Developing a Novel Therapy for Bacterial Pneumonia
Authors: Baer Brandon , Arsenault Christina , McCaig Lynda , Yamashita Cory , Veldhuizen Ruud 
Published: June 2021

Background

Bacterial pneumonia is a leading cause of death worldwide. Unfortunately, new treatments are faced with several major hurdles. Firstly, the incidence of antibiotic resistance is increasing. Secondly, both acute and chronic lung infections are often accompanied by maladaptive inflammatory responses linked to poor outcomes. Finally, the structure of the lung makes delivery of therapeutics to the sites of infection challenging. As a potential treatment for bacterial pneumonia, the current study combines a host‐defense peptide (CATH‐2), previously shown to kill antibiotic‐resistant bacteria and reduce inflammation, with an exogenous surfactant (BLES), capable of enhancing spreading throughout the lung.

Objectives

1) Quantify the transport CATH‐2 by BLES in vitro, 2) Assess the antimicrobial and anti‐inflammatory properties of BLES+CATH‐2 subsequent to spreading across a surface and 3) Investigate the immunomodulatory effects of BLES+CATH‐2 in vivo.

Hypothesis

The mixture of BLES+CATH‐2 will improve transport of CATH‐2 allowing for effective bacterial killing and reductions in inflammation at distal sites in vitro and in vivo.

Methods

Fluorescently‐labelled CATH‐2 was used to track its movement as it spread across a Wet Bridge Transfer system alone or in combination with BLES. Bacterial killing and anti‐inflammatory properties were assessed by seeding either a lab strain of Pseudomonas aeruginosa or RAW 264.7 macrophages to the distal well of the wet bridge system. The macrophages were stimulated with heat‐killed P. aeruginosa 15 minutes prior to the administration of saline, BLES, CATH‐2 or BLES+CATH‐2 in the proximal well. The fluid in each well was analyzed for cytokine content and bacterial killing. Additionally, a non‐infectious model of bacterial pneumonia was used, where mice were instilled with heat‐killed P. aeruginosa or saline. This first instillation was then followed by either saline, BLES, CATH‐2 or BLES+CATH‐2. All mice were monitored for 4 hours before being euthanized. Bronchoalveolar lavage fluid was collected and analyzed for cell counts, cell differentials, and cytokine concentrations.

Results

Fluorescence spectrometry revealed that significantly more CATH‐2 was transferred across the bridge when combined with BLES compared to CATH‐2 by itself. Additionally, only the combination of BLES+CATH‐2 showed significant improvements in bacterial killing and reducing inflammation across the wet bridge. Mice administered heat‐killed bacteria showed significant increases in the number of inflammatory cells, neutrophils and lavage IL‐6, TNF‐α and KC content compared to saline control. Instillation of BLES+CATH‐2 after an instillation of heat‐killed bacteria showed significant reductions across all markers of inflammation compared to saline, BLES or CATH‐2 alone.

Discussion

These results support BLES as an effective vehicle for the transport of CATH‐2 and that the mixture has potent antimicrobial and anti‐inflammatory properties. Our novel approach allowed us to rapidly assess the efficacy and spreading capabilities of BLES+CATH‐2. Additionally, the results support BLES+CATH‐2 as a therapy which can overcome the delivery problem hindering pulmonary therapies and reach distal sites of inflammation.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.