The effect of oxaloacetic acid on tyrosinase activity and structure: Integration of inhibition kinetics with docking simulation

Anti-cancer mechanisms of natural isoflavones against melanoma

The incidence of skin-related neoplasms has generally increased in recent years. Melanoma arises from malignant mutations in melanocytes in the basal layer of the epidermis and is a fatal skin cancer that seriously threatens human health. Isoflavones are polyphenolic compounds widely present in legumes and have drawn scientists' attention, because they have good efficacy against a variety of cancers, including melanoma, without significant toxic side effects and resistance. In this review article, we summarize the research progress of isoflavones in melanoma, including anti-melanoma roles and mechanisms of isoflavones via inhibition of tyrosinase activity, melanogenesis, melanoma cell growth, invasion of melanoma cells, and induction of apoptosis in melanoma cells. This information is important for the prevention, clinical treatment, and prognosis and survival of melanoma.

Inhibitory effect of acarbose on tyrosinase: application of molecular dynamics integrating inhibition kinetics

Due to its clinical and cosmetic applications, investigators have paid attention to tyrosinase (TYR) inhibitor development. In this study, a TYR inhibition study with acarbose was investigated to gain insights into the regulation of the catalytic function. Biochemical assay results indicated that acarbose was turned to be an inhibitor of TYR in a reversible binding manner and probed as a distinctive mixed-type inhibitor via measurement of double-reciprocal kinetic (Ki = 18.70 ± 4.12 mM). Time-interval kinetic measurement indicated that TYR catalytic function was gradually inactivated by acarbose in a time-dependent behavior displaying with a monophase process that was evaluated by semi-logarithmic plotting. Spectrofluorimetric measurement by integrating with a hydrophobic residue detector (1-anilinonaphthalene-8-sulfonate) showed that the high dose of acarbose derived a conspicuous local structural deformation of the TYR catalytic site pocket. Computational docking simulation showed that acarbose bound to key residues such as HIS61, TYR65, ASN81, HIS244, and HIS259. Our study extends an understanding of the functional application of acarbose and proposes that acarbose is an alternative candidate drug for a whitening agent via direct retardation of TYR catalytic function and it would be applicable for the relevant skin hyperpigmentation disorders concerning the dermatologic clinical purpose.Communicated by Ramaswamy H. Sarma.

Interactions studies of CYP2D6 with quercetin and hyperoside by spectral analysis and molecular dynamics simulations

Some ingredients from herbal medicine can significantly affect the activity of CYP2D6, thus leading to serious interactions between herbs and drugs. Quercetin and hyperoside are active ingredients widely found in vegetables, fruits, and herbal medicines. Quercetin and hyperoside have many biological activities. In this work, the characteristic bindings of CYP2D6 with quercetin/hyperoside are revealed by multi-spectroscopy analysis, molecular docking, and molecular dynamics simulations. The fluorescence of CYP2D6 is statically quenched by quercetin and hyperoside. The binding constant (Ka ) values of CYP2D6-quercetin/hyperoside range from 104  L mol-1 , which indicates that these two flavonoids bind moderately to CYP2D6. Meanwhile, quercetin has a stronger quenching ability to CYP2D6 than that of hyperoside. The secondary structure of CYP2D6 is obviously changed by binding with quercetin/hyperoside. The docking results reveal that the quercetin/hyperoside enters the active site of CYP2D6 near heme and binds to CYP2D6 by hydrogen bonds and van der Waals forces. The molecular dynamics simulation results indicate that the binding of quercetin/hyperoside can stabilize the two complexes, enhance the flexibility of CYP2D6 backbone atoms, and make a more unfolded and looser structure of CYP2D6.

Exploring the effect of a series of flavonoids on tyrosinase using integrated enzyme kinetics, multispectroscopic, and molecular modelling analyses

The control of food browning can be achieved by inhibiting tyrosinase (TY) activity, but current studies on the interaction of flavonoids as potent inhibitors with TY are inadequate. Herein, the effect of a library of flavonoids on TY was investigated using enzyme kinetics, multispectroscopic methods, and molecular modelling. Some flavonoids including 4, 8, 10, 17, 18, 28, 30, 33, and 34 exhibited potent TY inhibitory activity, with compound 10 demonstrating reversible inhibition in a mixed-competitive manner. Ultraviolet-visible spectral changes confirmed the formation of flavonoid-TY complexes. Fluorescence quenching analysis suggested effective intrinsic fluorescence quenching by flavonoids through static quenching with the ground-state complex formation. Synchronous fluorescence spectra showed the microenvironment change around the fluorophores induced by flavonoids. ANS-binding fluorescence assay indicated TY's surface hydrophobicity change by flavonoids and highlighted the change in secondary structure conformation, which was further confirmed by Fourier-transform infrared spectra. Molecular modelling results helped visualize the preferred binding conformation at the active site of TY, and demonstrated the important role of hydrophobic interaction and hydrogen bonding in stabilizing the flavonoid-TY complexes. These findings prove that diverse flavonoid structures distinctly impact their binding behavior on TY and contribute to understanding flavonoids' potential as TY inhibitors in controlling food browning.

Isolation, identification, and preparation of tyrosinase inhibitory peptides from Pinctada martensii meat

Recently, natural tyrosinase inhibitors have gained attention in clinical cosmetology research. In this study, the enzymatic hydrolysis of Pinctada martensii meat by protease from Bacillus licheniformis, 401 peptides with tyrosinase inhibitory were identified after isolated by ultrafiltration and Sephadex G-15 from the fraction F4. The peptide effects on the tyrosinase activity and structure were evaluated using molecular docking. Three synthetic peptides classified as W1 (WDRPKDDGGSPIK), W2 (DRGYPPVMF), and W3 (SGGGGGGGLGSGGSIRSSY), which had the lowest binding energies were selected for in vitro synthesis and biological activity investigation. The W3 peptide (5 mg/mL) had the highest tyrosinase activity, SPF, DPPH, and ABTS clearance values, and total antioxidant capacity. W3 did not affect the survival rate of mouse melanoma B16-F10 cells (1.0-5.0 mg/mL) but decreased the melanin content. Hence, W3 could be suitable for multifunctional tyrosinase inhibition and provides a novel method to use marine organisms as natural tyrosinase inhibitor sources.

An Epigenetic Role of Mitochondria in Cancer

Mitochondria are not only the main energy supplier but are also the cell metabolic center regulating multiple key metaborates that play pivotal roles in epigenetics regulation. These metabolites include acetyl-CoA, α-ketoglutarate (α-KG), S-adenosyl methionine (SAM), NAD⁺, and O-linked beta-N-acetylglucosamine (O-GlcNAc), which are the main substrates for DNA methylation and histone post-translation modifications, essential for gene transcriptional regulation and cell fate determination. Tumorigenesis is attributed to many factors, including gene mutations and tumor microenvironment. Mitochondria and epigenetics play essential roles in tumor initiation, evolution, metastasis, and recurrence. Targeting mitochondrial metabolism and epigenetics are promising therapeutic strategies for tumor treatment. In this review, we summarize the roles of mitochondria in key metabolites required for epigenetics modification and in cell fate regulation and discuss the current strategy in cancer therapies via targeting epigenetic modifiers and related enzymes in metabolic regulation. This review is an important contribution to the understanding of the current metabolic-epigenetic-tumorigenesis concept.

Novel insights into the inhibitory mechanism of (+)-catechin against trimethylamine-N-oxide demethylase

Trimethylamine-N-oxide demethylase (TMAOase) is a key enzyme for the decomposition of trimethylamine oxide into formaldehyde. The study investigated the inhibitory effects of (+)-catechin on TMAOase and involved mechanism to minimize the formaldehyde (FA) content of seafood during storage. TMAOase was purified by DEAE-52 cellulose and Sephacryl S-300 chromatography and the inhibitory mechanism of TMAOase was studied by Lineweaver-Burk plots, fluorescence spectroscopy, and circular dichroism. Specific activity of 37 ± 0.7 U/mg was obtained with 205 -fold purification and 15% yield, and molecular mass was 25 kDa. (+)-Catechin was a reversible inhibitor of TMAOase and its induced mechanism was the non-competitive inhibition type. (+)-Catechin binding to TMAOase formed a complex with the binding constant (K_sv) of 0.72 × 10³ at 298 K. The formation of complex induced the static fluorescence quenching and changes in the conformation of TMAOase, leading to a reduction in the rate of catalysis.

One-pot biofabrication and characterization of Tara gum/Riceberry phenolics-silver nanogel: A cytocompatible and green nanoplatform with multifaceted biological applications

This work proposed a one-pot green route for the development of a biocompatible Tara gum-Riceberry phenolics‑silver nanosphere hybrid nanocomposite (TG/RiPE-SNG) with manifold biological potentialities. The reaction system comprised of AgNO₃ as nanosilver precursor, Riceberry phenolic extract as the green in situ reductant, and Tara gum as stabilizing and anchoring agent. TG/RiPE-SNG was extensively characterized using UV-vis spectroscopy, FTIR, RAMAN, TEM, FESEM, EDX, DLS/zeta potential, XRD, and TGA analyses. Small, stable, spherical, well-dispersed SNP with an average particle size of 13.01 nm and λ_max of 421 nm were synthesized in situ, and uniformly distributed within the gel-like TG/RiPE composite. The prepared nanocomposite demonstrated superior antibacterial properties (MIC of 12.5 μg/mL) against S. aureus and S. epidermidis compared to the gum or extract. Additionally, TG/RiPE-SNG exhibited strong light barrier, tyrosinase inhibitory and antioxidant functionalities. TG/RiPE-SNG also exhibited high stability at different pH and was more thermally stable relative to the plain TG/RiPE composite. Furthermore, TG/RiPE-SNG showed good biocompatibility towards mouse L929 fibroblasts and rat erythrocytes. The obtained findings revealed a simple, benign, and inexpensive approach using only natural ingredients for the preparation of gum-based biopolymer-nanosilver hybrid nanocomposite and underscored the strong attributes of TG/RiPE-SNP as a nanomaterial with desirable biomedical potentials.

Insights on the Inhibitory Power of Flavonoids on Tyrosinase Activity: A Survey from 2016 to 2021

Tyrosinase is a multifunctional copper-containing oxidase enzyme that initiates melanin synthesis in humans. Excessive accumulation of melanin pigments or the overexpression of tyrosinase may result in skin-related disorders such as aging spots, wrinkles, melasma, freckles, lentigo, ephelides, nevus, browning and melanoma. Nature expresses itself through the plants as a source of phytochemicals with diverse biological properties. Among these bioactive compounds, flavonoids represent a huge natural class with different categories such as flavones, flavonols, isoflavones, flavan-3-ols, flavanones and chalcones that display antioxidant and tyrosinase inhibitor activities with a diversity of mechanistic approaches. In this review, we explore the role of novel or known flavonoids isolated from different plant species and their participation as tyrosinase inhibitors reported in the last five years from 2016 to 2021. We also discuss the mechanistic approaches through the different studies carried out on these compounds, including in vitro, in vivo and in silico computational research. Information was obtained from Google Scholar, PubMed, and Science Direct. We hope that the updated comprehensive data presented in this review will help researchers to develop new safe, efficacious, and effective drug or skin care products for the prevention of and/or protection against skin-aging disorders.

Antioxidant and tyrosinase inhibitory activities of traditional fermented Rosa from Dali Bai communities, Northwest Yunnan, China

Traditional fermented Rosa (TFR) is a typical food and medical product among the Dali Bai people, and its popularity is growing. A few studies have looked into TFR's medicinal advantages, linked germplasm resources, traditional processing procedures, and functional food qualities. Our goal was to look into Rosa's traditional processing, examine the dominant strains in TFR, and prove how these strains affected antioxidant and tyrosinase inhibitory activities. We used a snowball selection strategy to pick 371 informants for a semi-structured interview, supplemented with direct observations and sample collection. A microbial strain was isolated and identified from a TFR sample collected in the field. We synthesized TFR in the lab using the traditional way. Both of 2, 2-diphenyl-1 picrylhydrazyl (DPPH) free radical scavenging and tyrosinase inhibitory properties of the fermented solution of Rosa 'Dianhong' have been tested in this study. Altogether 15 species belonging to the genus Rosa, which are utilized in herbal medicine and fermented foods. Rosa 'Dianhong' was the Bai community's principal species with considerable cultural value and consumption. Raw Rosa petals included 15 major flavonoids and phenols, which were identified as TFR's active components. TFR-1 was discovered to be the dominating microbial strain in TFR, increasing total phenolic and flavonoid content in the fermented solution of Rosa 'Dianhong' by 0.45 mg GAE/ml and 0.60 mg RE/ml, respectively, after 30 days. TFR-1 also exhibited promising activity in terms of DPPH free radical scavenging and tyrosinase inhibition. TFR showed potent antioxidant and free-radical scavenger properties and is beneficial in skincare and nutrition, according to the findings. TFR's medicinal and edible properties suggest that it could be used as a cosmetic or nutraceutical product.

Inhibitory mechanism of two homoisoflavonoids from Ophiopogon japonicus on tyrosinase activity: insight from spectroscopic analysis and molecular docking

The inhibition mechanism of two homoisoflavonoids from Ophiopogon japonicus including methylophiopogonanone A (MO-A) and methylophiopogonanone B (MO-B) on tyrosinase (Tyr) was studied by multiple spectroscopic techniques and molecular docking. The results showed that the two homoisoflavonoids both inhibited Tyr activity via a reversible mixed-inhibition, with a half inhibitory concentration (IC50) of (10.87 ± 0.25) × 10-5 and (18.76 ± 0.14) × 10-5 mol L-1, respectively. The fluorescence quenching and secondary structure change of Tyr caused by MO-A and B are mainly driven by hydrophobic interaction and hydrogen bonding. Molecular docking analysis indicated that phenylmalandioxin in MO-A and methoxy in MO-B could coordinate with a Cu ion in the active center of Tyr, and interacted with amino acid Glu322 to form hydrogen bonding, occupying the catalytic center to block the entry of the substrate and consequently inhibit Tyr activity. This study may provide new perspectives on the inhibition mechanism of MO-A and MO-B on Tyr and serve a scientific basis for screening effective Tyr inhibitors.

Campanula macrostachya: biological activity and identification of phenolics using a liquid chromatography electrospray ionization tandem mass spectrometry system

It is known that some Campanula species are traditionally used because of their anti-allergic, spasmolytic, antiphlogistic, antioxidant, and antiviral properties. This study was designed to evaluate the phytochemical composition, antioxidant, α-amylase, and tyrosinase inhibitory activity of ethyl acetate, methanol, and water extracts of Campanula macrostachya Waldst. & Kit. ex Willd. Chemical compositions were analyzed by spectrophotometric and chromatographic methods. Antioxidant activities of the samples were tested by using five different test systems. Enzyme inhibitory activities of the extracts were also studied. As a result of the LC-ESI-MS/MS analyses, chlorogenic acid, hesperidin, and hyperoside were found to be the major compounds of the extracts, especially the MeOH extract (6559.59, 2499.22, and 2047.66 μg/g extract, respectively). Antioxidant activity tests have proven that MeOH extract showed higher activity than others (DPPH: 4.15 mg/mL, ABTS: 2.05 mg/mL, CUPRAC: 1.80 mg/mL, FRAP: 0.83 mg/mL, phosphomolybdenum: 1.69 mg/mL). Ferrous ion chelating activity of the water extract was 1.03 mg/mL. In α-amylase and tyrosinase inhibitory assays, EtOAc (IC₅₀: 2.54 mg/mL) and MeOH (IC₅₀: 1.51 mg/mL) extracts showed higher activity than the others did. In phosphomolybdenum, CUPRAC, FRAP, and tyrosinase inhibitory assays, the activity was strongly correlated with flavonoids, chlorogenic acid, hesperidin, and hyperoside. On the other hand, phenolic compounds have been found to contribute more to radical scavenging activity. Pearson correlation analysis showed that phenolics and flavonoids were not responsible for the α-amylase inhibitory activity of EtOAc extract.

Inhibitory effects and molecular mechanism on mushroom tyrosinase by condensed tannins isolation from the fruit of Ziziphus jujuba Mill. var. spinosa (Bunge) Hu ex H. F. Chow

The structure of extracted condensed tannin (CT) from the fruit of Sour jujube (Ziziphus jujuba Mill. var. spinosa (Bunge) Hu ex H. F. Chow) and the molecular mechanisms by which CT inhibits the activity of mushroom tyrosinase were investigated. The structure of CT was characterized by high performance liquid chromatography electrospray ionization mass spectrometry, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The kinetic assays were used to detect inhibition effect, type and mechanism. UV scanning, fluorescence quenching, copper interacting, o-quinone interaction and molecular docking assays were also used to reveal the molecular mechanisms by which CT inhibit tyrosinase. The results showed the structural units of CT containing afzelechin/epiafzelechin, catechin/epicatechin, and gallocatechin/epigallocatechin. Kinetic analysis showed that CT inhibits both the monophenolase and diphenolase activities of tyrosinase and exhibits reversible, mixed type mechanism. The fruit CT interacts primarily with the copper ions and specific amino acid residue (Asn191, Thr203, Ala202, Ser206, Met201, His194, His54, Glu182 and Ile42) in the active site of tyrosinase to disturb oxidation of substrates by tyrosinase. These results suggested the sour jujube fruit is a potential natural source of tyrosinase inhibitors, and has a potential to be used in food preservation, whitening cosmetics.

Characterization of antioxidant, α-glucosidase and tyrosinase inhibitors from the rhizomes of Potentilla anserina L. and their structure-activity relationship

Five new flavonoids (1-5), along with 25 known compounds, were isolated from the rhizomes of Potentilla anserina L. and their structures were identified using spectroscopic and chemical evidence. The extract, all fractions, and all isolated compounds were evaluated for their antioxidant, α-glucosidase, and tyrosinase inhibitory activities, and their structure-activity relationship was interpreted. The biflavanols and quercetin-3-O-α-l-rhamnopyranoside-2″-gallate (14) exhibited significant antioxidant and α-glucosidase inhibition activities. In this study, anti-tyrosinase activity and its mechanism of active compounds (potenserin C (4), potenserin D (5), and quercetin-3-O-α-l-rhamnopyranoside-2″-gallate (14)) were explored by a combination of computational simulations and kinetic studies. Kinetic studies indicated that potenserin C (4) and quercetin-3-O-α-l-rhamnopyranoside-2″-gallate (14) inhibited tyrosinase in a competitive manner, whereas potenserin D (5) acted in a reversible noncompetitive manner. The molecular docking result indicated that the substitution of the glucose moiety with galloyl and the presence of 3', 4', 5'-OH in flavonoid aglycones played a crucial role for the tyrosinase inhibiting effect. Moreover, the presence of biflavanols increased the activity against tyrosinase because of strong hydrogen binding, π-alkyl binding, and electrostatic interaction. Thus, the presented experiments developed several new lead compounds that could act as antioxidants and α-glucosidase inhibitors. Furthermore, biflavanols and quercetin-3-O-α-l-rhamnopyranoside-2″-gallate played important roles in the anti-browning activity during food processing.

Inhibitory Effect of Azamacrocyclic Ligands on Polyphenol Oxidase in Model and Food Systems

Enzymatic browning is one of the main problems faced by the food industry due to the enzyme polyphenol oxidase (PPO) provoking an undesirable color change in the presence of oxygen. Here, we report the evaluation of 10 different azamacrocyclic compounds with diverse morphologies as potential inhibitors against the activity of PPO, both in model and real systems. An initial screening of 10 ligands shows that all azamacrocyclic compounds inhibit to some extent the enzymatic browning, but the molecular structure plays a crucial role on the power of inhibition. Kinetic studies of the most active ligand (L2) reveal a S-parabolic I-parabolic noncompetitive inhibition mechanism and a remarkable inhibition at micromolar concentration (IC₅₀ = 10 μM). Furthermore, L2 action has been proven on apple juice to significantly reduce the enzymatic browning.

LC-ESI-QTOF-MS for the Profiling of the Metabolites and in Vitro Enzymes Inhibition Activity of Bryophyllum pinnatum and Oxalis corniculata Collected from Ramechhap District of Nepal

The objective of this study was to profile the chemical components and biological activity analysis of crude extract of Bryophyllum pinnatum and Oxalis corniculata. Results revealed that the analyzed plant materials encompass the high amount of total phenolic and flavonoids content and have significant antioxidant activities. Furthermore, methanol extracts are the potential source of α-amylase, α-glucosidase, lipase, tyrosinase and elastase inhibitors. High resolution mass spectrometry revealed the presence of diverse metabolites such as quercetin 3-O-α-L-rhamnopyranoside, myricetin 3-rhamnoside, bersaldegenin 1,3,5-orthoacetate, bryophyllin C, syringic acid, caffeic acid, p-coumaric acid, and quercetin in B. pinnatum and isoorientin, swertisin, apigenin 7,4'-diglucoside, vitexin, 4-hydroxybenzoic acid, vanillic acid, ethyl gallate, 3,3',4'-trihydroxy-5,7-dimethoxyflavone, and diosmetin-7-O-β-D-glucopyranoside in O. corniculata. Our finding suggested that these two plant species have high medicinal importance and are potential source of inhibitors for modern pharmaceuticals, nutraceuticals and cosmetics industries.

Flavones as tyrosinase inhibitors: kinetic studies in vitro and in silico

INTRODUCTION

Tyrosinase is a multifunctional copper-containing oxidase enzyme that catalyses the first steps in the formation of melanin pigments. Identification of tyrosinase inhibitors is of value for applications in cosmetics, medicine and agriculture.

OBJECTIVE

To develop an analytical method that allows identification of drug-like natural products that can be further developed as tyrosinase inhibitors. Results of in vitro and in silico studies will be compared in order to gain a deeper insight into the mechanism of action of enzyme inhibition.

METHOD

Using an in vitro assay we tested tyrosinase inhibitor effects of five structurally related flavones, i.e. luteolin (1), eupafolin (2), genkwanin (3), nobiletin (4), and chrysosplenetin (5). The strongest inhibitors were further investigated in silico, using enzyme docking simulations.

RESULTS

All compounds tested showed modest tyrosinase inhibitory effect compared to the positive control, kojic acid. The polymethoxy flavones 4 and 5 exhibited the strongest tyrosinase inhibitory effect with the half maximal inhibitory concentration (IC₅₀ ) values of 131.92 ± 1.75 μM and 99.87 ± 2.38 μM respectively. According to kinetic analysis 2, 4 and 5 were competitive inhibitors, whereas 1 and 3 were non-competitive inhibitors of tyrosinase. Docking studies indicated that methoxy groups on 4 and 5 caused steric hindrance which prevented alternative binding modes in the tyrosinase; the methoxy groups on the B-ring of these flavones faced the catalytic site in the enzyme.

CONCLUSIONS

The docking simulations nicely complemented the in vitro kinetic studies, opening the way for the development of predictive models for use in drug design.

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.

Simultaneous Determination of Six Isoflavones from Puerariae Lobatae Radix by CPE-HPLC and Effect of Puerarin on Tyrosinase Activity

Tyrosinase inhibitors with excellent inhibitory activities and lower side effects have promising applications in the fields of medicine, agriculture, food sciences and cosmetics. In this study, a method for simultaneous separation and determination of six target compounds (puerarin, daidzin, genistein, daidzein, genistin, and formononetin) in Puerariae Lobatae Radix was established by cloud point extraction (CPE) and concentration combined with high performance liquid chromatography (HPLC). To achieve high extraction yields, an ultrasound-assisted extraction method was developed based on a salt-modified Triton X-100 system. The optimal extraction conditions are: surfactant Triton X-100 concentration 0.07 g/mL, liquid-solid ratio 80:1 (mL/g), NaCl addition amount 0.6 g, equilibrium time 40 min, equilibrium temperature 70 °C. Under the optimal conditions, the total maximum extraction yield of the six target isoflavones reached 8.92 mg/g. Using l-tyrosine and l-dopa as substrates, the effects of puerarin on the monophenolase and diphenolase activity of tyrosinase activity were investigated by the enzyme kinetics method. The results showed that puerarin inhibited monophenolase activity with an IC₅₀ of 0.537 mg/mL and activated diphenolase activity. The inhibition type of puerarin on monophenolase and the activation type of puerarin on diphenolase were analyzed by Lineweaver-Burk plots which show that puerarin showed mixed inhibition on monophenolase and mixed activation on diphenolase. Therefore, puerarin can be used as both a tyrosinase inhibitor and a tyrosinase activator.

Inhibitory mechanism of epicatechin gallate on tyrosinase: inhibitory interaction, conformational change and computational simulation

Epicatechin gallate can inhibit the activity of tyrosinase in a mixed-type manner.

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.

Tyrosinase and α-glucosidase inhibitory potential of compounds isolated from Quercus coccifera bark: In vitro and in silico perspectives

Bark of Quercus coccifera is widely used in folk medicine. We tested tyrosinase and α-glucosidase inhibitory effects of Q. coccifera bark extract and isolated compounds from it. The extract inhibited tyrosinase with an IC₅₀ value of 75.13 ± 0.44 µg/mL. Among the isolated compounds, polydatin (6) showed potent tyrosinase inhibition compared to the positive control, kojic acid, with an IC₅₀ value of 4.05 ± 0.30 µg/mL. The Q. coccifera extract also inhibited α-glucosidase significantly with an IC₅₀ value of 3.26 ± 0.08 µg/mL. (-)-8-Chlorocatechin (5) was the most potent isolate, also more potent than the positive control, acarbose, with an IC₅₀ value of 43.60 ± 0.67 µg/mL. According to the kinetic analysis, 6 was a noncompetitive and 5 was a competitive inhibitor of tyrosinase, and 5 was a noncompetitive α-glucosidase inhibitor. In the light of these findings, we performed in silico molecular docking studies for 5 and 6 with QM/MM optimizations to predict their tyrosinase inhibition mechanisms at molecular level and search for correlations with the in vitro results. We found that the ionized form of 5 (5i) showed higher affinity and more stable binding to tyrosinase catalytic site than its neutral form, while 6 bound to the predicted allosteric sites of the enzyme better than the catalytic site.

A Comparative Assessment of Biological Effects and Chemical Profile of Italian Asphodeline lutea Extracts

The present study aims to highlight the therapeutic potential of Asphodeline lutea (AL), a wild edible plant of the Mediterranean diet. Roots, aerial parts, and flowers of AL at two different phenological stages were collected from three locations in Italy. The inhibitory activities of extracts on strategic enzymes linked to human diseases were assessed. The antioxidant properties were evaluated in vitro, using six standard bioassays. The phenolic and anthraquinone profiles were also established using HPLC-PDA. Zinc, cadmium, lead, and copper contents were also determined. All the samples inhibited acetylcholinesterase (from 1.51 to 2.20 mg GALAEs/g extract), tyrosinase (from 7.50 to 25.3 mg KAEs/g extract), and α-amylase (from 0.37 to 0.51 mmol ACAEs/g extract). Aloe-emodin and physcion were present in all parts, while rhein was not detected. The phenolic profile and the heavy metals composition of specimens gathered from three different regions of Italy were different. It can be argued that samples collected near the street can contain higher concentrations of heavy metals. The experimental data confirm that the A. lutea species could be considered as a potential source of bioactive metabolites, and its consumption could play a positive and safe role in human health maintenance.