He-Ne (633 nm) low power laser irradiation stimulates proliferation of keratinocyte cultures involving reactive oxygen species

Low power He-Ne (633 nm) lasers have been reported to exert opposite effects on proliferation of keratinocytes. The purpose of this study was to determine irradiation parameters of He-Ne laser (10 mW) leading to enhanced proliferation of cultured normal human keratinocytes (NHK), varying energy density, and frequency of exposures, and to evaluate the possible role of reactive oxygen species (ROS) in this response. Proliferation parameters studied reflected the rate of DNA synthesis, metabolic activity and mitotic activity of the cells. The rate of NHK proliferation was significantly enhanced within the first 72 h following exposure to a single dose of 1.9-5.5 J/cm², but the rate of NHK differentiation was not affected. The proliferative response was unique to proliferating cells, diminished with time, and was not observed following frequent exposures. Suppression of He-Ne laser-stimulated proliferation by added enzymatic and non-enzymatic antioxidants suggested that ROS were involved in mediating this response. The results indicate that under specific conditions, low energy He-Ne laser irradiation enhances keratinocyte proliferation in vitro. Furthermore, the results imply the value of future inclusion of low energy laser irradiation in improved protocols for cultivation of keratinocytes as skin substitutes, and in treatment modalities that promote in vivo keratinocyte proliferation and enhance wound healing.