Wavelength dependence of ultraviolet-induced DNA damage distribution: involvement of direct or indirect mechanisms and possible artefacts.

DNA damage profiles have been established in plasmid DNA using purified DNA repair enzymes and a plasmid relaxation assay, following exposure to UVC, UVB, UVA or simulated sunlight (SSL). Cyclobutane pyrimidine dimers (CPDs) are revealed as T4 endonuclease V-sensitive sites, oxidation products at purine and pyrimidine as Fpg- and Nth-sensitive sites, and abasic sites are detected by Nfo protein from Escherichia coli. CPDs are readily detected after UVA exposure, though produced 10(3) and 10(5) times less efficiently than by UVB or UVC, respectively. We demonstrate that CPDs are induced by UVA radiation and not by contaminating UVB wavelengths. Furthermore, they are produced at doses compatible with human exposure and are likely to contribute to the mutagenic specificity of UVA [E. Sage et al., Proc. Natl. Acad. Sci. USA 93 (1996) 176-180]. Oxidative damage is induced with a linear dose dependence, for each region of the solar spectrum, with the exception of oxidized pyrimidine and abasic sites, which are not detectable after UVB irradiation. The distribution of the different classes of photolesions varies markedly, depending on wavelengths. However, the unexpectedly high yield of oxidative lesions, as compared to CPDs, by UVA and SSL led us to investigate their production mechanism. An artificial formation of hydroxyl radicals is observed, which depends on the material of the sample holder used for UVA irradiation and is specific for long UV wavelengths. Our study sheds light on a possible artefact in the production of oxidative damage by UVA radiation. Meanwhile, after eliminating some potential sources of the artefact ratios of CPDs to oxidized purine of three and five upon irradiation with UVA and SSL, respectively, are still observed, whereas these ratios are about 140 and 200 after UVC and UVB irradiation.

Cell survival and shuttle vector mutagenesis induced by ultraviolet A and ultraviolet B radiation in a human cell line.

Although it is known that sunlight is carcinogenic,few molecular data are available concerning the mutagenic effects of ultraviolet (UV) B (290-320 nm) and UVA (320-400 nm) radiation in human cells. To analyze the biologic effects of UVA and UVB, we irradiated the 293 human cell line, derived from adenovirus-transformed human embryonic kidney cells, in which we had stably introduced a shuttle vector harboring the lacZ' bacterial gene as the mutagenesis target. Identical cell survival occurred after UVA doses 700-fold higher than UVB. This comparable to the UVA/UVB ratio that reaches the basal cell layer of the skin after sunlight exposure with UVB sunscreen. The frequency of UVA- and UVB- induced mutations increased with the UV dose as cell survival decreased. At cell survival levels greater than 10%, UVA and UVB induced similar frequencies of mutations in the episomal lacZ gene, whereas for cell survival lower than 10%, UVA induced twice as many mutations as UVB. Sequence analysis of 81 independent lacZ mutants (36 UVA- and 45 UVB-induced) revealed specific characteristics for some UV-induced-mutations, particularly for UVB. Mutations at A/T base pairs were induced more frequently by UVA than by UVB. The UVA-induced mutation spectrum that we have observed in human cells may help help to elucidate the mechanism of skin carcinogenesis.

[Dermatologic risks of quartz-halogen lamps]. / Risques dermatologiques des sources quartz-halogène.

Halogene sources are used increasingly in general illumination. Their quartz envelop is technically necessary, but presents the disadvantage of to letting the emitted UVA, UVB and UVC go through. Originally used as in indirect lighting, they have been introduced as desk-top lamps, without filter. We have proceeded to the verification of their output with a spectrophotometer calibrated by actinometry and we have calculated their relative erythemal efficacy according to the Parrish's action spectrum for human erythema. We found that, at 10 cm from the human skin, the irradiance was able to induce a minimal erythema in about 10 minutes on clear back skin. At working distance (50 cm), a barely perceptible erythema could be observed on the back of the hands after 8 consecutive hours working. We also found that sunburn cells were present in the skin sensitized with a potent phototoxic agent (8-methoxypsoralen) applied 15 minutes before a 4-6 minutes irradiation with the halogen source (at 20 cm), thus, indicating a potential risk for local phototoxicity and photoallergy. The cumulative doses per year, for 4 hours exposure per day, five days a week, reaches 125 minimal erythemal doses, equivalent to the average yearly exposure of individuals for work and leisure. If one assumes that this regimen is maintained for 30 years, the risk for induction of skin cancers on the dorsal aspect of the hands and the forearms, may be increased by a 3.4 factor, according to the widely accepted previsional models.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythema induced by quartz-halogen sources.

The erythemal effect of 100-W quartz-halogen sources, previously predicted from radiation measurements, was directly measured on humans at a distance of 10 cm. Minimal erythema was produced in 15 min for skin type I. These data show that normal use of a desktop lamp should not usually lead to erythema in one day, but that long-term effects cannot be ignored, because for lifetime use at work, the relative risk for squamous cell carcinoma on the back of the hands is 3.4.

Determination of 23 polycyclic aromatic hydrocarbons in atmospheric particulate matter of the Paris area and photolysis by sunlight.

Twenty-three polycyclic aromatic hydrocarbons (PAH) were determined in atmospheric particulate matter in 4 places of the Paris area at several times of the year. Fractionation was performed by reversed-phase high-pressure liquid chromatography. Determination was done by recording emission or excitation fluorescence spectra via a stopped-flow technique. Triphenylene was also extemporaneously determined by its phosphorescence spectrum at low temperature. Among the PAH determined dibenz(e,ghi)perylene has not been detected before in atmospheric particulate matter. The 10 more abundant PAH ranged from 0.1 to 40 ng/m3 of filtered air. Concentrations in August are from 14 to 250 times less than in January depending on the PAH. The reasons for this difference of behaviour among the PAH were investigated with regard to their photochemical and non-photochemical reactivity.

Relative efficiencies of three ultraviolet radiation wavelengths for cell killing and transformation in mouse cells in vitro.

C3H 10 T 1/2 clone 8 mouse cells were irradiated in vitro with three U.V. wavelengths 280, 254, and 230 nm. Two effects were investigated, survival and malignant transformation, and the relative efficiencies were determined for the three radiations. For transformation, these efficiencies were: 280nm:3.9; 254nm:5.1; 230nm:2.3 (transformations produced by 5 Jm-2 of U.V. for 1000 surviving cells). For cell killing the efficiencies were, in relative units, 34, 100, and 50 respectively. These efficiencies are in agreement with the hypothesis that the main chromophore for both effects is the nucleic acid, and not the protein moiety of the genome. This conclusion agrees with that previously reached by other investigators, but our present results obtained with the short wave-length 230 nm provide an especially strong new argument.