To investigate whether icariin (ICA) ameliorates cognitive impairment and modulates relevant endocrine hormone alterations in Alzheimer’s disease (AD) model mice by regulating osteocalcin (OCN) secretion.

An AD mouse model was established by intraventricular injection of okadaic acid (OA). Using a stratified design, 4-week-old male SPF mice (weighing 18 to 22 g) were randomly divided into 8 groups (n=6): wild-type (WT) control group (intragastric administration of 60 mg/kg normal saline); WT-AD group (WT mice with left intracerebroventricular injection of 1 µL OA); WT+ICA group (60 mg/kg ICA daily); WT-AD+ICA group (WT-AD mice with daily 60 mg/kg ICA); OCN^-/- control group (OCN^-/- mice with 60 mg/kg normal saline); OCN^-/--AD group (OCN^-/- mice with left intracerebroventricular injection of 1 µL OA); OCN^-/-+ICA group (OCN^-/- mice with 60 mg/kg ICA daily); and OCN^-/--AD+ICA group (OCN^-/--AD mice with 60 mg/kg ICA daily). The Morris water maze test was conducted to assess learning and memory abilities, while open field test was performed to evaluate anxiety levels. Hippocampal histopathological changes were observed with HE staining and silver impregnation staining; Nissl bodies in hippocampal neurons were detected with Nissl staining. Immunohistochemistry assay was employed to determine the expression of amyloid β-protein (Aβ) and OCN, and Western blotting was used to measure the protein levels of Aβ and OCN. ELISA was applied to detect the expression levels of corticotropin-releasing hormone (CRH), glucose (GLU), glucocorticoid (GC), and cortisol (COR).

Morris water maze test demonstrated that compared with the WT-AD group, the WT-AD+ICA group exhibited significantly shortened escape latency, prolonged time spent in the target quadrant, and increased platform crossing frequency (all P<0.05); similarly, the OCN^-/--AD+ICA group showed improvements than the OCN-/--AD group (all P<0.05). Open field test results indicated that compared with the WT-AD group, the WT-AD+ICA group displayed significantly increased total exploration distance, distance in the center, and time in the center, enhanced activity willingness, and reduced time in peripheral zone and distance in peripheral zone (all P<0.05); similar improvements were observed in the OCN^-/--AD+ICA group compared with the OCN^-/--AD group (all P<0.05). Staining results revealed that ICA intervention attenuated hippocampal pathology, restored hippocampal morphological architecture, reduced neurofibrillary tangles (NFTs), and promoted gradual recovery of Nissl bodies; however, the OCN^-/- mice failed to achieve complete normalization. Immunohistochemistry assay showed that compared with the WT-AD group, the WT-AD+ICA group exhibited decreased Aβ levels and increased OCN levels (all P<0.05); similar trends were observed in the OCN^-/--AD+ICA group relative to the OCN^-/--AD group (all P<0.05). Western blotting demonstrated that compared with the WT-AD group, the WT-AD+ICA group showed reduced Aβ expression and elevated OCN expression (both P<0.05); comparable changes were found in the OCN^-/--AD+ICA group compared with the OCN^-/--AD group (both P<0.05). ELISA indicated that compared with the WT-AD group, the WT-AD+ICA group exhibited significantly decreased levels of CRH, GLU, GC, and COR (all P<0.05); similar reductions were observed in the OCN^-/--AD+ICA group compared with the OCN^-/--AD group (all P<0.05).

ICA ameliorates cognitive impairment and reduces levels of related hyperactive endocrine hormones in AD model mice through regulating OCN secretion.