Double-transgenic amyloid precursor protein/presenilin 1 (APP/PS1) mice express a chimeric mouse/human APP bearing the Swedish mutation (Mo/HuAPP695swe) and a mutant human PS1-dE9 both causative of familial Alzheimer's disease (FAD). Transgenic mice show impaired memory and learning performance from the age of 6 months onwards. Double-transgenic APP/PS1 mice express altered APP and PS1 mRNAs and proteins, reduced β-secretase 1 (BACE1) mRNA and normal BACE1 protein, all of which suggest a particular mechanism of amyloidogenesis when compared with sporadic AD. The first β-amyloid plaques in APP/PS1 mice appear at 3 months, and they increase in number and distribution with disease progression in parallel with increased levels of brain soluble β-amyloid 1-42 and 1-40, but also with reduced 1-42/1-40 ratio with age. Amyloid deposition in plaques is accompanied by altered mitochondria and increased oxidative damage, post-translational modifications and accumulation of altered proteins at the dystrophic neurites surrounding plaques. Degradation pathways are also modified with disease progression including activation of the immunoproteasome together with variable alterations of the different protease activities of the ubiquitin-proteasome system. Present observations show modifications in the production of β-amyloid and activation and malfunction of the subcellular degradation pathways that have general implications in the pathogenesis of AD and more particularly in specificities of FAD amyloidogenesis.

Diets containing a high proportion of fat with respect to protein plus carbohydrates are capable of inducing ketone body production in the liver, which provides an energetic alternative to glucose. Some ketogenic diets have been tested as therapeutic strategies for treating metabolic disorders related to a deficiency in glucose-driven ATP generation. However, ketone bodies are not capable of providing extra tricarboxylic acid cycle intermediates, limiting the anabolic capacity of the cell. Therefore, it is reasonable to hypothesize that supplementing a ketogenic diet with anaplerotic compounds such as triheptanoin may improve ketogenic diet effectiveness. The present study tests this hypothesis in APP/PS1 (APPswe/PS1dE9) transgenic mice, used as a model of familial Alzheimer's disease because impaired energy supply to neurons has been linked to this neurodegenerative process. Triheptanoin supplementation to a ketogenic diet for three months and starting at the age of three months reduces the memory impairment of APP/PS1 mice at the age of 6 months. The Aβ production and deposition were not significantly altered by the ketogenic diet, supplemented or not by triheptanoin. However, mice fed with triheptanoin-rich ketogenic diet have shown decreased astroglial response in the vicinity of Aβ plaques and decreased expression of the pro-inflammatory cytokine interferon-γ in astrocytes. These findings correlate with transcriptional up-regulation of the ROS detoxifying mechanisms Sirt1 and Pparg, thus linking triheptanoin with improved mitochondrial status. Present findings support the concept that ketogenic diets supplemented with anaplerotic compounds can be considered potential therapeutic strategies at early stages of Alzheimer's disease.

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