Selective Inhibitors of Human Neuraminidase 1 (NEU1)

Bioisosteres at C9 of 2-Deoxy-2,3-didehydro-N-acetyl Neuraminic Acid Identify Selective Inhibitors of NEU3

Human neuraminidases play critical roles in many physiological and pathological processes. Humans have four isoenzymes of NEU, making selective inhibitors important tools to investigate the function of individual isoenzymes. A typical scaffold for NEU inhibitors is 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (DANA) where C9 modifications can be critical for potency and selectivity against human NEU. To design improved DANA analogues, we generated a library of compounds with either a short alkyl chain or a biphenyl substituent linked to the C9 position through one of six amide bioisosteres. Bioisostere linkers included triazole, urea, thiourea, carbamate, thiocarbamate, and sulfonamide groups. Within this library, we identified a C9 biphenyl carbamate derivative (963) that showed high selectivity and potency for NEU3 (Ki = 0.12 ± 0.01 μM). In contrast, NEU1 and NEU4 isoenzymes preferred amide and triazole linkers, respectively. Finally, analogues with urea, sulfonamide, and amide linkers showed enhanced inhibitory activity for a bacterial NEU, NanI from Clostridium perfringens.

Multivalent inhibition of the Aspergillus fumigatus KDNase

Aspergillus fumigatus is a saprophytic fungus and opportunistic pathogen often causing fatal infections in immunocompromised patients. Recently AfKDNAse, an exoglycosidase hydrolyzing 3-deoxy-D-galacto-D-glycero-nonulosonic acid (KDN), a rare sugar from the sialic acid family, was identified and characterized. The principal function of AfKDNAse is still unclear, but a study suggests a critical role in fungal cell wall morphology and virulence. Potent AfKDNAse inhibitors are required to better probe the enzyme's biological role and as potential antivirulence factors. In this work, we developed a set of AfKDNAse inhibitors based on enzymatically stable thio-KDN motifs. C2, C9-linked heterodi-KDN were designed to fit into unusually close KDN sugar binding pockets in the protein. A polymeric compound with an average of 54 KDN motifs was also designed by click chemistry. Inhibitory assays performed on recombinant AfKDNAse showed a moderate and strong enzymatic inhibition for the two classes of compounds, respectively. The poly-KDN showed more than a nine hundred fold improved inhibitory activity (IC50 = 1.52 ± 0.37 μM, 17-fold in a KDN molar basis) compared to a monovalent KDN reference, and is to our knowledge, the best synthetic inhibitor described for a KDNase. Multivalency appears to be a relevant strategy for the design of potent KDNase inhibitors. Importantly, poly-KDN was shown to strongly decrease filamentation when co-cultured with A. fumigatus at micromolar concentrations, opening interesting perspectives in the development of antivirulence factors.

Synthetic Sialosides Terminated with 8-N-Substituted Sialic Acid as Selective Substrates for Sialidases from Bacteria and Influenza Viruses

Sialosides containing C8-modified sialic acids are challenging synthetic targets but potentially useful probes for diagnostic substrate profiling of sialidases and elucidating the binding specificity of sialic acid-interacting proteins. Here, we demonstrate efficient chemoenzymatic methods for synthesizing para-nitrophenol-tagged α2-3- and α2-6-linked sialyl galactosides containing C8-acetamido, C8-azido, or C8-amino derivatized N-acetylneuraminic acid (Neu5Ac). High-throughput substrate specificity studies showed that the C8-modification of sialic acid significantly changes its recognition by sialidases from humans, various bacteria, and different influenza A and B viruses. Sialosides carrying Neu5Ac with a C8-azido modification were generally well tolerated by all the sialidases we tested, whereas sialosides containing C8-acetamido-modified Neu5Ac were only cleaved by selective bacterial sialidases. In contrast, sialosides with C8-amino-modified Neu5Ac were cleaved by a combination of selective bacterial and influenza A virus sialidases. These results indicate that sialosides terminated with a C8-amino or C8-acetamido-modified sialic acid can be used with other sialosides for diagnostic profiling of disease-causing sialidase-producing pathogens.

Inhibition of neuraminidase-1 sialidase activity by interfering peptides impairs insulin receptor activity in vitro and glucose homeostasis in vivo

Neuraminidases (NEUs) also called sialidases are glycosidases which catalyze the removal of terminal sialic acid residues from glycoproteins, glycolipids, and oligosaccharides. Mammalian NEU-1 participates in regulation of cell surface receptors such as insulin receptor (IR), epithelial growth factor receptor, low-density lipoprotein receptor, and toll-like receptor 4. At the plasma membrane, NEU-1 can be associated with the elastin-binding protein and the carboxypeptidase protective protein/cathepsin A to constitute the elastin receptor complex. In this complex, NEU-1 is essential for elastogenesis, signal transduction through this receptor and for biological effects of the elastin-derived peptides on atherosclerosis, thrombosis, insulin resistance, nonalcoholic steatohepatitis, and cancers. This is why research teams are developing inhibitors targeting this sialidase. Previously, we developed interfering peptides to inhibit the dimerization and the activation of NEU-1. In this study, we investigated the effects of these peptides on IR activation in vitro and in vivo. Using cellular overexpression and endogenous expression models of NEU-1 and IR (COS-7 and HepG2 cells, respectively), we have shown that interfering peptides inhibit NEU-1 dimerization and sialidase activity which results in a reduction of IR phosphorylation. These results demonstrated that NEU-1 positively regulates IR phosphorylation and activation in our conditions. In vivo, biodistribution study showed that interfering peptides are well distributed in mice. Treatment of C57Bl/6 mice during 8 weeks with interfering peptides induces a hyperglycemic effect in our experimental conditions. Altogether, we report here that inhibition of NEU-1 sialidase activity by interfering peptides decreases IR activity in vitro and glucose homeostasis in vivo.

From genomic insights to clinical hope: Targeting NEU1 in IgA nephropathy

BACKGROUND

IgA Nephropathy (IgAN), the primary form of glomerulonephritis, presents significant clinical challenges due to its obscure pathogenesis and lack of targeted treatments. We conducted a proteome-wide Mendelian randomization (MR) study to identify therapeutic targets for IgAN.

METHODS

Utilizing a plasma proteome dataset comprising 4907 blood plasma proteins as the exposure variable, and renal biopsy-confirmed IgAN cases as the outcome, this study employed MR to pinpoint proteins potentially pathogenic to IgAN. The robustness of our findings was affirmed through external dataset validation, reverse causation testing, and Bayesian colocalization analysis. Additionally, we conducted phenotypic scanning and analyzed downstream metabolites to investigate candidate proteins's biological function.

RESULTS

In our study, a significant association was identified between an increase in neuraminidase 1 (NEU1) expression and the risk of IgAN. Specifically, a one standard deviation increase in NEU1 expression was associated with an odds ratio of 11.80 for the development of IgAN (95% confidence interval: 4.03-34.54). This association was substantiated across various statistical models and external validations. Colocalization analysis indicated a shared causal variant between NEU1 expression and IgAN. Furthermore, an increased influenza risk associated with NEU1 was observed, supporting the therapeutic potential of NEU1 inhibitors for IgAN. However, our study found no significant role for neuraminic acid-related metabolites in IgAN's development, suggesting an independent pathway for NEU1's influence.

CONCLUSION

This study identifies NEU1 as a promising therapeutic target for IgAN, backed by robust genetic evidence. Future research should explore NEU1's therapeutic potential in diverse populations and clinical scenarios, further establishing its role in IgAN.

The Exploitation of the Glycosylation Pattern in Asthma: How We Alter Ancestral Pathways to Develop New Treatments

Asthma has reached epidemic levels, yet progress in developing specific therapies is slow. One of the main reasons for this is the fact that asthma is an umbrella term for various distinct subsets. Due to its high heterogeneity, it is difficult to establish biomarkers for each subset of asthma and to propose endotype-specific treatments. This review focuses on protein glycosylation as a process activated in asthma and ways to utilize it to develop novel biomarkers and treatments. We discuss known and relevant glycoproteins whose functions control disease development. The key role of glycoproteins in processes integral to asthma, such as inflammation, tissue remodeling, and repair, justifies our interest and research in the field of glycobiology. Altering the glycosylation states of proteins contributing to asthma can change the pathological processes that we previously failed to inhibit. Special emphasis is placed on chitotriosidase 1 (CHIT1), an enzyme capable of modifying LacNAc- and LacdiNAc-containing glycans. The expression and activity of CHIT1 are induced in human diseased lungs, and its pathological role has been demonstrated by both genetic and pharmacological approaches. We propose that studying the glycosylation pattern and enzymes involved in glycosylation in asthma can help in patient stratification and in developing personalized treatment.

The role of sialidase Neu1 in respiratory diseases

Neu1 is a sialidase enzyme that plays a crucial role in the regulation of glycosylation in a variety of cellular processes, including cellular signaling and inflammation. In recent years, numerous evidence has suggested that human NEU1 is also involved in the pathogenesis of various respiratory diseases, including lung infection, chronic obstructive pulmonary disease (COPD), asthma, and pulmonary fibrosis. This review paper aims to provide an overview of the current research on human NEU1 and respiratory diseases.

Facile synthesis of C5-azido derivatives of thiosialosides and 2,3-dehydro-5-N-acetylneuraminic acid (DANA)

Neuraminic acid (Neu5Ac, also known as sialic acid) is an important monosaccharide found in glycoproteins and glycolipids which plays a vital role in regulation of physiological functions and pathological conditions. The study of sialoglycans has benefitted from the development of glycomimetic probes and inhibitors for proteins and enzymes that interact with and modify neuraminic acid in glycan chains. Methods to access sialoside intermediates with high yield are needed to facilitate the design of new targets. Here, we report the synthesis of C5-azido thiosialosides using a mild method to deprotect the C5-acetamido functional group followed by the use of a diazo-transfer reagent. We examined two diazo-transfer strategies and compared their yields and tolerance of acetate protecting groups. The same methods and comparisons were also performed for the 2,3-dehydro-5-N-acetylneuraminic acid (DANA) scaffold which is commonly used to generate inhibitors of neuraminidase (sialidase) enzymes. We found that C5-azido derivatives of both thiosialosides and DANA could be produced in five or six steps with yields up to 76 % and 83 %, respectively. Diazo-transfer reagents compared in this study were trifluoromethanesulfonyl azide (TfN3) and imidazole-1-sulfonyl azide (ImzSO2N3). We found that both reagents were compatible with this method and showed comparable yields. Finally, we show that C5-azido derivatives can help to avoid O, N-acyl protecting group migration which was observed in C5-NHAc analogs.

New insights into the glycobiology of immune thrombocytopenia

PURPOSE OF REVIEW

The platelet surface harbors a lush forest of glycans (carbohydrate polymers) attached to membrane proteins and lipids. Accumulating evidence suggests that these glycans may be relevant to the pathophysiology of immune thrombocytopenia (ITP). Here, we critically evaluate data that point to a possible role for loss of sialic acid in driving platelet clearance in ITP, comment on the potential use of neuraminidase inhibitors for treatment of ITP, and highlight open questions in this area.

RECENT FINDINGS

Multiple lines of evidence suggest a role for loss of platelet sialic acid in the pathophysiology of thrombocytopenia. Recent work has tested the hypothesis that neuraminidase-mediated cleavage of platelet sialic acid may trigger clearance of platelets in ITP. Some clinical evidence supports efficacy of the viral neuraminidase inhibitor oseltamivir in ITP, which is surprising given its lack of activity against human neuraminidases.

SUMMARY

Further study of platelet glycobiology in ITP is necessary to fill key knowledge gaps. A deeper understanding of the roles of platelet glycans in ITP pathophysiology will help to guide development of novel therapies.

Structure of the immunoregulatory sialidase NEU1

Sialic acids linked to glycoproteins and glycolipids are important mediators of cell and protein recognition events. These sugar residues are removed by neuraminidases (sialidases). Neuraminidase-1 (sialidase-1 or NEU1) is a ubiquitously expressed mammalian sialidase located in lysosomes and on the cell membrane. Because of its modulation of multiple signaling processes, it is a potential therapeutic target for cancers and immune disorders. Genetic defects in NEU1 or in its protective protein cathepsin A (PPCA, CTSA) cause the lysosomal storage diseases sialidosis and galactosialidosis. To further our understanding of this enzyme's function at the molecular level, we determined the three-dimensional structure of murine NEU1. The enzyme oligomerizes through two self-association interfaces and displays a wide substrate-binding cavity. A catalytic loop adopts an inactive conformation. We propose a mechanism of activation involving a conformational change in this loop upon binding to its protective protein. These findings may facilitate the development of selective inhibitor and agonist therapies.

Conformationally locked sugar derivatives and analogues as potential neuraminidase inhibitors

The influenza virus remains a major health concern for mankind because it tends to mutate frequently and cause high morbidity. Influenza prevention and treatment are greatly aided by the use of antivirals. One such class of antivirals is neuraminidase inhibitors (NAIs), effective against influenza viruses. A neuraminidase on the virus's surface serves a vital function in viral propogation by assisting in the release of viruses from infected host cells. Neuraminidase inhibitors are the backbone in stoping such virus propagation thus helps in the treatment of influenza viruses infections. Two NAI medicines are licensed globally: Oseltamivir (Tamiflu™) and Zanamivir (Relanza™). There are two molecules that have acquired Japanese approval recently: Peramivir and Laninamivir, whereas Laninamivir octanoate is in Phase III clinical trials. The need for novel NAIs is due to frequent mutations in viruses and the rise in resistance against existing medication. The NA inhibitors (NAIs) are designed to have (oxa)cyclohexene scaffolds (a sugar scaffold) to mimic the oxonium transition state in the enzymatic cleavage of sialic acid. This review discusses in details and comprises all such conformationally locked (oxa)cyclohexene scaffolds and their analogues which have been recently designed and synthesized as potential neuraminidase inhibitors, thus as antiviral molecules. The structure-activity relationship of such diverese molecules has also been discussed in this review.

Structural and enzymatic characterization of the sialidase SiaPG from Porphyromonas gingivalis

The sialidases, which catalyze the hydrolysis of sialic acid from extracellular glycoconjugates, are a group of major virulence factors in various pathogenic bacteria. In Porphyromonas gingivalis, which causes human periodontal disease, sialidase contributes to bacterial pathogenesis via promoting the formation of biofilms and capsules, reducing the ability for macrophage clearance, and providing nutrients for bacterial colonization. Here, the crystal structure of the P. gingivalis sialidase SiaPG is reported at 2.1 Å resolution, revealing an N-terminal carbohydrate-binding domain followed by a canonical C-terminal catalytic domain. Simulation of the product sialic acid in the active-site pocket together with functional analysis enables clear identification of the key residues that are required for substrate binding and catalysis. Moreover, structural comparison with other sialidases reveals distinct features of the active-site pocket which might confer substrate specificity. These findings provide the structural basis for the further design and optimization of effective inhibitors to target SiaPG to fight against P. gingivalis-derived oral diseases.

Neuraminidase 1 promotes renal fibrosis development in male mice

The functions of the influenza virus neuraminidase has been well documented but those of the mammalian neuraminidases remain less explored. Here, we characterize the role of neuraminidase 1 (NEU1) in unilateral ureteral obstruction (UUO) and folic acid (FA)-induced renal fibrosis mouse models. We find that NEU1 is significantly upregulated in the fibrotic kidneys of patients and mice. Functionally, tubular epithelial cell-specific NEU1 knockout inhibits epithelial-to-mesenchymal transition, inflammatory cytokines production, and collagen deposition in mice. Conversely, NEU1 overexpression exacerbates progressive renal fibrosis. Mechanistically, NEU1 interacts with TGFβ type I receptor ALK5 at the 160-200aa region and stabilizes ALK5 leading to SMAD2/3 activation. Salvianolic acid B, a component of Salvia miltiorrhiza, is found to strongly bind to NEU1 and effectively protect mice from renal fibrosis in a NEU1-dependent manner. Collectively, this study characterizes a promotor role for NEU1 in renal fibrosis and suggests a potential avenue of targeting NEU1 to treat kidney diseases.

Co-infection of the respiratory epithelium, scene of complex functional interactions between viral, bacterial, and human neuraminidases

The activity of sialic acids, known to play critical roles in biology and many pathological processes, is finely regulated by a class of enzymes called sialidases, also known as neuraminidases. These are present in mammals and many other biological systems, such as viruses and bacteria. This review focuses on the very particular situation of co-infections of the respiratory epithelium, the scene of complex functional interactions between viral, bacterial, and human neuraminidases. This intrinsically multidisciplinary topic combining structural biology, biochemistry, physiology, and the study of host-pathogen interactions, opens up exciting research perspectives that could lead to a better understanding of the mechanisms underlying virus-bacteria co-infections and their contribution to the aggravation of respiratory pathology, notably in the context of pre-existing pathological contexts. Strategies that mimic or inhibit the activity of the neuraminidases could constitute interesting treatment options for viral and bacterial infections.

Sialidase Inhibitors with Different Mechanisms

Sialidases, or neuraminidases, are enzymes that catalyze the hydrolysis of sialic acid (Sia)-containing molecules, mostly removal of the terminal Sia (desialylation). By desialylation, sialidase can modulate the functionality of the target compound and is thus often involved in biological pathways. Inhibition of sialidases with inhibitors is an important approach for understanding sialidase function and the underlying mechanisms and could serve as a therapeutic approach as well. Transition-state analogues, such as anti-influenza drugs oseltamivir and zanamivir, are major sialidase inhibitors. In addition, difluoro-sialic acids were developed as mechanism-based sialidase inhibitors. Further, fluorinated quinone methide-based suicide substrates were reported. Sialidase product analogue inhibitors were also explored. Finally, natural products have shown competitive inhibiton against viral, bacterial, and human sialidases. This Perspective describes sialidase inhibitors with different mechanisms and their activities and future potential, which include transition-state analogue inhibitors, mechanism-based inhibitors, suicide substrate inhibitors, product analogue inhibitors, and natural product inhibitors.

NEU1 and NEU3 enzymes alter CD22 organization on B cells

The B cell membrane expresses sialic-acid-binding immunoglobulin-like lectins, also called Siglecs, that are important for modulating immune response. Siglecs have interactions with sialoglycoproteins found on the same membrane (cis-ligands) that result in homotypic and heterotypic receptor clusters. The regulation and organization of these clusters, and their effect on cell activation, is not clearly understood. We investigated the role of human neuraminidase enzymes NEU1 and NEU3 on the clustering of CD22 on B cells using confocal microscopy. We observed that native NEU1 and NEU3 activity influence the cluster size of CD22. Using single-particle tracking, we observed that NEU3 activity increased the lateral mobility of CD22, which was in contrast to the effect of exogenous bacterial NEU enzymes. Moreover, we show that native NEU1 and NEU3 activity influenced cellular Ca²⁺ levels, supporting a role for these enzymes in regulating B cell activation. Our results establish a role for native NEU activity in modulating CD22 organization and function on B cells.

Azido Groups Hamper Glycan Acceptance by Carbohydrate Processing Enzymes

Azido sugars have found frequent use as probes of biological systems in approaches ranging from cell surface metabolic labeling to activity-based proteomic profiling of glycosidases. However, little attention is typically paid to how well azide-substituted sugars represent the parent molecule, despite the substantial difference in size and structure of an azide compared to a hydroxyl. To quantitatively assess how well azides are accommodated, we have used glycosidases as tractable model enzyme systems reflecting what would also be expected for glycosyltransferases and other sugar binding/modifying proteins. In this vein, specificity constants have been measured for the hydrolysis of a series of azidodeoxy glucosides and N-acetylhexosaminides by a large number of glycosidases produced from expressed synthetic gene and metagenomic libraries. Azides at secondary carbons are not significantly accommodated, and thus, associated substrates are not processed, while those at primary carbons are productively recognized by only a small subset of the enzymes and often then only very poorly. Accordingly, in the absence of careful controls, results obtained with azide-modified sugars may not be representative of the situation with the natural sugar and should be interpreted with considerable caution. Azide incorporation can indeed provide a useful tool to monitor and detect glycosylation, but careful consideration should go into the selection of sites of azide substitution; such studies should not be used to quantitate glycosylation or to infer the absence of glycosylation activity.

The Janus-like role of neuraminidase isoenzymes in inflammation

The processes of activation, extravasation, and migration of immune cells to a site are early and essential steps in the induction of an acute inflammatory response. These events are an essential part of the inflammatory cascade, which involves multiple regulatory steps. Using a murine air pouch model of inflammation with LPS as an inflammation inducer, we demonstrate that isoenzymes of the neuraminidase family (NEU1, 3, and 4) play essential roles in these processes by acting as positive or negative regulators of leukocyte infiltration. In genetically knocked‐out (KO) mice for different NEU genes (Neu1 KO, Neu3 KO, Neu4 KO, and Neu3/4 double KO mice) with LPS‐induced air pouch inflammation, leukocytes at the site of inflammation were counted, and the inflamed tissue was analyzed using immunohistochemistry. Our data show that leukocyte recruitment was decreased in NEU1‐ and NEU3‐deficient mice, while it was increased in NEU4‐deficient animals. Consistent with these results, systemic as well as pouch exudate levels of pro‐inflammatory cytokines were reduced in Neu1 and increased in Neu4 KO mice. Pharmacological inhibitors specific for NEU1, NEU3, and NEU4 isoforms also affected leukocyte recruitment. Together our data demonstrate that NEU isoenzymes have distinct—and even opposing—effects on leukocyte recruitment, and therefore warrant further investigation to determine their mechanisms and importance as regulators of the inflammatory cascade.

Inhibitors of Human Neuraminidase Enzymes Block Transmigration in vitro

Cell migration to a site of inflammation is an important step of the immune response. This process is coordinated by cytokines, receptors, and the signal processing machinery of the cell. Many cellular receptors are glycosylated, and their activity can be modulated through changes in glycan structure. Furthermore, glycosylation can be critical to the folding and trafficking of receptors. In this work, we investigated the role of native human neuraminidase enzymes (NEU) in transmigration. We used a cultured T cell line (Jurkat) and a transwell assay with fibronectin (FN) coated wells and cytokines (IL-4 and TNF-α) as chemoattractants in the bottom chamber. We observed that NEU1, NEU3, and NEU4 were positive regulators of transmigration using an siRNA knockdown. Furthermore, we found that pharmacological inhibition of these enzymes inhibited transmigration. We conclude that human NEU isoenzymes NEU1, NEU3, and NEU4 can act as positive regulators of transmigration and should be investigated as targets for anti-inflammatory strategies.

Anomeric 1,2,3-triazole-linked sialic acid derivatives show selective inhibition towards a bacterial neuraminidase over a trypanosome trans-sialidase

Sialic acid is the natural substrate for sialidases and its chemical modification has been a useful approach to generate potent and selective inhibitors. Aiming at advancing the discovery of selective Trypanosoma cruzi trans-sialidase (TcTS) inhibitors, we have synthesised a small series of anomeric 1,2,3-triazole-linked sialic acid derivatives in good yields and high purity via copper-catalysed azide–alkyne cycloaddition (CuAAC, click chemistry) and evaluated their activity towards TcTS and neuraminidase. Surprisingly, the compounds showed practically no TcTS inhibition, whereas ca. 70% inhibition was observed for neuraminidase in relation to the analogues bearing hydrophobic substituents and ca. 5% for more polar substituents. These results suggest that polarity changes are less tolerated by neuraminidase due to the big difference in impact of hydrophobicity upon inhibition, thus indicating a simple approach to differentiate both enzymes. Moreover, such selectivity might be reasoned based on a possible steric hindrance caused by a bulky hydrophobic loop that sits over the TcTS active site and may prevent the hydrophobic inhibitors from binding. The present study is a step forward in exploiting subtle structural differences in sialidases that need to be addressed in order to achieve selective inhibition.

Human Neuraminidases: Structures and Stereoselective Inhibitors

This Perspective describes the classification, structures, substrates, mechanisms of action, and implications of human neuraminidases (hNEUs) in various pathologies. Some inhibitors have been developed for each isoform, leading to more precise interactions with hNEUs. Although crystal structure data are available for NEU2, most of the findings are based on NEU1 inhibition, and limited information is available for other hNEUs. Therefore, the synthesis of new compounds would facilitate the enrichment of the arsenal of inhibitors to better understand the roles of hNEUs and their mechanisms of action. Nevertheless, due to the already known inhibitors of human neuraminidase enzymes, a structure-activity relationship is presented along with different approaches to inhibit these enzymes for the development of potent and selective inhibitors. Among the different emerging strategies, one is the inhibition of the dimerization of NEU1 or NEU3, and the second is the inhibition of certain receptors located close to hNEU.

A stereo-electronic interpretation of a challenging orthoamide Overman rearrangement rationalized by molecular modelling

The Overman rearrangement difficulties are tentatively explained using stereo-electronic considerations, helping chemists to understand their troubles in this process.

The Elastin Receptor Complex: An Emerging Therapeutic Target Against Age-Related Vascular Diseases

The incidence of cardiovascular diseases is increasing worldwide with the growing aging of the population. Biological aging has major influence on the vascular tree and is associated with critical changes in the morphology and function of the arterial wall together with an extensive remodeling of the vascular extracellular matrix. Elastic fibers fragmentation and release of elastin degradation products, also known as elastin-derived peptides (EDPs), are typical hallmarks of aged conduit arteries. Along with the direct consequences of elastin fragmentation on the mechanical properties of arteries, the release of EDPs has been shown to modulate the development and/or progression of diverse vascular and metabolic diseases including atherosclerosis, thrombosis, type 2 diabetes and nonalcoholic steatohepatitis. Most of the biological effects mediated by these bioactive peptides are due to a peculiar membrane receptor called elastin receptor complex (ERC). This heterotrimeric receptor contains a peripheral protein called elastin-binding protein, the protective protein/cathepsin A, and a transmembrane sialidase, the neuraminidase-1 (NEU1). In this review, after an introductive part on the consequences of aging on the vasculature and the release of EDPs, we describe the composition of the ERC, the signaling pathways triggered by this receptor, and the current pharmacological strategies targeting ERC activation. Finally, we present and discuss new regulatory functions that have emerged over the last few years for the ERC through desialylation of membrane glycoproteins by NEU1, and its potential implication in receptor transactivation.

Sialidase and Sialyltransferase Inhibitors: Targeting Pathogenicity and Disease

Sialidases (SAs) and sialyltransferases (STs), the enzymes responsible for removing and adding sialic acid to other glycans, play essential roles in viruses, bacteria, parasites, and humans. Sialic acid is often the terminal sugar on glycans protruding from the cell surface in humans and is an important component for recognition and cell function. Pathogens have evolved to exploit this and use sialic acid to either “cloak” themselves, ensuring they remain undetected, or as a mechanism to enable release of virus progeny. The development of inhibitors against SAs and STs therefore provides the opportunity to target a range of diseases. Inhibitors targeting viral, bacterial, or parasitic enzymes can directly target their pathogenicity in humans. Excellent examples of this can be found with the anti-influenza drugs Zanamivir (Relenza™, GlaxoSmithKline) and Oseltamivir (Tamiflu™, Roche and Gilead), which have been used in the clinic for over two decades. However, the development of resistance against these drugs means there is an ongoing need for novel potent and specific inhibitors. Humans possess 20 STs and four SAs that play essential roles in cellular function, but have also been implicated in cancer progression, as glycans on many cancer cells are found to be hyper-sialylated. Whilst much remains unknown about how STs function in relation to disease, it is clear that specific inhibitors of them can serve both as tools to gain a better understanding of their activity and form the basis for development of anti-cancer drugs. Here we review the recent developments in the design of SA and ST inhibitors against pathogens and humans.

Prospects for the Use of Sialidase Inhibitors in Anti-atherosclerotic Therapy

The most typical feature of atherogenesis in humans at its early stage is the formation of foam cells in subendothelial arterial intima, which occurs as the consequence of intracellular cholesterol deposition. The main source of lipids accumulating in the arterial wall is circulating low-density lipoprotein (LDL). However, LDL particles should undergo proatherogenic modification to acquire atherogenic properties. One of the known types of atherogenic modification of LDL is enzymatic deglycosilation, namely, desialylation, which is the earliest change in the cascade of following multiple LDL modifications. The accumulating data make sialidases an intriguing and plausible therapeutic target, since pharmacological modulation of activity of these enzymes may have beneficial effects in several pathologies, including atherosclerosis. The hypothesis exists that decreasing LDL enzymatic desialylation may result in the prevention of lipid accumulation in arterial wall, thus breaking down one of the key players in atherogenesis at the cellular level. Several drugs acting as glycomimetics and inhibiting sialidase enzymatic activity already exist, but the concept of sialidase inhibition as an anti-atherosclerosis strategy remains unexplored to date. This review is focused on the potential possibilities of the repurposing of sialidase inhibitors for pathogenetic anti-atherosclerotic therapy.

Adverse Effects of Oseltamivir Phosphate Therapy on the Liver of LDLR-/- Mice Without Any Benefit on Atherosclerosis and Thrombosis

ABSTRACT

Desialylation, governed by sialidases or neuraminidases, is strongly implicated in a wide range of human disorders, and accumulative data show that inhibition of neuraminidases, such as neuraminidases 1 sialidase, may be useful for managing atherosclerosis. Several studies have reported promising effects of oseltamivir phosphate, a widely used anti-influenza sialidase inhibitor, on human cancer cells, inflammation, and insulin resistance. In this study, we evaluated the effects of oseltamivir phosphate on atherosclerosis and thrombosis and potential liver toxicity in LDLR-/- mice fed with high-fat diet. Our results showed that oseltamivir phosphate significantly decreased plasma levels of LDL cholesterol and elastin fragmentation in aorta. However, no effect was observed on both atherosclerotic plaque size in aortic roots and chemically induced thrombosis in carotid arteries. Importantly, oseltamivir phosphate administration had adverse effects on the liver of mice and significantly increased messenger RNA expression levels of F4/80, interleukin-1β, transforming growth factor-β1, matrix metalloproteinase-12, and collagen. Taken together, our findings suggest that oseltamivir phosphate has limited benefits on atherosclerosis and carotid thrombosis and may lead to adverse side effects on the liver with increased inflammation and fibrosis.

Identification and Evaluation of New Potential Inhibitors of Human Neuraminidase 1 Extracted from Olyra latifolia L.: A Preliminary Study

Sialidases, also called neuraminidases, are involved in several human pathologies such as neurodegenerative disorders, cancers, as well as infectious and cardiovascular diseases. Several studies have shown that neuraminidases, such as neuraminidase 1 (NEU-1), may be promising pharmacological targets. Therefore, the discovery of new selective inhibitors of NEU-1 are necessary to better understand the biological functions of this sialidase. In the present study, we describe the isolation and characterization of nine known compounds from Olyra latifolia L. leaves. This plant, known to have several therapeutic properties, belongs to the family of Poaceae and is found in the neotropics and in tropical Africa and Madagascar. Among the purified compounds, feddeiketone B, 2,3-dihydroxy-1-(4-hydroxy-3,5-diméthoxyphényl)-l-propanone, and syringylglycerol were shown to present structural analogy with DANA, and their effects on membrane NEU-1 sialidase activity were evaluated. Our results show that they possess inhibitory effects against NEU-1-mediated sialidase activity at the plasma membrane. In conclusion, we identified new natural bioactive molecules extracted from Olyra latifolia as inhibitors of human NEU-1 of strong interest to elucidate the biological functions of this sialidase and to target this protein involved in several pathophysiological contexts.

The Function of Sialidase Revealed by Sialidase Activity Imaging Probe

Sialidase cleaves sialic acid residues from glycans such as glycoproteins and glycolipids. In the brain, desorption of the sialic acid by sialidase is essential for synaptic plasticity, learning and memory and synaptic transmission. BTP3-Neu5Ac has been developed for sensitive imaging of sialidase enzyme activity in mammalian tissues. Sialidase activity in the rat hippocampus detected with BTP3-Neu5Ac increases rapidly by neuronal depolarization. It is presumed that an increased sialidase activity in conjunction with neural excitation is involved in the formation of the neural circuit for memory. Since sialidase inhibits the exocytosis of the excitatory neurotransmitter glutamate, the increased sialidase activity by neural excitation might play a role in the negative feedback mechanism against the glutamate release. Mammalian tissues other than the brain have also been stained with BTP3-Neu5Ac. On the basis of information on the sialidase activity imaging in the pancreas, it was found that sialidase inhibitor can be used as an anti-diabetic drug that can avoid hypoglycemia, a serious side effect of insulin secretagogues. In this review, we discuss the role of sialidase in the brain as well as in the pancreas and skin, as revealed by using a sialidase activity imaging probe. We also present the detection of influenza virus with BTP3-Neu5Ac and modification of BTP3-Neu5Ac.

Neuraminidases 1 and 3 Trigger Atherosclerosis by Desialylating Low-Density Lipoproteins and Increasing Their Uptake by Macrophages

Background Chronic vascular disease atherosclerosis starts with an uptake of atherogenic modified low-density lipoproteins (LDLs) by resident macrophages, resulting in formation of arterial fatty streaks and eventually atheromatous plaques. Increased plasma sialic acid levels, increased neuraminidase activity, and reduced sialic acid LDL content have been previously associated with atherosclerosis and coronary artery disease in human patients, but the mechanism underlying this association has not been explored. Methods and Results We tested the hypothesis that neuraminidases contribute to development of atherosclerosis by removing sialic acid residues from glycan chains of the LDL glycoprotein and glycolipids. Atherosclerosis progression was investigated in apolipoprotein E and LDL receptor knockout mice with genetic deficiency of neuraminidases 1, 3, and 4 or those treated with specific neuraminidase inhibitors. We show that desialylation of the LDL glycoprotein, apolipoprotein B 100, by human neuraminidases 1 and 3 increases the uptake of human LDL by human cultured macrophages and by macrophages in aortic root lesions in Apoe^-/- mice via asialoglycoprotein receptor 1. Genetic inactivation or pharmacological inhibition of neuraminidases 1 and 3 significantly delays formation of fatty streaks in the aortic root without affecting the plasma cholesterol and LDL levels in Apoe^-/- and Ldlr^-/- mouse models of atherosclerosis. Conclusions Together, our results suggest that neuraminidases 1 and 3 trigger the initial phase of atherosclerosis and formation of aortic fatty streaks by desialylating LDL and increasing their uptake by resident macrophages.

Using Bibliometric Analysis and Machine Learning to Identify Compounds Binding to Sialidase-1

Rare diseases impact hundreds of millions of individuals worldwide. However, few therapies exist to treat the rare disease population because financial resources are limited, the number of patients affected is low, bioactivity data is often nonexistent, and very few animal models exist to support preclinical development efforts. Sialidosis is an ultrarare lysosomal storage disorder in which mutations in the NEU1 gene result in the deficiency of the lysosomal enzyme sialidase-1. This enzyme catalyzes the removal of sialic acid moieties from glycoproteins and glycolipids. Therefore, the defective or deficient protein leads to the buildup of sialylated glycoproteins as well as several characteristic symptoms of sialidosis including visual impairment, ataxia, hepatomegaly, dysostosis multiplex, and developmental delay. In this study, we used a bibliometric tool to generate links between lysosomal storage disease (LSD) targets and existing bioactivity data that could be curated in order to build machine learning models and screen compounds in silico. We focused on sialidase as an example, and we used the data curated from the literature to build a Bayesian model which was then used to score compound libraries and rank these molecules for in vitro testing. Two compounds were identified from in vitro testing using microscale thermophoresis, namely sulfameter (K d 2.15 ± 1.02 μM) and mexenone (K d 8.88 ± 4.02 μM), which validated our approach to identifying new molecules binding to this protein, which could represent possible drug candidates that can be evaluated further as potential chaperones for this ultrarare lysosomal disease for which there is currently no treatment. Combining bibliometric and machine learning approaches has the ability to assist in curating small molecule data and model building, respectively, for rare disease drug discovery. This approach also has the capability to identify new compounds that are potential drug candidates.

An iPSC-based neural model of sialidosis uncovers glycolytic impairment-causing presynaptic dysfunction and deregulation of Ca2+ dynamics

Sialidosis is a neuropathic lysosomal storage disease caused by a deficiency in the NEU1 gene-encoding lysosomal neuraminidase and characterized by abnormal accumulation of undigested sialyl-oligoconjugates in systemic organs including brain. Although patients exhibit neurological symptoms, the underlying neuropathological mechanism remains unclear. Here, we generated induced pluripotent stem cells (iPSCs) from skin fibroblasts with sialidosis and induced the differentiation into neural progenitor cells (NPCs) and neurons. Sialidosis NPCs and neurons mimicked the disease-like phenotypes including reduced neuraminidase activity, accumulation of sialyl-oligoconjugates and lysosomal expansions. Functional analysis also revealed that sialidosis neurons displayed two distinct abnormalities, defective exocytotic glutamate release and augmented α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptor (AMPAR)-mediated Ca²⁺ influx. These abnormalities were restored by overexpression of the wild-type NEU1 gene, demonstrating causative role of neuraminidase deficiency in functional impairments of disease neurons. Comprehensive proteomics analysis revealed the significant reduction of SNARE proteins and glycolytic enzymes in synaptosomal fraction, with downregulation of ATP production. Bypassing the glycolysis by treatment of pyruvate, which is final metabolite of glycolysis pathway, improved both the synaptsomal ATP production and the exocytotic function. We also found that upregulation of AMPAR and L-type voltage dependent Ca²⁺ channel (VDCC) subunits in disease neurons, with the restoration of AMPAR-mediated Ca²⁺ over-load by treatment of antagonists for the AMPAR and L-type VDCC. Our present study provides new insights into both the neuronal pathophysiology and potential therapeutic strategy for sialidosis.

Polyvalent Transition-State Analogues of Sialyl Substrates Strongly Inhibit Bacterial Sialidases*

Bacterial sialidases (SA) are validated drug targets expressed by common human pathogens such as Streptococcus pneumoniae, Vibrio cholerae, or Clostridium perfringens. Noncovalent inhibitors of bacterial SA capable of reaching the submicromolar level are rarely reported. In this work, multi- and polyvalent compounds are developed, based on the transition-state analogue 2-deoxy-2,3-didehydro-N-acetylneuraminic (DANA). Poly-DANA inhibits the catalytic activity of SA from S. pneumoniae (NanA) and the symbiotic microorganism B. thetaiotaomicron (BtSA) at the picomolar and low nanomolar levels (expressed in moles of molecules and of DANA, respectively). Each DANA grafted to the polymer surpasses the inhibitory potential of the monovalent analogue by more than four orders of magnitude, which represents the highest multivalent effect reported so far for an enzyme inhibition. The synergistic interaction is shown to operate exclusively in the catalytic domain, and not in the flanked carbohydrate-binding module (CBM). These results offer interesting perspectives for the multivalent inhibition of other SA families lacking a CBM, such as viral, parasitic, or human SA.

Recent progress in chemical approaches for the development of novel neuraminidase inhibitors

Influenza virus is the main cause of an infectious disease called influenza affecting the respiratory system including the throat, nose and lungs. Neuraminidase inhibitors are reagents used to block the enzyme called neuraminidase to prevent the influenza infection from spreading. Neuraminidase inhibitors are widely used in the treatment of influenza infection, but still there is a need to develop more potent agents for the more effective treatment of influenza. Complications of the influenza disease lead to death, and one of these complications is drug resistance; hence, there is an urgent need to develop more effective agents. This review focuses on the recent advances in chemical synthesis pathways used for the development of new neuraminidase agents along with the medicinal aspects of chemically modified molecules, including the structure-activity relationship, which provides further rational designs of more active small molecules.

Transmembrane Peptides as a New Strategy to Inhibit Neuraminidase-1 Activation

Sialidases, or neuraminidases, are involved in several human disorders such as neurodegenerative, infectious and cardiovascular diseases, and cancers. Accumulative data have shown that inhibition of neuraminidases, such as NEU1 sialidase, may be a promising pharmacological target, and selective inhibitors of NEU1 are therefore needed to better understand the biological functions of this sialidase. In the present study, we designed interfering peptides (IntPep) that target a transmembrane dimerization interface previously identified in human NEU1 that controls its membrane dimerization and sialidase activity. Two complementary strategies were used to deliver the IntPep into cells, either flanked to a TAT sequence or non-tagged for solubilization in detergent micelles. Combined with molecular dynamics simulations and heteronuclear nuclear magnetic resonance (NMR) studies in membrane-mimicking environments, our results show that these IntPep are able to interact with the dimerization interface of human NEU1, to disrupt membrane NEU1 dimerization and to strongly decrease its sialidase activity at the plasma membrane. In conclusion, we report here new selective inhibitors of human NEU1 of strong interest to elucidate the biological functions of this sialidase.

Therapeutic Effect of Neuraminidase-1-Selective Inhibition in Mouse Models of Bleomycin-Induced Pulmonary Inflammation and Fibrosis

Pulmonary fibrosis remains a serious biomedical problem with no cure and an urgent need for better therapies. Neuraminidases (NEUs), including NEU1, have been recently implicated in the mechanism of pulmonary fibrosis by us and others. We now have tested the ability of a broad-spectrum neuraminidase inhibitor, 2,3-dehydro-2-deoxy-N-acetylneuraminic acid (DANA), to modulate the in vivo response to acute intratracheal bleomycin challenge as an experimental model of pulmonary fibrosis. A marked alleviation of bleomycin-induced body weight loss and notable declines in accumulation of pulmonary lymphocytes and collagen deposition were observed. Real-time polymerase chain reaction analyses of human and mouse lung tissues and primary human lung fibroblast cultures were also performed. A predominant expression and pronounced elevation in the levels of NEU1 mRNA were observed in patients with idiopathic pulmonary fibrosis and bleomycin-challenged mice compared with their corresponding controls, whereas NEU2, NEU3, and NEU4 were expressed at far lower levels. The levels of mRNA for the NEU1 chaperone, protective protein/cathepsin A (PPCA), were also elevated by bleomycin. Western blotting analyses demonstrated bleomycin-induced elevations in protein expression of both NEU1 and PPCA in mouse lungs. Two known selective NEU1 inhibitors, C9-pentyl-amide-DANA (C9-BA-DANA) and C5-hexanamido-C9-acetamido-DANA, dramatically reduced bleomycin-induced loss of body weight, accumulation of pulmonary lymphocytes, and deposition of collagen. Importantly, C9-BA-DANA was therapeutic in the chronic bleomycin exposure model with no toxic effects observed within the experimental timeframe. Moreover, in the acute bleomycin model, C9-BA-DANA attenuated NEU1-mediated desialylation and shedding of the mucin-1 ectodomain. These data indicate that NEU1-selective inhibition offers a potential therapeutic intervention for pulmonary fibrotic diseases. SIGNIFICANCE STATEMENT: Neuraminidase-1-selective therapeutic targeting in the acute and chronic bleomycin models of pulmonary fibrosis reverses pulmonary collagen deposition, accumulation of lymphocytes in the lungs, and the disease-associated loss of body weight-all without observable toxic effects. Such therapy is as efficacious as nonspecific inhibition of all neuraminidases in these models, thus indicating the central role of neuraminidase-1 as well as offering a potential innovative, specifically targeted, and safe approach to treating human patients with a severe malady: pulmonary fibrosis.

Human neuraminidases have reduced activity towards modified sialic acids on glycoproteins

Multiple levels of diversity in sialic acid presentation can influence the substrate activity of sialosides for glycoside hydrolases. Few reports have investigated the specificity of human neuraminidase (hNEU) activity towards modified sialic acid residues that can occur on glycoproteins. Previously, we evaluated hNEU activity towards 9-O-acetylated sialic acid in glycolipid substrates and found that hNEU generally discriminated against 9-O-acetylated sialic acid over Neu5Ac. Here, we have investigated the substrate specificity of hNEU enzymes for a glycoprotein substrate (bovine submaxillary mucin) containing 9-O-acetylated and Neu5Gc residues. Using this model substrate, we observe a general trend for hNEU tolerance of Neu5Ac > Neu5Gc ≫ Neu5,9Ac₂, consistent with our previous results with glycolipid substrates. These results expand our understanding of hNEU enzyme specificity and suggest that naturally occurring modifications of sialic acids can play a role in regulating hNEU activity.

Isoenzyme-Selective Inhibitors of Human Neuraminidases Reveal Distinct Effects on Cell Migration

The human neuraminidase enzymes (NEU1, NEU2, NEU3, and NEU4) are a class of enzymes implicated in pathologies including cancer and diabetes. Several reports have linked neuraminidase activity to the regulation of cell migration in cancer cells. Using an in vitro cell migration assay on fibronectin (FN) coated surfaces, we have investigated the role of these enzymes in integrin-mediated cell migration. We observed that neuraminidase inhibition caused significant retardation of cell migration in breast cancer (MDA-MB-231) and prostate cancer (PC-3) cell lines when using inhibitors of NEU3 and NEU4. In contrast, inhibition of NEU1 caused a significant increase in cell migration for the same cell lines. We concluded that the blockade of human neuraminidase enzymes with isoenzyme-selective inhibitors can lead to disparate results and has significant potential in the development of anticancer or wound healing therapeutics.

The sialidase inhibitor 2,3-dehydro-2-deoxy-N-acetylneuraminic acid is a glucose-dependent potentiator of insulin secretion

Sialidase cleaves sialic acid residues from a sialoglycoconjugate: oligosaccharides, glycolipids and glycoproteins that contain sialic acid. Histochemical imaging of the mouse pancreas using a benzothiazolylphenol-based sialic acid derivative (BTP3-Neu5Ac), a highly sensitive histochemical imaging probe used to assess sialidase activity, showed that pancreatic islets have intense sialidase activity. The sialidase inhibitor 2,3-dehydro-2-deoxy-N-acetylneuraminic acid (DANA) remarkably enhances glutamate release from hippocampal neurons. Since there are many similar processes between synaptic vesicle exocytosis and secretory granule exocytosis, we investigated the effect of DANA on insulin release from β-cells. Insulin release was induced in INS-1D cells by treatment with 8.3 mM glucose, and the release was enhanced by treatment with DANA. In a mouse intraperitoneal glucose tolerance test, the increase in serum insulin levels was enhanced by intravenous injection with DANA. However, under fasting conditions, insulin release was not enhanced by treatment with DANA. Calcium oscillations induced by 8.3 mM glucose treatment of INS-1D cells were not affected by DANA. Blood insulin levels in sialidase isozyme Neu3-deficient mice were significantly higher than those in WT mice under ad libitum feeding conditions, but the levels were not different under fasting conditions. These results indicate that DANA is a glucose-dependent potentiator of insulin secretion. The sialidase inhibitor may be useful for anti-diabetic treatment with a low risk of hypoglycemia.

Elastic fibers and elastin receptor complex: Neuraminidase-1 takes the center stage

Extracellular matrix (ECM) has for a long time being considered as a simple architectural support for cells. It is now clear that ECM presents a fundamental influence on cells driving their phenotype and fate. This complex network is highly specialized and the different classes of macromolecules that comprise the ECM determine its biological functions. For instance, collagens are responsible for the tensile strength of tissues, proteoglycans and glycosaminoglycans are essential for hydration and resistance to compression, and glycoproteins such as laminins facilitate cell attachment. The largest structures of the ECM are the elastic fibers found in abundance in tissues suffering high mechanical constraints such as skin, lungs or arteries. These structures present a very complex composition whose core is composed of elastin surrounded by a microfibrils mantle. Elastogenesis is a tightly regulated process involving the sialidase activity of the Neuraminidase-1 (Neu-1) sub-unit of the Elastin Receptor Complex. Interestingly, Neu-1 subunit also serves as a sensor of elastin degradation via its ability to transmit elastin-derived peptides signaling. Finally, reports showing that neuraminidase activity is able to regulate TGF-β activation raises questions about a possible role for Neu-1 in elastic fibers remodeling. In this mini review, we develop the concept of the regulation of the whole life of elastic fibers through an original scope, the key role of Neu-1 sialidase enzymatic activity.