Comparisons of the effects of single and multi-wavelength irradiation photodynamic therapy using 5-aminolevulinic acid

Protoporphyrin 9 induced by a photosensitizer such as 5-aminolevulinic acid has five absorption peak wavelengths: 410 nm, 510 nm, 545 nm, 580 nm, and 630 nm. The absorption coefficient of the 410 nm wavelength is the highest, but the tissue penetration depth of this wavelength is relatively low. Generally, red light from 600 nm to 800 nm is used as the light source for photodynamic therapy (PDT) due to its ability to deeply penetrate tissue. Treatment duration at this wavelength must be extended, however, because the absorption coefficient of red light is very low. Therefore, we investigated PDT using multiple wavelengths to improve the PDT effects. HaCaT cells were incubated with 5-aminolevulinic acid (1 mM) for 4 h and irradiated with light at a single wavelength or multiple wavelengths using light-emitting diodes with peak wavelengths of 405 nm, 505 nm, 545 nm, 570 nm, or 635 nm. After irradiation, the cells were incubated and survival rate was examined using an XTT-assay. Irradiation with a dual wavelength combination significantly increased the PDT effects in all cases compared with irradiation using only a single wavelength. The irradiation dose was the same for both single and double wavelengths. In contrast, there was no significant difference between single wavelength irradiation and triple or quadruple wavelength irradiations. These findings indicate that irradiation with dual wavelengths is the most efficient strategy for improving the effects of PDT.