The induction of DNA repair in X-ray irradiated Friend erythroleukaemia and human myeloid HL60 cells by low intensity laser irradiation

Friend erythroleukaemia (FEL), and human myeloid HL60 cells were x-ray irradiated (3.0∼3.5 Gy), and then irradiated with low intensity laser irradiation (LILI) (660 nm, 12 mW, 5 kHz, 20 J/cm2). During the irradiation sessions the cell suspensions were maintained at 0∼4°C to minimize the normal processes of DNA repair. As a control for DNA repair, x-ray irradiated HL60 cells were incubated at 37°C (0∼15 minutes). Using the Comet Assay and a sensitive ELISA to quantify the percentage of single-stranded DNA, a significant reduction in DNA damage was demonstrated for the x-ray, laser irradiated cells, and also for the x-ray irradiated HL60 cells incubated for 5 or 15 minutes at 37°C, These results suggest that LILI facilitates the repair of x-ray induced DNA damage in cell suspensions held at 0∼4°C. LILI has no observable thermal effect on the medium surrounding cell suspensions. However, in view of these current results the possibility of an LILI mediated intracellular thermal effect should be considered.