Activation of Sphingomyelinase-Ceramide-Pathway in COVID-19 Purposes Its Inhibition for Therapeutic Strategies

Abstract

Effective treatment strategies for severe coronavirus disease (COVID-19) remain scarce. Hydrolysis of membrane-embedded, inert sphingomyelin by stress responsive sphingomyelinases is a hallmark of adaptive responses and cellular repair. As demonstrated in experimental and observational clinical studies, the transient and stress-triggered release of a sphingomyelinase, SMPD1, into circulation and subsequent ceramide generation provides a promising target for FDA-approved drugs. Here, we report the activation of sphingomyelinase-ceramide pathway in 23 intensive care patients with severe COVID-19. We observed an increase of circulating activity of sphingomyelinase with subsequent derangement of sphingolipids in serum lipoproteins and from red blood cells (RBC). Consistent with increased ceramide levels derived from the inert membrane constituent sphingomyelin, increased activity of acid sphingomyelinase (ASM) accurately distinguished the patient cohort undergoing intensive care from healthy controls. Positive correlational analyses with biomarkers of severe clinical phenotype support the concept of an essential pathophysiological role of ASM in the course of SARS-CoV-2 infection as well as of a promising role for functional inhibition with anti-inflammatory agents in SARS-CoV-2 infection as also proposed in independent observational studies. We conclude that large-sized multicenter, interventional trials are now needed to evaluate the potential benefit of functional inhibition of this sphingomyelinase in critically ill patients with COVID-19.

Keywords: FIASMA; ceramide; drug repurposing; molecular biology of critical care; molecular markers; organ failure; sphingomyelinase.

Figure 1

Heatmap of spingolipids (SM and ceramides) as well as ASM activity either in (A) serum and (B) RBC. Shown are hierarchical cluster analyses from data obtained by monitoring the profile of sphingomyelins and ceramides as well as ASM activity (measured in serum samples). Specimen of sphingolipids are given in rows, individual patients samples in columns comparing patients (P1 –P23, marked in green) and healthy controls (HC 1-6, gray). Color code: increase in sphingolipid content is given in red, decrease in blue. Distance measure is given in euclidian manner.

Figure 2

Reprogramming of ceramide generation. Variation of ceramide profile either in RBC (A) or serum (B) in patients with COVID-19 compared to healthy volunteers. Principal component analysis (PCA) based on concentration profile of six ceramide specimen (16:0, 18:0, 20:0, 22:0, 24:0, 24:1) that passed the quality screen. Each circle represents the centroid of all samples in the representative group at day 1 of intensive care of COVID-19 patients). Healthy controls are given as asterisks, patients in triangles.

Figure 3

Ceramide profile in lipid extracts obtained from RBC and from serum samples. In patients with COVID-19, ceramide synthesis is increased in all specimen passing quality screen in RBC, and nearly in all investigated in serum (one exception: 24:0). Total amount of ceramide specimen is differing as expected between serum and RBC, absolute values are given in Table 3 . Statistical analysis was performed using Mann-Whitney U-Test and p-values <0.05 were considered to be significant. COVID-19 vs. healthy controls: *p < 0.05; **p < 0.01; ***p < 0.001. Exact parameters indicating statistical difference area also given in Table 2 .

Figure 4

Activity levels of acid sphingomyelinase (ASM) in serum samples. Shown are medians with interquartile ranges of ASM activity levels from 23 severe COVID-19 patients and six volunteers as healthy controls, measured in separate aliquots used for ceramide profiling. Statistical significance was tested using the Mann-Whitney U-test; statistical difference is indicated by asterisks: ***p < 0.0001.