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Biomedical subjects

F Bruckert

Publications and source records attributed to F Bruckert.

At least 19 recordsLinked to original sources
PubMed2005

Kinetics of cell spreading.

Cell spreading is a fundamental event where the contact area with a solid substrate increases because of actin polymerization. We propose in this Letter a physical model to study the growth of the contact area with time. This analysis is compared with experimental data using the ameoba Dictyostelium discoideum. Our model couples the stress, which builds up at the margin of the contact area when the cell spreads, to the biochemical processes of actin polymerization. This leads to a scaling analysis of experimental data with a characteristic time whose order of magnitude compares well with our experimental results.

Actins↗
PubMed2002

Peeling model for cell detachment.

In many experimental situations, the adhesion of cells to solid substrates is due to non-covalent chemical bonds. It is the thesis of this paper that many phenomena occurring in cell detachment experiments, such as in I (E. Decavé, G. Garriver, Y. Brechet, B. Fourcade, F. Bruckert, Biophys. J. 82, 2383 (2002)), result from the static and dynamic properties of the adhesive bridges at the extreme margin of the cell. This region defines the adhesive belt where the distribution of connected bonds crosses over to zero where the membrane leaves the substrate. The theoretical model we introduce in this paper discusses the threshold force together with the peeling velocity in the same theoretical framework. In this one-dimensional model, the threshold force results from a non-homogeneous distribution of anchor proteins along the membrane so that the adhesive belt increases its capacity to resist motion with increasing the external force. Analyzing the kinetics of the the contact line motion, we derive the characteristic relationship speed versus external force and we describe the non-equilibrium state of the adhesive belt as a function of the speed. We discuss our model in view of the experimental results obtained with D. discoideum for hydrodynamic shear experiments. Our results could be also confronted to single-cell observations.

Journal Article↗
PubMed2001

Aromatic di-alanine repeats (AdAR) are structural motifs characteristic of the soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) family.

The aromatic di-alanine repeat is a novel 12-amino acid-long motif constituting alternate small and large hydrophobic residues that mediate the close packing of alpha-helices. A hidden Markov model profile was constructed from the motifs initially described in Soluble N-ethyl maleimide-sensitive factor attachment proteins (SNAP), a family of soluble proteins involved in intracellular membrane fusion. Scanning different sets of protein sequences showed unambiguously that this profile defines a structural motif independent of the tetratrico peptide repeat, another widespread alpha-helical motif. In addition to SNAP, aromatic di-alanine repeats are found in selective LIM homeodomain binding proteins (SLB) and in proteins from the Pyrococcus and Archaeoglobus prokaryotes.

Alanine↗
PubMed2001

New CT index to quantify arterial obstruction in pulmonary embolism: comparison with angiographic index and echocardiography.

OBJECTIVE: This study was designed to define and evaluate a specific index to quantify arterial obstruction with helical CT in acute pulmonary embolism. MATERIALS AND METHODS: Fifty-four patients (mean age, 56 years) with proven pulmonary emboli among 158 consecutive patients, who had undergone both CT and pulmonary angiography for clinically suspected pulmonary embolism, were eligible for the study. The CT obstruction index was defined as (n. d) (n, value of the proximal clot site, equal to the number of segmental branches arising distally; d, degree of obstruction scored as partial obstruction [value of 1] or total obstruction [value of 2]). We compared the CT obstruction index with pulmonary arterial obstruction on angiography (assessed by the Miller index), using linear regression, and correlated it with findings on echocardiography. Interobserver variability was determined for both CT and pulmonary angiography indexes. RESULTS: The CT obstruction index (29% +/- 17%) and the Miller index (43% +/- 25%) were well correlated (r = 0.867, p < 0.0001) with an excellent concordance between investigators for both the CT index (r = 0.944, p < 0.0001) and the Miller index (r = 0.904, p < 0.0001). A CT obstruction index greater than 40% identified more than 90% of patients with right ventricular dilatation. CONCLUSION: The degree of arterial obstruction in pulmonary embolism may be quantified by a specific CT index that appears reproducible and highly correlated to the previously described index with pulmonary angiography. Further evaluations are needed to investigate the usefulness of the CT obstruction index for stratification of patient risk and determining therapeutic options.

Angiography↗
PubMed2000

A syntaxin 7 homologue is present in Dictyostelium discoideum endosomes and controls their homotypic fusion.

Endo-phagocytic activity is prominent in Dictyostelium discoideum and makes it a good model organism to study the molecular organization of membrane traffic in this pathway. We have identified a syntaxin 7 homologue (26% identity and 54% similarity to human syntaxin 7) in Dictyostelium cDNA and genomic data banks. In addition to the Habc and H3 helices and the C-terminal transmembrane domain characteristic of syntaxins, this protein contains a repetitive N-terminal extension of 68 amino acids. We first showed that Dictyostelium syntaxin 7 was able to form a complex with N-ethylmaleimide-sensitive fusion protein and alpha- and gamma-soluble N-ethylmaleimide-sensitive fusion protein attachment protein. Its intracellular localization was then studied by cell fractionation techniques and magnetic purification of the endocytic compartments. Most of D. discoideum syntaxin 7 is contained in endosomes. Finally, an in vitro endosome homotypic fusion assay (Laurent, O., Bruckert, F., Adessi, C., and Satre, M. (1998) J. Biol. Chem. 273, 793-799) was used to study a possible role for syntaxin 7 in this process. Purified anti-syntaxin 7 antibodies and a recombinant soluble fragment of syntaxin 7 both strongly inhibited fusion activity, indicating that this protein was necessary for endosome-endosome fusion. These results demonstrate the importance of this syntaxin 7 homologue in the early phases of Dictyostelium endo-phagocytic pathway.

Amino Acid Sequence↗
PubMed2000

Functional and molecular identification of novel members of the ubiquitous membrane fusion proteins alpha- and gamma-SNAP (soluble N-ethylmaleimide-sensitive factor-attachment proteins) families in Dictyostelium discoideum.

The soluble N-ethylmaleimide-sensitive-factor-attachment proteins (SNAP) are eukaryotic soluble proteins required for membrane fusion. Based on their initial identification in bovine brain cytosol, they are divided in alpha/beta and gamma subfamilies. SNAPs act as adapters between N-ethylmaleimide-sensitive factor (NSF), a hexameric ATPase, and membrane SNARE proteins (SNAP receptors). Within the NSF/SNAP/SNARE complex, SNAPs contribute to the catalysis of an ATP-driven conformational change in the SNAREs, resulting in dissociation of the complex. We have constructed a Dictyostelium discoideum strain overexpressing a c-myc-tagged form of D. discoideum NSF (NSF-myc). Its immunoprecipitation from detergent-solubilized membrane extracts reveals two associated polypeptides with apparent molecular masses of 33 and 36 kDa (p33 and p36) that are absent in NSF-myc immunoprecipitates from cytosol. Analysis of trypsin-digested peptides by microsequencing and mass spectrometry and comparison with cDNA sequences identify p33 and p36 as the D. discoideum homologues of alpha- and gamma-SNAP, respectively. The alpha-/gamma-SNAP molar ratio is close to 3 in vegetative amoebae from this organism. The molecular identification of gamma-SNAP in plants (Arabidopsis thaliana) and insects (Drosophila melanogaster) documents, for the first time, the wide distribution of the gamma subtype. Altogether, these results suggest a specific role for gamma-SNAP, distinct from that of alpha-SNAP.

Amino Acid Sequence↗
PubMed2000

Pulmonary embolism detection: prospective evaluation of dual-section helical CT versus selective pulmonary arteriography in 157 patients.

PURPOSE: To evaluate the accuracy of dual-section helical computed tomography (CT) in acute pulmonary embolism (PE) diagnosis. MATERIALS AND METHODS: Of 204 consecutive patients with clinically suspected acute PE (mean age, 58 years +/- 14 [SD]), 158 were enrolled. All patients underwent dual-section helical CT (2.7-mm effective section thickness) and selective pulmonary arteriography within 12 hours of each other. Each image was analyzed independently by two observers, who determined image quality and presence of PE among arterial segments, including at the subsegmental level. The final diagnosis was made with consensus. RESULTS: Selective pulmonary arteriography was considered optimal in 147 (93%), suboptimal in 10 (6%), and inconclusive in one (0.6%) of 158 patients. Dual-section helical CT findings were considered technically optimal in 140 (89%), suboptimal in 11 (7%), and inconclusive in six (4%). Selective pulmonary arteriography demonstrated PE in 62 patients. Four (6%) of 62 patients had isolated subsegmental PE. The sensitivity of dual-section helical CT was 90%, and the specificity was 94%. The positive and negative predictive values were 90% and 94%, respectively. CONCLUSION: Dual-section helical CT is an improvement in helical CT that offers a high sensitivity and specificity for the depiction of PE, including at the subsegmental level. Dual-section helical CT can replace pulmonary arteriography for the direct demonstration of PE in a majority of patients.

Acute Disease↗
PubMed1999

Helical CT phlebography of the superior vena cava: diagnosis and evaluation of venous obstruction.

OBJECTIVE: The purpose of this study was to determine the feasibility of helical CT phlebography of the superior vena cava (SVC) and to evaluate the role of this imaging technique in the diagnosis and treatment of SVC obstruction. SUBJECTS AND METHODS: Twenty-three helical CT phlebograms were obtained of patients with clinical findings that were suggestive of SVC obstruction (n = 19) and of patients undergoing posttherapeutic evaluation for SVC obstruction (n = 4). CT examinations consisted of helical acquisitions obtained in the craniocaudal direction with simultaneous bilateral antecubital vein injection of 2 x 90 ml of 12% iodinated contrast material at 2 ml/sec. Combined analysis of axial, multiplanar, and maximum-intensity-projection reformatted images was used for all patients. Image quality, venous stenosis or obstruction, intraluminal thrombus, and collateral pathways were evaluated. Comparison with digital phlebographic data was available for 16 patients; this comparison was performed in a nonblinded manner. RESULTS: CT phlebograms were considered technically optimal in 91% of the patients. In all these patients, helical CT phlebograms showed the venous obstruction: the site, extent, cause, and collateral pathways. CT phlebography appeared to be well correlated with digital phlebography in 16 patients regarding the degree of obstruction, the presence of collateral pathways, and the presence of thrombus. CONCLUSION: Helical CT phlebography may be a useful technique for imaging the SVC and its tributaries. This imaging technique is simple to perform and can provide all the information necessary to diagnose and treat SVC obstruction.

Feasibility Studies↗
PubMed1999

[Positional occlusion of the descending scapular artery in transverse thoraco-brachial syndrome with neurologic symptoms].

We report a thoracic outlet syndrome revealed by neurological complications. Angiography of the subclavian artery depicted an isolated positional occlusion of the descending scapular artery. This side branch of the subclavian artery is anatomically located close to and supplies the brachial plexus. Surgical treatment led to improvement of most symptoms and post-operative control angiography was normal. Not previously described, this sign illustrates the objective compression of the brachial plexus. Ischemia is perhaps intricated with compression, a well-known pathophysiological mechanism of neurological complications in this syndrome. This artery feeding the brachial plexus is usually ligated during surgical neurolysis but must be preserved in order to improve recovery of neurological function and prevent surgical failures.

Angiography↗
PubMed1999

[Post-traumatic aneurysmal dissection of the extracranial internal carotid artery; helical computed tomographic and angiographic aspects: a case].

A 20-year-old man presented with mild intracranial bleeding, a Horner's syndrome, and left neck swelling following head injury. Following noncontrast CT of the brain, a contrast-enhanced helical CT was performed through the neck that showed a hematoma in the poststyloid space (carotid sheath) with irregular diameter of the ICA. Selective digital subtraction angiography confirmed the presence of left cervical ICA dissection with pseudoaneurysm formation. The aneurysm was resected and an end-to-end anastomosis was done using an inverted saphenous graft. Histology confirmed a diagnosis of traumatic ICA dissection with pseudoaneurysm formation and there was no evidence of pre-existing pathology. Helical CT is a simple, widely available, and relatively non-invasive imaging technique that correlates well with angiography. It should be considered in the evaluation of patients with suspected cervical ICA dissection.

Accidents, Traffic↗
PubMed1999

[Arterial lipiodol chemoembolization of a left liver metastasis through the right internal thoracic artery].

The purpose of this article is to illustrate the efficacy of the chemoembolization in patients with hypervascular metastases and to describe the post-embolization change in vascularization pattern. Unusual collaterals may develop following embolization. A 59-year-old woman, followed for unresectable small bowel carcinoid tumor since 1991, underwent successful chemoembolization of several liver metastases. Only one liver lesion, located in segment IV, showed interval increase in size. This lesion was supplied by the right internal mammary artery. A branch of the right internal mammary artery was catheterized using a microcatheter and embolization was performed using doxorubicine-Lipiodol (Adriblastine, Lipiodol) and gelfoam (Spongel). No complications occurred after the procedure. The right internal mammary artery should be considered as a possible source of collateral arterial supply to the liver and should be evaluated in patients with local progression of disease.

Antibiotics, Antineoplastic↗
PubMed1999

[Bronchial and pulmonary vaso-occlusions].

The technique of vaso-occlusion (or embolisation) consists in occluding one or several vessels which are causing haemoptysis. Either of the pulmonary circulations (systemic bronchial or pulmonary) may be the cause and sometimes both are. In systemic pulmonary hypervascularization the pathological issues are affected by high pressure vascularisation at the expense of functional vascularisation and are the source of frequent episodes of bleeding. Bronchial and systemic vaso-occlusion has proven efficacy and safety on condition that strict rules are respected to avoid complications; the detection of potentially dangerous arteries (spinal, coronary and visceral) and a choice of material for embolisation which is adapted to the therapeutic strategy and the clinical and angiographic presentation. The indications for the procedure are dictated by severe or recurrent haemoptysis. Vaso-occlusion of pulmonary arteries which is a rarer indication dominated by conditions such as arteriovenous malformation (MAVP). The technique is adapted to the number, to the size and to the diffusion of MAVP which is characterised precisely by computed tomography. Vaso-occlusion is the treatment of first choice for MAVP only leaving failures of vaso-occlusion to surgery and certain pedicular forms have a very short afferent of large calibre.

Arteriovenous Malformations↗
PubMed1999

[Late solitary metastasis of a renal cancer to the contralateral adrenal gland].

We report a case of metachronous metastasis from renal cell carcinoma to the contralateral adrenal gland detected one year after radical nephrectomy. The initial tumor was incidentally discovered in the setting of acute aortic dissection. A large left adrenal tumor was detected on CT follow-up at two years. Retrospectively, a hypervascular lesion was present on the first yearly CT examination. Adrenalectomy was performed. There is no evidence of recurrent disease at 12 months. The patient was also treated with oral steroids. Because of their location and of the particularities of available therapeutic options, and because these metastases can occur late, long-term sonographic and CT follow-up should be performed. The clinical, imaging, therapeutic and prognostic aspects of these lesions will be discussed.

Adrenal Gland Neoplasms↗
PubMed1998

Identification of the Dictyostelium discoideum homolog of the N-ethylmaleimide-sensitive fusion protein.

The N-ethylmaleimide-sensitive fusion protein (NSF) is required for vesicular membrane fusion in multiple cellular functions. We have cloned a cDNA encoding the Dictyostelium discoideum homolog of the NSF protein. This cDNA hybridizes with a single fragment in Southern blots suggesting that NSF is encoded by a single gene in the amoeba. It is expressed constitutively during vegetative growth and throughout the differentiation cycle. The encoded gene product comprises 738 aa with a predicted molecular mass of 82 kDa. It shows the characteristic three-domain structure of NSF proteins. A more divergent amino-terminal part is followed by two highly conserved ATP-binding domains featuring Walker A and B signature sequences. The D. discoideum protein presents an overall aa sequence identity of 44% when compared to known NSF homologs. The monoclonal antibody 2E5 directed against Cricetellus griseus NSF recognizes a protein with a molecular weight of approx. 80 000 in a D. discoideum crude extract and the recombinant D. discoideum His6-NSF expressed in Escherichia coli.

Amino Acid Sequence↗
PubMed1998

In vitro reconstituted Dictyostelium discoideum early endosome fusion is regulated by Rab7 but proceeds in the absence of ATP-Mg2+ from the bulk solution.

We characterized the in vitro fusion of endosomal compartments from Dictyostelium discoideum. Fusion activity was restricted to early compartments, was dependent on cytosolic proteins, and was activated by GTP and guanosine 5'-O(3-thio)triphosphate (GTPgammaS). This stimulation suggests the involvement of a small G protein, which we propose to be Rab7 on the basis of the strong inhibitory effect of anti-Rab7 antibodies. It is noteworthy that in the presence of GTPgammaS, the concentration of ATP-Mg2+ could be reduced to less than 1 nM without loss of fusion activity. Under these conditions, competing residual ATP with adenosine 5'-O-(3-thio)triphosphate-Mg2+ also failed to inhibit endosome fusion. The presence of an ATP-depleting system alone blocked fusion probably because endogenous GTP was removed by coupling through NDP kinase. Moreover, whether ATP was present or not, GTPgammaS-activated fusion was equally sensitive to anti-Rab7 antibodies or N-ethylmaleimide and was restricted to early compartments. These results show that soluble ATP-Mg2+ is not needed for endosome fusion. Since homotypic fusion of endosomes in D. discoideum has been shown to depend on the ATPase N-ethylmaleimide-sensitive factor (Lenhard, J. M., Mayorga, L. , and Stahl, P. D. (1992) J. Biol. Chem. 267, 1896-1903), the nucleotide exchange on the N-ethylmaleimide sensitive factor must take place before GTPgammaS activation in this system.

Adenosine Triphosphate↗
PubMed1997

Sternal abscess due to Bartonella (Rochalimaea) henselae in a renal transplant patient.

Bartonella henselae, previously called Rochalimaea henselae, is the causative agent of cat scratch disease (CSD) in immunocompetent subjects and bacillary angiomatosis in immunocompromised ones. Bone lesions are common in bacillary angiomatosis, but not in CSD. We present the case of a patient with a renal transplant treated by immunosuppressive therapy who developed a sternal abscess with a histological pattern of CSD. The CT pattern was that of a lytic bone lesion with adjacent fluid collection. The diagnosis was made on the basis of a polymerase chain reaction amplification performed on bone material. Bartonella henselae is a newly described bacteria that causes CSD in a normal host and bacillary angiomatosis in immunocompromised patients. We report a case of an osteolytic lesions of the sternum with adjacent fluid collection related to CSD, which occurred in a patient with a renal transplant.

Abscess↗