Istradefylline reduces memory deficits in aging mice with amyloid pathology

Abstract

Adenosine A_2A receptors are putative therapeutic targets for neurological disorders. The adenosine A_2A receptor antagonist istradefylline is approved in Japan for Parkinson's disease and is being tested in clinical trials for this condition elsewhere. A_2A receptors on neurons and astrocytes may contribute to Alzheimer's disease (AD) by impairing memory. However, it is not known whether istradefylline enhances cognitive function in aging animals with AD-like amyloid plaque pathology. Here, we show that elevated levels of Aβ, C-terminal fragments of the amyloid precursor protein (APP), or amyloid plaques, but not overexpression of APP per se, increase astrocytic A_2A receptor levels in the hippocampus and neocortex of aging mice. Moreover, in amyloid plaque-bearing mice, low-dose istradefylline treatment enhanced spatial memory and habituation, supporting the conclusion that, within a well-defined dose range, A_2A receptor blockers might help counteract memory problems in patients with Alzheimer's disease.

Keywords: Adenosine receptors; Alzheimer's disease; Amyloid plaques; Antagonist; Astrocytes; Behavior; Inhibition; Istradefylline; Memory; Therapy.

Fig. 1. Increases in A_2A levels in mice with amyloid-β accumulation

(A and B) Representative photomicrographs of hippocampal and neocortical sections from 9–10-month-old APP^NL-G-F (A) and hAPP-I5 (B) mice and age-matched wildtype (WT) controls (A and B) immunostained for the A_2AR (green), GFAP (red) and Aβ (magenta). Overlay of A_2AR and GFAP is shown in yellow. Insets (i–ii) show magnified views of the boxed regions. Scale bars: 200 μm. (C–F) Levels of A_2AR and GFAP immunoreactivities in CA1 and neocortex normalized to total selected brain areas and averages in WT littermates. A_2AR: n=4 WT mice (from APP^NL-G-F line), 14 APP^NL-G-F mice, 6 WT mice (from hAPP-I5 line), 15 hAPP-I5 mice. GFAP: n=4 WT mice (APP^NL-G-F line), 9 APP^NL-G-F mice, 6 WT mice (hAPP-I5 line), 10 hAPP-I5 mice. **P<0.01, ***P<0.001 vs. WT littermate controls (t test with Welch’s correction). Values are means ± SEM.

Fig. 2. Istradefylline enhances spatial memory in hAPP mice

14–15-month-old WT and hAPP-J20 mice treated with vehicle (Veh) or istradefylline (Istra, 10 mg/kg/day) were tested in the Morris water maze. (A) Distance traveled during hidden platform training (four trials/day). Linear regression analysis: t=2.966, P=0.0045 for genotype effect; t=−1.583, P=0.112 for drug effect; t=−0.019, P=0.99 for interaction effect. n=14–16 mice per genotype and treatment. (B–I) Probe trials 1 day (B–F) and 3 days (G–I) after training. (B) Time in target and nontarget (other) quadrants. Two-way ANOVA of target quadrant time: F(1,52)=5.66, P=0.0211 for drug effect; F(1,52)=6.42, P=0.0143 for genotype effect. t test with FDR correction for multiple comparisons (target vs. other quadrants): P=0.044 (WT/Veh), 0.012 (WT/Istra), 0.008 (hAPP/Veh), 0.14 (hAPP/Istra). n=13–15 mice per genotype and treatment. (C–E) Distance from the platform location. Average distance in 60 seconds (C–D) and the first 20 seconds (E) of the 24-hour probe trial. Two-way ANOVA: (C) F(1,53)=4.93, P=0.0307 for drug effect; F(1,53)=13.37, P=0.0006 for genotype effect. n=13–16 mice per genotype and treatment. (E) F(1,51)=14.46, P=0.0004 for drug effect; F(1,51)=42.22, P<0.0001 for genotype effect. n=3–15 mice per genotype and treatment. (F) Swim speed. Two-way ANOVA: F(1,52)=12.40, P=0.0009 for genotype effect. n=14–16 mice per genotype and treatment. (G and H) Distance from the platform location. Average distance in 60 seconds (G) and the first 20 seconds (H) of the 72-hour probe trial. Two-way ANOVA: (H) F(1,52)=7.20, P=0.0098 for interaction effect; F(1,52)=44.54, P<0.0001 for genotype effect. n=13–16 mice per genotype and treatment. (I) Swim speed. Two-way ANOVA: F(1,53)=8.30, P=0.0057 for genotype effect. n=13–16 mice per genotype and treatment. *P<0.05, **P<0.01, ***P<0.001 vs. other quadrants by t test (B) or WT/Veh group by Dunnett’s test (C, E, F, H, I), or as indicated by the brackets (Bonferroni test). Green shading indicates the first 20 seconds of the probe trial. Values are means ± SEM.