Showing papers on "Ultraviolet light published in 2000"

Role of oxygen vacancy in the plasma-treated TiO2 photocatalyst with visible light activity for NO removal

Abstract: The photocatalytic activity for NO removal under an oxidative atmosphere has been studied over commercial TiO 2 and plasma-treated TiO 2 powders. By the plasma treatment, the photocatalytic activity for NO removal appeared in the visible light region up to 600 nm without a decrease in the ultraviolet light activity. It was found that the NO was removed as nitrate (NO 3 − ) by photocatalytic oxidation over the TiO 2 powders, where NO 3 − was accumulated. No difference in the crystal structure, the crystallinity, and the specific surface area was observed between the raw TiO 2 and the plasma-treated TiO 2 photocatalysts. In electron spin resonance (ESR) measurements, a sharp signal at g =2.004, which was identified as the electrons trapped on oxygen vacancies, was detected only for plasma-treated TiO 2 under visible light irradiation. The saturated intensity of the ESR signal at g =2.004 was proportional to the removal percentage of nitrogen oxides, suggesting that the number of trapped electrons determined the activity for the photocatalytic oxidation of NO to NO 3 − . The appearance of the visible light activity in the plasma-treated TiO 2 photocatalyst was ascribed to the newly formed oxygen vacancy state between the valence and the conduction bands in the TiO 2 band structure.

P53 Binding Protein 1 (53bp1) Is an Early Participant in the Cellular Response to DNA Double-Strand Breaks

Abstract: p53 binding protein 1 (53BP1), a protein proposed to function as a transcriptional coactivator of the p53 tumor suppressor, has BRCT domains with high homology to the Saccharomyces cerevisiae Rad9p DNA damage checkpoint protein. To examine whether 53BP1 has a role in the cellular response to DNA damage, we probed its intracellular localization by immunofluorescence. In untreated primary cells and U2OS osteosarcoma cells, 53BP1 exhibited diffuse nuclear staining; whereas, within 5–15 min after exposure to ionizing radiation (IR), 53BP1 localized at discreet nuclear foci. We propose that these foci represent sites of processing of DNA double-strand breaks (DSBs), because they were induced by IR and chemicals that cause DSBs, but not by ultraviolet light; their peak number approximated the number of DSBs induced by IR and decreased over time with kinetics that parallel the rate of DNA repair; and they colocalized with IR-induced Mre11/NBS and γ-H2AX foci, which have been previously shown to localize at sites of DSBs. Formation of 53BP1 foci after irradiation was not dependent on ataxia-telangiectasia mutated (ATM), Nijmegen breakage syndrome (NBS1), or wild-type p53. Thus, the fast kinetics of 53BP1 focus formation after irradiation and the lack of dependency on ATM and NBS1 suggest that 53BP1 functions early in the cellular response to DNA DSBs.

Existing and potential applications of ultraviolet light in the food industry - a critical review

Abstract: Short-wave ultraviolet light (UVC, 254 nm) can reduce dramatically the microbial load in air or on hard surfaces free from food residues, and can eliminate pathogens from potable water filtered to remove organic residues and 'clumps' of bacteria. More recently, approval of the Food and Drug Administration (USA) has been sought for a system for the destruction of pathogenic bacteria in fruit juices using UVC, and the same approach could perhaps be applied to remove spoilage organisms from cider or wines. In contrast, long-wave UV light (UVA, >320 nm) has limited microbiocidal properties, and for practical applications its effectiveness has to be enhanced by the presence of photosensitive compounds (eg furocoumarins) that will diffuse into a microbial cell prior to irradiation. The penetration of UVA into water is better than that of UVC, and its bacteriocidal action in the presence of photosensitisers can be rapid. However, pure furocoumarins are expensive and their addition to foodstuffs might be questioned on safety grounds. © 2000 Society of Chemical Industry.

Photoreactivity of Unsaturated Compounds with Hydrogen-Terminated Silicon(111)

Abstract: We report the photoreactivity of H−Si(111) with dioxygen and terminally unsaturated hydrocarbons. Illumination of H−Si(111) in air with ultraviolet light of wavelength of 350 nm or shorter produces oxidized silicon; longer wavelengths cause no oxidation. When H−Si(111) is immersed in unsaturated hydrocarbons (1-octene, 1-octadecene, 1-octyne, styrene, and phenylacetylene) that have been deoxygenated, illumination with a Hg lamp results in densely packed hydrocarbon films of molecular thickness. Previous work and the results presented here suggest that the H−Si bond adds across the unsaturated bond in these reactions similar to hydrosilylation reactions known for small-molecule chemistry and produce adsorbates covalently bonded to the surface. We present spectroscopic evidence showing films resulting from terminal acetylenes consist of adsorbates linked to the surface by a vinyl group. We propose that all of these reactions occur through a radical-chain mechanism initiated by the wavelength-dependent photo...

ATM phosphorylation of Nijmegen breakage syndrome protein is required in a DNA damage response.

Abstract: Nijmegen breakage syndrome (NBS) is characterized by extreme radiation sensitivity, chromosomal instability and cancer1 The phenotypes are similar to those of ataxia telangiectasia mutated (ATM) disease, where there is a deficiency in a protein kinase that is activated by DNA damage, indicating that the Nbs and Atm proteins may participate in common pathways Here we report that Nbs is specifically phosphorylated in response to γ-radiation, ultraviolet light and exposure to hydroxyurea Phosphorylation of Nbs mediated by γ-radiation, but not that induced by hydroxyurea or ultraviolet light, was markedly reduced in ATM cells In vivo, Nbs was phosphorylated on many serine residues, of which S343, S397 and S615 were phosphorylated by Atm in vitro At least two of these sites were underphosphorylated in ATM cells Inactivation of these serines by mutation partially abrogated Atm-dependent phosphorylation Reconstituting NBS cells with a mutant form of Nbs that cannot be phosphorylated at selected, ATM-dependent serine residues led to a specific reduction in clonogenic survival after γ-radiation Thus, phosphorylation of Nbs by Atm is critical for certain responses of human cells to DNA damage

Molecular pathology of cyclooxygenase-2 in neoplasia

Abstract: Cyclooxygenase (COX)-2 levels are elevated in several types of human cancer tissues. Nonselective nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit both the COX-1 and COX-2 protein, the two enzymes that convert arachidonic acids to prostaglandins. Regular use of such NSAIDs significantly reduces the risk and spread of some cancers. The objective of this study was to elucidate the molecular pathology of neoplasms that overexpress COX-2. Epidemiological data and clinical studies were analyzed and compared with results of studies of human tumor tissues, animal models, and cultured tumor cells. COX-2, but not COX-1, is highly expressed in human colon carcinoma, squamous cell carcinoma of the esophagus, and skin cancer. COX-2 is inducible by oncogenes ras and scr, interleukin-1, hypoxia, benzo[a]pyrene, ultraviolet light, epidermal growth factor, transforming growth factor beta, and tumor necrosis factor alpha. Dexamethasone, antioxidants, and tumor-suppressor protein p53 suppress COX-2 expression. COX-2 synthesizes prostaglandin E2 (PGE2) which stimulates bcl-2 and inhibits apoptosis, and induces interleukin-6 (IL-6) which enhances haptoglobin synthesis. PGE2 is associated with tumor metastases, IL-6 with cancer cell invasion, and haptoglobin with implantation and angiogenesis. Drastic reduction in polyp number results from COX-2 gene knockout as well as from selective COX-2 inhibition in a mouse model of human familial adenomatous polyposis. Nonselective NSAIDs, for instance aspirin, and selective COX-2 inhibitors such as celecoxib (SC-58635) and NS-398 suppress azoxymethane-induced colon carcinogenesis in rats. Aspirin, indomethacin, and ibuprofen decrease cultured lung cancer cell proliferation. Selective inhibition of COX-2 is preferable to nonselective inhibition. It reduces cancer cell proliferation, induces cancer cell apoptosis, and spares COX-1-induced cytoprotection of the gastrointestinal tract.

Photocrosslinkable chitosan as a biological adhesive.

Abstract: A photocrosslinkable chitosan to which both azide and lactose moieties were introduced (Az-CH-LA) was prepared as a biological adhesive for soft tissues and its effectiveness was compared with that of fibrin glue. Introduction of the lactose moieties resulted in a much more water-soluble chitosan at neutral pH. Application of ultraviolet light (UV) irradiation to photocrosslinkable Az-CH-LA produced an insoluble hydrogel within 60 s. This hydrogel firmly adhered two pieces of sliced ham with each other, depending upon the Az-CH-LA concentration. The binding strength of the chitosan hydrogel prepared from 30-50 mg/mL of Az-CH-LA was similar to that of fibrin glue. Compared to the fibrin glue, the chitosan hydrogel more effectively sealed air leakage from pinholes on isolated small intestine and aorta and from incisions on isolated trachea. Neither Az-CH-LA nor its hydrogel showed any cytotoxicity in cell culture tests of human skin fibroblasts, coronary endothelial cells, and smooth muscle cells. Furthermore, all mice studied survived for at least 1 month after implantation of 200 microL of photocrosslinked chitosan gel and intraperitoneal administration of up to 1 mL of 30 mg/mL of Az-CH-LA solution. These results suggest that the photocrosslinkable chitosan developed here has the potential of serving as a new tissue adhesive in medical use.

Sample preparation in the determination of phenolic compounds in fruits

Abstract: Phenolic compounds occur as secondary metabolites in all plants.1 They embrace a considerable range of substances possessing an aromatic ring bearing one or more hydroxy substituents, although a more precise definition is based on metabolic origin as those substances derived from the shikimate pathway and phenylpropanoid metabolism.2 A convenient classification of the plant phenols distinguishes the number of constitutive carbon atoms in conjunction with the structure of the basic phenolic skeleton (Table 1). The range of known phenolics is thus vast and also includes polymeric lignins and condensed tannins. Some plant phenols may be involved in primary metabolism whereas others have an effect on plant growth or protect the more vulnerable cell constituents against photooxidation by ultraviolet light by virtue of their strong UV absorption.3 Plant phenols also play an important role in disease resistance in the plant. Intense interest in fruit phenolics is also related to their physiological activity which depends on their antioxidant activity, the ability to scavenge both active oxygen species and electrophiles, the ability to inhibit nitrosation and to chelate metal ions, the potential for autooxidation and the capability to modulate certain cellular enzyme activities.4–7 Thus, knowledge of the levels of these compounds in plants is of considerable interest but is limited by problems of analysis. The structural diversity of the phenolics and its effect on physicochemical behaviour such as solubility and analyte recovery presents a challenging analytical problem. Moreover, a number of phenolic compounds are easily hydrolysed and many are relatively easily oxidized, which further complicates sample handling.8,9 This review emphasises the importance of sample preparation in the determination of phenolic compounds in plant materials particularly fruits. Fruits are an important dietary source of phenolic substances although interest is also shifting to other parts of the plant as potential commercial sources of phenols. Sample preparation is a critical step in analysis and this is even more significant with real samples where the matrix components are biologically active and the analytes represent a diverse spectrum of numerous compounds, many having an unknown identity. Thus, methods of extraction of phenols from fruits are generally dependent on several factors while the usual quantification procedures involve the separation sciences and are universally applicable. Soleas et al.10 illustrated this point. They developed a derivatization procedure for determination of 15 phenolic constituents in solid vitaceous plant materials and concluded that the method ‘should be suitable to measure polyphenols in fruit, vegetables, and other foods provided that efficient extraction techniques are employed’. Such statements are seen frequently in the analytical literature but they tend to belittle the importance of this step (or perhaps they serve to underline its critical importance). Rhodes and Price11 observed that the determination of phenolic species in foods is an important outstanding problem and reviewed methods for the extraction and purification of phenolic antioxidants as the conjugated forms that exist in plant foods. Knowledge of the extraction of phenolics is also desirable outside the analytical context for it has important practical applications in the food industry. For instance, the mechanism and kinetics of phenolic extraction from wood to wine during ageing in barrels12 has significant consequences for the production of quality wines.

Autofluorescence imaging system for endoscopy

Abstract: A system and method for imaging tissue autofluorescence through a video endoscope is described, comprising a light source capable of providing both ultraviolet light capable of inducing tissue autofluorescence and visible light which induces little or no autofluorescence, an optical system to deliver both wavelength bands to the tissue with the same apparent spatial and angular intensity distribution, a means for digitally acquiring the resulting, visible fluorescence and visible reflectance images using a single imaging detector at the distal tip of the endoscope and a means for digitally processing said images to generate a final, false-color image for display which indicates regions of tissue dysplasia. This system can either be added on to an existing video endoscope or integrated into its structure. The combined system can be electronically switched between normal white light imaging and fluorescence imaging.

Oxidative Processes Occurring When Pulsed High Voltage Discharges Degrade Phenol in Aqueous Solution

Abstract: In this investigation, results obtained using a pulsed discharge for organic compound removal are presented. The degradation of phenol by a streamer corona discharge and spark discharge, the effects of hydrogen peroxide additive on removal efficiency, and photochemical oxidation by ultraviolet light from the discharge plasma channel were investigated. The intermediate products and final byproducts formed by the spark discharge were also studied. A preliminary study of the degradation mechanism inside and outside the plasma channel was carried out. It was found that the removal efficiency of organic contaminants in the aqueous solution was higher for the spark discharge than for the streamer corona discharge and was greatly influenced by the discharge type and additive. The energy efficiency was the highest (6.91 × 10-3 μmol/J) for the case with hydrogen peroxide injection and spark discharge. The main intermediate products produced by the spark discharge during the treatment process were hydroquinone, pyr...

Vaccinia as a vector for tumor-directed gene therapy: Biodistribution of a thymidine kinase-deleted mutant

Abstract: Tumor-directed gene therapy, such as "suicide gene" therapy, requires high levels of gene expression in a high percentage of tumor cells in vivo to be effective. Current vector strategies have been ineffective in achieving these goals. This report introduces the attenuated (thymidine kinase (TK)-negative) replication-competent vaccinia virus (VV) as a potential vector for tumor-directed gene therapy by studying the biodistribution of VV in animal tumor models. A TK-deleted recombinant VV (Western Reserve strain) expressing luciferase on a synthetic promoter was constructed. Luciferase activity was measured in vitro after transduction of a variety of human and murine tumor cell lines and in vivo after intraperitoneal (i.p.) delivery in C57BL/6 mice with 7-day i.p. tumors (10(6) MC-38 cells). Three other in vivo tumor models were examined for tumor-specific gene expression after intravenous delivery of VV (human melanoma in nude mice, adenocarcinoma liver metastasis in immunocompetent mice, and subcutaneous sarcoma in the rat). In addition, a replication-incompetent vaccinia (1 microg of psoralen and ultraviolet light, 365 nm, 4 minutes) was tested in vitro and in vivo and compared with active virus. Luciferase activity in i.p. tumors at 4 days after i.p. injection of VV was >7000-fold higher than lung, >3000-fold higher than liver, and >250-fold higher than ovary. In addition, intravenous injection of VV resulted in markedly higher tumor luciferase activity compared with any other organ in every model tested (up to 188,000-fold higher than liver and 77,000-fold higher than lung). Inactivation of the virus resulted in negligible gene expression in vivo. In summary, VV has a high transduction efficiency in tumor cells with high levels of gene expression. The results suggest a selective in vivo replication of TK-deleted VV in tumor cells. Replication competent, TK-deleted VV appears to be an ideal vector for testing the in vivo delivery of toxic genes to tumor cells.

Green Tea Polyphenol Treatment to Human Skin Prevents Formation of Ultraviolet Light B-induced Pyrimidine Dimers in DNA

Abstract: Cancer chemopreventive effects of polyphenols from green tea (GTP) in mouse models of photocarcinogenesis are established. The present study is extended from mouse model to human system in vivo to determine the effect of topical application of GTP to human individuals against UV light-induced DNA damage in the form of cyclobutane pyrimidine dimers (CPDs) in the skin. UVB-induced CPDs were detected by immunohistochemical technique using monoclonal antibodies to thymine dimers. With the gradual increase in UVB dose, both erythema response and CPD formation in the skin was increased. GTP treatment inhibited both UVB-induced erythema response as well as CPD formation. Topical treatment with GTP (approximately 1 mg/cm2 of skin area) 20 min before human buttock skin (sun-protected site) exposure to UVB inhibited CPD formation in epidermis by 81, 70, 60, and 60% at 0.5, 1.0, 2.0, and 4.0 minimal erythema dose of UV exposure, respectively. Treatment of human skin with varying doses of GTP (1-4 mg/2.5 cm2 of skin area) before a single dose of UVB exposure (4.0 minimal erythema dose) decreased dose dependently the formation of UVB-induced CPDs in both epidermis and dermis. The inhibition of UVB-induced CPDs by GTP treatment may be, at least in part, responsible for the inhibition of photocarcinogenesis. Our data suggest that GTP may be used as a novel chemopreventive candidate and possible strategy to reduce UV-induced skin cancer risk in the human population.

Far Ultraviolet Imaging from the Image Spacecraft. 2. Wideband FUV Imaging

Abstract: The Far Ultraviolet Wideband Imaging Camera (WIC) complements the magnetospheric images taken by the IMAGE satellite instruments with simultaneous global maps of the terrestrial aurora. Thus, a primary requirement of WIC is to image the total intensity of the aurora in wavelength regions most representative of the auroral source and least contaminated by dayglow, have sufficient field of view to cover the entire polar region from spacecraft apogee and have resolution that is sufficient to resolve auroras on a scale of 1 to 2 latitude degrees. The instrument is sensitive in the spectral region from 140-190 nm. The WIC is mounted on the rotating IMAGE spacecraft viewing radially outward and has a field of view of 17° in the direction parallel to the spacecraft spin axis. Its field of view is 30° in the direction perpendicular to the spin axis, although only a 17° x 17° image of the Earth is recorded. The optics was an all-reflective, inverted Cassegrain Burch camera using concentric optics with a small convex primary and a large concave secondary mirror. The mirrors were coated by a special multi-layer coating, which has low reflectivity in the visible and near UV region. The detector consists of a MCP-intensified CCD. The MCP is curved to accommodate the focal surface of the concentric optics. The phosphor of the image intensifier is deposited on a concave fiberoptic window, which is then coupled to the CCD with a fiberoptic taper. The camera head operates in a fast frame transfer mode with the CCD being read approximately 30 full frames (512 x 256 pixel) per second with an exposure time of 0.033 s. The image motion due to the satellite spin is minimal during such a short exposure. Each image is electronically distortion corrected using the look up table scheme. An offset is added to each memory address that is proportional to the image shift due to satellite rotation, and the charge signal is digitally summed in memory. On orbit, approximately 300 frames will be added to produce one WIC image in memory. The advantage of the electronic motion compensation and distortion correction is that it is extremely flexible, permitting several kinds of corrections including motions parallel and perpendicular to the predicted axis of rotation. The instrument was calibrated by applying ultraviolet light through a vacuum monochromator and measuring the absolute responsivity of the instrument. To obtain the data for the distortion look up table, the camera was turned through various angles and the input angles corresponding to a pixel matrix were recorded. It was found that the spectral response peaked at 150 nm and fell off in either direction. The equivalent aperture of the camera, including mirror reflectivities and effective photocathode quantum efficiency, is about 0.04 cm2. Thus, a 100 Rayleigh aurora is expected to produce 23 equivalent counts per pixel per 10 s exposure at the peak of instrument response.

Efficient Nonlinear Frequency Conversion in an All-Resonant Double- Λ System

Abstract: We demonstrate efficient, pulsed, gas-phase, nonlinear frequency conversion in a quadruply resonant, double- $\ensuremath{\Lambda}$ system and, simultaneously, verify theoretical predictions of Rabi-frequency matching unique to absorbing nonlinear media. This system is used to up-convert ultraviolet light at 233 nm to the vacuum ultraviolet at 186 nm in atomic Pb vapor with small-signal conversion efficiencies exceeding $30%$ and with modest atomic density-length (NL) products (scale ${10}^{14}{\mathrm{cm}}^{\ensuremath{-}2}$) and optical power densities $(10--100\mathrm{kW}/{\mathrm{cm}}^{2})$.

A new application of UV-ozone treatment in the preparation of substrate-supported, mesoporous thin films

Abstract: A nominally room temperature photochemical method, simply employing ultraviolet light- (187−254 nm) generated ozone environment, is shown to provide an efficient alternative for the removal of surfactant templates for a routine production of mesoporous silica thin films at low temperatures. The treatment concomitantly strengthens the silicate phase by fostering the condensation of unreacted silanols leading to mesoporous thin films with well-defined mesoscopic morphologies. The surfactant/silicate thin film mesophases were prepared onto a polycrystalline Au surface by dip-coating or spin-casting methods using sub-critical micelle concentration (cmc) nonionic ethylene oxide surfactant in an oligomeric silica sol mixture. The structures and compositions of the thin film mesophases before and after exposure to UV/ozone were determined using a combination of reflection−absorption Fourier transform infrared spectroscopy, transmission electron microscopy, and thin film X-ray diffraction measurements. The pore c...

Immobilizing the Moving Parts of Voltage-Gated Ion Channels

Abstract: Voltage-gated ion channels have at least two classes of moving parts, voltage sensors that respond to changes in the transmembrane potential and gates that create or deny permeant ions access to the conduction pathway. To explore the coupling between voltage sensors and gates, we have systematically immobilized each using a bifunctional photoactivatable cross-linker, benzophenone-4-carboxamidocysteine methanethiosulfonate, that can be tethered to cysteines introduced into the channel protein by mutagenesis. To validate the method, we first tested it on the inactivation gate of the sodium channel. The benzophenone-labeled inactivation gate of the sodium channel can be trapped selectively either in an open or closed state by ultraviolet irradiation at either a hyperpolarized or depolarized voltage, respectively. To verify that ultraviolet light can immobilize S4 segments, we examined its relative effects on ionic and gating currents in Shaker potassium channels, labeled at residue 359 at the extracellular end of the S4 segment. As predicted by the tetrameric stoichiometry of these potassium channels, ultraviolet irradiation reduces ionic current by approximately the fourth power of the gating current reduction, suggesting little cooperativity between the movements of individual S4 segments. Photocross-linking occurs preferably at hyperpolarized voltages after labeling residue 359, suggesting that depolarization moves the benzophenone adduct out of a restricted environment. Immobilization of the S4 segment of the second domain of sodium channels prevents channels from opening. By contrast, photocross-linking the S4 segment of the fourth domain of the sodium channel has effects on both activation and inactivation. Our results indicate that specific voltage sensors of the sodium channel play unique roles in gating, and suggest that movement of one voltage sensor, the S4 segment of domain 4, is at least a two-step process, each step coupled to a different gate.

Stimulatory effect of oral administration of green tea or caffeine on ultraviolet light-induced increases in epidermal wild-type p53, p21(WAF1/CIP1), and apoptotic sunburn cells in SKH-1 mice.

Abstract: Pretreatment of SKH-1 mice with p.o.-administered 0.6% green tea (6 mg of lyophilized tea solids/ml) or 0.044% caffeine (0.44 mg/ml; concentration present in 0.6% green tea) for 2 weeks enhanced UV-induced increases in the number of p53-positive cells, p21(WAF1/CIP1)-positive cells, and apoptotic sunburn cells in the epidermis. These effects of p.o.-administered green tea or caffeine on early adaptive responses to UV provide the first demonstration of in vivo up-regulation of a tumor suppressor gene by a chemopreventive agent. The stimulatory effect of green tea and caffeine on UV-induced increases in the number of p53-positive cells, p21(WAF1/CIP1)-positive cells, and apoptotic sunburn cells may play a role in the inhibitory effects of tea and caffeine on UV-induced carcinogenesis.

Phosphors for down converting ultraviolet light of LEDs to blue-green light

Abstract: There is provided a blue-green illumination system, comprising a light emitting diode, and at least one luminescent material having at least two peak emission wavelengths, wherein the emission CIE color coordinates of the at least two peak emission wavelengths are located within an area of a pentagon on a CIE chromaticity diagram, whose corners have the following CIE color coordinates: e) x=0.0137 and y=0.4831; b) x=0.2240 and y=0.3890; c) x=0.2800 and y=0.4500; g) x=0.2879 and y=0.5196; and h) x=0.0108 and y=0.7220. The illumination system may be used as the green light of a traffic signal. The luminescent material may be a blend of (Ba 1-x Eu x )Mg 2 Al 6 O 27 (“BAM”) and (Ba 1-x Eu x )Mg 2-y Mn y Al 16 O 27 (“BAMMn”) phosphors, where 0

UV-Induced stabilization of c-fos and other short-lived mRNAs.

Abstract: Irradiation of cells with short-wavelength ultraviolet light (UVC) changes the program of gene expression, in part within less than 15 min. As one of the immediate-early genes in response to UV, expression of the oncogene c-fos is upregulated. This immediate induction is regulated at the transcriptional level and is transient in character, due to the autocatalyzed shutoff of transcription and the rapid turnover of c-fos mRNA. In an experiment analyzing the kinetics of c-fos mRNA expression in murine fibroblasts irradiated with UVC, we found that, in addition to the initial transient induction, c-fos mRNA accumulated in a second wave starting at 4 to 5 h after irradiation, reaching a maximum at 8 h, and persisting for several more hours. It was accompanied by an increase in Fos protein synthesis. The second peak of c-fos RNA was caused by an UV dose-dependent increase in mRNA half-life from about 10 to 60 min. With similar kinetics, the mRNAs of other UV target genes (i.e., the Kin17 gene, c-jun, IkappaB, and c-myc) were stabilized (e.g., Kin17 RNA from 80 min to more than 8 h). The delayed response was not due to autocrine cytokine secretion with subsequent autostimulation of the secreting cells or to UV-induced growth factor receptor activation. Cells unable to repair UVC-induced DNA damage responded to lower doses of UVC with an even greater accumulation of c-fos and Kin17 mRNAs than repair-proficient wild-type cells, suggesting that a process in which a repair protein is involved regulates mRNA stability. Although resembling the induction of p53, a DNA damage-dependent increase in p53 was not a necessary intermediate in the stabilization reaction, since cells derived from p53 knockout mice showed the same pattern of c-fos and Kin17 mRNA accumulation as wild-type cells. The data indicate that the signal flow induced by UV radiation addresses not only protein stability (p53) and transcription but also RNA stability, a hitherto-unrecognized level of UV-induced regulation.

Protective effect of topically applied olive oil against photocarcinogenesis following UVB exposure of mice

Abstract: Reactive oxygen species have been shown to play a role in ultraviolet light (UV)-induced skin carcinogenesis. Vitamin E and green tea polyphenols reduce experimental skin cancers in mice mainly because of their antioxidant properties. Since olive oil has also been reported to be a potent antioxidant, we examined its effect on UVB-induced skin carcinogenesis in hairless mice. Extra-virgin olive oil was applied topically before or after repeated exposure of mice to UVB. The onset of UVB-induced skin tumors was delayed in mice painted with olive oil compared with UVB control mice. However, with increasing numbers of UVB exposures, differences in the mean number of tumors between UVB control mice and mice pretreated with olive oil before UVB exposure (pre-UVB group) were lost. In contrast, mice that received olive oil after UVB exposure (post-UVB group) showed significantly lower numbers of tumors per mouse than those in the UVB control group throughout the experimental period. The mean number of tumors per mouse in the UVB control, pre-UVB and post-UVB groups was 7.33, 6.69 and 2.64, respectively, in the first experiment, and 8.53, 9.53 and 3.36 in the second experiment. Camellia oil was also applied, using the same experimental protocol, but did not have a suppressive effect. Immunohistochemical analysis of DNA damage in the form of cyclobutane pyrimidine dimers (CPD), (6-4) photoproducts and 8-hydroxy-2'-deoxyguanosine (8-OHdG) in samples taken 30 min after a single exposure of UVB showed no significant difference between UVB-irradiated control mice and the pre-UVB group. In the post-UVB group, there were lower levels of 8-OHdG in epidermal nuclei, but the formation of CPD and (6-4) photoproducts did not differ. Exposure of olive oil to UVB before application abrogated the protective effect on 8-OHdG formation. These results indicate that olive oil topically applied after UVB exposure can effectively reduce UVB-induced murine skin tumors, possibly via its antioxidant effects in reducing DNA damage by reactive oxygen species, and that the effective component may be labile to UVB.

The melanosome: the perfect model for cellular responses to the environment.

Abstract: Melanocytes play critical roles in mammals, including the regulation of constitutive pigmentation in the skin, hair, and eyes, in embryological development, and in photoprotection from ionizing radiation. The pigments themselves, possibly due to the inherent cytotoxic properties of their precursors, are synthesized and deposited within membrane-bound organelles known as melanosomes. However, the structure of melanosomes, and thus their characteristic properties, varies widely, from relatively disorganized, poorly pigmented pheomelanosomes to highly structured, melanized eumelanosomes. Melanocytes respond to various physiological stimuli, such as melanocyte-stimulating hormone (MSH), agouti signal protein (ASP), endothelins and/or ultraviolet light (UVL) by highly complex intracellular signaling mechanisms that can elicit dramatic changes in melanosome and melanocyte morphology. MSH and UVL stimulate transcription of melanogenic genes that elicit dramatic increases in the amount of eumelanins produced, whereas ASP serves as an antagonist of MSH and inhibits the transcription of those same genes. Recent studies have shown that melanocyte-specific transcription factors, such as MITF, play important roles in these responses, but ubiquitous transcription factors, such as ITF2 and E2A, are also involved. Virtually all known intracellular signaling pathways affect one or more parameters of pigmentation, and it is clear that both melanocyte-specific and basic housekeeping processes are affected by such modulation. The properties of melanins, including their photoprotective function, may be optimized by such stimulatory responses. Studies targeted at elucidating the regulatory mechanisms involved and the functional changes that result demonstrate that the melanosome is the perfect model to study such biological response mechanisms.