Hyperpigmentation in human solar lentigo is promoted by heparanase-induced loss of heparan sulfate chains at the dermal–epidermal junction

Ethanolic Extract of Bergenia purpurascens Exhibits Antimelanogenic Effects in B16F10 Cells through Multiple Mechanisms That Suppress Tyrosinase

Bergenia purpurascens, renowned for its antibacterial and antioxidant properties, remains relatively unexplored in its impact on melanogenesis. This study delves into the antimelanogenic potential of the ethanol extract derived from B. purpurascens (BPE). Our investigations reveal the robust antioxidant capabilities of the BPE, along with its effective inhibition of mushroom tyrosinase activity. Remarkably, these effects were significantly stronger than those observed with arbutin, the positive control. In vitro assays demonstrate the BPE's efficacy in reducing the melanin content and tyrosinase activity in α-MSH-stimulated B16F10 cells. Immunofluorescence and qPCR analyses further reveal the BPE's ability to inhibit MITF-mediated gene expression levels associated with melanogenesis, including Trp-1, Trp-2, and tyrosinase. These findings suggest that the extract operates through dual mechanisms, suppressing both tyrosinase activity and key transcription factor-mediated downstream signaling. Utilizing UPLC-MS/MS analysis, we identified six key compounds implicated in tyrosinase activity inhibition and melanogenesis suppression. Docking simulations confirm moderate binding affinities between these compounds and tyrosinase. This study highlights the potential of B. purpurascens as a novel natural agent for depigmentation in medicinal and cosmetic applications, elucidating its dual mechanism of action in melanogenesis inhibition.

Role of Dermal Factors Involved in Regulating the Melanin and Melanogenesis of Mammalian Melanocytes in Normal and Abnormal Skin

Mammalian melanin is produced in melanocytes and accumulated in melanosomes. Melanogenesis is supported by many factors derived from the surrounding tissue environment, such as the epidermis, dermis, and subcutaneous tissue, in addition to numerous melanogenesis-related genes. The roles of these genes have been fully investigated and the molecular analysis has been performed. Moreover, the role of paracrine factors derived from epidermis has also been studied. However, the role of dermis has not been fully studied. Thus, in this review, dermis-derived factors including soluble and insoluble components were overviewed and discussed in normal and abnormal circumstances. Dermal factors play an important role in the regulation of melanogenesis in the normal and abnormal mammalian skin.

Multi-System-Level Analysis Reveals Differential Expression of Stress Response-Associated Genes in Inflammatory Solar Lentigo

Although the pathogenesis of solar lentigo (SL) involves chronic ultraviolet (UV) exposure, cellular senescence, and upregulated melanogenesis, underlying molecular-level mechanisms associated with SL remain unclear. The aim of this study was to investigate the gene regulatory mechanisms intimately linked to inflammation in SL. Skin samples from patients with SL with or without histological inflammatory features were obtained. RNA-seq data from the samples were analyzed via multiple analysis approaches, including exploration of core inflammatory gene alterations, identifying functional pathways at both transcription and protein levels, comparison of inflammatory module (gene clusters) activation levels, and analyzing correlations between modules. These analyses disclosed specific core genes implicated in oxidative stress, especially the upregulation of nuclear factor kappa B in the inflammatory SLs, while genes associated with protective mechanisms, such as SLC6A9, were highly expressed in the non-inflammatory SLs. For inflammatory modules, Extracellular Immunity and Mitochondrial Innate Immunity were exclusively upregulated in the inflammatory SL. Analysis of protein-protein interactions revealed the significance of CXCR3 upregulation in the pathogenesis of inflammatory SL. In conclusion, the upregulation of stress response-associated genes and inflammatory pathways in response to UV-induced oxidative stress implies their involvement in the pathogenesis of inflammatory SL.

A chronic pro-inflammatory environment contributes to the physiopathology of actinic lentigines

Actinic lentigines (AL) or age spots, are skin hyperpigmented lesions associated with age and chronic sun exposure. To better understand the physiopathology of AL, we have characterized the inflammation response in AL of European and Japanese volunteers. Gene expression profile showed that in both populations, 10% of the modulated genes in AL versus adjacent non lesional skin (NL), i.e. 31 genes, are associated with inflammation/immune process. A pro-inflammatory environment in AL is strongly suggested by the activation of the arachidonic acid cascade and the plasmin pathway leading to prostaglandin production, along with the decrease of anti-inflammatory cytokines and the identification of inflammatory upstream regulators. Furthermore, in line with the over-expression of genes associated with the recruitment and activation of immune cells, immunostaining on skin sections revealed a significant infiltration of CD68+ macrophages and CD4+ T-cells in the dermis of AL. Strikingly, investigation of infiltrated macrophage subsets evidenced a significant increase of pro-inflammatory CD80+/CD68+ M1 macrophages in AL compared to NL. In conclusion, a chronic inflammation, sustained by pro-inflammatory mediators and infiltration of immune cells, particularly pro-inflammatory M1 macrophages, takes place in AL. This pro-inflammatory loop should be thus broken to normalize skin and improve the efficacy of age spot treatment.

Characteristics of dermal vascularity in melasma and solar lentigo

BACKGROUND /PURPOSE

Melasma and solar lentigo (SL) are major benign hyperpigmented lesions, and both have been shown to involve the dermal vasculature. This review discusses current knowledge regarding the clinical characteristics of dermal vascularity in melasma and SL, as well as the results of relevant molecular biological investigations.

METHODS

PubMed and Google Scholar were searched in December 2023 to identify articles related to melasma, SL, and the dermal vasculature in these lesions.

RESULTS

Vascular morphologies in melasma and SL have been detected by histological and non-invasive methods, including modalities such as optical coherence tomography. Biological studies have indicated that factors secreted from vascular endothelial cells, such as stem cell factor and endothelin-1, can promote melanogenesis. With respect to phototherapy, blood vessel-targeting laser treatments are expected to provide long-term suppression of pigmentation, but this regimen is only effective when dilated capillaries are visible.

CONCLUSION

In both melasma and SL, clinical and experimental investigations are revealing the contributions of dermal vascularity to hyperpigmentation. More effective treatment may require identification of hyperpigmentation subtypes. In the future, knowledge of treatment (including phototherapy) is expected to accumulate through reliable and validated non-invasive measurements.

A mechanism of melanogenesis mediated by E-cadherin downregulation and its involvement in solar lentigines

OBJECTIVE

Intensive studies have revealed that pleiotropic melanocytic factors are associated with age-spot formation. Dysfunctional keratinocyte differentiation is thought to be an upstream cause of age-spot formation. Although it has been shown that keratinocyte differentiation is mediated by the cell-cell contact factor E-cadherin, its involvement in age-spot formation remains unknown. Thus, to determine the origin of age-spots and an integrated solution for the same, we focused on E-cadherin expression in the present study.

METHODS

First, we assessed the solar lentigines in cutaneous and cultured cells by means of immunofluorescence staining. Following that, keratinocytes treated with siRNAs against E-cadherin were co-cultured with melanocytes, and the secreted factors were identified by means of proteomic analysis of the culture supernatants. We also performed quantitative PCR to assess melanogenesis activity and screen ingredients. For behavioural analysis of melanocytes, we performed time-lapse imaging using confocal laser scanning microscopy.

RESULTS

E-cadherin expression was downregulated in the epidermis of the solar lentigines, suggesting its involvement in age-spot formation. E-cadherin knocked down keratinocytes not only promoted the secretion of melanocytic/inflammatory factors but also increased melanogenesis by upregulating the expression of melanogenesis factors. Furthermore, live-imaging showed that the downregulation of E-cadherin inhibited melanocyte dynamics and accelerated melanin uptake. Finally, we identified Rosa multiflora fruit extract as a solution that can upregulate E-cadherin expression in keratinocytes.

CONCLUSION

Our findings showed that E-cadherin downregulation triggers various downstream melanocytic processes, such as the secretion of melanocytic factors and melanogenesis. Additionally, we showed that the Rosa multiflora fruit extract upregulated E-cadherin expression in keratinocytes.

Skin aging from mechanisms to interventions: focusing on dermal aging

Skin aging is a multifaceted process that involves intrinsic and extrinsic mechanisms that lead to various structural and physiological changes in the skin. Intrinsic aging is associated with programmed aging and cellular senescence, which are caused by endogenous oxidative stress and cellular damage. Extrinsic aging is the result of environmental factors, such as ultraviolet (UV) radiation and pollution, and leads to the production of reactive oxygen species, ultimately causing DNA damage and cellular dysfunction. In aged skin, senescent cells accumulate and contribute to the degradation of the extracellular matrix, which further contributes to the aging process. To combat the symptoms of aging, various topical agents and clinical procedures such as chemical peels, injectables, and energy-based devices have been developed. These procedures address different symptoms of aging, but to devise an effective anti-aging treatment protocol, it is essential to thoroughly understand the mechanisms of skin aging. This review provides an overview of the mechanisms of skin aging and their significance in the development of anti-aging treatments.

Influence of environmental factors on facial pigmented spots: Epidemiological survey of women living in the northern and southern regions of Japan

BACKGROUND

Several epidemiological studies have been conducted to understand the relationship between environmental factors (including chronic sun exposure) and clinical signs of pigmented spots. However, no quantitative analysis has focused on the adverse effects of the detailed features of pigmented spots, including their color intensity, size, and number on the cheek. This study was performed to elucidate the adverse effects of environmental factors on clinical signs of pigmented spots.

METHODS

We conducted an epidemiological survey of 102 Japanese women in 2 regions of high and low sun exposure (southern and northern regions, respectively). Using image analysis of high-resolution digital facial photographs, individual pigmented spots were quantified according to color, size, and total number on the cheek. Each indicator was then compared between the groups.

RESULTS

For the number of pigmented spots on the cheek, the age-related increase curve showed a large slope in the southern group. For the size of pigmented spots, no significant difference was found between the two groups, and large pigmented spots were observed on the cheek even in the northern group. For the color intensity of the spots, the southern group showed a marked age-related change; among older subjects, the pigmented spots were significantly darker in the southern than northern group.

CONCLUSION

Our results may indicate that environmental factors, including chronic exposure to sunlight, mainly increase the number of pigmented spots and darkening of these spots. However, the occurrence of large pigmented spots may be related to intrinsic factors represented by heredity rather than environmental factors.

Prediction and association analyses of skin phenotypes in Japanese females using genetic, environmental, and physical features

BACKGROUND

Skin characteristics show great variation from person to person and are affected by multiple factors, including genetic, environmental, and physical factors, but details of the involvement and contributions of these factors remain unclear.

OBJECTIVES

We aimed to characterize genetic, environmental, and physical factors affecting 16 skin features by developing models to predict personal skin characteristics.

METHODS

We analyzed the associations of skin phenotypes with genetic, environmental, and physical features in 1472 Japanese females aged 20-80 years. We focused on 16 skin characteristics, including melanin, brightness/lightness, yellowness, pigmented spots, wrinkles, resilience, moisture, barrier function, texture, and sebum amount. As genetic factors, we selected 74 single-nucleotide polymorphisms of genes related to skin color, vitamin level, hormones, circulation, extracellular matrix (ECM) components and ECM-degrading enzymes, inflammation, and antioxidants. Histories of ultraviolet (UV) exposure and smoking as environmental factors and age, height, and weight as physical factors were acquired by means of a questionnaire.

RESULTS

A linear association with age was prominent for increase in the area of crow's feet, increase in number of pigmented spots, decrease in forehead sebum, and increase in VISIA wrinkle parameters. Associations were analyzed by constructing linear regression models for skin feature changes and logistic regression models to predict whether subjects show lower or higher skin measurement values in the same age groups. Multiple genetic factors, history of UV exposure and smoking, and body mass index were statistically selected for each skin characteristic. The most important association found for skin spots, such as lentigines and wrinkles, was adolescent sun exposure.

CONCLUSION

Genetic, environmental, and physical factors associated with interindividual differences of the selected skin features were identified. The developed models should be useful to predict the skin characteristics of individuals and their age-related changes.

Brassinin Abundant in Brassicaceae Suppresses Melanogenesis through Dual Mechanisms of Tyrosinase Inhibition

Brassinin is a phytoalexin abundant in plants, especially in cabbage, and has been reported to act as an anti-cancer and anti-inflammatory agent. However, limited studies are available to elucidate the functionalities of brassinin. Here, we tested the effects of brassinin on melanogenesis using cell-free and cell-based biochemical analysis and docking simulation. Cell-free experiments exhibited that brassinin has antioxidant and anti-tyrosinase activities. When applied to B16F10 cells stimulated with a melanogenesis inducer α-MSH, brassinin pretreatment significantly reduced melanin accumulation and cellular tyrosinase activity. Docking simulation indicates that the docking score of brassinin to the binding pocket of tyrosinase is better than that of kojic acid or arbutin, anti-melanogenic positive controls, indicating that brassinin inhibits melanogenesis at least partially by binding to and inactivating tyrosinase. In addition, qPCR results showed that brassinin reduced tyrosinase mRNA levels. Together, these results suggest that brassinin exerts anti-melanogenesis effects by inhibiting both the activity and mRNA expression levels of tyrosinase. Therefore, our study showed that brassinin has the potential to be used in pharmaceutical or cosmetic products for depigmentation.

Post-Inflammatory Hyperpigmentation in Dark Skin: Molecular Mechanism and Skincare Implications

Human skin is characterized by significant diversity in color and tone, which are determined by the quantity and distribution of melanin pigment in the epidermis. Melanin absorbs and reflects ultraviolet radiation (UVR), preventing the damage to genomic DNA in the epidermis and degradation of collagen in the dermis; therefore, darker skin types are thought to be well protected from the photodamage because of the high melanin content. However, increased content of melanin in combination with the extrinsic stress factors causing inflammation such as excess UVR, allergic reactions, or injury can also frequently lead to cosmetic problems resulting in discoloration and scarring. This review summarizes current knowledge on histopathology and likely molecular signatures of one of the most common problems, post-inflammatory hyperpigmentation (PIH). The mechanisms proposed so far are subsequently discussed in the context of other factors characterizing darker skin types. This includes the common cellular features, organization of upper skin layers, and major biomarkers, with particular emphasis on increased propensities to systemic and localized inflammation. Enhanced or prolonged inflammatory responses can not only affect the process of melanogenesis but also have been implicated in injury-related skin pathologies and aging. Finally, we summarize the major cosmetic treatments for PIH and their known anti-inflammatory targets, which can be beneficial for darker skin tones and combined with broad-spectrum filters against UVR.

Update on Melasma-Part I: Pathogenesis

Melasma is a multifactorial dyschromia that results from exposure to external factors (such as solar radiation) and hormonal factors (such as sex hormones and pregnancy), as well as skin inflammation (such as contact dermatitis and esthetic procedures), in genetically predisposed individuals. Beyond hyperfunctional melanocytes, skin with melasma exhibits a series of structural and functional alterations in the epidermis, basement membrane, and upper dermis that interact to elicit and sustain a focal hypermelanogenic phenotype. Evolution in the knowledge of the genetic basis of melasma and the cutaneous response to solar radiation, as well as the roles of endocrine factors, antioxidant system, endothelium proliferation, fibroblast senescence, mast cell degranulation, autophagy deficits of the melanocyte, and the paracrine regulation of melanogenesis, will lead to the development of new treatments and preventive strategies. This review presents current knowledge on these aspects of the pathogenesis of melasma and discusses the effects of specific treatments and future research on these issues.

Morphological and transcriptional evaluation of multiple facial cutaneous hyperpigmented spots

Background

Morphological characteristics of major facial hyperpigmented spots have been well documented. However, detailed alterations of respective transcriptional profile for each spot and in-depth comparisons across multiple spot types have not been reported.

Objectives

To comprehensively assess and compare multiple facial hyperpigmented spot types at the morphological and molecular levels by utilising transcriptional expression profiling with correlation to quantified histological features.

Methods

Multiple types of facial spot biopsies were collected from Chinese women and compared to additional biopsies taken from adjacent healthy skin. The types of spots included Solar Lentigos with both elongated dermal-epidermal junction (DEJ) (SL[E]) and flat DEJ (SL[F]), Seborrhoeic Keratosis (SK), Melasma, Freckles, Post-inflammatory hyperpigmentation of resolving acne (PIH[A]) and other stimuli (PIH[O]). Combined histomorphometry, immunohistology, and transcriptome analysis for suprabasal-epidermis, basal-epidermis, and dermal compartments dissected by Laser Capture Microdissection (LCM) were conducted and compared across different spot types.

Results

Each spot type was confirmed to have the unique histological pathology already documented elsewhere. Most of the spot types except Melasma and PIH (A) revealed similar melanocyte density to adjacent skin. All spots exhibited increased melanin synthesis, melanosome transportation, as well as enhanced melanocyte dendricity, however, each spot revealed a distinct transcriptome regulation pattern in pigmentation pathways. Upregulation of pigmentation genes was also observed in the dermis of SL(F), SL(E), SK and PIH(O), associated with significant modulation of DEJ related genes in basal-epidermis and/or dermal compartments, suggesting potential melanocyte infiltration into the dermis due to impaired DEJ quality. Beyond upregulated pigmentation, for most spots, gene expression in the suprabasal-epidermis regulating keratinisation was significantly upregulated in conjunction with thickened stratum corneum. Furthermore, downregulation of tight junction related genes represented by claudin-1 was observed in majority of spot types, suggesting compromised barrier function could be a similarity across spots. Additionally, Cyclin-Dependent Kinase Inhibitor 2A (CDKN2A) was upregulated in all types of spots, indicating involvement of cell senescence as a common theme.

Conclusion

This comprehensive and comparative study based on the histological and transcriptional analysis of three skin compartments provided unique insights into specific causations as well as differences and similarities across multiple hyperpigmented spot types.

A Clinical and Biochemical Evaluation of a Temperature-Controlled Continuous Non-Invasive Radiofrequency Device for the Treatment of Melasma

Background

Melasma shows characteristic histological features of photoaged skin.

Objective

We evaluated the effect of dermal rejuvenation using a temperature-controlled continuous non-invasive radiofrequency (RF) device on melasma.

Methods

Continuous skin heating at the temperature of 43°C for 20 minutes was performed in ten subjects with melasma who underwent 3 tri-weekly RF sessions. Pigmentation was evaluated with Mexameter® and investigator’s global assessment (IGA). Immunohistochemical staining and image analysis was performed to evaluate biopsies from melasma skin before and after the treatment.

Results

The lesional melanin index was decreased by 13.7% at week 9. IGA score was improved from 3.50 at baseline to 2.95 at week 9. No significant adverse event was reported. Histologic analysis revealed reduced melanin and increased collagen density and thickness. The expression of procollagen-1 and type IV collagen was increased after the treatment. The number of p16^INK4A-positive senescent fibroblasts was reduced after the treatment, while the expression of heat shock protein 70 and 90 was increased. Stromal derived factor-1, a senescence-associated anti-melanogenic factor secreted from the fibroblasts, was up-regulated after the treatment, while the level of c-kit was not changed.

Conclusion

Thermal skin stimulation by the temperature-controlled continuous RF device improved melasma through dermal rejuvenation.

The pathogenesis of melasma and implications for treatment

BACKGROUND

Melasma is a complex and poorly understood disorder, with high rates of treatment failure and recurrences.

OBJECTIVES

We aimed to review the current knowledge of the pathogenesis of melasma and apply this knowledge to clinical implications on relevant therapeutic interventions.

METHODS

A systematic PubMed search was performed using the search term "((melasma[Text Word]) OR facial melanosis[Text Word]) AND (pathogenesis OR causality[MeSH Terms])" for articles published between 1990 and 2020. Included articles were then evaluated by two authors and assessed for relevant pathomechanistic pathways, after which they were divided into groups with minimal overlap. We then reviewed current treatment modalities for melasma and divided them according to the involved pathomechanistic pathway.

RESULTS

A total of 309 search results were retrieved among which 76 relevant articles were identified and reviewed. Five main pathomechanisms observed in melasma were identified: (1) melanocyte inappropriate activation; (2) aggregation of melanin and melanosomes in dermis and epidermis; (3a) increased mast cell count and (3b) solar elastosis; (4) altered basement membrane; and (5) increased vascularization. Treatment modalities were then divided based on these five pathways and detailed in 6 relevant tables.

CONCLUSION

The pathophysiology of melasma is multifactorial, resulting in treatment resistance and high recurrence rates. This wide variety of pathomechanisms should ideally be addressed separately in the treatment regimen in order to maximize results.

Participation of keratinocyte- and fibroblast-derived factors in melanocyte homeostasis, the response to UV, and pigmentary disorders

Human epidermal melanocytes play a central role in sensing the environment and protecting the skin from the drastic effects of solar ultraviolet radiation and other environmental toxins or inflammatory agents. Melanocytes survive in the epidermis for decades, which subjects them to chronic environmental insults. Melanocytes have a poor self-renewal capacity; therefore, it is critical to ensure their survival with genomic stability. The function and survival of melanocytes is regulated by an elaborate network of paracrine factors synthesized mainly by epidermal keratinocytes and dermal fibroblasts. A symbiotic relationship exists between epidermal melanocytes and keratinocytes on the one hand, and between melanocytes and dermal fibroblasts on the other hand. Melanocytes protect epidermal keratinocytes and dermal fibroblasts from the damaging effects of solar radiation, and the latter cells synthesize biochemical mediators that maintain the homeostasis, and regulate the stress response of melanocytes. Disruption of the paracrine network results in pigmentary disorders, due to abnormal regulation of melanin synthesis, and compromise of melanocyte survival or genomic stability. This review provides an update of the current knowledge of keratinocyte- and fibroblast-derived paracrine factors and their contribution to melanocyte physiology, and how their abnormal production is involved in the pathogenesis of common pigmentary disorders.

Deciphering skin re-pigmentation patterns in vitiligo: an update on the cellular and molecular events involved

Current treatment of vitiligo is still a great challenge, since most cases of vitiligo have variable re-pigmentation outcomes due to their unpredictable responses to existing therapeutic regimens. There is an urgent need to identify this re-pigmentation process and to develop novel therapies. This review illustrates the most current research and latest understanding of vitiligo skin re-pigmentation and related regulatory mechanisms. Literature was collected from PubMed until January 2020, using the search terms including "vitiligo," "re-pigmentation," "phototherapy," "narrow-band ultraviolet B, " "excimer," "fractional carbon dioxide laser," and "melanocyte stem cells." Literature was mainly derived from English articles. Article type was not limited. Emerging evidence suggests that patients with vitiligo present various re-pigmentation patterns following ultraviolet B phototherapy, which relies on different cell reservoirs from the perilesional margins and/or from uninvolved hair follicles to replenish functional melanocytes that are lost in vitiliginous skin. The following events are likely to be involved in this re-pigmentation process, including: 1) changes in the paracrine secretion and distribution of transforming growth factor-β1 in the bulge area and in the epidermis; 2) the enhanced transfer of dermal pro-melanogenic growth factors to the epidermis; and 3) the induction of a C-X-C motif chemokine ligand (CXCL) 12-enriched micro-environment that efficiently recruits CXCR4- or CXCR7-positive melanocytes. Ongoing studies on the cellular and molecular events underlying vitiligo re-pigmentation will help design new therapeutic strategies to improve treatment outcomes.

Paracrine regulation of melanogenesis

Melanocytes are generally characterized by the basic ability of melanin synthesis and transfer to adjacent keratinocytes. This constitutes an individual skin phenotype and provides epidermal protection from various stimuli, such as ultraviolet irradiation, through a complex process called melanogenesis, which can be regulated by autocrine or paracrine factors. Recent evidence has revealed the paracrine effects of keratinocytes on melanogenesis by secreting cytokines, including α-melanocyte stimulating hormone and endothelin-1. In addition to keratinocytes, there are other types of cells in the skin, such as fibroblasts and immune cells, which are also actively involved in the regulation of melanocyte behaviour through the production of paracrine factors. In addition, extracellular matrix proteins, which are secreted mainly by skin-resident cells, not only play direct roles in regulating melanocyte morphology and functions but also provide structural support between the epidermis and dermis to control the distribution of various secreted cytokines from keratinocytes and/or fibroblasts, which are potentially involved in the regulation of melanogenesis. Moreover, understanding the origin of melanocytes (neural crest cells) and the presence of nerve endings in the epidermis can reveal the intimate contact between melanocytes and cutaneous specific nervous system proteins. Melanocytes are associated with all these networks with corresponding receptors expressed on the cell surface. In this review, we provide an overview of recent advances in determining the intimate relationships between melanocytes and their surrounding elements, which provide insights into the complex nature of the regulation of melanogenesis.

Molecular and histological characterization of age spots

Age spots, also called solar lentigines and lentigo senilis, are light brown to black pigmented lesions of various sizes that typically develop in chronically sun-exposed skin. It is well known that age spots are strongly related to chronic sun exposure and are associated with photodamage and an increased risk for skin cancer; however, the mechanisms underlying their development remain poorly understood. We used immunohistochemical analysis and microarray analysis to investigate the processes involved in their formation, focusing on specific markers associated with the functions and proliferation of melanocytes and keratinocytes. A total of 193 genes were differentially expressed in age spots, but melanocyte pigment genes were not among them. The increased expression of keratins 5 and 10, markers of basal and suprabasal keratinocytes, respectively, in age spots suggests that the increased proliferation of basal keratinocytes combined with the decreased turnover of suprabasal keratinocytes leads to the exaggerated formation of rete ridges in lesional epidermis which in turn disrupts the normal processing of melanin upwards from the basal layer. Based on our results, we propose a model for the development of age spots that explains the accumulation of melanin and the development of extensive rete ridges in those hyperpigmented lesions.

Heparanase Inhibitors Facilitate the Assembly of the Basement Membrane in Artificial Skin

Recent research suggests that the basement membrane at the dermal-epidermal junction of the skin plays an important role in maintaining a healthy epidermis and dermis, and repeated damage to the skin can destabilize the skin and accelerate the aging process. Skin-equivalent models are suitable for studying the reconstruction of the basement membrane and its contribution to epidermal homeostasis because they lack the basement membrane and show abnormal expression of epidermal differentiation markers. By using these models, it has been shown that reconstruction of the basement membrane is enhanced not only by supplying basement membrane components, but also by inhibiting proteinases such as urokinase and matrix metalloproteinase. Although matrix metalloproteinase inhibitors assist in the reconstruction of the basement membrane structure, their action is not sufficient to promote its functional recovery. However, heparanase inhibitors stabilize the heparan sulfate chains of perlecan (a heparan sulfate proteoglycan) and promote the regulation of heparan sulfate binding growth factors in the basement membrane. Heparan sulfate promotes effective protein-protein interactions, thereby facilitating the assembly of type VII collagen anchoring fibrils and elastin-associated microfibrils. Using both matrix metalloproteinase inhibitors and heparanase inhibitors, the basement membrane in a skin-equivalent model comes close to recapitulating the structure and function of an in vivo basement membrane. Therefore, by using an appropriate dermis model and suitable protease inhibitors, it may be possible to produce skin-equivalent models that are more similar to natural skin

Skin Pigmentation and Pigmentary Disorders: Focus on Epidermal/Dermal Cross-Talk

Variation in human skin and hair color is the most notable aspect of human variability and several studies in evolution, genetics and developmental biology contributed to explain the mechanisms underlying human skin pigmentation, which is responsible for differences in skin color across the world's populations. Despite skin pigmentation is primarily related to melanocytes functionality, the surrounding keratinocytes and extracellular matrix proteins and fibroblasts in the underlying dermal compartment actively contribute to cutaneous homeostasis. Many autocrine/paracrine secreted factors and cell adhesion mechanisms involving both epidermal and dermal constituents determine constitutive skin pigmentation and, whenever deregulated, the occurrence of pigmentary disorders. In particular, an increased expression of such mediators and their specific receptors frequently lead to hyperpigmentary conditions, such as in melasma and in solar lentigo, whereas a defect in their expression/release is related to hypopigmented disorders, as seen in vitiligo. All these interactions underline the relevant role of pigmentation on human evolution and biology.

Platelet-derived growth factor regulates the proliferation and differentiation of human melanocytes in a differentiation-stage-specific manner

BACKGROUND

Although many kinds of keratinocyte-derived factors are known to regulate the proliferation and differentiation of human melanocytes, it is not well defined whether dermis-derived factors work in a similar way.

OBJECTIVE

The aim of this study is to clarify whether dermal factors are involved in regulating the proliferation and differentiation of human melanocytes.

METHODS

Human epidermal melanoblasts were cultured serially in a serum-free growth medium. Platelet-derived growth factor-BB (PDGF-BB) was supplemented to the medium, and the effects on the proliferation of melanoblasts/melanocytes and the differentiation of melanocytes were studied.

RESULTS

PDGF-BB stimulated the proliferation of melanoblasts cultured in melanoblast-proliferation medium, but inhibited the proliferation of melanocytes cultured in melanocyte-proliferation medium. By contrast, PDGF-BB stimulated the differentiation, dendritogenesis, and melanogenesis of melanocytes through the stimulation of tyrosinase activity and the expressions of tyrosinase and tyrosinase-related protein-1.

CONCLUSION

These results suggest that PDGF-BB regulates the proliferation and differentiation of human melanocytes in a differentiation-stage-specific manner. PDGF-BB seems to be one of the dermal factors that regulate the proliferation and differentiation of human melanocytes.

Biological processes in solar lentigo: insights brought by experimental models

Common in ageing patient, the solar lentigo is a macular hyperpigmented skin lesion that results from chronic exposure to ultraviolet irradiations. Despite sharing numerous features with other pigmented spots, the diagnostic of this benign lesion is well characterized at the tissue level. Recent studies shed lights on several factors and their pathogenic mechanisms involved in the development of the solar lentigo. This review summarizes how diverse experimental approaches allowed the identification of several biomarkers, which contribute to a better understanding on the initiation and the maintenance of this pigmentary disorder.

Structural characterization and in vitro antioxidant activity of kojic dipalmitate loaded w/o/w multiple emulsions intended for skin disorders

Multiple emulsions (MEs) are intensively being studied for drug delivery due to their ability to load and increase the bioavailability of active lipophilic antioxidant, such as kojic dipalmitate (KDP). The aim of this study was to structurally characterize developed MEs by determining the average droplet size (Dnm) and zeta potential (ZP), performing macroscopic and microscopic analysis and analyzing their rheological behavior and in vitro bioadhesion. Furthermore, the in vitro safety profile and antioxidant activity of KDP-loaded MEs were evaluated. The developed MEs showed a Dnm of approximately 1 micrometer and a ZP of -13 mV, and no change was observed in Dnm or ZP of the system with the addition of KDP. KDP-unloaded MEs exhibited ''shear thinning" flow behavior whereas KDP-loaded MEs exhibited Newtonian behavior, which are both characteristic of antithixotropic materials. MEs have bioadhesion properties that were not influenced by the incorporation of KDP. The results showed that the incorporation of KDP into MEs improved the safety profile of the drug. The in vitro antioxidant activity assay suggested that MEs presented a higher capacity for maintaining the antioxidant activity of KDP. ME-based systems may be a promising platform for the topical application of KDP in the treatment of skin disorders.

Regulation of pigmentation by substrate elasticity in normal human melanocytes and melanotic MNT1 human melanoma cells

The elasticity of the cellular microenvironment is a key regulator of cellular physiology in many cell types. To investigate the effects of substrate stiffness on the pigmentation process, we cultured normal human melanocytes (NHM) and MNT1 melanoma cells on laminin-coated polydimethylsiloxane (PDMS) substrates of different stiffness. The dendricity of NHM and MNT1 cells was reduced as the substrate stiffness decreased, and the degree of melanosome transfer from NHM or MNT1 cells to normal human keratinocytes was decreased on softer substrates with the reduced dendricity. Gene and protein expressions of MITF, tyrosinase, TRP2, and gp100/PMEL17 exhibited a consistent decreasing trend with the decreasing stiffness. Because the stiffness sensing is mediated by focal adhesion complex through integrin receptors, we checked laminin specific integrin alpha 6 and p-FAK for MNT1 cells to observe that the substrate adhesion was weakened as the substrate stiffness decreased. Weaker adhesion on a softer substrate was accompanied by dynamic shape changes in MNT1 cells with higher speed and larger scattering. Dendritic MNT1 cells cultured on a stiffer substrate exhibited lower migration with smaller root mean squared displacement. These results demonstrate the possibility that skin pigmentation can be influenced by mechanical properties of the cellular microenvironment and can increase when the skin becomes stiff.

Vitiligo: characterization of melanocytes in repigmented skin after punch grafting

BACKGROUND

Punch grafting is a surgical technique mainly applied in therapy-resistant, stable and circumscribed vitiligo.

OBJECTIVE

(i) To characterize in detail the features of the repigmented skin among punch grafts; and (ii) to correlate the ex vivo results with clinical data and punch grafting outcome.

METHODS

We evaluated by immunohistochemistry and image analysis the expression of a panel of specific melanocyte markers including HMB45, MITF, c-kit, MART-1 and TRP1, the proliferation marker Ki67 and the cell-cell adhesion molecule E-cadherin in tissue samples collected from nine patients after punch grafting.

RESULTS

Cells positive for MITF, c-kit, MART-1 and TRP1 were detected in the repigmented skin of all biopsies, whereas no reactivity was observed for HMB45. Melanocytes were identified along the entire length of the sections, and their mature state was assessed by the immuno-reactivity for the differentiation marker MART-1, the absence of cells positively stained for Ki67 and by the co-expression of c-kit and TRP1, a marker of a differentiated and pigmented state. Clinically, smaller punch grafts aimed at repigmenting lesional areas on the face gave the faster clinical results with no side-effects. Patients subjected to bigger punch grafts on the knee exhibited a longer repigmentation time and presented cobble stoning.

CONCLUSION

Our results suggest that the repigmentation observed in the areas between the grafts is due to the activation of the melanocytes located in the donor sites. These cells start to horizontally migrate towards the lesional skin thanks to successively the enlargement of intercellular spaces in relation to a decrease of E-cadherin reactivity and the up-modulation of pro-melanogenic mediators. Production and transfer of melanin in the surrounding keratinocytes and their persistence were assessed by the reactivity for MITF, c-kit, MART-1 and TRP1 but not for the pre-melanosome marker (HMB45).

Effects of fibroblast-derived factors on the proliferation and differentiation of human melanocytes in culture

BACKGROUND

Although keratinocyte-derived factors are known to promote the proliferation and differentiation of human epidermal melanocytes, it is not fully understood whether fibroblast-derived factors work in a similar way.

OBJECTIVE

The aim of this study is to clarify whether fibroblast-derived factors are involved in regulating the proliferation and differentiation of human melanocytes with or without keratinocytes using serum-free culture system.

METHODS

Human epidermal melanoblasts and melanocytes were cultured in a serum-free growth medium supplemented with fibroblast-derived factors such as keratinocyte growth factor (KGF) with or without keratinocytes, and the effects of KGF on the proliferation and differentiation of melanocytes were studied.

RESULTS

KGF stimulated the proliferation of melanoblasts in the presence of dibutyryl cAMP (DBcAMP), basic fibroblast growth factor (bFGF), transferrin (Tf), and endothelin-1 (ET-1). Although KGF stimulated the differentiation, melanogenesis, and dendritogenesis in the presence of DBcAMP, Tf, and ET-1 without keratinocytes, KGF required the presence of keratinocytes for the stimulation of melanocyte proliferation.

CONCLUSION

These results suggest that fibroblast-derived KGF stimulates the proliferation of human melanoblasts in synergy with cAMP, bFGF, Tf, and ET-1, the differentiation of melanocytes in synergy with cAMP, Tf, and ET-1, and the proliferation of melanocytes in synergy with cAMP, Tf, ET-1, and undefined keratinocyte-derived factors.

Manassantin B inhibits melanosome transport in melanocytes by disrupting the melanophilin-myosin Va interaction

Human skin hyperpigmentation disorders occur when the synthesis and/or distribution of melanin increases. The distribution of melanin in the skin is achieved by melanosome transport and transfer. The transport of melanosomes, the organelles where melanin is made, in a melanocyte precedes the transfer of the melanosomes to a keratinocyte. Therefore, hyperpigmentation can be regulated by decreasing melanosome transport. In this study, we found that an extract of Saururus chinensis Baill (ESCB) and one of its components, manassantin B, inhibited melanosome transport in Melan-a melanocytes and normal human melanocytes (NHMs). Manassantin B disturbed melanosome transport by disrupting the interaction between melanophilin and myosin Va. Manassantin B is neither a direct nor an indirect inhibitor of tyrosinase. The total melanin content was not reduced when melanosome transport was inhibited in a Melan-a melanocyte monoculture by manassantin B. Manassantin B decreased melanin content only when Melan-a melanocytes were co-cultured with SP-1 keratinocytes or stimulated by α-MSH. Therefore, we propose that specific inhibitors of melanosome transport, such as manassantin B, are potential candidate or lead compounds for the development of agents to treat undesirable hyperpigmentation of the skin.

Oral administration of French maritime pine bark extract (Flavangenol(®)) improves clinical symptoms in photoaged facial skin

BACKGROUND

French maritime pine bark extract (PBE) has gained popularity as a dietary supplement in the treatment of various diseases due to its polyphenol-rich ingredients. Oligometric proanthocyanidins (OPCs), a class of bioflavonoid complexes, are enriched in French maritime PBE and have antioxidant and anti-inflammatory activity. Previous studies have suggested that French maritime PBE helps reduce ultraviolet radiation damage to the skin and may protect human facial skin from symptoms of photoaging. To evaluate the clinical efficacy of French maritime PBE in the improvement of photodamaged facial skin, we conducted a randomized trial of oral supplementation with PBE.

METHODS

One hundred and twelve women with mild to moderate photoaging of the skin were randomized to either a 12-week open trial regimen of 100 mg PBE supplementation once daily or to a parallel-group trial regimen of 40 mg PBE supplementation once daily.

RESULTS

A significant decrease in clinical grading of skin photoaging scores was observed in both time courses of 100 mg daily and 40 mg daily PBE supplementation regimens. A significant reduction in the pigmentation of age spots was also demonstrated utilizing skin color measurements.

CONCLUSION

Clinically significant improvement in photodamaged skin could be achieved with PBE. Our findings confirm the efficacy and safety of PBE.