Photosensitization of phycocyanin extracted from Microcystis in human hepatocellular carcinoma cells: Implication of mitochondria-dependent apoptosis

The aim of this study was to explore the possibility that Microcystis phycocyanin (MC-PC) functions as a photosensitizer and to investigate the mechanism for the apoptosis induced by Microcystis phycocyanin-mediated photodynamic therapy (MC-PC-PDT) in human hepatocellular carcinoma cells (HepG2). After incubation with MC-PC, HepG2 cells were exposed to a He-Ne Laser beam and the cell survival rate was detected by MTT and Colony forming assay. The mechanism of apoptosis was determined by ultra-structural observation, reactive oxygen species (ROS) and mitochondrial membrane potential (Delta psi m) assay, activity detection of caspase-3 and cytosol cytochrome c and flow cytometry (FCM) for cell cycle analysis. Our results demonstrated that MC-PC-PDT effectively inhibits HepG2 proliferation with a half-lethal dose of 100 mu g/mL and induces apoptosis at 24 h with a dose of 200 mu g/mL MC-PC. MC-PC was found to localized in mitochondria, it could induce a high level of ROS accumulation at 16 h after PDT treatment, cause mitochondrial damage and the release of mitochondrial cytochrome c into the cytosol. These cellular changes are accompanied by a reduction of the Delta psi m, activation of caspase-3 and G2/M phase arrest, finally leading to apoptosis through a mitochondria-dependent pathway after 24 h. Meanwhile, necrosis was also contributed to cell death in MC-PC PDT process. The present study also identified a new source of phycocyanin from Microcystis as a safe and effective photosensitizer. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.