Gaseous Nitric Oxide (gNO) as a Potential Antimicrobial Therapy during Ex Vivo Lung Perfusion: An Efficacy and Safety Study

Abstract

Microbial infection in donor lungs decreases organ utilization in transplantation. Previous studies have demonstrated high-dose gaseous Nitric Oxide (gNO) to be effective against bacteria, however, this concept has not been studied in the context of lung transplantation. The present study explores the antimicrobial effects and the safety of continuously inhaled high-dose gNO. Effects of gNO on strains of P. aeruginosa, S. aureus, E. coli and Burkholderia cepacia (purchased from American Type Culture Collection) were performed in vitro. Agar plates were inoculated and transferred into either control (medical air) or treatment chamber (medical air + 200 ppm gNO) for 6 h. Safety of continuously inhaled high-dose gNO were studied in a porcine normothermic ex vivo lung perfusion (EVLP) model. Donor lungs with minimal cold ischemia (2h) were randomized (n=4 each) into control (normal ventilation setting) and treatment (normal ventilation setting + high-dose of gNO) group. Physiologic and biologic measures were monitored over 12 h of EVLP. gNO significantly reduced all strains of bacteria when compared to control (n=3 per group, Fig.1A): P. aeruginosa (5.8 ±1.27 vs 9.2 ±0.40 Log10CFU/mL, p= 0.01), S. aureus (5.6 ±0.65 vs 9.1 ±0.66 Log10CFU/mL, p= 0.002), E. coli (5.3 ±1.20 vs 9.4 ±0.47 Log10CFU/mL, p= 0.005) and Burkholderia cepacia (7.0 ±0.51 vs 8.9 ±0.57 Log10CFU/mL, p= 0.01). No significant adverse effects in lung function during EVLP were observed in lungs receiving 12h of continuous high-dose of gNO (Fig. 1B). Inflammatory cytokines at 1, 6 and 12h were similar between control and treatment (Fig. 1C). NO2 levels were <2.8 ppm throughout the treatment. Continuous high dose gNO at 200 ppm is effective towards reducing common respiratory pathogens in vitro. Inhaled high-dose gNO appears to be safe during 12h EVLP. We are further exploring this treatment using infected human lungs. If successful high dose gNO could be part of EVLP clinical protocols.