Processo inflamatório durante o reparo do músculo esquelético em idosos: o papel da fotobiomodulação

Abstract

The interaction between the immune system and the tissue determines the success of the muscle repair after the occurrence of injuries. With aging, however, sarcopenia and immunosenescence make this process slower and sometimes incomplete, indicating the need for more efficient therapeutic resources. There is evidence that photobiomodulation (FBM) potentiates muscle repair in young animals, but its effect has still been poorly evaluated in the elderly. This work aims to identify if there is a difference between young and old in the composition of the cells of the inflammatory infiltrate present in muscle tissue after acute injury, as well as to elucidate the role of FBM on these components and their products in elderly animals. For this, 30 Wistar rats, 20 months old, underwent cryoinjury in the anterior tibialis muscle (TA), the half treated with FBM. Creoles were performed with two direct applications of a metallic stick cooled in liquid nitrogen. Another 15 Wistar rats (2 months old) also underwent cryosurgery. The FBM (780nm, 40mW, 3,2J) was applied daily in 8 points (10 seconds / point) in the elderly animals. After 1, 3 and 7 days, the muscles of young and old animals (treated or not with FBM) were evaluated for the presence of neutrophils (elastase +) and macrophages of phenotype M1 and M2 (CD68 +; CD206 +). The expression of IL-6, TNF-α and TGF-β (by qPCR) and VEGF (by immunohistochemistry) was also evaluated in the muscles of the elderly animals (treated or not with FBM). The comparative analysis between young and old animals showed a lower presence of neutrophils and macrophages M1 and M2 after 1 day in the muscle of the elderly animals. After 3 days, the elderly continue to present only minor amounts of M2 macrophages, whereas after 7 days of injury, the number of M1 macrophages becomes greater in the elderly rats. In the muscles of elderly animals treated with FBM, it was possible to observe a lower number of neutrophils after 1 day of treatment and a larger number of macrophages M1 and M2 after 3 days of treatment. Already after 7 days of treatment, the amount of macrophages of the two profiles was lower in the irradiated muscles. FBM also generated an increase in the expression of IL-6, TNF-α and TGF-β after 3 days of treatment, with TNF-α expression only being maintained in this group after 7 days of treatment. Immunoblotting of VEGF was also increased in the FBM-treated group at the 3 and 7 day periods. The alterations found in the composition of the inflammatory infiltrate in the muscles of the elderly certainly contribute to the prolongation of the inflammatory

process and the repair impairment of this tissue when compared to that of young people. FBM makes the composition of the inflammatory infiltrate and its products chronologically closer to those observed in young animals, which would increase the chance of a better and faster repair in the elderly.