Low UV Doses Research Articles

Photoinduced fibrils formation of chicken egg white lysozyme under native conditions

AbstractRecent findings showed that transiently accessing structurally native‐like yet energetically higher conformational states is sufficient to trigger the formation of protein fibrils. Typically, these conformational states are made available through changing solvent conditions or introducing mutations. Here we show a novel way to initialize fibril formation for Chicken egg white lysozyme (CEWL) under native conditions via controlled UV illumination. Through a cassette of tryptophan‐based photochemistry, the two terminal disulfide bonds in CEWL can be selectively reduced. The reduced CEWL is then converted to conformational states with the C‐terminal fragment floppy upon thermal fluctuation. These states serve as precursors for the fibrillar aggregation. Intriguingly, the CEWL fibrils are stabilized by intermolecular disulfide bonds instead of noncovalent β‐sheet structures, distinct from the amyloid‐like lysozyme fibrils reported before. Based on the experimental evidences and all‐atom molecular dynamics simulation, we proposed a “runaway domain‐swapping” model for the structure of the CEWL fibrils, in which each CEWL molecule swaps the C‐terminal fragment into the complementary position of the adjacent molecule along the fibrils. We anticipate that this fibrillation mechanism can be extended to many other disulfide‐containing proteins. Our study stands for the first example of formation of protein fibrils under native conditions upon UV illumination and poses the potential danger of low UV dose to organisms at the protein level. Proteins 2012. © 2012 Wiley Periodicals, Inc.

Chronic low-dose ultraviolet-induced mutagenesis in nucleotide excision repair-deficient cells

UV radiation induces two major types of DNA lesions, cyclobutane pyrimidine dimers (CPDs) and 6-4 pyrimidine–pyrimidine photoproducts, which are both primarily repaired by nucleotide excision repair (NER). Here, we investigated how chronic low-dose UV (CLUV)-induced mutagenesis occurs in rad14Δ NER-deficient yeast cells, which lack the yeast orthologue of human xeroderma pigmentosum A (XPA). The results show that rad14Δ cells have a marked increase in CLUV-induced mutations, most of which are C→T transitions in the template strand for transcription. Unexpectedly, many of the CLUV-induced C→T mutations in rad14Δ cells are dependent on translesion synthesis (TLS) DNA polymerase η, encoded by RAD30, despite its previously established role in error-free TLS. Furthermore, we demonstrate that deamination of cytosine-containing CPDs contributes to CLUV-induced mutagenesis. Taken together, these results uncover a novel role for Polη in the induction of C→T transitions through deamination of cytosine-containing CPDs in CLUV-exposed NER deficient cells. More generally, our data suggest that Polη can act as both an error-free and a mutagenic DNA polymerase, depending on whether the NER pathway is available to efficiently repair damaged templates.

Killed but Metabolically Active Leishmania infantum as a Novel Whole-Cell Vaccine for Visceral Leishmaniasis

There are currently no effective vaccines for visceral leishmaniasis, the second most deadly parasitic infection in the world. Here, we describe a novel whole-cell vaccine approach using Leishmania infantum chagasi promastigotes treated with the psoralen compound amotosalen (S-59) and low doses of UV A radiation. This treatment generates permanent, covalent DNA cross-links within parasites and results in Leishmania organisms termed killed but metabolically active (KBMA). In this report, we characterize the in vitro growth characteristics of both KBMA L. major and KBMA L. infantum chagasi. Concentrations of S-59 that generate optimally attenuated parasites were identified. Like live L. infantum chagasi, KBMA L. infantum chagasi parasites were able to initially enter liver cells in vivo after intravenous infection. However, whereas live L. infantum chagasi infection leads to hepatosplenomegaly in mice after 6 months, KBMA L. infantum chagasi parasites were undetectable in the organs of mice at this time point. In vitro, KBMA L. infantum chagasi retained the ability to enter macrophages and induce nitric oxide production. These characteristics of KBMA L. infantum chagasi correlated with the ability to prophylactically protect mice via subcutaneous vaccination at levels similar to vaccination with live, virulent organisms. Splenocytes from mice vaccinated with either live L. infantum chagasi or KBMA L. infantum chagasi displayed similar cytokine patterns in vitro. These results suggest that KBMA technology is a potentially safe and effective novel vaccine strategy against the intracellular protozoan L. infantum chagasi. This approach may represent a new method for whole-cell vaccination against other complex intracellular pathogens.

Combination of O3/H2O2 and UV for multiple barrier micropollutant treatment and bromate formation control - an economic attractive option

Advanced Oxidation Processes (AOP) are known as an effective treatment barrier for micropollutants. Well known AOP combinations are UV/H2O2 and O3/H2O2. This paper will present a more detailed view on how to use the different options combining UV; ozone and H2O2. The focus of this investigation is on treatment effects (reduction of specific contaminats), water matrix, energy consumption and cost calculation (CAPEX, OPEX). The presented data are extracted from extended pilot trials carried out at DUNEA in 2009 and 2010. Dunea (The Netherlands,The Hague) produces drinking water from the Meuse River, which contains a variety of organic micropollutants as a result from upstream activity. Dunea is performing research to extend the current multiple barrier treatment (e.g. pre-treatment, artificial recharge and recovery (ARR), post-treatment) with an advanced oxidation processes (AOP), situated at the pre-treatment location in Bergambacht, before ARR. The degradation of organic micropollutants as a result of advanced oxidation using different combinations of hydrogen peroxide, ozone, low pressure (LP) UV lamps has been assessed by means of pilot-scale (5 m3/h) experiments. The influent was pre-treated river water, with an yearly average UV-transmission of 80% and a DOC concentration of 4 mg/L.The peroxide doses were varied as 0, 5 and 10 ppm, the ozone doses were varied as 1, 2 and 3 g ozone/m3. The UV doses were varied between 300 and 650 mJ/cm2. The installed power for the LP reactor was 0.26 kWh/m3. Atrazine, bromacil, ibuprofen and NDMA were spiked (10-20 µg/L) and used as model compounds. Bromacil was completely (>99%) removed by ozone/peroxide. Atrazine and ibuprofen were good (58% and 85% respectively) removed by O3/H2O2 and NDMA was not (9%) removed by this technique, whereas NDMA showed good (82%) removal by UV/H2O2. Atrazine, bromacil and ibuprofen were degraded by UV/H2O2 at 53, 46 and 59 %, respectively. In addition also combined AOP was tested; spiked water was treated by O3/H2O2 first and let over the LP-UV reactor directly afterwards. All four compounds showed highest degradation during combined AOP treatment. With this combined AOP, lower ozone dose and lower UV dose result in comparable degradation compared to single AOP treatment. For all these techniques a detailed capital expenditure operational expenditure (CAPEX / OPEX) evaluation was carried out based on a daily water flow of 240,000 m3/d. This evaluation resulted in the finding, that the combined AOP is the most economical solution with the best treatment result. Other advantages of the combined AOP are limited by-product formation, especially bromate, and a future barrier against OMPs encompassing a broad spectrum of properties.

A randomized comparison of excimer laser versus narrow‐band ultraviolet B phototherapy after punch grafting in stable vitiligo patients

Background Ultraviolet radiation following punch grafting may stimulate the migration of melanocytes from the grafts into the vitiliginous skin, thereby increasing the rate of repigmentation. We compared the effects of the 308-nm xenon chloride excimer laser (EL) vs. narrow-band ultraviolet B (NB-UVB) after punch grafting in patients with vitiligo. Objectives The aims of this study were to evaluate (i) repigmentation (%); (ii) treatment satisfaction; and (iii) patient preferences for EL vs. NB-UVB therapy after punch grafting in vitiligo. Methods Fourteen patients were treated with the punch-grafting technique on two symmetrical vitiligo patches. Starting 1 week after the punch grafting, the vitiligo patches were treated twice a week during 3 months, with EL on one side and with NB-UVB on the other side. Repigmentation (%) was measured by a digital image analysis system. Patients' satisfaction and preference for treatment were also assessed. Results Whereas both treatment modalities induced repigmentation, no statistically significant difference was found in grade of repigmentation after 3 months. With EL, 71.4% lower cumulative dose was reached. Patients were significantly more satisfied with NB-UVB and preferred it over EL. Conclusions The choice between EL and NB-UVB cannot solely be based on repigmentation, but rather on other factors, such as patients' preferences. However, given the lower UV dose of EL, we recommend its use in vulnerable populations, such as in small children and patients with sun-damaged skin with a history of long-term UVB treatment.

Disinfection of greywater effluent and regrowth potential of selected bacteria

Chlorination and UV irradiation of RBC (rotating biological contactor)-treated light GW (greywater) was investigated. The ability of chlorine and UV to inactivate indictor bacteria (FC - Faecal Coliforms, HPC - Heterotrophic Plate Count) and specific pathogens (P.a. - Pseudomonas aeruginosa sp., S.a. - Staphylococcus aureus sp.), was assessed and their regrowth potential was examined. The RBC removed 88.5-99.9% of all four bacteria groups. Nevertheless, the treated GW had to be disinfected. Most of the chlorine was consumed during the first 0.5 h, while later its decay rate decreased significantly, leaving enough residual after 6 h to prevent regrowth and to further inactivate bacteria in the stored GW effluent. Under exposure to low UV doses (≤69 mJ/cm(2)) FC was the most resistant bacteria group, followed by HPC, P.a. and S.a. Exposure to higher doses (≤439 mJs/cm(2)) completely inactivated FC, P.a. and S.a., while no further HPC inactivation was observed. FC, P.a. and S.a. did not exhibit regrowth after exposure to all the UV doses applied (up to 6 h storage). HPC did not exhibit regrowth after exposure to low UV doses (19-69 mJ/cm2), while it presented statistically significant regrowth in un-disinfected effluent and after exposure to higher UV doses (147-439 mJ/cm(2)).

Inactivation of human adenovirus by sequential disinfection with an alternative UV technology and free chlorine

There has been growing concern over human exposure to adenoviruses through drinking water due to the extreme resistance of human adenoviruses to the traditional UV technology (low-pressure (LP) UV). As an effort to develop an effective treatment strategy against human adenoviruses in drinking water, we determined the effectiveness of sequential disinfection with an alternative UV technology (medium-pressure (MP) UV) and free chlorine. Human adenovirus 2 (Ad2) was irradiated with a low dose of MP UV irradiation (10 mJ/cm(2)) through UV collimated apparatus and then exposed to a low dose of free chlorine (0.17 mg/L) at pH 8 and 5°C using a bench-scale chemical disinfection system. A significant inactivation (e.g. 4 log(10)) of Ad2 was achieved with the low doses of MP UV and free chlorine within a very short contact time (∼1.5 min) although there was no apparent synergistic effect on Ad2 between MP UV and free chlorine. Overall, it is likely that the sequential disinfection with UV irradiation and free chlorine should control the contamination of drinking water by human adenoviruses within practical doses of UV and free chlorine typically used in drinking water treatment processes.

Photo-Induced Fibrillar Formation of Chicken Egg White Lysozyme Under Native Conditions

Recent findings showed that transiently accessing structurally native-like yet energetically higher conformational states is sufficient to trigger the formation of protein fibrils. Typically, these conformational states are made available through changing solvent conditions or introducing mutations. Here we show a novel way to initialize fibril formation for Chicken egg white lysozyme (CEWL) under native conditions via controlled UV illumination. Through a cassette of tryptophan-based photochemistry, the two terminal disulfide bonds in CEWL can be selectively reduced. The reduced CEWL is then converted to conformational states with the C-terminal fragment floppy upon thermal fluctuation. These states serve as precursors for the fibrillar aggregation. Intriguingly, the CEWL fibrils are stabilized by intermolecular disulfide bonds instead of noncovalent β-sheet structures, distinct from the amyloid-like lysozyme fibrils reported before. Based on the experimental evidences and all-atom molecular dynamics simulation, we proposed a runaway domain-swapping model for the structure of the CEWL fibrils, in which each CEWL molecule swaps the C-terminal fragment into the complementary position of the adjacent molecule along the fibrils. We anticipate that this fibrillation mechanism can be extended to many other disulfide-containing proteins. Our study stands for the first example of formation of protein fibrils under native conditions upon UV illumination and poses the potential danger of low UV dose to organisms at the protein level.

Damage-specific DNA binding protein 1 (DDB1) is involved in ubiquitin-mediated proteolysis of p27Kip1 in response to UV irradiation

Damage-specific DNA binding protein 1 (DDB1) is a conserved protein component of the damaged DNA binding protein complex (DDB) that recognizes UV-induced DNA lesions and initiates the nucleotide excision repair process. DDB1 is also part of an E3 ubiquitin-ligase complex that targets a variety of substrates for proteolysis including the cyclin-dependent kinase inhibitor p27Kip1. The mechanism regulating the trafficking of DDB1 and its relationship with UV irradiation is not known, although cell cycle progression is implicated in the molecular machinery driving DDB1 into the nucleus. We evaluated the involvement of DDB1 in ubiquitination of the cdk inhibitor p27Kip1 in response to UV irradiation. First, we observed that low and high doses of UV irradiation exert different effects on p27Kip1 protein levels. Indeed, low but not high UV doses induced p27Kip1 protein proteolysis in several human cell lines and UV-dependent degradation is dominant over other genotoxic agents such as cisplatin. We also demonstrate that p27Kip1 reduction is not due to transcriptional regulation and that the proteasome inhibitor MG132 affects p27Kip1 degradation.We observed that at low UV doses the decrease in p27Kip1 nuclear protein related with DDB1 translocation into the nucleus; conversely, high doses of UV-induced p27Kip1 accumulation and unchanged level of DDB1. The knockdown of DDB1 or Skp2 prevents UV-induced degradation of p27Kip1 suggesting that DDB1 is essential to regulation of p27kip1 turnover after a mild DNA damage. Our findings support the concept that DDB1 contributes to the activation of DNA repair mechanisms and could be a key factor in regulating the cell cycle in response to UV-induced DNA damage. Although the temporal order with which DDB1 contributes to ubiquitination of p27Kip1 or initiates the nucleotide excision repair process remains to be established, our results represent a major step towards clarifying these issues.

UV Exposure Boosts Transcutaneous Immunization and Improves Tumor Immunity: Cytotoxic T-Cell Priming through the Skin

Immunologic approaches to combat cancer aim at the induction of tumor-reactive immune responses to achieve long-term protection. In this context, we recently developed a transcutaneous immunization (TCI) method using the Toll-like receptor (TLR) 7 agonist imiquimod and a peptide epitope. Application onto intact skin induces potent cytotoxic T lymphocyte (CTL) responses and protection against transplanted tumors. The purpose of this study was to explore the effects of UV irradiation on imiquimod-based TCI. Here we show that skin exposure to low-dose UV light before TCI with imiquimod strongly boosts specific CTL responses leading to memory formation and enhanced tumor protection. Toward the mechanisms, we show that the activation of bone-marrow-derived dermal dendritic cells (DCs), but not Langerin-expressing DCs, is responsible for enhanced CTL activation. We describe an optimized TCI method that mediates enhanced CTL and antitumor responses by a DC- and TLR-dependent mechanism. These data may provide the basis for the future development of advanced vaccination protocols against tumors and persistent virus infections.

Srs2 Plays a Critical Role in Reversible G2 Arrest upon Chronic and Low Doses of UV Irradiation via Two Distinct Homologous Recombination-Dependent Mechanisms in Postreplication Repair-Deficient Cells

Differential posttranslational modification of proliferating cell nuclear antigen (PCNA) by ubiquitin or SUMO plays an important role in coordinating the processes of DNA replication and DNA damage tolerance. Previously it was shown that the loss of RAD6-dependent error-free postreplication repair (PRR) results in DNA damage checkpoint-mediated G(2) arrest in cells exposed to chronic low-dose UV radiation (CLUV), whereas wild-type and nucleotide excision repair-deficient cells are largely unaffected. In this study, we report that suppression of homologous recombination (HR) in PRR-deficient cells by Srs2 and PCNA sumoylation is required for checkpoint activation and checkpoint maintenance during CLUV irradiation. Cyclin-dependent kinase (CDK1)-dependent phosphorylation of Srs2 did not influence checkpoint-mediated G(2) arrest or maintenance in PRR-deficient cells but was critical for HR-dependent checkpoint recovery following release from CLUV exposure. These results indicate that Srs2 plays an important role in checkpoint-mediated reversible G(2) arrest in PRR-deficient cells via two separate HR-dependent mechanisms. The first (required to suppress HR during PRR) is regulated by PCNA sumoylation, whereas the second (required for HR-dependent recovery following CLUV exposure) is regulated by CDK1-dependent phosphorylation.

Investigation of thermoluminescence characteristics of CaSrS: Ce nanophosphors

Thermoluminescence characteristics of Ca 0.75Sr 0.25S: Ce nanophosphors exposed to UV radiations have been investigated. Solid state diffusion method was employed to synthesize the nanophosphors. The confirmation for the formation of the mixed lattice was done by XRD. The particles formed were found to have 45 nm size as calculated by the Debye Scherrer formula. TEM results were in close agreement with the XRD as the nanoparticles formed possess capsule like structure with an average diameter of 50 nm. TL glow curves for the low doses (110–1680 mJ/cm 2) of UV show a main peak around 381 K and another peak of very low intensity around 570 K. The TL intensity increases up to 450 mJ/cm 2 of UV exposure. At higher doses (3.5–80 J/cm 2) the peak position varies slightly but the high temperature peak becomes more intense. Thermoluminescence characteristics of UV irradiated Ca 1− x Sr x S: Ce as a function of x (0.25, 0.50, and 0.75) have also been investigated. TL glow curves of Ca 1− x Sr x S: Ce (0.25, 0.50, and 0.75) recorded after 450 mJ/cm 2 of exposure of UV radiations show almost similar structure except slight variation in the peak position. Ca 0.25Sr 0.75S: Ce and Ca 0.50Sr 0.50S: Ce have single peak at 373 and 367 K, respectively, while Ca 0.75Sr 0.25S: Ce has a main peak at 381 K and a less intense peak at 570 K. Ca 0.75Sr 0.25S: Ce shows the most intense TL peak. The trap parameters namely, activation energy ( E), order of kinetics ( b), and frequency factor ( s) of Ca 0.75Sr 0.25S: Ce have been determined using Chen’s peak shape method and GCD function suggested by Kitis for second order kinetics.

Nicotinamide Prevents Ultraviolet Radiation‐induced Cellular Energy Loss

UV radiation is carcinogenic by causing mutations in the skin and also by suppressing cutaneous antitumor immunity. We previously found nicotinamide (vitamin B3) to be highly effective at reducing UV-induced immunosuppression in human volunteers, with microarray studies on in vivo irradiated human skin suggesting that nicotinamide normalizes subsets of apoptosis, immune function and energy metabolism-related genes that are downregulated by UV exposure. Using human adult low calcium temperature keratinocytes, we further investigated nicotinamide's effects on cellular energy metabolism. We found that nicotinamide prevented UV-induced cellular ATP loss and protected against UV-induced glycolytic blockade. To determine whether nicotinamide alters the effects of UV-induced oxidative stress posttranslationally, we also measured UV-induced reactive oxygen species (ROS). Nicotinamide had no effect on ROS formation, and at the low UV doses used in these studies, equivalent to ambient daily sun exposure, there was no evidence of apoptosis. Hence, nicotinamide appears to exert its UV protective effects on the skin via its role in cellular energy pathways.

Dynamic changes to survivin subcellular localization are initiated by DNA damage

Subcellular distribution of the apoptosis inhibitor survivin and its ability to relocalize as a result of cell cycle phase or therapeutic insult has led to the hypothesis that these subcellular pools may coincide with different survivin functions. The PIK kinases (ATM, ATR and DNA-PK) phosphorylate a variety of effector substrates that propagate DNA damage signals, resulting in various biological outputs. Here we demonstrate that subcellular repartitioning of survivin in MCF-7 cells as a result of UV light-mediated DNA damage is dependent upon DNA damage-sensing proteins as treatment with the pan PIK kinase inhibitor wortmannin repartitioned survivin in the mitochondria and diminished it from the cytosol and nucleus. Mitochondrial redistribution of survivin, such as was recorded after wortmannin treatment, occurred in cells lacking any one of the three DNA damage sensing protein kinases: DNA-PK, ATM or ATR. However, failed survivin redistribution from the mitochondria in response to low-dose UV occurred only in the cells lacking ATM, implying that ATM may be the primary kinase involved in this process. Taken together, this data implicates survivian's subcellular distribution is a dynamic physiological process that appears responsive to UV light-initiated DNA damage and that its distribution may be responsible for its multifunctionality.

Requirement for functional DNA polymerase eta in genome-wide repair of UV-induced DNA damage during S phase

The autosomal recessive disorder Xeroderma pigmentosum- variant (XPV) is characterized (i) at the cellular level by dramatic hypermutability and defective recovery of DNA synthesis following UV exposure, and (ii) clinically by abnormal sunlight sensitivity and remarkable predisposition to skin cancer. These phenotypes are clearly attributable to germline mutations in POLH, encoding DNA polymerase eta (polη) normally required for accurate translesion DNA synthesis (TLS) past UV-induced cyclobutane pyrimidine dimers. Here we demonstrate that patient-derived XPV-skin fibroblasts exposed to 15 J/m 2 of UV also exhibit (in addition to abnormal TLS) a significant defect in global-genomic nucleotide excision repair (GG-NER) exclusively during S phase. This cell cycle-specific GG-NER defect can be complemented by ectopic expression of wild-type polη, but not of polη variants deficient in either nuclear relocalization or PCNA interaction. We highlight a previous study from our laboratory demonstrating that UV-exposed, ATR-deficient Seckel syndrome fibroblasts, like XPV fibroblasts, manifest strong attenuation of GG-NER uniquely in S phase populations. We now present further evidence suggesting that deficient S phase repair can be rescued in both XPV- and Seckel syndrome-cells if the formation of blocked replication forks post-UV is either prevented or substantially reduced, i.e., following, respectively, pharmacological inhibition of DNA synthesis prior to UV irradiation, or exposure to a relatively low UV dose (5 J/m 2). Our findings in cultured cells permit speculation that abrogation of GG-NER during S phase might partially contribute (in a synergistic manner with defective, atypically error-prone TLS) to the extreme state of UV-hypermutability leading to accelerated skin cancer development in XPV patients. Moreover, based on the overall data, we postulate that loss of either functional polη or -ATR engenders abnormal persistence of stalled replication forks at UV-adducted sites in DNA which, in turn, can actively and/or passively trigger GG-NER inhibition.

Effect of pre- and post-UV disinfection conditions on photoreactivation of fecal coliforms in wastewater effluents

Photoreactivation of microorganisms following UV disinfection can represent a disadvantage to using UV technology for wastewater treatment since recovery may, in some cases, reach several logs. Thus, decreasing photoreactivation can lead to considerable savings in capital and operating costs. Objectives of this study were to determine pre- and post-UV irradiation conditions which could decrease fecal coliform (FC) photoreactivation in wastewater effluents. Results indicated that delaying exposure to photoreactivating light for 3 h suppressed photoreactivation after relatively low UV doses of 10 and 20 mJ/cm 2. Moreover, at least 440 lux (0.065 mW/cm 2) of visible light was needed to initiate photoreactivation. Additionally, photoreactivation decreased significantly when samples were exposed to visible light simultaneously or prior to UV irradiation. This was more significantly observed for winter samples, where photoreactivation decreased by nearly 50%. Finally, summer FC populations were more sensitive to inactivation and less able to photoreactivate than winter populations. The effect of visible light on photoreactivation levels may be explained by several photo-mechanisms of FC photolyase, such as photodecomposition of the MTHF co-factor and reduction of FAD.

Photodegradation of 4-chlorophenol using XeBr, KrCl and Cl2 barrier-discharge excilamps: A comparative study

Abstract A study on 4-chlorophenol (4CP) photodegradation has been carried out using UV radiation delivered from three different excimer lamps: XeBr, KrCl and Cl 2 , with maximum emission wavelengths of 283, 222 and 259 nm, respectively. The influence of initial 4-chlorophenol concentration on the photodegradation process was examined with pollutant concentrations ranging from 50 to 500 mg L −1 , and degradation progress was followed by determining the residual 4-chlorophenol, as well as that of the main photoproducts, hydroquinone (HQ) and benzoquinone (BQ). All excilamps were able to degrade 4CP. XeBr and the KrCl excilamps achieved almost total 4-chlorophenol degradation, with the removal efficiency of the Cl 2 excilamp being considerably lower. The KrCl excilamp, in spite of requiring longer exposure times compared with the XeBr, needed a much lower UV dose and, consequently, a lower energy consumption for degradation and, as a result, has been considered the most effective and efficient in 4CP removal. Additionally, and by defining the limit of 4-chlorophenol degradation, a modified pseudo-first order kinetic model was used to fit the kinetics of the 4-chlorophenol degradation process where good agreement between experimental data and those predicted by the model was found. Shielding effects are considered to have an influence on 4-chlorophenol degradation as there is a decrease in the pseudo-first order rate constant with increasing 4-chlorophenol concentrations for the three excilamps. In addition, there is a noticeable decrease in the maximum removal of 4-chlorophenol for the Cl 2 excilamp due to the same effect.

Acclimation to ultraviolet irradiation affects UV-B sensitivity of Daphnia magna to several environmental toxicants

Phototoxicity of several environmental contaminants by UV light has been reported in many studies. Nevertheless, field observations suggest the presence of certain defense mechanisms that would protect aquatic organisms against phototoxic damages. The current study was conducted to understand the responses of aquatic receptors to phototoxic chemicals in a natural environment where low dose UV light is present and long-term acclimation to UV might have been taken place. For this purpose, the water flea Daphnia magna was acclimated to a non-lethal, environmentally relevant level of UV-B light for >20 successive generations. The differences in toxicity response were evaluated between the UV-B acclimated and the non-acclimated daphnids when they were exposed to phototoxic compounds such as polynuclear aromatic hydrocarbons (fluoranthene and pyrene), a pharmaceutical (sulfathiazole), or metals (Cd and Cu) under UV-B light. Following the UV-B acclimation, toxicity of metals under UV-B light significantly decreased ( P < 0.1) suggesting the defense/repair system which might be developed through acclimation. For PAHs and sulfathiazole, however the acclimation rendered organisms more susceptible ( P < 0.05). The metabolic cost incurred during the acclimation to UV-B stress may in part explain the organisms’ reduced capacity to deal with other stressors. Addition of vitamin C significantly increased the resistance of UV-B acclimated individuals against Cu, while no change was observed for the other chemicals, suggesting that the mode of Cu phototoxicity is different from those of the other phototoxicants under UV-B light. Two-dimensional gel electrophoresis analyses showed that long-term acclimation to UV-B lead to notable changes in protein expression, which may be further evaluated to explain varying susceptibilities of the acclimated daphnids to different phototoxicants.

The Pathogenesis of Photoaging: The Role of Neutrophils and Neutrophil-Derived Enzymes

The hallmark of photoaged skin is solar elastosis, which is probably an end product of elastic fiber degradation. Exposure of human skin to a certain threshold of UV, infrared radiation (IR), and heat leads to an influx of neutrophils. These neutrophils are packed with potent proteolytic enzymes capable of degrading collagen and, particularly, elastic fibers. Neutrophil-derived proteolytic enzymes are held responsible for the extracellular matrix (ECM) damage observed in several non-dermatological conditions. Furthermore, neutrophil elastase, a major product of neutrophils, is strongly associated with solar elastosis in mice. Taken together with our data that show in vivo proteolytic activity of neutrophil-derived elastase and matrix metalloproteinases (MMPs) in UV-exposed skin, we have hypothesized earlier that neutrophils are major contributors to the photoaging process. Although several groups have shown that MMPs are also induced in skin exposed to relatively low doses of UV, IR, and heat, clinical data indicate that high(er) doses of UV, IR, and heat are necessary to induce photoaging or photoaging-like pathology in the skin. Therefore, we propose that MMPs generated by suberythemogenic doses of UV and low doses of IR/heat are involved in cellular processes other than ECM degradation.Journal of Investigative Dermatology Symposium Proceedings (2009) 14, 67-72; doi:10.1038/jidsymp.2009.15.

UV-DDB-dependent regulation of nucleotide excision repair kinetics in living cells

Although the basic principle of nucleotide excision repair (NER), which can eliminate various DNA lesions, have been dissected at the genetic, biochemical and cellular levels, the important in vivo regulation of the critical damage recognition step is poorly understood. Here we analyze the in vivo dynamics of the essential NER damage recognition factor XPC fused to the green fluorescence protein (GFP). Fluorescence recovery after photobleaching analysis revealed that the UV-induced transient immobilization of XPC, reflecting its actual engagement in NER, is regulated in a biphasic manner depending on the number of (6-4) photoproducts and titrated by the number of functional UV-DDB molecules. A similar biphasic UV-induced immobilization of TFIIH was observed using XPB-GFP. Surprisingly, subsequent integration of XPA into the NER complex appears to follow only the low UV dose immobilization of XPC. Our results indicate that when only a small number of (6-4) photoproducts are generated, the UV-DDB-dependent damage recognition pathway predominates over direct recognition by XPC, and they also suggest the presence of rate-limiting regulatory steps in NER prior to the assembly of XPA.