Cell-cycle delay is induced in cells of a U937 promonocytic cell line by low-intensity light irradiation at 660 nm

Visible-light irradiation (VLI) at 660 nm and 11.5 J/cm2 inhibits proliferation of cells of the U937 promonocytic cell line, as monitored by autoradiographical analysis. The S-phase cell population is reduced at 6 h post-radiation treatment. Flow cytometric analysis confirms this, and also shows that light irradiation of cells induces a statistically significant increase in G2/M cells at 6 h post-radiation treatment. It has been postulated that VLI at 660 nm can alter cell-cycle progression by affecting intracellular concentrations of ions, in particular pH and calcium. However, no significant effects of light irradiation on these intracellular ions have been observed. These effects of VLI are not a consequence of radiation-induced DNA strand breaks, therefore events other than direct DNA damage are involved. These findings demonstrate a direct photobiological effect of VLI at 660 nm on the cell cycle, and indicate a previously unsuspected mechanism for the induction of cell-cycle delay that is neither a result of changes in the concentration of intracellular ions nor initiated by DNA strand breaks.

Detection by fluorescence analysis of DNA unwinding and unscheduled DNA synthesis, of DNA damage and repair induced in vitro by direct-acting mutagens on human lymphocytes

The sensitivity and reliability of UDS and FADU in detecting mutagenic effects were compared by measuring DNA damage and repair in PBL treated in vitro with UV light, MMS and BPDE. The results indicate that FADU is more sensitive than UDS, as it is able to detect DNA damage at doses 3-4-fold lower. We also determined the DNA damage and repair induced by the above agents on lymphocyte samples from different donors by FADU and UDS, confirming that the DNA repair process in humans is characterized by interindividually variable efficiency.