Bacteremia Does Not Affect Cellular Uptake of Ultrafine Particles in the Lungs of Rats

Abstract

To assess the effects of intra-abdominal bacteremia on lung cellular function in vivo, we used electron microscopy to quantify the uptake of 6 nm diameter, albumin-coated colloidal gold particles (overall diam. 20.8 nm) by cells in the lungs of rats made septic by the introduction of live bacteria (E.coli and B. fragilis) into their abdomens. Gold particles were instilled into the trachea 24 hr after bacteremia induction, and lungs were harvested and prepared for electron microscopy 24 hr later. Because bacteremia produces an increase in metabolism, we hypothesized that this might be associated with increased cellular uptake of these particles and also with increased permeability of the alveolar epithelial barrier to them, as bacteremia is also associated with lung injury. We quantified particle uptake by counting particle densities (particles/μm²) within type I and type II epithelial cells, capillary endothelial cells, erythrocytes and neutrophils in the lungs of five septic rats and five sham-sepsis controls. We also counted particle densities within organelles of these cells (nuclei, mitochondria, type II cell lamellar bodies) and within the alveolar interstitium. We found particles to be present within all of these compartments, although we found no differences in particle densities between bacteremic rats and sham-sepsis controls. Our results suggest that these 6 nm particles were able to freely cross cell and organelle membranes, and further suggest that this ability was not altered by bacteremia.