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P Chacón

Publications and source records attributed to P Chacón.

At least 19 recordsLinked to original sources
PubMed2002

Effects of oleic-rich and omega-3-rich diets on serum lipid pattern and lipid oxidation in mildly hypercholesterolemic patients.

AIMS: To evaluate which dietary fat elicits the best response in terms of plasma lipids, lipoproteins, and oxidative processes. METHODS: After a 4-week run-in period, 14 mildly hypercholesterolemic subjects were fed two balanced diets for 6-week periods. During the first intervention period, patients received a monounsaturated fatty acid (MUFA)-enriched diet (olive oil diet). During the second period this diet was supplemented by n-3 polyunsaturated fatty acids (PUFAs) (n-3 diet). RESULTS: After the olive oil diet, a significant decrease in total serum cholesterol (-8.54%, P<0.01), and in apolipoprotein B (Apo B) (-10.0%, P<0.01) was observed. With the addition of n-3 fatty acids no further significant changes in serum lipid concentrations were found. However, the n-3 diet was followed by an increase in lipoperoxides in isolated native low-density lipoprotein (LDL) (67.23%, P<0.01). CONCLUSIONS: A beneficial effect on the serum lipid pattern was observed with the olive oil-enriched diet. The lack of further beneficial modifications on blood lipids and lipoproteins and the increase in the oxidative susceptibility of LDL observed after the addition of n-3 PUFA to the olive oil diet does not favor the use of this diet in hypercholesterolemic patients if it is not associated with a high intake of antioxidants.

Analysis of Variance↗
PubMed2001

SOMCD: method for evaluating protein secondary structure from UV circular dichroism spectra.

This article presents SOMCD, an improved method for the evaluation of protein secondary structure from circular dichroism spectra, based on Kohonen's self-organizing maps (SOM). Protein circular dichroism (CD) spectra are used to train a SOM, which arranges the spectra on a two-dimensional map. Location in the map reflects the secondary structure composition of a protein. With SOMCD, the prediction of beta-turn has been included. The number of spectra in the training set has been increased, and it now includes 39 protein spectra and 6 reference spectra. Finally, SOM parameters have been chosen to minimize distortion and make the network produce clusters with known properties. Estimation results show improvements compared with the previous version, K2D, which, in addition, estimated only three secondary structure components; the accuracy of the method is more uniform over the different secondary structures.

Algorithms↗
PubMed2001

Differential influence of LDL cholesterol and triglycerides on lipoprotein(a) concentrations in diabetic patients.

OBJECTIVE: To evaluate the relationship between plasma lipid profiles and lipoprotein(a) [Lp(a)] concentrations in diabetic patients, taking into account the Lp(a) phenotype. RESEARCH DESIGN AND METHODS: We included 191 consecutive diabetic outpatients (69 type 1 and 122 type 2 diabetic patients) in a cross-sectional study Serum Lp(a) was determined by enzyme-linked immunosorbent assay, and Lp(a) phenotypes were assessed by SDS-PAGE followed by immunoblotting. The statistical methods included a stepwise multiple regression analysis using the Lp(a) serum concentration as the dependent variable. The lipid profile consisted of total cholesterol, HDL cholesterol, LDL cholesterol, corrected LDL cholesterol, triglycerides, and apolipoproteins AI and B. RESULTS: In the multiple regression analysis, LDL cholesterol (positively) and triglycerides (negatively) were independently related to the Lp(a) concentration, and they explained the 6.6 and 7.8% of the Lp(a) variation, respectively. After correcting LDL cholesterol, the two variables explained 3.8 and 6.4% of the Lp(a) variation, respectively. In addition, we observed that serum Lp(a) concentrations were significantly lower in patients with type IV hyperlipidemia (mean 1.0 mg/dl [range 0.5-17], n = 16) than in normolipidemic patients (6.5 mg/dl [0.5-33.5], n = 117) and in type II hyperlipidemic patients (IIa 15.5 mg/dl [3.5-75], n = 13; IIb 9 mg/dl [1-80], n = 45); P < 0.001 by analysis of variance. CONCLUSIONS: Lp(a) concentrations were directly correlated with LDL cholesterol and negatively correlated with triglyceride levels in diabetic patients. Therefore, our results suggest that the treatment of diabetic dyslipemia may indirectly affect Lp(a) concentrations.

Adult↗
PubMed2000

Relationship between lipoprotein(a) phenotypes and plaminogen activator inhibitor type 1 in diabetic patients.

It has been demonstrated in vitro that lipoprotein(a) [Lp(a)] increases the endothelial synthesis of plasminogen activator inhibitor 1 (PAI-1). However, this effect in vivo is controversial, and the possible relationship between PAI-1 and Lp(a) phenotypes has not been evaluated. The aim of the study was to determine the influence of Lp(a) and its phenotypes on PAI-1 serum concentrations in diabetic patients. For this purpose we include 75 Caucasian diabetic patients (34 consecutive type I and 41 consecutive type II) without late diabetic complications. Lp(a) and PAI-1 were assessed by ELISA. Lp(a) phenotypes were determined by SDS-PAGE followed by immunoblotting, and grouped according to size in small (F,B,S1,S2), big (S3,S4), and null. A linear correlation between Lp(a) and PAI-1 was not observed either as a whole or when type I and type II diabetic patients were analyzed separately. However, significant differences were detected in PAI-1 levels when Lp(a) phenotypes were considered (small: 42.1+/-31.8 ng/mL; big: 37.2+/-26.1 ng/mL; null: 14.4+/-14.4; p< 0.05). The significant differences were due to the low PAI-1 concentrations observed in patients with null phenotype. Our results suggest that fibrinolytic activity might be preserved in diabetic patients with null Lp(a) phenotype. Furthermore, it could be speculated that diabetic patients with null phenotype should be considered at low risk to develop cardiovascular disease.

Adult↗
PubMed2000

Reconstruction of protein form with X-ray solution scattering and a genetic algorithm.

We have reconstructed, from experimental approximately 2 nm resolution X-ray solution scattering profiles, the corresponding shapes and sizes of myoglobin, troponin C, spermadhesin PSP-I/PSP-II, chymotrypsinogen A, superoxide dismutase, ovalbumin, tubulin, nitrite reductase, catalase, the structural change of troponin C upon dissociation of the two high affinity Ca(2+), and the solution model structure of a tandem pair of fibronectin type III cytoplasmic domains of integrin alpha6beta4 before determination of its crystal structure. To this purpose we have designed a new genetic algorithm which gradually explores a discrete search space and evolves convergent models made of several hundred beads (down to 0.3 nm radius) best fitting the scattering profile upon Debye calculation, without geometrical constraints or penalty for loose beads. This is a procedure of effective numerical transformation of the one-dimensional scattering profiles into three-dimensional model structures. The number of beads in models is correlated with the protein molecular mass (with one exception). The shape and approximate dimensions of each protein have been retrieved by a set of ten solution models, essentially superimposable with the available crystal structures.

Algorithms↗
PubMed2000

Influence of surgical stress and parenteral nutrition on serum leptin concentration.

UNLABELLED: Experimental studies suggest that leptin may be an important metabolic signal for energy regulation. AIM: To assess whether surgical stress produces changes in serum leptin concentration and to investigate and compare the effect of total parenteral nutrition and hypocaloric parenteral nutrition on serum leptin levels. PATIENTS AND METHODS: Twenty-two surgical patients (11 male and 11 female) in need of parenteral nutrition were recruited. Parenteral nutrition was always initiated 24 h after surgical procedure. Group I (n=15) received total parenteral nutrition, while Group II (n=7) were treated with hypocaloric parenteral nutrition. Serum leptin concentration was determined before surgical procedure (day -1), after surgery and before parenteral nutrition was started (day +1), and after 5 days of treatment with parenteral nutrition (day +6). RESULTS: A tendency to increase serum leptin levels was observed after surgical procedure (6.0+/-1.9 vs 9.9+/-2.7 ng/ml;P= 0.07). After starting parenteral nutrition no significant changes on serum leptin concentrations were found in both groups, but a trend to raise serum leptin was observed in Group I (6.2+/-1.7 vs 8.3+/-2.7 ng/ml) whereas a trend to decrease serum leptin was detected in Group II (4.6+/-2.5 vs 1.6+/-0.5 ng/ml). On day +6 an increase of serum leptin and insulin levels was observed in Group I in comparison with Group II (8.3+/-2.7 vs 1.6+/-0.5 ng/ml;P<< 0.05 and 58+/-41 vs 12+/-15 microU/l;P<< 0.05 respectively). Finally, a positive correlation at day +6 between insulin and serum leptin levels was observed (r= 0.66;P<< 0.01). CONCLUSIONS: a) Surgical stress is associated to an increase of serum leptin concentrations; b) Total and hypocaloric parenteral nutrition produces quite different effects on serum leptin levels that could be related to distinct insulin response.

Energy Intake↗
PubMed2000

Relationship of lipoprotein(a) and its phenotypes with the albumin excretion rate in diabetic patients: a multivariate analysis.

BACKGROUND/AIM: The possible association between lipoprotein(a) [Lp(a)] and albumin excretion rate (AER) is a topic that has generated conflicting views. The aim of this study was to determine the relationship between serum Lp(a) concentrations and AER in diabetic patients, taking into account Lp(a) phenotypes in a multivariate analysis. METHODS: For this purpose 191 consecutive diabetic patients (69 type 1 and 122 type 2) were included in the study. Lp(a) was determined by ELISA and its phenotypes by SDS-PAGE followed by immunoblotting. Lp(a) phenotypes were grouped by size in small (F, B, S1, S2), big (S3, S4) and null. RESULTS: Diabetic patients with an AER >20 microg/min presented higher Lp(a) concentrations than patients with an AER <20 microg/min: median 19 mg/dl versus 5 mg/dl (p < 0.0001). The differences remained at a significant level when the type of diabetes was considered. A linear correlation was observed between Lp(a) concentration and AER (type 1: r = 0.32, p = 0.01; type 2: r = 0.25, p < 0.05). The AER was independently correlated with Lp(a) concentrations in a multiple regression analysis (p < 0.01), and Lp(a) was independently associated with the presence of diabetic nephropathy in the logistic regression analysis. The overall frequency distribution of Lp(a) phenotypes differed significantly between patients with or without microalbuminuria (p < 0.05). In addition, the AER (microg/min) was different among the Lp(a) phenotypes: small 55 +/- 122 (median 4.9), big 58 +/- 123 (median 5.7) and null 3 +/- 2 (median 2.3); p = 0.01. The significant difference mainly resulted from low AER (<10 microg/min) detected in all patients with the null phenotype. CONCLUSIONS: In diabetic patients the serum Lp(a) concentration is associated with AER. Thus, the elevated cardiovascular risk observed in diabetic patients with a high AER could be related to the Lp(a) concentration. Finally, patients with the null Lp(a) phenotype can be considered as a group at low risk of the development of diabetic nephropathy.

Adult↗
PubMed1999

[Lipoprotein (a) and the evaluation of low density cholesterol by the Friedewald formula: a new problem for an old equation].

BACKGROUND: To evaluate the influence of lipoprotein(a) [Lp(a)] concentration on the LDL-cholesterol calculated by the Friedewald formula. MATERIAL AND METHODS: Lp(a) was determined to a worker population of 947 subject in order to perform a correction of LDL-cholesterol obtained by the Friedewald formula. RESULTS: In subjects in whom Lp(a) was > 30 mg/dl (12.9%) LDL-cholesterol levels were overestimated 10 mg/dl at least. CONCLUSION: Lp(a) should be considered in order to reduce Friedewald's formula error on the estimation of LDL-cholesterol.

Cholesterol, HDL↗
PubMed1998

Changes in microtubule protofilament number induced by Taxol binding to an easily accessible site. Internal microtubule dynamics.

We have investigated the accessibility of the Taxol-binding site and the effects of Taxol binding on the structures of assembled microtubules. Taxol and docetaxel readily bind to and dissociate from microtubules, reaching 95% ligand exchange equilibrium in less than 3 min under our solution conditions (microtubules were previously assembled from GTP-tubulin, GTP-tubulin and microtubule-associated proteins, or GDP-tubulin and taxoid). Microtubules assembled from purified tubulin with Taxol are known to have typically one protofilament less than with the analogue docetaxel and control microtubules. Surprisingly, Taxol binding and exchange induce changes in the structure of preformed microtubules in a relatively short time scale. Cryoelectron microscopy shows changes toward the protofilament number distribution characteristic of Taxol or docetaxel, with a half-time of approximately 0.5 min, employing GDP-tubulin-taxoid microtubules. Correspondingly, synchrotron x-ray solution scattering shows a reduction in the mean microtubule diameter upon Taxol binding to microtubules assembled from GTP-tubulin in glycerol-containing buffer, with a structural relaxation half-time of approximately 1 min. These results imply that microtubules can exchange protofilaments upon Taxol binding, due to internal dynamics along the microtubule wall. The simplest interpretation of the relatively fast taxoid exchange observed and labeling of cellular microtubules with fluorescent taxoids, is that the Taxol-binding site is at the outer microtubule surface. On the contrary, if Taxol binds at the microtubule lumen in agreement with the electron crystallographic structure of tubulin dimers, our results suggest that the inside of microtubules is easily accessible from the outer solution. Large pores or moving lattice defects in microtubules might facilitate the binding of taxoids, as well as of possible endogenous cellular ligands of the inner microtubule wall.

Animals↗
PubMed1998

Low-resolution structures of proteins in solution retrieved from X-ray scattering with a genetic algorithm.

Small-angle x-ray solution scattering (SAXS) is analyzed with a new method to retrieve convergent model structures that fit the scattering profiles. An arbitrary hexagonal packing of several hundred beads containing the problem object is defined. Instead of attempting to compute the Debye formula for all of the possible mass distributions, a genetic algorithm is employed that efficiently searches the configurational space and evolves best-fit bead models. Models from different runs of the algorithm have similar or identical structures. The modeling resolution is increased by reducing the bead radius together with the search space in successive cycles of refinement. The method has been tested with protein SAXS (0.001 < S < 0.06 A(-1)) calculated from x-ray crystal structures, adding noise to the profiles. The models obtained closely approach the volumes and radii of gyration of the known structures, and faithfully reproduce the dimensions and shape of each of them. This includes finding the active site cavity of lysozyme, the bilobed structure of gamma-crystallin, two domains connected by a stalk in betab2-crystallin, and the horseshoe shape of pancreatic ribonuclease inhibitor. The low-resolution solution structure of lysozyme has been directly modeled from its experimental SAXS profile (0.003 < S < 0.03 A(-1)). The model describes lysozyme size and shape to the resolution of the measurement. The method may be applied to other proteins, to the analysis of domain movements, to the comparison of solution and crystal structures, as well as to large macromolecular assemblies.

Algorithms↗
PubMed1997

A prediction of DPP IV/CD26 domain structure from a physico-chemical investigation of dipeptidyl peptidase IV (CD26) from human seminal plasma.

Human DPP IV, isolated from seminal plasma by means of immobilised adenosine deaminase, occurs in different forms which are distinguishable by net charge and native molecular weight. Charge differences arise primarily from different degrees of glycosylation containing various amounts of sialic acid. The majority of DPP IV isolated from total seminal plasma consists of the extracellular part of the protein starting at Gly-31. It is a very stable protein resisting high concentrations of denaturant. Unfolding experiments under reducing conditions are indicative of the existence of at least two domains which function independently. One of these domains is highly stabilised by disulfide bonds. Disruption of the disulfide bonds does not affect the activity, the dimeric state nor the adenosine deaminase binding properties of the protein but renders it more susceptible to proteolysis. The low-angle X-ray scattering spectrum is consistent with a model for a protein containing two subunits, each composed of three domains linked by flexible regions with low average mass. The secondary structure composition, determined by FTIR spectrometry, indicates that 45% of the protein consists of beta-sheets, which is higher than expected from computed secondary structure predictions. Our results provide compelling experimental evidence for the three-domain structure of the extracellular part of DPP IV.

Amino Acid Sequence↗
PubMed1997

Relationship between lipoprotein(a) phenotypes and albumin excretion rate in non-insulin-dependent diabetes mellitus: protective effect of 'null' phenotype?

The possible association between lipoprotein(a) [Lp(a)] and albumin excretion rate (AER) is a topic that generates conflicting views. In addition, Lp(a) phenotypes have not previously been considered as factors influencing AER. In order to clarify this issue, we studied 70 non-insulin-dependent diabetes mellitus (NIDDM) patients without clinically detectable macroangiopathy, 27 with microalbuminuria and 43 without it. Both groups were matched for the known variables that could influence AER and serum Lp(a) levels. Lp(a) was determined by enzyme-linked immunosorbent assay (ELISA), and Lp(a) phenotypes were assessed by electrophoresis followed by immunoblotting. Lp(a) phenotypes were grouped as follows: 'small' (F, S1 and S2), 'big' (S3 and S4) and 'null'. The NIDDM patients with microalbuminuria presented higher serum Lp(a) concentrations than the patients without it [15.7 mg dL-1 (95% CI 0.5-36.5) vs. 4.5 mg dL-1 (95% CI 0.1-18.5); P < 0.001] and a direct correlation between Lp(a) and AER was observed (r = 0.34; P < 0.01). AER was significantly different when Lp(a) phenotypes were considered ['small': median 19 micrograms min-1 (range 1-195); 'big': median 9.5 micrograms min-1 (range 1-186); 'null': 4 micrograms min-1 (range 1-9); P = 0.04]. None of the NIDDM patients with a 'null' phenotype showed an AER of > 10 micrograms min-1. In conclusion, this case-control study provides evidence that microalbuminuria is associated with high serum Lp(a) in NIDDM without clinically detectable macroangiopathy. Furthermore, NIDDM patients with a 'null' phenotype could be considered at low risk for the development of microalbuminuria.

Aged↗
PubMed1996

Tubulin secondary structure analysis, limited proteolysis sites, and homology to FtsZ.

The far-ultraviolet circular dichroism spectrum of the alpha beta-tubulin dimer analyzed by six different methods indicates an average content of approximately 33% alpha helix, 21% beta sheet, and 45% other secondary structure. Deconvolution of Fourier transform infrared spectra indicates 24% sheet, 37% (maximum) helix, and 38% (minimum) other structure. Separate alignments of 75 alpha-tubulin, 106 beta-tubulin, and 14 gamma-tubulin sequences and 12 sequences of the bacterial cell division protein FtsZ have been employed to predict their secondary structures with the multiple-sequence method PHD [Rost, B., & Sander, C. (1993a) J. Mol. Biol. 232, 584-599]. The predicted secondary structures average of 33% alpha helix, 24% beta sheet, and 43% loop for the alpha beta dimer. The predictions have been compared with sites of limited proteolysis by 12 proteases at the surfaces of the heterodimer and taxol-induced microtubules [de Pereda, J. M., & Andreu, J. M. (1996) Biochemistry 35, 14184-14202]. From 24 experimentally determined nicking sites, 18 are at predicted loops or at the extremes of secondary structure elements. Proteolysis zone A (including acetylable Lys40 and probably Lys60 in alpha-tubulin and Gly93 in beta-tubulin) and proteolysis zone B (extending between residues 167 and 183 in both chains) are accessible in microtubules. Proteolysis zone C, between residues 278 and 295, becomes partially occluded in microtubules. The alpha-tubulin nicking site Arg339-Ser340 is at a loop following a predicted alpha helix in proteolysis zone D. This site is protected in taxol microtubules; however, a new tryptic site appears which is probably located at the N-terminal end of the same helix. Zone D also contains beta-tubulin Cys354, which is accessible in microtubules. Proteolysis zone E includes the C-terminal hypervariable loops (10-20 residues) of each tubulin chain. These follow the two larger predicted helical zones (residues 372-395 and 405-432 in beta-tubulin), which also are the longer conserved part of the alpha- and beta-tubulin sequences. Through combination of this with other biochemical information, a set of surface and distance constraints is proposed for the folding of beta-tubulin. The FtsZ sequences are only 10-18% identical to the tubulin sequences. However, the predicted secondary structures show two clearly similar (85-87 and 51-78%) regions, at tubulin positions 95-175 and 305-350, corresponding to FtsZ 65-135 and 255-300, respectively. The first region is flanked by tubulin proteolysis zones A and B. It consists of a predicted loop1-helix-loop2-sheet-loop3-helix-loop4-sheet fold, which contains the motif (KR)GXXXXG (loop1), and the tubulin-FtsZ signature G-box motif (SAG)GGTG(SAT)G (loop3). A simple working model envisages loop1 and loop3 together at the nucleotide binding site, while loops 2 and 4 are at the surface of the protein, in agreement with proteolytic and antigenic accessibility results in tubulin. The model is compatible with studies of tubulin and FtsZ mutants. It is proposed that this region constitutes a common structural and evolutionary nucleus of tubulins and FtsZ which is different from typical GTPases.

Amino Acid Sequence↗
PubMed1996

Prospective case control study to determine the effect of lovastatin on serum testosterone and cortisol concentrations in hyperlipidemic nephrotic patients with chronic renal failure.

In order to investigate the effects of lovastatin on adrenal and gonadal function, we prospectively determined the basal and gonadorelin-stimulated concentrations of testosterone, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and the cortisol response to adrenocorticotropic hormone (ACTH) in a sample of 25 male patients with advanced chronic renal failure, hypercholesterolemia and proteinuria. Hormone studies were done prior to and after lovastatin treatment. The values of these patients were compared with those of a matched healthy control group. Before starting treatment with lovastatin, the patients showed significantly lower testosterone concentration and higher LH concentration than the control group. After stimulation with gonadorelin, they also showed a lower increase in testosterone and LH. After 12 months of lovastatin treatment, a significant decrease in the concentration of cholesterol, LDL C, VLDL C and apo B was observed, but neither the basal testosterone concentration nor the response to gonadorelin stimulation was modified. Before treatment, basal and ACTH-stimulated serum cortisol levels did not differ from those of the control group. After lovastatin treatment, neither the basal serum cortisol levels nor the response to ACTH was modified. We conclude that in the patients studied, although the decrease in testosterone concentration may be partially attributable to a decrease in its synthesis, lovastatin treatment does not increase testosterone deficit. This is either because this drug does not inhibit gonadal hydroxymethylglutaryl CoA reductase at the does given or because the cholesterol which LDL C provides the cell with is enough to maintain testosterone synthesis.

Adult↗
PubMed1995

Serum lipoprotein (a) levels in patients with chronic renal failure--evolution after renal transplantation and relationship with other parameters of lipoprotein metabolism: a prospective study.

In order to analyze the relationship between lipoprotein (a) [Lp (a)] and other lipoproteins during chronic renal failure and once renal function is restored after kidney transplantation, we determined the serum levels of total lipoprotein, high-density lipoprotein, low-density lipoprotein, and very-low-density lipoprotein cholesterols, total and very-low-density lipoprotein triglycerides, apolipoproteins A-I, B, C-II, C-III, and E, and E, and Lp (a) in 30 patients with chronic renal failure before and 12 months after renal transplantation. During the 1st year after transplantation, all patients were treated only with ciclosporin and prednisone and had serum creatinine levels < 1.6 mg/dl (140 mumol/l) and proteinuria < 500 mg/day. No patients had chronic hepatic disease. To determine reference values we studied a control group of 60 healthy volunteers. Before renal transplantation, the study group showed higher concentrations of triglycerides, very-low-density triglycerides, very-low density lipoprotein cholesterol, apolipoproteins, C-II and C-III, and Lp(a) than the control group. There was no correlation between Lp(a) and any of the studied variables. After renal transplantation, the serum levels of total lipoprotein, high-density lipoprotein, and low-density lipoprotein and apolipoproteins A-I and B increased significantly. Apolipoproteins C-II and C-III and Lp(a) decreased and normalized. After these changes had taken place, there was no relationship between Lp(a) and other parameters of lipoprotein metabolism. We conclude that the increase in Lp(a) during the chronic renal failure phase is basically related to the loss of renal function and does not depend on the resultant alterations which are produced in other lipoprotein variables.

Adult↗