The modulation of oxygen radical production by nitric oxide in mitochondria

Calcium-Dependent Interaction of Nitric Oxide Synthase with Cytochrome c Oxidase: Implications for Brain Bioenergetics

Targeted nitric oxide production is relevant for maintaining cellular energy production, protecting against oxidative stress, regulating cell death, and promoting neuroprotection. This study aimed to characterize the putative interaction of nitric-oxide synthase with mitochondrial proteins. The primary finding of this study is that cytochrome c oxidase (CCO) subunit IV (CCOIV) is associated directly with NOS in brain mitochondria when calcium ions are present. The matrix side of CCOIV binds to the N-terminus of NOS, supported by the abrogation of the binding by antibodies towards the N-terminus of NOS. Evidence supporting the interaction between CCOIV and NOS was provided by the coimmunoprecipitation of NOS from detergent-solubilized whole rat brain mitochondria with antibodies to CCOIV and the coimmunoprecipitation of CCOIV from crude brain NOS preparations using antibodies to NOS. The CCOIV domain that interacts with NOS was identified using a series of overlapping peptides derived from the primary sequence of CCOIV. As calcium ions not only activate NOS, but also facilitate the docking of NOS to CCOIV, this study points to a dynamic mechanism of controlling the bioenergetics by calcium changes, thereby adapting bioenergetics to cellular demands.

Mitochondrial bioenergetics decay in aging: beneficial effect of melatonin

Aging is a biological process characterized by progressive decline in physiological functions, increased oxidative stress, reduced capacity to respond to stresses, and increased risk of contracting age-associated disorders. Mitochondria are referred to as the powerhouse of the cell through their role in the oxidative phosphorylation to generate ATP. These organelles contribute to the aging process, mainly through impairment of electron transport chain activity, opening of the mitochondrial permeability transition pore and increased oxidative stress. These events lead to damage to proteins, lipids and mitochondrial DNA. Cardiolipin, a phospholipid of the inner mitochondrial membrane, plays a pivotal role in several mitochondrial bioenergetic processes as well as in mitochondrial-dependent steps of apoptosis and in mitochondrial membrane stability and dynamics. Cardiolipin alterations are associated with mitochondrial bienergetics decline in multiple tissues in a variety of physiopathological conditions, as well as in the aging process. Melatonin, the major product of the pineal gland, is considered an effective protector of mitochondrial bioenergetic function. Melatonin preserves mitochondrial function by preventing cardiolipin oxidation and this may explain, at least in part, the protective role of this compound in mitochondrial physiopathology and aging. Here, mechanisms through which melatonin exerts its protective role against mitochondrial dysfunction associated with aging and age-associated disorders are discussed.

Endogenous nitric oxide formation in cardiac myocytes does not control respiration during β-adrenergic stimulation

KEY POINTS

In the heart, endothelial nitric oxide (NO) controls oxygen consumption in the working heart through paracrine mechanisms. While cardiac myocytes contain several isoforms of NO synthases, it is unclear whether these can control respiration in an intracrine fashion. A long-standing controversy is whether a NOS exists within mitochondria. By combining fluorescence technologies with electrical field stimulation or the patch-clamp technique in beating cardiac myocytes, we identified a neuronal NO synthase (nNOS) as the most relevant source of intracellular NO during β-adrenergic stimulation, while no evidence for a mitochondria-located NOS was obtained. The amounts of NO produced by non-mitochondrial nNOS were insufficient to regulate respiration during β-adrenergic stimulation, arguing against intracrine control of respiration by NO within cardiac myocytes.

ABSTRACT

Endothelial nitric oxide (NO) controls cardiac oxygen (O₂ ) consumption in a paracrine way by slowing respiration at the mitochondrial electron transport chain. While NO synthases (NOSs) are also expressed in cardiac myocytes, it is unclear whether they control respiration in an intracrine way. Furthermore, the existence of a mitochondrial NOS is controversial. Here, by combining fluorescence imaging with electrical field stimulation, the patch-clamp method and knock-out technology, we determined the sources and consequences of intracellular NO formation during workload transitions in isolated murine and guinea pig cardiac myocytes and mitochondria. Using 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF) as a fluorescent NO-sensor that locates to the cytosol and mitochondria, we observed that NO increased by ∼12% within 3 min of β-adrenergic stimulation in beating cardiac myocytes. This NO stems from neuronal NOS (nNOS), but not endothelial (eNOS). After patch clamp-mediated dialysis of cytosolic DAF, the remaining NO signals (mostly mitochondrial) were blocked by nNOS deletion, but not by inhibiting the mitochondrial Ca²⁺ uniporter with Ru360. While in isolated mitochondria exogenous NO inhibited respiration and reduced the NAD(P)H redox state, pyridine nucleotide redox states were unaffected by pharmacological or genetic disruption of endogenous nNOS or eNOS during workload transitions in cardiac myoctyes. We conclude that under physiological conditions, nNOS is the most relevant source for NO in cardiac myocytes, but this nNOS is not located in mitochondria and does not control respiration. Therefore, cardiac O₂ consumption is controlled by endothelial NO in a paracrine, but not intracrine, fashion.

Novel Perspectives in Redox Biology and Pathophysiology of Failing Myocytes: Modulation of the Intramyocardial Redox Milieu for Therapeutic Interventions-A Review Article from the Working Group of Cardiac Cell Biology, Italian Society of Cardiology

The prevalence of heart failure (HF) is still increasing worldwide, with enormous human, social, and economic costs, in spite of huge efforts in understanding pathogenetic mechanisms and in developing effective therapies that have transformed this syndrome into a chronic disease. Myocardial redox imbalance is a hallmark of this syndrome, since excessive reactive oxygen and nitrogen species can behave as signaling molecules in the pathogenesis of hypertrophy and heart failure, leading to dysregulation of cellular calcium handling, of the contractile machinery, of myocardial energetics and metabolism, and of extracellular matrix deposition. Recently, following new interesting advances in understanding myocardial ROS and RNS signaling pathways, new promising therapeutical approaches with antioxidant properties are being developed, keeping in mind that scavenging ROS and RNS tout court is detrimental as well, since these molecules also play a role in physiological myocardial homeostasis.

Oxidative stress, cardiolipin and mitochondrial dysfunction in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is today considered the most common form of chronic liver disease, affecting a high proportion of the population worldwide. NAFLD encompasses a large spectrum of liver damage, ranging from simple steatosis to steatohepatitis, advanced fibrosis and cirrhosis. Obesity, hyperglycemia, type 2 diabetes and hypertriglyceridemia are the most important risk factors. The pathogenesis of NAFLD and its progression to fibrosis and chronic liver disease is still unknown. Accumulating evidence indicates that mitochondrial dysfunction plays a key role in the physiopathology of NAFLD, although the mechanisms underlying this dysfunction are still unclear. Oxidative stress is considered an important factor in producing lethal hepatocyte injury associated with NAFLD. Mitochondrial respiratory chain is the main subcellular source of reactive oxygen species (ROS), which may damage mitochondrial proteins, lipids and mitochondrial DNA. Cardiolipin, a phospholipid located at the level of the inner mitochondrial membrane, plays an important role in several reactions and processes involved in mitochondrial bioenergetics as well as in mitochondrial dependent steps of apoptosis. This phospholipid is particularly susceptible to ROS attack. Cardiolipin peroxidation has been associated with mitochondrial dysfunction in multiple tissues in several physiopathological conditions, including NAFLD. In this review, we focus on the potential roles played by oxidative stress and cardiolipin alterations in mitochondrial dysfunction associated with NAFLD.

Mitochondrial ion channels/transporters as sensors and regulators of cellular redox signaling

SIGNIFICANCE

Mitochondrial ion channels/transporters and the electron transport chain (ETC) serve as key sensors and regulators for cellular redox signaling, the production of reactive oxygen species (ROS) and nitrogen species (RNS) in mitochondria, and balancing cell survival and death. Although the functional and pharmacological characteristics of mitochondrial ion transport mechanisms have been extensively studied for several decades, the majority of the molecular identities that are responsible for these channels/transporters have remained a mystery until very recently.

RECENT ADVANCES

Recent breakthrough studies uncovered the molecular identities of the diverse array of major mitochondrial ion channels/transporters, including the mitochondrial Ca2+ uniporter pore, mitochondrial permeability transition pore, and mitochondrial ATP-sensitive K+ channel. This new information enables us to form detailed molecular and functional characterizations of mitochondrial ion channels/transporters and their roles in mitochondrial redox signaling.

CRITICAL ISSUES

Redox-mediated post-translational modifications of mitochondrial ion channels/transporters and ETC serve as key mechanisms for the spatiotemporal control of mitochondrial ROS/RNS generation.

FUTURE DIRECTIONS

Identification of detailed molecular mechanisms for redox-mediated regulation of mitochondrial ion channels will enable us to find novel therapeutic targets for many diseases that are associated with cellular redox signaling and mitochondrial ion channels/transporters.

Metabolic Stimulation of Plant Phenolics for Food Preservation and Health

Plant phenolics as secondary metabolites are key to a plant's defense response against biotic and abiotic stresses. These phytochemicals are also increasingly relevant to food preservation and human health in terms of chronic disease management. Phenolic compounds from different food crops with different chemical structures and biological functions have the potential to act as natural antioxidants. Plant-based human foods are rich with these phenolic phytochemicals and can be used effectively for food preservation and bioactive enrichments through metabolic stimulation of key pathways. Phenolic metabolites protect against microbial degradation of plant-based foods during postharvest storage. Phenolics not only provide biotic protection but also help to counter biochemical and physical food deteriorations and to enhance shelf life and nutritional quality. This review summarizes the role of metabolically stimulated plant phenolics in food preservation and their impact on the prevention of oxidative stress–induced human diseases.

Mitochondrial pathways, permeability transition pore, and redox signaling in cardioprotection: therapeutic implications

Reperfusion therapy is the indispensable treatment of acute myocardial infarction (AMI) and must be applied as soon as possible to attenuate the ischemic insult. However, reperfusion is responsible for additional myocardial damage likely involving opening of the mitochondrial permeability transition pore (mPTP). A great part of reperfusion injury occurs during the first minute of reperfusion. The prolonged opening of mPTP is considered one of the endpoints of the cascade to myocardial damage, causing loss of cardiomyocyte function and viability. Opening of mPTP and the consequent oxidative stress due to reactive oxygen and nitrogen species (ROS/RNS) are considered among the major mechanisms of mitochondrial and myocardial dysfunction. Kinases and mitochondrial components constitute an intricate network of signaling molecules and mitochondrial proteins, which interact in response to stressors. Cardioprotective pathways are activated by stimuli such as preconditioning and postconditioning (PostC), obtained with brief intermittent ischemia or with pharmacological agents, which drastically reduce the lethal ischemia/reperfusion injury. The protective pathways converging on mitochondria may preserve their function. Protection involves kinases, adenosine triphosphate-dependent potassium channels, ROS signaling, and the mPTP modulation. Some clinical studies using ischemic PostC during angioplasty support its protective effects, and an interesting alternative is pharmacological PostC. In fact, the mPTP desensitizer, cyclosporine A, has been shown to induce appreciable protections in AMI patients. Several factors and comorbidities that might interfere with cardioprotective signaling are considered. Hence, treatments adapted to the characteristics of the patient (i.e., phenotype oriented) might be feasible in the future.

Effect of garlic-derived organosulfur compounds on mitochondrial function and integrity in isolated mouse liver mitochondria

The objectives of this work were to evaluate the direct effects of diallysulfide (DAS) and diallyldisulfide (DADS), two major organosulfur compounds of garlic oil, on mitochondrial function and integrity, by using isolated mouse liver mitochondria in a cell-free system. DADS produced concentration-dependent mitochondrial swelling over the range 125-1000μM, while DAS was ineffective. Swelling experiments performed with de-energized or energized mitochondria showed similar maximal swelling amplitudes. Cyclosporin A (1μM), or ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA, 1mM) were ineffective in inhibiting DADS-induced mitochondrial swelling. DADS produced a minor (12%) decrease in mitochondrial membrane protein thiols, but did not induce clustering of mitochondrial membrane proteins. Incubation of mitochondria with DADS (but not DAS) produced an increase in the oxidation rate of 2',7' dichlorofluorescein diacetate (DCFH-DA), together with depletion of reduced glutathione (GSH) and increased lipid peroxidation. DADS (but not DAS) produced a concentration-dependent dissipation of the mitochondrial membrane potential, but did not induce cytochrome c release. DADS-dependent effects, including mitochondrial swelling, DCFH-DA oxidation, lipid peroxidation and loss of mitochondrial membrane potential, were inhibited by antioxidants and iron chelators. These results suggest that DADS causes direct impairment of mitochondrial function as the result of oxidation of the membrane lipid phase initiated by the GSH- and iron-dependent generation of oxidants.

Regulation of endothelial function by mitochondrial reactive oxygen species

Mitochondria are well known for their central roles in ATP production, calcium homeostasis, and heme and steroid biosynthesis. However, mitochondrial reactive oxygen species (ROS), including superoxide and hydrogen peroxide, once thought to be toxic byproducts of mitochondrial physiologic activities, have recently been recognized as important cell-signaling molecules in the vascular endothelium, where their production, conversion, and destruction are highly regulated. Mitochondrial reactive oxygen species appear to regulate important vascular homeostatic functions under basal conditions in a variety of vascular beds, where, in particular, they contribute to endothelium-dependent vasodilation. On exposure to cardiovascular risk factors, endothelial mitochondria produce excessive ROS in concert with other cellular ROS sources. Mitochondrial ROS, in this setting, act as important signaling molecules activating prothrombotic and proinflammatory pathways in the vascular endothelium, a process that initially manifests itself as endothelial dysfunction and, if persistent, may lead to the development of atherosclerotic plaques. This review concentrates on emerging appreciation of the importance of mitochondrial ROS as cell-signaling molecules in the vascular endothelium under both physiologic and pathophysiologic conditions. Future potential avenues of research in this field also are discussed.

Ischemia/reperfusion injury and cardioprotective mechanisms: Role of mitochondria and reactive oxygen species

Reperfusion therapy must be applied as soon as possible to attenuate the ischemic insult of acute myocardial infarction (AMI). However reperfusion is responsible for additional myocardial damage, which likely involves opening of the mitochondrial permeability transition pore (mPTP). In reperfusion injury, mitochondrial damage is a determining factor in causing loss of cardiomyocyte function and viability. Major mechanisms of mitochondrial dysfunction include the long lasting opening of mPTPs and the oxidative stress resulting from formation of reactive oxygen species (ROS). Several signaling cardioprotective pathways are activated by stimuli such as preconditioning and postconditioning, obtained with brief intermittent ischemia or with pharmacological agents. These pathways converge on a common target, the mitochondria, to preserve their function after ischemia/reperfusion. The present review discusses the role of mitochondria in cardioprotection, especially the involvement of adenosine triphosphate-dependent potassium channels, ROS signaling, and the mPTP. Ischemic postconditioning has emerged as a new way to target the mitochondria, and to drastically reduce lethal reperfusion injury. Several clinical studies using ischemic postconditioning during angioplasty now support its protective effects, and an interesting alternative is pharmacological postconditioning. In fact ischemic postconditioning and the mPTP desensitizer, cyclosporine A, have been shown to induce comparable protection in AMI patients.

Altered zinc transport disrupts mitochondrial protein processing/import in fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder that affects individuals who are carriers of small CGG premutation expansions in the fragile X mental retardation 1 (FMR1) gene. Mitochondrial dysfunction was observed as an incipient pathological process occurring in individuals who do not display overt features of FXTAS (1). Fibroblasts from premutation carriers had lower oxidative phosphorylation capacity (35% of controls) and Complex IV activity (45%), and higher precursor-to-mature ratios (P:M) of nDNA-encoded mitochondrial proteins (3.1-fold). However, fibroblasts from carriers with FXTAS symptoms presented higher FMR1 mRNA expression (3-fold) and lower Complex V (38%) and aconitase activities (43%). Higher P:M of ATPase β-subunit (ATPB) and frataxin were also observed in cortex from patients that died with FXTAS symptoms. Biochemical findings observed in FXTAS cells (lower mature frataxin, lower Complex IV and aconitase activities) along with common phenotypic traits shared by Friedreich's ataxia and FXTAS carriers (e.g. gait ataxia, loss of coordination) are consistent with a defective iron homeostasis in both diseases. Higher P:M, and lower ZnT6 and mature frataxin protein expression suggested defective zinc and iron metabolism arising from altered ZnT protein expression, which in turn impairs the activity of mitochondrial Zn-dependent proteases, critical for the import and processing of cytosolic precursors, such as frataxin. In support of this hypothesis, Zn-treated fibroblasts showed a significant recovery of ATPB P:M, ATPase activity and doubling time, whereas Zn and desferrioxamine extended these recoveries and rescued Complex IV activity.

Different effects of SNP and GSNO on mitochondrial O2 .- /H 2O2 production

Sodium Nitroprusside (SNP) and S-Nitrosoglutathione (GSNO) differently affect mitochondrial H(2)O(2) release at Complex-I. mM SNP increases while GSNO decreases the release induced by succinate alone or added on top of NAD-linked substrates. Stimulation likely depends on Nitric Oxide ((.)NO) (released by SNP but not by GSNO) inhibiting cytochrome oxidase and mitochondrial respiration. Preincubations with SNP or high GSNO (10 mM plus DTE to increases its (.)NO release) induces an inhibition of the succinate dependent H(2)O(2) production consistent with a (.)NO dependent covalent modification. However maximal inhibition of the succinate dependent H(2)O(2) release is obtained in the presence of low GSNO (20-100 μM), but not with SNP. This inhibition appears independent of (.)NO release since μM GSNO does not affect mitochondrial respiration, or the H(2)O(2) detection systems and its effect is very rapid. Inhibition may be partly due to an increased removal of O (2) (.-) since GSNO chemically competes with NBT and cytochrome C in O (2) (.-) detection.

Mitochondrial injury and protection in ischemic pre- and postconditioning

Mitochondrial damage is a determining factor in causing loss of cardiomyocyte function and viability, yet a mild degree of mitochondrial dysfunction appears to underlie cardioprotection against injury caused by postischemic reperfusion. This review is focused on two major mechanisms of mitochondrial dysfunction, namely, oxidative stress and opening of the mitochondrial permeability transition pore. The formation of reactive oxygen species in mitochondria will be analyzed with regard to factors controlling mitochondrial permeability transition pore opening. Finally, these mitochondrial processes are analyzed with respect to cardioprotection afforded by ischemic pre- and postconditioning.

Basal bioenergetic abnormalities in skeletal muscle from ryanodine receptor malignant hyperthermia-susceptible R163C knock-in mice

Malignant hyperthermia (MH) and central core disease in humans have been associated with mutations in the skeletal ryanodine receptor (RyR1). Heterozygous mice expressing the human MH/central core disease RyR1 R163C mutation exhibit MH when exposed to halothane or heat stress. Considering that many MH symptoms resemble those that could ensue from a mitochondrial dysfunction (e.g. metabolic acidosis and hyperthermia) and that MH-susceptible mice or humans have a higher than normal cytoplasmic Ca(2+) concentration at rest, we evaluated the role of mitochondria in skeletal muscle from R163C compared with wild type mice under basal (untriggered) conditions. R163C skeletal muscle exhibited a significant increase in matrix Ca(2+), increased reactive oxygen species production, lower expression of mitochondrial proteins, and higher mtDNA copy number. These changes, in conjunction with lower myoglobin and glycogen contents, Myh4 and GAPDH transcript levels, GAPDH activity, and lower glucose utilization suggested a switch to a compromised bioenergetic state characterized by both low oxidative phosphorylation and glycolysis. The shift in bioenergetic state was accompanied by a dysregulation of Ca(2+)-responsive signaling pathways regulated by calcineurin and ERK1/2. Chronically elevated resting Ca(2+) in R163C skeletal muscle elicited the maintenance of a fast-twitch fiber program and the development of insulin resistance-like phenotype as part of a metabolic adaptation to the R163C RyR1 mutation.

Hydrogen sulphide: novel opportunity for drug discovery

Hydrogen sulphide (H(2)S) is emerging as an important endogenous modulator, which exhibits the beneficial effects of nitric oxide (NO) on the cardiovascular (CV) system, without producing toxic metabolites. H(2)S is biosynthesized in mammalian tissues by cystathionine-β-synthase and cystathionine-γ-lyase. H(2)S exhibits the antioxidant properties of inorganic and organic sulphites, behaving as a scavenger of reactive oxygen species. There is also clear evidence that H(2)S triggers other important effects, mainly mediated by the activation of ATP-sensitive potassium channels (K(ATP)). This mechanism accounts for the vasorelaxing and cardioprotective effects of H(2)S. Furthermore, H(2)S inhibits smooth muscle proliferation and platelet aggregation. In non-CV systems, H(2)S regulates the functions of the central nervous system, as well as respiratory, gastroenteric, and endocrine systems. Conversely, H(2)S deficiency contributes to the pathogenesis of hypertension. Likewise, impairment of H(2)S biosynthesis is involved in CV complications associated with diabetes mellitus. There is also evidence of a cross-talk between the H(2)S and the endothelial NO pathways. In particular, recent observations indicate a possible pathogenic link between deficiencies of H(2 S activity and the progress of endothelial dysfunction. These biological aspects of endogenous H(2)S have led several authors to look at this mediator as "the new NO" that has given attractive opportunities to develop innovative classes of drugs. In this review, the main biological actions of H(2)S are discussed. Moreover, some examples of H(2)S-donors are shown, as well as some hybrids, in which H(2)S-releasing moieties are added to well-known drugs, for improving their pharmacodynamic profile or reducing the potential for adverse effects, are reported.

Melatonin, cardiolipin and mitochondrial bioenergetics in health and disease

Melatonin is a natural occurring compound with well-known antioxidant properties. Melatonin is ubiquitously distributed and because of its small size and amphiphilic nature, it is able to reach easily all cellular and subcellular compartments. The highest intracellular melatonin concentrations are found in mitochondria, raising the possibility of functional significance for this targeting with involvement in situ in mitochondrial activities. Mitochondria, the powerhouse of the cell, are considered to be the most important cellular organelles to contribute to degenerative processes mainly through respiratory chain dysfunction and formation of reactive oxygen species, leading to damage to mitochondrial proteins, lipids and DNA. Therefore, protecting mitochondria from oxidative damage could be an effective therapeutic strategy against cellular degenerative processes. Many of the beneficial effects of melatonin administration may depend on its effect on mitochondrial physiology. Cardiolipin, a phospholipid located at the level of inner mitochondrial membrane is known to be intimately involved in several mitochondrial bioenergetic processes as well as in mitochondrial-dependent steps of apoptosis. Alterations to cardiolipin structure, content and acyl chain composition have been associated with mitochondrial dysfunction in multiple tissues in several physiopathological situations and aging. Recently, melatonin was reported to protect the mitochondria from oxidative damage by preventing cardiolipin oxidation and this may explain, at least in part, the beneficial effect of this molecule in mitochondrial physiopathology. In this review, we discuss the role of melatonin in preventing mitochondrial dysfunction and disease.

Gases in the mitochondria

Gasomodulators - nitric oxide, carbon monoxide and hydrogen sulphide - are important physiological mediators that have been implicated in disorders such as neurodegeneration and sepsis. Some of their biological functions involve the mitochondria. In particular, their inhibition of cytochrome c oxidase has received much attention as this can cause energy depletion and cytotoxicity. However, reports that cellular energy production and cell survival are maintained even in the presence of gasomodulators are not uncommon. In both cases, modulation of mitochondrial targets by the gasomodulators appears to be an important event. We provide an overview of the effects of the gasomodulators on the mitochondria.

Mitochondria and vascular pathology

Functional and structural changes in mitochondria are caused by the opening of the mitochondrial permeability transition pore (PTP) and by the mitochondrial generation of reactive oxygen species (ROS). These two processes are linked in a vicious cycle that has been extensively documented in ischemia/reperfusion injuries of the heart, and the same processes likely contribute to vascular pathology. For instance, the opening of the PTP causes cell death in isolated endothelial and vascular smooth muscle cells. Indeed, atherosclerosis is exacerbated when mitochondrial antioxidant defenses are hampered, but a decrease in mitochondrial ROS formation reduces atherogenesis. Determining the exact location of ROS generation in mitochondria is a relevant and still unanswered question. The respiratory chain is generally believed to be a main site of ROS formation. However, several other mitochondrial components likely contribute to ROS generation. Recent reports highlight the relevance of monoamine oxidases (MAO) and p66(Shc). For example, the absence of p66(Shc) in hypercholesterolemic mice has been reported to reduce the occurrence of foam cells and early atherogenic lesions. On the other hand, MAO inhibition has been shown to reduce oxidative stress in many cell types eliciting significant protection from myocardial ischemia. In conclusion, evidence will be presented to demonstrate that (i) mitochondria are major sites of ROS formation; (ii) an increase in mitochondrial ROS formation and/or a decrease in mitochondrial antioxidant defenses exacerbate atherosclerosis; and (iii) mitochondrial dysfunction is likely a relevant mechanism underlying several risk factors (i.e., diabetes, hyperlipidemia, hypertension) associated with atherosclerosis.

Mitochondrial pathways for ROS formation and myocardial injury: the relevance of p66(Shc) and monoamine oxidase

Although mitochondria are considered the most relevant site for the formation of reactive oxygen species (ROS) in cardiac myocytes, a major and unsolved issue is where ROS are generated in mitochondria. Respiratory chain is generally indicated as a main site for ROS formation. However, other mitochondrial components are likely to contribute to ROS generation. Recent reports highlight the relevance of monoamine oxidases (MAO) and p66(Shc). The importance of these systems in the irreversibility of ischemic heart injury will be discussed along with the cardioprotective effects elicited by both MAO inhibition and p66(Shc) knockout. Finally, recent evidence will be reviewed that highlight the relevance of mitochondrial ROS formation also in myocardial failure and atherosclerosis.

Mitochondrial pathophysiology, reactive oxygen species, and cardiovascular diseases

This article discusses mitochondrial pathophysiology, reactive oxygen species, and cardiovascular diseases. Mitochondrial respiratory chains are responsible for energy metabolism/ATP production through the tricyclic antidepressant cycle, coupling of oxidative phosphorylation, and electron transfer. The mitochondrion produces reactive oxygen species as "side products" of respiration. The mitochondrial derived reactive oxygen species is involved in the pathogenesis of various clinical disorders including heart failure, hypoxia, ischemia/reperfusion injury, diabetes, neurodegenerative diseases, and the physiologic process of aging. Observational and mechanistical studies of these pathologic roles of mitochondria are discussed in depth in this article.

Effects of endogenous nitric oxide induced by 5-fluorouracil and L-Arg on liver carcinoma in nude mice

AIM: To study the effects of endogeous nitric oxide induced by 5-fluorouracil (5-FU) and L-arginine (L-Arg) on the human liver carcinoma model in nude mice.

METHODS: The human liver carcinoma model in nude mice was established with BEL-7402 cells and normal saline (NS), 5-FU and 5-FU + L-Arg injected intraperitoneally. The tumor size was measured. The necrotic degree and range were observed under microscope. The apoptosis of cancer cell was detected by turmina deoxynucleotidyl transferanse mediated dUTP nick end labeling (TUNEL) method. Immunohistochemical method was performed to determine the expression of iNOS, P16, BAX. The chemical colorimetry was used to test the activity and nitrate reductase method was adopted to test the concentration of nitric oxide (NO) in the tumor tissue. The BI2000 pathological image analyzer was used to analyze the result of immunohistochemistry.

RESULTS: 5-FU combined with L-Arg could inhibit the tumor growth apparently. In NS, 5-FU and 5-FU+L-Arg groups, the changes of tumor volumes were 257.978 ± 59.0, 172.232 ± 66.0 and 91.523 ± 26.7 mm³, respectively (P < 0.05 5-FU vs 5-FU + L-Arg group; P < 0.05 NS vs 5-FU + L-Arg group; P < 0.05, NS vs 5-FU group). The necrotic range and apoptosis index were significantly increased after the drug injection. The necrotic range was biggest in 5-FU + L-Arg group (χ² = 15.963, P < 0.05).

The apoptosis indexes were as follows: NS, 17.4% ± 6.19%; 5-FU, 31.3% ± 12.3%; and 5-FU + L-Arg, 46% ± 15.24% (P < 0.05, 5-FU vs 5-FU + L-Arg; P < 0.05, NS vs 5-FU + L-Arg; P < 0.05, NS vs 5-FU). The expression and activity of iNOS were increased in the tumor tissue. The concentration of NO was also increased. F of optical density of iNOS, iNOS activity and NO concentration are 31.693, 21.949, and 33.909, respectively, P < 0.05. The concentration of NO was related to the expression of P16 and BAX. The correlation coefficient was 0.764 and 0.554.

CONCLUSION: 5-FU combined with L-Arg can inhibit the growth of tumor in nude mice. The effect may be related to inducing the synthesis and increasing the activity of iNOS. The production of NO is increased, and it can enhance the expression of apoptosis-related gene and antioncogene.

A bio-psycho-socio-molecular approach to pain and stress management

Stress and trauma are interconnected with the experience of pain. This connection is due to a physiological coupling of underlying molecular autoregulatory mechanisms, as well as phenomenological similarities. Nonpharmaceutical therapeutic approaches such as the relaxation response, a process that supports physiological stress reduction and decreases the negative mental and physical effects of stress, also facilitate pain relief, again demonstrating physiological commonalities. These behavioral approaches have a critical impact on molecular patterns of autoregulation, leading to the assumption of a bio-psycho-socio-molecular model of autoregulation, including stress and pain. Thus, molecules and behavior may be seen as two sides of the same problem in pain and stress relief.

Nitric oxide regulation of mitochondrial oxygen consumption II: Molecular mechanism and tissue physiology

Nitric oxide (NO) is an intercellular signaling molecule; among its many and varied roles are the control of blood flow and blood pressure via activation of the heme enzyme, soluble guanylate cyclase. A growing body of evidence suggests that an additional target for NO is the mitochondrial oxygen-consuming heme/copper enzyme, cytochrome c oxidase. This review describes the molecular mechanism of this interaction and the consequences for its likely physiological role. The oxygen reactive site in cytochrome oxidase contains both heme iron (a(3)) and copper (Cu(B)) centers. NO inhibits cytochrome oxidase in both an oxygen-competitive (at heme a(3)) and oxygen-independent (at Cu(B)) manner. Before inhibition of oxygen consumption, changes can be observed in enzyme and substrate (cytochrome c) redox state. Physiological consequences can be mediated either by direct "metabolic" effects on oxygen consumption or via indirect "signaling" effects via mitochondrial redox state changes and free radical production. The detailed kinetics suggest, but do not prove, that cytochrome oxidase can be a target for NO even under circumstances when guanylate cyclase, its primary high affinity target, is not fully activated. In vivo organ and whole body measures of NO synthase inhibition suggest a possible role for NO inhibition of cytochrome oxidase. However, a detailed mapping of NO and oxygen levels, combined with direct measures of cytochrome oxidase/NO binding, in physiology is still awaited.

Mitochondrial function and nitric oxide metabolism are modified by enalapril treatment in rat kidney

The renal and cardiac benefits of renin-angiotensin system (RAS) inhibition in hypertension exceed those attributable to blood pressure reduction, and seem to involve mitochondrial function changes. To investigate whether mitochondrial changes associated with RAS inhibition are related to changes in nitric oxide (NO) metabolism, four groups of male Wistar rats were treated during 2 wk with a RAS inhibitor, enalapril (10 mg x kg(-1) x day(-1); Enal), or a NO synthase (NOS) inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME) (1 mg x kg(-1) x day(-1)), or both (Enal+L-NAME), or were untreated (control). Blood pressure and body weight were lower in Enal than in control. Electron transfer through complexes I to III and cytochrome oxidase activity were significantly lower, and uncoupling protein-2 content was significantly higher in kidney mitochondria isolated from Enal than in those from control. All of these changes were prevented by L-NAME cotreatment and were accompanied by a higher production/bioavailability of kidney NO. L-NAME abolished mitochondrial NOS activity but failed to inhibit extra-mitochondrial kidney NOS, underscoring the relevance of mitochondrial NO in those effects of enalapril that were suppressed by L-NAME cotreatment. In Enal, kidney mitochondria H(2)O(2) production rate and MnSOD activity were significantly lower than in control, and these effects were not prevented by L-NAME cotreatment. These findings may clarify the role of NO in the interactions between RAS and mitochondrial metabolism and can help to unravel the mechanisms involved in renal protection by RAS inhibitors.

Renal mitochondrial dysfunction in spontaneously hypertensive rats is attenuated by losartan but not by amlodipine

Mitochondrial dysfunction is associated with cardiovascular damage; however, data on a possible association with kidney damage are scarce. Here, we aimed at investigating whether 1) kidney impairment is related to mitochondrial dysfunction; and 2) ANG II blockade, compared with Ca2+ channel blockade, can reverse potential mitochondrial changes in hypertension. Eight-week-old male spontaneously hypertensive rats (SHR) received water containing losartan (40 mg·kg−1·day−1, SHR+Los), amlodipine (3 mg·kg−1·day−1, SHR+Amlo), or no additions (SHR) for 6 mo. Wistar-Kyoto rats (WKY) were normotensive controls. Glomerular and tubulointerstitial damage, systolic blood pressure, and proteinuria were higher, and creatinine clearance was lower in SHR vs. SHR+Los and WKY. In SHR+Amlo, blood pressure was similar to WKY, kidney function was similar to SHR, and renal lesions were lower than in SHR, but higher than in SHR+Los. In kidney mitochondria from SHR and SHR+Amlo, membrane potential, nitric oxide synthase, manganese-superoxide dismutase and cytochrome oxidase activities, and uncoupling protein-2 content were lower than in SHR+Los and WKY. In SHR and SHR+Amlo, mitochondrial H2O2 production was higher than in SHR+Los and WKY. Renal glutathione content was lower in SHR+Amlo relative to SHR, SHR+Los, and WKY. In SHR and SHR+Amlo, glutathione was relatively more oxidized than in SHR+Los and WKY. Tubulointerstitial α-smooth muscle actin labeling was inversely related to manganese-superoxide dismutase activity and uncoupling protein-2 content. These findings suggest that oxidant stress is associated with renal mitochondrial dysfunction in SHR. The mitochondrial-antioxidant actions of losartan may be an additional or alternative way to explain some of the beneficial effects of AT1-receptor antagonists.

Mitochondrial glutathione transport: physiological, pathological and toxicological implications

Although most cellular glutathione (GSH) is in the cytoplasm, a distinctly regulated pool is present in mitochondria. Inasmuch as GSH synthesis is primarily restricted to the cytoplasm, the mitochondrial pool must derive from transport of cytoplasmic GSH across the mitochondrial inner membrane. Early studies in liver mitochondria primarily focused on the relationship between GSH status and membrane permeability and energetics. Because GSH is an anion at physiological pH, this suggested that some of the organic anion carriers present in the inner membrane could function in GSH transport. Indeed, studies by Lash and colleagues in isolated mitochondria from rat kidney showed that most of the transport (>80%) in that tissue could be accounted for by function of the dicarboxylate carrier (DIC, Slc25a10) and the oxoglutarate carrier (OGC, Slc25a11), which mediate electroneutral exchange of dicarboxylates for inorganic phosphate and 2-oxoglutarate for other dicarboxylates, respectively. The identity and function of specific carrier proteins in other tissues is less certain, although the OGC is expressed in heart, liver, and brain and the DIC is expressed in liver and kidney. An additional carrier that transports 2-oxoglutarate, the oxodicarboxylate or oxoadipate carrier (ODC; Slc25a21), has been described in rat and human liver and its expression has a wide tissue distribution, although its potential function in GSH transport has not been investigated. Overexpression of the cDNA for the DIC and OGC in a renal proximal tubule-derived cell line, NRK-52E cells, showed that enhanced carrier expression and activity protects against oxidative stress and chemically induced apoptosis. This has implications for development of novel therapeutic approaches for treatment of human diseases and pathological states. Several conditions, such as alcoholic liver disease, cirrhosis or other chronic biliary obstructive diseases, and diabetic nephropathy, are associated with depletion or oxidation of the mitochondrial GSH pool in liver or kidney.

Hypoxia induces production of nitric oxide and reactive oxygen species in glomus cells of rat carotid body

The carotid body is an arterial chemoreceptor organ that senses arterial pO(2) and pH. Previous studies have indicated that both reactive oxygen species (ROS) and nitric oxide (NO) are important potential mediators that may be involved in the response of the carotid body to hypoxia. However, whether their production by the chemosensitive elements of the carotid body is indeed oxygen-dependent is currently unclear. Thus, we have investigated their production under normoxic (20% O(2)) and hypoxic (1% O(2)) conditions in slice preparations of the rat carotid body by using fluorescent indicators and confocal microscopy. NO-synthesizing enzymes were identified by immunohistochemistry and histochemistry, and the subcellular localization of the NO-sensitive indicator diaminofluorescein was determined by a photoconversion technique and electron microscopy. Glomus cells of the carotid body responded to hypoxia by increases in both ROS and NO production. The hypoxia-induced increase in NO generation required (to a large extent, but not completely) extracellular calcium. Glomus cells were immunoreactive to endothelial NO synthase but not to the neuronal or inducible isoforms. Ultrastructurally, the NO-sensitive indicator was observed in mitochondrial membranes after exposure to hypoxia. The data show that glomus cells respond to exposure to hypoxia by the enhanced production of both ROS and NO. NO production by glomus cells is probably mediated by endothelial NO synthase, which is activated by calcium influx. The presence of NO indicator in mitochondria suggests the hypoxic regulation of mitochondrial function via NO in glomus cells.

Role of nitric oxide-induced mtDNA damage in mitochondrial dysfunction and apoptosis

An increasing body of evidence suggests that nitric oxide (NO) can be cytotoxic and induce apoptosis. NO can also be genotoxic and cause DNA damage and mutations. It has been shown that NO damages mitochondrial DNA (mtDNA) to a greater extent than nuclear DNA. Previously, we reported that conditional targeting of the DNA repair protein hOGG1 into mitochondria using a mitochondria targeting sequence (MTS) augmented mtDNA repair of oxidative damage and enhanced cellular survival. To determine whether enhanced repair resulting from augmented expression of hOGG1 could also protect against the deleterious effects of NO, we used HeLa TetOff/MTS-OGG1-transfected cells to conditionally express hOGG1 in mitochondria. The effects of additional hOGG1 expression on repair of NO-induced mtDNA damage and cell survival were evaluated. These cells, along with vector transfectants, in either the presence or absence of doxycycline (Dox), were exposed to NO produced by the rapid decomposition of 1-propanamine, 3-(2-hydroxy-2-nitroso-1-propylhydrazino) (PAPA NONOate). Functional studies revealed that cells expressing recombinant hOGG1 were more proficient at repairing NO-induced mtDNA damage, which led to increased cellular survival following NO exposure. Moreover, the results described here show that conditional expression of hOGG1 in mitochondria decreases NO-induced inhibition of ATP production and protects cells from NO-induced apoptosis.

Persistent S-nitrosation of complex I and other mitochondrial membrane proteins by S-nitrosothiols but not nitric oxide or peroxynitrite: implications for the interaction of nitric oxide with mitochondria

S-nitrosation of mitochondrial proteins has been proposed to contribute to the pathophysiological interactions of nitric oxide (NO) and its derivatives with mitochondria but has not been shown directly. Furthermore, little is known about the mechanism of formation or the fate of these putative S-nitrosothiols. Here we have determined whether mitochondrial membrane protein thiols can be S-nitrosated on exposure to free NO from 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene (DETA-NONOate) by interaction with S-nitrosoglutathione or S-nitroso-N-acetylpenicillamine (SNAP) and by the NO derivative peroxynitrite. S-Nitrosation of protein thiols was measured directly by chemiluminescence detection. S-Nitrosoglutathione and S-nitroso-N-acetylpenicillamine led to extensive protein thiol oxidation, with about 30% of the modified protein thiols persistently S-nitrosated. In contrast, there was no protein thiol oxidation or S-nitrosation on exposure to 3,3-bis (aminoethyl)-1-hydroxy-2-oxo-1-triazene. Peroxynitrite extensively oxidized protein thiols but produced negligible amounts of S-nitrosothiols. Therefore, mitochondrial membrane protein thiols are S-nitrosated by preformed S-nitrosothiols but not by NO or by peroxynitrite. These S-nitrosated protein thiols were readily reduced by glutathione, so S-nitrosation will only persist when the mitochondrial glutathione pool is oxidized. Respiratory chain complex I was S-nitrosated by S-nitrosothiols, consistent with it being an important target for S-nitrosation during nitrosative stress. The S-nitrosation of complex I correlated with a significant loss of activity that was reversed by thiol reductants. S-Nitrosation was also associated with increased superoxide production from complex I. These findings point to a significant role for complex I S-nitrosation and consequent dysfunction during nitrosative stress in disorders such as Parkinson disease and sepsis.

Determination of mitochondrial nitric oxide synthase activity

The main biological targets of nitric oxide (NO) are hemoproteins, thiols, and superoxide anion (O2-). Mitochondria possess several hemoproteins, thiol-containing molecules, and they are one of the prime cellular producers of O2-. Thus, these organelles remain one of the main biological targets for NO. Reports on the existence of a Ca2+-sensitive mitochondrial NO synthase (mtNOS) have opened a new window in the field of NO and mitochondria research (Ghafourifar and Richter, 1997). mtNOS-derived NO reversibly decreases the activity of the mitochondrial hemoprotein, cytochrome c oxidase. This function of mtNOS regulates mitochondrial respiration and transmembrane potential (Deltapsi). The NO generated by mtNOS reacts with mitochondrial thiol-containing proteins including caspase-3. Because the S-nitrosated caspase-3 remains apoptotically silent as long as it is located within the mitochondria, this function of mtNOS portrays an anti-apoptotic property for mtNOS. mtNOS-derived NO also reacts with O2- to generate peroxynitrite. mtNOS-derived peroxynitrite induces oxidative stress and releases cytochrome c from the mitochondria, which represents a pro-apoptotic role for mtNOS. How mitochondria harmonize the reversible functions of mtNOS for mitochondrial respiration, its anti-apoptotic actions via S-nitrosation of caspase-3, versus the pro-apoptotic properties of peroxynitrite remains to be fully understood. However, intramitochondrial ionized Ca2+ concentration ([Ca2+]m) and the status of mitochondrial reducing defense barriers seem to play crucial roles in orchestrating the functions of mtNOS for mitochondria and cells (Ghafourifar and Cadenas, 2005).

Decrease in salivary secretion by radiation mediated by nitric oxide and prostaglandins

OBJECTIVE

In the present work, we evaluated the effect of exposing the submandibular glands (SMG) to radiation, studying different functional parameters such as salivary secretion, nitric oxide (NO) production, reactive oxygen species formation, prostaglandin (PGE) content and apoptosis.

METHODS

We irradiated rats in the head and neck region with a single dose of gamma-ray radiation of 15 Gy. Two hours after radiation, we measured norepinephrine-induced salivary secretion. After that, the SMG were dissected, and in this tissue, we measured the activity of NO synthase (NOS), the PGE content, the amount of reactive oxygen species, apoptotic cells and mitochondrial inducible NOS (iNOS) expression.

RESULTS

We found that radiation decreased salivary secretion when 10 and 30 microg/kg of norepinephrine was administered via the right femoral vein. We observed that iNOS activity was reduced and PGE content increased after radiation in SMG, indicating that NO and PGEs may participate in salivary secretion. The expression of mitochondrial NOS was increased after radiation leading to the formation of large amounts of NO that acts as a proapoptotic signal. In fact, we observed an augmentation in apoptotic cells. In this study, we also observed an increase in lipid peroxidation induced by radiation that may contribute to tissue damage.

CONCLUSIONS

Our results indicate that radiation induced a decrease in salivary secretion and SMG iNOS activity, meanwhile the PGE content, the lipid peroxidation and apoptosis increased in the tissue. These modifications decrease salivary secretion.

Oxidative stress and nitric oxide deficiency in the kidney: a critical link to hypertension?

There is growing evidence that oxidative stress contributes to hypertension. Oxidative stress can precede the development of hypertension. In almost all models of hypertension, there is oxidative stress that, if corrected, lowers BP, whereas creation of oxidative stress in normal animals can cause hypertension. There is overexpression of the p22(phox) and Nox-1 components of NADPH oxidase and reduced expression of extracellular superoxide dismutase (EC-SOD) in the kidneys of ANG II-infused rodents, whereas there is overexpression of p47(phox) and gp91(phox) and reduced expression of intracellular SOD with salt loading. Several mechanisms have been identified that can make oxidative stress self-sustaining. Reactive oxygen species (ROS) can enhance afferent arteriolar tone and reactivity both indirectly via potentiation of tubuloglomerular feedback and directly by microvascular mechanisms that diminish endothelium-derived relaxation factor/nitric oxide responses, generate a cyclooxygenase-2-dependent endothelial-derived contracting factor that activates thromboxane-prostanoid receptors, and enhance vascular smooth muscle cells reactivity. ROS can diminish the efficiency with which the kidney uses O(2) for Na(+) transport and thereby diminish the P(O(2)) within the kidney cortex. This may place a break on further ROS generation yet could further enhance vasculopathy and hypertension. There is a tight relationship between oxidative stress in the kidney and the development and maintenance of hypertension.

Functional characterization of brain mitochondrial nitric oxide synthase during hypertension and aging

Nitric oxide (NO*) plays an important role in various physiological processes. The aim of the present study was to investigate if brain mitochondrial nitric oxide synthase (mtNOS) is active and functional during hypertension. L-citrulline production, an indicator of nitric oxide synthesis, was concentration-dependent on L-arginine in all strains and all ages tested, and was inhibited by 7-Nitroindazole (7-NI). Brain mitochondria of 1 month-old (prehypertensive) spontaneously hypertensive rats (SHR) exhibited a significantly (p < 0.05) low basal L-citrulline content as compared to age-matched Wistar (W) and Wistar-Kyoto (WKY) rats. L-citrulline synthesis in SHR rats showed a significant (p < 0.01) low response to L-arginine in 3 and 7 months-old rats. Respiratory rates in states 3 and 4 increased with low L-arginine concentration in all strains and all ages. The results suggest that in rat brain mitochondria, L-citrulline synthesis is constant once age-related hypertension is installed and NO* does not regulate oxidative phosphorylation.

Glutathionylation of mitochondrial proteins

Many proteins contain free thiols that can be modified by the reversible formation of mixed disulfides with low-molecular-weight thiols through a process called S-thiolation. As the majority of these modifications result from the interaction of protein thiols with the endogenous glutathione pool, protein glutathionylation is the predominant alteration. Protein glutathionylation is of significance both for defense against oxidative damage and in redox signaling. As mitochondria are at the heart of both oxidative damage and redox signaling within the cell, the glutathionylation of mitochondrial proteins is of particular importance. Here we review the mechanisms and physiological significance of the glutathionylation of mitochondrial thiol proteins.

Melatonin and nitric oxide: two required antagonists for mitochondrial homeostasis

The presence of nitric oxide (NO* ) in the mitochondria led to analysis of its source and functions in mitochondrial homeostasis. Studies have revealed the existence of a mtNOS isoform with similar features to nNOS, with some post-traslational modifications, although without the typical signal peptide responsible for addressing proteins to mitochondrion. This isoform may account for the physiological production of NO* related to the respiratory control. During inflammatory conditions there is an excess of NO* in the mitochondria responsible for an increase in reactive oxygen and nitrogen species in sufficient amounts to compromise mitochondrial function. These conditions led to the discovery of the presence of an inducible mtNOS isoform with kinetic properties similar to iNOS. Experiments with knockout mice lacking either nNOS or iNOS further confirmed the existence of these two mtNOS isoforms in mitochondria. Although the increase in NO* in sepsis by inducible mtNOS may have important regulatory functions including the redistribution of oxygen into other pathways under hypoxia, it causes the production of excess NO* that is deleterious for the cell. Melatonin, an endogenous antioxidant, regulates mitochondrial respiration and bioenergetics and protects mitochondria from excess NO* by controlling the activity of mtNOS.

Mitochondrial nitric-oxide synthase: enzyme expression, characterization, and regulation

Nitric oxide is generated in vivo by nitric-oxide synthase (NOS) during the conversion of L-Arg to citrulline. Using a variety of biological systems and approaches emerging evidence has been accumulated for the occurrence of a mitochondrial NOS (mtNOS), identified as the alpha isoform of neuronal or NOS-1. Under physiological conditions, the production of nitric oxide by mitochondria has an important implication for the maintenance of the cellular metabolism, i.e. modulates the oxygen consumption of the organelles through the competitive (with oxygen) and reversible inhibition of cytochrome c oxidase. The transient inhibition suits the continuously changing energy and oxygen requirements of the tissue; it is a short-term regulation with profound pathophysiological consequences. This review describes the identification of mtNOS and the role of posttranslational modifications on mtNOS' activity and regulation.

mitoKATP channel activation in the postanoxic developing heart protects E-C coupling via NO-, ROS-, and PKC-dependent pathways

Whereas previous studies have shown that opening of the mitochondrial ATP-sensitive K+ (mitoKATP) channel protects the adult heart against ischemia-reperfusion injury, it remains to be established whether this mechanism also operates in the developing heart. Isolated spontaneously beating hearts from 4-day-old chick embryos were subjected to 30 min of anoxia followed by 60 min of reoxygenation. The chrono-, dromo-, and inotropic disturbances, as well as alterations of the electromechanical delay (EMD), reflecting excitation-contraction (E-C) coupling, were investigated. Production of reactive oxygen species (ROS) in the ventricle was determined using the intracellular fluorescent probe 2′,7′-dichlorofluorescin (DCFH). Effects of the specific mitoKATP channel opener diazoxide (Diazo, 50 μM) or the blocker 5-hydroxydecanoate (5-HD, 500 μM), the nitric oxide synthase (NOS) inhibitor NG-nitro-l-arginine methyl ester (l-NAME, 50 μM), the antioxidant N-(2-mercaptopropionyl)glycine (MPG, 1 mM), and the PKC inhibitor chelerythrine (Chel, 5 μM) on oxidative stress and postanoxic functional recovery were determined. Under normoxia, the baseline parameters were not altered by any of these pharmacological agents, alone or in combination. During the first 20 min of postanoxic reoxygenation, Diazo doubled the peak of ROS production and, interestingly, accelerated recovery of ventricular EMD and the PR interval. Diazo-induced ROS production was suppressed by 5-HD, MPG, or l-NAME, but not by Chel. Protection of ventricular EMD by Diazo was abolished by 5-HD, MPG, l-NAME, or Chel, whereas protection of the PR interval was abolished by l-NAME exclusively. Thus pharmacological opening of the mitoKATP channel selectively improves postanoxic recovery of cell-to-cell communication and ventricular E-C coupling. Although the NO-, ROS-, and PKC-dependent pathways also seem to be involved in this cardioprotection, their interrelation in the developing heart can differ markedly from that in the adult myocardium.

Long-term calorie restriction reduces proton leak and hydrogen peroxide production in liver mitochondria

Calorie restriction (CR) without malnutrition increases maximal life span in diverse species. It has been proposed that reduction in energy expenditure and reactive oxygen species (ROS) production could be a mechanism for life span extension with CR. As a step toward testing this theory, mitochondrial proton leak, H2O2 production, and markers of oxidative stress were measured in liver from FBNF1 rats fed control or 40% CR diets for 12 or 18 mo. CR was initiated at 6 mo of age. Proton leak kinetics curves, generated from simultaneous measures of oxygen consumption and membrane potential, indicated a decrease in proton leak after 18 mo of CR, while only a trend toward a proton leak decrease was observed after 12 mo. Significant shifts in phosphorylation and substrate oxidation curves also occurred with CR; however, these changes occurred in concert with the proton leak changes. Metabolic control analysis indicated no difference in the overall pattern of control of the oxidative phosphorylation system between control and CR animals. At 12 mo, no significant differences were observed between groups for H2O2 production or markers of oxidative stress. However, at 18 mo, protein carbonyl content was lower in CR animals, as was H2O2 production when mitochondria were respiring on either succinate alone or pyruvate plus malate in the presence of rotenone. These results indicate that long-term CR lowers mitochondrial proton leak and H2O2 production, and this is consistent with the idea that CR may act by decreasing energy expenditure and ROS production.

Involvement of Mitochondrial Peroxynitrite in Nitric Oxide-Induced Glutathione Synthesis

Cells respond to oxidative stress including nitric oxide (NO) by increasing cellular glutathione concentration, as a part of adaptive response against oxidative injury. To elucidate the mechanism by which NO induces glutathione we investigated the reactive oxygen species (ROS) generated in the cell. Treatment of RAW264.7 cells with NO donor, sodium nitroprusside (SNP), resulted in a temporary increase in glutathione in a dose-dependent manner, which peaked between 6 h and 12 h after treatment, whereas expression of gamma-glutamylcysteine synthetase (gamma-GCS) mRNA peaked around 3 h after treatment. The increase was inhibited by NO scavengers, oxyhemoglobin and carboxyl-2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). N-Acetyl-L-cysteine (NAC) also reduced the increase in glutathione to some extent, whereas both peroxynitrite scavenger ebselen and hydroxyl radical scavenger DMSO inhibited the increase in glutathione in a dose-dependent manner and complete inhibition was observed. Hydrogen peroxide exogenously added to the cell did not increase either glutathione or gamma-GCS expression at any concentration, indicating that involvement of hydrogen peroxide is not likely. Flow cytometric analysis showed that SNP induced a marked dose-dependent increase in Rhodamine123 fluorescence, which was completely inhibited by ebselen in a dose-dependent manner, whereas, little increase in 2',7'-dichlorofluorescin (DCF) fluorescence was observed. Generation of peroxynitrite in mitochondria by SNP was confirmed by elevated level of nitrotyrosine in a mitochondria fraction isolated from SNP-treated cells, and the elevation was completely inhibited by ebselen as well. These results suggest that induction of glutathione (GSH) synthesis by SNP treatment is mediated by peroxynitrite generated in mitochondria.