Preparation of a copper-based fluorescent probe for nitric oxide and its use in mammalian cultured cells

2-Amino-3'-dialkylaminobiphenyl-based fluorescent intracellular probes for nitric oxide surrogate N2O3

Fluorescent probes for nitric oxide (NO), or more frequently for its oxidized surrogate dinitrogen trioxide (N2O3), have enabled scientists to study the contributions of this signaling molecule to many physiological processes. Seeking to improve upon limitations of other probes, we have developed a family of fluorescent probes based on a 2-amino-3'-dialkylaminobiphenyl core. This core condenses with N2O3 to form benzo[c]cinnoline structures, incorporating the analyte into the newly formed fluorophore, which results in product fluorescence with virtually no background contribution from the initial probe. We varied the substituents in the core in order to optimize both the reactivity of the probes with N2O3 and their cinnoline products' fluorescence wavelengths and brightness. The top candidates were then applied to cultured cells to verify that they could respond to NO within cellular milieus, and the top performer, NO530, was compared with a "gold standard" commercial probe, DAF-FM, in a macrophage-derived cell line, RAW 264.7, stimulated to produce NO. NO530 demonstrated similar or better sensitivity and higher selectivity for NO than DAF, making it an attractive potential alternative for NO tracking in various applications.

Nitric oxide donor [Ru(terpy)(bdq)NO]3+ induces uncoupling and phosphorylation of endothelial nitric oxide synthase promoting oxidant production

[Ru(terpy)(bdq)NO]3+ (TERPY) is a nitric oxide (NO) donor that promotes relaxation of the mesenteric artery and aorta in rats. We sought to investigate whether it acts as both an NO donor and endothelial NO synthase (eNOS) activator, as shown previously for nitroglycerin. Human umbilical vein endothelial cells (HUVECs) and human embryonic kidney 293 cells transfected with empty vector (HEK) or eNOS cDNA (HEK-eNOS) were treated with TERPY (1µM) for different lengths of time. eNOS expression, dimerization, and Ser1177 phosphorylation, caveolin-1 (Cav-1) oligomerization, Cav-1 Tyr14 phosphorylation were evaluated by Western blotting. Studies also assessed the production of reactive oxygen/nitrogen species (ROS/RNS) in HUVECs and HEK-eNOS cells. In HEK cells devoid of eNOS, TERPY released NO without additional stimulus indicating that is an NO donor. Moreover, in HEK-eNOS cells, TERPY-induced NO production that was blocked by L-NAME. In addition, TERPY increased ROS and ONOO- production which were blocked by more than 80% by BH4 (essential eNOS co-factor) and eNOS siRNA. These results suggest that TERPY-induced ROS and ONOO- production were originated from eNOS. HUVECs stimulated with TERPY showed increased eNOS Ser1177 and Cav-1 Tyr14 phosphorylation, and decreased eNOS dimerization, Cav-1 oligomerization, and Cav-1/eNOS interaction after 20min. It suggests that TERPY induces eNOS hyperactivation and uncoupling by disrupting Cav-1/eNOS interaction and depleting BH4. Endothelium-dependent vasodilation in response to NO donor TERPY is associated with eNOS activation and uncoupling, and thereby appears to be mediated, at least in part, via eNOS-dependent ROS/RNS production.

Taking up the cudgels for the traditional reactive oxygen and nitrogen species detection assays and their use in the cardiovascular system

Reactive oxygen and nitrogen species (RONS such as H2O2, nitric oxide) confer redox regulation of essential cellular functions (e.g. differentiation, proliferation, migration, apoptosis), initiate and catalyze adaptive stress responses. In contrast, excessive formation of RONS caused by impaired break-down by cellular antioxidant systems and/or insufficient repair of the resulting oxidative damage of biomolecules may lead to appreciable impairment of cellular function and in the worst case to cell death, organ dysfunction and severe disease phenotypes of the entire organism. Therefore, the knowledge of the severity of oxidative stress and tissue specific localization is of great biological and clinical importance. However, at this level of investigation quantitative information may be enough. For the development of specific drugs, the cellular and subcellular localization of the sources of RONS or even the nature of the reactive species may be of great importance, and accordingly, more qualitative information is required. These two different philosophies currently compete with each other and their different needs (also reflected by different detection assays) often lead to controversial discussions within the redox research community. With the present review we want to shed some light on these different philosophies and needs (based on our personal views), but also to defend some of the traditional assays for the detection of RONS that work very well in our hands and to provide some guidelines how to use and interpret the results of these assays. We will also provide an overview on the "new assays" with a brief discussion on their strengths but also weaknesses and limitations.

Detection of Zn2+ release in nitric oxide treated cells and proteome: dependence on fluorescent sensor and proteomic sulfhydryl groups

Nitric oxide (NO) is both an important regulatory molecule in biological systems and a toxic xenobiotic. Its oxidation products react with sulfhydryl groups and either nitrosylate or oxidize them. The aerobic reaction of NO supplied by diethylamine NONOate (DEA-NO) with pig kidney LLC-PK₁ cells and Zn-proteins within the isolated proteome was examined with three fluorescent zinc sensors, zinquin (ZQ), TSQ, and FluoZin-3 (FZ-3). Observations of Zn²⁺ labilization from Zn-proteins depended on the specific sensor used. Upon cellular exposure to DEA-NO, ZQ sequestered about 13% of the proteomic Zn²⁺ as Zn(ZQ)₂ and additional Zn²⁺ as proteome·Zn-ZQ ternary complexes. TSQ, a sensor structurally related to ZQ with lower affinity for Zn²⁺, did not form Zn(TSQ)₂. Instead, Zn²⁺ mobilized by DEA-NO was exclusively bound as proteome·Zn-TSQ adducts. Analogous reactions of proteome with ZQ or TSQ in vitro displayed qualitatively similar products. Titration of native proteome with Zn²⁺ in the presence of ZQ resulted in the sole formation of proteome·Zn-ZQ species. This result suggested that sulfhydryl groups are involved in non-specific proteomic binding of mobile Zn²⁺ and that the appearance of Zn(ZQ)₂ after exposure of cells and proteome to DEA-NO resulted from a reduction in proteomic sulfhydryl ligands, favoring the formation of Zn(ZQ)₂ instead of proteome·Zn-ZQ. With the third sensor, FluoZin-3, neither Zn-FZ-3 nor proteome·Zn-FZ-3 was detected during the reaction of proteome with DEA-NO. Instead, it reacted independently with DEA-NO with a modest enhancement of fluorescence.

Oxidized extracellular DNA suppresses nitric oxide production by endothelial NO synthase (eNOS) in human endothelial cells (HUVEC)

Circulating DNA from patients with cardiovascular diseases reduce the synthesis of NO in endothelial cells, which is probably related to oxidative modification of DNA. To test this hypothesis, HUVEC cells were cultured in the presence of DNA containing ~1 (nonoxidized DNA), 700, or 2100 8-oxodG/10(6) nucleosides. Nonoxidized DNA stimulated the synthesis of NO, which was associated with an increase in the expression of endothelial NO synthase. Oxidized NO decreased the amount of mRNA and protein for endothelial NO synthase, but increased the relative content of its low active form. These changes were accompanied by reduction of NO production. These findings suggest that oxidative modification of circulating extracellular DNA contributes to endothelial dysfunction manifested in suppression of NO production.

Identification and rescue of α-synuclein toxicity in Parkinson patient-derived neurons

The induced pluripotent stem (iPS) cell field holds promise for in vitro disease modeling. However, identifying innate cellular pathologies, particularly for age-related neurodegenerative diseases, has been challenging. Here, we exploited mutation correction of iPS cells and conserved proteotoxic mechanisms from yeast to humans to discover and reverse phenotypic responses to α-synuclein (αsyn), a key protein involved in Parkinson's disease (PD). We generated cortical neurons from iPS cells of patients harboring αsyn mutations, who are at high risk of developing PD dementia. Genetic modifiers from unbiased screens in a yeast model of αsyn toxicity led to identification of early pathogenic phenotypes in patient neurons. These included nitrosative stress, accumulation of endoplasmic reticulum (ER)-associated degradation substrates, and ER stress. A small molecule identified in a yeast screen (NAB2), and the ubiquitin ligase Nedd4 it affects, reversed pathologic phenotypes in these neurons.

Toll-like receptor 7 rapidly relaxes human airways

RATIONALE

Toll-like receptors (TLRs) 7 and 8 detect respiratory virus single-stranded RNA and trigger an innate immune response. We recently described rapid TLR7-mediated bronchodilation in guinea pigs.

OBJECTIVES

To characterize TLR7 expression and TLR7-induced airway relaxation in humans and in eosinophilic airway inflammation in guinea pigs. To evaluate the relaxant effects of other TLRs.

METHODS

Human airway smooth muscle strips were contracted with methacholine in vitro, and responses to TLR7 and TLR8 agonists were assessed. TLR7-mediated nitric oxide production was measured using a fluorescent indicator, and TLR7 expression was characterized using immunofluorescence. TLR7 signaling was also evaluated in ovalbumin-challenged guinea pigs.

MEASUREMENTS AND MAIN RESULTS

The TLR7 agonist imiquimod (R837) caused rapid dose-dependent relaxation of methacholine-contracted human airways in vitro. This was blocked by the TLR7 antagonist IRS661 and by inhibiting nitric oxide production but not by inhibiting prostaglandin production. TLR7 activation markedly increased fluorescence of a nitric oxide detector. TLR7 was expressed on airway nerves, but not airway smooth muscle, implicating airway nerves as the source of TLR7-induced nitric oxide production. TLR7-mediated relaxation persisted in inflamed guinea pigs airways in vivo. The TLR8 agonists polyuridylic acid and polyadenylic acid also relaxed human airways, and this was not blocked by the TLR7 antagonist or by blocking nitric oxide or prostaglandin production. No other TLRs relaxed the airways.

CONCLUSIONS

TLR7 is expressed on airway nerves and mediates relaxation of human and animal airways through nitric oxide production. TLR7-mediated bronchodilation may be a new therapeutic strategy in asthma.

[Use of the most recent reagent (CuFL) for stimulation of NO synthesis by the medicinal leech salivary cell secretion in the cultures of human endothelium cells (HUVEC) and in rat cardiomiocytes]

The medicinal leech salivary cell secretion (SCS) may stimulate NO-production in cultures of human endothelium cells (HUVEC) and rat cardiomiocytes (RCM). This effect was detected using a NO specific reagent, - the complex Cu2+ with a fluorescein derivative (Cu-Fl). NO had also been detected in the cells by fluorescent electronic microscopy and determined quantitatively in the cells and in culture fluid by the fluorescence method. SCS stimulated NO synthesis in HUVEC cells (but not in RCM) is accompanied by NO release into intercellular space. Localization of NO synthesis centers is presented and it is shown that the increase in NO levels during the SCS action on HUVEC and RCM is associated with the increase in the activity of eNOS/nNOS, but not iNOS. In endothelial cells SCS activates nitrosylation processes, assessed by the increase of nitrite-ions in the culture medium. It is therefore important to use Cu-Fl, other than Griss-reagent, during the first hour of analysis of NO synthesis. The NO-depended mechanism of SCS action on endothelial cells might be a factor in providing of its positive action in hirudotheraphy.

Role of extracellular DNA oxidative modification in radiation induced bystander effects in human endotheliocytes

The development of the bystander effect induced by low doses of irradiation in human umbilical vein endothelial cells (HUVECs) depends on extracellular DNA (ecDNA) signaling pathway. We found that the changes in the levels of ROS and NO production by human endothelial cells are components of the radiation induced bystander effect that can be registered at a low dose. We exposed HUVECs to X-ray radiation and studied effects of ecDNA(R) isolated from the culture media conditioned by the short-term incubation of irradiated cells on intact HUVECs. Effects of ecDNA(R) produced by irradiated cells on ROS and NO production in non-irradiated HUVECs are similar to bystander effect. These effects at least partially depend on TLR9 signaling. We compared the production of the nitric oxide and the ROS in human endothelial cells that were (1) irradiated at a low dose; (2) exposed to the ecDNA(R) extracted from the media conditioned by irradiated cells; and (3) exposed to human DNA oxidized in vitro. We found that the cellular responses to all three stimuli described above are essentially similar. We conclude that irradiation-related oxidation of the ecDNA is an important component of the ecDNA-mediated bystander effect.

Enhanced expression of iNOS in human endothelial cells during long-term culturing with extracellular DNA fragments

NO synthesis by endothelial cells plays an important role in normal function of the cardiovascular system. This work was designed to evaluate the role of variations in properties of extracellular DNA in the regulation of NO synthesis. We studied the effect of four DNA samples with various base sequences (50 ng/ml) on functional activity of endothelial cells HUVEC during 24-h culturing. Human DNA fragments with high content of CG repeats increased intracellular content of NO and its metabolites (nitrites and nitrates) and accelerated oxidation of nitrites to nitrates. Changes in the content of NO metabolites after 24-h culturing was shown to depend on the expression of gene for inducible, but not for endothelial NO synthase. Increased expression of inducible NO synthase positively correlated with an increase in the content of mRNA for the adapter protein MyD88, but did not depend on TLR9 gene expression that encodes protein receptor for CG-DNA recognition. The intracellular concentration of MyD88 mRNA did not depend on the content of TLR9 mRNA. The existence of a variety of DNA-binding receptors apart from TLR9 receptor on the surface of endothelial cells was hypothesized. Activation of these receptors by extracellular DNA fragments stimulates expression of the adapter protein MyD88.

Interaction of a specific population of human embryonic stem cell-derived progenitor cells with CD11b+ cells ameliorates sepsis-induced lung inflammatory injury

Human embryonic stem cells differentiated under mesoderm-inducing conditions have important therapeutic properties in sepsis-induced lung injury in mice. Single cell suspensions obtained from day 7 human embryoid bodies (d7EBs) injected i.v. 1 hour after cecal ligation and puncture significantly reduced lung inflammation and edema as well as production of tumor necrosis factor-α and interferon-γ in lungs compared with controls, whereas interleukin-10 production remained elevated. d7EB cell transplantation also reduced mortality to 50% from 90% in the control group. The protection was ascribed to d7EB cell interaction with lung resident CD11b+ cells, and was correlated with the ability of d7EB cells to reduce it also reduced production of proinflammatory cytokines by CD11+ cells, and to endothelial NO synthase–derived NO by d7EB cells, leading to inhibition of inducible macrophage-type NO synthase activation in CD11b+ cells. The protective progenitor cells were positive for the endothelial and hematopoietic lineage marker angiotensin converting enzyme (ACE). Only the ACE+ fraction modulated the proinflammatory profile of CD11b+ cells and reduced mortality in septic mice. In contrast to the nonprotective ACE-cell fraction, the ACE+ cell fraction also produced NO. These findings suggest that an ACE+ subset of human embryonic stem cell–derived progenitor cells has a highly specialized anti-inflammatory function that ameliorates sepsis-induced lung inflammation and reduces mortality.

Multimodality imaging of nitric oxide and nitric oxide synthases

Nitric oxide (NO) and NO synthases (NOSs) are crucial factors in many pathophysiological processes such as inflammation, vascular/neurological function, and many types of cancer. Noninvasive imaging of NO or NOS can provide new insights in understanding these diseases and facilitate the development of novel therapeutic strategies. In this review, we will summarize the current state-of-the-art multimodality imaging in detecting NO and NOSs, including optical (fluorescence, chemiluminescence, and bioluminescence), electron paramagnetic resonance (EPR), magnetic resonance (MR), and positron emission tomography (PET). With continued effort over the last several years, these noninvasive imaging techniques can now reveal the biodistribution of NO or NOS in living subjects with high fidelity which will greatly facilitate scientists/clinicians in the development of new drugs and/or patient management. Lastly, we will also discuss future directions/applications of NO/NOS imaging. Successful development of novel NO/NOS imaging agents with optimal in vivo stability and desirable pharmacokinetics for clinical translation will enable the maximum benefit in patient management.