Characterization of Stimulative Properties of Red Light on Cell Cultures

Objectives: We wish to identify the mechanism of cell growth induction by red laser light. Methods: Characterization of the mechanism of the mitogenic capacity of red light was performed on both a molecular biology and biochemical level on fibroblasts and endothelial cells. For both studies, experimental cells were plated into 100mm tissue culture dishes and irradiated with 665nm light at 3.5mW/cm2. Control cells were treated similarly with the exception of being occluded from the light source. Half the cells were segregated into growth curve experiments to verify that the dose was sufficient to cause an increase in the growth rate. For the molecular experiments, polyA RNA from experimental and control cells was harvested and exposed to a murine gene array. Differences in gene expression were noted for biochemical analysis. Biochemical analysis was predicated upon being able to block the effect of light stimulation with pathway inhibitors Results: Molecular studies indicate that a number of changes occur in the gene expression of cells exposed to laser light compared to nonirradiated cells. Based upon biochemical studies it would appear that the growth factors bFGF and PDGF play a key role in the mitogenesis. bFGF contributed 50+/-5.1% of the stimulus with PDGF adding 23.2+/-6.2%. Both of the growth factors as well as their receptors are upregulated in irradiated cells. However, there appears to be an oxidative component to the increase in cell growth. Adding free radical traps to the media was sufficient to cause a significant decrease in the growth rates of irradiated cells. Conclusions: The data suggest that the mitogenic stimulus elicited by intense red light is primarily due to autocrine release of bFGF and PDGF as well as upregulation of the receptors. An alternate causal source is the formation of oxidative molecules which stimulate growth via an as yet unexplained mechanism.