Photobiomodulation induces in vitro re-epithelialization via nitric oxide production

Photobiomodulation is a widely used tool in regenerative medicine thanks to its ability to modulate a plethora of physiological responses. Wound re-epithelialization is strictly regulated by locally produced chemical mediators, such as nitric oxide (NO), a highly reactive free radical generated by the nitric oxide synthase (NOS) enzymatic family. In this study, it has been hypothesized that a 980-nm low-level laser stimulation could increase NO production in human keratinocytes and that such event might be directly related to the re-epithelialization process. Human keratinocytes were irradiated with increasing energy outputs (10-75 J) in the absence or presence of L-NAME, a NOS inhibitor. Laser stimulation induced an increase in NO production, resulting in an energy-dependent increase in both keratinocytes proliferation and re-epithelialization ability. The direct link between increased NO production and the observed physiological responses was confirmed by their inhibition in L-NAME pre-treated samples. Since NO production increase is a quick event, it is conceivable that it is due to an increase in existing NOS activity rather than to a de novo protein synthesis. For this reason, it could be hypothesized that photobiomodulation-derived NO positive effects on keratinocytes behavior might rely on a near infrared mediated increase in NOS conformational stability and cofactors as well as substrate binding ability, finally resulting in an increased enzymatic activity.