Biomedical subjects

P Magni

Publications and source records attributed to P Magni.

At least 37 records · Page 2Linked to original sources

PubMed2000

Leptin: a possible link between food intake, energy expenditure, and reproductive function.

Several regulatory substances participate in the regulation of both food intake/energy metabolism and reproduction in mammals. Most of these neuropeptides originate and act in the central nervous system, mainly at specific hypothalamic areas. Leptin represents a signal integrating all these functions, but originating from the periphery (adipose tissue) and carrying information mainly to central structures. Observations in rodent models of leptin deficiency have suggested that leptin participates in the control of reproduction, in conjunction with that of food intake and energy expenditure. Indeed, leptin administration resulted in the restoration of normal body weight, food intake, and fertility in the ob mouse, lacking circulating leptin. Specific targets of leptin in the hypothalamus are neurons expressing neuropeptide Y, proopiomelanocortin and gonadotropin-releasing hormone, but the presence of leptin receptors in peripheral reproductive structures suggests that leptin might also act at these sites. Human obesity is often associated with reproductive disturbances. The situation in humans is more complex than in the animal models of leptin deficit and the presence of leptin resistance in these subjects is suggested. In conclusion, leptin fits many requirements for a molecule linking the regulation of energy balance and the control of reproduction.

Animals↗

PubMed2000

Retinoic acid negatively regulates neuropeptide Y expression in human neuroblastoma cells.

Retinoids are involved in the regulation of development and differentiation in many tissues, including the nervous system, where they have been associated with some neurotransmitter systems. In the present study, we evaluated the effects of all-trans retinoic acid (RA) on the biosynthesis and secretion of neuropeptide Y (NPY), a widely expressed neuroregulatory peptide. The SH-SY5Y human neuroblastoma cell line has been used as the in vitro model system. Treatment with 10 microM RA induced a marked decrease in NPY gene expression after as little as 3-6 h of incubation and resulted in its almost complete suppression at 12-24 h and after a 6-day differentiating treatment. The NPY content in cell extracts and the NPY secreted and accumulated in the culture medium were also reduced by exposure to 10 microM RA at 12 and 24 h and at 6 days. Moreover, RA treatment for 6 days, but not for 24 h, resulted in a marked stimulation of proNPY processing to mature NPY. The presence of negative retinoic acid-response elements in the human NPY promoter (up to -1078 bp) was excluded by a computer search. When SH-SY5Y cells were treated simultaneously with 20 nM TPA and 10 microM RA for 24 h, the marked stimulatory effect of TPA alone was completely suppressed. These observations suggest that the expression of NPY in SH-SY5Y human neuroblastoma cells is negatively regulated by RA at the level of gene expression, probably by mechanisms involving the interaction of activated RARs with transcription factors (such as AP-1).

Blotting, Northern↗

PubMed2000

Intelligent analysis of clinical time series: an application in the diabetes mellitus domain.

This paper describes the application of a method for the intelligent analysis of clinical time series in the diabetes mellitus domain. Such a method is based on temporal abstractions and relies on the following steps: (i) 'pre-processing' of raw data through the application of suitable filtering techniques: (ii) 'extraction' from the pre-processed data of a set of abstract episodes (temporal abstractions); and (iii) 'post-processing' of temporal abstractions; the post-processing phase results in a new set of features that embeds high level information on the patient dynamics. The derived features set is used to obtain new knowledge through the application of machine learning algorithms. The paper describes in detail the application of this methodology and presents some results obtained on simulated data and on a data-set of four diabetic patients monitored for > 1 year.

Artificial Intelligence↗

PubMed2000

Deciding when to intervene: a Markov decision process approach.

The aim of this paper is to point out the difference between static and dynamic approaches to choosing the optimal time for intervention. The paper demonstrates that classical approaches, such as decision trees and influence diagrams, hardly cope with dynamic problems: they cannot simulate all the real-world strategies and consequently can only calculate suboptimal solutions. A dynamic formalism based on Markov decision processes (MPPs) is then proposed and applied to a medical problem: the prophylactic surgery in mild hereditary spherocytosis. The paper compares the proposed approach with a static approach on the same medical problem. The policy provided by the dynamic approach achieved significant gain over the static policy by delaying the intervention time in some categories of patients. The calculations are carried out with DT-Planner, a graphical decision aid specifically built for dealing with dynamic decision processes.

Cholecystectomy↗

PubMed2000

Bayesian analysis of blood glucose time series from diabetes home monitoring.

This paper describes the application of a novel Bayesian estimation technique to extract the structural components, i.e., trend and daily patterns, from blood glucose level time series coming from home monitoring of insulin dependent diabetes mellitus patients. The problem is formulated through a set of stochastic equations, and is solved in a Bayesian framework by using a Markov chain Monte Carlo technique. The potential of the method is illustrated by analyzing data coming from the home monitoring of a 14-year old male patient.

Adolescent↗

PubMed2000

Bayesian identification of a population compartmental model of C-peptide kinetics.

When models are used to measure or predict physiological variables and parameters in a given individual, the experiments needed are often complex and costly. A valuable solution for improving their cost effectiveness is represented by population models. A widely used population model in insulin secretion studies is the one proposed by Van Cauter et al. (Diabetes 41:368-377, 1992), which determines the parameters of the two compartment model of C-peptide kinetics in a given individual from the knowledge of his/her age, sex, body surface area, and health condition (i.e., normal, obese, diabetic). This population model was identified from the data of a large training set (more than 200 subjects) via a deterministic approach. This approach, while sound in terms of providing a point estimate of C-peptide kinetic parameters in a given individual, does not provide a measure of their precision. In this paper, by employing the same training set of Van Cauter et al., we show that the identification of the population model into a Bayesian framework (by using Markov chain Monte Carlo) allows, at the individual level, the estimation of point values of the C-peptide kinetic parameters together with their precision. A successful application of the methodology is illustrated in the estimation of C-peptide kinetic parameters of seven subjects (not belonging to the training set used for the identification of the population model) for which reference values were available thanks to an independent identification experiment.

Adult↗

PubMed1999

Expression of a leptin receptor in immortalized gonadotropin-releasing hormone-secreting neurons.

Leptin is secreted by adipocytes and regulates food intake and energy balance through the activation of specific receptors (OB-R). Recent evidence suggests that it is also involved in the control of reproductive processes, by possibly acting on central and peripheral targets. In particular, it has been shown that leptin may indirectly stimulate GnRH release from hypothalamic fragments by acting on interneurons impinging on GnRH-secreting neurons. The possibility that leptin might additionally modulate the activity of GnRH-secreting neurons in a direct way has been addressed in the present study, by using the immortalized GnRH-secreting cell line GT1-7. The presence of OB-R messenger RNA (mRNA) (long form) was detected by RT-PCR analysis of total RNA from GT1-7 cells. An OB-R protein is also expressed in these cells, as shown by immunocytochemistry and by Western blot analysis. The latter has revealed the presence of a single immunoreactive OB-R with an approximate size of 130 kDa. To study the functionality of these receptors, the effect of leptin treatment on GnRH secretion and gene expression in GT1-7 cells were evaluated. Under static conditions, GnRH release was stimulated by exposure to low concentrations of leptin (10(-12) M after 30 min; 10(-10) M after 60 min). The 10(-12) M dose was selected for studying the effect of leptin on GnRH secretion under dynamic conditions. To this purpose, GT1-7 cells were placed in a perifusion system; treatment with leptin (10(-12) M) for 60 min stimulated GnRH release with no changes of pulse frequency. On the contrary, exposure to leptin (10(-12)-10(-10) M) for 1, 3, 6, and 24 h did not affect GnRH gene expression in GT1-7 cells. The present results indicate that GT1-7 cells possess OB-Rs and that leptin may directly affect their function. Taken together with the available reports, these findings suggest that leptin might participate in the regulation of reproductive processes by acting at multiple levels, both centrally and peripherally.

Animals↗

PubMed1998

Cholinergic muscarinic mechanisms regulate neuropeptide Y gene expression via protein kinase C in human neuroblastoma cells.

Neuropeptide Y (NPY) participates in the control of several functions in the nervous system. NPYergic neurons present in brain areas involved in cognitive processes are linked to ascending projections of the cholinergic system, a finding that suggests a role for acetylcholine in the control of these cells. In the present study, the effect of the activation of cholinergic muscarinic receptors on the expression of the human NPY gene was assessed. The SH-SY5Y neuroblastoma cell line was used as an in vitro model of human neurons; NPY mRNA levels were evaluated by Northern blot analysis. The results indicate that: (a) the expression of the human NPY gene in SH-SY5Y cells is stimulated by the cholinergic muscarinic agonist, carbachol; (b) this effect is mediated by the M3 muscarinic receptor subtype, as indicated by the inhibitory effect of the M3 antagonist 4-DAMP; (c) protein kinase C (PKC) activation plays an important role in the induction of NPY gene expression in this system, as suggested by experiments with the PKC activator, TPA, and the PKC inhibitor, GF 109203X; (d) the stimulation of NPY mRNA levels by TPA and by carbachol in SH-SY5Y cells requires de novo synthesis of RNA and protein. In conclusion, the present study shows that the activation of PKC-coupled muscarinic receptors as the M3 subtype positively modulates the expression of the human NPY gene in SH-SY5Y neuroblastoma cells, via PKC-related mechanisms.

Carbachol↗

PubMed1998

Presence of 5alpha-reductase isozymes and aromatase in human prostate cancer cells and in benign prostate hyperplastic tissue.

BACKGROUND: Prostate trophism depends on DHT formed from T by the enzyme 5alpha-R. Two 5alpha-R isoforms with different biochemical characteristics have been cloned. Also estrogens might contribute to the prostate growth; however, their intraglandular formation by the enzyme aromatase is still debated. The aim of the present study was to verify whether (a) only one or both isoforms of the 5alpha-Rs are expressed in the prostate cancer cell line LNCaP and in BPH, or (b) the aromatase is present in these samples. METHODS: The profile of the pH optimum of the 5alpha-Rs was evaluated "in vitro" in LNCaP cells by the production of labeled 5alpha-reduced metabolites either from [14C]-T or [14C]-D4 at pH 3.5-8. The gene expression of the two 5alpha-Rs and of the aromatase in LNCaP cells and in BPH specimens was analyzed by RT-PCR combined to Southern blot analysis, using specific sets of oligonucleotides. The tissue localization of 5alpha-R1 was analyzed by immunohistochemistry using an anti-5alpha-R1 polyclonal antibody. RESULTS: (a) In LNCaP cells, the formation of 5alpha-reduced metabolites from the respective precursors increases progressively as a function of pH, being the highest at neutral pH values; (b) the 5alpha-R1 isoform is expressed in both LNCaP cells and in BPH, while the 5alpha-R2 mRNA is present only in BPH, but not in LNCaP cells; and (c) no aromatase transcripts were observed either in BPH or in LNCaP cells. CONCLUSIONS: A careful examination of the possible differential expression of T-activating enzymes, particularly in prostate cancer, would be of help to choose the appropriate treatment.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗

PubMed1998

Mining biomedical time series by combining structural analysis and temporal abstractions.

This paper describes the combination of Structural Time Series analysis and Temporal Abstractions for the interpretation of data coming from home monitoring of diabetic patients. Blood Glucose data are analyzed by a novel Bayesian technique for time series analysis. The results obtained are post-processed using Temporal Abstractions in order to extract knowledge that can be exploited "at the point of use" from physicians. The proposed data analysis procedure can be viewed as a Knowledge Discovery in Data Base process that is applied to time-varying data. The work here described is part of a Web-based telemedicine system for the management of Insulin Dependent Diabetes Mellitus patients, called T-IDDM.

Algorithms↗

PubMed1998

A new approach to optimal dynamic therapy planning.

Therapy planning is a very complex task. One of its crucial aspect is the derivation of therapeutic plans taking into account the dynamic aspect of the decision problem. This paper deals with dynamic decision problems using Influence Views, a novel graphical formalism based on Markov Decision Processes (MDPs) framework, in order to solve decision problems in which the optimal choice has to be revised periodically in accordance to the evolution of the patient's conditions. The proposed methodology has been applied to the plan of the prophylaxis in patients affected by a mild Hereditary Spherocytosis.

Child↗

PubMed1997

DT-Planner: an environment for managing dynamic decision problems.

The problem of formulating plans under uncertainty and coping with dynamic decision problems is a major task of both artificial intelligence and control theory applications in medicine. In this paper we will describe a software package, called DT-Planner, designed to represent and solve dynamic decision problems that can be modelled as Markov decision processes, by exploiting a novel graphical formalism, called influence view. An influence view is a directed acyclic graph that depicts the probabilistic relationships between the problem state variables in a generic time transition; additional variables, called event variables, may be added, in order to describe the conditional independencies between state variables. By using the specified conditional independence structure, an influence view may allow a parsimonious specification of a Markov decision process. DT-Planner lets the user specify and manage models through a user-friendly graphical interface, and implements efficient for policy determination algorithms. DT-Planner is written in C with Open Interface libraries and can be obtained, for non commercial use, via anonymous ftp without charge.

Algorithms↗

PubMed1995

Sphingomyelin is synthesized at the plasma membrane of oligodendrocytes and by purified myelin membranes: a study with fluorescent- and radio-labelled ceramide analogues.

In most cell types sphingomyelin is synthesized predominantly in the cis-medial compartments of the Golgi stacks whereas the contribution of the plasma membrane is much lower. The aim of this study was to assess the contribution of both compartments to the synthesis of sphingomyelin in myelinating cells. Therefore, oligodendrocytes from rat spinal cord were incubated in culture with fluorescently- or radiolabelled ceramides, and the effects of a block in the vesicular flow (monensin, brefeldin A, low temperature) on surface synthesis of sphingomyelin were evaluated. The results indicate that approximately 50% of the sphingomyelin synthase is present at the plasma and myelin membranes of oligodendrocytes.

Animals↗

PubMed1995

Purification of LamB proteins using continuous elution electrophoresis: a comparison with immunoaffinity chromatography.

LamB is a membrane protein that allows the exposition of a foreign peptide on the surface of a recombinant E. coli cells. An immunopurified hybrid LamB protein has been used to elicit high-titre antibodies to a foreign epitope. Looking for a simpler purification procedure we have compared the traditional approach, which includes affinity chromatography, to continuous elution electrophoresis, in the purification of two different hybrid LamB proteins as foreign epitopes. The results obtained showed that both methods yielded the same purification, although the electrophoretic procedure had a higher yield. Continuous-elution electrophoresis could be a useful tool for the purification of membrane proteins.

Antibodies, Monoclonal↗

PubMed1993

An early and transient period of protein synthesis is required for induction of neuropeptide Y-mRNA by phorbol ester and forskolin in aggregate cultures of fetal brain cells.

We have previously shown that both forskolin (F) and phorbol ester (P) induce neuropeptide Y (NPY) production by aggregate cultures formed from dissociated fetal rat brains. In this study, we addressed the question: Do F/P induce NPY-mRNA in aggregate cultures and if so, does induction require active protein kinases and on-going protein synthesis? On Northern blots, the NPY cDNA hybridized to a single species of about 0.8 kb. F and P each induced a time-dependent increase in NPY-mRNA relative abundance, and this was inhibited by staurosporine, an inhibitor of both protein kinase A and C. Cycloheximide (CHX) inhibited F/P induction of mRNA in a time-dependent manner. When aggregates were incubated with F+P for a total 12 h period, CHX added along with F+P (0 h) completely inhibited, CHX added 1.5 h after F+P partially inhibited, and CHX added 6 h after F+P did not inhibit the increase in NPY-mRNA. To rule out the possibility that this inhibitory profile reflects toxicity of CHX, blots were re-hybridized with a SRIF cRNA probe and, as expected for SRIF gene, a 12 h exposure to CHX did not inhibit F+P induction of SRIF-mRNA. Close inspection of the blots (derived from 1.5% agarose gels) suggested the presence in F/P-treated aggregates of 2 species NPY-mRNA [approximately 0.75 and approximately 0.85 kb, most likely differing in the length of poly(A) tail (Jamal et al., 1991)]; size-fractionation on a higher resolution gel (3% agarose) resolved the F/P induced mRNA into 2 distinct bands, while mRNA from untreated cultures migrated as a single band--the 0.75 kb.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Forskolin and phorbol ester stimulation of neuropeptide Y (NPY) production and secretion by aggregating fetal brain cells in culture: evidence for regulation of NPY biosynthesis at transcriptional and posttranscriptional levels.

Using fetal brain cells in culture, we have previously shown that activation of the cAMP pathway by forskolin induces the production and secretion of neuropeptide Y (NPY). In this study we wished to ascertain 1) if activation of the protein kinase C pathway induces NPY production and/or secretion and if there is synergism between the pathways, and 2) the role of protein/RNA synthesis and influx of extracellular calcium. Aggregates, formed from dissociated cells obtained from the hypothalamus-olfactory tubercle area of 17-day-old rat fetuses, were cultured in serum-free medium for 12 days. The NPY content of aggregates incubated for 24 h with solvent (control) was 4.4 ng/flask, and the medium content was 7.6 ng. Forskolin (10 microM) or phorbol 12-myristate 13-acetate (PMA; 20 nM) marginally affected aggregate content, but each increased medium content 2- to 3-fold; forskolin and PMA were additive. When cycloheximide (75 microM) was included along with forskolin, PMA, or forskolin plus PMA for a period of 10 h, the increase in NPY medium content was abolished. Actinomycin D (Act-D; 5 micrograms/ml) inhibited the response to each secretagogue in a time-dependent manner. When Act-D was included along with forskolin, PMA, or forskolin plus PMA for a total period of 12 or 24 h, the 12 h increase in content was not affected, whereas the 24 h increase was abolished. When the presence of Act-D was limited to 0-24, 6-24, or 12-24 h, and forskolin plus PMA were included for the entire 24-h period, the increase in NPY content was inhibited by 94%, 57%, and 12%, respectively. Verapamil (100 microM) totally inhibited the 24 h response to forskolin and partially (40-50%) inhibited the response to PMA or forskolin plus PMA. In none of these conditions was the inhibition of the increase in medium NPY content accompanied by an increase in aggregate content, nor was the NPY content of aggregate/medium of control cultures affected.(ABSTRACT TRUNCATED AT 400 WORDS)

1-Methyl-3-isobutylxanthine↗

PubMed1991

A potential mechanism for copper amplification of prostaglandin E2 action: attenuation of prostaglandin E2-induced efflux of cyclic AMP from median eminence explants.

It is known that prostaglandin E2 (PGE2) stimulation of LHRH release from the median eminence-arcuate nucleus (MEA) is mediated by the cAMP pathway, and a short pretreatment with copper markedly amplifies this release process. Because stimulation of cAMP accumulation is accompanied by cAMP efflux in many tissues, we considered the possibility that attenuation of cAMP efflux is one mechanism by which copper can enhance PGE2 action. When rat MEA explants were incubated in vitro, PGE2 induced a rapid (less than 2.5 min) and sustained (15 min) increase in cAMP efflux, the degree of which was a function of [PGE2]: by 5 min exposure to 10 microM PGEs2, efflux was 8-fold greater than the control (no PGE2) and it accounted for 12.4% of the total (tissue + medium) cAMP. Unlike the dramatic increase in cAMP efflux, PGE2 induced a moderate increase in cAMP content (49%) and in the incorporation of [3H] adenine into [3H] cAMP (78%); this increase was transient: it was evident after a 2.5 but not after a 5 min period of PGE2 exposure. Copper pretreatment did not alter this PGE2-induced increase in tissue cAMP content. In contrast, copper markedly inhibited (by 49%-66%) PGE2-induced cAMP efflux and this inhibition was noted regardless of the length of PGE2 exposure and PGE2 concentration. There was no evidence for hydrolysis of [3H]3',5'-cAMP included in the medium during the incubation with PGE2 with and without copper pretreatment. In summary, copper attenuated PGE2-induced cAMP efflux from MEA explants and this attenuation is not a consequence of a reduction in the availability of intracellular cAMP nor of hydrolysis of cAMP extracellularly.

Animals↗

PubMed1991

Regulated production and secretion of immunoreactive neuropeptide Y by aggregating fetal brain cells in cultures.

The aim of this study was to establish a culture system of fetal brain cells that could serve as a model for the study of the developmental regulation of the neuropeptide Y (NPY) neuron. Single cell suspensions were prepared from the hypothalamic-olfactory tubercle region of 18-day-old rat fetuses, and aggregates were formed by incubation in serum-free medium under constant rotation. Aggregate formation was complete within 24-48 h, and cultures were maintained for up to 23 days. The content of immunoreactive (IR) NPY in the medium and in the aggregates increased progressively with time in culture and at each time point, the medium contained 5- to 10-fold more NPY-IR. A 48-hour exposure to forskolin resulted in a 2-fold increase in the accumulation of NPY-IR in the aggregates and in the medium, indicating that both production and secretion of NPY are regulated by the cAMP intracellular pathway. Sephadex gel filtration revealed the presence of proNPY- and NPY-size substances. The ratio of NPY- to proNPY-size substances increased progressively with age of the aggregates as well as in tissues obtained from perinatal rats of comparable age. Thus, production and secretion of NPY-IR in the cultured aggregates are regulated processes and hence, this culture system can serve as a model to study regulatory processes in the developing NPY neuron.

Animals↗