Combined chemical and electron microscopic studies of pheomelanosomes in human red hair

Comparative transcriptome elucidates key genes and pathways related to golden phenotype of Crassostrea gigas

Marine bivalves are economically important and exhibit a remarkable diversity in shell color. The Pacific oyster Crassostrea gigas stands out as an important economic species, with the successful development of four distinct color strains through selective breeding. While previous studies have shed light on the genetic mechanism underlying color segregation, the precise molecular regulatory mechanisms responsible for shell coloration in oysters remains elusive. In this study, we confirmed that the golden phenotype is primarily attributed to pheomelanin by histological and ultrastructural observations. Additionally, we conducted a comparative transcriptome analysis of the black and golden shell color oysters to explore the potential genes and pathways contributing to the golden phenotype in C. gigas. Our results revealed a significant increase in differentially expressed genes in the golden phenotype associated with pathways such as glutathione metabolism, and calcium signaling pathway, suggesting a potential role in the synthesis of pheomelanin. Of particular note, we highlighted the potential role of two-pore channel 2 (TPC2) in modulating tyrosinase activity and melanosomal pH, ultimately determining the shade of pigmentation. Our study in this work provided a preliminary exploration of the mechanism, shedding light on the melanosome microenvironment and shell color.

A Comprehensive Review of Mammalian Pigmentation: Paving the Way for Innovative Hair Colour-Changing Cosmetics

The natural colour of hair shafts is formed at the bulb of hair follicles, and it is coupled to the hair growth cycle. Three critical processes must happen for efficient pigmentation: (1) melanosome biogenesis in neural crest-derived melanocytes, (2) the biochemical synthesis of melanins (melanogenesis) inside melanosomes, and (3) the transfer of melanin granules to surrounding pre-cortical keratinocytes for their incorporation into nascent hair fibres. All these steps are under complex genetic control. The array of natural hair colour shades are ascribed to polymorphisms in several pigmentary genes. A myriad of factors acting via autocrine, paracrine, and endocrine mechanisms also contributes for hair colour diversity. Given the enormous social and cosmetic importance attributed to hair colour, hair dyeing is today a common practice. Nonetheless, the adverse effects of the long-term usage of such cosmetic procedures demand the development of new methods for colour change. In this context, case reports of hair lightening, darkening and repigmentation as a side-effect of the therapeutic usage of many drugs substantiate the possibility to tune hair colour by interfering with the biology of follicular pigmentary units. By scrutinizing mammalian pigmentation, this review pinpoints key targetable processes for the development of innovative cosmetics that can safely change the hair colour from the inside out.

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.

Barriers and Promises of the Developing Pigment Organelle Field

Many colors and patterns in nature are regulated by the packaging and processing of intracellular pigment-containing organelles within cells. Spanning both molecular and tissue-level spatial scales with chemical and physical (structural) elements of coloration, pigment organelles represent an important but largely understudied feature of every biological system capable of coloration. Although vertebrate melanosomes have historically been the best-known and most studied pigment organelle, recent reports suggest a surge in studies focusing on other pigment organelles producing a variety of non-melanic pigments, optic crystals and structural colors through their geometric arrangement. In this issue, we showcase the importance these integrative and comparative studies and discuss their results which aid in our understanding of organelle form and function in their native environment. Specifically, we highlight how pigment organelles can be studied at different scales of organization, across multiple species in biology, and with an interdisciplinary approach to better understand the biological and chemical mechanisms underlying color. This type of comparative approach provides evidence for a common origin and identity of membrane-bound pigment organelles not only in vertebrates, as was originally postulated 40 years ago, but in all animals. This indicates that we have much to gain by studying a variety of pigment organelles, as the specific biological context may provide important and unique insights into various aspects of its life. We conclude by highlighting some barriers to this research and discussing strategies to overcome them through a discussion of future directions for pigment organelle research.

Melanosomes: Biogenesis, Properties, and Evolution of an Ancient Organelle

Melanosomes are organelles that produce and store melanin, a widespread biological pigment with a unique suite of properties including high refractive index, semiconducting capabilities, material stiffness, and high fossilization potential. They are involved in numerous critical biological functions in organisms across the tree of life. Individual components such as melanin chemistry and melanosome development have recently been addressed, but a broad synthesis is needed. Here, we review the hierarchical structure, development, functions, and evolution of melanosomes. We highlight variation in melanin chemistry and melanosome morphology and how these may relate to function. For example, we review what is known of the chemical differences between different melanin types (eumelanin, pheomelanin, allomelanin) and whether/how melanosome morphology relates to chemistry and color. We integrate the distribution of melanin across living organisms with what is known from the fossil record and produce hypotheses on its evolution. We suggest that melanin was present in life forms early in evolutionary history and that melanosomes evolved at the origin of organelles. Throughout, we discuss the (sometimes gaping) holes in our knowledge and suggest areas that need particular attention as we move forward in our understanding of these still-mysterious organelles and the materials that they contain.

Amyloids, melanins and oxidative stress in melanomagenesis

Melanoma has traditionally been viewed as an ultraviolet (UV) radiation-induced malignancy. While UV is a common inducing factor, other endogenous stresses such as metal ion accumulation or the melanin pigment itself may provide alternative pathways to melanoma progression. Eumelanosomes within melanoma often exhibit disrupted membranes and fragmented pigment which may be due to alterations in their amyloid-based striated matrix. The melanosomal amyloid can itself be toxic, especially in combination with reactive oxygen species (ROS) and reactive nitrogen species (RNS) generated by endogenous NADPH oxidase (NOX) and nitric oxide synthase (NOS) enzymes, a toxic mix that may initiate melanomagenesis. Further understanding of the loss of the melanosomal organization, the behaviour of the exposed melanin and the induction of ROS/RNS in melanomas may provide critical insights into this deadly disease.

MC1R, eumelanin and pheomelanin: their role in determining the susceptibility to skin cancer

Skin pigmentation is due to the accumulation of two types of melanin granules in the keratinocytes. Besides being the most potent blocker of ultraviolet radiation, the role of melanin in photoprotection is complex. This is because one type of melanin called eumelanin is UV absorbent, whereas the other, pheomelanin, is photounstable and may even promote carcinogenesis. Skin hyperpigmentation may be caused by stress or exposure to sunlight, which stimulates the release of α-melanocyte stimulating hormone (α-MSH) from damaged keratinocytes. Melanocortin 1 receptor (MC1R) is a key signaling molecule on melanocytes that responds to α-MSH by inducing expression of enzymes responsible for eumelanin synthesis. Persons with red hair have mutations in the MC1R causing its inactivation; this leads to a paucity of eumelanin production and makes red-heads more susceptible to skin cancer. Apart from its effects on melanin production, the α-MSH/MC1R signaling is also a potent anti-inflammatory pathway and has been shown to promote antimelanoma immunity. This review will focus on the role of MC1R in terms of its regulation of melanogenesis and influence on the immune system with respect to skin cancer susceptibility.

A Study of Immunohistochemical and Electron Microscopic Changes in Dowling-Degos Disease

Previous investigations have focused on the skin manifestations, histopathology, and pedigree of patients with Dowling-Degos disease (DDD). Little is known about its immunohistochemical staining, and electron microscopy. Our purpose was to study the immunohistochemistry and electron microscopy of lesions from patients with DDD. A biopsy specimen revealed elongated epidermal rete ridges with basilar hyperpigmentation in a filiform pattern. All pigmented cells in the basal layer were recognized by Anti-PEP-1, anti-PEP-2, HMB-45 and NKI/beteb antibodies. The melanocytes were localized in the basal layer and accounted for 10% of the total keratinocytes. There were supranuclear "caps" of brown granules within most basal kerotinocytes in the hyperpigmentation area. The melanocytes contained many mitochondria, Golgi apparati, and regular melanosomes in all stages of maturation in their cytoplasms; melanosome-laden dendrites were readily detected by transmission electron microscepe. Melanosomes, mainly of stages III and IV, were present within keratinocytes, distributed either as scattered patterns or forming "caps" over the nucleus.

Pheomelanin-induced oxidative stress: bright and dark chemistry bridging red hair phenotype and melanoma

The complex interplay of genetic and epigenetic factors linking sun exposure to melanoma in the red hair phenotype hinges on the peculiar physical and chemical properties of pheomelanins and the underlying biosynthetic pathway, which is switched on by the effects of inactivating polymorphisms in the melanocortin 1 receptor gene. In addition to the long recognized UV-dependent pathways of toxicity and cell damage, a UV-independent pro-oxidant state induced by pheomelanin within the genetically determined background of the red hair phenotype has recently been disclosed. This review provides a detailed discussion of the possible UV-dependent and UV-independent chemical mechanisms underlying pheomelanin-mediated oxidative stress, with special reference to the oxygen-dependent depletion of glutathione and other cell antioxidants. The new concept of pheomelanin as a 'living' polymer and biocatalyst that may grow by exposure to monomer building blocks and may trigger autooxidative processes is also discussed. As a corollary, treatment of inflammatory skin diseases in RHP patients is briefly commented. Finally, possible concerted strategies for melanoma prevention in the red hair phenotype are proposed.

Red human hair pheomelanin is a potent pro-oxidant mediating UV-independent contributory mechanisms of melanomagenesis

The highest incidence of melanoma in red haired individuals is attributed to the synthesis and phototoxic properties of pheomelanin pigments. Recently, pheomelanin has also been implicated in UV-independent pathways of oxidative stress; however, the underlying mechanisms have remained uncharted. Herein, we disclose the unprecedented property of purified red human hair pheomelanin (RHP) to promote (i) the oxygen-dependent depletion of major cell antioxidants, for example glutathione and NADH; (ii) the autoxidative formation of melanin pigments from their precursors. RHP would thus behave as a unique 'living' polymer and biocatalyst that may grow by simple exposure to monomer building blocks and may trigger autoxidative processes. These results yield new clues as to the origin of the pro-oxidant state in the red hair phenotype, uncover non-enzymatic pathways of melanogenesis, and pave the way to innovative strategies for melanoma prevention.

Nonlinear microscopy of eumelanin and pheomelanin with subcellular resolution

Pump-probe microscopy non-destructively differentiates eumelanin and pheomelanin and can be used to quantify melanin distributions in thin biopsy slices. Here we have extended that work for imaging eumelanin and pheomelanin distributions on a sub-cellular scale, allowing elucidation of characteristics of different cell types. The results show that melanin heterogeneity, previously found to be characteristic of melanomas, persists on the sub-cellular scale. We have also found spectral changes associated with melanin located in melanophages, which could potentially differentiate invasive pigmented melanocytes from melanophages without immunohistochemical staining.

In vivo characterization of melanin in melanocytic lesions: spectroscopic study on 1671 pigmented skin lesions

The purpose of this study is to determine the role of melanin in the various steps of progression of melanocytic neoplasia. To this aim, we perform a retrospective analysis on 1671 multispectral images of in vivo pigmented skin lesions previously recruited in the framework of a study focused on the computer-assisted diagnosis of melanoma. The series included 288 melanomas in different phases of progression, i.e., in situ, horizontal and vertical growth phase invasive melanomas, 424 dysplastic nevi, and other 957 melanocytic lesions. Analysis of the absorbance spectra in the different groups shows that the levels of eumelanin and pheomelanin increase and decrease, respectively, from dysplastic nevi to invasive melanomas. In both cases, the trend of melanin levels is associated to the progression from dysplastic nevi to vertical growth phase melanomas, reflecting a possible hierarchy in the natural history of the early phases of the disease. Our results suggest that diffuse reflectance spectroscopy used to differentiate eumelanin and pheomelanin in in vivo lesions is a promising technique useful to develop better strategies for the characterization of various melanocytic lesions, for instance, by monitoring melanin in a time-lapse study of a lesion that was supposed to be benign.

Regulatory factors of pheo- and eumelanogenesis in melanogenic compartments

Melanogenesis, i.e., synthesis of melanin and melanosomes, is a "cascade" of event which is channelled by internal and external regulatory factors. The recognition and selection of this information and subsequent differentiation of melanogenesis (melanin type and melanosomal development) would be regulated significantly by melanosomal membrane. The melanogenesis type could be switched relatively easily by UV light, hormone, and availability of tyrosinase substrate. The role of sulphydryl compounds as a regulatory factor in melanogenesis type (in particular for pheomelanogenesis) may not be tied to its absolute presence or absence, but rather, to the effective concentration within the melanocyte at a given time. It is, therefore, probable that the morphogenesis of melanosomes may not follow immediately in response to melanogenesis-type changes, hence the melanocyte revealing more often mosaic forms of melanosomes in nature after exposure to non-genetic factors. The switch of melanogenesis would be significantly controlled by structural and functional availability of vesiculoglobular bodies which are encoded or associated with HMSA-5 (69 kDa) glycoprotein. This HMSA-5 protein shares a significant homology with gp75 "b-locus" protein. However, because of our hypothesis that vesiculoglobular bodies carry post- (and pre-) tyrosinase regulatory factors involving in both pheo- and eumelanogenesis, the term "b-protein" which focuses only on eumelanogenesis may not be applied to HMSA-5.

Comparison of structural and chemical properties of black and red human hair melanosomes

Melanosomes in black and red human hair are isolated and characterized by various chemical and physical techniques. Different yields of 4-amino-hydroxyphenolanaline by HI hydrolysis (a marker for pheomelanin) and pyrrole-2,3,5-tricarboxylic acid by KMnO(4)/H(+) oxidation (a marker for eumelanin) indicate that the melanosomes in black hair are eumelanosomes, whereas those in red hair are mainly pheomelanosomes. Atomic force microscopy reveals that eumelanosomes and pheomelanosomes have ellipsoidal and spherical shapes, respectively. Eumelanosomes maintain structural integrity upon extraction from the keratin matrix, whereas pheomelanosomes tend to fall apart. The black-hair eumelanosomes have an average of 14.6 +/- 0.5% amino acids content, which is attributed to the internal proteins entrapped in the melanosomes granules. The red-hair melanosomes contain more than 44% of amino acid content even after extensive proteolytic digestion. This high content of amino acids and the poorly reserved integrity of red-hair melanosomes suggest that some proteins are possibly covalently bonded with the melanin constituents in addition to those that are entrapped inside the melanin species. Soluene solubilization assay indicates the absorbance of melanin per gram of sample, adjusted for the amino acid content, is a factor of 2.9 greater for the black-hair melanosomes than the red-hair melanosomes. Metal analysis reveals significant amounts of diverse heavy metal ions bound to the two types of melanosomes. The amount of Cu(II) and Zn(II) are similar but Fe(III) content is four times higher in the red-hair melanosomes. (13)C solid-state nuclear magnetic resonance spectra and infrared spectra are presented and are shown to be powerful techniques for discerning differences in the amino acid contents, the 5,6-dihydroxyindole-2-carboxylic acid:5,6-dihydroxyindole ratio, and the degree of cross-linking in the pigment. Excellent agreement is observed between these spectral results and the chemical degradation data.

Isolation and culture of amelanotic melanocytes from human hair follicles

We report a method to establish amelanotic melanocytes (AMMC) in culture and we investigate the effects of various components in the culture medium. Normal human scalp from cadaver donors was transected 1 mm below the epidermis, and hair follicles in the remaining dermis were isolated by a two-step enzyme treatment. The individual hair follicles were washed exhaustively and suspensions of hair follicle cells were prepared and cultured in Eagle's minimum essential medium supplemented with 12-o-tetradecanoyl-phorbol-13-acetate (TPA), cholera toxin and keratinocyte serum-free medium (K-SFM). Geneticin was used to eliminate contaminating fibroblasts. Proliferation of AMMC was observed after addition of TPA and K-SFM including bovine pituitary extract (BPE) into the culture medium. Cell type was determined by staining with monoclonal antibodies, NKI/beteb and HMB-45, which recognize premelanosomal and melanosomal antigens, respectively. The AMMC were also examined using transmission electron microscopy. Treatment with geneticin eliminates the majority of fibroblasts and does not impair the growth of keratinocytes or AMMC. After contaminating fibroblasts and keratinocytes were removed, two distinct cell morphologies remained: (1) large, dendritic and deeply pigmented cells, which did not proliferate and which disappeared by the third passage, and (2) small bipolar cells, which initially were unpigmented and proliferated very rapidly. We observed that TPA at various concentrations stimulated the proliferation of the cells, and at high concentrations could induce the formation of multiple dendrites. K-SFM including BPE accelerated the proliferation of the cells in a dose-dependent manner. After passage 3, almost all cells expressed premelanosomal and melanosomal antigens, recognized by NKI/beteb and HMB-45, respectively. Active mitochondria, abundant rough endoplasmic reticulum, Golgi complexes, ribosomes and melannosomes (predominantly in stages I, II or III with some at stage IV in some AMMC) were observed ultrastructurally in the cytoplasm of the cultured cells.

Comparisons of the Structural and Chemical Properties of Melanosomes Isolated from Retinal Pigment Epithelium, Iris and Choroid of Newborn and Mature Bovine Eyes¶

Melanosomes were isolated from the retinal pigment epithelium (RPE), iris and choroid of mature (age >2 years) and newborn (age <1 week) bovine eyes. Scanning electron microscopy was utilized to analyze the morphology of the melanosomes, which were found to vary among different tissues and different ages. While the total content of amino acids differs slightly (ranging from 9% to 15% by mass), the distributions of the amino acids are similar. The pheomelanin content is low in the choroid and the RPE (0.1-0.5%), and moderate in the iris (<2%); therefore, the major melanin component of bovine eye melanosomes is eumelanin, independent of the shape of the melanosomes. The yields of pyrrole-2,3,5-tricarboxylic acid from melanosomes decrease in the following order: choroid > iris > RPE, and exhibit decreasing yields with age. 13C solid-state nuclear magnetic resonance (NMR) spectroscopic analysis of iris and choroid melanosomes indicates the same trends. These observations suggest that the 5,6-dihydroxyindole-2-carboxylic acid contents decrease in the following order: choroid > iris > RPE, and decrease with age. Moreover, the 13C solid-state NMR spectra show (1) for the same age samples, the CH:Cq ratio for choroid is larger than that for iris melanosomes; and (2) an increase in the concentration of carbonyl groups with age within each type of melanosome.

Tyrosine-induced melanogenesis shows differences in morphologic and melanogenic preferences of melanosomes from light and dark skin types

The quality, quantity and distribution of melanosomes in epidermis play a crucial role in the determination of skin color and its sensitivity to UV radiation. Melanocyte cultures originating from individuals with light and dark skin types were grown in media with varying concentration of L-tyrosine. Melanosomal melanin content and the size of the organelles were measured after subcellular fractionation. In light-skin type cells, increased melanin production resulted in a more elliptical shape of melanosomes. In melanosomes that constitutively produce more melanin, the tyrosine-induced melanogenesis caused enlargement in all dimensions. X-ray microanalysis provided evidence that the increase in sulfur content induced by high tyrosine concentration was more prominent in the melanosomes from light skin types. A ratio between pheomelanin and eumelanin found in light-skin type melanosomes by HPLC was increased more markedly than that in melanosomes from dark skin melanocytes. These findings suggest that the melanocytes of light-skinned individuals exhibit a preference for pheomelanogenesis. Pheomelanin production is a thiol-consuming process and that might increase the risk of oxidation stress in these cells. This fact, together with the limited ability of pheomelanin to absorb UV radiation may lead to an elevated skin cancer risk among light-skinned individuals.

Quantitative analysis of eumelanin and pheomelanin in humans, mice, and other animals: a comparative review

The color of hair, skin, and eyes in animals mainly depends on the quantity, quality, and distribution of the pigment melanin, which occurs in two types: black to brown eumelanin and yellow to reddish pheomelanin. Microanalytical methods to quantify the amounts of eumelanin and pheomelanin in biological materials were developed in 1985. The methods are based on the chemical degradation of eumelanin to pyrrole-2,3,5-tricarboxylic acid and of pheomelanin to aminohydroxyphenylalanine isomers, which can be analyzed and quantitated by high performance liquid chromatography. This review summarizes and compares eumelanin and pheomelanin contents in various pigmented tissues obtained from humans, mice, and other animals. These methods have become valuable tools to study the functions of melanin, the control of melanogenesis, and the actions and interactions of pigmentation genes. The methods have also found applications in many clinical studies. High levels of pheomelanin are found only in yellow to red hairs of mammals and in red feathers of birds. It remains an intriguing question why lower vertebrates such as fishes do not synthesize pheomelanin. Detectable levels of pheomelanin are detected in human skin regardless of race, color, and skin type. However, eumelanin is always the major constituent of epidermal melanin, and the skin color appears to be determined by the quantity of melanin produced but not by the quality.

Screening of human primary melanocytes of defined melanocortin-1 receptor genotype: pigmentation marker, ultrastructural and UV-survival studies

Recent population studies have demonstrated an association with the red-hair and fair-skin phenotype with variant alleles of the melanocortin-1 receptor (MC1R) which result in amino acid substitutions within the coding region leading to an altered receptor activity. In particular, Arg151Cys, Arg160Trp and Asp294His were the most commonly associated variants seen in the south-east Queensland population with at least one of these alleles found in 93% of those with red hair. In order to study the individual effects of these variants on melanocyte biology and melanocytic pigmentation, we established a series of human melanocyte strains genotyped for the MC1R receptor which included wild-type consensus, variant heterozygotes, compound heterozygotes and homozygotes for Arg151Cys, Arg160Trp, Val60Leu and Val92Met alleles. These strains ranged from darkly pigmented to amelanotic, with all strains of consensus sequence having dark pigmentation. UV sensitivity was found not to be associated with either MC1R genotype or the level of pigmentation with a range of sensitivities seen across all genotypes. Ultrastructural analysis demonstrated that while consensus strains contained stage IV melanosomes in their terminal dendrites, Arg151Cys and Arg160Trp homozygote strains contained only stage II melanosomes. This was despite being able to show expression of tyrosinase and tyrosinase-related protein-1 markers, although at reduced levels and an ability to convert exogenous 3,4-dihydroxyphenyl-alanine (DOPA) to melanin in these strains.

Advanced chemical methods in melanin determination

Among the biopolymers, melanins are unique in many respects. The other essential biopolymers - proteins, nucleic acids, and carbohydrates - are chemically well characterized; their precursors (monomer units) and modes of connection between the monomer units are known, and sequences of their connection can be determined with well-established methodologies. In contrast, we still do not have a method to determine accurately the ratio of various units present in melanins. This is largely because of the chemical properties of melanins, such as their insolubility over a broad range of pH, the heterogeneity in their structural features, and also because of the lack of methods that can split melanin polymers into their monomer units (all other biopolymers can be hydrolysed to the corresponding monomer units). To overcome this difficulty, we developed a rapid and sensitive method for quantitatively analysing eumelanin and pheomelanin in biological samples by chemical degradation methods followed by HPLC determination. This HPLC microanalytical method for characterizing eumelanin and pheomelanin has become a useful tool for the study of melanogenesis. This review will summarize the usefulness and limitations of the various chemical and spectrophotometric methods used to analyse melanins at the biochemical, cellular, and tissue levels. Emphasis is given on the usefulness of 4-amino-3-hydroxyphenylalanine as a specific marker of pheomelanin.

The usefulness of 4-amino-3-hydroxyphenylalanine as a specific marker of pheomelanin

Reductive hydrolysis of pheomelanin with hydriodic acid (HI) gives two aminohydroxyphenylalanine isomers, 4-amino-3-hydroxyphenylalanine ('specific AHP') and 3-amino-4-hydroxyphenylalanine (3-aminotyrosine, AT), which derive from the oxidative polymerization of 5-S-cysteinyldopa, and 2-S-cysteinyldopa, respectively. Since we first introduced this analytical method, the combined amount of AHP and AT ('total AHP') has been extensively used as a marker of pheomelanin. However, one problem with using total AHP as a marker is that background levels originate from precursors other than pheomelanin. Considerable and variable amounts of background AT are produced from other sources, most likely nitrotyrosine residues in proteins. In order to overcome this problem, we developed HPLC conditions which enable the direct injection of the HI reduction products into the HPLC system allowing good separation of AHP and AT. In this way we could study the importance of both degradation products separately and their specificity as markers for pheomelanin. The usefulness of the present method is validated using human hair samples of various colours which were divided into dark, fair or red colours. The combined amount of specific AHP and AT shows an excellent correlation with total AHP, and the amount of specific AHP also correlates with the amount of total AHP. We also examined total AHP and specific AHP values against pyrrole-2,3,5-tricarboxylic acid (PTCA) values in the human hair samples. These results show that specific AHP measurement gives a more prominent segregation for the ratio of specific AHP to PTCA among hairs of various colours than the ratio of total AHP to PTCA. Thus, we conclude that 'specific AHP' is a more specific marker of pheomelanin than is 'total AHP'.

Noise-induced hearing loss: the effect of melanin in the stria vascularis

Conflicting investigations regarding the potential protective effect of melanin against noise-induced sensorineural hearing loss have suggested that eumelanin and pheomelanin may have differing effects within the stria vascularis. Three strains of C57BL/6J mice, (+/+, a/a) wild-types (dark coats/black eyes), (c2j/c2j, a/a), albinos (white coats/pink eyes), and (+/+, Ay/Ay) yellow mice (yellow coats/black eyes), were subjected to five consecutive days of broad band noise exposure at 112 dB(A) SPL for 3 h/day. Cochlear function was evaluated with auditory brainstem response audiometry to pure tones immediately pre-exposure, 5-6 h postexposure, and 14 days post-exposure. No significant difference in the degree of sensorineural hearing loss induced in the three strains of mice was identified. The eumelanin and pheomelanin content of each stria vascularis and amount of protein per stria for both mouse and guinea pig (2/NCR) were determined via high performance liquid chromatography. No pheomelanin was found in the stria of yellow mice, suggesting that coat color is not an accurate predictor of strial melanin content. The melanin content per mg of strial protein was higher in mice than in guinea pigs. A species-specific difference in melanin content does not explain the absence of a protective effect in mice.

Melanin density and melanin type predict melanocytic naevi in 19-20 year olds of northern European ancestry

Recent advances in estimating the density of cutaneous melanin by spectrophotometry and the concentration of the two types of melanin (eumelanin and phaeomelanin) in hair offer the potential to define the risk of skin cancer in individuals more accurately. The presence of common melanocytic naevi on the arm is associated with an increased risk of melanoma, and in this study the associations of arm naevi with melanin density at the upper inner arm and with melanin type in hair samples were examined in a representative sample (n = 267) of 19-20 year olds of northern European ancestry. Particularly in men, the association with naevus count was stronger for cutaneous melanin density than for follicular melanin type. Adjusted for recreational sun exposure, the rank correlation coefficients were r = -0.25, 0.12 and 0.01 for men, and r = -0.17, -0.12 and 0.14 for women, for cutaneous melanin, hair eumelanin and hair phaeomelanin, respectively. The associations with less objective markers of phenotype (hair colour, eye colour, nurse-assessed skin colour, and self-reported skin reaction to unaccustomed sun) were weaker. These findings provide important new information that human susceptibility to mutations of melanocytes can be estimated by objective biological measures. The next step is to determine whether these measures also predict the risk of melanoma.

Theoretical considerations in laser hair removal

A systematic and logical approach for laser hair removal demands an understanding of its biologic and physical bases. This article presents an overview of hair anatomy and physiology followed by a mathematically nonrigorous review of tissue optics and thermal responses to laser irradiation. The reader is provided with a step by step approach to laser hair removal.

Comparison of HPLC and stereologic image analysis for the quantitation of eu- and pheomelanins in nevus cells and stimulated melanoma cells

The aim of the study was to compare two methods of quantitating eumelanins and pheomelanins, pigments synthesized by melanocytes. One is based on the high performance liquid chromatography quantitation of specific degradation products of each melanin type. The other requires image analysis, transmission electron microscopy, and stereology. In a previous study, we showed good correlations between both methods for total melanin but not for eumelanins or pheomelanins. We describe here the same comparison in more pigmented cells (nevus cells and stimulated HBL melanoma cells). Transmission electron microscopy micrographs were image analyzed to generate several primary parameters. Stereology was used for estimating melanosomal maturation, intracellular melanin content, and the number of melanized melanosomes per cell, for total melanin, eumelanins, or pheomelanins. Our results showed a good correlation between both methods for total melanin, eumelanins, and pheomelanins with an r equal to 0.99, 0.91, and 0.93, respectively, when all the points were used in the linear regression analyses. In the melanoma cell group (HBL cells cultured in media of different compositions), the chemical and morphometric estimations were not parallel in the case of eumelanins and pheomelanins. In addition, the stereologic and high performance liquid chromatography pheomelanins to eumelanins ratios were still not correlated. These results demonstrate the relevancy of the stereologic method, but the low level of melanization, the possible lack of specificity of melanogenesis in melanoma cells, and a problem of sensitivity of the stereologic method in this context seem to be obstacles in obtaining better results. The utilization of normal human melanocytes could give some answers to our hypotheses.

Comparison of high performance liquid chromatography and stereological image analysis for the quantitation of eumelanins and pheomelanins in melanoma cells

The aim of the study was to compare two methods quantifying eumelanins and pheomelanins, pigments synthesized by melanocytes. One is based on the high performance liquid chromatography (HPLC) quantitation of specific degradation products of each melanin type. The other requires image analysis, transmission electron microscopy (TEM), and stereology. This study was carried out in cultured human melanoma cells and for each line, melanins were measured by HPLC and cells were fixed and embedded as pellets for TEM. Ultrathin sections were treated or not by the alkali elution method allowing the elimination of pheomelanins. The obtained micrographs were analyzed with our image analysis program permitting the estimation of several primary parameters. Stereology was used for estimating melanosomal maturation, intracellular melanins content, and number of melanized melanosomes per cell, for total melanin, eumelanins, or pheomelanins. Our results show a good correlation between both methods for total melanin, particularly when using the cytoplasmic volume density of melanin (r=0.93). Moreover, we report that the number of melanized melanosomes per cell and not the melanosomal maturation is responsible for the differences in total melanin content observed between the different cell lines. However, none of the stereological melanization parameters was correlated in the case of eumelanins or pheomelanins. In order to demonstrate the utter relevancy of this stereological approach, utilization of more pigmented melanoma cells, comparative study of HPLC and stereology, in normal epidermal melanocytes and a new evaluation of the alkali elution method in appropriate animal models would help us to explain the present results.

Ultrastructural recognition of gap junctions between melanocytes in human vestibular organs by tannic acid containing fixative preparation and freeze-fracture technique

BACKGROUND

The purpose of the present study was to obtain additional information about the ultrastructural characteristics of gap junctions between melanocytes in human vestibular organs by using various ultrastructural techniques.

METHODS

All materials were obtained from patients with vestibular schwannoma. Glutaraldehyde-fixed specimens and specimens treated with fixative containing glutaraldehyde and tannic acid were processed for conventional ultrathin transmission electron microscopic (TEM) examination. Others were prepared for freeze-fracture replica and examined by TEM.

RESULTS

Gap junctions were present between adjacent subepithelial melanocytes. The gaps between the inner leaflets of the apposed plasma membranes at the gap junctions were 10-12 nm, and the gaps between the outer leaflets were 2-4 nm. The intercellular space between the apposed plasma membranes of gap junctions showed the deposition of high electron-dense material in specimens prepared with fixative containing glutaraldehyde and tannic acid. At the highest magnification specimens fixed by glutaraldehyde with or without tannic acid and cut obliquely to the plasma membranes showed periodic substructures with constant repeating lattices or a small porous structure at the junctions. Study by freeze fracture revealed that these gap junctions between melanocytes consisted of 100-200 aggregations of connexon particles that were approximately 8.8 nm in diameter.

CONCLUSIONS

We suggest that melanocytes may construct a cellular network involved in the maintenance of the homeostasis of human vestibular organs through the intimate transmission of various signals or intercellular informations via well-developed gap junctions.

Characterization of melanogenesis in normal human epidermal melanocytes by chemical and ultrastructural analysis

Chemical and ultrastructural studies were conducted to define the relationship between type of melanogenesis and fine structures of melanosomes in normal human epidermal melanocytes. Chemical analysis of epidermal melanin demonstrated that the ratio of eumelanin/pheomelanin varied individually, ranging from 1.31 to exclusively eumelanic. Ultrastructural analysis of fine structures of melanosomes revealed that spheroid melanosomes were frequently observed in melanocytes of the epidermis whose eumelanin/ pheomelanin ratio was less than 5. Conversely, ellipsoid melanosomes predominated in melanocytes of the epidermis whose ratio was more than 10. On the basis of these findings, it seems reasonable to conclude that 1) normal human epidermal melanocytes synthesize both eumelanin and pheomelanin and 2) pheomelanin synthesis may be characterized by the presence of spheroid melanosomes whereas eumelanin synthesis is ascribed to ellipsoid melanosomes.

A prospective study on the association between red hair color and endometriosis in infertile patients

OBJECTIVE

To determine if red-haired infertile women have an increased prevalence of endometriosis.

DESIGN

Prospective, nonblinded.

SETTING

Large, metropolitan, private hospital, associated with a university. Subspeciality care provided by reproductive endocrinologists.

PATIENTS

One hundred forty-three consecutive women undergoing laparoscopy or laparotomy for infertility.

INTERVENTIONS

Laser ablation of any endometriosis present.

MAIN OUTCOME MEASURE

Presence of endometriosis.

RESULTS

Of 143 women entered into the study, 12 had natural red hair. The ages of these women ranged between 23 and 41 years. Ten of 12 (83%) of the red-haired women were found to have endometriosis compared with 55 of 131 (42%) of nonredheads. By statistical analysis, the 95% confidence intervals for the presence of endometriosis in redheads was 55% to 100% versus 34% to 51% for nonredheads.

CONCLUSION

The results suggest an association between the occurrence of natural red hair and those factors that lead to the development of endometriosis.

Isoenzymic patterns of tyrosinase in the rabbit choroid and retina/retinal pigment epithelium

Tyrosinase in crude extracts from the adult rabbit choroid and retina/retinal pigment epithelium was found to be differently affected by the inhibitors sodium metabisulfite, cyanide, diethyldithiocarbamate and 2,2'-dipyridyl:the latter inhibited the activity in the retina/retinal pigment epithelium extract after 24 hr of incubation, but not that in the choroid. The first three inhibitors, on the other hand, inhibited the activity in the choroid extract, but not in the retina/retinal pigment epithelium extract, after 3 hr of incubation. Both extracts contained one insoluble and two soluble isoenzymes. The mobilities and the apparent molecular weights of the soluble isoenzymes (more markedly so for the most rapidly migrating) differed, as revealed by polyacrylamide gel electrophoresis, resulting in distinct isoenzymic patterns. We suggest that such patterns may be related to the characteristic melanogenic features of the retina/retinal pigment epithelium and choroid.

Ultrastructural evidence of cell communication between epithelial dark cells and melanocytes in vestibular organs of the human inner ear

BACKGROUND

The possibility of interaction between epithelial dark cells and melanocytes in the mammalian inner ear has been pointed out because of their morphological and biochemical characteristics, although very few studies have dealt directly with communication between these two types of cells. We investigated the dark cell area of human vestibular organs in order to clarify the ultrastructural evidence for cell interaction between epithelial dark cells and melanocytes.

METHODS

All of the material was obtained from vestibular schwannoma operations. Paraffin sections were stained with hematoxylin and eosin (H&E) and by the Fontana-Masson technique. Other paraffin sections were also stained immunohistochemically for S-100 protein. Glutaraldehyde fixed specimens were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

RESULTS

Light microscopy revealed melanin pigment granules in the cytoplasm of epithelial dark cells. Melanocytes in the subepithelial layer stained positively for S-100 protein. The presence of intraepithelial melanocytes was confirmed by the presence of cell profiles with a large number of melanin pigment granules and S-100 protein in the cytoplasm. SEM showed that the dark cells had a pentagonal surface with microvilli on the apical surface edge. They had complicated structures at the basal portion of their cytoplasm. Melanocytes extending cytoplasmic processes to adjacent areas were observed under the dark cells. TEM showed that the dark cells were tightly linked by junctional complexes in the upper lateral portion of their cytoplasmic membrane and interdigitated by lateral infoldings. Compound melanosomes (phagosomes or secondary lysosomes) found in the cytoplasm of the dark cells contained poorly pigmented melanosomes with a periodic internal structure. Gap junctions were clearly showed between adjacent melanocytes in the subepithelial layer.

CONCLUSIONS

The characteristic substructures of dark cells and melanocytes suggested the presence of intimate cell interaction between these two types of cells in the vestibular organs of the human inner ear, although it is not clear at this stage whether such cell interaction is specific only for patients with vestibular schwannoma. Dark cells and melanocytes form a cell community that serves to maintain homeostasis in vestibular organs through communication in which cell information obtained by both dark cells and melanocytes serves to facilitate the system.

An ultrastructural study of melanocytes and melanosomes in the skin and hair bulbs of rufous albinos

We have examined hair bulb and skin melanocytes of rufous albinos from Southern Africa to further characterize this form of albinism. In the skin melanocytes we find both eumelanosomes and pheomelanosomes at various stages of melanization and, in addition, there appeared to be many aberrant incompletely melanized melanosomes. On average, rufous melanosomes are 30% smaller than normal black skin melanosomes. In the keratinocytes, the melanosomes are packaged into distinct aggregations, whereas in normal black skin, they occur singly. We suggest that the reddish skin color of these albinos is a consequence of an increase in the pheomelanin synthesis resulting in a raised pheomelanin/eumelanin ratio and that the aggregation of melanosomes results in a skin color slightly lighter than normal. In hair bulb melanocytes, only eumelanosomes were seen and these were mostly incompletely melanized. These findings correlate with our visual observations that the hair color of Southern African albinos is very pale (light brown or ginger). Based on our observations, we speculate on the possible cause of rufous albinism.

Hair melanins and hair color: ultrastructural and biochemical aspects

The color variants of mammalian hair, including spotting and albinism, are the result of melanocyte activity and have been shown to be determined by the action of multiple genes, some of which operate through the milieu in which the pigment cell resides; others appear to act intracellularly to control the type of melanogenesis. Although there has been much descriptive work on the mode of action of these genes, it has only been with the recent advances in the chemistry and molecular biology of melanin pigmentation that some progress is being made in understanding the nature and origin of hair color. It is the purpose of this article to provide an integrated overview of the major advances so made and to draw attention to certain peculiarities of the melanization processes of hair with respect to those underlying skin pigmentation. Key words: melanins, melanocytes, melanogenesis, hair.

Melanin pigments and melanosomal proteins as differentiation markers unique to normal and neoplastic melanocytes

This report introduces some aspects of our current basic research focus on the unique metabolic pathways within the melanocyte. Using this approach, we hope to gain a better understanding of the pathophysiology of malignant melanoma and develop early laboratory diagnostic tests for this disease. Specifically, we will discuss that: 1) the synthesis of pheomelanin is markedly increased in malignant melanoma and dysplastic melanocytic nevi; 2) high levels of metabolites of pheomelanin and eumelanin can be detected in the urine and blood of patients with metastatic melanoma; 3) this release of melanin metabolites appears to correlate with tumor thickness and tumor load, including the extent of metastasis; 4) the synthesis of melanosomal proteins also becomes aberrant in malignant melanoma; and 5) this abnormal melanosome synthesis can be utilized in the identification of antigenic epitopes that are uniquely expressed in malignant melanoma. We believe that this synthesis and secretion of abnormal melanin pigment and melanosomal proteins (human melanosome-specific antigen) would be useful for the development of early laboratory diagnostic and monitoring tools for malignant melanoma. In addition, we also report the detection of pheomelanin component in "normal" unexposed skin; however, the relative amount of pheomelanin in the skin does not reflect hair color (e.g., red hair). The nature of this pheomelanin component in the skin needs to be further clarified.

Dysplastic melanocytic nevi contain high levels of pheomelanin: quantitative comparison of pheomelanin/eumelanin levels between normal skin, common nevi, and dysplastic nevi

The degree and type of melanogenesis, i.e., either eumelanin of pheomelanin, has been shown to be a reliable marker for the differentiation of the melanocyte. If exposed to UV light, these two melanins were reported to behave differently; eumelanin was photoprotective whereas pheomelanin was phototoxic to cultured tumor cells. Our previous study indicated that dysplastic melanocytic nevus (DMN) undergoes altered melanogenesis, forming pheomelanosome-like granules. The present study examined chemically the type and degree of melanin synthesized in 31 melanocytic nevi excised from 27 patients as compared with that occurring in the surrounding normal skin. The tissue content of eumelanin and pheomelanin was expressed by the amounts of pyrrole-2,3,5-tricarboxylic acid (PTCA) and aminohydroxyphenylalanine (AHP), respectively. We found that DMN lesions contain significantly higher amounts of pheomelanin than either common melanocytic nevus (CMN) or normal skin. Differences in pheomelanin content between DMN and CMN could not be accounted for by inherently higher levels of pheomelanin within the skin in general from DMN patients. Our present finding substantiates our previous claim that epidermal melanocytes in DMN undergo deranged melanogenesis.

Pheomelanin as well as eumelanin is present in human epidermis

There are two types of melanin in mammals, the brownish black eumelanin and the reddish yellow pheomelanin. Eumelanin and pheomelanin are present in human hair and this study was carried out to see whether both pigments are also present in human epidermis. Samples of epidermis were obtained from suction blisters raised in the upper arm of 13 Caucasian subjects of skin types I, II, and III and analyzed for both eumelanin and pheomelanin using a procedure involving high-performance liquid chromatography. Eumelanin and pheomelanin were found in all epidermal samples and their relative proportions correlated well with those found in samples of hair taken from the same subjects. The lowest concentrations of eumelanin were found in subjects of skin type I, with higher levels in skin types II and III. The concentrations of pheomelanin were more variable and showed no relationship to skin type. Increases in the concentrations of both pigments occurred following PUVA therapy, but whereas the largest increases in eumelanin were seen in skin types II and III, the increases in pheomelanin showed little relationship to skin type. Unlike eumelanin, epidermal pheomelanin also showed little relationship to PUVA-induced tanning. The present findings could be particularly significant in view of recent suggestions that pheomelanin, rather than protecting the skin against UV radiation, may actually contribute to UV-induced skin damage.