Acid sphingomyelinase (ASM) and COVID-19: A review of the potential use of ASM inhibitors against SARS-CoV-2.

In the last 2 years, different pharmacological agents have been indicated as potential inhibitors of SARS-CoV-2 in vitro. Specifically, drugs termed as functional inhibitors of acid sphingomyelinase (FIASMAs) have proved to inhibit the SARS-CoV-2 replication using different types of cells. Those therapeutic agents share several chemical structure characteristics and some well-known representatives are fluoxetine, escitalopram, fluvoxamine, and others. Most of the FIASMAs are primarily used as effective therapeutic agents to treat different pathologies, therefore, they are natural drug candidates for repositioning strategy. In this review, we summarize the two main proposed mechanisms mediating acid sphingomyelinase (ASM) inhibition and how they can explain the inhibition of SARS-CoV-2 replication by FIASMAs. The first mechanism implies a disruption in the lysosomal pH fall as the endosome-lysosome moves toward the interior of the cell. In fact, changes in cholesterol levels in endosome-lysosome membranes, which are associated with ASM inhibition is thought to be mediated by lysosomal proton pump (ATP-ase) inactivation. The second mechanism involves the formation of an extracellular ceramide-rich domain, which is blocked by FIASMAs. The ceramide-rich domains are believed to facilitate the SARS-CoV-2 entrance into the host cells.

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

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.

Association Between FIASMAs and Reduced Risk of Intubation or Death in Individuals Hospitalized for Severe COVID-19: An Observational Multicenter Study.

Several medications commonly used for a number of medical conditions share a property of functional inhibition of acid sphingomyelinase (ASM), or FIASMA. Preclinical and clinical evidence suggest that the ASM/ceramide system may be central to severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection. We examined the potential usefulness of FIASMA use among patients hospitalized for severe coronavirus disease 2019 (COVID-19) in an observational multicenter study conducted at Greater Paris University hospitals. Of 2,846 adult patients hospitalized for severe COVID-19, 277 (9.7%) were taking an FIASMA medication at the time of their hospital admission. The primary end point was a composite of intubation and/or death. We compared this end point between patients taking vs. not taking an FIASMA medication in time-to-event analyses adjusted for sociodemographic characteristics and medical comorbidities. The primary analysis was a Cox regression model with inverse probability weighting (IPW). Over a mean follow-up of 9.2 days (SD = 12.5), the primary end point occurred in 104 patients (37.5%) receiving an FIASMA medication, and 1,060 patients (41.4%) who did not. Despite being significantly and substantially associated with older age and greater medical severity, FIASMA medication use was significantly associated with reduced likelihood of intubation or death in both crude (hazard ratio (HR) = 0.71, 95% confidence interval (CI) = 0.58-0.87, P < 0.001) and primary IPW (HR = 0.58, 95%CI = 0.46-0.72, P < 0.001) analyses. This association remained significant in multiple sensitivity analyses and was not specific to one particular FIASMA class or medication. These results show the potential importance of the ASM/ceramide system in COVID-19 and support the continuation of FIASMA medications in these patients. Double-blind controlled randomized clinical trials of these medications for COVID-19 are needed.

Inhibition of acid sphingomyelinase by ambroxol prevents SARS-CoV-2 entry into epithelial cells.

The acid sphingomyelinase/ceramide system has been shown to be important for cellular infection with at least some viruses, for instance, rhinovirus or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Functional inhibition of the acid sphingomyelinase using tricyclic antidepressants prevented infection of epithelial cells, for instance with SARS-CoV-2. The structure of ambroxol, that is, trans-4-[(2,4-dibromanilin-6-yl)-methyamino]-cyclohexanol, a mucolytic drug applied by inhalation, suggests that the drug might inhibit the acid sphingomyelinase and thereby infection with SARS-CoV-2. To test this, we used vesicular stomatitis virus pseudoviral particles presenting SARS-CoV-2 spike protein on their surface (pp-VSV-SARS-CoV-2 spike), a bona fide system for mimicking SARS-CoV-2 entry into cells. Viral uptake and formation of ceramide localization were determined by fluorescence microscopy, activity of the acid sphingomyelinase by consumption of [14C]sphingomyelin and ceramide was quantified by a kinase method. We found that entry of pp-VSV-SARS-CoV-2 spike required activation of acid sphingomyelinase and release of ceramide, events that were all prevented by pretreatment with ambroxol. We also obtained nasal epithelial cells from human volunteers prior to and after inhalation of ambroxol. Inhalation of ambroxol reduced acid sphingomyelinase activity in nasal epithelial cells and prevented pp-VSV-SARS-CoV-2 spike-induced acid sphingomyelinase activation, ceramide release, and entry of pp-VSV-SARS-CoV-2 spike ex vivo. The addition of purified acid sphingomyelinase or C16 ceramide restored entry of pp-VSV-SARS-CoV-2 spike into ambroxol-treated epithelial cells. We propose that ambroxol might be suitable for clinical studies to prevent coronavirus disease 2019.

Pharmacological Inhibition of Acid Sphingomyelinase Prevents Uptake of SARS-CoV-2 by Epithelial Cells.

The acid sphingomyelinase/ceramide system plays an important role in bacterial and viral infections. Here, we report that either pharmacological inhibition of acid sphingomyelinase with amitriptyline, imipramine, fluoxetine, sertraline, escitalopram, or maprotiline or genetic downregulation of the enzyme prevents infection of cultured cells or freshy isolated human nasal epithelial cells with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or vesicular stomatitis virus (VSV) pseudoviral particles (pp-VSV) presenting SARS-CoV-2 spike protein (pp-VSV-SARS-CoV-2 spike), a bona fide system mimicking SARS-CoV-2 infection. Infection activates acid sphingomyelinase and triggers a release of ceramide on the cell surface. Neutralization or consumption of surface ceramide reduces infection with pp-VSV-SARS-CoV-2 spike. Treating volunteers with a low dose of amitriptyline prevents infection of freshly isolated nasal epithelial cells with pp-VSV-SARS-CoV-2 spike. The data justify clinical studies investigating whether amitriptyline, a safe drug used clinically for almost 60 years, or other antidepressants that functionally block acid sphingomyelinase prevent SARS-CoV-2 infection.