Detecting and monitoring NO, SNO and nitrite in vivo

Myoglobin deficiency impairs maximal oxygen uptake and exercise performance: a lesson from Mb-/- mice

Myoglobin (Mb) plays an important role at rest and during exercise as a reservoir of oxygen and has been suggested to regulate NO• bioavailability under hypoxic/acidic conditions. However, its ultimate role during exercise is still a subject of debate. We aimed to study the effect of Mb deficiency on maximal oxygen uptake (V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ ) and exercise performance in myoglobin knockout mice (Mb-/- ) when compared to control mice (Mb+/+ ). Furthermore, we also studied NO• bioavailability, assessed as nitrite (NO2 - ) and nitrate (NO3 - ) in the heart, locomotory muscle and in plasma, at rest and during exercise at exhaustion both in Mb-/- and in Mb+/+ mice. The mice performed maximal running incremental exercise on a treadmill with whole-body gas exchange measurements. The Mb-/- mice had lower body mass, heart and hind limb muscle mass (P < 0.001). Mb-/- mice had significantly reduced maximal running performance (P < 0.001).V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ expressed in ml min-1 in Mb-/ - mice was 37% lower than in Mb+/+ mice (P < 0.001) and 13% lower when expressed in ml min-1  kg body mass-1 (P = 0.001). Additionally, Mb-/- mice had significantly lower plasma, heart and locomotory muscle NO2 - levels at rest. During exercise NO2 - increased significantly in the heart and locomotory muscles of Mb-/- and Mb+/+ mice, whereas no significant changes in NO2 - were found in plasma. Our study showed that, contrary to recent suggestions, Mb deficiency significantly impairsV ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ and maximal running performance in mice. KEY POINTS: Myoglobin knockout mice (Mb-/- ) possess lower maximal oxygen uptake (V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ ) and poorer maximal running performance than control mice (Mb+/+ ). Respiratory exchange ratio values at high running velocities in Mb-/- mice are higher than in control mice suggesting a shift in substrate utilization towards glucose metabolism in Mb-/- mice at the same running velocities. Lack of myoglobin lowers basal systemic and muscle NO• bioavailability, but does not affect exercise-induced NO2 - changes in plasma, heart and locomotory muscles. The present study demonstrates that myoglobin is of vital importance forV ̇ O 2 max ${\dot V_{{{\mathrm{O}}_2}\max }}$ and maximal running performance as well as explains why previous studies have failed to prove such a role of myoglobin when using the Mb-/- mouse model.

Graphene nanocomposites for real-time electrochemical sensing of nitric oxide in biological systems

Nitric oxide (NO) signaling plays many pivotal roles impacting almost every organ function in mammalian physiology, most notably in cardiovascular homeostasis, inflammation, and neurological regulation. Consequently, the ability to make real-time and continuous measurements of NO is a prerequisite research tool to understand fundamental biology in health and disease. Despite considerable success in the electrochemical sensing of NO, challenges remain to optimize rapid and highly sensitive detection, without interference from other species, in both cultured cells and in vivo. Achieving these goals depends on the choice of electrode material and the electrode surface modification, with graphene nanostructures recently reported to enhance the electrocatalytic detection of NO. Due to its single-atom thickness, high specific surface area, and highest electron mobility, graphene holds promise for electrochemical sensing of NO with unprecedented sensitivity and specificity even at sub-nanomolar concentrations. The non-covalent functionalization of graphene through supermolecular interactions, including π-π stacking and electrostatic interaction, facilitates the successful immobilization of other high electrolytic materials and heme biomolecules on graphene while maintaining the structural integrity and morphology of graphene sheets. Such nanocomposites have been optimized for the highly sensitive and specific detection of NO under physiologically relevant conditions. In this review, we examine the building blocks of these graphene-based electrochemical sensors, including the conjugation of different electrolytic materials and biomolecules on graphene, and sensing mechanisms, by reflecting on the recent developments in materials and engineering for real-time detection of NO in biological systems.

Nitrite Concentration in the Striated Muscles Is Reversely Related to Myoglobin and Mitochondrial Proteins Content in Rats

Skeletal muscles are an important reservoir of nitric oxide (NO^•) stored in the form of nitrite [NO₂⁻] and nitrate [NO₃⁻] (NO_x). Nitrite, which can be reduced to NO^• under hypoxic and acidotic conditions, is considered a physiologically relevant, direct source of bioactive NO^•. The aim of the present study was to determine the basal levels of NO_x in striated muscles (including rat heart and locomotory muscles) with varied contents of tissue nitrite reductases, such as myoglobin and mitochondrial electron transport chain proteins (ETC-proteins). Muscle NO_x was determined using a high-performance liquid chromatography-based method. Muscle proteins were evaluated using western-immunoblotting. We found that oxidative muscles with a higher content of ETC-proteins and myoglobin (such as the heart and slow-twitch locomotory muscles) have lower [NO₂⁻] compared to fast-twitch muscles with a lower content of those proteins. The muscle type had no observed effect on the [NO₃⁻]. Our results demonstrated that fast-twitch muscles possess greater potential to generate NO^• via nitrite reduction than slow-twitch muscles and the heart. This property might be of special importance for fast skeletal muscles during strenuous exercise and/or hypoxia since it might support muscle blood flow via additional NO^• provision (acidic/hypoxic vasodilation) and delay muscle fatigue.

Sodium borohydride and thiol mediated nitrite release from nitroaromatic antibiotics

Nitroaromatic antibiotics are used to treat a variety of bacterial and parasitic infections. These prodrugs require reductive bioactivation for activity, which provides a pathway for the release of nitrogen oxide species such as nitric oxide, nitrite, and/or nitroxyl. Using sodium borohydride and 2-aminoethanol as model reductants, this work examines release of nitrogen oxide species from various nitroaromatic compounds through several characterization methods. Specifically, 4- and 5-nitroimidazoles reproducibly generate higher amounts of nitrite (not nitric oxide or nitroxyl) than 2-nitroimidazoles during the reaction of model hydride donors or thiols. Mass spectrometric analysis shows clean formation of products resulting from nucleophile addition and nitro group loss. 2-Nitrofurans generate nitrite upon addition of sodium borohydride or 2-aminoethanethiol, but these complex reactions do not produce clean organic products. A mechanism that includes nucleophile addition to the carbon βto the nitro group to generate a nitronate anion followed by protonation and nitrous acid elimination explains the observed products and labeling studies. These systematic studies give a better understanding of the release mechanisms of nitrogen oxide species from these compounds allowing for the design of more efficient therapeutics.

Nitroaromatic Antibiotics as Nitrogen Oxide Sources

Nitroaromatic antibiotics show activity against anaerobic bacteria and parasites, finding use in the treatment of Heliobacter pylori infections, tuberculosis, trichomoniasis, human African trypanosomiasis, Chagas disease and leishmaniasis. Despite this activity and a clear need for the development of new treatments for these conditions, the associated toxicity and lack of clear mechanisms of action have limited their therapeutic development. Nitroaromatic antibiotics require reductive bioactivation for activity and this reductive metabolism can convert the nitro group to nitric oxide (NO) or a related reactive nitrogen species (RNS). As nitric oxide plays important roles in the defensive immune response to bacterial infection through both signaling and redox-mediated pathways, defining controlled NO generation pathways from these antibiotics would allow the design of new therapeutics. This review focuses on the release of nitrogen oxide species from various nitroaromatic antibiotics to portend the increased ability for these compounds to positively impact infectious disease treatment.

Nitric oxide inhibition of lipopolysaccharide-stimulated RAW 247.6 cells by ibuprofen-conjugated iron oxide nanoparticles

Aim: To develop a series of superparamagnetic iron oxide nanoparticles (SPIONs) by coconjugating them with ibuprofen (ibu) and glycerol phosphate (glycerol) or ibu and glucose-1-phosphate and to assess capacity of these conjugates to inhibit the release of nitric oxide (NO) in macrophages, even at low concentrations. Materials & methods: The SPION conjugates were characterized and their properties evaluated showing the influence of those ligands on colloidal stability and inhibition of NO-release demonstrated. The cytotoxicity and possible anti-inflammatory activity were evaluated using murine macrophages (RAW 247.6). Results: SPION-glycerol phosphate/ibu conjugates inhibited the NO production induced by lipopolysaccharides, indicating a potential anti-inflammatory activity. Conclusion: SPION conjugated with ibu was shown to inhibit NO-release even at very low concentrations, suggesting possible action against inflammatory diseases.

A Comparison of Different Approaches to Quantify Nitric Oxide Release from NO-Releasing Materials in Relevant Biological Media

The development of solid materials that deliver nitric oxide (NO) are of interest for several therapeutic applications. Nevertheless, due to NO’s reactive nature, rapid diffusion and short half-life, reporting their NO delivery characteristics is rather complex. The full knowledge of this parameter is fundamental to discuss the therapeutic utility of these materials, and thus, the NO quantification strategy must be carefully considered according to the NO-releasing scaffold type, to the expected NO-releasing amounts and to the medium of quantification. In this work, we explore and discuss three different ways of quantifying the release of NO in different biological fluids: haemoglobin assay, Griess assay and NO electrochemical detection. For these measurements, different porous materials, namely zeolites and titanosilicates were used as models for NO-releasing platforms. The oxyhaemoglobin assay offers great sensitivity (nanomolar levels), but it is only possible to monitor the NO release while oxyhaemoglobin is not fully converted. On the other hand, Griess assay has low sensitivity in complex biological media, namely in blood, and interferences with media make NO measurements questionable. Nevertheless, this method can measure micromolar amounts of NO and may be useful for an initial screening for long-term release performance. The electrochemical sensor enabled real-time measurements in a variety of biological settings. However, measured NO is critically low in oxygenated and complex media, giving transient signals, which makes long-term quantification impossible. Despite the disadvantages of each method, the combination of all the results provided a more comprehensive NO release profile for these materials, which will help to determine which formulations are most promising for specific therapeutic applications. This study highlights the importance of using appropriate NO quantification tools to provide accurate reports.

Ethanol Withdrawal Alters the Oxidative State of the Heart Through AT1-Dependent Mechanisms

Aims

We investigated the cardiac effects of ethanol withdrawal and the possible role of AT1 receptors in such response.

Methods

Male Wistar rats were treated with increasing doses of ethanol (3 to 9%, vol./vol.) for 21 days. The cardiac effects of ethanol withdrawal were investigated 48 h after abrupt discontinuation of ethanol. Some animals were orally treated with losartan (10 mg/kg/day), a selective AT1 receptor antagonist.

Results

Ethanol withdrawal did not affect serum levels of creatine kinase (CK)-MB. Losartan prevented ethanol withdrawal-induced increase in superoxide anion (O2•−) production in the left ventricle (LV). However, ethanol withdrawal did no alter the levels of thiobarbituric acid reactive substances (TBARS) or the expression of Nox1, Nox2 or Nox4 were found in the LV. Ethanol withdrawal reduced the concentration of hydrogen peroxide (H2O2) in the LV and this response was prevented by losartan. Ethanol withdrawal increased catalase activity in the LV and losartan attenuated this response. No changes on superoxide dismutase (SOD) activity or expression were detected in the LV during ethanol withdrawal. The expression of AT1, AT2 or angiotensin converting enzyme (ACE) was not affected by ethanol withdrawal. Similarly, no changes on the expression of ERK1/2, SAPK/JNK, COX-1 or COX-2 were found in the LV during ethanol withdrawal.

Conclusions

Ethanol withdrawal altered the cardiac oxidative state through AT1-dependent mechanisms. Our findings showed a role for angiotensin II/AT1 receptors in the initial steps of the cardiac effects induced by ethanol withdrawal.

Current approaches to measure nitric oxide in plants

Nitric oxide (NO) is now established as an important signalling molecule in plants where it influences growth, development, and responses to stress. Despite extensive research, the most appropriate methods to measure and localize these signalling radicals are debated and still need investigation. Many confounding factors such as the presence of other reactive intermediates, scavenging enzymes, and compartmentation influence how accurately each can be measured. Further, these signalling radicals have short half-lives ranging from seconds to minutes based on the cellular redox condition. Hence, it is necessary to use sensitive and specific methods in order to understand the contribution of each signalling molecule to various biological processes. In this review, we summarize the current knowledge on NO measurement in plant samples, via various methods. We also discuss advantages, limitations, and wider applications of each method.

A quasi-reagentless point-of-care test for nitrite and unaffected by oxygen and cyanide

The ubiquitous nitrite is a major analyte in the management of human health and environmental risks. The current analytical methods are complex techniques that do not fulfil the need for simple, robust and low-cost tools for on-site monitoring. Electrochemical reductase-based biosensors are presented as a powerful alternative, due to their good analytical performance and miniaturization potential. However, their real-world application is limited by the need of anoxic working conditions, and the standard oxygen removal strategies are incompatible with point-of-care measurements. Instead, a bienzymatic oxygen scavenger system comprising glucose oxidase and catalase can be used to promote anoxic conditions in aired environments. Herein, carbon screen-printed electrodes were modified with cytochrome c nitrite reductase together with glucose oxidase and catalase, so that nitrite cathodic detection could be performed by cyclic voltammetry under ambient air. The resulting biosensor displayed good linear response to the analyte (2–200 µM, sensitivity of 326 ± 5 mA M⁻¹ cm⁻² at −0.8 V; 0.8–150 µM, sensitivity of 511 ± 11 mA M⁻¹ cm⁻² at −0.5 V), while being free from oxygen interference and stable up to 1 month. Furthermore, the biosensor’s catalytic response was unaffected by the presence of cyanide, a well-known inhibitor of heme-enzymes.

Nitric oxide sensing by chlorophyll a

Nitric oxide (NO) acts as a signalling molecule that has direct and indirect regulatory roles in various functional processes in biology, though in plant kingdom its role is relatively unexplored. One reason for this is the fact that sensing of NO is always challenging. There are very few probes that can classify the different NO species. The present paper proposes a simple but straightforward way for sensing different NO species using chlorophyll, the source of inspiration being hemoglobin that serves as NO sink in mammalian systems. The proposed method is able to classify NO from DETA-NONOate or (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl) amino] diazen-1-ium-1,2-diolate, nitrite, nitrate and S-nitrosothiol or SNO. This discrimination is carried out by chlorophyll a (chl a) at nano molar (nM) order of sensitivity and at 293 K-310 K. Molecular docking reveals the differential binding effects of NO and SNO with chlorophyll, the predicted binding affinity matching with the experimental observation. Additional experiments with a diverse range of cyanobacteria reveal that apart from the spectroscopic approach the proposed sensing module can be used in microscopic inspection of NO species. Binding of NO is sensitive to temperature and static magnetic field. This provides additional support for the involvement of the porphyrin ring structures to the NO sensing process. This also, broadens the scope of the sensing methods as hinted in the text.

Hydrogen sulfide alleviates hypertensive kidney dysfunction through an epigenetic mechanism

Hypertension is a major risk factor for chronic kidney disease (CKD), and renal inflammation is an integral part in this pathology. Hydrogen sulfide (H₂S) has been shown to mitigate renal damage through reduction in blood pressure and ROS; however, the exact mechanisms are not clear. While several studies have underlined the role of epigenetics in renal inflammation and dysfunction, the mechanisms through which epigenetic regulators play a role in hypertension are not well defined. In this study, we sought to identify whether microRNAs are dysregulated in response to angiotensin II (ANG II)-induced hypertension in the kidney and whether a H₂S donor, GYY4137, could reverse the microRNA alteration and kidney function. Wild-type (C57BL/6J) mice were treated without or with ANG II and GYY4137 for 4 wk. Blood pressure, renal blood flow, and resistive index (RI) were measured. MicroRNA microarrays were conducted and subsequent target prediction revealed genes associated with a proinflammatory response. ANG II treatment significantly increased blood pressure, decreased blood flow in the renal cortex, increased RI, and reduced renal function. These effects were ameliorated in mice treated with GYY4137. Microarray analysis revealed downregulation of miR-129 in ANG II-treated mice and upregulation after GYY4137 treatment. Quantitation of proteins involved in the inflammatory response and DNA methylation revealed upregulation of IL-17A and DNA methyltransferase 3a, whereas H₂S production enzymes and anti-inflammatory IL-10 were reduced. Taken together, our data suggest that downregulation of miR-129 plays a significant role in ANG II-induced renal inflammation and functional outcomes and that GYY4137 improves renal function by reversing miR-129 expression.NEW & NOTEWORTHY We investigated epigenetic changes that occur in the hypertensive kidney and how H₂S supplementation reverses adverse effects. Inflammation, aberrant methylation, and dysfunction were observed in the hypertensive kidney, and these effects were alleviated with H₂S supplementation. We identify miR-129 as a potential regulator of blood pressure and H₂S regulation.

Synthesis and biological activity of furoxan derivatives against Mycobacterium tuberculosis

Tuberculosis (TB) remains a serious health problem responsible to cause millions of deaths annually. The scenario becomes alarming when it is evaluated that the number of new drugs does not increase proportionally to the emergence of resistance to the current therapy. Furoxan derivatives, known as nitric oxide (NO) donors, have been described to exhibit antitubercular activity. Herein, a novel series of hybrid furoxan derivatives (1,2,5-oxadiazole 2-N-oxide) (compounds 4a-c, 8a-c and 14a-c) were designed, synthesized and evaluated in vitro against Mycobacterium tuberculosis (MTB) H37Rv (ATCC 27294) and a clinical isolate MDR-TB strain. The furoxan derivatives have exhibited MIC90 values ranging from 1.03 to 62 μM (H37Rv) and 7.0-50.0 μM (MDR-TB). For the most active compounds (8c, 14a, 14b and 14c) the selectivity index ranged from 3.78 to 52.74 (MRC-5 cells) and 1.25-34.78 (J774A.1 cells). In addition, it was characterized for those compounds logPo/w values between 2.1 and 2.9. All compounds were able to release NO at levels ranging from 0.16 to 44.23%. Among the series, the phenylsulfonyl furoxan derivatives (compounds 14a-c) were the best NO-donor with the lowest MIC90 values. The most active compound (14c) was also stable at different pHs (5.0 and 7.4). In conclusion, furoxan derivatives were identified as new promising compounds useful to treat tuberculosis.