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Biomedical subjects

M Falconi

Publications and source records attributed to M Falconi.

At least 73 records · Page 4Linked to original sources
PubMed2001

Structure and stability of the insulin dimer investigated by molecular dynamics simulation.

Molecular dynamics simulation indicates that the dynamical behaviour of the insulin dimer is asymmetric. Atomic level knowledge of the interaction modes and protein conformation in the solvation state identifies dynamical structures, held by hydrogen bonds that stabilize, mainly in one monomer, the interaction between the chains. Dynamic cross-correlation analysis shows that the two insulin monomers behave asymmetrically and are almost independent. Solvation energy, calculated to evaluate the contribute of each interface residue to the dimer association pattern, well compares with the experimental association state found in protein mutants indicating that this parameter is an important factor to explain the association properties of mutated insulin dimers.

Computer Simulation↗
PubMed2001

Role of the helix capping in the stability of the mouse prion (180-213) segment: investigation through molecular dynamics simulations.

Molecular dynamics simulation of the 180-213 segment, forming the B and C helices in the mouse prion protein, and of three mutants, where the capping box residues or the hydrophobic staple motif residues were selectively mutated, have been carried out. The results indicate that the wild type segment is stable over all the trajectory, whilst the mutants display different degrees of destabilization. In detail mutation of Asp202 brings to a rapid unfolding of helix C likely because of the concomitant loss of a hydrogen bond and of a negative charge able to stabilize the dipole in the first turn of the helix. A lower destabilizing effect is observed upon mutation Thr199. On the other hand mutation of Phe198 and Val203, the hydrophobic staple residues, brings to an incorrect orientation of the first helix relative to the second one due to a weakening of the hydrophobic interaction. The results confirm the importance of the presence of both motifs for the structural integrity of the isolated fragment and suggest that these residues may have a main role in the structural transition observed in the inherited human prion diseases.

Amino Acid Sequence↗
PubMed2001

Surgical strategy in the treatment of gastrointestinal neuroendocrine tumours.

The aim of this study was to analyze the indications and type of surgery to be performed in patients suffering from the more common gastrointestinal neuroendocrine tumours. The different patterns of tumour spread are considered (local, locoregional and metastatic disease) along with the indications according to three main objectives, namely, identification of the disease, cure and care. The surgical procedures of choice in relation to the different tumour subtypes are also analyzed, and the main controversies relating to cytoreductive surgery are discussed.

Gastrointestinal Neoplasms↗
PubMed2001

Previous cholecystectomy, gastrectomy, and diabetes mellitus are not crucial risk factors for pancreatic cancer in patients with chronic pancreatitis.

INTRODUCTION: In the general population, cholecystectomy, diabetes, and chronic pancreatitis seem to be associated with an increased risk of developing pancreatic cancer. AIMS: We assessed whether previous cholecystectomy, gastrectomy, or diabetes mellitus may be risk factors for pancreatic cancer in patients with chronic pancreatitis. METHODOLOGY: We analyzed 853 patients with chronic pancreatitis (110 women, 743 men) with a median follow-up period of 14 years with particular reference to establishing which patients had previously undergone cholecystectomy or distal gastric resection (Billroth II anastomosis) or had diabetes or gallstone disease and the respective time scales involved. RESULTS: Pancreatic cancer developed in 17 patients with chronic pancreatitis after a median period of 8 years from onset of pancreatitis symptoms (range, 3-38 years). Excluding two cholecystectomies performed 1 year before diagnosis of cancer, cholecystectomy was performed in 7/17 (41%) patients with pancreatic cancer and in 381/836 (46%) of the other patients with chronic pancreatitis. Forty-nine (10%) patients with chronic pancreatitis and no pancreatic cancer had undergone cholecystectomy during the years before the onset of chronic pancreatitis, whereas none of the patients in whom a pancreatic malignancy developed had undergone cholecystectomy before the onset of chronic pancreatitis symptoms. Gastrectomies were performed in 116 patients (14%), 47 before the onset of chronic pancreatitis. Only 2/17 patients with pancreatic cancer had undergone previous gastrectomy, though in both cases only shortly before diagnosis of the cancer. Diabetes was diagnosed in 353 patients, but only in 30 (4%) before onset of chronic pancreatitis. Only 1/17 patients (6%) with pancreatic cancer had long-standing diabetes, whereas diabetes developed in 3/17 shortly before diagnosis of pancreatic cancer. CONCLUSIONS: Cholecystectomy, gastrectomy, and diabetes are not major risk factors for the development of pancreatic cancer in patients with chronic pancreatitis.

Cholecystectomy↗
PubMed2001

The relevance of gastrointestinal fistulae in clinical practice: a review.

Gastrointestinal fistulae most frequently occur as complications after abdominal surgery (75-85%) although they can also occur spontaneously--for example, in patients with inflammatory bowel disease (IBD) such as diverticulitis or following radiation therapy. Abdominal trauma can also lead to fistula formation although this is rare. Postoperative gastrointestinal fistulae can occur after any abdominal procedure in which the gastrointestinal tract is manipulated. Regardless of the cause, leakage of intestinal juices initiates a cascade of events: localised infection, abscess formation and, as a result of a septic focus, fistulae formation. The nature of the underlying disease may also be important, with some studies showing that fistula formation is more frequent following surgery for cancer than for benign disease. Fistula formation can result in a number of serious or debilitating complications, ranging from disturbance of fluid and electrolyte balance to sepsis and even death. The patient will almost always suffer from severe discomfort and pain. They may also have psychological problems, including anxiety over the course of their disease, and a poor body image due to the malodorous drainage fluid. Postoperative fistula formation often results in prolonged hospitalisation, patient disability, and enormous cost. Therapy has improved over time with the introduction of parental nutrition, intensive postoperative care, and advanced surgical techniques, which has reduced mortality rates. However, the number of patients suffering from gastrointestinal fistulae has not declined substantially. This can partially be explained by the fact that with improved care, more complex surgery is being performed on patients with more advanced or complicated disease who are generally at higher risk. Therefore, gastrointestinal fistulae remain an important complication following gastrointestinal surgery.

Humans↗
PubMed2001

Management of complications after pancreaticoduodenectomy in a high volume centre: results on 150 consecutive patients.

Pancreaticoduodenectomy (PD) is still a difficult procedure with significant morbidity. We report 150 consecutive PDs performed during a 3-year period. All the cases have been prospectively evaluated with regard to the surgical outcome. Mortality in this series was 3/150 (2%) with a re-operation rate of 5/150 (3.3%); surgical complications were experienced in 57/150 (38%). The most frequent complications were collections in 25/150 (16.6%) and pancreatic fistulas in 16/150 (10.7%). The majority of these complications were conservatively managed: only one abscess and one fistula due to an anastomotic dehiscence required re-operation. The complication most responsible for mortality was haemorrhage secondary to arterial pseudoaneurysms in patients with severe post-operative pancreatitis. The continued high morbidity of PDs is compensated by the ability to treat complications non-operatively, resulting in a surgical risk that should now be considered medium to low in high volume centres.

Acute Disease↗
PubMed2001

In vivo octreotide administration acutely reduces exocrine granule size in the human pancreas.

BACKGROUND: Octreotide has been found to be effective in the prevention of postoperative complications of pancreatic surgery, but the benefit of preoperative octreotide administration has not been assessed. AIMS: To evaluate the ability of octreotide in reducing the amount of digestive enzymes in the pancreas before surgery, a morphometric ultrastructural study of the gland was undertaken in patients undergoing demolitive pancreatic surgery. METHODS: Twenty-three inpatients received saline (n = 8) or octreotide (100 micrograms s.c.) before surgery either once (n = 5), or three (n = 5) or six (n = 5) times at 8-hour intervals. At surgery, biopsies of the pancreas were taken and processed for electron microscopy. Several parameters were assessed in exocrine cells by means of ultrastructural morphometry. RESULTS: A single administration of octreotide significantly reduced the exocrine granule number and the mean and total granular surface sectional area, and the ratio between granule area and cytoplasmic area. Repeated octreotide administrations were associated with partial (3 administrations) and complete (6 administrations) recovery of all parameters to control values. CONCLUSION: Preoperative administration of octreotide, the synthetic analogue of somatostatin, acutely reduces exocrine granule number and size in the pancreatic cell. This finding can partially explain the prophylactic effect of the drug on early complications of pancreatic surgery. Such an effect is not maintained over multiple administrations of the somatostatin analogue. Possible explanations for this latter finding are discussed.

Adult↗
PubMed2001

Chromatin fibers organization within the nucleus.

In order to evaluate at the ultrastructural level the three dimensional arrangement of the dispersed chromatin during the intephase, the immunogold detection of Bromodeoxyuridine (BrdU), of the DNA polymerase alpha and of the proliferating cell nuclear antigen (PCNA) was performed on human HL60 leukemia cells and nuclear matrices extracted from the same cellular model. The Field Emission In lens Scanning Electron Microscopy analysis of the ultrathin cryosectioned cells revealed the presence of a chromatin three dimensional network where the different constituents appeared repetitively assembled. Also the nuclear matrix showed a repetitive structure, on which the deprivation of the DNA corresponded to the selective loss of particular class sized fibers. The single or multiple combined immunolocalization of different structures involved in the DNA replication, where BrdU, DNA polymerase alpha and PCNA represent, respectively, the substratum, the polymerizing enzyme and a regulator of the reaction, allowed the understanding of its reciprocal spatial relationship on the dispersed interphasic chromatin and the role of the nuclear matrix in the replicative process.

Bromodeoxyuridine↗
PubMed2000

Insulin selectively stimulates nuclear phosphoinositide-specific phospholipase C (PI-PLC) beta1 activity through a mitogen-activated protein (MAP) kinase-dependent serine phosphorylation.

Using NIH 3T3 cells, we have investigated nuclear phosphoinositide metabolism in response to insulin, a molecule which acts as a proliferating factor for this cell line and which is known as a powerful activator of the mitogen-activated protein (MAP) kinase pathway. Insulin stimulated inositol lipid metabolism in the nucleus, as demonstrated by measurement of the diacylglycerol mass produced in vivo and by in vitro nuclear phosphoinositide-specific phospholipase C (PI-PLC) activity assay. Despite the fact that nuclei of NIH 3T3 cells contained all of the four isozymes of the beta family of PI-PLC (i.e. beta1, beta2, beta3, and beta4), insulin only activated the beta1 isoform. Insulin also induced nuclear translocation of MAP kinase, as demonstrated by Western blotting analysis, enzyme activity assays, and immunofluorescence staining, and this translocation was blocked by the specific MAP kinase kinase inhibitor PD98059. By means of both a monoclonal antibody recognizing phosphoserine and in vivo labeling with [(32)P]orthophosphate, we ascertained that nuclear PI-PLC-beta1 (and in particular the b subtype) was phosphorylated on serine residues in response to insulin. Both phosphorylation and activation of nuclear PI-PLC-beta1 were substantially reduced by PD98059. Our results conclusively demonstrate that activation of nuclear PI-PLC-beta1 strictly depends on its phosphorylation which is mediated through the MAP kinase pathway.

3T3 Cells↗
PubMed2000

Single mutation at the intersubunit interface confers extra efficiency to Cu,Zn superoxide dismutase.

The Val28-->Gly single mutant at the subunit interface of Cu,Zn superoxide dismutase from Photobacterium leiognathi displays a k(cat)/K(M) value of 1.7x10(10) M(-1) s(-1), twice that of the native enzyme. Analysis of the three-dimensional structure indicates that the active site Cu,Zn center is not perturbed, slight structural deviations being only localized in proximity of the mutation site. The enzyme-substrate association rate, calculated by Brownian dynamics simulation, is identical for both enzymes, indicating that the higher catalytic efficiency of the Val28-->Gly mutant is not due to a more favorable electrostatic potential distribution. This result demonstrates the occurrence of an intramolecular communication between the mutation site and the catalytic center, about 18 A away and indicates a new strategy to encode extra efficiency within other members of this enzymatic family.

Amino Acid Substitution↗
PubMed2000

Molecular dynamics simulation of solvated azurin: correlation between surface solvent accessibility and water residence times.

A system containing the globular protein azurin and 3,658 water molecules has been simulated to investigate the influence on water dynamics exerted by a protein surface. Evaluation of water mean residence time for elements having different secondary structure did not show any correlation. Identically, comparison of solvent residence time for atoms having different charge and polarity did not show any clear trend. The main factor influencing water residence time in proximity to a specific site was found to be its solvent accessibility. In detail for atoms belonging to lateral chains and having solvent-accessible surface lower than approximately 16 A(2)a relation is found for which charged and polar atoms are surrounded by water molecules characterized by residence times longer than the non polar ones. The involvement of the low accessible protein atom in an intraprotein hydrogen bond further modulates the length of the water residence time. On the other hand for surfaces having high solvent accessibility, all atoms, independently of their character, are surrounded by water molecules which rapidly exchange with the bulk solvent. Proteins 2000;39:56-67.

Azurin↗
PubMed2000

Plasmid curing effect of trovafloxacin.

The effect of sub-inhibitory concentrations of trovafloxacin, a recently developed fluoroquinolone molecule, on the capability of Escherichia coli cells to maintain three different types of plasmids has been investigated by a number of approaches, including the quantification of the loss of plasmid-borne functions and of plasmid DNA by quantitative PCR. The results obtained demonstrate that at concentrations ranging from the MIC to 1/8 of the MIC, trovafloxacin induces a clear, albeit incomplete, 'episome-curing' effect which was observed with plasmids differing in copy number, size and nature of the replication origin of the episome. This effect was most likely not due to an alteration of DNA supercoiling.

Anti-Infective Agents↗
PubMed2000

Pancreatic acinar carcinoma shows a distinct pattern of chromosomal imbalances by comparative genomic hybridization.

Pancreatic acinar cell carcinoma (PAC) is a rare pancreatic tumor for which no information about chromosomal anomalies is available. We examined six primary PACs by comparative genomic hybridization (CGH). All cases showed chromosomal changes. A total of 106 gains and 48 losses was detected. Consensus regions of gain were identified on chromosomes 1, 12, and X: 1q21 in four cases, 1q42 in three cases, 12p11.2 in four cases, and Xq12-21 in three cases. Recurrent losses were found at 16p13.2-p13.1 in three cases and at 16q23 in three cases. To verify these chromosomal imbalances, microsatellite analysis of matched normal and tumor DNA was performed using PCR-amplified markers for chromosomes 1, 12, and 16 in the regions showing nonrandom gains or losses. This analysis showed allelic imbalances in tumor DNA consistent with the CGH profiles. Our CGH study suggests that PAC shows a characteristic pattern of chromosomal alterations, involving gain at 1q, 12p, and Xq and loss of sequences at 16p and 16q. This pattern appears unique among solid tumors and is markedly different from that detected in pancreatic ductal carcinomas by the same technique. This suggests that PAC tumorigenesis involves different molecular pathways than those involved in the more common pancreatic ductal tumors. Genes Chromosomes Cancer 28:294-299, 2000.

Adult↗
PubMed2000

Role of octreotide in the treatment of external pancreatic pure fistulas: a single-institution prospective experience.

INTRODUCTION: Octreotide was studied in the treatment of pure external pancreatic fistulas. METHODS: Eighteen cases (12 males, 6 females) were prospectively observed. Six patients (four after radical surgery for periampullary cancer, one endocrine tumor enucleation and one pancreojejunostomy in chronic pancreatitis) were treated as outpatients with octreotide alone because of low basal fistula output (mean+/-SD: 96.6+/-27.4 cc/24 h). Twelve (five radical surgery for cancer, five surgery for severe pancreatitis, one enucleation and one pancreojejunostomy) were treated as inpatients with octreotide plus total parenteral nutrition because of the high output (mean+/-SD: 448.4+/-248.2 cc/24 h). RESULTS: Ten of the 12 high-output fistulas healed in 27.8+/-27.7 days, whereas all low-output fistulas healed in 12.1+/-6.6 days. CONCLUSION: Octreotide appears useful in the treatment of external pancreatic fistulas. For optimal results to be achieved, there must be no local infection and no mechanical or anatomical obstacles to the free flow of juice.

Adolescent↗