Chloromethyltetramethylrosamine (Mitotracker Orange) induces the mitochondrial permeability transition and inhibits respiratory complex I. Implications for the mechanism of cytochrome c release

Mitochondria-targeted BODIPY dyes for small molecule recognition, bio-imaging and photodynamic therapy

Mitochondria are essential for a diverse array of biological functions. There is increasing research focus on developing efficient tools for mitochondria-targeted detection and treatment. BODIPY dyes, known for their structural versatility and excellent spectroscopic properties, are being actively explored in this context. Numerous studies have focused on developing innovative BODIPYs that utilize optical signals for imaging mitochondria. This review presents a comprehensive overview of the progress made in this field, aiming to investigate mitochondria-related biological events. It covers key factors such as design strategies, spectroscopic properties, and cytotoxicity, as well as mechanism to facilitate their future application in organelle imaging and targeted therapy. This work is anticipated to provide valuable insights for guiding future development and facilitating further investigation into mitochondria-related biological sensing and phototherapy.

Performance of TMRM and Mitotrackers in mitochondrial morphofunctional analysis of primary human skin fibroblasts

Mitochondrial membrane potential (Δψ) and morphology are considered key readouts of mitochondrial functional state. This morphofunction can be studied using fluorescent dyes ("probes") like tetramethylrhodamine methyl ester (TMRM) and Mitotrackers (MTs). Although these dyes are broadly used, information comparing their performance in mitochondrial morphology quantification and Δψ-sensitivity in the same cell model is still scarce. Here we applied epifluorescence microscopy of primary human skin fibroblasts to evaluate TMRM, Mitotracker Red CMXros (CMXros), Mitotracker Red CMH2Xros (CMH2Xros), Mitotracker Green FM (MG) and Mitotracker Deep Red FM (MDR). All probes were suited for automated quantification of mitochondrial morphology parameters when Δψ was normal, although they did not deliver quantitatively identical results. The mitochondrial localization of TMRM and MTs was differentially sensitive to carbonyl cyanide-4-phenylhydrazone (FCCP)-induced Δψ depolarization, decreasing in the order: TMRM ≫ CHM2Xros = CMXros = MDR > MG. To study the effect of reversible Δψ changes, the impact of photo-induced Δψ "flickering" was studied in cells co-stained with TMRM and MG. During a flickering event, individual mitochondria displayed subsequent TMRM release and uptake, whereas this phenomenon was not observed for MG. Spatiotemporal and computational analysis of the flickering event provided evidence that TMRM redistributes between adjacent mitochondria by a mechanism dependent on Δψ and TMRM concentration. In summary, this study demonstrates that: (1) TMRM and MTs are suited for automated mitochondrial morphology quantification, (2) numerical data obtained with different probes is not identical, and (3) all probes are sensitive to FCCP-induced Δψ depolarization, with TMRM and MG displaying the highest and lowest sensitivity, respectively. We conclude that TMRM is better suited for integrated analysis of Δψ and mitochondrial morphology than the tested MTs under conditions that Δψ is not substantially depolarized.

Exploring the limitations of mitochondrial dye as a genuine horizontal mitochondrial transfer surrogate

Rosamine-based mitochondrial dyes, such as Mitotracker Red, have commonly been employed to visualize mitochondrial localization within cells due to their preferential accumulation in organelles with membrane potential. Consequently, Mitotracker Red has often served as a surrogate indicator for tracking mitochondrial movement between neighboring cells. However, it is important to note that the presence of membrane potential in the cell membrane and other organelles may lead to the non-specific partial enrichment of Mitotracker Red in locations other than mitochondria. This study comprehensively investigates the reliability of mitochondrial dye as a marker for studying horizontal mitochondrial transfer (HMT). By meticulous replicating of previous experiments and comparing the efficiency of mitochondrial dye transfer with that of mito-targeted GFP, our findings confirm that HMT occurs at significantly lower efficiency than previously indicated by Mitotracker dye. Subsequent experiments involving mitochondria-deficient cells robustly demonstrates the non-specificity of mitochondrial dye as indicator for mitochondria. We advocate for a thorough reevaluation of existing literature in this field and propose exploration of alternative techniques to enhance the investigation of HMT. By addressing these pivotal aspects, we can advance our understanding of cellular dynamics and pave the way for future explorations in this captivating field.

Galactosylceramide Upregulates the Expression of the BCL2 Gene and Downregulates the Expression of TNFRSF1B and TNFRSF9 Genes, Acting as an Anti-Apoptotic Molecule in Breast Cancer Cells

Galactosylceramide (GalCer) increases the resistance of breast cancer cells to doxorubicin, paclitaxel, and cisplatin by acting as an anti-apoptotic molecule. GalCer was found to specifically downregulate the levels of the pro-apoptotic TNFRSF1B and TNFRSF9 genes and upregulate the levels of the anti-apoptotic BCL2 gene, suggesting that this glycosphingolipid regulates their expression at the transcriptional level. Consistent with this hypothesis, MDA-MB-231 and MCF7 breast cancer cells with high levels of GalCer showed lower activity of the TNFRSF1B and TNFRSF9 promoters than cells lacking GalCer. In contrast, the activity of the BCL2 promoter was higher in MCF7 cells overproducing GalCer than in MCF7 cells without GalCer. However, no difference in BCL2 promoter activity was observed between MDA-MB-231 cells with high and no GalCer content. Instead, we found that high levels of GalCer increased the stability of Bcl-2 mRNA. Subsequent studies showed that breast cancer cells with high levels of GalCer are characterized by significantly lower expression of P53. Importantly, inhibition of P53 expression by siRNA in MCF7 and MDA-MB-231 cells lacking GalCer resulted in decreased expression and promoter activity of the TNFRS1B and TNFRSF9 genes. On the other hand, increased expression and promoter activity of the BCL2 gene was found in such MCF7 cells, and increased stability of Bcl-2 transcripts was observed in such MDA-MB-231 cells. Taken together, these data strongly suggest that the regulatory protein that simultaneously increases the expression of the TNFRSF1B and TNFRSF9 genes and decreases the expression of the BCL2 gene and the stability of Bcl-2 transcripts is most likely P53, the expression of which is GalCer dependent.

MitoTracker: A useful tool in need of better alternatives

The fluorescence viewing of mitochondria is commonly performed by MitoTracker, a lipophilic cationic dye that is taken up by the mitochondria. In this forum, we highlight several issues that may occur with MitoTracker, including staining of other organelles. Our aim is to offer alternative dyes and discuss their advantages and disadvantages. We also offer options for software with alternatives to MitoTracker to expedite future experimental design.

Effect of Senna plant on the mitochondrial activity of Hymenolepis diminuta

The peculiarity of energy metabolism in helminths is the ability to undergo transition from aerobic to anaerobic under low oxygen tension. during its adult stage. Fumarate reductase and succinate dehydrogenase of mitochondria are the two enzymes responsible during this transition and adaptation to this hypoxic environment. Earlier we had reported that three species of Senna plant, S. alata, S. alexandrina and S. occidentalis altered the morphology, ionic concentration and neurotransmission of the cestode parasite Hymenolepis diminuta. The present study aimed at exploring the mechanism of leaf extracts of the three plant species of Senna on the mitochondrial activity of the parasite that chiefly involve the NADH-fumarate reductase system which is the terminal step in phosphoenolpyruvate carboxykinase succinate pathway. The structure of mitochondria was observed through electron microsopy and its density was detected through confocal microscopy, spectroflourimetry and spectrophotometry, while enzyme activities were assayed through native gel and spectrophotometric assays. Praziquantel was tested on the parasites as a reference drug to compare its effects with that of the plant extracts. The mitochondria architecture was altered, and enzymes activity decraeased by 60% in all three plant species of Senna treated parasites which suggested that these three Senna species posses potent chemotherapeutic properties.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12639-021-01415-9.

Icaritin alleviates docetaxel-induced skin injury by suppressing reactive oxygen species via estrogen receptors

Background

Docetaxel (DTX) exhibits antitumor effects against breast cancer by stabilizing microtubules and increasing the accumulation of reactive oxygen species (ROS). DTX extravasation during infusion often causes skin injury. The present study aimed to investigate the effects and mechanisms of icaritin (ICT) on DTX‐induced skin injury.

Methods

The effects of ICT on the viability and apoptosis of HaCaT cells were measured by SRB assay and flow cytometry, respectively. Endogenous LC3 puncta and microtubules were determined by immunofluorescence. The number of mitochondria was measured by MitoTracker orange staining. ROS were determined by dihydroethidium staining. The expression of markers of ROS and autophagy were measured by western blotting. Chloroquine, compound D, and tamoxifen were employed as the inhibitor for autophagy and AMPK, estrogen receptors (ERs) modulator, respectively.

Results

DTX inhibited the viability and decreased apoptosis of HaCaT cells, which can be rescued by ICT. ICT decreased microtubule bundles, increased the number of mitochondria, and attenuated ROS of HaCaT cells induced by DTX. ICT blocks autophagy and the autophagic flux. Compound C or tamoxifen diminished the protection effects of ICT on DTX‐treated HaCaT cells.

Conclusion

ICT alleviates DTX‐induced skin injury by suppressing ROS, reducing microtubule bundles, and blocking autophagy via ERs. Our study indicated that ICT may be a potential candidate for DTX‐induced skin injury.

Strategies for organelle targeting of fluorescent probes

Fluorescent tools have emerged as an important tool for studying the distinct chemical microenvironments of organelles, due to their high specificity and ability to be used in non-destructive, live cellular studies. These tools fall largely in two categories: exogenous fluorescent dyes, or endogenous labels such as genetically encoded fluorescent proteins. In both cases, the probe must be targeted to the organelle of interest. To date, many organelle-targeted fluorescent tools have been reported and used to uncover new information about processes that underpin health and disease. However, the majority of these tools only apply a handful of targeting groups, and less-studied organelles have few robust targeting strategies. While the development of new, robust strategies is difficult, it is essential to develop such strategies to allow for the development of new tools and broadening the effective study of organelles. This review aims to provide a comprehensive overview of the major targeting strategies for both endogenous and exogenous fluorescent cargo, outlining the specific challenges for targeting each organelle type and as well as new developments in the field.

Shadow Electrochemiluminescence Microscopy of Single Mitochondria

Mitochondria are the subcellular bioenergetic organelles. The analysis of their morphology and topology is essential to provide useful information on their activity and metabolism. Herein, we report a label-free shadow electrochemiluminescence (ECL) microscopy based on the spatial confinement of the ECL-emitting reactive layer to image single living mitochondria deposited on the electrode surface. The ECL mechanism of the freely-diffusing [Ru(bpy)₃ ]²⁺ dye with the sacrificial tri-n-propylamine coreactant restrains the light-emitting region to a micrometric thickness allowing to visualize individual mitochondria with a remarkable sharp negative optical contrast. The imaging approach named "shadow ECL" (SECL) reflects the negative imprint of the local diffusional hindrance of the ECL reagents by each mitochondrion. The statistical analysis of the colocalization of the shadow ECL spots with the functional mitochondria revealed by classical fluorescent biomarkers, MitoTracker Deep Red and the endogenous intramitochondrial NADH, validates the reported methodology. The versatility and extreme sensitivity of the approach are further demonstrated by visualizing single mitochondria, which remain hardly detectable with the usual biomarkers. Finally, by alleviating problems of photobleaching and phototoxicity associated with conventional microscopy methods, SECL microscopy should find promising applications in the imaging of subcellular structures.

Magnetic Characterization and Moderate Cytotoxicity of Magnetic Mesoporous Silica Nanocomposite for Drug Delivery of Naproxen

In this study, we describe the magnetic and structural properties and cytotoxicity of drug delivery composite (DDC) consisting of hexagonally ordered mesoporous silica, iron oxide magnetic nanoparticles (Fe2O3), and the drug naproxen (Napro). The nonsteroidal anti-inflammatory drug (NSAID) naproxen was adsorbed into the pores of MCM-41 silica after the ultra-small superparamagnetic iron oxide nanoparticles (USPIONs) encapsulation. Our results confirm the suppression of the Brownian relaxation process caused by a "gripping effect" since the rotation of the whole particle encapsulated in the porous system of mesoporous silica was disabled. This behavior was observed for the first time, to the best of our knowledge. Therefore, the dominant relaxation mechanism in powder and liquid form is the Néel process when the rotation of the nanoparticle's magnetic moment is responsible for the relaxation. The in vitro cytotoxicity tests were performed using human glioma U87 MG cells, and the moderate manifestation of cell death, although at high concentrations of studied systems, was observed with fluorescent labeling by AnnexinV/FITC. All our results indicate that the as-prepared MCM-41/Napro/Fe2O3 composite has a potential application as a drug nanocarrier for magnetic-targeted drug delivery.

Determinants, and implications, of the shape and size of thylakoids and cristae

Thylakoids are flattened sacs isolated from other membranes; cristae are attached to the rest of the inner mitochondrial membrane by the crista junction, but the crista lumen is separated from the intermembrane space. The shape of thylakoids and cristae involves membranes with small (5-30 nm) radii of curvature. While the mechanism of curvature is not entirely clear, it seems to be largely a function of Curt proteins in thylakoids and Mitochondrial Organising Site and Crista Organising Centre proteins and oligomeric F_OF₁ ATP synthase in cristae. A subordinate, or minimal, role is attributable to lipids with areas of their head group area greater (convex leaflet) or smaller (concave leaflet) than the area of the lipid tail; examples of the latter group are monogalactosyldiglyceride in thylakoids and cardiolipin in cristae. The volume per unit area on the lumen side of the membrane is less than that of the chloroplast stroma or cyanobacterial cytosol for thylakoids, and mitochondrial matrix for cristae. A low volume per unit area of thylakoids and cristae means a small lumen width that is the average of wider spaces between lipid parts of the membranes and the narrower gaps dominated by extra-membrane components of transmembrane proteins. These structural constraints have important implications for the movement of the electron carriers plastocyanin and cytochrome c₆ (thylakoids) and cytochrome c (cristae) and hence the separation of the membrane-associated electron donors to, and electron acceptors from, these water-soluble electron carriers. The donor/acceptor pairs, are the cytochrome fb₆Fe_nh complex and P₇₀₀⁺ in thylakoids, and Complex III and Complex IV of cristae. The other energy flux parallel to the membranes is that of the proton motive force generated by redox-powered H⁺ pumps into the lumen to the proton motive force use in ATP synthesis by H⁺ flux from the lumen through the ATP synthase. For both the electron transport and proton motive force movement, concentration differences of reduced and oxidised electron carriers and protonated and deprotonated pH buffers are involved. The need for diffusion along a congested route of these energy transfer agents may limit the separation of sources and sinks parallel to the membranes of thylakoids and cristae.

Influence of Oxidative Stress on Time-Resolved Oxygen Detection by [Ru(Phen)3]2+ In Vivo and In Vitro

Detection of tissue and cell oxygenation is of high importance in fundamental biological and in many medical applications, particularly for monitoring dysfunction in the early stages of cancer. Measurements of the luminescence lifetimes of molecular probes offer a very promising and non-invasive approach to estimate tissue and cell oxygenation in vivo and in vitro. We optimized the evaluation of oxygen detection in vivo by [Ru(Phen)₃]²⁺ in the chicken embryo chorioallantoic membrane model. Its luminescence lifetimes measured in the CAM were analyzed through hierarchical clustering. The detection of the tissue oxygenation at the oxidative stress conditions is still challenging. We applied simultaneous time-resolved recording of the mitochondrial probe MitoTracker^TM OrangeCMTMRos fluorescence and [Ru(Phen)₃]²⁺ phosphorescence imaging in the intact cell without affecting the sensitivities of these molecular probes. [Ru(Phen)₃]²⁺ was demonstrated to be suitable for in vitro detection of oxygen under various stress factors that mimic oxidative stress: other molecular sensors, H₂O₂, and curcumin-mediated photodynamic therapy in glioma cancer cells. Low phototoxicities of the molecular probes were finally observed. Our study offers a high potential for the application and generalization of tissue oxygenation as an innovative approach based on the similarities between interdependent biological influences. It is particularly suitable for therapeutic approaches targeting metabolic alterations as well as oxygen, glucose, or lipid deprivation.

Automated Quantification of Mitochondrial Fragmentation in an In Vitro Parkinson's Disease Model

Neuronal mitochondrial fragmentation is a phenotype exhibited in models of neurodegeneration such as Parkinson's disease. Delineating the dysfunction in mitochondrial dynamics found in diseased states can aid our understanding of underlying mechanisms of disease progression and possibly identify novel therapeutic approaches. Advances in microscopy and the availability of intuitive open-access software have accelerated the rate of image acquisition and analysis, respectively. These developments allow routine biology researchers to rapidly turn hypotheses into results. In this protocol, we describe the utilization of cell culture techniques, high-content imaging (HCI), and the subsequent open-source image analysis pipeline for the quantification of mitochondrial fragmentation in the context of a rotenone-based in vitro Parkinson's disease model. © 2020 The Authors. Basic Protocol 1: SN4741 neuron culture and treatment in a rotenone-based model of Parkinson's disease Basic Protocol 2: Identification of cell nuclei, measurement of mitochondrial membrane potential, and measurement of mitochondrial fragmentation in mouse-derived midbrain dopaminergic neurons.

Live cell imaging of mitochondrial redox state in mammalian cells and yeast

The redox state of mitochondria is determined by the levels of reducing and oxidizing species in the organelle, which reflects mitochondrial metabolic activity and overall fitness. Mitochondria are also the primary endogenous source of reactive oxygen species (ROS). This chapter describes methods to measure the mitochondrial superoxide levels and the redox state of the organelle in mammalian cells and yeast. We describe the use of dihydroethidium (DHE) and MitoSOX (a derivative of dihydroethidium bound to a lipophilic cation) to detect mitochondrial superoxide in yeast and mammalian cells, respectively. We also describe the use of genetically encoded fluorescent biosensors for quantitative analysis of mitochondrial NADPH levels (iNap) in mammalian cells and mitochondrial redox state (mito-roGFP) in yeast.

Polyethyleneimine renders mitochondrial membranes permeable by interacting with negatively charged phospholipids in them

Polyethyleneimines (PEIs) are used for transfection of cells with nucleic acids. Meanwhile, the interaction of PEI with mitochondria causes cytochrome c release prior to apoptosis; the mechanisms how PEI causes this permeabilization of mitochondrial membranes and the release of cytochrome c remain unclear. To clarify these mechanisms, we examined the effects of branched-type PEI and linear-type PEI, each of which was 25 kDa in size, on mitochondria. The permeabilization potency of mitochondrial membranes by branched PEI was stronger than that by linear PEI. The permeabilization by PEIs were insensitive to permeability-transition inhibitors, indicating that PEI-induced permeabilization was not attributed to permeability transition. Meanwhile, PEIs caused permeabilization of artificial lipid vesicles; again, the permeabilization potency of branched PEI was stronger than that of linear PEI. Such a difference in this potency was close to that in the case of isolated mitochondria, signifying that the PEI-induced permeabilization of mitochondrial membranes could be attributed to PEI's interaction with the phospholipid phase. Furthermore, this PEI-induced permeabilization of the lipid vesicles was observed only in the case of lipid vesicles including negatively charged phospholipids. These results indicate that PEIs interacted with negatively charged phospholipids in the mitochondrial membranes to directly lead to their permeabilization.

In vitro identification of mitochondrial oxidative stress production by time-resolved fluorescence imaging of glioma cells

Oxidative phosphorylation and glycolysis are important features, by which cells could bypass oxidative stress. The level of oxidative stress, and the ability of cells to promote oxidative phosphorylation or glycolysis, significantly determined proliferation or cell demise. In the present work, we have employed selective mitochondrial probe MitoTracker™ Orange CMTM/Ros (MTO) to estimate the level of oxidative stress in cancer cells at different stressed conditions. MTO is partially sensitive to decrease of mitochondrial membrane potential and to reactive oxygen species (ROS) generated in mitochondria. We have demonstrated, that fluorescence lifetime of MTO is much more sensitive to oxidative stress than intensity-based approaches. This method was validated in different cancer cell lines. Our approach revealed, at relatively low ROS levels, that Gö 6976, a protein kinase C (PKC) α inhibitor, and rottlerin, an indirect PKCδ inhibitor, increased mitochondrial ROS level in glioma cell. Their involvement in oxidative phosphorylation and apoptosis was investigated with oxygen consumption rate estimation, western blot and flow-cytometric analysis. Our study brings new insight to identify feeble differences in ROS production in living cells.

Mitochondrial transfer between cells: Methodological constraints in cell culture and animal models

Interest in the recently discovered phenomenon of mitochondrial transfer between mammalian cells has gained momentum since it was first described in cell culture systems more than a decade ago. Mitochondria-targeting fluorescent dyes have been repurposed and are now widely used in these studies and in acute disease models, sometimes without due consideration of their limitations, while vectors containing mitochondrially-imported fluorescent proteins have complemented the use of mitochondria-targeting dyes. Genetic approaches that use mitochondrial DNA polymorphisms have also been used in some in vitro studies and in tumor models and are particularly useful where mtDNA is damaged or deleted. These approaches can also be used to study the long-term consequences of mitochondrial transfer such as in bone marrow and organ transplantation and in tumour biology where inherent mitochondrial damage is often a key feature. As research on intercellular mitochondrial transfer moves from cell culture into animal models and human diseases it will be important to understand the limitations of the various techniques in order to apply appropriate methodologies to address physiological and pathophysiological conditions.

Mitochondria-Targeted Triphenylphosphonium-Based Compounds: Syntheses, Mechanisms of Action, and Therapeutic and Diagnostic Applications

Mitochondria are recognized as one of the most important targets for new drug design in cancer, cardiovascular, and neurological diseases. Currently, the most effective way to deliver drugs specifically to mitochondria is by covalent linking a lipophilic cation such as an alkyltriphenylphosphonium moiety to a pharmacophore of interest. Other delocalized lipophilic cations, such as rhodamine, natural and synthetic mitochondria-targeting peptides, and nanoparticle vehicles, have also been used for mitochondrial delivery of small molecules. Depending on the approach used, and the cell and mitochondrial membrane potentials, more than 1000-fold higher mitochondrial concentration can be achieved. Mitochondrial targeting has been developed to study mitochondrial physiology and dysfunction and the interaction between mitochondria and other subcellular organelles and for treatment of a variety of diseases such as neurodegeneration and cancer. In this Review, we discuss efforts to target small-molecule compounds to mitochondria for probing mitochondria function, as diagnostic tools and potential therapeutics. We describe the physicochemical basis for mitochondrial accumulation of lipophilic cations, synthetic chemistry strategies to target compounds to mitochondria, mitochondrial probes, and sensors, and examples of mitochondrial targeting of bioactive compounds. Finally, we review published attempts to apply mitochondria-targeted agents for the treatment of cancer and neurodegenerative diseases.

A novel ATP-synthase-independent mechanism coupling mitochondrial activation to exocytosis in insulin-secreting cells

Pancreatic β-cells sense glucose, promoting insulin secretion. Glucose sensing requires the sequential stimulation of glycolysis, mitochondrial metabolism and Ca²⁺ entry. To elucidate how mitochondrial activation in β-cells contributes to insulin secretion, we compared the effects of glucose and the mitochondrial substrate methylsuccinate in the INS-1E insulin-secreting cell line at the respective concentrations at which they maximally activate mitochondrial respiration. Both substrates induced insulin secretion with distinct respiratory profiles, mitochondrial hyperpolarization, NADH production and ATP-to-ADP ratios. In contrast to glucose, methylsuccinate failed to induce large [Ca²⁺] rises and exocytosis proceeded largely independently of mitochondrial ATP synthesis. Both glucose- and methylsuccinate-induced secretion was blocked by diazoxide, indicating that Ca²⁺ is required for exocytosis. Dynamic assessment of the redox state of mitochondrial thiols revealed a less marked reduction in response to methylsuccinate than with glucose. Our results demonstrate that insulin exocytosis can be promoted by two distinct mechanisms one of which is dependent on mitochondrial ATP synthesis and large Ca²⁺ transients, and one of which is independent of mitochondrial ATP synthesis and relies on small Ca²⁺ signals. We propose that the combined effects of Ca²⁺ and redox reactions can trigger insulin secretion by these two mechanisms.

Boron-containing delocalised lipophilic cations for the selective targeting of cancer cells

To limit the incidence of relapse, cancer treatments must not promote the emergence of drug resistance in tumour and cancer stem cells. Under the proviso that a therapeutic amount of boron is selectively delivered to cancer cells, Boron Neutron Capture Therapy (BNCT) may represent one approach that meets this requirement. To this end, we report the synthesis and pharmacology of several chemical entities, based on boron-rich carborane moieties that are functionalised with Delocalized Lipophilic Cations (DLCs), which selectively target the mitochondria of tumour cells. The treatment of tumour and cancer stem cells (CSCs) with such DLC-functionalized carboranes (DLC-carboranes) induces cell growth arrest that is both highly cancer-cell-selective and permanent. Experiments involving cultures of normal and cancer cells show that only normal cells exhibit recapitulation of their proliferation potential upon removal of the DLC-carborane treatment. At the molecular level, the pharmacological effect of DLC-carboranes is exerted through activation of the p53/p21 axis.

Preincubation with green tea polyphenol extract is beneficial for attenuating sperm injury caused by freezing-thawing in swine

Polyphenols (PFs) extracted from green tea, known to be potent anti-oxidants, have been reported to be effective in increasing the motility and viability of mammalian sperm, preserved in a liquid form. Therefore, we tested whether PFs might also be effective for maintaining the integrity of frozen-thawed boar spermatozoa. Ejaculates, collected from Clawn miniature pigs, were diluted in a semen extender containing various amounts of PFs (0, 0.01, 0.05, 0.1 and 0.2% w/v) and then stored at 15°C overnight. The semen samples were processed, using the straw freezing procedure, and then frozen in liquid nitrogen. After rapid thawing at 40°C, the spermatozoa were subjected to several assays to evaluate semen quality. Spermatozoa frozen in a medium containing 0.01% w/v PFs exhibited significantly (P < 0.05) higher degrees of post-thawed viability and acrosomal integrity than those stored in the absence of PFs. However, no change in the mitochondrial activity was noted between the two groups. The inclusion of 0.01% PFs in the semen extender was significantly (P < 0.05) effective in increasing both the rates of monospermic oocyte formation and of blastocyst formation. These findings indicate that preincubation with the semen extender, containing 0.01% PFs prior to freezing, exerts a protective effect on boar sperm by preventing injuries associated with freezing-thawing.

Tl+ induces the permeability transition pore in Ca2+-loaded rat liver mitochondria energized by glutamate and malate

It is known that Ca2+ and heavy metals more actively induce MPTP opening in mitochondria, energized by the I complex substrates. Thus, a rise in a Tl+-induced MPTP was proposed in experiments on isolated rat liver mitochondria energized by the complex I substrate (glutamate and malate). Expose of the mitochondria to Ca2+ into a medium containing TlNO3, glutamate, and malate as well as sucrose or KNO3 resulted in a decrease in state 3, state 4, or DNP-stimulated respiration as well as an increase of both mitochondrial swelling and ΔΨmito dissipation. The MPTP inhibitors, CsA and ADP, almost completely eliminated the effect of Ca2+, which was more pronounced in the presence of the complex I substrates than the complex II substrate (succinate) and rotenone (Korotkov and Saris, 2011). The present study concludes that Tl+-induced MPTP opening is more appreciable in mitochondria energized by glutamate and malate but not succinate in the presence of rotenone. We assume that the Tl+-induced MPTP opening along with followed swelling and possible structural deformations of the complex I in Ca2+-loaded mitochondria may be a part of the thallium toxicity mechanism on mitochondria in living organisms. At the same time, oxidation of Tl+ to Tl3+ by mitochondrial oxygen reactive species is proposed for the mechanism.

Oxidative damage to mitochondria at the nodes of Ranvier precedes axon degeneration in ex vivo transected axons

Oxidative stress and mitochondrial dysfunction appear to contribute to axon degeneration in numerous neurological disorders. However, how these two processes interact to cause axonal damage-and how this damage is initiated-remains unclear. In this study we used transected motor axons from murine peripheral roots to investigate whether oxidative stress alters mitochondrial dynamics in myelinated axons. We show that the nodes of Ranvier are the initial sites of mitochondrial damage induced by oxidative stress. There, mitochondria became depolarized, followed by alterations of the external morphology and disruption of the cristae, along with reduced mitochondrial transport. These mitochondrial changes expanded from the nodes of Ranvier bidirectionally towards both internodes and eventually affected the entire mitochondrial population in the axon. Supplementing axonal bioenergetics by applying nicotinamide adenine dinucleotide and methyl pyruvate, rendered the mitochondria at the nodes of Ranvier resistant to these oxidative stress-induced changes. Importantly, this inhibition of mitochondrial damage protected the axons from degeneration. In conclusion, we present a novel ex vivo approach for monitoring mitochondrial dynamics within axons, which proved suitable for detecting mitochondrial changes upon exogenous application of oxidative stress. Our results indicate that the nodes of Ranvier are the site of initial mitochondrial damage in peripheral axons, and suggest that dysregulation of axonal bioenergetics plays a critical role in oxidative stress-triggered mitochondrial alterations and subsequent axonal injury. These novel insights into the mechanisms underlying axon degeneration may have implications for neurological disorders with a degenerative component.

Mitochondrial channels: ion fluxes and more

The field of mitochondrial ion channels has recently seen substantial progress, including the molecular identification of some of the channels. An integrative approach using genetics, electrophysiology, pharmacology, and cell biology to clarify the roles of these channels has thus become possible. It is by now clear that many of these channels are important for energy supply by the mitochondria and have a major impact on the fate of the entire cell as well. The purpose of this review is to provide an up-to-date overview of the electrophysiological properties, molecular identity, and pathophysiological functions of the mitochondrial ion channels studied so far and to highlight possible therapeutic perspectives based on current information.

Fluctuating vs. continuous exposure to H₂O₂: the effects on mitochondrial membrane potential, intracellular calcium, and NF-κB in astroglia

The effects of H2O2 are widely studied in cell cultures and other in vitro systems. However, such investigations are performed with the assumption that H2O2 concentration is constant, which may not properly reflect in vivo settings, particularly in redox-turbulent microenvironments such as mitochondria. Here we introduced and tested a novel concept of fluctuating oxidative stress. We treated C6 astroglial cells and primary astrocytes with H2O2, using three regimes of exposure - continuous, as well as fluctuating at low or high rate, and evaluated mitochondrial membrane potential and other parameters of mitochondrial activity - respiration, reducing capacity, and superoxide production, as well as intracellular ATP, intracellular calcium, and NF-κB activation. When compared to continuous exposure, fluctuating H2O2 induced a pronounced hyperpolarization in mitochondria, whereas the activity of electron transport chain appears not to be significantly affected. H2O2 provoked a decrease of ATP level and an increase of intracellular calcium concentration, independently of the regime of treatment. However, fluctuating H2O2 induced a specific pattern of large-amplitude fluctuations of calcium concentration. An impact on NF-κB activation was observed for high rate fluctuations, whereas continuous and low rate fluctuating oxidative stress did not provoke significant effects. Presented results outline the (patho)physiological relevance of redox fluctuations.

Transient Influx of nickel in root mitochondria modulates organic acid and reactive oxygen species production in nickel hyperaccumulator Alyssum murale

Mitochondria are important targets of metal toxicity and are also vital for maintaining metal homeostasis. Here, we examined the potential role of mitochondria in homeostasis of nickel in the roots of nickel hyperaccumulator plant Alyssum murale. We evaluated the biochemical basis of nickel tolerance by comparing the role of mitochondria in closely related nickel hyperaccumulator A. murale and non-accumulator Alyssum montanum. Evidence is presented for the rapid and transient influx of nickel in root mitochondria of nickel hyperaccumulator A. murale. In an early response to nickel treatment, substantial nickel influx was observed in mitochondria prior to sequestration in vacuoles in the roots of hyperaccumulator A. murale compared with non-accumulator A. montanum. In addition, the mitochondrial Krebs cycle was modulated to increase synthesis of malic acid and citric acid involvement in nickel hyperaccumulation. Furthermore, malic acid, which is reported to form a complex with nickel in hyperaccumulators, was also found to reduce the reactive oxygen species generation induced by nickel. We propose that the interaction of nickel with mitochondria is imperative in the early steps of nickel uptake in nickel hyperaccumulator plants. Initial uptake of nickel in roots results in biochemical responses in the root mitochondria indicating its vital role in homeostasis of nickel ions in hyperaccumulation.

Label-free photoacoustic microscopy of cytochromes

Photoacoustic microscopy (PAM) has achieved submicron lateral resolution in showing subcellular structures; however, relatively few endogenous subcellular contrasts have so far been imaged. Given that the hemeprotein, mostly cytochromes in general cells, is optically absorbing around the Soret peak (~420 nm), we implemented label-free PAM of cytochromes in cytoplasm for the first time. By measuring the photoacoustic spectra of the oxidized and reduced states of fibroblast lysate and fitting the difference spectrum with three types of cytochromes, we found that the three cytochromes account for more than half the optical absorption in the cell lysate at 420 nm wavelength. Fixed fibroblasts on slides were imaged by PAM at 422 and 250 nm wavelengths to reveal cytoplasms and nuclei, respectively, as confirmed by standard staining histology. PAM was also applied to label-free histology of mouse ear sections by showing cytoplasms and nuclei of various cells. PAM of cytochromes in cytoplasm is expected to be a high-throughput, label-free technique for studying live cell functions, which cannot be accomplished by conventional histology.

Application of a homogenous membrane potential assay to assess mitochondrial function

Decreases in mitochondrial membrane potential (MMP) have been associated with mitochondrial dysfunction that could lead to cell death. The MMP is generated by an electrochemical gradient via the mitochondrial electron transport chain coupled to a series of redox reactions. Measuring the MMP in living cells is commonly used to assess the effect of chemicals on mitochondrial function; decreases in MMP can be detected using lipophilic cationic fluorescent dyes. To identify an optimal dye for use in a high-throughput screening (HTS) format, we compared the ability of mitochondrial membrane potential sensor (Mito-MPS), 5,5',6,6'-tetrachloro-1,1',3,3' tetraethylbenzimidazolylcarbocyanine iodide, rhodamine 123, and tetramethylrhodamine to quantify a decrease in MMP in chemically exposed HepG2 cells cultured in 1,536-well plates. Under the conditions used, the optimal dye for this purpose is Mito-MPS. Next, we developed and optimized a homogenous cell-based Mito-MPS assay for use in 1,536-well plate format and demonstrated the utility of this assay by screening 1,280 compounds in the library of pharmacologically active compounds in HepG2 cells using a quantitative high-throughput screening platform. From the screening, we identified 14 compounds that disrupted the MMP, with half-maximal potencies ranging from 0.15 to 18 μM; among these, compound clusters that contained tyrphostin and 3'-substituted indolone analogs exhibited a structure-activity relationship. Our results demonstrate that this homogenous cell-based Mito-MPS assay can be used to evaluate the ability of large numbers of chemicals to decrease mitochondrial function.

Targeting of mitochondria-endoplasmic reticulum by fluorescent macrocyclic compounds

Background

Useful probes of the intracellular environment that target a specific organelle in order to allow direct observation of the changes in these regions is of high current interest. Macrocyclic ligands have already revealed themselves as important selective hosts in some biological applications, forming stable and specific complexes. Therefore, in this paper, several macrocyclic ligands are evaluated as potential molecular probes.

Methodology

Four polyammonium macrocycles and one macrotricyclic bearing pyridine and phenanthroline chromophores have been synthesised and evaluated as molecular probes. The cytotoxicity of the compounds has been analyzed using human breast cancer cells (MCF-7), non-cancerous human dermal fibroblasts (NHDF) and human adult dermal skin fibroblasts from a breast cancer patient (P14). All the compounds showed low toxicity at concentrations ranging from 10 nM to 10 µM, except for [32]phen₂N₄ which proved to be highly cytotoxic for MCF-7 cells. Flow cytometry studies evidenced that the percentage of apoptotic and necrotic MCF-7 and NHDF cells induced by the compounds is considerably low. Also, flow cytometry analysis showed that some compounds seem to modify the mitochondrial membrane potential (MMP) of the cells. Fluorescence microscopy evidenced that compounds easily cross the plasma membrane (5 min) and accumulated into the mitochondria, as confirmed by co-localization with MitoTracker Green™. The fluorescence images also evidenced an intact mitochondria structure after 48 h. Moreover, reticular staining suggestive of endoplasmic reticulum (ER) localization, in addition to the mitochondrial one, has been found by confocal microscopy.

Conclusion

Our study reveals that compounds Me₂[28]py₂N₆, cryptphen, [16]phenN₂, [30]phen₂N₆, have low toxicity and localize in mitochondria and ER. The ability of these compounds for translocating the cellular membrane (5 min) without special conditioning of the cells or derivatization of the probe, the time-dependent localization (48 h) and the cellular viability provide a proof-of-concept towards their use as promising probes towards biomedical studies.

Plasma membrane domains participate in pH banding of Chara internodal cells

We investigated the identity and distribution of cortical domains, stained by the endocytic marker FM 1-43, in branchlet internodal cells of the characean green algae Chara corallina and Chara braunii. Co-labeling with NBD C(6)-sphingomyelin, a plasma membrane dye, which is not internalized, confirmed their location in the plasma membrane, and co-labelling with the fluorescent pH indicator Lysotracker red indicated an acidic environment. The plasma membrane domains co-localized with the distribution of an antibody against a proton-translocating ATPase, and electron microscopic data confirmed their identity with elaborate plasma membrane invaginations known as charasomes. The average size and the distribution pattern of charasomes correlated with the pH banding pattern of the cell. Charasomes were larger and more frequent at the acidic regions than at the alkaline bands, indicating that they are involved in outward-directed proton transport. Inhibition of photosynthesis by DCMU prevented charasome formation, and incubation in pH buffers resulted in smaller, homogenously distributed charasomes irrespective of whether the pH was clamped at 5.5 or 8.5. These data indicate that the differential size and distribution of charasomes is not due to differences in external pH but reflects active, photosynthesis-dependent pH banding. The fact that pH banding recovered within several minutes in unbuffered medium, however, confirms that pH banding is also possible in cells with evenly distributed charasomes or without charasomes. Cortical mitochondria were also larger and more abundant at the acid bands, and their intimate association with charasomes and chloroplasts suggests an involvement in carbon uptake and photorespiration.

Protective role of fructose in the metabolism of astroglial C6 cells exposed to hydrogen peroxide

Astroglial cells represent the main line of defence against oxidative damage related to neurodegeneration. Therefore, protection of astroglia from an excess of reactive oxygen species could represent an important target of the treatment of such conditions. The aim of our study was to compare the abilities of glucose and fructose, the two monosaccharides used in diet and infusion, to protect C6 cells from hydrogen peroxide (H(2)O(2))-mediated oxidative stress. It was observed using confocal microscopy with fluorescent labels and the MTT test that fructose prevents changes of oxidative status of the cells exposed to H(2)O(2) and preserves their viability. Even more pronounced protective effects were observed for fructose 1,6-bis(phosphate). We propose that fructose and its intracellular forms prevent H(2)O(2) from participating in the Fenton reaction via iron sequestration. As fructose and fructose 1,6-bis(phosphate) are able to pass the blood-brain barrier, they could provide antioxidative protection of nervous tissue in vivo. So, in contrast to the well-known negative effects of frequent consumption of fructose under physiological conditions, acute infusion or ingestion of fructose or fructose 1,6-bis(phosphate) could be of benefit in the cytoprotective therapy of neurodegenerative disorders related to oxidative stress.

The molecular composition of the mitochondrial permeability transition pore

Uncontrolled cell death is a fundamental cause of organ disease in humans. However, despite the need for us to delineate the molecular machinery that underlies cardiomyocyte death, our knowledge of these lethal cellular processes is still limited. The discovery that mitochondrial dysfunction, and in particular the mitochondrial permeability transition (MPT) pore, is often a common cause of the cardiac cell mortality that underlies numerous cardiac diseases has been a first crucial step. The purpose of this review is to outline our current understanding of the molecular identity of the MPT pore and the many questions that still need to be answered.

Analysis of intracellular organelles by flow cytometry or microscopy

Functional analysis of cellular organelles can be accomplished by staining cells with suitable organelle-specific dyes and analyzing the fluorescence of the stained cells with a flow cytometer. With this methodology it is possible to resolve suspected heterogeneity in organelle function or content within a population of cells. Morphological information can be provided by quantitative microscopy (confocal microscope or video microscope with digital image-analysis system). The thirteen protocols cover flow cytometry and microscopy for both live and fixed cells.

The protein kinase C pathway mediates cardioprotection induced by cardiac-specific overexpression of fibroblast growth factor-2

Elucidation of protective mechanisms against ischemia-reperfusion injury is vital to the advancement of therapeutics for ischemic heart disease. Our laboratory has previously shown that cardiac-specific overexpression of fibroblast growth factor-2 (FGF2) results in increased recovery of contractile function and decreased infarct size following ischemia-reperfusion injury and has established a role for the mitogen-activated protein kinase (MAPK) signaling cascade in the cardioprotective effect of FGF2. We now show an additional role for the protein kinase C (PKC) signaling cascade in the mediation of FGF2-induced cardioprotection. Overexpression of FGF2 (FGF2 Tg) in the heart resulted in decreased translocation of PKC-delta but had no effect on PKC-alpha, -epsilon, or -zeta. In addition, multiple alterations in PKC isoform translocation occur during ischemia-reperfusion injury in FGF2 Tg hearts as assessed by Western blot analysis and confocal immunofluorescent microscopy. Treatment of FGF2 Tg and nontransgenic (NTg) hearts with the PKC inhibitor bisindolylmaleimide (1 micromol/l) revealed the necessity of PKC signaling for FGF2-induced reduction of contractile dysfunction and myocardial infarct size following ischemia-reperfusion injury. Western blot analysis of FGF2 Tg and NTg hearts subjected to ischemia-reperfusion injury in the presence of a PKC pathway inhibitor (bisindolylmaleimide, 1 micromol/l), an mitogen/extracellular signal-regulated kinase/extracellular signal-regulated kinase (MEK/ERK) pathway inhibitor (U-0126, 2.5 micromol/l), or a p38 pathway inhibitor (SB-203580, 2 micromol/l) revealed a complicated signaling network between the PKC and MAPK signaling cascades that may participate in FGF2-induced cardioprotection. Together, these data suggest that FGF2-induced cardioprotection is mediated via a PKC-dependent pathway and that the PKC and MAPK signaling cascades are integrally connected downstream of FGF2.

Generation of reactive oxygen species is an early event in dolichyl phosphate-induced apoptosis

The mechanism of induction of apoptosis by dolichyl phosphate (Dol-P) was investigated in U937 cells. Studies using isolated mitochondria revealed that the respiratory complex II activity was almost completely inhibited by 20 microg/ml of Dol-P but not by the same concentration of dolichol. Activities of complex I and III were also inhibited by Dol-P, but nearly 50% of activity still remained at 20 microg/ml. Dol-P induced release of cytochrome-c from the isolated mitochondria. Fluorometric microtiter plate assay revealed that generation of reactive oxygen species (ROS) increased in a time-dependent manner. Flow cytometric analysis also indicated that Dol-P caused loss of mitochondrial membrane potential (Deltapsi(m)) and increased ROS generation. The addition of the antioxidant pyrrolidine dithiocarbamate (PDTC) significantly inhibited Dol-P-induced ROS generation and activation of caspase-3. A specific inhibitor of respiratory complex II, thenoyltrifluoroacetone (TTFA), increased ROS generation, potentially mimicking the consequence of inhibition of electron flow at complex II by Dol-P in U937 cells. Electron microscopy revealed that mitochondria became swollen and spherical in shape by the treatment with Dol-P. Neither the tyrosine kinase inhibitor k252a nor mitogen activated protein kinase/extracellular signal-regulated kinase kinase (MEK) inhibitors PD98059 and U0126 inhibited the Dol-P-induced apoptosis. Together, these results suggest that the direct disruption of mitochondrial respiratory complexes and the consequent ROS generation play a critical role in the initiation of Dol-P-induced apoptosis.

Ganglioside GM3 promotes cell migration by regulating MAPK and c-Fos/AP-1

Gangliosides have been proposed as modulators of transmembrane signaling. Recently, GM3, a glycosphingolipid containing monosaialic acids, is thought to be one of the key molecules of signal transduction in mammalian cells. In this study, we used mouse embryonic fibroblast cell lines (MEFs) established from sialyltransferase-I knockout mice (GM3 synthase KO mice) to evaluate the regulation of mitogenic signals by gangliosides. Cell proliferation assay revealed a higher growth potential of GM3 KO MEFs. Immunoblots showed upregulation of Ras/Raf/MEK/ERK pathway in GM3 KO MEFs, and these signals resulted in enhanced translocation of ERK into the nuclei. Further, both exogenous and endogenous add-back of GM3 decreased the activities of MAPK in GM3 KO MEFs. In addition, GM3 KO MEFs formed foci in high-density culture condition, and analyses of cell cycle modulators revealed the resistance of GM3 KO MEFs for entering cell cycle arrest. Finally, sustained expressions of c-Fos in GM3 KO MEFs were shown to correlate with DNA-binding activity between c-Fos and AP-1. These results demonstrate that the deletion of sialyltransferase-I changes the character of MEFs to a highly activated state of the MAPK pathway, indicating the critical role of GM3 as a regulator of membrane-transmitted signals.

Ischemic preconditioning requires increases in reactive oxygen release independent of mitochondrial K+ channel activity

Mitochondrial ATP-sensitive K+ channels (mitoKATP) mediate ischemic preconditioning, a cardioprotective procedure. MitoKATP activity has been proposed to either enhance or prevent the release of reactive oxygen species. This study tested the redox effects of mitoKATP in order to clarify the role of these channels during preconditioning. We found no evidence that mitoKATP channels increase mitochondrial reactive oxygen species release directly. In addition, neither ischemic preconditioning nor the mitoKATP agonist diazoxide increased antioxidant defenses. Furthermore, increases in reactive oxygen species observed during ischemic preconditioning were not inhibited by mitoKATP antagonists, suggesting that they occur upstream of channel activity. Antioxidants were tested to verify if diazoxide-promoted ischemic protection was dependent on reactive oxygen species. N-Acetylcysteine proved to be an inadequate antioxidant for these tests since it directly interfered with the ability of diazoxide to activate mitoKATP. Catalase reversed the beneficial effect of preconditioning, but not of diazoxide, indicating that reactive oxygen species mediating preconditioning occur upstream of mitoKATP. Taken together, these results demonstrate that ischemic preconditioning increases reactive oxygen release independently of mitoKATP and suggest that the activity of this channel prevents oxidative reperfusion damage by decreasing reactive oxygen species production.

Tissue protection mediated by mitochondrial K+ channels

Two distinct K+ uniporters have been described in mitochondria, ATP-sensitive and Ca2+-activated. Both are capable of protecting tissues against ischemia and other forms of injury when active. These findings indicate a central role for mitochondrial K+ uptake in tissue protection. This review describes the characteristics of mitochondrial K+ uniport, physiological consequences of this transport, forms of tissue damage in which K+ channels are implicated and possible mechanisms through which protection occurs.

Efficacy of MitoTracker Green and CMXrosamine to measure changes in mitochondrial membrane potentials in living cells and tissues

BACKGROUND

Chloromethyl-X-rosamine (CMXRos) and MitoTracker Green (MTG) have proved to be useful dyes with which to measure mitochondrial function. CMXRos is a lipophilic cationic fluorescent dye that is concentrated inside mitochondria by their negative mitochondrial membrane potential (MMP). MTG fluorescence has been used as a measure of mitochondrial mass independent of MMP. The fluorescence ratio of the two dyes is a relative measure of the MMP independent of mitochondrial mass. Because MTG was recently reported to be sensitive to MMP, we have reevaluated the effects of loss of MMP on MTG and CMXRos fluorescence, using both flow cytometry and laser scanning confocal microscopy (LSCM).

METHODS

Using flow cytometry, the relative fluorescence of CMXRos, R123, and MTG was determined in human lymphoblastoid cell lines (LCLs) with or without carbonyl cyanide p-trifluoromethoxylphenyl-hydrazone (FCCP), used to collapse the MMP. LSCM analysis was also used to evaluate the effect of FCCP on MTG and CMXRos fluorescence of mouse cells and viable lenses in culture. The cytotoxicity of the dyes was determined using flow analysis of endogenous NADH fluorescence. The sensitivity of MTG fluorescence to H(2)O(2) was also evaluated using flow cytometry.

RESULTS

CMXRos fluorescence was dependent on MMP, whereas MTG fluorescence was not affected by MMP, using either flow or LSCM. Specific staining of mitochondria was seen with both dyes in all cell types tested, without evidence of cytotoxicity, as determined by NADH levels. H(2)O(2) damage slightly increased MTG staining of cells.

CONCLUSIONS

Our results indicate that CMXRos is a nontoxic sensitive indicator of relative changes in MMP, whereas MTG is relatively insensitive to MMP and oxidative stress, using both flow and LSCM analyses, provided optimal staining conditions are used. In addition, these dyes can be useful for the study of mitochondrial morphology and function in whole tissues, using LSCM.

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

Bilirubin is the principal end product of heme degradation. Prompted by epidemiologic analyses demonstrating an inverse correlation between serum bilirubin levels and cancer mortality, we examined the effect(s) of bilirubin on the growth and survival of colon adenocarcinoma cells. Adenocarcinoma cell monolayers were treated with bilirubin over a range of bilirubin:BSA molar ratios (0-0.6), and viability was assessed colorimetrically. Apoptosis was characterized by TUNEL assay, annexin V staining and caspase-3 activation. The mechanism(s) by which bilirubin induces apoptosis was investigated by Western blotting for cytochrome c release, assaying for caspase-8 and caspase-9 activation and for mitochondrial depolarization by JC-1 staining. The direct effect of bilirubin on the membrane potential of isolated mitochondria was evaluated using light-scattering and fluorescence techniques. Bilirubin decreased the viability of all colon cancer cell lines tested in a dose-dependent manner. Cells exhibited substantial apoptosis when exposed to bilirubin concentrations ranging 0-50 microM, as demonstrated by an 8- to 10-fold increase in TUNEL and annexin V staining and in caspase-3 activity. Bilirubin treatment evokes specific activation of caspase-9, enhances cytochrome c release into the cytoplasm and triggers the mitochondrial permeability transition in colon cancer monolayers. Additionally, bilirubin directly induces the depolarization of isolated rat liver mitochondria, an effect that is not inhibited by cyclosporin A. Bilirubin stimulates apoptosis of colon adenocarcinoma cells in vitro through activation of the mitochondrial pathway, apparently by directly dissipating mitochondrial membrane potential. As this effect is triggered at concentrations normally present in the intestinal lumen, we postulate a physiologic role for bilirubin in modulating colon tumorigenesis.

A novel role of Mgm1p, a dynamin-related GTPase, in ATP synthase assembly and cristae formation/maintenance

In Saccharomyces cerevisiae, two mitochondrial inner-membrane proteins play critical roles in organellar morphology. One is a dynamin-related GTPase, Mgm1p, which participates in mitochondrial fusion. Another is Tim11p, which is required for oligomeric assembly of F1Fo-ATP synthase, which generates ATP through oxidative phosphorylation. Our data bring these findings together and define a novel role for Mgm1p in the formation and maintenance of mitochondrial cristae. We show that Mgm1p serves as an upstream regulator of Tim11p protein stability, ATP synthase assembly, cristae morphology and cytochrome c storage within cristae.

Multiple effects of DiS-C3(5) on mitochondrial structure and function

3,3'-Dipropyl-2,2'-thiadicarbocyanine iodide [DiS-C(3)(5)], often used as a tracer dye to assess the mitochondrial membrane potential, was investigated in detail regarding its effects on the structure and function of isolated mitochondria. As reported previously, DiS-C(3)(5) had an inhibitory effect on NADH-driven mitochondrial electron transfer. On the contrary, in the presence of inorganic phosphate, DiS-C(3)(5) showed dose-dependent biphasic effects on mitochondria energized by succinate. At higher concentrations, such as 50 micro m, DiS-C(3)(5) accelerated mitochondrial oxygen consumption. Measurements of the permeability of DiS-C(3)(5)-treated mitochondrial membranes to poly(ethylene glycol) and analysis of mitochondrial configuration by transmission electron microscopy revealed that the accelerating effect of DiS-C(3)(5) on mitochondrial oxygen consumption reflects the induction of the mitochondrial permeability transition (PT). When the mitochondrial PT was induced by DiS-C(3)(5), release of mitochondrial cytochrome c was observed, as in the case of the PT induced by Ca(2+). On the contrary, at a low concentration such as 5 micro m, DiS-C(3)(5) showed an inhibitory effect on the latent oxygen consumption by mitochondria. This effect was shown to reflect inhibition of the PT induced by a low concentration of Ca(2+). Furthermore, in the absence of inorganic phosphate, DiS-C(3)(5) caused mitochondrial swelling. Under this condition, DiS-C(3)(5) caused changes in the membrane status of the mitochondria, but did not induce a release of mitochondrial cytochrome c.

Cloning and identification of hepatocellular carcinoma down-regulated mitochondrial carrier protein, a novel liver-specific uncoupling protein

We report the identification of a novel cDNA fragment that shows significantly reduced expression in cancerous tissue compared with paired non-cancerous liver tissue in patients with hepatocellular carcinoma (HCC). The full-length transcript of 1733 bp encodes a protein of 308 amino acids that has all the hallmark features of mitochondrial carrier proteins. We designate the novel protein as HDMCP (HCC-down-regulated mitochondrial carrier protein). The HDMCP orthologs in human, mouse, and rat are found to exhibit close similarity in protein sequence and gene organization, as well as exclusive expression in the liver. Moreover, conserved syntenic regions have been demonstrated at the HDMCP gene locus in the human, mouse, and rat genome. Taken together, we suggest that HDMCP might have a conserved and unique biological function in the liver. Overexpression of HDMCP in transiently transfected cancer cells results in the loss of staining by MitoTracker dye, indicating that HDMCP could induce the dissipation of mitochondrial membrane potential (DeltaPsim). However, HDMCP-mediated disruption of DeltaPsim is not related to mitochondrial permeability transition or apoptosis. In addition, we further demonstrate that the dissipation of DeltaPsim is accompanied by significant reduction of cellular ATP in 293T cells overexpressing HDMCP or uncoupling protein 2 (UCP2). Our present findings suggest that HDMCP might be one of the long postulated uncoupling proteins that catalyze the physiological "proton leak" in the liver. The down-regulation of HDMCP in HCC cancer cells might result in the elevation of DeltaPsim, a common phenomenon found in cancer cells.