Characterization of Equine Platelet Lysate for Nebulization in the Horse

Platelet lysate (PL) demonstrates antimicrobial and anti-inflammatory properties and may offer potential for treatment of bacterial pneumonia in horses. It remains unknown whether nebulization represents a suitable method of administration of PL in horses. This study characterized particle size and flow rate of pooled equine PL nebulized using an equine-specific nebulizer (Flexivent). Protein composition and antimicrobial activity were compared before and after nebulization. Protein composition was evaluated according to growth factor, antimicrobial peptide and cytokine concentrations and proteomic analysis. To evaluate antimicrobial activity, bacterial growth inhibition [maximum growth (µmax); carrying capacity (K)] were determined for E.coli, Streptococcus equi subsp zooepidemicus and Rhodococcus equi (WT and MDR) using pre- and post-nebulized PL concentrations of 50%. Flow rate and median particle size were 0.8 ml/min and 4.991 µm with 52% of particles ≤ 5 µm. Cytokine, growth factor, and antimicrobial peptide concentrations and proteomic profiles were similar pre- and post-nebulization. For all bacteria, nebulization did not alter effect of PL on growth parameters. Negative effects of PL treatments on K were noted for S. zooepidemicus (p= 0.009 all) compared to BHI. No effect of PL was observed on µmax for S.zooepidemicus and on K and µmax for E.coli. For R. equi (WT and MDR), K and µ were positively affected by PL treatments (p≤ 0.05). We concluded that nebulization does not appear to meaningfully impact PL bacterial growth inhibition or protein composition. Further research is recommended to better characterize PL antimicrobial activity against clinically relevant pathogens and suitability for nebulization in horses.