Blue light does not impair wound healing in vitro

Irradiation with red or near infrared light promotes tissue repair, while treatment with blue light is known to be antimicrobial. Consequently, it is thought that infected wounds could benefit more from combined blue and red/infrared light therapy; but there is a concern that blue light may slow healing. We investigated the effect of blue 470 nm light on wound healing, in terms of wound closure, total protein and collagen synthesis, growth factor and cytokines expression, in an in vitro scratch wound model. Human dermal fibroblasts were cultured for 48 h until confluent. Then a linear scratch wound was created and irradiated with 3, 5, 10 or 55 J/cm². Control plates were not irradiated. Following 24 h of incubation, cells were fixed and stained for migration and fluorescence analyses and the supernatant collected for quantification of total protein, hydroxyproline, bFGF, IL-6 and IL-10. The results showed that wound closure was similar for groups treated with 3, 5 and 10 J/cm², with a slight improvement with the 5 J/cm² dose, and slower closure with 55 J/cm² p < 0.001). Total protein concentration increased after irradiation with 3, 5 and 10 J/cm², reaching statistical significance at 5 J/cm² compared to control (p < 0.0001). However, hydroxyproline levels did not differ between groups. Similarly, bFGF and IL-10 concentrations did not differ between groups, but IL-6 concentration decreased progressively as fluence increased (p < 0.0001). Fluorescence analysis showed viable cells regardless of irradiation fluence. We conclude that irradiation with blue light at low fluence does not impair in vitro wound healing. The significant decrease in IL-6 suggests that 470 nm light is anti-inflammatory.