Regulation of Melanin Synthesis by Selenium-Containing Carbohydrates

Analysis of the antimelanogenic activity of zinc and selenium in vitro

Melasma is an acquired chronic condition characterized by hyperchromic patches in photo-exposed areas. The search for new compounds for the treatment of melasma without side effects is constant. In this context, the aim of this study was to investigate the in vitro cytotoxic and antimelanogenic effects of the trace elements Zinc (Zn) and Selenium (Se). In this study, we evaluated the effects of 30 µM hydroquinone, this concentration did not alter mitochondrial function (MTT assay), but increased the percentage of necrotic cells and levels of reactive species. Furthermore, it showed no influence on tyrosinase activity and melanin content. Unlike hydroquinone, exposure for 48 h to 100 µM Zn and 1 and 5 µM Se had no significant influence on the analysis of reactive species, as well as on the percentage of necrotic cells. Still, specifically in relation to 100 µM Zn, it decreased the melanin content. Given the above, the trace elements Zn and Se did not show toxicity at the concentrations tested and Zn showed a promising effect, however, the mechanism needs to be better explored in order to contribute to new and updated research in the fight against melasma with a perspective of therapeutic 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.

The Skin-Whitening and Antioxidant Effects of Protocatechuic Acid (PCA) Derivatives in Melanoma and Fibroblast Cell Lines

The skin is the most voluminous organ of the human body and is exposed to the outer environment. Such exposed skin suffers from the effects of various intrinsic and extrinsic aging factors. Skin aging is characterized by features such as wrinkling, loss of elasticity, and skin pigmentation. Skin pigmentation occurs in skin aging and is caused by hyper-melanogenesis and oxidative stress. Protocatechuic acid (PCA) is a natural secondary metabolite from a plant-based source widely used as a cosmetic ingredient. We chemically designed and synthesized PCA derivatives conjugated with alkyl esters to develop effective chemicals that have skin-whitening and antioxidant effects and enhance the pharmacological activities of PCA. We identified that melanin biosynthesis in B16 melanoma cells treated with alpha-melanocyte-stimulating hormone (α-MSH) is decreased by PCA derivatives. We also found that PCA derivatives effectively have antioxidant effects in HS68 fibroblast cells. In this study, we suggest that our PCA derivatives are potent ingredients for developing cosmetics with skin-whitening and antioxidant effects.

Development of Stilbenoid and Chalconoid Analogues as Potent Tyrosinase Modulators and Antioxidant Agents

A number of stilbenoid and chalconoid derivatives were prepared by straightforward methods, and their ability to modulate tyrosinase activity and to scavenge free radicals were evaluated in vitro. The cell-free in vitro evaluation revealed two diarylpropanes, 24 and 25, as potent tyrosinase inhibitors, whereas diarylpropenoic acids seemed to enhance the enzymatic activity. An in silico evaluation of the binding affinity of the selected compounds with the crystal structure of tyrosinase was also conducted in order to obtain better insight into the mechanism. Representative synthetic compounds with inhibitory and activating properties were further evaluated in melanoma cell lines B16F1 and B16F10 for their ability to moderate tyrosinase activity and affect melanin production. Dihydrostilbene analogues I and II, exhibited a stronger anti-melanogenic effect than kojic acid through the inhibition of cellular tyrosinase activity and melanin formation, while diarylpropanoic acid 44 proved to be a potent melanogenic factor, inducing cellular tyrosinase activity and melanin formation. Moreover, the antioxidant evaluation disclosed two analogues (29 and 11) with significant free-radical-scavenging activity (12.4 and 20.3 μM), which were 10- and 6-fold more potent than ascorbic acid (122.1 μΜ), respectively.

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.

Implications of Oxidative Stress in the Pathogenesis and Treatment of Hyperpigmentation Disorders

Oxidative stress represents an imbalance between the generation of reactive oxygen and nitrogen species and the ability of antioxidant systems to decompose those products. Oxidative stress is implicated in the pathogenesis of hyperpigmentation, hypopigmentation, melanoma, and other skin diseases. Regulatory networks involving oxidative stress and related pathways are widely represented in hypopigmentation diseases, particularly vitiligo. However, there is no complete review into the role of oxidative stress in the pathogenesis of hyperpigmentation disorders, especially regarding associations involving oxidative stress and cellular signaling pathways. Here, we review oxidative and antioxidant systems, oxidative stress-induced signal transduction mechanisms, and effects of antioxidant drugs used in preclinical and clinical settings in hyperpigmentation disorders.

Discovery of Resorcinol-Based Polycyclic Structures as Tyrosinase Inhibitors for Treatment of Parkinson's Disease

Tyrosinase is involved in the synthesis of neuromelanin in the substantia nigra, which is closely correlated with the pathogenesis of Parkinson's disease. Herein, we identified S05014 (l-Tyr, IC₅₀ = 6.25 ± 1.43 nM; l-Dopa, IC₅₀ = 0.64 ± 0.40 μM) as a highly effective tyrosinase inhibitor. It could inhibit the tyrosinase function from different origins and decrease the expression of tyrosinase. S05014 presented good medication safety and inhibited melanogenesis in a dose-dependent manner. Moreover, as a resorcinol derivative, S05014 could scavenge the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical and significantly reduce the overproduction of LPS-induced reactive oxidative species (ROS), indicating its antioxidative profile. S05014 exhibited an excellent neuroprotective effect against methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) impairment in vitro and could remarkably alleviate movement abnormalities and exploratory activities in vivo. Altogether, S05014 is considered as a promising inhibitor for tyrosinase, melanogenesis, and oxidative stress and has great potential to be utilized in anti-Parkinsonian syndrome. From this point of view, tyrosinase inhibition has been further confirmed to be a novel strategy to improve locomotor capacity and treat Parkinson's disease.

Antioxidant and Antimelanogenic Activities of Kimchi-Derived Limosilactobacillus fermentum JNU532 in B16F10 Melanoma Cells

Melanin is a natural skin pigment produced by specialized cells called melanocytes via a multistage biochemical pathway known as melanogenesis, involving the oxidation and polymerization of tyrosine. Melanogenesis is initiated upon exposure to ultraviolet (UV) radiation, causing the skin to darken, which protects skin cells from UVB radiation damage. However, the abnormal accumulation of melanin may lead to the development of certain skin diseases, including skin cancer. In this study, the antioxidant and antimelanogenic activities of the cell-free supernatant (CFS) of twenty strains were evaluated. Based on the results of 60% 2,2-diphenyl-1-picrylhydrazyl scavenging activity, 21% 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) scavenging capacity, and a 50% ascorbic acid equivalent ferric reducing antioxidant power value, Limosilactobacillus fermentum JNU532 was selected as the strain with the highest antioxidant potential. No cytotoxicity was observed in cells treated with the CFS of L. fermentum JNU532. Tyrosinase activity was reduced by 16.7% in CFStreated B16F10 cells (but not in the cell-free system), with >23.2% reduction in melanin content upon treatment with the L. fermentum JNU532-derived CFS. The inhibitory effect of the L. fermentum JNU532-derived CFS on B16F10 cell melanogenesis pathways was investigated using quantitative reverse transcription polymerase chain reaction and western blotting. The inhibitory effects of the L. fermentum JNU532-derived CFS were mediated by inhibiting the transcription of TYR, TRP-1, TRP-2, and MITF and the protein expression of TYR, TRP-1, TRP-2, and MITF. Therefore, L. fermentum JNU532 may be considered a potentially useful, natural depigmentation agent.

Inhibitory Effect of Olive Phenolic Compounds Isolated from Olive Oil By-Product on Melanosis of Shrimps

Melanosis is an unsolved problem of the crustacean industry and the cause of great loss of value. This study investigates the effect of two potent, natural antioxidants isolated from olive waste (hydroxytyrosol, HT and 3,4-dihydroxyphenylglycol, DHPG) and three novel HT-derivatives containing selenium and sulfur (dihydroxytyrosyl diselenide, N-hydroxytyrosyl selenourea, and N-hydroxytyrosyl thiourea) on the prevention of melanosis in Atlantic ditch shrimp (Palaemonetes varians) during refrigerated storage. These results clearly demonstrate the positive inhibitory effect of DHPG and dihydroxytyrosyl diselenide on delaying melanosis in vivo, although this effect was not dose dependent. The effect was associated with a concomitant-inhibitory effect on tyrosinase activity in vitro. To our knowledge, so far no studies on the prevention of melanosis have been conducted on this small specie of shrimp which is available in large quantities at any time of the year at low cost. Studies with these promising compounds could then be extended to other more economically important species with a greater guarantee of success.

On-water synthesis of glycosyl selenocyanate derivatives and their application in the metal free organocatalytic preparation of nonglycosidic selenium linked pseudodisaccharide derivatives

Glycosyl selenocyanate derivatives were prepared in very good yield by the treatment of glycosyl halide or triflate derivatives with potassium selenocyanate in water. A variety of selenium linked pseudodisaccharide derivatives were prepared in excellent yield using glycosyl selenocyanates as stable building blocks in the presence of hydrazine hydrate under metal-free organocatalytic reaction conditions.

SAR and QSAR research on tyrosinase inhibitors using machine learning methods

Tyrosinase is a key rate-limiting enzyme in the process of melanin synthesis, which is closely related to human pigmentation disorders. Tyrosinase inhibitors can down-regulate tyrosinase to effectively reduce melanin synthesis. In this work, we conducted structure-activity relationship (SAR) study on 1097 diverse mushroom tyrosinase inhibitors. We applied five kinds of machine learning methods to develop 15 classification models. Model 5B built by fully connected neural networks and ECFP4 fingerprints achieved the highest prediction accuracy of 91.36% and Matthews correlation coefficient (MCC) of 0.81 on the test set. The applicability domains (AD) of classification models were defined by d S T D - P R O method. Moreover, we clustered the 1097 inhibitors into eight subsets by K-Means to figure out inhibitors' structural features. In addition, 10 quantitative structure-activity relationship (QSAR) models were constructed by four machine learning methods based on 813 inhibitors. Model 6 J, the best QSAR model, was developed by fully connected neural networks with 50 RDKit descriptors. It resulted in a coefficient of determination (r ²) of 0.770 and a root mean squared error (RMSE) of 0.482 on the test set. The AD of Model 6 J was visualized by Williams plot. The models built in this study can be obtained from the authors.

Thiosemicarbazide binds with the dicopper center in the competitive inhibition of mushroom tyrosinase enzyme: Synthesis and molecular modeling of theophylline analogues

Theophylline is long known for its anti-ageing and anti-oxidative properties. Moreover, Tyrosinase is a crucial enzyme that regulates the melanin synthetic pathway, which is involved in various physiological metabolic processes including aging. The current paper describes the synthesis of various heterocyclic systems coupled with theophylline moiety along with their tyrosinase inhibition activity in view to identify the potent nucleus. Around 19 compounds were synthesized and screened for enzyme inhibition. Based on the current study, it is suggested that compound 18 having thiosemicarbazide has strong enzyme inhibition potential. The enzyme kinetics and docking studies provide important insights into how the compound interacts with the mushroom tyrosinase active site. The work will provide clue to developing new, potent tyrosinase inhibitors for drug development.

Serum level of antioxidant vitamins and minerals in patients with vitiligo, a systematic review and meta-analysis

BACKGROUND

Antioxidant status is considered as important factor in the pathogenesis of vitiligo. However, there are controversial findings about serum status of antioxidants in vitiligo patients. The purpose of this study was to systematically review the evidences comparing the serum levels of antioxidant vitamins and minerals between vitiligo patients and controls, and performing meta-analysis of the results.

METHODS

A comprehensive search was performed for studies comparing the serum status of antioxidant vitamins and minerals using following databases since inception up to 30 April 2020; PubMed, EMBASE, Scopus, and Web of Science. Data extraction was done by two independent reviewers. The data was pooled for serum level of each antioxidant comparing between vitiligo and control groups.

RESULTS

Thirteen studies were included in this systematic review. The serum level of vitamin A, C, E, selenium, zinc and copper were compared between vitiligo patients and controls in these studies. Eleven studies including 570 vitiligo cases and 580 controls were included in the meta-analysis. Serum vitamin A and copper level in vitiligo patients were only evaluated in single studies and not included in meta-analysis. Based on fixed effect model, there were no statistical difference between two groups regarding serum vitamin C (OR = 1.17, 95 % CI, 0.74-1.84, P = 0.495), and vitamin E (OR = 0.61, 95 % CI, 0.30-1.25, P = 0.180). Higher serum zinc can decrease the risk of vitiligo based on sensitivity analysis of the results. (OR = 0.29, 95 % CI 0.15-0.54, P < 0.001). Higher serum selenium level significantly increased the risk of vitiligo (OR = 4.31, 95 % CI, 2.72-6.81, P < 0.001). Vitamin A was not significantly different in two reported groups (6.35 ± 1.53 vs 6.77 ± 1.46 μg/mL, P > 0.05). Copper was significantly higher in vitiligo patients compared to controls (129 ± 33 vs 99 ± 19 μg /100 mL, P = 0.002).

CONCLUSION

The current meta-analysis of data on serum level of most studied antioxidants (vitamin C, vitamin E, zinc and selenium) in patients suffering vitiligo showed that higher serum selenium (OR = 4.31) and lower zinc level (OR = 0.29) can increased the risk of vitiligo. Potential mechanism associated with preventive effects of zinc and the depigmentation effect of selenium should be more elucidated in further studies.

Sweet Selenium: Synthesis and Properties of Selenium-Containing Sugars and Derivatives

In the last decades, organoselenium compounds gained interest due to their important biological features. However, the lack of solubility, which characterizes most of them, makes their actual clinical exploitability a hard to reach goal. Selenosugars, with their intrinsic polarity, do not suffer from this issue and as a result, they can be conceived as a useful alternative. The aim of this review is to provide basic knowledge of the synthetic aspects of selenosugars, selenonium salts, selenoglycosides, and selenonucleotides. Their biological properties will be briefly detailed. Of course, it will not be a comprehensive dissertation but an analysis of what the authors think is the cream of the crop of this interesting research topic.

Tyrosinase-Targeting Gallacetophenone Inhibits Melanogenesis in Melanocytes and Human Skin-Equivalents

Demands for safe depigmentation compounds are constantly increasing in the pharmaceutical and cosmetic industry, since the numerous relevant compounds reported to date have shown undesirable side effects or low anti-melanogenic effects. In this study, we reported three novel inhibitors of tyrosinase, which is the key enzyme in melanogenesis, identified using docking-based high throughput virtual screening of an in-house natural compound library followed by mushroom tyrosinase inhibition assay. Of the three compounds, gallacetophenone showed high anti-melanogenic effect in both human epidermal melanocytes and a 3D human skin model, MelanoDerm. The inhibitory effect of gallacetophenone on tyrosinase was elucidated by computational molecular modeling at the atomic level. Binding of gallacetophenone to the active site of tyrosinase was found to be stabilized by hydrophobic interactions with His367, Ile368, and Val377; hydrogen bonding with Ser380 and a water molecule bridging the copper ions. Thus, our results strongly suggested gallacetophenone as an anti-melanogenic ingredient that inhibits tyrosinase.

THE SAFE TRANSDERMAL COSMETIC PRODUCT WITH ANTITYROSINASE ACTIVITY

The possibility of developing a cosmetic product with antipigmentation properties has been considered. The cream is based on extracts, selected by monitoring, from plant components spread in Ukraine, able to inhibit tyrosinase and thus impart antipigmentation properties to the product. As active components expanding the range of the product’s cosmetic properties, ingredients were selected that strengthen the skin matrix and saturate it with essential substances. To enhance the effectiveness of the biologically active constituents of the product, liquid crystals based on cholesterics as modern systems of transdermal delivery of active components (0.1%) were included in its composition. For the cosmetic product, it has been suggested to use the following thermotropic cholesteric composition: cholesteryl nonanoate – 45%, cholesteryl pentanoate – 25%, cholesteryl-4-nonylbutanedioate – 30%. According to the complex of the organoleptic, physico-chemical, biochemical, and microbiological quality parameters of the new product after its manufacture and storage during three months, it has been established that it complies with the general sanitary and hygienic requirements to perfumes and cosmetics of the 3rd group. Biotesting on the testing cultures Allium cepa L. and Saccharomyces cerevisiae has proved the complete integral safety and growth potentiation of both testing cultures by 9.6–19.3% to the control, even in the presence of a preservative. This is an evidence of the safety, biological activity, and advisability of the developed cosmetic product with antipigmentation properties, containing cholesteric liquid crystals. The cosmetic product, based on the formulation developed, has been tested on female volunteers. Its effectiveness has been established and a simultaneous increase in the face skin humidity has been proved instrumentally.

Synthesis of N-arylindazole-3-carboxamide and N-benzoylindazole derivatives and their evaluation against α-MSH-stimulated melanogenesis

We have designed and synthesized twenty-six N-arylindazole-3-carboxamide (3a-p) and N-benzoylindazole (6a-j) derivatives to discover with excellent inhibition activities of α-MSH-stimulated melanogenesis. In the bio evaluation studies of these compounds, we discovered eighteen compounds, out of twenty-six exhibited more potent inhibition than the positive control arbutin. From the SAR studies, we identified 3k and 6g as lead compounds which displayed almost 5 and 9 times more potent inhibition of α-MSH-stimulated melanogenesis respectively than the reference arbutin. It is also evident the presence of electron withdrawing group at para position (R³) for the compounds (3a-p) and presence of +M group at ortho position (R⁵) for the compounds (6a-j) were crucial for their excellent inhibition activities of α-MSH-stimulated melanogenesis.

Antioxidant, anti-tyrosinase and anti-melanogenic effects of (E)-2,3-diphenylacrylic acid derivatives

During our continued search for strong skin whitening agents over the past ten years, we have investigated the efficacies of many tyrosinase inhibitors containing a common (E)-β-phenyl-α,β-unsaturated carbonyl scaffold, which we found to be essential for the effective inhibition of mushroom and mammalian tyrosinases. In this study, we explored the tyrosinase inhibitory effects of 2,3-diphenylacrylic acid (2,3-DPA) derivatives, which also possess the (E)-β-phenyl-α,β-unsaturated carbonyl motif. We synthesized fourteen (E)-2,3-DPA derivatives 1a-1n and one (Z)-2,3-DPA-derivative 1l' using a Perkin reaction with phenylacetic acid and appropriate substituted benzaldehydes. In our mushroom tyrosinase assay, 1c showed higher tyrosinase inhibitory activity (76.43 ± 3.53%, IC₅₀ = 20.04 ± 1.91 µM) with than the other 2,3-DPA derivatives or kojic acid (21.56 ± 2.93%, IC₅₀ = 30.64 ± 1.27 μM). Our mushroom tyrosinase inhibitory results were supported by our docking study, which showed compound 1c (-7.2 kcal/mole) exhibited stronger binding affinity for mushroom tyrosinase than kojic acid (-5.7 kcal/mole). In B16F10 melanoma cells (a murine cell-line), 1c showed no cytotoxic effect up to a concentration of 25 μM and exhibited greater tyrosinase inhibitory activity (68.83%) than kojic acid (49.39%). In these cells, arbutin (a well-known tyrosinase inhibitor used as the positive control) only inhibited tyrosinase by 42.67% even at a concentration of 400 μM. Furthermore, at 25 µM, 1c reduced melanin contents in B16F10 melanoma cells by 24.3% more than kojic acid (62.77% vs. 38.52%). These results indicate 1c is a promising candidate treatment for pigmentation-related diseases and potential skin whitening agents.

Natural product inspired allicin analogs as novel anti-cancer agents

A series of novel analogs of Allicin (S-allyl prop-2-ene-1-sulfinothioate) present in garlic has been synthesized in high yield. Synthesized 23 compounds were evaluated against different breast cancer cells (MDA-MB-468 and MCF-7) and non-cancer cells (WI38). Four compounds (3f, 3h, 3m and 3u) showed significant cytotoxicity against cancer cells whereas nontoxic to the normal cells. Based on the LD₅₀ values and selectivity index (SI), compound 3h (S-p-methoxybenzyl (p-methoxyphenyl)methanesulfinothioate) was considered as most promising anticancer agent amongst the above three compounds. Further bio-chemical studies confirmed that compound 3h promotes ROS generation, changes in mitochondrial permeability transition and induced caspase mediated DNA damage and apoptosis.

Improvement of Biological Activity of Morchella esculenta Protein Hydrolysate by Microwave-Assisted Selenization

Morchella esculenta protein hydrolysate (MPH) from a valued medicinal and edible fungus M. esculenta (L.) is an excellent material for functional food development. To promote MPH utilization, selenization of MPH was performed by applying a simple and environmentally friendly microwave irradiation procedure. The physicochemical characteristics of selenized MPH (Se-MPH) were investigated by SEM-EDX, FTIR, CD, and amino acid analyzer, and its biological activity were assessed by ABTS, DPPH, H₂ O₂ scavenging, and reducing power assays, as well as α-glucosidase, α-amylase, and tyrosinase inhibition tests. The results showed that MPH was successfully selenized, Se content in Se-MPH reached 59.0 ± 0.64 mg/g, and amino groups, hydroxyl groups, and sulfur atoms of methionine residues in the MPH molecule may participate in selenization. Furthermore, Se-MPH exhibited significantly enhanced antioxidant, antidiabetic, and tyrosinase inhibitory activities, compared with the native MPH and microwave-irradiated MPH. Thus, the microwave-assisted selenization is a feasible strategy for preparing organic Se and improving the biological activity of MPH. PRACTICAL APPLICATION: In this study, selenized Morchella esculenta protein hydrolysate (Se-MPH) was successfully prepared via conjugation with sodium selenite using the microwave-assisted method. The results showed that Se-MPH, synthesized with the aid of microwave, exhibited favorable selenium content and improved antioxidant, antidiabetic, and tyrosinase inhibitory activities. Therefore, microwave can be employed as an innovative and effective avenue for the production of organic selenium in nutraceutical and functional food industry.

Carbazole and hydrazone derivatives as new competitive inhibitors of tyrosinase: Experimental clues to binuclear copper active site binding

In this work a total of 12 carbazoles and hydrazone-bridged thiazole-pyrrole derivatives have been identified as new competitive inhibitors of tyrosinase. Carbazole derivative with 2-benzoimidazole substitution showed most potent inhibition in the series. Other carbazole derivatives containing benzothiazole and benzoxazole substitutions showed comparable levels of tyrosinase inhibition. The hydrazone derivatives also showed potent tyrosinase inhibitory activity with comparable K_i values except one with fluoride at its terminal position. Kinetic studies showed competitive inhibition of tyrosinase by all compounds that increased the substrate K_m without changing the V_max value. Moreover, experimental evidence suggests that the target compounds specifically bind to the binuclear copper center of the tyrosinase active site in an apparent mono-dentate fashion. Carbazoles and hydrazones are new and emerging classes of compounds as tyrosinase inhibitors that may provide new structural avenues to discovery of drugs targeting the treatment of hyperpigmentation and related dermatological disorders.

Inhibitors of Melanogenesis: An Updated Review

Melanins are pigment molecules that determine the skin, eye, and hair color of the human subject to its amount, quality, and distribution. Melanocytes synthesize melanin and provide epidermal protection from various stimuli, such as harmful ultraviolet radiation, through the complex process called melanogenesis. However, serious dermatological problems occur when there is excessive production of melanin in different parts of the human body. These include freckles, melasma, senile lentigo, pigmented acne scars, and cancer. Therefore, controlling the production of melanin is an important approach for the treatment of pigmentation related disorderes. In this Perspective, we focus on the inhibitors of melanogenesis that directly/indirectly target a key enzyme tyrosinase as well as its associated signaling pathways.

Skin whitening agents: medicinal chemistry perspective of tyrosinase inhibitors

Melanogenesis is a process to synthesize melanin, which is a primary responsible for the pigmentation of human skin, eye and hair. Although numerous enzymatic catalyzed and chemical reactions are involved in melanogenesis process, the enzymes such as tyrosinase and tyrosinase-related protein-1 (TRP-1) and TRP-2 played a major role in melanin synthesis. Specifically, tyrosinase is a key enzyme, which catalyzes a rate-limiting step of the melanin synthesis, and the downregulation of tyrosinase is the most prominent approach for the development of melanogenesis inhibitors. Therefore, numerous inhibitors that target tyrosinase have been developed in recent years. The review focuses on the recent discovery of tyrosinase inhibitors that are directly involved in the inhibition of tyrosinase catalytic activity and functionality from all sources, including laboratory synthetic methods, natural products, virtual screening and structure-based molecular docking studies.

Recent development of signaling pathways inhibitors of melanogenesis

Human skin, eye and hair color rely on the production of melanin, depending on its quantity, quality, and distribution, Melanin plays a monumental role in protecting the skin against the harmful effect of ultraviolet radiation and oxidative stress from various environmental pollutants. However, an excessive production of melanin causes serious dermatological problems such as freckles, solar lentigo (age spots), melasma, as well as cancer. Hence, the regulation of melanin production is important for controlling the hyper-pigmentation. Melanogenesis, a biosynthetic pathway to produce melanin pigment in melanocyte, involves a series of intricate enzymatic and chemical catalyzed reactions. Several extrinsic factors include ultraviolet radiation and chemical drugs, and intrinsic factors include molecules secreted by surrounding keratinocytes or melanocytes, and fibroblasts, all of which regulate melanogenesis. This article reviews recent advances in the development of melanogenesis inhibitors that directly/indirectly target melanogenesis-related signaling pathways. Efforts have been made to provide a description of the mechanism of action of inhibitors on various melanogenesis signaling pathways.

Involvement of monoaminergic system in the antidepressant-like effect of (octylseleno)-xylofuranoside in the mouse tail suspension test

Depression is one of the most commonly diagnosed neuropsychiatric disorders and several studies have demonstrated a role for selenium in mood disorders. For this reason, the present study investigated the role of the monoaminergic system in the antidepressant-like action of (octylseleno)-xylofuranoside (OSX), an organoselenium compound, in the tail suspension test (TST) in mice. For this purpose, OSX (0.001–10 mg/kg) was administered orally (p.o.) 30 min prior to testing, and all of the tested doses reduced the immobility time in the TST without changing the locomotor activity measured in the open field test (OFT). Furthermore, the antidepressant-like effect of OSX (0.01 mg/kg, p.o.) in the TSTwas prevented by pre-treatment in mice with ketanserin (1 mg/kg, intraperitoneal route (i.p.); a 5-HT2A/2C receptor antagonist),WAY100635 (0.1mg/kg, subcutaneous (s.c.); a selective 5-HT1A receptor antagonist), p-chlorophenylalaninemethyl ester-PCPA (100mg/kg, i.p.; a selective inhibitor of tryptophan hydroxylase), prazosin (1 mg/kg, i.p.; an α1-adrenoceptor antagonist), yohimbine (1 mg/kg, i.p.; an α2-adrenoceptor antagonist), SCH233390 (0.05 mg/kg, s.c., a dopaminergic D1 receptor antagonist) and sulpiride (50 mg/kg, i.p., a dopaminergic D2 receptor antagonist), but not with ondansetron (1 mg/kg, i.p.; a selective 5-HT3 receptor antagonist). Taken together, these data demonstrate that OSX has a potent antidepressant like effect in TST at lower doses (0.001–10 mg/kg), which is dependent on its interaction with the serotonergic, noradrenergic and dopaminergic systems.

Lipoteichoic acid isolated from Lactobacillus plantarum inhibits melanogenesis in B16F10 mouse melanoma cells

Lipoteichoic acid (LTA) is a major component of the cell wall of Gram-positive bacteria. Its effects on living organisms are different from those of lipopolysaccharide (LPS) found in Gram-negative bacteria. LTA contributes to immune regulatory effects including anti-aging. In this study, we showed that LTA isolated from Lactobacillus plantarum (pLTA) inhibited melanogenesis in B16F10 mouse melanoma cells. pLTA reduced the cellular activity of tyrosinase and the expression of tyrosinase family members in a dose-dependent manner. The expression of microphthalmia-associated transcription factor (MITF), a key factor in the synthesis of melanin, was also decreased by pLTA. Further, we showed that pLTA activated melanogenesis signaling, such as extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinse (PI3K)/AKT. In addition, the expression of heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) and HuR, which are important RNA-binding proteins (RBPs), was reduced. pLTA likely degrades MITF via regulation of melanogenic signaling and RNA stability of melanogenic proteins, resulting in the reduction of melanin. Thus, our data suggest that pLTA has therapeutic potential for treating hyperpigmentation disorders and can also be used as a cosmetic whitening agent.

S-(-)-10,11-dihydroxyfarnesoic acid methyl ester inhibits melanin synthesis in murine melanocyte cells

The development of antimelanogenic agents is important for the prevention of serious aesthetic problems such as melasmas, freckles, age spots, and chloasmas. In the course of screening for melanin synthesis inhibitors, we found that the culture broth from an insect morphopathogenic fungus, Beauveria bassiana CS1029, exhibits potent antimelanogenic activity. We isolated and purified an active metabolite and identified it as S-(−)-10,11-dihydroxyfarnesoic acid methyl ester (dhFAME), an insect juvenile hormone. To address whether dhFAME inhibits melanin synthesis, we first measured the size of the melanin biosynthesis inhibition zone caused by dhFAME. dhFAME also showed inhibitory activity against mushroom tyrosinase in Melan-a cells. Intracellular, dose-dependent tyrosinase inhibition activity was also confirmed by zymography. In addition, we showed that dhFAME strongly inhibits melanin synthesis in Melan-a cells. Furthermore, we compared levels of TYR, TRP-1, TRP-2, MITF, and MC1R mRNA expression by reverse-transcription polymerase chain reaction and showed that treatment of Melan-a cells with 35 μM dhFAME led to an 11-fold decrease in TYR expression, a 6-fold decrease in TRP-2 expression, and a 5-fold decrease in MITF expression. Together, these results indicate that dhFAME is a potent inhibitor of melanin synthesis that can potentially be used for cosmetic biomaterial(s).

Aromatic-turmerone inhibits α-MSH and IBMX-induced melanogenesis by inactivating CREB and MITF signaling pathways

This study investigated the anti-melanogenic effect of aromatic (ar)-turmerone on alpha-melanocyte stimulating hormone (α-MSH) and 3-isobuty-1-methxlzanthine (IBMX)-induced tyrosinase (Tyr), tyrosinase-related protein 1 (TRP-1), and tyrosinase-related protein 2 (TRP-2) expression in B16F10 melanoma cells. We demonstrated that ar-turmerone inhibits α-MSH and IBMX-induced melanin synthesis and tyrosinase activity. Data also showed that ar-turmerone inhibits the expression of tyrosinase, TRP-1, and TRP-2 in α-MSH- and IBMX-stimulated B16F10 cells. In addition, ar-turmerone exhibits stronger anti-melanogenic effects than curcumin. Furthermore, ar-turmerone strongly inhibited α-MSH- and IBMX-induced microphthalmia-associated transcription factor by suppressing the activity of cyclic adenosine monophosphate (cAMP)-responsive element binding protein in α-MSH-stimulated B16F10 cells. Our data revealed that ar-turmerone is a novel, effective, anti-melanogenic agent that functions by downregulating tyrosinase, Trp-1, and Trp-2 gene expression. Therefore, ar-turmerone may be a useful therapeutic agent for treating hyperpigmentation disorders, such as freckles and melasma, and as a beneficial additive in whitening cosmetics.

Inhibitory effects of 5-chloroacetyl-2-piperidino-1,3-selenazole, a novel selenium-containing compound, on skin melanin biosynthesis

Objectives

Increased production and accumulation of melanin leads to many hyperpigmentation disorders such as melasma, freckles and geriatric pigment spots. Thus, there is a need for the development of depigmenting agents. Based on our previous reports, selenium derivatives as anti-melanogenic lead compounds could be very important. The aim of this study was to investigate the depigmenting effect of novel selenium-containing compounds.

Methods

The inhibitory effects of 5-chloroacetyl-2-piperidino-1,3-selenazole (CS1), a novel selenium-containing compound, on melanogenesis were investigated in B16F10 melanoma cells and cultured brownish guinea pig skin tissue with α-melanocyte-stimulating hormone stimulation.

Key findings

We found that CS1 inhibited melanin production in B16F10 cells by suppressing tyrosinase activity and its protein expression. In addition, Western blotting analysis revealed that CS1 suppressed the expression of tyrosinase-related protein (TRP)-1 and TRP-2. Therefore, the depigmenting effect of CS1 might have been due to inhibition of tyrosinase activity and expression of melanogenic enzymes. Furthermore, CS1 had inhibitory effects on melanin biosynthesis of primary cultured skin of brownish guinea pig.

Conclusions

The results suggested that CS1 could be a useful candidate for the treatment of skin hyperpigmentation.

An updated review of tyrosinase inhibitors

Tyrosinase is a multifunctional, glycosylated, and copper-containing oxidase, which catalyzes the first two steps in mammalian melanogenesis and is responsible for enzymatic browning reactions in damaged fruits during post-harvest handling and processing. Neither hyperpigmentation in human skin nor enzymatic browning in fruits are desirable. These phenomena have encouraged researchers to seek new potent tyrosinase inhibitors for use in foods and cosmetics. This article surveys tyrosinase inhibitors newly discovered from natural and synthetic sources. The inhibitory strength is compared with that of a standard inhibitor, kojic acid, and their inhibitory mechanisms are discussed.