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Biomedical subjects

M A Tanner

Publications and source records attributed to M A Tanner.

At least 19 recordsLinked to original sources
PubMed2006

Myocardial iron loading in patients with thalassemia major on deferoxamine chelation.

BACKGROUND: Heart failure secondary to myocardial iron loading remains the leading cause of death in thalassemia major (TM). We used cardiovascular magnetic resonance (CMR) to assess the prevalence of myocardial iron overload and ventricular dysfunction in a large cohort of TM patients maintained on conventional chelation treatment with deferoxamine. METHODS: A mobile CMR scanner was transported from London, UK, to Sardinia, Italy where 167 TM patients were assessed for myocardial iron loading, B-natriuretic peptide (BNP), and ferritin. In patients with myocardial iron loading CMR assessments of ventricular function were also made. RESULTS: Myocardial iron loading (T2* < 20 ms) was present in 108 (65%) patients, which was severe (T2* < 8 ms) in 22 (13%). Impaired (< 56%) left ventricular (LV) ejection fraction (EF) was present in 5%, 20% and 62% of patients with mild, moderate or severe iron loading. Increasing myocardial iron was related to impaired LVEF (Rs = 0.57, p < 0.001), weakly related to serum ferritin (Rs = -0.34, p < 0.001), and not related to liver iron (Rs = 0.11, p = 0.26). BNP was weakly related to myocardial iron (Rs = -0.35, p < 0.001) and was abnormal in only 5 patients. CONCLUSIONS: Myocardial siderosis was found in two-thirds of thalassemia major patients on maintenance deferoxamine treatment. This was combined with a high prevalence of impaired LV function, the severity of which tracked the severity of iron deposition. BNP was not useful to assess myocardial siderosis.

Cardiomyopathies↗
PubMed2003

Percutaneous technique for the reduction of knotted coronary catheters.

During coronary angiography knotting of a coronary catheter is a recognised complication. It commonly results through excessive manipulation of a catheter in an attempt to engage the right coronary artery. Although simple manoeuvres of the catheter can often result in resolution of a kink, tighter knots may not be amenable to such measures. There is, however, little published material regarding its best management. We present five cases of cardiac catheterisation complicated by catheter knotting and present a novel percutaneous technique for their reduction.

Aged↗
PubMed2003

Clozapine associated dilated cardiomyopathy.

A 31-year-old white man was referred for investigation of a persistent sinus tachycardia. His only significant past medical history was of chronic schizophrenia for which he had been taking clozapine for six years. An electrocardiogram demonstrated sinus tachycardia, voltage criteria for left ventricular hypertrophy, and a prolonged QTc. Echocardiographic findings were consistent with a dilated cardiomyopathy. Serious cardiac complications of clozapine use are rare but have been reported previously. It is important to note that sinus tachycardia may be the only obvious clinical sign, and that complications can manifest months or even years (as in this case) after starting the drug. Patients on clozapine should be informed of potential cardiac symptoms and doctors should maintain a high degree of clinical suspicion throughout the duration of treatment.

Adult↗
PubMed2002

Substantial changes in gene expression level due to the storage temperature and storage duration of human whole blood.

Blood is a valuable clinical sample for high-throughput analysis of gene expression and is likely to become more popular as a diagnostic tool and as a predictive measure of disease progression and drug responsiveness. Gene expression data from blood that has been stored at ambient temperature for greater than 1 h vs. blood samples that have been lysed immediately post-collection shows dramatic changes in relative gene expression for a number of cytokines, chemokines, and transcription factors. Results indicate significant changes in the relative expression of several genes, many of which were either up-regulated or down-regulated, because of storage at ambient temperature: (1) In only 4 h of storage at ambient temperature, greater than 10-fold increases in relative gene expression were observed for interleukin-8 (IL-8), c-myc, and c-fos; (2) Up-regulation of IL-8, a chemokine that mediates inflammatory cell migration, took place only 1-h after collection and increased nearly 100-fold by 4 h; (3) Down-regulation of several anti-inflammatory genes was observed for blood stored at ambient temperature; and (4) A general trend toward selective enhancement of inflammatory responses was observed, mediated by possible mRNA transcription and turnover. These results validate the need for the rapid lysis of whole blood after removal from the source.

Blood Preservation↗
PubMed2000

Endothelial cell regulation of nitric oxide production during hypoxia in coronary microvessels and epicardial arteries.

Nitric oxide (NO) synthesized by endothelial cell nitric oxide synthase (eNOS) elicits vasodilation of resistance-sized coronary microvessels. Since coronary blood flow increases during hypoxia, we tested the hypotheses that: (1) hypoxia results in increased blood flow through increased NO production mediated by the upregulation of both eNOS mRNA and protein and (2) the regulation of NO production in response to hypoxia differs in microvascular endothelial cells and nonresistance, epicardial endothelial cells. Monocultures of vascular endothelium from resistance (approximately 100 micro) and nonresistance epicardial arteries were established and characterized. Nitric oxide was quantitated using a chemiluminescence method. Hypoxia (pO(2) = 10 mmHg) significantly increased NO production in both cell lines, with less NO produced in microvascular endothelium. Western blots demonstrated that hypoxia caused a time-dependent increase in eNOS protein in both lines, with an average 2.5-fold increase in nonresistance, epicardial endothelial cells compared to an average 1.7-fold increase in protein from microvascular endothelium. Total mRNA recovery increased 2.4 +/- 0.6-fold within 30 min of hypoxia in nonresistance, epicardial endothelial cells with no increase in microvascular endothelial cells. Although hypoxia increased NO production in both populations of endothelial cells, the increase in NO production and eNOS protein in microvascular endothelium was less compared to nonresistance, epicardial endothelial cells. Furthermore, there was no significant upregulation of total mRNA for eNOS in microvascular endothelium. The data indicate that increased NO production in microvascular endothelium during hypoxia may be through translational or posttranslational modifications of the enzyme, whereas transcriptional upregulation may account for the increased NO production in nonresistance, epicardial endothelial cells. Oxygen-sensitive response mechanisms that modulate NO production may be different in endothelium from different coronary artery vascular beds.

Animals↗
PubMed2000

Molecular phylogenetic evidence for noninvasive zoonotic transmission of Staphylococcus intermedius from a canine pet to a human.

rRNA-based molecular phylogenetic techniques were used to identify the bacterial species present in the ear fluid from a female patient with otitis externa. We report the identification of Staphylococcus intermedius from the patient and a possible route of transmission. Analysis of 16S ribosomal DNA restriction fragment length polymorphisms indicated that the dominant species present was S. intermedius. A pet dog owned by the patient also was tested and found to harbor S. intermedius. In humans, the disease is rare and considered a zoonosis. Previously, S. intermedius has been associated with dog bite wounds, catheter-related injuries, and surgery. This study represents the first reported case of a noninvasive infection with S. intermedius.

Adult↗
PubMed1999

On the approximation rate of hierarchical mixtures-of-experts for generalized linear models.

We investigate a class of hierarchical mixtures-of-experts (HME) models where generalized linear models with nonlinear mean functions of the form psi (alpha + xT beta) are mixed. Here psi (.) is the inverse link function. It is shown that mixtures of such mean functions can approximate a class of smooth functions of the form psi (h(x)), where h(.) epsilon W2;K infinity (a Sobolev class over [0, 1]s), as the number of experts m in the network increases. An upper bound of the approximation rate is given as O(m-2/s) in Lp norm. This rate can be achieved within the family of HME structures with no more than s-layers, where s is the dimension of the predictor x.

Algorithms↗
PubMed1999

The direct release of nitric oxide by gypenosides derived from the herb Gynostemma pentaphyllum.

Herbal medicines are increasingly being utilized to treat a wide variety of disease processes. Gypenosides are triterpenoid saponins contained in an extract from Gynostemma pentaphyllum and are reported to be effective in the treatment of cardiovascular diseases; however, the mechanism underlying the therapeutic effect is not known. We tested the hypothesis that gypenosides extracted from G. pentaphyllum elicit vasorelaxation through the direct release of endothelium-derived nitric oxide. Nitric oxide production in bovine aortic endothelial cells grown under standard tissue culture conditions was quantitated using a chemiluminescence method. Arterial vasomotion was assayed using isolated porcine coronary artery rings under standard isometric recording conditions. The extract of G. pentaphyllum at 0.1-100 microg/ml elicited concentration-dependent vasorelaxation of porcine coronary rings that was antagonized by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester. Indomethacin had no significant effect on G. pentaphyllum-induced relaxation. The G. pentaphyllum extract elicited a concentration-dependent increase in nitric oxide production from cultured bovine aortic endothelial cells. At the concentrations utilized, there was no morphological evidence for cellular toxicity. These results demonstrate that extracts of G. pentaphyllum directly stimulate nitric oxide release, but not prostanoid production. Nitric oxide production in response to gypenosides may be one mechanism whereby this herbal medicine elicits its therapeutic effects.

Animals↗
PubMed1999

The upregulation of endothelin and its receptors in porcine coronary arteries in a double balloon injury model of restenosis.

Endothelin, a potent vasoconstrictor, mitogen, and stimulant of collagen synthesis, is reported to be increased after vascular injury. We tested the hypothesis that tissue endothelin levels and its receptor expression are increased following double balloon injury in a porcine coronary artery model of restenosis. Male miniature swine maintained on a hyperlipidemic diet underwent oversized balloon injury to both the proximal right coronary artery and left circumflex coronary artery. Two weeks following the initial injury, the arteries were repeat injured at the same site and subsequently harvested four weeks later. Proximal balloon injured (BI) and distal non-balloon-injured (NBI) segments from the same artery were collected. Tissue endothelin-1 (ET-1) levels were measured by ELISA. Endothelin receptors were assayed by radioligand binding using 125I-ET-1 and also immunolabeling. Tissue endothelin levels were 4-5 fold greater in BI arteries as compared to NBI. There was a significant increase in tissue ET-1 levels and endothelin receptor binding following double balloon injury relative to NBI control arteries. Western blots showed an increased expression of ET(A) receptor protein in injured vessels compared to non-injured arteries. Immunohistochemistry using an ET(A) receptor specific antibody confirmed increased receptor density following balloon injury. Thus, in an in vivo double balloon injury model for coronary artery restenosis, the response to vascular injury is increased tissue ET-1 content and upregulation of ET(A) receptor density associated with increased receptor protein.

Animals↗
PubMed1999

Approximate Monte Carlo conditional inference in exponential families.

This article presents an algorithm for approximate frequentist conditional inference on two or more parameters for any regression model in the Generalized Linear Model (GLIM) family. We thereby extend highly accurate inference beyond the cases of logistic regression and contingency tables implimented in commercially available software. The method makes use of the double saddlepoint approximations of Skovgaard (1987, Journal of Applied Probability 24, 875-887) and Jensen (1992, Biometrika 79, 693-703) to the conditional cumulative distribution function of a sufficient statistic given the remaining sufficient statistics. This approximation is then used in conjunction with noniterative Monte Carlo methods to generate a sample from a distribution that approximates the joint distribution of the sufficient statistics associated with the parameters of interest conditional on the observed values of the sufficient statistics associated with the nuisance parameters. This algorithm is an alternate approach to that presented by Kolassa and Tanner (1994, Journal of the American Statistical Association 89, 697-702), in which a Markov chain is generated whose equilibrium distribution under certain regularity conditions approximates the joint distribution of interest. In Kolassa and Tanner (1994), the Gibbs sampler was used in conjunction with these univariate conditional distribution function approximations. The method of this paper does not require the construction and simulation of a Markov chain, thus avoiding the need to develop regularity conditions under which the algorithm converges and the need for the data analyst to check convergence of the particular chain. Examples involving logistic and truncated Poisson regression are presented.

Algorithms↗
PubMed1999

Small-sample confidence regions in exponential families.

This article presents an algorithm for small-sample conditional confidence regions for two or more parameters for any discrete regression model in the generalized linear interactive model family. Regions are constructed by careful inversion of conditional hypothesis tests. This method presupposes the use of approximate or exact techniques for enumerating the sample space for some components of the vector of sufficient statistics conditional on other components. Such enumeration may be performed exactly or by exact or approximate Monte Carlo, including the algorithms of Kolassa and Tanner (1994, Journal of the American Statistical Association 89, 697-702; 1999, Biometrics 55, 246-251). This method also assumes that one can compute certain conditional probabilities for a fixed value of the parameter vector. Because of a property of exponential families, one can use this set of conditional probabilities to directly compute the conditional probabilities associated with any other value of the vector of the parameters of interest. This observation dramatically reduces the computational effort required to invert the hypothesis test to obtain the confidence region. To construct a region with confidence level 1 - alpha, the algorithm begins with a grid of values for the parameters of interest. For each parameter vector on the grid (corresponding to the current null hypothesis), one transforms the initial set of conditional probabilities using exponential tilting and then calculates the p value for this current null hypothesis. The confidence region is the set of parameter values for which the p value is at least alpha.

Algorithms↗
PubMed1999

Prevalence of corynebacterial 16S rRNA sequences in patients with bacterial and "nonbacterial" prostatitis.

The etiology of chronic prostatitis syndromes in men is controversial, particularly when positive cultures for established uropathogens are lacking. Although identification of bacteria in prostatic fluid has relied on cultivation and microscopy, most microorganisms in the environment, including some human pathogens, are resistant to cultivation. We report here on an rRNA-based molecular phylogenetic approach to the identification of bacteria in prostate fluid from prostatitis patients. Positive bacterial signals were seen for 65% of patients with chronic prostatitis overall. Seven of 11 patients with bacterial signals but none of 6 patients without bacterial signals were cured with antibiotic-based therapy. Results indicate the occurrence in the prostate fluid of a wide spectrum of bacterial species representing several genera. Most rRNA genes were closely related to those of species belonging to the genera Corynebacterium, Staphylococcus, Peptostreptococcus, Streptococcus, and Escherichia. Unexpectedly, a wide diversity of Corynebacterium species was found in high proportion compared to the proportions of other bacterial species found. A subset of these 16S rRNA sequences represent those of undescribed species on the basis of their positions in phylogenetic trees. These uncharacterized organisms were not detected in control samples, suggesting that the organisms have a role in the disease or are the consequence of the disease. These studies show that microorganisms associated with prostatitis generally occur as complex microbial communities that differ between patients. The results also indicate that microbial communities distinct from those associated with prostatitis may occur at low levels in normal prostatic fluid.

Bacterial Infections↗
PubMed1999

Kinetics of mammary clonogenic cells and rat mammary cancer induction by X-rays or fission neutrons.

Following the hormonal treatment of rats with high prolactin levels and glucocorticoid deficiency (Prl+/Glc-) for 48 days (Day +48), total recoverable mammary DNA was increased by more than sevenfold, tritiated thymidine uptake by nearly fourfold, and total mammary clonogens by about fivefold. Irradiation with 4, 40, and 80 cGy X-rays on Day +48 increased total mammary carcinomas per rat-day-at-risk linearly with dose, and 40 and 80 cGy significantly decreased first carcinoma latency. A dose of 40 cGy X-rays before hormone treatment (Day -1) yielded tumor latencies and frequencies insignificantly different from unirradiated controls but significantly different from those when the dose was given on Day +48. Total carcinomas per rat-day-at-risk were fitted better by a function of dose to the power 0.4 than by a linear function after exposure to 1, 10. and 20 cGy fission neutrons, and 10 and 20 cGy significantly shortened the time to appearance of the first cancer. In contrast to results with X-rays, 10 cGy neutrons on Day -1 yielded tumor frequencies and latencies insignificantly different from 10 cGy neutrons on Day +48. The carcinogenic action of X-rays, but not of neutrons, was thus influenced by total clonogen numbers and/or proliferation rates.

Animals↗
PubMed1999

Ethanol increases endothelial nitric oxide production through modulation of nitric oxide synthase expression.

Moderate alcohol consumption has been shown to reduce the risk of ischemic heart disease potentially through its effect on specific endothelial-derived compounds. We tested the hypothesis that ethanol increases the expression of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) production in bovine aortic endothelial cells (BAEC). Primary cultures of BAEC grown to confluence under standard conditions were treated 3-6 h with 0.1% ethanol in the presence of indomethacin. Ethanol induced a significant increase in both basal and stimulated NO production as determined by chemiluminescence method. This effect was accompanied by a rapid increase of eNOS protein and mRNA expression levels. eNOS mRNA increased two-fold within 3 h and gradually declined, but the increased levels of mRNA persisted for >24 h. A similar increase of eNOS expression was observed in human umbilical endothelial cells exposed to ethanol. These results demonstrate that ethanol augments both basal and stimulated NO production and that this effect is associated with increased eNOS protein and mRNA expression levels. The data are consistent with the hypothesis that the reduced incidence of ischemic heart disease associated with alcohol may be related, at least in part, to the modulation of vascular endothelial cell production of NO.

Animals↗
PubMed1998

Specific ribosomal DNA sequences from diverse environmental settings correlate with experimental contaminants.

Phylogenetic analysis of 16S ribosomal DNA (rDNA) clones obtained by PCR from uncultured bacteria inhabiting a wide range of environments has increased our knowledge of bacterial diversity. One possible problem in the assessment of bacterial diversity based on sequence information is that PCR is exquisitely sensitive to contaminating 16S rDNA. This raises the possibility that some putative environmental rRNA sequences in fact correspond to contaminant sequences. To document potential contaminants, we cloned and sequenced PCR-amplified 16S rDNA fragments obtained at low levels in the absence of added template DNA. 16S rDNA sequences closely related to the genera Duganella (formerly Zoogloea), Acinetobacter, Stenotrophomonas, Escherichia, Leptothrix, and Herbaspirillum were identified in contaminant libraries and in clone libraries from diverse, generally low-biomass habitats. The rRNA sequences detected possibly are common contaminants in reagents used to prepare genomic DNA. Consequently, their detection in processed environmental samples may not reflect environmentally relevant organisms.

Animals↗
PubMed1998

Vascular endothelial cell regulation of extracellular matrix collagen: role of nitric oxide.

Endothelium-derived products have been implicated in the regulation of vascular wall structure through their effects on extracellular matrix metabolism. The purpose of this study was to further understand the paracrine mechanisms underlying endothelial cell regulation of extracellular matrix metabolism by testing the hypothesis that endothelium-derived nitric oxide decreases the concentration of soluble collagens derived from vascular smooth muscle cells (VSMCs). Porcine coronary endothelium and VSMCs were grown under a coculture configuration to assess the paracrine effects of nitric oxide produced by the endothelium on VSMC collagen types I and III. Endogenous endothelial cell nitric oxide production was blocked with N(omega)-nitro-L-arginine methyl ester. Collagen type I and type III were quantitatively measured using an enzyme-linked immunosorbent assay method. The endothelium elicited a time-dependent increase in the concentration of soluble VSMC-derived collagen type I; in contrast, collagen type III was decreased. After inhibition of nitric oxide production, there was a marked increase in both collagen types I and III concentration. These results demonstrated that endothelium-derived nitric oxide differentially alters collagen subtypes produced by VSMCs. The data support the hypothesis that nitric oxide functions via a paracrine mechanism to decrease VSMC collagen types I and III concentration, a finding consistent with an integral role for the endothelium in modulating extracellular matrix metabolism.

Animals↗
PubMed1997

Joining the two domains of a group I ribozyme to form the catalytic core.

Self-splicing group I introns, like other large catalytic RNAs, contain structural domains. Although the crystal structure of one of these domains has been determined by x-ray analysis, its connection to the other major domain that contains the guanosine-binding site has not been known. Site-directed mutagenesis and kinetic analysis of RNA splicing were used to identify a base triple in the conserved core of both a cyanobacterial (Anabaena) and a eukaryotic (Tetrahymena) group I intron. This long-range interaction connects a sequence adjacent to the guanosine-binding site with the domain implicated in coordinating the 5' splice site helix, and it thereby contributes to formation of the active site. The resulting five-strand junction, in which a short helix forms base triples with three separate strands in the Tetrahymena intron, reveals exceptionally dense packing of RNA.

Anabaena↗