Chemotherapeutic induction of mitochondrial oxidative stress activates GSK-3α/β and Bax, leading to permeability transition pore opening and tumor cell death

The mechanisms of action of mitochondrial targeting agents in cancer: inhibiting oxidative phosphorylation and inducing apoptosis

The tumor microenvironment affects the structure and metabolic function of mitochondria in tumor cells. This process involves changes in metabolic activity, an increase in the amount of reactive oxygen species (ROS) in tumor cells compared to normal cells, the production of more intracellular free radicals, and the activation of oxidative pathways. From a practical perspective, it is advantageous to develop drugs that target mitochondria for the treatment of malignant tumors. Such drugs can enhance the selectivity of treatments for specific cell groups, minimize toxic effects on normal tissues, and improve combinational treatments. Mitochondrial targeting agents typically rely on small molecule medications (such as synthetic small molecules agents, active ingredients of plants, mitochondrial inhibitors or autophagy inhibitors, and others), modified mitochondrial delivery system agents (such as lipophilic cation modification or combining other molecules to form targeted mitochondrial agents), and a few mitochondrial complex inhibitors. This article will review these compounds in three main areas: oxidative phosphorylation (OXPHOS), changes in ROS levels, and endogenous oxidative and apoptotic processes.

The effects of two gold-N-heterocyclic carbene (NHC) complexes in ovarian cancer cells: a redox proteomic study

PURPOSE

Ovarian cancer is the fifth leading cause of cancer-related deaths in women. Standard treatment consists of tumor debulking surgery followed by platinum and paclitaxel chemotherapy; yet, despite the initial response, about 70-75% of patients develop resistance to chemotherapy. Gold compounds represent a family of very promising anticancer drugs. Among them, we previously investigated the cytotoxic and pro-apoptotic properties of Au(NHC) and Au(NHC)2PF6, i.e., a monocarbene gold(I) complex and the corresponding bis(carbene) complex. Gold compounds are known to alter the redox state of cells interacting with free cysteine and selenocysteine residues of several proteins. Herein, a redox proteomic study has been carried out to elucidate the mechanisms of cytotoxicity in A2780 human ovarian cancer cells.

METHODS

A biotinylated iodoacetamide labeling method coupled with mass spectrometry was used to identify oxidation-sensitive protein cysteines.

RESULTS

Gold carbene complexes cause extensive oxidation of several cellular proteins; many affected proteins belong to two major functional classes: carbohydrate metabolism, and cytoskeleton organization/cell adhesion. Among the affected proteins, Glyceraldehyde-3-phosphate dehydrogenase inhibition was proved by enzymatic assays and by ESI-MS studies. We also found that Au(NHC)2PF6 inhibits mitochondrial respiration impairing complex I function. Concerning the oxidized cytoskeletal proteins, gold binding to the free cysteines of actin was demonstrated by ESI-MS analysis. Notably, both gold compounds affected cell migration and invasion.

CONCLUSIONS

In this study, we deepened the mode of action of Au(NHC) and Au(NHC)2PF6, identifying common cellular targets but confirming their different influence on the mitochondrial function.

Tumor growth of neurofibromin-deficient cells is driven by decreased respiration and hampered by NAD+ and SIRT3

Neurofibromin loss drives neoplastic growth and a rewiring of mitochondrial metabolism. Here we report that neurofibromin ablation dampens expression and activity of NADH dehydrogenase, the respiratory chain complex I, in an ERK-dependent fashion, decreasing both respiration and intracellular NAD⁺. Expression of the alternative NADH dehydrogenase NDI1 raises NAD⁺/NADH ratio, enhances the activity of the NAD⁺-dependent deacetylase SIRT3 and interferes with tumorigenicity in neurofibromin-deficient cells. The antineoplastic effect of NDI1 is mimicked by administration of NAD⁺ precursors or by rising expression of the NAD⁺ deacetylase SIRT3 and is synergistic with ablation of the mitochondrial chaperone TRAP1, which augments succinate dehydrogenase activity further contributing to block pro-neoplastic metabolic changes. These findings shed light on bioenergetic adaptations of tumors lacking neurofibromin, linking complex I inhibition to mitochondrial NAD⁺/NADH unbalance and SIRT3 inhibition, as well as to down-regulation of succinate dehydrogenase. This metabolic rewiring could unveil attractive therapeutic targets for neoplasms related to neurofibromin loss.

Current Progress and Perspectives on Using Gold Compounds for the Modulation of Tumor Cell Metabolism

Altered cellular metabolism, which is essential for the growth and survival of tumor cells in a specific microenvironment, is one of the hallmarks of cancer. Among the most significant changes in the metabolic pattern of tumor cells is the shift from oxidative phosphorylation to aerobic glycolysis for glucose utilization. Tumor cells also exhibit changes in patterns of protein and nucleic acid metabolism. Recently, gold compounds have been shown to target several metabolic pathways and a number of metabolites in tumor cells. In this review, we summarize how gold compounds modulate glucose, protein, and nucleic acid metabolism in tumor cells, resulting in anti-tumor effects. We also discuss the rationale underlying the anti-tumor effects of these gold compounds and highlight how to effectively utilize against various types of tumors.

Au2phen and Auoxo6, Two Dinuclear Oxo-Bridged Gold(III) Compounds, Induce Apoptotic Signaling in Human Ovarian A2780 Cancer Cells

Au₂phen ((2,9-dimethyl-1,10-phenanthroline)₂Au₂(µ-O)₂)(PF₆)₂ and Auoxo6 ((6,6′-dimethyl-2,2′-bipyridine)₂Au₂(µ-O)₂)(PF₆)₂ are two structurally related gold(III) complexes that were previously reported to display relevant and promising anticancer properties in vitro toward a large number of human cancer cell lines. To expand the knowledge on the molecular mechanisms through which these gold(III) complexes trigger apoptosis in cancer cells, further studies have been performed using A2780 ovarian cancer cells as reference models. For comparative purposes, parallel studies were carried out on the gold(III) complex AuL12 (dibromo(ethylsarcosinedithiocarbamate)gold(III)), whose proapoptotic profile had been earlier characterized in several cancer cell lines. Our results pointed out that all these gold(III) compounds manifest a significant degree of similarity in their cellular and proapoptotic effects; the main observed perturbations consist of potent thioredoxin reductase inhibition, disruption of the cell redox balance, impairment of the mitochondrial membrane potential, and induction of associated metabolic changes. In addition, evidence was gained of the remarkable contribution of ASK1 (apoptosis-signal-regulating kinase-1) and AKT pathways to gold(III)-induced apoptotic signaling. Overall, the observed effects may be traced back to gold(III) reduction and subsequent formation and release of gold(I) species that are able to bind and inhibit several enzymes responsible for the intracellular redox homeostasis, in particular the selenoenzyme thioredoxin reductase.

Design, physico-chemical characterization and in vitro biological activity of organogold(III) glycoconjugates

To develop new metal-based glycoconjugates as potential anticancer agents, four organometallic gold(iii)-dithiocarbamato glycoconjugates of the type [AuIII(2-Bnpy)(SSC-Inp-GlcN)](PF6) (2-Bnpy: 2-benzylpyridine; Inp: isonipecotic moiety; GlcN: amino-glucose scaffold; Au3-Au6) and the corresponding model non-glycosylated counterparts [AuIII(2-Bnpy)(SSC-Inp-R)](PF6) (R: OEt (Au1), NH2 (Au2)) have been generated and characterized by means of several analytical techniques (elemental analysis, FT-IR, 1H-/13C-NMR, ESI-MS, UV-Vis, X-ray crystallography). Their stability under physiologically-relevant conditions (PBS solution) and n-octanol/PBS distribution coefficient (D7.4) have also been evaluated. Gold(iii) glycoconjugates showed an antiproliferative effect against ovarian carcinoma A2780 cells, with GI50 values in the low micromolar range. Remarkably, their cell growth inhibitory effect increases upon the addition of a glucose transporter 1 (GLUT1) inhibitor, thus ruling out the involvement of GLUT1 in their transport inside the cell. Additional mechanistic studies have been carried out in A2780 cells, supporting the hypothesis of a facilitated diffusion mechanism (possibly mediated by glucose transporters other than GLUT1), and revealing their capability to act as topoisomerase I and II inhibitors and to disrupt mitochondrial membrane integrity, leading to the generation of ROS, thus resulting in the promotion of oxidative stress and, eventually, cell death.

Targeting mitochondrial ion channels for cancer therapy

Pharmacological targeting of mitochondrial ion channels is emerging as a promising approach to eliminate cancer cells; as most of these channels are differentially expressed and/or regulated in cancer cells in comparison to healthy ones, this strategy may selectively eliminate the former. Perturbation of ion fluxes across the outer and inner membranes is linked to alterations of redox state, membrane potential and bioenergetic efficiency. This leads to indirect modulation of oxidative phosphorylation, which is/may be fundamental for both cancer and cancer stem cell survival. Furthermore, given the crucial contribution of mitochondria to intrinsic apoptosis, modulation of their ion channels leading to cytochrome c release may be of great advantage in case of resistance to drugs triggering apoptotic events upstream of the mitochondrial phase. In the present review, we give an overview of the known mitochondrial ion channels and of their modulators capable of killing cancer cells. In addition, we discuss state-of-the-art strategies using mitochondriotropic drugs or peptide-based approaches allowing a more efficient and selective targeting of mitochondrial ion channel-linked events.

A novel piperine analogue exerts in vivo antitumor effect by inducing oxidative, antiangiogenic and immunomodulatory actions

Structural diversity characterizes natural products as prototypes for design of lead compounds. The aim of this study was to synthetize, and to evaluate the toxicity and antitumor action of a new piperine analogue, the butyl 4-(4-nitrobenzoate)-piperinoate (DE-07). Toxicity was evaluated against zebrafish, and in mice (acute and micronucleus assays). To evaluate the DE-07 antitumor activity Ehrlich ascites carcinoma model was used in mice. Angiogenesis, Reactive Oxygen Species (ROS) production and cytokines levels were investigated. Ninety-six hours exposure to DE-07 did not cause morphological or developmental changes in zebrafish embryos and larvae, with estimated LC₅₀ (lethal concentration 50%) higher than 100 μg/mL. On the acute toxicity assay in mice, LD₅₀ (lethal dose 50%) was estimated at around 1000 mg/kg, intraperitoneally (i.p.). DE-07 (300 mg/kg, i.p.) did not induce increase in the number of micronucleated erythrocytes in mice, suggesting no genotoxicity. On Ehrlich tumor model, DE-07 (12.5, 25 or 50 mg/kg, i.p.) induced a significant decrease on cell viability. In addition, there was an increase on ROS production and a decrease in peritumoral microvessels density. Moreover, DE-07 induced an increase of cytokines levels involved in oxidative stress and antiangiogenic effect (IL-1β, TNF-α and IL-4). No significant clinical toxicological effects were recorded in Ehrlich tumor transplanted animals. These data provide evidence that DE-07 presents low toxicity, and antitumor effect via oxidative and antiangiogenic actions by inducing modulation of inflammatory response in the tumor microenvironment.

Combined Use of Astragalus Polysaccharide and Berberine Attenuates Insulin Resistance in IR-HepG2 Cells via Regulation of the Gluconeogenesis Signaling Pathway

Insulin resistance (IR) is likely to induce metabolic syndrome and type 2 diabetes mellitus (T2DM). Gluconeogenesis (GNG) is a complex metabolic process that may result in glucose generation from certain non-carbohydrate substrates. Chinese herbal medicine astragalus polysaccharides and berberine have been documented to ameliorate IR, and combined use of astragalus polysaccharide (AP) and berberine (BBR) are reported to synergistically produce an even better effect. However, what change may occur in the GNG signaling pathway of IR-HepG2 cells in this synergistic effect and whether AP-BBR attenuates IR by regulating the GNG signaling pathway remain unclear. For the first time, we discovered in this study that the optimal time of IR-HepG2 cell model formation was 48 h after insulin intervention. AP-BBR attenuated IR in HepG2 cells and the optimal concentration was 10 mg. AP-BBR reduced the intracellular H2O2 content with no significant effect on apoptosis of IR-HepG2 cells. In addition, a rapid change was observed in intracellular calcium current of the IR-HepG2 cell model, and AP-BBR intervention attenuated this change markedly. The gene sequencing results showed that the GNG signaling pathway was one of the signaling pathways of AP-BBR to attenuate IR in IR-Hepg2 cells. The expression of p-FoxO1Ser256 and PEPCK protein was increased, and the expression of GLUT2 protein was decreased significantly in the IR-HepG2 cell model, and both of these effects could be reversed by AP-BBR intervention. AP-BBR attenuated IR in IR-HepG2 cells, probably by regulating the GNG signaling Pathway.

A Proteomic View of Cellular Responses to Anticancer Quinoline-Copper Complexes

Metal-containing drugs have long been used in anticancer therapies. The mechansims of action of platinum-based drugs are now well-understood, which cannot be said of drugs containing other metals, such as gold or copper. To gain further insights into such mechanisms, we used a classical proteomic approach based on two-dimensional elelctrophoresis to investigate the mechanisms of action of a hydroxyquinoline-copper complex, which shows promising anticancer activities, using the leukemic cell line RAW264.7 as the biological target. Pathway analysis of the modulated proteins highlighted changes in the ubiquitin/proteasome pathway, the mitochondrion, the cell adhesion-cytoskeleton pathway, and carbon metabolism or oxido-reduction. In line with these prteomic-derived hypotheses, targeted validation experiments showed that the hydroxyquinoline-copper complex induces a massive reduction in free glutathione and a strong alteration in the actin cytoskeleton, suggesting a multi-target action of the hydroxyquinoline-copper complex on cancer cells.

Redox Regulation of Hexokinases

SIGNIFICANCE

Hexokinases are key enzymes that are responsible for the first reaction of glycolysis, but they also moonlight other cellular processes, including mitochondrial redox signaling regulation. Modulation of hexokinase activity and spatiotemporal location by reactive oxygen and nitrogen species as well as other gasotransmitters serves as the basis for a unique, underexplored method of tight and flexible regulation of these fundamental enzymes. Recent Advances: Redox modifications of thiols serve as a molecular code that enables the precise and complex regulation of hexokinases. Redox regulation of hexokinases is also used by multiple parasites to cause widespread and severe diseases, including malaria, Chagas disease, and sleeping sickness. Redox-active molecules affect each other, and the moonlighting activity of hexokinases provides another feedback loop that affects the cellular redox status and is hijacked in malignantly transformed cells.

CRITICAL ISSUES

Several compounds affect the redox status of hexokinases in vivo. These include the dehydroascorbic acid (oxidized form of vitamin C), pyrrolidinium porrolidine-1-carbodithioate (contraceptive), peroxynitrite (product of ethanol metabolism), alloxan (a glucose analog), and isobenzothiazolinone ebselen. However, very limited information is available regarding which amino acid residues in hexokinases are affected by redox signaling. Except in cases of monogenic diabetes, direct evidence is absent for disease phenotypes that are associated with variations within motifs that are susceptible to redox signaling.

FUTURE DIRECTIONS

Further studies should address the propensity of hexokinases and their disease-associated variants to participate in redox regulation. Robust and straightforward proteomic methods are needed to understand the context and consequences of hexokinase-mediated redox regulation in health and disease.

Tauopathy: A common mechanism for neurodegeneration and brain aging

Tau, a microtubule-associated protein promotes assembly and stability of microtubules which is related to axoplasmic flow and critical neuronal activities upon physiological conditions. Under neurodegenerative condition such as in Alzheimer's Disease (AD), tau-microtubule binding dynamics and equilibrium are severely affected due to its aberrant post-translational modifications including acetylation and hyperphosphorylation. This event results in its conformational changes to form neurofibrillary tangles (NFT) after aggregation in the cytosol. The formation of NFT is more strongly correlated with cognitive decline than the distribution of senile plaque, which is formed by polymorphous beta-amyloid (Aβ) protein deposits, another pathological hallmark of AD. In neurodegenerative conditions, other than AD, the disease manifestation is correlated with mutations of the MAPT gene. In Primary age-related tauopathy (PART), which is commonly observed in the brains of aged individuals, tau deposition is directly correlated with cognitive deficits even in the absence of Aβ deposition. Thus, tauopathy has been considered as an essential hallmark in neurodegeneration and normal brain aging. In this review, we highlighted the recent progress about the tauopathies in the light of its posttranslational modifications and its implication in AD and the aged brain.

Pharmacological modulation of mitochondrial ion channels

The field of mitochondrial ion channels has undergone a rapid development during the last three decades, due to the molecular identification of some of the channels residing in the outer and inner membranes. Relevant information about the function of these channels in physiological and pathological settings was gained thanks to genetic models for a few, mitochondria-specific channels. However, many ion channels have multiple localizations within the cell, hampering a clear-cut determination of their function by pharmacological means. The present review summarizes our current knowledge about the ins and outs of mitochondrial ion channels, with special focus on the channels that have received much attention in recent years, namely, the voltage-dependent anion channels, the permeability transition pore (also called mitochondrial megachannel), the mitochondrial calcium uniporter and some of the inner membrane-located potassium channels. In addition, possible strategies to overcome the difficulties of specifically targeting mitochondrial channels versus their counterparts active in other membranes are discussed, as well as the possibilities of modulating channel function by small peptides that compete for binding with protein interacting partners. Altogether, these promising tools along with large-scale chemical screenings set up to identify new, specific channel modulators will hopefully allow us to pinpoint the actual function of most mitochondrial ion channels in the near future and to pharmacologically affect important pathologies in which they are involved, such as neurodegeneration, ischaemic damage and cancer. LINKED ARTICLES: This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Glycogen synthase kinase 3β promotes liver innate immune activation by restraining AMP-activated protein kinase activation

BACKGROUND & AIMS

Glycogen synthase kinase 3β (Gsk3β [Gsk3b]) is a ubiquitously expressed kinase with distinctive functions in different types of cells. Although its roles in regulating innate immune activation and ischaemia and reperfusion injuries (IRIs) have been well documented, the underlying mechanisms remain ambiguous, in part because of the lack of cell-specific tools in vivo.

METHODS

We created a myeloid-specific Gsk3b knockout (KO) strain to study the function of Gsk3β in macrophages in a murine liver partial warm ischaemia model.

RESULTS

Compared with controls, myeloid Gsk3b KO mice were protected from IRI, with diminished proinflammatory but enhanced anti-inflammatory immune responses in livers. In bone marrow-derived macrophages, Gsk3β deficiency resulted in an early reduction of Tnf gene transcription but sustained increase of Il10 gene transcription on Toll-like receptor 4 stimulation in vitro. These effects were associated with enhanced AMP-activated protein kinase (AMPK) activation, which led to an accelerated and higher level of induction of the novel innate immune negative regulator small heterodimer partner (SHP [Nr0b2]). The regulatory function of Gsk3β on AMPK activation and SHP induction was confirmed in wild-type bone marrow-derived macrophages with a Gsk3 inhibitor. Furthermore, we found that this immune regulatory mechanism was independent of Gsk3β Ser9 phosphorylation and the phosphoinositide 3-kinase-Akt signalling pathway. In vivo, myeloid Gsk3β deficiency facilitated SHP upregulation by ischaemia-reperfusion in liver macrophages. Treatment of Gsk3b KO mice with either AMPK inhibitor or SHP small interfering RNA before the onset of liver ischaemia restored liver proinflammatory immune activation and IRI in these otherwise protected hosts. Additionally, pharmacological activation of AMPK protected wild-type mice from liver IRI, with reduced proinflammatory immune activation. Inhibition of the AMPK-SHP pathway by liver ischaemia was demonstrated in tumour resection patients.

CONCLUSIONS

Gsk3β promotes innate proinflammatory immune activation by restraining AMPK activation.

LAY SUMMARY

Glycogen synthase kinase 3β promotes macrophage inflammatory activation by inhibiting the immune regulatory signalling of AMP-activated protein kinase and the induction of small heterodimer partner. Therefore, therapeutic targeting of glycogen synthase kinase 3β enhances innate immune regulation and protects liver from ischaemia and reperfusion injury.

Pim kinase inhibition sensitizes FLT3-ITD acute myeloid leukemia cells to topoisomerase 2 inhibitors through increased DNA damage and oxidative stress

Internal tandem duplication of fms-like tyrosine kinase-3 (FLT3-ITD) is frequent (30 percent) in acute myeloid leukemia (AML), and is associated with short disease-free survival following chemotherapy. The serine threonine kinase Pim-1 is a pro-survival oncogene transcriptionally upregulated by FLT3-ITD that also promotes its signaling in a positive feedback loop. Thus inhibiting Pim-1 represents an attractive approach in targeting FLT3-ITD cells. Indeed, co-treatment with the pan-Pim kinase inhibitor AZD1208 or expression of a kinase-dead Pim-1 mutant sensitized FLT3-ITD cell lines to apoptosis triggered by chemotherapy drugs including the topoisomerase 2 inhibitors daunorubicin, etoposide and mitoxantrone, but not the nucleoside analog cytarabine. AZD1208 sensitized primary AML cells with FLT3-ITD to topoisomerase 2 inhibitors, but did not sensitize AML cells with wild-type FLT3 or remission bone marrow cells, supporting a favorable therapeutic index. Mechanistically, the enhanced apoptosis observed with AZD1208 and topoisomerase 2 inhibitor combination treatment was associated with increased DNA double-strand breaks and increased levels of reactive oxygen species (ROS), and co-treatment with the ROS scavenger N-acetyl cysteine rescued FLT3-ITD cells from AZD1208 sensitization to topoisomerase 2 inhibitors. Our data support testing of Pim kinase inhibitors with topoisomerase 2 inhibitors, but not with cytarabine, to improve treatment outcomes in AML with FLT3-ITD.

Apoptosis in human liver carcinoma caused by gold nanoparticles in combination with carvedilol is mediated via modulation of MAPK/Akt/mTOR pathway and EGFR/FAAD proteins

In cancers, apoptosis signaling pathways and cell survival and growth pathways responsible for resistance to conventional treatments, such as Pi3K/Akt/mTOR and mitogen-activated protein kinase (MAPK) become dysregulated. Recently, alternative treatments to promote tumor cell death have become important. The present study reports on the antitumor and cytoprotective action of gold nanoparticles (GNPs) and carvedilol in combination and in isolated application. Apoptosis was analyzed by FITC/propidium iodide staining flow cytometry; caspase-3, caspase-8, Bcl-2 and MAPK/ERK activity by immunofluorescence microscopy; gene expression of proteins related to cell death as Akt, mTOR, EGFR, MDR1, survivin, FADD and Apaf, by the real-time PCR; and western blot analysis for MAPK/ERK, Akt and mTOR. Oxidative stress evaluation was performed by reduced glutathione (GSH) and malondialdehyde (MDA) levels. Intracellular GNPs targets were identified by transmission electron microscopy. After exposure to a combination of GNPs (6.25 µg/ml) and carvedilol (3 µM), death as promoted by apoptosis was detected using flow cytometry, for expression of pro-apoptotic proteins FADD, caspase-3, caspase-8 and sub-regulation of anti-apoptotic MAPK/ERK, Akt, mTOR, EGFR and MDR1 resistance. Non-tumor cell cytoprotection with GSH elevation and MDA reduction levels was detected. GNPs were identified within the cell near to the nucleus when combined with carvedilol. The combination of GNP and carvedilol promoted downregulation of anti-apoptotic and drug resistance genes, over-regulation of pro-apoptotic proteins in tumor cells, as well as cytoprotection of non-tumor cells with reduction of apoptosis and oxidative stress.

CoQ0-induced mitochondrial PTP opening triggers apoptosis via ROS-mediated VDAC1 upregulation in HL-60 leukemia cells and suppresses tumor growth in athymic nude mice/xenografted nude mice

Coenzyme Q (CoQ) analogs with variable numbers of isoprenoid units have been demonstrated as anticancer and antioxidant/pro-oxidant molecules. This study examined the in vitro and in vivo antitumor and apoptosis activities of CoQ₀ (2,3-dimethoxy-5-methyl-1,4-benzoquinone, zero isoprenoid side-chains) through upregulation of the Voltage-dependent anion channel 1 (VDAC1) signaling pathway on human promyelocytic leukemia. CoQ₀ (0-40 μg/mL) treatment significantly reduced HL-60 cell viability, and up-regulated mitochondrial VDAC1 expression. CoQ₀ treatment triggers intracellular ROS generation, calcium release, ΔΨm collapse and PTP opening in HL-60 cells. CoQ₀ treatment induced apoptosis, which was associated with DNA fragmentation, cytochrome c release, caspase-3 and PARP activation, and Bax/Bcl-2 dysregulation. Annexin V-PI staining indicated that CoQ₀ promotes late apoptosis. Furthermore, the blockade of CoQ₀-induced ROS production by antioxidant NAC pretreatment substantially attenuated CoQ₀-induced apoptosis. The activation of p-GSK3β expression, cyclophilin D inhibition, and p53 activation through ROS are involved in CoQ₀-induced HL-60 apoptotic cell death. Notably, ROS-independent p38 activation is involved in CoQ₀-mediated apoptosis in HL-60 cells. In addition, the silencing of VDAC1 also prevented CoQ₀-induced mitochondrial translocation of Bax, activation of caspase-3, and reduction in Bcl-2. Intriguingly, VDAC1 silencing did not prevent ROS production induced by CoQ₀, which in turn indicates that CoQ₀ induced ROS-mediated VDAC1 and then mitochondrial apoptosis in HL-60 cells. In vivo results revealed that CoQ₀ is effective in delaying tumor incidence and reducing the tumor burden in HL-60-xenografted nude mice. Taken together, CoQ₀ could be a promising anticancer agent for the treatment of human promyelocytic leukemia through upregulation of VDAC1 signaling pathways.

The role of hypernitrosylation in the pathogenesis and pathophysiology of neuroprogressive diseases

There is a wealth of data indicating that de novo protein S-nitrosylation in general and protein transnitrosylation in particular mediates the bulk of nitric oxide signalling. These processes enable redox sensing and facilitate homeostatic regulation of redox dependent protein signalling, function, stability and trafficking. Increased S-nitrosylation in an environment of increasing oxidative and nitrosative stress (O&NS) is initially a protective mechanism aimed at maintaining protein structure and function. When O&NS becomes severe, mechanisms governing denitrosylation and transnitrosylation break down leading to the pathological state referred to as hypernitrosylation (HN). Such a state has been implicated in the pathogenesis and pathophysiology of several neuropsychiatric and neurodegenerative diseases and we investigate its potential role in the development and maintenance of neuroprogressive disorders. In this paper, we propose a model whereby the hypernitrosylation of a range of functional proteins and enzymes lead to changes in activity which conspire to produce at least some of the core abnormalities contributing to the development and maintenance of pathology in these illnesses.

P7C3 inhibits GSK3β activation to protect dopaminergic neurons against neurotoxin-induced cell death in vitro and in vivo

Parkinson’s disease (PD) is the second most prevalent neurodegenerative disease. Although its pathogenesis remains unclear, mitochondrial dysfunction plays a vital role in the pathology of PD. P7C3, an aminopropyl carbazole, possesses a significant neuroprotective ability in several neurodegenerative disorders, including PD. Here, we showed that P7C3 stabilized mitochondrial membrane potential, reduced reactive oxygen species production, and inhibited cytochrome c release in MES23.5 cells (a dopaminergic (DA) cell line) exposed to 1-methyl-4-phenylpyridinium (MPP⁺). In MES23.5 cells, P7C3 inhibited glycogen synthase kinase-3 beta (GSK3β) activation induced by MPP⁺. P7C3 also inhibited p53 activity and repressed Bax upregulation to protect cells from MPP⁺ toxicity. In addition, the activation of p53 was significantly attenuated with the inhibition of GSK3β activity by P7C3. Furthermore, P7C3 blocked GSK3β and p53 activation in the midbrain, and prevented DA neuronal loss in the substantia nigra in 1-methyl-4-phenyl-1,2,3,4-tetrahydropyridine mice. Thus, our study demonstrates that P7C3 protects DA neurons from neurotoxin-induced cell death by repressing the GSK3β-p53-Bax pathway both in vitro and in vivo, thus providing a theoretical basis for P7C3 in the potential clinical treatment of PD.

Novel p53-dependent anticancer strategy by targeting iron signaling and BNIP3L-induced mitophagy

This study identifies BNIP3L as the key regulator of p53-dependent cell death mechanism in colon cancer cells targeted by the novel gallium based anticancer drug, KP46. KP46 specifically accumulated into mitochondria where it caused p53-dependent morphological and functional damage impairing mitochondrial dynamics and bioenergetics. Furthermore, competing with iron for cellular uptake, KP46 lowered the intracellular labile iron pools and intracellular heme. Accordingly, p53 accumulated in the nucleus where it activated its transcriptional target BNIP3L, a BH3 only domain protein with functions in apoptosis and mitophagy. Upregulated BNIP3L sensitized the mitochondrial permeability transition and strongly induced PARKIN-mediated mitochondrial clearance and cellular vacuolization. Downregulation of BNIP3L entirely rescued cell viability caused by exposure of KP46 for 24 hours, confirming that early induced cell death was regulated by BNIP3L. Altogether, targeting BNIP3L in wild-type p53 colon cancer cells is a novel anticancer strategy activating iron depletion signaling and the mitophagy-related cell death pathway.

Inhibiting mitochondrial respiration prevents cancer in a mouse model of Li-Fraumeni syndrome

Li-Fraumeni syndrome (LFS) is a cancer predisposition disorder caused by germline mutations in TP53 that can lead to increased mitochondrial metabolism in patients. However, the implications of altered mitochondrial function for tumorigenesis in LFS are unclear. Here, we have reported that genetic or pharmacologic disruption of mitochondrial respiration improves cancer-free survival in a mouse model of LFS that expresses mutant p53. Mechanistically, inhibition of mitochondrial function increased autophagy and decreased the aberrant proliferation signaling caused by mutant p53. In a pilot study, LFS patients treated with metformin exhibited decreases in mitochondrial activity concomitant with activation of antiproliferation signaling, thus reproducing the effects of disrupting mitochondrial function observed in LFS mice. These observations indicate that a commonly prescribed diabetic medicine can restrain mitochondrial metabolism and tumorigenesis in an LFS model, supporting its further consideration for cancer prevention in LFS patients.

The mitochondrial permeability transition pore in AD 2016: An update

Over the past 30years the mitochondrial permeability transition - the permeabilization of the inner mitochondrial membrane due to the opening of a wide pore - has progressed from being considered a curious artifact induced in isolated mitochondria by Ca(2+) and phosphate to a key cell-death-inducing process in several major pathologies. Its relevance is by now universally acknowledged and a pharmacology targeting the phenomenon is being developed. The molecular nature of the pore remains to this day uncertain, but progress has recently been made with the identification of the FOF1 ATP synthase as the probable proteic substrate. Researchers sharing this conviction are however divided into two camps: these believing that only the ATP synthase dimers or oligomers can form the pore, presumably in the contact region between monomers, and those who consider that the ring-forming c subunits in the FO sector actually constitute the walls of the pore. The latest development is the emergence of a new candidate: Spastic Paraplegia 7 (SPG7), a mitochondrial AAA-type membrane protease which forms a 6-stave barrel. This review summarizes recent developments of research on the pathophysiological relevance and on the molecular nature of the mitochondrial permeability transition pore. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

Breast Cancer: A Molecular and Redox Snapshot

SIGNIFICANCE

Breast cancer is a unique disease characterized by heterogeneous cell populations causing roadblocks in therapeutic medicine, owing to its complex etiology and primeval understanding of the biology behind its genesis, progression, and sustenance. Globocan statistics indicate over 1.7 million new breast cancer diagnoses in 2012, accounting for 25% of all cancer morbidities.

RECENT ADVANCES

Despite these dismal statistics, the introduction of molecular gene signature platforms, progressive therapeutic approaches in diagnosis, and management of breast cancer has led to more effective treatment strategies and control measures concurrent with an equally reassuring decline in the mortality rate.

CRITICAL ISSUES

However, an enormous body of research in this area is requisite as high mortality associated with metastatic and/or drug refractory tumors continues to present a therapeutic challenge. Despite advances in systemic chemotherapy, the median survival of patients harboring metastatic breast cancers continues to be below 2 years.

FUTURE DIRECTIONS

Hence, a massive effort to scrutinize and evaluate chemotherapeutics on the basis of the molecular classification of these cancers is undertaken with the objective to devise more attractive and feasible approaches to treat breast cancers and improve patients' quality of life. This review aims to summarize the current understanding of the biology of breast cancer as well as challenges faced in combating breast cancer, with special emphasis on the current battery of treatment strategies. We will also try and gain perspective from recent encounters on novel findings responsible for the progression and metastatic transformation of breast cancer cells in an endeavor to develop more targeted treatment options. Antioxid. Redox Signal. 25, 337-370.

Gsk3 Signalling and Redox Status in Bipolar Disorder: Evidence from Lithium Efficacy

Objective. To discuss the link between glycogen synthase kinase-3 (GSK3) and the main biological alterations demonstrated in bipolar disorder (BD), with special attention to the redox status and the evidence supporting the efficacy of lithium (a GSK3 inhibitor) in the treatment of BD. Methods. A literature research on the discussed topics, using Pubmed and Google Scholar, has been conducted. Moreover, a manual selection of interesting references from the identified articles has been performed. Results. The main biological alterations of BD, pertaining to inflammation, oxidative stress, membrane ion channels, and circadian system, seem to be intertwined. The dysfunction of the GSK3 signalling pathway is involved in all the aforementioned "biological causes" of BD. In a complex scenario, it can be seen as the common denominator linking them all. Lithium inhibition of GSK3 could, at least in part, explain its positive effect on these biological dysfunctions and its superiority in terms of clinical efficacy. Conclusions. Deepening the knowledge on the molecular bases of BD is fundamental to identifying the biochemical pathways that must be targeted in order to provide patients with increasingly effective therapeutic tools against an invalidating disorder such as BD.

Nitrosative Stress, Hypernitrosylation, and Autoimmune Responses to Nitrosylated Proteins: New Pathways in Neuroprogressive Disorders Including Depression and Chronic Fatigue Syndrome

Nitric oxide plays an indispensable role in modulating cellular signaling and redox pathways. This role is mainly effected by the readily reversible nitrosylation of selective protein cysteine thiols. The reversibility and sophistication of this signaling system is enabled and regulated by a number of enzymes which form part of the thioredoxin, glutathione, and pyridoxine antioxidant systems. Increases in nitric oxide levels initially lead to a defensive increase in the number of nitrosylated proteins in an effort to preserve their function. However, in an environment of chronic oxidative and nitrosative stress (O&NS), nitrosylation of crucial cysteine groups within key enzymes of the thioredoxin, glutathione, and pyridoxine systems leads to their inactivation thereby disabling denitrosylation and transnitrosylation and subsequently a state described as "hypernitrosylation." This state leads to the development of pathology in multiple domains such as the inhibition of enzymes of the electron transport chain, decreased mitochondrial function, and altered conformation of proteins and amino acids leading to loss of immune tolerance and development of autoimmunity. Hypernitrosylation also leads to altered function or inactivation of proteins involved in the regulation of apoptosis, autophagy, proteomic degradation, transcription factor activity, immune-inflammatory pathways, energy production, and neural function and survival. Hypernitrosylation, as a consequence of chronically elevated O&NS and activated immune-inflammatory pathways, can explain many characteristic abnormalities observed in neuroprogressive disease including major depression and chronic fatigue syndrome/myalgic encephalomyelitis. In those disorders, increased bacterial translocation may drive hypernitrosylation and autoimmune responses against nitrosylated proteins.

Soluble guanylate cyclase activation during ischemic injury in mice protects against postischemic inflammation at the mitochondrial level

The aim was to determine whether treatment with BAY 60-2770, a selective activator of oxidized soluble guanylate cyclase (sGC), near the end of an ischemic event would prevent postischemic inflammation and mitochondrial dysfunction in wild-type (WT) and heme oxygenase-1 KO (HO-1(-/-)) mice. This protocol prevented increases in leukocyte rolling (LR) and adhesion (LA) to intestinal venules along with elevated TNFα and circulating neutrophil levels that accompany ischemia-reperfusion (I/R) in both animal models. We further hypothesized that a component of BAY 60-2770 treatment involves maintenance of mitochondrial membrane integrity during I/R. Measurements on isolated enterocytes of calcein fluorescence (mitochondrial permeability) and JC-1 fluorescence ratio (mitochondrial membrane potential) were reduced by I/R, indicating formation of mitochondrial permeability transition pores (mPTP). These effects were abrogated by BAY 60-2770 as well as cyclosporin A and SB-216763, which prevented mPTP opening and inhibited glycogen synthase kinase-3β (GSK-3β), respectively. Western blots of WT and HO-1(-/-) enterocytes indicated that GSK-3β phosphorylation on Ser(9) (inhibitory site) was reduced by half following I/R alone (increased GSK-3β activity) and increased by one-third (reduced GSK-3β activity) following BAY 60-2770. Other investigators have associated phosphorylation of the GSK-3β substrate cyclophilin D (pCyPD) with mPTP formation. We observed a 60% increase in pCyPD after I/R, whereas BAY 60-2770 treatment of sham and I/R groups reduced pCyPD by about 20%. In conclusion, selective activation of oxidized sGC of WT and HO-1(-/-) during ischemia protects against I/R-induced inflammation and preserves mucosal integrity in part by reducing pCyPD production and mPTP formation.

Exposure to a 50-Hz magnetic field induced mitochondrial permeability transition through the ROS/GSK-3β signaling pathway

PURPOSE

To investigate the biological effects of a 50-Hz magnetic field (MF) on mitochondrial permeability.

MATERIALS AND METHODS

Human amniotic epithelial cells were exposed to MF (50 Hz, 0.4 mT) for different durations. Mitochondrial permeability, mitochondrial membrane potential (ΔΨm), cytochrome c (Cyt-c) release and the related mechanisms were explored.

RESULTS

Exposure to the MF at 0.4 mT for 60 min transiently induced mitochondrial permeability transition (MPT) and Cyt-c release, although there was no significant effect on mitochondrial membrane potential (ΔΨm). Other than decreasing the total Bcl-2 associated X protein (Bax) level, MF exposure did not significantly affect the levels of Bax and B-cell lymphoma-2 (Bcl-2) in mitochondria. In addition, cells exposed to the MF showed increased intracellular reactive oxidative species (ROS) levels and glycogen synthase kinase-3β (GSK-3β) dephosphorylation at 9 serine residue (Ser(9)). Moreover, the MF-induced MPT was attenuated by ROS scavenger (N-acetyl-L-cysteine, NAC) or GSK-3β inhibitor, and NAC pretreatment prevented GSK-3β dephosphorylation (Ser(9)) caused by MF exposure.

CONCLUSION

MPT induced by MF exposure was mediated through the ROS/GSK-3β signaling pathway.

Lithium in the Kidney: Friend and Foe?

Trace amounts of lithium are essential for our physical and mental health, and administration of lithium has improved the quality of life of millions of patients with bipolar disorder for >60 years. However, in a substantial number of patients with bipolar disorder, long-term lithium therapy comes at the cost of severe renal side effects, including nephrogenic diabetes insipidus and rarely, ESRD. Although the mechanisms underlying the lithium-induced renal pathologies are becoming clearer, several recent animal studies revealed that short-term administration of lower amounts of lithium prevents different forms of experimental AKI. In this review, we discuss the knowledge of the pathologic and therapeutic effects of lithium in the kidney. Furthermore, we discuss the underlying mechanisms of these seemingly paradoxical effects of lithium, in which fine-tuned regulation of glycogen synthase kinase type 3, a prime target for lithium, seems to be key. The new discoveries regarding the protective effect of lithium against AKI in rodents call for follow-up studies in humans and suggest that long-term therapy with low lithium concentrations could be beneficial in CKD.

The Mitochondrial Permeability Transition Pore: Channel Formation by F-ATP Synthase, Integration in Signal Transduction, and Role in Pathophysiology

The mitochondrial permeability transition (PT) is a permeability increase of the inner mitochondrial membrane mediated by a channel, the permeability transition pore (PTP). After a brief historical introduction, we cover the key regulatory features of the PTP and provide a critical assessment of putative protein components that have been tested by genetic analysis. The discovery that under conditions of oxidative stress the F-ATP synthases of mammals, yeast, and Drosophila can be turned into Ca(2+)-dependent channels, whose electrophysiological properties match those of the corresponding PTPs, opens new perspectives to the field. We discuss structural and functional features of F-ATP synthases that may provide clues to its transition from an energy-conserving into an energy-dissipating device as well as recent advances on signal transduction to the PTP and on its role in cellular pathophysiology.

Remote ischemic preconditioning for kidney protection: GSK3β-centric insights into the mechanism of action

Preventing acute kidney injury (AKI) in high-risk patients following medical interventions is a paramount challenge for clinical practice. Recent data from animal experiments and clinical trials indicate that remote ischemic preconditioning, represented by limb ischemic preconditioning, confers a protective action on the kidney. Ischemic preconditioning is effective in reducing the risk for AKI following cardiovascular interventions and the use of iodinated radiocontrast media. Nevertheless, the underlying mechanisms for this protective effect are elusive. A protective signal is conveyed from the remote site undergoing ischemic preconditioning, such as the limb, to target organs, such as the kidney, by multiple potential communication pathways, which may involve humoral, neuronal, and systemic mechanisms. Diverse transmitting pathways trigger a variety of signaling cascades, including the reperfusion injury salvage kinase and survivor activating factor enhancement pathways, all of which converge on glycogen synthase kinase 3β (GSK3β). Inhibition of GSK3β subsequent to ischemic preconditioning reinforces the Nrf2-mediated antioxidant defense, diminishes the nuclear factor-κB-dependent proinflammatory response, and exerts prosurvival effects ensuing from the desensitized mitochondria permeability transition. Thus, therapeutic targeting of GSK3β by ischemic preconditioning or by pharmacologic preconditioning with existing US Food and Drug Administration-approved drugs having GSK3β-inhibitory activities might represent a pragmatic and cost-effective adjuvant strategy for kidney protection and prophylaxis against AKI.

The Ambiguous Relationship of Oxidative Stress, Tau Hyperphosphorylation, and Autophagy Dysfunction in Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia. The pathological hallmarks of AD are amyloid plaques [aggregates of amyloid-beta (Aβ)] and neurofibrillary tangles (aggregates of tau). Growing evidence suggests that tau accumulation is pathologically more relevant to the development of neurodegeneration and cognitive decline in AD patients than Aβ plaques. Oxidative stress is a prominent early event in the pathogenesis of AD and is therefore believed to contribute to tau hyperphosphorylation. Several studies have shown that the autophagic pathway in neurons is important under physiological and pathological conditions. Therefore, this pathway plays a crucial role for the degradation of endogenous soluble tau. However, the relationship between oxidative stress, tau protein hyperphosphorylation, autophagy dysregulation, and neuronal cell death in AD remains unclear. Here, we review the latest progress in AD, with a special emphasis on oxidative stress, tau hyperphosphorylation, and autophagy. We also discuss the relationship of these three factors in AD.

Molecular mechanisms of mTOR regulation by stress

Tumors are prime examples of cell growth in unfavorable environments that elicit cellular stress. The high metabolic demand and insufficient vascularization of tumors cause a deficiency of oxygen and nutrients. Oncogenic mutations map to signaling events via mammalian target of rapamycin (mTOR), metabolic pathways, and mitochondrial function. These alterations have been linked with cellular stresses, in particular endoplasmic reticulum (ER) stress, hypoxia, and oxidative stress. Yet tumors survive these challenges and acquire highly energy-demanding traits, such as overgrowth and invasiveness. In this review we focus on stresses that occur in cancer cells and discuss them in the context of mTOR signaling. Of note, many tumor traits require mTOR complex 1 (mTORC1) activity, but mTORC1 hyperactivation eventually sensitizes cells to apoptosis. Thus, mTORC1 activity needs to be balanced in cancer cells. We provide an overview of the mechanisms contributing to mTOR regulation by stress and suggest a model wherein stress granules function as guardians of mTORC1 signaling, allowing cancer cells to escape stress-induced cell death.

Reprint of "The mitochondrial permeability transition pore and its adaptive responses in tumor cells"

This review covers recent progress on the nature of the mitochondrial permeability transition pore (PTP) – a key effector in the mitochondrial pathways to cell death – and on the adaptive responses of tumor cells that desensitize the PTP to Ca(2+) and reactive oxygen species (ROS), thereby playing an important role in the resistance of tumors to cell death. The discovery that the PTP forms from dimers of F-ATP synthase; and the definition of the Ca(2+)- and ROS-dependent signaling pathways affecting the transition of the F-ATP synthase from an energy-conserving to an energy-dissipating device open new perspectives for therapeutic intervention in cancer cells.

Molecular mechanisms of cell death: central implication of ATP synthase in mitochondrial permeability transition

The term mitochondrial permeability transition (MPT) is commonly used to indicate an abrupt increase in the permeability of the inner mitochondrial membrane to low molecular weight solutes. Widespread MPT has catastrophic consequences for the cell, de facto marking the boundary between cellular life and death. MPT results indeed in the structural and functional collapse of mitochondria, an event that commits cells to suicide via regulated necrosis or apoptosis. MPT has a central role in the etiology of both acute and chronic diseases characterized by the loss of post-mitotic cells. Moreover, cancer cells are often relatively insensitive to the induction of MPT, underlying their increased resistance to potentially lethal cues. Thus, intense efforts have been dedicated not only at the understanding of MPT in mechanistic terms, but also at the development of pharmacological MPT modulators. In this setting, multiple mitochondrial and extramitochondrial proteins have been suspected to critically regulate the MPT. So far, however, only peptidylprolyl isomerase F (best known as cyclophilin D) appears to constitute a key component of the so-called permeability transition pore complex (PTPC), the supramolecular entity that is believed to mediate MPT. Here, after reviewing the structural and functional features of the PTPC, we summarize recent findings suggesting that another of its core components is represented by the c subunit of mitochondrial ATP synthase.

Gold(III)-pyrrolidinedithiocarbamato Derivatives as Antineoplastic Agents

Transition metals offer many possibilities in developing potent chemotherapeutic agents. They are endowed with a variety of oxidation states, allowing for the selection of their coordination numbers and geometries via the choice of proper ligands, leading to the tuning of their final biological properties. We report here on the synthesis, physico-chemical characterization, and solution behavior of two gold(III) pyrrolidinedithiocarbamates (PDT), namely [Au^IIIBr₂(PDT)] and [Au^IIICl₂(PDT)]. We found that the bromide derivative was more effective than the chloride one in inducing cell death for several cancer cell lines. [Au^IIIBr₂(PDT)] elicited oxidative stress with effects on the permeability transition pore, a mitochondrial channel whose opening leads to cell death. More efficient antineoplastic strategies are required for the widespread burden that is cancer. In line with this, our results indicate that [Au^IIIBr₂(PDT)] is a promising antineoplastic agent that targets cellular components with crucial functions for the survival of tumor cells.

SERPINB3 protects from oxidative damage by chemotherapeutics through inhibition of mitochondrial respiratory complex I

SERPINB3 (SB3) is a serine protease inhibitor overexpressed in several malignancies of epithelial origin, including primary liver cancer, where it inhibits apoptosis through poorly defined mechanisms. In the present study we analyze the effect of SB3 on hepatoma cell death elicited by a panel of chemotherapeutic agents. We report that SB3 shields cells from the toxicity of drugs with a pro-oxidant action such as doxorubicin, cisplatin and EM20-25. The rapid rise in ROS levels prompted by these compounds causes opening of the mitochondrial permeability transition pore (PTP), irreversibly committing cells to death. We find that a fraction of SB3 locates in mitochondrial inner compartments, and that this mitochondrial fraction increases under conditions of oxidative stress. Mitochondrial SB3 inhibits ROS generation and the ensuing PTP induction and cell death through an inhibitory interaction with respiratory Complex I. These findings identify a novel mechanism of action of SB3 that contributes to tumor cell resistance to anti-neoplastic drugs

How the location of superoxide generation influences the β-cell response to nitric oxide

Cytokines impair the function and decrease the viability of insulin-producing β-cells by a pathway that requires the expression of inducible nitric oxide synthase (iNOS) and generation of high levels of nitric oxide. In addition to nitric oxide, excessive formation of reactive oxygen species, such as superoxide and hydrogen peroxide, has been shown to cause β-cell damage. Although the reaction of nitric oxide with superoxide results in the formation of peroxynitrite, we have shown that β-cells do not have the capacity to produce this powerful oxidant in response to cytokines. When β-cells are forced to generate peroxynitrite using nitric oxide donors and superoxide-generating redox cycling agents, superoxide scavenges nitric oxide and prevents the inhibitory and destructive actions of nitric oxide on mitochondrial oxidative metabolism and β-cell viability. In this study, we show that the β-cell response to nitric oxide is regulated by the location of superoxide generation. Nitric oxide freely diffuses through cell membranes, and it reacts with superoxide produced within cells and in the extracellular space, generating peroxynitrite. However, only when it is produced within cells does superoxide attenuate nitric oxide-induced mitochondrial dysfunction, gene expression, and toxicity. These findings suggest that the location of radical generation and the site of radical reactions are key determinants in the functional response of β-cells to reactive oxygen species and reactive nitrogen species. Although nitric oxide is freely diffusible, its biological function can be controlled by the local generation of superoxide, such that when this reaction occurs within β-cells, superoxide protects β-cells by scavenging nitric oxide.

[Application of the Ca2+ indicator fluo-3 and fluo-4 in the process of H2O2 induced apoptosis of A549 cell]

BACKGROUND AND OBJECTIVE

Lung cancer is a common malignant tumor all over the world, and Ca(2+) is a critical regulator for apoptosis of cancer cells. The monitoring of cytoplastic Ca(2+) level in real-time will contribute to further investigate the molecular mechanisms of apoptosis mediated by Ca2+ in lung cancer cells. To evaluate the Ca(2+) indicator fluo-3 and fluo-4 in the process of H2O2 induced the apoptosis of lung adenocarcinoma A549 cells. The cytoplastic Ca(2+) concentration ([Ca(2+)]i) was determined in real-time, and the correlations between [Ca(2+)]i and cell apoptosis were investigated. The differences in fluorescence intensity and measured value were compared between the two Ca(2+) indicators.

METHODS

Cells were loaded with the Ca(2+) indicator fluo-3 or fluo-4 for 1 h, and then stimulated with 50 mM H2O2. Laser scanning confocal microscope was applied to perform real-time monitoring on the variation of [Ca(2+)]i in selected cells. DAPI staining was used to observe apoptosis in H2O2 treated cells.

RESULTS

Our results showed that the fluorescence intensity of fluo-4 was stronger than that of fluo-3 in the same condition of dye concentration, loading time and image acquisition parameters before or after H2O2 stimulation. The cytoplastic [Ca(2+)]i was rapidly elevated in H2O2 stimulated A549 cells. The range of [Ca(2+)]i in selected cells loaded with fluo-3 was 112.2 nM-1,069.6 nM, and that in selected cells loaded with fluo-4 was 7.6 nM-505.4 nM. Moreover, the apoptotic rate was significantly increased in H2O2 treated cells, compared with untreated ones (P<0.01).

CONCLUSION

In summary, H2O2 promoted Ca(2+) release in A549 cells, and induced cell apoptosis. Ca(2+) indicator fluo-4 was probably more applicable to measure [Ca(2+)]i in cells with less content of Ca(2+).

The mitochondrial permeability transition pore and its adaptive responses in tumor cells

This review covers recent progress on the nature of the mitochondrial permeability transition pore (PTP) - a key effector in the mitochondrial pathways to cell death - and on the adaptive responses of tumor cells that desensitize the PTP to Ca(2+) and reactive oxygen species (ROS), thereby playing an important role in the resistance of tumors to cell death. The discovery that the PTP forms from dimers of F-ATP synthase; and the definition of the Ca(2+)- and ROS-dependent signaling pathways affecting the transition of the F-ATP synthase from an energy-conserving to an energy-dissipating device open new perspectives for therapeutic intervention in cancer cells.

Translocation of glycogen synthase kinase-3β (GSK-3β), a trigger of permeability transition, is kinase activity-dependent and mediated by interaction with voltage-dependent anion channel 2 (VDAC2)

Glycogen synthase kinase-3β (GSK-3β) is a major positive regulator of the mitochondrial permeability transition pore (mPTP), a principle trigger of cell death, under the condition of oxidative stress. However, the mechanism by which cytosolic GSK-3β translocates to mitochondria, promoting mPTP opening, remains unclear. Here we addressed this issue by analyses of the effect of site-directed mutations in GSK-3β on mitochondrial translocation and protein/protein interactions upon oxidative stress. H9c2 cardiomyoblasts were transfected with GFP-tagged GSK-3β (WT), a mutant GSK-3β insensitive to inhibitory phosphorylation (S9A), or kinase-deficient GSK-3β (K85R). Time lapse observation revealed that WT and S9A translocated from the cytosol to the mitochondria more promptly than did K85R after exposure to oxidative stress. H2O2 increased the density of nine spots on two-dimensional gel electrophoresis of anti-GSK-3β-immunoprecipitates by more than 3-fold. MALDI-TOF/MS analysis revealed that one of the spots contained voltage-dependent anion channel 2 (VDAC2). Knockdown of VDAC2, but not VDAC1 or VDAC3, by siRNA attenuated both the mitochondrial translocation of GSK-3β and mPTP opening under stress conditions. The mitochondrial translocation of GSK-3β was attenuated also when Lys-15, but not Arg-4 or Arg-6, in the N-terminal domain of GSK-3β was replaced with alanine. The oxidative stress-induced mitochondrial translocation of GSK-3β was associated with an increase in cell death, which was suppressed by lithium chloride (LiCl), a GSK-3β inhibitor. These results demonstrate that GSK-3β translocates from the cytosol to mitochondria in a kinase activity- and VDAC2-dependent manner in which an N-terminal domain of GSK-3β may function as a mitochondrial targeting sequence.

Preclinical activity of multiple-target gold(III)-dithiocarbamato peptidomimetics in prostate cancer cells and xenografts

Background: Recently, novel gold(III)-dithiocarbamato peptidomimetics, designed to target peptide transporters upregulated in several tumor cells have shown promise as anticancer agents. Results: The biological behavior of the most promising derivatives AuD8 and AuD9 was studied in PC3 and DU145 prostate cancer cells. They exert higher cytotoxicity in vitro than the reference drug cisplatin and induce apoptosis, promoting mitochondrial membrane permeabilization and stimulating reactive oxygen species generation. Moreover, they inhibit both selenoenzyme thioredoxin reductase and proteasome activity. Additionally, AuD8 effectively reduces tumor growth in prostate tumor-bearing nude mice with minimal systemic toxicity. Conclusion: Altogether, our results provide insights into the anticancer activity of these gold(III)-dithiocarbamato peptidomimetics and support their potential as new agents for prostate cancer treatment.

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.

Cracking the cytotoxicity code: apoptotic induction of 10-acetylirciformonin B is mediated through ROS generation and mitochondrial dysfunction

A marine furanoterpenoid derivative, 10-acetylirciformonin B (10AB), was found to inhibit the proliferation of leukemia, hepatoma, and colon cancer cell lines, with selective and significant potency against leukemia cells. It induced DNA damage and apoptosis in leukemia HL 60 cells. To fully understand the mechanism behind the 10AB apoptotic induction against HL 60 cells, we extended our previous findings and further explored the precise molecular targets of 10AB. We found that the use of 10AB increased apoptosis by 8.9%-87.6% and caused disruption of mitochondrial membrane potential (MMP) by 15.2%-95.2% in a dose-dependent manner, as demonstrated by annexin-V/PI and JC-1 staining assays, respectively. Moreover, our findings indicated that the pretreatment of HL 60 cells with N-acetyl-l-cysteine (NAC), a reactive oxygen species (ROS) scavenger, diminished MMP disruption and apoptosis induced by 10AB, suggesting that ROS overproduction plays a crucial rule in the cytotoxic activity of 10AB. The results of a cell-free system assay indicated that 10AB could act as a topoisomerase catalytic inhibitor through the inhibition of topoisomerase IIα. On the protein level, the expression of the anti-apoptotic proteins Bcl-xL and Bcl-2, caspase inhibitors XIAP and survivin, as well as hexokinase II were inhibited by the use of 10AB. On the other hand, the expression of the pro-apoptotic protein Bax was increased after 10AB treatment. Taken together, our results suggest that 10AB-induced apoptosis is mediated through the overproduction of ROS and the disruption of mitochondrial metabolism.

Indirubin-3'-oxime reverses bone loss in ovariectomized and hindlimb-unloaded mice via activation of the Wnt/β-catenin signaling

Osteoporosis is a major global health issue in elderly people. Because Wnt/β-catenin signaling plays a key role in bone homeostasis, we screened activators of this pathway through cell-based screening, and investigated indirubin-3'-oxime (I3O), one of the positive compounds known to inhibit GSK3β, as a potential anti-osteoporotic agent. Here, we show that I3O activated Wnt/β-catenin signaling via inhibition of the interaction of GSK3β with β-catenin, and induced osteoblast differentiation in vitro and increased calvarial bone thickness ex vivo. Intraperitoneal injection of I3O increased bone mass and improved microarchitecture in normal mice and reversed bone loss in an ovariectomized mouse model of age-related osteoporosis. I3O also increased thickness and area of cortical bone, indicating improved bone strength. Enhanced bone mass and strength correlated with activated Wnt/β-catenin signaling, as shown by histological analyses of both trabecular and cortical bones. I3O also restored mass and density of bone in hindlimb-unloaded mice compared with control, suspended mice, demonstrating bone-restoration effects of I3O in non-aged-related osteoporosis as well. Overall, I3O, a pharmacologically active small molecule, could be a potential therapeutic agent for the treatment and prevention of osteoporosis.

Redox-sensitive glycogen synthase kinase 3β-directed control of mitochondrial permeability transition: rheostatic regulation of acute kidney injury

Mitochondrial dysfunction plays a pivotal role in necroapoptotic cell death and in the development of acute kidney injury (AKI). Evidence suggests that glycogen synthase kinase (GSK) 3β resides at the nexus of multiple signaling pathways implicated in the regulation of mitochondrial permeability transition (MPT). In cultured renal tubular epithelial cells, a discrete pool of GSK3β was detected in mitochondria. Coimmunoprecipitation assay confirmed that GSK3β physically interacts with cyclophilin F and voltage-dependent anion channel (VDAC), key MPT regulators that possess multiple GSK3β phosphorylation consensus motifs, suggesting that GSK3β has a direct control of MPT. Upon a strong burst of reactive oxygen species elicited by the pro-oxidant herbicide paraquat, the activity of the redox-sensitive GSK3β was drastically enhanced. This was accompanied by augmented phosphorylation of cyclophilin F and VDAC, associated with MPT and cell death. Inhibition of GSK3β by either the selective inhibitor 4-Benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8) or forced expression of a kinase-dead mutant obliterated paraquat-induced phosphorylation of cyclophilin F and VDAC, prevented MPT, and improved cellular viability. Conversely, ectopic expression of a constitutively active GSK3β amplified the effect of paraquat on cyclophilin F and VDAC phosphorylation and sensitized cells to paraquat-induced MPT and death. In vivo, paraquat injection elicited marked oxidant stress in the kidney and resulted in acute kidney dysfunction and massive tubular apoptosis and necrosis. Consistent with in vitro findings, the activity of GSK3β was augmented in the kidney after paraquat injury, associated with increased phosphorylation of cyclophilin F and VDAC and sensitized MPT. TDZD-8 blocked GSK3β activity in the kidney, intercepted cyclophilin F and VDAC phosphorylation, prevented MPT, attenuated tubular cell death, and ameliorated paraquat-induced AKI. Our data suggest that the redox-sensitive GSK3β regulates renal tubular injury in AKI by controlling the activity of MPT regulators.

Dibenzofuran-induced mitochondrial dysfunction: Interaction with ANT carrier

Exposure to environmental pollutants such as dibenzofurans and furans is linked to the pathophysiology of several diseases. Dibenzofuran (DBF) is listed as a pollutant of concern due to its persistence in the environment, bioaccumulation and toxicity to humans, being associated with the development of lung diseases and cancers, due to its extremely toxic properties such as carcinogenic and teratogenic. Mitochondria play a key role in cellular homeostasis and keeping a proper energy supply for eukaryotic cells is essential in the fulfillment of the tissues energy-demand. Therefore, interference with mitochondrial function leads to cell death and organ failure. In this work, the effects of DBF on isolated rat liver mitochondria were analyzed. DBF exposure caused a markedly increase in the lag phase that follows depolarization induced by ADP, indicating an effect in the phosphorylative system. This was associated with a dose-dependent decrease in ATPase activity. Moreover, DBF also increased the threshold to the induction of the mitochondrial permeability transition (MPT) by calcium. Pretreatment of mitochondria with DBF also increased the concentration of carboxyatractyloside (CAT) necessary to abolish ADP phosphorylation and to induce the MPT, suggesting that DBF may interfere with mitochondria through an effect on the adenine nucleotide translocase (ANT). By co-immunoprecipitating ANT and Cyclophilin D (CypD) following MPT induction, we observed that in the presence of DBF, the ratio CypD/ANT was decreased. This demonstrates that DBF interferes with the ANT and so prevents CypD binding to the ANT, causing decreased phosphorylative capacity and inhibiting the MPT, which is also reflected by an increase in calcium retention capacity. Clarifying the role of pollutants in some mechanisms of toxicity, such as unbalance of bioenergetics status and mitochondrial function, may help to explain the progressive and chronic evolution of diseases derived from exposure to environmental pollutants.

Myotonic dystrophy protein kinase (DMPK) prevents ROS-induced cell death by assembling a hexokinase II-Src complex on the mitochondrial surface

The biological functions of myotonic dystrophy protein kinase (DMPK), a serine/threonine kinase whose gene mutations cause myotonic dystrophy type 1 (DM1), remain poorly understood. Several DMPK isoforms exist, and the long ones (DMPK-A/B/C/D) are associated with the mitochondria, where they exert unknown activities. We have studied the isoform A of DMPK, which we have found to be prevalently associated to the outer mitochondrial membrane. The kinase activity of mitochondrial DMPK protects cells from oxidative stress and from the ensuing opening of the mitochondrial permeability transition pore (PTP), which would otherwise irreversibly commit cells to death. We observe that DMPK (i) increases the mitochondrial localization of hexokinase II (HK II), (ii) forms a multimeric complex with HK II and with the active form of the tyrosine kinase Src, binding its SH3 domain and (iii) it is tyrosine-phosphorylated by Src. Both interaction among these proteins and tyrosine phosphorylation of DMPK are increased under oxidative stress, and Src inhibition selectively enhances death in DMPK-expressing cells after HK II detachment from the mitochondria. Down-modulation of DMPK abolishes the appearance of muscle markers in in vitro myogenesis, which is rescued by oxidant scavenging. Our data indicate that, together with HK II and Src, mitochondrial DMPK is part of a multimolecular complex endowed with antioxidant and pro-survival properties that could be relevant during the function and differentiation of muscle fibers.