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Biomedical subjects

M Micheletti

Publications and source records attributed to M Micheletti.

At least 19 recordsLinked to original sources
PubMed2005

Microscale process evaluation of recombinant biocatalyst libraries: application to Baeyer-Villiger monooxygenase catalysed lactone synthesis.

Microscale processing techniques are rapidly emerging as a cost- effective means for parallel experimentation and hence the evaluation of large libraries of recombinant biocatalysts. In this work, the potential of an automated microscale process is demonstrated in a linked sequence of operations comprising fermentation, enzyme induction and bioconversion using three whole-cell biocatalysts each expressing cyclohexanone monoxygenase (CHMO). The biocatalysts, Escherichia coli TOP 10 [pQR239], E. coli JM107 and Acinetobacter calcoaceticus NCIMB 9871, were first produced in 96-deep square well fermentations at various carbon source concentrations (10 and 20 g L(-1) glycerol). Following induction of CHMO activity biomass concentrations of up to 6 gDCW L(-1) were obtained. Cells from each fermentation were subsequently used for the Baeyer-Villiger oxidation of bicyclo[3.2.0]hept-2-en-6-one, cyclohexanone and cyclopentanone. Each bioconversion was performed at two initial substrate concentrations (0.5 and 1.0 g L(-1)) in order to simultaneously explore both substrate specificity and inhibition. The microscale process sequences yielded quantitative and reproducible data for each biocatalyst on maximum growth rate, biomass yield, initial rate of lactone formation, specific biocatalyst activity and bioconversion yield. E. coli TOP 10 [pQR239] was demonstrated to be an efficient biocatalyst showing substrate specificities and substrate inhibition effects in line with previous studies. Finally, in order to show that the data obtained with E. coli TOP 10 [pQR239] at microwell scale (1,000 microL) could be related to larger scales of operation, the process was performed in a 2-L stirred-tank bioreactor. Using conditions designed to enable microwell kinetic measurements under none oxygen-limited conditions, the fermentation and bioconversion data obtained at the two scales showed good quantitative agreement. This study therefore confirms the potential of automated microscale experimentation for the whole-process evaluation of recombinant biocatalyst libraries and the specification of pilot and process scale operating conditions.

Acinetobacter calcoaceticus↗
PubMed2005

A novel pattern of fast calcium oscillations points to calcium and electrical activity cross-talk in rat chromaffin cells.

Slow oscillations of cytosolic calcium ion concentration - [Ca(2+)](c) - typically originate from release by intracellular stores, but in some cell types can be triggered and sustained by Ca(2+) influx as well. In this study we simultaneously monitored changes in [Ca(2+)](c) and in the electrical activity of the cell membrane by combining indo-1 and patch-clamp measurements in single rat chromaffin cells. By this approach we observed a novel type of spontaneous [Ca(2+)](c) oscillations, much faster than those previously described in these cells. These oscillations are triggered and sustained by complex electrical activity (slow action potentials and spike bursts), require Ca(2+) influx and do not involve release from intracellular stores. The possible physiological implications of this new pathway of intracellular signalling are discussed.

Action Potentials↗
PubMed2003

Prolonged treatment with imatinib mesylate in patients with advanced chronic myeloid leukemia causes a reduction of bcr/abl mRNA levels independent of cytogenetic response.

Bcr/abl mRNA levels were monitored in 13 patients with chronic myeloid leukemia receiving imatinib mesylate over a period of 78 weeks. During treatment median bcr/abl mRNA levels progressively declined from 77.2 normalized dose (nD) at baseline to 11.28 nD after 13 weeks ( P<0.05) and to 1.28 nD after 78 weeks ( P<0.05). After 13 weeks, bcr/abl mRNA levels were significantly lower in cytogenetic responders compared to nonresponders ( P<0.05), but subsequent decrease in the transcript levels caused the loss of any correlation to the cytogenetic status. These results suggest that bcr/abl mRNA levels may reflect cytogenetic response only during the early phases of imatinib therapy.

Antineoplastic Agents↗
PubMed2001

Calcium protects differentiating neuroblastoma cells during 50 Hz electromagnetic radiation.

Despite growing concern about electromagnetic radiation, the interaction between 50- to 60-Hz fields and biological structures remains obscure. Epidemiological studies have failed to prove a significantly correlation between exposure to radiation fields and particular pathologies. We demonstrate that a 50- to 60-Hz magnetic field interacts with cell differentiation through two opposing mechanisms: it antagonizes the shift in cell membrane surface charges that occur during the early phases of differentiation and it modulates hyperpolarizing K channels by increasing intracellular Ca. The simultaneous onset of both mechanisms prevents alterations in cell differentiation. We propose that cells are normally protected against electromagnetic insult. Pathologies may arise, however, if intracellular Ca regulation or K channel activation malfunctions.

Animals↗
PubMed1999

Lidocaine inhibition of the hyperpolarization-activated current (I(f)) in sinoatrial myocytes.

The aim of this study was to provide information on the dose dependence and biophysical details of lidocaine blockade of the hyperpolarization-activated current (I(f)) in the sinoatrial node. Isolated rabbit sinoatrial myocytes were patch-clamped in the whole-cell configuration at 36+/-0.5 degrees C, in the presence of 1 mM Ba2+ and 2 mM Mn2+ to minimize contamination by K+ and Ca2+ currents, respectively. Lidocaine inhibited I(f) dose-dependently with a maximal inhibition of 69.5% at 75 microM and a half-maximal effect at 38.2 microM. Lidocaine reduced the conductance of fully activated I(f), without affecting the current reversal potential; the blocking effect was independent of membrane potential. Voltage dependence of I(f) activation gating was not affected by lidocaine, whose effect was independent of use and rate. Lidocaine did not modify the time course of I(f) activation. At therapeutic concentrations, lidocaine significantly inhibited I(f) by reducing fully activated channel conductance. Lack of voltage and rate dependence of effect differentiates lidocaine from most of other blockers of this current.

Animals↗
PubMed1997

Ionic currents during sustained pacemaker activity in rabbit sino-atrial myocytes.

1. The contribution of various ionic currents to diastolic depolarization (DD) in rabbit sinoatrial myocytes was evaluated by the action potential clamp technique. Individual currents were identified, during sustained pacemaking activity reproduced under voltage clamp conditions, according to their sensitivity to specific channel blockers. 2. The current sensitive to dihydropyridines (DHPs), blockers of L-type Ca2+ current (ICa,L), was small and outward during most of DD. Diastolic DHP-sensitive current was affected by changes in the driving force for K+, but it was insensitive to E-4031, which blocks the current termed IK,r; it was abolished by cell dialysis with a Ca2+ chelator. 3. The current sensitive to 2 mM Cs+ (ICs), a blocker of hyperpolarization-activated current (I(f)), was inward during the whole DD and it was substantially larger than the net inward current flowing during this phase. However, diastolic IK,r, identified in the same cells as the current sensitive to the blocker E-4031, exceeded ICs 2-fold. 4. These findings suggest that: (a) Ca2+ influx during the pacemaker cycle increases a K+ conductance, thus inverting the direction of the net current generated by L-type Ca2+ channel activity during DD; (b) the magnitude of I(f) would be adequate to account fully for DD; however, the coexistence of a larger IK,r suggests that other channels besides I(f) contribute inward current during this phase.

Action Potentials↗
PubMed1996

G-CSF-mobilized peripheral blood progenitor cells for allogeneic transplantation of resistant or relapsing acute leukemias.

Peripheral blood progenitor cells (PBPC) were mobilized by G-CSF in normal HLA identical siblings and used for allogeneic transplantation in eight patients with refractory or relapsed acute leukemias. G-CSF administration was well tolerated and no significant side-effects were registered. The number of circulating WBC peaked at day 5 after G-CSF (range: 22.6-74.6 x 10(9)/l) with a median of 65 CD34+ cells/microl (38-155). As a consequence of leukaphereses, platelets progressively decreased, reaching the nadir after the last procedure (84-205 x 10(9)/l). A mean of two aphereses (1-3) were performed between day +4 and +7 during which 10 liters of blood were processed each time by a cell separator. Conditioning regimens were: fractionated total body irradiation (FTBI) plus either HDAra-C (2 g/m2 x 2/day for 6 days) (n=5) or melphalan (110 mg/m2) (n= 1) and busulfan (4 mg/kg/day for 4 days) and melphalan (110 mg/m2) in two patients relapsed after a previous FTBI-based allogeneic or autologous BMT. At transplantation, a median of 6.9 x 10(6) CD34+ cells/kg (4.2-16.5) and 279 x 10(6) CD3+ cells/kg (161-786) were infused. Engraftment of both neutrophils (> or v=1.5 x 10(9)/l) and platelets (> or v=20 x 10(9)/l) was observed in all patients after a median time of 18 days (range: 11-20 and 10-26, respectively). The evaluation of engraftment after transplantation was accomplished by PCR analysis of four hypervariable genomic regions (VNTR) (ApoB, ApoC2, YNZ-22, and MCT 118) which allowed to demonstrate the condition of donor chimaera in all patients after transplantation. As far as the clinical outcome, two patients died of interstitial pneumonitis at day +243 and +69 and two patients died at day +62 and +152 of pulmonary aspergillosis. Four patients remain alive in remission between day +88 and +287 with grade 0-l GVHD. Allogeneic PBPC transplantation is associated with a complete hematologic recovery and despite the infusion of a large amount of mature CD3+ lymphocytes, apparently acute GVHD is not worse than expected after transplantation of bone marrow progenitors.

Adolescent↗
PubMed1989

[Use of diverse prosthetic materials in preparation of sequential bypasses in combined lesions of the aorto-iliac-femoral axis].

A series regarding three years of surgery is analysed with regard to the preparation of four sequential by-passes out of 23 aorto-bifemoral revascularisations. Indications and the eminently technical aspects are discussed, the latter consisting of the adoption of two types of different prostheses sutured one to the other, such as the Dacron and the PTFE prostheses, which proved to be very compatible and long-lasting. The results were excellent as is testified by the follow-up.

Aorta, Abdominal↗
PubMed1989

[Stapler reconstruction after total gastrectomy contrasted with manual anastomosis].

A personal series (1985-1987) of 22 cases of total gastrectomy for cancer is analysed, a comparison being made between 11 cases treated with manual anastomosis and 11 reconstructed using a stapler. The advantages and disadvantages of the various techniques are examined and although no substantial difference is noted between the two reconstructive modalities, at least as regards morbidity and mortality, stress is laid on the unquestionable advantages of mechanical staplers. These are essentially speed of execution, suture perfection and excellent long-term results.

Esophagoplasty↗
PubMed1989

[Follow-up of revascularization. Our echotomographic experience with 20 aorto-femoral by-pass patients].

Twenty patients submitted to aortobifemoral bypass and controlled every six months with echotomography, echoflow and digitalised angiography were followed up and the results reported. The value of the technique emerges clearly. It is risk-free and possesses high sensitivity for the analysis of peripheral vascular anastomosis. The limitations of the technique would appear to be connected solely to poor evaluation of the aortic anastomosis.

Angiography, Digital Subtraction↗
PubMed1989

[Methods for preparing patients to vascular surgery. Our experience].

A personal series covering two years of vascular surgery involving 58 cases without problems of sepsis has been examined. The modalities employed for preventing wound infections and prosthesis suppuration when it occurred and consisting of showers, antibiotic prophylaxis and shaving are reported. In conclusion it is maintained that a specific, disciplined protocol must be followed in all candidates for prosthesis.

Anti-Bacterial Agents↗
PubMed1981

[Frequency and semeiological evolution of epileptic seizures occurring between 40 and 65 years of age (author's transl)].

458 patients who had their first epileptic fit between the ages of 40 and 65 are classified into 5 groups according to the seizure symptomatology: when the symptomatology remains unchanged, the frequency of fits is less than 1 per month in 84% of generalized fits and more than 1 per month in 52% of focal fits. When the symptomatology changes, the frequency of fits is less than 1 per month when the inaugural fit is generalized (23 out of 27) and more than 1 per month when the inaugural fit is focal (15 out of 21). Modifications of the symptomatology correlate positively with a prevalence of tumor aetiology. Primary generalized epilepsies are rare (4.4%). Non-specific secondary generalized epilepsies (including vascular, metabolic or toxic encephalopathies) account for 24.4% of the cases. Focal epilepsies are the most common form (40.7%), elementary fits being four times more frequent than complex fits.

Adult↗
PubMedDate not supplied

[Semiological comparison of spontaneous and bemegride-induced epileptic seizures (author's transl)].

The authors view an epileptic seizure as a series of symptoms which they can localize on the bases of data taken from stereoelectroencephalography literature. They reconstruct and compare the presumed organization (origin and propagation) of the discharge in 100 epileptic subjects. Both spontaneous and megimide-induced seizures are considered. The results involve 34 subjects with quite similar spontaneous and induced seizures. Comparison of the two critical modalities show that : 1) There is no variation in the chronological relationship of the symptoms. 3) There are differences in the symptomatology. These differences may be interpreted as non-uniform response of involved structures to the source of activation, or as involvement of new structures.

Bemegride↗