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Biomedical subjects

T Martín

Publications and source records attributed to T Martín.

At least 19 recordsLinked to original sources
PubMed2005

Mechanisms for dynamic crack branching in brittle elastic solids: strain field kinematics and reflected surface waves.

We report on a numerical simulation study of dynamic fracture in strip-shaped plates in which we implement a fracture criterion that fully respects mode-I symmetry. The crack dynamics is studied as a function of the length of the initial notch. The cracks show accelerated straight motion until branching appears. We show that branching can be triggered by two different mechanisms: namely, the kinematics of the strain field and back-reflected surface waves traveling on the crack lip. We also propose a qualitative explanation for the kinematic branching mechanism in terms of the effects of the lattice discretization on Yoffe's stress field. The kinematic branching mechanism is understood by analyzing the disconnection times of the nodes ahead and aside of the crack tip.

Journal Article↗
PubMed2005

Efficacy of high loading doses of liposomal amphotericin B in the treatment of experimental invasive pulmonary aspergillosis.

This study aimed to investigate whether initial treatment of experimental pulmonary aspergillosis with high loading doses can be used as an alternative to standard therapeutic regimens. Steroid-immunosuppressed rats, infected intratracheally with Aspergillus fumigatus, received either amphotericin B deoxycholate (d-AmB) 1 mg/kg/day, liposomal amphotericin B (L-AmB) 5 mg/kg/day, or underwent a 3-day course of L-AmB 10 mg/kg, or 10 mg/kg for the first 3 or 4 days of treatment, followed by 3 mg/kg until the end of treatment. Therapy started 24 h after fungal challenge and lasted for 7 days. Compared to controls, survival was improved significantly in animals receiving any L-AmB regimen (p <or= 0.003), but not d-AmB. Compared with d-AmB, L-AmB at initial doses of 10 mg/kg followed by 3 mg/kg/day was consistently more effective, but only when measured in terms of survival, lung weight and glucosamine levels, and not log CFU. Despite the absence of significant differences between any of the L-AmB regimens, a trend towards better response rates with the higher loading dose was observed.

Amphotericin B↗
PubMed2001

Double cationic propargylation: from linear to polycyclic ethers.

[reaction: see text]. The trapping of cations generated from Co2(CO)6-bispropargylic alcohols provided diethers in good yield. The procedure is also valid when two vicinal acetylenes are present. The methodology can be applied to the synthesis of symmetrical or unsymmetrical linear or cyclic propargylic ethers. The use of substrates with a stereochemically defined secondary nucleophilic alcohol provided cyclic ethers with a high degree of stereocontrol.

Journal Article↗
PubMed2001

Chiral softballs: synthesis and molecular recognition properties.

Studies on the different congeners of the softball were undertaken to explore structural variants for enantioselective encapsulation. Two different spacer elements in the monomeric subunit render the dimeric softball chiral although the monomer itself is achiral. The dimers represent capsules with dissymmetric cavities with volumes ranging from 190 to 390 A(3). The cavities are distorted spheres, and asymmetric guests, such as naturally occurring terpenes, generally prefer one enantiomer of the capsule to its mirror image. The selectivities are moderate (up to 4:1). The complexation studies show that the host capsules are flexible enough to arrange themselves comfortably around a guest but still maintain enough rigidity to be influenced by the occupancy of a chiral guest. The enantiomeric capsules can interconvert (racemize) by dissociation and recombination of their subunits.

Journal Article↗
PubMed2001

Beta-hydroxy-gamma-lactones as chiral building blocks for the enantioselective synthesis of marine natural products.

The enantioselective synthesis of trans-(+)-laurediol, (2S,3S,5R)-5-[(1R)-1-hydroxy-9-decenyl]-2-pentyltetrahydro-3-furanol, and (2S,3S,5S)-5-[(1S)-1-hydroxy-9-decenyl]-2-pentyltetrahydro-3-furanol are described. In addition, a formal synthesis of trans-(-)-kumausyne is also developed. All the synthetic procedures have in common the use of enantiomerically enriched beta-hydroxy-gamma-lactones, easily available by Sharpless asymmetric dihydroxylation (AD) from the suitable beta,gamma-unsaturated ester. The use of Katsuki-Sharpless asymmetric epoxidation (AE) as an additional enantioselective reaction provides cyclic compounds of high enantiomeric purity.

Biological Products↗
PubMed1999

Guest exchange in an encapsulation complex: a supramolecular substitution reaction.

Encapsulation complexes are reversibly formed assemblies in which small molecule guests are completely surrounded by large molecule hosts. The assemblies are held together by weak intermolecular forces and are dynamic: they form and dissipate on time scales ranging from milliseconds to days-long enough for many interactions, even reactions, to take place within them. Little information is available on the exchange process, how guests get in and out of these complexes. Here we report that these events can be slow enough for conventional kinetic studies, and reactive intermediates can be detected. Guest exchange has much in common with familiar chemical substitution reactions, but differs in some respects: no covalent bonds are made or broken, the substrate is an assembly rather than a single molecule, and at least four molecules are involved in multiple rate-determining steps.

Adamantane↗
PubMed1999

Serum zinc, copper, insulin and lipids in Alzheimer's disease epsilon 4 apolipoprotein E allele carriers.

BACKGROUND: Copper (Cu) and zinc (Zn) have been implicated in the development of Alzheimer's disease (AD) and, in this regard, Cu and Zn serum concentrations have been analysed but with inconclusive results. Serum insulin, glucose and cholesterol concentrations have been related to the apolipoprotein E genotype in non-AD populations. DESIGN: In this study, we have analysed the relationship between serum Cu, Zn, insulin, glucose and lipid parameters (cholesterol, triglycerides, apoA and apoB apolipoproteins) in AD and AD epsilon 4 apolipoprotein E carriers by multivariate analysis using logistic regression, including the variables that showed a significance of P < 0.05 in the bivariate analysis. RESULTS: The results obtained show that epsilon 4 apoE allele is an independent AD risk factor (OR = 6. 67, 95% CI = 2.59-17.16). In AD epsilon 4 apoE allele carriers, we found significantly higher Zn, Cu and insulin serum concentrations. Non-demented control subjects with at least one epsilon 4 apoE allele had the lowest serum insulin concentrations. There was no significant association between epsilon 4 apolipoprotein E allele and lipid parameters in the sample studied. CONCLUSIONS: In AD we have found a significant association between higher serum Zn, Cu and insulin concentrations and the presence of an epsilon 4 apoE allele, but only greater serum Zn concentration appears to be an independent risk factor associated with the development of AD.

Age Factors↗
PubMed1999

[Levels of evidence in the prevention and control of nosocomial infection].

BACKGROUND: Sanitary, economic and social importance of nosocomial infections justifies the introduction and development of control and surveillance systems in hospitals. The practice of a rational medicine needs the scientific evidence evaluation of the control measures employed, in terms of efficacy, efficiency and effectivity. METHODS: Critical appraisal of medical literature with special emphasis in recommendations provided by Centers for Disease Control and Prevention (CDC). RESULTS: A minimum proportion of prevention and control recommendations provided by Centers for Disease Control and Prevention (CDC) are included in the Category IA (demonstrated evidence in well-designed epidemiological or experimental studies), while sanitary impact (reduction of the nosocomial infection incidence or prevalence) or economic impact (the benefit derived of this nosocomial infection frequency reduction) of numerous interventions keeps being a motive for study and discussion because its evidence level is not demonstrated due to internal or external validity problems. CONCLUSIONS: An appropriate strategy to be adopted by sanitary professionals in charge of nosocomial infection control is the application of the evidence-based medicine methodology and principles.

Bacterial Infections↗
PubMed1998

Molecular assembly and encapsulation directed by hydrogen-bonding preferences and the filling of space.

Multiple copies of a molecule, held together in finite aggregates, give rise to properties and functions that are unique to their assembled states. Because these aggregates are held together by weak forces operating over short distances, a premium is placed on complementarity: The molecular surfaces must facilitate specific interactions that direct the assembly to one aggregate rather than another. Hydrogen-bonding preferences can be combined with molecular curvature to favor the assembly of four self-complementary subunits into a pseudo-spherical capsule. Filling the capsule with smaller, complementary molecules provides the final instruction for the assembly process.

Adamantane↗
PubMed1998

[Detection of human herpesvirus 8 in patients with Kaposi's sarcoma or Castleman's disease associated with AIDS].

A new herpesvirus provisionally termed as KSHV or HHV-8 has been detected in lesions from AIDS-based Kaposi's sarcoma (KS) and from other KS clinical forms, and also in other tumors such as body cavity-based lymphomas or Castleman's disease (CD). We have assessed the presence of this novel herpesvirus in specimens from patients diagnosed with either AIDS and KS or AIDS and CD. DNA samples from skin lesions and peripheral blood obtained from 8 patients diagnosed with AIDS, seven with KS and one with multicentric CD were analyzed; skin specimens and peripheral blood samples from volunteer blood donors or from KS and CD free HIV seronegative patients were used as controls. Detection of the virus was done by PCR amplification of KS330 region, one of the HHV-8 sequences first reported. All skin lesions analysed tested positive for KS330; peripheral blood samples from 5 of the patients, including the one diagnosed with CD, showed also the virus sequence. All skin specimens and peripheral blood samples from controls were negative. From our results it can be concluded that the novel herpesvirus HHV-8 can also be detected in patients with AIDS-associated KS and AIDS-associated CD in Spain.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Chiral spaces: dissymmetric capsules through self-assembly.

Molecules with self-complementary surfaces interact through weak intermolecular forces to form assemblies, and the assembled states frequently exhibit distinctive properties. Described here are systems in which symmetrical molecules assemble through hydrogen bonding to produce capsules with dissymmetric cavities. The capsules form and dissipate on a time scale that permits their direct observation by nuclear magnetic resonance measurements, and they act as hosts for smaller molecular guests. Molecular recognition of chiral guests, such as naturally occurring terpenes, determines which dissymmetric cavities are preferentially formed in the assembly process.

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed1998

BN 52021 (a platelet activating factor-receptor antagonist) decreases alveolar macrophage-mediated lung injury in experimental extrinsic allergic alveolitis.

Several lines of research indirectly suggest that platelet activating factor (PAF) may intervene in the pathogenesis of extrinsic allergic alveolitis (EAA). The specific aim of our study was to evaluate the participation of PAF on macrophage activation during the acute phase of EAA in an experimental model of this disease developed in guinea pigs. Initially we measured the concentration of PAF in bronchoalvedar lavage fluid, blood and lung tissue. In a second phase we evaluate the participation of PAF on alveolar macrophage activation and parenchymal lung injury. The effect of PAF on parenchymal lung injury was evaluated by measuring several lung parenchymatous lesion indices (lung index, bronchoalvedar lavage fluid (BALF) lactic hydrogenase activity and BALF alkaline phosphatase activity) and parameters of systemic response to the challenge (acute phase reagents). We observed that induction of the experimental EAA gave rise to an increase in the concentration of PAF in blood and in lung tissue. The use of the PAF-receptor antagonist BN52021 decreases the release of lysosomal enzymes (beta-glucuronidase and tartrate-sensitive acid phosphatase) to the extracellular environment both in vivo and in vitro. Furthermore, antagonism of the PAF receptors notably decreases pulmonary parenchymatous lesion. These data suggest that lung lesions from acute EAA are partly mediated by local production of PAF.

Alveolitis, Extrinsic Allergic↗
PubMed1998

[Visceral leishmaniasis in immunocompromised patients].

OBJECTIVE: Most patients who developed visceral leishmaniasis (VL) in our country are ímmunocompromised (IC) host, frequently HIV-infected patients. One objective was to know if there were differences about the clinical manifestations, diagnostic tests or prognosis in IC patients who were infected or not with HIV (HIV+ and HIV-, respectively). Also we wonder if some features were associated with death during the initial episodes of VL. METHOD: We studied 16 IC patients with VL, 9 were VIH+ and 7 were VIH-. Most frequently observed findings were fever (94%), splenomegaly (81%), hepatomegaly (69%), and constitutional syndrome (50%). HIV+ patients had symptoms during a lapse of time (70 +/- 78 days) larger than the VIH- cases had (17 +/- 12 days, p < 0.05). RESULTS: We performed a serology to Leishmania sp in 15 cases (94%) and were positive in 13 patients (77% in HIV+ and 100% in VIH patients). Seven patients (44%, 4 VIH- and 3 VIH+) died during the initial episode of VL. Nine patients (66%) who survived to it were followed-up during 68 +/- 49 months. Seven patients (4 VIH+ and 3 VIH-) showed several relapses (2.5 +/- 1.6 relapses/patient) through the follow-up. The patients who died during the initial episode had more frequently (p < 0.05) concentrations of albumin below 3 g/dl or of globulins below 4 g/dl, than the survivors had. The CD4+ lymphocyte counts in HIV+ patients were lower in patients who died during the initial episode of VL (19 +/- 15/mm) than in survivors (108 +/- 67/mm3, p = 0.07).

AIDS-Related Opportunistic Infections↗