Icariin decreases the expression of APP and BACE-1 and reduces the β-amyloid burden in an APP transgenic mouse model of Alzheimer's disease

Abstract

Objective: The purpose of this study was to investigate the effects and pharmacological mechanisms of icariin, which is the main component in the traditional Chinese herb Epimedium, on β-amyloid (Aβ) production in an amyloid precursor protein (APP) transgenic (Tg) mouse model of Alzheimer's disease (AD).

Methods: APPV717I Tg mice were randomly divided into a model group and icariin-treated (30 and 100 μmol/kg per day) groups. Learning-memory abilities were determined by Morris water maze and object recognition tests. Aβ contents were measured by enzyme-linked immunosorbent assays and immunohistochemistry. Amyloid plaques were detected by Congo red staining and Bielschowsky silver staining. The levels of expression of APP and β-site APP-cleaving enzyme 1 (BACE-1) were measured by western blotting and immunohistochemistry.

Results: Ten-month-old Tg mice showed obvious learning-memory impairments, and significant increases in Aβ contents, amyloid plaques, and APP and BACE-1 levels in the hippocampus. The intragastric administration of icariin to Tg mice for 6 months (from 4 to 10 months of age) improved the learning-memory abilities and significantly decreased the Aβ contents, amyloid plaques, and APP and BACE-1 levels in the hippocampus.

Conclusion: Icariin reduced the Aβ burden and amyloid plaque deposition in the hippocampus of APP transgenic mice by decreasing the APP and BACE-1 levels. These novel findings suggest that icariin may be a promising treatment in patients with AD.

Keywords: APPV717I transgenic mice; Alzheimer's disease; BACE-1; Icariin; amyloid plaque; amyloid precursor protein; β-amyloid.

Fig 1

Effects of icariin on learning and memory impairments in APP V717I transgenic mice (Morris water maze). Icariin (ICA) at the doses of 30 μmol/kg (L) and 100 μmol/kg (H) was intragastrically administered to APP Tg mice for 6 months (from 4 to 10 months of age). “Escape latency” is the data in the last trial after 4 day's training. A. Comparison of escape latencies in different mice groups at 4 months of age and 10 months of age. B. Effects of icariin on escape latencies in 10-month-old APP transgenic (Tg) mice. C. Group differences of the mean percentage searching time in the target quadrant compared to the whole pool during the probe trial. D. Effects of icariin on the time in the target quadrant. n=18. The data are shown as mean ± standard deviation (SD); ^▲P<0.05, ^▲▲P<0.01, compared with transgenic-negative [Tg(-)] mice; ^△△P<0.01, compared with 4-month-old APP Tg mice; **P<0.01, compared with APP Tg(+) model mice.

Fig 2

Effects of icariin on learning and memory impairments in APP V717I transgenic mice (object recognition test, ORT). Icariin (ICA) at the doses of 30 μmol/kg (L) and 100 μmol/kg (H) was intragastrically administered to APP Tg mice for 6 months (from 4 to 10 months of age). A. Comparison of the discrimination index (DI) in different mice groups at 4 months of age and 10 months of age. B. Effects of icariin on DI in 10-month-old APP Tg mice. On day 2, there was no significant difference in the exploration time to 2 identical objects among groups. On day 3, there was no significant difference in total exploration time (N+F) among groups. n=18. The data are shown as mean ± SD; ^▲P<0.05, compared with Tg(-) mice; ^△△P<0.01, compared with 4-month-old APP Tg mice; *P<0.05, compared with APP Tg(+) model mice.

Fig 3

Effects of icariin on Aβ contents in the hippocampus of 10-month-old APP V717I transgenic mice. Icariin (ICA) at the doses of 30 μmol/kg (L) and 100 μmol/kg (H) was intragastrically administered to APP Tg mice for 6 months (from 4 to 10 months of age). A. Aβ burden in the hippocampal CA1 region that was detected with immunohistochemical staining by using anti-Aβ1-16 antibody (scale bar = 50 μm). n=5. B. Aβ1-42 contents in the whole hippocampus that were measured with enzyme-linked immunosorbent assays. n=8-10. The data are shown as mean ± SD; ^▲▲ P < 0.01, compared with Tg(-) mice; ** P < 0.01, compared with Tg(+) model mice.

Fig 4

Effects of icariin on amyloid plaques in the hippocampus of 10-month-old APP V717I transgenic mice. Icariin (ICA) at the doses of 30 μmol/kg (L) and 100 μmol/kg (H) was intragastrically administered to APP Tg mice for 6 months (from 4 to 10 months of age). A. Congo red staining. B. Semiquantitative analysis of Congo red staining. C. Bielschowsky silver staining. n=5. The data are shown as mean ± SD; ^▲▲P<0.01, compared with Tg(-) mice; **P<0.01, compared with APP Tg(+) model mice. Scale bar = 50 μm.

Fig 5

Effects of icariin on amyloid precursor protein (APP) expression in the hippocampus of 10-month-old APP V717I transgenic mice. Icariin (ICA) at the doses of 30 μmol/kg (L) and 100 μmol/kg (H) was intragastrically administered to APP Tg mice for 6 months (from 4 to 10 months of age). A. Western blot. B. Semiquantitative analysis of western blot. C. Immunohistochemical staining (scale bar = 50 μm). n=5. The data are shown as mean ± SD; ^▲P<0.05, compared with Tg(-) mice; *P<0.05, **P<0.01, compared with Tg(+) model mice.

Fig 6

Effects of icariin on β-site APP-cleaving enzyme 1 (BACE-1) expression in the hippocampus of 10-month-old APP V717I transgenic mice. Icariin (ICA) at the doses of 30 μmol/kg (L) and 100 μmol/kg (H) was intragastrically administered to APP Tg mice for 6 months (from 4 to 10 months of age). A. Western blot. B. Semiquantitative analysis of western blot. C. Immunohistochemical staining (scale bar = 50 μm). n=5. The data are shown as mean ± SD; ^▲▲P<0.01, compared with Tg(-) mice; *P<0.05, compared with Tg(+) model mice.