Inactivation of cholinesterase induced by non-steroidal anti-inflammatory drugs with horseradish peroxidase: Implication for Alzheimer's disease

AimsTo clarify the mechanism of the protective effect of non-steroidal anti-inflammatory drugs (NSAIDs) on Alzheimer's disease, inactivation of cholinesterase (ChE) induced by NSAIDs was examined.Main methodsEquine ChE and rat brain homogenate were incubated with NSAIDs and horseradish peroxidase (HRP) and H₂O₂ (HRP–H₂O₂). ChE activity was measured by using 5,5'-dithiobis(nitrobenzoic acid). By using electron spin resonance, NSAID radicals induced by reaction with HRP–H₂O₂ were detected in the presence of spin trap agents.Key findingsEquine ChE was inactivated by mefenamic acid with HRP–H₂O₂. ChE activity in rat brain homogenate decreased dependent on the concentration of mefenamic acid in the presence of HRP–H₂O₂. NSAIDs diclofenac, indomethacin, phenylbutazone, piroxicam and salicylic acid inactivated ChE. Oxygen radical scavengers did not prevent inactivation of ChE induced by mefenamic acid with HRP–H₂O₂. However, spin trap agents 5,5-dimethyl-1-pyrroline-l-oxide and N-methyl-nitrosopropane, reduced glutathione and ascorbic acid strongly inhibited inactivation of ChE, indicating participation of mefenamic acid radicals. Fluorescent emission of ChE peaked at 400 nm, and the Vmax value of ChE changed during interaction of mefenamic acid with HRP–H₂O₂, indicating that ChE may be inactivated through modification of tyrosine residues by mefenamic radicals.SignificanceThe protective effect of NSAIDs on Alzheimer's disease seems to occur through inactivation of ChE induced by NSAIDs radicals.