Synthesis and biomedical applications of Cerium oxide nanoparticles - A Review

Combined Raman and AFM detection of changes in HeLa cervical cancer cells induced by CeO2 nanoparticles – molecular and morphological perspectives

Raman and AFM analyses represent a tool for the evaluation of cytotoxic and anti-proliferative effects in cells induced by CeO₂ nanoparticles.

The Aquilegia pubiflora (Himalayan columbine) mediated synthesis of nanoceria for diverse biomedical applications

Herein, we report an eco-friendly, facile, one-pot, green synthesis of nanoceria for multiple biomedical applications. In the study, cerium oxide nanoparticles (CeO₂-NPs) were synthesized using a simple aqueous extract of Aquilegia pubiflora as an effective reducing and capping agent. The biosynthesized nanoparticles were characterized via UV-vis spectroscopy, X-ray powder diffraction (XRD), high-performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The NPs were highly stable, exhibited high purity, and had a spherical morphology and mean size of 28 nm. FTIR and HPLC studies confirmed the successful capping of bioactive compounds on the nanoparticles. The well-characterized NPs were evaluated for a number of biomedical applications, and their antimicrobial (antifungal, antibacterial, and antileishmanial), protein kinase inhibition, anticancer, antioxidant, anti-diabetic and biocompatibility properties were studied. Our results showed that the Aquilegia pubiflora mediated CeO₂-NPs were highly active against fungal strains, compared to the tested bacterial strains, with Aspergillus niger resulting in the largest zone of inhibition (15.1 ± 0.27 mm). The particles also exhibited dose dependent leishmanicidal activity with significant LC₅₀ values toward both the amastigote (114 μg mL⁻¹) and promastigote (97 μg mL⁻¹) forms of the parasite Leishmania tropica (KWH23). The NPs were found to be moderately active against the HepG2 cell line, showing 26.78% ± 1.16% inhibition at 200 μg mL⁻¹. Last but not least, their highly biocompatible nature was observed with respect to freshly isolated human red blood cells (hRBCs), making the greenly synthesized CeO₂-NPs a novel candidates for multidimensional medical applications.

Graphical illustration of eco-friendly, facile, one-pot, green synthesis of nanoceria for multiple biomedical applications.

Ophthalmic Applications of Cerium Oxide Nanoparticles

Cerium oxide nanoparticles (CeO₂-NPs; or nanoceria) have been largely studied for biomedical applications due to their peculiar auto-regenerative antioxidant activity. This review focuses on ophthalmic applications of nanoceria. Many in vivo data indicate that nanoceria protect the retina from neurodegeneration. In particular, they have been tested in animal models of age-related macular degeneration and retinitis pigmentosa and their neuroprotective properties have been shown to persist for a long time, without any collateral effects. In vitro cytotoxicity studies have shown that CeO₂-NPs could be safe for lens cells and could represent a new therapy for cataract treatment, but further studies are needed. To date, different pharmaceutical formulations based on nanoceria have been created looking at future clinical ophthalmic applications, such as water-soluble nanoceria, glycol chitosan-coated ceria nanoparticles (GCCNPs), and alginate-gelatin hydrogel loaded GCCNPs. GCCNPs were also effective in preventing choroidal neovascularization in vivo. Based on the nanosize of nanoceria, corneal permeation could be achieved to allow topical treatment of nanoceria. PEGylation and encapsulation in liposomes represent the main strategies to support corneal permeation, without altering nanoceria chemical-physical properties. Based on their great antioxidant properties, safety, and nanosize, nanoceria represent a new potential therapeutic for the treatment of several eye disorders.

Metal Oxide Nanoparticles in Therapeutic Regulation of Macrophage Functions

Macrophages are components of the innate immune system that control a plethora of biological processes. Macrophages can be activated towards pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes depending on the cue; however, polarization may be altered in bacterial and viral infections, cancer, or autoimmune diseases. Metal (zinc, iron, titanium, copper, etc.) oxide nanoparticles are widely used in therapeutic applications as drugs, nanocarriers, and diagnostic tools. Macrophages can recognize and engulf nanoparticles, while the influence of macrophage-nanoparticle interaction on cell polarization remains unclear. In this review, we summarize the molecular mechanisms that drive macrophage activation phenotypes and functions upon interaction with nanoparticles in an inflammatory microenvironment. The manifold effects of metal oxide nanoparticles on macrophages depend on the type of metal and the route of synthesis. While largely considered as drug transporters, metal oxide nanoparticles nevertheless have an immunotherapeutic potential, as they can evoke pro- or anti-inflammatory effects on macrophages and become essential for macrophage profiling in cancer, wound healing, infections, and autoimmunity.

In vitro and in vivo biocompatibility assessment of free radical scavenging nanocomposite scaffolds for bone tissue regeneration

Bone is the second most transplanted tissue in the world, resulting in increased demand for bone grafts leading to the fabrication of synthetic scaffold grafting alternatives. Fracture sites are under increased oxidative stress after injuries, affecting osteoblast function and hindering fracture healing and remodeling. To counter oxidative stress, free radical scavenging agents, such as cerium oxide nanoparticles, have gained traction in tissue engineering. Toward the goal of developing a functional synthetic system for bone tissue engineering, we characterized the biocompatibility of a porous, bioactive, free radical scavenging nanocomposite scaffold composed of poly(1,8 octanediol-co-citrate), beta-tricalcium phosphate, and cerium oxide nanoparticles. We studied cellular and tissue compatibility utilizing in vitro and in vivo models to assess nanocomposite interactions with both human osteoblast cells and rat subcutaneous tissue. We found the scaffolds were biocompatible in both models and supported cell attachment, proliferation, mineralization, and infiltration. Using hydrogen peroxide, we simulated oxidative stress to study the protective properties of the nanocomposite scaffolds via a reduction in cytotoxicity and recovered mineralization of osteoblast cells in vitro. We also found after implantation in vivo the scaffolds exhibited biocompatible properties essential for successful scaffolds for bone tissue engineering. Cells were able to infiltrate through the scaffolds, the surrounding tissues elicited a minimal immune response, and there were signs of scaffold degradation after 30 days of implantation. After the array of biological characterization, we had confirmed the development of a nanocomposite scaffold system capable of supporting bone-remodeling processes while providing a protective free radical scavenging effect.

Simultaneous enzyme mimicking and chemical reduction mechanisms for nanoceria as a bio-antioxidant: a catalytic model bridging computations and experiments for nanozymes

The bio-antioxidant ability of nanoceria has been mainly ascribed to its ability to mimic superoxide dismutase (SOD) and catalase (CAT), and its mechanisms are thought to be analogous to those of the natural enzymes. Accordingly, nanoceria has been called a nanozyme, a nanomaterial mimicking enzymes. Because they overlook the real structural features of nanoceria, these hypothetical mechanisms cannot explain the important antioxidant experiments of nanoceria and have little predictive power. We hereby study the O₂˙^- and H₂O₂ scavenging mechanisms of nanoceria using first principles calculations, taking into account the role of oxygen vacancies that are practically abundant in nanoceria. The results reveal atomistic-level mechanisms responsible for the SOD and CAT mimetic activities of nanoceria. The newly created surface defect states in the electronic band structures of the shortly-lived intermediate species, called transient surface defect states (TSDSs), play critical roles in the enzyme mimetic catalysis and can serve as the bridge between computations and experiments at the atomistic level. The energy levels of TSDSs, which depend on the concentration and distribution of oxygen vacancies, determine whether the nanoceria is eligible for the catalysis. Besides the known enzyme mimicking mechanisms, the non-catalytic chemical reduction mechanisms are also responsible for the scavenging of O₂˙^- and H₂O₂, in which nanoceria serves as a reducing agent rather than a catalyst. The chemical reduction pathways poison the active sites of nanoceria which serve to mimic SOD and thus deteriorate its SOD mimetic activity. The results provide guidance for the engineering of nanoceria for bio-antioxidant applications. In particular, the proposed catalytic model can be generalized for the screening and design of high-performance nanozymes based on semiconductor nanomaterials.

Synthesis and biomedical applications of nanoceria, a redox active nanoparticle

Background

Nanoceria has recently received much attention, because of its widespread biomedical applications, including antibacterial, antioxidant and anticancer activity, drug/gene delivery systems, anti-diabetic property, and tissue engineering.

Main body

Nanoceria exhibits excellent antibacterial activity against both Gram-positive and Gram-negative bacteria via the generation of reactive oxygen species (ROS). In healthy cells, it acts as an antioxidant by scavenging ROS (at physiological pH). Thus, it protects them, while in cancer cells (under low pH environment) it acts as pro-oxidant by generating ROS and kills them. Nanoceria has also been effectively used as a carrier for targeted drug and gene delivery in vitro and in vivo models. Besides, nanoceria can also act as an antidiabetic agent and confer protection towards diabetes-associated organ pathophysiology via decreasing the ROS level in diabetic subjects. Nanoceria also possesses excellent potential in the field of tissue engineering. In this review, firstly, we have discussed the different methods used for the synthesis of nanoceria as these are very important to control the size, shape and Ce³⁺/Ce⁴⁺ ratio of the particles upon which the physical, chemical, and biological properties depend. Secondly, we have extensively reviewed the different biomedical applications of nanoceria with probable mechanisms based on the literature reports.

Conclusion

The outcome of this review will improve the understanding about the different synthetic procedures and biomedical applications of nanoceria, which should, in turn, lead to the design of novel clinical interventions associated with various health disorders.

Graphical abstract

Layer-by-Layer Cerium Oxide Nanoparticle Coating for Antioxidant Protection of Encapsulated Beta Cells

In type 1 diabetes, the replacement of the destroyed beta cells could restore physiological glucose regulation and eliminate the need for exogenous insulin. Immunoisolation of these foreign cellular transplants via biomaterial encapsulation is widely used to prevent graft rejection. While highly effective in blocking direct cell-to-cell contact, nonspecific inflammatory reactions to the implant lead to the overproduction of reactive oxygen species, which contribute to foreign body reaction and encapsulated cell loss. For antioxidant protection, cerium oxide nanoparticles (CONPs) are a self-renewable, ubiquitous, free radical scavenger currently explored in several biomedical applications. Herein, 2-12 alternating layers of CONP/alginate are assembled onto alginate microbeads containing beta cells using a layer-by-layer (LbL) technique. The resulting nanocomposite coatings demonstrate robust antioxidant activity. The degree of cytoprotection correlates with layer number, indicating tunable antioxidant protection. Coating of alginate beads with 12 layers of CONP/alginate provides complete protection to the entrapped beta cells from exposure to 100 × 10-6 m H2 O2 , with no significant changes in cellular metabolic activity, oxidant capacity, or insulin secretion dynamics, when compared to untreated controls. The flexibility of this LbL method, as well as its nanoscale profile, provides a versatile approach for imparting antioxidant protection to numerous biomedical implants, including beta cell transplantation.

Atherosclerosis Treatment with Stimuli-Responsive Nanoagents: Recent Advances and Future Perspectives

Atherosclerosis is the root of approximately one-third of global mortalities. Nanotechnology exhibits splendid prospects to combat atherosclerosis at the molecular level by engineering smart nanoagents with versatile functionalizations. Significant advances in nanoengineering enable nanoagents to autonomously navigate in the bloodstream, escape from biological barriers, and assemble with their nanocohort at the targeted lesion. The assembly of nanoagents with endogenous and exogenous stimuli breaks down their shells, facilitates intracellular delivery, releases their cargo to kill the corrupt cells, and gives imaging reports. All these improvements pave the way toward personalized medicine for atherosclerosis. This review systematically summarizes the recent advances in stimuli-responsive nanoagents for atherosclerosis management and its progress in clinical trials.

Facile synthesis of IrO2/rGO nanocomposites with high peroxidase-like activity for sensitive colorimetric detection of low weight biothiols

In this work, we reported a novel nanozyme synthesized by decorating highly dispersed ultrafine IrO₂ nanoparticles on reduced graphene oxide (rGO) nanosheets via a simple hydrothermal method. The as-prepared IrO₂/rGO nanocomposites exhibited intrinsic peroxidase-like activity and could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue product in the presence of H₂O₂. Catalytic kinetic of IrO₂/rGO nanocomposites followed Michaelis-Menten behavior, exhibiting a higher affinity to TMB than horseradish peroxidase (HRP) enzyme. Catalytic mechanism studies suggested that the peroxidase-like activity of IrO₂/rGO nanocomposites originated from their ability of electron transfer between substrate and H₂O₂. On the basis of high peroxidase-like activity of IrO₂/rGO nanocomposites, a colorimetric strategy for rapid and sensitive detection of low weight biothiols was developed. The colorimetric detection assays for low weight biothiols showed high selectivity against other amino acids. Therefore, the IrO₂/rGO nanozyme is expected for promising potential applications in the biosensor, diagnostics and environment.

In vivo immunomodulatory and antioxidant properties of nanoceria (nCeO2) in the marine mussel Mytilus galloprovincialis

Cerium nanoparticles (nCeO₂) are increasingly utilized in a wide variety of industrial, environmental and biomedical applications, and are therefore expected to be released in the aquatic environment. Due to its peculiar redox properties, nCeO₂ may present unique hazards to environmental and human health. Previous data showed that in the hemocytes of the marine bivalve Mytilus galloprovincialis, in vitro exposure to a particular type of nCeO₂ (9 nm, characterized by negative ζ-potential, high H₂O₂ scavenging capacity and Ce³⁺/Ce⁴⁺ surface ratio) reduced basal ROS production, lysosomal membrane stability and phagocytic activity in the presence of hemolymph serum; the effects observed were partly ascribed to the formation of a SOD-protein corona in the hemolymph. In this work, the in vivo effects of this type of nCeO₂ were investigated in mussels exposed to 100 μg/L nCeO₂ for 96 h; several lysosomal, immune, inflammatory and antioxidant biomarkers were measured at cellular (hemocytes) and tissue (gills, digestive gland) level. Molecular responses were evaluated in hemocytes and digestive gland by determining expression of 11 selected genes related to known biological functions. The results show specific immunomodulatory and antioxidant effects of nCeO₂ at different levels of biological organization in the absence of Cerium tissue accumulation. These data further support the redox mechanisms at the basis of the physiological effects of nCeO₂. Finally, in order to evaluate the possible impact at the whole organism level, the effects of nCeO₂ were evaluated in the 48 h embryotoxicity assay in a wide concentration range. However, nCeO₂ exposure resulted in a small reduction in normal embryo development. Overall, the results demonstrate that in mussels nCeO₂ can selectively modulate different physiological processes at different levels of biological organization.

NiO decorated CeO2 nanostructures as room temperature isopropanol gas sensors

Heterostructures developed using CeO2 show promising peculiarities in the field of metal oxide gas sensors due to the great variations in the resistance during the adsorption and desorption processes. NiO decorated CeO2 nanostructures (NiO/CeO2) were synthesized via a facile two-step process. High resolution transmission electron microscopy (HRTEM) results revealed the perfect decoration of NiO on the CeO2 surface. The porous nature of the NiO/CeO2 sensor surface was confirmed from scanning electron microscopy (SEM) analysis. Gas sensing studies of pristine CeO2 and NiO/CeO2 sensors were performed under room conditions and enhanced gas sensing properties for the NiO/CeO2 sensor towards isopropanol were observed. Decoration of NiO on the CeO2 surface develops a built-in potential at the interface of NiO and CeO2 which played a vital role in the superior sensing performance of the NiO/CeO2 sensor. Sharp response and recovery times (15 s/19 s) were observed for the NiO/CeO2 sensor towards 100 ppm isopropanol at room temperature. Long-term stability of the NiO/CeO2 sensor was also studied and discussed. From all the results it is concluded that the decoration of NiO on the CeO2 surface could significantly enhance the sensing performance and it has great advantages in designing best performing isopropanol gas sensors.

Antioxidant activity of cerium dioxide nanoparticles and nanorods in scavenging hydroxyl radicals

Cerium oxide nanoparticles (CeNPs) have been shown to exhibit antioxidant capabilities, but their efficiency in scavenging reactive oxygen species (ROS) and the underlying mechanisms are not yet well understood. In this study, cerium dioxide nanoparticles (CeNPs) and nanorods (CeNRs) were found to exhibit much stronger scavenging activity than ·OH generation in phosphate buffered saline (PBS) and surrogate lung fluid (SLF). The larger surface area and higher defect density of CeNRs may lead to higher ·OH scavenging activity than for CeNPs. These insights are important to understand the redox activity of cerium nanomaterials and provide clues to the role of CeNPs in biological and environmental processes.

Design, Fabrication, and In Vitro Evaluation of Nanoceria-Loaded Nanostructured Lipid Carriers for the Treatment of Neurological Diseases

Neurodegenerative diseases comprise a large group of disorders characterized by a dramatic synaptic connections loss, occurring as a result of neurodegeneration, which is closely related to the overproduction of reactive oxygen and nitrogen species. Currently, the treatment of neurodegenerative diseases has been limited mainly because of the inability of the synthesized delivery systems to cross the blood-brain barrier and to successfully deliver their therapeutic cargo to the diseased tissue. Taking into consideration the aforementioned limitations, we designed a lipid-based nanotherapeutic vector composed of biomimetic lipids and CeO₂ nanoparticles (nanoceria, NC). NC have shown to be a promising tool for the treatment of several pathological conditions ranging from cancer to neurological diseases, mainly because of their antioxidant properties, while lipid-based structures have been shown to have an inherent ability to cross the blood-brain barrier. The lipid-based nanotherapeutics were successfully fabricated using a combination of ultrasonication and high-pressure homogenization techniques, and they were fully characterized morphologically and physicochemically. Their antioxidant ability was demonstrated using electron paramagnetic resonance spectroscopy and antioxidant assays. These innovative nanotherapeutics demonstrated a higher colloidal stability with respect to free NC, preserving at the same time their antioxidant properties. Finally, the ability of the lipid carriers to cross a model of the blood-brain barrier and to be internalized by neurons, acting both as neuroprotective and pro-neurogenic agents, was demonstrated using single- and triple-culture systems.

Biomedical applications of nanoceria: new roles for an old player

The use of different biomaterials with the ability to accelerate the repair and regeneration processes is of great importance in tissue engineering strategies. On this point, cerium oxide nanoparticles (CNPs or nanoceria) have recently attracted much attention due to their excellent biological properties including anti-oxidant, anti-inflammation and antibacterial activities as well as high angiogenic potential. The results of incorporation of these nano-sized particles into various constructs and scaffolds designed for tissue engineering applications have proven the success of this strategy in terms of improving healing process of different tissues. In this review, we first summarize the physicochemical and biological properties of nanoceria in brief and then present its usability in tissue engineering strategies based on the currently available published reports.

The nanotechnology among US: are metal and metal oxides nanoparticles a nano or mega risk for soil microbial communities?

Metal nanoparticles and metal oxides nanoparticles (MNPs/MONPs) have been widely included in a great diversity of products and industrial applications and they are already a part of our everyday life. According to estimation studies, their production is expected to increase exponentially in the next few years. Consequently, soil has been suggested as the main sink of MNPs/MONPs once they are deliberately or accidentally released into the environment. The potential negative perturbations that may result on soil microbial communities and ecological processes are resulting in concerns. Several nano-toxicological studies of MNPs/MONPs, reported so far, have focused on aquatic organisms, animals, and soil invertebrates. However, during recent years, the studies have been oriented to understand the effects of MNPs/MONPs on microbial communities and their interaction with soil components. The studies have suggested that MNPs/MONPs are one of the most toxic type to soil biota, amongst different types of nanomaterials. This may threaten soil health and fertility, since microbial communities are known to support important biological processes and ecosystem services such as the nutrient cycling, whereby their protection against the environmental pollution is imperative. Therefore, in this review we summarize the actual knowledge available from the last five years (2013-2018) and gaps about the potential negative, positive or neutral effects produced on soil by different classes of MNPs/MONPs. A particular emphasis has been placed on the associated soil microorganisms and biological processes. Finally, perspectives about future research are discussed.