Comparative protection efficiency of UVA- and UVB-induced tans against erythema and formation of endonuclease-sensitive sites in DNA by UVB in human skin

UVA- and UVB-induced tans which were visually identical with each other were induced in separate sites on the lower back of 5 normal human volunteers of good tanning ability. Tanning was achieved by 4 exposures to UVA and UVB administered over an 8-day period. One week after the last exposure the protection afforded by the two types of tan against UVB-induced erythema and against UVB-induced DNA damage was measured. Protection against erythema was measured by comparison of the minimal erythema doses of UVB in tanned and untanned skin. Protection against DNA damage was assessed by comparing the numbers of endonuclease-sensitive sites in epidermal DNA extracted from biopsies taken from tanned and untanned sites exposed to the same dose of UVB. The UVB tans conferred significant protection (mean 2.98-fold) against UVB-induced erythema. UVA tans were not associated with significant protection (mean 1.4-fold). In contrast, both UVA- and UVB-induced tans were associated with a similar reduction in yield of endonuclease-sensitive sites in epidermal DNA (in UVA tan to 47% and in UVB tan to 45% of the yield in untanned skin). Protection conferred by the tans against erythema was therefore not paralleled by protection against DNA damage.     

UVA sunbeds: tanning, photoprotection, acute adverse effects and immunological changes

The effects on 31 normal subjects following exposure to sunbeds containing UVA lamps with minimal UVB emission have been compared in a double-blind study with the effects on nine control subjects of a similar exposure course three times weekly for 4 weeks to sunbeds emitting visible light. On previously untanned areas, all those subjects on active treatment developed a mild tan; in tanned areas they all developed a moderate tan, while all control subjects developed a minimal to mild tan. The mean protection factor against later UVB-induced erythema was 3.2 +/- 0.3 after the active course and 1.6 +/- 0.2 among the controls. Significantly more frequent adverse cutaneous effects for active subjects were pruritus, erythema, freckling, burning sensation, dryness and polymorphic light eruption. Cutaneous Langerhans cell numbers, and blood CD3+ (pan T-cell) and CD4+ (helper T-cell) lymphocyte subsets were reduced in both active and control groups. CD8+ (cytotoxic/suppressor T-cell) counts were similarly but not significantly reduced in both groups. Pityrosporum yeast counts were significantly reduced in both groups. The changes found in both groups seem attributable to small amounts of UVB emission from both active and control lamps.     

Immunoprotective UVA (320-400 nm) irradiation upregulates heme oxygenase-1 in the dermis and epidermis of hairless mouse skin

The induction of heme oxygenase-1 (HO-1) by ultraviolet A (UVA) (320-400 nm) radiation provides a protective cellular defence against oxidative stress, and has been well demonstrated in cultured human skin fibroblasts, although keratinocytes were unreactive. The UVA responsiveness of HO-1 however, has not been confirmed in intact skin. Previously, we reported that UVA-inducible HO enzyme activity in mouse skin is protective against UVB-induced immunosuppression. This study identifies the induced HO isoform and its localization in mouse skin irradiated in vivo with such an immunoprotective UVA dose. We found that HO-1 mRNA was expressed in UVA-irradiated skin, but not in normal or UVB-irradiated skin, whereas constitutive HO-2 was always present. UVA-irradiated skin had increased HO enzyme activity and bilirubin content, and decreased heme content, consistent with HO-1 induction. In situ hybridization and immunohistochemical staining localized HO-1 mRNA and protein to both epidermis and dermis, with strongest expression in basal keratinocytes and weaker expression in dermal fibroblast-like and other cells, in contrast with UVA-induced HO-1 in cultured human skin fibroblasts. This suggests that cultured skin cells may not fully represent skin functions in vivo, or that there may be inherent differences between human and hairless mouse skin HO-1 responses.     

The contributions of UVA and UVB to connective tissue damage in hairless mice

UVA, in high-dose single exposures, can, like UVB, be deleterious to skin. Dermal damage resulting from chronic exposure to UVA has not been studied. To investigate the long-term effects, we irradiated albino hairless mice for 30-34 weeks with UVA radiation, alone, from two sources with differing spectral qualities, and in combination with UVB as solar-simulating radiation. The results were compared to UVB alone. Like UVB, the UVA waveband, especially that with a spectral distribution similar to solar UVA, caused elastic fiber damage, increased glycosaminoglycan levels, and produced hypertrophy of deep dermal tissues. There were, however, striking differences between UVB- and UVA-irradiated skin. A combination of UVA and UVB summated the effects of both wavebands. Substantial protection against these effects was afforded by a broad-spectrum sunscreen.     

EFFECTS OF EXPOSURE TO ULTRAVIOLET LIGHT IN A COMMERCIAL SOLARIUM ON LANGERHANS CELLS AND MELANOCYTES IN HUMAN EPIDERMIS

Nine subjects of Celtic and mixed European descent were exposed to small (1/2 hour) doses of ultraviolet light (UVL) on 10 consecutive days in a commercial solarium to determine the effects of UVL on epidermal melanocytes and immunocompetent Langerhans cells (LCs). Tanned and non-tanned subjects were studied to determine whether pigmentation from melanocytes provided the LCs with any protection against these UVL effects. A transient reduction in the number of LCs occurred in response to UVL exposure, returning to near pre-exposure levels two weeks after cessation of the solarium course. The tan which developed or deepened following the UVL exposure appeared to provide little or no protection against this reduction, regardless of whether the subjects were lightly tanned or untanned prior to the solarium course. Even though the number of subjects examined was small these results indicate that exposure to solarium UVL irradiation, even in small doses, may adversely affect the skin immune system and therefore is not recommended as a safe means of acquiring a tan.     

Demonstration of giant and anular nexus in the psoriatic epidermis

Summary To determine whether a tan produced by 8-MOP and UVA protects from subsequent solar light irradiation, volunteers were irradiated with unfiltered Xenon arc light before and 10 days after a 1 week's course of four 8-MOP-UVA treatments. Evaluation of the minimal erythema doses and of histological changes before and after 8-MOP-UVA treatment revealed that the 8-MOP-UVA induced tan protected against the erythemogenic and cell damaging effects of Xenon arc light. Unscheduled repair DNA synthesis, used as a measure for UVB-induced DNA damage and repair, was also investigated in skin irradiated with the Xenon arc before and after 8-MOP-UVA induced tanning. Both the number of grains per sparse labeled cell and the number of sparse labeled cells per 1000 cells, were found to be significantly lower in tanned skin; taking decreased unscheduled repair DNA synthesis as a measure for decreased DNA-damage, these findings also demonstrate a photoprotective effect of the 8-MOP-UVA induced tan.     

Decreased human epidermal antigen-presenting cell activity after ultraviolet A exposure: dose-response effects and protection by sunscreens

BACKGROUND: Ultraviolet (UV) exposure of human skin causes immunosuppression that contributes to the growth of skin cancer. The contribution of UVA in these processes is still a matter of debate. OBJECTIVES: The purpose of our study was first to find a dose-response effect of UVA exposure on human epidermal antigen-presenting cell (APC) activity and to evaluate the protective capacity of two sunscreen formulations against a high level of acute UVA exposure. We also tried to evaluate the protective capacity afforded by the same sunscreens against UVA-induced clinical changes such as redness and pigmentation. METHODS: The functional assessment of the alloantigen-presenting capacity of epidermal cells prepared from skin keratotome samples 3 days after UVA exposure was measured with a mixed epidermal cell-lymphocyte reaction (MECLR) in each healthy volunteer (n = 16). Redness and pigmentation were assessed by chromametry 24 h after exposure to a single UVA dose. RESULTS: In vivo UVA exposure to 15, 30 and 60 J cm(-2) resulted in a dose-dependent decrease in purified allogeneic T cell (CD4+ T cells) proliferation induced by UVA-irradiated epidermal cells. The epidermal APC function was significantly decreased with a suberythemal exposure corresponding to 15 J cm(-2). The decrease, partial and not statistically different between 30 and 60 J cm(-2), exhibits a plateau-response effect. There was no correlation between the decrease of the epidermal APC function and the intensity of erythema and persistent pigment darkening. Both sunscreen formulations strongly inhibited the UVA-induced reduction of MECLR at 90 J cm(-2). CONCLUSION: Our results clearly demonstrate that UVA impairs the APC activity of the epidermal cells and thus may contribute to UV-induced immunosuppression in humans. They also indicate that erythema and immunosuppression have different dose-response curves in the UVA range. The two sunscreen formulations afforded a significant protection against the decrease in epidermal APC activity induced by exposure to a high UVA dose (90 J cm(-2)).     

Protective effects of tanning on cutaneous DNA damage in situ

BACKGROUND: The incidence of skin cancer, the most common type of cancer in the Western world, has been shown to be associated with the degree of exposure to solar radiation. However, little is known on how human skin can be protected against UV-induced DNA damage by constitutive and induced pigmentation. OBJECTIVE: To study the effect of skin pigmentation induced by a sunbed-type of treatment on the formation of UV-induced DNA damage in human skin in situ. METHODS: A photoproduct assay was performed in untanned and tanned skin of healthy volunteers. RESULTS: There is no significant difference in the induction of photoproducts between untanned and tanned skin. CONCLUSION: Our data demonstrate that constitutive skin pigmentation is more efficient than the induced one in protection against formation of photoproducts.     

UVA radiation impairs phenotypic and functional maturation of human dermal dendritic cells

There is now strong evidence that the ultraviolet A (UVA) part of the solar spectrum contributes to the development of skin cancers. Its effect on the skin immune system, however, has not been fully investigated. Here, we analyzed the effects of UVA radiation on dermal dendritic cells (DDC), which, in addition, provided further characterization of these cells. Dermal sheets were obtained from normal human skin and irradiated, or not, with UVA at 2 or 12 J per cm2. After a 2 d incubation, the phenotype of emigrant cells was analyzed by double immunostaining and flow cytometry. Results showed that migratory DDC were best characterized by CD1c expression and that only few cells co-expressed the Langerhans cell marker Langerin. Whereas the DC extracted from the dermis displayed an immature phenotype, emigrant DDC showed increased expression of HLA-DR and acquired co-stimulation and maturation markers. We showed here that UVA significantly decreased the number of viable emigrant DDC, a process related to increased apoptosis. Furthermore, UVA irradiation impaired the phenotypic and functional maturation of migrating DDC into potent antigen-presenting cells, in a concentration-dependent manner. The results provide further evidence that UVA are immunosuppressive and suggest an additional mechanism by which solar radiation impairs immune response.     

Role of NF-κB–p53 crosstalk in ultraviolet A-induced cell death and G1 arrest in human dermal fibroblasts

Photoaging is the premature aging of the skin caused by repeated exposure to sunlight and is characterized by a depletion of the dermal extracellular matrix. This depletion is due to the loss of fibroblast cells and their multiple functions. UVA was revealed as a major inducer of photoaging in various clinical studies. As UVA photons have long wavelength spectra, UVA penetrates deeper into the dermis than UVB and UVC, leading to the induction of cell death, the destruction of the dermal extracellular matrix through the induction of matrix metalloproteinase expression, and the repression of collagen expression. However, the exact effects of UVA on the skin remain a matter of debate. Here, we assess cell cycle stage to demonstrate that NF-κB–p53 crosstalk induces apoptosis and growth arrest in UVA-irradiated human dermal fibroblasts. In addition, UVA irradiation led to an increase of NF-κB–HDAC1 complexes, which in turn repressed cyclin D1 expression in UVA-irradiated human dermal fibroblasts. We provide direct evidence that UVA irradiation induces changes in the p53-dependent NF-κB complex that lead to growth arrest and apoptosis through the repression of cyclin D1. These studies uncovered that NF-κB–p53 crosstalk is a key regulator of UVA-dependent growth arrest and apoptosis.     

Sunburn protection by longwave ultraviolet radiation-induced pigmentation

The role of melanin pigment in sunburn protection was investigated. Deep tans were induced over the backs of volunteers with repeated exposure to longwave ultraviolet radiation (UV-A). Melanogenesis was stimulated without an appreciable thickening of the stratum corneum. Two to three times the minimal erythema dose was required to produce redness in UV-A-tanned skin. Transmission studies through isolated corneum sheets revealed that specimens from tanned skin were about twice as efficient in filtering sunburn rays as stratum corneum from untanned skin. Tanning with UV-A does not provide a substantial resistance against sunburn.     

Effects of UVA (320-400 nm) on the barrier characteristics of the skin

The stratum corneum serves as the major barrier to the entrance of most molecules into the skin. In the studies presented here, the effects of UVA radiation (320-400 nm) on the barrier capacity of human stratum corneum were examined. Penetration of a homologous series of primary alcohols through unirradiated (control) and UVA-irradiated (test) human epidermis was determined in vitro. Permeability constants, kp, were calculated. Mean ratios of permeability constants for UVA-irradiated and unirradiated epidermis (mean kp test)/(mean kp control) ranged from 2.3 to 3.0 for methanol and from 2.2 to 2.5 for ethanol. These mean ratios were determined using different pieces of epidermis from the same piece of skin for test and control samples. When kp control and kp test were determined on the same piece of epidermis on successive days, the ratios (kp test/kp control) were similar to the mean ratios determined on different pieces of epidermis. For other primary alcohols, propanol, butanol, hexanol, and heptanol, UVA radiation did not alter their permeability constants significantly. Partition coefficients, Km, were determined for ethanol and heptanol using UVA-irradiated and unirradiated stratum corneum. For ethanol, irradiation resulted in a 1.5 to 2.6 times increase in Km. For heptanol, irradiation caused no change in Km. These results demonstrate that the barrier capacity of stratum corneum for small, polar, primary alcohols is diminished (permeability increases) and for higher molecular weight less polar alcohols, is unaffected by small doses of UVA radiation. This increased permeability of small polar alcohols through human skin may be due to enhanced partitioning into UVA-irradiated stratum corneum, which was not apparent for a higher molecular weight less polar alcohol.     

Trioxsalen bath plus UVA effective and safe in the treatment of psoriasis

Seventy-four patients with psoriasis were treated using a trioxsalen bath (50 mg/150 1 of water) and long wave ultraviolet light (UVA) given in an ordinary PUVA-cabin. Good or excellent results were observed in 92% of the patients in the initial phase and in 63% during the maintenance treatment. Because of local side-effects the therapy was discontinued in two patients. One of them developed contact hypersensitivity to trioxsalen and the other developed blisters with such low doses of UVA that it was difficult to maintain the proper dose. The therapy was started with 0-28 J/cm² of UVA and after an average of 18 treatments, when the average dose was 1.70 J/cm², the patients were moved to maintenance treatment which took place at 1-4 week intervals. The therapy was well tolerated and cosmetically very acceptable. The final tan was even on all but the face, which remained untanned.     

Tirilazad amelioriates extracellular effects of photooxidative stress by sealing the membrane of UVA irradiated human dermal fibroblasts

The evaluation of antioxidant medication might provide further tools to protect the skin against the detrimental effects of photooxidative stress. In this context we have previously shown that the lazaroid tirilazad protects fibroblasts effectively against lipid peroxidation (LPO). Now we investigated whether and how tirilazad also influences two typical stress responses after UVA exposure, i.e. IL-6 and collagenase (MMP-1) release. Fibroblasts pre-incubated with tirilazad at a concentration of 30 microM show significantly less IL-6 in the extracellular medium after UVA exposure. Correspondingly, pre-incubation with tirilazad also significantly diminishes the extracellular MMP-1 protein concentration 24h post-irradiation. These effects observed are due to a membrane stabilisation, as tirilazad neither diminishes IL-6 mRNA production nor intracellular IL-6/MMP-1 protein levels after UVA exposure and thus most likely acts by sealing off the cell, delaying the typical leakage of IL-6 and MMP-1.     

UVA does not photoreactivate pyrimidine dimers in cultured human fibroblasts

Abstract Pyrimidine dimers were induced in duplicates of cultured human skin fibroblasts by irradiation with various doses of UVB radiation. Subsequently, one set of cells was further exposed to either 5 or 10 J/cm² of UVA radiation to assess the photoreactivating activity of this spectral range in a human cell system. Following irradiation, pyrimidine dimers were quantified in all cells by determining the number of endonuclease-sensitive sites (ESS). No difference in the yield of ESS was observed between cells which had been irradiated with UVB only as compared to cells which subsequently had been exposed to 5 or 10 J/cm² UVA. In contrast, subsequent exposure of UVB-irradiated cells of Monodelphis domestica to 10 J/cm² UVA resulted in an almost 50% reduction of UVB-induced pyrimidine dimers. These data indicate that UVA does not induce photoenzymatic repair in human fibroblasts.     

Chronic UVA (365-nm) irradiation induced scratching in hairless mice: dose-time dependency and the effect of ketanserin

Abstract In a study on the dose–response relationship for longwave UVA (UVAI; 340–400 nm) carcinogenesis in hairless mice scratch marks appeared after months of daily exposure as an unwanted side effect. Tumor induction in the highest of the 4 tested dose groups (receiving a daily dose of 430 kJ/m² of 365-nm radiation) could not be determined because extensive scarification occurred prior to the development of any tumors. The induction of scratch marks could be scored and quantified in all 4 dose groups tested. The UVA I dose-dependencies for the induction of tumors and scratch marks were compared. We found that the induction of scratch marks depended mainly on the cumulative UVA1 exposure, whereas tumor induction showed a lesser dose-dependency. An attempt was made to prevent the apparent pruritogenic effect of UVA1 irradiation and to understand its mechanism. The influence of ketanserin, a serotonin/histamine antagonist, on the UVA1 induction of scratch marks was tested in groups of 8 mice daily irradiated with 430 kJ/m². No difference was found between treated and untreated animals. Histological examination of skin biopsies from irradiated mice from the 430-kJ/m² dose group from the UVA1 careinogenic experiment, showed no changes in numbers of mast cells or other inflammatory features when compared to skin biopsies from unirradiated control mice. This indicated that UVA1-induced scratching is not mediated through mast cell release of scrotonin and/or histamine. An adequate therapeutic treatment which can prevent UVA1-induccd scratching would enable us to lest tumor induction with UVA1 over a larger close range, and may provide additional insight in how this radiation damages the skin. It remains conjectural whether there exists an analogous UVA-induccd pruritus in human skin.     

Photoprotection of bacterial-derived melanin against ultraviolet A–induced cell death and its potential application as an active sunscreen

Background  The increase in the incidence of non-melanoma skin tumours, photoaging, and immunosuppression demand for more effective sunscreen on ultraviolet A (UVA) irradiation.
Objectives  The aim of the study is to evaluate the photoprotective effects of a bacterial-derived melanin against UVA-induced damages in vitro and in vivo .
Methods  Human fibroblasts were used to assess the role of the bacterial-derived melanin on cell viability against UVA. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and nuclear morphology were employed to evaluate the photoprotection at the cellular level. Fluorometric assays were performed to detect the formation of reactive oxygen species (ROS) in the cells. Evaluations of the bacterial-derived melanin as a sunscreen were measured by transmission test and persistent pigment darkening on human skin.
Results  Bacterial-derived melanin efficiently scavenged ROS in the fibroblasts after UVA irradiation. The cell viability of xeroderma pigmentosum (XP) fibroblast treated with varied doses of melanin increased dramatically in comparison with untreated control and the treated XP fibroblasts became more resistant to UVA-induced apoptosis than normal fibroblasts. Although the relative transmission didn't change too much with different concentration of bacterial-derived melanin, this melanin could keep UVA-irradiated skin from pigment darkening and act as an active sunscreen on skin.
Conclusions  The bacterial-derived melanin provided significant protection to fibroblast cell and human skin against the UVA radiation. It has the potential to be developed as an active sunscreen for the patients with photosensitivity skin to sun exposure.     

Penetration kinetics of 8-methoxypsoralen after 8-methoxypsoralen bath procedure with and without UVA irradiation.

Administration of 8-methoxypsoralen (8-MOP) in a dilute bath water solution is an effective therapeutic alternative for systemic application of 8-MOP, avoiding systemic side effects such as nausea and cataractogenesis. The aim of our study was to determine the epicutaneous penetration of 8-MOP in a dilute bath water solution with and without additional UVA irradiation in human skin under in vitro conditions. To simulate the PUVA bath procedure, 8 skin samples were exposed to radioactively labeled 8-MOP in a water solution. After 20 min, the test solution was removed and the skin surface was dried. Immediately after the bath procedure, 4 of the skin samples were irradiated with 0.5 J/cm2 UVA. During a test period of 15 h, the 8-MOP penetration was observed. In both test groups (with and without UVA irradiation) 8-MOP permeated through all skin layers between 30 min and 1 h after application. Compared to the unirradiated skin samples, the UVA-irradiated skin samples showed a significantly slower increase and a lower maximum of 8-MOP permeation. Following our results, UVA irradiation of 8-MOP-exposed skin samples led to a significantly decreased permeation rate. This might be due to UVA-induced links between 8-MOP molecules and human DNA. In addition, we investigated the levels of radioactivity emitted by tritium-labeled 8-MOP in stratum corneum, epidermis and dermis up to 30 min after 8-MOP bath in two further test groups with and without additional UVA irradiation. The statistical analysis revealed no significant differences between these two test groups. Thus, the levels of radioactivity remained constant in the epidermis and dermis during the test period of 30 min. Since the levels of radioactivity were constant up to 30 min after UVA irradiation, a previously supposed marked loss of 8-MOP concentration might not be responsible for the rapid extinction of observed in vivo photosensitivity within 1 h after PUVA bath observed in vivo in human skin.     

UVA1 phototherapy: a concise and practical review

High intensity long-wavelength ultraviolet A (340-400 nm; UVA1) lamps were initially developed as skin research tools; over time they have proven to be useful for treating a number of chronic dermatoses. UVA1 units and dosimetry are strikingly different from conventional UV phototherapy. The therapeutic effect of UVA1 is related to the fact that its long wavelength penetrates the dermis more deeply than UVB. UVA1 radiation induces collagenase (matrix metalloproteinase-1) expression, T-cell apoptosis, and depletes Langerhans and mast cells in the dermis. UVA1 exposure stimulates endothelial cells to undergo neovascularization. Ultraviolet A1 exerts significant therapeutic effects in atopic dermatitis and morphea; there is also evidence for its use in other skin diseases, including cutaneous T-cell lymphoma and mastocytosis.