PROCESSING OF HCG IN NORMAL AND ABNORMAL PREGNANCIES

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Preliminary studies in our laboratory are consistent with a relationship between hyperglycosylation (additional antennae and fucose residues on N-linked oligosaccharides) and nicking or cleavage of hCG. Other preliminary studies indicate the structural instability and diminished biological activity of hyperglycosylated and of nicked hCG molecules, and how they may be the source of free Beta-subunit in the circulation and Beta-core fragment in urine samples. A large number of papers have been published showing raised hCG levels, and raised proportions of free Beta-subunit and Beta-core fragment levels in serum or urine samples from patients with Down syndrome pregnancies, preeclampsia, trophoblast disease, or hyperemesis gravidarum. It is our hypothesis, that all of these raised levels arise from the hyperglycosylation of hCG, through a pathway involving nicking of hyperglycosylated hCG, ineffective autocrine control of hCG production, and rapid dissociation to generate nicked free Beta-subunit, and degradation to Beta-core fragment. Five sets of experiments are proposed to test this hypothesis and investigate the clinical ramification of the observations in normal and abnormal pregnancies. Studies are proposed to confirm and compare the levels of hCG, free Beta-subunit and Beta-core fragment in 720 sets of parallel serum and urine samples from normal and abnormal pregnancies (Aim 1A); to purify hCG from normal first, second, and third trimester pregnancy urine samples and trophoblast disease, preeclampsia, hyperemesis gravidarum and Down syndrome pregnancy urine samples (3 each) and compare the extents and sites of nicking, and the type, amounts and locations of hyperglycosylated N-linked oligosaccharides (Aim 2); to investigate the hyperglycosylation-nicking relationship by comparing normal and hyperglycosylated hCG as substrates for nicking enzymes (Aim 3); to examine the biological activities of normal and abnormal pregnancy hCG and abilities to feedback through to the placenta and control hCG synthesis (Aim 4); to investigate the and compare the stabilities of hCG from normal and abnormal pregnancy, and determine whether dissociation could explain the raised proportion of free Beta- subunit (Aim 5); and to use the parallel serum and urine samples to investigate the clinical utility of new immunoassays specifically measuring nicked or hyperglycosylated hCG molecules (Aim 1B).