Lack of durable protection against cotton smoke‐induced acute lung injury in sheep by nebulized single chain urokinase plasminogen activator or tissue plasminogen activator

Abstract

Background Airway fibrin casts are clinically important complications of severe inhalational smoke-induced acute lung injury (ISIALI) for which reliable evidence-based therapy is lacking. Nebulized anticoagulants or a tissue plasminogen activator; tPA, has been advocated, but airway bleeding is a known and lethal potential complication. We posited that nebulized delivery of single chain urokinase plasminogen activator, scuPA, is well-tolerated and improves physiologic outcomes in ISIALI. To test this hypothesis, we nebulized scuPA or tPA and delivered these agents every 4 h to sheep with cotton smoke induced ISIALI that were ventilated by either adaptive pressure ventilation/controlled mandatory ventilation (APVcmv; Group 1, n = 14) or synchronized controlled mandatory ventilation (SCMV)/limited suctioning; Group 2, n = 32). Physiologic readouts of acute lung injury included arterial blood gas analyses, PaO 2 /FiO 2 ratios, peak and plateau airway pressures, lung resistance and static lung compliance. Lung injury was further assessed by histologic scoring. Biochemical analyses included determination of antigenic and enzymographic uPA and tPA levels, plasminogen activator and plasminogen activator inhibitor-1 activities and d -dimer in bronchoalveolar lavage (BAL). Plasma levels of uPA, tPA antigens, d -dimers and α-macroglobulin-uPA complex levels were also assessed. Results In Group 1, tPA at the 2 mg dose was ineffective, but at 4 mg tPA or scuPA, the PaO 2 /FiO 2 ratios, peak/plateau pressures improved during evolving injury (p < 0.01) without significant differences at 48 h. To improve delivery of the interventions, the experiments were repeated in Group 2 with limited suctioning/SCMV, which generally increased PAs in (BAL). In Group 2, tPA was ineffective, but scuPA (4 or 8 mg) improved physiologic outcomes (p < 0.01) and plateau pressures remained lower at 48 h. Airway bleeding occurred at 8 mg tPA. BAL plasminogen activator (PA) levels positively correlated with physiologic outcomes at 48 h. Conclusions Physiologic outcomes improved in sheep in which better delivery of the PAs occurred. The benefits of nebulized scuPA were achieved without airway bleeding associated with tPA, but were transient and largely abrogated at 48 h, in part attributable to the progression and severity of ISIALI. Electronic supplementary material The online version of this article (10.1186/s40169-018-0196-3) contains supplementary material, which is available to authorized users.

Perfluorochemical‐facilitated plasminogen activator delivery to the airways: A novel treatment for inhalational smoke‐induced acute lung injury

“…Animals were managed according to the Guiding Principles in the Care and Use of Animals of the National Institutes of Health. Spontaneously breathing anesthetized adult female merino sheep were instrumented and exposed to cotton smoke‐induced ISALI (n = 36; 30‐45 kg; 6/group), as previously described 7,26 . Briefly, the sheep were surgically prepared for vascular access, pressure monitoring, blood sampling, and thermodilution cardiac output measurements under anesthesia and analgesia.…”

“…The experimental schedule is shown in Figure 1. The animals were supported with time‐cycled (20 br/min), volume‐controlled (12 mL/kg), pressure limited (35/5 cmH 2 O) mechanical ventilation (Hamilton G5 ventilator; Hamilton Medical, Inc., Reno, NV) with heated (33°C)/humidified inspired gas for a total of 48 h while conscious, as we previously reported 7,26 …”

“…We found that high‐dose nebulized tPA delivery was confounded by airway bleeding complications, while scuPA was well tolerated and supported transient improvement in gas exchange and lung mechanics. The better response to scuPA appeared to relate to its relative resistance to plasminogen activator inhibitor (PAI‐1) and ability to form bioactive complexes amenable to low‐grade release of uPA for up to 24 h 7,8 . However, neither of the aerosolized interventions achieved durable reduction in cast burden or improvements in physiologic responses in this severe lung injury model 7 …”

“…We inferred that smoke‐induced local impairment of fibrinolytic activity contributes to deposition and persistence of airway casts. We used a well‐established sheep model of cotton ISALI and investigated aerosolized delivery of tissue plasminogen activator (tPA) or single‐chain urokinase plasminogen activator (scuPA) in saline 7 . We found that high‐dose nebulized tPA delivery was confounded by airway bleeding complications, while scuPA was well tolerated and supported transient improvement in gas exchange and lung mechanics.…”

“…Building on our experience with PFC biomedical applications, development of PFC/drug suspensions for intrapulmonary drug administration, as well as extensive experience with the sheep model of ISALI, 3,4,7,25‐27 we also hypothesized that PFC delivery of PA agents mitigates the airway cast formation in ISALI. On the basis of our previous findings using the same sheep model of ISALI, we inferred that better delivery of scuPA using PFC would more effectively improve outcomes by virtue of resistance to PAI‐1 and durable release of PA activity 7,8 . With more effective local PA delivery, we postulated that cast management would be improved and result in sustained physiologic improvement for the 48‐h study period.…”