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Biomedical subjects

Luis Vázquez

Publications and source records attributed to Luis Vázquez.

13 recordsLinked to original sources
PubMed2006

Remote temperature retrieval from heating or cooling targets.

We propose a simple pyrometric algorithm to retrieve the temperature from a radiating body during heating or cooling with no prior knowledge of the spectral emissivity. We ratio the measured fluxes at two different temperatures in two narrow bands. The error budget of this method is calculated. We consider its application for the rover-based exploration of the Martian ground, which is subjected to daily and seasonal temperature variations. The method is optimized to increase accuracy in the retrieval of temperature variation, which is the most interesting parameter for ground heat-flux studies.

Journal Article↗
PubMed2006

Gelation under dynamic conditions: a strategy for in vitro cell ordering.

Ordered gelation under spin-coating conditions, as reported here, is a suitable method to order cells in biogels. Cell ordering is of great importance for functional repair of central nervous system (CNS) injuries, because therapies must include strategies to bridge chystic gaps and facilitate axon growth towards its target. Organized biocompatible and biodegradable substrates may be used for this purpose, to supply trophic support and provide directional cues for neuronal process outgrowth. Atomic force microscopy (AFM) and low temperature scanning electron microscopy (LTSEM), confirmed that fibrils in kappa-carrageenan/chitosan and fibrin hydrogels prepared under spin-coating conditions, were longitudinally arranged. The cell model was conveniently tested using rat C6 glioma cells. C6 cells were distributed regularly in fibrin gels formed under centrifugal force. The ability of ordered fibrin scaffolds to promote uniform distribution of transplanted cells, was confirmed by fluorescence microscopy.

Animals↗
PubMed2006

Vascular ophthalmological side effects associated with antiviral therapy for chronic hepatitis C are related to vascular endothelial growth factor levels.

We have screened for the incidence of vascular ophthalmological side effects (VOSE) in chronic hepatitis C (CHC) patients undergoing pegylated interferon (peg-IFN) plus ribavirin (RBV) therapy and sought evidence for angiogenesis activation. Thirty-four CHC patients were prospectively evaluated (18 patients with 180 microg/week of peg-IFN-alpha2a plus 800mg/day of RBV and 16 with 1.5 microg/kg/week of peg-IFN-alpha2b plus 800-1,200mg/day of RBV). Complete ophthalmological evaluation and serum vascular endothelial growth factor (VEGF) levels were assessed before and at the end of therapy. Thirteen patients (38.2%) developed VOSE, eight (23.5%) featured subconjunctival haemorrhage, and five (14.7%) had evidence of retinopathy - all were unrelated to age, sex, genotype, the type of antiviral schedule used and response to therapy. At the end of treatment, the VOSE group had significantly higher serum VEGF levels than the group of patients without detectable side effects (median 281 [range 106-386] vs 117 [83-225] pg/ml, P=0.05). These differences increased when VEGF values were corrected by platelet count. In the VOSE group, baseline VEGF and VEGF/platelet values were also significantly higher (164 [55-260] vs 64 [21-172] pg/ml, P=0.046; and 0.920 [0.217-1.543] vs 0.320 [0.100-0.661] pg/10(6) platelets, P=0.024, respectively]. In a multivariate model VEGF/platelet values at end of treatment and hepatic fibrosis stage were the only predictors of VOSE development. In 3 out of 13 patients visual acuity was affected and 2 had residual lesions in the follow-up. In this exploratory study, antiviral therapy of CHC frequently induces VOSE, apparently through an activation of angiogenesis.

Adult↗
PubMed2005

A complementary microscopy analysis of Sticholysin II crystals on lipid films: Atomic force and transmission electron characterizations.

A new crystal form of the cytotoxin Sticholysin II (StnII) formed on lipid monolayers of 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) has been characterized by transmission electron microscopy (TEM) and by tapping mode atomic force microscopy (AFM) under nearly physiological conditions. Both approaches show the existence of single- and double-layered 2D crystals possessing hexagonal symmetry and unit cell dimensions of a = b =10 nm and gamma = 120 degrees. However, single-layered StnII crystals could only be analysed by TEM and double-layered crystals by AFM. Considering the previously known atomic structure of native StnII and that of a tetrameric assembly, a model is proposed for this new crystal form in which StnII conserves its monomeric state upon interaction with the lipid monolayer. These results are in agreement with the existence of the so called M2 state of the actinoporins.

Animals↗
PubMed2005

Study of the analysis of alkoxyglycerols and other non-polar lipids by liquid chromatography coupled with evaporative light scattering detector.

An HPLC method with evaporative light scattering detection (ELSD) for the simultaneous analysis of various lipid classes, particularly alkoxyglycerols and acylglycerols with very similar structure and polarity, has been developed. These lipid classes are frequently found in numerous fats and oils such as shark liver oils and can serve as substrates for lipase-catalyzed reactions. This method utilizes a silica column and a gradient elution of isooctane, methyl tert-butyl ether and 2-propanol in different proportions. Separation between squalene, sterol esters, and fatty acid ethyl esters has been achieved in a time of analysis slightly higher than 8 min. In addition, a good resolution between 1,3-diacylglycerols and free sterols was also attained in the same run, with a broad range of concentrations. Excellent precision regarding the retention times was obtained. The limit of detection for the different lipid classes studied was below 1 microg. Intra-day and inter-day variation of retention times and areas was also evaluated. The relative standard deviation of intra-day variation for retention times and areas never exceeded of 0.1 and 10, respectively. The HPLC-ELSD method was also optimized to separate and quantify the hydrolysis products of alkoxyglycerols and acylglycerols (mono-esterified and non-esterified alkoxyglycerols and mono-esterified and di-esterified acylglycerols) at the same time, rendering a useful method for the study of lipase-catalyzed reactions and a wide variety of fats and oils. The present methodology not only separates 18 different lipid classes with a good reproducibility, but it is also able to estimate the relative proportion in which they are found in a broad range of concentrations.

Animals↗
PubMed2005

Influence of a fluorescent probe on the nanostructure of phospholipid membranes: dipalmitoylphosphatidylcholine interfacial monolayers.

Monolayers of dipalmitoylphosphatidylcholine (DPPC), both in the absence and in the presence of 1% (mol/mol) of a fluorescent phospholipid probe, have been spread at the air-liquid interface of a surface balance, compressed up to pressures in the liquid-expanded/liquid-condensed plateau of the isotherm, transferred onto mica supports, and analyzed by scanning force microscopy (SFM). Supported DPPC films showed micrometer-sized condensed domains with morphology and size that were entirely analogous to those observed in situ at the air-liquid interface by epifluorescence microscopy. The analysis by SFM, however, allowed the study and comparison of monolayers in the absence and in the presence of the fluorescent marker. This analysis revealed that the presence of dye reduced by 10-20% the total amount of the liquid-condensed phase in the DPPC films. The presence of the dye also decreased the mechanical stability of the film and increased the time required for the monolayer to equilibrate. The resolution of SFM permitted the determination that the structures of both the liquid-expanded and the liquid-condensed regions of DPPC films were heterogeneous at the nanometer scale. Liquid-condensed DPPC microdomains contained nanoholes covering 4-8% of their area whereas 60-80% of the surface detected as liquid-expanded by fluorescence microscopy consisted of a condensed-like framework of nanodomains. The total area, the shape of the nanodomains, and their interconnectivity were affected by the presence of the probe, suggesting that care must be taken when studying the structure, especially at the nanometer scale, and properties of model lipid films in the presence of extrinsic probes.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2005

In situ conformational analysis of fibrinogen adsorbed on Si surfaces.

Fibrinogen is a major plasma protein. Previous investigations of structural changes of fibrinogen due to adsorption are mostly based on indirect evidence after its desorption, whereas our measurements were performed on fibrinogen in its adsorbed state. Specific enzyme-linked immunosorption experiments showed that the amount of adsorbed fibrinogen increased as the surface became more hydrophobic. Atomic force microscopy (AFM) investigations revealed the trinodular shape of fibrinogen molecules adsorbed on hydrophilic surfaces, whereas all of the molecules appeared globular on hydrophobic surfaces. The distribution of secondary structures in adsorbed fibrinogen was quantified by in situ Fourier-transform infrared (FTIR) analysis. Substrates of identical chemical bulk composition but different surface hydrophobicity permit direct comparison among them. Adsorption properties of fibrinogen are different for each degree of hydrophobicity. Although there is some increase of turn structure and decrease of beta-sheet structure, the secondary structure of adsorbed fibrinogen on hydrophilic surface turned out to be rather similar to that of the protein in solution phase with a major alpha-helix content. Hydrophilic surfaces exhibit superior blood compatibility as required for medical applications.

Adsorption↗
PubMed2005

Self-organized ordering of nanostructures produced by ion-beam sputtering.

We study the self-organized ordering of nanostructures produced by ion-beam sputtering of targets amorphizing under irradiation. By introducing a model akin to models of pattern formation in aeolian sand dunes, we extend consistently the current continuum theory of erosion by IBS. We obtain new nonlinear effects responsible for the in-plane ordering of the structures, whose strength correlates with the degree of ordering found in experiments. Our results highlight the importance of redeposition and surface viscous flow to this nanopattern formation process.

Journal Article↗
PubMed2005

Molding and replication of ceramic surfaces with nanoscale resolution.

The design of reproducible and more efficient nanofabrication routes has become a very active research field in recent years. In particular, the development of new methods for micro- and nanopatterning materials surfaces has attracted the attention of many researchers in industry and academia as a consequence of the growing relevance of patterned surfaces in many technological fields, ranging from optoelectronics to biotechnology. In this work we explore, discuss, and demonstrate the possibility of extending the well-known molding and replication strategy for patterning ceramic materials with nanoscale resolution. To achieve this goal we have combined physical deposition methods, molecule-thick anti-sticking coatings, and nanostructured substrates as master surfaces. This new perspective on an "old technology", as molding is, provides an interesting alternative for high-resolution, direct surface-relief patterning of materials that currently requires expensive and time-consuming lithographic approaches.

Biocompatible Materials↗
PubMed2005

Insulin resistance impairs sustained response rate to peginterferon plus ribavirin in chronic hepatitis C patients.

BACKGROUND & AIMS: We evaluated the effect of insulin resistance and viral factors on sustained virological response in patients with chronic hepatitis C treated with peginterferon plus ribavirin. METHODS: Patients (n=159; 94 men; age, 41.7 +/- 11.1 years) with chronic hepatitis C (genotype 1, n=113; non-1 genotype, n=46) received treatment with interferon plus ribavirin. Serum levels of leptin and insulin were measured, and the insulin resistance index (HOMA-IR: homeostasis model of assessment) and body mass index were calculated. RESULTS: A sustained virological response was associated with lower age, insulin resistance index, body mass index, and gamma-glutamyltranspeptidase and serum leptin levels. There was no association with viral load, sex, type of interferon, or cholesterol levels. A sustained virological response was achieved in 43.4% (46/113) of genotype 1 and 89% (32/36) of genotype 2 and 3 (P=.0001) patients. Necroinflammatory activity and steatosis were not associated with the sustained virological response rate. Multivariate regression analysis indicated that the independent variables related to sustained virological response were genotype (odds ratio, 3.57; 95% confidence interval, 1.49-8.3; P=.001), insulin resistance index (odds ratio, 1.82; 95% confidence interval, 1.08-3.06; P=.012), and fibrosis (odds ratio, 1.36; 95% confidence interval, 1.01-1.84; P=.029). A sustained virological response in patients with genotype 1 and insulin resistance (HOMA-IR > 2) occurred in 23 of 70 (32.8%; 95% confidence interval, 21.9%-43.9%) patients, vs. 26 of 43 (60.5%; 95% confidence interval, 45.9%-75.1%) genotype 1 patients without insulin resistance (P=.007; odds ratio, 3.12, 95% confidence interval, 1.42-6.89). CONCLUSIONS: Insulin resistance, fibrosis, and genotype are independent predictors of the response to antiviral therapy in chronic hepatitis C patients treated with peginterferon plus ribavirin.

Adult↗
PubMed2004

Effect of pulmonary surfactant protein SP-B on the micro- and nanostructure of phospholipid films.

Monolayers of dipalmitoylphosphatidylcholine (DPPC) and DPPC/dipalmitoylphosphatidylglycerol (DPPG) (7:3, w/w) in the absence or in the presence of 2, 5, 10, or 20 weight percent of porcine surfactant protein SP-B were spread at the air-liquid interface of a surface balance, compressed up to surface pressures in the liquid-expanded/liquid-condensed (LE-LC) plateau of the isotherm, transferred onto mica supports, and analyzed by scanning force microscopy. In the absence of protein, the films showed micrometer-sized condensed domains with morphology and size that were analogous to those observed in situ at the air-liquid interface by epifluorescence microscopy. Scanning force microscopy permits examination of the coexisting phases at a higher resolution than previously achieved with fluorescent microscopy. Both LE and LC regions of DPPC films were heterogeneous in nature. LC microdomains contained numerous expanded-like islands whereas regions apparently liquid-expanded were covered by a condensed-like framework of interconnected nanodomains. Presence of increasing amounts of pulmonary surfactant protein SP-B affected the distribution of the LE and LC regions of DPPC and DPPC/DPPG films both at the microscopic and the nanoscopic level. The condensed microdomains became more numerous but their size decreased, resulting in an overall reduction of the amount of total LC phase in both DPPC and DPPC/DPPG films. At the nanoscopic level, SP-B also caused a marked reduction of the size of the condensed-like nanodomains in the LE phase and an increase in the length of the LE/LC interface. SP-B promotes a fine nanoscopic framework of lipid and lipid-protein nanodomains that is associated with a substantial mechanical resistance to film deformation and rupture as observed during film transference and manipulation. The effect of SP-B on the nanoscopic structure of the lipid films was greater in DPPC/DPPG than in pure DPPC films, indicating additional contributions of electrostatic lipid-protein interactions. The alterations of the nanoscopic structures of phospholipid films by SP-B provide the structural framework for the protein simultaneously sustaining structural stability as well as dynamical flexibility in surfactant films at the extreme conditions imposed by the respiratory mechanics. SP-B also formed segregated two-dimensional clusters that were associated with the boundaries between LC microdomains and the LE regions of DPPC and DPPC/DPPG films. The presence of these clusters at protein-to-lipid proportions above 2% by weight suggests that the concentration of SP-B in the surfactant lipid-protein complexes may be close to the solubility limit of the protein in the lipid films.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2002

Immobilization of peroxidase glycoprotein on gold electrodes modified with mixed epoxy-boronic Acid monolayers.

The development of bioelectronic enzyme applications requires the immobilization of active proteins onto solid or colloidal substrates such as gold. Coverage of the gold surface with alkanethiol self-assembled monolayers (SAMs) reduces nonspecific adsorption of proteins and also allows the incorporation onto the surface of ligands with affinity for complementary binding sites on native proteins. We present in this work a strategy for the covalent immobilization of glycosylated proteins previously adsorbed through weak, reversible interactions, on tailored SAMs. Boronic acids, which form cyclic esters with saccharides, are incorporated into SAMs to weakly adsorb the glycoprotein onto the electrode surface through their carbohydrate moiety. To prevent protein release from the electrode surface, we combine the affinity motif of boronates with the reactivity of epoxy groups to covalently link the protein to heterofunctional boronate-epoxy SAMs. The principle underlying our strategy is the increased immobilization rate achieved by the weak interaction-induced proximity effect between slow reacting oxyrane groups in the SAM and nucleophilic residues from adsorbed proteins, which allows the formation of very stable covalent bonds. This approach is exemplified by the use of phenylboronates-oxyrane mixed monolayers as a reactive support and redox-enzyme horseradish peroxidase as glycoprotein for the preparation of peroxidase electrodes. Quartz crystal microbalance, atomic force microscopy, and electrochemical measurements are used to characterize these enzymatic electrodes. These epoxy-boronate functional monolayers are versatile, stable interfaces, ready to incorporate glycoproteins by incubation under mild conditions.

Adsorption↗