Biomedical subjects

Luis González

Publications and source records attributed to Luis González.

10 recordsLinked to original sources

PubMed2006

Optics of the average normal cornea from general and canonical representations of its surface topography.

Generally, the analysis of corneal topography involves fitting the raw data to a parametric geometric model that includes a regular basis surface, plus some sort of polynomial expansion to adjust the more irregular residual component. So far, these parametric models have been used in their canonical form, ignoring that the observation (keratometric) coordinate system is different from corneal axes of symmetry. Here we propose, instead, to use the canonical form when the topography is referenced to the intrinsic corneal system of coordinates, defined by its principal axes of symmetry. This idea is implemented using the general expression of an ellipsoid to fit the raw data given by the instrument. Then, the position and orientation of the three orthogonal semiaxes of the ellipsoid, which define the intrinsic Cartesian system of coordinates for normal corneas, can be identified by passing to the canonical form, by standard linear algebra. This model has been first validated experimentally obtaining significantly lower values for rms fitting error as compared with previous standard models: spherical, conical, and biconical. The fitting residual was then adjusted by a Zernike polynomial expansion. The topographies of 123 corneas were analyzed obtaining their radii of curvature, conic constants, Zernike coefficients, and the direction and position of the optical axis of the ellipsoid. The results were compared with those obtained using the standard models. The general ellipsoid model provides more negative values for the conic constants and lower apex radii (more prolate shapes) than the standard models applied to the same data. If the data are analyzed using standard models, the resulting mean shape of the cornea is consistent with previous studies, but when using the ellipsoid model we find new interesting features: The mean cornea is a more prolate ellipsoid (apical power 50 D), the direction of the optical axis is about 2.3 degrees nasal, and the residual term shows three Zernike coefficients significantly higher than zero (third-order trefoil and fourth- and sixth-order spherical). These three nonzero Zernike coefficients are responsible for most of the higher-order aberrations of the average cornea. Finally, we propose and implement a simple method for three-dimensional registration of corneal topographies, passing from the general to the canonical form of the ellipsoid.

Adult↗

PubMed2005

Quantitative study of the structure-retention index relationship in the imine family.

The Kováts retention index is one of the most popular descriptors of the performance of organic compounds in gas chromatography (GC). The mathematical modeling of this index is an interesting and open problem in analytical chemistry. In this paper, two models for the prediction of the Kováts retention index are presented. Topologic, topographic and quantum-chemical descriptors were used as structural descriptors. Multiple linear regression (MLR) analysis provides the first model using the forward stepwise procedure for the variable selection. For the second one, an ensemble of artificial neural network (ANN) was constructed using the pruning algorithm. Both methods were validated by an external set of compounds, by the Golbraikh and Tropsha method and by the leave-one-out (LOO) and the leave many out (LMO) procedures. The R2, RMScv and Q2, values for the training sets were 0.884, 0.589 and 0.830 for NN and 0.974, 0.417 and 0.970 for MLR models, respectively. The robustness of both models was demonstrated. Both portrait the chromatographic performance of the sample but in this case, the results of MLR equation are better than the NN ones. The MLR model is recommended because of its simplicity.

Imines↗

PubMed2005

Rapid molecular diagnosis of ataxia-telangiectasia by optimised RT-PCR and direct sequencing analysis.

Ataxia-telangiectasia (A-T) is a severe autosomal recessive disorder involving cerebellar degeneration, immunodeficiency, chromosomal instability, radiosensitivity, and cancer predisposition. A-T results from mutations in a single gene (ataxia-telangiectasia mutated, ATM) on chromosome 11 that encodes a 3056 amino acid protein (ATM). The purpose of this study is the design of an easy and rapid method for the molecular diagnosis of A-T which could be applied to clinical diagnosis, genetic counselling, carrier prediction, and prenatal diagnosis. Sixteen primer pairs were designed for RT-PCR. The PCR conditions were optimised to obtain a unique profile for the amplification of the 16 PCR products. These fragments were purified, directly sequenced and interpreted. The mutations found in three Spanish A-T families were reconfirmed with the optimised PCR and direct sequencing analysis. Up to now more than 400 A-T associated mutations have been reported in the ATM gene that do not support the existence of one or several hotspots. The immense size (transcript with 9168 nucleotides) and the structure of this gene (66 exons) greatly complicate the process of screening for all sequence variations. Our simple method allows identification of mutations in the coding region of the ATM gene from cDNA and represents a very useful tool for early diagnosis and genetic counselling in families with A-T.

Ataxia Telangiectasia↗

PubMed2004

HLA haplotypes associated with hemochromatosis mutations in the Spanish population.

BACKGROUND: The present study is an analysis of the frequencies of HLA-A and -B antigens and HLA haplotypes in two groups of individuals homozygous for the two main HFE mutations (C282Y and H63D) and a group heterozygous for the S65C mutation. METHODS: The study population includes: 1123 healthy individuals, 100 homozygous for the C282Y mutation, 138 homozygous for the H63D mutation and 17 heterozygous for the S65C mutation. HFE and HLA alleles were detected using DNA-based and microlymphocytotoxicity techniques respectively. RESULTS: An expected significant association between C282Y and the HLA-A3/B7 haplotype was found, but other HLA haplotypes carrying the -A3 antigen were found: HLA-A3/B62 and HLA-A3/B44. Also, a significant association between H63D mutation and HLA-A29/B44 haplotype was found, and again other HLA haplotypes carrying the HLA-A29 antigen were also found: HLA-A29/B14 and HLA-A29/B62. In addition, the S65C mutation seems to be associated with a HLA haplotype carrying the HLA-A26 antigen. CONCLUSION: These findings clearly suggest that HLA-A3/B7 and HLA-A29/B44 are the ancestral haplotypes from which the C282Y and H63D mutations originated, respectively. The frequencies of these mutations in different populations, their geographical distribution, and the degree of the statistical association to the ancestral haplotypes, suggest that the H63D mutation must have occurred earlier than the C282Y mutation.

Gene Frequency↗

PubMed2004

A sliding mode control proposal for open-loop unstable processes.

This papers presents a sliding mode controller based on a first-order-plus-dead-time model of the process for controlling open-loop unstable systems. The proposed controller has a simple and fixed structure with a set of tuning equations as a function of the desired performance. Both linear and nonlinear models were used to study the controller performance by computer simulations.

Algorithms↗

PubMed2004

Changes in iNOS activity, oxidative stress and melatonin levels in hypertensive patients treated with lacidipine.

OBJECTIVE(S): To study the changes in macrophage inducible nitric oxide synthase (iNOS) activity, plasma levels of nitrite, lipid peroxidation (LPO) and melatonin in human essential hypertension before and 6 months after 4 mg/day lacidipine treatment. DESIGN: The study was carried out in a total of 25 subjects--11 healthy subjects and 14 hypertensive patients. Blood pressure and peripheral blood samples were taken before and after 6 months of lacidipine treatment (4 mg/day). METHODS: Systolic (SBP) and diastolic blood pressure (DBP), renal function, lipid and carbohydrate metabolism, renin, aldosterone and catecholamine levels were measured by routine methods. The activity of macrophage iNOS and plasma nitrite, LPO and melatonin levels were also measured. CONCLUSIONS: Besides reducing blood pressure, lacidipine treatment significantly decreased plasma LPO and macrophage iNOS activity, without changes in NO. Melatonin significantly increases in hypertensive patients, returning to control after lacidipine. Thus, lacidipine reduced blood pressure and free radicals, avoiding the oxidative damage to endothelium. It is suggested that administration of lacidipine plus melatonin may enhance the beneficial effects of each drug in essential hypertension.

Adult↗

PubMed2003

[Clinical study of measure of parasitemia in patients infected with Trypanosoma cruzi in Atacama, Chile].

BACKGROUND: Trypanosoma cruzi infection is endemic in Northern/Central Chile. AIM: To perform a clinical assessment of patients infected with Trypanosoma cruzi. PATIENTS AND METHODS: Two hundred sixty three subjects with a positive serology for Trypanosoma cruzi, were invited by mail to a clinical assessment in a Regional Hospital. In a subsample of these, a polymerase chain reaction for Trypanosoma cruzi, was done. RESULTS: Of all the invited subjects, 183 responded and were assessed at the hospital. Of these, 60 had cardiac affections, 52 had colon problems and 17, esophageal disease. Seventy four were asymptomatic. Of the 64 patients in whom polymerase chain reaction was done, 35 had a positive result. CONCLUSIONS: A high percentage of subjects infected with Trypanosoma cruzi, had clinical consequences of the infection. Polymerase chain reaction showed persistency of the parasite in more than half of the infected patients.

Adult↗

PubMed2002

[Detection of BCR-ABL gene sequences using RT-PCR in patients with leukemia in the IX region. Chile].

BACKGROUND: The BCR-ABL fusion gene is the molecular expression of the Philadelphia chromosome. This cytogenetic aberration is the most frequent alteration found in leukemias, which is produced by the translocation t(9;22). Two different fusion proteins are produced depending on the break point (210 kD and 190 kD). The detection of this gene has both diagnostic and prognostic importance, associated with poor prognosis in acute lymphoblastic leukemia (ALL). AIM: To detect BCR-ABL gene sequences in patients with leukemia from the IX Region of Chile. MATERIAL AND METHODS: We studied 58 patients: 5 chronic myeloid leukemia (CML), 35 ALL, 15 acute myeloid leukemia (AML) and 3 biphenotypic leukemia. The gene sequences were detected using reverse transcriptase polymerase chain reaction (RT-PCR). RESULTS: BRC-ABL gene sequences were positive in all patients with CML, 2 of 35 ALL (one child and one adult). The remaining patients were negative. We found p210 and p190 co-expression in 2 CML and 1 ALL. CONCLUSIONS: Our results are in agreement with other reports. The detection of these and other genetic alterations will allow us to have invaluable diagnostic and prognostic information from our patients with leukemia.

Acute Disease↗

PubMedDate not supplied

In vitro and in vivo study of octacosanol metabolism.

BACKGROUND: Policosanol is a mixture of very-long-chain aliphatic alcohols purified from sugar cane wax with cholesterol-lowering effects, whose main component is octacosanol. Scarce data about the metabolism of octacosanol and the other fatty alcohols composing policosanol have been published. METHODS: Human fibroblasts were cultured in presence of (3)H-octacosanol during 0.5, 2 and 4 h. Lipid extracts were analyzed by thin layer chromatography, and the spots corresponding to octacosanol and octacosanoic acid were identified comparing with authentic standards. Spots were scraped, transferred to vials and radioactivity was measured. For corroborating the presence of octacosanol and octacosanoic acid, samples were analyzed by gas chromatography-mass spectrometry (GC-MS). The in vivo study of octacosanol metabolism was conducted in rats and Macaca arctoides monkeys. Rats were orally administered with policosanol (60 mg/kg) and free octacosanol and octacosanoic acid were identified in liver and plasma by GC-MS at various time intervals. Monkeys were orally and endovenously treated with policosanol (10 mg/kg) and the presence of free octacosanol, octacosanoic acid and some chain-shortened FA was investigated. RESULTS: When fibroblasts were cultured in presence of (3)H-octacosanol, three spots were found: a first one corresponded to octacosanoic acid, a second to octacosanol and a third one remained unidentified. The radioactivity on the spot of octacosanoic acid slightly decreased throughout the incubation but increased in the third spot. Octacosanol and free octacosanoic acids were also identified in plasma of monkeys orally administered with policosanol. In addition, plasma samples showed free saturated acids, palmitic acid being the most abundant, followed by oleic and mystiric acids. Unsaturated acids (oleic and palmitoleic) were also observed. CONCLUSIONS: The present study demonstrates that octacosanoic acid is formed after incubation of fibroblast cultures with (3)H-octacosanol and after oral dosing with policosanol to rats. In addition, we demonstrated that shortened saturated (myristic, palmitic and stearic) and unsaturated (oleic, palmitoleic) FA are also formed after oral dosing with policosanol to monkeys. The present results are consistent with the fact that octacosanol metabolism is linked to FA metabolism via beta-oxidation, but further studies need to explore the occurrence of more metabolites proving such hypothesis.

Animals↗

PubMedDate not supplied

Accuracy and reproducibility of Zywave, Tracey, and experimental aberrometers.

PURPOSE: To compare the accuracy and verify the reliability of different commercial and experimental prototypes of aberrometers using a small group of normal subjects with low myopia. METHODS: Three different devices were used to measure the wavefront aberration of five normal myopic eyes: 1) Zywave--commercial aberrometer based on a Hartmann-Shack wavefront sensor; 2) Tracey--commercial system based on the laser ray tracing principle; and 3) an experimental laboratory laser ray tracing instrument working at two different wavelengths (532 and 786 nm). A series of five measurements were taken for each subject. Pupil diameter and alignment were controlled. All wave aberration maps were reduced to a common 6.5-mm pupil diameter, and then the mean and standard deviation were computed for the series, as well as the global average and standard deviation for each subject. RESULTS: Despite several important differences among devices and sessions, the results obtained with the different devices were equivalent. The main difference found between aberrometers was due to the longitudinal chromatic aberration caused by the use of different wavelengths. The signal-to-noise ratio estimated from the raw data was moderate, 12, but could be improved by a factor of 2 by discarding those measurements with a higher deviation from the mean and averaging the remaining data, which was the approach implemented in the Zywave instrument. CONCLUSION: The aberrometers tested were reliable in normal eyes with low myopia. Aberrometry is a robust but noisy technique. Accuracy is limited by noise and other sources of variability, including the size and alignment of the pupil. These conclusions might not apply to eyes with large aberrations.

Adult↗