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Biomedical subjects

M Falconi

Publications and source records attributed to M Falconi.

At least 55 records · Page 3Linked to original sources
PubMed2001

Superefficient enzymes.

Diffusion-controlled enzymes are characterized by second-order rate constants in the range 10(8)-10(10) M(-1)s(-1). These values are at the upper end of the observed rates of many enzyme-substrate reactions and have been predicted by theoretical studies on bimolecular reaction in solution. Such enzymes are considered to be perfect, since their rate-limiting step is not due to any chemical event but to the diffusional association rate between the enzyme and the substrate. Often the enzyme-substrate encounter is facilitated either through the presence of a strong attractive electric field, produced by charges on the enzyme surface, or through the reduction in the dimension of the search process. Here we provide a brief review of some of the enzymes characterized by a very fast second-order constant, focusing attention on triose phosphate isomerase and Cu,Zn superoxide dismutase taken as typical examples of such highly tuned enzymes.

Animals↗
PubMed2001

Nonfunctioning endocrine tumors of the pancreas: possibilities of spiral CT characterization.

The aim of this study was to assess the ability of spiral CT to adequately characterize the nonfunctioning endocrine tumors (NFETs) of the pancreas, distinguishing this lesion from the other pancreatic tumors. The spiral CT examinations of 21 cases of histologically proven NFETs, along with those of 29 cases of other pancreatic tumors and tumor-like lesions, were retrospectively reviewed in a blinded fashion by two radiologists, in order to correctly classify the lesions, highlighting the typical signs reported in the literature. Discordant cases were further analyzed in the presence of a third radiologist. The final diagnosis was acquired by means of a majority or overall consensus. The histopathologic examination was considered the gold standard. The sensitivity, specificity, and positive and negative predictive values of CT were calculated. After the consensus evaluation, the correct diagnosis was reached in 72% of cases, with 10% of nonspecific diagnoses of solid pancreatic tumor and 18% of wrong diagnoses. The sensitivity and specificity of spiral CT in identifying NFETs were 66.6 and 82.7%, respectively. The positive and negative predictive values were 73.7 and 77.4%, respectively. In up to 70% of cases the NFET demonstrates a typical aspect of a mass hyperdense in the arterial contrastographic phase eventually associated with hyperdense hepatic metastases in more than half of the patients. This finding does allow the diagnosis of NFET but without certainty indeed, since other tumors can show a similar densitometric behavior and among them particularly the ductal adenocarcinoma. On the other hand, both the solid, hypovascularized NFETs, and the cystic form, cannot be differentiated from the other solid and cystic tumors of the pancreas.

Adenoma, Islet Cell↗
PubMed2001

Successful xenografting of cryopreserved primary pancreatic cancers.

In order to assess the suitability of cryopreserved neoplastic tissues for xenografting into nude (nu/nu) mice, we compared the take rate in 28 samples of pancreatic ductal carcinoma. Eleven fresh samples were implanted in nu/nu mice, and 17 were frozen in cryopreserving solution and implanted at a later time. All samples were examined for the presence of neoplastic tissue in cryostat sections. A total of 15 tumors grew in the animals; five from the freshly implanted samples and ten from those cryopreserved. Ten xenografted tumors were characterized for alterations in p53, K-ras, and p16 genes, which were found in six, eight, and nine cases, respectively. Our results demonstrate that the take rate for xenografting is comparable between cryopreserved and fresh tissue samples. The procedure allows for the exchange of tumor material between institutions and permits the establishment of centralized facilities for the storage of an array of different primary tumor samples suitable for the production of in vivo models of cancers.

Adult↗
PubMed2001

A method for sex assignment in mixed samples.

A method for male sex assignment in mixed samples by amplifying a specific amelogenin Y sequence is described. The specificity and the high sensitivity make it suitable for basic research, forensic evaluations and clinical applications.

Amelogenin↗
PubMed2001

Prophylaxis for septic complications in acute necrotizing pancreatitis.

Because the mortality of severe pancreatitis is higher when infected necrosis supervenes, prevention of infections has become a relevant endpoint for management. The "ideal" drug should be characterized by specific activity against the bacteria known to be responsible for infection and should be able to penetrate the gland in a sufficient concentration. To date there have been eight prospective trials with antibiotics, one on selective digestive decontamination, and others with enteral nutrition. A meta-analysis regarding experiences with antimicrobial drugs reports a significant reduction in the incidence of infected necrosis and pancreatic abscesses during severe pancreatitis. In conclusion, among the several options aimed at reducing infections during necrotizing pancreatitis, the prophylactic use of antibacterial drugs is the only one to have been tested to date in several randomized studies. Strong consideration should be given to treating patients with severe pancreatitis with broadspectrum antibiotics, selective digestive decontamination, and enteral nutrition.

Animals↗
PubMed2001

Phospholipase C delta2 expression characterizes the neoplastic transformation of the human gastric mucosa.

The expression, cellular distribution, and activity of PIP(2)-specific phospholipase C (PLC) in healthy human gastric-mucosa cells have been recently studied in our laboratories and a direct evidence for an almost exclusive expression of PLC beta isoforms, with the exception of PLC beta4, has been provided. These results addressed our attention to possible modification of PLC expression and activity during neoplastic transformation of the human gastric mucosa. In the present article we present results indicating that PLC delta2 is markedly expressed in type II intestinal metaplasia and in the adenocarcinoma whereas traces of other PLC isoforms were sometime detected. Interestingly, we found that type I intestinal metaplasia was in the majority of the cases PLC delta2-negative, but when expressed, this type of metaplasia generally considered as benignant, always evolved toward neoplastic transformation. These results therefore readdress the question of surveillance of the patients with type I intestinal metaplasia and suggest that PLC delta2 expression might be a possible marker of gastric malignant transformation.

Adenocarcinoma↗
PubMed2001

Molecular characterization of pancreatic serous microcystic adenomas: evidence for a tumor suppressor gene on chromosome 10q.

Pancreatic serous microcystic adenomas (SCAs) are rare, benign tumors with a striking female preference. Virtually no information is available about chromosomal or genetic anomalies in this disease. We performed extensive molecular characterization of 21 cases of formalin-fixed, paraffin-embedded sporadic SCAs consisting in genome-wide allelic loss analysis with 79 microsatellite markers covering all 22 autosomes, assessment of microsatellite instability, and mutational analysis of the VHL, K-ras, and p53 genes in nine cases for which frozen tissue was available. Although no case showed microsatellite instability of the type seen in mismatch repair-deficient tumors, a relatively low fractional allelic loss of 0.08 was found. Losses on chromosome 10q were the most frequent event in SCAs (50% of cases), followed by allelic losses on chromosome 3p (40% of cases). Moderately frequent losses (>25% of cases) were found on chromosomes 1q, 2q, and 7q. The VHL gene, located on chromosome 3p, had somatic inactivating mutations in two of nine cases (22%), whereas no mutations were found in either K-ras or p53, in agreement with the finding that all 21 cases stained negative for p53 by immunohistochemistry. Our study indicates that the involvement of chromosomal arms 10q and 3p is characteristic of SCAs and that the VHL gene is involved in a subset of sporadic cases.

Aged↗
PubMed2001

Dynamics-function correlation in Cu, Zn superoxide dismutase: a spectroscopic and molecular dynamics simulation study.

A single mutation (Val29-->Gly) at the subunit interface of a Cu, Zn superoxide dismutase dimer leads to a twofold increase in the second order catalytic rate, when compared to the native enzyme, without causing any modification of the structure or the electric field distribution. To check the role of dynamic processes in this catalytic enhancement, the flexibility of the dimeric protein at the subunit interface region has been probed by the phosphorescence and fluorescence properties of the unique tryptophan residue. Multiple spectroscopic data indicate that Trp83 experiences a very similar, and relatively hydrophobic, environment in both wild-type and mutant protein, whereas its mobility is distinctly more restrained in the latter. Molecular dynamics simulation confirms this result, and provides, at the molecular level, details of the dynamic change felt by tryptophan. Moreover, the simulation shows that the loops surrounding the active site are more flexible in the mutant than in the native enzyme, making the copper more accessible to the incoming substrate, and being thus responsible for the catalytic rate enhancement. Evidence for increased, dynamic copper accessibility also comes from faster copper removal in the mutant by a metal chelator. These results indicate that differences in dynamic, rather than structural, features of the two enzymes are responsible for the observed functional change.

Amino Acid Sequence↗
PubMed2001

Evaluation of the F2000 bonding procedure: a high resolution SEM study.

OBJECTIVES: The aim of this study was to define the morphological bonding of the F2000 Restorative System (3M Dental Product) to enamel and dentin. For this purpose, high resolution scanning electron microscope (SEM) in conjunction with a tensile bond strength analysis was used to correlate the morphological findings to the bonding potential. Scotchbond 1 (SB1) adhesive system was utilized as a control. MATERIALS AND METHODS: Teeth were prepared in vivo and prepared as: (1) F2000 PA for 15s, (2) F2000 PA for 30s, (3) 35% phosphoric acid for 15s and SB1 and (4) 35% phosphoric acid for 30s and SB1. All teeth were then restored with the F2000 compomer restorative material, extracted, sectioned and analyzed by means of a field emission in-lens SEM (FEISEM). The conditioning/etching patterns of the two adhesive systems were also evaluated in vitro on dentin disks in order to show high resolution details of every single step of the bonding procedure. RESULTS: FEISEM images showed a repetitive pattern of the enamel crystals with several microporosities after the 30s application of F2000 PA; moreover a good adaptation of the adhesive resin on the conditioned enamel was observable. FEISEM analysis of the dentin surface revealed no evidence of a smear layer after the application of F2000 PA for 30s. Residual smear plugs were partially obliterating the tubule orifices when F2000 PA was used, while they were completely absent after etching with 35% phosphoric acid. The total etching technique revealed open tubules and resin tags formation after the application of SB1. CONCLUSIONS: The one step etching/priming/bonding procedure of the F2000 PA showed favorable results at ultra-structural level when applied on both the enamel and the dentin surface for 30s (as per manufacturers' instructions), but the bond strength analysis showed higher values of bonding of the F2000 compomer when the SB1 adhesive agent (after etching with 35% phosphoric acid) was used (7.7+/-2.2 vs 19.0+/-4.4MPa).

Acid Etching, Dental↗
PubMed2001

Digestive neuroendocrine tumours: diagnosis and treatment in Italy. A survey by the Oncology Study Section of the Italian Society of Gastroenterology (SIGE).

BACKGROUND: New insights in the diagnosis and treatment of digestive neuroendocrine tumours have prompted a renewed interest in these rare and complex diseases. AIM: To establish how many new cases of digestive neuroendocrine tumours were diagnosed, and how they were treated, at gastroenterological centres across Italy during a two-year period (1997-1998). METHODS: The 12 centres taking part filled in a data collection form reporting type of tumour, methods of diagnosis and therapeutic strategies adopted in each case. Data were collected and analysed by the authors of the present report. RESULTS: Data refer to 98 patients, 22 with functioning and 76 with non-functioning digestive neuroendocrine tumours [50 carcinoids, 48 pancreatic endocrine tumour syndromes]. Primary tumours were localised in 96% (38% with metastases) of non-functioning and 81% (50% with metastases) of functioning tumours. These were surgically removed in >80% of patients in both groups. Somatostatin analogue treatment, with or without interferon, was administered in 35% of patients, while chemotherapy was used in 9% and 23% of functioning and non-functioning tumours, respectively. The imaging study always included a computed tomography scan (20% helical computed tomography). Magnetic resonance and somatostatin receptor scintigraphy were also performed, the former in 41% and 21% of the two (functioning and non-functioning tumour) groups, the latter in 45% and 30%. CONCLUSIONS: The number of functioning digestive neuroendocrine tumours reported was lower than expected. Surgery plays a major role in the treatment of these tumours in all centres. Overall, in only a small number of patients was a multidisciplinary approach applied.

Adolescent↗
PubMed2001

Molecular dynamics simulation of the antimicrobial salivary peptide histatin-5 in water and in trifluoroethanol: a microscopic description of the water destructuring effect.

The results of 520 ps molecular dynamics simulation of histatin-5, a small peptide present in human saliva and possessing antimicrobial activity, dissolved in water and in 2,2,2-trifluoroethanol, are reported. The simulations indicate that histatin-5 is destabilized in water and begins to unfold after 250 ps, while in organic solvent it maintains a regular secondary structure throughout the trajectory. Analysis of the peptide-solvent hydrogen bonds indicates that 2,2,2-trifluoroethanol is a poorer proton acceptor than water. The fluorine atom of the alcohol is almost never engaged in a hydrogen bond and the organic solvent interacts mainly with the peptide through its hydroxyl group. For some residues analysis of the solvent residence time indicated longer values for 2,2,2-trifluoroethanol than for water. The most striking difference is related to the number of times the solvent enters and leaves the first coordination shell of the peptide. This value was more than one order of magnitude higher for water than for the alcohol, suggesting that this may be the main cause of alpha-helix destabilization perpetrated by water.

Amino Acid Sequence↗
PubMed2001

Interleukin 2 and interleukin 15 differentially predispose natural killer cells to apoptosis mediated by endothelial and tumour cells.

Human natural killer (NK) cells constitutively express the beta- and gamma-chains of the interleukin 2 (IL-2)/IL-15 receptor, and both IL-2 and IL-15 are able to activate NK cell proliferation and cytotoxicity. When IL-2-primed human NK cells are exposed to sensitive targets (i.e. K562) they undergo apoptosis mediated by the beta(2)-integrin CD18. Here, we demonstrate that: (i) endothelial cells, similar to K562 tumour target cells, induce apoptosis of IL-2-primed NK cells; (ii) endothelial- and K562 cell-induced apoptosis is significantly lower in IL-15 than in IL-2-stimulated NK cells; (iii) a critical role in the apoptosis of IL-2-primed NK cells is played by the alpha-chain of the IL-2 receptor. Our data show for the first time that IL-2-activated NK cells can die by apoptosis upon contact with the vascular endothelium, which is a necessary step for their extravasation, with a direct pathophysiological relevance on the strategy of adoptive immunotherapy of cancer. On the other hand, IL-15, although generating a similar level of activation of NK cells, largely prevents their apoptotic fate. Therefore, IL-15 produced early in the immune response, when T cells are not yet activated, generates lymphokine-activated killer cells that are efficient killers relatively protected from apoptosis. Once activated, T cells produce IL-2 that overcomes the effect of IL-15 on NK cells, paving the way for their death by apoptosis.

Apoptosis↗
PubMed2001

Clinicopathological features and treatment of intraductal papillary mucinous tumour of the pancreas.

BACKGROUND: The surgical strategy in patients with a pancreatic intraductal papillary mucinous tumour (IPMT) is still controversial. In this study the pathological findings in a series of patients were used to rationalize surgical choice. METHODS: Fifty-one patients with IPMT were observed between 1988 and 1998 and treated by pancreatic resection. Factors evaluated included symptoms, tumour site, type of operation, histological findings and resection margins, tumour stage, follow-up and survival. RESULTS: Pancreaticoduodenectomy was the most frequent surgical treatment (33 patients; 65 per cent), followed by left pancreatectomy (ten), total pancreatectomy (five) and middle pancreatectomy (three). Histological assessment revealed the tumour to be an adenoma in 13 patients (25 per cent), a borderline tumour in ten (20 per cent) and a carcinoma in 28 (55 per cent), 19 of which were invasive. Mild to moderate dysplasia was present at the resection margin in 20 specimens (41 per cent), and carcinoma in one. Local recurrence was observed in four patients (8 per cent), all of whom underwent a second resection. The 3-year actuarial survival rate for benign and malignant disease was 94 and 69 per cent respectively (P = 0.03). CONCLUSION: These results suggest that resection should be the treatment for IPMT. Management of the resection margin could be crucial in avoiding tumour recurrence.

Adenocarcinoma, Mucinous↗
PubMed2001

Involvement of FIS in the H-NS-mediated regulation of virF gene of Shigella and enteroinvasive Escherichia coli.

The mechanism of pathogenicity in Shigella and enteroinvasive Escherichia coli (EIEC) requires the co-ordinated expression of several genes located on both the virulence plasmid and the chromosome. We found that cells lacking a functional FIS protein (factor for inversion stimulation) are partially impaired in expressing the virulence genes and that full expression is totally restored when Shigella wild-type fis gene is offered in trans. We also identified virF, among the virulence genes, as a target of FIS-mediated activation and showed that FIS binds to four specific sites in the promoter region of virF. Previous studies have demonstrated that the expression of VirF, the first positive activator of a multistep regulatory cascade, is subject to temperature-dependent regulation by H-NS, one of the main nucleoid-associated proteins. We now demonstrate that two of the four FIS sites overlap one of the two H-NS sites responsible for thermoregulation (H-NS site I). FIS was found to exercise a direct positive transcriptional control at permissive temperature (37 degrees C), when H-NS fails to repress virF, as well as an indirect effect by partially counteracting H-NS inhibition at the transition temperature (32 degrees C). Our data indicate that FIS may be relevant for the rapid increase in virF expression after penetration of bacteria into the host.

Bacterial Proteins↗
PubMed2001

Role of the electrostatic loop of Cu,Zn superoxide dismutase in the copper uptake process.

Cu,Zn superoxide dismutases are characterized by the presence of four highly conserved charged residues (Lys120, Glu/Asp130, Glu131 and Lys134), which are placed at the edge of the active site channel and have been shown to be individually involved in the electrostatic attraction of the substrate toward the catalytically active copper ion. By genetic engineering we mutated these four residues into neutrally charged ones (Leu120, Gln130, Gln131, Thr134). The effects of these mutations on the rate of superoxide dismutation were not dramatic. In fact, at two different pH and ionic strength values, the mutant enzyme had a catalytic constant even higher with respect to the wild-type protein, showing that electrostatic interaction at these surface sites is not essential for high catalytic efficiency of the enzyme. The mutant and the wild-type enzyme showed the same degree of inhibition by CN(-), and both were not affected by I(-), showing that mutations did not alter the sensitivity of the enzyme to anions. On the other hand, reconstitution of active enzyme from either the wild-type or mutant copper-free enzymes with a copper(I)-glutathione [Cu(I)-GSH] complex showed that metal uptake by the mutant was much slower than by the wild-type enzyme. The demonstration that the 'electrostatic loop' is apparently conserved to assure optimal copper uptake by the enzyme, rather than fast dismutation, may provide further support to the idea that Cu,Zn superoxide dismutase is a bifunctional protein, acting in cellular defense against oxidative stress both as a copper buffer and as a superoxide radical scavenger.

Binding Sites↗
PubMed2001

Infection prevention in necrotizing pancreatitis: an old challenge with new perspectives.

Necrotizing pancreatitis still remains a life-threatening disease despite several improvements in diagnosis, prevention and treatment. In recent years, some important questions have been answered such as the need for early intensive medical treatment rather than early surgery, but others are still strongly debated. The aim of this paper is to present an up-to-date assessment of current challenges in the management of necrotizing pancreatitis in order to prevent infection.

Antibiotic Prophylaxis↗
PubMed2001

Pancreatic tumours: molecular pathways implicated in ductal cancer are involved in ampullary but not in exocrine nonductal or endocrine tumorigenesis.

Alterations of K- ras, p53, p16 and DPC4/Smad4 characterize pancreatic ductal cancer (PDC). Reports of inactivation of these latter two genes in pancreatic endocrine tumours (PET) suggest that common molecular pathways are involved in the tumorigenesis of pancreatic exocrine and endocrine epithelia. We characterized 112 primary pancreatic tumours for alterations in p16 and DPC4 and immunohistochemical expression of DPC4. The cases included 34 PDC, 10 intraductal papillary-mucinous tumours (IPMT), 6 acinar carcinomas (PAC), 5 solid-pseudopapillary tumours (SPT), 16 ampulla of Vater cancers (AVC) and 41 PET. All tumours were also presently or previously analysed for K- ras and p53 mutations and allelic loss at 9p, 17p and 18q. Alterations in K- ras, p53, p16 and DPC4 were found in 82%, 53%, 38% and 9% of PDC, respectively and in 47%, 60%, 25% and 6% of AVC. Alterations in these genes were virtually absent in PET, PAC or SPT, while in IPMT only K- ras mutations were present (30%). Positive immunostaining confirmed the absence of DPC4 alterations in all IPMT, SPT, PAC and PET, while 47% of PDC and 38% of AVC were immunonegative. These data suggest that pancreatic exocrine and endocrine tumourigenesis involves different genetic targets and that among exocrine pancreatic neoplasms, only ductal and ampullary cancers share common molecular events.

Adenocarcinoma, Mucinous↗