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Biomedical subjects

J Méndez

Publications and source records attributed to J Méndez.

At least 19 recordsLinked to original sources
PubMed1997

Male-predominant carboxylesterase expression in the reproductive system of molluscs and insects: immunochemical and biochemical similarity between Mytilus male associated polypeptide (MAP) and Drosophila sex-specific esterase S.

We suggested that sexual differentiation of the reproductive system in gonochoric species of invertebrates can be characterized by common molecular mechanisms in spite of high morphological divergences of reproductive tract organs in different animal groups. The present study focused on this problem and report our observations on biochemical characteristics of male-associated polypeptide (MAP) identified in the gonad tissue of bivalve molluscs, Mytilus galloprovincialis, in comparison to those of male-specific carboxylesterase (esterase S) of Drosophila virilis ejaculatory bulbs. We provide evidences for the immunochemical similarity of Mytilus MAP and Drosophila esterase S. We also show that MAP is characterized by esterase activity toward both, alpha- and beta-naphthyl acetates. Using immunofluorescence, we found MAP in the gonad (mantle) connective tissue, membranes of follicles and around gonad ducts but not in sperm cells. Nevertheless, the levels of MAP expression depend on presence or absence of ripe spermatozoa in the gonad follicles. In mature gonads before spawning, MAP is expressed at high level, while in the spent gonads only traces of this polypeptide could be detected. Using Western immunoblot, MAP was not observed in spermatozoa obtained by biopsy of gonad follicles. In contrast, we found this protein in spawned sperm cells. Thus, we suggest that spawning may be required to establish the trafficking mechanisms that control whether MAP is retained or excreted by the gonad. Taken together, the results indicate that MAP of M. galloprovincialis is structurally and functionally related to esterase S of D. virilis ejaculatory bulbs.

Amino Acids↗
PubMed1997

Analysis of NORs and NOR-associated heterochromatin in the mussel Mytilus galloprovincialis Lmk.

The chromosomes of the mussel Mytilus galloprovincialis were analysed by means of chromomycin A3 (CMA), distamycin A/DAPI (DA/DAPI), DAPI/actinomycin D (DAPI/AMD) and chromomycin A3/distamycin A/DAPI (CDD) fluorescence banding techniques, C-banding, silver staining, N-banding and in situ hybridization with 18S+28S rDNA and telomere probes. 18S+28S rDNA clusters were located on the telomeres of two pairs of submeta/subtelocentric chromosomes. The nucleolar organizing regions (NORs) were associated with bright CMA fluorescence, dull DAPI fluorescence and C- and N-positive bands, but not all four NOR-associated heterochromatin bands showed bright CMA fluorescence in a given cell; intra- and interindividual variability was found in this character. Additional non-ribosomal C-bands did not show any differential fluorescent behaviour.

Animals↗
PubMed1997

Occupational allergic disease in cereal workers by stored grain pests.

It is well known that workers occupationally exposed to grain dust have a high prevalence of respiratory symptoms, but their pathogenesis remains obscure when sensitization to cereal flour cannot be demonstrated. Storage mites, tenebroids, and cockroaches are stored-grain pests found in grain and cereal products frequently in our area, where the cereal industry is the most important industry. An epidemiological analysis of sensitization of these stored-grain pests was performed on 4379 patients residing in an area of cereal industries. Fifty grain workers were selected for in vivo diagnostic tests with nine genera of mites, Tenebrio molitor and Blatta orientalis. Specific IgE antibodies to the extracts were demonstrated by prick tests and RAST. Association between respiratory symptoms and occupational exposure was confirmed by challenge tests (specific and methacholine). The prevalence of mite sensitization in the total sample studied (4379) was 18.96% (SEM 0.58, 95% CI 16.93-19.19). The prevalence of sensitization to storage mites among mite-sensitive patients was 11.88% (SEM 1.15, 95% CI 9.63-14.3). Among the 50 selected patients the most frequent sensitization was that to Dermatophagoides pteronyssinus (58%), followed by Dermatophagoides frinae (48%), Lepidoglyphus destructor and Tyrophagus putrescentiae (38%), Blomia kulagini (34%), and Acarus siro and Chortoglyphus arcuatus (24%). In addition, 22% of the patients presented negative prick tests and RAST for Dermatophagoides species with positive test to storage mites. Fifty percent of the 50 patients were sensitizated to Tenebrio molitor (SEM 0.7, CI 95% 36-64), and 36% to Blatta orientalis (SEM 0.67, CI 95% 23-49). The identification of mites, tenebroids, and cockroaches in dust samples yields useful data for the diagnosis of our patients.

Adolescent↗
PubMed1997

Effect of pancreatic islets on splenic hepatocellular transplantation.

PURPOSE OF THE STUDY: To determine whether Langerhans' islets exert a beneficial effect on splenic hepatocellular transplantation. HYPOTHESIS: the addition of pancreatic islets to hepatocytes would improve their normal function through the support of insulin and glucagon in the same proportions as they usually receive in the hepatic environment. EXPERIMENTAL DESIGN: Potential improvement in the hepatocellular function to be evaluated by means of regenerative activity recorded after applying a specific stimulus (partial hepatectomy and/or cyclosporine A). METHODS: An immunohistochemical technique (antinuslin antibodies) was used to confirm the presence of active islets of Langerhans in the spleen. Microcytophotometry was used to quantify hepatocyte regeneration. RESULTS: Although demonstrating the presence of active (insulin-positive) islets together with hepatocytes in the spleen was feasible, the expected positive influence on the regenerative activity of hepatocytes was impossible to prove. CONCLUSIONS: Further study is needed to reach definitive conclusions about the real usefulness of pancreatic islets in hepatocyte transplantation.

Animals↗
PubMed1996

In vitro protein-primed initiation of pneumococcal phage Cp-1 DNA replication occurs at the third 3' nucleotide of the linear template: a stepwise sliding-back mechanism.

Phage Cp-1 from Streptoccocus pneumoniae makes use of a protein-priming mechanism to start replication of its linear DNA: the first reaction consists of the addition of 5' dAMP to a molecule of the primer protein, an initiation event occurring at both DNA ends. After elongation of the initiation complex, the primer protein remains linked to the 5' end of the nascent DNA chain, and is subsequently referred to as terminal protein (TP). In this paper, using DNA-free extracts from Cp-1-infected S. pneumoniae, we provide evidence that the formation of the covalent complex TP-dAMP is a template-instructed reaction and that ssDNA molecules can serve as templates for TP-primed replication. A mutational analysis of the 3' terminal nucleotides of Cp-1 DNA reveals that a precise DNA sequence is required for efficient template recognition, and that in vitro initiation of Cp-1 DNA replication is directed by the third nucleotide of the template. However, the two terminal nucleotides are recovered during the first steps of elongation. A new variant of the sliding-back mechanism for protein-primed initiation, firstly described for Bacillus subtilis phage phi29, is proposed to account for the maintenance of Cp-1 DNA ends. The results presented here reinforce the hypothesis that sliding-back must be a common feature in all genomes that use protein-priming to initiate replication.

Bacillus Phages↗
PubMed1996

Hepatotrophic effect of folinic acid in rats.

Hepatic ischemia hinders the proliferative response of hepatocytes, necessary to restore the liver/body ratio after liver resection/transplantation. Folinic acid administered during the ischemic period following 70% hepatectomy plus 15 min of normothermic liver ischemia has restored the regenerative response to the levels of normoperfused livers. This unexpected finding has guided us to design the present study in order to find out whether the folinic acid is an hepatotrophic substance or not. Sprague-Dawley rats submitted to partial (40 or 70%) hepatectomies were used. Saline (2 cc) or folinic acid (2.5 mg/kg) have been administered i.v. Forty-eight hours after hepatectomy the hepatocyte's DNA content has been assessed by means of a cytophotometric technique, and the percentage of regenerating hepatocytes (PRH) has been calculated. Folinic acid administration has significantly increased the PRH in both resting (5.1 vs 1.2) and regenerating livers (70% hepatectomy) (22.2 vs 41) when compared with nontreated groups. Folinic acid administration after liver ischemia plus hepatectomy has shown similar results, corroborating our previous study. Although its mechanisms of augmentation of liver regeneration remain unclear and further studies are required, folinic acid seems to be a promising therapeutic tool in liver surgery.

Animals↗
PubMed1996

Turner syndrome: a study of chromosomal mosaicism.

We report the results of a molecular investigation of 25 patients who had Turner syndrome and who had previously been subject to analysis using cytogenetic techniques. When in situ hybridization and polymerase chain reaction (PCR) techniques were applied, a larger number of mosaic individuals were observed than were detected by cytogenetic methods. This was mainly because of the presence of the cell line 46,XX. The most frequent mosaics were 45,X/46,XX (36%); the presence of isochromosomes comprised 24% and fragments 12%. The patients who had been previously diagnosed with mosaicism displayed a higher complexity in their karyotypes because of the presence of new cellular lines. The isodicentric X chromosome for the long arm, idic(Xq), gave rise to complex mosaics of up to nine cell lines. The application of fluorescence in situ hybridization and PCR led to a clearer definition of alterations at the centromeric level and the identification of the nature of chromosome fragments.

DNA Probes↗
PubMed1996

Endotoxin depletes ascorbate in the guinea pig heart. Protective effects of vitamins C and E against oxidative stress.

The effect of acute endotoxin-induced septic shock on myocardium oxidative stress after low or high vitamin C and/or E dietary supplementation was studied in guinea pigs, laboratory animals which, like human, do not have capacity for ascorbate synthesis. Neither the antioxidant enzymes or GSH were modified by endotoxin and vitamin treatments. Vitamin E showed a strong capacity to protect the myocardium against both enzymatic and non-enzymatic lipid peroxidation even in the presence of endotoxin. Vitamin C supplementation increased heart ascorbate whereas endotoxic shock totally depleted the heart ascorbate of vitamin C supplemented animals without changing vitamin E. Endotoxin significantly increased myocardium uric acid, a marker of ischemia induced oxidative stress, in animals fed with low vitamin C levels. This increase was totally prevented in vitamin C supplemented, but not in vitamin E supplemented animals. Strongly depressed levels of plasma vitamin C have been recently described in sepsis in human patients. The results suggest that ascorbate is a primary antioxidant target in the heart of endotoxin treated mammals lacking the capacity to synthesize ascorbate and that ascorbate can have a protective value against endotoxin-induced free radical damage in the myocardium. Implications of these results for the possible preventive role of vitamin C in humans during sepsis are discussed.

Analysis of Variance↗
PubMed1996

Vitamin E decreases urine lipid peroxidation products in young healthy human volunteers under normal conditions.

An experimental study on the effects of supplementation with antioxidant vitamins on urine lipid peroxidation products was performed in 21 young healthy men. The subjects ingested placebo, 1 g of vitamin C, or 100 mg of vitamin E per day just after the midday meal during 30 days. Urine samples were obtained 0, 15 and 30 days after the beginning of the study. These samples were analyzed by spectrophotometry or fluorometry after reaction with thiobarbituric acid. Prescan fluorometric studies of the thiobarbituric acid reactive substances in both malondialdehyde standards and urine samples indicated 503 nm and 548 nm as optimum excitation and emission wavelengths. The fluorescence measurements proved to be superior both in terms of selectivity and capacity of detection of antioxidant effects in relation to spectrophotometry. Identical emission peaks were obtained with malondialdehyde standards and urine samples, showing the specificity of the fluorometric method. When measured by fluorometry, the urine of the subjects supplemented with vitamin E showed significantly and progressively smaller lipid peroxidation products as the time of supplementation increased, reaching a 27% decrease at the end of the longitudinal trial. The results indicate the usefulness of the fluorescent measurement of urine thiobarbituric acid reactive substances to easily and rapidly detect variations in whole body oxidative stress in humans. They also show the capacity of safe vitamin E dietary doses to decrease endogenous oxidative stress in healthy humans routinely performing their normal activities.

Adult↗
PubMed1996

Growth hormone responses to growth hormone-releasing hormone and clonidine before and after erythropoietin therapy in CAPD patients.

Correction of anemia with recombinant human erythropoietin (rhEPO) in patients with end-stage renal disease has been associated with improvement of several abnormalities in hypothalamo-hypophyseal functions. The aim of the present work was to evaluate the growth hormone (GH) responses to GH-releasing hormone (GHRH) and clonidine stimulation, as well as the baseline concentrations of insulin-like growth factor I(IGF-I), before and after the correction of anemia with rhEPO in a group of uremic patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Nine clinically stable patients (1 male, 8 female; mean age 55.4 years; mean duration of CAPD 14.1 months) were studied. Twelve normal volunteers were studied as controls. GHRH and clonidine stimulation tests were performed prior to starting rhEPO and again after partial correction of anemia with rhEPO therapy (60-130 U/kg/week, s.c., for 12 weeks). Blood samples for GH were collected during 2 h after GHRH (100 micrograms i.v. in bolus) or clonidine (0.15 mg/m2, p.o.) administration. In basal plasma samples IGF-I concentrations were also measured. Mean (+/- SEM) blood hemoglobin concentration rose from 5.32 +/- 0.25 to 7.22 +/- 0.25 mmol/l (p < 0.001) after rhEPO treatment. GH responses to GHRH were characterized by marked differences in single patients when compared with the control group. However, the GH peak and the area under the secretory curves (AUC) of GH responses in CAPD patients (9.89 +/- 4.01 micrograms/l and 15.06 +/- 6.02 micrograms.h/l, respectively) did not differ from those obtained in control subjects (14.58 +/- 3.25 microgram/l and 16.94 +/- 4.31 microgram.h/l, respectively). The study after correction of anemia showed an evident potentiation of GH values that reached statistically significant values at 60 and 90 min. GH AUC after rhEPO therapy rose to 25.61 +/- 9.25 micrograms.h/l (p = 0.01). In control subjects, clonidine administration was followed by a GH release that reached a maximum at 90 min (7.67 +/- 2.24 micrograms/l). However, CAPD patients exhibited a blunted response to clonidine both before (2.00 +/- 0.78 microgram/l) and after (2.78 +/- 0.76 microgram/l, NS) correction of the anemia with rhEPO. On the other hand, IGF-I concentrations after rhEPO therapy (32.05 +/- 5.52 nmol/l) were not significantly different from those found prior to starting therapy (38.13 +/- 8.44 nmol/l). In conclusion, these results suggest that correction of the anemia with rhEPO therapy potentiates GH responses to direct pituitary stimulation with GHRH although it is unable to restore the blunted response of GH to clonidine that is found in CAPD patients.

Adrenergic alpha-Agonists↗
PubMed1996

Carrier detection in Duchenne and Becker muscular dystrophy using dinucleotide repeat polymorphisms. A study in Mexican families.

In order to improve carrier detection of Duchenne and Becker muscular dystrophy, dinucleotide sequences repeats (CA) of introns 44, 45, 49 and 50 were used as well as two markers located at the 5' and 3' ends of the dystrophin gene. Haplotypes of the unaffected and affected persons of ten DMD/ BMD Mexican families were determined. Fifty eight females were studied, 30 of whom were at-risk STR haplotypes. Furthermore, it was possible to identify a recombination event in the dystrophin gene in one family, and a gonadal mosaicism was found in another family.

Genetic Carrier Screening↗
PubMed1996

Serum insulin and insulin-like growth factor binding protein-1 levels in adult patients undergoing peritoneal dialysis.

It is known that serum insulin-like growth factor binding protein-1 (IGFBP-1) concentrations are inversely related to insulin levels both in healthy and diabetic subjects. The aim of the present study was to assess serum IGFBP-1 levels in a group of patients undergoing peritoneal dialysis (PD) and to evaluate their relationship with serum insulin concentrations. Thirty-five patients [19 males, 16 females; age (mean +/- SEM) 53.2 +/- 2.5 years; range 18-78; duration of continuous ambulatory peritoneal dialysis 33.1 +/- 6.0 months; Kt/V 2.00 +/- 0.05; normalized protein catabolic rate 1.00 +/- 0.05 g/kg/day] were studied. Nine patients were diabetics. In all patients, baseline IGFBP-1, insulin, and growth hormone (GH) levels were determined. Fasting IGFBP-1 levels were elevated in 19 (54%) patients and were normal in 16 patients. In all patients, high levels of serum insulin levels (> 25 microU/mL) were observed. Baseline IGFBP-1 levels were only slightly higher in diabetic patients (53.7 +/- 14.6 vs 40.5 +/- 8.2 micrograms/L,NS), however, serum levels of GH were similar in both groups (3.0 +/- 1.8 vs 2.9 +/- 0.5 microgram/L, NS). There was no correlation between fasting insulin and IGFBP-1 levels both in the whole group (r = 0.2; NS) and the diabetic (r = 0.2; NS) and nondiabetic (r = 0.3; NS) subgroups, despite high fasting insulin levels. We could only find a significant positive correlation between fasting glucose and IGFBP-1 levels in the diabetic group (r = 0.7, p < 0.05). Our data suggest that adult patients undergoing PD show hyperinsulinemia associated with normal or high serum IGFBP-1 levels. This suggests that insulin does not affect IGFBP-1 production in this group of patients. It could be explained, at least in part, by the insulin resistance present in uremia.

Adolescent↗
PubMed1995

Primer terminus stabilization at the phi 29 DNA polymerase active site. Mutational analysis of conserved motif KXY.

phi 29 DNA polymerase shares with other DNA-dependent DNA polymerases several regions of amino acid homology along the primary structure. A conserved amino acid motif, located in the C-terminal portion of the polypeptide and characterized by the amino acid sequence KK(K/R)Y, is conserved in the group of eukaryotic-type DNA polymerases. In the subgroup of DNA polymerases that have a protein-priming mechanism, this motif is restricted to the sequence KXY, X never being a positively charged amino acid. Residues Lys498 and Tyr500 form this conserved motif in phi 29 DNA polymerase. Mutant K498T, in which the positive charge of the motif has been eliminated, was strongly affected both in initiation (terminal protein-dAMP formation, using terminal protein as primer) and DNA polymerization reactions. Mutants K498R and Y500S were able to carry out the initiation reaction to a higher or similar extent, respectively, than wild-type phi 29 DNA polymerase but were affected in DNA polymerization reactions. All of the mutations severely affected the stable binding of the polymerase to a primer-template DNA. In addition, all of the mutant polymerases analyzed in this work showed an unusually strong 3'-5' exonuclease activity both under polymerization or non-polymerization conditions. The results obtained suggest a role of the conserved residues of the KXY motif in stabilizing the primer terminus at the polymerization active site, the positive charge of residue Lys498 being critical for the synthetic activities of phi 29 DNA polymerase.

Amino Acid Sequence↗
PubMed1995

Protein-nucleic acid interactions in bacteriophage phi 29 DNA replication.

phi 29 DNA replication starts at both DNA ends by a protein priming mechanism. The formation of the terminal protein-dAMP initiation complex is directed by the second nucleotide from the 3' end of the template. The transition from protein-primed initiation to normal DNA elongation has been proposed to occur by a sliding-back mechanism that is necessary for maintaining the sequences at the phi 29 DNA ends. Structure-function studies have been carried out in the phi 29 DNA polymerase. By site-directed mutagenesis of amino acids conserved among distantly related DNA polymerases we have shown that the N-terminal domain of phi 29 DNA polymerase contains the 3'-5' exonuclease activity and the strand-displacement capacity, whereas the C-terminal domain contains the synthetic activities (protein-primed initiation and DNA polymerization). Viral protein p6 stimulates the initiation of phi 29 DNA replication. The structure of the protein p6-DNA complex has been determined, as well as the main signals at the phi 29 DNA ends recognized by protein p6. The DNA binding domain of protein p6 has been studied. The results indicate that an alpha-helical structure located in the N-terminal region of protein p6 is involved in DNA binding through the minor groove. The phi 29 protein p5 is the single-stranded DNA binding (SSB) protein involved in phi 29 DNA replication, by binding to the displaced single-stranded DNA (ssDNA) in the replication intermediates. In addition, protein p5 is able to unwind duplex DNA. The properties of the phi 29 SSB-ssDNA complex are described. Using the four viral proteins, terminal protein, DNA polymerase, protein p6 and the SSB protein, it was possible to amplify the 19,285-bp phi 29 DNA molecule by a factor of 4000 after 1 h of incubation at 30 degrees C. The infectivity of the in vitro amplified DNA was identical to that of phi 29 DNA obtained from virions.

Bacillus Phages↗