Hydroxyphenyl thiosemicarbazones as inhibitors of mushroom tyrosinase and antibrowning agents

Integrated transcriptome and DNA methylome analysis reveal the browning mechanism in Agaricus bisporus

The white button mushroom (Agaricus bisporus), widely cultivated worldwide as an edible mushroom, is susceptible to browning, which significantly impacts its nutritional and commercial value. Extensive research has enhanced our understanding of the mechanisms underlying this browning process. Although the role of DNA methylation in regulating gene expression has been studied in many fungi, information specifically concerning DNA methylation during the browning in A. bisporus is still limited. In this study, we initially evaluated the impact of temperatures (4 ℃ and room temperature) on discoloration in A. bisporus, and samples with similar discoloration under different temperatures were collected for transcriptome and DNA methylation sequencing. The results revealed that DNA methylation was positively correlated with browning, suggesting its involvement during the browning in A. bisporus. Further analysis showed the heightened methylation levels were primarily attributed to increased methylation at CHG and CHH sites. By joint analysis of transcriptome and DNA methylome, 342 genes with significant expression changes were identified to be affected by DNA methylation, and finally 13 genes were considered as important browning genes under different signaling pathways, such as ABA/ET pathway. Notably, four DNA methyltransferases were identified and validated to play important role during browning in A. bisporus. Altogether, this study provides theoretical insights into the functions of DNMTs in A. bisporus, and offers new perspectives on the role of DNA methylation in edible mushrooms.

Cannabidiol-Based Thiosemicarbazones: A Preliminary Study Evaluating Their Anti-Tyrosinase Properties

Cannabidiol (CBD), a non-psychoactive cannabinoid, has attracted significant research interest due to its antioxidant, anti-inflammatory, and neuroprotective properties. As a versatile scaffold in drug discovery, CBD has been widely explored for developing novel therapeutics. In this study, we synthesized and evaluated the anti-tyrosinase activity of CBD-based thiosemicarbazones. Structure-activity relationship (SAR) analyses were conducted to assess the impact of various functional groups on tyrosinase inhibition, including an evaluation of inhibitory kinetics for selected compounds. The synthesized derivatives demonstrated potent tyrosinase inhibition, with activity comparable to kojic acid, a standard tyrosinase inhibitor. Given the crucial role of tyrosinase in melanin biosynthesis, these findings suggest that CBD-based thiosemicarbazones could serve as promising candidates for managing tyrosinase-related disorders, including hyperpigmentation and melanogenesis-related conditions. Moreover, the presence of thiosemicarbazone moieties may contribute to the observed inhibitory effects, potentially through metal chelation at the enzyme's active site. This study provides valuable insights into the design of CBD-derived inhibitors targeting tyrosinase. Further optimization and in-depth biological evaluation are warranted to explore their full therapeutic potential.

Structural and mechanistic insights into the anti-tyrosinase, anti-melanogenesis, and anti-browning effect of proanthocyanidins from seed coats of Acer truncatum Bunge

Acer truncatum is a multifunctional tree species with broad applications in ornamental, healthy drink, and seed oil. In the present study, proanthocyanidins were isolated from the seed coats of A. truncatum, which were largely discarded as industrial wastes in seed oil production. Meanwhile, structural features, effects and mechanisms of anti-tyrosinase, anti-melanogenesis, and anti-browning of A. truncatum seed coat proanthocyanidins (ASPs) were systematically investigated. The joint application of FT-IR, MALDI-TOF-MS, hiolysis-coupled reverse-phase LC-ESI-MS, together with normal-phase LC confirmed that ASPs were predominately constituted by procyanidins with a mean polymerization degree of 12.09. Furthermore, ASPs powerfully inhibited both monophenolase and diphenolase activities of tyrosinase, and the inhibition of diphenolase was proved to be reversible and competitive-uncompetitive mixed type. Analyses of fluorescence quenching, UV spectra, and copper-ion chelation indicated that ASPs could inhibit tyrosinase in varied stages, and molecular docking and dynamic simulation further revealed the interaction mode between ASPs and tyrosinase. Cell assays further suggested that ASPs exhibited a strong inhibition against intracellular tyrosinase activity and melanin production through suppressing the expression of tyrosinase and microphthalmia transcription factor (MITF) at transcription level and caused apoptosis in B16F10 cells at higher concentrations. Antioxidant and anti-browning studies demonstrated that ASPs possessed high capacities of antioxidant, and potently suppress the browning of fresh-cut potatoes. Therefore, this study confirmed that seed coats of Acer truncatum is a potential natural source of tyrosinase, melanogenesis, and browning inhibitor, which provided a theoretical basis for the utilization of ASPs in the cosmetics, pharmaceutical, and food industries.

Inhibitory potential of 7-hydroxycoumarin-3-carboxylic acid against tyrosinase and its effect on the preservation of fresh-sliced apples

Excessive tyrosinase expression leads to pigmented diseases in humans and browning in plants, necessitating effective tyrosinase inhibitors. This study investigated the inhibitory effect and mechanism of 7-hydroxycoumarin-3-carboxylic acid (7-HC-3-CA) on tyrosinase. Using UV-visible absorption spectroscopy, we found that 7-HC-3-CA effectively inhibited tyrosinase activity, with an IC50 value of 364 ± 1.3 μM. Enzyme kinetics, fluorescence methods and molecular simulation techniques revealed that 7-HC-3-CA acted as a reversible and competitive inhibitor, forming a stable complex with tyrosinase through hydrophobic interactions and hydrogen bonding. This altered the microenvironment of Tyr and Trp residues, causing the structural stretching and conformational changes that diminish catalytic activity. Preservation experiments demonstrated that 0.5 mM 7-HC-3-CA significantly reduced mass loss and decreased browning of fresh-sliced apples. It also lowered polyphenol oxidase activity from 0.22 to 0.18 and delayed phenolic oxidation, enhancing total phenolic content from 0.34 to 0.54, thereby controlling browning and extending storage life. Cell assays indicated that 0.5 mM 7-HC-3-CA had no significant impact on cell proliferation, with viability over 80 %. Acute toxicity tests proved that 0.5 mM of 7-HC-3-CA is completely non-lethal to KM mice. In conclusion, this study confirmed 7-HC-3-CA was a viable and safe antibrowning agent and revealed its potential application in the field of food preservation.

Inhibition of polyphenol oxidase for preventing browning in edible mushrooms: A review

Edible mushrooms are rich in nutrients and bioactive compounds, but their browning affects their quality and commercial value. This article reviews various methods to inhibit polyphenol oxidase (PPO)-induced browning in mushrooms. Physical methods such as heat treatment, low temperatures, irradiation, and ultrasound effectively reduce PPO activity but may affect mushroom texture and flavor. Chemical inhibitors, including synthetic chemicals and natural plant extracts, provide effective PPO inhibition but require careful monitoring of their content. Biological methods, including gene editing and microbial fermentation, show promise in targeting PPO genes and enhancing antioxidant production. Combining these methods offers a comprehensive strategy for preserving mushroom quality, extending shelf life, and maintaining nutritional value. PRACTICAL APPLICATION: These approaches can be applied in the food industry to improve post-harvest mushroom preservation, enhance product quality, and reduce waste, benefiting both producers and consumers. Further research and innovation are needed to optimize the practical application of these methods in large-scale processing and storage conditions.

Inhibitory activity and mechanism of thiosemicarbazide derivatives on tyrosinase and their anti-browning activity in fresh apple juice

Exploring tyrosinase inhibitors has been an effective way to find promising anti-browning agents in the food industry. Therefore, a class of thiosemicarbazide derivatives (4a-4m) were synthesized and we investigated the inhibitory mechanism on tyrosinase by fluorescence quenching, copper ion chelating and UV spectra study etc. 2-(2-Chlorobenzyl) hydrazine-1-carbothioamide (4f) (IC50 = 1.21 ± 0.02 μM) is the most active compound of all derivatives, which was defined as a mix-type inhibitor. Additionally, molecular docking and copper ions chelating studies indicated that compound 4f has the ability to inhibit the tyrosinase activity by chelating the copper ions in the active region. Furthermore, compound 4f also exhibited lower cytotoxicity, excellent aqueous solubility and outstanding anti-browning capacity in fresh apple juice. These findings indicated these derivatives could provide more possibility for developing more safer and effective anti-browning agents.

A new strategy for the treatment of Parkinson's disease: Discovery and bio-evaluation of the first central-targeting tyrosinase inhibitor

The high level of tyrosinase leads to the generation of neuromelanin, further causing the abnormality of redox-related protein level and mediating the occurrence and development of Parkinson's disease (PD). However, the existing tyrosinase inhibitors are mostly natural product extracts or polyphenolic derivatives, which hindered them from penetrating the blood-brain barrier (BBB). Herein, we obtained a novel tyrosinase inhibitor, 2-06 (tyrosinase: monophenolase IC50 = 70.44 ± 22.69 μM, diphenolase IC50 = 1.89 ± 0.64 μM), through the structure-based screening method. The compound 2-06 presented good in vitro and in vivo safety, and can inhibit the tyrosinase and melanogenesis in B16F10. Moreover, this compound showed neuroprotective effects and Parkinsonism behavior improving function. 2-06 was proved to penetrate the BBB and enter the central nervous system (CNS). The exploration of the binding mode between 2-06 and tyrosinase provided the foundation for the subsequent structural optimization. This is the first research to develop a central-targeting tyrosinase inhibitor, which is crucial for in-depth study on the new strategy for utilizing tyrosinase inhibitors to treat PD.

Cyrene™ as a tyrosinase inhibitor and anti-browning agent

The tyrosinase pathway takes part in the enzymatic process of food browning and is primarily responsible for food spoilage - manifesting itself from a decrease in its nutritional value to a deterioration of taste, which consequently leads to a gradual loss of shelf life. Finding safe and bio-based tyrosinase inhibitors and anti-browning agents may be of great importance in agriculture and food industries. Herein, we showed that Cyrene™ exhibits tyrosinase inhibitory activity (IC50: 268.2 µM), the 1.44 times higher than ascorbic acid (IC50: 386.5 μM). Binding mode studies demonstrated that the carbonyl oxygen of Cyrene™ coordinates with both copper ions. Surprisingly, both hydroxyl groups of Cyrene gem-diol perform a monodentate binding mode with both copper ions, at similar distances. This fact suggests that both compounds could have a similar binding mode and, as consequence, similar biological activities in tyrosinase inhibition assays and anti-browning activities.

Synthesis, anti-browning effect and mechanism research of kojic acid-coumarin derivatives as anti-tyrosinase inhibitors

Thirteen kojic acid-coumarin derivatives were synthesized using the principle of molecular hybridization, and their structures were characterized by 1H NMR, 13C NMR, and HRMS. In vitro enzyme inhibition experiments showed that all newly synthesized derivatives have excellent inhibition of tyrosinase (TYR) activity. As a mixed inhibitor, compound 6f has the strongest activity, with an IC50 value of 0.88 ± 0.10 µM. Multispectral experiments have confirmed that the mode of action of compound 6f on TYR was static quenching. In addition, compound 6f formed a new complex with TYR, which increased the hydrophobicity of the enzyme microenvironment, reduced the content of the α-helix in the enzyme, and changed the secondary structure. The experimental results showed that compound 6f effectively inhibited the browning of lotus root slices and had low cytotoxicity. Therefore, compound 6f is believed to have great development potential as a TYR inhibitor in the food industry.

Recent advances in triazoles as tyrosinase inhibitors

The tyrosinase enzyme, which is widely found in microorganisms, animals and plants, has a significant position in melanogenesis, plays an important role in undesirable browning of fruits and vegetables, antibiotic resistance, skin pigment formation, sclerotization of cuticle, neurodegeneration, etc. Therefore, with the wide potential application fields of tyrosinase in food, agriculture, cosmetics and pharmaceutical industries, which has become the target enzyme for the development of therapeutic agents such as antibrowning, anticancer, antibacterial, skin whitening, insecticides, etc., a large number of synthetic tyrosinase inhibitors have been widely reported in recent years. The triazole ring, which has a broad spectrum of biological action, is of increasing interest in the synthesis of new tyrosinase inhibitors. In this review, tyrosinase inhibition effects, structure-activity relationships, enzyme inhibition kinetics and mechanisms of action of 1,2,3- or 1,2,4-triazole derivatives were investigated. The data gathered is anticipated to supply rational guidance and an influential strategy for the development of novel, potent and safe tyrosinase inhibitors for better practical application in the future.

From polyphenol to o-quinone: Occurrence, significance, and intervention strategies in foods and health implications

Polyphenol oxidation is a chemical process impairing food freshness and other desirable qualities, which has become a serious problem in fruit and vegetable processing industry. It is crucial to understand the mechanisms involved in these detrimental alterations. o-Quinones are primarily generated by polyphenols with di/tri-phenolic groups through enzymatic oxidation and/or auto-oxidation. They are highly reactive species, which not only readily suffer the attack by nucleophiles but also powerfully oxidize other molecules presenting lower redox potentials via electron transfer reactions. These reactions and subsequent complicated reactions are capable of initiating quality losses in foods, such as browning, aroma loss, and nutritional decline. To attenuate these adverse influences, a variety of technologies have emerged to restrain polyphenol oxidation via governing different factors, especially polyphenol oxidases and oxygen. Despite tremendous efforts devoted, to date, the loss of food quality caused by quinones has remained a great challenge in the food processing industry. Furthermore, o-quinones are responsible for the chemopreventive effects and/or toxicity of the parent catechols on human health, the mechanisms by which are quite complex. Herein, this review focuses on the generation and reactivity of o-quinones, attempting to clarify mechanisms involved in the quality deterioration of foods and health implications for humans. Potential innovative inhibitors and technologies are also presented to intervene in o-quinone formation and subsequent reactions. In future, the feasibility of these inhibitory strategies should be evaluated, and further exploration on biological targets of o-quinones is of great necessity.

Inhibitory Activities of Samples on Tyrosinases Were Affected by Enzyme Species and Sample Addition Methods

The inhibition of tyrosinase (TYR) activity is an effective measure to inhibit melanin synthesis. At present, there are many methods with discrepant details that study the TYR inhibitory activity of samples. Under the same experimental conditions, this paper systematically studies whether enzyme species and sample addition methods are the key factors that determine the TYR inhibitory activity of samples. TYRs extracted from B16F10 cells, apple and mushroom, called BTYR, ATYR and MTYR, respectively, were selected to implement this study. Results showed that TYR inhibitory activities of samples were obviously affected by the above two factors. It was necessary to select the appropriate enzyme according to the problems to be explained. It was speculated that indirectly inhibitory activity reflected the comprehensive effects of samples on TYR catalytic activity and intracellular TYR synthesis pathway, while directly inhibitory activity reflected the effects of samples on TYR catalytic activity. Additionally, kojic acid could be used as a positive control for both B16F10 cells and MTYR models. The TYR inhibitory activity of β-arbutin was complicated and fickle, while that of epigallocatechin gallate (EGCG) was universal and stable, which is to say, EGCG always inhibited TYR activity in a dose-dependent manner. In conclusion, the TYR inhibitory activities of samples were affected by enzyme species and sample addition methods. Compared with the unstable β-arbutin, EGCG was more valuable for clinical research.

A potentiometric and spectrofluorimetric approach to unravel inhibitory effects of semi- and thiosemicarbazones on mushroom tyrosinase activity

The inhibitory effects on mushrooms tyrosinase activity of some semi- and thiosemicarbazones were investigated. While the semicarbazones are inactive, the thiosemicarbazones are, in general, more active than the reference (kojic acid, IC₅₀ = 70 μM), with maximum activity obtained with benzaldehyde thiosemicarbazone (IC₅₀ = 7 μM). These inhibitors probably act by coordination of the copper(II) metal ions in the active site of tyrosinase: effectively, potentiometric studies conducted in water solutions confirm that the most active thiosemicarbazone is a good ligand for copper(II) ions. The tyrosinase CD spectra do not show any significant difference by addition of an inhibitor or an inactive compound. On the contrary, interesting results were obtained by spectrofluorimetric titrations of mushrooms tyrosinase aqueous solutions with some of the investigated compounds, giving helpful information about possible mechanism of action. The thiosemicarbazones here reported are not cytotoxic on human fibroblasts and do not activate cells in a pro-inflammatory way.

Modulation of the lipophilicity and molecular size of thiosemicarbazone inhibitors to regulate tyrosinase activity

A group of 5-methylsalicylaldehyde thiosemicarbazone derivatives (HMTs) bearing different lipophilic and steric substituents attached at the 3-position of cresol ring were synthesized and investigated as mushroom tyrosinase (TYR) inhibitors. The ability of HMTs to inhibit the diphenolase activity of TYR was evaluated with L-DOPA as substrate by determining IC₅₀ values in relation to their structure modifications. HMTs displayed distinct inhibitory competencies towards TYR activity with IC₅₀ values in the range of 1.02-143.56 μM. A close correlation between their inhibition potency and both lipophilicity and molecular size was observed. The inhibitory effect of the hydroxyethyl-containing derivatives was much higher than the hydroxyethyl-free ones overall. Among them, HMT-NBO exhibited the most potent effect with IC₅₀ of 5.85 μM, which was nearly 25-fold and 3.8-fold lower than its parent HMT-NBE and the control kojic acid, respectively. The hydroxyethyl clearly benefited the improvement of the inhibitory competences and acted as a regulating group of lipophilicity of the inhibitors. The kinetic analyses showed that HMTs were reversible and mixed type inhibitors against mushroom TYR. The inhibition mechanism was studied by means of fluorescence spectroscopy, FT-IR, ESI-MS and molecular docking analysis. The results indicated that the observed inhibitory effect of HMTs was accomplished by acting on the amino acid residues rather than by chelating the centre copper ions of TYR. Each of HMTs can insert the hydrophobic pocket and interact with the residues of TYR through Van der Waals forces and hydrogen bonds, with additional electrostatic interactions for HMT-NEE and HMT-NEO further strengthening the affinity. Meanwhile, the inhibitors were observed to bind with L-DOPA or/and L-DOPAquinone forming 1:1 stoichiometric complexes, probably exerting indirect inhibition against TYR activity.

Design and synthesis of novel stilbene-hydroxypyridinone hybrids as tyrosinase inhibitors and their application in the anti-browning of freshly-cut apples

In order to develop the tyrosinase inhibitors with potential application in food industry, a series of stilbene-hydroxypyridinone hybrids were prepared. Among these compounds, 1h was found to possess the most potent tyrosinase inhibitory effect on both monophenolase and diphenolase activities, with IC₅₀ values of 2.72 μM and 15.86 μM, respectively. The inhibitory effect of 1h on monophenolase activity was 4.6 times that of kojic acid. An inhibition kinetic assay indicated that 1h was a mixed-type and reversible inhibitor. The copper-binding and reducing ability assays, molecular docking study, intrinsic and ANS-binding fluorescence assays indicated that copper coordination and reduction is likely to be the causative mechanism for 1h-induced inhibition on tyrosinase. The results of color measurement and browning index determination indicated that treatment with 1h retarded effectively the browning of freshly-cut apples during their storage. Meanwhile, PPO and POD activities in apple slices were found to be effectively inhibited.

Synthesis and Tyrosinase Inhibitory Activity of (E)-5-Benzyl-7- (3-Bromobenzylidene)-3-(3-Bromophenyl)-2-Phenyl-3,3a, 4,5,6,7-Hexahydro-2H-Pyrazolo[4,3-c]Pyridine

The tyrosinase enzyme plays an essential role in the pigmentation of human skin, fruits, and vegetables. It has been tied with several human skin diseases and post-harvest problems. Hence, the tyrosinase enzyme becomes an excellent therapeutic target to overcome these issues. This study aimed to screen tyrosinase inhibitors by synthesizing halogen-substituted pyrazolopyridine derivatives. The pyrazolopyridine compound was obtained through two stages of synthesis. First, the intermediate compound, a derivative of 3,5-bis(arylidene)-4-piperidone, was synthesized through the Cleisen-Schmidt condensation reaction of 4-piperidone and benzaldehyde derivatives. Furthermore, the intermediate compound was reacted with phenylhydrazine through a cyclocondensation reaction to produce the titled compound with an 11% yield. The chemical structure of the target compound was identified through the interpretation of UV, FTIR, NMR, and HRMS spectra. Then an in vitro assay was conducted on the tyrosinase enzyme of the fungus Agaricus bisporus by detecting the presence of dopachrome at a wavelength of 492 nm. As a result, the in vitro assay showed that the titled compound had a weak inhibitory activity, and the IC50 value was > 500 µM. Thus, the synthesized compound is considered inactive.

Kojic Acid Showed Consistent Inhibitory Activity on Tyrosinase from Mushroom and in Cultured B16F10 Cells Compared with Arbutins

Kojic acid, β-arbutin, α-arbutin, and deoxyarbutin have been reported as tyrosinase inhibitors in many articles, but some contradictions exist in their differing results. In order to provide some explanations for these contradictions and to find the most suitable compound as a positive control for screening potential tyrosinase inhibitors, the activity and inhibition type of the aforementioned compounds on monophenolase and diphenolase of mushroom tyrosinase (MTYR) were studied. Their effects on B16F10 cells melanin content, tyrosinase (BTYR) activity, and cell viability were also exposed. Results indicated that α-arbutin competitively inhibited monophenolase activity, whereas they uncompetitively activated diphenolase activity of MTYR. β-arbutin noncompetitively and competitively inhibited monophenolase activity at high molarity (4000 µM) and moderate molarity (250–1000 µM) respectively, whereas it activated the diphenolase activity of MTYR. Deoxyarbutin competitively inhibited diphenolase activity, but could not inhibit monophenolase activity and only extended the lag time. Kojic acid competitively inhibited monophenolase activity and competitive–noncompetitive mixed-type inhibited diphenolase activity of MTYR. In a cellular experiment, deoxyarbutin effectively inhibited BTYR activity and reduced melanin content, but it also potently decreased cell viability. α-arbutin and β-arbutin dose-dependently inhibited BTYR activity, reduced melanin content, and increased cell viability. Kojic acid did not affect cell viability at 43.8–700 µM, but inhibited BTYR activity and reduced melanin content in a dose-dependent manner. Therefore, kojic acid was considered as the most suitable positive control among these four compounds, because it could inhibit both monophenolase and diphenolase activity of MTYR and reduce intercellular melanin content by inhibiting BTYR activity without cytotoxicity. Some explanations for the contradictions in the reported articles were provided.

Recent advances in the design and discovery of synthetic tyrosinase inhibitors

Tyrosinase is a copper-containing metalloenzyme that is responsible for the rate-limiting catalytic step in the melanin biosynthesis and enzymatic browning. As a promising target, tyrosinase inhibitors can be used as skin whitening agents and food preservatives, thus having broad potential in the fields of food, cosmetics, agriculture and medicine. From 2015 to 2020, numerous synthetic inhibitors of tyrosinase have been developed to overcome the challenges of low efficacy and side effects. This review summarizes the enzyme structure and biological functions of tyrosinase and demonstrates the recent advances of synthetic tyrosinase inhibitors from the perspective of medicinal chemistry, providing a better understanding of the catalytic mechanisms and more effective tyrosinase inhibitors.

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.

Spectroscopic studies and molecular docking on the interaction of delphinidin-3-O-galactoside with tyrosinase

The inhibitory effects of delphinidin-3-O-galactoside (DG) on the activities of tyrosinase (EC 1.14.18.1) (TY) from the edible Agaricus bisporus mushroom were investigated by enzyme kinetics, multispectroscopic methods, and molecular docking. As a result, DG showed strong inhibition on TY with the IC₅₀ of 34.14 × 10^-6  mol L^-1 . The inhibition mode of DG against TY was mixed type with α values of 5.09. The binding constant K_a and related thermodynamic parameters at the three different temperatures showed that the fluorescence quenching of TY by DG was static quenching. Synchronous fluorescence, three-dimensional fluorescence, ultraviolet-visible spectroscopy, and circular dichroism spectroscopies confirmed that the conformation or microenvironment of the TY protein were changed after binding with DG. Molecular docking revealed that DG had strong binding affinity to TY through hydrogen bonding and van der Waals force, and the results were consistent with the fluorescence data. Our findings suggested that DG may be potential TY inhibitor.

Design, synthesis, molecular modeling, and biological evaluation of novel kojic acid derivatives containing bioactive heterocycle moiety as inhibitors of tyrosinase and antibrowning agents

Tyrosinase plays an important role in melanin biosynthesis and enzymatic browning of fresh-cut fruit and vegetables. To discover potent tyrosinase inhibitors and antibrowning agents, a series of novel kojic acid derivatives containing bioactive heterocycle moiety (4a-4l) were designed and synthesized. Thereinto, 4d displayed the most potent tyrosinase inhibitory activity with IC₅₀ of 3.23 ± 0.26 μM and behaved as a competitive inhibitor with a K_i of 1.96 μM, compared to kojic acid (IC₅₀ = 32.23 ± 2.01 μM). Besides, copper-chelating assay, fluorescence spectrum quenching experiment, ANS-binding fluorescence quenching analysis, and molecular modeling studies indicated that 4d may inhibit tyrosinase activity by chelating with copper ions in the active site of tyrosinase. Furthermore, 4d exhibited low cytotoxic activity and significant antibrowning effects.This study suggests that these compounds may serve as lead molecules for developing novel tyrosinase inhibitors and antibrowning agents.

Antityrosinase Mechanism and Antimelanogenic Effect of Arbutin Esters Synthesis Catalyzed by Whole-Cell Biocatalyst

Tyrosinase is a key enzyme responsible for enzymatic browning of fruits and vegetables and skin disorders due to overproduction of melanin. Arbutin is an inhibitor of tyrosinase; however, its high polarity and weak transdermal absorption capacity limit its applications. In this paper, a green solvent system was developed to successfully synthesize arbutin esters with improved liposolubilities (Clog P values = 0.27-5.03). Among the obtained esters, arbutin undecenoate (AU) showed the strongest tyrosinase-inhibiting activity (15.6%), which was 9.0 times higher than that of arbutin. An enzyme kinetics study indicated that AU was a competitive inhibitor with reversible inhibition. The esters inhibited tyrosinase by making the secondary structure of tyrosinase looser and less stable; moreover, the interactions between tyrosinase and AU driven by metal interactions and hydrogen bonds also offered a mechanism for inhibition of AU on tyrosinase. In addition, AU (100 μM) reduced the melanin content of B16 mouse melanoma cells to 61.3% of the control group.

Electrocatalytic performance of tyrosinase detection in Penaeus vannamei based on a [(PSS/PPy)(P2Mo18/PPy)5] multilayer composite film modified electrode

Polyoxometalates (POMs) are widely used in the preparation of sensors that detect the content of substances because of their excellent electron transfer capabilities. In this paper, a [(PSS/PPy)(P₂Mo₁₈/PPy)₅] multilayer composite film modified electrode was prepared by the potentiostatic deposition method. The electrochemical performance of the modified electrode was studied by cyclic voltammetry under the conditions of different modified layers, different supporting electrolytes and different sweep rates. Different concentrations of tyrosinase were catalyzed by the modified electrode under a suitable supporting electrolyte, and the electrochemical sensing of tyrosinase by the modified electrode was studied. The research results show that the modified electrode has good stability and reproducibility for electrochemical sensing of tyrosinase, and the response current has a good linear relationship with the amount of tyrosinase added. Taking peak III as an example, the detection limit (S/N = 3) was 2.7649 U mL^-1. It can be known from the timing ampere curve that as the concentration of tyrosinase in the reaction system continues to increase, its response current increases stepwise, providing a linear curve in the range of 3.66 U mL^-1 to 26.87 U mL^-1, and the minimum detection limit (S/N = 3) reaches 0.0021 U mL^-1. The [(PSS/PPy)(P₂Mo₁₈/PPy)₅] multilayer composite membrane modified electrode was used to detect tyrosinase in Penaeus vannamei. The spiked recovery of the sample was 96.3-100.8%, indicating that the modified electrode has high accuracy and can be used for the detection of tyrosinase in actual samples.

A comprehensive review on phenolic compounds from edible mushrooms: Occurrence, biological activity, application and future prospective

Phenolic compounds are minor metabolites usually present in mushroom species. Because of their potential advantages for human health, such as antioxidant and other biological activities, these bioactive components have been gaining more interest as functional foods, nutraceutical agents for providing better health conditions. This review aims to comprehensively discuss the recent advances in mushroom phenolic compounds, including new sources, structural characteristics, biological activities, potential uses and its industrial applications as well as the future perspectives. Phenolic acids as well as flavonoids are considered the most common phenolics occurring in mushroom species. These are responsible for its bioactivities, including antioxidant, anti-inflammatory, antitumor, antihyperglycaemic, antiosteoporotic, anti-tyrosinase and antimicrobial activities. Several edible mushroom species with good phenolic content and show higher biological activity were highlighted, in a way for its futuristic applications. Trends on mushroom research highlighting new research areas, such as nanoformulation were discussed. Furthermore, the use of phenolic compounds as nutraceutical and cosmeceutical agents as well as the future perspectives and recommendations were made.

Separation, identification, and molecular docking of tyrosinase inhibitory peptides from the hydrolysates of defatted walnut (Juglans regia L.) meal

Defatted walnut meal protein was hydrolyzed using alcalase to yield tyrosinase inhibitory peptides. After separation by ultrafiltration and Sephadex G-25, the fraction with the highest tyrosinase inhibitory activity was identified using liquid chromatography-tandem mass spectrometry and 606 peptides were obtained. Then, molecular docking was used to screen for tyrosinase inhibitory peptides and to clarify the theoretical interaction mechanism between the peptides and tyrosinase. A peptide with the sequence Phe-Pro-Tyr (FPY, MW: 425.2 Da) was identified and the synthesized peptide inhibited tyrosine monophenolase and diphenolase with IC₅₀ values of 1.11 ± 0.05 and 3.22 ± 0.09 mM, respectively. The inhibition of tyrosinase by FPY was competitive and reversible. Good stability of FPY toward digestion was observed in an in vitro gastrointestinal digestion simulation experiment. These results indicated that FPY can be used as a potential tyrosinase inhibitor in the food, medicine, and cosmetics industries.

Synthesis, antioxidant and anti-tyrosinase activity of 1,2,4-triazole hydrazones as antibrowning agents

A series of 1,2,4-triazole hydrazones (1-16) were synthesized, and their inhibitory activities and mechanisms on tyrosinase were investigated by ultraviolet spectrophotometry, fluorescence quenching, molecular docking study, etc. Most of compounds possessed potent tyrosinase inhibitory activity. Thereinto, compound 9 presented the superior activity with IC₅₀ of 0.9 μM, which was markedly lower than the standard kojic acid (IC₅₀ = 64.1 μM). Compound 9 not only interacted with copper ions in the active center of the enzyme but also bound to the enzyme-substrate complex, indicating that it was a competitive-noncompetitive mixed inhibitor. Additionally, it also displayed potent DPPH scavenging activity. Antibrowning test showed that compound 9 effectively reduced the enzymatic browning of fresh-cut potatoes. Furthermore, compound 9 exhibited low cytotoxic activity against human normal cell line with IC₅₀ of 49.9 µM. Overall, the present study suggests that these compounds may serve as lead molecules for developing novel antibrowning agents in food industry.

Effect directed synthesis of a new tyrosinase inhibitor with anti-browning activity

The inhibition of enzymatic browning is an attractive target to elevate the quality of foods. The objective of this work is to describe a novel platform for the discovery of tyrosinase inhibitors, based on (a) one-pot preparation of a library of thiosemicarbazide compounds, (b) biological evaluation using tyrosinase TLC bioautography, (c) inhibitor identification via mass spectrometry coupled to bioautography. During these proof-of-concept experiments, the approach led to the straightforward identification of a new thiosemicarbazone with improved tyrosinase inhibition properties and fresh-cut apple slices antibrowning effect when compared to kojic acid. In conclusion, the platform represents an interesting strategy for the discovery of this type of inhibitors.

Assessment of the Pharmacological Properties and Phytochemical Profile of Bruguiera gymnorhiza (L.) Lam Using in Vitro Studies, in Silico Docking, and Multivariate Analysis

Bruguiera gymnorhiza (L.) Lam. is claimed to effectively manage a number of ailments including diabetes and associated complications. Nonetheless, no attempt has been made to delineate its pharmacological propensities and phytochemical profile. This study was designed to appraise the antioxidant and enzymatic inhibitory properties relevant to the management of diabetes mellitus, obesity, and neurodegenerative and skin disorders. A combination of colorimetric assays and ultra-high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS) were applied for the phytochemical screening of leaf, root, twig, and fruit extracts (methanol and ethyl acetate). In vitro antioxidant evaluations were via radical scavenging abilities (DPPH, ABTS), reducing potential (FRAP, CUPRAC), chelating power, and total antioxidant capacity (phosphomolybdenum). Seven key metabolic enzymes (α-amylase, α-glucosidase, tyrosinase, elastase, lipase, AChE, and BChE) were targeted to determine the inhibitory effects. Multivariate and in silico docking analysis were performed on collected data. Methanolic fruit extract yielded the highest total phenolic, tannin, and triterpenoid contents (174.18 ± 4.27 mg GAE/g, 176.24 ± 3.10 mg CE/g, 63.11 ± 3.27 mg OAE/g, respectively); significantly depressed tyrosinase, elastase, and α-amylase activities (155.35 ± 0.29 mg KAE/g, 4.56 ± 0.10 mg CAE/g, 1.00 ± 0.05 mmol ACAE/g, accordingly); and harboured the most potent antioxidant capacities with DPPH, CUPRAC, FRAP (492.62 ± 5.31, 961.46 ± 11.18, 552.49 ± 8.71 mg TE/g, respectively), and phosphomolybdenum (4.17 ± 0.31 mmol TE/g) assays. Multivariate analysis suggested that the type of solvents used influenced the biological activities more compared to plant parts. Docking analysis showed that azelaic acid binds with tyrosinase by Van der Waals and conventional hydrogen bonds. We anticipate that the present study may establish baseline data on this halophyte that could open new avenues for the development of biomedicine.

The Guanidine Pseudoalkaloids 10-Methoxy-Leonurine and Leonurine Act as Competitive Inhibitors of Tyrosinase

Tyrosinase plays a key role in the production of melanin. A variety of industrial fields have shown interest in the development of tyrosinase inhibitors from plants. In this study, compounds 1–5 derived from Leonurus japonicas were evaluated to determine their ability to inhibit tyrosinase. Of these, 10-methoxy-leonurine (1) and leonurine (2) exhibited IC₅₀ values of 7.4 ± 0.4 and 12.4 ± 0.8 μM, respectively, and acted as competitive inhibitors of tyrosinase, with Ki values in the micromolar range. In silico modeling revealed a guanidine group located in the inner cavity and a benzene ring docked within the active site of these compounds. These guanidine pseudoalkaloids show potential not only as tyrosinase inhibitors but also as lead compounds in new scaffolds for the development of novel inhibitors.