The Role of Arachidonic Acid and Its Metabolites in Controlling Inositol Lipid Metabolism in Swiss 3T3 Cells

Swiss 3T3 fibroblasts were chosen as a model system to study the role of arachidonic acid and/or its metabolites in controlling sermuM- and PDGF-induced inositol lipid metabolism. (0.01 - 10 muM) caused a rapid stimulation of inositol phospholipid hydrolysis which was maximal within 1-2 minutes of stimulation with the agonist. The level of Ptdlns was not significantly affected by PGF2a. The time course of [3H]-InsP accmuMulation suggests that InsP was not produced directly from Ptdlns, but was formed by the dephosphorylation of InsP2 and InsP3 at least within 1 minute after the PGF2a addition. 1.6 muM PGF2a caused a two-three fold increase in [3H] -PtdA levels, but did not affect the levels of any other major phospholipid measured. Having shown that PGF2a stimulated inositol lipid metabolism in 3T3 cells, it was postulated that the formation of prostaglandins from AA might be intermediatory in the action of PDGF on inositol phospholipid hydrolysis. In order to prove this, it was necessary to be able to inhibit their formation. Surprisingly, the cyclooxygenase inhibitors tested, (flurbiprofen and indomethacin), on their own caused a stimulation of inositol lipid metabolism. This was observed as an increase in [3H]-InsP levels and in [3H]-PtdA levels. The inhibitors had no effect on the levels of any other major phospholipid. The effect of flurbiprofen on inositol lipid metabolism was shown to be dose-related, with 100 muM flurbiprofen producing the maximmuM stimulation. By inhibiting cyclooxygenase activity, it seemed possible that flurbiprofen might have re-directed free AA towards the lipoxygenase pathway and thus the possibility that a stimulatory lipoxygenase metabolite was responsible for the increase in inositol phospholipid hydrolysis was investigated. BW755C, an inhibitor of both cyclooxygenase and lipoxygenase also caused a stimulation of inositol lipid metabolism, in a dose-related manner. The effect was maximal with 100 muM BW755C. Although it remains possible that BW755C did not inhibit all the 1.o. enzymes, it seemed more likely that the stimulation of inositol phospholipid hydrolysis was due to AA itself. Further evidence which suggested this to be the case was that flurbiprofen and BW755C, in a dose-dependent manner caused an increase in the level of free [3H]-AA in the medimuM surrounding the cells. The drugs also caused an increase in the level of [3H] -arachidonyl PtdA. Exogenously applied AA increased the level of [3H]-InsP in a dose-related manner which was maximal with 100 muM AA. This concentration of AA was thought too high to be of physiological significance. However, one contributing factor here was that the majority of the exogenously applied AA bound to albmuMin in the BSS surrounding the cells. In albmuMin-free BSS 0.1 muM AA gave almost an equivalent increase in InsP formation as 100 muM AA in cells surrounded by albmuMin-containing BSS. Also, in experiments where the effects of BW755C and indomethacin on [3H]-AA release and on [3H]-arachidonyl PtdA formation were studied, the results were consistent with the idea that endogenously released AA was binding to albmuMin in the BSS surrounding the cells. Further support for the theory that AA itself stimulated inositol lipid metabolism in 3T3 cells was that flurbiprofen and BW755C were not additive with exogenously applied AA in stimulating inositol phospholipid hydrolysis. This suggests that they have the same pathway of action. Studies were then carried out to investigate the pathway by which AA was liberated. Melittin, a PLA2 activator, stimulated both AA release and inositol lipid metabolism in a dose-related manner. Dexamethasone, an indirect inhibitor of PLA2 abolished the BW755C- and flurbiprofen-induced increase in inositol lipid metabolism in a dose-related manner. These results suggest that the pathway is involved in the liberation of AA from the membrane phospholipids in 3T3 cells. (Abstract shortened by ProQuest.)

Managing student expectations online

In contrast to other studies of students in online environments, which examine the skills and attitudes that students bring to an online university learning environment, we are interested in the expectations with which students come to online university study. Four expectational barriers, which arise from students&rsquo; background and cultural history, are identified as being: who is responsible for learning, who is responsible for student interaction with content, who is responsible for the use of appropriate learning strategies and who is responsible for required ancillary skills. There is a discussion of how these barriers arise and how one might attempt to manage the students&rsquo; expectations and ameliorate their effects.<br /

Structured development of an asynchronous forth processor using trace theory

This thesis examines the use of a structured design methodology in the design of asynchronous circuits so that high level constructs can be specified purely in terms of signal exchanges and without the intrusion of lower level concepts. Trace theory is used to specify a multi-processor Forth machine at a high level then part of the design is further elaborated using trace theory operations to (insure that the behaviours of the lower level constructs will combine to give the high level specified behaviour without locking or other hazards. A novel form of threaded language to take advantage of the machine architecture is developed. At suitable points the design is tested by simulation. The stack element which is designed is reduced to an electric circuit which is itself tested by simulation to verify the design

Convex hulls in concept induction

Classification learning is dominated by systems which induce large numbers of small axis-orthogonal decision surfaces. This strongly biases such systems towards particular hypothesis types but there is reason believe that many domains have underlying concepts which do not involve axis orthogonal surfaces. Further, the multiplicity of small decision regions mitigates against any holistic appreciation of the theories produced by these systems, notwithstanding the fact that many of the small regions are individually comprehensible. This thesis investigates modeling concepts as large geometric structures in n-dimensional space. Convex hulls are a superset of the set of axis orthogonal hyperrectangles into which axis orthogonal systems partition the instance space. In consequence, there is reason to believe that convex hulls might provide a more flexible and general learning bias than axis orthogonal regions. The formation of convex hulls around a group of points of the same class is shown to be a usable generalisation and is more general than generalisations produced by axis-orthogonal based classifiers, without constructive induction, like decision trees, decision lists and rules. The use of a small number of large hulls as a concept representation is shown to provide classification performance which can be better than that of classifiers which use a large number of small fragmentary regions for each concept. A convex hull based classifier, CH1, has been implemented and tested. CH1 can handle categorical and continuous data. Algorithms for two basic generalisation operations on hulls, inflation and facet deletion, are presented. The two operations are shown to improve the accuracy of the classifier and provide moderate classification accuracy over a representative selection of typical, largely or wholly continuous valued machine learning tasks. The classifier exhibits superior performance to well-known axis-orthogonal-based classifiers when presented with domains where the underlying decision surfaces are not axis parallel. The strengths and weaknesses of the system are identified. One particular advantage is the ability of the system to model domains with approximately the same number of structures as there are underlying concepts. This leads to the possibility of extraction of higher level mathematical descriptions of the induced concepts, using the techniques of computational geometry, which is not possible from a multiplicity of small regions

Editorial: Building and delivering real-world, integrated sustainability solutions: Insights, methods and case-study applications

This Research Topic aims to showcase research, development and technology (RDT) work toward devising and delivering integrated solutions that support and enhance the climate smart landscape (CSL)-based approach. This Research Topic comprises 13 articles, including 10 Original Research articles,1 Review, 1 Hypothesis and Theory article, and 1 Technology Report. State-of-the-art modeling approaches and sampling technologies are showcased. Contributed papers present new methodological/technological innovation, findings, and/or insights across four themes: (1) landscape productivity and crop suitability, (2) variable crop requirements for water and nutrients,(3) crop health status, phenology and phenotyping, (4)crop disease assessment and prediction under integrated pest management (IPM) and the CSL approach

Establishment and operation of a Good Manufacturing Practice-compliant allogeneic Epstein-Barr virus (EBV)-specific cytotoxic cell bank for the treatment of EBV-associated lymphoproliferative disease

Funded by Wellcome Trust Translational Award SNBTSPeer reviewedPublisher PD

Qualitative study exploring the key determinants of information gathering to inform the management of over-the-counter (OTC) consultations in community pharmacies

Peer reviewedPublisher PD