Selective Brain-Targeted Antagonism of p38 MAPKα Reduces Hippocampal IL-1β Levels and Improves Morris Water Maze Performance in Aged Rats

Abstract

Background: P38 mitogen activated protein kinase (MAPK) α modulates microglia-mediated inflammatory responses and a number of neuronal physiological processes.

Objective: To evaluate pre-clinically the pharmacological effects in the brain of p38 MAPKα inhibition with a brain-penetrant specific chemical antagonist.

Methods: VX-745, a blood-brain barrier penetrant, highly selective p38 MAPKα inhibitor, and clinical stage investigational drug, was utilized. Initially, a pilot study in 26-month-old Tg2576 mice was conducted. Subsequently, a definitive dose-response study was conducted in aged (20-22 months) rats with identified cognitive deficits; n = 15 per group: vehicle, 0.5, 1.5, and 4.5 mg/kg VX-745 by oral gavage twice daily for 3 weeks. Assessments in aged rats included IL-1β, PSD-95, TNFα protein levels in hippocampus; and Morris water maze (MWM) test for cognitive performance.

Results: Drug effect could not be assessed in Tg2576 mice, as little inflammation was evident. In cognitively-impaired aged rats, VX-745 led to significantly improved performance in the MWM and significant reduction in hippocampal IL-1β protein levels, though the effects were dissociated as the MWM effect was evident at a lower dose level than that required to lower IL-1β. Drug concentration-effect relationships and predicted human doses were determined.

Conclusions: Selective inhibition of p38 MAPKα with VX-745 in aged rats reduces hippocampal IL-1β levels and improves performance in the MWM. As the two effects occur at different dose levels, the behavioral effect appears to be via a mechanism that is independent of reducing cytokine production. The predicted human doses should minimize risks of systemic toxicity.

Keywords: Aged rats; Alzheimer’s disease; IL-1β; Tg2576 mouse; amyloid plaque; cognition; p38 MAPKα.

Fig.1

Effects of VX-745 on the area of amyloid plaque in the hippocampus and cortex of Tg2576 mice. Expressed as Mean (±SEM) percentage of total area by immunohistochemistry staining for Aβ. Mice treated with VX-745 (3 mg/kg) demonstrated a statistical trend toward decreased number of amyloid plaques in the hippocampus (p = 0.069, unpaired two-sided t-test), compared to vehicle treated transgenic mice. In addition, amyloid plaque load was numerically lower in the cortex of VX-745-treated lower (p = not significant).

Fig.2

Morris water maze test results during acquisition phase. Results in vehicle-treated young rats and aged rats treated with 0.5, 1.5, or 4.5 mg/kg VX-745 shown as mean (±SEM) Latency (a) and mean (±SEM) Distance (b) by Day of testing.  ^*p <  0.05, for 1.5 mg/kg VX-745 versus aged-vehicle treated rats at last day of testing.

Fig.3

Normalized Morris water maze test results during acquisition phase. Results in vehicle-treated young rats and aged rats treated with 0.5, 1.5, or 4.5 mg/kg VX-745 shown as Latency (c) and Distance (d) as percentage change from initial testing results at day 8.  ^**p <  0.01 and  ^*p <  0.05 by t-test for latency and distance, respectively, for 1.5 mg/kg VX-745 versus aged-vehicle treated rats at last day of testing.

Fig.4

Protein levels of IL-1β (a) and PSD95 (b) in hippocampal homogenate. Obtained at sacrifice at end of treatment in vehicle-treated young rats and aged rats treated with vehicle or 0.5, 1.5, or 4.5 mg/kg of VX-745. 4.5 mg/kg VX-745 demonstrated significantly reduced IL-1β levels (p = 0.038 by Mann-Whitney rank sum test) and a trend toward increased PSD95 levels (p = 0.06) compared to vehicle-treated aged rats.