Genotoxic effects in bacteria of the light emitted by halogen tungsten lamps having treated quartz bulbs

The risk of ultraviolet radiation exposure from indoor lamps in lupus erythematosus

It is well known that ultraviolet radiation can exacerbate skin disease in patients with lupus erythematosus. While many patients are advised to avoid sunlight and artificial tanning, it is not clear how best to counsel patients regarding the use of indoor lamps. Indeed, many of the light bulbs commonly used in the home and workplace emit low-dose ultraviolet radiation. The irradiance is considerably lower than that of the sun, however the exposure time can last for hours and is typically repeated on a daily basis. Therefore, it is possible that this chronic exposure could ultimately result in a significant accumulation of damage.

Modulation of light-induced skin tumors by N -acetylcysteine and/or ascorbic acid in hairless mice

The light emitted by halogen quartz bulbs contains a broad spectrum of UV wavelengths, is strongly genotoxic and is a potent inducer of skin tumors in hairless mice. By using a UVC filter, this light mimics solar radiation and induces a variety of genomic and transcriptional alterations in mouse skin. UV-related carcinogenesis involves depletion of antioxidants and glutathione in skin cells. On this basis, we evaluated modulation of carcinogenicity of UVC-filtered halogen lamps in SKH-1 hairless mice by the antioxidants N-acetyl-l-cysteine (NAC) and ascorbic acid (AsA). Both agents were given in the drinking water, either individually or in combination. The earliest skin lesions were detected after 300 days' exposure to light and became confluent in a number of mice after 480 days. NAC administration prolonged the latency time by 90 days. Moreover, NAC considerably and significantly decreased both incidence and multiplicity of light-induced skin tumors, prevented the occurrence of malignant lesions (squamocellular carcinomas) and reduced the tumor size. In contrast, AsA, which may behave as a prooxidant rather than an antioxidant, increased the multiplicity of total skin tumors, carcinomas in situ and squamocellular carcinomas. Co-administration of NAC with AsA significantly attenuated the negative effect of AsA, presumably due to the ability of this thiol to maintain a reduced environment. Therefore, in agreement with our previous in vitro findings, oral NAC is able to attenuate the detrimental effects of AsA.

Dermatological Risk of Indoor Ultraviolet Exposure from Contemporary Lighting Sources¶†‡§

Discussions of risks and implications of cutaneous exposure to indoor lighting, including hypothetical contribution to causality of melanoma, have mainly concentrated on ultraviolet (UV) A and B (UVA, UVB) spectral emissions from fluorescent bulbs. Only studies of quartz halogen lamps have suggested that users might sustain UVC-induced injury. Examination of light sources in the home and school of a child with xeroderma pigmentosum revealed that several different types emitted surprising levels of UV. Our purpose was to assess the extent of UV emissions from a variety of commonly used light sources to identify potential dermatological risks. UV and visible spectral emissions of commercially obtained lamps of several types were measured using a calibrated spectral radiometer traceable to the National Institute of Standards and Technology. Indoor light sources including fluorescent, quartz halogen and even tungsten filament incandescent lamps provided UVA, UVB and sometimes UVC emissions. Intensities of some emissions were of similar magnitude to those in sunlight. Chronic exposure to indoor lighting may deliver unexpected cumulative UV exposure to the skin and eyes. Patients with UV-exacerbated dermatoses should be cautioned about potential adverse reactions from indoor lighting.

Lethality of visible light for Escherichia coli hemH1 mutants influence of defects in DNA repair

The hemH gene encodes ferrochelatase, the final enzyme of the heme biosynthetic pathway. Defects of this enzyme lead to accumulation of protoporphyrin IX and an increase in reactive oxygen species, causing susceptibility to blue and white light in bacteria and protoporphyria in humans. Here we show that the photosensitivity of hemH1 strains is much increased when the bacteria are devoid of ability to repair abasic sites. The sensitivity is increased 10- or 50-fold, in mutants bearing single xth or triple xth-nth-nfo mutations, respectively, but is not changed in mutants bearing nth, fpg, mutY, and mutT that are positive or negative for uvrA. This may indicate that in hemH1 mutants abasic sites are accumulated to a greater degree than oxidised bases, and/or that protoporphyrin, in the presence of abasic sites, increases the photosensitivity of hemH1 cells. It was shown in this work that the level of abasic sites (and/or strand breaks) in DNA of hemH1 strains increases greatly. Abasic sites and oxidative bases are potential mutagenic lesions. Nevertheless, the sensitivity of hemH1 bacteria to the lethal effect of visible light is not accompanied by increase in mutations. One of the possible explanations is that the genotoxic effect due to damage of hemH, shortage of heme and/or accumulating of protoporphyrin IX makes mutagenesis impossible.