Cardiolipin-Specific Peroxidase Reactions of Cytochrome c in Mitochondria During Irradiation-Induced Apoptosis

Permeabilization of the outer mitochondrial membrane: Mechanisms and consequences

Permeabilization of the outer mitochondrial membrane is а physiological process that can allow certain molecules to pass through it, such as low molecular weight solutes required for cellular respiration. This process is also important for the development of various modes of cell death. Depending on the severity of this process, cells can die by autophagy, apoptosis, or necrosis/necroptosis. Distinct types of pores can be opened at the outer mitochondrial membrane depending on physiological or pathological stimuli, and different mechanisms can be activated in order to open these pores. In this comprehensive review, all these types of permeabilization, the mechanisms of their activation, and their role in various diseases are discussed.

HILPDA-mediated lipidomic remodelling promotes radiotherapy resistance in nasopharyngeal carcinoma by accelerating mitophagy

Radiotherapy resistance is a major obstacle to nasopharyngeal carcinoma (NPC) therapy and contributes to tumour recurrence and metastasis. Lipid metabolism is a key regulatory mechanism in cancer biology; however, its role in NPC radiotherapy resistance remains unclear. In this study, we identified hypoxia-inducible lipid droplet-associated protein (HILPDA) as a newly discovered regulator of radioresistance that induces not only lipid droplet (LD) formation but also intracellular lipid remodelling, notably changing mitochondrial cardiolipin (CL) levels. Additionally, we found that the upregulation of CL promotes mitophagy in response to irradiation exposure. Mechanistically, HILPDA inhibits PINK1-mediated CLS1 ubiquitination and degradation. The combination of a mitophagy inhibitor and irradiation significantly increases the radiosensitivity of NPC cells. Human cancer-derived data confirmed that the HILPDA-CLS1 pathway promotes NPC radioresistance. Collectively, these findings suggest that HILPDA plays a critical role in promoting NPC radioresistance and might be targeted to overcome radiotherapeutic resistance in NPC patients in the clinic.

Integration of glucose and cardiolipin anabolism confers radiation resistance of HCC

BACKGROUND AND AIMS

Poor response to ionizing radiation (IR) due to resistance remains a clinical challenge. Altered metabolism represents a defining characteristic of nearly all types of cancers. However, how radioresistance is linked to metabolic reprogramming remains elusive in hepatocellular carcinoma (HCC).

APPROACH AND RESULTS

Baseline radiation responsiveness of different HCC cells were identified and cells with acquired radio-resistance were generated. By performing proteomics, metabolomics, metabolic flux, and other functional studies, we depicted a metabolic phenotype that mediates radiation resistance in HCC, whereby increased glucose flux leads to glucose addiction in radioresistant HCC cells and a corresponding increase in glycerophospholipids biosynthesis to enhance the levels of cardiolipin. Accumulation of cardiolipin dampens the effectiveness of IR by inhibiting cytochrome c release to initiate apoptosis. Mechanistically, mammalian target of rapamycin complex 1 (mTORC1) signaling-mediated translational control of hypoxia inducible factor-1α (HIF-1α) and sterol regulatory element-binding protein-1 (SREBP1) remodels such metabolic cascade. Targeting mTORC1 or glucose to cardiolipin synthesis, in combination with IR, strongly diminishes tumor burden. Finally, activation of glucose metabolism predicts poor response to radiotherapy in cancer patients.

CONCLUSIONS

We demonstrate a link between radiation resistance and metabolic integration and suggest that metabolically dismantling the radioresistant features of tumors may provide potential combination approaches for radiotherapy in HCC.

Activation of Cytochrome C Peroxidase Function Through Coordinated Foldon Loop Dynamics upon Interaction with Anionic Lipids

Cardiolipin (CL) is a mitochondrial anionic lipid that plays important roles in the regulation and signaling of mitochondrial apoptosis. CL peroxidation catalyzed by the assembly of CL-cytochrome c (cyt c) complexes at the inner mitochondrial membrane is a critical checkpoint. The structural changes in the protein, associated with peroxidase activation by CL and different anionic lipids, are not known at a molecular level. To better understand these peripheral protein-lipid interactions, we compare how phosphatidylglycerol (PG) and CL lipids trigger cyt c peroxidase activation, and correlate functional differences to structural and motional changes in membrane-associated cyt c. Structural and motional studies of the bound protein are enabled by magic angle spinning solid state NMR spectroscopy, while lipid peroxidase activity is assayed by mass spectrometry. PG binding results in a surface-bound state that preserves a nativelike fold, which nonetheless allows for significant peroxidase activity, though at a lower level than binding its native substrate CL. Lipid-specific differences in peroxidase activation are found to correlate to corresponding differences in lipid-induced protein mobility, affecting specific protein segments. The dynamics of omega loops C and D are upregulated by CL binding, in a way that is remarkably controlled by the protein:lipid stoichiometry. In contrast to complete chemical denaturation, membrane-induced protein destabilization reflects a destabilization of select cyt c foldons, while the energetically most stable helices are preserved. Our studies illuminate the interplay of protein and lipid dynamics in the creation of lipid peroxidase-active proteolipid complexes implicated in early stages of mitochondrial apoptosis.

Redox Epiphospholipidome in Programmed Cell Death Signaling: Catalytic Mechanisms and Regulation

A huge diversification of phospholipids, forming the aqueous interfaces of all biomembranes, cannot be accommodated within a simple concept of their role as membrane building blocks. Indeed, a number of signaling functions of (phospho)lipid molecules has been discovered. Among these signaling lipids, a particular group of oxygenated polyunsaturated fatty acids (PUFA), so called lipid mediators, has been thoroughly investigated over several decades. This group includes oxygenated octadecanoids, eicosanoids, and docosanoids and includes several hundreds of individual species. Oxygenation of PUFA can occur when they are esterified into major classes of phospholipids. Initially, these events have been associated with non-specific oxidative injury of biomembranes. An alternative concept is that these post-synthetically oxidatively modified phospholipids and their adducts with proteins are a part of a redox epiphospholipidome that represents a rich and versatile language for intra- and inter-cellular communications. The redox epiphospholipidome may include hundreds of thousands of individual molecular species acting as meaningful biological signals. This review describes the signaling role of oxygenated phospholipids in programs of regulated cell death. Although phospholipid peroxidation has been associated with almost all known cell death programs, we chose to discuss enzymatic pathways activated during apoptosis and ferroptosis and leading to peroxidation of two phospholipid classes, cardiolipins (CLs) and phosphatidylethanolamines (PEs). This is based on the available LC-MS identification and quantitative information on the respective peroxidation products of CLs and PEs. We focused on molecular mechanisms through which two proteins, a mitochondrial hemoprotein cytochrome c (cyt c), and non-heme Fe lipoxygenase (LOX), change their catalytic properties to fulfill new functions of generating oxygenated CL and PE species. Given the high selectivity and specificity of CL and PE peroxidation we argue that enzymatic reactions catalyzed by cyt c/CL complexes and 15-lipoxygenase/phosphatidylethanolamine binding protein 1 (15LOX/PEBP1) complexes dominate, at least during the initiation stage of peroxidation, in apoptosis and ferroptosis. We contrast cell-autonomous nature of CLox signaling in apoptosis correlating with its anti-inflammatory functions vs. non-cell-autonomous ferroptotic signaling facilitating pro-inflammatory (necro-inflammatory) responses. Finally, we propose that small molecule mechanism-based regulators of enzymatic phospholipid peroxidation may lead to highly specific anti-apoptotic and anti-ferroptotic therapeutic modalities.

Activated clotting factor X mediates mitochondrial alterations and inflammatory responses via protease-activated receptor signaling in alveolar epithelial cells

There is growing evidence for the contribution of the activated coagulation factor X (FXa) in the development of chronic inflammatory lung diseases. Therefore, we aimed to investigate effects of exogenous FXa on mitochondrial and metabolic function as well as the induction of inflammatory molecules in type II alveolar epithelial cells. Effects of FXa on epithelial cells were investigated in A549 cell line. Activation of extracellular signal-regulated kinase (ERK) and induction of inflammatory molecules were examined by immunoblot and gene expression analysis. Mitochondrial function was assessed by the measurement of oxygen consumption during maximal oxidative phosphorylation and quantitative determination of cardiolipin oxidation. Apoptosis was tested using a caspase 3 antibody. Metabolic activity and lactate dehydrogenase assay were applied for the detection of cellular viability. FXa activated ERK1/2 and induced an increase in the expression of pro-inflammatory cytokines, which was prevented by an inhibitor of FXa, edoxaban, or an inhibitor of protease-activated receptor 1, vorapaxar. Exposure to FXa caused mitochondrial alteration with restricted capacity for ATP generation, which was effectively prevented by edoxaban, vorapaxar and GB83 (inhibitor of protease-activated receptor 2). Of note, exposure to FXa did not initiate apoptosis in epithelial cells. FXa-dependent pro-inflammatory state and impairment of mitochondria did not reach the level of significance in lung epithelial cells. However, these effects might limit regenerative potency of lung epithelial cells, particular under clinical circumstances where lung injury causes exposure to clotting factors.

Microalgae in modern cancer therapy: Current knowledge

Cancer is an everyday medical concern which requires an appropriate treatment strategy. The malfunction of cell cycle is a well-established cause for cancer induction. Chemotherapy and radiation are the standard available therapeutic approach for cancer treatment; however severe side effects were reported in association to such treatments, for instance, the efficacy of patients' immune system is adversely affected in apart by radiation. These side effects may be minimized by providing novel remedial preparations. Complementary and alternative medicinal compounds, which were obtained from fresh or marine flora particularly micro and macro algae, were reported to its anti-cancerous activities. Several types of bioactive molecules are also present in microalgae, such as carotenoids, various forms of polysaccharides, vitamins, sterol, fibres, minerals…ect; the great unused biomass of microalgae and their excellent diversity of chemical constituents may introduce a major step in developing of anti-malignant drugs. Previously, such characteristic of microalgal bio-diversity was commercially exploited to make food supplements and gelling substances. However, recently, several investigations were designed to study the potential anti-carcinogenic effect of microalgal extracts, where they mostly concluded their ability to induce apoptotic cancer cell death via caspase dependent or independent pathways. In this review paper, we reported the various species of microalgae that possessed anti-tumor activity, the tumor cell lines altered through using microalgal extracts along with the levels of such extracts that reported to its inhibitor effect against cell cycle and proliferation.

What modulates animal longevity? Fast and slow aging in bivalves as a model for the study of lifespan

Delineating the physiological and biochemical causes of aging process in the animal kingdom is a highly active area of research not only because of potential benefits for human health but also because aging process is related to life history strategies (growth and reproduction) and to responses of organisms to environmental conditions and stress. In this synthesis, we advocate studying bivalve species as models for revealing the determinants of species divergences in maximal longevity. This taxonomic group includes the longest living metazoan on earth (Arctica islandica), which insures the widest range of maximum life span when shorter living species are also included in the comparative model. This model can also be useful for uncovering factors modulating the pace of aging in given species by taking advantages of the wide disparity of lifespan among different populations of the same species. For example, maximal lifespan in different populations of A islandica range from approximately 36 years to over 500 years. In the last 15 years, research has revealed that either regulation or tolerance to oxidative stress is tightly correlated to longevity in this group which support further investigations on this taxon to unveil putative mechanistic links between Reactive Oxygen Species and aging process.

The Cytotoxic Action of Cytochrome C/Cardiolipin Nanocomplex (Cyt-CL) on Cancer Cells in Culture

PURPOSE

The effect of existing anti-cancer therapies is based mainly on the stimulation of apoptosis in cancer cells. Here, we have demonstrated the ability of a catalytically-reactive nanoparticle-based complex of cytochrome c with cardiolipin (Cyt-CL) to induce the apoptosis and killing of cancer cells in a monolayer cell culture.

METHODS

Cyt-CL nanoparticles were prepared by complexing CytC with different molar excesses of CL. Following characterization, cytotoxicity and apoptosis inducing effects of nanoparticles were investigated. In an attempt to identify the anticancer activity mechanism of Cyt-CL, pseudo-lipoxygenase and lipoperoxidase reaction kinetics were measured by chemiluminescence.

RESULTS

Using chemiluminescence, we have demonstrated that the Cyt-CL complex produces lipoperoxide radicals in two reactions: by decomposition of lipid hydroperoxides, and by lipid peroxidation under the action of H₂O₂. Antioxidants inhibited the formation of lipid radicals. Cyt-CL nanoparticles, but not the CytC alone, dramatically enhanced the level of apoptosis and cell death in two cell lines: drug-sensitive (A2780) and doxorubicin-resistant (A2780-Adr). The proposed mechanism of the cytotoxic action of Cyt-CL involves either penetration through the cytoplasm and outer mitochondrial membrane and catalysis of lipid peroxidation reactions at the inner mitochondrial membrane, or/and activation of lipid peroxidation within the cytoplasmic membrane.

CONCLUSIONS

Here we propose a new type of anticancer nano-formulation, with an action based on the catalytic action of Cyt-CL nanoparticles on the cell membrane and and/or mitochondrial membranes that results in lipid peroxidation reactions, which give rise to activation of apoptosis in cancer cells, including multidrug resistant cells.

Known unknowns of cardiolipin signaling: The best is yet to come

Since its discovery 75years ago, a wealth of knowledge has accumulated on the role of cardiolipin, the hallmark phospholipid of mitochondria, in bioenergetics and particularly on the structural organization of the inner mitochondrial membrane. A surge of interest in this anionic doubly-charged tetra-acylated lipid found in both prokaryotes and mitochondria has emerged based on its newly discovered signaling functions. Cardiolipin displays organ, tissue, cellular and transmembrane distribution asymmetries. A collapse of the membrane asymmetry represents a pro-mitophageal mechanism whereby externalized cardiolipin acts as an "eat-me" signal. Oxidation of cardiolipin's polyunsaturated acyl chains - catalyzed by cardiolipin complexes with cytochrome c. - is a pro-apoptotic signal. The messaging functions of myriads of cardiolipin species and their oxidation products are now being recognized as important intracellular and extracellular signals for innate and adaptive immune systems. This newly developing field of research exploring cardiolipin signaling is the main subject of this review. This article is part of a Special Issue entitled: Lipids of Mitochondria edited by Guenther Daum.

Conversion of amyloid fibrils of cytochrome c to mature nanorods through a honeycomb morphology

Amyloid species with various morphologies have been found for different proteins and disease systems. In this article, we aim to ask if these morphologies are unique to a particular protein or if they convert from one to another. Using a heme protein containing iron as the transition-metal activator of aggregation and a negatively charged surfactant, partial unfolding of the protein and its aggregation have been induced. In the pathway of aggregation, we have observed the formation of several morphological structures of a single protein, which were visualized directly using atomic force microscopy (AFM). These structures have been found to appear and disappear with time, and their formation could be monitored under normal buffer conditions and at room temperature without requiring any sophisticated chemical or biological methodologies. In addition, we have observed the formation of honeycomb-shaped morphology, which may serve as an intermediate. These amyloid-based nanostructures may have the potential to be explored in therapeutics delivery and other biomedical applications.

Cardiolipin-cytochrome c complex: Switching cytochrome c from an electron-transfer shuttle to a myoglobin- and a peroxidase-like heme-protein

Cytochrome c (cytc) is a small heme-protein located in the space between the inner and the outer membrane of the mitochondrion that transfers electrons from cytc-reductase to cytc-oxidase. The hexa-coordinated heme-Fe atom of cytc displays a very low reactivity toward ligands and does not exhibit significant catalytic properties. However, upon cardiolipin (CL) binding, cytc achieves ligand binding and catalytic properties reminiscent of those of myoglobin and peroxidase. In particular, the peroxidase activity of the cardiolipin-cytochrome c complex (CL-cytc) is critical for the redistribution of CL from the inner to the outer mitochondrial membranes and is essential for the execution and completion of the apoptotic program. On the other hand, the capability of CL-cytc to bind NO and CO and the heme-Fe-based scavenging of reactive nitrogen and oxygen species may affect apoptosis. Here, the ligand binding and catalytic properties of CL-cytc are analyzed in parallel with those of CL-free cytc, myoglobin, and peroxidase to dissect the potential mechanisms of CL in modulating the pro- and anti-apoptotic actions of cytc.

Antioxidant Approaches to Management of Ionizing Irradiation Injury

Ionizing irradiation induces acute and chronic injury to tissues and organs. Applications of antioxidant therapies for the management of ionizing irradiation injury fall into three categories: (1) radiation counter measures against total or partial body irradiation; (2) normal tissue protection against acute organ specific ionizing irradiation injury; and (3) prevention of chronic/late radiation tissue and organ injury. The development of antioxidant therapies to ameliorate ionizing irradiation injury began with initial studies on gene therapy using Manganese Superoxide Dismutase (MnSOD) transgene approaches and evolved into applications of small molecule radiation protectors and mitigators. The understanding of the multiple steps in ionizing radiation-induced cellular, tissue, and organ injury, as well as total body effects is required to optimize the use of antioxidant therapies, and to sequence such approaches with targeted therapies for the multiple steps in the irradiation damage response.

Resonant inelastic X-ray scattering on ferrous and ferric bis-imidazole porphyrin and cytochrome c: nature and role of the axial methionine-Fe bond

Axial Cu-S(Met) bonds in electron transfer (ET) active sites are generally found to lower their reduction potentials. An axial S(Met) bond is also present in cytochrome c (cyt c) and is generally thought to increase the reduction potential. The highly covalent nature of the porphyrin environment in heme proteins precludes using many spectroscopic approaches to directly study the Fe site to experimentally quantify this bond. Alternatively, L-edge X-ray absorption spectroscopy (XAS) enables one to directly focus on the 3d-orbitals in a highly covalent environment and has previously been successfully applied to porphyrin model complexes. However, this technique cannot be extended to metalloproteins in solution. Here, we use metal K-edge XAS to obtain L-edge like data through 1s2p resonance inelastic X-ray scattering (RIXS). It has been applied here to a bis-imidazole porphyrin model complex and cyt c. The RIXS data on the model complex are directly correlated to L-edge XAS data to develop the complementary nature of these two spectroscopic methods. Comparison between the bis-imidazole model complex and cyt c in ferrous and ferric oxidation states show quantitative differences that reflect differences in axial ligand covalency. The data reveal an increased covalency for the S(Met) relative to N(His) axial ligand and a higher degree of covalency for the ferric states relative to the ferrous states. These results are reproduced by DFT calculations, which are used to evaluate the thermodynamics of the Fe-S(Met) bond and its dependence on redox state. These results provide insight into a number of previous chemical and physical results on cyt c.

Cardiolipin remodeling: a regulatory hub for modulating cardiolipin metabolism and function

Cardiolipin (CL), the signature phospholipid of mitochondria, is involved in a plethora of cellular processes and is crucial for mitochondrial function and architecture. The de novo synthesis of CL in the mitochondria is followed by a unique remodeling process, in which CL undergoes cycles of deacylation and reacylation. Specific fatty acyl composition is acquired during this process, and remodeled CL contains predominantly unsaturated fatty acids. The importance of CL remodeling is underscored by the life-threatening genetic disorder Barth syndrome (BTHS), caused by mutations in tafazzin, which reacylates monolysocardiolipin (MLCL) generated from the deacylation of CL. Just as CL-deficient yeast mutants have been instrumental in elucidating functions of this lipid, the recently characterized CL-phospholipase mutant cld1Δ and the tafazzin mutant taz1Δ are powerful tools to understand the functions of CL remodeling. In this review, we discuss recent advances in understanding the role of CL in mitochondria with specific focus on the enigmatic functions of CL remodeling.

Oxidized but not native cardiolipin has pro-inflammatory effects, which are inhibited by Annexin A5

OBJECTIVE

Cardiolipin (CL) is a phospholipid with an unusual dimeric structure containing four double-bonds and is easily oxidized. CL is present in mitochondria. Here we explored potential pro-inflammatory properties implicated in cardiovascular disease (CVD): activation of endothelial cells, 5-lipoxygenase (5-LOX) and leukotriene B4 (LTB4), by oxidized CL (oxCL) and inhibitory effects of Annexin A5, an antithrombotic and antiinflammatory plasma protein.

METHODS

In monocytes/macrophages and neutrophils, calcium mobilization was monitored spectrophotometrically with Fura-2 and synthesis of LTB4 was analyzed by EIA. Expression of adhesion molecules on endothelial cells was studied by FACScan. Binding of Annexin A5 were analyzed by ELISA. The mRNA expression of 5-LOX and cyclooxygenase-2 was assessed by Real-Time PCR.

RESULTS

We demonstrate that oxCL but not its non-oxidized counterpart CL induces biosynthesis of LTB4 and increases intracellular concentrations of calcium in monocytes/macrophages and neutrophils. oxCL rather than CL selectively elevates gene expression of 5-LOX but not COX-2 in human macrophages. Furthermore, oxCL but not CL raises levels of adhesion molecules ICAM-1 and VCAM-1 in endothelial cells. Annexin A5 can bind oxCL to abolish all these oxCL-induced effects.

CONCLUSIONS

oxCL may promote inflammation and related diseases especially in conditions involving unresolved apoptosis and necrosis, such as atherosclerosis, where free oxCL is likely to be released from liberated mitochondria. Increased intracellular calcium could activate 5-LOX to produce Leukotriene B4 (LTB4). Annexin A5 inhibits the pro-inflammatory effects of oxCL and its potential therapeutic use when oxCL is implicated in inflammation could be of interest.

Metabolism and function of mitochondrial cardiolipin

Since it has been recognized that mitochondria are crucial not only for energy metabolism but also for other cellular functions, there has been a growing interest in cardiolipin, the specific phospholipid of mitochondrial membranes. Indeed, cardiolipin is a universal component of mitochondria in all eukaryotes. It has a unique dimeric structure comprised of two phosphatidic acid residues linked by a glycerol bridge, which gives rise to unique physicochemical properties. Cardiolipin plays an important role in the structural organization and the function of mitochondrial membranes. In this article, we review the literature on cardiolipin biology, focusing on the most important discoveries of the past decade. Specifically, we describe the formation, the migration, and the degradation of cardiolipin and we discuss how cardiolipin affects mitochondrial function. We also give an overview of the various phenotypes of cardiolipin deficiency in different organisms.

Cardiolipin asymmetry, oxidation and signaling

Cardiolipins (CLs) are ancient and unusual dimeric phospholipids localized in the plasma membrane of bacteria and in the inner mitochondrial membrane of eukaryotes. In mitochondria, two types of asymmetries--trans-membrane and molecular--are essential determinants of CL functions. In this review, we describe CL-based signaling mitochondrial pathways realized via modulation of trans-membrane asymmetry and leading to externalization and peroxidation of CLs in mitophagy and apoptosis, respectively. We discuss possible mechanisms of CL translocations from the inner leaflet of the inner to the outer leaflet of the outer mitochondrial membranes. We present redox reaction mechanisms of cytochrome c-catalyzed CL peroxidation as a required stage in the execution of apoptosis. We also emphasize the significance of CL-related metabolic pathways as new targets for drug discovery. Finally, a remarkable diversity of polyunsaturated CL species and their oxidation products have evolved in eukaryotes vs. prokaryotes. This diversity--associated with CL molecular asymmetry--is presented as the basis for mitochondrial communications language.

Radiation-induced cytochrome c release and the neuroprotective effects of the pan-caspase inhibitor z-VAD-fmk in the hypoglossal nucleus

Numerous studies have demonstrated that neuronal cell death occurs via extrinsic (death receptors) and intrinsic (mitochondria) pathways. Radiation induces caspase activation fundamentally via the mitochondrial pathway. To investigate the role of caspase, a cell permeable pan-caspase inhibitor, z-VAD-fmk [N-benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone], was used to investigate the effects of caspase blockade in vivo following irradiation. Adult male Sprague-Dawley rats (weight, 250–300 g) underwent irradiation at room temperature with a 4-Gy dose of radiation. Since z-VAD-fmk does not penetrate the blood-brain barrier, it was applied intracerebroventricularly via a bolus injection (0.2 μg/h for 1 h). Terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) demonstrated that z-VAD-fmk reduced the numbers of TUNEL-positive cells within the hypoglossal nucleus, suggesting that intervention in the caspase cascade following radiation may have therapeutic applications. The caspase inhibitor z-VAD-fmk reduced the expression and activation of caspase-3, caspase-8 and caspase-9 in the irradiated rats, indicating that caspase may be a potential therapeutic target in the treatment of brain radiation injury. Treatment with z-VAD-fmk also reduced the appearance of cytochrome c within the cytosolic fraction following radiation. The hypoglossal nucleus may be used as a model of radiation-induced injury in the central nervous system, providing visual information and displaying apoptotic nuclear morphology.

Microalgal compounds modulate carcinogenesis in the gastrointestinal tract

Gastrointestinal cancers rank second in overall cancer-related deaths. Carotenoids, sulfated polysaccharides, and polyunsaturated fatty acids (PUFAs) from microalgae exhibit cancer chemopreventive features at different stages of carcinogenesis. For instance, sulfated polysaccharides bear a prophylactic potential via blocking adhesion of pathogens to the gastric surface, whereas carotenoids are effective against Helicobacter pylori infection. This effect is notable because H. pylori has been targeted as the primary cause of gastric cancer. Recent results on antitumor and antibacterial compounds synthesized by microalgae are reviewed here, with an emphasis on their impact upon H. pylori infection and derived pathologies accompanying the progression of gastric carcinogenesis.

Neuroprotective effects of anthocyanins on apoptosis induced by mitochondrial oxidative stress

OBJECTIVES

Mitochondrial oxidative stress (MOS) is a major factor in the underlying pathology of many neurodegenerative diseases. Here, we investigated the neuroprotective effects of a unique class of nutraceutical antioxidants, anthocyanins, against MOS-induced death of cultured cerebellar granule neurons (CGNs). Callistephin and kuromanin are anthocyanins derived from strawberries and black rice, respectively, whose neuroprotective properties have yet to be examined in detail.

METHODS

Glutathione (GSH)-sensitive MOS and intrinsic apoptosis were induced in CGNs by incubation with the Bcl-2 inhibitor, HA14-1. The effects of anthocyanin co-incubation on CGN survival were assessed.

RESULTS

The anthocyanins demonstrated significant protection from MOS-induced apoptosis which was equivalent to that provided by the green tea polyphenol, epigallocatechin 3-gallate; however, neither anthocyanin was as effective as GSH at rescuing CGNs. Inhibition of Bcl-2 caused a significant reduction of mitochondrial GSH which was prevented by the anthocyanins. Furthermore, the anthocyanins inhibited iron-induced lipid peroxidation in rat brain homogenates and prevented cardiolipin oxidation induced by MOS in CGNs. MOS-induced mitochondrial fragmentation and proteolytic cleavage of the optic atrophy 1 (OPA1) fusion GTPase were also attenuated by the anthocyanins. Finally, the anthocyanins significantly enhanced GSH peroxidase activity in a cell-free assay.

DISCUSSION

These data show that anthocyanins suppress MOS-induced apoptosis by preserving mitochondrial GSH and inhibiting cardiolipin oxidation and mitochondrial fragmentation. These nutraceutical antioxidants warrant further study as potential therapeutic agents for neurodegenerative diseases caused by MOS.

Strategies for discovery of small molecule radiation protectors and radiation mitigators

Mitochondrial targeted radiation damage protectors (delivered prior to irradiation) and mitigators (delivered after irradiation, but before the appearance of symptoms associated with radiation syndrome) have been a recent focus in drug discovery for (1) normal tissue radiation protection during fractionated radiotherapy, and (2) radiation terrorism counter measures. Several categories of such molecules have been discovered: nitroxide-linked hybrid molecules, including GS-nitroxide, GS-nitric oxide synthase inhibitors, p53/mdm2/mdm4 inhibitors, and pharmaceutical agents including inhibitors of the phosphoinositide-3-kinase pathway and the anti-seizure medicine, carbamazepine. Evaluation of potential new radiation dose modifying molecules to protect normal tissue includes: clonogenic radiation survival curves, assays for apoptosis and DNA repair, and irradiation-induced depletion of antioxidant stores. Studies of organ specific radioprotection and in total body irradiation-induced hematopoietic syndrome in the mouse model for protection/mitigation facilitate rational means by which to move candidate small molecule drugs along the drug discovery pipeline into clinical development.

Oxidative lipidomics of γ-radiation-induced lung injury: mass spectrometric characterization of cardiolipin and phosphatidylserine peroxidation

Oxidative damage plays a significant role in the pathogenesis of γ-radiation-induced lung injury. Endothelium is a preferred target for early radiation-induced damage and apoptosis. Given the newly discovered role of oxidized phospholipids in apoptotic signaling, we performed oxidative lipidomics analysis of phospholipids in irradiated mouse lungs and cultured mouse lung endothelial cells. C57BL/6NHsd female mice were subjected to total-body irradiation (10 Gy, 15 Gy) and euthanized 24 h thereafter. Mouse lung endothelial cells were analyzed 48 h after γ irradiation (15 Gy). We found that radiation-induced apoptosis in vivo and in vitro was accompanied by non-random oxidation of phospholipids. Cardiolipin and phosphatidylserine were the major oxidized phospholipids, while more abundant phospholipids (phosphatidylcholine, phosphatidylethanolamine) remained non-oxidized. Electrospray ionization mass spectrometry analysis revealed the formation of cardiolipin and phosphatidylserine oxygenated molecular species in the irradiated lung and cells. Analysis of fatty acids after hydrolysis of cardiolipin and phosphatidylserine by phospholipase A(2) revealed the presence of mono-hydroperoxy and/or mono-hydroxy/mono-epoxy, mono-hydroperoxy/mono-oxo molecular species of linoleic acid. We speculate that cyt c-driven oxidations of cardiolipin and phosphatidylserine associated with the execution of apoptosis in pulmonary endothelial cells are important contributors to endothelium dysfunction in γ-radiation-induced lung injury.

Ascorbate peroxidase activity of cytochrome c

The peroxidase-type reactivity of cytochrome c is proposed to play a role in free radical production and/or apoptosis. This study describes cytochrome c catalysis of peroxide consumption by ascorbate. Under conditions where the sixth coordination position at the cytochrome c heme iron becomes more accessible for exogenous ligands (by carboxymethylation, cardiolipin addition or by partial denaturation with guanidinium hydrochloride) this peroxidase activity is enhanced. A reaction intermediate is detected by stopped-flow UV-vis spectroscopy upon reaction of guanidine-treated cytochrome c with peroxide, which resembles the spectrum of globin Compound II species and is thus proposed to be a ferryl species. The ability of physiological levels of ascorbate (10-60 µM) to interact with this species may have implications for mechanisms of cell signalling or damage that are based on cytochrome c/peroxide interactions.

Mitochondrial targeting of electron scavenging antioxidants: Regulation of selective oxidation vs random chain reactions

Effective regulation of highly compartmentalized production of reactive oxygen species and peroxidation reactions in mitochondria requires targeting of small molecule antioxidants and antioxidant enzymes into the organelles. This review describes recently developed approaches to mitochondrial targeting of small biologically active molecules based on: (i) preferential accumulation in mitochondria because of their hydrophobicity and positive charge (hydrophobic cations), (ii) binding with high affinity to an intra-mitochondrial constituent, and (iii) metabolic conversions by specific mitochondrial enzymes to reveal an active entity. In addition, targeted delivery of antioxidant enzymes via expression of leader sequences directing the proteins into mitochondria is considered. Examples of successful antioxidant and anti-apoptotic protection based on the ability of targeted cargoes to inhibit cytochrome c-catalyzed peroxidation of a mitochondria-specific phospholipid cardiolipin, in vitro and in vivo are presented. Particular emphasis is placed on the employment of triphenylphosphonium- and hemi-gramicidin S-moieties as two effective vehicles for mitochondrial delivery of antioxidants.

Mass-spectrometric analysis of hydroperoxy- and hydroxy-derivatives of cardiolipin and phosphatidylserine in cells and tissues induced by pro-apoptotic and pro-inflammatory stimuli

Oxidation of two anionic phospholipids--cardiolipin (CL) in mitochondria and phosphatidylserine (PS) in extramitochondrial compartments--is important signaling event, particularly during the execution of programmed cell death and clearance of apoptotic cells. Quantitative analysis of CL and PS oxidation products is central to understanding their molecular mechanisms of action. We combined the identification of diverse phospholipid molecular species by ESI-MS with quantitative assessments of lipid hydroperoxides using a fluorescence HPLC-based protocol. We characterized CL and PS oxidation products formed in a model system (cyt c/H(2)O(2)), in apoptotic cells (neurons, pulmonary artery endothelial cells) and mouse lung under inflammatory/oxidative stress conditions (hyperoxia, inhalation of single walled carbon nanotubes). Our results demonstrate the usefulness of this approach for quantitative assessments, identification of individual molecular species and structural characterization of anionic phospholipids that are involved in oxidative modification in cells and tissues.

Double E1B 19 kDa- and E1B 55 kDa-deleted oncolytic adenovirus in combination with radiotherapy elicits an enhanced anti-tumor effect

Radiation therapy, a mainstay for anti-tumor therapeutic regimens for a variety of tumor types, triggers tumor cell apoptotic pathways by either directly eliciting DNA damage or indirectly inducing the formation of oxygen radicals. In an effort to augment radiation therapy, we generated a double E1B 19 kDa- and E1B 55 kDa-deleted oncolytic adenovirus (Ad-DeltaE1B19/55). In combination with radiotherapy, greater cytotoxicity was observed for Ad-DeltaE1B19/55 than for the single E1B 55 kDa-deleted oncolytic Ad (Ad-DeltaE1B55). Consistent with this observation, higher levels of p53, phospho-p53, phospho-Chk1, phospho-Chk2, PI3K (phosphatidylinositol-3-kinase), phospho-AKT, cytochrome c, and cleavage of PARP (poly (ADP-ribose) polymerase) and caspase-3 were observed in cells treated with Ad-DeltaE1B19/55 compared with those treated with Ad-DeltaE1B55, indicating that the E1B 19 kDa present in Ad-DeltaE1B55 may partially block radiation-induced apoptosis. A significant therapeutic benefit was also observed in vivo when oncolytic Ads and radiation were combined. Tumors treated with Ad-DeltaE1B19/55 and radiation showed large areas of necrosis and apoptosis with the corresponding induction of p53. Finally, consistent with in vitro observations, the combination of Ad-DeltaE1B19/55 and radiation was more efficacious than the combination of Ad-DeltaE1B55 and radiation. Taken together, these results present a strong therapeutic rationale for combining radiation therapy with E1B 19 kDa-deleted oncolytic Ad.

Cytochrome c/cardiolipin relations in mitochondria: a kiss of death

Recently, phospholipid peroxidation products gained a reputation as key regulatory molecules and participants in oxidative signaling pathways. During apoptosis, a mitochondria-specific phospholipid, cardiolipin (CL), interacts with cytochrome c (cyt c) to form a peroxidase complex that catalyzes CL oxidation; this process plays a pivotal role in the mitochondrial stage of the execution of the cell death program. This review is focused on redox mechanisms and essential structural features of cyt c's conversion into a CL-specific peroxidase that represent an interesting and maybe still unique example of a functionally significant ligand change in hemoproteins. Furthermore, specific characteristics of CL in mitochondria--its asymmetric transmembrane distribution and mechanisms of collapse, the regulation of its synthesis, remodeling, and fatty acid composition--are given significant consideration. Finally, new concepts in drug discovery based on the design of mitochondria-targeted inhibitors of cyt c/CL peroxidase and CL peroxidation with antiapoptotic effects are presented.

Mitochondria-targeted disruptors and inhibitors of cytochrome c/cardiolipin peroxidase complexes: a new strategy in anti-apoptotic drug discovery

The critical role of mitochondria in programmed cell death leads to the design of mitochondriotropic agents as a strategy in regulating apoptosis. For anticancer therapy, stimulation of proapoptotic mitochondrial events in tumor cells and their suppression in surrounding normal cells represents a promising paradigm for new therapies. Different approaches targeting regulation of components of mitochondrial antioxidant system such as Mn-SOD demonstrated significant antitumor efficiency, particularly in combination therapy. This review is focused on a newly discovered early stage of mitochondria-dependent apoptosis - oxidative lipid signaling involving a mitochondria-specific phospholipid cardiolipin (CL). Cytochrome c (cyt c) acts as a CL-specific peroxidase very early in apoptosis. At this stage, the hostile events are still secluded within the mitochondria and do not reach the cytosolic targets. CL oxidation process is required for the release of pro-apoptotic factors into the cytosol. Manipulation of cyt c interactions with CL, inhibition of peroxidase activity, and prevention of CL peroxidation are prime targets for the discovery of anti-apoptotic drugs acting before the "point-of-no-return" in the fulfillment of the cell death program. Therefore, mitochondria-targeted disruptors and inhibitors of cyt c/CL peroxidase complexes and suppression of CL peroxidation represent new strategies in anti-apoptotic drug discovery.

Mitochondrial kinases and their molecular interaction with cardiolipin

Mitochondrial isoforms of creatine kinase (MtCK) and nucleoside diphosphate kinase (NDPK-D) are not phylogenetically related but share functionally important properties. They both use mitochondrially generated ATP with the ultimate goal of maintaining proper nucleotide pools, are located in the intermembrane/cristae space, have symmetrical oligomeric structures, and show high affinity binding to anionic phospholipids, in particular cardiolipin. The structural basis and functional consequences of the cardiolipin interaction have been studied and are discussed in detail in this review. They mainly result in a functional interaction of MtCK and NDPK-D with inner membrane adenylate translocator, probably by forming proteolipid complexes. These interactions allow for privileged exchange of metabolites (channeling) that ultimately regulate mitochondrial respiration. Further functions of the MtCK/membrane interaction include formation of cardiolipin membrane patches, stabilization of mitochondria and a role in apoptotic signaling, as well as in case of both kinases, a role in facilitating lipid transfer between two membranes. Finally, disturbed cardiolipin interactions of MtCK, NDPK-D and other proteins like cytochrome c and truncated Bid are discussed more generally in the context of apoptosis and necrosis.

Nitration of solvent-exposed tyrosine 74 on cytochrome c triggers heme iron-methionine 80 bond disruption. Nuclear magnetic resonance and optical spectroscopy studies

Cytochrome c, a mitochondrial electron transfer protein containing a hexacoordinated heme, is involved in other physiologically relevant events, such as the triggering of apoptosis, and the activation of a peroxidatic activity. The latter occurs secondary to interactions with cardiolipin and/or post-translational modifications, including tyrosine nitration by peroxynitrite and other nitric oxide-derived oxidants. The gain of peroxidatic activity in nitrated cytochrome c has been related to a heme site transition in the physiological pH region, which normally occurs at alkaline pH in the native protein. Herein, we report a spectroscopic characterization of two nitrated variants of horse heart cytochrome c by using optical spectroscopy studies and NMR. Highly pure nitrated cytochrome c species modified at solvent-exposed Tyr-74 or Tyr-97 were generated after treatment with a flux of peroxynitrite, separated, purified by preparative high pressure liquid chromatography, and characterized by mass spectrometry-based peptide mapping. It is shown that nitration of Tyr-74 elicits an early alkaline transition with a pKa = 7.2, resulting in the displacement of the sixth and axial iron ligand Met-80 and replacement by a weaker Lys ligand to yield an alternative low spin conformation. Based on the study of site-specific Tyr to Phe mutants in the four conserved Tyr residues, we also show that this transition is not due to deprotonation of nitro-Tyr-74, but instead we propose a destabilizing steric effect of the nitro group in the mobile Omega-loop of cytochrome c, which is transmitted to the iron center via the nearby Tyr-67. The key role of Tyr-67 in promoting the transition through interactions with Met-80 was further substantiated in the Y67F mutant. These results therefore provide new insights into how a remote post-translational modification in cytochrome c such as tyrosine nitration triggers profound structural changes in the heme ligation and microenvironment and impacts in protein function.

Mass-spectrometric characterization of phospholipids and their hydroperoxide derivatives in vivo: effects of total body irradiation

Combination of electrospray ionization mass spectrometry (ESI-MS), fluorescence high-performance liquid chromatography (HPLC), and 2D-high-performance thin-layer chromatography (2D-HPTLC) is a powerful approach to identify and quantitatively analyze oxidized phospholipids in vivo. We describe application of this methodology in assessments of phospholipid hydroperoxides using as an example their characterization and quantitative determinations in different tissues of mice exposed to total body irradiation (TBI, 10 and 15 Gy). Using ESI-MS, we identified individual molecular species - with particular emphasis on polyunsaturated molecules as preferred peroxidation substrates - in major classes of phospholipids: cardiolipin (CL), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylinositol (PI) isolated from mouse brain, lung, muscles, small intestine, and bone marrow. We show that the pattern of phospholipid oxidation 24 h after TBI is nonrandom and does not follow the phospholipid abundance in tissues. The anionic phospholipids - CL, PS, and PI - are the preferred peroxidation substrates. We identified and structurally characterized individual hydroperoxides in these three classes of phospholipids. The protocols described may be utilized in studies of signaling functions of oxidized phospholipids in cell physiology and pathology.

Denervation induces cytosolic phospholipase A2-mediated fatty acid hydroperoxide generation by muscle mitochondria

Previously, we demonstrated that mitochondria from denervated muscle exhibited dramatically higher Amplex Red dependent fluorescence (thought to be highly specific for hydrogen peroxide) compared with control muscle mitochondria. We now demonstrate that catalase only partially inhibits the Amplex Red signal in mitochondria from denervated muscle. In contrast, ebselen (a glutathione peroxidase mimetic and inhibitor of fatty acid hydroperoxides) significantly inhibits the Amplex Red signal. This suggests that the majority of the Amplex Red signal in mitochondria from denervated muscle is not derived from hydrogen peroxide. Because Amplex Red cannot react with substrates in the lipid environment, we hypothesize that lipid hydroperoxides formed within the mitochondrial lipid bilayer are released as fatty acid hydroperoxides and react with the Amplex Red probe. We also suggest that the release of fatty acid hydroperoxides from denervated muscle mitochondria may be an important determinant of muscle atrophy. In support of this, muscle atrophy and the Amplex Red signal are inhibited in caloric restricted mice and in transgenic mice that overexpress the lipid hydroperoxide-detoxifying enzyme glutathione peroxidase 4. Finally, we propose that cytosolic phospholipase A2 may be a potential source of these hydroperoxides.

Mass-spectrometric characterization of phospholipids and their primary peroxidation products in rat cortical neurons during staurosporine-induced apoptosis

The molecular diversity of phospholipids is essential for their structural and signaling functions in cell membranes. In the current work, we present, the results of mass spectrometric characterization of individual molecular species in major classes of phospholipids -- phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), phosphatidylserine (PtdSer), phosphatidylinositol (PtdIns), sphingomyelin (CerPCho), and cardiolipin (Ptd(2)Gro) -- and their oxidation products during apoptosis induced in neurons by staurosporine (STS). The diversity of molecular species of phospholipids in rat cortical neurons followed the order Ptd(2)Gro > PtdEtn >> PtdCho >> PtdSer > PtdIns > CerPCho. The number of polyunsaturated oxidizable species decreased in the order Ptd(2)Gro >> PtdEtn > PtdCho > PtdSer > PtdIns > CerPCho. Thus a relatively minor class of phospholipids, Ptd(2)Gro, was represented in cortical neurons by the greatest variety of both total and peroxidizable molecular species. Quantitative fluorescence HPLC analysis employed to assess the oxidation of different classes of phospholipids in neuronal cells during intrinsic apoptosis induced by STS revealed that three anionic phospholipids -- Ptd(2)Gro >> PtdSer > PtdIns -- underwent robust oxidation. No significant oxidation in the most dominant phospholipid classes -- PtdCho and PtdEtn -- was detected. MS-studies revealed the presence of hydroxy-, hydroperoxy- as well as hydroxy-/hydroperoxy-species of Ptd(2)Gro, PtdSer, and PtdIns. Experiments in model systems where total cortex Ptd(2)Gro and PtdSer fractions were incubated in the presence of cytochrome c (cyt c) and H(2)O(2), confirmed that molecular identities of the products formed were similar to the ones generated during STS-induced neuronal apoptosis. The temporal sequence of biomarkers of STS-induced apoptosis and phospholipid peroxidation combined with recently demonstrated redox catalytic properties of cyt c realized through its interactions with Ptd(2)Gro and PtdSer suggest that cyt c acts as a catalyst of selective peroxidation of anionic phospholipids yielding Ptd(2)Gro and PtdSer peroxidation products. These oxidation products participate in mitochondrial membrane permeability transition and in PtdSer externalization leading to recognition and uptake of apoptotic cells by professional phagocytes.

Molecular markers of radiation-related normal tissue toxicity

Over the past five decades, those interested in markers of radiation effect have focused primarily on tumor response. More recently, however, the view has broadened to include irradiated normal tissues-markers that predict unusual risk of side-effects, prognosticate during the prodromal and therapeutic phases, diagnose a particular toxicity as radiation-related, and, in the case of bioterror, allow for tissue-specific biodosimetry. Currently, there are few clinically useful radiation-related biomarkers. Notably, levels of some hormones such as thyroid-stimulating hormone (TSH) have been used successfully as markers of dysfunction, indicative of the need for replacement therapy, and for prevention of cancers. The most promising macromolecular markers are cytokines: TGFbeta, IL-1, IL-6, and TNFalpha being lead molecules in this class as both markers and targets for therapy. Genomics and proteomics are still in nascent stages and are actively being studied and developed.

Oxidative lipidomics of gamma-irradiation-induced intestinal injury

Although gamma-irradiation-induced tissue injury has been associated with lipid peroxidation, the individual phospholipid molecular targets have not been identified. We employed oxidative lipidomics to qualitatively and quantitatively characterize phospholipid peroxidation in a radiosensitive tissue, the small intestine, of mice exposed to total body irradiation (TBI) (10 and 15 Gy). Using electrospray ionization mass spectrometry we found that the major classes of intestine phospholipids-phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol-included clusters with highly oxidizable molecular species containing docosahexaenoic fatty acid. Molecular species of cardiolipin were represented by only two major less oxidizable individual molecular species-tetralinoleoylcardiolipin and trilinoleoyl-mono-oleoylcardiolipin. Selective and robust oxidation of two anionic phospholipids-cardiolipin in mitochondria and phosphatidylserine outside of mitochondria-was observed 24 h after gamma-irradiation. MS analysis detected several TBI-induced molecular species of oxidized cardiolipin: (C(18:2))(3)(C(18:2)-OOH), (C(18:2))(2)(C(18:2)-OOH)(2), (C(18:2))(1)(C(18:2)-OOH)(3), and (C(18:2)-OOH)(4). The major molecular species involved in TBI-triggered peroxidation of phosphatidylserine included C(18:0)/C(22:6)-OOH, C(18:0)/C(22:5)-OOH, and C(18:0)/C(22:4)-OOH. More abundant phospholipids-phosphatidylcholine and phosphatidylethanolamine-did not reveal any oxidative stress responses despite the presence of highly oxidizable docosahexaenoic fatty acid residues in their molecular species. A marked activation of caspases 3/7 that was detected in the intestine of gamma-irradiated mice indicates the involvement of apoptotic cell death in the TBI injury. Given that oxidized molecular species of cardiolipin and phosphatidylserine accumulate during apoptosis of different cells in vitro we speculate that cardiolipin and phosphatidylserine oxidation products may be useful as potential biomarkers of gamma-irradiation-induced intestinal apoptosis in vivo and may represent a promising target for the discovery of new radioprotectors and radiosensitizers.