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M Salazar

Publications and source records attributed to M Salazar.

At least 37 records · Page 2Linked to original sources
PubMed1999

Medical clearance for respirator use: sensitivity and specificity of a questionnaire.

BACKGROUND: OSHA regulations require that workers receive medical clearance prior to respirator use, and recently, a detailed questionnaire has been provided to assist with this purpose. However, there are limited published data on the sensitivity and specificity of self-administered questionnaires for identifying individuals who may safely wear a respirator. METHODS: We tested 474 consecutive workers at a Department of Energy complex. After completing the self-administered questionnaire, all workers received a standardized physician evaluation including interview, physical examination, and spirometry. The outcomes of the questionnaire assessment were compared to the outcomes of physician evaluation. RESULTS: Data for analysis were available from 413 of workers (87%). All workers received medical clearance; only 10 workers (2.4%) received work restrictions. The questionnaire demonstrated 100% sensitivity in identifying workers who required work restrictions, but had specificity of only 19%. Compared to physician evaluation, the questionnaire had modest sensitivity to the detection of chronic medical conditions. CONCLUSIONS: These data suggest that the rates of medical clearance for respirator use are very high, and that a self-administered questionnaire may be appropriate for medical clearance in certain settings. It is recommended that the policy of routine physician evaluation and spirometry for respirator clearance be re-examined.

Adult↗
PubMed1999

Dominant lethal study of alpha-asarone in male and female mice after sub-chronic treatment.

Dominant lethal studies were conducted in male and female mice with alpha-asarone, the active hypolipidaemic component of Guatteria gaumeri Greenman, by per os sub-chronic treatment (10 and 20 mg/kg, 5 days/week, for 8 weeks) and subsequent mating. alpha-Asarone did not produce germinal mutations in either males or females. Epididymal sperm examination of male mice immediately after treatment failed to reveal any alteration in sperm count on shape. No significant alterations were observed in testicular or epididymal weights or testicular histology.

Allylbenzene Derivatives↗
PubMed1999

An electrocardiographic algorithm for the prediction of the culprit lesion site in acute anterior myocardial infarction.

BACKGROUND: Although the 12-lead electrocardiogram (ECG) has been found useful in identifying the left anterior descending (LAD) coronary artery as the infarct-related artery in acute myocardial infarction (MI), it has traditionally been felt to be incapable of localizing the culprit lesion within the LAD itself. Such a capability would be important, because anterior MI due to proximal LAD lesions carry a much worse prognosis than those due to more distal or branch vessel lesions. HYPOTHESIS: This study investigated whether certain ECG variables--especially an ST-segment injury pattern in leads aVL and/or V1--would correlate with culprit lesion site, and an ECG algorithm was developed to predict culprit lesion site. METHODS: The initial ECGs of 55 patients who had undergone cardiac catheterization after an anterior or lateral MI were reviewed to identify the leads with an ST-segment injury pattern; the corresponding catheterization films were then reviewed to identify the location of the culprit lesion; and these separate findings were then compared. RESULTS: The sensitivity and specificity of an ST-injury pattern in aVL in predicting a culprit lesion before the first diagonal branch were 91 and 90%, respectively; the same values in predicting a lesion prior to the first septal branch were 85 and 78%. ST-segment elevation in V1, on the other hand, was a much less sensitive and specific predictor of a preseptal lesion. Overall, our algorithm correctly identified the culprit lesion location in 82% of our patients. CONCLUSION: Based on our findings, we conclude that a ST-segment injury pattern in aVL during an anterior myocardial infarction predominantly reflects a proximal LAD lesion and therefore constitutes a high-risk finding.

Algorithms↗
PubMed1999

Synthesis and hypolipidaemic evaluation of a series of alpha-asarone analogues related to clofibrate in mice.

A series of alpha-asarone analogues related to clofibrate, containing an acetic acid group at C-2 of the aromatic ring, has been prepared as the acids or as the ethyl and methyl esters. The corresponding alcohols were also synthesized by reduction of the ethyl esters. The compounds were examined in hyperlipidaemic male mice to evaluate their ability to modify serum lipoprotein cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol and triglycerides after oral administration of 40 and 80 mg kg(-1) for 6 days. Except for methyl 2-methoxy-5-nitro-4-(2-propenyl)phenoxyacetate at either dose, these clofibrate-related phenoxyacetic acid derivatives were found to have significant hypocholesterolaemic activity. Levels of low-density lipoprotein cholesterol and triglycerides were significantly reduced and those of high-density lipoprotein cholesterol were elevated. 2-Methoxy-5-nitro-4-(2-propenyl)phenoxyacetic acid was active at both doses in all the tests. Clofibrate (150 mg kg(-1)) was more potent at reducing low-density lipoprotein cholesterol. No activity was detected for the alcohol derivatives. These preliminary results suggest that this class of compound might have more promise as potential hypolipidaemic agents than other alpha-asarone derivatives. Further investigation and characterization should be performed to determine the mode of action of these agents on lipid metabolism.

Allylbenzene Derivatives↗
PubMed1998

Dominant lethal study of alpha-asarone in male mice.

Alpha-asarone is a hypolipidaemic agent obtained from Guatteria gaumeri, a medical plant used in Mexico to treat hypercholesteraemia and cholelithiasis. alpha-Asarone has been shown to be hepatocarcinogenic and mutagenic in a human lymphocyte assay, a murine bone marrow cell assay and in an unscheduled DNA synthesis assay. In this study, alpha-asarone was tested for dominant lethal effects in male CF1 mice. The drug was given orally at doses of 0, 10 and 30 mg/kg per day for 5 days. Males were mated weekly with eight consecutive batches of naive, nulliparous female mice. Repeated matings revealed no perceptible effect of alpha-asarone on the incidence of pregnancy. Examination of surgically exposed uteri and ovaries of pregnant females on day 13-15 of gestation revealed an increased incidence of post-implantation loss. Semen examination of a separate group of mice showed a decreased concentration and motility of spermatozoa. These results suggest a dominant lethal mutation as well as direct alpha-asarone toxicity to spermatozoa by in treated mice.

Allylbenzene Derivatives↗
PubMed1998

NMR-Based model of a telomerase-inhibiting compound bound to G-quadruplex DNA.

The single-stranded (TTAGGG)n tail of human telomeric DNA is known to form stable G-quadruplex structures. Optimal telomerase activity requires the nonfolded single-stranded form of the primer, and stabilization of the G-quadruplex form is known to interfere with telomerase binding. We have identified 3,4,9, 10-perylenetetracarboxylic diimide-based ligands as potent inhibitors of human telomerase by using a primer extension assay that does not use PCR-based amplification of the telomerase primer extension products. A set of NMR titrations of the ligand into solutions of G-quadruplexes using various oligonucleotides related to human telomeric DNA showed strong and specific binding of the ligand to the G-quadruplex. The exchange rate between bound and free DNA forms is slow on the NMR time scale and allows the unequivocal determination of the binding site and mode of binding. In the case of the 5'-TTAGGG sequence, the ligand-DNA complex consists of two quadruplexes oriented in a tail-to-tail manner with the ligand sandwiched between terminal G4 planes. Longer telomeric sequences, such as TTAGGGTT, TTAGGGTTA, and TAGGGTTA, form 1:1 ligand-quadruplex complexes with the ligand bound at the GT step by a threading intercalation mode. On the basis of 2D NOESY data, a model of the latter complex has been derived that is consistent with the available experimental data. The determination of the solution structure of this telomerase inhibitor bound to telomeric quadruplex DNA should help in the design of new anticancer agents with a unique and novel mechanism of action.

Anthracenes↗
PubMed1998

Generation of coated intermediates of clathrin-mediated endocytosis on protein-free liposomes.

Clathrin-coated buds and dynamin-coated tubules morphologically similar to corresponding structures observed in synaptic membranes can be generated on protein-free liposomes by incubation with cytosol, or with clathrin coat proteins and purified dynamin, respectively. Dynamin- and clathrin-coated intermediates may form independently of each other, despite the coupling between the two processes typically observed in synaptic membranes. Formation of both structures on liposomes can occur in the absence of nucleotides. These findings indicate that interfaces between lipids and cytosolic proteins are fully sufficient to deform lipids bilayers into buds and tubules. They suggest that a main function of membrane proteins is to act as positive and negative regulators of coat assembly, therefore controlling these processes in time and space.

Animals↗
PubMed1998

Effect of DNA secondary structure on human telomerase activity.

Telomeres are specialized DNA-protein complexes located at the chromosome ends. The guanine-rich telomeric sequences have the ability to form G-quadruplex structures under physiological ionic conditions in vitro. Human telomeres are maintained through addition of TTAGGG repeats by the enzyme telomerase. To determine a correlation between DNA secondary structure and human telomerase, telomerase activity in the presence of various metal cations was monitored. Telomerase synthesized a larger proportion of products corresponding to four, five, eight, and nine full repeats of TTAGGG in 100 mM K+ and to a lesser extent in 100 mM Na+ when a d(TTAGGG)3 input primer was used. A more even product distribution was observed when the reaction mixture contained no added Na+ or K+. Increasing concentrations of Cs+ resulted in a loss of processivity but not in the distinct manner observed in K+. When the input primer contained 7-deaza-dG, the product distribution resembled that of reactions without K+ even in the presence of 100 mM K+. Native polyacrylamide gel electrophoresis indicated that d(TTAGGG)4, d(TTAGGG)5, d(TTAGGG)8, and d(TTAGGG)9 formed compact structures in the presence of K+. The oligonucleotide d(TTAGGG)4 had a UV spectrum characteristic of that of the G-quadruplex only in the presence of K+ and Na+. A reasonable explanation for these results is that four, five, eight, and nine repeats of TTAGGG form DNA secondary structures which promote dissociation of the primer from telomerase. This suggests that telomerase activity in cells can be modulated by the secondary structure of the DNA template. These findings are of probable relevance to the concept of telomerase as a therapeutic target for drug design.

Cesium↗
PubMed1998

Subchronic toxicity study in mice fed Spirulina maxima.

The purpose of this study was to evaluate the toxicity of Spirulina maxima, a blue-green alga used as food supplement and food coloring, after 13 weeks of treatment. Groups of ten mice of each sex were given S. maxima in the diet at concentrations of 0 (control), 10, 20 or 30% (w/w) for 13 weeks. The alga ingestion had no effect on behavior, food and water intake, growth or survival. Terminal values in hematology and clinical chemistry did not reveal differences between treated and control groups. However, male and female mice showed significant changes in serum cholesterol levels at 20 and 30% algal concentrations, but a toxic effect of S. maxima was excluded. Post-mortem examination revealed no differences in gross or microscopic findings. Our results show that S. maxima up to high feeding levels did not produce adverse effects in mice after subchronic treatment.

Animals↗
PubMed1998

Typing of HLA-B*15 alleles using sequence-specific primers.

We have developed a DNA based typing method to detect 38 known B*15 alleles using sequence-specific primers (PCR-SSP). This method involves 38 primers and 39 PCR-SSP reactions with results that can be obtained in 3 hours. The method is easy, fast and suitable for clinical typing for bone marrow and organ transplantation. We have typed 106 HLA-B15 samples using this method. For homozygous HLA-B15 samples, some B*15 allele combinations need to be resolved by additional PCR reactions not included in this article. The method allows the detection of potential new alleles requiring sequencing for confirmation, and it is useful to resolve unusual serological reaction patterns for different HLA-B15 serological specificities. In addition, it could be used to resolve ambiguous PCR-SSOP typing results and for recognition of mismatches in serologically matched unrelated individuals.

Alleles↗
PubMed1997

Defect in Th1-like cells of nonresponders to hepatitis B vaccine.

Peripheral blood lymphocytes from nonresponders to hepatitis B vaccine (HBsAg) failed to undergo a proliferative response to recombinant HBsAg in vitro, whereas cells from responders proliferated vigorously. The lack of proliferative response was not due to defective antigen presentation in that MHC-identical responder and nonresponder antigen presenting cells were equally effective in stimulating responder T cells. Nonresponder T cells did not proliferate in response to antigen-pulsed MHC identical responder antigen presenting cells. The present study demonstrated that: 1) there were no detectable (1 in < 20 x 10(4) HBsAg-precursor T cells in any of the nonresponders, while in responders the frequency of HBsAg-precursor T cells ranged from 1 in 3.2 x 10(3) to 1 in 40 x 10(3); 2) nonresponder cell cultures did not secrete IL-2 in response to HBsAg stimulation; 3) exogenous recombinant IL-2 did not restore the proliferative response of the T cells in HBsAg-pulsed cultures of nonresponders. These results suggest that the cellular basis for the lack of response to HBsAg is a defect in HBsAg-specific Th1-like cells; either there is an absence of the Th1 cells or cells with TCR specificity for HBsAg are present but are unresponsive to the HBsAg peptide-MHC complex (i.e., anergy or tolerance).

Adult↗
PubMed1997

Accurate typing of HLA-A antigens and analysis of serological deficiencies.

We are reporting the results of HLA-A typing by PCR-SSOP complemented by PCR-SSP of samples obtained from the National Marrow Donor Program (NMDP). These samples were a representative group from 2486 tested in duplicate by serology. A total of 390 samples gave HLA-A discrepant results. Comparing the molecular typing results of 238 samples (samples with available DNA) with the serological typing results, 54 homozygotes and 184 heterozygotes produced a total of 422 assignments by molecular methods. We found assignment discrepancies in 147/422 (35%) in laboratory 1 and 144/422 (34%) in laboratory 2 (a combined group of 4 NMDP laboratories; laboratory 1 is not included). The serological discrepancies found were of 3 categories: a) false negatives, b) incomplete typing (discrepancies due to the level of resolution within a cross-reactive or CREG group) and c) false positives. Major problems were identified using serology for typing HLA-A antigens: a) inability to identify all WHO-recognized specificities, more frequently in non-Caucasians or in HLA-A specificities known to be found more frequently in non-Caucasians for laboratory 1 and incorrect assignments of A19 specificities in laboratory 2, b) incorrect assignments in cells with poor viability and c) false-positive assignments in homozygotes. We propose a possible strategy to type HLA-A specificities with two steps: a) a minimum of serology for typing specificities for common CREG groups: A1, A2, A3, A11, A9, A10, A28, A19. However, a given laboratory can determine the level of serological assignments needed as a first step. And b) molecular methods to identify splits: A23, A24, A29, A30, A31, A32, A33, A34, A36, A66, A74 and A80. The technique described is useful for large-scale bone marrow donor typings for cells with poor viability, and for resolving ambiguous results including false-positive assignments of homozygous cells.

DNA↗
PubMed1997

Error rate for HLA-B antigen assignment by serology: implications for proficiency testing and utilization of DNA-based typing methods.

Until recently, the majority of HLA class I typing has been performed by serology. Expensive commercial typing trays are frequently used for testing non-Caucasian subjects and new strategies using DNA-based methods have been adopted for improving clinical histocompatibility testing results and adapted as supplements in proficiency testing. A double-blind comparison of the typing of HLA-B specificities in 40 samples was carried out between serology and two polymerase chain reaction (PCR) methods, PCR amplification with sequence-specific primers (PCR-SSP) and PCR amplification and subsequent hybridization with sequence-specific oligonucleotide probes (PCR-SSOP). The results demonstrated 22.5% misassignments of HLA-B antigens by serology. There was complete concordance between the results obtained with the two PCR based typing methods. A second panel of 20 donor samples with incomplete or ambiguous serologic results was analyzed by PCR-SSP and SSOP Both PCR methods identified correctly the HLA-B antigens. Our results suggest that more accurate typing results can be achieved by complementing serologic testing with DNA-based typing techniques. The level of resolution for HLA-B antigen assignment can be obtained by this combination of serology and limited DNA-based typing is equivalent to the HLA-B specificities defined by the WHO-HLA Committee. This level of resolution cannot routinely be achieved in clinical histocompatibility testing or in proficiency testing using serologic reagents only.

DNA↗
PubMed1996

Thermally induced DNA.RNA hybrid to G-quadruplex transitions: possible implications for telomere synthesis by telomerase.

Telomerase is a specialized reverse transcriptase that contains its own RNA template for synthesis of telomeric DNA [Greider, C. W., & Blackburn, E. H. (1989) Nature 337, 331-337; Shippen-Lentz, D., & Blackburn, E. H. (1990) Science 247, 546-552]. The activity of this ribonucleoprotein enzyme has been associated with cancer cells [Kim et al. (1994) Science 266, 2011-2015] and is thus a potential target for anticancer chemotherapy. Telomeric DNA.RNA hybrids are important intermediates in telomerase function and form after extension of the growing telomere on the telomerase RNA template. Translocation is a critical step in telomerase function and consists of unwinding of the telomeric DNA.telomerase RNA hybrid followed by repositioning of the 3'-end of the extended telomere. A central question in telomerase function is how translocation of the extended telomere occurs in the absence of ATP or GTP. It has been hypothesized that unwinding of the telomeric hybrid may be facilitated by the formation of stable hairpins or G-quadruplexes by the telomere product (i.e., a hybrid to G-quadruplex transition) and that this may provide at least part of the driving force for translocation [Shippen-Lentz & Blackburn, 1990; Zahler et al. (1991) Nature 350, 718-720]. However, so far there has been no effort aimed at examining the possibility that a hybrid/G-quadruplex equilibrium can occur and to what extent this equilibrium depends on buffer and concentration conditions. Examination of these transitions may provide insight into telomerase function and may also provide clues for the development of anti-telomerase agents. Using a model system consisting of the DNA.RNA hybrid d(GGTTAGGGTTAG).r(cuaacccuaacc), we present evidence that a thermally induced transition of telomeric DNA.RNA hybrid to G-quadruplex can occur under certain conditions. These results provide support for the hypothesis that G-quadruplex formation by the telomere product may in fact regulate telomerase function at the translocation step (Zahler et al., 1991) and suggest an Achilles' heel for indirectly targeting telomerase. Thus, on the basis of the insight gained from the present studies and the results of Zahler et al. (1991), we propose that ligands that selectively bind or cleave G-quadruplex structures may modulate telomerase processivity.

Base Sequence↗
PubMed1996

Human telomerase inhibition by 7-deaza-2'-deoxypurine nucleoside triphosphates.

Telomeres play an important role in chromosome organization and stability. Human telomerase is a terminal transferase that adds TTAGGG units onto the telomere end. In general, telomerase activity is not detected in normal somatic cells but is present in immortalized cells. Consequently, telomerase might be a selective target for cancer chemotherapy. Using cell-free biochemical telomerase assay, we have found that 7-deaza-2'-deoxyguanosine-5'-triphosphate (7-deaza-dGTP) and 7-deaza-2'-deoxyadenosine-5'-triphosphate (7-deaza-dATP) were potent telomerase inhibitors. The concentrations of inhibitors in which 50% of the telomerase activity was inhibited (IC50 values) were 11 and 8 microM for 7-deaza-dGTP and 7-deaza-dATP, respectively. Additional studies show that both 7-deaza-dGTP and 7-deaza-dATP were also incorporated into telomeric DNA by telomerase. However, incorporation of 7-deaza-dATP or 7-deaza-dGTP results in a telomeric ladder that is prematurely shortened. No difference in the number or position of pause sites were observed when 7-deaza-dATP was compared to dATP as substrates. On the other hand, both a shift and an increase in pause sites was observed when dGTP was replaced by 7-deaza-dGTP. Incorporation of 7-deaza nucleotides by telomerase may be used as a tool for the study of telomerase mechanism and function. In addition, this may be a novel approach in the design of new telomerase inhibitors.

Cells, Cultured↗
PubMed1996

Structural variation among retroviral primer-DNA junctions: solution structure of the HIV-1 (-)-strand Okazaki fragment r(gcca)d(CTGC).d(GCAGTGGC).

The three-dimensional solution structure of the hybrid-chimeric duplex r(gcca)d(CTGC).d(GCAGTGGC) has been determined by two-dimensional NMR, restrained molecular dynamics (rMD), and NOE back-calculation methods. This chimera, consisting of a chimeric RNA-DNA strand and its complementary DNA strand, is formed after priming (-)-strand DNA synthesis by tRNA(Lys3) and subsequent (+)-strand DNA synthesis by reverse transcriptase and is an obligatory intermediate in the formation of double-stranded DNA prior to HIV-1 retrovirus integration. The duplex consists of two different types of double helix: a hybrid form (H-form) and a B-form structure connected by a junction. It is chemically similar to several other Okazaki fragments whose structures have been previously determined in our laboratory. However, some structural parameters are not the same and were found to be sequence dependent. In particular, the sugar conformations at the DNA base pair proximal to the hybrid segment vary from O4'-endo to C2'-endo depending on the base composition. The position of the transition from the relatively wide groove of H-form to the narrow groove of B-form is also sequence dependent, occurring either exactly at the RNA-DNA junction or within the purely DNA segment of the chimera-as is the case in the structure of the present HIV-1 (-)-strand primer. This structural change produces a kink at the DNA-DNA step adjacent to the RNA-DNA junction in the HIV-1 (-)-strand primer. The sequence dependence of structures of RNA-DNA chimeric duplexes may be responsible for the variable cleavage pattern of different Okazaki fragments by reverse transcriptase RNase H.

Base Composition↗