Feline insular amyloid: immunohistochemical and immunochemical evidence that the amyloid is insulin-related

Utilizing islet amyloid-laden pancreatic tissues from six diabetic cats, we demonstrated substantial immunoreactivity (peroxidase-antiperoxidase technique) of the islet amyloid with antiserum to a B chain-rich insulin fraction, but no reactivity with antisera to insulin, glucagon, or somatostatin. Islet amyloid was purified from two cats and a protein unique to the diabetic and islet amyloid-laden cats was separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Immunoreactivity of this protein with antiserum to the B chain-rich insulin fraction was also shown by immunoblotting. Attempts to obtain the amino acid composition of the purified unique protein (represented by a single 25,000 dalton band on gel electrophoresis) were not successful because the amount of protein was too small. These results provide important additional evidence that an insulin-related protein is involved in the formation of islet amyloid. Our study also shows that the diabetic cat provides several advantages for the continued study of the etiopathogenic relationship of islet amyloid and diabetes mellitus.