Novel mitochondrial deletions in human epithelial cells irradiated with an FS20 ultraviolet light source in vitro

The formation of mitochondrial deletions brought about by FS20 irradiation was examined in a line of human epithelial cells. In this system, Mt DNA deletions were found to be induced within 24 h following a single irradiation as low as 1.4 mJ/cm2 from an FS20 light source. We observed at least two distinct FS20-induced Mt deletions: the widely observed 4977 bp common deletion (CD) and a novel 5128 bp deletion flanked by TAGG repeats at nt 8247–8250 and 13,375–13,378 that has not, to our knowledge been previously described. While glutathione (GSH) at concentrations between 50 and 200 μM was found to block the formation of the CD in a dose-dependent manner, GSH at higher concentration induced the CD even in unirradiated cells. This is consistent with the idea that low dose GSH inhibits CD formation via reductive elimination of peroxides while higher concentrations may act as an electron donor to produce reactive oxygen species. Interestingly, in irradiated cells, GSH at intermediate concentrations (50 μM) induced a second, shorter, deletion similar to the novel deletion induced by FS20 alone but involving a different TAGG repeat spanning nt 13,175–13,178.