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Background Analyses of blood biomarkers involved in the host response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral infection can reveal distinct biological pathways and inform development and testing of therapeutics for COVID-19. Our objective was to evaluate host endothelial, epithelial and inflammatory biomarkers in COVID-19. Methods We prospectively enrolled 171 ICU patients, including 78 (46%) patients positive and 93 (54%) negative for SARS-CoV-2 infection from April to September, 2020. We compared 22 plasma biomarkers in blood collected within 24 h and 3 days after ICU admission. Results In critically ill COVID-19 and non-COVID-19 patients, the most common ICU admission diagnoses were respiratory failure or pneumonia, followed by sepsis and other diagnoses. Similar proportions of patients in both groups received invasive mechanical ventilation at the time of study enrollment. COVID-19 and non-COVID-19 patients had similar rates of acute respiratory distress syndrome, severe acute kidney injury, and in-hospital mortality. While concentrations of interleukin 6 and 8 were not different between groups, markers of epithelial cell injury (soluble receptor for advanced glycation end products, sRAGE) and acute phase proteins (serum amyloid A, SAA) were significantly higher in COVID-19 compared to non-COVID-19, adjusting for demographics and APACHE III scores. In contrast, angiopoietin 2:1 (Ang-2:1 ratio) and soluble tumor necrosis factor receptor 1 (sTNFR-1), markers of endothelial dysfunction and inflammation, were significantly lower in COVID-19 (p Conclusions These studies demonstrate that, unlike other well-studied causes of critical illness, endothelial dysfunction may not be characteristic of severe COVID-19 early after ICU admission. Pathways resulting in elaboration of acute phase proteins and inducing epithelial cell injury may be promising targets for therapeutics in COVID-19.

Critically ill patients manifest many of the same immune features seen in coronavirus disease 2019 (COVID-19), including both “cytokine storm” and “immune suppression.” However, direct comparisons of molecular and cellular profiles between contemporaneously enrolled critically ill patients with and without severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are limited. We sought to identify immune signatures specifically enriched in critically ill patients with COVID-19 compared with patients without COVID-19. We enrolled a multisite prospective cohort of patients admitted under suspicion for COVID-19, who were then determined to be SARS-CoV-2-positive ( n = 204) or -negative ( n = 122). SARS-CoV-2-positive patients had higher plasma levels of CXCL10, sPD-L1, IFN-γ, CCL26, C-reactive protein (CRP), and TNF-α relative to SARS-CoV-2-negative patients adjusting for demographics and severity of illness (Bonferroni P value < 0.05). In contrast, the levels of IL-6, IL-8, IL-10, and IL-17A were not significantly different between the two groups. In SARS-CoV-2-positive patients, higher plasma levels of sPD-L1 and TNF-α were associated with fewer ventilator-free days (VFDs) and higher mortality rates (Bonferroni P value < 0.05). Lymphocyte chemoattractants such as CCL17 were associated with more severe respiratory failure in SARS-CoV-2-positive patients, but less severe respiratory failure in SARS-CoV-2-negative patients ( P value for interaction < 0.01). Circulating T cells and monocytes from SARS-CoV-2-positive subjects were hyporesponsive to in vitro stimulation compared with SARS-CoV-2-negative subjects. Critically ill SARS-CoV-2-positive patients exhibit an immune signature of high interferon-induced lymphocyte chemoattractants (e.g., CXCL10 and CCL17) and immune cell hyporesponsiveness when directly compared with SARS-CoV-2-negative patients. This suggests a specific role for T-cell migration coupled with an immune-checkpoint regulatory response in COVID-19-related critical illness.

RATIONALE: Several studies have identified host immune signatures that are associated with COVID-19. However, it is unclear whether these immune signatures are specific to COVID-19 or are merely reflective of illness severity. In vitro studies have demonstrated that human T-cell responses to SARS-CoV-2-specific antigens are mediated through interferon-gamma (IFN-γ). Methods: We prospectively enrolled a multi-site cohort of patients admitted to the ICU under suspicion for COVID-19 who were then determined to be SARS-CoV-2-positive (n = 82) or-negative (n = 97) by RT-PCR. We measured multiple molecular and cellular immune profiles from blood and endotracheal aspirates (ETAs) collected on ICU admission. Our primary analysis tested for associations between IFN-γ and interferon-inducible mediators (CXCL10 and soluble PD-L1 (sPD-L1)) in blood or ETAs and SARS-CoV-2 status. We then stratified our cohort into SARS-CoV-2-negative and-positive groups and tested for associations between interferon-inducible mediators and clinical outcomes and SARS-CoV-2-copy-number. We used cytometry time-of-flight (CyTOF) to simultaneously measure 39 cell surface and intracellular markers on peripheral blood mononuclear cells collected from a subset of patients with ARDS. We then compared immune cell signatures in subjects with vs. without SARS-CoV-2. Results: The mean APACHE III score was higher in SARS-CoV-2-negative vs.-positive subjects (80±30 vs. 69±29), but the groups were otherwise well-matched. SARS-CoV-2-positive subjects had higher plasma concentrations of IFN-γ, CXCL10, and sPD-L1 relative to SARSCoV-2-negative patients adjusting for age, sex, and severity of illness (all p ≤ 0.01). The levels of IL-6, TNF-α, IL-8, MCP-1, and IL-17A were not significantly different between the two groups. SARS-CoV-2-positive subjects also had higher CXCL10 concentrations in ETAs than SARS-CoV-2-negative subjects. Higher plasma concentrations of CXCL10 and sPD-L1 were associated with higher mortality (Table 1) and more severe respiratory disease (ventilator-free days (VFDs), ARDS) in SARS-CoV-2-positive, but not-negative, patients. In contrast, higher IL-6 was associated with a lower number of VFDs and ARDS in both groups. IFN-γ and CXCL10 (but not IL-6) were associated with SARS-CoV-2-copy-number. Using CyTOF, we found SARS-CoV-2-positive subjects had a lower proportion of CXCR3+ (CXCL10 receptor) T-cells, a higher proportion of PD-L1+ monocytes, and less T-cell and monocyte intracellular cytokine staining vs. SARS-CoV-2-negative patients. Conclusion: Our findings suggest interferon-inducible mediator responses and immune cell hypofunction are characteristic of critically ill subjects with SARS-CoV-2 compared with similar patients without SARS-CoV-2. Our identification of immune signatures that are associated with SARS-CoV-2 infection but are distinct from other forms of critical illness clarifies COVID-19 pathophysiology.

Rationale: Analyses of blood biomarkers involved in the host response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral infection can reveal distinct biological pathways and inform development and testing of therapeutics for COVID-19. Objective: To evaluate host endothelial, epithelial and inflammatory biomarkers in COVID-19Methods: We prospectively enrolled 169 ICU patients with suspicion of COVID-19 infection, including 78 (46%) patients positive and 91 (54%) negative for SARS-CoV-2 infection from April to September, 2020. We compared 22 plasma biomarkers in blood collected within 24 hours and 3 days after ICU admission. Measurement and Main Results: ICU patients with and without COVID-19 had similar rates of severe acute kidney injury, shock, thromboembolism and in-hospital mortality. Rates of ARDS were higher in COVID-19 (aRR = 5.9, 95% CI: 3.2-11.0). While concentrations of interleukin 6 and 8 were not different between groups, markers of epithelial cell injury (soluble receptor for advanced glycation end products, sRAGE) and acute phase proteins (serum amyloid A, SAA) were significantly higher in COVID-19 compared to non-COVID-19, adjusting for demographics and APACHE III scores (Figure 1). In contrast, angiopoietin 2:1 (Ang-2:1 ratio) and soluble tumor necrosis factor receptor 1 (sTNFR-1), markers of endothelial dysfunction and inflammation, were significantly lower in COVID-19 (Bonferroni corrected p

Additional file 1. Table S1: Coefficient of variation of plasma biomarkers. Table S2: Admission Diagnoses within Cohorts. Table S3: Day 1 plasma biomarkers at study enrollment between COVID-19 and non-COVID-19. Table S4: Plasma biomarkers restricted to patients with a primary ICU diagnosis of pneumonia or respiratory failure. Table S5: Trend in plasma biomarkers over Day 1 and 3 between COVID-19 and non-COVID-19. Table S6: Association of baseline biomarkers with ARDS. Table S7: Association of baseline biomarkers with severe AKI. Figure S1: Similar set of plasma biomarkers are different between critically ill patients with COVID-19 compared to without COVID-19 adjusting for receipt of corticosteroids.

BACKGROUND Serum creatinine concentrations (SCrs) are used to determine the presence and severity of acute kidney injury (AKI). SCr is primarily eliminated by glomerular filtration; however, most mechanisms of AKI in critical illness involve kidney proximal tubules, where tubular secretion occurs. Proximal tubular secretory clearance is not currently estimated in the intensive care unit (ICU). Our objective was to estimate the kidney clearance of secretory solutes in critically ill adults. METHODS We collected matched blood and spot urine samples from 170 ICU patients and from a comparison group of 70 adults with normal kidney function. We measured 7 endogenously produced secretory solutes using liquid chromatography–tandem mass spectrometry. We computed a composite secretion score incorporating all 7 solutes and evaluated associations with 28-day major adverse kidney events (MAKE28), defined as doubling of SCr, dialysis dependence, or death. RESULTS The urine-to-plasma ratios of 6 of 7 secretory solutes were lower in critically ill patients compared with healthy individuals after adjustment for SCr. The composite secretion score was moderately correlated with SCr and cystatin C (r = –0.51 and r = –0.53, respectively). Each SD higher composite secretion score was associated with a 25% lower risk of MAKE28 (95% CI 9% to 38% lower) independent of severity of illness, SCr, and tubular injury markers. Higher urine-to-plasma ratios of individual secretory solutes isovalerylglycine and tiglylglycine were associated with MAKE28 after accounting for multiple testing. CONCLUSION Among critically ill adults, tubular secretory clearance is associated with adverse outcomes, and its measurement could improve assessment of kidney function and dosing of essential ICU medications. FUNDING Grants from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK/NIH) K23DK116967, the University of Washington Diabetes Research Center P30DK017047, an unrestricted gift to the Kidney Research Institute from the Northwest Kidney Centers, and the Vanderbilt O’Brien Kidney Center (NIDDK 5P30 DK114809-03). The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript.

Background We previously identified two acute kidney injury (AKI) sub-phenotypes (AKI-SP1 and AKI-SP2) with different risk of poor clinical outcomes and response to vasopressor therapy. Plasma biomarkers of endothelial dysfunction (tumor necrosis factor receptor-1, angiopoietin-1 and 2) differentiated the AKI sub-phenotypes. However, it is unknown whether these biomarkers are simply markers or causal mediators in the development of AKI sub-phenotypes. Methods We tested for associations between single-nucleotide polymorphisms within the Angiopoietin-1, Angiopoietin-2, and Tumor Necrosis Factor Receptor 1A genes and AKI- SP2 in 421 critically ill subjects of European ancestry. Top performing single-nucleotide polymorphisms (FDR Results A genetic variant, rs2920656C > T, near ANGPT2 was associated with reduced risk of AKI-SP2 (odds ratio, 0.45; 95% CI, 0.31–0.66; adjusted FDR = 0.003) and decreased plasma angiopoietin-2 (p = 0.002). Causal inference analysis showed that for each minor allele (T) the risk of developing AKI-SP2 decreases by 16%. Plasma angiopoietin-2 mediated 41.5% of the rs2920656 related risk for AKI-SP2. Human kidney microvascular endothelial cells carrying the T allele of rs2920656 produced numerically lower levels of angiopoietin-2 although this was not statistically significant (p = 0.07). Finally, analyses demonstrated that angiopoietin-2 is minimally renally cleared in critically ill subjects. Conclusion Genetic mediation analysis provides supportive evidence that angiopoietin-2 plays a causal role in risk for AKI-SP2.

Additional file 1: Supplement Data File. Includes supplement tables referenced in the manuscript.