COVID-19 is a novel coronavirus that can cause severe and potentially fatal respiratory infections. COVID-19 has many similarities to previously seen coronaviruses, such as those that caused the Middle Eastern Respiratory Syndrome (MERS) that emerged in 2011 and the Severe Acute Respiratory Syndrome (SARS) in 2002-2003. Based on early reports, many patients may present with mild to moderate respiratory symptoms, but approximately 20% developed severe symptoms. These severe cases developed a multitude of life threatening complications, like acute lung injury (ALI), acute respiratory distress syndrome (ARDS), and shock.~An early investigation into the patients with severe presentations, revealed high levels of inflammatory cytokines like interleukin 2 (IL-2), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), and monocyte chemoattractant protein 1 (MCP-1). This upregulation of inflammatory cytokines, also referred to as a cytokine storm, is similar to the innate immune response triggered by the previous coronaviruses.5,6 The increased production of these cytokines is the expected anti-viral response of the innate immune system, which is trigged by viral RNA replication. Viral replication triggers downstream inflammatory signaling cascades like NF-κB and IRF3 leading to increased neutrophil and monocyte-macrophages infiltrating the tissue. While effective against viral infection, this process is also believed to be responsible for the development of the significant respiratory complications associated with COVID-19.~ALI and ARDS are not unique to COVID-19 and develop with many viral respiratory infections. Several therapeutic strategies have been evaluated in ALI and ARDS and demonstrated benefit outside of the current pandemic. Heparin, a commonly used anticoagulant, has been shown to exhibit anti-inflammatory properties within the respiratory system. An in vitro study of heparin in a pulmonary cell model of ALI found that heparin significantly inhibited the NF-κB pathway. This inhibition led to a reduced levels of IL-6 and TNF-α in human alveolar macrophages exposed to an E. coli lipopolysaccharide to simulate inflammatory ALI. Additionally, heparin significantly reduced IL-6, TNF-α, and MCP-1 in human alveolar type II cell models. No increases in necrosis or apoptosis were observed.~In addition to these immunomodulation effects, heparin is primarily an anticoagulant and systemic administration carries a risk of bleeding. Due to this, several investigations were conducted in animal models and in humans to determine if administering the heparin via nebulization could take advantage of the immunomodulation, without increasing the risk of bleeding. Nebulized heparin was studied in a rat model of ARDS and was observed to attenuate ALI through reduction of pro-coagulant and pro-inflammatory pathways. Significant reductions in IL-6 and TNF-α were observed. Additionally, reductions in the expression of NF-κB were observed in the alveolar macrophages.~Several clinical investigations in humans with ARDS have also been completed. In a randomized, placebo controlled study of 60 patients with severe ARDS, patients were randomized to nebulized heparin, streptokinase and placebo. Patients in the heparin group received 10,000 units via nebulizer every 4 hours and had significant improvements in their ARDS by day 8. No effect on systemic coagulation markers like APTT and INR were observed. Additionally, no major bleeding events or blood transfusions were observed. A second, randomized placebo controlled trial of 50 patients requiring more than 48 hours of mechanical ventilation was conducted to determine the possible benefit of nebulized heparin. Patients with ALI that received nebulized heparin had a significant reduction in the time on the ventilator as compared to placebo. Patients that received heparin had higher APTT values than those that received placebo, but no significant bleeding events occurred. This study utilized a heparin dose of 25,000 units every 4 hours, which may explain the difference between the laboratory effects in the two human studies.~Heparin has demonstrated the ability to reduce the inflammatory cytokines believed to be responsible for the development of ALI and ARDS in COVID-19 and it may prove to be beneficial in this patient population. When administered via nebulization, no adverse effects were observed in the previously conducted studies and may provide a safe therapeutic option to improve the outcomes of patients with COVID-19 related ALI and ARDS.
Randomized, placebo controlled study to determine if nebulized heparin may reduce the severity of lung injury caused by the novel coronavirus, also known as COVID-19