Oxygen Toxicity Is Reduced by Acetylcholinesterase Inhibition in the Developing Rat Brain

Abstract

The cholinergic anti-inflammatory pathway is a neural mechanism that suppresses the innate inflammatory response and controls inflammation employing acetylcholine as the key endogenous mediator. In this study, we investigated the effects of the cholinergic agonists, physostigmine and donepezil, on neurodegeneration, inflammation and oxidative stress during oxygen toxicity in the developing rat brain. The aim of this study was to investigate the level of neurodegeneration, expression of proinflammatory cytokines, glutathione and lipid peroxidation after hyperoxia and treatment with the acetylcholinesterase (AChE) inhibitors, physostigmine and donepezil in the brain of neonatal rats. Six-day-old Wistar rats were exposed to 80% oxygen for 12-24 h and received 100 μg/kg physostigmine or 200 μg/kg donepezil intraperitoneally. Sex-matched littermates kept in room air and injected with normal saline, physostigmine or donepezil served as controls. Treatment with both inhibitors significantly reduced hyperoxia-triggered activity of AChE, neural cell death and the upregulation of the proinflammatory cytokines IL-1β and TNF-α in the immature rat brain on the mRNA and protein level. In parallel, hyperoxia-induced oxidative stress was reduced by concomitant physostigmine and donepezil administration, as shown by an increased reduced/oxidized glutathione ratio and attenuated malondialdehyde levels, as a sign of lipid peroxidation. Our results suggest that a single treatment with AChE inhibitors at the beginning of hyperoxia attenuated the detrimental effects of oxygen toxicity in the developing brain and may pave the way for AChE inhibitors, which are currently used for the treatment of Alzheimer's disease, as potential candidates for adjunctive neuroprotective therapies to the immature brain.

Inhibition of Acetylcholinesterase Modulates NMDA Receptor Antagonist Mediated Alterations in the Developing Brain

“…As acetylcholinesterase is rapidly modulated under a variety of stress conditions and is induced during cell death [26,51–54], we investigated the regulation of AChE activity after administration of the non-competitive NMDA receptor antagonist MK801 (0.5 mg/kg at 0, 8, and 16 h) and the AChE inhibitor physostigmine (100 μg/kg at 0 h) to the immature rat brain. A marked up-regulation of AChE activity in brain hemispheres of rat pups at 6 (47.63 + 0.24 U/mg protein), 12 (43.50 + 1.87 U/mg protein) and 24 h (46.13 + 1.92 U/mg protein) after the last MK801 treatment (dark grey bars) was detected (Figure 1).…”

“…Since we have recently demonstrated a neuroprotective effect of physostigmine in a neonatal rat model of oxygen toxicity [26] we investigated whether this pharmacological intervention might also regulate mechanisms of NMDA receptor-induced neurodegeneration. Physostigmine is used especially for treatment of myasthenia gravis and glaucoma [58], reduces diisopropyl fluorophosphate-induced mortality [59] and improves survival in a model of experimental sepsis [60].…”

“…Cholinesterase inhibitors are able to ameliorate impaired working memory in adult rats and behavioural deficits in adult mice induced by MK801 (dizocilpine) [24,25]. We have previously demonstrated a neuroprotective effect of AChE inhibition in a neonatal rat model of oxygen toxicity [26]. These findings led to the question of whether administration of the prototypical AChE inhibitor, physostigmine, might regulate mechanisms of NMDA receptor antagonist-induced neurodegeneration in the developing brain.…”

Hyperoxia and the Immature Brain

“…In hyperoxiainduced neonatal brain injury, the upregulation of AChE has been detected [72] . After 12-24 h of hyperoxia exposure to 6-day-old rat pups, pretreatment with the AChE inhibitors physiostigmin (100 μg/kg) and donezepil (200 μg/kg) resulted in the reduction of AChE activity, and IL-1β, TNF-α mRNA and protein expression as well as the amelioration of oxidative stress and neuronal cell death [102] . Dextromethorphan (DM) is an antitussive agent widely used in paediatric care [202,203] .…”

“…It has been shown that hyperoxia triggers an increase in oxidative stress by modulating intracellular redox homeostasis, via an increase in oxidised glutathione and a decrease in reduced glutathione and heme oxygenase 1 (HO-1) as well as an increase in lipid peroxidation in the immature brain of 6-day-old rats after 2-48 h of hyperoxia [72,102] . In this model, even short exposures to nonphysiologic oxygen levels can change the balance of the ROS-dependent thioredoxin/peroxiredoxin system.…”