Alteration of racial differences in melanosome distribution in human epidermis after exposure to ultraviolet light

Assessment of Variability in Free Flap Color Match to Facial Skin by Donor Site and Race

OBJECTIVES

To use portable colorimetry to quantify color differences between facial skin and potential three head and neck microvascular free tissue transfer (MFTT) donor sites-radial forearm (RF), anterolateral thigh (ALT), and fibula (FF)-and compare these differences by pigmentation of the donor site skin and self-identified race.

METHODS

In this cross-sectional cohort study, healthy volunteers consented to handheld colorimeter measurements at the three potential MFTT donor sites (RF, ALT, FF) to quantify color match to the facial skin using the CIE color space (DeltaE). The comparison of ipsilateral to contralateral cheek served as control for measurements. Cross-sectional measurements in healthy volunteers were then compared to measurements obtained in postoperative head and neck MFTT patients.

RESULTS

DeltaE measurements were obtained for 128 healthy controls and 24 postoperative patients (N = 152). With increasing lightness (decreased pigmentation) of the skin at the donor site, the color match significantly worsened (higher DeltaE) across all potential MFTT donor sites (all p < 0.05). DeltaE from healthy controls closely approximated postoperative color match measurements in patients who underwent cervicofacial MFTT (DeltaE RF: 5.3 vs. 6.0, p = 0.432; DeltaE ALT: 6.2 vs. 6.4, p = 0.822; DeltaE FF: 6.0 vs. 6.4, p = 0.806).

CONCLUSION

Patients with decreased skin pigmentation who are undergoing head and neck MFTT may experience worse color discrepancy between cervicofacial skin and the transferred skin paddle than those with more pigmented skin. Portable colorimetry may identify patients who could benefit from interventions such as dermis-resected free tissue reconstruction with skin grafting to improve postoperative appearance.

LEVEL OF EVIDENCE

3 Laryngoscope, 134:3581-3586, 2024.

Wavelength-dependent threshold fluences for melanosome disruption to evaluate the treatment of pigmented lesions with 532-, 730-, 755-, 785-, and 1064-nm picosecond lasers

BACKGROUND AND OBJECTIVES

A threshold fluence for melanosome disruption has the potential to provide a robust numerical indicator for establishing clinical endpoints for pigmented lesion treatment using a picosecond laser. Although the thresholds for a 755-nm picosecond laser were previously reported, the wavelength dependence has not been investigated. In this study, wavelength-dependent threshold fluences for melanosome disruption were determined. Using a mathematical model based on the thresholds, irradiation parameters for 532-, 730-, 755-, 785-, and 1064-nm picosecond laser treatments were evaluated quantitatively.

STUDY DESIGN/MATERIALS AND METHODS

A suspension of melanosomes extracted from porcine eyes was irradiated using picosecond lasers with varying fluence. The mean particle size of the irradiated melanosomes was measured by dynamic light scattering, and their disruption was observed by scanning electron microscopy to determine the disruption thresholds. A mathematical model was developed, combined with the threshold obtained and Monte Carlo light transport to calculate irradiation parameters required to disrupt melanosomes within the skin tissue.

RESULTS

The threshold fluences were determined to be 0.95, 2.25, 2.75, and 6.50 J/cm² for 532-, 730-, 785-, and 1064-nm picosecond lasers, respectively. The numerical results quantitatively revealed the relationship between irradiation wavelength, incident fluence, and spot size required to disrupt melanosomes distributed at different depths in the skin tissue. The calculated irradiation parameters were consistent with clinical parameters that showed high efficacy with a low incidence of complications.

CONCLUSION

The wavelength-dependent thresholds for melanosome disruption were determined. The results of the evaluation of irradiation parameters from the threshold-based analysis provided numerical indicators for setting the clinical endpoints for 532-, 730-, 755-, 785-, and 1064-nm picosecond lasers.

Skin of color in dermatopathology: does color matter?

Skin of color (SoC) remains an understudied and under taught area of dermatology despite its rising importance. Race and ethnicity play a particularly important role in dermatology as skin pigmentation can affect the manifestation and presentation of many common dermatoses. With this review, we seek to review pertinent differences in SoC histology, as well as highlight the histopathology of conditions more common in SoC and address inherent bias that may affect accurate dermatopathology sign out.

An update on cosmetic procedures in people of color. Part 1: Scientific background, assessment, preprocedure preparation

Increased life expectancy, focus on appearance, and readily available and accessible cosmetic procedures have served to drive an increase in the number of nonsurgical cosmetic procedures performed in the last 20 years. Demographic shifts in the United States, with increases in diverse populations that seek nonsurgical cosmetic procedures, have resulted in the need for a better understanding of cultural preferences as well as structural and biological differences in the skin of people of color (POC). Although many advances in the form of cosmeceuticals, cosmetics, and photoprotection have been made to address the aesthetic needs of and minimize complications in POC, nonsurgical cosmetic procedures are required to address common aesthetic concerns. Gaps remain in the education of dermatologists regarding the appropriate selection and execution of nonsurgical cosmetic procedures in POC. This educational initiative will facilitate a favorable outcome and optimal cosmetic results for POC.

Factors affecting superficial vein visibility at the upper limb in healthy young adults: A cross-sectional observational study

OBJECTIVE

Venipuncture is an invasive procedure, and repeated puncture attempts may be uncomfortable or even traumatic for patients. Vein visibility is one of the most influential variables for the failure of venipuncture; however, the factors affecting vein visibility remain unclear. The present study was conducted to identify the factors influencing vein visibility at the upper limb in healthy young adults.

METHODS

Twenty-seven healthy volunteers were included. All measurements were performed at the right arm, right cubital fossa, and right forearm. The depth and cross-sectional area of superficial veins were measured by ultrasonography. Skin color was assessed by a spectrophotometer and quantified according to Commission International d'Eclairage L*a*b* values.

RESULTS

Invisible superficial veins were significantly deeper and had a larger cross-sectional area than visible superficial veins. Skin color b* of invisible superficial veins was significantly higher than that of visible superficial veins. Vein depth, skin color b*, and gender markedly affected superficial vein visibility at the upper limb. The cutoff for vein depth was 2.3 mm (area under the curve = 0.91).

CONCLUSION

The present results confirmed that vein depth, skin color b*, and gender strongly influenced vein visibility at the upper limb. The cutoff for vein depth was 2.3 mm.

Considerations When Treating Cosmetic Concerns in Men of Color

BACKGROUND

Men of color include a diverse population encompassing individuals with Fitzpatrick skin Types IV through VI. Yet, there is a paucity of data describing the cosmetic concerns of this population.

OBJECTIVE

To review the basic science of advantages and disadvantages of skin of color and pathophysiology, incidence, and treatment of disorders of cosmetic concern in men of color.

METHODS

A MEDLINE search was performed for publications on sex and racial differences in basic science of skin, common disorders in men of color, and evidence-based treatments.

RESULTS

There are intrinsic differences in skin and hair of darker-complexioned men, particularly in Hispanics, African Americans, Asians, and Afro-Caribbeans. Advantages of darker skin include increased photoprotection, slowed aging, and a lower incidence of skin cancer. However, the increased content of melanin is associated with myriad dyschromias including melasma and postinflammatory hyperpigmentation (PIH). Additional common skin conditions of concern in men of color include pseudofolliculitis barbae, acne keloidalis nuchae, and keloids.

CONCLUSION

A skin color conscious approach should be administered in caring for the cosmetic concerns of men of color that is cognizant of differences in biology of the skin and hair, associated PIH of disorders, and cultural/social practices among this population.

Tyrosinase Depletion Prevents the Maturation of Melanosomes in the Mouse Hair Follicle

The mechanisms that lead to variation in human skin and hair color are not fully understood. To better understand the molecular control of skin and hair color variation, we modulated the expression of Tyrosinase (Tyr), which controls the rate-limiting step of melanogenesis, by expressing a single-copy, tetracycline-inducible shRNA against Tyr in mice. Moderate depletion of TYR was sufficient to alter the appearance of the mouse coat in black, agouti, and yellow coat color backgrounds, even though TYR depletion did not significantly inhibit accumulation of melanin within the mouse hair. Ultra-structural studies revealed that the reduction of Tyr inhibited the accumulation of terminal melanosomes, and inhibited the expression of genes that regulate melanogenesis. These results indicate that color in skin and hair is determined not only by the total amount of melanin within the hair, but also by the relative accumulation of mature melanosomes.

Ultraviolet Radiation-Induced Cytogenetic Damage in White, Hispanic and Black Skin Melanocytes: A Risk for Cutaneous Melanoma

Cutaneous Melanoma (CM) is a leading cause of cancer deaths, with reports indicating a rising trend in the incidence rate of melanoma among Hispanics in certain U.S. states. The level of melanin pigmentation in the skin is suggested to render photoprotection from the DNA-damaging effects of Ultraviolet Radiation (UVR). UVR-induced DNA damage leads to cytogenetic defects visualized as the formation of micronuclei, multinuclei and polymorphic nuclei in cells, and a hallmark of cancer risk. The causative relationship between Sun exposure and CM is controversial, especially in Hispanics and needs further evaluation. This study was initiated with melanocytes from White, Hispanic and Black neonatal foreskins which were exposed to UVR to assess their susceptibility to UVR-induced modulation of cellular growth, cytogenetic damage, intracellular and released melanin. Our results show that White and Hispanic skin melanocytes with similar levels of constitutive melanin are susceptible to UVR-induced cytogenetic damage, whereas Black skin melanocytes are not. Our data suggest that the risk of developing UVR-induced CM in a skin type is correlated with the level of cutaneous pigmentation and its ethnic background. This study provides a benchmark for further investigation on the damaging effects of UVR as risk for CM in Hispanics.

In vivo quantification of epidermis pigmentation and dermis papilla density with reflectance confocal microscopy: variations with age and skin phototype

Reflectance confocal microscopy (RCM) may help to quantify variations of skin pigmentation induced by different stimuli such as UV radiation or therapeutic intervention. The objective of our work was to identify RCM parameters able to quantify in vivo dermis papilla density and epidermis pigmentation potentially applicable in clinical studies. The study included 111 healthy female volunteers with phototypes I-VI. Photo-exposed and photo-protected anatomical sites were imaged. The effect of age was also assessed. Four epidermis components were specifically investigated: stratum corneum, stratum spinosum, basal epidermal layer and dermo-epidermal junction. Laser power, diameter of corneocytes and upper spinous keratinocytes, brightness of upper spinous and interpapillary spinous keratinocytes, number of dermal papillae and papillary contrast were systematically assessed. Papillary contrast measured at the dermo-epidermal junction appeared to be a reliable marker of epidermis pigmentation and showed a strong correlation with skin pigmentation assessed clinically using the Fitzpatrick's classification. Brightness of upper spinous and interpapillary spinous keratinocytes was not influenced by the skin phototype. The number of dermal papillae was significantly lower in subjects with phototypes I-II as compared with darker skin subjects. A dramatic reduction in the number of dermal papillae was noticed with age, particularly in subjects with fair skin. The method presented here provides a new in vivo investigation tool for quantification of dermis papilla density and epidermal pigmentation. Papillary contrast measured at the dermo-epidermal junction may be selected as a marker of skin pigmentation for evaluation in clinical studies.

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.

Inhibitory effect of proanthocyanidin on ultraviolet B irradiation-induced melanogenesis

Repetitive exposure of the skin to ultraviolet (UV) radiation induces various adverse effects, including skin thickening, wrinkle formation, inflammation, and pigmentation. Various natural and synthetic compounds were studied to determine whether they might prevent UV induction of these adverse effects. In particular, naturally occurring antioxidants were used for regulating skin damage induced by UV radiation since several antioxidants were found to inhibit photoaging through prevention of collagen synthesis via inhibition of matrix metalloproteinases (MMP) and/or decrease of melanin synthesis. The L values in pigmented skin were lower at 4 wk (52.97 +/- 2.09) than at the start of this study (0 wk, 62.89 +/- 0.56) in the control. In the proanthocyanidin mixture group, the L value was increased (56.83 +/- 1.71) similar to the control (52.97 +/- 2.09). Proanthocyanidin also suppressed the expression levels of tyrosinase by 20-40%, and blocked the expression of MITF, TRP-1, and TRP-2, which are factors implicated in the control of melanogenesis. Taken together, these data indicate that proanthocyanidin may be useful to attenuate UVB-induced melanogenesis.

Ultrastructural findings in progressive macular hypomelanosis indicate decreased melanin production

BACKGROUND

The pathogenesis of progressive macular hypomelanosis (PMH) is unknown. Recently, Westerhof et al. (Arch Dermatol 2004; 140: 210-214) hypothesized that Propionibacterium acnes produces a depigmenting factor that interferes with melanogenesis in the skin, resulting in hypopigmented spots. The purpose of the study is to gain an insight into the pathogenesis of PMH.

MATERIALS AND METHODS

We took a biopsy of 2-mm diameter from normal and lesional skin in eight PMH patients. Using electron microscopy, we compared melanization of melanosomes, melanosome transfer and amount of epidermal melanin in normal and lesional skin.

RESULT

Compared to non-lesional skin, we observed a decrease of epidermal melanin and less melanized melanosomes in lesional skin of all patients. When comparing normal and lesional skin of patients with skin type V and VI, we observed a difference in melanosome size and maturation and a switch of transferred melanosomes from single stage IV transferred melanosomes to aggregated stage I, II and III transferred melanosomes, as seen in healthy skin of skin type I to IV.

CONCLUSION

Hypopigmentation in PMH seems to be the result of an altered melanogenesis based on a decrease in melanin formation and a change in the distribution of melanosomes. In lesional skin of PMH patients with skin type V and VI less melanized, aggregated melanosomes in stead of single, mature melanosomes are transferred from melanocytes to keratinocytes. This results in a decrease of epidermal melanin. Further investigations are needed to determine the precise role of Propionibacterium acnes in this alteration of melanogenesis.

Dermatologia na pele negra

Este estudo aborda a dermatologia na pele negra. Inicialmente, discute os conceitos de raça e etnia, assim como os critérios de classificação da população brasileira, indicando as regiões em que a população negra se concentra. A seguir, faz breve explanação sobre os sistemas de classificação da cor da pele e descreve particularidades estruturais, biológicas e funcionais da epiderme, derme e anexos cutâneos que diferenciam as peles clara e escura. Posteriormente, mostra algumas alterações fisiológicas comumente observadas na pele, nas unhas e nas mucosas dos indivíduos negros. Aponta, também, alguns padrões de reações e modificações da cor das lesões, decorrentes da hiperpigmentação cutânea, que determinam aspectos inusitados às dermatoses, dificultando seu reconhecimento. Finalmente, destaca algumas doenças em especial, enfatizando particularidades inerentes ao padrão das lesões e à freqüência de algumas dermatoses na pele negra. Nesse contexto, a intenção foi fornecer dados para auxiliar o dermatologista a se familiarizar com as diferentes nuanças que as doenças podem adquirir na pele mais pigmentada.

Human skin pigmentation: melanocytes modulate skin color in response to stress

All organisms, from simple invertebrates to complex human beings, exist in different colors and patterns, which arise from the unique distribution of pigments throughout the body. Pigmentation is highly heritable, being regulated by genetic, environmental, and endocrine factors that modulate the amount, type, and distribution of melanins in the skin, hair, and eyes. In addition to its roles in camouflage, heat regulation, and cosmetic variation, melanin protects against UV radiation and thus is an important defense system in human skin against harmful factors. Being the largest organ of the body that is always under the influence of internal and external factors, the skin often reacts to those agents by modifying the constitutive pigmentation pattern. The focus of this review is to provide an updated overview of important physiological and biological factors that increase pigmentation and the mechanisms by which they do so. We consider endocrine factors that induce temporary (e.g., during pregnancy) or permanent (e.g., during aging) changes in skin color, environmental factors (e.g., UV), certain drugs, and chemical compounds, etc. Understanding the mechanisms by which different factors and compounds induce melanogenesis is of great interest pharmaceutically (as therapy for pigmentary diseases) and cosmeceutically (e.g., to design tanning products with potential to reduce skin cancer risk).

Ethnic considerations in the treatment of Hispanic and Latin-American patients with hyperpigmentation

Latin-Americans have a heterogeneous ancestry that is defined by their place of domicile, while Hispanics are defined as those persons of Spanish descent. These two groups have a diverse range of skin phototypes and pigmentation and are prone to an increased incidence of melasma and post-inflammatory hyperpigmentation. Little research has been conducted to evaluate the frequency, course, effects, tolerability and treatment response of skin diseases in Hispanic and Latin-American populations. From the limited data that are available it is considered that the treatment of melasma in these two groups does not differ from the general population. First-line therapy of melasma should consist of effective topical therapies, mainly a fixed triple combination of hydroquinone, retinoic acid and fluocinolone acetonide. Where patients have either sensitivity or triple combination therapy is unavailable, other compounds with dual ingredients may be considered as an alternative. Options for second-line therapy include peels either alone or in combination with topical therapy. Lasers should rarely be used in the treatment of melasma and then only as third-line therapy in cases of melasma which is resistant to all other therapies. If applied, skin type must be taken into account. Irritation and sensitivity can be a concern in darker-skinned Hispanic patients and for this reason, the risk of post-inflammatory hyperpigmentation (PIH) following treatment should be considered.

The combination of 2% 4-hydroxyanisole (mequinol) and 0.01% tretinoin effectively improves the appearance of solar lentigines in ethnic groups

While the efficacy and safety of topical 4-hydroxyanisole (mequinol) 2%/tretinoin 0.01% therapy has been established in Caucasian populations, those with skin types I-II, little research has focused on individuals with darker skin types. The purpose of this open-label study was to evaluate the efficacy and safety of mequinol 2%/tretinoin 0.01% solution in the treatment of solar lentigines in Asian, Latin/Hispanic, and African American ethnic groups with skin types II-V. Subjects were required to have >or= 10 solar lentigines on the dorsal forearms/hands and >or= 3 on the face. One lesion was designated the target lesion, however, all lesions were treated. Patients were treated with topical mequinol 2%/tretinoin 0.01% and clinically evaluated at 4, 8, 12, 16, 20, and 24 weeks as well as 4 weeks following treatment cessation. At each visit, lesions were evaluated using Target and Overall Lesion Pigmentation Index scores ranging from 0 (lightest) to 8 (darkest), where 4 indicated equal pigment with surrounding skin. Efficacy was determined based on pigmentation index scores, and safety was assessed using laboratory monitoring and adverse event (AE) reporting. Over 80% of the 259 subjects completing this study responded to mequinol 2%/tretinoin 0.01% therapy, with a majority of subjects maintaining clinical benefit at 4 weeks post-treatment. Most AEs reported were tolerable and overall mequinol 2%/tretinoin 0.01% therapy had a favorable benefit-to-risk ratio. This study therefore supports the theory that topical mequinol 2%/tretinoin 0.01% is an effective and safe treatment of solar lentigines in ethnic populations, and in those with dark skin types.

Genetic and environmental influences on skin pattern deterioration

Sun exposure has been known to cause histological changes in the dermal layer of the skin. Using deterioration in the fine reticular patterning of the epidermal stratum corneum (skin pattern, as measured on the Beagley-Gibson scale) as a proxy measure of histological changes in the dermal layer, previous studies have typically assumed that degradation of skin pattern is largely caused by sun exposure. A twin study comprising 332 monozygotic twin pairs and 488 dizygotic twin pairs at ages 12, 14, and 16 was used to investigate the etiology of variation in skin pattern, particularly in relation to measured sun exposure and skin color. Our results indicate that although self-reported sun exposure is a significant contributor to variation in skin pattern, its effect is small, explaining only 3.4% of variation in skin pattern at age 14. Additive genetic effects explain 86% of variation in skin pattern at age 12 but these effects reduce with age so that 75% of variation is due to additive genetic effects at age 14 and 72% at age 16. This trend of diminishing genetic influences continues into adulthood, with 62% of variation due to non-additive genetic factors in a smaller adult sample (aged 32-86). Skin color explains 10.4% of variation in skin pattern at age 12, which is due to additive genetic influences common to both. Melanin content appears to provide a protective effect against skin pattern deterioration, perhaps because of the structural differences in melanosomes between different skin types or the free radical scavenging properties of melanin.

Skin ageing: A comparison between Chinese and European populations

BACKGROUND

Although limited data are available, it is commonly considered that Europeans and Asians have different skin ageing features.

OBJECTIVES

The present studies have been carried out to evaluate the influence of age and sun-exposure on the main clinical signs of Asian skin ageing.

METHODS

One hundred and sixty Chinese and 160 French age-matched women (age range: 20-60 years old) were clinically examined and scored by the same dermatologist. Facial wrinkles (crow's-feet, glabella and perioral wrinkles) and pigmented spots (on face and hands) were assessed in situ and standardized photographs of the face were taken. Lifelong sun-exposure was estimated from answers to a questionnaire. Comparisons were made between 10-year age groups.

RESULTS

Results show that, for each facial skin area, wrinkle onset is delayed by about 10 years in Chinese women as compared to French women. Facial wrinkling rate over the years is linear in French women and not linear in Chinese women who appear to experience a fast ageing process between age 40 and 50. Pigmented spot intensity is a much more important ageing sign in Chinese women (severe for 30% of women over 40) than in French women (severe for less than 8% of women, irrespective of age).

CONCLUSION

These first results underline that main skin ageing features (wrinkles, spots) progress differently in the Chinese and French women we have studied. They require to be confirmed on broad multicentre studies involving larger cohorts.

The Expression and Activation of Protease-Activated Receptor-2 Correlate with Skin Color

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

What controls variation in human skin color?

There is a large range of human skin color, yet we know very little about the underlying genetic architecture. Is the number of skin color genes close to five, 50, or 500?

Structure and function of ethnic skin and hair

Differences have been found among blacks, whites, Asians, and Hispanics in various areas of skin structure and function. Among them is the stratum corneum lipid (ceramide) content, which is highest in Asians, then Hispanics, then whites, and lowest in blacks. Melanosomal packaging and percutaneous absorption rates for specific compounds also vary among the different races. Reports supporting the occurrence of difference in TEWL, tyrosinase levels, skin elasticity, and water absorption rates between blacks and whites, and reaction to skin irritation have been conflicting. No significant differences in corneocyte size, skin thickness, and skin biomechanics have been reported.

Genetics of dark skin in mice

Chemical mutagenesis in the mouse is a powerful approach for phenotype-driven genetics, but questions remain about the efficiency with which new mutations ascertained by their phenotype can be localized and identified, and that knowledge applied to a specific biological problem. During a global screen for dominant phenotypes in about 30,000 animals, a novel class of pigmentation mutants were identified by dark skin (Dsk). We determined the genetic map location, homozygous phenotype, and histology of 10 new Dsk and 2 new dark coat (Dcc) mutations, and identified mutations in Agouti (Met1Leu, Dcc4), Sox18 (Leu220ter, Dcc1), Keratin 2e (Thr500Pro, Dsk2), and Egfr (Leu863Gln, Dsk5). Cutaneous effects of most Dsk mutations are limited to melanocytes, except for the Keratin 2e and Egfr mutations, in which hyperkeratosis and epidermal thickening precede epidermal melanocytosis by 3-6 wk. The Dsk2 mutation is likely to impair intermediate filament assembly, leading to cytolysis of suprabasal keratinocytes and secondary hyperkeratosis and melanocytosis. The Dsk5 mutation causes increased tyrosine kinase activity and a decrease in steady-state receptor levels in vivo. The Dsk mutations represent genes or map locations not implicated previously in pigmentation, and delineate a developmental pathway in which mutations can be classified on the basis of body region, microscopic site, and timing of pigment accumulation.

Skin of color: biology, structure, function, and implications for dermatologic disease

People with skin of color constitute a wide range of racial and ethnic groups-including Africans, African Americans, African Caribbeans, Chinese and Japanese, Native American Navajo Indians, and certain groups of fair-skinned persons (eg, Indians, Pakistanis, Arabs), and Hispanics. It has been predicted that people with skin of color will constitute a majority of the United States and international populations in the 21st century. There is not a wealth of data on racial and ethnic differences in skin and hair structure, physiology, and function. What studies do exist involve small patient populations and often have methodologic flaws. Consequently, few definitive conclusions can be made. The literature does support a racial differential in epidermal melanin content and melanosome dispersion in people of color compared with fair-skinned persons. Other studies have demonstrated differences in hair structure and fibroblast size and structure between black and fair-skinned persons. These differences could at least in part account for the lower incidence of skin cancer in certain people of color compared with fair-skinned persons; a lower incidence and different presentation of photo aging; pigmentation disorders in people with skin of color; and a higher incidence of certain types of alopecia in Africans and African Americans compared with those of other ancestry. However, biologic or genetic factors are not the only ones impacting on these differences in dermatologic disorders. Cultural practices also can have a significant impact. Further studies are needed to help dermatologists optimally treat people with skin of color.

Video-rate confocal scanning laser microscope for imaging human tissues in vivo

We have built a video-rate confocal scanning laser microscope for reflectance imaging of human skin and oral mucosa in vivo. Design and imaging parameters were determined for optimum resolution and contrast. Mechanical skin-holding fixtures and oral tissue clamps were made for stable objective lens-to-tissue contact such that gross tissue motion relative to the microscope was minimized. Confocal imaging was possible to maximum depths of 350 microm in human skin and 450 microm in oral mucosa, with measured lateral resolution of 0.5-1 microm and axial resolution (section thickness) of 3-5 microm at the 1064-nm wavelength. This resolution is comparable with that of conventional microscopy of excised biopsies (histology). Normal and abnormal tissue morphology and dynamic processes were observed.

Human pigmentation genetics: the difference is only skin deep

There is no doubt that visual impressions of body form and color are important in the interactions within and between human communities. Remarkably, it is the levels of just one chemically inert and stable visual pigment known as melanin that is responsible for producing all shades of humankind. Major human genes involved in its formation have been identified largely using a comparative genomics approach and through the molecular analysis of the pigmentary process that occurs within the melanocyte. Three classes of genes have been examined for their contribution to normal human color variation through the production of hypopigmented phenotypes or by genetic association with skin type and hair color. The MSH cell surface receptor and the melanosomal P-protein are the two most obvious candidate genes influencing variation in pigmentation phenotype, and may do so by regulating the levels and activities of the melanogenic enzymes tyrosinase, TRP-1 and TRP-2.

Diffuse hyperpigmentation of the skin: a clinicopathologic approach to diagnosis

There are multiple causes of diffuse hyperpigmentation of the skin (DHP) and determination of the exact etiology can sometimes be difficult. A systematic classification based on both clinical and pathological findings that should aid the clinician who is confronted with this situation is presented in this article. The skin diseases that cause DHP are classified based on the pigment characteristics (melanin, non-melanin), pigment distribution (epidermal, epidermal-dermal, dermal) and density of melanocytes (normal, increased). The intent of this review is to provide a "histopathological tool" that increases diagnostic accuracy in the evaluation of a patient with DHP.

In vivo confocal scanning laser microscopy of human skin: melanin provides strong contrast

Confocal scanning laser microscopy of live human skin was performed to investigate the correlation of in vivo cellular and morphologic features to histology, the effect of wavelength on imaging, and the role of melanin as a contrast agent. We built a video-rate confocal scanning laser microscope for in vivo imaging of human skin. Using a 100 x microscope objective, we imaged high-contrast optical "sections" of normal skin, vitiliginous skin, and a compound nevus. In vivo "confocal histology" correlated well with conventional histology. The maximum imaging depth increased with wavelength: the epidermis was imaged with visible 400-700-nm wavelengths; the superficial papillary dermis and blood cells (erythrocytes and leukocytes) in the deeper capillaries were imaged with the near infrared 800-900-nm wavelengths. For confocal reflectance imaging, melanin provided strong contrast by increased backscattering of light such that the cytoplasm in heavily pigmented cells imaged brightly. In vivo confocal microscopy potentially offers dermatologists a diagnostic tool that is instant and entirely non-invasive compared to conventional histopathology.

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.

C32 human melanoma cell endogenous lectins: characterization and implication in vesicle-mediated melanin transfer to keratinocytes

To optimize skin pigmentation in order to help body prevention against UV radiation, the mechanism of melanin pigment transfer from melanocytes to keratinocytes must be elucidated. Melanin transfer to keratinocytes requires specific recognition between keratinocytes and melanocytes or melanosomes. Cell surface sugar-specific receptor (membrane lectin) expression was studied in human C32 melanoma cells, an amelanotic melanoma, by flow cytometry analysis of neoglycoprotein binding as an approach to the molecular specificity. Sugar receptors on melanocytes are mainly specific for alpha-L-fucose. Their expression is enhanced upon treatment by the diacylglycerol analogue 1-oleoyl-2-acetylglycerol, which can induce melanin synthesis in amelanotic human melanoma cells in a dose-dependent manner. Flow cytometry analyses showed a small-sized population of vesicles distinguishable from large cells by their fluorescence properties upon neoglycoprotein binding. Sorting indicated that the small-sized subpopulation is composed of vesicles produced by melanocytic cells. Upon vesicle formation, a selective concentration of sugar receptors specific for 6-phospho-beta-D-galactosides appears in the resulting melanocytic vesicles. Vesicles are recognized and taken up by cultured keratinocytes and a partial inhibitory effect was obtained upon cell incubation in the presence of neoglycoproteins, indicating a possible participation of sugar receptors in this recognition. The validity for such a model to help in understanding the natural melanin transfer by melanosomes is confirmed by electron microscopy, which demonstrates the presence of melanin inside keratinocytic cells upon incubation with melanocytic vesicles.

The geography of non-ocular malignant melanoma in India: its association with latitude, ozone levels and UV light exposure

Ultraviolet light from sunlight is implicated in the aetiology of non-ocular malignant melanoma, mostly from Western studies. This study reports the relation of such melanomas from 7 cancer registries in different parts of India with latitude, altitude, ozone levels and ultraviolet (UV) light exposure. A log linear model was fitted using GLIM, assuming Poisson errors in incidence; linear and non-linear regression techniques were also used. Results show slight negative associations of melanoma with latitude, chi 2 = -3.37, p = 0.07, and statistically non-significant ones with atmospheric ozone levels (r = -0.36, n.s.), and a positive association with UV (r = 0.30, n.s.). Melanoma incidence from 4 places relates in a parabolic curve with latitude (y = 1-0.09 chi 2 + 0.003 chi 2 in males and y = 1.73-0.17 chi 2 + 0.005 chi 2 in females). Patients originally from west coastal ethnic/linguistic communities predominate in Bombay. Geographic patterns of melanoma in Indians are similar with those in white Caucasians. Ultraviolet light exposure may also be involved in its aetiology in non-white Caucasians, such as Indians.

Melanocytic lesions and melanocyte populations in human epidermis

Basal melanocytes were counted and atypia assessed on an arbitrary scale in punch biopsies from the sun-exposed extensor aspect of the forearm of normal skin and from the covered skin of the buttock of patients with pigmented naevi and control subjects. The difference in melanocyte counts and in the presence of atypia between sun-exposed and covered skin was statistically highly significant. The only other difference was between melanocyte counts in covered skin from those with multiple atypical naevi and all other groups; the counts in the former were greater than those in the latter. No further difference was attributable to sun exposure, skin type or diagnostic group. Some degree of melanocyte atypia was seen in approximately half of the biopsies of sun-exposed skin, but atypia was seen in only six of 84 biopsies of covered skin. In each case atypia was present in the corresponding forearm biopsy and all six subjects had pigmented lesions (four with melanoma and two with multiple atypical naevi). It seems possible that while increased melanocyte counts in covered skin could correlate with the presence of atypical naevi, atypia of covered epidermal melanocytes could possibly relate to melanoma risk.

Biology of hypopigmentation

A review of the basics of pigment cell biology is followed by a discussion of the characteristics of several disorders of hypopigmentation. By determining such features as inheritance pattern, time of onset (congenital, childhood, adulthood), natural history (stable vs progressive), type of pigment loss (diffuse or circumscribed), distribution of lesions (generalized vs localized), degree of pigment loss (incomplete or complete), number of melanocytes, if any, in biopsy specimens of affected areas, type of melanocytic dysfunction, and associated inflammation or infection, one can classify the disorders of hypopigmentation. The proposed pathophysiology for each disorder of hypomelanosis is presented.