Syringaresinol from Cinnamomum cassia (L.) J.Presl ameliorates cognitive deficits and AD pathology via AMPK in a DM-AD mouse model

Abstract

Ethnopharmacological relevance: Syringaresinol (SYR), a major lignan in food analogous TCM (Cinnamomum cassia (L.) J.Presl) possesses antioxidant, anti-inflammatory, antidiabetic, and antiaging effects. However, its protective role and mechanisms in diabetes-related cognitive dysfunction (DM-AD) remain unclear.

Aim of the study: We aimed to assess the protective effects of SYR on metabolic dysfunction associated cognitive decline through the modulation of oxidative stress, neuroinflammation and AMPK activation.

Materials and methods: This study involved extraction of C. cassia bark and isolation of SYR, structurally characterized by HR-MS and ¹H NMR. A DM-AD mouse model was established using HFD and STZ. In vivo assessments included body weight, food intake, fasting glucose, GTT, and ITT. Cognitive function was evaluated using Y-maze, MWM, and NOR tests. SYR's interaction with AMPK was examined through western blotting, molecular docking, and AMPK inhibitor experiments. Oxidative stress markers and neuroinflammatory cytokines were analyzed via biochemical assays and RT-PCR.

Results: SYR treatments at 5 and 15 mg/kg significantly improved metabolic parameters by reducing body weight gain, enhancing glucose tolerance and insulin sensitivity, and restoring hepatic lipid balance. It also alleviated cognitive impairments with improved memory and learning. Mechanistically, SYR activated AMPK, supported by phosphorylation and molecular docking (-8.7 kcal/mol). In addition, SYR also enhanced antioxidant defense and suppressed neuroinflammatory and increased anti-inflammatory cytokines in the DM-AD brain. Co-treatment with the AMPK inhibitor abolished SYR's cognitive and anti-inflammatory benefits to confirm AMPK's key role in neuroprotective effects of SYR.

Conclusions: In conclusion, SYR demonstrates metabolic and neuroprotective effects comparable to metformin, primarily through AMPK activation therefore it could be used as a promising natural therapeutic candidate for DM-associated AD.

Keywords: AMPK; Anti-diabetic; Cinnamomum cassia Presl; Syringaresinol; anti-Alzheimer's disease.