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PubMed1997

Transgenic overproduction of islet amyloid polypeptide (amylin) is not sufficient for islet amyloid formation.

Islet amyloid polypeptide forms islet amyloid deposits in non-insulin-dependent diabetes mellitus. We have generated transgenic mice which express human islet amyloid polypeptide in their pancreatic beta cells yet do not develop islet amyloid deposits despite producing levels of the amyloidogenic human peptide 2 - 3 fold higher than the native (mouse) peptide. To determine whether marked overproduction of islet amyloid polypeptide is a potential cause of islet amyloid formation, we increased expression of this transgene by producing homozygous transgenic animals and by making heterozygous mice experimentally insulin resistant with nicotinic acid. Pancreatic content of islet amyloid polypeptide-like immunoreactivity in homozygous and nicotinic acid-treated mice was 2-fold (25 +/- 7 fmol/microg; n = 6) and 3.5-fold (47 +/- 20 fmol/microg; n = 3) higher, respectively, than that of untreated heterozygous animals (13+/-2 fmol/microg; n = 11; both p < 0.05). Despite this marked increase in production of islet amyloid polypeptide, neither group of mice developed gross islet amyloid deposits even after 16 months of age. We conclude that overproduction of islet amyloid polypeptide, even as produced by extreme insulin resistance, is not in itself sufficient for islet amyloid formation.

Amyloid↗

PubMed1993

On the association between amyloid fibrils and glycosaminoglycans; possible interactive role of Ca2+ and amyloid P-component.

We have previously reported the specific association of glycosaminoglycans (GAG) and proteoglycans (PG) with amyloid fibrils and characterized the polysaccharides directly extracted from amyloid-laden tissues. In the present study we further elucidate the association between purified amyloid fibrils and GAG/PG with special reference to those GAG/PG associated with amyloid P-component (AP) and the interactive role of Ca2+ ions. Amyloid fibrils were isolated from human hepatic AA amyloid employing water extraction with and without preceding removal of AP, an extrafibrillar protein component of all amyloids, using sodium citrate. GAG/PG co-isolated with the amyloid extracts, with and without AP, were isolated and characterized. Agarose-affinity chromatography of extracts containing AP was performed, and the GAG associated with this extrafibrillary protein were characterized as well. Several different GAG/PG populations were demonstrated in the various extracts. The abolition of calcium-dependent binding markedly influenced the amount of GAG/PG recovered in the fibril extracts, as well as the total amount of amyloid material obtained. Thus, it seems that calcium plays an important role in the association between the fibrils and the sugar moieties, and that a significant fraction of the GAG found in amyloid exhibits a Ca(2+)-dependent fibril-GAG interaction. No significant difference in the proportion between galactosaminoglycans and glucosamines was, however, disclosed when the two extraction protocols were compared, suggesting that no particular GAG species has a higher affinity for the fibrils themselves. Both dermatan/chondroitin sulphate and heparan sulphate identified in the present study exhibited a Ca(2+)-dependent interaction with AP, supporting previous findings. However, the amyloid-associated galactosaminoglycans found, especially the large PG appearing in small amounts, seemed to have a higher affinity for the extrafibrillar AP than the other GAG.

Amyloid↗

PubMed2005

Immunohistochemical identification of amyloid, using an anti-human serum amyloid P component (SAP) antibody, is possible in ruminants but not in dogs and cats.

Amyloidosis represents a heterogenous group of diseases that have in common the deposition of fibrils composed of proteins of beta-pleated sheet structure, a structure which can be specifically identified by histochemistry using the Congo red or similar stains. Amyloid consists primarily of the amyloid fibrils but also of the amyloid P component (AP). This component, which is identical with the serum counterpart (SAP), is found in all types of human amyloid, and immunohistochemical identification of AP has been proposed as an adjunct to the universal, type-independent diagnosis of human amyloidosis. In the present study of animal amyloidosis, we compared the amyloid-specific Congo red stain with an immunohistochemical protocol using an anti-human SAP antibody for the identification of amyloid in formalin fixed tissue samples. The species and types of amyloidoses investigated were: (i) seven cows, one yak (Bos grunniens), and one sheep affected with amyloidosis of presumed AA type, (ii) one dog with a pancreatic endocrine tumour producing amyloid of presumed AIAPP type, (iii) two cats with presumed AIAPP-amyloidosis of the islets of Langerhans, one cat with presumed AA-amyloidosis, and one cat with an amyloid-producing odontogenic tumour. Intense immunostaining co-localized with amyloid, identified by its congophilia and green birefringence, using a protocol without any antigen retrieval in each of the seven cows, the yak and the sheep. The method seemed more sensitive in the ruminants than the Congo red stain, but was unable to detect amyloid in the dog and the cats regardless of the application of various antigen retrieval protocols. However, specific identification of amyloid still rests on the Congo red method or similar histochemical techniques.

Amyloid↗

PubMed1991

Transthyretin-type cerebral amyloid angiopathy in type I familial amyloid polyneuropathy.

To clarify the pathogenesis of cerebrovascular amyloid deposits, histological and immunocytochemical studies were performed on the central nervous system (CNS) in ten cases with type I familial amyloid polyneuropathy (FAP). They commonly suffered from peripheral somatic and autonomic nerve disorders without any CNS dysfunctions. However, all cases showed CNS amyloid deposits, mainly on the leptomeningeal vessels and pia-arachnoid membranes, with arteries and arterioles in the subarachnoidal space being the predominant site of cerebral amyloid accumulation. Using immunocytochemical staining methods with antibodies to amyloid beta-protein, human cystatin C and transthyretin (prealbumin), all of these amyloid deposits were specifically immunolabeled by the anti-human transthyretin antibody. However, there was no transthyretin-related amyloid deposits in the brain parenchyma. It is concluded that CNS transthyretin-immunoreactive amyloid deposition with cerebral amyloid angiopathy (CAA) is a common pathological finding in this disease. Moreover, the patients with type I FAP are known to have an amyloid protein precursor (a variant of transthyretin) in serum. This transthyretin type of CAA, therefore, seems to be an example of cerebrovascular amyloid deposits derived from a serum precursor.

Adolescent↗

PubMed2004

Characterization of splenic glycosaminoglycans accumulated in vivo in experimentally induced amyloid-susceptible and amyloid-resistant mice.

The pathogenesis of the amyloid deposition diseases is poorly understood. The CE/J mouse, which is naturally protected from amyloid A (AA) protein amyloidosis, has provided a tool to study mechanisms that may be implicated in amyloid deposition diseases by means of comparison of findings with those in an AA-susceptible mouse strain. We have compared proteoglycan/glycosaminoglycan accumulation in vivo in amyloid-protected CE/J mouse strain and in AA-susceptible CBA/J mouse strain in homeostasis and when injected with amyloid-inducing agents. Results indicate that there is an overall increase in [(35)S]proteoglycan/glycosaminoglycan accumulation in the spleens of both strains of mice, but with a specific increase in heparan sulfate in only CBA/J mouse spleens that are rich in amyloid. Further, we report the absence of heparan sulfate in the splenic perifollicular areas of amyloid-free CE/J mouse, whereas in the amyloid-laden CBA/J mouse there is co-localization of heparan sulfate with the AA deposits. We have also examined the glycosaminoglycan disaccharide products in both these strains of mice for their sulfation positions and found no differences in the disaccharide composition of chondroitin/dermatan sulfate and heparan sulfate isolated from the control CBA/J and control CE/J mice. There were no differences in chondroitin/dermatan sulfate in both strains after experimental induction. However, analysis of the heparan sulfate disaccharides by means of capillary high-performance liquid chromatography linked to microelectrospray ionization time-of-flight mass spectrometry indicated that the disaccharide composition of the splenic heparan sulfate obtained from the treated CBA/J mice that had developed amyloid was markedly different from that obtained from the control CBA/J mice and the treated amyloid-resistant CE/J mice. These findings suggest that unique heparan sulfates play a fundamental role in the pathogenesis of amyloid.

Amyloidosis↗

PubMed1982

Senile aortic amyloid. A third distinctive type of age-related cardiovascular amyloid.

Aortic tissues from 22 elderly patients were analyzed by Congo red staining for amyloid deposits. All samples contained amyloid, which was resistant to the potassium permanganate reaction. Tryptophan was present in all amyloid deposits. The amyloid failed to react with antiserums to amyloid fibril protein ASc1 or human prealbumin, proteins previous demonstrated in generalized senile cardiac amyloid. It also differed from age-related isolated atrial amyloid, which has been shown to lack tryptophan. Deposits did not react with antiserums specific for amyloid fibril proteins of the A lambda IV, A lambda VI, AA, or AEt types. These results indicate that senile aortic amyloid is distinct from amyloid present in primary and secondary amyloidosis and appears to represent a third form of cardiovascular amyloid associated with the aging process.

Aged↗

PubMed1995

Serum amyloid P component prevents proteolysis of the amyloid fibrils of Alzheimer disease and systemic amyloidosis.

Extracellular deposition of amyloid fibrils is responsible for the pathology in the systemic amyloidoses and probably also in Alzheimer disease [Haass, C. & Selkoe, D. J. (1993) Cell 75, 1039-1042] and type II diabetes mellitus [Lorenzo, A., Razzaboni, B., Weir, G. C. & Yankner, B. A. (1994) Nature (London) 368, 756-760]. The fibrils themselves are relatively resistant to proteolysis in vitro but amyloid deposits do regress in vivo, usually with clinical benefit, if new amyloid fibril formation can be halted. Serum amyloid P component (SAP) binds to all types of amyloid fibrils and is a universal constituent of amyloid deposits, including the plaques, amorphous amyloid beta protein deposits and neurofibrillary tangles of Alzheimer disease [Coria, F., Castano, E., Prelli, F., Larrondo-Lillo, M., van Duinen, S., Shelanski, M. L. & Frangione, B. (1988) Lab. Invest. 58, 454-458; Duong, T., Pommier, E. C. & Scheibel, A. B. (1989) Acta Neuropathol. 78, 429-437]. Here we show that SAP prevents proteolysis of the amyloid fibrils of Alzheimer disease, of systemic amyloid A amyloidosis and of systemic monoclonal light chain amyloidosis and may thereby contribute to their persistence in vivo. SAP is not an enzyme inhibitor and is protective only when bound to the fibrils. Interference with binding of SAP to amyloid fibrils in vivo is thus an attractive therapeutic objective, achievement of which should promote regression of the deposits.

Alzheimer Disease↗

PubMed2003

Amyloid beta protein toxicity mediated by the formation of amyloid-beta protein precursor complexes.

The amyloid-beta protein precursor, a type 1 transmembrane protein, gives rise to the amyloid beta-protein, a neurotoxic peptide postulated to be involved in the pathogenesis of Alzheimer's disease. Here, we show that soluble amyloid beta protein accelerates amyloid precursor protein complex formation, a process that contributes to neuronal cell death. The mechanism of cell death involves the recruitment of caspase-8 to the complex, followed by intracytoplasmic caspase cleavage of amyloid precursor protein. In vivo, the levels of soluble amyloid beta protein correlated with caspase-cleaved fragments of the amyloid precursor protein in brains of Alzheimer's disease subjects. These findings suggest that soluble amyloid beta protein-induced multimerization of the amyloid precursor protein may be another mechanism by which amyloid beta protein contributes to synapse loss and neuronal cell death seen in Alzheimer's disease.

Amyloid beta-Peptides↗

PubMed1986

Characterization of amyloid deposits in biopsies of 15 with "sporadic" (non-familial or plasma cell dyscrasia amyloid polyneuropathy.

Review of the clinical and laboratory findings of 39 patients with amyloid polyneuropathy (AP) showed 12 cases to be hereditary and 12 to be associated with plasma cell dyscrasia (PCD). The remaining 15, termed "sporadic" AP, had neuropathy clinically indistinguishable from the other two groups but without a clinicopathologically identified PCD or positive family history. In an attempt to identify the type of amyloid in "sporadic" AP, the immunoreactivity of amyloid deposits was investigated using specific antisera raised against the following different chemical types of amyloid fibril proteins: variable regions of amyloid light chains kappa (A kappa) and lambda (A lambda), amyloid protein AA, and prealbumin. It was found that the amyloid in "sporadic" AP had A lambda antigenic determinants in ten cases, A kappa in one and prealbumin in three; in one case, the A lambda nature of amyloid was confirmed biochemically on the extracted amyloid fibrills. Thus, the most common type of AP in our population appears to be the "sporadic" form. In "sporadic" AP, the amyloid is most commonly of immunoglobulin light chain origin, even in the absence of overt PCD, and it can be rapidly categorized immunocytochemically to determine therapeutic directions or provide genetic guidance.

Amyloid↗

PubMed1990

Alzheimer cortical neurons containing abundant amyloid mRNA. Relationship to amyloid deposition and senile plaques.

Since the detailed molecular events leading to the formation of amyloid-containing senile plaques of the Alzheimer's disease (AD) brain are incompletely understood, the present studies were undertaken to address this issue using a combination of molecular and cytochemical approaches. Amyloid precursor protein riboprobes containing the A4 (beta-amyloid) domain were applied to cortex using the in situ hybridization method to examine the distribution of neuronal amyloid mRNA in relation to the laminar pattern of amyloid deposition and the localization of plaques. The derived data indicated that high levels of amyloid mRNA can be synthesized by AD cortical neurons that appeared to be morphologically intact. The distribution of these cells was not coincident with the cortical laminar pattern that is typical of amyloid deposits observed after immunostaining with anti-A4 monoclonal antibodies. Further, there was no obvious relationship between neurons containing abundant amyloid mRNA and the distribution of plaques identified by thioflavin S staining. While the neuronal synthesis of amyloid may be a significant factor at some point during plaque formation, it may not be the exclusive determinant. The possibility is raised that processes affecting secretion, diffusion, and/or transport of amyloid away from neuronal or non-neuronal cells of origin to sites of deposition may be meaningful aspects of the molecular pathology of Alzheimer's disease.

Aged↗

PubMed1999

Differences in amyloid deposition in islets of transgenic mice expressing human islet amyloid polypeptide versus human islets implanted into nude mice.

Islet amyloid polypeptide (IAPP)-derived amyloid is frequently deposited in the islets of Langerhans in patients with chronic non-insulin-dependent diabetes mellitus (NIDDM). When human islets were implanted under the renal capsule in nude mice, amyloid occurred in 73% of the grafts within 2 weeks. In this study, we compare the deposition of amyloid in islets from a transgenic mouse strain expressing human IAPP (hIAPP) and in normal human islets after implantation in nude mice. The implantations were performed as follows: (1) nondiabetic recipients were given islets from transgenic mice alone, (2) human islets were implanted in the upper pole of the kidney and islets from transgenic mice were implanted in the lower pole of the kidney, (3) grafts containing a mixture of human and transgenic islets were implanted, and (4) transgenic islets and islets from nontransgenic littermates were implanted in therapeutic numbers into recipients made diabetic by a single injection of alloxan prior to implantation. The implants were removed after various periods from 4 days to 8 weeks. The implants were either fixed in Formalin, stained for amyloid, and viewed in polarized light, or processed for immunoelectron microscopy and studied after immunolabeling with specific antibodies against IAPP. We found that the course of amyloid deposition differed significantly between human islets and hIAPP-expressing mouse islets. In human islets, amyloid was mainly deposited intracellularly and only small amounts of amyloid were found extracellularly. In contrast, in islets from transgenic mice, amyloid was exclusively deposited extracellularly and deposition in this site was preceded by an aggregation of immunoreactive material along the basement membrane. These findings point to separate mechanisms for amyloid formation in these two models.

Amyloid↗

PubMed1998

Adenoviral expression of murine serum amyloid A proteins to study amyloid fibrillogenesis.

Serum amyloid A (SAA) proteins are one of the most inducible acute-phase reactants and are precursors of secondary amyloidosis. In the mouse, SAA1 and SAA2 are induced in approximately equal quantities in response to amyloid induction models. These two isotypes differ in only 9 of 103 amino acid residues; however, only SAA2 is selectively deposited into amyloid fibrils. SAA expression in the CE/J mouse species is an exception in that gene duplication did not occur and the CE/J variant is a hybrid molecule sharing features of SAA1 and SAA2. However, even though it is more closely related to SAA2 it is not deposited as amyloid fibrils. We have developed an adenoviral vector system to overexpress SAA proteins in cell culture to determine the ability of these proteins to form amyloid fibrils, and to study the structural features in relation to amyloid formation. Both the SAA2 and CE/J SAA proteins were synthesized in large quantities and purified to homogeneity. Electron microscopic analysis of the SAA proteins revealed that the SAA2 protein was capable of forming amyloid fibrils, whereas the CE/J SAA was incapable. Radiolabelled SAAs were associated with normal or acute-phase high-density lipoproteins (HDLs); we examined them for their clearance from the circulation. In normal mice, SAA2 had a half-life of 70 min and CE/J SAA had a half-life of 120 min; however, in amyloid mice 50% of the SAA2 cleared in 55 min, compared with 135 min for the CE/J protein. When the SAA proteins were associated with acute-phase HDLs, SAA2 clearance was decreased to 60 min in normal mice compared with 30 min in amyloidogenic mice. Both normal and acute-phase HDLs were capable of depositing SAA2 into preformed amyloid fibrils, whereas the CE/J protein did not become associated with amyloid fibrils. This established approach opens the doors for large-scale SAA production and for the examination of specific amino acids involved in the fibrillogenic capability of the SAA2 molecule in vitro and in vivo.

Acute-Phase Proteins↗

PubMed1990

Islet amyloid polypeptide: pinpointing amino acid residues linked to amyloid fibril formation.

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.

Amino Acid Sequence↗

PubMed1996

Islet amyloid formation associated with hyperglycemia in transgenic mice with pancreatic beta cell expression of human islet amyloid polypeptide.

Pancreatic islet amyloid deposits are a characteristic pathologic feature of non-insulin-dependent diabetes mellitus and contain islet amyloid polypeptide (IAPP; amylin). We used transgenic mice that express human IAPP in pancreatic beta cells to explore the potential role of islet amyloid in the pathogenesis of non-insulin-dependent diabetes mellitus. Extensive amyloid deposits were observed in the pancreatic islets of approximately 80% of male transgenic mice > 13 months of age. Islet amyloid deposits were rarely observed in female transgenic mice (11%) and were never seen in nontransgenic animals. Ultrastructural analysis revealed that these deposits were composed of human IAPP-immunoreactive fibrils that accumulated between beta cells and islet capillaries. Strikingly, approximately half of the mice with islet amyloid deposits were hyperglycemic (plasma glucose > 11 mM). In younger (6- to 9-month-old) male transgenic mice, islet amyloid deposits were less commonly observed but were always associated with severe hyperglycemia (plasma glucose > 22 mM). These data indicate that expression of human IAPP in beta cells predisposes male mice to the development of islet amyloid and hyperglycemia. The frequent concordance of islet amyloid with hyperglycemia in these mice suggests an interdependence of these two conditions and supports the hypothesis that islet amyloid may play a role in the development of hyperglycemia.

Amyloid↗

PubMed1998

Progression of cerebral amyloid angiopathy: accumulation of amyloid-beta40 in affected vessels.

Cerebrovascular deposits of amyloid (cerebral amyloid angiopathy, or CAA) are generally asymptomatic, but in advanced cases, they can lead to vessel rupture and hemorrhage. The process of progression in CAA was studied by comparison of postmortem brains with asymptomatic ("mild") CAA to brains with the form of the disease associated with hemorrhage ("severe CAA"). Cortical and meningeal vessels were immunostained for beta-amyloid and examined by confocal microscopy and by systematic quantitative sampling. We focused on 2 quantitative parameters: the proportion of vessels affected by amyloid (a measure of amyloid seeding of vessels) and the amount of amyloid per affected vessel (a measure of growth of existing lesions). Surprisingly, there was no difference between the proportion of affected cortical vessels in mild and severe CAA (0.29 vs 0.32, p = 0.65), but rather an increase in the area of the 40 amino acid form of beta-amyloid per affected cortical vessel (198.5 +/- 38.7 vs 455.8 +/- 100.9 microm2/vessel, p < 0.007). Increasing doses (from 0 to 1 to 2 copies) of the apolipoprotein E epsilon4 allele were also associated with greater amyloid per vessel without change in the proportion of affected vessels within each class of CAA severity. These findings suggest that progression from asymptomatic to advanced CAA reflects progressive accumulation of amyloid in vessels previously seeded with amyloid, and that this process is selectively enhanced by apolipoprotein E epsilon4.

Aging↗

PubMed2005

Genetic background determines the extent of islet amyloid formation in human islet amyloid polypeptide transgenic mice.

Genetic background is important in determining susceptibility to metabolic abnormalities such as insulin resistance and beta-cell dysfunction. Islet amyloid is associated with reduced beta-cell mass and function and develops in the majority of our C57BL/6J x DBA/2J (F(1)) male human islet amyloid polypeptide (hIAPP) transgenic mice after 1 yr of increased fat feeding. To determine the relative contribution of each parental strain, C57BL/6J (BL6) and DBA/2J (DBA2), to islet amyloid formation, we studied male hIAPP mice on each background strain (BL6, n = 13; and DBA2 n = 11) and C57BL/6J x DBA/2J F(1) mice (n = 17) on a 9% (wt/wt) fat diet for 1 yr. At the end of 12 mo, islet amyloid deposition was quantified from thioflavin S-stained pancreas sections. The majority of mice in all groups developed islet amyloid (BL6: 91%, F(1): 76%, DBA2: 100%). However, the prevalence (%amyloid-positive islets; BL6: 14 +/- 3%, F(1): 44 +/- 8%, DBA2: 49 +/- 9%, P < 0.05) and severity (%islet area occupied by amyloid; BL6: 0.03 +/- 0.01%, F(1): 9.2 +/- 2.9%, DBA2: 5.7 +/- 2.3%, p < or = 0.01) were significantly lower in BL6 than F(1) and DBA2 mice. Increased islet amyloid severity was negatively correlated with insulin-positive area per islet, in F(1) (r(2) = 0.75, P < 0.001) and DBA2 (r(2) = 0.87, P < 0.001) mice but not BL6 mice (r(2) = 0.07). In summary, the extent of islet amyloid formation in hIAPP transgenic mice is determined by background strain, with mice expressing DBA/2J genes (F(1) and DBA2 mice) being more susceptible to amyloid deposition that replaces beta-cell mass. These findings underscore the importance of genetic and environmental factors in studying metabolic disease.

Amyloid↗

PubMed1999

The mechanism of islet amyloid polypeptide toxicity is membrane disruption by intermediate-sized toxic amyloid particles.

NIDDM is characterized by islet amyloid deposits and decreased beta-cell mass. Islet amyloid is derived from the locally expressed protein islet amyloid polypeptide (IAPP). While it is now widely accepted that abnormal aggregation of IAPP has a role in beta-cell death in NIDDM, the mechanism remains unknown. We hypothesized that small IAPP aggregates, rather than mature large amyloid deposits, are cytotoxic. Consistent with this hypothesis, freshly dissolved human (h)-IAPP was cytotoxic when added to dispersed mouse and human islet cells, provoking the formation of abnormal vesicle-like membrane structures in association with vacuolization and cell death. Human islet cell death occurred by both apoptosis and necrosis, predominantly between 24 and 48 h after exposure to h-IAPP. In contrast, the addition to dispersed islet cells of matured h-IAPP containing large amyloid deposits of organized fibrils was seldom associated with vesicle-like structures or features of cell death, even though the cells were often encased in the larger amyloid deposits. Based on these observations, we hypothesized that h-IAPP cytotoxicity is mediated by membrane damage induced by early h-IAPP aggregates. Consistent with this hypothesis, application of freshly dissolved h-IAPP to voltage-clamped planar bilayer membranes (a cell-free in vitro system) also caused membrane instability manifested as a marked increase in conductance, increased membrane electrical noise, and accelerated membrane breakage, effects that were absent using matured h-IAPP or rat IAPP solutions. Light-scattering techniques showed that membrane toxicity corresponded to h-IAPP aggregates containing approximately 25-6,000 IAPP molecules, an intermediate-sized amyloid particle that we term intermediate-sized toxic amyloid particles (ISTAPs). We conclude that freshly dissolved h-IAPP is cytotoxic and that this cytotoxicity is mediated through an interaction of ISTAPs with cellular membranes. Once ISTAPs mature into amyloid deposits comprising >10(6) molecules, the capacity of h-IAPP to cause membrane instability and islet cell death is significantly reduced or abolished. These data may have implications for the mechanism of cell death in other diseases characterized by local amyloid formation (such as Alzheimer's disease).

Amyloid↗

PubMed2003

Increased dietary fat promotes islet amyloid formation and beta-cell secretory dysfunction in a transgenic mouse model of islet amyloid.

Transgenic mice expressing the amyloidogenic human islet amyloid polypeptide (hIAPP) in their islet beta-cells are a model of islet amyloid formation as it occurs in type 2 diabetes. Our hIAPP transgenic mice developed islet amyloid when fed a breeder chow but not regular chow. Because the breeder chow contained increased amounts of fat, we hypothesized that increased dietary fat enhances islet amyloid formation. To test this hypothesis, we fed male hIAPP transgenic and nontransgenic control mice diets containing 15% (low fat), 30% (medium fat), or 45% (high fat) of calories derived from fat for 12 months, and we measured islet amyloid, islet endocrine cell composition, and beta-cell function. Increased dietary fat in hIAPP transgenic mice was associated with a dose-dependent increase in both the prevalence (percentage of islets containing amyloid deposits; 34 +/- 8, 45 +/- 8, and 58 +/- 10%, P < 0.05) and severity (percentage of islet area occupied by amyloid; 0.8 +/- 0.5, 1.0 +/- 0.5, and 4.6 +/- 2.5%, P = 0.05) of islet amyloid. In addition, in these hIAPP transgenic mice, there was a dose-dependent decrease in the proportion of islet area comprising beta-cells, with no significant change in islet size. In contrast, nontransgenic mice adapted to diet-induced obesity by increasing their islet size more than twofold. Increased dietary fat was associated with impaired insulin secretion in hIAPP transgenic (P = 0.05) but not nontransgenic mice. In summary, dietary fat enhances both the prevalence and severity of islet amyloid and leads to beta-cell loss and impaired insulin secretion. Because both morphologic and functional defects are present in hIAPP transgenic mice, this would suggest that the effect of dietary fat to enhance islet amyloid formation might play a role in the pathogenesis of the islet lesion of type 2 diabetes in humans.

Amyloid↗