Diabetes mellitus is characterized by a lack of insulin, and by high serum glucose concentrations (hyperglycemia) which can be correlated with some carbohydrate abnormalities and many pathological effects of the disease, including elevated levels of several serum glycoproteins, abnormalities in tissue glycoproteins such as basement membrane proteins, and altered cell surface glycoproteins in lymphocytes and other cells. The effects of diabetes, high glucose or low insulin concentrations on oligosaccharide structure and synthesis are unknown.
The aim of this proposal is to examine serum glycoprotein structure and synthesis in vivo and in vitro in the BB/W diabetic rat, a model for type I (juvenile onset) diabetes. Many of the studies proposed here will focus on the structure and synthesis of haptoglobin, since our preliminary studies have shown that this diabetic protein apparently has a novel abnormality in its Asn-linked oligosaccharides. Additional studies will be performed on lentil-lectin binding proteins, since our preliminary studies showed altered lentil-lectin binding of several BB/W diabetic rat serum glycoproteins. Studies will be performed on haptoglobin and other serum proteins synthesized in vivo by prediabetic, well-controlled diabetic and poorly controlled diabetic rats, in order to determine the correlation between the glycoprotein changes observed, the onset of diabetes, and good versus poor glucose control. In order to determine the effects of hyperglycemia on glycoprotein biosynthesis in vitro, synthesis of haptoglobin and other glycoproteins will be examined in perfused rat liver or hepatocytes under conditions of normal or excess glucose, and normal or absent insulin, mimicking conditions found in normal and diabetic serum. Methods of structural analysis of oligosaccharides synthesized in vivo and in vitro will include carbohydrate composition, lectin affinity chromatography, exo- and endoglycosidase digestion, and methylation.
