Biomedical subjects

J T Nguyen

Publications and source records attributed to J T Nguyen.

23 records · Page 2Linked to original sources

PubMed1993

Alpha 1-antichymotrypsin binding to Alzheimer A beta peptides is sequence specific and induces fibril disaggregation in vitro.

The serine protease inhibitor alpha 1-antichymotrypsin (ACT) consistently colocalizes with amyloid deposits of Alzheimer's disease (AD) and may contribute to the generation of amyloid proteins and/or physically affect fibril assembly. AD amyloid fibrils are composed primarily of A beta, which is a proteolytic fragment of the larger beta-amyloid precursor protein. Using negative-stain and immunochemical electron microscopy, we have investigated the binding of ACT to the fibrils formed by four synthetic A beta analogues corresponding to the wild-type human 1-40 sequence [Hwt(1-40)], a 1-40 peptide [HDu(1-40)] containing the Glu22-->Gln mutation found in hereditary cerebral hemorrhage with amyloidosis of the Dutch type, the N-terminal 1-28 residues [beta(1-28)], and an internal fragment of A beta containing residues 11-28 [beta(11-28)]. Each of these peptide analogues assembled into 70-90-A-diameter fibrils resembling native amyloid and, except for beta(11-28), bound ACT, as indicated by the appearance of 80-100-A globular particles that adhered to preformed fibrils and that could be decorated with anti-ACT antibodies. Under the conditions used, ACT binding destabilized the in vitro fibrils and produced a gradual dissolution of the macromolecular assemblies into constituent filaments and shorter fragments. The internal fragment (11-28) did not exhibit ACT binding or any structural changes. These results suggest that a specific sequence likely contained within the N-terminal 10 residues of A beta is responsible for the formation of the ACT-amyloid complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Alzheimer Disease↗

PubMed1992

Fibril formation by primate, rodent, and Dutch-hemorrhagic analogues of Alzheimer amyloid beta-protein.

Deposition of extraneuronal fibrils that assemble from the 39-43 residue beta/A4 amyloid protein is one of the earliest histopathological features of Alzheimer's disease. We have used negative-stain electron microscopy, Fourier-transform infrared (FT-IR) spectroscopy, and fiber X-ray diffraction to examine the structure and properties of synthetic peptides corresponding to residues 1-40 of the beta/A4 protein of primate [Pm(1-40); human and monkey], rodent [Ro(1-40); with Arg5-->Gly, Tyr10-->Phe, and His13-->Arg], and hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D) [Du(1-40); with Glu22-->Gln]. As controls, we examined a reverse primate sequence [Pm*(40-1)] and an extensively substituted primate peptide [C(1-40); with Glu3-->Arg, Arg5-->Glu, Asp7-->Val, His13-->Lys, Lys16-->His, Val18-->Asp, Phe19-->Ser, Phe20-->Tyr, Ser26-->Pro, Ala30-->Val, Ile31-->Ala, Met35-->norLeu, Gly38-->Ile, Val39-->Ala, and Val40-->Gly]. The assembly of these peptides was studied to understand the relationship between species-dependent amyloid formation and beta/A4 sequence and the effect of a naturally occurring point mutation of fibrillogenesis. The three N-terminal amino acid differences between Pm(1-40) and Ro(1-40) had virtually no effect on the morphology or organization of the fibrils formed by these peptides, indicating that the lack of amyloid deposits in rodent brain is not due directly to specific changes in its beta/A4 sequence. beta-Sheet and fibril formation, judged by FT-IR, was maximal within the pH range 5-8 for Pm(1-40), pH 5-10.5 for Du(1-40), and pH 2.5-8 for Ro(1-40).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1992

Effects of sulfate ions on Alzheimer beta/A4 peptide assemblies: implications for amyloid fibril-proteoglycan interactions.

To model the possible involvement of sulfated proteoglycans in amyloidogenesis, we examined the influence of sulfate ions, heparan, and Congo red on the conformation and morphology of peptides derived from the Alzheimer beta/A4 amyloid protein. The peptides included residues 11-28, 13-28, 15-28, and 11-25 of beta/A4. Negative-stain electron microscopy revealed a sulfate-specific tendency of the preformed peptide fibrillar assemblies of beta(11-28), beta(13-28), and beta(11-25), but not beta(15-28), to undergo extensive lateral aggregation and axial growth into "macrofibers" that were approximately 0.1-0.2 micron wide by approximately 20-30 microns long. Such effects were observed at low sulfate concentrations (e.g., 5-50 mM) and could not be reproduced under comparable conditions with Na2HPO4, Na2SeO4, or NaCl. Macrofibers in NaCl were only observed at 1,000 mM. At physiological ionic strength of NaCl, fibril aggregation was observed only with addition of sulfate ions at 5-50 mM. Selenate ions, by contrast with sulfate ions, induced only axial and not substantial lateral aggregation of fibrils. X-ray diffraction indicated that the original cross-beta peptide conformation remained unchanged; however, sulfate binding did produce an intense approximately 65 A meridional reflection not recorded with control peptides. This new reflection probably arises from the periodic deposition of the electron-dense sulfate along the (long) axis of the fibril. The sulfate binding could provide sites for the binding of additional fibrils that generate the observed lateral and axial aggregation. The binding of heparan to beta(11-28) also produced extensive aggregation, suggesting that in vivo sulfated compounds can promote macrofibers. The amyloid-specific, sulfonated dye Congo red, even in the presence of sulfate ions, produced limited aggregation and reduced axial growth of the fibrils. Therefore, electrostatic interactions are important in the binding of exogenous compounds to amyloid fibrils. Our findings suggest that the sulfate moieties of certain molecules, such as glycosaminoglycans, may affect the aggregation and deposition of amyloid fibrils that are observed as extensive deposits in senile plaques and cerebrovascular amyloid.

Amyloid↗

PubMed1991

pH-dependent structural transitions of Alzheimer amyloid peptides.

To understand the molecular interactions leading to the assembly of beta/44 protein into the hallmark fibrils of Alzheimer's disease (AD), we have examined the ability of synthetic peptides that correspond to the beta/A4 extracellular sequence to form fibrils over the range of pH 3-10. Peptides included the sequences 1-28, 19-28, 17-28, 15-28, 13-28, 11-28, and 9-28 of beta/A4. The model fibrils were compared with isolated amyloid with respect to morphology, conformation, tinctorial properties, and stability under denaturing conditions. Electron microscopy, Fourier-transform infrared (FT-IR) spectroscopy, and x-ray diffraction revealed that the ionization states of the amino acid sidechains appeared to be a crucial feature in fibril formation. This was reflected by the ability of several peptides to undergo fibril assembly and disassembly as a function of pH. Comparisons between different beta/A4 sequences demonstrated that the fibrillar structure representative of AD amyloid was dependent upon electrostatic interactions, likely involving His-13 and Asp-23, and hydrophobic interactions between uncharged sidechains contained within residues 17-21. The results also indicated an exclusively beta-sheet conformation for the synthetic (and possibly AD fibrils) in contrast to certain other (e.g., systemic) amyloids.

Amino Acid Sequence↗

PubMed1990

The cytokine CSF-1 (M-CSF) expressed by endometrial carcinomas in vivo and in vitro, may also be a circulating tumor marker of neoplastic disease activity in endometrial carcinoma patients.

Endometrial epithelial cell expression of CSF-1 and FMS antigens was studied in vivo and in vitro in 24 human endometrial carcinoma and 11 benign endometrial biopsy specimens. Twenty-one of 24 adenocarcinomas and 4 of 11 benign lesions stained positively (by IHC) with rabbit anti-human CSF-1 antibodies, while all 24 carcinomas and 3 out of 11 benign lesions (all secretory endometrial specimens) showed significant IHC staining (1+ or greater) of epithelial elements and tissue macrophages with a mouse anti-FMS (CSF-1 receptor) monoclonal antibody. CSF-1 levels in plasma from endometrial carcinoma patients (85 samples, 24 patients) were also found to be markedly elevated (some greater than 100 ng/ml) in patients with active or recurrent disease. In vitro, several endometrial carcinoma cell lines were shown to express FMS complementary transcripts and FMS antigen which were very similar if not identical to those expressed in choriocarcinoma cell line positive controls. Autocrine and paracrine effects mediated by tumor or stromally produced CSF-1 and a tumor epithelial cell CSF-1 receptor may therefore contribute to the biological behavior of endometrial neoplasms in vivo and in vitro.

Adenocarcinoma↗