Photochemical Nitric Oxide Research Articles

Influence of Pluronic F127 microenvironments on the photochemical nitric oxide release from S-nitrosoglutathione

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) (F127) hydrogels have been used to deliver nitric oxide (NO) topically in biomedical applications. Here, the effect of F127 microenvironments on the photochemical NO release from S-nitrosoglutathione (GSNO) was investigated in F127 solutions 7.6 wt% 15 wt% and 22.5 wt% at 15 °C and 37 °C. Small-angle X-ray Scattering (SAXS) and Differential Scanning Calorimetry (DSC) measurements, along with proton Nuclear Magnetic Resonance (1H NMR) spectral shifts and T2 relaxation data at six different concentration-temperature conditions, allowed identifying F127 microphases characterized by: a sol phase of unimers; micelles in non-defined periodic order, and a gel phase of cubic packed micelles. Kinetic measurements showed that GSNO photodecompositon proceeds faster in micellized F127 where GSNO is segregated to the intermicellar microenvironment. Real time kinetic monitoring of NO release and T2 relaxation profiles showed that NO is preferentially partitioned into the hydrophobic PPO cores of the F127 micelles, with the consequent decrease in its rate of release to the gas phase. These results show that F127 microphases affect both the kinetics of GSNO photodecomposition and the rate of NO escape and can be used to modulate the photochemical NO delivery from F127/GSNO solutions.

Nitric oxide release from a photoactive water-soluble ruthenium nitrosyl. Biological effects

This research presents the synthesis and characterization of the photochemical nitric oxide (NO) precursor Ru(salenCO2H)(NO)Cl (1, salenCO2H = N,N’-ethylenebis(3,3’-bis-carboxylsalicylideneiminato). This water-soluble ruthenium nitrosyl releases NO upon photolysis with a quantum yield that is pH dependent owing to the nitrosyl to nitrite conversion of that axial ligand at higher pH. Also described are the water, oxygen, and thermal stability of 1 and the cytotoxicity and the vascular relaxivity properties of 1 in the dark and under photolysis.

Topical photochemical nitric oxide release from porous poly(vinyl alcohol) membrane for visible light modulation of dermal vasodilation

Abstract Complications of functional peripheral artery disease (PAD), like chronic wounds and Raynaud’s disease and phenomenon, have stimulated the development of topical nitric oxide (NO)-releasing biomaterials capable of restoring the blood flow locally. In this work, we used phase inversion technique to prepare porous membranes of poly(vinyl alcohol) (PVA) functionalized with NO-releasing S-nitrosothiol (SNO) moieties. This strategy led to crosslinked amorphous membranes with swelling degree of 750 wt% and interconnected macropores with diameters greater than 600 μm. Controlling the extent of the S-nitrosation reaction allowed obtaining PVA-SNO membranes that spontaneously release NO in the range of 33–53 nmol/cm 2 in the dark. Irradiation of these membranes with visible light, led to first order NO release kinetics with rate constant of (5.6 ± 0.2) × 10 −3 s −1 and increased the amount of NO released to 64–101 nmol/cm 2 . Topical application of PVA-SNO membrane for 4 min on the healthy skin, led to a fast and localized 300% increase in the dermal blood flow, which was enhanced to 900% when the membrane was irradiated with visible light, during the same period. These results show that the photochemical NO release from macroporous PVA-SNO membrane is an effective tool for modulating NO actions in the treatment/prevention of PAD symptoms and other biomedical applications.

Nitrous Oxide Metabolism in Nitrate-Reducing Bacteria: Physiology and Regulatory Mechanisms.

Nitrous oxide (N2O) is an important greenhouse gas (GHG) with substantial global warming potential and also contributes to ozone depletion through photochemical nitric oxide (NO) production in the stratosphere. The negative effects of N2O on climate and stratospheric ozone make N2O mitigation an international challenge. More than 60% of global N2O emissions are emitted from agricultural soils mainly due to the application of synthetic nitrogen-containing fertilizers. Thus, mitigation strategies must be developed which increase (or at least do not negatively impact) on agricultural efficiency whilst decrease the levels of N2O released. This aim is particularly important in the context of the ever expanding population and subsequent increased burden on the food chain. More than two-thirds of N2O emissions from soils can be attributed to bacterial and fungal denitrification and nitrification processes. In ammonia-oxidizing bacteria, N2O is formed through the oxidation of hydroxylamine to nitrite. In denitrifiers, nitrate is reduced to N2 via nitrite, NO and N2O production. In addition to denitrification, respiratory nitrate ammonification (also termed dissimilatory nitrate reduction to ammonium) is another important nitrate-reducing mechanism in soil, responsible for the loss of nitrate and production of N2O from reduction of NO that is formed as a by-product of the reduction process. This review will synthesize our current understanding of the environmental, regulatory and biochemical control of N2O emissions by nitrate-reducing bacteria and point to new solutions for agricultural GHG mitigation.

Pluronic F127/poly(vinyl alcohol) hydrogels for controlling the photochemical nitric oxide delivery in topical applications

Pluronic F127/poly(vinyl alcohol) hydrogels for controlling the photochemical nitric oxide delivery in topical applications

Light-controlled release of nitric oxide from solid polymer composite materials using visible and near infra-red light.

Photochemical Nitric oxide releasing composite materials (Photo-NORMs) were prepared using biocompatible polymers and the photochemical nitric oxide donor complex (CrONO). We have demonstrated nitric oxide (NO) release from the solid composites for extended (>30 hours) and controlled (20-100 pmoles s(-1)) durations after visible light irradiation. Quantitation of the efficiency of NO release from the composites shows that polymer gas permeability most dramatically affects the overall efficiency (QY) of photochemical NO release, where polymers with higher gas permeability have a higher QY of nitric oxide release. Composites were also prepared with β-phase lanthanide-doped NaYF4 upconverting nanoparticles (UCNPs). Controlled Nitric oxide release was achieved via near infrared (NIR) irradiation. A prototype LED device shows proof-of-concept that such photoresponsive NO-releasing composites could be applied to implantable systems, where the amount of NO released is modulated by changing irradiation time and light intensity. This research provides the guidelines necessary to move towards device fabrication and testing in actual tissue to evaluate the photo-NORMS as a reliable option for nitric oxide release in vivo.

Enhanced photochemical nitric oxide release from a flutamide derivative incorporated in Pluronic F127 micelles

The incorporation of nitric oxide (NO) photodonors into nontoxic vehicles may allow for the tunable control of topical NO release to treat pathological conditions associated with the impairment of NO production in the dermal vasculature. Pluronic F127 is a PEO–PPO–PEO triblock copolymer that is used as a nontoxic vehicle that undergoes thermally reversible micellization and gelation. In this study, we synthesized a thermally stable flutamide derivative, N-(3-aminopropyl)-3-(trifluoromethyl)-4-nitrobenzenamine (ATN), which is capable of releasing NO upon irradiation with visible light, as shown by real-time chemiluminescence NO detection. We demonstrated that the incorporation of ATN into the hydrophobic nuclei of F127 micelles leads to an enhancement of its photochemical NO release, which is consistent with the photodecomposition route associated with the nitro-to-nitrite photorearrangement of ATN. This mechanism underscores a new role of the F127 micelles as concentrating “nanoreactors” for hydrophobic NO releasing drugs. In this case, this effect may represent a new strategy for enhancing photochemical NO release from ATN, which makes the micellar F127/ATN solutions promising for topical NO application.

Nitric Oxide Releasing Materials Triggered by Near-Infrared Excitation Through Tissue Filters

Novel materials for the phototherapeutic release of the bioregulator nitric oxide (nitrogen monoxide) are described. Also reported is a method for scanning these materials with a focused NIR beam to induce photouncaging while minimizing damage from local heating. The new materials consist of poly(dimethylsiloxane) composites with near-infrared-to-visible upconverting nanoparticles (UCNPs) that are cast into a biocompatible polymer disk (PD). These PDs are then impregnated with the photochemical nitric oxide precursor Roussin's black salt (RBS) to give UCNP_RBS_PD devices that generate NO when irradiated with 980 nm light. When the UCNP_RBS_PD composites were irradiated with NIR light through filters composed of porcine tissue, physiologically relevant NO concentrations were released, thus demonstrating the potential of such devices for minimally invasive phototherapeutic applications.

Nitric oxide and nitrous oxide turnover in natural and engineered microbial communities: biological pathways, chemical reactions, and novel technologies

Nitrous oxide (N2O) is an environmentally important atmospheric trace gas because it is an effective greenhouse gas and it leads to ozone depletion through photo-chemical nitric oxide (NO) production in the stratosphere. Mitigating its steady increase in atmospheric concentration requires an understanding of the mechanisms that lead to its formation in natural and engineered microbial communities. N2O is formed biologically from the oxidation of hydroxylamine (NH2OH) or the reduction of nitrite (NO−2) to NO and further to N2O. Our review of the biological pathways for N2O production shows that apparently all organisms and pathways known to be involved in the catabolic branch of microbial N-cycle have the potential to catalyze the reduction of NO−2 to NO and the further reduction of NO to N2O, while N2O formation from NH2OH is only performed by ammonia oxidizing bacteria (AOB). In addition to biological pathways, we review important chemical reactions that can lead to NO and N2O formation due to the reactivity of NO−2, NH2OH, and nitroxyl (HNO). Moreover, biological N2O formation is highly dynamic in response to N-imbalance imposed on a system. Thus, understanding NO formation and capturing the dynamics of NO and N2O build-up are key to understand mechanisms of N2O release. Here, we discuss novel technologies that allow experiments on NO and N2O formation at high temporal resolution, namely NO and N2O microelectrodes and the dynamic analysis of the isotopic signature of N2O with quantum cascade laser absorption spectroscopy (QCLAS). In addition, we introduce other techniques that use the isotopic composition of N2O to distinguish production pathways and findings that were made with emerging molecular techniques in complex environments. Finally, we discuss how a combination of the presented tools might help to address important open questions on pathways and controls of nitrogen flow through complex microbial communities that eventually lead to N2O build-up.

Photochemistry of trans-Cr(cyclam)(ONO)2+, a Nitric Oxide Precursor

Experimental and density functional theory (DFT) studies are described that are focused on outlining the reactivity of the known photochemical nitric oxide precursor trans-Cr(cyclam)(ONO)(2)(+) ("CrONO", cyclam = 1,4,8,11-tetrazacycltetradecane). Studies in both aerated and deaerated aqueous media are described as are the roles of both the oxidant O(2) and a reductant such as glutathione in trapping the apparent Cr(IV) photoreaction intermediate trans-Cr(cyclam)(O)(ONO)(+). Also reported and characterized structurally is the Cr(V) product of long-term photolysis in the absence of reducing agents, the trans-dioxo species [trans-Cr(cyclam)(O)(2)](ClO(4)). Photosensitization experiments indicate that at least a significant fraction of the reaction occurs from the lowest energy doublet excited state(s). Lastly, cell culture experiments demonstrate that CrONO has little or no acute toxicity either before or after photolysis.

Metal complexes as photochemical nitric oxide precursors: Potential applications in the treatment of tumors

The bioregulatory molecule NO plays key roles in cancer biology and has been implicated in both tumor growth and suppression. Furthermore, it is a gamma-radiation sensitizer that may enhance selective killing of neoplastic tissues. For these reasons, there is considerable interest in developing methods for NO delivery to specific physiological targets. In this Perspective, we describe ongoing investigations focused on photochemical methodologies to deliver therapeutic doses of NO to such targets utilizing transition metal complexes that are nitric oxide precursors. The photochemical strategy has the advantages that it allows for precise control of the timing, location, and dosage for the targeted delivery of a bioactive agent.

Chromium(III) Complexes for Photochemical Nitric Oxide Generation from Coordinated Nitrite: Synthesis and Photochemistry of Macrocyclic Complexes with Pendant Chromophores, trans-[Cr(L)(ONO)2]BF4

Several new dinitritochromium(III) complexes of the type trans-[Cr(L)(ONO)(2)]BF(4), where L is a derivative of the macrocyclic ligand cyclam having pendant aromatic chromophores attached (L = 5,7-dimethyl-6-(substituted)-1,4,8,11-tetraazacyclotetradecane), have been prepared and characterized. Photoexcitation of aqueous solutions containing these complexes at wavelengths corresponding to the pendant chromophore absorption bands led to the generation of NO as detected by an electrochemical sensor. Photophysical data show that the expected fluorescence of the pendant chromophores is largely quenched when the macrocyclic ligand is coordinated to these Cr(III) centers, and this is interpreted in terms of fast energy transfer processes from the ligand-centered pipi states to the Cr(III)-centered ligand field states leading to subsequent cleavage of the Cr(III)-coordinated nitrito ligand. Thus, the chromophores tethered to the coordinated cyclam serve as light-gathering antennae for the intramolecular sensitization of the NO-generating photoreactions at the metal center.

Thermal and photochemical nitric oxide release from S-nitrosothiols incorporated in Pluronic F127 gel: potential uses for local and controlled nitric oxide release

The local delivery of nitric oxide (nitrogen monoxide, NO) by thermal or photochemical means to target cells or organs has a great potential in several biomedical applications, especially if the NO donors are incorporated into non-toxic viscous matrices. In this work, we have shown that the NO donors S-nitrosoglutathione (GSNO) and S-nitroso- N-acetylcysteine (SNAC) can be incorporated into F127 hydrogels, from where NO can be released thermally or photochemically (with λ irr>480 nm). High sensitivity differential scanning calorimetry (HSDSC) and a new spectrophotometric method, were used to characterize the micellization and the reversal thermal gelation processes of the F127 hydrogels containing NO donors, and to modulate the gelation temperatures to the range 29–32°C. Spectral monitoring of the S–NO bond cleavage showed that the initial rates of thermal and photochemical NO release (ranging from 2 to 45 μmol l −1 min −1) are decreased in the hydrogel matrices, relative to those obtained in aqueous solutions. This stabilization effect was assigned to a cage recombination mechanism and offers an additional advantage for the storage and handling of S-nitrosothiols. These results indicate that F127 hydrogels might be used for the thermal and photochemical delivery of NO from S-nitrosothiols to target areas in biomedical applications.

Heat and Photolytic Nitric Oxide are Essential Factors for Light-induced Vascular Tension Changes

. Light induces various vascular tension changes, but these phenomena and their mechanisms remain controversial. We hypothesise that photocontraction results from the thermal effect, and that photorelaxation results from the non-thermal effect of photochemical nitric oxide generation. The isometric tension of a rat aortic ring was measured during laser light irradiation at various wavelengths with constant heat generation. Visible irradiation (458 nm, 514.5 nm) induced either photorelaxation (the tension increment was −20% of the contracted state induced by noradrenaline) or photocontraction (+7.8%); UV irradiation (351 nm) induced only photorelaxation (−41%), and near-IR irradiation (800 nm) produced only photocontraction (+11%). In the vascular tissue, photocontraction increased with deposited light energy, which was proportional to the temperature elevation. Simply heating the vascular tissue also resulted in vasocontraction. Photorelaxation by UV occurred even in the absence of endothelium, and was significantly reduced to 49% of control levels of photorelaxation by the guanylate cyclase inhibitor, methylene blue. Photorelaxation was not reduced by the nitric oxide synthetase inhibitors, N ω-monomethyl-l-arginine (l-NMMA) and N ω-nitro-l-arginine methyl ester (l-NAME). We conclude that photocontraction is produced by the thermal effect resulting from deposited light energy. Photorelaxation might be induced by endothelium-independent nitric oxide generation, which seems to result from the photochemical effect due to photon energy.