Decreased renal expression of PAQR5 is associated with the absence of a nephroprotective effect of progesterone in a rat UUO model

Fibrosis is a severe complication of chronic kidney disease (CKD). Progesterone, like other sex hormones, plays an important role in renal physiology, but its role in CKD is poorly understood. We investigated progesterone effect on renal fibrosis progression in the rat model of unilateral ureteral obstruction (UUO). Female rats were exposed to UUO, ovariectomy and progesterone administration after UUO with ovariectomy. Expression of key fibrosis markers, proinflammatory cytokines, levels of membrane-bound (PAQR5) and nuclear (PGR) progesterone receptors, and matrix metalloproteinase (MMP) activity were analyzed in the obstructed and intact rat kidney. In all groups exposed to UUO, decreased PAQR5 expression was observed in the obstructed kidney while in the contralateral kidney, it remained unaffected. We found increased mRNA levels for profibrotic COL1A1, FN1, MMP2, TIMP1, TIMP2, proinflammatory IL1α, IL1β, and IL18, as well as elevated α-SMA and MMP9 proteins, collagen deposition, and MMP2 activity in all UUO kidneys. Progesterone had slight or no effect on the change in these markers. Thus, we demonstrate for the first time diminished sensitivity of the kidney to progesterone associated with renal fibrosis due to a severe decrease in PAQR5 expression that was accompanied by the lack of nephroprotection in a rat UUO model.

Linking 7-Nitrobenzo-2-oxa-1,3-diazole (NBD) to Triphenylphosphonium Yields Mitochondria-Targeted Protonophore and Antibacterial Agent

Appending lipophilic cations to small molecules has been widely used to produce mitochondria-targeted compounds with specific activities. In this work, we obtained a series of derivatives of the well-known fluorescent dye 7-nitrobenzo-2-oxa-1,3-diazole (NBD). According to the previous data [Denisov et al. (2014) Bioelectrochemistry, 98, 30-38], alkyl derivatives of NBD can uncouple isolated mitochondria at concentration of tens of micromoles despite a high pK_a value (~11) of the dissociating group. Here, a number of triphenylphosphonium (TPP) derivatives linked to NBD via hydrocarbon spacers of varying length (C5, C8, C10, and C12) were synthesized (mitoNBD analogues), which accumulated in the mitochondria in an energy-dependent manner. NBD-C10-TPP (C10-mitoNBD) acted as a protonophore in artificial lipid membranes (liposomes) and uncoupled isolated mitochondria at micromolar concentrations, while the derivative with a shorter linker (NBD-C5-TPP, or C5-mitoNBD) exhibited no such activities. In accordance with this data, C10-mitoNBD was significantly more efficient than C5-mitoNBD in suppressing the growth of Bacillus subtilis. C10-mitoNBD and C12-mitoNBD demonstrated the highest antibacterial activity among the investigated analogues. C10-mitoNBD also exhibited the neuroprotective effect in the rat model of traumatic brain injury.

Targeting Inflammation and Oxidative Stress as a Therapy for Ischemic Kidney Injury

Inflammation and oxidative stress are the main pathological processes that accompany ischemic injury of kidneys and other organs. Based on this, these factors are often chosen as a target for treatment of acute kidney injury (AKI) in a variety of experimental and clinical studies. Note, that since these two components are closely interrelated during AKI development, substances that treat one of the processes often affect the other. The review considers several groups of promising nephroprotectors that have both anti-inflammatory and antioxidant effects. For example, many antioxidants, such as vitamins, polyphenolic compounds, and mitochondria-targeted antioxidants, not only reduce production of the reactive oxygen species in the cell but also modulate activity of the immune cells. On the other hand, immunosuppressors and non-steroidal anti-inflammatory drugs that primarily affect inflammation also reduce oxidative stress under some conditions. Another group of therapeutics is represented by hormones, such as estrogens and melatonin, which significantly reduce severity of the kidney damage through modulation of both these processes. We conclude that drugs with combined anti-inflammatory and antioxidant capacities are the most promising agents for the treatment of acute ischemic kidney injury.

Rapamycin Is Not Protective against Ischemic and Cisplatin-Induced Kidney Injury

Autophagy plays an important role in the pathogenesis of acute kidney injury (AKI). Although autophagy activation was shown to be associated with an increased lifespan and beneficial effects in various pathologies, the impact of autophagy activators, particularly, rapamycin and its analogues on AKI remains obscure. In our study, we explored the effects of rapamycin treatment in in vivo and in vitro models of ischemic and cisplatin-induced AKI. The impact of rapamycin on the kidney function after renal ischemia/reperfusion (I/R) or exposure to the nephrotoxic agent cisplatin was assessed by quantifying blood urea nitrogen and serum creatinine and evaluating the content of neutrophil gelatinase-associated lipocalin, a novel biomarker of AKI. In vitro experiments were performed on the primary culture of renal tubular cells (RTCs) that were subjected to oxygen-glucose deprivation (OGD) or incubated with cisplatin under various rapamycin treatment protocols. Cell viability and proliferation were estimated by the MTT assay and real-time cell analysis using an RTCA iCELLigence system. Although rapamycin inhibited mTOR (mammalian target of rapamycin) signaling, it failed to enhance the autophagy and to ameliorate the severity of AKI caused by ischemia or cisplatin-induced nephrotoxicity. Experiments with RTCs demonstrated that rapamycin exhibited the anti-proliferative effect in primary RTCs cultures but did not protect renal cells exposed to OGD or cisplatin. Our study revealed for the first time that the mTOR inhibitor rapamycin did not prevent AKI caused by renal I/R or cisplatin-induced nephrotoxicity and, therefore, cannot be considered as an ideal mimetic of the autophagy-associated nephroprotective mechanisms (e.g., those induced by caloric restriction), as it had been suggested earlier. The protective action of such approaches like caloric restriction might not be limited to mTOR inhibition and can proceed through more complex mechanisms involving alternative autophagy-related targets. Thus, the use of rapamycin and its analogues for the treatment of various AKI forms requires further studies in order to understand potential protective or adverse effects of these compounds in different contexts.

Effect of Silk Fibroin on Neuroregeneration After Traumatic Brain Injury

Traumatic brain injury is one of the leading causes of disability among the working-age population worldwide. Despite attempts to develop neuroprotective therapeutic approaches, including pharmacological or cellular technologies, significant advances in brain regeneration have not yet been achieved. Development of silk fibroin-based biomaterials represents a new frontier in neuroregenerative therapies after brain injury. In this study, we estimated the short and long-term effects of silk fibroin scaffold transplantation on traumatic brain injury and biocompatibility of this biomaterial within rat neuro-vascular cells. Silk fibroin microparticles were injected into a brain damage area 1 day after the injury. Silk fibroin affords neuroprotection as judged by diminished brain damage and recovery of long-term neurological functions. We did not detect considerable toxicity to neuro-vascular cells cultured on fibroin/fibroin-gelatin microparticles in vitro. Cultivation of primary cell cultures of neurons and astrocytes on silk fibroin matrices demonstrated their higher viability under oxygen-glucose deprivation compared to 2D conditions on plastic plates. Thus, we conclude that scaffolds based on silk fibroin can become the basis for the creation of constructs aimed to treat brain regeneration after injury.

Dysfunction of Kidney Endothelium after Ischemia/Reperfusion and Its Prevention by Mitochondria-Targeted Antioxidant

One of the most important pathological consequences of renal ischemia/reperfusion (I/R) is kidney malfunctioning. I/R leads to oxidative stress, which affects not only nephron cells but also cells of the vascular wall, especially endothelium, resulting in its damage. Assessment of endothelial damage, its role in pathological changes in organ functioning, and approaches to normalization of endothelial and renal functions are vital problems that need to be resolved. The goal of this study was to examine functional and morphological impairments occurring in the endothelium of renal vessels after I/R and to explore the possibility of alleviation of the severity of these changes using mitochondria-targeted antioxidant 10-(6'-plastoquinonyl)decylrhodamine 19 (SkQR1). Here we demonstrate that 40-min ischemia with 10-min reperfusion results in a profound change in the structure of endothelial cells mitochondria, accompanied by vasoconstriction of renal blood vessels, reduced renal blood flow, and increased number of endothelial cells circulating in the blood. Permeability of the kidney vascular wall increased 48 h after I/R. Injection of SkQR1 improves recovery of renal blood flow and reduces vascular resistance of the kidney in the first minutes of reperfusion; it also reduces the severity of renal insufficiency and normalizes permeability of renal endothelium 48 h after I/R. In in vitro experiments, SkQR1 provided protection of endothelial cells from death provoked by oxygen-glucose deprivation. On the other hand, an inhibitor of NO-synthases, L-nitroarginine, abolished the positive effects of SkQR1 on hemodynamics and protection from renal failure. Thus, dysfunction and death of endothelial cells play an important role in the development of reperfusion injury of renal tissues. Our results indicate that the major pathogenic factors in the endothelial damage are oxidative stress and mitochondrial damage within endothelial cells, while mitochondria-targeted antioxidants could be an effective tool for the protection of tissue from negative effects of ischemia.

Do Mitochondria Have an Immune System?

The question if mitochondria have some kind of immune system is not trivial. The basis for raising this question is the fact that bacteria, which are progenitors of mitochondria, do have an immune system. The CRISPR system in bacteria based on the principle of RNA interference serves as an organized mechanism for destroying alien nucleic acids, primarily those of viral origin. We have shown that mitochondria are also a target for viral attacks, probably due to a related organization of genomes in these organelles and bacteria. Bioinformatic analysis performed in this study has not given a clear answer if there is a CRISPR-like immune system in mitochondria. However, this does not preclude the possibility of mitochondrial immunity that can be difficult to decipher or that is based on some principles other than those of CRISPR.

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.

Intercellular Transfer of Mitochondria

Recently described phenomenon of intercellular transfer of mitochondria attracts the attention of researchers in both fundamental science and translational medicine. In particular, the transfer of mitochondria results in the initiation of stem cell differentiation, in reprogramming of differentiated cells, and in the recovery of the lost mitochondrial function in recipient cells. However, the mechanisms of mitochondria transfer between cells and conditions inducing this phenomenon are studied insufficiently. It is still questionable whether this phenomenon exists in vivo. Moreover, it is unclear, how the transfer of mitochondria into somatic cells is affected by the ubiquitination system that, for example, is responsible for the elimination of "alien" mitochondria of the spermatozoon in the oocyte during fertilization. Studies on these processes can provide a powerful incentive for development of strategies for treatment of mitochondria-associated pathologies and give rise a new avenue for therapeutic approaches based on "mitochondrial transplantation".

Microbiota and mitobiota. Putting an equal sign between mitochondria and bacteria

The recent revival of old theories and setting them on modern scientific rails to a large extent are also relevant to mitochondrial science. Given the widespread belief that mitochondria are symbionts of ancient bacterial origin, the processes inherent to mitochondrial physiology can be revised based on their comparative analysis with possible involvement of bacteria. Such comparison combined with discussion of the role of microbiota in pathogenesis allows discussion of the role of "mitobiota" (we introduce this term) as the combination of different phenotypic manifestations of mitochondria in the organism reflecting pathological changes in the mitochondrial genome. When putting an equal sign between mitochondria and bacteria, we find similarity between the mitochondrial and bacterial theories of cancer. The presence of the term "bacterial infection" suggests "mitochondrial infection", and mitochondrial (oxidative) theory of aging can in some way be transformed into a "bacterial theory of aging". The possible existence of such processes and the data confirming their presence are discussed in this review. If such a comparison has the right to exist, the homeostasis of "mitobiota" is of not lesser physiological importance than homeostasis of microbiota, which has been so intensively discussed recently.

[Pathological changes after brain ischemia are similar to those observed in Alzheimer disease]

We studied the influence of ischemia/reperfusion of the middle cerebral artery in the rat's brain on the deferred violation of cognitive functions of the brain which are similar to main symptoms observed in the development of Alzheimer's disease. Using 8-hose radial labyrinth we demonstrated that 6 months after incidence of cerebral ischemia a significant impairment of working memory and a decrease in animals the ability to learn are developed. 7 months after focal cerebral ischemia we could observe the accumulation of a mature amyloid peptide and hyperphosphorylated form of the Tau pro- tein in ipsilateral cerebral hemisphere and of the the beta-amyloid peptide precursor in the contralateral hemisphere. Thus, after an experimental stroke in the brain pathological chanres occur as those typical of Alzheimer's disease.

Mild uncoupling of respiration and phosphorylation as a mechanism providing nephro- and neuroprotective effects of penetrating cations of the SkQ family

It is generally accepted that mitochondrial production of reactive oxygen species is nonlinearly related to the value of the mitochondrial membrane potential with significant increment at values exceeding 150 mV. Due to this, high values of the membrane potential are highly dangerous, specifically under pathological conditions associated with oxidative stress. Mild uncoupling of oxidative phosphorylation is an approach to preventing hyperpolarization of the mitochondrial membrane. We confirmed data obtained earlier in our group that dodecylrhodamine 19 (C(12)R1) (a penetrating cation from SkQ family not possessing a plastoquinone group) has uncoupling properties, this fact making it highly potent for use in prevention of pathologies associated with oxidative stress induced by mitochondrial hyperpolarization. Further experiments showed that C(12)R1 provided nephroprotection under ischemia/reperfusion of the kidney as well as under rhabdomyolysis through diminishing of renal dysfunction manifested by elevated level of blood creatinine and urea. Similar nephroprotective properties were observed for low doses (275 nmol/kg) of the conventional uncoupler 2,4-dinitrophenol. Another penetrating cation that did not demonstrate protonophorous activity (SkQR4) had no effect on renal dysfunction. In experiments with induced ischemic stroke, C(12)R1 did not have any effect on the area of ischemic damage, but it significantly lowered neurological deficit. We conclude that beneficial effects of penetrating cation derivatives of rhodamine 19 in renal pathologies and brain ischemia may be at least partially explained by uncoupling of oxidation and phosphorylation.

Perspectives of mitochondrial medicine

Mitochondrial medicine was established more than 50 years ago after discovery of the very first pathology caused by impaired mitochondria. Since then, more than 100 mitochondrial pathologies have been discovered. However, the number may be significantly higher if we interpret the term "mitochondrial medicine" more widely and include in these pathologies not only those determined by the genetic apparatus of the nucleus and mitochondria, but also acquired mitochondrial defects of non-genetic nature. Now the main problems of mitochondriology arise from methodology, this being due to studies of mitochondrial activities under different models and conditions that are far from the functioning of mitochondria in a cell, organ, or organism. Controversial behavior of mitochondria ("friends and foes") to some extent might be explained by their bacterial origin with possible preservation of "egoistic" features peculiar to bacteria. Apparently, for normal mitochondrial functioning it is essential to maintain homeostasis of a number of mitochondrial elements such as mitochondrial DNA structure, membrane potential, and the system of mitochondrial quality control. Abrogation of these elements can cause a number of pathologies that have become subjects of mitochondrial medicine. Some approaches to therapy of mitochondrial pathologies are discussed.

Role of oxidative stress and mitochondria in onset of urinary bladder dysfunction under acute urine retention

Acute urine retention is a frequent complication in patients with benign hyperplasia of the prostate gland. According to studies made on experimental animals and people, it is accompanied by the deterioration of the bladder blood supply. This study attempts to explore the relationship of intramural blood flow, production of reactive oxygen species, and functional state of the bladder detrusor in modeling of acute urine retention in rats, as well as the impact of mitochondria-targeted antioxidants (which are supposed to alleviate the effects of oxidative stress induced by experimental ischemia) on these parameters. The study showed beneficial effects of mitochondria-targeted antioxidant SkQR1 in preventing damage of the bladder caused by acute urinary retention, which suggests the therapeutic use of this type of compounds for the treatment of ischemic abnormalities of the urinary bladder.

Nephroprotective effect of GSK-3β inhibition by lithium ions and δ-opioid receptor agonist dalargin on gentamicin-induced nephrotoxicity

Nephrotoxicity and ototoxicity are the most considerable side effects of aminoglycoside antibiotics, such as gentamicin that seriously limits its application in medicine. The major mechanism of negative effect of gentamicin on kidney cells involves damage of mitochondria and induction of an oxidative stress that causes cell death resulting in kidney dysfunction. In this work we compared effects of the lithium ions and δ-opioid receptors agonist, dalargin on gentamicin-induced kidney injury. It was revealed that LiCl and dalargin treatment reduced renal tubular cell death and diminished kidney injury caused by gentamicin. Both LiCl and dalargin were found to enhance phosphorylation of glycogen synthase kinase 3β in the kidney which points to induction of nephroprotective signaling pathways. Thus, we conclude that lithium ions and dalargin might be considered as novel promising agents for future use to prevent negative consequences of therapy with aminoglycoside antibiotics.

Mitochondria-targeted antioxidant SkQR1 ameliorates gentamycin-induced renal failure and hearing loss

The influence of the mitochondria-targeted antioxidant SkQR1 on gentamycin-induced nephrotoxicity and ototoxicity has been analyzed. SkQR1 reduces the death of kidney epithelium cells and decreases the severity of renal failure caused by gentamycin application and also lowers the animals' mortality. Treatment with SkQR1 also decreases gentamycin-induced hearing loss. Mitochondria-targeted antioxidants, such as SkQR1, are new promising agents for preventing negative consequences of therapy with antibiotics.

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.

Mechanisms of nephroprotective effect of mitochondria-targeted antioxidants under rhabdomyolysis and ischemia/reperfusion

Oxidative stress-related renal pathologies apparently include rhabdomyolysis and ischemia/reperfusion phenomenon. These two pathologies were chosen for study in order to develop a proper strategy for protection of the kidney. Mitochondria were found to be a key player in these pathologies, being both the source and the target for excessive production of reactive oxygen species (ROS). A mitochondria-targeted compound which is a conjugate of a positively charged rhodamine molecule with plastoquinone (SkQR1) was found to rescue the kidney from the deleterious effect of both pathologies. Intraperitoneal injection of SkQR1 before the onset of pathology not only normalized the level of ROS and lipid peroxidized products in kidney mitochondria but also decreased the level of cytochrome c in the blood, restored normal renal excretory function and significantly lowered mortality among animals having a single kidney exposed to ischemia/reperfusion. The SkQR1-derivative missing plastoquinone (C12R1) possessed some, although limited nephroprotective properties and enhanced animal survival after ischemia/reperfusion. SkQR1 was found to induce some elements of nephroprotective pathways providing ischemic tolerance such as an increase in erythropoietin levels and phosphorylation of glycogen synthase kinase 3β in the kidney. SkQR1 also normalized renal erythropoietin level lowered after kidney ischemia/reperfusion and injection of a well-known nephrotoxic agent gentamicin.

New-generation Skulachev ions exhibiting nephroprotective and neuroprotective properties

A mitochondria-targeted chimeric compound consisting of a rhodamine derivative linked to a plastoquinone molecule (10-(6'-plastoquinonyl)decylrhodamine, SkQR1) was studied under conditions of acute brain or kidney damage. A protective effect of this compound was demonstrated in a model of focal brain ischemia, rat kidney ischemia/reperfusion, myoglobinuria (rhabdomyolysis, or crush syndrome), and pyelonephritis. We found that a single intraperitoneal injection of SkQR1 diminishes the size of the ischemic zone in the brain and improves performance of a test characterizing neurological deficit in ischemic animals. Control substance not containing plastoquinone appeared to be not neuroprotective. The data show that SkQR1 is a nephroprotectant and neuroprotectant, which can be due to the antioxidative action of this Skulachev cation.

Role of acidosis, NMDA receptors, and acid-sensitive ion channel 1a (ASIC1a) in neuronal death induced by ischemia

This review collects data on the influence of intracellular and extracellular acidosis on neuronal viability and the effect of acidosis on neuronal damage progressing under brain ischemia/hypoxia. Particular attention is devoted to the involvement of ionotropic glutamic receptors and acid-sensitive ion channel 1a in these processes.

Cell-to-cell cross-talk between mesenchymal stem cells and cardiomyocytes in co-culture

The goals of the study were: (1) to explore the communication between human mesenchymal stem cells (MSC) and rat cardiac myocytes resulting in differentiation of the stem cells and, (2) to evaluate the role of mitochondria in it. Light and fluorescence microscopy as well as scanning electron microscopy revealed that after co-cultivation, cells formed intercellular contacts and transient exchange with cytosolic elements could be observed. The transport of cytosolic entity had no specific direction. Noticeably, mitochondria also could be transferred to the recipient cells in a unidirectional fashion (towards cardiomyocytes only). Transmission electron microscopy revealed significant variability in both the diameter of intercellular contacting tubes and their shape. Inside of these nanotubes mitochondria-resembling structures were identified. Moreover, after co-cultivation with cardiomyocytes, expression of human-specific myosin was revealed in MSC. Thus, we speculate that: (1) transport of intracellular elements to MSC possibly can determine the direction of their differentiation and, (2) mitochondria may be involved in the mechanism of the stem cell differentiation. It looks plausible that mitochondrial transfer to recipient cardiomyocytes may be involved in the mechanism of failed myocardium repair after stem cells transplantation.

The role of mitochondria in oxidative and nitrosative stress during ischemia/reperfusion in the rat kidney

Reoxygenation following ischemia causes tissue oxidative stress. We studied the role of oxidative stress caused by kidney ischemia/reperfusion (I/R) on the mitochondria of renal tissue slices. I/R caused the mitochondria to be swollen, fragmented, and have lower membrane potential. The mitochondria generated more reactive oxygen species (ROS) and nitric oxide (NO) in situ as measured by fluorescence of ROS- and NO-sensitive probes. Infusion of lithium ion, an inhibitor of glycogen kinase synthase-3, caused phosphorylation of its Ser-9 and restored the membrane potential and decreased ROS production of the mitochondrial fraction. Ischemic kidney and hypoxic rat preconditioning improved mitochondrial membrane potential and lowered ROS production caused by subsequent I/R similar to lithium ion infusion. Preconditioning normalized NO production in mitochondria as well. The drop in the mitochondrial membrane potential was prevented by NO synthase inhibition, demonstrating a strong contribution of NO to changes in mitochondrial energy metabolism during the I/R transition. Mitochondria in the I/R-stressed kidney contained less cytochrome c and more pro-apoptotic Bax, consistent with apoptotic degradation.

Reactive oxygen and nitrogen species: Friends or foes?

Chemical and physiological functions of molecular oxygen and reactive oxygen species (ROS) and existing equilibrium between pools of pro-oxidants and anti-oxidants providing steady state ROS level vital for normal mitochondrial and cell functioning are reviewed. The presence of intracellular oxygen and ROS sensors is postulated and few candidates for this role are suggested. Possible involvement of ROS in the process of fragmentation of mitochondrial reticulum made of long mitochondrial filaments serving in the cell as "electric cables", as well as the role of ROS in apoptosis and programmed mitochondrial destruction (mitoptosis) are reviewed. The critical role of ROS in destructive processes under ischemia/reoxygenation and ischemic preconditioning is discussed. Mitochondrial permeability transition gets special consideration as a possible component of the apoptotic cascade, resulting in excessive "ROS-induced ROS release".