TIP peptide inhalation in oleic acid-induced experimental lung injury: a post-hoc comparison

Challenges and perspectives in porcine model of acute lung injury using oleic acid

The oleic acid (OA) models of lung injury try to simulate the findings of human Acute Respiratory Distress Syndrome (ARDS). However, these models are difficult to replicate because they vary in terms of animals species, OA doses, time for establishment of lung injury, different observation periods and settings of mechanical ventilation. The objective of this study was to evaluate a protocol of administration of OA in lung injury model, challenges in its development and its effects on respiratory mechanics, hemodynamic changes, histology, gas exchange and mortality. We then submitted ten Large White pigs to acute lung injury through intravenous infusion of acid oleic in the pulmonary artery. The mortality of the model was 50%, due to an intense hemodynamic instability during OA administration, even with early use of vasoactive drugs. Three animals required additional doses of OA to achieve criteria for acute lung injury. Histology showed findings consistent with acute lung injury. However, more pulmonary edema was observed in lower segments than in upper segments of both lungs (p = 0.01). IL-6 and IL-8 were significantly increased compared to normal lungs (p < 0.05), and IL-6 showed higher levels in upper segments compared to lower segments (p = 0.03). Positive cells for Caspase 3 were present in all samples, localized mainly in respiratory epithelial cells and macrophages. In conclusion, this model shows histological findings of acute lung injury and inflammatory response similar to those of clinical ARDS, it presents high mortality, inconsistent reproducibility and hardly controlled hemodynamic instability.

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

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.

TIP peptide inhalation in experimental acute lung injury: effect of repetitive dosage and different synthetic variants

Background

Inhalation of TIP peptides that mimic the lectin-like domain of TNF-α is a novel approach to attenuate pulmonary oedema on the threshold to clinical application. A placebo-controlled porcine model of acute respiratory distress syndrome (ARDS) demonstrated a reduced thermodilution-derived extravascular lung water index (EVLWI) and improved gas exchange through TIP peptide inhalation within three hours. Based on these findings, the present study compares a single versus a repetitive inhalation of a TIP peptide (TIP-A) and two alternate peptide versions (TIP-A, TIP-B).

Methods

Following animal care committee approval ARDS was induced by bronchoalveolar lavage followed by injurious ventilation in 21 anaesthetized pigs. A randomised-blinded three-group setting compared the single-dosed peptide variants TIP-A and TIP-B as well as single versus repetitive inhalation of TIP-A (n = 7 per group). Over two three-hour intervals parameters of gas exchange, transpulmonary thermodilution, calculated alveolar fluid clearance, and ventilation/perfusion-distribution were assessed. Post-mortem measurements included pulmonary wet/dry ratio and haemorrhage/congestion scoring.

Results

The repetitive TIP-A inhalation led to a significantly lower wet/dry ratio than a single dose and a small but significantly lower EVLWI. However, EVLWI changes over time and the derived alveolar fluid clearance did not differ significantly. The comparison of TIP-A and B showed no relevant differences. Gas exchange and ventilation/perfusion-distribution significantly improved in all groups without intergroup differences. No differences were found in haemorrhage/congestion scoring.

Conclusions

In comparison to a single application the repetitive inhalation of a TIP peptide in three-hour intervals may lead to a small additional reduction the lung water content. Two alternate TIP peptide versions showed interchangeable characteristics.