Reformulating Surfactant for the Delivery of Cathelicidins
Authors: Baer Brandon , Possmayer Fred , Yamashita Cory , Veldhuizen Ruud 
Published: June 2021

Background

The complex branching structure of the lung makes direct delivery of drugs, such as the antimicrobial peptides cathelicidins, to the small and distal airways a major challenge. To address this issue our lab has been investigating the use of exogenous surfactant (BLES), to facilitate the pulmonary delivery of cathelicidins. BLES is a lipoprotein complex capable of spreading through the lung. Its major lipid components are phosphatidylglycerol (PG; 10%), phosphatidylcholine (PC; 40%) and dipalmitoylphosphatidylcholine (DPPC;40%). Although, BLES in combination with cathelicidins has shown promising results, the presence of BLES has also been shown to significantly reduce the ability of these peptides to kill bacteria.

Objectives

1) Determine the lipid components of BLES that are limiting the bactericidal effects of cathelicidins, 2) reconstitute BLES to reduce its inhibitory effect on the antimicrobial properties of cathelicidins, and 3) assess the spreading and bacterial killing of reformulated BLES/cathelicidin preparations at a distal site.

Hypothesis

A reformulated BLES will improve the bacterial killing of BLES/cathelicidin mixtures, without reducing spreading to distal sites in vitro.

Methods

Antimicrobial assays were performed against a lab strain of Pseudomonas aeruginosa for four cathelicidins in the presence of individual surfactant lipids. BLES was also supplemented with different lipids to generate different relative amounts of PG (5–40%), PC (20–70%) and DPPC (20–70%). These different versions of BLES were combined with cathelicidins for bacterial killing curves and assessment on our newly developed wet bridge transfer system. This in vitro system was utilized to assess spreading and bacterial killing at distal sites. P. aeruginosa was seeded to the distal well and cathelicidins alone or resuspended in a reformulated BLES were administered to the delivery well.

Results

At concentrations found in BLES, PG was the only lipid component to significantly inhibit the bacterial killing of all cathelicidins tested. Furthermore, all reformulated surfactant preparations with lower PG concentrations than BLES were shown to significantly enhance peptide function compared to BLES. Experiments performed on the wet bridge transfer system showed that altering BLES to limit PG content (6–9%) significantly enhanced bacterial killing in the distal dish for suspended cathelicidins compared to BLES/cathelicidin. However, reducing the PG content of BLES to 5% was shown to significantly inhibit its ability to spread across the wet bridge transfer system. Moreover, when combined with cathelicidins it was shown have significantly lower bacterial killing in the distal dish compared to BLES.

Discussion

These results suggest that PG is the major component of BLES inhibiting the bacterial killing properties of cathelicidins. Furthermore, the data from the wet bridge experiments indicated that altering the lipid composition of BLES to limit PG‐content creates a more effective cathelicidin/surfactant preparation. Therefore, future studies should utilize artificial surfactants with lower levels of PG to delivery cathelicidins to the peripheral airways. However, some PG may be needed for peptide transfer and normal surfactant function.

Support or Funding Information

Lawson Internal Research Fund

This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.