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Biomedical subjects

V Viti

Publications and source records attributed to V Viti.

At least 19 recordsLinked to original sources
PubMed1992

Prony-Householder method applied to 31P NMR signals: II. Study of conjugates of ara-AMP with lactosaminated albumin.

Conjugates of 9-beta-D-arabinofuranosyladenine 5'-monophosphate (ara-AMP) with lactosaminated albumin (L-SA), obtained by using two different coupling procedures, produce antibodies in rats and mice which display only a small cross-reactivity. 31P NMR signals from the two conjugates have been examined to clarify whether different lysine and histidine residues are involved in the two reaction pathways. The occurrence of different chemical shifts and linewidths between the two conjugates, as evidenced by processing the signals with the Prony-Householder method, indicates the formation of two different complexes.

Animals↗
PubMed1992

23Na-NMR study of cation cotransport in human red blood cells.

Na(+)-K+ cotransport in human erythrocytes from healthy subjects has been studied by means of 23Na-nuclear magnetic resonance (NMR) in the presence of the anionic paramagnetic shift reagent dysprosium (III) tripolyphosphate [Dy(PPP)2(7-)]. The intra- and extracellular 23Na-NMR signals were well separated, giving values of 6 +/- 1 mM for internal sodium concentration. Determination of the furosemide-sensitive Na+ efflux, in the presence of ouabain, was obtained by correlating the chemical shift variation of the external signal with changes in external Na+ concentration. For this purpose, calibration curves were generated. The values of the maximum efflux velocity (Vmax; 0.29-1 mmol.h-1.l cells-1) measured in 10 healthy adult male subjects were found to be within the range of values obtained by other authors. The NMR method proposed for the study of Na(+)-K+ cotransport is relatively simple and allows quick evaluation of cotransport Vmax values for a number of samples, being a good candidate for the study of this transport mechanism in the presence of different pathologies.

Biological Transport↗
PubMed1992

Localized and transient changes in plasma membrane fluidity during in vitro myoblast fusion: an 1H-NMR study.

High resolution proton NMR was used to study the cell surface molecular events which take place during in vitro myoblast differentiation and fusion. The CH3 and (CH2)n spectral signals were followed throughout in vitro myogenic development. The results show that although both the T1 and T2 relaxation times of the CH3 and (CH2)n groups are sensitive to the fusion process, T1 is the most sensitive. Both T1 of CH3 and (CH2)n increased before fusion indicating a higher degree of molecular motion and then returned to their original values. These results demonstrate how mobile lipid domains observed with proton NMR can be used to study the changes taking place during myoblast differentiation, particularly myoblast membrane fusion.

Animals↗
PubMed1991

Interaction of HIV-1 with susceptible lymphoblastoid cells. 1H NMR studies.

Different strains of HIV susceptible lymphoblastoid cells have been infected by HIV-1 and examined by means of 1H NMR spectroscopy at different times after infection, taking advantage of the presence of high resolution lipid signals from the plasma membrane of tumor cells. A transient decrease in intensity of fatty acid signals, originated by changes in membrane structure, has been observed early after viral infection. Marked alterations in membrane-dependent steps of phospholipid synthesis can also be inferred by the observed transient depression in peaks from choline-based metabolites. Spectral modifications deriving from changes in lipid metabolism are also produced both in infected cells a few days after infection and in permanently infected cells. 1H NMR can, therefore, monitor structural and metabolic effects induced by HIV infection.

Cell Membrane↗
PubMed1991

Metabolic and structural effects of HIV infection in human peripheral blood mononuclear cells can be monitored with 1H NMR spectroscopy.

Infection of human peripheral blood lymphocytes by human immunodeficiency virus type 1 (HIV-1) was investigated by means of 1H nuclear magnetic resonance spectroscopy, taking advantage of the presence of signals from fluid lipid domains in the membrane of stimulated lymphocytes. A transient decrease of the lipid methylene signal intensity was observed at the time of HIV internalization, monitoring a general rearrangement of membrane structure associated with virus entry. A similar effect was also observed a few days after infection, when HIV particles are released by infected cells as demonstrated by high reverse transcriptase activity in cell supernatant. Signals arising from choline-based metabolites were also affected by HIV infection, indicating a possible slowing down of phospholipid synthesis.

Cell-Free System↗
PubMed1990

Effects of decreased pH on membrane structural organization of Escherichia coli grown in different fatty acid-supplemented media: a 31P NMR study.

Total membranes from Escherichia coli cells grown in different fatty acid-supplemented media have been examined by 31P NMR at different pH values. The isolated inner and outer membranes were also studied and compared to the liposomes formed with the corresponding extracted lipids. While the liposomes show structures that are correlated with lipid composition, degree of fatty acid unsaturation, and pH, the membrane structure is mainly bilayer. The presence of two bilayer phases characterized by different chemical shift anisotropy values (delta nu csa) is detectable at neutral pH; a perturbation of the bilayer phase characterized by the smallest delta nu csa is produced by low pH. Moreover, an isotropic peak is always present in the membrane NMR spectra: its attribution to cardiolipin molecules is discussed on the basis of digestion experiments with phospholipase C.

Cell Membrane↗
PubMed1990

A new glucose-clamp algorithm--theoretical considerations and computer simulations.

The commonly used setup of an automatic glucose-clamp was analyzed as a control system, modeling the measuring device and the patient in a simple but effective way. Strict limits in response time, parasitic oscillation amplitude, and accuracy were defined in order to approach the physician's requirements. We developed a new control algorithm and defined the gain coefficients which can lead the system within these limits. Computer simulations with model parameters from literature (patient) and from experimental data (measuring device) are presented. Preliminary in vivo trials are also presented.

Algorithms↗
PubMed1989

Biochemical and NMR studies on structure and release conditions of RNA-containing vesicles shed by human colon adenocarcinoma cells.

Large amounts of particulate material, mostly lipid vesicles, are released by human colon adenocarcinoma HCT-8R cells when they are packed at high density in saline solution. RNA is also present in the released structures. Vesicle sheding is displayed only by healthy and viable cells. The process, in our experimental conditions, lasts up to 40 min, and can be restored by supplementing cells with nutrients and oxygen. RNA and lipids give rise to IH and 3IP NMR signals. The process is somehow related to a thermotropic transition observed by means of IH NMR spectroscopy for peculiar lipid domains in the plasma membrane. Analysis of 3IP NMR spectra of the phosphodiester groups, upon pH variation, indicates strong interaction between RNA and proteins in an assembled structure. A constant amount of polyA+ RNA can be recovered from the vesicles. The electrophoretic pattern and in vitro protein synthesis indicate that mRNA can be isolated as a functionally active molecule with a major 5 Kb fraction.

Adenocarcinoma↗
PubMed1989

Characterization of vesicles, containing an acylated oligopeptide, released by human colon adenocarcinoma cells. NMR and biochemical studies.

RNA-containing vesicles, recovered from the supernatant of high-density cell samples of human colon carcinoma, produce a high-resolution 1H NMR spectrum of lipids characterized by isotropic tumbling; these vesicles contain large amounts of triglycerides and cholesterol esters. Both findings have strict analogies to what is displayed by the proteolipid complexes isolated from the sera of tumor-bearing patients [(1985) Proc. Natl. Acad. Sci. USA 82, 3455-3459; (1986) FEBS Lett. 203, 164-168]. Lipid analysis and enzymatic tests indicate that these vesicles are selected micromaps of plasma membranes, analogous to those that can be recovered from culture media in which tumor cells are grown [(1985) Dev. Biol. 3, 33-57]. Peculiar lipids, an acylated oligopeptide and a modified phospholipid, are also present in the vesicles.

Acylation↗
PubMed1988

RNA-lipid complexes released from the plasma membrane of human colon carcinoma cells.

Cultured cells from human colon adenocarcinoma spontaneously release structures which display an intense 31P NMR signal from RNA and mobile phospholipids. Furthermore, the DPH probe in the cell supernatant shows an intense fluorescence, thus indicating its insertion in lipid vesicles. The total membranes, prepared from the same cells, also release similar structures. The fatty acid chain signals from the mobile lipids, observable in the H NMR spectrum, and the fluorescence polarization of the DPH probe are strongly affected by RNAase digestion, thus indicating an association between RNA molecules and lipids. The enzymatic marker cytochrome c reductase was assayed to rule out possible contamination from endoplasmatic reticulum. A high alkaline phosphatase activity was instead found in the supernatant samples, thus indicating that the shed material is released by the plasma membrane.

Adenocarcinoma↗
PubMed1987

Mobile phospholipid signals in NMR spectra of cultured human adenocarcinoma cells.

An intense peak is visible in the phosphodiester region of the 31P NMR spectra of human colon adenocarcinoma HCT-8R cells. A signal at the same frequency, partially deriving from mobile phospholipids, is also observable in the spectra of total membranes and of perchloric acid extracts prepared from the same cells. The phosphodiester signals of glycerophosphorylcholine, glycerophosphorylethanolamine, and glycerophosphorylserine resonate at lower fields with respect to this broader peak and appear only in aged samples. Enzymatic treatments of the extracts would indicate that ribonucleic acid also contributes to the broad phosphodiester signal. Moreover, 1H NMR spectra show the presence of lipid structures, characterized by high mobility, in the cell and in the membrane samples, similar to what was already observed in other tumor cells and tissues.

Adenocarcinoma↗
PubMed1987

Effects of gamma-irradiation on the erythrocyte membrane: ESR, NMR and biochemical studies.

The effects of gamma-irradiation on resealed erythrocyte ghosts have been examined with different techniques. Phospholipid analysis reveals peroxidative damage on the polyunsaturated chains of phosphatidylethanolamine. Gel electrophoresis and ESR measurements indicate modifications of the cytoskeletal proteins. 31P Nuclear magnetic resonance data show bilayer modifications that can be interpreted as changes in lipid-protein interactions. The overall picture from the present results favours interaction between lipids and proteins in the inner monolayer of the membrane.

Cobalt Radioisotopes↗
PubMed1987

Studies of structural modifications induced by gamma-irradiation in distearoylphosphatidylcholine liposomes.

An investigation of the structural and thermodynamical modifications induced by gamma-irradiation in model membranes is reported. Differential scanning calorimetry and X-ray diffraction were used to study the different phases and associated transitions of distearoylphosphatidylcholine multilamellar liposomes after 60Co gamma-irradiation. Changes were observed in the shape of the calorimetric peaks and in the corresponding phase transition temperatures. In particular a shoulder was observed at about 20 kGy. The three phases characteristic of lecithins with identical acyl chains were detected also for the highest radiation dose. The formation of lysolecithin and stearic acid upon phospholipid degradation was observed. The lysolecithin concentration increases as a function of irradiation dose, until a saturation value is reached at 40 kGy. These results correlate quite well with those obtained for interlayer and interchain distances and for the width of the main phase transition calorimetric peak. At the highest dose (approximately equal to 80 kGy) cross-linked adjacent radicals and other molecular species are also formed. Appreciable differences, and some similarities, in the behaviour of DSPC and DPPC liposomes under gamma-irradiation were observed.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1987

All trans-retinol effects on human colon adenocarcinoma cultured cells: biological and nmr studies.

The effect of all-trans-retinol on tumor cell line HCT-8R from human colon adenocarcinoma has been examined. Growth inhibition in the absence of cytotoxic effect has been observed. T1 and T2 relaxation times of 1H NMR resonances from mobile lipid domains are shortened by adding the vitamin A to the culture medium. Furthermore, the 31P NMR phosphodiester signal, attributed to a RNA-proteolipid complex from plasma membrane, is affected by retinol treatment. A possible correlation between growth inhibition and NMR results is discussed.

Adenocarcinoma↗
PubMed1987

Nonlinear methods in spectral analysis of NMR signals from living systems.

Two autoregressive procedures, namely Burg's maximum entropy method and Prony's method, have been applied to the processing of 31P NMR signals (free induction decays) of human cells. A comparison of the main advantages obtained by using these methods in the field of the NMR spectral analysis of signals from living samples is here illustrated. Improvements in sensitivity and resolution are obtained with respect to Fourier transform method by using only very few data points.

Adenine Nucleotides↗
PubMed1979

1H NMR study on the interaction of cupric ion with ribonuclease A.

The reassignment of the 1H NMR C-2 histidine signals of the bovine pancreatic ribonuclease A has required a revision of the 1H NMR data on the role of the different histidines in their interaction with the Cu2+. The results of our measurements carried out at p2H 5.5 and 7.0 reduce the importance of His-12 as main site of interaction. At p2H 5.5 a very strong binding site involves His-119, while a weaker one contains certainly His-105. On the contrary, at p2H 7.0 the histidines 105 and 119 seem to possess binding constants of the same order of magnitude and in addition they provide stronger ligands for the Cu2+ than His-12. The comparison with X-ray data in the crystal shows numerous analogies. Finally, preliminary results on the competitive inhibition effect between the Cu2+ and 2',3'-cytidine monophosphoric acid are discussed.

Animals↗