[Toxicological evaluation of colloidal nano-sized silver stabilized polyvinylpyrrolidone. IV. Influence on intestinal microbiota, immune indexes].

Nano-sized colloidal silver (NCS) stabilized with polyvinylpyrrolidone (PVP) containing nanoparticles (NPs) of silver with a diameter of 10-80 nm was administered to growing male rats (body weight 80±10 g) during the first 30 days by intragastric gavage and then for 62 days with diet consumed in doses of 0.1, 1.0 and 10 mg/kg of body weight per day based on silver (Ag). The control animals received deionized water and PVP. The composition of microbiota from the cecum was studied using standard microbiological methods with determination of the main and transient components, together with antagonistic activity of symbiotic bifidobacteria. Expression of antigens CD45RA, CD3, CD4, CD8, CD161a on lymphocytes (Ly) of peripheral blood was determined by flow cytometry; blood serum levels of cytokines IL10, IL13, TNFα were examined by ELISA. It was shown that subacute administration of colloidal Ag in all studied doses did not lead to significant changes in the composition of the main components of normal microbiota, providing, however, the inhibitory effect on the growth of some transitory components probably including opportunistic species of microorganisms. Among the studied immunological parameters decreased amount of B-Ly was noticed at the highest dose of the NCS, while changes in the other parameters of the immune system were depended ambiguously on the dose of the product. The results were analyzed in conjunction with the data of previous publications concerning the impact on the NCS on integrated, morphological, hematological, biochemical and enzymological indexes of animals in the 92-day experiment. It was concluded that significant symptoms of NCS sub-acute oral toxicity manifested starting from a dose of 1 mg/kg body weight of Ag, and the maximum not observed adverse effect dose (NOAEL) can be estimated as 0.1 mg/kg body weight.