Photosensitized biostimulation of keratinocytes and fibroblasts by low-energy visible light

There has been much interest in the biological effects of low energy visible and near infrared lasers. Most of the experiments show that low energy visible and near infrared lasers do have specific bioeffects which seem to change from stimulatory to damaging with increasing doses. In the present work we irradiated keratinocytes with various light sources (360 nm, 540 nm, 630 nm, and 780 nm) and found that at a specified, relatively low energy dose there is an accelerated cell mitosis. The percentage of dividing cells 24 hrs following exposure increased by 2 - 3 fold. Cell number in the treated cultures increased between 48 and 72 hrs by a factor of 1.3 - 2. We have suggested that the effect is due to light absorption by either endogenous porphyrins or cytochromes in the cell. Porphyrins and cytochromes are photosensitizers. At low irradiation doses, small amounts of singlet oxygen (¹O²) or other oxyradicals are produced, providing the energy needed for cell proliferation. We have examined our assumption by introducing very small amounts of hematoporphyrin derivatives (HPD) into the fibroblast cells, measuring their proliferation after light irradiation. We have found that in comparison to previous results a smaller energy dose of 360 nm light is needed to enhance proliferation. These preliminary results have important implications in phototherapy and in photodynamic therapy.