Agrimonia pilosa Ledeb., Cinnamomum cassia Blume, and Lonicera japonica Thunb. protect against cognitive dysfunction and energy and glucose dysregulation by reducing neuroinflammation and hippocampal insulin resistance in β-amyloid-infused rats

Abstract

Objectives: The water extracts of Cinnamomum cassia Blume bark (CCB; Lauraceae), Lonicera japonica Thunb. flower (LJT; Caprifoliaceae), and Agrimonia pilosa Ledeb. leaves (APL; Rosaceae) prevented amyloid-β (25–35)-induced cell death in PC12 cells in our preliminary study. We evaluated whether long-term oral consumption of CCB, LJT, and APL improves cognitive dysfunction and glucose homeostasis in rats with experimentally induced AD-type dementia.

Methods: Male rats received hippocampal CA1 infusions of amyloid-β (25–35, AD) or amyloid-β (35–25, non-plaque forming, normal-controls, Non-AD-CON), at a rate of 3.6 nmol/day for 14 days. AD rats were divided into four groups receiving either 2% lyophilized water extracts of CCB, LJT, or APL or 2% dextrin (AD-CON) in high-fat diets (43% energy as fat).

Results: Hippocampal amyloid-β deposition, tau phosphorylation, and expressions of tumor necrosis factor (TNF)-α and inducible nitric oxide synthase (iNOS) (neruoinflammation markers) were increased, and insulin signaling decreased in AD-CON. CCB, LJT, and APL all prevented hippocampal amyloid-β accumulation and enhanced hippocampal insulin signaling. CCB, LJT, and APL decreased TNF-α and iNOS in the hippocampus and especially APL exhibited the greatest decrease. AD-CON exhibited cognitive dysfunction in passive avoidance and water maze tests, whereas CCB, LJT, and APL protected against cognitive dysfunction, and APL was most effective and was similar to Non-AD-CON. AD-CON had less fat oxidation as an energy fuel, but it was reversed by CCB, LJT, and especially APL. APL-treated rats had less visceral fat than AD-CON rats. AD-CON rats exhibited impaired insulin sensitivity and increased insulin secretion during oral glucose tolerance test compared with Non-AD-CON, but CCB and APL prevented the impairment.

Discussion: These results supported that APL, LJT, and CCB effectively prevent the cognitive dysfunction and the impairment of energy and glucose homeostasis induced by amyloid-β deposition by reducing neuroinflammation and enhancing insulin signaling. APL exhibited the greatest effectiveness for improving cognitive function.

Keywords:

• Lonicera japonica Thunb
• Agrimonia pilosa Ledeb
• Cinnamon
• Amyloid-β
• Cognitive dysfunction
• Glucose metabolism