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      Effect of ultraviolet C emitted from KrCl excimer lamp with or without bandpass filter to mouse epidermis

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          Abstract

          It has been reported that 222-nm ultraviolet C (UVC) exerts a germicidal effect on bacteria and viruses as well as UV radiation emitted from a conventional germicidal lamp but is less toxic to the mammalian cells than that from a germicidal lamp. An excimer lamp filled with krypton chloride (KrCl) gas principally emits 222-nm UVC. However, the lamp also emits a wide band of wavelengths other than 222 nm, especially UVC at a longer wavelength than 222 nm and ultraviolet B, which cause DNA damage. There are some reports on the critical role of bandpass filters in reducing the harmful effect of UVC emitted from a KrCl excimer lamp in a human skin model and human subjects. However, the effectiveness of a bandpass filter has not been demonstrated in animal experiments. In the present study, mice were irradiated with UVC emitted from a KrCl excimer lamp with or without a bandpass filter. UVC emitted from an unfiltered KrCl lamp at doses of 50, 150 and 300 mJ/cm 2 induced cyclobutyl pyrimidine dimer (CPD)-positive cells, whereas UVC emitted from a filtered lamp did not significantly increase CPD-positive cells in the epidermis. The present study suggested that the bandpass filter serves a critical role in reducing the harmful effect of emission outside of 222 nm to mouse keratinocytes.

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          Mutations induced by ultraviolet light.

          The different ultraviolet (UV) wavelength components, UVA (320-400 nm), UVB (280-320 nm), and UVC (200-280 nm), have distinct mutagenic properties. A hallmark of UVC and UVB mutagenesis is the high frequency of transition mutations at dipyrimidine sequences containing cytosine. In human skin cancers, about 35% of all mutations in the p53 gene are transitions at dipyrimidines within the sequence 5'-TCG and 5'-CCG, and these are localized at several mutational hotspots. Since 5'-CG sequences are methylated along the p53 coding sequence in human cells, these mutations may be derived from sunlight-induced pyrimidine dimers forming at sequences that contain 5-methylcytosine. Cyclobutane pyrimidine dimers (CPDs) form preferentially at dipyrimidines containing 5-methylcytosine when cells are irradiated with UVB or sunlight. In order to define the contribution of 5-methylcytosine to sunlight-induced mutations, the lacI and cII transgenes in mouse fibroblasts were used as mutational targets. After 254 nm UVC irradiation, only 6-9% of the base substitutions were at dipyrimidines containing 5-methylcytosine. However, 24-32% of the solar light-induced mutations were at dipyrimidines that contain 5-methylcytosine and most of these mutations were transitions. Thus, CPDs forming preferentially at dipyrimidines with 5-methylcytosine are responsible for a considerable fraction of the mutations induced by sunlight in mammalian cells. Using mouse cell lines harboring photoproduct-specific photolyases and mutational reporter genes, we showed that CPDs (rather than 6-4 photoproducts or other lesions) are responsible for the great majority of UVB-induced mutations. An important component of UVB mutagenesis is the deamination of cytosine and 5-methylcytosine within CPDs. The mutational specificity of long-wave UVA (340-400 nm) is distinct from that of the shorter wavelength UV and is characterized mainly by G to T transversions presumably arising through mechanisms involving oxidized DNA bases. We also discuss the role of DNA damage-tolerant DNA polymerases in UV lesion bypass and mutagenesis.
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            Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses

            A direct approach to limit airborne viral transmissions is to inactivate them within a short time of their production. Germicidal ultraviolet light, typically at 254 nm, is effective in this context but, used directly, can be a health hazard to skin and eyes. By contrast, far-UVC light (207–222 nm) efficiently kills pathogens potentially without harm to exposed human tissues. We previously demonstrated that 222-nm far-UVC light efficiently kills airborne influenza virus and we extend those studies to explore far-UVC efficacy against airborne human coronaviruses alpha HCoV-229E and beta HCoV-OC43. Low doses of 1.7 and 1.2 mJ/cm2 inactivated 99.9% of aerosolized coronavirus 229E and OC43, respectively. As all human coronaviruses have similar genomic sizes, far-UVC light would be expected to show similar inactivation efficiency against other human coronaviruses including SARS-CoV-2. Based on the beta-HCoV-OC43 results, continuous far-UVC exposure in occupied public locations at the current regulatory exposure limit (~3 mJ/cm2/hour) would result in ~90% viral inactivation in ~8 minutes, 95% in ~11 minutes, 99% in ~16 minutes and 99.9% inactivation in ~25 minutes. Thus while staying within current regulatory dose limits, low-dose-rate far-UVC exposure can potentially safely provide a major reduction in the ambient level of airborne coronaviruses in occupied public locations.
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              Germicidal Efficacy and Mammalian Skin Safety of 222-nm UV Light

              We have previously shown that 207-nm ultraviolet (UV) light has similar antimicrobial properties as typical germicidal UV light (254 nm), but without inducing mammalian skin damage. The biophysical rationale is based on the limited penetration distance of 207-nm light in biological samples (e.g. stratum corneum) compared with that of 254-nm light. Here we extended our previous studies to 222-nm light and tested the hypothesis that there exists a narrow wavelength window in the far-UVC region, from around 200–222 nm, which is significantly harmful to bacteria, but without damaging cells in tissues. We used a krypton-chlorine (Kr-Cl) excimer lamp that produces 222-nm UV light with a bandpass filter to remove the lower- and higher-wavelength components. Relative to respective controls, we measured: 1. in vitro killing of methicillin-resistant Staphylococcus aureus (MRSA) as a function of UV fluence; 2. yields of the main UV-associated premutagenic DNA lesions (cyclobutane pyrimidine dimers and 6-4 photoproducts) in a 3D human skin tissue model in vitro ; 3. eight cellular and molecular skin damage endpoints in exposed hairless mice in vivo . Comparisons were made with results from a conventional 254-nm UV germicidal lamp used as positive control. We found that 222-nm light kills MRSA efficiently but, unlike conventional germicidal UV lamps (254 nm), it produces almost no premutagenic UV-associated DNA lesions in a 3D human skin model and it is not cytotoxic to exposed mammalian skin. As predicted by biophysical considerations and in agreement with our previous findings, far-UVC light in the range of 200–222 nm kills bacteria efficiently regardless of their drug-resistant proficiency, but without the skin damaging effects associated with conventional germicidal UV exposure.
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                Author and article information

                Contributors
                Role: ConceptualizationRole: Formal analysisRole: InvestigationRole: ValidationRole: Writing – original draft
                Role: ConceptualizationRole: Writing – original draft
                Role: InvestigationRole: Writing – original draft
                Role: ConceptualizationRole: Writing – original draft
                Role: ConceptualizationRole: Writing – original draft
                Role: ConceptualizationRole: Project administrationRole: SupervisionRole: Writing – original draft
                Role: Editor
                Journal
                PLoS One
                PLoS One
                plos
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                3 May 2022
                2022
                : 17
                : 5
                : e0267957
                Affiliations
                [1 ] Department of Microbiology and Immunology, Hirosaki University Graduate School of Medicine, Hirosaki, Aomori, Japan
                [2 ] Institute for Animal Experimentation, Hirosaki University Graduate School of Medicine, Hirosaki, Aomori, Japan
                [3 ] Department of Biopolymer and Health Science, Hirosaki University Graduate School of Medicine, Hirosaki, Aomori, Japan
                [4 ] Ushio Inc., Chiyoda-ku, Tokyo, Japan
                Massachusetts General Hospital, UNITED STATES
                Author notes

                Competing Interests: I have read the journal’s policy and the authors of this manuscript Kyosuke Yamane, Hiroyuki Ohashi and Tatsushi Igarashi have the following competing interests: Kyosuke Yamane, Hiroyuki Ohashi and Tatsushi Igarashi are provided support in the form of salaries from Ushio Inc., Tokyo, Japan. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

                Author information
                https://orcid.org/0000-0002-9583-8919
                Article
                PONE-D-21-33285
                10.1371/journal.pone.0267957
                9064105
                35503791
                23615bdd-a8cf-4cb0-abc2-2b8ffed9de75
                © 2022 Narita et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 18 October 2021
                : 19 April 2022
                Page count
                Figures: 2, Tables: 0, Pages: 8
                Funding
                Funded by: USHIO Inc.
                Award ID: 3310200001
                Award Recipient :
                This work was supported by USHIO Inc., Tokyo, Japan. The funder provided support in the form of salaries for authors [K. Y., H. O and T. I.] but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Physical sciences
                Physics
                Electromagnetic radiation
                Light
                Ultraviolet radiation
                Ultraviolet C
                Engineering and Technology
                Signal Processing
                Signal Filtering
                Bandpass Filters
                Physical Sciences
                Physics
                Electromagnetic Radiation
                Light
                Ultraviolet Radiation
                Biology and Life Sciences
                Anatomy
                Integumentary System
                Skin
                Epidermis
                Medicine and Health Sciences
                Anatomy
                Integumentary System
                Skin
                Epidermis
                Physical sciences
                Physics
                Electromagnetic radiation
                Light
                Ultraviolet radiation
                Ultraviolet B
                Biology and Life Sciences
                Anatomy
                Integumentary System
                Skin
                Medicine and Health Sciences
                Anatomy
                Integumentary System
                Skin
                Biology and Life Sciences
                Cell Biology
                Cellular Types
                Animal Cells
                Epithelial Cells
                Keratinocytes
                Biology and Life Sciences
                Anatomy
                Biological Tissue
                Epithelium
                Epithelial Cells
                Keratinocytes
                Medicine and Health Sciences
                Anatomy
                Biological Tissue
                Epithelium
                Epithelial Cells
                Keratinocytes
                Physical Sciences
                Chemistry
                Chemical Compounds
                Chlorides
                Custom metadata
                All relevant data are within the paper.

                Uncategorized
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