Search PubMed⌕ Search

Biomedical subjects

S Paoletti

Publications and source records attributed to S Paoletti.

At least 37 records · Page 2Linked to original sources
PubMed1997

Noninvasive in vivo quantitative assessment of fat content in human liver.

BACKGROUND/AIMS: Since the introduction of ultrasonography, liver steatosis has become an increasingly frequent diagnosis. Both ultrasonography (US) and computerized tomography (CT) provide qualitative rather than quantitative assessment of fatty infiltration. The objective of this study was to develop a noninvasive method for the quantification of the hepatic fat content in vivo. A test object containing solutions with CT scan density (CTD) similar to normal liver ("liver-equivalent") or "fat-equivalent material" in variable proportions was prepared to measure patients with variable degrees of steatosis in vivo. RESULTS: A linear correlation (r=0.99, p<0.001) linked CTD and the increasing percentage of fat-equivalent material. A CTD calibration curve was derived as a reference for the in vivo determinations. In 29 consecutive patients with steatosis diagnosed by histology, CTD was linearly correlated (r=0.83, p<0.001) with the hepatic fat content (HFC) expressed as percent of the whole liver, obtained by a computerized histomorphometric analysis. Based on the calibration curve obtained in 29 subjects who underwent liver biopsy, 38 additional consecutive steatotic patients were examined and the degree of hepatic fat content was calculated. The HFC was linearly correlated (r=-0.86, p<0.001) with the liver-to-spleen ratio. CONCLUSIONS: We conclude that the use of test objects allows an accurate and reproducible noninvasive quantitative assessment of hepatic fat infiltration in humans. This technique may prove useful in the evaluation of the natural course and treatment of hepatic steatosis as well as in the assessment of donor livers prior to transplantation.

Adult↗
PubMed1997

Effect of monomer composition on proton dissociation of weak polyacids.

The study of the proton dissociation process of weak polyacids (eg a carboxylic poly(monoprotic)acid) is based on the knowledge of the change in electrostatic free energy, G(el), as a function of the variation of the number of charges on the polymer chain. The original treatment proposed by Manning can be used to describe the proton dissociation process of weak poly(monoprotic)acids, in the absence of pH-induced conformational transitions. In order to describe the alpha dependence of pKa of weak co-poly(monoprotic)acids containing two different acidic groups in different amounts along the polymer chain, a simple modification of the model is proposed.

Carboxylic Acids↗
PubMed1996

Complete synthesis of 3'-sialyl-N-acetyllactosamine by regioselective transglycosylation.

Transglycolytic synthesis of 3'-sialyl-N-acetyllactosamine by sequential use of beta-galactosidase from Bacillus circulans and trans-sialidase from Trypanosoma cruzi was described. These reactions depicted the first complete synthesis of a biologically important oligosaccharide with high regioselectivity avoiding use of glycosyltransferases and NDP sugars.

Amino Sugars↗
PubMed1996

Azide, cyanide, fluoride, imidazole and pyridine binding to ferric and ferrous native horse heart cytochrome c and to its carboxymethylated derivative: a comparative study.

Azide, cyanide, fluoride, imidazole, and pyridine binding to ferric and ferrous native horse heart cytochrome c and to its carboxymethylated derivative has been investigated, from the thermodynamic viewpoint, at pH 7.5 and 25.0 degrees C. Ligand affinity for ferric and ferrous carboxymethylated cytochrome c is higher by about 30- and 400-fold, respectively, than that observed for the native protein. The results here reported: (i) allow the estimation, for the first time, of the ligand-independent free energy associated with the heme-iron sixth coordination bond in ferric and ferrous native cytochrome c, which turns out to be +8.4 kJ mol-1 and +14.6 kJ mol-1, at 25.0 degrees C, respectively, and (ii) suggest an interplay between redox, structural, ligand binding, and recognition properties of cytochrome c.

Animals↗
PubMed1996

High-yield synthesis of N-acetyllactosamine by regioselective transglycosylation.

The synthesis of N-acetyllactosamine (D-Galp beta 1-4D-GlcpNAc) with very low contamination of its isomer N-acetyllactosamine (D-Galp beta 1-6D-GlcpNAc) was obtained by use of regioselective transglycosylation activity of beta-galactosidase from Bacillus circulans using lactose as the donor of D-Galp and D-GlcpNAc as the acceptor. The reaction was conducted at 15 degrees C and at pH 5.0. The incubation time was considerably reduced and the yield improved 100% with respect to the best results so far described in the literature.

Amino Sugars↗
PubMed1996

Structural determinants of fluoride and formate binding to hemoglobin and myoglobin: crystallographic and 1H-NMR relaxometric study.

The x-ray crystal structure of the fluoride derivative of ferric sperm whale (Physeter catodon) myoglobin (Mb) has been determined at 2.5 A resolution (R = 0.187) by difference Fourier techniques. The fluoride anion, sitting in the central part of the heme distal site and coordinated to the heme iron, is hydrogen bonded to the distal His(64)E7 NE2 atom and to the W195 solvent water molecule. This water molecule also significantly interacts with the same HisE7 residue, which stabilizes the coordinated fluoride ion. Moreover, fluoride and formate binding to ferric Aplysia limacina Mb, sperm whale (Physeter catodon) Mb, horse (Caballus caballus) Mb, loggerhead sea turtle (Caretta caretta) Mb, and human hemoglobin has been investigated by 1H-NMR relaxometry. A strong solvent proton relaxation enhancement is observed for the fluoride derivatives of hemoproteins containing HisE7. Conversely, only a small outer-sphere contribution to the solvent relaxation rate has been observed for all of the formate derivatives considered and for the A. limacina Mb:fluoride derivative, where HisE7 is replaced by Val.

Animals↗
PubMed1996

1H-NMR relaxometric study of pancreatic serine (pro)enzyme inhibition by a Gd(III) chelate bearing boronic functionalities.

Binding of the paramagnetic N,N"-bis(m-boroxyphenylcarbamoylmethyl)-diethylenetriamine-N,N', N"-triacetic acid Gd(III) [sequence: see text] complex (GdBB) to chymotrypsin, chymotrypsinogen, trypsin, trypsinogen and pancreatic elastase has been investigated by 1H-NMR relaxometry, between pH 6.0 and 8.5, at 25.0 degrees C. Values of Ki for the competitive inhibition of serine proteinases by GdBB are in excellent agreement with values of Kd obtained by 1H-NMR relaxometry, suggesting that the substrate and the paramagnetic complex bind to the same region. Moreover, 1H-NMR relaxometry allowed to determine values of Kd for GdBB binding to chymotrypsinogen and trypsinogen, both devoid of catalytic activity. The increase of the water proton relaxation rate upon GdBB binding to serine (pro)enzymes may be useful in the design of novel functional contrast agents for magnetic resonance imaging.

Boron↗
PubMed1995

NMR relaxometric investigation on human methemoglobin and fluoromethemoglobin. An improved quantitative in vitro assay of human methemoglobin.

Longitudinal water proton relaxation rates of methemoglobin solutions show a strong dependence on temperature and pH. The increase of the relaxation rates with temperature is associated with shortened exchange lifetime of the coordinated water molecule. An accurate measurement of the relaxation rate of methemoglobin solutions thus requires careful control of the experimental temperature. This observation prompted the authors to look for an improved version of the relaxometric in vitro determination of methemoglobin. The method is based on transforming methemoglobin into the corresponding fluoromethemoglobin derivative, which shows both a higher relaxivity and a negligible dependence on temperature. The proposed method has been found to be in good agreement with data from spectrophotometric assays.

Humans↗
PubMed1995

Detection and quantitation of phosphorus metabolites in crude tissue extracts by 1H and 31P NMR: use of gradient assisted 1H-31P HMQC experiments, with selective pulses, for the assignment of less abundant metabolites.

The analysis of crude tissue extracts by NMR has proven to be of use in the study of metabolism due to the non-destructive and non-selective character of the technique. Lists of 1H and 31P NMR assignments of phosphorus metabolites in water solution at specified pH and ionic composition are of large general value but their usefulness may be limited when analysing complex mixtures of metabolites at low concentrations. In this work we report on the use of gradient-assisted proton detected multiple quantum 1H and 31P coherence experiments with selective pulses for the rapid and unambiguous assignments of some crowded regions in 1H and 31P spectra of crude extracts from rat liver. The amplitudes of the gradient episodes were calibrated to optimize the coherence transfer pathway between proton and phosphorus, and the delay for the evolution of the long-range coupling was calculated from values of 3JPH and 4JPH ranging from 1.4 to 7.5 Hz. Moreover, a selective 90 degrees Gaussian pulse on the 31P channel was introduced to increase the resolution in the F1-domain and make the method even faster. The procedure was then applied to unambiguously assign the ID 31P and 1H spectra of perchloric acid extracts of rat livers that had been stimulated with phenylephrine, dBcAMP and glucagon and thus detect changes in the concentration of less abundant metabolites such as phosphoenolpyruvate, UDP-glucose and AMP. The fact that the quantification of these metabolites by either 31P and 1H methods lead to different results is discussed, and the use of 1H NMR spectroscopy for the quantification of phosphorus metabolites whose signal are too weak or poorly resolved in a 31P spectrum is proposed.

Adenosine Monophosphate↗
PubMed1995

Conformational analysis of segments of oxidized cellulose. Part I: Molecular modelling of glucuronic acid dimers considering the effect of counter-ions and a polar environment.

Conformational analysis of various forms of glucuronic acid dimers as the model structures of oxidized cellulose has been performed using molecular mechanics with a CVFF force field. The effects of ionization of carboxyl groups, ion pairing with explicit consideration of counter-ions (Na+, Mg2+) and the implicit inclusion of a solvent effect via the dielectric constant, epsilon, have been simulated. The non-ionized glucuronic acid dimer shows conformational behaviour similar to that of unoxidized cellobiose. The ionization of COOH groups leads to strong destabilization of C and D conformers (with both COO- groups on the same side of the molecule), while complexation with counter-ions leads to strong stabilization of these forms which yield highly wound low-pitch helices. An increase in the solvent polarity has an attenuating effect on the behaviour described above.

Anions↗
PubMed1994

NMR analysis of succinoglycans from different microbial sources: partial assignment of their 1H and 13C NMR spectra and location of the succinate and the acetate groups.

In order to obtain information on the location of succinate and acetate groups, comparative NMR analyses were carried out on succinoglycans from different microbial sources by using conventional and advanced NMR techniques. In particular, one-dimensional, 1H and 13C NMR spectra were recorded for qualitative and quantitative analysis on native high-molecular-weight succinoglycans (both in the Na+ salt and free-acid forms) from Pseudomonas sp. NCIB 11592, Agrobacterium radiobacter A201-25, Rhizobium meliloti YE-2, and Rhizobium sp. isolated from Vicia faba and compared with those of the deacylated and deacylated-depyruvated, partially depolymerised exopolysaccharides from Rhizobium meliloti YE-2. Moreover, a series of two-dimensional experiments was performed on all the exopolysaccharides aiming at the partial assignment of the NMR spectra. The NMR data showed that succinate is located on O-6 of either one or both of the two side chain 3-linked beta-D-Glc residues, whereas the acetate (when it is present) is located on one of the O-6 of backbone 4-linked beta-D-Glc units, but the specific site could not be determined. In addition, the spectral features of the succinate substituent were found to be sensitive to pH changes.

Acetates↗
PubMed1994

On the specificity of a bacteriophage-borne endoglycanase for the native capsular polysaccharide produced by Klebsiella pneumoniae SK1 and its derived polymers.

The specificity of the endoglycanase associated with the bacteriophage phi SK1 particles was tested on the native capsular polysaccharide produced by Klebsiella pneumoniae serotype SK1 and on three chemically modified polymers derived from it. The primary structure of the SK1 capsular polysaccharide is: [formula: see text] and the beta 1-3 linkage between the glucose and the galactose residues is the one cleaved by the phage enzyme. The enzyme activity was assayed on the deacetylated polysaccharide and on two derivatives obtained by removal of both the side-chain sugars and of only the alpha-D-galactosyl unit, respectively. The endoglycanase was more active on the deacetylated polysaccharide than on the native one, suggesting that the presence of the acetyl groups interferes with the enzyme-polysaccharide interaction. A possible role of the acetyl groups in the control of the polysaccharide chain length and hence on the rheological behaviour of the capsule cannot be ruled out, as already indicated for other bacterial polysaccharides. On the contrary, the removal of the side chains, either complete or selective, caused the modification of the recognition site in such a way that the enzymatic depolymerization no longer occurred. Therefore, it can be inferred that the phi SK1 endoglycanase requires the presence of both the side chain sugars to exhibit its cleaving activity, although this latter is in the main chain.

Bacteriophages↗
PubMed1994

Energy metabolism, replicative ability, intracellular calcium concentration, and ionic channels of horse articular chondrocytes.

Some aspects of the physiology of chondrocytes from horse articular cartilage were studied, since this animal model can be helpful in understanding arthritic processes. The replicative ability of articular chondrocytes, measured by the incorporation of [3H]thymidine, and their capacity of proteoglycan production, evaluated from the incorporation of [35S] sulfate, are very low. In addition, these cells do not differentiate in vitro as shown by the constant specific activity of alkaline phosphatase measured at different times in culture. Two types of potassium channels were identified by patch clamp experiments in the cell-attached configuration, one characterized by a conductance of 40 pS and the other of 100 pS. No active K+ channels were found at Vpip = 0. It was shown by Fura-2 experiments that the low replicative ability is paralleled by a modest variation of the intracellular calcium concentration after a mitogenic stimulus. 31P NMR experiments, both on slices of whole articular cartilage and on isolated cells, demonstrate that chondrocytes derive their energy mainly from the glycolytic pathway.

Animals↗
PubMed1994

Solution properties of the capsular polysaccharide produced by Klebsiella pneumoniae K40.

This paper reports some physicochemical properties of the capsular polysaccharide produced by Klebsiella pneumoniae serotype K40 (K40-CPS) in aqueous solution. The polymer has a linear hexasaccharide repeating unit containing one glucuronic acid residue as the only ionizable group. Potentiometric, viscometric, chiro-optical and rheological measurements have been carried out over a range of ionic strength, pH and temperature, with the aim of characterizing the conformational state of the polysaccharide in aqueous solution. All the data reported indicate that the K40-CPS does not undergo a cooperative conformational transition under the investigated experimental conditions. Furthermore, the viscosity data and the viscoelastic spectra suggest that the K40-CPS is rather flexible and adopts a random coil conformation in solution.

Carbohydrate Sequence↗
PubMed1993

NMR studies of oligosaccharides derived from hyaluronate: complete assignment of 1H and 13C NMR spectra of aqueous di- and tetra-saccharides, and comparison of chemical shifts for oligosaccharides of increasing degree of polymerisation.

A series of oligosaccharides was prepared from hyaluronate by depolymerisation with bovine testicular hyaluronidase. Complete assignment of the 1H and 13C NMR spectra was obtained for the disaccharide, the tetrasaccharide, and the NaBH4-treated tetrasaccharide, by using various 1D and 2D NMR methods. The 1H assignments for the tetrasaccharide differ from the incomplete data reported recently (ref. 11). The 13C NMR spectra of the aqueous di-, tetra-, hexa-, and octa-saccharides of this series show that all resonances, apart from those subject to obvious end effects, have chemical shifts comparable to those of the corresponding resonances of hyaluronate in D2O. The observed 13C chemical shifts suggests that cooperative intramolecular hydrogen bonds probably play a minor role in determining the conformation of hyaluronate in water.

Animals↗
PubMed1993

Hyaluronan can be protected from free-radical depolymerisation by 2,6-diisopropylphenol, a novel radical scavenger.

The scavenging effect of 2,6-diisopropylphenol on hydroxy radicals produced by xanthine oxidase was assessed by evaluating the in vitro depolymerisation of hyaluronan in artificial synovial fluid by size-exclusion chromatography. After 1 hour, the number-average molecular weight of hyaluronan remained unchanged (100%) with 2,6-diisopropylphenol, whereas it dropped to 90% with methylprednisolone added, to 55% with the antioxidant 2,6-tert-butyl-4-methylphenol added, and to 10% of its initial value in the absence of scavenger.

Chromatography, Gel↗