Neuroprotective Effects of Oleanolic Acid and Erythrodiol in Prodromal Alzheimer's Disease

NEUROLEA is a multicenter, randomized, double-blind, controlled dietary intervention trial coordinated by the Instituto de la Grasa (CSIC). Participants will be recruited at the Neurology Units of Hospital Universitario Virgen del Rocío, Hospital Universitario Reina Sofía and Hospital Universitario de Valme. Study oils. High-purity crystalline oleanolic acid (\>95%) will be obtained from olive leaves following a procedure developed by the research team (Spanish Patent ES2160553) and used to prepare an oleanolic acid-enriched olive oil (600 mg/kg) according to European Patent EP18382510. A commercial olive oil 0.4° will serve as the control oil, as it has the same fatty acid composition as the other oils but a very low content of minor bioactive components. Pomace olive oil, which naturally contains oleanolic acid and erythrodiol, will be purchased from local markets. Oil composition will be verified by gas chromatography and differential scanning calorimetry before the intervention begins. Randomization and blinding. Allocation will follow computer-generated random numbers prepared by the trial coordinator. Participants, clinical and nutritional research staff, and the neuropsychologists scoring the cognitive assessments will be blinded to group assignment. Sample size. Thirty-four participants per arm are required for 90% power to detect a 10% reduction in dementia incidence in the functional oil arms compared with a 25% incidence in the control arm over 12 months (alpha 0.05). Allowing for up to 15% attrition in a long-term dietary intervention, the target is 40 participants per arm (120 in total). Intervention and follow-up. Participants will consume 55 mL/day of the assigned oil, preferably raw and distributed across the three main meals, for 12 months. Adherence will be assessed with the self-reported Haynes-Sackett compliance test and by return of empty bottles, methods previously used by this team in the PREDIABOLE and OLTRAD trials. Participants and their caregivers will receive general healthy-eating guidance throughout the study. Assessments. Evaluations will be performed at baseline and after 6 and 12 months, and will include a comprehensive neuropsychological battery, clinical examination, anthropometry and body composition by bioimpedance, dietary intake and diet quality questionnaires, and fasting blood and urine sampling. Serum concentrations of oleanolic acid and erythrodiol will be measured by HPLC-MS to verify exposure. Mechanistic analyses. Beyond the clinical endpoints, the trial will examine circulating markers of lipid and glucose metabolism, oxidative stress and inflammation, and advanced glycation end product metabolism, together with the expression of related genes in peripheral blood mononuclear cells. Blood-based markers of Alzheimer's disease pathology (p-tau 217, neurofilament light chain, glial fibrillary acidic protein, and the amyloid beta 42/40 ratio) will be quantified at baseline and 12 months. Data will be managed in REDCap and stored in pseudonymized form in accordance with the General Data Protection Regulation.