Optimization of red to near-infrared stimulation by light-emitting diodes to increase cellular metabolism

Abstract

Learning objectives: Light-emitting diodes (LEDs) in near-infrared spectrum (810, 850 and 940 nm) enhanced cellular metabolism in a dose-dependent manner. Operation mode, power density, duration and periodicity must be considered in tailoring photobiomodulation (PBM) protocols for specific clinical scenarios. PBM by LEDs enhanced cells´ activity with minimal temperature increase, being a feasible and safe alternative to lasers. Brief introduction: Although PBM is used for tissue repair, it is not yet clinically implemented due to conflicting evidence in the literature. This may arise from the lack of studies investigating the most adequate stimulation parameters to elicit therapeutic effects at cellular level. This study aims to investigate the impact of different PBM parameters in cellular metabolism. Methods: Human-derived cells were stimulated by PBM, applied by an array of LEDs, on top of each well, at: 600, 655, 810, 850 and 940 nm wavelengths; 4, 7, 10, 14 and 17 mW/cm2 power densities; continuous mode for 1 min or pulsed mode for 2 min (with 1 Hz pulse frequency and 50% duty cycle); daily or every other day. Stimulation time was further increased up to 4 min to assess the PBM dose response. The applied energy density and total energy varied from 0.2 to 4.1 J/cm2 and 1.2 to 20 J, respectively. Temperature increase during stimulation was measured. After three days of stimulation, cellular metabolism was assessed by metabolic activity. Significant differences were represented at p-value < 0.01. Results: Cellular metabolism was significantly improved by 810 nm at 17 mW/cm2 (continuous, every other day, p = 0.000); 850 nm at 4 mW/cm2 (pulsed, every other day, p = 0.001), 7 mW/cm2 (continuous, daily, p = 0.000); and 10 mW/cm2 (continuous, daily, p = 0.000); 940 nm at 4 mW/cm2 (continuous, daily, p = 0.006); 14 mW/cm2 (pulsed, daily, p = 0.0003); 17 mW/cm2 (continuous, daily, p = 0.000). A dose response was demonstrated, being distinct among the PBM parameters. The temperature rise during stimulation was minimal. Conclusions: Stimulation with near-infrared LEDs was efficient in promoting cellular metabolism. These findings will significantly impact and improve the current knowledge of PBM effectiveness by LEDs.