Reversal of allodynia and enhanced tendon repair in rats via 660 and 808 nm photobiomodulation.

Abstract

Our study aimed to explore the potential of Photobiomodulation (PBM) as a treatment for Tendinopathy (TP), a chronic condition characterized by tendon degeneration, inflammation, and pain, for which current treatment options often yield unsatisfactory outcomes. PBM, utilizing low-level laser, has shown promise in reducing inflammatory markers, stimulating cell proliferation, and alleviating pain, thus presenting itself as a promising alternative therapy for TP. Using an experimental rat model of tendinopathy, male Wistar rats weighing 250-370 g were induced with TP through the injection of type I collagenase into the calcaneal tendon. Animals were divided into four equal groups (control, TP, TP + 660 nm, TP + 808 nm), with 10 animals in each group for the nociceptive behavioral tests and 5 in each for the biomolecular analysis. Fifteen days later, PBM was administered to the tendons once daily for seven consecutive sessions using two wavelengths (660 and 808 nm), with 3 J for 30 s, irradiating an area of 0.028 cm² totaling 107.14 J/cm². Mechanical nociception and thermal cold sensitivity were assessed, and tendon samples were collected for analysis of collagen types and total cell count. Spinal cord samples were also collected and immunostained to evaluate specific markers. Our results demonstrated that collagenase injection induced mechanical allodynia and cold hypersensitivity, both of which were reversed by PBM at both 660 and 808 nm wavelengths (**p < 0.005 and *p < 0.05). Additionally, TP led to an increase in collagen type III and a decrease in collagen type I expression, with these effects being reversed by PBM treatment (*p < 0.05). Moreover, TP increased astrocyte immunoreactivity, while PBM at both wavelengths led to a decrease in astrocyte and IL-1β expression. In conclusion, PBM emerged as an effective treatment for TP, as it not only alleviated pain symptoms but also modulated collagen expression and reduced astrocyte and IL-1β expression (**p < 0.01). These findings suggest that PBM could serve as a beneficial adjunctive therapy for analgesia and regeneration in TP management.