Investigating the effects of low intensity visible light on human keratinocytes using a customized LED exposure system

Photobiomodulation (PBM) refers to the use of light to modulate cellular processes, and has demonstrated utility in improving wound healing outcomes, and reducing pain and inflammation. Despite the potential benefits of PBM, the precise molecular mechanisms through which it influences cell behavior are not yet well understood. Inconsistent reporting of key light parameters has created uncertainty around optimal exposure profiles. In addition, very low intensities of light, <0.1 J/cm(2), have not been thoroughly examined for their use in PBM. Here, we present a custom-made compact, and modular LED-based exposure system for studying the effects of very low-intensity visible light (cell proliferation, migration, ROS production, and mitochondria) membrane potential) of three different wavelengths in a parallel manner. The device allows for six repeats of three different exposure conditions plus a non-irradiated control on a single 24-well plate. The immortalised human keratinocyte cell line, HaCaT, was selected as a major cellular component of the skin epidermal barrier. Furthermore, an in vitro wound model was developed by allowing the HaCaT to form a confluent monolayer, then scratching the cells with a pipette tip to form a wound. Cells were exposed to yellow (585 nm, 0.09 mW, similar to 3.7 mJ/cm(2)), orange (610 nm, 0.8 mW, similar to 31 mJ/cm(2)), and red (660 nm, 0.8 mW, similar to 31 mJ/cm(2)) light for 10 min. 48 h post-irradiation, immunohistochemistry was performed to evaluate cell viability, proliferation, ROS production, and mitochondrial membrane potential. The results demonstrate increased proliferation and decreased scratch area for all exposure conditions, however only red light increased the mitochondrial activity. Oxidative stress levels did not increase for any of the exposures. The present exposure system provides opportunities to better understand the complex cellular mechanisms driven by the irradiation of skin cells with visible light.

Automated summary

Photobiomodulation (PBM) utilizes light to modulate cellular processes, and shows potential benefits in wound healing and pain reduction. However, the molecular mechanisms underlying PBM's effects are not fully understood. This study developed a custom-made LED-based exposure system to study the effects of very low-intensity visible light on skin cells. The results demonstrate increased proliferation and mitochondrial activity with red light exposure. This research provides insights into the complex cellular mechanisms driven by visible light irradiation of skin cells.