Effects of zinc phthalocyanine tetrasulfonate-based photodynamic therapy on rat brain isolated mitochondria

Abstract

PDT has been used in the treatment of malignant brain tumors for the last 2 decades. It is based on the interaction of a photosensitizer (PS) and light of an appropriate wavelength, with generation of oxygen species, mainly singlet oxygen. Brain is particularly susceptible to oxidative stress; therefore the study of PDT effects on cerebral mitochondria might provide mechanistic insights into the action of the therapy, contributing to its optimization. In the present study, we addressed the mitochondrial toxicity of the second generation PS, zinc phthalocyanine tetrasulfonate (ZnPcS 4), on rat brain isolated mitochondria, by investigating both intrinsic toxicity and photodynamic action. At higher concentrations (15 and 25 μM/mg protein) ZnPcS 4 caused (a) inhibition of state-3 respiration and (b) decrease of RCR and ADP/O. Electrochemical potential, state-4 respiration and Ca 2+ retention capacity were not affected. Cytochrome c release was not observed. Coupled with 600 or 1800 mJ/cm 2 laser irradiation, ZnPcS 4 (5 μM/mg protein) caused more intense effects on state 3, RCR and ADP/O; moreover state-4 respiration and membrane potential were affected. Besides that, Ca 2+ and cytochrome c release were induced. Cyclosporine A (CsA) decreased Ca 2+ release and ameliorated the electrochemical potential, suggesting that membrane permeability transition (MPT) might be involved in the photodynamic effect. The low intrinsic toxicity and the high photodynamic effect on rat brain mitochondria induced by ZnPcS 4, allied to its improved photophysical properties, might indicate its potential for the treatment of malignant brain tumors.