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      Introduction of an agent-based multi-scale modular architecture for dynamic knowledge representation of acute inflammation

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      1 ,
      Theoretical Biology & Medical Modelling
      BioMed Central

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          Abstract

          Background

          One of the greatest challenges facing biomedical research is the integration and sharing of vast amounts of information, not only for individual researchers, but also for the community at large. Agent Based Modeling (ABM) can provide a means of addressing this challenge via a unifying translational architecture for dynamic knowledge representation. This paper presents a series of linked ABMs representing multiple levels of biological organization. They are intended to translate the knowledge derived from in vitro models of acute inflammation to clinically relevant phenomenon such as multiple organ failure.

          Results and Discussion

          ABM development followed a sequence starting with relatively direct translation from in-vitro derived rules into a cell-as-agent level ABM, leading on to concatenated ABMs into multi-tissue models, eventually resulting in topologically linked aggregate multi-tissue ABMs modeling organ-organ crosstalk. As an underlying design principle organs were considered to be functionally composed of an epithelial surface, which determined organ integrity, and an endothelial/blood interface, representing the reaction surface for the initiation and propagation of inflammation. The development of the epithelial ABM derived from an in-vitro model of gut epithelial permeability is described. Next, the epithelial ABM was concatenated with the endothelial/inflammatory cell ABM to produce an organ model of the gut. This model was validated against in-vivo models of the inflammatory response of the gut to ischemia. Finally, the gut ABM was linked to a similarly constructed pulmonary ABM to simulate the gut-pulmonary axis in the pathogenesis of multiple organ failure. The behavior of this model was validated against in-vivo and clinical observations on the cross-talk between these two organ systems

          Conclusion

          A series of ABMs are presented extending from the level of intracellular mechanism to clinically observed behavior in the intensive care setting. The ABMs all utilize cell-level agents that encapsulate specific mechanistic knowledge extracted from in vitro experiments. The execution of the ABMs results in a dynamic representation of the multi-scale conceptual models derived from those experiments. These models represent a qualitative means of integrating basic scientific information on acute inflammation in a multi-scale, modular architecture as a means of conceptual model verification that can potentially be used to concatenate, communicate and advance community-wide knowledge.

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          Most cited references57

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          Nitric oxide regulates exocytosis by S-nitrosylation of N-ethylmaleimide-sensitive factor.

          Nitric oxide (NO) inhibits vascular inflammation, but the molecular basis for its anti-inflammatory properties is unknown. We show that NO inhibits exocytosis of Weibel-Palade bodies, endothelial granules that mediate vascular inflammation and thrombosis, by regulating the activity of N-ethylmaleimide-sensitive factor (NSF). NO inhibits NSF disassembly of soluble NSF attachment protein receptor (SNARE) complexes by nitrosylating critical cysteine residues of NSF. NO may regulate exocytosis in a variety of physiological processes, including vascular inflammation, neurotransmission, thrombosis, and cytotoxic T lymphocyte cell killing.
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            In silico experiments of existing and hypothetical cytokine-directed clinical trials using agent-based modeling.

            W. An (2004)
            To introduce a form of mathematical modeling, agent-based modeling (ABM), and demonstrate its potential uses in the evaluation of the dynamics of the innate immune response (IIR) and the development of possible treatments for systemic inflammatory response syndrome (SIRS)/multiple organ failure (MOF). The IIR can be categorized as a complex system that responds to interventions in a nonintuitive fashion, leading to difficulty in translating basic science knowledge into effective treatments for SIRS/MOF. It is proposed that ABM is particularly well suited to examining the complex interactions of the IIR and its disordered states of SIRS/MOF. Computer simulation and mathematical modeling. Review articles on components and mechanisms involved in the IIR. Published results from phase III anticytokine/mediator trials. Published results from smaller clinical trials and animal studies. An abstract ABM of the IIR was created. The model reproduces the general behavior of the IIR with respect to outcome and cause of system "death." Patterns of levels of individual cytokines matched patterns of measured cytokines reported in the existing literature. Clinical trials of anticytokine therapy were simulated and produced outcomes qualitatively similar to those reported in the literature. A series of hypothetical treatment regimes (variation of dose and length of treatment [anti-tumor necrosis factor and anti-interleukin-1], anti-CD-18, and multiple-drug regimes [combination of anti-tumor necrosis factor, anti-interleukin-1, and anti-CD-18]) were formulated and implemented in the ABM. None of the simulated therapies showed a statistically significant improvement in system mortality. Presented herein is an abstracted ABM of the IIR. This model is intended primarily as an introduction to and demonstration of this technique. However, even this relatively simple model demonstrates counterintuitive system responses and the difficulty of effectively manipulating a complex system like the IIR. ABM may provide a synthetic, analytical platform to integrate basic science data on the IIR, thus eventually aiding in formulating and testing future mediator-directed therapies for SIRS/MOF before clinical trials, and it may provide insights into directions of future research.
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              Coarse-grained molecular simulation of diffusion and reaction kinetics in a crowded virtual cytoplasm.

              We present a general-purpose model for biomolecular simulations at the molecular level that incorporates stochasticity, spatial dependence, and volume exclusion, using diffusing and reacting particles with physical dimensions. To validate the model, we first established the formal relationship between the microscopic model parameters (timestep, move length, and reaction probabilities) and the macroscopic coefficients for diffusion and reaction rate. We then compared simulation results with Smoluchowski theory for diffusion-limited irreversible reactions and the best available approximation for diffusion-influenced reversible reactions. To simulate the volumetric effects of a crowded intracellular environment, we created a virtual cytoplasm composed of a heterogeneous population of particles diffusing at rates appropriate to their size. The particle-size distribution was estimated from the relative abundance, mass, and stoichiometries of protein complexes using an experimentally derived proteome catalog from Escherichia coli K12. Simulated diffusion constants exhibited anomalous behavior as a function of time and crowding. Although significant, the volumetric impact of crowding on diffusion cannot fully account for retarded protein mobility in vivo, suggesting that other biophysical factors are at play. The simulated effect of crowding on barnase-barstar dimerization, an experimentally characterized example of a bimolecular association reaction, reveals a biphasic time course, indicating that crowding exerts different effects over different timescales. These observations illustrate that quantitative realism in biosimulation will depend to some extent on mesoscale phenomena that are not currently well understood.
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                Author and article information

                Journal
                Theor Biol Med Model
                Theoretical Biology & Medical Modelling
                BioMed Central
                1742-4682
                2008
                27 May 2008
                : 5
                : 11
                Affiliations
                [1 ]Department of Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
                Article
                1742-4682-5-11
                10.1186/1742-4682-5-11
                2442588
                18505587
                97cf9f51-9b12-484f-b80e-ac8734c299dd
                Copyright © 2008 An; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 3 October 2007
                : 27 May 2008
                Categories
                Research

                Quantitative & Systems biology
                Quantitative & Systems biology

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