Stimulation of Sigma Receptors with Afobazole Blocks Activation of Microglia and Reduces Toxicity Caused by Amyloid-β25-35

Alzheimer’s disease (AD) is a progressive neurodegenerative disease and the leading cause of senile dementia in the United States. Accumulation of amyloid- β (A β ) and the effects of this peptide on microglial cells contribute greatly to the etiology of AD. Experiments were carried out to determine whether the pan-selective σ -receptor agonist afobazole can modulate microglial response to the cytotoxic A β fragment, A β 25–35 . Treatment with afobazole decreased microglial activation in response to A β , as indicated by reduced membrane ruffling and cell migration. The effects of afobazole on A β 25–35 -evoked migration were concentration dependent and consistent with σ -receptor activation. When afobazole was coapplied with either BD-1047 [ N -[2-(3,4-dichlorophenyl)ethyl]- N -methyl-2-(dimethylamino)ethylamine dihydrobromide] or rimcazole, which are σ -1- and σ -2-selective antagonists, respectively, the inhibition of A β 25–35 -induced migration by afobazole was reduced. Prolonged exposure of microglia to A β 25–35 resulted in glial cell death that was associated with increased expression of the proapoptotic protein Bax and the death protease caspase-3. Coapplication of afobazole with A β 25–35 decreased the number of cells expressing both Bax and caspase-3 and resulted in a concomitant enhancement in cell survival. Although afobazole inhibited activation of microglia cells by A β 25–35 , it preserved normal functional responses in these cells after exposure to the amyloid peptide. Intracellular calcium increases induced by ATP were depressed in microglia after 24-hour exposure to A β 25–35 . However, coincubation in afobazole returned these responses to near control levels. Therefore, stimulation of σ -1 and σ -2 receptors by afobazole prevents A β 25–35 activation of microglia and inhibits A β 25–35 -associated cytotoxicity, suggesting that afobazole may be useful for AD therapeutics.