New silver nanoparticles induce apoptosis-like process in E. coli and interfere with mammalian copper metabolism

Iurii A Orlov,1,2 Tatiana P Sankova,1,2 Polina S Babich,3 Ilya M Sosnin,1,4 Ekaterina Yu Ilyechova,1,5 Demid A Kirilenko,1,6 Pavel N Brunkov,1,6 Gennadii L Ataev,3 Alexey E Romanov,1,4,6 Ludmila V Puchkova1,2,5 1International Research and Education Center “Functional materials and devices of optoelectronics and microelectronics”, ITMO University, 2Department of Biophysics, Peter the Great St Petersburg Polytechnic University, 3Department of Zoology, Herzen State Pedagogical University of Russia, St Petersburg, 4Nanocatalysts and Functional Materials Laboratory, Togliatti State University, Togliatti, 5Department of Molecular Genetics, Research Institute of Experimental Medicine, 6Ioffe Institute, St Petersburg, Russia Abstract: Silver nanoparticles (SNPs) are new functional materials that are widely used in biomedical and industrial technologies. Two main features that make SNPs valuable are their strong antibacterial effects and low toxicity to eukaryotes. In this study, SNPs were synthesized using a modified method of reducing the metal ions to their atomic state followed by crystallization. SNPs were characterized by UV/vis spectroscopy, X-ray diffractometry, atomic force microscopy, and transmission electron microscopy (TEM). The SNPs were spherically shaped with an average linear dimension of 20 nm. In aqueous solution, the SNPs were beige-yellow in color, and they formed a black color in bacteria-rich growth media. The toxicity and bioavailability of the SNPs were tested using Escherichia coli cells and C57Bl/6 mice. Although the SNPs displayed bactericidal activity, an E. coli cell strain transformed with an expression plasmid carrying a human CTR1 ectodomain with three motives that bind Cu(II), Cu(I), and Ag(I) demonstrated increased resistance to treatment with SNPs. TEM showed that the SNPs were absorbed by the E. coli cell, and flow cytometry showed that the SNPs induced apoptosis-like death. In mice treated with SNPs (daily intraperitoneal injection of 10 µg SNPs/g body weight over 4 days), the ceruloplasmin (Cp) oxidase activity in the blood serum decreased. However, level of Cp gene expression, the relative contents of the Cp protein in the Golgi complex and in the serum did not change. Treatment with SNPs did not influence the activity of superoxide dismutase 1 in the liver and had no apparent toxic effects in mice. These findings expand the scope of application for the use of new SNPs. The data are discussed in a paradigm, in which the effects of SNPs are caused by the interference of silver ions with copper metabolism. Keywords: silver nanoparticles, bioavailability, apoptosis-like death, mammalian copper metabolism, copper status