Physiological Roles of Eumelanin- and Melanogenesis-Associated Diseases: A Look at the Potentialities of Engineered and Microbial Eumelanin in Clinical Practice

This paper aims to highlight the physiological actions exerted by eumelanin present in several organs/tissues of the human body and to rationalise the often conflicting functional roles played by this biopolymer on the basis of its peculiar properties. Besides pigmentary disorders, a growing number of organ injuries and degenerative pathologies are presently ascribed to the modification of physiological eumelanin levels in terms of alterations in its chemical/structural features, and of a partial loss or uneven distribution of the pigment. The present review analyses the more recent research dedicated to the physiological and pathological actions of eumelanin and provides an insight into some melanogenesis-associated diseases of the skin, eye, ear, and brain, including the most significant neurodegenerative disorders. Also described are the potentialities of therapies based on the localised supply of exogeneous EU and the opportunities that EU produced via synthetic biology offers in order to redesign therapeutical and diagnostic applications.

New insight into melanin for food packaging and biotechnology applications

Melanin is a dark brown to black biomacromolecule with biologically active multifunctional properties that do not have a precise chemical structure, but its structure mainly depends on the polymerization conditions during the synthesis process. Natural melanin can be isolated from various animal, plant, and microbial sources, while synthetic melanin-like compounds can be synthesized by simple polymerization of dopamine. Melanin is widely used in various areas due to its functional properties such as photosensitivity, light barrier property, free radical scavenging ability, antioxidant activity, etc. It also has an excellent ability to act as a reducing agent and capping agent to synthesize various metal nanoparticles. Melanin nanoparticles (MNP) or melanin-like nanoparticles (MLNP) have the unique potential to act as functional materials to improve nanocomposite films' physical and functional properties. Various food packaging and biomedical applications have been made alone or by mixing melanin or MLNP. In this review, the general aspects of melanin that highlight biological activity, along with a description of MNP and the use as nanofillers in packaging films as well as reducing and capping agents and biomedical applications, were comprehensively reviewed.

Effect of Mechanical Compression on Invasion Process of Malignant Melanoma Using In Vitro Three-Dimensional Cell Culture Device

Malignant melanoma in the plantar surface of the foot is subjected to various mechanical stimuli generated by daily human activity such as walking. Some studies have reported that mechanical compression affects the development and progression of melanoma. However, little is known about how mechanical compression affects the behavior of malignant melanoma cells in a physiological condition due to the complexity of the invasion mechanisms. In this study, we developed an in vitro three-dimensional cell culture device using microporous membrane in order to evaluate the effects of mechanical compression on the invasion process of malignant melanoma. Our results suggest that the invasion of melanoma cells under the compressive stress for 8 h of culture was promoted with the elongation of F-actin filaments compared to control groups, whereas there was no significant difference between both groups at 32 h of culture, with increasing cell death associated with promoting melanin synthesis. The results of this study contribute to the elucidation of the invasion mechanisms of malignant melanoma caused by mechanical stimulation.

Dyspigmented hypertrophic scars: Beyond skin color

Although pigment synthesis is well understood, relevant mechanisms of psychologically debilitating dyspigmentation in nascent tissue after cutaneous injuries are still unknown. Here, differences in genomic transcription of hyper- and hypopigmented tissue relative to uninjured skin were investigated using a red Duroc swine scar model. Transcription profiles differed based on pigmentation phenotypes with a trend of more upregulation or downregulation in hyper- or hypopigmented scars, respectively. Ingenuity Pathway Analysis of significantly modulated genes in both pigmentation phenotypes showed pathways related to redox, metabolic, and inflammatory responses were more present in hypopigmented samples, while those related to stem cell development differentiation were found mainly in hyperpigmented samples. Cell-cell and cell-extracellular matrix interactions and inflammation responses were predicted (z-score) active in hyperpigmented and inactive in hypopigmented. The proinflammatory high-mobility group box 1 pathway showed the opposite trend. Analysis of differentially regulated mutually exclusive genes showed an extensive presence of metabolic, proinflammatory, and oxidative stress pathways in hypopigmented scars, while melanin synthesis, glycosaminoglycans biosynthesis, and cell differentiation pathways were predominant in hyperpigmented scar. Several potential therapeutic gene targets have been identified.

Ultraviolet B, melanin and mitochondrial DNA: Photo-damage in human epidermal keratinocytes and melanocytes modulated by alpha-melanocyte-stimulating hormone

Alpha-melanocyte-stimulating hormone (alpha-MSH) increases melanogenesis and protects from UV-induced DNA damage. However, its effect on mitochondrial DNA (mtDNA) damage is unknown. We have addressed this issue in a pilot study using human epidermal keratinocytes and melanocytes incubated with alpha-MSH and irradiated with UVB. Real-time touchdown PCR was used to quantify total and deleted mtDNA. The deletion detected encompassed the common deletion but was more sensitive to detection. There were 4.4 times more mtDNA copies in keratinocytes than in melanocytes. Irradiation alone did not affect copy numbers. Alpha-MSH slightly increased copy numbers in both cell types in the absence of UVB and caused a similar small decrease in copy number with dose in both cell types. Deleted copies were nearly twice as frequent in keratinocytes as in melanocytes. Alpha-MSH reduced the frequency of deleted copies by half in keratinocytes but not in melanocytes. UVB dose dependently led to an increase in the deleted copy number in alpha-MSH-treated melanocytes. UVB irradiation had little effect on deleted copy number in alpha-MSH-treated keratinocytes. In summary, alpha-MSH enhances mtDNA damage in melanocytes presumably by increased melanogenesis, while α-MSH is protective in keratinocytes, the more so in the absence of irradiation.

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.

Cellular Mechanisms of Oxidative Stress and Action in Melanoma

Most melanomas occur on the skin, but a small percentage of these life-threatening cancers affect other parts of the body, such as the eye and mucous membranes, including the mouth. Given that most melanomas are caused by ultraviolet radiation (UV) exposure, close attention has been paid to the impact of oxidative stress on these tumors. The possibility that key epigenetic enzymes cannot act on a DNA altered by oxidative stress has opened new perspectives. Therefore, much attention has been paid to the alteration of DNA methylation by oxidative stress. We review the current evidence about (i) the role of oxidative stress in melanoma initiation and progression; (ii) the mechanisms by which ROS influence the DNA methylation pattern of transformed melanocytes; (iii) the transformative potential of oxidative stress-induced changes in global and/or local gene methylation and expression; (iv) the employment of this epimutation as a biomarker for melanoma diagnosis, prognosis, and drug resistance evaluation; (v) the impact of this new knowledge in clinical practice for melanoma treatment.

Melanocytes as instigators and victims of oxidative stress

Epidermal melanocytes are particularly vulnerable to oxidative stress owing to the pro-oxidant state generated during melanin synthesis, and to the intrinsic antioxidant defenses that are compromised in pathologic conditions. Melanoma is thought to be oxidative stress driven, and melanocyte death in vitiligo is thought to be instigated by a highly pro-oxidant state in the epidermis. We review the current knowledge about melanin and the redox state of melanocytes, how paracrine factors help counteract oxidative stress, the role of oxidative stress in melanoma initiation and progression and in melanocyte death in vitiligo, and how this knowledge can be harnessed for melanoma and vitiligo treatment.

Biochemical composition and antioxidant properties of Lavandula angustifolia Miller essential oil are shielded by propolis against UV radiations

UV radiations are principal causes of skin cancer and aging. Suntan creams were developed to protect epidermis and derma layers against photodegradation and photooxidation. The addition of antioxidant plant extracts (i.e. essential oil) to sunscreens is habitually performed, to increase their UV protective effects and to contrast pro-radical and cytotoxic compounds present in these solutions. According to these observations, in the present work, the alteration of chemical composition and bioactive properties of Lavandula angustifolia Miller essential oil, exposed to UV light, was investigated. UV induced a significant deterioration of lavender oil biochemical profile. Moreover, the antioxidant activity of this solution, in in vitro tests and directly on B16-F10 melanoma cells, greatly decreased after UV treatment. Our results also showed that essential oil was shielded from UV stress by propolis addition. Even after UV treatment, bee glue highly protected lavender oil secondary metabolites from degradation and also preserved their antiradical properties, both in in vitro antioxidant assays and in cell oxidative damage evaluations. This research proposed propolis as highly efficient UV protective and antiradical additive for sunscreens, cosmetics and alimentary or pharmaceutical products containing plant extracts.

Melanoma induction by ultraviolet A but not ultraviolet B radiation requires melanin pigment

Malignant melanoma of the skin (CMM) is associated with ultraviolet radiation exposure, but the mechanisms and even the wavelengths responsible are unclear. Here we use a mammalian model to investigate melanoma formed in response to precise spectrally defined ultraviolet wavelengths and biologically relevant doses. We show that melanoma induction by ultraviolet A (320-400 nm) requires the presence of melanin pigment and is associated with oxidative DNA damage within melanocytes. In contrast, ultraviolet B radiation (280-320 nm) initiates melanoma in a pigment-independent manner associated with direct ultraviolet B DNA damage. Thus, we identified two ultraviolet wavelength-dependent pathways for the induction of CMM and describe an unexpected and significant role for melanin within the melanocyte in melanomagenesis.

Shining light on skin pigmentation: the darker and the brighter side of effects of UV radiation

The term barrier function as applied to human skin often connotes the physical properties of this organ that provides protection from its surrounding environment. This term does not generally include skin pigmentation. However, skin pigmentation, which is the result of melanin produced in melanocytes residing in the basal layer of the skin and exported to the keratinocytes in the upper layers, serves equally important protective function. Indeed, changes in skin pigmentation are often the most readily recognized indicators of exposure of skin to damaging agents, especially to natural and artificial radiation in the environment. Several recent studies have shed new light on (1) the mechanisms involved in selective effects of subcomponents of UV radiation on human skin pigmentation and (2) the interactive influences between keratinocytes and melanocytes, acting as "epidermal melanin unit," that manifest as changes in skin pigmentation in response to exposure to various forms of radiation. This article provides a concise review of our current understanding of the effects of the nonionizing solar radiation, at cellular and molecular levels, on human skin pigmentation.

Investigating the role of melanin in UVA/UVB- and hydrogen peroxide-induced cellular and mitochondrial ROS production and mitochondrial DNA damage in human melanoma cells

Skin cancer incidence is dramatically increasing worldwide, with exposure to ultraviolet radiation (UVR) a predominant factor. The UVA component initiates oxidative stress in human skin, although its exact role in the initiation of skin cancer, particularly malignant melanoma, remains unclear and is controversial because there is evidence for a melanin-dependent mechanism in UVA-linked melanoma studies. Nonpigmented (CHL-1, A375), moderately pigmented (FM55, SKmel23), and highly pigmented (FM94, hyperpigmented FM55) human melanoma cell lines have been used to investigate UVA-induced production of reactive oxygen species using FACS analysis, at both the cellular (dihydrorhodamine-123) and the mitochondrial (MitoSOX) level, where most cellular stress is generated. For the first time, downstream mtDNA damage (utilizing a quantitative long-PCR assay) has been investigated. Using UVA, UVB, and H(2)O(2) as cellular stressors, we have explored the dual roles of melanin as a photoprotector and photosensitizer. The presence of melanin has no influence over cellular oxidative stress generation, whereas, in contrast, melanin protects against mitochondrial superoxide generation and mtDNA damage (one-way ANOVA with post hoc Tukey's analysis, P<0.001). We show that if melanin binds directly to DNA, it acts as a direct photosensitizer of mtDNA damage during UVA irradiation (P<0.001), providing evidence for the dual roles of melanin.

Solar radiation induced skin damage: review of protective and preventive options

PURPOSE

Solar energy has a number of short- and long-term detrimental effects on skin that can result in several skin disorders. The aim of this review is to summarise current knowledge on endogenous systems within the skin for protection from solar radiation and present research findings to date, on the exogenous options for such skin photoprotection.

RESULTS

Endogenous systems for protection from solar radiation include melanin synthesis, epidermal thickening and an antioxidant network. Existing lesions are eliminated via repair mechanisms. Cells with irreparable damage undergo apoptosis. Excessive and chronic sun exposure however can overwhelm these mechanisms leading to photoaging and the development of cutaneous malignancies. Therefore exogenous means are a necessity. Exogenous protection includes sun avoidance, use of photoprotective clothing and sufficient application of broad-spectrum sunscreens as presently the best way to protect the skin. However other strategies that may enhance currently used means of protection are being investigated. These are often based on the endogenous protective response to solar light such as compounds that stimulate pigmentation, antioxidant enzymes, DNA repair enzymes, non-enzymatic antioxidants.

CONCLUSION

More research is needed to confirm the effectiveness of new alternatives to photoprotection such as use of DNA repair and antioxidant enzymes and plant polyphenols and to find an efficient way for their delivery to the skin. New approaches to the prevention of skin damage are important especially for specific groups of people such as (young) children, photosensitive people and patients on immunosuppressive therapy. Changes in public awareness on the subject too must be made.

The protective role of melanin against UV damage in human skin

Human skin is repeatedly exposed to UVR that influences the function and survival of many cell types and is regarded as the main causative factor in the induction of skin cancer. It has been traditionally believed that skin pigmentation is the most important photoprotective factor, as melanin, besides functioning as a broadband UV absorbent, has antioxidant and radical scavenging properties. Besides, many epidemiological studies have shown a lower incidence for skin cancer in individuals with darker skin compared to those with fair skin. Skin pigmentation is of great cultural and cosmetic importance, yet the role of melanin in photoprotection is still controversial. This article outlines the major acute and chronic effects of UVR on human skin, the properties of melanin, the regulation of pigmentation and its effect on skin cancer prevention.

Increased melanogenesis is a risk factor for oxidative DNA damage--study on cultured melanocytes and atypical nevus cells

Melanin synthesis is an oxygen-dependent process that acts as a potential source of reactive oxygen species (ROS) inside pigment-forming cells. The synthesis of the lighter variant of melanin, pheomelanin, consumes cysteine and this may limit the capacity of the cellular antioxidative defense. We show that tyrosine-induced melanogenesis in cultured normal human melanocytes (NHM) is accompanied by increased production of ROS and decreased concentration of intracellular glutathione. Clinical atypical (dysplastic) nevi (DN) regularly contain more melanin than do normal melanocytes (MC). We also show that in these cultured DN cells three out of four exhibit elevated synthesis of pheomelanin and this is accompanied by their early senescence. By using various redox-sensitive molecular probes, we demonstrate that cultured DN cells produce significantly more ROS than do normal MC from the same donor. Our experiments employing single-cell gel electrophoresis (comet assay) usually reveal higher fragmentation of DNA in DN cells than in normal MC. Even if in some cases the normal alkaline comet assay shows no differences in DNA fragmentation between DN cells and normal MC, the use of the comet assay with formamidopyrimidine DNA glycosylase can disclose that the DNA of the cultured DN cells harbor more oxidative damage than the DNA of normal MC from the same person.

Melanoma, long wavelength ultraviolet and sunscreens: Controversies and potential resolutions

Although sunlight is known to cause melanoma, there has been considerable controversy as to the importance of short (UVB) and long (UVA) ultraviolet (UV) wavelengths in causing melanoma, leading to uncertainty in how best to prevent this cancer. This uncertainty has been compounded by the difficulties in assaying the UVA protection abilities of sunscreens, as compared to widely accepted measures of UVB screening by the sun protection factor (SPF). This review discusses the controversies surrounding UVA causation of melanoma in both human and animal models and the use of sunscreens to prevent melanoma. In addition, it details the development of an electron paramagnetic resonance (EPR) technique, initially used to determine the wavelength dependence (or action spectrum) of intramelanocyte radical generation to resolve these controversies in the Xiphophorus model. It is shown how this EPR technique allows a sunscreen protection factor to be determined, that is weighted to the melanocyte, and how this also allows study of the wavelength-dependent screening ability of sunscreens.

Development of genotoxicity test procedures with Episkin®, a reconstructed human skin model: Towards new tools for in vitro risk assessment of dermally applied compounds?

Today reconstructed skin models that simulate human skin, such as Episkin, are widely used for safety or efficacy pre-screening. Moreover, they are of growing interest for regulatory purposes in the framework of alternatives to animal testing. In order to reduce and eventually replace results of in vivo genotoxicity testing with in vitro data, there is a need to develop new complementary biological models and methods with improved ability to predict genotoxic risk. This can be achieved if these new assays do take into account exposure conditions that are more relevant than in the current test systems. In an attempt to meet this challenge, two new applications using a human reconstructed skin model for in vitro genotoxicity assessment are proposed. The skin is the target organ for dermally exposed compounds or environmental stress. Although attempts have been made to develop genotoxicity test procedures in vivo on mouse skin, human reconstructed skin models have not been used for in vitro genotoxicity testing so far, although they present clear advantages over mouse skin for human risk prediction. This paper presents the results of the development of a specific protocol allowing to perform the comet assay, a genotoxicity test procedure, on reconstructed skin. The comet assay was conducted after treatment of Episkin with UV, Lomefloxacin and UV or 4-nitroquinoline-N-oxide (4NQO). Treatment with the sunscreen Mexoryl was able to reduce the extent of comet signal. A second approach to use reconstructed epidermis in genotoxicity assays is also proposed. Indeed, the skin is a biologically active barrier driving the response to exposure to chemical agents and their possible metabolites. A specific co-culture system (Figure 1) using Episkin to perform the regular micronucleus assay is presented. Micronucleus induction in L5178Y cells cultured underneath Episkin was assessed after treatment of the reconstructed epidermis with mitomycin C, cyclophosphamide or apigenin. This second way of using human reconstructed skin for genotoxicity testing aims at improving the relevance of exposure conditions in in vitro genotoxicity assays for dermally applied compounds.

Do adolescent indoor tanners exhibit dependency?

BACKGROUND

Indoor tanning is a common adolescent risk behavior that has been hypothesized to be motivated and maintained by the mood-altering effects of ultraviolet light.

OBJECTIVE

Our purpose was to explore heretofore anecdotal reports that indoor tanning leads to dependency.

METHODS

A telephone interview was conducted among 1275 adolescents, ages 14 to 17 years. Self-reported difficulty in quitting indoor tanning was assessed among 267 adolescents (20.9% of total) who tanned indoors more than once in the previous year in relation to age of initiation, frequency of use, and positive or negative consequences of the practice.

RESULTS

Difficulty in quitting was more likely with younger age at initiation (age 13 years or younger vs ages 16 to 17; odds ratio = 4.3, 95% confidence interval 1.3-14.7) and higher frequency of use (P = .009), even after accounting for positive or negative consequences of indoor tanning and other demographic characteristics.

LIMITATIONS

This was a cross-sectional study design with a limited outcome measure.

CONCLUSION

Although preliminary, our findings for age at initiation and frequency of use in relation to difficulty in quitting indoor tanning are consistent with other potentially addictive behaviors taken up during adolescence.

UVA-induced modification of catalase charge properties in the epidermis is correlated with the skin phototype

The harmful effects of UVA radiation (320-400 nm) on the skin have been related to the generation of reactive oxygen species. Pheomelanin, the pigment characteristic of fair-skinned individuals, amplifies these effects. In vitro, in the presence of photosensitizing agents, UVA light produces singlet oxygen, which reacts with several targets. We have investigated a possible correlation between melanin-type and the antioxidant defense system after UV, focusing on the activities of superoxide dismutase and catalase, which correlated with the phototype of epidermal reconstructs. UVA was more effective than UVB in damaging these enzymatic activities, especially catalase. Furthermore, UVA irradiation induced a free-radical-mediated damage in the cells, leading to an oxidation of cell proteins. On catalase, synthetic pheomelanin amplified this effect on specific targets, such as residues of tryptophan and methionine. UVA irradiation of low phototype reconstructed epidermis and of U937 through synthetic pheomelanin induced a modification in the electrophoretic properties of native catalase, which was counteracted by histidine, a quencher of singlet oxygen. These results demonstrate that pheomelanin could act as a photosensitizing agent, following UVA irradiation, inducing charge modifications of native catalase, by a mechanism involving singlet oxygen or its downstream products.

Endogenous UVA-photosensitizers: mediators of skin photodamage and novel targets for skin photoprotection

Endogenous chromophores in human skin serve as photosensitizers involved in skin photocarcinogenesis and photoaging. Absorption of solar photons, particularly in the UVA region, induces the formation of photoexcited states of skin photosensitizers with subsequent generation of reactive oxygen species (ROS), organic free radicals and other toxic photoproducts that mediate skin photooxidative stress. The complexity of endogenous skin photosensitizers with regard to molecular structure, pathways of formation, mechanisms of action, and the diversity of relevant skin targets has hampered progress in this area of photobiology and most likely contributed to an underestimation of the importance of endogenous sensitizers in skin photodamage. Recently, UVA-fluorophores in extracellular matrix proteins formed posttranslationally as a consequence of enzymatic maturation or spontaneous chemical damage during chronological and actinic aging have been identified as an abundant source of light-driven ROS formation in skin upstream of photooxidative cellular stress. Importantly, sensitized skin cell photodamage by this bystander mechanism occurs after photoexcitation of sensitizers contained in skin structural proteins without direct cellular photon absorption thereby enhancing the potency and range of phototoxic UVA action in deeper layers of skin. The causative role of photoexcited states in skin photodamage suggests that direct molecular antagonism of photosensitization reactions using physical quenchers of photoexcited states offers a novel chemopreventive opportunity for skin photoprotection.

Indoor tanning by adolescents: prevalence, practices and policies

Despite known acute and chronic health effects from the use of indoor tanning, including the potential for all forms of skin cancer, the practice is popular in the United States (US) and Europe. A review of the scientific literature that examines adolescents and indoor tanning use was undertaken, summarising what is known about prevalence and practices among adolescents, characteristics associated with adolescent use, and policies that regulate adolescent access to indoor tanning facilities. The prevalence of indoor tanning is consistently found to be higher among girls than boys and to increase with age in both Europe and the US. An examination of other demographic characteristics, skin cancer risk factors, knowledge, attitudes and social factors points to higher prevalence of the behaviour among adolescents with positive attitudes towards tans and whose friends or parents also tan indoors. Adolescent access to indoor tanning is rarely regulated in the US or Europe, and where regulations exist, business compliance is low. In addition, businesses actively market their product to adolescents as they organise to limit further regulations prohibiting adolescent access. Pricing, licensure, advertising restrictions and media campaigns, in combination with adolescent-targeted interventions, are possible strategies that could be tested for their effectiveness to reduce adolescent indoor tanning use. Harm reduction policies, such as eye protection, that reduce risk for adolescents who choose to tan indoors, are also important.

Ectopic expression of tyrosinase increases melanin synthesis and cell death following UVB irradiation in fibroblasts from familial atypical multiple mole and melanoma (FAMMM) patients

Patients with familial atypical multiple mole and melanoma (FAMMM) [so-called familial dysplastic naevus syndrome (FDNS)] have a high risk for the development of malignant melanoma. The underlying gene defect has an autosomal dominant inheritance with variable expression and incomplete penetrance. Fibroblasts derived from FAMMM patients have high sensitivity to UVC and mutagens, e.g. 4-nitroquinoline-1-oxide. We were interested in identifying how the combination of inherent sensitivity to UV light and abnormal melanin synthesis interacts in the development of melanoma in FAMMM patients. Intermediates of melanin synthesis produce free radicals that are toxic to cells. Atypical moles (dysplastic naevi) are engaged in the biosynthesis of abnormal melanin pigments. This study examined whether there was any abnormal melanin pigmentation or cell damage after the ectopic expression of tyrosinase in fibroblasts from FAMMM patients when compared with fibroblasts from normal subjects. Fibroblasts from FAMMM patients (3012T and 3072T) were associated with a higher sensitivity than normal human fibroblasts to the toxicity of UVB. When cells were infected with tyrosinase-expressing adenovirus (Ad-HT) and irradiated with UVB, FAMMM fibroblasts showed higher tyrosinase activity, produced more melanin pigments and were degraded more significantly than normal human fibroblasts. Western blot analysis revealed that Ad-HT-infected 3072T produced a larger amount of tyrosinase protein than did Ad-HT-infected normal fibroblasts after UVB irradiation. Our findings suggest: (1) that FAMMM fibroblasts have an unknown machinery which enhances tyrosinase expression by UVB irradiation; and (2) that the resulting increase in melanin synthesis affects the cytotoxicity of UVB to FAMMM fibroblasts. All of these processes may be involved in the genomic instability and development of melanoma in FAMMM patients.

Molecular responses to photogenotoxic stress induced by the antibiotic lomefloxacin in human skin cells: from DNA damage to apoptosis

Photo-unstable chemicals sometimes behave as phototoxins in skin, inducing untoward clinical side-effects when exposed to sunlight. Some drugs, such as psoralens or fluoroquinolones, can damage genomic DNA, thus increasing the risk of photocarcinogenesis. Here, lomefloxacin, an antibiotic from the fluoroquinolone family known to be involved in skin tumor development in photoexposed mice, was studied using normal human skin cells in culture: fibroblasts, keratinocytes, and Caucasian melanocytes. When treated cells were exposed to simulated solar ultraviolet A (320-400 nm), lomefloxacin induced damage such as strand breaks and pyrimidine dimers in genomic DNA. Lomefloxacin also triggered various stress responses: heme-oxygenase-1 expression in fibroblasts, changes in p53 status as shown by the accumulation of p53 and p21 proteins or the induction of MDM2 and GADD45 genes, and stimulation of melanogenesis by increasing the tyrosinase activity in melanocytes. Lomefloxacin could also lead to apoptosis in keratinocytes exposed to ultraviolet A: caspase-3 was activated and FAS-L gene was induced. Moreover, keratinocytes were shown to be the most sensitive cell type to lomefloxacin phototoxic effects, in spite of the well-established effectiveness of their antioxidant equipment. These data show that the phototoxicity of a given drug can be driven by different mechanisms and that its biologic impact varies according to cell type.

Comet assay combined with p53 detection as a sensitive approach for DNA photoprotection assessment in vitro

A simple in vitro approach where sun formulations are spread on a quartz slide and placed over human skin cells in culture is proposed as a convenient test for photoprotection assessment at the DNA level. Using the comet assay, DNA strand breaks and oxidative DNA damage were detected. Then, accumulation of p53 protein was studied as a marker for UV-induced genotoxic stress. Such a method was used to compare formulations with different photostability. Spectroradiometry showed that a photo-unstable formulation lost its effectiveness in UVA screening when pre-irradiated by simulated sunlight. As a consequence, such a formulation was not as protective as a photostable one at the genomic level.

Comparative tolerability of systemic treatments for plaque-type psoriasis

Psoriasis is a chronic, debilitating skin condition that affects millions of people and is attributed to both genetic and environmental factors. Topical therapy is generally considered to be the first-line treatment of psoriasis. However, many patients do not respond to topical therapy or have disease so extensive that topical therapy is not practical. For these patients, systemic therapy is indicated. Presently, there are four available systemic treatments, psoralen with ultraviolet A (PUVA), methotrexate, oral retinoids (acitretin), and cyclosporin. Unfortunately, all of these treatments have significant potential adverse effects. PUVA may acutely cause nausea, pruritus and sunburn. More chronic and concerning is the development of PUVA lentigines, ocular complications and skin cancer. Non-melanoma skin cancer has been directly linked to PUVA; however, the association with melonoma is more elusive. Methotrexate use most notably carries the risk of hepatic fibrosis and cirrhosis, which is not always evident on liver function tests. Other more rare, but potentially life-threatening adverse effects include pancytopenia, lymphoproliferative disorders and acute pneumonitis. The addition of folic acid may help to reduce the risk of increasing liver enzymes and haematological toxicity seen in those taking methotrexate. Both methotrexate and oral retinoids are teratogenic and should never be used in pregnancy. Oral retinoids are probably the least effective available systemic medication for the treatment of plaque psoriasis. The effects are improved with the addition of other systemic therapies. Acitretin has replaced the formerly used etretinate primarily because of the significantly shorter half-life. The adverse effects are generally mild and reversible, making the drug fairly safe for long-term use. The most commonly seen adverse effects include elevated serum lipids, generalised xerosis and alopecia. Bony abnormalities, while somewhat controversial, have also been described and include diffuse idiopathic skeletal hyperostosis, skeletal calcifications and osteoporosis. Cyclosporin is the most recently approved systemic medication for plaque psoriasis. The nephrotoxicity associated with the use of cyclosporin can be minimised when used in lower doses and for a limited duration. Hypertension is usually mild and can be seen in up to about one-third of patients receiving long-term therapy. Cutaneous and internal malignancies have also been reported with cyclosporin and tend to be correlated with duration of treatment. In this review, we will examine the potential adverse effects with these US Food and Drug Administration-approved treatments in adults, with specific emphasis on the controversies that surround long-term therapy with these agents and their cumulative adverse effects.

Modulatory effects of an algal extract containing astaxanthin on UVA-irradiated cells in culture

UV radiation from sunlight is the most potent environmental risk factor in skin cancer pathogenesis. In the present study the ability of an algal extract to protect against UVA-induced DNA alterations was examined in human skin fibroblasts (1BR-3), human melanocytes (HEMAc) and human intestinal CaCo-2 cells. The protective effects of the proprietary algal extract, which contained a high level of the carotenoid astaxanthin, were compared with synthetic astaxanthin. DNA damage was assessed using the single cell gel electrophoresis or comet assay. In 1BR-3 cells, synthetic astaxanthin prevented UVA-induced DNA damage at all concentrations (10 nM, 100 nM, 10 microM) tested. In addition, the synthetic carotenoid also prevented DNA damage in both the HEMAc and CaCo-2 cells. The algal extract displayed protection against UVA-induced DNA damage when the equivalent of 10 microM astaxanthin was added to all three-cell types, however, at the lower concentrations (10 and 100 nM) no significant protection was evident. There was a 4.6-fold increase in astaxanthin content of CaCo-2 cells exposed to the synthetic compound and a 2.5-fold increase in cells exposed to algal extract. In 1BR-3 cells, exposure to UVA for 2 h resulted in a significant induction of cellular superoxide dismutase (SOD) activity, coupled with a marked decrease in cellular glutathione (GSH) content. However pre-incubation (18 h) with 10 microM of the either the synthetic astaxanthin or the algal extract prevented UVA-induced alterations in SOD activity and GSH content. Similarly, in CaCo-2 cells a significant depletion of GSH was observed following UVA-irradiation which was prevented by simultaneously incubating with 10 microM of either synthetic astaxanthin or the algal extract. SOD activity was unchanged following UVA exposure in the intestinal cell line. This work suggests a role for the algal extract as a potentially beneficial antioxidant.

Measurement of UVB-Induced DNA damage and its consequences in models of immunosuppression

Exposure to UVB results in formation of cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts in DNA. These can be quantified by a variety of techniques including alkaline gel electrophoresis, ELISAs, Southwestern blotting, and immunohistochemistry. Damage to DNA results in activation of damage response pathways, as indicated by Western blotting using antibodies specific for p53 and breast cancer-associated gene 1 (BRCA1) phosphorylation. The signal from DNA damage to activation of these response pathways appears to be mediated by FKBP12-rapamycin-associated protein (FRAP), since these phosphorylation events are blocked by rapamycin. UVB-induced DNA damage also leads to induction of immunosuppressive cytokines including tumor necrosis factor alpha (TNF-alpha) and interleukin (IL)-10 in skin. Induction of TNF-alpha by UVB is readily detectable in cultured normal human epidermal keratinocytes (NHEKs) using ELISA, while induction of IL-10 is readily detectable in cultured mouse keratinocytes but not in NHEKs. Induction of DNA damage by liposome-encapsulated HindIII results in induction of immunosuppressive responses similar to UVB. Clinical testing shows that liposome-encapsulated T4 endonuclease V or photolyase stimulates repair of CPDs in the skin of human subjects, and prevents UVB-induced immunosuppression. Stimulation of repair and prevention of immunosuppression have been linked to prevention of skin cancer by liposome-encapsulated T4 endonuclease V in repair-deficient xeroderma pigmentosum patients.

Photogenotoxicity of mammalian cells: a review of the different assays for in vitro testing

During the past several years, phototoxicity has been studied at the molecular level, and these studies have provided new insights in the field of DNA lesion characterization, DNA repair and cell response to ultraviolet (UV)-induced stress. The development of new antibiotics and antiinflammatory drugs has highlighted the necessity to develop the assessment of phototoxicity in the safety evaluation of new chemical compounds. This paper aims at reviewing the known molecular mechanisms of the cellular response to UV-induced stress, the in vitro methods that can be proposed and used to screen for toxicity of sunlight and the photosensitization process resulting from the activation of drugs by light. UV sources, biological systems and endpoints of interest in that particular objective are listed. Phototoxic effects span from the cytotoxic-apoptotic effect to the induction of primary DNA damage, DNA repair and a variety of stress genes acting on the cell cycle and the fate of the cell. Ultimately, it can lead to the induction of hereditary DNA modification. A variety of assays are proposed to specifically address all these particular consequences of UV-induced toxicity.

The expression of genes induced in melanocytes by exposure to 365-nm UVA: study by cDNA arrays and real-time quantitative RT-PCR

Ultraviolet A radiation (UVA; 320-400 nm) constitutes more than 90% of the terrestrial UV solar energy. This type of radiation generates reactive oxygen species and consequently induces DNA damage. UVA irradiation is now considered to be an important carcinogen agent especially in the development of melanoma. UVA radiation is known to activate several pathways in mammalian cells. We have used cDNA arrays to analyze differential gene expression in primary cultures of human melanocytes in response to 365-nm UVA. Among 588 genes studied, 11 were overexpressed. These genes included genes involved in cell cycle regulation (GADD45, CIP1/WAF1), in stress response (HSP70, HSP40, HSP86), in apoptosis (GADD153, tristetraproline) and genes encoding transcription factors (EGR-1, ETR-101, c-JUN, ATF4). This coordinate gene regulation was confirmed by real-time quantitative RT-PCR.

Melanin offers protection against induction of cyclobutane pyrimidine dimers and 6-4 photoproducts by UVB in cultured human melanocytes

The goal of this investigation was to correlate the melanin content in human pigmentary cells with the generation of UVB-induced photoproducts and to examine the relationship between the melanin content and the removal of the photoproducts. Cultured melanocytes from light-skinned individuals synthesized less melanin and produced more cyclobutane pyrimidine dimers and 6-4 photoproducts upon UVB exposure than did melanocytes from black skin. Tyrosine-stimulated melanogenesis provided protection against DNA damage in both cell types. In another set of pigmented cell lines a ratio between eumelanin and pheomelanin was determined. The assessment of association between DNA damage induction and the quantity and quality of melanin revealed that eumelanin concentration correlated better with DNA protection than pheomelanin. Skin type-I and skin type-VI melanocytes, congenital nevus (CN)-derived cells and skin type-II melanocytes from a multiple-melanoma patient were grown in media with low or high L-tyrosine concentration. The cells were irradiated with 200 J/m2 UVB, and the levels of the photoproducts were determined immediately and after 6 and 24 h. Once again the induction of the photoproducts was mitigated by increased melanogenesis, and it was inversely correlated with the skin type. No significant differences were found for the removal of photoproducts in the cultures of skin types I and VI and CN cells. No indications of a delay in the removal of photoproducts in the melanocytes from the multiple-melanoma patient were found either.

Evaluation of sunscreen protection in human melanocytes exposed to UVA or UVB irradiation using the alkaline comet assay

The in vivo assessment of sunscreen protection does not include the photogenotoxicity of UVA or UVB solar radiation. Using the comet assay we have developed a simple and rapid technique to quantify sunscreen efficacy against DNA damage induced by UV light. Cutaneous human melanocytes from primary cultures were embedded in low-melting point (LPM) agarose and exposed to UVA (0.8 J/cm2) or to UVB (0.06 J/cm2) through a quartz slide covered with 10 microL volumes of sunscreens. DNA single-strand breaks induced directly by UVA at 4 degrees C and indirectly through nucleotide excision repair by UVB following a 35 min incubation period at 37 degrees C were quantified using the comet assay. Tail moments (TM) (tail length x %tail DNA) of 100 cells/sample were determined by image analysis. DNA damage was evaluated with a nonlinear regression analysis on the normalized distribution frequencies of TM using a chi 2 function. The coefficients of genomic protection (CGP) were defined as the percentage of inhibition of DNA lesions caused by the sunscreens. Twenty-one sunscreens were evaluated, and the calculated CGP were compared with the in vivo sun protective factor (SPF) and with the protection factor UVA (PFA). Nonlinear relationships were found between SPF and CGPUVB and between PFA and CGPUVA.

Melanin content of cultured human melanocytes and UV-induced cytotoxicity

Cultured melanocytes originating from persons with different skin phototypes were utilized for measurement of endonuclease sensitive sites induced by UVB and the determination of cell survival after UVA or UVB irradiation. During culture, the melanocytes largely maintained their phenotypic characteristics according to their original skin phototype. Total melanin concentrations were 4.9 times higher in the darker skin phototype (IV-VI) melanocytes when compared to the cells from lighter skin phototypes (I-III). Also phaeomelanin contents were higher (2.5 times) in the skin phototype (IV-VI) melanocytes which implies that the cells from light skin types contain less melanin, but a relatively high proportion of phaeomelanin. After UVB irradiation a stronger induction of endonuclease sensitive sites was found for melanocytes with a lower level of total melanin and a high content of pheomelanin. By measuring the clone forming ability in different melanocyte cultures after UVB irradiation, significant better survival was found in case of the cells with the higher melanin content. Despite the large variations in melanin content, no significant difference in survival after UVA irradiation could be demonstrated in this way. Our results suggest a protective effect of melanin for UVB and indicate the importance of the measurements of melanin content and composition when different parameters of UV-induced damage are studied in melanin producing cells.

Ultraviolet A and melanoma: a review

The incidence and mortality rates of melanoma have risen for many decades in the United States. Increased exposure to ultraviolet (UV) radiation is generally considered to be responsible. Sunburns, a measure of excess sun exposure, have been identified as a risk factor for the development of melanoma. Because sunburns are primarily due to UVB (280-320 nm) radiation, UVB has been implicated as a potential contributing factor to the pathogenesis of melanoma. The adverse role of UVA (320-400 nm) in this regard is less well studied, and currently there is a great deal of controversy regarding the relationship between UVA exposure and the development of melanoma. This article reviews evidence in the English-language literature that surrounds the controversy concerning a possible role for UVA in the origin of melanoma. Our search found that UVA causes DNA damage via photosensitized reactions that result in the production of oxygen radical species. UVA can induce mutations in various cultured cell lines. Furthermore, in two animal models, the hybrid Xiphophorus fish and the opossum (Mondelphis domestica), melanomas and melanoma precursors can be induced with UVA. UVA radiation has been reported to produce immunosuppression in laboratory animals and in humans. Some epidemiologic studies have reported an increase in melanomas in users of sunbeds and sunscreens and in patients exposed to psoralen and UVA (PUVA) therapy. There is basic scientific evidence of the harmful effects of UVA on DNA, cells and animals. Collectively, these data suggest a potential role for UVA in the pathogenesis of melanoma. To date evidence from epidemiologic studies and clinical observations are inconclusive but seem to be consistent with this hypothesis. Additional research on the possible role of UVA in the pathogenesis of melanoma is required.

Fluoroquinolones as chemical tools to define a strategy for photogenotoxicity in vitro assessment

Today's lifestyle is often associated with frequent exposure to sunlight, but some xenobiotics used in drugs, cosmetics or food chemicals can produce adverse biological effects when irradiated. In particular, they can increase the risk of photogenotoxicity already due to UV radiation itself. There is thus a need to design appropriate approaches in order to obtain relevant data at the molecular and cellular level in this field. For ethical and practical reasons, in vitro models can be very convenient at least for first evaluation tests. Here, we propose a strategy based on complementary experiments to study the photogenotoxic potential of a compound. The fluoroquinolones BAYy3118 and lomefloxacin were used as standards to demonstrate the performance of each test: photoinduced interaction with supercoiled circular DNA, photomutagenicity in the yeast Saccharomyces cerevisae, induction of DNA photodamage in cultured human skin cells as revealed by comet assay, and finally induction of specific phototoxic stress responses such as p53 activation or melanogenesis stimulation. Such a strategy should help to ensure the safety of products likely to undergo environmental sunlight exposure.

The phototumorigenic fluoroquinolone, lomefloxacin, photosensitises p53 accumulation and transcriptional activity in human skin cells

The fluoroquinolone antibiotic, lomefloxacin, is phototoxic in human skin exposed to UVA radiation, photosensitises DNA strand breaks and pyrimidine dimers in human keratinocytes in vitro, and is phototumorigenic in mouse skin. The p53 tumour suppressor protein is activated by a variety of cellular insults including UV radiation, to become a transcription factor for downstream markers such as the cyclin-kinase inhibitor p21CIP1/WAF1 or cause caspase transactivation which cleaves poly ADP ribose polymerase (PARP) as an early step in apoptosis. We have investigated these molecular defence responses in human skin cells treated with lomefloxacin and UVA radiation in vitro. Western blots revealed that lomefloxacin photosensitised the stabilisation of p53 protein in human fibroblasts. Lomefloxacin also photosensitised p53 transcriptional activity in amelanotic melanoma cells expressing wild-type p53 and stably transfected with a construct containing a beta-galactosidase reporter gene downstream from a p53 consensus binding sequence. Neither photosensitised production of H2O2 nor the resultant DNA strand breaks, appeared to be involved in this effect. Interestingly, p21CIP1/WAFI protein was upregulated by lomefloxacin in the dark by a p53-independent mechanism. Lomefloxacin also photosensitised the degradation of nuclear PARP, suggestive of caspase mediated, early apoptotic events.