The Nature of the Amyloid in the Islets of Langerhans: A Novel Polypeptide Hormone?
The novel peptide, islet (or insulinoma) amyloid polypeptide (IAPP), is described. IAPP is produced by normal and neoplastic islet β-cells and is the major constituent of islet amyloid, which occurs mainly in type 2 diabetic individuals but also to a lesser extent in persons without diabetes. The function of IAPP is unknown, but it has partial sequence identity with the neurohormone calcitonin gene-related peptide, making hormonal nature probable.
Deposition of a hyaline material in the islets of Langerhans in connection with diabetes mellitus was described almost 90 years ago (1). During a time when amyloid was regarded as a single substance, there was a debate about whether or not the deposited material was actually amyloid (2). With modern definition (3), there is now no doubt that islet hyaline is a form of localized amyloidosis.
Islet amyloid is strictly limited to the islets, and electron microscopic studies have revealed evidence for its origin from β-cells (4). Similarly, amyloid deposits are very common in insulinomas and are much more rare in other hormone-producing pancreatic tumors (5). These observations indicate that islet amyloid contains a protein expressed by the β-cells. For that reason, an insulin-related molecule was long suspected as the major subunit of islet amyloid. It is the aim of this presentation to review recent unexpected findings on the composition of islet amyloid.
KeywordsAmyloid Deposit Amyloid Fibril Human Islet Hormonal Nature Islet Amyloid Polypeptide
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