Mutagenesis and Cytotoxicity in Human Epithelial Cells by Far- and Near-Ultraviolet Radiations: Action Spectra

Abstract

Action spectra were determined for cell killing and mutation by monochromatic ultraviolet and visible radiations (254-434 nm) in cultured human epithelial P3 cells. Cell killing was more efficient following radiation at the shorter wavelengths (254-434 nm) than at longer wavelengths (365-434 nm). At 254 nm, for example, a fluence of 11 Jm-2 gave 37% cell survival, while at 365 nm, 17 X 10(5) Jm-2 gave equivalent survival. At 434 nm little killing was observed with fluences up to 3 X 10(6) Jm-2. Mutant induction, determined at the hypoxanthine-guanine phosphoribosyltransferase locus, was caused by radiation at 254, 313, and 365 nm. There was no mutant induction at 334 nm although this wavelength was highly cytotoxic. Mutagenesis was not induced by 434 nm radiation, either. There was a weak response at 405 nm; the mutant frequencies were only slightly increased above background levels. For the mutagenic wavelengths, log-log plots of the mutation frequency against fluence showed linear regressions with positive slopes of 2.5, consistent with data from a previous study using Escherichia coli. The data points of the action spectra for lethality and mutagenesis were similar to the spectrum for DNA damage at wavelengths shorter than 313 nm, whereas at longer wavelengths the lethality spectrum had a shoulder, and the mutagenesis spectrum had a secondary peak at 365 nm. No correlation was observed for the P3 cells between the spectra for cell killing and mutagenesis caused by wavelengths longer than 313 nm and the induction of DNA breakage or the formation of DNA-to-protein covalent bonds in these cells.

Blue Light Induces Mitochondrial DNA Damage and Free Radical Production in Epithelial Cells

“…Forty-eight hours after plating, the medium was replaced with serum-free medium. MTT assays were performed at four time points (1,3,6, and 9 h). At each time point, cell viability was measured using the MTT assay as described previously (15).…”

“…Most studies have concentrated on the role of UV irradiation due to its high energy, photoreactivity, wide range of biological chromophores, specific cellular responses, and association with pathologies such as skin melanoma and cataract (1)(2)(3)(4). However, the role of visible light has been less extensively investigated, even though studies have demonstrated that visible light can induce cellular dysfunction and cell death both in vitro and in vivo (1)(2)(3)(5)(6)(7). The blue region (400 -500 nm) of the visible spectrum is likely to be particularly important because it has a relatively high energy, can penetrate tissue(s), and is associated with the occurrence of malignant melanoma in animal models (6,7).…”

Endogenous glutathione levels modulate the frequency of both spontaneous and long wavelength ultraviolet induced mutations in human cells

“…Reports of mutation induction by broad-band sources fail to exclude the contribution of shorter wavelengths and results using monochromatic radiation at various UVA wavelengths vary with die wavelength and cell type employed (5)(6)(7). For example the results of our own study (5) did not demonstrate mutation induction at the hypoxanthine guanine phosphoribosyl transferase (HGPRT*) locus by radiation at a wavelength of 365 nm in cultured human lymphoblastoid cells whereas such radiation does appear to be mutagenic in a human teratocarcinoma cell line (6) and in cultured human fibroblasts (7).…”

High‐throughput laser‐mediated in situ cell purification with high purity and yield

“…First, UVA irradiation (Ͼ320 nm) is far less mutagenic than UVB (290 -320 nm) or UVC (Ͻ290 nm) irradiation (31,32), and is supported by the safe use of UVA in human clinical studies (33,34). Second, although different cells exhibit different sensitivities to UVA damage, it is far less variable than cell type sensitivities to UVB and UVC damage (31,35,36). The results of the present work are consistent with this expectation, demonstrating a modest range of sensitivities (3.2-fold) among seven diverse cell types.…”