Nitric Oxide Delivery

Nitric oxide, NO, is a broad-spectrum antibacterial agent, making it an attractive alternative to traditional antibiotics for treating infections. To date, a direct comparison of the antibacterial activity of gaseous NO, gNO, versus water-soluble NO-releasing biopolymers has not been reported.

In work published in ACS Biomaterials, researchers in the Schoenfisch Group compare the bactericidal action of NO-releasing chitosan oligosaccharides to gNO treatment against cystic fibrosis-relevant Gram-positive and Gram-negative bacteria.

 

Schematic

 

Schematic of the gaseous NO exposure chamber. The flow rates of the gases were separately controlled to obtain precise concentrations of gNO. The combined mixture enters the humidified chamber through a single port while exiting through PTFE and HEPA filters to remove water vapor and aerosolized bacteria, respectively. The NO concentration of the output gas was analyzed using a chemiluminescence nitric oxide analyzer, NOA. The valves, connecting the gas cylinders to the exposure chamber and between the HEPA filter and NOA, allow for the creation of a closed, gas-tight system.

 

A NO exposure chamber was constructed to enable the dosing of bacteria with gNO at concentrations up to 800 ppm under both aerobic and anaerobic conditions. Bacteria viability, solution properties, such as, pH, NO concentration, and toxicity to mammalian cells were monitored to ensure a thorough understanding of bactericidal action and reproducibility for each delivery method. The NO-releasing chitosan oligosaccharides required significantly lower NO doses relative to gNO therapy to elicit antibacterial action against Pseudomonas aeruginosa and Staphylococcus aureus under both aerobic and anaerobic conditions.

A standardized protocol was developed to compare the antibacterial action of gNO to a water-soluble biopolymer releasing NO in solution. Exposure conditions, such as, pH, NO concentration, and solution depth, bacteria viability versus CF-relevant bacteria under aerobic and anaerobic environments, and toxicity to mammalian cells were investigated for both NO delivery methodologies.

Under all tested conditions, COS-EA/NO required significantly lower doses of NO in solution to achieve a 3-log reduction in bacterial viability compared to gNO. The NO-releasing biopolymer system allows for a more direct treatment approach, releasing the NO payload over time in solution. Such delivery necessitates shorter NO diffusion distances to bacteria, leading to reduced NO scavenging and greater antibacterial action at lower doses.

Additionally, the positively charged chitosan scaffold may provide unique targeting features by associating with the negatively charged biofilm, further reducing the required NO diffusion distance to the bacteria. Although NO-releasing chitosan was utilized as a model biopolymer system in this study, the methodology described in the group's publication allows for comparison of gNO to any water-soluble NO donor.