PubMed Health⌕ Search

Biomedical subjects

C Alexander

Publications and source records attributed to C Alexander.

At least 37 records · Page 2Linked to original sources
PubMed1995

Phosphorylation of elongation factor Tu prevents ternary complex formation.

The elongation factor Tu (EF-Tu) is a member of the GTP/GDP-binding proteins and interacts with various partners during the elongation cycle of protein biosynthesis thereby mediating the correct binding of amino-acylated transfer RNA (aa-tRNA) to the acceptor site (A-site) of the ribosome. After GTP hydrolysis EF-Tu is released in its GDP-bound state. In vivo, EF-Tu is post-translationally modified by phosphorylation. Here we report that the phosphorylation of EF-Tu by a ribosome associated kinase activity is drastically enhanced by EF-Ts. The antibiotic kirromycin, known to block EF-Tu function, inhibits the modification. This effect is specific, since kirromycin-resistant mutants do become phosphorylated in the presence of the antibiotic. On the other hand, phosphorylated wild-type EF-Tu does not bind kirromycin. Most interestingly, the phosphorylation of EF-Tu abolishes its ability to bind aa-tRNA. In the GTP conformation the site of modification is located at the interface between domains 1 and 3 and is involved in a strong interdomain hydrogen bond. Introduction of a charged phosphate group at this position will change the interaction between the domains, leading to an opening of the molecule reminiscent of the GDP conformation. A model for the function of EF-Tu phosphorylation in protein biosynthesis is presented.

Anti-Bacterial Agents↗
PubMed1995

Hypoosmotic volume regulation of astrocytes in elevated extracellular potassium.

Cellular volume and potassium contents were determined in rat astrocytes from primary culture following suspension in isoosmotic (269 mOsm) and hypoosmotic (136 mOsm) phosphate-buffered saline (PBS) containing various potassium concentrations. Within 1 min of suspension in hypoosmotic PBS, cells swelled to 135% of their volume in isoosmotic PBS. This initial swelling was not altered by varying the potassium concentration of the hypoosmotic PBS. After suspension in hypoosmotic PBS containing 3.2 mM potassium, a regulatory volume decrease (RVD) was observed. Higher concentrations of potassium in hypoosmotic PBS inhibited RVD following osmotic swelling. Cells swollen in hypoosmotic PBS containing 50 mM potassium continued to swell for 7 min, reaching a volume of 141% of their initial isoosmotic volume. After 7 min, these cells demonstrated a subsequent decrease in volume. The swelling observed between 1-7 min after suspension in hypoosmotic PBS containing 50 mM potassium was not affected by 10 microM gadolinium, 1 mM quinine, 1 mM DIDS (4,4'-diisothiocyanato-2,2'-stilbenedisulfonic acid), 1 mM SITS (4-acetamido-4'-isothiocyanato-2,2'-stilbenedisulfonic acid), 1 mM furosemide, or 100 microM bumetanide. Normal RVD was obtained in hypoosmotic PBS containing 50 mM potassium, if chloride was replaced with gluconate (but not nitrate) to reduce the extracellular K.Cl product to that of hypoosmotic PBS containing 3.2 mM potassium. The volume decrease seen between 7-30 min after exposure to hypoosmotic PBS containing 50 mM potassium was blocked by 1 mM DIDS, 1 mM SITS, or 1 mM furosemide. Cellular potassium content was elevated by approximately 60% after 7 min exposure to isoosmotic or hypoosmotic PBS containing 50 mM potassium. In hypoosmotic PBS, this increase in cellular potassium was reduced with replacement of chloride by gluconate, but not by nitrate. The results indicate that astrocytes swollen in PBS containing elevated potassium concentrations continue to swell, in part, by accumulation of potassium plus chloride mediated by an approach to Donnan equilibrium. Cotransport carriers or stretch-activated channels do not play a role in the enhanced swelling observed in hypoosmotic PBS containing 50 mM potassium. We suggest that a voltage-sensitive chloride channel mediates this continuation of cell swelling. This mechanism may be important in the persistent swelling of astrocytes observed in pathologic conditions such as trauma and seizures where extracellular potassium is elevated, or when other factors are present which may cause astroglial depolarization.

Animals↗
PubMed1995

Radioimmunoscintigraphy of ovarian tumours with technetium-99m labelled monoclonal antibody-170: first clinical experiences.

The recently developed technetium-99m-labelled monoclonal antibody-170 (MAb-170) was designed for diagnostic use in patients suffering from gynaecological adenocarcinoma. Following in vitro studies which showed immunoreactivity of this antibody to more than 90% of human adenocarcinomas, the present investigation was initiated to verify its usefulness for radioimmunoscintigraphy of ovarian tumours. Most of the 30 patients participating in this study underwent immunoscintigraphy prior to first-look surgery. Biokinetic evaluation in two patients showed a plasma half-time of 18.9 h (mean value, n = 2, r = 0.98) and a biexponential total body curve with values of 7.7 h and 17 days (r = 0.98). The mean 24-h urinary excretion was 12% of the injected dose. Radioimmunoscintigraphy using the MAb-170 recognised 12 of 13 cases of adenocarcinoma of the ovaries, corresponding to an overall sensitivity of 92.3%. Specificity was 94.1% (16/17). The calculation of accuracy yielded a figure of 93.3% (28/30). Of 33 known lesions, 26 were visualised successfully; thus the locoregional sensitivity was 78.8%. Of 29 benign tumour sites, 28 showed no evidence of tracer accumulation, corresponding to a locoregional specificity of 96.6%. The smallest lesion visualised was an adenocarcinoma of the corpus uteri with a diameter of 1.5 cm. Technetium-99m labelled MAb-170 is a promising new radiopharmaceutical for immunoscintigraphy of ovarian adenocarcinoma.

Adenocarcinoma↗
PubMed1995

Myocardial scintigraphy.

Nuclear cardiology continues to be of particular importance in nuclear medicine. In this domain, myocardial scintigraphy has become the eminent diagnostic tool in the diagnosis of cardiac disorders like coronary artery disease, myocarditis, heart transplant rejection, chemotherapy-induced cardiotoxicity, and others. In a comparison of the latest worldwide trends, European investigators seem to be more interested in recently developed myocardial tracers than those in the US. Besides research into antimyosin monoclonal antibodies for the detection of myocardial damage, the technetium 99m-labeled perfusion markers are being studied as potential substitutes for thallous chloride TI 201. In recent years, the dual use of 201TICI/99mTc-sestamibi taught us the comparable clinical value of these two radiopharmaceutics in the detection of coronary artery disease. In the future, additional 99mTc-labeled perfusion markers may contribute to the ongoing decrease in thallium's widespread use. In the area of viability (ie, the preinterventional detection of potentially reversible myocardial wall-motion abnormalities), 201TICI is still not fully accepted. The most reliable diagnostic tool for this procedure is 13N-NH3 (ammonia)/fluorine F18 fluorodeoxyglucose (FDG) positron emission tomography because of its options for quantification and high-resolution imaging. In the near future, the limited number of these sophisticated but expensive positron emission tomography centers will not satisfy the growing clinical demand for viability studies. Thus, European nuclear cardiologists are developing alternative techniques for positron imaging. They have shown that by means of a conventional gamma camera with special high-energy collimators, a reliable perfusion/viability assessment is feasible.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Disease↗
PubMed1995

[Image fusion of MRI and immunoscintigraphy with MAb-170 in ovarian tumors].

In recent years multimodality imaging achieved growing importance. It is mostly performed by means of quite expensive software and hardware solutions. In the present pilot study a simple and low-cost procedure was developed to achieve image fusion in the pelvis. The image data of immunoscintigraphy (SPECT) and MRI were transferred to a personal computer and combined by standard software for image manipulation. The results in eleven patients with space-occupying lesions in the pelvis showed that adequate anatometabolic slices could be achieved. The results show a tendency to increased specificity and precision of multimodality imaging in comparison with SPECT and MRI alone. In conclusion, the low-cost solution, as developed by us, is feasible in clinical practice. Its results are reliable in clinical decision making.

Adult↗
PubMed1995

[18FDG in the primary staging of lung tumors. Results with a gamma camera and a 511 keV collimator].

The diagnosis of primary lung tumors requires a precise staging according to the TNM classification. In contrast to established imaging methods 18FDG describes the functional metabolic processes in the tumor tissue due to increased glycolysis. This paper describes the use of 18FDG in the primary staging of lung tumors and metastases. 44 patients were studied with a gamma camera and a 511 keV collimator. In comparison to pulmonary tumors and metastases detected by other imaging methods (107) the accumulation of 18FDG has a sensitivity of 85%, in lesions verified by histology (50) of 89%, in primary tumors (35) of 100% and in metastases (63) of 76%. As an alternative to FDG PET studies, primary staging of lung tumors is possible with a gamma camera, suitable for ECT and fitted with a 511 keV collimator.

Adult↗
PubMed1995

Expression of molecules associated with neuronal plasticity in the striatum after aspiration and thermocoagulatory lesions of the cerebral cortex in adult rats.

Like the hippocampus, the striatum receives excitatory afferents from the cerebral cortex but, in the case of the striatum, very little is known about the molecular events associated with plasticity after lesions of this pathway. Using immunohistochemical techniques, we have examined the effects of cortical lesions induced either by aspiration of the frontoparietal cortex or by thermocoagulation of pial blood vessels on axonal and glial molecules associated with neuronal plasticity in the striatum. The growth associated protein GAP-43, a molecule present in axons and growth cones, decreased in the dorsolateral striatum after aspiration but not after thermocoagulatory lesions. In contrast, synaptophysin, a marker of synaptic vesicles, remained unchanged in the denervated striatum after both types of lesions. Immunostaining for basic fibroblast growth factor (bFGF) markedly decreased in striatal astrocytes after both lesions, despite an increased staining for glial fibrillary acidic protein (GFAP). The adhesion molecules tenascin, chondroitin sulfate proteoglycans, highly polysialylated neural cell adhesion molecule (PSA-NCAM), and laminin did not change significantly in the gray matter of the dorsolateral striatum after either type of lesion. These effects differed from those observed after partial denervation of the hippocampus and spinal cord, revealing marked regional differences in the response of axonal and glial proteins to afferent lesions. In addition, the results further indicate that cortical lesions have both similar and distinct consequences, depending on the procedure by which the lesions are induced, suggesting that cortical lesions associated with different types of pathology may differentially affect subcortical structures.

Animals↗
PubMed1995

Unfinished business: adult immunization against tetanus.

Where effective child immunization schemes have been established virtually all cases of tetanus occur in persons aged over 50 years. Adult immunization programmes should be introduced in order to protect this age group against the disease.

Age Factors↗
PubMed1994

Myocardial metabolic imaging by means of fluorine-18 deoxyglucose/technetium-99m sestamibi dual-isotope single-photon emission tomography.

The detection of preserved glucose uptake in hypoperfused dysfunctional myocardium by fluorine-18 deoxyglucose (FDG) positron emission tomography (PET) represents the method of choice in myocardial viability diagnostics. As the technique is not available for the majority of patients due to cost and the limited capacity of the PET centres, it was the aim of the present work to develop and test FDG single-photon emission tomography (SPET) with the means of conventional nuclear medicine. The perfusion marker sestamibi (MIBI) was used together with the metabolic tracer FDG in dual-isotope acquisition. A conventional SPET camera was equipped with a 511-keV collimator and designed to operate with simultaneous four-channel acquisition. In this way, the scatter of 18F into the technetium-99m energy window could be taken into account by a novel method of scatter correction. Thirty patients with regional wall motion abnormalities at rest were investigated. The results of visual wall motion analysis by contrast cine-ventriculography in nine segments/heart were compared with the results of quantitative scintigraphy. The scintigraphic patterns of MIBI and FDG tracer accumulation were defined as normal, matched defects and perfusion-metabolism mismatches. Spatial resolution of the system was satisfactory, with a full width at half maximum (FWHM) of 15.2 mm for 18F and 14.0 mm for 99mTc, as measured by planar imaging in air at 5 cm distance from the collimator. Image quality allowed interpretation in all 30 patients. 88% of segments without relevant wall motion abnormalities presented normal scintigraphic results. Seventy-five akinetic segments showed mismatches in 27%, matched defects in 44% and normal perfusion in 29%. We conclude that FDG-MIBI dual-isotope SPET is technically feasible with the means of conventional nuclear medicine. Thus, the method is potentially available for widespread application in patient care and may represent an alternative to the 201Tl reinjection technique.

Coronary Disease↗
PubMed1994

High resolution ECG and left ventricular volume after acute myocardial infarction.

The presence of ventricular late potentials (LPs) early after acute myocardial infarction (AMI) was recently reported to correlate with left ventricular dilatation subsequent to AMI. We assessed prospectively the relationship between LP (time domain) in the late phase of AMI and left ventricular end-diastolic volume (EDV) measured by equilibrium radionuclide angiocardiography 4 weeks and 12 months after AMI. In 80 consecutive patients 4 weeks and 12 months after thrombolytic therapy for AMI, LP and EDV were determined (EDV1, EDV2). There was no significant correlation between QRS duration (r = 0.18), RMS40 (r = 0.08), or LAS40 (r = 0.1) and EDV1 or EDV2 in patients with or without LP at baseline. In both groups (patients with [n = 15] and without LP [n = 65]), EDV1 and EDV2 were comparable (128 +/- 32 mL vs 126 +/- 35 mL; 114 +/- 40 mL vs 117 +/- 36 mL; P = NS). In addition, there was no significant difference between EDV1 and EDV2 in patients who developed new LP (n = 6) or lost LP (n = 9) 12 months after AMI. In contrast to LP in the very early phase after AMI, there seems to be no significant correlation between the high resolution ECG in the late phase after thrombolytic therapy for AMI and left ventricular EDV.

Electrocardiography↗
PubMed1993

High prevalence of unsuspected abdominal aortic aneurysm in patients with confirmed symptomatic peripheral or cerebral arterial disease.

A group of 561 consecutive patients with proven symptomatic peripheral or cerebral arterial disease attending a vascular clinic was screened for abdominal aortic aneurysm (AAA) using B-mode ultrasonography. An aneurysm was present in 40 of 358 men (11.2 per cent) and 13 of 203 women (6.4 per cent), a total prevalence of 9.4 per cent. Thirty-three aneurysms were 3-4 cm in diameter. The prevalence of AAA was similar in patients referred with lower-limb and with cerebral ischaemia. Physical examination for AAA was performed in 200 patients before ultrasonography. The sensitivity of physical examination in the detection of aneurysm was 43 per cent (57 per cent for AAA > or = 4 cm in diameter, 29 per cent for AAA < 4 cm in diameter). Physical examination was an inadequate method of screening. Initial follow-up showed a mean aneurysm expansion rate of 0.20 cm/year. Patients with arterial disease have a high risk of AAA; routine ultrasonographic screening should be considered.

Aortic Aneurysm, Abdominal↗
PubMed1993

Rapid measurement of blood leakage during regional chemotherapy.

In order to avoid complications after regional chemotherapy (isolated hyperthermic perfusion) of the extremities, rapid measurement of blood leakage from the extracorporeal to the systemic circulation is important. A method using technetium-99m in vivo red blood cell (RBC) labelling is reported that provides results within 3 min. Blood samples drawn from the systemic and the extracorporeal circulation were measured for 99mTc activity using a mobile well counter, and the leakage values calculated. The mean result was 7.6% +/- 6.5%/15 min (n = 209). The corresponding flow rate was 100.2 +/- 85.7 ml/15 min (mean +/- SD). The values for isolation perfusion of the upper and the lower extremities are compared. The leakage results using 99mTc RBC labelling were correlated with other blood pool markers. Iodine-125 human serum albumin and indium-113 m transferrin were administered in subgroups of 4 and 19 patients simultaneously. Using linear regression, the coefficient of correlation was 0.72 for 99mTc/113mIn and 0.58 for 99mTc/125I. Comparison with the alternatives suggests that the rapid method of leakage measurement after 99mTc RBC labelling can be considered one of the most practicable and reliable methods available.

Chemotherapy, Cancer, Regional Perfusion↗
PubMed1993

Anxiety in children with asthma.

The purpose of this study was to examine associations between levels of state and trait anxiety in children with asthma and increased asthma morbidity immediately following an acute asthmatic attack. A total of 155 children, aged 7-12 years, diagnosed with asthma, were administered the State-Trait Anxiety Inventory for Children (STAIC) while the State-Trait Anxiety Inventory Form Y (STAI) was administered to the mother. The mother's state and trait anxiety scores were consistently higher than the child's scores, and there was no significant correlation between child and mother anxiety levels. Almost two-thirds of children reported feeling "panic" at the beginning of the index asthma attack, which was significantly associated with child state anxiety. Health professionals must be sensitive to child as well as maternal anxiety in families of children with asthma.

Adult↗
PubMed1992

Sequence of the tufA gene encoding elongation factor EF-Tu from Thermus aquaticus and overproduction of the protein in Escherichia coli.

The sequence of the tufA gene from the extreme thermophilic eubacterium Thermus aquaticus EP 00276 was determined. The GC content in third positions of codons is 89.5%, with an unusual predominance of guanosine (60.7%). The derived protein sequence differs from tufA- and tufB-encoded sequences for elongation factor Tu (EF-Tu) of Thermus thermophilus HB8, another member of the genus Thermus, in 10 of the 405 amino acid residues. Three exchanges are located in the additional loop of ten amino acids (182-191). The loop, probably involved in nucleotide binding, is absent in EF-Tu of the mesophile Escherichia coli. Since EF-Tu from E. coli is quite unstable, the protein is well-suited for analyzing molecular changes that lead to thermostabilization. Comparison of the EF-Tu domain I from E. coli and Thermus strains revealed clustered amino acid exchanges in the C-terminal part of the first helix and in adjacent residues of the second loop inferred to interact with the ribosome. Most other exchanges in the guanine nucleotide binding domain are located in loops or nearest vicinity of loops suggesting their importance for thermostability. The T. aquaticus EF-Tu was overproduced in E. coli using the tac expression system. Identity of the recombinant T. aquaticus EF-Tu was verified by Western blot analysis, N-terminal sequencing and GDP binding assays.

Amino Acid Sequence↗
PubMed1992

Epidermal growth factor (EGF)-stimulated tyrosine phosphorylation and EGF receptor degradation in cells expressing EGF receptors truncated at residue 973.

Epidermal growth factor (EGF)-stimulated tyrosine phosphorylation of proteins was examined in cells expressing wild-type (WT-EGFR) EGF receptors or EGF receptors truncated at residue 973 (973-EGFR). A much broader spectrum of tyrosine phosphorylated proteins was found following EGF treatment of 973-EGFR expressing cells compared with cells expressing wild-type receptors. Several additional ras GTPase activating protein-associated tyrosine phosphorylated proteins were found in EGF-treated 973-EGFR cells relative to WT-EGFR cells. Additional tyrosine-phosphorylated proteins were also found to co-immunoprecipitate with phospholipase C gamma 1 (PLC gamma 1) following EGF treatment of cells expressing 973-EGFR relative to cells expressing WT-EGFR. EGF-stimulated tyrosine phosphorylation of PLC gamma 1 was found in cells expressing WT-EGFR, but not in cells expressing 973-EGFR. WT-EGF receptor from EGF-treated cells bound well to bacterially expressed src homology (SH) regions of PLC gamma 1 and to a lesser extent to bacterially expressed GTPase activating protein SH regions. No binding of 973-EGF receptor to SH regions of either protein could be detected. EGF treatment greatly reduced the half-life of WT-EGFR, but had relatively little effect on the half-life of 973-EGFR. EGF induced internalization of 973-EGFR at a slower rate than WT-EGFR and caused the appearance of discrete receptor degradation products for both cell types. The data indicate that truncation of the EGF receptor at residue 973 alters receptor substrate specificity, decreases the rate of receptor internalization, and has an inhibitory effect on receptor degradation.

3T3 Cells↗