Accurate Nitric Oxide Measurements from Donors in Cell Media: Identification of Scavenging Agents

Nitric oxide releasing coatings for the prevention of viral and bacterial infections

Healthcare associated infections (HCAI) represent a significant burden worldwide contributing to morbidity and mortality and result in substantial economic consequences equating to billions annually. Although the impacts of HCAI have been felt for many years, the coronavirus pandemic has had a profound effect, escalating rates of HCAI, even with extensive preventative measures such as vaccination, personal protective equipment, and deep cleaning regimes. Therefore, there is an urgent need for new solutions to mitigate this serious health emergency. In this paper, the fabrication of nitric oxide (NO) releasing dual action polymer coatings for use in healthcare applications is described. The coatings are doped with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) and release high payloads of NO in a sustained manner for in excess of 50 hours. These coatings are extensively characterized in multiple biologically relevant solutions and the antibacterial/antiviral efficacy is studied. For the first time, we assess antibacterial activity in a time course study (1, 2, 4 and 24 h) in both nutrient rich and nutrient poor conditions. Coatings exhibit excellent activity against Pseudomonas aeruginosa and methicillin resistant Staphylococcus aureus (MRSA), with up to complete reduction observed over 24 hours. Additionally, when tested against SARS-CoV-2, the coatings significantly reduced active virus in as little as 10 minutes. These promising results suggest that these coatings could be a valuable addition to existing preventative measures in the fight against HCAIs.

Versatile metal-organic frameworks as a catalyst and an indicator of nitric oxide

The imaging of nitric oxide (NO) and its donors is crucial to explore NO-related physiological and pathological processes. In this work, we demonstrate the use of Cu-based metal-organic frameworks (Cu-MOFs) as nanoprobes for NO detection and as a catalyst for the generation of NO from the biologically occurring substrate, S-nitrosothiols (RSNOs). The paramagnetic Cu²⁺ in the MOFs could quench the luminescence of triphenylamine; Cu-MOFs only exhibited weak emission at 450 nm. Upon the addition of NO, the paramagnetic Cu²⁺ was reduced to diamagnetic Cu⁺, and thus the luminescence was recovered directly. Cu-MOFs exhibited high selectivity for other species in the reaction system, including NO₂^-, H₂O₂, AA, NO₃^- and ¹O₂. More significantly, the Cu⁺ can react with s-nitrosoglutathione (GSNO), s-nitrosocysteine (CysNO), and s-nitrosocysteamine (CysamNO) to generate NO and then oxidize to Cu²⁺-MOFs with quenched luminescence, respectively, and thus the catalysis is inhibited, noted as a self-controlled process. The Cu-MOFs catalyst was confirmed by powder X-ray diffraction to remain structurally intact in aqueous environments. The Cu-MOFs have been successfully employed in the biological imaging of NO in living cells. The bifunctional MOFs could offer a novel platform for the real-time monitoring of NO species, provide potential for exploiting NO in cancer therapy and improve the methodologies to elucidate the NO-related biological processes.

A metal-organic framework with multienzyme activity as a biosensing platform for real-time electrochemical detection of nitric oxide and hydrogen peroxide

A Metal-Organic Framework (MOFs) with large surface area, exposed active site, excellent catalytic performance and high chemical stability has been used as an artificial enzyme and designed for nonenzymatic electrochemical sensors. Here, a strategy of using an enhanced electrochemical sensing platform for the detection of nitic oxide (NO) and hydrogen peroxide (H2O2) was designed via a nano-metalloporphyrinic metal-organic framework (NporMOF(Fe)) as an electrode material. By taking advantage of the small size, high surface area and exposed Fe active site, the obtained NporMOF(Fe) displays excellent electrocatalytic activity toward NO and H2O2. The NporMOF(Fe) modified electrode shows high sensing ability toward the in situ generated NO in NO2- containing phosphate buffer (PB) solution with a wide linear detection range of 5 μM to 200 μM and a very low detection limit of 1.3 μM. Moreover, NporMOF(Fe) exhibits high electrocatalytic activity toward the reduction of H2O2 and the practical detection of H2O2 released from HeLa cells. Furthermore, the NporMOF(Fe) modified electrode shows excellent selectivity toward the detection of NO and H2O2 in the presence of other physiologically important analytes. This method shows excellent biosensing performance, implying the universal applicability of MOFs-based artificial nanozymes for biosensors and the potential application for third generation biosensors.

Antimicrobial Nitric Oxide Releasing Contact Lens Gels for the Treatment of Microbial Keratitis

Microbial keratitis is a serious sight threatening infection affecting approximately two million individuals worldwide annually. While antibiotic eye drops remain the gold standard treatment for these infections, the significant problems associated with eye drop drug delivery and the alarming rise in antimicrobial resistance has meant that there is an urgent need to develop alternative treatments. In this work, a nitric oxide releasing contact lens gel displaying broad spectrum antimicrobial activity against two of the most common causative pathogens of microbial keratitis is described. The contact lens gel is composed of poly-ε-lysine (pεK) functionalized with nitric oxide (NO) releasing diazeniumdiolate moieties which enables the controlled and sustained release of bactericidal concentrations of NO at physiological pH over a period of 15 h. Diazeniumdiolate functionalization was confirmed by Fourier transform infrared (FTIR), and the concentration of NO released from the gels was determined by chemiluminescence. The bactericidal efficacy of the gels against Pseudomonas aeruginosa and Staphylococcus aureus was ascertained, and between 1 and 4 log reductions in bacterial populations were observed over 24 h. Additional cell cytotoxicity studies with human corneal epithelial cells (hCE-T) also demonstrated that the contact lens gels were not cytotoxic, suggesting that the developed technology could be a viable alternative treatment for microbial  keratitis.

A Novel Ruthenium-based Molecular Sensor to Detect Endothelial Nitric Oxide

Nitric oxide (NO) is a key regulator of endothelial cell and vascular function. The direct measurement of NO is challenging due to its short half-life, and as such surrogate measurements are typically used to approximate its relative concentrations. Here we demonstrate that ruthenium-based [Ru(bpy)₂(dabpy)]²⁺ is a potent sensor for NO in its irreversible, NO-bound active form, [Ru(bpy)₂(T-bpy)]²⁺. Using spectrophotometry we established the sensor’s ability to detect and measure soluble NO in a concentration-dependent manner in cell-free media. Endothelial cells cultured with acetylcholine or hydrogen peroxide to induce endogenous NO production showed modest increases of 7.3 ± 7.1% and 36.3 ± 25.0% respectively in fluorescence signal from baseline state, while addition of exogenous NO increased their fluorescence by 5.2-fold. The changes in fluorescence signal were proportionate and comparable against conventional NO assays. Rabbit blood samples immediately exposed to [Ru(bpy)₂(dabpy)]²⁺ displayed 8-fold higher mean fluorescence, relative to blood without sensor. Approximately 14% of the observed signal was NO/NO adduct-specific. Optimal readings were obtained when sensor was added to freshly collected blood, remaining stable during subsequent freeze-thaw cycles. Clinical studies are now required to test the utility of [Ru(bpy)₂(dabpy)]²⁺ as a sensor to detect changes in NO from human blood samples in cardiovascular health and disease.

Critical nitric oxide concentration for Pseudomonas aeruginosa biofilm reduction on polyurethane substrates

Bacterial colonies that reside on a surface, known as biofilms, are intrinsically impenetrable to traditional antibiotics, ultimately driving research toward an alternative therapeutic approach. Nitric oxide (NO) has gained attention for its biologically beneficial properties, particularly centered around its antibacterial capabilities. NO donors that can release the molecule under physiological conditions (such as S-nitrosothiols) can be utilized in clinical settings to combat bacterial biofilm infections. Herein the authors describe determining a critical concentration of NO necessary to cause >90% reduction of a Pseudomonas aeruginosa biofilm grown on medical grade polyurethane films. The biofilm was grown under optimal culture conditions [in nutrient broth media (NBM) at 37 °C] for 24 h before the addition of the NO donor S-nitrosoglutathione (GSNO) in NBM for an additional 24 h. The cellular viability of the biofilm after the challenge period was tested using varying concentrations of NO to determine the critical amount necessary to cause at least a 90% reduction in bacterial biofilm viability. The critical GSNO concentration was found to be 10 mM, which corresponds to 2.73 mM NO. Time kill experiments were performed on the 24 h biofilm using the critical amount of NO at 4, 8, 12, and 16 h and it was determined that the 90% biofilm viability reduction occurred at 12 h and was sustained for the entire 24 h challenge period. This critical concentration was subsequently tested for total NO release via a nitric oxide analyzer. The total amount of NO released over the 12 h challenge period was found to be 5.97 ± 0.66 × 10(-6) mol NO, which corresponds to 1.49 ± 0.17 μmol NO/ml NBM. This is the first identification of the critical NO concentration needed to elicit this biological response on a medically relevant polymer.

Efficient Eradication of Mature Pseudomonas aeruginosa Biofilm via Controlled Delivery of Nitric Oxide Combined with Antimicrobial Peptide and Antibiotics

Fast eradication of mature biofilms is the ‘holy grail’ in the clinical management of device-related infections. Endogenous nitric oxide (NO) produced by macrophages plays an important role in host defense against intracellular pathogens, and NO is a promising agent in preventing biofilms formation in vitro. However, the rate of delivery of NO by various NO donors (e.g., diazeniumdiolates, S-nitrosothiols, etc.) is difficult to control, which hinders fundamental studies aimed at understanding the role of NO in biofilm control. In this study, by using a novel precisely controlled electrochemical NO releasing catheter device, we examine the effect of physiological levels of NO on eradicating mature Pseudomonas aeruginosa biofilm (7 days), as well as the potential application of the combination of NO with antimicrobial agents. It is shown that physiological levels of NO exhibit mixed effects of killing bacteria and dispersing ambient biofilm. The overall biofilm-eradicating effect of NO is quite efficient in a dose-dependent manner over a 3 h period of NO treatment. Moreover, NO also greatly enhances the efficacy of antimicrobial agents, including human beta-defensin 2 (BD-2) and several antibiotics, in eradicating biofilm and its detached cells, which otherwise exhibited high recalcitrance to these antimicrobial agents. The electrochemical NO release technology offers a powerful tool in evaluating the role of NO in biofilm control as well as a promising approach when combined with antimicrobial agents to treat biofilm-associated infections in hospital settings, especially infections resulting from intravascular catheters.

Reprint of: Nitric oxide-releasing polysaccharide derivative exhibits 8-log reduction against Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus

Health-care associated infections (HAIs) and the increasing number of antibiotic-resistant bacteria strains remain significant public health threats worldwide. Although the number of HAIs has decreased by using improved sterilization protocols, the cost related to HAIs is still quantified in billions of dollars. Furthermore, the development of multi-drug resistant strains is increasing exponentially, demonstrating that current treatments are inefficient. Thus, the quest for new methods to eradicate bacterial infection is increasingly important in antimicrobial, drug delivery and biomaterials research. Herein, the bactericidal activity of a water-soluble NO-releasing polysaccharide derivative was evaluated in nutrient broth media against three bacteria strains that are commonly responsible for HAIs. Data confirmed that this NO-releasing polysaccharide derivative induced an 8-log reduction in bacterial growth after 24h for Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus. Additionally, the absence of bacteria after 72 h of exposure to NO illustrates the inability of the bacteria to recover and the prevention of biofilm formation. The presented 8-log reduction in bacterial survival after 24h is among the highest reduction reported for NO delivery systems to date, and reaches the desired standard for industrially-relevant reduction. More specifically, this system represents the only water-soluble antimicrobial to reach such a significant bacterial reduction in nutrient rich media, wherein experimental conditions more closely mimic the in vivo environment than those in previous reports. Furthermore, the absence of bacterial activity after 72 h and the versatility of using a water-soluble compound suggest that this NO-releasing polysaccharide derivative is a promising route for treating HAIs.

Co-delivery of nitric oxide and antibiotic using polymeric nanoparticles

The rise of hospital-acquired infections, also known as nosocomial infections, is a growing concern in intensive healthcare, causing the death of hundreds of thousands of patients and costing billions of dollars worldwide every year. In addition, a decrease in the effectiveness of antibiotics caused by the emergence of drug resistance in pathogens living in biofilm communities poses a significant threat to our health system. The development of new therapeutic agents is urgently needed to overcome this challenge. We have developed new dual action polymeric nanoparticles capable of storing nitric oxide, which can provoke dispersal of biofilms into an antibiotic susceptible planktonic form, together with the aminoglycoside gentamicin, capable of killing the bacteria. The novelty of this work lies in the attachment of NO-releasing moiety to an existing clinically used drug, gentamicin. The nanoparticles were found to release both agents simultaneously and demonstrated synergistic effects, reducing the viability of Pseudomonas aeruginosa biofilm and planktonic cultures by more than 90% and 95%, respectively, while treatments with antibiotic or nitric oxide alone resulted in less than 20% decrease in biofilm viability.

Nitric oxide-releasing polysaccharide derivative exhibits 8-log reduction against Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus

Health-care associated infections (HAIs) and the increasing number of antibiotic-resistant bacteria strains remain significant public health threats worldwide. Although the number of HAIs has decreased by using improved sterilization protocols, the cost related to HAIs is still quantified in billions of dollars. Furthermore, the development of multi-drug resistant strains is increasing exponentially, demonstrating that current treatments are inefficient. Thus, the quest for new methods to eradicate bacterial infection is increasingly important in antimicrobial, drug delivery and biomaterials research. Herein, the bactericidal activity of a water-soluble NO-releasing polysaccharide derivative was evaluated in nutrient broth media against three bacteria strains that are commonly responsible for HAIs. Data confirmed that this NO-releasing polysaccharide derivative induced an 8-log reduction in bacterial growth after 24h for Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus. Additionally, the absence of bacteria after 72h of exposure to NO illustrates the inability of the bacteria to recover and the prevention of biofilm formation. The presented 8-log reduction in bacterial survival after 24h is among the highest reduction reported for NO delivery systems to date, and reaches the desired standard for industrially-relevant reduction. More specifically, this system represents the only water-soluble antimicrobial to reach such a significant bacterial reduction in nutrient rich media, wherein experimental conditions more closely mimic the in vivo environment than those in previous reports. Furthermore, the absence of bacterial activity after 72h and the versatility of using a water-soluble compound suggest that this NO-releasing polysaccharide derivative is a promising route for treating HAIs.

S-Nitrosothiol analysis via photolysis and amperometric nitric oxide detection in a microfluidic device

A 530 nm light emitting diode was coupled to a microfluidic sensor to facilitate photolysis of nitrosothiols (i.e., S-nitrosoglutathione, S-nitrosocysteine, and S-nitrosoalbumin) and amperometric detection of the resulting nitric oxide (NO). This configuration allowed for maximum sensitivity and versatility, while limiting potential interference from nitrate decomposition caused by ultraviolet light. Compared to similar measurements of total S-nitrosothiol content in bulk solution, use of the microfluidic platform permitted significantly enhanced analytical performance in both phosphate-buffered saline and plasma (6-20× improvement in sensitivity depending on nitrosothiol type). Additionally, the ability to reduce sample volumes from milliliters to microliters provides increased clinical utility. To demonstrate its potential for biological analysis, this device was used to measure basal nitrosothiol levels from the vasculature of a healthy porcine model.