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Biomedical subjects

J Cobb

Publications and source records attributed to J Cobb.

At least 37 records · Page 2Linked to original sources
PubMed1998

Cerebrospinal fluid cytology in patients with cancer: minimizing false-negative results.

BACKGROUND: Detection of malignant cells on cytologic examination of the cerebrospinal fluid (CSF) is the diagnostic gold standard for leptomeningeal carcinomatosis. The absence of cells is a primary endpoint for most therapeutic trials. Unfortunately, false-negative results are common. Practical strategies are necessary to remedy this problem. METHODS: Four physician-dependent variables (CSF sample volume, site of CSF sampling, processing time, and frequency of CSF sampling) were identified, and their contributions to the false-negative rate of CSF cytology were evaluated prospectively in 39 patients with leptomeningeal carcinomatosis. Retrospective data were analyzed to estimate the importance of these variables in daily practice. RESULTS: False-negative CSF cytology results correlated with small CSF volume (P < 0.001), delayed processing (P < 0.001), not obtaining CSF from a site of symptomatic or radiographically demonstrated disease (P = 0.02), and sampling fewer than two times (P < 0.001). In 1 year, 97% of CSF specimens at the study institution were of inadequate volume; >25% were processed too slowly. CONCLUSIONS: False-negative CSF cytology results are common, but can be minimized by: 1) withdrawing at least 10.5 mL of CSF for cytologic analysis; 2) processing the CSF specimen immediately; 3) obtaining CSF from a site of known leptomeningeal disease; and 4) repeating this procedure once if the initial cytology is negative.

Cerebrospinal Fluid↗
PubMed1998

Dynamics of meiotic prophase I during spermatogenesis: from pairing to division.

This review focuses on recent developments in our understanding of meiotic chromosome behavior in mammalian spermatogenesis, with a special emphasis on prophase I events in the best characterized organism, the laboratory mouse. The dynamics of chromosome movement prior to pairing and synapsis of chromosomes are complex and implicate function for both centromeres and telomeres in getting homologous chromosomes together in intimate synapsis. Likely candidates for mediating pairing and recombination include a host of proteins implicated in DNA repair and recombination, which have been shown to localize to the synaptonemal complex during meiotic prophase I. Precocious induction of meiotic metaphase in cultured pachytene spermatocytes has led to new information about requirements for MPF and topoisomerase II activity during the transition from meiotic prophase to metaphase. Together, the studies reviewed here increase our understanding of how chromosomes get together with their homologous partners and how these partners subsequently come apart.

Animals↗
PubMed1998

Meiotic prophase arrest with failure of chromosome synapsis in mice deficient for Dmc1, a germline-specific RecA homolog.

DMC1 is a meiosis-specific gene first discovered in yeast that encodes a protein with homology to RecA and may be component of recombination nodules. Yeast dmc1 mutants are defective in crossing over and synaptonemal complex (SC) formation, and arrest in late prophase of meiosis I. We have generated a null mutation in the Dmc1 gene in mice and show that homozygous mutant males and females are sterile with arrest of gametogenesis in the first meiotic prophase. Chromosomes in mutant spermatocytes fail to synapse, despite the formation of axial elements that are the precursor to the SC. The strong similarity of phenotypes in Dmc1-deficient mice and yeast suggests that meiotic mechanisms have been highly conserved through evolution.

Adenosine Triphosphatases↗
PubMed1998

Sudden coronary death in women.

OBJECTIVES: The objective of this study was to examine prospectively the incidence, predisposing cardiovascular conditions, and risk factors for sudden death in women compared with men. METHODS AND RESULT: The study design was a prospective general population examination of a cohort of 2873 women for development of sudden coronary death in relation to antecedent overt coronary heart disease (CHD), cardiac failure, and risk factors for coronary heart disease. Participants were women aged 30 to 62 years participating in the Framingham Study, receiving routine biennial examinations for risk factors and cardiovascular conditions. Among women monitored over a period of 38 years, there were 750 initial coronary events, of which 94 (12%) were sudden cardiac deaths. Of the 292 CHD fatalities in women, 32% were sudden cardiac deaths and 37% of the women had a history of prior CHD. Sudden death incidence in women logged behind that in men by >10 years. However, above age 75 years, 17% of all CHD events in women were sudden deaths. Sudden death risk in women with CHD was half as high as in men if they had CHD. In both sexes, a myocardial infarction conferred twice the risk of angina. Cardiac failure escalated sudden death risk of women 5-fold but was only one fourth that of men with failure or CHD. Ventricular ectopy increased sudden death risk only in women without prior overt CHD. Except for diabetes, CHD risk factors imposed a lower sudden death risk in women than men. However, even in women, sudden death risk increased over a 17-fold range in relation to their burden of CHD risk factors. CONCLUSIONS: Sudden death is a prominent feature of CHD in women as well as men, particularly in advanced age. A higher fraction of sudden deaths in women than men is unexpected occurring in the absence of prior overt CHD. It is subject to the same risk factors and as predictable in women as in men. However, at any level of multivariate risk, women are less vulnerable to sudden death than men.

Adult↗
PubMed1997

Analysis of expression and function of topoisomerase I and II during meiosis in male mice.

Topoisomerases are nuclear enzymes that remove torsional stress in DNA. Their function is important for replication, transcription, chromosome condensation, and chromosome segregation during mitosis and meiosis. The goal of this work is to analyze both expression and function of topoisomerases during the meiotic stages of mammalian spermatogenesis. The patterns of expression of topoisomerase I and topoisomerase II alpha genes were followed on Northern blots of RNA from testes of mice of different ages and from specific germ cell populations. The transcript of the topoisomerase I gene was highest in somatic cells of the testis and in the mitotically proliferating spermatogonia and meiotic prophase spermatocytes, with the level of transcript decreasing dramatically in postmeiotic spermatids. In contrast, the levels of topoisomerase II alpha transcript were negligible in germ-cell free testes and highest in late meiotic prophase cells and round spermatids. Enzyme activity for both topoisomerase I and topoisomerase II was detected in both pachytene spermatocytes and in round spermatids; topoisomerase II exhibited a higher level of activity in meiotic spermatocytes than in round spermatids. In cultured cells, camptothecin, an inhibitor of topoisomerase I, caused some abnormalities of paired meiotic homologs, but did not inhibit the transition to metaphase. In contrast, teniposide and ICRF-193, inhibitors of topoisomerase II, dramatically inhibited the formation of metaphase chromosomes in cells induced to progress from prophase to metaphase. However, the disassembly of the synaptonemal complex was not inhibited, indicating that this process could be uncoupled from condensation of chromatin to form chromosomes. These studies constitute evidence for a functional requirement for topoisomerase II activity in the transition from meiotic prophase to meiotic metaphase I in mammalian spermatocytes.

Animals↗
PubMed1997

Expression cloning and receptor pharmacology of human calcitonin receptors from MCF-7 cells and their relationship to amylin receptors.

Human breast cell carcinoma MCF-7 cells were found to bind 125I-labeled rat amylin (rAmylin) and the peptide amylin antagonist radioligand 125I-AC512 with high affinity. This high affinity binding possessed characteristics unique to the already defined high affinity binding site for amylin in the rat nucleus accumbens [Mol. Pharmacol. 44:493-497 (1993); J. Pharmacol. Exp. Ther. 270:779-787 (1994); Eur. J. Pharmacol. 262:133-141 (1994)]. To further define this receptor, we report results of expression cloning studies from an MCF-7 cell library. We isolated two variants of a seven-transmembrane receptor that were identical to two previously described human calcitonin receptors (hCTR1 and hCTR2). These receptors were characterized by expression in different surrogate host cell systems. Transient expression of hCTR1 in COS cells yielded membranes that bound 125I-AC512 and 125I-salmon calcitonin with high affinity, but no high affinity binding was observed with 125I-human calcitonin (hCAL) or 125I-rAmylin. Stable expression of hCTR1 in HEK 293 cells produced similar data. In contrast, expression of hCTR2 in COS cells yielded membranes that bound 125I-AC512, 125I-hCAL, and 125I-rAmylin with high affinity. The agonists 125I-hCAL and 125I-rAmylin bound 65% and 1.5%, respectively, of the sites bound by the antagonist radioligand 125I-AC512 in this expression system. This pattern of binding was repeated in HEK 293 cells stably transfected with hCTR2 (125I-hCAL = 24.8% Bmax, 125I-rAmylin = 8% Bmax). In both expression systems, the agonists hCAL and rAmylin were much more potent in displacing their radioligand counterparts than was the antagonist radioligand 125I-AC512. For example, the pKi value for displacement of 125I-AC512 by rAmylin was 7.2 in HEK 293 cells but rose to 9.1 when displacing 125I-rAmylin. Finally, hCTR2 was expressed in baculovirus-infected Ti ni cells. In this system, only specific binding to the antagonist 125I-AC512 and agonist 125I-hCAL was observed; no binding to 125I-rAmylin could be detected. These data are discussed in terms of two working hypotheses. The first is that amylin is a weak agonist for hCTR2 and that this receptor is unrelated to the amylin receptor found in this cell line. The second is that hCTR2 couples to different G proteins for calcitonin and amylin function in different cells. At present, these data cannot be used to disprove conclusively either hypothesis.

Amino Acid Sequence↗
PubMed1995

Detection and analysis of an alternatively spliced isoform of interleukin-6 mRNA in peripheral blood mononuclear cells.

Oligonucleotide primers for human interleukin-6 (IL-6) that bracketed the entire coding region of the gene were used in reverse transciptase-polymerase chain reaction (RT-PCR) studies to examine lL-6 expression in peripheral blood mononuclear cells (PBMC). In addition to the predicted 0.64-kb RT-PCR product, a second 0.45-kb product was observed. Cloning and dideoxy sequence analysis of this product revealed evidence for an alternatively spliced lL-6 transcript lacking exon II. Further RT-PCR analysis using forward primers ending at or one base before the exon I donor splice site again yielded both products. Additional primers were designed and successfully used to selectively distinguish the two forms of IL-6 transcript. Both transcripts were prominent in peripheral blood monocytes and lymphocytes, whereas only the 0.64-kb, full-length transcript was prominent in the lL-6-producing 5637 (human bladder carcinoma) cell line. Northern analysis revealed, in addition to the predominant 1.3-kb transcript, several minor transcripts at 1.9 to 4.8 kb that hybridized with the alternatively spliced cDNA probe but not with an exon II probe. Western analysis revealed lL-6 polypeptides of predicted size (26 to 29 kD) in culture medium from PBMC, while showing an immunoreactive band at 17 kD in cell lysates. These findings suggest the existence of an alternatively spliced form of lL-6 mRNA, which would encode for a polypeptide missing the gp130 interactive (signal-transducing) domain contained in exon II while retaining the lL-6 receptor (p80) domain. Such a molecule could in theory function as a natural antagonist of lL-6, as it would be expected to bind to the IL-6 receptor but not lead to signal transduction.

Amino Acid Sequence↗
PubMed1995

Ubiquitin fusion proteins are overexpressed in colon cancer but not in gastric cancer.

A cDNA clone (AF3) encoding the ubiquitin A gene 52 amino acid extension fusion protein (UbA52) was isolated from a subtracted cDNA library of human colorectal carcinoma minus adjacent normal mucosa. In Northern hybridization the mRNA signal for UbA52 was greater in surgical samples of colonic carcinoma (T) than in paired adjacent normal (N) tissues in 24 of 29 cases (T/N = 3.4 +/- 0.5, P < 0.01). An oligonucleotide probe specific for only the 52 amino acid extension confirmed the overexpression of UbA52. In contrast, there was no overexpression of UbA52 mRNA in gastric cancer samples (n = 7, T/N = 1.0 +/- 0.3). The mRNA of several ribosomal proteins, and of another ubiquitin A gene fusion protein, UbA80, with an 80 amino acid extension of ribosomal protein S27a, have been reported to be over-expressed in colon cancer, but not as yet at the protein level. Using rabbit antisera to the ribosomal protein component S27a we demonstrate over-expression of S27a at the protein level in colonic (n = 5), but not gastric (n = 6) carcinomas. Therefore it is likely that both UbA80 and UbA52 are overexpressed in colon cancer, but not in gastric cancer.

Base Sequence↗
PubMed1995

Determination of strontium-90 in milk samples using a controlled precipitation clean-up step prior to ion-chromatography.

Strontium-90 may be determined by beta-counting its yttrium-90 daughter following separation by ion-chromatography, using a three column system comprising a chelating concentrator column, a cation-exchange column and an anion-exchange separator column. The column system has previously been applied to the determination of strontium-90 in water and urine samples. The applicability of the system to the analysis of milk is hampered by the large concentrations of calcium present, which significantly reduces the extraction of yttrium-90 by the concentrator column. A maximum of approximately 200 mg of calcium can be present for the successful extraction of yttrium-90, which greatly limits the quantity of milk that can be analysed. The quantity of milk analysed can be increased by the inclusion of a controlled precipitation step prior to the ion-chromatographic separation. The precipitation is carried out on acid digested milk samples by the addition of ammonia solution until the addition of one drop causes a reduction in pH resulting in the precipitation of calcium hydrogenphosphate. Under these conditions, approximately 20% of the calcium present in the original milk sample is precipitated, yttrium-90 is precipitated whereas strontium-90 is not precipitated. Dissolution of the precipitate, followed by separation of yttrium-90 using the ion-chromatography system facilitates the analysis of a litre of milk with recoveries of greater than 80%.

Animals↗
PubMed1995

Transducers for foot pressure measurement: survey of recent developments.

Recent advances in the development of transducers for the measurement of vertical and shear forces acting on the plantar surface of the foot are reviewed. Barefoot and in-shoe discrete and matrix transducers are reviewed in terms of structure, operation, performance and limitations. Examples of capacitive, piezo-electric, optical, conductive and resistive types of transducer are presented. Where available, the current clinical status is specified.

Biomechanical Phenomena↗
PubMed1995

Does number of children increase the rate of coronary heart disease in men?

We examined the association between number of children and coronary heart disease risk among men in two large prospective cohort studies. Data from the Framingham Heart Study comprised a group of 1,632 men who were followed for 30 years; data from the first National Health and Nutrition Examination Survey National Epidemiologic Follow-up Study included 2,584 men who were followed for 3-5 years. We found no relation between number of children and coronary heart disease incidence in these cohorts. This lack of association in men contrasts with the previous positive association found between pregnancy and coronary heart disease in women.

Adult↗
PubMed1994

Determination of strontium-90 in water and urine samples using ion chromatography.

A semi-automated method was developed for the determination of 90Sr in water and urine samples using ion chromatography. Yttrium-90 in secular equilibrium with 90Sr was initially extracted from the sample solution buffered to pH 5 using a high-capacity iminodiacetate chelating resin. At this pH, transition metals, lanthanides and actinides were extracted by the resin. The extracted metals were then transferred on to a separator column where they were separated and eluted as weak acid anionic complexes. The transition metals were eluted first by using a pyridine-2,6-dicarboxylate eluent, then the lanthanides, actinides and 90Y were eluted from the column by using an oxalate-diglycolate eluent. The fraction containing 90Y was then collected and beta-counted. For water samples, a minimum of sample preparation was required prior to chromatography, whereas an oxalate coprecipitation was included as a preconcentration step for urine samples. The derived recoveries for 90Sr for surface water, rain water and urine samples were 91.7 +/- 1.8, 91.9 +/- 1.6 and 90.0 +/- 2.7%, respectively, and the minimum detectable activity using gas flow proportional counting was 8 mBq.

Chromatography↗
PubMed1993

Benefits and adverse effects of weight loss. Observations from the Framingham Study.

OBJECTIVE: To identify the benefits and adverse effects of weight loss. DESIGN: Longitudinal, epidemiologic study in a defined population. PARTICIPANTS: Men and women (n = 2500) who were between 35 and 54 years old at baseline, followed for 20 years in Framingham, Massachusetts. MEASUREMENTS: Height, weight, lipid levels, blood pressure, smoking status, diet, physical activity, prevalent and incident cardiovascular disease, diabetes, other diseases, and mortality rate were assessed. RESULTS: Compared with those whose body mass index (BMI) or weight changed least, men and women who lost weight during a 10-year period were older, heavier, and had higher blood pressures and cholesterol levels initially but had the smallest gains in blood pressure and cholesterol levels. However, rates of cigarette smoking were higher, and rates of smoking cessation were lower. During 20 years of further follow-up, death rates were highest in those whose BMI decreased and in those with the highest BMI at study entry. Relative risks for death from cardiovascular disease, coronary heart disease, and all causes were significantly greater by 33% to 61% in men whose BMI decreased after adjusting for age and risk factors for cardiovascular disease. In women, weight loss and weight gain were associated with higher relative risks for cardiovascular disease and coronary heart disease, but only the 38% increase in total mortality rate among women who lost weight was statistically significant after adjusting for age. CONCLUSIONS: Weight loss was associated with improvements in blood pressure and cholesterol levels but also with continued cigarette smoking, prevalent and incident cardiovascular disease, diabetes mellitus, other diseases, and higher death rates. Leanness and maintenance of stable weight were beneficial to risk factors, and to the prevention of morbidity, and death.

Adult↗
PubMed1993

Untreated blood pressure level is inversely related to cognitive functioning: the Framingham Study.

It was hypothesized that blood pressure would be inversely related to cognitive functioning, if unconfounded with antihypertensive medication and measured over many occasions prior to neuropsychological testing. For stroke-free Framingham Study participants aged 55-88 years (n = 1,702), blood pressure levels were averaged over five biennial examinations (1956-1964) when few hypertensives were being treated, and examined in relation to neuropsychological tests administered between 1976 and 1978. With age, education, occupation, cigarette smoking, alcohol consumption, and gender controlled, blood pressure levels and chronicity of hypertension were inversely related to the composite score and measures of attention and memory. This was true for the full sample, for a subsample untreated during blood pressure measurement (n = 1,485), and for a subsample untreated throughout the entire study period (n = 1,038). For example, decline per 10 mmHg increment in blood pressure ranged from -0.04 to -0.07 standard score units (z) for the composite score. A negative finding previously was most likely due to blood pressure measurement concurrently with neuropsychological testing, or too few measurements. Hypertension-associated pathogenic processes may cause mild cognitive impairment, but other mechanisms need to be considered.

Aged↗
PubMed1993

Number of pregnancies and the subsequent risk of cardiovascular disease.

BACKGROUND: Whether increasing parity or gravidity is a risk factor for coronary heart disease has been debated, but the question remains unresolved. METHODS: We tested the association between the number of pregnancies and a variety of cardiovascular end points in two groups of women who had completed childbearing. One group comprised 2357 women who were followed for 28 years through the Framingham Heart Study, and the other 2533 women followed for at least 12 years through the first National Health and Nutrition Examination Survey National Epidemiologic Follow-up Study (NHEFS). RESULTS: The rates of coronary heart disease were higher among multigravid women than among women who had never been pregnant, in both the Framingham Heart Study and the NHEFS, but in both studies, the higher rates were statistically significant only in women with six or more pregnancies. For the women in the Framingham Study, the rate ratio adjusted for age and educational level in the group with six or more pregnancies (as compared with women who had never been pregnant) was 1.6 (95 percent confidence interval, 1.1 to 2.2). For the women in the NHEFS, the same adjusted rate ratio was 1.5 (95 percent confidence interval, 1.1 to 1.9). Adjustments for other known cardiovascular risk factors, including weight, did not markedly alter this risk. The rate of total cardiovascular disease was also significantly higher among multigravid women in the Framingham Study than in the women who had never been pregnant. CONCLUSIONS: In two prospective American studies, having six or more pregnancies was associated with a small but consistent increase in the risk of coronary heart disease and cardiovascular disease. Whether gravidity itself or some other unmeasured factor accounts for the increase in risk that we observed requires further investigation.

Aged↗