Natural, semisynthetic and synthetic tyrosinase inhibitors

From Fish Scale Gelatin to Tyrosinase Inhibitor: A Novel Peptides Screening Approach Application

Bioaffinity ultrafiltration combined with LC-Orbitrap-MS/MS was applied for the first time to achieve rapid screening and identification of tyrosinase inhibitory peptides (TYIPs) from grass carp scale gelatin hydrolysates. The binding mode of TYIPs with tyrosinase was investigated by molecular docking technology. The whitening effect of TYIPs was further studied by evaluating the tyrosinase activity and melanin content in mouse B16F10 cells. Four new TYIPs were screened from hydrolysates, among which DLGFLARGF showed the strongest tyrosinase inhibition with an IC50 value of 3.09 mM. Molecular docking showed that hydrogen bonds were the main driving force in the interaction between the peptide DLGFLARGF and tyrosinase. The addition of DLGFLARGF significantly inhibited the tyrosinase activity and melanin production of B16F10 melanoma cells. These results suggest that DLGFLARGF is a promising skin whitening agent for the treatment of potential pigment-related diseases.

Fast screening of tyrosinase inhibitors from traditional Chinese medicinal plants by ligand fishing in combination with in situ fluorescent assay

A simple and rapid method for screening of tyrosinase (TYR) inhibitors present in traditional Chinese medicines (TCMs) was developed by combining ligand fishing and the fluorescent enzymatic assay based on dopamine-functionalized carbon quantum dots (CQDs-Dopa). Ligands of the enzyme present in the TCM extractions were firstly adsorbed on the enzyme-modified magnetic beads, and then the beads were magnetically separated and subjected directly to the CQDs-Dopa-based fluorescent assay. Finally, compounds were desorbed from the "active" beads and identified with ultra-performance liquid chromatography-triple quadrupole mass spectrometry. A known natural TYR inhibitor quercetin was selected to assess the feasibility and quantification performance of this method, and good linearity in the range of 0.01-0.16 mM (R² = 0.992) with a low detection limit of 0.004 mM was obtained. This method was then applied to screen TYR inhibitors present in Scutellaria baicalensis and Sophora flavescens. Six TYR inhibitors including baicalin (1), baicalein (2), wogonin (3), oroxylin A (4), kurarinone (5), and sophoraflavanone G (6) were found, among which 1-4 were firstly discovered in this work. This is the first report on the in situ assessment of the target compounds obtained by ligand fishing in the form of a mixture, which exhibited the combined advantages of specific extraction ability of ligand fishing and the high sensitivity of CQDs-based fluorescent assay, showing great potential for fast screening of enzyme inhibitors from TCMs.

Role of Phenolic Compounds in Human Disease: Current Knowledge and Future Prospects

Inflammation is a natural protective mechanism that occurs when the body's tissue homeostatic mechanisms are disrupted by biotic, physical, or chemical agents. The immune response generates pro-inflammatory mediators, but excessive output, such as chronic inflammation, contributes to many persistent diseases. Some phenolic compounds work in tandem with nonsteroidal anti-inflammatory drugs (NSAIDs) to inhibit pro-inflammatory mediators' activity or gene expression, including cyclooxygenase (COX). Various phenolic compounds can also act on transcription factors, such as nuclear factor-κB (NF-κB) or nuclear factor-erythroid factor 2-related factor 2 (Nrf-2), to up-or downregulate elements within the antioxidant response pathways. Phenolic compounds can inhibit enzymes associated with the development of human diseases and have been used to treat various common human ailments, including hypertension, metabolic problems, incendiary infections, and neurodegenerative diseases. The inhibition of the angiotensin-converting enzyme (ACE) by phenolic compounds has been used to treat hypertension. The inhibition of carbohydrate hydrolyzing enzyme represents a type 2 diabetes mellitus therapy, and cholinesterase inhibition has been applied to treat Alzheimer's disease (AD). Phenolic compounds have also demonstrated anti-inflammatory properties to treat skin diseases, rheumatoid arthritis, and inflammatory bowel disease. Plant extracts and phenolic compounds exert protective effects against oxidative stress and inflammation caused by airborne particulate matter, in addition to a range of anti-inflammatory, anticancer, anti-aging, antibacterial, and antiviral activities. Dietary polyphenols have been used to prevent and treat allergy-related diseases. The chemical and biological contributions of phenolic compounds to cardiovascular disease have also been described. This review summarizes the recent progress delineating the multifunctional roles of phenolic compounds, including their anti-inflammatory properties and the molecular pathways through which they exert anti-inflammatory effects on metabolic disorders. This study also discusses current issues and potential prospects for the therapeutic application of phenolic compounds to various human diseases.

Antimelanogenic activity of patuletin from Inula japonica flowers in B16F10 melanoma cells and zebrafish embryos

During the search for natural melanogenesis inhibitors, patuletin, a flavonoid, was isolated from Inula japonica flowers. We investigated the antimelanogenic effects of patuletin on B16F10 melanoma cells and zebrafish embryos. Patuletin dose-dependently reduced melanocyte-stimulating hormone-induced melanogenesis and L-DOPA oxidation in B16F10 cells. Western blot analysis showed that patuletin reduced cellular tyrosinase expression in a dose-dependent manner. Patuletin treatment significantly decreased melanin pigmentation in the embryo compared to the untreated controls.

Three New Isoprenylated Flavones from Artocarpus chama Stem and Their Bioactivities

Phytochemical investigation of Artocarpus chama stem was performed by chromatographic techniques, resulting from the isolation and structure elucidation of three new compounds, namely 3′-farnesyl-apigenin (1), 3-(hydroxyprenyl) isoetin (2), and 3-prenyl-5,7,2′,5′-tetrahydroxy-4′-methoxyflavone (3), and five known compounds, namely homoeriodictyol (4), isocycloartobilo-xanthone (5), artocarpanone (6), naringenin (7), and artocarpin (8). From the screening result, A. chama extract showed a potent tyrosinase inhibitory effect. Ihe isolated compounds 1, 4 and 6 also exhibited tyrosinase inhibition with IC50 of 135.70, 52.18, and 38.78 µg/mL, respectively. Moreover, compounds 3, 4, 5, 6, and 8 showed strong activity against Staphylococcus epidermidis, S. aureus, methicillin-resistant S. aureus, and Cutibacterium acnes. This study is the first report on phytochemical investigation with new compounds and biological activities of A. chama. Skin infection can cause dark spots or hyperpigmentation. The isolated compounds that showed both anityrosinase and antimicrobial activities will be further studied in in vivo and clinical trials in order to develop treatment for hyperpigmentation, which is caused by infectious diseases by microorganisms.

Synergistic effects and antityrosinase mechanism of four plant polyphenols from Morus and Hulless Barley

Sanggenone C, oxyresveratrol, catechin and l-epicatechin exist in Morus and Hulless Barley as natural polyphenols with antityrosinase activity. Little research on their synergistic and structure-function relationships of them has been reported in recent years. In this paper, the inhibition mechanisms of these four plant polyphenols were investigated by enzyme kinetics, HPLC, fluorescence spectra, and molecular docking methods. The results showed that oxyresveratrol (IC₅₀ = 1.096 ± 0.048 μg/mL), sanggenone C (IC₅₀ = 13.360 ± 1.029 μg/mL), l-epicatechin (IC₅₀ = 55.730 ± 1.762 μg/mL), and catechin (IC₅₀ = 148.500 ± 3.355 μg/mL) exhibited tyrosinase inhibition activity. When sangenone C (14 μg/mL) was mixed with l-epicatechin (56 μg/mL) at 4:1 (40 μL + 10 μL), the highest tyrosinase inhibition was achieved. Molecular docking showed that the number and position of phenolic hydroxyls of polyphenols were the key for tyrosinase inhibition activity. This study provided new ideas for the application of these four plant polyphenols from Hulless Barley and Morus as tyrosinase inhibitors in food preservation.

Characterization of Phenethyl Cinnamamide Compounds from Hemp Seed and Determination of Their Melanogenesis Inhibitory Activity

Hyperpigmentation is induced by the overactivation of tyrosinase, which is a rate-limiting enzyme in melanogenesis. The defatted extract of hemp (Cannabis sativa L.) seed is known to have inhibitory effects on melanogenesis; however, effective compounds in the extract have not been identified yet. In this study, three phenethyl cinnamamides present in hemp seed extract were prepared by purification and chemical synthesis and were assessed for their inhibitory effect on melanogenesis in B16F10 melanoma cells. A comparison of the anti-melanogenesis and anti-tyrosinase activity of hemp seed solvent fractions revealed that the ethyl acetate fraction possessed the greatest potential for suppressing melanogenesis in melanoma cells by decreasing tyrosinase activity. We tentatively identified 26 compounds in the ethyl acetate fraction by comparing spectroscopic data with the literature. Three phenethyl cinnamamides such as N-trans-caffeoyltyramine, N-trans-coumaroyltyramine, and N-trans-feruloyltyramine present abundantly in the ethyl acetate fraction were prepared and their anti-melanogenesis and anti-tyrosinase activities in melanoma cells were evaluated. We found that N-trans-caffeoyltyramine and N-trans-feruloyltyramine inhibited alpha melanocyte stimulating hormone (α-MSH)-induced melanogenesis without cytotoxicity, while N-trans-coumaroyltyramine inhibited melanogenesis with cytotoxicity. IC₅₀ values of N-trans-caffeoyltyramine, N-trans-feruloyltyramine, and N-trans-coumaroyltyramine for inhibition of α-MSH-mediated tyrosinase activation were 0.8, 20.2, and 6.3 μM, respectively. Overall, N-trans-caffeoyltyramine possessed the strongest anti-melanogenesis activity among the three phenethyl cinnamamides evaluated. The inhibitory effect of N-trans-caffeoyltyramine was verified by determining the melanin content and tyrosinase activity in melanoma after treating the cells with synthetic compounds. Thus, N-trans-caffeoyltyramine isolated from hemp seed extract could be useful in cosmetics as a skin-whitening agent.

Exploring the Potential of Icelandic Seaweeds Extracts Produced by Aqueous Pulsed Electric Fields-Assisted Extraction for Cosmetic Applications

A growing concern for overall health is driving a global market of natural ingredients not only in the food industry but also in the cosmetic field. In this study, a screening on potential cosmetic applications of aqueous extracts from three Icelandic seaweeds produced by pulsed electric fields (PEF) was performed. Produced extracts by PEF from Ulva lactuca, Alaria esculenta and Palmaria palmata were compared with the traditional hot water extraction in terms of polyphenol, flavonoid and carbohydrate content. Moreover, antioxidant properties and enzymatic inhibitory activities were evaluated by using in vitro assays. PEF exhibited similar results to the traditional method, showing several advantages such as its non-thermal nature and shorter extraction time. Amongst the three Icelandic species, Alaria esculenta showed the highest content of phenolic (mean value 8869.7 µg GAE/g dw) and flavonoid (mean value 12,098.7 µg QE/g dw) compounds, also exhibiting the highest antioxidant capacities. Moreover, Alaria esculenta extracts exhibited excellent anti-enzymatic activities (76.9, 72.8, 93.0 and 100% for collagenase, elastase, tyrosinase and hyaluronidase, respectively) for their use in skin whitening and anti-aging products. Thus, our preliminary study suggests that Icelandic Alaria esculenta-based extracts produced by PEF could be used as potential ingredients for natural cosmetic and cosmeceutical formulations.

4H-benzochromene derivatives as novel tyrosinase inhibitors and radical scavengers: synthesis, biological evaluation, and molecular docking analysis

A series of ethyl 2-amino-4H-benzo[h]chromene-3-carboxylate derivatives, having phenyl ring with diverse substituents at C4 position of 4H-benzochromene nucleus, were synthesized via one-pot three-component reaction between various aromatic aldehydes, α-naphthol, and ethyl cyanoacetate. The synthesized compounds were screened for their antityrosinase activity. Compound 4i, bearing 4-dimethylamino substitution on C4-phenyl ring, was the most potent tyrosinase inhibitor (IC50 = 34.12 μM). The inhibition kinetic analysis of 4i indicated that the compound was a competitive tyrosinase inhibitor. Compounds 4a, 4g, 4i and 4j were the effective radical scavengers with EC50s in the range of 0.144-0.943 mM. According to the in silico drug-like and ADME predictions, 4i can be considered as a suitable candidate. Molecular docking results confirmed that the derivative was well accommodated within the mushroom tyrosinase binding site. Therefore, 4i can be introduced as a novel tyrosinase inhibitor that might be a promising lead in medicine, cosmetics, and food industry.

Evaluation of quercetin omega-6 and -9 esters on activity and structure of mushroom tyrosinase: Spectroscopic and molecular docking studies

Quercetin is one of the most ubiquitous dietary flavonoids widely distributed in plants and foods of plant origin, and is a potent tyrosinase inhibitor. Quercetin fatty esters could lead to an improve in quercetin lipophilicity which could positively affect its pharmacological activity. In this study, the inhibitory effect of two novel esters of quercetin-linoleic acid (ligand A) and quercetin-oleic acid (ligand B) has been investigated on structure and diphenolase activity of mushroom tyrosinase (MT) by experimental and molecular docking techniques. The inhibitory kinetics study using UV-visible spectrophotometry in the presence of its substrate 3,4-dihydroxyphenylalanine (L-dopa), revealed that both esters successfully inhibit the activity of tyrosinase and reduce the formation of dopaquinone. Results showed that the binding of ligands to MT induced rearrangement and conformational changes of the enzyme. Thermodynamic parameters of these interactions (K_a , ∆G°, ∆H° and ∆S°) were obtained at pH = 6.8 and temperatures of 298 and 310 K. Molecular docking studies further was applied to calculation of binding energies (ΔG_bA  = -21.84 kJ/mol, ΔG_bB  = -20.92 kJ/mol), inhibition constant values (K_IA  = 160 µM, K_IB  = 220 µM) and the special binding site. It can be deduced that ligands act as a potential tyrosinase inhibitor and it was found that the best possible interaction condition with binding modes visualize was achieved by ligand A and exhibited the potent tyrosinase inhibitory activity. These findings may be helpful to understand the inhibition mechanism of quercetin fatty acids esters on tyrosinase and provide a convenient screening method to differentiate phenolic tyrosinase inhibitors. PRACTICAL APPLICATIONS: Bioavailability and antioxidant activity of conjugated fatty acids with their bioequivalence in several biological effects and metabolic processes such as beta-oxidation from various forms has been reported to be highly variable and useful. Quercetin shows beneficial role in human health, but its biological effects in vivo is limited by poor bioavailability, low skin permeability and solubility. This study design new tyrosinase inhibitors which helpful to functional research of unsaturated fatty acid esters in the treatment of inflammatory diseases and hyperpigmentation disorders. In addition, undesirable enzymatic browning of plant derived-foods by tyrosinase causes a decrease in market value and economic loss of food products. The results suggest that the conjugation of quercetin with linoleic and oleic acids resulted in novel stronger tyrosinase inhibitors which may have therapeutic applications and replacement of toxic tyrosinase inhibitors and contribute as anti- browning agents in food, cosmetic and pharmaceutical industry.

E. coli Ribonucleotide Reductase β2 Subunit Inactivation by Triapine Occurs through Binding of a Triapine-Fe(II) Adduct

Ribonucleotide reductase (RNR), which supplies the building blocks for DNA biosynthesis and its repair, has been linked to human diseases and is emerging as a therapeutic target. Here, we present a mechanistic investigation of triapine (3AP), a clinically relevant small molecule that inhibits the tyrosyl radical within the RNR β₂ subunit. Solvent kinetic isotope effects reveal that proton transfer is not rate-limiting for inhibition of Y122· of E. coli RNR β₂ by the pertinent 3AP-Fe(II) adduct. Vibrational spectroscopy further demonstrates that unlike inhibition of the β₂ tyrosyl radical by hydroxyurea, a carboxylate containing proton wire is not at play. Binding measurements reveal a low nanomolar affinity (K_d ∼ 6 nM) of 3AP-Fe(II) for β₂. Taken together, these data should prompt further development of RNR inactivators based on the triapine scaffold for therapeutic applications.

Phytochemical profile of Cespedesia spathulata leaves (Ochnaceae) and its effect on tyrosinase enzyme

Phytochemical studies of Cespedesia spathulata (Ochnaceae) leaves using 1H, 13C NMR, and GC-MS have led to the isolation of some metabolites identified for the first time in these species such as cathechin, epicatechin, vitexin, orientin, 6''-O-acetyl-vitexin, sitosterol, stigmasterol, phytol, 4,5-dihydrovomifoliol and a mixture of aliphatic methyl esters, together with ochnaflavone, which was previously isolated from this plant. The modulating activity of some fractions and compounds from Cespedesia spathulata towards tyrosinase enzyme was assayed by spectroscopic and theoretical means/experiments. The dichloromethane fraction (133 μg mL-1) and ochnaflavone (333 μM) inhibited tyrosinase activity by 20 % and 2.0 %, respectively, whereas the ethyl acetate fraction (666 μg mL-1) and ±catechins (catechin and epicatechin - 800 μM) activated it by 104 % and 384 %, respectively. Quantum chemical calculations suggested that catechin and epicatechin are better activators than L-DOPA by interacting with Cu (II) ions. Molecular docking results suggested that hydrogen bonding and hydrophobic interactions are the main binding forces between each tyrosinase activator and the amino acid residues inside the active protein binding pocket.

Spectrophotometric Assays for Sensing Tyrosinase Activity and Their Applications

Tyrosinase (TYR, E.C. 1.14.18.1), a critical enzyme participating in melanogenesis, catalyzes the first two steps in melanin biosynthesis including the ortho-hydroxylation of L-tyrosine and the oxidation of L-DOPA. Previous pharmacological investigations have revealed that an abnormal level of TYR is tightly associated with various dermatoses, including albinism, age spots, and malignant melanoma. TYR inhibitors can partially block the formation of pigment, which are always used for improving skin tone and treating dermatoses. The practical and reliable assays for monitoring TYR activity levels are very useful for both disease diagnosis and drug discovery. This review comprehensively summarizes structural and enzymatic characteristics, catalytic mechanism and substrate preference of TYR, as well as the recent advances in biochemical assays for sensing TYR activity and their biomedical applications. The design strategies of various TYR substrates, alongside with several lists of all reported biochemical assays for sensing TYR including analytical conditions and kinetic parameters, are presented for the first time. Additionally, the biomedical applications and future perspectives of these optical assays are also highlighted. The information and knowledge presented in this review offer a group of practical and reliable assays and imaging tools for sensing TYR activities in complex biological systems, which strongly facilitates high-throughput screening TYR inhibitors and further investigations on the relevance of TYR to human diseases.

Biological insights and NMR metabolic profiling of different extracts of Spermacoce verticillata (L.) G. Mey

Spermacoce verticillata (L.) G. Mey. is commonly used in the folk medicine by various cultures to manage common diseases. Herein, the chemical and biological profiles of S. verticillata were studied in order to provide a comprehensive characterization of bioactive compounds and also to highlight the therapeutic properties. The in vitro antioxidant activity using free-radical scavenging, phosphomolybdenum, ferrous-ion chelating and reducing power assays, and the inhibitory activity against key enzymes such as acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), tyrosinase, α-amylase and α-glucosidase of S. verticillata extracts (dichloromethane, ethyl acetate, methanol and water) were investigated. The highest total phenolic and flavonoid content were observed in the methanolic and aqueous extracts. Exhaustive 2DNMR investigation has revealed the presence of rutin, ursolic and oleanoic acids. The methanolic extract, followed by aqueous extract have showed remarkable free radical quenching and reducing ability, while the dichloromethane extract was the best source of metal chelators. The tested extracts showed notable inhibitory activity against cholinesterases (AChE: 1.63 - 4.99 mg GALAE/g extract and BChE: 12.40 - 15.48 mg GALAE/g extract) and tyrosinase (60.85 - 159.64 mg KAE/g extract). No inhibitory activity was displayed by ethyl acetate and aqueous extracts against BChE and tyrosinase, respectively. All the tested extracts showed modest α-amylase inhibitory activity, while only the ethyl acetate and aqueous extracts were potent against α-glycosidase. This study further validates the use of S. verticillata in the traditional medicine, while advocating for further investigation for phytomedicine development.

Phytochemical Study and In Vitro Screening Focusing on the Anti-Aging Features of Various Plants of the Greek Flora

Skin health is heavily affected by ultraviolet irradiation from the sun. In addition, senile skin is characterized by major changes in the collagen, elastin and in the hyaluronan content. Natural products (NPs) have been shown to delay cellular senescence or in vivo aging by regulating age-related signaling pathways. Moreover, NPs are a preferable source of photoprotective agents and have been proven to be useful against the undesirable skin hyperpigmentation. Greek flora harvests great plant diversity with approximately 6000 plant species, as it has a wealth of NPs. Here, we report an extensive screening among hundreds of plant species. More than 440 plant species and subspecies were selected and evaluated. The extracts were screened for their antioxidant and anti-melanogenic properties, while the most promising were further subjected to various in vitro and cell-based assays related to skin aging. In parallel, their chemical profile was analyzed with High-Performance Thin-Layer Chromatography (HPTLC) and/or Ultra-Performance Liquid Chromatography High-Resolution Mass Spectrometry (UPLC-HRMS). A variety of extracts were identified that can be of great value for the cosmetic industry, since they combine antioxidant, photoprotective, anti-melanogenic and anti-aging properties. In particular, the methanolic extracts of Sideritis scardica and Rosa damascena could be worthy of further attention, since they showed interesting chemical profiles and promising properties against specific targets involved in skin aging.

5-Substituted isatin thiosemicarbazones as inhibitors of tyrosinase: Insights of substituent effects

Seven isatin-thiosemicarbazone analogues bearing different substituents (R) attached at C-5 of the indoline ring, TSC-ISA-R (R = -H, -CH₃, -OCH₃, -OCF₃, -F, -Cl and -NO₂), were synthesized and evaluated as inhibitors of mushroom tyrosinase (TYR). The inhibitory behaviour and performance of TSC-ISA-R were investigated spectroscopically in relation to the substituent modifications through examining their inhibition against the diphenolase activity of TYR using L-DOPA as a substrate. The IC₅₀ values of TSC-ISA-R were determined to be in the range of 81-209 μM. The kinetic analysis showed that TSC-ISA-R were reversible and mixed type inhibitors. Three potential non-covalent interactions rather than complexation including the binding of TSC-ISA-R with free TYR, TYR-L-DOPA complex, and with substrate L-DOPA were found to be involved in the inhibition. The substituent modifications affected these interactions by varying the characters of the resulting TSC-ISA-R in different degrees. The thiosemicarbazido moiety of each TSC-ISA-R contributed predominantly to the inhibition, and the isatin moiety seemed to play a regulatory role in the binding of TSC-ISA-R to the target molecules. The results of theoretical calculations using density functional theory method indicated a different effect of -R on the electron distribution in HOMO of TSC-ISA-R. The LUMO-HOMO energy gap of TSC-ISA-R almost accords with the trend of their experimental inhibition potency.

Natural and synthetic flavonoid derivatives as new potential tyrosinase inhibitors: a systematic review

Tyrosinase is a multifunctional glycosylated and copper-containing oxidase that is highly prevalent in plants and animals and plays a pivotal role in catalyzing the two key steps of melanogenesis: tyrosine's hydroxylation to dihydroxyphenylalanine (DOPA), and oxidation of the latter species to dopaquinone. Melanin guards against the destructive effects of ultraviolet radiation which is known to produce considerable pathological disorders such as skin cancer, among others. Moreover, the overproduction of melanin can create aesthetic problems along with serious disorders linked to hyperpigmented spots or patches on skin. Several skin-whitening products which reduce melanogenesis activity and alleviate hyperpigmentation are commercially available. A few of them, particularly those obtained from natural sources and that incorporate a phenolic scaffold, have been exploited in the cosmetic industry. In this context, synthetic tyrosinase inhibitors (TIs) with elevated efficacy and fewer side effects are direly needed in the pharmaceutical and cosmetic industries owing to their protective effect against pigmentation and dermatological disorders. Furthermore, the biological significance of the chromone skeleton and its associated medicinal and bioactive properties has drawn immense interest and inspired many researchers to design and develop novel anti-tyrosinase agents based on the flavonoid core (2-arylchromone). This review article is oriented to provide an insight and a deeper understanding of the tyrosinase inhibitory activity of an array of natural and bioinspired phenolic compounds with special emphasis on flavonoids to demonstrate how the position of ring substituents and their interaction with tyrosinase could be correlated with their effectiveness or lack thereof against inhibiting the enzyme.

Anti-Melanogenic Properties of Velutin and Its Analogs

Velutin, one of the flavones contained in natural plants, has various beneficial activities, such as skin whitening, as well as anti-inflammatory, anti-allergic, antioxidant, and antimicrobial activities. However, the relationship between the structure of velutin and its anti-melanogenesis activity is not yet investigated. In this study, we obtained 12 velutin derivatives substituted at C5, C7, C3′, and C4′ of the flavone backbone with hydrogen, hydroxyl, and methoxy functionalities by chemical synthesis, to perform SAR analysis of velutin structural analogues. The SAR study revealed that the substitution of functional groups at C5, C7, C3′, and C4′ of the flavone backbone affects biological activities related to melanin synthesis. The coexistence of hydroxyl and methoxy at the C5 and C7 position is essential for inhibiting tyrosinase activity. However, 1,2-diol compounds substituted at C3′ and C4′ of flavone backbone induce apoptosis of melanoma cells. Further, substitution at C3′ and C4′ with methoxy or hydrogen is essential for inhibiting melanogenesis. Thus, this study would be helpful for the development of natural-derived functional materials to regulate melanin synthesis.

Naturally occurring and synthetic peptides: Efficient tyrosinase inhibitors

Tyrosinase is a copper-containing enzyme involved in the biosynthesis of melanin pigment, which is the most important photo protective agent against skin photo carcinogenesis. Excess production of melanin causes hyperpigmentation leading to undesired browning in human skin, fruits, and vegetable as well as plant-derived foods. Moreover, the role of tyrosinase in the onset and progression of various diseases such as cancers, Alzheimer's, and Parkinson diseases has been well documented in the literature. In this respect, tyrosinase inhibitors have been in the center of attention particularly as the efficient skin whitening agents. Among a wide range of compounds possessing anti-tyrosinase activity, peptides both natural and synthetic derivatives have attracted attention due to high potency and safety.

Morin Induces Melanogenesis via Activation of MAPK Signaling Pathways in B16F10 Mouse Melanoma Cells

Morin is a well-known flavonoid, and has been reported to have various properties, such as anti-cell death, antioxidant, and anti-inflammatory properties. Although studies on the biochemical and biological actions of morin have been reported, the melanin biosynthesis effects and molecular mechanisms are unknown. In this study, we first found that morin has the effect of enhancing melanin biosynthesis in B16F10 mouse melanoma cells, and analyzed the molecular mechanism. In this study, we examined the effects of morin on the melanin contents and tyrosinase activity, as well as the protein expression levels of the melanogenic enzymes TRP-1, TRP-2, and microphtalmia-associated transcription factor (MITF) in B16F10 mouse melanoma cells. Morin showed no cytotoxicity in the concentration range of 5–100 μM, and significantly increased the intracellular tyrosinase activity and melanin contents. In mechanism analysis, morin increased the protein expression of TRP-1, TRP-2, and MITF associated with melanogenesis. Furthermore, morin increased phosphorylated ERK and p38 at the early time, and decreased phosphorylated ERK after 12 h. The results suggest that morin enhances melanin synthesis through the MAPK signaling pathways in B16F10 mouse melanoma cells.

Functionality study of chalcone-hydroxypyridinone hybrids as tyrosinase inhibitors and influence on anti-tyrosinase activity

In an attempt to synthesise new tyrosinase inhibitors, we designed and synthesised a series of chalcone-hydroxypyridinone hybrids as potential tyrosinase inhibitors adopting strategic modifications of kojic acid. All the newly synthesised compounds were characterised by NMR and mass spectrometry. Initial screening of the target compounds demonstrated that compounds 1a, 1d, and 1n had relatively strong inhibitory activities against tyrosinase monophenolase, with IC₅₀ values of 3.07 ± 0.85, 2.25 ± 0.8 and 2.75 ± 1.19 μM, respectively. The inhibitory activity against monophenolase was 6- to 8-fold higher than that of kojic acid. Compounds 1a, 1d, and 1n also showed inhibition of diphenolase, with IC₅₀ values of 17.05 ± 0.07, 11.70 ± 0.03 and 19.3 ± 0.28 μM, respectively. The inhibition kinetics of diphenolase indicates that compounds 1a and 1d induce reversible inhibition on tyrosinase. Finally, we found that copper coordination should be one of the important inhibitory mechanism of these compounds in tyrosinase.

Chemical composition, biological properties and bioinformatics analysis of two Caesalpina species: A new light in the road from nature to pharmacy shelf

Caesalpinia bonduc and C. decapeleta var. japonica have great importance in traditional medicine systems but scientific information's are still lacking for their potentials. To explore their bioactivity, we assessed the antioxidant, enzyme inhibitory abilities of the dichloromethane (DCM), ethyl acetate, methanol, and water extracts prepared from the leaves and bark. The cytotoxicity and anticancer properties of the extracts were also assessed in vitro. The water extract of C. decapeleta leaves possessed highest phenolic content (108.16 mg gallic acid equivalent (GAE)/g extract), while the highest flavonoid content was recorded for the C. bonduc leaf methanolic extract (27.89 mg rutin equivalent (RE)/g extract). In general, C. decapeleta extracts possessed higher radical scavenging potential compared to C. bonduc extracts. C. decapeleta DCM leaves extract (10.20 mg galantamine equivalent (GALAE)/g extract) showed highest inhibition against butyrylcholinesterase. The cytotoxicity of the most potent methanolic and aqueous extracts were assessed against four cell lines. The chemical profiles of both species appeared to be different. C. bonduc was abundant in organic and phenolic acids as well as their esters. Flavonoid glycosides, bonducellin and its derivatives and caesalminaxins were identified. Whereas, C. decalpetala possessed many galloylated compounds. The cytotoxicity of C. bonduc and C. decapetala extracts was tested using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) based assay on VERO (kidney of an adult African Green monkey cells), HeLa (human cervical adenocarcinoma cells), RKO (human colon carcinoma cells), FaDu (human hypopharyngeal squamous carcinoma cells) cell lines. C. bonduc bark water extract exhibited the highest cytotoxicity towards HeLa (50 % cytotoxic concentration (CC₅₀): 28.5 μg/mL) cancer cell line, as compared to normal VERO cells (CC₅₀:35.87 μg/mL). For C. decapetala, the highest cytotoxicity was found for bark methanol extract on the HeLa cells with CC₅₀ of 46.08 μg/mL and selectivity index of 3.33. In the gene ontology analysis, prostate cancer, nuclear factor kappa B (NF-kappa B) signaling, proteoglycans in cancer pathways might support the results of the cytotoxic assays. These results showed that the tested Caesalpinia species, showing potent inhibitory action against butyrylcholinesterase, might represent novel phytotherapeutic avenues for the management of Alzheimer's disease.

Dopamine-Mediated Vanillin Multicomponent Derivative Synthesis via Grindstone Method: Application of Antioxidant, Anti-Tyrosinase, and Cytotoxic Activities

Purpose

This study aimed to determine the extent of contribution of dopamine to antioxidant and anti-tyrosinase activities, by dopamine addition to vanillin. This study achieved the synthesis of dopamine-associated vanillin Mannich base derivatives prepared via a one-step reaction involving a green chemistry approach, and investigation of antioxidant and anti-tyrosinase activities.

Methods

Novel one-pot synthesis of Mannich base dopamine-connected vanillin (1a-l) derivatives can be achieved via green chemistry without using a catalyst. Newly-prepared compounds were characterised with FTIR and NMR (¹H and ¹³C) spectra, mass spectra, and elemental analyses. In total, 12 compounds (1a-l) were synthesised and their antioxidant and anti-tyrosinase activities evaluated. Antioxidant activities of 2,2-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide (NO), hydrogen peroxide (H₂O₂), and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and diammonium assays, ABTS^•+ radical scavenging, and linoleic acid peroxidation were used to screen all synthesised compounds (1a-l) for anti-tyrosinase activities and cytotoxicity against MCF-7 and Vero cell lines;.

Results

The compound 1k inhibited (IC₅₀:11.02µg/mL) the DPPH-scavenging activity to a greater extent than the standard BHT (IC₅₀:25.17µg/mL), and showed high activity in H₂O₂ and NO scavenging assays. Compound 1e was more potent (96.21%) against ABTS and compound 1k was more potent (95.28%) against 2,2ʹ-azobis(2-amidinopropane)dihydrochloride antioxidant than the standard trolox. All synthesised compounds were screened for anti-tyrosinase inhibitory activity. Compound 1e had higher activity against tyrosinase (IC₅₀=10.63 µg/mL), than kojic acid (IC₅₀=21.52µg/mL), and was more cytotoxic (GI₅₀ 0.01µM) against MCF-7 cell line than the doxorubicin standard and other tested compounds.

Conclusion

In this study, all compounds were found to possess significant antioxidant and anti-tyrosinase activities. Compounds 1e and 1k performed well, compared with other compounds, in all assays. In addition, this study successfully identified several promising molecules that exhibited antioxidant and anti-tyrosinase activities.

Ditopic Chelators of Dicopper Centers for Enhanced Tyrosinases Inhibition

Tyrosinase enzymes (Tys) are involved in the key steps of melanin (protective pigments) biosynthesis and molecules targeting the binuclear copper active site on tyrosinases represent a relevant strategy to regulate enzyme activities. In this work, the possible synergic effect generated by a combination of known inhibitors is studied. For this, derivatives containing kojic acid (KA) and 2-hydroxypyridine-N-oxide (HOPNO) combined with a thiosemicarbazone (TSC) moiety were synthetized. Their inhibition activities were evaluated on purified tyrosinases from different sources (mushroom, bacterial, and human) as well as on melanin production by lysates from the human melanoma MNT-1 cell line. Results showed significant enhancement of the inhibitory effects compared with the parent compounds, in particular for HOPNO-TSC. To elucidate the interaction mode with the dicopper(II) active site, binding studies with a tyrosinase bio-inspired model of the dicopper(II) center were investigated. The structure of the isolated adduct between one ditopic inhibitor (KA-TSC) and the model complex reveals that the binding to a dicopper center can occur with both chelating sites. Computational studies on model complexes and docking studies on enzymes led to the identification of KA and HOPNO moieties as interacting groups with the dicopper active site.

Molecular modeling and phenoloxidase inhibitory activity of arbutin and arbutin undecylenic acid ester

Excessive melanin formation has been linked to various skin disorders such as hyperpigmentation and skin cancer. Tyrosinase is the most prominent target for inhibitors of melanin production. In this study, we investigated whether arbutin and its prodrug, arbutin undecylenic acid ester, might inhibit phenoloxidase (PO), a tyrosinase-like enzyme. Molecular docking simulation results suggested that arbutin and arbutin undecylenic acid ester can bind to the substrate-binding pocket of PO. Arbutin undecylenic acid ester with an IC₅₀ 6.34 mM was effective to inhibit PO compared to arbutin (IC₅₀ 29.42 mM). In addition, arbutin undecylenic acid ester showed low cytotoxicity in Drosophila S2 cells and the compound inhibited the melanization reaction. Therefore, the results of this study have demonstrated that arbutin undecylenic acid ester as a potential inhibitor of PO. We successfully designed a new platform utilizing Drosophila melanogaster and Bombyx mori as animal models propounding fast, cheap, and high effectiveness in method to screen tyrosinase inhibitors.

Screening of perhydrolases to optimize glucose oxidase-perhydrolase-in situ chemical oxidation cascade reaction system and its application in melanin decolorization

A novel glucose oxidase (GOD)-perhydrolase-in situ chemical oxidation (ISCO) cascade reaction system was designed, optimized, and verified the operation feasibility in this research. Among the determined four perhydrolases, acyltransferase from Mycobacterium smegmatis (MsAcT) displayed the highest specific activity for perhydrolysis reaction (76.4 U/mg) and the lowest K_m value to hydrogen peroxide (13.9 mmol/L). GOD-MsAcT cascade reaction system also displayed high catalytic efficiency. Under the optimal parameters (50:1 activity unit ratio of GOD to MsAcT, pH 8.0, 50 mmol/L of β-d-glucose, and 15 mmol/L of glyceryl triacetate), the melanin decolorization rate using GOD-MsAcT-ISCO cascade reaction system reached 86.8 %. Kinetics of GOD-MsAcT-ISCO cascade reaction system for melanin decolorization fitted the kinetic model of Boltzmann sigmoid. As a substitutive skin whitening technology, GOD-MsAcT-ISCO cascade reaction system displayed an excellent application prospect.

Monosubstituted Acetophenone Thiosemicarbazones as Potent Inhibitors of Tyrosinase: Synthesis, Inhibitory Studies, and Molecular Docking

A set of 12 monosubstituted acetophenone thiosemicarbazone derivatives (TSCs) were synthesized and their inhibitory properties toward tyrosinase activity were tested. Moreover, their ability to inhibit melanogenesis in the B16F10 murine melanoma cell line was studied. In order to investigate the nature of interactions between the enzyme and the inhibitors, molecular docking to the active site was performed. TSCs 5, 6, 8, and 9 revealed a half maximal inhibitory concentration (IC₅₀) below 1 µM. Compound 6 turned out to be the most potent tyrosinase inhibitor. All investigated compounds showed reversible inhibition of competitive or mixed type. The para-substituted TSCs had higher affinity for the enzyme as compared to their ortho- and meta-analogues. All investigated compounds inhibited melanin production in B16F10 cells at the micromolar level. Molecular docking showed that the sulfur atom of the thiourea moiety penetrates the active site and interacts with copper ions. The above outcomes might be helpful in the design of new tyrosinase inhibitors in the food and cosmetic industries.

Characterization of Caffeoylquinic Acids from Lepisorus thunbergianus and Their Melanogenesis Inhibitory Activity

Hyperpigmentation resulting from the overactivation of tyrosinase leads to darker spots or patches on the human skin. Although these phenomena are harmless, there is still great demand for melanogenesis inhibitors to prevent hyperpigmentation by inhibiting the tyrosinase, a rate-limiting enzyme in melanogenesis. Although Lepisorus thunbergianus has been used in folk remedies as a diuretic and hemostatic agent, its effect on melanogenesis has not yet been reported. In this study, we prepared an L. thunbergianus extract and its solvent fractions and evaluated their biological activity against free radical and melanin synthesis. The extract of L. thunbergianus inhibited mushroom tyrosinase activity more efficiently than, and with similar antioxidant activity to, arbutin in vitro. Comparative evaluation of the anti-melanogenesis and anti-tyrosinase activity of L. thunbergianus solvent fractions demonstrated that, by inhibiting tyrosinase activity, the butanol fraction has the highest potential for the inhibition of melanogenesis in melanoma cells. We found by structural analysis using high-performance liquid chromatography (HPLC) and NMR spectroscopy that the major compounds in butanol fraction were three caffeoylquinic acid derivatives. The three derivatives had similar radical scavenging and anti-tyrosinase activities in vitro, while only 5-caffeoylquinic acid had an inhibitory effect on α-MSH-induced melanogenesis. The inhibitory effect of 5-caffeoylquinic acid was verified by the determination of the melanin content and tyrosinase activity in melanoma after treating the cells with a commercial compound. Further, we revealed that 5-caffeoylquinic acid inhibited melanogenesis by chelating a copper cation from a copper-tyrosinase complex. Thus, 5-caffeoylquinic acid or butanol fraction isolated from L. thunbergianus might be useful in cosmetics as a skin-whitening agent.

Extracts of Antrodia cinnamomea mycelium as a highly potent tyrosinase inhibitor

BACKGROUND

Ganoderma has been known as a cure for diseases since ancient times, and been used as a medicinal mushroom for more than 2000 years. By many accounts, Ganoderma lucidum extracts from fruit bodies exhibited the comparable tyrosinase inhibition activity.

AIMS

To validate A. cinnamomea mycelia anti-melanogenesis activity. Ethanolic extracts of A. cinnamomea mycelia were evaluated using in vitro cell-free tyrosinase assay, cell-based and zebrafish phenotype-based method. Meanwhile, safety assessment was also conducted to ensure the feasibility as the novel ingredients in cosmetic and pharmaceutic industries.

METHODS

The major regulatory enzymes being in charge of cutaneous pigmentation, was investigated in both cell-free and cellular enzyme systems, and in phenotype-based zebrafish model. A high-throughput TLC in vitro screening system was introduced to perform the initial evaluation of those with anti-melanin formation activity.

RESULTS

Among the fractions, 50% ethanol extracted fraction (AC_Et50_Hex) exhibited highest anti-melanin formation activity. AC_Et50_Hex (at 100 ppm) reduced 30% intracellular melanin of B16-F10 cells through suppression of tyrosinase activity and its protein expression. For animal study, not only does AC_Et50_Hex exhibited similar depigmenting efficacy to kojic acid (56.1% vs 52.3%) with lower dosage (50 ppm vs 1400 ppm), but showed less toxicity to zebrafish.

CONCLUSION

A. cinnamomea mycelium extracts can be an ideal candidate/substitute for skin-whitening since kojic acid has been reported with carcinogenic effect. AC_Et50_Hex was recognized as a potential tyrosinase inhibitor throughout in vitro and in vivo analysis studies. The mass production of A. cinnamomea mycelium from agitated fermentation realizes the natural mushroom extracts for commercial application.

Adsorbed hollow fiber immobilized tyrosinase for the screening of enzyme inhibitors from Pueraria lobata extract

In this study, a method based on adsorbed hollow fiber immobilized tyrosinase (TYR) was developed to screening potential TYR inhibitors from Pueraria lobate extract. Kojic acid and ranitidine were used as positive and negative control to verify the reliability of the proposed method, respectively. Several significant parameters of the screening process, including the amount of P. lobata extract, adsorption time and incubation time, were optimized. After investigating the repeatability of the developed method, seven potential active compounds in P. lobata extract were successfully detected and their chemical structures were tentatively identified by liquid chromatography - mass spectrometry analysis. Furthermore, the inhibitory activity of four identified compounds on TYR was tested in vitro, and three of them, namely, puerarin, puerarin-6″-O-xyloside and puerarin apioside were verified to have good TYR inhibitory activity with IC₅₀ value of 478.5, 513.8, and 877.3 μM, respectively. In addition, the molecular docking results indicated that these compounds could bind to the amino acid residues in TYR catalytic pocket. These results proved that the proposed method is a feasible approach for screening of TYR inhibitors from plant extract.

Tyrosinase and Melanogenesis Inhibition by Indigenous African Plants: A Review

The indiscriminate use of non-regulated skin lighteners among African populations has raised health concerns due to the negative effects associated with skin lightener toxicity. For this reason, there is a growing interest in the cosmetic development of plants and their metabolites as alternatives to available chemical-derived skin lightening formulations. Approximately 90% of Africa’s population depends on traditional medicine, and the continent’s biodiversity holds plant material with various biological activities, thus attracting considerable research interest. This study aimed to review existing evidence and document indigenous African plant species capable of inhibiting the enzyme tyrosinase and melanogenesis for potential incorporation into skin lightening products. Literature search on melanin biosynthesis, skin lightening, and tyrosinase inhibitors resulted in the identification of 35 plant species were distributed among 31 genera and 21 families across 15 African countries and 9 South African provinces. All plants identified in this study showed competent tyrosinase and melanogenesis inhibitory capabilities. These results indicate that African plants have the potential to serve as alternatives to current chemically-derived skin lighteners.

Clinical efficacy of dissolvable microneedles armed with anti-melanogenic compounds to counter hyperpigmentation

BACKGROUND

Hyperpigmentation is a complex physiological process associated with alterations of skin color due to melanin overproduction and distribution. Both intrinsic and extrinsic factors influence discoloration with the involvement of multiple pathways in cooperative manners. Restoring natural skin color requires a multi-targeted approach. Latest advances in anti-melanogenic compounds and microneedle delivery system have presented opportunities for tackling hyperpigmentationsuccessfully.

AIMS

This work was aimed at assessing the dermal tolerability and efficacy of hyaluronic acid-based microneedle patches loaded with anti-melanogenic actives for improvements of skin discoloration.

PATIENTS/METHODS

The test products consist of hyaluronic acid with niacinamide, ascorbic acid 2-glucoside, tranexamic acid, resveratrol, 4-n-butyl-resorcinol, and Halidrys siliquosa extract. In a monocentric 12 weeks clinical trial, the HA-MNs patches were applied to the affected areas of the faces on subjects with hyperpigmented skin. The color properties of the skin were analyzed spectrophotometrically.

RESULTS

The products were tolerated remarkably; none of the subjects informed any primary or cumulative skin responses. Evaluation of color related measurable skin properties provided insight into the general effectiveness: The individual topology measurements showed 51.4% noticeable improvements in hyperpigmented zones, which were also in good agreement with the personal impressions of the subjects determined by questionnaires before and after the treatments.

CONCLUSIONS

The concentrated blends of actives in microneedle patches act in a multi-targeted manner, and they could be worked in a complementary fashion for the improvement of skin color and appearance. The study has established the overall convenience of the HA-MNs with the formulation of anti-melogenic compounds against skin discoloration.

Traditional Asian Herbs in Skin Whitening: The Current Development and Limitations

In Asia, the market for whitening cosmetics is expanding rapidly, more and more people prefer to use natural products. Driven by natural product demand and technical advances, herbal research is also developing fast. Lots of studies reported that Asian herbal reagents can reduce melanogenesis, these findings provide evidence for the whitening application of Asian herbs. However, the current development status and challenges of herbal research need attention too. By reviewing these studies, different problems in studying herbal formulas, extracts, and active ingredients were presented. One of the most influential troubles is that the components of herbs are too complex to obtain reliable results. Thus, an understanding of the overall quality of herbal research is necessary. Further, 90 most cited Asian herbal studies on whitening were collected, which were conducted between 2017 and 2020, then statistical analysis was carried out. This work provided a comprehensive understanding of Asian herbal research in skin whitening, including the overall status and quality, as well as the focuses and limitations of these studies. By proactively confronting and analyzing these issues, it is suggested that the focus of herbal medicine research needs to shift from quantity to quality, and the new stage of development should emphasize transformation from research findings to whitening products.

Marine-Derived Compounds with Potential Use as Cosmeceuticals and Nutricosmetics

The cosmetic industry is among the fastest growing industries in the last decade. As the beauty concepts have been revolutionized, many terms have been coined to accompany the innovation of this industry, since the beauty products are not just confined to those that are applied to protect and enhance the appearance of the human body. Consequently, the terms such as cosmeceuticals and nutricosmetics have emerged to give a notion of the health benefits of the products that create the beauty from inside to outside. In the past years, natural products-based cosmeceuticals have gained a huge amount of attention not only from researchers but also from the public due to the general belief that they are harmless. Notably, in recent years, the demand for cosmeceuticals from the marine resources has been exponentially on the rise due to their unique chemical and biological properties that are not found in terrestrial resources. Therefore, the present review addresses the importance of marine-derived compounds, stressing new chemical entities with cosmeceutical potential from the marine natural resources and their mechanisms of action by which these compounds exert on the body functions as well as their related health benefits. Marine environments are the most important reservoir of biodiversity that provide biologically active substances whose potential is still to be discovered for application as pharmaceuticals, nutraceuticals, and cosmeceuticals. Marine organisms are not only an important renewable source of valuable bulk compounds used in cosmetic industry such as agar and carrageenan, which are used as gelling and thickening agents to increase the viscosity of cosmetic formulations, but also of small molecules such as ectoine (to promote skin hydration), trichodin A (to prevent product alteration caused by microbial contamination), and mytiloxanthin (as a coloring agent). Marine-derived molecules can also function as active ingredients, being the main compounds that determine the function of cosmeceuticals such as anti-tyrosinase (kojic acid), antiacne (sargafuran), whitening (chrysophanol), UV protection (scytonemin, mycosporine-like amino acids (MAAs)), antioxidants, and anti-wrinkle (astaxanthin and PUFAs).

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.

Synthesis, biological evaluation and molecular docking analysis of vaniline-benzylidenehydrazine hybrids as potent tyrosinase inhibitors

In this work, 11 novel compounds based on vaniline and benzylidenehydrazine structure were synthesized with various substituents on phenyl aromatic ring of the molecule and evaluated as tyrosinase inhibitors. These new derivatives showed significant anti-tyrosinase activities, among which 4i demonstrated to be the most potent compound, with IC₅₀ values of 1.58 µM . The structure–activity relationship study of the novel constructed analogs was fully discussed. Kinetic study of compound 4i showed uncompetitive inhibition towards tyrosinase. Furthermore, the high potency of 4i was supported theoretically by molecular docking evaluations.

Inhibition of melanin production and promotion of collagen production by the extract of Kuji amber

Kuji amber is fossilized tree resin of the Late Cretaceous in Japan. In this study, new biological activities of ethanol extract of Kuji amber (EtOH ext.) and supercritical carbon dioxide fluid extract of Kuji amber (scCO2 ext.) were examined. Both EtOH ext. and scCO2 ext. inhibited melanin production in B16 mouse melanoma cells and promoted collagen production in human skin fibroblast SF-TY cells. The scCO2 ext. had more potent activity than that of EtOH ext. and may depend on the efficiency of the extraction. The main new biologically active compound in Kuji amber, kujigamberol had no activities against melanin production, however, it promoted collagen production at low concentrations. A biologically active compound having a different structure, spirolactone norditerpenoid, showed both the inhibition activity against melanin production and the promotion activity of collagen production in a dose dependent manner. EtOH ext. and scCO2 ext., which include both kujigamberol and spirolactone norditerpenoid, have not only anti-allergy activity, but also inhibit melanin production and promote collagen production.

Improving the antioxidant and anti-tyrosinase activities of Stemonae Radix by solid-state fermentation with Mucor circinelloides T2-12

Stemonae Radix, a medicinal and edible herb, has been reported to possess various pharmacological effects. In the present study, Stemonae Radix was fermented by fungi to improve the antioxidant and anti-tyrosinase activities. The results showed that Stemonae Radix fermented by Mucor circinelloides T2-12 exhibited two-folds more antioxidant and anti-tyrosinase activities than non-fermented material. The increased activity might be ascribed to the improvement of total phenolic content, hydrolyzation of glucosides and esters of phenolics and metabolism of saccharides according to ultraviolet and nuclear paramagnetic resonance spectroscopy. This paper suggested that fermenting Stemonae Radix with M. circinelloides T2-12 is effective to increase antioxidant and anti-tyrosinase effects and Stemonae Radix fermented by M. circinelloides T2-12 might be newly alternative of natural antioxidant and tyrosinase inhibitor. The present study is the first to report that pure strain fermentation processing is effective in improving the antioxidant and anti-tyrosinase activities of Stemonae Radix.

Phloretin as both a substrate and inhibitor of tyrosinase: Inhibitory activity and mechanism

Tyrosinase is the rate-limiting enzyme for controlling the production of melanin in the human body, and overproduction of melanin can lead to a variety of skin disorders. In this paper, the inhibitory kinetics of phloretin on tyrosinase and their binding mechanism were determined using spectroscopy, molecular docking, antioxidant assays and chromatography. The spectroscopic results indicate that phloretin reversibly inhibits tyrosinase in a mix-type manner through a multiphase kinetic process with the IC₅₀ of 169.36 μmol/L. It is shown that phloretin has a strong ability to quench the intrinsic fluorescence of tyrosinase mainly through a static quenching procedure, suggesting that a stable phloretin-tyrosinase complex is generated. Molecular docking results suggest that the dominant conformation of phloretin binds to the gate of the active site of tyrosinase. Moreover, the antioxidant assays demonstrate that phloretin has powerful antioxidant capacity and has the ability to reduce o-dopaquinone to l-dopa just like ascorbic acid. Interestingly, the results of spectroscopy and chromatography indicate that phloretin is a substrate of tyrosinase but also an inhibitor. The possible inhibitory mechanism is proposed, which will be helpful to design and search for tyrosinase inhibitors.