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The biology of trophoblast cell development can be investigated using in vitro model systems. The Rcho-1 trophoblast stem cell line was derived from a rat choriocarcinoma and is an effective tool for elucidating regulatory mechanisms controlling trophoblast cell differentiation. In this chapter, we describe methods used in the maintenance and manipulation of the Rcho-1 trophoblast cell line.
The MCF-7 cell line was derived from a patient with metastatic breast cancer in 1970. Since then it has become a prominent model system for the study of estrogen receptor-positive breast cancer. With this model as a focus, this review summarizes important studies addressing tumor necrosis factor-alpha as a prototypical apoptosis-inducing cytokine in MCF-7 cells. Both survival and death receptor signaling pathways are discussed in terms of their role in chemotherapy-induced apoptosis as well as in chemoresistance. Novel therapeutic approaches to the treatment of breast cancer are proposed utilizing knowledge of these signaling pathways as targets. Specifically, ceramide metabolism is proposed as a novel target for chemosensitivity, perhaps combined with selective inhibitors of Bcl-2 or PI3K/Akt/nuclear factor-kappaB. Suggested areas of future research include translational studies manipulating candidate survival and death signaling pathways.
Mental health treatment teams are living systems at the group level and comprise key productive subsystems of organizations providing mental health care. Effective treatment teams, like effective organizations, are anticipatory systems that contain subsystems that model and predict future system and environmental conditions and enable responses that increase system viability. A systems analysis of treatment teams highlights their potential instability due to their tendencies to regress toward dysfunctional partial systems and their active maintenance in nonequilibrium steady states with their organizational and external environments. Team subsystems are analyzed from the viewpoints of system processes and also with regard to individuals and their roles. Boundary processes are central to effective team functioning, assure constancy of team membership, and regulate the team's interfaces with its parent agency and with the external environment. Various causes and forms of disturbed information processing within hierarchical organizations are examined, and their effects at the treatment team level are discussed. The conclusion of the discussion focuses on team leadership and how leadership expands upon the concept of the decider subsystem to include role and personal factors to the team's leaders, and functions that are anticipatory and integrative in nature. Effective leaders must set appropriate thresholds for feedback regulation processes, and balance several pairs of seemingly opposing forces, including homeostasis and development, role differentiation and role overlap, and personal accountability and empowerment of others.
Analysis of the resultant mathematical models demonstrated that exposure of liver tissue to aqueous solutions of acids leads to an increase of pH, and its contact with alkaline solutions results in an appreciable decrease of the pH of the model system. This should be borne in mind when creating and analyzing analog models describing the process of extraction of various organic compounds from biological material.
Family nursing is in the early stages of development, and there is often difficulty in translating nursing conceptual frameworks into terms that are less abstract and more readily usable in the family practice arena. Yet the conversion of abstract ideas to concrete descriptions is necessary if nursing theory-based practice is to expand. This article describes the client system known as family within the Neuman systems model. Based on clinical data and the experience of nurses using the Neuman model in practice, a description of the family as client is developed. The five variables of Neuman's model are identified and the terms used in describing the family system are clarified. A rationale for the application is also presented.
Excitotoxicity is defined as a mode of neural cell death triggered by overactivation of receptors for the amino acid transmitter glutamate. There is considerable evidence that excitotoxicity is responsible for cell death in several neuropathological states, including some retinal diseases. The isolated retina, particularly from chick embryos, has been used extensively as an experimental system to characterize this process. This paper summarizes the use of isolated retina as a model system for studies of excitotoxicity from a theoretical and methodological point of view, and reviews results obtained from studies utilizing this system.
Bicarbonate markedly enhances ethylene production from 1-aminocyclopropane-1-carboxylic acid (ACC) in model chemical systems where the conversion is free radical-mediated, in thylakoid membrane suspensions of Phaseolus vulgaris L. cv Kinghorn where the reaction is light-dependent, and in microsomal membrane suspensions and intact tissues where the reaction is enzymically mediated. In two model systems generating free radicals-the Fenton reaction and a reaction mixture containing xanthine/xanthine oxidase, NaHCO(3) (200 millimolar) increased the formation of ethylene from ACC by 84-fold and 54-fold, respectively. Isolated thylakoid membranes also proved capable of ACC-dependent ethylene production, but only upon illumination, and this too was enhanced by added NaHCO(3). As well, light-induced inhibition of ACC-dependent ethylene production by leaf discs was relieved by adding 200 millimolar NaHCO(3). Finally, NaHCO(3) (200 millimolar) augmented ACC-dependent ethylene production from young carnation flowers by about 4-fold, and the conversions of ACC to ethylene by microsomes isolated from carnation flowers and etiolated pea epicotyls were higher by 1900 and 62%, respectively, in the presence of 200 millimolar NaHCO(3).This increased production of ethylene appears not to be due to bicarbonate or CO(2)-induced release of the gas from putative receptor sites, since the addition of NaHCO(3) to sealed reaction mixtures after the ACC to ethylene conversion had been terminated had no effect. Spin-trapping studies have confirmed that bicarbonate does not facilitate the formation of free radicals thought to be involved in the conversion of ACC to ethylene. Nor did bicarbonate alter the physical properties of the membrane bilayer, which might indirectly modulate the activity of the membrane-associated enzyme capable of converting ACC to ethylene. Rather, bicarbonate appears to directly facilitate the conversion of ACC to ethylene, and the data are consistent with the view that CO(2) derived from bicarbonate is the active molecular species.
The bacterium Vibrio cholerae, like other human pathogens that reside in environmental reservoirs, survives predation by unicellular eukaryotes. Strains of the O1 and O139 serogroups cause cholera, whereas non-O1/non-O139 strains cause human infections through poorly defined mechanisms. Using Dictyostelium discoideum as a model host, we have identified a virulence mechanism in a non-O1/non-O139 V. cholerae strain that involves extracellular translocation of proteins that lack N-terminal hydrophobic leader sequences. Accordingly, we have named these genes "VAS" genes for virulence-associated secretion, and we propose that these genes encode a prototypic "type VI" secretion system. We show that vas genes are required for cytotoxicity of V. cholerae cells toward Dictyostelium amoebae and mammalian J774 macrophages by a contact-dependent mechanism. A large number of Gram-negative bacterial pathogens carry genes homologous to vas genes and potential effector proteins secreted by this pathway (i.e., hemolysin-coregulated protein and VgrG). Mutations in vas homologs in other bacterial species have been reported to attenuate virulence in animals and cultured macrophages. Thus, the genes encoding the VAS-related, type VI secretion system likely play an important conserved function in microbial pathogenesis and represent an additional class of targets for vaccine and antimicrobial drug-based therapies.
The Escherichia coli ammonium transport protein (AmtB) has become the model system of choice for analysis of the process of ammonium uptake by the ubiquitous Amt family of inner membrane proteins. Over the past 6 years we have developed a range of genetic and biochemical tools in this system. These have allowed structure/function analysis to develop rapidly, offering insight initially into the membrane topology of the protein and most recently leading to the solution of high-resolution 3D structures. Genetic analysis has revealed a novel regulatory mechanism that is apparently conserved in prokaryotic Amt proteins and genetic approaches are also now being used to dissect structure/function relationships in Amt proteins. The now well-recognised homology between the Amt proteins, found in archaea, eubacteria, fungi and plants, and the Rhesus proteins, found characteristically in animals, also means that studies on E. coli AmtB can potentially shed light on structure/function relationships in the clinically important Rh proteins.
We have studied the antitumor effects of Bacillus Calmette-Guerin (RIVM strain) in the syngeneic rat bladder tumor model RBT323. In an immunohistochemical infiltrate study we compared the antitumor effects of BCG with the immunopathological findings in order to get more insight into the possible effector mechanisms of BCG. The antitumor effects of BCG appeared not to be dose-dependent, in the dose range tested. In rechallenge experiments no difference in growth of control tumors was seen between rats pretreated- or not pretreated with BCG. There was, however, a significant increase in antitumor effect of BCG after pretreatment with BCG. Immunohistological examination of BCG treated tumors revealed infiltrates consisting of macrophages, B-cells and T-cells. These results imply that whereas no specific response against the RBT323 cells is generated by BCG treatment, possibly BCG induced antigens do serve as immunogens in this nonimmunogenic syngeneic rat bladder tumor model system.
Acrylamide levels in cooked/processed food can be reduced by treatment with citric acid or glycine. In a potato model system cooked at 180 degrees C for 10-60 min, these treatments affected the volatile profiles. Strecker aldehydes and alkylpyrazines, key flavor compounds of cooked potato, were monitored. Citric acid limited the generation of volatiles, particularly the alkylpyrazines. Glycine increased the total volatile yield by promoting the formation of certain alkylpyrazines, namely, 2,3-dimethylpyrazine, trimethylpyrazine, 2-ethyl-3,5-dimethylpyrazine, tetramethylpyrazine, and 2,5-diethyl-3-methylpyrazine. However, the formation of other pyrazines and Strecker aldehydes was suppressed. It was proposed that the opposing effects of these treatments on total volatile yield may be used to best advantage by employing a combined treatment at lower concentrations, especially as both treatments were found to have an additive effect in reducing acrylamide. This would minimize the impact on flavor but still achieve the desired reduction in acrylamide levels.
Phosphate was found to dramatically enhance the formation of 2-methyl-2-acetylthiazolidine from a cysteamine/2,3-butanedione model system. In addition to the major component, 2-methyl-2-acetylthiazolidine, significant amounts of two structurally closely related compounds, 2-acetyl-2,3,5,6-tetrahydro-1,4-thiazine and 5-acetyl-2,3-dihydro-1,4-thiazine, were characterized by using GC/MS (CI and EI). There was an oxidative transformation of 2-acetyl-2,3,5,6-tetrahydro-1,4-thiazine to 5-acetyl-2,3-dihydro-1,4-thiazine in the presence of azodicarbonamide. A formation mechanism for 2-methyl-2-acetylthiazolidine and structurally related 2-acetyl-2,3,5,6-tetrahydro-1,4-thiazine and 5-acetyl-2,3-dihydro-1,4-thiazine is proposed.
[structure: see text] A model system has been developed to study the synergy between aromatic stacking and hydrogen bonding in the binding of a flavin derivative. The results show that the identity of both the hydrogen bonding and pi-stacking units strongly determine the overall receptor affinity for flavin in both the oxidized and radical anion forms.
To study responses to Mycobacterium leprae antigens, we developed an in vitro model system in which latex particles coated with M. leprae sonic extract (MLSON) antigen were presented to monocytes. Uptake and oxidative response as measured by superoxide production to these antigens were investigated. Phagocytosis of MLSON-coated particles was greater than that of control particles in monocytes from both leprosy patients and controls from leprosy-endemic areas; uptake of MLSON-coated particles was higher in monocytes from lepromatous leprosy patients than in cells from tuberculoid leprosy patients and controls. In both patients and controls, uptake of latex particles coated with leprosy antigens triggered very little reduction of nitroblue tetrazolium although the cells were capable of mounting a respiratory burst. Antigen-coated latex particles can therefore be used as a tool to investigate monocyte responses to M. leprae and individual recombinant antigens.
The precision, accuracy, and durability of the Reflotron were evaluated by the Massachusetts Model Systems for Blood Cholesterol Screening Program. Screenings were conducted in diverse community settings over 16 months. Fingerstick samples from 10,428 individuals were tested. None of the four analyzers met the 1992 standards for precision, although two met the 1992 standards for accuracy. More than 40% of Reflotron values differed from the reference laboratory values by upwards of 5%. More than 16% of individuals were misclassified in terms of their risk category. All four instruments malfunctioned during the project.
A novel model system was developed for studying the effects of colloidal Ca phosphate (CCP) concentration on the rheological properties of Cheddar cheese, independent of proteolysis and any gross compositional variation. Cheddar cheese slices (disks; diameter = 50 mm, thickness = 2 mm) were incubated in synthetic Cheddar cheese aqueous phase solutions for 6 h at 22 degrees C. Control (unincubated) Cheddar cheese had a total Ca and CCP concentration of 2.80 g/100 g of protein and 1.84 g of Ca/100 g of protein, respectively. Increasing the concentration of Ca in the synthetic Cheddar cheese aqueous phase solution incrementally in the range from 1.39 to 8.34 g/L significantly increased the total Ca and CCP concentration of the cheese samples from 2.21 to 4.59 g/100 g of protein and from 1.36 to 2.36 g of Ca/100 g of protein, respectively. Values of storage modulus (index of stiffness) at 70 degrees C increased significantly with increasing concentrations of CCP, but the opposite trend was apparent at 20 degrees C. The maximum in loss tangent (index of meltability/flowability) decreased significantly with increasing concentration of CCP, and there was no significant effect on the temperature at which the maximum in loss tangent occurred (68 to 70 degrees C). Fourier transform mechanical spectroscopy showed the frequency dependence of all of the cheese samples increased with increasing temperature; however, solubilization of CCP increased the frequency dependence of the cheese matrix only in the high temperature region (i.e., >35 degrees C). These results support earlier studies that hypothesized that the concentration of CCP strongly modulates the rheological properties of cheese.
The overall goal of our research is to elucidate the cellular mechanisms involved in the process of luteinizing hormone (LH)-stimulated down-regulation of the LH receptor. Towards this end, we became interested in determining whether cultured granulosa cells could be used as a physiologic model system to study this important process. In this report, we show that a very brief exposure (2 min) to physiologic concentrations of LH causes down-regulation of the LH receptor in granulosa cells cultured in serum-free medium. These data represent the first in vitro demonstration of down-regulation of the LH receptor in the granulosa cell. Furthermore, the dose dependency and kinetics of down-regulation of the LH receptor in vitro, as described here, are very similar to those reported for LH receptor down-regulation in vivo. Thus, this granulosa cell culture system is a powerful new model for studying the biochemical events involved in LH receptor down-regulation.
Experiments have been performed to demonstrate and quantify cross-relaxation between water and methylene resonances in a simple model system. Inversion recovery experiments on aqueous solutions of polyethylene glycol produce a transient nuclear Overhauser effect that alters the recovery of the methylene resonance. The relevant equations and parameters that describe this effect are identified and their values are explicitly quantified by analyzing the experimental results. It is shown that cross-relaxation is measurable and significant in this system even though there are no strong hydrophilic interactions available to immobilize water. In studies of dog bile, the water and lipid resonances behave in a qualitatively similar fashion, lending support to the contention that cross-relaxation cannot be neglected in solutions of biological macromolecules.