Neutrophil extracellular trap (NET) degradation attenuates acute lung injury and protects mice from ricin-induced acute respiratory distress syndrome (ARDS)

ARDS is a life-threatening respiratory condition associated with pulmonary vascular hyperpermeability and loss of aerated lung tissue. Ricin is a plant-toxin derived from the seeds of Ricinus communis, irreversibly inactivates ribosomes and arrests protein synthesis. Pulmonary exposure to ricin represents a bona fide model for ARDS, is characterized by pulmonary inflammation with massive neutrophil recruitment and severe disruption of the alveolar-capillary barrier leading to pulmonary edema, compromised gas exchange and respiratory failure. We have shown that upon ricin exposure, neutrophil infiltration into lungs, a hallmark of ARDS, mediate proteolysis of junction proteins. Recently, there is an increasing concern about the deleterious effect of NETs in sterile inflammation, such as in ricin case. During NETosis, PAD4 drives histone citrullination and chromatin decondensation. Decondensed chromatin decorated with citrullinated histones (citH3) and cytoplasmic granular enzymes, such as MPO is expelled from the neutrophil. Herein, we show increasing levels of PAD4, citH3 and MPO in the BALF of ricin exposed mice. BALF neutrophils efficiently produced NETs which were associated with MPO and citH3. Immunohistology of lung sections upon ricin exposure demonstrated propagating NETosis. Treatment of ricin exposed mice with recombinant DNase, targeted against NET-associated extracellular DNA, administrated with anti-ricin antibodies, dramatically decreased the level of extracellular DNA and proinflammatory cytokines in the lungs and conferred higher protection levels to mice in comparison to sole administration of antitoxin. This data highlights the potential clinical benefit of NET inhibiting drugs in ARDS.