Naringin ameliorates memory deficits and exerts neuroprotective effects in a mouse model of Alzheimer's disease by regulating multiple metabolic pathways

Abstract

The aim of the present study was to investigate the neuroprotective effects of naringin on the memory impairment of hydrocortisone mice, and to elucidate the potential underlying molecular mechanisms. In the present study, a hydrocortisone model was constructed. Novel object recognition, Morris water maze and step‑down tests were performed in order to assess the learning and memory abilities of mice. Hematoxylin and eosin staining was used to observe pathological changes in the hippocampus and hypothalamus. Transmission electron microscopy was used to observe the ultrastructural changes in the hippocampus. Immunohistochemistry was used to detect the expression of ERα and ERβ. Western blotting was performed to detect the expression of each protein in the relevant system. It was found that naringin can significantly improve cognitive, learning and memory dysfunction in mice with hydrocortisone memory impairment. In addition, naringin can exert neuroprotective effects through a variety of mechanisms, including amyloid β metabolism, Tau protein hyperphosphorylation, acetylcholinergic system, glutamate receptor system, oxidative stress and cell apoptosis. Naringin can also affect the expression of phosphorylated‑P38/P38, indicating that the neuroprotective effect of naringin may also involve the MAPK/P38 pathway. The results of the present study concluded that naringin can effectively improve the cognitive abilities of mice with memory impairment and exert neuroprotective effects. Thus, naringin may be a promising target drug candidate for the treatment of Alzheimer's disease.

Keywords: Alzheimer's disease; memory impairment; naringin; amyloid‑β; apoptosis.

Figure 1.

Structure of naringin.

Figure 2.

Flowchart of animal experimental procedures. TEM, transmission electron microscopy.

Figure 3.

Naringin improved memory and cognition in mice with memory impairment. (A) The comparison of new object recognition index of each group. (B) Escape latencies, the number of mice crossing the quadrant of platform and the time of crossing target quadrant in the Morris water maze in each group. (C) Number of errors and the escape latencies in the step-down test of each group. **P<0.01 vs. sham group; ^##P<0.01 vs. model group; ^&P<0.05, ^&&P<0.01 vs. naringin group.

Figure 4.

Pathological observation with H&E staining. H&E staining of the (A) hippocampus and (B) hypothalamus. H&E, hematoxylin and eosin. Magnification, х200.

Figure 5.

Microstructure observation of hippocampus with TEM. Scale bar, 50 nm. TEM, transmission electron microscopy.

Figure 6.

Naringin upregulates the expression of ERα and ERβ. (A) ERα protein level and (B) ERβ protein level in each group was detected by immunohistochemistry. Scale bar, 50 µm. ER, estrogen receptor.

Figure 7.

Naringin exerts neuroprotective effects by affecting Aβ metabolism and the hyperphosphorylation of Tau. (A) Protein levels of APP, BACE1 and Aβ; (B) CDK5 and p-Tau. **P<0.01 vs. sham group; ^##P<0.01 vs. model group; ^&P<0.05 vs. naringin group. APP, amyloid protein; BACE1, β-site APP cleaving enzyme 1; Aβ, amyloid β; CDK5, cyclin-dependent kinase 5.

Figure 8.

Naringin exerts neuroprotective effects by regulating the glutamate receptor system and apoptosis. (A) Protein levels of NMDAR1, GluR2 and CAMKII. (B) Protein levels of Bad, Bcl-2 and cleaved-caspase-3. **P<0.01 vs. sham group; ^#P<0.05 and ^##P<0.01 vs. model group; ^&P<0.05, ^&&P<0.01 vs. naringin group. NMDAR1, glutamate receptor subunit 1; GluR2, glutamate receptor 2; CAMKII, calcium/calmodulin-dependent protein kinase type II.

Figure 9.

Naringin exerts neuroprotective effects by regulating the acetylcholinergic system and oxidative stress. (A) Naringin significantly increased the Ach content and ChAT activity, but decreasing AchE activity. (B) Naringin significantly decreased the content of MDA and NO in the hippocampus, and the increased the content of SOD. **P<0.01 vs. sham group; ^##P<0.01 vs. model group; ^&P<0.05 vs. naringin group. Ach, acetylcholine; ChAT, choline acetyltransferase; AchE, acetylcholine esterase; MDA, malondialdehyde; NO, nitric oxide; SOD, superoxide dismutase.

Figure 10.

Naringin upregulates the expression of ERβ and downregulates the expression of P38/P-P38 in the hippocampus. **P<0.01 vs. sham group; ^##P<0.01 vs. model group; ^&P<0.05 vs. naringin group. ER, estrogen receptor; p-, phosphorylated.