Dominika Malinska

Methods to monitor ROS production by fluorescence microscopy and fluorometry.

Mitochondria are considered one of the main sources of reactive oxygen species (ROS). The overgeneration of ROS can evoke an intracellular state of oxidative stress, leading to permanent cell damage. Thus, the intracellular accumulation of ROS may not only disrupt the functions of specific tissues and organs but also lead to the premature death of the entire organism. Less severe increases in ROS levels may lead to the nonlethal oxidation of fundamental cellular components, such as proteins, phospholipids, and DNA, hence exerting a mutagenic effect that promotes oncogenesis and tumor progression. Here, we describe the use of chemical probes for the rapid detection of ROS in intact and permeabilized adherent cells by fluorescence microscopy and fluorometry. Moreover, after discussing the limitations described in the literature for the fluorescent probes presented herein, we recommend methods to assess the production of specific ROS in various fields of investigation, including the study of oncometabolism.

Sites of generation of reactive oxygen species in homogenates of brain tissue determined with the use of respiratory substrates and inhibitors

Reactive oxygen species (ROS) have been widely implicated in the pathogenesis of various neurological diseases and aging. But the exact sites of ROS generation in brain tissue remained so far elusive. Here, we provide direct experimental evidence that at least 50% of total ROS generation in succinate-oxidizing homogenates of brain tissue can be attributed to complex I of mitochondrial respiratory chain. Applying quantitative methods for ROS detection we observed in different preparations from human, rat and mouse brain (digitonin-permeabilized tissue homogenates and isolated mitochondria) a linear relationship between rate of oxygen consumption and ROS generation with succinate as mitochondrial substrate. This quantitative relationship indicates, that under the particular conditions of oxygen saturation about 1% of the corresponding respiratory chain electron flow is redirected to form superoxide. Since we observed in mouse and rat brain mitochondria a unique dependency of both forward and reverse electron flow-dependent mitochondrial H(2)O(2) production on NAD redox state, we substantiated previous evidence that the FMN moiety of complex I is the major donor of electrons for the single electron reduction of molecular oxygen.

Pharmacology of mitochondrial potassium channels: dark side of the field

Mitochondrial potassium channels play an important role in cytoprotection. Potassium channels in the inner mitochondrial membrane are modulated by inhibitors and activators (potassium channel openers) previously described for plasma membrane potassium channels. The majority of mitochondrial potassium channel modulators exhibit a broad spectrum of off‐target effects. These include uncoupling properties, inhibition of the respiratory chain and effects on cellular calcium homeostasis. Therefore, the rational application of channel inhibitors or activators is crucial to understanding the cellular consequences of mitochondrial channel inhibition or activation. Moreover, understanding their side‐effects should facilitate the design of a specific mitochondrial channel opener with cytoprotective properties. In this review, we discuss the complex interactions of potassium channel inhibitors and activators with cellular structures.

Mitochondrial potassium channels and reactive oxygen species

Pretreatment of tissues with potassium channel openers (KCOs) has been observed to be cytoprotective in a broad variety of insults. This phenomenon has been proposed to be intimately linked to activation of mitochondrial potassium channels which apparently modulate the mitochondrial production of reactive oxygen species (ROS). This critical review summarizes literature findings about the mitochondrial production of ROS, the action of KCOs on mitochondrial ROS production and the putative link to the cytoprotective action of these drugs.

Polyethylenimine-mediated impairment of mitochondrial membrane potential, respiration and membrane integrity: implications for nucleic acid delivery and gene therapy.

The 25 kDa branched polyethylenimine (PEI) is a highly efficient synthetic polycation used in transfection protocols, but also triggers mitochondrial-mediated apoptotic cell death processes where the mechanistic issues are poorly understood. We now demonstrate that PEI in a concentration- and time-dependent manner can affect functions (membrane potential, swelling and respiration) and ultrastructural integrity of freshly isolated rat liver mitochondria. The threshold concentration for detection of PEI-mediated impairment of rat liver mitochondrial functions is 3 μg/mL, however, lower PEI levels still exert some effects on mitochondrial morphology and respiration, and these may be related to the inherent membrane perturbing properties of this polycation. The PEI-mediated mitochondrial swelling phase is biphasic, with a fast decaying initial period (most prominent from 4 μg/mL PEI) followed by a slower, linear swelling response. The slow phase is presumably the result of a time-dependent transition permeability opening in mitochondria initially resistant to swelling/depolarization, but may further be related to PEI-induced nanoscale structural defects and/or formation of pores in the outer membrane. Respiration assessments further suggested that PEI in the presence of exogenous ADP behaves in a similar fashion to a slow-acting inhibitory compound. PEI further shows an uncoupling property that is detectable at low respiration rates. The relevance of these findings to PEI-mediated initiation of intrinsic apoptotic pathway is discussed.

Changes in mitochondrial reactive oxygen species synthesis during differentiation of skeletal muscle cells

Myogenesis is accompanied by an intensive metabolic remodeling. We investigated the mitochondrial reactive oxygen species (ROS) generation at different levels of skeletal muscle differentiation: in C2C12 myoblasts, in C2C12 myotubes and in adult mouse skeletal muscle. Differentiation was accompanied by an increase in mitochondrial content and respiratory chain activity. The detected ROS production levels correlated with mitochondrial content, being the lowest in the myoblasts. Unlike the adult skeletal muscle, myoblast ROS production was significantly stimulated by the complex I inhibitor rotenone. Our results show that mitochondria are an important ROS source in skeletal muscle cells. The substantial changes in mitochondrial ROS synthesis during skeletal muscle differentiation can be explained by intensive bioenergetic remodeling.

Effect of mtDNA point mutations on cellular bioenergetics.

This overview discusses the results of research on the effects of most frequent mtDNA point mutations on cellular bioenergetics. Thirteen proteins coded by mtDNA are crucial for oxidative phosphorylation, 11 of them constitute key components of the respiratory chain complexes I, III and IV and 2 of mitochondrial ATP synthase. Moreover, pathogenic point mutations in mitochondrial tRNAs and rRNAs generate abnormal synthesis of the mtDNA coded proteins. Thus, pathogenic point mutations in mtDNA usually disturb the level of key parameter of the oxidative phosphorylation, i.e. the electric potential on the inner mitochondrial membrane (Δψ), and in a consequence calcium signalling and mitochondrial dynamics in the cell. Mitochondrial generation of reactive oxygen species is also modified in the mutated cells. The results obtained with cultured cells and describing biochemical consequences of mtDNA point mutations are full of contradictions. Still they help elucidate the biochemical basis of pathologies and provide a valuable tool for finding remedies in the future. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).

Large-conductance K+ channel opener CGS7184 as a regulator of endothelial cell function.

Large-conductance Ca(2+)-activated potassium (BK(Ca)) channels are present in endothelium, but their regulatory role remains uncharacterized. The aim of the present study was to investigate the pharmacological effects of the BK(Ca) channel opener ethyl-1-[[(4-chlorophenyl)amino]oxo]-2-hydroxy-6-trifluoromethyl-1H-indole-3-carboxylate (CGS7184) on endothelium in the aorta and coronary circulation, particularly with regard to nitric oxide (NO)-dependent regulation of vascular tone, as well as effects of CGS7184 on NO production, calcium homeostasis, and mitochondrial function in cultured endothelial cells. The vasorelaxant action of CGS7184 was studied in coronary circulation and in the aorta using isolated perfused guinea pig heart and rat aortic rings, respectively. The effects of CGS7184 on calcium homeostasis, mitochondrial membrane potential, NO production, and mitochondrial respiration were tested in cultures of EA.hy 926 endothelial cells. The BK(Ca) channel opener CGS7184 caused a concentration-dependent (0.03-3 microM) relaxation of the rat aorta and coronary vasodilatation in the isolated guinea pig heart. Both responses were profoundly inhibited by the nitric oxide (NO) synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) (100 microM). CGS7184 (5 microM) also increased basal NO production in EA.hy 926 cells by approximately two-fold. Moreover, CGS7184 induced a concentration-dependent (0.1-10 microM) elevation in intracellular calcium concentration. Interestingly, CGS7184 affected mitochondrial function by causing mitochondrial potential depolarization and an increase in oxygen consumption in EA.hy 926 endothelial cells. The BK(Ca) channel opener CGS7184 activates NOS pathways and modulates mitochondrial function in the endothelium. Both effects may be triggered by the CGS7184-induced modulation of intracellular Ca(2+) homeostasis in EA.hy 926 endothelial cells.

Effects of resorcylidene aminoguanidine (RAG) on selected parameters of isolated rat liver mitochondria.

In the present investigation, we attempted to study possible mechanisms of the interactions of resorcylidene aminoguanidine (RAG), the agent with a recognized anti-glycation and antioxidative activity, with rat liver mitochondria. We hypothesized that RAG affects organization of the lipid bilayer in mitochondrial membranes and thus impairs transmembrane Ca(2+) redistribution, transmembrane potential, and respiration capacity. Isolated mitochondria were exposed to RAG (50-200 microM) and several parameters of their function monitored employing spectrofluorimetric, cytometric, and respirometric techniques. Mitochondrial membrane potential and membrane fluidity were tracked using the staining with rhodamine 123 (Rh123) and 1,6-diphenyl-1,3,5-hexatriene (DPH), respectively. Mitochondrial respiration and oxidative phosphorylation was monitored with a high-resolution respirometry, and mobilization of Ca(2+) was detected using spectrofluorimetry with Calcium Green 5-N. RAG depolarized and fluidized mitochondrial membrane, as deduced from reduced fluorescence of intramitochondrial Rh123 and decreased DPH fluorescence anisotropy. The slight inhibitory effect of 100-200 microM RAG on mitochondrial respiratory capacity was observed merely when monitored in the presence of ADP. The reduced sensitivity of mitochondria to calcium-induced depolarization was significant only at higher RAG concentrations (100-200 microM). Moreover, RAG induced pronounced conformational changes in two model proteins: bovine serum albumin and cytochrome c. These findings indicate that regardless of its depolarizing and fluidizing properties, RAG does not largely affect the mitochondrial respiration, although it may significantly lower oxidative phosphorylation when used at higher concentrations.

The Cytoprotective Action of the Potassium Channel Opener BMS-191095 in C2C12 Myoblasts is Related to the Modulation of Calcium Homeostasis

BMS-191095 is an opener of the mitochondrial ATP-regulated potassium channel, which has been shown to provide cytoprotection in models of ischemia-reperfusion induced injury in various tissues. This study aimed at checking the protective action of BMS-191095 under the conditions of oxidative stress or disruption of intracellular calcium homeostasis. Methods: The cytoprotective potential of BMS-191095 was tested in C2C12 myoblasts injured by treatment with H2O2 or calcium ionophore A23187. The influence of the opener on intracellular calcium levels, calpain activity and respiration rates were determined. Results: BMS-191095 protected myoblasts from calcium ionophore A23187-induced injury, but not from H H2O2-induced injury. A23187-mediated cell damage was also prevented by calpain inhibitor PD 150606. A23187 administration led to a transient increase in cytosolic calcium levels, concomitant activation of calpains and a decrease in state 3 respiration rates, indicating mitochondrial dysfunction. Co-administration of BMS-191095 diminished calpain activation in A23187-treated cells but did not prevent mitochondrial damage. In the presence of BMS-191095, restoration of cytosolic calcium concentrations to basal levels after A23187 treatment was considerably faster which may underly the reduced activation of calpains. Conclusion: The BMS-191095-mediated cytoprotection observed in C2C12 myoblasts results probably from modulation of intracellular calcium transients leading to prevention of calpain activation.