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.

12-O-retinoylphorbol-13-acetate (RPA) behaves like a retinoid-derivative in binding to retinol-binding-protein: a correlation with its specific action as an incomplete tumor promoter?

12-O-retinoylphorbol-13-acetate (RPA), an incomplete tumor promoter of the phorbol ester type and protein kinase C (PKC) activator, consists of two characteristic structural elements: the phorbol body and the retinoyl ester chain. Therefore, possible binding of the incomplete tumor promoter RPA to the human transport protein retinol-binding-protein (RBP) has been examined by molecular modeling methods and experimental binding studies. The calculated prediction of binding properties was primarily based on a comparative geometrical approach. It was shown that the beta-ionone-ring of RPA was not altered within the binding pocket of RBP (molecular modeling) compared to retinoic acid (X-ray crystallographic data). The torsion angle C5'-C6'-C7'-C8', determining the conformation of the RBP-beta-ionone-ring relative to the isoprene tail, is rotated by 42 degrees for RPA compared to retinol and to retinoic acid, respectively. Combining all the results from force field calculations, MD simulations and geometrical comparisons, the conclusion could be drawn that RPA should be able to bind to RBP. This interaction should be less strong than that with its natural ligand retinol or with retinoic acid. This prediction was proven experimentally. RPA was able to compete with retinoic acid for binding at RBP in human plasma. The binding properties were investigated using 3H-labeled retinoic acid in homologous and heterologous competition studies in a one-dimensional native polyacrylamide gel electrophoresis system. An approximately 2000-fold weaker binding of RPA to RBP as compared to retinoic acid was determined experimentally, confirming the prediction of the molecular modeling approach. The characteristic behaviour of RPA as an incomplete promoter, due to possible binding to PKC and RBP, is discussed.

Differential expression of human chorionic gonadotropin (hCG) glycosylation isoforms in failing and continuing pregnancies: preliminary characterization of the hyperglycosylated hCG epitope

Human chorionic gonadotropin (hCG) glycoforms change as pregnancy progresses. We have developed an antibody (B152) which can measure a hyperglycosylated early pregnancy isoform of hCG. This putative hyperglycosylated form of hCG arises very early in pregnancies and is rapidly replaced by an isoform that predominates for the remainder of the pregnancy. The profiles of these hCG glycoforms are measured as a ratio of values of two immunometric assays. The profiles of these ratios differ between pregnancies which persist and those which will experience early failure. In this report, daily urine hCG isoform ratios from donor eggs (no exogenous hCG pretreatment), in vitro fertilization pregnancies were profiled and analyzed from the first day following embryo transfer (ET). Significant differences were found between continuing pregnancy and pregnancy loss throughout days 5-20 post-ET. When hCG isoform ratios were analyzed from the first day of detectable hCG, pregnancy loss could be predicted in the case of a single fetus both during the 5- to 10-day time segment (P=0.018) and the 10- to 15-day time segment (P=0.045). When single and multiple fetus pregnancies were analyzed together significance was approached in the 10- to 15-day time period (P=0.058). In a second population of pregnant women who conceived naturally, in whom urine samples were collected at approximately weekly intervals to either term birth or clinical spontaneous abortion, the ratio could discriminate between miscarriages and normal term pregnancies (P=0.043). In later pregnancy, the ratio of hCG isoforms declined more rapidly in miscarriages than in term pregnancy. Antibody B152 was produced using a choriocarcinoma-derived hCG (C5), which was hyperglycosylated at both N- and O-linked sites and was 100% nicked at position beta(47-48). Western blot analyses supported the assay results showing that early pregnancy urine does not contain nicked C5-like hCG. Also, the early pregnancy hCG appeared to be the same size as later pregnancy hCG as judged by SDS gel electrophoresis. A series of Western blot analyses and immunoassays conducted with the samples either non-reduced or reduced showed that B152 is directed to a linear epitope located in the COOH-terminal peptide region of the beta subunit. This indicated that only the O-glycan groups and not the N-linked glycans are part of the antibody epitope.

Development and characterization of antibodies to a nicked and hyperglycosylated form of hCG from a choriocarcinoma patient: generation of antibodies that differentiate between pregnancy hCG and choriocarcinoma hCG

Human chorionic gonadotropin (hCG) exists in blood and urine as a variety of isoforms one of which contains peptide bond cleavages within its beta-subunit loop 2 and is referred to as nicked hCG (hCGn). This hCG isoform appears to be more prevalent in the urine of patients with certain malignancies and possibly in some disorders of pregnancy. Until now, only indirect immunoassays could be used to quantify hCGn. We report the development of two monoclonal antibodies (MAbs) to a form of hCGn isolated from a choriocarcinoma patient. This hCG isoform was not only 100% nicked, but also contained 100% tetrasaccharide-core O-linked carbohydrate moieties in its beta COOH-terminal region. Two-site immunometric assays have been developed using these new antibodies, B151 and B152. The former exhibits good specificity for hCGn independent of the source of the hCGn, the form excreted by choriocarcinoma patients or the form of hCGn from normal pregnancies. The latter antibody, B152, is sensitive to the carbohydrate moieties and possibly other differences in hCG isoforms, but is not for nicking of the beta-subunit. These two immunometric assays provide potential novel diagnostic tools for direct measurement of hCG isoforms which could not be accurately quantified earlier before development of the assays using these newly generated antibodies.

Evaluation of nicked human chorionic gonadotropin content in clinical specimens by a specific immunometric assay

We report the development and characterization of an IRMA for the direct measurement of nicked human chorionic gonadotropin (hCGn) in blood and urine. hCGn derived from a reference preparation of hCG used as an immunogen elicits monoclonal antibodies (mAbs) with enhanced recognition of human luteinizing hormone epitopes. The most specific assay for pregnancy hCGn is an IRMA composed of one mAb to choriocarcinoma-derived hCGn (C5) and a second mAb developed from immunization with normal-pregnancy hCGn. This assay was used to evaluate hCGn profiles in normal, in vitro fertilization, Down syndrome, and ectopic pregnancies. In all pregnancies, hCGn was usually present in much lower concentrations than the non-nicked hCG isoform. Our results suggest that some form of physical separation from the overwhelming quantities of non-nicked hCG present in clinical specimens will be required before accurate immunochemical estimations of hCGn can be made.

Differential urinary gonadotrophin profiles in early pregnancy and early pregnancy loss

Early pregnancy loss (EPL), detected by patterns of human chorionic gonadotrophin (hCG) in urine, is the biomarker employed in investigations of the impact of personal, workplace or environmental reproductive toxins on human fertility. An issue central to these studies is what, in terms of urinary hCG expression, constitutes an EPL. This report describes the urinary molecular forms of hCG expressed in menstrual cycles in which a normal pregnancy was conceived, or an EPL occurred, or no apparent conception occurred. Qualitative and significant quantitative differences in the expression of hCG-associated analytes were found between normal pregnancy cycles and EPL cycles. Discriminant analysis calculation based on mole fractions of the different hCG-associated molecules afforded 91 per cent and 80 per cent correct classification of clinical pregnancy cycles and EPL cycles, respectively. Although hCG-associated molecules unique to either EPL or normal pregnancy were not found, what is thought to be an early form of hCG is expressed both at a high frequency and at a significantly higher concentration in early normal pregnancy when compared with EPL. The relative absence of this molecule very early in pregnancy may signal a pregnancy loss.

HLH beta core fragment immunoreactivity in the urine of ovulating women: a sensitive and specific immunometric assay for its detection

Recently, we isolated an hLH beta core fragment (hLHβcf) from human pituitaries. This molecule is homologous to the hCG beta core fragment (hCGβcf), which may be a marker of normal pregnancy, Down syndrome, and certain cancers. We now report antibodies to the hLHβcf, four of which have been applied in sensitive immunoradiometric assays for urinary measurements. One of the antibodies recognizes an epitope on the hLHβcf, which is not present on the hCGβcf, hLH, or hLHβ. This specific hLHβcf antibody acts cooperatively with other newly-developed antibodies reported here to produce an assay with a sensitivity of 1 fmol/ml of hLHβcf. The specificity of these new IRMA systems will make it possible to measure the hLHβcf in urine in the presence of hLH, hLH beta, or the hCGβcf. Although the hLHβcf used to develop specific antibodies was purified from pituitaries, the assays developed recognize this metabolite in urine. Measurements of heterodimeric hLH as compared to hLHβcf in the urine of cycling women indicated that the concentration of hLHβcf rose as high as 6-7 times the concentration of hLH starting a day after the midcycle surge. The new measuring systems allow the precise quantitation of this hLH metabolite in urine.

Development and characterization of a new, highly specific antibody to the human chorionic gonadotropin-beta fragment

In addition to high concentrations of hCG, pregnancy urine contains even higher concentrations of a fragment of the hCG beta-subunit. This biologically inactive material complicates immunological measurement of hCG, since it cross-reacts with many polyclonal and monoclonal antibodies to the hCG beta-subunit that are employed for assays of hCG in urine. Although we and others have developed antibodies to this fragment, specific measurement of the fragment in the presence of free hCG beta has remained difficult due to intrinsic cross-reactivity of these antibodies with the intact hCG beta. Rather than attempt to increase specificity by assay optimization, we developed a new, highly specific monoclonal antibody, designated B210, which cross-reacts less than 0.1% with the free hCG beta-subunit in both liquid and solid phase immunoassay formats. We have used this new monoclonal antibody in immunoradiometric assays to measure specifically the hCG beta fragment in urine throughout pregnancy as well as in the sera of two individuals with cancers producing the hCG beta-subunit. We discovered that the hCG beta fragment can bind three monoclonal antibodies simultaneously, indicating that although the epitope for antibody B210 is a new determinant exposed on the hCG beta fragment and not on intact hCG or on free hCG beta-subunit, the hCG beta fragment retains at least two other hCG beta-related epitopes intact, i.e. those that bind monoclonal antibodies B108 and B201.

Preparation and characterization of antibodies to the urinary fragment of the human chorionic gonadotropin beta-subunit

hCG is a glycoprotein hormone composed of two dissimilar subunits (alpha and beta) and is normally synthesized by trophoblastic tissue. Its measurement by immunoassay is widely employed as a test for pregnancy, but can be complicated by cross-reactivity with human (h) LH. Immunoassays based on the beta-subunit of hCG have been employed to decrease this cross-reactivity with hLH, but when these assays are used with urine specimens, the antibodies employed also detect a fragment of hCG beta, which can lead to significant differences in measurement. To overcome these problems, we have developed a series of monoclonal antibodies to the beta fragment of hCG recovered from pregnancy urine. Some of the antibodies that bind to this beta fragment are directed to a region of hCG beta that is different from the epitopes recognized by antibodies raised against the intact beta-subunit. The new epitopes available in the hCG beta fragment form the basis for novel immunoassays. These beta fragment antibodies are used in conjunction with other antibodies, directed to different epitopes of the hormone, to produce a series of immunoradiometric assays that can discriminate among intact hormone, free hCG beta, and hCG beta fragment. The hCG beta fragment antibodies described herein have affinities between 10(9) and 10(11) M-1 for the beta fragment and exhibit varying degrees of discrimination between the hCG beta fragment, the beta-subunits of hCG and hLH, and intact hCG and hLH.