Neuroprotection by caffeine and adenosine A2A receptor blockade of beta-amyloid neurotoxicity

Abstract

Adenosine is a neuromodulator in the nervous system and it has recently been observed that pharmacological blockade or gene disruption of adenosine A(2A) receptors confers neuroprotection under different neurotoxic situations in the brain. We now observed that coapplication of either caffeine (1-25 micro M) or the selective A(2A) receptor antagonist, 4-(2-[7-amino-2(2-furyl)(1,2,4)triazolo (2,3-a)(1,3,5)triazin-5-ylamino]ethyl)phenol (ZM 241385, 50 nM), but not the A receptor antagonist, 8-cyclopentyltheophylline (200 nM), prevented the neuronal cell death caused by exposure of rat cultured cerebellar granule neurons to fragment 25-35 of beta-amyloid protein (25 micro M for 48 h), that by itself caused a near three-fold increase of propidium iodide-labeled cells. This constitutes the first in vitro evidence to suggest that adenosine A(2A) receptors may be the molecular target responsible for the observed beneficial effects of caffeine consumption in the development of Alzheimer's disease.

Figures

Figure 1

Caffeine and adenosine A2A receptor antagonists are neuroprotective against β-amyloid-induced neurotoxicity. Rat cerebellar neurons were cultured for 5 days and serum was withdrawn at day 5 for 48 h, which led to a discrete pattern of propidium iodide-labeled cells, indicative of low number of nonviable cells (a-1) and first column from the left in (b) and (c). The exposure of cells to Aβ25–35 (25 μM) in parallel with serum withdrawal increased the number of nonviable cells ((a-2), third and fourth columns from the left in (b) and (c), respectively) in comparison with the withdrawal of serum only (considered as control, 100% being the number of nonviable cells in this situation). (b) Administration of increasing concentrations of caffeine (1–25 μM) together with Aβ25–35 (25 μM) attenuated and fully prevented the Aβ25–35-induced neurotoxicity (see also (a-3)), but addition of caffeine (25 μM) failed to modify the number of nonviable cells upon serum withdrawal in the absence of Aβ25–35 (second column in (b)). The data are mean±s.e.m. of five experiments. (c) A selective A2A receptor antagonist, ZM 241385 (50 nM, second column from the right), but not an A1 receptor antagonist, CPT (200 nM, first column from the right), blocked the Aβ25–35 (25 μM)-induced neurotoxicity, but failed to modify the number of nonviable cells upon serum withdrawal in the absence of Aβ25–35 (second and third columns from the left). The data are mean±s.e.m. of three experiments. *P<0.05 versus control (first column from the left); **versus effect of 25 μM Aβ25–35 (third and fourth columns from the left in (b) and (c), respectively).