The dose-effect response of combined red and infrared photobiomodulation on insulin resistance in skeletal muscle cells

Obesity is a major public health problem and is a major contributor to the development of insulin resistance. In previous studies we observed that single-wavelength red or infrared photobiomodulation (PBM) improved insulin signaling in adipocytes and skeletal muscle of mice fed a high-fat diet, but information about the combination of different wavelengths, as well as the effect of different light doses (J/cm(2)) is lacking. Therefore, the aim of this study was to investigate the effects of different doses of dual-wavelength PBM on insulin signaling in muscle cell, and explore potential mechanisms involved. Mouse myoblasts (C2C12) were differentiated into myotubes and cultured in palmitic acid, sodium oleate and L-carnitine (PAL) to induce insulin resistance high or in glucose medium (CTRL). Then, they received SHAM treatment (lights off, 0 J/cm(2)) or PBM (660 + 850 nm; 2, 4 or 8 J/cm(2)). PAL induced insulin resistance (assessed by Akt phosphorylation at ser473), attenuated maximal citrate synthase activity, and increased the phosphorylation of c-Jun NH(2) terminal kinase (JNK) (T183/Y185). PBM at doses of 4 or 8 J/cm(2) reversed these PAL-induced responses. Furthermore, at doses of 2, 4 or 8 J/cm2, PBM reversed the increase in mitofusin-2 content induced by PAL. In conclusion, the combination of dualwavelength red and infrared PBM at doses of 4 and 8 J/cm(2) improved intracellular insulin signaling in musculoskeletal cells, and this effect appears to involve the modulation of mitochondrial function and the attenuation of the activation of stress kinases.