Publications by authors named "Thierry Douki"

166 Publications

Wavelengths and temporal effects on the response of mammalian cells to UV radiation: Limitations of action spectra illustrated by genotoxicity.

Authors:
Thierry Douki

J Photochem Photobiol B 2021 Apr 2;217:112169. Epub 2021 Mar 2.

Univ. Grenoble Alpes, CEA, CNRS, IRIG, SyMMES, F-38000 Grenoble, France. Electronic address:

All photobiological events depend on the wavelength of the incident radiation. In real-life situations and in the vast majority of laboratory experiments, exposure always involves sources with various emission spectra spreading over a wide wavelength range. Action spectra are often used to describe the efficiency of a process at different wavelengths and to predict the effects of a given light source by summation of the individual effects at each wavelength. However, a full understanding of the biological effects of complex sources requires more than considering these concomitant events at each specific wavelength. Indeed, photons of different energies may not have additive but synergistic or inhibitory effects on photochemical processes and cellular responses. The evolution of a photobiological response with post-irradiation time must also be considered. These two aspects may represent some limitations to the use of action spectra. The present review, focused on mammalian cells, illustrates the concept of action spectrum and discusses its drawbacks using theoretical considerations and examples taken from the literature. Emphasis is placed on genotoxicity for which wavelength effects have been extensively studied. Other effects of UV exposure are also mentioned.
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http://dx.doi.org/10.1016/j.jphotobiol.2021.112169DOI Listing
April 2021

Glutathione conjugates of the mercapturic acid pathway and guanine adduct as biomarkers of exposure to CEES, a sulfur mustard analog.

Anal Bioanal Chem 2021 Feb 7;413(5):1337-1351. Epub 2021 Jan 7.

Univ. Grenoble Alpes, CEA, CNRS, IRIG, SyMMES, 38000, Grenoble, France.

Sulfur mustard (SM), a chemical warfare agent, is a strong alkylating compound that readily reacts with numerous biomolecules. The goal of the present work was to define and validate new biomarkers of exposure to SM that could be easily accessible in urine or plasma. Because investigations using SM are prohibited by the Organisation for the Prohibition of Chemical Weapons, we worked with 2-chloroethyl ethyl sulfide (CEES), a monofunctional analog of SM. We developed an ultra-high-pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) approach to the conjugate of CEES to glutathione and two of its metabolites: the cysteine and the N-acetylcysteine conjugates. The N7-guanine adduct of CEES (N7Gua-CEES) was also targeted. After synthesizing the specific biomarkers, a solid-phase extraction protocol and a UHPLC-MS/MS method with isotopic dilution were optimized. We were able to quantify N7Gua-CEES in the DNA of HaCaT keratinocytes and of explants of human skin exposed to CEES. N7Gua-CEES was also detected in the culture medium of these two models, together with the glutathione and the cysteine conjugates. In contrast, the N-acetylcysteine conjugate was not detected. The method was then applied to plasma from mice cutaneously exposed to CEES. All four markers could be detected. Our present results thus validate both the analytical technique and the biological relevance of new, easily quantifiable biomarkers of exposure to CEES. Because CEES behaves very similar to SM, the results are promising for application to this toxic of interest.
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http://dx.doi.org/10.1007/s00216-020-03096-4DOI Listing
February 2021

Dark cyclobutane pyrimidine dimers are formed in the epidermis of Fitzpatrick skin types I/II and VI in vivo after exposure to solar-simulated radiation.

Pigment Cell Melanoma Res 2021 May 20;34(3):575-584. Epub 2021 Jan 20.

St John's Institute of Dermatology, King's College London, London, UK.

Introduction: Unlike "light" cylobutane pyrimidine dimers (CPD) formed during ultraviolet radiation (UVR) exposure, dark CPD (dCPD) are formed afterwards. Studies have attributed this to delayed melanin sensitization. There are no data on the role of melanin in dCPD formation in human skin.

Methods And Results: Volunteers of Fitzpatrick skin types (FST I/II vs. VI) were exposed to erythemally equivalent doses of solar simulated radiation. CPD were assessed by semi-quantitative immunostaining in whole epidermis and in three epidermal zones, and quantitative HPLC-MS/MS (whole epidermis) at different times post-exposure up to 24 hr. A CPD peak that appeared at 1-2 hr post-exposure in whole epidermis measurements, in all skin types, demonstrated dCPD. However, both dCPD and light CPD were absent in the basal layer of FST VI with the greatest melanin concentration. Modelling the whole epidermis data showed no differences between the repair kinetics of FST I/II and VI.

Discussion: Melanin may be a sensitizer or "sunscreen" for dCPD depending on its location and concentration. Previous CPD repair studies in human skin have assumed peak CPD immediately after UVR exposure and so have overestimated total repair.
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http://dx.doi.org/10.1111/pcmr.12956DOI Listing
May 2021

Seasonal Differences in the UVA/UVB Ratio of Natural Sunlight Influence the Efficiency of the Photoisomerization of (6-4) Photoproducts into their Dewar Valence Isomers.

Photochem Photobiol 2021 May 22;97(3):582-588. Epub 2020 Dec 22.

Medical Genetics Research Center, Nara Medical University, Kashihara, Japan.

The UVA and UVB components of sunlight can produce three classes of bipyrimidine DNA photolesions [cyclobutane pyrimidine dimers (CPDs), pyrimidine (6-4) pyrimidone photoproducts (6-4PPs) and related Dewar valence isomers (DewarPPs)]. The UVA/UVB ratio of sunlight is high in winter and low in summer in the Northern Hemisphere. Since UVB radiation produces 6-4PPs and UVA radiation converts them into DewarPPs through photoisomerization, it is expected that there may be differences in the photoisomerization of 6-4PPs between summer and winter, although that has never been documented. To determine that, isolated DNA was exposed to natural sunlight for 8 h in late summer and in winter, and absolute levels of the three classes of photolesions were quantified using calibrated ELISAs. It was found that sunlight produces CPDs and 6-4PPs in DNA at a ratio of about 9:1 and converts approximately 80% of 6-4PPs into DewarPPs within 3 h. Moreover, photoisomerization is more efficient in winter than in late summer after sunlight irradiation for the same duration, at similar solar UV doses and with the same induction level of CPDs. These results demonstrate that seasonal differences in the UVA/UVB ratio influence the efficiency of the photoisomerization of 6-4PPs into DewarPPs.
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http://dx.doi.org/10.1111/php.13361DOI Listing
May 2021

Impairment of Base Excision Repair in Dermal Fibroblasts Isolated From Nevoid Basal Cell Carcinoma Patients.

Front Oncol 2020 7;10:1551. Epub 2020 Aug 7.

SYMMES/CIBEST UMR 5819 UGA-CNRS-CEA, Univ. Grenoble Alpes, Grenoble, France.

The nevoid basal cell carcinoma syndrome (NBCCS), also called Gorlin syndrome is an autosomal dominant disorder whose incidence is estimated at about 1 per 55,600-256,000 individuals. It is characterized by several developmental abnormalities and an increased predisposition to the development of basal cell carcinomas (BCCs). Cutaneous fibroblasts from Gorlin patients have been shown to exhibit an increased sensitivity to ionizing radiations. Mutations in the tumor suppressor gene , which is part of the Sonic Hedgehog (SHH) signaling pathway, are responsible for these clinical manifestations. As several genetic mutations in the DNA repair genes are responsible of photo or radiosensitivity and high predisposition to cancers, we hypothesized that these effects in Gorlin syndrome might be due to a defect in the DNA damage response (DDR) and/or the DNA repair capacities. Therefore, the objective of this work was to investigate the sensitivity of skin fibroblasts from NBCCS patients to different DNA damaging agents and to determine the ability of these agents to modulate the DNA repair capacities. Gorlin fibroblasts showed high radiosensitivity and also less resistance to oxidative stress-inducing agents when compared to control fibroblasts obtained from healthy individuals. Gorlin fibroblasts harboring mutations were more sensitive to the exposure to ionizing radiation and to UVA. However, no difference in cell viability was shown after exposure to UVB or bleomycin. As BER is responsible for the repair of oxidative DNA damage, we decided to assess the BER pathway efficacy in Gorlin fibroblasts. Interestingly, a concomitant decrease of both BER gene expression and BER protein activity was observed in Gorlin fibroblasts when compared to control. Our results suggest that low levels of DNA repair within Gorlin cells may lead to an accumulation of oxidative DNA damage that could participate and partly explain the radiosensitivity and the BCC-prone phenotype in Gorlin syndrome.
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http://dx.doi.org/10.3389/fonc.2020.01551DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7427476PMC
August 2020

Guanine Radicals Induced in DNA by Low-Energy Photoionization.

Acc Chem Res 2020 08 27;53(8):1511-1519. Epub 2020 Jul 27.

Université Paris-Saclay, CEA, CNRS, LIDYL, F-91191 Gif-sur-Yvette, France.

Guanine () radicals are precursors to DNA oxidative damage, correlated with carcinogenesis and aging. During the past few years, we demonstrated clearly an intriguing effect: radicals can be generated upon direct absorption of UV radiation with energy significantly lower than the ionization potential. Using nanosecond transient absorption spectroscopy, we studied the primary species, ejected electrons and guanine radicals, which result from photoionization of various DNA systems in aqueous solution.The DNA propensity to undergo electron detachment at low photon energies greatly depends on its secondary structure. Undetected for monomers or unstacked oligomers, this propensity may be 1 order of magnitude higher for -quadruplexes than for duplexes. The experimental results suggest nonvertical processes, associated with the relaxation of electronic excited states. Theoretical studies are required to validate the mechanism and determine the factors that come into play. Such a mechanism, which may be operative over a broad excitation wavelength range, explains the occurrence of oxidative damage observed upon UVB and UVA irradiation.Quantification of radical populations and their time evolution questions some widespread views. It appears that radicals may be generated with the same probability as pyrimidine dimers, which are considered to be the major lesions induced upon absorption of low-energy UV radiation by DNA. As most radical cations undergo deprotonation, the vast majority of the final reaction products is expected to stem from long-lived deprotonated radicals. Consequently, when radical cations are involved, the widely used oxidation marker 8-oxodG is not representative of the oxidative damage.Beyond the biological consequences, photogeneration of electron holes in -quadruplexes may inspire applications in nanoelectronics; although four-stranded structures are currently studied as molecular wires, their behavior as photoconductors has not been explored so far.In the present Account, after highlighting some key experimental issues, we first describe the photoionization process, and then, we focus on radicals. We use as show-cases new results obtained for genomic DNA and -quadruplexes. Generation and reaction dynamics of radicals in these systems provide a representative picture of the phenomena reported previously for duplexes and -quadruplexes, respectively.
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http://dx.doi.org/10.1021/acs.accounts.0c00245DOI Listing
August 2020

Structural, biochemical and functional analyses of tRNA-monooxygenase enzyme MiaE from Pseudomonas putida provide insights into tRNA/MiaE interaction.

Nucleic Acids Res 2020 09;48(17):9918-9930

Univ. Grenoble Alpes, CEA, CNRS, CBM-UMR 5249, 17 avenue des martyrs, Grenoble, France.

MiaE (2-methylthio-N6-isopentenyl-adenosine37-tRNA monooxygenase) is a unique non-heme diiron enzyme that catalyzes the O2-dependent post-transcriptional allylic hydroxylation of a hypermodified nucleotide 2-methylthio-N6-isopentenyl-adenosine (ms2i6A37) at position 37 of selected tRNA molecules to produce 2-methylthio-N6-4-hydroxyisopentenyl-adenosine (ms2io6A37). Here, we report the in vivo activity, biochemical, spectroscopic characterization and X-ray crystal structure of MiaE from Pseudomonas putida. The investigation demonstrates that the putative pp-2188 gene encodes a MiaE enzyme. The structure shows that Pp-MiaE consists of a catalytic diiron(III) domain with a four alpha-helix bundle fold. A docking model of Pp-MiaE in complex with tRNA, combined with site directed mutagenesis and in vivo activity shed light on the importance of an additional linker region for substrate tRNA recognition. Finally, krypton-pressurized Pp-MiaE experiments, revealed the presence of defined O2 site along a conserved hydrophobic tunnel leading to the diiron active center.
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http://dx.doi.org/10.1093/nar/gkaa667DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7515727PMC
September 2020

Comparative study on gene expression profile in rat lung after repeated exposure to diesel and biodiesel exhausts upstream and downstream of a particle filter.

Environ Pollut 2020 Nov 26;266(Pt 2):115264. Epub 2020 Jul 26.

Univ Rennes, CHU Rennes, Inserm, EHESP, Irset (Institut de Recherche en Santé, Environnement et Travail), UMR_S 1085, 35000, Rennes, France.

Biodiesel is considered as a valuable and less toxic alternative to diesel. However, cellular and molecular effects of repeated exposure to biodiesel emissions from a recent engine equipped with a diesel particle filter (DPF) remain to be characterized. To gain insights about this point, the lung transcriptional signatures were analyzed for rats (n = 6 per group) exposed to filtered air, 30% rapeseed biodiesel (B30) blend or reference diesel (RF0), upstream and downstream a DPF, for 3 weeks (3 h/day, 5 days/week). Genomic analysis revealed a modest regulation of gene expression level (lower than a 2-fold) by both fuels and a higher number of genes regulated downstream the DPF than upstream, in response to either RF0 or to B30 exhaust emissions. The presence of DPF was found to notably impact the lung gene signature of rats exposed to B30. The number of genes regulated in common by both fuels was low, which is likely due to differences in concentrations of regulated pollutants in exhausts, notably for compound organic volatiles, polycyclic aromatic hydrocarbons, NO or NOx. Nevertheless, we have identified some pathways that were activated for both exhaust emissions, such as integrin-, IGF-1- and Rac-signaling pathways, likely reflecting the effects of gas phase products. By contrast, some canonical pathways relative to "oxidative phosphorylation" and "mitochondrial dysfunction" appear as specific to B30 exhaust emission; the repression of transcripts of mitochondrial respiratory chain in lung of rats exposed to B30 downstream of DPF supports the perturbation of mitochondria function. This study done with a recent diesel engine (compliant with the European IV emission standard) and commercially-available fuels reveals that the diesel blend composition and the presence of an after treatment system may modify lung gene signature of rats repeatedly exposed to exhaust emissions, however in a rather modest manner.
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http://dx.doi.org/10.1016/j.envpol.2020.115264DOI Listing
November 2020

Toxicity to RAW264.7 Macrophages of Silica Nanoparticles and the E551 Food Additive, in Combination with Genotoxic Agents.

Nanomaterials (Basel) 2020 Jul 21;10(7). Epub 2020 Jul 21.

Université Grenoble-Alpes, CEA, CNRS, IRIG-DIESE, SyMMES, Chemistry Interface Biology for the Environment, Health and Toxicology (CIBEST), F-38000 Grenoble, France.

Synthetic amorphous silica (SAS) is used in a plethora of applications and included in many daily products to which humans are exposed via inhalation, ingestion, or skin contact. This poses the question of their potential toxicity, particularly towards macrophages, which show specific sensitivity to this material. SAS represents an ideal candidate for the adsorption of environmental contaminants due to its large surface area and could consequently modulate their toxicity. In this study, we assessed the toxicity towards macrophages and intestinal epithelial cells of three SAS particles, either isolated SiO nanoparticles (LS30) or SiO particles composed of agglomerated-aggregates of fused primary particles, either food-grade (E551) or non-food-grade (Fumed silica). These particles were applied to cells either alone or in combination with genotoxic co-contaminants, i.e., benzo[a]pyrene (B[a]P) and methane methylsulfonate (MMS). We show that macrophages are much more sensitive to these toxic agents than a non-differenciated co-culture of Caco-2 and HT29-MTX cells, used here as a model of intestinal epithelium. Co-exposure to SiO and MMS causes DNA damage in a synergistic way, which is not explained by the modulation of DNA repair protein mRNA expression. Together, this suggests that SiO particles could adsorb genotoxic agents on their surface and, consequently, increase their DNA damaging potential.
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http://dx.doi.org/10.3390/nano10071418DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7408573PMC
July 2020

TiO genotoxicity: An update of the results published over the last six years.

Mutat Res 2020 Jun - Jul;854-855:503198. Epub 2020 May 15.

Univ. Grenoble Grenoble Alpes, CEA, CNRS, IRIG-SyMMES, CIBEST, 38000, Grenoble, France. Electronic address:

TiO particles are broadly used in daily products, including cosmetics for their UV-absorbing property, food for their white colouring property, water and air purification systems, self-cleaning surfaces and photoconversion electrical devices for their photocatalytic properties. The toxicity of TiO nano- and microparticles has been studied for decades, and part of this investigation has been dedicated to the identification of their potential impact on DNA, i.e., their genotoxicity. This review summarizes data retrieved from their genotoxicity testing during the past 6 years, encompassing both in vitro and in vivo studies, mostly performed on lung and intestinal models. It shows that TiO particles, both nano- and micro-sized, produce genotoxic damage to a variety of cell types, even at low, realistic doses.
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http://dx.doi.org/10.1016/j.mrgentox.2020.503198DOI Listing
October 2020

Photoinduced DNA Lesions in Dormant Bacteria: The Peculiar Route Leading to Spore Photoproducts Characterized by Multiscale Molecular Dynamics*.

Chemistry 2020 Nov 30;26(62):14236-14241. Epub 2020 Sep 30.

Université de Lorraine and CNRS, LPCT UMR 7019, 54000, Nancy, France.

Some bacterial species enter a dormant state in the form of spores to resist to unfavorable external conditions. Spores are resistant to a wide series of stress agents, including UV radiation, and can last for tens to hundreds of years. Due to the suspension of biological functions, such as DNA repair, they accumulate DNA damage upon exposure to UV radiation. Differently from active organisms, the most common DNA photoproducts in spores are not cyclobutane pyrimidine dimers, but rather the so-called spore photoproducts. This noncanonical photochemistry results from the dry state of DNA and its binding to small, acid-soluble proteins that drastically modify the structure and photoreactivity of the nucleic acid. Herein, multiscale molecular dynamics simulations, including extended classical molecular dynamics and quantum mechanics/molecular mechanics based dynamics, are used to elucidate the coupling of electronic and structural factors that lead to this photochemical outcome. In particular, the well-described impact of the peculiar DNA environment found in spores on the favored formation of the spore photoproduct, given the small free energy barrier found for this path, is rationalized. Meanwhile, the specific organization of spore DNA precludes the photochemical path that leads to cyclobutane pyrimidine dimer formation.
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http://dx.doi.org/10.1002/chem.202002484DOI Listing
November 2020

Oxidative Stress and Genotoxicity in Melanoma Induction: Impact on Repair Rather Than Formation of DNA Damage?

Authors:
Thierry Douki

Photochem Photobiol 2020 09 8;96(5):962-972. Epub 2020 Jun 8.

Université Grenoble Alpes, CEA, CNRS, IRIG, SyMMES, Grenoble, France.

Keratinocytes and melanocytes, two cutaneous cell types located within the epidermis, are the origin of most skin cancers, namely carcinomas and melanomas. These two types of tumors differ in many ways. First, carcinomas are almost 10 times more frequent than melanomas. In addition, the affected cellular pathways, the mutated genes and the metastatic properties of the tumors are not the same. This review addresses another specificity of melanomas: the role of photo-oxidative stress. UVA efficiently produces reactive oxygen species in melanocytes, which results in more frequent oxidatively generated DNA lesions than in other cell types. The question of the respective contribution of UVB-induced pyrimidine dimers and UVA-mediated oxidatively generated lesions to mutagenesis in melanoma remains open. Recent results based on next-generation sequencing techniques strongly suggest that the mutational signature associated with pyrimidine dimers is overwhelming in melanomas like in skin carcinomas. UVA-induced oxidative stress may yet be indirectly linked to the genotoxic pathways involved in melanoma through its ability to hamper DNA repair activities.
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http://dx.doi.org/10.1111/php.13278DOI Listing
September 2020

DNA Damage Kills Bacterial Spores and Cells Exposed to 222-Nanometer UV Radiation.

Appl Environ Microbiol 2020 04 1;86(8). Epub 2020 Apr 1.

Department of Molecular Biology and Biophysics, UConn Health, Farmington, Connecticut, USA

This study examined the microbicidal activity of 222-nm UV radiation (UV), which is potentially a safer alternative to the 254-nm UV radiation (UV) that is often used for surface decontamination. Spores and/or growing and stationary-phase cells of , , , , and and a herpesvirus were all killed or inactivated by UV and at lower fluences than with UV spores and cells lacking the major DNA repair protein RecA were more sensitive to UV, as were spores lacking their DNA-protective proteins, the α/β-type small, acid-soluble spore proteins. The spore cores' large amount of Ca-dipicolinic acid (∼25% of the core dry weight) also protected and spores against UV, while spores' proteinaceous coat may have given some slight protection against UV Survivors among spores treated with UV acquired a large number of mutations, and this radiation generated known mutagenic photoproducts in spore and cell DNA, primarily cyclobutane-type pyrimidine dimers in growing cells and an α-thyminyl-thymine adduct termed the spore photoproduct (SP) in spores. Notably, the loss of a key SP repair protein markedly decreased spore UV resistance. UV-treated spores germinated relatively normally, and the generation of colonies from these germinated spores was not salt sensitive. The latter two findings suggest that UV does not kill spores by general protein damage, and thus, the new results are consistent with the notion that DNA damage is responsible for the killing of spores and cells by UV Spores of a variety of bacteria are resistant to common decontamination agents, and many of them are major causes of food spoilage and some serious human diseases, including anthrax caused by spores of Consequently, there is an ongoing need for efficient methods for spore eradication, in particular methods that have minimal deleterious effects on people or the environment. UV radiation at 254 nm (UV) is sporicidal and commonly used for surface decontamination but can cause deleterious effects in humans. Recent work, however, suggests that 222-nm UV (UV) may be less harmful to people than UV yet may still kill bacteria and at lower fluences than UV The present work has identified the damage by UV that leads to the killing of growing cells and spores of some bacteria, many of which are human pathogens, and UV also inactivates a herpesvirus.
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http://dx.doi.org/10.1128/AEM.03039-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7117916PMC
April 2020

Metabolism and genotoxicity of polycyclic aromatic hydrocarbons in human skin explants: mixture effects and modulation by sunlight.

Arch Toxicol 2020 02 17;94(2):495-507. Epub 2019 Dec 17.

Univ. Grenoble Alpes, UGA, CEA, CNRS, IRIG, SyMMES, 38000, Grenoble, France.

Cutaneous exposure to carcinogenic polycyclic aromatic hydrocarbons (PAH) occurs frequently in the industrialized workplace. In the present study, we addressed this topic in a series of experiments using human skin explants and organic extracts of relevant industrial products. PAH mixtures were applied topically in volumes containing either 10 or 1 nmol B[a]P. We first observed that although mixtures were very efficient at inducing expression of CYP450 1A1, 1A2, and 1B1, formation of adducts of PAH metabolites to DNA, like those of benzo[a]pyrene diol epoxide (BPDE), was drastically reduced as the complexity of the surrounding matrix increased. Interestingly, observation of a nonlinear, dose-dependent response with the least complex mixture suggested the existence of a threshold for this inhibitory effect. We then investigated the impact of simulated sunlight (SSL) on the effects of PAH in skin. SSL was found to decrease the expression of CYP450 genes when applied either after or more efficiently before PAH treatment. Accordingly, the level of DNA-BPDE adducts was reduced in skin samples exposed to both PAH and SSL. The main conclusion of our work is that both increasing chemical complexity of the mixtures and co-exposure to UV radiation decreased the production of adducts between DNA and PAH metabolites. Such results must be taken into account in risk management.
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http://dx.doi.org/10.1007/s00204-019-02650-zDOI Listing
February 2020

Toxicity and DNA repair in normal human keratinocytes co-exposed to benzo[a]pyrene and sunlight.

Toxicol In Vitro 2020 Mar 11;63:104744. Epub 2019 Dec 11.

Univ. Grenoble Alpes, SyMMES/CIBEST UMR 5819 UGA-CNRS-CEA, INAC/CEA-Grenoble LAN, F-38000 Grenoble, France. Electronic address:

Skin has the potential to be exposed to both solar UV radiation and polycyclic aromatic hydrocarbons, especially in occupational environments. In the present work, we investigated how benzo[a]pyrene (B[a]P) modulates cellular phototoxicity and impacts formation and repair of pyrimidine dimers induced by simulated sunlight (SSL) in normal human keratinocytes (NHK). We were especially interested in determining whether the aryl hydrocarbon receptor (AhR) was involved since it was recently shown to negatively impact repair. Addition of 1 μM B[a]P after exposure to 2 minimal erythemal doses of SSL had little impact on NHK. The inverse protocol involving incubation with B[a]P followed by irradiation led to a strong increase in phototoxicity. Repair of DNA photoproducts was drastically impaired. Using agonists and antagonists of AhR allowed us to conclude that this factor was not involved in these results. Observation of a strong increase in the level of the oxidative marker 8-oxo-7,8-dihydroguanine in the protocol involving B[a]P treatment followed by exposure to SSL strongly suggested that a photosensitized oxidative stress was responsible for cell death and inhibition of DNA repair. Accordingly, both adverse effects were diminished with a lower concentration of B[a]P and a lower SSL dose, leading to less oxidative stress.
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http://dx.doi.org/10.1016/j.tiv.2019.104744DOI Listing
March 2020

Toxicological impact of acute exposure to E171 food additive and TiO nanoparticles on a co-culture of Caco-2 and HT29-MTX intestinal cells.

Mutat Res 2019 09 22;845:402980. Epub 2018 Nov 22.

Univ. Grenoble-Alpes, CEA, CNRS, INAC-SyMMES, Chimie Interface Biologie pour l'Environnement, la Santé et la Toxicologie (CIBEST), 38000, Grenoble, France. Electronic address:

TiO particles are widely used in products for everyday consumption, such as cosmetics and food; their possible adverse effects on human health must therefore be investigated. The aim of this study was to document in vitro impact of the food additive E171, i.e. TiO, and of TiO nanoparticles, on a co-culture of Caco-2 and HT29-MTX cells, which is an in vitro model for human intestine. Cells were exposed to TiO particles three days after seeding, i.e. while they were not fully differentiated. Cell viability, reactive oxygen species (ROS) levels and DNA integrity were assessed, by MTT assay, DCFH-DA assay, alkaline and Fpg-modified comet assay and 8-oxo-dGuo measurement by HPLC-MS/MS. The mRNA expression of genes involved in ROS regulation, DNA repair via base-excision repair, and endoplasmic reticulum stress was assessed by RT-qPCR. Exposure to TiO particles resulted in increased intracellular ROS levels, but did not impair cell viability and did not cause any oxidative damage to DNA. Only minor changes in mRNA expression were detected. Altogether, this shows that E171 food additive and TiO nanoparticles only produce minor effects to this in vitro intestinal cell model.
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http://dx.doi.org/10.1016/j.mrgentox.2018.11.004DOI Listing
September 2019

Wavelength- and Tissue-dependent Variations in the Mutagenicity of Cyclobutane Pyrimidine Dimers in Mouse Skin.

Photochem Photobiol 2020 01 15;96(1):94-104. Epub 2019 Oct 15.

Department of Medical Biochemistry, Tohoku University Graduate School of Medicine, Sendai, Japan.

The cyclobutane pyrimidine dimer (CPD) is a main mutagenic photolesion in DNA produced by UVR. We previously studied the wavelength-dependent kinetics of mutation induction efficiency using monochromatic UVR sources and transgenic mice developed for mutation assay and established the action spectra of UVR mutagenicity in the mouse epidermis and dermis. Here, we further established the action spectra of CPD and pyrimidine(6-4)pyrimidone photoproduct formation in the same tissues and in naked DNA using the same sources and mouse strain. Quantitative ELISA helped us estimate the photolesion formation efficiencies on a molecule-per-nucleotide basis. Using these action spectra, we confirmed that the UVR mutation mostly depends on CPD formation. Moreover, the mutagenicity of a CPD molecule (CPD mutagenicity) was found to vary by wavelength, peaking at approximately 313 nm in both the epidermis and dermis with similar wavelength-dependent patterns. Thus, the CPD formation efficiency is a main determinant of UVR mutagenicity in mouse skin, whereas a wavelength-dependent variation in the qualitative characteristics of CPD molecules also affects the mutagenic consequences of UVR insults. In addition, the CPD mutagenicity was always higher in the epidermis than in the dermis, suggesting different cellular responses to UVR between the two tissues irrespective of the wavelength.
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http://dx.doi.org/10.1111/php.13159DOI Listing
January 2020

Influence of exposure dose, complex mixture, and ultraviolet radiation on skin absorption and bioactivation of polycyclic aromatic hydrocarbons ex vivo.

Arch Toxicol 2019 08 8;93(8):2165-2184. Epub 2019 Jul 8.

Equipe Environnement et Prédiction de la Santé des Populations, Laboratoire TIMC-IMAG (UMR 5525 UGA-CNRS), Université Grenoble Alpes, Faculté de Médecine, Domaine de la Merci, 38706, La Tronche Cedex, France.

Combined exposure to complex mixtures of polycyclic aromatic hydrocarbons (PAHs) and ultraviolet radiation (UVR) is suspected to enhance PAH skin permeability and skin cancer risk depending on PAH bioactivation. The impact of PAH mixtures (exposure dose, composition, and complexity) and UVR was assessed for PAH cutaneous absorption and metabolism using realistic exposure conditions and human skin explants. PAH complex mixtures were extracted from the industrial products coal tar pitch (CTP-I) and petroleum coke (PC-I). The synthetic mixture (CTP-S) was identically reconstituted using PAH standards. The applied dose was adjusted to 1 (PC-I, CTP-I) or 10 nmol (CTP-I, CTP-S) of benzo[a]pyrene (B[a]P). Unmetabolized PAHs were recovered from the skin surface, skin and medium, and then quantified by HPLC-fluorescence detection. PAH metabolites were collected from the medium and analyzed by GC-MS/MS. B[a]P and PAH penetration was lower for the highest B[a]P dose, industrial mixtures, and CTP-I compared to PC-I. Skin irradiation increased PAH penetration only for CTP-I. PAH uptake was poorly influenced by the different experimental conditions. PAH metabolism markedly decreased in the application of mixtures, leading to unmetabolized PAH accumulation in human skin. PAH metabolism was similar between CTP-I and PC-I, but was lower for the highest dose and the industrial mixtures, suggesting a saturation of xenobiotic metabolizing enzymes, as confirmed in a time-course study. UVR strongly inhibited all PAH metabolism. Altogether, these results underline the necessity to consider the reality of human exposure (PAH complex mixtures and UVR) during in vitro experiments to properly estimate skin absorption and metabolism.
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http://dx.doi.org/10.1007/s00204-019-02504-8DOI Listing
August 2019

Radicals Generated in Tetramolecular Guanine Quadruplexes by Photoionization: Spectral and Dynamical Features.

J Phys Chem B 2019 06 31;123(23):4950-4957. Epub 2019 May 31.

LIDYL, CEA, CNRS, Université Paris-Saclay , F-91191 Gif-sur-Yvette , France.

G-quadruplexes are four-stranded DNA structures playing a key role in many biological functions and are promising for applications in the field of nanoelectronics. Characterizing the generation and fate of radical cations (electron holes) within these systems is important in relation to the DNA oxidative damage and/or conductivity issues. This study focuses on guanine radicals in G-quadruplexes formed by association of four TGGGGT strands in the presence of Na cations, (TG4T)/Na. Using nanosecond transient spectroscopy with 266 nm excitation, we quantitatively characterize hydrated ejected electrons and three types of guanine radicals. We show that, at an energy lower by 2.7 eV than the guanine ionization potential, one-photon ionization occurs with quantum yield of (3.5 ± 0.5) × 10. Deprotonation of the radical cations is completed within 20 μs, leading to the formation of (G-H2) radicals, following a strongly nonexponential decay pattern. Within 10 ms, the latter undergoes tautomerization to deprotonated (G-H1) radicals. The dynamics of the various radicals determined for (TG4T)/Na, in connection to those reported previously for telomeric G-quadruplexes TEL21/Na, is correlated with energetic factors computed by quantum chemical methods. The faster deprotonation of radical cations in (TG4T)/Na compared to TEL21/Na explains that irradiation of the former does not generate 8-oxodGuo, which is readily detected by high-performance liquid chromatography/mass spectrometry in the case of TEL21/Na.
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http://dx.doi.org/10.1021/acs.jpcb.9b02637DOI Listing
June 2019

A realistic human skin model to study benzo[a]pyrene cutaneous absorption in order to determine the most relevant biomarker for carcinogenic exposure.

Arch Toxicol 2019 01 22;93(1):81-93. Epub 2018 Oct 22.

Equipe Environnement et Prédiction de la Santé des Populations, Faculté de Médecine, Laboratoire TIMC-IMAG (UMR 5525 UGA-CNRS), Université Grenoble Alpes, 38706, La Tronche, France.

Polycyclic aromatic hydrocarbons (PAH) are ubiquitous pollutants, among which benzo[a]pyrene (B[a]P) is the only compound classified carcinogenic to humans. Besides pulmonary uptake, skin is the major route of PAH absorption during occupational exposure. Health risk due to PAH exposure is commonly assessed among workers using biomonitoring. A realistic human ex vivo skin model was developed to explore B[a]P diffusion and metabolism to determine the most relevant biomarker following dermal exposure. Three realistic doses (0.88, 8.85 and 22.11 nmol/cm) were topically applied for 8, 24, and 48 h. B[a]P and its metabolites were quantified by liquid chromatography coupled with fluorimetric detection. The impact of time, applied dose, and donor age were estimated using a linear mixed-effects model. B[a]P vastly penetrated the skin within 8 h. The major metabolites were 3-hydroxybenzo[a]pyrene (3-OHB[a]P) and 7,8,9,10-tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene (B[a]P-tetrol). This latter predominantly derives from the most carcinogenic metabolite of B[a]P, benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE), as well as benzo[a]pyrene-9,10-diol-7,8-epoxide (reverse-BPDE). Benzo[a]pyrene-trans-7,8-dihydrodiol (B[a]P-7,8-diol) was a minor metabolite, and benzo[a]pyrene-trans-4,5-dihydrodiol (B[a]P-4,5-diol) was never quantified. Unmetabolized B[a]P bioavailability was limited following dermal exposure since less than 3% of the applied dose could be measured in the culture medium. B[a]P was continuously absorbed and metabolized by human skin over 48 h. B[a]P-tetrol production became saturated as the applied dose increased, while no effect was measured on the other metabolic pathways. Age had a slight positive effect on B[a]P absorption and metabolism. This work supports the relevance of B[a]P-tetrol to assess occupational exposure and carcinogenic risk after cutaneous absorption of B[a]P.
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http://dx.doi.org/10.1007/s00204-018-2329-2DOI Listing
January 2019

Solar simulated light exposure alters metabolization and genotoxicity induced by benzo[a]pyrene in human skin.

Sci Rep 2018 10 2;8(1):14692. Epub 2018 Oct 2.

Univ. Grenoble Alpes, CEA, CNRS, INAC-SyMMES-CIBEST, Grenoble, France.

Skin is a major barrier against external insults and is exposed to combinations of chemical and/or physical toxic agents. Co-exposure to the carcinogenic benzo[a]pyrene (B[a]P) and solar UV radiation is highly relevant in human health, especially in occupational safety. In vitro studies have suggested that UVB enhances B[a]P genotoxicity by activating the AhR pathway and overexpressing the cytochrome P450 enzymes responsible for the conversion of B[a]P into DNA damaging metabolites. Our present work involved more realistic conditions, namely ex vivo human skin explants and simulated sunlight (SSL) as a UV source. We found that topically applied B[a]P strongly induced expression of cutaneous cytochrome P450 genes and formation of DNA adducts. However, gene induction was significantly reduced when B[a]P was combined with SSL. Consequently, formation of BPDE-adducts was also reduced when B[a]P was associated with SSL. Similar results were obtained with primary cultures of human keratinocytes. These results indicate that UV significantly impairs B[a]P metabolism, and decreases rather than increases immediate toxicity. However, it cannot be ruled out that decreased metabolism leads to accumulation of B[a]P and delayed genotoxicity.
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http://dx.doi.org/10.1038/s41598-018-33031-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6168490PMC
October 2018

The UV/Visible Radiation Boundary Region (385-405 nm) Damages Skin Cells and Induces "dark" Cyclobutane Pyrimidine Dimers in Human Skin in vivo.

Sci Rep 2018 08 24;8(1):12722. Epub 2018 Aug 24.

St. John's Institute of Dermatology, King's College London, Guy's Hospital, London, SE1 9RT, UK.

The adverse effects of terrestrial solar ultraviolet radiation (UVR) (~295-400 nm) on the skin are well documented, especially in the UVB region (~295-320 nm). The effects of very long-wave UVA (>380 nm) and visible radiation (≥400 nm) are much less known. Sunscreens have been beneficial in inhibiting a wide range of photodamage, however most formulations provide very little protection in the long wave UVA region (380-400 nm) and almost none from shortwave visible wavelengths (400-420 nm). We demonstrate photodamage in this region for a number of different endpoints including cell viability, DNA damage (delayed cyclobutane pyrimidine dimers), differential gene expression (for genes associated with inflammation, oxidative stress and photoageing) and induction of oxidizing species in vitro in HaCaT keratinocytes and in vivo in human volunteers. This work has implications for phototherapy and photoprotection.
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http://dx.doi.org/10.1038/s41598-018-30738-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6109054PMC
August 2018

The AHR represses nucleotide excision repair and apoptosis and contributes to UV-induced skin carcinogenesis.

Cell Death Differ 2018 11 16;25(10):1823-1836. Epub 2018 Jul 16.

IUF-Leibniz-Research Institute for Environmental Medicine, 40225, Düsseldorf, Germany.

Ultraviolet B (UVB) radiation induces mutagenic DNA photoproducts, in particular cyclobutane pyrimidine dimers (CPDs), in epidermal keratinocytes (KC). To prevent skin carcinogenesis, these DNA photoproducts must be removed by nucleotide excision repair (NER) or apoptosis. Here we report that the UVB-sensitive transcription factor aryl hydrocarbon receptor (AHR) attenuates the clearance of UVB-induced CPDs in human HaCaT KC and skin from SKH-1 hairless mice. Subsequent RNA interference and inhibitor studies in KC revealed that AHR specifically suppresses global genome but not transcription-coupled NER. In further experiments, we found that the accelerated repair of CPDs in AHR-compromised KC depended on a modulation of the p27 tumor suppressor protein. Accordingly, p27 protein levels were increased in AHR-silenced KC and skin biopsies from AHR mice, and critical for the improvement of NER. Besides increasing NER activity, AHR inhibition was accompanied by an enhanced occurrence of DNA double-strand breaks triggering KC apoptosis at later time points after irradiation. The UVB-activated AHR thus acts as a negative regulator of both early defense systems against carcinogenesis, NER and apoptosis, implying that it exhibits tumorigenic functions in UVB-exposed skin. In fact, AHR mice developed 50% less UVB-induced cutaneous squamous cell carcinomas in a chronic photocarcinogenesis study than their AHR littermates. Taken together, our data reveal that AHR influences DNA damage-dependent responses in UVB-irradiated KC and critically contributes to skin photocarcinogenesis in mice.
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http://dx.doi.org/10.1038/s41418-018-0160-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6180092PMC
November 2018

Sub-optimal Application of a High SPF Sunscreen Prevents Epidermal DNA Damage in Vivo.

Acta Derm Venereol 2018 Oct;98(9):880-887

St John's Institute of Dermatology, Kings College London, SE1 9RT London, United Kingdom.

The cyclobutane pyrimidine dimer (CPD) is a potentially mutagenic DNA photolesion that is the basis of most skin cancers. There are no data on DNA protection by sunscreens under typical conditions of use. The study aim was to determine such protection, in phototypes I/II, with representative sunscreen-user application. A very high SPF formulation was applied at 0.75, 1.3 and 2.0 mg/cm2. Unprotected control skin was exposed to 4 standard erythema doses (SED) of solar simulated UVR, and sunscreen-treated sites to 30 SED. Holiday behaviour was also simulated by UVR exposure for 5 consecutive days. Control skin received 1 SED daily, and sunscreen-treated sites received 15 (all 3 application thicknesses) or 30 (2.0 mg/cm2) SED daily. CPD were assessed by quantitative HPLC-tandem mass spectrometry (HPLC-MS/MS) and semi-quantitative immunostaining. In comparison with unprotected control sites, sunscreen significantly (p ≤ 0.001-0.05) reduced DNA damage at 1.3 and 2.0 mg/cm2 in all cases. However, reduction with typical sunscreen use (0.75 mg/cm2) was non-significant, with the exception of HPLC-MS/MS data for the 5-day study (p <0.001). Overall, these results support sunscreen use as a strategy to reduce skin cancer, and demonstrate that public health messages must stress better sunscreen application to get maximal benefit.
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http://dx.doi.org/10.2340/00015555-2992DOI Listing
October 2018

Energy Metabolism Rewiring Precedes UVB-Induced Primary Skin Tumor Formation.

Cell Rep 2018 06;23(12):3621-3634

Inserm U 1035, BMGIC, 33076 Bordeaux, France; Université de Bordeaux, 146 rue Léo Saignat, 33076 Bordeaux, France; Centre de Référence pour les Maladies Rares de la Peau, CHU de Bordeaux, France. Electronic address:

Although growing evidence indicates that bioenergetic metabolism plays an important role in the progression of tumorigenesis, little information is available on the contribution of reprogramming of energy metabolism in cancer initiation. By applying a quantitative proteomic approach and targeted metabolomics, we find that specific metabolic modifications precede primary skin tumor formation. Using a multistage model of ultraviolet B (UVB) radiation-induced skin cancer, we show that glycolysis, tricarboxylic acid (TCA) cycle, and fatty acid β-oxidation are decreased at a very early stage of photocarcinogenesis, while the distal part of the electron transport chain (ETC) is upregulated. Reductive glutamine metabolism and the activity of dihydroorotate dehydrogenase (DHODH) are both necessary for maintaining high ETC. Mice with decreased DHODH activity or impaired ETC failed to develop pre-malignant and malignant lesions. DHODH activity represents a major link between DNA repair efficiency and bioenergetic patterning during skin carcinogenesis.
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http://dx.doi.org/10.1016/j.celrep.2018.05.060DOI Listing
June 2018

6-Formylindolo[3,2-b]carbazole (FICZ) is a Very Minor Photoproduct of Tryptophan at Biologically Relevant Doses of UVB and Simulated Sunlight.

Photochem Photobiol 2019 01 12;95(1):237-243. Epub 2018 Jul 12.

Univ. Grenoble Alpes, CEA, CNRS, INAC, SyMMES/CIBEST, Grenoble, France.

Exposure to solar UV is at the origin of numerous photodegradation pathways in biomolecules. Tryptophan is readily modified by UVB radiation into ring-opened and oxidized photoproducts. One of them, 6-formylindolo[3,2-b]carbazole (FICZ), has been extensively studied in the recent years because it very efficiently binds to AhR, a major factor in numerous biologic processes, such as metabolism of xenobiotics. Unfortunately, little information is available on the actual yield of FICZ upon exposure to low and biologically relevant doses of UV radiation. In the present work, we used a sensitive and specific HPLC-tandem mass spectrometry assay to quantify a series of photoproducts induced by UVB and simulated sunlight (SSL) in solutions of tryptophan. FICZ represented only a minute amount of the photoproducts (0.02 and 0.03%, respectively). Experiments were repeated in culture medium where the yield of FICZ was also found to be very low, even when Trp was added. Last, no FICZ could be detected in cytosolic fractions of cultured cells exposed to SSL. Altogether, the present results show that FICZ is a very minor photoproduct and that it cannot be considered the only endogenous photoproduct responsible for the induction of AhR-dependent responses in UV-irradiated cells.
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http://dx.doi.org/10.1111/php.12950DOI Listing
January 2019

The Photochemistry of Unprotected DNA and DNA inside Bacillus subtilis Spores Exposed to Simulated Martian Surface Conditions of Atmospheric Composition, Temperature, Pressure, and Solar Radiation.

Astrobiology 2018 04 28;18(4):393-402. Epub 2018 Mar 28.

3 Univ. Grenoble Alpes , CEA, CNRS, INAC, SyMMES/CIBEST, Grenoble, France .

DNA is considered a potential biomarker for life-detection experiments destined for Mars. Experiments were conducted to examine the photochemistry of bacterial DNA, either unprotected or within Bacillus subtilis spores, in response to exposure to simulated martian surface conditions consisting of the following: temperature (-10°C), pressure (0.7 kPa), atmospheric composition [CO (95.54%), N (2.7%), Ar (1.6%), O (0.13%), and HO (0.03%)], and UV-visible-near IR solar radiation spectrum (200-1100 nm) calibrated to 4 W/m of UVC (200-280 nm). While the majority (99.9%) of viable spores deposited in multiple layers on spacecraft-qualified aluminum coupons were inactivated within 5 min, a detectable fraction survived for up to the equivalent of ∼115 martian sols. Spore photoproduct (SP) was the major lesion detected in spore DNA, with minor amounts of cyclobutane pyrimidine dimers (CPD), in the order TT CPD > TC CPD > CT CPD. In addition, the (6-4)TC, but not the (6-4)TT, photoproduct was detected in spore DNA. When unprotected DNA was exposed to simulated martian conditions, all photoproducts were detected. Surprisingly, the (6-4)TC photoproduct was the major photoproduct, followed by SP ∼ TT CPD > TC CPD > (6-4)TT > CT CPD > CC CPD. Differences in the photochemistry of unprotected DNA and spore DNA in response to simulated martian surface conditions versus laboratory conditions are reviewed and discussed. The results have implications for the planning of future life-detection experiments that use DNA as the target, and for the long-term persistence on Mars of forward contaminants or their DNA. Key Words: Bacillus subtilis-DNA-Mars-Photochemistry-Spore-Ultraviolet. Astrobiology 18, 393-402.
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http://dx.doi.org/10.1089/ast.2017.1721DOI Listing
April 2018

Quantitative analysis of UV photolesions suggests that cyclobutane pyrimidine dimers produced in mouse skin by UVB are more mutagenic than those produced by UVC.

Photochem Photobiol Sci 2018 Apr;17(4):404-413

Department of Medical Biochemistry, Tohoku University Graduate School of Medicine, Sendai, Japan.

The amount of photolesions produced in DNA after exposure to physiological doses of ultraviolet radiation (UVR) can be estimated with high sensitivity and at low cost through an immunological assay, ELISA, which, however, provides only a relative estimate that cannot be used for comparisons between different photolesions such as cyclobutane pyrimidine dimer (CPD) and pyrimidine(6-4)pyrimidone photoproduct (64PP) or for analysis of the genotoxicity of photolesions on a molecular basis. To solve this drawback of ELISA, we introduced a set of UVR-exposed, calibration DNA whose photolesion amounts were predetermined and estimated the absolute molecular amounts of CPDs and 64PPs produced in mouse skin exposed to UVC and UVB. We confirmed previously reported observations that UVC induced more photolesions in the skin than UVB at the same dose, and that both types of UVR produced more CPDs than 64PPs. The UVR protection abilities of the cornified and epidermal layers for the lower tissues were also evaluated quantitatively. We noticed that the values of absorbance obtained in ELISA were not always proportional to the molecular amounts of the lesion, especially for CPD, cautioning against the direct use of ELISA absorbance data for estimation of the photolesion amounts. We further estimated the mutagenicity of a CPD produced by UVC and UVB in the epidermis and dermis using the mutation data from our previous studies with mouse skin and found that CPDs produced in the epidermis by UVB were more than two-fold mutagenic than those by UVC, which suggests that the properties of CPDs produced by UVC and UVB might be different. The difference may originate from the wavelength-dependent methyl CpG preference of CPD formation. In addition, the mutagenicity of CPDs in the dermis was lower than that in the epidermis irrespective of the UVR source, suggesting a higher efficiency in the dermis to reduce the genotoxicity of CPDs produced within it. We also estimated the minimum amount of photolesions required to induce the mutation induction suppression (MIS) response in the epidermis to be around 15 64PPs or 100 CPDs per million bases in DNA as the mean estimate from UVC and UVB-induced MIS.
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http://dx.doi.org/10.1039/c7pp00348jDOI Listing
April 2018

Formation of UV-induced DNA damage contributing to skin cancer development.

Photochem Photobiol Sci 2018 Dec;17(12):1816-1841

Département de Médecine Nucléaire et Radiobiologie, Faculté de Médecine, 3001 12e Avenue Nord, Université de Sherbrooke, Sherbrooke, Québec JIH 5N4, Canada.

UV-induced DNA damage plays a key role in the initiation phase of skin cancer. When left unrepaired or when damaged cells are not eliminated by apoptosis, DNA lesions express their mutagneic properties, leading to the activation of proto-oncogene or the inactivation of tumor suppression genes. The chemical nature and the amount of DNA damage strongly depend on the wavelength of the incident photons. The most energetic part of the solar spectrum at the Earth's surface (UVB, 280-320 nm) leads to the formation of cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts (64PPs). Less energetic but 20-times more intense UVA (320-400 nm) also induces the formation of CPDs together with a wide variety of oxidatively generated lesions such as single strand breaks and oxidized bases. Among those, 8-oxo-7,8-dihydroguanine (8-oxoGua) is the most frequent since it can be produced by several mechanisms. Data available on the respective yield of DNA photoproducts in cells and skin show that exposure to sunlight mostly induces pyrimidine dimers, which explains the mutational signature found in skin tumors, with lower amounts of 8-oxoGua and strand breaks. The present review aims at describing the basic photochemistry of DNA and discussing the quantitative formation of the different UV-induced DNA lesions reported in the literature. Additional information on mutagenesis, repair and photoprotection is briefly provided.
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http://dx.doi.org/10.1039/c7pp00395aDOI Listing
December 2018