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Regulatory Mechanisms
in Biosystems
Regulatory Mechanisms
in Biosystems
ISSN 2519-8521 (Print) ISSN 2520-2588 (Online) Regul. Mech. Biosyst., 9(3), 469-476 doi: 10.15421/021870
Enzyme-like activity of nanomaterials
S. I. Tsekhmistrenko*, V. S. Bityutskyy*, O. S. Tsekhmistrenko*, V. M. Polishchuk*, S. A. Polishchuk*, N. V. Ponomarenko*, Y. O. Melnychenko*, M. Y. Spivak**
*Bila Tserkva National Agrarian University, Bila Tserkva, Ukraine
**Zabolotny Institute ofMicrobiology and Virology ofNAS of Ukraine, Kyiv, Ukraine
Tsekhmistrenko, S. I., Bityutskyy, V. S., Tsekhmistrenko, O. S., Polishchuk, V. M., Polishchuk, S. A., Ponomarenko, N. V., Melnychenko, Y. O., & Spivak, M. Y. (2018). Enzyme-like activity of nanomaterials. Regulatory Mechanisms in Biosystems, 9(3), 469-476. doi:10.15421/021870
In modern conditions, nanomaterials, especially nanoparticles of metals and nonmetals, are increasingly used in various industries. Due to their unique properties, in particular, the ability of nanoparticles to exhibit an enzyme-like effect they are widely used in biology, medicine, biotechnology, the food industry and agriculture. Important advantages of nanoparticles are their size, which enables specific properties to be present: their large surface area, the ability to transfer molecules and the ability to protect them from degradation and release over a long time, the location of action and the specificity of interaction with biological structures. Nanoparticles play a special role in the processes of neutralizing the active forms of oxygen. It has been established that a number of nanoparticles, in particular, Fe, Mn, Zn, Ce, Si and Se oxides, have an enzyme-like activity mimicking that of some enzymes. By changing the degree of oxidation, these particles can regenerate and continuously catalyze the reaction of neutralizing superoxide anion radicals, thus fulfilling the function of SOD and being the first link in protecting tissues and cells from oxidative stress in physiological and pathological conditions. It is proved that nanoparticles Mn3O4, Fe3O4, Co3O4, CeO2, LaCoO3 and other elements can effectively dispose of hydrogen peroxide and other peroxides, showing catalase-like and peroxidase-like activity. Nanozymes are characterized that exhibit the activity of oxidases, peroxidases and phosphatase. The prospect of using mimetics for complex in vitro analyzes of high-sensitivity biomarker disease detection is shown. The possibility of effective multi-use of nanoparticles as antioxidants is indicated. There are good prospects for further research on properties and the use of polyfunctional particles that are easily synthesized, reliable and inexpensive. More work is needed to determine the interaction of enzymomimetics with biological molecules such as proteins, carbohydrates and lipids, and also to take into account the peculiarities of their metabolism, clearance, degradation, biocompatibility and side effects, since individual nanoparticles have the potential to be deposited in separate organs.
Keywords: mimetics; superoxide dismutase; catalase; oxidase; peroxidase; phosphatase.
Article info
Received 11.06.2018 Received in revised form
07.07.2018 Accepted 08.07.2018
Bila Tserkva National Agrarian University, Soborna ploshcha, 8/1, Bila Tserkva, 09100, Ukraine. Tel.: +38-045-635-12-88.
Zabolotny Institute ofMicrobiology and Virology ofNAS of Ukraine, Akad. Zabolotny st., 154, Kyiv, 03680, Ukraine. Tel.: +38-068-034-48-48. E-mail:
svetlana.tsehmistrenko@gmail.com
Introduction
The 21st century is considered to be the period of global usage of nanotechnology, which deals with a set of theoretically sound and practical methods of research, analysis and synthesis, as well as the production and use of products with a predictable atomic structure through controlled manipulation of individual atoms and molecules (Gordon et al., 2007). Due to the extremely small dimensions (up to 100 nm) and the large surface area per unit volume, nanomaterials have specific chemical, physical and biological properties that are useful for many new applications. Many nanoparticles (NPs) have been found to exhibit enzymatic activity and are potentially capable of being used in various industries, particularly in the food industry, pharmacy, and biotechnology. The creation of artificial enzymes simulating the complexity and functioning of natural systems is one of the greatest achievements of the last two decades.
Use of nanoparticles
Rapid development of nanotechnology around the world has created numerous catalytically active nanomaterials (Cormode et al., 2018). Currently, nanomaterials of different origin are used in biology, medicine and biotechnology (Fig. 1). This category includes nanomaterials
with enzyme-mimetic properties, such as nanoparticles of metals and nonmetals, their oxides, magnetic nanoparticles, liposomes, carbon and polymer nanomaterials. They are characterized as a potential alternative to natural enzymes and are widely used in many industries such as immunoassay, biosensorica, pharmaceutical processes, oncotherapy, the food industry, ecology, etc. (Chen et al., 2012, 2014; Fu, 2014; Lu et al., 2015; Li & Zhang, 2016). This demonstrates the great importance and commercial interest of using nanomaterials as enzyme mimetics. Compared to enzymes of natural origin, agonists or mimetics on the basis of nanomaterials can change catalytic activity, are stable in harsh conditions, their production is relatively easy and economically justified (Cheng et al., 2015). The cyclic action of nanoparticles and the possibility of recovery without significant loss in subsequent cycles of catalytic activity makes them unique compounds (Wei & Wang, 2013). In addition, the surface of nanomaterials, unlike natural enzymes which have only one active site in a molecule, may have more catalytic centers (Liu et al., 2015; Gao et al., 2017). These enzyme mimetics are of great importance in practice (Gordon et al., 2007; Wei & Wang, 2013; Lin et al., 2014; Xu et al., 2014).
The basic requirements for nanoparticles regarding their use in biology and medicine are low toxicity or absence of it, high biocompatibility, biodegradational property and the ability to be removed from the organism naturally (Fu, 2014; Kozik et al., 2016; Bityutskyy et al., 2017; Chekman et al., 2017).
The catalytic activity of nanoparticles and the ability to inactivate active forms of oxygen can be used to simulate the catalytic activity of natural enzymes. Different nanoparticles have been studied to date, and their enzymomimetic activity, in particular superoxide dismutase, oxidase-like, peroxidase-like, catalase- and phosphatase-like, have been determined (He et al., 2014; Cormode et al., 2018).
nanoparticles ofmetal oxides
magnetic nanoparticles
metal nanoparticles (Au, Ag, Cu, Ce. Zn. _Fe etc)
H
Nanomaterials what are used in biology and medicine
\ I Nanoparticles of j I nonmetals (Se, I
JI_h._J
liposomes (single layer, I double layer) J
carbon nanomaterials (fuierenes, carbon nanotubes, nanodiamonds)
polymer nanoparticles (micelles, chitosan, polymerprotein conjugates)
Fig. 1. Nanomaterials used in biology and medicine
General characteristics of mimetics
Agonists or mimetics are compounds that imitate the action of other substances, being similar to the ones formed in the organism (enzymes, hormones, mediators). Cell receptors react to mimetics as a substance which they interact with (Singh, 2016). According to physical and chemical properties, mimetics are similar to natural signaling molecules, but they have a number of important qualities (Fig. 2).
Fig. 2. Properties of mimetic enzymes
They bind to molecular receptors not intended for them, and substitute natural regulatory substances. Mimetics can act more strongly or weakly than the compounds that they replace, that is, their impact varies. They can compete with natural signaling molecules for binding to receptors (by concentration and affinity). The period of functioning of the mimetics in the unchanged state of the organism and the time of binding to the receptors are different from natural compounds. Formation in the body of its own regulatory substances due to the feedback between the concentration of regulators and their production is conditioned by the presence of mimetics (Chekman et al., 2017).
The term "nanozymes" was introduced for nanomaterials with their own enzyme-like activity to distinguish these nanocomplexes from immobilized enzymes (Wei & Wang, 2013). The development of highly effective non-protein analogues of enzymes is an relevant task for modern biology, biotechnology, medicine and agriculture (Dong et al., 2012; Bityutskyy et al., 2017). Currently, several types of artificial enzymes have been created to replace natural analogues (Kozik et al., 2016; Nelson et al., 2016; Wang et al., 2017).
Natural enzymes and mimetics have many properties in common: they accelerate the chemical reactions and can regenerate (Kozik et al., 2016; Chekman et al., 2017). Natural enzymes, unlike the artificial ones,
require special environmental conditions, in particular a certain temperature and pH (Grulke et al., 2014). Such unique properties of nanomaterials can be used for the prevention, diagnosis and treatment of diseases. Many nanomaterials have powerful antioxidant properties that can potentially act as inhibitors of active forms of oxygen. However, it has also been proven that certain nanomaterials have prooxidant properties that contribute to the formation of active forms of oxygen, which can lead to the formation of oxidative stress, which is known to promote the development of various pathologies (Amani et al., 2017; Sims et al.,
2017). One of the important features of nanoenzymes compared to the natural enzymes and other mimetics is that their activity can be regulated by altering the structure, size, surface modification, introduction of protective coverings, etc. (Liu et al., 2015; Kozik et al., 2016; Fa et al.,
2018). A relationship between catalytic activity, therapeutic efficiency and biocompatibility of particular mimetics has been determined (Cor-mode et al., 2018). It was found that the smaller are the particles, the higher is their catalytic activity. This phenomenon is conditioned by the fact that smaller nanoparticles have a larger surface area for interaction with the substrate. This indicates the possibility of synthesizing nano-particles with a particular activity and properties (Gao et al., 2017). The enzyme-mimetic activity of nanomaterials is influenced by several factors, in particular, their chemical composition, surface charge, particle size, and surface covering (Sharpe et al., 2011; Samuel et al., 2014; Ver-ma, 2014; Sandhir et al., 2015; Cîrcu et al., 2016; Shah et al., 2017). However, both the positive and the toxic effects of NPs may be differ-rent, since the synthesis method, the choice of stabilizers which cover the particles, can lead to a different biological effect (Estevez et al., 2017). It is important to understand which physical-chemical properties correlate with biological activity, and are critical for determining the conditions that contribute to the positive effect and for determining the circumstances which lead to formation of toxic properties.
There is a prospect of using nanomaterials for medical and industrial purposes (Armstrong et al., 2013; Sandhir et al., 2015). It is believed that their significant activity provides more effective neutralization of various types of active forms of oxygen (Sandhir et al., 2015). Recently, antioxidant activity was determined for various metallic nanocomposi-tes such as gold (Esumi et al., 2003; BarathManiKanth et al., 2010), platinum (Kajita et al., 2007; Kim et al., 2008; Moglianetti et al., 2016), iron (Paul et al., 2009; Szekeres et al., 2014; Toth et al., 2014; Shah et al., 2017), nickel (Saikia et al., 2010), cerium (Kim et al., 2012) and yttrium (Schubert et al., 2006). Nanoparticles (NPs) of metal oxides are intensively studied (Kozik et al., 2016; Tsekhmistrenko et al., 2018). They are successfully used in the treatment of a number of pathologies, have high colloidal resistance and biocompatibility (Grillone et al., 2017).
Nanoparticles with their antioxidant activity conditioned by the ability to exhibit enzyme-mimetic action, can be promising therapeutic agents that can be used for targeted drug delivery (Morry et al., 2017). However, with nanoparticles, one should take into account such issues as metabolism, clearance, degradation, biocompatibility and side effects, since individual nanoparticles have the potential for prolonged maintenance in the organs, in particular, the liver and spleen (Cormode et al., 2018). The interaction of nanoparticles with the local environment plays an important role in their distribution and long-teim stability (Dhall et al., 2017).
Nanomaterials as SOD mimetics
Superoxide dismutase is an enzyme that functions for the catalytic conversion of a superoxide radical to oxygen and hydrogen peroxide. The catalytically active metal of this enzyme can be Cu, Fe, Mn.
A superoxide radical which is formed predominantly in mitochondria and, when protons are added is capable of being converted into hydroperoxide (Fig. 3), is one of the most destructive forms of oxygen (Lushchak, 2015; Wang et al., 2017). It is known that SOD inactivates superoxide anion in two stages with formation of hydrogen peroxide and oxygen (Shin et al., 2009). In this case, the general reaction of superoxide anion dismutation for nanoparticles also includes two stages (Korsvik et al., 2007).
SOD-like activity is typical for various metal oxide nanoparticles, in particular nano-TiO2 (Zheng et al., 2017), ZnO (Li et al., 2018),
Fe3O4 (Khedri et al., 2018), NiO-NPs (Faisal et al., 2013), Mn3O4 (Yao et al., 2018), LaCoO3 (Wang et al., 2017), CeNPs (BatiniC-Haberle et al., 2010; Heckert et al., 2008), Pt (Wei & Wang, 2013), Au (Lin et al., 2014) and nonmetals: SiO2 (Farhangi-Abriz et al., 2018; Soares et al., 2018) and Se (Guo et al. 2016). These mimetics provide considerable interest, as they are characterized by increased stability, multifunction-nality and regulated activity.
Fig. 3. Enzyme-like properties of nanomaterials: TMB (3,3,5,5-tetramethylbenzidine), DOPA (dihydroxyphenylalanine) (adopted from Singh, 2017)
One of the first superoxide dismutase activities determined was for cerium dioxide nanoparticles (Korsvik et al., 2007; Singh, 2016). In the case of superoxide anion dismutration, the formation of hydrogen peroxide and transitional compound - cerium hydroperoxide Се(ООН)(ОН)3 on the surface of the nanodispersed cerium dioxide occurs, ie, three reactions actually occur (Batinic-Haberle et al., 2010): Oxidation of О2- - e ^ О2; Restoration of О2-+e + 2Н+ ^ Н2О2; Oxidation-reduction Се3+ + 4Н2О^ Се(ОН)4+4Н++ e.
The treatment of cerium nanoparticles with Н2О2 causes a complete loss of SOD-like activity, but after a certain period of time, the activity is restored, which confirms the process of spontaneous regeneration of the nanoparticle surface (in relation to oxygen non-stoichiometry) and recovery to trivalent cerium (Gil et al., 2017; Baldim et al., 2018). The activity of nanoparticles depends on their size. NPs, the size of which is 3-5 nm, more intensively inactivate superoxide anion than larger nano-particles (5-8 nm). The effectiveness of nanocerium to act as a SOD mimetic is proportional to the concentration of Ce3+ ions on the surface of particles (Nelson et al., 2016). The presence of other ions, in particular titanium ions, inhibits this activity (Zhu et al., 2012). SOD-like activity of nanoparticles depends on the ionic composition of the solution (McCormack et al., 2014). During the action of phosphate ions, phosphorylation of the surface of particles occurs, which reduces their ability to manifest the functions of SOD and catalase.
Nanomaterials as catalase mimetics
Along with superoxide radionuclide, hydrogen peroxide is also an active form of oxygen that is neutralized due to catalase. It was determined that a number of nanoparticles effectively protect the cells and tissues from the toxic effects of Н2О2 (Grinko et al., 2015; Wang et al., 2017) and other peroxides (Sun et al., 2017).
Nanoparticles of Mn3O4 (Yao et al., 2018), Fe3O4, Co3O4 and CeO2 (Wei & Wang, 2013), LaCoO3 (Wang et al., 2017), NiO-NPs (Faisal et al., 2013), Au (Lin et al., 2014) simulate the activity of catalase. In conditions of physiological reactions, including the substrate, the optimal values of pH and temperature, some nanoparticles, particularly of ferrum oxide, demonstrate catalase- and peroxidase-like activity (Gao et al., 2017). The Fe2O3 and Fe3O4 nanoparticles decompose Н2О2 in a neutral and alkaline medium, but it was found that Fe3O4 was characterized by higher catalase mimetic activity. Similarly to peroxidase-like activity, the pH range is essential in the effectiveness of this reaction (Chen et al., 2012; Gao et al., 2017). Singh et al. (2017) reported that the ability of
graphenes to simulate the catalase function at pH > 7.2. The mechanism of mimetic action of nanoparticles is complex and remains incompletely studied. Grinko et al. (2015) mention that the process of decomposition of Н2О2 by nanoparticles is similar to the mechanism of catalase activity. The intensity of the catalase-mimetic activity of nanoparticles of transition metals, in particular cerium, is conditioned by the number of ions of trivalent Ce on their surface (Das et al., 2013; Nelson et al., 2016; Yang et al., 2016). The reactivity of hydrogen peroxide is affected by the size of nanoparticles and surface ligands (Lee et al., 2013; Gil et al., 2017). Small СеО2 nanoparticles, and those containing more oxide, exhibit increased reactivity to Н2О2. Reaction of the decomposition is not hindered by the surface ligand. Concentrations of Ce3+ ions on the surface of СеО2 nanoparticles have a proportional effect on their catalase-like activity (Nelson et al., 2016).
The possibility of effective use and reuse of СеО2 nanoparticles as an antioxidant has been proved. Such effect occurs due to the fact that at first the Се3+ ions located on the surface of nanoparticles, are oxidized with hydrogen peroxide, forming Се41.
At the same time, Н2О2 is irreversibly adsorbed on the surface of hydrated Се4+ ions, forming cerium perhydroxide. Perhydroxide is decomposed with the formation of oxygen. After using all of the hydrogen peroxide in the system, part of the quaternary cerium ions due to the restoration (recovery) of the crystalline lattice of the nanoparticle returns to the initial Се31 state (Celardo et al., 2011; Grinko et al., 2015; Kozik et al., 2016). These processes are possible due to the occurrence of oxygen vacancies which contribute to the formation of oxygen non-stoichiometry and increase in the number of cerium atoms with the Ш degree of oxidation. The set of processes which occurs on the surface of cerium nanoparticles can be represented in the form of a scheme: NP-Ce31 + H2O2 ^ NP-Ce4+=0 + H2O, NP-Ce4+=0 + H2O2^ NP-Ce3+ + H2O + O2. Ions of various metals can modify the catalase-like activity of nanoparticles (Tsai et al., 2007). Therefore, in the case of doping into a crystalline lattice of cerium dioxide of zirconium ions, there was observed the activation of the decomposition of hydrogen peroxide, which was directly proportional to the molar Zr/Ce ratio. Celardo et al. (2011) mentioned the opposite effect after introducing Samarium ions into the crystalline lattice of CeNPs. The authors observed a monotonic decrease in the speed of decomposition of hydrogen peroxide, which depended on the content of Samaria.
It was determined that nanopolyhedrons with a high concentration of Ce4+ ions contributed to the mimetic activity of catalase, while nano-tubes and nanopowders with high concentration of Ce3+ ions increased the mimetic activity of SOD (Naganuma, 2017). These results should be used to construct nanoparticles aimed at enhancing enzyme mimetic activity for therapeutic purposes. It was determined that biomimetic artificial enzymes based on antioxidant CeO2 nanoparticles become luminescent during their Eu3+ doping (Pratsinis et al., 2017).
Nanomaterials as oxidase mimetics
Over the recent decades, the enzyme-like properties of nanomaterials have been widely studied, but for the most part, attention has been paid to SOD-like, peroxidase- and catalase-like activity of these nanomaterials. Now, research is becoming focused on nanomaterials with oxidase-like properties.
Oxidases are enzymes from the oxidoreductase class, which catalyze the oxidation-recovery reaction, which includes molecular oxygen as an acceptor of electrons. In the course of reactions which are catalyzed by oxidase, the substrate oxidizes by molecular oxygen, forming water, hydrogen peroxide or free oxygen radicals (Singh, 2016). These enzymes catalyze a number of reactions:
Glucose + O2 ^ Gluconic acid+H2O2 (Glucose oxidase) Galactose + O2 ^ 1,6-Diadehyde + H2O2 (Galactose oxidase)
Alcohol+O2 ^ Aldehyde + H2O2 (Alcohol oxidase) Cholesterol+O2 ^ Cholesteon+H2O2 (Cholesterol oxidase)
Choline ^ Betaine + H2O2 (Choline oxidase) Recently, research has increasingly focussed on the oxidase-mimetic activity of nanoparticles. The studies by Cao et al. (2017) revealed that
ruthenium nanoparticles (Ru) exhibit their own oxidase activity, catalyzing the oxidation of tetramethylbenzidine (TMB) and sodium L-ascor-bate with dissolved oxygen. Similar activity was demonstrated by Pt nanoparticles (Deng et al., 2017), Au (He et al., 2011), Ir (Cui et al., 2017), CoFe2O4 (Zhang et al., 2013), ZnFe2O4 (Su et al., 2012), MnO2 (Yan et al., 2017), CeO2 (Dalapati, 2017; Estevez et al., 2017), NiCo2O4 (Song et al., 2018), Se (Guo et al., 2016) and other metals and composites. It was determined that the maximum mimetic activity depends on particular physical parameters. Thus, the nanoparticles of Se exhibited optimal catalytic activity at pH 4 and 30 °C, and the oxidase-like activity was higher as the concentrations increased and the size reduced (Guo et al., 2016). The maximum activity ofiridium nanoparticles (IrNP) which were synthesized using sodium citrate and NaBHi, occured at their average diameter of 2.5 nm (Cui et al., 2017). Chen et al. (2017) reported the first attempt of using graphene nanoparticles (GQD/AgNP hybrids). These NPs demonstrate high oxidase activity and remained stable in neutral media at temperature of up to 60 °C. The doping of CeO2 nanoparticles by titanium caused no reduction in their oxidase mimetic activity, but was accompanied by a change in the shape of the spherical nanostructure (Zhu et al., 2012).
Nanomaterials as peroxidase mimetics
Peroxidase is an enzyme that catalyzes the oxidation of polyphenols and some aromatic amines with oxygen, hydrogen peroxide or organic peroxides. Peroxidase forms a complex compound with hydrogen peroxide, resulting in peroxide being activated and becoming able to act as an acceptor of hydrogen (Pandey et al., 2017).
2RH+H2O2 ^ 2R+2H2O.
Peroxidases, as a cofactor in active centers, contain gem, or redox-active cysteine or selenium (van Bloois et al., 2010). There are several types of peroxidases, such as glutathione peroxidase, myeloperoxidase, haloperoxidase, lactoperoxidase, etc. (Pandey et al., 2017).
Since 2007, when the enzyme-like peroxidase activity of Fe3O4 nanoparticles was first recorded, over 40 nanomaterials have been identified (Jiang et al., 2018). It was determined that nanomaterials are characterized by peroxidase activity, including high stability and low cost of synthesis (He et al., 2014; Singh, 2016).
Peroxidation activity is characteristic for Co3O4 nanoparticles (Jia et al., 2016), Cu2O (Chen et al., 2012; Guo et al., 2017), FeS (Dutta et al., 2012), CeO2 (Sun et al., 2017), Au/CeO2 (Bhagat et al., 2018), CoFe2O4 (Fan & Huang, 2012), BiFeO3 (Luo et al., 2010), MnFe2O4 (Vernekar, et al., 2016), CdS (Garai-Ibabe et al., 2014), FeSe (Dutta et al., 2012), FeTe (Jiang et al., 2013), rhodium (Choleva et al., 2018), ZnFe2O4 (Zhao et al., 2013), graphene oxide (Vineh et al., 2017), fullerene (Voei-kov & Yablonskaya, 2015) and carbon nanotubes (Wang et al., 2014). This allows them to be applied for immunoassay, glucose detection, protection against free radicals, etc. Significant enzymic activity of such nanoparticles (in the presence of the nucleus and the shell) is maintained at extreme values of pH (2-11) and high temperature (up to 90 °C), which indicates their superiority over natural enzymes.
Antioxidants based on selenium and tellurium can act as mimetics of glutathione peroxidase, can reduce oxidative stress during inflammatory processes and other pathological conditions (Huang et al., 2014; Lu et al., 2017; Hosnedlova et al., 2018). Nano-Se has a better antioxidant effect than other chemical forms of selenium, at the same time reducing the risk of its toxicity (Wang et al., 2007). The antioxidant properties of SeNPs nanoparticles are more effective compared to other selenium compounds and less toxic than selenomethionine (SeMet).
The internal triple enzyme-mimetic activity of nickel-palladium nanoparticles (NiPd HNPs) (Wang et al., 2016), LaCoO3 was also studied (Wang et al., 2017) and V6O13 (Li et al., 2018). The multimimetic particles of NiPd and V6O13 exhibit oxidase-like, peroxidase-like and cata-lase-like activity, are reliable, inexpensive and easily synthesized. On the basis of oxidase-like and peroxidase-like activity, a colorimetric biosensor was developed to detect glutathione and a fluorescence system for the detection of Н2О2 and glucose. Recently, there was discovered the "hidden talent" of gold to exhibit mimetic activity (Lin et al., 2014). Gold nanoparticles, similarly to the multimimetics, were observed simu-
lating peroxidase, nucleases, esterases, glucose oxidases, catalase and superoxide dismutase. The authors mention that these enzyme-like characteristics are conditioned by nanogold itself or functional groups present in the surrounding monolayer.
Zhao et al. (2018) for the first time reported the construction of mesoporous nanostructures based on Co3O4 for the dispersion of cata-lytically active sites for the purpose of doping iron nanoparticles (FeNP). Composites (FeNP @ Co3O4 HNCs) have high peroxidase activity, which is significantly higher compared to iron nanoparticles (F eNP) and Co3O4. The high catalytic activity of FeNP @ Co3O4 nanoparticles occurs due to its porous-hollow structure, which is convenient for dispersion of formed nanoparticles and to reduction of agglomeration.
Nanoparticles Au, MnO2, Fe3O4, CuO, Co3O4 NP and CeO2 caused increased glutathione peroxidase activity (Wei & Wang, 2013). Liu et al. (2012) have shown that stabilized nanoparticles of MnO2 imitate the activity of peroxidase, therefore they were started to be used in immunoassay for colorimetric measurements. New nanoparticles of Co9S8 type with effective intrinsic peroxidase activity can be used for colori-metric ionisation of copper ions (Mu et al., 2018).
Ions of transition metals, such as Fe, have peroxidase activity and can inactivate hydroxyl radicals using a general mechanism similar to Fenton's reaction (Singh, 2016; Gao et al., 2017). Khedri et al. (2018) mention that the peroxidase activity of chitosan coated Fe3O4NPs nano-particles. Similarly to natural enzymes, the enzyme-mimetic activity of nanoparticles may be stimulated or inhibited by certain chemical compounds. Thus, nucleotides, in particular, AMP, can enhance the peroxi-dase activity of Fe3O4 nanoparticles at neutral pH by forming a complex (Yang et al., 2017). Inhibitors of this mimetic activity can be sodium azide, ascorbic acid and catecholamines (Liu et al., 2012). Liao et al. (2018) report that sulfide ions are capable of inhibiting peroxidase-like activity of copper nanoclusters (CuNCs).
It was determined that TiO2 nanoparticles demonstrated mimetic activity, can be incorporated into a photosensitive biocatalytic cascade, activate alkaline phosphatase, and subsequently peroxidase (Li et al., 2018). Brominated graphene (GBR) containing about 3% bromine had a mimetic peroxidase activity in relation to 3,3', 5,5'-tetramethylben-zidine (TMB). The optimum activity was observed at pH 4.48 (Singh et al., 2016).
Nanomaterials as phosphate mimetics
Phosphatase catalyzes the hydrolysis of complex esters of phosphoric acid in living organisms. The function of phosphatase is maintaining the phosphate level required for various biochemical processes. Phos-phatase is involved in biological processes such as cell proliferation, transduction of signals, metabolism, intercellular communication, etc. For the first time, phosphatase-like activity was studied in cerium nano-particles (Kuchma et al., 2010). Nanoparticles of SeO2 exhibit phospha-tasomimetic activity in relation to the hydrolysis of organic phosphate esters, and the dependence between of the reaction speed on the pH of the medium was determined (Singh, 2016). It is assumed that in the case of this reaction, splitting of phosphate and its adsorption on the surface of nanoparticles occur. According to Kozik et al. (2016), cerium dioxide nanoparticles are not complete phosphatase analogues, since the phosphate group binds to the surface of the nanoparticle irreversibly. Subsequently, cerium phosphate is desorbed, and the surface of nano-particles is able to be involved in catalytic reactions again. Nanodisper-sive cerium dioxide is used for concentration and quantitative dephos-phorylation of phosphoproteins (Jia et al., 2012). It also can stimulate phosphorylation of mitogen-active protein kinase in human bronchial epithelial cells (Beas2B), manifesting pro-oxidant properties (Park et al., 2008).
The activation of the nuclear transcription factor NF-kB depends on phosphorylation of the protein-inhibitor of iKBa-kinases (IKK) (Popov et al., 2017). NF-kB functions as one of the most important intracellular messengers which combines a variety of environmental signals with the expression of numerous cellular genes. NF-kB regulates a variety of biological processes: cell growth, their survival, tissue development, immune response and inflammatory processes. Disorders in regulation of
signaling mechanisms which are based on NF-kB aie associated with such severe human diseases as cancer, autoimmune diseases, chronic inflammation, metabolic disorders, diabetes and neurodegenerative diseases (Ghosh, 2007; Pushkarev et al., 2015).
The ability to purposefully regulate the activity of the factor NF-kB is promising for controlling and treating a large number of pathological processes in the cell. Research has shown that cerium dioxide nanoparticles inhibit phosphorylation of 1кВа, thereby reducing the translocation of the p65 subunit, which occurs due to activation of NF-kB (Popov et al., 2017).
Nanopartides with low ratios of the Се3+/Се4+ oxidation state demonstrate both mimetic activity of catalase and phosphatase (Dhall et al., 2017). The ability to manifest the activity of acid phosphatase was observed for Pt nanoparticles (Deng et al., 2017), and the activity of alkaline phosphatase simulates fullerene nanoparticles (Voeikov & Yablonska-ya, 2015). Reverse phosphorylation and dephosphorylation reactions are the basis of energy and signaling metabolism in the cells, and such molecular activity opens a new perspective in the evaluation and prediction of biological properties of nanoparticles (Celardo et al., 2011).
Conclusions
This paper demonstrates separate results on the study of the enzymatic activity of nanoparticles and their positive effects. However, there are a number of studies on the risks of their use (Bandas et al., 2015; Fu, 2014). As a result of the conducted analysis, we can state that nanoparticles have a large number of applications in various fields - biology, medicine, the food industry, etc. However, the development of new nanosy stems raises a number of new questions. It has been found that nanoparticles are highly biologically active, which is determined by the polyfactor action, which needs to be determined. The interaction between nanoparticles and biological molecules, such as proteins, carbohydrates, and lipids, remain poorly studied. Practical application of nano-particles in biology requires an integrated analysis of the duration of their stay in the organism and the need for targeted delivery to organs and tissues, which accelerates further spread (Grillone et al., 2017). Due to their mimetic properties, it is promising to use nanoparticles for the purpose of early diagnosis of dangerous diseases, development of fundamentally new methods and molecular instruments in therapy and surgery, as well as solving other biological and biotechnological problems. In future, research on this topic requires a safe, responsible and integrated approach with scientific research and assessments of possible medical-sanitary and environmental risks, which is the basis of the European Union policy in the field of nanotechnology (Regulation, 2012).
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