Endocrine Abstracts (2004) 7 P72

Maternal serum hCG binding to immobilised wheat germ agglutinin in women with and without type 1 diabetes mellitus

R Nayar1, J Harris2, L Marley2 & J Chapman1

1Department of Metabolic Medicine, City Hospital Sunderland NHS Trust, Sunderland, UK; 2Department of Clinical Biochemistry, City Hospital Sunderland NHS Trust, Sunderland, UK.

The binding characteristics of maternal serum human chorionic gonadotrophin (hCG) to immobilised lectins, specifically Concanavalin A (Con A), Lens culinaris agglutinin (LCA) and Wheat germ agglutinin (WGA), have been shown be compatible with the proposed glycosyl structures of hCG as inferred from other analytical methods. We have shown that serum hCG from groups of pregnant women with or without type 1 diabetes show identical affinity for Con A and LCA, but serum hCG from the diabetes group contained hCG isoforms binding less strongly to WGA (Pharmacia) than serum hCG from women without diabetes. We have now compared serum hCG binding to WGA taking into account gestational length and total maternal serum hCG concentration.

Serum, 50mcl, was made up to 2.5 ml by the addition of 20 mmol. Tris HCl, pH 7.4, 500 mmol NaCl. and chromatographed on 1 ml. columns of WGA; Sepharose 6B (Sigma) equilibrated in the same buffer. Bound hCG was eluted in a gradient 3-15 mmol. N-acetyl glucosamine (Glc.NAc.) over 70 column bed volumes at 0.2 ml/minute. Fractions, 2ml., were assayed for hCG using a commercial assay system (Immulite). Comparison was made between samples from women with and without diabetes at 8,9,10,11 and 12 weeks gestation. Each pair was matched for maternal serum hCG concentration as well as length of gestation.

Lectin affinity chromatography identified 5 major and 2 minor subfractions of hCG in all samples. At 8 weeks gestation samples from both diabetic and non-diabetic pregnancies were identical. With increasing length of gestation from 8 to 12 weeks there was a clear increase in the proportion of more weakly bound hCG isoforms. These data indicate that maternal serum hCG glycosylation is modified in the presence of maternal type 1 diabetes and that these changes are related to gestational length and are independent of maternal serum hCG concentration.

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