Inhibitors of Melanogenesis: An Updated Review

Interactions of Phenylalanine Derivatives with Human Tyrosinase: Lessons from Experimental and Theoretical tudies

The pigmentation of the skin, modulated by different actors in melanogenesis, is mainly due to the melanins (protective pigments). In humans, these pigments' precursors are synthetized by an enzyme known as tyrosinase (TyH). The regulation of the enzyme activity by specific modulators (inhibitors or activators) can offer a means to fight hypo- and hyper-pigmentations responsible for medical, psychological and societal handicaps. Herein, we report the investigation of phenylalanine derivatives as TyH modulators. Interacting with the binuclear copper active site of the enzyme, phenylalanine derivatives combine effects induced by combination with known resorcinol inhibitors and natural substrate/intermediate (amino acid part). Computational studies including docking, molecular dynamics and free energy calculations combined with biological activity assays on isolated TyH and in human melanoma MNT-1 cells, and X-ray crystallography analyses with the TyH analogue Tyrp1, provide conclusive evidence of the interactions of phenylalanine derivatives with human tyrosinase. In particular, our findings indicate that an analogue of L-DOPA, namely (S)-3-amino-tyrosine, stands out as an amino phenol derivative with inhibitory properties against TyH.

Chemical composition analysis and transcriptomics reveal the R2R3-MYB genes and phenol oxidases regulating the melanin formation in black radish

Melanins are dark-brown to black-colored biomacromolecules which have been thoroughly studied in animals and microorganisms. However, the biochemical and molecular basis of plant melanins are poorly understood. We first characterized melanin from the black radish (Raphanus sativus var. niger) 'HLB' through spectroscopic techniques. p-Coumaric acid was identified as the main precursor of radish melanin. Moreover, a joint analysis of transcriptome and coexpression network was performed for the two radish accessions with black and white cortexes, 'HLB' and '55'. A set of R2R3-type RsMYBs and enzyme-coding genes exhibited a coexpression pattern, and were strongly correlated with melanin formation in radish. Transient overexpression of two phenol oxidases RsLAC7 (laccase 7) or RsPOD22-1 (peroxidase 22-1) resulted in a deeper brown color around the infiltration sites and a significant increase in the total phenol content. Furthermore, co-injection of the transcriptional activator RsMYB48/RsMYB97 with RsLAC7 and/or RsPOD22-1, markedly increased the yield of black extracts. Spectroscopic analyses revealed that these extracts are similar to the melanin found in 'HLB'. Our findings advance the understanding of structural information and the transcriptional regulatory mechanism underlying melanin formation in radish.

Synthesis and evaluation of 3-hydroxyquinolin-2(1H)-one derivatives as inhibitors of tyrosinase

The tyrosinase (TYR) enzyme catalyses sequential reactions in the melanogenesis pathway: l-tyrosine is oxidised to yield L-3,4-dihydroxyphenylalanine (l-dopa), which in turn is converted to dopaquinone. These two reactions are the first two steps of melanin biosynthesis and are rate limiting. The accumulation or overproduction of melanin may cause skin hyperpigmentation and inhibitors of TYR are thus of interest to the cosmeceutical industry. Several TYR inhibitors are used to treat skin hyperpigmentation, however, some are ineffective and possess questionable safety profiles. This emphasises the need to develop novel TYR inhibitors with better safety and efficacy profiles. The small molecule, 3-hydroxycoumarin, has been reported to be a good potency TYR inhibitor (IC50 = 2.49 µM), and based on this, a series of eight structurally related 3-hydroxyquinolin-2(1H)-one derivatives were synthesised with the aim to discover novel TYR inhibitors. The results showed that four of the derivatives inhibited TYR from the champignon mushroom Agaricus bisporus (abTYR) with IC50 < 6.11 µM. The most potent inhibitor displayed an IC50 value of 2.52 μM. Under the same conditions, the reference inhibitors, thiamidol and kojic acid, inhibited abTYR with IC50 values of 0.130 and 26.4 μM, respectively. Based on the small molecular structures of the active 3-hydroxyquinolin-2(1H)-one inhibitors which are amenable to structure optimisation, it may be concluded that this class of compounds are good leads for the design of TYR inhibitors for cosmeceutical applications.

Considerations about the inhibition of monophenolase and diphenolase activities of tyrosinase. Characterization of the inhibitor concentration which generates 50 % of inhibition, type and inhibition constants. A review

Tyrosinase is a copper oxidase enzyme which catalyzes the first two steps in the melanogenesis pathway, L-tyrosine to L-dopa conversion and, then, to o-dopaquinone and dopachrome. Hypopigmentation and, above all, hyperpigmentation issues can be originated depending on their activity. This enzyme also promotes the browning of fruits and vegetables. Therefore, control of their activity by regulators is research topic of great relevance. In this work, we consider the use of inhibitors of monophenolase and diphenolase activities of the enzyme in order to accomplish such control. An experimental design and data analysis which allow the accurate calculation of the degree of inhibition of monophenolase activity (iM) and diphenolase activity (iD) are proposed. The IC50 values (amount of inhibitor that causes 50 % inhibition at a fixed substrate concentration) can be calculated for the two activities and from the values of IC50M (monophenolase) and IC50D(diphenolase). Additionally, the strength and type of inhibition can be deduced from these values. The data analysis from these IC50D values allows to obtain the values of [Formula: see text] or [Formula: see text] , or and [Formula: see text] from the values of IC50M. In all cases, the values of the different must satisfy their relationship with IC50M and IC50D.

Tricholoma matsutake polysaccharides suppress excessive melanogenesis via JNK-mediated pathway: Investigation in 8- methoxypsoralen induced B16-F10 melanoma cells and clinical study

Skin hyperpigmentation is a worldwide condition associated with augmented melanogenesis. However, conventional therapies often entail various adverse effects. Here, we explore the safety range and depigmentary effects of polysaccharides extract of Tricholoma matsutake (PETM) in an in vitro model and further evaluated its efficacy at the clinical level. An induced-melanogenesis model was established by treating B16-F10 melanoma cells with 8-methoxypsoralen (8-MOP). Effects of PETM on cell viability and melanin content were examined and compared to a commonly used depigmentary agent, α-arbutin. Expressions of key melanogenic factors and upstream signaling pathway were analysed by quantitative PCR and western blot. Moreover, a placebo-controlled clinical study involving Chinese females with skin hyperpigmentation was conducted to measure the efficacy of PETM on improving facial pigmented spots, melanin index, and individual typology angle (ITA°). Results demonstrated that PETM (up to 0.5 mg/mL) had little effect on the viability and motility of B16-F10 cells. Notably, it significantly suppressed the melanin content and expressions of key melanogenic factors induced by 8-MOP in B16-F10 melanoma cells. Western blotting results revealed that PETM inhibited melanogenesis by inactivating c-Jun N-terminal kinase (JNK), and this inhibitory role could be rescued by JNK agonist treatment. Clinical findings showed that PETM treatment resulted in a significant reduction of facial hyperpigmented spot, decreased melanin index, and improved ITA° value compared to the placebo-control group. In conclusion, these in vitro and clinical evidence demonstrated the safety and depigmentary efficacy of PETM, a novel polysaccharide agent. The distinct mechanism of action of PETM on melanogenic signaling pathway positions it as a promising agent for developing alternative therapies.

Artificial Intelligence-Assisted Optimization of Antipigmentation Tyrosinase Inhibitors: De Novo Molecular Generation Based on a Low Activity Lead Compound

Artificial intelligence (AI) de novo molecular generation is a highly promising strategy in the drug discovery, with deep reinforcement learning (RL) models emerging as powerful tools. This study introduces a fragment-by-fragment growth RL forward molecular generation and optimization strategy based on a low activity lead compound. This process integrates fragment growth-based reaction templates, while target docking and drug-likeness prediction were simultaneously performed. This comprehensive approach considers molecular similarity, internal diversity, synthesizability, and effectiveness, thereby enhancing the quality and efficiency of molecular generation. Finally, a series of tyrosinase inhibitors were generated and synthesized. Most compounds exhibited more improved activity than lead, with an optimal candidate compound surpassing the effects of kojic acid and demonstrating significant antipigmentation activity in a zebrafish model. Furthermore, metabolic stability studies indicated susceptibility to hepatic metabolism. The proposed AI structural optimization strategies will play a promising role in accelerating the drug discovery and improving traditional efficiency.

Anti-skin ageing activities of rice (Oryza sativa) bran soft and hard waxes in cultured skin cells

OBJECTIVE

Rice (Oryza sativa) bran waxes, the by-products of rice bran oil manufacturing, are widely used as inactive components in several preparations. Nevertheless, the function of rice bran waxes against skin ageing has never been reported. This study aimed to investigate thermal property and fatty acid profile of rice bran waxes, including rice bran soft (RBS) and hard (RBH) waxes, and the activities against skin ageing in cultured skin cells.

METHODS

Thermal property and fatty acid profile of rice bran waxes were analysed by differential scanning calorimetry and gas chromatography-mass spectrometry, respectively. The cytotoxicity assay of waxes was performed in B16F10 melanoma cells, human skin fibroblasts and co-culture cells of HaCaT cells and human skin fibroblasts. The non-cytotoxic concentrations of waxes were evaluated for their activities against skin ageing, including melanogenesis assay, antioxidant activity, collagen content analysis, matrix metalloproteinase-1 and matrix metalloproteinase-2 inhibitory assay and anti-inflammatory activity.

RESULTS

Thermal property indicated the endotherm peaks with melting temperatures at 40.89 ± 0.27°C and 69.64 ± 0.34°C for RBS and RBH, respectively. The main fatty acids in RBS were oleic (31.68 ± 0.75%) and linoleic acids (27.19 ± 0.40%), whereas those in RBH were palmitic (36.24 ± 1.08%) and stearic acids (35.21 ± 4.51%). The cytotoxicity assay in single cells and co-culture cells showed the non-cytotoxicity of RBS (0.0001-1 mg/mL) and RBH (0.0001-0.1 mg/mL). The anti-skin ageing activities of 1 mg/mL RBS and 0.1 mg/mL RBH included the melanogenesis inhibition by suppression of tyrosinase and tyrosinase-related protein-2 enzymes, the antioxidant activity by cellular protection against cell damage and cell death, the collagen stimulation, the matrix metalloproteinase-1 and matrix metalloproteinase-2 suppression and the anti-inflammation.

CONCLUSIONS

The study results suggest that RBS and RBH can potentially be applied as the functional ingredients in formulations against skin ageing as well as provide the superior benefit on skin moisturization.

Targeted intradermal delivery of alpha-arbutin-loaded dissolving polymeric microneedles visualized by three-dimensional Orbitrap secondary ion mass spectrometry (3D OrbiSIMS)

Hyperpigmentation, a prevalent dermatological condition characterized by melanin overproduction, poses treatment challenges due to the hydrophilicity of alpha-arbutin, a widely utilized tyrosinase inhibitor. This study investigates the efficacy of dissolving microneedles (DMNs) in augmenting skin permeation for alpha-arbutin delivery to the targeted epidermal site. Porcine full-thickness skin was employed in a 24-hour Franz cell study, commencing with the assessment of commercial alpha-arbutin-containing products. Solid steel microneedles (CMNs) from Dermapen® were utilized as both pre- and post-treatment modalities to evaluate the influence of different applications on alpha-arbutin delivery. Additionally, alpha-arbutin-loaded polyvinylpyrrolidone-co-vinyl acetate (PVPVA) DMNs, containing 2 % w/w alpha-arbutin, were fabricated and examined for their permeation-enhancing capabilities. HPLC analysis and 3D Orbitrap Secondary Ion Mass Spectrometry (OrbiSIMS) were employed to quantify and visualize alpha-arbutin in various Franz cell components. Results indicate that alpha-arbutin permeation to the skin was restricted (less than 1 %) without microneedle application and significantly increased by 6-fold (4-5 %) with post-treatment CMNs and DMNs, but not with pre-treatment CMNs. Notably, DMNs exhibited a more sustainable and robust capacity than post-treatment CMNs. OrbiSIMS imaging analysis revealed that DMNs visually enhance skin permeation of alpha-arbutin by delivering the compound to the basal layer of the targeted skin location. Overall, this study underscores the potential of DMNs as a promising delivery system for promoting targeted intradermal delivery of alpha-arbutin, providing a comprehensive exploration of various methodologies to identify innovative and improved microneedle approaches for alpha-arbutin permeation.

Design and synthesis of 4-amino-2',4'-dihydroxyindanone derivatives as potent inhibitors of tyrosinase and melanin biosynthesis in human melanoma cells

Melanogenesis inhibition constitutes a privileged therapeutic solution to treat skin hyperpigmentation, a major dermatological concern associated with the overproduction of melanin by human tyrosinase (hsTYR). Despite the existence of many well-known TYR (tyrosinase) inhibitors commercialized in skin formulations, their hsTYR-inhibition efficacy remains poor since most of them were investigated over mushroom tyrosinase (abTYR), a model with low homology relative to hsTYR. Considering the need for new potent hsTYR inhibitors, we designed and synthesized a series of indanones starting from 4-hydroxy compound 1a, one of the two most active derivatives reported to date against the human enzyme, together with marketed thiamidol. We observed that analogues featuring 4-amino and 4-amido-2',4'-dihydroxyindanone motifs showed two-to ten-fold increase in activity over human melanoma MNT-1 cell lysates, and a ten-fold improvement in a 4-days whole-cell experiment, compared to parent analogue 1a. Molecular docking investigation was performed for the most promising 4-amido derivatives and suggested a plausible interaction pattern with the second coordination sphere of hsTYR, notably through hydrogen bonding with Glu203, confirming their impact in the binding mode with hsTYR active site.

Synthesis and Tyrosinase Inhibitory Activity of Novel Benzimidazole/Thiazolidin-4-one Hybrid Derivatives

In this study, novel 3-(phenylamino)thiazolidin-4-one 2 a-d and 3-(phenyl)thiazolidin-4-one 3 a-g derivatives which are having benzimidazole moiety were synthesized and their tyrosinase inhibitory activity were investigated. The structures of the target compounds were elucidated using 1 H/13 C-NMR, IR and MS. The structure of 2 b was also characterized using HSQC NMR technique. Among the target compounds, 3 b-g demonstrated stronger tyrosinase inhibitory activity (IC50 values for 3 b-g ranged from 80.93 to 119.20 μM), compared to the positive control kojic acid (IC50 : 125.08 μM). With IC50 value of 80.93 μM, 5-(2-(4-(1H-benzimidazol-1-yl)phenyl)-4-oxothiazolidin-3-yl)-2-methylbenzenesulfonamide 3 g was found to be the most active derivative of the series. Molecular docking studies were conducted to elucidate the binding interactions between compounds and tyrosinase. The MTT assay studies used to determine the cytotoxicity of 3 b-g showed that 3 c, 3 d, 3 f and 3 g were not cytotoxic in the range of 0-200 μM. Considering its tyrosinase inhibitory activity and cytotoxic effect, 3 g exhibits promising potential for further research and development as a novel tyrosinase inhibitor.

Evaluation of systemic oxidative stress in patients with melasma

BACKGROUND

The significance of oxidative stress has been assessed and proven in the etiopathogenesis of many cutaneous disorders, but there are few studies that evaluated the role of only some factors involved in oxidative stress in patients with melasma.

OBJECTIVE

This study aimed to examine the role of oxidative stress in melasma and assess the relationship between systemic oxidative stress and the severity and extension of this disease.

METHODS

In this study, the serum levels of superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT), malondialdehyde (MDA), protein carbonyl (PC), selenium (Se), vitamin E (vit E), and vitamin C (vit C) of fifty patients with melasma were compared with those of fifty controls.

RESULTS

The serum level of MDA was significantly higher in the melasma group (3.08 vs. 2.35 U/mL; p < 0.05), and it was positively correlated with the severity (r = 0.4; p < 0.001) and extension (r = 0.3; p < 0.05) of the disease. Furthermore, the serum level of vit C was significantly lower in melasma patients (2.16 vs. 2.57 μg/mL; p < 0.001).

CONCLUSION

Systemic oxidative stress has a key role in the etiopathogenesis of melasma. Serum concentrations of MDA and vitamin C are indicators of this impairment.

Tyrosinase inhibitory peptides: Structure-activity relationship study on peptide chemical properties, terminal preferences and intracellular regulation of melanogenesis signaling pathways

BACKGROUND

Bioactive peptides have gained attention as potential alternatives to chemical-based skin lightening agents. Based on literature search, the reported articles focused mainly on the sources and preparation methods of tyrosinase inhibitory peptides and there is lacking information regarding the structure-activity relationship (SAR) between peptide property and tyrosinase inhibition. It was hypothesized that peptide properties such as hydrophobicity/hydrophilicity and the amino acid type and position/arrangement at the terminal positions could affect peptide mode of binding hence result in various degrees of tyrosinase inhibition.

METHODS

In this study, the sequences of 128 tyrosinase inhibitory peptides were collected from peer-reviewed articles. The hydrophobicity/hydrophilicity property and the amino acid profile of peptides at the N- and C-terminals were analyzed using bioinformatics tools. Molecular docking analysis was employed to further elucidate the roles of reactive amino acids in tyrosinase-peptide binding interactions. The peptide-regulated intracellular melanogenesis pathways were also compiled and discussed.

RESULTS

It was found that hydrophobic and/or polar neutral properties may facilitate or stabilize peptide binding with tyrosinase. Moreover, short peptides featuring a cysteine and tyrosine at the N- and C- terminal ultimate positions tend to bind to the active site of tyrosinase whereas positively charged amino acid such as arginine at the N-terminal does not favor peptide binding to tyrosinase.

CONCLUSIONS

These findings provide detailed explanation on how peptide/amino acid structures are related and what function they play in tyrosinase inhibition. It could also inspire researchers to account for tyrosinase-peptide SAR and the underlying anti-melanogenesis mechanisms in formulating peptide-based treatments or strategies against skin hyperpigmentation.

Synthesis, in silico modelling, and in vitro biological evaluation of substituted pyrazole derivatives as potential anti-skin cancer, anti-tyrosinase, and antioxidant agents

Twenty-five azole compounds (P1-P25) were synthesised using regioselective base-metal catalysed and microwave-assisted approaches, fully characterised by high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR), and infrared spectra (IR) analyses, and evaluated for anticancer, anti-tyrosinase, and anti-oxidant activities in silico and in vitro. P25 exhibited potent anticancer activity against cells of four skin cancer (SC) lines, with selectivity for melanoma (A375, SK-Mel-28) or non-melanoma (A431, SCC-12) SC cells over non-cancerous HaCaT-keratinocytes. Clonogenic, scratch-wound, and immunoblotting assay data were consistent with anti-proliferative results, expression profiling therewith implicating intrinsic and extrinsic apoptosis activation. In a mushroom tyrosinase inhibition assay, P14 was most potent among the compounds (half-maximal inhibitory concentration where 50% of cells are dead, IC50 15.9 μM), with activity greater than arbutin and kojic acid. Also, P6 exhibited noteworthy free radical-scavenging activity. Furthermore, in silico docking and absorption, distribution, metabolism, excretion, and toxicity (ADMET) simulations predicted prominent-phenotypic actives to engage diverse cancer/hyperpigmentation-related targets with relatively high affinities. Altogether, promising early-stage hits were identified - some with multiple activities - warranting further hit-to-lead optimisation chemistry with further biological evaluations, towards identifying new skin-cancer and skin-pigmentation renormalising agents.

Tripeptides conjugated with thiosemicarbazones: new inhibitors of tyrosinase for cosmeceutical use

The development of skin-care products is recently growing. Cosmetic formulas containing active ingredients with proven efficacy, namely cosmeceuticals, are based on various compounds, including peptides. Different whitening agents featuring anti-tyrosinase activity have been applied in the cosmeceutical field. Despite their availability, their applicability is often limited due to several drawbacks including toxicity, lack of stability, and other factors. In this work, we present the inhibitory effect on diphenolase activity of thiosemicarbazone (TSC)-peptide conjugates. Tripeptides FFY, FWY, and FYY were conjugated with three TSCs bearing one or two aromatic rings via amide bond formation in a solid phase. Compounds were then examined as tyrosinase and melanogenesis inhibitors in murine melanoma B16F0 cell line, followed by the cytotoxicity assays of these cells. In silico investigations explained the differences in the activity, observed among tested compounds. Mushroom tyrosinase was inhibited by TSC1-conjugates at micromolar level, with IC₅₀ lower than this for kojic acid, a widely used reference compound. Up to now, this is the first report regarding thiosemicarbazones conjugated with tripeptides, synthesised for the purpose of tyrosinase inhibition.

Dietary flavonoid myricetin 3-O-galactoside suppresses α-melanocyte stimulating hormone-induced melanogenesis in B16F10 melanoma cells by regulating PKA and ERK1/2 activation

Melanogenesis is the process where skin pigment melanin is produced through tyrosinase activity. Overproduction of melanin causes skin disorders such as freckles, spots, and hyperpigmentation. Myricetin 3-O-galactoside (M3G) is a dietary flavonoid with reported bioactivities. M3G was isolated from Limonium tetragonum and its anti-melanogenic properties were investigated in α-melanocyte stimulating hormone-stimulated B16F10 melanoma cells. The in vitro anti-melanogenic capacity of M3G was confirmed by inhibited tyrosinase and melanin production. M3G-mediated suppression of melanogenic proteins, tyrosinase, microphthalmia-associated transcription factor (MITF), and tyrosinase-related proteins (TRP)-1 and TRP-2, were confirmed by mRNA and protein levels, analyzed by RT-qPCR and Western blot, respectively. Furthermore, M3G suppressed Wnt signaling through the inhibition of PKA phosphorylation. M3G also suppressed the consequent phosphorylation of CREB and nuclear levels of MITF. Analysis of MAPK activation further revealed that M3G increased the activation of ERK1/2 while p38 and JNK activation remained unaffected. Results showed that M3G suppressed melanogenesis in B16F10 cells by decreasing tyrosinase production and therefore inhibiting melanin formation. A possible action mechanism was the suppression of CREB activation and upregulation of ERK phosphorylation which might cause the decreased nuclear levels of MITF. In conclusion, M3G was suggested to be a potential nutraceutical with anti-melanogenic properties.

Computational methods to analyze and predict the binding mode of inhibitors targeting both human and mushroom tyrosinase

Tyrosinase, a copper-containing enzyme critical in melanin biosynthesis, is a key drug target for hyperpigmentation and melanoma in humans. Testing the inhibitory effects of compounds using tyrosinase from Agaricus bisporus (AbTYR) has been a common practice to identify potential therapeutics from synthetic and natural sources. However, structural diversity among human tyrosinase (hTYR) and AbTYR presents a challenge in developing drugs that are therapeutically effective. In this study, we combined retrospective and computational analyses with experimental data to provide insights into the development of new inhibitors targeting both hTYR and AbTYR. We observed contrasting effects of Thiamidol™ and our 4-(4-hydroxyphenyl)piperazin-1-yl-derivative (6) on both enzymes; based on this finding, we aimed to investigate their binding modes in hTYR and AbTYR to identify residues that significantly improve affinity. All the information led to the discovery of compound [4-(4-hydroxyphenyl)piperazin-1-yl](2-methoxyphenyl)methanone (MehT-3, 7), which showed comparable activity on AbTYR (IC50 = 3.52 μM) and hTYR (IC50 = 5.4 μM). Based on these achievements we propose the exploitation of our computational results to provide relevant structural information for the development of newer dual-targeting molecules, which could be preliminarily tested on AbTYR as a rapid and inexpensive screening procedure before being tested on hTYR.

In Vitro and In Vivo Biological Evaluation of Indole-thiazolidine-2,4-dione Derivatives as Tyrosinase Inhibitors

Tyrosinase is an important rate-limiting enzyme in melanin biosynthesis. To find potential tyrosinase inhibitors with anti-melanogenic activity, a series of indole-thiazolidine-2,4-dione derivatives 5a~5z were synthesized by incorporating indole with thiazolidine-2,4-dione into one compound and assayed for their biological activities. All compounds displayed tyrosinase inhibitory activities and 5w had the highest anti-tyrosinase inhibitory activity with an IC50 value of 11.2 μM. Inhibition kinetics revealed 5w as a mixed-type tyrosinase inhibitor. Fluorescence quenching results indicated that 5w quenched tyrosinase fluorescence in a static process. CD spectra and 3D fluorescence spectra results suggested that the binding of 5w with tyrosinase could change the conformation and microenvironment of tyrosinase. Molecular docking also represented the binding between 5w and tyrosinase. Moreover, 5w could inhibit tyrosinase activity and melanogenesis both in B16F10 cells and the zebrafish model. Therefore, compound 5w could serve as a tyrosinase inhibitor with anti-melanogenic activity.

Natural tyrosinase enzyme inhibitors: A path from melanin to melanoma and its reported pharmacological activities

The skin containing melanin pigment acts as a protective barrier and counteracts the UVR and other environmental stressors to maintain or restore disrupted cutaneous homeostasis. The production of melanin pigment is dependent on tyrosine levels. L-tyrosine and L-dihydroxyphenylalanine (L-DOPA) can serve both as a substrates and intermediates of melanin synthetic pathway and as inducers and positive regulators of melanogenesis. The biosynthesis of melanin is stimulated upon exposure to UVR, which can also stimulate local production of hormonal factors, which can stimulate melanoma development by altering the chemical properties of eu- and pheomelanin. The process of melanogenesis can be altered by several pathways. One involves activation of POMC, with the production of POMC peptides including MSH and ACTH, which increase intracellular cAMP levels, which activates the MITF, and helps to stimulate tyrosinase (TYR) expression and activity. Defects in OCA1 to 4 affects melanogenic activity via posttranslational modifications resulting in proteasomal degradation and reducing pigmentation. Further, altering, the MITF factor, helps to regulate the expression of MRGE in melanoma, and helps to increase the TYR glycosylation in ER. CRH stimulates POMC peptides that regulate melanogenesis and also by itself can stimulate melanogenesis. The POMC, P53, ACTH, MSH, MC1R, MITF, and 6-BH4 are found to be important regulators for pigmentation. Melanogenesis can affect melanoma behaviour and inhibit immune responses. Therefore, we reviewed natural products that would alter melanin production. Our special focus was on targeting melanin synthesis and TYR enzyme activity to inhibit melanogenesis as an adjuvant therapy of melanotic melanoma. Furthermore, this review also outlines the current updated pharmacological studies targeting the TYR enzyme from natural sources and its consequential effects on melanin production.

Design, synthesis, in vitro, and in silico evaluations of kojic acid derivatives linked to amino pyridine moiety as potent tyrosinase inhibitors

In the present study, novel series of kojic acid derivatives conjugated to amino pyridine moiety were designed and synthesized to explore their inhibitory activity against tyrosinase. To this end, the structure of all derivatives was characterized by 1H NMR, 13C NMR, FT-IR, and elemental analysis. Next, all derivatives were evaluated against tyrosinase compared to the kojic acid as positive control and exhibited different inhibitory potencies. Furthermore, the antioxidant potential of all derivatives was determined. The kinetic analysis of the most active agent revealed that 3-hydroxy-6-(hydroxymethyl)-2-((3-nitrophenyl)(pyridin-2-ylamino)methyl)-4H-pyran-4-one (4h) binds to the enzyme in the uncompetitive mode of action. The docking analysis and molecular dynamic simulations showed considerable binding affinity and significant interactions with tyrosinase enzyme to target the melanogenesis pathway, proposing them as potent candidates to control hyperpigmentation in the future.

Potent Antioxidant and Anti-Tyrosinase Activity of Butein and Homobutein Probed by Molecular Kinetic and Mechanistic Studies

Butein (BU) and homobutein (HB) are bioactive polyhydroxylated chalcones widespread in dietary plants, whose antioxidant properties require mechanistic definition. They were investigated by inhibited autoxidation kinetic studies of methyl linoleate in Triton™ X-100 micelles at pH 7.4, 37 °C. Butein had kinh = (3.0 ± 0.9) × 104 M-1s-1 showing a chain-breaking mechanism with higher antioxidant activity than reference α-tocopherol (kinh = (2.2 ± 0.6) × 104 M-1s-1), particularly concerning the stoichiometry or peroxyl radical trapping n = 3.7 ± 1.1 vs. 2.0 for tocopherol. Homobutein had kinh = (2.8 ± 0.9) × 103 M-1s-1, pairing the relative BDEOH measured by radical equilibration EPR as 78.4 ± 0.2 kcal/mol for BU and estimated as 82.6 kcal/mol for HB. The inhibition of mushroom tyrosinase (mTYR) by HB and BU was also investigated. BU gives a reversible uncompetitive inhibition of monophenolase reaction with KI' = 9.95 ± 2.69 µM and mixed-type diphenolase inhibition with KI = 3.30 ± 0.75 µM and KI' = 18.75 ± 5.15 µM, while HB was nearly competitive toward both mono- and diphenolase with respective KI of 2.76 ± 0.70 µM and 2.50 ± 1.56 µM. IC50 values (monophenolase/diphenolase at 1 mM substrate) were 10.88 ± 2.19 µM/15.20 ± 1.25 µM, 14.78 ± 1.05 µM/12.36 ± 2.00 µM, and 33.14 ± 5.03 µM/18.27 ± 3.42 µM, respectively, for BU, HB, and reference kojic acid. Molecular docking studies confirmed the mechanism. Results indicate very potent antioxidant activity for BU and potent anti-tyrosinase activity for both chalcones, which is discussed in relation to bioactivity toward protection from skin disorders and food oxidative spoilage.

Mechanism of melanogenesis inhibition by Keggin-type polyoxometalates

Abnormal melanin overproduction can result in hyperpigmentation syndrome in human skin diseases and enzymatic browning of fruits and vegetables. Recently, our group found that Keggin-type polyoxometalates (POMs) can efficiently inhibit tyrosinase activity. However, it remains unclear whether Keggin-type POMs exhibit optimal effects in vivo. Additionally, the inhibitory effect and mechanism of action of POMs on cellular tyrosinase activity and melanogenesis have been rarely reported. Here we demonstrate that our screened and synthesised PMo11Zn and GaMo12 show superior inhibitory effects on melanin formation as well as inhibition of cellular tyrosinase activity compared to other Keggin-type POMs. Intriguingly, we reveal that Keggin-type POMs competitively bind to tyrosinase mainly through more interactions with Cu2+ ions and the amino acid residue is capable of forming van der Waals, cation-π and hydrogen bonds, resulting in a reversible non-covalent complex formation. Our findings provide valuable insights into the design, synthesis and screening of polyoxometalates as multifunctional metallodrugs and food preservatives against hyperpigmentation.

Expression and tissue distribution analysis of vimentin and transthyretin proteins associated with coat colors in sheep (Ovis aries)

OBJECTIVE

Pigment production and distribution are controlled through multiple proteins, resulting in different coat color phenotypes of sheep.

METHODS

The expression distribution of vimentin (VIM) and transthyretin (TTR) in white and black sheep skins was detected by liquid chromatography-electrospray ionization tandem MS (LC-ESI-MS/MS), gene ontology (GO) statistics, immunohistochemistry, Western blot, and quantitative real time polymerase chain reaction (qRT-PCR) to evaluate their role in the coat color formation of sheep.

RESULTS

LC-ESI-MS/MS results showed VIM and TTR proteins in white and black skin tissues of sheep. Meanwhile, GO functional annotation analysis suggested that VIM and TTR proteins were mainly concentrated in cellular components and biological process, respectively. Further research confirmed that VIM and TTR proteins were expressed at significantly higher levels in black sheep skins than in white sheep skins by Western blot, respectively. Immunohistochemistry notably detected VIM and TTR in hair follicle, dermal papilla, and outer root sheath of white and black sheep skins. qRT-PCR results also revealed that the expression of VIM and TTR mRNAs was higher in black sheep skins than in white sheep skins.

CONCLUSION

The expression of VIM and TTR were higher in black sheep skins than in white sheep skins and the transcription and translation were unanimous in this study. VIM and TTR proteins were expressed in hair follicles of white and black sheep skins. These results suggested that VIM and TTR were involved in the coat color formation of sheep.

UVB promotes melanogenesis by regulating METTL3

Ultraviolet (UV) radiation is the primary exogenous inducer of skin pigmentation, although the mechanism has not been fully elucidated. N6-methyladenosine (m6 A) modification is one of the key epigenetic form of gene regulation that affects multiple biological processes. The aim of this study was to explore the role and underlying mechanisms of m6 A modification in UVB-induced melanogenesis. Low-dose UVB increased global m6 A modification in melanocytes (MCs) and MNT1 melanoma cell line. The GEPIA database predicted that methyltransferase METTL3 is positively correlated with the melanogenic transcription factor MITF in the sun-exposed skin tissues. After METTL3 respectively overexpressed and knocked down in the MNT1, the melanin content and melanogenesis-related genes were significantly upregulated after overexpression of METTL3, especially with UVB irradiation, and downregulated after METTL3 knockdown. METTL3 levels were also higher in melanocytic nevi with high melanin content. METTL3 overexpression and knockdown also altered the protein level of YAP1. SRAMP analysis predicted four high-potential m6 A modification sites on YAP1 mRNA, of which three were confirmed by methylated RNA immunoprecipitation. Inhibition of YAP1 expression can partially reverse melanogenesis induced by overexpression of METTL3. In conclusion, UVB irradiation promotes global m6 A modification in MCs and upregulates METTL3, which increases the expression level of YAP1 through m6 A modification, thereby activating the co-transcription factor TEAD1 and promoting melanogenesis.

Synthesis and evaluation of the antioxidant and anti-tyrosinase activities of thiazolyl hydrazone derivatives and their application in the anti-browning of fresh-cut potato

Tyrosinase is a key enzyme in the biosynthesis of melanin, which is responsible for the browning of foods as well as many skin disorders. In order to develop new anti-browning agents with dual antioxidant and anti-tyrosinase capacities, a series of 30 thiazolyl hydrazone derivatives were synthesized. Among the molecules prepared, 6 and 30 were found to be the most potent tyrosinase inhibitors with IC₅₀ values ​​comparable to that of kojic acid. Interestingly, 6 also has the highest radical scavenging activity among the prepared molecules. The inhibition kinetics study indicated that 6 is a non-competitive inhibitor while 30 inhibits tyrosinase competitively. The anti-browning assay of fresh-cut potato slices revealed that 6 and 30 are potent anti-browning agents with a capacity as high as kojic acid. The mechanisms of free radical scavenging and tyrosinase inhibition have been fully investigated in silico using computational kinetics, molecular docking, and molecular dynamics simulations.

Sensitive Quantitative In Vivo Assay for Evaluating the Effects of Biomolecules on Hair Growth and Coloring Using Direct Microinjections into Mouse Whisker Follicles

Many people suffer from hair loss and abnormal skin pigmentation, highlighting the need for simple assays to support drug discovery research. Current assays have various limitations, such as being in vitro only, not sensitive enough, or unquantifiable. We took advantage of the bilateral symmetry and large size of mouse whisker follicles to develop a novel in vivo assay called "whisker follicle microinjection assay". In this assay, we plucked mouse whiskers and then injected molecules directly into one side of the whisker follicles using microneedles that were a similar size to the whiskers, and we injected solvent on the other side as a control. Once the whiskers grew out again, we quantitatively measured their length and color intensity to evaluate the effects of the molecules on hair growth and coloring. Several chemicals and proteins were used to test this assay. The chemicals minoxidil and ruxolitinib, as well as the protein RSPO1, promoted hair growth. The effect of the clinical drug minoxidil could be detected at a concentration as low as 0.001%. The chemical deoxyarbutin inhibited melanin production. The protein Nbl1 was identified as a novel hair-growth inhibitor. In conclusion, we successfully established a sensitive and quantitative in vivo assay to evaluate the effects of chemicals and proteins on hair growth and coloring and identified a novel regulator by using this assay. This whisker follicle microinjection assay will be useful when investigating protein functions and when developing drugs to treat hair loss and abnormal skin pigmentation.

Baicalein Inhibits α-Melanocyte-stimulating Hormone-stimulated Melanogenesis via p38 Mitogen-activated Protein Kinase Pathway in B16F10 Mouse Melanoma Cells

Excessive UVB exposure causes development of both malignant and non-malignant melanoma via the secretion of α-melanocyte-stimulating hormone (α-MSH). We investigated whether baicalein (5,6,7-trihydroxyflavone) could inhibit α-MSH-stimulated melanogenesis. Baicalein prevented UVB- and α-MSH-induced melanin production and attenuated α-MSH-stimulated tyrosinase (monophenol monooxygenase) activity, and expression of tyrosinase and tyrosine-related protein-2. In addition, baicalein prevented melanogenesis and pigmentation via the p38 mitogen-activated protein kinases signaling pathway. These findings suggest that baicalein represents a natural compound for attenuating melanogenesis.

Secondary Metabolites from the Cultures of Medicinal Mushroom Vanderbylia robiniophila and Their Tyrosinase Inhibitory Activities

Vanderbylia robiniophila (Huaier in Chinese) has been used as a traditional herbal medicine in China for over 1600 years. However, the secondary metabolites of V. robiniophila have not been systematically examined. Corresponding chemical investigation in this study led to the discovery of two new compounds, (22E, 24R)-6β, 7α-dimethoxyergosta-8(14), 22-diene-3β, 5α-diol (1) and vanderbyliolide A (8), along with eight known ones (2-7, 9-10). Their structures were determined by extensive spectroscopic analyses and electronic circular dichroism (ECD) calculations. The tyrosinase inhibitory activity of all isolated compounds was evaluated, and compound 10 showed a potential tyrosinase inhibitory effect with an IC₅₀ value of 60.47 ± 2.63 μM. Kinetic studies of the inhibition reactions suggested that 10 provides the inhibitory ability on tyrosinase in an uncompetitive way.

Plant-Derived Vesicle-Like Nanoparticles as Promising Biotherapeutic Tools: Present and Future

Extracellular vesicles (EVs) are heterogeneous, phospholipid bilayer-enclosed biological particles that regulate cell communication by molecular cargo delivery and surface signaling. EVs are secreted by almost all living cells, including plant cells. Plant-derived vesicle-like nanoparticles (PDVLNs) is a generic term referring to vesicle-like nanostructure particles isolated from plants. Their low immunogenicity and wide availability make PDVLNs safer and more economical to be developed as therapeutic agents and drug carriers. Accumulating evidence indicates the key roles of PDVLNs in regulating interkingdom crosstalk between humans and plants. PDVLNs are capable of entering the human-body systemand delivering effector molecules to cells that modulate cell-signaling pathways. PDVLNs released by or obtained from plants thus have great influenceon human health and diseases. In this review, the biogenesis, detailed preparation methods, various physical and biochemical characteristics, biosafety, and preservation of PDVLNs are introduced, along with how these characteristics pertain to their biosafety and preservability. The potential applications of PDVLNs on different plant and mammalian diseases and PDVLN research standardization are then systematically discussed.

In silico and in vitro studies of novel derivatives of tyrosol and raspberry ketone as the mushroom tyrosinase inhibitors

Tyrosinase is the key enzyme for melanin biosynthesis. Overproduction and deposition of this pigment cause different problems in various industries including agriculture and food. Finding safe tyrosinase inhibitors thus attracts great research interest. The goal of this study is evaluation of inhibitory potencies of some novel synthetic derivatives of tyrosol and raspberry ketone on diphenolase activity of mushroom tyrosinase. The ligands inhibited enzyme activity and compound 4-(2-(4-(hydroxymethyl)-2-methyl-1,3-dioxolan-2-yl)ethyl)phenol (1d) exhibited the most inhibitory potency (77% inhibition, IC₅₀ = 0.32 µmol L^-1) via the mixed inhibition mode. This compound was also safe according to the results of in vitro analyses. The enzyme-ligands interactions were theoretically and experimentally investigated using molecular docking and fluorescence quenching approaches, respectively. Modes of quenching and related parameters were also determined and molecular docking data showed that the ligands bind to important sites of the enzyme. These compounds, especially 1d, can be suggested as efficient candidates for further investigations.

Leveraging the 3-Chloro-4-fluorophenyl Motif to Identify Inhibitors of Tyrosinase from Agaricus bisporus

Tyrosinase (EC 1.14.18.1) is implicated in melanin production in various organisms. There is a growing body of evidence suggesting that the overproduction of melanin might be related to several skin pigmentation disorders as well as neurodegenerative processes in Parkinson's disease. Based on this consideration, the development of tyrosinase inhibitors represents a new challenge to identify new agents in pharmaceutical and cosmetic applications. With the goal of identifying tyrosinase inhibitors from a synthetic source, we employed a cheap and facile preliminary assay using tyrosinase from Agaricus bisporus (AbTYR). We have previously demonstrated that the 4-fluorobenzyl moiety might be effective in interactions with the catalytic site of AbTYR; moreover, the additional chlorine atom exerted beneficial effects in enhancing inhibitory activity. Therefore, we planned the synthesis of new small compounds in which we incorporated the 3-chloro-4-fluorophenyl fragment into distinct chemotypes that revealed the ability to establish profitable contact with the AbTYR catalytic site. Our results confirmed that the presence of this fragment is an important structural feature to improve the AbTYR inhibition in these new chemotypes as well. Furthermore, docking analysis supported the best activity of the selected studied compounds, possessing higher potency when compared with reference compounds.

Fungal production of kojic acid and its industrial applications

Kojic acid has gained its importance after it was known worldwide that the substance functions primarily as skin-lightening agent. Kojic acid plays a vital role in skin care products, as it enhances the ability to prevent exposure to UV radiation. It inhibits the tyrosinase formation which suppresses hyperpigmentation in human skin. Besides cosmetics, kojic acid is also greatly used in food, agriculture, and pharmaceuticals industries. Conversely, according to Global Industry Analysts, the Middle East, Asia, and in Africa especially, the demand of whitening cream is very high, and probably the market will reach to $31.2 billion by 2024 from $17.9 billion of 2017. The important kojic acid-producing strains were mainly belongs to the genus Aspergillus and Penicillium. Due to its commercial potential, it continues to attract the attention for its green synthesis, and the studies are still widely conducted to improve kojic acid production. Thus, the present review is focused on the current production processes, gene regulation, and limitation of its commercial production, probable reasons, and possible solutions. For the first time, detailed information on the metabolic pathway and the genes involved in kojic acid production, along with illustrations of genes, are highlighted in the present review. Demand and market applications of kojic acid and its regulatory approvals for its safer use are also discussed. KEY POINTS: • Kojic acid is an organic acid that is primarily produced by Aspergillus species. • It is mainly used in the field of health care and cosmetic industries. • Kojic acid and its derivatives seem to be safe molecules for human use.

Design, Synthesis, and Biological Evaluation of Novel Hybrids Containing Dihydrochalcone as Tyrosinase Inhibitors to Treat Skin Hyperpigmentation

Excessive melanin deposition may lead to a series of skin disorders. The production of melanin is carried out by melanocytes, in which the enzyme tyrosinase performs a key role. In this work, we identified a series of novel tyrosinase inhibitor hybrids with a dihydrochalcone skeleton and resorcinol structure, which can inhibit tyrosinase activity and reduce the melanin content in the skin. Compound 11c possessed the most potent activity against tyrosinase, showing IC₅₀ values at nanomolar concentration ranges, along with significant antioxidant activity and low cytotoxicity. Furthermore, in vitro permeation tests, supported by HPLC analysis and 3D OrbiSIMS imaging visualization, revealed the excellent permeation of 11c. More importantly, compound 11c reduced the melanin content on UV-induced skin pigmentation in a guinea pig model in vivo. These results suggest that compound 11c may serve as a promising potent tyrosinase inhibitor for the development of a potential therapy to treat skin hyperpigmentation.

Oxidation of baicalein by tyrosinase and by o-quinones

Baicalein (5,6,7-trihydroxyflavone) has been previously described as an inhibitor of tyrosinase (Guo et al. Int. J. Biol. Macromol. 118 (2018) 57-68). However, long before this article was published this flavonoid had been shown to be a substrate of this enzyme and a catecholic cofactor partially abolishing the lag-phase during oxidation of l-tyrosine. Other compounds with a 1,2,3-triphenol moiety, such as pyrogallol, gallic acid and its esters are also oxidized by tyrosinase. Gallic acid was also shown to reduce tyrosinase-generated o-quinones. We have demonstrated that baicalein is also rapidly oxidized by o-quinones generated from catechols by tyrosinase or by treatment with sodium periodate. Smaller changes of absorbance at 475 nm during oxidation of l-dopa by tyrosinase in the presence of baicalein do not result from enzyme inhibition but from reduction of dopaquinone by baicalein. This reaction prevents formation of dopachrome giving an effect of inhibition, which is only apparent. The actual reaction rates did not decrease but increased in the presence of baicalein, which we demonstrated by measurements of oxygen consumption.

Exploiting HOPNO-dicopper center interaction to development of inhibitors for human tyrosinase

In human, Tyrosinase enzyme (TyH) is involved in the key steps of protective pigments biosynthesis (in skin, eyes and hair). The use of molecules targeting its binuclear copper active site represents a relevant strategy to regulate TyH activities. In this work, we targeted 2-Hydroxypyridine-N-oxide analogs (HOPNO, an established chelating group for the tyrosinase dicopper active site) with the aim to combine effects induced by combination with a reference inhibitor (kojic acid) or natural substrate (tyrosine). The HOPNO-MeOH (3) and the racemic amino acid HOPNO-AA compounds (11) were tested on purified tyrosinases from different sources (fungal, bacterial and human) for comparison purposes. Both compounds have more potent inhibitory activities than the parent HOPNO moiety and display strictly competitive inhibition constant, in particular with human tyrosinase. Furthermore, 11 appears to be the most active on the B16-F1 mammal melanoma cells. The investigations were completed by stereospecificity analysis. Racemic mixture of the fully protected amino acid 10 was separated by chiral HPLC into the corresponding enantiomers. Assignment of the absolute configuration of the deprotected compounds was completed, based on X-ray crystallography. The inhibition activities on melanin production were tested on lysates and whole human melanoma MNT-1 cells. Results showed significant enhancement of the inhibitory effects for the (S) enantiomer compared to the (R) enantiomer. Computational studies led to an explanation of this difference of activity based for both enantiomers on the respective position of the amino acid group versus the HOPNO plane.

Thioquinoline derivatives conjugated to thiosemicarbazide as potent tyrosinase inhibitors with anti-melanogenesis properties

In the present study, a series of aryl-substituted thioqunoline conjugated to thiosemicarbazide were rationally designed and synthesized. The formation of target compounds was confirmed by spectral characterization techniques such as IR, ¹H-NMR, ¹³C-NMR, ESI-MS, and elemental analysis. Among the synthesized derivatives, compound 10g bearing para-chlorophenyl moiety was proved to be the most potent tyrosinase inhibitor with an IC₅₀ value of 25.75 ± 0.19 µM. Compound 10g as the most potent derivative exhibited a noncompetitive inhibition pattern against tyrosinase in the kinetic study. Furthermore, the in silico cavity detection, as well as the molecular docking assessments, were performed to follow the behavior of 10g within the proposed binding site. Besides, the toxicity of 10g and its potency to reduce the melanin content on A375 cell lines were also measured. Consequently, aryl-substituted thioqunolines conjugated to thiosemicarbazide might be a promising candidate in the cosmetics, medicine, and food industry as tyrosinase inhibitors.

A Comprehensive Review of Mammalian Pigmentation: Paving the Way for Innovative Hair Colour-Changing Cosmetics

The natural colour of hair shafts is formed at the bulb of hair follicles, and it is coupled to the hair growth cycle. Three critical processes must happen for efficient pigmentation: (1) melanosome biogenesis in neural crest-derived melanocytes, (2) the biochemical synthesis of melanins (melanogenesis) inside melanosomes, and (3) the transfer of melanin granules to surrounding pre-cortical keratinocytes for their incorporation into nascent hair fibres. All these steps are under complex genetic control. The array of natural hair colour shades are ascribed to polymorphisms in several pigmentary genes. A myriad of factors acting via autocrine, paracrine, and endocrine mechanisms also contributes for hair colour diversity. Given the enormous social and cosmetic importance attributed to hair colour, hair dyeing is today a common practice. Nonetheless, the adverse effects of the long-term usage of such cosmetic procedures demand the development of new methods for colour change. In this context, case reports of hair lightening, darkening and repigmentation as a side-effect of the therapeutic usage of many drugs substantiate the possibility to tune hair colour by interfering with the biology of follicular pigmentary units. By scrutinizing mammalian pigmentation, this review pinpoints key targetable processes for the development of innovative cosmetics that can safely change the hair colour from the inside out.

Synthesis and discovery of potential tyrosinase inhibitor of new coumarin-based thiophenyl-pyrazolylthiazole nuclei: In vitro evaluation, cytotoxicity, kinetic, and computational studies

A well-known key enzyme in melanogenesis and hyperpigmentation is tyrosinase. The present study introduces a novel series of thiophenyl-pyrazolylthiazole-coumarin hybrids (6a-6h) as tyrosinase inhibitors. The in-vitro tyrosinase inhibition results indicated that all compounds have strong tyrosinase inhibitory activity, particularly compound 6g (IC₅₀  = 0.043 ± 0.006 μM), was identified as the most active compound compared to the positive control (kojic acid, IC₅₀  = 18.521 ± 1.162 μM). Lineweaver-Burk plots were employed to analyze the kinetic mechanism, and compound 6g formed an enzyme-inhibitor complex by inhibiting tyrosinase non-competitively. Furthermore, all compounds demonstrated excellent antioxidant activity against DPPH. MTT assay was used to screen the cytotoxicity of all compounds on B16F10 melanoma cells, and they had no toxic effect on the cells. The binding affinity of compounds with tyrosinase was also investigated using molecular docking, and the ligands displayed good binding energy values. These molecules could be a promising lead for skin pigmentation and associated diseases as nontoxic pharmacological scaffolds.

Depigmenting topical therapy based on a synergistic combination of compounds targeting the key pathways involved in melasma pathophysiology

Melasma has a complex pathophysiology with different cell types and signalling pathways involved. Paracrine factors secreted by keratinocytes, fibroblasts and endothelial cells act on melanocytes and stimulate melanogenesis. These paracrine factors are involved in the oxidative stress, inflammatory, vascular and hormonal pathways, among others. Damage of the dermoepidermal barrier also occurs and facilitates melanin deposition in the dermis, also known as dermal or mixed melasma. We used artificial intelligence tools to define the best combination of compounds for skin pigmentation inhibition. Mathematical models suggested the combination of retinol, diosmin and ferulic acid to be the most effective one. In vitro cellular tyrosinase activity assay proved that this combination had a synergistic depigmenting effect. Further assays proved that the combination could inhibit key pathways involved in melasma by downregulating ET-1 and COX-2 gene expression and IBMX-induced dendricity in human melanocytes, and upregulated the gene expression of IL-1b, TIMP3 and several endogenous antioxidant enzymes. The combination also reduced melanin levels in a phototype VI 3D epidermis model. These results indicate that the combination of retinol, diosmin and ferulic acid is an effective synergistic complex for the treatment of melasma by regulating the key molecular pathways involved in skin hyperpigmentation pathophysiology.

Anti-Melanogenic Potential of Natural and Synthetic Substances: Application in Zebrafish Model

Melanogenesis is a biosynthetic pathway for the formation of the pigment melanin in human skin. A key enzyme in the process of pigmentation through melanin is tyrosinase, which catalyzes the first and only limiting step in melanogenesis. Since the discovery of its methanogenic properties, tyrosinase has been the focus of research related to the anti-melanogenesis. In addition to developing more effective and commercially safe inhibitors, more studies are required to better understand the mechanisms involved in the skin depigmentation process. However, in vivo assays are necessary to develop and validate new drugs or molecules for this purpose, and to accomplish this, zebrafish has been identified as a model organism for in vivo application. In addition, such model would allow tracking and studying the depigmenting activity of many bioactive compounds, important to genetics, medicinal chemistry and even the cosmetic industry. Studies have shown the similarity between human and zebrafish genomes, encouraging their use as a model to understand the mechanism of action of a tested compound. Interestingly, zebrafish skin shares many similarities with human skin, suggesting that this model organism is suitable for studying melanogenesis inhibitors. Accordingly, several bioactive compounds reported herein for this model are compared in terms of their molecular structure and possible mode of action in zebrafish embryos. In particular, this article described the main metabolites of Trichoderma fungi, in addition to substances from natural and synthetic sources.

In Vitro, In Vivo, and In Silico Analyses of Molecular Anti-Pigmentation Mechanisms of Selected Thai Rejuvenating Remedy and Bioactive Metabolites

Thai rejuvenating remedies are mixed herbal formulas promoting longevity. Due to the complexity, the biological activities of these remedies are minimal. Therefore, in this study, the authors evaluated the anti-pigmentation effect at the molecular level of the selected Thai rejuvenating remedy to fulfill the knowledge gap. First, the authors found that the selected remedy showed promising activity against the tyrosinase enzyme with an IC₅₀ value of 9.41 µg/mL. In the comparison, kojic acid (positive control) exhibited an IC₅₀ value of 3.92 µg/mL against the same enzyme. Later, the authors identified glabridin as a bioactive molecule against tyrosinase with an IC₅₀ value of 0.08 µg/mL. However, ethyl p-methoxycinnamate was the most abundant metabolite found in the remedy. The authors also found that the selected remedy and glabridin reduced the melanin content in the cell-based assay (B16F1) but not in the zebrafish larvae experiment. Finally, the authors conducted a computational investigation through molecular docking proposing a theoretical molecular interplay between glabridin, ethyl p-methoxycinnamate, and target proteins (tyrosinase and melanocortin-1 receptor, MC1R). Hence, in this study, the authors reported the molecular anti-pigmentation mechanism of the selected Thai rejuvenating remedy for the first time by combining the results from in silico, in vitro, and in vivo experiments.

Resorcinol-based hemiindigoid derivatives as human tyrosinase inhibitors and melanogenesis suppressors in human melanoma cells

Human tyrosinase (hsTYR) catalyzes the key steps of melanogenesis, making it a privileged target for reducing melanin production in vivo. However, very few hsTYR inhibitors have been reported so far in the literature, whereas thousands of mushroom tyrosinase (abTYR) inhibitors are known. Yet, as these enzymes are actually very different, including at their active sites, there is an urgent need for new true hsTYR inhibitors in order to enable human-directed pharmacological and dermocosmetic applications without encountering the inefficiency and toxicity issues currently triggered by kojic acid or hydroquinone. Starting from the two most active compounds reported to date, i.e. a 2-hydroxypyridine-embedded aurone and thiamidol, we combined herein key structural elements and developed new nanomolar hsTYR inhibitors with cell-based activity. From a complete series of thirty-eight synthesized derivatives, excellent inhibition values were obtained for two compounds in both human melanoma cell lysates and purified hsTYR assays, and a promising improvement was observed in whole cell experiments.

Chemical Composition and Tyrosinase Inhibitory Activities of Fatty Acids Obtained from Heterotrophic Microalgae, S. limacinum and C. cohnii

Tyrosinase is the rate-limiting enzyme for melanin production in plant and mammalian cells. Upregulation of this enzyme results in hyperpigmentation disorders. In order to treat pigmentation problems, novel skin whitening compounds are extremely screened. It is found that fatty acids based on their saturation levels either increase or decrease tyrosinase enzyme activity. Thus, fatty acids and their compositions are promising candidates for the treatment of hyperpigmentation or hypopigmentation disorders. Microalgae are rich in both saturated and unsaturated fatty acids, as well. In this study, C. cohnii and S. limacinum fatty acids were evaluated as tyrosinase inhibitor candidates. Mushroom tyrosinase activity studies displayed that both extracts increase tyrosinase enzyme activity dose-dependently. On the other hand, S. limacinum at 200 µg ml^-1 concentration almost decreased half of tyrosinase enzyme activity in B16-F10 cells. Besides, it was 3 times more efficient for tyrosinase enzyme activity inhibition and 2 times more effective to decrease melanin synthesis compared to C. cohnii. Considering low toxicity to B16-F10 melanoma and healthy keratinocyte cells (HaCaT), S. limacinum fatty acids could be a suitable source for lipid-based tyrosinase inhibitory functional cosmetics products.

Application of traditional Chinese medicine as skin depigmentation agents

Traditional Chinese medicine (TCM) has been frequently used as skin lightning agents. However, the mechanism of action of their effect is unclear. The present study aims to evaluate anti-tyrosinase activity of 10 commonly used TCM on mushroom (ab), human (hs) and mouse melanoma B16F0 (mm) tyrosinase (TYR) respectively. The results showed that at 1.0 mg/mL, extracts from Rosa rugosa Thumb, Morus alba L. and Paeonia lactiflora Pall were active against both abTYR and hsTYR (>50% inhibition), extracts from Bletilla striata (Thunb.) Rchb. F., Centella asiatica (L.) Urb, Cynanchum atratum L., Rosa canina L., Rhus chinensis Mill. and Glycyrrhiza urolensis Fisch. Ex DC. inhibited either abTYR or hsTYR (>50%), while extract from Tribulus terrestris L. had no/minimal activity (<10% inhibition). When treated with melanoma B16F0 cells, M. alba also significantly reduced mmTYR activity (70% at 250 μg/mL) and melanin content (50% at 250 μg/mL). These findings demonstrated inhibitory effects of 9 TCM against TYR and hence support their application as skin lightning agents. Our results also showed discrepancies in TYR activity from different sources, suggesting a testing regime of combining abTYR, hsTYR and mmTYR when developing depigmentation agents for human application.

Effect of Chicken Egg White-Derived Peptide and Hydrolysates on Abnormal Skin Pigmentation during Wound Recovery

Abnormal skin pigmentation commonly occurs during the wound healing process due to the overproduction of melanin. Chicken egg white (CEW) has long been used to improve skin health. Previous published works had found CEW proteins house bioactive peptides that inhibit tyrosinase, the key enzyme of melanogenesis. The current study aimed to evaluate the anti-pigmentation potential and mechanism of the CEW-derived peptide (GYSLGNWVCAAK) and hydrolysates (CEWH_mono and CEWH_di), using a cell-based model. All of these peptide and hydrolysates inhibited intracellular tyrosinase activity and melanin level up to 45.39 ± 1.31 and 70.01 ± 1.00%, respectively. GYSLGNWVCAAK and CEWH_di reduced intracellular cAMP levels by 13.38 ± 3.65 and 14.55 ± 2.82%, respectively; however, CEWH_mono did not affect cAMP level. Moreover, the hydrolysates downregulated the mRNA expression of melanogenesis-related genes, such as Mitf, Tyr, Trp-1 and Trp-2, but GYSLGNWVCAAK only suppressed Tyr gene expression. Downregulation of the genes may lower the catalytic activities and/or affect the structural stability of TYR, TRP-1 and TRP-2; thus, impeding melanogenesis to cause an anti-pigmentation effect in the cell. Outcomes from the current study could serve as the starting point to understand the underlying complex, multifaceted melanogenesis regulatory mechanism at the cellular level.

New Butyroside D from Argan Press Cake Possess Anti-Melanogenesis Effect via MITF Downregulation in B16F10 and HEM Cells

Hyperpigmentation is a skin condition where patches of skin become darker in color due to excess melanin production upon UV exposure leading to melasma, which are lentigines or post inflammatory hyperpigmentation that psychologically affecting a great number of people. The present study investigates the anti-melanogenic effect of Butyroside D and the underling mechanism. After the confirmation of the non-cytotoxic effect of Butyroside D on B16F10 cells, we proceeded with analyzing the impact of the treatment at low and high concentration (i.e., 0.2 μM and 2 μM) using gene profiling analysis and examined the differentiation in gene expression. Our results identify cyclic adenosine monophosphate (cAMP), Wnt/β-catenin and Mitogen-Activated Protein Kinase (MAPK) signaling pathways to be downregulated upon treatment with Butyroside D. These pathways were targeted to further validate the effect of Butyroside D on membrane receptors melanocortin 1 receptor (MC1R) and receptor tyrosine kinase (c-Kit), related microphthalmia-associated transcription factor (MITF) and consequently tyrosinase (TYR), and tyrosine-related protein-1 (TYRP-1) that were all shown to be downregulated and, therefore, leading to the repression of melanin biosynthesis. Finally, the anti-melanogenic effect of Butyroside D was confirmed on human epidermal melanocytes (HEM) cells by inhibiting the activation of cAMP pathway generally mediated through α-melanocyte-stimulating hormone (α-MSH) and MC1R. Overall, this study suggests the potential applicability of this purified compound for the prevention of hyperpigmentation conditions.

Persulfate-promoted synthesis of biphenyl compounds in water from biomass-derived triacetic acid lactone

A metal-free, persulfate-promoted route in water to access substituted biphenyl compounds is described. In our approach, the biomass-derived triacetic acid lactone (TAL) and phenylacetylenes are employed to generate targeted products in high yields and regioselectivity. The present method contributes to the green synthesis initiative to harness renewable biomass-derived compounds in environmentally friendly methodologies.