Inhalation therapy with the synthetic TIP-like peptide AP318 attenuates pulmonary inflammation in a porcine sepsis model

Abstract

Background: The lectin-like domain of TNF-α can be mimicked by synthetic TIP peptides and represents an innovative pharmacologic option to treat edematous respiratory failure. TIP inhalation was shown to reduce pulmonary edema and improve gas exchange. In addition to its edema resolution effect, TIP peptides may exert some anti-inflammatory properties. The present study therefore investigates the influence of the inhaled TIP peptide AP318 on intrapulmonary inflammatory response in a porcine model of systemic sepsis.

Methods: In a randomized-blinded setting lung injury was induced in 18 pigs by lipopolysaccharide-infusion and a second hit with a short period of ventilator-induced lung stress, followed by a six-hour observation period. The animals received either two inhalations with the peptide (AP318, 2×1 mg kg(-1)) or vehicle. Post-mortem pulmonary expression of inflammatory and mechanotransduction markers were determined by real-time polymerase chain reaction (IL-1β, IL-6, TNF-α, COX-2, iNOS, amphiregulin, and tenascin-c). Furthermore, regional histopathological lung injury, edema formation and systemic inflammation were quantified.

Results: Despite similar systemic response to lipopolysaccharide infusion in both groups, pulmonary inflammation (IL-6, TNF-α, COX-2, tenascin-c) was significantly mitigated by AP318. Furthermore, a Western blot analysis shows a significantly lower of COX-2 protein level. The present sepsis model caused minor lung edema formation and moderate gas exchange impairment. Six hours after onset pathologic scoring showed no improvement, while gas exchange parameters and pulmonary edema formation were similar in the two groups.

Conclusion: In summary, AP318 significantly attenuated intrapulmonary inflammatory response even without the presence or resolution of severe pulmonary edema in a porcine model of systemic sepsis-associated lung injury. These findings suggest an anti-inflammatory mechanism of the lectin-like domain beyond mere edema reabsorption in endotoxemic lung injury in vivo.

Figure 1

Experimental protocol.

Figure 2

Pulmonary expression of inflammatory cytokines and enzymes. Intrapulmonary mRNA expression [mRNA copies] of inflammatory cytokines normalized to peptidylprolyl isomerase A (PPIA): IL-1β, IL-6, TNF-α, and iNOS. Significant intergroup differences indicated by P values.

Figure 3

COX-2 and mechanotransduction. Intrapulmonary mRNA expression [mRNA copies] of COX-2, amphiregulin and tenascin-c normalized to peptidylprolyl isomerase A (PPIA). COX-2 protein expression by Western Blot analysis. Significant intergroup differences indicated by P values.

Figure 4

Systemic hematological parameters and inflammatory cytokines. Time courses of systemic TNF-α, IL-6, lactate, leucocytes, and platelets. *Indicates P < 0.05 vs. baseline value, # P < 0.05 vs. Sepsis/VILI and × P < 0.05 vs. 3 h value. No significant intergroup differences. Sepsis/VILI values of TNF-α exceed the detection capacities of the available assays.

Figure 5

Gas exchange and respiratory mechanics. Time courses of PaO₂/FiO₂ and C_dyn. *P < 0.05 vs. Baseline. No intergroup differences.

Figure 6

Pathological assessment of the lungs. Global histopathological respectively macroscopic lung injury scoring and pulmonary wet to dry ratio. No significant intergroup differences.