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Biomedical subjects

R López

Publications and source records attributed to R López.

At least 73 records · Page 4Linked to original sources
PubMed2001

Liver transplantation in patients with portal vein thrombosis.

The aim of this study is to analyze the incidence, risk factors, management, and follow-up of patients with portal vein thrombosis (PVT) undergoing primary orthotopic liver transplantation (OLT). Four hundred fifteen OLTs were performed in 391 patients. In 62 patients, partial (group 1; n = 48) or complete (group 2; n = 14) PVT was found at the time of surgery. Portal flow was reestablished by venous thrombectomy. In this study, we compare 62 primary OLTs performed in patients with PVT at the time of OLT with a group of 329 primary OLTs performed in patients without PVT (group 3) and analyze the incidence of PVT, use of diagnostic methods, surgical management, and outcome. We found no significant differences among the 3 groups for length of surgery, cold and warm ischemic times, and postoperative stay in the intensive care unit. With the piggyback technique, groups 1 and 2 had greater blood losses and required more blood transfusions than group 3. The early reoperation rate was greater in group 2. The incidence of rethrombosis was 4.8% (group 1, 2%; group 2, 14.3%). Reexploration and thrombectomy (2 patients) and retransplantation (1 patient) had a 100% mortality rate. In particular, the mortality rate of patients with complete PVT with extension into the splanchnic veins is high (33%). Three-month and 4-year patient survival rates were statistically similar in the 3 groups. The presence of PVT at the time of OLT is not a contraindication for OLT. However, if PVT extends into the splanchnic veins, the outcome is guarded.

Adult↗
PubMed2001

Molecular characterization of the pneumococcal teichoic acid phosphorylcholine esterase.

A search to identify proteins with high affinity for choline-containing pneumococcal cell walls (choline-binding proteins) has permitted the localization, cloning, sequencing, and overexpression of a gene (pce), coding for a protein (Pce) that liberates phosphorylcholine from purified cell walls of Streptococcus pneumoniae. The pce gene of the pneumococcal strain R6 encodes a protein of 627 amino acids with a predicted Mr of 72,104. Pce can remove a maximum of 20% phosphorylcholine residues from the cell wall teichoic acid. In silico analysis of Pce shows a modular organization of the enzyme where the choline-binding domain, involved in cell wall substrate recognition, and the catalytic domain are located at the carboxy- and amino-terminal moieties of the protein, respectively. Remarkably, a long tail of 85 amino acids follows the carboxy-terminal domain, a structural feature that had not been described for the published choline-binding proteins. The carboxy-terminal moiety of Pce is assembled by 10 repeated motifs, and the protein has also a cleavable signal peptide of 25 amino acids that renders after its cleavage a mature protein of 69,426 Da (602 amino acids). The pce gene has been expressed in Escherichia coli, and Pce was active when assayed on pneumococcal walls. We have also found that the signal peptide of Pce was functional in E. coli. Biochemical analysis suggested that Pce is the teichoic acid phosphorylcholine esterase of S. pneumoniae that had been biochemically characterized previously. Construction of two pce pneumococcal mutants (R6D and M31D) by insertion-duplication mutagenesis revealed that these mutants grew at a doubling-time similar to those of the parental strains of the wild-type R6 and the lytA-mutant M31, respectively. R6D and M31D were morphologically indistinguishable from the parental strains when whole-mounted cells were observed under the electron microscope and exhibited levels of competence for genetic transformation slightly lower than those reported for R6 and M31.

Amino Acid Sequence↗
PubMed2001

Role of COX-2-derived metabolites in regulation of the renal hemodynamic response to norepinephrine.

The objective of this study was to examine the role of cylcooxygenase (COX)-2-derived prostaglandins (PG) in modulating the renal hemodynamic effects of norepinephrine (NE) during low or normal sodium intake. The relative contribution of each COX isoform in producing the PG that attenuate the renal NE effects during normal sodium intake was also evaluated. The renal response to three doses of NE (50, 100, and 250 ng. kg(-1). min(-1)) was evaluated in anesthetized dogs pretreated with vehicle, a selective COX-2 inhibitor (nimesulide), or a nonselective COX inhibitor (meclofenamate). Intrarenal infusion of the two lower doses of NE in vehicle-pretreated dogs with normal sodium intake (n = 8) elicited an increase in renal vascular resistance (RVR; 21 and 34%) without inducing changes in glomerular filtration rate (GFR). The highest dose of NE in this group induced a further increment in RVR (113%) and a decrease in GFR (33%). Pretreatment with nimesulide in dogs with normal sodium intake (n = 7) did not modify the NE-induced increments in RVR but enhanced the decreases in GFR induced by the three NE doses (12, 26, and 64%). The renal hemodynamic response to NE in meclofenamate-pretreated dogs with normal sodium intake (n = 7) was similar to that found in dogs pretreated with nimesulide. Infusion of the lowest dose of NE to vehicle-pretreated dogs with low sodium intake (n = 6) did not modify GFR and elicited an increase in RVR (42%). Infusion of the second and third doses of NE led to a decrease in GFR (35 and 91%) and a rise in RVR (82 and 587%). Infusion of the first two doses of NE in nimesulide-pretreated dogs with low sodium intake (n = 5) induced a fall in GFR (64 and 92%) and an increase in RVR (174 and 2,293%) that were greater (P < 0.05) than those induced by NE in vehicle-pretreated dogs. The elevation in the urinary excretion rates of PGE(2) and 6-keto-PGF(1alpha) elicited by NE was prevented in the nimesulide-pretreated dogs. Our results show that COX-2 inhibition potentiates the renal hemodynamic effects of NE and propose that the PG involved in modulating them are mainly derived from COX-2 activity.

6-Ketoprostaglandin F1 alpha↗
PubMed2001

Epidemiology of clinical attachment loss in adolescents.

BACKGROUND: Relatively little is known about the prevalence, severity, and determinants of clinical attachment loss among adolescents. METHODS: A multi-stage random sampling procedure was used to obtain a sample of 9,203 high school students aged 12 to 21 years from the Province of Santiago, Chile. All but 41 students were examined for clinical attachment loss in 6 sites of first and second molars and incisors. The students were interviewed with respect to tooth brushing habits, smoking habits, dental visits, and diabetic status. Logistic regression analyses were used to assess the relative strength of the associations between age, gender, smoking, tooth brushing habits, dental attendance patterns, diabetic status, and governmental school support and the occurrence of clinical attachment loss. RESULTS: Overall, clinical attachment loss > or = 1 mm was seen in 69.2% of the students; > or = 2 mm in 16% of the students; and > or = 3 mm in 4.5%. The distribution of clinical attachment loss was markedly skewed, but followed a continuum of disease severity. Logistic regression analyses showed that attachment loss was associated with higher age, female gender, infrequent tooth brushing, infrequent dental visits, and attending a high school receiving governmental support. CONCLUSIONS: No sharp distinction exists between periodontal health and disease among Chilean adolescents. Higher age, poor oral hygiene, and a lower socioeconomic background play a role in the occurrence of clinical attachment loss.

Adolescent↗
PubMed2001

Genetic bases and medical relevance of capsular polysaccharide biosynthesis in pathogenic streptococci.

Many streptococci are human and/or animal pathogens and the frequent cause of life-threatening diseases. Among various streptococcal virulence factors, capsular polysaccharides (CPs) are recognized as essential to prevent phagocytosis by macrophages and neutrophils. In the last decade, an impressive advance on the knowledge of the genetic bases underlying capsule formation has been achieved. The capsular gene cluster driving the formation of the CP of Streptococcus pyogenes and other hyaluronate-producing streptococci, represents one of the simplest cases of gene organization to synthesize a capsule. A more complex situation has been found in Streptococcus pneumoniae, Streptococcus agalactiae, Streptococcus suis, and other streptococci. On the whole, there exists a direct relationship between the structural and chemical complexity of the repeating unit of the polysaccharide and the number of genes found in the corresponding capsular locus. Streptococcal vaccines, either polysaccharide or conjugate, are currently being tested in clinical trials to overcome the rise of worldwide antibiotic resistance, although, for different reasons, none of these vaccines are expected to provide the required full coverage in a near future. This concern has prompted to explore alternative possibilities with an improved therapeutic potential against streptococcal diseases.

Animals↗
PubMed2001

The evidence for an etiological relationship between oral contraceptive use and dysplastic change in cervical tissue.

A case-control study of 112 patients with cervical intraepithelial neoplasia (CIN) and 131 control subjects was conducted. Estradiol receptor levels were determined in the total (cytosolic-nucleosolic) fraction of the neoplastic cervical specimens taken during the late proliferative phase of their cycle from 58 premenopausal patients who had been oral contraceptive (OC) users for at least 2 years and from 54 premenopausal women who had not been OC users. All specimens contained variable amount of estradiol receptor (from 7.6 to 53.0 fmol estradiol/mg protein and 7.2 to 29.3 fmol estradiol/mg protein in patients who were OC users and non-users, respectively). A significant correlation was found between estradiol receptor concentration and histological grading in both groups, likewise higher levels of estradiol receptor were observed in the low-grade CIN group tissue from patients who were OC users (p < 0.05). At the same time 17 beta-estradiol and progesterone levels were also determined in the serum of all women who had not used an OC for at least 12 months. The mean +/- SD estradiol serum levels in non-users of OC with CIN (0.189 +/- 0.08 ng/ml, follicular phase) were greater than the mean +/- SD (1.163 +/- 0.33 ng/ml, luteal phase) progesterone serum concentration. Serum estradiol levels were significantly higher (p < 0.05) in OC users, whereas progesterone levels were not (p > 0.05). OC users had an increased risk (odds ratio = 1.31, 95% CI 1.0-2.3) of cervical neoplasia.

Adult↗
PubMed2001

A model for forecasting emergency hospital admissions: effect of environmental variables.

This study modeled patterns and trends in emergency hospital admissions at a hospital in Madrid, Spain. The purpose was to quantify qualitative associations that have been detected between such admissions and a number of environmental variables. The following data were used: unscheduled daily emergency hospital admissions, Madrid air pollution data, and meteorological data. Time-series analysis was performed, with Box-Jenkins modeling. A multivariate model was constructed, incorporating the different causes of admissions and the respective environmental variables. Statistically significant associations were found between hospital admissions and other variables, indicating relationships with temperature, relative humidity, and mean daily tropospheric ozone concentrations. Whereas the effect of heat on admissions was short term, that of cold was in evidence from the second week. The association with ozone showed a seven-day lag and basically manifested itself as an influence on admissions for circulatory disease.

Cardiovascular Diseases↗
PubMed2000

HLA class I alleles associated with susceptibility or resistance to human immunodeficiency virus type 1 infection among a population in Chaco Province, Argentina.

Host genetic factors, such as HLA alleles, are important in human immunodeficiency virus (HIV) infection and its progression to AIDS. HLA class I gene products are involved in peptide presentation, and each allele is responsible for presenting a different set of peptides to cytotoxic T lymphocytes. The increase or decrease in the frequency of certain alleles in HIV-1-positive versus control subjects would suggest that alleles play a role in susceptibility to or protection against this viral infection. In the present study, 56 HIV-1-positive patients in Chaco Province, Argentina, were typed for the HLA-A and HLA-B loci, using polymerase chain reaction and sequence-specific oligonucleotide probes. The frequency of alleles A*24, B*18, and B*39 was increased in HIV-1-positive subjects, suggesting that these alleles play a role in susceptibility to HIV-1 infection. Alleles B*44 and B*55 were not found in HIV-1-positive subjects, suggesting that they have a protective effect against the disease. The P values of the alleles B*39 and B*44 were statistically significant (P<.05).

Acquired Immunodeficiency Syndrome↗
PubMed2000

Plasmodium falciparum: red blood cell binding studies of peptides derived from histidine-rich KAHRP-I, HRP-II and HRP-III proteins.

Histidine-rich proteins have been associated with Plasmodium falciparum infected red blood cells (RBC) cytoadherence, and RBC rosetting; these phenomena may cause clogging of the post-capillary venules, this being one of the main causes of severe cerebral malaria. They may also participate in parasite mature stages' evasion of the immune system and their subsequent destruction in the spleen. Non-overlapping synthetic peptides, corresponding to entire amino acid sequences reported for the KAHRP-I, HRP-II and HRP-III proteins, were used in RBC binding assays. Peptides with high and low binding activity were recognized. The KAHRP-I protein shows 3 peptides with high binding affinity to RBCs, two of them variable (peptide 6783, sequence 321QNYVHPWSGYSAPYGVPHGA(340) and peptide 6789, sequence 441KKREKSIMEKNHAAKKLTKK(460)) and the other conserved (peptide 6786, sequence 381KSKKHKDHDGEKKKSKKHKD(400)) having affinity constant of around 190 nM and 1000 binding sites per cell. Interestingly, this peptide shares aminoacid sequences with one reported as being recognized by malaria exposed human antibodies. The HRP-I protein also presents one conserved peptide (peptide 6800, sequence 24NNSAFNNNLCSKNAKGLNLN(43)) with high affinity, located in the amino terminal region of the native protein, having 210 nM affinity constant and 6000 receptor sites. The HRP-III protein only contains peptides with low binding activity. Treatment of red blood cells with neuraminidase reduces the binding of the conserved high binding 6786 and 6800 peptides. Anti-glycophorins A, B and C antibodies inhibit the binding of the conserved high binding 6786 and 6800 peptides. Furthermore, the specific determination of glycoproteins by chemioluminescenoe, in SDS/PAGE western blot, suggests that these glycophorins could be the receptor for these high binding peptides. High binding peptides' critical amino acids, involved in RBC binding were determined by means of competition binding assays.

Amino Acid Sequence↗
PubMed2000

Mobilization kinetics of peripheral blood progenitor cells after IAPVP-16 salvage chemotherapy plus G-CSF in lymphoproliferative disorders.

We have explored the efficacy of salvage chemotherapy combination, IAPVP-16 (ifosfamide 5 g/m2 on day 1; VP-16 100 mg/m2 on days 1-3; ara-C 1.2 g/m2/12 h on days 1 and 2; methylprednisolone 80 mg/m2 on days 1-5) plus G-CSF for PBPC mobilization. This protocol was used in 45 patients with relapsed or refractory lymphoproliferative diseases who underwent 85 leukaphereses. In 41 patients > 2 x 106/kg CD34+ cells were obtained after a median of two procedures. The median number of CD34+ cells harvested was 3.2 x 106/kg per apheresis and 8.4 x 106/kg per patient. Seven of 10 patients who had failed previous mobilization attempts achieved more than 2 x 106 CD34+ cells/kg in a maximum of three aphereses. A history of previous mobilization failure and a low platelet count (<150 x 109/l) negatively influenced the CD34+ cell yield in univariate and multivariate analyses. A good correlation was found between the circulating CD34+ cells/microl and the CD34+ cells and CFU-GM in the leukaphereses products (r = 0.93 and r = 0.73, P < 0.001), and > or =17 CD34+ cells/microl predicted the achievement of > 2 x 106/kg CD34+ cells in a single leukapheresis in more than 90% of cases. IAPVP-16 plus G-CSF may be specially indicated in tandem transplantations or CD34+ selection and in patients who have failed previous mobilization attempts.

Adult↗
PubMed2000

Clonal origin of the type 37 Streptococcus pneumoniae.

It has been recently reported that different type 37 clinical isolates of Streptococcus pneumoniae have an identical tts gene directing the formation of type 37 capsular polysaccharide. Here we show that type 37 S. pneumoniae strains isolated in two different continents (Europe and America) some 60 years apart frequently gave rise to nontypable variants upon in vitro cultivation. The tts gene from three independent nontypable mutants was PCR amplified and sequenced showing different classes of inactivating mutations. Furthermore, pulsed-field gel electrophoresis and multilocus sequence typing demonstrated that the type 37 pneumococcal isolates studied so far constitute a highly related strain cluster (a clonal complex), and strongly suggested that every type 37 pneumococcus has spread globally from a single, old clone.

Bacterial Typing Techniques↗
PubMed2000

Percutaneous toxicity of uranyl nitrate: its effect in terms of exposure area and time.

Different groups have undertaken research work focusing their attention on the biological effects of uranium and have described kidney and bone to be the main target organs in uranium poisoning. In this study we used the skin as the route of entry of uranium. We carried out two sets of experiments in adult rats: in one of them topical applications with uranyl nitrate (UN) over different areas were performed; in the other topical applications with UN on a given area over different times were carried out. In the latter experiment the exposure to UN was stopped by removing it from skin with soap and water. Kidney and bone samples were removed for histological studies. This work is based on the determination of the survival rate of the exposed animals and on the effects elicited in kidney and bone. There is a relation between the area of the surface exposed to uranium and the time of exposure and the subsequent percutaneous toxicity. There were no surviving animals following topical application of UN to an 8 cm2 area nor when the time of exposure was 24 h. The survival rate of the animals increased when either the topical area or the time of exposure to UN was reduced. Although the inhibition of bone formation in metaphysical bone has been previously described by our group as a result of UN poisoning, this is the first time that such an effect is found after percutaneous exposure for such short periods of time. The general toxic effects of UN, evidenced as kidney histological alterations, increased in severity as either one of the two variables studied increased. This is a condition that could be considered as hazardous for those workers engaged in uranium processing and purification. It is noteworthy that a simple method such as washing with soap and water is an effective method to reduce the lethality of UN percutaneous intoxication.

Administration, Topical↗
PubMed2000

Retrobulbar anaplastic astrocytoma in a dog: clinicopathological and ultrasonographic features.

An 11-year-old entire female German shepherd dog was presented with a progressive non-painful exophthalmos of the right eye. Ultrasonographic examination revealed a solid and well-defined orbital mass compressing the globe. Thoracic radiography revealed multiple pulmonary metastases of different sizes. The histopathological and immunohistochemical features of both the retrobulbar tumour and pulmonary metastases were consistent with an anaplastic astrocytoma. This represents an unusual case of an extracranial astrocytoma with multiple pulmonary metastases. The clinical features and the ultrasonographic, histopathological and immunohistochemical findings are described.

Animals↗
PubMed2000

MM1, a temperate bacteriophage of the type 23F Spanish/USA multiresistant epidemic clone of Streptococcus pneumoniae: structural analysis of the site-specific integration system.

We have characterized a temperate phage (MM1) from a clinical isolate of the multiply antibiotic-resistant Spanish/American 23F Streptococcus pneumoniae clone (Spain(23F)-1 strain). The 40-kb double-stranded genome of MM1 has been isolated as a DNA-protein complex. The use of MM1 DNA as a probe revealed that the phage genome is integrated in the host chromosome. The host and phage attachment sites, attB and attP, respectively, have been determined. Nucleotide sequencing of the attachment sites identified a 15-bp core site (5'-TTATAATTCATCCGC-3') that has not been found in any bacterial genome described so far. Sequence information revealed the presence of an integrase gene (int), which represents the first identification of an integrase in the pneumococcal system. A 1.5-kb DNA fragment embracing attP and the int gene contained all of the genetic information needed for stable integration of a nonreplicative plasmid into the attB site of a pneumococcal strain. This vector will facilitate the introduction of foreign genes into the pneumococcal chromosome. Interestingly, DNAs highly similar to that of MM1 have been detected in several clinical pneumococcal isolates of different capsular types, suggesting a widespread distribution of these phages in relevant pathogenic strains.

Amino Acid Sequence↗
PubMed2000

Uveal melanoma model with metastasis in rabbits: effects of different doses of cyclosporine A.

OBJECTIVE: To compare the toxicity and efficacy of different doses of cyclosporine A (CsA) in a rabbit model of uveal melanoma. METHODS: We used four experimental groups: control, no CsA; group 1, 15 to 10 mg/kg/day; group 2, 15 mg/kg/day; and group 3, 20 mg/kg/day. The MKT-BR cell line was implanted in the choroid. All animals underwent ophthalmoscopic evaluation; the animals were weighed and blood levels of CsA, blood urea nitrogen (BUN), creatinine and alanine aminotransferase (ALT) were measured weekly. Necropsies and histologic study were performed to detect intraocular tumors and metastasis. RESULTS: A difference in survival rates was found between groups 2 and 3 (p = 0.0042). Differences were observed in the mean BUN and creatinine levels (p < 0.001 and p < 0.003, respectively) between groups but not in the ALT. Intraocular tumors were detected ophthalmoscopically in 50%, 65%, and 70% of the animals in groups 1, 2, and 3 respectively, and histologically in 70%, 90%, and 100% of the same groups. Lung metastases were found in 26.8% of animals with intraocular tumors. Differences were observed in mean CsA blood levels between animals with and without histologically demonstrated uveal tumors (p = 0.001) but not in animals with or without metastasis. CONCLUSIONS: Different doses of CsA affect survival, tumor development and renal toxicity. Metastatic disease is independent of CsA dose and the subsequent CsA blood levels. A blood level of CsA ranging from 500 to 1000 ng/ml and doses of 10 to 15 mg/kg/day may effectively develop this model of uveal melanoma.

Alanine Transaminase↗
PubMed2000

[Physicochemical and microbiological evaluation of 3 commercial guava jams (Psidium guajava L.)].

Four different production batches were taken from each brand. Samples were purchased from retail markets in Maracay, Cagua and Turmero. (Venezuela). The average physical and chemical values were: vacuum = 38.81 cm Hg; pH = 3.28; titrable acidity (%citric acid) = 0.59%; degree Brix = 67.24; reducing sugars = 55.28%; total sugars = 62.28, and the color parameters a = +14.44, b = +8.77 and L = 17.09. Molds, yeast and aerobic plate counts were lower than 10 UFC/g; it reveals an excellent microbiological quality of the product. The studied jams degree Brix and acidity fulfil COVENIN (1) requirements for jam products, but not pH range. In agreement with variance analysis, there were highly significance differences between the samples and among the shares of each sample for all physical and chemical properties evaluated.

Analysis of Variance↗