Anti-inflammatory effect of photobiomodulation in the brain following local peripheral carrageenan-induced inflammation

Photobiomodulation (PBM) has been suggested as a potential anti-inflammatory therapy, presenting excellent outcomes for several disorders. Reduction in COX-2 mRNA expression in subplantar and brain tissues by PBM was demonstrated, using the classic model of oedema formation and hyperalgesia induced by Carrageenan (Carr). This work investigated the effect of PBM on mRNA expression of key inflammation-related genes (IL-1β, mPGES-1, mPGES-2 and EP) in subplantar and brain tissues obtained from rats receiving Carr.

The animals were treated with Carr, treated with PBM after 1 h and sacrificed after 1, 3 and 6 h. The light source used was a diode laser, with output power of 30 mW and a wavelength of 660 nm. The laser beam illuminated an area of 0.785 cm², resulting in an energy dosage of 7.5 J/cm², applied for 196 s. IL-1β, mPGES-1, mPGES-2 and EP mRNAs were determined by RT-PCR.

It was observed a reduction in IL-1β expression as in subplantar tissue as in brain parenchyma in animals treated with PBM. In addition, the expression of both mPGES-1 and mPGES-2 mRNA was decreased after PBM.

These results suggested that PBM could reduce the production of IL-1β and subsequently decreasing the effects of PGE2. Therefore, the possible mechanism by which PBM alleviates hyperalgesia could involve its ability to decrease the expression of inflammatory markers in the CNS, reducing the production of PGE₂ in the spinal cord.