Metal Oxide Nanoparticles: Review of Synthesis, Characterization and Biological Effects

In the last few years, the progress made in the field of nanotechnology has allowed researchers to develop and synthesize nanosized materials with unique physicochemical characteristics, suitable for various biomedical applications. Amongst these nanomaterials, metal oxide nanoparticles (MONPs) have gained increasing interest due to their excellent properties, which to a great extent differ from their bulk counterpart. However, despite such positive advantages, a substantial body of literature reports on their cytotoxic effects, which are directly correlated to the nanoparticles' physicochemical properties, therefore, better control over the synthetic parameters will not only lead to favorable surface characteristics but may also increase biocompatibility and consequently lower cytotoxicity. Taking into consideration the enormous biomedical potential of MONPs, the present review will discuss the most recent developments in this field referring mainly to synthesis methods, physical and chemical characterization and biological effects, including the pro-regenerative and antitumor potentials as well as antibacterial activity. Moreover, the last section of the review will tackle the pressing issue of the toxic effects of MONPs on various tissues/organs and cell lines.

Enzyme Nanoscale Interactions with Manganese Zinc Sulfide Give Insight into Potential Antiviral Mechanisms and SARS-CoV-2 Inhibition

Recent interest in nanomedicine has skyrocketed because of mRNA vaccine lipid nanoparticles (LNPs) against COVID-19. Ironically, despite this success, the innovative nexus between nanotechnology and biochemistry, and the impact of nanoparticles on enzyme biochemical activity is poorly understood. The studies of this group on zinc nanoparticle (ZNP) compositions suggest that nanorod morphologies are preferred and that ZNP doped with manganese or iron can increase activity against model enzymes such as luciferase, DNA polymerase, and β-galactosidase (β-Gal), with the latter previously being associated with antimicrobial activity. SARS-CoV-2 encodes several of these types of oxido-reductase, polymerase, or hydrolase types of enzymes, and while metamaterials or nanoparticle composites have become important in many fields, their application against SARS-CoV-2 has only recently been considered. Recently, this group discovered the antiviral activity of manganese-doped zinc sulfide (MnZnS), and here the interactions of this nanoparticle composite with β-Gal, angiotensin converting enzyme (ACE), and human ACE2 (hACE2), the SARS-CoV-2 receptor, are demonstrated. Low UV, circular dichroism, and zeta potential results confirm their enzyme interaction and inhibition by fluorometric area under the curve (AUC) measurements. The IC₅₀ of enzyme activity varied depending on the manganese percentage and surface ranging from 20 to 50 μg/mL. MnZnS NPs give a 1–2 log order inhibition of SARS-CoV-2; however, surface-capping with cysteine does not improve activity. These data suggest that Mn substituted ZNP interactions to hACE2 and potentially other enzymes may underlie its antiviral activity, opening up a new area of pharmacology ready for preclinical translation.

Inspirations of Cobalt Oxide Nanoparticle Based Anticancer Therapeutics

Cobalt is essential to the metabolism of all animals due to its key role in cobalamin, also known as vitamin B12, the primary biological reservoir of cobalt as an ultra-trace element. Current cancer treatment strategies, including chemotherapy and radiotherapy, have been seriously restricted by their side effects and low efficiency for a long time, which urges us to develop new technologies for more effective and much safer anticancer therapies. Novel nanotechnologies, based on different kinds of functional nanomaterials, have been proved to act as effective and promising strategies for anticancer treatment. Based on the important biological roles of cobalt, cobalt oxide nanoparticles (NPs) have been widely developed for their attractive biomedical applications, especially their potential for anticancer treatments due to their selective inhibition of cancer cells. Thus, more and more attention has been attracted to the preparation, characterization and anticancer investigation of cobalt oxide nanoparticles in recent years, which is expected to introduce novel anticancer treatment strategies. In this review, we summarize the synthesis methods of cobalt oxide nanoparticles to discuss the advantages and restrictions for their preparation. Moreover, we emphatically discuss the anticancer functions of cobalt oxide nanoparticles as well as their underlying mechanisms to promote the development of cobalt oxide nanoparticles for anticancer treatments, which might finally benefit the current anticancer therapeutics based on functional cobalt oxide nanoparticles.

Extraction of Chlorobenzenes and PCBs from Water by ZnO Nanoparticles

Metal oxide nanoparticles have great potential for selective adsorption and catalytic degradation of contaminants from aqueous solutions. In this study, we employ mass spectrometry and molecular dynamics simulations to better understand the chemical and physical mechanisms determining the affinity of chlorobenzenes and polychlorinated biphenyls (PCBs) for zinc oxide nanoparticles (ZnO NPs). The experiments and simulations both demonstrate that the adsorption coefficients for chlorobenzenes increase steadily with the number of chlorine atoms, while, for PCBs, the relation is more complex. The simulations link this complexity to chlorine atoms at ortho positions hindering coplanar conformations. For a given number of chlorine atoms, the simulations predict decreasing adsorption affinity with increasing numbers of ortho substitutions. Consequently, the simulations predict that some of the highest adsorption affinities for ZnO NPs are exhibited by dioxin-like PCBs, suggesting the possibility of selective sequestration of these most acutely toxic PCBs. Remarkably, the experiments show that the PCB adsorption coefficients of ZnO NPs with diameters ≤ 80 nm exceed those of a soil sample by 5–7 orders of magnitude, meaning that a single gram of ZnO NPs could sequester low levels of PCB contamination from as much as a ton of soil.

Zn-based physiometacomposite nanoparticles: distribution, tolerance, imaging, and antiviral and anticancer activity

The aim of this study was to investigate the distribution, tolerance, and anticancer and antiviral activity of Zn-based physiometacomposites (PMCs). Manganese, iron, nickel and cobalt-doped ZnO, ZnS or ZnSe were synthesized. Cell uptake, distribution into 3D culture and mice, and biochemical and chemotherapeutic activity were studied by fluorescence/bioluminescence, confocal microscopy, flow cytometry, viability, antitumor and virus titer assays. Luminescence and inductively coupled plasma mass spectrometry analysis showed that nanoparticle distribution was liver >spleen >kidney >lung >brain, without tissue or blood pathology. Photophysical characterization as ex vivo tissue probes and LL37 peptide, antisense oligomer or aptamer delivery targeting RAS/Ras binding domain (RBD) was investigated. Treatment at 25 μg/ml for 48 h showed ≥98-99% cell viability, 3D organoid uptake, 3-log inhibition of β-Galactosidase and porcine reproductive respiratory virus infection. Data support the preclinical development of PMCs for imaging and delivery targeting cancer and infectious disease.

Interaction of Ras Binding Domain (RBD) by chemotherapeutic zinc oxide nanoparticles: Progress towards RAS pathway protein interference

Zinc oxide (ZnO) NP is considered as a nanoscale chemotherapeutic. Thus, the drug delivery of this inorganic NP is of considerable importance. Ras mutations are common in cancer and the activation of this signaling pathway is a hallmark in carcinoma, melanoma and many other aggressive malignancies. Thus, here we examined the binding and delivery of Ras binding domain (RBD), a model cancer-relevant protein and effector of Ras by ZnO NP. Shifts in zeta potential in water, PBS, DMEM and DMEM supplemented with FBS supported NP interaction to RBD. Fluorescence quenching of the NP was concentration-dependent for RBD, Stern-Volmer analysis of this data was used to estimate binding strength which was significant for ZnO-RBD (Kd < 10-5). ZnO NP interaction to RBD was further confirmed by pull-down assay demonstrated by SDS-PAGE analysis. The ability of ZnO NP to inhibit 3-D tumor spheroid was demonstrated in HeLa cell spheroids-the ZnO NP breaking apart these structures revealing a significant (>50%) zone of killing as shown by light and fluorescence microscopy after intra-vital staining. ZnO 100 nm was superior to ZnO 14 nm in terms of anticancer activity. When bound to ZnO NP, the anticancer activity of RBD was enhanced. These data indicate the potential diagnostic application or therapeutic activity of RBD-NP complexes in vivo which demands further investigation.

Translating Nanomedicine to Comparative Oncology-the Case for Combining Zinc Oxide Nanomaterials with Nucleic Acid Therapeutic and Protein Delivery for Treating Metastatic Cancer

The unique anticancer, biochemical, and immunologic properties of nanomaterials are becoming a new tool in biomedical research. Their translation into the clinic promises a new wave of targeted therapies. One nanomaterial of particular interest are zinc oxide (ZnO) nanoparticles (NPs), which has distinct mechanisms of anticancer activity including unique surface, induction of reactive oxygen species, lipid oxidation, pH, and also ionic gradients within cancer cells and the tumor microenvironment. It is recognized that ZnO NPs can serve as a direct enzyme inhibitor. Significantly, ZnO NPs inhibit extracellular signal-regulated kinase (ERK) and protein kinase B (AKT) associated with melanoma progression, drug resistance, and metastasis. Indeed, direct intratumoral injection of ZnO NPs or a complex of ZnO with RNA significantly suppresses ERK and AKT phosphorylation. These data suggest ZnO NPs and their complexes or conjugates with nucleic acid therapeutic or anticancer protein may represent a potential new strategy for the treatment of metastatic melanoma, and potentially other cancers. This review focuses on the anticancer mechanisms of ZnO NPs and what is currently known about its biochemical effects on melanoma, biologic activity, and pharmacokinetics in rodents and its potential for translation into large animal, spontaneously developing models of melanoma and other cancers, which represent models of comparative oncology.

Comparative functional dynamics studies on the enzyme nano-bio interface

Introduction

Biomedical applications of nanoparticles (NPs) as enzyme inhibitors have recently come to light. Oxides of metals native to the physiological environment (eg, Fe, Zn, Mg, etc.) are of particular interest-especially the functional consequences of their enzyme interaction.

Materials and methods

Here, Fe₂O₃, zinc oxide (ZnO), magnesium oxide (MgO) and nickel oxide (NiO) NPs are compared to copper (Cu) and boron carbide (B₄C) NPs. The functional impact of NP interaction to the model enzyme luciferase is determined by 2-dimensional fluorescence difference spectroscopy (2-D FDS) and 2-dimensional photoluminescence difference spectroscopy (2-D PLDS). By 2-D FDS analysis, the change in maximal intensity and in 2-D FDS area under the curve (AUC) is in the order Cu~B₄C>ZnO>NiO>>Fe₂O₃>MgO. The induced changes in protein conformation are confirmed by tryptic digests and gel electrophoresis.

Results

Analysis of possible trypsin cleavage sites suggest that cleavage mostly occurs in the range of residues 112-155 and 372-439, giving a major 45 kDa band. By 2-D PLDS, it is found that B₄C NPs completely ablate bioluminescence, while Cu and Fe₂O₃ NPs yield a unique bimodal negative decay rate, -7.67×10³ and -3.50×10¹ relative light units respectively. Cu NPs, in particular, give a remarkable 271% change in enzyme activity. Molecular dynamics simulations in water predicted that the surfaces of metal oxide NPs become capped with metal hydroxide groups under physiological conditions, while the surface of B₄C becomes populated with boronic acid or borinic acid groups. These predictions are supported by the experimentally determined zeta potential. Thin layer chromatography patterns further support this conception of the NP surfaces, where stabilizing interactions were in the order ionic>polar>non-polar for the series tested.

Conclusion

Overall the results suggest that B₄C and Cu NP functional dynamics on enzyme biochemistry are unique and should be examined further for potential ramifications on other model, physiological or disease-relevant enzymes.

ZnO Nanoparticles Protect RNA from Degradation Better than DNA

Gene therapy and RNA delivery require a nanoparticle (NP) to stabilize these nucleic acids when administered in vivo. The presence of degradative hydrolytic enzymes within these environments limits the nucleic acids’ pharmacologic activity. This study compared the effects of nanoscale ZnO and MgO in the protection afforded to DNA and RNA from degradation by DNase, serum or tumor homogenate. For double-stranded plasmid DNA degradation by DNase, our results suggest that the presence of MgO NP can protect DNA from DNase digestion at an elevated temperature (65 °C), a biochemical activity not present in ZnO NP-containing samples at any temperature. In this case, intact DNA was remarkably present for MgO NP after ethidium bromide staining and agarose gel electrophoresis where these same stained DNA bands were notably absent for ZnO NP. Anticancer RNA, polyinosinic-polycytidylic acid (poly I:C) is now considered an anti-metastatic RNA targeting agent and as such there is great interest in its delivery by NP. For it to function, the NP must protect it from degradation in serum and the tumor environment. Surprisingly, ZnO NP protected the RNA from degradation in either serum-containing media or melanoma tumor homogenate after gel electrophoretic analysis, whereas the band was much more diminished in the presence of MgO. For both MgO and ZnO NP, buffer-dependent rescue from degradation occurred. These data suggest a fundamental difference in the ability of MgO and ZnO NP to stabilize nucleic acids with implications for DNA and RNA delivery and therapy.

Determinants of Alanine Dipeptide Conformational Equilibria on Graphene and Hydroxylated Derivatives

Understanding the interaction of carbon nanomaterials with proteins is essential for determining the potential effects of these materials on health and in the design of biotechnology based on them. Here we leverage explicit-solvent molecular simulation and multidimensional free-energy calculations to investigate how adsorption to carbon nanomaterial surfaces affects the conformational equilibrium of alanine dipeptide, a widely used model of protein backbone structure. We find that the two most favorable structures of alanine dipeptide on graphene (or large carbon nanotubes) correspond to the two amide linkages lying in the same plane, flat against the surface, rather than the nonplanar α-helix-like and β-sheet-like conformations that predominate in aqueous solution. On graphenic surfaces, the latter conformations are metastable and most often correspond to amide-π stacking of the N-terminal amide. The calculations highlight the key role of amide-π interactions in determining the conformational equilibrium. Lesser but significant contributions from hydrogen bonding to the high density interfacial water layer or to the hydroxy groups of hydroxylated graphene also define the most favorable conformations. This work should yield insight on the influence of carbon nanotubes, graphene, and their functionalized derivatives on protein structure.