Changes in surface activity of lung surfactant and bronchoalveolar cell profile upon COVID-19-related Acute Respiratory Distress Syndrome

Abstract

A contribution of Lung Surfactant (LS) inactivation to COVID-19-related ARDS (cvARDS) has been argued, but not been clearly demonstrated to date. In the present study, we have characterised the extent of lung neutrophil infiltration along with the surface-active properties and protein composition of LS in bronchoalveolar lavages (BALs) collected from 12 cvARDS patients. A control group of 9 subjects without respiratory diseases was also enrolled.

BAL cell sorting was performed by flow cytometry. The adsorption of LS at the air-liquid interface was assessed by Surfactant Adsorption Test (SAT), whereas the level of surfactant hydrophobic proteins was measured by Western Blot analysis. Results were normalised by phosphatidylcholine (PC) total amount.

Significant increase in neutrophil [61.3(47.5-84.6)% vs 1.6(0.9-4.9)%, p<0.0001] and decrease in macrophage percentages [13.6(6.1-28.9)% vs 90.8(87.1-92-6)%, p<0.0001] of total BAL cells were detected in cvARDS patients. A lower overtime LS adsorption/accumulation at the air-liquid interface was also observed in those patients compared to the control group from 60min onward [14003(10232-19736) vs 24501(16386-28489) RFU, p=0.0471]. Moreover, cvARDS patients under the acute phase showed the lowest surfactant activity at the end of SAT (12191(11588-20159) RFU, p=0.048). An increase in both SP-B and SP-C/PC was also evident in cvARDS BALs.

Here, we report for the first time on the reduction of LS surface-active properties during the acute period and even under the recovery phases of cvARDS. This may confirm how LS inactivation may be involved in both early and late consequences of severe cvARDS.