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M Vives

Publications and source records attributed to M Vives.

At least 19 recordsLinked to original sources
PubMed2002

Study of the influence of metal ions on tRNA(Phe) thermal unfolding equilibria by UV spectroscopy and multivariate curve resolution.

The influence of metal ions (Na(+), Mg(2+) and Cd(2+)) on the thermal unfolding of phenylalanine transfer ribonucleic acid (tRNA(Phe)) was studied by UV spectroscopy-monitored melting experiments. Absorbance data were obtained during the unfolding process in the range 220-340 nm and later analyzed by a multivariate curve resolution approach (MCR-ALS) based on factor analysis. This procedure determines the number of spectroscopically distinct conformations present during the unfolding process and reveals their concentration profiles and pure spectra, without any initial assumption having to be made about the number of steps in the unfolding pathway. From the concentration profiles and pure spectra, information such as T(m) values can be recovered. The results were compared with those obtained previously in spectroscopic and calorimetric unfolding experiments, showing that the multivariate approach recovers information that complements that obtained in traditional spectroscopic melting experiments.

Cadmium↗
PubMed2001

Analytical characterization of the conformational transitions of polynucleotides by means of different molecular spectroscopies and multivariate curve resolution.

A general procedure for the study of conformational transitions of polynucleotides is described. The equilibria between different conformations induced by salt, ethidium bromide, and temperature of poly(dG-dC). poly(dG-dC) and induced by salt and temperature of poly(A). poly(U) are investigated using molecular absorption, circular dichroism, and fluorescence spectroscopies. Spectral data obtained from experiments are analyzed by means of a factor analysis method, namely, multivariate curve resolution, which allows possible intermediate states to be detected and the pure spectra and the concentration profiles of all species present in the system to be estimated. This work shows the application of this procedure for the analysis of data matrices obtained in individual experiments but also for the analysis of several data matrices simultaneously.

Circular Dichroism↗
PubMed2001

Three-way multivariate curve resolution applied to speciation of acid-base and thermal unfolding transitions of an alternating polynucleotide.

Analytical speciation of acid-base equilibria and thermal unfolding transitions of an alternating random polynucleotide containing cytosine and hypoxanthine, poly(C, I), is studied. The results are compared with those obtained previously for single-stranded polynucleotides, poly(I) and poly(C), and for the double-stranded poly(I). poly(C), to examine the influence of the secondary structure on the acid-base properties of bases. This study is based on monitoring acid-base titrations and thermal unfolding experiments by molecular absorption, CD, and molecular fluorescence spectroscopies. Experimental data were analyzed by a novel chemometric approach based on a recently developed three-way Multivariate Curve Resolution method, which allowed the simultaneous analysis of data from several spectroscopies. This procedure improves the resolution of the concentration profiles and pure spectra for the species and conformations present in folding-unfolding and acid-base equilibria. The results from acid-base studies showed the existence of only three species in the pH range 2-12 at 37 degrees C and 0.15M ionic strength. No cooperative effects were detected from the resolved concentration profiles, showing that equilibria concerning alternating polynucleotides like poly(C, I) are simpler than those involving poly(I). poly(C). Thermal unfolding experiments at neutral pH confirmed the existence of two transitions and one intermediate conformation. This intermediate conformation could only be detected and resolved without ambiguities when molecular absorption and CD spectral data were analyzed simultaneously.

Algorithms↗
PubMed2001

Protonation studies and multivariate curve resolution on oligodeoxynucleotides carrying the mutagenic base 2-aminopurine.

2-Aminopurine (P) is a mutagen causing A.T to G.C transitions in prokaryotic systems. To study the base-pairing schemes between P and cytosine (C) or thymine (T), two self-complementary dodecamers containing P paired with either C or T were synthesized, and their protonation equilibria were studied by acid-base titrations and melting experiments. The mismatches were incorporated into the self-complementary sequence d(CGCPCCGGXGCG), where X was C or T. Spectroscopic data obtained from molecular absorption, circular dichroism (CD), and molecular fluorescence spectroscopy were analyzed by a factor-analysis-based method, multivariate curve resolution based on the alternating least squares optimization procedure (MCR-ALS). This procedure allows determination of the number of acid-base species or conformations present in an acid-base or melting experiment and the resolution of the concentration profiles and pure spectra for each of them. Acid-base experiments have shown that at pH 7, 150 mM ionic strength, and 37 degrees C, both C and P are deprotonated. At pH near 4, the majority of species shows C protonated and P deprotonated. Finally, at pH values near 3, the majority of species shows both protonated C and P. These results are in agreement with NMR studies showing a wobble geometry for the P x C base pair and a Watson-Crick geometry for the P x T base pair at neutral pH. Melting experiments were carried out to confirm the proposed acid-base distribution profile. For the sequence including the P x T mismatch, only one transition was observed at neutral pH. However, for the sequence including the P x C mismatch, two transitions were detected by CD but only one by molecular absorption. This behavior agrees with that observed by other authors for oligonucleotides of similar sequence and suggests the following sequence of conformational changes during melting: duplex --> hairpin --> random coil.

2-Aminopurine↗
PubMed2001

Study of the interaction of cis-dichloro-(1,2 diethyl-3-aminopyrrolidine)Pt(II) complex with poly(I), poly(C) and poly(I) x poly(C).

The interaction of cis-dichloro-(1,2 diethyl-3-aminopyrrolidine)platinum(II) (Ptpyrr) with the polynucleotides poly(I), poly(C) and poly(I) x poly(C) acids was studied by circular dichroism, molecular fluorescence and (1)H NMR spectroscopies. Multivariate Curve Resolution, a factor analysis method, was applied for the analysis and interpretation of spectroscopic data obtained in mole ratio and kinetics studies. This procedure allows the determination of the number of different interaction complexes present during the experiments and the resolution of both concentration profiles and pure spectra for all of them. Two different interaction complexes were observed at the experimental conditions studied. The first one, at low Ptpyrr:polynucleotide ratio (r(Ptpyrr:poly)) values, corresponds to the interaction of Ptpyrr with hypoxanthine bases in the poly(I) moiety. This interaction leads to the destabilization and dissociation of the double-stranded conformation. The second complex was observed at higher r(Ptpyrr:poly) values and corresponds to the interaction of Ptpyrr to cytosine bases in poly(C) moiety. The formation of both complexes showed that the interaction of Ptpyrr with hypoxanthine bases occurred at the first stages of the reaction and with cytosine bases at longer reaction times. The results obtained show the utility of the Multivariate Curve Resolution approach for the analysis of data obtained by monitoring spectroscopically the interaction equilibria of platinum compounds with nucleic acids.

Circular Dichroism↗
PubMed2001

Useful tests on pleural fluid that distinguish transudates from exudates.

We aimed to compare the classic Light's criteria with different testing strategies in an effort to improve the accuracy of pleural fluid (PF) categorization. Thirty-two patients with transudates and 140 with exudates on the basis of their clinical diagnosis were entered into the study. We examined the discriminative properties of 10 analytes in the identification of PF, both singly and in combination with an 'or' rule, to see which was best in distinguishing a transudate from an exudate. A combination of PF lactate dehydrogenase (LD) > 307 U/L (two-thirds of the upper limit of the serum LD reference range) with either PF cholesterol > 1.55 mmol/L or PF to serum protein ratio > 0.5 had a diagnostic accuracy similar to that of Light's criteria. We suggest the use of PF LD and cholesterol in combination as an alternative method for distinguishing pleural transudates from exudates. This test combination avoids the need for venepuncture and the simultaneous collection of a blood sample.

Adult↗
PubMed2000

Community-acquired pneumonia: development of a bedside predictive model and scoring system to identify the aetiology.

Although initial presentation has been commonly used to select empirical therapy in patients with community-acquired pneumonia (CAP), few studies have provided a quantitative estimation of its value. The objective of this study was to analyse whether a combination of basic clinical and laboratory information performed at bedside can accurately predict the aetiology of pneumonia. A prospective study was developed among patients admitted to the Emergency Department University Hospital Arnau de Vilanova, Lleida, Spain, with CAP. Informed consent was obtained from patients in the study. At entry, basic clinical (age, comorbidity, symptoms and physical findings) and laboratory (white blood cell count) information commonly used by clinicians in the management of respiratory infections, was recorded. According to microbiological results, patients were assigned to the following categories: bacterial (Streptococcus pneumoniae and other pyogenic bacteria), virus-like (Mycoplasma pneumoniae, Chlamydia spp and virus) and unknown pneumonia. A scoring system to identify the aetiology was derived from the odds ratio (OR) assigned to independent variables, adjusted by a logistic regression model. The accuracy of the prediction rule was tested by using receiver operating characteristic curves. One hundred and three consecutive patients were classified as having virus-like (48), bacterial (37) and unknown (18) pneumonia, respectively. Independent predictors related to bacterial pneumonia were an acute onset of symptoms (OR 31; 95% CI, 6-150), age greater than 65 or comorbidity (OR 6.9; 95% CI, 2-23), and leukocytosis or leukopenia (OR 2; 95% CI, 0.6-7). The sensitivity and specificity of the scoring system to identify patients with bacterial pneumonia were 89% and 94%, respectively. The prediction rule developed from these three variables classified the aetiology of pneumonia with a ROC curve area of 0.84. Proper use of basic clinical and laboratory information is useful to identify the aetiology of CAP. The prediction rule may help clinicians to choose initial antibiotic therapy.

Adolescent↗
PubMed2000

Pleural SC5b-9: a test for identifying complicated parapneumonic effusions.

UNLABELLED: BACKGROUND AND OBJECTIVES We have tested whether the complement activation products SC5b-9 and C3a-desArg are useful to distinguish complicated (CPE) from uncomplicated parapneumonic effusions (UPE). DESIGN: A total of 66 patients were enrolled in the study: 5 with empyema, 19 with CPE, 12 with UPE, and 30 transudates who served as controls. SC5b-9 and C3a-desArg were measured by commercial ELISA tests, and their performances were evaluated using receiver operating characteristic (ROC) analysis. RESULTS: Patients with CPE had higher mean levels of pleural SC5b-9 (8,218 microg/l) and C3a-desArg (8,790 microg/l) than those with UPE (2,227 and 3,772 microg/l, respectively; p < 0.0001), whereas concentrations in the latter were comparable with controls for the SC5b-9 test. Empyemas had a wide range of pleural complement activation product values. Pleural SC5b-9 and C3a-desArg showed very high diagnostic accuracy in the diagnosis CPE (90.3 and 77.8%, respectively) when corresponding cutoff points of 2,000 and 4,000 microg/l were used. In a stepwise logistic regression analysis, the combination of SC5b-9 >/=2,000 microg/l, LDH >/=1,000 U/l and a pleural polymorphonuclear percentage >/=85% provided the highest discriminative power for the diagnosis of CPE (area under ROC curve 0.97). CONCLUSION: This pilot study suggests that measurement of pleural SC5b-9 can be useful in the workup of patients with a parapneumonic effusion in order to differentiate CPE from UPE.

Adult↗
PubMed2000

Usefulness of pleural complement activation products in differentiating tuberculosis and malignant effusions.

OBJECTIVE: To determine whether measurement of the complement activation products SC5b-9 and C3a-desArg in pleural fluid can reliably differentiate tuberculous from malignant pleural effusions. DESIGN: Twenty-four patients with tuberculous pleuritis, 29 with malignant pleural effusion, and 30 control subjects with transudates were enrolled in the study. SCSb-9 and C3a-desArg were measured in pleural fluid using commercial ELISA tests, and their performances were evaluated using receiver operating characteristic (ROC) analysis. RESULTS: Patients with tuberculous pleuritis had higher mean levels of pleural SC5b-9 (5052 microg/L) and C3a-desArg (7436 microg/L) than those with malignant effusions (1048 and 2835 microg/L, respectively), whereas only SC5b-9 concentrations in the latter were comparable with controls. The area under the ROC curve (AUC) was 0.84 for SC5b-9 and 0.81 for C3a-desArg. Pleural SC5b-9 showed an accuracy of 80.8%, compared with 78.8% for C3a-desArg, when cut-off points of 1500 and 4500 microg/L, respectively, were used. Using a stepwise logistic regression model, the combination of pleural SCSb-9 > or =1500 microg/L, age < or =35 years, and pleural monocyte percentage > or =90% provided the highest accuracy for tuberculous pleurisy (88.5%, AUC 0.95). CONCLUSION: This pilot study suggests that pleural SC5b-9 is clinically useful for differentiating tuberculous and malignant pleural effusions.

Adult↗
PubMed2000

Diagnosis of tuberculous pleuritis by the measurement of soluble interleukin 2 receptor in pleural fluid.

OBJECTIVE: As soluble interleukin-2 receptor (sIL-2R) is a marker of T-lymphocyte activation, we sought to determine whether its measurement in pleural fluid is diagnostically useful in tuberculous pleurisy. DESIGN: We compared the concentrations of sIL-2R in pleural samples of 23 patients with tuberculous pleurisy and 109 patients with non-tuberculous effusions (34 malignant, 34 parapneumonic, 27 transudates and 14 miscellaneous). sIL-2R was measured by a commercial ELISA test and its performance was evaluated using receiver operating characteristic (ROC) analysis. RESULTS: The mean values of pleural sIL-2R were 9179 U/mL in patients with tuberculous pleurisy vs 3664 U/mL in patients with malignancy, 2603 U/mL in patients with parapneumonic effusions, 1016 U/mL in patients with transudates, and 1906 U/mL in patients with miscellaneous diseases (P < 0.0001). A ROC curve identified the best cut-off at 4700 U/mL, yielding measures for sensitivity (0.91), specificity (0.94) and accuracy (0.94). CONCLUSIONS: The results of this pilot study suggest that pleural sIL-2R appears to be clinically useful for differentiating between tuberculous and non-tuberculous pleural effusions.

Adolescent↗
PubMed1998

Comparative analysis of Light's criteria and other biochemical parameters for distinguishing transudates from exudates.

OBJECTIVES: To compare the accuracy of Light's criteria for categorizing a pleural effusion as an exudate with several alternative criteria. DESIGN: Prospective evaluation of patients who underwent a diagnostic thoracocentesis. SETTING: Community teaching hospital in Lleida, Spain. PATIENTS AND METHODS: Medical records and pleural fluid characteristics of 241 consecutive patients with pleural effusion admitted over a 29-month period were reviewed. Forty eight of these patients were excluded for different reasons. Light's criteria and a different cutoff level for the pleural fluid cholesterol level were applied and their accuracies were calculated. RESULTS: Of the 193 patients included, 38 (20%) had transudates and 155 (80%) exudates. The accuracy of Light's criteria for identifying exudates was 92% [confidence intervals (CI), 88-96%], with a sensitivity of 97% (CI, 94-100%) and specificity of 71% (CI, 57-85%). A cutoff level of 50 mg dl-1 was selected for pleural cholesterol, which yielded a sensitivity and specificity of 84% (CI, 79-90%), with an accuracy of 84% (CI, 72-96%). Overall, pleural cholesterol misclassified more exudates as transudates than Light's criteria (15 vs. 3.2%, P < 0.001). The combination of pleural cholesterol with lactate dehydroegnase (LDH) or pleural fluid/serum protein ratio revealed a comparable accuracy to that achieved with Light's criteria. CONCLUSIONS: Light's criteria are just as useful as the association of pleural cholesterol and LDH to detect exudates. In the present study, no parameter, including pleural cholesterol, was superior to Light's criteria.

Adolescent↗
PubMed1998

Elecsys CEA, PSA and AFP. Clinical results of a multicentre evaluation.

Three tumormarker assays, Elecsys CEA, PSA and AFP, have been evaluated in an international multicentre study to characterize their clinical performance and to verify the comparability with the corresponding tests of the Enzymun-Test product line and other methods. For each of the markers results were obtained from four laboratories. On the basis of 314 and 199 specimens respectively, (preliminary) reference ranges could be established for CEA and PSA. For the prostate marker, the age dependence of the antigen level could be clearly confirmed. Mean concentrations range between 0.51 ng/ml (< 40 years) and 3.57 ng/ml (> 70 years). Referring to CEA, 95th percentiles of 4.31 ng/ml and 2.69 ng/ml were elaborated for smokers and nonsmokers. In general, good to excellent correlations (r > 0.98) were found between the Elecsys and Enzymun-Tests. Regarding the systematic comparability of both systems, most of the slopes derived from the individual method comparison studies are within the +/- 10% range of the respective standardization results. The specific distribution pattern of the individual tumormarker values elaborated with sample material of known clinical background, reflects the well established categorization of different benign and malignant diseases according to their characteristic marker levels. Of utmost importance, however, is the excellent comparability of the Elecsys assays with the corresponding Enzymun-Tests and the FDA approved AIA 1200 tests from TOSOH in follow-up studies. Almost superimposable concentration curves guarantee that identical diagnostic information is derived from all three methods. Especially for PSA, a series of measurements on sera of prostatectomized patients proved the usability and clinical value of the test also for this particular indication. For either one of the Elecsys tests, the feasibility of using plasma as sample material was verified.

Adult↗
PubMed1997

Nasopharyngeal colonization in Costa Rican children during the first year of life.

BACKGROUND: The establishment of the nasopharyngeal flora was followed in Costa Rican children from birth to 1 year of age. METHODS: Nasopharyngeal cultures were obtained at 1 (n = 413), 3 (n = 393), 6 (n = 376) and 12 months (n = 356) of age from children representative of the population in the Puriscal district. Weekly cultures were obtained from a subcohort of these children (n = 101). Mother-infant diads (n = 95) and preschool children (n = 208) attending day-care centers were also studied. RESULTS: The estimated proportion of colonized children in the population differed markedly depending on the frequency of culture. Quarterly cultures showed a slow increase in carrier rates from 3.9% for Haemophilus influenzae, 3.1% for Streptococcus pneumoniae and 6.5% for Moraxella catarrhalis at 1 month of age to 10.1% carrying H. influenzae and 19.4% carrying S. pneumoniae by the end of the first year. By quarterly culture the proportion of children colonized at least once was 36% for S. pneumoniae, 26% for H. influenzae and 28% for M. catarrhalis. In contrast weekly sampling showed that 95 to 100% of the children were colonized at least once during the first year of life with H. influenzae, S. pneumoniae or M. catarrhalis. Nasopharyngeal carriage of H. influenzae, S. pneumoniae and M. catarrhalis was low in the mothers, and very few mother-infant pairs carried identical bacteria at the same time. In contrast carrier rates were high in the siblings attending day care (H. influenzae 27.9%, S. pneumoniae 39.4%, both organisms 26.6%). Infants with siblings had significantly higher bacterial carriage at all ages than infants without siblings. CONCLUSIONS: Quarterly nasopharyngeal cultures showed that Costa Rican infants acquire their nasopharyngeal flora at a rate comparable with that for infants in developed countries and that siblings are an important source of the bacteria. Weekly samplings showed that virtually all children were colonized at least once during the first year of life.

Adult↗
PubMed1997

Beta-cell function abnormalities in islets from an adult subject with nesidioblastosis and autoantibodies against the islet cells.

Human islets from an adult subject with nesidioblastosis were isolated and used to perform in vitro studies. Isolated nesidioblastotic islets showed an increased basal rate of insulin secretion (nesidioblastotic islets, 81.3 +/- 6.4 vs. control islets, from cadaveric organ normal donors, 10.2 +/- 0.9 microU/islet/90 min) without any further release with increasing glucose concentration. In addition, islets isolated from the pancreas with nesidioblastosis contained more insulin than control islets, 1,547.0 +/- 128.7 vs. 935.0 +/- 51.7 microU/islet, and the levels of insulin mRNA were also higher than those measured in controls. Interestingly, the serum of the subject with nesidioblastosis contained autoantibodies that stained brightly and selectively a population of islet cells whose distribution coincided with that expected of alpha cells. In summary, pancreatic islets in nesidioblastosis display beta-cell functional abnormalities. Moreover, the finding of antibodies against islet cells is a common feature in the serum of nesidioblastotic subjects; nevertheless, their pathological significance warrants further investigation.

Adolescent↗