B cell granule peptides affect human islet amyloid polypeptide (IAPP) fibril formation in vitro.

Islet amyloid polypeptide (IAPP) forms fibrils spontaneously. We examined whether other B cell granule peptides affect formation of beta-pleated sheet fibrils in vitro from human IAPP. Quantitative radioassay (radioactivity of soluble IAPP after adding 125I-IAPP) and thioflavine fluorescence spectroscopy showed that insulin, C-peptide, and pancreastatin inhibited fibril formation by 60-100% at ratio 100:1 (peptide:IAPP), whereas at 1:10 or 1:100, i.e., IAPP in excess, a potentiated IAPP fibril formation was induced by the peptides. Semi-quantitative analysis by electron microscopy yielded similar effects. Thus, spontaneous IAPP fibrillisation is influenced by other B cell secretory granule peptides in a molar ratio dependent manner.