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Said I Kaba, Elena M Egorova Institute of General Pathology and Pathophysiology, Moscow, Russia Abstract: In the last decade, much attention has been paid to studies of the effect of silver nanoparticles (Ag NPs) on tumor cells. Apart from elucidation of the mechanism of NPs’ interaction with mammalian cells, these studies are aimed at discovering new effective antitumor drugs. In this work, we report about the toxic effects of Ag NPs observed on two types of tumor cells: HeLa (adhesive cells) and U937 (suspension cells). The Ag NPs were obtained by an original method of biochemical synthesis. Particle size was 13.2±4.72 nm, and zeta potential was -61.9±3.2 mV. The toxicity of Ag NPs in the concentration range 0.5–8.0 µg Ag/mL was determined by means of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and cytofluorometry after 4 and 24 hours' incubation. It was found that Ag NPs had high toxicity toward both cell types. The minimal concentrations where a toxicity effect was registered (toxicity thresholds) lied in the range 0.5–2.0 µg Ag/mL. In parallel with the Ag NP solution, cells were incubated with water solutions of the NP stabilizer (aerosol-OT) and Ag+ ions (as silver nitrate). It was shown that aerosol-OT had no effect on the viability on HeLa cells, but was moderately toxic toward U937, though less dangerous for these cells than Ag NPs. With Ag+ ions, for HeLa no toxic effect was observed, while for U937 they were as toxic as the Ag NPs. The data obtained indicate that Ag NPs as used in this study may prove to be useful for the creation of medicines for cancer therapy. Keywords: silver nanoparticles, cell viability, apoptosis, tumor cells

We have used a combined geometrical-topological approach to analyze 21,697 intermetallic crystal structures stored in the Inorganic Crystal Structure Database. Following a geometrical scheme of close packing of balls, we have considered the three most typical polyhedral atomic environments of the icosahedral, cuboctahedral, or twinned cuboctahedral shape as well as multi-shell (up to four shells) local atomic configurations (LACs) based on these cores in 10,657 unique crystal structure determinations. In total, half of intermetallic structures have been found to contain one of these configurations, with the icosahedral LACs being the most frequent. We have revealed that even a two-shell configuration strongly predetermines the overall connectivity (topological type) of an intermetallic crystal structure. The chemical and stoichiometric composition of the multi-shell LACs generally obeys the close-packing model: the number of atoms in the subsequent shells ( N k ) varies around the value N k = 10 k 2 + 2, which is valid for the same size atoms, to reach the densest packing for the k th shell. Deviations from the revealed regularities often indicate inconsistencies in the crystallographic information, unusual features of the structure, or the existence of more stable phases that can be used for the validation of experimental and modeling data.

The toxic action of surfactant used as a stabilizer of metal nanoparticles have been studied with the aim to determine separate contributions of surfactant monomers and micelles to cell viability decrease. Basing on (1) the well-known ability of surfactant molecules to form micelles in solution at a critical micelle concentration (CMC) and (2) the results reported in literature, showing that toxicity of various surfactants increases when their concentration exceeds CMC, we supposed that surfactant molecules and micelles may differ in their toxic effect on cells. This supposition was verified on the anionic surfactant aerosol-OT (AOT) used as a stabilizer of silver nanoparticles (AgNPs) in studies of their cytotoxicity on Jurkat cells by means of the MTT test. Two samples of AgNPs stabilized with AOT in concentrations higher (3 mM) and lower (1 mM) than its CMC in water were introduced to the cell medium as water solutions diluted to obtain nanoparticle concentrations in the range 1-7 μg/mL. Cell viability changes were registered after 24 h incubation. It was found that AgNPs of similar average size (about 16 nm), synthesized by the same procedure, introduced to the same concentrations in cell medium, produced a different effect on cell viability. Namely, decrease in cell viability was observed for AgNPs with 3 mM AOT, while no noticeable changes were registered for AgNPs with 1 mM AOT. A similar difference was detected for the corresponding dilutions of 3 mM and 1 mM AOT water solutions. We assumed that the toxicity dependence on AOT concentration originated from the difference in toxic action of the two different AOT forms - molecules (monomers) and micelles - present in the AgNPs and AOT solution. The approach was suggested for estimation of the separate contributions of monomers and micelles to the total AOT toxicity; changes of these contributions with AgNPs or AOT concentration were also determined. The results obtained may prove to be useful in studies of the biological activity of surfactants applied both as nanoparticle stabilizers and as agents working in medicine as suppressors of various infections., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The toxic and genotoxic effects of silver nanoparticles were studied on injected mice (BALB/c line) in vivo. A water solution of silver nanoparticles (SNP) with particle sizes of 9±6 nm was obtained by means of the original method of biochemical synthesis. The effect of the SNP solution was compared to those of AOT (anionic surfactant used as SNP stabilizer) and silver nitrate (i.e. Ag+ ions) introduced as water solutions. In studies of the toxic effects, the death of mice was registered 12-24 hours after injection only at two maximum dozes of SNP (equivalent to 0.54 and 0.36 gAg/l). It is shown that the toxic effect decreases in the sequence SNP>AOT>>AgNO3. The LE50/30 values for SNP and AOT are equal to 0.30±0.07 gAg/l and 13.3±2.1 gAg/l, respectively. Genotoxic effects were assessed by the abnormal sperm heads test and neutral Comet assay. The frequencies of abnormal sperm heads (ASHs) did not differ after treatment by SNP and AOT, but both were significantly higher than those found with AgNO3 and in control mice. Comet assay showed an increase of the DNA percentage in the comet tail in spleen cells after the injection of SNP and AOT in concentrations of ≤ LE50/30. Tail DNA % was 32.8±1.3 and 26.3±1.7%, respectively, vs 16.2±0.7% for the untreated control. To sum up, these tests showed that the genotoxic effects of the SNP solution are associated with the presence of AOT rather than SNP.

A new polymer composite based on carboxymethylchitin and silver nanoparticles was obtained in order to produce biodegradable wound coating films. The number of metal nanoparticles in the composite may be easily regulated as was verified by UV-VIS-spectroscopy data. A comparative evaluation of silver nanoparticle size in the initial system and in the polymer composition was performed by means of photon correlation spectroscopy. Composite films revealed a pronounced concentration-dependent antibacterial activity towards strains Salmonella typhimurium and Staphilococcus aureus.

A method for assessing the abiotic efficiency of water-dispersed nano-sized silver particles is suggested. Nanoparticles were obtained by the method of biochemical synthesis in reversed micelles made from anionic surfactant bis-(2-ethylhexyl) sodium sulfosuccinate (AOT). A water dispersion of nanoparticles was prepared from the micellar solution in organic solvent by means of a special procedure. The abiotic efficiency assay is based on the capacity of cells to respond by the negative chemotaxis to chemical agents with harmful metabolic action. In plasmodium of myxomicete Physarum polycephalum, the biocide and repellent effects of silver nanoparticles, Ag+ ions, and AOT were tested in order to compare the abiotic efficiency of these substances in water solution and after introduction into agar substrate. The increase in the oscillation period, the reduction in the area of spreading, and the avoidance reaction in the spatial test, taken together, revealed a much higher repellent efficiency of silver nanoparticles as compared with that of Ag+ ions and AOT. The NSP concentrations lethal for Physarum were similar to those found earlier for bacteria and viruses. The chemotaxis-based tests applied in this study allow one to quantitatively assess cell reactions and monitor their time course. Besides, they have a much higher resolving capacity than the tests based on lethal effects of abiotic substances.

Electrokinetic behaviour of human lymphocytes was studied by photon correlation spectroscopy technique on laser IR-spectrometer. The electrophoretic mobilities (EPMs) were measured for peripheral blood lymphocytes (PBL) and CEM-C12 T cell line in 1:1 electrolyte at 22 degrees C. Plots of mobility vs ionic strength in the range 0.001-0.1 M were compared with theoretical curves calculated from (i) the Smoluchowsky formula, (ii) the simplified form of the Dukhin-Deryaguin equation which takes into account the fact that the mobility decreases due to the relaxation effect and (iii) the equation suggested by Donath and Pastushenko, which takes into account the influence of cell glycoprotein layer (GPL) on the EPM values. It has been found that the first two equations describe the experimental data with the assumption that surface charge density (sigma) decreases and width of the hydrodynamically immobile layer (L) increases with decreasing ionic strength; the relaxation effect turns out to be insignificant for the cell charges and sizes under consideration. In agreement with these findings, the third equation is approximately consistent with experimental data on the condition that GPL is allowed to expand with decreasing ionic strength, with simultaneous decrease of its full charge density (sigma(f)). The results are compared with relevant evidence for erythrocytes. The possible applications of the inferences arrived at in electrophoretic studies of cell behaviour are also discussed.

The Dukhin-Deryaguin equation, used in the modern theory of electrophoresis for the calculation of electrophoretic mobility (EPM) in the region of double layer polarization, is known from literature [4-6] in its form (DD1) valid for the equal mobilities of the cation and anion in solutions of symmetrical electrolytes. Here we describe the other version of this equation (DD2), for arbitrary ion mobilities in 1:1 electrolytes. The EPMs calculated from this latter version are in good agreement with an exact computer solution [12]. The use of DD2 is illustrated in a series of EMP vs. IgC curves, calculated for selected examples of negatively charged lipid membranes. In addition, we describe two simplified versions of DD2, which are valid, respectively, for the high zeta potentials and when the electroosmotic component of ions' fluxes at the charged surface is neglected. Comparing DD2 with DD1 shows that the latter equation results in an error which may exceed the experimental dispersion of EPM values in the absence of specific ion binding. This error is reduced if the counter-ion binding is not small; hence, DD1 may also be used in some cases for solutions with arbitrary ion mobilities.

The Helmholtz-Smoluchowski theory, widely used for the calculation of zeta potential from the measured electrophoretic mobility (EPM), is known to be invalid in the region where the mobility is affected by the surface conductivity and polarization of the electrical double layer. In this region, the zeta potential found according to the Smoluchowski equation (zeta sm) is not identical to the true electrostatic potential at the hydrodynamic plane of shear (zeta), which is considered in the Gouy-Chapman-Stern theory of the electrical double layer. As a result, zeta sm cannot be used for the subsequent calculation of surface potential and surface charge density of a membrane studied. here we suggest a simple way, allowing one to decide between the validity and nonvalidity of the Smoluchowski equation in various sets of experimental conditions used in electrophoretic measurements on lipid membranes. We calculated the dimensionless criterion Rel, accepted in the Dukhin theory of electrophoresis as a measure of the extent of the influence of surface conductivity and double layer polarization on EPM. The Rel changes, with membrane charge density, ionic strength and vesicle radius, were found to be helpful in finding the combinations of these three parameters, corresponding to the validity of the Smoluchowski equation.

Lipid suspensions with a low polydispersity (delta = 0.15 +/- 0.05, as given by photon correlation spectroscopy (PCS)) were used to elucidate the origin of the disagreement between the experimental zeta potential values (zeta sm), obtained from the electrophoretic mobilities through the Smoluchowski equation, and double-layer theory prediction (zeta potential) at low salt concentrations. The values of zeta sm, measured for cardiolipin and phosphatidylserine suspensions in monovalent electrolytes, were compared with the correspondent theoretical values of the zeta potentials correlated for the relaxation effect; the correction was made according to the S.S. Dukhin theory of electrophoresis. It was found, that this correction eliminates the disagreement for cardiolipin in NaCl entirely; it partly solves the problem for cardiolipin in KCl but fails to improve the situation for phosphatidylserine in NaCl.

Electrophoretic mobilities were measured for cardiolipin, phosphatidylinositol and phosphatidylserine liposomes in solutions of potassium chloride. The zeta potential as a function of ionic strength deviates significantly from the predictions of the double-layer theory in the 10(-3)-5.10(-2) M range. This might be due to changes in pH in the course of the experiment and/or to the inapplicability of the Smoluchowski equation at low ionic strengths. Taking into account the relaxation effects results in theoretical curves, calculated for various particle sizes at low ionic strength, which are in better agreement with the experiment. However, for quantitative comparison with experimental data, further investigations are necessary.

Changes of surface potential difference of neutral BLM in the presence of negatively charged liposomes were controlled by means of potentiodynamic method. The liposomes were prepared by sonication of PS-suspension in buffer solution. BLM was formed conventionally from lecithin--decane mixture. Measurements were carried out in buffer solution 2 mM KCL, 5 mM Tris-Cl pH 7.6) at 30 degrees C. It is shown that the liposomes are irreversibly bound to BLM, but do not fuse with it under the conditions investigated.

Potentiodynamic method was used for investigating bilayer lipid membrane (BLM)- liposomes (LS) interaction. BLM was formed from egg lecithin and its mixture with phosphatidylserine (PS); LS-from PS. It is shown that in the presence of calcium in the aqueous phase (1-10 mM) and charged phospholipids in both LS and BLM, fusion of LS with BLM is observed. The fusion event was registered by measuring the increase of negative charge density on BLM surface opposite to that facing the LS.

Synthesis of cardiolipin analogues containing an ionophore residue in the fatty acid moiety is described. The ionophore, dibenzo-18-crown-6, has been incorporated into second position of the glycerol residue by acylating mono- and dilysocardiolipin with a modified fatty acid anhydride. Lyso-derivatives of cardiolipin have been prepared by enzymatic hydrolysis of beef heart cardiolipin by snake venom phospholipase A2 (Naja naja oxiana).