Uncovering lipid biomarkers linked to methylphenidate efficacy in treating apathy in Alzheimer’s disease: insights from the ADMET 2 trial

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BACKGROUND: Apathy is a prevalent neuropsychiatric symptom (NPS) in Alzheimer's disease (AD), linked to functional impairment and reduced quality of life. The Apathy in Dementia Methylphenidate Trial 2 (ADMET-2) found methylphenidate (MPH) had modest efficacy for treating apathy, but treatment responses varied. MPH blocks dopamine and noradrenaline transporters, inhibiting dopamine and noradrenaline reuptake. Lipids are closely tied to monamine transporter function through their structural and signaling roles in neurotransmission, neuroinflammation, and synaptic plasticity. This study aimed to identify lipid species associated with MPH response and explore lipid pathway disruptions in responders versus non-responders. METHODS: Participants from ADMET-2 with baseline lipidomic data were included. Responders were defined by a ≥4-point improvement on the Neuropsychiatric Inventory Apathy subscale (NPI-A), or moderate-to-marked improvement on the ADCS-Clinicians Global Impression-Change (ADCS-CGIC). Baseline plasma samples underwent lipidomic profiling. Sparse Partial Least Squares Discriminant Analysis (sPLS-DA) in the MPH group was used to identify lipid species distinguishing responders from non-responders. Model performance was evaluated by area under the curve (AUC). Identified lipid species were analyzed in MetaboAnalyst for pathway enrichment. A secondary analysis in the placebo group assessed specificity of findings to MPH. RESULTS: Of the 43 MPH-treated participants, 28 were NPI-apathy responders, and 10 were ADCS-CGIC responders. The PLS-DA model achieved robust discrimination between responders and non-responders (NPI-apathy: AUC = 0.82 +/- 0.05; ADCS-CGIC: AUC=0.84 +/- 0.07). Pathway analysis revealed disruptions in ceramide, phosphosphingolipid, and glycosphingolipid metabolism for NPI-apathy responders, and ceramide and glycosphingolipid metabolism for ADCS-CGIC responders. In 55 placebo-treated participants (30 NPI-apathy responders), an AUC of 0.79 +/- 0.05 was achieved, with pathway analysis indicating disruption in glycosphingolipid metabolism only. CONCLUSIONS: This study demonstrates the utility of lipidomic profiling in identifying biomarkers of response to MPH in AD patients with apathy. The identified lipidomic species are broadly related to monoamine transporter function, reflecting their role in neurotransmission and synaptic plasticity. While glycosphingolipid metabolism appears broadly linked to changes in apathy, disruptions in ceramide and phospholipid metabolism may be specific to MPH treatment. Further study of these pathways may offer insights into the molecular mechanisms underlying apathy and treatment response, and could inform future biomarker-guided interventions.

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