Lithium as a Treatment for Alzheimer's Disease: The Systems Pharmacology Perspective

Systems pharmacology is a novel framework for drug research that models traditional and innovative pharmacological parameters and provides the overall efficacy and safety profile of a drug across body systems and complex, non-linear, molecular interactions. Lithium chloride, a pharmacological compound approved for the therapy of psychiatric disorders, represents a poorly explored compound for the treatment of Alzheimer's disease (AD). Lithium has been shown to reduce downstream effects associated with the aberrant overactivation of certain molecular pathways, such as glycogen synthase kinase 3 subunit β (GSK3-β)-related pathways, involved in AD-related pathophysiology. It seems that overactivation and overexpression of GSK3-β lead to an impairment of long-term potentiation and amyloid-β induced neurotoxicity that can be normalized using lithium. Moreover, a growing body of evidence has demonstrated that lithium's GSK3-β inhibitory effect prevents tau phosphorylation in mouse models of tauopathies. Clinical data have been inconclusive, partly due to methodological limitations. The lack of studies exploring the dynamics of protein misfolding in AD and investigating the specific tau-isoforms appearing prior to the accumulation of neurofibrillary tangles calls for new and optimized clinical trials. Advanced computer modeling based on a formal implementation of quantitative parameters and basic enzymatic insights into a mechanism-based model would present a good start to tackle these non-linear interactions. This innovative approach will pave the way for developing "molecularly" biomarker-guided targeted therapies, i.e., treatments specifically adapted ("tailored") to the individual, consistently with the primary objectives and key conceptual points of precision medicine and precision pharmacology.Program “PHOENIX” led by the Sorbonne University Foundation and sponsored by la Fondation pour la Recherche sur Alzheimer

A path toward precision medicine for neuroinflammatory mechanisms in Alzheimer's disease

Neuroinflammation commences decades before Alzheimer's disease (AD) clinical onset and represents one of the earliest pathomechanistic alterations throughout the AD continuum. Large-scale genome-wide association studies point out several genetic variants—TREM2, CD33, PILRA, CR1, MS4A, CLU, ABCA7, EPHA1, and HLA-DRB5-HLA-DRB1—potentially linked to neuroinflammation. Most of these genes are involved in proinflammatory intracellular signaling, cytokines/interleukins/cell turnover, synaptic activity, lipid metabolism, and vesicle trafficking. Proteomic studies indicate that a plethora of interconnected aberrant molecular pathways, set off and perpetuated by TNF-α, TGF-β, IL-1β, and the receptor protein TREM2, are involved in neuroinflammation. Microglia and astrocytes are key cellular drivers and regulators of neuroinflammation. Under physiological conditions, they are important for neurotransmission and synaptic homeostasis. In AD, there is a turning point throughout its pathophysiological evolution where glial cells sustain an overexpressed inflammatory response that synergizes with amyloid-β and tau accumulation, and drives synaptotoxicity and neurodegeneration in a self-reinforcing manner. Despite a strong therapeutic rationale, previous clinical trials investigating compounds with anti-inflammatory properties, including non-steroidal anti-inflammatory drugs (NSAIDs), did not achieve primary efficacy endpoints. It is conceivable that study design issues, including the lack of diagnostic accuracy and biomarkers for target population identification and proof of mechanism, may partially explain the negative outcomes. However, a recent meta-analysis indicates a potential biological effect of NSAIDs. In this regard, candidate fluid biomarkers of neuroinflammation are under analytical/clinical validation, i.e., TREM2, IL-1β, MCP-1, IL-6, TNF-α receptor complexes, TGF-β, and YKL-40. PET radio-ligands are investigated to accomplish in vivo and longitudinal regional exploration of neuroinflammation. Biomarkers tracking different molecular pathways (body fluid matrixes) along with brain neuroinflammatory endophenotypes (neuroimaging markers), can untangle temporal–spatial dynamics between neuroinflammation and other AD pathophysiological mechanisms. Robust biomarker–drug codevelopment pipelines are expected to enrich large-scale clinical trials testing new-generation compounds active, directly or indirectly, on neuroinflammatory targets and displaying putative disease-modifying effects: novel NSAIDs, AL002 (anti-TREM2 antibody), anti-Aβ protofibrils (BAN2401), and AL003 (anti-CD33 antibody). As a next step, taking advantage of breakthrough and multimodal techniques coupled with a systems biology approach is the path to pursue for developing individualized therapeutic strategies targeting neuroinflammation under the framework of precision medicine.Sorbonne University Foundation and sponsored by la Fondation pour la Recherche sur Alzheimer. HH is an employee of Eisai Inc. During his previous work (until April 2019), he was supported by the AXA Research Fund, the Fondation partenariale Sorbonne Université and the Fondation pour la Recherche sur Alzheimer, Paris, Franc