Cerium oxide nanoparticles have long attracted the attention of biomedics due to their antioxidant and anti-inflammatory properties. It can help in the treatment of difficult-to-heal ulcers, liver diseases, and retinal degeneration. However, the issue of safety remained open for a long time: due to their tiny size, particles are able to penetrate into cells and theoretically can harm them. Most of the previous studies in which scientists have tested the safety of cerium oxide nanoparticles have been conducted in vitro or on cell cultures. Experiments on laboratory animals have so far been few in number due to their complexity and high cost. Therefore, scientists are looking for simpler, but no less reliable ways to study such particles.

Scientists from Southern Federal University, Sechenov University, the Russian National Research Medical University named after N.I. Pirogov and the Institute of Bioorganic Chemistry named after Academicians M.M. Shemyakin and Yu.A. Ovchinnikov of the Russian Academy of Sciences investigated the safety of cerium oxide nanoparticles using bacterial biosensors. These are E. coli cells that have been artificially "embedded" with glow genes. The brightness of their glow varies depending on the environmental conditions: for example, in response to DNA damage or the presence of strong oxidizing agents (peroxide and superoxide radicals), it decreases as cells begin to die.

It was this effect that the authors used to evaluate the toxicity of cerium oxide nanoparticles. They placed a small amount of nanoparticles in the bacterial culture, after which the glow of the cells was measured for two hours. At the same time, the authors used three popular variants of nanoparticles: coated with citric acid (citrate) or dextran polysaccharide, as well as uncoated.

It turned out that none of the nanoparticle variants affected the bacterial community, since the glow of the cultures remained virtually unchanged. The authors also tested the antioxidant properties of cerium oxide nanoparticles and its ability to prevent mutations in DNA using bacterial biosensors. For this purpose, hydrogen peroxide and a mutagen substance were additionally added to the bacterial cultures. Oxidation was best suppressed by nanoparticles with citric acid: they reduced cell damage caused by peroxide by 65.6%. In experiments with a mutagen, the nanoparticles studied partially (with an efficiency of up to 56%) avoided damage to the genetic material in cells.

"Together with Sechenov University, we participated in testing new antioxidant materials. We have tested the effect of cerium nanoparticles on bacterial biosensors – genetically modified strains of E. coli that respond to oxidative stress by glowing.

Among several variants, citrate-modified nanoparticles proved to be the best antioxidant, while dextran-modified nanoparticles showed the highest antimutagenic potential, reducing DNA damage caused by dioxydin by more than 56%. The results suggest the potential use of these nanoparticles as antioxidant and antimutagenic agents in medicine and veterinary medicine," says Evgeniya Idelnova, Doctor of Biological Sciences, Head of the Youth Laboratory "Molecular Genetics of Microbial Consortia" at the SFedU Academy of Biology and Medicine.

The results of the study, supported by a grant from the Russian Science Foundation (RSF), are published in the International Journal of Molecular Sciences.

"We have not only proven the safety of different variants of cerium oxide nanoparticles, but also demonstrated their powerful antioxidant and antimutagenic properties. At the same time, it turned out that the effect of different nanoparticles is somewhat different, so for various practical applications it is worth choosing a specific composition. In general, such nanomaterials can help in the treatment of chronic wounds and ulcers, as well as inflammatory liver diseases and degenerative retinal diseases. In the future, we plan to continue the research necessary to start clinical trials of the drugs being developed. In particular, in a week we will begin an animal experiment with the treatment of wounds infected with antibiotic-resistant strains of bacteria. This is an important issue, as the constantly recurring theme of microbial resistance is added in our case to the problem of the need to achieve scar-free wound healing while preserving all functional layers of the skin. In addition, the antioxidant and antimutagenic properties of the developed products are useful for creating not only regenerative and antimicrobial products, but also for protection against various forms of radiation. Last December, together with the Lomonosov Moscow State University Research Institute of Nuclear Physics, we launched the space part of an experiment with selected biosensors on methods of protecting living organisms during long-term space flights. The ground—based part of the study and the first months of testing in space have already shown encouraging results," said Ekaterina Silina, MD, Professor of the Department of Pathological Physiology, Head of the Laboratory of Life Sciences at Moscow State Medical University named after I.M. Sechenov.