Selective vulnerability of synaptic signaling and metabolism to nitrosative stress

Structural Analysis of Plasmodium falciparum Hexokinase Provides Novel Information about Catalysis Due to a Plasmodium-Specific Insertion

The protozoan parasite Plasmodium falciparum is the causative pathogen of the most severe form of malaria, for which novel strategies for treatment are urgently required. The primary energy supply for intraerythrocytic stages of Plasmodium is the production of ATP via glycolysis. Due to the parasite's strong dependence on this pathway and the significant structural differences of its glycolytic enzymes compared to its human counterpart, glycolysis is considered a potential drug target. In this study, we provide the first three-dimensional protein structure of P. falciparum hexokinase (PfHK) containing novel information about the mechanisms of PfHK. We identified for the first time a Plasmodium-specific insertion that lines the active site. Moreover, we propose that this insertion plays a role in ATP binding. Residues of the insertion further seem to affect the tetrameric interface and therefore suggest a special way of communication among the different monomers. In addition, we confirmed that PfHK is targeted and affected by oxidative posttranslational modifications (oxPTMs). Both S-glutathionylation and S-nitrosation revealed an inhibitory effect on the enzymatic activity of PfHK.

The effect of intranasal administration of an IL-1b antagonist (RAIL) on the state of the nitroxydergic system of the brain during modeling of acute cerebrovascular accident

Introduction: This study was designed to evaluate the effect activity of RAIL-gel in comparison with Citicoline on nitroxydergic system during acute cerebrovascular accident.

Methods: In this study, 80 white nonlinear rats were randomly assigned to 4 groups (20 rats in each): 1) intact; 2) control - untreated with acute cerebrovascular accident (ACVA), examined on the 4th day; 3) animals with ACVA, receiving RAIL, examined on the 18th day; 4) animals with ACVA, treated with Citicoline, examined on the 4th day. The expression of inducible NOS was determined by Western blotting. The nitrosative stress marker, nitrotyrosine, was determined using the ELISE kit NITROTYROSINE (kit no. HK501-02, series 12825k1212-k). To assess the state of iNOS mRNA expression, we used the method of polymerase chain reaction with reverse transcription in real time (RT-PCR).

Results: Our research demonstrated that course administration of the RAIL and Citicoline to animals with ACVA for 4 days leads to the stabilization of the parameters of the brain nitroxydergic system. However, Citicoline does not provide a full effect on the shifts of the NO system in the brain. It does not have the proper effect on such an important link in the pathogenesis of ischemic brain damage as nitrosative stress. RAIL leads to a significant decrease in NOS activity due to its inducible form (decrease in the expression of iNOS and iNOS mRNA) and a decrease in NO metabolits, and inhibition of nitrosative stress (decrease in nitrotyrosine).

Conclusion: IL-1b antagonist RAIL (Intranal Gel) significantly exceeds Citicoline in terms of the severity of the effect on the nitroxydergic system indicators.

The synthetic peptide PnPP-19 potentiates erectile function via nNOS and iNOS

PnPP-19 peptide has a primary sequence design based on molecular modeling studies of PnTx2-6 toxin. It comprises the amino acid residues that are potentially significant for the pharmacological action of PnTx2-6. Ex vivo and in vivo experiments in normotensive, hypertensive, or diabetic murine models have shown a significant improvement in penile erection after administration of PnPP-19. Given the potential use of PnPP-19 in pharmaceutical formulations to treat erectile dysfunction and the lack of information concerning its mode of action, the present work investigates its activities on the nitrergic system. PnPP-19 induced a significant increase in nitric oxide (NO) and cGMP levels in corpus cavernosum (cc). These effects were inhibited by l-NAME, a non-selective inhibitor of nitric oxide synthase (NOS); were partially inhibited by 7- Nitroindazole, a selective inhibitor of neuronal NOS (nNOS); and were abolished by L-NIL, a selective inhibitor of inducible NOS (iNOS). This potentiating effect was not affected by atropine. PnPP-19 also led to changes in mRNA levels, protein expression and phosphorylation at specific sites of NOS, in cc. Assays using cavernous tissue from knockout mice to endothelial NOS (eNOS), nNOS or iNOS showed that PnPP-19 potentiates relaxation only in eNOS-knockout mice, which suggests an essential role for nNOS. Surprisingly, iNOS enhanced the potentiation of erectile function evoked by PnPP-19. Our results demonstrate that this new synthetic peptide potentiates erectile function via nitric oxide activation and reinforce its role as a new pharmacological tool for the treatment of erectile dysfunction.

Regional Brain Recovery from Acute Synaptic Injury in Simian Immunodeficiency Virus-Infected Rhesus Macaques Associates with Heme Oxygenase Isoform Expression

Brain injury induced by acute simian (or human) immunodeficiency virus infection may persist or spontaneously resolve in different brain regions. Identifying the host factor(s) that promotes spontaneous recovery from such injury may reveal targets for therapeutic drug strategies for promoting recovery from acute neuronal injury. The gradual recovery from such injury observed in many, but not all, brain regions in the rhesus macaque model is consistent with the possible existence of a therapeutic window of opportunity for intervening to promote recovery, even in those regions not showing spontaneous recovery. In persons living with human immunodeficiency virus infection, such neuroprotective treatments could ultimately be considered as adjuncts to the initiation of antiretroviral drug therapy.

Brain injury occurs within days in simian immunodeficiency virus (SIV) or human immunodeficiency virus (HIV) infection, and some recovery may occur within weeks. Inflammation and oxidative stress associate with such injury, but what drives recovery is unknown. Chronic HIV infection associates with reduced brain frontal cortex expression of the antioxidant/anti-inflammatory enzyme heme oxygenase-1 (HO-1) and increased neuroinflammation in individuals with cognitive impairment. We hypothesized that acute regional brain injury and recovery associate with differences in regional brain HO-1 expression. Using SIV-infected rhesus macaques, we analyzed multiple brain regions through acute and chronic infection (90 days postinfection [dpi]) and quantified viral (SIV gag RNA), synaptic (PSD-95; synaptophysin), axonal (neurofilament/neurofilament light chain [NFL]), inflammatory, and antioxidant (enzymes, including heme oxygenase isoforms [HO-1, HO-2]) markers. PSD-95 was reduced in the brainstem, basal ganglia, neocortex, and cerebellum within 13 dpi, indicating acute synaptic injury throughout the brain. All areas except the brainstem recovered. Unchanged NFL was consistent with no acute axonal injury. SIV RNA expression was highest in the brainstem throughout infection, and it associated with neuroinflammation. Surprisingly, during the synaptic injury and recovery phases, HO-2, and not HO-1, progressively decreased in the brainstem. Thus, acute SIV synaptic injury occurs throughout the brain, with spontaneous recovery in regions other than the brainstem. Within the brainstem, the high SIV load and inflammation, along with reduction of HO-2, may impair recovery. In other brain regions, stable HO-2 expression, with or without increasing HO-1, may promote recovery. Our data support roles for heme oxygenase isoforms in modulating recovery from synaptic injury in SIV infection and suggest their therapeutic targeting for promoting neuronal recovery.

IMPORTANCE Brain injury induced by acute simian (or human) immunodeficiency virus infection may persist or spontaneously resolve in different brain regions. Identifying the host factor(s) that promotes spontaneous recovery from such injury may reveal targets for therapeutic drug strategies for promoting recovery from acute neuronal injury. The gradual recovery from such injury observed in many, but not all, brain regions in the rhesus macaque model is consistent with the possible existence of a therapeutic window of opportunity for intervening to promote recovery, even in those regions not showing spontaneous recovery. In persons living with human immunodeficiency virus infection, such neuroprotective treatments could ultimately be considered as adjuncts to the initiation of antiretroviral drug therapy.

Mechanism Underlying the Protective Effect of Selenium on NO-Induced Oxidative Damage in Bovine Mammary Epithelial Cells

This experiment was conducted to investigate the effects and mechanism of selenium (Se) on antioxidant and immune function of bovine mammary epithelial cells (BMEC) damaged by nitric oxide (NO). The third-generation BMEC was randomly divided into eight treatments with six replicates. The BMEC in the control group was cultured in the medium without Se and diethylenetriamine/NO (DETA/NO) for 30 h. For the DETA/NO group and Se protection group BMEC were exposed to different concentrations of Se (0, 10, 20, 50, 100, 150, and 200 nmol/L) for 24 h, followed by treatment with DETA/NO (1000 μmol/L) for 6 h. Compared with the control group, DETA/NO decreased proliferation rate and activity of thioredoxin reductase (TrxR; P < 0.05). Additionally, DETA/NO decreased the gene expression of both nuclear factor-E2-related factor 2 (Nrf2) and TrxR, as well as the protein expression level of TrxR. However, the activity, and expression levels of inducible nitric oxide synthase (iNOS), as well as the concentration and gene expression level of interleukin-1β (IL-1β) and the concentration of NO significantly increased (P < 0.05). The gene expression levels of indexes related to the mitogen-activated protein kinase (MAPK) signaling pathway showed similar changes. Treatment of BMEC with Se significantly reversed DETA/NO-induced changes in a linear or quadratic dose-dependent manner (P < 0.05), with greatest benefit at 50 nmol/L. These data suggests that Se improves the antioxidant function of BMEC, and protects cells from DETA/NO-induced oxidative damage, primarily by enhancing the activity of TrxR and decreasing the concentration of NO through modulation of Nrf2 and MAPK signaling pathways.

Redox Regulation of Hexokinases

SIGNIFICANCE

Hexokinases are key enzymes that are responsible for the first reaction of glycolysis, but they also moonlight other cellular processes, including mitochondrial redox signaling regulation. Modulation of hexokinase activity and spatiotemporal location by reactive oxygen and nitrogen species as well as other gasotransmitters serves as the basis for a unique, underexplored method of tight and flexible regulation of these fundamental enzymes. Recent Advances: Redox modifications of thiols serve as a molecular code that enables the precise and complex regulation of hexokinases. Redox regulation of hexokinases is also used by multiple parasites to cause widespread and severe diseases, including malaria, Chagas disease, and sleeping sickness. Redox-active molecules affect each other, and the moonlighting activity of hexokinases provides another feedback loop that affects the cellular redox status and is hijacked in malignantly transformed cells.

CRITICAL ISSUES

Several compounds affect the redox status of hexokinases in vivo. These include the dehydroascorbic acid (oxidized form of vitamin C), pyrrolidinium porrolidine-1-carbodithioate (contraceptive), peroxynitrite (product of ethanol metabolism), alloxan (a glucose analog), and isobenzothiazolinone ebselen. However, very limited information is available regarding which amino acid residues in hexokinases are affected by redox signaling. Except in cases of monogenic diabetes, direct evidence is absent for disease phenotypes that are associated with variations within motifs that are susceptible to redox signaling.

FUTURE DIRECTIONS

Further studies should address the propensity of hexokinases and their disease-associated variants to participate in redox regulation. Robust and straightforward proteomic methods are needed to understand the context and consequences of hexokinase-mediated redox regulation in health and disease.

Cell Volume Control in Healthy Brain and Neuropathologies

Regulation of cellular volume is a critical homeostatic process that is intimately linked to ionic and osmotic balance in the brain tissue. Because the brain is encased in the rigid skull and has a very complex cellular architecture, even minute changes in the volume of extracellular and intracellular compartments have a very strong impact on tissue excitability and function. The failure of cell volume control is a major feature of several neuropathologies, such as hyponatremia, stroke, epilepsy, hyperammonemia, and others. There is strong evidence that such dysregulation, especially uncontrolled cell swelling, plays a major role in adverse pathological outcomes. To protect themselves, brain cells utilize a variety of mechanisms to maintain their optimal volume, primarily by releasing or taking in ions and small organic molecules through diverse volume-sensitive ion channels and transporters. In principle, the mechanisms of cell volume regulation are not unique to the brain and share many commonalities with other tissues. However, because ions and some organic osmolytes (e.g., major amino acid neurotransmitters) have a strong impact on neuronal excitability, cell volume regulation in the brain is a surprisingly treacherous process, which may cause more harm than good. This topical review covers the established and emerging information in this rapidly developing area of physiology.

'SNO'-Storms Compromise Protein Activity and Mitochondrial Metabolism in Neurodegenerative Disorders

The prevalence of neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), is currently a major public health concern due to the lack of efficient disease-modifying therapeutic options. Recent evidence suggests that mitochondrial dysfunction and nitrosative/oxidative stress are key common mediators of pathogenesis. In this review, we highlight molecular mechanisms linking NO-dependent post-translational modifications, such as cysteine S-nitrosylation and tyrosine nitration, to abnormal mitochondrial metabolism. We further discuss the hypothesis that pathological levels of NO compromise brain energy metabolism via aberrant S-nitrosylation of key enzymes in the tricarboxylic acid (TCA) cycle and oxidative phosphorylation, contributing to neurodegenerative conditions. A better understanding of these pathophysiological events may provide a potential pathway for designing novel therapeutics to ameliorate neurodegenerative disorders.

Nitric oxide induces hypoxia ischemic injury in the neonatal brain via the disruption of neuronal iron metabolism

We have recently shown that increased hydrogen peroxide (H₂O₂) generation is involved in hypoxia–ischemia (HI)-mediated neonatal brain injury. H₂O₂ can react with free iron to form the hydroxyl radical, through Fenton Chemistry. Thus, the objective of this study was to determine if there was a role for the hydroxyl radical in neonatal HI brain injury and to elucidate the underlying mechanisms. Our data demonstrate that HI increases the deposition of free iron and hydroxyl radical formation, in both P7 hippocampal slice cultures exposed to oxygen–glucose deprivation (OGD), and the neonatal rat exposed to HI. Both these processes were found to be nitric oxide (NO) dependent. Further analysis demonstrated that the NO-dependent increase in iron deposition was mediated through increased transferrin receptor expression and a decrease in ferritin expression. This was correlated with a reduction in aconitase activity. Both NO inhibition and iron scavenging, using deferoxamine administration, reduced hydroxyl radical levels and neuronal cell death. In conclusion, our results suggest that increased NO generation leads to neuronal cell death during neonatal HI, at least in part, by altering iron homeostasis and hydroxyl radical generation.

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HI increases the deposition of free iron and hydroxyl radical formation in the neonatal brain.

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Both these processes are NO dependent.

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Increased iron deposition is mediated via increased TfR and decreased ferritin expression.

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These processes are involved in the neuronal cell death associated with neonatal HI.

Cancer cell metabolism and the modulating effects of nitric oxide

Altered metabolic phenotype has been recognized as a hallmark of tumor cells for many years, but this aspect of the cancer phenotype has come into greater focus in recent years. NOS2 (inducible nitric oxide synthase of iNOS) has been implicated as a component in many aggressive tumor phenotypes, including melanoma, glioblastoma, and breast cancer. Nitric oxide has been well established as a modulator of cellular bioenergetics pathways, in many ways similar to the alteration of cellular metabolism observed in aggressive tumors. In this review we attempt to bring these concepts together with the general hypothesis that one function of NOS2 and NO in cancer is to modulate metabolic processes to facilitate increased tumor aggression. There are many mechanisms by which NO can modulate tumor metabolism, including direct inhibition of respiration, alterations in mitochondrial mass, oxidative inhibition of bioenergetic enzymes, and the stimulation of secondary signaling pathways. Here we review metabolic alterations in the context of cancer cells and discuss the role of NO as a potential mediator of these changes.

Nitric oxide and energy metabolism in mammals

Nitric oxide (NO) is a signaling molecule synthesized from L-arginine by NO synthase in animals. Increasing evidence shows that NO regulates the mammalian metabolism of energy substrates and that these effects of NO critically depend on its concentrations at the reaction site and the period of exposure. High concentrations of NO (in the micromolar range) irreversibly inhibit complexes I, II, III, IV, and V in the mitochondrial respiratory chain, whereas physiological levels of NO (in the nanomolar range) reversibly reduce cytochomrome oxidase. Thus, NO reduces oxygen consumption by isolated mitochondria to various extents. In intact cells, through cGMP and AMP-activated protein kinase signaling, physiological levels of NO acutely stimulate uptake and oxidation of glucose and fatty acids by skeletal muscle, heart, liver, and adipose tissue, while inhibiting the synthesis of glucose, glycogen and fat in the insulin-sensitive tissues, and enhancing lipolysis in white adipocytes. Chronic effects of physiological levels of NO in vivo include stimulation of angiogenesis, blood flow, mitochondrial biogenesis, and brown adipocyte development. Modulation of NO-mediated pathways through dietary supplementation with L-arginine or its precursor L-citrulline may provide an effective, practical strategy to prevent and treat metabolic syndrome, including obesity, diabetes, and dyslipidemia in mammals, including humans.

Characterization of adult rat astrocyte cultures

Astrocytes, a major class of glial cells, regulate neurotransmitter systems, synaptic processing, ion homeostasis, antioxidant defenses and energy metabolism. Astrocyte cultures derived from rodent brains have been extensively used to characterize astrocytes' biochemical, pharmacological and morphological properties. The aims of this study were to develop a protocol for routine preparation and to characterize a primary astrocyte culture from the brains of adult (90 days old) Wistar rats. For this we used enzymatic digestion (trypsin and papain) and mechanical dissociation. Medium exchange occurred from 24 h after obtaining a culture and after, twice a week up to reach the confluence (around the 4^th to 5^th week). Under basal conditions, adult astrocytes presented a polygonal to fusiform and flat morphology. Furthermore, approximately 95% the cells were positive for the main glial markers, including GFAP, glutamate transporters, glutamine synthetase and S100B. Moreover, the astrocytes were able to take up glucose and glutamate. Adult astrocytes were also able to respond to acute H₂O₂ exposure, which led to an increase in reactive oxygen species (ROS) levels and a decrease in glutamate uptake. The antioxidant compound resveratrol was able to protect adult astrocytes from oxidative damage. A response of adult astrocytes to an inflammatory stimulus with LPS was also observed. Changes in the actin cytoskeleton were induced in stimulated astrocytes, most likely by a mechanism dependent on MAPK and Rho A signaling pathways. Taken together, these findings indicate that the culture model described in this study exhibits the biochemical and physiological properties of astrocytes and may be useful for elucidating the mechanisms related to the adult brain, exploring changes between neonatal and adult astrocytes, as well as investigating compounds involved in cytotoxicity and cytoprotection.

saRNA guided iNOS up-regulation improves erectile function of diabetic rats

PURPOSE

Promoter targeted saRNAs mediate sequence specific up-regulation of gene expression. We explored the therapeutic effect of RNA activation mediated iNOS gene activation on improving erectile function in a rat model of diabetes mellitus.

MATERIALS AND METHODS

An optimal saRNA sequence specific for iNOS promoter was cloned into an adenoviral vector, resulting in AdU6/shiNOS and AdU6/shControl. The corresponding viruses were used to transduce cultured rat cavernous smooth muscle cells. Streptozotocin induced diabetes models were established in rats and used to test the effects of intracavernous delivery of iNOS saRNA viruses on erectile function. iNOS expression in the cavernous smooth muscle cells or penile tissue of treated rats was assessed by reverse transcriptase-polymerase chain reaction and Western blot. Cyclic guanosine monophosphate was analyzed by enzyme-linked immunosorbent assay. Intracavernous pressure in response to cavernous nerve stimulation was measured using a data acquisition system on post-injection days 1, 3, 5, 7, 10 and 14.

RESULTS

Adenovirus mediated expression of iNOS saRNA caused sustained up-regulation of iNOS in cavernous smooth muscle cells. Intracavernous injection of AdU6/shiNOS activated iNOS expression in vivo and significantly increased peak intracavernous pressure in streptozotocin induced diabetic rats via nitric oxide/intracellular cyclic guanosine monophosphate activation.

CONCLUSIONS

Results show that saRNA mediated iNOS over expression in the penis can restore erectile function in streptozocin diabetic rats via the nitric oxide-cyclic guanosine monophosphate pathway.

S-nitrosation: current concepts and new developments

The S-nitrosation (also referred to as S-nitrosylation) of cysteine residues is an important post-translational protein modification that regulates protein function and cell signaling. The original research articles and reviews in this Forum cover important concepts in protein S-nitrosation and identify key developments and opportunities for progress in this area. Defining the mechanisms by which S-nitrosothiols (RSNOs) may be formed and decomposed in cells and tissues, the integration of the biological chemistry associated with nitric oxide (NO) and other derivatives such as nitrite, and the development of new methodologies merging proteomics and direct quantitation are all key issues that we believe would require detailed attention.