Sunday Sep 14, 2014 (foodconsumer.org) -- The potential neurotoxicity of silica (also known as silicon dioxide) nanoparticles or its effect on the risk of Alzheimer's disease remains largely untested, according to a new study report in Toxicology Letters, although silica nanoparticles have been used in all sorts of dietary supplements, processed foods, and personal care products.

The Chinese study now suggests intake of silica engineered silica nanoparticles can increase risk of Alzheimer's disease, which affects more than five million American older people, according to the U.S. Centers for Disease Control and Prevention.

The study was not to study the effect of silica on risk of human Alzheimer's disease.  Rather it was intended to examine the cellular uptake of silica nanoparticles in human SK-N-Sh and mouse neuro2a (N2a) neuroblastoma cells treated with 10 ug/mL of 15 nm silica nanoparticles for 24 hours.

The study found silica nanoparticles applied to the cell lines were mainly localized in the cytoplasm of the cells and impaired the morphology of SK-N-SH and N2a cells.  Specifically, the treatment increased the number of round cells, diminished dendrite-like processes and decreased cell density.  Chemically, silica nanoparticles decreased cell viability, induced apoptosis, and increased intracellular reactive oxygen species (ROS) in a dose dependent manner.

In both cell lines, exposure to silica nanoparticles increased deposit of intracellular  β-amyloid 1-42 (Aβ(1-42)) and phosphorylation of tau at Ser262 and Ser396, two hallmarks of Alzheimer's disease.  Also, the expression of amyloid precursor protein increased while amyloid β-degrading enzyme neprilysin decreased in cells exposed to silica nanoparticles. This and other evidence suggests that exposure to silica can be a risk factor for Alzheimer's disease.

The study concluded "exposure to SiNPs (silica nanoparticles) induced neurotoxicity and pathological signs of Alzheimer's disease." 

Another study shows that silicon dioxide or simply silica with size ranging from 10 to 15 nm can damage multiple organs including the liver, kidney, lung and testis. (David Liu, PHD)

Yang X, He C, Li J, Chen H, Ma Q, Sui X, Tian S, Ying M, Zhang Q, Luo Y, Zhuang Z, Liu J.  Uptake of silica nanoparticles: neurotoxicity and Alzheimer-like pathology in human SK-N-SH and mouse neuro2a neuroblastoma cells.   Toxicol Lett. 2014 Aug 17;229(1):240-9.