Search PubMed⌕ Search

Biomedical subjects

A Keller

Publications and source records attributed to A Keller.

At least 73 records · Page 4Linked to original sources
PubMed1999

Sequence-tagged connectors: a sequence approach to mapping and scanning the human genome.

The sequence-tagged connector (STC) strategy proposes to generate sequence tags densely scattered (every 3.3 kilobases) across the human genome by arraying 450,000 bacterial artificial chromosomes (BACs) with randomly cleaved inserts, sequencing both ends of each, and preparing a restriction enzyme fingerprint of each. The STC resource, containing end sequences, fingerprints, and arrayed BACs, creates a map where the interrelationships of the individual BAC clones are resolved through their STCs as overlapping BAC clones are sequenced. Once a seed or initiation BAC clone is sequenced, the minimum overlapping 5' and 3' BAC clones can be identified computationally and sequenced. By reiterating this "sequence-then-map by computer analysis against the STC database" strategy, a minimum tiling path of clones can be sequenced at a rate that is primarily limited by the sequencing throughput of individual genome centers. As of February 1999, we had deposited, together with The Institute for Genomic Research (TIGR), into GenBank 314,000 STCs ( approximately 135 megabases), or 4.5% of human genomic DNA. This genome survey reveals numerous genes, genome-wide repeats, simple sequence repeats (potential genetic markers), and CpG islands (potential gene initiation sites). It also illustrates the power of the STC strategy for creating minimum tiling paths of BAC clones for large-scale genomic sequencing. Because the STC resource permits the easy integration of genetic, physical, gene, and sequence maps for chromosomes, it will be a powerful tool for the initial analysis of the human genome and other complex genomes.

Chromosome Mapping↗
PubMed1999

Presence of enolase in the M-band of skeletal muscle and possible indirect interaction with the cytosolic muscle isoform of creatine kinase.

Glycerol-skinned skeletal muscle fibres retain the defined sarcomeric structure of the myofibrils. We show here that a small fraction of two enzymes important for energy metabolism, the cytosolic muscle isoform of creatine kinase (EC 2.7.3.2), MM-creatine kinase (MM-CK), and enolase (EC 4.2.1.11), remains bound to skinned fibres. CK is slowly exchangeable, whereas enolase is firmly bound. Two-dimensional gel electrophoresis followed by Western blot analyses demonstrates that both alpha (ubiquitous) and beta (muscle-specific) subunits of enolase are present in these preparations. Enolase and CK were co-localized at the M-band of the sarcomeres, as observed by indirect immunofluorescence and confocal microscopy. Cross-linking experiments were performed on skinned fibres with three bifunctional succinimidyl esters of different lengths and yielded a protein complex of 150 kDa that reacted with antibodies directed against either M-CK or beta-enolase. The cross-linking efficiency was greatest for the longest reagent and zero for the shortest one. The length of the cross-linker giving a covalent complex between the two enzymes does not support the notion of a direct interaction between M-CK and enolase. This is the first demonstration of the presence of an enzyme of energy metabolism other than CK at the M-band of myofibres.

Animals↗
PubMed1999

Predictors of isokinetic back muscle strength in patients with low back pain.

STUDY DESIGN: Testing for trunk muscle strength was performed on 105 patients with chronic low back pain. OBJECTIVES: To investigate prediction of isokinetic back muscle strength in patients with low back pain. SUMMARY OF BACKGROUND DATA: The clinical evaluation of patients with chronic low back pain often in difficult because of discrepancy between disability and impairment. The isokinetic trunk device was developed as a tool for objective assessment of back muscle strength. However, the performance of patients depends on radiologic abnormalities of the spine, conditions of the back muscles, and various psychosocial factors. Studies are warranted that address how these variables influence back muscle strength. METHODS: The patients with chronic low back pain were tested by an isokinetic trunk muscle strength test (Cybex TEF, Ronkonkoma, NY). In addition, the following variables were recorded: gender, age, body mass index, emotional distress, pain on exertion, self-efficacy for pain, degenerative changes of the lumbar spine, cross-sectional area, and density of the erector spinae muscles. The three latter variables were estimated by computed tomography scans. The sum of the total work performed during isokinetic extension strength test was the dependent variable in a multiple regression analysis, and anthropometric, demographic, psychological, and radiologic factors were independent variables. RESULTS: Gender, cross-sectional muscle area, and pain on exertion were the most powerful predictors of isokinetic back muscle strength. The final regression model, which included these variables, could account for approximately 40% of the variability in back muscle strength. CONCLUSION: For assessing the results of an isokinetic trunk muscle strength test, cross-sectional muscle area, gender, and pain on exertion should be taken into account.

Adult↗
PubMed1999

The beta enolase subunit displays three different patterns of microheterogeneity in human striated muscle.

In higher vertebrates, the glycolytic enzyme enolase (2-phospho-D-glycerate hydrolyase; EC 4.2.1.11) is active as a dimeric protein formed from three subunits--alpha: ubiquitous, beta: muscle specific, and gamma: neuron specific--encoded by different genes. In the present study, we have shown that an antiserum previously produced against the mouse beta beta enolase is also a specific reagent for the muscle specific human enolase. Using this antiserum to study human muscles, we demonstrated novel patterns of the beta subunit microheterogeneity which are distinctive from those observed previously in rodents and which appear to be independent of age, gender and muscular activity. Two variants of the beta subunit differing by their size have been detected: one heavy form of 46 kDa (beta H) and one light form of 45 kDa (beta L). Muscle biopsies expressed either beta H or beta L or beta H + beta L, and all muscles of an individual expressed the same variants. The products of in vitro translation of RNA prepared from human muscle displayed beta subunit variants identical to those of the protein present in the biopsy. Therefore the differences observed between individuals reveal a difference already present at the level of the RNA transcripts. These observations suggest the existence of an yet undescribed polymorphism of the human beta enolase gene which could affect the coding sequence. Comparative immunocytochemical and histochemical analyses of biopsies demonstrated that the beta subunit was expressed in all fast fibres (type II), but not in slow fibres (type I). No difference was observed in the intensity of beta enolase immunolabelling between the various types (IIA, IIAB, IIB) of fast fibres. No significant difference in fibre type composition and histological appearance was visible between muscles presenting either one of the three patterns of microheterogeneity.

Adult↗
PubMed1999

Denervation of rabbit gastrocnemius and soleus muscles: effect on muscle-specific enolase.

We report here, for the first time, the expression of the muscle-specific isoform of the glycolytic enzyme, enolase (EC 4.2.1. 11) (beta enolase), in rabbit skeletal muscles. We have analysed the fast-twitch gastrocnemius and the slow-twitch soleus muscles during normal postnatal development and following denervation. We show that, in rabbit, as already described in rodents, beta enolase gene expression behaves as a good marker of the fast-twitch fibers. In soleus muscle, the beta enolase transcript level is 10-20% of that found in gastrocnemius. Denervation, performed at 8 postnatal days, induces an important drop of beta enolase transcript levels in both developing soleus and gastrocnemius muscles, with a 80% decrease observed 1 week after denervation in the operated muscles, as compared to the corresponding contralateral muscles. Thereafter, the beta enolase transcript level continues to decrease in the fast-twitch muscle, with the beta enolase subunit being detectable only in the atrophic fast-twitch fibers. In contrast, the beta transcript level tends to increase in the denervated slow-twitch muscle, reaching about 50% of that in contralateral soleus, at 7 weeks after surgery. The level of beta enolase transcripts still expressed after denervation seems to stabilize at the same low level in both types of inactive muscles. This suggests that the small fraction of beta enolase expression which is not controlled by the nerve, or by the contractile activity imposed by it, is independent of the muscle phenotype.

Animals↗
PubMed1999

A 96-well microfiltration assay for measurement of total clottable fibrinogen.

In clinical routine use, fibrinogen is measured by clotting-time methods, or by clot turbidity in photometric prothrombin time determination. For calibration of these assays measurement of total thrombin-clottable protein has been recommended. We have now developed a microfiltration assay for total thrombin-clottable protein. Plasma samples were mixed with thrombin in a 96-well microfiltration device. After clot formation, the fluid was extracted by vacuum suction, and fibrin adherent to the filter membranes washed with buffer. Membrane segments with adherent fibrin were recovered from the 96-well manifold with a punch and transferred to tubes containing denaturing buffer solution. After dissolution of fibrin, protein concentration was determined by optical absorption at 280 nm. The microfiltration assay displayed a high correlation with the total clottable protein method (R = 0.95), and fibrinogen antigen (r = 0.96). Correlation with clotting time assays, and PT-derived fibrinogen in 150 clinical plasma samples was in the range of r = 0.84 to r = 0.97. Intraassay and day-to-day variability of the assay was comparable to the conventional total clottable fibrinogen assay. The novel microfiltration assay appears to be well suited for measurement of large series of samples for calibration, screening purposes, and clinical trials.

Blood Coagulation↗
PubMed1998

Functional organization of rat olfactory bulb glomeruli revealed by optical imaging.

The functional organization and synaptic physiology of olfactory bulb glomeruli were studied in rat in vitro slice preparations stained with the voltage-sensitive dye RH-155. Optical signals were recorded with a 100-element photodiode array at high temporal resolution. Pharmacological and ionic manipulations were used to investigate synaptic responses to stimulation of the olfactory nerve layer (ONL). ONL stimulation evoked a sodium-mediated compound action potential that propagated across the ONL and invaded individual glomeruli. This presynaptic volley evoked calcium-dependent synaptic responses the amplitudes of which were largest within the glomerular layer (GL); smaller amplitude responses were recorded in deeper layers of the olfactory bulb. Synaptic responses in the GL were attenuated by the non-NMDA ionotropic glutamate receptor antagonist CNQX; the residual component was suppressed by the NMDA glutamate receptor antagonist AP-5. The GABAA receptor antagonist bicuculline methiodide had little effect, whereas the GABAB receptor agonist baclofen dramatically attenuated ONL-evoked synaptic responses. The effects of baclofen were reversed by the GABAB receptor antagonist CGP35348. Paired-pulse depression of ONL-evoked synaptic responses in the GL was partially reversed by CGP35348. These findings suggest that olfactory nerve axons release glutamate to activate both NMDA and non-NMDA receptors on GL neurons, that GABAA receptor-mediated inhibition has little effect on these responses, and that GABAB receptor-mediated inhibition may act presynaptically on olfactory nerve axons to modulate their inputs to olfactory bulb neurons.

2-Amino-5-phosphonovalerate↗
PubMed1998

Internal jugular vein thrombosis following modified neck dissection: implications for head and neck flap reconstruction.

BACKGROUND: The incidence of internal jugular vein thrombosis (IJVT) following a modified neck dissection remains uncertain. The effect of, or consequences following, IJVT upon pedicled and free flap head and neck reconstructions remains unexplored. METHODS: Twenty-nine preserved internal jugular veins in 24 patients undergoing modified neck dissection were available for prospective study. All patients required a pedicled or free flap reconstruction and received a modified, unilateral or bilateral cervical lymphadenectomy. The patency of all jugular veins was determined preoperatively and postoperatively using a combination of computed tomography (CT) scanning, high-resolution ultrasound, and color-flow Doppler (CFD). RESULTS: The IJVT rate was 14%. The presence of a pedicled myocutaneous flap and left-sided jugular dissections may represent risks to the postoperative patency of the internal jugular vein. Preoperative radiotherapy did not appear to impact negatively upon the thrombosis rate. CONCLUSIONS: Thrombosis of the internal jugular vein may result in significant morbidity for the postoperative oncologic patient. An internal jugular-dependent-free-tissue transfer may risk venous compromise of the flap, whereas the use of a pedicled flap may place the jugular at increased risk for thrombosis. Strategies for deep venous system microvascular recipient recruitment in the head and neck are discussed. Wherever possible, we employ two deep venous systems, the internal jugular, and subclavian (via the external jugular) for flap drainage.

Aged↗
PubMed1998

Revisions of endoprosthetic reconstructions after limb salvage in musculoskeletal oncology.

Of 91 limb-salvage procedures using prosthetic reconstructions because of primary or metastatic bone and soft-tissue tumors 26 revisions were performed in 16 patients. Revision was due to polyethylene wear (9 cases), aseptic loosening (8 cases), recurrent hip dislocation (3 cases), prosthetic stem fracture (2 cases), infection (2 cases), leg length discrepancy (1 case), and traumatic dislocation of a saddle prosthesis (1 case). The follow-up period for tumor control varied from 1.5 to 22 years with a median of 13.5 years. The follow-up period after the last revision operation varied from 0.5 to 12 years with a median of 3 years. At the last follow-up, the functional results had deteriorated compared with after the primary operation in 5 patients and had improved in 2 patients. In the remaining patients, the results did not change.

Adolescent↗
PubMed1998

A randomized study of combined zidovudine-lamivudine versus didanosine monotherapy in children with symptomatic therapy-naive HIV-1 infection. The Pediatric AIDS Clinical Trials Group Protocol 300 Study Team.

OBJECTIVE: The Pediatric AIDS Clinical Trials Group (PACTG) Protocol 300 assessed the clinical efficacy and safety of combination zidovudine/lamivudine (ZDV/3TC) compared with either didanosine (ddI) alone or combination ZDV/ddI. STUDY DESIGN: Children with symptomatic human immunodeficiency virus (HIV) infection, 6 weeks through 15 years of age, were stratified according to age and randomly assigned to receive ddI, ZDV/3TC, or ZDV/ddI. The primary endpoint was time to first progression of HIV disease or death. Enrollment in the ZDV/ddI arm stopped after 11 months on the basis of results of PACTG Protocol 152, but blinded follow-up continued. RESULTS: For the 471 children who could be evaluated, the median age was 2.7 years, median CD4 cell count was 699 cells/mm3, and median log10 HIV RNA was 5.1/mL. Median follow-up was 9.4 months. Patients receiving ZDV/3TC had a lower risk of HIV disease progression or death than those receiving ddI alone (15 vs 38 failures, P = .0006) and a lower risk of death (3 vs 15 deaths, P = .0039). Weight and height growth rates, CD4+ cell counts, and RNA concentrations showed results favoring ZDV/3TC. For patients concurrently randomized to all 3 treatment arms, both ZDV/3TC and ZDV/ddI recipients had lower risk of HIV disease progression than those who received ddI alone (P = .0026 and P = .0045). CONCLUSIONS: Combination therapy with either ZDV/3TC or ZDV/ddI was superior, as determined by clinical and laboratory measures, to monotherapy with ddI.

Adolescent↗
PubMed1998

Distribution of inhibitory synapses on the somata of pyramidal neurons in cat motor cortex.

The mechanisms by which cortical neurons perform spatial and temporal integration of synaptic inputs are dependent, in large part, on the numbers, types, and distributions of their synapses. To further our understanding of these integrative mechanisms, we examined the distribution of synapses on identified classes of cortical neurons. Pyramidal cells in the cat motor cortex projecting either to the ipsilateral somatosensory cortex or to the spinal cord were labeled by the retrograde transport of horseradish peroxidase. Entire soma of selected corticocortical and corticospinal cells were examined using serial-section electron microscopy. The profiles of these somata and the synapses formed with each of these profiles were reconstructed from each thin section with a computer-aided morphometry system. All somatic synapses were of the symmetrical, presumably inhibitory type. For both cell types, these synapses were not homogeneously distributed over the somatic membrane, but were clustered at several discrete zones. The number and density of synapses on the somata of different corticocortical and corticospinal neurons were not significantly different. However, the density of these synapses was inversely correlated with the size of their postsynaptic somata. We discuss the significance of these findings to the integrative properties of cortical neurons.

Animals↗
PubMed1998

5-Fluorouracil and leucovorin therapy in patients with hormone refractory prostate cancer: an Eastern Cooperative Oncology Group phase II study (E1889).

This report is a multi-institutional phase II study designed to obtain the response rate, survival, and toxicity profile for patients having hormone-refractory prostate cancer. Patients who had bidimensionally measurable prostate carcinoma in first or second remission after previous hormonal therapy but no history of chemotherapy were eligible. Patients were treated with leucovorin, 20 mg/m2 intravenously, followed by 5-fluorouracil (5-FU), 425 mg/m2 intravenously daily for 5 days, with cycles repeated every 28 days. Of 38 eligible patients, 3 (7.9%) had partial responses to therapy and 20 (52.6%) had stable disease. Median survival was 11.6 months for all 38 patients and median time to progression was 4.4 months. Most of the serious side effects were gastrointestinal or hematologic and overall, 23 of 38 patients (60.5%) experienced at least one grade 3 or 4 treatment-related toxicity of any type, as measured by the National Cancer Institute common toxicity criteria. Five patients (13.2%) withdrew from the study because of adverse reactions from chemotherapy. We conclude that treatment of hormone-refractory prostate cancer patients with 5-FU and leucovorin chemotherapy produced few responses at the cost of significant side effects. Further investigation of this combination is not warranted in this setting.

Adenocarcinoma↗
PubMed1998

Noninvasive rejection monitoring of cardiac transplants using high resolution intramyocardial electrograms: initial US multicenter experience.

Endomyocardial biopsy (EMB) remains the mainstay for the diagnosis of acute cellular rejection in cardiac transplant patients. A noninvasive alternative that would supplant or reduce the number of EMBs would be a highly desirable and cost-effective tool. To evaluate one potential alternative, a pacemaker with high resolution telemetry capabilities and two fractally coated epimyocardial leads were implanted in 30 patients at five transplant centers during the heart transplant procedure. Ventricular electrograms were recorded during intrinsic and paced activity and digitized to a laptop-based data acquisition device. Electrograms were recorded at frequent intervals and systematically on days when EMBs were performed. The electrogram data were then transferred via the Internet to a central data processing site. Clinical patient management was blinded to the electrogram results and varied considerably among the five centers. Using EMB together with clinical assessment of the transplant revealed 18 cases of clinically significant rejection beyond postoperative day 27 that required antirejection therapy. The normalized parameter values extracted from the electrogram recordings during pacing (the ventricular evoked response) that were associated with significant rejection were statistically lower (86% +/- 16% versus 96% +/- 22%, P < 0.005). The application of a single-threshold diagnosis model to the parameter values allowed detection of significant rejection with a negative predictive value of 98%. This analysis also showed that as many as 55% of the routine surveillance EMBs could have been eliminated had the pacemaker monitoring technique been used as a screening tool prior to EMB. A prospective study should further define the role of this technique in the detection and management of cardiac transplant patients.

Electrocardiography↗
PubMed1998

Serum and cerebrospinal fluid pharmacokinetics of intravenous and oral lamivudine in human immunodeficiency virus-infected children.

We studied the pharmacokinetics of intravenously and orally administered lamivudine at six dose levels ranging from 0.5 to 10 mg/kg of body weight in 52 children with human immunodeficiency virus infection. A two-compartment model with first-order elimination from the central compartment was simultaneously fitted to the serum drug concentration-time data obtained after intravenous and oral administration. The maximal concentration at the end of the 1-h intravenous infusion and the area under the concentration-time curve after oral and intravenous administration increased proportionally with the dose. The mean clearance of lamivudine (+/- standard deviation) in the children was 0.53 +/- 0.19 liter/kg/h (229 +/- 77 ml/min/m2 of body surface area), and the mean half-lives at the distribution and elimination phases were 0.23 +/- 0.18 and 2.2 +/- 2.1 h, respectively. Clearance was age dependent when normalized to body weight but age independent when normalized to body surface area. Lamivudine was rapidly absorbed after oral administration, and 66% +/- 25% of the oral dose was absorbed. Serum lamivudine concentrations were maintained above 1 microM for >/=8 h of 24 h on the twice daily oral dosing schedule with doses of >/=2 mg/kg. The cerebrospinal fluid drug concentration measured 2 to 4 h after the dose was 12% (range, 0 to 46%) of the simultaneously measured serum drug concentration. A limited-sampling strategy was developed to estimate the area under the concentration-time curve for concentrations in serum at 2 and 6 h.

Administration, Oral↗
PubMed1998

Long-term pamidronate treatment of advanced multiple myeloma patients reduces skeletal events. Myeloma Aredia Study Group.

PURPOSE: To determine the efficacy and safety of 21 monthly cycles of pamidronate therapy in patients with advanced multiple myeloma. PATIENTS AND METHODS: Patients with stage III myeloma and at least one lytic lesion received either placebo or pamidronate 90 mg intravenously administered as a 4-hour infusion monthly for 21 cycles. At study entry, the patients were stratified according to whether they were to receive first-line (stratum 1) or second-line (stratum 2) antimyeloma chemotherapy. Skeletal events (pathologic fracture, radiation or surgery to bone, and spinal cord compression) and hypercalcemia were assessed monthly. RESULTS: The results of the first nine previously reported cycles are extended to 21 cycles. Of the 392 randomized patients, efficacy could be evaluated in 198 who received pamidronate and 179 who received placebo. After 21 cycles, the proportion of patients who developed any skeletal event was lower in the pamidronate-group (P = .015). The mean number of skeletal events per year was less in the pamidronate-group (1.3) than in placebo-treated patients (2.2; P = .008). Although survival was not different between the pamidronate-treated group and placebo patients overall, stratum 2 patients who received pamidronate lived longer than those who received placebo (14 v 21 months, P = .041). Pamidronate was safe and well tolerated during the 21 cycles of therapy. CONCLUSION: Long-term monthly infusions of pamidronate as an adjunct to chemotherapy are superior to chemotherapy alone in reducing skeletal events in stage III multiple myeloma patients, and may improve the survival of patients on salvage therapy.

Diphosphonates↗