Improvement of aminolevulinic acid (ALA)-mediated photodynamic diagnosis using n-propyl gallate.

Photodynamic diagnosis (PDD) using aminolevulinic acid (ALA) is widely used in clinical fields. In PDD, protoporphyrin IX (PpIX) is generated from ALA in tumors, allowing the detection of the tumors by PpIX fluorescence. However, it is well known that PpIX is bleached by light irradiation (photobleaching) resulting in reduced PDD efficiency. In this study, n-propyl gallate (NPG) was investigated as an enhancer of PDD efficiency. Tumor cells were incubated with NPG after treatment with ALA, and reactive oxygen species and PpIX fluorescence were measured. The antioxidant NPG suppressed the production of reactive oxygen species from light-irradiated porphyrins and ameliorated photobleaching of PpIX generated from ALA in vitro and in vivo. Incubation with NPG decreased the production of reactive oxygen species from PpIX and suppressed PpIX photobleaching. These results indicate that the antioxidant NPG may significantly improve PDD efficiency.