Investigation of plant derived compounds mediating cell signalling effectson FOXO1a and AMPK

  • Sandra Bacon

    Student thesis: Doctoral ThesisDoctor of Philosophy


    In recent years there has been a considerable increase in human obesity levels with an associated increase in the incidence of type 2 diabetes mellitus (T2DM), a disorder of glucose metabolism characterised by insulin resistance. It is unclear why obesity and insulin resistance should frequently exist comorbidly but the current prevalence of polypharmacy suggests the underlying mechanisms may be multifactorial in origin. This project has highlighted plant compounds and extracts with:
    Insulin-like properties in cell culture experiments in that they induce phosphorylation and therefore inactivation of the transcription factor FOXO1a, which is a major downstream effector insulin and
    Properties similar to the T2D drugs metformin and pioglitazone, which both activate AMOK signalling and reduce phosphorylation of the ribosomal protein S6.
    The project began with an analysis of plant extracts which can mediate intracellular cell signalling effects on FOXO1a and AMPK. The pilot data established that one extract (grape seed, GSE) induces regulation of AMPK and FOXO1a much more readily than another (pine bark, PBE). GSE and PBE were subjected to multiple fractionation methods and mass spectrometry to learn more about the active agent(s) in the extracts. Another chapter adopted a candidate-approach, investigating effects of the plant compound gallic acid (GA) on AMPK. Although GA cannot explain the effects of GSE on AMPK, the availability of a variety of analogues of GA allowed investigation of structural requirements for cell responses. Two more extracts, cranberry and lingonberry, were then investigated using the techniques established earlier with GSE and PBE. These studies discovered that fractions containing B-type linkages were more effective at phosphorylating of FOXO1a than those containing A-type linkages, suggesting B-type linkages may be required for these effects.
    Metformin itself is a synthetic analogue of a plant compound and metformin analogues known as diguanides were synthesised and structure/activity relationships were assessed. Diguanides and biguanides were found ti induce similar responses but diguanides were much more toxic than biguanides, suggesting they may be less specific in their mechanism of action, or alternatively that they have different intramitochondrial targets.
    The aims of this project were
    1. To extract polyphenolic compounds from grape seed, pine bark and berries using chromatography techniques and to characterise these compound using liquid chromatography/mass spectrometry
    2. To exclude or confirm insulin-like or metformin-like properties by application to cell culture models to assess effects on regulation of glucose and energy homeostasis by measuring phosphorylation of the transcription factor FOXO1a, AMPK and the ribosomal protein S6.
    Date of Award2012
    Original languageEnglish
    SupervisorGraham Rena (Supervisor) & Gordon McDougall (Supervisor)

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