UVB Dose Research Articles

UVB damage onset and progression 24h post exposure in human-derived skin cells.

The focus of this research was on UVB radiation (280-320nm) responsible for cellular changes in skin of acute and chronically exposed individuals. This study investigated the acute cellular damages triggered by UVB exposure of cultured human fibroblasts and keratinocyte cells immediately and 24h post exposure in order to understand damage onset and progression. The study evaluated a number of cellular parameters including mitochondria, lysosomes, cell membrane, DNA damages as well as pro and anti-apoptotic protein expression levels. Cellular organelle damages were assessed by a battery of in vitro toxicological assays using MTS and Neutral red cytotoxicity assays. Cell membrane damages were also assessed by measuring lactate dehydrogenase (LDH) enzyme leakage from UVB exposed cells. Lastly DNA damages was assessed using the comet assay while protein expression was evaluated using Western Blot. In this study we reported in all our assay systems (MTS, NR and LDH) that cellular damages were UVB dose dependent with damages amplified 24h post exposure. Our results also indicated that incubation of exposed cells for a period of 24h increased the sensitivity of the assay systems used. The increased sensitivity in detecting early cytotoxic damages was manifested though organelle damage measurement at very low doses which were not manifested immediately post exposure. The data also indicated that HaCaT cells were most sensitive in detecting UVB triggered damages immediately and 24h post exposure using the MTS assay. We also established upregulation and downregulation of various apoptotic proteins at various time points post exposure. The presented data clearly indicated the need for a comprehensive assessment of UVB damages 4 and 24h post exposure due to the different assay sensitivities in addition to various signaling mechanisms activated at different time points post exposure.

Egg hatching response to a range of ultraviolet-B (UV-B) radiation doses for four predatory mites and the herbivorous spider mite Tetranychus urticae.

Egg hatchability of four predatory mites-Phytoseiulus persimilis Athias-Henriot, Iphiseius [Amblyseius] degenerans Berlese, Amblyseius swirskii Athias-Henriot, and Euseius finlandicus Oudemans (Acari: Phytoseiidae)-and the spider mite Tetranychus urticae Koch (Acari: Tetranychidae) was determined under various UV-B doses either in constant darkness (DD) or with simultaneous irradiation using white light. Under UV-B irradiation and DD or simultaneous irradiation with white light, the predator's eggs hatched in significantly lower percentages than in the control non-exposed eggs, which indicates deleterious effects of UV-B on embryonic development. In addition, higher hatchability percentages were observed under UV-B irradiation and DD in eggs of the predatory mites than in eggs of T. urticae. This might be caused by a higher involvement of an antioxidant system, shield effects by pigments or a mere shorter duration of embryonic development in predatory mites than in T. urticae, thus avoiding accumulative effects of UV-B. Although no eggs of T. urticae hatched under UV-B irradiation and DD, variable hatchability percentages were observed under simultaneous irradiation with white light, which suggests the involvement of a photoreactivation system that reduces UV-B damages. Under the same doses with simultaneous irradiation with white light, eggs of T. urticae displayed higher photoreactivation and were more tolerant to UV-B than eggs of the predatory mites. Among predators variation regarding the tolerance to UV-B effects was observed, with eggs of P. persimilis and I. degenerans being more tolerant to UV-B radiation than eggs of A. swirskii and E. finlandicus.

Cutaneous malignant melanoma incidences analyzed worldwide by sex, age, and skin type over personal Ultraviolet-B dose shows no role for sunburn but implies one for Vitamin D3.

ABSTRACTBecause the incidence of cutaneous malignant melanoma (CMM) was reported to increase with increasing terrestrial UVR (290–400 nm) doses in the US back in 1975 and a recent publication showed no association exists with UVR exposure at all, we set out to fully elucidate the role of UVR in CMM. To achieve this goal, we analyzed the CMM incidences over latitude and estimated the average personal UVR dose in the US and numerous countries (> 50) on 5 continents around the world. Using data from the International Agency for Research on Cancer in 2005, we performed worldwide analysis of CMM over UVR dose by sex, age group (0–14, 15–29, 30–49, 50–69, 70–85+) and Fitzpatrick skin types I-VI. Surprisingly, increasing UVR doses, which represent erythemally-weighted doses comprised primarily of UVB (290–315 nm) radiation, did not significantly correlate with increasing CMM incidence for people with any skin type anywhere in the world. Paradoxically, we found significant correlations between increasing CMM and decreasing UVB dose in Europeans with skin types I-IV. Both Europeans and Americans in some age groups have significant increasing CMM incidences with decreasing UVB dose, which shows UVB is not the main driver in CMM and suggests a possible role for lower cutaneous vitamin D3 levels and UVA (315–400 nm) radiation. CMM may be initiated or promoted by UVA radiation because people are exposed to it indoors through windows and outdoors through some sunscreen formulations. Thus, our findings may explain why some broad-spectrum sunscreen formulations do not protect against getting CMM.

UV-B radiation increases anthocyanin levels in cotyledons and inhibits the growth of common buckwheat seedlings

The impact of short-term UV-B treatment on the content of individual flavonoids and photosynthetic pigments in cotyledons and the growth of common buckwheat (Fagopyrum esculentum Moench) seedlings was investigated. Seeds of four common buckwheat cultivars were germinated in darkness over a period of 4 days and acclimatized for 2 days under a 16/8 h light/dark photoperiod at 24/18 °C day/night, and exposure to 100-120 μmol ∙ m-2 ∙ s-1 of photosynthetically active radiation (PAR). Seedlings were divided into three batches, including two batches subjected to different doses of UV-B (5 W ∙ m-2 and 10 W ∙ m-2, one hour per day) for 5 days, and a control group exposed to PAR only. Exposure to UV-B increased anthocyanin levels in the cotyledons of all examined cultivars, it inhibited hypocotyl elongation, but did not affect the content of photosynthetic pigments. Flavone concentrations increased in cv. Red Corolla and Kora, remained constant in cv. Panda and decreased in cv. Hruszowska. Exposure to UV-B decreased rutin levels in cv. Hruszowska, but not in the remaining cultivars. Cultivars Hruszowska, Panda and Kora appeared to be less resistant to UV-B than Red Corolla. Higher resistance to UV-B radiation in Red Corolla can probably be attributed to its higher content of anthocyanins and rutin in comparison with the remaining cultivars.

Effects of UVB radiation on freshwater biota: a meta‐analysis

AbstractAimStratospheric ozone depletion and simultaneous increases in UVB radiation due to human activities have the potential to affect freshwater biota. The goal of our study is to summarize the impacts of UVB on freshwater biota by comparing the differences in the general patterns, including the directions and the magnitudes of the impacts of UVB on four major freshwater taxa (phytoplankton, zooplankton, fish and amphibians). The potential driving forces for these differences are also explored.LocationGlobal.MethodsWe performed a meta‐analysis on a database consisting of 146 studies including 127 species from four taxonomic groups. We tested for the effects of taxonomic group, experimental venue, developmental stage, UVB dosage and the latitude of organism provenance.ResultsUVB had significant negative effects on freshwater biota from the molecular–cellular to individual–population levels. However, these effects were highly variable among the taxonomic groups. In general, zooplankton was the most negatively affected group, whereas fish and amphibians were less affected. As direct fitness components, survival and reproduction were the two responses most affected by UVB. The sensitivities of individuals to UVB at different developmental stages were different for the same taxon, while the stage‐dependent sensitivity patterns also differed among different taxa. Additionally, effects of different experimental venues, UVB dosages and latitudes of organism provenance on the effects of UVB were detected.Main conclusionsOur results suggest that UVB has significant negative effects on freshwater biota. We found that the effects of UVB varied among taxonomic groups, developmental stages, experimental venues, UVB dosages and latitudes of organism provenance. The variation in sensitivity among the different taxa has important implications for ecosystem responses. Given that stratospheric ozone is unlikely to recover to the levels of the 1980s in the upcoming decades, more conservation efforts should be taken to protect freshwater habitats from further damage by UVB.

Screening sunscreens: protecting the biomechanical barrier function of skin from solar ultraviolet radiation damage.

Solar ultraviolet (UV) radiation is ubiquitous in human life and well known to cause skin damage that can lead to harmful conditions such as erythema. Although sunscreen is a popular form of protection for some of these conditions, it is unclear whether sunscreen can maintain the mechanical barrier properties of skin. The objective of this study was to determine whether in vitro thin-film mechanical analysis techniques adapted for biological tissue are able to characterize the efficacy of commonly used UV inhibitors and commercial sunscreens to protect the biomechanical barrier properties of stratum corneum (SC) from UV exposure. The biomechanical properties of SC samples were assayed through measurements of the SC's drying stress profile and delamination energy. The drying stresses within SC were characterized from the curvature of a borosilicate glass substrate onto which SC had been adhered. Delamination energies were characterized using a double-cantilever beam (DCB) cohesion testing method. Successive DCB specimens were prepared from previously separated specimens by adhering new substrates onto each side of the already tested specimen to probe delamination energies deeper into the SC. These properties of the SC were measured before and after UV exposure, both with and without sunscreens applied, to determine the role of sunscreen in preserving the barrier function of SC. The drying stress in SC starts increasing sooner and rises to a higher plateau stress value after UVA exposure as compared to non-UV-exposed control specimens. For specimens that had sunscreen applied, the UVA-exposed and non-UV-exposed SC had similar drying stress profiles. Additionally, specimens exposed to UVB without protection from sunscreen exhibited significantly lower delamination energies than non-UV-exposed controls. With commercial sunscreen applied, the delamination energy for UV-exposed and non-UV-exposed tissue was consistent, even up to large doses of UVB. In vitro thin-film mechanical analysis techniques can readily characterize the effects of SC's exposure to UV radiation. The methods used in this study demonstrated commercial sunscreens were able to preserve the biomechanical properties of SC during UV exposure, thus indicating the barrier function of SC was also maintained.

UV-B radiation reduces biocontrol ability of Clonostachys rosea against Botrytis cinerea

ABSTRACTThere is a lack of information comparing UV-B radiation conidial sensitivity of the biocontrol agent Clonostachys rosea (Cr) and its target pathogen, Botrytis cinerea (Bc). We investigated the interactions in vitro and on strawberry leaf discs between previously selected Cr and Bc strains tolerant to UV-B radiation. Strawberry leaf discs inoculated with Bc, Cr, or combinations of both fungi were exposed to UV-B doses (2.9, 5.9, and 8.9 kJ m−2). Incidence and sporulation of both fungi were evaluated, and the Area Under Incidence Progress Curve (AUIPC) and Area Under Sporulation Progress Curve (AUSPC) were calculated. AUIPC and AUSPC of Cr on leaf discs were negatively correlated to increased UV-B. When inoculated alone on leaf discs, Bc was not affected by UV-B, but when inoculated with Cr the incidence and sporulation of Bc were positively correlated to UV-B radiation dose. In the absence of UV-B, Cr reduced incidence and sporulation of Bc. However, the ability of Cr to control Bc was reduced by 20% to 50% with increasing UV-B radiation. Increasing the applied concentration of Cr conidia 10-fold partially overcame the deleterious effects of UV-B on the ability of the biocontrol agent to reduce Bc sporulation in strawberry leaves. The selection of antagonists must fulfil many requirements; besides being active against the specific targeted plant pathogens, they must be cost-effective and have ecological characteristics suitable for the desired use conditions. We suggest that UV-B exposure must be taken into account during the development of bio-fungicides based on Cr.

Oxygen toxicity and antioxidative responses in arsenic stressed Helianthus annuus L. seedlings against UV-B

In order to know the impact of elevated level of UV-B on arsenic stressed Helianthus annuus L. var. DRSF-113 plants, certain physiological (growth – root and shoot lengths, their fresh masses and leaf area; photosynthetic competence and respiration) and biochemical parameters (pigments – Chl a and b, Car, anthocyanin and flavonoids; reactive oxygen species – superoxide radicals, H2O2; reactive carbonyl group, electrolyte leakage; antioxidants – superoxide dismutase, peroxidise, catalase, glutathione-S-transferase, proline) of their seedlings were analysed under the simultaneous exposures of two arsenic doses (6mgkg−1 soil, As1; and 12mgkg−1 soil, As2) and two UV-B doses (1.2kJm−2d−1, UV-B1; and 3.6kJm−2d−1, UV-B2). As1 and As2 alone declined all the studied growth parameters – along with photosynthetic pigments which were further aggravated after the simultaneous exposures of predefined levels of UV-B. Each As exposure was accompanied by significant accumulation of As in root, shoot and leaves and was substantiated by simultaneous exposures of UV-B doses which manifested into suppressed growth, decreased chlorophyll contents and photosynthesis. In similar conditions, other photo-shielding pigments, viz. carotenoids, anthocyanin and flavonoids along with respiration and oxidative stress markers such as O2•¯, H2O2; and indicators of cell membrane damage like MDA (malondialdehyde), RCG (reactive carbonyl group), electrolyte leakage were enhanced by As, and became more pronounced after the simultaneous exposures of UV-B doses. As doses stimulated the activities of SOD, POD, CAT, GST and Pro which got further accelerated after the simultaneous exposures of UV-B doses.

Redox proteomic evaluation of oxidative modification and recovery in a 3D reconstituted human skin tissue model exposed to UVB.

Exposure to UV in humans resulting in sunburn triggers a complex series of events that are a mix of immediate and delayed damage mediation and healing. While studies on the effects of UV exposure on DNA damage and repair have been reported, changes in the oxidative modification of skin proteins are poorly understood at the molecular level, despite the important role played by structural proteins in skin tissue, and the effect of the integrity of these proteins on skin appearance and health. Proteomic molecular mapping of oxidation was here applied to try to enhance understanding of skin damage and recovery from oxidative damage and UVB exposure. A redox proteomic-based approach was applied to evaluating skin protein modification when exposed to varying doses of UVB after initial oxidative stress, via tracking changes in protein oxidation during the healing process in vitro using a full-thickness reconstituted human skin tissue model. Bioassays and structural evaluation confirmed that our cultured skin tissues underwent a normal physiological response to UVB exposure. A set of potential skin marker peptides was generated, for use in tracking skin protein oxidative modification. Exposure to UVB after thermal oxidative stress was found to result in higher levels of skin protein oxidation than a non-irradiated control for up to seven days after exposure. Recovery of the skin proteins from oxidative stress, as assessed by the overall protein oxidation levels, was found to be impaired by UVB exposure. Oxidative modification was largely observed in skin structural proteins. Exposure of skin proteins to UVB exacerbates oxidative damage to structural skin proteins, with higher exposure levels leading to increasingly impaired recovery from this damage. This has potential implications for the functional performance of the proteins and inter-related skin health and cosmetic appearance.

Investigation of suitable starting doses of narrowband UVB in Asian vitiligo patients: a pilot study.

Phototherapy is the preferred treatment modality for active and generalized vitiligo. One of the widely accepted consensus on starting dose of phototherapy is using a uniform dose of 280 mJ/cm2 regardless of patients' Fitzpatrick skin phototype (SPT). However, in many clinical experiences with Asian vitiligo patients, the protocol seems suboptimal. To gather more evidence on establishing a higher starting dosage for Asian vitiligo patients undergoing phototherapy. We enrolled generalized vitiligo patients with lesions sized adequate enough for phototest. Minimal erythema dose (MED) of vitiligo lesion and non-lesion was measured along with melanin index (MI). Relatively, a wide range of MED and MI was observed even among patients with similar SPT. The range of MED for lesional skin was 300-700 mJ/cm2 and the MED for non-lesion was 500-800 mJ/cm2 . Correlation was noted between lesional MED and non-lesional MI (Spearman correlation, ρ = 0.664 [P < 0.036]) and mean lesional MED was approximately 65% of mean non-lesional MED. Results from phototest and tolerability of patients to doses higher than 280 mJ/cm2 may indicate that higher starting doses might be appropriate for Asian vitiligo patients.

Relative sensitivity of DNA and photosystem II in Ulva intestinalis (Chlorophyta) under natural solar irradiation

High intensities of sunlight can result in DNA and photosystem II (PSII) damage. However, the relative sensitivity of both these targets under natural sunlight and especially over a long period has not been studied in algae so far. Although DNA damage is highly specifically induced by ultraviolet-B radiation (UVB, 280-315 nm), PSII is inactivated by a broad spectrum. The green macroalga Ulva intestinalis is an appropriate and interesting study organism with which to investigate the relative importance of the 2 different targets of sunlight because this alga contains no UV-screening protective pigments, although it is exposed to strong solar irradiation in its natural habitat. This entails a high risk of DNA damage. Therefore, diel time courses and long-term development of DNA damage and the optimal quantum yield of PSII (F-v/F-m) were studied in situ. F-v/F-m was extremely reduced at noon, but a fast recovery was observed in the afternoon. As dark-adapted basal fluorescence (F-o) of PSII was substantially decreased during the day, non-photochemical quenching is suggested to be a key photoprotective strategy in U. intestinalis. In contrast, even in samples with strongly reduced F-v/F-m, only very low DNA damage was found, irrespective of the accumulated UVB dose. We propose that efficient photoreactivation driven by natural sunlight balances the induction of dimers. This leads to a higher UVB tolerance of DNA than that observed in algae under experimental UVB irradition. In this field study, U. intestinalis suffered more from photoinhibition than from DNA damage.

Dead Sea ultraviolet climatotherapy for children with atopic dermatitis.

Atopic dermatitis (AD) is a common, chronic, and relapsing inflammatory skin disorder. Moderate to severe cases represent an extremely disabling disease, for both children and their parents. Dead Sea climatotherapy (DSC), recognized as a natural treatment for patients with skin diseases, takes advantage of the selectively scattered ultraviolet irradiation (UV) present at the lowest terrestrial site on the earth. To investigate the impact on short-term results of DSC in moderate to severe AD children from the Czech Republic treated 4 weeks at the Deutsches Medizinisches Zentrum (DMZ), Israel, and to correlate their results to the cumulative UVA and UVB irradiation doses received during treatment. Seventy-two patients aged <19 years were divided into three groups and treated in March 2014, October 2014, and March 2015 with gradually increasing sun exposure during 28 consecutive days. Daily and cumulative exposure doses of UVB and UVA were calculated through patients' recorded sun exposure logs. The SCORing Atopic Dermatitis (SCORAD) index was recorded immediately after DSC and 3 months later by the same dermatologist. Good clinical results were observed in all groups, with overall improvement in SCORAD reaching 87.5 ± 13.4% and 71.3 ± 21.3% immediately after DSC and 3 months later, respectively. No side effects were observed during the treatments. Higher cumulative exposure times correlated with better results and enhanced remission. Dead Sea climatotherapy represents a valuable option for the treatment of AD in children. Medically controlled and prescribed sun exposure seems to directly and positively influence the results obtained.

Topical application of superoxide dismutase mediated by HIV-TAT peptide attenuates UVB-induced damages in human skin

The purpose of this study was to evaluate whether topical application of superoxide dismutase with cell penetrating peptide (HIV-TAT) could protect against skin damage induced by UVB irradiation in humans. The permeability through stratum corneum of large proteins linked to TAT peptide was firstly confirmed by confocal microscopy and tape stripping. Ten healthy volunteers with either Fitzpatrick skin type II or III were recruited in this clinical study. TAT-SOD (300units/cm2) and vehicle cream were applied on two symmetric areas of both inner upper arms 1h prior to UVB irradiation. After one hour of pretreatment, subjects received 10 incremental doses of UVB on pretreated areas. 24h later, erythema, blood flow and apoptotic cells were measured. Pretreatment with TAT-SOD 1h prior to UVB radiation promoted a mean minimal erythema dose (MED) increase of 36.6±18.4% (p=0.013<0.05. n=10) compared to vehicle control. The median blood flow values of all subjects following 2 and 3-MED of UVB were 107.8±51.0units and 239.5±88.0units respectively, which account for 26% and 25% decrease with respect to vehicle groups. These data suggest that TAT-SOD significantly suppresses UVB induced erythema formation and blood flow rise. Furthermore, pretreatment with TAT-SOD 1h prior to 2-MED of UVB irradiation reduced the apoptotic sunburn cell formation by 47.6±8.6% (p<0.0001) in all subjects. Evaluating results generated from all measurements, we conclude that topical application of TAT-SOD significantly attenuates UVB-induced skin damage in man. These biological effects of TAT-SOD are probably mediated via its free radical scavenging properties, clearly differentiating it from other physical sunscreen agents.

Abstract 900: In vivo modeling of NRAS-mutant melanoma reveals differential preventative efficacy amongst SPF30 sunscreens

Abstract Cutaneous melanoma claims the life of one American every hour, and while the etiology of this tumor type is not entirely understood, exposure to ultraviolet (UV) radiation (280-340nm) is a major risk factor. For this reason, the use of UV-blocking sunscreens is strongly advocated; however, few studies have tested the relative efficacy of these agents in preventing melanoma formation in vivo. Here, we employed a new genetically engineered mouse model (TpN61R) to examine the ability of 6 chemically distinct SPF30 sunscreens to prevent melanoma. In this TpN61R model, topical 4-hydroxytamoxifen (4OHT) treatment induces the melanocyte-specific expression of oncogenic NRas as well as inactivation of the p16INK4a tumor suppressor. These genetic lesions co-occur in ∼24% of all human melanomas, making the TpN61R model biologically relevant. Since NRAS mutations are an early and UV-independent event in human melanoma, TpN61R mice were first painted with 4OHT and then exposed to a single dose of 4.5 kJ/m2 UVB light one day later. Exposed skin from TpN61R mice showed transient cyclobutane pyrimidine dimer (CPD) formation, however no evidence of edema or inflammation was observed. Despite these mild effects, UVB exposure reduced the melanoma-free survival of TpN61R mice by 80% and increased tumor incidence rate from 1.2 to 3.4 tumors/mouse. Further experiments using a variety of UVB doses (0.25, 1.0, 2.3 and 9.0 kJ/m2) in the TpN61R model revealed a dose-dependent increase in early melanoma incidence. Together, these data establish the exquisite cooperation of UV light and oncogenic NRas mutations in driving melanoma. Taking advantage of this unique model, we tested the preventative efficacy of SPF30 sunscreens with differing chemical composition. Sunscreens components included UVA (avobenzene), UVB (homosalate, octisalate) and broad spectrum (oxybenzone, octocrylene, zinc oxide) blocking agents. Application of sunscreen prior to UVB exposure decreased DNA damage, delayed melanoma onset and reduced tumor incidence in a sunscreen-dependent manner. Thus, SPF30 sunscreens do not equally prevent UVB-induced, NRAS mutant melanoma. This work establishes the first in vivo system to test sunscreen efficacy in NRAS-driven melanoma and will help direct the development of improved melanoma preventatives. Citation Format: Andrea M. Holderbaum, Rebecca C. Hennessey, James E. Gillahan, Anamaria Bonilla, Conor Delaney, Raleigh D. Kladney, Kathleen L. Tober, Tatiana M. Oberyszyn, Christin E. Burd. In vivo modeling of NRAS-mutant melanoma reveals differential preventative efficacy amongst SPF30 sunscreens. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 900.

Elevated ROS-scavenging enzymes contribute to acclimation to UV-B exposure in transplastomic tobacco plants, reducing the role of plastid peroxidases

Leaf peroxidases play a key role in the successful acclimation of plants to low UV-B doses. The aim of the present study was to examine whether selective enhancement of alternative chloroplast antioxidant pathways achieved by chloroplast transformation affected the need for peroxidase defense. Transplastomic tobacco lines expressing glutathione reductase in combination with either dehydroascorbate reductase or glutathione-S-transferase in their plastids exhibited better tolerance to supplemental UV-B than wild type plants. After 10days UV treatment, both the maximum and effective quantum yields of PSII decreased in the wild type by 10% but were unaffected in either of the transformed lines. Activities of total peroxidase and ascorbate peroxidase, in addition to dehydroascorbate reductase and gluthatione-S-transferase, were increased by UV in all lines. Gluthatione reductase activity was unaffected by UV in the transplastomic line engineered to have a higher constitutive level of this enzyme, but increased in the two other genotypes. However, the observed more successful acclimation required less activation of peroxidases in the doubly transformed plants than in the wild type and less increase in non-enzymatic hydroxyl radical neutralization in the dehydroascorbate reductase plus glutathione reductase fortified plants than in either of the other lines. These results highlight the fundamental role of efficient glutathione, and especially ascorbate, recycling in the chloroplast in response to exposure of plants to UV-B. They also identify chloroplast localized peroxidases among the large variety of leaf peroxidases as essential elements of defense, supporting our earlier hypothesis on hydrogen peroxide UV-B photo-cleavage as the primary mechanism behind damage.

Relative Contributions of UVB and UVA to the Photoconversion of (6-4) Photoproducts into their Dewar Valence Isomers.

Dewar valence isomers are photoisomerization products of pyrimidine (6-4) pyrimidone photoproducts, a major class of UV-induced DNA lesions, which exhibits a maximal absorption around 320nm. However, Dewar isomers are not produced in significant amounts in cells exposed to biologically relevant doses of UVB. In contrast, they are readily produced when cells are exposed to a combination of UVA and UVB. The present computational work demonstrates that, on the basis of known absorption properties and formation quantum yields, the difference in Dewar formation between the two types of radiation can be explained by the role of normal bases. In the UVB range, at the low level of (6-4) photoproducts present in cells exposed to realistic doses, normal bases are present in overwhelming amounts and absorb the vast majority of the incident photons. In contrast, the absorption of DNA bases is much weaker in the UVA range while that of (6-4) photoproducts is still significant, making photoisomerization possible. This two-photon process makes it difficult to define an action spectrum for the formation of Dewar isomers.

Impact on Vitamin D2, Vitamin D4 and Agaritine in Agaricus bisporus Mushrooms after Artificial and Natural Solar UV Light Exposure.

Commercial mushroom production can expose mushrooms post-harvest to UV light for purposes of vitamin D2 enrichment by converting the naturally occurring provitamin D2 (ergosterol). The objectives of the present study were to artificially simulate solar UV-B doses occurring naturally in Central Europe and to investigate vitamin D2 and vitamin D4 production in sliced Agaricus bisporus (button mushrooms) and to analyse and compare the agaritine content of naturally and artificially UV-irradiated mushrooms. Agaritine was measured for safety aspects even though there is no rationale for a link between UV light exposure and agaritine content. The artificial UV-B dose of 0.53J/cm(2) raised the vitamin D2 content to significantly (P<0.001) higher levels of 67.1±9.9μg/g dry weight (DW) than sun exposure (3.9±0.8μg/g dry DW). We observed a positive correlation between vitamin D4 and vitamin D2 production (r(2)=0.96, P<0.001) after artificial UV irradiation, with vitamin D4 levels ranging from 0 to 20.9μg/g DW. The agaritine content varied widely but remained within normal ranges in all samples. Irrespective of the irradiation source, agaritine dropped dramatically in conjunction with all UV-B doses both artificial and natural solar, probably due to its known instability. The biological action of vitamin D from UV-exposed mushrooms reflects the activity of these two major vitamin D analogues (D2, D4). Vitamin D4 should be analysed and agaritine disregarded in future studies of UV-exposed mushrooms.

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

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

Photosensitivity of murine skin greatly depends on the genetic background: clinically relevant dose as a new measure to replace minimal erythema dose in mouse studies.

Artificial UV irradiation of murine skin is a frequently used method for testing photosensitivity, study carcinogenesis and photoprotective effects of different compounds. However, doses of UV radiation and mouse strains used in experiments vary greatly. The genetic background of mice may influence the photosensitivity as melanin content, pigmentation and hair cycle parameters are dissimilar. Doses of UV are often expressed in relation to the minimal erythema dose (MED) that was not necessarily determined for the given strain. We set out to standardize the method of measuring photosensitivity in three commonly used mouse strains, C57BL/6N, Balb/c and SKH-1. We found that MED may not be determined for some strains as erythema development in mice with diverse genotypes differs greatly. We measured the oedema response in vivo and ex vivo by using OCT. Given the strain-specific variability of erythema, we introduced Clinically Relevant Dose (CRD) as a new term to replace MED in experiments, to describe the lowest dose that triggers a perceptible skin reaction in mice. Not only the CRD but the proportion of erythema and oedema were different in strains examined. C57BL/6N mice display skin reactions at the lowest UVB dose, while SKH-1 hairless mice show changes, mostly oedema, after higher doses of UVB. The cellular composition and skin thickness were examined by histopathology. IL-1beta and IL-6 levels in skin correlated with the increasing doses of UVB. Despite the variations in the degree of erythema and oedema, no major differences in cytokine expressions were seen among various strains of mice.

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

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