The protective role of melanin against UV damage in human skin

Bacterial tyrosinases: old enzymes with new relevance to biotechnology

Tyrosinases are copper-containing dioxygen activating enzymes found in many species of bacteria and are usually associated with melanin production. These proteins have a strong preference for phenolic and diphenolic substrates and are somewhat limited in their reaction scope, always producing an activated quinone as product. Despite this fact they have potential in several biotechnological applications, including the production of novel mixed melanins, protein cross-linking, phenolic biosensors, production of l-DOPA, phenol and dye removal and biocatalysis. Although most studies have used Streptomyces sp. enzymes, there are several other examples of these proteins that are also of potential interest. For instance a solvent tolerant enzyme has been described, as well as an enzyme with both tyrosinase and laccase activities, enzymes with altered substrate preferences, an enzyme produced as an inactive zymogen as well as examples which do not require auxiliary proteins for copper insertion (unlike the Streptomyces sp. enzymes which do require such a protein). This article will summarise the reports on the biotechnological applications of bacterial tyrosinases as well as the current information available on the different types of this enzyme.

Skin tissue engineering--in vivo and in vitro applications

Significant progress has been made over the years in the development of in vitro-engineered substitutes that mimic human skin, either to be used as grafts for the replacement of lost skin or for the establishment of human-based in vitro skin models. This review summarizes these advances in in vivo and in vitro applications of tissue-engineered skin. We further highlight novel efforts in the design of complex disease-in-a-dish models for studies ranging from disease etiology to drug development and screening.

Catechol Redox Induced Formation of Metal Core-Polymer Shell Nanoparticles

A novel strategy was developed to synthesize polymer-coated metal nanoparticles (NPs) through reduction of metal cations with 3,4-dihydroxyphenylalanine (DOPA)-containing polyethylene glycol (PEG) polymers. Catechol redox chemistry was used to both synthesize metal NPs and simultaneously form a cross-linked shell of PEG polymers on their surfaces. DOPA reduced gold and silver cations into neutral metal atoms, producing reactive quinones that covalently cross-linked the PEG molecules around the surface of the NP. Importantly, these PEG-functionalized metal NPs were stable in physiological ionic strengths and under centrifugation, and hold broad appeal since they absorb and scatter light in aqueous solutions.

Photoaging under recreational sunbeds

BACKGROUND

Artificial sources of restricted light wavelength, particularly tanning beds, are progressively gaining importance in photoaging.

OBJECTIVE

To assess the kinetics and the long-term evolution of skin pigmentation and tensile functions in sunbed worshippers over a period of 8 years.

METHODS

Photoaging was explored in women who were both sunshine and sunbed worshippers. A series of 65 phototype III women aged 31-46 years completed a 100-month survey. Quarterly assessments were performed on the forearms to measure (a) the skin color individual typology angle (ITA°), (b) the extent in mottled subclinical melanoderma (MSM) using the ultraviolet light-enhanced visualization method and (c) the rheological properties of skin.

RESULTS

A progressive increase in both skin extensibility and hysteresis was observed, contrasting with a decrease in biologic elasticity. These rheological changes were correlated with the ITA° changes, but not with the MSM extent. The kinetics of evolution of each test variable were distinct over time.

DISCUSSION

This work is the first attempt at evaluating the kinetics of changes in physical parameters during a long period of frequent exposures to tanning sunbeds and sunshine for lifestyle purposes. The alterations were quite important in the color, MSM and rheological functions of the skin.

Ultraviolet radiation and skin cancer

Skin cancer is the most common type of cancer in fair-skinned populations in many parts of the world. The incidence, morbidity and mortality rates of skin cancers are increasing and, therefore, pose a significant public health concern. Ultraviolet radiation (UVR) is the major etiologic agent in the development of skin cancers. UVR causes DNA damage and genetic mutations, which subsequently lead to skin cancer. A clearer understanding of UVR is crucial in the prevention of skin cancer. This article reviews UVR, its damaging effects on the skin and its relationship to UV immunosuppression and skin cancer. Several factors influence the amount of UVR reaching the earth's surface, including ozone depletion, UV light elevation, latitude, altitude, and weather conditions. The current treatment modalities utilizing UVR (i.e. phototherapy) can also predispose to skin cancers. Unnecessary exposure to the sun and artificial UVR (tanning lamps) are important personal attributable risks. This article aims to provide a comprehensive overview of skin cancer with an emphasis on carefully evaluated statistics, the epidemiology of UVR-induced skin cancers, incidence rates, risk factors, and preventative behaviors & strategies, including personal behavioral modifications and public educational initiatives.

The deceptive nature of UVA tanning versus the modest protective effects of UVB tanning on human skin

The relationship between human skin pigmentation and protection from ultraviolet (UV) radiation is an important element underlying differences in skin carcinogenesis rates. The association between UV damage and the risk of skin cancer is clear, yet a strategic balance in exposure to UV needs to be met. Dark skin is protected from UV-induced DNA damage significantly more than light skin owing to the constitutively higher pigmentation, but an as yet unresolved and important question is what photoprotective benefit, if any, is afforded by facultative pigmentation (i.e. a tan induced by UV exposure). To address that and to compare the effects of various wavelengths of UV, we repetitively exposed human skin to suberythemal doses of UVA and/or UVB over 2 weeks after which a challenge dose of UVA and UVB was given. Although visual skin pigmentation (tanning) elicited by different UV exposure protocols was similar, the melanin content and UV-protective effects against DNA damage in UVB-tanned skin (but not in UVA-tanned skin) were significantly higher. UVA-induced tans seem to result from the photooxidation of existing melanin and its precursors with some redistribution of pigment granules, while UVB stimulates melanocytes to up-regulate melanin synthesis and increases pigmentation coverage, effects that are synergistically stimulated in UVA and UVB-exposed skin. Thus, UVA tanning contributes essentially no photoprotection, although all types of UV-induced tanning result in DNA and cellular damage, which can eventually lead to photocarcinogenesis.

Infant skin physiology and development during the first years of life: a review of recent findings based on in vivo studies

Infant skin is often presented as the cosmetic ideal for adults. However, compared to adult skin it seems to be more prone to develop certain pathological conditions, such as atopic dermatitis and irritant contact dermatitis. Therefore, understanding the physiology of healthy infant skin as a point of reference is of interest both from the cosmetic as well as from the clinical point of view. Clinical research on healthy infants is, however, limited because of ethical considerations of using invasive methods and therefore until recently data has been scarce. Technical innovations and the availability of non-invasive in vivo techniques, such as evaporimetry, electrical impedance measurement, in vivo video and confocal microscopy, and in vivo fibre-optic based spectroscopy, opened up the field of in vivo infant skin physiology research. Studies incorporating such methods have demonstrated that compared to adult, infant skin continues to develop during the first years of life. Specifically, infant skin appears to have thinner epidermis and stratum corneum (SC) as well as smaller corneocytes at least until the second year of life. The water-handling properties are not fully developed before the end of the first year and infant SC contains more water and less amounts of natural moisturizing factors. Such findings re-evaluate the old notions that skin is fully matured at birth. Armed with this knowledge, we are in a position not only to better understand infant dermatological conditions but also to design better skin care products respecting the distinct qualities of infant skin.

Genetics of pigmentation in skin cancer--a review

Skin pigmentation is one of the most overt human physical traits with consequences on susceptibility to skin cancer. The variations in skin pigmentation are dependent on geographic location and population ethnicity. Skin colouration is mainly due to the pigmentation substance melanin, produced in specialized organelles (melanosomes) within dendritic melanocytes, and transferred to neighbouring keratinocytes. The two types of melanin synthesized in well defined chemical reactions are the protective dark coloured eumelanin and the sulphur containing light red-yellow pheomelanin. The events leading to the synthesis of melanin are controlled by signalling cascades that involve a host of genes encoding ligands, receptors, transcription factors, channel transporters and many other crucial molecules. Several variants within the genes involved in pigmentation have been associated with high risk phenotypes like fair skin, brown-red hair and green-blue eyes. Many of those variants have also been implicated in the risk of various skin cancers. The variants within the key pigmentation gene, melanocortin-receptor 1 (MC1R), in particular have been ubiquitously linked with high risk traits and skin cancers involving both pigmentary and non-pigmentary functions and likely interaction with variants in other genes. Many of the variants in other genes, functional in pigmentation pathway, have also been associated with phenotypic variation and risk of skin cancers. Those genes include agouti signalling protein (ASIP), tyrosinase (TYR), tyrosinase-related protein 1 (TYRP1), oculocutaneous albinism II (OCA2), various solute carrier genes and transporters. Most of those associations have been confirmed in genome wide association studies that at the same time have also identified new loci involved in phenotypic variation and skin cancer risk. In conclusion, the genetic variants within the genes involved in skin pigmentation besides influencing phenotypic traits are important determinants of risk of several skin cancers. However, ultimate risk of skin cancer is dependent on interplay between genetic and host factors.

Is UV radiation beneficial in postburn wound healing?

Currently strict ultraviolet (UV) light avoidance strategies and utilizing sunblock containing products are generally advocated during the reepithelialization process as well as after wound closure. These recommendations are guided by a common appreciation of UV radiation as a predominant cause of skin cancer development. It is possible however that the currently accepted practice of near continuous UV protection abrogates the normal cutaneous response to injury, with melanocyte redistribution and pigmentation creating hypopigmented scars. We hypothesize that judicious UV exposure might in fact be beneficial for wound healing and skin homeostasis. UV light should be investigated as a potential modulator of keratinocyte-melanocyte cross-talk in wound healing. In vitro studies will have to prove whether UV radiation induced melanocyte activation might have a stimulatory paracrine effect on keratinocyte proliferation which could beneficially affect wound healing. We further hypothesize that UV exposure to wounds might stimulate and restore normal melanocyte distribution and melanin content in reepithelialized wounds preventing hypopigmentation. Furthermore, exposure of reepithelialized wounds to UV light might exert a photo protective effect in the skin by the production of melanin. This in turn may protect the epidermis from UV-induced damage and carcinogenesis. It is therefore proposed that moderate UV exposure should be commenced early in the healing process of cutaneous wounds. At present, current practice and literature do not support the notion that UV-sun block is necessary in postburn scar management. Burn scars do not seem to exert an enhanced risk for melanomagenesis, the occurrence of which has only very rarely been reported in burn scars. Different mutations in susceptibility genes or in genes involved in the control of the cell cycle or maintenance of cellular integrity which are UV radiation independent are involved in the initiation and promotion steps of skin cancer.

New wrinkles on wrinkling: an 8-year longitudinal study on the progression of expression lines into persistent wrinkles

BACKGROUND

While cumulative lifetime sun exposure is well recognized as having an important role in the progression of facial wrinkling, the role of facial expression has largely been overlooked, in part due to the lack of comprehensive longitudinal data on the change in both expression lines and persistent wrinkles with age.

OBJECTIVES

To track the detailed pattern of facial wrinkling in the same group of people over several years and to verify that expression lines evolve into persistent wrinkles. In addition, to identify factors predictive of a faster or slower rate of wrinkling.

METHODS

Standardized images were captured at baseline and at 8 years of 122 women (ages 10-72 years, skin types I-VI) with and without a smiling expression. The wrinkle pattern with expression at baseline was compared with the pattern without expression at 8 years. Severity of facial wrinkling was quantified using computer-based image analysis. Skin colour, hydration, sebum and pH were measured at baseline. A structured questionnaire captured demographic and lifestyle data at baseline and at 8 years.

RESULTS

Each subject's unique pattern of persistent facial wrinkling observed without expression at year 8 was predicted by the pattern of lines observed with a smiling expression at baseline. Having a drier, more alkaline stratum corneum, a lighter complexion, being middle-aged (40s) or becoming menopausal were associated with faster persistent wrinkling.

CONCLUSIONS

Repeated skin flexure during facial expression causes persistent wrinkles. The pattern of expression lines predicts the pattern of future persistent wrinkles. Certain intrinsic and extrinsic factors are not causative, but influence the rate, of facial wrinkling.

The melanocortin-1 receptor gene polymorphism and association with human skin cancer

The melanocortin-1 receptor (MC1R) is a key gene involved in the regulation of melanin synthesis and encodes a G-protein coupled receptor expressed on the surface of the melanocyte in the skin and hair follicles. MC1R activation after ultraviolet radiation exposure results in the production of the dark eumelanin pigment and the tanning process in humans, providing physical protection against DNA damage. The MC1R gene is highly polymorphic in Caucasian populations with a number of MC1R variant alleles associated with red hair, fair skin, freckling, poor tanning, and increased risk of melanoma and nonmelanoma skin cancer. Variant receptors have shown alterations in biochemical function, largely due to intracellular retention or impaired G-protein coupling, but retain some signaling ability. The association of MC1R variant alleles with skin cancer risk remains after correction for pigmentation phenotype, indicating regulation of nonpigmentary pathways. Notably, MC1R activation has been linked to DNA repair and may also contribute to the regulation of immune responses.

Chromophore concentrations, absorption and scattering properties of human skin in-vivo

Absorption and reduced scattering coefficients of in-vivo human skin provide critical information on non-invasive skin diagnoses for aesthetic and clinical purposes. To date, very few in-vivo skin optical properties have been reported. Previously, we reported absorption and scattering properties of in-vivo skin in the wavelength range from 650 to 1000 nm using the diffusing probe in the "modified two-layer geometry". In this study, we determine the spectra of skin optical properties continuously in the range from 500 to 1000 nm. It was found that the concentration of chromophores, such as oxy-hemoglobin, deoxy-hemoglobin, and melanin, calculated based on the absorption spectra of eighteen subjects at wavelengths above and below 600 nm were distinct because of the inherent difference in the interrogation region. The scattering power, which is related to the average scatterer's size, demonstrates a clear contrast between skin phototypes, skin sites, and wavelengths. We also applied venous occlusion on forearms and found that the concentrations of oxy- and deoxy-hemoglobin as assessed at wavelengths above and below 600 nm were different. Our results suggest that diffuse reflectance techniques with the visible and near infrared light sources can be employed to investigate the hemodynamics and optical properties of upper dermis and lower dermis.

Short- and long-term effects of UV radiation on the pigmentation of human skin

The incidence of skin cancer, including cutaneous melanoma, has risen substantially in recent years, and epidemiological and laboratory studies show that UV radiation is a major causative factor of this increase. UV damage also underlies photoaging of the skin, and these deleterious effects of UV can be, in part, prevented in skin with higher levels of constitutive pigmentation. We review the clinical studies we have made in recent years regarding the rapid and the long-term responses of the pigmentary system in human skin to UV exposure.Journal of Investigative Dermatology Symposium Proceedings (2009) 14, 32-35; doi:10.1038/jidsymp.2009.10.

Current challenges in understanding melanogenesis: bridging chemistry, biological control, morphology, and function

Melanin is a natural pigment produced within organelles, melanosomes, located in melanocytes. Biological functions of melanosomes are often attributed to the unique chemical properties of the melanins they contain; however, the molecular structure of melanins, the mechanism by which the pigment is produced, and how the pigment is organized within the melanosome remains to be fully understood. In this review, we examine the current understanding of the initial chemical steps in the melanogenesis. Most natural melanins are mixtures of eumelanin and pheomelanin, and so after presenting the current understanding of the individual pigments, we focus on the mixed melanin systems, with a critical eye towards understanding how studies on individual melanin do and do not provide insight in the molecular aspects of their structures. We conclude the review with a discussion of important issues that must be addressed in future research efforts to more fully understand the relationship between molecular and functional properties of this important class of natural pigments.

Genetic risk factors for melanoma

The genetic basis of melanoma is complex and has both inherited and acquired components. Different genomic approaches have been used to identify a number of inherited risk factors, which can be stratified by penetrance and prevalence. Rare high-penetrance factors are expressed in familial clustering of melanoma and include mutations in CDKN2A (encoding p16(INK4a) and p14(ARF)) and CDK4. These genes are involved in cell-cycle arrest and melanocyte senescence and are nearly invariably targeted by somatic mutations during melanoma progression. Low-penetrance factors are common in the general population and include single-nucleotide polymorphisms in or near MC1R, ASIP, TYR and TYRP1. These genes are major determinants of hair and skin pigmentation, but their role in melanoma development remains unclear. This review describes the efforts that have led to the current understanding of melanoma susceptibility as the result of complex gene-gene and gene-environment interactions. Despite the significant advances, the majority of familial cases remain unaccounted for.

Skin cancer in skin of color

In general, skin cancer is uncommon in people of color when compared to Caucasians. When it does occur, it is often associated with increased morbidity and mortality. Differences in survival rates may be attributed to skin cancers being diagnosed at a more advanced stage, and socioeconomic factors such as lack of adequate insurance coverage and lack of transportation can function as barriers to timely diagnosis and early treatment. In addition to advanced stage at presentation, malignant skin lesions in skin of color often present in an atypical fashion. Because skin cancer prevention and screening practices historically have been lower among Hispanics, Blacks, and Asians, and given the changing demographics in the United States, interventions that are tailored to each of these groups will be needed. Public educational campaigns should be expanded to educate people of all skin types with emphasis on skin cancers occurring in areas not exposed to the sun (Byrd-Miles et al., 2007), since sunlight is not as important an etiologic factor in the pathogenesis of skin cancer in people of color. Dermatologists and primary care physicians should instruct their darker-skinned patients on how to perform routine skin self-examinations. Physicians should also encourage patients to ask their specialists such as their gynecologist, dentist, and ophthalmologist to look for abnormal pigmentation during routine exams. To reduce the burden of skin cancer, several prevention methods for all people have been strongly encouraged, including monthly self-examinations, daily use of SPF 30 or greater sunscreen, sunglasses with UV-absorbing lenses, and avoiding tanning booths (American Cancer Society, 2008) (see Table 7). In addition, recommendations for clinicians to promote the prevention of skin cancer in skin of color have also been made, including closely monitoring changing pigmented lesions on the palms and soles and hyperkeratotic or poorly healing ulcers in immunosuppressed patients (Halder & Bridgeman-Shah, 1995) (see Table 7).

Chemical analysis of late stages of pheomelanogenesis: conversion of dihydrobenzothiazine to a benzothiazole structure

Pheomelanogenesis is a complex pathway that starts with the oxidation of tyrosine (or DOPA, 3,4-dihydroxyphenylalanine) by tyrosinase in the presence of cysteine, which results in the production of 5-S-cysteinyldopa and its isomers. Beyond that step, relatively little has been clarified except for a possible intermediate produced, dihydro-1,4-benzothiazine-3-carboxylic acid (DHBTCA). We therefore carried out a detailed study on the course of pheomelanogenesis using DOPA and cysteine and the physiological enzyme tyrosinase. To elucidate the later stages of pheomelanogenesis, chemical degradative methods of reductive hydrolysis with hydroiodic acid and alkaline peroxide oxidation were applied. The results show that: (1) DHBTCA accumulates after the disappearance of the cysteinyldopa isomers, (2) DHBTCA is then oxidized by a redox exchange with dopaquinone to form ortho-quinonimine, which leads to the production of pheomelanin with a benzothiazine moiety, and (3) the benzothiazine moiety gradually degrades to form a benzothiazole moiety. This latter process is consistent with the much higher ratio of benzothiazole-derived units in human red hair than in mouse yellow hair. These findings may be relevant to the (photo)toxic effects of pheomelanin.

Nonlinear absorption microscopy

For the past two decades, nonlinear microscopy has been developed to overcome the scattering problem in thick tissue imaging. Owing to its increased imaging depth and high spatial resolution, nonlinear microscopy becomes the first choice for imaging living tissues. The use of nonlinear optical effects not only facilitates the signal originating from an extremely small volume defined by light focusing but also provides novel contrast mechanisms with molecular specificity. Nonlinear absorption is a nonlinear optical effect in which the absorption coefficient depends on excitation intensity. As a commonly used spectroscopy tool, nonlinear absorption measurement uncovers many photophysical and photochemical processes correlated with electronic states of molecules. Recently we have been focusing on adapting this spectroscopy method to a microscopy imaging technique. The effort leads to a novel modality in nonlinear microscopy-nonlinear absorption microscopy. This article summarizes the principles and instrumentation of this imaging technique and highlights some of the recent progress in applying it to imaging skin pigmentation and microvasculature under ex vivo or in vivo conditions.

Effect of untreated and photobleached bovine RPE melanosomes on the photoinduced peroxidation of lipids

Melanin is usually considered a photoprotective pigment and antioxidant agent, but it is unclear how melanosomes protect pigmented cells against oxidative stress induced by light and whether aging modulates its photoprotective function, particularly in long-lived post-mitotic cells such as the retinal pigment epithelium (RPE). To address these issues, we analyzed the effects of untreated and experimentally photobleached melanosomes from cow RPE on the peroxidation of liposomal lipids induced by irradiation with intense visible light or by a rose Bengal photosensitized reaction. Photobleached melanosomes were used as a model of photo-aged pigment granules, and the progress of lipid peroxidation was monitored by electron spin resonance (EPR) oximetry and the iodometric determination of lipid hydroperoxides. We observed that while untreated melanosomes inhibited the rose Bengal induced peroxidation of lipids only moderately, partially photobleached melanosomes had very little effect on this process. Untreated melanosomes also inhibited peroxidation of liposomal lipids induced by intense visible light; however, the inhibitory effect markedly changed with the irradiation time. On the other hand, partially photobleached pigment granules accelerated the photoinduced peroxidation of lipids. The observed effects illustrate the limited efficiency of melanin within granules to scavenge and quench reactive oxygen species randomly generated by photosensitized reactions. The photosensitizing ability of photobleached melanosomes may arise from their capacity to photogenerate hydrogen peroxide. Collectively, our data indicate that natural melanin is only a moderately efficient photoprotective pigment, which upon photoaging may lose its antioxidant efficiency and even become a photosensitizer.

Melanin from epidermal human melanocytes: study by pyrolytic GC/MS

Pigmentation of human skin is determined by the presence of melanin, the polymeric pigment that is produced in melanocytes and transferred to adjacent keratinocytes. Epidermal melanocytes produce two distinct types of melanin pigments: eumelanin, composed mainly of indole-type monomers, and pheomelanin that contains benzothiazine-type backbone. Eumelanin protects skin against UV-induced damages, whereas pheomelanin is believed to act as a potent UV photosensitizer and promote carcinogenesis. In this study, pyrolysis in combination with gas chromatography and mass spectrometry (Py-GC/MS) was applied for structural studies of the epidermal pigment isolated from the cultured human melanocytes. The analysis was preceded by investigations of DOPA-originated synthetic eumelanin and pheomelanin standards. This allowed determination of pyrolytic markers for both types of melanin pigments. To obtain additional information on the natural pigment structure, the samples were thermally degraded in the presence of tetramethylammonium hydroxide as the derivatizing agent. It was shown that the analyzed pigment from normal human epidermal melanocytes derived from moderately pigmented skin is of eumelanin type with little incorporation of a pheomelanin component. The results indicate that Py-GC/MS is a rapid and efficient technique for the differentiation of epidermal melanin types and may be an alternative to commonly used methods based on chemical degradation.

Challenges in applying photoemission electron microscopy to biological systems

Photoemission electron microscopy (PEEM) is a unique surface-sensitive instrument capable of providing real-time images with high spatial resolution. While similar to the more common electron microscopies, scanning electron microscopy and transmission electron microscopy, the imaging technology relies on the photogeneration of electrons emitted from a sample through light excitation. This imaging technique has found prominence in surface and materials sciences, being well suited for imaging flat surfaces, and changes that occur to that surface as various parameters are changed (e.g. temperature, exposure to reactive gases). Biologically focused PEEM received significant attention in the 1970s, but was not aggressively advanced since that pioneering work. PEEM is capable of providing important insights into biological systems that extend beyond simple imaging. In this article, we identify and establish important issues that affect the acquisition and analysis of biological samples with PEEM. We will briefly review the biological impact and importance of PEEM with respect to our work. The article also concludes with a discussion of some of the current challenges that must be addressed to enable PEEM to achieve its maximum potential with biological samples.

Insights into melanosomes and melanin from some interesting spatial and temporal properties

Melanosomes are organelles found in a wide variety of tissues throughout the animal kingdom and exhibit a range of different shapes: spheres of up to approximately 1 mum diameters and ellipsoids with lengths of up to approximately 2 mum and varying aspect ratios. The functions of melanosomes include photoprotection, mitigation of the effects of reactive oxygen species, and metal chelation. The melanosome contains a variety of biological molecules, e.g., proteins and lipids, but the dominant constituent is the pigment melanin, and the functions ascribed to melanosomes are uniquely enabled by the chemical properties of the melanins they contain. In the past decade, there has been significant progress in understanding melanins and their impact on human health. While the molecular details of melanin production and how the pigment is organized within the melanosome determine its properties and biological functions, the physical and chemical properties of the surface of the melanosome are central to their range of ascribed functions. Surprisingly, few studies designed to probe this biological surface have been reported. In this article, we discuss recent work using surface-sensitive analytic, spectroscopic, and imaging techniques to examine the structural and chemical properties of many types of natural pigments: sepia melanin granules, human and bovine ocular melanosomes, human hair melanosomes, and neuromelanin. N 2 adsorption/desorption measurements and atomic force microscopy provide novel insights into surface morphology. The chemical properties of the melanins present on the surface are revealed by X-ray photoelectron spectroscopy and photoemission electron microscopy. These technologies are also applied to elucidate changes in surface properties that occur with aging. Specifically, studies of the surface properties of human retinal pigment epithelium melanosomes as a function of age are stimulating the development of models for their age-dependent behaviors. The article concludes with a brief discussion of important unanswered research questions in this field.