UV-induced Melanogenesis Research Articles

Co-Treatment with Phlorotannin and Extracellular Vesicles from Ecklonia cava Inhibits UV-Induced Melanogenesis.

Hyperpigmentation due to ultraviolet (UV)-induced melanogenesis causes various esthetic problems. Phlorotannin (PT) and extracellular vesicles (EVs) derived from various plants suppress melanogenesis pathways. We used UV-exposed keratinocytes and animal skin to determine if co-treatment with PT and EVs from Ecklonia cava (EVE) could inhibit melanogenesis by reducing UV-induced oxidative stress and the expression of the thioredoxin-interacting protein (TXNIP)/nucleotide-binding oligomerization domain-like receptor family pyrin domain containing the 3 (NLRP3)/interleukin-18 (IL-18) pathway, which are upstream signals of the microphthalmia-associated transcription factor. UV exposure increased oxidative stress in keratinocytes and animal skin, as evaluated by 8-OHdG expression, and this effect was reduced by co-treatment with PT and EVE. UV also increased binding between NLRP3 and TXNIP, which increased NLRP3 inflammasome activation and IL-18 secretion, and this effect was reduced by co-treatment with PT and EVE in keratinocytes and animal skin. In melanocytes, conditioned media (CM) from UV-exposed keratinocytes increased the expression of melanogenesis-related pathways; however, these effects were reduced with CM from UV-exposed keratinocytes treated with PT and EVE. Similarly, PT and EVE treatment reduced melanogenesis-related signals, melanin content, and increased basement membrane (BM) components in UV-exposed animal skin. Thus, co-treatment with PT and EVE reduced melanogenesis and restored the BM structure by reducing oxidative stress and TXNIP/NLRP3/IL-18 pathway expression.

Effects of tea polyphenols on UVA-induced melanogenesis via inhibition of α-MSH-MC1R signalling pathway.

IntroductionUltraviolet (UV) irradiation is a major environmental factor affecting photoaging, which is characterized by skin wrinkle formation and hyperpigmentation. Although many factors are involved in the melanogenesis progress, UV is thought to play a major role in tanning. The pathway of α-melanocyte-stimulating hormone (α-MSH)-melanocortin receptor 1 (MC1R) is associated with UV-induced melanogenesis. Thus, α-MSH antagonists may have applications in the prevention of melanogenesis.AimTo investigate the effects of tea polyphenols (TPS) on pigmentation, and further explore the underlying mechanism.Material and methodsHuman keratinocyte cell line (HaCaT) cells and Human epidermal melanocytes (HEM) were exposed to UVA and treated with different concentrations of TPS or Nonapeptide-1 acetate salt (N-1A). Then, cell viability, melanin content, and tyrosinase activity of both kinds of cells were detected. Quantification of α-MSH in HaCaT cells and HEM cells determined by ELISA assays. Immunohistochemistry of HEM cells was employed to further investigate the expression of melanogenesis-related proteins.ResultsThe different concentrations of TPS were found to decrease the melanin content, tyrosinase activity and melanogenesis-related proteins such as microphthalmia-associated transcription factor (MITF), tyrosinase-related protein (TRP)1, and TRP2. Besides, TPS inhibited α-MSH-MC1R signalling through directly suppressed α-MSH expression rather than the down-regulated expression level of MC1R.ConclusionsOur findings indicate that TPS may be a potential whitening agent for use in cosmetics and the medical treatment of hyperpigmentation disorders.

Protective effects of Thai silk sericins and their related mechanisms on UVA-induced phototoxicity and melanogenesis: Investigation in primary melanocyte cells using a proteomic approach

UV radiation causes excess production of melanin as a result of hyperpigmentation and skin disorders. Silk sericin exhibited bioactivities to skin and inhibited UV-induced phototoxicity and melanogenesis in skin cells; however, the mechanism related to sericin against UV-induced melanogenesis has not been investigated. This study aimed to investigate the protective effects of Thai silk sericins against UVA-induced phototoxicity and melanogenesis and their related mechanisms. Thai silk sericins exhibited cytoprotective effects against UV-induced toxicity in human primary melanocytes by attenuation of cytotoxicity, intracellular ROS generation, and mitochondrial potential impairment. Pre- and post-treatment with sericin significantly inhibited melanin synthesis and tyrosinase activity against UVA exposure. In addition, sericin S2 could reduce the basal melanin content in zebrafish embryos. The proteomic analysis demonstrated that Thai silk sericins altered the protein expression in melanocytes especially proteins related to stress, inflammatory, cytokine stimulation, cell proliferation, and cell survival processes that contribute to cytoprotective effect and inhibitory effect on melanogenesis of sericin. Moreover, we demonstrated the novel mechanism of Thai silk sericins in inhibiting UVA-induced melanogenesis via increasing BMP4 expression in MAPK/ERK signaling pathway. These evidences support the potential use of Thai silk sericins in prevention of hyperpigmentation in skin disorders especially after UVA exposure.

Oxidative stress in the skin: Impact and related protection.

Skin, our first interface to the external environment, is subjected to oxidative stress caused by a variety of factors such as solar ultraviolet, infrared and visible light, environmental pollution, including ozone and particulate matters, and psychological stress. Excessive reactive species, including reactive oxygen species and reactive nitrogen species, exacerbate skin pigmentation and aging, which further lead to skin tone unevenness, pigmentary disorder, skin roughness and wrinkles. Besides these, skin microbiota are also a very important factor ensuring the proper functions of skin. While environmental factors such as UV and pollutants impact skin microbiota compositions, skin dysbiosis results in various skin conditions. In this review, we summarize the generation of oxidative stress from exogenous and endogenous sources. We further introduce current knowledge on the possible roles of oxidative stress in skin pigmentation and aging, specifically with emphasis on oxidative stress and skin pigmentation. Meanwhile, we summarize the science and rationale of using three well-known antioxidants, namely vitamin C, resveratrol and ferulic acid, in the treatment of hyperpigmentation. Finally, we discuss the strategy for preventing oxidative stress-induced skin pigmentation and aging.

Critical Role of ATP-P2X7 Axis in UV-Induced Melanogenesis

Purinergic signaling participates in skin physiology and pathology, such as hair growth, wound healing, inflammation, pain, and skin cancer. However, few studies have investigated the involvement of purinergic signaling in skin pigmentation. This study demonstrated that extracellular adenosine 5'-triphosphate (ATP) released from keratinocytes by UVB radiation promotes melanin production in primary human epidermal melanocytes and exvivo skin cultures. Intracellular calcium ion and protein kinase C/CREB signaling contributed to ATP-mediated melanogenesis. Also, P2X7 receptor was proven to play a pivotal role in ATP-mediated melanogenesis because P2X7 receptor blockade abrogated ATP-induced melanin production. In addition, MNT1 cells with P2X7 receptor knockout using CRISPR/Cas9 system did not show any increase in MITF expression when co-cultured with UV-irradiated keratinocytes compared to MNT1 cells with intact P2X7 receptor, which showed increased expression of MITF. In conclusion, our results indicate that the extracellular ATP-P2X7 signaling axis is an adjunctive mechanism in UV-induced melanogenesis. Furthermore, ATP-induced purinergic signaling in melanocytes may alter skin pigmentation.

Apigenin inhibit UV-induced melanogenesis through activation of MIF and PAR-2 expression in keratinocytes

Apigenin inhibit UV-induced melanogenesis through activation of MIF and PAR-2 expression in keratinocytes

Skin protective effect of guava leaves against UV-induced melanogenesis via inhibition of ORAI1 channel and tyrosinase activity.

Ultraviolet (UV) irradiation is a major environmental factor affecting photoageing, which is characterized by skin wrinkle formation and hyperpigmentation. Although many factors are involved in the photoageing process, UV irradiation is thought to play a major role in melanogenesis. Tyrosinase is the key enzyme in melanin synthesis; therefore, many whitening agents target tyrosinase through various mechanisms, such as direct interference of tyrosinase catalytic activity or inhibition of tyrosinase mRNA expression. Furthermore, the highly selective calcium channel ORAI1 has been shown to be associated with UV-induced melanogenesis. Thus, ORAI1 antagonists may have applications in the prevention of melanogenesis. Here, we aimed to identify the antimelanogenesis agents from methanolic extract of guava leaves (Psidium guajava) that can inhibit tyrosinase and ORAI1 channel. The n-butanol (47.47%±7.503% inhibition at 10μg/mL) and hexane (57.88%±7.09% inhibition at 10μg/mL) fractions were found to inhibit ORAI1 channel activity. In addition, both fractions showed effective tyrosinase inhibitory activity (68.3%±0.50% and 56.9%±1.53% inhibition, respectively). We also confirmed that the hexane fraction decreased the melanin content induced by UVB irradiation and the ET-1-induced melanogenesis in murine B16F10 melanoma cells. These results suggest that the leaves of P.guajava can be used to protect against direct and indirect UV-induced melanogenesis.

Foeniculum vulgare extract and its constituent, trans-anethole, inhibit UV-induced melanogenesis via ORAI1 channel inhibition

BackgroundUltraviolet radiation exposure is the most important cause of extrinsic skin aging (photoaging), which causes skin wrinkling and hyperpigmentation. Although many factors are involved in the photoaging process, calcium release-activated calcium channel protein 1 (ORAI1) has been reported to be involved in UV-induced melanogenesis. ObjectiveThe aim of the present study was to find inhibitory effects of the extract of Foeniculum vulgare (fennel) fruits on ORAI1 ion channels and UV-induced melanogenesis in melanoma cells and to identify its active constituents. MethodsActive compounds were isolated and quantitatively analyzed. An electrophysiological assay was performed by using the whole-cell patch-clamp technique. Intracellular free calcium concentration was measured by Fura-2. Tyrosinase activity was evaluated by levodopa colorimetry. Effects of the most active compound on cell viability of murine B16F10 melanoma cells and inhibition of melanin content after UVB irradiation were determined. ResultsF. vulgare fruits extract and its hexane fraction strongly blocked ORAI1 currents and tyrosinase activity and significantly inhibited UV-induced melanogenesis. Of the 13 compounds isolated from the hexane fraction, trans-anethole (TA) exhibited inhibitory effects on ORAI1 (IC50=8.954±1.36μM) and increased cytoplasmic Ca2+ concentrations in response. TA inhibited UV-induced melanogenesis without affecting tyrosinase activity. ConclusionOur findings suggest that the fruits extract of F. vulgare and its active constituent, TA, provide a possible novel approach for treating and preventing UV-induced melanogenesis.

514 Efficacy of apigenin on UV-induced melanogenesis through activation of MIF and PAR-2 expression in keratinocytes

514 Efficacy of apigenin on UV-induced melanogenesis through activation of MIF and PAR-2 expression in keratinocytes

Valencene from the Rhizomes of Cyperus rotundus Inhibits Skin Photoaging-Related Ion Channels and UV-Induced Melanogenesis in B16F10 Melanoma Cells.

Ultraviolet (UV) radiation deeply penetrates skin and causes inflammation and pigmentary changes and triggers immune responses. Furthermore, accumulating evidence suggests that calcium ion channels, such as TRPV1 and ORAI1, mediate diverse dermatological processes including melanogenesis, skin wrinkling, and inflammation. The rhizomes of Cyperus rotundus have been used to treat inflammatory diseases including dermatitis. However, their effects on UV-induced photoaging-related ion channels remain unknown. Therefore, this study was undertaken to evaluate the antagonistic effects of C. rotundus extract and their constituents on TRPV1 and ORAI1 channels. Electrophysiological analysis revealed that valencene (1) isolated from the hexane fraction potently inhibited capsaicin-induced TRPV1 and ORAI1 currents at 90 μM (69 ± 15% and 97 ± 2% at -60 and -120 mV, respectively). The inhibitory effect of 1 on cytoplasmic Ca(2+) concentrations in response to ORAI1 activation (85 ± 2% at 50 μM) was also confirmed. Furthermore, 1 concentration-dependently decreased the melanin content after UVB irradiation in murine B16F10 melanoma cells by 82.66 ± 2.14% at 15 μg/mL. These results suggest that C. rotundus rhizomes have potential therapeutic effects on UV-induced photoaging and indicate that the therapeutic and cosmetic applications of 1 are worth further investigation.

Recent progress in melasma pathogenesis.

Melasma is a common skin pigmentation condition. Given therapeutic difficulty as one of the biggest concerns, understanding of the etiology and pathogenesis of melasma becomes essential. UV irradiation, female sex hormones, and inflammatory processes are addressed as triggering factors with genetic predisposition. The mechanism of UV-induced melanogenesis has been extensively investigated as a model system to study melasma pathogenesis. Hitherto, treatment modalities for melasma are similar to other hyperpigmentation disorders. However, individual triggering factors induce a separate pigmentation disease, whose pathogenic mechanisms and clinical phenotypes are different from the ones encountered in melasma. Fortunately, there have been ongoing updates on melasma pathogenesis with regard to major triggering factors. Presence of certain factors working independently of UV exposure and role of dermal factors and microRNAs are being identified as novel discoveries about melasma pathogenesis. In this review, the melasma pathogenesis is reviewed in association with updated and new findings.

An updated review of melasma pathogenesis

Melasma is a pigmentation disorder characterized by common clinical findings. However, the pathogenic mechanisms involved are heterogeneous in different individuals and ethnic groups. We have reviewed the pathophysiological mechanisms involved in melasma. Although the pathogenesis has not entirely been elucidated thus far, new findings are being identified by research groups. Epidemiologic studies may provide clues on the involvement of genetic factor(s), UV irradiation, or hormones in melasma. Some of the mechanisms of altered skin pigmentation, such as UV-induced pigmentation, may also be applicable to the pathogenesis of melasma. In fact, an increase in similar keratinocyte-derived melanogenic factors and their receptors occur in both UV-induced melanogenesis and melasma. Increased expression of female sex hormone receptors and the identification of the PDZ domain containing 1 (PDZK1) signaling mechanism provide insights to further our understanding of melasma. In addition to keratinocyte-derived paracrine factors, the role of paracrine factors from dermal fibroblasts, such as stem cell factor (SCF) and Wnt inhibitory factor-1 (WIF-1), is elucidated in melasma. Furthermore, the involvement of ion exchangers and microRNAs (miRNAs), such as H19 miRNA (miR-675), are also suggested.

Synthesis of alkyl coumarate esters by celite-bound lipase of Bacillus licheniformis SCD11501

• A water-free reaction system was successfully employed to synthesize a series of alkyl coumarates by using a celite-immobilized lipase from B. licheniformis strain SCD11501. • The optimal yields of methyl coumarate (69.0%), ethyl coumarate (63.1%), propyl coumarate (59.8%) and butyl coumarate (55.1%) were obtained. • A high yield of methyl coumarate was achieved possibly because methyl group may cause relatively less stearic hindrance. • Addition of molecular sieves to the reaction system had a modulatory effect on the ester synthesis. • The characterization of synthesized esters was done by FTIR spectroscopy and 1 H NMR spectra. Coumaric acid and its derivatives are known to inhibit UV-induced melanogenesis, skin erythema, angiogenesis, platelet accumulation and osteoclastogenesis besides regulation of bone formation, anti-oxidant and anti-microbial activities. The present study is a novel piece of work in which the syntheses of a series of alkyl coumarates (methyl coumarate, ethyl coumarate, propyl coumarate and butyl coumarate) have been achieved using celite-immobilized lipase of Bacillus licheniformis strain SCD11501 in a water-free medium at 55 °C under shaking in a chemical reactor. The maximum yield(s) of coumaric acid based esters i.e. methyl coumarate (69.0%), ethyl coumarate (63.1%), n -propyl coumarate (59.8%) and n -butyl coumarate (55.1%) using celite-immobilized lipase could be achieved after optimizing various reaction parameters such as incubation time, incubation temperature, relative molar concentration of reactants, biocatalyst concentration and amount of molecular sieves added to the reaction system. Molecular sieves had an important effect on the ester synthesis resulting in an enhanced yield. Maximum yield was recorded for methyl coumarate (69.0%) possibly because methyl group causes less stearic hindrance to the catalytic site of the lipase due to which it becomes more accessible for immobilized lipase to undergo esterification. The characterization of synthesized esters was done through FTIR spectroscopy and 1 H NMR spectra.

Comparable down-regulation of TYR, TYRP1 and TYRP2 genes and inhibition of melanogenesis by tyrostat, tocotrienol-rich fraction and tocopherol in human skin melanocytes improves skin pigmentation.

Antioxidant has been recognized to inhibit UV-induced melanogenesis. This study aimed to elucidate the molecular mechanism of tyrostat, tocopherol and tocotrienol-rich fraction in inhibiting melanogenesis in human skin melanocytes. Primary culture of melanocytes was exposed to repeated doses of 0.6 J/cm2 UVA for 6 days and treated with tyrostat, tocotrienol-rich fraction or tocopherol alone or in combination. UVA irradiation increased melanin content and tyrosinase activity and up-regulated TYR, TYRP1 and TYRP2 genes. Treatment with tyrostat, tocotrienol-rich fraction or tocopherol decreased melanin content and down-regulated TYR, TYRP1 and TYRP2 genes with decreased tyrosinase activity. Combined treatment exerted better effects as compared to treatment with single compound in decreasing the melanin content and down-regulating TYR, TYRP1 and TYRP2 genes. These findings indicated that tyrostat, tocotrienol-rich fraction and tocopherol inhibit melanogenesis by modulating the expression of genes involved in the regulation of melanin synthesis and inhibiting tyrosinase activity. Tyrostat, tocopherol and tocotrienol-rich fraction possessed anti-melanogenic properties and might be useful in improving skin pigmentation caused by UVA exposure.

Telomere-Mediated Effects on Melanogenesis and Skin Aging

UV-induced melanogenesis (tanning) and "premature aging" or photoaging result in large part from DNA damage. This article reviews data tying both phenomena to telomere-based DNA damage signaling and develops a conceptual framework in which both responses may be understood as cancer-avoidance protective mechanisms.Journal of Investigative Dermatology Symposium Proceedings (2009) 14, 25-31; doi:10.1038/jidsymp.2009.9.

IL-01 UV-induced melanogenesis: A telomere-mediated DNA damage response

IL-01 UV-induced melanogenesis: A telomere-mediated DNA damage response

The melanocortin-1 receptor: red hair and beyond.

Although human pigmentation is genetically complex, to date polymorphism at only 1 locus, the melanocortin-1 receptor (MC1-R), has been associated with physiologic variation in hair and skin color. The MC1-R, a G protein-coupled receptor with 7 transmembrane-spanning domains, plays a key role in determining the type of melanin (eumelanin vs pheomelanin) that is produced within melanocytes. This article begins with an overview of melanocortin receptors, proopiomelanocortin-derived ligands, and the agouti antagonist, with particular focus on their functions in regulating eumelanin and pheomelanin synthesis, including UV-induced melanogenesis. A brief description of mouse-coat-color genetics is then followed by a discussion of human MC1-R variants, which are present in approximately 50% of white populations. We review the increasing evidence that loss-of-function MC1-R mutations largely account for the red hair phenotype in humans (which approximates an autosomal recessive trait) and also have a strong association with fair skin and a decreased ability to tan, with a significant heterozygote effect in individuals without red hair. Finally, we examine recent work showing that loss-of-function MC1-R variants may increase the risk of developing melanoma and nonmelanoma skin cancer beyond their effects on pigmentation phenotype.

Possible involvement of ERK 1/2 in UVA-induced melanogenesis in cultured normal human epidermal melanocytes.

UV-induced melanogenesis is a well known physiological response of human skin exposed to solar radiation; however, the signaling molecules involved in the stimulation of melanogenesis in melanocytes following UV exposure remain unclear. In this study we induced melanogenesis in vitro in normal human epidermal melanocytes using a single irradiation with UVA at 1 kJ/m2 and examined the potential involvement of mitogen-activated protein kinases (MAPK) as UVA-responsive signaling molecules in those cells. UVA irradiation did not affect the proliferation of melanocytes, but it did increase tyrosinase mRNA expression, which reached a maximum level 4 hr after UVA irradiation. The amount of tyrosinase protein, as quantitated by immunoblotting, was also increased at 24 hr following UVA irradiation. Among the MAPK examined, extracellular signal-related kinase (ERK) 1/2 was phosphorylated within 15 min of UVA irradiation, but no such phosphorylation was observed for c-Jun N-terminal kinases (JNK) or p38. Accordingly, the activity of ERK1/2 was also increased shortly after UVA irradiation. These responses of ERK1/2 to UVA irradiation were markedly inhibited when cells were pre-treated with N-acetyl-L-cysteine, an antioxidant, or with suramin, a tyrosine kinase receptor inhibitor. The formation of (6-4)photoproducts or cyclobutane pyrimidine dimers was not detected in cellular DNA after UVA irradiation. These findings suggest that a single UVA irradiation-induced melanogenesis is associated with the activation of ERK1/2 by upstream signals that originate from reactive oxygen species or from activated tyrosine kinase receptors, but not from damaged DNA.

The Melanocortin‐1 Receptor and Human Pigmentation

alpha-Melanocyte stimulating hormone (alpha-MSH) is known to be the main physiologic regulator for integumental pigmentation of various vertebrate species. However, the role of alpha-MSH and related melanocortins in the regulation of human cutaneous pigmentation is only beginning to be understood. Cloning of the melanocortin-1 receptor (MC1R), and the feasibility of establishing normal human epidermal melanocyte cultures have made it possible to demonstrate direct and specific biological effects of alpha-MSH on these cells. It is now recognized that both alpha-MSH and ACTH have similar mitogenic and melanogenic effects on human epidermal melanocytes. These effects are mediated by binding of these hormones to the specific MC1R that recognizes them both with similar affinity. Human MC1R is homologous to its mouse counterpart in that its activation leads to stimulation of eumelanin synthesis. MC1R is also the binding site for agouti signaling protein (ASP), the product of the agouti locus. Human epidermal melanocytes respond to purified recombinant mouse or human ASP, with a reduction in basal tyrosinase activity, and complete abrogation of the mitogenic and melanogenic effects of alpha-MSH. These results suggest that ASP induces pheomelanin synthesis by competing with alpha-MSH for binding to the MC1R. This receptor seems to be subject to regulation by a variety of paracrine and/or autocrine factors that are synthesized in response to exposure of the skin to ultraviolet radiation (UVR). Activation of MC1R seems to be pivotal for UV-induced melanogenesis, since stimulation of the cAMP pathway plays a key role in the melanogenic response of human epidermal melanocytes. The melanogenic response to UVR might be influenced by the presence of allelic variants of the MC1R gene. Allelic variants have been identified and shown to be associated with red hair, poor tanning ability, and possibly melanoma. The possible influence of these variants on the function of the MC1R needs to be investigated, in order to understand the physiological consequence of these mutations. Also, the interaction of alpha-MSH with other factors that are known to affect pigmentation needs to be better understood in order to define the role possible of this hormone and its receptor in acquired human cutaneous hyper- or hypopigmentation.

DNA photodamage stimulates melanogenesis and other photoprotective responses.

Ultraviolet (UV) irradiation is a major source of environmental damage to skin. Melanin pigmentation protects against this damage by absorbing UV photons and UV-generated free radicals before they can react with DNA and other critical cellular components; and UV-induced melanogenesis or tanning is widely recognized as exposed skin's major defense against further UV damage. This article reviews extensive data suggesting DNA damage or DNA repair intermediates directly triggers tanning and other photoprotective responses. Evidence includes the observations that tanning is enhanced in cultured pigment cells by accelerating repair of UV-induced cyclobutane pyrimidine dimers or by treating the cells with UV-mimetic DNA-damaging chemicals. Moreover, small single stranded DNA fragments such as thymidine dinucleotides (pTpT), the substrate for almost all DNA photoproducts, also stimulates tanning when added to cultured pigment cells or applied topically to intact skin. In bacteria, single stranded DNA generated by DNA damage or its repair activates a protease that in turn derepresses over 20 genes whose protein products enhance DNA repair and otherwise promote cell survival, a phenomenon termed the SOS response. Interestingly, pTpT also enhances repair of UV-induced DNA damage in human cells and animal skin, at least in part by activating the tumor suppressor protein and transcription factor p53 and thus upregulating a variety of gene products involved in DNA repair and cell cycle regulation. Together, these data suggest that human cells have an evolutionarily conserved SOS-like response in which UV-induced DNA damage serves as signal to induce photoprotective responses such as tanning and increased DNA repair capacity. The responses can also be triggered in the absence of DNA damage by addition of small single-stranded DNA fragments such as pTpT.