Current and future treatment of amyloid diseases

There are more than 30 human proteins whose aggregation appears to cause degenerative maladies referred to as amyloid diseases or amyloidoses. These disorders are named after the characteristic cross-β-sheet amyloid fibrils that accumulate systemically or are localized to specific organs. In most cases, current treatment is limited to symptomatic approaches and thus disease-modifying therapies are needed. Alzheimer's disease is a neurodegenerative disorder with extracellular amyloid β-peptide (Aβ) fibrils and intracellular tau neurofibrillary tangles as pathological hallmarks. Numerous clinical trials have been conducted with passive and active immunotherapy, and small molecules to inhibit Aβ formation and aggregation or to enhance Aβ clearance; so far such clinical trials have been unsuccessful. Novel strategies are therefore required and here we will discuss the possibility of utilizing the chaperone BRICHOS to prevent Aβ aggregation and toxicity. Type 2 diabetes mellitus is symptomatically treated with insulin. However, the underlying pathology is linked to the aggregation and progressive accumulation of islet amyloid polypeptide as fibrils and oligomers, which are cytotoxic. Several compounds have been shown to inhibit islet amyloid aggregation and cytotoxicity in vitro. Future animal studies and clinical trials have to be conducted to determine their efficacy in vivo. The transthyretin (TTR) amyloidoses are a group of systemic degenerative diseases compromising multiple organ systems, caused by TTR aggregation. Liver transplantation decreases the generation of misfolded TTR and improves the quality of life for a subgroup of this patient population. Compounds that stabilize the natively folded, nonamyloidogenic, tetrameric conformation of TTR have been developed and the drug tafamidis is available as a promising treatment.

Alkali-degradation of amyloid: an ancient method useful for making monoclonal antibodies against amyloid fibril proteins

The systemic amyloidoses constitute a group of life-threatening disorders at which one out of about 15 different proteins have polymerized into fibrils. Prognosis and treatment varies widely and depends on the biochemical type. Determination of this has usually to be performed by immunohistochemistry which is a challenge because of lack of monospecific antibodies that can be used on formaldehyde-fixed tissue sections. We have here used an old method to create immunogenic fragments of AL-amyloid fibrils by partial degradation and solubilization with sodium hydroxide. The mouse monoclonal antibody pwlam raised against this material, labelled AL-amyloid deposits of lambda origin strongly and specifically in sections of formaldehyde-fixed and paraffin-embedded tissues.

Peroxisome proliferator activated receptor gamma activity is low in mature primary human visceral adipocytes

AIMS/HYPOTHESIS

The amount of visceral fat mass strongly relates to insulin resistance in humans. The transcription factor peroxisome proliferator activated receptor gamma (PPARG) is abundant in adipocytes and regulates genes of importance for insulin sensitivity. Our objective was to study PPARG activity in human visceral and subcutaneous adipocytes and to compare this with the most common model for human disease, the mouse.

MATERIALS AND METHODS

We transfected primary human adipocytes with a plasmid encoding firefly luciferase controlled by PPARG response element (PPRE) from the acyl-CoA-oxidase gene and measured PPRE activity by emission of light.

RESULTS

We found that PPRE activity was 6.6-fold higher (median) in adipocytes from subcutaneous than from omental fat from the same subjects (n = 23). The activity was also 6.2-fold higher in subcutaneous than in intra-abdominal fat cells when we used a PPARG ligand-binding domain-GAL4 fusion protein as reporter, demonstrating that the difference in PPRE activity was due to different levels of activity of the PPARG receptor in the two fat depots. Stimulation with 5 micromol/l rosiglitazone did not induce a PPRE activity in visceral adipocytes that was as high as basal levels in subcutaneous adipocytes. Interestingly, in mice of two different strains the PPRE activity was similar in visceral and subcutaneous fat cells.

CONCLUSIONS/INTERPRETATION

We found considerably lower PPARG activity in visceral than in subcutaneous primary human adipocytes. Further studies of the molecular mechanisms behind this difference could lead to development of drugs that target the adverse effects of visceral obesity.

Intracellular amyloid-like deposits contain unprocessed pro-islet amyloid polypeptide (proIAPP) in beta cells of transgenic mice overexpressing the gene for human IAPP and transplanted human islets

AIMS/HYPOTHESIS

Islet amyloid is a frequent finding in the islets of Langerhans of individuals with type 2 diabetes. The main amyloid constituent is the beta cell-derived polypeptide hormone islet amyloid polypeptide (IAPP). In general, amyloid refers to an extracellular deposit of a congophilic material, but intracellular amyloid is seen in some beta cells of transgenic mice expressing the gene for human IAPP and in human islets transplanted into nude mice. The aim of this study was to immunohistochemically characterise the intracellular amyloid.

METHODS

Antisera against the N- and C-terminal processing sites of proIAPP (which were therefore specific for proIAPP), the C-terminal flanking peptide and mature IAPP were used for immunoelectron microscopy.

RESULTS

Fibrillar aggregates were seen in the halo region of the secretory granules in some beta cells in human IAPP transgenic mice. These aggregates were labelled with proIAPP-specific antisera. Also, proIAPP reactivity was more widespread in the intracellular amyloid-like aggregates in beta cells of transgenic mice than in human islet transplants, in which the intracellular amyloid-like deposits were larger, but the proIAPP labelling was restricted to small spots within the amyloid deposits.

CONCLUSIONS/INTERPRETATION

We suggest that proIAPP forms the first amyloid fibrils and that this can occur already in the secretory granules of the beta cells. The proIAPP-derived fibrils can act as seed for further amyloid formation, now made up by IAPP. The observed difference between human islet transplants and human IAPP transgenic animals may reflect differences in stages of amyloid development.

Enhanced in vitro production of amyloid-like fibrils from mutant (S20G) islet amyloid polypeptide

Islet amyloid polypeptide (IAPP, "amylin") is the amyloid-fibril-forming polypeptide in the islets of Langerhans associated with type 2 diabetes mellitus. A missense mutation in the IAPP gene associated with early-onset type 2 diabetes has been identified in the Japanese population. This mutation results in a glycine for serine substitution at position 20 of the mature IAPP molecule. Whether or not formation of islet amyloid with resulting destruction of islet tissue is the cause of this diabetes is yet not known. The present in vitro study was performed in order to investigate any influence of the amino acid substitution on the fibril formation capacity. Synthetic full-length wild type (IAPPwt) and mutant (IAPPS20G) as well as corresponding truncated peptides (position 18-29) were dissolved in dimethylsulfoxide (DMSO) or in 10% acetic acid at a concentration of 10 mg/mL and their fibril forming capacity was checked by Congo red staining, electron microscopy, a Congo red affinity assay and Thioflavine Tfluorometric assay. It was found that full-length and truncated IAPPS20G both formed more amyloid-like fibrils and did this faster compared to IAPPwt. The fibril morphology differed slightly between the preparations.

CONCLUSION

The amino acid substitution (S20G) is situated close to the region of the IAPP molecule implicated in the IAPP fibrillogenesis. The significantly increased formation of amyloid-like fibrils by IAPPS20G is highly interesting and may be associated with an increased islet amyloid formation in vivo and of fundamental importance in the pathogenesis of this specific form of diabetes.

Codeposition of apolipoprotein A-IV and transthyretin in senile systemic (ATTR) amyloidosis

Protein material was extracted from amyloid-rich sections of formalin-fixed and paraffin-embedded heart tissue from an individual with senile systemic amyloidosis, known to contain wild-type transthyretin as major amyloid fibril protein. Amino acid sequence analysis of tryptic peptides of this material revealed in addition to transthyretin sequences, also amino acid sequence corresponding to an N-terminal fragment of apolipoprotein A-IV. In immunohistochemistry, an antiserum to a synthetic apolipoprotein A-IV peptide labeled amyloid specifically. This peptide formed spontaneously amyloid-like fibrils in vitro and enhanced fibril formation from wild-type transthyretin. We conclude that several apolipoproteins, including apolipoprotein A-IV, may be important minor amyloid constituents, promoting fibril formation.

Islet amyloid development in a mouse strain lacking endogenous islet amyloid polypeptide (IAPP) but expressing human IAPP

BACKGROUND

Several mouse strains expressing human islet amyloid polypeptide (IAPP) have been created to study development of islet amyloid and its impact on islet cell function. The tendency to form islet amyloid has varied strongly among these strains by factors that have not been elucidated. Because some beta cell granule components are known to inhibit IAPP fibril formation in vitro, we wanted to determine whether a mouse strain expressing human IAPP but lacking the nonamyloidogenic mouse IAPP is more prone to develop islet amyloidosis.

MATERIALS AND METHODS

Such a strain was created by cross-breeding a transgenic mouse strain and an IAPP null mouse strain.

RESULTS

When fed a fat-enriched diet, male mice expressing only human IAPP developed islet amyloid earlier and to a higher extent than did mice expressing both human and mouse IAPP. Supporting these results, we found that mouse IAPP dose-dependently inhibits formation of fibrils from human IAPP.

CONCLUSIONS

Female mice did not develop amyloid deposits, although small extracellular amorphous IAPP deposits were found in some islets. When cultivated in vitro, amyloid deposits occurred within 10 days in islets from either male or female mice expressing only human IAPP. The study shows that formation of islet amyloid may be dependent on the environment, including the presence or absence of fibril inhibitors or promoters.

Amyloid in human islets of Langerhans: immunologic evidence that islet amyloid polypeptide is modified in amyloidogenesis

Amyloid derived from the beta-cell product islet amyloid polypeptide (IAPP) has been implicated for a beta-cell lesion in Type II diabetes mellitus. The pathogenesis of islet amyloid is poorly understood, and in addition to an amyloidogenic IAPP molecule and possibly increased concentration of IAPP, other unknown factors seem to be included. It was shown previously that polyclonal rabbit IAPP antisera label beta cells close to amyloid only weakly. Whether this lack of immunoreactivity depends on lack of IAPP or on hidden epitopes is in question. In the present study, we show that the IAPP immunoreactivity of these beta cells is possible to retrieve. On the other hand, the monoclonal IAPP antibody 4A5, which labels IAPP in beta cells, does not label IAPP in its native amyloid form. We show evidence that this lack of immunoreactivity is not dependent on conformational change of the IAPP molecules in the amyloidogenesis but is likely owing to glycation of IAPP in human islet amyloid deposits.

Pro islet amyloid polypeptide (ProIAPP) immunoreactivity in the islets of Langerhans

Islet amyloid is typically found in type 2 diabetes mellitus and is believed to participate in the beta cell deterioration. The islet amyloid fibril consists of the 37-amino-acid islet amyloid polypeptide (IAPP) but its pathogenesis is only partly understood. We developed several different rabbit antisera against the flanking peptides of the IAPP precursor (proIAPP) and the proIAPP processing sites in order to study the possible occurrence of unprocessed proIAPP or parts thereof in islet amyloid. We applied these antisera in an immunohistochemical study on, islet amyloid deposits present in a newly generated mouse strain that over-expresses human IAPP but is devoid of mouse IAPP. Male mice of this strain develop severe islet amyloidosis when given a high fat diet. Generally, the antisera showed no immunoreactivity with the amyloid. However, in scattered single beta cells, where amyloid could be seen intracellularly, immunoreactivity with one or more of the antisera co-localized with the amyloid. Although virtually all amyloid in human islets of Langerhans is found extracellularly, we propose that the initial amyloid formation occurs intracellularly, perhaps by not fully processed or folded (pro)IAPP. This amyloid, which may develop rapidly under certain circumstances, probably leads to cell death. If not degraded these amyloid spots may then act as nidus for further amyloid formation from fully processed IAPP, secreted from surrounding beta cells.

Medin: an integral fragment of aortic smooth muscle cell-produced lactadherin forms the most common human amyloid

Aortic medial amyloid is a form of localized amyloid that occurs in virtually all individuals older than 60 years. The importance and impact of the amyloid deposits are unknown. In this study we have purified a 5.5-kDa aortic medial amyloid component, by size-exclusion chromatography and RP-HPLC, from three individuals, and we have shown by amino acid sequence analysis that the amyloid is derived from an integral proteolytic fragment of lactadherin. Lactadherin is a 364-aa glycoprotein, previously known to be expressed by mammary epithelial cells as a cell surface protein and secreted as part of the milk fat globule membrane. The multidomain protein has a C-terminal domain showing homology to blood coagulation factors V and VIII. We found that the main constituent of aortic medial amyloid is a 50-aa-long peptide, here called medin, that is positioned within the coagulation factor-like domain of lactadherin. Our result is supported by the specific labeling of aortic medial amyloid in light and electron microscopy with two rabbit antisera raised against two synthetic peptides corresponding to different parts of medin. By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. Furthermore, one of the synthetic peptides forms amyloid-like fibrils in vitro. Lactadherin was not previously known to be an amyloid precursor protein or to be expressed in aortic tissue. The structure of lactadherin may implicate an important regulatory function in the aorta.

Islet amyloid polypeptide tonally inhibits beta-, alpha-, and delta-cell secretion in isolated rat pancreatic islets

Islet amyloid polypeptide (IAPP, or amylin) is produced in pancreatic beta-cells. The intraislet significance of IAPP is still uncertain. In the present study, paracrine effects of endogenous IAPP and somatostatin were investigated in isolated rat pancreatic islets. The intraislet IAPP activity was inhibited with an IAPP antiserum or a specific antagonist [IAPP-(8-37)]. Somatostatin activity was inhibited by immunoneutralization. Basal insulin and glucagon secretion were not affected by the somatostatin and/or IAPP blockade. Arginine-stimulated insulin and glucagon secretion were dose dependently increased by IAPP antiserum, IAPP-(8-37), and somatostatin antiserum, respectively. Arginine-stimulated somatostatin secretion was dose dependently potentiated by IAPP antiserum. Insulin secretion induced by 16.7 mM glucose was enhanced by IAPP antiserum and IAPP-(8-37), respectively. A combination of somatostatin antiserum with IAPP antiserum or IAPP-(8-37) further enhanced the arginine-stimulated insulin and glucagon secretion compared with effects when the blocking reagents were used individually. These results indicate that endogenously produced IAPP tonally inhibits stimulated insulin, glucagon, and somatostatin secretion. Furthermore, the paracrine effects of IAPP and somatostatin are additive.

Quantitative immunohistochemical analysis of islet amyloid polypeptide (IAPP) in normal, impaired glucose tolerant, and diabetic cats

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 immunohistochemistry, we examined the IAPP and insulin content in pancreatic 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.

Increased release of IAPP in response to long-term high fat intake in mice

In the present study, mice were fed high-fat diet or standard animal chow during 6 months. Animals fed high-fat diet showed a 4.5-fold increase in the fasting plasma IAPP levels compared to animals fed standard chow. No significant change in plasma insulin levels occurred between the groups. These differences in hormone response result in a change of the molar ratio between IAPP and insulin in the group fed high-fat diet. An increased IAPP to insulin molar ratio might be important in the pathogenesis of islet amyloid in man.

Altered immunoreactivity of islet amyloid polypeptide (IAPP) may reflect major modifications of the IAPP molecule in amyloidogenesis

We have developed a mouse monoclonal antibody against rat/mouse islet amyloid polypeptide (IAPP). The antibody recognises an epitope in the N-terminal part of the molecule, which is conserved between different species. The antibody immunohistochemically labelled beta cells in normal islets of most different mammalian species including man and in one avian species. Previous immunohistochemical studies of human pancreatic tissue from individuals with non-insulin-dependent diabetes mellitus (NIDDM) have revealed a paradoxical and unexplained lack of IAPP immunoreactivity in beta cells close to amyloid in spite of the presence of IAPP mRNA. In contrast to these findings we show that the newly developed monoclonal IAPP antibody strongly labels such beta cells while islet amyloid deposits which are labelled by polyclonal antisera do not bind the monoclonal antibody. These findings with the polyclonal antisera and the monoclonal antibody indicate that IAPP undergoes one or several structural changes during the amyloidogenesis. Knowledge of these structural changes that may include abnormal folding or chemical modification of IAPP is probably important for the understanding of the amyloidogenesis and the pathogenesis of the islet lesion in NIDDM.

Amyloidosis: a global problem common in Papua New Guinea

The increase in different precursor proteins that have been shown to form amyloid fibrils and the identification of common properties have not yet led to any unifying theory or mechanism for the pathogenesis of amyloidogenesis. Papua New Guinea holds a unique place in the story of amyloidosis and in this article we review the current status of amyloidosis research indicating how this relates to those forms relevant to Papua New Guinea. This review concentrates on secondary reactive amyloid (AA), which is found in the highest frequency in the world in parts of Papua New Guinea, and kuru, in which the amyloid protein itself is infectious. The history, pathogenesis and future prospects for these diseases are discussed in the light of what is known about other forms of amyloidosis.

A protein AA-variant derived from a novel serum AA protein, SAA1 delta, in an individual from Papua New Guinea

A major protein AA amyloid protein was purified and characterised from a Papua New Guinnean 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 Papua New Guinea this AAdelta must originate from a novel SAAdelta which may represent a particularly amyloidogenic variant.

Effects of beta cell granule components on human islet amyloid polypeptide fibril formation

Formation of amyloid-like fibrils in a solution of human islet amyloid polypeptide (hIAPP) with and without the presence of other beta-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, Ca2+ and Zn2+ each individually enhanced fibril formation. C-peptide combined with Ca2+ 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, Ca2+ 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.

Expression of cone transducin, Gz alpha, and other G-protein alpha-subunit messenger ribonucleic acids in pancreatic islets

The G-proteins are a family of heterotrimeric guanine nucleotide-binding proteins that play important roles in signal transduction and whose expression is regulated in a tissue-specific manner. Here we have surveyed the expression of G-protein alpha-subunits in mouse pancreatic islets. Degenerate oligonucleotide primers corresponding to conserved primary sequences in known G alpha-subunits were used in a reverse transcriptase-polymerase chain reaction, and the amplified complementary DNA (cDNA) fragments were subcloned and sequenced. Over 100 clones were analyzed, from which we determined that islet cells express at least seven G alpha-subunits: G8 alpha, Gi1 alpha or Gi3 alpha, Gi2 alpha, G11 alpha, G14 alpha, Gz alpha, and Gt2 alpha (cone transducin). In particular, the identification of Gz alpha and Gt2 alpha was of interest in that previous studies had indicated that the expression of Gz alpha was restricted mainly to the brain, retina, and adrenal gland, whereas Gt2 alpha was expressed predominantly in retinal cone photoreceptors. By Western blot analysis, we estimated that the amount of Gz alpha protein present in mouse islets was about 40% of that in retina. To further investigate the expression of Gt2 alpha, mouse Gt2 alpha cDNA was cloned from a retinal library and sequenced. The cDNA was used as a probe for Northern blot analysis, and the results confirmed that mouse islets contained a substantial level of Gt2 alpha messenger RNA (mRNA), albeit less than that found in retina (approximately 5-fold lower). Gt2 alpha mRNA was also shown to be present in a clonal mouse pancreatic alpha-cell line (alpha TC1-6) as well as in adrenal gland, pituitary, and a clonal mouse anterior pituitary cell line (AtT20). In situ hybridization revealed that Gt2 alpha mRNA was expressed essentially throughout the islet, suggesting that it is normally expressed in the abundant islet beta-cells and possibly others. In situ analysis also showed that Gt2 alpha mRNA expressed in the pituitary was limited to the intermediate and anterior lobes. We conclude that islet cells express multiple G-proteins, including several that are normally expressed at high levels in certain neuronal cells.

Islet amyloid polypeptide in patients with pancreatic cancer and diabetes

BACKGROUND

The diabetes mellitus that occurs in patients with pancreatic cancer is characterized by marked insulin resistance that declines after tumor resection. Islet amyloid polypeptide (IAPP), a hormonal factor secreted from the pancreatic beta cells, reduces insulin sensitivity in vivo and glycogen synthesis in vitro. In this study, we examined the relation between IAPP and diabetes in patients with pancreatic cancer.

METHODS

We measured IAPP in plasma from 30 patients with pancreatic cancer, 46 patients with other cancers, 23 patients with diabetes, and 25 normal subjects. IAPP immunoreactivity and IAPP messenger RNA were studied in pancreatic cancers, pancreatic tissue adjacent to cancers, and normal pancreatic tissue.

RESULTS

Plasma IAPP concentrations were elevated in the patients with pancreatic cancer as compared with the normal subjects (mean [+/- SD], 22.3 +/- 13.6 vs. 8.0 +/- 5.0 pmol per liter; P < 0.001), normal in the patients with other cancers, and normal or low in the patients with diabetes. Among the patients with pancreatic cancer, the concentrations were 25.0 +/- 8.7 pmol per liter in the 7 patients with diabetes who required insulin, 31.4 +/- 12.6 pmol per liter in the 11 patients with diabetes who did not require insulin, and 12.2 +/- 2.4 pmol per liter in the 9 patients with normal glucose tolerance (3 patients had impaired glucose tolerance; their mean plasma IAPP concentration was 11.7 +/- 5.5 pmol per liter). Plasma IAPP concentrations decreased after surgery in the seven patients with pancreatic cancer who were studied before and after subtotal pancreatectomy (28.9 +/- 16.4 vs. 5.6 +/- 3.4 pmol per liter, P = 0.01). Pancreatic cancers contained IAPP, but the concentrations were lower than in normal pancreatic tissue (17 +/- 16 vs. 183 +/- 129 pmol per gram, P < 0.001). In samples from the patients with both pancreatic cancer and diabetes, immunostaining for IAPP was reduced in islets of pancreatic tissue surrounding the tumor; in situ hybridization studies suggested that transcription occurred normally in these islets.

CONCLUSIONS

Plasma IAPP concentrations are elevated in patients with pancreatic cancer who have diabetes. Since IAPP may cause insulin resistance, its overproduction may contribute to the diabetes that occurs in these patients.

Human G(olf) alpha: complementary deoxyribonucleic acid structure and expression in pancreatic islets and other tissues outside the olfactory neuroepithelium and central nervous system

G(olf) alpha is a G-protein originally believed to mediate signal transduction exclusively within the olfactory neuroepithelium and subsequently found to be a major stimulatory G-protein in the basal ganglia. Here we present evidence that G(olf) alpha is expressed in several other tissues. The human isoform of G(olf) alpha was isolated from two human insulinoma cDNA libraries. Comparison of the human sequence with rat G(olf) alpha shows 91% nucleotide identity (within the coding region) and 99% identity at the amino acid level. Northern and reverse transcriptase-polymerase chain reaction analyses indicated that G(olf) alpha is expressed in all human insulinomas examined thus far as well as in normal pancreatic islets. G(olf) alpha mRNA was also detected in testis, retina, brain, and liver. Western blot analysis of various mouse tissues demonstrated that the level of G(olf) alpha protein in islets is lower than that in the olfactory neuroepithelium and other parts of the brain; its expression in retina, lung, and spleen was moderately higher than that in islets, and its expression in testis approached that in olfactory neuroepithelium. G(olf) alpha was also detected by immunohistochemistry in mouse islets, human insulinomas, the epithelial lining of mouse epididymis, photoreceptor cells of mouse retina, and mouse lung alveoli. These findings suggest a role for G(olf) alpha in a diverse population of cells located outside the olfactory neuroepithelium and central nervous system.

Human islet amyloid polypeptide transgenic mice as a model of non-insulin-dependent diabetes mellitus (NIDDM)

To model islet amyloidogenesis in NIDDM and explore the glucoregulatory role of islet amyloid polypeptide (IAPP), we have created transgenic mice 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 abnormalities 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.

Islet amyloid polypeptide: demonstration of mRNA in human pancreatic islets by in situ hybridization in islets with and without amyloid deposits

Islet amyloid polypeptide which is normally coexpressed with insulin in beta cells, forms amyloid deposits especially in islets of Type 2 (non-insulin-dependent) diabetic subjects. Occurrence of islet amyloid is paradoxically associated with loss of islet amyloid polypeptide immunoreactivity in beta cells. The present study was undertaken to examine whether the islet amyloid polypeptide gene is expressed in islets with decreased islet amyloid polypeptide immunoreactivity. Pancreatic tissue from 14 patients, 7 with Type 2 diabetes and 7 non-diabetic, were obtained at autopsy or surgery and studied for islet amyloid polypeptide expression by in situ hybridization and for presence of insulin and islet amyloid polypeptide by immunohistochemistry. Six of the specimens from the diabetic and three of those from the non-diabetic patients had varying degrees of islet amyloid polypeptide-derived islet amyloid. Amyloid deposits were associated with decreased numbers of beta cells with islet amyloid polypeptide immunoreactivity despite an apparent normal frequency of insulin-containing cells. This discrepancy might reflect an alteration in islet amyloid polypeptide production or processing at a transcriptional or post-transcriptional level. In contrast to the varying immunohistochemical patterns, islets of all categories showed strong labelling using an islet amyloid polypeptide probe for in situ hybridization. It is concluded that islet amyloid polypeptide production is not altered at the transcriptional level. The following possibilities remain: (1) islet amyloid polypeptide production may be altered at a post-transcriptional level or (2) that islet amyloid polypeptide production is normal but the reduced immunoreactivity of the cells reflects a reduced storage of IAPP in secretory granules.(ABSTRACT TRUNCATED AT 250 WORDS)

Seminal vesicle amyloid: the first example of exocrine cell origin of an amyloid fibril precursor

Amyloid fibrils have been extracted from seminal vesicles, and a dominant 14 kD amyloid fibril protein has been identified. An antiserum to this protein reacted both with amyloid and with epithelial cells in some normal seminal vesicles. These reactions were blocked with seminal vesicle secretion and seminal vesicle amyloid fibril protein, but not by degraded amyloid fibrils or fibril protein from other types of amyloid. It is concluded that seminal vesicle amyloid is derived from secretory proteins of the seminal vesicles. As such, it is the first amyloid described which appears to be the product of an exocrine secretory cell.

The complete amino acid sequence of bovine serum amyloid protein A (SAA) and of subspecies of the tissue-deposited amyloid fibril protein A

Bovine serum amyloid A (SAA) was isolated from the acute phase high density lipoprotein (HDL) fraction of a cow suffering from acute mastitis. The elucidated primary structure revealed a protein consisting of 112 amino acid residues. Compared with SAA proteins from other species, the bovine protein was shown to have an insertion of nine amino acid residues between positions 69 and 70. No microheterogeneity could be observed in the protein. Amyloid fibrils extracted from the kidneys were found to contain at least three subspecies of protein AA, consisting of 68, 81 and about 110 amino acid residues. The amino acid sequences established for the protein AA subspecies revealed no microheterogeneity, and were identical to that elucidated for protein SAA.

The N-terminal segment of protein AA determines its fibrillogenic property

The amyloid fibril protein AA consists of a varying long N-terminal part of the precursor protein serum AA. By using synthetic peptides corresponding to human and murine protein AA segments and cyanogen bromide fragments of human protein AA, we show evidence that the amyloidogenic part of the molecule is the first 10-15 amino acid long segment. Amino acid substitutions in this part of the molecule may explain why only one of the two mouse SAA isoforms is amyloidogenic.

Fibronectin and basement membrane components in renal amyloid deposits in patients with primary and secondary amyloidosis

Kidney biopsies from one patient with primary (AL) and three with secondary (AA) amyloidosis were used for an ultrastructural study of the collocalization of basement membrane proteins and the extracellular matrix protein fibronectin within amyloid deposits. Antibodies against amyloid P component, laminin, and heparan sulphate proteoglycan core protein all reacted with the basement membranes and the amyloid depositions in AA and AL amyloidosis. Monoclonal and polyclonal antibodies against collagen type IV reacted only with the basement membranes. Anti-fibronectin reaction was found in association with the basement membranes in all four cases, while labelling of amyloid depositions was found only in one of the AA amyloid cases and in the AL amyloid depositions. It is concluded that basement membrane components may be of importance for the formation of amyloid fibrils.

AA-amyloidosis. Tissue component-specific association of various protein AA subspecies and evidence of a fourth SAA gene product

Protein AA, the major repetitive protein subunit present in fibrils deposited in AA-amyloidosis, is an N-terminal cleavage product of a 104-amino acid precursor, serum amyloid A (SAA). Protein AA subspecies varying between 45 and 94 amino acids in length have been described. In this study it is shown that the different protein AA subspecies are not evenly distributed in amyloid deposits and that in single patients, certain subspecies of protein AA are deposited in specific tissue component sites. Thus larger protein AA subspecies occur in lower concentration in amyloid in the glomeruli compared to other sites and are especially found in amyloid in vessel walls. Three different SAA forms have been predicted from genomic and complementary DNA studies. The existence of a fourth type has been suspected from amino acid sequence studies of purified SAA. Protein AA derived from this fourth type of SAA is now shown to be present in amyloid fibrils in one of the patients studied in this paper.

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.

Massive vascular AA-amyloidosis: a histologically and biochemically distinctive subtype of reactive systemic amyloidosis

Amyloid protein AA consists of several subspecies which mainly arise through proteolytic cleavage at various sites of the precursor, serum protein AA. The most common protein AA subspecies (the protein AA prototype) contains 76 amino-acid residues. In previous studies we have shown that distinctive patterns of amyloid infiltration occur in AA-amyloidosis. The amyloid in different patterns of infiltration seems to consist of distinctive protein AA subspecies. In the present study we have analysed protein AA in three patients with a form of AA-amyloidosis with heavy vascular infiltration and show that the amyloid fibrils contain two groups of protein AA subspecies. One, quantitatively predominating, group contains large subspecies of up to 94 amino-acid residues and a second group of protein AA-molecules contains around 50 amino-acid residues. The AA molecules lack the N-terminal arginine residue. It is concluded that AA-amyloidosis with massive vascular infiltration is a distinctive subform with typical clinical and histological appearance and with fibrils containing characteristic protein AA subspecies.

Islet amyloid polypeptide (IAPP) and pro-IAPP immunoreactivity in human islets of Langerhans

Islet amyloid polypeptide (IAPP) is a 37-amino-acid putative hormone which is expressed by islet B-cells and most probably is co-released with insulin. IAPP is synthesized as an 89-amino-acid prepropeptide in which IAPP is flanked by two short peptides. The two short peptides are ultimately cleaved off at basic residues. In the present study, we used antisera to three different synthetic peptides corresponding to positions 18-30, 40-50 and 53-62 of prepro-IAPP. The two latter peptides fall within the mature IAPP molecule while the first peptide corresponds to the N-terminal flanking peptide. We demonstrate that normal B-cells and islet amyloid both react immunohistochemically with all of these antisera. Using the immunogold labelling technique, we also demonstrate electron microscopically that both the IAPP immunoreactivity and the pro1-IAPP immunoreactivity in amyloid deposits are confined to the amyloid fibrils per se. These data indicate that not only mature IAPP but also the N-terminal flanking peptide is present in islet amyloid deposits. It remains to be shown if the propeptide segments are involved in the pathogenesis of these amyloid depositions.

Islet amyloid polypeptide (IAPP):cDNA cloning and identification of an amyloidogenic region associated with the species-specific occurrence of age-related diabetes mellitus

We have cloned and sequenced a human islet amyloid polypeptide (IAPP) cDNA. A secretory 89 amino acid IAPP protein precursor is predicted from which the 37 amino acid IAPP molecule is formed by amino- and carboxyterminal proteolytic processing. The IAPP peptide is 43-46% identical in amino acid sequence to the two members of the calcitonin gene-related peptide (CGRP) family. Evolutionary conserved proteolytic processing sites indicate that similar proteases are involved in the maturation of IAPP and CGRP and that the IAPP amyloid polypeptide is identical to the normal proteolytic product of the IAPP precursor. A synthetic peptide corresponding to a carboxyteminal fragment of human IAPP is shown to spontaneously form amyloid-like fibrils in vitro. Antibodies against this peptide cross-react with IAPP from species that develop amyloid in pancreatic islets in conjunction with age-related diabetes mellitus (human, cat, racoon), but do not cross-react with IAPP from other tested species (mouse, rat, guinea pig, dog). Thus, a species-specific structural motif in the putative amyloidogenic region of IAPP is associated with both amyloid formation and the development of age-related diabetes mellitus. This provides a new molecular clue to the pathogenesis of this disease.

Co-localization of islet amyloid polypeptide and insulin in the B cell secretory granules of the human pancreatic islets

Islet amyloid polypeptide is a novel 37 amino-acid-residues polypeptide which has been isolated from amyloid deposits in an insulinoma, and in human and cat islets of Langerhans. The molecule has 46% homology with the calcitonin gene-related peptide. Light microscopy examination of the pancreas shows that islet amyloid polypeptide immunoreactivity is restricted to the islet B cells. The present study utilized a rabbit antiserum against a synthetic peptide corresponding to positions 20-29 of islet amyloid polypeptide, a sequence without any amino-acid identity with calcitonin gene-related peptide. By applying the immunogold technique at the ultrastructural level, it was shown that both insulin and islet amyloid polypeptide immunoreactivity occurs in the central granular core of the human B cell secretory granules, while the A cells remain unlabelled. The demonstration that islet amyloid polypeptide is a granular protein of the B cells may indicate that it is released together with insulin. Further studies are necessary to evaluate the functional role of islet amyloid polypeptide.

Amino acid sequence variations in protein AA of cats with high and low incidences of AA amyloidosis

1. Amyloid isolated from the liver of a domestic short-haired (DSH) cat was dissolved and purified by gel filtration for amino acid sequence analysis. 2. Sequences of two major peptides corresponding to positions 18-23 and 25-75 of human amyloid protein AA were obtained when cyanogen bromide-cleaved protein was applied to an amino acid sequenator. 3. Comparison of these regions of amyloid protein from the Abyssinian cat (high incidence of AA amyloidosis) and DSH cat (low incidence of AA amyloidosis) revealed three amino acid differences, two of which occurred within regions that are completely conserved in the Abyssinian cat and all other species. 4. Secondary prediction plots showed less potential for amyloidogenicity (i.e., less beta-sheet conformation) in protein AA of the DSH cat as compared to the Abyssinian cat and other animal species. 5. These differences in protein AA of the DSH cat may, therefore, be linked to the comparatively uncommon occurrence of AA amyloidosis in the DSH cat as compared to the Abyssinian cat and other animals species.

Immunohistochemical identification of heparan sulphate proteoglycan in secondary systemic amyloidosis

The distribution of proteoglycans in kidneys from patients with secondary (AA) systemic amyloidosis was investigated. Antisera reacting with the protein cores of chondroitin sulphate proteoglycan (CSPG), dermatan sulphate proteoglycan (DSPG) and heparan sulphate proteoglycan (HSPG) were used in conjunction with the peroxidase-antiperoxidase (PAP) method. HSPG was the only proteoglycan found to be specifically localized to the amyloid deposits. The staining was most intense on the endothelial side of the deposits in both the glomeruli and in the vessel walls. No staining was observed after absorption of the HSPG antiserum with a fraction of the amyloid preparations, corresponding in size to that reported for glomerular HSPG. The possible role of HSPG and endothelial cells in the pathogenesis of the amyloid deposits is discussed.

Insulin as an amyloid-fibril protein at sites of repeated insulin injections in a diabetic patient

A patient with Type 1 (insulin-dependent) diabetes mellitus developed localised amyloidosis at the sites of his injections of porcine insulin. A major amyloid fibril protein was extracted and, by means of its amino acid composition and amino acid sequence, it was shown to contain intact insulin molecules. Porcine insulin is the tenth protein and the first foreign protein to be chemically identified in human amyloid fibrils.

Islet amyloid polypeptide-like immunoreactivity in the islet B cells of type 2 (non-insulin-dependent) diabetic and non-diabetic individuals

A novel peptide, islet amyloid polypeptide (IAPP), with structural resemblance to calcitonin gene-related peptide has recently been purified from amyloid deposits in an insulinoma and from islets of Langerhans. By immunohistochemical methods, using antisera to a synthetic undecapeptide of IAPP and to insulin, we show that freshly fixed islet B cells in man, guinea pig, rat, mouse and hamster exhibit strong IAPP-immunoreactivity while A cells are unreactive. In human autopsy material, all of 11 non-diabetic individuals had IAPP immunoreactivity of the islets. In comparison 8 of the 13 patients with Type 2 (non-insulin-dependent) diabetes had no IAPP immunoreactive cells. The proportion of islet cells having IAPP immunoreactivity exceeded 10% in only 1 of the 5 remaining diabetic patients while in all 13 patients substantially more than 10% of the islet cells contained immunoreactive insulin. IAPP-positive amyloid deposits were found in 20-99% of the islets in 12 of the Type 2 diabetic patients while 6 of 11 non-diabetic subjects had amyloid in 3-11% of their islets. In islets with IAPP-immunoreactive amyloid, very few IAPP-cells were seen despite a strong reaction of the B cells with antiserum to insulin. This study shows that IAPP is a normal islet B cell component and that IAPP immunoreactivity in B cells is diminished in Type 2 diabetes while IAPP is deposited as amyloid fibrils in the islets of Langerhans. Although the function of IAPP is unknown, its occurrence in the islet B cells and its structural relation to calcitonin gene-related peptide makes a hormonal nature probable.(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloid fibril protein AA. Characterization of uncommon subspecies from a patient with rheumatoid arthritis

Protein AA, the main fibril protein in secondary systemic amyloidosis, is a mixture of protein fragments (subspecies) of different length, probably arising by enzymatic cleavage of a serum precursor, SAA. We have purified amyloid fibril protein AA from a patient with rheumatoid arthritis and secondary amyloidosis with an unusual amyloid distribution in organs. This protein AA contained two major subspecies of which one consisted of 50 amino acid residues shown by complete amino acid sequence analysis. The other major AA subspecies, characterized by N- and C-terminal sequence analysis and amino acid determination of proteolytic peptides, contained 45 amino acid residues. The pI of these AA-variants differed considerably, 8.1 to 5.5, respectively. Several minor protein AA subspecies were also identified, among them one with a blocked N-terminal. The findings indicate that AA proteins of different length are connected to varying AA amyloid syndromes.

Bovine amyloid protein AA: isolation and amino acid sequence analysis

Amyloid-laden renal glomeruli were selectively isolated from a cow with a history of multiple organ inflammatory diseases which terminated in amyloid-induced glomerulopathy and severe proteinuria. Lyophilized amyloid fibrils obtained by water extraction procedures were dissolved in 6M guanidine hydrochloride and gel filtered on Sepharose CL6B and Sephacryl S-300 Superfine columns for slab gel electrophoresis, analytic isoelectric focusing, and amino acid sequence analyses. Electrophoresis of material from the major retarded peak of the elution profile revealed that bovine protein AA moves as one band with an apparent molecular mass of about 14,000 Daltons. Several distinct bands between approximately pH 4.0 and 5.0 were observed when this material was evaluated by analytic isoelectric focusing, thus having a pattern resembling that of human and dog protein AA. A blocked N-terminus was demonstrated when protein from the major retarded peak was subjected to amino acid sequencing, but cyanogen bromide cleavage followed by gel filtration produced 3 peptide fragments for amino acid sequence analysis. These peptides had a high degree of homology with positions 4-14, 18-24 and 25-49 of human protein AA. An apparent complete homology between bovine protein AA and protein AA from other species was apparent at positions 35-45, providing further evidence that this is a functionally significant part of the serum protein AA (SAA) molecule.