Emerging toolset of three-dimensional pulmonary cell culture models for simulating lung pathophysiology towards mechanistic elucidation and therapeutic treatment of SARS-COV-2 infection.

The ongoing COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) poses a never before seen challenge to human health and the world economy. However, it is difficult to widely use conventional animal and cell culture models in understanding the underlying pathological mechanisms of COVID-19, which in turn hinders the development of relevant therapeutic treatments, including drugs. To overcome this challenge, various three-dimensional (3D) pulmonary cell culture models such as organoids are emerging as an innovative toolset for simulating the pathophysiology occurring in the respiratory system, including bronchial airways, alveoli, capillary network, and pulmonary interstitium, which provide a robust and powerful platform for studying the process and underlying mechanisms of SARS-CoV-2 infection among the potential primary targets in the lung. This review introduces the key features of some of these recently developed tools, including organoid, lung-on-a-chip, and 3D bioprinting, which can recapitulate different structural compartments of the lung and lung function, in particular, accurately resembling the human-relevant pathophysiology of SARS-CoV-2 infection in vivo. In addition, the recent progress in developing organoids for alveolar and airway disease modeling and their applications for discovering drugs against SARS-CoV-2 infection are highlighted. These innovative 3D cell culture models together may hold the promise to fully understand the pathogenesis and eventually eradicate the pandemic of COVID-19.

Toward an optimized strategy of using various airway mucus clearance techniques to treat critically ill COVID-19 patients

Coronavirus disease 2019 (COVID-19) caused by acute respiratory syndrome coronavirus 2 (SARS-Cov-2) is still threatening the human life and society throughout the world. For those critically ill patients, mechanical ventilation (MV) is essential to provide life support during treatment. However, both the virus infection and MV disrupt the balance between secretion and elimination of airway mucus and lead to mucus accumulation in the lung. Postmortem examination verified that the lungs in patients died of COVID-19 are indeed filled with sticky mucus, suggesting a great need to improve airway mucus clearance in critically ill COVID-19 patients. Therefore, it may be helpful to comprehensively review the current understanding regarding the changes of biochemical and rheological features of airway mucus associated with the disease, as well as the physiological principles and algorithm to decide airway clearance techniques suitable for the critically ill COVID-19 patients. Based on these considerations, optimized strategies may be developed to eliminate the airway mucus accumulated in the airways of critically ill COVID-19 patients.

Biomechanical issues of mechanical ventilation in Covid-19 therapy

The critically ill coronavirus disease 2019 (Covid-19) patients usually present acute respiratory distress syndrome (ARDS), or even acute respiratory failure, and require mechanical ventilation (MV) to provide support for breathing. However, clinical studies have found an extraordinarily high mortality rate (50%) for those Covid-19 patients who underwent MV. Considering the mechanical nature of MV, the high mortality rate is highly possible to be associated with mechanical stretch-induced lung injury during MV. Thus, it is imperative to understand the MV-induced pathological alterations in the respiratory system and corresponding mitigation measures in order to improve the therapy of critically ill Covid-19 patients. Ventilator-induced lung injury in therapy of critically ill Covid-19 patients involves several biomechanical factors and mechanisms, including changes in respiratory parameters, inflammatory cytokines storm, ciliary-mucus system, airway smooth muscle cells, lung fibrosis, and stretch-activated cell signaling. It is hoped that these biomechanical issues can be diligently investigated, so as to provide insights for optimizing the therapy for Covid-19 as well as other respiratory diseases.