Concentration and fluence dependence of the disturbance of the membrane integrity of human fibroblasts by the photodynamic action of Photosan III

Two human fibroblast cell lines were treated with varying concentrations of the photosensitizer Photosan III for different incubation times, and subsequently irradiated with an He-Ne laser. The biological parameter investigated was trypan blue exclusion by the cells. For each given drug concentration and incubation time, a threshold fluence was observed, which resulted in the complete loss of the cell membrane integrity. Using the equation tcr = b X CPS-a, the correlation between threshold light dose (tcr) and the concentration of the photosensitizer (CPS) can be described for all three incubation times (10 min, 2 h, 20 h) characterized by different sets of a and b values. This power function implies that these parameters are inversely correlated to each other. A correlation of incubation time with critical exposure time for different drug concentrations gave saturation curves. No differences were observed between the two cell lines. The method applied may be useful for a fast comparison of the sensitizing efficiencies of different treatment protocols for the in vitro investigation of photodynamic laser therapy.