Open Access
Photochemistry and Photobiology
First published: 27 November 2022
Safety Evaluation of Far-UV-C Irradiation to Epithelial Basal Cells in the Corneal Limbus
Sachiko Kaidzu 1, Kazunobu Sugihara 1, Masahiro Sasaki 2, Aiko Nishiaki 2, Hiroyuki Ohashi 2, Tatsushi Igarashi 2, Masaki Tanito 1
1 Department of Ophthalmology, Shimane University Faculty of Medicine, Izumo, Japan.
2 Ushio Inc., Tokyo, Japan.
Far-UVCは生理的ターンオーバーにより24時間で剥がれ落ちる角膜上皮最表層にしか到達しないため傷害を起こしにくいことを報告した。しかし、角膜上皮の幹細胞が存在する角膜輪部基底部に傷害が及ぶと長期的には角膜傷害に繋がる。そこで我々は、照射したＵＶが角膜輪部に及ぼす影響について調べた。
254 nm UVC、311 nm UVB照射直後のラット角膜輪部では、上方下方ともに輪部上皮基底部までCPDが観察された。235 nm UVCでは上方は中間層まで、下方は表層にCPDが観察された。一方、207および222 nm UVCでは最表層の細胞にしかCPDは観察されなかった。ブタ角膜輪部においても222 nm UVCは輪部上皮最表層の細胞までしか到達しなかった。
角膜上皮幹細胞は角膜輪部の基底部に存在するため、最表層までしか到達しないFar-UVCは組織幹細胞に対して傷害を与えることはなく、角膜組織に長期的な影響を及ぼす可能性は低いと考えられる。
We reported that Far-UVC is unlikely to cause injury because it only reaches the superficial layer of the corneal epithelium, which peels off in 24 hours due to physiological turnover. However, if the basal portion of the corneal ring, where the stem cells of the corneal epithelium reside, is injured, this may lead to corneal injury in the long term. Therefore, we investigated the effects of irradiated UV on the corneal ring.
In the rat corneal rings immediately after 254 nm UVC and 311 nm UVB irradiation, CPD was observed up to the basal portion of the epithelium of the rings both in the upper and lower regions. 235 nm UVC showed CPD in the upper region up to the middle layer and in the lower region in the superficial layer. In contrast, at 207 and 222 nm UVC, CPD was observed only in the superficial layer of cells. In the porcine corneal ring, 222 nm UVC reached only the superficial layer of the ring epithelium.
Since corneal epithelial stem cells reside in the basal portion of the corneal ring, Far-UVC, which only reaches the superficial layer, does not injure tissue stem cells and is unlikely to have long-term effects on corneal tissue.
