The Effect of Deflazacort Treatment on the Functioning of Skeletal Muscle Mitochondria in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a severe hereditary disease caused by a lack of dystrophin, a protein essential for myocyte integrity. Mitochondrial dysfunction is reportedly responsible for DMD. This study examines the effect of glucocorticoid deflazacort on the functioning of the skeletal-muscle mitochondria of dystrophin-deficient mdx mice and WT animals. Deflazacort administration was found to improve mitochondrial respiration of mdx mice due to an increase in the level of ETC complexes (complexes III and IV and ATP synthase), which may contribute to the normalization of ATP levels in the skeletal muscle of mdx animals. Deflazacort treatment improved the rate of Ca2+ uniport in the skeletal muscle mitochondria of mdx mice, presumably by affecting the subunit composition of the calcium uniporter of organelles. At the same time, deflazacort was found to reduce the resistance of skeletal mitochondria to MPT pore opening, which may be associated with a change in the level of ANT2 and CypD. In this case, deflazacort also affected the mitochondria of WT mice. The paper discusses the mechanisms underlying the effect of deflazacort on the functioning of mitochondria and contributing to the improvement of the muscular function of mdx mice.

The Effect of S-15176 Difumarate Salt on Ultrastructure and Functions of Liver Mitochondria of C57BL/6 Mice with Streptozotocin/High-Fat Diet-Induced Type 2 Diabetes

Simple Summary

Type II diabetes mellitus (T2DM) is one of the most common diseases, which currently represents a major medical and social problem due to the chronic course, high rates of disability and mortality among patients. Mitochondria of the liver and other vital organs are one of the main targets of T2DM at the intracellular level. The pathological changes in the structure of mitochondria, hyperproduction of reactive oxygen species by the organelles, disorders in mitochondrial transport systems and ATP synthesis are now widely recognized as important factors in the development of diabetes. Therefore, treatment strategies to attenuate mitochondrial injury may result in cellular reprogramming and alleviation of the diabetes-related pathological complications. The aim of present work was to investigate the possible protective effect of S-15176, a potent derivative of the anti-ischemic agent trimetazidine, against mitochondrial damage in the liver of mice with experimental T2DM. The data indicate that S-15176 attenuates mitochondrial dysfunction and ultrastructural abnormalities in the liver of T2DM mice. The mechanisms underlying the protective effect of S-15176 are related to the stimulation of mitochondrial biogenesis and the inhibition of lipid peroxidation in the organelles. One may assume that the compound acts as a mitochondria-targeted metabolic reprogramming agent in T2DM.

Abstract

S-15176, a potent derivative of the anti-ischemic agent trimetazidine, was reported to have multiple effects on the metabolism of mitochondria. In the present work, the effect of S-15176 (1.5 mg/kg/day i.p.) on the ultrastructure and functions of liver mitochondria of C57BL/6 mice with type 2 diabetes mellitus (T2DM) induced by a high-fat diet combined with a low-dose streptozotocin injection was examined. An electron microscopy study showed that T2DM induced mitochondrial swelling and a reduction in the number of liver mitochondria. The number of mtDNA copies in the liver in T2DM decreased. The expression of Drp1 slightly increased, and that of Mfn2 and Opa1 somewhat decreased. The treatment of diabetic animals with S-15176 prevented the mitochondrial swelling, normalized the average mitochondrial size, and significantly decreased the content of the key marker of lipid peroxidation malondialdehyde in liver mitochondria. In S-15176-treated T2DM mice, a two-fold increase in the expression of the PGC-1α and a slight decrease in Drp 1 expression in the liver were observed. The respiratory control ratio, the level of mtDNA, and the number of liver mitochondria of S-15176-treated diabetic mice tended to restore. S-15176 did not affect the decrease in expression of Parkin and Opa1 in the liver of diabetic animals, but slightly suppressed the expression of these proteins in the control. The modulatory effect of S-15176 on dysfunction of liver mitochondria in T2DM can be related to the stimulation of mitochondrial biogenesis and the inhibition of lipid peroxidation in the organelles.

Prospects for the use of regulators of oxidative stress in the comprehensive treatment of the novel Coronavirus Disease 2019 (COVID-19) and its complications

Some surface proteins of the newly identified severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can bind to the hemoglobin molecule of an erythrocyte, which leads to the destruction of the structure of the heme and the release of harmful iron ions to the bloodstream. The degradation of hemoglobin results in the impairment of oxygen-carrying capacity of the blood, and the accumulation of free iron enhances the production of reactive oxygen species. Both events can lead to the development of oxidative stress. In this case, oxidative damage to the lungs leads then to the injuries of all other tissues and organs. The use of uridine, which preserves the structure of pulmonary alveoli and the air-blood barrier of the lungs in the course of experimental severe hypoxia, and dihydroquercetin, an effective free radical scavenger, is promising for the treatment of COVID-19. These drugs can also be used for the recovery of the body after the severe disease.

Diabetes Mellitus, Mitochondrial Dysfunction and Ca2+-Dependent Permeability Transition Pore

Diabetes mellitus is one of the most common metabolic diseases in the developed world, and is associated either with the impaired secretion of insulin or with the resistance of cells to the actions of this hormone (type I and type II diabetes, respectively). In both cases, a common pathological change is an increase in blood glucose—hyperglycemia, which eventually can lead to serious damage to the organs and tissues of the organism. Mitochondria are one of the main targets of diabetes at the intracellular level. This review is dedicated to the analysis of recent data regarding the role of mitochondrial dysfunction in the development of diabetes mellitus. Specific areas of focus include the involvement of mitochondrial calcium transport systems and a pathophysiological phenomenon called the permeability transition pore in the pathogenesis of diabetes mellitus. The important contribution of these systems and their potential relevance as therapeutic targets in the pathology are discussed.

Structural and Functional Features of Ca2+ Transport Systems in Liver Mitochondria of Rats with Experimental Hyperthyroidism

We analyzed structural and functional features of the main mitochondrial Ca2+-transporting systems, mitochondrial Ca2+ uniporter complex (MCUC) and Ca2+-dependent cyclosporin A-sensitive mitochondrial permeability transition pore (MPT pore), in rats with hyperthyroid state. It was found that, the rate of Ca2+ accumulation by rat liver mitochondria in this pathology increases by 1.3 times, which can be associated with higher level of the channel-forming subunit of the uniporter MCU and lower content of dominant-negative subunit of this complex MCUb. At the same time, the level of the regulatory subunit MICU1 remained unchanged. It was shown that calcium retention capacity of liver mitochondria in rats with experimental hyperthyroidism decreased by 2 times in comparison with the control, which attested to reduced resistance of liver mitochondria of hyperthyroid rats to induction of the MPT pore. The observed changes are consistent with the data on increased amount of cyclophilin D, a mitochondrial matrix peptidyl-prolyl isomerase that is known to modulate the MPT pore opening and expression of the Ppif gene that encodes mitochondrial cyclophilin D in rats with experimental hyperthyroidism.

Transport of Ca2+ and Ca2+-Dependent Permeability Transition in the Liver and Heart Mitochondria of Rats with Different Tolerance to Acute Hypoxia

The work examines the kinetic parameters of Ca²⁺ uptake via the mitochondrial calcium uniporter complex (MCUC) and the opening of the Ca²⁺-dependent permeability transition pore (MPT pore) in the liver and heart mitochondria of rats with high resistance (HR) and low resistance (LR) to acute hypoxia. We found that the rate of Ca²⁺ uptake by mitochondria of the liver and heart in HR rats is higher than that in LR rats, which is associated with a higher level of the channel-forming subunit MCU in liver mitochondria of HR rats and a lower content of the dominant-negative channel subunit MCUb in heart mitochondria of HR rats. It was shown that the liver mitochondria of HR rats are more resistant to the induction of the MPT pore than those of LR rats (the calcium retention capacity of liver mitochondria of HR rats was found to be 1.3 times greater than that of LR rats). These data correlate with the fact that the level of F₀F₁-ATP synthase, a possible structural element of the MPT pore, in the liver mitochondria of HR rats is lower than in LR rats. In heart mitochondria of rats of the two phenotypes, no statistically significant difference in the formation of the MPT pore was revealed. The paper discusses how changes in the expression of the MCUC subunits and the putative components of the MPT pore can affect Ca²⁺ homeostasis of mitochondria in animals with originally different tolerance to hypoxia and in hypoxia-induced tissue injury.

Transport of Ca2+ and Ca2+-Dependent Permeability Transition in Rat Liver Mitochondria under the Streptozotocin-Induced Type I Diabetes

Although diabetes mellitus is known to be a disease associated with mitochondrial dysfunction, not everything is clear about mitochondrial Ca²⁺ transport and Ca²⁺-induced permeability transition in diabetic cells. The objective of this work was to study the operation of MCU and Ca²⁺-dependent mitochondrial permeabilization in the liver cells of Sprague-Dawley rats under the streptozotocin-induced type I diabetes. It was shown that two weeks after the induction of diabetes, the rate of Ca²⁺ uptake by the mitochondria of diabetic animals increased ~1.4-fold. The expression of MCU and MICU1 subunits did not change, yet the quantity of dominant-negative MCUb channel subunits was almost twice as lower. The organelles also became more resistant to the induction of CsA-sensitive MPT pore and less resistant to the induction of CsA-insensitive palmitate/Ca²⁺-induced pore. The mitochondria of diabetic liver cells also showed changes in the lipid matrix of their membranes. The content of fatty acids in the membranes grew, and microviscosity of the lipid bilayer (assessed with laurdan) increased. At the same time, lipid peroxidation (assessed by the production of malonic dialdehyde) was stimulated. The paper discusses the consequences of the diabetes-related changes in mitochondria in the context of cell physiology.

Effect of hypoxia on mitochondrial enzymes and ultrastructure in the brain cortex of rats with different tolerance to oxygen shortage

The mitochondrial structure and the contents of subunits (NDUFV2, SDHA, Cyt b, COX1) of mitochondrial respiratory complexes I-IV as well as of the hypoxia-inducible factor (HIF-1α) in the brain cortex (BC) of rats with high resistance (HR) and low resistance (LR) to hypoxia were studied for the first time depending on the severity of hypoxia. Different regimes of 30-min hypobaric hypoxia (pO₂ 14, 10, and 8%) were used. It was found that cortical mitochondria responded to 30-min hypobaric hypoxia of different severity with typical and progressing changes in mitochondrial structure and function of mitochondrial enzymes. Under 14 and 10% hypoxia, animals developed compensatory structural and metabolic responses aimed at supporting the cell energy homeostasis. Consequently, these hypoxia regimes can be used for treatment in pressure chambers. At the same time, decreasing the oxygen concentration in the inhaled air to 8% led to the appearance of destructive processes in brain mitochondria. The features of mitochondrial ultrastructure and the function of respiratory enzymes in the BC of HR and LR rats exposed to normoxic and hypoxic conditions suggest that the two types of animals had two essentially distinct functional and metabolic patterns determined by different efficiency of the energy apparatus. The development of adaptive and destructive responses involved different metabolic pathways of the oxidation of energy substrates and different efficiency of the functioning of mitochondrial respiratory carriers.

Uridine as a protector against hypoxia-induced lung injury

The effect of the activation of the mitochondrial ATP-dependent potassium channel (mitoKATP) on the ultrastructure of rat lung in acute hypoxic hypoxia (7% of oxygen in nitrogen, exposure 30 min) was studied. It was shown that uridine, a precursor of the mitoKATP activator UDP, exerted a protective effect against hypoxic damage to the lung. The administration of uridine to animals prior to hypoxia decreased the number of mitochondria with altered ultrastructure and prevented the hypoxia-induced mitochondrial swelling. Uridine also protected the epithelial, interstitial and endothelial layers of the air-blood barrier from the hypoxia-induced hyperhydration. The protective action of uridine against hypoxia-induced lung injury was eliminated by the selective blocker of mitoKATP 5-hydroxydecanoate. These data suggest that one of the mechanisms of the positive effect of uridine is related to the activation of the mitoKATP channel, which, according to the literature and our data, is involved in the protection of tissues from hypoxia and leads to adaptation to it. A possible role of uridine in the maintenance of the mitochondrial structure upon hypoxia-induced lung injury and the optimization of oxygen supply of the organism is discussed.

Mitochondrial Ca2+ Transport: Mechanisms, Molecular Structures, and Role in Cells

Mitochondria are among the most important cell organelles involved in the regulation of intracellular calcium homeostasis. During the last decade, a number of molecular structures responsible for the mitochondrial calcium transport have been identified including the mitochondrial Ca2+ uniporter (MCU), Na+/Ca2+ exchanger (NCLX), and Ca2+/H+ antiporter (Letm1). The review summarizes the data on the structure, regulation, and physiological role of such structures. The pathophysiological mechanism of Ca2+ transport through the cyclosporine A-sensitive mitochondrial permeability transition pore is discussed. An alternative mechanism for the mitochondrial pore opening, namely, formation of the lipid pore induced by saturated fatty acids, and its role in Ca2+ transport are described in detail.

Dynamic Restructuring of the Myocardial Mitochondria in Response to Uridine Modulation of the Activity of Mitochondrial ATP-Dependent Potassium Channel under Conditions of Acute Hypoxic Hypoxia

We studied the effects of in vivo modulation of activity of mitochondrial ATP-dependent potassium channel (mitoK_ATP) by uridine on the morphofunctional state of mitochondria in rat cardiomyocytes under conditions of acute hypoxia. Preinjection of uridine to animals reduced the number of structurally modified mitochondria, but had practically no effect on their morphogenesis after hypoxia. Uridine in vivo stimulated the formation of micromitochondria and their release into the cytoplasm. The number of "maternal" mitochondria containing three and more new micromitochondria, increased as well. The use of mitoK_ATP blocker 5-hydroxydecanoate in parallel with uridine abolished its protective effect, as it significantly inhibited the formation of micromitochondria in rat cardiomyocytes after acute hypoxic exposure.

The role of mitochondrial KATP channel in anti-inflammatory effects of uridine in endotoxemic mice

In this study, we examined the effects of uridine on plasma cytokine levels, heat shock protein (HSP) 72 expression, and nuclear factor (NF)-κB signaling in spleen lymphocytes after exposure of male BALB/c mice to Escherichia coli lipopolysaccharide (LPS). Mice were treated with uridine (30 mg/kg body weight, intraperitoneal injection [i.p.]) or saline solution of LPS (2.5 mg/kg, i. p.). Endotoxin increased plasma levels of tumor necrosis factor-α, interferon-γ, interleukin (IL)-1, IL-2, and IL-6 by 2.1-, 1.9-, 1.7-, 1.6-, and 2.3-fold, respectively. Prior treatment with uridine prevented LPS-induced increases in all studied cytokines. In splenic lymphocytes, LPS treatment increased the expression of HSP 72 by 2.4-fold, whereas preliminary treatment with uridine completely prevented this effect. LPS also activated NF-κB signaling in splenic lymphocytes, and uridine decreased NF-κB pathway activity. Inhibitory analysis showed that the mechanism of uridine action was associated with the formation of the UDP-metabolic activator of the mitochondrial ATP-dependent potassium channel (mitoK_ATP) and the UTP-activator of glycogen synthesis in the tissues. A specific inhibitor of mitoK_ATP, 5-hydroxydecanoate (5 mg/kg), and an inhibitor of glycogen synthesis, galactosamine (110 mg/kg), prevented the effects of uridine. Thus, uridine itself or uridine phosphates, which increased after uridine treatment, appeared to inhibit pro-inflammatory responses induced by LPS application. Overall, these findings demonstrated that the mechanisms mediating the effects of uridine were regulated by activation of glycogen synthesis and opening of the mitoK_ATP, which in turn increased the energy potential of the cell and reduced oxidative stress.

Study of Uridine Effect on the Development of Audiogenic Tonic Seizures in Krushinsky-Molodkina Strain Rats

The latency of tonic seizure in response to loud sound (in rats of the Krushinsky-Molodkina strain with audiogenic epilepsy) had been slightly (although statistically significantly) longer after chronic uridine injections (100 mg/kg, i.p., three times a day during 9 or 12 days). The recovery time from the tonic seizure was shorter after 12 days of injections in comparison to the 9-day injection period. At the same time, the intensity of tonic seizures provoked by loud sound did not change after chronic uridine injections. The lack of uridine anticonvulsive effect demonstrated in the audiogenic epilepsy model contradicts the anticonvulsant effects of uridine in experiments with other seizure models, in which the epileptic foci were localized in the forebrain structures.

Energetic, oxidative and ionic exchange in rat brain and liver mitochondria at experimental audiogenic epilepsy (Krushinsky-Molodkina model)

The role of brain and liver mitochondria at epileptic seizure was studied on Krushinsky-Molodkina (KM) rats which respond to sound with an intensive epileptic seizure (audiogenic epilepsy). We didn't find significant changes in respiration rats of brain and liver mitochondria of KM and control rats; however the efficiency of АТР synthesis in the KM rat mitochondria was 10% lower. In rats with audiogenic epilepsy the concentration of oxidative stress marker malondialdehyde in mitochondria of the brain (but not liver) was 2-fold higher than that in the control rats. The rate of H₂O₂ generation in brain mitochondria of КМ rats was twofold higher than in the control animals when using NAD-dependent substrates. This difference was less pronounced in liver mitochondria. In KM rats, the activity of mitochondrial ATP-dependent potassium channel was lower than in liver mitochondria of control rats. The comparative study of the mitochondria ability to retain calcium ions revealed that in the case of using the complex I and complex II substrates, permeability transition pore is easier to trigger in brain and liver mitochondria of KM and КМs rats than in the control ones. The role of the changes in the energetic, oxidative, and ionic exchange in the mechanism of audiogenic epilepsy generation in rats and the possible correction of the epilepsy seizures are discussed.

Effect of surface-potential modulators on the opening of lipid pores in liposomal and mitochondrial inner membranes induced by palmitate and calcium ions

The effect of surface-potential modulators on palmitate/Ca2+-induced formation of lipid pores was studied in liposomal and inner mitochondrial membranes. Pore formation was monitored by sulforhodamine B release from liposomes and swelling of mitochondria. ζ-potential in liposomes was determined from electrophoretic mobility. Replacement of sucrose as the osmotic agent with KCl decreased negative ζ-potential in liposomes and increased resistance of both mitochondria and liposomes to the pore inducers, palmitic acid, and Ca2+. Micromolar Mg2+ also inhibited palmitate/Ca2+-induced permeabilization of liposomes. The rate of palmitate/Ca2+-induced, cyclosporin A-insensitive swelling of mitochondria increased 22% upon increasing pH from 7.0 to 7.8. At below the critical micelle concentration, the cationic detergent cetyltrimethylammonium bromide (10 μM) and the anionic surfactant sodium dodecylsulfate (10-50 μM) made the ζ-potential less and more negative, respectively, and inhibited and stimulated opening of mitochondrial palmitate/Ca2+-induced lipid pores. Taken together, the findings indicate that surface potential regulates palmitate/Ca2+-induced lipid pore opening.

[The influence of spermine on Ca(2+)-dependent permeability transition in mitochondria and liposomes induced by palmitic and α,Ω-hexadecanedioic acids]

The effect of spermine on Ca(2+)-dependent permeability transition in mitochondria and liposomes induced by palmitic and α,Ω-hexadecanedioic acid was studied. It has been shown that spermine inhibited the cyclosporin A-insensitive mitochondrial swelling induced by palmitic acid and Ca2+ and α,Ω-hexadecanedioic acid and Ca2+. 100 μM spermine did not influence the mitochondrial respiration in state V2 and the respiration stimulated by palmitic acid, α,Ω-hexadecanedioic acid and Ca2+. Pre-incubation of liposomes with 100 μM spermine resulted in the inhibition of palmitic acid/Ca(2+)- and α,Ω-hexadecanedioic acid/Ca(2+)-induced release of the fluorescent dye sulforhodamine B from liposomes. At the same time, spermine added to fatty acids-contained membranes of liposomes stimulated Ca(2+)-dependent release of sulforhodamine B from liposomes. It was shown that an addition of spermine to liposomes resulted in a significant increase in z-potential of liposomal membranes (from -39.8 mV to -18.6 mV). A possible mechanism of spermine influence on palmitic acid/Ca(2+)- and α,Ω-hexadecanedioic acid/Ca(2+)-induced permeability transition in mitochondria and liposomes is discussed.

Interaction of phospholipase A of the E. coli outer membrane with the inhibitors of eucaryotic phospholipases A₂ and their effect on the Ca²⁺-induced permeabilization of the bacterial membrane

Phospholipase A of the bacterial outer membrane (OMPLA) is a β-barrel membrane protein which is activated under various stress conditions. The current study examines interaction of inhibitors of eucaryotic phospholipases A₂--palmitoyl trifluoromethyl ketone (PACOCF₃) and aristolochic acid (AA)--with OMPLA and considers a possible involvement of the enzyme in the Ca²⁺-dependent permeabilization of the outer membrane of Escherichia coli. Using the method of molecular docking, it has been predicted that PACOCF₃ and AA bind to OMPLA at the same site and with the same affinity as the OMPLA inhibitors, hexadecanesulfonylfluoride and bromophenacyl bromide, and the substrate of the enzyme palmitoyl oleoyl phosphatidylethanolamine. It has also been shown that PACOCF₃, AA, and bromophenacyl bromide inhibit the Ca²⁺-induced temperature-dependent changes in the permeability of the bacterial membrane for the fluorescent probe propidium iodide and suppressed the transformation of E. coli cells with plasmid DNA induced by Ca²⁺ and heat shock. The cell viability was not affected by the eucaryotic phospholipases A₂ inhibitors. The study discusses a possible involvement of OMPLA in the mechanisms of bacterial transmembrane transport based on the permeabilization of the bacterial outer membrane.

[Study of the mechanisms of cytotoxic effect of uranyl nitrate]

The mechanisms of cytotoxic effect of uranyl nitrate were studied. It was shown that uranyl nitrate induced HEp-2 cell death, mainly by necrotic way. In the experiments in vitro, uranyl nitrate caused an appearance of 8-oxoguanine in DNA, indicating the induction of oxidative stress. The experiments with isolated rat liver mitochondria revealed that 1 mM uranyl nitrate decreased the respiration rates of mitochondria in state 3 and DNP-induced respiration. At the same time, uranyl nitrate had no influence on the opening of the mitochondrial permeability transition pore and decreased the rate of formation of H2O2 by mitochondria. Possible molecular mechanisms of uranyl-induced necrosis are discussed.

[Mitochondria and hepatotoxicity of ethanol]

The current understanding of the effects of alcohol intoxication on the basic mitochondrial functions has been presented. Both, the direct toxic effect of ethanol on biological membranes and various cellular systems and the toxicity of acetaldehyde and reactive oxygen species (the products of ethanol oxidation) are discussed, with emphasis on the effect of ethanol on the basic functions of mitochondria and Ca(2+)-dependent mitochondrial permeability transition. Based on the available experimental data, it is demonstrated that acute alcohol intoxication causes a global mitochondrial dysfunction in the liver, resulting in considerable disturbance of the whole cellular metabolism. Alcohol poisoning of the liver leads to a decreased ability of cells to withstand oxidative stress, to support the synthesis of vital metabolic intermediates (e.g., methyl groups), as well as to produce urea from ammonia, due to a decreased permeability of the outer membrane and impaired exchange of substrates between the cytoplasm and the mitochondrial matrix. This review emphasizes the role of the voltage-dependent anion channels of the outer mitochondrial membrane in ethanol-mediated disturbances of basic mitochondrial functions and its consequences for the entire cell metabolism in the liver.

[Effect of cholesterol on the formation of palmitate/Ca(2+)-activated pore in mitochondria and liposomes]

The influenc of cholesterol on the formation of the mitochondrial cyclosporin A (CsA)-insensitive palmitate/Ca(2+)-activated pore has been studied. It has been established that increasing the cholesterol level in mitochondrial membranes results in an increase in the of rate of mitochondrial swelling induced by palmitic acid (> or = 20 microM) and Ca2+ (30 microM). This effect is not related to changes in the functional activity of organelles since cholesterol did not influence the mitochondrial respiration in different metabolic states. At the same time, it was shown that the palmitate/Ca(2+)-induced permeabilization of cholesterol-containing azolectin liposomes was Stronger than that of azolectin liposomes. It was found that, in the liposomal membrane, the Ca(2+)-induced phase separation of palmitic acid into distinct membrane domains takes place. The presence of cholesterol in membranes increases the extent of segregation.