Abstract
Background: Coronavirus disease-19 (COVID-19) is an acute respiratory illness caused by the SARS-COV-2 virus. Patients with COVID-19 infection can present with thrombosis in the setting of inflammation (thromboinflammation), presumably from endothelial dysfunction, or "endotheliopathy".
Yu et al demonstrated in vitro that the spike protein subunit of SARS-COV2 acts as a potent activator of the alternative complement pathway (AP), one of three complement pathways within the innate immune system. Satyam et alreported the deposition of complement components on lung tissue of patients who succumbed to COVID-19, consistent with activation of classical and alternate pathways. These studies suggest complement dysregulation potentially causing endotheliopathy in COVID-19 patients.
Thrombomodulin (TM) is an endothelial glycoprotein that plays two crucial roles in maintaining a healthy endothelium - as a natural anticoagulant and a negative regulator of complement. TM shed into the circulation due to endothelial injury can be measured in the plasma as soluble TM (sTM). Goshua et al showed elevated sTM in an adult cohort of patients with COVID-19. However, it is yet to be demonstrated if there is any correlation between endothelial injury and AP activation in COVID-19, or if either play a role in clinical outcome in the pediatric population.
Objective: To 1) assess endothelial injury and AP activation in a cohort of critically ill pediatric patients with COVID-19 by measuring sTM and Ba (an AP activation product); 2) determine the correlation between endothelial injury and AP activation; and 3) analyze the utility of sTM and Ba in predicting pediatric clinical outcomes.
Methods:
We collected plasma samples of patients admitted to the Pediatric Intensive Care Unit and found to be positive for SARS-CoV-2 between Dec 2, 2020 and Jan 22, 2021 at Texas Children's Hospital. For controls, we collected plasma samples from pediatric patients undergoing preoperative clearance, all at their baseline state of health.
sTM levels and Ba levels were measured in plasma samples using commercially available TM and Ba ELISA kits. sTM greater than 7.6 ng/ml (based on the assay range in adults) and Ba greater than 1080 ng/ml (based on data from adult healthy controls) were considered elevated.
Data regarding demographics, length of ICU stay, clinical indicators of end organ damage- mechanical ventilation, dialysis, use of vasopressors, ECMO, mortality were obtained retrospectively via chart review. Inclusion criteria included all patients with a positive SARS-COV2 PCR admitted to the ICU. Exclusion criteria was age greater than 21 years, pregnant female, patients with known inflammatory or complement-mediated disorders.
Statistical analysis: For sTM and Ba levels between control and COVID-19 patients, mean +/- standard deviation was calculated and significance determined with an unpaired t-test. Fischer exact test, Wilcoxon rank sum and Pearson product-moment correlation tests were used for statistical analysis of clinical outcomes as appropriate. A p-value <0.05 was considered statistically significant.
Results:
A total of 38 control patients and 33 COVID-19 patients were enrolled. Ba and sTM levels were both significantly higher in the COVID-19 pediatric patients compared to the controls (Fig. 1). Within the COVID-19 patient cohort, 61% (n=20) had elevated sTM and 42% (n=14) had elevated Ba levels. There was a moderately positive correlation between sTM and plasma Ba levels in the COVID-19 cohort (Fig. 2).
Within the COVID-19 patients' cohort, though higher Ba levels were not associated with an increased rate of intubation, they were associated with an increased duration of mechanical ventilation (p=.039) for those intubated (Table 1). Elevated sTM was associated with increased vasopressor use (p=.011). Although other clinical outcome variables did not reach statistical significance likely owing to small numbers, overall trend indicated worse outcomes in patients with elevated sTM.
Conclusions:
Our findings are consistent with the hypothesis that SARS-COV-2 activates AP and causes endothelial injury in children. The positive correlation between sTM and Ba suggest interplay between inflammation, coagulation and endotheliopathy supporting thromboinflammation in COVID-19. Higher sTM and Ba levels indicated worse clinical outcomes in children, but larger studies are needed to confirm our findings.
Sartain: Alexon Pharamaceuticals: Membership on an entity's Board of Directors or advisory committees.
