Low-intensity laser favors muscle regeneration in a malnourished and recovered experimental model

ABSTRACT Low-Level Laser Therapy - LLLT is used frequently on muscle lesions, but needs to be investigated in a malnutrition model. The aim of this study was to analyze the effects of LLLT on muscle regeneration of rats subjected to malnutrition and protein recovery. Forty recently weaned Wistar rats were used, divided into control group (C), subjected to a normal-protein diet (14% casein), and the malnourished group (D), subjected to a low-protein diet (6% casein) for 45 days and to a normal-protein diet until the end of the experiment. Subsequently, the right tibialis anterior muscle was subjected to cryogenic cooling and treated with LLLT (830 nm AsGaAl, 30 mW, 20 J/cm²), three times a week, for 7 and 21 days. There was a reduction of the inflammation/regeneration area in the C21 group compared to D21 (p<0.05), which became more evident with the LLLT (C21L and D21L). The TNF-α contents were reduced after 21 days of the injury. The connective tissue density area (CTDA) was lower in the C21 and C21L groups compared to the respective malnourished groups (p<0.05). LLLT reduced the CTDA in group D21L in comparison to D21 (p<0.05), but the TGF-β1 contents were not influenced. The cross-sectional area (CSA) of the muscle fiber increased in the 21-day groups. Higher levels of m-TOR were found in the C21L group when compared to D21L (p<0.05). It was concluded that LLLT favored muscle regeneration in the late stage of the experimental model of postnatal malnutrition and subsequent protein recovery.