Abstract

Levels of circulating angiopoietin-2 (Ang-2) increase in sepsis, raising the possibility that Ang-2 acts as a modulator in the sepsis cascade. To investigate this, experimental sepsis was induced in male C57BL6 mice by a multidrug-resistant isolate of Pseudomonas aeruginosa; survival was determined along with neutrophil tissue infiltration and release of proinflammatory cytokines. Survival was significantly increased either by pretreatment with recombinant Ang-2 2 h before or treatment with recombinant Ang-2 30 min after bacterial challenge. Likewise, Ang-2 pretreatment protected against sepsis-related death elicited by Escherichia coli; however, Ang-2 failed to provide protection in lipopolysaccharide (LPS)-challenged mice. The survival advantage of Ang-2 in response to P. aeruginosa challenge was lost in tumor necrosis factor (TNF)-deficient mice or neutropenic mice. Infiltration of the liver by neutrophils was elevated in the Ang-2 group compared with saline-treated animals. Serum TNF-α levels were reduced by Ang-2, whereas those of interleukin (IL)-6 and IL-10 remained unchanged. This was accompanied by lower release of TNF-α by stimulated splenocytes. When applied to U937 cells in vitro, heat-killed P. aeruginosa induced the secretion of IL-6 and TNF-α; low levels of exogenous TNF-α synergized with P. aeruginosa. This synergistic effect was abolished after the addition of Ang-2. These results put in evidence a striking protective role of Ang-2 in experimental sepsis evoked by a multidrug-resistant isolate of P. aeruginosa attributed to modulation of TNF-α production and changes in neutrophil migration. The protective role of Ang-2 is shown when whole microorganisms are used and not LPS, suggesting complex interactions with the host immune response.