Surfactant protein A is a principal and oxidation-sensitive microbial permeabilizing factor in the alveolar lining fluid.
We have reported that surfactant protein A kills some Gram-negative organisms by increasing membrane permeability. In this study, we investigated the physiologic importance of this activity and the effect of oxidative stress on the antimicrobial functions of SP-A in vitro and in vivo. Concentrated bronchoalveolar lavage fluids from SP-A+/+ mice increased the permeability of the Escherichia coli K12 cell membrane to a greater extent than lavage from SP-A-/- animals. Similarly, calcium-dependent surfactant-binding proteins of SP-A+/+ mice increased membrane permeability more than those from SP-A-/- mice and produced greater zonal killing of agar-embedded bacteria in a radial diffusion assay. Exposure of human SP-A to copper-initiated surfactant phospholipid peroxidation or to free radicals generated by human neutrophils in vitro increased the level of SP-A-associated carbonyl moieties and blocked the permeabilizing function of the protein. We also found that exposure of mice to 90% O2 for 4 days, sufficient to lead to consumption of glutathione, oxidation of protein thiols, and accumulation of airspace protein-associated carbonyl moieties, blocked the permeabilizing activity of lavage fluid from SP-A+/+ mice. We conclude that SP-A is a major microbial permeablizing factor in lavage fluid and that oxidative stress inhibits the antibacterial activity of SP-A by a mechanism that includes oxidative modification and functional inactivation of the protein.
Kuzmenko
Alexander I
AI
Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Cincinnati School of Medicine, Cincinnati, Ohio 45267-0564, USA.
Wu
Huixing
H
Wan
Sijue
S
McCormack
Francis X
FX
D000818:Animals; D001992:Bronchoalveolar Lavage Fluid; D002118:Calcium / Q000378:metabolism; D037222:Collectins / Q000378:metabolism; D004927:Escherichia coli Infections / Q000378:metabolism*; D006801:Humans; D018496:Hyperoxia / Q000378:metabolism; D015227:Lipid Peroxidation; D051379:Mice; D008817:Mice, Mutant Strains; D010084:Oxidation-Reduction; D010539:Permeability; D011014:Pneumonia / Q000378:metabolism*; D011649:Pulmonary Alveolar Proteinosis / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000378:metabolism* / Q000382:microbiology; D037662:Pulmonary Surfactant-Associated Protein A / Q000235:genetics / Q000378:metabolism*
D037222:Collectins; D037662:Pulmonary Surfactant-Associated Protein A; D002118:Calcium