Nitric oxide and viral infection: Recent developments in antiviral therapies and platforms

Varying material thickness of silicone rubber for tunable nitric oxide release

Silicone rubber (SR), a common medical-grade polymer used in medical devices, has previously been modified for nitric oxide (NO) releasing capabilities. However, the effects of material properties such as film thickness on NO release kinetics are not well explored. In this study, SR is used in the first analysis of how a polymer's thickness affects the storage and uptake of an NO donor and subsequent release properties. Observed NO release trends show that a polymer's thickness results in tunable NO release. These results indicate how crucial a polymer's thickness is to optimize the NO release in an efficient and effective method.

Cyclooxygenase-2/prostaglandin E2 pathway regulates infectious bronchitis virus replication in avian macrophages

Infectious bronchitis virus (IBV) is a significant respiratory pathogen that affects chickens worldwide. As an avian coronavirus, IBV leads to productive infection in chicken macrophages. However, the effects of IBV infection in macrophages on cyclooxygenase-2 (COX-2) expression are still to be elucidated. Therefore, we investigated the role of IBV infection on the production of COX-2, an enzyme involved in the synthesis of prostaglandin E2 (PGE2) in chicken macrophages. The chicken macrophage cells were infected with two IBV strains, and the cells and culture supernatants were harvested at predetermined time points to measure intracellular and extracellular IBV infection. IBV infection was quantified as has been the COX-2 and PGE2 productions. We found that IBV infection enhances COX-2 production at both mRNA and protein levels in chicken macrophages. When a selective COX-2 antagonist was used to reduce the COX-2 expression in macrophages, we observed that IBV replication decreased. When IBV-infected macrophages were treated with PGE2 receptor (EP2 and EP4) inhibitors, IBV replication was reduced. Upon utilizing a selective COX-2 antagonist to diminish PGE2 expression in macrophages, a discernible decrease in IBV replication was observed. Treatment of IBV-infected macrophages with a PGE2 receptor (EP2) inhibitor resulted in a reduction in IBV replication, whereas the introduction of exogenous PGE2 heightened viral replication. Additionally, pretreatment with a Janus-kinase two antagonist attenuated the inhibitory effect of recombinant chicken interferon (IFN)-γ on viral replication. The evaluation of immune mediators, such as inducible nitric oxide (NO) synthase (iNOS), NO, and interleukin (IL)-6, revealed enhanced expression following IBV infection of macrophages. In response to the inhibition of COX-2 and PGE2 receptors, we observed a reduction in the expressions of iNOS and IL-6 in macrophages, correlating with reduced IBV infection. Overall, IBV infection increased COX-2 and PGE2 production in addition to iNOS, NO, and IL-6 expression in chicken macrophages in a time-dependent manner. Inhibition of the COX-2/PGE2 pathway may lead to increased macrophage defence mechanisms against IBV infection, resulting in a reduction in viral replication and iNOS and IL-6 expressions. Understanding the molecular mechanisms underlying these processes may shed light on potential antiviral targets for controlling IBV infection.

Nitric Oxide: Physiological Functions, Delivery, and Biomedical Applications

Nitric oxide (NO) is a gaseous molecule that has a central role in signaling pathways involved in numerous physiological processes (e.g., vasodilation, neurotransmission, inflammation, apoptosis, and tumor growth). Due to its gaseous form, NO has a short half-life, and its physiology role is concentration dependent, often restricting its function to a target site. Providing NO from an external source is beneficial in promoting cellular functions and treatment of different pathological conditions. Hence, the multifaceted role of NO in physiology and pathology has garnered massive interest in developing strategies to deliver exogenous NO for the treatment of various regenerative and biomedical complexities. NO-releasing platforms or donors capable of delivering NO in a controlled and sustained manner to target tissues or organs have advanced in the past few decades. This review article discusses in detail the generation of NO via the enzymatic functions of NO synthase as well as from NO donors and the multiple biological and pathological processes that NO modulates. The methods for incorporating of NO donors into diverse biomaterials including physical, chemical, or supramolecular techniques are summarized. Then, these NO-releasing platforms are highlighted in terms of advancing treatment strategies for various medical problems.

Isolation of Latilactobacillus curvatus with Enhanced Nitric Oxide Synthesis from Korean Traditional Fermented Food and Investigation of Its Probiotic Properties

Nitric oxide (NO) is a free radical associated with physiological functions such as blood pressure regulation, cardiovascular health, mitochondrial production, calcium transport, oxidative stress, and skeletal muscle repair. This study aimed to isolate Latilactobacillus curvatus strains with enhanced NO production from the traditional Korean fermented food, jangajji, and evaluate their probiotic properties for industrial purposes. When cells were co-cultured with various bacterial stimulants, NO production generally increased, and NO synthesis was observed in the range of 20-40 mg/mL. The selected strains of Lat. curvatus were resistant to acid and bile conditions and with variable effectiveness (1-14%) in adhering to Caco-2 cells. Most bacterial strains can inhibit the growth of various pathogens. In addition, they are capable of reducing cholesterol levels via assimilation of cholesterol at 10-50%. Among the selected NO synthases from Lat. curvatus strains, the strain JBCC38 showed the highest capacity to scavenge ABTS (30.1%) and DPPH radicals (39.4%). Moreover, these strains exhibited immunomodulatory properties. The production of TNF-α and IL-6 in the macrophages treated with various bacterial stimulants was induced in all the selected strains.

Advanced Nitric Oxide Generating Nanomedicine for Therapeutic Applications

Nitric oxide (NO), a gaseous transmitter extensively present in the human body, regulates vascular relaxation, immune response, inflammation, neurotransmission, and other crucial functions. Nitrite donors have been used clinically to treat angina, heart failure, pulmonary hypertension, and erectile dysfunction. Based on NO's vast biological functions, it further can treat tumors, bacteria/biofilms and other infections, wound healing, eye diseases, and osteoporosis. However, delivering NO is challenging due to uncontrolled blood circulation release and a half-life of under five seconds. With advanced biotechnology and the development of nanomedicine, NO donors packaged with multifunctional nanocarriers by physically embedding or chemically conjugating have been reported to show improved therapeutic efficacy and reduced side effects. Herein, we review and discuss recent applications of NO nanomedicines, their therapeutic mechanisms, and the challenges of NO nanomedicines for future scientific studies and clinical applications. As NO enables the inhibition of the replication of DNA and RNA in infectious microbes, including COVID-19 coronaviruses and malaria parasites, we highlight the potential of NO nanomedicines for antipandemic efforts. This review aims to provide deep insights and practical hints into design strategies and applications of NO nanomedicines.

Derivatization of graphene oxide nanosheets with tunable nitric oxide release for antibacterial biomaterials

Graphene oxide (GO) nanosheets are a promising class of carbon-based materials suitable for application in the construction of medical devices. These materials have inherent antimicrobial properties based on sheet size, but these effects must be carefully traded off to maintain biocompatibility. Chemical modification of functional groups to the lattice structure of GO nanosheets enables unique opportunities to introduce new surface properties to bolster biological effects. Herein, we have developed nitric oxide (NO)-releasing GO nanosheets via immobilization of S-nitrosothiol (RSNO) moieties to GO nanosheets (GO-[NH]x -SNO). These novel RSNO-based GO nanosheets were characterized for chemical functionality via Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and colorimetric assays for functional group quantification. Stoichiometric control of the available RSNO groups functionalized onto the nanosheets was studied using chemiluminescence-based NO detection methods, showing highly tunable NO release kinetics. Studies of electrical stimulation and subsequent electrochemical reduction of the nanosheets demonstrated further tunability of the NO release based on stimuli. Finally, nanosheets were evaluated for cytotoxicity and antibacterial effects, showing strong cytocompatibility with human fibroblasts in parallel to broad antibacterial and anti-biofilm effects against both Gram-positive and Gram-negative strains. In summary, derivatized GO-(NH)x -SNO nanosheets were shown to have tunable NO release properties, enabling application-specific tailoring for diverse biomedical applications such as antimicrobial coatings and composite fillers for stents, sensors, and other medical devices.

Synthesis and Characterization of Nitric Oxide-Releasing Ampicillin as a Potential Strategy for Combatting Bacterial Biofilm Formation

Biofilm formation on biomaterial interfaces and the development of antibiotic-resistant bacteria have decreased the effectiveness of traditional antibiotic treatment of infections. In this project, ampicillin, a commonly used antibiotic, was conjugated with S-nitroso-N-acetylpenicillamine (SNAP), an S-nitrosothiol compound (RSNO) used for controlled nitric oxide (NO) release. This novel multifunctional molecule is the first of its kind to provide combined antibiotic and NO treatment of infectious pathogens. Characterization of the molecule included NMR, FTIR, and mass spectrometry. NO release behavior was also measured and compared to pure, unmodified SNAP. When evaluating the antimicrobial efficacy, the synthesized SNAPicillin molecule showed the lowest MIC value against Gram-negative Pseudomonas aeruginosa and Gram-positive methicillin-resistant Staphylococcus aureus compared to ampicillin and SNAP alone. SNAPicillin also displayed enhanced biofilm dispersal and killing of both bacterial strains when treating a 48 h biofilm preformed on a polymer surface. The antibacterial results combined with the biocompatibility of the molecule show great promise for infection prevention and treatment of polymeric interfaces to reduce medical device-related infections.

Polymeric Amines Induce Nitric Oxide Release from S-Nitrosothiols

Catalytic generation of nitric oxide (NO) from NO donors by nanomaterials has enabled prolonged NO delivery for various biomedical applications, but this approach requires laborious synthesis routes. In this study, a new class of materials, that is, polymeric amines including polyethyleneimine (PEI), poly-L-lysine, and poly(allylamine hydrochloride), is discovered to induce NO generation from S-nitrosothiols (RSNOs) at physiological conditions. Controlled NO generation can be readily achieved by tuning the concentration of the NO donors (RSNOs) and polymers, and the type and molecular weight of the polymers. Importantly, the mechanism of NO generation by these polymers is deciphered to be attributed to the nucleophilic reaction between primary amines on polymers and the SNO groups of RSNOs. The NO-releasing feature of the polymers can be integrated into a suite of materials, for example, simply by embedding PEI into poly(vinyl alcohol) (PVA) hydrogels. The functionality of the PVA/PEI hydrogels is demonstrated for Pseudomonas aeruginosa biofilm prevention with a ≈4 log reduction within 6 h. As NO has potential therapeutic implications in various diseases, the identification of polymeric amines to induce NO release will open new opportunities in NO-generating biomaterials for antibacterial, antiviral, anticancer, antithrombotic, and wound healing applications.

Manipulation of Oxidative Stress Responses by Non-Thermal Plasma to Treat Herpes Simplex Virus Type 1 Infection and Disease

Herpes simplex virus type 1 (HSV-1) is a contagious pathogen with a large global footprint, due to its ability to cause lifelong infection in patients. Current antiviral therapies are effective in limiting viral replication in the epithelial cells to alleviate clinical symptoms, but ineffective in eliminating latent viral reservoirs in neurons. Much of HSV-1 pathogenesis is dependent on its ability to manipulate oxidative stress responses to craft a cellular environment that favors HSV-1 replication. However, to maintain redox homeostasis and to promote antiviral immune responses, the infected cell can upregulate reactive oxygen and nitrogen species (RONS) while having a tight control on antioxidant concentrations to prevent cellular damage. Non-thermal plasma (NTP), which we propose as a potential therapy alternative directed against HSV-1 infection, is a means to deliver RONS that affect redox homeostasis in the infected cell. This review emphasizes how NTP can be an effective therapy for HSV-1 infections through the direct antiviral activity of RONS and via immunomodulatory changes in the infected cells that will stimulate anti-HSV-1 adaptive immune responses. Overall, NTP application can control HSV-1 replication and address the challenges of latency by decreasing the size of the viral reservoir in the nervous system.

Strategies of Pathogens to Escape from NO-Based Host Defense

Nitric oxide (NO) is an essential signaling molecule present in most living organisms including bacteria, fungi, plants, and animals. NO participates in a wide range of biological processes including vasomotor tone, neurotransmission, and immune response. However, NO is highly reactive and can give rise to reactive nitrogen and oxygen species that, in turn, can modify a broad range of biomolecules. Much evidence supports the critical role of NO in the virulence and replication of viruses, bacteria, protozoan, metazoan, and fungi, thus representing a general mechanism of host defense. However, pathogens have developed different mechanisms to elude the host NO and to protect themselves against oxidative and nitrosative stress. Here, the strategies evolved by viruses, bacteria, protozoan, metazoan, and fungi to escape from the NO-based host defense are overviewed.

Nitric Oxide-Releasing Silicone Oil with Tunable Payload for Antibacterial Applications

Bacterial infections are a hurdle to the application of medical devices, and in the United States alone, more than one million infection cases are reported annually from indwelling medical devices. Infections not only affect the function of medical devices but also risk the lives and health of patients. Nitric oxide (NO) has been used as an antibacterial therapy that kills bacteria without causing resistance and provides many therapeutic effects such as anti-inflammation, antithrombosis, and angiogenesis. Silicone oils have been widely utilized in manufacturing consumer goods, healthcare products, and medical products. Specifically, liquid silicone oils are used as a medical lubricant that creates lubricated interfaces between medical devices and the exterior physiological environment to improve the performance of medical devices. Herein, we report the first primary S-nitrosothiol-based NO-releasing silicone oil (RSNO-Si) that exhibits proactive antibacterial effects. S-nitrosothiol silicone oils (RSNO-Si) were synthesized and the NO payloads ranged from 34.0 to 603.9 μM. The increased NO payload induced higher-viscosity RSNO-Si oils, as RSNO0.1-Si, RSNO0.5-Si, and RSNO1-Si had viscosities of 12.8 ± 0.1 cP, 32.0 ± 0.2 cP, and 35.1 ± 0.3 cP, respectively. RSNO-Si-SR interfaces were fabricated by infusing silicone rubber (SR) in RSNO-Si oil, and the resulting RSNO-Si-SR disks demonstrated NO release without NO donor leaching. RSNO0.1-Si-SR, RSNO0.5-Si-SR, and RSNO1-Si-SR exhibited maximum NO flux at 0.8, 6.5, and 21.5 × 10 ^-10 mol cm^-2 min^-1 in 24 h, respectively. RSNO-Si-SR disks also demonstrated 97.45, 95.40, and 96.08% of inhibition against S. aureus in a 4 h bacterial adhesion assay. Considering the easy synthesis, simple fabrication of non-leaching NO-releasing interfaces, tunable payloads, NO flux levels, and antimicrobial effects, RSNO-Si oils exhibited their potential use as platform chemicals for creating antimicrobial medical device surfaces and other antibacterial materials.

Dual Action Nitric Oxide and Fluoride Ion-Releasing Hydrogels for Combating Dental Caries

Demineralization and breakdown of tooth enamel are characterized by a condition called dental caries or tooth decay, which is caused by two main factors: (1) highly acidic food intake without proper oral hygiene and (2) overactive oral bacteria generating acidic metabolic byproducts. Fluoride treatments have been shown to help rebuild the hydroxyapatite structures that make up 98% of enamel but do not tackle the bacterial overload that continues to threaten future demineralization. Herein, we have created a dual-function Pluronic F127-alginate hydrogel with nitric oxide (NO)- and fluoride-releasing capabilities for the two-pronged treatment of dental caries. Analysis of the hydrogels demonstrated porous, shear-thinning behaviors with tunable mechanical properties. Varying the weight percent of the NO donor S-nitrosoglutathione (GSNO) within the hydrogel enabled physiologically actionable NO release over 4 h, with the fabricated gels demonstrating storage stability over 21 days. This NO-releasing capability resulted in a 97.59% reduction of viable Streptococcus mutans in the planktonic state over 4 h and reduced the preformed biofilm mass by 48.8% after 24 h. Delivery of fluoride ions was confirmed by a fluoride-sensitive electrode, with release levels resulting in the significant prevention of demineralization of hydroxyapatite discs after treatment with an acidic demineralization solution. Exposure to human gingival fibroblasts and human osteoblasts showed cytocompatibility of the hydrogel, demonstrating the potential for the successful treatment of dental caries in patients.

NO in Viral Infections: Role and Development of Antiviral Therapies

Nitric oxide is a ubiquitous signaling radical that influences critical body functions. Its importance in the cardiovascular system and the innate immune response to bacterial and viral infections has been extensively investigated. The overproduction of NO is an early component of viral infections, including those affecting the respiratory tract. The production of high levels of NO is due to the overexpression of NO biosynthesis by inducible NO synthase (iNOS), which is involved in viral clearance. The development of NO-based antiviral therapies, particularly gaseous NO inhalation and NO-donors, has proven to be an excellent antiviral therapeutic strategy. The aim of this review is to systematically examine the multiple research studies that have been carried out to elucidate the role of NO in viral infections and to comprehensively describe the NO-based antiviral strategies that have been developed thus far. Particular attention has been paid to the potential mechanisms of NO and its clinical use in the prevention and therapy of COVID-19.

Control of Orthodontic Tooth Movement by Nitric Oxide Releasing Nanoparticles in Sprague-Dawley Rats

Orthodontic treatment commonly requires the need to prevent movement of some teeth while maximizing movement of other teeth. This study aimed to investigate the influence of locally injected nitric oxide (NO) releasing nanoparticles on orthodontic tooth movement in rats.

MATERIALS AND METHODS

Experimental tooth movement was achieved with nickel-titanium alloy springs ligated between the maxillary first molar and ipsilateral incisor. 2.2 mg/kg of silica nanoparticles containing S-nitrosothiol groups were injected into the mucosa just mesial to 1^st molar teeth immediately prior to orthodontic appliance activation. NO release from nanoparticles was measured in vitro by chemiluminescence. Tooth movement was measured using polyvinyl siloxane impressions. Bones were analyzed by microcomputed tomography. Local tissue was assessed by histomorphometry.

RESULTS

Nanoparticles released a burst of NO within the first hours at approximately 10 ppb/mg particles that diminished by 10 × to approximately 1 ppb/mg particles over the next 1-4 days, and then diminished again by tenfold from day 4 to day 7, at which point it was no longer measurable. Molar but not incisor tooth movement was inhibited over 50% by injection of the NO releasing nanoparticles. Inhibition of molar tooth movement occurred only during active NO release from nanoparticles, which lasted for approximately 1 week. Molar tooth movement returned to control levels of tooth movement after end of NO release. Alveolar and long bones were not impacted by injection of the NO releasing nanoparticles, and serum cyclic guanosine monophosphate (cGMP) levels were not increased in animals that received the NO releasing nanoparticles. Root resorption was decreased and periodontal blood vessel numbers were increased in animals with appliances that were injected with the NO releasing nanoparticles as compared to animals with appliances that did not receive injections with the nanoparticles.

CONCLUSION

Nitric oxide (NO) release from S-nitrosothiol containing nanoparticles inhibits movement of teeth adjacent to the site of nanoparticle injection for 1 week. Additional studies are needed to establish biologic mechanisms, optimize efficacy and increase longevity of this orthodontic anchorage effect.

Nitric Oxide-Releasing Lock Solution for the Prevention of Catheter-Related Infection and Thrombosis

Although frequently used, venous catheters are often associated with serious complications such as infection and thrombosis. Lock solution therapies are clinically used to deter these issues but generally address only infection or thrombosis with limited success. Here, we report the development of a dual-functional lock therapy using nitric oxide (NO) donor molecule, S-nitrosoglutathione (GSNO). NO is a potent, broad-spectrum antimicrobial agent that also temporarily inhibits platelet activation, preventing thrombosis. Furthermore, NO has antibiofilm actions, an ability that traditional antibiotic lock solutions lack, thus limiting their efficacy. In this work, different concentrations of GSNO were characterized via NO analysis to determine a range of NO-releasing lock solution (NOreLS) concentrations to investigate and to demonstrate prolonged potential efficacy. Tested against clinically used vancomycin and gentamicin lock solutions, GSNO-based NOreLS repeatedly outperformed in models of different stages of catheter infections. NOreLS also prevented clot formation when exposed to whole blood, showing increased efficacy compared to a heparin lock solution. Moreover, NOreLS was demonstrated to be biocompatible via hemolysis and cytotoxicity assays. NOreLS has excellent potential for safely and effectively preventing infection and thrombosis related to catheter usage.

Advances in the Prophylaxis of Respiratory Infections by the Nasal and the Oromucosal Route: Relevance to the Fight with the SARS-CoV-2 Pandemic

In this time of COVID-19 pandemic, the strategies for prevention of the infection are a primary concern. Looking more globally on the subject and acknowledging the high degree of misuse of protective face masks from the population, we focused this review on alternative pharmaceutical developments eligible for self-defense against respiratory infections. In particular, the attention herein is directed to the nasal and oromucosal formulations intended to boost the local immunity, neutralize or mechanically “trap” the pathogens at the site of entry (nose or mouth). The current work presents a critical review of the contemporary methods of immune- and chemoprophylaxis and their suitability and applicability in topical mucosal dosage forms for SARS-CoV-2 prophylaxis.

Surface-Catalyzed Nitric Oxide Release via a Metal Organic Framework Enhances Antibacterial Surface Effects

It has been previously demonstrated that metal nanoparticles embedded into polymeric materials doped with nitric oxide (NO) donor compounds can accelerate the release rate of NO for therapeutic applications. Despite the advantages of elevated NO surface flux for eradicating opportunistic bacteria in the initial hours of application, metal nanoparticles can often trigger a secondary biocidal effect through leaching that can lead to unfavorable cytotoxic responses from host cells. Alternatively, copper-based metal organic frameworks (MOFs) have been shown to stabilize Cu^2+/1+ via coordination while demonstrating longer-term catalytic performance compared to their salt counterparts. Herein, the practical application of MOFs in NO-releasing polymeric substrates with an embedded NO donor compound was investigated for the first time. By developing composite thermoplastic silicon polycarbonate polyurethane (TSPCU) scaffolds, the catalytic effects achievable via intrapolymeric interactions between an MOF and NO donor compound were investigated using the water-stable copper-based MOF H₃[(Cu₄Cl)₃(BTTri)₈-(H₂O)₁₂]·72H₂O (CuBTTri) and the NO donor S-nitroso-N-acetyl-penicillamine (SNAP). By creating a multifunctional triple-layered composite scaffold with CuBTTri and SNAP, the surface flux of NO from catalyzed SNAP decomposition was found tunable based on the variable weight percent CuBTTri incorporation. The tunable NO surface fluxes were found to elicit different cytotoxic responses in human cell lines, enabling application-specific tailoring. Challenging the TSPCU-NO-MOF composites against 24 h bacterial growth models, the enhanced NO release was found to elicit over 99% reduction in adhered and over 95% reduction in planktonic methicillin-resistant Staphylococcus aureus, with similar results observed for Escherichia coli. These results indicate that the combination of embedded MOFs and NO donors can be used as a highly efficacious tool for the early prevention of biofilm formation on medical devices.

Reduction in Foreign Body Response and Improved Antimicrobial Efficacy via Silicone-Oil-Infused Nitric-Oxide-Releasing Medical-Grade Cannulas

Foreign body response and infection are two universal complications that occur with indwelling medical devices. In response, researchers have developed different antimicrobial and antifouling surface strategies to minimize bacterial colonization and fibrous encapsulation. In this study, the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) and silicone oil were impregnated into silicone rubber cannulas (SR-SNAP-Si) using a solvent swelling method to improve the antimicrobial properties and decrease the foreign body response. The fabricated SR-SNAP-Si cannulas demonstrated a stable, prolonged NO release, exhibited minimal SNAP leaching, and maintained sliding angles < 15° for 21 days. SR-SNAP-Si cannulas displayed enhanced antimicrobial efficacy against Staphylococcus aureus in a 7-day biofilm bioreactor study, reducing the viability of adhered bacteria by 99.2 ± 0.2% compared to unmodified cannulas while remaining noncytotoxic toward human fibroblast cells. Finally, SR-SNAP-Si cannulas were evaluated for the first time in a 14- and 21-day subcutaneous mouse model, showing significantly enhanced biocompatibility compared to control cannulas by reducing the thickness of fibrous encapsulation by 60.9 ± 6.1 and a 60.8 ± 10.5% reduction in cell density around the implant site after 3 weeks. Thus, this work demonstrates that antifouling, NO-releasing surfaces can improve the lifetime and safety of indwelling medical devices.

Organosilica colloids as nitric oxide carriers: Pharmacokinetics and biocompatibility

Nitric oxide (NO) is a potential therapeutic agent for various diseases. However, it is challenging to deliver this unstable, free-radical gaseous molecule in the body. Various nanoparticle-based drug delivery systems have been investigated as promising NO carriers without detailed characterization of their biological fate. The purpose of this study is to investigate the pharmacokinetics and biocompatibility of organosilica-based NO-delivering nanocarriers. Two distinct NO nanoformulations, namely NO-SiNP-1 and NO-SiNP-2, were prepared from a thiol-functionalized organosilane using nanoprecipitation and direct aqueous synthesis, respectively. During the preparation, the thiol group was converted to S-nitrosothiol (SNO) under a nitrosation condition. The final products contain SNO-loaded organosilica particles of similar sizes (~130 nm), but of different morphologies and surface charges (between the two formulations). In the in vitro release kinetics study, NO-SiNP-1 exhibited a much slower NO release rate than NO-SiNP-2 (by 5-fold); therefore, the former is considered as a slow NO releaser, and the latter a fast NO releaser. However, in the rat pharmacokinetic study (IV bolus of 50 μmol/kg), NO-SiNP-1 was rapidly eliminated from the blood (within 20 min); in contrast, NO-SiNP-2 was slowly eliminated with an extended circulation time of 12 h for plasma SNO, along with markedly higher plasma levels of nitrite and nitrate. The two formulations are generally biocompatible. In conclusion, the paper presents contrast biological fates of two organosilica colloidal formulations for nitric oxide delivery.

A Synergistic New Approach Toward Enhanced Antibacterial Efficacy via Antimicrobial Peptide Immobilization on a Nitric Oxide-Releasing Surface

Despite technological advancement, nosocomial infections are prevalent due to the rise of antibiotic resistance. A combinatorial approach with multimechanistic antibacterial activity is desired for an effective antibacterial medical device surface strategy. In this study, an antimicrobial peptide, nisin, is immobilized onto biomimetic nitric oxide (NO)-releasing medical-grade silicone rubber (SR) via mussel-inspired polydopamine (PDA) as a bonding agent to reduce the risk of infection. Immobilization of nisin on NO-releasing SR (SR-SNAP-Nisin) and the surface characteristics were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy and contact angle measurements. The NO release profile (7 days) and diffusion of SNAP from SR-SNAP-Nisin were quantified using chemiluminescence-based nitric oxide analyzers and UV-vis spectroscopy, respectively. Nisin quantification showed a greater affinity of nisin immobilization toward SNAP-doped SR. Matrix-assisted laser desorption/ionization mass spectrometry analysis on surface nisin leaching for 120 h under physiological conditions demonstrated the stability of nisin immobilization on PDA coatings. SR-SNAP-Nisin shows versatile in vitro anti-infection efficacy against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus in the planktonic and adhered states. Furthermore, the combination of NO and nisin has a superior ability to impair biofilm formation on polymer surfaces. SR-SNAP-Nisin leachates did not elicit cytotoxicity toward mouse fibroblast cells and human umbilical vein endothelial cells, indicating the biocompatibility of the material in vitro. The preventative and therapeutic potential of SR-SNAP-Nisin dictated by two bioactive agents may offer a promising antibacterial surface strategy.

Bactericidal Activity of Bulk Nanobubbles through Active Oxygen Species Generation

We investigated the bactericidal activity of bulk nanobubbles (NBs) using E. coli, a model bacterium. Bulk NBs were produced by forcing gas through a porous alumina membrane with an ordered arrangement of nanoscale straight holes in contact with water. NBs with different gas contents, including CO2, O2, and N2, were generated and evaluated for their bactericidal effects. The survival rate of E. coli was significantly reduced in a suspension of CO2-containing NB (CO2-NB water). The N2-NB water demonstrated a small amount of bactericidal behavior, but its impact was not as significant as that of CO2-NB water. When E. coli was retained in O2-NB water, the survival rate was even higher than that in pure water (PW). We investigated the generation of reactive oxygen species (ROS) in NB suspensions by electron spin resonance spectroscopy. The main ROS generated in the NB water were hydroxyl radicals and OH·, and the production of ROS was the strongest in CO2-NB water, which was consistent with the results of the bactericidal effect measurements. We assumed that NB mediated by ROS would exhibit bactericidal behavior and proposed a kinetic model to explain the retention time variation of the survival rate. The results calculated based on the proposed model matched closely with the experimental results.

Nitric Oxide System and Bronchial Epithelium: More Than a Barrier

Airway epithelium forms a physical barrier that protects the lung from the entrance of inhaled allergens, irritants, or microorganisms. This epithelial structure is maintained by tight junctions, adherens junctions and desmosomes that prevent the diffusion of soluble mediators or proteins between apical and basolateral cell surfaces. This apical junctional complex also participates in several signaling pathways involved in gene expression, cell proliferation and cell differentiation. In addition, the airway epithelium can produce chemokines and cytokines that trigger the activation of the immune response. Disruption of this complex by some inflammatory, profibrotic, and carcinogens agents can provoke epithelial barrier dysfunction that not only contributes to an increase of viral and bacterial infection, but also alters the normal function of epithelial cells provoking several lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF) or lung cancer, among others. While nitric oxide (NO) molecular pathway has been linked with endothelial function, less is known about the role of the NO system on the bronchial epithelium and airway epithelial cells function in physiological and different pathologic scenarios. Several data indicate that the fraction of exhaled nitric oxide (F_ENO) is altered in lung diseases such as asthma, COPD, lung fibrosis, and cancer among others, and that reactive oxygen species mediate uncoupling NO to promote the increase of peroxynitrite levels, thus inducing bronchial epithelial barrier dysfunction. Furthermore, iNOS and the intracellular pathway sGC-cGMP-PKG are dysregulated in bronchial epithelial cells from patients with lung inflammation, fibrosis, and malignancies which represents an attractive drug molecular target. In this review we describe in detail current knowledge of the effect of NOS-NO-GC-cGMP-PKG pathway activation and disruption in bronchial epithelial cells barrier integrity and its contribution in different lung diseases, focusing on bronchial epithelial cell permeability, inflammation, transformation, migration, apoptosis/necrosis, and proliferation, as well as the specific NO molecular pathways involved.