Novel synthetic kojic acid-methimazole derivatives inhibit mushroom tyrosinase and melanogenesis

Mechanism of inhibition of melanoma by fucoxanthin simulated in vitro digestion products in cell models constructed using human malignant melanoma cells (A375) and keratinocytes (HaCaT)

Recently, the increasing incidence of malignant melanoma has become a major public health concern owing to its poor prognosis and impact on quality of life. Consuming foods with potent antitumor compounds can help prevent melanoma and maintain skin health. Fucoxanthin (FX), a naturally occurring carotenoid found in brown algae, possesses antitumor properties. However, its bioavailability, safety risks, and in vivo effects and mechanisms against melanoma remain unclear. This research focused on evaluating the safety and prospective antimelanoma impact of simulated gastrointestinal digestion products (FX-ID) on HaCaT and A375 cells.The results indicate that FX-ID exerts negative effects on mitochondria in A375 cells, increases Bax expression, releases Cytochrome C, and activates cleaved caspase-3, ultimately promoting apoptosis. Additionally, FX-ID influences the mitogen-activated protein kinase (MAPK) pathway by enhancing cyclooxygenase-2 (COX-2) and nuclear factor kappa B (NF-κB) levels, consequently facilitating apoptosis and inflammation without significantly impacting HaCaT cells. These findings provide insight into inhibitory mechanism of FX-ID against melanoma, guiding the development of functional foods for prevention.

Targeting Tyrosinase in Hyperpigmentation: Current Status, Limitations and Future Promises

Hyperpigmentation is a common and distressing dermatologic condition. Since tyrosinase (TYR) plays an essential role in melanogenesis, its inhibition is considered a logical approach along with other therapeutic methods to prevent the accumulation of melanin in the skin. Thus, TYR inhibitors are a tempting target as the medicinal and cosmetic active agents of hyperpigmentation disorder. Among TYR inhibitors, hydroquinone is a traditional lightening agent that is commonly used in clinical practice. However, despite good efficacy, prolonged use of hydroquinone is associated with side effects. To overcome these shortcomings, new approaches in targeting TYR and treating hyperpigmentation are desperately requiredessentialneeded. In line with this purpose, several non-hydroquinone lightening agents have been developed and suggested as hydroquinone alternatives. In addition to traditional approaches, nanomedicine and nanotheranostic platforms have been recently proposed in the treatment of hyperpigmentation. In this review, we discuss the available strategies for the management of hyperpigmentation with a focus on TYR inhibition. In addition, alternative treatment options to hydroquinone are discussed. Finally, we present nano-based strategies to improve the therapeutic effect of drugs prescribed to patients with skin disorders.

Evaluation of whitening and antimicrobial activity of two strains of Bletilla striata WT and HL20

ETHNOPHARMACOLOGICAL RELEVANCE

Bletilla striata (Thunb.) Reixchb.f. is a perennial herb of the Orchid-aceae Bletilla and have various ethnopharmacological uses. As a traditional astringent hemostatic Chinese herbal medicine, B. striata has been widely used in the treatment of 127 different kinds of hemorrhagic diseases. Moreover, B. striata has been a beauty medicine since ancient times, with the first ancient records dating back to 2000 years ago, traditionally used to removing freckle and smooth the skin. Because of the high content of polysaccharides, which is considered the primary active substance of B. striata and having anti-aging, whitening, and anti-oxidation functions, this is also widely used in the cosmetics industry.

AIM

We screened the germplasm resources of B. striata in the early stage and the superior HL20 strain was obtained. Our research aims to analyze and compare the whitening and antimicrobial activities of different extracts (aqueous extract, ethanol extract, and aqueous extract from ethanol extract filter residue) of the selected superior varieties (HL20) and the control (WT).

MATERIALS AND METHODS

L-tyrosine and L-dopa were used as substrates to establish a tyrosinase inhibition system with arbutin as the positive control and the whitening activity was measured by the inhibition rate of TYR-M and TYR-D. Besides, an in vitro antimicrobial susceptibility test was performed to assess the antimicrobial activity of the B. striata extracts. In a nutshell, the method of punching diffusion was used to thoroughly examine the effects of three extracts from two strains on the antimicrobial activity of five types of microorganism in cosmetics microbiological testing products. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of different extracts were also assessed.

RESULTS

Results showed that the whitening and antimicrobial properties of the HL20 strain were found to be more potent than those of the WT strain. Compared with the other two extraction methods, the aqueous extract from ethanol extract filter residue of B. striata exhibited better inhibition of tyrosinase activity. The antimicrobial assay manifested that only the ethanol extract of B. striata had an inhibitory effect and had a potent antimicrobial impact on E. faecalis.

CONCLUSIONS

In summary, we evaluated the pharmacological activity of the pre-selected excellent variety (HL20) in terms of whitening and antimicrobial activity. Our results reveal that the selected strain (HL20) has certain advantages over the control (WT). These characteristics make it a candidate additive for whitening cosmetics. Our study also provides a further contribution to the product application of B. striata in cosmetics and antimicrobial agents and the selected HL20 also lays a foundation for the breeding of superior B. striata varieties.

Advances in Biomedical Functions of Natural Whitening Substances in the Treatment of Skin Pigmentation Diseases

Pigmentation diseases can lead to significant color differences between the affected part and the normal part, resulting in severe psychological and emotional distress among patients. The treatment of pigmentation diseases with good patient compliance is mainly in the form of topical drugs. However, conventional hydroquinone therapy contributes to several pathological conditions, such as erythema, dryness, and skin desquamation, and requires a longer treatment time to show significant results. To address these shortcomings, natural whitening substances represented by kojic acid and arbutin have gradually become the candidate ingredients of traditional local preparations due to their excellent biological safety. This review focuses on several natural whitening substances with potential therapeutic effects in pigmentation disease and their mechanisms, and a thorough discussion has been conducted into the solution methods for the challenges involved in the practical application of natural whitening substances.

Regulation of Tyrosinase Enzyme Activity by Glutathione Peroxidase Mimics

Hydrogen peroxide plays a crucial role in the melanogenesis process by regulating the activity of the key melanin-forming enzyme tyrosinase, responsible for the browning of fruits, vegetables, and seafood. Therefore, a molecule with dual activities, both efficient tyrosinase inhibition and strong hydrogen peroxide degrading ability, may act as a promising antibrowning agent. Herein, we report highly efficient selone-based mushroom tyrosinase inhibitors 2 and 3 with remarkable glutathione peroxidase (GPx) enzyme-like activity. The presence of benzimidazole moiety enhances the tyrosinase inhibition efficiency of selone 2 (IC₅₀ = 0.4 μM) by almost 600 times higher than imidazole-based selone 1 (IC₅₀ = 238 μM). Interestingly, the addition of another aromatic ring to the benzimidazole moiety has led to the development of an efficient lipid-soluble tyrosinase inhibitor 3 (IC₅₀ = 2.4 μM). The selenium center and the -NH group of 2 and 3 are extremely crucial to exhibit high GPx-like activity and tyrosinase inhibition potency. The hydrophobic moiety of the inhibitors (2 and 3) further assists them in tightly binding at the active site of the enzyme and facilitates the C═Se group to strongly coordinate with the copper ions. Inhibitor 2 exhibited excellent antibrowning and polyphenol oxidase inhibition properties in banana and apple juice extracts.

Structural and inhibitory effects of fulvic and humic acids against tyrosinase

Inhibition of tyrosinase activity can control fruit browning and preserve the flavor and nutritional value of food. The impacts of fulvic acid (FA) and humic acid (HA) on tyrosinase activity were investigated utilizing circular dichroism (CD) and fluorescence spectroscopy, molecular docking (MD), and molecular dynamics simulations. HA and FA demonstrated a mixed type of inhibition with K_i 2.02 and 5.2 μM, respectively. The thermodynamic parameters displayed that the hydrogen bond and hydrophobic force play a major role in the FA-tyrosinase and HA-tyrosinase interaction, respectively. Fluorescence experiments demonstrated changes in tyrosinase tertiary structures. HA could not destroy the tyrosinase secondary structure significantly, however, FA has a significant influence on the tyrosinase secondary structure. The molecular dynamics findings demonstrated the minimal fluctuations and the lowest flexibility in the complex amino acids in the HA-tyrosinase and FA-tyrosinase interaction. Altogether, HA and FA could be utilized in food industries as an accessible natural source for tyrosinase inhibition. PRACTICAL APPLICATIONS: Recently, the investigation of tyrosinase inhibitors from the biosphere for hindrance of undesired browning in the food industry has increased considerably. Mushroom tyrosinase is a suitable model for kinetic research owing to its availability as well as close conformational similarity to tyrosinase in a mammal. Natural sources and their effective compounds could have wonderful potential on tyrosinase activity and structure, thus, in this study, the interactions between tyrosinase and fulvic acid (FA) and Humic acid (HA) were investigated. Previously, it has been shown that HA and FA have antioxidant properties and they can improve the quality of food via retarding lipid oxidation. Altogether, further investigations are warranted to draw firm conclusions, HA and FA could be utilized in food industries not only as antioxidant agents but also as an accessible natural source for tyrosinase inhibition.

PEPPSI complexes as potential prodrugs: enzyme inhibition, antioxidant activity, electrochemical characterization, molecular docking analysis

In this study, enzyme inhibition and antioxidant activity analyzes of previously characterized pyridine-enhanced precatalyst preparation stabilization and initiation (PEPPSI)-type Palladium(II) complexes with benzimidazole-type ligands {dichloro[L]pyridine palladium(II), L1: 1-(2-methyl-2-propenyl)-3-[benzylbenzimidazole]-2-ylidene, L2: 1-(2-methyl-2-propenyl)-3-[4-chloro benzylbenzimidazole]-2-ylidene, L3: 1-(2-methyl-2-propenyl)-3-[3-methylbenzylbenzimidazole]-2-ylidene, L4: 1-(2-methyl-2-propenyl)-3-[3,4,5-thrimethoxybenzylbenzimidazole]-2-ylidene, L5: 1-(2-methyl-2-propenyl)-3-[3-naphthylbenzylbenzimidazole]-2-ylidene, L6: 1-(2-methyl-2-propenyl)-3-[anthracen-9-ylmethylbenzimidazole]-2-ylidene} were performed and evaluated as potential drugs for neurodegenerative disorders such as Alzheimer disease and Parkinson disease. Inhibition of tyrosinase enzyme of N-heterocyclic carbenes (NHC) complexes was determined for the first time in literature. Chelating activities of the complexes were determined and compared with EDTA. Electrochemical characterization was performed using cyclic voltammetry method. Moreover, global reactivity descriptors and electronic transitions were evaluated by DFT/TDDFT methods and molecular docking interactions with human acetylcholine esterase, human butyrylcholine esterase and oxidoreductase were studied.

An overview of hydroxypyranone and hydroxypyridinone as privileged scaffolds for novel drug discovery

Hydroxypyranone and hydroxypyridinone are important oxygen-containing or nitrogen-containing heterocyclic nucleus and attracted increasing attention in medicinal chemistry and drug discovery over the past decade. Previous literature reports revealed that hydroxypyranone and hydroxypyridinone derivatives exhibit a wide range of pharmacological activities such as antibacterial, antifungal, antiviral, anticancer, anti-inflammatory, antioxidant, anticonvulsant, and anti-diabetic activities. In this review, we systematically summarized the literature reported biological activities of hydroxypyranone and hydroxypyridinone derivatives. In particular, we focus on their biological activity, structure-activity relationship (SAR), mechanism of action, and interaction mechanisms with the target. The collected information is expected to provide rational guidance for the development of clinically useful agents from these pharmacophores.

Biochemical Properties of Tyrosinase from Aspergillus terreus and Penicillium copticola; Undecanoic Acid from Aspergillus flavus, an Endophyte of Moringa oleifera, Is a Novel Potent Tyrosinase Inhibitor

Tyrosinase is a copper-containing monooxygenase catalyzing the O-hydroxylation of tyrosine to 3,4-dihydroxyphenylalanine then to dopaquinone that is profoundly involved in melanin synthesis in eukaryotes. Overactivation of tyrosinase is correlated with hyperpigmentation that is metabolically correlated with severe pathological disorders, so, inhibition of this enzyme is the most effective approach in controlling the overproduction of melanin and its hazardous effects. Thus, searching for a powerful, selective inhibitor of human tyrosinase to limit the hyper-synthesis of melanin is a challenge. Unlike the difficulty of overexpression of human tyrosinase, using fungal tyrosinase as a model enzyme to the human one to evaluate the mechanistics of enzyme inhibition in response to various compounds is the most feasible strategy. Thus, the purification of highly catalytic-efficient fungal tyrosinase, exploring a novel inhibitor, and evaluating the mechanistics of enzyme inhibition are the main objectives of this work. Aspergillus terreus and Penicillium copticola were reported as the most potential tyrosinase producers. The biochemical properties suggest that this enzyme displays a higher structural and catalytic proximity to human tyrosinase. Upon nutritional bioprocessing by Plackett–Burman design, the yield of tyrosinase was increased by about 7.5-folds, compared to the control. The purified tyrosinase was strongly inhibited by kojic acid and A. flavus DCM extracts with IC₅₀ values of 15.1 and 12.6 µg/mL, respectively. From the spectroscopic analysis, the main anti-tyrosinase compounds of A. flavus extract was resolved, and verified as undecanoic acid. Further studies are ongoing to unravel the in vivo effect and cytotoxicity of this compound in fungi and human, that could be a novel drug to various diseases associated with hyperpigmentation by melanin.

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.

5-Methoxy-2-mercaptobenzimidazole as an efficient inhibitor on tyrosinase: Inhibitory activity and mechanism

In this study, 5-methoxy-2-mercaptobenzimidazole (5-M-2-MB) was confirmed as an efficient tyrosinase inhibitor by methods of enzyme kinetic, fluorescence quenching, ANS-binding, thermodynamics, energy transfer, and molecular docking in combination. The results proved that 5-M-2-MB significantly inhibited the tyrosinase (IC₅₀ = 60 ± 2 nM) in a reversible and competitive way with the K_i value of 80 ± 1 nM. It quenched the intrinsic fluorescence of tyrosinase through a static mechanism, and caused conformational change of the enzyme by increasing the hydrophobic region. Moreover, this compound could bind to tyrosinase and form 5-M-2-MB-tyrosinase complex by hydrogen bond and hydrophobic interaction. The interactions were generated between 5-M-2-MB and specific amino acid residues (Trp-358, Thr-308, Glu-356, and Asp-357) located on the A chain of tyrosinase. Therefore, this study would offer a theoretical foundation for developing the new tyrosinase inhibitor.

Phenolic compounds profile, neuroprotective effect and antioxidant potential of a commercial Turkish coffee

ABSTRACT Objective The purpose of this study is to determine the phenolic and flavonoid contents, and antioxidant activities and neuroprotective effects of powdered coffee sample of a commercial coffee brand originated from Sivas, Turkey. Methods Total phenolic, flavonoid and antioxidant contents, enzymatic and non-enzymatic antioxidative activities based on 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity, metal chelating potential, reducing power, superoxide dismutase and catalase activity tests and lipid peroxidation inhibition potentials of the ethanolic and aqueous extracts of the coffee sample were assayed using the commonly preferred spectrophotometric methods. Furthermore the extracts’ cholinesterase and tyrosinase inhibition potentials were evaluated. Phenolic profiles of the coffee sample were investigated using high performance liquid chromatography. Results Catechin was the most frequently detected phenolic acid. In addition, it was demonstrated that the water extract has a significant impact when compared with standard antioxidants. While the SC50 (sufficient concentration to obtain 50% of a maximum scavenging capacity) value for the scavenging activity of 2,2-diphenyl-1-picrylhydrazyl free radical was calculated as being 0.08mg/mL for water extract, the amount of chelating agents with half Fe2+ ions in the medium was found to be 0.271mg/mL. Additionally, it was shown that 0.1mg/mL concentration of both extracts prevents lipid peroxidation by 8%. Compared with standard drugs, inhibition potentials of cholinesterase and tyrosinase enzymes were considered as moderately acceptable in these samples. Conclusion Besides the extracts’ enzymatic antioxidant activity, their inhibition potential on cholinesterase and tyrosinase enzymes – which are important clinical enzymes – reveal that this natural source can be used as a valuable resource in different fields, especially in medicine.

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.

Exploiting the 1-(4-fluorobenzyl)piperazine fragment for the development of novel tyrosinase inhibitors as anti-melanogenic agents: Design, synthesis, structural insights and biological profile

The development of Tyrosinase inhibitors (TYRIs) could represent an efficacious strategy for pharmacological intervention on skin pathologies related to aberrant production of melanin. Based on in silico studies we designed and tested a library of twenty-four compounds bearing the 4-(4-fluorobenzyl)piperazin-1-yl]-fragment. As result, we identified several compounds with excellent inhibit effects at low micromolar concentration against TYR from Agaricus bisporus (TyM). Among them, compound 25 (IC₅₀ = 0.96 μM) proved to be ∼20-fold more potent than the reference compound kojic acid (IC₅₀ = 17.76 μM) having wide applications in the cosmetics and pharmaceutical industries. The mode of interaction of active inhibitor 25 was deciphered by means of crystallography as well as molecular docking and these results were consistent with kinetic experiments. Moreover, the identified compound 25 exhibited no considerable cytotoxicity and showed anti-melanogenic effects on B16F10 melanoma cells. Therefore, a combination of computational and biochemical approaches could represent a rational guidelines for further structural modification of this class of compounds as future anti-melanogenic 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.

Antioxidation and Melanogenesis Inhibition of Various Dendrobium tosaense Extracts

This study investigated the polyphenol content, antioxidant activity, and inhibition ability of mushroom tyrosinase and melanogenesis of Dendrobium tosaense (DT) extract. Ground DT was extracted using deionized water (W) or 50% ethanol (50E) at room temperature (RT) or 50 °C (50T) for 20 min. The 50T + 50E extract exhibited the highest total phenol content 47.0 ± 4.0 mg gallic acid equivalent/g DT extract, the highest level of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) free-radical scavenging 66.0 ± 3.0 mg Trolox equivalent/g DT extract, and the highest reducing power 12.00 ± 0.50 mg vitamin C equivalent/g DT extract. The RT + W extract had the highest total flavonoid content 110.0 ± 3.0 mg quercetin equivalent/g DT extract. The RT + 50E extract had the lowest half maximal inhibitory concentration 1.30 ± 0.00 mg/mL for 2,2-diphenyl-1-picrylhydrazyl free-radical scavenging, and the lowest half maximal inhibitory concentration 6.40 ± 0.30 mg/mL for mushroom tyrosinase inhibition activity. DT extracts, especially RT + W and 50T + W, exhibited potent inhibitory effects on melanogenesis of B16/F10 cells. These results demonstrated the application potential of DT extract for skincare.

Synthesis and biological evaluation of caffeic acid derivatives as potent inhibitors of α-MSH-stimulated melanogenesis

We have disclosed our effort to develop caffeic acid derivatives as potent and non-toxic inhibitors of α-MSH-stimulated melanogenesis to treat pigmentation disorders and skin medication including a cosmetic skin-whitening agent. The SAR studies revealed that cyclohexyl ester and secondary amide derivatives of caffeic acid showed significant inhibitory activities.