Suppression of melanogenesis by induction of endogenous intracellular metallothionein in human melanocytes

Phoenix dactylifera L. Seed Extract Exhibits Antioxidant Effects and Attenuates Melanogenesis in B16F10 Murine Melanoma Cells by Downregulating PKA Signaling

Background: The mode of action of Phoenix dactylifera seed extract in skin care has never been explored. Methods: P. dactylifera L. seeds were extracted by ultrasonic extraction. The antioxidant characteristics of the extract were determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-di-(3-ethylbenzthiazoline sulfonic acid) (ABTS⁺) assays and scavenging methods. The total phenolic content, reducing capacity, iron (II) ion-chelation, and intracellular reactive oxygen species (ROS)-scavenging capacities were also investigated. The effects of P. dactylifera L. seed extract on melanogenesis were evaluated spectrophotometrically by a mushroom tyrosinase activity assay, determination of intracellular tyrosinase activity, and melanin content. The expression levels of melanogenesis-related proteins were analyzed by Western blotting. Results: The results revealed that the P. dactylifera L. seed extract exerted apparent antioxidant capacity and significantly decreased intracellular ROS content at concentrations of 0.245 and 0.49 (mg/mL). Furthermore, the extract decreased the expression of melanocortin 1 receptor (MC1R), microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein-1 (TRP1), and tyrosinase-related protein-2 (TRP2), and inhibited melanogenesis in B16F10 cells. Conclusions: Our results revealed that P. dactylifera L. seed extract attenuated melanogenesis in B16F10 cells by downregulating protein kinase A (PKA) signaling pathways. Hence, the extract could be used as a type of skin-whitening agent in skin care products.

Traditional Chinese Herbal Medicine for Whitening

Melanin is the chief pigment responsible for the pigmentation of human skin. Increasing evidence indicates that traditional Chinese drugs with skin-whitening effects are attracting the attention of consumers and researchers because they are perceived to be milder, safer, and healthier than synthetic alternatives. This commentary summarizes the current research on Chinese herbal medicines that inhibit melanin and their biological activities. The findings presented in this study suggest that these traditional Chinese herbal medicines might be potential candidates for novel skin-whitening agents.

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.

Snails in the sun: Strategies of terrestrial gastropods to cope with hot and dry conditions

Terrestrial gastropods do not only inhabit humid and cool environments but also habitat in which hot and dry conditions prevail. Snail species that are able to cope with such climatic conditions are thus expected to having developed multifaceted strategies and mechanisms to ensure their survival and reproduction under heat and desiccation stress. This review paper aims to provide an integrative overview of the numerous adaptation strategies terrestrial snails have evolved to persist in hot and dry environments as well as their mutual interconnections and feedbacks, but also to outline research gaps and questions that remained unanswered. We extracted relevant information from more than 140 publications in order to show how biochemical, cellular, physiological, morphological, ecological, thermodynamic, and evolutionary parameters contribute to provide an overall picture of this classical example in stress ecology. These mechanisms range from behavioral and metabolic adaptations, including estivation, to the induction of chaperones and antioxidant enzymes, mucocyte and digestive gland cell responses and the modification and frequency of morphological features, particularly shell pigmentation. In this context, thermodynamic constraints call for processes of complex adaptation at varying levels of biological organization that are mutually interwoven. We were able to assemble extensive, mostly narrowly focused information from the literature into a web of network parameters, showing that future work on this subject requires multicausal thinking to account for the complexity of relationships involved in snails' adaptation to insolation, heat, and drought.

Vanillic acid in Panax ginseng root extract inhibits melanogenesis in B16F10 cells via inhibition of the NO/PKG signaling pathway

Panax ginseng C. A. Meyer has been widely used in skin care. Our previous study showed that the phenolic acids in ginseng root extract (GRE) impart inhibitory effects on melanogenesis. In this study, we found that as the most abundant component of phenolic acids in GRE, vanillic acid decreased tyrosinase activity and melanin levels with or without α-MSH stimulation and suppressed the expression of microphthalmia-associated transcription factor (MITF) and melanogenic enzymes in B16F10 cells. Furthermore, vanillic acid downregulated NOS activity, nitric oxide (NO) content, cGMP level, guanylate cyclase (GC) and protein kinase G (PKG) activity, and the phosphorylation of cAMP-response element-binding protein (CREB), whereas arbutin had no effect on the NO/PKG pathway. These findings indicate that vanillic acid in GRE suppressed melanogenesis by inhibiting the NO/PKG signaling pathways. This study provides a potential mechanism underlying the inhibitory effect of ginseng on melanogenesis.

MALDI MSI of MeLiM melanoma: Searching for differences in protein profiles

Background

Treatment of advanced cutaneous melanoma remains challenging, and new data on melanoma biology are required. The most widely accepted criteria for the prognostic evaluation of melanoma are histopathological and clinical parameters, and the identification of additional tumor markers is thus of paramount importance. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI), an important tool in cancer research, is useful for unraveling the molecular profile of melanoma.

Methodology/Principal findings

In this report, we used the melanoma-bearing Libechov minipig (MeLiM), a unique animal model that allows observation of the complete spontaneous regression of invasive cutaneous melanoma, to investigate i) the differences between melanoma and healthy skin protein profiles and ii) the proteins potentially involved in spontaneous regression. The MeLiM tissues were cryosected, histologically characterized, analyzed by MALDI MSI, and immunohistologically stained. Multivariate statistical analyses of the MALDI MSI data revealed ten relevant m/z ions, of which the expression levels varied significantly among the studied MeLiM tissues. These ion peaks were used to create mass ion images/maps and visualize the differences between tumor and healthy skin specimens, as well as among histologically characterized tissue regions.

Conclusions/Significance

Protein profiles comprising ten statistically significant mass ion peaks useful for differentiating cutaneous melanoma and healthy skin tissues were determined. Peaks at m/z 3044, 6011, 6140 and 10180 were overexpressed in melanoma compared with healthy skin tissue. More specifically, m/z 6140 was expressed at significantly (p < 0.05) higher levels in normally growing melanoma regions than in regions with early and late spontaneous regression. This study demonstrates the clinical utility of MALDI MSI for the analysis of tissue cryosections at a molecular level.

Candidate genes for shell colour polymorphism in Cepaea nemoralis

The characteristic ground colour and banding patterns on shells of the land snail Cepaea nemoralis form a classic study system for genetics and adaptation as it varies widely between individuals. We use RNAseq analysis to identify candidate genes underlying this polymorphism. We sequenced cDNA from the foot and the mantle (the shell-producing tissue) of four individuals of two phenotypes and produced a de novo transcriptome of 147,397 contigs. Differential expression analysis identified a set of 1,961 transcripts that were upregulated in mantle tissue. Sequence variant analysis resulted in a set of 2,592 transcripts with single nucleotide polymorphisms (SNPs) that differed consistently between the phenotypes. Inspection of the overlap between the differential expression analysis and SNP analysis yielded a set of 197 candidate transcripts, of which 38 were annotated. Four of these transcripts are thought to be involved in production of the shell’s nacreous layer. Comparison with morph-associated Restriction-site Associated DNA (RAD)-tags from a published study yielded eight transcripts that were annotated as metallothionein, a protein that is thought to inhibit the production of melanin in melanocytes. These results thus provide an excellent starting point for the elucidation of the genetic regulation of the Cepaea nemoralis shell colour polymorphism.

UVB induces epidermal 11β-hydroxysteroid dehydrogenase type 1 activity in vivo

Detrimental consequences of ultraviolet radiation (UVR) in skin include photoageing, immunosuppression and photocarcinogenesis, processes also significantly regulated by local glucocorticoid (GC) availability. In man, the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) generates the active GC cortisol from cortisone (or corticosterone from 11-dehydrocorticosterone in rodents). 11β-HSD1 oxo-reductase activity requires the cofactor NADPH, generated by hexose-6-phosphate dehydrogenase. We previously demonstrated increased 11β-HSD1 levels in skin obtained from photoexposed versus photoprotected anatomical regions. However, the direct effect of UVR on 11β-HSD1 expression remains to be elucidated. To investigate the cutaneous regulation of 11β-HSD1 following UVR in vivo, the dorsal skin of female SKH1 mice was irradiated with 50, 100, 200 and 400 mJ/cm(2) UVB. Measurement of transepidermal water loss, 11β-HSD1 activity, mRNA/protein expression and histological studies was taken at 1, 3 and 7 days postexposure. 11β-HSD1 and hexose-6-phosphate dehydrogenase mRNA expression peaked 1 day postexposure to 400 mJ/cm(2) UVB before subsequently declining (days 3 and 7). Corresponding increases in 11β-HSD1 protein and enzyme activity were observed 3 days postexposure coinciding with reduced GC receptor mRNA expression. Immunofluorescence studies revealed 11β-HSD1 localization to hyperproliferative epidermal keratinocytes in UVB-exposed skin. 11β-HSD1 expression and activity were also induced by 200 and 100 (but not 50) mJ/cm(2) UVB and correlated with increased transepidermal water loss (indicative of barrier disruption). UVB-induced 11β-HSD1 activation represents a novel mechanism that may contribute to the regulation of cutaneous responses to UVR exposure.

Versatile antitumor potential of isoxanthohumol: Enhancement of paclitaxel activity in vivo

Isoxanthohumol (IXN), a prenylated flavonoid from hops, exhibits diverse biological activities, e.g. antitumor, antiinflammatory, antioxidant and antiangiogenic. In this study, the effect of IXN is evaluated on two melanoma cell lines with dissimilar molecular background, B16 and A375. The treatment of both cell lines with IXN resulted in dose-dependent decrease of cell viability. Abolished viability was in correlation with changed morphology and loss of dividing potential indicating phenotypical alteration of both tested cell lines. While modified B16 cells underwent the process of non-classic differentiation followed by tyrosinase activity without enhancement of melanin content, inhibition of Notch 1, β-catenin and Oct-3/4 was observed in A375 cells indicating loss of their pluripotent characteristics. In parallel with this, distinct subpopulations in both cell cultures entered the process of programmed cell death-apoptosis in a caspase independent manner. The described changes in cultures upon exposure to IXN could be connected with the suppression of reactive oxygen (ROS) and nitrogen species (RNS) induced by the drug. Despite the differences in which IXN promoted modifications in the upper part of the PI3K/Akt and MEK-ERK signaling pathways between B16 and A375 cells, p70S6K and its target S6 protein in both types of melanoma cells, after transient activation, became inhibited. In addition to direct input of IXN on cell viability, this study for the first time shows that IXN strongly sensitizes melanoma cells to the treatment with paclitaxel in vivo, in concordance with data obtained in vitro on B16 cells as well as their highly invasive F10 subclone.

Inhibitory effects of adlay extract on melanin production and cellular oxygen stress in B16F10 melanoma cells

The aim of this study was to determine the effects of adlay extract on melanin production and the antioxidant characteristics of the extract. The seeds were extracted by the supercritical fluid CO₂ extraction (SFE) method. The effect of adlay extract on melanin production was evaluated using mushroom tyrosinase activity assay, intracellular tyrosinase activity, antioxidant properties and melanin content. Those assays were performed spectrophotometrically. In addition, the expression of melanogenesis-related proteins was determined by western blotting. The results revealed that the adlay extract suppressed intracellular tyrosinase activity and decreased the amount of melanin in B16F10 cells. The adlay extract decreased the expression of microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase related protein-1 (TRP-1) and tyrosinase related protein-2 (TRP-2). The extract also exhibited antioxidant characteristics such as free radical scavenging capacity and reducing power. It effectively decreased intracellular reactive oxygen species (ROS) levels in B16F10 cells. We concluded that the adlay extract inhibits melanin production by down-regulation of MITF, tyrosinase, TRP-1 and TRP-2. The antioxidant properties of the extract may also contribute to the inhibition of melanogenesis. The adlay extract can therefore be applied as an inhibitor of melanogenesis and could also act as a natural antioxidant in skin care products.

Poly-γ-glutamate from Bacillus subtilis inhibits tyrosinase activity and melanogenesis

Poly-γ-glutamate (γ-PGA) has been considered as one of the most promising biomaterials with a wide range of applications, but there has been no report that directly shows the anti-tyrosinase and anti-melanogenesis properties of γ-PGA. In the present study, we investigated the inhibitory effects of γ- PGA with low molecular weight (Mw; lγ-PGA) and high Mw (hγ-PGA) on mushroom tyrosinase and murine tyrosinase activities and on melanogenesis in B16 melanoma cells. First, we showed that both lγ-PGA and hγ-PGA could effectively inhibit mushroom tyrosinase activities including monophenolase and diphenolase activities in a dose-dependent manner. Second, both lγ-PGA and hγ-PGA showed strong anti-tyrosinase activity and anti-melanogenesis in B16 melanoma cells. Third, both lγ-PGA and hγ-PGA inhibited forskolin-induced tyrosinase activity and melanogenesis by decreasing the levels of intracellular reactive oxygen species and nitric oxide while increasing the catalase activity in B16 cells. This is the first report on the anti-melanogenesis effect of γ-PGA, which suggests that γ-PGA could have a potential in the cosmetic skin whitening business, therapeutic applications and the food industry.

Dual bioactivities of essential oil extracted from the leaves of Artemisia argyi as an antimelanogenic versus antioxidant agent and chemical composition analysis by GC/MS

The study was aimed at investigating the antimelanogenic and antioxidant properties of essential oil when extracted from the leaves of Artemisia argyi, then analyzing the chemical composition of the essential oil. The inhibitory effect of the essential oil on melanogenesis was evaluated by a mushroom tyrosinase activity assay and B16F10 melanoma cell model. The antioxidant capacity of the essential oil was assayed by spectrophotometric analysis, and the volatile chemical composition of the essential oil was analyzed with gas chromatography-mass spectrometry (GC/MS). The results revealed that the essential oil significantly inhibits mushroom tyrosinase activity (IC₅₀ = 19.16 mg/mL), down-regulates B16F10 intracellular tyrosinase activity and decreases the amount of melanin content in a dose-dependent pattern. Furthermore, the essential oil significantly scavenged 2,2-diphenyl-1-picryl-hydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzthiazoline- 6-sulphonic acid) ABTS radicals, showed an apparent reduction power as compared with metal-ion chelating activities. The chemicals constituents in the essential oil are ether (23.66%), alcohols (16.72%), sesquiterpenes (15.21%), esters (11.78%), monoterpenes (11.63%), ketones (6.09%), aromatic compounds (5.01%), and account for a 90.10% analysis of its chemical composition. It is predicted that eucalyptol and the other constituents, except for alcohols, in the essential oil may contribute to its antioxidant activities. The results indicated that essential oil extracted from A. argyi leaves decreased melanin production in B16F10 cells and showed potent antioxidant activity. The essential oil can thereby be applied as an inhibitor of melanogenesis and could also act as a natural antioxidant in skin care products.

Salicin regulates the expression of functional 'youth gene clusters' to reflect a more youthful gene expression profile

There are a variety of biological mechanisms that contribute to specific characteristics of ageing skin; for example, the loss of skin structure proteins, increased susceptibility to UV-induced pigmentation and/or loss of hydration. Each of these biological processes is influenced by specific groups of genes. In this research, we have identified groups of genes associated with specific clinical signs of skin ageing and refer to these as functional 'youth gene clusters'. In this study, quantitative real-time polymerase chain reaction (qPCR) was used to investigate the effects of topical application of salicin in regulating the expression of functional 'youth gene clusters' to reflect a more youthful skin profile and reduce the appearance of attributes associated with skin ageing. Results showed that salicin significantly influences the gene expression profiles of treated human equivalent full-thickness skin, by regulating the expression of genes associated with various biological processes involving skin structure, skin hydration, pigmentation and cellular differentiation. Based on the findings from this experiment, salicin was identified as a key ingredient that may regulate functional 'youth gene clusters' to reflect a more youthful gene expression profile by increasing the expression of genes responsible for youthful skin and decreasing the expression of genes responsible for the appearance of aged skin.

The two faces of metallothionein in carcinogenesis: photoprotection against UVR-induced cancer and promotion of tumour survival

Metallothionein is a multi-functional protein that protects the host against toxic heavy metals. Under stressful situations it can protect against oxidative damage, contribute to tissue repair, modulate immune responses and limit inflammatory processes. Recently, metallothionein's role in ultraviolet radiation (UVR)-induced injury has been investigated. These studies have shown that when metallothionein is upregulated following exposure to UVR, it can protect against UVR-induced damage and the subsequent development of skin cancer. We propose that this initial protection is achieved through its anti-oxidant role resulting in reduced oxidative stress, reduced apoptosis, reduced NFkappaB activation and enhanced repair of DNA damage. However, once UVR-induced neoplasia has occurred, the cancer cells can hijack metallothionein's protective functions, resulting in increased tumour progression and malignancy. These two discordant sets of attributes are context-dependent, and represent the two faces of metallothionein.

Role of antioxidants in the skin: anti-aging effects

Intracellular and extracellular oxidative stress initiated by reactive oxygen species (ROS) advance skin aging, which is characterized by wrinkles and atypical pigmentation. Because UV enhances ROS generation in cells, skin aging is usually discussed in relation to UV exposure. The use of antioxidants is an effective approach to prevent symptoms related to photo-induced aging of the skin. In this review, the mechanisms of ROS generation and ROS elimination in the body are summarized. The effects of ROS generated in the skin and the roles of ROS in altering the skin are also discussed. In addition, the effects of representative antioxidants on the skin are summarized with a focus on skin aging.

Inhibitory effect of the water-soluble polymer-wrapped derivative of fullerene on UVA-induced melanogenesis via downregulation of tyrosinase expression in human melanocytes and skin tissues

The C60-fullerene derivatives are expected, as novel and potent anti-oxidants, to more effectively protect skin cells against oxidative stress. UVA-induced oxidative stress is considered to promote melanogenesis and serious skin damage. The effect of any fullerene derivatives on UVA-induced melanogenesis is still unknown. Here, we evaluated effects of a water-soluble polyvinylpyrrolidone (PVP)-wrapped fullerene derivative (named "Radical Radical Sponge" because of its anti-oxidant ability) on melanogenesis, which was promoted by UVA-irradiation to human melanocytes and skin tissues. Radical Sponge markedly scavenged UVA-induced reactive oxygen species (ROS) inside human melanocytes as shown by fluorometry using the redox indicator CDCFH-DA. After treatment with Radical Sponge or other agents, human melanocytes and skin tissues were irradiated by UVA. Then, cellular melanin content, tyrosinase activity and the ultrastructural change of skin melanosomes were examined. Radical Sponge showed to significantly inhibit UVA-promoted melanogenesis in normal human epidermis melanocytes (NHEM) and human melanoma HMV-II cells within a non-cytotoxicity dose range. As compared with two whitening agents, arbutin and L-ascorbic acid, Radical Sponge demonstrated the stronger anti-melanogenic potential according to spectrophotometric quantification for extracted melanin. In human skin cultures also, UVA-promoted melanin contents were repressed by Radical Sponge according to Fontana-Masson stain, suggesting its ability to repress UVA-induced tanning. Transmission electron microscopic ultrastructural images also proved that UVA-increased melanosomes in human skin tissue were obviously reduced by Radical Sponge. The UVA-enhanced tyrosinase enzymatic activity in NHEM melanocytes was inhibited by Radical Sponge more markedly than by arbutin and L-ascorbic acid. The UVA-enhanced tyrosinase protein expression, together with cell-size fatness and dendrite-formation, was also inhibited more markedly by Radical Sponge according to immunostain and flow cytometry using anti-tyrosinase antibody. Thus the depigmentating action of Radical Sponge might be due to its down-regulating effect on the tyrosinase expression, which is initiated by UVA-caused ROS generation.