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At least 919 records · Page 51Linked to original sources
PubMed2001

Encystation of Acanthamoeba castellanii: dye uptake for assessment by flow cytometry and confocal laser scanning microscopy.

AIMS: To develop rapid means of distinguishing between cysts and trophozoites of the opportunistic pathogen, Acanthamoeba castellanii, the causative agent of keratitis. METHODS AND RESULTS: Fluorescence of Congo Red, Calcoflor White was specific for the endocyst wall; trophozoites did not become fluorescent. The anionic oxonol dye, DiBAC4(3), did not penetrate the cytoplasmic membrane after short-term (<5 min) exposure, whereas cysts are permeable and become fluorescent. Confocal scanning laser microscopy confirmed these properties and large populations of organisms were analysed by flow cytometry. CONCLUSION: These data provide a rapid alternative to traditional haemocytometer or plate counts for discrimination of trophozoites from cysts. SIGNIFICANCE AND IMPACT OF THE STUDY: Rapid and precise determination of the growth cycle of a dangerous ocular pathogen.

Acanthamoeba↗
PubMed1992

Live oral auxotrophic Shigella flexneri SFL124 vaccine with a deleted aroD gene: characterization and monkey protection studies.

Shigella flexneri SFL124, with a deletion encompassing all, or nearly all, of the coding sequence of gene aroD was obtained after selection on a fusaric acid medium supplemented with 2,3-dihydroxybenzoic acid for tetracycline-sensitive mutants of S. flexneri SFL114 which is an aroD::Tn10 transductant. Two of 20 tetracycline-sensitive mutants tested in colony hybridization with a 32P-labelled DNA probe of approximately 1400 base pairs (comprising all except the 75 N-terminal base pairs of the coding region of gene aroD) did not hybridize. The selected mutant SFL124 is Congo-red positive, invades and shows a limited multiplication in HeLa cells and does not cause keratoconjunctivitis in guinea-pigs. It is well tolerated by Macaca fascicularis monkeys, is excreted for up to 4 days, elicits a slight inflammatory reaction in the colonic mucosa, stimulates significant secretory IgA responses in the intestine and serum IgA and IgG responses against the S. flexneri cell envelope lipopolysaccharide. The immune response conferred a complete protection against challenge with 1 x 10(11) (equivalent to a 100 LD50 dose) live S. flexneri SFL1.

Administration, Oral↗
PubMed2006

Identification of an amyloidogenic region on keratoepithelin via synthetic peptides.

Mutations of keratoepithelin (KE) gene in human chromosome 5q31 have been linked with corneal epithelial or stromal dystrophies characterized by the abnormal deposits of amyloid fibrils and/or non-amyloid aggregations in corneal tissue. We report herein that synthetic peptide containing amino acid (a.a.) residues of 515-532 of native KE protein can readily form beta-sheet-containing amyloid fibrils in vitro. Amyloid fibrils formed in various conditions from short synthetic peptides (containing a.a. 515-532 and 515-525, respectively) were characterized by thioflavin T (ThT) fluorescence assay, Congo red staining, electron microscopy (EM) and circular dichroism (CD). Triple-N-methylation of the synthetic peptides prevented the beta-sheet polymerization and related amyloid fibril formation. Comparison study with ThT fluorescence further demonstrated that synthetic peptides containing corneal dystrophy-related mutations within this region formed amyloid fibrils to various extents. Our results suggest that each individual dystrophy-related mutation by itself does not necessarily potentiate amyloid fibril formation of KE. Roles of these intrinsically amyloidogenic foci in abnormal KE aggregations and amyloid deposits of stromal corneal dystrophies await further investigation.

Amino Acid Sequence↗
PubMed2000

A de novo designed helix-turn-helix peptide forms nontoxic amyloid fibrils.

We report here that a monomeric de novo designed alpha-helix-turn-alpha-helix peptide, alpha t alpha, when incubated at 37 degrees C in an aqueous buffer at neutral pH, forms nonbranching, protease resistant fibrils that are 6-10 nm in diameter. These fibrils are rich in beta-sheet and bind the amyloidophilic dye Congo red. alpha t alpha fibrils thus display the morphologic, structural, and tinctorial properties of authentic amyloid fibrils. Surprisingly, unlike fibrils formed by peptides such as the amyloid beta-protein or the islet amyloid polypeptide, alpha t alpha fibrils were not toxic to cultured rat primary cortical neurons or PC12 cells. These results suggest that the potential to form fibrils under physiologic conditions is not limited to those proteins associated with amyloidoses and that fibril formation alone is not predictive of cytotoxic activity.

Amino Acid Sequence↗
PubMed1990

Nonamyloidotic fibrillar glomerulopathy and recurrent gestational anasarca.

Congo-red-negative microfibrils have been described in various glomerular diseases, some of which have no known etiology. We report the unusual case of a young woman who, over a period of 17 years, developed recurrent gestational anasarca but was asymptomatic between pregnancies except for proteinuria. Her blood pressure and renal function have remained normal over the years. A renal biopsy done 5 years after her third pregnancy showed diffuse mesangial expansion and irregular thickening of the glomerular basement membrane, both caused by the deposition of nonamyloidotic microfibrils. We discuss the differential diagnosis of this case and review the pertinent literature.

Adult↗
PubMed1999

Synthesis and amyloid binding properties of rhenium complexes: preliminary progress toward a reagent for SPECT imaging of Alzheimer's disease brain.

The definitive diagnosis of Alzheimer's disease (AD) requires the detection of amyloid plaques in postmortem brain. Although the amount of fibrillar amyloid roughly correlates with the severity of symptoms at the time of death, the temporal relationship between amyloid deposition, neuronal loss, and cognitive decline is unclear. To elucidate this relationship, a noninvasive, practical method for the quantitation of brain amyloid deposition is required. We describe herein the initial stages of a strategy to accomplish this goal by single photon computed tomographic imaging. The amyloid-binding dye Congo Red was modified to allow its conjugation to the monoamine-monoamide bis(thiol) ligand. This ligand complexes technetium(V) in its neutral oxo form. A biphenyl-containing building block was conjugated to the protected ligand, and the product was coupled to the relevant aromatic compounds. Rhenium oxo complexes, which are isosteric, but nonradioactive, analogues of the potential imaging agent technetium oxo complexes, were synthesized. These complexes bound to Abeta amyloid fibrils produced in vitro and stained amyloid plaques and vascular amyloid in AD brain sections.

Alzheimer Disease↗
PubMed1991

Nonamyloidotic fibrillary glomerulopathy, immunotactoid glomerulopathy, and the differential diagnosis of filamentous glomerulopathies.

Kidney biopsies from 12 patients between the ages of 10 and 63 yr were diagnosed as nonamyloidotic fibrillary glomerulopathy (NAFG) or immunotactoid glomerulopathy (IG) on the basis of the electron microscopic finding of filamentous or tubular material within the glomerular capillaries and mesangium. Six patients were male and six were female. Eleven presented with nephrotic syndrome and one with acute renal failure. Eight were hypertensive, and four of these patients had gross or microscopic hematuria as well. Biopsies from 11 patients were Congo red negative; one was weakly positive. By light microscopy, the predominant glomerular change was thickening of the capillary basement membrane with or without widening of the mesangium; these changes were suggestive of membranous glomerulonephritis. Immunofluorescent studies performed in four of the cases were positive for immunoglobulin G (IgG). Immunoperoxidase staining for beta 2-microglobulin was negative in four patients. Ultrastructurally, filaments or tubules were identified in the glomerular capillary basement membrane and/or mesangium in each patient. The filaments in NAFG, IG, amyloidosis, and other paraprotein deposits can be differentiated by size, arrangement, and location of filamentous material.

Actin Cytoskeleton↗
PubMed2001

Chaperonin-mediated de novo generation of prion protein aggregates.

The infectious prion protein, PrP(Sc), a predominantly beta-sheet aggregate, is derived from PrP(C), the largely alpha-helical cellular isoform of PrP. Conformational conversion of PrP(C) into PrP(Sc) has been suggested to involve a chaperone-like factor. Here we report that the bacterial chaperonin GroEL, a close homolog of eukaryotic Hsp60, can catalyze the aggregation of chemically denatured and of folded, recombinant PrP in a model reaction in vitro. Aggregates form upon ATP-dependent release of PrP from chaperonin and have certain properties of PrP(Sc), including a high beta-sheet content, the ability to bind the dye Congo red, detergent-insolubility and increased protease-resistance. A conserved sequence segment of PrP (residues 90-121), critical for PrP(Sc) generation in vivo, is also required for chaperonin-mediated aggregate formation in vitro. Initial binding of refolded, alpha-helical PrP to chaperonin is mediated by the unstructured N-terminal segment of PrP (residues 23-121) and is followed by a rearrangement of the globular PrP core-domain. These results show that chaperonins of the Hsp60 class can, in principle, mediate PrP aggregation de novo, i.e. independently of a pre-existent PrP(Sc) template.

Adenosine Triphosphate↗
PubMed1999

Amyloid and Pro501 Thr-mutated (beta)ig-h3 gene product colocalize in lattice corneal dystrophy type IIIA.

PURPOSE: To assess the relative distribution in the cornea of amyloid and (beta)ig-h3 gene product in lattice corneal dystrophy type IIIA (LCD-IIIA). METHODS: Serial sections from the cornea of a patient with LCD-IIIA were subjected to either Congo red staining or immunohistochemistry employing an antibody to (beta)ig-h3. Also, genomic DNA was isolated from peripheral blood and used as a template for polymerase chain reaction to amplify all exons of (beta)ig-h3. RESULTS: Exon 11 of (beta)ig-h3 was mutated (Pro501Thr). Subepithelial and intrastromal congophilic deposits exhibited a birefringency characteristic of amyloid. These regions of the tissue were also highly immunoreactive with the antibody to the (beta)ig-h3 gene product. CONCLUSION: Amyloid and Pro501Thr-mutated (beta)ig-h3 protein accumulate and colocalize in LCD-IIIA.

Aged↗
PubMed2005

Beta-amyloid peptides stimulate endozepine biosynthesis in cultured rat astrocytes.

Accumulation of beta-amyloid peptide (Abeta), which is a landmark of Alzheimer's disease, may alter astrocyte functions before any visible symptoms of the disease occur. Here, we examined the effects of Abeta on biosynthesis and release of diazepam-binding inhibitor (DBI), a polypeptide primarily expressed by astroglial cells in the CNS. Quantitative RT-PCR and specific radioimmunoassay demonstrated that aggregated Abeta(25-35), at concentrations up to 10(-4) m, induced a dose-dependent increase in DBI mRNA expression and DBI-related peptide release from cultured rat astrocytes. These effects were totally suppressed when aggregation of Abeta(25-35) was prevented by Congo red. Measurement of the number of living cells revealed that Abeta(25-35) induced a trophic rather than a toxic effect on astrocytes. Administration of cycloheximide blocked Abeta(25-35)-induced increase of DBI gene expression and endozepine accumulation in astrocytes, indicating that protein synthesis is required for DBI gene expression. Altogether, the present data suggest that Abeta-induced activation of endozepine biosynthesis and release may contribute to astrocyte proliferation associated with Alzheimer's disease.

Amyloid beta-Peptides↗
PubMed2000

Gelsolin inhibits the fibrillization of amyloid beta-protein, and also defibrillizes its preformed fibrils.

Amyloid beta-protein (Abeta) is present in soluble form in the plasma and cerebrospinal fluid (CSF) of normal people and patients with Alzheimer's disease (AD). However, in AD patients, Abeta gets fibrillized as the main constituent of amyloid plaques in the brain. Soluble synthetic Abeta also forms amyloid-like fibrils when it is allowed to age. The mechanism that prevents soluble Abeta from fibrillization in biological fluids is not clear. We recently reported that gelsolin, a secretory protein, binds to Abeta, and that gelsolin/Abeta complex is present in the plasma [V.P.S. Chauhan, I. Ray, A. Chauhan, H.M. Wisniewski, Biochem. Biophys. Res. Commun. 258 (1999) 241-246.]. We now studied the effect of gelsolin on Abeta fibrillization. Congo red staining and electron microscopic examination in negative staining of aged samples of Abeta alone and Abeta incubated with gelsolin showed that gelsolin inhibits the fibrillization of synthetic Abeta 1-40 and Abeta 1-42 at gelsolin to Abeta molar ratio of 1:40. In addition, gelsolin also defibrillized the preformed fibrils of Abeta 1-40 and Abeta 1-42 in a time-dependent manner. These results suggest that gelsolin functions as an anti-amyloidogenic protein in the plasma and CSF, where it prevents Abeta from fibrillization, and helps to maintain it in the soluble form.

Amyloid beta-Peptides↗
PubMed2004

Beta-amyloid-derived pentapeptide RIIGLa inhibits Abeta(1-42) aggregation and toxicity.

Pr-IIGL(a), a derivative of the tetrapeptide beta-amyloid 31-34 (Abeta(31-34)), exerts controversial effects: it is toxic in a neuroblastoma culture, but it protects glial cells from the cytotoxic action of Abeta(1-42). For an understanding of this phenomenon, a new pentapeptide, RIIGL(a) was synthetized, and both compounds were studied by different physicochemical and biological methods. Transmission electron microscopic (TEM) studies revealed that Pr-IIGL(a) forms fibrillar aggregates, whereas RIIGL(a) does not form fibrils. Congo red binding studies furnished the same results. Aggregated Pr-IIGL(a) acts as a cytotoxic agent in neuroblastoma cultures, but RIIGL(a) does not display inherent toxicity. RIIGL(a) co-incubated with Abeta(1-42) inhibits the formation of mature amyloid fibres (TEM studies) and reduces the cytotoxic effect of fibrillar Abeta(1-42). These results indicate that RIIGL(a) is an effective inhibitor of both the aggregation and the toxic effects of Abeta(1-42) and can serve as a lead compound for the design of novel neuroprotective peptidomimetics.

Amyloid beta-Peptides↗
PubMed2000

Controlling polymerization of beta-amyloid and prion-derived peptides with synthetic small molecule ligands.

The Alzheimer beta-amyloid peptide (Abeta) and a fragment of the prion protein have the capacity of forming amyloid-like fibrils when incubated under physiological conditions in vitro. Here we show that a small amyloid ligand, RO-47-1816/001, enhances this process severalfold by binding to amyloid molecules and apparently promote formation of the peptide-to-peptide bonds that join the monomers of the amyloid fibrils. This effect could be antagonized by other ligands, including analogues of RO-47-1816/001, as well as the structurally unrelated ligand Congo red. Analogues of RO-47-1816/001 with low affinity for amyloid did not display any antagonistic effect. In conclusion, these data suggest that synthetic molecules, and possibly also small natural substances present in the brain, may act in a chaperone-like fashion, promoting Abeta polymerization and growth of amyloid fibrils in vitro and possibly also in vivo. Furthermore, we demonstrate that small organic molecules can be used to inhibit the action of amyloid-enhancing compounds.

Amyloid beta-Peptides↗
PubMed1999

Protofibrillar intermediates of amyloid beta-protein induce acute electrophysiological changes and progressive neurotoxicity in cortical neurons.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is thought to be caused in part by the age-related accumulation of amyloid beta-protein (Abeta). The presence of neuritic plaques containing abundant Abeta-derived amyloid fibrils in AD brain tissue supports the concept that fibril accumulation per se underlies neuronal dysfunction in AD. Recent observations have begun to challenge this assumption by suggesting that earlier Abeta assemblies formed during the process of fibrillogenesis may also play a role in AD pathogenesis. Here, we present the novel finding that protofibrils (PF), metastable intermediates in amyloid fibril formation, can alter the electrical activity of neurons and cause neuronal loss. Both low molecular weight Abeta (LMW Abeta) and PF reproducibly induced toxicity in mixed brain cultures in a time- and concentration-dependent manner. No increase in fibril formation during the course of the experiments was observed by either Congo red binding or electron microscopy, suggesting that the neurotoxicity of LMW Abeta and PF cannot be explained by conversion to fibrils. Importantly, protofibrils, but not LMW Abeta, produced a rapid increase in EPSPs, action potentials, and membrane depolarizations. These data suggest that PF have inherent biological activity similar to that of mature fibrils. Our results raise the possibility that the preclinical and early clinical progression of AD is driven in part by the accumulation of specific Abeta assembly intermediates formed during the process of fibrillogenesis.

Amyloid beta-Peptides↗
PubMed2005

Single-site mutations in a hyperthermophilic variant of the B1 domain of protein G result in self-assembled oligomers.

We have characterized two homologous, single-point core mutants of a 57-residue, hyperthermophilic variant of the B1 domain of protein G (HTB1). These single-point mutations in HTB1 replace a Phe residue in the hydrophobic core with either a Glu or Asp residue. Both of these homologous core-variant mutants undergo significant structural rearrangement from the native, monomeric fold and exist as stable soluble oligomeric species of 5 and 30 nm in diameter. Gel-filtration, dynamic light scattering, circular dichroism spectroscopy, fluorescence spectroscopy, along with Congo Red and Thioflavin T binding clearly demonstrated that these core-variants undergo significant structural rearrangement from the native, monomeric ubiquitin fold. The two oligomeric species did not equilibrate over extended periods of time and displayed distinct secondary structures. The larger of the two species was found to possess structural features that are reminiscent of an emerging class of protein assemblies prone to beta-sheet-mediated aggregation. These results are significant as there are very few examples of extensive conformational or oligomerization switching brought about by single-point mutations in a stable protein-fold.

Amino Acid Sequence↗
PubMed2001

Age-dependent induction of congophilic neurofibrillary tau inclusions in tau transgenic mice.

Intraneuronal filamentous tau inclusions such as neurofibrillary tangles (NFTs) are neuropathological hallmarks of Alzheimer's disease (AD) and related sporadic and familial tauopathies. NFTs identical to those found in AD brains have also been detected in the hippocampus and entorhinal cortex of cognitively normal individuals as they age. To recapitulate age-induced NFT formation in a mouse model, we examined 12- to 24-month-old transgenic (Tg) mice overexpressing the smallest human brain tau isoform. These Tg mice develop congophilic tau inclusions in several brain regions including the hippocampus, amygdala, and entorhinal cortex. NFT-like inclusions were first detected in Tg mice at 18 to 20 months of age and they were detected by histochemical dyes that bind specifically to crossed beta-pleated sheet structures (eg, Congo red, Thioflavin S). Moreover, ultrastructurally these lesions contained straight tau filaments comprised of both mouse and human tau proteins but not other cytoskeletal proteins (eg, neurofilaments, microtubules). Isolated tau filaments were also recovered from detergent-insoluble tau fractions and insoluble tau proteins accumulated in brain in an age-dependent manner. Thus, overexpression of the smallest human brain tau isoform resulted in late onset and age-dependent formation of congophilic tau inclusions with properties similar to those in the tangles of human tauopathies, thereby implicating aging in the pathogenesis of fibrous tau inclusions.

Aging↗
PubMed1983

Localized amyloidosis in basal cell carcinoma. A pathologic study.

Congo-red screening demonstrated intratumor deposits of amyloid in 35 of 53 unselected cases of basal cell carcinoma. Male subjects had a higher amyloid positivity rate than female subjects. The amyloid deposits were permanganate-resistant and located in the stroma between clumps of tumor cells, as well as abutting the advancing front of the neoplasm. Solar elastosis was often observed in the overlying and adjacent subepidermis. The relationship between amyloid positivity and the different histological subtypes of basal cell carcinoma, tumor ulceration, and density of the lymphoplasmacytic stromal infiltrate were also studied. The possibility that amyloid originates from the tumor cells and is a result of tumor apoptosis (degeneration) is discussed.

Amyloid↗
PubMed1975

Ultrastructural variation in granular dystrophy of the cornea.

Corneal deposits of granular dystrophy were studies in six corneas from five patients. Two additional corneas from two patients with lattice dystrophy were used for comparison. The diagnoses were confirmed by light and electron microscopy. Three types of ultrastructural features were distinguished in the electron-dense rod-shaped deposits of granular dystrophy, i.e., Type 1 with homogenous structure, Type 2 with fibrillar constituents, and Type 3 with a moth-eaten or sponge-like appearance. In polarization microscopy of Congo-red stained sections, the Type 2 tended to show an increased birefringence without green dichroism, while the other types were less birefringent than the stroma. Three different components were found immediately around the deposits, i.e., 1. normal collagen fibrils, 2. finely filamentous substance, and 3. areas of thin fibrils (70-100 A in diameter). While the second component appeared non-specific, the third component was found only in two corneas, superimposed on the lesions of granular dystrophy, and showed light and electron microscopic characteristics of the lesions of amyloid as well as of lattice dystrophy.

Aged↗