Antimicrobial and immuno-modulatory peptides as a treatment for lung disease and delivery by nebulisation

Abstract

Respiratory infections are of significant concern for individuals with chronic inflammatory lung diseases and there is an unmet need for novel antibiotics. Antimicrobial peptides possess antibiotic potential due to their antimicrobial and/or immunomodulatory properties. The project aim was to assess the therapeutic potential of several snake-derived AMPs and to evaluate the suitability of peptide delivery by nebulisation.

In in vitro assays the peptides exhibited antimicrobial activity and/or anti-inflammatory effects with minimal cytotoxicity. We considered the impact of lung proteases on the peptides. Peptide incubation with CF sputum and protease inhibitors revealed the peptides were susceptible to proteolytic cleavage. Cleavage predictions highlighted neutrophil elastase (NE) as most likely responsible. All peptides were susceptible to cleavage by NE, and several peptides retained function following NE-incubation. Mass spectrometric analysis and cleavage predictions informed truncated derivative development, aiming to reduce production cost and potential immunogenicity. SnE1 and derivatives were tested as therapeutics for acute lung infection using a murine model of chronic lung disease. SnE1N treatment reduced lung bacterial load, whereas, SnE1 did not. SnE1 increased
protein and IL6 concentration in the BAL fluid and reduced the number of immune cells, possibly due to cytotoxic effects, indicating increased inflammation; whereas, SnE1N did not. In nebulised delivery suitability testing, nebulisation did not alter peptide function. Sn1b and C2 were shown to be respirable in an adult spontaneously breathing model and all test peptides were found to be respirable in a mechanically ventilated breathing model.

Assessment of nebulised droplet distributions suggested all test peptides would likely reach the lower airways. To conclude, AMPs remain an attractive candidate for antibiotic development. In this study, we found that SnE1N reduced the bacterial burden during acute lung infection in mice with chronic lung inflammation, warranting further investigation. Additionally, peptide delivery via nebulisation is likely feasible.

Date of Award	Jul 2021
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Cliff Taggart (Supervisor), John Dalton (Supervisor) & Sinead Weldon (Supervisor)