PubMed Health⌕ Search

Biomedical subjects

M A Leon

Publications and source records attributed to M A Leon.

At least 19 recordsLinked to original sources
PubMed2000

Alpha2-HSG, a specific inhibitor of insulin receptor autophosphorylation, interacts with the insulin receptor.

Human fetuin, [alpha2-Heremans Schmid Glycoprotein (alpha2-HSG)], is a natural inhibitor of insulin receptor tyrosine kinase activity (IR-TKA). Previously, we have demonstrated that alpha2-HSG inhibits the mitogenic pathway without affecting the metabolic arm of insulin signal transduction. In this study, we demonstrate the time-course and specificity of inhibition, its interaction with IR and probable physiological role. In intact rat1 fibroblasts overexpressing the human insulin receptor (HIRc B), incubation of recombinant human alpha2-HSGbac (1.8 microM) inhibited insulin-induced IR autophosphorylation by over 80%. This inhibitory effect of alpha2-HSGbac on insulin-induced IR autophosphorylation was blunted by half in 60 min. Interestingly, alpha2-HSGbac at similar concentrations (0.9 or 1.8 microM), had no effect on EGF- or IGF-I-induced cognate receptor autophosphorylation. Anti-alpha2-HSG immunoprecipitates of alpha2-HSGbac-treated HIRc B cell lysates demonstrated the presence of IR. Our data suggest that alpha2-HSGbac preferentially interacts with the activated IR. To further characterize the site(s) of interaction, the effect of alpha2-HSGbac on trypsin-treated IR autophosphorylation was studied. Trypsin-treatment of intact HIRc B cells results in proteolysis of the IR alpha-chain and constitutive activation of IR-TKA. We demonstrate that alpha2-HSGbac (0.1 microM) completely inhibited trypsin-activated IR autophosphorylation and TKA in vitro indicating that this effect was not mediated by its interaction with the proximal 576 amino acid residues of the IR alpha-subunit. The physiological relevance of these observations was explored by characterizing the effects of alpha2-HSG injection in rats. Alpha2-HSGbac (2 microM), acutely injected through the portal vein of normal rats, inhibited insulin-stimulated IR autophosphorylation and IRS-1 phosphorylation in liver and hindlimb muscle. Taken together our results suggest that alpha2-HSG, by interacting with IR, specifically inhibits insulin-stimulated IR autophosphorylation and may play a physiological role in the regulation of insulin signaling.

Animals↗
PubMed1998

H-NS regulates DNA repair in Shigella.

We report a new role for H-NS in Shigella spp.: suppression of repair of DNA damage after UV irradiation. H-NS-mediated suppression of virulence gene expression is thermoregulated in Shigella, being functional at 30 degrees C and nonfunctional at 37 to 40 degrees C. We find that H-NS-mediated suppression of DNA repair after UV irradiation is also thermoregulated. Thus, Shigella flexneri M90T, incubated at 37 or 40 degrees C postirradiation, shows up to 30-fold higher survival than when incubated at 30 degrees C postirradiation. The hns mutants BS189 and BS208, both of which lack functional H-NS, show a high rate of survival (no repression) whether incubated at 30 or 40 degrees C postirradiation. Suppression of DNA repair by H-NS is not mediated through genes on the invasion plasmid of S. flexneri M90T, since BS176, cured of plasmid, behaves identically to the parental M90T. Thus, in Shigella the nonfunctionality of H-NS permits enhanced DNA repair at temperatures encountered in the human host. However, pathogenic Escherichia coli strains (enteroinvasive and enterohemorrhagic E. coli) show low survival whether incubated at 30 or 40 degrees C postirradiation. E. coli K-12 shows markedly different behavior; high survival postirradiation at both 30 and 40 degrees C. These K-12 strains were originally selected from E. coli organisms subjected to both UV and X irradiation. Therefore, our data suggest that repair processes, extensively described for laboratory strains of E. coli, require experimental verification in pathogenic strains which were not adapted to irradiation.

Bacterial Proteins↗
PubMed1997

Gamma radiation induces CD69 expression on lymphocytes.

Gamma radiation activates protooncogenes that are involved in early signal transduction, e.g., Raf-1. Most studies of effects of gamma radiation on lymphocytes deal with regulation of gene expression. However, early surface receptor expression in response to radiation has not been reported. We studied the effect of radiation on lymphocyte CD69 expression and BrdU uptake in the absence or presence of phytohemagglutinin (PHA). Radiation induces CD69 expression on T and B cells in a dose- and time-dependent manner. Four hours after a dose of 906 cGy, approximately 90% of B and 12% of T cells express CD69. CD69 expression diminishes after 6 h and requires de novo protein synthesis and protein phosphorylation. Radiation alone does not stimulate cell proliferation, as measured by BrdU incorporation, at any radiation dose tested. Furthermore, radiation enhances PHA induced CD69 expression at 2 h, but inhibits BrdU incorporation at day 3 in a dose-dependent fashion. CD69 functions as a marker for response to radiation, but unlike antigen or mitogen, radiation-induced CD69 expression does not lead to proliferation.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1997

Ventilation mode recognition using artificial neural networks.

This study investigated the capabilities of artificial neural networks to identify spontaneous and pressure support ventilation modes from gas flow and airway pressure signals. After receiving written informed consent, flow and pressure waveforms were recorded from 13 patients undergoing general anesthesia. During analysis, the inspiratory phase of each breath was extracted and normalized in amplitude and wavelength. Neural networks were configured to input flow, pressure, or both waveforms and to output the ventilatory mode. Neural network training was accomplished with data from 500 breaths obtained from 7 patients. Neural network performance was tested with 433 breaths from the remaining 6 patients. Networks using flow, pressure, and both waveforms recognized correctly 78% (337), 97% (423), and 100% (433) of the test waveforms, respectively. Results indicate that neural networks can be used effectively for breathing pattern recognition and encourage the application of neural networks in other types of respiratory pattern recognition problems.

Aged↗
PubMed1997

Bovine fetuin is an inhibitor of insulin receptor tyrosine kinase.

Fetuin has been identified earlier as the bovine homolog of the human plasma protein, alpha2-Heremans Schmid glycoprotein (alpha2-HSG). Although bovine fetuin shares over 70% amino acid sequence similarity with alpha2-HSG and rat fetuin, no common function(s) have been identified. We report that immunoaffinity purified bovine fetuin acts as an inhibitor of insulin receptor tyrosine kinase activity (IR-TKA) with half-maximal inhibition at 1.5 microM. In vitro, bovine fetuin (1.5 microM) blocked insulin-induced autophosphorylation of the human IR completely and the half-maximal inhibitory effect was observed at 0.5 microM. Incubation of HIRcB cells (rat1 fibroblasts transfected with wild-type human insulin receptor cDNA) with bovine fetuin (1.5 microM) inhibited insulin-induced tyrosine phosphorylation of the IR beta-subunit by 40%. In addition, bovine fetuin (2 microM) completely blocked insulin-stimulated DNA synthesis in H-35 rat hepatoma cells. Our results, together with earlier reports on rat fetuin and human alpha2-HSG, indicate a common IR-TK inhibitory function for fetuin homologs.

Animals↗
PubMed1997

Toward implementation of artificial neural networks that "really work".

Artificial neural networks are established analytical methods in bio-medical research. They have repeatedly outperformed traditional tools for pattern recognition and clinical outcome prediction while assuring continued adaptation and learning. However, successful experimental neural networks systems seldom reach a production state. That is, they are not incorporated into clinical information systems. It could be speculated that neural networks simply must undergo a lengthy acceptance process before they become part of the day to day operations of health care systems. However, our experience trying to incorporate experimental neural networks into information systems lead us to believe that there are technical and operational barriers that greatly difficult neural network implementation. A solution for these problems may be the delineation of policies and procedures for neural network implementation and the development a new class of neural network client/server applications that fit the needs of current clinical information systems.

Hospital Information Systems↗
PubMed1997

A personal digital assistant for determination of fluid needs for burn patients.

In most instances, the treatment of major burn victims begins in the emergency room of the hospital closest to the accident site. It can be assumed that the emergency room personnel in most hospitals rarely see patients with major burns. Thus, their experience with burn fluid resuscitation is often limited. Yet it is critical that primary early treatment of burn injury with fluid resuscitation begin before the patient is admitted locally or transferred to a burn unit. To assist these individuals a fluid resuscitation calculation application has been developed to run on a hand-held personal digital assistant (Palm Pilot). This hand-held application is meant to assist in emergency situations where time is short, thoughtful computation is not possible, and a quick determination of fluid replacement therapy is important for the survival of the patient.

Adult↗
PubMed1997

Distributed neural networks for biomedical research.

To facilitate the application of neural networks in bio-medical sciences, we have developed a new client-server neural network concept that enhances user operation and reduces processing time. The client component allows users to enter all information required to create and control a complete neural network project. The server component provides the actual tools for neural network development. The server is able to distribute the burden of neural network processing among remote machines, if available. To date, the system has been applied successfully to problems in the of chromosome recognition and horse gait analysis domains.

Computer Communication Networks↗
PubMed1997

Delivery of laboratory data with World Wide Web technology.

We have developed an experimental World Wide Web (WWW) based system to deliver laboratory results to clinicians in our Veterinary Medical Teaching Hospital. Laboratory results are generated by the clinical pathology section of our Veterinary Medical Diagnostic Laboratory and stored in a legacy information system. This system does not interface directly to the hospital information system, and it cannot be accessed directly by clinicians. Our "meta" system first parses routine print reports and then instantiates the data into a modern, open-architecture relational database using a data model constructed with currently accepted international standards for data representation and communication. The system does not affect either of the existing legacy systems. Location-independent delivery of patient data is via a secure WWW based system which maximizes usability and allows "value-added" graphic representations. The data can be viewed with any web browser. Future extensibility and intra- and inter-institutional compatibility served as key design criteria. The system is in the process of being evaluated using accepted methods of assessment of information technologies.

Animals↗
PubMed1996

Recombinant human alpha 2-HS glycoprotein inhibits insulin-stimulated mitogenic pathway without affecting metabolic signalling in Chinese hamster ovary cells overexpressing the human insulin receptor.

Insulin acts on its target tissues by specific interaction with the cell surface insulin receptor (IR). The IR possesses an intrinsic tyrosine kinase (TK) activity which is stimulated by insulin binding. This TK activity is required for many aspects of insulin signalling. We had earlier reported that human plasma alpha 2-HS glycoprotein (alpha 2-HSG) inhibits insulin-stimulated mitogenesis at the level of IR-TK (Mol Endo 7: 1445-1455, 1993). In the present study, using recombinant alpha 2-HSG, which possesses 50-100 times the specific activity of plasma alpha 2-HSG, we have further investigated the molecular basis of this effect. We examined the insulin-stimulated Ras signalling pathway in Chinese Hamster Ovary cells overexpressing the human IR. alpha 2-HSG inhibits insulin-induced tyrosine phosphorylation of IRS-1 and the subsequent association of GRB2, as well as Sos, with IRS-1. This inhibition results in reduced guanine nucleotide exchange in p21ras. alpha 2-HSG also inhibits the stimulation of Raf phosphorylation, in response to insulin, leading to inhibition of MEK activity. In a parallel pathway, alpha 2-HSG also inhibits insulin-induced tyrosine phosphorylation of Shc. However, alpha 2-HSG does not affect any of the metabolic actions of insulin rested in these cells. These results suggest that, while insulin's mitogenic effects can be abolished by inhibition of insulin-induced IR-TK, propagation of signals for metabolic activities might utilize alternate of rescue mechanisms.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Multiple neural network response variability as a predictor of neural network accuracy for chromosome recognition.

Human chromosome classification requires all chromosome appearing in a microphotograph of a dividing human cell to be classified within the known normal or abnormal 24 chromosome types. In recent years, research has focused on the use of neural networks for classification of normal chromosomes. Experimental work in this area led us to question whether learning variability, resulting when multiple neural networks are trained to solve the same problem, could be used as a predictor of classification performance. The Copenhagen chromosome data bank, consisting of 30-component feature vectors from 8106 chromosomes isolated from 180 cells, was divided into a training and a test subsets. Back propagation neural networks with 30 input nodes, 1 to 100 nodes in the hidden layer, and 24 output nodes were trained with the same learning parameters. After training, each neural network was tested. The neural network yielding the best classification was labeled as the optimal neural network. An error variability score was calculated for each test chromosome. This score was a function of all (100) neural network outputs obtained for that chromosome. The error variability scores ranged from 0.16 to 1.31 with a mean value of 0.41 and a SD of 0.12. There was significant difference (p < 0.0001) between the variability scores from chromosomes classified correctly (mean = 0.4, SD = 0.1, n = 3804) and incorrectly (mean = 0.62, SD = 0.19, n = 241) by the optimal neural network. When the variability score was used as a threshold to decide whether or not to accept the output of the optimal neural network, a peak classification rate of 98.93% was observed for chromosomes with an error variability score < 0.35. Results indicate that the error variability of multiple neural network responses can be used as a confidence indicator for a optimal neural network.

Humans↗
PubMed1993

Serum alpha 2-HS-glycoprotein is an inhibitor of the human insulin receptor at the tyrosine kinase level.

The insulin-dependent tyrosine kinase activity (TKA) of the insulin receptor (IR) plays an essential role in insulin signaling. Thus, dysregulation of IR-TKA might be an important element in the states of insulin resistance. A phosphorylated rat hepatic glycoprotein (pp63) acting as an inhibitor of IR-TK has been described. In search of the human homolog of pp63, we isolated a cDNA clone from a human liver lambda gt11 cDNA library. DNA sequence analysis reveals identity with the mRNA product of a human gene AHSG encoding a serum protein, alpha 2-Heremans Scmid-glycoprotein (alpha 2HSG), with heretofore unknown physiological function. Northern blot analysis demonstrates a 1.8-kilobase mRNA in human liver and HepG2 hepatoma cells. alpha 2HSG, purified from human serum, specifically inhibits insulin-stimulated IR autophosphorylation in vitro and in vivo as well as exogenous substrate tyrosine phosphorylation. alpha 2HSG also inhibits both insulin-induced tyrosine phosphorylation of IRS-1 and the association of IRS-1 with the p85 subunit of phosphatidylinositol-3 kinase in H-35 hepatoma cells. alpha 2HSG inhibits insulin-dependent mitogenesis, but does not affect insulin-stimulated induction of the metabolic enzyme tyrosine aminotransferase. alpha 2HSG does not compete with insulin for binding to IR. Finally, the action of alpha 2HSG is specific toward the IR-TK; its effect does not extend to insulin-like growth factor-I-stimulated TKA. Our results allow us to assign a biochemical function for human alpha 2HSG, namely regulation of insulin action at the IR-TK level.

Amino Acid Sequence↗
PubMed1991

Environmental signals induce major changes in virulence of Shigella spp.

Growth conditions play a major role in expression of virulence by Shigella spp. both in vitro (adherence and internalization in eukaryotic host cells) and in vivo (keratoconjunctivitis). Optimized expression of virulence required anaerobic growth to log phase in particular media such as brain heart infusion broth. Kinetic studies of guinea pig eye infections showed that as few as 2 x 10(5) S. dysenteriae CG097 or S. flexneri M90T, grown under these optimized conditions, produced keratoconjunctivitis in 15 h. In vitro studies demonstrated that adherence to and invasion of Henle 407 cells, at 37 degrees C, by organisms grown under these optimized conditions, were significantly greater than when organisms were grown aerobically under the same conditions.

Anaerobiosis↗
PubMed1991

Shigella dysenteriae 60R strain adheres to and invades tissue culture cells in the absence of virulence plasmid.

Evidence is presented that a high level Shiga toxin-producing strain Shigella dysenteriae 60R adheres to and invades the epithelial cell lines Hct8 and Henle 407. The invasive phenotype of S. dysenteriae 60R differs in four ways from the heretofore studied invasive Shigella phenotypes. First, S. dysenteriae 60R lacks the virulence plasmid characteristic of other invasive Shigella spp. and enteroinvasive Escherichia coli. Second, hybridization studies show that the known ipa genes are neither present in the chromosome nor in the small plasmid of 60R. Third, 60R adheres to and invades Hct8 and Henle 407 cells at 37 degrees C as well as at 30 degrees C. Fourth, the phenotype of adherence and invasion of 60R is remarkably stable, even during prolonged growth in laboratory media and storage.

Antigens, Bacterial↗
PubMed1989

Cloning and DNA sequence of plasmid determinant iss, coding for increased serum survival and surface exclusion, which has homology with lambda DNA.

Escherichia coli K12 cells carrying a cloned 1.4 kb HindIII fragment from plasmid ColV2-K94, showed increased survival in guinea pig serum. The recombinant plasmid also conferred group II surface exclusion, i.e. the cells were reduced in recipient ability towards the incoming plasmid R538drd in conjugation experiments. Southern blotting suggested homology with bacteriophage lambda DNA and to the insertion element IS2. Determination of the DNA sequence of the fragment demonstrated the presence of a truncated IS2 (165 bp), separated by 250 bp from a 900 bp stretch of homology with lambda DNA, beginning within the Rz gene and continuing in the rightward direction on the lambda map. A 97 amino acid open reading frame (ORF) adjacent to Rz and on the opposite strand, remained intact in iss, with several amino acid changes. The ORF in iss is preceded by sequences resembling prokaryotic ribosome binding sites and promoters.

Amino Acid Sequence↗
PubMed1987

The carbohydrate specificity of conglutinin and its homology to proteins in the hepatic lectin family.

Inhibition experiments with D-mannose oligosaccharides establish that conglutinin recognises terminal alpha 1----2 mannobiosyl units present in the glycopeptide of the alpha-chain of the complement component C3b. On the basis of its three domain structure and the homology of its N-terminal amino-acid sequence to that of the dog pulmonary surfactant protein, it is proposed that conglutinin is a member of the hepatic lectin family.

Animals↗