Spin trapping of nitric oxide with the iron-dithiocarbamate complex: chemistry and biology

Electrophilic characteristics and aqueous behavior of fatty acid nitroalkenes

Fatty acid nitroalkenes (NO2-FA) are endogenously-generated products of the reaction of metabolic and inflammatory-derived nitrogen dioxide (.NO2) with unsaturated fatty acids. These species mediate signaling actions and induce adaptive responses in preclinical models of inflammatory and metabolic diseases. The nitroalkene substituent possesses an electrophilic nature, resulting in rapid and reversible reactions with biological nucleophiles such as cysteine, thus supporting post-translational modifications (PTM) of proteins having susceptible nucleophilic centers. These reactions contribute to enzyme regulation, modulation of inflammation and cell proliferation and the regulation of gene expression responses. Herein, focus is placed on the reduction-oxidation (redox) characteristics and stability of specific NO2-FA regioisomers having biological and clinical relevance; nitro-oleic acid (NO2-OA), bis-allylic nitro-linoleic acid (NO2-LA) and the conjugated diene-containing nitro-conjugated linoleic acid (NO2-cLA). Cyclic and alternating-current voltammetry and chronopotentiometry were used to the study of reduction potentials of these NO2-FA. R-NO2 reduction was observed around -0.8 V (vs. Ag/AgCl/3 M KCl) and is related to relative NO2-FA electrophilicity. This reduction process could be utilized for the evaluation of NO2-FA stability in aqueous milieu, shown herein to be pH dependent. In addition, electron paramagnetic resonance (EPR) spectroscopy was used to define the stability of the nitroalkene moiety under aqueous conditions, specifically under conditions where nitric oxide (.NO) release could be detected. The experimental data were supported by density functional theory calculations using 6-311++G (d,p) basis set and B3LYP functional. Based on experimental and computational approaches, the relative electrophilicities of these NO2-FA are NO2-cLA >> NO2-LA > NO2-OA. Micellarization and vesiculation largely define these biophysical characteristics in aqueous, nucleophile-free conditions. At concentrations below the critical micellar concentration (CMC), monomeric NO2-FA predominate, while at greater concentrations a micellar phase consisting of self-assembled lipid structures predominates. The CMC, determined by dynamic light scattering in 0.1 M phosphate buffer (pH 7.4) at 25 °C, was 6.9 (NO2-LA) 10.6 (NO2-OA) and 42.3 μM (NO2-cLA), respectively. In aggregate, this study provides new insight into the biophysical properties of NO2-FA that are important for better understanding the cell signaling and pharmacological potential of this class of mediators.

Development of a Red-Light-Controllable Nitric Oxide Releaser to Control Smooth Muscle Relaxation in Vivo

We designed and synthesized a novel Si-rhodamine derivative, NORD-1, as a red-light-controllable nitric oxide (NO) releaser, on the basis of photoredox parameter analysis. Red-light-responsive NO release from NORD-1 was confirmed by ESR spin trapping and quantified with an NO electrode and by means of Griess assay. The NO release cross section (ε_656 nm·Φ_NO) of NORD-1 was calculated to be 3.65 × 10², which is larger than that of a previously reported yellowish-green-light-controllable NO releaser, NO-Rosa5. The photoresponsiveness of NO release from NORD-1 was precise and efficient enough to induce vasodilation ex vivo under Magnus test conditions. Finally, we showed that intracavernous pressure (ICP) could be controlled in rats in vivo with the combination of NORD-1 and a red-light source without increasing systemic blood pressure, which is a serious side effect of usual NO releasers, such as nitroglycerin and isopentyl nitrite. NORD-1 is expected to be a useful chemical tool for NO research, as well as a candidate agent to control the circulatory system.

Synthesis, evaluation, and biological applications of visible-light-controllable nitric oxide releasers

Nitric oxide (NO) is biologically synthesized in human body and mediates various signal pathway. Because NO is too unstable to handle for biological assay, NO releasers had been developed for NO research. Among them, light-controllable NO releasers are quite useful tool because their NO release can be spatiotemporally controlled by light irradiation. This article shows how to synthesize visible-light controllable NO releasers based on N-nitrosoaminophenol structure, evaluate NO releasing efficiency in various methods, and apply them for biological experiments.

Near-Infrared Photoactivatable Nitric Oxide Donors with Integrated Photoacoustic Monitoring

Photoacoustic (PA) tomography is a noninvasive technology that utilizes near-infrared (NIR) excitation and ultrasonic detection to image biological tissue at centimeter depths. While several activatable small-molecule PA sensors have been developed for various analytes, the use of PA molecules for deep-tissue analyte delivery and monitoring remains an underexplored area of research. Herein, we describe the synthesis, characterization, and in vivo validation of photoNOD-1 and photoNOD-2, the first organic, NIR-photocontrolled nitric oxide (NO) donors that incorporate a PA readout of analyte release. These molecules consist of an aza-BODIPY dye appended with an aryl N-nitrosamine NO-donating moiety. The photoNODs exhibit chemostability to various biological stimuli, including redox-active metals and CYP450 enzymes, and demonstrate negligible cytotoxicity in the absence of irradiation. Upon single-photon NIR irradiation, photoNOD-1 and photoNOD-2 release NO as well as rNOD-1 or rNOD-2, PA-active products that enable ratiometric monitoring of NO release. Our in vitro studies show that, upon irradiation, photoNOD-1 and photoNOD-2 exhibit 46.6-fold and 21.5-fold ratiometric turn-ons, respectively. Moreover, unlike existing NIR NO donors, the photoNODs do not require encapsulation or multiphoton activation for use in live animals. In this study, we use PA tomography to monitor the local, irradiation-dependent release of NO from photoNOD-1 and photoNOD-2 in mice after subcutaneous treatment. In addition, we use a murine model for breast cancer to show that photoNOD-1 can selectively affect tumor growth rates in the presence of NIR light stimulation following systemic administration.

A yellowish-green-light-controllable nitric oxide donor based on N-nitrosoaminophenol applicable for photocontrolled vasodilation

Nitric oxide (NO) has been known as a gaseous chemical mediator, which modulates several physiological functions. Spatial and temporal control of NO release facilitates further study and medical application of NO. Herein, we report design and synthesis of a novel NO donor, NO-Rosa. NO-Rosa has a rosamine moiety, which absorbs yellowish green light. Upon irradiation with yellowish green light (530-590 nm), NO is released from NO-Rosa, presumably via photoinduced electron transfer from the N-nitrosoaminophenol moiety to the rosamine moiety. NO release from NO-Rosa was detected by ESR spin trapping and a NO fluorescent probe. Cellular NO release control was achieved in HEK293 cells using a NO fluorescent probe, DAF-FM DA. Furthermore, temporally controlled NO-induced vasodilation was demonstrated by treatment of a rat aortic strip with NO-Rosaex vivo and irradiation by yellowish green light. NO-Rosa is expected to be utilized for further study of NO-related physiological functions, utilizing its ability of spatiotemporal release of NO as a photocontrollable compound with harmless yellowish-green light.

Regulation of nitric oxide signaling by formation of a distal receptor-ligand complex

The binding of nitric oxide (NO) to the heme cofactor of heme-nitric oxide/oxygen binding (H-NOX) proteins can lead to the dissociation of the heme-ligating histidine residue and yield a five-coordinate nitrosyl complex, which is an important step for NO-dependent signaling. In the five-coordinate nitrosyl complex, NO can reside either on the distal or proximal side of the heme, which could have a profound influence over the lifetime of the in vivo signal. To investigate this central molecular question, the Shewanella oneidensis H-NOX (So H-NOX)–NO complex was biophysically characterized under limiting and excess NO. The results show that So H-NOX preferably forms a distal NO species under both limiting and excess NO. Therefore, signal strength and complex lifetime in vivo will be dictated by the dissociation rate of NO from the distal complex and the return of the histidine ligand to the heme.

Visible Light-Controlled Nitric Oxide Release from Hindered Nitrobenzene Derivatives for Specific Modulation of Mitochondrial Dynamics

Nitric oxide (NO) is a physiological signaling molecule, whose biological production is precisely regulated at the subcellular level. Here, we describe the design, synthesis, and evaluation of novel mitochondria-targeted NO releasers, Rol-DNB-mor and Rol-DNB-pyr, that are photocontrollable not only in the UV wavelength range but also in the biologically favorable visible wavelength range (530-590 nm). These caged NO compounds consist of a hindered nitrobenzene as the NO-releasing moiety and a rhodamine chromophore. Their NO-release properties were characterized by an electron spin resonance (ESR) spin trapping method and fluorometric analysis using NO probes, and their mitochondrial localization in live cells was confirmed by costaining. Furthermore, we demonstrated visible light control of mitochondrial fragmentation via activation of dynamin-related protein 1 (Drp1) by means of precisely controlled NO delivery into mitochondria of cultured HEK293 cells, utilizing Rol-DNB-pyr.

Plant-pathogenic Streptomyces species produce nitric oxide synthase-derived nitric oxide in response to host signals

Nitric oxide (NO) is a potent intercellular signal for defense, development, and metabolism in animals and plants. In mammals, highly regulated nitric oxide synthases (NOSs) generate NO. NOS homologs exist in some prokaryotes, but direct evidence for NO production by these proteins has been lacking. Here, we demonstrate that a NOS in plant-pathogenic Streptomyces species produces diffusible NO. NOS-dependent NO production increased in response to cellobiose, a plant cell wall component, and occurred at the host-pathogen interface, demonstrating induction by host signals. These data document in vivo production of NO by prokaryotic NOSs and implicate pathogen-derived NO in host-pathogen interactions. NO may serve as a signaling molecule in other NOS-containing bacteria, including the medically and environmentally important organisms Bacillus anthracis, Staphylococcus aureus, and Deinococcus radiodurans.

Specific detection of gaseous NO and 15NO in the headspace from liquid-phase reactions involving NO-generating organic, inorganic, and biochemical samples using a mid-infrared laser

Nitric oxide (NO) is an important biological signaling agent. The specific detection of NO represents a continuing challenge in the field of NO research. Many methods are currently employed for the detection of NO. Here, we report a qualitative but specific detection method for gaseous NO liberated in and from solution taking advantage of its low solubility. Importantly, our mid-infrared laser absorption method does not depend on any chemical derivatization of NO, and is applicable over a wide range of concentrations for both protein work and in organic-inorganic modeling work. We also apply this method to the specific detection of 15NO.

Spin trapping nitric oxide from neuronal nitric oxide synthase: A look at several iron-dithiocarbamate complexes

The free radical, nitric oxide ( radicalNO), is responsible for a myriad of physiological functions. The ability to verify and study radicalNO in vivo is required to provide insight into the events taking place upon its generation and in particular the flux of radicalNO at relevant cellular sites. With this in mind, several iron-chelates (Fe2+(L)2) have been developed, which have provided a useful tool for the study and identification of radicalNO through spin-trapping and electron paramagnetic resonance (EPR) spectroscopy. However, the effectiveness of radicalNO detection is dependent on the Fe2+(L)2 complex. The development of more efficient and stable Fe2+(L)2 chelates may help to better understand the role of radicalNO in vivo. In this paper, we present data comparing several proline derived iron-dithiocarbamate complexes with the more commonly used spin traps for radicalNO, Fe2+-di(N-methyl-D-glutamine-dithiocarbamate) (Fe2+(MGD)2) and Fe2+-di(N-(dithiocarboxy)sarcosine) (Fe2+(DTCS)2). We evaluate the apparent rate constant (kapp) for the reaction of radicalNO with these Fe2+(L)2complexes and the stability of the corresponding Fe2+(NO)(L)2 in presence of NOS I.