Brain Blood Flow and Sugar Transport in Alzheimer's Disease With and Without Diabetes - A Pilot Imaging Study

Alzheimer Dementia (AD), Diabete Type 2

neuroimaging, Alzheimer's disease, amyloid, glucose transport, glucose metabolism

Alzheimer's disease is the most common cause of dementia and affects a growing number of older adults. Although harmful proteins build up in the brain, we still do not fully understand why some brain regions are affected earlier or more severely than others. Many people with Alzheimer's disease also have problems with blood flow and sugar handling in the brain, and these changes may play an important role in disease development. People with type 2 diabetes are at especially high risk of developing Alzheimer's disease and often experience a more severe disease course. This pilot study aims to improve our understanding of how brain blood flow and sugar use are altered in Alzheimer's disease, and whether these changes differ in people with and without type 2 diabetes. We will study three groups: people with Alzheimer's disease without diabetes, people with Alzheimer's disease and type 2 diabetes, and healthy older individuals. By comparing these groups, we aim to identify early brain changes that may contribute to cognitive decline. Participants will undergo advanced brain imaging using positron emission tomography (PET) scans. One scan uses a radioactive sugar tracer to measure how the brain takes up and uses glucose. Importantly, a new non-invasive method will also allow us to estimate how efficiently glucose is transported from the blood into the brain. This is a key process that may be impaired in Alzheimer's disease, but has previously required invasive procedures. The new approach avoids arterial cannulation, making the study safer and more comfortable for participants. A second PET scan will assess brain blood flow and blood vessel function, including how well the vessels can respond to increased demand. Participants will also complete cognitive tests to assess memory and thinking abilities. Ultimately, this research may contribute to earlier diagnosis, better monitoring of disease progression, and development of new treatment strategies for Alzheimer's disease.

1. Synopsis / Summary Design: Comparative imaging study. Population: 60 participants: Group A: 20 patients with suspected Alzheimer's disease (AD) without type 2 diabetes (T2D) Group B: 20 patients with suspected AD + T2D Group C: 20 healthy age-matched controls Procedures: Dynamic \[11C\]PiB positron emission tomography (PET) after acetazolamide: early phase as perfusion/vascular function marker; late phase as β-amyloid load. Dynamic \[18F\]FDG PET with heart scans and prebolus method: glucose transport and cerebral metabolic rate of glucose (CMRglc). Magnetic resonance imaging (MRI) (if not available within 5 years and clinically acceptable): assessment of white matter lesions (Fazekas score) and vascular markers. Neuropsychological testing (if not already available clinically). Primary endpoint: Volume and overlap of abnormal regions across imaging biomarkers (with diabetes status considered). Secondary endpoints: Correlation between cognitive index score and biomarker volumes. Timeline: First subject first visit Sep 2025; last subject last visit Dec 2026; end of trial Sep 2027. 2. Background and Rationale Dementia prevalence is rising; Alzheimer's disease and vascular dementia account for the majority of cases, often co-existing ("mixed dementia"). AD is characterized by early β-amyloid deposition and later neurodegeneration, with hypometabolism and perfusion abnormalities in characteristic parietotemporal regions. T2D is associated with cognitive impairment and increased dementia risk, potentially via impaired insulin signaling and altered brain glucose handling. A key methodological barrier has been robust, clinically feasible quantification of glucose transport across the blood-brain barrier (BBB). Prior work suggests blood-brain glucose transport is sensitive to AD-related changes and may respond to metabolic interventions. Conventional glucose transport estimation requires arterial cannulation and high temporal resolution. We have developed a non-invasive approach using an image-derived input function with heart scanning and a prebolus strategy (method manuscript in preparation), enabling estimation of CMRglc and glucose transport in the same FDG session. For vascular reserve, acetazolamide challenge probes endothelial-mediated vasodilation. We will use early-phase \[11C\]PiB as a perfusion proxy (validated against FDG/perfusion measures in prior studies). Overall aim: Map and compare regional extent and overlap of quantitative imaging biomarkers in suspected AD with and without T2D versus healthy controls. 3. Hypotheses Patients with suspected AD are amyloid-positive on \[11C\]PiB PET. Aside from amyloid load, biomarkers show broadly similar regional patterns within subjects, but differ in affected volume. Glucose transport impairment affects a larger cortical volume than glucose metabolism impairment (CMRglc). Perfusion during vasodilation shows larger affected volume than glucose metabolism. White matter lesion burden co-localizes with affected regions and differs by diabetes status. 4. Objectives and Endpoints 4.1 Primary objective Map neurodegenerative PET biomarkers and vascular MRI markers in suspected AD and compare the volume and overlap of regional involvement across biomarkers (accounting for T2D). 4.2 Secondary objectives Relate imaging biomarker volumes to cognitive performance. 4.3 Primary endpoint Volume and overlap of: Reduced glucose transport from FDG PET Reduced CMRglc from FDG PET Increased amyloid load from late \[11C\]PiB PET (standard uptake value ratio, (SUVR) \> 1.5, cortex vs cerebellum) Reduced perfusion during vasodilation from early \[11C\]PiB PET White matter lesions (none / some / confluent; incl. Fazekas scoring) 4.4 Secondary endpoints Association between cognitive index score and volumes of the above abnormalities. 4.5 Exploratory endpoints Associations between imaging volumes and metabolic/clinical measures (body mass index (BMI), waist, fasting glucose/insulin measures, etc.). 5. Methods 5.1 Design Comparative cross-sectional imaging study with prespecified group comparisons (A vs B vs C). 5.2 Schedule Procedures are conducted over 2-3 study visits. 6. Trial Population 6.1 Recruitment Patients (A, B): Identified through the memory clinic at Herlev or referrals to clinical brain FDG PET. A health professional asks permission for research contact; written information is provided. Research staff contacts the patient ≥3 days later to screen and offer an information meeting. Controls (C): Recruitment via approved advertisements (TrialTree, forskningnu.dk, local media, posters, social media) with safeguards against tagging/comment disclosure. 6.2 Inclusion criteria Written informed consent before any study procedures Age 60-90 years Group A/B: clinically suspected AD Group B: documented T2D Group C: no significant somatic/psychiatric disease Ability and willingness to comply with protocol 6.3 Exclusion criteria Suspicion of non-AD dementia Significant brain disease unrelated to dementia Medication affecting perfusion or glucose metabolism (e.g., GLP-1 receptor agonists; metformin/insulin allowed in Group B) Active cancer treatment Alcohol/drug abuse history Severe claustrophobia Pregnancy/breastfeeding MRI contraindications (metal fragments, pacemaker, incompatible implants, etc.) For controls: significant cardiovascular disease or diabetes (atrial fibrillation acceptable) 6.4 Informed consent Consent is voluntary; withdrawal is allowed anytime without consequences for clinical care. Participants are offered up to 7 days to consider participation and may bring a relative/friend to the information meeting. After trial completion, participants will be informed of overall results; individual results will be handled with respect for the right not to know. Permission may be requested for future contact regarding follow-up trials. 6.5 Demography and clinical data DOB, sex, height/weight/BMI, waist, blood pressure/pulse, smoking/alcohol history, medication list, diabetes history (if applicable), relevant clinical cognitive test results. 6.7 Biobank No research biobank is created. 7. Study Procedures 7.1 \[18F\]FDG PET Visit \ 2 hours; replaces routine clinical FDG PET where applicable. 4-hour fasting. Venous access for tracer injection. Dynamic brain scan (\ 55 min) with heart scans before and after for non-invasive input function. Total injected activity \ 200 MBq split (prebolus + bolus). Plasma glucose measured if needed. 7.2 \[11C\]PiB PET + acetazolamide Visit \ 2 hours. Venous access. Acetazolamide 1 g in 50 mL saline infused over 5 min. After \ 10 min, dynamic brain \[11C\]PiB PET (\ 60 min), activity 100-500 MBq. 7.3 MRI (if needed) If brain MRI is \<5 years old and clinically acceptable with no suspected major change, MRI is not repeated. Otherwise \ 20 min MRI including sequences relevant for vascular markers and white matter lesions. No contrast. 7.4 Neuropsychological testing Up to 60 min in quiet setting; attention, memory, learning, language, processing speed tests. 8. Safety, Risks, and Discomfort Long dynamic PET sessions may be tiring; staff monitor participants throughout. Adverse events from FDG, PiB and MRI are rare and typically mild. Acetazolamide may cause headache, tingling, increased diuresis, or altered taste of carbonated drinks; serious events are very rare. Radiation: FDG (\ 4.8 mSv), PiB (\ 3.4 mSv), CT (\ 3 mSv), total \ 11.2 mSv (approx. \<3 years background radiation in Denmark). Many patients would otherwise have routine FDG PET clinically. Only participants ≥60 years are included. Incidental findings: Scans are not intended as diagnostic exams. If potentially clinically significant incidental findings are suspected, a radiologist will be consulted; participant and GP will be informed where relevant. Participants who do not wish to be informed of incidental findings with potential health implications will not be scanned. 9. Data Handling / GDPR Data stored for 15 years; thereafter transferred to "Privacy" in anonymised form. Data stored coded in accordance with GDPR and Danish Data Protection rules and registered with the Danish Data Protection Agency. Paper documents destroyed after completion of processing (planned by Dec 2027). Access to medical records occurs only after signed consent and is used for eligibility assessment, safety, and analysis variables (diagnoses, medication, relevant labs, prior imaging, cognitive tests). Monitoring authorities may access data under confidentiality obligations. 10. Statistical Plan 10.1 General Descriptive statistics including missingness and reasons. Analyses are non-blinded. Deviations from analysis plan will be documented in publications. 10.2 Image analyses (key outcomes) \[11C\]PiB early phase: first 10 min reconstructed as "vascular/perfusion" image; outcome = regional uptake relative to cerebellar grey matter; z-scores vs controls. \[11C\]PiB late phase: 40-60 min reconstructed for amyloid SUVr; cortical volume with SUVr \> 1.5 recorded. \[18F\]FDG heart IDIF: VOI in LV cavity; prebolus/bolus ratio applied; late point from last heart scan; plasma conversion via population-based ratio. \[18F\]FDG brain: dynamic modelling (two-compartment); lumped constant 0.76; plasma glucose included. Outcomes: CMRglc and K1-based glucose transport estimate. MRI: neuroradiologist rates Fazekas score, regional white matter lesions, and other vascular findings. 10.3 Sample size Exploratory. n=20 per group) accounts for \ 10% drop-out, expected \ 15% differences in affected volumes, power 90%, alpha 5%, and \ 14% variation. Participants unable to complete study visits may be replaced. 11\. End of Trial / Discontinuation Ethics Committee informed within 90 days after completion. Participants may discontinue at any time; discontinuation does not affect clinical care. 12\. Administrative Procedures Insurance: Covered under Danish patient insurance law. Finances/COI: Investigator-initiated; no investigators have financial stake. Operating expenses covered by involved departments. 13\. Publication Data owned by Region Hovedstaden. Results will be published regardless of outcome in peer-reviewed journals, following Vancouver authorship guidelines.

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