key: cord-0332278-grc5tyys
authors: Welch, David; de Muro, Marilena Aquino; Buonanno, Manuela; Brenner, David J
title: Wavelength-dependent DNA photodamage in a 3-D human skin model over the far-UVC and germicidal-UVC wavelength ranges from 215 to 255 nm
date: 2021-12-16
journal: bioRxiv
DOI: 10.1101/2021.12.14.472653
sha: 381ab0af78f12826fb82052da219b3f5ad23f650
doc_id: 332278
cord_uid: grc5tyys

The effectiveness of UVC to reduce airborne-mediated disease transmission is well-established. However conventional germicidal UVC (~254 nm) cannot be used directly in occupied spaces because of the potential for damage to the skin and eye. A recently studied alternative with the potential to be used directly in occupied spaces is far-UVC (200 to 235 nm, typically 222 nm), as it cannot penetrate to the key living cells in the epidermis. Optimal far-UVC use is hampered by limited knowledge of the precise wavelength dependence of UVC-induced DNA damage, and thus we have used a monochromatic UVC exposure system to assess wavelength-dependent DNA damage in a realistic 3-D human skin model. We exposed a 3-D human skin model to mono-wavelength UVC exposures of 100 mJ/cm2, at UVC wavelengths from 215 to 255 nm (5-nm steps). At each wavelength we measured yields of DNA-damaged keratinocytes, and their distribution within the layers of the epidermis. No increase in DNA damage was observed in the epidermis at wavelengths from 215 to 235 nm, but at higher wavelengths (240-255 nm) significant levels of DNA damage were observed. These results support use of far-UVC light to safely reduce the risk of airborne disease transmission in occupied locations.

Far-UVC safety is premised on the fact that, because its effective range in biological material is 51 much shorter than for conventional (254 nm wavelength) germicidal UVC (16, 21-23), far-UVC 52 incident on the skin is absorbed primarily in the superficial stratum corneum (see Fig. 1 

In this study, we used a monochromatic exposure system designed for narrow bandwidth 78 UVC exposures, with which we irradiated realistic 3-D models of human skin which recapitulates 79 the key components of human skin. Using this system we assessed the wavelength dependence 

The monochromator spectral output was characterized using a BTS-2048UV 100 Spectroradiometer (Gigahertz-Optik, Inc., Amesbury, MA). With a 600 µm slit width and the 101 1201.6 g/mm grating, the resolution of the monochromator was 1.9 nm. The measured full width 102 at half maximum was between 2.0 nm and 2.2 nm for all peak wavelengths used in this study.

The monochromatic spectral output for wavelengths between 215 nm and 255 nm is shown in 

The tissues were exposed to a radiant exposure dose of 100 mJ/cm 2 using narrow 

With a full width half maximum between 2.0 nm and 2.2 nm for all peak wavelengths used in this 149 study, we exposed multiple 3-D models of normal human skin to 100 mJ/cm 2 of narrow bandwidth 

To put these stratum-specific results into context (and see Fig. 1 ), the stratum basale is 177 the deepest layer of the epidermis, where basal cells, including melanocytes, are constantly 178 dividing and migrating upwards; above the stratum basale is the stratum spinosum which contains 179 squamous cells and provides the skin's structural integrity; and above the stratum spinosum is 180 the stratum granulosum which contains dead or dying cells whose nuclei and other organelles are 181 disintegrating as the cells move up into the stratum corneum (37). Thus from a long-term safety 182 perspective, the concern relates to DNA damage to cells in the stratum basale and stratum 183 spinosum, which contain living basal cells, melanocytes and squamous cells (24, 25, 38). DNA 9 damage to cells in the stratum granulosum or, of course, the stratum corneum is of much less 185 concern, as these contain dead or dying cells.

We may conclude from these results that, at UVC exposures of 100 mJ/cm 2 , far-UVC (215 187 to 235 nm) did not produce a significant increase in photodamage averaged over the epithelium, 

In conclusion, these results provide quantitative wavelength-specific data supporting the 199 safe use of far-UVC in occupied public settings. The data were generated using a realistic 3-D 200 human skin model exposed to UVC exposures of 100 mJ/cm 2 , somewhat higher than the current 

Percentage of the total keratinocytes positive for CPD counted in A) the whole epidermis and B) 364 each layer (see Fig. 1 )of the epidermis. Error bars indicate standard deviations.

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