Conquering Insulin Network Dysfunctions in Alzheimer’s Disease: Where Are We Today?

Issue title: Therapeutic Trials in Alzheimer’s Disease: Where Are We Now?

Guest editors: Paula I. Moreira, Jesus Avila, Daniela Galimberti, Miguel A. Pappolla, Germán Plascencia-Villa, Aaron A. Sorensen, Xiongwei Zhu and George Perry

Article type: Review Article

Authors: de la Monte, Suzanne M.^{; *}

Affiliations: Departments of Pathology and Laboratory Medicine, Medicine, Neurology and Neurosurgery, Rhode Island Hospital, Lifespan Academic Institutions, and the Warren Alpert Medical School of Brown University, Providence, RI, USA

Correspondence: [*] Correspondence to: Dr. Suzanne M. de la Monte, MD MPH, Department of Medicine, Rhode Island Hospital, Providence, RI 02908, USA. Tel.: +1 401 444 7364; Fax: +1 401 444 2939; E-mail: Suzanne_DeLaMonte_MD@Brown.edu.

Abstract: Functional impairments in the brain’s insulin and insulin-like growth factor (IGF) signal transduction networks are recognized mediators of dysregulated energy metabolism, a major driver of the Alzheimer’s disease (AD) neurodegeneration cascade. AD-associated insulin-deficient and insulin-resistant states mimic those of diabetes mellitus and affect all cell types in the brain. Besides accounting for abundant amyloid-β and hyperphosphorylated tau lesions in AD, insulin/IGF pathway dysfunctions cause cortical atrophy, loss of synaptic plasticity, white matter myelin/oligodendrocyte degeneration, astrocyte and microglial neuroinflammation and oxidative stress, deficits in energy metabolism, mitochondrial dysfunction, and microvascular disease. These same neuropathological processes have been linked to cognitive impairment in type 2 diabetes mellitus, Parkinson’s disease, and vascular dementia. Strategies to address metabolic mediators of cognitive impairment have been borrowed from diabetes and other insulin-resistant diseases and leveraged on preclinical AD model data. The repurposing of diabetes drugs led to clinical trials with intranasal insulin, followed by insulin sensitizers including metformin and peroxisome-proliferator-activated receptor agonists, and then incretin mimetics primarily targeting GLP-1 receptors. In addition, other glucose-lowering agents have been tested for their efficacy in preventing cognitive declines. The strengths and limitations of these approaches are discussed. The main conclusion of this review is that we have now arrived at a stage in which it is time to address long-term deficits in trophic factor availability and receptor responsiveness, signaling abnormalities that extend beyond insulin and include IGFs and interconnected pathways, and the need for multi-pronged rather than single-pronged therapeutic targeting to remediate AD and other forms of neurodegeneration.

Keywords: Alzheimer’s disease, diabetes drugs, incretin, insulin resistance, insulin sensitizer, intranasal insulin, neurodegeneration, PPAR agonist, type 3 diabetes, vascular dementia

DOI: 10.3233/JAD-240069

Journal: Journal of Alzheimer's Disease, vol. 101, no. s1, pp. S317-S343, 2024