Combined kinetic studies and computational analysis on kojic acid analogous as tyrosinase inhibitors

Isolation, Characterization, Genome Annotation, and Evaluation of Tyrosinase Inhibitory Activity in Secondary Metabolites of Paenibacillus sp. JNUCC32: A Comprehensive Analysis through Molecular Docking and Molecular Dynamics Simulation

A potential strain, Paenibacillus sp. JNUCC32, was isolated and subjected to whole-genome sequencing. Genome functional annotation revealed its active metabolic capabilities. This study aimed to investigate the pivotal secondary metabolites in the biological system. Fermentation and extraction were performed, resulting in the isolation of seven known compounds: tryptophol (1), 3-(4-hydroxyphenyl)propionic acid (2), ferulic acid (3), maculosin (4), brevianamide F (5), indole-3-acetic acid (6), and butyric acid (7). Tryptophol exhibited favorable pharmacokinetic properties and demonstrated certain tyrosinase inhibitory activity (IC50 = 999 μM). For further analysis of its inhibition mechanism through molecular docking and molecular dynamics (MD) simulation, tryptophol formed three hydrogen bonds and a pro-Michaelis complex with tyrosinase (binding energy = -5.3 kcal/mol). The MD simulation indicated favorable stability for the tryptophol-mushroom tyrosinase complex, primarily governed by hydrogen bond interactions. The crucial residues VAL-283 and HIS-263 in the docking were also validated. This study suggests tryptophol as a potential candidate for antibrowning agents and dermatological research.

Bacterial Tyrosinase Inhibition, Hemolytic and Thrombolytic Screening, and In Silico Modeling of Rationally Designed Tosyl Piperazine-Engrafted Dithiocarbamate Derivatives

Piperazine is a privileged moiety that is a structural part of many clinical drugs. Piperazine-based scaffolds have attracted the attention of pharmaceutical and medicinal scientists to develop novel, efficient therapeutic agents owing to their significant and promising biological profile. In the current study, an ecofriendly ultrasonic-assisted synthetic approach was applied to achieve a novel series of 1-tosyl piperazine dithiocarbamate acetamide hybrids 4a-4j, which was evaluated for in vitro tyrosinase inhibition and thrombolytic and hemolytic cytotoxic activities. Among all the piperazine-based dithiocarbamate acetamide target molecules 4a-4j, the structural analogs 4d displayed excellent tyrosinase inhibition efficacy (IC50 = 6.88 ± 0.11 µM) which was better than the reference standard drugs kojic acid (30.34 ± 0.75 µM) and ascorbic acid (11.5 ± 1.00 µM), respectively, which was further confirmed by in silico induced-fit docking (IFD) simulation Good tyrosinase activities were exhibited by 4g (IC50 = 7.24 ± 0.15 µM), 4b (IC50 = 8.01 ± 0.11 µM) and 4c (IC50 = 8.1 ± 0.30 µM) dithiocarbamate acetamides, which were also better tyrosinase inhibitors than the reference drugs but were less active than the 4d structural hybrid. All the derivatives are less toxic, having values in the 0.29 ± 0.01% to 15.6 ± 0.5% range. The scaffold 4b demonstrated better hemolytic potential (0.29 ± 0.01%), while a remarkably high thrombolytic chemotherapeutic potential was displayed by analog 4e (67.3 ± 0.2%).

Inhibitory mechanism of scutellarein on tyrosinase by kinetics, spectroscopy and molecular simulation

Tyrosinase plays an important role in melanin synthesis. Inhibition against tyrosinase activity has been extensively focused on for pharmaceutical, food, cosmetic, and agricultural purpose. The inhibitory mechanism of scutellarein on tyrosinase was elaborated by coupling enzyme kinetics, multi-spectroscopy and computational simulation. Scutellarein remarkably inhibited tyrosinase activity with an IC₅₀ value of 91 μM. Scutellarein reversibly inhibited tyrosinase in a competitive manner. Fluorescence quenching validated that interaction of scutellarein with tyrosinase occurred to form a complex with a binding constant of 6.11 × 10⁴ M^-1. Thermodynamic parameters suggested that scutellarein spontaneously bound with tyrosinase via hydrogen bond and van der Waals force. Three-dimensional fluorescence spectra and circular dichroism spectra revealed that scutellarein induced an obvious conformational change in tyrosinase. Molecular docking result predicted that scutellarein mainly bound with tyrosinase via Arg268 residue. Scutellarein effectively controlled the enzymatic browning of apple slices during storage. This research could give theoretical guiding significance in various application for tyrosinase inhibitors.

Coumarin-Based Compounds as Inhibitors of Tyrosinase/Tyrosine Hydroxylase: Synthesis, Kinetic Studies, and In Silico Approaches

Cancer represents the main cause of morbidity and mortality worldwide, constituting a serious health problem. In this context, melanoma represents the most aggressive and fatal type of skin cancer, with death rates increasing every year. Scientific efforts have been addressed to the development of inhibitors targeting the tyrosinase enzyme as potential anti-melanoma agents due to the importance of this enzyme in melanogenesis biosynthesis. Coumarin-based compounds have shown potential activity as anti-melanoma agents and tyrosinase inhibitors. In this study, coumarin-based derivatives were designed, synthesized, and experimentally evaluated upon tyrosinase. Compound FN-19, a coumarin-thiosemicarbazone analog, exhibited potent anti-tyrosinase activity, with an IC50 value of 42.16 ± 5.16 µM, being more active than ascorbic acid and kojic acid, both reference inhibitors. The kinetic study showed that FN-19 acts as a mixed inhibitor. Still, for this compound, molecular dynamics (MD) simulations were performed to determine the stability of the complex with tyrosinase, generating RMSD, RMSF, and interaction plots. Additionally, docking studies were performed to elucidate the binding pose at the tyrosinase, suggesting that the hydroxyl group of coumarin derivative performs coordinate bonds (bidentate) with the copper(II) ions at distances ranging from 2.09 to 2.61 Å. Then, MM/PBSA calculations revealed that van der Waals interactions are the most relevant intermolecular forces for complex stabilization. Furthermore, it was observed that FN-19 has a binding energy (ΔEMM) value similar to tropolone, a tyrosinase inhibitor. Therefore, the data obtained in this study will be useful for designing and developing novel coumarin-based analogs targeting the tyrosinase enzyme.

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.

Biological control of melanin biosynthesis pathway on prolific and pleochromatic induction of Lasiodiplodia theobromae

To obtain a kind of microbial pigment with high yield and variety coloration by regulating the pigment synthesis pathway in this experiment, Lasiodiplodia theobromae was used to induce pigment secretion by prolific inducing factors (tyrosinase, Cu²⁺, stilbene glycoside) and pleochromatic inducing factors (L-tyrosine, L-cysteine, tricyclazole). The results showed that through single factor and compound culture, the most reasonable inducing formula was 150 ku/L tyrosinase, while tricyclazole at 10 mg/L for 30 days had a maximum color difference of 42.92 NBS with a reddish-brown color in 10 days. The melanin content increased gradually with the extension of culture time, and the pleochromatic inducing group was up to 3.47 mg/mL, higher than that of the prolific inducing group. However, the poor solubility of purified melanin with a diameter of 100-200 nm was observed in conventional solvents. Through effective induction, it is expected that L. theobromae can secrete melanin stably and be widely used in printing, dyeing, electronics, and the chemical industry.

Computational Analysis of Triazole-Based Kojic Acid Analogs as Tyrosinase Inhibitors by Molecular Dynamics and Free Energy Calculations

Molecular docking, molecular dynamics (MD) simulations and the linear interaction energy (LIE) method were used here to predict binding modes and free energy for a set of 1,2,3-triazole-based KA analogs as potent inhibitors of Tyrosinase (TYR), a key metalloenzyme of the melanogenesis process. Initially, molecular docking calculations satisfactorily predicted the binding mode of evaluated KA analogs, where the KA part overlays the crystal conformation of the KA inhibitor into the catalytic site of TYR. The MD simulations were followed by the LIE method, which reproduced the experimental binding free energies for KA analogs with an r² equal to 0.97, suggesting the robustness of our theoretical model. Moreover, the van der Waals contributions performed by some residues such as Phe197, Pro201, Arg209, Met215 and Val218 are responsible for the binding recognition of 1,2,3-triazole-based KA analogs in TYR catalytic site. Finally, our calculations provide suitable validation of the combination of molecular docking, MD, and LIE approaches as a powerful tool in the structure-based drug design of new and potent TYR inhibitors.

Inhibition of Melanization by Kojic Acid Promotes Cell Wall Disruption of the Human Pathogenic Fungus Fonsecaea sp

Chromoblastomycosis (CBM) is a chronic human subcutaneous mycosis caused by various aetiologic agents. CBM does not have an established treatment but may be managed using antifungal agents, surgical removal of the lesions, or cryotherapy. Kojic acid (KA), a known tyrosinase inhibitor with a variety of biological actions, including fungistatic action against the fungus Cryptococcus neoformans, mediated by inhibiting melanin production, seems to be an alternative to improve the treatment of CBM. The aim of the present study was to analyze the action of KA against the pathogenic fungus Fonsecaea sp., an aetiological agent of CBM. The fungal culture was incubated with KA, and the amount of melanin was assessed, followed by cytochemical detection. Subsequently, the samples were analyzed by light microscopy, transmission and scanning electron microscopy. Culture analysis revealed that 100 g/mL KA significantly decreased the melanization of the fungus and the exocytosis of melanin into the culture supernatant. Additionally, KA induced less growth of biofilm formation and intense disruption of the cell wall, and decreased the number of melanin-containing vesicles in the culture supernatant. Finally, KA inhibited fungal filamentation in culture and the subsequent phagocytosis process. Thus, KA may be a promising substance to help in the treatment of CBM.

Discovery of Novel Tyrosinase Inhibitors From Marine Cyanobacteria

Tyrosinase, an important oxidase involved in the primary immune response in humans, can sometimes become problematic as it can catalyze undesirable oxidation reactions. Therefore, for decades there has been a strong pharmaceutical interest in the discovery of novel inhibitors of this enzyme. Recent studies have also indicated that tyrosinase inhibitors can potentially be used in the treatment of melanoma cancer. Over the years, many new tyrosinase inhibitors have been discovered from various natural sources; however, marine natural products (MNPs) have contributed only a small number of promising candidates. Therefore, in this study we focused on the discovery of new MNP tyrosinase inhibitors of marine cyanobacterial and algal origins. A colorimetric tyrosinase inhibitory assay was used to screen over 4,500 marine extracts against mushroom tyrosinase (A. bisporus). Our results revealed that scytonemin monomer (ScyM), a pure compound from our compound library and also the monomeric last-step precursor in the biosynthesis of the well-known cyanobacterial sunscreen pigment “scytonemin,” consistently showed the highest tyrosinase inhibitory score. Determination of the half maximal inhibitory concentration (IC₅₀) further indicated that ScyM is more potent than the commonly used commercial inhibitor standard “kojic acid” (KA; IC₅₀ of ScyM: 4.90 μM vs. IC₅₀ of KA: 11.31 μM). After a scaled-up chemical synthesis of ScyM as well as its O-methyl analog (ScyM-OMe), we conducted a series of follow-up studies on their structures, inhibitory properties, and mode of inhibition. Our results supported ScyM as the second case ever of a novel tyrosinase inhibitory compound based on a marine cyanobacterial natural product. The excellent in vitro performance of ScyM makes it a promising candidate for applications such as a skin-whitening agent or an adjuvant therapy for melanoma cancer treatment.

In silico ADMET, molecular docking and molecular simulation-based study of glabridin’s natural and semisynthetic derivatives as potential tyrosinase inhibitors

Hyper-pigmentation conditions may develop due to erroneous melanogenesis cascade which leads to excess melanin production. Recently, inhibition of tyrosinase is the main focus of investigation as it majorly contributes to melanin production. This inhibition property can be exploited in medicine, agriculture, and in cosmetics. Present study aims to find a natural and safe alternative molecule as tyrosinase inhibitor. In this study, human tyrosinase enzyme was modelled due to unavailability of its crystal structure to look into the degree of efficacy of glabridin and its 15 derivatives as tyrosinase inhibitor. Docking was performed by Autodock Vina at the catalytic core enzyme. Glabridin effects on melanoma cell lines was also elucidated by analysing cytotoxicity and effect on melanin production. Computational ADME analysis was done by SwissADME. Molecular dynamic simulation was also performed to further evaluate the interaction profile of these molecules and kojic acid (positive inhibitor) with respect to apo protein. Notably, four derivatives 5′-formylglabridin, glabridin dimer, 5′-prenyl glabridin and R-glabridin exhibited better binding affinity than glabridin. Glabridin effectively inhibited melanin production in a dose dependent manner. Among these, 5′-formylglabridin displayed highest binding affinity with docking score − 9.2 kcal/mol. Molecular properties and bioactivity analysis by Molinspiration web server and by SwissADME also presented these molecules as potential drug candidates. The study explores the understanding for the development of suitable tyrosinase inhibitor/s for the prevention of hyperpigmentation. However, a detailed in vivo study is required for glabridin derivatives to suggest these molecules as anti-melanogenic compound.

Theoretical Studies of Cyanophycin Dipeptides as Inhibitors of Tyrosinases

The three-dimensional structure of tyrosinase has been crystallized from many species but not from Homo sapiens. Tyrosinase is a key enzyme in melanin biosynthesis, being an important target for melanoma and skin-whitening cosmetics. Several studies employed the structure of tyrosinase from Agaricus bisporus as a model enzyme. Recently, 98% of human genome proteins were elucidated by AlphaFold. Herein, the AlphaFold structure of human tyrosinase and the previous model were compared. Moreover, tyrosinase-related proteins 1 and 2 were included, along with inhibition studies employing kojic and cinnamic acids. Peptides are widely studied for their inhibitory activity of skin-related enzymes. Cyanophycin is an amino acid polymer produced by cyanobacteria and is built of aspartic acid and arginine; arginine can be also replaced by other amino acids. A new set of cyanophycin-derived dipeptides was evaluated as potential inhibitors. Aspartate–glutamate showed the strongest interaction and was chosen as a leading compound for future studies.

Wells-Dawson phosphotungstates as mushroom tyrosinase inhibitors: a speciation study

In order to elucidate the active polyoxotungstate (POT) species that inhibit fungal polyphenol oxidase (AbPPO4) in sodium citrate buffer at pH 6.8, four Wells-Dawson phosphotungstates [α/β-P^V₂W^VI₁₈O₆₂]^6- (intact form), [α₂-P^V₂W^VI₁₇O₆₁]^10- (monolacunary), [P^V₂W^VI₁₅O₅₆]^12- (trilacunary) and [H₂P^V₂W^VI₁₂O₄₈]^12- (hexalacunary) were investigated. The speciation of the POT solutions under the dopachrome assay (50 mM Na-citrate buffer, pH 6.8; L-3,4-dihydroxyphenylalanine as a substrate) conditions were determined by ¹⁸³W-NMR, ³¹P-NMR spectroscopy and mass spectrometry. The intact Wells-Dawson POT [α/β-P^V₂W^VI₁₈O₆₂]^6- shows partial (~ 69%) disintegration into the monolacunary [α₂-P^V₂W^VI₁₇O₆₁]^10- anion with moderate activity (K_i = 9.7 mM). The monolacunary [α₂-P^V₂W^VI₁₇O₆₁]^10- retains its structural integrity and exhibits the strongest inhibition of AbPPO4 (K_i = 6.5 mM). The trilacunary POT [P^V₂W^VI₁₅O₅₆]^12- rearranges to the more stable monolacunary [α₂-P^V₂W^VI₁₇O₆₁]^10- (~ 62%) accompanied by release of free phosphates and shows the weakest inhibition (K_i = 13.6 mM). The hexalacunary anion [H₂P^V₂W^VI₁₂O₄₈]^12- undergoes time-dependent hydrolysis resulting in a mixture of [H₂P^V₂W^VI₁₂O₄₈]^12-, [P^V₈W^VI₄₈O₁₈₄]^40-, [P^V₂W^VI₁₉O₆₉(H₂O)]^14- and [α₂-P^V₂W^VI₁₇O₆₁]^10- which together leads to comparable inhibitory activity (K_i = 7.5 mM) after 48 h. For the solutions of [α/β-P^V₂W^VI₁₈O₆₂]^6-, [α₂-P^V₂W^VI₁₇O₆₁]^10- and [P^V₂W^VI₁₅O₅₆]^12- the inhibitory activity is correlated to the degree of their rearrangement to [α₂-P^V₂W^VI₁₇O₆₁]^10-. The rearrangement of hexalacunary [H₂P^V₂W^VI₁₂O₄₈]^12- into at least four POTs with a negligible amount of monolacunary anion interferes with the correlation of activity to the degree of their rearrangement to [α₂-P^V₂W^VI₁₇O₆₁]^10-. The good inhibitory effect of the Wells-Dawson [α₂-P^V₂W^VI₁₇O₆₁]^10- anion is explained by the low charge density of its protonated forms H_x[α₂-P^V₂W^VI₁₇O₆₁]^(10-x)- (x = 3 or 4) at pH 6.8.

Gonçalves Vianez JL, Santana da Costa K, de Molfetta FA, Nahum Alves C. Analysis of Kojic Acid Derivatives as Competitive Inhibitors of Tyrosinase: A Molecular Modeling Approach

Tyrosinases belong to the functional copper-containing proteins family, and their structure contains two copper atoms, in the active site, which are coordinated by three histidine residues. The biosynthesis of melanin in melanocytes has two stages depending on the actions of the natural substrates L-DOPA and L-tyrosine. The dysregulation of tyrosinase is involved in skin cancer initiation. In the present study, using molecular modeling tools, we analyzed the inhibition activity of tyrosinase activity using kojic acid (KA) derivatives designed from aromatic aldehydes and malononitrile. All derivatives showed conformational affinity to the enzyme active site, and a favorable distance to chelate the copper ion, which is essential for enzyme function. Molecular dynamics simulations revealed that the derivatives formed promising complexes, presenting stable conformations with deviations between 0.2 and 0.35 Å. In addition, the investigated KA derivatives showed favorable binding free energies. The most stable KA derivatives showed the following binding free energies: -17.65 kcal mol-1 (D6), -18.07 kcal mol-1 (D2), -18.13 (D5) kcal mol-1, and -10.31 kcal mol-1 (D4). Our results suggest that these derivatives could be potent competitive inhibitors of the natural substrates of L-DOPA (-12.84 kcal mol-1) and L-tyrosine (-9.04 kcal mol-1) in melanogenesis.

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.

Melanins as Sustainable Resources for Advanced Biotechnological Applications

Melanins are a class of biopolymers that are widespread in nature and have diverse origins, chemical compositions, and functions. Their chemical, electrical, optical, and paramagnetic properties offer opportunities for applications in materials science, particularly for medical and technical uses. This review focuses on the application of analytical techniques to study melanins in multidisciplinary contexts with a view to their use as sustainable resources for advanced biotechnological applications, and how these may facilitate the achievement of the United Nations Sustainable Development Goals.

Pellucidin A promotes antinociceptive activity by peripheral mechanisms inhibiting COX-2 and NOS: In vivo and in silico study

Peperomia pellucida (PP) belongs to the Peperomia genus, which has a pantropic distribution. PP is used to treat a wide range of symptoms and diseases, such as pain, inflammation, and hypertension. Intriguingly, PP extract is used by different tropical countries for its anti-inflammatory and antinociceptive effects. In fact, these outcomes have been shown in animal models, though the exact bioactive products of PP that exert such results are yet to be discovered. To determine and elucidate the mechanism of action of one of these compounds, we evaluated the antinociceptive effect of the novel dimeric ArC2 compound, Pellucidin A by using in vivo and in silico models. Animals were then subjected to chemical, biphasic and thermal models of pain. Pellucidin A induced an antinociceptive effect against chemical-induced pain in mice, demonstrated by the decrease of the number of writhes, reaching a reduction of 43% and 65% in animals treated with 1 and 5 mg/kg of Pellucidin A, respectively. In the biphasic response (central and peripheral), animals treated with Pellucidin A showed a significant reduction of the licking time exclusively during the second phase (inflammatory phase). In the hot-plate test, Pellucidin A did not have any impact on the latency time of the treated animals. Moreover, in vivo and in silico results show that Pellucidin A’s mechanism of action in the inflammatory pain occurs most likely through interaction with the nitric oxide (NO) pathway. Our results demonstrate that the antinociceptive activities of Pellucidin A operate under mechanism(s) of peripheral action, involving inflammatory mediators. This work provides insightful novel evidence of the biological properties of Pellucidin A, and leads to a better understanding of its mechanism of action, pointing to potential pharmacological use.

Evaluating the Performance of a Non-Bonded Cu2+ Model Including Jahn-Teller Effect into the Binding of Tyrosinase Inhibitors

Tyrosinase (TYR) is a metalloenzyme classified as a type-3 copper protein, which is involved in the synthesis of melanin through a catalytic process beginning with the conversion of the amino acid l-Tyrosine (l-Tyr) to l-3,4-dihydroxyphenylalanine (l-DOPA). It plays an important role in the mechanism of melanogenesis in various organisms including mammals, plants, and fungi. Herein, we used a combination of computational molecular modeling techniques including molecular dynamic (MD) simulations and the linear interaction energy (LIE) model to evaluate the binding free energy of a set of analogs of kojic acid (KA) in complex with TYR. For the MD simulations, we used a dummy model including the description of the Jahn–Teller effect for Cu²⁺ ions in the active site of this enzyme. Our results show that the LIE model predicts the TYR binding affinities of the inhibitor in close agreement to experimental results. Overall, we demonstrate that the classical model provides a suitable description of the main interactions between analogs of KA and Cu²⁺ ions in the active site of TYR.

Evaluation of Cytotoxic and Tyrosinase Inhibitory Activities of 2-phenoxy(thiomethyl) pyridotriazolopyrimidines: In Vitro and Molecular Docking Studies

BACKGROUND

The use of tyrosinase has confirmed to be the best means of recognizing safe, effective, and potent tyrosinase inhibitors for whitening skin. Twenty-four 2-phenoxy(thiomethyl)pyridotriazolopyrimidines were synthesized and characterized in our previous studies.

OBJECTIVE

The present work aimed to evaluate their cytotoxicity against HepG2 (hepatocellular carcinoma), A549 (pulmonary adenocarcinoma), MCF-7 (breast adenocarcinoma) and WRL 68 (embryonic liver) cell lines.

METHODS

MTT assay was employed to investigate the cytotoxicity, and a tyrosinase inhibitor screening kit was used to evaluate the Tyrosinase (TYR) inhibitory activity of the targets.

RESULTS

The tested compounds exhibited no considerable cytotoxicity, and nine of them were selected for a tyrosinase inhibitory test. Compounds 2b, 2m, and 5a showed good inhibitory percentages against TYR compared to that of kojic acid (reference substance). Molecular docking was performed to rationalize the Structure-Activity Relationship (SAR) of the target pyridotriazolopyrimidines and analyze the binding between the docked-selected compounds and the amino acid residues in the active site of tyrosinase.

CONCLUSION

The target pyridotriazolopyrimidines were identified as a new class of tyrosinase inhibitors.

A comprehensive review on tyrosinase inhibitors

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

Kinetic and computational molecular docking simulation study of novel kojic acid derivatives as anti-tyrosinase and antioxidant agents

The novel kojic acid derivatives KAD1 and KAD2 have been demonstrated that they exhibited potent anti-melanogenesis activity in our previous report. In this study, we further study the inhibitory mechanism on mushroom tyrosinase. The inhibitory types of both KADs on diphenolase were classified as mixed type based on the results of the kinetic model. The interaction between KADs and tyrosinase was illustrated by fluorescence quenching, molecular docking and copper chelate activity. The KADs were also evaluated with respect to their antioxidant activities by DPPH and ABTS⁺ assays. The results showed that KADs have more potent antioxidant activities than kojic acid. Our study could provide new ideas for the development of new anti-tyrosinase and antioxidant agents.

Synthesis, computational molecular docking analysis and effectiveness on tyrosinase inhibition of kojic acid derivatives

Tyrosinase inhibitors have become increasingly important as whitening agents and for the treatment of pigmentary disorders. In this study, the synthesis of kojic acid derivatives having 2-substituted-3-hydroxy-6-hyroxymethyl/chloromethyl/methyl/morpholinomethylpiperidinyl- methyl/pyrrolidinylmethyl-4H-pyran-4-one structure (compounds 1-30) with inhibitory effects on tyrosinase enzyme were described. One-pot Mannich reaction was carried out by using kojic acid/chlorokojic acid/allomaltol and substituted benzylpiperazine derivatives in presence of formaline. Subsequently, cyclic amine (morpholine, piperidine and pyrrolidine) derivatives of the 6th-position of chlorokojic acid were obtained with nucleophilic substitutions in basic medium. The structures of new compounds were identified by FT-IR, ¹H- and ¹³C NMR, ESI-MS and elemental analysis data. The potential mushroom tyrosinase inhibitory activity of the compounds were evaluated by the spectrophotometric method using l-DOPA as a substrate and kojic acid as the control agent. The potential inhibitory activity was also investigated in silico using molecular docking simulation method. Tyrosinase inhibitory action was significantly more efficacious for several compounds (IC₅₀: 86.2-362.1 µM) than kojic acid (IC₅₀: 418.2). Compound 3 bearing 3,4-dichlorobenzyl piperazine moiety was proven to have the highest inhibitory activity. The results of docking studies showed that according to the predicted conformation of compound 3 in the enzyme binding site, hydroxymethyl group provides a metal complex with copper ions and enzyme. Thus, this interaction explain the high inhibitory activities of the compounds 1, 3 and 4 possessing hydroxymethyl substituent supporting the mushroom assay results with docking studies. In accordance with the results, it is suggested that Mannich bases of kojic acid bearing substituted benzyl piperazine groups (compounds 1, 3, 4, 11, 13, 14, 23, 24, 28, and 29) could be promising antityrosinase agents. Additionally, considering the relationship between tyrosinase inhibitory activity results and molecular docking, a new tyrosinase inhibition mechanism can be proposed.

Keggin-type polyoxotungstates as mushroom tyrosinase inhibitors - A speciation study

Mushroom tyrosinase abPPO4 is a commercially relevant polyphenol oxidase and has been being targeted for numerous inhibition studies including polyoxometalates (POMs). In the present work, its diphenolase activity was inhibited at pH 6.8 by a series of structurally related polyoxotungstates (POTs) of the α-Keggin archetype, exhibiting the general formula [Xⁿ⁺W₁₂O₄₀]⁽⁸⁻ⁿ⁾⁻ in order to elucidate charge-dependent activity correlations. Kinetic data were obtained from the dopachrome assay and ¹⁸³W NMR was applied to obtain crucial insights into the actual Keggin POT speciation in solution, facilitating a straightforward assignment of inhibition effects to the identified POT species. While [PW₁₂O₄₀]³⁻ was completely hydrolyzed to its moderately active lacunary form H_x[PW₁₁O₃₉]^(7−x)− (K_i = 25.6 mM), [SiW₁₂O₄₀]⁴⁻ showed the most pronounced inhibition effects with a K_i of 4.7 mM despite of partial hydrolysis to its ineffective lacunary form H_x[SiW₁₁O₃₉]^(8−x)−. More negative Keggin cluster charges of 5− and 6− generally resulted in preclusion of inhibitory efficacy as well as hydrolysis, but with the Ni-substituted cluster [PW₁₁O₃₉{Ni(H₂O)}]⁵⁻ enzymatic inhibition was clearly restored (K_i = 9.7 mM). The inhibitory capacity of the structurally intact Keggin POTs was found to be inversely correlated to their net charge. The here applied speciation strategy is of utmost importance for any biological POM application to identify the actually active POM species.

Antioxidant, photoprotective and inhibitory activity of tyrosinase in extracts of Dalbergia ecastaphyllum

Dalbergia ecastaphyllum is a native Brazil plant with importance for beekeeping, and widely used in folk medicine. For the first time, the extracts of this plant were assessed for the presence of hydrophilic and lipophilic antioxidants, as well as inhibition of tyrosinase, free radicals scavenging and sunscreen protection. The antioxidant activity was evaluated by free radical scavenging (DPPH) and β-carotene bleaching assay. The tyrosinase inhibitory activity was evaluated and calculated the EC50. The photoprotective activity was measured using different concentrations of D. ecastaphyllum extracts. The Sun Protection Factor (SPF) of the samples was higher than 6, and the sample from Ilhéus showed the most pronounced photoprotective effect. Sample from Canavieiras presented the highest antioxidant activity by free radical scavenging DPPH and β-carotene bleaching method, with 92.41% and 48.34%, respectively. All samples inhibited the tyrosinase, especially the sample from Prado that was most effective (124.62 μg.mL^-1). Significant negative correlation was found between flavonoid contents and inhibition of tyrosinase. The overall results provide relevant information about the Dalbergia ecastaphyllum species, indicating as potential material to cosmetic and pharmaceutical industry.

Inhibition of tyrosinase by 4H-chromene analogs: Synthesis, kinetic studies, and computational analysis

Inhibition of mushroom tyrosinase was observed with synthetic dihydropyrano[3,2-b]chromenediones. Among them, DHPC04 displayed the most potent tyrosinase inhibitory activity with a K_i value of 4 μm, comparable to the reference standard inhibitor kojic acid. A kinetic study suggested that these synthetic heterocyclic compounds behave as competitive inhibitors for the L-DOPA binding site of the enzyme. Furthermore, molecular modeling provided important insight into the mechanism of binding interactions with the tyrosinase copper active site.

Tyrosinase inhibitory activity, molecular docking studies and antioxidant potential of chemotypes of Lippia origanoides (Verbenaceae) essential oils

The essential oils (EOs) of the aerial parts of Lippia origanoides (LiOr), collected in different localities of the Amazon region, were obtained by hydrodistillation and analyzed by GC and CG-MS. Principle component analysis (PCA) based on chemical composition grouped the oils in four chemotypes rich in mono- and sesquiterpenoids. Group I was characterized by 1,8-cineole and α-terpineol (LiOr-1 and LiOr-4) and group II by thymol (LiOr-2). The oil LiOr-3 showed β-caryophyllene, α-phellandrene and β-phellandrene as predominant and LiOr-5 was rich in (E)-nerolidol and β-caryophyllene. All samples were evaluated for antioxidant activity and inhibition of tyrosinase in vitro and in silico. The highest antioxidant activity by the DPPH free radical method was observed in LiOr-2 and LiOr-5 oils (132.1 and 82.7 mg TE∙mL^-1, respectively). The tyrosinase inhibition potential was performed using L-tyrosine and L-DOPA as substrates and all samples were more effective in the first step of oxidation. The inhibition by samples LiOr-2 and LiOr-4 were 84.7% and 62.6%, respectively. The samples LiOr-1, LiOr-4 and LiOr-5 displayed an interaction with copper (II) ion with bathochromic shift around 15 nm. In order to elucidate the mechanism of inhibition of the main compounds, a molecular docking study was carried out. All compounds displayed an interaction between an oxygen and Cu or histidine residues with distances less than 4 Å. The best docking energies were observed with thymol and (E)-nerolidol (-79.8 kcal.mol^-1), which suggested H-bonding interactions with Met281 and His263 (thymol) and His259, His263 ((E)-nerolidol).

The unravelling of the complex pattern of tyrosinase inhibition

Tyrosinases are responsible for melanin formation in all life domains. Tyrosinase inhibitors are used for the prevention of severe skin diseases, in skin-whitening creams and to avoid fruit browning, however continued use of many such inhibitors is considered unsafe. In this study we provide conclusive evidence of the inhibition mechanism of two well studied tyrosinase inhibitors, KA (kojic acid) and HQ (hydroquinone), which are extensively used in hyperpigmentation treatment. KA is reported in the literature with contradicting inhibition mechanisms, while HQ is described as both a tyrosinase inhibitor and a substrate. By visualization of KA and HQ in the active site of TyrBm crystals, together with molecular modeling, binding constant analysis and kinetic experiments, we have elucidated their mechanisms of inhibition, which was ambiguous for both inhibitors. We confirm that while KA acts as a mixed inhibitor, HQ can act both as a TyrBm substrate and as an inhibitor.

Estimation of Inhibitory Effect against Tyrosinase Activity through Homology Modeling and Molecular Docking

Tyrosinase is a key enzyme in melanogenesis. Generally, mushroom tyrosinase from A. bisporus had been used as a model in skin-whitening agent tests employed in the cosmetic industry. The recently obtained crystal structure of bacterial tyrosinase from B. megaterium has high similarity (33.5%) to the human enzyme and thus it was used as a template for constructing of the human model. Binding of tyrosinase to a series of its inhibitors was simulated by automated docking calculations. Docking and MD simulation results suggested that N81, N260, H263, and M280 are involved in the binding of inhibitors to mushroom tyrosinase. E195 and H208 are important residues in bacterial tyrosinase, while E230, S245, N249, H252, V262, and S265 bind to inhibitors and are important in forming pi interaction in human tyrosinase.