Alzheimer’s disease (AD) is characterized by brain amyloid beta plaque formation, neuroinflammation and neuronal degradation, which lead to cognitive impairment and decline in normal circadian rhythm (CR). Bioactive steroid marinobufagenin (MBG) modulates neuroinflammation. In 16-mo old double transgenic APPswe/PS1dE9 AD mice with advanced AD, amyloid precursor protein (APP) and interleukin 6 (IL6) mRNAs were upregulated vs. wild type (WT) control, and treatment with MBG reduced mRNA expression. Here, we investigated whether treatment with MBG at early-stage AD may impact AD development in this AD mouse model.
Methods:
Five months old male AD mice and WT mice were administered MBG (100 µg/day/kg) (AD-MBG, n= 8; WT-MBG, n= 14) or vehicle for control (AD-C, n= 7; WT-C, n= 14) via ALZET osmotic minipumps for 3 months. At 8-mo of age, the mice underwent turn-based discrimination learning in a water T-maze (WTM) to assess procedural learning and home cage activity (HCA) analysis during three consecutive days of single housing. Higher number of trials required to achieve criterion indicates greater difficulty with learning the task in WTM. The inflammatory and AD gene profile (by qPCR) and MBG levels (by immunoassay) were measured in hippocampus and plasma. Data was analyzed by 2-way ANOVA followed by Tukey’s test and presented as mean ±SE.
Results:
WT-C and AD-C mice had similar plasma MBG levels (243 ± 34 vs. 307 ± 65 pmol/L). MBG was higher in WT-MBG (447 ± 59 pmol/L; p lt; 0.05 vs. WT-C) and AD-MBG mice (554 ± 57 pmol/L; p lt; 0.05 vs. AD-C). In HCA, AD-C showed greater disruption in nightly CR, represented by greater activation during the first 6 hours of the night (Fig. 1a, b). While MBG did not significantly affect behavioral performance in WT or AD mice, trends show that MBG may worsen CR in WT and improve CR in AD mice. In WTM, AD-C required more trials than WT-C to reach criterion (Fig. 1c). MBG treatment numerically decreased the number of trials in AD-MBG vs. AD-C. MBG shows potential protective effect against cognitive impairment in AD mice. WT-MBG exhibited numerical increase in the number of trials, thus, MBG may reduce procedural learning ability in WT mice in WTM (Fig. 1c). Hippocampal inflammatory marker IL10 mRNA was 2-fold lower (plt;0.01) and IL6 mRNA was the same in AD-C vs. WT-C. AD markers were higher in AD-C vs. WT-C: APP mRNA 1.7-fold (Plt;0.01) and glial fibrillary acidic protein (GFAP) mRNA 1.6-fold (plt;0.05). MBG treatment did not affect this gene expression.
Conclusions:
AD mice in comparison to WT mice exhibited early-stage AD procedural learning impairment and CR disorder, which were accompanied by upregulated hippocampal AD markers without inflammatory marker activation. MBG treatment may have a protective effect against early-stage AD-related learning impairment and CR disruption. Future studies will examine the effects of MBG on the different cognitive domains in AD mice.
Supported by the NIH/NIA Intramural Research Program.
Figure 1: Home cage activity (HCA) and water T-maze (WTM) behavioral test results. (a) Average of activation in HCA during first six hours of nighttime; strain effect: p<0.05. (b) Overall activation in HCA for 24 hours. Grey area: nighttime between 6:30 p.m. and 6:30 a.m. (c) Number of trials required to learn turn-based acquisition in WTM. Strain*treatment: p<0.05. WT-C (n=14), AD-C (7), control WT and AD mice treated with vehicle; WT-MBG (n=14), AD-MBG (n=8): WT and AD mice treated with MBG.
