Wavelength-dependent photobiomodulation attenuates synovial inflammation in fibroblast-like synoviocytes and a collagenase-induced osteoarthritis model.

Photobiomodulation (PBM) using light-emitting diodes (LEDs) has demonstrated promising anti-inflammatory effects in musculoskeletal disorders. However, the optimal parameters for modulating synovitis and joint degeneration in osteoarthritis (OA) remain unclear. This study aimed to examine the wavelength- and dose-dependent effects of PBM on inflammatory responses in fibroblast-like synoviocytes (FLS) and evaluate the in vivo therapeutic efficacy of selected wavelengths in a murine model of collagenase-induced OA (CIOA). Primary rat FLS were stimulated with TNF-α and irradiated using PBM at 625, 810, 940, or 1050 nm with fluences ranging from 13 to 78 J/cm2 (fixed irradiance of 44 mW/cm2). mRNA levels of IL-1β, IL-6, COX-2, and iNOS were quantified by RT-qPCR. The in vivo study involved daily PBM (810 or 940 nm at 39 J/cm2) for two weeks in CIOA mice, starting one week post-induction. Pain-related behavior was assessed weekly using the incapacitance test. Synovial inflammation and cartilage degradation were evaluated by histology and immunofluorescence staining for IL-1β and IL-6. Among tested parameters, 810 nm at 39 J/cm2 showed the most potent suppression of inflammatory gene expression in FLS. In vivo, 810 nm PBM significantly improved pain-related behavior by week 4, reduced synovitis and cartilage damage, and downregulated IL-1β and IL-6 expression in synovium. While 940 nm PBM also demonstrated anti-inflammatory effects in vitro, it did not show significant efficacy in vivo. These findings suggest that PBM at 810 nm exerts stronger anti-inflammatory and chondroprotective effects in inflammatory OA compared with 940 nm, supporting its potential as a non-pharmacological intervention for inflammatory OA phenotypes.