Adsorption and inhibition of acetylcholinesterase by different nanoparticles.

Manufactured nanoparticles can be toxic via interactions with proteins and enzymes. Acetylcholinesterase (AChE) is a key enzyme present in the brain, blood and nervous system. Therefore, adsorption and inhibition of AChE by eight nanoparticles, SiO(2), TiO(2), Al(2)O(3), Al, Cu, Cu-C (carbon-coated copper), multi-walled carbon nanotubes (MWCNT) and single-walled carbon nanotubes (SWCNT), were examined. A modified Ellman assay was used to measure AChE activity because nanoparticles could adsorb the yellowish product, 5'-mercapto-2'-nitrobenzoic acid (5-MNBA) during the color development. Adsorption and inhibition rates by nanoparticles were estimated by decrease of AChE activities compared to controls. Carbon nanotubes had high affinity for AChE adsorption, the highest being SWCNT (94%). Nano SiO(2) and Al(2)O(3) showed the lowest adsorption. Inhibition by the tested nanoparticles was primarily caused by adsorption. However, Cu(2+) release in Cu and Cu-C nanoparticle suspensions caused 40% and 45% of AChE activity reduction, respectively. AChE inhibition by bulk Cu and activated carbon particles was also measured for comparison, showing that the inhibition by bulk particles was lower than their counterpart nanoparticles. For bulk Cu particles, AChE inhibition was primarily caused by dissolved ions, but mainly by adsorption for activated carbon. AChE inhibition by Cu, Cu-C, MWCNT and SWCNT had dose-response relationships, and their median inhibitory concentrations (IC(50)) were 4, 17, 156 and 96mgL(-1), respectively, showing that these nanoparticles may have neurotoxicity and AChE may have potential to be used as a biomarker for nanoparticles.