Molecular responses to stress induced in normal human caucasian melanocytes in culture by exposure to simulated solar UV

Melanocytes play a central role in the response of skin to sunlight exposure. They are directly involved in UV-induced pigmentation as a defense mechanism. However, their alteration can lead to melanoma, a process where the role of sun overexposure is highly probable. The transformation process whereby UV damage may result in melanoma initiation is poorly understood, especially in terms of UV-induced genotoxicity in pigmented cells, where melanin can act either as a sunscreen or as a photosensitizer. The aim of this study was to analyze the behavior of melanocytes from fair skin under irradiation mimicking environmental sunlight in terms of spectral power distribution. To do this, normal human Caucasian melanocytes in culture were exposed to simulated solar UV (SSUV, 300-400 nm). Even at relatively high doses (until 20 min exposure, corresponding to 12 kJ/m2 UV-B and 110 kJ/m2 UV-A), cell death was limited, as shown by cell viability and low occurrence of apoptosis (caspase-3 activation). Moreover, p53 accumulation was three times lower in melanocytes than in unpigmented cells such as fibroblasts after SSUV exposure. However, an important fraction of melanocyte population was arrested in G2-M phase, and this correlated well with a high induction level of the gene GADD45, 4 h after exposure. Among the genes involved in DNA repair, gene XPC was the most inducible because its expression increased more than two-fold 15 h after a 20 min exposure, whereas expression of P48 was only slightly increased. In addition, an early induction of Heme Oxygenase 1 (HO1) gene, a typical response to oxidative stress, was also observed for the first time in melanocytes. Interestingly, this induction remained significant when melanocytes were exposed to UV-A radiation only (320-400 nm), and stimulation of melanogenesis before irradiation further increased HO1 induction. These results were obtained with normal human cells after exposure to SSUV radiation, which mimicked natural sunlight. They provide new data related to gene expression and suggest that melanin in light skin could contribute to sunlight-induced genotoxicity and maybe to melanocyte transformation.     

Phlorotannin and antioxidant responses upon short-term exposure to UV radiation and elevated temperature in three south Pacific kelps

Rapid adjustments of the photosynthetic machinery and efficient antioxidant mechanisms to scavenge harmful ROS are physiologic adaptions exhibited by intertidal seaweeds to persist in temperate regions. This study examines short-term (3 h) responses of three large kelps from the cold-temperate coast of Chile, normally adapted to water temperatures <16°C, but exposed abruptly to simultaneous high temperatures and UV radiation during low tide in summer. The kelps were exposed in the laboratory to three temperatures (10, 20 and 28°C) with and without UV radiation, and photochemical reactions, concentration of phlorotannins and antioxidant activity were examined. The exposure to elevated temperature (slightly exacerbated by the presence of UV radiation) decreased photochemical processes (measured as fluorescence kinetics) in the three studied species and increased lipid peroxidation in two of them. The concentration of total soluble phlorotannins was variable and correlated with the antioxidant activity in the presence of UV radiation. Insoluble phlorotannins did not change during the exposure. In all, the downregulation of the photochemical machinery, which was expressed as dynamic photoinhibition, and the rapid induction of soluble phlorotannins triggered by UV radiation minimized the effects of oxidative stress and maintained the operation of photochemical processes during short-term thermal stress.     

UV exposure of elementary school children in five Japanese cities

A 1 week UV‐exposure measurement and outdoor‐activity pattern survey was conducted for elementary school children for four seasons at five sites in Japan, i.e. Sapporo (43°05′N, altitude 40 m), Tsukuba (36°05′N, 20 m), Tokyo (35°40′N, 45 m), Miyazaki (31°60′N, 40 m) and Naha (26°10′N, 5 m), and UV exposure was measured directly and estimated using outdoor‐activity records. The study site with largest UV exposure was Miyazaki, a southern rural area. Comparing the results for boys and girls, UV exposure was larger in boys. UV exposure was large in spring and summer and small in winter. The total amount of UV exposure in spring and summer contributed 57.7–73.4% of total exposure for the year. As a whole, 8.1% and 1.8% of the schoolchildren were exposed to more than 1 minimum erythemal dose (MED) and 2 MED of solar UV in a day, respectively. The estimated yearly UV exposure ranged from 49 207 J/m² in Miyazaki to 31 520 J/m² in Tsukuba. The actual UV exposure correlated to potential UV exposure, estimated using outdoor‐activity records and ambient UV irradiance, but the ratio differed by season and site. The yearly average of percent UV exposure to ambient UV on a horizontal plane ranged from 9.9% in Tokyo to 4.0% in Naha. In the questionnaire survey on outdoor‐activity pattern, a short question “How long did you spend time outdoors between 0900 and 1500 h?” gives the best estimates of UV exposure.     

Estimation of pedestrian level UV exposure under trees

Trees influence the amount of solar UV radiation that reaches pedestrians. A three-dimensional model was developed to predict the ultraviolet-B (UV-B) irradiance fields in open-tree canopies where the spacing between trees is equal to or greater than the width of individual tree crowns. The model predicted the relative irradiance (fraction of above-canopy irradiance) under both sunlit and shaded conditions under clear skies with a mean bias error of less than 0.01 and a root mean square error of 0.07. Both model and measurements showed that the locations people typically perceive as shady, low-irradiance locations in the environment can actually have significant UV-B exposure (40-60% of that under direct sunlight). The relationship of tree cover in residential neighborhoods to erythemal UV-B exposure for children and adults was modeled for the 4 h around noon in June and July. Results showed that human exposures (on the horizontal) in cities located at 15 and 30 degrees latitudes are nearly identical. For latitudes between 15 and 60 degrees, ultraviolet protection factors (UPF) were less than 2 for less than 50% tree cover. A UPF of 10 was possible at all latitudes for tree cover of 90%.     

Mean exposure fractions of human body solar UV exposure patterns for application in different ambient climates

In this research, the erythemally effective UV measured using miniaturized polysulphone dosimeters to over 1250 individual body sites and collected over a 4-year period is presented relative to the total exposed skin surface area (SSA) of a life-size manikin model. A new term is also introduced, the mean exposure fraction (MEF). The MEF is used to weight modeled or measured horizontal plane UV exposures to the total unprotected SSA of an individual and is defined as the ratio of exposure per unit area received by the unprotected skin surfaces of the body relative to the exposure received on a horizontal plane. The MEF has been calculated for a range of solar zenith angles (SZA) to provide a sunburning energy data set weighted to the actual SSA of a typically clothed individual. For this research, the MEF was determined as 0.15, 0.26 and 0.41 in the SZA ranges 0°-30°, 30°-50° and 50°-80° providing information that can be used in a variety of different ambient, latitudinal and seasonal climates where total human body UV exposure information is not available.     

Laboratory UV exposure: risk assessment and protective measures

In research laboratories ultraviolet radiation is widely used, particularly in photochemistry and photobiology, as a sterilizing agent and for the characterization of samples. The results of a survey conducted near several university laboratories are presented with the aim of quantifying exposure levels to UV-incoherent radiation and to assess individual risk for researchers and students. It has been shown that exposure is not negligible, especially if safety procedures are neglected and personal protective equipments, described in this study, are not used.     

Facial solar UV exposure of Austrian farmers during occupation

Optoelectronic personal UV-meters were used to monitor the occupational facial solar erythemally effective exposure of 12 Austrian full-time farmers with high temporal resolution. To ensure high quality measurements several quality assurance procedures were applied, like calibration with respect to solar elevation and total ozone column. From April to October the test persons carried the UV-meters on the forehead during working hours. A digital diary (activity, location, weather, photoprotective measures) was completed on an hourly basis. Our field test produced 1427 complete daily records (measurement and diary). The total exposures showed high variability (77 –757 standard erythema dose [SED]) which correlates with the number of working days and even stronger with the little numbers of days with high exposure (>10 SED). Risk factors for high exposures were: mixed-culture farms with aggravated working conditions, low degree of automation of working processes, inadequate operating logistics (summarized as manual work outdoor), driving machines without cabins, and female gender. UV exposure of female farmers was approximately twice as high as that of men: Women received 15% of ambient radiation while men got 8%. Avoiding daily exposure >10 SED could reduce exposure down to 40% and the risk in developing skin cancer by a factor of 40.     

Degradation products formed during UV exposure of polyethylene-ZnO nano-composites

Photodegradation of low density polyethylene (LDPE) containing nano-particulate ZnO has been studied using FTIR to follow the development of oxidation products in the polymer film and to monitor carbon dioxide evolved as a principal product of oxidation. The degradation behaviour of ZnO-free LDPE has been compared with that of compounds containing 0.25% and 0.75% ZnO and these results are compared with those obtained using similar films containing nano-particulate TiO₂. Under UV exposure, the presence of ZnO accelerated the development of carbonyl groups and CO₂ production. The carbonyl group development was more rapid when TiO₂ was used whereas ZnO caused greater CO₂ generation. Carbonyl group development seemed to correlate better with the reduction in mechanical properties whereas CO₂ generation correlated better with weight change measurements. The influence of ZnO on the oxidation pathways in LDPE is discussed; it is proposed that photo-oxidation is relatively much more likely to occur at terminal sites (rather than at pendent sites) when ZnO is present.     

UVA exposure affects UVB and cis-urocanic acid-induced systemic suppression of immune responses in Listeria monocytogenes-infected Balb/c mice

Ultraviolet radiation can inhibit immune responses locally as well as systemically. Such effects have been measured in animals and humans exposed to ultraviolet B (wavelength 280-315 nm) (UVB) and ultraviolet A (315-400 nm) (UVA). The precise wavelength dependence is important for the identification of possible molecular targets and for assessments of risk of different artificial UV sources and solar UV. In such analyses, it is commonly assumed that radiation energy from each wavelength contributes to the effect independent of the other wavelengths. Here we show that this assumption does not hold good. In the present study, it was investigated whether exposure to broadband UVA or longwave ultraviolet A 1 (340-400 nm) (UVA 1) prior to the standard immunosuppressive UVB protocol might modulate the immunosuppressive effects induced by UVB. Preexposure to broadband UVA or longwave UVA 1, 1 day prior to the standard immunosuppressive UVB protocol, inhibited the UVB-induced suppression of delayed type hypersensitivity (DTH) to Listeria monocytogenes significantly. This effect was not associated with restoring the number of interleukin (IL-12)-positive cells in the spleen. Since isomerization of trans-urocanic acid (UCA) into the immunosuppressive cis-UCA isomer plays a crucial role in UVB-induced immunomodulation, in a second set of experiments it was investigated whether immunosuppression induced by cis-UCA might also be downregulated by preexposure to UVA. Animals were exposed to broad-band UVA or longwave UVA 1 prior to application of an immunosuppressive dose of cis- or trans-UCA as a control. Both UVA and UVA 1 appear to inhibit the cis-UCA-induced systemic immunosuppression (DTH and IL-12) to L. monocytogenes. These studies clearly show that UVA radiation modulates both UVB and cis-UCA-induced immunomodulation. In general, our studies indicate that both broadband UVA and longwave UVA 1 could induce modulation of UVB and cis-UCA-induced immunomodulation. As sunlight contains both UVA and UVB radiation the balance between these two radiations apparently determines the net immunomodulatory effect.     

Pretilt angle generation by UV exposure during imidization of polyimide

We investigated pretilt angle generation and liquid crystal (LC) alignment by ultraviolet exposure during the imidization of polyimide (PI). The generated pretilt angle of a nematic (N) LC using an in situ photo-alignment method is smaller than that using a conventional photo-alignment method on a surface of PI having side chains. The NLC pretilt angles using an in situ photo-alignment method injected at isotropic phase increased with annealing were observed.     

Pretilt angle generation by UV exposure during imidization of polyimide

We investigated pretilt angle generation and liquid crystal (LC) alignment by ultraviolet exposure during the imidization of polyimide (PI). The generated pretilt angle of a nematic (N) LC using an in situ photo-alignment method is smaller than that using a conventional photo-alignment method on a surface of PI having side chains. The NLC pretilt angles using an in situ photo-alignment method injected at isotropic phase increased with annealing were observed.     

Short-term UV exposure of sunbathers at a Mediterranean Sea site

The aim of this study was to investigate whether systematic differences in solar UV exposure on a specific anatomical site (chest) exist among three groups of Italian sunbathers: healthy subjects (suntanned and non-suntanned individuals) and subjects affected by abnormally high sensitivity to solar exposure. A second aim of the study was to search for a possible relation among biological markers of individual response to UV exposure (such as skin colorimetric parameters, skin temperature and changes in free radical amounts [FR] in the blood) and photosensitivity. FR in the blood were analyzed because of their possible influence on UV carcinogenesis. Measurements of ambient doses (i.e. incident erythemally weighted irradiance on a horizontal surface over a specified period of time) and erythemally effective UV dose received by an anatomical site (here called personal dose or exposure on a specific anatomical site) were investigated. Personal doses received by the chest were determined using polysulfone dosimetry. Exposure Ratio (ER), defined as the ratio between the personal dose and the corresponding ambient dose during the same exposure period, was then calculated. Measuring of skin color in the Commission Internationale de l'Eclairage L (luminance), a (redness), b (yellowness) system and skin temperature were also carried out on the inner upper arm (nonexposed skin site) and on the chest. It was found that the median value of ER was 0.20 (min: 0.09 and max: 0.34) for suntanned individuals, it was 0.17 (min: 0.13 and max: 0.42) for non-suntanned individuals and it was 0.19 (min: 0.14 and max: 0.34) for photosensitive individuals. There were no significant differences across the groups in their median ER scores. In addition, the statistical analysis showed that L on the exposed site before exposure demonstrated consistently higher median scores after exposure in all groups. The b value after exposure was significantly lower than before exposure in all participants, while no significant differences for a were observed before or after exposure between or within the groups. Our findings suggest that photodermatoses are not significantly related to ER and to the changes in biological markers due to too short-term UV exposure.     

Adjusting timing of weathering test to account for seasonal variations in UV exposure

Satellite-derived UV climatology has been used to design a timetable for the outdoor UV exposure of polymeric material specimens. By pre-exposure computation, fixed time increments are transformed into a schedule with a predicted average accumulation of UV dose. The method was applied to produce a timetable for an ongoing exposure programme in a network of seven European test sites over the latitude range 28.5-67.4°N. The effect of the average seasonal variability of solar UV irradiance on the predicted accumulated UV exposure is shown to be notably diminished by the method. Relative underestimations of 5-82% of cumulative UV stress are estimated to be avoided by extensions of 6-167 days exposure durations as suggested by the adjustment procedure. Hence, more reproducible degradation data are expected to be obtainable for exposures that are not multiples of the full annual cycle of UV, especially for those with a duration <1 year.     

Evaluation of a high exposure solar UV dosimeter for underwater use

Solar ultraviolet radiation (UV) is known to have a significant effect upon the marine ecosystem. This has been documented by many previous studies using a variety of measurement methods in aquatic environments such as oceans, streams and lakes. Evidence gathered from these investigations has shown that UVB radiation (280-320 nm) can negatively affect numerous aquatic life forms, while UVA radiation (320-400 nm) can both damage and possibly even repair certain types of underwater life. Chemical dosimeters such as polysulphone have been tested to record underwater UV exposures and in turn quantify the relationship between water column depth and dissolved organic carbon levels to the distribution of biologically damaging UV underwater. However, these studies have only been able to intercept UV exposures over relatively short time intervals. This paper reports on the evaluation of a high exposure UV dosimeter for underwater use. The UV dosimeter was fabricated from poly 2,6-dimethyl-1,4-phenylene oxide (PPO) film. This paper presents the dose response, cosine response, exposure additivity and watermarking effect relating to the PPO dosimeter as measured in a controlled underwater environment and will also detail the overnight dark reaction and UVA and visible radiation response of the PPO dosimeter, which can be used for error correction to improve the reliability of the UV data measured by the PPO dosimeters. These results show that this dosimeter has the potential for long-term underwater UV exposure measurements.     

Near-infrared exposure changes cellular responses to ionizing radiation

Near infrared (NIR) and X-rays are radiations from different sides of the wavelength spectrum but both are used during medical treatments, as they have severe impacts on cellular processes, including metabolism, gene expression, proliferation and survival. However, both radiations differ strictly in their consequences for exposed patients: NIR effects are generally supposed to be positive, mostly ascribed to a stimulation of metabolism, whereas X-ray leads to genetic instability, an increase of reactive oxygen species (ROS) and DNA damages and finally to cellular death by apoptosis in tumor cells. Since genomic stability after X-irradiation depends on the mitochondrial metabolism, which is well known to be regulated by NIR, we analyzed the impact of NIR on cellular responses of fibroblasts, retinal progenitor cells and keratinocytes to X-radiation. Our data show that previous exposure to naturally occurring doses of nonthermal NIR combined with clinically relevant X-ray doses leads to (1) increased genomic instability, indicated by elevated ratios of mitotic catastrophes, (2) increased ROS, (3) higher amounts of X-irradiated cells entering S-phase and (4) impaired DNA double-strand break repair. Taken together, our data show tremendous effects of NIR on cellular responses to X-rays, probably affecting the results of radiotherapy after NIR exposure during cancer treatment.     

Ultrasound measurements of skin thickness after UV exposure: a feasibility study

High-frequency ultrasound images were used to measure the thickness of the dermis and epidermis of four human subjects. These measurements were performed before and after a single exposure to ultraviolet radiation (UV). Doses ranging from 0.5 to 3 minimal erythema doses (MED) were delivered to the skin of the back of four human subjects, and thickness measurements were made over a period of 16 days. We found: (1) exposures > or = 2 MED caused a 10-30% increase in the thickness of the dermis-epidermis layer; (2) the thickening response was not always in direct proportion to the UV dose; (3) maximum thickening response time was 48 h for the 2.8-3.0 MED exposure levels; (4) "diffusion" or spreading of the thickening response to neighboring areas occurred in some cases, as far as 4 cm from the exposed region (center-to-center), with changes ranging from 12% to 17%; (5) decreased thickness of the dermis-epidermis layer of up to 12% was observed for 3 out of 4 of the subjects.     

Retinal phototoxicity induced by hydrochlorothiazide after exposure to a UV tanning device

Abstract UV radiation is known to cause acute and chronic eye and skin damage. The present case report describes the occurrence of hydrochlorothiazide-induced retinal phototoxicity immediately after exposure to UV light emanated from a sunbed in a 40-year-old myopic woman. During the tanning session she had always worn UV protective eyewear, except for a few minutes when she took the protective goggles off to put her spectacles on to locate and turn the timer switch off. At baseline her visual acuity was 10/25 in OD and 10/80 in OS. Fundus examination revealed the presence of retinal lesions in both eyes. More specific tests confirmed the presence of a phototoxic macular damage. Hydrochlorothiazide was discontinued, and she was recommended to wear UV filtering glasses. Over the follow-up period (12 months), a slow and progressive visual acuity recovery in both eyes occurred. At the last check the visual acuity improvement was of about 60% from baseline in both eyes. Fundus examination showed only a juxtafoveal flat pigmented scar of the retinal pigment epithelium in both eyes, milder in OD. The constant rise in the number of sunbed users makes the knowledge of UV-related side effects a problem that cannot be postponed further. Awareness of the general public about the harmful effects of UV exposure must represent one of the leading preventive health strategies. Therefore, a careful analysis of the medical history before the admission to a sunbed session throughout a questionnaire could represent an economic and effective measure to avoid further cases of a phototoxic macular damage in patients taking photosensitizing compounds.     

Vibrational spectroscopic characterization of ethylene-Co-vinyl cinnamate copolymers before and after UV exposure

Vibrational spectroscopic studies of a series of ethylene-co-vinyl cinnamate (EVCIN) copolymers, before and after exposure to UV radiation, are reported. The purpose of these studies is to determine whether or not significant reaction (photo-crosslinking) of the cinnamate groups in EVCIN copolymers occurs upon UV exposure in the solid state as the concentration (fraction) of cinnamate groups is systematically reduced. By increasing the ethylene concentration in the EVCIN copolymers the cinnamate groups are “diluted” and progressively spaced apart in the copolymer. Somewhat surprisingly, we find that an EVCIN copolymer containing only 5 mole % vinyl cinnamate still undergoes a facile crosslinking in the solid state upon UV exposure.     

Sensitivity of erythemally effective UV irradiance and daily exposure to temporal variability in total ozone

The provision of information to the public about current levels of the erythemally effective UV radiation is an important issue in health care. The quality of promoted values is therefore of special importance. The atmospheric parameter which affects the erythemally effective UV radiation under clear sky most is the total ozone content of the atmosphere. In this paper we examined the sensitivity of the erythemally effective irradiance and daily radiant exposure to the temporal variability of total ozone on time scales from 1 to 15 days. The results show that the sensitivity is highest for the first 24 h. Larger time scales do not exhibit a similar influence. Total ozone measurements of the previous day may already cause uncertainties higher than 0.5 UV index (UVI) independent of the geolocation. For comparison, a temporal persistence of 15 days may cause uncertainties of 1.2 UVI at 50°N, 1 UVI at 30°S and less than 1 UVI at the equator. The results of this study allow finding the necessary temporal resolution of total ozone values when a certain accuracy for the UVI or for the purpose of sun protection is required. The results are compared with those of two preceding studies where we quantified the influence of measurement uncertainties and spatial total ozone variability to the erythemally effective irradiance at noon and to the daily dose. We conclude that temporal variability of total ozone is the most critical issue, but also measurement uncertainties do have a noticeable influence on the erythemally effective radiation.