Biomedical subjects

A Luquita

Publications and source records attributed to A Luquita.

7 recordsLinked to original sources

PubMed2005

Blood viscosity changes in experimentally Trypanosoma cruzi-infected rats.

Microcirculatory alterations would explain focal lesions found in Chagas' cardiomyopathy. Trypanosoma cruzi (T. cruzi) infection induces host blood properties modifications and defensive responses capable of producing blood hyperviscosity, an ischemic risk factor able to affect microvascular blood flow. We studied whole blood viscosity (eta(b)) and plasmatic and cellular factors influencing it in rats, 7 and 14 days after experimental infection with T. cruzi. Increased plasma viscosity (eta(p)) was found in infected versus control rats and it was correlated with high blood parasite levels at 7 days and enhanced gamma-globulin fraction concentration at 14 days. The hematocrit, mean corpuscular volume (MCV) and eta(b) were higher in 14 days infected rats vs. 7 days and control animals. Also, electron microscopy observation showed morphological changes in red blood cells (RBC) at 7 and 14 days post-infection, with increased proportion of echinocyte and stomatocyte shapes transformation. In our rat model of Chagas' disease, BPL, increased plasmatic protein concentration, enhanced MCV and RBC shapes transformation would determine blood hyperviscosity, cause of microvascular blood flow abnormalities.

Animals↗

PubMed2004

Haemorheological variables as a rheumatoid arthritis activity indicator.

OBJECTIVE: To investigate if blood hyperviscosity in RA patients is due to a reduced erythrocyte deformability and, therefore, turning it into a reliable activity indicator, as well as a therapy follow-up marker for this pathology. METHODS: (1) The haemorheological profile consisting of erythrocyte deformability, blood and plasma viscosity, and erythrocyte membrane fluidity was determined in 24 AR patients and 17 healthy controls. (2) A 4 year follow-up was carried on in 16 patients monitoring blood viscosity, erythrocyte deformability and biochemical variables in relation to clinical assessment of disease activity (Disease Activity Score "DAS 28-4"). RESULTS: Erythrocyte deformability and membrane fluidity were impaired in RA patients compared to controls (p<0.001). Blood viscosity was significantly increased and correlated with the cell rigidity index (r=0.85, p<0.0000) in RA patients. The follow-up showed a good correlation between haemorheological parameters and DAS 28-4 during disease evolution. CONCLUSION: our results support the hypothesis that in RA, blood hyperviscosity is determined by deformability loss, which in turn is due to a membrane rigidization. This could evidenced that a widespread cell membrane damage is expressed through an impaired erythrocyte deformability, turning haemorheological parameters into reliable tools to study disease evolution. The follow-up study enabled us to confirm that erythrocyte deformability is an efficient indicator of rheumatoid arthritis activity.

Adult↗

PubMed2001

Probing the determinants of coenzyme specificity in ferredoxin-NADP+ reductase by site-directed mutagenesis.

On the basis of sequence and three-dimensional structure comparison between Anabaena PCC7119 ferredoxin-NADP(+) reductase (FNR) and other reductases from its structurally related family that bind either NADP(+)/H or NAD(+)/H, a set of amino acid residues that might determine the FNR coenzyme specificity can be assigned. These residues include Thr-155, Ser-223, Arg-224, Arg-233 and Tyr-235. Systematic replacement of these amino acids was done to identify which of them are the main determinants of coenzyme specificity. Our data indicate that all of the residues interacting with the 2'-phosphate of NADP(+)/H in Anabaena FNR are not involved to the same extent in determining coenzyme specificity and affinity. Thus, it is found that Ser-223 and Tyr-235 are important for determining NADP(+)/H specificity and orientation with respect to the protein, whereas Arg-224 and Arg-233 provide only secondary interactions in Anabaena FNR. The analysis of the T155G FNR form also indicates that the determinants of coenzyme specificity are not only situated in the 2'-phosphate NADP(+)/H interacting region but that other regions of the protein must be involved. These regions, although not interacting directly with the coenzyme, must produce specific structural arrangements of the backbone chain that determine coenzyme specificity. The loop formed by residues 261-268 in Anabaena FNR must be one of these regions.

Amino Acid Sequence↗

PubMed2001

Influence of adsorbed plasma proteins on erythrocyte rheological properties: in vitro and ex vivo studies.

The influence of plasma protein adsorption on the mechanical properties characterizing erythrocyte behaviour under flow was studied in human and rats. The deformability index, elastic modulus and surface viscosity were measured by laser diffractometry. In in vitro studies, human and rat erythrocytes were washed to remove their original protein coating, and then incubated in saline-diluted plasma media. For erythrocytes incubated in the most diluted solutions (plasma/saline 1:3, v/v), the deformability index increased 30% for both species (human, P<0.01 and rat, P<0.2); the elastic modulus decreased 20% (human, P<0.05) and 60% (rat, P<0.01); and surface viscosity decreased 20% (human, P<0.05) and 40% (rat, P<0.01), relative to values for erythrocytes incubated in pure plasma. Ex vivo experiments were performed using rats. Plasma proteins were diluted replacing 15% volemic plasma by saline in three consecutive plasmapheresis steps. The rheological properties of erythrocytes, tested after each step, followed the general trends of the in vitro pattern. These results suggest that the decrease in plasma protein concentration affects blood rheology in two ways. The first is the well known decrease in plasma viscosity, and the second is an improvement of erythrocyte deformability, as has been shown in this work. Thus, a new argument supporting the benefits of normovolemic hemodilution in patients with poor peripheral perfusion is provided.

Adsorption↗

PubMed1998

Apoflavodoxin: structure, stability, and FMN binding.

Flavodoxins are one domain alpha/beta electron transfer proteins that participate in photosynthetic reactions. All flavodoxins carry a molecule of flavin mononucleotide (FMN), non-covalently bound, that confers redox properties to the protein. There are two structurally distinct flavodoxins, short ones and long flavodoxins; the latter contain an extra loop with unknown function. We have undertaken the study of the stability and folding of the apoflavodoxin from Anabaena (a long flavodoxin) and the analysis of the interaction between the apoflavodoxin and FMN. Our studies indicate that apoflavodoxin folds in a few seconds to a form that is competent in FMN binding. The stability of this apoflavodoxin is low and its urea denaturation can be described by a two-state mechanism. The role of the different parts of the apoflavodoxin in the stability and structure of the whole protein is being investigated using mutagenesis and specific cleavage to generate apoflavodoxin fragments. The X-ray structure of apoflavodoxin is very similar to that of its complex with FMN, the main difference being the conformation of the two aromatic residues that sandwich FMN in the complex. In apoflavodoxin these groups interact with each other so closing the FMN binding site. Despite this fact, apoflavodoxin binds FMN tightly and rapidly, and the resulting holoflavodoxin displays a high conformational stability. We have found that one role of the aromatic residues that interact with FMN is to help to retain bound the reduced form of the cofactor whose complex with apoflavodoxin is otherwise too weak.

Anabaena↗

PubMed1998

Effect of complement on the rheological properties of the erythrocyte membrane.

The effect of complement (C) on the erythrocyte deformability was investigated. Sheep erythrocytes (E) were sensitized with specific antibodies (A) and treated with various doses of human C. Gravity filtration of unlysed EAC showed a C dose-dependent decrease in whole cell deformability, which was shown to be due to an impairment of the membrane rheological properties. As the fluidity of the lipid bilayer, sensed by a spin label, was not modified, the observed effects should be related to an interaction between C and the cytoskeleton. The influence of C3b and C3d in these processes seems unlikely, as similar hemagglutination titers were found, respectively, for anti-C3c and anti-C3d antisera against the varying EAC. The study of the degree of spontaneous hemolysis of EAC in buffers with solutes of different Stokes radii showed that differing-sized functional C lesions were produced, and that the formation of larger-sized lesions was favored by incubation with higher C doses. These results suggest that the insertion of proteins from the membrane attack complex, C5b-9 (MAC), into the erythrocyte membrane may be responsible for the effect of C on the rheological properties of the erythrocyte membrane.

Animals↗

PubMed1996

Comparison between internal microviscosity of low-density erythrocytes and the microviscosity of hemoglobin solutions: an electron paramagnetic resonance study.

The hypothesis that the internal viscosity of erythrocytes is governed by the intracellular hemoglobin (Hb) concentration is examined. Here viscosity is determined by labeling of the cytoplasmic reduced glutathione with the spin label maleimido-Tempo. Erythrocyte populations with different Hb concentrations in isosmotic conditions were obtained through incomplete lysis, followed by cell resealing, and discontinuous density gradient separation. This procedure maintains normal cell shape and volume. Microviscosity of membrane-free Hb solutions was measured by addition of spin labeled glutathione. It was found that microviscosity values are similar for the erythrocyte cytoplasm and for Hb solutions of equivalent concentrations, showing that the erythrocyte membrane does not have any influence on internal microviscosity. The dependence of the microviscosity on the concentration of Hb solutions was compared with results of macroscopic viscosity obtained by other authors. It is concluded that microviscosity is sensitive to individual properties of the Hb molecule (intrinsic viscosity), but that it is not sensitive to intermolecular interactions. As the microviscosity behavior as a function of Hb concentration is the same in Hb solutions as in the erythrocyte cytoplasm, the inferences regarding macroscopic viscosity in Hb solutions could be translated to the rheological properties of the erythrocyte cytoplasm. Thus, these properties could be predicted from the values of the mean corpuscular Hb concentration.

Biophysical Phenomena↗