Nitric oxide signaling: systems integration of oxygen balance in defense of cell integrity

Hyaluronic Acid-Coated Silica Nanoparticles for Targeted Delivery of Nitric Oxide to Cancer Cells

Drug resistance and off-target toxicity are two of the greatest challenges to chemotherapeutic melanoma treatments. Nitric oxide (NO) represents an attractive alternative to conventional therapeutics due to its numerous anticancer properties and low probability of engendering resistance. As NO is highly reactive, macromolecular NO donors are needed for the controlled and targeted delivery of NO for therapeutic applications. Herein, mesoporous silica nanoparticles (MSNs) coated with hyaluronic acid (HA) were developed as a NO delivery system to facilitate controlled delivery to cancer cells through both passive and active targeting via the enhanced permeation and retention effect and directed binding of HA with CD44 receptors, respectively. The aminosilane modification, HA concentration, and HA molecular weight were systematically evaluated to facilitate the MSN coating and NO loading. The hydrodynamic diameter and dispersity of the nanoparticles increased after HA coating due to the hydrophilic nature of HA, with greater increases observed at higher HA molecular weight. Lower starting concentrations of HA and aminosilanes with longer alkyl chains favored more efficient HA coating. Faster NO-release kinetics and lower NO payloads were observed for the HA-coated MSNs relative to uncoated MSNs. However, the localized delivery of NO to cancer cells through the active targeting conferred by HA increased levels of oxidative stress and induced mitochondria-mediated apoptosis in melanoma cells. Cytotoxicity was also evaluated against human dermal fibroblasts, with the use of 6 kDa HA-coated MSNs resulting in the greatest therapeutic indices. Enhanced internalization of HA-coated nanoparticles into melanoma cells versus uncoated nanoparticles was visualized with confocal microscopy and quantified by fluorescence spectroscopy. In total, HA-coated MSNs represent a promising NO delivery system for potential use as a chemotherapeutic for skin melanomas.

The premetazoan ancestry of the synaptic toolkit and appearance of first neurons

Neurons, especially when coupled with muscles, allow animals to interact with and navigate through their environment in ways unique to life on earth. Found in all major animal lineages except sponges and placozoans, nervous systems range widely in organization and complexity, with neurons possibly representing the most diverse cell-type. This diversity has led to much debate over the evolutionary origin of neurons as well as synapses, which allow for the directed transmission of information. The broad phylogenetic distribution of neurons and presence of many of the defining components outside of animals suggests an early origin of this cell type, potentially in the time between the first animal and the last common ancestor of extant animals. Here, we highlight the occurrence and function of key aspects of neurons outside of animals as well as recent findings from non-bilaterian animals in order to make predictions about when and how the first neuron(s) arose during animal evolution and their relationship to those found in extant lineages. With advancing technologies in single cell transcriptomics and proteomics as well as expanding functional techniques in non-bilaterian animals and the close relatives of animals, it is an exciting time to begin unraveling the complex evolutionary history of this fascinating animal cell type.

Synergistic anti-inflammatory effects and mechanisms of the combination of resveratrol and curcumin in human vascular endothelial cells and rodent aorta

Chronic increased pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) play critical roles in the development of endothelial dysfunction and therefore induce cardiovascular disease. Although phytochemicals have the potential ability to reduce the risk of CVD, the big gap between required high concentration in cells and the low bioavailability in the blood of phytochemicals compromise their therapeutic potentials. This study aims to investigate if combined phytochemicals at low levels exert a synergistic anti-inflammatory effect and to define relevant molecular mechanisms. Our results found that combined curcumin (5 µM) and resveratrol (5 µM) synergistically (combination index is 0.78) inhibited TNF-α-induced monocytes adhesion to human endothelial EA.hy 926 cells while the individual chemicals did not have such effect at the selected concentrations. The concentrations of curcumin (5 µM) and resveratrol (5 µM) are very close to the maximum level of curcumin (3.56 µM) and resveratrol (2 µM) in human blood. Dietary supplementation of combined curcumin (500mg/kg) and resveratrol (200mg/kg) synergistically reduced TNF-α-induced vascular inflammation in C57BL/6 mice with a similar pattern in cells. Moreover, the combination ameliorated the TNF-α-induced protein expressions and circulating levels of vascular cell adhesion molecule 1 and monocyte chemotactic protein-1 in EA.hy 926 cells, mice aorta and serum. Furthermore, combined curcumin and resveratrol significantly inhibited TNF-α-induced nuclear factor-kappaB (NF-κB) p65 nuclear protein expression than that by the individual chemical alone in EA.hy 926 cells, indicating that the synergistic effect of the combination may result from that curcumin reduces the required minimum concentration for resveratrol to inhibit the nuclear translocation of NF-κB. In conclusion, the combination of curcumin and resveratrol protects against TNF-α-induced vascular inflammation by suppressing NF-κB signaling in vitro and in vivo models. This study suggests that dietary intake of a combination of curcumin and resveratrol or its foods may be a practical, safe approach to prevent vascular inflammation and therefore prevent/treat vascular diseases in humans.

Chlorogenic acid alleviates thioacetamide-induced toxicity and promotes liver development in zebrafish (Danio rerio) through the Wnt signaling pathway

Chlorogenic acid (CGA) is a phenylpropanoid compound that is well known to improve the antioxidant capacity and other biological activities. However, the roles of CGA in the liver development of organisms are unclear. In the present study, we aimed to investigate the function of CGA in the hepatic development in thioacetamide (TAA)-induced zebrafish embryos. We found that CGA exerted certain beneficial effects on zebrafish larvae from TAA-exposed zebrafish embryos, such as increasing the liver size, body length, heart rate, acetylcholinesterase activity, and motor ability. In addition, CGA displayed an antioxidant effect on TAA-induced zebrafish embryos by enhancing the activities of superoxide dismutase (SOD), catalase (CAT), and glucose-6-phosphate dehydrogenase (G6PDH), and decreasing of the contents of malondialdehyde (MDA), reactive oxygen species (ROS), and nitric oxide (NO). The results of western blotting analysis showed that CGA inhibited cell apoptosis by increasing the levels of Bcl2 apoptosis regulator and decreasing the levels of Bcl2 associated X (Bax), apoptosis regulator and tumor protein P53. Moreover, CGA promoted cell proliferation in TAA-induced zebrafish larvae, as detected using proliferating cell nuclear antigen fluorescence immunostaining. In addition, CGA inhibited the expression of Wnt signaling pathway genes Dkk1 (encoding Dickkopf Wnt signaling pathway inhibitors), and promoted the expression of Lef1 (encoding lymphoid enhancer binding factor 1) and Wnt2bb (encoding wingless-type MMTV integration site family, member 2Bb). When the Wnt signal inhibitor IWR-1 was added, there was no significant change in liver development in the IWR-1 + TAA group compared with the IWR-1 + TAA + CGA group (p <0.05), which suggested that CGA regulates liver development via Wnt signaling pathway. Overall, our results suggested that CGA might alleviate TAA-induced toxicity in zebrafish and promote liver development through the Wnt signaling pathway, which provides a basis for the therapeutic effect of CGA on liver dysplasia.

New Functions of Vav Family Proteins in Cardiovascular Biology, Skeletal Muscle, and the Nervous System

Simple Summary

In this review, we provide information on the role of Vav proteins, a group of signaling molecules that act as both Rho GTPase activators and adaptor molecules, in the cardiovascular system, skeletal muscle, and the nervous system. We also describe how these functions impact in other physiological and pathological processes such as sympathoregulation, blood pressure regulation, systemic metabolism, and metabolic syndrome.

Abstract

Vav proteins act as tyrosine phosphorylation-regulated guanosine nucleotide exchange factors for Rho GTPases and as molecular scaffolds. In mammals, this family of signaling proteins is composed of three members (Vav1, Vav2, Vav3) that work downstream of protein tyrosine kinases in a wide variety of cellular processes. Recent work with genetically modified mouse models has revealed that these proteins play key signaling roles in vascular smooth and skeletal muscle cells, specific neuronal subtypes, and glia cells. These functions, in turn, ensure the proper regulation of blood pressure levels, skeletal muscle mass, axonal wiring, and fiber myelination events as well as systemic metabolic balance. The study of these mice has also led to the discovery of new physiological interconnection among tissues that contribute to the ontogeny and progression of different pathologies such as, for example, hypertension, cardiovascular disease, and metabolic syndrome. Here, we provide an integrated view of all these new Vav family-dependent signaling and physiological functions.

Protein kinase A activity and NO are involved in the regulation of crucian carp (Carassius carassius) red blood cell osmotic fragility

Activation of the cAMP pathway by β-adrenergic stimulation and cGMP pathway by activation of guanylate cyclase substantially affects red blood cell (RBC) membrane properties in mammals. However, whether similar mechanisms are involved in RBC regulation of lower vertebrates, especially teleosts, is not elucidated yet. In this study, we evaluated the effects of adenylate cyclase activation by epinephrine and forskolin, guanylate cyclase activation by sodium nitroprusside, and the role of Na⁺/H⁺-exchanger in the changes of osmotic fragility and regulatory volume decrease (RVD) response in crucian carp RBCs. Western blot analysis of protein kinase A and protein kinase G substrate phosphorylation revealed that changes in osmotic fragility were regulated via the protein kinase A, but not protein kinase G signaling pathway. At the same time, the RVD response in crucian carp RBCs was not affected either by activation of adenylate or guanylate cyclase. Adenylate cyclase/protein kinase A activation significantly decreased RBC osmotic fragility, i.e., increased cell rigidity. Inhibition of Na⁺/H⁺-exchanger by amiloride had no effect on the epinephrine-mediated decrease of RBC osmotic fragility. NO donor SNP did not activate guanylate cyclase, however affected RBCs osmotic fragility by protein kinase G-independent mechanisms. Taken together, our data demonstrated that the cAMP/PKA signaling pathway and NO are involved in the regulation of crucian carp RBC osmotic fragility, but not in RVD response. The authors confirm that the study has no clinical trial.

Induction of nitric oxide synthesis: a strategy to defend against high environmental ammonia-induced oxidative stress in primary hepatocytes of air-breathing catfish, Clarias magur

Air-breathing magur catfish (Clarias magur) regularly face the problem of exposure to high environmental ammonia (HEA) as one of the major pollutants in their natural habitats that causes considerable toxic effects at the cellular level, including that of oxidative stress. The major objective of the present study was to demonstrate the antioxidant activity of endogenously produced nitric oxide (NO) to defend against ammonia-induced oxidative stress in primary hepatocytes of magur catfish during exposure to HEA. Exposure to NH4Cl (5 mmol l-1) led to a significant increase in intracellular ammonia concentration with a sharp rise of hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations within 3 h in primary hepatocytes, which decreased gradually at later stages of treatment. This phenomenon was accompanied by a significant increase in superoxide dismutase (SOD) and catalase (CAT) activity as a consequence of induction of corresponding genes. HEA exposure also led to the stimulation of NO production due to induction of inducible nitric oxide synthase (iNOS) activity, as a consequence of up-regulation of the nos2 gene. Most interestingly, when NO production by hepatocytes under ammonia stress was blocked by adding certain inhibitors [aminoguanidine and 3-(4-methylphenylsulfonyl)-2-propenenitrile] to the culture medium, there was a further rise of H2O2 and MDA concentrations in hepatocytes. These were accompanied by the lowering of SOD and CAT activity with less expression of corresponding genes. Thus, it can be contemplated that magur catfish use the strategy of stimulation of NO production, which ultimately induces the SOD-CAT enzyme system to defend against ammonia-induced oxidative stress.

Hyper-ammonia stress causes induction of inducible nitric oxide synthase gene and more production of nitric oxide in air-breathing magur catfish, Clarias magur (Hamilton)

Nitric oxide (NO) is an important signalling molecule that plays diverse physiological functions in several vertebrates including that of adaptation to various stressful stimuli. The air-breathing magur catfish (Clarias magur) is known to tolerate a very high external ammonia (HEA) stress in its natural habitats. We report here the possible induction of inducible nitric oxide (inos) gene and more generation of NO in magur catfish exposed to HEA. Exposure to HEA (25 mM NH₄Cl) for 14 days led to the higher accumulation of NO in different tissues of magur catfish and also more efflux of NO from the perfused liver of NH₄Cl-treated fish as a consequence of high build of toxic ammonia in body tissues. More synthesis and accumulation of NO in body tissues was associated with the induction of iNOS activity, which otherwise was not detectable in control fish. The stimulation of iNOS activity in HEA exposed fish was mainly due to induction of inos gene as evidenced by more expression of inos mRNA and also more abundance of iNOS protein in different tissues of magur catfish. Immunocytochemical analysis indicated the zonal specific expression of iNOS protein in different tissues of magur catfish. The augmentation of iNOS in the fish under HEA could be an adaptive strategy of the fish to defend against the ammonia stress through the generation of NO. Therefore, the present finding identifies the potential role of iNOS to enhance the adaptive capacity and survivability of catfish under various adverse environmental and pathological conditions that it faces in its natural habitats.

Transport Stress Changes Blood Biochemistry, Antioxidant Defense System, and Hepatic HSPs mRNA Expressions of Channel Catfish Ictalurus punctatus

Transport procedures usually cause fish stress. The purpose of this study was to investigate the effect of transport stress on blood biochemical profiles, oxidative stress biomarkers, and hepatic heat shock proteins (HSPs) of channel catfish (Ictalurus punctatus). Fish (body weight 55.57 ± 5.13 g) were randomly distributed to two groups, the control, and the treatment. The control group was kept under the normal culture conditions. The treatment group was exposed to the process of transport (3.5 h). Fish samples were collected before transport, after packing and at 0, 1, 6, 24, 72, and 168 h after transport, respectively. Transport caused a significant increase in the serum concentrations of cortisol, glucose, total cholesterol, and triglyceride, as well as, the activity of aspartate aminotransferase at 0 and 1 h after transport compared with non-transported fish and the basal level. Blood total protein content significantly declined in the transported fish. Total antioxidant capacity (T-AOC), malonaldehyde content, and the activities of both glutathione peroxidase and catalase significantly increased in fish within 6 h after transport. The transported fish exhibited a significant higher level in either the concentration of nitric oxide or the mRNA expressions of both hepatic HSP70 and HSP90. It is concluded that transport triggers stress response of I. punctatus, leading to the obvious change in antioxidant capacity. I. punctatus need to be more care after transport to recover from transport stress.

Mussel (Mytilus coruscus) Water Extract Containing Taurine Prevents LPS-Induced Inflammatory Responses in Zebrafish Model

Mussel (Mytilus coruscus) water extract had strong anti-inflammatory activities, but the effects and its mechanisms of mussel on anti-inflammatory properties in vivo remain to be determined. This study, therefore, was designed to investigate anti-inflammatory activities of mussel water extract containing a large amounts of taurine (151.96 nmol/mg) using the lipopolysaccharide (LPS)-induced inflammatory zebrafish model. In this study, mussel water extract containing taurine shows potent protective effects against the cell death stimulated by LPS exposure in zebrafish embryos. In addition, zebrafish subjected to LPS treatment exhibited significantly increased reactive oxygen species (ROS) and nitric oxide (NO) levels. However, mussel water extract markedly suppressed LPS-induced ROS and NO production. Our results indicate that mussel water extract attenuated inflammation by inhibiting the LPS-induced intracellular ROS and NO production in zebrafish embryos. These findings could demonstrate the anti-inflammatory activity of mussel water extract containing taurine, which might have a protective effects on inflammatory diseases.

Induction of Inducible Nitric Oxide Synthase by Lipopolysaccharide and the Influences of Cell Volume Changes, Stress Hormones and Oxidative Stress on Nitric Oxide Efflux from the Perfused Liver of Air-Breathing Catfish, Heteropneustes fossilis

The air-breathing singhi catfish (Heteropneustes fossilis) is frequently being challenged by bacterial contaminants, and different environmental insults like osmotic, hyper-ammonia, dehydration and oxidative stresses in its natural habitats throughout the year. The main objectives of the present investigation were to determine (a) the possible induction of inducible nitric oxide synthase (iNOS) gene with enhanced production of nitric oxide (NO) by intra-peritoneal injection of lipopolysaccharide (LPS) (a bacterial endotoxin), and (b) to determine the effects of hepatic cell volume changes due to anisotonicity or by infusion of certain metabolites, stress hormones and by induction of oxidative stress on production of NO from the iNOS-induced perfused liver of singhi catfish. Intra-peritoneal injection of LPS led to induction of iNOS gene and localized tissue specific expression of iNOS enzyme with more production and accumulation of NO in different tissues of singhi catfish. Further, changes of hydration status/cell volume, caused either by anisotonicity or by infusion of certain metabolites such as glutamine plus glycine and adenosine, affected the NO production from the perfused liver of iNOS-induced singhi catfish. In general, increase of hydration status/cell swelling due to hypotonicity caused decrease, and decrease of hydration status/cell shrinkage due to hypertonicity caused increase of NO efflux from the perfused liver, thus suggesting that changes in hydration status/cell volume of hepatic cells serve as a potent modulator for regulating the NO production. Significant increase of NO efflux from the perfused liver was also observed while infusing the liver with stress hormones like epinephrine and norepinephrine, accompanied with decrease of hydration status/cell volume of hepatic cells. Further, oxidative stress, caused due to infusion of t-butyl hydroperoxide and hydrogen peroxide separately, in the perfused liver of singhi catfish, resulted in significant increase of NO efflux accompanied with decrease of hydration status/cell volume of hepatic cells. However, the reasons for these cell volume-sensitive changes of NO efflux from the liver of singhi catfish are not fully understood with the available data. Nonetheless, enhanced or decreased production of NO from the perfused liver under osmotic stress, in presence of stress hormones and oxidative stress reflected its potential role in cellular homeostasis and also for better adaptations under environmental challenges. This is the first report of osmosensitive and oxidative stress-induced changes of NO production and efflux from the liver of any teleosts. Further, the level of expression of iNOS in this singhi catfish could also serve as an important indicator to determine the pathological status of the external environment.

Trigeminocardiac reflex by mandibular extension on rat pial microcirculation: role of nitric oxide

In the present study we have extended our previous findings about the effects of 10 minutes of passive mandibular extension in anesthetized Wistar rats. By prolonging the observation time to 3 hours, we showed that 10 minutes mandibular extension caused a significant reduction of the mean arterial blood pressure and heart rate respect to baseline values, which persisted up to 160 minutes after mandibular extension. These effects were accompanied by a characteristic biphasic response of pial arterioles: during mandibular extension, pial arterioles constricted and after mandibular extension dilated for the whole observation period. Interestingly, the administration of the opioid receptor antagonist naloxone abolished the vasoconstriction observed during mandibular extension, while the administration of N_ω-Nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, abolished the vasodilation observed after mandibular extension. Either drug did not affect the reduction of mean arterial blood pressure and heart rate induced by mandibular extension. By qRT-PCR, we also showed that neuronal nitric oxide synthase gene expression was significantly increased compared with baseline conditions during and after mandibular extension and endothelial nitric oxide synthase gene expression markedly increased at 2 hours after mandibular extension. Finally, western blotting detected a significant increase in neuronal and endothelial nitric oxide synthase protein expression. In conclusion mandibular extension caused complex effects on pial microcirculation involving opioid receptor activation and nitric oxide release by both neurons and endothelial vascular cells at different times.

Genetic dissection of the vav2-rac1 signaling axis in vascular smooth muscle cells

Vascular smooth muscle cells (vSMCs) are key in the regulation of blood pressure and the engagement of vascular pathologies, such as hypertension, arterial remodeling, and neointima formation. The role of the Rac1 GTPase in these cells remains poorly characterized. To clarify this issue, we have utilized genetically engineered mice to manipulate the signaling output of Rac1 in these cells at will using inducible, Cre-loxP-mediated DNA recombination techniques. Here, we show that the expression of an active version of the Rac1 activator Vav2 exclusively in vSMCs leads to hypotension as well as the elimination of the hypertension induced by the systemic loss of wild-type Vav2. Conversely, the specific depletion of Rac1 in vSMCs causes defective nitric oxide vasodilation responses and hypertension. Rac1, but not Vav2, also is important for neointima formation but not for hypertension-driven vascular remodeling. These animals also have allowed us to dismiss etiological connections between hypertension and metabolic disease and, most importantly, identify pathophysiological programs that cooperate in the development and consolidation of hypertensive states caused by local vascular tone dysfunctions. Finally, our results suggest that the therapeutic inhibition of Rac1 will be associated with extensive cardiovascular system-related side effects and identify pharmacological avenues to circumvent them.

The Rho/Rac exchange factor Vav2 controls nitric oxide-dependent responses in mouse vascular smooth muscle cells

The regulation of arterial contractility is essential for blood pressure control. The GTPase RhoA promotes vasoconstriction by modulating the cytoskeleton of vascular smooth muscle cells. Whether other Rho/Rac pathways contribute to blood pressure regulation remains unknown. By studying a hypertensive knockout mouse lacking the Rho/Rac activator Vav2, we have discovered a new signaling pathway involving Vav2, the GTPase Rac1, and the serine/threonine kinase Pak that contributes to nitric oxide-triggered blood vessel relaxation and normotensia. This pathway mediated the Pak-dependent inhibition of phosphodiesterase type 5, a process that favored RhoA inactivation and the subsequent depolymerization of the F-actin cytoskeleton in vascular smooth muscle cells. The inhibition of phosphodiesterase type 5 required its physical interaction with autophosphorylated Pak1 but, unexpectedly, occurred without detectable transphosphorylation events between those 2 proteins. The administration of phosphodiesterase type 5 inhibitors prevented the development of hypertension and cardiovascular disease in Vav2-deficient animals, demonstrating the involvement of this new pathway in blood pressure regulation. Taken together, these results unveil one cause of the cardiovascular phenotype of Vav2-knockout mice, identify a new Rac1/Pak1 signaling pathway, and provide a mechanistic framework for better understanding blood pressure control in physiological and pathological states.

The oxygen status of the developing seed

Recent applications of oxygen-sensitive microsensors have demonstrated steep oxygen gradients in developing seeds of various crops. Here, we present an overview on oxygen distribution, major determinants of the oxygen status in the developing seed and implications for seed physiology. The steady-state oxygen concentration in different seed tissues depends on developmental parameters, and is determined to a large extent by environmental factors. Photosynthetic activity of the seed significantly diminishes hypoxic constraints, and can even cause transient, local hyperoxia. Changes in oxygen availability cause rapid adjustments in mitochondrial respiration and global metabolism. We argue that nitric oxide (NO) is a key player in the oxygen balancing process in seeds, avoiding fermentation and anoxia in vivo. Molecular approaches aiming to increase oxygen availability within the seed are discussed.

Aging and cardioprotection

Advanced age is a strong independent predictor for death, disability, and morbidity in patients with structural heart disease. With the projected increase in the elderly population and the prevalence of age-related cardiovascular disabilities worldwide, the need to understand the biology of the aging heart, the mechanisms for age-mediated cardiac vulnerability, and the development of strategies to limit myocardial dysfunction in the elderly have never been more urgent. Experimental evidence in animal models indicate attenuation in cardioprotective pathways with aging, yet limited information is available regarding age-related changes in the human heart. Human cardiac aging generates a complex phenotype, only partially replicated in animal models. Here, we summarize current understanding of the aging heart stemming from clinical and experimental studies, and we highlight targets for protection of the vulnerable senescent myocardium. Further progress mandates assessment of human tissue to dissect specific aging-associated genomic and proteomic dynamics, and their functional consequences leading to increased susceptibility of the heart to injury, a critical step toward designing novel therapeutic interventions to limit age-related myocardial dysfunction and promote healthy aging.

The paracrine hormone hypothesis of colorectal cancer

Colorectal carcinogenesis originates in the context of dysregulated epithelial cell homeostasis, wherein hyperproliferation, hypodifferentiation, metabolic reprogramming, and mesenchymal remodeling reflect recursive mutually reinforcing mechanisms contributing to progressive genomic instability. Although genotypic and phenotypic elements characterizing the terminal integration of these pathophysiological processes defining cancer are well enumerated, events initiating, coordinating, and sustaining this hierarchical maladaptive systems evolution remain elusive for most tumors. In the intestine, guanylyl cyclase C (GCC) and its paracrine ligands organize and regulate the homeostatic integrity of the crypt-villus axis, forming a hormonal tumor suppressor signaling sequence, whose dysfunction defines the initiation of neoplastic transformation and creates a permissive niche for tumor progression.

Chronic treatment with sildenafil improves energy balance and insulin action in high fat-fed conscious mice

Stimulation of nitric oxide-cGMP signaling results in vascular relaxation and increased muscle glucose uptake. We show that chronically inhibiting cGMP hydrolysis with the phosphodiesterase-5 inhibitor sildenafil improves energy balance and enhances in vivo insulin action in a mouse model of diet-induced insulin resistance. High-fat-fed mice treated with sildenafil plus L-arginine or sildenafil alone for 12 weeks had reduced weight and fat mass due to increased energy expenditure. However, uncoupling protein-1 levels were not increased in sildenafil-treated mice. Chronic treatment with sildenafil plus L-arginine or sildenafil alone increased arterial cGMP levels but did not adversely affect blood pressure or cardiac morphology. Sildenafil treatment, with or without l-arginine, resulted in lower fasting insulin and glucose levels and enhanced rates of glucose infusion, disappearance, and muscle glucose uptake during a hyperinsulinemic (4 mU x kg(-1) x min(-1))-euglycemic clamp in conscious mice. These effects occurred without an increase in activation of muscle insulin signaling. An acute treatment of high fat-fed mice with sildenafil plus l-arginine did not improve insulin action. These results show that phosphodiesterase-5 is a potential target for therapies aimed at preventing diet-induced energy imbalance and insulin resistance.

Proteomic analysis of age dependent nitration of rat cardiac proteins by solution isoelectric focusing coupled to nanoHPLC tandem mass spectrometry

Protein nitration occurs as a result of oxidative stress induced by reactive oxygen (ROS) and reactive nitrogen species (RNS). Therefore, protein nitration serves as a hallmark for protein oxidation in vivo. We have previously reported on age dependent protein nitration in cardiac tissue of Fisher 344 BN-F1 rats analyzed by two-dimensional gel electrophoresis; however, only one specific nitration site was identified [Kanski, J., Behring, A., Pelling, J., Schöneich, C., 2005a. Proteomic identification of 3-nitrotyrosine-containing rat cardiac proteins: effects of biological aging. Am. J. Physiol. Heart Circ. Physiol. 288, H371-381]. In the present report, we used solution phase isoelectric focusing (IEF) followed by nanoHPLC-ESI-MS/MS that allowed us to obtain good MS/MS data to identify specific sites of protein nitration in cardiac tissue. As expected, more nitrated proteins were detected in cardiac tissue of old rats, including myosin heavy chain, neurofibromin, tropomyosin and nebulin-related anchoring protein. The post-translational modification of these cytoskeletal proteins may provide some rationale for the age-dependent functional decline of the heart.

Nitric oxide in physiologic concentrations targets the translational machinery to increase the proliferation of human breast cancer cells: involvement of mammalian target of rapamycin/eIF4E pathway

Nitric oxide (NO) in nanomolar (nmol/L) concentrations is consistently detected in tumor microenvironment and has been found to promote tumorigenesis. The mechanism by which NO enhances tumor progression is largely unknown. In this study, we investigated the possible mechanisms and identified cellular targets by which NO increases proliferation of human breast cancer cell lines MDA-MB-231 and MCF-7. DETA-NONOate, a long acting NO donor, with a half-life of 20 h, was used. We found that NO (nmol/L) dramatically increased total protein synthesis in MDA-MB-231 and MCF-7 and also increased cell proliferation. NO specifically increased the translation of cyclin D1 and ornithine decarboxylase (ODC) without altering their mRNA levels or half-lives. Critical components in the translational machinery, such as phosphorylated mammalian target of rapamycin (mTOR) and its downstream targets, phosphorylated eukaryotic translation initiation factor and p70 S6 kinase, were up-regulated following NO treatment, and inhibition of mTOR with rapamycin attenuated NO induced increase of cyclin D1 and ODC. Activation of translational machinery was mediated by NO-induced up-regulation of the Raf/mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase/ERK (Raf/MEK/ERK) and phosphatidylinositol 3-kinase (PI-3 kinase)/Akt signaling pathways. Up-regulation of the Raf/MEK/ERK and PI-3 kinase/Akt pathways by NO was found to be mediated by activation of Ras, which was cyclic guanosine 3',5'-monophosphate independent. Furthermore, inactivation of Ras by farnesyl transferase inhibitor or K-Ras small interfering RNA attenuated NO-induced increase in proliferation signaling and cyclin D1 and ODC translation, further confirming the involvement of Ras activation during NO-induced cell proliferation.

Assessing NO-dependent vasodilatation using vessel bioassays at defined oxygen tensions

Results from vessel bioassays have provided the foundation for much of our understanding of the mechanisms that control vascular homeostasis and blood flow. The seminal observations that led to the discovery that nitric oxide (NO) is a critical mediator of vascular relaxation were made with the use of such methodology, and many studies have used NO-dependent vessel relaxation as an experimental readout for understanding mechanisms that regulate vascular NO function. Studies have coupled controlling oxygen tensions within vessel bioassay chambers to begin to understand how oxygen-specifically hypoxia-regulate NO function, and this context has identified red cells-specifically hemoglobin within-as critical modulators. Alone, vessel bioassays or measuring oxygen partial pressures (pO2) is relatively straightforward, but the combination necessitates consideration of several factors. We use the example of deoxygenated red cells/hemoglobin-dependent potentiation of nitrite-dependent dilation to illustrate the salient factors that are critical to consider in designing and interpreting experiments aimed at understanding the interplay between oxygen and NO function in the vasculature.

Non-lesional vitiliginous melanocytes are not characterized by an increased proneness to nitric oxide-induced apoptosis

Nitric oxide (NO) is a reactive endogenous molecule with multiple functions including inflammation and immunity. NO stimulates melanogenesis by activating soluble guanylyl cyclase (sGC) resulting in increases in intracellular guanosine 3',5'-cyclic monophosphate (cGMP). In vitro experiments showed that NO could inhibit the de novo attachment of melanocytes to extracellular matrix (ECM) suggesting that NO-induced aberrant perturbation of melanocyte-ECM interaction could be a reason for melanocyte loss in vitiliginous lesions. Here, we examined whether there might be differences between normal melanocytes and vitiliginous melanocytes (VMs) with respect to NO-induced detachment from ECM and whether cGMP is involved. We used the direct NO donor (Z)-1-[N-(3-ammoniopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2-diolate and the peroxynitrite donor 3-morpholino-sydnonimine for the present studies. These donors induced detachment of both normal melanocytes and non-lesional VMs in a time- and concentration-dependent manner with comparable susceptibility and similar expression profile of sGC. Treatment of melanocytes with caspase inhibitors reduced cell detachment, indicating that a major part of the detachment is due to apoptosis. The NO-induced detachment but not apoptosis was partly inhibited in the presence of sGC and cGMP-dependent protein kinase inhibitors. In addition, the membrane-permeable cGMP analog 8-(4-chlorophenyethio/guanosine-3',5'-cyclic monophosphate (PCPT) cGMP was not able to induce apoptosis in melanocytes, suggesting that NO-induced detachment of melanocytes via apoptosis is cGMP-independent. The present results also indicate that there are no apparent differences between NO-induced detachment of non-lesional vitiliginous and normal melanocytes from ECM.

Effect of MnSOD (E. coli) on the relaxation caused by sodium nitroprusside on isolated rat renal artery

In this study themolecular foundation of nitric oxide induced relaxation of arteries, with or without endothelium, of normotensive and spontanously hypertensive ratswas re-examined. With this purpose in mind, the effects of the nitric oxide donor sodium nitroprusside (NaNP), with and without manganese containing superoxide dismutase (MnSOD E.C. 1.15.1.1), on rat renal artery relaxation was strudied. The results show that the relaxation effect of NaNP is two times higher in normotensive, compared to spontaneously hypertensive rats. Similar differences exist in the relaxation effects of NaNP on isolated renal arteries without endothelium, indicating that besides the difference in the function of an endothelium, concerning basal NO production in normotensive and hypertensive rats, there is a differencewith respect to NO relaxation in the smoothmuscle that is induced by hypertension. MnSOD decreased the relaxation effect of NaNP in all the examined renal arteries, more in normotensive than in hypertensive ones regardless of the presence of an endothelium. These results show that MnSOD, by modifying the chemical versatility of NO into redox active forms - nitrosonium (NO+) and nitroxyl (NO-), produces different relaxation effects in normotensive and hypertensive arteries of rats, with or without an endothelium, potentiating the role of nitroxyl induced relaxation in sponteneously hypertensive rats. The results prove the need for the synthesis of complex NO donors, as the mechanisms of artery relaxation are different due to an endothel and smooth mouscle changes in hypertensive, as compared to normotensive rats.

Nitric Oxide as a Unique Bioactive Signaling Messenger in Physiology and Pathophysiology

Nitric oxide (NO) is an intra- and extracellular messenger that mediates diverse signaling pathways in target cells and is known to play an important role in many physiological processes including neuronal signaling, immune response, inflammatory response, modulation of ion channels, phagocytic defense mechanism, penile erection, and cardiovascular homeostasis and its decompensation in atherogenesis. Recent studies have also revealed a role for NO as signaling molecule in plant, as it activates various defense genes and acts as developmental regulator. In plants, NO can also be produced by nitrate reductase. NO can operate through posttranslational modification of proteins (nitrosylation). NO is also a causative agent in various pathophysiological abnormalities. One of the very important systems, the cardiovascular system, is affected by NO production, as this bioactive molecule is involved in the regulation of cardiovascular motor tone, modulation of myocardial contractivity, control of cell proliferation, and inhibition of platelet activation, aggregation, and adhesion. The prime source of NO in the cardiovascular system is endothelial NO synthase, which is tightly regulated with respect to activity and localization. The inhibition of chronic NO synthesis leads to neurogenic and arterial hypertensions, which later contribute to development of myocardial fibrosis. Overall, the modulation of NO synthesis is associated with hypertension. This review briefly describes the physiology of NO, its synthesis, catabolism, and targeting, the mechanism of NO action, and the pharmacological role of NO with special reference to its essential role in hypertension.