Melanin Distribution Research Articles

Mechanisms of Skin Tanning in Different Racial/Ethnic Groups in Response to Ultraviolet Radiation

Ultraviolet radiation stimulates pigmentation in human skin, but the mechanism(s) whereby this increase in melanin production (commonly known as tanning) occurs is not well understood. Few studies have examined the molecular consequences of UV on human skin of various racial backgrounds in situ. We investigated the effects of UV on human skin of various races before and at different times after a single 1 minimal erythemal dose UV exposure. We measured the distribution of DNA damage that results, as well as the melanin content/distribution and the expression of various melanocyte-specific genes. The density of melanocytes at the epidermal:dermal junction in different types of human skin are remarkably similar and do not change significantly within 1 wk after UV exposure. The expression of melanocyte-specific proteins (including TYR (tyrosinase), TYRP1 (tyrosinase-related protein 1), DCT (tyrosinase-related protein 2), MART1 (melanoma antigens recognized by T-cells) gp100 (Pmel17/silver), and MITF (micropthalmia transcription factor)) increased from 0 to 7 d after UV exposure, but the melanin content of the skin increased only slightly. The most significant change, however, was a change in the distribution of melanin from the lower layer upwards to the middle layer of the skin, which was more dramatic in the darker skin. These results provide a basis for understanding the origin of different skin colors and responses to UV within different races.

Hormone influence on melanogenesis and spots formation

Hormone influence on melanogenesis and spots formation

Architectural characteristics of sun exposed and sun protected south‐east Asian skin

Architectural characteristics of sun exposed and sun protected south‐east Asian skin

Epidermal dermal junction and spots in human skin

Epidermal dermal junction and spots in human skin

Non-Invasive Visualization of Melanin and Melanocytes by Reflectance-Mode Confocal Microscopy

In vivo visualization of epidermal melanin was performed by reflectance-mode confocal microscopy (RCM). Firstly, we examined the distribution of epidermal melanin in pigmented animals and compared with that of the human skin. Melanocytes in the skin of pigmented animals were found to accumulate a large amount of melanin that can be easily visualized because of its brightness. Their RCM images correlated well with the Fontana-Masson-stained sections for melanin. In contrast, in the human skin, typical dendritic melanocytes were hardly observed even in pigmented lesions, although supranuclear melanin caps were easily visible. These results suggested that human melanocytes rapidly transfer the produced melanin to keratinocytes and do not accumulate it. Secondly, to elucidate the production of melanin by human melanocytes, we evaluated the changes of melanin after a single ultraviolet (UV) exposure. The melanin-accumulating melanocytes were clearly visualized during the skin pigmentation process. The RCM images showed the brightness because of melanin gradually increased from day 4, then dendrite-elongated melanocytes appearing from day 8, and finally melanin caps formed from day 29. In conclusion, RCM successfully evidenced the difference in melanin distribution between the pigmented animals and humans, and the UV-induced pigmentation process in vivo as well.

Melanin Pigment Uptake Within Paget Cells

Background: The differential diagnosis of intraepidermal neoplasms showing cell clusters and/or single units with upward migration includes Pagets disease, melanoma in‐situ, Bowens disease, and Pagetoid reticulosis. Purpose: We describe three cases of Pagets disease of the nipple with melanin pigment uptake by Paget cells. Results: Clinical and pathologic material of three women with biopsy proven Pagets disease of the nipple was reviewed. Clinically, two cases demonstrated an excoriated nipple, one of which also showed a zone of depigmentation. The clinical appearance of the third case was not available. Histologically, each case demonstrated Paget cells singly and in clusters with cytoplasmic uptake of melanin pigment. Melanocytes were found in each case, but were neither increased in number nor showed atypical forms. The dendritic processes of melanocytes were found to encase single Paget cells. Pigment was also found dispersed in the papillary dermis and within melanophages. Conclusions: Melanin pigment uptake by Paget cells represents a significant potential pitfall in ultimately arriving at the correct diagnosis. Misdiagnosing these cases as a melanocytic lesion could potentially delay the management of an underlying breast cancer. Careful examination of melanocyte and melanin distribution with respect to Paget cells is warranted in such cases.

Dark-cell areas in the dog vestibular endorgans: an immunohistochemical study.

The stria vascularis in the cochlea and the dark-cell areas in the vestibular endorgans are structures involved in the production of endolymphatic fluid. This study investigated the dark-cell areas in the vestibular endorgans of the dog by classical staining and by immunohistochemistry (anti-Na,K-ATPase beta2 isoform, anti-cytokeratins (against cytokeratins 5 and 8), anti-vimentin and anti-S100A6) from birth to 110 postnatal days. Using classical staining, it was not possible to discriminate dark cells from other epithelial cells lining the vestibular endolymphatic spaces. From birth, the Na,K-ATPase beta2 isoform was expressed in the lateral and basal cell membranes of a subset of cells located in the utricular wall, at the base of the cristae ampullaris and was identified as dark cells. From birth, anti-cytokeratins labelled all the cells forming the epithelial lining, including the dark cells, while anti-vimentin labelled the underlying mesenchymal cells. From postnatal day 10, anti-S100A6 labelled subepithelial cells exclusively located underneath the dark-cell areas and were identified as vestibular melanocyte-like cells. From birth, Fontana staining evidenced fine melanin granules in the subepithelial layer. The amount of melanin granules increased during the first month. Melanin distribution was closely associated with the region where S100A6-positive cells were located. The cell-specific antigen expression in the dog dark-cell areas was clearly comparable to that of the dog stria vascularis previously described. The present investigation also suggested an earlier histological and immunohistological maturity in the dark-cell areas than in the stria vascularis of dogs. This preliminary morphological description of the normal dark-cell areas in dogs by means of immunomarkers may be instrumental in studying pathological processes involving the fluid-secreting structures in vestibular endorgans.

Ultrastructural characterization of the distribution of melanin and epidermal macrophages in photodamaged skin.

We examined the characteristics of melanin distribution, the possible mechanisms underlying the histological incontinence of pigment, and the significance of epidermal macrophages in photodamaged skin. We used electron microscopy to compare and quantitate melanin distribution in various types of cells and structures, to qualitatively observe associations of melanin granules with melanophages, and to examine morphological differences of epidermal macrophages in sun-exposed versus sun-protected facial skin. Melanin-containing cells (such as Langerhans' cells) and melanin-containing structures (such as colloid bodies) in photodamaged skin were more numerous than in sun-protected skin, in proportion to differences in melanocyte density and in epidermal melanin content. Although the precise mechanism(s) of histological incontinence of pigment in photoaging skin appear to be very complicated, it is certainly one of the morphological hallmarks of photodamaged facial skin, and the degeneration of keratinocytes (noted by their electron-lucent properties), a feature characteristic of photoaging, contributes to that process. Furthermore, the increased numbers of epidermal macrophages in sun-exposed skin may be associated with photoaging processes (probably through their phagocytic function) as well as alterations of the cutaneous immune system.

The expression and activation of protease-activated receptor-2 correlate with skin color.

Skin color results from the production and distribution of melanin in the epidermis. The protease-activated receptor-2 (PAR-2), expressed on keratinocytes but not on melanocytes, is involved in melanosome uptake via phagocytosis, and modulation of PAR-2 activation affects skin color. The pattern of melanosome distribution within the epidermis is skin color-dependent. In vitro, this distribution pattern is regulated by the ethnic origin of the keratinocytes, not the melanocytes. Therefore, we hypothesized that PAR-2 may play a role in the modulation of pigmentation in a skin type-dependent manner. We examined the expression of PAR-2 and its activator, trypsin, in human skins with different pigmentary levels. Here we show that PAR-2 and trypsin are expressed in higher levels, and are differentially localized in highly pigmented, relative to lightly pigmented skins. Moreover, highly pigmented skins exhibit an increase in PAR-2-specific protease cleavage ability. Microsphere phagocytosis was more efficient in keratinocytes from highly pigmented skins, and PAR-2 induced phagocytosis resulted in more efficient microsphere ingestion and more compacted microsphere organization in dark skin-derived keratinocytes. These results demonstrate that PAR-2 expression and activity correlate with skin color, suggesting the involvement of PAR-2 in ethnic skin color phenotypes.

Toxicity of chromium and heptachlor epoxide on liver of Rana kl. esculenta: A morphological and histochemical study

Over the last 50 years, many species of amphibians have declined markedly, and even become extinct throughout the world. The cause of this is not clear, and several factors may be involved, including exposure to contaminants. The effects of some pollutants (i.e., chromium and heptachlor epoxide) on the green frog (.Rana kl. esculenta) were assessed experimentally, using morpho‐histological techniques. At the lowest doses used (0.5 ppm for Cr, 4 ppb ‐ 40 ppb for heptachlor epoxide), the hepatocytes showed no relevant structural or functional changes. The highest dose (5 ppm for chromium and 400 ppb for heptachlor epoxide) proved to affect the hepatocytes, as revealed mainly by intense ROS reactivity and by increased SDH activity. In addition, relevant variations in melanin content and distribution, as well as in hemo‐siderin deposits, were observed in melanomacrophages. These cells also showed an intense dose‐dependent reactivity for both acid phosphatase and catalase in the liver of treated animals. In general, the results suggest that the role of the melanomacrophag‐ic component is fundamental, possibly due to the action of melanin pigment and to catalase activity towards hepatocytes in detoxification. The 50 ppm dose of chromium was lethal.

Evolutionary genetics of the melanocortin-1 receptor in vertebrates.

The molecular genetic basis of adaptive change in phenotype is a major outstanding issue in evolutionary biology. Evolutionary change in coat and plumage color is a promising system for making progress in this field. Most notably, recent work on the molecular genetic basis of hair and feather color has identified several genes which are candidates for involvement in evolutionary color change in mammals and birds. We have investigated the evolution of one of these candidate genes, the melanocortin-1 receptor (MC1R) gene, in relation to changes in melanin distribution among a wide variety of primate species, and in bananaquits (Coereba flaveola), which are a classic case of melanic plumage polymorphism in birds. In primates, a role of the MC1R coding region in coat color evolution can be ruled out in several cases in which closely related species have drastically different distributions of eumelanin and/or pheomelanin. However, reconstruction of MC1R sequences over primate evolution shows the presence of mutations at important functional sites in several lineages. Most notably, the lion tamarins (Leontopithecus) show a striking pattern of MC1R evolution, including deletions and several nonconservative amino acid changes. In the bananaquit, an E92K substitution in the MC1R is strongly associated with melanism, and this is likely to be the causative mutation. Reconstruction of the evolution of bananaquit MC1R alleles shows that melanism is a derived trait in this species. These results confirm the utility of a candidate gene approach to color evolution in vertebrates and open the way for extensive future research.

Evolution of yellow Gene Regulation and Pigmentation in Drosophila

Background: Changes in developmental gene expression are central to phenotypic evolution, but the genetic mechanisms underlying these changes are not well understood. Interspecific differences in gene expression can arise from evolutionary changes in cis-regulatory DNA and/or in the expression of trans-acting regulatory proteins, but few case studies have distinguished between these mechanisms. Here, we compare the regulation of the yellow gene, which is required for melanization, among distantly related Drosophila species with different pigment patterns and determine the phenotypic effects of divergent Yellow expression.Results: Yellow expression has diverged among D. melanogaster, D. subobscura, and D. virilis and, in all cases, correlates with the distribution of black melanin. Species-specific Yellow expression patterns were retained in D. melanogaster transformants carrying the D. subobscura and D. virilis yellow genes, indicating that sequence evolution within the yellow gene underlies the divergence of Yellow expression. Evolutionary changes in the activity of orthologous cis-regulatory elements are responsible for differences in abdominal Yellow expression; however, cis-regulatory element evolution is not the sole cause of divergent Yellow expression patterns. Transformation of the D. melanogaster yellow gene into D. virilis altered its expression pattern, indicating that trans-acting factors that regulate the D. melanogaster yellow gene have also diverged between these two species. Finally, we found that the phenotypic effects of evolutionary changes in Yellow expression depend on epistatic interactions with other genes.Conclusions: Evolutionary changes in Yellow expression correlate with divergent melanin patterns and are a result of evolution in both cis- and trans-regulation. These changes were likely necessary for the divergence of pigmentation, but evolutionary changes in other genes were also required.

Monte Carlo simulation of reflection spectra of random multilayer media strongly scattering and absorbing light

The reflection spectra of a multilayer random medium — the human skin — strongly scattering and absorbing light are numerically simulated. The propagation of light in the medium and the absorption spectra are simulated by the stochastic Monte Carlo method, which combines schemes for calculations of real photon trajectories and the statistical weight method. The model takes into account the inhomogeneous spatial distribution of blood vessels, water, and melanin, the degree of blood oxygenation, and the hematocrit index. The attenuation of the incident radiation caused by reflection and refraction at Fresnel boundaries of layers inside the medium is also considered. The simulated reflection spectra are compared with the experimental reflection spectra of the human skin. It is shown that a set of parameters that was used to describe the optical properties of skin layers and their possible variations, despite being far from complete, is nevertheless sufficient for the simulation of the reflection spectra of the human skin and their quantitative analysis.

Effect of adenovirus-mediated expression of Sonic hedgehog gene on hair regrowth in mice with chemotherapy-induced alopecia.

The Sonic hedgehog (Shh) gene is involved in the initiation of hair growth. We have shown that localized, transient, enhanced expression of the Shh gene in mouse skin mediated by an adenovirus (AdShh) vector accelerates initiation of the anagen (i.e., growth) phase of hair follicle development. Because hair regrowth in chemotherapy-induced alopecia is associated with follicle cell proliferation and active melanogenesis similar to that observed in the anagen phase of normal hair growth, we examined whether AdShh-mediated Shh expression would accelerate hair regrowth in the skin of mice with chemotherapy-induced alopecia. After establishment of cyclophosphamide-induced alopecia, in either 3- or 7-week-old mice, AdShh or a control vector (AdNull) was delivered to dorsal skin by intradermal injection. Hair regrowth and melanogenesis were assessed by histology and gross morphology. Fisher's exact test was used to compare differences in outcomes between AdShh-treated and control (AdNull-treated or not injected with any vector [naive]) mice. All statistical tests were two-sided. Northern blot analysis confirmed enhanced Shh expression after AdShh administration in 7-week-old mice. Two weeks after AdShh administration, the injection site (all of five mice) showed large, anagen-phase hair follicles with a normal distribution of melanin. In contrast, both skin treated with AdNull (all of five mice) and skin from naive mice (all of five mice) showed dystrophic hair follicles with irregular distribution of melanin (P<.001 in both comparisons). Gross morphologic observations confirmed that AdShh-treated mice, but not naive mice or AdNull-treated mice, showed skin darkening at the injection site indicative of entry into anagen phase (P<.001 in both comparisons). AdShh treatment of 3-week-old mice with cyclophosphamide-induced alopecia was followed by accelerated hair follicle recovery (19 of 22 mice); such recovery was not observed at this rate in AdNull-treated or naive skin (P<.001 for both comparisons). Localized, transient, enhanced expression of Shh gene in skin, mediated by an adenovirus vector, might be a future strategy to accelerate hair follicle regrowth after chemotherapy-induced alopecia.

A mechanistic link between parasite resistance and expression of a sexually selected trait in a damselfly.

This paper examines a field-based insect system in which a signal trait and an immune effector system responsible for parasite resistance rely on the same melanin-producing enzyme cascade (phenoloxidase, PO). Observations and experiments on males of the calopterygid damselfly Calopteryx splendens xanthostoma revealed that resistance to the prevalent parasite in the study system (a eugregarine protozoan infecting the mid-gut) was correlated with quantitative aspects of the sexually dimorphic melanized wingspot of males, a trait that is produced and fixed before the host comes into contact with the sporozsoites of the parasite. Regulation of PO during experimental immune challenge showed that males with dark, homogenous melanin distribution in their wings showed no change in PO levels 24 h after challenge. By contrast males with lighter and/or more heterogenous melanin distribution in their wings tended to show higher PO levels 2-h after immune challenge. The changes in PO levels occur despite the lack of a relationship between wing-pigment distribution and the cellular encapsulation response. These results suggest a shared, limiting resource may form the mechanistic basis of the trade-off between a condition-dependent signal trait and immune function in this system.

Histamine Induces Melanogenesis and Morphologic Changes by Protein Kinase A Activation via H2 Receptors in Human Normal Melanocytes

Hyperpigmentation frequently accompanies chronic or acute inflammation. A number of inflammatory mediators have been shown to stimulate melanin synthesis in human melanocytes. Although histamine is ubiquitous as an inflammatory factor, its involvement in pigmentation remains obscure. In this work, we examined the effects of histamine on cultured human melanocytes. Treatment of human melanocytes with 0.1-10 microM histamine evoked morphologic changes and increases in tyrosinase activity. The concomitant increases in melanin content of the histamine-treated melanocytes indicated an elevation of melanin synthesis by tyrosinase activation. These stimulatory effects of histamine were completely inhibited by an H2 antagonist, famotidine, whereas H1 and H3 antagonists had no inhibitory effect whatsoever. In addition, an H2 agonist, dimaprit, induced the same degree of melanogenesis as histamine at concentrations of 0.1-10 microM. We observed an increase in the intracellular cAMP contents of human melanocytes induced by histamine via the H2 receptors. We know that this cAMP accumulation and subsequent protein kinase A activation plays a critical role in histamine-induced melanogenesis, because a specific protein kinase A inhibitor, H-89, completely suppressed these stimulatory effects of histamine, and because dibutylic cAMP, a specific protein kinase A activator, stimulated human melanocytes as potently as histamine. Taken together, we show here that histamine induces melanogenesis of human cultured melanocytes by protein kinase A activation via H2 receptors.

Independent-component analysis of skin color image.

The spatial distributions of melanin and hemoglobin in human skin are separated by independent-component analysis of a skin color image. The analysis is based on the skin color model with three assumptions: (1) Spatial variation of color in the skin is caused by two pigments, melanin and hemoglobin; (2) the quantities of the two pigments are mutually independent spatially; and (3) linearity holds among the quantities and the observed color signals in the optical density domain. The results of the separation agree well with physiological knowledge. The separated components are synthesized to simulate the various facial color images by changing the quantities of the two separated pigments.

Temporal sequence of changes in rat retina after UV-A and blue light exposure

Two spectral types of retinal light damage were induced in pigmented rats by irradiating small retinal patches at either 380 or 470 nm. The temporal sequence of changes in the retina was followed for up to 2 months by funduscopy and histology. For both damage types, fundus changes were best visible after 3 days. Histology showed that 380 nm specifically damaged photoreceptor cells, particularly the rods. All cell compartments of the rods, including the nucleus were affected already after 3 h. In the next days, damaged rods degenerated. At high doses (2.5×the funduscopic threshold dose) all rods in the irradiated area were lost, resulting in a local photoreceptor lesion, which was still present at 2 months after the irradiation. At 470 nm, damage occurred both in the photoreceptor layer and in the pigment epithelium. Acute changes, at 1 h after irradiation, consisted mainly of damaged mitochondria in these layers. Next, the pigment epithelium showed swelling, an altered melanin distribution and, at high doses (2.5×threshold), interruptions of the monolayer. Degeneration of photoreceptor cells was initially limited to a few scattered cells, but 3 days after high doses focal areas of massive degeneration were seen. At late stages, the cells of the pigment epithelium recovered and the photoreceptor layer showed a loss of cells. The results show that the spectral damage types are distinct in the early phases, indicating that different mechanisms are involved. Yet, the end effect of both damage types after exposure at doses up to 2.5×the funduscopic threshold is remarkably similar and consists of local photoreceptor lesions.

Melanin distribution in corneocytes and fine patterns of pigmentation on pigmented areas in pigmentary disorders

Background/aims:Hyperpigmentation on the face, such as chloasma, ephelides, and senile pigmentation, is a common problem in the dermatological field. It is desirable to obtain precise data on melanin distribution and hyperpigmentation patterns for correct diagnosis and suitable treatment; however, there are few reports of non‐invasive studies of hyperpigmentation of the face skin.Methods:In this study, we examined melanin distribution in corneocytes and fine patterns of pigmentation. Using adhesive tape, we stripped the skin on both pigmented areas and adjacent normal areas of the face. The melanin granules in the cells of the stripped specimens were stained by the Fontana‐Masson stain method. The melanin distribution of corneocytes was categorized into five types, and the frequency of each type was calculated. Pigmentation patterns were imaged by a videomicroscope equipped with a polarizer. The fine patterns of pigmentation were categorized into three basic patterns: reticulated, granulated and flat pigmentation.Results:Melanin granules were concentrated around the nuclei in pigmented areas compared with normal areas. The frequency of each fine pattern was different in each pigmented disease.Conclusions:This study will be useful in assisting dermatologists in correcting clinical diagnoses of pigmented skin diseases.

Evidence of Retinal Light Damage in Rana cascadae: A Declining Amphibian Species

Diurnal wildlife populations that inhabit high-altitude environments may be at risk of cumulative retinal injury from increased penetration of solar ultraviolet radiation resulting from a declining concentration of stratospheric ozone. Previously, the deleterious effect of ultraviolet radiation on the eggs and hatching success has been shown in Rana cascadae, a high-altitude species undergoing major population declines. To assess whether the retinas of this species may be showing signs of injury resulting from cumulative exposure to solar radiation, both the histological condition and photoreceptor densities were compared in R. cascadae, in experimentally light-damaged R. pipiens, and in control R. pipiens. Distinctive outer-retinal abnormalities observed in the inferior retina of R. cascadae were similar to those observed in light-damaged R. pipiens. These included an abnormal distribution of retinal pigment epithelial melanin, damaged photoreceptors and the presence of large, pigment-filled macrophages. Statistically significant, negative correlations were found between extent of outer-retinal histopathology and cone photoreceptor densities both in light-damaged R. pipiens (r = -0.54) and R. cascadae (r = -0.59). Overall cone photoreceptor densities were lower in the inferior versus superior retina of R.cascadae and in light-damaged R. pipiens compared with controls. In R. pipiens, experimental light damage significantly reduced green-rod and miniature-cone densities in the inferior retina; both contain a short-wavelength sensitive photopigment. The lowest densities of these two photoreceptor types were found in the inferior retina of R. cascadae as well. Similarities between the major abnormalities observed in R. cascadae and in experimentally light-damaged R. pipiens suggest that environmental solar radiation is damaging the retinas of R. cascadae and perhaps other highaltitude species as well.