Serum Sphingosine-1-Phosphate as Novel Prognostic and Predictive Biomarker for COVID-19 Severity and Morbidity and Its Implications in Clinical Management

Abstract

Background: Since December 2019, COVID-19 has widely spread throughout the world, causing thousands of deaths. Clinical characteristics of COVID-19 patients have been widely reported, but significative disease-associated biomarkers are needed. We aimed to evaluate the prognostic power of circulating sphingosine-1-phosphate (S1P) in COVID-19, to propose S1P as a novel prognostic and predictive biomarker. Methods: Clinical and blood parameters were investigated in 111 COVID-19 patients (COV) and 47 healthy subject (HLT), with a particular focus on patients who required intensive care unit (ICU) admission. We measured serum levels of S1P and its main transporter apolipoprotein M (apoM) by ELISA assay. Correlation with clinical and blood parameters were performed by Pearson correlations. Univariable and multivariable regression analysis were performed to assess the interaction between clinically significant factors and ICU admission. Further, Cox regression was used to evaluate the prognostic power of S1P for ICU admission and mortality. Findings: We reported statistically significant alterations of several blood parameters in COV, as an increase of white blood cells, neutrophil-to-lymphocyte ratio, ferritin, D-dimer and fibrinogen, and a decrease in hemoglobin, lymphocyte count and total proteins. Our major finding is the drop of serum S1P level in COV, strongly associated with the decrease of red blood cells, the major source of plasmatic S1P, and both apoM and albumin, the most important transporters of circulating S1P. The multivariable regression analysis revealed that S1P is the most important predictor for ICU admission (OR:39·45, [95%CI:1·51-1031·60]; p=0·027), and Cox proportional-hazards model demonstrated a high power of S1P in predicting patient’s outcome. Interpretation: COVID-19 patients showed a drastic decrease of serum S1P, suggesting that circulating S1P levels may be clinically used as negative biomarkers to predict severity/mortality of COVID-19. Taken together, our results suggest that restoring S1P at physiological level may represent a novel therapeutic strategy. Funding: Italian Ministry of Health. Declaration of Interests: All authors declare no competing interests. Ethics Approval Statement:This prospective, case-control study was approved by the Ethic Committee of Ospedale San Paolo in Milan, Lombardy, Italy (COST Action n.2020/ST/057).