Regular articleA ketone ester diet exhibits anxiolytic and cognition-sparing properties, and lessens amyloid and tau pathologies in a mouse model of Alzheimer's disease
Introduction
By 2050, the number of patients with Alzheimer's disease (AD) in the United States is expected to approach 13 million (Thies and Bleiler, 2011). Although there have been advances in the diagnosis of probable AD (McKhann et al., 2011), all clinical trials of interventions aimed at slowing disease progression in patients with mild cognitive impairment (MCI) and AD have failed (Feldman et al., 2007, Petersen et al., 2005, Winblad et al., 2008). The self-aggregation and accumulation of extracellular amyloid β-peptide (Aβ) and intracellular hyperphosphorylated tau (pTau) with cognitive impairment are defining features of AD (Selkoe, 1997). Although mutations in the β-amyloid precursor protein (APP) and the APP-cleaving enzyme presenilin-1 cause rare cases of early-onset familial AD (Bertram et al., 2010), most cases of AD occur after the age of 65 years and have no known cause.
Increasing evidence suggests a role for a chronic positive energy balance resulting from excessive caloric intake and a sedentary lifestyle (and associated insulin resistance) during midlife as AD risk factors (Kapogiannis and Mattson, 2011, Xu et al., 2011). Aβ pathology and cognitive deficits are exacerbated by a high-fat diet (Julien et al., 2010) and diabetes (Takeda et al., 2010), and are ameliorated by dietary energy restriction (Halagappa et al., 2007, Patel et al., 2005, Wang et al., 2005) in mouse models of AD. Moreover, pilot clinical studies have reported improvement in cognitive function and reduced progression of hypometabolism assessed by fluorodeoxyglucose (FDG) positron emission tomography (PET) in patients with AD after intranasal administration of insulin (Craft et al., 2012).
Ketone bodies are an alternative fuel for brain cells when glucose availability is insufficient. The neuroprotective potential of ketones is supported by the well-known efficacy of fasting and ketogenic diets in the treatment of epilepsy (Conklin, 1922, Wilder, 1921). The metabolism of ketone bodies mimics some actions of insulin (Sato et al., 1995) and can overcome insulin resistance (Kashiwaya et al., 1997), suggesting a potential therapeutic benefit of ketone bodies in AD (Kashiwaya et al., 2000). Consistent with the latter possibility, intermittent energy restriction increases levels of circulating β-hydroxybutyrate (Johnson et al., 2007) and ameliorates cognitive impairment in a mouse model of AD (Halagappa et al., 2007).
A ketogenic diet decreased Aβ levels in the brain of AD mice (Van Der Auwera et al., 2005), suggesting that ketone bodies might suppress the pathogenic processes associated with cognitive impairment in AD. However, the latter study did not evaluate the therapeutic potential of ketone bodies per se, and it is not known if ketone bodies can ameliorate behavioral deficits in AD models. There have been no published reports of ketone bodies improving behavioral function and decreasing progression of Aβ and pTau pathologies in AD models. In this study, a novel ketone ester comprised of d-β-hydroxybutyrate and (R)-1,3-butanediol, a precursor of the physiological forms of ketone bodies, was used. The impact of the ketone ester–based diet on the progression of AD-like Aβ and pTau pathologies and behavioral abnormalities in the triple transgenic mouse model of AD, 3xTgAD mice, was examined (Oddo et al., 2003).
Section snippets
Animals, diet, and study overview
The initial generation and characterization of 3xTgAD mice have been reported previously (Oddo et al., 2003). The mice used in the present study were from a colony that had been backcrossed onto a C57BL/6 genetic background for 8 generations and characterized in our previous studies (Liu et al., 2010, Romberg et al., 2011, Rothman et al., 2012). Mice were housed at the National Institute on Aging Biomedical Research Center in Baltimore, MD. Thirty male 3xTgAD mice were housed in groups of 2 to
3xTgAD mice fed a KET diet exhibit a lower average body weight and a higher β-hydroxybutyrate concentration
During the first 50 days on the experimental diets, the mice in both the KET and control (CHO) diet groups exhibited fluctuations in body weight as they adapted to the diets (Fig. 1). Thereafter, the mice on the KET diet maintained body weight approximately 10% to 12% lower than the body weight of mice in the CHO group (KET 38.0 ± 0.7 g, CHO 42.6 ± 1.9 g). There was no difference in the body weight of mice assigned to each group at the time of diet initiation (KET 38.8 g, CHO 37.9 g). Levels of
Discussion
A diet containing a specific ketone ester was found to ameliorate behavioral abnormalities (anxiety and memory deficits) and reduce the amounts of Aβ and pTau in brain regions known to mediate those behaviors in 3xTgAD mice. Previous studies have demonstrated a positive association between levels of endogenous ketone bodies and cognitive function in human subjects and animal models (see Maalouf et al., 2009 for a review). In addition, dietary interventions that increase levels of ketone bodies,
Disclosure statement
The authors declare no competing financial interests.
Acknowledgement
The authors thank Andrew Holmes, Elizabeth Gratton, and Shireesh Srivastava for scientific advice and technical assistance. This research was supported by the Intramural Research Programs of the National Institute on Aging and the National Institute on Alcohol Abuse and Alcoholism.
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Current affiliation: Christian Bergman is a student at University of Virginia School of Medicine.
The first 2 authors contributed equally to this project.