Time-dependent effects of low-level laser therapy on the morphology and oxidative response in the skin wound healing in rats

This study aims to investigate the effect of different energy densities provided by low-level laser therapy (LLLT) on the morphology of scar tissue and the oxidative response in the healing of secondary intention skin wounds in rats. Twenty-four male adult Wistar rats were used. Skin wounds were made on the backs of the animals, which were randomized into three groups of eight animals each as follows, 0.9% saline (control); laser GaAsAl 30 J/cm² (L30); laser GaAsAl 90 J/cm² (L90). The experiment lasted 21 days. Every 7 days, the wound contraction index (WCI) was calculated and tissue from different wounds was removed to assess the proportion of cells and blood vessels, collagen maturation index (CMI), thiobarbituric acid reactive substance (TBARS) levels and catalase activity (CAT). On the 7th and 14th days, the WCI and the proportion of cells were significantly higher in groups L30 and L90 compared to the control (p < 0.05). At all the time points analyzed, there was a greater proportion of blood vessels and a higher CMI in group L90 compared to the other groups (p < 0.05). On the 7th and 14th days, lower TBARS levels and increased CAT activity were found in the L90 group compared to the control (p < 0.05). On the 7th day, a moderately negative correlation was found between TBARS levels and WCI, CMI and CAT in all the groups. LLLT may modulate the oxidative status of wounded tissue, constituting a possible mechanism through which the LLLT exerts its effects in the initial phases of tissue repair.