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Are silver supplements always useful?
JINR Press Service
Scientists of the Neutron Physics Laboratory in cooperation with the Institute of Microbiology and Biotechnology of the participating country of the Joint Institute for Nuclear Research - Moldova – studied how silver nanoparticles behave in the body of animals, as well as how they affect the state of their body. Silver nanoparticles are widely used in various industries, including food and cosmetics production. The results of the study suggest the toxicity of these nanoparticles, and may in the future mean that their use will have to be limited or, at least, strictly regulated.
Nanotechnology is a new area of science and technology that has been actively developing in recent decades. Nanomaterials are increasingly entering human life, and nanoparticles, thanks to their unique properties, have improved many industries of production and consumption, including medicine, where they are used for the delivery of medicines. The most studied to date are silver nanoparticles (AgNPs), which have pronounced antibacterial properties with low toxicity and no negative effect on the indigenous microflora of animals. The properties of nanoparticles also depend on the shape and size of the particles, which determines their scope or limitations.
The staff of the JINR Neutron Physics Laboratory together with colleagues from the Institute of Microbiology and Biotechnology (Chisinau, Moldova) have started a cycle of work on the toxicity of metal nanoparticles for animals. The main purpose of this study was to study the effect of unmodified (AgNPs) and modified cyanobacterium Spirulina platensis (AgNPs-Spirulina) silver nanoparticles on rats with prolonged oral administration. Modification of the surface of nanoparticles (Fig. 1) by various biomolecules in a controlled manner is necessary to change their properties, such as preventing aggregation or enhancing antimicrobial action.
"In this study, both ordinary silver nanoparticles and "enhanced" ones with blue-green algae, namely spirulina, were considered. Unmodified silver nanoparticles have the property of "sticking together", which leads to a change in their physical, chemical and antimicrobial properties. To avoid aggregation, we tried adding spirulina, which is non-toxic to living organisms and has been well studied. Unlike many cyanobacteria, it does not produce algotoxins in response to the action of metals and other pollutants," comments Inga Zinkovskaya, Head of the JINR Research Department, Head of the Neutron Activation Analysis and Applied Research of the JINR LNF.
Fig. 1 Silver nanoparticles modified with Spirulina platensis biomass
Experiments with animals were carried out in the vivarium of the Laboratory of Stress Physiology, Adaptation and General Sanocreatology Institute of Physiology and Sanocreatology (Chisinau, Moldova). The animals were divided into 4 groups with different diets: 1. negative control group (K1) — standard diet; 2. positive control group (C2) — standard diet with the addition of spirulina biomass; 3. experimental group 1 (AgNP) — standard diet with the addition of AgNP; and 4. experimental group 2 (AgNPs-Sp) is a standard diet with the addition of AgNPs-spirulina. The experiment lasted 28 days.
The silver content in rat organs (brain, liver, spleen, kidneys, testicles and ovaries) was determined by neutron activation analysis (NAA) at the IBR-2 reactor REGATTA facility. According to the results obtained, silver was found in all the analyzed animal organs, with the exception of the ovaries and testes, in which only modified nanoparticles accumulated. The highest silver content accumulated in the brain, liver and kidneys — 0.145–0.150 mcg/g. It should be noted that in animals injected with unmodified nanoparticles, the highest silver content was determined in the brain and kidneys, whereas in animals injected with AgNPs-Spirulina, silver mainly accumulated in the brain and testicles (Fig. 2).
Some of the animals were transferred to a standard diet at the end of the experiment and after a half-life (28 days), the silver content in the organs was determined by NAA. As the NAA data showed, silver was excreted from the spleen, liver and kidneys. Thus, its content in the liver decreased by 76%. However, the excretion from the brain was very low, regardless of the type of nanoparticles used.
Fig. 2 Silver content in rat organs: (A) animals injected with AgNPs and AgNPs-Spirulina for 28 days, measured immediately after the end of the experiment; (B) animals injected with AgNP for 28 days, measured after the half-life; (C) animals injected with AgNPs-Spirulina in within 28 days measured after half-life
Hematological and biochemical tests were performed to detect the effect of nanoparticles on rats. A significant difference was found in the content of eosinophils in the experimental and control groups. Hematological parameters of rats under the influence of silver nanoparticles did not change significantly, except for the content of reticulocytes and eosinophils, which increased significantly. Changes in biochemical parameters did not go beyond the norm. However, changes in the values of kidney and liver function indicators may indicate possible toxicity of silver nanoparticles. Silver nanoparticles with a size of 8-20 nm can easily penetrate the blood-brain barrier, and their low excretion from the brain indicates the irreversibility of this process.
"Nanoparticles of this size range are most often used in industry. Especially in cosmetics. And although we see that they did not affect the blood formula and the functional state of animal organs, it is obvious that they accumulate in the brain. This requires close attention, because over time, accumulated nanoparticles can have a toxic effect that will affect the cognitive functions of the brain," Inga Zinkovskaya summed up. — Thus, silver nanoparticles should be used with caution. We will continue our research in this direction."
Article by Rudi et al. Accumulation and effect of silver nanoparticles functionalized with Spirulina platensis on rats is published in the journal Nanomaterials.
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