Objective: Huannao Yicong Decoction (, HYD), an effective herbal formula against Alzheimer's disease (AD), has been proven to have neuroprotective action in amyloid β-protein_1-42 (Aβ_1-42)-induced rat model. This study was designed to characterize mechanisms by which HYD leads to suppression of inflflammation and apoptosis in the brains of Aβ_1-42-induced rat.

Methods: A total of 72 rats were divided into 6 groups, which were referred to as: sham operation group, model group, donepezil-treated group, HYD low-dose group (HYDL), HYD middle-dose group (HYDM) and HYD high-dose group (HYDH). Rats in HYDL, HYDM and HYDH were injected with Aβ_1-42 at the CA1 region of hippocampus to form AD model and were fed the HYD extract at different dose of 3.78, 7.56 and 18.90 g crude drug/kg. The behavioral changes of rats were evaluated by Morris water maze (MWM) before sacrififice. Pathological changes of the brain tissue were evaluated using hematoxylin eosin (HE) staining. The levels of interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α) were measured by radioimmunoassay. The levels of Aβ and proteins that are associated with apoptosis such as B-cell lymphoma-2 protein (Bcl-2), Bcl-2-associated X protein (Bax), cysteine-aspartic protease (caspase)-3, -8, -9 and -12 in serum were measured by immunohistochemistry.

Results: Compared with the sham operation group, the spatial learning and memory abilities of AD rats were signifificantly decreased (P<0.05 or P<0.01; Expressions of IL-1, TNF-α, Aβ and apoptosis-signaling proteins caspase-3, -8, -9, -12 were signifificantly up-regulated (P<0.05 or P<0.01). The ratio of Bcl-2 to Bax were signifificantly decreased in the model group (P<0.01). When treated with HYD extract, the spatial learning and memory abilities of AD-model rats were significantly increased (P<0.05 or P<0.01), IL-1, TNF-α, Aβ, caspase-3, -8, -9 and -12 were down-regulated (P<0.05 or P<0.01), and the ratio of Bcl-2 to Bax were reduced (P<0.05 or P<0.01).

Conclusions: HYD extract can improve the learning and memory ability defificits, alleviate the inflflammatory response and pathological manifestations induced by Aβ_1-42 injection in the rat model of AD. HYD down-regulates the levels of IL-1, TNF-α and Aβ, and decreases the rate of apoptosis by modulating apoptosis-signaling-related proteins such as caspase-3, -8, -9, and -12.