Arbutin increases the pigmentation of cultured human melanocytes through mechanisms other than the induction of tyrosinase activity

Newly identified peptide Nigrocin-OA27 inhibits UVB induced melanin production via the MITF/TYR pathway

Melasma is a common skin disease induced by an increase in the content of melanin in the skin, which also causes serious physical and mental harm to patients. In this research, a novel peptide (Nigrocin-OA27) from Odorrana andersonii is shown to exert a whitening effect on C57 mice pigmentation model. The peptide also demonstrated non-toxic and antioxidant capacity, and can significantly reduce melanin content in B16 cells. Topical application effectively delivered Nigrocin-OA27 to skin's epidermal and dermal layers and exhibited significant preventive and whitening effects on the UVB-induced ear pigmentation model in C57 mice. The whitening mechanism of Nigrocin-OA27 may be related to reduced levels of the microphthalmia-associated transcription factor and the key enzyme for melanogenesis-tyrosinase (TYR). Nigrocin-OA27 also inhibited the catalytic activity by adhering to the active core of TYR, thereby reducing melanin formation and deposition. In conclusion, Nigrocin-OA27 may be a potentially effective external agent to treat melasma by inhibiting aberrant skin melanin synthesis.

Peptide OA-VI12 restrains melanogenesis in B16 cells and C57B/6 mouse ear skin via the miR-122-5p/Mitf/Tyr axis

Excessive melanogenesis leads to hyperpigmentation, which is one of the common skin conditions in humans. Existing whitening cosmetics cannot meet market needs due to their inherent limitations. Thus, the development of novel skin-whitening agents continues to be a challenge. The peptide OA-VI12 from the skin of amphibians at high altitude has attracted attention due to its remarkable anti light damage activity. However, whether OA-VI12 has the skin-whitening effect of inhibiting melanogenesis is still. Mouse melanoma cells (B16) were used to study the effect of OA-VI12 on cell viability and melanin content. The pigmentation model of C57B/6 mouse ear skin was induced by UVB and treated with OA-VI12. Melanin staining was used to observe the degree of pigmentation. MicroRNA sequencing, quantitative real-time PCR (qRT-PCR), immunofluorescence analysis and Western blot were used to detect the change of factor expression. Double luciferase gene report experiment was used to prove the regulatory relationship between miRNA and target genes. OA-VI12 has no effect on the viability of B16 cells in the concentration range of 1-100 μM and significantly inhibits the melanin content of B16 cells. Topical application of OA-VI12, which exerted transdermal potency, prevented UVB-induced pigmentation of ear skin. MicroRNA sequencing and double luciferase reporter analysis results showed that miR-122-5p, which directly regulated microphthalmia-associated transcription factor (Mitf), had significantly different expression before and after treatment with OA-VI12. Mitf is a simple helix loop and leucine zipper transcription factor that regulates tyrosinase (Tyr) expression by binding to the M-box promoter element of Tyr. qRT-PCR, immunofluorescence analysis and Western blot showed that OA-VI12 up-regulated the expression of miR-122-5p and inhibited the expression of Mitf and Tyr. The effects of OA-VI12 on melanogenesis inhibition in vitro and in vivo may involve the miR-122-5p/Mitf/tyr axis. OA-VI12 represents the first report on a natural amphibian-derived peptide with skin-whitening capacity and the first report of miR-122-5p as a target for regulating melanogenesis, thereby demonstrating its potential as a novel skin-whitening agent and highlighting amphibian-derived peptides as an underdeveloped resource.

Inhibitory Activities of Samples on Tyrosinases Were Affected by Enzyme Species and Sample Addition Methods

The inhibition of tyrosinase (TYR) activity is an effective measure to inhibit melanin synthesis. At present, there are many methods with discrepant details that study the TYR inhibitory activity of samples. Under the same experimental conditions, this paper systematically studies whether enzyme species and sample addition methods are the key factors that determine the TYR inhibitory activity of samples. TYRs extracted from B16F10 cells, apple and mushroom, called BTYR, ATYR and MTYR, respectively, were selected to implement this study. Results showed that TYR inhibitory activities of samples were obviously affected by the above two factors. It was necessary to select the appropriate enzyme according to the problems to be explained. It was speculated that indirectly inhibitory activity reflected the comprehensive effects of samples on TYR catalytic activity and intracellular TYR synthesis pathway, while directly inhibitory activity reflected the effects of samples on TYR catalytic activity. Additionally, kojic acid could be used as a positive control for both B16F10 cells and MTYR models. The TYR inhibitory activity of β-arbutin was complicated and fickle, while that of epigallocatechin gallate (EGCG) was universal and stable, which is to say, EGCG always inhibited TYR activity in a dose-dependent manner. In conclusion, the TYR inhibitory activities of samples were affected by enzyme species and sample addition methods. Compared with the unstable β-arbutin, EGCG was more valuable for clinical research.

Concentration-dependent stimulation of melanin production as well as melanocyte and keratinocyte proliferation by melatonin in human eyelid epidermis

It remains unclear how the multifunctional indoleamine neurohormone, melatonin, alters melanin production and melanocytes within intact human epidermis under physiologically relevant conditions. In the current pilot study, we aimed to clarify this in long-term organ-cultured, full-thickness human eyelid skin, selected for its clinically recognized sensitivity to pigmentation-modulatory hormones. Warthin-Starry histochemistry showed that 100 μM melatonin significantly increased epidermal melanin content and melanocyte dendricity after 6 days of organ culture, even though tyrosinase activity in situ was inhibited, as assessed by quantitative immunohistomorphometry. While the higher melatonin dose tested here (200 μM) did not change epidermal melanization, but again inhibited tyrosinase activity, it increased the number and proliferation of both gp100⁺ epidermal melanocytes and keratinocytes as well as protein expression of the premelanosomal marker, gp100, ex vivo. Contrary to most previous studies, these eyelid skin organ culture results suggest that long-term melatonin application exerts overall stimulatory, dose-dependent effects on the epidermal pigmentary unit within intact human skin, which appear surprisingly tyrosinase-independent. While these provocative preliminary findings require further work-up and independent confirmation, they encourage one to systematically explore whether prolonged melatonin therapy can (re-)stimulate melanogenesis and increase the pool/activity of epidermal melanocytes in hypopigmented skin lesions.

The effect of Medicago sativa extract and light on skin hypopigmentation disorders in C57/BL6 mice

BACKGROUND

Vitiligo is a common depigmentation skin disease that affects the quality of life in many patients.

AIMS

This study aims to investigate the effect of Medicago sativa methanol extract on the treatment of skin hypopigmentation disorders.

METHODS

Antioxidant activity and phytochemical constituents of the extract were determined using DDPH assay, Folin-Ciocalteu, AlCl_3, and HPLC-MS/MS analysis. Oil in water (o/w) creams were prepared to contain the methanolic extract, and applied to hydroquinone-induced depigmentation in vivo model and further challenged in combination with UVA light exposure. Skin and hair colors were visually scored and evaluated at different time intervals, and histopathological examinations of skin layers and hair follicles were performed.

RESULTS

A total phenolic content of 187.70 mg/g, equivalent to gallic acid, and total flavonoid content of 21.97 mg/g, equivalent to quercetin, were recorded. Extract showed 71% antioxidant activity. Moreover, the HPLC-MS/MS detection revealed the presence of 18 compounds including P-coumaric acid and antioxidants flavonoids, of those are seven compounds not previously detected in this species. The in vivo study showed a remarkable skin and hair pigmentation effect on plant extract-treated groups, compared to the reference, placebo, and control groups. Histopathological examinations showed the growth of colored hair follicles in the dermis and epidermis layers of the extract-treated mice.

CONCLUSION

The study suggests the use of M. sativa extract in enhancing the pigmentation process in hypopigmented skin and hair if combined with UVA light. Therefore, M. sativa extract can be considered a potential treatment for vitiligo.

Cephalosporin as Potent Urease and Tyrosinase Inhibitor: Exploration through Enzyme Inhibition, Kinetic Mechanism, and Molecular Docking Studies

In present study, eleven cephalosporin drugs were selected to explore their new medically important enzyme targets with inherited safety advantage. To this end, selected drugs with active ingredient, cefpodoxime proxetil, ceftazidime, cefepime, ceftriaxone sodium, cefaclor, cefotaxime sodium, cefixime trihydrate, cephalexin, cefadroxil, cephradine, and cefuroxime, were evaluated and found to have significant activity against urease (IC50 = 0.06 ± 0.004 to 0.37 ± 0.046 mM) and tyrosinase (IC50 = 0.01 ± 0.0005 to 0.12 ± 0.017 mM) enzymes. Urease activity was lower than standard thiourea; however, tyrosinase activity of all drugs outperforms (ranging 6 to 18 times) the positive control: hydroquinone (IC50 = 0.18 ± 0.02 mM). Moreover, the kinetic analysis of the most active drugs, ceftriaxone sodium and cefotaxime sodium, revealed that they bind irreversibly with both the enzymes; however, their mode of action was competitive for urease and mixed-type, preferentially competitive for tyrosinase enzyme. Like in vitro activity, ceftriaxone sodium and cefotaxime sodium docking analysis showed their considerable binding affinity and significant interactions with both urease and tyrosinase enzymes sufficient for downstream signaling responsible for observed enzyme inhibition in vitro, purposing them as potent candidates to control enzyme-rooted obstructions in future.

Kojic Acid Showed Consistent Inhibitory Activity on Tyrosinase from Mushroom and in Cultured B16F10 Cells Compared with Arbutins

Kojic acid, β-arbutin, α-arbutin, and deoxyarbutin have been reported as tyrosinase inhibitors in many articles, but some contradictions exist in their differing results. In order to provide some explanations for these contradictions and to find the most suitable compound as a positive control for screening potential tyrosinase inhibitors, the activity and inhibition type of the aforementioned compounds on monophenolase and diphenolase of mushroom tyrosinase (MTYR) were studied. Their effects on B16F10 cells melanin content, tyrosinase (BTYR) activity, and cell viability were also exposed. Results indicated that α-arbutin competitively inhibited monophenolase activity, whereas they uncompetitively activated diphenolase activity of MTYR. β-arbutin noncompetitively and competitively inhibited monophenolase activity at high molarity (4000 µM) and moderate molarity (250–1000 µM) respectively, whereas it activated the diphenolase activity of MTYR. Deoxyarbutin competitively inhibited diphenolase activity, but could not inhibit monophenolase activity and only extended the lag time. Kojic acid competitively inhibited monophenolase activity and competitive–noncompetitive mixed-type inhibited diphenolase activity of MTYR. In a cellular experiment, deoxyarbutin effectively inhibited BTYR activity and reduced melanin content, but it also potently decreased cell viability. α-arbutin and β-arbutin dose-dependently inhibited BTYR activity, reduced melanin content, and increased cell viability. Kojic acid did not affect cell viability at 43.8–700 µM, but inhibited BTYR activity and reduced melanin content in a dose-dependent manner. Therefore, kojic acid was considered as the most suitable positive control among these four compounds, because it could inhibit both monophenolase and diphenolase activity of MTYR and reduce intercellular melanin content by inhibiting BTYR activity without cytotoxicity. Some explanations for the contradictions in the reported articles were provided.

Sargahydroquinoic Acid Suppresses Hyperpigmentation by cAMP and ERK1/2-Mediated Downregulation of MITF in α-MSH-Stimulated B16F10 Cells

Hyperpigmentation diseases of the skin require topical treatment with depigmenting agents. We investigated the hypopigmented mechanisms of sargahydroquinoic acid (SHQA) in alpha-melanocyte-stimulating hormone (α-MSH)-stimulated B16F10 cells. SHQA reduced cellular tyrosinase (TYR) activity and melanin content in a concentration-dependent manner and attenuated the expression of TYR and tyrosinase-related protein 1 (TRP1), along with their transcriptional regulator, microphthalmia-associated transcription factor (MITF). SHQA also suppressed α-MSH-induced cellular production of cyclic adenosine monophosphate (cAMP), which inhibited protein kinase A (PKA)-dependent cAMP-responsive element-binding protein (CREB) activation. Docking simulation data showed a potential binding affinity of SHQA to the regulatory subunit RIIβ of PKA, which may also adversely affect PKA and CREB activation. Moreover, SHQA activated ERK1/2 signaling in B16F10 cells, stimulating the proteasomal degradation of MITF. These data suggest that SHQA ameliorated hyperpigmentation in α-MSH-stimulated B16F10 cells by downregulating MITF via PKA inactivation and ERK1/2 phosphorylation, indicating that SHQA is a potent therapeutic agent against skin hyperpigmentation disorders.

Arbutin as a Skin Depigmenting Agent with Antimelanogenic and Antioxidant Properties

Arbutin is a compound of hydroquinone and D-glucose, and it has been over 30 years since there have been serious studies on the skin lightening action of this substance. In the meantime, there have been debates and validation studies about the mechanism of action of this substance as well as its skin lightening efficacy and safety. Several analogs or derivatives of arbutin have been developed and studied for their melanin synthesis inhibitory action. Formulations have been developed to improve the stability, transdermal delivery, and release of arbutin, and device usage to promote skin absorption has been developed. Substances that inhibit melanin synthesis synergistically with arbutin have been explored. The skin lightening efficacy of arbutin alone or in combination with other active ingredients has been clinically evaluated. Combined therapy with arbutin and laser could give enhanced depigmenting efficacy. The use of arbutin causes dermatitis rarely, and caution is recommended for the use of arbutin-containing products, especially from the viewpoint that hydroquinone may be generated during product use. Studies on the antioxidant properties of arbutin are emerging, and these antioxidant properties are proposed to contribute to the skin depigmenting action of arbutin. It is hoped that this review will help to understand the pros and cons of arbutin as a cosmetic ingredient, and will lead to future research directions for developing advanced skin lightening and protecting cosmetic products.

New Benzimidazothiazolone Derivatives as Tyrosinase Inhibitors with Potential Anti-Melanogenesis and Reactive Oxygen Species Scavenging Activities

Thirteen (Z)-2-(substituted benzylidene)benzimidazothiazolone analogs were synthesized and evaluated for their inhibitory activity against mushroom tyrosinase. Among the compounds synthesized, compounds 1–3 showed greater inhibitory activity than kojic acid (IC₅₀ = 18.27 ± 0.89 μM); IC₅₀ = 3.70 ± 0.51 μM for 1; IC₅₀ = 3.05 ± 0.95 μM for 2; and IC₅₀ = 5.00 ± 0.38 μM for 3, and found to be competitive tyrosinase inhibitors. In silico molecular docking simulations demonstrated that compounds 1–3 could bind to the catalytic sites of tyrosinase. Compounds 1–3 inhibited melanin production and cellular tyrosinase activity in a concentration-dependent manner. Notably, compound 2 dose-dependently scavenged ROS in B16F10 cells. Furthermore, compound 2 downregulated the protein kinase A (PKA)/cAMP response element-binding protein (CREB) and mitogen-activated protein kinase (MAPK) signaling pathways, which led to a reduction in microphthalmia-associated transcription factor (MITF) expression, and decreased tyrosinase, tyrosinase related protein 1 (TRP1), and TRP2 expression, resulting in anti-melanogenesis activity. Hence, compound 2 may serve as an anti-melanogenic agent against hyperpigmentation diseases.

New Insight into the Interactions of Arbutin with Mushroom Tyrosinase

As a safe substitute for hydroquinone, β-arbutin, a natural plant substance, and its synthetic counterpart, α-arbutin, are used in depigmentation formulations. However, there are debatable points regarding the impact of arbutin on tyrosinase and the pigmentation process. To shed light on this issue, the effects of Pyrus biossieriana leaves extract (PbLE) and β-arbutin, extracted from PbLE, on mushroom tyrosinase (MT) were comprehensively examined. The study was focused on cresolase activity as the characteristic reaction of a tyrosinase. Kinetics studies disclosed that β-arbutin can modulate MT monophenolase activity from inhibition to activation or vice versa. β-Arbutin inhibited L-tyrosine (LTy) oxidation at concentrations < 0.3 mM but it increased (more than 400%) the enzymatic oxidation of L-tyrosine at the concentrations > 0.3 mM. An opposite pattern (activation then inhibition) was observed when a synthetic substrate was used instead of LTy. Computational studies, focused on the heavy chain of MT, indicated that β-arbutin effect could be overruled by the enzyme's ability to provide the ligand with a non-specific binding site (MTPc). A plausible mechanism was presented to show the influence of MTPc on the substrate pose in the active site. The possible determinant correlation between the findings of this research and the current studies on human tyrosinase role in the pigmentation process has been presented.

Valorization of Bio-Residues from the Processing of Main Portuguese Fruit Crops: From Discarded Waste to Health Promoting Compounds

Food processing generates a large amount of bio-residues, which have become the focus of different studies aimed at valorizing this low-cost source of bioactive compounds. High fruit consumption is associated with beneficial health effects and, therefore, bio-waste and its constituents arouse therapeutic interest. The present work focuses on the main Portuguese fruit crops and revises (i) the chemical constituents of apple, orange, and pear pomace as potential sources of functional/bioactive compounds; (ii) the bioactive evidence and potential therapeutic use of bio-waste generated in the processing of the main Portuguese fruit crops; and (iii) potential applications in the food, nutraceutical, pharmaceutical, and cosmetics industries. The current evidence of the effect of these bio-residues as antioxidant, anti-inflammatory, and antimicrobial agents is also summarized. Conclusions of the revised data are that these bio-wastes hold great potential to be employed in specific nutritional and pharmaceutical applications.

Comparison of 2% deoxyarbutin and 4% hydroquinone as a depigmenting agent in healthy individuals: A double-blind randomized controlled clinical trial

BACKGROUND

Hydroquinone, which is considered the gold standard skin depigmenting agent, has been associated with multiple side effects. Lately, deoxyarbutin has been suggested to be an alternative of hydroquinone with better safety profile.

OBJECTIVE

To compare the depigmenting effect of 2% deoxyarbutin and 4% hydroquinone sera.

METHODS

This double-blind randomized controlled study was done on the right and left arms of healthy participants. Subjects were instructed to apply either 2% deoxyarbutin or 4% hydroquinone serum on each arm, which were randomly labeled as group A and B, every day for 12 weeks. Chromameter and mexameter analysis were done every 2 weeks to assess the color change. Paired and independent t-tests were used to assess the color change within and between both groups, respectively.

RESULTS

A total of 59 females participated in this study. Both groups showed significant improvement in skin depigmentation as shown by the chromameter (increase in L* value) and mexameter (decrease in melanin index) analysis at the end of the study (p < 0.05). No significant difference in both parameters was observed between both groups (p > 0.05). No side effects were reported in either groups.

CONCLUSION

2% deoxyarbutin and 4% hydroquinone sera showed comparable depigmenting efficacy.

Roles of inflammation factors in melanogenesis (Review)

The occurrence of hyperpigmentation or hypopigmentation after inflammation is a common condition in dermatology and cosmetology. Since the exact mechanism of its occurrence is not yet known, prevention and treatment are troublesome. Previous studies have confirmed that α-melanocyte-stimulating hormone, stem cell factor and other factors can promote melanogenesis-related gene expression through the activation of signaling pathways. Recent studies have revealed that a variety of inflammatory mediators can also participate in the regulation of melanogenesis in melanocytes. In this review, we summarized that interleukin-18, interleukin-33, granulocyte-macrophage colony stimulating factor, interferon-γ, prostaglandin E2 have the effect of promoting melanogenesis, while interleukin-1, interleukin-4, interleukin-6, interleukin-17 and tumor necrosis factor can inhibit melanogenesis. Further studies have found that these inflammatory factors may activate or inhibit melanogenesis-related signaling pathways (such as protein kinase A and mitogen activated protein kinase) by binding to corresponding receptors, thereby promoting or inhibiting the expression of melanogenesis-related genes and regulating skin pigmentation processes. This suggests that the development of drugs or treatment methods from the perspective of regulating inflammation can provide new ideas and new targets for the treatment of pigmented dermatosis. This review outlines the current understanding of the inflammation factors' roles in melanogenesis.

Topical treatment strategies to manipulate human skin pigmentation

Skin pigmentation is a result of melanin produced by melanocytes in the epidermis. Melanocyte activity, along with the type and distribution of melanins, is the main driver for diversity of skin pigmentation. Dark melanin acts to protect against the deleterious effects of ultraviolet (UV) radiation, including photo-aging and skin cancer formation. In turn, UV radiation activates skin melanocytes to induce further pigmentation (i.e., "tanning pathway"). The well-characterized MSH/MC1R-cAMP-MITF pathway regulates UV-induced melanization. Pharmacologic activation of this pathway ("sunless tanning") represents a potential strategy for skin cancer prevention, particularly in those with light skin or the "red hair" phenotype who tan poorly after UV exposure due to MC1R inactivating polymorphisms. Skin hyperpigmentation can also occur as a result of inflammatory processes and dermatological disorders such as melasma. While primarily of cosmetic concern, these conditions can dramatically impact quality of life of affected patients. Several topical agents are utilized to treat skin pigmentation disorders. Here, we review melanogenesis induced by UV exposure and the agents that target this pathway.

Novel Amide Derivatives as Potent Tyrosinase Inhibitors; In-vitro, In-vivo Antimelanogenic Activity and Computational Studies

BACKGROUND

Tyrosinase is involved in the melanin biosynthesis and the abnormal accumulation of melanin pigments leading to hyperpigmentation disorders. Controlling the melanogenesis could be an important strategy for treating abnormal pigmentation.

METHODS

In the present study, a series of amide derivatives (3a-e and 5a-e) were synthesized aiming to inhibit tyrosinase activity and melanin production. All derivatives were screened for tyrosinase inhibition in a cell-free system. The possible interactions of amide derivatives with tyrosinase enzyme and effect of these interactions on tyrosinase structure were checked by molecular docking in silico and by Circular Dichroism (CD) studies, respectively. The most potent amide derivative (5c) based on cell-free experiments, was further tested for cellular ROS inhibition and for tyrosinase activity using mouse skin melanoma (B16F10) cells.

RESULTS

The tyrosinase inhibitory concentration (IC50) for tested compounds was observed between the range of 68 to 0.0029 µg/ml with a lowest IC50 value of compound 5c which outperforms the reference arbutin and kojic acid. The cellular tyrosinase activity and melanin quantification assay demonstrate that 15µg/ml of 5c attenuates 36% tyrosinase, 24% melanin content of B16F10 cells without significant cell toxicity. Moreover, the zebrafish in vivo assay reveals that 5c effectively reduces melanogenesis without perceptible toxicity. Furthermore, the molecular docking demonstrates that compound 5c interacts with copper ions and multiple amino acids in the active site of tyrosinase with best glide score (-5.387 kcal/mol), essential for mushroom tyrosinase inhibition and the ability to diminish the melanin synthesis in-vitro and in-vivo.

CONCLUSION

Thus, we propose compound 5c as a potential candidate to control tyrosinase rooted hyperpigmentation in the future.

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

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

Anti-melanogenic effects of oyster hydrolysate in UVB-irradiated C57BL/6J mice and B16F10 melanoma cells via downregulation of cAMP signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Pacific oyster (Crassostrea gigas) has been used to treat pigmentary disorders such as freckles, melasma, and moles in Korea.

AIM OF THE STUDY

We aimed to investigate the inhibitory effects of oyster hydrolysate (OH) on melanogenesis in B16F10 melanoma cells and UVB-irradiated C57BL/6J mice.

MATERIAL AND METHODS

The molecular weight distribution and peptide sequences of OH were detected using MALDI-TOF and UHPLC. To evaluate the anti-melanogenic effects of OH, cell viability, melanin content, tyrosinase activity, intracellular cyclic adenosine monophosphate (cAMP) and protein expressions levels were measured in B16F10 cells. In addition, OH was orally administered to UVB-irradiated mice for 9 weeks. After sacrificing the mice, the whitening effects of OH were evaluated based on histological observations and protein expression levels.

RESULTS

In B16F10 cells, OH decreased melanin content and tyrosinase activity in a dose-dependent manner. OH exhibited anti-melanogenic activities via downregulation of cAMP signaling pathway, which consequently decreased melanin synthesis. In UVB-irradiated mice groups, OH decreased the number of active melanocytes and melanin granules. The expression of tyrosinase-related proteins and microphthalmia-associated transcription factor (MITF) decreased in the OH-administered groups.

CONCLUSIONS

These results show that OH inhibits melanin synthesis in B16F10 cells via downregulation of cAMP signaling pathway and in UVB-irradiated mice, by decreasing the number of active melanocytes and melanin granules.

Anti-melanogenesis potential of a new series of Morita-Baylis-Hillman adducts in B16F10 melanoma cell line

Melanin is a natural polymer pigment which provides skin photoprotection against ultraviolet radiation. An excessive synthesis of melanin leads to hyperpigmentation disorders. Tyrosinase catalyzes the rate limiting steps on melanogenesis. Therefore, tyrosinase inhibitors have potential applications in medicine and cosmetic fields. We carried out herein the screening of a family of cyclic Morita-Baylis-Hillman adducts (MBH) to find out their effects on tyrosinase activity and on melanogenesis in murine melanoma B16F10 cell line. Kinetic analysis of tyrosinase inhibition showed that compounds 1a (2-hydroxymethyl) cyclohex-2-enone) and 3f (diethyl (1-(6-oxocyclohex-1-en-1-yl) ethyl-phosphonate) were competitive inhibitors, whereas the compound 2b (6-oxocyclohex-1-en-1-yl) ethyl acetate) was a non-competitive one. Additionally we have found that (1a, 2b and 3f) compounds had a strong melanogenesis inhibition effect in isobutylmethylxanthine (IBMX)-treated murine melanoma B16F10 cells when tested at low and non cytotoxic dose (10-50 µM), by attenuating the melanin production, intracellular tyrosinase activity and tyrosinase expression. Thus, we suggest that these compounds could be used as effective skin-whitening agents.

De Novo Molecular Design of a Novel Octapeptide That Inhibits In Vivo Melanogenesis and Has Great Transdermal Ability

Cutaneous hyperpigmentation from excess melanogenesis causes serious pigmentary disorders and even melasma. Short peptides (SPs) are garnering attention lately owing to their therapeutic potential in dermatological diseases and low systemic side effects. Here, we show an octapeptide, ansin2, designed de novo from antioxidant SPs we previously reported, significantly inhibiting melanogenesis in B16 cells by decreasing tyrosinase production via regulating the MITF pathway. Ansin2 could also inhibit tyrosinase function by covering its catalytic pocket, which was simulated in docking and LIGPLOT studies. Topical application of ansin2 exhibited evident protection in UVB-induced pigmentation in guinea pig models both in terms of prophylaxis and treatment. Interestingly, unlike other hydrophilic and peptidic drugs that need delivery systems, ansin2 can be efficiently delivered topically to the epidermis and dermis per se without an affiliated moiety. Given that ansin2 lacks unwanted toxicities and immunogenicity, it holds great potential in treating hyperpigmentation in the cosmetics and pharmaceutical industries.

Sargaquinoic acid ameliorates hyperpigmentation through cAMP and ERK-mediated downregulation of MITF in α-MSH-stimulated B16F10 cells

Hyperpigmentation disorders of the skin adversely influence the quality of life. We previously demonstrated the hypopigmenting properties of the ethanolic extract from Sargassum serratifolium and identified sargaquinoic acid (SQA) as an active component. The current study aims to investigate the hypopigmenting action of SQA in α-melanocyte stimulating hormone (α-MSH)-stimulated B16F10 cells. SQA attenuated cellular melanin synthesis by inhibiting the expression of the melanogenic enzymes, including tyrosinase (TYR), tyrosinase-related protein 1 (TRP1), and TRP2. SQA also inhibited cellular TYR activity in a dose-dependent manner. Reduced intracellular cAMP accumulation by SQA treatment resulted in the suppressed phosphorylation of cAMP-responsive element-binding protein (CREB), leading to the downregulation of microphthalmia-associated transcription factor (MITF) in α-MSH-stimulated B16F10 cells. SQA increased the phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and MITF (Ser73), inducing proteasomal degradation of MITF. SQA showed high binding affinity to the cAMP binding domain of PKA; the direct binding of SQA to PKA may exert an additional inhibitory effect on the PKA-dependent CREB activation. Our data demonstrated that SQA suppressed melanin production through the cAMP/CREB- and ERK1/2-mediated downregulation of MITF in α-MSH-stimulated B16F10 cells and SQA has a potential therapeutic agent for the treatment of skin hyperpigmentation disorders.

Investigation of the pro-apoptotic effects of arbutin and its acetylated derivative on murine melanoma cells

Arbutin, a natural polyphenol isolated from the bearberry plant Arctostaphylos uvaursi, possesses whitening and anticancer properties. The effects of arbutin on melanogenesis and its pro-apoptotic effect on B16 murine melanoma cells have not yet been reported. In the present study, acetylated arbutin was prepared in order to improve the biological effects of arbutin, and it was found to significantly inhibit the biosynthesis of melanin and tyrosinase activity compared with parent arbutin in B16 murine melanoma cells. Interestingly, only acetylated arbutin strongly inhibited B16 murine melanoma cell migration in a dose-dependent manner. Both arbutin and acetylated arbutin significantly reduced cell viability, promoted cell apoptosis, caused G1 cell cycle arrest and induced mitochondrial disruption in B16 murine melanoma cells. Furthermore, reduced expression of B-cell lymphoma‑extra large (Bcl-xL) and Bcl-2 were observed in arbutin- and acetylated arbutin-treated cells. Therefore, arbutin and acetylated arbutin were found to exert pro-apoptotic effects on B16 murine melanoma cells, mediated through the mitochondrial pathway. The findings of the present study also support the use of acetylated arbutin as a new potential candidate agent for skin whitening and melanoma treatment.

Action of tyrosinase on alpha and beta-arbutin: A kinetic study

The known derivatives from hydroquinone, α and β-arbutin, are used as depigmenting agents. In this work, we demonstrate that the oxy form of tyrosinase (oxytyrosinase) hydroxylates α and β-arbutin in ortho position of the phenolic hydroxyl group, giving rise to a complex formed by met-tyrosinase with the hydroxylated α or β-arbutin. This complex could evolve in two ways: by oxidizing the originated o-diphenol to o-quinone and deoxy-tyrosinase, or by delivering the o-diphenol and met-tyrosinase to the medium, which would produce the self-activation of the system. Note that the quinones generated in both cases are unstable, so the catalysis cannot be studied quantitatively. However, if 3-methyl-2-benzothiazolinone hydrazone hydrochloride hydrate is used, the o-quinone is attacked, so that it becomes an adduct, which can be oxidized by another molecule of o-quinone, generating o-diphenol in the medium. In this way, the system reaches the steady state and originates a chromophore, which, in turn, has a high absorptivity in the visible spectrum. This reaction allowed us to characterize α and β-arbutin kinetically as substrates of tyrosinase for the first time, obtaining a Michaelis constant values of 6.5 ± 0.58 mM and 3 ± 0.19 mM, respectively. The data agree with those from docking studies that showed that the enzyme has a higher affinity for β-arbutin. Moreover, the catalytic constants obtained by the kinetic studies (catalytic constant = 4.43 ± 0.33 s-1 and 3.7 ± 0.29 s-1 for α and β-arbutin respectively) agree with our forecast based on 13 C NMR considerations. This kinetic characterization of α and β-arbutin as substrates of tyrosinase should be taken into account to explain possible adverse effects of these compounds.

Efficient Percutaneous Delivery of the Antimelanogenic Agent Glabridin Using Cationic Amphiphilic Chitosan Micelles

Partially myristoylated chitosan pyrrolidone carboxylate (PMCP) is a cationic amphiphilic chitosan derivative. Glabridin (Glab) from licorice root extracts is a hydrophobic antimelanogenic agent. Here we assessed the effects of cationic Glab-containing polymeric micelles derived from PMCP (Glab/PMCP-PM) on the ability of Glab to penetrate the skin and inhibit melanogenesis using a human skin model. The amount of Glab absorbed 24 h after the application of Glab/PMCP-PM was approximately four times higher than that of conventional oil-in-water micelles (control) prepared using Tween 60. Further, the release of IL-1α, a mediator of inflammation, was not detected. Treatment with Glab/PMCP-PM significantly increased the inhibition of melanogenesis compared with control. The inhibition of melanogenesis depends upon the enhanced ability of Glab to penetrate the skin, particularly the epidermis. Moreover, the inhibition of melanogenesis and the cationic potential of the Glab/PMCP-PM levels were increased by the cationic phospholipid copolymer. Therefore, Glab/PMCP-PM shows potential as an effective transdermal delivery system for treating skin hyperpigmentation.

Anti-melanogenic effects of Aster spathulifolius extract in UVB-exposed C57BL/6J mice and B16F10 melanoma cells through the regulation of MAPK/ERK and AKT/GSK3β signalling

OBJECTIVES

Pharmacological studies of Aster spathulifolius Maxim(AS) have demonstrated its anti-allergy, anti-viral and anti-obesity effects, however, its anti-melanogenic effects is still unclear. In this study, the effects of AS extract (ASE) on the inhibition of melanin synthesis were investigated in vitro and in vivo.

METHODS

To perform this study, the contents of melanin and tyrosinase activity were analysed in B16F10 melanoma cells. Western blotting was carried out to determine the underlyling mechanism. Additionally, we investigated the effect of this extract on hyperpigmentation in C57bL/6J mice induced by 3, 6 and 9 weeks of UVB irradiation.

KEY FINDINGS

AS extract led to reduced melanin synthesis through the regulation of MITF and its downstream signals. Furthermore, ASE increased the phosphorylation of MAPK/ERK and Akt/GSK3β signalling pathway components. In vivo study, hypopigmentation effects were also observed. The melanocyte activity and the distribution of melanin granules were decreased in UVB-irradiated mice treated with ASE.

CONCLUSIONS

These results suggest that the ASE may be promising as an active anti-melanogenic component, and further investigations should be performed regarding its potential as a whitening agent in the field of cosmetics.

Berberine regulates melanin synthesis by activating PI3K/AKT, ERK and GSK3β in B16F10 melanoma cells

Berberine, an isoquinoline alkaloid, has a wide range of beneficial properties, including anti-bacterial, anti-inflammatory, anti-cancer, and cholesterol-lowering effects. Recently findings suggest that berberine improves glucose and lipid metabolism disorders. In the present study, we examined the mechanism underlying the inhibitory effect of berberine on α-melanocyte-stimulating hormone (α-MSH)-stimulated B16F10 melanoma cells. The results showed that berberine attenuated α-MSH induction of the microphthalmia-associated transcription factor (MITF) and tyrosinase in a dose-dependent manner. To elucidate the mechanism underlying the inhibitory effect of berberine, we examined the effect of α-MSH-stimulated phosphorylation of PI3K/AKT, ERK, and GSK3β. The results showed that treatment with berberine resulted in a reduction in the phosphorylation of PI3K/AKT, ERK, and GSK3β. Taken together, the results suggested that berberine inhibits melanin synthesis and tyrosinase activity by downregulating the expression of MITF and tyrosinase. Thus, these findings may contribute to the potential application of berberine in the prevention and treatment of skin pigmentation disorders.

Synthesis, characterization and biological evaluation of paeonol thiosemicarbazone analogues as mushroom tyrosinase inhibitors

A series of hydroxy- and methoxy-substituted paeonol thiosemicarbazone analogues were synthesized as potential tyrosinase inhibitors and their inhibitory effects on mushroom tyrosinase and inhibitory mechanism were evaluated. Paeonol thiosemicarbazone analogues have been found exhibiting more remarkable inhibition than their indexcompounds on mushroom tyrosinase. Among them, compound 2,4-dihydroxy acetophenone-4-phenyl-3-thiosemicarbazone (d1) had the most potent inhibition activity with the IC50 value of 0.006 ± 0.001 mM, displayed as a reversible competitive inhibitor. The inhibitory ability of o- or p-substituted acetophenone thiosemicarbazones was: di-substituted acetophenone thiosemicarbazones>mono-substituted acetophenone thiosemicarbazones>non-substituted acetophenone thiosemicarbazones. Copper ions chelation assay explained that compound d1 exhibited competitive inhibition by forming a chelate with the copper ions at the catalytic domain of tyrosinase as well as indicate a 1.5:1 binding ratio of compound d1 with copper ions. In the fluorescence spectrum study, compound d1 behaved stronger fluorescence quenching on tyrosinase towards d1-Cu(2+) complex, inhibiting tyrosinase mainly by means of chelating the two copper ions in the active site. The newly synthesized compounds may serve as structural templates for designing and developing novel tyrosinase inhibitors.

Anti-melanogenic effect of (Z)-5-(2,4-dihydroxybenzylidene) thiazolidine-2,4-dione, a novel tyrosinase inhibitor

We synthesized (Z)-5-(2,4-dihydroxybenzylidene)thiazolidine-2,4-dione (MHY498) as a potential tyrosinase inhibitor. MHY498 potently inhibited mushroom tyrosinase activity (mean IC50 = 3.55 μM) in a dose-dependent manner. MHY498 was more potent than the well-known tyrosinase inhibitor, kojic acid (mean IC50 = 22.79 μM). When tested in B16F10 melanoma cells treated with α-melanocyte stimulating hormone (α-MSH), MHY498 inhibited murine tyrosinase activity and decreased melanin production without inducing cytotoxicity. Docking models showed that the binding affinity of MHY498 to tyrosinase was higher than that of kojic acid, and docking simulation results indicated that the tyrosinase binding moieties of MHY498 and kojic acid were similar. Western blotting showed that tyrosinase inhibition by MHY498 partly resulted from the expressional modulations of tyrosinase and its transcription factor, microphthalmia-associated transcription factor, via the cAMP-PKA-CREB pathway. These findings suggest that MHY498 could be useful as an antimelanogenic agent for the prevention and treatment of diseases associated with skin pigmentation.

A novel synthesized tyrosinase inhibitor: (E)-2-((2,4-dihydroxyphenyl)diazenyl)phenyl 4-methylbenzenesulfonate as an azo-resveratrol analog

We synthesized a novel series of (E)-2-((substituted phenyl)diazenyl)phenyl 4-methylbenzenesulfonate derivatives (2 and 3) and (E)-2-((substituted phenyl)diazenyl)phenol derivatives (4 and 5), and conducted an evaluation in order to determine their inhibitory effects on mushroom tyrosinase, with the aim of discovering a tyrosinase inhibitor. Most of the compounds (3-5) exhibited higher inhibitory effects than kojic acid (IC(50) = 49.08 µM), a representative tyrosinase inhibitor. A novel synthesized compound, (E)-2-((2,4-dihydroxyphenyl)diazenyl)phenyl 4-methylbenzenesulfonate (3), showed the best results with an IC(50) of 17.85 µM, and showed competitive inhibition on Lineweaver-Burk plots, as further confirmed by the docking results. In addition, active compounds 3-5 were not cytotoxic to cultured B16F10 cells at the concentrations tested, and inhibited both tyrosinase and melanin synthesis. Therefore the active compounds (3-5) might be considered excellent candidates for use in the development of therapeutic agents for diseases associated with hyperpigmentation.

High-yield enzymatic bioconversion of hydroquinone to α-arbutin, a powerful skin lightening agent, by amylosucrase

α-Arbutin (α-Ab) is a powerful skin whitening agent that blocks epidermal melanin biosynthesis by inhibiting the enzymatic oxidation of tyrosine and L-3,4-dihydroxyphenylalanine (L-DOPA). α-Ab was effectively synthesized from hydroquinone (HQ) by enzymatic biotransformation using amylosucrase (ASase). The ASase gene from Deinococcus geothermalis (DGAS) was expressed and efficiently purified from Escherichia coli using a constitutive expression system. The expressed DGAS was functional and performed a glycosyltransferase reaction using sucrose as a donor and HQ as an acceptor. The presence of a single HQ bioconversion product was confirmed by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). The HQ bioconversion product was isolated by silica gel open column chromatography and its chemical structure determined by 1H and 13C nuclear magnetic resonance (NMR). The product was determined to be hydroquinone-O-α-D-glucopyranoside with a glucose molecule linked to HQ through an α-glycosidic bond. However, the production yield of the transfer reaction was significantly low (1.3%) due to the instability of HQ in the reaction mixture. The instability of HQ was considerably improved by antioxidant agents, particularly ascorbic acid, implying that HQ is labile to oxidation. A maximum yield of HQ transfer product of 90% was obtained at a 10:1 molar ratio of donor (sucrose) and acceptor (HQ) molecules in the presence of 0.2 mM ascorbic acid.

Evaluation of in vitro and in vivo anti-melanogenic activity of a newly synthesized strong tyrosinase inhibitor (E)-3-(2,4 dihydroxybenzylidene)pyrrolidine-2,5-dione (3-DBP)

BACKGROUND

Tyrosinase inhibitors have become increasingly important because of their ability to inhibit the synthesis of the pigment melanin. A search for new agents with strong tyrosinase activity led to the synthesis of the tyrosinase inhibitor (E)-3-(2,4-dihydroxybenzylidene)pyrrolidine-2,5-dione (3-DBP).

METHODS

The inhibitory effect of 3-DBP on tyrosinase activity and melanin production was examined in murine melanoma B16F10 cells. Additional experiments were performed using HRM2 hairless mice to demonstrate the effects of 3-DBP in vivo.

RESULTS

The novel compound, 3-DBP, showed an inhibitory effect against mushroom tyrosinase (IC50=0.53 μM), which indicated that it was more potent than the well-known tyrosinase inhibitor kojic acid (IC50=8.2 μM). When tested in B16F10 melanoma cells treated with α-melanocyte stimulating hormone (α-MSH), 3-DBP also inhibited murine tyrosinase activity, which in turn induced a decrease in melanin production in these cells. The anti-melanogenic effect of 3-DBP was further verified in HRM2 hairless mice. The skin-whitening index (L value) of HRM2 hairless mice treated with 3-DBP before irradiation with UVB was greater than that of UVB-irradiated mice that were not treated with 3-DBP.

GENERAL SIGNIFICANCE

The newly synthesized 3-DBP has a potent inhibitory effect on tyrosinase. In addition to an in vitro investigation of the effects of 3-DBP on tyrosinase, in vivo studies using an HRM2 hairless mouse model demonstrated the anti-melanogenic potency of 3-DBP. Our newly synthesized 3-DBP showed efficient tyrosinase inhibitory effect in vivo and in vitro. Our finding suggests that 3-DBP can be an effective skin-whitening agent.

Kojic acid-induced IL-6 production in human keratinocytes plays a role in its anti-melanogenic activity in skin

BACKGROUND

Kojic acid is a fungal metabolite widely used in medicinal and cosmetic formulations as a skin-lightening agent based on its de-pigmenting activity. Although in human clinical studies kojic acid has been shown to be effective in the treatment of hyper-pigmentation disorders such as melasma, the reasons for its apparent lack of anti-melanogenic activity in cultured mammalian melanocytes are unclear.

OBJECTIVES

This study was aimed to elucidate pharmacological mechanisms of the in vivo anti-melanogenic activity of kojic acid in human skin.

METHODS

A primary human melanocyte and keratinocyte co-culture system was used to evaluate whether kojic-acid-induced changes in keratinocytes were associated with anti-melanogenic activities in melanocytes. The cytokine secretion profiles in response to kojic acid were analyzed.

RESULTS

Kojic acid increased interleukin (IL)-6 and IL-8 production in melanocyte/keratinocyte co-cultures; however, IL-6 directly inhibited melanogenesis whereas IL-8 did not. In melanocyte monocultures, kojic acid did not increase IL-6 production whereas in keratinocyte monocultures it significantly up-regulated IL-6 gene and protein expression. Therefore, the up-regulation of IL-6 in melanocyte/keratinocyte co-cultures seems to be originated from kojic acid-induced changes in keratinocytes. Anti-IL-6 antibody treatment antagonized the anti-melanogenic effect of kojic acid on the co-cultures.

CONCLUSIONS

The pharmacological mechanism of kojic acid to explain clinically effective anti-melanogenic activity on hyper-pigmented skin is associated with the kojic acid-induced IL-6 production in keratinocytes. The cross-talk between melanocytes and keratinocytes should be determined in future studies on the pharmacological mechanisms of clinically effective dermatological drugs acting on the epidermis.

Characterization of a novel tyrosinase inhibitor, (2RS,4R)-2-(2,4-dihydroxyphenyl)thiazolidine-4-carboxylic acid (MHY384)

BACKGROUND

We synthesized (2RS,4R)-2-(2,4-dihydroxyphenyl)thiazolidine-4-carboxylic acid (MHY384) as a potential tyrosinase inhibitor and investigated its antityrosinase activity.

METHODS

The structure of MHY384 was established using (1)H and (13)C NMR spectroscopy and mass spectral analyses. To investigate dual mechanisms of action of MHY384 for the inhibition of melanin synthesis, we confirmed the inhibitory effect of tyrosinase catalytic activity of MHY384. Then, we confirmed the inhibitory effect of MHY384 on transcription of tyrosinase mRNA through alpha-MSH-induced cAMP-PKA-MITF signaling. In addition, we supported the inhibitory mechanism of MHY384 against tyrosinase using a kinetic study and docking programs.

RESULTS

To determine how MHY384 regulates melanogenesis, we measured melanin levels and expression of the genes for microphthalmia-associated transcription factor (MITF) and tyrosinase in α-melanocyte-stimulating hormone (α-MSH)-induced B16F10 melanoma cells. MHY384 potently inhibited tyrosinase activity and melanin production in B16F10 melanoma cells. Through docking models, we were able to construct the tertiary structure of mushroom tyrosinase and simulate its docking with MHY384. The result supports that MHY384 strongly interacts with tyrosinase residues in the active site and it can directly inhibit tyrosinase. To investigate additional mechanisms of action of MHY384, we confirmed that the inhibition of tyrosinase activity was found to be due to the modulation of the expression of tyrosinase and its transcription factor, MITF, through cAMP, which regulates protein kinase A.

CONCLUSIONS

This study strongly indicates that the depigmenting effect of MHY384 results from the down-regulation of MITF and tyrosinase through direct tyrosinase inhibition.

GENERAL SIGNIFICANCE

Our findings suggest that MHY384 can be an effective skin-whitening agent.

Tyrosinase small interfering RNA effectively suppresses tyrosinase gene expression in vitro and in vivo

Tyrosinase is a bifunctional enzyme which oxidizes the initial step of melanin biosynthesis, that is, conversion of tyrosine to dopa and subsequently dopa to dopaquinone. It is a glycosylated protein and a major regulator of melanogenesis. To date, many approaches have been tried to regulate tyrosinase activity and melanin content. To that end, we screened small interfering RNA sequences for sequence-inhibited tyrosinase expression in B16 cells and in C57BL/6 mice. We analyzed tyrosinase mRNA levels by quantitative real-time PCR and determined tyrosinase activity and melanin content at 24, 48, and 72 hours after transfection. Results showed that siNM_011661_001 was the most efficient small interfering RNA sequence in suppressing tyrosinase mRNA expression, and cells transfected with this sequence showed lower tyrosinase activity. Moreover, intravitreous injection of siNM_011661_001 in C57BL/6 mice induced an efficient and stable gene-specific inhibition of expression at the posttranscriptional level.

Proteomics analysis of A375 human malignant melanoma cells in response to arbutin treatment

Although the toxicogenomics of A375 human malignant melanoma cells treated with arbutin have been elucidated using DNA microarray, the proteomics of the cellular response to this compound are still poorly understood. In this study, we performed proteomic analyses to investigate the anticancer effect of arbutin on the protein expression profile in A375 cells. After treatment with arbutin (8 microg/ml) for 24, 48 and 72 h, the proteomic profiles of control and arbutin-treated A375 cells were compared, and 26 differentially expressed proteins (7 upregulated and 19 downregulated proteins) were identified by MALDI-Q-TOF MS and MS/MS. Among these proteins, 13 isoforms of six identical proteins were observed. Bioinformatic tools were used to search for protein function and to predict protein interactions. The interaction network of 14 differentially expressed proteins was found to be correlated with the downstream regulation of p53 tumor suppressor and cell apoptosis. In addition, three upregulated proteins (14-3-3G, VDAC-1 and p53) and five downregulated proteins (ENPL, ENOA, IMDH2, PRDX1 and VIME) in arbutin-treated A375 cells were validated by RT-PCR analysis. These proteins were found to play important roles in the suppression of cancer development.

Inhibitory effects of plant extracts on tyrosinase, L-DOPA oxidation, and melanin synthesis

For medical, pharmacological, and cosmetic reasons, the demand for effective and safe depigmentating agents has increased. In this study, 101 plant extracts (methanol or water extracts) were screened for their inhibitory activities against tyrosinase, (L-3, 4,-dihydroxyphenylalanine) L-DOPA oxidation, and melanin biosynthesis in B16 mouse melanoma cells. Of the extracts examined, 31 showed over 50% inhibition of mushroom tyrosinase at a concentration of 666 microg/Ml, and 11 inhibited L-DOPA auto-oxidation at this concentration. In particular, extracts of Broussonetia kazinoki var. humilis (leaves and stems), Broussonetia papyrifera (leaves and bark), Cornus officinalis (fruit), Rhus javanica (gallnut), and Pinus densiflora (leaves) inhibited both tyrosinase activity and L-DOPA oxidation in a concentration-dependent manner. Seventeen plant extracts that inhibited tyrosinase were further tested for their inhibitory effects on melanogenesis. In B16 mouse melanoma cells, extracts of Acorus gramineus, Capsella bursa-pastoris, Morus bombycis, Perilla frutescens var. crispa, Quercus dentate (bark), Rhus javanica (gallnut), Schizopepon bryoniaefolius, or Sophora flavescens markedly inhibited (>50%) melanin synthesis at 50 microg/Ml. These plants represent a potential source of novel whitening agents for ultraviolet (UV)-sensitive skin.

Inhibition of Melanogenesis by Selina-4(14),7(11)-dien-8-one Isolated from Atractylodis Rhizoma Alba

To develop effective skin-lightening agents, we tested medicinal herbal extracts for their melanogenic-inhibitory activities. We isolated a sesquiterpenoid compound from the extract of Atractylodis Rhizoma Alba using the bioactivity-guided fractionation and identified it as selina-4(14),7(11)-dien-8-one (compound 1) with spectroscopic methods. Compound 1 dramatically reduced melanin synthesis of melan-a cells without any apparent cytotoxicity. Compound 1 did not inhibit cell-free tyrosinase activity but decreased tyrosinase activity in melanocytes. These effects were attributed to reduced expression of melanogenic enzymes such as tyrosinase, tyrosinase-related protein 1 (TRP-1), and tyrosinase-related protein 2 (TRP-2). These results suggest that compound 1 may be an effective skin-lightening agent that regulates expression of melanogenic enzymes.

Topical Methimazole as a New Treatment for Postinflammatory Hyperpigmentation: Report of the First Case

We have previously shown that the peroxidase inhibitor methimazole (1-methyl-2-mercapto imidazole; MMI) is a noncytotoxic inhibitor of melanin production in cultured B16 melanocytes. It was further demonstrated that the topical application of 5% MMI on brown guinea pig skin for 6 weeks causes a significant reduction in the amount of epidermal melanin, resulting in visually recognizable cutaneous depigmentation. Herein, we report a 27-year-old male with postinflammatory hyperpigmentation (due to acid burn), successfully treated with topical MMI as a new skin depigmenting agent. Topical 5% MMI caused a moderate to marked improvement of the hyperpigmented lesions within 6 weeks of once-daily application. Topical MMI was well tolerated by the patient and did not affect the level of serum thyroid hormones (free thyroxin, free triiodothyronine and the thyroid-stimulating hormone). Unlike most known depigmenting agents, such as hydroquinone and kojic acid, MMI is a noncytotoxic, nonmutagenic compound, and it is possible that MMI could serve as a novel agent for the treatment of hyperpigmentary disorders in human.

Inhibitory effects of active compounds isolated from safflower (Carthamus tinctorius L.) seeds for melanogenesis

In order to develop a new skin whitening agent, safflower (Carthamus tinctorius L.) seeds were evaluated for melanogenesis inhibitory activity and its active principles were identified following activity-guided isolation. The 80% aqueous methanol extract and ethyl acetate fraction from safflower seeds showed a significant inhibition for mushroom tyrosinase. Three active compounds, N-feruloylserotonin, N-(p-coumaroyl)serotonin, and acacetin, were isolated from the ethyl acetate fraction as the active principles. Compared with arbutin (IC50=0.223 mM), the IC50 values of these compounds were 0.023, 0.074, and 0.779 mM for N-feruloylserotonin, N-(p-coumaroyl)serotonin, and acacetin, respectively. It was also found that N-feruloylserotonin and N-(p-coumaroyl)serotonin strongly inhibited the melanin production of Streptomyces bikiniensis and B16 melanoma cells in comparison with a known melanogenesis inhibitor, arbutin.

Inhibitory effects of alpha-arbutin on melanin synthesis in cultured human melanoma cells and a three-dimensional human skin model

We studied the inhibitory effects of 4-hydroxyphenyl alpha-glucopyranoside (alpha-arbutin) on melanogenesis in cultured human melanoma cells, HMV-II, and in a three-dimensional cultured human skin model. alpha-Arbutin showed no inhibitory effect on HMV-II cell growth at a concentration below 1.0 mM. Melanin synthesis in cells treated with alpha-arbutin at 0.5 mM decreased to 76% of that in non-treated cells. The cellular tyrosinase activity of HMV-II cells also significantly decreased, while the expression of its mRNA was not affected. Melanin synthesis in a human skin model was also evaluated by the macro- and microscopic observation of its pigmentation as well as by quantitative measurements of melanin. Treatment of the human skin model with 250 microg of alpha-arbutin did not inhibit cell viability, while melanin synthesis was reduced to 40% of that in the control. These results indicate that alpha-arbutin is an effective and safe ingredient for skin-lightening.

The effect of antisense tyrosinase-related protein 1 on melanocytes and malignant melanoma cells

BACKGROUND

Tyrosinase-related proteins (TRPs) include tyrosinase, TRP-1 and TRP-2. The functions of tyrosinase and TRP-2 have been determined, but the biological role of TRP-1 is still controversial and is not well known in humans.

OBJECTIVES

To study further the biological role of the human TRP-1 gene in melanocytes and melanoma cells.

METHODS

TRP-1 cDNA was subcloned into eukaryotic expression vector pcDNA3.1 in the reverse direction, and antisense recombinant vector was transfected into melanocytes and a melanoma cell line using Lipofectamine 2000. Positive cells were selected by geneticin. TRP-1 mRNA level was measured by reverse transcription-polymerase chain reaction (RT-PCR), and TRP-1 protein level by Western blot. Cell cycles were determined by flow cytometry, and the activity of tyrosinase was evaluated by L-DOPA reaction. Light microscopy, electron microscopy and flow cytometry were used to observe cell morphology and apoptosis. For in vivo assays, the antitumour activity of antisense TRP-1 against the malignant melanoma (MM) cell line, Libr, was evaluated in an animal-tumour model of subcutaneous tumours.

RESULTS

Positive transfected cells steadily expressed TRP-1 antisense RNA. RT-PCR and Western blot showed a low level of TRP-1 mRNA and TRP-1 protein, respectively. Cell cycles were blocked in the G1 stage, and the activity of tyrosinase decreased significantly (P < 0.01). Light and electron microscopy showed abnormal cell morphology, and apoptosis was detected. The neoplasia activity of antisense TRP-1-transfected MM cells was significantly lower than that of MM cells (P < 0.01).

CONCLUSIONS

TRP-1 plays an important role in the proliferation, morphology and tyrosinase activity of melanocytes and melanoma cells.

Identification of oxidation product of arbutin in mushroom tyrosinase assay system

In order to elucidate whitening mechanisms of arbutin (hydroquinone-O-beta-D-glucopyranoside), its effects on mushroom tyrosinase were analyzed by spectrophotometric, polarographic, and HPLC experiments. It was found that as soon as catalytic amounts of L-DOPA become available as a cofactor, arbutin acts as a monophenol substrate. A significant enzymatic product was identified as 3,4-dihydroxyphenyl-O-beta-D-glucopyranoside by NMR and MS experiments.