suPAR links a dysregulated immune response to tissue inflammation and sepsis-induced acute kidney injury.

Acute kidney injury (AKI) secondary to sepsis results in poor outcomes and conventional kidney function indicators lack diagnostic value. Soluble urokinase plasminogen activator receptor (suPAR) is an innate immune-derived molecule implicated in inflammatory organ damage. We characterized the diagnostic ability of longitudinal serum suPAR levels to discriminate severity and course of sepsis-induced AKI (SI-AKI) in 200 critically ill patients meeting Sepsis-3 criteria. The pathophysiologic relevance of varying suPAR levels in SI-AKI was explored in a polymicrobial sepsis model in WT, (s)uPAR-knockout, and transgenic suPAR-overexpressing mice. At all time points studied, suPAR provided a robust classification of SI-AKI disease severity, with improved prediction of renal replacement therapy (RRT) and mortality compared with established kidney biomarkers. Patients with suPAR levels of greater than 12.7 ng/mL were at highest risk for RRT or death, with an adjusted odds ratio of 7.48 (95% CI, 3.00-18.63). suPAR deficiency protected mice against SI-AKI. suPAR-overexpressing mice exhibited greater kidney damage and poorer survival through inflamed kidneys, accompanied by local upregulation of potent chemoattractants and pronounced kidney T cell infiltration. Hence, suPAR allows for an innate immune-derived and kidney function-independent staging of SI-AKI and offers improved longitudinal risk stratification. suPAR promotes T cell-based kidney inflammation, while suPAR deficiency improves SI-AKI.

Detection of In Vivo Inflammasome Activation for Predicting Sepsis Mortality.

Sepsis is a severe life-threatening syndrome caused by dysregulated host responses to infection. Biomarkers that allow for monitoring the patient's immune status are needed. Recently, a flow cytometry-based detection of in vivo inflammasome activation by formation of cytoplasmic aggregates of ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) has been proposed. Here we report on the frequency of ASC-speck+ leukocytes correlating with the survival of sepsis. 25 patients with sepsis were sampled consecutively for 7 days. Blood, serum samples and patient data were collected according to the guidelines of the PredARRT-Sep-Trial. Flow cytometric analysis was performed on fresh whole blood samples to investigate the formation of ASC-specks in leukocyte subsets. Serum samples were analyzed for production of IL-1ß, IL-18 and additional inflammatory markers. ASC-speck formation was found to be increased in leukocytes from sepsis patients compared to healthy donor controls. The absolute number of ASC-speck+ neutrophils peaked on day 1. For monocytes, the highest percentage and maximum absolute number of ASC-speck+ cells were detected on day 6 and day 7. Inflammatory cytokines were elevated on day 1 and declined thereafter, with exception of IL-18. Survival analysis showed that patients with lower absolute numbers of ASC-speck+ monocytes (<1,650 cells/ml) on day 6 had a lower probability to survive, with a hazard ratio (HR) of 10.178. Thus, the frequency of ASC-speck+ monocytes on day 6 after onset of sepsis may serve to identify patients at risk of death from sepsis.

Cell Cycle Biomarkers and Soluble Urokinase-Type Plasminogen Activator Receptor for the Prediction of Sepsis-Induced Acute Kidney Injury Requiring Renal Replacement Therapy: A Prospective, Exploratory Study.

OBJECTIVES: Sepsis-induced acute kidney injury is the dominant acute kidney injury etiology in critically ill patients and is often associated with a need for renal replacement therapy. The indication and timing of renal replacement therapy are controversially discussed. We hypothesized that the product of the G1-cell cycle arrest biomarkers tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7 ([TIMP-2] × [IGFBP7]), and the soluble urokinase-type plasminogen activator receptor are of diagnostic value for the prediction of septic acute kidney injury courses requiring renal replacement therapy. DESIGN: In this prospective study, critically ill patients were enrolled immediately after the fulfillment of Sepsis-3 criteria. Urinary [TIMP-2] × [IGFBP7] levels over time and serum soluble urokinase-type plasminogen activator receptor levels once at inclusion were measured. The primary endpoint was the development of septic acute kidney injury with the need for renal replacement therapy. Area under the receiver operating characteristic curves, de Long's tests, and logistic regression models were calculated. SETTING: Two ICUs at Heidelberg University Hospital between May 2017 and July 2018. PATIENTS: One-hundred critically ill patients with positive Sepsis-3 criteria. INTERVENTIONS: None. MEASUREMENT AND MAIN RESULTS: Nineteen patients required renal replacement therapy. Diagnostic performance of urinary [TIMP-2] × [IGFBP7] improved over time with the highest area under the receiver operating characteristic curve of 0.89 (95% CI, 0.80-0.98) 24 hours after study inclusion. Soluble urokinase-type plasminogen activator receptor levels at inclusion showed an area under the receiver operating characteristic curve of 0.83 (0.75-0.92). The best discrimination ability for the primary outcome measure was achieved for [TIMP-2] × [IGFBP7] at 24 hours after inclusion by applying a cutoff value of greater than or equal to 0.6 (ng/mL)/1,000 (sensitivity 90.9, specificity 67.1). Soluble urokinase-type plasminogen activator receptor performed best by using a cutoff value of greater than or equal to 8.53 ng/mL (sensitivity 84.2, specificity 82.7). A combination of newly tested biomarkers with cystatin C resulted in a significantly improved diagnostic accuracy. Cystatin C in combination with [TIMP-2] × [IGFBP7] 24 hours outperformed all standard renal parameters (area under the receiver operating characteristic curve 0.93 [0.86-1.00]). CONCLUSIONS: [TIMP-2] × [IGFBP7] and soluble urokinase-type plasminogen activator receptor are promising biomarker candidates for the risk stratification of septic acute kidney injury patients with the need for renal replacement therapy.