The proliferative and toxic effects of ultraviolet light and inflammation on epidermal pigment cells

Fingerprinting of skin cells by live cell Raman spectroscopy reveals melanoma cell heterogeneity and cell-type-specific responses to UVR

Raman spectroscopy is an emerging dermatological technique with the potential to discriminate biochemically between cell types in a label-free and non-invasive manner. Here, we use live single-cell Raman spectroscopy and principal component analysis (PCA) to fingerprint mouse melanoblasts, melanocytes, keratinocytes and melanoma cells. We show the differences in their spectra are attributable to biomarkers in the melanin biosynthesis pathway and that melanoma cells are a heterogeneous population that sit on a trajectory between undifferentiated melanoblasts and differentiated melanocytes. We demonstrate the utility of Raman spectroscopy as a highly sensitive tool to probe the melanin biosynthesis pathway and its immediate response to ultraviolet (UV) irradiation revealing previously undescribed opposing responses to UVA and UVB irradiation in melanocytes. Finally, we identify melanocyte-specific accumulation of β-carotene correlated with a stabilisation of the UVR response in lipids and proteins consistent with a β-carotene-mediated photoprotective mechanism. In summary, our data show that Raman spectroscopy can be used to determine the differentiation status of cells of the melanocyte lineage and describe the immediate and temporal biochemical changes associated with UV exposure which differ depending on cell type, differentiation status and competence to synthesise melanin. Our work uniquely applies Raman spectroscopy to discriminate between cell types by biological function and differentiation status while they are growing in culture. In doing so, we demonstrate for the first time its utility as a tool with which to probe the melanin biosynthesis pathway.

The Expression of Melanogenic Proteins in Korean Skin after Ultraviolet Irradiation

For proper melanin production, several specific enzymes such as tyrosinase, tyrosinase-related protein 1 (TRP-1) and dopachrome tautomerase are required. Their expressions are increased after exposure to UVB. However, it is not known how long tyrosinase and TRP-1 activities continue after UV irradiation in vivo. The purpose of this study is to measure the changes in expressions of tyrosinase, TRP1, and MITF after exposure to UV on skin in a Korean population. We established an immunohistochemical staining protocol for specimens which were obtained from UV-irradiated skin in five healthy Korean males on the 2nd, 5th, 7th, 28th, and 56th days after UV irradiation. Tyrosinase, TRP-1, and MITF expressions increased until 7 days after UV irradiation and then dropped to the basal constitutive level 4 and 8 weeks later. Interestingly, tyrosinase increased prior to TRP-1. This study reveals the time-sequence of melanin-synthesized enzymes and provides important information for the clinical evaluation of the effectiveness of whitening agents.

Idiopathic guttate hypomelanosis-like lesions in patients with mycosis fungoides: a new adverse effect of phototherapy

BACKGROUND

Idiopathic guttate hypomelanosis (IGH) is a common pigmentary disorder, the aetiology and pathogenesis of which are largely unknown. The appearance of IGH-like lesions during phototherapy has been reported previously in only one patient.

OBJECTIVE

To describe the clinical and histological features of phototherapy-induced IGH-like lesions, their relation to ultraviolet dosimetry and the course of this eruption in patients with mycosis fungoides (MF).

METHODS

The files of all patients with MF who underwent phototherapy in our centre from 1992 to 2008 were searched to identify those in whom IGH-like lesions appeared during treatment. Results Among 87 patients with early-stage MF who underwent phototherapy, seven acquired IGH-like lesions during monotherapy with narrow-band ultraviolet B (NB-UVB; four patients) or psoralen and ultraviolet A (PUVA; three patients). All but one had a light complexion. The lesions appeared in areas exposed to ultraviolet light, and not exclusively on the skin previously involved by the disease. The mean number of exposures until appearance of the lesions was 92 for NB-UVB and 137 for PUVA. Biopsy study showed a decreased number of melanocytes. Phototherapy was discontinued in four patients, of whom three showed a partial or complete disappearance of the IGH-lesions. The other three patients are still receiving phototherapy, with no change in their IGH-like lesions.

CONCLUSIONS

Phototherapy may induce an eruption bearing similar clinical and histopathological features to IGH. The eruption is rare, appears to emerge only after prolonged therapy and seems to be reversible upon discontinuation of phototherapy. IGH-like eruption should be added to the list of side-effects of phototherapy.

Ultraviolet B-induced alterations of the skin barrier and epidermal calcium gradient

Ultraviolet irradiation induces a variety of cutaneous changes, including epidermal permeability barrier disruption. In the present study, we assessed the effects of ultraviolet B (UVB) irradiation in epidermal barrier function and calcium distribution in murine epidermis. Adult hairless mice were exposed to a single dose of UVB (0.15 J/cm(2)). Barrier function was evaluated by transepidermal water loss (TEWL), lanthanum perfusion. The morphological alterations were examined by histology, immunohistochemistry and electron microscopy using ruthenium tetroxide (RuO(4)) postfixation. For evaluation of the effect on epidermal calcium distribution, the ion-capture cytochemistry was employed. UVB irradiation caused a significant increase in TEWL, which peaked at day 4. In parallel, the increased number of sunburn cells and the changes in epidermal hyperplasia and proliferation were observed. Electron microscopic observation demonstrated that the water-soluble lanthanum tracer was present in the extracellular stratum corneum domains, and the increased intercellular permeability was correlated with defective organization of the extracellular lipid lamellar bilayers of the stratum corneum. Moreover, UVB irradiation also caused an appearance of calcium precipitates in the stratum corneum and transitional cell layers as well as the increased cytosolic calcium in the lower epidermis, reflecting the alterations of the epidermal calcium gradient. These results suggest that the changes of the epidermal calcium distribution pattern may correlate with the perturbation of the epidermal barrier induced by UVB irradiation.

Biophysical and morphological changes in the stratum corneum lipids induced by UVB irradiation

BACKGROUND

UV irradiation induces a variety of responses in the epidermis, including sunburn cell formation, epidermal hyperplasia, and epidermal permeability barrier disruption.

OBJECTIVE

The aim of present study was to assess the effects of UVB irradiation in the intercellular lipids in murine stratum corneum.

METHODS

Adult hairless mice were exposed to a single UVB dose (0.15 J/cm(2)), the Fourier transform infrared (FT-IR) spectroscopic study was performed to investigate the effect on the biophysical changes in the stratum corneum lipids, barrier function was monitored by transepidermal water loss (TEWL) measurement, and the morphological alterations of stratum corneum was examined by electron microscopy using ruthenium tetroxide postfixation.

RESULTS

The FT-IR spectroscopic study revealed that there was the shift to higher wavenumbers of the symmetric and asymmetric stretching peaks near 2850 and 2920 cm(-1) respectively at days 3-4 after a single UVB irradiation, reflecting to the increase in motional freedom of lipids hydrocarbon chains, call as disordering of lipids. Moreover, A single UVB irradiation also caused a significant increase in TEWL, the increase in TEWL began after 2 days and peaked at day 4. Electron microscopic observations revealed that marked morphological abnormalities in the intercellular domains, including abnormal profile of lamellar granules and its contents at the interface between stratum corneum and stratum granulosum and the persistence of the nuclei in the stratum corneum. Moreover, the separated fragmentary lipid lamellae, excessive numbers of lamellae in stacks, both the elongated and enlarged lacuna as well as the extracellular whorls were present within the widen space of the stratum corneum.

CONCLUSION

The both of biophysical and morphological changes of the stratum corneum lipids may reflect to the mechanisms of perturbation of the epidermal permeability barrier induced by UVB irradiation.

Increase of pro-opiomelanocortin mRNA prior to tyrosinase, tyrosinase-related protein 1, dopachrome tautomerase, Pmel-17/gp100, and P-protein mRNA in human skin after ultraviolet B irradiation

In ultraviolet-induced tanning, the protein levels of various gene products critical for pigmentation (including tyrosinase and tyrosinase-related protein-1) are increased in response to ultraviolet B irradiation, but changes in mRNA levels of these factors have not been investigated in vivo. We have established an in situ hybridization technique to investigate mRNA levels of pro-opiomelanocortin, tyrosinase, tyrosinase-related protein-1, dopachrome tautomerase, P-protein, Pmel-17/gp100, and microphthalmia-associated transcription factor, and have analyzed the changes in mRNA levels in the ultraviolet B-exposed skin in vivo. The right or left forearm of each volunteer was irradiated with ultraviolet B, and skin biopsies were obtained at 2 and 5 d postirradiation. mRNA level of pro- opiomelanocortin was increased 2 d after ultraviolet B irradiation, and returned to a near-basal level after 5 d, whereas the mRNA levels of tyrosinase, tyrosinase-related protein-1, dopachrome tautomerase, P-protein, and Pmel-17/gp100 showed some or no increase at 2 d, but were significantly increased 5 d after ultraviolet B irradiation. Microphthalmia-associated transcription factor mRNA was slightly increased on days 2 and 5 after ultraviolet B irradiation. Our results suggest that the mechanism of the tanning response of human skin may involve the transcriptional regulation of certain pigmentary genes, and that pro-opiomelanocortin-derived melanocortins such as alpha-melanocyte-stimulating hormone and adrenocorticotropic hormone may play a part in regulating these genes in vivo.

Vitiligo-like leucoderma during photochemotherapy for mycosis fungoides

We describe four patients with mycosis fungoides (MF) in whom depigmentation, and also leucotrichia in one, occurred following the resolution of the eruption during phototherapy (psoralen plus ultraviolet A treatment in three patients, climatotherapy in one). In all cases, the depigmentation was localized to the area of the pre-existing MF lesions. There was no clinically obvious phototoxicity. Biopsy study including S100 staining in all cases, and electron microscopy in one case, demonstrated the total absence of melanocytes, with no evidence of MF. It is suggested that the phototherapy may have activated a cell-mediated immunity leading to destruction of the melanocytes. We recommend that vitiligo-like leucoderma be added to the list of untoward effects of phototherapy in MF.

Seasonal pattern of the excision rate of melanoma and naevi

Based on available information that melanocytic skin lesions presenting a junctional component are more susceptible to the influence of ultraviolet radiation, this study compares the seasonal differences between the excision rates of melanocytic skin lesions with a junctional component to those without. The histological diagnoses of 1230 patients with melanocytic skin lesions were retrospectively analysed. Depending on the histological diagnosis four groups were formed: melanomas, dysplastic naevi, common naevi (junctional and compound naevi), and dermal naevi. All dates of operations were allocated to summer or winter halves of the year. The collected data were computer analysed for statistical description. The number of excisions of melanocytic lesions with a junctional component (melanoma, dysplastic naevi, common naevi) showed an impressive seasonal variation, with a peak during the summer months, while the excision frequency of dermal naevi was approximately constant during the year. In conclusion, we suggest that ultraviolet radiation may contribute to the seasonal pattern of excision of melanoma and naevi only when a junctional component is present.

Skin pigmentation enhancers

The highest incidences of cancer are found in the skin, but endogenous pigmentation is associated with markedly reduced risk. Agents that enhance skin pigmentation have the potential to reduce both photodamage and skin cancer incidence. The purpose of this review is to evaluate agents that have the potential to increase skin pigmentation. These include topically applied substances that simulate natural pigmentation: dihydroxyacetone and melanins; and substances that stimulate the natural pigmentation process: psoralens with UVA (PUVA), dimethylsulfoxide (DMSO), L-tyrosine, L-Dopa, lysosomotropic agents, diacylglycerols, thymidine dinucleotides, DNA fragments, melanocyte stimulating hormone (MSH) analogs, 3-isobutyl-1-methylxanthine (IBMX), nitric oxide donors, and bicyclic monoterpene (BMT) diols. These agents are compared with regards to efficacy when administered to melanoma cells, normal human epidermal melanocytes, animal skin, and human skin. In addition, mechanisms of action are reviewed since these may reveal issues related to both efficacy and safety. Both dihydroxyacetone and topically applied melanins are presently available to the consumer, and both of these have been shown to provide some photoprotection. Of the pigmentation stimulators, only PUVA and MSH analogs have been tested extensively on humans, but there are concerns about the safety and side effects of both. At least some of the remaining pigmentation stimulators under development have the potential to safely induce a photoprotective tan.

Topical all-trans retinoic acid augments ultraviolet radiation-induced increases in activated melanocyte numbers in mice

We have previously shown that daily application of 0.05% retinoic acid to the backs of lightly pigmented, hairless HRA:Skh-2 mice increases melanogenesis resulting from exposure to solar-simulated ultraviolet radiation. In this study we show that as early as 1 wk following commencement of treatment, there is a 2- fold increase in the number of epidermal 3,4-dihydroxyphenylalanine positive melanocytes in retinoic acid and ultraviolet radiation treated HRA:Skh-2 mice compared with mice that received ultraviolet radiation only. This increased to a 2.9-fold difference by 6 wk. Retinoic acid also augmented ultraviolet radiation-stimulated melanogenesis, with a 4-fold increase being observed after only 2 wk. These findings were also seen in C57BL mice. Ultraviolet radiation and retinoic acid needed to be applied to the same skin site for the augmentation in melanocyte activation to occur. Ultraviolet B rather than ultraviolet A was mainly responsible for melanogenesis and the retinoic acid primarily increased ultraviolet B-induced melanogenesis. Furthermore, retinoic acid on it's own, in the absence of ultraviolet radiation caused a small but statistically significant increase in 3,4-dihydroxyphenylalanine positive melanocyte numbers and melanogenesis. Thus topical retinoic acid is a potent modulator of melanocyte activation. Alone it is able to increase the number of activated epidermal melanocytes and make melanocytes more sensitive to activation by ultraviolet B.

One single erythemagenic UV irradiation is more effective in increasing the proliferative activity of melanocytes in melanocytic naevi compared with fractionally applied high doses

The effect of a single irradiation with UV light on the expression of Ki67 antigen, topoisomerase II alpha, proliferating cell nuclear antigen (PCNA), the melanocyte activation marker HMB-45 and protein p53 in melanocytic naevi was investigated 1 week after application of a single erythemagenic UV dose and after daily exposures with suberythemagenic doses over 4-6 weeks. To assess the effect of UV irradiation, one half of each naevus was shielded with black tape during the UV exposure, and the irradiated part and the non-irradiated parts were evaluated separately. Except for HMB-45, a double staining procedure was performed to distinguish between labelled melanocytes and keratinocytes. After semiquantitative assessment of the staining signal the irradiated part was compared with the non-irradiated part of the same naevus. Morphological changes and an enhanced proliferative/ reparative activity in melanocytes were much more frequent in the naevi irradiated with a single erythemagenic UV dose than in those given repeated suberythemagenic doses. In addition, the keratinocytes showed an increased labelling for PCNA and p53 after the single irradiation. These data may support the importance of intermittent UV exposure and sunburns in the development of both benign and malignant melanocytic lesions.

Melanocyte-stimulating properties of secretory phospholipase A2

Phospholipase A2 (PLA2) catalyzes the release of free fatty acids from membrane phospholipids, and its products derived from these fatty acids, such as prostaglandins and leukotrienes, significantly up-regulate the key melanogenic enzyme, tyrosinase, in melanocytes. This has led to suggestions that PLA2 itself triggers melanin synthesis in melanogenesis following UV irradiation or inflammation. We have examined the effect of secretory PLA2 (sPLA2) on melanogenesis in cultured human melanocytes. Secretory PLA2 stimulated DNA synthesis and melanin synthesis, and these phenomena were completely inhibited by treatment with a phospholipase inhibitor, p-bromophenacyl bromide, demonstrating that the catalytic activity of sPLA2 is required for melanogenesis. Secretory PLA2 also stimulated tyrosinase activity, increased the amount of tyrosinase-related protein-1 and up-regulated the expression of both mRNA. These findings suggest that sPLA2 is an important mediator of UV-induced or postinflammatory pigmentation.

Influence of phospholipid liposomes (PLL) on UVB-induced erythema formation

Application of liposomal phospholipids (Natipide II) caused a significant decrease in erythema induced by UVB (280-312 mm) in patients with skin types II and III (n = 31). In accordance with findings in other organs, e.g. liver, the present findings suggest that phospholipids are capable of reducing H2O2 formation and/or increasing glutathione synthesis in human skin, thus reducing erythema formation by preventing oxidative stress.

Ultrastructural study of vitiligo

BACKGROUND

Vitiligo is a relatively common skin disease characterised by development of patchy depigmented macules. A comparative ultrastructural study was undertaken between early developing (2-6 months duration) and long standing (1-5 years duration) lesions of vitiligo in a series of ten patients.

METHODS

Skin biopsy specimens from the ten patients were fixed, stained, and examined under an electron microscope.

RESULTS

No melanocytes were found in the sections taken from long standing lesions. The sections from early lesions showed junctional melanocytes exhibiting various cellular abnormalities. The epidermal keratinocytes were normal in all sections; however, some sections from the periphery of early lesions exhibited minor degenerative changes.

CONCLUSIONS

We can assume that because of the absence of melanocytes in long standing lesions, repigmentation may occur only from the melanocytic reservoir in the hair follicles. Repigmentation may also occur in lesions of short duration by reactivation of melanocytes present in the area, so an attempt should be made to treat vitiligo lesions in their early stage.

Effects of topical ammonium lactate on cutaneous atrophy from a potent topical corticosteroid

BACKGROUND

Topical corticosteroids produce atrophic changes in skin, including thinning of the epidermis and decrease in dermal ground substance. We observed that 12% ammonium lactate produced an increase in the thickness of epidermis and increased amounts of dermal glycosaminoglycans.

OBJECTIVE

Our purpose was to determine whether 12% ammonium lactate could minimize cutaneous atrophy produced by a potent topical corticosteroid.

METHODS

Clobetasol propionate, 12% ammonium lactate, and both agents were repetitively applied under occlusive patches as well as in open patches on the forearms of human volunteers for 3 to 4 weeks. Biopsy specimens were analyzed for thickness of the epidermis and dermal glycosaminoglycans by image analysis.

RESULTS

Twelve percent ammonium lactate produced a significant sparing of atrophy in both the epidermis and dermis without any influence on the bioavailability or antiinflammatory properties of the corticosteroid.

CONCLUSION

Twelve percent ammonium lactate may be useful in mitigating the adverse effects of corticosteroid on skin.

Evaluating the UVA photoprotection of sunscreens with murine skin edema

The acute and chronic deleterious effects of UVA on skin have prompted a growing interest in developing effective UVA-photoprotective sunscreens. The quantification of their UVA photoprotection remains, however, a major problem. In the present study, murine skin edema induced by 8-methoxypsoralen plus UVA (PUVA) is evaluated as a screening method for quantifying the UVA photoprotection of commercially available sunscreens. The PUVA-induced murine skin edema is provoked on the dorsa of female hairless albino mice and measured with a hand-held micrometer. A clear time course and a well-defined dose-response relationship are demonstrated. Therefore, a UVA-photoprotection factor (UVA-PF) could be defined by dividing the minimal edema dose with sunscreen by the minimal edema dose without sunscreen. The UVA-PF values obtained with this method were quantitatively and qualitatively very similar to those obtained in 8-methoxypsoralen-photosensitized murine skin by using the number of sunburn cells as the biologic end point and were qualitatively similar to UVA-PF values obtained in human skin using phototoxic erythema and UVASUN-induced tanning as the parameter. It is concluded that PUVA-induced murine skin edema offers an objective, reproducible, and easily applicable screening method for quantifying the degree of UVA photoprotection of a sunscreen.

Treatment of vitiligo with oral 5-methoxypsoralen

Thirty-six patients with vitiligo were treated with oral 5-methoxypsoralen (5-MOP) and subsequently exposed to UVA irradiation. The patients were treated once or twice weekly over a period of 2-10 months, taking 40-60 mg of 5-MOP 2 hours before exposure to UVA light. The amount of exposure to UVA light was slowly increased according to the patient's tolerance. Eleven (31%) patients showed remarkable repigmentation of the areas of vitiligo within six months. Overall, 78% of the patients showed effective repigmentation. Areas of vitiligo on the face and trunk were more responsive to treatment than those on the distal part of limbs. Adverse effects due to the drug included 2 patients with nausea and 1 patient with headache. It is suggested that treatment with systemic 5-MOP is effective, safe, and useful in selected cases of vitiligo.

Role of skin surface lipids in UV-induced epidermal cell changes

Ultraviolet irradiation is capable of affecting skin surface lipids, especially squalene and cholesterol, both in vitro and in vivo, with generation of active lipoperoxides. The photodecomposition of the skin lipid component was carefully evaluated by capillary gas-chromatography. The effects of UV-induced lipoperoxides on human keratinocytes in culture and on guinea pig ear slices were compared with those of synthetic lipoperoxides, i.e. cumene hydroperoxide and 13-hydroperoxylinoleate. A time- and dose-dependent effect on protein synthesis and mitotic activity was observed. In cell culture low concentrations (0.05-5 micrograms/ml) of peroxidated squalene and synthetic lipoperoxides stimulated the incorporation of radiolabelled thymidine and phenylalanine, while higher concentrations (greater than 10 micrograms/ml), or longer periods of treatment, induced cellular damage. In guinea pig ear slices, the lipoperoxides (5-50 micrograms/ml) increased aminoacid incorporation and the number of epidermal pigment cells; higher concentrations (greater than 100 micrograms/ml) caused a derangement of epidermal structure. The results suggest that UV irradiation of skin generates lipoperoxides from the surface lipids which, in vitro, are capable of producing a number of changes in epidermal cells.

Influence of depigmenting chemical agents on hair and skin color in yellow (pheomelanic) and black (eumelanic) mice

Topical applications of monobenzylether of hydroquinone (MBEH) or intraperitoneal injections of phenol induced graying of hair in eumelanic mice but had little effect on hair color in pheomelanic mice. Amcinonide, an anti-inflammatory agent, elicited whitening of a few hairs in both pheomelanic and eumelanic mice. In phenol-treated eumelanic mice, damaged follicular melanocytes were uprooted from hair bulbs and incorporated into the developing hair. The fate of follicular melanocytes in MBEH- or amcinonide-treated mice was not determined since hair growth and graying were more variable than in phenol-treated mice. In contrast to the susceptibility of eumelanic hair follicles to depigmentation by phenol or MBEH, the tail skin of eumelanic or pheomelanic mice was not depigmented by these agents. Overall, during the 3 week period of treatment that was sufficient for phenol or MBEH to elicit graying of hair, epidermal melanocytes of the tails of eumelanic or pheomelanic mice either failed to respond (phenol) or were stimulated in their "proliferative" and melanogenic activity (MBEH). In contrast, amcinonide brought about a marked reduction in the numbers of DOPA-positive epidermal melanocytes inhabiting the tails of eumelanic or pheomelanic mice. Amcinonide exerted a deleterious influence on the structure and function of tail epidermis. Its actions were partly reversed by simultaneous treatment with MBEH but not with prostaglandin (PGE2).

Regulation of human melanocyte growth, dendricity, and melanization by keratinocyte derived factors

Epidermal pigmentation involves the synthesis of melanin in melanocytes and its transfer to surrounding keratinocytes, where it functions in photoprotection. To investigate the possible role of the keratinocyte in regulating pigmentation, human keratinocytes were incubated for 24 h in a defined culture medium, which was then transferred to pure human melanocyte cultures. After 1 week, the conditioned medium produced a fourfold increase in melanocyte yield and a seven-fold increase in total melanin. Increased melanocyte dendricity was clearly visible within 24 h as well. Ultrafiltration of the keratinocyte-conditioned medium suggested approximately one-half of the growth promoting activity as well as most of the dendricity and melanization stimulating activities were of low molecular weight (less than 500 Da). High molecular weight fractions stimulated only melanocyte growth. Of the several known keratinocyte-derived factors tested, none could be implicated as a mediator of the observed effects. Basic fibroblast growth factor, known to stimulate melanocyte growth in some culture systems, failed to stimulate growth, dendricity, or melanin content when added to the complete non-conditioned medium. Interleukin-1 alpha, interleukin-1 beta, 12-hydroxyeicosatetraenoic acid, prostaglandin E2, leukotriene B4, and adenosine 3',5'-cyclic monophosphate analogues also had no effect. These studies demonstrate that keratinocytes in vitro release factors that modulate melanocyte behavior and expand our understanding of controls for human epidermal pigmentation.

Growth of melanocytes in a skin equivalent model in vitro

We have developed a pigmented human skin equivalent by inserting a punch biopsy of human infant foreskin as a source of epidermis into a collagen lattice (dermal equivalent). Using a conventional epidermal culture medium and stimulation with UVB irradiation or 8-MOP + UVA treatment, melanocytes were found to grow out from the biopsy with the epidermal sheet. In this newly formed epidermis, melanocytes and keratinocytes were maintained in an architectural relationship similar to that present in vivo and melanocyte outgrowth could be quantitatively evaluated. Consequently, this pigmented human skin equivalent is a useful model for investigating the biology and photobiology of human skin pigmentation.

Leukoderma punctata

Thirteen patients with vitiligo (1 segmental, 4 focal, 8 generalized) aged 7 to 38, most of them female children, developed numerous punctate hypopigmented and achromic spots. The spots measured 0.5 to 1.5 mm and were located primarily on the sun-exposed areas of the extremities; they appeared following treatment with PUVASOL. Two of these patients experienced a reduction of this leukodermic defect, whereas the remaining patients showed a stable clinical course. Dopa and Fontana stains disclosed, in most cases, decreased but not absent functional melanocytes and a marked reduction of melanin. Ultrastructural studies demonstrated slight to severe damage of keratinocytes and melanocytes similar to that previously reported in vitiligo patients. The phototoxic effect of PUVASOL therapy is suggested as a possible etiologic factor in these patients. A probable relationship among idiopathic guttate hypomelanosis, leukoderma punctata, and vitiligo is discussed.

Differential hypermelanosis induced by allergic contact dermatitis

In moderately colored guinea-pig skin, UVB, PUVA (psoralen plus UVA), and allergic contact dermatitis were shown to induce visibly well-defined hyperpigmentation that resembled the pigmentary changes observed in Mongoloid human skin. To clarify mechanisms of allergen-induced hyperpigmentation, we compared the effects of allergic contact dermatitis on pigmentation by using 6 different allergens: dinitrochlorobenzene (DNCB), 1-phenylazo-2-naphthol (PAN), benzyl salicylate (BS), jasmine oil (JO), hydroxycitronella (HC), and ylang ylang oil (YYO). The PAN-, JO-, HC-, and YYO-induced allergic reactions caused a definite visible hyperpigmentation that began to appear within 14 days, reaching maximum intensity about 40 days after the induction of the allergic reaction. These hyperpigmentations were accompanied by a significant increase in the population of dopa-positive melanocytes on day 24 following allergic reactions. In contrast, BS- and DNCB-induced allergic reactions did not give rise to visibly distinct hyperpigmentation in spite of the intensive allergic reactions following their challenge application. In a nonsensitized group, primary irritant reactions were induced by the application of 100% JO, but no distinctive hyperpigmentation was found 40 days after the last application. Quantitative analysis of the number of melanophages in the dermis showed that there was a marked increase in the number of melanophages in PAN, YYO, and HC allergy-induced hyperpigmented areas, with PAN showing a significant increase compared with those in non-treated areas of the same animals, whereas JO was associated with no such increase in hyperpigmented area, despite the stimulated pigmentation. In the case of the lack of induced hyperpigmentation, as seen in BS and DNCB allergy and JO irritation, there was also no substantial increase in the number of melanophages. Our findings indicate that allergic contact dermatitis is a unique melanogenic stimulant different from UV irradiation.

Sensitivity of mouse Skh:HR-2 to ultraviolet radiation: melanocyte inactivation

The hairless mouse, Skh:HR-2, was exposed to doses of ultraviolet (UV) radiation known to induce skin pigmentation. Three parameters associated with perturbations in skin pigmentation were monitored following UV exposure. These include spectroscopy (skin darkness), histology (melanocyte density), and biochemistry (melanin). Within 90 min of UV exposure, the skin became lighter. This was associated with a reduction of quantifiable melanin and the inactivation of epidermal melanocytes.

Ear swelling in response to UVB irradiation

The skin response to UVB irradiation in mice was evaluated by means of ear swelling. ICR albino mice were irradiated with 500 mJ/cm2 UVB and the effect of various drugs on ear swelling was examined 24 h after irradiation. Intravenous injections of betamethasone (0.8 microgram/g body wt.) or indomethacin (24 micrograms/g) remarkably inhibited ear swelling, whereas intraperitoneal injections of diphenhydramine (20 micrograms/g), cimetidine (10 micrograms/g), or a combination of both these antihistamines did not. In contrast, the number of sunburn cells counted 24 h after UVB irradiation (200 mJ/cm2) in mouse ears was not affected by these drugs. The amount of prostaglandin D2 (PGD2) in mice ears at various intervals after irradiation with 500 mJ/cm2 UVB was determined by radioimmunoassay. Compared with the values before irradiation, the PGD2 levels were significantly higher 3 and 6 h after irradiation and gradually decreased and returned to the basal level by 12 h, although ear swelling continued after 12 h. These results suggest that prostaglandins are responsible at least in part for the development of ear swelling, but not for sunburn cell formation induced by UVB, and that ear swelling represents a simple and useful response model for the rapid in vivo screening of nonsteroidal or steroidal anti-inflammatory agents.

Differential analysis of experimental hypermelanosis induced by UVB, PUVA, and allergic contact dermatitis using a brownish guinea pig model

In moderately colored guinea-pig skin, UVB, PUVA, and allergic contact dermatitis were shown to induce hyperpigmentation that resembled the pigmentary changes observed in mongoloid human skin. Using this model, we examined the effects of chemical agents, including tyrosinase inhibitors and sunscreen agents, on the color changes induced by UV irradiation. The daily exposure of brownish guinea-pig skin to UVB irradiation at a variety of energies for 3 successive days induced clearly visible black pigmentation on the irradiated rectangular areas of the flank within a few days of irradiation, the maximum being reached about 1 week after irradiation, i.e., similar to the changes that occur in pigmented human skin. Split epidermal sheets prepared from untreated pigmented guinea pigs exhibited 200-400 melanocytes/mm2; 1 week after UV irradiation, the applied areas show an increased number of strongly dopa-positive melanocytes with stout dendrites (800-1,000 cells/mm2). UVA irradiation following an intraperitoneal injection of 8-methoxypsoralen (8-MOP) also produced black pigmentation 1 week after irradiation, and this was paralleled by a marked increase in the number of dopa-positive melanocytes in dopa-reacted split epidermal sheets. Allergic contact dermatitis produced by the application of 1-phenylazo-2-naphthol induced hyperpigmentation after an interval of about 14 days in 10 of the 21 allergy-acquiring animals examined. This induced pigmentation was accompanied by an increase in the number of dopa-positive melanocytes as compared to the number seen in controls. In contrast, allergic contact dermatitis produced by the application of dinitrochlorobenzene failed to induce such a high ratio of postpigmentation, with only 3 of the 21 allergy-acquiring animals showing hyperpigmentation and 5 showing depigmentation; in the latter, there was a slight decrease in the number of dopa-positive melanocytes. To study the preventive effect of tyrosine inhibitors on UVB-induced pigmentation, daily topical applications of these compounds were performed after three daily UVB irradiations. Treatment with 10% hydroquinone for 10 days interrupted UVB-induced pigmentation and resulted in a marked reduction in the number of epidermal melanocytes as compared to the number found in UVB-irradiated, untreated control skin.

Prostaglandin E2 and D2 but not MSH stimulate the proliferation of pigment cells in the pinnal epidermis of the DBA/2 mouse

Epidermal melanocytes proliferate following a variety of physical stimuli, for example, mechanical injury to the skin or exposure to UV radiation. We suggest that some transducer in the epidermis converts the physical modality into a biochemical signal which is responsible for initiation of mitosis. Melanocyte stimulating hormone, both alpha and beta variants, administered parenterally for periods up to 4 weeks do not alter the number of melanocytes per mm2 in several strains of neonatal or adult mice. Ultraviolet B and arachidonic acid both stimulate proliferation of pigment cells. Indomethacin which inhibits cyclooxygenase and the formation of prostaglandins (PGs) blocks the proliferation induced by both agents. We tested a wide variety of PGs. We observed that PGD2 applied daily to the skin of a mouse causes a small increase in melanocyte density (cells/mm2). PGE2 in similar doses applied topically caused a large increase. PGE2 caused an increase in the uptake of tritiated thymidine by dopa-positive dendritic cells. This indicates that PGE2 stimulated some melanocytes to proliferate. Histologic studies indicate that PGE2 also enhances melanogenesis. PGE2 is synthesized in the skin and affects keratinocytes and Langerhans cells as well as pigment cells. We postulate that it is one compound that can modulate the interaction of these 3 main cells of the epidermis.

Quantitative assessment of phototoxicity in the skin of hairless mice

For determining threshold levels of inflammation resulting from a phototoxic regimen, measurement of ear thickness with a hand-held micrometer was compared with assessment by eye of the reaction on the dorsa of hairless mice. The ear-measurement technique was less sensitive with respect to the minimum concentration of 8-methoxypsoralen at which phototoxicity could be detected. However this technique was more quantifiable and more objective than detection of threshold responses by eye. Changes in ear thickness were detectable over an extended period of time with a maximum increase at 16 days; return to normal thickness occurred by 35 days. Compressibility of affected ears changed during the course of measurement, but repetitive measurement of the ears did not alter the development or resolution of the inflammatory response.

The occurrence of vitiligo after psoralens and ultraviolet a therapy

The ability of photochemotherapy with 8-methoxypsoralen in conjunction with high-intensity long-wave ultraviolet light (PUVA) to stimulate melanogenesis is well known. This effect on the pigmentary system is evidenced by the diffuse tanning of clinically normal skin in PUVA-treated patients with psoriasis and other disorders, as well as by the repigmentation of lesions in vitiligo. It is now recognized that there may be additional pigmentary effects, resulting in clinical lesions such as PUVA mottling, PUVA lentigines, and localized hypopigmentation. We have documented the occurrence of yet another association with PUVA therapy--the paradoxical appearance of widespread hypopigmentation consistent with vitiligo in three PUVA-treated patients, one with psoriasis and two with mycosis fungoides. Histologic and ultrastructural findings are presented.

The PUVA-induced pigmented macule: a lentiginous proliferation of large, sometimes cytologically atypical, melanocytes

Eleven PUVA-induced pigmented macules (PM) obtained from seven psoriatic adults 4 to 6 years after starting PUVA therapy were compared to eight sun-induced pigmented macules (SM) and five specimens of light-protected skin (LPS) from twelve nonpsoriatic control subjects who had not received ultraviolet radiation therapy. Unlike SM, many PM were darkly or irregularly pigmented. In a blind histologic assessment using routine and L-dihydroxyphenylalanine (dopa)-incubated tissue sections, both PM and SM were lentigines. Three of eleven PM had slight melanocytic atypism, compared to none of eight SM. When compared to SM and LPS, PM had a significantly increased proportion of hypertrophic melanocytes. These observations demonstrate that chronic PUVA induces pigmented macules characterized by a lentiginous proliferation of large melanocytes which, in some cases, may be slightly atypical. PUVA-treated individuals require continual monitoring for atypical melanocytic lesions.