Duration Of Nitric Oxide Release Research Articles

Post-exposure persistence of nitric oxide upregulation in skin cells irradiated by UV-A.

Evidence suggests that exposure to UV-A radiation can liberate nitric oxide from skin cells eliciting vasodilation in-vivo. However, the duration of nitric oxide release in skin cells after UV exposure is not well studied, with emphasis on UV-B mediated iNOS upregulation. The current study demonstrated persistence of nitric oxide release in a dark reaction after moderate UV-A exposure, peaking around 48 h post exposure; this effect was shown in keratinocytes, fibroblasts and endothelial cells from neonatal donors and keratinocytes from aged donors and confirmed the hypothesis that UV-A exposure appeared to upregulate cNOS alongside iNOS. Release of nitric oxide in the skin cells induced by a moderate exposure to UV-A in sunlight may be especially beneficial for some demographic groups such as the elderly, hypertensive patients or those with impaired nitric oxide function, not only during exposure but many hours and days after that.

Extended Nitric Oxide-Releasing Polyurethanes via S-Nitrosothiol-Modified Mesoporous Silica Nanoparticles.

S-Nitrosothiol (RSNO)-modified mesoporous silica nanoparticles (MSNs) were doped into polyurethane (PU) to achieve extended NO-releasing coatings. Parameters influencing the synthesis of RSNO-functionalized nitric oxide (NO)-releasing MSNs were evaluated to elucidate the impact of pore structure on NO release characteristics. The porous particles were characterized as having larger NO payloads and longer NO release durations than those of nonporous particles, a feature attributed to the recombination of the NO radical in confined intraporous microenvironments. NO release kinetics, particle leaching, and thermal stability of the RSNO-modified MSNs dispersed in PU were evaluated as a function of PU structure to determine the feasibility of preparing a range of NO-releasing polymers for biomedical device-coating applications. The NO release kinetics from the PUs proved to be highly extended (>30 d) and consistent over a range of PU properties. Furthermore, RSNO-modified MSN leaching was not observed from the PUs. The NO release payloads were also maintained for 4 days for polymers stored at 0 °C.

Progress and Promise of Nitric Oxide-Releasing Platforms.

Nitric oxide (NO) is a highly potent radical with a wide spectrum of physiological activities. Depending on the concentration, it can enhance endothelial cell proliferation in a growth factor‐free medium, mediate angiogenesis, accelerate wound healing, but may also lead to tumor progression or induce inflammation. Due to its multifaceted role, NO must be administered at a right dose and at the specific site. Many efforts have focused on developing NO‐releasing biomaterials; however, NO short half‐life in human tissues only allows this molecule to diffuse over short distances, and significant challenges remain before the full potential of NO can be realized. Here, an overview of platforms that are engineered to release NO via catalytic or noncatalytic approaches is presented, with a specific emphasis on progress reported in the past five years. A number of NO donors, natural enzymes, and enzyme mimics are highlighted, and recent promising developments of NO‐releasing scaffolds, particles, and films are presented. In particular, key parameters of NO delivery are discussed: 1) NO payload, 2) maximum NO flux, 3) NO release half‐life, 4) time required to reach maximum flux, and 5) duration of NO release. Advantages and drawbacks are reviewed, and possible further developments are suggested.

Influence of diabetes on the foreign body response to nitric oxide-releasing implants

The foreign body response (FBR) to nitric oxide (NO)-releasing subcutaneous implants was compared between healthy and streptozotocin-induced diabetic swine by evaluating inflammation, collagen capsule formation, and angiogenesis. Steel wire substrates were first modified with polyurethane membranes capable of diverse NO-release kinetics (NO fluxes and release durations of 0.8–630.0 pmol cm−2 s−1 and 2–13 d, respectively). The NO-releasing materials were implanted in the subcutis for 3, 10, or 25 d for histological and immunohistochemical evaluation of the FBR. A delayed, more severe inflammatory response to control (i.e., non-NO-releasing) implants was observed in diabetic pigs relative to healthy swine. Regardless of the animal disease state, each NO-releasing implant tested elicited reduced inflammation compared to controls at both 3 and 10 d. However, only the NO-release materials capable of releasing low NO fluxes (0.8–3.3 pmol cm−2 s−1) for 7–13 d durations mitigated the inflammatory response at 25 d. Using immunohistochemical staining for the endothelial cell surface marker CD-31, we also observed poor blood vessel development at non-NO-releasing implants in diabetic swine. Relative to controls, NO-releasing implants with the longest NO-release duration (13 d) increased blood vessel densities by 47.1 and 70.4% in the healthy and diabetic pigs, respectively. In the healthy model, tissues surrounding the long NO-release materials contained sparse amounts of collagen, whereas implants with shorter NO-release durations (2, 3, and 7 d) were characterized with a dense collagen encapsulation layer, similar to controls. Collagen deposition in diabetic swine was inhibited, and unaffected by NO. These results emphasize several key differences in the FBR in the setting of acute onset diabetes. The observation that NO release counteracts the more severe FBR in diabetic swine while simultaneously promoting tissue integration may help guide the design of medical implants (e.g., glucose sensors) with improved performance for diabetes management.

Functionalized Mesoporous Silica via an Aminosilane Surfactant Ion Exchange Reaction: Controlled Scaffold Design and Nitric Oxide Release.

Nitric oxide-releasing mesoporous silica nanoparticles (MSNs) were prepared using an aminosilane-template surfactant ion exchange reaction. Initially, bare silica particles were synthesized under basic conditions in the presence of cetyltrimethylammonium bromide (CTAB). These particles were functionalized with nitric oxide (NO) donor precursors (i.e., secondary amines) via the addition of aminosilane directly to the particle sol and a commensurate ion exchange reaction between the cationic aminosilanes and CTAB. N-Diazeniumdiolate NO donors were formed at the secondary amines to yield NO-releasing MSNs. Tuning of the ion exchange-based MSN modification approach allowed for the preparation of monodisperse particles ranging from 30 to 1100 nm. Regardless of size, the MSNs stored appreciable levels of NO (0.4–1.5 μmol mg–1) with tunable NO release durations (1–33 h) dependent on the aminosilane modification. Independent control of NO release properties and particle size was achieved, demonstrating the flexibility of this novel MSN synthesis over conventional co-condensation and surface grafting strategies.

Superhydrophobic nitric oxide-releasing xerogels

Superhydrophobic nitric oxide (NO)-releasing xerogels were prepared by spray-coating a fluorinated silane/silica composite onto N-diazeniumdiolate NO donor-modified xerogels. The thickness of the superhydrophobic layer was used to extend NO release durations from 59 to 105h. The resulting xerogels were stable, maintaining superhydrophobicity for up to 1month (the longest duration tested) when immersed in solution, with no leaching of silica or undesirable fragmentation detected. The combination of superhydrophobicity and NO release reduced viable Pseudomonas aeruginosa adhesion by >2-logs. The killing effect of NO was demonstrated at longer bacterial contact times, with superhydrophobic NO-releasing xerogels resulting in 3.8-log reductions in adhered viable bacteria vs. controls. With no observed toxicity to L929 murine fibroblasts, NO-releasing superhydrophobic membranes may be valuable antibacterial coatings for implants as they both reduce adhesion and kill bacteria that do adhere.

Quantitative nitric oxide release to study the effects on dorsal root ganglion cells

Nitric oxide (NO) has shown to play important and diverse biological roles. NO is suspected to be beneficial at low levels for a variety of cells, including retinal epithelial cells, lymphatic epithelial cells, and dorsal root ganglion cells, but can be detrimental at high levels or at certain periods of time in their growth. Currently, the beneficial or harmful levels and durations of NO have not been determined. We have developed an NO-generating polydimethylsiloxane (PDMS) that contains S-nitroso-N-acetyl- d -penicillamine (SNAP) covalently linked to its backbone which is capable of stable and dynamic control of NO release in response to light. A solid core waveguide device has also been fabricated to propagate controllable levels of light along its surfaces. By coating this surface with the photosensitive SNAP-PDMS and growing cells on an additional polymer layer, a device has been developed that allows for specified variation in NO release and duration the cultured cells experience, without exposing the cells directly to light. The waveguide system allows precise levels of NO to be generated that will allow the determination of beneficial and damaging levels of NO the cells experience. In these experiments dorsal root ganglion (DRG) cells were cultured with different levels of NO in order to determine cellular response. Future work includes varying the level and duration of NO release the cells are exposed to. This can lead to a better understanding of the effects of NO during spinal cord injury so that nerve growth and regeneration can become a possibility.

The effect of nitric oxide surface flux on the foreign body response to subcutaneous implants

Although the release of nitric oxide (NO) from biomaterials has been shown to reduce the foreign body response (FBR), the optimal NO release kinetics and doses remain unknown. Herein, polyurethane-coated wire substrates with varying NO release properties were implanted into porcine subcutaneous tissue for 3, 7, 21 and 42 d. Histological analysis revealed that materials with short NO release durations (i.e., 24 h) were insufficient to reduce the collagen capsule thickness at 3 and 6 weeks, whereas implants with longer release durations (i.e., 3 and 14 d) and greater NO payloads significantly reduced the collagen encapsulation at both 3 and 6 weeks. The acute inflammatory response was mitigated most notably by systems with the longest duration and greatest dose of NO release, supporting the notion that these properties are most critical in circumventing the FBR for subcutaneous biomedical applications (e.g., glucose sensors).

S-Nitroso-N-acetyl-D-penicillamine covalently linked to polydimethylsiloxane (SNAP–PDMS) for use as a controlled photoinitiated nitric oxide release polymer

Nitric oxide (NO) plays a critical role in the regulation of a wide variety of physiological processes. It is a potent inhibitor of platelet adhesion and aggregation, inhibits bacterial adhesion and proliferation, is implicated in mediating the inflammatory response toward implanted devices, plays a role in tumor growth and proliferation, and is a neurotransmitter. Herein, we describe the synthesis and NO-release properties of a modified polydimethylsiloxane that contains S-nitroso-N-acetyl-D-penicillamine covalently attached to the cross-linking agent (SNAP–DMS). Light from a C503B-BAN-CY0C0461 light-emitting diode (470 nm) was used as an external trigger to allow precise control over level and duration of NO release ranging from a surface flux of zero to approximately 3.5×10−10 mol cm-2 min-1. SNAP–PDMS films stored in the dark released NO after 297 days, indicating the long-term stability of SNAP–PDMS.

Characterization of GTMAC-Graft-Chitosan as a Bactericidal Agent for Nitric Oxide Release

This work aims to prepare and characterize one kind of nitric oxide (NO)-releasing conjugation of quaternary ammonium salt to chitosan, as well as to evaluate the anti-bacterial properties of diazeniumdiolates and the changes in NO release properties. The newly synthesized diazeniumdiolates are obtained from glycidyl-trimethyl-ammonium chloride (GTMAC)-bearing chitosan derivatives (HTCC) with different molecular weights (280 and 670 KDa) and are used as NO donor species. An HTCC with high molecular weight (670 KDa) exhibits higher storage capacity for NO (up to 357.70 nmol NO/mg) than one with a low molecular weight (280 kDa). The NO release durations (7 h) observed for the HTCC diazeniumliolates with higher molecular weight (670 kDa) was slightly higher than that of HTCC diazeniumliolates with lower molecular weight (280 kDa). By determining the inhibition zone diameter, HTCC-NO with lower molecular weight (280 kDa) showed significantly higher inhibition capabilities againstE. colithan HTCC, crude chitosan, and water control.

Controlled Nitric Oxide Delivery Platform Based onS-Nitrosothiol Conjugated Interpolymer Complexes for Diabetic Wound Healing

Nitric oxide (NO) is known to play a critical role in enhancing wound healing as topical NO administration has demonstrated enhanced wound healing in diabetic animal models. However, this approach has been limited by the short duration of NO release, short half-life of NO, and instability of available NO donors. To overcome these deficiencies, we have developed a new NO delivery platform based on grafting S-nitrosothiols (RSNOs), derived from endogenous glutathione (GSH) or its oligomeric derivatives, phytochelatins (PCs), onto poly(vinyl methyl ether-co-maleic anhydride) (PVMMA), and their subsequent formation of interpolymer complexes with poly(vinyl pyrrolidone) (PVP). Such interpolymer complexes provide controlled release of NO for an extended duration (>10 days) and exhibit enhanced stability in the solid state over that of free RSNOs. The existence of intermolecular hydrogen bonding in such complexes and the formation of disulfide bonds following the NO release have been confirmed by FTIR and Raman. Preliminary wound healing study in a diabetic rat model demonstrates that, with a single topical application, the present controlled release NO delivery system can effectively accelerate wound closure as compared with the control (p < 0.05). The results suggest that the present NO releasing interpolymer complexes could be potentially useful for diabetic wound healing.

Characterization of folate-graft-chitosan as a scaffold for nitric oxide release

The preparation and characterization of nitric oxide (NO)-releasing chitosan–folate conjugates were reported. The secondary amine chitosan–folate conjugates exhibited a high storage capacity for NO (up to 84.3 nmol NO/mg) (when the graft rate of folate was 12.5%), greatly increasing the “payload” of released NO with the graft rate of folate increasing. The NO release durations (12 h) observed for secondary amine the chitosan–folate conjugates with the high graft rate (12.5%) were largerly shorter compared to O 2-protected diazeniumliolates with BrCH 2CH 3 (24 h), thus illustrating a macromolecular effect on NO release kinetics.

Polymeric coatings that mimic the endothelium: Combining nitric oxide release with surface-bound active thrombomodulin and heparin

Multi-functional bilayer polymeric coatings are prepared with both controlled nitric oxide (NO) release and surface-bound active thrombomodulin (TM) alone or in combination with immobilized heparin. The outer-layer is made of CarboSil, a commercially available copolymer of silicone rubber (SR) and polyurethane (PU). The CarboSil is either carboxylated or aminated via an allophanate reaction with a diisocyanate compound followed by a urea-forming reaction between the generated isocyanate group of the polymer and the amine group of an amino acid (glycine), an oligopeptide (triglycine) or a diamine. The carboxylated CarboSil can then be used to immobilize TM through the formation of an amide bond between the surface carboxylic acid groups and the lysine residues of TM. Aminated CarboSil can also be employed to initially couple heparin to the surface, and then the carboxylic acid groups on heparin can be further used to anchor TM. Both surface-bound TM and heparin's activity are evaluated by chromogenic assays and found to be at clinically significant levels. The underlying NO release layer is made with another commercial SR–PU copolymer (PurSil) mixed with a lipophilic NO donor (N-diazeniumdiolated dibutylhexanediamine (DBHD/N2O2)). The NO release rate can be tuned by changing the thickness of top coatings, and the duration of NO release at physiologically relevant levels can be as long as 2 weeks. The combination of controlled NO release as well as immobilized active TM and heparin from/on the same polymeric surface mimics the highly thromboresistant endothelium layer. Hence, such multifunctional polymer coatings should provide more blood-compatible surfaces for biomedical devices.

Dendrimers as a Scaffold for Nitric Oxide Release

The preparation and characterization of nitric oxide (NO)-releasing dendrimer conjugates are reported. Generation 3 and 5 polypropylenimine dendrimers (DAB-Am-16 and DAB-Am-64) were modified at the exterior to impart different amine functionalities. The ability to store NO on a dendritic scaffold using N-diazeniumdiolate NO donors was examined via the reaction of primary amine, secondary amine, and amide functionalities with high pressures of NO (5 atm). The secondary amine dendrimer conjugates exhibited a high storage capacity for NO (up to 5.6 micromol NO/mg), greatly increasing the "payload" of released NO over existing macromolecular NO donors. The mechanism of diazeniumdiolate decomposition was proton initiated, generating NO spontaneously under physiological conditions (pH 7.4, 37 degrees C). The NO release durations (>16 h) observed for the secondary amine dendrimers were significantly longer compared to small molecule alkyl secondary amine diazeniumdiolates, thus illustrating a dendritic effect on NO release kinetics. The multivalent exterior of dendrimers allows for the future combination of NO donors and other functionalities on a single molecular scaffold, enabling diverse utility as NO storage/delivery systems.

A chronopharmacological preventive treatment for sleep-related migraine headaches and chronic morning headaches: Nitric oxide supersensitivity can cause sleep-related headaches in a subset of patients

Frequent and recurrent migraine headaches can, over time, pose the additional risks of stroke, brain damage, heart failure and attention deficit. This is why prevention should always be a part of the treatment. Nitric oxide supersensitivity is the hypothesis upon which this model is based. Its role in causing migraine headaches and chronic morning headaches can be triggered by both normal and abnormal characteristics of the sleep cycle and more specifically by the release of nitric oxide that occurs towards the end of the sleep cycle. Stress and the age-related loss of sleep continuity, together with the corresponding increase in cortisol levels, potentiate delta rebound. Delta rebound results in deeper sleep intensity. It is associated with increased nitric oxide production. Increased delta rebound then causes an increase in the amount and duration of nitric oxide release at night. Migraineurs are susceptible to migraine headaches because they are supersensitive to nitric oxide. The diurnal pattern of the incidence of sleep-related headaches in a subset of the general population is caused by the effect of nitric oxide supersensitivity during the sleep cycle. The proposed treatment is for both sleep-related migraine headaches and chronic morning headaches. It consists of melatonin and moclobemide taken during the night, close the end of the sleep cycle so as to achieve the maximum concentrations. Both melatonin and moclobemide affect three important aspects of sleep-related headaches: nitric oxide supersensitivity, stress system dysfunction and sleep pathology. Both melatonin and moclobemide have demonstrated effectiveness in preventing migraine headaches. Additionally, both melatonin and moclobemide are compatible with most of the other therapeutic agents used to prevent migraine headaches and with at least 1 therapeutic agent that is used to treat migraine headaches.

Nitric Oxide-Releasing Xerogel Microarrays Prepared with Surface-Tailored Poly(dimethylsiloxane) Templates

Surface graft polymerization with poly(ethylene glycol) acrylate is reported as an effective method for modifying the surface of poly(dimethylsiloxane) array templates thus enabling the preparation of nitric oxide (NO)-releasing xerogel micropatterns. The surface wettability of PEGA-grafted templates was sufficient to overcome the flow resistance of ethyltrimethoxysilane (ETMOS) sol solutions and allow the formation of xerogel microarrays via capillary action of sol through the template channels. Due to the combined versatility of both sol−gel chemistry and micropatterning, substrates were modified with a range of aminosilane-doped xerogel microarrays with variable NO release properties. Several parameters were studied including (1) NO surface flux as a function of type and concentration of aminosilane NO-donor precursor; (2) micropattern dimensions for maximizing surface flux and duration of NO release; and (3) the effect of microstructure separation on localized NO surface concentration as determined wi...

Direct measurement of nitric oxide release from saphenous vein: abolishment by surgical preparation

Background. Surgical preparation (distension) of the saphenous vein (SV) is applied routinely during harvesting in coronary artery bypass grafting (CABG). However, mechanical distension may impair the endothelium, which plays an important role in long-term patency. The present study investigated the effect of surgical preparation of the SV on nitric oxide (NO) release from the endothelium by direct measurement of NO. Methods. Saphenous vein segments taken from CABG patients were cut open longitudinally and placed in an organ chamber. An NO-sensitive electrode and NO meter were used to directly measure NO release induced by acetylcholine (ACh) and bradykinin (BK) from the surgically prepared veins (PV) compared with the control (nondistended) veins. Results. The basal release of NO in the PV group was significantly lower than that in the control group (3.4 ± 1.4 nM, n = 9 versus 9.9 ± 2.8 nM, n = 13, p = 0.002). The maximum concentrations of NO release induced by ACh and BK in the PV group were also significantly lower than those in the control veins (for ACh 10 −6 mol/L: 9.6 ± 3.1 nM, n = 8 versus 41.9 ± 11.2 nM, n = 12, p = 0.005; for BK 10 −8 mol/L: 8.3 ± 3.7 nM, n = 7 versus 37.9 ± 6.1 nM, n = 9, p = 0.003). Further, the duration of NO release in the PV group was significantly shorter than that in control veins (1.5 ± 1.3 minutes, n = 8 versus 8.1 ± 1.9 minutes, n = 8, p < 0.001). Conclusions. Surgical preparation almost abolishes NO release by the SV and this may significantly contribute to the low long-term patency rate of the vein graft.

Biotransformation and cytotoxic properties of NO-donors on MCF7 and U251 cell lines

Previous studies have shown a role for nitric oxide (NO) as a cytotoxic effector. In the present work, two chemically different NO-donors such as glyceryl trinitrate (GTN) and S-nitroso-N-acetylpenicillamine (SNAP) were evaluated for both NO release and cytostatic/cytotoxic properties. Nitrite accumulation in the supernatant of MCF-7 and U251 cell lines indicated a greater and quickly release of NO derived from SNAP. A time-course of hemoglobin absorption spectral changes showed a greater release of NO derived from GTN in presence of cells compared to the values observed in the media, confirming that the release of NO by GTN can be enzymatic and non-enzymatic. On the contrary, SNAP generated NO without contribution of cellular components and saturated oxyhemoglobin quickly, within 2 hours. Both NO-donors inhibited thymidine incorporation in a similar manner and dose-dependently in U251 cells, but not in MCF-7 cells, where SNAP at the highest tested dose of 1000 μM induced only a 33% cytostatic effect. About trypan blue exclusion test, after 24 h GTN and SNAP, releasing similar amounts of NO, showed comparable cytotoxic effects on U251 cells (50% dead cells), but not on MCF-7 cells, where GTN resulted more cytotoxic. From our data, the “in vitro” antitumoral activity of NO-donors seems to be related to the type of tumor cell lines, to the amount and duration of NO release.