ISLET AMYLOID POLYPEPTIDE AND ITS N-TERMINAL AND C-TERMINAL FLANKING PEPTIDES IMMUNOREACTIVITY IN ISLET AMYLOID OF DIABETIC-PATIENTS

We determined immunohistochemically whether the islet amyloid polypept ide (IAPP)/amylin precursor is one component of islet amyloid, using p olyclonal antibodies specific for human IAPP(8-17) and amino (N)-termi nal and carboxy (C)-terminal flanking peptides. To enhance immunostain ing of the amyloid, we pretreated the pancreatic tissue sections with 100% formic acid. In three non-diabetic subjects, pancreatic islet cel ls were immunoreactive to anti-IAPP(8-17) and anti-N-terminal and C-te rminal flanking peptide antibodies and the reactivity was enhanced wit h formic acid pretreatment. In six type 2 diabetic subjects and a subj ect with type A insulin resistance, islet amyloid deposits were reacti ve to anti-IAPP(8-17) antibody, but not to anti-N-terminal and C-termi nal flanking peptide antibodies. Formic acid pretreatment markedly enh anced the reactivity to anti-IAPP(8-17) antibody; however, it failed t o show the reactivity to anti-N-terminal and C-terminal flanking pepti de antibodies. Formic acid pretreatment of pancreatic tissue sections prepared for immunostaining is useful for visualization of buried epit opes of mature IAPP and its precursor molecules, either in islet amylo id deposits or in the islet cells. We conclude that the IAPP precursor and N-terminal and C-terminal flanking peptides are not constituents of human islet amyloid.