The mitochondrion is a major source of reactive oxygen species (ROS). Superoxide (O(2)(*-)) is generated under specific bioenergetic conditions at several sites within the electron-transport system; most is converted to H(2)O(2) inside and outside the mitochondrial matrix by superoxide dismutases. H(2)O(2) is a major chemical messenger that, in low amounts and with its products, physiologically modulates cell function. The redox state and ROS scavengers largely control the emission (generation scavenging) of O(2)(*-). Cell ischemia, hypoxia, or toxins can result in excess O(2)(*-) production when the redox state is altered and the ROS scavenger systems are overwhelmed. Too much H(2)O(2) can combine with Fe(2+) complexes to form reactive ferryl species (e.g., Fe(IV) = O(*)). In the presence of nitric oxide (NO(*)), O(2)(*-) forms the reactant peroxynitrite (ONOO(-)), and ONOOH-induced nitrosylation of proteins, DNA, and lipids can modify their structure and function. An initial increase in ROS can cause an even greater increase in ROS and allow excess mitochondrial Ca(2+) entry, both of which are factors that induce cell apoptosis and necrosis. Approaches to reduce excess O(2)(*-) emission include selectively boosting the antioxidant capacity, uncoupling of oxidative phosphorylation to reduce generation of O(2)(*-) by inducing proton leak, and reversibly inhibiting electron transport. Mitochondrial cation channels and exchangers function to maintain matrix homeostasis and likely play a role in modulating mitochondrial function, in part by regulating O(2)(*-) generation. Cell-signaling pathways induced physiologically by ROS include effects on thiol groups and disulfide linkages to modify posttranslationally protein structure to activate/inactivate specific kinase/phosphatase pathways. Hypoxia-inducible factors that stimulate a cascade of gene transcription may be mediated physiologically by ROS. Our knowledge of the role played by ROS and their scavenging systems in modulation of cell function and cell death has grown exponentially over the past few years, but we are still limited in how to apply this knowledge to develop its full therapeutic potential.

Reactive oxygen species (ROS) are believed to be involved in triggering cardiac ischemic preconditioning (IPC). Decreased formation of ROS on reperfusion after prolonged ischemia may in part underlie protection by IPC. In heart models, these contentions have been based either on the effect of ROS scavengers to abrogate IPC-induced preservation or on a measurement of oxidation products on reperfusion. Using spectrophotofluorometry at the left ventricular wall and the fluorescent probe dihydroethidium (DHE), we measured intracellular ROS superoxide (O(2)(-).) continuously in isolated guinea pig heart and tested the effect of IPC and the O(2)(-). scavenger manganese(III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) on O(2)(-). formation throughout the phases of preconditioning (PC), 30-min ischemia and 60-min reperfusion (I/R). IPC was evidenced by improved contractile function and reduced infarction; MnTBAP abrogated these effects. Brief PC pulses increased O(2)(-). during the ischemic but not the reperfusion phase. O(2)(-). increased by 35% within 1 min of ischemia, increased further to 95% after 20 min of ischemia, and decreased slowly on reperfusion. In the IPC group, O(2)(-). was not elevated over 35% during index ischemia and was not increased at all on reperfusion; these effects were abrogated by MnTBAP. Our results directly demonstrate how intracellular ROS increase in intact hearts during IPC and I/R and clarify the role of ROS in triggering and mediating IPC.

Chen Q, Camara AK, Stowe DF, Hoppel CL, Lesnefsky EJ. Modulation of electron transport protects cardiac mitochondria and decreases myocardial injury during ischemia and reperfusion. Am J Physiol Cell Physiol 292: C137-C147, 2007. First published September 13, 2006; doi:10.1152/ajpcell.00270.2006.-Mitochondria are increasingly recognized as lynchpins in the evolution of cardiac injury during ischemia and reperfusion. This review addresses the emerging concept that modulation of mitochondrial respiration during and immediately following an episode of ischemia can attenuate the extent of myocardial injury. The blockade of electron transport and the partial uncoupling of respiration are two mechanisms whereby manipulation of mitochondrial metabolism during ischemia decreases cardiac injury. Although protection by inhibition of electron transport or uncoupling of respiration initially appears to be counterintuitive, the continuation of mitochondrial oxidative phosphorylation in the pathological milieu of ischemia generates reactive oxygen species, mitochondrial calcium overload, and the release of cytochrome c. The initial target of these deleterious mitochondrial-driven processes is the mitochondria themselves. Consequences to the cardiomyocyte, in turn, include oxidative damage, the onset of mitochondrial permeability transition, and activation of apoptotic cascades, all favoring cardiomyocyte death. Ischemia-induced mitochondrial damage carried forward into reperfusion further amplifies these mechanisms of mitochondrial-driven myocyte injury. Interruption of mitochondrial respiration during early reperfusion by pharmacologic blockade of electron transport or even recurrent hypoxia or brief ischemia paradoxically decreases cardiac injury. It increasingly appears that the cardioprotective paradigms of ischemic preconditioning and postconditioning utilize modulation of mitochondrial oxidative metabolism as a key effector mechanism. The initially counterintuitive approach to inhibit mitochondrial respiration provides a new cardioprotective paradigm to decrease cellular injury during both ischemia and reperfusion.cardiolipin; cytochrome c; complex I; cytochrome oxidase MITOCHONDRIA are both targets and sources of injury during cardiac ischemia and reperfusion. This review addresses the emerging concept that modulation of mitochondrial oxidative metabolism during ischemia or early reperfusion protects mitochondrial function and decreases myocardial cell death. Mitochondria contribute to their own damage during ischemia, since blockade of electron transport immediately before ischemia dramatically attenuates damage to mitochondrial electron transport, with preserved oxidative phosphorylation, retention of cytochrome c, and decreased release of reactive oxygen species (ROS). Ischemic preconditioning (IPC) leads to a partial uncoupling of mitochondrial respiration, resulting in decreased mitochondrial injury following subsequent sustained ischemia. A substantial portion of damage to mitochondrial electron transport and oxi...

The mitochondrion is the most important organelle in determining continued cell survival and cell death. Mitochondrial dysfunction leads to many human maladies, including cardiovascular diseases, neurodegenerative disease, and cancer. These mitochondria-related pathologies range from early infancy to senescence. The central premise of this review is that if mitochondrial abnormalities contribute to the pathological state, alleviating the mitochondrial dysfunction would contribute to attenuating the severity or progression of the disease. Therefore, this review will examine the role of mitochondria in the etiology and progression of several diseases and explore potential therapeutic benefits of targeting mitochondria in mitigating the disease processes. Indeed, recent advances in mitochondrial biology have led to selective targeting of drugs designed to modulate and manipulate mitochondrial function and genomics for therapeutic benefit. These approaches to treat mitochondrial dysfunction rationally could lead to selective protection of cells in different tissues and various disease states. However, most of these approaches are in their infancy.

Mitochondria are the key source of ATP that fuels cellular functions, and they are also central in cellular signaling, cell division and apoptosis. Dysfunction of mitochondria has been implicated in a wide range of diseases, including neurodegenerative and cardiac diseases, and various types of cancer. One of the key proteins that regulate mitochondrial function is the voltage-dependent anion channel 1 (VDAC1), the most abundant protein on the outer membrane of mitochondria. VDAC1 is the gatekeeper for the passages of metabolites, nucleotides, and ions; it plays a crucial role in regulating apoptosis due to its interaction with apoptotic and anti-apoptotic proteins, namely members of the Bcl-2 family of proteins and hexokinase. Therefore, regulation of VDAC1 is crucial not only for metabolic functions of mitochondria, but also for cell survival. In fact, multiple lines of evidence have confirmed the involvement of VDAC1 in several diseases. Consequently, modulation or dysregulation of VDAC1 function can potentially attenuate or exacerbate pathophysiological conditions. Understanding the role of VDAC1 in health and disease could lead to selective protection of cells in different tissues and diverse diseases. The purpose of this review is to discuss the role of VDAC1 in the pathogenesis of diseases and as a potentially effective target for therapeutic management of various pathologies.

Aim Damage to the mitochondrial electron transport chain (ETC) occurs during ischaemia. Blockade of electron flow in the ETC just before ischaemia with the reversible complex I inhibitor amobarbital protects isolated mitochondria against ischaemic damage and preserves oxidative phosphorylation and cytochrome c content. We hypothesized that brief amobarbital perfusion just before ischaemia would improve cardiac recovery and decrease infarct size after ischaemia and reperfusion (IR) ] were significantly reduced, NADH-FAD redox state was preserved and cardiac function was markedly improved in the amobarbital group; infarct size was smaller in the amobarbital group compared to the untreated group. Conclusion Temporary blockade of mitochondrial complex I activity by amobarbital protects hearts by reducing production of O 2 2 † and mtCa 2þ loading during IR injury.

ATP-sensitive K+ channel opening in inner mitochondrial membranes protects hearts from ischemia-reperfusion (I/R) injury. Opening of the Big conductance Ca2+-sensitive K+ channel (BK(Ca)) is now also known to elicit cardiac preconditioning. We investigated the role of the pharmacological opening of the BK(Ca) channel on inducing mitochondrial preconditioning during I/R and the role of O2-derived free radicals in modulating protection by putative mitochondrial (m)BK(Ca) channel opening. Left ventricular (LV) pressure (LVP) was measured with a balloon and transducer in guinea pig hearts isolated and perfused at constant pressure. NADH, reactive oxygen species (ROS), principally superoxide (O2(-*)), and m[Ca2+] were measured spectrophotofluorometrically at the LV free wall using autofluorescence and fluorescent dyes dihydroethidium and indo 1, respectively. BK(Ca) channel opener 1-(2'-hydroxy-5'-trifluoromethylphenyl)-5-trifluoromethyl-2(3H)benzimid-axolone (NS; NS-1619) was given for 15 min, ending 25 min before 30 min of global I/R. Either Mn(III)tetrakis(4-benzoic acid)porphyrin (TB; MnTBAP), a synthetic dismutator of O2(-*), or an antagonist of the BK(Ca) channel paxilline (PX) was given alone or for 5 min before, during, and 5 min after NS. NS pretreatment resulted in a 2.5-fold increase in developed LVP and a 2.5-fold decrease in infarct size. This was accompanied by less O2(-*) generation, decreased m[Ca2+], and more normalized NADH during early ischemia and throughout reperfusion. Both TB and PX antagonized each preconditioning effect. This indicates that 1) NS induces a mitochondrial-preconditioned state, evident during early ischemia, presumably on mBK(Ca) channels; 2) NS effects are blocked by BK(Ca) antagonist PX; and 3) NS-induced preconditioning is dependent on the production of ROS. Thus NS may induce mitochondrial ROS release to initiate preconditioning.

Hypothermic perfusion at 17 degrees C caused moderate and reversible changes in mitochondrial function. However, hypothermia protects during ischemia, as shown by preservation of mitochondrial NADH energy balance and prevention of deleterious increases in m[Ca2+] and ROS formation. The close temporal relations of these factors during cooling and during ischemia suggest a causal link between mCa2+, mitochondrial energy balance, and ROS production.