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Biomedical subjects

C Fiorentini

Publications and source records attributed to C Fiorentini.

At least 109 records · Page 6Linked to original sources
PubMed1993

Signal transduction pathways and cellular intoxication with Clostridium difficile toxins.

In cultured cells the cytopathic effects (CPE) of Clostridium difficile toxins A and B are superficially similar. The irreversible CPEs involve a reorganization of the cytoskeleton, but the molecular details of the mechanism(s) of action are unknown. As part of the work to elucidate the events leading to the CPE, cultured cells were preincubated with agents known to either stimulate or inhibit some major signal transduction pathways, whereupon toxin was added and the development of the CPE was followed. Both toxin-induced CPEs were enhanced by phorbol esters and mezerein, which stimulate protein kinase C, while they were inhibited by the phospholipase A2 inhibitors quinacrine and 4-bromophenacylbromide. Agents affecting certain G-proteins, cGMP and cAMP levels, phosphatases, prostacyclin, lipoxygenase, and phospholipase C did not affect the development of the CPE of either toxin. Thus, the cytoskeletal effect induced by toxins A or B appears to require PLA2 activity and involves at least part of a protein kinase C-dependent pathway, but not pertussis toxin-sensitive G-proteins, cyclic nucleotides, eicosanoid metabolites, or phospholipase C activity. In addition, both toxins were shown to activate phospholipase A2.

Bacterial Proteins↗
PubMed1993

Percutaneous pericardiocentesis versus subxiphoid pericardiotomy in cardiac tamponade due to postoperative pericardial effusion.

In a retrospective study, 42 patients with acute cardiac tamponade due to pericardial effusion were evaluated following cardiac surgery, and the pericardial fluid was drained by one of two alternative methods: two-dimensional echocardiographic-guided pericardiocentesis (2D-echo) or subxiphoid surgical pericardiotomy. During the first period (from 1982 to 1986), one of the two methods was chosen by the treating physicians, whereas in the second period (from 1986 to 1991), 2D-echo-guided pericardiocentesis was the treatment of choice. Percutaneous pericardiocentesis was performed using local anesthesia in 29 patients. A Tuohy needle was inserted at the left xipho-costal junction and, when fluid was obtained, 6 mL of saline solution was injected during 2D-echo contrast monitoring, and a multiple-hole, 6F, 30-cm catheter was inserted by means of a guidewire and positioned into the posterior pericardium, as near as possible to the atrioventricular groove. Complete drainage of pericardial fluid by percutaneous pericardiocentesis was obtained in 26 patients (89%). This procedure also allowed the evacuation of posterior and loculated effusions. Complications included two right ventricular punctures, which were immediately recognized by 2D-echo contrast and produced no serious consequences. Sixteen patients who underwent surgical pericardiotomy had complete evacuation of pericardial fluid without major complications (two of them suffered atrial arrhythmias during the procedure). The average amount of fluid drained, as well as the localization of the effusions, were the same for both groups. 2D-echo-guided pericardiocentesis was found to be a useful, safe, and simple technique. It can be used as an alternative treatment to subxiphoid pericardiotomy for cardiac tamponade due to postoperative pericardial effusions.

Adult↗
PubMed1993

Induction of phagocytic behaviour in human epithelial cells by Escherichia coli cytotoxic necrotizing factor type 1.

Cytotoxic necrotizing factor type 1 (CNF1) from strains of pathogenic Escherichia coli induces in human epithelial HEp-2 cells, a profound reorganization of the actin cytoskeleton into prominent stress fibres and membrane ruffles. We report here that this process is associated with induction of phagocytic-like activity. CNF1-treated cells acquired the ability to ingest latex beads as well as non-invasive bacteria such as Listeria innocua, which were taken as a model system. Uptake of bacteria was similar to pathogen-induced phagocytosis, since L. innocua transformed with DNA coding for the pore-forming toxin listeriolysin O behaved, with respect to intracellular growth, like the invasive, pathogenic species L. monocytogenes. Our results raise the possibility that, in vivo, pathogenic CNF1-producing E. coli may invade epithelia by this novel induced phagocytic-like mechanism.

Actin Cytoskeleton↗
PubMed1993

Interaction of Escherichia coli cytotoxic necrotizing factor type 1 (CNF1) with cultured cells.

The cytotoxic necrotizing factor type 1 (CNF1) from E. coli causes necrosis in rabbit skin and multinucleation in cultured cells. Cells exposed to CNF1 were characterized by changes in actin organization, mainly consisting in the presence of well-developed stress fibers and membrane ruffles. The interaction of CNF1 with the cell cytoskeleton probably promotes the cell spreading and interferes with the cytokinesis, leading to the formation of giant multinucleated cells.

Actins↗
PubMed1993

[The improvement of the Doppler echocardiographic method for the estimation of pulmonary systolic pressure].

The formulas currently utilized for noninvasive evaluation of right ventricular systolic pressure (RVSP) include right ventricular-right atrial pressure gradient (RV-RAG) and right atrial pressure (RAP). The former is expressed by trans-tricuspid systolic flow velocity, the latter is generally assumed. We recently observed that ultrasound estimation of RAP through inferior vena cava collapsibility index (CI) may help in the choice of the more appropriate formula for the evaluation of RVSP. However, these traditional methods (method A:RV-RAG + 10; method B:RV-RAG x 1.1 + 14) have limitations, particularly when RAP is low. The present study was undertaken to improve noninvasive estimation of RVSP through new formulas based on CI prediction of RAP. One hundred and four patients, in whom tricuspid regurgitation was adequately documented with CW-Doppler, were included in this study. They were classified into 3 groups: Group 1 with CI > 45%, Group 2 with CI < or = 35%, Group 3 with CI 35-45%. RVSP was evaluated by 3 different methods: A, B, and C. Method C was based on CI, assigning 6, 16, or 9 mmHg to RAP (respectively, the mean values in the 3 groups of our previous study). Results indicate that method C improves noninvasive estimation of RVSP in Group 1 and Group 2, with respect to other methods, with reduction of the SEE and of the mean difference of the t-test between hemodynamic and echographic values. In Group 3, Doppler estimation by method A and C, and catheter measurements are comparable, whereas method B significantly overestimates the actual value.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

[Late ventricular potentials in the post-infarct patient. A follow-up at 4 years].

We performed a prospective study to evaluate the prognostic significance and the natural history of late ventricular potentials (LPs) in 209 patients (165 males and 44 females; mean age 59.8 +/- 10 years) who survived acute myocardial infarction. Signal-averaged electrocardiograms (SA-ECGs) were performed before hospital discharge (16 +/- 5 days) and after four years (mean follow-up 42 +/- 7 months). SA-ECGs were processed using a 40 Hz high-pass bidirectional filter. Duration of "filtered" QRS (normal value < 120 msec), duration of the low-amplitude signals (n.v. < 39 msec) and last 40 msec voltage of the QRS complex (n.v. > 20 microV) were measured. LPs were defined as the presence of two or more abnormal values. In addition, 24-hour Holter monitoring was performed in all patients, and left ventricular ejection fraction (LVEF) was determined by scintigraphy in 120 (57.4%). Sixty patients (28.7%) had LPs before hospital discharge (group 1), and 149 (71.3%) had normal SA-ECGs (group 2). During the follow-up period there were 10 arrhythmic events, 7 of which were sudden deaths, and three cases of sustained ventricular tachycardia. SA-ECG was repeated in 141 patients (68%). The mean values of SA-ECG's parameters did not change significantly between the two controls, and the correlation was good for all of them. Despite this, spontaneous normalization of SA-ECGs occurred in 21 patients (60%) and the subsequent appearance of LPs was seen in 13 (12%); in these latter, the SA-ECG's parameters measured before hospital discharge were "borderline" and significantly different from those who did not change. The sensitivity of SA-ECG as a predictor of arrhythmic events was 80% and the specificity 74%. Patients with arrhythmic events had a longer filtered QRS (126 +/- 33 vs 103 +/- 12 msec; p < 0.001), longer duration of the low-amplitude signals (57 +/- 23 vs 32 +/- 11 msec; p < 0.001), lower voltages (17 +/- 8 vs 36 +/- 24 microV; p < 0.001), and, moreover, higher peak CK values, lower LVEF and higher value of Lown modified class. In conclusion, SA-ECG confirms its value in identifying patients at risk of arrhythmic events after myocardial infarction. SA-ECG recordings taken before the discharge can be used to predict serial changes during follow-up.

Aged↗
PubMed1992

Cell injury and death caused by bacterial protein toxins.

Bacterial protein toxins, such as Clostridium difficile toxin A and the Escherichia coli cytotoxic necrotizing factor 1 are known to exert their cytotoxic action via a modification of some cytoskeletal components. The changes in actin organization caused by these toxins appear to be the primary events in the mechanism leading to cell death.

Actins↗
PubMed1992

Exercise performance in patients with uncomplicated essential hypertension. Effects of nifedipine-induced acute blood pressure reduction.

In untreated patients with uncomplicated essential hypertension, exercise induces an abnormal increase in blood pressure; the influences of this increase on exercise were evaluated by a cardiopulmonary exercise test (CPX) performed in control conditions (step 1) and during acute blood pressure reduction (step 2). Patients were classified as (1) normotensive (resting diastolic blood pressure [BPd] less than 90 mm Hg; n = 14), (2) mildly hypertensive (BPd of 90 to 104 mm Hg; n = 9), and (3) moderately to severely hypertensive (BPd greater than or equal to 105 mm Hg; n = 16). For the three groups, peak mean blood pressure during exercise was 125 +/- 5 mm Hg (mean +/- SEM), 144 +/- 3 mm Hg (p less than 0.01 vs normotensive), and 161 +/- 4 mm Hg (p less than 0.01 vs normotensive and p less than 0.01 vs mild hypertension), respectively. Oxygen consumption (VO2) at peak exercise and at ventilatory anaerobic threshold was 26.1 +/- 1.1 and 17.2 +/- 0.5 ml/min/kg, 25.4 +/- 1.1 and 16.9 +/- 0.8 ml/min/kg, and 26.4 +/- 1.3 and 17.5 +/- 1.2 ml/min/kg in normotensive subjects, those with mild hypertension, and those with moderate to severe hypertension, respectively. Fourteen normotensive subjects, six with mild hypertension, and nine with moderate to severe hypertension participated to step 2 (nifedipine vs placebo, double-blind crossover). Nifedipine reduced blood pressure at rest and at peak exercise in those with hypertension. Peak exercise VO2 was unaffected by nifedipine in both normotensive subjects and those with hypertension. With nifedipine, ventilatory anaerobic threshold occurred earlier and at a lower VO2 in mild and in moderate to severe hypertension (delta VO2 = -1.9 and -2.4 ml/min/kg, respectively). These findings might be due to nifedipine-induced redistribution of blood flow during exercise and might be the reason for the complaint of weakness after blood pressure reduction in hypertensive subjects.

Blood Pressure↗
PubMed1992

Clostridium difficile toxin A induces multinucleation in the human leukemic T cell line JURKAT.

Clostridium difficile toxin A is a cytotoxic enterotoxin known to be active on all mammalian cell lines tested up to now. It induces a disruption of the cytoskeleton, particularly the microfilament system, leading to inhibition of cell proliferation. Here, we describe some effects of toxin A on the leukemic T cell line JURKAT. Cells exposed to the toxin did not divide, as cell numbers remained constant for 3 days in the presence of 0.5 to 1.0 micrograms/ml of the toxin. However, these cells were found to become multinucleated, a phenomenon which was time- and dose-dependent. After treatment for 72 h with 0.5 micrograms/ml toxin A, 95% of the cells were multinucleated and had a considerably increased cell diameter. These effects in JURKAT cells were partially reversible upon removal of the toxin within 12 h after the beginning of toxin exposure, but irreversible after 24 h of toxin treatment. These results suggest a continuing nuclear division in the absence of cytoplasmic division, i.e., an effect of toxin A on contractile ring formation. The JURKAT cell is the first cell type reported to respond to toxin A with multinucleation.

Bacterial Toxins↗
PubMed1991

Enhancement of cell-mediated cytotoxicity by Clostridium difficile toxin A: an in vitro study.

Cells from the immune system exhibiting cytotoxic activity are able to kill tumor or infected cells in a major histocompatibility complex-restricted (cytotoxic lymphocytes) or non-restricted (natural killer cells) manner. In order to exert such a cytotoxicity they have to bind the target cell and release cytotoxic factors able to induce target cell death. Treatment of human peripheral blood mononuclear cells with toxin A from Clostridium difficile induced an enhancement of the cytotoxic efficiency of these effector cells. Morphological analysis of effector/target cell pairs seems to suggest that this could be related to an increased ability of cytotoxic effectors to establish close and intertwined contacts with target cells. These contacts involve adhesion molecules and lead to the formation of a "closed chamber" which probably improves the efficacy of lytic factors and results in an increased cytotoxicity.

Bacterial Toxins↗
PubMed1991

Clostridium difficile toxin A and its effects on cells.

Clostridium difficile toxin A in its native form is a high molecular weight (520-540 K) aggregate with five major biological activities. It is lethal, enterotoxic, cytotoxic and cytotonic, and induces hemagglutination of rabbit red blood cells. Possibly these activities are contained in separate components. A major subunit of c. 230-310 K has been defined but lower molecular weight components cannot be excluded. The major component has been cloned, and sequence analysis indicated a complicated pattern of repeating sequences in the C-terminal third of the molecule. This review deals mainly with the effects of toxin A on cultured cells. Most mammalian cells are sensitive to toxin A whose major effect is to stop cell division irreversibly. The toxin binds via its repeat sequences to a trisaccharide receptor expressed on rabbit red cells and on brush border membranes from hamster intestine. This receptor seems to be functional in the hemagglutination reaction and the enterotoxicity. Its role in the cytotoxic effect of the toxin is not clear, but no other receptor structure has as yet been identified. In order to exert its cytotoxic (antiproliferative) effect toxin A must first be internalized by endocytosis. Thus a latency period of at least 30 min after toxin binding to cells is consistently observed, and all cytotoxic effects can be prevented by blocking the endocytosis pathway. The first microscopically visible signs of cytotoxicity consist in retraction and rounding of intoxicated cells. In addition the nucleus becomes polarized to one side of the cell while other cell organelles are not significantly affected. These morphological changes seem to be the consequence of a cytoskeletal rearrangement, mainly involving some components of the microfilament system. Inhibition of macromolecular syntheses as well as permeabilization of the plasma membrane may follow the early cytoskeletal effects and finally lead to cell death. Attempts to identify metabolic pathways of significance in the cytotoxicity suggest that the cytosolic level of Ca2+ is not important, thus excluding certain mechanisms for cell killing. In this respect the cytotoxic mode of action of toxin A clearly differs from that of toxin B. However, the biochemical basis for the antiproliferative effect of toxin A remains unknown.

Animals↗
PubMed1991

[The noninvasive estimation of right atrial pressure improves the Doppler evaluation of the pulmonary systolic pressure].

The right ventricular systolic pressure can be evaluated with the Doppler method through the right ventricular-atrial gradient (RV-RA gradient) and the right atrial pressure. The former is expressed by the transtricuspid velocity of flow, the latter is generally assumed. In 50 patients with elevated pulmonary pressure we tested whether ultrasounds may be utilized for the evaluation of the right atrial pressure, and whether the derived values contribute to improve the accuracy of the method. We estimated the right ventricular systolic pressure with method A: RV-RA gradient + 10; and method B: RV-RA gradient x 1.1 + 14, where 10 and 14 are the assumed right atrial pressure (mmHg). Through the collapsibility index of the inferior vena cava, taken as an ultrasound-derived index of right atrial pressure, we were able to identify 3 groups of patients with normal (Group 1, 14 cases), elevated (Group 2, 21 cases) and moderately elevated (Group 3, 15 cases) right atrial pressure, respectively. In them the right ventricular systolic pressures obtained with both method A and method B were compared to those derived with catheter. In Group 1 the non-invasive values were significantly closer to the invasive ones when calculated with method A; the same was true of method B in Group 2. In Group 3 the accuracy of the 2 methods was similar. We conclude that ultrasound assists in the non-invasive approximation of the right atrial pressure as well as in the choice of the appropriate formula, so that Doppler estimation of the right ventricular systolic pressure is improved.

Adult↗
PubMed1991

Suicide behavior of target cells after binding with natural killer cells.

Human natural killer (NK) cell activity seems to be related to the integrity and function of the cytoskeletal apparatus. It has been hypothesized that microfilaments and microtubules play a pivotal role. In particular, the binding of the NK cell to the target cell requires microfilament integrity, and the lysis of bound targets seems to depend on microtubule assembly. We focused on the changes occurring in cytoskeletal elements and surface structures of NK cells and of target cells highly sensitive to NK activity (K562). Our observations, performed by fluorescence and scanning electron microscopy, besides confirming a rearrangement of the cytoskeletal apparatus in the effector cell, provide evidence that target cell cytoskeletal elements are involved in NK cell function. In K562 cells, after binding with NK cells, there is marginal rearrangement of actin and polarization of tubulin and vimentin in the contact regions, accompanied by modification of surface structures. These findings suggest that the target cell plays an active role in its own death by participating in the formation of an extended area of intimate contact with the killer cell. In addition, they lend credence to the surprising proposal that NK cells may induce a suicide mechanism in target cells.

Cell Survival↗
PubMed1990

Doppler assessment of left ventricular filling pattern in silent ischemia in patients with Prinzmetal's angina.

Spontaneous angina is an ideal condition in which to study left ventricular (LV) dysfunction induced by acute myocardial ischemia. In 6 patients with Prinzmetal's angina, LV diastolic function during 16 episodes of spontaneous angina was studied by simultaneous recordings of electrocardiographic (ECG), echocardiographic and hemodynamic parameters. In particular, pulsed Doppler echocardiography measured peak velocity of early (E) and late (A) transmitral flow and E/A ratio, as indexes of relative early versus late LV filling. During the ischemic attacks, the time sequence of pulsed Doppler echocardiographic and ECG changes showed 3 distinct phases: (1) "waxing phase: transmitral flow changes with minimal ECG modifications (E/A = 0.85 +/- 0.1); (2) "steady" phase: maximal ECG changes (E/A = 0.9 +/- 0.1); and (3) "waning" phase: regression of the ECG changes (E/A = 1.26 +/- 0.15). In each phase, E/A ratio showed a significant difference from the baseline value (E/A = 1.17 +/- 0.2) as a result of changes in E, suggesting that myocardial ischemia affects mainly the early phase of diastole. In the waxing phase, LV diastolic dysfunction preceded systolic abnormalities, as documented by a significant reduction of E/A ratio in the absence of alterations in LV ejection fraction, as well as in systemic arterial and pulmonary wedge pressures. Finally, all the recorded parameters were consistent with LV "contractile rebound" occurring in the waning phase and affecting both diastole and systole.

Angina Pectoris, Variant↗
PubMed1990

Surface blebbing and cytoskeletal changes induced in vitro by toxin B from Clostridium difficile: an immunochemical and ultrastructural study.

Clostridium difficile toxin B is a powerful cytopathic agent without enterotoxic activity which is believed to be involved in the pathogenesis of pseudomembranous colitis. Up until today, the mechanisms of toxin B cytotoxicity have not been elucidated. The results of in vitro studies performed on different cell lines by means of immunocytochemical and ultrastructural methods are reported here. Low doses (0.15 ng/ml) of toxin B cause cell rounding and arborization. Higher doses (up to 15 micrograms/ml) induce cell rounding and appearance of numerous surface protrusions with blister or bulb-like features. These "blebs" belong to the potocytotic type, the bleb matrix being devoid of cytoplasmic organelles and filled with ribosomes only. Furthermore, a peculiar role of cytoskeletal apparatus in this phenomenon has been detected. In fact, morphological rearrangement occurs in cytoskeletal elements, mainly represented by the presence, in the blebs, of tubulin and of the actin-binding proteins alpha-actinin, filamin, and calmodulin, while actin and intermediate filaments, keratin and vimentin, appear to be absent. Moreover, beta 2-microglobulin, considered as a surface protein marker, seems to undergo changes in its expression, being absent over the blebbing surface. The results of this study may support the view that C. difficile toxin B affects one or more subcellular components that regulate the structure and function of the actin cytoskeleton.

Bacterial Proteins↗