The genetic disease Fanconi anemia (FA), generally considered to be a DNA repair defect, has also been related to a deficiency in cellular defense against reactive oxygen species (ROS). Results show that mitochondrial matrix densification occurs rapidly and transiently in FA fibroblasts following 8-methoxypsoralen (8-MOP) photoreaction or ultraviolet A (320 to 380 nm) (UVA) irradiation. This effect is oxygen dependent because it is more important under 20 than under 5% oxygen tension. In contrast, in normal fibroblasts very little, if any, densification of mitochondrial matrix is induced by treatments even at the highest oxygen tension. The changes in matrix density in FA cells are accompanied by some modifications in transmembrane potential, linked to a Fenton-like reaction, and in mitochondrial cardiolipin content, differing from the responses of normal cells. These data are indicative of some sort of membrane damage induced by 8-MOP photoreaction and UVA irradiation, to which FA cells appear to be particularly sensitive.

The effects of vitamin E supplementation were evaluated in cultured human normal fibroblasts exposed to ultraviolet A radiation (320-380 nm) (UVA). Cells were incubated in medium containing alpha-tocopherol, alpha-tocopherol acetate or the synthetic analog Trolox for 24 h prior to UVA exposure. DNA damage in the form of frank breaks and alkali-labile sites, collectively termed single-strand breaks (SSB), was assayed by the technique of single cell gel electrophoresis (comet assay), immediately following irradiation or after different repair periods. The generation of hydrogen peroxide (H2O2) and superoxide ion (O2.-) was measured by flow cytometry through the oxidation of indicators into fluorescent dyes. It was observed that pretreatment of cells with any form of vitamin E resulted in an increased susceptibility to the photoinduction of DNA SSB and in a longer persistence of damage, whereas no significant change was observed in the production of H2O2 and O2.- reactive oxygen species, compared to untreated controls. These findings indicate that in human normal fibroblasts, exogenously added vitamin E exerts a promoting activity on DNA damage upon UVA irradiation and might lead to increased cytotoxic and mutagenic risks.

Fanconi anemia (FA) is an inherited cancer-susceptibility disorder, characterized by genomic instability, hypersensitivity to DNA cross-linking agents, and a prolonged G2 phase of the cell cycle. We observed a marked dose-dependent accumulation of FA cells in the G2 compartment after treatment with 4,5′,8-trimethylpsoralen (Me3Pso) in combination with 365 nm irradiation. Using bivariate DNA distribution methodology, we determined the proportion of replicating and arresting S-phase cells and observed that, whereas normal cells arrested DNA replication in the presence of Me3Pso cross-links and monoadducts, FA lymphoblasts failed to arrest DNA synthesis. Taken together, the above data suggest that, in response to damage induced by DNA cross-linking agents, the S-phase checkpoint is inefficient in FA cells. This would lead to accumulation of secondary lesions, such as single- and double-strand breaks and gaps. The prolonged time in G2 phase seen in FA cells therefore exists in order to allow the cells to remove lesions which accumulated during the preceding abnormal S phase.