Relationship between tyrosinase inhibitory action and oxidation-reduction potential of cosmetic whitening ingredients and phenol derivatives

Skin-whitening effects of Spergularia marina by suppressing MITF translocation

Spergularia marina is a plant that grows in salty regions along the coastline and exerts radical-scavenging and anti-inflammatory effects. In this study, we investigated the skin-whitening effects of S. marina extract (SME) in B16F10 melanoma cells. SME was found to exert radical-scavenging effects. It suppressed α-melanocyte-stimulating hormone-induced melanogenesis and tyrosinase activity. We also assessed the melanin production signaling pathway to identify the inhibitory action mechanism of SME on melanogenesis. SME decreased the protein expression levels of tyrosinase-related protein (TRP)-1, TRP-2, and tyrosinase, which play important roles in melanogenesis. Furthermore, western blotting revealed that SME inhibited the nuclear translocation of melanocyte inducing transcription factor (MITF), which is a transcription factor for TRP-1, TRP-2, and tyrosinase, suggesting that SME exerts its skin-whitening effect by inhibiting MITF nuclear translocation. Therefore, SME may potentially be used in skin-whitening medicines and cosmetics.

Tyrosinase Inhibitors Naturally Present in Plants and Synthetic Modifications of These Natural Products as Anti-Melanogenic Agents: A Review

Tyrosinase is a key enzyme target to design new chemical ligands against melanogenesis. In the current review, different chemical derivatives are explored which have been used as anti-melanogenic compounds. These are different chemical compounds naturally present in plants and semi-synthetic and synthetic compounds inspired by these natural products, such as kojic acid produced by several species of fungi; arbutin-a glycosylated hydroquinone extracted from the bearberry plant; vanillin-a phenolic aldehyde extracted from the vanilla bean, etc. After enzyme inhibition screening, various chemical compounds showed different therapeutic effects as tyrosinase inhibitors with different values of the inhibition constant and IC₅₀. We show how appropriately designed scaffolds inspired by the structures of natural compounds are used to develop novel synthetic inhibitors. We review the results of numerous studies, which could lead to the development of effective anti-tyrosinase agents with increased efficiency and safety in the near future, with many applications in the food, pharmaceutical and cosmetics industries.

Asparagus cochinchinensis: A review of its botany, traditional uses, phytochemistry, pharmacology, and applications

Asparagus cochinchinensis (Lour.) Merr. (A. cochinchinensis) is a traditional herbal medicine that is used to treat constipation, fever, pneumonia, stomachache, tracheitis, rhinitis, cataract, acne, urticaria. More than 90 compounds have been identified from different structural types in A. cochinchinensis, including steroidal saponins, C21-steroides, lignans, polysaccharides, amino acids, etc. These bioactive ingredients make A. cochinchinensis remarkable for its pharmacological effects on anti-asthma, anti-inflammatory, anti-oxidation, anti-tumor, improving Alzheimer’s disease, neuroprotection, gut health-promoting and so on. Moreover, A. cochinchinensis also plays an important role in food, health product, cosmetic, and other fields. This review focused on the research publications of A. cochinchinensis and aimed to summarize the advances in the botany, traditional uses, phytochemistry, pharmacology, and applications which will provide reference for the further studies and applications of A. cochinchinensis.

Enzymatic Biosynthesis of Simple Phenolic Glycosides as Potential Anti-Melanogenic Antioxidants

Simple phenolics (SPs) and their glycosides have recently gained much attention as functional skin-care resources for their anti-melanogenic and antioxidant activities. Enzymatic glycosylation of SP aglycone make it feasible to create SP glycosides with updated bioactive potentials. Herein, a glycosyltransferase (GT)-encoding gene was cloned from the fosmid libraries of Streptomyces tenjimariensis ATCC 31603 using GT-specific degenerate PCR followed by in silico analyses. The recombinant StSPGT was able to flexibly catalyze the transfer of two glycosyl moieties towards two SP acceptors, (hydroxyphenyl-2-propanol [HPP2] and hydroxyphenyl-3-propanol [HPP3]), generating stereospecific α-anomeric glycosides as follows: HPP2-O-α-glucoside, HPP2-O-α-2″-deoxyglucoside, HPP3-O-α-glucoside and HPP3-O-α-2″-deoxyglucoside. This enzyme seems not only to prefer UDP-glucose and HPP2 as a favorable glycosyl donor and acceptor, respectively but also differentiates the positional difference of the hydroxyl function as acceptor catalytic sites. Paired in vitro and in vivo antioxidant assays represented SPs and their corresponding glycosides as convincing antioxidants in a time- and concentration-dependent manner by scavenging DPPH radicals and intracellular ROS. Even compared to the conventional agents, HPP2 and glycoside analogs displayed improved tyrosinase inhibitory activity in vitro and still suppressed in vivo melanogenesis. Both HPP2 glycosides are further likely to exert the best inhibitory activity against elastase, eventually highlighting these glycosides with enhanced anti-melanogenic and antioxidant activities as promising anti-wrinkle hits.

Hop Tannins as Multifunctional Tyrosinase Inhibitor: Structure Characterization, Inhibition Activity, and Mechanism

The application of hops could be extended to obtain higher commercial values. Tannins from hops were assessed for their tyrosinase inhibition ability, and the associated mechanisms were explored. Nuclear magnetic resonance (NMR) and high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry (HPLC–ESI–MS/MS) revealed that the hop tannins were characterized as condensed tannins with (epi)catechin and (epi)gallocatechin as subunits and an average polymerization degree of 10.32. Tyrosinase inhibition assay indicated that hop tannins had an IC₅₀ = 76.52 ± 6.56 μM. Kinetic studies of the inhibition processes indicated the tannins provided inhibition through competitive–uncompetitive mixed reactions. In silico molecule docking showed that tannins were bound to the active site of tyrosinase via hydrogen and electrovalent bonds. Circular dichroism (CD) observed the structural variation in the tyrosinase after reacting with the tannins. Fluorescence quenching analysis and free radical scavenging assays indicated that the tannins had copper ion chelating and antioxidant activities, which may also contribute to inhibition. The intracellular inhibition assay revealed that the melanin was reduced by 34.50% in B16F10 cells. These results indicate that these tannins can be applied as whitening agents in the cosmetics industry.

Acceleration of the bio-reduction of methyl orange by a magnetic and extracellular polymeric substance nanocomposite

Extracellular electron transfer (EET) plays an important role in bio-reduction of environmental pollutants. Extracellular polymeric substances (EPS), a kind of biogenic macromolecule, contain functional groups responsible for acceleration of EET. In this study, azo dye-methyl orange (MO) was chosen as a model pollutant, and a Fe₃O₄ and EPS nanocomposite (Fe₃O₄@EPS) was prepared to evaluate its promotion on the bio-reduction of MO. The flower-like core-shell configuration of Fe₃O₄@EPS with a 12 nm of light layer of EPS was confirmed by TEM. The redox ability of EPS was well reserved on Fe₃O₄@EPS by FTIR and electrochemical test. The application of Fe₃O₄@EPS on sustained acceleration of MO decolorization were confirmed by batch experiments and anaerobic sequenced batch reactors. Due to biocompatibility of the biogenic shell, the as-prepared Fe₃O₄@EPS exhibited low toxic to microorganisms by the Live/dead cell test. Moreover, negligible leaching of EPS under high concentration of various anions and less than 10% of EPS was released under extreme acidic and basic pH condition. The results of study provided a new preparation method of biological intimate and environmentally friendly redox mediators and suggested a feasible way for its use on bio-reduction of pollutants.

Health Benefits and Pharmacological Properties of Hinokitiol

Hinokitiol is a natural bioactive compound found in several aromatic and medicinal plants. It is a terpenoid synthetized and secreted by different species as secondary metabolites. This volatile compound was tested and explored for its different biological properties. In this review, we report the pharmacological properties of hinokitiol by focusing mainly on its anticancer mechanisms. Indeed, it can block cell transformation at different levels by its action on the cell cycle, apoptosis, autophagy via inhibiting gene expression and dysregulating cellular signaling pathways. Moreover, hinokitiol also exhibits other pharmacological properties, including antidiabetic, anti-inflammatory, and antimicrobial effects. It showed multiple and several effects through its inhibition, interaction and/or activation of the main cellular targets inducing these pathologies.

Cylindromicin from Arctic-Derived Fungus Tolypocladium sp. SCSIO 40433

The fungus strain SCSIO 40433 was isolated from an Arctic-derived glacier sediment sample and characterized as Tolypocladium cylindrosporum. A new compound, cylindromicin (1), and seven known secondary metabolites (2–8) were isolated from this strain. The chemical structures of these compounds were elucidated by comprehensive spectroscopic analyses. Cylindromicin (1) featured a 3,4-dihydro-2H-pyran skeleton. The absolute configuration of compound 1 was assigned via interpretation of key Nuclear Overhauser Effect Spectroscopy (NOESY) correlations and Electronic Circular Dichroism (ECD) calculation. Cylindromicin (1) exhibited significant tyrosinase inhibition activity. This study highlights Polar fungi as a potential resource for new bioactive natural products.

SAR and QSAR research on tyrosinase inhibitors using machine learning methods

Tyrosinase is a key rate-limiting enzyme in the process of melanin synthesis, which is closely related to human pigmentation disorders. Tyrosinase inhibitors can down-regulate tyrosinase to effectively reduce melanin synthesis. In this work, we conducted structure-activity relationship (SAR) study on 1097 diverse mushroom tyrosinase inhibitors. We applied five kinds of machine learning methods to develop 15 classification models. Model 5B built by fully connected neural networks and ECFP4 fingerprints achieved the highest prediction accuracy of 91.36% and Matthews correlation coefficient (MCC) of 0.81 on the test set. The applicability domains (AD) of classification models were defined by d S T D - P R O method. Moreover, we clustered the 1097 inhibitors into eight subsets by K-Means to figure out inhibitors' structural features. In addition, 10 quantitative structure-activity relationship (QSAR) models were constructed by four machine learning methods based on 813 inhibitors. Model 6 J, the best QSAR model, was developed by fully connected neural networks with 50 RDKit descriptors. It resulted in a coefficient of determination (r ²) of 0.770 and a root mean squared error (RMSE) of 0.482 on the test set. The AD of Model 6 J was visualized by Williams plot. The models built in this study can be obtained from the authors.

Age-Deterring and Skin Care Function of a Polyphenol Rich Sugarcane Concentrate

Increasing evidence suggests that environmental stress, such as UV radiation, generates reactive oxygen and nitrogen species in skin cells, leading to histochemical changes including skin disorders and aging, hyper pigmentation, and increased formation of wrinkles. Besides the defensive system in skin composed of vitamins and intrinsic antioxidant enzymes, topical and skin conditioning products have been used commonly to eradicate or eliminate these skin ailments. Among various ingredients providing nourishing and moisturizing effect in skin, antioxidants have been reported to be a key ingredient to counteract skin aging processes and skin disorders. Derived from a patented extraction process, a polyphenol rich sugarcane concentrate (Officinol™) becomes the focus of this study due to its rich content of polyphenols known to be strong antioxidants. In this work, we carried out a series of cell-based in vitro studies to examine the use of Officinol™ in anti-aging and skin care functions. Our studies show that Officinol™ activated telomerase, a major biomarker that have been reported to be associated with slowed cellular aging process. When skin cells were under environmental stress such as UV radiation, Officinol™ inhibited MMP-1, an interstitial collagenase in skin cells, and deterred the breakdown of collagen that provides supple texture in skin. Officinol™ also inhibited cellular expression of melanin pigmentation and tyrosinase activity, two major biomarkers causing skin pigmentation and aging spots, and inhibited elastase, an enzyme that facilities the reduction of skin elasticity. At the end of the investigation, we carried out a 10-person, pilot study to examine the effect of Officinol™ on skin lightening and fine line and wrinkle reduction in human skin. The combination of the in vitro and the human pre-study indicates that Officinol™ could provide significant preventative and protective functions including antioxidant, anti-aging, wrinkle reduction, and skin brightening for human skin suffering from aging and other stress. These findings are to be confirmed with a larger scale clinical study at a later stage.

Anti-melanogenic activity of methanolic extract from leaves of Sorbaria sorbifolia var. stellipila Max. on α-MSH-stimulated B16 melanoma 4A5 cells

Background

Melanin is a pigment, which is widely distributed in organisms. In humans, melanin pigments determine eye, hair, and skin color and protect the skin from damage by ultraviolet radiation; however, immoderate distribution of melanin in the skin causes discoloration. In the present study, we screened methanolic extracts from leaves of 47 plant species, most of which are native to East Asia, for the inhibitory activity against melanogenesis.

Methods

B16 melanoma 4A5 cells were used in all assays conducted in this study. Melanin content assay was performed using methanolic extracts from leaves of 47 plant species. Cytotoxicity of the extract from leaves of Sorbaria sorbifolia var. stellipila Max. (SME) was evaluated by WST-8 assay. Tyrosinase activity was determined using the lysate of α-MSH-stimulated B16 melanoma 4A5 cells and L-dopa as a colorimetric substrate. Melanogenic gene expression was determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR).

Results

SME showed the highest inhibitory activity among tested samples without cytotoxicity. SME exhibited the inhibition potency for the enzymatic activity of tyrosinase. In addition, qRT-PCR result displayed that SME downregulates the expression of melanogenic genes including tyrosinase, TRP-1, TRP-2, and the transcription factor MITF.

Conclusion

Overall results revealed that the extract from leaves of S. sorbifolia var. stellipila Max. has a potential to be used as a skin whitening agent.

Inhibition of melanogenesis by sodium 2-mercaptoethanesulfonate

Sodium 2-mercaptoethanesulfonate (mesna) is a protective agent that is widely used in medicine because of its antioxidant effects. Recently, reactive oxygen species (ROS) were shown to increase pigmentation. Thus, ROS scavengers and inhibitors of ROS production may suppress melanogenesis. Forkhead box-O3a (FoxO3a) is an antimelanogenic factor that mediates ROS-induced skin pigmentation. In this study, we aimed to investigate the whitening effect of mesna and the signaling mechanism mediating this effect. Human melanoma (MNT-1) cells were used in this study. mRNA and protein expression were measured by real-time quantitative PCR and Western blotting analysis to track changes in FoxO3a-related signals induced by mesna. An immunofluorescence assay was performed to determine the nuclear translocation of FoxO3a. When MNT-1 melanoma cells were treated with mesna, melanin production and secretion decreased. These effects were accompanied by increases in FoxO3a activation and nuclear translocation, resulting in downregulation of four master genes of melanogenesis: MITF, TYR, TRP1, and TRP2. We found that mesna, an antioxidant and radical scavenger, suppresses melanin production and may therefore be a useful agent for the clinical treatment of hyperpigmentation disorders.

Safety and efficacy of parenteral glutathione as a promising skin lightening agent: A controlled assessor blinded pharmacohistologic and ultrastructural study in an animal model

Hyperpigmentation was induced in the skin of experimental animals using UVB at 6 J/cm² three times a week for three consecutive weeks. Subsequently, glutathione was injected intraperitoneally in the experimental animals at doses of 10, 20, and 40 mg/kg body weight three times a week for three consecutive weeks. At the end of the experiment, blood samples and lung, kidney, liver, and skin tissue specimens were collected from animals for hematological, biochemical, histological, and electron microscopy examination. Glutathione at 40 mg/kg body weight/day reduced skin hyperpigmentation significantly, except at low doses. The skin lightening effect assessed by a chromameter was dose-dependent. There were no statistically significant differences among the mean values of AST, ALT, creatinine, BUN, and CBC counts across the four groups. Lung, kidney, and liver tissue specimens did not show any histological toxic changes. The number of melanin granules was significantly lower in the group treated with the highest dose of glutathione compared to that in the control. Electron microscopy proved that glutathione at 20 and 40 mg/kg body weight/day was able to reduce the number of melanized cells significantly compared to that in the control. Parenteral glutathione was effective as a skin lightening agent and did not provoke any toxic effects in the employed animal model. The limitation of the study was conducted in guinea pigs and was of short-term duration.

Topical treatment strategies to manipulate human skin pigmentation

Skin pigmentation is a result of melanin produced by melanocytes in the epidermis. Melanocyte activity, along with the type and distribution of melanins, is the main driver for diversity of skin pigmentation. Dark melanin acts to protect against the deleterious effects of ultraviolet (UV) radiation, including photo-aging and skin cancer formation. In turn, UV radiation activates skin melanocytes to induce further pigmentation (i.e., "tanning pathway"). The well-characterized MSH/MC1R-cAMP-MITF pathway regulates UV-induced melanization. Pharmacologic activation of this pathway ("sunless tanning") represents a potential strategy for skin cancer prevention, particularly in those with light skin or the "red hair" phenotype who tan poorly after UV exposure due to MC1R inactivating polymorphisms. Skin hyperpigmentation can also occur as a result of inflammatory processes and dermatological disorders such as melasma. While primarily of cosmetic concern, these conditions can dramatically impact quality of life of affected patients. Several topical agents are utilized to treat skin pigmentation disorders. Here, we review melanogenesis induced by UV exposure and the agents that target this pathway.

A comprehensive review on tyrosinase inhibitors

Tyrosinase is a multi-copper enzyme which is widely distributed in different organisms and plays an important role in the melanogenesis and enzymatic browning. Therefore, its inhibitors can be attractive in cosmetics and medicinal industries as depigmentation agents and also in food and agriculture industries as antibrowning compounds. For this purpose, many natural, semi-synthetic and synthetic inhibitors have been developed by different screening methods to date. This review has focused on the tyrosinase inhibitors discovered from all sources and biochemically characterised in the last four decades.

Investigation of the pro-apoptotic effects of arbutin and its acetylated derivative on murine melanoma cells

Arbutin, a natural polyphenol isolated from the bearberry plant Arctostaphylos uvaursi, possesses whitening and anticancer properties. The effects of arbutin on melanogenesis and its pro-apoptotic effect on B16 murine melanoma cells have not yet been reported. In the present study, acetylated arbutin was prepared in order to improve the biological effects of arbutin, and it was found to significantly inhibit the biosynthesis of melanin and tyrosinase activity compared with parent arbutin in B16 murine melanoma cells. Interestingly, only acetylated arbutin strongly inhibited B16 murine melanoma cell migration in a dose-dependent manner. Both arbutin and acetylated arbutin significantly reduced cell viability, promoted cell apoptosis, caused G1 cell cycle arrest and induced mitochondrial disruption in B16 murine melanoma cells. Furthermore, reduced expression of B-cell lymphoma‑extra large (Bcl-xL) and Bcl-2 were observed in arbutin- and acetylated arbutin-treated cells. Therefore, arbutin and acetylated arbutin were found to exert pro-apoptotic effects on B16 murine melanoma cells, mediated through the mitochondrial pathway. The findings of the present study also support the use of acetylated arbutin as a new potential candidate agent for skin whitening and melanoma treatment.

Hair dyes resorcinol and lawsone reduce production of melanin in melanoma cells by tyrosinase activity inhibition and decreasing tyrosinase and microphthalmia-associated transcription factor (MITF) expression

Hair coloring products are one of the most important cosmetics for modern people; there are three major types of hair dyes, including the temporary, semi-permanent and permanent hair dyes. The selected hair dyes (such as ammonium persulfate, sodium persulfate, resorcinol and lawsone) are the important components for hair coloring products. Therefore, we analyzed the effects of these compounds on melanogenesis in B16-F10 melanoma cells. The results proved that hair dyes resorcinol and lawsone can reduce the production of melanin. The results also confirmed that resorcinol and lawsone inhibit mushroom and cellular tyrosinase activities in vitro. Resorcinol and lawsone can also downregulate the protein levels of tyrosinase and microphthalmia-associated transcription factor (MITF) in B16-F10 cells. Thus, we suggest that frequent use of hair dyes may have the risk of reducing natural melanin production in hair follicles. Moreover, resorcinol and lawsone may also be used as hypopigmenting agents to food, agricultural and cosmetic industry in the future.

Novel virtual screening approach for the discovery of human tyrosinase inhibitors

Tyrosinase is the key enzyme involved in the human pigmentation process, as well as the undesired browning of fruits and vegetables. Compounds inhibiting tyrosinase catalytic activity are an important class of cosmetic and dermatological agents which show high potential as depigmentation agents used for skin lightening. The multi-step protocol employed for the identification of novel tyrosinase inhibitors incorporated the Shape Signatures computational algorithm for rapid screening of chemical libraries. This algorithm converts the size and shape of a molecule, as well its surface charge distribution and other bio-relevant properties, into compact histograms (signatures) that lend themselves to rapid comparison between molecules. Shape Signatures excels at scaffold hopping across different chemical families, which enables identification of new actives whose molecular structure is distinct from other known actives. Using this approach, we identified a novel class of depigmentation agents that demonstrated promise for skin lightening product development.

Skin-whitening and skin-condition-improving effects of topical oxidized glutathione: a double-blind and placebo-controlled clinical trial in healthy women

Purpose

Glutathione is a tripeptide consisting of cysteine, glycine, and glutamate and functions as a major antioxidant. It is synthesized endogenously in humans. Glutathione protects thiol protein groups from oxidation and is involved in cellular detoxification for maintenance of the cell environment. Reduced glutathione (GSH) has a skin-whitening effect in humans through its tyrosinase inhibitory activity, but in the case of oxidized glutathione (GSSG) this effect is unclear. We examined the skin-whitening and skin-condition effects of topical GSSG in healthy women.

Subjects and methods

The subjects were 30 healthy adult women aged 30 to 50 years. The study design was a randomized, double-blind, matched-pair, placebo-controlled clinical trial. Subjects applied GSSG 2% (weight/weight [w/w]) lotion to one side of the face and a placebo lotion to the other side twice daily for 10 weeks. We objectively measured changes in melanin index values, moisture content of the stratum corneum, smoothness, wrinkle formation, and elasticity of the skin. The principal investigator and each subject also used subjective scores to investigate skin whitening, wrinkle reduction, and smoothness. Analysis of variance was used to evaluate differences between groups.

Results

The skin melanin index was significantly lower with GSSG treatment than with placebo from the early weeks after the start of the trial through to the end of the study period (at 10 weeks, P<0.001). In addition, in the latter half of the study period GSSG-treated sites had significant increases in moisture content of the stratum corneum, suppression of wrinkle formation, and improvement in skin smoothness. There were no marked adverse effects from GSSG application.

Conclusion

Topical GSSG is safe and effectively whitens the skin and improves skin condition in healthy women.

Whitening effects of marine pseudomonas extract

BACKGROUND

Bacteria associated with marine invertebrates are a rich source of bioactive metabolites.

OBJECTIVE

The effects of marine bacteria extracts on pigmentation were investigated to find novel whitening agents.

METHODS

The marine bacteria collected near Gangwha Island in Korea were isolated and extracted using organic solvent. The organic extracts were screened and selected using the cell free tyrosinase activity. The whitening effects of the selected extract were further investigated using cultured melanocytes, cultured skin and in vivo zebrafish. The whitening mechanism of the marine extract was also investigated.

RESULTS

The marine bacterial methylene chloride extract reduced the pigmentation of Melan-a cells, human melanocytes, cultured skin and in vivo zebrafish. The decrease in pigmentation was due to the inhibition of tyrosinase activity and the expression of tyrosinase and microphthalmia-associated transcription factor protein. These bacteria were identified as a novel Pseudomonas species.

CONCLUSION

The methylene chloride extract of marine pseudomonas species possesses a whitening effect. Further chemical isolation and characterization of the active compounds from this marine bacterial extract are needed.

Prediction of tyrosinase inhibition activity using atom-based bilinear indices

A set of novel atom-based molecular fingerprints is proposed based on a bilinear map similar to that defined in linear algebra. These molecular descriptors (MDs) are proposed as a new means of molecular parametrization easily calculated from 2D molecular information. The nonstochastic and stochastic molecular indices match molecular structure provided by molecular topology by using the kth nonstochastic and stochastic graph-theoretical electronic-density matrices, M(k) and S(k), respectively. Thus, the kth nonstochastic and stochastic bilinear indices are calculated using M(k) and S(k) as matrix operators of bilinear transformations. Chemical information is coded by using different pair combinations of atomic weightings (mass, polarizability, vdW volume, and electronegativity). The results of QSAR studies of tyrosinase inhibitors using the new MDs and linear discriminant analysis (LDA) demonstrate the ability of the bilinear indices in testing biological properties. A database of 246 structurally diverse tyrosinase inhibitors was assembled. An inactive set of 412 drugs with other clinical uses was used; both active and inactive sets were processed by hierarchical and partitional cluster analyses to design training and predicting sets. Twelve LDA-based QSAR models were obtained, the first six using the nonstochastic total and local bilinear indices and the last six with the stochastic MDs. The discriminant models were applied; globally good classifications of 99.58 and 89.96 % were observed for the best nonstochastic and stochastic bilinear indices models in the training set along with high Matthews correlation coefficients (C) of 0.99 and 0.79, respectively, in the learning set. External prediction sets used to validate the models obtained were correctly classified, with accuracies of 100 and 87.78 %, respectively, yielding C values of 1.00 and 0.73. This subset contains 180 active and inactive compounds not considered to fit the models. A simulated virtual screen demonstrated this approach in searching tyrosinase inhibitors from compounds never considered in either training or predicting series. These fitted models permitted the selection of new cycloartane compounds isolated from herbal plants as new tyrosinase inhibitors. A good correspondence between theoretical and experimental inhibitory effects on tyrosinase was observed; compound CA6 (IC(50)=1.32 microM) showed higher activity than the reference compounds kojic acid (IC(50)=16.67 microM) and L-mimosine (IC(50)=3.68 microM).

Oxazolones: New tyrosinase inhibitors; synthesis and their structure–activity relationships

The tyrosinase inhibitory potential of seventeen synthesized oxazolone derivatives has been evaluated and their structure-activity relationships developed in the present work. All the synthesized derivatives, 3-19, demonstrated excellent in vitro tyrosinase inhibitory properties having IC50 values in the range of 1.23+/-0.37-17.73+/-2.69 microM, whereas standard inhibitors l-mimosine and kojic acid have IC50 values 3.68+/-0.02 and 16.67+/-0.52 microM,, respectively. Compounds 4-8 having IC50 values 3.11+/-0.95, 3.51+/-0.25, 3.23+/-0.66, 1.23 +/- 0.37, and 2.15+/-0.75, respectively, were found to be very active members of the series, even better than both the standard inhibitors. However, compounds 3, 9-11, 13, 14, 16, 17, and 19 were found to be better than kojic acid but not l-mimosine. (2-Methyl-4-[E,2Z)-3-phenyl-2-propenyliden]-1,3-oxazol-5(4H)-one (7) bearing a cinnamyol residue at C-4 of oxazolone moiety and an IC50 = 1.23+/-0.37 microM was found to be the most active one among all tested compounds. These studies reveal that the substitution of functional group (s) at C-4 and C-2 positions plays a vital role in the activity of this series of compounds. It is concluded that compound 7 may act as a potential lead molecule to develop new drugs for the treatment of tyrosinase based disorders.

Differential regulation of melanosomal proteins after hinokitiol treatment

BACKGROUND

Melanogenesis is regulated by a series of enzymes under the control of microphthalmia-associated transcription factor (MITF).

OBJECTIVE

The aim of this study was to examine melanosome-associated protein levels in Mel-Ab cells after hinokitiol treatment.

METHODS

We measured melanin contents and analyzed melanosome-associated protein levels using Western blot and RT-PCR analysis.

RESULTS

Hinokitiol markedly inhibited melanin synthesis and also reduced the protein levels of tyrosinase (TYR), tyrosinase-related protein 1 (TYRP-1), tyrosinase-related protein 2 (TYRP-2) and MITF in Mel-Ab cells. In addition, hinokitiol significantly increased the phosphorylations of extracellular signal-regulated kinases 1 and 2 (ERK1/2). Furthermore, reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that TYR and MITF mRNA levels were significantly decreased but that levels of TYRP-1 and TYRP-2 mRNA were unaffected by hinokitiol treatment. These results suggest that hinokitiol-induced ERK phosphorylation reduces MITF and TYR transcription, and mediates the action of hinokitiol on melanogenesis. Interestingly, the mRNAs of TYRP-1 and TYRP-2 were unaffected, although the protein levels of TYRP-1 and TYRP-2 were down-regulated. Thus, the effects of hinokitiol on the transcription of TYR may differ from its effects on TYRP-1 and TYRP-2.

CONCLUSION

Therefore, we suggest that TYRP-1 and TYRP-2 may be regulated by post-translational degradation after hinokitiol treatment.

Hemocyanin in the exoskeleton of crustaceans: enzymatic properties and immunolocalization

We investigated the enzymatic properties and immunohistochemical localization of cuticular hemocyanin, a known oxygen transporter in the prawn Penaeus japonicus. The molecular weight of hemocyanin purified from the cuticle was estimated to be 67-77 k using SDS-PAGE, and the purified protein was effectively converted into a phenoloxidase-like enzyme by an SDS-treatment. The activated enzyme catalyzed the o-hydroxylation of monophenols and the oxidation of o-diphenols and was inhibited by typical inhibitors of phenoloxidase. These characteristics were nearly identical to the enzymatic properties of hemolymph hemocyanin. Immunological detection showed a diffuse distribution of hemocyanin over the exocuticle and endocuticle, and a higher signal level was observed in the latter. Based on these results, roles of hemocyanin in various physiological processes such as immune response and sclerotization of the cuticle were discussed.

An oxygen transporter hemocyanin can act on the late pathway of melanin synthesis

5,6-Dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) are precursors of eumelanin. The effects of crustacean hemolymph proteins on these eumelanin-related metabolites were investigated. Zymogram analysis indicated that polymers of hemocyanin (Hc) subunits converted DHI into black pigment while no effects were observed using DHICA as a substrate. Spectrum changes for mixtures of purified Hc and DHI showed a profile similar to oxidized DHI by mushroom tyrosinase while Hc had only slight effects on DHICA. Typical inhibitors of tyrosinase and phenoloxidase severely hampered the production of oxidized DHI. Taken together with previous results, these data indicate that Hc plays a crucial role in the conversion of DHI in the hemolymph of crustaceans, which promotes late reactions in the melanin synthetic pathway as well as early reactions (oxidation of tyrosine and DOPA to dopaquinone).

(-)-Epigallocatechin-3-gallate and hinokitiol reduce melanin synthesis via decreased MITF production

In this study, the effects of (-)-epigallocatechin-3-gallate (EGCG) and/or hinokitiol (beta-thujaplicin) on melanogenesis were investigated. Our results showed that both EGCG and hinokitiol significantly inhibited melanin synthesis in a concentration-dependent manner, and that their hypopigmenting effects were stronger than that of kojic acid, which is known to inhibit melanin formation in melanocytes and melanoma cells. Interestingly, EGCG did not show any additive hypopigmenting effect in combination with kojic acid, though EGCG did show a synergistic effect in combination with hinokitiol. Several reports indicate that the activation of extracellular signal-regulated kinase (ERK) induces microphthalmia-associated transcription factor (MITF) degradation. Accordingly, the effects of EGCG and hinokitiol on the ERK signaling pathway were examined. EGCG and hinokitiol induced neither ERK activation nor MITF degradation. On the other hand, both EGCG and hinokitiol reduced the protein levels of MITF and of tyrosinase, the rate limiting melanogenic enzyme, whereas kojic acid had no effect. In addition, hinokitiol strongly downregulated the activity of tyrosinase, whereas EGCG or kojic acid had only a little effect. These results show that both EGCG and hinokitiol reduce MITF production, and suggest that reduced tyrosinase activity by hinokitiol explains their synergistic effect on melanogenesis.

Downregulation of NF-kappaB activation in human keratinocytes by melanogenic inhibitors

BACKGROUND

Exposure of skin cells, particularly keratinocytes to various nuclear factor-kappaB (NF-kappaB) activators (e.g. tumor necrosis factor-alpha, interleukin-1, lipopolysaccharides, and ultraviolet light) leads to phosphorylation and degradation of the inhibitory protein, IkappaB. Liberated NF-kappaB is translocated into the nucleus where it can change or alter expression of target genes, resulting in the secretion of extracellular signaling molecules including melanotrophic factors affecting melanocyte.

OBJECTIVE

In order to demonstrate the possible role of NF-kappaB activation on the synthesis of melanotrophic factors from the keratinocytes, the activities of NF-kappaB induced by melanogenic inhibitors (MIs) were determined in human HaCaT keratinocytes transfected with pNF-kappaB-SEAP-NPT plasmid. Transfectant cells released the secretory alkaline phosphatase (SEAP) as a transcription reporter in response to the NF-kappaB activity and contain the neomycin phosphotransferase (NPT) gene for the dominant selection marker for geneticin resistance.

METHODS

MIs such as niacinamide, kojic acid, hydroquinone, resorcinol, arbutin, and glycolic acid were preincubated with transfectant HaCaT cells for 3 h and then ultraviolet B (UVB) was irradiated. NF-kappaB activation was measured with the SEAP reporter gene assay using a fluorescence detection method.

RESULTS

Of the MIs tested, kojic acid (IC(50)=60 microM) was found to be the most potent inhibitor of UVB-upregulating NF-kappaB activation in transfectant HaCaT cells, which is followed by niacinamide (IC(50)=540 microM). Pretreatment of the transfectant HaCaT cells with the MIs, especially kojic acid and niacinamide, effectively lowered NF-kappaB binding measured by electrophoretic mobility shift assay. Furthermore, these two inhibitors remarkably reduced the secretion level of IL-6, one of melanotrophic factors, triggered by UV-radiation of the HaCaT cells.

CONCLUSION

These observations suggest that MIs working at the in vivo level might act partially through the modulation of the synthesis of melanotrophic factors in keratinocyte.

Glabrene and isoliquiritigenin as tyrosinase inhibitors from licorice roots

Tyrosinase is known to be a key enzyme in melanin biosynthesis, involved in determining the color of mammalian skin and hair. Various dermatological disorders, such as melasama, age spots, and sites of actinic damage, arise from the accumulation of an excessive level of epidermal pigmentation. The inadequacy of current therapies to treat these conditions as well as high cytotoxicity and mutagenicity, poor skin penetration, and low stability of formulations led us to seek new whitening agents to meet the medical requirements for depigmenting agents. The inhibitory effect of licorice extract on tyrosinase activity was higher than that expected from the level of glabridin in the extract. This led us to test for other components that may contribute to this strong inhibitory activity. Results indicated that glabrene and isoliquiritigenin (2',4',4-trihydroxychalcone) in the licorice extract can inhibit both mono- and diphenolase tyrosinase activities. The IC(50) values for glabrene and isoliquiritigenin were 3.5 and 8.1 microM, respectively, when tyrosine was used as substrate. The effects of glabrene and isoliquiritigenin on tyrosinase activity were dose-dependent and correlated to their ability to inhibit melanin formation in melanocytes. This is the first study indicating that glabrene and isoliquiritigenin exert varying degrees of inhibition on tyrosinase-dependent melanin biosynthesis, suggesting that isoflavenes and chalcones may serve as candidates for skin-lightening agents.