Liquid biopsies to evaluate the effect of a ketogenic diet on molecular circuitries associated with mild cognitive impairment - Project Summary The discovery of brain cells-derived small extracellular vesicles (sEV), broadly known as exosomes, has led to studies examining their role as `liquid biopsies' for Alzheimer's disease and related dementias (ADRD). sEV offer a unique, repeatable, and less invasive tool to discover molecular changes in multiple cell types of the brain during Alzheimer's disease (AD) pathogenesis. Here, we propose to test the usefulness of brain cells-derived sEV to discover the molecular pathways targeted by a dietary intervention against AD and to identify individuals responsive to such intervention. Earlier studies have shown the beneficial effects of ketogenic diet (KD) against ADRD, and we have developed a KD version known as a `Modified Mediterranean-Ketogenic Diet (MMKD)' with improved nutrition and compliance, and recently in a pilot study published its promising beneficial effects in individuals with amnestic mild cognitive impairment (aMCI). Based upon these exciting results, a phase II study (BEAT-AD: Brain Energy for Amyloid Transformation in AD, R01AG055122, PI: Craft) was initiated to test MMKD efficacy in adults with aMCI in comparison to a low-fat American Heart Association Diet (AHAD). In BEAT-AD, all participants (100 adults with aMCI) undergo comprehensive cognitive testing, brain MRIs, apoE genotyping, and metabolic profiling. Additional assessments include CSF analysis of AD biomarkers and PET imaging of the brain for amyloid and tau deposition, ketone uptake, and glucose metabolism. Together, these `gold-standard' measures will assess the efficacy of MMKD against AD but are unlikely to establish the effect of MMKD on key molecular determinants of aMCI brain. Additionally, there is no known blood-based biomarker to identify those individuals who would be most responsive to MMKD. To demonstrate the usefulness of sEV in understanding the molecular action of MMKD at the neuronal level, we obtained plasma samples from the completed pilot study and generated solid feasibility data, published recently in the journal Brain Communications. Based upon these exciting findings, we propose to further establish the effect of MMKD on glutamate-glutamate receptor-Aβ signaling, oxidative stress, and neuroinflammation in the BEAT-AD study. In this ancillary study, we will isolate various brain cells-derived sEV from the plasma of all 100 participants (both pre- and post-MMKD and –AHAD) and characterize in the following aims: Aim I: sEV characterization to assess the effect of MMKD intervention on glutamate signaling and synaptic plasticity-related biomarkers in individuals with aMCI; Aim II: sEV characterization to determine the effect of MMKD intervention on oxidative stress and neuroinflammation in individuals with aMCI; and Aim III: To characterize brain cells-derived sEV to predict response to MMKD intervention in individuals with aMCI. Outcomes will establish brain cells-derived sEV as liquid biopsies to non- invasively assess the effect of MMKD on molecular circuitries in the aMCI brain and their clinical application in screening individuals responsive to MMKD, leading to an evidence-based `personalized approach' to AD.
