Identification and purification of cytolytic antibodies directed against O-acetylated sialic acid in childhood acute lymphoblastic leukemia

O-acetylesterase activity of Bifidobacterium bifidum sialidase facilities the liberation of sialic acid and encourages the proliferation of sialic acid scavenging Bifidobacterium breve

Bifidobacterium bifidum possesses two extracellular sialidases (SiaBb1 and SiaBb2) that release free sialic acid from mucin sialoglycans, which can be utilized via cross-feeding by Bifidobacterium breve that, otherwise, is prevented from utilizing this nutrient source. Modification of sialic acids with O-acetyl esters is known to protect mucin glycans from degradation by bacterial sialidases. Compared to SiaBb2, SiaBb1 has an additional O-acetylesterase (Est) domain. We aimed to elucidate the role of the SiaBb1 Est domain from B. bifidum in sialic acid cross-feeding within Bifidobacterium. Pre-treatment of mucin secreted from bovine submaxillary glands (BSM) using His₆ -tagged-Est and -SiaBb2 released a higher amount of sialic acid compared to the pre-treatment by His₆ -SiaBb2. Growth of B. breve increased with an increase in nanE expression when supplemented with both His₆ -Est- and His₆ -SiaBb2-treated BSM. These results indicate that the esterase activity of the SiaBb1 Est domain enhances the efficiency of SiaBb2 to cleave sialic acid from mucin. This free sialic acid can be utilized by coexisting sialic acid scavenging B. breve via cross-feeding. Here, we provide the molecular mechanism underlying the unique sialoglycan degradation property of B. bifidum which is mediated by the complementary activities of SiaBb1 and SiaBb2 in the context of sialic acid cross-feeding.

A Novel Compound Plumercine from Plumeria alba Exhibits Promising Anti-Leukemic Efficacies against B Cell Acute Lymphoblastic Leukemia

The current study was focused to evaluate the antioxidant and the anti-cancerous properties of Plumeria alba. Plumeria alba was chosen due to its existing medicinal values. Antioxidant assays like Superoxide radical scavenging assay, Nitrous Oxide radical scavenging assay, were performed, on the methanolic and ethyl acetate extracts of the plant, that depicts the pro-oxidant nature of the extract. Further, they were tested to check cell viability on B cell Acute Lymphoblastic Leukemia (ALL) Cell line (NALM 6), human lung cancer cell line (A549), T cell Acute Lymphoblastic Leukemia cell line (MOLT4), and PBMC isolated from normal donors utilizing MTT assay. Robust anti-proliferative activity was observed in the case of NALM 6 followed by A549, MOLT4, whereas negligible activity was observed in the case of PBMC. Intrigued by this finding, in silico docking was performed using three bioactive compounds namely Plumericine, Isoplumericine, and 13-O-p-Coumaroylplumieride, unique to Plumeria sp. They were docked against five different cyclins and Cdk proteins responsible for ALL. The compounds have shown satisfactory results and their druggability and ADMET properties were checked further. Plumercine turned out to be the most competent compound and hence can be considered as a potential leukemic drug candidate in the future.

Sialic acid and biology of life: An introduction

Sialic acids are important molecule with high structural diversity. They are known to occur in higher animals such as Echinoderms, Hemichordata, Cephalochorda, and Vertebrata and also in other animals such as Platyhelminthes, Cephalopoda, and Crustaceae. Plants are known to lack sialic acid. But they are reported to occur in viruses, bacteria, protozoa, and fungi. Deaminated neuraminic acid although occurs in vertebrates and bacteria, is reported to occur in abundance in the lower vertebrates. Sialic acids are mostly located in terminal ends of glycoproteins and glycolipids, capsular and tissue polysialic acids, bacterial lipooligosaccharides/polysaccharides, and in different forms that dictate their role in biology. Sialic acid play important roles in human physiology of cell-cell interaction, communication, cell-cell signaling, carbohydrate-protein interactions, cellular aggregation, development processes, immune reactions, reproduction, and in neurobiology and human diseases in enabling the infection process by bacteria and virus, tumor growth and metastasis, microbiome biology, and pathology. It enables molecular mimicry in pathogens that allows them to escape host immune responses. Recently sialic acid has found role in therapeutics. In this chapter we have highlighted the (i) diversity of sialic acid, (ii) their occurrence in the diverse life forms, (iii) sialylation and disease, and (iv) sialic acid and therapeutics.

Recent approaches for directly profiling cell surface sialoform

Sialic acids (SAs) are nine-carbon monosaccharides existing at the terminal location of glycan structures on the cell surface and secreted glycoconjugates. The expression levels and linkages of SAs on cells and tissues, collectively known as sialoform, present the hallmark of the cells and tissues of different systems and conditions. Accordingly, detecting or profiling cell surface sialoforms is very critical for understanding the function of cell surface glycans and glycoconjugates and even the molecular mechanisms of their underlying biological processes. Further, it may provide therapeutic and diagnostic applications for different diseases. In the past decades, several kinds of SA-specific binding molecules have been developed for detecting and profiling specific sialoforms of cells and tissues; the experimental materials have expanded from frozen tissue to living cells; and the analytical technologies have advanced from histochemistry to fluorescent imaging, flow cytometry and microarrays. This review summarizes the recent bioaffinity approaches for directly detecting and profiling specific SAs or sialylglycans, and their modifications of different cells and tissues.

Deacetylation of sialic acid by esterases potentiates pneumococcal neuraminidase activity for mucin utilization, colonization and virulence

Pneumococcal neuraminidase is a key enzyme for sequential deglycosylation of host glycans, and plays an important role in host survival, colonization, and pathogenesis of infections caused by Streptococcus pneumoniae. One of the factors that can affect the activity of neuraminidase is the amount and position of acetylation present in its substrate sialic acid. We hypothesised that pneumococcal esterases potentiate neuraminidase activity by removing acetylation from sialic acid, and that will have a major effect on pneumococcal survival on mucin, colonization, and virulence. These hypotheses were tested using isogenic mutants and recombinant esterases in microbiological, biochemical and in vivo assays. We found that pneumococcal esterase activity is encoded by at least four genes, SPD_0534 (EstA) was found to be responsible for the main esterase activity, and the pneumococcal esterases are specific for short acyl chains. Assay of esterase activity by using natural substrates showed that both the Axe and EstA esterases could use acetylated xylan and Bovine Sub-maxillary Mucin (BSM), a highly acetylated substrate, but only EstA was active against tributyrin (triglyceride). Incubation of BSM with either Axe or EstA led to the acetate release in a time and concentration dependent manner, and pre-treatment of BSM with either enzyme increased sialic acid release on subsequent exposure to neuraminidase A. qRT-PCR results showed that the expression level of estA and axe increased when exposed to BSM and in respiratory tissues. Mutation of estA alone or in combination with nanA (codes for neuraminidase A), or the replacement of its putative serine active site to alanine, reduced the pneumococcal ability to utilise BSM as a sole carbon source, sialic acid release, colonization, and virulence in a mouse model of pneumococcal pneumonia.

Immunoaffinity Chromatography: Concepts and Applications

Antibody-based separation methods, such as immunoaffinity chromatography (IAC), are powerful purification and isolation techniques. Antibodies isolated using these techniques have proven highly efficient in applications ranging from clinical diagnostics to environmental monitoring. Immunoaffinity chromatography is an efficient antibody separation method which exploits the binding efficiency of a ligand to an antibody. Essential to the successful design of any IAC platform is the optimization of critical experimental parameters such as (a) the biological affinity pair, (b) the matrix support, (c) the immobilization coupling chemistry, and (d) the effective elution conditions. These elements and the practicalities of their use are discussed in detail in this review. At the core of all IAC platforms is the high affinity interactions between antibodies and their related ligands; hence, this review entails a brief introduction to the generation of antibodies for use in immunoaffinity chromatography and also provides specific examples of their potential applications.

Cytotoxic activity against human neuroblastoma and melanoma cells mediated by IgM antibodies derived from peripheral blood of healthy donors

A small percentage of healthy donors identified in the Western population carry antibodies in their peripheral blood which convey cytotoxic activity against certain human melanoma and neuroblastoma cell lines. We measured the cytotoxic activity of sera and plasmas from healthy donors on the human neuroblastoma cell line Kelly and various melanoma cell lines. Antibodies of IgM isotype, presumably belonging to the class of naturally occurring antibodies, exerted cytotoxic activity in a complement-dependent fashion. Apart from complement-dependent tumor cell lysis, we observed C3 opsonization in all tumor cell lines upon treatment with cytotoxic plasmas. Cell lines tested primarily expressed membrane complement regulatory proteins (mCRP) CD46, CD55 and CD59 to various extents. Blocking of mCRPs by monoclonal antibodies enhanced cell lysis and opsonization, though some melanoma cells remained resistant to complement attack. Epitopes recognized by cytotoxic antibodies were represented by gangliosides such as GD2 and GD3, as evidenced by cellular sialidase pretreatment and enhanced expression of distinct gangliosides. It remains to be clarified why only a small fraction of healthy persons carry these antitumor cytotoxic antibodies.

Characterization of a sialate-O-acetylesterase (NanS) from the oral pathogen Tannerella forsythia that enhances sialic acid release by NanH, its cognate sialidase

We characterize a novel bacterial sialate-O-acetylesterase potentially important for the nutrition of oral pathogens causing periodontal disease by enhancing their ability to harvest sialic acid sugar. Its high activity and stability indicate that it can also be used in glycan pharmacoanalytics.

Two-step chromatography purification of IgGs possessing sialidase activity from human blood serum

Sialation of cell surface is known to be tightly connected with tumorigenicity, invasiveness, metastatic potential and clearance of aged cells, while sialation of immunoglobulin G (IgG) molecules determines their anti-inflammatory properties. Recently, we have found for the first time IgG-antibodies possessing sialidase-like activity (sialylic abzyme) in blood serum of multiple myeloma and systemic lupus erythematosis patients. This abzyme was detected in a pool of IgGs purified by a typical procedure including immunoglobulin's precipitation with ammonium sulfate and following chromatography on protein G-Sepharose column. Here we describe a novel matrix for affinity purification of sialylic abzyme that is based on using bovine submandibular gland mucin conjugated to Sepharose matrix (mucin-Sepharose). This matrix preferentially binds sialidase-like IgGs from a pool of sialidase-active fraction of proteins precipitated with 50% ammonium sulfate from blood serum of the systemic lupus erythematosis patients. That allowed us to develop a new scheme of double-step chromatography purification of sialidase-like IgGs from human blood serum.

Identification and analysis of o-acetylated sialoglycoproteins

5-N-acetylneuraminic acid, commonly known as sialic acid (Sia), constitutes a family of N- and O-substituted 9-carbon monosaccharides. Frequent modification of O-acetylations at positions C-7, C-8, or C-9 of Sias generates a family of O-acetylated sialic acid (O-AcSia) and plays crucial roles in many cellular events like cell-cell adhesion, proliferation, migration, etc. Therefore, identification and analysis of O-acetylated sialoglycoproteins (O-AcSGPs) are important. In this chapter, we describe several approaches for successful identification of O-AcSGPs. We broadly divide them into two categories, i.e., invasive and noninvasive methods. Several O-AcSias-binding probes are used for this purpose. Detailed methodologies for step-by-step identification using these probes have been discussed. We have also included a few invasive analytical methods for identification and quantitation of O-AcSias. Several indirect methods are also elaborated for such purpose, in which O-acetyl group from sialic acids is initially removed followed by detection of Sias by several approaches. For molecular identification, we have described methods for affinity purification of O-AcSGPs using an O-AcSias-binding lectin as an affinity matrix followed by sequencing using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF-TOF) mass spectroscopy (MS). In spite of special attention, loss of O-acetyl groups due to its sensitivity towards alkaline pH and high temperature along with migration of labile O-acetyl groups from C7-C8-C9 during sample preparation is difficult to avoid. Therefore there is always a risk for underestimation of O-AcSias.

Sialoglycosylation of RBC in visceral leishmaniasis leads to enhanced oxidative stress, calpain-induced fragmentation of spectrin and hemolysis

Visceral leishmaniasis (VL) caused by the intracellular parasite Leishmania donovani accounts for an estimated 12 million cases of human infection. It is almost always associated with anemia, which severely complicates the disease course. However, the pathological processes leading to anemia in VL have thus far not been adequately characterized to date. In studying the glycosylation patterns of peripheral blood cells we found that the red blood cells (RBC) of VL patients (RBC(VL)) express eight 9-O-acetylated sialoglycoproteins (9-O-AcSGPs) that are not detected in the RBC of healthy individuals (RBC(N)). At the same time, the patients had high titers of anti-9-O-AcSGP IgG antibodies in their sera. These two conditions appear to be linked and related to the anemic state of the patients, as exposure of RBC(VL) but not RBC(N) to anti-9-O-AcSGPs antibodies purified from patient sera triggered a series of responses. These included calcium influx via the P/Q-type but not L-type channels, activation of calpain I, proteolysis of spectrin, enhanced oxidative stress, lipid peroxidation, externalization of phosphatidyl serine with enhanced erythrophagocytosis, enhanced membrane fragility and, finally, hemolysis. Taken together, this study suggests that the enhanced hemolysis is linked to an impairment of membrane integrity in RBC(VL) which is mediated by ligand-specific interaction of surface 9-O-AcSGPs. This affords a potential explanation for the structural and functional features of RBC(VL) which are involved in the hemolysis related to the anemia which develops in VL patients.

Functions and Biosynthesis of O-Acetylated Sialic Acids

Sialic acids have a pivotal functional impact in many biological interactions such as virus attachment, cellular adhesion, regulation of proliferation, and apoptosis. A common modification of sialic acids is O-acetylation. O-Acetylated sialic acids occur in bacteria and parasites and are also receptor determinants for a number of viruses. Moreover, they have important functions in embryogenesis, development, and immunological processes. O-Acetylated sialic acids represent cancer markers, as shown for acute lymphoblastic leukemia, and they are known to play significant roles in the regulation of ganglioside-mediated apoptosis. Expression of O-acetylated sialoglycans is regulated by sialic acid-specific O-acetyltransferases and O-acetylesterases. Recent developments in the identification of the enigmatic sialic acid-specific O-acetyltransferase are discussed.

Immunoaffinity chromatography

Antibody-based separation methods, such as immunoaffinity chromatography (IAC), are powerful purification and isolation techniques. Antibodies isolated using these techniques have proven highly efficient in applications ranging from clinical diagnostics to environmental monitoring. IAC is an efficient antibody separation method which exploits the binding efficiency of a ligand to an antibody. Essential to the successful design of any IAC platform is the optimisation of critical experimental parameters such as: (a) the biological affinity pair, (b) the matrix support, (c) the immobilisation coupling chemistry, and (d) the effective elution conditions. These elements and the practicalities of their use are discussed in detail in this review. At the core of all IAC platforms is the high-affinity interactions between antibodies and their related ligands; hence, this review entails a brief introduction to the generation of antibodies for use in IAC and also provides specific examples of their potential applications.

Identification of a sulfonoquinovosyldiacylglyceride from Azadirachta indica and studies on its cytotoxic activity and DNA binding properties

Chromatographic separation of the methanolic extract of the leaves of Azadirachta indica led to the isolation of a sulfonoglycolipid characterized as a sulfonoquinovosyldiacylglyceride (SQDG), by extensive 2D NMR and mass spectral analysis. SQDG induces apoptosis in a dose dependent manner with IC(50) 8.3 μM against acute lymphoblastic leukemia (ALL) MOLT-4 cell lines. The compound showed significant DNA binding properties as evidenced by the enhancement of melting temperature and perturbation of the characteristic B-form in CD evidence of calf thymus DNA. The DNA binding was also characterized by isothermal calorimetry where a predominantly enthalpy driven binding to CT DNA was revealed.

Identification of pregnancy-associated CA125-reactive protein as a carbohydrate-binding immunoglobulin G

Cancer antigen 125 (CA125), also referred to as mucin 16, is expressed under both normal and pathological conditions and the complexity of its structure indicates multifunctionality, i.e. both the protein and carbohydrate parts may be involved in diverse interactions at different levels of cell and tissue organization. Its biological role is not understood, but involvement in immune response modulation and influence on cell adhesion have been speculated. This study aimed at isolation and characterization of endogenous ligands for CA125 as an initial step in gaining insight into its activity. A CA125-reactive fraction was separated from human placental extract by affinity chromatography. The isolated preparation was characterized by SDS-PAGE, immunoblotting, peptide mass fingerprinting and binding assay. The CA125-reactive fraction from placental extract was identified as carbohydrate-binding IgG. The glycan composition of inhibitors of carbohydrate-binding pointed to sialic acid as one determinant for recognition but indicated that sialylation was not alone and that glycotopes containing galactose, N-acetylgalactosamine and N-acetylglucosamine were also important. CA125-reactive IgG could be selectively enriched using fetuin as the ligand and represents a distinct IgG subfraction differing from abundant natural carbohydrate-binding antibodies. Taking advantage of the particular properties of ligands for CA125 may have biomedical potential for use as biological modifiers or delivery agents and have an impact beyond pregnancy, since many immunoregulatory molecular pathways are common to embryonic development and malignant transformation.

Disease-associated glycosylated molecular variants of human C-reactive protein activate complement-mediated hemolysis of erythrocytes in tuberculosis and Indian visceral leishmaniasis

Human C-reactive protein (CRP), as a mediator of innate immunity, removed damaged cells by activating the classical complement pathway. Previous studies have successfully demonstrated that CRPs are differentially induced as glycosylated molecular variants in certain pathological conditions. Affinity-purified CRPs from two most prevalent diseases in India viz. tuberculosis (TB) and visceral leishmaniasis (VL) have differential glycosylation in their sugar composition and linkages. As anemia is a common manifestation in TB and VL, we assessed the contributory role of glycosylated CRPs to influence hemolysis via CRP-complement-pathway as compared to healthy control subjects. Accordingly, the specific binding of glycosylated CRPs with erythrocytes was established by flow-cytometry and ELISA. Significantly, deglycosylated CRPs showed a 7-8-fold reduced binding with erythrocytes confirming the role of glycosylated moieties. Scatchard analysis revealed striking differences in the apparent binding constants (10(4)-10(5) M(-1)) and number of binding sites (10(6)-10(7)sites/erythrocyte) for CRP on patients' erythrocytes as compared to normal. Western blotting along with immunoprecipitation analysis revealed the presence of distinct molecular determinants on TB and VL erythrocytes specific to disease-associated CRP. Increased fragility, hydrophobicity and decreased rigidity of diseased-erythrocytes upon binding with glycosylated CRP suggested membrane damage. Finally, the erythrocyte-CRP binding was shown to activate the CRP-complement-cascade causing hemolysis, even at physiological concentration of CRP (10 microg/ml). Thus, it may be postulated that CRP have a protective role towards the clearance of damaged-erythrocytes in these two diseases.

Natural antibodies, intravenous immunoglobulin and their role in autoimmunity, cancer and inflammation

Natural antibodies are produced by B lymphocytes in the absence of external antigen stimulation. With their ability to recognize self, altered self and foreign antigens, they comprise an important first-line defence against invading pathogens, but are also important for tissue homeostasis. By recognizing oligosaccharides expressed on tumour cells and modified cell surface structures accompanying necrosis, natural antibodies have an important anti-tumorigenic function. IVIg contains a wide spectrum of specificities presented in normal plasma including natural antibodies and has been shown to exert inhibitory effects on tumour cells through a subfraction of anti-vascular endothelial growth factor immunoglobulin (Ig)G antibodies with anti-angiogenic properties. IgA antibodies also have potent immunomodulatory properties, being able to both induce and suppress immune responses. IgA-mediated inhibitory function is able to inhibit several inflammatory diseases including asthma and glomerulonephritis. Autoantibodies of the IgM type, on the other hand, have shown promising results in the treatment of multiple sclerosis. These autoantibodies promote remyelination rather than modulating inflammation. Oxidation-specific epitopes, as found in atherosclerotic lesions and on apoptotic cells, comprise one important target of natural antibodies. By recognizing these epitopes, natural antibodies neutralize proinflammatory responses and mediate atheroprotection.

O-acetylated sialic acids: multifaceted role in childhood acute lymphoblastic leukaemia

Childhood acute lymphoblastic leukaemia (ALL), a malignant transformation of the lymphoblasts, is highly responsive to chemotherapy. However, due to certain inadequacy in detection of minimal residual disease (MRD), relapse is a common phenomenon. To address this question, the present review deals with the induction of an unique O-acetyl derivative of sialic acid on a few disease-associated glycoproteins and glycolipids at the onset of childhood ALL, a finding of our group in the last decade. This information has been successfully utilized for diagnosis and prognosis of the disease. Existing literature is included for comparison. Additionally, cell surface overexpression of 9-O-acetylated sialoglycoproteins and antibodies against them present in patients' sera aid the survival of the malignant lymphoblasts and suggest a multifaceted role played by these molecules. Taken together, monitoring these molecules helps not only in unravelling the biology of this paediatric malignancy but also in personalizing the treatment strategies for the betterment of the patient population.

Co-expression of 9-O-acetylated sialoglycoproteins and their binding proteins on lymphoblasts of childhood acute lymphoblastic leukemia: an anti-apoptotic role

Enhanced levels of 9-O-acetylated sialoglycoproteins (Neu5,9Ac2GPs) as disease-associated molecules was reported to act as signaling molecules for promoting survival of lymphoblasts in childhood acute lymphoblastic leukemia (ALL). Here, we searched for potential physiological ligands for Neu5,9Ac2GPs that could be involved in modulating the survival of lymphoblasts. Accordingly, we examined the presence of binding proteins for Neu5,9Ac2GPs on cell lines and primary cells of patients with B- and T-ALL, at presentation of the disease. Peripheral blood mononuclear cells from normal healthy donors and cells from myeloid leukemia patients were used for comparison. Neu5,9Ac2GPs-binding proteins (BPs) were specifically detected on the surface of both T- and B-ALL-lymphoblasts and ALL-cell lines along with the consistent presence of Neu5,9Ac2GPs. The Neu5,9Ac2GPs and BPs also co-localized on the cell surface and interacted specificallyin vitro. Apoptosis of lymphoblasts, induced by serum starvation, was reversed in the presence of purified Neu5,9Ac2GPs due to possible engagement of BPs, and the anti-apoptotic role of this interaction was established. This is the first report of the presence of potential physiological ligands for disease-associated molecules like Neu5,9Ac2GPs, the interaction of which is able to trigger an anti-apoptotic signal conferring a survival advantage to leukemic cells in childhood ALL.

Chemo-enzymatic synthesis of C-9 acetylated sialosides

A chemo-enzymatic synthesis of [(5-acetamido-9-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galacto-2-nonulopyranosylonic acid)-(2-->3)-O-(beta-D-galactopyranosyl)-(1-->3)-O-(2-acetamido-2-deoxy-alpha-D-galactopyranosyl)]-l-serine acetate (1) has been accomplished by a regioselective chemical acetylation of Neu5Ac (2) to give 9-O-acetylated sialic acid 3, which was enzymatically converted into CMP-Neu5,9Ac(2) (4) employing a recombinant CMP-sialic acid synthetase from Neisseria meningitis [EC 2.7.7.43]. The resulting compound was then employed for the enzymatic glycosylation of the C-3' hydroxyl of chemically prepared glycosylated amino acid 10 using recombinant rat alpha-(2-->3)-O-sialyltransferase expressed in Spodooptera frugiperda [EC 2.4.99.4] to give, after deprotection of the N(alpha)-benzyloxycarbonyl (CBz)-protecting group of serine, target compound 1. The N(alpha)-CBz-protected intermediate 11 can be employed for the synthesis of glycolipopeptides for immunization purposes.

Flow-cytometric monitoring of disease-associated expression of 9-O-acetylated sialoglycoproteins in combination with known CD antigens, as an index for MRD in children with acute lymphoblastic leukaemia: a two-year longitudinal follow-up study

Background

Over expression of 9-O-acetylated sialoglycoproteins (Neu5,9Ac₂-GPs, abbreviated as OAcSGP) has been demonstrated as a disease-associated antigen on the lymphoblasts of childhood acute lymphoblastic leukaemia (ALL). Achatinin-H, a lectin, has selective affinity towards terminal 9-O-acetylated sialic acids-α2-6-Nacetylated galactosamine. Exploring this affinity, enhanced expression of OAcSGP was observed, at the onset of disease, followed by its decrease with chemotherapy and reappearance with relapse. In spite of treatment, patients retain the diseased cells referred to as minimal residual disease (MRD) responsible for relapse. Our aim was to select a suitable template by using the differential expression of OAcSGP along with other known CD antigens to monitor MRD in peripheral blood (PB) and bone marrow (BM) of Indian patients with B- or T-ALL during treatment and correlate it with the disease status.

Methods

A two-year longitudinal follow-up study was done with 109 patients from the onset of the disease till the end of chemotherapy, treated under MCP841protocol. Paired samples of PB (n = 1667) and BM (n = 999) were monitored by flow cytometry. Three templates selected for this investigation were OAcSGP⁺CD10⁺CD19⁺ or OAcSGP⁺CD34⁺CD19⁺ for B-ALL and OAcSGP⁺CD7⁺CD3⁺ for T-ALL.

Results

Using each template the level of MRD detection reached 0.01% for a patient in clinical remission (CR). 81.65% of the patients were in CR during these two years while the remaining relapsed. Failure in early clearance of lymphoblasts, as indicated by higher MRD, implied an elevated risk of relapse. Soaring MRD during the chemotherapeutic regimen predicted clinical relapse, at least a month before medical manifestation. Irrespective of B- or T-lineage ALL, the MRD in PB and BM correlated well.

Conclusion

A range of MRD values can be predicted for the patients in CR, irrespective of their lineage, being 0.03 ± 0.01% (PB) and 0.05 ± 0.015% (BM). These patients may not be stated as normal with respect to the presence of MRD. Hence, MRD study beyond two-years follow-up is necessary to investigate further reduction in MRD, thereby ensuring their disease-free survival. Therefore, we suggest use of these templates for MRD detection, during and post-chemotherapy for proper patient management strategies, thereby helping in personalizing the treatment.

O-acetylation of sialic acids is required for the survival of lymphoblasts in childhood acute lymphoblastic leukemia (ALL)

Exploiting the selective affinity of Achatinin-H towards 9-O-acetylneuraminic acid(alpha2-6)GalNAc, we have demonstrated the presence of 9-O-acetylated sialoglycoproteins (Neu5,9Ac(2)-GPs) on hematopoietic cells of children suffering from acute lymphoblastic leukemia (ALL), indicative of defective sialylation associated with this disease. The carbohydrate epitope of Neu5,9Ac(2)-GPs(ALL) was confirmed by using several synthetic sialic acid analogues. They are functionally active signaling molecules as demonstrated by their role in mediating lymphoproliferative responses and consequential increased production of IFN-gamma due to specific stimulation of Neu5,9Ac(2)-GPs on PBMC(ALL) with Achatinin-H. Cells devoid of 9-O-acetylations (9-O-AcSA(-)) revealed decreased nitric oxide production as compared to 9-O-AcSA(+) cells on exposure to IFN-gamma. Under this condition, a decrease in viability of 9-O-AcSA(-) cells as compared to 9-O-AcSA(+) cells was also observed which was reflected from increased caspase 3 activity and apoptosis suggesting the protective role of this glycotope. These Neu5,9Ac(2)-GPs are also capable of inducing disease-specific anti-Neu5,9Ac(2)-GPs antibodies in ALL children. Additionally, we have observed that disease-specific anti-Neu5,9Ac(2)-GPs have altered glycosylation profile, and they are incapable of exerting a few Fc-glycosylation-sensitive effector functions. These observations hint toward a disbalanced homeostasis, thereby enabling the cancer cells to escape host defense. Taken together, it may be hypothesized that Neu5,9Ac(2)-GPs and their antibodies play a prominent role in promoting the survival of lymphoblasts in ALL.

Genome-based identification and characterization of a putative mucin-binding protein from the surface of Streptococcus pneumoniae

Streptococcus pneumoniae open reading frame SP1492 encodes a surface protein that contains a novel conserved domain similar to the repeated fragments of mucin-binding proteins from lactobacilli and lactococci. To investigate the functional role(s) of this protein and its potential adhesive properties, the surface-exposed region of SP1492 was expressed in Escherichia coli, purified to homogeneity, and partially characterized by biophysical and immunological methods. Circular dichroism and sedimentation measurements confirmed that SP1492 is an all-beta protein that exists in solution as a monomer. The SP1492 protein has been shown to be expressed by S. pneumoniae and was experimentally localized to its surface. The protein functional domain binds to mucins II and III from porcine stomach and to purified submaxillary bovine gland mucin. It appears to be one of the very few unambiguous pneumococcal adhesin molecules known to date. A hypothetical model constructed by ab initio techniques predicts a novel beta-sandwich protein structure.

Identification of 9-O-acetyl-N-acetylneuraminic acid in normal canine pre-ocular tear film secreted mucins and its depletion in Keratoconjunctivitis sicca

O-Acetylated sialic acids have been reported in many sialoglycoproteins where they mediate a variety of immune and other biological events. We have previously demonstrated that the protective mucus barrier on the surface of the canine eye contains sialoglycoproteins. We have also investigated the occurrence of O-acetylated sialic acids in these ocular mucins. Mucus aspirated from the surface of normal dog eyes and those with keratoconjunctivitis sicca (KCS) was fractionated into three pools by density gradient centrifugation. Sialic acids comprised 0.6-0.9% of the dry weight of the mucins isolated. The sialic acid profile in these pools was examined using HPLC. O-Acetylated sialic acids, mainly Neu5,9Ac2, were detected in normal animals and made up 10-30% of the total sialic acids detected. A doubling of the sialic acid content was found in KCS mucins, but the level of 9-O-acetylated sialic acid was reduced below 4% of total. Histological analysis of conjunctival tissue from normal and KCS dogs showed the presence of sialic acids, detected with the alpha(2-6) sialic acid-specific lectin Sambucus nigra, in the goblet cells and corresponding to the staining pattern for MUC5AC, the major ocular-secreted mucin gene product. In KCS animals a disruption of the normal pattern of conjunctival goblet cells was seen with preservation of the pattern of lectin binding observed in normal animals. Thus the data demonstrate the presence of mono-O-Acetylated sialic acids in normal canine ocular mucins and a loss of this population of sialic acids in dry eye disease in spite of a significant increase in total sialic acids in KCS mucin.

Interferon gamma promotes survival of lymphoblasts overexpressing 9-O-acetylated sialoglycoconjugates in childhood acute lymphoblastic leukaemia (ALL)

An enhanced linkage-specific 9-O-acetylated sialic acid (9-O-AcSA) on peripheral blood mononuclear cells (PBMC) of children with acute lymphoblastic leukaemia, ALL (PBMC(ALL), 9-O-AcSA+ cells) was demonstrated by using a lectin, Achatinin-H, whose lectinogenic epitope was 9-O-AcSAalpha2-6GalNAc. Our aim was to evaluate the in vitro contributory role of this glycotope (9-O-AcSAalpha2-6GalNAc) towards the survival of these 9-O-AcSA+ cells in ALL patients. For direct comparison, 9-O-AcSA- cells were generated by removing O-acetyl group of 9-O-AcSA present on PBMC(ALL) using O-acetyl esterase. An elevated level of serum interferon gamma (IFN-gamma) in affected children led us to think that PBMC(ALL) are continuously exposed specifically to this cytokine. Accordingly, 9-O-AcSA+ and 9-O-AcSA- cells were exposed in vitro to IFN-gamma. A twofold increased NO release along with inducible NO synthase (iNOS) mRNA expression by the 9-O-AcSA+ cells was observed as compared to the 9-O-AcSA- cells. The decreased viability of IFN-gamma exposed 9-O-AcSA- cells as compared to 9-O-AcSA+ cells were reflected from a 5.0-fold increased caspase-3-like activity and a 10.0-fold increased apoptosis in the 9-O-AcSA- cells when production of NO was lowered by adding competitive inhibitor of iNOS in reaction mixture. Therefore, it may be envisaged that a link exists between induction of this glycotope and their role in regulating viability of PBMC(ALL). Taken together, it is reasonable to hypothesise that O-acetylation of sialic acids on PBMC(ALL) may be an additional mechanism that promotes the survival of lymphoblasts by avoiding apoptosis via IFN-gamma-induced NO production.

Increased interferon gamma production by peripheral blood mononuclear cells in response to stimulation of overexpressed disease-specific 9-O-acetylated sialoglycoconjugates in children suffering from acute lymphoblastic leukaemia

Disease-specific over-expression of 9-O-acetylated sialoglycoconjugates (9-O-AcSGs) on peripheral blood mononuclear cells (PBMC) of children with acute lymphoblastic leukaemia (ALL, PBMC(ALL)) has been demonstrated using a lectin, Achatinin-H, with specificity towards 9-O-AcSAalpha2-6GalNAc. This study investigated the contributory role of 9-O-AcSGs induced on PBMC(ALL). Stimulation of PBMC(ALL) with Achatinin-H through 9-O-AcSGs led to a lymphoproliferative response with a significantly increased interferon-gamma (IFN-gamma) production when compared with unstimulated cells as demonstrated by enzyme-linked immunosorbent assay and mRNA expression. Under identical conditions, PBMC(ALL) ablated of O-acetylations did not respond to such stimulation. In summary, it may be concluded that stimulation of over-expressed 9-O-AcSGs regulate signalling for proliferation, leading to the release of IFN-gamma. Controlled expression of these molecules may be exploited as potential targets for therapy, promising beneficial effects to children with ALL.

Detection of immune-complexed 9-O-acetylated sialoglycoconjugates in the sera of patients with pediatric acute lymphoblastic leukemia

Although childhood acute lymphoblastic leukemia (ALL) is highly responsive to chemotherapy, reliable techniques are needed to determine treatment outcome. Over expression of 9-O-acetylated sialoglycoconjugates (9-OAcSGs) on lymphoblasts and concomitant anti-9-OAcSGs was found to have a diagnostic and prognostic potential. However, the presence of circulatory immune-complexed antigens remains unknown. The present study was aimed to evaluate whether immune-complexed 9-OAcSGs can be harnessed for better disease management. Immune-complexed antigens were evaluated in ALL sera (n=262) by a Dot-blot using a 9-OAcSAalpha2-6GalNAc-specific lectin, Achatinin-H. Using three serum samples, the inter- and intra-assay imprecision was evaluated as 11-13% and 7-11%, respectively. The recovery of spiked 9-OAcSGs was 84.2-95.4%. The central 95% reference interval for immune-complexed 9-OAcSGs in normal human sera (NHS, n=144) was 2.9-3.4 mug/ml irrespective of sex and age. At disease presentation, the immune-complexed 9-OAcSGs were fivefold higher than NHS, decreased with remission induction and importantly, reappeared with clinical relapse. Sera from patients with other hematological disorders (n=86) showed negligible levels. The Dot-blot demonstrated the potential application of immune-complexed antigen as a disease-specific marker and its efficacy as a sensitive and specific method that could serve as an economical yet effective index for monitoring disease status.

Purification, characterization of O-acetylated sialoglycoconjugates-specific IgM, and development of an enzyme-linked immunosorbent assay for diagnosis and follow-up of indian visceral leishmaniasis patients

The surface expression of 9-O-acetylated sialic acid (9-OAcSA) is elevated on hematopoietic cells and erythrocytes of visceral leishmaniasis (VL) patients. In this study, we show that VL patients contain elevated levels of IgM antibodies directed against 9-O-acetylated sialoglycoconjugates (9-OAcSG). These antibodies were affinity purified with bovine submaxillary protein as the affinity matrix containing the terminal epitope, 9-OAcSAalpha2-6GalNAc. They also bound to 9-OAcSGs on hematopoietic cells of patients with VL and to epitopes in the cytosol of Leishmania donovani promastigotes. A novel enzyme-linked immunosorbent assay was employed that showed 4-fold higher anti-OAcSG titers in VL patients (n=38), mean +/- S.E.M. being 0.83 +/- 0.09 vs. 0.21 +/- 0.04 detected in normal donors (n=20) and patients with cross-reactive diseases such as malaria (n=4) or tuberculosis (n=4). Assay specificity and sensitivity was 100% and 92%, respectively, whereas positive and negative predictive values were 100% and 90%, respectively. Significantly, anti-OAcSG titers declined 30 days after completion of anti-leishmanial treatment, indicating that monitoring of anti-9-OAcSGs may be a valuable alternative toward increasing the efficiency of diagnosis and follow-up of VL.

Differential expression of 9-O-acetylated sialoglycoconjugates on leukemic blasts: a potential tool for long-term monitoring of children with acute lymphoblastic leukemia

Earlier studies have demonstrated overexpression of 9-O-acetylated sialoglycoconjugates (9-O-AcSGs) on lymphoblasts, concomitant with high titers of anti-9-O-AcSG antibodies in childhood acute lymphoblastic leukemia (ALL). Our aim was to evaluate the correlation between expression of different 9-O-AcSGs during chemotherapeutic treatment. Accordingly, expression of 9-O-AcSGs on lymphoblasts of ALL patients (n = 70) were longitudinally monitored for 6 years (1997-2002), using Achatinin-H, a 9-O-acetylated sialic acid (9-O-AcSA) binding lectin with preferential affinity for 9-O-AcSGs with terminal 9-O-AcSA alpha 2-->6GalNAc. Western blot analysis of patients (n = 30) showed that 3 ALL-specific 9-O-AcSGs (90, 120 and 135 kDa) were induced at presentation; all these bands disappeared after treatment in patients (n = 22) who had disease-free survival. The 90 kDa band persisted in 8 patients who subsequently relapsed with reexpression of the 120 kDa band. FACS analysis revealed that at presentation (n = 70) 90.1 +/- 5.0% cells expressed 9-O-AcSGs, which decreased progressively with chemotherapy, remained <5% during clinical remission and reappeared in relapse (80 +/- 10%, n = 18). Early clearance of 9-O-AcSG(+) cells, during 4-8 weeks of treatment showed a good correlation with low risk of relapse. Sensitivity of detection of 9-O-AcSG(+) cells was 0.1%. Numbers of both high- and low-affinity binding sites were maximum at presentation, decreased with treatment and increased again in clinical relapse. We propose that close monitoring of 90 and 120 kDa 9-O-AcSGs may serve as a reliable index for long-term management of childhood ALL and merits therapeutic consideration.

Discovery and characterization of sialic acid O-acetylation in group B Streptococcus

Group B Streptococcus (GBS) is the leading cause of human neonatal sepsis and meningitis. The GBS capsular polysaccharide is a major virulence factor and the active principle of vaccines in phase II trials. All GBS capsules have a terminal alpha 2-3-linked sialic acid [N-acetylneuraminic acid (Neu5Ac)], which interferes with complement-mediated killing. We show here that some of the Neu5Ac residues of the GBS type III capsule are O-acetylated at carbon position 7, 8, or 9, a major modification evidently missed in previous studies. Data are consistent with initial O-acetylation at position 7, and subsequent migration of the O-acetyl ester at positions 8 and 9. O-acetylation was also present on several other GBS serotypes (Ia, Ib, II, V, and VI). Deletion of the CMP-Neu5Ac synthase gene neuA by precise, in-frame allelic replacement gave intracellular accumulation of O-acetylated Neu5Ac, whereas overexpression markedly decreased O-acetylation. Given the known GBS Neu5Ac biosynthesis pathway, these data indicate that O-acetylation occurs on free Neu5Ac, competing with the CMP-Neu5Ac synthase. O-acetylation often generates immunogenic epitopes on bacterial capsular polysaccharides and can modulate human alternate pathway complement activation. Thus, our discovery has important implications for GBS pathogenicity, immunogenicity, and vaccine design.

Antibodies against 9-O-acetylated sialoglycans: a potent marker to monitor clinical status in childhood acute lymphoblastic leukemia

BACKGROUND

Although childhood acute lymphoblastic leukemia (ALL) is highly responsive to chemotherapy, reliable techniques are needed to determine treatment outcome and predict impending relapse. In ALL, the cell surface over expression of 9-O-acetylated sialoglycans (9-OAcSGs) on lymphoblasts and concomitant high antibody titers in patients' sera was reported.

OBJECTIVES

The present study was aimed to evaluate whether anti-9-OAcSG titers can be harnessed to monitor the clinical outcome of ALL.

DESIGN AND METHODS

Anti-9-OAcSGs were analyzed by ELISA in children receiving either UK ALL X (n = 69, Group I) in India or UK ALL 97 (n = 47, Group II) in UK along with age-matched normal healthy controls at different time points over a period of >2 years. An attempt was also made to investigate subclass distribution of disease-specific IgG. Moreover, 17 patients having a higher sample size were longitudinally monitored.

RESULTS

Antibody levels were raised at disease presentation, decreased with remission induction, and importantly, reappeared with clinical relapse. Sera from patients with other hematological disorders and normal controls showed negligible levels of circulating anti-9-OAcSGs. In patients of both Groups I and II, the assay showed high sensitivity (98.92% and 96.77%) and specificity (92.1% and 95.91%), respectively. IgG subclass analyses during different phases of treatment revealed that 9-OAcSG-specific IgG(1) could serve as a better prognostic marker in ALL.

CONCLUSIONS

This study demonstrated the potential of this disease-specific antibody as an alternate marker in diagnosis and long-term assessment of ALL patients, suggesting its application in detection and prediction of impending relapse. Therefore, the expression of anti-9-OAcSGs, irrespective of their treatment protocol, may serve as an economical yet effective index for monitoring of childhood ALL.

Induction of glycosylation in human C-reactive protein under different pathological conditions

As an acute-phase protein, human C-reactive protein (CRP) is clinically important. CRPs were purified from several samples in six different pathological conditions, where their levels ranged from 22 to 342 microg/ml. Small, but significant, variations in electrophoretic mobilities on native PAGE suggested differences in molecular mass, charge and/or shape. Following separation by SDS/PAGE, they showed single subunits with some differences in their molecular masses ranging between 27 and 30.5 kDa, but for a particular disease, the mobility was the same for CRPs purified from multiple individuals or pooled sera. Isoelectric focusing (IEF) also indicated that the purified CRPs differed from each other. Glycosylation was demonstrated in these purified CRPs by Digoxigenin kits, neuraminidase treatment and binding with lectins. The presence of N-linked sugar moiety was confirmed by N-glycosidase F digestion. The presence of sialic acid, glucose, galactose and mannose has been demonstrated by gas liquid chromatography, mass spectroscopic and fluorimetric analysis. Matrix-assisted laser-desorption ionization analysis of the tryptic digests of three CRPs showed systematic absence of two peptide fragments, one at the N-terminus and the other near the C-terminus. Model-building suggested that the loss of these fragments exposed two potential glycosylation sites on a cleft floor keeping the protein-protein interactions in pentraxins and calcium-dependent phosphorylcholine-binding qualitatively unaffected. Thus we have convincingly demonstrated that human CRP is glycosylated in some pathological conditions.

Cas1p is a membrane protein necessary for the O-acetylation of the Cryptococcus neoformans capsular polysaccharide

The capsule is certainly the most obvious virulence factor for Cryptococcus neoformans. The main capsule constituents are glucuronoxylomannans (GXM). Several studies have focused on the structure and chemistry of the GXM component of the capsule, yet little is known about the genetic basis of the capsule construction. Using a monoclonal antibody specific to a sugar epitope, we isolated a capsule-structure mutant strain and cloned by complementation a gene named CAS1 that codes for a putative membrane protein. Although no sequence homology was found with any known protein in the different databases, protein analysis using the PROPSEARCH software classified Cas1p as a putative glycosyltransferase. Cas1p is a well-conserved evolutionary protein, as we identified one orthologue in the human genome, one in the drosophila genome and four in the plant Arabidopsis thaliana genome. Analysis of the capsule structure after CAS1 deletion showed that it is required for GXM O-acetylation.

O-acetyl sialic acid specific IgM in childhood acute lymphoblastic leukaemia

Initial studies have revealed an enhanced surface expression of O-acetylated sialoglycoconjugates (O-AcSGs) on lymphoblasts concomitant with high titres of IgG in childhood Acute Lymphoblastic Leukaemia (ALL) (Mandal C, Chatterjee M, Sinha D, Br J Haematol 110, 801-12, 2000). In our efforts to identify disease specific markers for ALL, we have affinity-purified IgM directed against O-AcSGs that reacts with three disease specific O-AcSGs present on membrane proteins derived from peripheral blood mononuclear cells (PBMC) of ALL patients. Antibody specificity towards O-AcSGs was confirmed by selective binding to erythrocytes bearing surface O-AcSGs, decreased binding with de-O-acetylated BSM and following pretreatment with O-acetyl esterase. Competitive inhibition ELISA demonstrated a higher avidity of IgM for O-AcSG than IgG. Flow cytometry demonstrated the diagnostic potential of purified O-AcSA IgM as binding was specific with ALL patients and minimal with other haematological disorders and normal individuals. It therefore may be adopted as a non-invasive approach for detection of childhood ALL. Taken together, the data indicates that carbohydrate epitopes having terminal O-AcSA alpha2 --> 6 GalNAc determinants induce disease specific IgG and IgM, potentially useful molecular markers for childhood ALL.

Role of linkage specific 9-O-acetylated sialoglycoconjugates in activation of the alternate complement pathway in mammalian erythrocytes

Substitution of the -OH group at C-9 of sialic acid by an O-acetyl ester has been suggested to modify various biological phenomena that are regulated by sialic acids. Amongst them, enhancement of erythrocyte lysis by 9-O-acetylated sialic acid determinants through modulation of the alternate pathway of complement has been extensively studied on murine erythrocytes [1]. A variable expression of linkage specific 9-O-acetylated sialoglycoconjugates as defined by the lectinogenic epitope of Achatinin-H namely 9-O-acetylated sialic acid alpha2-->6Gal NAc was identified on rabbit, guinea pig, hamster, rat, mouse and human erythrocytes. This differential expression of linkage specific 9-O-acetylated sialoglycoconjugates strongly correlated with the susceptibility of mammalian erythrocytes to lysis by the alternate pathway of complement. Additionally, low levels of antibodies directed against O-acetylated sialic acids in these mammalian species suggested that these constitutively present determinants have low immunogenicity. Taken together, our results indicate that complement mediated hemolysis depends not simply upon the extent of surface 9-O-acetylated sialic acids present but more importantly upon the specific linkage.