Effects of photobiomodulation on human hair dermal papilla cells with various light modes and light parameters

Androgenetic alopecia (AGA) is a prevalent hair loss disorder and influenced by genetic, hormonal, and environmental factors. Minoxidil and finasteride have been widely used for treating AGA. However, the side effects associated with these drugs often lead to poor patient compliance. In contrast, photobiomodulation (PBM), due to its safety and non-invasiveness, holds promising prospects for use. Although the promoting effects of PBM on AGA have been reported, the mechanisms by which PBM affects dermal papilla cells (DPCs) remain largely unknown. Hence, this study explored the impacts of both continuous wave (CW) and pulsed wave (PW) PBM on DPCs, and revealed the underlying actions of light parameters in PBM. Orthogonal experiments were conducted to evaluate the effects of CW PBM on DPCs at varying irradiances and doses, indicating that irradiance was the crucial parameter, as well as cell viability and proliferation were maximized at 8 mW/cm² and 8 J/cm². For PW PBM, response surface methodology was employed to determine the influences of duty cycles, frequencies, and doses. The findings highlighted frequency as a primary factor, with the optimum cell viability observed at peak irradiance 10 mW/cm², duty cycle 80 %, 500 Hz, and 8.8 J/cm². Notably, PBM could enhance cell viability, proliferation, and migration in DPCs by activating the Wnt/β-Catenin signaling and suppressing Transforming Growth Factor signaling, particularly when applied in pulsed mode. Overall, this study determined the key light parameters that influence PBM effectiveness, further identified the optimal light conditions, and preliminary revealed into the mechanisms of PBM in DPCs, highlighting that PW PBM may be a competitive therapeutic option for alleviating AGA in the future.