Biomedical subjects
Publications and source records attributed to N Aubry.
The electrohydrodynamic instability of the interface between two liquids with different physical and electrical properties in plane Poiseuille flow is used to form monodisperse droplets in a square channel. The drop size and formation rate are controlled by simply controlling the flow rates and the amplitude of the electric field applied across the channel.
The point dipole (PD) model is routinely used for estimating the dielectrophoretic (DEP) force acting on a particle placed in the nonuniform electric fields of dielectrophoresis devices, such as square cages. We show that if the particle size is much smaller than the dielectrophoretic cage size, the PD model accurately approximates the actual DEP force, computed numerically using the Maxwell stress tensor method. However, when the two sizes are comparable, the actual DEP force differs significantly in both magnitude and direction from that given by the PD model.
This work describes the use of NMR as a medicinal chemistry tool for better understanding the binding characteristics of inhibitors of the HCV NS3 protease. The protease-bound structure of a tetrapeptide-like inhibitor that has an acid C-terminus, a norvaline at P1 and a naphthylmethoxy proline at P2 is described. Conformational comparisons are made with a similar compound having a 1-amino-cyclopropylcarboxylic acid at P1 and with a hexapeptide inhibitor. Differences between the free and bound states are identified. 19F NMR also helped in determining that a single complex is observed when an inhibitor is added to the protease at a 1:1 ratio.
The interactions of the NS3 protease domain with inhibitors that are based on N-terminal cleavage products of peptide substrates were studied by NMR methods. Transferred nuclear Overhauser effect experiments showed that these inhibitors bind the protease in a well defined, extended conformation. Protease-induced line-broadening studies helped identify the segments of inhibitors which come into contact with the protease. A comparison of the NMR data of the free and protease-bound states suggests that these ligands undergo rigidification upon complexation. This work provides the first structure of an inhibitor when bound to NS3 protease and should be valuable for designing more potent inhibitors.
Substrate hydrolysis by human cytomegalovirus (HCMV) protease is essential to viral capsid assembly. The interaction of HCMV protease and the N-terminal cleavage products of the hydrolysis of R- and M-site oligopeptide substrate mimics (R and M, respectively, which span the P9-P1 positions) was studied by NMR methods. Protease-induced differential line broadening indicated that ligand binding is mediated by the P4-P1 amino acid residues of the peptides. A well-defined extended conformation of R from P1 through P4 when complexed to HCMV protease was evidenced by numerous transferred nuclear Overhauser effect (NOE) correlations for the peptide upon addition of the enzyme. NOE cross-peaks between the P4 and P5 side chains placing these two groups in proximity indicated a deviation from the extended conformation starting at P5. Similar studies carried out for the M peptide also indicated an extended peptide structure very similar to that of R, although the conformation of the P5 glycine could not be established. No obvious variation in structure between bound R and M (notably at P4, where the tyrosine of the R-site has been suggested to play a key role in ligand binding) could be discerned that might explain the observed differences in processing rates between R- and M-sequences. Kinetic studies, utilizing R- and M-site peptide substrates for which the P5 and P4 residues were separately exchanged, revealed that these positions had essentially no influence on the specificity constants (kcat/KM). In sharp contrast, substitution of the P2 residue of an M-site peptide changed its specificity constant to that of an R-site peptide substrate, and vice versa.
Only a moderate degree of concordance has been reported between stress-redistribution-reinjection thallium-201 single photon emission computed tomography (SPECT) and dobutamine echocardiography for the identification of myocardial viability after acute myocardial infarction. SPECT with rest-reinjection performed 4 hours after exercise testing and digitized two-dimensional (2-D) ultrasound reconstruction of the left ventricle at baseline and after low-dose dobutamine (5 to 10 microg/kg/min) infusion were compared in 50 patients > or = 8 days (12 +/- 7 days) after acute myocardial infarction. Five patients were excluded because of technically inadequate echocardiograms. Both SPECT and dobutamine echocardiography were assessed in a 16-segment model and interpreted in the remaining 45 patients. Digitized 2-D reconstruction of the left ventricle in each wall motion was scored from 1 (normal) to 4 (dyskinesia). Myocardial viability was identified on ultrasound wall-motion improvement of one or more grades from baseline to echocardiography performed > or = 30 days (60 +/- 41 days) after systematic revascularization procedure of the infarct-related artery. Reversible defect under thallium-201 SPECT and wall-motion improvement under dobutamine echocardiography were concordant in 163 (69 percent) of the 235 baseline dyssynergic segments and in 30 (67 percent) patients. Myocardial viability was identified after angioplasty (n=37) or surgery (n=8) in 29 patients and 109 segments. Positive and negative predictive values per patient in the diagnosis of myocardial viability were 86 percent and 57 percent, respectively, for stress thallium-201 SPECT with reinjection, and 100 percent and 62 percent for dobutamine echocardiography. Positive and negative predictive values per segment were 80 percent and 69 percent for the isotopic method and 91 percent and 70 percent for dobutamine echocardiography. We conclude that dobutamine echocardiography and stress thallium-201 SPECT with reinjection have similar accuracies to identify myocardial viability after acute myocardial infarction, with excellent positive but relatively low negative predictive values.
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The solution conformations of three polyhydroxymonoamide renin inhibitors which differ in the relative configuration and position of the hydroxyl groups at the P3 position were investigated by NMR spectroscopy. The NMR data are consistent with a predominant conformation in DMSO with the exception that two inhibitors exhibit conformational averaging about a torsion angle along P3. Comparisons with the renin-bound structures determined by X-ray crystallography [Tong et al., (1995) J. Mol. Biol. 250, 211] show that the unbound and renin-bound conformations are similar (with exceptions in the P3 position). This similarity suggests that gross conformational changes of the inhibitor are not a prerequisite for binding to renin. Apart from being able to tolerate different dihydroxylated structures at P3, renin can also accommodate different conformations at P3. Differences were observed at the P3 position between the inhibitors in the unbound state, between the unbound and renin-bound states, and between the renin-bound states.
OBJECTIVES: This study evaluated the role of preload reserve in the stroke volume response to exercise in patients with left ventricular systolic dysfunction by assessing the relation between stroke volume and late left ventricular diastolic filling during exercise. BACKGROUND: In patients with left ventricular diastolic dysfunction, the absence of left ventricular distension is the fundamental mechanism explaining the nonaugmentation of stroke volume during exercise. METHODS: In 32 patients with left ventricular systolic dysfunction and 16 healthy control subjects, mitral and aortic velocities were recorded by Doppler echocardiography at rest and during submaximal supine bicycle exercise. Stroke volume, peak early (E) and late (A) mitral velocities, A/E ratio and end-diastolic filling were measured at rest and during exercise. RESULTS: Stroke volume increased significantly in control subjects but did not change in patients. Peak early mitral velocity increased significantly and to the same extent in both groups, whereas peak late mitral velocity and end-diastolic filling increased significantly in both groups but more so in control subjects; the A/E ratio increased significantly in control subjects but did not change in patients. In addition, stroke volume correlated significantly with peak late mitral velocity during exercise in patients (r = 0.72, p < 0.001). CONCLUSIONS: Compared with control subjects, patients with left ventricular systolic dysfunction exhibited limited increases in both stroke volume and late left ventricular filling during exercise. Furthermore, their stroke volume response correlated with the capacity of the left ventricle to increase late diastolic filling, that is, preload reserve.
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Atherosclerotic heart disease is the leading cause of death in patients with end stage renal disease, but its non invasive detection remains difficult because of a low efficacy of exercise testing. The aim of the study was to evaluate diagnostic accuracy of thallium myocardial imaging after dipyridamole combined with exercise. Forty two chronic dialysis patients (34 men, 8 women) aged 55 +/- 11 years (range: 36 to 75) without symptom of angina nor myocardial infarction were studied. In each patient, an echocardiography, a myocardial scintigraphy with dipyridamole combined with symptom-limited exercise, and coronarography were performed. A coronary heart disease was diagnosed by coronarography in 10 patients (4.5 and 1 respectively with 1, 2 and 3 vessels diseased). Echocardiography detected a left ventricular hypertrophy (LVH) in 26 patients and a regional asynergia in 14 patients. A positive scintigraphy was present in 11 patients. Three false-positive and 2 false-negative on scintigraphy were noted. Sensibility, specificity, positive predictive value and negative predictive value were respectively evaluated at 80, 73, 73 and 93%. All the five patients with either false-positive or false-negative scintigraphy exhibited a LVH. CONCLUSION. In chronic dialysis patients, coronary heart disease may be detected by thallium myocardial imaging after dipyridamole combined with exercise.
The C-terminus of the small subunit of class I ribonucleotide reductases is essential for subunit association and enzymatic activity. 1H NMR analysis of the small subunit (2 x 38 kDa as a homodimer) of herpes simplex virus ribonucleotide reductase shows that this critical binding site is mobile and exposed in relation to the rest of the protein. Assignments of six C-terminal amino acids are made by comparing the TOCSY and NOESY spectra of the small subunit with the spectra of an identical protein truncated by seven amino acids at the C-terminus and the spectra of an analogous 15 amino acid peptide. The mobility of the C-terminus may be important for subunit recognition and could be general for other ribonucleotide reductases. The spectral comparisons also suggest that the six C-terminal amino acids of the small subunit and peptide are conformationally similar. This observation may be important for the design of inhibitors of ribonucleotide reductase subunit association.
It is known that peptides corresponding to the C-terminus of the small subunit of herpes simplex virus type 1 and 2 ribonucleotide reductase can inhibit enzymatic activity by preventing the association of the enzyme's two subunits. In a quest for smaller, more potent inhibitors, we have conducted a structure activity investigation based on the pentapeptide H-Val-Val-Asn-Asp-Leu-OH. Potency increases of up to 4000 times (IC50 0.18 microM) have been achieved in an enzymatic assay by a combination of modifying the N-terminal valine to a diethylacetyl group, adding a methyl group to the beta-carbon of the adjacent valine, dialkylating the asparagine side-chain nitrogen and dimethylating the beta-carbon of the aspartic acid residue. In addition the relative contribution of various inhibitor functionalities to inhibitor potency has been investigated.
The authors studied retrospectively a series of 39 patients with a documented second restenosis after coronary angioplasty between January 1987 and November 1992, 33 of whom (31 men, 2 women) underwent a third procedure. The artery dilated was the left anterior descending (n = 17 including 9 proximal stenoses), the right coronary (n = 10), the left circumflex or its branches (n = 5) and the left main stem (n = 1). The lesions were confirmed to one vessel in 25 cases (75%) and affected two vessels in 8 cases (25%). The third angioplasty procedure was performed on a single artery in all cases. The average left ventricular ejection fraction was 60% (43%-75%). The diameter of the dilated artery was over 3.25 mm in 24% of cases (8/33). The primary success rate was 100% without any complications. The average period between the first and second angioplasties was 16 +/- 10 weeks, and between the second and third angioplasties 19 +/- 12 weeks. Angioplastic controls of the 3rd angioplasty were performed in 25 cases (75%). A third restenosis (n = 7) was treated by surgical bypass (n = 1), repeat angioplasty (n = 4), endocoronary stenting (n = 1) or medically (n = 1), with a global follow-up of 22 months (2-56 months), 2 patients underwent coronary bypass grafting, 2 have residual angina (contralateral lesion which could not be dilated), 1 had an infarct in the territory of an undilated artery, and 28 (85%) were asymptomatic. The restenosis rate after the third angioplasty procedure was 28% (7/25).(ABSTRACT TRUNCATED AT 250 WORDS)
The present report gives preliminary results of a new sensitive method for the amperometric determination of antigens in serum. This method, developed from the biological model 'hepatitis B surface antigen antibodies' is less time-consuming than most immunochemical techniques, and eliminates many inconveniences arising from use of isotopes. Specific antibodies immobilised onto a gelatin membrane are applied in a solid phase 'sandwich' procedure. The antibodies are labelled with glucose oxidase. The measurement consists of an immunological process and an enzymatic reaction. The second part is carried out by fixing the active membrane onto a pO2 electrode. The sensor is immersed in a standard glucose solution and a signal is obtained by measuring the consumption of oxygen due to the enzyme reaction. This response is correlated to the antigen concentration of the sample. It is a function of both the diffusional and the reactional characteristics of the active layer. Under software conditions, the signal is sampled when the stationary state is obtained. The difference between initial signal and the stationary state signal is measured and compared with the pre-set calibration curve. Use of the computerised enzyme immunosensor could easily be extended to assay of other antigens and haptens that are usually determined by radioimmunoassay.