Activation of nicotinic acetylcholine receptor prevents the production of reactive oxygen species in fibrillar β amyloid peptide (1-42)-stimulated microglia

Recent studies have reported that the "cholinergic anti-inflammatory pathway" regulates peripheral inflammatory responses via α 7 nicotinic acetylcholine receptors (α 7 nAChRs) and that acetylcholine and nicotine regulate the expression of proinflammatory mediators such as TNF-α and prostaglandin E2 in microglial cultures. In a previous study we showed that ATP released by β-amyloid-stimulated microglia induced reactive oxygen species (ROS) production, in a process involving the P2X7 receptor (P2X7R), in an autocrine fashion. These observations led us to investigate whether stimulation by nicotine could regulate fibrillar β amyloid peptide (1-42) (fAβ1-42)-induced ROS production by modulating ATP efflux-mediated Ca2+ influx through P2X7R. Nicotine inhibited ROS generation in fAβ1-42-stimulated microglial cells, and this inhibition was blocked by mecamylamine, a non-selective nAChR antagonist, and α-bungarotoxin, a selective α7 nAChR antagonist. Nicotine inhibited NADPH oxidase activation and completely blocked Ca2+ influx in fAβ1-42-stimulated microglia. Moreover, ATP release from fAβ1-42-stimulated microglia was significantly suppressed by nicotine treatment. In contrast, nicotine did not inhibit 2',3'-O-(4-benzoyl)-benzoyl ATP (BzATP)-induced Ca2+ influx, but inhibited ROS generation in BzATP-stimulated microglia, indicating an inhibitory effect of nicotine on a signaling process downstream of P2X7R. Taken together, these results suggest that the inhibitory effect of nicotine on ROS production in fAβ1-42-stimulated microglia is mediated by indirect blockage of ATP release and by directly altering the signaling process downstream from P2X7R.