Lipopolysaccharide protection from oxygen toxicity: effect on rat pulmonary selectins.

Sublethal doses of LPS result in increased tolerance to high concentrations of oxygen and this is associated with decreased pulmonary inflammation in a rat model. To investigate the mechanism of decreased neutrophil influx into the lung in this model, we measured levels of mRNA in the lung for the endothelial adhesion molecules, E-selectin and P-selectin. Immunostaining for E-selectin protein was also done in rat lungs, as well as measurement of soluble L-selectin in the blood. These levels were measured in the lungs of adult rats injected with 0.5 mg/kg LPS or placebo at 0 and 24 h and exposed to > 95% O2 for 60 h. Oxygen exposure resulted in significant increases in both E- and P-selectin mRNA and in E-selectin protein after 60 h. LPS resulted in an early rise in E-selectin protein followed by a decline to less than control (saline/O2) levels at 60 h. Messenger RNA for E-selectin followed a similar trend, although there were no differences at 60 h between LPS and control groups exposed to O2. P-selectin mRNA expression did not significantly differ between LPS and control O2 groups. Soluble L-selectin levels decreased by 6 h after LPS infusion and were significantly lower than saline/O2 controls through 24 h, suggesting binding to endothelium. In conclusion, the decrease in E-selectin expression on the surface of pulmonary endothelium after LPS could contribute to decreased inflammation in this model of oxygen toxicity. Soluble L-selectin may serve a further anti-inflammatory role after LPS infusion by binding to pulmonary endothelium.

Neutrophil adhesion molecule expression in the developing neonatal rat exposed to hyperoxia.

Neonatal rats have an increased tolerance to hyperoxia, which is associated with a diminished pulmonary inflammatory response compared with adults. To investigate this differing response, expression of the neutrophil adhesion molecules, L-selectin and CD18, and levels of soluble L-selectin, were examined using flow cytometry and sandwich enzyme-linked immunosorbent assay on air-exposed neonatal rat neutrophils at 0-24 and 72 h and 7, 10, 14, and 21 d of age compared with the adult and after exposure to hyperoxia (>/= 98% O2) for 56 h in adults and for 72 h and 7 d in neonates. Expression of L-selectin in 0-24-h neonates was similar to adults, but was significantly lower than adults at 72 h and 7 d (P = 0.011). Soluble L-selectin levels were significantly higher than those in adults in the 0-24- and 72-h neonates (P < 0.001). CD18 expression in unstimulated and activated neutrophils of neonatal rats was higher at 0-24 h than in the adult (P < 0.001), but thereafter did not differ from adults. After hyperoxic exposure, L-selectin did not differ between the exposure groups but soluble L-selectin tended to increase in neonates after 7 d of O2 exposure Finally, CD18 was significantly higher after hyperoxic exposure of the adult (P = 0.008), but did not change with oxygen exposure in the neonate. Based on these findings, we speculate that differences between neonatal and adult rats in expression of L-selectin may contribute to delayed oxygen toxicity in neonatal rats.

Endotoxin protection from oxygen toxicity: effect on pulmonary neutrophils and L-selectin.

The mechanisms by which sublethal doses of endotoxin protect against hyperoxic lung injury are not completely understood. We hypothesized that endotoxin treatment would result in a decreased inflammatory response to hyperoxia and that this would be accompanied by activation of neutrophils (as evidenced by loss of L-selectin) in the peripheral circulation. Adult rats were injected with endotoxin 0.5 mg/kg prior to and 24 hr after onset of exposure to > or = 98% O2. After 56 hr of hyperoxia, pulmonary neutrophils were lower in the O2/endotoxin group compared to O2 controls as measured by myeloperoxidase in lung homogenates and neutrophil counts in bronchoalveolar lavage fluid. Circulating neutrophils were also significantly lower in the O2/endotoxin group compared to O2 controls at 56 hr. Expression of the neutrophil adhesion molecule, L-selectin, was lower at 4 and 24 hr in the endotoxin-treated rats compared to O2 controls. There were no differences at 48 hr. Expression of CD18 rose significantly in the O2/endotoxin group after 4 hr, but thereafter did not differ from O2 controls. In summary, endotoxin protection from O2 toxicity was associated with reduced neutrophils in the lung and a loss of L-selectin from peripheral blood neutrophils.