Chronic administration of R-flurbiprofen attenuates learning impairments in transgenic amyloid precursor protein mice

Abstract

Background: Long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) is associated with a reduced incidence of Alzheimer's disease (AD). We and others have shown that certain NSAIDs reduce secretion of Abeta42 in cell culture and animal models, and that the effect of NSAIDs on Abeta42 is independent of the inhibition of cyclooxygenase by these compounds. Since Abeta42 is hypothesized to be the initiating pathologic molecule in AD, the ability of these compounds to lower Abeta42 selectively may be associated with their protective effect. We have previously identified R-flurbiprofen (tarenflurbil) as a selective Abeta42 lowering agent with greatly reduced cyclooxygenase activity that shows promise for testing this hypothesis. In this study we report the effect of chronic R-flurbiprofen treatment on cognition and Abeta loads in Tg2576 APP mice.

Results: A four-month preventative treatment regimen with R-flurbiprofen (10 mg/kg/day) was administered to young Tg2576 mice prior to robust plaque or Abeta pathology. This treatment regimen improved spatial learning as assessed by the Morris water maze, indicated by an increased spatial bias during the third probe trial and an increased utilization of a place strategy to solve the water maze. These results are consistent with an improvement in hippocampal- and medial temporal lobe-dependent memory function. A modest, though not statistically significant, reduction in formic acid-soluble levels of Abeta was also observed. To determine if R-flurbiprofen could reverse cognitive deficits in Tg2576 mice where plaque pathology was already robust, a two-week therapeutic treatment was given to older Tg2576 mice with the same dose of R-flurbiprofen. This approach resulted in a significant decrease in Abeta plaque burden but no significant improvement in spatial learning.

Conclusion: We have found that chronic administration of R-flurbiprofen is able to attenuate spatial learning deficits if given prior to plaque deposition in Tg2576 mice. Given its ability to selectively target Abeta42 production and improve cognitive impairments in transgenic APP mice, as well as promising data from a phase 2 human clinical trial, future studies are needed to investigate the utility of R-flurbiprofen as an AD therapeutic and its possible mechanisms of action.

Figure 1

Sensory motor and spatial learning ability measured in the water maze. 1A shows the latency to escape to the visible escape platform during cue training. There are no differences in the performance of any of the groups. 1B shows the search error during the acquisition of the spatial reference memory task. The 2-week R-flurbiprofen-treated mice (Therapeutic group) performed more poorly than the other groups (Preventative group) on days 4, 7, 8, 9 and 10. 1C shows that only the Tg2576 mice treated for 16 weeks (Preventative group) with R-flurbiprofen developed a spatial bias for the training quadrant. 1D shows representative swim paths of the Control and the Preventative groups during Probe Trial 3. Note that the R-flurbiprofen-treated mice focus their search in the training quadrant that contained the hidden escape platform (bottom left quadrant). 1E shows the percent of subjects that preferred using a cue or place strategy during the strategy competition. 80% of the Tg2576 mice in the Preventative group preferred using a place strategy compared to only 30% of the Control and 31% of the Therapeutic group (Chi-square = 11.23, p < .01).

Figure 2

ELISA quantitation of Aβ levels in Tg2576 from water maze experiments. The levels of detergent soluble (RIPA or SDS) and formic acid soluble Aβ1–40 and Aβ1–42 in R-flurbiprofen treated mice from the three water mazes are plotted as percent control. The mean Aβ levels +/- the standard error from control mice are shown below each graph. The absolute values (pmoles/gram tissue) of formic acid soluble Aβ40 and Aβ42 levels from individual animals are plotted against one another to show the distribution of individual animals from experimental groups. "Preventative 1 and Preventative 2" refers to two different experiments examining the effects of 4 months of administration of R-flurbiprofen to Tg2576 mice. "Therapeutic" refers to 2 weeks administration of R-flurbiprofen.

Figure 3

Effect of R-flurbiprofen treatment on amyloid-β plaques in Tg2576 mice. Brain sections of representative Control and R-flurbiprofen-treated mice from water maze Experiment 3 (20 months at sacrifice) were stained for Aβ plaques using antibody 33.1.1 (A) and thioflavin (B). In (C), the level of Aβ plaque burden (quantified as % Aβ immunoreactive area) in Control compared to R-flurbiprofen treated-Tg2576 mice from Experiments 2 and 3 are compared. Note the significant reduction in plaque burden in the R-flurbiprofen treated mice from Experiment 3 (*** p < 0.0001).