The Role of Mitochondrial Enzymes, Succinate-Coupled Signaling Pathways and Mitochondrial Ultrastructure in the Formation of Urgent Adaptation to Acute Hypoxia in the Myocardium.

The effect of a single one-hour exposure to three modes of hypobaric hypoxia (HBH) differed in the content of O in inhaled air (FiO-14%, 10%, 8%) in the development of mitochondrial-dependent adaptive processes in the myocardium was studied in vivo. The following parameters have been examined: (a) an urgent reaction of catalytic subunits of mitochondrial enzymes (NDUFV2, SDHA, Cyt b, COX2, ATP5A) in the myocardium as an indicator of the state of the respiratory chain electron transport function; (b) an urgent activation of signaling pathways dependent on GPR91, HIF-1α and VEGF, allowing us to assess their role in the formation of urgent mechanisms of adaptation to hypoxia in the myocardium; (c) changes in the ultrastructure of three subpopulations of myocardial mitochondria under these conditions. The studies were conducted on two rat phenotypes: rats with low resistance (LR) and high resistance (HR) to hypoxia.

Signaling Role of Mitochondrial Enzymes and Ultrastructure in the Formation of Molecular Mechanisms of Adaptation to Hypoxia.

This study was the first comprehensive investigation of the dependence of mitochondrial enzyme response (catalytic subunits of mitochondrial complexes (MC) I-V, including NDUFV2, SDHA, Cyt b, COX1 and ATP5A) and mitochondrial ultrastructure in the rat cerebral cortex (CC) on the severity and duration of in vivo hypoxic exposures. The role of individual animal's resistance to hypoxia was also studied. The respiratory chain (RC) was shown to respond to changes in environmental [O] as follows: (a) differential reaction of mitochondrial enzymes, which depends on the severity of the hypoxic exposure and which indicates changes in the content and catalytic properties of mitochondrial enzymes, both during acute and multiple exposures; and (b) ultrastructural changes in mitochondria, which reflect various degrees of mitochondrial energization.

[The effect of Mexidol on cerebral mitochondriogenesis at a young age and during aging].

Aim: To study the ability of mexidol to induce cerebral mitochondriogenesis in the brain of young and aging rats.

Material And Methods: Expression level of marker proteins of cerebral mitochondriogenesis was evaluated during treatment with mexidol (20, 40, 100 mg/kg; 20 days; intraperitoneally) in the cerebral cortex of young (3 month) and aging (6, 9, 12, and 15 month) outbred male rats, using the Western blot analysis.

Results: It has been shown for the first time that the course injections of mexidol in doses of 40 and 100 mg/kg is accompanied by dose-dependent induction of the succinate receptor SUCNR1 and protein markers of mitochondrial biogenesis: transcription coactivator PGC-1α, transcription factors (NRF1, TFAM), catalytic subunits of respiratory enzymes (NDUV2, NDUV2,cytb, COX2) and ATP synthase (ATP5A) in the cerebral cortex of young and aging outbred male rats.

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 (pO 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.

Peculiarities of Immediate Response of Respiratory Chain Enzymes in Rat Cerebral Cortex to Hypoxia.

We performed a complex study of the dependence of immediate reaction of catalytic subunits in mitochondrial enzymes (NDUFV2, SDHA, Cyt b, COX1, and ATP5A) in rat cerebral cortex (the most hypoxia-sensitive tissue) on the severity and duration of hypoxia in vivo and the role of individual resistance of rats to oxygen deficiency in this process. Three types of responses to hypoxia were revealed. The immediate response of mitochondria to oxygen deficiency appeared after its drop by 30-33% relatively to normal atmosphere level.

Specific Features of Immediate Ultrastructural Changes in Brain Cortex Mitochondria of Rats with Different Tolerance to Hypoxia under Various Modes of Hypoxic Exposures.

We performed ultrastructural study of cerebral cortex mitochondria in rats with different tolerance to oxygen deficiency (low resistant and highly resistant specimens). Low resistant rats were characterized by the prevalence of mitochondria with lightened matrix due to the nondense packing of cristae. By contrast, mitochondria of highly resistant animals had the dense packing of cristae.

The Role of Succinate in Regulation of Immediate HIF-1α Expression in Hypoxia.

Hypoxia-induced immediate expression of transcription factor HIF-1α in the brain cortex is regulated by succinate produced in both the tricarbonic acid cycle and GABA shunt reactions and is induced by succinate-containing drugs. These facts prove the existence of succinate-dependent signalling regulation involved in immediate and delayed molecular adaptation and increased body resistance to oxygen deficiency, where succinate acts as a signal molecule. The intensity of this process differs in animals with low and high resistance to hypoxia.

Specific Features of Immediate Expression of Succinate-Dependent Receptor GPR91 in Tissues during Hypoxia.

Under normoxic conditions, succinate-dependent receptor GPR91 was found in varying amounts in all analyzed aerobic tissues except erythrocytes. The maximum density of the receptor was observed in the myocardium: by 2.3 and 1.

[Urgent changes in the expression of hypoxia-inducible factor-1α (HIF-1α) in the neocortex of rats with different tolerance to acute hypoxia underwent focal ischemic stroke prefrontal cortex].

Using immunohistochemical method, it was demonstrated that neurons of the cerebral cortex have the capacity to express hypoxia-inducible factor-1 alpha (HIF-1α) in normoxia. Intensity of this process is different for rats having unequal tolerance to hypoxia. Basal HIF-1α expression in neurons of rats with low-resistance (LR) to hypoxia is higher compared to rats with high-resistance (HR).

Phenotypic features of the dynamics of HIF-1α levels in rat neocortex in different hypoxia regimens.

There are tissue-specific and phenotypic differences in the basal levels of HIF-1α under normoxic conditions. Induction of short-term adaptation to hypoxia and formation of long-term adaptation are genetically determined. These phenomena are observed only in animals with low resistance to hypoxia and are associated with biphasic expression of HIF-1α in the neocortex only during hypoxic preconditioning.

[Phenotypic characteristics of factor expression induced by hypoxia and redox status of the rat neocortical cells at different stages of adaptation to hypoxia].

Hypoxic preconditioning induces two-phase increase of HIF-1alpha expression in the neocortex of low-resistance rats. The first, brief phase appears after each hypoxic episode and rapidly disappears in normoxic conditions. The second increase in of HIF-1alpha expression occurs in 24 hours after the hypoxic episode.

Activity of mitochondrial ATP-dependent potassium channel in animals with different resistance to hypoxia before and after the course of hypoxic training.

Activity of mitochondrial ATP-dependent potassium channel in rats with high genetically determined resistance to hypoxia was higher than in sensitive animals. Adaptation of low resistant rats to hypoxia was accompanied by activation of the channel, facilitation of potassium recycling in mitochondria, and a decrease in the rate of H2O2 formation. Our results indicate that mitochondrial ATP-dependent potassium channel plays an important role in the delayed mechanisms of animal's adaptation to hypoxia.

Effects of preconditioning on the resistance to acute hypobaric hypoxia and their correction with selective antagonists of nicotinic receptors.

Hypobaric hypoxic preconditioning increased the resistance of low resistant and highly resistant rats to acute hypobaric hypoxia at a critical height. Intergroup differences in the resistance of rats to acute hypobaric hypoxia were not observed after hypobaric hypoxia and one variational series with a wide range of resistance (4.5-24.

Urgent reaction of the complement system to hypoxic exposure in rats sensitive to hypoxia.

Different modes of hypoxic exposure led to phasic changes in activities of the complement system components in rats sensitive to hypoxia starting from the first minutes of the posthypoxic period and persisting for 24 h and longer. The direction of shifts in the complement system depended on the duration and intensity of oxygen deficiency. Single one-hour interval hypoxia led to a moderate elevation of activities of virtually all the studied components.

Functioning of the mitochondrial ATP-dependent potassium channel in rats varying in their resistance to hypoxia. Involvement of the channel in the process of animal's adaptation to hypoxia.

The mechanism of tissue protection from ischemic damage by activation of the mitochondrial ATP-dependent K(+) channel (mitoK(ATP)) remains unexplored. In this work, we have measured, using various approaches, the ATP-dependent mitochondrial K(+) transport in rats that differed in their resistance to hypoxia. The transport was found to be faster in the hypoxia-resistant rats as compared to that in the hypoxia-sensitive animals.

Energotropic effect of succinate-containing derivatives of 3-hydroxypyridine.

Succinate-containing derivatives of 3-hydroxypyridine, mexidol and proxypin, serve as succinate donors for the respiratory chain and contribute to activation of the succinate oxidase pathway of oxidation. Under conditions of hypoxia, these changes promote recovery of aerobic energy production, normalization of intracellular ATP concentration, and development of the antihypoxic effect. Succinate-free analogues of the test compounds exhibit no such properties.

Development of resistance of an organism under various conditions of hypoxic preconditioning: role of the hypoxic period and reoxygenation.

Single exposure to moderate (10% O(2)) hypobaric, normobaric, and intermittent hypoxia is followed by a preconditioning response of the organism. The mechanisms for immediate adaptation are activated during the hypoxic period. Intermittent reoxygenation not only delays, but even suppresses this process.

Effect of several flavonoid-containing plant preparations on activity of mitochondrial ATP-dependent potassium channel.

Flavonoid-containing plant preparations (water soluble extracts of Pentaphylloides fruticosa [Extralife], Emblica officinalis Gaerth [Amla], and Bergenia crassifolia [Bergenia]) produced a dose-dependent and tissue-specific effect on activity of mitochondrial ATP-dependent potassium channel. The effect of these preparations was biphasic (activation and inhibition). The activating effect of Extralife was one order of magnitude higher than that of Amla and Bergenia and was observed in a wider concentration range.

Effect of intermittent normobaric hypoxia on kinetic properties of mitochondrial enzymes.

We studied the effect of intermittent normobaric hypoxia on the formation of adaptive signs and state of mitochondrial enzymes in the cerebral cortex of rats with different resistance to hypoxia. Kinetic parameters for mitochondrial enzymes in the substrate region of the respiratory chain of the cerebral cortex underwent various changes in low resistant and highly resistant rats over the first 2 h after 1-h intermittent normobaric hypoxia. Low resistant animals were characterized by more effective functioning of rotenone-sensitive NADH-cytochrome C reductase and succinate-cytochrome C reductase under conditions of increased reduction status of the cell.

[Energotropic, antihypoxic, and antioxidative effects of flavonoids].

Phytogenous flavonoid-containing agents (PFCA) are able to initiate electron flow bypassing the NAD-dependent region of respiratory chain, which is related with the activity of DT-diaphorase catalyzing two-electron reduction of quinones to hydroquinones and hydrogen peroxide in the presence of NADH and oxygen. This property is dramatically potentiated under the conditions of suppressed electron transport function of mitochondrial enzyme complex I (MEC I). In this process, part of the flow goes to the cytochrome region of respiratory chain and provides recovery of the MEC II and MEC III coupling function.

[The regulatory role of mitochondrial dysfunction in hypoxia and its interaction with transcription activity].

The mitochondrial respiratory chain participates in the performance of the signal system, which activates the realization of metabolic compensatory processes and coupled functional response to both single and repeated, long-term exposure to acute hypoxia. Under the conditions of reduced oxygen delivery to cells the mitochondrial respiratory chain is involved in the process of oxygen homeostasis regulation and modulates oxygen consumption, the rate of oxygen delivery from the extracellular milieu to mitochondria, and energy synthesis, activating hypoxia-specific transcription factors as well.

Behavioral peculiarities and reactions of brain dopaminergic systems in rats with different resistance to acute hypobaric hypoxia.

Locomotor activity in the open field test did not correlate with rat resistance to acute hypobaric hypoxia; there was a correlation between this resistance and rat behavior during acute stress. Immobility was characteristic of rats with low and particularly medium resistance to hypoxia; this reaction can be abolished by antidepressants. by contrast, highly resistant rats were mainly hyperactive.

[The long-term effect of one-time acute hypoxia on the behavior of rats with different typological characteristics].

Non-strain albino rats with the active type of behaviour (high motor activity and often visiting the center in the "open field" test) were found to be characterized by the longer time of survival at lifting to 11,000 m than the animals with the passive type of behaviour (low motor activity and lesser number of center visits). The latter were observed to increase their motor activity in the "open field" in 14 days after the single hypoxic influence.