Clinical protocols are recommended in device guidelines outlined for treating many diseases on empirical basis.
However, effects of low-intensity infrared lasers at fluences used in clinical protocols on DNA are controversial.
Excitation of endogenous chromophores in tissues and free radicals generation could be described as a consequence of
laser used. DNA lesions induced by free radicals cause changes in DNA structure, chromatin organization, ploidy
degrees and cell death. In this work, we investigated whether low-intensity infrared laser therapy could alter the
fibroblasts nuclei characteristics and induce DNA fragmentation. Tendons of Wistar rats were exposed to low-intensity
infrared laser (830 nm), at different fluences (1, 5 and 10 J/cm2), in continuous wave (power output of 10mW, power
density of 79.6 mW/cm2). Different frequencies were analyzed for the higher fluence (10 J/cm2), at pulsed emission
mode (2.5, 250 and 2500 Hz), with the laser source at surface of skin. Geometric, densitometric and textural parameters
obtained for Feulgen-stained nuclei by image analysis were used to define nuclear phenotypes. Significant differences
were observed on the nuclear phenotype of tendons after exposure to laser, as well as, high cell death percentages was
observed for all fluences and frequencies analyzed here, exception 1 J/cm2 fluence. Our results indicate that low-intensity
infrared laser can alter geometric, densitometric and textural parameters in tendon fibroblasts nuclei. Laser can also
induce DNA fragmentation, chromatin lost and consequently cell death, using fluences, frequencies and emission modes
took out from clinical protocols.