Comparison of the effect of LPS and PAM3 on ventilated lungs

Abstract

Background: While lipopolysaccharide (LPS) from Gram-negative bacteria has been shown to augment inflammation in ventilated lungs information on the effect of Gram-positive bacteria is lacking. Therefore the effect of LPS and a lipopetide from Gram-positive bacteria, PAM3, on ventilated lungs were investigated.

Methods: C57/Bl6 mice were mechanically ventilated. Sterile saline (sham) and different concentrations of LPS (1 microg and 5 microg) and PAM3 (50 nM and 200 nM) were applied intratracheally. Lung function parameters and expression of MIP-2 and TNFalpha as well as influx of neutrophils were measured.

Results: Mechanical ventilation increased resistance and decreased compliance over time. PAM3 but not LPS significantly increased resistance compared to sham challenge (P < 0.05). Both LPS and PAM3 significantly increased MIP-2 and TNFalpha mRNA expression compared to sham challenge (P < 0.05). The numbers of neutrophils were significantly increased after LPS at a concentration of 5 microg compared to sham (P < 0.05). PAM3 significantly increased the numbers of neutrophils at both concentrations compared to sham (P < 0.05).

Conclusions: These data suggest that PAM3 similar to LPS enhances ventilator-induced inflammation. Moreover, PAM3 but not LPS increases pulmonary resistance in ventilated lungs. Further studies are warranted to define the role of lipopetides in ventilator-associated lung injury.

Figure 1

Relative changes in resistance (A) and compliance (B) during mechanical ventilation alone and after challenge with sterile saline (sham), LPS (1 μg and 5 μg) and PAM3 (50 nM and 200 nM). Mean values are shown.

Figure 2

Relative changes of lung function parameters from time of stimulation (30 min) to the end of ventilation (120 min). A: Resistance (R) and tissue damping (G) significantly increased after PAM3 (P < 0.05) but not in the other groups. No significant change was observed for Newtonian resistance (Rn) (P > 0.05). B: Elastance (H) significantly increased with PAM3 (P < 0.05). C: Compliance (C) was significantly decreased after stimulation with PAM3 (P < 0.05).

Figure 3

MIP-2 (A) and TNFα (B) gene expression in the mouse lung of spontaneously breathing animals (w/o, without mechanical ventilation) and mechanical ventilated animals without challenge (control), with intratracheal saline challenge (sham) and with challenge with LPS or PAM3 at different doses. Bars indicate mean+SEM. *: P < 0.05 vs spontaneously breathing mice. **: P < 0.05 vs control. +: P < 0.05 vs sham. § P < 0.05 vs PAM3 challenge.

Figure 4

Numbers of polymorphonuclear cells (PMN) per high powered field in the mouse lung of spontaneously breathing animals (w/o, without mechanical ventilation) and mechanical ventilated animals without challenge (control), with intratracheal saline challenge (sham) and with challenge with LPS or PAM3 at different doses. Bars indicate mean+SEM. *: P < 0.05 vs sham.

Figure 5

Histology sections of mouse lungs with ventilation alone (A), after sham challenge (B), after LPS challenge (5 μg) (C), and after PAM3 challenge (200 nM) (D). HE staining. Original magnification ×100.