Biochemistry of mitochondrial nitric-oxide synthase

The emerging role of nitric oxide in the synaptic dysfunction of vascular dementia

With an increase in global aging, the number of people affected by cerebrovascular diseases is also increasing, and the incidence of vascular dementia-closely related to cerebrovascular risk-is increasing at an epidemic rate. However, few therapeutic options exist that can markedly improve the cognitive impairment and prognosis of vascular dementia patients. Similarly in Alzheimer's disease and other neurological disorders, synaptic dysfunction is recognized as the main reason for cognitive decline. Nitric oxide is one of the ubiquitous gaseous cellular messengers involved in multiple physiological and pathological processes of the central nervous system. Recently, nitric oxide has been implicated in regulating synaptic plasticity and plays an important role in the pathogenesis of vascular dementia. This review introduces in detail the emerging role of nitric oxide in physiological and pathological states of vascular dementia and summarizes the diverse effects of nitric oxide on different aspects of synaptic dysfunction, neuroinflammation, oxidative stress, and blood-brain barrier dysfunction that underlie the progress of vascular dementia. Additionally, we propose that targeting the nitric oxide-sGC-cGMP pathway using certain specific approaches may provide a novel therapeutic strategy for vascular dementia.

Products of oxidative and non-oxidative metabolism of L-arginine as potential regulators of Ca2+ transport in mitochondria of uterine smooth muscle

Mitochondria play a crucial role in maintaining Ca2+ homeostasis in cells. Due to the critical regulatory role of the products of oxidative and non-oxidative metabolism of L-arginine, it is essential to clarify their effect on Ca2+ transport in smooth muscle mitochondria. Experiments were performed on the uterine myocytes of rats and isolated mitochondria. The possibility of NO synthesis by mitochondria was demonstrated by confocal microscopy and spectrofluorimetry methods using the NO-sensitive fluorescent probe DAF-FM and Mitotracker Orange CM-H2TMRos. It was shown that 50 μM L-arginine stimulates the energy-dependent accumulation of Ca2+ in mitochondria using the fluorescent probe Fluo-4 AM. A similar effect occurred when using nitric oxide donors 100 μM SNP, SNAP, and sodium nitrite (SN) directly. The stimulating effect was eliminated in the presence of the NO scavenger C-PTIO. Nitric oxide reduces the electrical potential in mitochondria without causing them to swell. The stimulatory effect of spermine on the accumulation of Ca2+ by mitochondria is attributed to the enhancement of NO synthesis, which was demonstrated with the use of C-PTIO, NO-synthase inhibitors (100 μM NA and L-NAME), as well as by direct monitoring of NO synthesis fluorescent probe DAF-FM. A conclusion was drawn about the potential regulatory effect of the product of the oxidative metabolism of L-arginine - NO on the transport of Ca2+ in the mitochondria of the myometrium, as well as the corresponding effect of the product of non-oxidative metabolism -spermine by increasing the synthesis of NO in these subcellular structures.

The tissue-specific nature of physiological zebrafish mitochondrial bioenergetics

Zebrafish are a powerful tool to study a myriad of experimental conditions, including mitochondrial bioenergetics. Considering that mitochondria are different in many aspects depending on the tissue evaluated, in the zebrafish model there is still a lack of this investigation. Especially for juvenile zebrafish. In the present study, we examined whether different tissues from zebrafish juveniles show mitochondrial density- and tissue-specificity comparing brain, liver, heart, and skeletal muscle (SM). The liver and brain complex IV showed the highest O2 consumption of all ETC in all tissues (10x when compared to other respiratory complexes). The liver showed a higher potential for ROS generation. In this way, the brain and liver showed more susceptibility to O2- generation when compared to other tissues. Regarding Ca2+ transport, the brain showed greater capacity for Ca2+ uptake and the liver presented low Ca2+ uptake capacity. The liver and brain were more susceptible to producing NO. The enzymes SOD and Catalase showed high activity in the brain, whereas GPx showed higher activity in the liver and CS in the SM. TEM reveals, as expected, a physiological diverse mitochondrial morphology. The essential differences between zebrafish tissues investigated probably reflect how the mitochondria play a diverse role in systemic homeostasis. This feature may not be limited to normal metabolic functions but also to stress conditions. In summary, mitochondrial bioenergetics in zebrafish juvenile permeabilized tissues showed a tissue-specificity and a useful tool to investigate conditions of redox system imbalance, mainly in the liver and brain.

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.

L-Ornithine L-Aspartate Restores Mitochondrial Function and Modulates Intracellular Calcium Homeostasis in Parkinson's Disease Models

The altered crosstalk between mitochondrial dysfunction, intracellular Ca²⁺ homeostasis, and oxidative stress has a central role in the dopaminergic neurodegeneration. In the present study, we investigated the hypothesis that pharmacological strategies able to improve mitochondrial functions might prevent neuronal dysfunction in in vitro models of Parkinson’s disease. To this aim, the attention was focused on the amino acid ornithine due to its ability to cross the blood–brain barrier, to selectively reach and penetrate the mitochondria through the ornithine transporter 1, and to control mitochondrial function. To pursue this issue, experiments were performed in human neuroblastoma cells SH-SY5Y treated with rotenone and 6-hydroxydopamine to investigate the pharmacological profile of the compound L-Ornithine-L-Aspartate (LOLA) as a new potential therapeutic strategy to prevent dopaminergic neurons’ death. In these models, confocal microscopy experiments with fluorescent dyes measuring mitochondrial calcium content, mitochondrial membrane potential, and mitochondrial ROS production, demonstrated that LOLA improved mitochondrial functions. Moreover, by increasing NCXs expression and activity, LOLA also reduced cytosolic [Ca²⁺] thanks to its ability to modulate NO production. Collectively, these results indicate that LOLA, by interfering with those mitochondrial mechanisms related to ROS and RNS production, promotes mitochondrial functional recovery, thus confirming the tight relationship existing between cytosolic ionic homeostasis and cellular metabolism depending on the type of insult applied.

Nitric oxide-releasing biomaterials for promoting wound healing in impaired diabetic wounds: State of the art and recent trends

Impaired diabetic wounds are serious pathophysiological complications associated with persistent microbial infections including failure in the closure of wounds, and the cause of a high frequency of lower limb amputations. The healing of diabetic wounds is attenuated due to the lack of secretion of growth factors, prolonged inflammation, and/or inhibition of angiogenic activity. Diabetic wound healing can be enhanced by supplying nitric oxide (NO) endogenously or exogenously. NO produced inside the cells by endothelial nitric oxide synthase (eNOS) naturally aids wound healing through its beneficial vasculogenic effects. However, during hyperglycemia, the activity of eNOS is affected, and thus there becomes an utmost need for the topical supply of NO from exogenous sources. Thus, NO-donors that can release NO are loaded into wound healing patches or wound coverage matrices to treat diabetic wounds. The burst release of NO from its donors is prevented by encapsulating them in polymeric hydrogels or nanoparticles for supplying NO for an extended duration of time to the diabetic wounds. In this article, we review the etiology of diabetic wounds, wound healing strategies, and the role of NO in the wound healing process. We further discuss the challenges faced in translating NO-donors as a clinically viable nanomedicine strategy for the treatment of diabetic wounds with a focus on the use of biomaterials for the encapsulation and in vivo controlled delivery of NO-donors.

How and when abusive supervision influences knowledge hiding behavior: evidence from India

Purpose

This study aims to investigate the differential roles of self-esteem and co-rumination in the mediated relationship between abusive supervision and knowledge hiding via psychological safety.

Design/methodology/approach

The study used a three-wave time-lagged design and data were collected from 388 full-time employees in India.

Findings

The results show that psychological safety mediated the impact abusive supervision had on knowledge hiding. Further, this impact was weakened by higher self-esteem as employees with higher self-esteem were less affected by the impact of abusive supervision on psychological safety and knowledge hiding; but this impact was amplified by more co-rumination as employees who co-ruminated more were also more affected by abusive supervision in psychological safety and knowledge hiding.

Research limitations/implications

A cross-sectional design and the use of self-reported questionnaires are a few limitations of this study.

Originality/value

This study took a purposeful deviation from the traditional path of organizational justice to the study of abusive supervision and psychological safety and endeavored an alternate route, one of resource conservation. Further, employees have diverse reasons that heighten or dampen their inclination to hide knowledge from others in the workplace. The study examines co-rumination and self-esteem as possible boundary conditions.

Nitric oxide and dopamine metabolism converge via mitochondrial dysfunction in the mechanisms of neurodegeneration in Parkinson's disease

The molecular mechanisms underlying the degeneration and neuronal death associated with Parkinson's disease (PD) are not clearly understood. Several pathways and models have been explored in an overwhelming number of studies. Overall, from these studies, mitochondrial dysfunction and nitroxidative stress have emerged as major contributors to degeneration of dopaminergic neurons in PD. In addition, an excessive or inappropriate production of nitric oxide (^•NO) and an abnormal metabolism of dopamine have been independently implicated in both processes. However, the participation of ^•NO in reactions with dopamine relevant to neurotoxicity strongly suggests that dopamine or its metabolites may be potential targets for ^•NO, affecting the physiological chemistry of both, ^•NO and dopamine. In this short review, we provide a critical and integrative appraisal of the nitric oxide-dopamine pathway we have previously suggested and that might be operative in PD. This pathway emphasizes a connection between abnormal dopamine and ^•NO metabolism, which may potentially converge in an integrated mechanism with toxic cellular outcomes. In particular, it encompasses the synergistic interaction of ^•NO with 3,4-dihydroxyphenylacetic acid (DOPAC), a major dopamine metabolite, leading to dopaminergic cell death via mechanisms that involve mitochondrial dysfunction, gluthathione depletion and nitroxidative stress.

The heart is lost without the hypothalamus

Neuroanatomic and functional studies show the paraventricular (PVN) of the hypothalamus to have a central role in the autonomic control that supports cardiovascular regulation. Direct and indirect projections from the PVN preautonomic neurons to the sympathetic preganglionic neurons in the spinal cord modulate sympathetic activity. The preautonomic neurons of the PVN adjust their level of activation in response to afferent signals arising from peripheral viscerosensory receptors relayed through the nucleus tractus solitarius. The prevailing sympathetic tone is a balance between excitatory and inhibitory influences that arises from the preautonomic PVN neurons. Under physiologic conditions, tonic sympathetic inhibition driven by a nitric oxide-γ-aminobutyric acid-mediated mechanism is dominant, but in pathologic situation such as heart failure there is a switch from inhibition to sympathoexcitation driven by glutamate and angiotensin II. Angiotensin II, reactive oxygen species, and hypoxia as a result of myocardial infarction/ischemia alter the tightly regulated posttranslational protein-protein interaction of CAPON (carboxy-terminal postsynaptic density protein ligand of neuronal nitric oxide synthase (NOS1)) and PIN (protein inhibitor of NOS1) signaling mechanism. Within the preautonomic neurons of the PVN, the disruption of CAPON and PIN signaling leads to a downregulation of NOS1 expression and reduced NO bioavailability. These data support the notion that CAPON-PIN dysregulation of NO bioavailability is a major contributor to the pathogenesis of sympathoexcitation in heart failure.

Temporal evolution of cardiac mitochondrial dysfunction in a type 1 diabetes model. Mitochondrial complex I impairment, and H2O2 and NO productions as early subcellular events

The aim of this work was to study the early events that occur in heart mitochondria and to analyse the temporal evolution of cardiac mitochondrial dysfunction in a type 1 diabetes model. Male Wistar rats were injected with Streptozotocin (STZ, single dose, 60 mg × kg^-1, i.p.) and hyperglycemic state was confirmed 72 h later. The animals were sacrificed 10 or 14 days after STZ-injection. Heart mitochondrial state 3 O₂ consumption sustained by malate-glutamate (21%) or by succinate (16%), and complexes I-III (27%), II-III (24%) and IV (22%) activities were lower in STZ group, when animals were sacrificed at day 14, i.e. ~11 days of hyperglycemia. In contrast, after 10 days of STZ-injection (~7 days of hyperglycemia), only the state 3 O₂ consumption sustained by malate-glutamate (23%) and its corresponding respiratory control (30%) were lower in diabetic rats, in accordance with complex I-III activity reduction (17%). Therefore, this time (~7 days of hyperglycemia) has been considered as an "early stage" of cardiac mitochondrial dysfunction. At this point, mitochondrial production rates of H₂O₂ (117%), NO (30%) and ONOO^- (~225%), and mtNOS expression (29%) were higher; and mitochondrial SOD activity (15%) and [GSH + GSSG] (28%) were lower in diabetic rats. Linear correlations between the modified mitochondrial parameters and glycemias were observed. PGC-1α expression was similar between groups, suggesting that mitochondrial biogenesis was not triggered in this initial phase of mitochondrial dysfunction. Consequently, complex I, H₂O₂ and NO could be considered early subcellular signals of cardiac mitochondrial dysfunction, with NO and H₂O₂ being located upstream de novo synthesis of mitochondria.

Disruption of mitochondrial functions and oxidative stress contribute to neurologic dysfunction in organic acidurias

Organic acidurias (OADs) are inherited disorders of amino acid metabolism biochemically characterized by accumulation of short-chain carboxylic acids in tissues and biological fluids of the affected patients and clinically by predominant neurological manifestations. Some of these disorders are amenable to treatment, which significantly decreases mortality and morbidity, but it is still ineffective to prevent long-term neurologic and systemic complications. Although pathogenesis of OADs is still poorly established, recent human and animal data, such as lactic acidosis, mitochondrial morphological alterations, decreased activities of respiratory chain complexes and altered parameters of oxidative stress, found in tissues from patients and from genetic mice models with these diseases indicate that disruption of critical mitochondrial functions and oxidative stress play an important role in their pathophysiology. Furthermore, organic acids that accumulate in the most prevalent OADs were shown to compromise bioenergetics, by decreasing ATP synthesis, mitochondrial membrane potential, reducing equivalent content and calcium retention capacity, besides inducing mitochondrial swelling, reactive oxygen and nitrogen species generation and apoptosis. It is therefore presumed that secondary mitochondrial dysfunction and oxidative stress caused by major metabolites accumulating in OADs contribute to tissue damage in these pathologies.

The Peculiar Facets of Nitric Oxide as a Cellular Messenger: From Disease-Associated Signaling to the Regulation of Brain Bioenergetics and Neurovascular Coupling

In this review, we address the regulatory and toxic role of ^·NO along several pathways, from the gut to the brain. Initially, we address the role on ^·NO in the regulation of mitochondrial respiration with emphasis on the possible contribution to Parkinson's disease via mechanisms that involve its interaction with a major dopamine metabolite, DOPAC. In parallel with initial discoveries of the inhibition of mitochondrial respiration by ^·NO, it became clear the potential for toxic ^·NO-mediated mechanisms involving the production of more reactive species and the post-translational modification of mitochondrial proteins. Accordingly, we have proposed a novel mechanism potentially leading to dopaminergic cell death, providing evidence that NO synergistically interact with DOPAC in promoting cell death via mechanisms that involve GSH depletion. The modulatory role of NO will be then briefly discussed as a master regulator on brain energy metabolism. The energy metabolism in the brain is central to the understanding of brain function and disease. The core role of ^·NO in the regulation of brain metabolism and vascular responses is further substantiated by discussing its role as a mediator of neurovascular coupling, the increase in local microvessels blood flow in response to spatially restricted increase of neuronal activity. The many facets of NO as intracellular and intercellular messenger, conveying information associated with its spatial and temporal concentration dynamics, involve not only the discussion of its reactions and potential targets on a defined biological environment but also the regulation of its synthesis by the family of nitric oxide synthases. More recently, a novel pathway, out of control of NOS, has been the subject of a great deal of controversy, the nitrate:nitrite:NO pathway, adding new perspectives to ^·NO biology. Thus, finally, this novel pathway will be addressed in connection with nitrate consumption in the diet and the beneficial effects of protein nitration by reactive nitrogen species.

Glutathione and Nitric Oxide: Key Team Players in Use and Disuse of Skeletal Muscle

Glutathione (GSH) is the main non-enzymatic antioxidant playing an important role in detoxification, signal transduction by modulation of protein thiols redox status and direct scavenging of radicals. The latter function is not only performed against reactive oxygen species (ROS) but GSH also has a fundamental role in buffering nitric oxide (NO), a physiologically-produced molecule having-multifaceted functions. The efficient rate of GSH synthesis and high levels of GSH-dependent enzymes are characteristic features of healthy skeletal muscle where, besides the canonical functions, it is also involved in muscle contraction regulation. Moreover, NO production in skeletal muscle is a direct consequence of contractile activity and influences several metabolic myocyte pathways under both physiological and pathological conditions. In this review, we will consider the homeostasis and intersection of GSH with NO and then we will restrict the discussion on their role in processes related to skeletal muscle function and degeneration.

Nitric oxide and its derivatives in the cancer battlefield

Elevated levels of reactive nitrogen species, alteration in redox balance and deregulated redox signaling are common hallmarks of cancer progression and chemoresistance. However, depending on the cellular context, distinct reactive nitrogen species are also hypothesized to mediate cytotoxic activity and are thus used in anticancer therapies. We present here the dual face of nitric oxide and its derivatives in cancer biology. Main derivatives of nitric oxide, such as nitrogen dioxide and peroxynitrite cause cell death by inducing protein and lipid peroxidation and/or DNA damage. Moreover, they control the activity of important protein players within the pro- and anti-apoptotic signaling pathways. Thus, the control of intracellular reactive nitrogen species may become a sophisticated tool in anticancer strategies.

Differential impacts of brain stem oxidative stress and nitrosative stress on sympathetic vasomotor tone

Based on work-done in the rostral ventrolateral medulla (RVLM), this review presents four lessons learnt from studying the differential impacts of oxidative stress and nitrosative stress on sympathetic vasomotor tone and their clinical and therapeutic implications. The first lesson is that an increase in sympathetic vasomotor tone because of augmented oxidative stress in the RVLM is responsible for the generation of neurogenic hypertension. On the other hand, a shift from oxidative stress to nitrosative stress in the RVLM underpins the succession of increase to decrease in sympathetic vasomotor tone during the progression towards brain stem death. The second lesson is that, by having different cellular sources, regulatory mechanisms on synthesis and degradation, kinetics of chemical reactions, and downstream signaling pathways, reactive oxygen species and reactive nitrogen species should not be regarded as a singular moiety. The third lesson is that well-defined differential roles of oxidative stress and nitrosative stress with distinct regulatory mechanisms in the RVLM during neurogenic hypertension and brain stem death clearly denote that they are not interchangeable phenomena with unified cellular actions. Special attention must be paid to their beneficial or detrimental roles under a specific disease or a particular time-window of that disease. The fourth lesson is that, to be successful, future antioxidant therapies against neurogenic hypertension must take into consideration the much more complicated picture than that presented in this review on the generation, maintenance, regulation or modulation of the sympathetic vasomotor tone. The identification that the progression towards brain stem death entails a shift from oxidative stress to nitrosative stress in the RVLM may open a new vista for therapeutic intervention to slow down this transition.

Tempol Attenuates Neuropathic Pain by Inhibiting Nitric Oxide Production

Background

Neuropathic pain not only affects individual life quality but also increases economic burden for the society. Treatment to alleviate neuropathic pain is required.

Methodology

Fifty rats were randomly assigned into sham, spinal nerve ligation, and three treatment groups with different doses of Tempol (100, 200, and 300 mg/kg, respectively), with 10 rats in each group. A neuropathic pain model was created with spinal nerve L5 and L6 ligation. Mechanical allodynia and thermal hyperalgesia were tested preoperatively (day 0) and postoperatively (days 1, 3, 5, and 7). Spinal cord levels of nitric oxide, as well as activities of nitric oxide synthase and acetylcholinesterase, were tested in postoperative day 7.

Results

Compared with rats in the spinal nerve ligation group, rats in Tempol treatment groups had decreased responses to mechanical pain and cold plate stimulations. A high dose of Tempol produced more attenuating effects. The level of nitric oxide and activity of nitric oxide synthase were also decreased with Tempol treatments, whereas no significant changes were observed in the activity of acetylcholinesterase.

Conclusions

Tempol attenuated an experimental rat model with neuropathic pain by inhibiting nitric oxide production.

Complex I syndrome in striatum and frontal cortex in a rat model of Parkinson disease

Mitochondrial dysfunction named complex I syndrome was observed in striatum mitochondria of rotenone treated rats (2 mg rotenone/kg, i. p., for 30 or 60 days) in an animal model of Parkinson disease. After 60 days of rotenone treatment, the animals showed: (a) 6-fold increased bradykinesia and 60% decreased locomotor activity; (b) 35-34% decreases in striatum O₂ uptake and in state 3 mitochondrial respiration with malate-glutamate as substrate; (c) 43-57% diminished striatum complex I activity with 60-71% decreased striatum mitochondrial NOS activity, determined both as biochemical activity and as functional activity (by the NO inhibition of active respiration); (d) 34-40% increased rates of mitochondrial O₂^•- and H₂O₂ productions and 36-46% increased contents of the products of phospholipid peroxidation and of protein oxidation; and (e) 24% decreased striatum mitochondrial content, likely associated to decreased NO-dependent mitochondrial biogenesis. Intermediate values were observed after 30 days of rotenone treatment. Frontal cortex tissue and mitochondria showed similar but less marked changes. Rotenone-treated rats showed mitochondrial complex I syndrome associated with cellular oxidative stress in the dopaminergic brain areas of striatum and frontal cortex, a fact that describes the high sensitivity of mitochondrial complex I to inactivation by oxidative reactions.

Aβ1-42 increases the expression of neural KATP subunits Kir6.2/SUR1 via the NF-κB, p38 MAPK and PKC signal pathways in rat primary cholinergic neurons

ATP-sensitive potassium channels (KATP) may mediate a potential neuroprotective role in Alzheimer's disease (AD). Given that exposure to Aβ1-42 in cultured primary cholinergic neurons for 72 h significantly upregulates the expression of KATP subunits Kir6.2/SUR1, we aim to study the underlying signal transduction mechanisms that are involved in Aβ_1-42-induced upregulation of KATP subunits Kir6.2/SUR1. In the present study, we first identified the primary cultured rat cortical and hippocampal neurons using immunocytochemistry. 0.5 μM NF-κB inhibitor SN-50, 2 μM p38MAPK inhibitor SB203580 or 2 μM PKC inhibitor Chelerythrine chloride (CTC) were then added in three separate groups, followed by 2 μM Aβ_1-42 30 min later in all 3 groups. Western Blot was performed 72 h later to detect the expression of KATP subunits Kir6.2/SUR1. We found that Aβ_1-42 significantly increased the level of KATP subunits Kir6.2/SUR1 expression at 72 h when compared with the control group ( p < 0.05). However, when compared with the Aβ_1-42 group, the level of KATP subunits Kir6.2/SUR1 expression at 72 h significantly decreased in the SN50 + Aβ_1-42 group, SB203580 + Aβ_1-42 group, and the CTC + Aβ_1-42 group ( p < 0.05). Our findings suggest that the NF-κB, p38 MAPK, and PKC signal pathways are partially involved in the upregulation of KATP subunits Kir6.2/SUR1 expression induced by Aβ_1-42 cytotoxicity in neurons, which supports a potential theoretical basis of targeting these signal pathways in the treatment of AD.

(+)-Catechin inhibits heart mitochondrial complex I and nitric oxide synthase: functional consequences on membrane potential and hydrogen peroxide production

The aim was to study thein vitroeffect of nM to low μM concentration of (+)-catechin on the enzymatic activities of mitochondrial complex I and mtNOS, as well as the consequences on the membrane potential and H₂O₂production rate.

Gas Signaling Molecules and Mitochondrial Potassium Channels

Recently, gaseous signaling molecules, such as carbon monoxide (CO), nitric oxide (NO), and hydrogen sulfide (H₂S), which were previously considered to be highly toxic, have been of increasing interest due to their beneficial effects at low concentrations. These so-called gasotransmitters affect many cellular processes, such as apoptosis, proliferation, cytoprotection, oxygen sensing, ATP synthesis, and cellular respiration. It is thought that mitochondria, specifically their respiratory complexes, constitute an important target for these gases. On the other hand, increasing evidence of a cytoprotective role for mitochondrial potassium channels provides motivation for the analysis of the role of gasotransmitters in the regulation of channel function. A number of potassium channels have been shown to exhibit activity within the inner mitochondrial membrane, including ATP-sensitive potassium channels, Ca²⁺-activated potassium channels, voltage-gated Kv potassium channels, and TWIK-related acid-sensitive K⁺ channel 3 (TASK-3). The effects of these channels include the regulation of mitochondrial respiration and membrane potential. Additionally, they may modulate the synthesis of reactive oxygen species within mitochondria. The opening of mitochondrial potassium channels is believed to induce cytoprotection, while channel inhibition may facilitate cell death. The molecular mechanisms underlying the action of gasotransmitters are complex. In this review, we focus on the molecular mechanisms underlying the action of H₂S, NO, and CO on potassium channels present within mitochondria.

Hydrogen peroxide, nitric oxide and ATP are molecules involved in cardiac mitochondrial biogenesis in Diabetes

This study, in an experimental model of type I Diabetes Mellitus in rats, deals with the mitochondrial production rates and steady-state concentrations of H₂O₂ and NO, and ATP levels as part of a network of signaling molecules involved in heart mitochondrial biogenesis. Sustained hyperglycemia leads to a cardiac compromise against a work overload, in the absence of changes in resting cardiac performance and of heart hypertrophy. Diabetes was induced in male Wistar rats by a single dose of Streptozotocin (STZ, 60mg × kg^-1, ip.). After 28 days of STZ-injection, rats were sacrificed and hearts were isolated. The mitochondrial mass (mg mitochondrial protein × g heart^-1), determined through cytochrome oxidase activity ratio, was 47% higher in heart from diabetic than from control animals. Stereological analysis of cardiac tissue microphotographs showed an increase in the cytosolic volume occupied by mitochondria (30%) and in the number of mitochondria per unit area (52%), and a decrease in the mean area of each mitochondrion (23%) in diabetic respect to control rats. Additionally, an enhancement (76%) in PGC-1α expression was observed in cardiac tissue of diabetic animals. Moreover, heart mitochondrial H₂O₂ (127%) and NO (23%) productions and mtNOS expression (132%) were higher, while mitochondrial ATP production rate was lower (~ 40%), concomitantly with a partial-mitochondrial depolarization, in diabetic than in control rats. Changes in mitochondrial H₂O₂ and NO steady-state concentrations and an imbalance between cellular energy demand and mitochondrial energy transduction could be involved in the signaling pathways that lead to the novo synthesis of mitochondria. However, this compensatory mechanism triggered to restore the mitochondrial and tissue normal activities, did not lead to competent mitochondria capable of supplying the energetic demands in diabetic pathological conditions.

Effects of nitric oxide on large-conductance Ca2+ -activated K+ currents in human cardiac fibroblasts through PKA and PKG-related pathways

The human cardiac fibroblast (HCF) is the most abundant cell type in the myocardium, and HCFs play critical roles in maintaining normal cardiac function. However, unlike cardiomyocytes, the electrophysiology of HCFs is not well established. In the cardiovascular system, Ca²⁺ -activated K⁺ (KCa) channels have distinct physiological and pathological functions, and nitric oxide (NO) plays a key role. In this study, we investigated the potential effects of NO on KCa channels in HCFs. We recorded strong oscillating, well-maintained outward K⁺ currents without marked inactivation throughout the test pulse period and detected outward rectification in the I-V curve; these are all characteristics that are typical of KCa currents. These currents were blocked with iberiotoxin (IBTX, a BKCa blocker) but not with TRAM-34 (an IKCa blocker). The amplitudes of the currents were increased with SNAP (an NO donor), and these increases were inhibited with IBTX. The SNAP-stimulating effect on the BKCa currents was blocked by pretreatment with KT5823 (a protein kinase G [PKG] inhibitor) or 1 H-[1,-2, -4] oxadiazolo-[4,-3-a] quinoxalin-1-one (ODQ; a soluble guanylate cyclase inhibitor). Additionally, 8-bromo-cyclic guanosine 3',5'-monophosphate (8-Br-cGMP) stimulated the BKCa currents, and pretreatment with KT5720 (a protein kinase A [PKA] inhibitor) and SQ22536 (an adenylyl cyclase inhibitor) blocked the NO-stimulating effect on the BKCa currents. Furthermore, 8-bromo-cyclic adenosine 3',5'-monophosphate (8-Br-cAMP) activated the BKCa currents. These data suggest that BKCa current is the main subtype of the KCa current in HCFs and that NO enhances these currents through the PKG and PKA pathways.

NO control of mitochondrial function in normal and transformed cells

Nitric oxide (NO) is a signaling molecule with multiple facets and involved in numerous pathological process, including cancer. Among the different pathways where NO has a functionally relevant participation, is the control of mitochondrial respiration and biogenesis. NO is able to inhibit the electron transport chain, mainly at Complex IV, regulating oxygen consumption and ATP generation, but at the same time, can also induce increase in reactive oxygen and nitrogen species. The presence of reactive species can induce oxidative damage or participate in redox signaling. In this review, we discuss how NO affects mitochondrial respiration and mitochondrial biogenesis, and how it influences the development of mitochondrial deficiency and cancer. This article is part of a Special Issue entitled Mitochondria in Cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.

Molecular Bases of Brain Preconditioning

Preconditioning of the brain induces tolerance to the damaging effects of ischemia and prevents cell death in ischemic penumbra. The development of this phenomenon is mediated by mitochondrial adenosine triphosphate-sensitive potassium (KATP+) channels and nitric oxide signaling (NO). The aim of this study was to investigate the dynamics of molecular changes in mitochondria after ischemic preconditioning (IP) and the effect of pharmacological preconditioning (PhP) with the KATP+-channels opener diazoxide on NO levels after ischemic stroke in rats. Immunofluorescence-histochemistry and laser-confocal microscopy were applied to evaluate the cortical expression of electron transport chain enzymes, mitochondrial KATP+-channels, neuronal and inducible NO-synthases, as well as the dynamics of nitrosylation and nitration of proteins in rats during the early and delayed phases of IP. NO cerebral content was studied with electron paramagnetic resonance (EPR) spectroscopy using spin trapping. We found that 24 h after IP in rats, there is a two-fold decrease in expression of mitochondrial KATP+-channels (p = 0.012) in nervous tissue, a comparable increase in expression of cytochrome c oxidase (p = 0.008), and a decrease in intensity of protein S-nitrosylation and nitration (p = 0.0004 and p = 0.001, respectively). PhP led to a 56% reduction of free NO concentration 72 h after ischemic stroke simulation (p = 0.002). We attribute this result to the restructuring of tissue energy metabolism, namely the provision of increased catalytic sites to mitochondria and the increased elimination of NO, which prevents a decrease in cell sensitivity to oxygen during subsequent periods of severe ischemia.

Post-translational regulation of neuronal nitric oxide synthase: implications for sympathoexcitatory states

INTRODUCTION

Nitric oxide (NO) synthesized via neuronal nitric oxide synthase (nNOS) plays a significant role in regulation/modulation of autonomic control of circulation. Various pathological states are associated with diminished nNOS expression and blunted autonomic effects of NO in the central nervous system (CNS) including heart failure, hypertension, diabetes mellitus, chronic renal failure etc. Therefore, elucidation of the molecular mechanism/s involved in dysregulation of nNOS is essential to understand the pathogenesis of increased sympathoexcitation in these diseased states. Areas covered: nNOS is a highly regulated enzyme, being regulated at transcriptional and posttranslational levels via protein-protein interactions and modifications viz. phosphorylation, ubiquitination, and sumoylation. The enzyme activity of nNOS also depends on the optimal concentration of substrate, cofactors and association with regulatory proteins. This review focuses on the posttranslational regulation of nNOS in the context of normal and diseased states within the CNS. Expert opinion: Gaining insight into the mechanism/s involved in the regulation of nNOS would provide novel strategies for manipulating nNOS directed therapeutic modalities in the future, including catalytically active dimer stabilization and protein-protein interactions with intracellular protein effectors. Ultimately, this is expected to provide tools to improve autonomic dysregulation in various diseases such as heart failure, hypertension, and diabetes.

Diabetes impairs heart mitochondrial function without changes in resting cardiac performance

Diabetes is a chronic disease associated to a cardiac contractile dysfunction that is not attributable to underlying coronary artery disease or hypertension, and could be consequence of a progressive deterioration of mitochondrial function. We hypothesized that impaired mitochondrial function precedes Diabetic Cardiomyopathy. Thus, the aim of this work was to study the cardiac performance and heart mitochondrial function of diabetic rats, using an experimental model of type I Diabetes. Rats were sacrificed after 28days of Streptozotocin injection (STZ, 60mgkg^-1, ip.). Heart O₂ consumption was declined, mainly due to the impairment of mitochondrial O₂ uptake. The mitochondrial dysfunction observed in diabetic animals included the reduction of state 3 respiration (22%), the decline of ADP/O ratio (∼15%) and the decrease of the respiratory complexes activities (22-26%). An enhancement in mitochondrial H₂O₂ (127%) and NO (23%) production rates and in tyrosine nitration (58%) were observed in heart of diabetic rats, with a decrease in Mn-SOD activity (∼50%). Moreover, a decrease in contractile response (38%), inotropic (37%) and lusitropic (58%) reserves were observed in diabetic rats only after a β-adrenergic stimulus. Therefore, in conditions of sustained hyperglycemia, heart mitochondrial O₂ consumption and oxidative phosphorylation efficiency are decreased, and H₂O₂ and NO productions are increased, leading to a cardiac compromise against a work overload. This mitochondrial impairment was detected in the absence of heart hypertrophy and of resting cardiac performance changes, suggesting that mitochondrial dysfunction could precede the onset of diabetic cardiac failure, being H₂O₂, NO and ATP the molecules probably involved in mitochondrion-cytosol signalling.

Ketogenic diet decreases oxidative stress and improves mitochondrial respiratory complex activity

Cerebral metabolism of ketones after traumatic brain injury (TBI) improves neuropathology and behavior in an age-dependent manner. Neuroprotection is attributed to improved cellular energetics, although other properties contribute to the beneficial effects. Oxidative stress is responsible for mitochondrial dysfunction after TBI. Ketones decrease oxidative stress, increase antioxidants and scavenge free radicals. It is hypothesized that ketogenic diet (KD) will decrease post-TBI oxidative stress and improve mitochondria. Postnatal day 35 (PND35) male rats were given sham or controlled cortical impact (CCI) injury and placed on standard (STD) or KD. Ipsilateral cortex homogenates and mitochondria were assayed for markers of oxidative stress, antioxidant expression and mitochondrial function. Oxidative stress was significantly increased at 6 and 24 h post-injury and attenuated by KD while inducing protein expression of antioxidants, NAD(P)H dehydrogenase quinone 1 (NQO1) and superoxide dismutase (SOD1/2). Complex I activity was inhibited in STD and KD groups at 6 h and normalized by 24 h. KD significantly improved Complex II-III activity that was reduced in STD at 6 h. Activity remained reduced at 24 h in STD and unchanged in KD animals. These results strongly suggest that ketones improve post-TBI cerebral metabolism by providing alternative substrates and through antioxidant properties, preventing oxidative stress-mediated mitochondrial dysfunction.

Mitochondrial nitric oxide production supported by reverse electron transfer

Heart phosphorylating electron transfer particles (ETPH) produced NO at 1.2 ± 0.1 nmol NO. min(-1) mg protein(-1) by the mtNOS catalyzed reaction. These particles showed a NAD(+) reductase activity of 64 ± 3 nmol min(-1) mg protein(-1) sustained by reverse electron transfer (RET) at expenses of ATP and succinate. The same particles, without NADPH and in conditions of RET produced 0.97 ± 0.07 nmol NO. min(-1) mg protein(-1). Rotenone inhibited NO production supported by RET measured in ETPH and in coupled mitochondria, but did not reduce the activity of recombinant nNOS, indicating that the inhibitory effect of rotenone on NO production is due to an electron flow inhibition and not to a direct action on mtNOS structure. NO production sustained by RET corresponds to 20% of the total amount of NO released from heart coupled mitochondria. A mitochondrial fraction enriched in complex I produced 1.7 ± 0.2 nmol NO. min(-1) mg protein(-1) and reacted with anti-75 kDa complex I subunit and anti-nNOS antibodies, suggesting that complex I and mtNOS are located contiguously. These data show that mitochondrial NO production can be supported by RET, and suggest that mtNOS is next to complex I, reaffirming the idea of a functional association between these proteins.

The Dual Function of Reactive Oxygen/Nitrogen Species in Bioenergetics and Cell Death: The Role of ATP Synthase

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) targeting mitochondria are major causative factors in disease pathogenesis. The mitochondrial permeability transition pore (PTP) is a mega-channel modulated by calcium and ROS/RNS modifications and it has been described to play a crucial role in many pathophysiological events since prolonged channel opening causes cell death. The recent identification that dimers of ATP synthase form the PTP and the fact that posttranslational modifications caused by ROS/RNS also affect cellular bioenergetics through the modulation of ATP synthase catalysis reveal a dual function of these modifications in the cells. Here, we describe mitochondria as a major site of production and as a target of ROS/RNS and discuss the pathophysiological conditions in which oxidative and nitrosative modifications modulate the catalytic and pore-forming activities of ATP synthase.

Mitochondrial oxidative metabolism and uncoupling proteins in the failing heart

Despite significant progress in cardiovascular medicine, myocardial ischemia and infarction, progressing eventually to the final end point heart failure (HF), remain the leading cause of morbidity and mortality in the USA. HF is a complex syndrome that results from any structural or functional impairment in ventricular filling or blood ejection. Ultimately, the heart's inability to supply the body's tissues with enough blood may lead to death. Mechanistically, the hallmarks of the failing heart include abnormal energy metabolism, increased production of reactive oxygen species (ROS) and defects in excitation-contraction coupling. HF is a highly dynamic pathological process, and observed alterations in cardiac metabolism and function depend on the disease progression. In the early stages, cardiac remodeling characterized by normal or slightly increased fatty acid (FA) oxidation plays a compensatory, cardioprotective role. However, upon progression of HF, FA oxidation and mitochondrial oxidative activity are decreased, resulting in a significant drop in cardiac ATP levels. In HF, as a compensatory response to decreased oxidative metabolism, glucose uptake and glycolysis are upregulated, but this upregulation is not sufficient to compensate for a drop in ATP production. Elevated mitochondrial ROS generation and ROS-mediated damage, when they overwhelm the cellular antioxidant defense system, induce heart injury and contribute to the progression of HF. Mitochondrial uncoupling proteins (UCPs), which promote proton leak across the inner mitochondrial membrane, have emerged as essential regulators of mitochondrial membrane potential, respiratory activity and ROS generation. Although the physiological role of UCP2 and UCP3, expressed in the heart, has not been clearly established, increasing evidence suggests that these proteins by promoting mild uncoupling could reduce mitochondrial ROS generation and cardiomyocyte apoptosis and ameliorate thereby myocardial function. Further investigation on the alterations in cardiac UCP activity and regulation will advance our understanding of their physiological roles in the healthy and diseased heart and also may facilitate the development of novel and more efficient therapies.

Nitric oxide interacts with mitochondrial complex III producing antimycin-like effects

The effect of NO between cytochromes b and c of the mitochondrial respiratory chain were studied using submitochondrial particles (SMP) from bovine heart and GSNO and SPER-NO as NO sources. Succinate-cytochrome c reductase (complex II-III) activity (222 ± 4 nmol/min. mg protein) was inhibited by 51% in the presence of 500 μM GSNO and by 48% in the presence of 30 μM SPER-NO, in both cases at ~1.25 μM NO. Neither GSNO nor SPER-NO were able to inhibit succinate-Q reductase activity (complex II; 220 ± 9 nmol/min. mg protein), showing that NO affects complex III. Complex II-III activity was decreased (36%) when SMP were incubated with l-arginine and mtNOS cofactors, indicating that this effect is also produced by endogenous NO. GSNO (500 μM) reduced cytochrome b562 by 71%, in an [O2] independent manner. Hyperbolic increases in O2(•-) (up to 1.3 ± 0.1 nmol/min. mg protein) and H2O2 (up to 0.64 ± 0.05 nmol/min. mg protein) productions were observed with a maximal effect at 500 μM GSNO. The O2(•-)/H2O2 ratio was 1.98 in accordance with the stoichiometry of the O2(•-) disproportionation. Moreover, H2O2 production was increased by 72-74% when heart coupled mitochondria were exposed to 500 μM GSNO or 30 μM SPER-NO. SMP incubated in the presence of succinate showed an EPR signal (g=1.99) compatible with a stable semiquinone. This EPR signal was increased not only by antimycin but also by GSNO and SPER-NO. These signals were not modified under N2 atmosphere, indicating that they are not a consequence to the effect of NOx species on complex III area. These results show that NO interacts with ubiquinone-cytochrome b area producing antimycin-like effects. This behaviour comprises the inhibition of electron transfer, the interruption of the oxidation of cytochromes b, and the enhancement of [UQH(•)]ss which, in turn, leads to an increase in O2(•-) and H2O2 mitochondrial production rates.

Interaction of endothelial nitric oxide synthase with mitochondria regulates oxidative stress and function in fetal pulmonary artery endothelial cells

An increase in oxygen tension at birth is one of the key signals that initiate pulmonary vasodilation in the fetal lung. We investigated the hypothesis that targeting endothelial nitric oxide synthase (eNOS) to the mitochondrial outer membrane regulates reactive oxygen species (ROS) formation in the fetal pulmonary artery endothelial cells (PAEC) during this transition. We isolated PAEC and pulmonary arteries from 137-day gestation fetal lambs (term = 144 days). We exposed PAEC to a simulated transition from fetal to (3% O2) to normoxic (21%) or hyperoxic (95% O2) postnatal Po2 or to the nitric oxide synthase (NOS) agonist ATP. We assessed the effect of O2 and ATP on eNOS interactions with the mitochondrial outer membrane protein porin and with the chaperone hsp90. We also investigated the effect of decoy peptides that blocked eNOS interactions with porin or hsp90 on PAEC angiogenesis and vasodilator function of pulmonary arteries. Transition of fetal PAEC from 3 to 21% O2 but not to 95% O2 or exposure to ATP increased eNOS association with hsp90 and porin. Decoy peptides that blocked eNOS interactions decreased NO release, increased O2 consumption and mitochondrial ROS levels, and impaired PAEC angiogenesis. Decoy peptides also inhibited the relaxation responses of pulmonary artery rings and dilation of resistance size pulmonary arteries to ATP. The mitochondrial-antioxidant mito-ubiquinone restored the response to ATP in decoy peptide-treated pulmonary arteries. These data indicate that targeting eNOS to mitochondria decreases endothelial oxidative stress and facilitates vasodilation in fetal pulmonary circulation at birth.

Inducible NO synthase is constitutively expressed in porcine myocardium and its level decreases along with tachycardia-induced heart failure

BACKGROUND

The adverse effects of oxidative stress and the presence of proinflammatory factors in the heart have been widely demonstrated mainly on rodent models. However, larger clinical trials focusing on inflammation or oxidative stress in heart failure (HF) have not been carried out. This may be due to differences in the anatomy and physiology of the cardiovascular system between small rodents and large mammals. Thus, we investigated myocardial inflammatory factors, such as inducible NO synthase (iNOS) and oxidative stress indices in female pigs with chronic tachycardia-induced cardiomyopathy.

METHODS

Homogenous female siblings of Large White breed swine (n=15) underwent continuous right ventricular (RV) pacing at 170bpm, whereas five sham-operated subjects served as controls. In the course of RV pacing, animals developed a clinical picture of HF and were euthanized at subsequent stages of the disease: mild, moderate and severe HF. Left ventricle (LV) sections were examined with electron microscopy. The relative expression of iNOS in LV was determined by quantitative PCR. The protein level of iNOS was determined by Western blotting and immunohistochemistry. The level of the S-nitrosylated (S-NO) protein in LV was determined after S-NO moieties were substituted by biotin, followed by a colorimetrical detection with streptavidin. Malondialdehyde (MDA), a marker of lipid peroxidation, was evaluated in the LV and serum using thiobarbituric acid. The aconitase activity (based on measurement of the concomitant formation of NADPH from NADP(+)), a marker of oxidative stress, was analyzed in mitochondrial and cytosolic LV fractions. The concentration of interleukin-1β (IL-1β) was measured in LV homogenates using enzyme-linked immunosorbent assay.

RESULTS

RV pacing resulted in an impairment of LV systolic function, LV dilatation and neurohormonal activation. The electron microscopy revealed abnormalities within the cardiomyocytes of failing hearts, i.e. swollen mitochondria and myofibril derangement. iNOS was expressed in the control LV myocardium. The development of HF was accompanied by a decrease in iNOS mRNA (P<.05), which was also reflected at a protein level, and a decrease in the protein S-nitrosylation (P<.05). Both iNOS mRNA and S-NO relative moiety levels were inversely related to the dilatation of the LV (P<.05). There was no difference in the concentration of MDA in the LV and serum. Similarly, no differences in the concentration of IL-1β LV were found between diseased and healthy animals. Aconitase activity was decreased only in the LV mitochondrial fraction of pigs with severe HF.

CONCLUSIONS

iNOS was shown to be constitutively expressed within porcine LV. Its level decreases during the progression of systolic nonischemic HF in the pig model. Thus, it can be assumed that an up-regulation of proinflammatory factors is not involved in porcine tachycardia-induced cardiomyopathy and that the impact of oxidative stress may be restricted to the mitochondria in this HF model.

Sensitivity to anti-Fas is independent of increased cathepsin D activity and adrenodoxin reductase expression occurring in NOS-3 overexpressing HepG2 cells

Stable overexpression of endothelial nitric oxide synthase (NOS-3) in HepG2 cells (4TO-NOS) leads to increased nitro-oxidative stress and upregulation of the cell death mediators p53 and Fas. Thus, NOS-3 overexpression has been suggested as a useful antiproliferative mechanism in hepatocarcinoma cells. We aimed to identify the underlying mechanism of cell death induced by NOS-3 overexpression at basal conditions and with anti-Fas treatment. The intracellular localization of NOS-3, the nitro-oxidative stress and the mitochondrial activity were analysed. In addition, the protein expression profile in 4TO-NOS was screened for differentially expressed proteins potentially involved in the induction of apoptosis. NOS-3 localization in the mitochondrial outer membrane was not associated with changes in the respiratory cellular capacity, but was related to the mitochondrial biogenesis increase and with a higher protein expression of mitochondrial complex IV. Nitro-oxidative stress and cell death in NOS-3 overexpressing cells occurred with the expression increase of pro-apoptotic genes and a higher expression/activity of the enzymes adrenodoxin reductase mitochondrial (AR) and cathepsin D (CatD). CatD overexpression in 4TO-NOS was related to the apoptosis induction independently of its catalytic activity. In addition, CatD activity inhibition by pepstatin A was not effective in blocking apoptosis induced by anti-Fas. In summary, NOS-3 overexpression resulted in an increased sensitivity to anti-Fas induced cell death, independently of AR expression and CatD activity.

Interaction between connexin 43 and nitric oxide synthase in mice heart mitochondria

Connexin 43 (Cx43), which is highly expressed in the heart and especially in cardiomyocytes, interferes with the expression of nitric oxide synthase (NOS) isoforms. Conversely, Cx43 gene expression is down-regulated by nitric oxide derived from the inducible NOS. Thus, a complex interplay between Cx43 and NOS expression appears to exist. As cardiac mitochondria are supposed to contain a NOS, we now investigated the expression of NOS isoforms and the nitric oxide production rate in isolated mitochondria of wild-type and Cx43-deficient (Cx43(Cre-ER(T)/fl) ) mice hearts. Mitochondria were isolated from hearts using differential centrifugation and purified via Percoll gradient ultracentrifugation. Isolated mitochondria were stained with an antibody against the mitochondrial marker protein adenine-nucleotide-translocator (ANT) in combination with either a neuronal NOS (nNOS) or an inducible NOS (iNOS) antibody and analysed using confocal laser scanning microscopy. The nitric oxide formation was quantified in purified mitochondria using the oxyhaemoglobin assay. Co-localization of predominantly nNOS (nNOS: 93 ± 4.1%; iNOS: 24.6 ± 7.5%) with ANT was detected in isolated mitochondria of wild-type mice. In contrast, iNOS expression was increased in Cx43(Cre-ER(T)/fl) mitochondria (iNOS: 90.7 ± 3.2%; nNOS: 53.8 ± 17.5%). The mitochondrial nitric oxide formation was reduced in Cx43(Cre-ER(T)/fl) mitochondria (0.14 ± 0.02 nmol/min./mg protein) in comparison to wild-type mitochondria (0.24 ± 0.02 nmol/min./mg). These are the first data demonstrating, that a reduced mitochondrial Cx43 content is associated with a switch of the mitochondrial NOS isoform and the respective mitochondrial rate of nitric oxide formation.

Cysteine-mediated redox signalling in the mitochondria

This review represents a novel look at the many sources, cysteine targets, and signaling processes of ROS in the mitochondria.

Role of nitric oxide in the regulation of motor function. An overview of behavioral, biochemical and histological studies in animal models

A compelling body of evidence suggests that nitric oxide (NO), a unique gaseous neurotransmitter and neuromodulator plays a key role in the regulation of motor function. Recently, the interest of researchers concentrates on the NO - soluble guanylyl cyclase (sGC) - cyclic GMP (cGMP) signaling pathway in the striatum as a new target for the treatment of Parkinson's disease (PD). The aim of the study is to review the available literature referring to the role of NO in the integration of basal ganglia functions. First, attention has been focused on behavioral effects of NO donors and neuronal nitric oxide synthase (nNOS) inhibitors in the modulation of motor behavior. Then, disturbances in the nitrergic neurotransmission in PD and its 6-OHDA animal model have been presented. Moreover, the most current data demonstrating the contribution of both dopamine and glutamate to the regulation of NO biosynthesis in the striatum have been analyzed. Finally, the role of NO in the tonic and phasic dopamine release as well as in the regulation of striatal output pathways also has been discussed.

Abnormal mitochondrial L-arginine transport contributes to the pathogenesis of heart failure and rexoygenation injury

Background

Impaired mitochondrial function is fundamental feature of heart failure (HF) and myocardial ischemia. In addition to the effects of heightened oxidative stress, altered nitric oxide (NO) metabolism, generated by a mitochondrial NO synthase, has also been proposed to impact upon mitochondrial function. However, the mechanism responsible for arginine transport into mitochondria and the effect of HF on such a process is unknown. We therefore aimed to characterize mitochondrial L-arginine transport and to investigate the hypothesis that impaired mitochondrial L-arginine transport plays a key role in the pathogenesis of heart failure and myocardial injury.

Methods and Results

In mitochondria isolated from failing hearts (sheep rapid pacing model and mouse Mst1 transgenic model) we demonstrated a marked reduction in L-arginine uptake (p<0.05 and p<0.01 respectively) and expression of the principal L-arginine transporter, CAT-1 (p<0.001, p<0.01) compared to controls. This was accompanied by significantly lower NO production and higher 3-nitrotyrosine levels (both p<0.05). The role of mitochondrial L-arginine transport in modulating cardiac stress responses was examined in cardiomyocytes with mitochondrial specific overexpression of CAT-1 (mtCAT1) exposed to hypoxia-reoxygenation stress. mtCAT1 cardiomyocytes had significantly improved mitochondrial membrane potential, respiration and ATP turnover together with significantly decreased reactive oxygen species production and cell death following mitochondrial stress.

Conclusion

These data provide new insights into the role of L-arginine transport in mitochondrial biology and cardiovascular disease. Augmentation of mitochondrial L-arginine availability may be a novel therapeutic strategy for myocardial disorders involving mitochondrial stress such as heart failure and reperfusion injury.

The beneficial effects of melatonin against heart mitochondrial impairment during sepsis: inhibition of iNOS and preservation of nNOS

While it is accepted that the high production of nitric oxide (NO˙) by the inducible nitric oxide synthase (iNOS) impairs cardiac mitochondrial function during sepsis, the role of neuronal nitric oxide synthase (nNOS) may be protective. During sepsis, there is a significantly increase in the expression and activity of mitochondrial iNOS (i-mtNOS), which parallels the changes in cytosolic iNOS. The existence of a constitutive NOS form (c-mtNOS) in heart mitochondria has been also described, but its role in the heart failure during sepsis remains unclear. Herein, we analyzed the changes in mitochondrial oxidative stress and bioenergetics in wild-type and nNOS-deficient mice during sepsis, and the role of melatonin, a known antioxidant, in these changes. Sepsis was induced by cecal ligation and puncture, and heart mitochondria were analyzed for NOS expression and activity, nitrites, lipid peroxidation, glutathione and glutathione redox enzymes, oxidized proteins, and respiratory chain activity in vehicle- and melatonin-treated mice. Our data show that sepsis produced a similar induction of iNOS/i-mtNOS and comparable inhibition of the respiratory chain activity in wild-type and in nNOS-deficient mice. Sepsis also increased mitochondrial oxidative/nitrosative stress to a similar extent in both mice strains. Melatonin administration inhibited iNOS/i-mtNOS induction, restored mitochondrial homeostasis in septic mice, and preserved the activity of nNOS/c-mtNOS. The effects of melatonin were unrelated to the presence or the absence of nNOS. Our observations show a lack of effect of nNOS on heart bioenergetic impairment during sepsis and further support the beneficial actions of melatonin in sepsis.

The role of nNOS and PGC-1α in skeletal muscle cells

Neuronal nitric oxide synthase (nNOS) and peroxisome proliferator activated receptor γ co-activator 1α (PGC-1α) are two fundamental factors involved in the regulation of skeletal muscle cell metabolism. nNOS exists as several alternatively spliced variants, each having a specific pattern of subcellular localisation. Nitric oxide (NO) functions as a second messenger in signal transduction pathways that lead to the expression of metabolic genes involved in oxidative metabolism, vasodilatation and skeletal muscle contraction. PGC-1α is a transcriptional coactivator and represents a master regulator of mitochondrial biogenesis by promoting the transcription of mitochondrial genes. PGC-1α can be induced during physical exercise, and it plays a key role in coordinating the oxidation of intracellular fatty acids with mitochondrial remodelling. Several lines of evidence demonstrate that NO could act as a key regulator of PGC-1α expression; however, the link between nNOS and PGC-1α in skeletal muscle remains only poorly understood. In this Commentary, we review important metabolic pathways that are governed by nNOS and PGC-1α, and aim to highlight how they might intersect and cooperatively regulate skeletal muscle mitochondrial and lipid energetic metabolism and contraction.

Brain stem NOS and ROS in neural mechanisms of hypertension

SIGNIFICANCE

There is now compelling evidence to substantiate the notion that by depressing baroreflex regulation of blood pressure and augmenting central sympathetic outflow through their actions on the nucleus tractus solitarii (NTS) and rostral ventrolateral medulla (RVLM), brain stem nitric oxide synthase (NOS) and reactive oxygen species (ROS) are important contributing factors to neural mechanisms of hypertension. This review summarizes our contemporary views on the impact of NOS and ROS in the NTS and RVLM on neurogenic hypertension, and presents potential antihypertensive strategies that target brain stem NOS/ROS signaling.

RECENT ADVANCES

NO signaling in the brain stem may be pro- or antihypertensive depending on the NOS isoform that generates this gaseous moiety and the site of action. Elevation of the ROS level when its production overbalances its degradation in the NTS and RVLM underlies neurogenic hypertension. Interventional strategies with emphases on alleviating the adverse actions of these molecules on blood pressure regulation have been investigated.

CRITICAL ISSUES

The pathological roles of NOS in the RVLM and NTS in neural mechanisms of hypertension are highly complex. Likewise, multiple signaling pathways underlie the deleterious roles of brain-stem ROS in neurogenic hypertension. There are recent indications that interactions between brain stem ROS and NOS may play a contributory role.

FUTURE DIRECTIONS

Given the complicity of action mechanisms of brain-stem NOS and ROS in neural mechanisms of hypertension, additional studies are needed to identify the most crucial therapeutic target that is applicable not only in animal models but also in patients suffering from neurogenic hypertension.

The role of s-nitrosylation and s-glutathionylation of protein disulphide isomerase in protein misfolding and neurodegeneration

Neurodegenerative diseases involve the progressive loss of neurons, and a pathological hallmark is the presence of abnormal inclusions containing misfolded proteins. Although the precise molecular mechanisms triggering neurodegeneration remain unclear, endoplasmic reticulum (ER) stress, elevated oxidative and nitrosative stress, and protein misfolding are important features in pathogenesis. Protein disulphide isomerase (PDI) is the prototype of a family of molecular chaperones and foldases upregulated during ER stress that are increasingly implicated in neurodegenerative diseases. PDI catalyzes the rearrangement and formation of disulphide bonds, thus facilitating protein folding, and in neurodegeneration may act to ameliorate the burden of protein misfolding. However, an aberrant posttranslational modification of PDI, S-nitrosylation, inhibits its protective function in these conditions. S-nitrosylation is a redox-mediated modification that regulates protein function by covalent addition of nitric oxide- (NO-) containing groups to cysteine residues. Here, we discuss the evidence for abnormal S-nitrosylation of PDI (SNO-PDI) in neurodegeneration and how this may be linked to another aberrant modification of PDI, S-glutathionylation. Understanding the role of aberrant S-nitrosylation/S-glutathionylation of PDI in the pathogenesis of neurodegenerative diseases may provide insights into novel therapeutic interventions in the future.

Characterization of apoptosis induced by emodin and related regulatory mechanisms in human neuroblastoma cells

Emodin (1,3,8-trihydroxy-6-methylanthraquinone), a major constituent of rhubarb, has a wide range of therapeutic applications. Recent studies have shown that emodin can induce or prevent cell apoptosis, although the precise molecular mechanisms underlying these effects are unknown. Experiments from the current study revealed that emodin (10–20 μM) induces apoptotic processes in the human neuroblastoma cell line, IMR-32, but exerts no injury effects at treatment doses below 10 μM. Treatment with emodin at concentrations of 10–20 μM led to a direct increase in the reactive oxygen species (ROS) content in IMR-32 cells, along with significant elevation of cytoplasmic free calcium and nitric oxide (NO) levels, loss of mitochondrial membrane potential (MMP), activation of caspases-9 and -3, and cell death. Pretreatment with nitric oxide (NO) scavengers suppressed the apoptotic biochemical changes induced by 20 μM emodin, and attenuated emodin-induced p53 and p21 expression involved in apoptotic signaling. Our results collectively indicate that emodin at concentrations of 10–20 μM triggers apoptosis of IMR-32 cells via a mechanism involving both ROS and NO. Based on the collective results, we propose a model for an emodin-triggered apoptotic signaling cascade that sequentially involves ROS, Ca²⁺, NO, p53, caspase-9 and caspase-3.

Protective effect of curcuminoids on age-related mitochondrial impairment in female Wistar rat brain

The present study demonstrated the neuroprotective effect of curcuminoids, the active polyphenols of Curcuma longa (L.) rhizomes on mitochondrial dysfunctioning in middle aged and aged female Wistar rat brain. Rats were orally treated with curcuminoids (100 mg/kg) for 3 months and their brain was collected for evaluation of mitochondrial enzymes and complexes activity, ultra structural changes in mitochondria, neuronal nitric oxide synthase (nNOS) protein expression, adenosine triphosphate (ATP) and lipofuscin content. Significant alterations were observed in all the tested parameters in highly aged rat brain when compared with young control. Long term curcuminoids administration prevented this age associated loss of mitochondrial enzymes and complexes activity in middle aged rat brain except for malate dehydrogenase, Complex II and IV activity when compared with young control. Among aged rats, curcuminoids treatment specifically elevated isocitrate and NADH dehydrogenase, cytochrome c oxidase, Complex I and total ATP content. A significant down-regulation of nNOS protein expression along with reduced lipofuscin content was also observed in curucminoids treated middle aged and aged rats. Thus, it was suggested that curcuminoids may act as a putative drug candidate for the prevention of deleterious effects of ageing and age associated neurodegenerative disorders through amelioration of aberrant mitochondrial functioning.