Influence of Neurospora endonuclease on trenimon-induced structural chromosomal aberrations and sister-chromatid exchanges in human peripheral lymphocytes and Chinese hamster ovary cells

The induction of chromosomal aberrations and SCEs by visible light in combination with dyes. II. Cell cycle dependence, and the effect of hydroxyl radical scavengers during light exposure in cultures of Chinese hamster ovary cells sensitized with acridine orange

Chinese hamster ovary (CHO) cells were synchronized by mitotic shake-off, treated with the fluorochrome acridine orange (AO; 0.5 micrograms/ml), washed free of excess dye and subsequently exposed to visible light (2 X 40 W/8 Wm-2). The light exposure was performed on cells in the G1, G1/S, S or G2 phase of the cell cycle. AO + light induced high frequencies of aberration in the S phase and even higher in the G1 phase. The aberrations observed were all of the chromatid type. The chromosome-type aberrations (dicentrics, rings) obtained when cells in the G1 phase were exposed to X-rays were not found after corresponding treatments with AO + light. With the exception of an increased frequency of gaps, no chromosomal aberrations were induced in G2-phase cells. Sister-chromatid exchanges were efficiently produced by the photodynamic system in the G1, G1/S and S phase of the cell cycle. In other experiments, AO-treated unsynchronized CHO cells were exposed to light in the presence of the hydroxyl radical scavengers mannitol (100 mM) and 5-dimethyl thiourea (100 mM). In parallel experiments these scavengers were found to reduce markedly the chromosome breaking effects by X-rays but had no influence on the photodynamic induction of chromosomal alterations. The results presented show that the visible light-induced chromosomal alterations in CHO cells sensitized with the fluorochrome AO are obtained by an S-dependent mechanism. Furthermore, the results indicate that the hydroxyl free radical does not play a major role in the production of chromosomal alterations by AO + light.

The induction and repair of DNA damage detected by the DNA precipitation assay in Chinese hamster ovary cells treated with acridine orange + visible light

The photodynamic effect of the dye acridine orange (AO) in combination with visible light (400-700 nm) was studied in Chinese hamster ovary (CHO) cells, the endpoints investigated being induction, as well as repair, of DNA strand breaks. Cells were treated for 20 min with AO (0.1-3.0 micrograms/ml), washed free of excess dye and subsequently exposed to low doses of visible light (2 x 40 W/8 W/m2) for 5-15 min. AO proved to be an efficient sensitizer for light-induced DNA strand breaks, detected with the DNA precipitation assay, and expressed as percentage of DNA precipitated. The induction of breaks was linear up to 0.5 micrograms/ml AO + 10 min of light, which corresponds to 55% precipitated DNA, and was dependent on the concentration of AO as well as on the dose of light delivered. As a comparison, 18 Gy of X-rays was required to yield an equivalent amount of induced DNA strand breaks. The rejoining of the light-induced DNA strand breaks was studied by incubating the AO-sensitized cells for 30-120 min at 37 degrees C directly after light exposure. A fast recover of 67-91% of the damage (compared to initial damage, recovery time = 0, and dependent on the concentration of AO) was observed during the first 30 min of incubation. However, a significant amount of DNA damage remained after 2 h of recovery. These remaining, long-lived lesions might be involved in the photoinduced and acridine-sensitized chromosomal aberrations and sister-chromatid exchanges (SCE). The significance of these observations is discussed in relation to AO-sensitized and photoinduced DNA damage and chromosomal alterations.