Background: The incidence of acute kidney injury following severe sepsis is higher in the elderly. We hypothesized that microvascular endothelium is "primed" by aging and that sepsis represents a "second hit," resulting in more severe microvascular complications.
Methods: Three- and 18-months-old mice were intraperitoneally injected with 1,500 EU/g body weight lipopolysaccharide and sacrificed after 8 h. Flow cytometry and myeloperoxidase ELISA determined neutrophils in plasma. Quantitative reverse transcription polymerase chain reaction was used to analyze messenger ribonucleic acid levels of cell adhesion molecules P-selectin and E-selectin, vascular cell adhesion protein-1, intercellular adhesion molecule-1, angiopoietin receptor TIE-2, and angiopoietins Ang1 and Ang2. In kidney tissue we assessed neutrophil influx and E-selectin protein expression. Neutrophils were depleted with the monoclonal antibody NIMP.
Results: At basal conditions, microvascular endothelial cell activation status was similar in both groups, except for a higher Ang-2 expression (P < 0.05) in the kidney of aged mice. Lipopolysaccharide-induced increase in neutrophil count was higher in old (3.3-fold change) compared with young mice (2.2-fold change). Messenger ribonucleic acid analysis showed higher upregulation of P- and E-selectin (P = 0.0004, P = 0.0007) after lipopolysaccharide administration in kidneys of elderly mice, which was confirmed at the protein level for E-selectin. Renal neutrophil influx in lipopolysaccharide-treated aged mice was increased (2.5-fold induction in aged and 2.1-fold in young, P < 0.0001). Polymorphonuclear cell depletion exaggerated the lipopolysaccharide-induced kidney injury.
Conclusion: Ang-2 is increased in older mice, which might cause priming of the endothelial cells. Endothelium responded by a more extensive increase in expression of P- and E-selectin in older mice and increased polymorphonuclear cell influx.