Fluorescence Imaging of Heat-Stress Induced Mitochondrial Long-Term Depolarization in Breast Cancer Cells

Abstract

Various thermotherapies are based on the induction of lethal heat in target tissues. Spatial and temporal instabilities of elevated temperatures induced in therapy targets require optimized treatment protocols and reliable temperature control methods during thermotherapies. Heat-stress induced effects on mitochondrial transmembrane potentials were analyzed in breast cancer cells, species MX1, using the potential sensor JC-1 (Molecular Probes, Invitrogen, Germany). Potential dependant labeling of heat-stressed cells was imaged and evaluated by fluorescence microscopy and compared with control cells. JC-1 stains mitochondria in cells with high mitochondrial potentials by forming orange-red fluorescent J-aggregates while in cells with depolarized or damaged mitochondria the sensor dye exists as green fluorescent monomers. In MX1 cells orange-red and green fluorescence intensities were correlated with each other after various heat-stress treatments and states of mitochondrial membrane potentials were deduced from the image data. With increasing stress temperatures the intensity of red fluorescent J-aggregates decreased while the green fluorescence intensity of JC-1 monomers increased. This heat-stress response happened in a nonlinear manner with increasing temperatures resulting in a nonlinear increase of red/green fluorescence ratios. These data indicated that mitochondria in MX1 cells were increasingly depolarized in response to increasing ambient temperatures.

Effects of hyperthermia as a mitigation strategy in DNA damage-based cancer therapies

“…To this end, several studies have associated hyperthermia with increased ROS production [26]. For instance, there is evidence demonstrating that hyperthermia can disturb the mitochondrial membrane, consequently leading to alterations in the cellular redox status [27,28] which in turn can result in DNA damage induction.…”

Invited Review Article: Current State of Research on Biological Effects of Terahertz Radiation

“…Heat can cause several interrelated effects on mitochondria: (i) disrupt membrane potential (ΔΨ m ) [84,90]; (ii) change the redox status of cells; (iii) cause increased bursts of ROS; (iv) stimulate mitochondrial enzyme activity (i.e. citrate synthase) [87]; (v) inhibit ATP production; and (vi) destabilize intracellular proteins (Fig.…”

“…4a, c) [27]. Membrane disruption typically does not occur under mild heat stress (40 and 45°C for 30 min), but it becomes quite pronounced under severe conditions (50-56°C for 30 min) [90]. Membrane disruptions are believed to be mediated via the signaling of pro-apoptotic (Bax) and antiapopotic Bcl-2 family members, in particular caspase 2 [91].…”

Gold nanorods as photothermal agents and autofluorescence enhancer to track cell death during plasmonic photothermal therapy

“…3(b). The decrease in the measured intensity of the treated cells was due to the mitochondrial damage (cell damage) resulting in the alteration in the redox status of cells [8]. The fluorescence microscope images of the cells can illustrate the autofluorescence and cell viability for monitoring the treatment outcome.…”