UVB-exposed Skin Research Articles

Photoactivation of corticosteroids in UVB-exposed skin

The photodegradation of flumethasone (FM) and fluocinolone acetonide (FC) was studied in solution and in the pig skin. Both glucocorticosteroids applied to the pig skin were unstable under UVB light. The photoproducts formed in the skin were the lumi-, photolumi- and andro-derivatives for FM, the same found in vitro. Instead, FC hydroperoxide formed in solution was not found in the skin: the reactivity and oxidative ability of this photoproduct towards biological substrates (lipids, proteins) seems the reason of the lack of its detection in the ex vivo model. In fact, it demonstrated to quickly oxidize amino acids and peptides, and to react with BSA both in the dark and under irradiation. Moreover, the presence in the irradiated pig skin of the FC andro-derivative, which usually forms in H-donating environment, seems consistent with the mechanism of Norrish I fragmentation followed by H-abstraction, likely from the surrounding biological substrates. These findings indicate that photoreactivity of these compounds may take place in the skin of patients exposing themselves to sunlight and is a warning about possible skin damage as a result of that. Furthermore, photolability of these drugs in the skin might cause loss of their therapeutic activity.

RETRACTED: Aberrant DNA hypermethylation patterns lead to transcriptional silencing of tumor suppressor genes in UVB-exposed skin and UVB-induced skin tumors of mice

Overexposure of the human skin to solar ultraviolet (UV) radiation is the major etiologic factor for development of skin cancers. Here, we report the results of epigenetic modifications in UV-exposed skin and skin tumors in a systematic manner. The skin and tumor samples were collected after chronic exposure of the skin of SKH-1 hairless mice to UVB radiation using a well-established photocarcinogenesis protocol. We found a distinct DNA hypermethylation pattern in the UVB-exposed epidermal skin and UVB-induced skin tumors that was associated with the elevated expression and activity of the DNA methyltransferases (Dnmt) 1, Dnmt3a and Dnmt3b. To explore the role of hypermethylation in skin photocarcinogenesis, we focused on the p16(INK4a) and RASSF1A tumor suppressor genes, which are transcriptionally silenced on methylation. We established that the silencing of these genes in UVB-exposed epidermis and UVB-induced skin tumors is associated with a network of epigenetic modifications, including hypoacetylation of histone H3 and H4 and increased histone deacetylation, as well as recruitment of methyl-binding proteins, including MeCP2 and MBD1, to the methylated CpGs. Higher levels of DNA methylation and DNMT activity in human squamous cell carcinoma specimens than in normal human skin suggest that the data are relevant clinically. Our data indicate for the first time that UVB-induced DNA hypermethylation, enhanced Dnmt activity and histone modifications occur in UVB-exposed skin and UVB-induced skin tumors and suggest that these events are involved in the silencing of tumor suppressor genes and in skin tumor development.

Proanthocyanidins Inhibit Photocarcinogenesis through Enhancement of DNA Repair and Xeroderma Pigmentosum Group A–Dependent Mechanism

Dietary grape seed proanthocyanidins (GSP) inhibit photocarcinogenesis in mice; however, the molecular mechanisms underlying this effect have not been fully elucidated. As ultraviolet B (UVB)-induced DNA damage in the form of cyclobutane pyrimidine dimers (CPDs) has been implicated in skin cancer risk, we studied whether dietary GSPs enhance repair of UVB-induced DNA damage and, if so, what is the potential mechanism? Supplementation of GSPs (0.5%, w/w) with AIN76A control diet significantly reduced the levels of CPD(+) cells in UVB-exposed mouse skin; however, GSPs did not significantly reduce UVB-induced CPD(+) cells in the skin of interleukin-12p40 (IL-12) knockout (KO) mice, suggesting that IL-12 is required for the repair of CPDs by GSPs. Using IL-12 KO mice and their wild-type counterparts and standard photocarcinogenesis protocol, we found that supplementation of control diet with GSPs (0.5%, w/w) significantly reduced UVB-induced skin tumor development in wild-type mice, which was associated with the elevated mRNA levels of nucleotide excision repair genes, such as XPA, XPC, DDB2, and RPA1; however, this effect of GSPs was less pronounced in IL-12 KO mice. Cytostaining analysis revealed that GSPs repaired UV-induced CPD(+) cells in xeroderma pigmentosum complementation group A (XPA)-proficient fibroblasts from a healthy individual but did not repair in XPA-deficient fibroblasts from XPA patients. Furthermore, GSPs enhance nuclear translocation of XPA and enhanced its interactions with other DNA repair protein ERCC1. Together, our findings reveal that prevention of photocarcinogenesis by GSPs is mediated through enhanced DNA repair in epidermal cells by IL-12- and XPA-dependent mechanisms.

The deceptive nature of UVA tanning versus the modest protective effects of UVB tanning on human skin

The relationship between human skin pigmentation and protection from ultraviolet (UV) radiation is an important element underlying differences in skin carcinogenesis rates. The association between UV damage and the risk of skin cancer is clear, yet a strategic balance in exposure to UV needs to be met. Dark skin is protected from UV-induced DNA damage significantly more than light skin owing to the constitutively higher pigmentation, but an as yet unresolved and important question is what photoprotective benefit, if any, is afforded by facultative pigmentation (i.e. a tan induced by UV exposure). To address that and to compare the effects of various wavelengths of UV, we repetitively exposed human skin to suberythemal doses of UVA and/or UVB over 2 weeks after which a challenge dose of UVA and UVB was given. Although visual skin pigmentation (tanning) elicited by different UV exposure protocols was similar, the melanin content and UV-protective effects against DNA damage in UVB-tanned skin (but not in UVA-tanned skin) were significantly higher. UVA-induced tans seem to result from the photooxidation of existing melanin and its precursors with some redistribution of pigment granules, while UVB stimulates melanocytes to up-regulate melanin synthesis and increases pigmentation coverage, effects that are synergistically stimulated in UVA and UVB-exposed skin. Thus, UVA tanning contributes essentially no photoprotection, although all types of UV-induced tanning result in DNA and cellular damage, which can eventually lead to photocarcinogenesis.

Honokiol, a phytochemical from the Magnolia plant, inhibits photocarcinogenesis by targeting UVB-induced inflammatory mediators and cell cycle regulators: development of topical formulation

To develop newer and more effective chemopreventive agents for skin cancer, we assessed the effect of honokiol, a phytochemical from the Magnolia plant, on ultraviolet (UV) radiation-induced skin tumorigenesis using the SKH-1 hairless mouse model. Topical treatment of mice with honokiol in a hydrophilic cream-based topical formulation before or after UVB (180 mJ/cm(2)) irradiation resulted in a significant protection against photocarcinogenesis in terms of tumor multiplicity (28-60%, P < 0.05 to <0.001) and tumor volume per tumor-bearing mouse (33-80%, P < 0.05 to 0.001, n = 20). Honokiol also inhibited and delayed the malignant progression of papillomas to carcinomas. To investigate the in vivo molecular targets of honokiol efficacy, tumors and tumor-uninvolved skin samples from the tumor-bearing mice were analyzed for inflammatory mediators, cell cycle regulators and survival signals using immunostaining, western blotting and enzyme-linked immunosorbent assay. Treatment with honokiol significantly inhibited UVB-induced expression of cyclooxygenase-2, prostaglandin E(2) (P < 0.001), proliferating cell nuclear antigen and proinflammatory cytokines, such as tumor necrosis factor-α (P < 0.001), interleukin (IL)-1β (P < 0.01) and IL-6 (P < 0.001) in the skin as well as in skin tumors. Western blot analysis revealed that honokiol: (i) inhibited the levels of cyclins D1, D2 and E and associated cyclin-dependent kinases (CDKs)2, CDK4 and CDK6, (ii) upregulated Cip/p21 and Kip/p27 and (iii) inhibited the levels of phosphatidylinositol 3-kinase and the phosphorylation of Akt at Ser(473) in UVB-induced skin tumors. Together, our results indicate that honokiol holds promise for the prevention of UVB-induced skin cancer by targeting inflammatory mediators, cell cycle regulators and cell survival signals in UVB-exposed skin.

The Mandatory Role of IL-10–Producing and OX40 Ligand-Expressing Mature Langerhans Cells in Local UVB-Induced Immunosuppression

The mechanism underlying the local UVB-induced immunosuppression is a central issue to be clarified in photoimmunology. There have been reported a considerable number of cells and factors that participate in the sensitization phase-dependent suppression, including Langerhans cells (LCs), regulatory T cells, IL-10, and TNF-alpha. The recent important finding that LC-depleted mice rather exhibit enhanced contact hypersensitivity responses urged us to re-evaluate the role of LCs along with dermal dendritic cells (dDCs) in the mechanism of UVB-induced immunosuppression. We studied the surface expression of OX40 ligand (OX40L) and the intracellular expression of IL-10 in LCs and dDCs from UVB-irradiated (300 mJ/cm(2)) skin of BALB/c mice and those migrating to the regional lymph nodes from UVB-irradiated, hapten-painted mice. In epidermal and dermal cell suspensions prepared from the UVB-irradiated skin, LCs expressed OX40L as well as CD86 and produced IL-10 at a higher level than Langerin(-) dDCs. The UVB-induced immunosuppression was attenuated by the administration of IL-10-neutralizing or OX40L-blocking Abs. In mice whose UVB-irradiated, hapten-painted skin was dissected 1 d after hapten application, the contact hypersensitivity response was restored, because this treatment allowed dDCs but not LCs to migrate to the draining lymph nodes. Moreover, LC-depleted mice by using Langerin-diphtheria toxin receptor-knocked-in mice showed impaired UVB-induced immunosuppression. These results suggest that IL-10-producing and OX40L-expressing LCs in the UVB-exposed skin are mandatory for the induction of Ag-specific regulatory T cells.

Influences of p53 deficiency on the apoptotic response, DNA damage removal and mutagenesis in UVB-exposed mouse skin

p53 suppresses the genomic instability provoked by genotoxic agents. Ultraviolet (UV) B induces skin cancers by producing DNA damage and mutations in the skin genome, whereas the skin tissue responds to the UVB insult with cell cycle arrest and apoptosis as well as damage exclusion by DNA repair. To address the p53 contribution to these skin responses in vivo, we analyzed the time course of DNA damage removal, apoptosis induction and hyperplasia in the skin after UVB irradiation in p53-knockout mice. We also examined UVB-induced mutations in the skin. We found that p53 deficiency does not abolish the UVB-induced apoptotic response in the epidermis but delays the process and the following hyperplasia 12-24 h. Regardless of the p53 genotype, 1 kJ/m(2) UVB induced a total replacement of the epidermal layer by destroying the damaged epidermis by apoptosis and rebuilding a new one through hyperplasia. We failed to detect a clear defect in removal of UVB-induced DNA photolesions from the genome of the p53-deficient skin except for a delay in the epidermis, which seemed to result from the delay in the apoptotic response. However, we found that p53 deficiency enhanced UVB-induced mutagenesis. Furthermore, in a genetic study using Xpa-knockout mice, we showed that the enhanced mutagenic response depends on the activity of nucleotide excision repair (NER), which was also supported by the mutation spectrum observed in the UVB-exposed p53-knockout mice. These results indicate that p53 protects the skin genome from the UVB genotoxicity by facilitating NER, whereas its contribution to the UVB-induced apoptosis is limited.

Abstract 952: Nitric oxide donor sulindac inhibits photocarcinogenesis by modulating epithelial mesenchymal transition and mitogen activated protein kinase signaling in SKH-1 hairless mouse skin

Abstract Nitric oxide (NO)-releasing non-steroid anti-inflammatory drugs (NO-NSAIDs) have been shown to have anti-proliferative, proapoptotic and cancer inhibitory properties. Here, we have investigated the effects of NO-donor sulindac on UVB-induced skin cancer development in SKH-1 hairless mice. Mice (6-8 weeks old) were divided into three groups of ten mice each, which received either vehicle (acetone), vehicle+UVB (180mJ/cm 2) or topical application of NO-sulindac (5mg/mouse)+UVB after dissolving in acetone. Mice-treated with NO-sulindac developed significantly less number of tumors (60%) compared with non-NO-sulindac treated mice and tumor volume was also less by 90% on termination of the experiment at week 30th. Immunohistochemical and western blot analyses revealed that the expression levels of proliferation markers such as proliferating cell nuclear antigen (PCNA) and cell cycle regulatory cyclin D1 were markedly diminished in tumors of NO-sulindac treated mice. However, the treatment of NO-sulindac resulted in enhanced apoptosis in skin tumors as ascertained by the increased terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) assay, reduced Bcl-2 and enhanced Bax expression levels in the tumors and tumor uninvolved skin. To investigate the effects of NO-sulindac on the progression of benign lesions to invasive carcinomas, we examined squamous cell carcinomas (SCC) for various epithelial-mesenchymal transition (EMT) markers. NO-sulindac decreased the expression of mesenchymal markers such as Fibronectin, N-cadherin, SNAI, Slug and Twist whereas the epithelial polarity marker E-cadherin was found to be increased compared to the SCCs of non-NO-sulindac treated group. Down regulation of EMT by NO-sulindac was associated with a remarkable diminution of UVB-induced phosphorylation MAPK proteins such as, extracellular signal-regulated kinase 1/2 (Erk 1/2), c-Jun-NH2 terminal kinase 1/2 (JNK1/2) and p38 in both UVB-exposed skin and skin tumors. Together our results suggest that NO-sulindac is a potential chemopreventive agent for photocarcinogenesis and that inhibition of photocarcinogenesis by NO-sulindac is associated with the inhibition of EMT and MAPK protein expression in skin tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 952.

Abstract 1871: Honokiol, a natural plant product, inhibits ultraviolet radiation-induced skin tumorigenesis in mice through inhibition of inflammation and inflammatory mediators

Abstract Chronic exposure of solar ultraviolet (UV) radiation is the major etiologic agent for over one million new cases of non-melanoma skin cancers in the US each year. These cutaneous malignancies thus have a tremendous impact on public health and healthcare expenditures. The use of natural plant products has received considerable interest to protect skin from adverse biological effects of UV radiation since the protective clothing and use of sunscreens are not adequate for skin photoprotection. The photoprotective effect of honokiol, a plant product from Magnolia species, therefore assessed using SKH-1 hairless mouse model. To determine the skin cancer chemopreventive effect and associated mechanism of honokiol, a hydrophilic cream based topical formulation was developed. Different groups of mice (n=20) treated with or without honokiol were subjected to photocarcinogenesis protocol. Mice were irradiated to UVB (180 mJ/cm2) three times a week. At the termination of the experiment at 24th week, we found that topical application of honokiol (1mg &amp; 3mg/mouse) inhibited UVB-induced skin tumor development in terms of tumor incidence (10-20%), tumor multiplicity (40-60%) and tumor size (50-75%). Since UV-induced inflammation plays a crucial role in the development of skin tumors, we examined the effect of honokiol on UVB-induced biomarkers of inflammation, such as the expression levels of cyclooxygenase-2 (COX-2), prostaglandins (PG), proliferating cell nuclear antigen (PCNA), infiltration of inflammatory leukocytes, development of edema and epidermal hyperplastic response using immunostaining, western blotting and RT-PCR. Our data revealed that topical application of honokiol before each exposure of UVB radiation resulted in a dose-dependent inhibition of UVB-induced expression of COX-2, PGE2, developments of edema and infiltration of leukocytes at the UVB-irradiated skin sites. Honokiol also inhibited the levels of PCNA (hyperplastic potential) in epidermal keratinocytes of UVB-exposed skin. The inhibitory effects of honokiol on inflammatory mediators were also found in skin tumor samples. The results of this study suggest that honokiol has the ability to inhibit UVB radiation-induced skin tumor development in mice and it is associated with the inhibition of UVB-induced inflammation and inflammatory mediators in mouse skin and skin tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1871.

Dietary Grape Seed Proanthocyanidins Inhibit UVB-Induced Cyclooxygenase-2 Expression and Other Inflammatory Mediators in UVB-Exposed Skin and Skin Tumors of SKH-1 Hairless Mice

The purpose of this study was to determine the chemopreventive mechanism of dietary grape seed proanthocyanidins (GSPs) against ultraviolet (UV) radiation-induced skin tumor development in mice. Six-to-seven-week-old SKH-1 hairless mice were subjected to photocarcinogenesis protocol, and exposed to UVB radiation (180 mJ/cm(2)) three times/week for 24 weeks. Mice were fed a standard AIN76A control diet with or without supplementation with grape seed proanthocyanidins (GSPs; 0.2% or 0.5%, w/w). At the termination of the experiment, mice were sacrificed, and skin and skin tumor samples were harvested and subjected to the analysis of biomarkers related to inflammation using immunostaining, western blot analysis, ELISA and real-time PCR. Dietary GSPs inhibited UVB-induced infiltration of proinflammatory leukocytes and the levels of myeloperoxidase, cyclooxygenase-2 (COX-2), prostaglandin (PG) E(2), cyclin D1 and proliferating cell nuclear antigen (PCNA) in the skin and skin tumors compared to non-GSPs-treated UVB irradiated mouse skin and skin tumors. GSPs also significantly inhibited the levels of proinflammatory cytokines, tumor necrosis factor-alpha (P < 0.01), IL-1beta (P < 0.001) and IL-6 (P < 0.001), in UVB-exposed skin and skin tumors. The results from this study clearly suggest that dietary GSPs inhibit photocarcinogenesis in mice through the inhibition of UVB-induced inflammation and mediators of inflammation in mouse skin.

Leptin deficiency-induced obesity exacerbates ultraviolet B radiation-induced cyclooxygenase-2 expression and cell survival signals in ultraviolet B-irradiated mouse skin

Obesity has been implicated in several inflammatory diseases and in different types of cancer. Chronic inflammation induced by exposure to ultraviolet (UV) radiation has been implicated in various skin diseases, including melanoma and nonmelanoma skin cancers. As the relationship between obesity and susceptibility to UV radiation-caused inflammation is not clearly understood, we assessed the role of obesity on UVB-induced inflammation, and mediators of this inflammatory response, using the genetically obese (leptin-deficient) mouse model. Leptin-deficient obese (ob/ob) mice and wild-type counterparts (C57/BL6 mice) were exposed to UVB radiation (120 mJ/cm 2) on alternate days for 1 month. The mice were then euthanized and skin samples collected for analysis of biomarkers of inflammatory responses using immunohistochemistry, western blotting, ELISA and real-time PCR. Here, we report that the levels of inflammatory responses were higher in the UVB-exposed skin of the ob/ob obese mice than those in the UVB-exposed skin of the wild-type non-obese mice. The levels of UVB-induced cyclooxygenase-2 expression, prostaglandin-E 2 production, proinflammatory cytokines ( i.e., tumor necrosis factor-α, interleukin-1β, interleukin-6), and proliferating cell nuclear antigen and cell survival signals (phosphatidylinositol-3-kinase and p-Akt-Ser 473) were higher in the skin of the ob/ob obese mice than the those in skin of their wild-type non-obese counterparts. Compared with the wild-type non-obese mice, the leptin-deficient obese mice also exhibited greater activation of NF-κB/p65 and fewer apoptotic cells in the UVB-irradiated skin. Our study suggests for the first time that obesity in mice is associated with greater susceptibility to UVB-induced inflammatory responses and, therefore, obesity may increase susceptibility to UVB-induced inflammation-associated skin diseases, including the risk of skin cancer.

Effect of Date Seed Oil on p53 Expression in Normal Human Skin

A critical step to escape from the carcinogenic potential of UV radiation is mediated by the protein p53. P53 activates growth arrest, allowing for DNA repair, which removes damaged cells. The concept of photoprotection involves blocking apoptosis and the prevention of oxidative damage to cellular DNA. Date seed oil (DSO) extract has been reported to be beneficial in the reduction of chemically induced oxidative stress in normal human skin. In this study, we investigated the DNA-protective qualities of DSO as measured by p53 expression in human skin biopsies, one day after exposure to ultraviolet B (UVB) radiation. P53 expression was analyzed using immunohistochemistry. The results showed an increase in p53 expression in the basal cell compartment of UVB-exposed skin as compared to the non-UVB-exposed skin. However, DSO has significant photoprotective effects by inhibition of damage caused by UVB irradiation: a significantly lower fraction of cells was p53 positive as compared to the non-DSO-treated skin. We conclude that p53 expression is a sensitive parameter for the detection of UVB-induced damage in the skin and suggest that DSO could provide an efficient complement to photoprotective measures and may contribute to reduce the DNA damage.

High-fat diet exacerbates inflammation and cell survival signals in the skin of ultraviolet B-irradiated C57BL/6 mice

Inflammation induced by chronic exposure to ultraviolet (UV) radiation has been implicated in various skin diseases. We formulated the hypothesis that a high-fat diet may influence the UV-induced inflammatory responses in the skin. C57BL/6 mice were fed a high-fat diet or control diet and exposed to UVB radiation (120 mJ/cm 2) three times/week for 10 weeks. The mice were then sacrificed and skin and plasma samples collected for analysis of biomarkers of inflammatory responses using immunohistochemistry, western blotting, ELISA and real-time PCR. We found that the levels of inflammatory biomarkers were increased in the UVB-exposed skin of the mice fed the high-fat diet than the UVB-exposed skin of the mice fed the control diet. The levels of inflammatory biomarkers of early responses to UVB exposure (e.g., myeloperoxidase, cyclooxygenase-2, prostaglandin-E 2), proinflammatory cytokines (i.e., tumor necrosis factor-α, interleukin-1β, interleukin-6), and proliferating cell nuclear antigen and cell survival signals (phosphatidylinositol-3-kinase and p-Akt-Ser 473) were higher in high-fat-diet-fed mouse skin than control-diet-fed mouse skin. The plasma levels of insulin growth factor-1 were greater in the UVB-irradiated mice fed the high-fat diet than the UVB-irradiated mice fed the control diet, whereas the levels of plasma adiponectin were significantly lower. This pronounced exacerbation of the UVB-induced inflammatory responses in the skin of mice fed a high-fat diet suggests that high-fat diet may increase susceptibility to inflammation-associated skin diseases, including the risk of skin cancer.

Inhibition of UVB-Induced Skin Tumor Development by Drinking Green Tea Polyphenols Is Mediated Through DNA Repair and Subsequent Inhibition of Inflammation

Consumption of green tea polyphenols (GTPs) in drinking water prevents photocarcinogenesis in mice; however, the molecular mechanisms underlying this effect have not been fully elucidated. Using IL-12p40 knockout (KO) mice and their wild-type counterparts and an established photocarcinogenesis protocol, we found that although administration of GTPs (0.2%, w/v) in drinking water significantly reduced UVB-induced tumor development in wild-type mice, this treatment had a nonsignificant effect in IL-12-KO mice. GTPs resulted in reduction in the levels of markers of inflammation (cyclooxygenase-2, prostaglandin E(2), proliferating cell nuclear antigen, and cyclin D1) and proinflammatory cytokines (tumor necrosis factor-alpha, IL-6, and IL-1beta) in chronically UVB-exposed skin and skin tumors of wild-type mice but less effective in IL-12p40-KO mice. UVB-induced DNA damage (cyclobutane pyrimidine dimers) was resolved rapidly in GTPs-treated wild-type mice than untreated wild-type mice and this resolution followed the same time course as the GTPs-induced reduction in the levels of inflammatory responses. This effect of GTPs was less pronounced in IL-12-KO mice. The above results were confirmed by treatment of IL-12-KO mice with murine recombinant IL-12 and treatment of wild-type mice with neutralizing anti-IL-12 antibody. To our knowledge, it is previously unreported that prevention of photocarcinogenesis by GTPs is mediated through IL-12-dependent DNA repair and a subsequent reduction in skin inflammation.

Observation of dermal collagen fiber in wrinkled skin using polarization-resolved second-harmonic-generation microscopy

Optical probe methods for in vivo assessments of cutaneous photoaging are necessary in fields such as anti-aging dermatology and skin cosmetic development. We investigated the relation between wrinkle direction and collagen orientation in ultraviolet-B-exposed (UVB-exposed) skin using polarization-resolved second-harmonic-generation (SHG) microscopy. A polarization anisotropic image of the SHG light indicated that wrinkle direction in UVB-exposed skin is predominantly parallel to the orientation of dermal collagen fibers. Furthermore, collagen orientation in post-UVB-exposed skin with few wrinkles changed from that of UVB-exposed wrinkled skin to that of no-UVB-exposed skin. The method proposed has the potential to become a powerful non-invasive tool for assessment of cutaneous photoaging.

Impact of ultraviolet radiation on the expression of marker proteins of gap and adhesion junctions in human epidermis

We aimed to investigate the impact of ultraviolet B (UVB) as well as UVA1 on the epidermal expression of specific markers of gap and adhesion junctions. Twelve healthy subjects were enrolled in the study. The back of the subjects was irradiated with three MED-UVB as well as three MED-UVA1. Twenty-four hours later, punch biopsies were taken from irradiated and non-irradiated skin. Immunohistochemical procedures were used for the detection of connexin 43, E-cadherin, involucrin, Ki-67 using specific antibodies. Staining intensity of connexin 43 in UVB-exposed skin was significantly increased when compared with non-exposed and UVA1-exposed sites. By contrast, staining intensity of E-cadherin in UVB-exposed skin was significantly decreased when compared with non-exposed and UVA1-exposed sites. Involucrin and Ki-67 staining of keratinocytes was significantly increased in UVB-exposed sites as compared with non-exposed and UVA1-irradiated sites. UVB significantly alters the epidermal expression of gap and adhesion junction proteins possibly indicating a role of these proteins in the regulation of UV-induced inflammation and development and progression of skin cancer.

RETRACTED: IL-12 Deficiency Exacerbates Inflammatory Responses in UV-Irradiated Skin and Skin Tumors

IL-12 deficiency has been shown to promote photocarcinogenesis in mice. As UVB-induced inflammation is an important tumor-promoting event in the development of skin tumors, we determined the effects of IL-12-deficiency on UVB-induced inflammatory responses in mice. For this purpose, IL-12-knockout (IL-12 KO) and their wild-type counterparts were subjected to a photocarcinogenesis protocol; skin and tumor samples were collected at the termination of the experiment, and analyzed for biomarkers of inflammation and their mediators. We found that the levels of infiltrating leukocytes, myeloperoxidase, proliferating cell-nuclear antigen (PCNA), COX-2, PGE2, and the proinflammatory cytokines IL-1beta, TNF-alpha, and IL-6 were higher in the UVB-exposed skin of IL-12 KO than in that of wild-type mice. In a short-term experiment, pretreatment of IL-12 KO mice with rIL-12 (50 ng per mouse) before each exposure to UVB increased the repair rate of UVB-induced cyclobutane pyrimidine dimers, while inhibiting UVB-induced increases in myeloperoxidase, COX-2, PGE2, PCNA, TNF-alpha, and IL-1beta in the skin as compared with non-rIL-12-treated IL-12 KO mice. Similarly, tumors of IL-12 KO mice expressed higher levels of inflammatory responses than those of wild-type mice. Together, our data suggest that IL-12 KO mice are more susceptible to both UVB-induced inflammation and photocarcinogenesis because of the deficiency in the repair of UVB-induced DNA damage.

Pigmentation effects of solar‐simulated radiation as compared with UVA and UVB radiation

Different wavelengths of ultraviolet (UV) radiation elicit different responses in the skin. UVA induces immediate tanning and persistent pigment darkening through oxidation of pre-existing melanin or melanogenic precursors, while UVB induces delayed tanning which takes several days or longer to develop and requires activation of melanocytes. We compared the effects of a 2-week repetitive exposure of human skin to solar-simulated radiation (SSR), UVA or UVB at doses eliciting comparable levels of visible tanning and measured levels of melanins and melanin-related metabolites. Levels of eumelanin and pheomelanin were significantly higher in the order of SSR, UVB, UVA or unexposed control skin. Levels of free 5-S-cysteinyldopa (5SCD) were elevated about 4-fold in SSR- or UVB-exposed skin compared with UVA-exposed or control skin. Levels of protein-bound form of 5SCD tended to be higher in SSR- or UVB-exposed skin than in UVA-exposed or control skin. Total levels of 5-hydroxy-6-methoxyindole-2-carboxylic acid (5H6MI2C) and 6H5MI2C were higher in SSR- than in UVB-exposed or control skin. These results show that SSR is more effective in promoting delayed tanning than UVB radiation alone, suggesting a synergistic effect of UVA radiation. Furthermore, free 5SCD may serve as a good marker of the effect of SSR and UVB.

Ultrastructural studies bearing on the mechanism of UVB-impaired induction of contact hypersensitivity to DNCB in man.

In both murine and human experimental systems, acute, low dose exposure of skin to ultraviolet B light (UVB) impairs the induction of allergic contact dermatitis (ACD) by haptens such as dinitrochlorobenzene (DNCB) in a significant proportion of individuals. By light microscopy, epidermal Langerhans cells (LC) have been reported to be depleted by UVB exposure as well as by epicutaneous hapten application, implying that LC may be the locus of action of the effects of both UVB and DNCB. However, light microscopy can not readily distinguish cell density changes secondary to LC necrosis from changes resulting from down-modulation of expression of LC surface molecules. Using a highly sensitive immunogold electron microscopic approach, we have evaluated the differential effects of UVB and/or DNCB on human epidermal LC. The results reveal that DNCB alone caused significant up-regulation of cell surface HLA class II expression on a very small number of LC, the major fraction of LC expressing normal levels of HLA class II. Furthermore, DNCB alone caused a modest reduction in the density of LC at the treated sites without evidence of cell necrosis. Treatment with UVB alone or UVB exposure followed by DNCB resulted in a reduction in the density of LC, with widespread evidence of LC necrosis. However, the few remaining intact LC were all intensely HLA class II-positive after UVB exposure followed by DNCB, whereas treatment with UVB alone did not result in changes in LC HLA class II expression. The findings that after DNCB painting only a small proportion of the LC were strongly HLA class II-positive, but after UVB exposure followed by DNCB all intact LC displayed significant up-regulation of cell surface HLA class II expression, imply that UVB exposure inhibits the migration of epidermal LC. This is consistent with the view that DNCB fails to induce ACD when hapten is painted on UVB-exposed skin because insufficient LC are available to initiate T cell activation in the draining lymph node.

Interleukin-12 Deficiency Is Permissive for Angiogenesis in UV Radiation-Induced Skin Tumors

We have shown previously that endogenous deficiency of interleukin (IL)-12 promotes photocarcinogenesis in mice. To characterize the role of IL-12 deficiency in tumor angiogenesis, we developed IL-12p35 knockout (IL-12 KO) mice on a C3H/HeN background. IL-12 KO mice and their wild-type (WT) counterparts were subjected to a photocarcinogenesis protocol. When tumor yield was stabilized, samples of tumor and tumor-uninvolved UVB-exposed skin were collected and subjected to immunohistochemistry, gelatinolytic zymography, real-time PCR, and Western blot analysis of angiogenic factors. We found that the protein, mRNA expression and/or activity of the matrix metalloproteinases (MMP)-2, MMP-3, MMP-7, and MMP-9, and basic fibroblast growth factor, which play crucial roles in tumor growth, were significantly higher in UVB-exposed skin and tumors of IL-12 KO mice compared with WT mice. With respect to the tumor vasculature, the expression of CD31-positive cells and the expression of vascular endothelial growth factor were higher in the tumors of IL-12 KO mice than WTs. The proliferative capacity of tumor cells of the IL-12 KO mice was significantly higher than their WT counterparts when determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and by analyzing the expression of cyclin D1. The level of the proinflammatory cytokine IL-6 and the expression of IL-23 in tumors of IL-12 KO mice were markedly higher than in the tumors of WT mice. IL-23 has been shown to promote tumor growth. Together, these data indicate for the first time that IL-12 deficiency promotes proangiogenic stimuli in UVB-induced skin tumors and suggest that endogenous enhancement of IL-12 levels may be effective in the prevention and treatment of UV-induced skin cancers.