Research On The Bioaccumulation Behavior Of Silver Nanoparticles In Rats

With the wide application of nanosilver, specifically silver nanoparticles (AgNPs) in a diverse spectrum of fields, the environmental exposure of this kind of nanomaterials has become inevitable. Lots of attentions have been paid on its potential adverse effects based on multiple experimental models. Given that the translocation, distribution and the possible biotransformation of nanosilver in organisms are the essential prerequisites for its biological effects, comprehensive researches on the behaviors of nanosilver in vivo are paramount, thus bringing understanding of the toxicological effects of AgNPs and their potential hazards in human beings. In this thesis, the bioaccumulation and elimination behavior of nanosilver was studied in natal Sprague-Dawley (SD) rats through intranasal instillation.Using 2-day-postnatal SD rats as the experimental model, a kind of PVP coated nanosilver was used for the short-term (4 weeks) and long-term (12 weeks) exposure experiments followed by a 4-week recovery duration. The results indicated all tested organs or tissues contained silver accumulation during the exposure of AgNPs. Relatively high levels of silver existed in brain tissue after 12-week exposure of AgNPs (0.1 mg as Ag·kg-1·d-1), while it was the liver that accumulated the highest concentration of silver after a 4-week exposure. Time course studies for silver bioaccumulation showed that silver concentration in brain increased with the exposure duration while silver concentrations in the other tested organs increased during the first 4-6 weeks, then gradually declined to a negligible level. The most interesting finding was that the brain silver accumulation increased during the exposure period and showed no trend to decrease during the 4-week recovery stage, which implied the brain-targeted bioaccumulation of silver. Meanwhile, silver nitrate exposure was performed in the comparative experiment to evaluate the effects of silver ions. Similar bioaccumulation profile of silver was observed in the rats exposed to silver nitrate when compared with those treated with AgNPs. Nevertheless, tissue silver levels in silver ion exposure groups were significantly higher those in AgNPs exposure ones, which well explained the relatively higher toxicity of ionic silver than particulate one.Altogether, we investigated the distribution, translocation, retention of AgNPs in rats through intranasal instillation. The finding of brain-targeted distribution and persistent retention of silver implicated the potential neurological hazards from the nasal administration of silver colloid medications.