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

Rosa × damascena Herrm. essential oil: anti-tyrosinase activity and phytochemical composition

Tyrosinase is a key enzyme in melanin synthesis, and its natural inhibitors are receiving increasing attention. Rosa × damascena Herrm. essential oil (RDEO), as important functional metabolites, was widely known due to its biological activities. But its tyrosinase inhibitory activity has not been detailed investigated. Therefore, in this paper, RDEO was comprehensively investigated the tyrosinase inhibitory, followed by the phytochemical composition analysis. Activity screening results showed that RDEO exhibited effective anti-tyrosinase activity and was a reversible and mixed-type inhibitor. CD assay results revealed that RDEO could affect the conformation of tyrosinase to reduce the activity. In B16F10 cells, RDEO (25-100 μg/mL) could inhibit intracellular tyrosinase activity and decrease melanin content. Finally, GC-MS analysis of RDEO found that citronellol (21.22%), geraniol (14.1%), eicosane (11.03%), heneicosane (6.65%) and 1-nonadecene (5.16%) were its main phytochemical compositions. This study provided data support for Rosa × damascena Herrm. essential oil as one potential natural tyrosinase inhibitor and its applications in cosmetics and medicine.

Design, synthesis, and in vitro and in silico study of 1-benzyl-indole hybrid thiosemicarbazones as competitive tyrosinase inhibitors

Developing new anti-tyrosinase drugs seems crucial for the medical and industrial fields since irregular melanin synthesis is linked to the resurgence of several skin conditions, including melanoma, and the browning of fruits and vegetables. A novel series of N-1 and C-3 substituted indole-based thiosemicarbazones 5(a-r) are synthesized and further analyzed for their inhibition potential against tyrosinase enzyme through in vitro assays. The synthesized compounds displayed very good to moderate inhibition with half maximal inhibitory concentration in the range of 12.40 ± 0.26 μM to 47.24 ± 1.27 μM. Among all the derivatives 5k displayed the highest inhibitory activity. According to SAR analysis, the derivatives with 4-substitution at the benzyl or phenyl ring of the thiosemicarbazones exhibited better inhibitory potential against tyrosinase. In silico analysis (including ADMET prediction and molecular docking) was conducted and compared with the standard drug (kojic acid). These findings may help the hunt for new melanogenesis inhibitors that the food and cosmetics industries may find valuable.

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

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

Tyrosinase Inhibition and Antimelanogenic Effects of Resorcinol-Containing Compounds

Tyrosinases (TYRs) are copper-containing metalloenzymes present in a large diversity of species. In human, hTYR is responsible for pivotal steps in melanogenesis, catalysing the oxidation of l-tyrosine to l-DOPA and further to dopaquinone. While numerous TYR inhibitors have been reported, polyphenolic compounds tend to dominate the literature. However, many of these compounds, particularly monophenols and catechols, have been identified as alternative substrates rather than true inhibitors, given their structural similarity to natural substrates. Resorcinol-containing compounds have emerged as promising candidates to address this challenge, as the meta-dihydroxy moiety in resorcinol demonstrates resistance to TYR-mediated oxidation, while retaining the favourable interactions with copper ions provided by the hydroxy groups. Although their precise mechanism of action remains debated, resorcinol derivatives have yielded some of the most active compounds against isolated mushroom and human TYRs, as well as clinically used dermocosmetic agents like rucinol and thiamidol, which exhibited very promising effects in patients with facial melasma. This review outlines the development of resorcinol-containing TYR inhibitors, categorized by scaffold type, ranging from simple alkyl analogues to intricate synthetic derivatives. Mechanistic insights about the resorcinol-TYR interaction are also presented and debated.

Inhibition mechanism investigation of quercetagetin as a potential tyrosinase inhibitor

Tyrosinase is one important rate limiting enzyme in melanin synthesis, directly affecting the melanin synthesis. Quercetagetin is one active ingredient from marigold. Thence, the inhibition effects of quercetagetin against tyrosinase were investigated. The results showed quercetagetin could inhibit tyrosinase activity with IC50 value of 0.19 ± 0.01 mM and the inhibition type was a reversible mixed-type. Results of fluorescence quenching showed quercetagetin could quench tyrosinase fluorescence in static process. CD and 3D fluorescence results showed the interaction of quercetagetin to tyrosinase could change tyrosinase conformation to inhibit activity. Moreover, docking revealed details of quercetagetin's interactions with tyrosinase.

Synergistic Biomedical Potential and Molecular Docking Analyses of Coumarin-Triazole Hybrids as Tyrosinase Inhibitors: Design, Synthesis, In Vitro Profiling, and In Silico Studies

The tyrosinase enzyme has a vital role in the browning of vegetables and fruits and the biosynthesis of melanin. In this work, we synthesized a diverse library of coumarin-triazole hybrids, and these compounds were characterized by using suitable analytical techniques. Our research work extends beyond the synthetic effort to explore the therapeutic potential of these compounds. We put the synthesized compounds through meticulous in vitro screening against the tyrosinase enzyme, and these coumarin derivatives evinced good IC50 values in the range of 0.339 ± 0.25 µM to 14.06 ± 0.92 µM. In the library of synthesized compounds, six compounds were found to be more potent than standard ascorbic acid (IC50 = 11.5 ± 1.00), and among them, 17e and 17f, being the most active, exhibited remarkable anti-tyrosinase potential, with IC50 values of 0.339 ± 0.25 μM and 3.148 ± 0.23 μM, respectively. Furthermore, an in silico modeling study was carried out to determine the key interactions of these compounds with the tyrosinase protein (PDB ID: 2Y9X) and thus to authenticate our experimental findings. The quantitative SAR studies exhibited a good correlation between the synthesized derivatives of coumarin and their anti-tyrosinase activity. The docking studies verified the experimental results, and ligand 17e showed good interaction with the core residues of tyrosinase. This study not only expands the field of coumarin-triazole hybrid synthesis but also provides valuable insights for the development of novel tyrosinase inhibitors.

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.

Pour some sugar on me: The diverse functions of phenylpropanoid glycosylation

The phenylpropanoid metabolism is the source of a vast array of specialized metabolites that play diverse functions in plant growth and development and contribute to all aspects of plant interactions with their surrounding environment. These compounds protect plants from damaging ultraviolet radiation and reactive oxygen species, provide mechanical support for the plants to stand upright, and mediate plant-plant and plant-microorganism communications. The enormous metabolic diversity of phenylpropanoids is further expanded by chemical modifications known as "decorative reactions", including hydroxylation, methylation, glycosylation, and acylation. Among these modifications, glycosylation is the major driving force of phenylpropanoid structural diversification, also contributing to the expansion of their properties. Phenylpropanoid glycosylation is catalyzed by regioselective uridine diphosphate (UDP)-dependent glycosyltransferases (UGTs), whereas glycosyl hydrolases known as β-glucosidases are the major players in deglycosylation. In this article, we review how the glycosylation process affects key physicochemical properties of phenylpropanoids, such as molecular stability and solubility, as well as metabolite compartmentalization/storage and biological activity/toxicity. We also summarize the recent knowledge on the functional implications of glycosylation of different classes of phenylpropanoid compounds. A balance of glycosylation/deglycosylation might represent an essential molecular mechanism to regulate phenylpropanoid homeostasis, allowing plants to dynamically respond to diverse environmental signals.

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.

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.

Phenolic acids in Panax ginseng inhibit melanin production through bidirectional regulation of melanin synthase transcription via different signaling pathways

Background

Our previous investigation indicated that the preparation of Panax ginseng Meyer (P. ginseng) inhibited melanogenesis. It comprised salicylic acid (SA), protocatechuic acid (PA), p-coumaric acid (p-CA), vanillic acid (VA), and caffeic acid (CA). In this investigation, the regulatory effects of P. ginseng phenolic acid monomers on melanin production were assessed.

Methods

In vitro and in vivo impact of phenolic acid monomers were assessed.

Results

SA, PA, p-CA and VA inhibited tyrosinase (TYR) to reduce melanin production, whereas CA had the opposite effects. SA, PA, p-CA and VA significantly downregulated the melanocortin 1 receptor (MC1R), cycle AMP (cAMP), protein kinase A (PKA), cycle AMP-response element-binding protein (CREB), microphthalmia-associated transcription factor (MITF) pathway, reducing mRNA and protein levels of TYR, tyrosinase-related protein 1 (TYRP1), and TYRP2. Moreover, CA treatment enhanced the cAMP, PKA, and CREB pathways to promote MITF mRNA level and phosphorylation. It also alleviated MITF protein level in α-MSH-stimulated B16F10 cells, comparable to untreated B16F10, increasing the expression of phosphorylation glycogen synthase kinase 3β (p-GSK3β), β-catenin, p-ERK/ERK, and p-p38/p38. Furthermore, the GSK3β inhibitor promoted p-GSK3β and p-MITF expression, as observed in CA-treated cells. Moreover, p38 and ERK inhibitors inhibited CA-stimulated p-p38/p38, p-ERK/ERK, and p-MITF increase, which had negative binding energies with MC1R, as depicted by molecular docking.

Conclusion

P. ginseng roots' phenolic acid monomers can safely inhibit melanin production by bidirectionally regulating melanin synthase transcription. Furthermore, they reduced MITF expression via MC1R/cAMP/PKA signaling pathway and enhanced MITF post-translational modification via Wnt/mitogen-activated protein kinase signaling pathway.

Synthesis, Anti-Tyrosinase Activity, and Spectroscopic Inhibition Mechanism of Cinnamic Acid-Eugenol Esters

Tyrosinase plays crucial roles in mediating the production of melanin pigment; thus, its inhibitors could be useful in preventing melanin-related diseases. To find potential tyrosinase inhibitors, a series of cinnamic acid-eugenol esters (c1~c29) was synthesized and their chemical structures were confirmed by 1H NMR, 13C NMR, HRMS, and FT-IR, respectively. The biological evaluation results showed that all compounds c1~c29 exhibited definite tyrosinase inhibitory activity; especially, compound c27 was the strongest tyrosinase inhibitor (IC50: 3.07 ± 0.26 μM), being ~4.6-fold stronger than the positive control, kojic acid (IC50: 14.15 ± 0.46 μM). Inhibition kinetic studies validated compound c27 as a reversible mixed-type inhibitor against tyrosinase. Three-dimensional fluorescence and circular dichroism (CD) spectra results indicated that compound c27 could change the conformation and secondary structure of tyrosinase. Fluorescence-quenching results showed that compound c27 quenched tyrosinase fluorescence in the static manner with one binding site. Molecular docking results also revealed the binding interactions between compound c27 and tyrosinase. Therefore, cinnamic acid-eugenol esters, especially c27, could be used as lead compounds to find potential tyrosinase inhibitors.