Effect of catechins on 5-aminolevulinic acid-induced protoporphyrin IX accumulation and its photodynamic therapy for A549 cells cultured <i>in vitro</i>

We investigated the effects of four catechins, (-)-epicatechin (EC), (-)-epicatechin gallate (ECg), (-)-epigallocatechin (EGC), and (-)-epigallocatechin gallate (EGCg), on intracellular accumulation of 5-aminolevulinic acid-induced protoporphyrin IX (ALA-PpIX) in human lung alveolar carcinoma cells cultured in vitro. The extent of ALA-PpIX accumulation followed the order: ECg > EGCg > EGC > EC ≈ no catechin (ALA alone). Furthermore, fluorescence imaging of ferrous ions (Fe2+) using Mito-FerroGreen indicated that catechins chelated intracellular Fe2+, with chelating ability ranked as ECg > EGCg > EGC > EC. Accordingly, ECg and EGCg notably enhanced ALA-PpIX accumulation, presumably due to their higher ability to chelate intracellular Fe2+. However, the order of enhancement of ALA-based photodynamic therapy (ALA-PDT) efficacy among the catechins did not correlate to the order of intracellular ALA-PpIX accumulation. This discrepancy may be attributable to the scavenging of singlet oxygen generated from ALA-PpIX under LED light irradiation by the catechins.