Methylation of Phenyl Rings in Ester-Stabilized Phosphorus Ylides Vastly Enhances Their Protonophoric Activity

We have recently discovered that ester-stabilized phosphorus ylides, resulting from deprotonation of a phosphonium salt such as [Ph3PCH2COOR], can transfer protons across artificial and biological membranes. To create more effective cationic protonophores, we synthesized similar phosphonium salts with one ((heptyloxycarbonylmethyl)(p-tolyl)bromide) or two ((butyloxycarbonylmethyl)(3,5-xylyl)osphonium bromide) methyl substituents in the phenyl groups. The methylation enormously augmented both protonophoric activity of the ylides on planar bilayer lipid membrane (BLM) and uncoupling of mammalian mitochondria, which correlated with strongly accelerated flip-flop of their cationic precursors across the BLM.

Synthesis of Triphenylphosphonium-Linked Derivative of 3,5-Ditert-butyl-4-hydroxybenzylidene-malononitrile (SF6847) via Knoevenagel Reaction Yields an Effective Mitochondria-Targeted Protonophoric Uncoupler

Mitochondrial uncouplers are actively sought as potential therapeutics. Here, we report the first successful synthesis of mitochondria-targeted derivatives of the highly potent uncoupler 3,5-ditert-butyl-4-hydroxybenzylidene-malononitrile (SF6847), bearing a cationic alkyl(triphenyl)phosphonium (TPP) group. As a key step of the synthesis, we used condensation of a ketophenol with malononitrile via the Knoevenagel reaction. SF-C5-TPP with a pentamethylene linker between SF6847 and TPP, stimulating respiration and collapsing membrane potential of rat liver mitochondria at submicromolar concentrations, proved to be the most effective uncoupler of the series. SF-C5-TPP showed pronounced protonophoric activity on a model planar bilayer lipid membrane. Importantly, SF-C5-TPP exhibited rather low toxicity in fibroblast cell culture, causing mitochondrial depolarization in cells at concentrations that only slightly affected cell viability. SF-C5-TPP was more effective in decreasing the mitochondrial membrane potential in the cell culture than SF6847, in contrast to the case of isolated mitochondria. Like other zwitterionic uncouplers, SF-C5-TPP inhibited the growth of Bacillus subtilis in the micromolar concentration range.

Redox processes are major regulators of leukotriene synthesis in neutrophils exposed to bacteria Salmonella typhimurium; the way to manipulate neutrophil swarming

Neutrophils play a primary role in protecting our body from pathogens. When confronted with invading bacteria, neutrophils begin to produce leukotriene B4, a potent chemoattractant that, in cooperation with the primary bacterial chemoattractant fMLP, stimulates the formation of swarms of neutrophils surrounding pathogens. Here we describe a complex redox regulation that either stimulates or inhibits fMLP-induced leukotriene synthesis in an experimental model of neutrophils interacting with Salmonella typhimurium. The scavenging of mitochondrial reactive oxygen species by mitochondria-targeted antioxidants MitoQ and SkQ1, as well as inhibition of their production by mitochondrial inhibitors, inhibit the synthesis of leukotrienes regardless of the cessation of oxidative phosphorylation. On the contrary, antioxidants N-acetylcysteine and sodium hydrosulfide promoting reductive shift in the reversible thiol-disulfide system stimulate the synthesis of leukotrienes. Diamide that oxidizes glutathione at high concentrations inhibits leukotriene synthesis, and the glutathione precursor S-adenosyl-L-methionine prevents this inhibition. Diamide-dependent inhibition is also prevented by diphenyleneiodonium, presumably through inhibition of NADPH oxidase and NADPH accumulation. Thus, during bacterial infection, maintaining the reduced state of glutathione in neutrophils plays a decisive role in the synthesis of leukotriene B4. Suppression of excess leukotriene synthesis is an effective strategy for treating various inflammatory pathologies. Our data suggest that the use of mitochondria-targeted antioxidants may be promising for this purpose, whereas known thiol-based antioxidants, such as N-acetylcysteine, may dangerously stimulate leukotriene synthesis by neutrophils during severe pathogenic infection.

Relationship of Cytotoxic and Antimicrobial Effects of Triphenylphosphonium Conjugates with Various Quinone Derivatives

Quinone derivatives of triphenylphosphonium have proven themselves to be effective geroprotectors and antioxidants that prevent oxidation of cell components with participation of active free radicals - peroxide (RO2·), alkoxy (RO·), and alkyl (R·) radicals, as well as reactive oxygen species (superoxide anion, singlet oxygen). Their most studied representatives are derivatives of plastoquinone (SkQ1) and ubiquinone (MitoQ), which in addition to antioxidant properties also have a strong antibacterial effect. In this study, we investigated antibacterial properties of other quinone derivatives based on decyltriphenylphosphonium (SkQ3, SkQT, and SkQThy). We have shown that they, just like SkQ1, inhibit growth of various Gram-positive bacteria at micromolar concentrations, while being less effective against Gram-negative bacteria, which is associated with recognition of the triphenylphosphonium derivatives by the main multidrug resistance (MDR) pump of Gram-negative bacteria, AcrAB-TolC. Antibacterial action of SkQ1 itself was found to be dependent on the number of bacterial cells. It is important to note that the cytotoxic effect of SkQ1 on mammalian cells was observed at higher concentrations than the antibacterial action, which can be explained by (i) the presence of a large number of membrane organelles, (ii) lower membrane potential, (iii) spatial separation of the processes of energy generation and transport, and (iv) differences in the composition of MDR pumps. Differences in the cytotoxic effects on different types of eukaryotic cells may be associated with the degree of membrane organelle development, energy status of the cell, and level of the MDR pump expression.

The critical role of mitochondrial lipid peroxidation in ferroptosis: insights from recent studies

Ferroptosis is a regulated form of necrotic cell death reliant on iron-catalyzed lipid peroxidation. Although the precise involvement of mitochondria in ferroptosis remains incompletely elucidated, recent research indicates that mitochondrial oxidative events wield a pivotal influence in this mechanism. This article centers on the most recent discoveries, spotlighting the significance of mitochondrial lipid peroxidation in the occurrence of ferroptosis. Modern investigative tools, such as mitochondria-specific dyes responsive to lipid peroxidation and antioxidants targeting mitochondria, have been employed to delve into this phenomenon. The authors' recent empirical evidence demonstrates that mitochondrial lipid peroxidation, quantified using the innovative fluorescent ratiometric probe MitoCLox, takes place prior to the onset of ferroptotic cell death. The mitochondria-targeted antioxidant SkQ1 hinders mitochondrial lipid peroxidation and thwarts ferroptosis, all while leaving unaffected the buildup of reactive oxygen species within the cytoplasm, an antecedent to mitochondrial lipid peroxidation. Similarly, the redox agent methylene blue, impeding the genesis of reactive oxygen species in complex I of the electron transport chain, also imparts a comparable protective effect. These findings collectively imply that reactive oxygen species originating from complex I might hold particular significance in fomenting mitochondrial lipid peroxidation, a pivotal trigger of ferroptosis.

Six Functions of Respiration: Isn't It Time to Take Control over ROS Production in Mitochondria, and Aging Along with It?

Cellular respiration is associated with at least six distinct but intertwined biological functions. (1) biosynthesis of ATP from ADP and inorganic phosphate, (2) consumption of respiratory substrates, (3) support of membrane transport, (4) conversion of respiratory energy to heat, (5) removal of oxygen to prevent oxidative damage, and (6) generation of reactive oxygen species (ROS) as signaling molecules. Here we focus on function #6, which helps the organism control its mitochondria. The ROS bursts typically occur when the mitochondrial membrane potential (MMP) becomes too high, e.g., due to mitochondrial malfunction, leading to cardiolipin (CL) oxidation. Depending on the intensity of CL damage, specific programs for the elimination of damaged mitochondria (mitophagy), whole cells (apoptosis), or organisms (phenoptosis) can be activated. In particular, we consider those mechanisms that suppress ROS generation by enabling ATP synthesis at low MMP levels. We discuss evidence that the mild depolarization mechanism of direct ATP/ADP exchange across mammalian inner and outer mitochondrial membranes weakens with age. We review recent data showing that by protecting CL from oxidation, mitochondria-targeted antioxidants decrease lethality in response to many potentially deadly shock insults. Thus, targeting ROS- and CL-dependent pathways may prevent acute mortality and, hopefully, slow aging.

Ester-stabilized phosphorus ylides as protonophores on bilayer lipid membranes, mitochondria and chloroplasts

Triphenylphosphonium ylides are commonly used as key intermediates in the Wittig reaction. Based on the known acidities of stabilized ylide precursors, we proposed that a methylene group adjacent to phosphorus in these compounds can ensure proton shuttling across lipid membranes. Here, we synthesized (decyloxycarbonylmethyl)triphenylphosphonium bromide (CMTPP-C₁₀) by reaction of triphenylphosphine with decyl bromoacetate. This phosphonium salt precursor of the ester-stabilized phosphorus ylide along with its octyl (CMTPP-C₈) and dodecyl (CMTPP-C₁₂) analogues was found to be a carrier of protons in mitochondrial, chloroplast and artificial lipid membranes, suggesting that it can reversibly release hydrogen ions and diffuse through the membranes in both zwitterionic (ylide) and cationic forms. The CMTPP-C₁₀-mediated electrical current across planar bilayer lipid membranes exhibited pronounced proton selectivity. Similar to conventional protonophores, known to uncouple electron transport and ATP synthesis, CMTPP-C_n (n = 8, 10, 12) stimulated mitochondrial respiration, while decreasing membrane potential, at micromolar concentrations, thereby showing the classical uncoupling activity in mitochondria. CMTPP-C₁₂ also caused dissipation of transmembrane pH gradient on chloroplast membranes. Importantly, CMTPP-C₁₀ exhibited substantially lower toxicity in cell culture, than C₁₂TPP. Thus, we report the finding of a new class of ylide-type protonophores, which is of substantial interest due to promising therapeutic properties of uncouplers.

Current perspectives of mitochondria-targeted antioxidants in cancer prevention and treatment

Oxidative stress nearly always accompanies all stages of cancer development. At the early stages, antioxidants may help to reduce reactive oxygen species (ROS) production and exhibit anticarcinogenic effects. In the later stages, ROS involvement becomes more complex. On the one hand, ROS are necessary for cancer progression and epithelial-mesenchymal transition. On the other hand, antioxidants may promote cancer cell survival and may increase metastatic frequency. The role of mitochondrial ROS in cancer development remains largely unknown. This paper reviews experimental data on the effects of both endogenous and exogenous antioxidants on cancerogenesis focusing on the development and application of mitochondria-targeted antioxidants. We also discuss the prospects for antioxidant cancer therapy, focusing on the use of mitochondria-targeted antioxidants.

Mitochondrion-targeted antioxidant SkQ1 prevents rapid animal death caused by highly diverse shocks

The response to stress involves the activation of pathways leading either to protection from the stress origin, eventually resulting in development of stress resistance, or activation of the rapid death of the organism. Here we hypothesize that mitochondrial reactive oxygen species (mtROS) play a key role in stress-induced programmed death of the organism, which we called "phenoptosis" in 1997. We demonstrate that the synthetic mitochondria-targeted antioxidant SkQ1 (which specifically abolishes mtROS) prevents rapid death of mice caused by four mechanistically very different shocks: (a) bacterial lipopolysaccharide (LPS) shock, (b) shock in response to intravenous mitochondrial injection, (c) cold shock, and (d) toxic shock caused by the penetrating cation C₁₂TPP. Importantly, under all these stresses mortality was associated with a strong elevation of the levels of pro-inflammatory cytokines and administration of SkQ1 was able to switch off the cytokine storms. Since the main effect of SkQ1 is the neutralization of mtROS, this study provides evidence for the role of mtROS in the activation of innate immune responses mediating stress-induced death of the organism. We propose that SkQ1 may be used clinically to support patients in critical conditions, such as septic shock, extensive trauma, cooling, and severe infection by bacteria or viruses.

Mitochondrial Lipid Peroxidation Is Responsible for Ferroptosis

Ferroptosis induced by erastin (an inhibitor of cystine transport) and butionine sulfoximine (an inhibitor of glutathione biosynthesis) was prevented by the mitochondria-targeted antioxidants SkQ1 and MitoTEMPO. These effects correlate with the prevention of mitochondrial lipid peroxidation, which precedes cell death. Methylene blue, a redox agent that inhibits the production of reactive oxygen species (ROS) in complex I of the mitochondrial electron transport chain, also inhibits ferroptosis and mitochondrial lipid peroxidation. Activation of ROS production in complex I with rotenone in the presence of ferrous iron stimulates lipid peroxidation in isolated mitochondria, while ROS produced by complex III are ineffective. SkQ1 and methylene blue inhibit lipid peroxidation. We suggest that ROS formed in complex I promote mitochondrial lipid peroxidation and ferroptosis.

Innate Immunity and Phenoptosis

The hypothesis is proposed that activation of innate immunity is the primary mechanism of phenoptosis (programmed death of an organism). In support of the hypothesis, we discuss (i) the data on active release of signaling molecules from the cell producing excessive inflammation; (ii) the data on contribution of mitochondrial production of reactive oxygen species to immune response.

[Electrophysiological and psychophysical studies in assessment of visual functions in patients with hereditary optic neuropathy]

PURPOSE

To study the capabilities of electrophysiological and psychophysical examination methods for assessment of the functional state of ganglion cells, retina and optic nerve in patients with hereditary optic neuropathy (HON).

MATERIAL AND METHODS

The study included 60 patients (118 eyes) with a genetically confirmed diagnosis of HON. All study patients underwent visual field test (VFT), spectral optical coherence tomography (OCT), flash and pattern visual evoked potentials (VEP) (Flash-VEP, FVEP; Pattern-VEP, PVEP), photopic electroretinography with photonegative response (PhNR) registration and the color vision test. In 24 patients (46 eyes), these parameters were assessed before the start of treatment and one year later. The treatment involved the mitochondria-targeted antioxidant SkQ1 - plastoquinonyl-decyl-triphenylphosphonium bromide (PDTP) in the form of eye drops.

RESULTS

The main PVEP components for 1.0° and 0.3° were registered in 20% and in 14% of patient eyes with HON and high visual functions, respectively. After one year of PDTP use, a significant decrease in P100 peak latency was found only in the group with disease duration of ≤1.5 years as of the time of treatment start (p<0.05). Significant differences were observed in the PhNR amplitude (p<0.004) between patients of the main and the control groups, as well as in the PhNR amplitude between patients with visual acuity of ≤0.1 and ≥0.13 (p<0.01). Patients with high visual functions were found to have a correlation between the PhNR amplitude, GCC thickness and the global loss index (GLV).

CONCLUSION

Along with VFT, OCT and color vision tests, electrophysiological studies are one of the main methods of examining patients with HON. After one year of PDTP use, there was a significant decrease in the FVEP P2 peak latency in the group with a disease duration of ≤1.5 years as of the time of treatment start. The PhNR amplitude in patients with high visual functions was found to correlate with structural changes in the ganglion cell layer and the retinal nerve fiber layer.

Innate Immunity as an Executor of the Programmed Death of Individual Organisms for the Benefit of the Entire Population

In humans, over-activation of innate immunity in response to viral or bacterial infections often causes severe illness and death. Furthermore, similar mechanisms related to innate immunity can cause pathogenesis and death in sepsis, massive trauma (including surgery and burns), ischemia/reperfusion, some toxic lesions, and viral infections including COVID-19. Based on the reviewed observations, we suggest that such severe outcomes may be manifestations of a controlled suicidal strategy protecting the entire population from the spread of pathogens and from dangerous pathologies rather than an aberrant hyperstimulation of defense responses. We argue that innate immunity may be involved in the implementation of an altruistic programmed death of an organism aimed at increasing the well-being of the whole community. We discuss possible ways to suppress this atavistic program by interfering with innate immunity and suggest that combating this program should be a major goal of future medicine.

Mitoptosis, Twenty Years After

In 1999 V. P. Skulachev proposed the term "mitoptosis" to refer to the programmed elimination of mitochondria in living cells. According to the initial thought, mitoptosis serves to protect cells from malfunctioning of the damaged mitochondria. At the same time, a new mechanism of the complete mitochondria elimination was found under the conditions of massive mitochondrial damage associated with oxidative stress. In this experimental model, mitochondrial cluster formation in the perinuclear region leads to the formation of "mitoptotic body" surrounded by a single-layer membrane and subsequent release of mitochondria from the cell. Later, it was found that mitoptosis plays an important role in various normal and pathological processes that are not necessarily associated with the mitochondrial damage. It was found that mitoptosis takes place during cell differentiation, self-maintenance of hematopoietic stem cells, metabolic remodelling, and elimination of the paternal mitochondria in organisms with the maternal inheritance of the mitochondrial DNA. Moreover, the associated with mitoptosis release of mitochondrial components into the blood may be involved in the transmission of signals between cells, but also leads to the development of inflammatory and autoimmune diseases. Mitoptosis can be attributed to the asymmetric inheritance of mitochondria in the division of yeast and some animal cells, when the defective mitochondria are transferred to one of the newly formed cells. Finally, a specific form of mitoptosis appears to be selective elimination of mitochondria with deleterious mutations in whole follicular ovarian cells in mammals. During formation of the primary follicle, the mitochondrial DNA copy number is significantly reduced. After division, the cells that receive predominantly mitochondria with deleterious mutations in their mtDNA die, thereby reducing the likelihood of transmission of these mutations to offspring. Further study of the mechanisms of mitoptosis in normal and pathological conditions is important both for understanding the processes of development and aging, and for designing therapeutic approaches for inflammatory, neurodegenerative and other diseases.

Mitochondria-targeted 1,4-naphthoquinone (SkQN) is a powerful prooxidant and cytotoxic agent

An increase in the production of reactive oxygen species (ROS) in mitochondria due to targeted delivery of redox active compounds may be useful in studies of modulation of cell functions by mitochondrial ROS. Recently, the mitochondria-targeted derivative of menadione (MitoK₃) was synthesized. However, MitoK₃ did not induce mitochondrial ROS production and lipid peroxidation while exerting significant cytotoxic action. Here we synthesized 1,4-naphthoquinone conjugated with alkyltriphenylphosphonium (SkQN) as a prototype of mitochondria-targeted prooxidant, and its redox properties, interactions with isolated mitochondria, yeast cells and various human cell lines were investigated. According to electrochemical measurements, SkQN was more active redox agent and, due to the absence of methyl group in the naphthoquinone ring, more reactive as electrophile than MitoK₃. SkQN (but not MitoK₃) stimulated hydrogen peroxide production in isolated mitochondria. At low concentrations, SkQN stimulated state 4 respiration in mitochondria, decreased membrane potential, and blocked ATP synthesis, being more efficient uncoupler of oxidative phosphorylation than MitoK₃. In yeast cells, SkQN decreased cell viability and induced oxidative stress and mitochondrial fragmentation. SkQN killed various tumor cells much more efficiently than MitoK₃. Since many tumors are characterized by increased oxidative stress, the use of new mitochondria-targeted prooxidants may be a promising strategy for anticancer therapy.

Mitochondrial localization of SESN2

SESN2 is a member of the evolutionarily conserved sestrin protein family found in most of the Metazoa species. The SESN2 gene is transcriptionally activated by many stress factors, including metabolic derangements, reactive oxygen species (ROS), and DNA-damage. As a result, SESN2 controls ROS accumulation, metabolism, and cell viability. The best-known function of SESN2 is the inhibition of the mechanistic target of rapamycin complex 1 kinase (mTORC1) that plays a central role in support of cell growth and suppression of autophagy. SESN2 inhibits mTORC1 activity through interaction with the GATOR2 protein complex preventing an inhibitory effect of GATOR2 on the GATOR1 protein complex. GATOR1 stimulates GTPase activity of the RagA/B small GTPase, the component of RagA/B:RagC/D complex, preventing mTORC1 translocation to the lysosomes and its activation by the small GTPase Rheb. Despite the well-established role of SESN2 in mTORC1 inhibition, other SESN2 activities are not well-characterized. We recently showed that SESN2 could control mitochondrial function and cell death via mTORC1-independent mechanisms, and these activities might be explained by direct effects of SESN2 on mitochondria. In this work, we examined mitochondrial localization of SESN2 and demonstrated that SESN2 is located on mitochondria and can be directly involved in the regulation of mitochondrial functions.

Fluorescein Derivatives as Antibacterial Agents Acting via Membrane Depolarization

Appending a lipophylic alkyl chain by ester bond to fluorescein has been previously shown to convert this popular dye into an effective protonophoric uncoupler of oxidative phosphorylation in mitochondria, exhibiting neuro- and nephroprotective effects in murine models. In line with this finding, we here report data on the pronounced depolarizing effect of a series of fluorescein decyl esters on bacterial cells. The binding of the fluorescein derivatives to Bacillus subtilis cells was monitored by fluorescence microscopy and fluorescence correlation spectroscopy (FCS). FCS revealed the energy-dependent accumulation of the fluorescein esters with decyl(triphenyl)- and decyl(tri-p-tolyl)phosphonium cations in the bacterial cells. The latter compound proved to be the most potent in suppressing B. subtilis growth.

Three rare pathogenic mtDNA substitutions in LHON patients with low heteroplasmy

In this article we present clinical, molecular and biochemical investigations of three patients with LHON caused by rare point substitutions in mtDNA. One patient harbours the known mtDNA mutation (m.13513 G>A), the others have new variants (m.13379 A>G in MT-ND5 gene and m.14597 A>G in MT-ND6 gene, which has never been previously associated with LHON). NGS analysis of a whole mtDNA derived from patient's blood revealed a low mutation load (24%, 47%, 23% respectively). Our data, including family segregation analysis, measurement of reactive oxygen species (ROS) production and cytotoxic effect of paraquat and high-resolution respirometry, showed that nucleotide variant m.14597 A>G can be classified as pathogenic mutation.

Molecular Dynamics Modeling of the Interaction of Cationic Fluorescent Lipid Peroxidation-Sensitive Probes with the Mitochondrial Membrane

Cardiolipin (CL) plays a central role in lipid peroxidation (LPO) of the mitochondrial inner membrane due to higher content of unsaturated fatty acids in CL in comparison with the other phospholipids. CL oxidation plays an important role in the regulation of various intracellular signaling pathways and its excessive oxidation contributes to the development of various pathologies and, possibly, participates in the aging process. Mitochondria-targeted antioxidants containing triphenylphosphonium (TPP⁺) effectively protect CL from oxidation. It is assumed that fluorescent probes on the basis of the C11-BODIPY fluorophore sensitive to LPO and containing TPP⁺ can selectively register CL oxidation. To test this possibility, we carried out a molecular dynamic simulation of such probes in a model mitochondrial membrane. It is shown that the probes are located in the membrane at the same depth as the unsaturated bonds in CL molecules sensitive to oxidation. Increasing the length of the linker that binds the fluorophore and TPP⁺ residue ha little effect on the position of the probe in the membrane. This indicates the possibility of modifying the linker to increase the selectivity of the probes to CL.

Therapeutic Effect of the Mitochondria-Targeted Antioxidant SkQ1 on the Culture Model of Multiple Sclerosis

Multiple sclerosis (MS) is a heterogeneous autoimmune disease of unknown etiology characterized by inflammation, demyelination, and axonal degeneration that affects both the white and gray matter of CNS. Recent large-scale epidemiological and genomic studies identified several genetic and environmental risk factors for the disease. Among them are environmental factors of infectious origin, possibly causing MS, which include Epstein-Barr virus infection, reactivation of some endogenous retrovirus groups, and infection by pathogenic bacteria (mycobacteria, Chlamydia pneumoniae, and Helicobacter pylori). However, the nature of the events leading to the activation of immune cells in MS is mostly unknown and there is no effective therapy against the disease. Amazingly, whatever the cause of the disease, signs of damage to the nerve tissue with MS lesions were the same as with infectious leprosy, while in the latter case nitrozooxidative stress was suggested as the main cause of the nerve damage. With this in mind and following the hypothesis that excessive production of mitochondrial reactive oxygen species critically contributes to MS pathogenesis, we studied the effect of mitochondria-targeted antioxidant SkQ1 in an in vitro MS model of the primary oligodendrocyte culture of the cerebellum, challenged with lipopolysaccharide (LPS). SkQ1 was found to accumulate in the mitochondria of oligodendrocytes and microglial cells, and it was also found to prevent LPS-induced inhibition of myelin production in oligodendrocytes. The results implicate that mitochondria-targeted antioxidants could be promising candidates as components of a combined therapy for MS and related neurological disorders.

Does Oxidation of Mitochondrial Cardiolipin Trigger a Chain of Antiapoptotic Reactions?

Oxidative stress causes selective oxidation of cardiolipin (CL), a four-tail lipid specific for the inner mitochondrial membrane. Interaction with oxidized CL transforms cytochrome c into peroxidase capable of oxidizing even more CL molecules. Ultimately, this chain of events leads to the pore formation in the outer mitochondrial membrane and release of mitochondrial proteins, including cytochrome c, into the cytoplasm. In the cytoplasm, cytochrome c promotes apoptosome assembly that triggers apoptosis (programmed cell death). Because of this amplification cascade, even an occasional oxidation of a single CL molecule by endogenously formed reactive oxygen species (ROS) might cause cell death, unless the same CL oxidation triggers a separate chain of antiapoptotic reactions that would prevent the CL-mediated apoptotic cascade. Here, we argue that the key function of CL in mitochondria and other coupling membranes is to prevent proton leak along the interface of interacting membrane proteins. Therefore, CL oxidation should increase proton permeability through the CL-rich clusters of membrane proteins (CL islands) and cause a drop in the mitochondrial membrane potential (MMP). On one hand, the MMP drop should hinder ROS generation and further CL oxidation in the entire mitochondrion. On the other hand, it is known to cause rapid fission of the mitochondrial network and formation of many small mitochondria, only some of which would contain oxidized CL islands. The fission of mitochondrial network would hinder apoptosome formation by preventing cytochrome c release from healthy mitochondria, so that slowly working protein quality control mechanisms would have enough time to eliminate mitochondria with the oxidized CL. Because of these two oppositely directed regulatory pathways, both triggered by CL oxidation, the fate of the cell appears to be determined by the balance between the CL-mediated proapoptotic and antiapoptotic reactions. Since this balance depends on the extent of CL oxidation, mitochondria-targeted antioxidants might be able to ensure cell survival in many pathologies by preventing CL oxidation.

Induction of autophagy by depolarization of mitochondria

Mitochondrial dysfunction plays a crucial role in the macroautophagy/autophagy cascade. In a recently published study Sun et al. described the induction of autophagy by the membranophilic triphenylphosphonium (TPP)-based cation 10-(6'-ubiquinonyl) decyltriphenylphosphonium (MitoQ) in HepG2 cells (Sun C, et al. "MitoQ regulates autophagy by inducing a pseudo-mitochondrial membrane potential [PMMP]", Autophagy 2017, 13:730-738.). Sun et al. suggested that MitoQ adsorbed to the inner mitochondrial membrane with its cationic moiety remaining in the intermembrane space, adding a large number of positive charges and establishing a "pseudo-mitochondrial membrane potential," which blocked the ATP synthase. Here we argue that the suggested mechanism for generation of the "pseudo-mitochondrial membrane potential" is physically implausible and contradicts earlier findings on the electrophoretic displacements of membranophilic cations within and through phospholipid membranes. We provide evidence that TPP-cations dissipated the mitochondrial membrane potential in HepG2 cells and that the induction of autophagy in carcinoma cells by TPP-cations correlated with the uncoupling of oxidative phosphorylation. The mild uncoupling of oxidative phosphorylation by various mitochondria-targeted penetrating cations may contribute to their reported therapeutic effects via inducing both autophagy and mitochondria-selective mitophagy.

Mitodiversity

Here, in addition to the previously coined term "mitobiota", we introduce the term "mitodiversity" for various phenotypic and genetic heterogeneities of mitochondria within the same cell or organ. Based on data on the mitochondrial transmembrane potential determined both in situ and in vitro under normal conditions and after organ ischemia/reperfusion, such heterogeneity is most evident under pathologic conditions. Herein, a part of the mitochondrial population with transmembrane potential typical of the normal state is sustained even under a pathological condition that, perhaps, underlies the development of ways of reversing pathology back to the normal state. The membrane potentials of isolated mitochondria were shown to directly correlate with the magnitude of side-scattered light depicting internal structure of mitochondria. We analyzed possible interpretations of data on mitochondrial membrane potential obtained using fluorescent probes. We suggest a possible mechanism underlying retention of fluorescent probes inside the cells and mitochondria.

Low Concentrations of Uncouplers of Oxidative Phosphorylation Prevent Inflammatory Activation of Endothelial Cells by Tumor Necrosis Factor

In endothelial cells, mitochondria play an important regulatory role in physiology as well as in pathophysiology related to excessive inflammation. We have studied the effect of low doses of mitochondrial uncouplers on inflammatory activation of endothelial cells using the classic uncouplers 2,4-dinitrophenol and 4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazole, as well as the mitochondria-targeted cationic uncoupler dodecyltriphenylphosphonium (C12TPP). All of these uncouplers suppressed the expression of E-selectin, adhesion molecules ICAM1 and VCAM1, as well as the adhesion of neutrophils to endothelium induced by tumor necrosis factor (TNF). The antiinflammatory action of the uncouplers was at least partially mediated by the inhibition of NFκB activation due to a decrease in phosphorylation of the inhibitory subunit IκBα. The dynamic concentration range for the inhibition of ICAM1 expression by C12TPP was three orders of magnitude higher compared to the classic uncouplers. Probably, the decrease in membrane potential inhibited the accumulation of penetrating cations into mitochondria, thus lowering the uncoupling activity and preventing further loss of mitochondrial potential. Membrane potential recovery after the removal of the uncouplers did not abolish its antiinflammatory action. Thus, mild uncoupling could induce TNF resistance in endothelial cells. We found no significant stimulation of mitochondrial biogenesis or autophagy by the uncouplers. However, we observed a decrease in the relative amount of fragmented mitochondria. The latter may significantly change the signaling properties of mitochondria. Earlier we showed that both classic and mitochondria-targeted antioxidants inhibited the TNF-induced NFκB-dependent activation of endothelium. The present data suggest that the antiinflammatory effect of mild uncoupling is related to its antioxidant action.

Methodology for use of mitochondria-targeted cations in the field of oxidative stress-related research

For many pathological conditions, reactive oxygen species (ROS) generated in mitochondria are considered to have a role as a trigger. When mitochondrial ROS (mROS) are formed in the inner mitochondrial membrane, they initiate free radical-mediated chain reactions of lipid peroxidation and are thus especially damaging. The consequences of membrane damage are decreased electrical resistance of the membrane, oxidative damage to cardiolipin (a mitochondria specific lipid essential for functioning of respiratory chain proteins and H(+)-ATP synthase), and damage to mitochondrial DNA localized in close vicinity to the inner membrane, with consequent mitochondrial dysfunction and induction of apoptotic cascade and cell death. To target the starting point of such undesirable events, antioxidants conjugated with mitochondria-targeted, membrane-penetrating cations can be used to scavenge ROS inside mitochondria. The most demonstrative indications favoring this conclusion originate from recent discoveries of the in vivo effects of such cations belonging to the MitoQ and SkQ groups. Here we describe some essential methodological aspects of the application of mitochondria-targeted cations promising in treating oxidative stress-related pathologies.

Radioprotective effects of mitochondria-targeted antioxidant SkQR1

We show here that mitochondria-targeted antioxidant composed of plastoquinone conjugated through hydrocarbon linker with cationic rhodamine 19 (SkQR1) protected against nuclear DNA damage induced by gamma radiation in K562 erythroleukemia cells. We also demonstrate that SkQR1 prevented the early (1 h postirradiation) accumulation of phosphorylated histone H2AX (γ-H2AX) an indicator of DNA double-strand break formation, as well as the radiation-induced increase in chromosomal aberrations. These data suggested that nuclear DNA damage induced by gamma radiation may be mediated by mitochondrial reactive oxygen species (ROS) production. We show that SkQR1 suppressed delayed accumulation of ROS 32 h after irradiation probably by inhibiting mitochondrial ROS-induced ROS release mechanisms. This suggests that mitochondria-targeted antioxidants may protect cells from the late consequences of radiation exposure related to delayed oxidative stress. We have previously reported that SkQRl is the substrate of multidrug resistance pump P-glycoproten (Pgp 170) and selectively protects Pgp 170-negative cells against oxidative stress. In line with this finding, we demonstrate here that SkQR1 did not protect Pgp170-positive K562 subline against DNA damage induced by gamma radiation. The selective radioprotection of normal Pgp 170-negative cells by mitochondria-targeted antioxidants could be a promising strategy to increase the efficiency of radiotherapy for multidrug-resistant tumors.

[Mitochondria-targeted antioxidant SkQR1 selectively protects MDR-negative cells against ionizing radiation]

Radioprotection appeared to be an important problem of today due to atom energetic development and utilization of radiation material in the industry, science and medicine. It has been shown that mitochondrial targeted antioxidant SkQR1 could attenuate radiation injury of human erythroleukemia K562 cells. Pretreatment with SkQR1 before irradiation decreased DNA double strand breaks formation, diminished the number of chromosomal aberrations and suppressed delayed ROS production. Prevention of oxidative stress and normalization of mitochondrial function by mitochondria-targeted antioxidants may be a potential therapeutic strategy not only against immediate consequences of radiation, but, either against its late consequences such as genomic instability. SkQR1 did not protect against radiation-induced damage the K562 subline with high level of multidrug resistance (MDR) due to SkQR1 extrusion with Pgp 170 MDR pump. We suggest that mitochondria-targeted antioxidants might be used for selective protection of normal cells against radiation-induced damage without interference with radiotherapy of MDR-positive tumors.

Derivatives of the cationic plant alkaloids berberine and palmatine amplify protonophorous activity of fatty acids in model membranes and mitochondria

Previously it has been shown by our group that berberine and palmatine, penetrating cations of plant origin, when conjugated with plastoquinone (SkQBerb and SkQPalm), can accumulate in isolated mitochondria or in mitochondria of living cells and effectively protect them from oxidative damage. In the present work, we demonstrate that SkQBerb, SkQPalm, and their analogs lacking the plastoquinone moiety (C10Berb and C10Palm) operate as mitochondria-targeted compounds facilitating protonophorous effect of free fatty acids. These compounds induce proton transport mediated by small concentrations of added fatty acids both in planar and liposomal model lipid membranes. In mitochondria, such an effect can be carried out by endogenous fatty acids and the adenine nucleotide translocase.

Effects of the mitochondria-targeted antioxidant SkQ1 on lifespan of rodents

The effect of the mitochondria-targeted, plastoquinone-containing antioxidant SkQ1 on the lifespan of outbred mice and of three strains of inbred mice was studied. To this end, low pathogen (LP) or specific pathogen free (SPF) vivaria in St. Petersburg, Moscow, and Stockholm were used. For comparison, we also studied mole-voles and dwarf hamsters, two wild species of small rodents kept under simulated natural conditions. It was found that substitution of a LP vivarium for a conventional (non-LP) one doubled the lifespan of female outbred mice, just as SkQ1 did in a non-LP vivarium. SkQ1 prevented age-dependent disappearance of estrous cycles of outbred mice in both LP and non-LP vivaria. In the SPF vivarium in Moscow, male BALB/c mice had shorter lifespan than females, and SkQ1 increased their lifespan to the values of the females. In the females, SkQ1 retarded development of such trait of aging as heart mass increase. Male C57Bl/6 mice housed individually in the SPF vivarium in Stockholm lived as long as females. SkQ1 increased the male lifespan, the longevity of the females being unchanged. SkQ1 did not change food intake by these mice. Dwarf hamsters and mole-voles kept in outdoor cages or under simulated natural conditions lived longer if treated with SkQ1. The effect of SkQ1 on longevity of females is assumed to mainly be due to retardation of the age-linked decline of the immune system. For males under LP or SPF conditions, SkQ1 increased the lifespan, affecting also some other system(s) responsible for aging.

Effects of the mitochondria-targeted antioxidant SkQ1 on lifespan of rodents

The effect of the mitochondria-targeted, plastoquinone-containing antioxidant SkQ1 on the lifespan of outbred mice and of three strains of inbred mice was studied. To this end, low pathogen (LP) or specific pathogen free (SPF) vivaria in St. Petersburg, Moscow, and Stockholm were used. For comparison, we also studied mole-voles and dwarf hamsters, two wild species of small rodents kept under simulated natural conditions. It was found that substitution of a LP vivarium for a conventional (non-LP) one doubled the lifespan of female outbred mice, just as SkQ1 did in a non-LP vivarium. SkQ1 prevented age-dependent disappearance of estrous cycles of outbred mice in both LP and non-LP vivaria. In the SPF vivarium in Moscow, male BALB/c mice had shorter lifespan than females, and SkQ1 increased their lifespan to the values of the females. In the females, SkQ1 retarded development of such trait of aging as heart mass increase. Male C57Bl/6 mice housed individually in the SPF vivarium in Stockholm lived as long as females. SkQ1 increased the male lifespan, the longevity of the females being unchanged. SkQ1 did not change food intake by these mice. Dwarf hamsters and mole-voles kept in outdoor cages or under simulated natural conditions lived longer if treated with SkQ1. The effect of SkQ1 on longevity of females is assumed to mainly be due to retardation of the age-linked decline of the immune system. For males under LP or SPF conditions, SkQ1 increased the lifespan, affecting also some other system(s) responsible for aging.

A-to-I RNA editing: a contribution to diversity of the transcriptome and an organism's development

The complexity of multicellular organisms requires both an increase in genetic information and fine tuning in regulation of gene expression. One of the mechanisms responsible for these functions is RNA editing. RNA editing is a complex process affecting the mechanism of changes in transcriptome sequences. The best studied example of this process is A-to-I RNA editing. On the organism's level, RNA editing plays a key role during ontogenesis and in the defense against pathogens. Disorders in A-to-I RNA editing lead to serious abnormalities. The importance of RNA editing increases with an increase in the organism's complexity. Correct RNA editing is an indispensable factor of an organism's development and probably determines the lifespan of higher eukaryotes.

Mitochondrial-targeted plastoquinone derivatives. Effect on senescence and acute age-related pathologies

Plastoquinone, a very effective electron carrier and antioxidant of chloroplasts, was conjugated with decyltriphenylphosphonium to obtain a cation easily penetrating through membranes. This cation, called SkQ1, is specifically targeted to mitochondria by electrophoresis in the electric field formed by the mitochondrial respiratory chain. The respiratory chain also regenerates reduced SkQ1H(2) from its oxidized form that appears as a result of the antioxidant activity of SkQ1H(2). SkQ1H(2) prevents oxidation of cardiolipin, a mitochondrial phospholipid that is especially sensitive to attack by reactive oxygen species (ROS). In cell cultures, SkQ1 and its analog plastoquinonyl decylrhodamine 19 (SkQR1) arrest H(2)O(2)-induced apoptosis. When tested in vivo, SkQs (i) prolong the lifespan of fungi, crustaceans, insects, fish, and mice, (ii) suppress appearance of a large number of traits typical for age-related senescence (cataract, retinopathies, achromotrichia, osteoporosis, lordokyphosis, decline of the immune system, myeloid shift of blood cells, activation of apoptosis, induction of β-galactosidase, phosphorylation of H2AX histones, etc.) and (iii) lower tissue damage and save the lives of young animals after treatments resulting in kidney ischemia, rhabdomyolysis, heart attack, arrhythmia, and stroke. We suggest that the SkQs reduce mitochondrial ROS and, as a consequence, inhibit mitochondria-mediated apoptosis, an obligatory step of execution of programs responsible for both senescence and fast "biochemical suicide" of an organism after a severe metabolic crisis.

Mitochondria as source of reactive oxygen species under oxidative stress. Study with novel mitochondria-targeted antioxidants--the "Skulachev-ion" derivatives

Production of reactive oxygen species (ROS) in mitochondria was studied using the novel mitochondria-targeted antioxidants (SkQ) in cultures of human cells. It was shown that SkQ rapidly (1-2 h) and selectively accumulated in mitochondria and prevented oxidation of mitochondrial components under oxidative stress induced by hydrogen peroxide. At nanomolar concentrations, SkQ inhibited oxidation of glutathione, fragmentation of mitochondria, and translocation of Bax from cytosol into mitochondria. The last effect could be related to prevention of conformational change in the adenine nucleotide transporter, which depends on oxidation of critical thiols. Mitochondria-targeted antioxidants at nanomolar concentrations prevented accumulation of ROS and cell death under oxidative stress. These effects required 24 h or more (depending on the cell type) preincubation, and this was not related to slow induction of endogenous antioxidant systems. It is suggested that SkQ slowly accumulates in a small subpopulation of mitochondria that have decreased membrane potential and produce the major part of ROS under oxidative stress. This population was visualized in the cells using potential-sensitive dye. The possible role of the small fraction of "bad" mitochondria in cell physiology is discussed.

Reactive oxygen species produced in mitochondria are involved in age-dependent changes of hematopoietic and mesenchymal progenitor cells in mice. A study with the novel mitochondria-targeted antioxidant SkQ1

Lifelong treatment of mice with the effective mitochondria-targeted antioxidant SkQ1 [10-(6'-plastoquinonyl) decyltriphenylphosphonium] does not affect hematopoietic stem cells (HSC) and more differentiated hematopoietic progenitors but significantly decelerates age-dependent changes in peripheral blood. During the first 13 months, SkQ1 (0.9 or 28.8 nmol/kg day) prevents age-dependent myeloid shift (increase in the proportion of granulocytes and decrease in the proportion of lymphocytes). During the next year of treatment the effect disappears, and the hemogram of 2-year-old treated mice does not differ from the control. The number of mesenchymal stem cells (MSC) in the bone marrow does not change during 2 years of treatment with SkQ1, but the concentration of MSC progeny fibroblast colony-forming units (CFU-F) increases with dose of SkQ1. The concentration of CFU-F after 1 and 2 years treatment with SkQ1 is twice higher than in young mice. Our data indicate that the stromal environment of hematopoietic cells could be the primary target of age-dependent changes mediated by reactive oxygen species produced in mitochondria. The anti-aging effects of SkQ1 described here are in perfect agreement with the inhibitory effects of this antioxidant on aging observed in the other models.

Prevention of cardiolipin oxidation and fatty acid cycling as two antioxidant mechanisms of cationic derivatives of plastoquinone (SkQs)

The present state of the art in studies on the mechanisms of antioxidant activities of mitochondria-targeted cationic plastoquinone derivatives (SkQs) is reviewed. Our experiments showed that these compounds can operate as antioxidants in two quite different ways, i.e. (i) by preventing peroxidation of cardiolipin [Antonenko et al., Biochemistry (Moscow) 73 (2008) 1273-1287] and (ii) by fatty acid cycling resulting in mild uncoupling that inhibits the formation of reactive oxygen species (ROS) in mitochondrial State 4 [Severin et al. Proc. Natl. Acad. Sci. USA 107 (2009), 663-668]. The quinol and cationic moieties of SkQ are involved in cases (i) and (ii), respectively. In case (i) SkQH2 interrupts propagation of chain reactions involved in peroxidation of unsaturated fatty acid residues in cardiolipin, the formed SkQ- being reduced back to SkQH2 by heme bH of complex III in an antimycin-sensitive way. Molecular dynamics simulation showed that there are two stable conformations of SkQ1 with the quinol residue localized near peroxyl radicals at C9 or C13 of the linoleate residue in cardiolipin. In mechanism (ii), fatty acid cycling mediated by the cationic SkQ moiety is involved. It consists of (a) transmembrane movement of the fatty acid anion/SkQ cation pair and (b) back flows of free SkQ cation and protonated fatty acid. The cycling results in a protonophorous effect that was demonstrated in planar phospholipid membranes and liposomes. In mitochondria, the cycling gives rise to mild uncoupling, thereby decreasing membrane potential and ROS generation coupled to reverse electron transport in the respiratory chain. In yeast cells, dodecyltriphenylphosphonium (capital ES, Cyrillic12TPP), the cationic part of SkQ1, induces uncoupling that is mitochondria-targeted since capital ES, Cyrillic12TPP is specifically accumulated in mitochondria and increases the H+ conductance of their inner membrane. The conductance of the outer cell membrane is not affected by capital ES, Cyrillic12TPP.

Mitochondria-targeted plastoquinone derivatives as tools to interrupt execution of the aging program. 1. Cationic plastoquinone derivatives: synthesis and in vitro studies

Synthesis of cationic plastoquinone derivatives (SkQs) containing positively charged phosphonium or rhodamine moieties connected to plastoquinone by decane or pentane linkers is described. It is shown that SkQs (i) easily penetrate through planar, mitochondrial, and outer cell membranes, (ii) at low (nanomolar) concentrations, posses strong antioxidant activity in aqueous solution, BLM, lipid micelles, liposomes, isolated mitochondria, and cells, (iii) at higher (micromolar) concentrations, show pronounced prooxidant activity, the "window" between anti- and prooxidant concentrations being very much larger than for MitoQ, a cationic ubiquinone derivative showing very much lower antioxidant activity and higher prooxidant activity, (iv) are reduced by the respiratory chain to SkQH2, the rate of oxidation of SkQH2 being lower than the rate of SkQ reduction, and (v) prevent oxidation of mitochondrial cardiolipin by OH*. In HeLa cells and human fibroblasts, SkQs operate as powerful inhibitors of the ROS-induced apoptosis and necrosis. For the two most active SkQs, namely SkQ1 and SkQR1, C(1/2) values for inhibition of the H2O2-induced apoptosis in fibroblasts appear to be as low as 1x10(-11) and 8x10(-13) M, respectively. SkQR1, a fluorescent representative of the SkQ family, specifically stains a single type of organelles in the living cell, i.e. energized mitochondria. Such specificity is explained by the fact that it is the mitochondrial matrix that is the only negatively-charged compartment inside the cell. Assuming that the Deltapsi values on the outer cell and inner mitochondrial membranes are about 60 and 180 mV, respectively, and taking into account distribution coefficient of SkQ1 between lipid and water (about 13,000 : 1), the SkQ1 concentration in the inner leaflet of the inner mitochondrial membrane should be 1.3x10(8) times higher than in the extracellular space. This explains the very high efficiency of such compounds in experiments on cell cultures. It is concluded that SkQs are rechargeable, mitochondria-targeted antioxidants of very high efficiency and specificity. Therefore, they might be used to effectively prevent ROS-induced oxidation of lipids and proteins in the inner mitochondrial membrane in vivo.

Effect of oxidative stress on dynamics of mitochondrial reticulum

Fission of the mitochondrial reticulum (the thread-grain transition) and following gathering of mitochondria in the perinuclear area are induced by oxidative stress. It is shown that inhibitors of the respiratory chain (piericidin and myxothiazol) cause fission of mitochondria in HeLa cells and fibroblasts, whereas a mitochondria-targeted antioxidant (MitoQ) inhibits this effect. Hydrogen peroxide also induced the fission, which was stimulated by the inhibitors of respiration and suppressed by MitoQ. In untreated cells, the mitochondrial reticulum consisted of numerous electrically-independent fragments. Prolonged treatment with MitoQ resulted in drastic increase in size and decrease in number of these fragments. Local photodamage of mitochondria caused immediate depolarization of a large fraction of the mitochondrial network in MitoQ-treated cells. Our data indicate that the thread-grain transition of mitochondria depends on production of reactive oxygen species (ROS) in initial segments of the respiratory chain and is a necessary step in the process of elimination of mitochondria (mitoptosis).

Production of reactive oxygen species in mitochondria of HeLa cells under oxidative stress

Mitochondria can be a source of reactive oxygen species (ROS) and a target of oxidative damage during oxidative stress. In this connection, the effect of photodynamic treatment (PDT) with Mitotracker Red (MR) as a mitochondria-targeted photosensitizer has been studied in HeLa cells. It is shown that MR produces both singlet oxygen and superoxide anion upon photoactivation and causes photoinactivation of gramicidin channels in a model system (planar lipid bilayer). Mitochondria-targeted antioxidant (MitoQ) inhibits this effect. In living cells, MR-mediated PDT initiates a delayed ("dark") accumulation of ROS, which is accelerated by inhibitors of the respiratory chain (piericidin, rotenone and myxothiazol) and inhibited by MitoQ and diphenyleneiodonium (an inhibitor of flavin enzymes), indicating that flavin of Complex I is involved in the ROS production. PDT causes necrosis that is prevented by MitoQ. Treatment of the cell with hydrogen peroxide causes accumulation of ROS, and the effects of inhibitors and MitoQ are similar to that described for the PDT model. Apoptosis caused by H2O2 is augmented by the inhibitors of respiration and suppressed by MitoQ. It is concluded that the initial segments of the respiratory chain can be an important source of ROS, which are targeted to mitochondria, determining the fate of the cell subjected to oxidative stress.

Hydrogen peroxide produced inside mitochondria takes part in cell-to-cell transmission of apoptotic signal

In monolayer of HeLa cells treated with tumor necrosis factor (TNF), apoptotic cells formed clusters indicating possible transmission of apoptotic signal via the culture media. To investigate this phenomenon, a simple method of enabling two cell cultures to interact has been employed. Two coverslips were placed side by side in a Petri dish, one coverslip covered with apoptogen-treated cells (the inducer) and another with non-treated cells (the recipient). TNF, staurosporine, or H2O2 treatment of the inducer cells is shown to initiate apoptosis on the recipient coverslip. This effect is increased by a catalase inhibitor aminotriazole and is arrested by addition of catalase or by pre-treatment of either the inducer or the recipient cells with nanomolar concentrations of mitochondria-targeted cationic antioxidant MitoQ (10-(6 -ubiquinolyl)decyltriphenylphosphonium), which specifically arrests H2O2-induced apoptosis. The action of MitoQ is abolished by an uncoupler preventing accumulation of MitoQ in mitochondria. It is concluded that reactive oxygen species (ROS) produced by mitochondria in the apoptotic cells initiate the release of H2O2 from these cells. The H2O2 released is employed as a long-distance cell suicide messenger. In processing of such a signal by the recipient cells, mitochondrial ROS production is also involved. It is suggested that the described phenomenon may be involved in expansion of the apoptotic region around a damaged part of the tissue during heart attack or stroke as well as in "organoptosis", i.e. disappearance of organs during ontogenesis.

Bioenergetics and death

Specific inhibitors of mitochondrial functions were used in studies on the relation between bioenergetics and programmed cell death. The data of the authors are discussed in the review.

Selective elimination of mitochondria from living cells induced by inhibitors of bioenergetic functions

The inhibitors of oxidative phosphorylation induced fragmentation of mitochondria without any signs of apoptosis in CV-1 and HeLa cells. Prolonged treatment with the uncouplers (alone or in combination with the inhibitors of respiration) caused perinuclear clusterization of mitochondria, followed by their selective elimination. The fraction of mitochondria-depleted cells remained viable.

Inhibition of mitochondrial bioenergetics: the effects on structure of mitochondria in the cell and on apoptosis

The effects of specific inhibitors of respiratory chain, F(o)F(1)ATP synthase and uncouplers of oxidative phosphorylation on survival of carcinoma HeLa cells and on the structure of mitochondria in the cells were studied. The inhibitors of respiration (piericidin, antimycin, myxothiazol), the F(1)-component of ATP synthase (aurovertin) and uncouplers (DNP, FCCP) did not affect viability of HeLa cells, apoptosis induced by TNF or staurosporin and the anti-apoptotic action of Bcl-2. Apoptosis was induced by combined action of respiratory inhibitors and uncouplers indicating possible pro-apoptotic action of reactive oxygen species (ROS) generated by mitochondria. Short-term incubation of HeLa cells with the mitochondrial inhibitors and 2-deoxyglucose followed by 24-48 h recovery resulted in massive apoptosis. Apoptosis correlated to transient (3-4 h) and limited (60-70%) depletion of ATP. More prolonged or more complete transient ATP depletion induced pronounced necrosis. The inhibitors of respiration and uncouplers caused fragmentation of tubular mitochondria and formation of small round bodies followed by swelling. These transitions were not accompanied with release of cytochrome c into the cytosol and were fully reversible. The combined effect of respiratory inhibitors and uncouplers developed more rapidly indicating possible involvement of ROS generated by mitochondria. More prolonged (48-72 h) incubation with this combination of inhibitors caused clustering and degradation of mitochondria.