Light stimuli attenuates inflammatory activation in primary bone marrow-derived macrophages

Bone repair depends on a regulated macrophage-driven inflammatory response. Non-activated macrophages (M0) differentiate into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes in response to microenvironmental signals. This study evaluated, in vitro, the effects of photobiomodulation (PBM) on bone marrow-derived macrophage polarisation. Monocytes were isolated, differentiated into macrophages (M0), and induced to acquire M1- or M2-associated characteristics. Cells were irradiated using a PBM protocol for bone regeneration (equivalent dose of 2.1 E). Cells were analysed according to morphology, expression of M1 (iNOS, Tnf-α) or M2 markers (Arg1, Cd206), protein expression (iNOS and ARG1), and nitric oxide (NO) and reactive oxygen species (ROS) production. Data were analysed using 1-way analysis of variance or Student's t-test (p ≤ 0.05). PBM promoted selective and transient modulation of inflammatory and metabolic markers in M0, M1, and M2 macrophages. Compared to non-PBM-treated cells, M1^PBM cells had reduced NO levels, increased early ROS levels, and decreased gene and protein expression. In M2^PBM cells, transient changes in NO and ROS production were detected, with reduced Cd206 expression and similar Arg1 expression, although increased ARG1 protein expression was detected compared to non-irradiated controls. In M0^PBM cells, NO levels remained unchanged, while early ROS levels increased, accompanied by reduced iNos and Arg-1, and increased Cd206 expression. Under the selected parameters, PBM modulated macrophage inflammatory behaviour, but was insufficient to induce classical macrophage polarisation towards a specific phenotype. These findings suggest that modulation of macrophage-mediated inflammatory responses may contribute to the effects of this PBM protocol during bone repair.