Biomedical subjects

C Soto

Publications and source records attributed to C Soto.

At least 73 records · Page 4Linked to original sources

PubMed1996

Calcium and gadolinium ions stimulate the GTPase activity of purified chicken brain tubulin through a conformational change.

Ca2+ and Gd3+ stimulated the GTPase activity of chicken brain tubulin 13- and 26-fold, respectively. Mg2+, Tb3+, and Na+ had no effect. This GTPase activity showed a saturation behavior with Ca2+ and Gd3+ with a maximal activity of 0.26 +/- 0.026 and 1.15 +/- 0.78 nmol min-1 per mg of tubulin and semisaturation constants, expressed as the concentration of the cation needed for 50% of saturation, of 0.32 +/- 0.18 and 0.011 +/- 0.007 mM, respectively. In the presence of Ca2+, the GTPase activity was proportional to tubulin concentration in the range 0.9-31.8 microM. The semisaturation constants for the inhibition of tubulin polymerization and for the depolymerization of microtubules by Ca2+ were 0.71 +/- 0.1 and 0.049 +/- 0.043 mM, respectively. The similarity of the Ca2+ semisaturation constants for inhibition of tubulin assembly and stimulation of the GTPase activity suggests that these processes are correlated. These results support the hypothesis that the GTPase activity is related to but not directly involved in the mechanism of inhibition of Ca2+ -dependent tubulin assembly. This inhibition could be better explained by the formation of a nonfunctional conformational state of tubulin induced by Ca2+ that is responsible for the GTPase activity. Quenching of the intrinsic fluorescence of tryptophan induced by Ca2+ showed an apparent dissociation constant of 0.14 +/- 0.005 mM, in the range of values determined through tubulin polymerization inhibition or through the induction of GTPase activity by Ca2+. Acrylamide-induced quenching of the intrinsic fluorescence showed values of the Stern-Volmer constants of 5.4 +/- 0.12 and 5.0 +/- 0.15 M-1 in the absence and presence of Ca2+, respectively. These results support the hypothesis that the inhibition of tubulin polymerization and the induction of the GTPase activity by Ca2+ is mediated by a conformational change. Ca2+ failed to induce depolymerization of GDP-AIF4-microtubules; this could be explained by a model in which Ca-tubulin is unable to assemble into microtubules and the rate of dissociation of GDP-Pi-tubulin from the microtubule ends is extremely slow compared with the rate of GDP-subunit dissociation, supporting the concept that the GTP- and GDP-Pi-tubulin cap at the ends of microtubules regulates their dynamic instability.

Aluminum Compounds↗

PubMed1996

The interaction between apolipoprotein E and Alzheimer's amyloid beta-peptide is dependent on beta-peptide conformation.

An important feature of Alzheimer's disease (AD) is the cerebral deposition of amyloid. The main component of the amyloid is a 39-44-amino acid residue protein called amyloid beta (A beta), which also exists as a normal protein in biological fluids, known as soluble A beta. A major risk factor for late-onset AD is the inheritance of the apolipoprotein (apo) E4 isotype of apoE. How apoE is involved in the pathogenesis of AD is unclear; however, evidence exists for a direct apoE/A beta interaction. We and others have shown that apoE copurifies with A beta from AD amyloid plaques and that under certain in vitro conditions apoE promotes a beta-sheet structure in A beta peptides. Currently we document the high affinity binding of A beta peptides to both human recombinant apoE3 and -E4 with a KD of 20 nM. This interaction is greatly influenced by the conformational state of the A beta peptide used. Furthermore, we show that the fibril modulating effect of apoE is also influenced by the initial secondary structure of the A beta peptide. The preferential binding of apoE to A beta peptides with a beta-sheet conformation can in part explain the copurification of A beta and apoE from AD amyloid plaques.

Alzheimer Disease↗

PubMed1996

The conformation of Alzheimer's beta peptide determines the rate of amyloid formation and its resistance to proteolysis.

Amyloid beta-peptide (A beta) is found in an aggregated poorly soluble form in senile or neuritic plaques deposited in the brain of individuals affected by Alzheimer's disease (AD). In addition soluble A beta (sA beta) is identified normally circulating in human body fluids. In this study we report that synthetic peptides containing the sequences 1-40 and 1-42 of A beta, and A beta analogues bearing amino acid substitutions can adopt two major conformational states in solution: (1) an amyloidogenic conformer (A beta ac) with a high content of beta-sheet and partly resistant to proteases and (2) a non-amyloidogenic conformer (A beta nac) with a random coil conformation and protease-sensitive. The differences in the fibrillogenesis rate and in the protease resistance among the several A beta peptides studied depend mainly on the relative propensity for adopting the amyloidogenic conformation, which in the absence of external factors is largely conditioned by the primary structure of the peptide. A beta nac containing the sequence 1-40, 1-42 or bearing amino acid substitutions (Dutch variant of A beta) was protease-sensitive and unable to form a significant amount of amyloid even at high concentrations or after long incubations. The finding of the simultaneous existence of different A beta conformers with distinct abilities to form amyloid may help to explain why A beta is found in both soluble and fibrillar forms in vivo.

Alzheimer Disease↗

PubMed1996

Alzheimer's beta-amyloid peptide is conformationally modified by apolipoprotein E in vitro.

Amyloid beta-peptide (A beta) is a major component of neuritic plaques, a feature of Alzheimer's disease (AD) brains. Recently, we showed that A beta adopts two major conformational states in solution, which differ in their abilities to form amyloid. These are highly amyloidogenic conformer (A beta ac) with a high content of beta-sheet and a slowly amyloidogenic conformer (A beta nac) with a random coil conformation. Apolipoprotein E (apoE), particularly the E4 isoform, which is genetically associated with AD, binds to A beta and modulates fibrillogenesis in vitro. In the present work, the influence of apoE on the conformation of A beta peptides was studied. The results suggest that, under the conditions used, apoE enhances amyloid formation by inducing the conformational transition from A beta nac into A beta ac. We propose that an important step in A beta fibrillogenesis is the transformation induced by apoE of the soluble non-amyloidogenic into the pathological amyloidogenic conformer of A beta.

Alzheimer Disease↗

PubMed1996

Extracellular matrix regulates the amount of the beta-amyloid precursor protein and its amyloidogenic fragments.

We have studied the influence of the extracellular matrix (ECM) on the amount of beta-amyloid precursor protein (APP) and C-terminal amyloid-bearing fragments in 313 fibroblasts. After incubation with ECM components, the cellular APP content of 3T3 cells changed. Besides, different substrata including collagen, fibronectin, laminin, vitronectin, and heparin, determined changes in the amount of a C-terminal 22 kDa-fragment. The regulation of amyloidogenic fragments by the ECM was transient; in fact, when 3T3 cells were plated on tissue culture dishes coated with collagen or vitronectin, maximal levels of the 22 kDa fragment were observed 12 h after plating; in the presence of fibronectin, the maximum level of the amyloidogenic fragment was obtained 36 h after plating. These results indicate that the ECM modulates in a transient way the generation of APP-derived polypeptides containing the amyloid-beta-peptide (A beta). The ECM does not have a generalized effect on 3T3 fibroblasts, because no significant differences in cell attachment, growth rate, whole-cell polypeptide pattern beta 1 integrin and alpha-tubulin levels were observed on cells grown on various matrix proteins. Laminin, collagen, and heparin also influence the level of an amyloidogenic fragment of 35 kDa in Neuro 2A neuronal cells, without a significant change in the neuronal marker acetylcholinesterase. In this case, however, a long-lasting response to ECM molecules was observed. These observations provide evidence that ECM molecules influence APP biogenesis, including the generation of amyloidogenic fragments containing the A beta peptide. Our studies might prove significant to understand the localized increment of beta-amyloid deposition in selected areas of the brain of Alzheimer's patients.

3T3 Cells↗

PubMed1996

Is erythrocyte alkaline phosphatase activity a marker of zinc status in humans?

The identification of an enzyme activity that responds to changes in Zn intake may serve as a useful biomarker for Zn status. Alkaline phosphatase (ALP) is a dimeric protein with each subunit containing two Zn atoms. The activity of ALP in erythrocytes (E) decreases as a result of a low Zn diet, which suggests that this enzyme may be a marker of Zn status. To investigate this further, we determined the response of E-ALP in six healthy subjects following supplementation with 50 mg Zn (4.2 x RDI) daily for 4 wk. A small but significant increase in plasma Zn was observed with supplementation (p < 0.05), whereas there was no significant change in E-Zn over the same period. Plasma and E-Cu showed no change. Conversely, the activity of E-ALP increased in all subjects from 1.7 +/- 0.5 to 5.9 +/- 0.7 U/g protein (mean +/- SE) (p < 0.0001). The small change observed in plasma Zn is not biologically significant in view of the many documented factors that influence its concentration. Our data support the hypothesis that E-ALP is a marker of Zn status in humans.

Adult↗

PubMed1996

Transdiaphragmatic pressure gradients and the lower esophageal sphincter after tight abdominal wall plication in the rat.

BACKGROUND: Gastroesophageal reflux (GER) is increasingly recognized as a complication of surgical closure of gastroschisis and omphalocele. AIM: This study tests the hypothesis that forceful abdominal wall closure reinforces the transdiaphragmatic pressure gradients that constitute the main GER-driving force and challenges the antireflux barrier. MATERIALS AND METHODS: Abdominal and esophageal pressures as well as lower esophageal sphincter pressures (LESP) and length (LESL) were measured in 17 adult rats before tight abdominal wall plication, after it, and 1 week later. RESULTS: This maneuver increased the transdiaphragmatic expiratory gradient from 0.67 +/- 1.31 to 6.97 +/- 2.68 mm Hg (P < .01) and the inspiratory gradient from 4.36 +/- 1.13 to 10.79 +/- 2.31 mm Hg (P < .01) by markedly increasing both the expiratory (from 1.47 +/- 0.74 to 9.44 +/- 1.85 mm Hg; P < .01) and inspiratory (from 0.98 +/- 0.69 to 6.83 +/- 1.55 mm Hg; P < .01) intraabdominal pressures. These changes were transient, and all pressures became normal after 1 week. The antireflux barrier functioned properly under these new conditions because both LESP and the diaphragmatic pinch-cock pressure (DPP) increased, from 20.3 +/- 3.63 to 26.5 +/- 4.31 mm Hg (P < .01) and from 16.4 +/- 7.25 to 22.5 +/- 4.36 mm Hg (P < .01), respectively, while LESL remained unchanged. CONCLUSION: Tight abdominal wall plication in the rat generates high intraabdominal pressures and thus reinforces the transdiaphragmatic pressure gradients, but these conditions elicit a healthy barrier response with sphincteric reinforcement. In addition, these changes are transient and fade out some time after operation. These facts should be taken into account for understanding the pathogenesis of GER after repair of abdominal wall defects in human babies.

Abdominal Muscles↗

PubMed1996

Acetylcholinesterase accelerates assembly of amyloid-beta-peptides into Alzheimer's fibrils: possible role of the peripheral site of the enzyme.

Acetylcholinesterase (AChE), an important component of cholinergic synapses, colocalizes with amyloid-beta peptide (A beta) deposits of Alzheimer's brain. We report here that bovine brain AChE, as well as the human and mouse recombinant enzyme, accelerates amyloid formation from wild-type A beta and a mutant A beta peptide, which alone produces few amyloid-like fibrils. The action of AChE was independent of the subunit array of the enzyme, was not affected by edrophonium, an active site inhibitor, but it was affected by propidium, a peripheral anionic binding site ligand. Butyrylcholinesterase, an enzyme that lacks the peripheral site, did not affect amyloid formation. Furthermore, AChE is a potent amyloid-promoting factor when compared with other A beta-associated proteins. Thus, in addition to its role in cholinergic synapses, AChE may function by accelerating A beta formation and could play a role during amyloid deposition in Alzheimer's brain.

Acetylcholinesterase↗

PubMed1996

[Medullary cancer of the thyroid. Experience at the Hospital de Valdivia].

BACKGROUND: Medullary carcinoma of the thyroid is an infrequent type of thyroid tumor. AIM: To retrospectively study all cases of medullary carcinoma of the thyroid diagnosed at a regional hospital. PATIENTS AND METHODS: The charts and pathological studies of eight patients with medullary carcinoma of the thyroid, among 75 with thyroidal cancer, were reviewed. RESULTS: Solitary nodules were the presenting sign in seven patients and cachexia in one. Five patients were subjected to total thyroidectomy, five to cervical lymph node dissection and four to complementary radiotherapy. Pathological diagnosis was made with the surgical piece in seven patients and by aspiration cytology in one. Five of the eight patients are alive after 50 months of follow up as a mean, one patient with bone metastasis. CONCLUSIONS: The small sample size precludes conclusions on the prognosis and treatment of the disease.

Adolescent↗

PubMed1996

[Effects of diaphragmatic plication in the antireflux barrier in rats].

INTRODUCTION: There is increasing evidence of frequent occurrence of gastroesophageal reflux (GER) in patients surviving operations for congenital diaphragmatic hernia (CDH) and diaphragmatic eventration (DE). The murine model allows to study the behavior of the components of antireflux barrier. AIM: To study the changes introduced in esophageal-gastric junction by DE due to cervical transection of the left phrenic nerve and subsequent plication of the paralyzed diaphragm. MATERIAL AND METHODS: Adult male Wistar rats were divided into two groups: in one we measured the pressure conditions before and after phrenic nerve section (PNS) and in the other we evaluated such conditions in PNS rats before and after diaphragmatic plication (DP). RESULTS: Phrenic transection significantly lowered inspiratory pressure gradient (IPG), (2.79 +/- 1.05 vs 4.43 +/- 1.03, p < 0.05), without changes in expiratory pressure gradient (EPG) (0.31 +/- 1.03 vs 0.25 +/- 1, p > 0.05), or lower esophageal sphincter pressure (LESP) (20.88 +/- 7.73 vs 15.88 +/- 9.25, p > 0.05). Plication of the diaphragm reestablished normal IPG (4.04 +/- 0.75 vs 2.58 +/- 0.51, p < 0.05) while increased EPG (1 +/- 0.75 vs -0.32 +/- 1.05, p < 0.05) and decreased LESP (10.59 +/- 5.74 vs 17.15 +/- 5.59, p < 0.05). CONCLUSION: Paralyzed diaphragmatic eventration lowered inspiratory gradient pressure; diaphragmatic plication reestablished this gradient, but decreased LESP and increased expiratory gradient pressure. These modifications may contribute to induce GER.

Animals↗

PubMed1995

Fibrillogenesis of synthetic amyloid-beta peptides is dependent on their initial secondary structure.

Synthetic peptides containing the sequence of Alzheimer's amyloid-beta peptide (A beta) spontaneously form amyloid-like fibrils in vitro, and have been extensively used to study the factors that modulate fibrillogenesis. Contradictory observations have been reported regarding the neurotoxicity of A beta and the influence of some A beta-binding proteins on in vitro A beta amyloid formation. In this study, we show that A beta 1-40 synthetic peptides obtained from different suppliers, have significantly distinct fibrillogenic properties. No differences were detected in the chemical structure or in the initial assembly state by mass spectroscopy, reverse-phase high performance liquid chromatography and denaturing or non-denaturing gel electrophoresis. However, there was a direct correlation between the ability of soluble peptides to form amyloid and their percentage of beta-sheet structure, as determined by electron microscopy, fluorescence associated to thioflavine T bound to amyloid, and circular dichroism. The data suggest that the determinant factor of A beta fibrillogenesis is the secondary structure adopted by the peptide in its soluble state.

Amyloid↗

PubMed1995

Apolipoprotein E increases the fibrillogenic potential of synthetic peptides derived from Alzheimer's, gelsolin and AA amyloids.

Apolipoprotein E (apoE) has been found in association with several different types of systemic and cerebral amyloid deposits and the presence of the epsilon 4 allele constitutes a risk factor for Alzheimer's disease. It has been shown that apoE binds and promotes the fibrillogenesis in vitro of Alzheimer's amyloid beta-peptide, suggesting an important role for apoE in the modulation of amyloidogenesis. Due to the co-localization of apoE with several biochemically distinct amyloid deposits, it has been proposed that apoE plays a general role modulating and/or participating in amyloidosis. In the present study, we show for the first time that apoE, isolated from human plasma, increases fibril formation of synthetic peptides comprising the amyloidogenic sequences of gelsolin amyloid related to familial amyloidosis Finnish type, and amyloid A found in secondary amyloidosis and familial Mediterranean fever. Our results suggest that apoE acts as a general pathological chaperone in various amyloidoses by enhancing the transition from soluble peptides into amyloid-forming, pathological molecules.

Alzheimer Disease↗

PubMed1995

Fibrillogenesis in Alzheimer's disease of amyloid beta peptides and apolipoprotein E.

A central event in Alzheimer's disease is the conformational change from normally circulating soluble amyloid beta peptides (A beta) and tau proteins into amyloid fibrils, in the form of senile plaques and neurofibrillary tangles respectively. The apolipoprotein E (apoE) gene locus has recently been associated with late-onset Alzheimer's disease. It is not know whether apoE plays a direct role in the pathogenesis of the disease. In the present work we have investigated whether apoE can affect the known spontaneous in vitro formation of amyloid-like fibrils by synthetic A beta analogues using a thioflavine-T assay for fibril formation, electron microscopy and Congo Red staining. Our results show that, under the conditions used, apoE directly promotes amyloid fibril formation, increasing both the rate of fibrillogenesis and the total amount of amyloid formed. ApoE accelerated fibril formation of both wild-type A beta-(1-40) and A beta-(1-40A), an analogue created by the replacement of valine with alanine at residue 18, which alone produces few amyloid-like fibrils. However, apoE produced only a minimal effect on A beta-(1-40Q), found in the Dutch variant of Alzheimer's disease. When recombinant apoE isoforms were used, apoE4 was more efficient than apoE3 at enhancing amyloid formation. These in vitro observations support the hypothesis that apoE acts as a pathological chaperone, promoting the beta-pleated-sheet conformation of soluble A beta into amyloid fibres, and provide a possible explanation for the association of the apoE4 genetic isoform with Alzheimer's disease.

Alzheimer Disease↗

PubMed1995

Two conformational states of amyloid beta-peptide: implications for the pathogenesis of Alzheimer's disease.

Since the discovery of soluble amyloid-beta (sA beta), it became clear that the same amino acid sequence can have both a fibrillar or a soluble state. In this work, we describe the isolation of two different species derived from synthetic A beta(1-40) differing in their conformational and fibrillogenesis properties. The separation was performed taking advantage of the fact that only one species is sedimentable by centrifugation after 2 weeks of incubation at 1 mg/ml. One species is highly amyloidogenic (A beta ac) and has an antiparallel beta-sheet structure and the other one is poorly amyloidogenic (A beta nac) and contains mainly random coil or alpha-helix structure. Chemical changes were not detected in the primary structure of both species and the differences in the physical properties and very likely in biological behaviour are thought to have a conformational basis. We propose that the transformation of the non-amyloidogenic into the amyloidogenic conformation could be the fundamental event in the pathological polymerization of sA beta and in the development of Alzheimer's disease.

Algorithms↗

PubMed1995

The alpha-helical to beta-strand transition in the amino-terminal fragment of the amyloid beta-peptide modulates amyloid formation.

Amyloid-beta peptide (A beta) consists of a hydrophobic C-terminal domain (residues 29-42) that adopts beta-strand conformation and an N-terminal domain (amino acids 10-24) whose sequence permits the existence of a dynamic equilibrium between an alpha-helix and a beta-strand. In this paper we analyzed the effect of the alternate N-terminal conformations on amyloid fibril formation through the study of the analogous A beta peptides containing single amino acidic substitutions. The single mutation of valine 18 to alanine induces a significant increment of the alpha-helical content of A beta, determined by Fourier transform infrared spectroscopy and circular dichroism and dramatically diminishes fibrillogenesis, measured by turbidity, thioflavine T binding, Congo red staining, and electron microscopic examination. In hereditary Dutch cerebral hemorrhage with amyloidosis (a variant of Alzheimer's disease), the substitution of glutamine for glutamic acid at position 22 decreased the propensity of the A beta N-terminal domain to adopt an alpha-helical structure, with a concomitant increase in amyloid formation. We propose that A beta exists in an equilibrium between two species: one "able" and another "unable" to form amyloid, depending on the secondary structure adopted by the N-terminal domain. Thus, manipulation of the A beta secondary structure with therapeutical compounds that promote the alpha-helical conformation may provides a tool to control the amyloid deposition observed in Alzheimer's disease patients.

Alanine↗

PubMed1995

Cultured epidermal autograft in the management of critical pediatric burn patients.

We treated 4 patients with CEA at "La Paz" Children's Hospital between July 1992 and September 1993. All of them had acute flame burns. The total body surface area (TBSA) of burn injury ranged from 75% to 85% with an age range of two to five years. Before placement of CEA homografts and biosynthetic materials were used to prepare the wound bed. CEA take ranged from 40% to 90%. One of the children died after polyethylene glycol intoxication when the exposed areas were nearly totally covered. Two more have started rehabilitation therapy and the last patient was grafted just two months ago.

Burns↗

PubMed1995

[Modification of the lipid profile of human placenta by moderate maternal undernutrition].

The lipid composition of human placenta phospholipids, coming from 9 undernourished women that gave birth to low weight newborns and 9 well nourished women, was analyzed using gas-liquid chromatography. Phospholipids of placentas coming from undernourished women, when compared to well nourished women, had significantly lower amounts of w-6 and w-3 fatty acids (40.1 +/- 1.5 vs 42.4 +/- 1.4 and 6.0 +/- 0.7 vs 7.1 +/- 1.3% respectively). The calculated mean melting point was higher in plancetas coming from undernourished women. It these women, the low content of polyunsaturated fatty acids and its replacement by short chain fatty acids was not able to balance the high mean melting points. The relative deficiency of essential fatty acids, the low saturation index and the high mean melting point of undernourished women's placental phospholipids, may suggest a lower membrane fluidity and a subnormal essential fatty acid content of fetal organs, that are essential for normal growth and development.

Analysis of Variance↗

PubMed1994

Structural determinants of the Alzheimer's amyloid beta-peptide.

The hallmark event of Alzheimer's disease (AD) is the deposition of amyloid as insoluble fiber masses in extracellular neuritic plaques and around the walls of cerebral blood vessels. The main component of amyloid is a hydrophobic peptide, named amyloid beta-peptide (beta A4), which results from the processing of a much longer membrane amyloid precursor protein (APP). This review focuses on the structural features of beta A4 and the factors that determine beta A4 insolubilization. Theoretical and experimental studies of the primary structure of beta A4 have shown that it is composed of a completely hydrophobic C-terminal domain, which adopts beta-strand structure, and an N-terminal region, whose sequence permits different secondary structures. In fact, this region can exist as an alpha-helical or beta-strand conformation depending on the environmental condition (pH and hydrophobicity surrounding the molecule). The effects of pH and hydrophobicity on beta A4 structure may elucidate the mechanisms determining its aggregation and amyloid deposition in AD.

Alzheimer Disease↗