Liraglutide Protects Against Brain Amyloid-β1-42 Accumulation in Female Mice with Early Alzheimer's Disease-Like Pathology by Partially Rescuing Oxidative/Nitrosative Stress and Inflammation

Abstract

Alzheimer's disease (AD) is the most common form of dementia worldwide, being characterized by the deposition of senile plaques, neurofibrillary tangles (enriched in the amyloid beta (Aβ) peptide and hyperphosphorylated tau (p-tau), respectively) and memory loss. Aging, type 2 diabetes (T2D) and female sex (especially after menopause) are risk factors for AD, but their crosslinking mechanisms remain unclear. Most clinical trials targeting AD neuropathology failed and it remains incurable. However, evidence suggests that effective anti-T2D drugs, such as the GLP-1 mimetic and neuroprotector liraglutide, can be also efficient against AD. Thus, we aimed to study the benefits of a peripheral liraglutide treatment in AD female mice. We used blood and brain cortical lysates from 10-month-old 3xTg-AD female mice, treated for 28 days with liraglutide (0.2 mg/kg, once/day) to evaluate parameters affected in AD (e.g., Aβ and p-tau, motor and cognitive function, glucose metabolism, inflammation and oxidative/nitrosative stress). Despite the limited signs of cognitive changes in mature female mice, liraglutide only reduced their cortical Aβ_1-42 levels. Liraglutide partially attenuated brain estradiol and GLP-1 and activated PKA levels, oxidative/nitrosative stress and inflammation in these AD female mice. Our results support the earlier use of liraglutide as a potential preventive/therapeutic agent against the accumulation of the first neuropathological features of AD in females.

Keywords: Alzheimer’s disease; GLP-1 mimetics; brain protection; female sex; liraglutide.

Figure 1

Effect of liraglutide on brain cortical AD-like hallmarks in 3xTg-AD female mice. Brain cortical Aβ_1–42 (A), Aβ_1–40 (B) and Tau pSer396 levels (C) were determined. Data are the mean ± SE from 4–6 mice/group. Statistical significance: * p < 0.05, ** p < 0.01, *** p < 0.001 or **** p < 0.0001, by the one-way ANOVA with the Bonferroni and Fisher LSD post-hoc tests for multiple comparisons.

Figure 2

Effect of liraglutide on behavioral performance in female mice with early AD-like pathology. Total distance travelled (A), and distance travelled (B) and time spent in the center (C) of the open field area during the open field test; time spent in start arm during training (D) and number of entries into the novel arm during testing session (E) in the Y-maze test; escape latency across trainings days (F) and testing session (G), and the number of crossings during testing session (H) of the Morris Water Maze test were assessed. Data are the mean ± SE from 6–10 mice/group. Statistical significance: * p < 0.05 or ** p < 0.01, by the one-way ANOVA with the Fisher LSD post-hoc test for multiple comparisons (for a Gaussian distribution: A,B,D,E), or by the non-parametric Mann-Whitney test (for a non-Gaussian distribution: C,G,H). Regarding Figure 2F, statistical significance: * p < 0.05 in WT day 3 vs. WT day 2, ^£p < 0.05 in 3xTg-AD + Lira day 2 vs. 3xTg-AD + Lira day 1, **** p < 0.0001 by two-way ANOVA, with the Tukey post-hoc test for multiple comparisons.

Figure 2

Effect of liraglutide on behavioral performance in female mice with early AD-like pathology. Total distance travelled (A), and distance travelled (B) and time spent in the center (C) of the open field area during the open field test; time spent in start arm during training (D) and number of entries into the novel arm during testing session (E) in the Y-maze test; escape latency across trainings days (F) and testing session (G), and the number of crossings during testing session (H) of the Morris Water Maze test were assessed. Data are the mean ± SE from 6–10 mice/group. Statistical significance: * p < 0.05 or ** p < 0.01, by the one-way ANOVA with the Fisher LSD post-hoc test for multiple comparisons (for a Gaussian distribution: A,B,D,E), or by the non-parametric Mann-Whitney test (for a non-Gaussian distribution: C,G,H). Regarding Figure 2F, statistical significance: * p < 0.05 in WT day 3 vs. WT day 2, ^£p < 0.05 in 3xTg-AD + Lira day 2 vs. 3xTg-AD + Lira day 1, **** p < 0.0001 by two-way ANOVA, with the Tukey post-hoc test for multiple comparisons.

Figure 3

Effect of liraglutide on brain cortical inflammation markers in female mice with early AD-like pathology. Brain cortical C-Reactive Protein (A) and IL-10 (B) were determined. Data are the mean ± SE from 3–6 mice/group. Statistical significance: * p < 0.05 or ** p < 0.01, by the one-way ANOVA with the Fisher LSD or Games-Howell post-hoc tests for multiple comparisons.

Figure 4

Effect of liraglutide on brain cortical glucose levels and transporters in mature female mice with early AD-like pathology. Brain cortical glucose (A), and GLUT1 (B) and GLUT4 protein levels (C) were evaluated and normalized to β-actin levels, and representative Western blotting images displayed. Data are the mean ± SE from 5–6 mice/group. Statistical significance: * p < 0.05, by the one-way ANOVA with the Fisher LSD or Games-Howell post-hoc tests for multiple comparisons.

Figure 5

Effect of liraglutide on brain cortical glucose metabolism in female mice with early AD-like pathology. Brain cortical G6PDH activity (A), and pyruvate (B) and lactate levels (C) were determined. Data are the mean ± SE from 4–6 mice/group. Statistical significance: * p < 0.05, by the one-way ANOVA with the Fisher LSD post-hoc test for multiple comparisons (for a Gaussian distribution), or with the non-parametric Mann-Whitney test (for a non-Gaussian distribution: GAPDH activity and lactate levels).

Figure 6

Effect of liraglutide on brain cortical oxidative and nitrosative stress markers in female mice with early AD-like pathology. Brain cortical carbonyl groups formation (A), 8-OH-dG (B) and nitrites levels (C) were determined. Data are the mean ± SE from 5–7 mice/group. Statistical significance: * p < 0.05 or ** p < 0.01, by the one-way ANOVA with the Fisher LSD post-hoc test for multiple comparisons.

Figure 7

Effect of liraglutide on brain cortical mitochondrial fission/fusion markers in female mice with early AD-like pathology. Brain cortical Fis1 (A) and OPA1 protein levels (B) were determined and normalized to β-actin levels, and representative Western blotting images displayed. Data are the mean ± SE from 6 mice/group. Statistical significance: * p < 0.05, by the one-way ANOVA with the Fisher LSD post-hoc test for multiple comparisons.