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Biomedical subjects

J M Merino

Publications and source records attributed to J M Merino.

At least 19 recordsLinked to original sources
PubMed2007

Microstructure and macroscopic properties of bioactive CaO-SiO2-PDMS hybrids.

CaO-SiO2-PDMS (polydimethylsiloxane) hybrid materials were synthesized as crack-free monoliths presenting in vitro bioactivity, i.e. able to be coated with a calcium phosphate-rich layer after having been soaked in simulated body fluid (SBF). A wide physical-chemical characterization of these materials was carried out to relate their microscopic structure and macroscopic properties. The effect of PDMS and the amounts of water used for the tetraethoxysilane (TEOS) hydrolysis on the mechanical properties of hybrid materials was investigated by three-point bending tests. For a given amount of water, as PDMS content in hybrids increased, the elastic modulus decreased. Furthermore, keeping the PDMS content constant, when the amount of H2O decreased, the elastic modulus increased. Regarding in vitro bioactivity and mechanical properties, the hybrid material obtained with molar ratios H2O/TEOS = 2 and TEOS/PDMS = 3.5 proved to be the best candidate for either soft tissue substitution or metallic implant coating since the hybrid material would promote bond to bone formation, simultaneously dampening the mechanical charges.

Biocompatible Materials↗
PubMed2005

Budesonide/formoterol maintenance and reliever therapy: an effective asthma treatment option?

This 12-month dose-titration study assessed the effectiveness of budesonide/formoterol for maintenance plus relief with a control group using salmeterol/fluticasone for maintenance plus salbutamol for relief. Adolescents and adults (n = 2,143; mean forced expiratory volume in one second (FEV1) 73% predicted; mean inhaled corticosteroid (ICS) 884 microg.day(-1)) were randomised to budesonide/formoterol 160/4.5 microg two inhalations b.i.d. plus additional inhalations as needed, or salmeterol/fluticasone 50/250 microg b.i.d. plus salbutamol as needed. Treatment was prescribed open label; after 4 weeks, physicians could titrate maintenance doses in accordance with normal clinical practice. Maintenance plus as-needed budesonide/formoterol prolonged the time to first severe exacerbation versus salmeterol/fluticasone (25% risk reduction). The total number of severe exacerbations was significantly reduced in the budesonide/formoterol group (255 versus 329). Both regimens provided sustained improvements in symptoms, as-needed use, quality of life and FEV1, with differences in favour of the budesonide/formoterol group for as-needed use (0.58 versus 0.93 inhalations.day(-1)) and FEV1 (post-beta2-agonist values). Mean ICS dose during treatment was similar in both groups (653 microg budesonide.day(-1) (maintenance plus as-needed) versus 583 microg fluticasone.day(-1)). The simplified strategy using budesonide/formoterol for maintenance and reliever therapy is feasible, safe and at least as effective as salmeterol/fluticasone plus salbutamol.

Adolescent↗
PubMed2001

The content of glycogen phosphorylase and glycogen in preparations of sarcoplasmic reticulum-glycogenolytic complex is enhanced in diabetic rat skeletal muscle.

AIMS/HYPOTHESIS: We have examined the effect of diabetes and pharmacological insulin treatment on the content of glycogen phosphorylase and glycogen associated with the sarcoplasmic reticulum-glycogenolytic complex from rat skeletal muscle. METHODS: Diabetes was induced in rats by streptozotocin injection. Enzymatic activities were measured using spectrophotometric methods. Glycogen phosphorylase was determined measuring the pyridoxal-5' -phosphate content and using polyacrylamide gel electrophoresis. Glycogen content was measured by enzymatic and the phenol sulfuric methods. RESULTS: The content of glycogen phosphorylase associated with the sarcoplasmic reticulum glycogenolytic complex gradually arises after diabetes induction. The content of glycogen phosphorylase was restored to a control value by pharmacological insulin treatment. In addition, the content of glycogen in preparations of sarcoplasmic reticulum-glycogenolytic complex of diabetic animals was also increased, whereas the content of glycogen in total muscle of diabetic rats was similar to that of the control rats. The absolute and relative amount of glycogen associated with sarcoplasmic reticulum seemed to increase in diabetic animals. These effects on the compartmentalisation of glycogen were suppressed by insulin treatment. Additionally, the rate of conversion of glycogen phosphorylase b to a, an index of the phosphorylase kinase activity, was 50 % lower in diabetic rats, increasing the dephosphorylated form of glycogen phosphorylase and, as a consequence, its association with sarcoplasmic reticulum membranes. CONCLUSION/INTERPRETATION: These results suggest that under diabetic conditions, both glycogen phosphorylase and a small percentage of muscle glycogen are relocalized in the sarcoplasmic reticulum-glycogenolytic complex.

Animals↗
PubMed2001

Microbiology of pediatric primary pulmonary tuberculosis.

OBJECTIVE: To determine the sensitivity of bacteriologic studies in pediatric pulmonary tuberculosis. PATIENTS AND METHODS: Between January 1988 and December 1996, 104 consecutive patients aged 0 to 18 years received a diagnosis of primary pulmonary tuberculosis at our institution. Demographic, clinical, laboratory, and bacteriologic data were collected. Clinical specimens were studied for acid-fast bacilli detection by Ziehl-Neelsen stain and cultured for Mycobacterium recovery by Lowenstein-Jensen culture medium. Statistical analysis was performed utilizing chi(2), t tests, and multivariate logistic regression analysis. RESULTS: Bacteriologic results were available for 57 patients (54.8%). A positive smear or culture result for Mycobacterium tuberculosis was obtained in 9 of 54 patients (16.6%) and 25 of 50 patients (50%), respectively. Confirmation of M tuberculosis disease was achieved in 28 patients (49.1%). Ziehl-Neelsen stain and Lowenstein-Jensen culture recovery rates were 10.3% (14 of 135) and 52% (48 of 92) of specimens studied, respectively. Sputum, pleural fluid, and biopsy material cultures yielded M tuberculosis in 55%, 75%, and 63% of patients, respectively. Mean +/- SD age (13.7 +/- 4.5 years vs 9.6 +/- 4.5 years) and number of samples submitted for culture (1.93 +/- 0.94 vs 1.31 +/- 0.97) were significantly higher in the confirmed tuberculosis disease group (p < 0.05). The presence of a pleural effusion was also more commonly found in the confirmed tuberculosis disease group (p < 0.05). CONCLUSION: The sensitivity of bacteriologic studies in pediatric pulmonary tuberculosis disease was 49.1%. Age is the main factor associated with the positivity of culture results.

Adolescent↗
PubMed2000

Identification of an aspartic residue in the P-loop of the vanilloid receptor that modulates pore properties.

Vanilloid receptor subunit 1 (VR1) is a nonselective cation channel that integrates multiple pain-producing stimuli. VR1 channels are blocked with high efficacy by the well established noncompetitive antagonist ruthenium red and exhibit high permeability to divalent cations. The molecular determinants that define these functional properties remain elusive. We have addressed this question and evaluated by site-specific neutralization the contribution on pore properties of acidic residues located in the putative VR1 pore region. Mutant receptors expressed in Xenopus oocytes exhibited capsaicin-operated ionic currents akin to those of wild type channels. Incorporation of glutamine residues at Glu(648) and Glu(651) rendered minor effects on VR1 pore attributes, while Glu(636) slightly modulated pore blockade. In contrast, replacement of Asp(646) by asparagine decreased 10-fold ruthenium red blockade efficacy and reduced 4-fold the relative permeability of the divalent cation Mg(2+) with respect to Na(+) without changing the selectivity of monovalent cations. At variance with wild type channels and E636Q, E648Q, and E651Q mutant receptors, ruthenium red blockade of D646N mutants was weakly sensitive to extracellular pH acidification. Collectively, our results suggest that Asp(646) is a molecular determinant of VR1 pore properties and imply that this residue may form a ring of negative charges that structures a high affinity binding site for cationic molecules at the extracellular entryway.

Amino Acid Sequence↗
PubMed2000

Arginine-rich peptides are blockers of VR-1 channels with analgesic activity.

Vanilloid receptors (VRs) play a fundamental role in the transduction of peripheral tissue injury and/or inflammation responses. Molecules that antagonize VR channel activity may act as selective and potent analgesics. We report that synthetic arginine-rich hexapeptides block heterologously expressed VR-1 channels with submicromolar efficacy in a weak voltage-dependent manner, consistent with a binding site located near/at the entryway of the aqueous pore. Dynorphins, natural arginine-rich peptides, also blocked VR-1 activity with micromolar affinity. Notably, synthetic and natural arginine-rich peptides attenuated the ocular irritation produced by topical capsaicin application onto the eyes of experimental animals. Taken together, our results imply that arginine-rich peptides are VR-1 channel blockers with analgesic activity. These findings may expand the development of novel analgesics by targeting receptor sites distinct from the capsaicin binding site.

Amino Acid Sequence↗
PubMed1999

pH and ligand binding modulate the strength of protein-protein interactions in the Ca(2+)-ATPase from sarcoplasmic reticulum membranes.

The Ca(2+)-ATPase from sarcoplasmic reticulum (SR) membranes couples the Ca(2+) transport to ATP hydrolysis through phosphorylation in its cytoplasmic catalytic domain. Interactions between protein domains and the role of monomer-monomer interactions remain unclear. Here, we report a differential scanning calorimetric study of the thermal unfolding of this protein. In the pH range 6-8, thermal unfolding of the Ca(2+)-ATPase in glycogen phosphorylase-free SR membranes shows a major endothermic peak with a critical temperature midpoint ranging between 51 and 55 degrees C, depending on pH, Ca(2+), Mg(2+)-ADP and KCl concentrations. The enthalpy change of the overall unfolding process ranged between 250 and 300 kcal/mol of Ca(2+)-ATPase monomer. Thermal denaturation of the Ca(2+)-ATPase in SR membranes is well fitted to an irreversible process that can be rationalized in terms of a non-two state process, N (native)right harpoon over left harpoon I (intermediate)-->D (denatured). Thermodynamic analysis show that this protein has a compact structure, implying a tight structural interconnection between catalytic and Ca(2+) transport domains. The apparent cooperative unit, defined by the van 't Hoff enthalpy to the overall unfolding enthalpy ratio, increased from 1.1 at pH 6 to 1.8 at pH 8, showing that monomer-monomer interactions are stronger at weakly basic pH than at weakly acidic pH. While micromolar Ca(2+) concentrations had only a weak effect on the cooperativity of the unfolding process, this is clearly increased by millimolar Mg(2+)-ADP. In addition, high ionic strength lowered the apparent cooperative unit to approximately 1.0 in the pH range 6-8. Taken together, these results suggest that protein-protein interactions are altered by variables that modulate the catalytic activity of this enzyme.

Animals↗
PubMed1999

Plausible stoichiometry of the interacting nucleotide-binding sites in the Ca(2+)-ATPase from sarcoplasmic reticulum membranes.

The Ca(2+),Mg(2+)-ATPase from sarcoplasmic reticulum couples ATP hydrolysis to Ca(2+) transport toward the lumen of the muscular vesicular system. Combined structural and functional studies suggest that the Ca(2+) binding sites are formed by six amino acids of the same polypeptide and that cation translocation may take place through a channel inside a monomer of the ATPase. However, calorimetric, fluorescent, and kinetic studies suggest that the ATPase may assemble into functional oligomers of as yet unknown stoichiometry. We have addressed this question and attempted to determine the ATPase stoichiometry using a biophysical approach based on the analysis of the ATPase inhibition by fluorescein 5'-isothiocyanate in the presence of increasing ATP concentrations. For native SR membranes, our inhibition data are well described by a model consisting of two interacting nucleotide-binding sites per oligomer. This stoichiometry was disrupted in detergent C(12)E(8)-solubilized ATPase. Thus, these findings suggest that interacting nucleotide binding sites of the ATPase may appear as dimers, and imply that interactions of the globular cytoplasmic domains would play a modulatory role of the protein enzymatic activity.

Animals↗
PubMed1999

A multidimensional modeling of predictors influencing the adjustment to a colostomy.

PURPOSE: Factors contributing to the postoperative adjustment of patients who had undergone permanent colostomy surgery were studied. DESIGN: Cross-sectional study. SETTING AND SUBJECTS: Sixty patients who underwent colostomy surgery at 5 hospitals in Santiago, Chile, between 1987 and 1995 were evaluated. Subjects were between the ages of 27 and 89 and underwent colostomy surgery from 4 months to 19 years before data collection. METHODS AND INSTRUMENTS: A demographic questionnaire and a semistructured interview were used to elicit information concerning psychosocial reactions to a colostomy and perceptions about the changes in lifestyle created by the ostomy. Medical records were reviewed for information about disease-related characteristics and an ostomy self-care scale measured coping skills. Adjustment to the colostomy procedure was measured by means of the Olbrisch ostomy adjustment scale. RESULTS: Patient adaptation to a colostomy is primarily affected by the following factors: (1) the level of ostomy self-care, (2) psychological support, and (3) social support from family and significant others. CONCLUSION: Successful adjustment to a permanent colostomy is most likely to occur if the patient receives adequate instruction in self-care and has the appropriate psychological support to integrate the new physical changes into a healthy body image. This includes continued acceptance from family and the patient's social network.

Adaptation, Psychological↗
PubMed1999

Tuberculous pleural effusion in children.

STUDY OBJECTIVES: To describe the age distribution, clinical, laboratory, radiographic, and bacteriologic findings of pediatric patients with tuberculous pleural effusion. DESIGN: A retrospective study. PATIENTS AND METHODS: We have identified all cases of primary pulmonary tuberculosis in children < 18 years, reported to the health department. We have collected information from medical records regarding demographics, clinical findings, bacteriologic results, and evolution. Chest radiographs obtained at the time of initial evaluation were reviewed independently by two groups of radiologists who were blind to the clinical and epidemiologic data. RESULTS: Between January 1983 and December 1996, 175 children < 18 years were diagnosed as having primary pulmonary tuberculosis. Among them, 39 patients (22.1%) showed pleural effusion on chest radiograph. The mean age of patients with tuberculous pleural effusion was significantly higher (13.52+/-0.5 years vs 6.97+/-0.42 years). The sensitivity of the tuberculin test is 97.4% for an induration > or = 5 mm. Pleural fluid analysis shows a lymphocytic exudative effusion. Chest radiograph review showed unilateral pleural effusion in all cases. Pleural effusion was the sole radiographic manifestation in 41% of cases. Parenchymal disease is associated in 23 cases (59%). Bacteriologic confirmation of tuberculosis was achieved in 22 cases (56.4%). Cultures of pleural fluid and biopsy material both yielded Mycobacterium tuberculosis in 15 of 34 (44.1%) and 12 of 18 (66.6%), respectively, for samples under study. Pleural biopsy specimens showed granulomatous inflammation in 18 of 23 cases (78.3%). Antituberculous therapy for 6 to 9 months was effective in all cases. Transient side effects occurred in 1 of 39 patients (2.9%). CONCLUSIONS: Pleural effusion accounts for 22.1% of cases of pediatric pulmonary tuberculosis. Parenchymal consolidation is the most common associated radiographic finding. Bacteriologic confirmation was achieved in 56.4% of cases. A short course of chemotherapy is effective.

Adolescent↗
PubMed1999

[Factors which determine the psychological adjustment to permanent colostomies. An empirical study in Santiago, Chile].

BACKGROUND: The acceptance of a colostomy by a patient requires a great amount of psychological resources and social support. AIM: To identify factors that influence the postoperative adaptation to a colostomy. PATIENTS AND METHODS: Sixty patients subjected to a colostomy in 5 hospitals in Santiago were interviewed. The adaptation to the procedure was assessed using the Olsbrisch Ostomy Adjustment Scale. Three regression equations were elaborated to determine the main predictors associated to adaptation. Control variables such as sex, age and the lapse between the interview and the surgical procedure, were included in the model. RESULTS: The model used identified the simultaneous and combined effects of socioeconomic variables such as education and income on the adaptation to colostomy. A generalized detriment of the self image was detected. Patients valued the social support given by the family and friends. Multiple regression analysis determined that the main predictor of the patient's adaptation to colostomy was the level of self care developed. CONCLUSIONS: The better adaptation to a colostomy could be achieved by training the patient for an adequate self care and providing him with psychological and social support.

Adaptation, Psychological↗
PubMed1998

Structural determinants of the blocker binding site in glutamate and NMDA receptor channels.

Glutamate receptor channels of the NMDA-type (N-methyl-D-aspartate) and non-NMDA-type (GluR) differ in their pore properties. The N-site in the M2 transmembrane segment of NMDA receptors (NMDAR), or the corresponding Q/R-site in GluRs, is a pivotal structural determinant of their permeation and blockade characteristics. Substitutions at a second site in M2, the L-site (L577) in GluR1, drastically alter the receptor selectivity to divalent cations. Here we report that M2 mutants carrying an asparagine or a threonine residue at the Q-site of GluR1, along with a tryptophan residue at the L-site, form homomeric GluR1 channels that are highly sensitive to structurally diverse, uncompetitive NMDA antagonists such as arylcyclohexylamines, dibenzocycloheptenimines, and to morphinian and adamantane derivatives. Analysis of the voltage dependence of channel blockade locates the blocker binding site approximately 0.65 partway into the transmembrane electric field in both GluR1 mutants and NMDAR channels. Our results suggest that the homomeric GluR1 double mutants, L577W/Q582N and L577W/Q582T, fairly approximate the pore properties of the heteromeric NMDA receptor and support the structural kinship of their permeation pathways.

Amino Acid Substitution↗
PubMed1998

Selected peptides targeted to the NMDA receptor channel protect neurons from excitotoxic death.

Excitotoxic neuronal death, associated with neurodegeneration and stroke, is triggered primarily by massive Ca2+ influx arising from overactivation of glutamate receptor channels of the N-methyl-D-aspartate (NMDA) subtype. To search for channel blockers, synthetic combinatorial libraries were assayed for block of agonist-evoked currents by the human NR1-NR2A NMDA receptor subunits expressed in amphibian oocytes. A set of arginine-rich hexapeptides selectively blocked the NMDA receptor channel with IC50 approximately 100 nM, a potency similar to clinically tolerated blockers such as memantine, and only marginally blocked on non-NMDA glutamate receptors. These peptides prevent neuronal cell death elicited by an excitotoxic insult on hippocampal cultures.

Animals↗
PubMed1997

Structural changes of the sarcoplasmic reticulum Ca(II)-ATPase nucleotide binding domain by pH and La(III).

The Ca(2+)-ATPase from sarcoplasmic reticulum couples the hydrolysis of one molecule of ATP to the transport of two Ca2+ ions in skeletal muscle fibers. Here, we study the accessibility of the fluorescein covalently attached to the Lys515 at the nucleotide binding domain of the ATPase to the small collisional quencher iodide at pH 6 and 8, as well as the effect of ligand binding (La3+, La(3+)-nucleotide, and Ca2+). Our results indicate that bound fluorescein is significantly more accessible at pH 6 than at pH 8, suggesting that pH modulates the structure of the nucleotide binding domain of the ATPase. This notion was further substantiated by the finding that La(3+)-nucleotide only interacted with the catalytic center at acidic pH. Notably, the differential accessibility of the nucleotide binding domain at acidic and basic pH cannot be rationalized in terms of the ATPase E1/E2 conformational equilibrium since a shift of the ATPase toward the E1 (plus Ca2+) or E2 (plus EGTA) did not affect the accessibility of fluorescein-labeled ATPase to the quencher. Taken together, these findings show the presence of structural flexibility in the FITC binding site and suggest a structural modulation of the Ca(2+)-ATPase nucleotide binding domain by pH and La3+ binding through long-range link-age mechanisms.

Adenosine Diphosphate↗
PubMed1996

Pediatric experience with autologous peripheral blood progenitor cell transplantation: influence of CD34+ cell dose in engraftment kinetics.

The aim of this study was to analyze factors affecting mobilization and engraftment in 40 children undergoing autologous peripheral blood progenitor cell transplantation for different malignancies: 19 patients with haematological malignancies and 21 patients with solid tumors. Patients received 4-5 days of rhG-CSF (12 micrograms/kg/day) subcutaneously. Apheresis was performed by continuous flow blood cell separation beginning on the fifth day of rhG-CSF. For patients weighing < or = 25 kg, the extracorporeal line was primed with irradiated red blood cells. After myeloablative conditioning regimens, patients were grafted with 7.21 +/- 7.8 x 10(6)/kg CD34+ cells. Days to achieve an absolute neutrophil count > 0.5 x 10(9)/1 and a platelet count > 20 x 10(9)/1 without platelet support were 9.50 +/- 1.2 (range 7-13) and 18.1 +/- 8.3 (range 9-37), respectively. The number of CD34+ cells infused was highly correlated with engraftment kinetics (P = 0.0001). The patient's body weight and the number of previous chemotherapy courses had a negative influence on CD34+ cells collected.

Adolescent↗
PubMed1995

Mg(2+)-ADP protects against inactivation of sarcoplasmic reticulum Ca2+,Mg(2+)-ATPase by N-cyclohexyl-N'-(4-dimethylamino-alpha-naphthyl) carbodiimide.

N-cyclohexyl-N'-(4-dimethylamino-alpha-naphthyl) carbodiimide (NCD-4) inactivates the sarcoplasmic reticulum Ca(2+)-ATPase by covalent labelling at or near the high affinity (transport) Ca2+ sites. Mg(2+)-ADP protects against the inactivation of the Ca(2+)-ATPase produced by NCD-4, with a K0.5 of Mg(2+)-ADP of 28 +/- 6 microM for purified Ca(2+)-ATPase. With native and solubilized sarcoplasmic reticulum membranes millimolar Mg(2+)-ADP concentrations are needed to produce an effective protection of the Ca(2+)-ATPase against inactivation by NCD-4. These results suggest a tight structural interconnection between catalytic and transport Ca2+ sites in the Ca(2+)-ATPase, modulated by protein-protein interactions in the SR membrane.

Adenosine Diphosphate↗
PubMed1994

Thermal unfolding of monomeric Ca(II), Mg(II)-ATPase from sarcoplasmic reticulum of rabbit skeletal muscle.

The thermal unfolding of monomeric and delipidated Ca(2+)-ATPase, solubilized in C12E8, can be appropriately described as a non-two-state irreversible denaturation, with only one endothermic peak. In the Ca2+ concentration range (0-0.5 mM) which stimulates the ATPase activity of solubilized monomeric ATPase, Ca2+ shifts the critical temperature midpoint of the denaturation process (Tm) from 42 to 50 degrees C without segregation of the endothermic peak into two separate components. Because 20 mM Mg2+ only shifts the Tm from 42 to 44 degrees C, we conclude that the effect of Ca2+ upon the Tm is likely to be due to binding to the high affinity Ca2+ sites in the ATPase. The effect of Ca2+ upon the enthalpy of denaturation is biphasic, suggesting the presence of low affinity Ca2+ sites (K0.5 in the millimolar range) in monomeric and solubilized ATPase.

Animals↗