Enhanced cognition through dietary modulation of neuroinflammation in high risk APOE4 carriers

Currently 800,000 individuals in the UK have dementia, with a predicted rise to one million sufferers by 2025. An estimated 77% of those in elderly care homes suffer from dementia. Alzheimer's disease (AD), which is characterised by a loss of memory, mood changes, and communication and reasoning difficulties, is the most common form. An individual's risk of AD is determined by both lifestyle (exercise, smoking, diet etc) and genetic factors. Variations in our genes (DNA), which carry the information necessary for the manufacture of all proteins in the body, can affect both the structure of the protein or the levels produced. This may subsequently change body metabolism and risk of diseases such as AD. Variation in the APOE gene results in three possible versions of the protein, namely E2, E3 or E4. We all have two copies of each gene and those of us who are APOE3/E4 (25% UK population) or APOE4/E4 (2% UK population) are at 3- and 15-fold increased risk of AD compared to those with the most common APOE3/E3 (60% UK population). Furthermore APOE4 carriers develop the disease at a much younger age.
In cell, mice and human studies, we and others have demonstrated that a large component of the increased risk associated with an APOE4 genotype is likely to be due to increased (neuro)inflammation and oxidative stress. In AD, neuroinflammation and oxidative stress reduce the function of brain cells (neurons), and in particular the end region (the synapsis) which pass on signals to adjacent neurons.
Certain dietary components such as DHA (a fish oil fatty acid) and flavanols (plant derived compounds found in cocoa, berries and tea), have been shown to reduce inflammation and improve cognition. Although there is considerable 'overlap' between the beneficial impact of these dietary components and the negative impact of the APOE4 genotype on brain function, surprisingly the ability of DHA and flavanols to reduce the risk of dementia in APOE4 carriers is unknown. Furthermore given that DHA and flavanols have some distinct effects on brain biology, we hypothesise that the effect of the two components fed simultaneously will have a greater impact than either fed separately.
In brief, we will carry out a feeding study in mice which express either the human version of the APOE3 or APOE4 gene. Adult APOE3 or APOE4 mice will be fed a control chow diet, a high fat diet (HFD, similar to a human diet), HFD+DHA, HFD+flavanols, or HFD+DHA and flavanols, for 16 weeks. Brain function in the animals will be assessed every 4 weeks using a radial arm water maze, which is commonly used for the assessment of different forms of memory. At the end of the feeding period, the animals will be sacrificed and the brain tissue analysed for a range of factors which modulate brain inflammation and oxidative status, along with the levels of DHA (and other fats), flavanols and a range of compounds they produce. In addition the brains of the animals will be stained with 'dyes' enabling the visualisation (using sophisticated microscopy techniques) of markers of neuronal and function, growth and repair.
From a scientific point of view the outlined work is predicted to significantly advance current understanding of the interactive impact of APOE genotype and dietary components on cognitive abilities and the underlying biological mechanisms. From a public health view-point we aim to identify targeted dietary strategies, which will promote healthy brain ageing, in particular in the large 'at-risk' APOE4 population subgroup. This would be associated with considerable benefit with respect to quality of life in the elderly, and reductions in the ever increasing NHS spent associated with dementia.

The APOE4 genotype is the most significant common genetic risk factor for accelerated brain aging and Alzheimer's disease. We have demonstrated over the last 10 years using cell lines, targeted replacement rodents and in humans, that (neuro)inflammation and oxidative stress are likely to underlie the cognitive decline associated with the APOE4 allele (25% UK population). The anti-inflammatory properties of the fish oil fatty acids (EPA and DHA) have been relatively consistently described. Furthermore, in a series of recent publications in rodent models we report that plant derived flavanols improve memory in aged animals, reduce glial (inflammatory) cells activation, and alter inflammatory-dependent neuronal signalling and synaptic plasticity (an early defining feature of cognitive dysfunction) biomarkers.
Given the identified 'overlap' between the aetiological basis of APOE4-cognitive decline associations and the molecular and cellular targets of flavanols and DHA, we hypothesise that these dietary components will ameliorate the neuroinflammation, loss of synaptic plasticity and accelerated cognitive decline associated with the APOE4 allele.
APOE3 or APOE4 mice will be fed a control chow diet, high fat diet (HFD), HFD+DHA, HFD+flavanols, or HFD+DHA and flavanols, for 16 weeks. Spatial working and reference memory will be assessed every 4 weeks using the radial arm water maze methodology. Brain tissue will be isolated and quantified for a range of lipid-derived, NO-derived, and cytokine modulators of inflammation and oxidative status. The protein levels and phosphorylation status of key (often oxidative sensitive) signalling pathways involved in inflammation and synaptic plasticity will also be assessed. Furthermore DHA, flavonols and their metabolites will be quantified pre- and post-intervention to establish APOE genotype mediated differences in DHA and flavonols tissue uptake and metabolism.

In general the proposed work will broaden our understanding of the role of dietary components in healthy brain aging. The research addresses the BBSRC 2011-2015 and the Cross-Council research priority areas of 'Healthy and safe food', 'Research to inform public policy' and 'Aging research: lifelong health and well being' by:
-Conducting 'mechanistic research on the biology of ageing and its modulation by diet'
-'Identifying interventions to improve physical and mental well being later in life'
Dissemination will be carried out at a number of levels including; (1) Data presentation at scientific meetings and to industrial partners, (2) Publication of findings in high impact journals, such as the JBC, J Neurosci and AJCN, (3) Press releases, and (4) Inclusion in the material taught to our UG and PG Nutrition and Medical students.
The predicted beneficiaries of the research are likely to be:
(1) The academic community: see academic beneficiaries section
(2) Population at large: With rapidly ageing populations, and the exponential increase in AD risk with age (doubling every 5 years after the age of 60), a > 3-fold rise in the population prevalence of dementia is predicted by 2050. Currently there is a distinct lack of strategies to promote health brain ageing. An effective dietary approach (such as proposed in the current application) to aid cognition and delay the onset of disease, in particular in 'high-risk', early-onset APOE4 carriers, would contribute significantly to morbidity compression in the elderly and increase 'healthy life expectancy'.
(3) UK economy and National Health Service (NHS): Strategies associated with healthy brain ageing and a reduction in the population burden of dementia would undoubtedly be associated with large economic benefits to the NHS and UK economy at large. Individuals live with dementia for 2-20y, the vast majority of which is non-independent living. Approximately 77% of the >65y individuals living in residential care homes are demented (Dementia UK, 2007). It is estimated that the total annual cost of dementia to the UK economy is £17 billion (or £25k per person with advanced dementia). Predicted escalating costs are not sustainable.
(4) Public health policy makers: It is becoming likely that generic dietary recommendations will to a degree be replaced by more targeted advice based on an individual genetic make-up and other personal attributes. When genetic testing become more widely available, the APOE gene is likely to be included in a standard genetic test. The current research will provide considerable insight into what specific dietary guidelines should be given to the 'at-risk' APOE4 individuals who represent 25% of the UK population.
(5) Food and Nutraceutical/Pharmaceutical Industries: The general consumer, and in particular the elderly are motivated to purchase foods aimed at improving cognition. The data generated will provide the UK based and world-wide food industry with evidence to design and produce effective cognitive enhancing ingredients and products, which would lead to an improved market share. Although oily fish is currently the only significant source of dietary DHA, as part of the BBSRC Programme Grant (BB/I0153451, which began in April 2012), in collaboration with Prof Jonathan Napier and his group at BBSRC, Rothamsted, we are assessing the absorption and bio-efficacy of seed oil derived DHA produced by GM technology. A natural extension of this could be the production of high flavanols+DHA seed oils.

Note: It is recognised that the full realisation of impacts 2-4 will require some substantiation of the findings from our animal studies in human trials. The current work programme will provide the novel data needed to inform the design and focus of such follow on human RCTs.