Small extracellular vesicles in plasma reveal molecular effects of modified Mediterranean-ketogenic diet in participants with mild cognitive impairment

Extracellular vesicles have emerged as a less-invasive nano-tool for discovering biomarkers of Alzheimer’s disease and related dementia. Here, we analysed different neuron-enriched extracellular vesicles from plasma to predict response and molecular mechanisms of ketogenic diet’s efficacy in mild cognitive impairment participants. The study was a randomized crossover design in which cognitively normal and mild cognitive impairment participants consumed a modified Mediterranean-ketogenic diet or American Heart Association diet for 6 weeks, followed by other diet after washout. L1 cell adhesion molecule, synaptophysin and neural cell adhesion molecule surface markers were used to enrich for neuron-secreted small extracellular vesicles (sEV(L1CAM), sEV(SYP) and sEV(NCAM)). For the first time, we have presented multiple evidences, including immunogold labelling/transmission electron microscopy, clusters of differentiation 63-ELISA-based assay, confocal microscopy fluorescent images and flow cytometry data confirming the presence of L1 cell adhesion molecule on the surface of sEV(L1CAM), validating purity and relative abundance of sEV(L1CAM) in the plasma. Cargo analysis of sEV(L1CAM) showed that modified Mediterranean-ketogenic diet intervention reduces amyloid beta 1–42 (50.3%, P = 0.011), p181-tau (34.9%, P = 0.033) and neurofilament light (54.2%, P = 0.020) in mild cognitive impairment participants. Moreover, sEV(L1CAM)showed better sensitivity compared with CSF in analysing increased glutamate (6-folds, P < 0.0001) from mild cognitive impairment participants following modified Mediterranean-ketogenic diet intervention. sEV(L1CAM) characterization also suggested that modified Mediterranean-ketogenic diet differentially targets the expression of various glutamate receptors—glutamate receptor ionotropic NMDA1, glutamate receptor ionotropic NMDA2A, glutamate receptor ionotropic NMDA2B and glutamate receptor ionotropic AMPA type subunit 1. Importantly, these sEV(L1CAM) measures strongly correlated with corresponding clinical CSF biomarkers (neurogranin, amyloid beta 1–42, neurofilament light and tau). Furthermore, sEV(L1CAM) were loaded with less advanced glycation endproducts and exhibited anti-inflammatory activity following modified Mediterranean-ketogenic diet intervention. Most importantly, the expression of monocarboxylate transporter 2 on the surface of sEV(L1CAM) predicted the amyloid beta 1–42 response to modified Mediterranean-ketogenic diet intervention (area under the curve = 0.87, P = 0.0044) and offered a novel screening tool to identify participants responsive to this dietary intervention. Finally, sEV(L1CAM), sEV(SYP) and sEV(NCAM) showed significantly high concordance in analysing amyloid beta 1–42 (Pearson correlation coefficient ≥ 0.63, P < 0.01) and neurofilament light (Pearson correlation coefficient ≥ 0.49, P < 0.05). Together, small extracellular vesicles in plasma offers promise in assessing the efficacy of dietary/therapeutic intervention against mild cognitive impairment/Alzheimer’s disease.