Biomarkers, ketone bodies, and the prevention of Alzheimer's disease

Sporadic Alzheimer's disease (spAD) has three successive phases: preclinical, mild cognitive impairment, and dementia. Individuals in the preclinical phase are cognitively normal. Diagnosis of preclinical spAD requires evidence of pathologic brain changes provided by established biomarkers. Histopathologic features of spAD include (i) extra-cellular cerebral amyloid plaques and intracellular neurofibrillary tangles that embody hyperphosphorylated tau; and (ii) neuronal and synaptic loss. Amyloid-PET brain scans conducted during spAD's preclinical phase have disclosed abnormal accumulations of amyloid-beta (A beta) in cognitively normal, high-risk individuals. However, this measure correlates poorly with changes in cognitive status. In contrast, MRI measures of brain atrophy consistently parallel cognitive deterioration. By the time dementia appears, amyloid deposition has already slowed or ceased. When a new treatment offers promise of arresting or delaying progression of preclinical spAD, its effectiveness must be inferred from intervention-correlated changes in biomarkers. Herein, differing tenets of the amyloid cascade hypothesis (ACM) and the mitochondrial cascade hypothesis (MCH) are compared. Adoption of the ACH suggests therapeutic research continue to focus on aspects of the amyloid pathways. Adoption of the MCH suggests research emphasis be placed on restoration and stabilization of mitochondrial function. Ketone ester (KE)-induced elevation of plasma ketone body (KB) levels improves mitochondrial metabolism and prevents or delays progression of AD-like pathologic changes in several AD animal models. Thus, as a first step, it is imperative to determine whether KE-caused hyperketonemia can bring about favorable changes in biomarkers of AD pathology in individuals who are in an early stage of AD's preclinical phase. (C) 2015 Elsevier Inc. All rights reserved.