The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

GASEOUS NITRIC OXIDE BACTERICIDAL ACTIVITY RETAINED DURING INTERMITTENT HIGH-DOSE SHORT DURATION EXPOSURE

Chris C. Miller1, Bevin McMUllin3, Abdi Ghaffari2, Nora Pick1, Alex Stenzler5, Aziz Ghahary2, Diane Roscoe4, Jeremy Road3, Yossef Av-gay1



Background: Nitric oxide (NO) has been shown to play an important host defense role as part of the innate immune system. Previously, we have shown that gaseous NO (gNO) has great potential as an effective topical anti-infective agent for non-healing wounds due to its non specific antimicrobial properties. These same antimicrobial attributes may be useful for pulmonary infections. However, gNO would have limited usefulness as an inhaled antimicrobial agent as continuous exposure to the concentration required for a bactericidal effect (160-200ppm) leads to methemoglobinemia. To overcome this problem, we investigated whether a thirty minute exposure of 160 ppm every four hours would retain the same antimicrobial effects as continuous delivery. If successful, this approach would then make it feasible to deliver inhaled gNO and evaluate its antimicrobial properties in an animal model by allowing pulmonary methemoglobin concentrations developed during exposure to return to a safe level between exposures and also reduce the potential of tissue toxicity.

Methods/Results:
In vitro, exposure of clinical multi-drug resistant Staphylococcous aureus and Escherichia coli strains isolated from the lungs of nosocomial pneumonia patients and a lethal antibiotic-resistant strain of P. aeruginosa, isolated from a deceased cystic fibrosis patient resulted in over a 5 log10 reduction in bacterial load after multiple thirty minute treatments (4 cycles) every four hours to 160 ppm gNO. The intermittent regimen required 320 (SD=0) ppm hours for 100% lethality whereas the continuous exposure required 800 (SD=160) ppm-hours. We have also shown that selection for a gNO resistant phenotype did not lead to decrease sensitivity to gNO therapy (p>0.05). In addition, no host cellular toxicity was observed in human THP-1 monocytes and macrophages following intermittent delivery of a high concentration of gNO, and the proliferation and migration of pulmonary epithelial cells was not adversely affected by the administration of intermittent high dose gNO.

Conclusion:
These results justify further studies that should focus on whether intermittent delivery of 160 ppm of gNO every four hours can technically be administered while keeping inhaled NO2 levels less than 2 ppm and methemoglobin saturation less than 2.5 percent. If this can be achieved then the potential for a new era in inhaled antimicrobial therapy may be on the horizon.