Comparison of the effects of UV-visible irradiation of melanins and melanin-hematoporphyrin complexes from human black and red hair

Does Eumelanin Oxidation Play a Role on the Photostability of Ethyl Glucuronide in Hair Exposed to Simulated Solar Radiation?

The action of solar radiation on the concentration of the ethanol metabolite ethyl glucuronide (EtG) in 40 hair samples of nonabstinent subjects was investigated. Hair samples of different colors were analyzed before and after irradiation with artificial sunlight under a light dose corresponding to 3 months of sun exposure. After irradiation, an increase of EtG concentration was detected in 55% of the samples ranging from 5% to 141%. In 16 cases, a concentration reduction ranging from -2% to -74% was observed. The measure of the level of pyrrole-2,3,5-tricarboxylic acid (PTCA), a marker of eumelanin oxidation, demonstrated the largest increase in oxidation in light brown hair where the greatest degradation of EtG was observed after irradiation. However, the rise of PTCA in all hair tested was accompanied by increase in EtG concentration in 8/10 samples and by decrease in 2/10, suggesting no correlation between the two markers. To verify if hair structure was modified by light, scanning electron microscopy (SEM) analysis was performed on irradiated hair of different colors and compared with the dark samples. SEM revealed modification of hair structure in all samples showing partial shaft exfoliation and reduction of hair thickness under the treatment with solar radiation.

Cutaneous melanoma: how does ultraviolet light contribute to melanocyte transformation?

Ascribing a causal role to ultraviolet radiation in melanoma induction is problematic, as the relationship between total lifetime sun exposure and melanoma risk is not as strong as for some other skin cancers. Epidemiological studies show that heightened melanoma risk is most associated with intermittent sunburns. Despite this, lesions can develop on anatomical locations receiving intermittent (e.g., the trunk) or chronic exposures (e.g., the head and neck). Individuals developing melanoma on truncal sites tend to have more nevi, suggesting that in addition to the differences in forms of sun exposure, there may also be innate variation that makes one more susceptible to one or other mechanism of melanoma development. Such differences may depend upon different responses at the time of exposure (e.g., pigmentation characteristics, DNA repair capability and melanocyte proliferative response), and/or the role of the skin microenvironment in limiting proliferation of a ‘primed’ or mutated melanocyte during the latent period leading up to the appearance of a melanocytic lesion.

Synthetic melanin is a model for soluble natural eumelanin in UVA-photosensitised superoxide production

Studies to UV-irradiate natural eumelanins in vitro have used insoluble pigment obtained by acid hydrolysis, which lacks melanoprotein. Eumelanin synthesised in the presence of a protein is not insoluble, and the insoluble form of melanin from acid hydrolysis may not have the same physicochemical properties as the natural pigment synthesised in vivo in the melanosome. Here we investigated radical production by three natural eumelanins exposed to solar levels of UVA; sepia melanin from Sepia officinalis, and eumelanins isolated from Oriental human and domestic cat hair. UVA irradiation of sepia melanin in solution at pH 4.5 in the presence of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) gave hydroperoxyl and hydroxyl radical-adducts, maximal at 0.6-2.5 mg/ml melanin concentrations. Hydroperoxyl radical production was relatively low in acetate buffer, but detected in aqueous suspensions of sepia melanin. Hair eumelanins were photoreactive with hydroperoxyl radical-adduct production at low concentrations (0.1-0.4 mg/ml melanin). Synthetic pigment after synthesis undergoes photo-oxidation (producing superoxide) at low concentrations (0.3 mg/ml) and its oxidation increases the photoreactivity at higher melanin concentrations. These findings may be physiologically relevant to the properties and function of eumelanin in vivo when it is at low concentration (found in a small proportion of Caucasian melanocytes), and suggest that synthetic melanin has the potential for the basis of a model for natural eumelanin.

Worldwide polymorphism at the MC1R locus and normal pigmentation variation in humans

While there have been many advances in our understanding of the genetics of pathological skin pigmentation in humans, our knowledge about what determines variation in normal skin color is still incomplete. Variation in one gene, melanocortin 1 receptor (MC1R), has been associated with red hair and fair skin in Europeans. However, this gene might also play an important role in shaping pigmentation of other human populations, where it experiences different selective pressures. Below we review what is currently known about polymorphism and selection at the MC1R coding and promoter regions in human populations, the pattern of MC1R evolution in nonhuman primates, and the interaction of MC1R with other genes.

A novel RFP-RET transgenic mouse model with abundant eumelanin in the cochlea

We report on the cochlea of a novel metallothionein-I (MT)/RFP-RET transgenic mouse model with severe systemic melanosis. Electron microscopy revealed that these transgenic mice possess abundant quantities of melanin in the intermediate cells of the stria vascularis. High performance liquid chromatography analysis indicated that cochleae of these transgenic mice contained about twice as much eumelanin as cochleae of control C57BL/6 mice and that the amount of pheomelanin was approximately equal in these two strains. Auditory brainstem responses at 2, 4, 8, and 16 kHz were not significantly different between transgenic and control mice. This is the first report on a mouse model of overproduction of cochlear eumelanin, and our results suggest that this transgenic mouse is an excellent model for investigating the effects of overexpression of cochlear eumelanin. In addition, we provide evidence that eumelanin overproduction in the cochlea does not affect normal hearing.

Melanocortin 1 receptor variants, pigmentation, and skin cancer susceptibility

The melanocortin 1 receptor is a key regulator of variation in normal human pigmentation. Genetic variants of this receptor cause red hair and fair skin, and several case-control studies have demonstrated that these genetic variants increase the risk of skin cancer development in humans. The mechanism whereby the risks of skin cancer are increased is not entirely clear, and may be because of a combination of effects on pigmentation and non-pigmentary pathways.

Melanin acts as a potent UVB photosensitizer to cause an atypical mode of cell death in murine skin

Melanin protects the skin against DNA damage induced by direct absorption of sunlight's UV radiation. Yet, irradiating melanin in vitro or in cultured cells also generates active oxygen species such as superoxide, which can indirectly induce oxidative base lesions and DNA strand breaks. This photosensitization is greater for pheomelanin (yellow and red melanin) than for eumelanin (brown and black). The in vivo photosensitizing ability of melanin is unknown. We used congenic mice of black, yellow, and albino coat colors to investigate the induction of DNA lesions and apoptosis after exposure to predominantly UVB (280-320 nm) or UVA (320-400 nm) radiation. Cyclobutane pyrimidine dimers induced by direct UVB absorption were equal in all three strains, as was apoptosis measured as sunburn cells or as keratinocytes containing active caspase-3. However, terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling (TUNEL)-positive cells were approximately 3-fold more frequent in black and yellow mice after UVB or UVA irradiation than in albino. In epidermal sheets, TUNEL-positive cells lined the upper portion of the hair follicle, consistent with UV-induced photosensitization by melanin in the hair shaft. Because the concentration of eumelanin in black mice was three times that of pheomelanin in yellow mice, pheomelanin had 3-fold greater specific activity. We conclude that UV-irradiated melanin, particularly pheomelanin, photosensitizes adjacent cells to caspase-3 independent apoptosis, and this occurs at a frequency greater than the apoptosis induced by direct DNA absorption of UV. Melanin-induced apoptosis may contribute to the increased sensitivity of individuals with blonde and red hair to sunburn and skin cancer.

Effects of melanogenesis-inducing nitric oxide and histamine on the production of eumelanin and pheomelanin in cultured human melanocytes

Melanin pigments produced in human melanocytes are classified into two categories; black coloured eumelanin and reddish-yellow pheomelanin. Stimulation of melanocytes with alpha-melanocyte-stimulating hormone (alpha-MSH), one of several melanogenic factors, has been reported to enhance eumelanogenesis to a greater degree than pheomelanogenesis, which contributes to hyperpigmentation in skin. Nitric oxide (NO) and histamine are also melanogenesis-stimulating factors that are released from cells surrounding melanocytes following ultraviolet (UV) irradiation. In this study, the effects of NO and histamine on the ratio of eumelanin and pheomelanin were examined in human melanocytes, and then compared with that of alpha-MSH. The amounts of eumelanin and pheomelanin were quantified using high-performance liquid chromatography analysis after oxidation and hydrolysis of melanin. Melanogenesis was induced by the addition of alpha-MSH, NO, or histamine to melanocytes. The amount of eumelanin production significantly increased with independent stimulation by these melanogenic factors, especially histamine, while that of pheomelanin significantly increased with alpha-MSH and NO, but only slightly with histamine. As a result, the ratio of eumelanin and pheomelanin increased significantly with the addition of NO or histamine. These results suggest that NO and histamine, as in the case of alpha-MSH, may contribute to UV-induced hyperpigmentation by enhancing eumelanogenesis.

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.

Photoprotective actions of natural and synthetic melanins

Melanins are thought to be important modulators of photochemistry in skin. Eumelanin, a black-brown pigment, is believed to protect against UV-induced photodamage, whereas pheomelanin, a red-yellow pigment, is believed to possess photosensitizing properties. To investigate the hypothesized dichotomy of melanins as both photoprotectants and photosensitizers, we examined the effects of melanins on UV-induced liposomal lipid peroxidation. Sepia melanin, a representative eumelanin, and both red hair pheomelanin and synthetic pheomelanin were employed in these studies. Both eumelanin and pheomelanin inhibited UVA/B- and UVA-induced liposomal lipid peroxidation in a concentration-dependent manner as measured by inhibition of conjugated diene formation. No change in protective properties of the melanins was observed in the presence of saturating levels of O2 during UVA irradiation. Pheomelanin irradiated with UVA/B or UVA induced superoxide-catalyzed reduction of nitroblue tetrazolium, whereas eumelanin did not. Melanins are known to bind various metals, and we examined the effect of iron on the photoproperties of melanins. Eumelanin complexed with Fe(III) did not inhibit UVA/B-induced lipid peroxidation, whereas pheomelanin complexed with Fe(III) stimulated UVA/B-induced lipid peroxidation. Thus, complexation with iron reversed the antioxidant effect of eumelanin and converted pheomelanin into a prooxidant. Analysis of lipid peroxidation products indicated that the oxidation was mediated by free radicals rather than by singlet oxygen. These data indicate that both eumelanin and pheomelanin exert antioxidant effects against UV-induced lipid peroxidation but that the prooxidant activities of pheomelanin result from pheomelanin-metal complexation.

Physiological doses of ultraviolet irradiation induce DNA strand breaks in cultured human melanocytes, as detected by means of an immunochemical assay

An immunochemical assay, i.e. sandwich enzyme-linked immunosorbent assay, has been modified to detect UV-induced damage in cellular DNA of monolayer-grown human melanocytes. The method is based on the binding of a monoclonal antibody to single-stranded DNA. The melanocytes derived from human foreskin of skin type II individuals were suspended and exposed to UVA, UVB, solar-simulated light or gamma-rays. Following physiological doses of UVA, UVB or solar-simulated light, a dose-related DNA unwinding comprising a considerable number of single-strand breaks (ssb) was observed. No correlation was found between different seeded cell densities or different culturing periods and the UVA sensitivity of the cells. After UVA irradiation, 0.07 ssb/10(10) Da/kJ/m2 were detected and after UVB irradiation 1.9 ssb/10(10) Da/kJ/m2 were seen. One minimal erythema dose of solar-simulated light induced 2.25 ssb/10(10) Da. Our results from melanocytes expressed in ssb/Da DNA are comparable and have the same sensitivity toward UVA as well as toward UVB as nonpigmented skin cells. As low doses of UVA have already been shown to induce detectable numbers of ssb, this assay is of great interest for further investigations about the photoprotecting and/or photosensitizing effects of melanins in human melanocytes derived from different skin types.

Determination of pheomelanin by measurement of aminohydroxyphenylalanine isomers with high-performance liquid chromatography

We describe an improved method for the analysis of pheomelanin in biological samples. The method is based on a chemical degradation of the melanin polymer and HPLC analysis of specific degradation products. Hydriodic hydrolysis provides 4-amino-3-hydroxyphenylalanine (AHP) and 3-amino-l-tyrosine (AT) which are detected with an electrochemical detector. We have examined each step of the analysis and the results are presented in this paper. First the samples are hydrolyzed for 16 h. AT and AHP are then isolated from the hydrolysates by ion-exchange chromatography and then separated and quantitated by HPLC and electrochemical detection. The method shows good reproducibility with a total imprecision below 5.6%. The linearity of the method was shown from 0 to 490 ng AT and 0 to 850 ng AHP per sample, using a melanoma cell suspension (27 mg protein/ml) with up to 24-fold dilutions of the original sample. For cultured "normal" human melanocytes a minimal amount of 0.1 mg protein is sufficient for analysis of pheomelanin in the samples. This method provides the opportunity to study the composition of the formed melanin in cell lines, cultured in different growth media.

Comparative studies on the tolerance to photoinduced cutaneous inflammatory reactions by psoralen and rose bengal

The photochemotherapeutic value of topical 8-methoxypsoralen (8-MOP) plus UVA irradiation has been well recognized. The phototoxicity associated with psoralen plus UVA (PUVA) therapy is hallmarked by an increase in vascular permeability (iVP), the accumulation of polymorphonuclear leukocytes (aPMN) and erythema formation in situ. Rose bengal (RB) plus UVA-VIS light (320-700 nm) produces a similar acute inflammatory response, but without immediate or delayed erythema and perceptible edema. This study describes some of the parameters involved in inflammatory reactions evoked by PUVA and the results are compared with RB-induced phototoxic reactions. The rates of iVP and aPMN with a 3 h pulse were quantified using 125I-albumin and 51Cr-labelled PMNs respectively. The erythemal response was graded visually. 8-MOP cream was applied topically, while RB was injected intradermally in rabbit skin before UVA-VIS (9.4 J cm-2) irradiation. The data show that there is no significant difference in the rates of iVP, aPMN and erythema formation between normal skin sites and mast cell-depleted skin sites when challenged with 8-MOP plus light. These results suggest that in situ mast cells do not play a significant role in 8-MOP-photoinduced acute cutaneous inflammatory reactions, in contrast with RB-photoinduced reactions. The iVP and aPMN responses are minimal or absent in sites subjected to repeated exposure to 8-MOP plus light for three or more consecutive days, suggesting the establishment of a desensitized/unresponsive state. Moreover, 8-MOP-photo-desensitized sites do not produce iVP and aPMN of the same magnitude as the normal (naive) skin sites when challenged with RB plus light. Similarly, RB-photo-desensitized sites do not produce iVP and aPMN of the same magnitude as the native skin sites when challenged with 8-MOP plus light. The desensitization and cross-desensitization of skin sites to 8-MOP- or RB-photoinduced reactions suggest that there is either direct attack on the target cell(s), thereby removing the ability to express adhesion molecules, such as endothelial leukocyte adhesion molecule 1 (ELAM-1) or intercellular adhesion molecule 1 (ICAM-1), involved in the accumulation of inflammatory cells, or downregulation of the secretion/release of putative agent(s), such as interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF-alpha), responsible for the initiation and progression of cutaneous inflammations.

Scavenger effect of vitamin E and derivatives on free radicals generated by photoirradiated pheomelanin

The free radical scavenger properties of vitamin E (DL-alpha-tocopherol), a natural antioxidant, and derivatives were studied using an original in vitro method consisting of free radical production by photoirradiation of pheomelanin and direct detection of the free radicals by a physical, specific technique, electron spin resonance. Validation of this method has been realized using well-known biological free radical scavengers, superoxide dismutase and reduced glutathione. DL-alpha-Tocopherol, tocopheryl acetate, tocopheryl linoleate, and tocopheryl polyoxyethylene (POE) succinate induced a significant diminution of the free radical production. In order of efficiency, tocopheryl POE succinate was the best scavenger (37.6% inhibition at 0.25%) followed by tocopheryl linoleate (25.6% inhibition at 1%) and tocopheryl acetate (23.9% inhibition at 0.5%) and finally DL-alpha-tocopherol (16.2% inhibition at 0.05%). The results reported a decrease of the inhibitory effect for high concentrations of DL-alpha-tocopherol (0.1%) and tocopheryl acetate (1%), showing a tendency of this compound to act as a prooxidant. Used in optimal concentrations in cosmetologic or dermatologic formulations, Vitamin E and these derivatives should prevent or reduce the harmful activity of free radicals in the skin.

Nle4DPhe7 alpha-melanocyte-stimulating hormone increases the eumelanin:phaeomelanin ratio in cultured human melanocytes

In mammals, melanin exists in two chemically distinct forms: the red-yellow phaeomelanin and the brown-black eumelanin. Although administration of the pigmentary hormone alpha-melanocyte-stimulating hormone (alpha MSH) and its synthetic analogue Nle4DPhe7 alpha MSH induces skin darkening in man, the increases in melanogenesis in cultured human melanocytes in response to these peptides are relatively small. However, it is possible that MSH affects the eumelanin:phaeomelanin ratio rather than total cellular melanin. Thus, this study examined the specific effects of Nle4DPhe7 alpha MSH on the two melanins in cultured human melanocytes, quantifying eumelanin and phaeomelanin by high performance liquid chromatography. Nle4DPhe7 alpha MSH induced significant increases in the eumelanin content of these cells while having lesser and varied effects on the levels of phaeomelanin. As a consequence, the eumelanin:phaoemelanin ratio was increased in every culture. These results demonstrate that Nle4DPhe7 alpha MSH affects melanin type in human melanocytes and suggest a possible mechanism by which this peptide induces skin darkening in man.

Premature avian melanocyte death due to low antioxidant levels of protection: fowl model for vitiligo

Feather melanocytes in the Barred Plymouth Rock (BPR) and White Leghorn (WL) chickens die prematurely in vivo when compared to the wild type Jungle Fowl (JF) chicken. Since these mutant melanocytes live in vitro, an environmental factor in the feather must precipitate their death. Results show that the addition of selected antioxidants, glutathione (GSH) and superoxide dismutase (SOD), can rescue these mutant melanocytes in vitro that have been placed under stress conditions that cause their premature cell death. Measurements of in vivo levels of GSH, catalase, and SOD show no significant difference in catalase activity between the JF, BPR, and WL feathers but do show a significant reduction in GSH activity in both the BPR and WL feathers to approximately 66% of the GSH concentration found in JF feathers. SOD activity in the BPR tissue is reduced significantly to approximately 50% of the JF activity and the WL SOD activity is reduced significantly to approximately 50% of the BPR SOD activity. Preliminary results of measurements of glutathione peroxidase activity indicate there is no difference in the levels of this enzyme in JF, BPR and WL feathers. A working hypothesis, based on current results, is proposed for premature cell death in BPR and WL feather melanocytes. The BPR melanocytes are genetically sensitive due to a defect in their SOD and GSH levels caused by the barring gene (B) and their death, due to reactive species of oxygen radicals, is precipitated in the poorly vascularized feather by the accumulation of oxygen radicals due to the low turnover of tissue fluids. The WL chicken carries the dominant white gene (I) in addition to the B gene. This gene directs the further reduction of the level of SOD and, when combined with the cell death mechanism already present in the BPR chicken, causes the WL feather melanocytes to die much earlier than the BPR feather melanocytes which in turn die much earlier than the wild type JF melanocytes. This same mechanistic hypothesis could apply as a cause of premature melanocyte cell death in human vitiligo wherein the vitiliginous melanocytes may have a genetic defect in their oxygen radical protection system.

The presence of tyrosinase and related proteins in human epidermis and their relationship to melanin type

The present study was carried out to investigate the abundance of tyrosinase and related proteins (TRP-1 and TRP-2) in human epidermis and their relationship to melanin type. Positive immunocytochemical staining was seen for all three proteins in epidermal melanocytes. For each protein the numbers of positively stained melanocytes were similar in all subjects studied irrespective of skin type. Following 5 daily suberythemal doses of UVB the melanocytes were larger, more dendritic, and increased in number. With TRP-1 and TRP-2 the increase in number in response to UVB was unrelated to skin type and, hence, with melanin type but with tyrosinase there was a much greater increase in skin types III and IV than in skin type I and II. The enhanced numbers of tyrosinase-positive melanocytes were accompanied by increased staining intensity, suggesting a greater expression of tyrosinase in the melanocytes from skin types III and IV compared with skin types I and II. This increase in tyrosinase could be related to the greater levels of eumelanin found in skin types III and IV, and this is in keeping with the view that higher levels of tyrosinase are associated with the production of eumelanin than phaeomelanin.

Etiology of melanoma

Although the precise etiology of melanoma remains unknown, much data link sunlight to melanoma. The imperfect evidence associating sun exposure (particularly UVB radiation) with melanoma emerges from human data, obviating problems inherent in extrapolation from animal and other models. However, the mechanism by which sunlight might possibly initiate or promote melanoma remains obscure. Some clarification should emerge from the potential isolation of genes that carry susceptibility to melanoma in families prone to the disease; such work could serve as a basis to distinguish genetic and environmental influences in melanoma [167]. Continued studies of faulty DNA repair in XP patients may elucidate the steps in mutagenesis and carcinogenesis. Future case-control studies must address the limits on the accuracy of recall and the limits on statistical methods to separate the cluster of phenotypic risk needed in determining biologically effective dose. Animal and in vitro studies must contribute more insight. Further research in the South American opossum models appears promising [72]. Although ozone depletion has been documented, there has been little definitive evidence of subsequent increase of UVB at the Earth's surface. Nevertheless, the threat posed by ozone depletion deserves continued environmental action and public education. The role of precursor lesions, particularly dysplastic nevi/atypical moles, must be clarified with future research. The distribution of melanoma among various work forces suggests that occupational risk factors may play an important role in the etiology of this disease [168-170]. The consistent reports of excess melanoma among accountants, clerical workers, professional workers, and teachers deserve further study. Furthermore, evidence of excesses in printing and press, petrochemical, and the telecommunications industries require follow-up. Carefully planned studies that account for nonoccupational risk factors are recommended. Research over the last four decades has brought much information about melanoma etiology. More work is needed to learn the precise cause and ultimately to prevent avoidable mortality from malignant melanoma.

Cultured human melanocytes from black and white donors have different sunlight and ultraviolet A radiation sensitivities

Short-term and long-term survival of cultured neonatal foreskin melanocytes from black and white individuals were assessed following a single exposure to simulated sunlight or ultraviolet A (UVA) radiation. Melanocytes from black individuals contained significantly more melanin than melanocytes from white individuals (p less than 0.05). Black and white melanocytes had similar survival profiles following simulated sunlight exposure, whereas black melanocytes were significantly more resistant to UVA cytotoxicity than melanocytes from white subjects (p less than 0.05) at UVA doses above 15 J/cm2. There was no difference in unscheduled DNA synthesis in the black or white melanocytes following simulated sunlight exposure and no unscheduled DNA synthesis was measurable following melanocyte exposure to UVA radiation. Low-dose UVA (1 or 5 J/cm2) was mitogenic to both black and white melanocytes. By analysis of co-variance, the melanin content of melanocytes of black and white subjects was significantly (p less than 0.05) associated with susceptibility to UVA killing; melanocytes with high melanin content had high resistance to UVA cytotoxicity and those with low melanin content had low resistance to UVA cytotoxicity. From these data we suggest that the higher melanin content of melanocytes of black subjects confers increased resistance to UVA damage. This is likely to be of importance in epidermal photodamage.

Photoinduced cutaneous inflammatory response by psoralens

Our studies describe the inflammatory response in rabbit skin induced by topical application of 8-methoxypsoralen (8-MOP) and UVA-visible irradiation (320-700 nm). Increase in vascular permeability (iVP) and accumulation of polymorphonuclear leucocytes (aPMN) at the test sites were quantitated using 125I-albumin and 51Cr-labelled PMNs respectively. Erythema was graded visually. 8-MOP cream was applied topically and irradiated. The erythemal response, aPMN and iVP at the test sites were quantitated at 6, 24, 48 and 72 h post-irradiation. The iVP and aPMN were maximal at 24 h; the erythemal response was the same at 24-48 h. The responses were dependent on 8-MOP concentration and irradiation dose. Topical application of 200 micrograms 8-MOP cream followed by irradiation for 2 h (9.4 J cm-2) produced 3-7 times iVP, 2-4 times aPMN and intense erythema at the test sites after 24 h. Neither aPMN nor iVP was detected before 6 h and erythemal response was not observable up to 16 h after irradiation. The aPMN and iVP gradually subsided in 72 h, although the erythemal response was still present. The repeated exposure of 8-MOP-treated sites for three consecutive days 24 h apart did not produce appreciable iVP or aPMN at 72 h or 24 h after the last exposure; however, erythema persisted. The 8-MOP-treated sites previously exposed for three consecutive days on reapplication of 8-MOP cream plus irradiation showed significantly less response compared with non-pretreated sites. Our results suggest that the erythemal response is not directly related to either iVP or aPMN.

Antioxidative activity of synthetic melanins. Cardiolipin liposome model

The inhibiting effect of melanin synthesized from dihydroxyphenylalanine (DOPA), dopamine, adrenaline and adrenolutin on the ultraviolet- or the Fe(2+)-ascorbic acid-induced peroxidation of cardiolipin liposomes has been studied. All these melanins are able to inhibit both the ultraviolet- and the Fe(2+)-ascorbic acid-induced lipid peroxidation. Antioxidative activity of melanins enhances in the order: dopamine-melanin less than melanin synthesized from dopamine in the presence of Cu(2+) less than DOPA--melanin less than melanin synthesized from adrenaline in the presence of Cu(2+) approximately equal to adrenolutin-melanin, and correlates with their ability to scavenge superoxide anion radical. The optical screening effect of the investigated melanins in the inhibition of lipid peroxidation was not higher than 15% for the most active melanins.

Free radicals and aging of the skin

Cutaneous aging is the result of genetically determined or intrinsic aging superimposed by degenerative changes due to actinic irradiation, also called photoaging. The manifestations of cutaneous aging, as it relates to the perception of age, is caused by ultraviolet light, in particular in those parts of the body exposed daily to solar radiation. Free radical generation in the skin by UV light and from other sources, such as cellular infiltrations or the xanthine oxidase reaction, may be detected by direct and indirect methods. The decrease in antioxidant enzymes and small molecular weight antioxidants such as glutathione, vitamin E and ubiquinone upon exposure to UV light is an indication that the pro-antioxidant balance can be overwhelmed by acute or chronic photo-oxidative stress. Antioxidant supplementation is therefore a means for prevention or at least retardation of premature cutaneous aging.

Modification of membrane fluidity in melanin-containing cells by low-level microwave radiation

The treatment of a B16 melanoma cell line with 2.45-GHz pulsed microwaves (10 mW/cm2, 10-microseconds pulses at 100 pps, 1-h exposure; SAR, 0.2 W/kg) resulted in changes of membrane ordering as measured by EPR (electron paramagnetic resonance) reporter techniques. The changes reflected a shift from a more fluid-like phase to a more solid (ordered) state of the cell membrane. Exposure of artificially prepared liposomes that were reconstituted with melanin produced similar results. In contrast, neither B16 melanoma cells treated with 5-Bromo-2-Deoxyuridine (3 micrograms/day x 7 days) to render them amelanotic, nor liposomes prepared without melanin, exhibited the microwave-facilitated increase of ordering. Inhibition of the ordering was achieved by the use of superoxide dismutase (SOD), which strongly implicates oxygen radicals as a cause of the membrane changes. The data indicate that a significant, specific alteration of cell-membrane ordering followed microwave exposure. This alteration was unique to melanotic membranes and was due, at least in part, to the generation of oxygen radicals.

Role of iron in the photosensitization by uroporphyrin

The role of iron in the mechanism of photosensitivity due to uroporphyrin was investigated. There is frequently increased levels of Fe in the serum from patients with porphyria cutanea tarda, where the photosensitivity is due to uroporphyrin. It has been reported that H2O2 has a major role in the uroporphyrin induced photosensitivity. Hence we examined the hypothesis that Fe would catalyze the production of OH from H2O2 and the OH thus formed may have a significant role in the uroporphyrin photosensitivity. This was examined by studying the effects of the Fe chelating compound deferoxamine in an in vitro system. Our results show that deferoxamine inhibited the uroporphyrin photosensitivity, but not the photosensitivity due to protoporphyrin. This indicates that Fe may play a role in the uroporphyrin photosensitization in the skin, by accelerating the formation of OH, which may be a major reactive species responsible for the photosensitization in porphyria cutanea tarda.

Disparate antioxidant enzyme activities in cultured human cutaneous fibroblasts, keratinocytes, and melanocytes

Antioxidant enzyme activities of cultured human foreskin fibroblasts, keratinocytes, and melanocytes from healthy black and Caucasian donors were measured and compared. Fibroblasts had more (p less than 0.05) peroxidase, catalase, glutathione peroxidase, and superoxide dismutase activity than keratinocytes. Keratinocytes had more (p less than 0.05) peroxidase, catalase, glutathione peroxidase, and superoxide dismutase activity than melanocytes. No differences in antioxidant enzyme activities were observed between the cells of any type taken from black or Caucasian people. Antioxidant enzyme activities may affect resistance to damage by oxidants induced by ultraviolet radiation and inflammation.

Pheomelanin as well as eumelanin is present in human epidermis

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

Quantitation of hydrogen peroxide formed during UV-visible irradiation of protoporphyrin, coproporphyrin and uroporphyrin

Free porphyrins are strong photosensitizers. Previously reported findings indicate that the in vitro cell lysis induced by irradiation in the presence of coproporphyrin (CP) and uroporphyrin (UP) is mediated by H2O2 and that induced by irradiation with protoporphyrin (PP) is not mediated by H2O2. In the present study the possible role of H2O2 in the porphyrin photosensitization was investigated by direct measurement of the H2O2 formed during the irradiation of PP, CP and UP. Our results show that the amount of H2O2 formed decreased in the following order: UP, CP, PP. The amounts of H2O2 formed during irradiation of CP and PP were approximately 86% and 38% respectively in comparison to the H2O2 formed during the irradiation of UP. The formation of H2O2 was inhibited by sodium azide, a strong quencher of singlet oxygen. These observations are in good agreement with the previous report that the in vitro photolysis of Ehrlich ascites carcinoma cells by UP and CP, but not that by PP, was inhibited by catalase and clinical findings with patients with erythropoietic protoporphyria (EPP) and porphyria cutanea tarda (PCT). The patients with EPP, where the photosensitivity is due to PP, respond well to beta-carotene while beta-carotene does not protect against the photosensitivity in PCT, in which case the photosensitivity is due to uroporphyrin.

A comparison of the phototoxicity of protoporphyrin, coproporphyrin and uroporphyrin using a cellular system in vitro

The photobiological effects of protoporphyrin (PP), coproporphyrin (CP) and uroporphyrin (UP) were investigated using an in vitro model. Suspensions of Ehrlich ascites carcinoma cells were labelled with 51Cr and irradiated in the presence of a wide range of concentrations of PP, CP and UP. It was found that PP was the most potent photosensitizer in this system; CP was less effective than PP and UP was the least potent. The cell lysis by CP was enhanced by superoxide dismutase (SOD) and inhibited by catalase; the lysis by UP was also inhibited by catalase; on the other hand, the lysis by PP was not affected by SOD or catalase. These indicate that the cell lysis by CP and UP was largely due to hydrogen peroxide produced from superoxide formed during the irradiation. The lysis produced by PP was not mediated by hydrogen peroxide. These differences in the mechanisms of the phototoxicity of the various porphyrins may have relevance in the etiology and treatment of the porphyrias.

UVB-induced melanogenesis may be mediated through the MSH-receptor system

Ultraviolet B radiation (UVB) elicits an increase in melanin production in mammalian skin. The mechanisms regulating this process are not understood, although it is well documented that there is an increase in the number of melanin-producing melanocytes. The melanotropins (MSH) are a family of peptides that increase the melanin content of melanocytes through an interaction with high affinity receptors. We have obtained evidence that the effects of UVB on melanogenesis may be mediated through an increase in MSH receptor activity on melanocytes. First, exposure of Cloudman S91 mouse melanoma cells to UVB resulted in increased binding of 125I-MSH to cells within 24 h. In five separate experiments, UVB-irradiated cultures displayed 2-10-fold increases in MSH binding capacity over that of unirradiated control cultures (optimum doses 10-20 mJ/cm2). Second, UVB and MSH potentiated one another in promoting cutaneous melanogenesis in both mice and guinea pigs. In the areas of guinea pig skin that received both UVB and MSH, there was a fivefold increase in active melanocytes/mm2 over the sum of active melanocytes/mm2 in areas receiving either MSH or UVB separately. Our results suggest that UVB light causes an increase in MSH receptor activity on cutaneous melanocytes, thus increasing cellular responsiveness to MSH. Implicit in this mechanism is a transduction of radiant energy into chemical energy during the process of UVB-induced melanogenesis.

Human melanocytic neoplasms and their etiologic relationship with sunlight

Two hypotheses have been presented. The first states that melanomas commonly evolve from normal melanocytes by a tumor progression pathway from a banal nevus to a nevus with dysplasia, to a micro-invasive, and then to a fully evolved, tumorigenic, primary melanoma which has competence for metastasis. It is important to note that not all melanomas follow this complete pathway. As Foulds noted long ago, tumors may bypass any of the stages of tumor progression. Thus, many melanomas do not, apparently, arise in nevi, and melanomas may evolve "fully formed" as pure tumorigenic nodules. However, from the biological point of view, study of the benign potential precursors (nevi and, especially, dysplastic nevi as well as microinvasive melanomas) may well reveal mechanisms of progression that are applicable to all melanomas, and perhaps to other solid tumors as well. From a clinical viewpoint, follow-up and education of patients at increased risk for melanoma, and early diagnosis of melanomas in their curable, microinvasive stages may result in a reduction of mortality from the disease, even without influencing its overall incidence. The melanomas that occur on plantar and palmar (acral) skin appear to progress through a microinvasive stage similar to that of other cutaneous melanomas. However, the significance of precursor and marker lesions (if any exist) in acral melanoma remains to be elucidated by clinicopathologic and epidemiologic studies. The possibility of etiologic agents other than UV light, such as chemical carcinogens and/or viruses, should be investigated in these cases. The second hypothesis presented here, that UV light is etiologic for the common cutaneous melanoma of white populations, has support from clinical, epidemiologic, and biologic observations. From a biologic viewpoint, ultraviolet light has all of the properties that might enable it to act as a complete carcinogen, and to enhance tumor progression in melanocytic "potential-precursor" lesions. Clinically, it seems appropriate to encourage patients (and members of the general population, as well) to adopt sensible attitudes to sun exposure. By such means, it is possible that some melanomas might be prevented, or that the rate and incidence of progression to more-advanced stages might be inhibited.

Skin type, hair color, and freckles are predictors of decreased minimal erythema ultraviolet radiation dose

In a group of 190 white healthy subjects the skin type classification method was found valuable for differentiating subgroups with various degrees of sun sensitivity (except for 33% with borderline or unclassifiable skin type). Sun-sensitive skin types I and II were significantly more common among persons with light hair color or freckles, or both (p less than 0.001). In each skin type category the proportion of subjects with a minimal erythema dose (MED) lower than the median MED of the entire group (%LMED) decreased significantly with increasing skin type number, and distinguished between skin types I through III better than did their mean MED values. Independent predictors of %LMED were skin type and hair color. The contribution of freckles to %LMED was skin type dependent. Age, sex, or eye color had no independent effect on %LMED. The association of skin types I and II, red or blond hair, and freckles with decreased MED may reflect genetically controlled predominance of pheomelanin (a photosensitizing molecule) in the skin of subjects with these phenotypes.

Ultrastructural changes produced in Ehrlich ascites carcinoma cells by ultraviolet-visible radiation in the presence of melanins

Irradiation of Ehrlich ascites carcinoma (EAC) cells in the presence of pheomelanin, i.e., red hair melanin (RHM), has been reported to produce extensive cell lysis. Irradiation in the presence of eumelanin, i.e., black hair melanin (BHM), or irradiation in the absence of either type of melanin did not produce this effect. We observed that RHM particles penetrated the cell membrane without apparent structural damage to the cell or the cell membrane. Irradiation of the cells in the absence of melanin did not produce any changes in the ultrastructure of the cells. Incubation of the cells in the dark in the presence of RHM produced only minor structural, mainly cytoplasmic changes. Irradiation of the cells in the presence of RHM produced extensive ultrastructural changes prior to complete cell lysis; these changes were more severe than the effects of incubation of the cells in the dark in the presence of RHM. When the cells incubated in the dark or irradiated in the presence of latex particles or either one of the eumelanins particles, viz. BHM or synthetic dopa melanin, these particles did not penetrate into the cells or produce any ultrastructural changes. These particles were in fact not even ingested by the cells.

Is there any difference in the photobiological properties of melanins isolated from human blue and brown eyes?

Investigations were carried out to determine whether the melanin present in the blue and brown eyes were eumelanin, the melanin present in black hair and dark skin, or pheomelanin, the melanin present in red hair and the skin of people with red hair. Our results showed that UV-visible irradiation of blue or brown eye melanin did not produce any superoxide. Irradiation of 51Cr-labelled Ehrlich ascites carcinoma cells in the presence of blue or brown eye melanin did not produce significant cell lysis. The electron spin resonance (ESR) signals of blue and brown eye melanins were very similar to those of eumelanin. Comparison of these findings with our previous results indicated that the blue and brown eye melanins are essentially eumelanin. The ESR signals further suggested that in the case of both blue and brown eye melanins the iris, ciliary body, choroid, and retinal pigment epithelium did not differ.

Reaction of superoxide anions with melanins: electron spin resonance and spin trapping studies

Scavenging of superoxide radicals by melanin is a possible factor in the photoprotection afforded by melanin pigments. The reaction between superoxide anions and melanins has been studied by electron spin resonance and spin trapping methods. It was found that superoxide anions react to produce melanin free radicals in a reaction inhibited by superoxide dismutase but not by catalase. The rate of radical formation depends on the concentration of melanin and superoxide, the pH of the medium and the presence of diamagnetic metal ions. The melanin pigment competes with the enzyme superoxide dismutase for removal of superoxide radicals. It was found that the xanthine-xanthine oxidase system is not suitable for studying the reaction of superoxide with melanin, as the enzymatic activity of xanthine oxidase is considerably inhibited by melanin.

Effects of melanin-induced free radicals on the isolated rat peritoneal mast cells

Pheomelanin from human red hair (RHM) produces considerably more cellular damage in Ehrlich ascites carcinoma cells when subjected to radiations of wavelength 320-700 nm than eumelanin from black hair (BHM). Irradiation of RHM generated large amounts of superoxide while BHM did not produce detectable amounts of superoxide. The present investigations describe the effects of irradiation of mast cells in the presence of various natural and synthetic melanins. Irradiation of mast cells in the presence of RHM and red hair melanoprotein released large amounts of histamine while BHM and synthetic melanins prepared from dopa, cysteinyldopa, or a mixture of dopa and cysteinyldopa did not release histamine. The release of histamine at lower concentrations of RHM was not accompanied by the release of 51Cr from chromium-loaded cells, suggesting that this release was of noncytotoxic nature. On the other hand, the release of histamine at higher concentrations of RHM was due to cell lysis since both histamine and cytoplasmic marker 51Cr were released to the same extent. The release evoked by large concentration RHM was not inhibited by superoxide dismutase or catalase. This suggests that the cell lysis under these conditions was not due to H2O2 or O-2. The finding that mast cells release histamine when irradiated in the presence of RHM suggests that the immediate and late-phase reactions seen in sunburn may in part be due to the release of mediators from these cells.

Free radicals from eumelanins: quantum yields and wavelength dependence

Formation of light-induced free radicals from natural eumelanin (from bovine eyes) and synthetic melanin (from oxidation of 3,4-dihydroxyphenylalanine) has been studied by electron spin resonance spectroscopy. Action spectra measured for natural melanins are very similar to that found for synthetic melanin, and are unaffected by the removal of associated protein. A comparison of action spectra with optical absorbance spectra shows that the former has a more marked wavelength dependence, suggesting that the chromophore that is most active in free-radical production is not the major melanin chromophore that absorbs visible light. Measurements of quantum yields for free-radical production have been made over a wavelength range from 600 to 230 nm. The efficiency of radical production from natural eumelanin is about three times greater than from the synthetic material. Although production of the melanin radicals detected is independent of oxygen, some correlation with oxygen consumption is evident; quantum yields for radical production are approximately three times those for oxygen consumption obtained under similar conditions. Possible reasons for this are discussed.