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Biomedical subjects

A Ortiz

Publications and source records attributed to A Ortiz.

At least 55 records · Page 3Linked to original sources
PubMed2001

Hypertrophic cardiomyopathy caused by a novel alpha-tropomyosin mutation (V95A) is associated with mild cardiac phenotype, abnormal calcium binding to troponin, abnormal myosin cycling, and poor prognosis.

BACKGROUND: We report hypertrophic cardiomyopathy (HCM) in a Spanish-American family caused by a novel alpha-tropomyosin (TPM1) mutation and examine the pathogenesis of the clinical disease by characterizing functional defects in the purified mutant protein. METHODS AND RESULTS: HCM was linked to the TPM1 gene (logarithm of the odds [LOD] score 3.17). Sequencing and restriction digestion analysis demonstrated a TPM1 mutation V95A that cosegregated with HCM. The mutation has been associated with 13 deaths in 26 affected members (11 sudden deaths and 2 related to heart failure), with a cumulative survival rate of 73+/-10% at the age of 40 years. Left ventricular wall thickness (mean 16+/-6 mm) and disease penetrance (53%) were similar to those for the ss-myosin mutations L908V and G256E previously associated with a benign prognosis. Left ventricular hypertrophy was milder than with the ss-myosin mutation R403Q, but the prognosis was similarly poor. With the use of recombinant tropomyosins, we identified several functional alterations at the protein level. The mutation caused a 40% to 50% increase in calcium affinity in regulated thin filament-myosin subfragment-1 (S1) MgATPase assays, a 20% decrease in MgATPase rates in the presence of saturating calcium, a 5% decrease in unloaded shortening velocity in in vitro motility assays, and no change in cooperative myosin S1 binding to regulated thin filaments. CONCLUSIONS: In contrast to other reported TPM1 mutations, V95A-associated HCM exhibits unusual features of mild phenotype but poor prognosis. Both myosin cycling and calcium binding to troponin are abnormal in the presence of the mutant tropomyosin. The genetic diagnosis afforded by this mutation will be valuable in the management of HCM.

Adult↗
PubMed2001

Aggregational behavior of aqueous dispersions of the antifungal lipopeptide iturin A.

Iturin A, a lipopeptide isolated from Bacillus subtilis, possesses a strong antifungal activity, and has been devoted to a great deal of attention. Since iturin is an amphiphilic compound with a great propensity to self-associate in solution as well as inside the membrane, the question arises to whether its aggregational behavior is dependent on the concentration of the lipopeptide. In order to test this, the ability of iturin suspensions to encapsulate water-soluble molecules has been examined. Iturin was dispersed at different concentrations above its critical micellar concentration, in a buffer containing the water-soluble dye 5,6-carboxyfluorescein. For iturin A micelles, a Stokes radius of 1.3 nm and an aggregational number of 7 was obtained. The results shown in this work clearly demonstrate that iturin dispersions in water, at concentrations of 0.7, 1.4 and 3 mM, i.e. far above the critical micellar concentration (40 microM), are capable of encapsulating carboxyfluorescein, probably by adopting a type of aggregate different from the micelle. Negative-staining electron microscopy shows the presence of vesicles with an average size of 150 nm. By using (14)C-iturin, it is shown that, at 3 mM concentration, 40 % of the iturin molecules adopt this vesicular state. It is proposed that iturin molecules form a fully interdigitated bilayer, where each hydrocarbon tail span the entire hydrocarbon width of the bilayer, resulting in multilamellar vesicles capable of encapsulating an aqueous compartment. The possible implications of these results to the membrane destabilizing effect of iturin A, are discussed according to the dynamic cone-shape of the iturin molecule.

Anti-Bacterial Agents↗
PubMed2001

In vitro evaluation of trichoderma and gliocladium antagonism against the symbiotic fungus of the leaf-cutting ant Atta cephalotes.

The antagonistic activity of Trichoderma and Gliocladium isolates against Attamyces sp., a symbiotic fungus of the leaf-cutting ant Atta cephalotes, was investigated. A. cephalotes cultures this fungus as the primary food source. Most of the Trichodema and Gliocladium isolates tested in vitro (82.6%) inhibited the Attamyces sp. mycelial growth. which was probably due to their colonization ability and competition for nutrients, both of them known mechanisms of some species of these genera. T. lignorum strain T-26 was the strongest inhibitor achieving a colonization of 23%. Microscopical observations indicate that the inhibitory effect was caused by an interaction that took place in close contact with the host hypha, causing wall deformation that led to the collapse of the turgor pressure.

Agaricales↗
PubMed2001

Expression of bilirubin UDP-glucuronosyltransferase (bUGT) throughout fetal development: intrasplenic transplantation into Gunn rats to correct enzymatic deficiency.

The aim of this work was to determine the pattern of expression of hepatic bilirubin UDP-glucuronosyltransferase throughout fetal development in rats, with the purpose of using fetal hepatocytes at the most appropiate stage of development for transplantation into Gunn rats lacking bilirubin UDP-glucuronosyltransferase activity and then assessing the therapeutic capacity of the implants. The results show that at day 13 of gestational life there is already bilirubin UDP-glucuronosyltransferase gene expression. Twenty-one-day fetal hepatocyte transplantation was also performed into the spleens of hyperbilirubinemic Gunn rats, when alpha-fetoprotein mRNA is still detectable. At 15, 30, and 90 days after transplantation, a mild decrease in total bilirubin serum levels was observed. An increase in bile conjugated bilirubin also was observed at 30 and 90 days. These data suggest the favorable evolution of transplanted cells and show its feasibility for therapy.

Animals↗
PubMed2001

Targeting acute ischemic stroke with a calcium-sensitive opener of maxi-K potassium channels.

During ischemic stroke, neurons at risk are exposed to pathologically high levels of intracellular calcium (Ca++), initiating a fatal biochemical cascade. To protect these neurons, we have developed openers of large-conductance, Ca++-activated (maxi-K or BK) potassium channels, thereby augmenting an endogenous mechanism for regulating Ca++ entry and membrane potential. The novel fluoro-oxindoles BMS-204352 and racemic compound 1 are potent, effective and uniquely Ca++-sensitive openers of maxi-K channels. In rat models of permanent large-vessel stroke, BMS-204352 provided significant levels of cortical neuroprotection when administered two hours after the onset of occlusion, but had no effects on blood pressure or cerebral blood flow. This novel approach may restrict Ca++ entry in neurons at risk while having minimal side effects.

Animals↗
PubMed2001

Role of type of vascular access in erythropoietin and intravenous iron requirements in haemodialysis.

BACKGROUND: Recent data have suggested the existence of a relationship between the use of synthetic vascular accesses and increased erythropoietin (Epo) requirements. The present study aimed to evaluate the possible role of the type of vascular access in both Epo and intravenous (i.v.) iron requirements. METHODS: One-hundred-and-seven individuals without recognized causes of Epo resistance, 62 of them undergoing chronic haemodialysis through native arteriovenous fistulae (AVF) and 45 through PTFE grafts, were retrospectively studied (one-year follow-up). Sixty-nine patients, i.e. all but three with a PTFE graft and 27 with native AVF, were taking anti-platelet agents. Doses of i.v. iron and Epo and laboratory parameters were recorded. RESULTS: Erythropoietin and i.v. iron requirements were higher in the patients dialysed through PTFE grafts compared with those with native AVF (Epo: 103.8+/-58.4 vs 81.0+/-44.5 U/kg/week, P=0.025; i.v. iron: 178.9+/-111 vs. 125.9+/-96 mg/month, P=0.01). On a yearly basis, the difference in Epo dose represented a total of 94582+/-16789 U Epo/patient/year. Moreover, the patients with PTFE grafts received more red blood cell transfusions than patients with native AVF (P=0.021). No differences between laboratory, dialysis kinetics, demographic or comorbidity parameters were found. The type of vascular access was the best predictor of the requirement of > or =150 U/kg/week Epo (P=0.03). Even though the patients who received anti-platelet therapy required more i.v. iron (167.5+/-103.6 vs. 114.5+/-101.4 mg/month, P=0.008) but not more Epo (P=NS), the possibility of an accessory role of anti-platelet agents in the increased Epo requirements with PTFE grafts cannot be ruled out. CONCLUSIONS: The use of a PTFE graft and anti-platelet drugs represents a previously undescribed association related to higher Epo and i.v. iron requirements. The association described herein adds new arguments to the debate concerning the choice of vascular access in chronic haemodialysis patients.

Aged↗
PubMed2001

Intestinal metaplasia in patients with columnar lined esophagus is associated with high levels of duodenogastroesophageal reflux.

OBJECTIVE: To evaluate the rate of duodenogastroesophageal reflux in patients with columnar lined esophagus compared with patients with gastroesophageal reflux disease without columnar lined esophagus, and to analyze whether it is related to the presence of specialized columnar epithelium in the metaplastic segment. SUMMARY BACKGROUND DATA: The carcinomatous degeneration of columnar lined esophagus originates from a specialized columnar epithelium. The appearance of this metaplastic phenomenon is clearly related to severe prolonged gastroesophageal reflux, but only some of these patients finally develop columnar lined esophagus. For this reason other factors have been suggested, particularly the role played by the reflux of duodenal contents into the esophagus. METHODS: The authors studied 15 healthy volunteers (control group), 10 patients with reflux symptoms but without endoscopic lesions, 20 patients with reflux esophagitis without columnar lined esophagus, and 35 patients with columnar lined esophagus (complicated with ulcers or stenosis in 8 cases), of whom 22 had intestinal metaplasia. To assess the reflux of duodenal contents into the esophagus, all the patients underwent Bilitec 2000 and 24-hour esophageal pH monitoring. RESULTS: The presence of bilirubin in the material refluxed into the esophagus was greater in the patients with columnar lined esophagus than in the rest of the groups. Likewise, duodenogastroesophageal reflux was greater in the columnar lined esophagus patients who had intestinal metaplasia. CONCLUSIONS: Duodenogastroesophageal reflux may play a major role in the development of columnar lined esophagus, especially in patients with intestinal metaplasia.

Adult↗
PubMed2001

Mechanism of thiamine uptake by human colonocytes: studies with cultured colonic epithelial cell line NCM460.

Thiamine (vitamin B(1)) is essential for normal cellular functions and growth. Mammals cannot synthesize thiamine and thus must obtain the vitamin via intestinal absorption. The intestine is exposed to a dietary thiamine source and a bacterial source in which the vitamin is synthesized by the normal microflora of the large intestine. Very little is known about thiamine uptake in the large intestine. The aim of this study was, therefore, to address this issue. Our results with human-derived colonic epithelial NCM460 cells as a model system showed thiamine uptake to be 1) temperature- and energy dependent, 2) Na(+) independent, 3) increased with increasing buffer pH from 5 to 8 and after cell acidification but inhibited by amiloride, 4) saturable as a function of concentration, 5) inhibited by thiamine structural analogs but not by unrelated organic cations, and 6) inhibited by modulators of a Ca(2+)/calmodulin-mediated pathway. NCM460 cells and native human colonic mucosa expressed the recently cloned human thiamine transporter THTR-1 (product of the SLC19A2 gene) at both mRNA and protein levels. These results demonstrate for the first time that human NCM460 colonocytes possess a specific carrier-mediated system for thiamine uptake that appears to be under the regulation of an intracellular Ca(2+)/calmodulin-mediated pathway. It is suggested that bacterially synthesized thiamine in the large intestine may contribute to thiamine nutrition of the host, especially toward cellular nutrition of the local colonocytes.

Carrier Proteins↗
PubMed2000

Role and regulation of apoptotic cell death in the kidney. Y2K update.

Apoptosis is an active form of cell death that, in balance with mitosis, regulates cell number. Cell number abnormalities are a frequent feature of renal disease. We now review current concepts on the molecular regulation of apoptotic cell death, including the influence of survival and lethal factors from the extracellular microenvironment as well as the role of intracellular regulators of apoptosis, such as death receptors, proapoptotic and antiapoptotic bcl2-related proteins, the mitochondria and caspases. In addition the role of apoptosis in the genesis, persistence and progression and remodeling and resolution of renal injury is discussed. Information on the expression and function of apoptosis regulatory proteins in specific renal syndromes is summarized. Finally, future perspectives in research and clinical intervention are discussed.

Apoptosis↗
PubMed2000

A biophysical study of the interaction of the lipopeptide antibiotic iturin A with aqueous phospholipid bilayers.

Iturin A is a lipopeptide extracted from the culture media of Bacillus subtilis which shows a strong antifungal action. The interaction of iturin A with multilamellar vesicles of dimyristoylphosphatidylcholine (DMPC) induced structures which did not sediment during centrifugation. Electron microscopy after negative staining showed that, at 30 mol%, iturin A/DMPC vesicles were visible but smaller than those formed by pure DMPC. Thermograms of DMPC/iturinA obtained after differential scanning calorimetry, at low concentrations of iturin A, were interpreted as indicating the presence of two laterally separated phases, one formed by pure phospholipid and the other by lipopeptide-phospholipid complexes, these two separated phases being already detected even at low concentrations such as 2 mol%. Fluorescence quenching experiments showed that the D-Tyr residue of the lipopeptide was fully accessible to the aqueous medium, indicating that the polar part of iturin A is located outside of the membrane hydrophobic palisade. It was concluded that the membrane barrier properties are likely to be damaged in the area where the lipid complexes are accumulated, due to structural fluctuations, and this may be one of the bases of its biological activity. Iturin-A was also able to greatly destabilize dielaidoylphosphatidylethanolamine (DEPE) membranes in the fluid form, producing a new structure which had a poor correlation in X-ray diffraction, and in 31P NMR spectroscopy gave rise to a spectrum containing a double isotropic signal. Iturin A was shown to induce DEPE to adopt phases other than H(II) inverted hexagonal, underlining that this lipopeptide is capable of modifying the curvature of the membrane, which may also be important in explaining the tendency of iturin A to create small vesicles and which may be another of the bases of its biological activity.

Anti-Bacterial Agents↗
PubMed2000

Membrane fusion activity of tick-borne encephalitis virus and recombinant subviral particles in a liposomal model system.

We present a kinetic analysis of the membrane fusion activity of tick-borne encephalitis (TBE) virus and TBE-derived recombinant subviral particles (RSPs) in a liposomal model system. Fusion was monitored using a fluorescence assay involving pyrene-labeled phospholipids. Fusion was strictly dependent on low pH, with the optimum being at pH 5.3-5.5 and the threshold at pH 6.8. Fusion did not require a protein or carbohydrate receptor in the target liposomes. Preexposure to low pH of the virus alone resulted in inactivation of its fusion activity. At the optimum pH for fusion and 37 degrees C, the rate and extent of fusion were very high, with more than 50% of the virus fusing within 2 s and the final extent of fusion being 70%. Lowering of the temperature did not result in a significant decrease in the rate and extent of fusion, suggesting that TBE virus fusion is a facile process with a low activation energy, possibly due to the flat orientation of the E glycoprotein on the viral surface facilitating the establishment of direct intermembrane contact. The fusion characteristics of TBE virus and RSPs were similar, indicating that RSPs provide a reliable and convenient model for further study of the membrane fusion properties of TBE virus.

Animals↗
PubMed2000

Derivation of protein-specific pair potentials based on weak sequence fragment similarity.

A method is presented for the derivation of knowledge-based pair potentials that corrects for the various compositions of different proteins. The resulting statistical pair potential is more specific than that derived from previous approaches as assessed by gapless threading results. Additionally, a methodology is presented that interpolates between statistical potentials when no homologous examples to the protein of interest are in the structural database used to derive the potential, to a Go-like potential (in which native interactions are favorable and all nonnative interactions are not) when homologous proteins are present. For cases in which no protein exceeds 30% sequence identity, pairs of weakly homologous interacting fragments are employed to enhance the specificity of the potential. In gapless threading, the mean z score increases from -10.4 for the best statistical pair potential to -12.8 when the local sequence similarity, fragment-based pair potentials are used. Examination of the ab initio structure prediction of four representative globular proteins consistently reveals a qualitative improvement in the yield of structures in the 4 to 6 A rmsd from native range when the fragment-based pair potential is used relative to that when the quasichemical pair potential is employed. This suggests that such protein-specific potentials provide a significant advantage relative to generic quasichemical potentials.

Amino Acids↗
PubMed2000

Fluorescence study on the interaction of a multiple antigenic peptide from hepatitis A virus with lipid vesicles.

The interaction of the multiple antigenic peptide MAP4VP3 with lipid membranes has been studied by spectroscopic techniques. MAP4VP3 is a multimeric peptide that corresponds to four units of the sequence 110-121 of the capsid protein VP3 of hepatitis A virus. In order to evaluate the electrostatic and hydrophobic components on the lipid-peptide interaction, small unilamelar vesicles of different compositions, including zwitterionic dipalmitoylphosphatidylcholine (DPPC), anionic dipalmitoylphosphatidylcholine/phatidylinositol (DPPC:PI 9:1), and cationic dipalmitoylphosphatidylcholine/stearylamine (DPPC:SA 9.5:0.5), were used as membrane models. Intrinsic tryptophan fluorescence changes and energy transfer experiments show that MAP4VP3 binds to all three types of vesicles with the same stoichiometry, indicating that the electrostatic component of the interaction is not important for binding of this anionic peptide. Steady-state polarization experiments with vesicles labeled with 1,6-diphenyl-1,3,5-hexatriene or with 1-anilino-8-naphtalene sulphonic acid indicate that MAP4VP3 induces a change in the packing of the bilayers, with a decrease in the fluidity of the lipids and an increase in the temperature of phase transition in all the vesicles. The percentage of lipid exposed to the bulk aqueous phase is around 60% in intact vesicles, and it does not change upon binding of MAP4VP3 to DPPC vesicles, indicating that the peptide does not alter the permeability of the membrane. An increase in the amount of lipid exposed to the aqueous phase in cationic vesicles indicates either lipid flip-flop or disruption of the vesicles. Binding to DPPC vesicles occurs without leakage of entrapped carboxyfluorescein, even at high mol fractions of peptide. However, a time-dependent leakage is seen with cationic DPPC/SA and anionic DPPC/PI vesicles, indicating that the peptide induces membrane destabilization and not lipid flip-flop. Resonance energy transfer experiments show that MAP4VP3 leakage from cationic vesicles is due to membrane fusion, whereas leakage from anionic vesicles is not accompanied by lipid mixing. Results show that MAP4VP3 interacts strongly with the lipid components of the membrane, and although binding is not of electrostatic nature, the bound form of the peptide has different activity depending on the membrane net charge; thus, it is membrane disruptive in cationic and anionic vesicles, whereas no destabilizing effect is seen in DPPC vesicles.

Antigens, Viral↗