic effects at the effective concentrations. Moreover, CHEH dose-dependently inhibited tyrosinase activity in B16 melanoma cells, as confirmed by Western blot analysis of the tyrosinase protein levels. However, tyrosinase transcript levels remained unchanged under the same experimental conditions. These results indicate that CHEH inhibited melanogenesis in B16 melanoma cells by regulating tyrosinase activity at the post-transcriptional level. On the other hand, in a cell-free system, CHEH did not inhibit tyrosinase activity. This indicated that CHEH suppressed the pigmentation of melanocytes by indirectly regulating tyrosinase activity. Finally, in a clinical trial, a cream containing 1.0% CHEH showed good whitening effect on UV-induced pigmented human skin without adverse effects. In conclusion, we suggest that CHEH may be an effective inhibitor of melanogenesis and useful effects in the treatment of hyperpigmented disorders.

Characterization of tyrosinase inhibitors in the twigs of Cudrania tricuspidata and their structure-activity relationship study

The twigs of Cudrania tricuspidata were found to show strong tyrosinase inhibitory activity, and further detailed component analysis resulted in the isolation of a new flavanol glucoside, (2S,3S)-2,3-trans-dihydromorin-7-O-β-d-glucoside (1), plus twenty-seven known compounds (2-28). Their structures were elucidated on the basis of ESI-MS and NMR spectral data. Among the isolated compounds, trans-dihydromorin (8), oxyresveratrol (9), and steppogenin (12) were found to exhibit significant tyrosinase inhibition activities. Moreover, the structure-activity relationship of these isolated compounds was also discussed.

Natural Melanogenesis Inhibitors Acting Through the Down-Regulation of Tyrosinase Activity

Melanogenesis is a biosynthetic pathway for the formation of the pigment melanin in human skin. A key enzyme, tyrosinase, catalyzes the first and only rate-limiting steps in melanogenesis, and the down-regulation of enzyme activity is the most reported method for the inhibition of melanogenesis. Because of the cosmetically important issue of hyperpigmentation, there is a big demand for melanogenesis inhibitors. This encourages researchers to seek potent melanogenesis inhibitors for cosmetic uses. This article reviews melanogenesis inhibitors that have been recently discovered from natural sources. The reaction mechanisms of the inhibitors on tyrosinase activity are also discussed.

Extraction of dihydroquercetin from Larix gmelinii with ultrasound-assisted and microwave-assisted alternant digestion

An ultrasound and microwave assisted alternant extraction method (UMAE) was applied for extracting dihydroquercetin (DHQ) from Larix gmelinii wood. This investigation was conducted using 60% ethanol as solvent, 1:12 solid to liquid ratio, and 3 h soaking time. The optimum treatment time was ultrasound 40 min, microwave 20 min, respectively, and the extraction was performed once. Under the optimized conditions, satisfactory extraction yield of the target analyte was obtained. Relative to ultrasound-assisted or microwave-assisted method, the proposed approach provides higher extraction yield. The effect of DHQ of different concentrations and synthetic antioxidants on oxidative stability in soy bean oil stored for 20 days at different temperatures (25 °C and 60 °C) was compared. DHQ was more effective in restraining soy bean oil oxidation, and a dose-response relationship was observed. The antioxidant activity of DHQ was a little stronger than that of BHA and BHT. Soy bean oil supplemented with 0.08 mg/g DHQ exhibited favorable antioxidant effects and is preferable for effectively avoiding oxidation. The L. gmelinii wood samples before and after extraction were characterized by scanning electron microscopy. The results showed that the UMAE method is a simple and efficient technique for sample preparation.

Involvement of the p38 MAPK and ERK signaling pathway in the anti-melanogenic effect of methyl 3,5-dicaffeoyl quinate in B16F10 mouse melanoma cells

Methyl 3,5-dicaffeoyl quinate (MDQ), an active compound present in Kalopanax pictus, Salicornia herbacea L., Aster oharai and Solidago virga-aurea var. gigantean, is a dicaffeoylquinic acid derivative esterified by methanol. Recent studies have revealed that MDQ possesses multiple pharmacological activities, such as antitumor, antioxidative and cytoprotective activities. To date, there has been no attempt to test the action of MDQ in melanocytes. In this study, we investigated the effect of MDQ on melanogenesis in B16F10 mouse melanoma cells. MDQ inhibited melanin production and tyrosinase activity in B16F10 mouse melanoma cells without a direct inhibitory effect on mushroom tyrosinase activity. Furthermore, we also found that MDQ decreased protein expression levels of microphthalmia-associated transcription factor (MITF) and tyrosinase in B16F10 melanin cells. Meanwhile, phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) was significantly reduced after 6h MDQ treatment, and this expression recovered at 48 h. The phosphorylation of extracellular signal-regulated kinase (ERK) was significantly enhanced at 12-48 h, whereas no effect was observed in the phosphorylation of Akt. In addition, MDQ treatment did not significantly alter the expression levels of total p38 MAPK, ERK, and Akt. Thus, it seems that inhibition of phospho-p38 MAPK and activation of phospho-ERK may lead to the suppression of melanogenesis in MDQ-treated B16F10 mouse melanoma cells.

Inhibitory effects of Sargassum polycystum on tyrosinase activity and melanin formation in B16F10 murine melanoma cells

ETHNOPHARMACOLOGICAL RELEVANCE

Sargassum polycystum, a type of brown seaweed, has been used for the treatment of skin-related disorders in traditional medicine.

AIM OF THE STUDY

The aim of the present study is to investigate the antimelanogenesis effect of Sargassum polycystum extracts by cell-free mushroom tyrosinase assay followed by cell viability assay, cellular tyrosinase assay and melanin content assay using B16F10 murine melanoma cells.

MATERIALS AND METHODS

Sargassum polycystum was extracted with 95% ethanol and further fractionated with hexane, ethyl acetate and water. The ethanolic crude extract and its fractionated extracts were tested for their potential to act as antimelanogenesis or skin-whitening agents by their abilities to inhibit tyrosinase activity in the cell-free mushroom tyrosinase assay and cellular tyrosinase derived from melanin-forming B16F10 murine melanoma cells. The tyrosinase inhibitory activity was correlated to the inhibition of melanin production in α-MSH-stimulated and unstimulated B16F10 cells.

RESULTS

Sargassum polycystum ethanolic extract and its fractions had little or no inhibitory effect on mushroom tyrosinase activity. However, when tested on cellular tyrosinase, the ethanolic extract and its non-polar fraction, hexane fraction (SPHF), showed significant inhibition of cellular tyrosinase activity. In parallel to its cellular tyrosinase inhibitory activity, SPHF was also able to inhibit basal and α-MSH-stimulated melanin production in B16F10 cells.

CONCLUSIONS

Our findings showed that (i) cellular tyrosinase assay is more reliable than mushroom tyrosinase assay in the initial testing of potential antimelanogenesis agents and, (ii) SPHF inhibited melanogenesis by inhibiting cellular tyrosinase activity. SPHF may be useful for treating hyperpigmentation and as a skin-whitening agent in cosmetics industry.

Comparison of the antimelanogenic effects of p-coumaric acid and its methyl ester and their skin permeabilities

BACKGROUND

p-Coumaric acid (PCA) inhibits human tyrosinase (TYR) activity and melanin synthesis in human epidermal melanocytes.

OBJECTIVE

The purpose of the current study was to examine the potential of PCA and its hydrophobic derivative, methyl p-coumarate (MPC), as hypopigmenting agents for topical use.

METHODS

PCA and MPC were comparatively tested against in vitro human TYR enzyme activity and cellular melanin synthesis in human epidermal melanocytes. Permeation studies were undertaken using an artificial lipophilic membrane and an excised porcine skin. In vivo hypopigmenting efficacy was assessed on the skin of melanin-possessing hairless mice exposed to UVB.

RESULTS

Although PCA was a stronger inhibitor than MPC against TYR activity in vitro, the former inhibited cellular melanin synthesis less effectively than the latter. A non-cell based permeability assay indicated that PCA was practically impermeable through the lipophilic barrier while MPC was highly permeable. In contrast, an ex vivo skin permeation study demonstrated that topically applied PCA in the form of a cream can diffuse into the aqueous medium underneath the skin. No MPC was released from a MPC cream but PCA was released instead as a bio-converted product. Topical application of PCA cream attenuated the UVB-induced erythema formation and pigmentation in mice models, more effectively compared with MPC cream.

CONCLUSION

PCA may be useful as an active ingredient for topical applications for a hypopigmenting effect. MPC has potential as a hypopigmenting agent but requires rather invasive methods for its delivery to the target cells.

Inhibitory effect of rose hip (Rosa canina L.) on melanogenesis in mouse melanoma cells and on pigmentation in brown guinea pigs

The compounds present in rose hips exerting an inhibitory action against melanogenesis in B16 mouse melanoma cells were investigated by dividing an aqueous extract of rose hips (RE) into four fractions. The 50% ethanol eluate from a DIAION HP-20 column significantly reduced the production of melanin and was mainly composed of procyanidin glycosides. We also found that this 50% ethanol eluate reduced the intracellular tyrosinase activity and also had a direct inhibitory effect on tyrosinase obtained as a protein mixture from the melanoma cell lysate. We also investigated the effect of orally administering RE on skin pigmentation in brown guinea pigs, and found that the pigmentation was inhibited together with the tyrosinase activity in the skin. These data collectively suggest that proanthocyanidins from RE inhibited melanogenesis in mouse melanoma cells and guinea pig skin, and could be useful as a skin-whitening agent when taken orally.

Quercetin inhibits α-MSH-stimulated melanogenesis in B16F10 melanoma cells

Quercetin is known to inhibit tyrosinase activity and melanin production in melanocytes. However, several reports suggest that quercetin has different and opposite effects on melanogenesis. This study examined the precise effects of quercetin on melanogenesis using cell-free assay systems and melanocytes. Quercetin inhibited the monophenolase and diphenolase activities of tyrosinase, and melanin synthesis in cell-free assay systems. Quercetin induced mild stimulation of the tyrosinase activity and dihydroxyphenylalaminechrome tautomerase (TRP-2) expression but only at low concentrations (<20 μm) in B16F10 melanoma cells. In contrast, the addition of 50 μm quercetin to the cells led to a significant decrease in the activity and synthesis of tyrosinase, as well as a decrease in the expression of tyrosinase-related protein-1 and TRP-2 proteins, regardless of the presence or absence of α-melanocyte stimulating hormone (α-MSH). Quercetin also reduced the intracellular cAMP and the phosphorylated protein kinase A levels in α-MSH-stimulated B16F10 cells. Moreover, quercetin (20 μm) diminished the expression and activity of tyrosinase, and melanin content in cultured normal human epidermal melanocytes. These effects were not related to its cytotoxic action. Although the in vivo effects of quercetin are still unclear, these results suggest that quercetin could play important roles in controlling melanogenesis.

The melanogenesis and mechanisms of skin-lightening agents--existing and new approaches

Skin-lightening products are commercially available for cosmetic purposes to obtain lighter skin complexion. Clinically, they are also used for treatment of hyperpigmentary disorders such as melasma, café au lait spot and solar lentigo. All of these target naturally melanin production, and many of the commonly used agents are known as competitive inhibitors of tyrosinase, one of the key enzymes in melanogenesis. In this review, we present an overview of commonly used skin-whitening ingredients that are commercialized, but we also hypothesize on other mechanisms that could be important targets to control skin pigmentation such as for example regulation of the adrenergic and glutaminergic signalling and also control of tetrahydrobiopterins in the human skin.

Inhibitory effect of quercetin isolated from rose hip (Rosa canina L.) against melanogenesis by mouse melanoma cells

We investigated the effects of compounds isolated from a methanolic extract of rose hips on melanin biosynthesis in B16 mouse melanoma cells and the possible mechanisms responsible for the inhibition of melanin biosynthesis. We found that, among the isolated compounds, quercetin was a particularly potent melanogenesis inhibitor. To reveal the mechanism for this inhibition, the effects on tyrosinase of B16 mouse melanoma were measured. Quercetin decreased the intracellular tyrosinase activity as well as the tyrosinase activity in a cell culture-free system. We also examined the cellular level of tyrosinase protein and found that quercetin dose-dependently inhibited tyrosinase protein expression. We consider from these results that the inhibition of melanogenesis by quercetin was due to the inhibition of both tyrosinase activity and of the protein expression.

Inhibition of melanogenesis by tyrosinase siRNA in human melanocytes

Tyrosinase (TYR) plays a critical role in cellular melanogenesis and, thus, has been the major target of pharmacological approaches for the control of skin pigmentation. This study examined an alternative molecular approach using TYR-small interfering RNA (siRNA) to control melanogenesis in the human melanocytes. Both the mRNA and protein levels of TYR were significantly lowered by TYR-siRNA treatment, whereas TYR-related protein 1 and TYR-related protein 2 displayed no such changes. TYR-siRNA treatment inhibited the cellular melanin synthesis from the externally supplied TYR substrate L-tyrosine. TYR-siRNA also suppressed melanin synthesis and decreased the viability of cells exposed to ultraviolet radiation, supporting a critical role of melanin in protection against ultraviolet radiation. These results suggest that molecular approaches using siRNA targeted to the enzymes of melanogenic pathway may provide a novel strategy for the control of cell pigmentation.

An updated review of tyrosinase inhibitors

Tyrosinase is a multifunctional, glycosylated, and copper-containing oxidase, which catalyzes the first two steps in mammalian melanogenesis and is responsible for enzymatic browning reactions in damaged fruits during post-harvest handling and processing. Neither hyperpigmentation in human skin nor enzymatic browning in fruits are desirable. These phenomena have encouraged researchers to seek new potent tyrosinase inhibitors for use in foods and cosmetics. This article surveys tyrosinase inhibitors newly discovered from natural and synthetic sources. The inhibitory strength is compared with that of a standard inhibitor, kojic acid, and their inhibitory mechanisms are discussed.