Effects of short-wavelength blue light on fibroblasts. Experimental evidence in wound healing and cutaneous fibrosis

Wound healing and skin fibrosis are antithetical processes where fibroblasts play a key-role. PhotoBioModulation therapy (PBM) is a physical treatment proposed in recent years in wound care. Here, we show the results obtained from in vivo and in vitro experiments about the PBM effects of short-wavelength blue LED light (emission range 410-430 nm). In vivo studies were performed in superficial wound in animal model (33 CD1 male mice). Wounds were treated with blue light (20.6 J/cm²), and biopsies were collected at 0-1-3-6-9-12-18-24-72-144 hours. Unwounded skin was used as a control. Histology, fluorescence analysis, scratch-test assay and multiphoton microscopy were performed. Skin fibrosis was studied by in vitro experiments on human cultured fibroblasts isolated from keloid tissues. Six doses were tested: 3.43–6.87–13.7–20.6–30.9-41.2 J/cm². Colourimetric assays, electrophysiological recordings, micro-Raman measurements and electron microscopy were used to study cell viability, proliferation and some features of mitochondria before and after irradiation. Fibroblasts from healthy donors were used as a control. The in vivo study evidenced a faster recovery in blue light-treated wounds, accompanied by collagen deposition and a tissue morphology close to the one typical of an intact healthy skin. From in vitro experiments we pointed out that at low light dose (3.43 J/cm²) the cell metabolism increases, while at high light dose (30.9 and 41.2 J/cm²) its reduction is observed. In the electrophysiology test, the application of 20.6 J/cm² increases the outward currents only in keloid fibroblasts, while mitochondria (observed with TEM) increase their dimension in a dose-dependent manner. In conclusion, blue light does not have the same effect on different cell types, while modulates their activity in different ways. Our results demonstrated that short-wavelength blue LED light has PBM properties: fibroblasts activity is modulated, thus obtaining a faster tissue remodelling accompanied by a better scarring outcome, especially in subjects predisposed to form keloids and hypertrophic scars.