The importance of fluorescence distribution and kinetics of ALA-induced PpIX in the bladder in photodynamic therapy

Photodynamic therapy (PDT) is a new anticancer technique directed at the selective destruction of neoplastic tissue. Aminolevulinic acid (ALA), a precursor in the biosynthesis of heme, induces the production of the endogenous photosensitizer protoporphyrin IX (PpIX). In this study the fluorescence distribution of ALA-induced PpIX was investigated in the rat bladder wall by fluorescence microscopy. The fluorescence studies showed that PpIX concentrates in bladder mucosa and that the highest fluorescence levels are achieved after four hours of 300 mg/kg ALA administration. A clear trend in difference between mucosa and muscularis layers was found in all samples taken after 1, 2, 4 and 6 hours of ALA administration. Our results suggest that to get the highest PpIX fluorescence intensity in bladder mucosa it is best to use 300 mg/kg ALA administration. Four hours is the time point when the highest difference in fluorescence between mucosa and muscularis is reached.