Chronic low dose of AM404 ameliorates the cognitive impairment and pathological features in hyperglycemic 3xTg-AD mice

Abstract

Rationale: Hyperglycemia accelerates the progression of Alzheimer’s disease (AD), and GSK3β plays a potential link between AD and hyperglycemia. Therefore, a direct or indirect GSK3β inhibition may have potential to delay the progression of AD. Our previous biochemical assay identified AM404 as a GSK3β inhibitor at high dose (IC50 = 5.353 μM); however, other study suggests that AM404 impaired synaptic plasticity of hippocampus at high dose (10 mg/kg; i.p.). Therefore, the dose and duration of treatment are crucial for the effects of AM404. Objective: The effects and molecular mechanisms of AM404 at low dose were evaluated from in vitro to in vivo models. Methods: AM404 (0.1–0.5 μM) was tested on tau hyperphosphorylated mouse hippocampal primary cultures treated with Wortmannin (WT) and GF109203X (GFX). Hyperglycemic triple transgenic AD (3×Tg-AD) mice at 6 months old were intraperitoneally injected with AM404 (0.25 mg/kg) for 4 weeks. The spatial learning and memory of mice were measured using the Morris water maze. Mouse brain and serum samples were collected for pathological analyses. Results: AM404 (0.5 μM) exhibited significantly augmented neuroprotection toward tau hyperphosphorylation in primary cultures. The chronic systemic administration of AM404 (0.25 mg/kg) attenuated cognitive deficits in hyperglycemic 3×Tg-AD mice. Moreover, chronic low dose of AM404 significantly attenuated Aβ production, tau protein phosphorylation, and inflammation associated with an increase of pS473Akt and pS9-GSK3β. Therefore, AM404 at low dose, not only increased neuroprotection, but also ameliorated cognitive deficit, could be partly by regulating the Akt/GSK3β signaling, which may contribute to downregulation of Aβ, tau hyperphosphorylation, and inflammation in hyperglycemic 3×Tg-AD mice. Conclusions: These results highlight that chronic administration of AM404 at low dose may be through the Akt/GSK3β pathway to ameliorate the impairment in hyperglycemic 3×Tg-AD mice.