Dissociation of mitochondrial depolarization from cytochrome c release during apoptosis induced by photodynamic therapy

Abstract

Photodynamic therapy (PDT) with the phthalocyanine photosensitizer Pc 4 induces rapid apoptosis in mouse lymphoma (LY-R) cells, initiating with the release of cytochrome c from mitochondria. It has been proposed that the opening of the mitochondrial membrane permeability transition pores, which results in the dissipation of the mitochondrial membrane potential (Δψ m ), is essential for the escape of cytochrome c from mitochondria into the cytosol as well as for apoptotic cell death. Therefore, we have assessed the correlation between the loss of Δψ m and the release of cytochrome c following PDT. Treatment of LY-R cells with 300 nM Pc 4 and 60, 90 or 120 mJ/cm 2 of red light resulted in apoptosis of 80–90% of the cells, accompanied by >20-fold elevation in caspase-3-like activity within one h. At all 3 doses of PDT employed here, the majority of the cytochrome c was released from mitochondria at 15 min after irradiation, as determined by an immunohistochemical method. In contrast, the loss of Δψ m following PDT, as monitored by the uptake of JC-1 or Rh-123, depended on the PDT dose and the post-treatment time. In spite of the release of cytochrome c at 15 min after each of the 3 doses, a corresponding loss of Δψ m was observed only for those cells that received the highest dose of PDT. Virtually all cells that received one of the lower doses of PDT (300 nM Pc 4 plus 60 or 90 mJ/cm 2 ) maintained normal Δψ m . Hence, our results support the conclusion that the release of cytochrome c from mitochondria resulting from Pc 4-PDT-induced photodamage is independent of the loss of Δψ m . Therefore, it is important to consider a range of doses of this or other apoptotic stimuli in deciphering the relationship of metabolic responses that contribute to apoptosis. © 2001 Cancer Research Campaign http://www.bjcancer.com

Nitric oxide-induced genotoxicity, mitochondrial damage, and apoptosis in human lymphoblastoid cells expressing wild-type and mutant p53

“…Amounts of cytosolic cytochrome c were essentially equal, despite the higher MMP loss in WTK-1 versus TK6 cells. These findings are consistent with previous reports that cytochrome c release was independent of MMP loss after treatment of cells with diverse agents (39,40). In addition, many investigations have revealed that the antiapoptotic proteins Bcl-2 and Bcl-x͞l block p53-regulated release of cytochrome c from mitochondria (6,10,38).…”

Unconjugated bilirubin induces apoptosis in colon cancer cells by triggering mitochondrial depolarization

“…Following a PBS wash, cells were suspended in culture medium containing the fluorescent probe JC-1 (10 g/ml) for 10 min and then analyzed by flow cytometry. 42 …”

Pheophorbide�a-mediated photodynamic therapy induces apoptotic cell death in murine oral squamous cell carcinoma in vitro and in vivo

“…Most types of cancers are especially active in both the uptake and accumulation of photosensitizer agents than normal tissues, which makes tumors especially vulnerable to PDT (8). PDT employs a photosensitizer and visible light to produce singlet oxygen and other reactive oxygen species, which cause an oxidative stress in cells and membrane damage which eventually leads to cell death and tumor ablation (9)(10)(11). PDT was reported to inhibit cancer through different cell death pathways and its effectiveness is dependent on the types of cancer cell lines and photosensitizers (12)(13)(14).…”