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J Torrent

Publications and source records attributed to J Torrent.

At least 19 recordsLinked to original sources
PubMed2006

Pressure-jump-induced kinetics reveals a hydration dependent folding/unfolding mechanism of ribonuclease A.

Pressure-jump (p-jump)-induced relaxation kinetics was used to explore the energy landscape of protein folding/unfolding of Y115W, a fluorescent variant of ribonuclease A. Pressure-jumps of 40 MPa amplitude (5 ms dead-time) were conducted both to higher (unfolding) and to lower (folding) pressure, in the range from 100 to 500 MPa, between 30 and 50 degrees C. Significant deviations from the expected symmetrical protein relaxation kinetics were observed. Whereas downward p-jumps resulted always in single exponential kinetics, the kinetics induced by upward p-jumps were biphasic in the low pressure range and monophasic at higher pressures. The relative amplitude of the slow phase decreased as a function of both pressure and temperature. At 50 degrees C, only the fast phase remained. These results can be interpreted within the framework of a two-dimensional energy surface containing a pressure- and temperature-dependent barrier between two unfolded states differing in the isomeric state of the Asn-113-Pro-114 bond. Analysis of the activation volume of the fast kinetic phase revealed a temperature-dependent shift of the unfolding transition state to a larger volume. The observed compensation of this effect by glycerol offers an explanation for its protein stabilizing effect.

Animals↗
PubMed2005

The powerful high pressure tool for protein conformational studies.

The pressure behavior of proteins may be summarized as a the pressure-induced disordering of their structures. This thermodynamic parameter has effects on proteins that are similar but not identical to those induced by temperature, the other thermodynamic parameter. Of particular importance are the intermolecular interactions that follow partial protein unfolding and that give rise to the formation of fibrils. Because some proteins do not form fibrils under pressure, these observations can be related to the shape of the stability diagram. Weak interactions which are differently affected by hydrostatic pressure or temperature play a determinant role in protein stability. Pressure acts on the 2 degrees, 3 degrees and 4 degrees structures of proteins which are maintained by electrostatic and hydrophobic interactions and by hydrogen bonds. We present some typical examples of how pressure affects the tertiary structure of proteins (the case of prion proteins), induces unfolding (ataxin), is a convenient tool to study enzyme dissociation (enolase), and provides arguments to understand the role of the partial volume of an enzyme (butyrylcholinesterase). This approach may have important implications for the understanding of the basic mechanism of protein diseases and for the development of preventive and therapeutic measures.

Ataxin-3↗
PubMed2004

High pressure, an alternative approach to understand protein misfolding diseases.

Protein folding is essential for the flow of genetic information to biological activity. A failure in this process can result in disease, by causing cell damage and sometimes death. The misfolding of proteins often induces their aggregation, initiating the fibril formation seen in a range of human and animal diseases. Because misfolding and aggregation are of fundamental importance in vivo, there is currently great interest in understanding their mechanisms. To gain insight into the folding and unfolding processes of proteins, for nearly a century, an original biophysical approach has been successfully used: the application of high hydrostatic pressure combined with various spectroscopic and kinetic techniques. Because high pressure provides new insight into protein structure and folding which cannot be obtained by other techniques, the conformations of pressure-induced unfolding intermediates and species involved in the initial states of aggregation of proteins associated with specific diseases are currently being investigated. Our contention is that by exploring folding kinetics, misfolding pathways and stability under pressure, it will be possible to understand the mechanisms of amyloidogenesis, with the ultimate goal to design therapeutic strategies to prevent progression of the disease.

Amyloid↗
PubMed2001

Morphologic changes in breast biopsies after duct endoscopy.

Duct endoscopy is a recent technique used for a direct view of the breast ductal system. The aim of this study is to determine any morphological changes in breast tissue attributable to low-pressure irrigation with saline solution that the technique requires. A total of 26 breast biopsies from patients who underwent ductal endoscopy before surgery were compared with 26 breast specimens from the retroareolar region. Breast specimens from duct endoscopy showed more frequent epithelial detachment (73%), epithelial loss (35%), periductal clefts (77%), stromal disaggregation (46%) and displacement of epithelial cells into the stroma (27%) than the control group in which epithelial detachment was seen in 4% of patients, periductal clefts in 15%, and stromal disaggregation in 15%. Epithelial loss and epithelial displacement where not seen in the control group. Although low-pressure fluid perfusion used for duct endoscopy induced morphological changes in breast tissue, these can easily be distinguished from malignancy, and are most likely to occur as the result of duct rupture.

Journal Article↗
PubMed2001

Pressure versus temperature unfolding of ribonuclease A: an FTIR spectroscopic characterization of 10 variants at the carboxy-terminal site.

FTIR spectroscopy was used to characterize and compare the temperature- and pressure-induced unfolding of ribonuclease A and a set of its variants engineered in a hydrophobic region of the C-terminal part of the molecule postulated as a CFIS. The results show for all the ribonucleases investigated, a cooperative, two-state, reversible unfolding transition using both pressure and temperature. The relative stabilities, among the different sites and different variants at the same site, monitored either through the changes in the position of the maximum of the amide I' band and the tyrosine band, or the maximum of the band assigned to the beta-sheet structure, corroborate the results of a previous study using fourth-derivative UV absorbance spectroscopy. In addition, variants at position 108 are the most critical for ribonuclease structure and stability. The V108G variant seems to present a greater conformational flexibility than the other variants. The pressure- and temperature-denaturated states of all the ribonucleases characterized retained some secondary structure. However, their spectral maxima were centered at different wavenumbers, which suggests that pressure- and temperature-denaturated states do not have the same structural characteristics. Nevertheless, there was close correlation between the pressure and temperature midpoint transition values for the whole series of protein variants, which indicated a common tendency of stability toward pressure and heat.

Amino Acid Substitution↗
PubMed1999

Pressure versus heat-induced unfolding of ribonuclease A: the case of hydrophobic interactions within a chain-folding initiation site.

To investigate the characteristics of the postulated carboxy terminal chain-folding initiation site in bovine pancreatic ribonuclease A (RNase A) (residues 106-118), important in the early stages of the folding pathway, we have engineered by site-directed mutagenesis a set of 14 predominantly conservative hydrophobic variants of the protein. The stability of each variant has been compared by pressure and temperature-induced unfolding, monitored by fourth derivative UV absorbance spectroscopy. Apparently simple two-state, reversible unfolding transitions are observed, suggesting that the disruption of tertiary structure of each protein at high pressure or temperature is strongly cooperative. Within the limits of the technique, we are unable to detect significant differences between the two processes of denaturation. Both steady-state kinetic parameters for the enzyme reaction and UV CD spectra of each RNase A variant indicate that truncation of hydrophobic side chains in this region has, in general, little or no effect on the native structure and function of the enzyme. Furthermore, the decreases in free energy of unfolding upon pressure and thermal denaturation of all the variants, particularly those modified at residues 106 and 108, suggest that the hydrophobic residues and side chain packing interactions of this region play an important role in maintaining the conformational stability of RNase A. We also demonstrate the potential of Tyr115 replacement by Trp as a non-destabilizing fluorescence probe of conformational changes local to the region.

Animals↗
PubMed1999

Valine 108, a chain-folding initiation site-belonging residue, crucial for the ribonuclease A stability.

Thermal denaturation of bovine pancreatic ribonuclease A and a set of its single variants, carrying replacements of hydrophobic residues in the postulated 106-118 chain folding initiation site, has been studied by differential scanning calorimetry. Ribonuclease A variants undergo a two-state thermal transition denaturation except for those with replacement of valine 108. Most mutations cause a significant destabilization of the protein compared to the wild-type, thus demonstrating the importance of hydrophobic residues at the 106-118 region in maintaining the stability of the molecule. Among them, those of valine 108 promote the greatest (14-27 degrees C) destabilization of the molecule. Therefore, valine 108 plays a crucial role for ribonuclease A stability.

Animals↗
PubMed1999

Absolute bioavailability and absorption profile of cyanamide in man.

A pharmacokinetic study of cyanamide, an inhibitor of aldehyde dehydrogenase (EC1.2.1.3) used as an adjuvant in the aversive therapy of chronic alcoholism, has been carried out in healthy male volunteers following intravenous and oral administration. Cyanamide plasma levels were determined by a sensitive HPLC assay, specific for cyanamide. After intravenous administration cyanamide displayed a disposition profile according to a two-compartmental open model. Elimination half-life and total plasma clearance values ranged from 42.2 to 61.3 min and from 0.0123 to 0.0190 L.kg-1.min-1, respectively. After oral administration of 0.3, 1.0, and 1.5 mg/kg x +/- SEM values of Cmax, tmax (median) and AUC were 0.18 +/- 0.03, 0.91 +/- 0.11, and 1.65 +/- 0.27 micrograms.ml-1; 13.5, 13.5, and 12 min; and 8.59 +/- 1.32, 45.39 +/- 1.62, and 77.86 +/- 17.49 micrograms.ml-1.min, respectively. Absorption was not complete and the oral bioavailability, 45.55 +/- 9.22, 70.12 +/- 4.73, and 80.78 +/- 8.19% for the 0.3, 1.0, and 1.5 mg/kg doses, respectively, increased with the dose administered. The models that consider a first-order absorption process alone (whether with a fixed or variable bioavailability value as a function of dose) or with loss of drug due to presystemic metabolism (with zero-order or Michaelis-Menten kinetics) were simultaneously fitted to plasma level data obtained following 1 mg/kg i.v. and 0.3, 1.0, and 1.5 mg/kg oral administrations. The model that best fit the data was that with a first-order absorption process plus a loss by presystemic metabolism with Michaelis-Menten kinetics, suggesting the presence of a saturable first-pass effect.

Absorption↗
PubMed1996

A drug interaction study between cicletanine and tolbutamide in healthy volunteers.

OBJECTIVE: To determine the possible interaction between the antihypertensive agent cicletanine and the hypoglycaemic drug tolbutamide. METHODS: Time-courses of glycaemia and serum immunoreactive insulin (IRI) were followed in 10 healthy subjects after two tolbutamide infusions in each volunteer; initially alone and 9 days later concomitantly with repeated oral cicletanine. Any drug interaction was quantified on the basis of a decrease or increase in the AUC with time of glycaemia and IRI by subtraction of baseline concentration (AUC0(240)-GLY and AUC0(60)-IRI). Peak glycaemia and peak IRI, and the corresponding time to peaks, were also assessed. RESULTS: Following tolbutamide, mean AUC0(240)-GLY values were 97.7 and 98.8 mmol.l-1.min, without or with cicletanine, respectively; the corresponding AUC0(60)-IRI were 485 and 321 mU.l-1.min. Mean peak glycaemia values were 0.996 and 1.071 mmol.l-1. Regarding the peak IRI, a decrease was observed after tolbutamide and cicletanine: median values were 29.2 and 17.4 mU.l-1. The corresponding median time to peak glycaemia and IRI values were 30 and 30 min and 5 (all subjects) and 5 min. CONCLUSION: No clinically relevant interaction was shown after the concomitant administration of repeated oral doses of cicletanine and acute intravenous tolbutamide to healthy volunteers.

Administration, Oral↗
PubMed1995

Evaluation of the central effects of alcohol and caffeine interaction.

1. The dynamic and kinetic interactions of alcohol and caffeine were studied in a double-blind, placebo controlled, cross-over trial. Treatments were administered to eight healthy subjects in four experimental sessions, leaving a 1 week wash-out period between each, as follows: 1) placebo, 2) alcohol (0.8 g kg-1), 3) caffeine (400 mg) and 4) alcohol (0.8 g kg-1) + caffeine (400 mg). 2. Evaluations were performed by means of: 1) objective measures: a) psychomotor performance (critical flicker fusion frequency, simple reaction time and tapping test), b) long latency visual evoked potentials ('pattern reversal'); 2) subjective self-rated scales (visual analogue scales and profile of mood states); 3) caffeine and alcohol plasma concentration determinations. 3. The battery of pharmacodynamic tests was conducted at baseline and at +0.5 h, +1.5 h, +2.5 h, +4 h and +6 h. An analysis of variance was applied to the results, accepting a P < 0.05 as significant. The plasma-time curves for caffeine and alcohol were analysed by means of model-independent methods. 4. Results obtained with caffeine in the objective measures demonstrated a decrease in simple reaction time and an increase in the amplitude of the evoked potentials; the subjects' self-ratings showed a tendency to be more active. Alcohol increased simple reaction time and decreased amplitude of the evoked potentials, although the subjects rated themselves as being active. The combination of alcohol + caffeine showed no significant difference from placebo in the objective tests; nevertheless, the subjective feeling of drunkenness remained. The area under the curve (AUC) for caffeine was significantly higher when administered with alcohol.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Technical note: assessing the consistency of measurement procedures in animal energetics and nutrition.

Our objective was to assess the consistency of representative digestion and energetics determinations used in animal nutrition. We used distribution theory of quadratic forms that allow for the attainment of width of confidence intervals (WI) for intraclass correlations. Three models commonly used in animal nutrition were analyzed, and their respective programs were coded to obtain the required confidence limits. Data sets were obtained from previous research published by our laboratory. Urinary, CH4, and ME were analyzed assuming a two-factor nested balanced variance component model. Rate of ruminal NDF disappearance (kd) and DM digestibility by an 8-d conventional collection trial were fitted to a two-factor crossed variance component model without interaction with a single observation per cell. Empty BW (EBW), carcass energy, and EBW energy were fitted to a two-factor crossed variance component model with interaction. Widths of confidence intervals varied with the example data set and variable tested. The narrowest WI was that of DM digestibility, less than .07 at a 95% confidence level for all the intraclass correlations, which shows the high consistency of the DM digestibility measurement in the specific study. Medium to large WI were found for kd and EBW; WI estimates were less than .70 at a 95% confidence level. Large WI, from .8 to 1.0 at a 95% confidence level, were found for the remaining variables, indicating the greater variability of these measurements. This methodology allows the assessment of the consistency of a measurement process and provides a method to monitor it each time a determination is made.

Analysis of Variance↗
PubMed1995

[Treatment of a hemorrhagic duodenal varice by endoscopic sclerotherapy].

We report the case of a duodenal varix rupture in a 37-year-old man revealing an alcoholic cirrhosis. Endoscopic diagnosis of this duodenal varix was difficult because of its atypical and changing appearance. Endoscopic sclerotherapy was completely successful and there was no recurrent bleeding. Although duodenal varix is rare, this case and the literature emphasize the importance of considering this diagnosis in all patients with duodenal tumoral lesions and suspected portal hypertension. In this context, duodenal biopsy can be dangerous and should be avoided. In case of duodenal varix rupture, endoscopic sclerotherapy appears to be a safe and efficient first-choice therapy.

Adult↗
PubMed1995

[Endoscopic diagnosis of a biliodigestive fistula of tuberculous origin revealing acquired immunodeficiency syndrome].

We report the case of a 32-year-old Malian man with abdominal tuberculosis revealing acquired immunodeficiency syndrome. A gastroscopy was made for epigastric pain and showed caseum in a digestive fistula with acid fast bacilli. Mycobacterium tuberculosis infection was confirmed by sputum culture. An early antituberculous therapy was prescribed. Outcome was good with rapid fistula closing and slower mass diminution of the abdominal lymph nodes. This case report confirms nodal tuberculosis as a possible cause of digestive fistulae. Rapid endoscopic diagnosis of this tuberculous fistula led to diagnosis of acquired immunodeficiency syndrome and early adapted medical treatment without invasive diagnostic methods.

AIDS-Related Opportunistic Infections↗
PubMed1995

Dual bite demonstrated by kinesiography: a case report.

A 60-year-old man sought treatment for extensive tooth wear resulting from bruxism. He had no signs of temporomandibular joint dysfunction. The kinesiographic study revealed that he had a dual bite, with two intercuspal positions, separated by 3 mm anteroposteriorly and by 7 mm laterally. The dentition was restored with metal-ceramic crowns to restore a normal occlusion. The kinesiographic follow-up studies revealed that, initially, it was difficult for the patient to adapt to a new occlusal design, but 6 years later, the dual bite had disappeared. However, the disoccluding angle had flattened where the second intercuspal position had previously existed, corresponding, clinically, to a change from canine guidance to anterior-canine guidance.

Bruxism↗
PubMed1994

Co-product fiber digestibility: kinetic and in vivo assessment.

Nutrient digestion and kinetic characteristics of alfalfa hay, brewers grains, beet pulp, and cottonseed hulls were studied in two experiments. In the first experiment, these feedstuffs were fed with a mineral/vitamin supplement in a 4 x 4 Latin square to eight ewes to determine total tract digestibilities by 8-d total collection and rates of passage using Yb as a marker. In the second experiment samples of the same feedstuffs were incubated in situ in four ruminally fistulated steers in a 4 x 4 Latin square design to quantify ruminal disappearance of NDF and ADF. Three Dacron bags were placed in the rumen for each of six time periods: 6, 12, 24, 48, 72, and 96 h. Total tract digestibilities of DM ranged from 33% for cottonseed hulls to 78% for beet pulp. Digestibilities of NDF ranged from 32% for cottonseed hulls to 81% for beet pulp. Total tract retention times ranged from 74 h for beet pulp to 44 h for alfalfa. Retention time for alfalfa was lower (P < .05) than those for beet pulp or cottonseed hulls. Calculation of TDN values yielded values similar to those of NRC other than for cottonseed hulls, for which NRC values were 18 to 29% higher. Alfalfa hay and beet pulp were the feedstuffs with the most rapidly disappearing NDF, .124/h for alfalfa and .116/h for beet pulp, which were faster (P < .05) than those found in brewers grains and cottonseed hulls, .035 and .043/h, respectively. Potentially digestible NDF ranged from 55% for alfalfa hay to 94% for beet pulp.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1993

Evaluation of the methodological quality of clinical trial protocols. A preliminary experience in Spain.

The methodological quality of 50 clinical trial protocols submitted to our hospital has been assessed by means of a check-list. The most frequent methodological deficiencies found were related to statistical analysis, selection criteria, sample size, incorrect use of placebo, homogeneity of the groups, concomitant medication, randomisation plan, monitoring of adverse events and study design. Lack of insurance for the patients and inadequacies in the investigators' brochure and case report forms were observed in a significant number of cases. The results suggest the importance of a multidisciplinary team in the elaboration of clinical trial protocols to prevent methodological errors.

Clinical Protocols↗