THE KD IN ALZHEIMER DISEASE
There is growing realization that neuronal excitability is enhanced in patients with Alzheimer disease (AD; Noebels, 2011; Roberson et al., 2011). While the essential pathological processes of AD involves neuronal degeneration with accumulation of abnormal cellular products such as fibrillary plaques and tangles, recent evidence points to alterations in the function of extant neural circuits and mitochondrial homeostasis (Kapogiannis and Mattson, 2011). This view is bolstered by the higher incidence of seizures in
patients with AD as compared to the unaffected population (Palop and Mucke, 2009). Therefore, there is a rationale for hypothesizing that the KD might have a beneficial role in patients with Frontiers in Pharmacology | Neuropharmacology April 2012 | Volume 3 | Article 59 | 2Stafstrom and Rho Ketogenic diet in neurological diseases AD (Balietti et al., 2010a), in addition to the potential benefits
to the aging process as noted above. One should note, importantly, that if ketone bodies are indeed the primary mediators that counter aging and neurodegeneration in AD, implementation of the KD should be tempered by known age-related differences in
the production and extraction of ketones (i.e., this is more efficient in young animals), as well as age-specific regional differences in
ketone utilization within the brain (Nehlig, 1999). Clinical studies to date have been equivocal but promising. A randomized double-blind, placebo-controlled trial of a MCT KD resulted in significantly improved cognitive functioning in APOε4-negative patients with AD but not in patients with a APOε4 mutation (Henderson et al., 2009). In this study, the primary cognitive end-points measured were the mean change from baseline in the AD Assessment Scale-Cognitive subscale, and global scores in the AD Cooperative Study – Clinical Global Impression of Change (Henderson et al.,2009). This significant clinical improvement was considered to be secondary to improved mitochondrial function, since ketone bodies (specifically, beta-hydroxybutyrate or BHB) have been shown to protect against the toxic effects of β-amyloid on neurons in culture (Kashiwaya et al., 2000). Alternatively, the KD may actually decrease amounts of β-amyloid deposition (VanderAuwera et al., 2005). Interestingly, other diets such as the Mediterranean diet are showing some promise in AD (Gu et al.,2010), possibly through a reduction in systemic inflammation and improved metabolic profiles.
Recent studies have shown a closer linkage of AD to epilepsy. For example, animal models of AD exhibit neuronal hyperexcitability and enhanced propensity to seizures (Palop et al., 2007; Roberson et al., 2011); these models may ultimately allow for detailed analyses of both cognitive and anticonvulsant effects of the KD or other dietary manipulations such as calorie restriction.
Transgenic AD mice fed 2DG demonstrated better mitochondrial function, less oxidative stress, and reduced expression of amyloid
precursor protein and β-amyloid compared to control animals (Yao et al., 2011). Another pathophysiological mechanism hypothesized to operate in AD ties together altered mitochondrial function and glucose metabolism,i.e., accumulation of advanced glycation nd products (AGE; Srikanth et al., 2011). AGE accumulation is a process of normal aging that is accelerated in AD; proteins are non-enzymatically glycosylated and this cross-linking of proteins accentuates their dysfunction. One proposed mechanism is increased ROS and free radical formation, which, as discussed above, hampers mitochondrial function. The intriguing possibility that AGE inhibitors (e.g., aminoguanidine, tenilsetam, carnosine) could act in concert with the KD or antioxidants in retarding AD progression remains speculative at this time. Thus, there is growing evidence that the KD may be an effective treatment for AD through a variety of metabolism-induced mechanisms that reduce oxidative stress and neuroinflammation, and enhance bioenergetic profiles – largely through enhanced mitochondrial functioning. However, caution should be exercised in extrapolating findings in animals to humans, as discrepancies in terms of both clinical efficacy and untoward side-effects have been noted. For example, adverse reactions to calorie restriction have been reported in some rodent models (Maalouf et al., 2009),and in hippocampus, abnormal morphological synaptic changes have been observed in CA1 stratum moleculare (Balietti et al., 2008).