BLES‐Cath‐2 Intratracheal Administration in an in vivo P. aeruginosa Pneumonia Model

Background Increasing patterns of antibiotic resistance, especially in individuals with chronic lung disease, have mandated the development of novel therapies. Host‐defense peptides HDP such as cathelicidin‐2 (CATH‐2), possess excellent antimicrobial activities in vitro however in vivo efficacy has not been well established. Furthermore, in order to enhance in vivo distribution, a novel approach using CATH‐2 combined with bovine lipid extract surfactant (BLES) as a delivery vehicle was utilized. It was hypothesized that CATH‐2/ BLES would be superior to CATH‐2 alone in decreasing bacterial burden and improving physiologic parameters in an in vivo model of Pseudomonas aeruginosa (PA) infection with mechanical ventilation. Methods Adult male Sprague‐Dawley rats were intubated, mechanically ventilated for 30 minutes, followed by an intratracheal inoculum of 8 x 10^8 CFU/mL of PA. One hour following PA administration, rats were randomized to receive an intratracheal administration of either: i) Saline, ii) Air, iii) BLES, iv) Cath‐2, or v) BLES/Cath‐2. Mechanical ventilation continued for three hours during which peak inspiratory pressure (PIP) and arterial blood gases were recorded. At the completion of the ventilation protocol, animals were sacrificed and whole lungs were homogenized and the bacterial burden was assessed by growth analysis of lung homogenates on Cetrimide Agar plates incubated overnight at 37 C. Statistical analysis was performed using a one‐way ANOVA. Results Physiological measurements revealed a significant decline of arterial oxygenation (PaO2) in air and saline control groups. At the three‐hour time point, the BLES/Cath‐2 group had a significantly (p < 0.01) higher PaO2 and compared to the Cath‐2 treated animals. Interestingly, the Cath‐2 group had PIP values at 30 minutes following PA instillation that were significantly higher compared to all groups. Colony growth data demonstrated a significant difference between the Cath‐2 treated animals and the control groups; however there was no difference compared to the BLES/Cath‐2 group. Conclusion Our findings demonstrate that Cath‐2 has excellent anti‐microbial activity against PA in an in vivo model of pneumonia and mechanical ventilation, although significant reduction in lung function was observed. Cath‐2 alone worsens lung function by possibly causing an overwhelming inflammatory response. Furthermore, CATH‐2/ BLES significantly improved physiological parameters compared to Cath‐2 alone. This suggests that the combination of BLES/Cath‐2 allows for both improved lung function and while maintaining antimicrobial activity. Future analysis includes extension of the time points and lavage inflammatory markers. Support or Funding Information Physician Services Inc. and the Canadian Cystic Fibrosis foundation

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