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Biomedical subjects

F Marchetti

Publications and source records attributed to F Marchetti.

At least 91 records · Page 5Linked to original sources
PubMed1989

Identifying weak signals in the presence of noise: a new method of locating potential ligand contact residues in immunoglobulin-related molecules.

We develop and apply a new method for estimating the locations of hypervariable residues in immunoglobulin-related molecules. The method differs from the standard introduced by Wu and Kabat in two essential ways: (1) we take explicit account of the type of substitution at a given position, rather than just the total number of substitutions, and (2) we use an explicit statistical decision criterion for classifying a site into either the complementarity determining or framework category. Simulations indicate that the method is reliable with relatively little data, approximately 5% of the sites being misclassified when 10 sequences are aligned. The method is applied to immunoglobulin light chains and to class 1 and class 2 products of the major histocompatibility complex.

Filtration↗
PubMed1989

[Pharmacokinetics of intravenous anesthetics in aged patients].

This paper reviews the pharmacokinetic modifications of anaesthetic intravenous drugs in elderly reported in the literature. With benzodiazepines, the elimination half-life is prolonged and can increase the duration of the sedative effect. With hypnotics, the increase of pharmacological effect (intensity and duration) is due to a decrease of initial volume of distribution and total body clearance. Except morphine, the pharmacokinetic of opioids is slightly changed and can't explain the increase of the pharmacodynamic sensibility.

Adult↗
PubMed1988

Structural and chemical characterization of gallstones resistant to dissolution therapy.

X-ray diffraction, i.r. spectroscopic, and chemical analyses have been carried out on radiolucent gallstones resistant to dissolution therapy. Cholesterol represents the main component of all the examined stones, while the ratio between the amounts of pigmented material and calcium carbonate is about 1 in the inner and outer layers of the stones and 3 in the medial layer. Calcium carbonate is present in two distinct crystalline forms: vaterite, which is the main inorganic crystalline phase, and calcite. The cell parameters of vaterite and calcite are shorter in the inner and outer layers of the stones than in the medial layer. The observed variation of the cell parameters has been related to the substitution of copper to calcium in the carbonate structures, on the basis of the data obtained on vaterite and calcite synthesized in presence of different copper concentrations in solution. The results indicate that the failure of the dissolution therapy can be related to the inhomogeneous distribution in the stones of calcium carbonate and calcium bilirubinate.

Calcium↗
PubMed1984

The behaviour of apatite-based ceramics in relation to the critical 1150 degrees-1250 degrees C temperature range.

Characterization of synthetic calcium phosphates is reported and compared with previous studies. Barium hydroxyapatite was also synthesized. Shrinkage on sintering, water absorption, tensile strength, porosity and X-ray diffraction patterns were studied. Hydroxyapatite and beta-tricalcium phosphate show compositional and mechanical property variation dependent on sintering temperatures. The property change on introduction of barium removes the practical value. X-ray diffraction analysis is considered essential before clinical use due to sensitivity of composition to sintering conditions.

Barium Compounds↗
PubMed1983

[A rapid method for assay of 25-hydroxyvitamin D in serum].

A simplified assay for 25-hydroxyvitamin D is reported. In this procedure ethanol extraction is used in order to obtain a better protein precipitation and a higher recovery of added tritiated 25-hydroxyvitamin D3. Extraction is followed by column chromatography on Sep-pak Silica cartridges. The eluate is dried and directly used for competitive protein binding assay. The method shows two main advantages: it is less time consuming and is easier to perform than existing procedures.

25-Hydroxyvitamin D 2↗
PubMed1983

[Assay of 24,25-dihydroxyvitamin D by competitive protein binding].

A competitive protein binding radioassay for 24,25-dihydroxyvitamin D in human serum has been developed, which is relatively simple and rapid. Acetonitrile is used for sample extraction and protein precipitation. column chromatography is then performed in a Sep-pak cartridge. High pressure liquid chromatography follows. The dried eluate is assayed using rat serum as the source of binding protein. Since 25-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 are equipotent in their competitive displacement of tritiated 25-hydroxyvitamin D3 from at serum, 25-hydroxyvitamin D3 can be used as the assay standard.

24,25-Dihydroxyvitamin D 3↗
PubMed1983

A theory of measurement error and its implications for spatial and temporal gradient sensing during chemotaxis. II. The effects of non-equilibrated ligand binding.

Cells generally chemotax along a direction in which their receptor occupancy gradient--whether spatial or temporal--is maximum. Occupancy differentials are, however, often so small as to be masked by thermal noise; i.e., by fluctuations inherent in the stochastic nature of ligand binding. Such fluctuations therefore impose a fundamental limit on the sensitivity of a cell's ability to detect a chemoattractant gradient. In order to pursue the implications of this limit, fluctuation theories have been developed. The theories assume that the signal is some function of the receptor occupancy gradient, allow an estimate of the standard deviation about the mean signal, and permit an evaluation of, among other things, the extent to which a receptor defect can impair an effective response. Previous theories have assumed an equilibrated ligand-receptor interaction. In this paper we introduce a generalized definition of a signal caused by a receptor occupancy gradient that allows us to develop a non-equilibrium theory of thermal noise. We show that previous formulations are a special case of the current development. More specifically, we find the following. Swimming cells subject to Brownian tumbling must generally average their signals over a very long time period to achieve a signal-to-noise ratio less than or equal to 1. Spatial gradient detection is possible with ligand-receptor equilibrium constants less than 10(3)M-1, but since such ligands are rare, theory predicts that tumbling cells will generally not detect gradients by measuring spatial occupancy differentials. These conclusions hold irrespective of whether chemical equilibrium is achieved. For crawling cells not subject to Brownian tumbling, a range of affinities exists in which spatial or temporal gradient detection is possible. In general a spatial mechanism is more efficient for low affinity ligands (dissociation times less than 0.3 s), whereas a temporal mechanism is more efficient for higher K. In this case the detection of gradients in slowly dissociating ligand will be facilitated if signal processing begins prior to chemical equilibration. An important new parameter is indicated by the theory. The definitions of a temporal gradient signal is based on estimating and comparing average occupancy over two time intervals displaced by a time t1. The theory predicts an optimal t1, of order milliseconds, that leads to the shortest minimum averaging time. For t1 values at and longer than the optimum, and for all averaging times exceeding some minimum, the cell will detect a temporal signal.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Predictive value of cord blood IgE levels in 'at-risk' newborn babies and influence of type of feeding.

Cord serum IgE levels were examined in 101 newborn infants of atopic parents, and reviewed at the ages of 3, 6, 9, 12, 15, 18, 21 and 24 months, in order to determine any relation with signs and symptoms of allergic rhinitis, bronchial asthma, atopic dermatitis, urticaria and food allergy. Cord blood IgE levels were 1.06 +/- 1.02 U/ml in the group of infants who developed atopic disease, and 0.34 +/- 0.79 U/ml in the group of infants who did not develop atopy (P less than 0.001). In the breast-fed group 37.5% of the infants with cord blood IgE more than 0.8 U/ml and 11.5% with IgE below 0.8 U/ml had atopic disease. In the soy-fed group 33.3% of the infants with cord blood IgE more than 0.8 U/ml and 15.8% with cord blood IgE less than 0.8 U/ml developed atopy. Ninety percent of the cow's milk-fed infants with cord blood IgE above 0.8 U/ml and 16% with cord blood IgE below 0.8 U/ml showed atopy during the follow-up period. No correlation was found between the IgE levels in maternal and respective cord blood.

Animals↗
PubMed1983

Prevention of atopic disease in "at-risk newborns" by prolonged breast-feeding.

The protective effect of breast feeding against atopic disease (AD) has been confirmed in several prospective studies, while some retrospective studies have yielded controversial results. We have evaluated the prophylactic effect of prolonged breast feeding on the development of AD in 101 newborns at hereditary risk for allergic disease. The study design also included a strict dietary avoidance regimen of the nursing mothers. Our data demonstrate that breast feeding or breast feeding supplemented with soy milk exert a prophylactic effect on the development of AD in these at-risk infants. Mechanisms by which breast feeding protects from atopy are discussed.

Breast Feeding↗
PubMedDate not supplied

A theory of measurement error and its implications for spatial and temporal gradient sensing during chemotaxis.

In order that cells respond to environmental cues, they must be able to measure ambient ligand concentration. Concentrations fluctuate, however, because of thermal noise, and one can readily show that estimates based on concentration values at a particular moment will be subject to substantial error. Cells are therefore expected to average their estimates over some limited time period. In this paper we assume that a cell uses fractional receptor occupancy as a measure of ambient ligand concentration and develop general expressions for the error a cell makes because the length of the averaging period is necessarily limited. Our analysis is general, relieving many of the assumptions underlying the seminal work of Berg and Purcell. The most important formal difference is our inclusion of occupancy-dependent dissociation--a phenomenon that has been well-documented for many systems. In addition, our formulation permits signal averaging to begin before chemical equilibrium has been established and it allows binding kinetics to be nonlinear (i.e., biomolecular rather than pseudo-first-order). The results are applied to spatial and temporal concentration gradients. In particular we estimate the minimum averaging times required for cells to detect such gradients under typical in vitro conditions. These estimates involve assigning numerical values to receptor ligand rate constants. If the rate constants are at their maximum possible values (limited only by center of mass diffusion), then either temporal or spatial gradients can be detected in minutes or less. If, however, as suggested by experiments, the rate constants are several orders of magnitude below their diffusion-limited values, then under typical constant gradient conditions the time required to detect a spatial gradient is prohibitively long, whereas temporal gradients can still be detected in reasonable lengths of time. This result was obtained for large cells such as lymphocytes, as well as for the smaller, bacterial cells. The ratio of averaging times for the two mechanisms--amounting to several orders of magnitude--is well beyond what could be reconciled by limitations of the calculation, and strongly suggests heavy reliance on temporal sensing mechanisms under typical in vitro conditions with constant spatial gradients.

Animals↗