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

Wang, Chun-yan, Wang, Xinyan, Wang, Yu, Zhou, Tao, Bai, Yu, Li, Yu-cheng, Huang, Bei
Journal of photochemistry and photobiology 2012 v.117 pp. 70-79
Microcystis, apoptosis, caspase-3, cell cycle, cell viability, cytochrome c, cytosol, flow cytometry, hepatoma, human cell lines, humans, membrane potential, mitochondria, mitochondrial membrane, necrosis, neoplasm cells, photobiology, photochemistry, photosensitivity, phycocyanin, reactive oxygen species, survival rate, therapeutics
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 ultrastructural observation, reactive oxygen species (ROS) and mitochondrial membrane potential (Δψm) 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 100μg/mL and induces apoptosis at 24h with a dose of 200μg/mL MC-PC. MC-PC was found to localized in mitochondria, it could induce a high level of ROS accumulation at 16h 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 Δψm, activation of caspase-3 and G2/M phase arrest, finally leading to apoptosis through a mitochondria-dependent pathway after 24h. 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.