UV‐Mediated DNA Strand Breaks in Corneal Epithelial Cells Assessed Using the Comet Assay Procedure^¶

Abstract

Ultraviolet (UV)‐mediated DNA damage in various tissues has been well documented. However, research on the damaging effect of UV irradiation on the DNA of corneal epithelium is scarce, even though this is of interest because the cornea is directly exposed to damaging solar (UV) radiation. In this study, we developed a corneal epithelium Comet assay model to to assess the background DNA damage (as strand breaks) n cells retrieved from different layers of the porcine corneal epithelium, and to investigated the effect of UV irradiation on DNA damage in corneal epithelial cells. Results show that the background DNA strand breaks decreased significantly (P < 0.001) toward deeper layers of the epithelium. Exposure to the same intensity (0.216 J/cm2) of UVA, UVB and UVC caused a significant (P < 0.001) increased in DNA strand breaks of deeper‐layer cells: mean ± SD %DNA scores (10 gels per treatment, with 100 irradiated cells scored per gel) were 10.2%± 1.4% for UVA, 27.4%± 4.6% for UVB, and 14.7%± 1.8% for UVC compared with 4.2%± 0.05% for controls (ambient room light). This study has shown for the first time that the Comet assay for DNA strand breaks can be used successfully with corneal epithelial cells. This report will support future studies investigating environmental influences on corneal health and the assessment of possible protective strategies, and in applying DNA lesion‐specific versions of the Comet assay in this corneal epithelial cell model.

Efficacy and safety assessment of a novel ultraviolet C device for treating corneal bacterial infections

“…The most damaging, by a factor of almost two over UVA and UVC, was found to be UVB. 19 Such an assessment of DNA damage is likely to be a more sensitive test of the effect of UV on cells compared with the current study, where a less sensitive, but more clinically applicable live/dead staining technique was used. Again, putting this in context, a 1-s exposure to the UVC LED in the current study, with an output of 1.93mW/cm 2 , would equate to a dose of 1.93 mJ/cm 2 , and even the 30-s exposure would amount to only 57.95 mJ/cm 2 .…”

“…Despite the considerable cumulative lifetime exposure of the cornea to both UVB and UVA, as well as to visible ambient light, a retrospective study by Lee and Hirst in 1992 reported an incidence of histologically proven dysplasia, carcinoma in situ, and invasive carcinoma of the cornea and conjunctiva of only 1.9 per 100 000 per year, averaged over a 10-year period. 21 Given the similarity in damage observed histologically for UVA and UVC, 19 it would seem unlikely that a short additional exposure to UVC would significantly increase the risk of carcinogenicity. 21 Naturally, the potential risk to ocular structures would depend, not only on the DNA-damaging potential of the light itself, but, also, on penetration to deeper structures.…”

Levels of oxidative DNA damage are low in ex vivo engineered human limbal epithelial tissue

“…Scant information is available regarding types and levels of DNA damage in the corneal epithelium in the human eye. A gradient of DNA damage has been described in the corneal epithelium in animal eyes where levels of DNA strand breaks were observed to decrease from the surface towards the basal layer (Choy et al 2005). Levels of DNA strand breaks and levels of oxidized bases are generally very low in the epithelium on human donor corneas maintained in cold storage.…”

“…Increases in levels of strand breaks and also in levels of oxidized bases in the epithelium may be observed after transfer of the donor corneas to organ culture ). Environmental stressors such as UV-irradiation and airborne particulate matter have been shown to induce DNA strand breaks in cultivated human and animal epithelial cells (Choy et al 2005;Gao et al 2016). Unrepaired, such damage may act to destabilize cell function through an increased level of transcriptional errors (Ishibashi et al 2005).…”