Comparative study of the mucin-type sugar chains of human chorionic gonadotropin present in the urine of patients with trophoblastic diseases and healthy pregnant women

Analysis of Ser/Thr-Linked Sugar Chains

Analysis of carbohydrate structures is an integral part of understanding the structure-function relationship of glycans as well as whole glycoproteins. Glycan profiling by HPLC with fluorescence detection is a powerful technique that sheds considerable light into understanding glycan structures. Profiling of N-linked glycans by HPLC and mass spectrometry is well established. However procedures for profiling Ser/Thr-linked sugar chains are still a challenge since there is no enzyme capable of releasing the intact glycans. Simplistic profiling of O-linked sugar chains is possible only by the virtue of anthranilic acid (AA, 2-aminobenzoic acid, 2-AA) labeling chemistry (Anumula, Anal Biochem 457:31-37, 2014), which eliminates the need for intermediary isolation steps, e.g., desalting and chromatographic purification, for labeling. O-linked sugar chains were released by hydrazinolysis at 60 °C for 6 h. Hydrazine was evaporated, and sugar chains were N-acetylated and derivatized with 2-AA in the same reaction mixture and separated on an Amide-80 column. Such simple hydrazinolysis protocols should benefit not only the biotechnology industry but also academic laboratories for characterization of glycoproteins. Detailed structure analysis is possible with AA-labeled glycans using mass spectrometry and NMR.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

Humanization of JAA-F11, a Highly Specific Anti-Thomsen-Friedenreich Pancarcinoma Antibody and InVitro Efficacy Analysis

JAA-F11 is a highly specific mouse monoclonal to the Thomsen-Friedenreich Antigen (TF-Ag) which is an alpha-O-linked disaccharide antigen on the surface of ~80% of human carcinomas, including breast, lung, colon, bladder, ovarian, and prostate cancers, and is cryptic on normal cells. JAA-F11 has potential, when humanized, for cancer immunotherapy for multiple cancer types. Humanization of JAA-F11, was performed utilizing complementarity determining regions grafting on a homology framework. The objective herein is to test the specificity, affinity and biology efficacy of the humanized JAA-F11 (hJAA-F11). Using a 609 target glycan array, 2 hJAA-F11 constructs were shown to have excellent chemical specificity, binding only to TF-Ag alpha-linked structures and not to TF-Ag beta-linked structures. The relative affinity of these hJAA-F11 constructs for TF-Ag was improved over the mouse antibody, while T20 scoring predicted low clinical immunogenicity. The hJAA-F11 constructs produced antibody-dependent cellular cytotoxicity in breast and lung tumor lines shown to express TF-Ag by flow cytometry. Internalization of hJAA-F11 into cancer cells was also shown using a surface binding ELISA and confirmed by immunofluorescence microscopy. Both the naked hJAA-F11 and a maytansine-conjugated antibody (hJAA-F11-DM1) suppressed in vivo tumor progression in a human breast cancer xenograft model in SCID mice. Together, our results support the conclusion that the humanized antibody to the TF-Ag has potential as an adjunct therapy, either directly or as part of an antibody drug conjugate, to treat breast cancer, including triple negative breast cancer which currently has no targeted therapy, as well as lung cancer.

An Automated Micro-Total Immunoassay System for Measuring Cancer-Associated α2,3-linked Sialyl N-Glycan-Carrying Prostate-Specific Antigen May Improve the Accuracy of Prostate Cancer Diagnosis

The low specificity of the prostate-specific antigen (PSA) for early detection of prostate cancer (PCa) is a major issue worldwide. The aim of this study to examine whether the serum PCa-associated α2,3-linked sialyl N-glycan-carrying PSA (S2,3PSA) ratio measured by automated micro-total immunoassay systems (μTAS system) can be applied as a diagnostic marker of PCa. The μTAS system can utilize affinity-based separation involving noncovalent interaction between the immunocomplex of S2,3PSA and Maackia amurensis lectin to simultaneously determine concentrations of free PSA and S2,3PSA. To validate quantitative performance, both recombinant S2,3PSA and benign-associated α2,6-linked sialyl N-glycan-carrying PSA (S2,6PSA) purified from culture supernatant of PSA cDNA transiently-transfected Chinese hamster ovary (CHO)-K1 cells were used as standard protein. Between 2007 and 2016, fifty patients with biopsy-proven PCa were pair-matched for age and PSA levels, with the same number of benign prostatic hyperplasia (BPH) patients used to validate the diagnostic performance of serum S2,3PSA ratio. A recombinant S2,3PSA- and S2,6PSA-spiked sample was clearly discriminated by μTAS system. Limit of detection of S2,3PSA was 0.05 ng/mL and coefficient variation was less than 3.1%. The area under the curve (AUC) for detection of PCa for the S2,3PSA ratio (%S2,3PSA) with cutoff value 43.85% (AUC; 0.8340) was much superior to total PSA (AUC; 0.5062) using validation sample set. Although the present results are preliminary, the newly developed μTAS platform for measuring %S2,3PSA can achieve the required assay performance specifications for use in the practical and clinical setting and may improve the accuracy of PCa diagnosis. Additional validation studies are warranted.

Direct analysis of hCGβcf glycosylation in normal and aberrant pregnancy by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The analysis of human chorionic gonadotropin (hCG) in clinical chemistry laboratories by specific immunoassay is well established. However, changes in glycosylation are not as easily assayed and yet alterations in hCG glycosylation is associated with abnormal pregnancy. hCGβ-core fragment (hCGβcf) was isolated from the urine of women, pregnant with normal, molar and hyperemesis gravidarum pregnancies. Each sample was subjected to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) analysis following dithiothreitol (DTT) reduction and fingerprint spectra of peptide hCGβ 6–40 were analyzed. Samples were variably glycosylated, where most structures were small, core and largely mono-antennary. Larger single bi-antennary and mixtures of larger mono-antennary and bi-antennary moieties were also observed in some samples. Larger glycoforms were more abundant in the abnormal pregnancies and tri-antennary carbohydrate moieties were only observed in the samples from molar and hyperemesis gravidarum pregnancies. Given that such spectral profiling differences may be characteristic, development of small sample preparation for mass spectral analysis of hCG may lead to a simpler and faster approach to glycostructural analysis and potentially a novel clinical diagnostic test.

Measurement of aberrant glycosylation of prostate specific antigen can improve specificity in early detection of prostate cancer

INTRODUCTION

We previously identified prostate cancer (PCa)-associated aberrant glycosylation of PSA, where α2,3-linked sialylation is an additional terminal N-glycan on free PSA (S2,3PSA). We then developed a new assay system measuring S2,3PSA using a magnetic microbead-based immunoassay. We compared the diagnostic accuracy of conventional PSA and percent-free PSA (%fPSA) tests.

METHODS

We used MagPlex beads to measure serum S2,3PSA levels using anti-human fPSA monoclonal antibody (8A6) for capture and anti-α2,3-linked sialic acid monoclonal antibody (HYB4) for detection. We determined the cutoff values in a training test and measured serum S2,3PSA levels in 314 patients who underwent biopsy, including 138 PCa and 176 non-PCa patients with PSA of <10.0 ng/ml. Serum S2,3PSA levels were presented as mean fluorescence intensity (MFI). Receiver operating characteristic curves were used to evaluate the diagnostic accuracy of total PSA, %fPSA, and S2,3PSA.

RESULTS

We determined an MFI cutoff value of 1130 with a sensitivity of 95.0% and specificity of 72.0% for the diagnosis of PCa in the training test. In the validation study, the area under the curve for the detection of PCa with S2,3PSA was 0.84, which was significantly higher than that with PSA or %fPSA.

CONCLUSIONS

Although the present study is small and preliminary, these results suggest that the measurement of serum S2,3PSA using a magnetic microbead-based immunoassay may improve the accuracy of early detection of PCa and reduce unnecessary prostate biopsy.

Competition between core-2 GlcNAc-transferase and ST6GalNAc-transferase regulates the synthesis of the leukocyte selectin ligand on human P-selectin glycoprotein ligand-1

The binding of selectins to carbohydrate ligands expressed on leukocytes regulates immunity and inflammation. Among the human selectin ligands, the O-linked glycans at the N-terminus of the leukocyte cell-surface molecule P-selectin glycoprotein ligand-1 (PSGL-1, CD162) are important because they bind all selectins (L-, E-, and P-selectin) with high affinity under hydrodynamic shear conditions. Analysis of glycan microheterogeneity at this site is complicated by the presence of 72 additional potential O-linked glycosylation sites on this mucinous protein. To overcome this limitation, truncated forms of PSGL-1, called "PSGL-1 peptide probes," were developed. Ultra-high sensitivity mass spectrometry analysis of glycans released from such probes along with glycoproteomic analysis demonstrate the presence of both the sialyl Lewis-X (sLe(X)) and the di-sialylated T-antigen (NeuAcα2,3Galβ1,3(NeuAcα2,6)GalNAc) at the PSGL-1 N-terminus. Overexpression of glycoprotein-specific ST6GalNAc-transferases (ST6GalNAc1, -2, or -4) in human promyelocytic HL-60 cells altered glycan structures and cell adhesion properties. In particular, ST6GalNAc2 overexpression abrogated cell surface HECA-452/CLA expression, reduced the number of rolling leukocytes on P- and L-selectin-bearing substrates by ~85%, and increased median rolling velocity of remaining cells by 80-150%. Cell rolling on E-selectin was unaltered although the number of adherent cells was reduced by 60%. ST6GalNAc2 partially co-localizes in the Golgi with the core-2 β(1,6)GlcNAc-transferase C2GnT-1. Overall, the data describe the glycan microheterogeneity at the PSGL-1 N-terminus. They suggest that a competition between ST6GalNAc2 and C2GnT-1 for the core-1/Galβ1,3GalNAc glycan may regulate leukocyte adhesion under fluid shear.

hCG and hyperglycosylated hCG in the establishment and evolution of hemochorial placentation

The evolution of regular chorionic gonadotropin (CG) and hyperglycosylated CG are linked with the evolution of hemochorial placentation in primates. Recent research with humans shows that regular CG promotes spiral artery angiogenesis and hyperglycosylated CG controls invasion by implanting trophoblast cells. It is inferred that the evolution of regular CG and hyperglycosylated CG in early simian primates, the first species to produce these CG forms, established hemochorial placentation in this species. The circulating half-lives, and thus the circulating concentrations, of regular CG and hyperglycosylated CG increased in advanced simian primates and increased further in humans, seemingly causing greater myometrial invasion and superior angiogenesis in hemochorial placentation in advanced primates and humans. Advanced hemochorial placentation is associated with relatively high proportions of pregnancy failures in humans. This can be explained by considering human implantation inadequate in terms of invasion requirements. The demanding implantation required by the human embryo is seemingly dependent on adequate production of hyperglycosylated CG. Failures in hemochorial placentation invasion lead to anoxia and cause preeclampsia and eclampsia uniquely in humans, which can also be attributed to inadequate hyperglycosylated CG signaling. We propose here that inadequate regular CG and hyperglycosylated CG molecules are the evolutionary causes of these obstetric complications in humans.

Human chorionic gonadotropin and associated molecules

When considering human chorionic gonadotropin (hCG) and hCG tests, it is important to realize that it is not a single biological molecule. The regular form of hCG produced by differentiated syncytotrophoblast cells (regular hCG) is a hormone made with the primary function of maintaining the myometrial and decidual spiral arteries and the vascular supply of the placenta during the full course of pregnancy. Hyperglycosylated hCG (hCG with double-size O-linked oligosaccharides) is made by undifferentiated cytotrophoblast cells. This is an autocrine hormone with separate functions, it maintains invasion as in implantation of pregnancy and malignancy in gestational trophoblastic diseases. A hyperglycosylated free beta-subunit is produced by a high proportion of all malignancies. This functions as an autocrine hormone to promote the growth and invasion of the malignancy. It is important to realize when ordering an hCG test what you are measuring and whether the test ordered will detect appropriately these three variant of hCG as well as their degradation products. Most automated commercial laboratory tests, point-of-care test and over-the-counter tests are limited in what is detected, focusing only on regular hCG. This is in part due to the US FDA, who only consider hCG as a pregnancy test, and to whom only detection of regular hCG is critical. This may be a cause of test errors since primarily hyperglycosylated hCG is produced in early pregnancy, choriocarcinoma and germ cell testicular malignancies, and only free beta-subunit may be produced in other germ cell malignancies (all applications for hCG test). The exceptions are the older style hCGbeta radioimmunoassay and the Siemen's Immulite platform hCG test which detect all variant and their degradation product appropriately. Regardless of test specificity limitations, assays for hCG variants are widely used clinically in pregnancy detection, early pregnancy detection, prediction of spontaneously aborting and ectopic pregnancies and prediction of trisomy pregnancies. hCG tests are essential in managing gestational trophoblastic diseases, whether hydatidiform mole, invasive mole or choriocarcinoma, and are very useful in management of testicular malignancies and other germ cell malignancies.

New discoveries on the biology and detection of human chorionic gonadotropin

Human chorionic gonadotropin (hCG) is a glycoprotein hormone comprising 2 subunits, alpha and beta joined non covalently. While similar in structure to luteinizing hormone (LH), hCG exists in multiple hormonal and non-endocrine agents, rather than as a single molecule like LH and the other glycoprotein hormones. These are regular hCG, hyperglycosylated hCG and the free beta-subunit of hyperglycosylated hCG. For 88 years regular hCG has been known as a promoter of corpus luteal progesterone production, even though this function only explains 3 weeks of a full gestations production of regular hCG. Research in recent years has explained the full gestational production by demonstration of critical functions in trophoblast differentiation and in fetal nutrition through myometrial spiral artery angiogenesis. While regular hCG is made by fused villous syncytiotrophoblast cells, extravillous invasive cytotrophoblast cells make the variant hyperglycosylated hCG. This variant is an autocrine factor, acting on extravillous invasive cytotrophoblast cells to initiate and control invasion as occurs at implantation of pregnancy and the establishment of hemochorial placentation, and malignancy as occurs in invasive hydatidiform mole and choriocarcinoma. Hyperglycosylated hCG inhibits apoptosis in extravillous invasive cytotrophoblast cells promoting cell invasion, growth and malignancy. Other non-trophoblastic malignancies retro-differentiate and produce a hyperglycosylated free beta-subunit of hCG (hCG free beta). This has been shown to be an autocrine factor antagonizing apoptosis furthering cancer cell growth and malignancy. New applications have been demonstrated for total hCG measurements and detection of the 3 hCG variants in pregnancy detection, monitoring pregnancy outcome, determining risk for Down syndrome fetus, predicting preeclampsia, detecting pituitary hCG, detecting and managing gestational trophoblastic diseases, diagnosing quiescent gestational trophoblastic disease, diagnosing placental site trophoblastic tumor, managing testicular germ cell malignancies, and monitoring other human malignancies. There are very few molecules with such wide and varying functions as regular hCG and its variants, and very few tests with such a wide spectrum of clinical applications as total hCG.

Identification of Monosialylated N-glycoforms in the CDG Urinome by Ion Mobility Tandem Mass Spectrometry: The Potential for Clinical Applications

Introduction

A novel approach of ion mobility tandem mass spectrometry (IMS-MS/MS) is applied to analysis of human glycourinome to obtain carbohydrate pattern data of congenital disorders of glycosylation patient. Overlapping of the complex carbohydrate mass range landscape has been highly reduced upon IMS-MS procedure, allowing more efficient identification by mapping and sequencing of glycan precursor ions, following their separation by mobility, according to difference in drift time through the traveling wave IMS cell. Intact and truncated N- and O-glycan structures modified by sialylation and fucosylation were identified according to their drift time separated molecular ions and submitted to fragmentation in a narrow mass window.

IMS CID MS/MS Analysis

The fragmentation spectra generated from the IMS separated precursor ions contain series of fragment ions maintaining the same mobility as their parent ions, and the assignment accuracy can be significantly enhanced.

Conclusion

According to the specific fragment ion patterns, carbohydrate epitopes described to be involved in pathological processes were assigned. A high potential of this glycomics-based strategy for clinical applications can be presented.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update covering the period 2001-2002

This review is the second update of the original review on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates that was published in 1999. It covers fundamental aspects of the technique as applied to carbohydrates, fragmentation of carbohydrates, studies of specific carbohydrate types such as those from plant cell walls and those attached to proteins and lipids, studies of glycosyl-transferases and glycosidases, and studies where MALDI has been used to monitor products of chemical synthesis. Use of the technique shows a steady annual increase at the expense of older techniques such as FAB. There is an increasing emphasis on its use for examination of biological systems rather than on studies of fundamental aspects and method development and this is reflected by much of the work on applications appearing in tabular form.

MALDI-QTOFMS/MS identification of glycoforms from the urine of a CDG patient

Identification of single glycoconjugate components in a complex mixture from the urine of a patient suffering from a congenital disorder of glycosylation was probed by MALDIMS analysis on a hybrid quadrupole time-of-flight instrument. In negative ion mode, complex maps containing more than 50 ionic species were obtained and a number of molecular ions directly as-signed using a previously developed computer-assisted algorithm. To confirm the data and determine the carbohydrate sequence, single molecular ions were selected and submitted to fragmentation experiments. Interpretation of fragmentation spectra was also assisted by the soft-ware using alignment with spectra generated in silico. According to fragmentation data, the majority of glycoconjugate ionic species could be assigned to free oligosaccharides along with ten species tentatively assigned to glycopeptides. Following this approach for glycan identification by a combination of MALDI-QTOFMS and MS/MS experiments, computer-assisted assignment and fragment analysis, data for a potential glycan data base are produced. Of high benefit for this approach are two main factors: low sample consumption due to the high sensitivity of ion formation, and generation of only singly charged species in MALDIMS allowing interpretation with-out any deconvolution. In this experimental set-up, sequencing of single components from the MALDI maps by low energy CID followed by computer-assisted assignment and data base search is proposed as a most efficient strategy for the rapid identification of complex carbohydrate structures in clinical glycomics.

Characterization of the N-linked oligosaccharides from human chorionic gonadotropin expressed in the methylotrophic yeast Pichia pastoris

Human chorionic gonadotropin (hCG) is a heterodimeric, placental glycoprotein hormone involved in the maintenance of the corpus luteum during the first trimester of pregnancy. Biologically active hCG has been successfully expressed in the yeast Pichia pastoris (phCG). In the context of structural studies and therapeutic applications of phCG, detailed information about its glycosylation pattern is a prerequisite. To this end N-glycans were released with peptide-N(4)-(N-acetyl-beta-glucosaminyl)asparagine amidase F and fractionated via anion-exchange chromatography (Resource Q) yielding both neutral (80%) and charged, phosphate-containing (20%) high-mannose-type structures. Subfractionations were carried out via normal phase (Lichrosorb-NH(2)) and high-pH anion-exchange (CarboPac PA-1) chromatography. Structural analyses of the released N-glycans were carried out by using HPLC profiling of fluorescent 2-aminobenzamide derivatives, MALDI-TOF mass spectrometry, and 500-MHz(1)H-NMR spectroscopy. Detailed neutral oligosaccharide structures, in the range of Man(8)GlcNAc(2) to Man(11)GlcNAc(2) including molecular isomers, could be established, and structures up to Man(15)GlcNAc(2) were indicated. Phosphate-containing oligosaccharides ranged from Man(9)PGlcNAc(2) to Man(13)PGlcNAc(2). Mannosyl O-glycans were not detected. Profiling studies carried out on different production batches showed that the oligosaccharide structures are similar, but their relative amounts varied with the culturing media.

Hyperglycosylated hCG

Hyperglycosylated hCG (hCG-H) is a glycosylation variant of the hormone hCG. Here we review all that is known about this independently functioning molecule. As discussed, it is a very different molecule to the hormone hCG. First, hCG-H is produced by cytotrophoblast cells while regular hCG is made in syncytiotrophoblast cell. Second, it is an autocrine acting directly on the cells which produce it, while regular hCG is an endocrine acting on maternal corpus luteal cells. Third, hCG-H has minimal biological activity in promoting progesterone production compared to regular hCG. Fourth, hCG-H functions unlike regular hCG as an invasion promoter, whether invasion as in choriocarcinoma and testicular germ cell malignancies, or as in implantation of pregnancy. These functions seemingly occur through action on cytotrophoblast cell TGFbeta receptors. Fifth, hCG-H is an essential component for successful human implantation to prevent early pregnancy loss and spontaneous abortion. Sixth, hCG-H is critical for promoting the midtrimester hemochorial implantation, and for preventing preeclampsia. Seventh, measurements of hCG-H have advantages over measurements of regular hCG or total hCG, in detecting pregnancy, pregnancy outcome (failing or term pregnancy), predicting preeclampsia in pregnancy, or as a tumor marker for gestational trophoblastic diseases.

Hyperglycosylated HCG expression in pregnancy: cellular origin and clinical applications

Employing a monoclonal antibody (B152) specific for a carbohydrate epitope found on a choriocarcinoma derived hCG, it was discovered that a similar hCG isoform is expressed during early pregnancy. This form differs from later pregnancy hCG in carbohydrate moieties. Profiling of these two hCG isoforms throughout pregnancy utilized two IRMA's: B152-B207 ("hyperglycosylated hCG"-specific assay) and B109-B108 (an IRMA for standard intact hCG isoforms in the WHO hCG reference preparation). The WHO hCG standard was used in both assays. Values were presented as a ratio of hCG isoform concentrations (B152/B109 ratio). In early pregnancy urine concentrations of B152 hCG were significantly higher in normal pregnancy (NP) compared to early pregnancy loss (EPL). Matched serum-urine samples from the first and third trimesters revealed that the B152 hCG form is predominant in both serum and urine in the first trimester compared with the third trimester. The proportion of the B152 hCG (HhCG) form is higher in urine than in matched serum. There was a significant difference in the B152/B109 ratio between days 5 and 20 from time of embryo transfer in normally developing pregnancy versus EPL in the urine of IVF patients. In spontaneous abortion (SA) the level of B109 hCG remained higher in NP compared with SA. However, the B152/B109 ratio declined with gestational age faster in SA than in NP suggesting perhaps a different loss mechanism in SA versus EPL. The cellular origin of the different hCG glycoforms was identified by assay of cell media from cytotrophoblasts (CTBs) and syncytiotrophoblasts (STBs). Isolated CTBs expressed predominantly HhCG. The level of expression was the highest in the first trimester. STBs were the source of the less glycosylated B109 hCG isoform. Analysis of hCG glycoforms during early pregnancy can distinguish pregnancies that will fail from those that will proceed normally. Since the B152 assay does not effectively discriminate between intact HhCG and free beta HhCG (HhCGbeta), a new HhCGbeta assay was developed. This assay recognizes the HhCGbeta which is produced by CTBs. We hypothesize that the measurement of HhCGbeta may have a potential use in screening for Down syndrome and perhaps other pregnancy disorders and certain types of cancer.

Hyperglycosylated hCG: a variant with separate biological functions to regular hCG

Hyperglycosylated hCG (hCG-H) is an over-glycosylated variant of hCG. While regular hCG is produced by differentiated syncytotrophoblast cells, hCG-H is independently secreted by stem cytotrophoblast cells. hCG-H has an independent function to regular hCG. It is the direct promoter of trophoblast invasion and malignancy. Invasion as in implantation of pregnancy and malignancy as in choriocarcinoma. Neither will occur in the absence of hCG-H. hCG-H measurements have multiple functions. Primarily or exclusively hCG-H is produced at the time of implantation of pregnancy and in the 2 weeks that follows. As such, a good pregnancy test should measure regular hCG and hCG-H equally. This is not commonly the case. Most tests poorly detect hCG-H. New pregnancy tests are needed, including those that measure only hCG-H. Considering that hCG-H is critical for implantation, hCG-H is also invaluable for determining pregnancy outcome and detecting failures. It makes a considerable more accurate test for detecting pregnancy failures and ectopic pregnancies than regular hCG. Down syndrome pregnancies are marked by poor trophoblast differentiation. As such, they are very well marked by using a combination of hCG-H measurements and other screening tests. hCG-H is also an absolute tumor marker for malignant or invasive gestational trophoblastic disease, it can discriminate active and inactive (quiescent) disease, and the need for chemotherapy.

Determination of hyperglycosylated human chorionic gonadotropin produced by malignant gestational trophoblastic neoplasias and male germ cell tumors using a lectin-based immunoassay and surface plasmon resonance

The ability to reliably detect aberrant glycosylation of human chorionic gonadotropin (hCG) may have profound implications for the diagnosis and monitoring of malignant gestational trophoblastic neoplasia, germ cell tumors, other malignancies, and pregnancy complications. To become a clinically useful assay, however, this discrimination of glycoforms should be possible on minimally treated biological specimens. Towards this end, we have developed a lectin-based sandwich-type immunoassay to compare the glycosylation patterns of hCG among urine specimens from patients presenting with a normal pregnancy, invasive mole, choriocarcinoma, and male germ cell tumors using carbohydrate-free antibody fragments as capture reagents and a panel of eight lectins, five recognizing neutral sugars and three recognizing sialic acid. There was no significant difference in the binding of any of the lectins to hCG in the urine of women over the gestational range of 6-38 weeks. Three lectins, however, exhibited differential binding to urinary hCG derived from these normal pregnant controls and that from patients with malignant forms of gestational trophoblastic disease and male germ cell tumors. Galanthus nivalis agglutinin and Maackia amurensis lectin, which bind terminal mannose and alpha(2-3)sialic acid, respectively, preferentially bound pregnancy-derived hCG, whereas the lectin, wheat germ agglutinin, which binds sialic acid and beta(1-4)N-acetylglucosamine, exhibited decreased binding to pregnancy-derived hCG compared to that from patients with male germ cell tumors and malignant gestational trophoblastic neoplasia. The differential binding observed with these three promising lectins is most encouraging and warrants further examination. The experimental paradigm also holds promise for the development of comparable assays for other glycosylated tumor markers.

A single serum test for measuring early pregnancy outcome with high predictive value

OBJECTIVES

Current testing to determine a failing pregnancy requires two separate clinic visits to measure the hCG doubling rate. Diagnosing a failing pregnancy is often done in emergency departments where simplified and accelerated testing methods are needed. Here, we investigated hyperglycosylated hCG (hCG-H) for predicting pregnancy failure.

DESIGN AND METHODS

We studied two independent sets of patient samples collected in the early weeks of gestation. One set was urine samples, and the other was serum samples. In all cases, hCG and hCG-H were measured using automated chemiluminescence immunoassays. Concentrations of hCG and hCG-H were plotted on a scattergram, and levels in failing pregnancies were compared to those in continuing pregnancies.

RESULTS

Data indicated that a threshold level of hCG-H (13 microg/L) in both serum and urine samples defined the concentration below where pregnancies were likely to fail. This cut-off corresponded to 73% detection of failures at a 2.9% false positive rate using serum and 75% detection at a 15% false positive rate using urine. Using an hCG cut-off that corresponded to the same false positive rates, hCG detected only 42% of failures using serum and 43% of failures using urine.

CONCLUSIONS

Our data indicate that hCG-H provides a much more accurate single test than hCG for assessing pregnancy outcome. Compatible with the use of serum or urine samples, a single hCG-H test might provide simpler, faster, and more accurate results for predicting the progress of a pregnancy than standard hCG testing.

Gestational trophoblastic diseases: 1. Pathophysiology of hyperglycosylated hCG

OBJECTIVE

Hyperglycosylated hCG (hCG-H) is a glycosylation variant of hCG produced by cytotrophoblast cells at implantation of pregnancy and in choriocarcinoma. We investigated the biological function of hCG-H in invasion in vitro and in vivo and the use of hCG-H antibodies in blocking tumorigenesis and cancer growth in vivo.

METHODS AND RESULTS

hCG-H accounts for 43% to 100% of total hCG immunoreactivity in the culture fluid of choriocarcinoma cell lines and 100% in primary cultures of pregnancy cytotrophoblast cells. We investigated the action of hCG and hCG-H on isolated cytotrophoblast cell primary cultures and on 3 different lines of choriocarcinoma cells cultured on Matrigel basement membrane inserts (culture models for assessing tumor invasion). The addition of hCG-H to medium significantly promoted invasion of membranes with both pregnancy and cancer cell line sources, while regular hCG had no significant effect. JEG-3 human choriocarcinoma cells were transplanted subcutaneously into athymic nude mice. Tumors rapidly formed. B152, mouse monoclonal antibody against hCG-H, and non-specific mouse IgG (control) were administered twice weekly once tumors were clearly visible. While a correlation between time and growth was observed with the control group (r(2)=0.97), no correlation was observed with the B152-treated mice (r(2)=0.15). B152 blocked tumor growth (t test, IgG vs. B152, P=0.003). In a second experiment, antibody B152 or IgG was administered to mice at the time of choriocarcinoma transplantation. B152 significantly inhibited tumorigenesis (t test P=0.0071).

CONCLUSIONS

hCG-H is a critical promoter in human cytotrophoblast and human choriocarcinoma cell invasion in vivo and in vitro, promoting tumor growth and invasion through an autocrine mechanism. hCG-H is a signal for choriocarcinoma cell invasion, making it a biological tumor marker. Antibodies against hCG-H block tumor formation and growth. Human or humanized antibodies against hCG-H may be useful in treating and managing choriocarcinoma and other gestational trophoblastic malignancies.

Identification of glycoconjugates in the urine of a patient with congenital disorder of glycosylation by high-resolution mass spectrometry

More than 150 molecular species were detected in a single glycoconjugate fraction obtained from urine of a congenital disorders of glycosylation (CDG) patient by use of high-resolution FT-ICR MS. With respect to its high-mass accuracy and resolving power, FT-ICR MS represents an ideal tool for analysis of single components in complex glycoconjugate mixtures obtained from body fluids. The presence of overlapping nearly isobaric ionic species in glycoconjugate mixtures obtained from CDG patient's urine was postulated from fragmentation data of several precursor ions obtained by nanoESI Q-TOF CID. Their existence was confirmed by high-resolution/high-mass accuracy FT-ICR MS detection. High-resolution FT-ICR mass spectra can, therefore, be generally considered for glycoscreening of complex mixture samples in a single stage. From the accurate molecular ion mass determinations the composition of glycoconjugate species can be identified. Particular enhancement of identification is offered by computer-assisted calculations in combination with monosaccharide building block analysis, which can be extended by considerations of non-carbohydrate modifications, such as amino acids, phosphates and sulfates. Taking advantage of this strategy, the number of compositions assigned to mass peaks was significantly increased in a fraction obtained from urine by size exclusion and anion exchange chromatography.

Lectin immunoassays using antibody fragments to detect glycoforms of human chorionic gonadotropin secreted by choriocarcinoma cells

Immobilized antibodies are commonly used to recognize and bind proteins of interest from heterogeneous samples; however, subsequent probing of the glycan(s) of captured glycoproteins with lectins is limited by interference due to the competing oligosaccharides inherently present on antibodies. To prepare capture antibodies with significantly reduced binding of any lectin, the glycosylated protein domains (F(c)) of two anti-human chorionic gonadotropin antibodies were proteolytically removed. Depending on the individual antibody, usable fragments were generated either directly or effectively separated after cleavage through partial reduction and thiol coupling to an appropriate matrix. Importantly, neither method required additional purification of the antibody fragments before immobilization. Binding of a variety of lectins to the functional fragments was reduced by approximately 90% compared with intact immunoglobulin G in both an enzyme-linked immunosorbent assay and a biosensor format. These carbohydrate-free antibody fragments were used to bind the glycoprotein hormone, human chorionic gonadotropin, produced during normal pregnancy and that secreted by three human choriocarcinoma cell lines. Lectins bound to the unpurified gonadotropin glycoforms in distinct patterns consistent with glycan structures previously elucidated by others on hormone samples purified from the urine of pregnant women and of patients with choriocarcinoma. The methods described in this article are applicable for generating capture reagents universally suitable for lectin immunoassays of glycoproteins.

Specific Measurement of O-Linked Core 2 Sugar-Containing Isoforms of Hyperglycosylated Human Chorionic Gonadotropin by Antibody B152

There have been a significant number of reports on the clinical utility of measurement of 'hyperglycosylated' isoforms of the pregnancy hormone, human chorionic gonadotropin (hCG). Although there are a variety of hCG isoforms which can be termed 'hyperglycosylated', the measurements were all made using a unique antibody designated B152. This antibody was raised using a choriocarcinoma-derived form of hCG, which was hyperglycosylated with N- and O-glycans and was also 100% 'nicked' hCG. Antibody B152 was recently mapped to a linear epitope around a single O-glycan on the beta-subunit of hCG at residue number 132. Thus, the antibody can only measure isoforms of hCG that possess a core 2 type of branched O-glycan on this portion of the hCG beta-subunit. Isoforms that are hyperglycosylated in the hCG alpha-subunit or only on the N-glycans of hCGbeta will not be recognized by antibody B152. Apparently, measurements of these core 2 hCG isoforms have important clinical application in early pregnancy during which they are the predominant isoform of hCG until the 6th week of gestation. The secretory pattern of these isoforms can be used to predict the health status of the pregnancy in fertility clinics. Moreover, the measurements of these core 2 hCG isoforms are more useful than standard hCG for the prediction of Down syndrome pregnancies. The core 2 isoforms are also of important use in cancer diagnosis and monitoring since their concentration appears to correlate with malignancy.

Biochemical screening for congenital defects

This article discusses biochemical screening for congenital defects. Biochemical screening remains the standard for estimating the risk of aneuploidy in pregnancy. The combination of first and second trimester markers promises to further improve diagnostic accuracy for anomaly detection.

Hyperglycosylated hCG (invasive trophoblast antigen, ITA) a key antigen for early pregnancy detection

OBJECTIVES

Hyperglycosylated human chorionic gonadotrophin (hCG) is an hCG variant with extra-large O-linked oligosaccharides, produced by phenotypically invasive cytotrophoblast cells in choriocarcinoma and pregnancy. It is the principal form of hCG produced in the first weeks of gestation. We investigated the importance of hyperglycosylated hCG in pregnancy testing and its detection by current hCG tests.

DESIGN AND METHODS

We measured the concentration of hyperglycosylated hCG and total hCG in 512 pregnancies throughout gestation. We assessed and compared the abilities of 14 commonly used commercial laboratory hCG tests and 18 home pregnancy tests to detect regular and hyperglycosylated hCG.

RESULTS

Hyperglycosylated hCG is the principal source of hCG-related immunoreactivity in early pregnancy. In the week following missing menses, hyperglycosylated hCG measurements may be more sensitive than regular hCG measurements in detecting pregnancy. Of 14 commercial laboratory hCG tests, 3 appropriately detected hyperglycosylated hCG standard. Of 18 different home pregnancy products 11 poorly or very poorly detected this key antigen.

CONCLUSIONS

Hyperglycosylated hCG may be the key molecule in the detection of early pregnancy. However, the majority of tests poorly detected or failed to detect this key antigen. New pregnancy tests are needed that either solely detect hyperglycosylated hCG or equally detect regular hCG and hyperglycosylated hCG.

Processing of O-linked glycosylation in the chimera consisting of alpha-subunit and carboxyl-terminal peptide of the human chorionic gonadotropin beta-subunit is affected by dimer formation with follicle-stimulating hormone beta-subunit

hCG, LH, FSH, and TSH are a family of heterodimeric glycoprotein hormones that contain a common alpha-subunit, but differ in their hormone-specific beta-subunits. hCGbeta is unique among beta-subunits due to a carboxyl-terminal peptide (CTP) bearing four O-linked oligosaccharides. We previously reported that there were differences in O-glycosylation between two chimeras consisting of alpha-subunit and CTP, i.e. a variant with CTP at the N-terminal region (Calpha) and another analog with CTP at the C-terminus (alphaC) of the alpha-subunit. To address whether O-glycosylation is influenced by the heterodimer formation, Calpha and alphaC were expressed alone or with FSHbeta-subunit in Chinese hamster ovary cells. The O-linked glycosylation was assessed by continuous labeling with [(35)S]methionine/cysteine, immunoprecipitation with anti-alpha or anti-FSH serum, serial digestion with endoglycosidase-F and neuraminidase, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The decrease in molecular weight of dimeric chimeras digested with endoglycosidase-F was greater in Calpha than that in alphaC after treatment with neuraminidase, revealing that both chimeras have different numbers of sialic acids on O-linked carbohydrates. By treating with endoglycosidase-F, the dimeric alphaC migrated faster than its free form, whereas the mobility difference between assembled and unassembled forms of Calpha was very little. These data indicate that processing of O-glycosylation is affected by the backbone polypeptide chain(s).

The reaction of acetylacetone with amino sugars: implications for the formation of glycosylpyrazole derivatives

Glycosylpyrazoles are efficiently formed by reaction of saccharide hydrazones with pentan-2,4-dione (acetylacetone), but in aqueous buffer, pyrazole derivatives of amino sugars couple with a further equivalent of acetylacetone affording high yields of ketoenamines. These ketoenamines were considerably more stable than the ketoenamines formed from 2-amino-2-deoxy aldoses that have been described as intermediates in the classical Elson-Morgan reaction. Moreover, high yields of perketoenamine derivatives were achieved with oligosaccharides derived from hydrolysis of chitosan. The removal of the ketoenamine moieties to regenerate the free amine was readily accomplished with aqueous hydrazine.

Trophoblast origin of hCG isoforms: cytotrophoblasts are the primary source of choriocarcinoma-like hCG

We have previously demonstrated that a hyperglycosylated isoform of chorionic gonadotropin (hCG) (B152 hCG) is detected in the blood and urine in early pregnancy and is subsequently rapidly replaced by the hCG isoform (B109 hCG) characteristic of later pregnancy. In the current study we have extended our work on the origin of these isoforms. We have used a combination of in situ and in vitro approaches. Localization studies in placental tissues showed that monoclonal antibody B109 stained very specifically syncytiotrophoblast (STBs) from first and second trimester tissues. At term, STBs exhibited no B109 staining at all. Immunostaining with B152 antibody, that recognize the hyperglycosylated isoform of hCG, revealed only punctate staining of STBs in most villi of first trimester tissue. Both antibodies B109 and B152 failed to stain cytotrophoblasts (CTBs). To assess the functional relevance of these observations we analyzed conditioned media from purified CTBs using two immunometric assays, one of which (B152-B207*) has primary specificity for the hyperglycosylated, choriocarcinoma-like hCG and the other (B109-B108*) having primary specificity for the later pregnancy hCG isoform. Regardless of gestational age, isolated CTBs secreted predominantly B152 hCG isoform in contrast to placental villi (predominantly STBs), which released primarily the B109 hCG isoform. Isolated CTBs, however, failed to immunostain with both B109 and B152 antibodies. To resolve this contradiction, we cultured CTBs in the presence of brefeldin A, a drug known to block secretion by inhibiting protein translocation from the endoplasmic reticulum to the Golgi vesicles. Brefeldin A treated CTBs stained strongly with B109 and did not stain or stained weakly with B152 antibody. We assume that treatment with brefeldin A impaired glycosylation of beta subunit and consequently inhibited the production of hyperglycosylated form of hCG recognized by B152. In summary, our in vitro experiments indicate that both isoforms of hCG are produced by villus CTBs and that the dominant isoform is the one recognized by antibody B152. STBs produce primarily the less glycosylated B109 hCG isoform. This data suggests that at the beginning of pregnancy villus CTBs are the major source of the B152 hCG isoform. This finding is supported by our clinical data that show that the dominant hCG isoform in the blood and urine of pregnant women in the first 6 weeks of pregnancy is recognized by B152 (). The inversion of the B152/B109 ratio observed after 6-7 weeks of pregnancy can be explained by the reduction of number of villus CTBs and/or by maturation of STBs.

Unmasking a new recognition signal for O-linked glycosylation in the chorionic gonadotropin beta subunit

hCGbeta subunit is distinguished among the other members of the family of the glycoprotein hormones by the presence of four serine O-linked oligosaccharide units in the last 25 amino acids. This carboxy terminal peptide (CTP) influences the intracellular behavior of the subunit and is important for maintaining the biological half-life of hCG. To examine how the O-linked oligosaccharides affect the metabolic behavior of hCG, we generated a CGbeta mutant devoid of the native O-linked acceptor sites. An alternative site not used in the native subunit was glycosylated and the structure of this oligosaccharide differed from the wild-type O-linked carbohydrates. This glycosylation occurred at serine 130 in the CTP and in contrast to the wild type O-linked oligosaccharides, sialic acid is a major component of the alternatively linked carbohydrate. The data show that deleting the native acceptor sites exposes a new site for O-glycosylation and promotes a differential intracellular processing of the beta subunit. These results support the hypothesis that the CTP participates in the folding of the newly synthesized subunit, which is manifested by the post-translational changes reported here.

An analytical and structural database provides a strategy for sequencing O-glycans from microgram quantities of glycoproteins

A sensitive, rapid, quantitative strategy has been developed for O-glycan analysis. A structural database has been constructed that currently contains analytical parameters for more than 50 glycans, enabling identification of O-glycans at the subpicomole level. The database contains the structure, molecular weight, and both normal and reversed-phase HPLC elution positions for each glycan. These observed parameters reflect the mass, three-dimensional shape, and hydrophobicity of the glycans and, therefore, provide information relating to linkage and arm specificity as well as monosaccharide composition. Initially the database was constructed by analyzing glycans released by mild hydrazinolysis from bovine serum fetuin, synthetic glycopeptides, human glycophorin A, and serum IgA1. The structures of the fluorescently labeled sugars were determined from a combination of HPLC data, mass spectrometric composition and mass fragmentation data, and exoglycosidase digestions. This approach was then applied to human neutrophil gelatinase B and secretory IgA, where 18 and 25 O-glycans were identified, respectively, and the parameters of these glycans were added to the database. This approach provides a basis for the analysis of subpicomole quantities of O-glycans from normal levels of natural glycoproteins.

Pathways of O-glycan biosynthesis in cancer cells

Glycoproteins with O-glycosidically linked carbohydrate chains of complex structures and functions are found in secretions and on the cell surfaces of cancer cells. The structures of O-glycans are often unusual or abnormal in cancer, and greatly contribute to the phenotype and biology of cancer cells. Some of the mechanisms of changes in O-glycosylation pathways have been determined in cancer model systems. However, O-glycan biosynthesis is a complex process that is still poorly understood. The glycosyltransferases and sulfotransferases that synthesize O-glycans appear to exist as families of related enzymes of which individual members are expressed in a tissue- and growth-specific fashion. Studies of their regulation in cancer may reveal the connection between cancerous transformation and glycosylation which may help to understand and control the abnormal biology of tumor cells. Cancer diagnosis may be based on the appearance of certain glycosylated epitopes, and therapeutic avenues have been designed to attack cancer cells via their glycans.

Structural analysis of O-linked oligosaccharide-alditols by electrospray-tandem mass spectrometry after mild periodate oxidation and derivatization with 2-aminopyridine

O-linked oligosaccharide-alditols were analyzed by a combination of high-performance liquid chromatography (HPLC) and electrospray-tandem mass spectrometry (ESI-MS/MS). First, oligosaccharide-alditols were treated with sodium meta-periodate under conditions where core N-acetylgalactosaminitol is specifically degraded. The resulting fragments were labeled with 2-aminopyridine and purified on a reversed-phase column. Pyridylamino oligosaccharides yielded protonated molecular ions in positive-ion ES-MS and gave Y-series sequence ions, arising from glycosidic cleavages, by ESI-tandem mass spectrometry. Information on sugar sequence and branching of oligosaccharides linked at C6 and C3 to the N-acetylgalactosaminitol can be obtained. A systematic study of various oligosaccharide-alditols demonstrated that this approach constitutes a powerful tool for the structural characterization of O-glycans available only in limited quantities.

Analysis of O-linked oligosaccharide alditols by high-pH anion-exchange chromatography with pulsed amperometric detection

To apply high-pH anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) to the accurate and sensitive analysis of O-linked oligosaccharide alditol, removal of glycopeptides and peptides from oligosaccharide samples obtained by beta-elimination was first investigated. The results obtained by using fetuin as a model glycoprotein indicated that (glyco)peptides derivatized by fluorescamine are easily removed from the beta-eliminated oligosaccharide sample by means of a Sep-Pak C18 cartridge due to their increased hydrophobicity. This clean-up procedure was also effectively applied to the beta-eliminated oligosaccharide sample obtained from delipidated sheep erythrocyte ghosts. Furthermore, structural analysis of the oligosaccharide alditols by HPAEC-PAD was successfully performed in combination with partial and complete desialylation, composition analysis, periodate oxidation, and glycosidase digestion and revealed that sheep erythrocyte membrane glycoproteins contain Gal beta 1-->3Gal-NAc and Gal beta 1-->4GlcNAc beta 1-->3Gal beta 1-->3GalNac, to which one or two residues of Neu5Ac and Neu5Gc are attached in different combinations.

Carbohydrate and peptide structure of the alpha- and beta-subunits of human chorionic gonadotropin from normal and aberrant pregnancy and choriocarcinoma

Human chorionic gonadotropin (hCG), purified from the urine of 14 individuals with normal pregnancy, diabetic pregnancy, hydatidiform mole, or choriocarcinoma, plus two hCG standard preparations, was examined for concurrent peptide-sequence and asparagine (N)- and serine (O)-linked carbohydrate heterogeneity. Protein-sequence analysis was used to measure amino-terminal heterogeneity and the "nicking" of internal peptide bonds. The use of high-pH anion-exchange chromatography coupled with the increased sensitivity of pulsed amperometric detection (HPAE/PAD) revealed that distinct proportions of both hCG alpha- and beta-subunits from normal and aberrant pregnancy are hyperglycosylated, and that it is the extent of the specific subunit hyperglycosylation that significantly increases in malignant disease. Peptide-bond nicking was restricted to a single linkage (beta 47-48) in normal and diabetic pregnancy, but occurred at two sites in standard preparations, at three sites in hydatidiform mole, and at three sites in choriocarcinoma beta-subunit. In the carbohydrate moiety, alpha-subunit from normal pregnancy hCG contained nonfucosylated, mono- and biantennary N-linked structures (49.3 and 36.7%, means); fucosylated biantennary and triantennary oligosaccharides were also identified (7.3 and 6.9%). In choriocarcinoma alpha-subunit, the level of fucosylated biantennary increased, offset by a parallel decrease in the predominant biantennary structure of normal pregnancy (P < 0.0001). The beta-subunit from normal pregnancy hCG contained fucosylated and nonfucosylated biantennary N-linked structures; however, mono- and triantennary oligosaccharides were also identified (4.6 and 13.7%). For O-linked glycans, in beta-subunit from normal pregnancy, disaccharide-core structure predominated, whereas tetrasaccharide-core structure was also detected (15.6%). A trend was demonstrated in beta-subunit: the proportions of the nonpredominating N- and O-linked oligosaccharides increased stepwise from normal pregnancy to hydatidiform mole to choriocarcinoma. The increases were: for monoantennary oligosaccharide, 4.6 to 6.8 to 11.2%; for triantennary, 13.7 to 26.7 to 51.5% and, for O-linked tetrasaccharide-core structure, 15.6 to 23.0 to 74.8%. For hCG from individual diabetic pregnancy, the principal N-linked structure (34.7%) was consistent with a biantennary oligosaccharide previously reported only in carcinoma; and sialylation of both N- and O-linked antennae was significantly decreased compared to that of normal pregnancy. Taken collectively, the distinctive patterns of subunit-specific, predominant oligosaccharides appear to reflect the steric effect of local protein structure during glycosylation processes. The evidence of alternative or "hyperbranched" glycoforms on both alpha- and beta-subunits, seen at low levels in normal pregnancy and at increased or even predominant levels in malignant disease, suggests alternative substrate accessibility for Golgi processing enzymes, alpha 1,6 fucosyltransferase and N-acetylglucosaminyltransferase IV, in distinct proportions of subunit molecules.

Metabolism of hCG and hLH to multiple urinary forms

Human chorionic gonadotropin (hCG) is synthesized primarily in the placenta while human luteinizing hormone (hLH) is produced in the pituitary. Both hormones are highly homologous in structure and both appear to be altered to analogous molecular forms as the hormones are proteolytically processed, or metabolized, from tissue of origin, through the circulation, and finally to the urine. Placental hCG is excreted into urine as heterodimeric hormone, heterodimeric nicked hCG, free subunits (some nicked), and predominantly as the hCG beta core fragment. A pituitary form of heterodimeric hCG, which is partly sulfated as is pituitary hLH, was recently isolated and is likely the form of hCG observed in the urine of healthy postmenopausal women and nonpregnant premenopausal women as well. A pituitary form of the hLH beta core fragment, highly analogous in structure to that of urinary hCG beta core fragment, has been used to develop specific monoclonal antibody assays to measure urinary hLH beta core fragment which is excreted at significantly higher molar concentrations than is hLH in the urine of ovulating women 1 or 2 days after the LH surge. This fragment of LH appears in the urine of postmenopausal women as well. The development of the capability to distinguish the hCG beta core fragment from the hLH beta core fragment in urine may have useful applications in tumor marker assays, pregnancy tests, and menopause. While hCG urinary assays have been widely employed, urinary assays for hCG and hLH metabolites are much less used since the urinary molecular forms are only partly known. Our studies of hCG and hLH urinary metabolites are directed towards improvement of the utility of urinary measurements of molecules derived from these hormones. Since many of the molecular forms of these two hormones in urine differ from their forms in blood, it may be necessary to produce new immunoassays as well as novel urinary reference preparations to accurately measure these molecules within their urinary matrix.

Molecular cloning of a developmentally regulated N-acetylgalactosamine alpha2,6-sialyltransferase specific for sialylated glycoconjugates

A cDNA encoding a novel sialyltransferase has been isolated employing the polymerase chain reaction using degenerate primers to conserved regions of the sialylmotif that is present in all eukaryotic members of the sialyltransferase gene family examined to date. The cDNA sequence revealed an open reading frame coding for 305 amino acids, making it the shortest sialyltransferase cloned to date. This open reading frame predicts all the characteristic structural features of other sialyltransferases including a type II membrane protein topology and both sialylmotifs, one centrally located and the second in the carboxyl-terminal portion of the cDNA. When compared with all other sialyltransferase cDNAs, the predicted amino acid sequence displays the lowest homology in the sialyltransferase gene family. Northern analysis shows this sialyltransferase to be developmentally regulated in brain with expression persisting through adulthood in spleen, kidney, and lung. Stable transfection of the full-length cDNA in the human kidney carcinoma cell line 293 produced an active sialyltransferase with marked specificity for the sialoside, Neu5Ac-alpha2,3Gal-beta1,3GalNAc and glycoconjugates carrying the same sequence such as G(M1b) and fetuin. The disialylated tetrasaccharide formed by reacting the sialyltransferase with the aforementioned sialoside was analyzed by one- and two-dimensional 1H and 13C NMR spectroscopy and was shown to be the Neu5Ac-alpha2,3Gal-beta1,3(Neu5Ac-alpha2,6)GalNAc sialoside. This indicates that the enzyme is a GalNAc alpha-2,6-sialyltransferase. Since two other ST6GalNAc sialyltransferase cDNAs have been isolated, this sialyltransferase has been designated ST6GalNAc III. Of these three, ST6GalNAc III displays the most restricted acceptor specificity and is the only sialyltransferase cloned to date capable of forming the developmentally regulated ganglioside G(D1alpha) from G(M1b).

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

Hepatocyte growth factor is linked by O-glycosylated oligosaccharide on the alpha chain

The glycosylation site and the structure of O-glycosylated oligosaccharide of recombinant human HGF were investigated. N-acetylgalactosamine (GalNAc) in the alpha chain suggested the presence of O-glycosylated oligosaccharide. Sugar analysis and amino acid sequence analysis of peptide fragments produced by limited degradation revealed that O-glycosylated oligosaccharide linked to Thr445 of the alpha chain. The molecular weight of the oligosaccharide was determined with ion spray mass spectrometry. From these studies, the structure of the O-glycosylated oligosaccharide on the alpha chain of HGF was concluded as [formula: see text].

Structures and functions of the sugar chains of glycoproteins

Most proteins within living organisms contain sugar chains. Recent advancements in cell biology have revealed that many of these sugar chains play important roles as signals for cell-surface recognition phenomena in multi-cellular organisms. In order to elucidate the biological information included in the sugar chains and link them with biology, a novel scientific field called 'glycobiology' has been established. This review will give an outline of the analytical techniques for the structural study of the sugar chains of glycoproteins, the structural characteristics of the sugar chains and the biosynthetic mechanism to produce such characteristics. Based on this knowledge, functional aspects of the sugar chains of glycohormones and of those in the immune system will be described to help others understand this new scientific field.

The carbohydrate chains of the beta subunit of human chorionic gonadotropin produced by the choriocarcinoma cell line BeWo. Novel O-linked and novel bisecting-GlcNAc-containing N-linked carbohydrates

The N-linked carbohydrate chains of the beta subunit of human chorionic gonadotropin (hCG-beta) isolated from the culture fluid of the choriocarcinoma cell line BeWo were released enzymatically by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. Subsequently, the O-linked oligosaccharides were split off from the N-deglycosylated protein by mild alkaline borohydride treatment. The carbohydrate chains were purified in their intact sialylated forms by FPLC anion-exchange chromatography on Mono Q, HPLC on Lichrosorb-NH2, and high-pH anion-exchange chromatography on CarboPac PA1. 1H-NMR spectroscopic analysis of the major fractions demonstrates the occurrence of the following sialylated diantennary and triantennary N-linked oligosaccharides. Residues not written in bold letters are variably present. [formula: see text] The incidence of triantennary carbohydrate chains is much higher than in normal urinary hCG-beta (26% vs 2%). The same holds for the alpha 1-6-fucosylation of the asparagine-bound GlcNAc (95% vs 42%). The presence of a bisecting GlcNAc and the occurrence of alpha 2-6-linked Neu5Ac in the most abundant N-glycans, are new features for hCG-beta. The major O-linked carbohydrate chains identified are the tetrasaccharide Neu5Ac alpha 2-3Gal beta 1-3(Neu5Ac alpha 2-6)GalNAc-ol and the hexasaccharide Neu5Ac alpha 2-3Gal beta 1-4GlcNAc beta 1-6(Neu5Ac alpha 2-3Gal beta 1-3)GalNAc-ol, both also found in normal urinary hCG. In addition, two novel O-glycans were characterized: [formula: see text]