Accuracy of single-photon emission computed tomography myocardial perfusion imaging in patients with stents in native coronary arteries

Strategies to noninvasively evaluate patients after coronary stenting have not been evaluated. To determine the accuracy of single-photon emission computed tomography (SPECT) myocardial perfusion imaging in patients after coronary stenting, 209 patients who had undergone stenting followed by late stress SPECT myocardial perfusion imaging were evaluated. Quantitative coronary angiography was performed in 33 patients following SPECT imaging. SPECT restenosis was defined as a reversible or fixed defect within the stented vascular territory. Angiographic restenosis was examined using 2 definitions: total area narrowing > or =50% or > or =70% of the stent site or stented artery. The SPECT and angiographic findings were concordant in 22 of 33 stented vascular territories using the 50% definition of restenosis and in 29 of 33 stented territories using the 70% definition. Use of the 70% definition of restenosis resulted in improved accuracy of SPECT to detect a significant stenosis in the stented artery. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of SPECT were 95%, 73%, 88%, 89%, and 88% respectively. In patients with positive SPECT scans, the most significant stenosis in the stented artery was outside the stent site in 50% of cases. SPECT imaging appears to be accurate to predict significant stenosis in the stented artery, although the most severe stenosis is frequently distant from the stent site.     

The role of threonine in the P2 position of Bowman-Birk proteinase inhibitors: studies on P2 variation in cyclic peptides encompassing the reactive site loop

Previously, we have described a template-assisted combinatorial peptide library based on the anti-tryptic reactive site loop of a Bowman-Birk inhibitor (BBI). Sequences that displayed inhibitory activity re-directed towards chymotrypsin were found to have a consensus binding motif, with their most striking feature being that exclusively threonine was found at the P2 position. The present study investigates the reason for this surprising specificity by maintaining the binding motif but systematically varying the P2 residue. From analysis of 26 variants, it is found that the requirements for inhibitory activity at P2 are finely tuned, and in agreement with the library work, threonine at P2 provides optimal inhibition. In addition, peptides with threonine at P2 are significantly less susceptible to hydrolysis. Examination of all available BBI sequences shows that threonine is very highly conserved at P2, which implies that the functional requirement extends to the full-length BBI protein. Our results are consistent with a dual requirement for hydrophobic recognition within the S2 pocket and maintenance of an inhibitory conformation via hydrogen bonding within the reactive-site loop. As the isolated peptide loop reproduces the active region of full-length BBI, these results explain why threonine is well conserved at P2 in this class of inhibitor. Furthermore, they illustrate that proteinase inhibitor specificity can have characteristics that are not easily predicted from information on the substrate preferences of a proteinase.     

Diphtheria toxin fused to granulocyte-macrophage colony-stimulating factor eliminates acute myeloid leukemia cells with the potential to initiate leukemia in immunodeficient mice, but spares normal hemopoietic stem cells

We studied the cell kill induced by granulocyte-macrophage colony-stimulating factor (GM-CSF ) fused to Diphtheria Toxin (DT-GM-CSF ) in acute myeloid leukemia (AML) samples and in populations of normal primitive hemopoietic progenitor cells. AML samples from three patients were incubated in vitro with 100 ng/mL DT-GM-CSF for 48 hours, and AML cell kill was determined in a proliferation assay, a clonogenic assay colony-forming unit-AML (CFU-AML) and a quantitative long-term bone marrow (BM) culture ie, the leukemic-cobblestone area forming cell assay (L-CAFC). To measure an effect on cells with in vivo leukemia initiating potential DT-GM-CSF exposed AML cells were transplanted into immunodeficient mice. In two out of three samples it was shown that all AML subsets, including those with long-term abilities in vivo (severe combined immunodeficient mice) and in vitro (L-CAFC assay) were reduced in number by DT-GM-CSF. Cell kill induced by DT-GM-CSF could be prevented by coincubation with an excess of GM-CSF, demonstrating that sensitivity to DT-GM-CSF is specifically mediated by the GM-CSF receptor. Therefore, binding and internalization of GM-CSF probably occur in immature AML precursors of these two cases of AML. The third AML sample was not responsive to either GM-CSF or DT-GM-CSF. The number of committed progenitors of normal bone marrow (burst-forming unit-erythroid, colony-forming unit granulocyte- macrophage, and cobble stone area forming cell [CAFC] week 2) and also the number of cells with long-term repopulating ability, assayed as week 6 CAFC, were unchanged after exposure to DT-GM-CSF (100 ng/mL, 48 hours). These studies show that DT-GM-CSF may be used to eliminate myeloid leukemic cells with long-term potential in vitro and in immunodeficient mice, whereas normal hemopoietic stem cells are spared.     

Ultrasound evaluation of piglet diaphragm function before and after fatigue

Clinically, a noninvasive measure of diaphragm function is needed. The purpose of this study is to determine whether ultrasonography can be used to 1) quantify diaphragm function and 2) identify fatigue in a piglet model. Five piglets were anesthetized with pentobarbital sodium and halothane and studied during the following conditions: 1) baseline (spontaneous breathing); 2) baseline + CO2 [inhaled CO2 to increase arterial PCO2 to 50-60 Torr (6.6-8 kPa)]; 3) fatigue + CO2 (fatigue induced with 30 min of phrenic nerve pacing); and 4) recovery + CO2 (recovery after 1 h of mechanical ventilation). Ultrasound measurements of the posterior diaphragm were made (inspiratory mean velocity) in the transverse plane. Images were obtained from the midline, just inferior to the xiphoid process, and perpendicular to the abdomen. M-mode measures were made of the right posterior hemidiaphragm in the plane just lateral to the inferior vena cava. Abdominal and esophageal pressures were measured and transdiaphragmatic pressure (Pdi) was calculated during spontaneous (Sp) and paced (Pace) breaths. Arterial blood gases were also measured. Pdi(Sp) and Pdi(Pace) during baseline + CO2 were 8 +/- 0.7 and 49 +/- 11 cmH2O, respectively, and decreased to 6 +/- 1.0 and 27 +/- 7 cmH2O, respectively, during fatigue + CO2. Mean inspiratory velocity also decreased from 13 +/- 2 to 8 +/- 1 cm/s during these conditions. All variables returned to baseline during recovery + CO2. Ultrasonography can be used to quantify diaphragm function and identify piglet diaphragm fatigue.     

Revision of the Scheme for Extraction and Classification of Dyes from Polyacrylonitrile Fibres

The simple sequential scheme for the extraction and classification of dyes from 1–2–cm lengths of polyacrylonitrile fibres reported by Beattie et al., J. S. D. C, 95 (1979) 295, is revised to avoid misclassification of some basic dyes.     

Effect of thermal treatment on the growth,structure and luminescence of nitride-passivated silicon nanoclusters

Silicon nanoclusters (Si-ncs) embedded in silicon nitride films have been studied to determine the effects that deposition and processing parameters have on their growth, luminescent properties, and electronic structure. Luminescence was observed from Si-ncs formed in silicon-rich silicon nitride films with a broad range of compositions and grown using three different types of chemical vapour deposition systems. Photoluminescence (PL) experiments revealed broad, tunable emissions with peaks ranging from the near-infrared across the full visible spectrum. The emission energy was highly dependent on the film composition and changed only slightly with annealing temperature and time, which primarily affected the emission intensity. The PL spectra from films annealed for duration of times ranging from 2 s to 2 h at 600 and 800°C indicated a fast initial formation and growth of nanoclusters in the first few seconds of annealing followed by a slow, but steady growth as annealing time was further increased. X-ray absorption near edge structure at the Si K- and L_3,2-edges exhibited composition-dependent phase separation and structural re-ordering of the Si-ncs and silicon nitride host matrix under different post-deposition annealing conditions and generally supported the trends observed in the PL spectra.     

Homology modelling of two subtilisin-like proteases from the hyperthermophilic archaea Pyrococcus furiosus and Thermococcus stetteri

The hyperthermophilic archaeon Pyrococcus furiosus produces an extracellular, glycosylated hyperthermostable subtilisin-like serine protease, termed pyrolysin (Voorhorst,W.G.B., Eggen,R.I.L., Geerling,A.C.M., Platteeuw,C., Siezen,R.J. and de Vos,W.M. (1996) J. Biol. Chem., 271, 20426-20431). Based on the pyrolysin coding sequence, a pyrolysin-like gene fragment was cloned and characterized from the extreme thermophilic archaeon Thermococcus stetteri. Like pyrolysin, the deduced sequence of this serine protease, designated stetterlysin, contains a catalytic domain with high homology with other subtilases, allowing homology modelling starting from known crystal structures. Comparison of the predicted three-dimensional models of the catalytic domain of stetterlysin and pyrolysin with the crystal structure of subtilases from mesophilic and thermophilic origin, i.e. subtilisin BPN' and thermitase, and the homology model of subtilisin S41 from psychrophilic origin, led to the identification of features that could be related to protein stabilization. Higher thermostability was found to be correlated with an increased number of residues involved in pairs and networks of charge-charge and aromatic-aromatic interactions. These highly thermostable proteases have several extra surface loops and inserts with a relatively high frequency of aromatic residues and Asn residues. The latter are often present in putative N-glycosylation sites. Results from modelling of known substrates in the substrate- binding region support the broad substrate range and the autocatalytic activation previously suggested for pyrolysin.