Elevated Levels of α - Haptoglobin in the Type II Diabetic KKA Y Mouse Model

Abstract

K KAY mice are a Japanese native strain exhibiting diabetic traits at an early age. Such traits are likely to include impaired glucose tolerance, hyperglycemia, hyperinsulinemia, insulin resistence of peripheral tissue, and renal glomerular changes. Plasma of KKA Y mice as well as C57 BL A/J control mice subjected to two-dimensional gel electrophoresis revealed a protein of approximate pI 4.5 and molecular weight 11 kD which is 3X more concentrated in the diabetic mice than in the control mice. Two-Dimensional electrophoresis followed by zinc staining and passive elution were used as a means of isolating approximately 50 µg of the unknown protein. Following cleavage of the isolated protein, high performance liquid chromatography (HPLC) served to separate the 11 Kd protein from contaminants found in the elution buffer. Subsequent NH2-terminal sequence analysis resulted in the identification of this protein as an α-haptoglobin-like peptide, showing 80% identity with the first 25 residues of rat haptoglobin. Haptoglobin is a serum glycoprotein responsible for the removal of free hemoglobin from the blood. An irreversibly bound haptoglobin-hemoglobin complex is taken up by the liver and delivered to the bile where it is made accessible todegrative enzymes. In so doing, the kidney glomerulus is protected against damage caused by free hemoglobin. Haptoglobin has in the past been associated with the occurrence of hypertension. This paper now points out that haptoglobin is a marker of diabetes in the KKA Y model.