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Amyloidosis is a protein conformational disorder with the distinctive feature of extracellular accumulation of amyloid fibrils that come from different proteins. In the ligamentum flavum of the lumbar spine, amyloid deposits were frequently found in elderly patients with lumbar spinal canal stenosis and were at least partially formed by wild-type transthyretin. However, how amyloid deposits in the ligamentum flavum affect lumbar spinal canal stenosis has remained unclear. In this study, we analyzed clinical, pathologic, and radiologic findings of patients with lumbar spinal canal stenosis who had amyloid deposits in the ligamentum flavum. We studied 95 ligamentum flavum specimens obtained from 56 patients with lumbar spinal canal stenosis and 21 ligamentum flavum specimens obtained from 19 patients with lumbar disk herniation. We evaluated histopathologic findings and clinicoradiologic manifestations, such as thickness of the ligamentum flavum and lumbar spinal segmental instability. We found that all 95 ligamentum flavum specimens resected from patients with lumbar spinal canal stenosis had amyloid deposits, which we classified into two types, transthyretin-positive and transthyretin-negative, and that transthyretin amyloid formation in the ligamentum flavum of patients with lumbar spinal canal stenosis was an age-associated phenomenon. The amount of amyloid in the ligamentum flavum was related to clinical manifestations of lumbar spinal canal stenosis, such as thickness of the ligamentum flavum and lumbar spinal segmental instability, in the patients with lumbar spinal canal stenosis with transthyretin-positive amyloid deposits. To our knowledge, this report is the first to show clinicopathologic correlations in transthyretin amyloid deposits of the ligamentum flavum. In conclusion, transthyretin amyloid deposits in the ligamentum flavum may be related to the pathogenesis of lumbar spinal canal stenosis in elderly patients.

Islet amyloid polypeptide (IAPP, “amylin”) has been proposed as having important roles in the pathogenesis of type 2 diabetes mellitus via its biological activity and by forming islet amyloid. The domestic cat develops a type of diabetes that closely resembles type 2 diabetes in humans, including the frequent formation of islet amyloid deposits in the impaired glucose tolerant (IGT) and diabetic state. With the aid of computerized image analysis and immuno-histochemistry, we examined the IAPP and insulin content inpancreatic islets of normal, IGT and diabetic cats. IAPP immunoreactivity in beta cells from IGT cats was significantly stronger (p < 0.01) as compared with cells from normal cats, while the insulin labelling strength was unchanged. Overtly diabetic cats were usually almost devoid of beta cells. As in humans, cellular IAPP but not IAPP in islet amyloid deposits was labelled by the newly developed monoclonal antibody to IAPP 4A5, thus providing further evidence that IAPP is modified by a yet unknown mechanism during the amyloidogenic process. The study provides evidence that an increased beta cell storage of IAPP independent of insulin may be an important factor in the early phase of the development of islet amyloid in this form of diabetes.

Islet amyloid polypeptide (IAPP or amylin) is costored and cosecreted with insulin and may regulate insulin secretion and blood glucose handling. However, the role and importance of endogenous IAPP in the regulation of insulin release and glucose homeostasis have been controversial. Here we report on the generation and phenotypic analysis of IAPP-deficient mice. These mice have normal, or near to normal, basal levels of circulating insulin and glucose. However, following glucose administration, IAPP-deficient males presented increased insulin responses paralleled with a more rapid blood glucose elimination compared to wild-type controls. Blood glucose elimination was also found to be enhanced in IAPP-deficient females, but the insulin response in this gender did not differ from controls. In a transgenic rescue experiment, using an insulin-promoter human-IAPP fusion gene, insulin responses and blood glucose elimination were reversed in IAPP-deficient males, whereas the female phenotype appeared unaffected. Our results provide the first firm evidence of a physiological role for endogenous IAPP and indicate that IAPP, apparently in a gender-dependent manner, limits the degree of glucose-induced insulin secretion and the rate of blood glucose elimination.

A major protein AA amyloid protein was purified and characterised from a Papua New Guinean individual. This AA protein differed from all previously characterised SAA variants by the combination of Ala52, Val57, Asn60, Phe68, Phe69 and Gly72. Since the prevalence of AA-amyloidosis is unusually high in PapuaNew Guinea this AAδ must originate from a novel SAAδ which may represent a particularly amyloidogenicvariant.

Formation of amyloid-like fibrils in a solution of human islet amyloid polypeptide (hIAPP) with and without the presence of other β-cell granule components was studied in vitro. Insulin at less than equimolar concentration strongly inhibited hIAPP fibrillogenesis. Proinsulin had a weaker inhibitory effect while C-peptide, Ca 2+and Zn 2+each individually enhanced fibril formation. C-peptide combined with Ca 2+had an inhibitory effect. Since IAPP was found almost exclusively in the halo fractions of isolated islet secretory granules, primarily the concentrations of C-peptide, Ca 2+and possibly proinsulin may be crucial for the native state of IAPP. It is concluded that an imbalance between fibril formation enhancers and inhibitors may be of importance in the pathogenesis of amyloid in the islets of Langerhans.

Background: Human, but not mouse, islet amyloid polypeptide (IAPP) is amyloidogenic. Transgenic mice overexpressing human IAPP in the βcells of the islets of Langerhans should be useful in identifying factors important for the deposition of IAPP as insoluble amyloid fibrils. Materials and Methods: Transgenic mice expressing human IAPP were examined using several experimental models for the production of persistent hyperglycemia, as well as for the overstimulation and/or inhibition of βcell secretion. Obesity was induced by aurothioglucose. Persistent hyperglycemia was produced by long-term administration of glucocorticosteroids or by partial pancreatectomy. Inhibition of normal βcell exocytosis by diazoxide administration, with or without concurrent dexamethasone injections, was carried out to increase crinophagy of secretory granules. The human IAPP gene was also introduced into the dband obmouse models for diabetes. Finally, isolated islets cultivated in vitro at high glucose concentration were also examined. Results: No amyloid deposits were found in the pancreata of any of the animals, either by light microscopy after Congo red staining or by electron microscopy after immunogold labeling with antibodies specific for human IAPP. Aurothioglucose treatment resulted in increased numbers of granules in the βcell and the appearance of large lysosomal bodies without amyloid. However, islets from dband obmice expressing human IAPP cultivated in vitro in the presence of glucocorticosteroid and/or growth hormone, were found to contain extracellular amyloid deposits reacting with antibodies to human IAPP. Conclusions: Oversecretion of human IAPP or increased crinophagy are not sufficient for amyloid formation. This indicates that other factors must influence amyloid deposition; one such factor may be the local clearance of IAPP.

Islet amyloid polypeptide (IAPP), a putative polypeptide hormone, is a product of pancreatic beta-cells and the major constituent of the amyloid deposits seen mainly in islets of type 2 diabetic humans and diabetic cats. The connection between IAPP amyloid formation and diabetes is unknown, but a limited segment of the IAPP molecule, positions 20-29, seems responsible for the aggregation to fibrils. Differences in the amino acid sequence of this region probably determine whether or not islet amyloid can develop in a particular species. Amyloid fibril formation can be mimicked in vitro with the aid of synthetic peptides. With this technique we show that peptides corresponding to IAPP positions 20-29 of human and cat, species that develop IAPP-derived islet amyloid, form amyloid-like fibrils in vitro. The corresponding IAPP segment from three rodent species that do not develop IAPP-derived amyloid did not give rise to fibrils. Substitution of the human IAPP-(20-29) decapeptide with one or two amino acid residues from species without islet amyloid generally reduced the capacity to form fibrils. We conclude that the sequence Ala-Ile-Leu-Ser-Ser, corresponding to positions 25-29 of human IAPP, is strongly amyloidogenic and that a proline-for-serine substitution in position 28, as in several rodents, almost completely inhibits formation of amyloid fibrils.

To model islet amyloidogenesis in NIDDM and explore the glucoregulatory role of islet amyloid polypeptide (IAPP), we have created transgenic micye containing a rat insulin-I promoter-human IAPP fusion gene. Expression of human IAPP was localized to the islets of Langerhans, anterior pituitary and brain in transgenic animals; blood IAPP levels were elevated 5-fold while fasting glucose levels remained normal. Amyloid deposits have not been detected in transgenic islets suggesting that other co-existing abnormalitites in NIDDM may be required for the formation of islet amyloid. These animals provide a unique model for exploring this hypothesis and other proposed functions of IAPP.