REACTIVE OXYGEN SPECIES INDUCIBLE BY LOW-INTENSITY LASER IRRADIATION ALTER DNA-SYNTHESIS IN THE HEMATOPOIETIC-CELL LINE U937

Background and Objective: The purpose of this study was to evaluate th e possible role of reactive oxygen species (ROS) in mediating previous ly recorded alterations in DNA synthesis, inducible by low-intensity l aser irradiation (LILI), in the haemopoietic cell line U937. Study Des ign/Materials and Methods: The ability of LILI (660 nm, 12 mW, 5 kHz) to induce ROS from U937 cells was assessed spectrophotometrically at e nergy densities (E.D.) from 1.0 to 11.5 J/cm(2). In order to assess wh ether laser-induced ROS could alter cellular proliferation DNA synthes is was measured, post-irradiation, by the incorporation of tritiated t hymidine (H-3-TdR) into the cells in both the presence and absence of the antioxidant catalase (CAT). Results: Detectable ROS were produced post-irradiation only from the differentiated form of the cell line. A nalysis by Student's t-test for unrelated groups showed a significant difference, at E.D.s 2.9 and 8.6 J/cm(2), in the extent of DNA synthes is occurring in cells irradiated in the presence of CAT or in its abse nce. Conclusion: These findings demonstrate that laser-inducible ROS c an mediate laser's effects on this cell line. (C) 1996 Wiley-Liss, Inc .