A Dietary Ketone Ester Normalizes Abnormal Behavior in a Mouse Model of Alzheimer's Disease.

Because of a decreased sensitivity toward insulin, a key regulator of pyruvate dehydrogenase (PDH), Alzheimer's patients have lower brain glucose utilization with reductions in Tricarboxylic Acid (TCA) cycle metabolites such as citrate, a precursor to n-acetyl-aspartate. In the 3xTgAd mouse model of Alzheimer's disease (AD), aging mice also demonstrate low brain glucose metabolism. Ketone metabolism can overcome PDH inhibition and restore TCA cycle metabolites, thereby enhancing amino acid biosynthesis. A ketone ester of d-ß-hydroxybutyrate was incorporated into a diet (Ket) and fed to 3xTgAd mice. A control group was fed a calorically matched diet (Cho). At 15 months of age, the exploratory and avoidance-related behavior patterns of the mice were evaluated. At 16.5 months of age, the animals were euthanized, and their hippocampi were analyzed for citrate, α-ketoglutarate, and amino acids. In the hippocampi of the Ket-fed mice, there were higher concentrations of citrate and α-ketoglutarate as well as higher concentrations of glutamate, aspartate and n-acetyl-aspartate compared with controls. There were positive associations between (1) concentrations of aspartate and n-acetyl-aspartate (n = 14, R = 0.9327), and (2) α-ketoglutarate and glutamate (n = 14, R = 0.8521) in animals maintained on either diet. Hippocampal n-acetyl-aspartate predicted the outcome of several exploratory and avoidance-related behaviors. Ketosis restored citrate and α-ketoglutarate in the hippocampi of aging mice. Higher concentrations of n-acetyl-aspartate corresponded with greater exploratory activity and reduced avoidance-related behavior.

Effects of a dietary ketone ester on hippocampal glycolytic and tricarboxylic acid cycle intermediates and amino acids in a 3xTgAD mouse model of Alzheimer's disease.

In patients with Alzheimer's disease (AD) and in a triple transgenic (3xTgAD) mouse model of AD low glucose metabolism in the brain precedes loss of memory and cognitive decline. The metabolism of ketones in the brain by-passes glycolysis and therefore may correct several deficiencies that are associated with glucose hypometabolism. A dietary supplement composed of an ester of D-ß-hydroxybutyrate and R-1,3 butane diol referred to as ketone ester (KE) was incorporated into a rodent diet and fed to 3xTgAD mice for 8 months. At 16.5 months of age animals were killed and brains dissected. Analyses were carried out on the hippocampus and frontal cortex for glycolytic and TCA (Tricarboxylic Acid) cycle intermediates, amino acids, oxidized lipids and proteins, and enzymes. There were higher concentrations of d-ß-hydroxybutyrate in the hippocampus of KE-fed mice where there were also higher concentrations of TCA cycle and glycolytic intermediates and the energy-linked biomarker, N-acetyl aspartate compared to controls. In the hippocampi of control-fed animals the free mitochondrial [NAD+ ]/[NADH] ratio were highly oxidized, whereas, in KE-fed animals the mitochondria were reduced. Also, the levels of oxidized protein and lipids were lower and the energy of ATP hydrolysis was greater compared to controls. 3xTgAD mice maintained on a KE-supplemented diet had higher concentrations of glycolytic and TCA cycle metabolites, a more reduced mitochondrial redox potential, and lower amounts of oxidized lipids and proteins in their hippocampi compared to controls. The KE offers a potential therapy to counter fundamental metabolic deficits common to patients and transgenic models. Read the Editorial Highlight for this article on page 162.