Abstract
BackgroundSynthetic Amorphous Silica (SAS) is commonly used in food and drugs. Recently, a consumer intake of silica from food was estimated at 9.4 mg/kg bw/day, of which 1.8 mg/kg bw/day was estimated to be in the nano-size range. Food products containing SAS have been shown to contain silica in the nanometer size range (i.e. 5 – 200 nm) up to 43% of the total silica content. Concerns have been raised about the possible adverse effects of chronic exposure to nanostructured silica.MethodsRats were orally exposed to 100, 1000 or 2500 mg/kg bw/day of SAS, or to 100, 500 or 1000 mg/kg bw/day of NM-202 (a representative nanostructured silica for OECD testing) for 28 days, or to the highest dose of SAS or NM-202 for 84 days.ResultsSAS and NM-202 were extensively characterized as pristine materials, but also in the feed matrix and gut content of the animals, and after in vitro digestion. The latter indicated that the intestinal content of the mid/high-dose groups had stronger gel-like properties than the low-dose groups, implying low gelation and high bioaccessibility of silica in the human intestine at realistic consumer exposure levels. Exposure to SAS or NM-202 did not result in clearly elevated tissue silica levels after 28-days of exposure. However, after 84-days of exposure to SAS, but not to NM-202, silica accumulated in the spleen. Biochemical and immunological markers in blood and isolated cells did not indicate toxicity, but histopathological analysis, showed an increased incidence of liver fibrosis after 84-days of exposure, which only reached significance in the NM-202 treated animals. This observation was accompanied by a moderate, but significant increase in the expression of fibrosis-related genes in liver samples.ConclusionsAlthough only few adverse effects were observed, additional studies are warranted to further evaluate the biological relevance of observed fibrosis in liver and possible accumulation of silica in the spleen in the NM-202 and SAS exposed animals respectively. In these studies, dose-effect relations should be studied at lower dosages, more representative of the current exposure of consumers, since only the highest dosages were used for the present 84-day exposure study.
Highlights
Synthetic Amorphous Silica (SAS) is commonly used in food and drugs
Suspensions of both SAS and NM-202 in water containing 0.05% bovine serum albumine (BSA) as a stabilizing agent, showed the presence of agglomerates, which appeared to be larger in the feed mixture (Figure 1A-D), as assessed by scanning electron microscopy (SEM)
We conclude that, oral exposure of rats to NM-202 resulted in biological effects on the liver after 84 days of exposure, whereas exposure to SAS did not, which might have been caused by minor variations in the starting material
Summary
Synthetic Amorphous Silica (SAS) is commonly used in food and drugs. SAS intended for application in foodstuffs is predominantly produced by a standard pyrogenic process in which SiCl4 is burned in a hydrogen flame at temperatures ranging from 1000 to 2500°C. This results in the generation of primary silica nanoparticles of ~10 nm that aggregate into particles with sizes in the order of 100 nm, which agglomerate into particles in the larger nano- or micro-size range [1,2,6]
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