CSF sphingomyelins in Alzheimer’s disease, neurodegeneration, and neuroinflammation

INTRODUCTION Sphingomyelin (SM) levels have been associated with Alzheimer’s disease (AD), but the association direction has been inconsistent and research on cerebrospinal fluid (CSF) SMs has been limited by sample size, breadth of SMs examined, and diversity of biomarkers available. METHODS Leveraging two longitudinal AD cohorts with metabolome-wide CSF metabolomics data (n=502), we analyzed the relationship between the levels of 12 CSF SMs, and AD diagnosis and biomarkers of pathology, neurodegeneration, and neuroinflammation using logistic, linear, and linear mixed effects models. RESULTS No SMs were significantly associated with AD diagnosis, mild cognitive impairment, or amyloid biomarkers. Phosphorylated tau, neurofilament light, α-synuclein, neurogranin, soluble triggering receptor expressed on myeloid cells 2, and chitinase-3-like-protein 1 were each significantly, positively associated with at least 5 of the SMs. DISCUSSION The associations between SMs and biomarkers of neurodegeneration and neuroinflammation, but not biomarkers of amyloid or diagnosis of AD, point to SMs as potential biomarkers for neurodegeneration and neuroinflammation that may not be AD-specific. ### Competing Interest Statement Author EJ's spouse is an employee of, and owns stock options in, Epic. HZ, author, has served at scientific advisory boards and/or as a consultant for Alector, Eisai, Denali, Roche Diagnostics, Wave, Samumed, Siemens Healthineers, Pinteon Therapeutics, Nervgen, AZTherapies, CogRx and Red Abbey Labs, has given lectures in symposia sponsored by Cellectricon, Fujirebio, Alzecure and Biogen, and is a co-founder of Brain Biomarker Solutions in Gothenburg AB (BBS), which is a part of the GU Ventures Incubator Program (outside submitted work). KB has served as a consultant, at advisory boards, or at data monitoring committees for Abcam, Axon, Biogen, JOMDD/Shimadzu. Julius Clinical, Lilly, MagQu, Novartis, Prothena, Roche Diagnostics, and Siemens Healthineers, and is a co-founder of Brain Biomarker Solutions in Gothenburg AB (BBS), which is a part of the GU Ventures Incubator Program, all unrelated to the work presented in this paper. SCJ, author, has served at advisory boards for Roche Diagnostics and was a consultant to Roche Diagnostics in 2018. Authors GK and AB are employees of Roche Diagnostics GmbH; AB owns stock in Hoffmann-La Roche Ltd. Author IS is an employee of Roche Diagnostics International Ltd. ### Funding Statement This research is supported by National Institutes of health (NIH) grants R01AG27161 (WRAP: Biomarkers of Preclinical AD), R01AG054047 (Genomic and Metabolomic Data Integration in a Longitudinal Cohort at Risk for AD), P30AG017266 (Center for Demography of Health and Aging), P50AG033514 and P30AG062715 (Wisconsin ADRC Grant), R01 AG021155 (Longitudinal Course of Imaging Biomarkers in People At Risk for AD); UL1TR000427 (Clinical and Translational Science Award (CTSA) program through the NIH National Center for Advancing Translational Sciences (NCATS), P2CHD047873 (core grant to the Center for Demography and Ecology at the University of Wisconsin-Madison, S10 OD025245-01 (Biomedical Research Support Shared Instrumentation grant from NIH). Author YKD was supported by a training grant from the National Institute on Aging (T32AG000213). Author HZ is a Wallenberg Scholar supported by grants from the Swedish Research Council (#2018-02532), the European Research Council (#681712), Swedish State Support for Clinical Research (#ALFGBG-720931), the Alzheimer Drug Discovery Foundation (ADDF), USA (#201809-2016862), the AD Strategic Fund and the Alzheimer’s Association (#ADSF-21-831376-C, #ADSF-21-831381-C and #ADSF-21-831377-C), the Olav Thon Foundation, the Erling-Persson Family Foundation, Stiftelsen för Gamla Tjänarinnor, Hjärnfonden, Sweden (#FO2019-0228), the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 860197 (MIRIADE), and the UK Dementia Research Institute at UCL. Author KB is supported by the Swedish Research Council (#2017-00915), the Alzheimer Drug Discovery Foundation (ADDF), USA (#RDAPB-201809-2016615), the Swedish Alzheimer Foundation (#AF-742881), Hjärnfonden, Sweden (#FO2017-0243), the Swedish state under the agreement between the Swedish government and the County Councils, the ALF-agreement (#ALFGBG-715986), the European Union Joint Program for Neurodegenerative Disorders (JPND2019-466-236), the National Institute of Health (NIH), USA, (grant #1R01AG068398-01), and the Alzheimer’s Association 2021 Zenith Award (ZEN-21-848495). Author TJB and PET data processing and analyses are supported by the Alzheimer’s Association (AARF-19-614533). Author EV was supported by the Center for Demography of Health and Aging (P30 AG17266) and a NIA Training Grant (Population, Life Course and Aging) (T32 AG00129). The Roche NeuroToolKit is a panel of robust prototype biomarker assays designed to evaluate key pathologic events characteristic of AD and other neurological disorders, used for research purposes only and not approved for clinical use. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study was approved by the University of Wisconsin Health Sciences Institutional Review Board as part of the Generations of WRAP (GROW) study. Participants in the WADRC and WRAP studies provided written informed consent. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes The datasets analyzed in this study may be requested from the Wisconsin ADRC at . * Aβ : amyloid beta AD : Alzheimer’s disease Dementia-AD : clinical diagnosis of dementia with AD as a suspected cause ADRC : Alzheimer’s Disease Research Center α-synuclein : alpha synuclein ANOVA : analysis of variance CSF : cerebrospinal fluid CU : cognitively unimpaired DVR : distribution volume ratio IL6 : interleukin-6 LMM : linear mixed effects model LP : lumbar puncture MCI : mild cognitive impairment MRI : magnetic resonance imaging NfL : neurofilament light NTK : NeuroToolKit PET : positron emission tomography PiB : Pittsburgh compound B p-tau181 : phosphorylated tau p-tau181/Aβ42 : p-tau181 to amyloid beta 42 ratio QC : quality control ROI : region of interest SM : sphingomyelin sTREM2 : soluble triggering receptor found on myeloid cells 2 WRAP : Wisconsin Registry for Alzheimer’s Prevention YKL40 : chitinase-3-like protein 1