Current pharmacological interventions mostly target symptoms. Most recently, disease-modifying therapies targeting beta-amyloid aggregation have been developed. Randomized controlled trials using these drugs (Lacenemab and Donanemab) in patients with early symptomatic AD showed a modest impact in terms of slowing cognitive decline and reducing amyloid biomarkers, associated with significant adverse effects. Yet, to date, no pharmacological intervention has been shown to reverse the loss in cognitive function associated with AD, nor to prevent the development of AD pathology. The risk of developing AD is influenced by both genetic and acquired factors, which include APOE genotype and insulin resistance. A better understanding of the association between insulin resistance and AD has important implications, both from a pathophysiological perspective and to foster the development of new therapeutic and preventive strategies. Observational studies have unambiguously demonstrated the bidirectional link between AD and type 2 diabetes mellitus (T2DM). Moreover, recent studies have shown that AD patients without T2DM have impaired insulin signalling at the brain level, which has led the field to define AD as "type 3 diabetes". Insulin is a hormone normally synthesized by the pancreas to regulate blood glucose levels and its utilization within the cells of our body, including the brain. To date, studies using intranasal insulin (INI) administration to investigate brain insulin signalling have shown significant variations in fMRI BOLD signal and improved cognition in healthy subjects. In AD patients, chronic INI administration for months showed that it significantly slowed down the progressive brain metabolism alteration as measured by positron emission tomography (PET) with 18-fluorodeoxyglucose (FDG), and to reduce the ratio of tau on amyloids deposit levels in cerebro-spinal fluid(tau-P181 to CSF Aβ42). Taken together, these findings raise the possibility that insulin is modifying AD-related processes.However, the effects of acute INI administration on brain function and cognition in healthy and AD subjects is not fully characterized yet. Acute INI could help to identify pathophysiologic processes occurring after a single doses, mainly insulin signalling and not due to any long term exposure event (genetic expression or modulation of the receptors).
PET-FDG is a neuroimaging technique that enables the quantification of human brain metabolism. Magnetic Resonance Imaging (MRI) utilizes a magnetic field to capture high-precision structural information about the humain brain. Functional MRI (fMRI) extends the capabilities of traditional MRI by capturing information on the modulation of brain perfusion during tasks and resting state. Finally, electroencephalography (EEG) allows direct and dynamic acquisition of cortical electric activity and allow to study functional brain connectivity.
Using simultaneous multimodal neuroimaging (FDG-PET, fMRI, EEG), this research project will aim to further investigate in vivo brain insulin signalling by exploring the effects of acute INI administration on neurometabolic and neurovascular coupling, and on cortical electrical activity, both in individuals with normal cognitive function and those affected by MCI/AD.
