BACKGROUND

Alzheimer's disease (AD) is a devastating neurodegenerative disease (AD) and has no treatment that can cure or halt the disease progression. This study explored the therapeutic potential of lithium salt dissolved in Ryanodex formulation vehicle (RFV) and delivered to the brain by intranasal application. We first compared lithium concentrations in the brain and blood of wild-type mice following intranasal or oral administration of lithium chloride (LiCl) dissolved in either RFV or water. The beneficial and side effects of intranasal versus oral LiCl in RFV in these mice were assessed and potential mechanisms underlying the efficacy of anti-inflammation and anti-pyroptosis in the brains were also investigated in both wild-type (WT) and 5XFAD Alzheimer's Disease (AD) mice brains.

METHODS

For the study of brain versus blood lithium concentrations, WT B6SJLF1/J mice at 2 months of age were treated with intranasal or oral LiCl (3 mmol/kg) dissolved in RFV or in water. Brain and blood lithium concentrations were measured at various times after drugs administration. Brain/blood lithium concentration ratios were then determined. For studying therapeutic efficacy versus side effects and their underlying mechanisms, 5XFAD and WT B6SJLF1/J mice were treated with intranasal LiCl (3 mmol/kg) daily, Monday to Friday each week, in RFV beginning at 2 or 9 months of age with a 12-week treatment duration. Animal behaviors were assessed for depression (tail suspension), cognition (fear conditioning and Y maze), olfaction (buried food test), and motor functions (rotarod) at the age of 5 and 12 months. Blood and brain tissue were harvested from these mice at 13 months. Blood biomarkers for the functions of thyroid (thyroid stimulating hormone, TSH) and kidney (creatinine) were measured using ELISA. Changes in protein expression levels of the endoplasmic reticulum Ca release channels type 1 InsP receptors (InsPR-1), malondialdehyde (MDA)-modified proteins and 4-hydroxy-2-nonenal (4-HNE), pyroptosis regulatory proteins (NLR family pyrin domain containing 3 (NLRP3), cleaved caspase-1, N-terminal of Gasdermin D (GSDMD)), cytotoxic (IL-1β, IL-18, IL-6, TNF-α) and cytoprotective (IL-10) cytokines and synapse proteins (PSD-95, synapsin-1) were determined using immunoblotting. Mouse body weights were monitored regularly.

RESULTS

Compared to oral LiCl in RFV nanoparticles, intranasal treatment of WT mice with LiCl in RFV markedly decreased blood concentrations at the time frame of 30-120 minutes. The ratio of brain/blood lithium concentration after Intranasal lithium chloride in RFV significantly increased, in comparison to those after oral administration lithium chloride in RFV or intranasal administration of lithium chloride in water. Intranasal lithium chloride in RFV inhibited both memory loss and depressive behavior in adult and aged 5XFAD mice. Additionally intranasal treatment of aged 5XFAD mice with LiCl in RFV effectively suppressed the increases in InsPR-1, intracellular oxidative stress markers (4-HNE-bound and MDA-modified proteins), pyroptosis activation proteins (NLRP3, cleaved caspase-1, N-terminal GSDMD) and cytotoxic cytokines (IL-1β, IL-6, TNF-α), but reversed the down-regulation of cytoprotective cytokine IL-10. Intranasal LiCl in RFV also alleviated the loss of the postsynaptic synapse protein PSD-95, but not synapsin-1, in aged 5XFAD mice. Blood level of the kidney function marker creatinine was significantly increased in 5XFAD than in WT mice in an age-dependent manner and this elevation was abolished by intranasal delivery of LiCl in RFV. Intranasal LiCl in RFV for 12 weeks in both WT or 5XFAD mice did not affect blood biomarkers for thyroid function, nor did it affect smell or muscle function or body weight.

CONCLUSION

Intranasal administration of LiCl in RFV significantly decreased lithium blood concentrations and increased brain/blood lithium concentration ratio, in comparison to its oral administration. Intranasal administration of LiCl in RFV robustly protected against both memory loss and depressive-like behavior, while had no side effects concerning thyroid and kidney toxicity in 5XFAD mice. These lithium-induced beneficial effects were strongly associated with lithium's suppression of InsPR-1 Ca channel receptor increase, pathological neuroinflammation and activation of the pyroptosis pathway, as well as the loss of some synaptic proteins. Intranasal delivery of lithium salt in RFV could become an effective and potent inhibitor of pathological inflammation/pyroptosis in the CNS and serve as a new treatment for both AD-associated dementia and depression with minimal unwanted side effects including peripheral organ toxicity.