Preservation of the in vivo state of mitochondrial network for ex vivo physiological study of mitochondria

The Protective Effect of Uridine in a Rotenone-Induced Model of Parkinson's Disease: The Role of the Mitochondrial ATP-Dependent Potassium Channel

The effect of the modulators of the mitochondrial ATP-dependent potassium channel (mitoKATP) on the structural and biochemical alterations in the substantia nigra and brain tissues was studied in a rat model of Parkinson's disease induced by rotenone. It was found that, in experimental parkinsonism accompanied by characteristic motor deficits, both neurons and the myelin sheath of nerve fibers in the substantia nigra were affected. Changes in energy and ion exchange in brain mitochondria were also revealed. The nucleoside uridine, which is a source for the synthesis of the mitoKATP channel opener uridine diphosphate, was able to dose-dependently decrease behavioral disorders and prevent the death of animals, which occurred for about 50% of animals in the model. Uridine prevented disturbances in redox, energy, and ion exchanges in brain mitochondria, and eliminated alterations in their structure and the myelin sheath in the substantia nigra. Cytochemical examination showed that uridine restored the indicators of oxidative phosphorylation and glycolysis in peripheral blood lymphocytes. The specific blocker of the mitoKATP channel, 5-hydroxydecanoate, eliminated the positive effects of uridine, suggesting that this channel is involved in neuroprotection. Taken together, these findings indicate the promise of using the natural metabolite uridine as a new drug to prevent and, possibly, stop the progression of Parkinson's disease.

Uridine as a Regulator of Functional and Ultrastructural Changes in the Brain of Rats in a Model of 6-OHDA-Induced Parkinson's Disease

Using a model of Parkinson's disease (PD) induced by the bilateral injection of neurotoxin 6-hydroxydopamine (6-OHDA) into rat brain substantia nigra (SN), we showed uridine to exert a protective effect associated with activation of the mitochondrial ATP-dependent potassium (mitoK-ATP) channel. Injection of 4 µg neurotoxin evoked a 70% decrease in the time the experimental animal spent on the rod in the RotaRod test, an increase in the amount of lipid peroxides in blood serum and cerebral-cortex mitochondria and the rate of reactive oxygen species formation, and a decrease in Ca2+ retention in mitochondria. Herewith, lymphocytes featured an increase in the activity of lactate dehydrogenase, a cytosolic enzyme of glycolysis, without changes in succinate-dehydrogenase activity. Structural changes occurring in the SN and striatum manifested themselves in the destruction of mitochondria, degeneration of neurons and synapses, and stratification of myelin sheaths in them. Subcutaneous injections of 30 µg/kg uridine for 22 days restored the neurotoxin-induced changes in these parameters to levels close to the control. 5-Hydroxydecanoate (5 mg/kg), a specific mitoK-ATP channel inhibitor, eliminated the beneficial effect of uridine for almost all characteristics tested, indicating the involvement of the mitoK-ATP channel in the protective effect of uridine. The mechanism of the protective effect of uridine and its therapeutic applications for the prevention and treatment of PD are discussed.

Comparative Study of Functional Changes in Heart Mitochondria in Two Modes of Epinephrine Exposure Modeling Myocardial Injury in Rats

The parameters of coupled respiration and transport of calcium ions in mitochondria isolated from the heart of rats were studied in two modes of exposure to epinephrine for modelling myocardial damage. In 24 h after injection of 1.5 mg/kg epinephrine to rats, we observed a decrease in the efficiency of oxidative phosphorylation in heart mitochondria in the presence of both NADH- and FADH-dependent respiratory substrates. Increasing the epinephrine dose and exposure (2 mg/kg, 72 h) led to a more pronounced decrease in the ADP/O coefficient when succinate was used as a substrate, which indicated a predominant decrease in the activity of complex II of the respiratory chain. The injection of epinephrine in the two modes resulted in a decrease in the rate of calcium entry in rat heart mitochondria, but had no effect on mitochondrial calcium retention capacity, which reflects the resistance of the organelles to the induction of the Са²⁺-dependent pore. These findings suggest that both cardiomyopathy models in rats can be used to study the effectiveness of pharmacological therapy using mitochondria-targeted agents.

Activities of Succinate Dehydrogenase and Lactate Dehydrogenase in Blood Lymphocytes in Yakut Ground Squirrels Spermophilus undulatus During Hibernation and in the Active State

We studied energy metabolism in blood lymphocytes of Yakut ground squirrels Spermophilus undulatus in active state and during hibernation. Activities of succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH), marker enzymes of mitochondrial respiration and glycolysis, were measured by a cytobiochemical method based on quantitative assessment of a product of NBT reduction to diformazan in blood lymphocytes immobilized on glass. To measure SDH and LDH activities, cytobiochemical staining of immobilized cells was performed with succinate, lactate, and NAD. In the state of hibernation, SDH activity decreased by 3 times and LDH activity decreased by 10 times or more. These results suggest that the decrease in metabolic activity in lymphocytes of ground squirrels during hypothermia is associated with inhibition of glycolysis, rather than with mitochondrial energy supply.

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.

Mitochondrial plasticity in the cerebellum of two anoxia-tolerant sharks: contrasting responses to anoxia/reoxygenation

Exposure to anoxia leads to rapid ATP depletion, alters metabolic pathways and exacerbates succinate accumulation. Upon re-oxygenation, the preferential oxidation of accumulated succinate most often impairs mitochondrial function. Few species can survive prolonged periods of hypoxia and anoxia at tropical temperatures and those that do may rely on mitochondria plasticity in response to disruptions to oxygen availability. Two carpet sharks, the epaulette shark (Hemiscyllium ocellatum; ES) and the grey carpet shark (Chiloscyllium punctatum; GCS) display different adaptive responses to prolonged anoxia: while the ES enters energy conserving metabolic depression, the GCS temporarily elevates its haematocrit prolonging oxygen delivery. High-resolution respirometry was used to investigate mitochondrial function in the cerebellum, a highly metabolically active organ that is oxygen sensitive and vulnerable to injury after anoxia/re-oxygenation (AR).

Succinate was titrated into cerebellar preparations in vitro, with or without pre-exposure to AR, then the activity of mitochondrial complexes was examined. Like most vertebrates, GCS mitochondria significantly increased succinate oxidation rates, with impaired complex I function post-AR. In contrast, ES mitochondria inhibited succinate oxidation rates and both complex I and II capacities were conserved, resulting in preservation of oxidative phosphorylation capacity post-AR.

Divergent mitochondrial plasticity elicited by elevated succinate post A/R parallels the inherently divergent physiological adaptations of these animals to prolonged anoxia, namely the absence (GCS) and presence of metabolic depression (ES). Since anoxia tolerance in these species also occurs at temperatures close to that of humans, examining their mitochondrial responses to AR could provide insights for novel interventions in clinical settings.

Mitochondria in smooth muscle cells of viscera

The spatial density of mitochondria was studied by thin-section electron microscopy in smooth muscles of bladder, iris and gut in mice, rats, guinea-pigs and sheep. Morphometric data included areas of muscle cell profiles (~6,000 muscle cells were measured) and areas of their mitochondria (more than three times as many). The visual method delivers accurate estimates of the extent of the chondrioma (the ensemble of mitochondria in a cell), measuring all and only the mitochondria in each muscle cell and no other cells. The digital records obtained can be used again for checks and new searches. Spatial density of mitochondria varies between about 2 and 10% in different muscles in different species. In contrast, there is consistency of mitochondrial density within a given muscle in a given species. For each muscle in each species there is a characteristic mitochondrial density with modest variation between experiments. On the basis of data from serial sections in the rat detrusor muscle, mitochondrial density varies very little between the muscle cells, each cell having a value close to that for the whole muscle. Mitochondrial density is different in a given muscle, e.g., ileal circular muscle, from the four mammalian species, with highest values in mouse and lowest in sheep; in mice the mitochondrial density is nearly three time higher that in sheep. In a given species there are characteristic variations between different muscles. For example, the bladder detrusor muscle has markedly fewer mitochondria than the ileum, and the iris has markedly more.

Fermentation Conditions and Media Optimization for Isocitric Acid Production from Ethanol by Yarrowia lipolytica

Isocitric acid exists in the form of four stereoisomers, of which only the threo-Ds-form (ICA) is a natural active compound, an intermediate of Krebs cycle, and suitable for nutritional and pharmaceutical use. In this paper, we propose a method for ICA production from ethanol by yeast Yarrowia lipolytica. The effects of temperature, pH of the medium, and aeration on the growth of the producer Y. lipolytica VKM Y-2373 and synthesis of ICA were studied. An optimal fermentation regime, which ensures a good growth of the producer and directed synthesis of the target product, was determined. The producer is advised to carry out cultivation at 29°C and various pH of the medium and the oxygen concentration (pH 5 and pO₂ 20–25% (of saturation) during the growth period and pH 6 and pO₂ 50–55% (of saturation) during the acid formation) on a nutrient medium containing an increased content of zinc (0.6 mg/L), iron (1.2 mg/L), and 30 mM itaconic acid (inhibitor of isocitrate lyase—the key enzyme of ICA metabolism) should also be introduced into the nutrition medium. Such fermentation production mode provides 90.5 g/L ICA with process selectivity of 80%, mass yield (Y_ICA) of 0.77 g/g, and energy yield (η_ICA) of 0.278 g/g.

Substrate-Specific Reduction of Tetrazolium Salts by Isolated Mitochondria, Tissues, and Leukocytes

Tetrazolium salts are commonly used in cytochemical and biochemical studies as indicators of metabolic activity of cells. Formazans, formed by reduction of tetrazolium salts, behave as pseudo-solutions during initial incubation, which allows monitoring their optical density throughout incubation. The criteria and conditions for measuring oxidative activity of mitochondria and dehydrogenase activity in reduction of nitroblue tetrazolium (NBT) and methyl thiazolyl tetrazolium (MTT) in suspensions of isolated mitochondria, tissue homogenates, and leukocytes were investigated in this work. We found that the reduction of these two acceptors depended on the oxidized substrate - NBT was reduced more readily during succinate oxidation, while MTT - during oxidation of NAD-dependent substrates. Reduction of both acceptors was more sensitive to dehydrogenase inhibitors that to respiratory chain inhibitors. The reduction of NBT in isolated mitochondria, in leukocytes in the presence of digitonin, and in liver and kidney homogenates was completely blocked by succinate dehydrogenase inhibitors - malonate and TTFA. Based on these criteria, activation of succinate oxidation was revealed from the increase in malonate-sensitive fraction of the reduced NBT under physiological stress. The effect of progesterone and its synthetic analogs on oxidation of NAD-dependent substrates by mitochondria was investigated using MTT. Both acceptors are also reduced by superoxide anion; the impact of this reaction is negligible or completely absent under physiological conditions, but can become detectable on generation of superoxide induced by inhibitors of individual enzyme complexes or in the case of mitochondrial dysfunction. The results indicate that the recording of optical density of reduced NBT and MTT is a highly sensitive method for evaluation of metabolic activity of mitochondria applicable for different incubation conditions, it offers certain advantages in comparison with other methods (simultaneous incubation of a large set of probes in spectral cuvettes or plates); moreover, it allows determination of activity of separate redox-dependent enzymes when selective inhibitors are available.

Impairment of mitochondrial function of rat hepatocytes by high fat diet and oxidative stress

Fatty liver disease associated with obesity is an important medical problem and the mechanisms for lipid accumulation in hepatocytes are not fully elucidated yet. Recent findings indicate that mitochondria play an important role in this process. Our data on hepatocytes in which mitochondria are in contact with other cytosolic structures important for their function, extend observations obtained on isolated mitochondria and confirm inhibition of Complex I activity in hepatocytes isolated from rats fed by high fat diet (HFD) compared with controls fed by standard diet (STD). Furthermore we have found that HFD-hepatocytes are more sensitive to the peroxidative stress because under these conditions also Complex II activity is disturbed. Therefore in HFD animals decrease of Complex I activity cannot be compensated by Complex II substrates as in STD hepatocytes. Our data thus indicates that combination of HFD and peroxidative stress potentiates HFD damaging effect of mitochondria because both branches of the respiratory chain (NADH- and flavoprotein-dependent) are disturbed.

Biguanides inhibit complex I, II and IV of rat liver mitochondria and modify their functional properties

In this study, we focused on an analysis of biguanides effects on mitochondrial enzyme activities, mitochondrial membrane potential and membrane permeability transition pore function. We used phenformin, which is more efficient than metformin, and evaluated its effect on rat liver mitochondria and isolated hepatocytes. In contrast to previously published data, we found that phenformin, after a 5 min pre-incubation, dose-dependently inhibits not only mitochondrial complex I but also complex II and IV activity in isolated mitochondria. The enzymes complexes inhibition is paralleled by the decreased respiratory control index and mitochondrial membrane potential. Direct measurements of mitochondrial swelling revealed that phenformin increases the resistance of the permeability transition pore to Ca(2+) ions. Our data might be in agreement with the hypothesis of Schäfer (1976) that binding of biguanides to membrane phospholipids alters membrane properties in a non-specific manner and, subsequently, different enzyme activities are modified via lipid phase. However, our measurements of anisotropy of fluorescence of hydrophobic membrane probe diphenylhexatriene have not shown a measurable effect of membrane fluidity with the 1 mM concentration of phenformin that strongly inhibited complex I activity. Our data therefore suggest that biguanides could be considered as agents with high efficacy but low specifity.

Effects of phospholipid hepatoprotectors on apoptosis during experimental liver pathology induced by isoniazid and paracetamol

Phospholipid hepatoprotectors essentiale, eplir, and their combinations with succinic acid decreased the relative content of apoptotic lymphocytes and granulocytes in the blood, content of TNF-α, total and indirect bilirubin, and activities of transaminases and alkaline phosphatase and increase the content of IL-10 in rats with experimental intoxication induced by isoniazid and paracetamol. A combination of eplir and succinic acid was most effective in preventing the development of leukocyte apoptosis.

Burst of succinate dehydrogenase and α-ketoglutarate dehydrogenase activity in concert with the expression of genes coding for respiratory chain proteins underlies short-term beneficial physiological stress in mitochondria

Conditions for the realization in rats of moderate physiological stress (PHS) (30-120 min) were selected, which preferentially increase adaptive restorative processes without adverse responses typical of harmful stress (HST). The succinate dehydrogenase (SDH) and α-ketoglutarate dehydrogenase (KDH) activity and the formation of reactive oxygen species (ROS) in mitochondria were measured in lymphocytes by the cytobiochemical method, which detects the regulation of mitochondria in the organism with high sensitivity. These mitochondrial markers undergo an initial 10-20-fold burst of activity followed by a decrease to a level exceeding the quiescent state 2-3-fold by 120 min of PHS. By 30-60 min, the rise in SDH activity was greater than in KDH activity, while the activity of KDH prevailed over that of SDH by 120 min. The attenuation of SDH hyperactivity during PHS occurs by a mechanism other than oxaloacetate inhibition developed under HST. The dynamics of SDH and KDH activity corresponds to the known physiological replacement of adrenergic regulation by cholinergic during PHS, which is confirmed here by mitochondrial markers because their activity reflects these two types of nerve regulation, respectively. The domination of cholinergic regulation provides the overrestoration of expenditures for activity. In essence, this phenomenon corresponds to the training of the organism. It was first revealed in mitochondria after a single short-time stress episode. The burst of ROS formation was congruous with changes in SDH and KDH activity, as well as in ucp2 and cox3 expression, while the activity of SDH was inversely dependent on the expression of the gene of its catalytic subunit in the spleen. As the SDH activity enhanced, the expression of the succinate receptor decreased with subsequent dramatic rise when the activity was becoming lower. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaption and therapy.

Evaluation of basic mitochondrial functions using rat tissue homogenates

The primary attempt in diagnostic and experimental studies of numerous pathological states associated with mitochondrial dysfunction is a precise evaluation of changes in function, content and structure of mitochondrial OXPHOS system. The analysis of rat heart, liver, brain and kidney by oxygraphy, enzyme activities, membrane potential, and BN/SDS-PAGE western blotting demonstrated that tissue homogenates can substitute for isolated mitochondria, providing comparable qualitative mitochondrial parameters. The use of homogenate avoids the loss of the majority of mitochondria during their isolation. Only 50-100mg of the tissue is required for the complex OXPHOS analysis, i.e. five times less as compared with isolated mitochondria.