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Biomedical subjects

C Sierra

Publications and source records attributed to C Sierra.

At least 19 recordsLinked to original sources
PubMed1998

Antioxidant enzymes and fatty acid status in erythrocytes of Down's syndrome patients.

The excess of genetic information in patients with Down's syndrome (DS) produces an increase in the catalytic activity of superoxide dismutase (SOD1), an antioxidant enzyme coded on chromosome 21. It has been suggested that an increase in oxidative stress in DS patients may cause adverse effects in the cell membranes through the oxidation of polyunsaturated fatty acids (PUFAs). The aim of this study was to evaluate the cellular antioxidant system by determining the catalytic activity of the SOD1, glutathione peroxidase (GPx), catalase (CAT), and glutathione reductase (GR) enzymes and the concentrations of alpha-tocopherol in red blood cells (RBCs) in a group of 72 DS patients. The profile of fatty acids in the phospholipids of RBC membranes was also evaluated. The activity of the erythrocyte antioxidant enzymes is significantly higher in the DS group than in the control group (SOD1, 635 +/- 70 U/g Hb vs 476 +/- 67 U/g Hb; CAT, 1843 +/- 250 U/g Hb vs 1482 +/- 250 U/g Hb; GPx, 23.2 +/- 5.3 U/g Hb vs 21.5 +/- 3.6 U/g Hb; and GR, 9.32 +/- 1.4 U/g Hb vs 6.9 +/- 1.3 U/g Hb, respectively). No differences were observed in RBC alpha-tocopherol concentrations between the two groups studied. Long-chain n6 PUFA (C20:3n6, C20:4n6) concentrations were increased in DS patients, suggesting enhanced delta-6-desaturase activity. The long-chain n3 PUFA (docosahexenoic acid) does not appear to be affected by increased oxidative stress, probably because of the existence of compensatory antioxidant mechanisms.

Adolescent↗
PubMed1997

Tocopherol in inborn errors of intermediary metabolism.

Red blood cell tocopherol was measured in a group of 92 children with inborn errors of intermediary metabolism to evaluate the peroxidative damage in different mitochondrial and cytosolic defects, and to consider the need for treatment or vitamin supplementation. Tocopherol was determined by HPLC with UV detection. Results were expressed in nanomoles red blood cell tocopherol per gram protein. Significant differences (Mann-Whitney; P < 0.001) were found between tocopherol levels in untreated patients: 19 with mitochondrial defects versus 23 with cytosolic enzyme or transport defects, and versus 58 age-matched reference values. In conclusion, mitochondrial enzyme deficiencies, either amino and organic acidurias or defects of energy metabolism, seem to produce an excess of free radicals with the consequent utilization of tocopherol as antioxidant. This is not apparent in the cytosolic enzyme defects studied, whose tocopherol levels are in the normal range. Treatment with tocopherol completely corrects the deficient antioxidant status.

Adolescent↗
PubMed1997

Comparison of statistical indicators for the automatic detection of 80 Hz auditory steady state responses.

OBJECTIVE: To evaluate, using receiver operation characteristic (ROC) curves, the performance of several statistical indicators in the objective detection of 80 Hz steady state auditory evoked responses. DESIGN: Steady state auditory evoked responses elicited by amplitude modulated tones of 500 and 1000 Hz, were obtained in 16 normal adults. Recordings were made at intensities ranging from 80 to 30 dB SPL and without stimulation. Four statistics: coherence synchrony measure, circular T2, a new variant of Hotelling T2 (labeled HT2) and a test for hidden periodicity (F test) were calculated. The statistics were compared using ROC curves and bootstrapping techniques. Two outcome measures were considered: behavioral threshold prediction and averaging efficiency. RESULTS: All indicators were highly accurate to detect a response (8 to 9 dB above mean behavioral threshold for the 1000 Hz and 14 to 16 dB for the 500 Hz carrier). Responses could be reliable detected after averaging about five individual epochs of long duration. No statistically significant differences were evidenced though in their capability to predict behavioral threshold or their averaging efficiency. CONCLUSIONS: Despite the more adequate statistical properties of some of these indicators no significant differences were found in their performance. Thus all of these indicators could be recommended for automatic detection of 80 Hz auditory steady state responses.

Adolescent↗
PubMed1995

Effect of long-term antihypertensive therapy with angiotensin converting enzyme inhibitors on red cell sodium transport.

Several sodium transport abnormalities have been reported in erythrocytes from essential hypertensive patients. The possible modification of these parameters under antihypertensive treatment remains controversial. We have measured the maximal rates of the Na+/K+ pump, Na+/K+/Cl- cotransport, and Na+/Li+ countertransport and the rate constant of Na+ leak in erythrocytes from 22 essential hypertensive patient responders to angiotensin converting enzyme inhibitors quinapril or captopril, and from 17 patient nonresponders to these drugs. In the former group, sodium transport measurements were performed at the baseline placebo period and after 6 months of active treatment. The maximal rate of Na+/Li+ countertransport decreased significantly after 6 months of treatment, without differences between both groups of treatment. Angiotensin converting enzyme inhibitors did not significantly modify other sodium transport parameters. The basal activity of erythrocyte sodium transport was not different between patients who responded or not to antihypertensive treatment with those drugs, excluding a predictive value of these measurements concerning the response to angiotensin converting enzyme inhibitors.

Adult↗
PubMed1995

Assessment of salt sensitivity in essential hypertension by 24-h ambulatory blood pressure monitoring.

We used ambulatory blood pressure monitoring (ABPM) in the assessment of salt sensitivity in 40 essential hypertensive patients, comparing 24-h mean blood pressure during 7 days of low salt (20 mmol NaCl/day) and high salt (260 mmol NaCl/day) intake. Salt sensitivity was diagnosed in 18 essential hypertensive patients (45%), each of them showing a significant increase in mean blood pressure (P < .05) from low to high salt diet. Salt-sensitive patients exhibited a high-salt-dependent increase in all blood pressure parameters including 24-h systolic, mean, diastolic blood pressure, blood pressure load, area under the curve, and awake and asleep blood pressure values. These patients exhibited a nondipper profile on both low-salt and high-salt diets. Salt-resistant patients (55%) showed a decrease in awake, and an increase in asleep blood pressure values after high salt intake, thus tending to flatten the circadian blood pressure profile. We conclude that ABPM is a useful method to assess salt sensitivity. In salt-resistant patients high salt intake induces a significant increase in asleep blood pressure with no significant changes in 24-h blood pressure, promoting a flattened blood pressure curve and tending to transform a dipper into a nondipper profile, which could have important implications in end-organ damage.

Adult↗
PubMed1995

Catch in the primary spines of the sea urchin Eucidaris tribuloides: a brief review and a new interpretation.

Previous models of reversible catch in echinoid spines, as a property of muscle or of collagen, are briefly reviewed and discussed. This brief review offers a new interpretation of catch in primary spines of Eucidaris tribuloides, viewing the collagen and small muscles of the catch ligament working together as a variable-length tendon. In the model presented, changes in ligament length when out of catch are accommodated by sliding of discontinuous, interdigitating and cross-link-stabilized columns of collagen fibrils, the muscle layer external to the ligament effecting spine movement. Catch is viewed as a consequence of contraction of small muscles inserted on the collagen columns within the ligament. Ligament shortening tightens the profuse (ca. 30,000/mm2) and highly ordered collagen insertion loops within the stereoms of the spine base and test, and catch results from the multiplicative effect of these friction sites in series. New data are presented on novel structural cross-links between collagen fibrils. The cross-links stabilize the ligament columns. The central ligament in Eucidaris plays a purely passive mechanical role in maintaining the alignment of the spine-test articulation. It contains no muscle and neither contracts nor undergoes catch; its insertions are simple, unlike the complex stereom insertions of the main ligament.

Animals↗
PubMed1994

Validation of the medical expert system RENOIR.

RENOIR is an expert system developed to assist the diagnosis of 37 diseases of connective tissue and inflammatory arthropathies. Precise diagnosis of rheumatic diseases implies great uncertainty and there is no gold standard with which to compare the expert system output. To overcome this problem a set of clinical cases was submitted to RENOIR and its diagnoses were compared with those of clinicians. Medical records of 81 patients with rheumatic diseases were interpreted by RENOIR and by 12 clinicians at three different expertise levels in rheumatology. Distances between the likelihoods of the 37 considered diseases provided by clinicians and RENOIR were computed as a disagreement measure. Mahalanobis distance was used to correct the collinearity between the possibilities of each pair of diseases. Using the resulting matrices of distances between experts, cluster analyses were carried out to classify RENOIR among human experts. Greater differences between RENOIR and clinicians than among clinicians themselves were not found.

Cluster Analysis↗
PubMed1993

Pharmacological sensitivity of the articular capsule of the primary spines of Eucidaris tribuloides.

1. This paper describes the effects of several cholinergic agonists and antagonists, and of beta-phenylethylamine (PEA) and some of its derivatives, on the articular capsule, or ligament, of the primary spines of Eucidaris tribuloides. 2. Carbamylcholine (CCh), methacholine (MeACh), nicotine, and muscarine exert a stiffening effect similar to that of acetylcholine (ACh), although the time course of their actions varies widely. 3. Atropine induced stiffening and blocked and responses to muscarine and MeACh. The responses to MeACh were blocked also by 4-diphenylacetoxy-N-methylpiperidine, suggesting the presence in the ligament of type M3 muscarinic receptors, in addition to nicotinic ones. d-Tubocurarine induced stiffness of the ligament and failed to block the responses to ACh and nicotine. 4. While ACh induced only a slight desensitization, CCh caused a long-lasting blockade of the stiffening effects of the cholinergic agonists. This shows that the receptors for ACh have a site or sites that recognize the ester moieties of these molecules. 5. Eserine and neostigmine potentiate the responses to acetylcholine, indicating the presence of acetylcholinesterase in the ligament. 6. beta-Phenylethylamine, epinephrine, norepinephrine, and dopamine induce diphasic responses; usually a brief softening followed by a slow and irreversible stiffening of the ligament. 7. In contrast to the above, tyramine and octopamine elicit a simple softening of ligaments which are stiff as a result of handling or by exposure to cholinergic agonists. However, tyramine and octopamine do not soften ligaments which become stiff as a result of exposure to adrenergic agonists.

Acetylcholine↗
PubMed1993

Serum and erythrocyte tocopherol in uremic patients: effect of hemodialysis versus peritoneal dialysis.

alpha-Tocopherol is transferred from serum to erythrocytes by high-density lipoproteins (HDL). We have studied total serum, HDL and erythrocyte tocopherol concentration in uremic patients on hemodialysis (HD; n = 18) and continuous ambulatory peritoneal dialysis (CAPD; n = 14), and the relationship between HDL and erythrocyte tocopherol content. Serum and erythrocyte tocopherol were determined by high-performance liquid chromatography. Serum tocopherol levels were higher in CAPD patients (p < 0.05) than in control (n = 30) and HD groups. Erythrocyte tocopherol was lower in HD patients than in the controls but there were no differences between CAPD patients and the control group. Bioavailable tocopherol was found to be normal in both HD and CAPD patients. HDL-tocopherol was lower in both HD and CAPD groups, but probably enough to reach a normal level of tocopherol in erythrocytes, as has been demonstrated in CAPD patients. So, although a defect in the transfer of tocopherol to red blood cells is possible, some other causes could influence it too, as a greater antioxidant consumption in HD patients.

Adult↗
PubMed1992

Validation of the medical expert system PNEUMON-IA.

The present study validates the expert system PNEUMON-IA. The aim of PNEUMON-IA is assessing the etiology of community-acquired pneumonias from clinical, radiological, and laboratory data obtained at the onset of the disease. Validation was performed using data from medical records of 76 patients with proven clinical diagnosis of pneumonia. The etiological diagnoses provided by PNEUMON-IA were compared to those established by five specialists unrelated to the development of the expert system. For each etiological possibility, both PNEUMON-IA and the experts provided a causal possibility, expressed as a linguistic label (i.e., "almost impossible"). Linguistic labels were then converted to numeric values. In the majority of cases, an etiological diagnosis was unavailable to be used as a gold standard. To overcome this limitation, distances between arrays of etiological possibilities given by specialists and by PNEUMON-IA were considered as an agreement measure between diagnoses. Cluster analysis based on those distances was used to classify PNEUMON-IA among experts. Results showed the same differences between specialists and PNEUMON-IA as among the specialists themselves. The method used to validate PNEUMON-IA could prove useful to assess the performance of expert systems in fields where no gold standard is available.

Adolescent↗
PubMed1992

[Nutritional changes caused by the germination of legumes commonly eaten in Chile].

The changes promoted by germination on phytates, oligosaccharides, crude protein, amino acids and riboflavin contents of black and white cultivars of beans, lentils, chicken-pea and peas, were studied. Seeds germination was carried out in darkness at 25 degrees C and 85% RH during 72 hours, previously soaked overnight in a solution of sodium hypochlorite at a concentration of 50 ppm. Germination capacity was assessed by determining hypocotyl and epicotyl lengths and percent of sprouted seed. The seeds were milled and freeze-dried for the chemical analysis. Germination promoted a significant increase in crude protein content and reduction also significant in phytates levels. These changes were attributed to an increase of proteases and phytase activities. In fact, this enzyme would make a solubilization of phytates and would release soluble protein and minerals. A significant reduction of flatulence oligosaccharides took place, which was also explained by an increase of alpha-galactosidase concentration. Sprouted seeds showed a higher content of almost all amino acid than crude legumes, although this change was variable. Significant increase of riboflavin was also found. Finally, germination decreased ashes and fat contents. These findings were determined in all legumes, although both cultivars of beans showed a higher response to the biochemical changes.

Amino Acids↗
PubMed1991

Nutritional quality of lupine (Lupinus albus cv. Multolupa) as affected by lactic acid fermentation.

The effects of selected NRRL strains of Lactobacillus acidophilus, L. buchneri, L. cellobiosus and L. fermentum upon oligosaccharide, phytate and alkaloid contents, as well as on the nutritive value of lupine, were investigated. Lupine was processed to a 12% total solids suspension, inoculated with 1% (v/v) cultures and fermented until a final desired pH of 4.5. L. acidophilus B-2092 and L. buchneri B-1837 growth was related to a significant sucrose breakdown and decreases of phytates, whereas L. acidophilus B-1910 and L. fermentum B-585 reduced the content of flatulence oligosaccharides. The activity of L. acidophilus B-1910 was particularly associated with lowering of alkaloids and increase of riboflavin. Lactic acid fermentation produced slight changes in lysine and methionine contents. No significant differences in net protein ratio values and protein digestibility were found between fermented and unfermented lupine (P less than 0.05). A 1:1 ratio mixture of B-1910 and B-2092 strains of L. acidophilus lead to a final fermented lupine with nutritional advantages to those given by the individual cultures.

Alkaloids↗