Secretory Acid Sphingomyelinase Research Articles

Increased acid sphingomyelinase levels in pediatric patients with obesity

The level of secretory acid sphingomyelinase (S-ASM), a key enzyme in the sphingolipid metabolism, is elevated in a variety of human diseases, including in the serum of obese adults. Alterations in S-ASM were also found to induce morphological changes in erythrocytes. Consequently, the inhibition of S-ASM by functional Inhibitors of ASM (FIASMA) may have broad clinical implications. The purpose of this study was to assess S-ASM activity in pediatric patients with obesity and healthy matched controls, as well as to investigate the erythrocyte morphology using transmission electron microscopy. We recruited 46 obese patients (mean age 11 ± 2.9 years) and 44 controls (mean age 10.8 ± 2.9 years). S-ASM activity was significantly higher (Wilcoxon signed-rank test p-value: 0.004) in obese patients (mean 396.4 ± 49.7 pmol/ml/h) than in controls (mean 373.7 ± 23.1 pmol/ml/h). No evidence of morphological differences in erythrocytes was found between the two populations. We then carried out a case–control study based on the spontaneous reporting system database to compare FIASMAs with NON-FIASMAs in terms of weight gain risk. Children who received FIASMA had a significantly lower frequency of weight gain reports than patients who took NON-FIASMA agents (p < 0.001). Our findings suggest there is an intriguing possibility that S-ASM may play a role in pediatric obesity. This pilot study could serve as the basis for future studies in this interesting field of research.

Characterization of the small molecule ARC39, a direct and specific inhibitor of acid sphingomyelinase in vitro

Inhibition of acid sphingomyelinase (ASM), a lysosomal enzyme that catalyzes the hydrolysis of sphingomyelin into ceramide and phosphorylcholine, may serve as an investigational tool or a therapeutic intervention to control many diseases. Specific ASM inhibitors are currently not sufficiently characterized. Here, we found that 1-aminodecylidene bis-phosphonic acid (ARC39) specifically and efficiently (>90%) inhibits both lysosomal and secretory ASM in vitro. Results from investigating sphingomyelin phosphodiesterase 1 (SMPD1/Smpd1) mRNA and ASM protein levels suggested that ARC39 directly inhibits ASM’s catalytic activity in cultured cells, a mechanism that differs from that of functional inhibitors of ASM. We further provide evidence that ARC39 dose- and time-dependently inhibits lysosomal ASM in intact cells, and we show that ARC39 also reduces platelet- and ASM-promoted adhesion of tumor cells. The observed toxicity of ARC39 is low at concentrations relevant for ASM inhibition in vitro, and it does not strongly alter the lysosomal compartment or induce phospholipidosis in vitro. When applied intraperitoneally in vivo, even subtoxic high doses administered short-term induced sphingomyelin accumulation only locally in the peritoneal lavage without significant accumulation in plasma, liver, spleen, or brain. These findings require further investigation with other possible chemical modifications. In conclusion, our results indicate that ARC39 potently and selectively inhibits ASM in vitro and highlight the need for developing compounds that can reach tissue concentrations sufficient for ASM inhibition in vivo.

Secretory Acid Sphingomyelinase in the Serum of Medicated Patients Predicts the Prospective Course of Depression.

Major depressive disorder (MDD) is a highly prevalent and devastating psychiatric illness with strong individual and societal burdens. However, biomarkers to improve the limited preventive and therapeutic approaches are scarce. Multilevel evidence suggests that the pathophysiological involvement of sphingolipids particularly increases the levels of ceramides and the ceramide hydrolyzing enzyme, acid sphingomyelinase. The activity of secretory acid sphingomyelinase (S-ASM) and routine blood parameters were determined in the serum of patients with current (unmedicated n = 63, medicated n = 66) and remitted (n = 39) MDD and healthy subjects (n = 61). Depression severity and anxiety and their 3-weeks prospective course of treatment were assessed by psychometric inventories. S-ASM activity was not different between the four groups, did not decrease during treatment, and was not lower in individuals taking medication that functionally inhibited ASM. However, S-ASM correlated positively with depression severity only in remitted patients. High enzyme activity at inclusion predicted milder clinician-evaluated and self-rated depression severity (HAM-D, MADRS, BDI-II) and state anxiety at follow-up, and was related to stronger improvement in these scores in medicated patients. S-ASM was strongly and contrariwise associated with serum lipids in unmedicated and medicated females. These findings contribute to a better understanding of the pathomechanisms underlying depression and the development of clinical strategies and biomarkers.

Solving the secretory acid sphingomyelinase puzzle: Insights from lysosome-mediated parasite invasion and plasma membrane repair.

Acid sphingomyelinase (ASM) is a lysosomal enzyme that cleaves the phosphorylcholine head group of sphingomyelin, generating ceramide. Recessive mutations in SMPD1, the gene encoding ASM, cause Niemann-Pick Disease Types A and B. These disorders are attributed not only to lipid accumulation inside lysosomes but also to changes on the outer leaflet of the plasma membrane, highlighting an extracellular role for ASM. Secretion of ASM occurs under physiological conditions, and earlier studies proposed two forms of the enzyme, one resident in lysosomes and another form that would be diverted to the secretory pathway. Such differential intracellular trafficking has been difficult to explain because there is only one SMPD1 transcript that generates an active enzyme, found primarily inside lysosomes. Unexpectedly, studies of cell invasion by the protozoan parasite Trypanosoma cruzi revealed that conventional lysosomes can fuse with the plasma membrane in response to elevations in intracellular Ca2+ , releasing their contents extracellularly. ASM exocytosed from lysosomes remodels the outer leaflet of the plasma membrane, promoting parasite invasion and wound repair. Here, we discuss the possibility that ASM release during lysosomal exocytosis, in response to various forms of stress, may represent a major source of the secretory form of this enzyme.

Immunoregulatory role of acid sphingomyelinase in allergic asthma.

Acid sphingomyelinase (ASM) is one of the enzymes that catalyzes the breakdown of sphingomyelin to ceramide and phosphorylcholine. In this study, we aimed at elucidating the role of ASM in allergic asthma. We used an ovalbumin-induced murine model of asthma where we compared wild-type and ASM-deficient mice. In wild-type mice, secretory ASM activity in the bronchoalveolar lavage fluid was increased in the acute ovalbumin model, but not in a tolerogenic model. Furthermore, in the absence of ASM, the serum IgE level was reduced, compared with wild-type mice, while an accumulation of interstitial macrophages and foreign antigen-induced regulatory T cells along with exhausted CD4+ PD1+ T cells was observed in the lungs of ASM-/- mice. In conclusion, in the absence of ASM, we observed an accumulation of immunosuppressive antigen-induced regulatory T cells expressing Foxp3 and CTLA4 in the lung as well as multinucleated interstitial macrophages and exhausted CD4+ PD1+ T cells associated with inhibition of serum IgE in asthma.

Peripheral Acid Sphingomyelinase Activity Is Associated with Biomarkers and Phenotypes of Alcohol Use and Dependence in Patients and Healthy Controls.

By catalyzing the hydrolysis of sphingomyelin into ceramide, acid sphingomyelinase (ASM) changes the local composition of the plasma membrane with effects on receptor-mediated signaling. Altered enzyme activities have been noted in common human diseases, including alcohol dependence. However, the underlying mechanisms remain largely unresolved. Blood samples were collected from early-abstinent alcohol-dependent in-patients (n[♂] = 113, n[♀] = 87) and matched healthy controls (n[♂] = 133, n[♀] = 107), and analyzed for routine blood parameters and serum ASM activity. We confirmed increased secretory ASM activities in alcohol-dependent patients compared to healthy control subjects, which decreased slightly during detoxification. ASM activity correlated positively with blood alcohol concentration, withdrawal severity, biomarkers of alcohol dependence (liver enzyme activities of gamma-glutamyl transferase, alanine aminotransferase, aspartate aminotransferase; homocysteine, carbohydrate-deficient transferrin; mean corpuscular volume, and creatine kinase). ASM activity correlated negatively with leukocyte and thrombocyte counts. ASM and gamma-glutamyl transferase were also associated in healthy subjects. Most effects were similar for males and females with different strengths. We describe previously unreported associations between ASM activity and markers of liver damage and myelosuppression. Further research should investigate whether this relationship is causal, or whether these parameters are part of a common pathway in order to gain insights into underlying mechanisms and develop clinical applications.

Elevation of Serum Acid Sphingomyelinase Activity in Children with Acute Respiratory Syncytial Virus Bronchiolitis.

Acid sphingomyelinase (ASM) is a lysosomal enzyme that hydrolyzes sphingomyelin into ceramide, a bioactive lipid to regulate cellular physiological functions. Thus, ASM activation has been reported as a key event in pathophysiological reactions including inflammation, cytokine release, oxidative stress, and endothelial damage in human diseases. Since ASM activation is associated with extracellular ASM secretion through unknown mechanisms, it can be detected by recognizing the elevation of secretory ASM (S-ASM) activity. Serum S-ASM activity has been reported to increase in chronic diseases, acute cardiac diseases, and systemic inflammatory diseases. However, the serum S-ASM has not been investigated in common acute illness. This study was designed to evaluate serum S-ASM activity in children with common acute illness. Fifty children with common acute illness and five healthy children were included in this study. The patients were categorized into five groups based on clinical diagnoses: acute respiratory syncytial virus (RSV) bronchiolitis, adenovirus infection, streptococcal infection, asthma, and other infections due to unknown origin. The serum S-ASM activity was significantly elevated at 6.9 ± 1.6 nmol/0.1 mL/6 h in the group of acute RSV bronchiolitis patients compared with healthy children who had a mean level of 1.8 ± 0.8 nmol/0.1 mL/6 h (p < 0.05). In the other illness groups, the serum S-ASM activity was not significantly elevated. The results suggest an association of ASM activation with RSV infection, a cause for common acute illness. This is the first report to describe the elevation of serum S-ASM activity in respiratory tract infection.

Elevation of ceramide and activation of secretory acid sphingomyelinase in patients with acute coronary syndromes

Although there are several reported evidences for a pathogenic role of sphingolipid signaling in atherosclerosis, peripheral blood levels of ceramide and secretory acid sphingomyelinase (S-SMase) activity in patients with acute coronary syndromes (ACS) have not been evaluated. A total of 304 CAD patients and 52 healthy individuals were divided into four groups: control group (n=52), stable angina pectoris (SAP) group (n=98), unstable angina pectoris (UAP) group (n=92), and acute myocardial infarction (AMI) group (n=114). Plasma levels of sphingomyelin (SPM) were elevated in patients with UAP and AMI compared with those in the control and SAP participants. Plasma ceramide levels and S-SMase activity in patients with ACS (including UAP and AMI) on day 0 were significantly higher than those in the control and SAP participants. Elevation in plasma ceramide levels in patients with UAP and AMI was sustained until a day after percutaneous coronary intervention or day 7, respectively. Moreover, in patients with UAP, S-SMase activity elevation on day 0 was followed by a gradual decrease toward the SAP range up to a day after percutaneous coronary intervention. In patients with AMI, elevation in S-SMase activity showed a peak on day 3. Serial changes in plasma ceramide and S-SMase activity were documented in patients with ACS. These findings provide an insight into the molecular mechanism of plaque destabilization.

Characterization of Acid Sphingomyelinase Activity in Human Cerebrospinal Fluid

BackgroundAs a key enzyme in sphingolipid metabolism, acid sphingomyelinase (ASM) is involved in the regulation of cell fate and signaling via hydrolysis of sphingomyelin to form ceramide. While increased activity of the lysosomal form has been associated with various pathological conditions, there are few studies on secretory ASM limited only to cell models, plasma or serum.MethodsAn optimized assay based on a fluorescent substrate was applied to measure the ASM activity in cerebrospinal fluid (CSF) collected from mice and from 42 patients who were classified as controls based on normal routine CSF values.ResultsWe have detected ASM activity in human CSF, established a sensitive quantitative assay and characterized the enzyme’s properties. The enzyme resembles plasmatic ASM including protein stability and Zn2+-dependence but the assays differ considerably in the optimal detergent concentration. Significantly increased activities in the CSF of ASM transgenic mice and undetectable levels in ASM knock-out mice prove that the measured ASM activity originates from the ASM-encoding gene SMPD1. CSF localized ASM activities were comparable to corresponding serum ASM levels at their respective optimal reaction conditions, but no correlation was observed. The large variance in ASM activity was independent of sex, age or analyzed routine CSF parameters.ConclusionsHuman and mouse CSF contain detectable levels of secretory ASM, which are unrelated to serum ASM activities. Further investigations in humans and in animal models will help to elucidate the role of this enzyme in human disease and to assess its value as a potential biomarker for disease type, severity, progress or therapeutic success.

ACTIVATION OF SECRETORY ACID SPHINGOMYELINASE AND ELEVATION OF CERAMIDE IN PLASMA IS ASSOCIATED WITH CHRONIC HEART FAILURE

ObjectivesThe sphingolipid pathway generates bioactive molecules that are crucial to the regulation of a variety of physiological and pathological processes. Recent studies indicate that plasma secretory acid sphingomyelinase (S-SMase) activity...

Proteolysis sensitizes LDL particles to phospholipolysis by secretory phospholipase A2 group V and secretory sphingomyelinase

LDL particles that enter the arterial intima become exposed to proteolytic and lipolytic modifications. The extracellular hydrolases potentially involved in LDL modification include proteolytic enzymes, such as chymase, cathepsin S, and plasmin, and phospholipolytic enzymes, such as secretory phospholipases A2 (sPLA2-IIa and sPLA2-V) and secretory acid sphingomyelinase (sSMase). Here, LDL was first proteolyzed and then subjected to lipolysis, after which the effects of combined proteolysis and lipolysis on LDL fusion and on binding to human aortic proteoglycans (PG) were studied. Chymase and cathepsin S led to more extensive proteolysis and release of peptide fragments from LDL than did plasmin. sPLA2-IIa was not able to hydrolyze unmodified LDL, and even preproteolysis of LDL particles failed to enhance lipolysis by this enzyme. However, preproteolysis with chymase and cathepsin S accelerated lipolysis by sPLA2-V and sSMase, which resulted in enhanced fusion and proteoglycan binding of the preproteolyzed LDL particles. Taken together, the results revealed that proteolysis sensitizes the LDL particles to hydrolysis by sPLA2-V and sSMase. By promoting fusion and binding of LDL to human aortic proteoglycans, the combination of proteolysis and phospholipolysis of LDL particles potentially enhances extracellular accumulation of LDL-derived lipids during atherogenesis.

Ceramide Causes Pulmonary Cell Apoptosis and Emphysema: A Role for Sphingolipid Homeostasis in the Maintenance of Alveolar Cells

Alveolar cell apoptosis is a critical element of experimental and human emphysema, in that it accounts for alveolar destruction and interacts with oxidative stress, inflammation, and protease activation, all contributing to the unique nature of the disease. Prompted by our finding of up-regulated ceramide levels in lungs of patients with smoking-induced emphysema (1), we demonstrate that ceramide, a second messenger lipid, is a critical mediator and amplifier of alveolar cell apoptosis in experimental emphysema. Inhibition of enzymes of the de novo ceramide synthesis prevented lung ceramide increases, alveolar cell apoptosis, oxidative stress, and emphysema caused by blockade of vascular endothelial growth factor receptor (VEGFR) with SU5416 in both rats and mice. The lung alterations seen with VEGFR blockade were reproduced with intratracheal instillation of ceramide in naive mice. Furthermore, reduction of lung levels of very long ceramides after administration of a neutralizing ceramide antibody in vivo and the inability of acid sphingomyelinase–deficient fibroblasts to augment endogenous ceramide synthesis in response to exogenous ceramide indicated a feed-forward mechanism of ceramide regulation mediated via the secretory acid sphingomyelinase. Finally, the finding that supplementation of sphingosine-1-phosphate (S1-P) prevented lung cell apoptosis due to VEGFR blockade suggests that ceramide–S1-P balance might be critical in the maintenance of alveolar septal integrity. We have therefore identified ceramide as a critical pathogenetic element in emphysema and a promising target for pharmacologic intervention in a disease with no available therapies. Conflict of Interest Statement: None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

Ceramide upregulation causes pulmonary cell apoptosis and emphysema-like disease in mice

Alveolar cell apoptosis is involved in the pathogenesis of emphysema, a prevalent disease primarily caused by cigarette smoking. We report that ceramide, a second messenger lipid, is a crucial mediator of alveolar destruction in emphysema. Inhibition of enzymes controlling de novo ceramide synthesis prevented alveolar cell apoptosis, oxidative stress and emphysema caused by blockade of the vascular endothelial growth factor (VEGF) receptors in both rats and mice. Emphysema was reproduced with intratracheal instillation of ceramide in naive mice. Excessive ceramide triggers a feed-forward mechanism mediated by activation of secretory acid sphingomyelinase, as suggested by experiments with neutralizing ceramide antibody in mice and with acid sphingomyelinase-deficient fibroblasts. Concomitant augmentation of signaling initiated by a prosurvival metabolite, sphingosine-1-phosphate, prevented lung apoptosis, implying that a balance between ceramide and sphingosine-1-phosphate is required for maintenance of alveolar septal integrity. Finally, increased lung ceramides in individuals with smoking-induced emphysema suggests that ceramide upregulation may be a crucial pathogenic element and a promising target in this disease that currently lacks effective therapies.

Distribution of acid sphingomyelinase in human various body fluids.

Enzyme activities of acid sphingomyelinase (ASM) were determined in various human cell-free body fluids, serum, cerebrospinal fluid, urine, salivary fluid, tear fluid, and synovial fluid, using assay buffers with or without Zn2+ -cation. Although ASM activity was not detected in the cerebrospinal fluid, the other fluids demonstrated significant enzyme activities of ASM. All ASMs detected in the fluids were stimulated by the addition of Zn2+ -cation, suggesting that those enzymes are secretory ASM derived from ASM gene. We suggest a possible enzymatic diagnosis of Niemann-Pick disease types A and B using those body fluids. Interestingly, salivary and tear fluids showed much higher activities of ASM than those of the other fluids. Because sphingolipids, especially sphingomyelin, are major constituents of a normal diet, especially, milk, eggs, and meat products, we suggest that ASM in the salivary gland may play an important role in the digestion of sphingomyelin in a normal diet.