Pheomelanin Content Research Articles

Effects of Dietary Cystine and Tyrosine Supplementation on Melanin Synthesis in the Pacific Oyster (Crassostrea gigas).

Melanogenesis is a multistep process to produce melanin for dark pigmentation in skin coloration. Previous studies in vertebrates demonstrated that cystine and tyrosine amino acids are involved in the melanin synthesis. However, very little is known about the melanogenesis in bivalve. In this study, cystine supplementation for 30days significantly upregulated the expression of CgB-aat1, CgCbs and CgTyr and pheomelanin content in the Pacific oyster Crassostrea gigas. Transmission electron microscope (TEM) results revealed more melanosomes in the connective tissue and melanin granules were secreted in epithelium of mantle. In contrast, tyrosine supplementation had no clear effect on melanogenesis except the gene expression changes of CgB-aat1 and CgCbs. In addition, prolonged supplementation of cystine or tyrosine for 60days had a negative impact on melanogenesis. Indeed, after 60days, expression of most of the melanin synthesis-related genes under study was decreased, and melanin content was significantly reduced, indicating that cystine and tyrosine might inhibit production of eumelanin and pheomelanin, respectively. In addition, in vitro analysis using primary cell culture from mantle tissue indicated that incubation with cystine, tyrosine, or B-AAT1 polypeptide, CBS/TYR recombinant proteins induced the increase of CgB-aat1 and CgCbs expression in a dose-dependent manner, suggesting the presence of a regulatory network in response to cystine and tyrosine amino acids intakes in pheomelanin synthesis-related gene expression. Taken together, these data indicate that cystine-CgB-aat1-CgCbs-CgTyr axis is a potential regulator of the pheomelanin biosynthesis pathway, and thus plays an important role in the mantle pigmentation in C. gigas. This work provides a new clue for selective cultivation of oyster strains with specific shell colors in bivalve breeding.

Exposure to sulfur in soil explains pigmentation by pheomelanin in birds inhabiting Iceland

Melanins are the most common pigments in birds and mammals. The synthesis of the sulfurated form of melanin, termed pheomelanin, is promoted by high levels of thiols in melanocytes. Exposure to elemental sulfur in the environment can potentially influence intracellular thiol levels in terrestrial animals, but this has never been investigated in the wild. This is particularly relevant in areas with a high volcanic activity that facilitate sulfur exposure. We explored for an association between the pheomelanin content of feathers in 35 breeding birds from 13 phylogenetically diverse species and 29 locations in Iceland, and the sulfur content of nearby soil samples. After controlling for the effect of phylogenetic relatedness between species, we found that the pheomelanin content of feathers was significantly correlated with the sulfur content of soil, indicating that pheomelanin production increases with sulfur exposure. Our results suggest that environmental exposure to relatively high levels of elemental sulfur promotes the expression of pheomelanin-based pigmentation phenotypes in birds, likely by an influence on intracellular thiols during development. This is the first evidence that soil chemistry can affect the phenotype of animals. Highly volcanic areas such as Iceland are thus potential sources of global phenotypic diversity by promoting sulfur exposure in animals.

Identification of Polymorphism in the MC1R Gene and Its Association with the Melanin Content in Feathers of Chinese Yellow Quails

MC1R plays a crucial role in controlling the type of melanin synthesized in the melanocytes, which greatly affects plumage color in birds. One g.16796362G/T SNP was found in the MC1R gene coding region, which caused a Met120Ile mutation in the amino acid sequence. The Met120Ile mutation was located in the third transmembrane domain of the MC1R protein and decreased protein stability. The g.16796362G/T locus achieved medium polymorphism and had significant association with feather melanin content in Chinese yellow quails. The contents of total melanin and pheomelanin with AA genotype were significant lower than those with AB or BB genotypes in skin tissues, while the expression levels of MC1R mRNA had no significant difference in feathers with different genotypes. This experiment indicated that the Met120Ile mutation could affect the function of the MC1R protein and change the biosynthesis of melanin in Chinese yellow quails.

Development of a method for isolation of melanin from archival FFPE tissues of human melanoma for structural studies by pyrolysis-gas chromatography-tandem mass spectrometry

Abstract Introduction There is some evidence that pheomelanin produced in skin melanocytes may be involved in the development of cutaneous melanoma, particularly in individuals with a light skin/red hair phenotype. However, nothing is known about possible correlation between the type and/or clinical stage of melanoma and the content of pheomelanin in the tumor tissue. We believe that archival formalin-fixed and paraffin-embedded (FFPE) melanoma tissues could be a good source of melanin pigment for future large-scale research on that issue. Aim The aim of this work was to develop a method for isolation and purification of melanin from FFPE samples of human melanoma. To test the suitability of the isolation protocol for planned structural studies, the obtained melanin was analyzed for pheomelanin content by the method based on pyrolysis (Py) coupled with gas chromatography and tandem mass spectrometry (GC/MS/MS). Material and methods For melanin isolation, microtome sections of FFPE tissue of primary lesion and lymph node metastases were subjected to a multistep procedure of paraffin removal, tissue rehydration, homogenization, and digestion with the set of proteolytic enzymes. The pigment samples were then pyrolyzed at 500 °C, and the GC-separated thermal degradation products were identified using a triple quadrupole mass spectrometer operating in the multiple reaction monitoring mode. Results GC/MS/MS analysis of the pyrolysis products revealed the presence of pheomelanin markers, which allowed quantitation of a pheomelanin component of each of the isolated pigments. Melanin from the FFPE primary melanoma was found to contain 6.6%, and the pigment from FFPE metastatic lymph node 7.5% of pheomelanin. Conclusions The developed protocol allows for the isolation of melanin from FFPE melanoma specimens. The pigment can be successfully studied for pheomelanin content by Py-GC/MS/MS method. The results of our study indicate that archival FFPE tumor tissues can be used as a good source of melanin for future structural studies aimed at shedding more light on the role of pheomelanin in the pathomechanism of cutaneous melanoma.

The pigmentation phenotype of melanocytes affects their response to nitric oxide in vitro.

It has been shown that nitric oxide (NO) can modulate the immune properties of epidermal melanocytes, and that overexpression of NO in the skin may contribute to inflammation-related pigmentary disorders. Little is known about whether constitutive cell pigmentation affects the sensitivity of melanocytes to NO. To compare the effect of NO on melanin synthesis and the expression of key melanogenesis-related genes in normal human melanocytes of various degrees of constitutive pigmentation. Human epidermal melanocytes derived from lightly and darkly pigmented skin (HEMn-LP and HEMn-DP, respectively) were cultured with or without a NO donor (SPER/NO). Then the total melanin content, the pheomelanin content, the activity and concentration of tyrosinase, and the expressions of TYR and DCT were assessed. NO released from SPER/NO did not alter the total amount of melanin produced by cultured cells but increased the proportion of pheomelanin, especially in HEMn-DP. Transcriptional activity of the melanogenesis-related genes, in particular DCT, was downregulated in HEMn-DP and upregulated in HEMn-LP cultured with SPER/NO. NO can promote pheomelanogenesis in human epidermal melanocytes, and the cell response in this respect is associated with the pigmentation phenotype. During exposure to NO, melanocytes from dark skin produce much more pheomelanin than lightly pigmented cells. NO-induced overproduction of pheomelanin in the skin could be one of the factors responsible for the greater propensity to develop severe inflammatory dermatoses in dark-skinned individuals, or even melanoma de novo formation based on local chronic inflammation.

Pheomelanin subunit non-destructive quantification by Raman spectroscopy and multivariate curve resolution-alternating least squares (MCR-ALS)

To date no direct methods are available for the subunit quantification of pheomelanin, the sulfur-containing melanin form whose structure increases melanoma risk. Here we apply Raman spectroscopy combined with chemometrics (MCR-ALS method) to quantify benzothiazine (BT) and benzothiazole (BZ), the constituent monomers of pheomelanin. The Raman spectra of synthetic pheomelanins only composed of BT or BZ were markedly different from those of natural pheomelanins composed of mixed BT-BZ, indicating the necessity of using a multivariate curve resolution method to extract the pure profiles of these monomers in complex samples. MCR-ALS with correlation constraint was applied to the Raman spectra of pheomelanized feathers from 26 bird species to predict BT-BZ concentrations. The methodology was able to quantify BT with R2 ​= ​0.91 and a relative error of 9%, for the range of 100–1000 ​ng/mg. However, the model did not perform well for BZ quantification. In addition, the MCR-ALS model could retrieve a pure profile associated to keratin, a major component (interference) in feathers. The deconvolution of Raman spectra, which predicts total pheomelanin content, combined with MCR-ALS, which predicts BT content, can therefore provide a complete pheomelanin determination at the monomeric level. This represents a direct and non-destructive analytical method for pheomelanin subunits, opening the door to investigate the differential cytotoxicity of these subunits in a high diversity of biological samples, including melanoma.

Identification of L-Cysteinamide as a Potent Inhibitor of Tyrosinase-Mediated Dopachrome Formation and Eumelanin Synthesis.

The purpose of this study is to identify amino acid derivatives with potent anti-eumelanogenic activity. First, we compared the effects of twenty different amidated amino acids on tyrosinase (TYR)-mediated dopachrome formation in vitro and melanin content in dark-pigmented human melanoma MNT-1 cells. The results showed that only L-cysteinamide inhibited TYR-mediated dopachrome formation in vitro and reduced the melanin content of cells. Next, the antimelanogenic effect of L-cysteinamide was compared to those of other thiol compounds (L-cysteine, N-acetyl L-cysteine, glutathione, L-cysteine ethyl ester, N-acetyl L-cysteinamide, and cysteamine) and positive controls with known antimelanogenic effects (kojic acid and β-arbutin). The results showed the unique properties of L-cysteinamide, which effectively reduces melanin content without causing cytotoxicity. L-Cysteinamide did not affect the mRNA and protein levels of TYR, tyrosinase-related protein 1, and dopachrome tautomerase in MNT-1 cells. L-Cysteinamide exhibited similar properties in normal human epidermal melanocytes (HEMs). Experiments using mushroom TYR suggest that L-cysteinamide at certain concentrations can inhibit eumelanin synthesis through a dual mechanism by inhibiting TYR-catalyzed dopaquinone synthesis and by diverting the synthesized dopaquinone to the formation of DOPA-cysteinamide conjugates rather than dopachrome. Finally, L-cysteinamide was shown to increase pheomelanin content while decreasing eumelanin and total melanin contents in MNT-1 cells. This study suggests that L-cysteinamide has an optimal structure that can effectively and safely inhibit eumelanin synthesis in MNT-1 cells and HEMs, and will be useful in controlling skin hyperpigmentation.

Feather Gene Expression Elucidates the Developmental Basis of Plumage Iridescence in African Starlings.

Iridescence is widespread in the living world, occurring in organisms as diverse as bacteria, plants, and animals. Yet, compared to pigment-based forms of coloration, we know surprisingly little about the developmental and molecular bases of the structural colors that give rise to iridescence. Birds display a rich diversity of iridescent structural colors that are produced in feathers by the arrangement of melanin-containing organelles called melanosomes into nanoscale configurations, but how these often unusually shaped melanosomes form, or how they are arranged into highly organized nanostructures, remains largely unknown. Here, we use functional genomics to explore the developmental basis of iridescent plumage using superb starlings (Lamprotornis superbus), which produce both iridescent blue and non-iridescent red feathers. Through morphological and chemical analyses, we confirm that hollow, flattened melanosomes in iridescent feathers are eumelanin-based, whereas melanosomes in non-iridescent feathers are solid and amorphous, suggesting that high pheomelanin content underlies red coloration. Intriguingly, the nanoscale arrangement of melanosomes within the barbules was surprisingly similar between feather types. After creating a new genome assembly, we use transcriptomics to show that non-iridescent feather development is associated with genes related to pigmentation, metabolism, and mitochondrial function, suggesting non-iridescent feathers are more energetically expensive to produce than iridescent feathers. However, iridescent feather development is associated with genes related to structural and cellular organization, suggesting that, while nanostructures themselves may passively assemble, barbules and melanosomes may require active organization to give them their shape. Together, our analyses suggest that iridescent feathers form through a combination of passive self-assembly and active processes.

Improved HPLC Conditions to Determine Eumelanin and Pheomelanin Contents in Biological Samples Using an Ion Pair Reagent.

Alkaline hydrogen peroxide oxidation (AHPO) of eumelanin and pheomelanin, two major classes of melanin pigments, affords pyrrole-2,3,5-tricarboxylic acid (PTCA), pyrrole-2,3-dicarboxylic acid (PDCA) and pyrrole-2,3,4,5-tetracarboxylic acid (PTeCA) from eumelanin and thiazole-2,4,5-tricarboxylic acid (TTCA) and thiazole-4,5-dicarboxylic acid (TDCA) from pheomelanin. Quantification of these five markers by HPLC provides useful information on the quantity and structural diversity of melanins in various biological samples. HPLC analysis of these markers using the original method of 0.1 M potassium phosphate buffer (pH 2.1):methanol = 99:1 (85:15 for PTeCA) on a reversed-phase column had some problems, including the short lifetime of the column and, except for the major eumelanin marker PTCA, other markers were occasionally overlapped by interfering peaks in samples containing only trace levels of these markers. These problems can be overcome by the addition of an ion pair reagent for anions, such as tetra-n-butylammonium bromide (1 mM), to retard the elution of di-, tri- and tetra-carboxylic acids. The methanol concentration was increased to 17% (30% for PTeCA) and the linearity, reproducibility, and recovery of the markers with this improved method is good to excellent. This improved HPLC method was compared to the original method using synthetic melanins, mouse hair, human hair, and human epidermal samples. In addition to PTCA, TTCA, a major marker for pheomelanin, showed excellent correlations between both HPLC methods. The other markers showed an attenuation of the interfering peaks with the improved method. We recommend this improved HPLC method for the quantitative analysis of melanin markers following AHPO because of its simplicity, accuracy, and reproducibility.

Kojic acid alters pheomelanin content in human induced pluripotent stem cell-derived melanocytes.

Kojic acid alters pheomelanin content in human induced pluripotent stem cell-derived melanocytes.

Knockdown of microRNA‑143‑5p by STTM technology affects eumelanin and pheomelanin production in melanocytes.

MicroRNAs (miRNAs) serve various roles in the regulation of melanogenesis in mammalian melanocytes that contribute to the development of hair color. The manipulation of the melanocyte action is a new target for genetic improvement. Short tandem target mimic (STTM) is a potent approach for silencing miRNAs in plants and animals. To investigate the function of miR-143-5p in melanogenesis, STTM was used to block the expression of miR-143-5p (STTM-miR-143-5p). The molecular analysis and luciferase reporter assay identified myosin Va gene (MYO5A) as one of the miR-143-5p targets. STTM-miR-143-5p overexpression resulted in an increased expression of downstream melanogenesis genes including microphthalmia-associated transcription factor (MITF), tyrosinase family members [tyrosinase (TYR) and tyrosinase-related protein 1 (TYRP1)], melanophilin (MLPH), and Rab27a, thereby contributing to melanocyte pigmentation by promoting total alkali-soluble melanogenesis (ASM) and eumelanin (EM) contents; conversely, STTM-miR-143-5p overexpression resulted in decreased expression of the tyrosinase-related protein 2 (TYRP2)/dopachrome tautomerase (DCT), which is responsible for decreased pheomelanin (PM) content in mouse melanocytes. The results indicated that melanin production in melanocytes could be increased by manipulating miR-143-5p expression using STTM which resulted in ASM and EM production.

Pheomelanin synthesis varies with protein food abundance in developing goshawks.

The accumulation of the amino acid cysteine in lysosomes produces toxic substances, which are avoided by a gene (CTNS) coding for a transporter that pumps cystine out of lysosomes. Melanosomes are lysosome-related organelles that synthesize melanins, the most widespread pigments in animals. The synthesis of the orange melanin, termed pheomelanin, depends on cysteine levels because the sulfhydryl group is used to form the pigment. Pheomelanin synthesis may, therefore, be affected by cysteine homeostasis, although this has never been explored in a natural system. As diet is an important source of cysteine, here we indirectly tested for such an effect by searching for an association between food abundance and pheomelanin content of feathers in a wild population of Northern goshawk Accipiter gentilis. As predicted on the basis that CTNS expression may inhibit pheomelanin synthesis and increase with food abundance as previously found in other strictly carnivorous birds, we found that the feather pheomelanin content in nestling goshawks, but not in adults, decreased as the abundance of prey available to them increased. In contrast, variation in the feather content of the non-sulphurated melanin form (eumelanin) was only explained by sex in both nestlings and adults. We also found that the feather pheomelanin content of nestlings was negatively related to that of their mothers, suggesting a relevant environmental influence on pheomelanin synthesis. Overall, our findings suggest that variation in pheomelanin synthesis may be a side effect of the maintenance of cysteine homeostasis. This may help explaining variability in the expression of pigmented phenotypes.

Differential gene regulation underlies variation in melanic plumage coloration in the dark-eyed junco (Junco hyemalis).

Colour plays a prominent role in species recognition; therefore, understanding the proximate basis of pigmentation can provide insight into reproductive isolation and speciation. Colour differences between taxa may be the result of regulatory differences or be caused by mutations in coding regions of the expressed genes. To investigate these two alternatives, we studied the pigment composition and the genetic basis of coloration in two divergent dark-eyed junco (Junco hyemalis) subspecies, the slate-coloured and Oregon juncos, which have evolved marked differences in plumage coloration since the Last Glacial Maximum. We used HPLC and light microscopy to investigate pigment composition and deposition in feathers from four body areas. We then used RNA-seq to compare the relative roles of differential gene expression in developing feathers and sequence divergence in transcribed loci under common-garden conditions. Junco feathers differed in eumelanin and pheomelanin content and distribution. Within subspecies, in lighter feathers melanin synthesis genes were downregulated (including PMEL, TYR, TYRP1, OCA2 and MLANA), and ASIP was upregulated. Feathers from different body regions also showed differential expression of HOX and WNT genes. Feathers from the same body regions that differed in colour between the two subspecies showed differential expression of ASIP and three other genes (MFSD12, KCNJ13 and HAND2) associated with pigmentation in other taxa. Sequence variation in the expressed genes was not related to colour differences. Our findings support the hypothesis that differential regulation of a few genes can account for marked differences in coloration, a mechanism that may facilitate the rapid phenotypic diversification of juncos.

Solar and terrestrial radiations explain continental-scale variation in bird pigmentation.

Animals living on the earth's surface are protected from the damaging effects of solar ultraviolet (UV) radiation by melanin pigments that color their integument. UV levels that reach the earth's surface vary spatially, but the role of UV exposure in shaping clinal variations in animal pigmentation has never been tested. Here, we show at a continental scale in Europe that golden eagles Aquila chrysaetos reared in territories with a high solar UV-B radiation exposure deposit lower amounts of the sulphurated form of melanin (pheomelanin) in feathers and consequently develop darker plumage phenotypes than eagles from territories with lower radiation exposure. This clinal variation in pigmentation is also explained by terrestrial γ radiation levels in the rearing territories by a similar effect on the pheomelanin content of feathers, unveiling natural radioactivity as a previously unsuspected factor shaping animal pigmentation. These findings show for the first time the potential of solar and terrestrial radiations to explain pigmentation phenotype diversity in animals, including humans, at large spatial scales.

Variation in melanin pigmentation of a sexually selected plumage trait and its adaptive value in the Common SnipeGallinago gallinago

There is increasing evidence that melanin‐based plumage coloration correlates with different components of fitness and that it may act as a social or sexual signal of individual quality. We analysed variation in melanin pigmentation in the outermost tail feathers of the Common SnipeGallinago gallinago. During courtship flights, male Snipe use their outermost tail feathers to generate a drumming sound, which plays a role in territory establishment and mate choice. As the outermost tail feathers are displayed to females during these flights, we predicted that conspicuous variation in their rusty‐brown (pheomelanin‐based) coloration may act as an honest signal of individual quality. To test this prediction, we spectrophotometrically measured brightness (an indicator of total melanin content) and red chroma (an indicator of pheomelanin content) of the outermost tail feathers in 180 juvenile and adult Common Snipe. An age‐related decline in feather brightness was found exclusively in females, suggesting that melanization could have evolved by natural selection to camouflage incubating birds. In both sexes, brightness of the tail feathers was inversely correlated with their structural quality (as measured with mass–length residuals), suggesting that melanization could increase mechanical properties of feathers and, in males, enhance the quality of courtship sonation. Red chroma positively correlated with total plasma protein concentration, supporting our prediction that pheomelanin pigmentation of tail feathers may act as an honest signal of condition. Our study indicated that variation in the melanin‐based coloration of the outermost tail feathers in the Common Snipe could have evolved as a result of several different selection pressures and it emphasizes the complexity of the processes that underlie the evolution of melanin‐based plumage coloration in birds.

Isolation and characterization of melanin pigment from yesso scallop Patinopecten yessoensis

Melanin is one of the essential compounds in the pigments of molluscan shells. However, the effects of melanin on color variations in molluscs are largely unknown. Our previous study suggests that Yesso scallop Patinopecten yessoensis might contain melanin pigment in the dark brown shell. We therefore isolated melanin from the pigmented shells using hydrochloric acid method, and characterized the types of melanin pigments by spectrophotometry. The purified melanin, which was verified by spectrophotometry scanning and HPLC analysis, showed the typical characteristics of melanin absorption spectra and HPLC chromatograms. The contents of pheomelanin and eumelanin in pigmented shells, which were determined by the linear standard curve of melanin at 405 nm and 350 nm absorbance, were 48.23 ± 1.350 and 157.65 ± 5.905 mg, respectively. The present results indicate that the brown-pigmented shells of scallops comprise approximately 76.6% of eumelanin and 23.4% of pheomelanin, which supports the presence of eumelanin-rich pigment in scallop shells. Therefore, the combination of hydrochloric acid extraction and spectrophotometric quantification is a rapid and efficient method to isolate and quantify melanin in shells. This will facilitate the melanin studies related to shell color polymorphism and the selective breeding of bivalves with different shell colors.

Pheomelanin content of cultured human melanocytes from lightly and darkly pigmented skin: A pyrolysis-gas chromatography/tandem mass spectrometry study

The diverse susceptibility of human skin with various degree of constitutive pigmentation to UV-induced damage, including carcinogenesis, may result from the differences in both total melanin content and the pigment composition, in particular the proportion of potentially harmful pheomelanin. The aim of this study was to compare a pheomelanin content of human epidermal melanocytes derived from lightly and darkly pigmented neonatal skin, using the previously developed method based on the thermal degradation of the pigment. Melanin was isolated from the cultured cells and pyrolysed at 500°C with a microfurnace-type device. The obtained pyrolysates were analyzed for the presence of the marker degradation products using a gas chromatography/tandem mass spectrometry system operating in a multiple reaction monitoring mode. The pheomelanin content was calculated from a calibration curve, generated with the use of a series of synthetic melanin pigments with known percentages of incorporated pheomelanin. We have found that the pheomelanin content of human epidermal melanocytes from neonatal skin does not exceed 10pg per cell, and depends on the degree of constitutive pigmentation. Heavily pigmented melanocytes derived from dark skin produce approximately four times as much pheomelanin as the cells from light skinned donors.

MC1R variants affect the expression of melanocortin and melanogenic genes and the association between melanocortin genes and coloration.

The melanocortin-1 receptor (MC1R) gene influences coloration by altering the expression of genes acting downstream in the melanin synthesis. MC1R belongs to the melanocortin system, a genetic network coding for the ligands that regulate MC1R and other melanocortin receptors controlling different physiological and behavioural traits. The impact of MC1R variants on these regulatory melanocortin genes was never considered, even though MC1R mutations could alter the influence of these genes on coloration (e.g. by decreasing MC1R response to melanocortin ligands). Using barn owl growing feathers, we investigated the differences between MC1R genotypes in the (co)expression of six melanocortin and nine melanogenic-related genes and in the association between melanocortin gene expression and phenotype (feather pheomelanin content). Compared to the MC1R rufous allele, responsible for reddish coloration, the white allele was not only associated with an expected lower expression of melanogenic-related genes (TYR, TYRP1, OCA2, SLC45A2, KIT, DCT) but also with a lower MC1R expression and a higher expression of ASIP, the MC1R antagonist. More importantly, the expression of PCSK2, responsible for the maturation of the MC1R agonist, α-melanocyte-stimulating hormone, was positively related to pheomelanin content in MC1R white homozygotes but not in individuals carrying the MC1R rufous allele. These findings indicate that MC1R mutations not only alter the expression of melanogenic-related genes but also the association between coloration and the expression of melanocortin genes upstream of MC1R. This suggests that MC1R mutations can modulate the regulation of coloration by the pleiotropic melanocortin genes, potentially decoupling the often-observed associations between coloration and other phenotypes.

Non‐invasive quantification of melanin in the stratum corneum: a novel indicator of skin lesions in pigmentation diseases

Skin melanin content is an important indicator for ascertaining the pathology of skin pigmentation diseases, but its analysis necessitates a biopsy or other means of collecting tissue, posing a considerable burden to the patient, and making it difficult to observe how a given skin site changes over time. Here, we aimed to establish a non-invasive method for quantifying the eumelanin and pheomelanin content of the stratum corneum. Sun-exposed and non-exposed samples from 10 healthy Japanese subjects were compared. We harvested the outermost layer of the stratum corneum by tape-stripping, considering the outer side of the forearm as a sun-exposed area, and medial side of the upper arm as a non-exposed area. Four additional subjects were included in the analysis of change in melanin content over time at the same skin site. The anterior lower leg received a single exposure to two minimal erythema dose sunlight, and the stratum corneum was harvested from the same site over a period of 20 weeks; we subsequently quantified the levels of eumelanin and pheomelanin using high-performance liquid chromatography. We were able to accurately quantify the eumelanin and pheomelanin contents of the stratum corneum, and to observe the evolution of the same skin site over time. Eumelanin levels were significantly higher in the sun-exposed area, with a peak in melanin observed after 11-15 weeks of sun exposure. This non-invasive method can serve as a marker for pathology of skin pigmentation diseases such as malignant tumors.

Quantifying variation in human scalp hair fiber shape and pigmentation.

This study aims to evaluate the use of quantitative methods of measuring variation in scalp hair fiber shape and pigmentation and carry out exploratory data analysis on a limited sample of individuals from diverse populations in order to inform future avenues of research for the evolution of modern human hair variation. Cross-sectional area and shape and average curvature of scalp hair fibers were quantified using ImageJ. Pigmentation was analyzed using chemical methods estimating total melanin content through spectrophotometric methods, and eumelanin and pheomelanin content through HLPC analysis of melanin-specific degradation products. The initial results reinforced findings from earlier, traditional studies. African and African Diaspora scalp hair was significantly curled, (East) Asian hair was significantly thick, and European hair was significantly lighter in color. However, pigmentation analyses revealed a high level of variability in the melanin content of non-European populations and analysis of curvature found a large range of variation in the average curvature of East African individuals. Overall, these results suggest the usefulness of chemical methods for the elucidation of nonperceptible differences in scalp hair color and highlight the need for improvements in our assessment and understanding of hair fiber curvature. Am J Phys Anthropol 160:341-352, 2016. © 2016 Wiley Periodicals, Inc.