Strategies Employed to Design Biocompatible Metal Nanoparticles for Medical Science and Biotechnology Applications

The applicability of nanomaterials has evolved in biomedical domains thanks to advances in biocompatibility strategies and the mitigation of cytotoxic effects, allowing diagnostics, imaging, and therapeutic approaches. The application of nanoparticles (NP), particularly metal nanoparticles (mNPs), such as gold (Au) and silver (Ag), includes inherent challenges related to the material characteristics, surface modification, and bioconjugation techniques. By tailoring the surface properties through appropriate coating with biocompatible molecules or functionalization with active biomolecules, researchers can reach a harmonious interaction with biological systems or samples (mostly fluids or tissues). Thus, this review highlights the mechanisms associated with the obtention of biocompatible mNP and presents a comprehensive overview of methods that facilitate safe and efficient production. Therefore, we consider this review to be a valuable resource for all researchers navigating this dynamic field.

In vitro cytocompatibility and antibacterial studies on biodegradable Zn alloys supplemented by a critical assessment of direct contact cytotoxicity assay

In vitro cytotoxicity assessment is indispensable in developing new biodegradable implant materials. Zn, which demonstrates an ideal corrosion rate between Mg- and Fe-based alloys, has been reported to have excellent in vivo biocompatibility. Therefore, modifications aimed at improving Zn's mechanical properties should not degrade its biological response. As sufficient strength, ductility and corrosion behavior required of load-bearing implants has been obtained in plastically deformed Zn-3Ag-0.5Mg, the effect of simultaneous Ag and Mg additions on in vitro cytocompatibility and antibacterial properties was studied, in relation to Zn and Zn-3Ag. Direct cell culture on samples and indirect extract-based tests showed almost no significant differences between the tested Zn-based materials. The diluted extracts of Zn, Zn-3Ag, and Zn-3Ag-0.5Mg showed no cytotoxicity toward MG-63 cells at a concentration of ≤12.5%. The cytotoxic effect was observed only at high Zn²⁺ ion concentrations and when in direct contact with metallic samples. The highest LD₅₀ (lethal dose killing 50% of cells) of 13.4 mg/L of Zn²⁺ ions were determined for the Zn-3Ag-0.5Mg. Similar antibacterial activity against Escherichia coli and Staphylococcus aureus was observed for Zn and Zn alloys, so the effect is attributed mainly to the released Zn²⁺ ions exhibiting bactericidal properties. Most importantly, our experiments indicated the limitations of water-soluble tetrazolium salt-based cytotoxicity assays for direct tests on Zn-based materials. The discrepancies between the WST-8 assay and SEM observations are attributed to the interference of Zn²⁺ ions with tetrazolium salt, therefore favoring its transformation into formazan, giving false cell viability quantitative results.

Investigating nanoplastics toxicity using advanced stem cell-based intestinal and lung in vitro models

Plastic particles in the nanometer range-called nanoplastics-are environmental contaminants with growing public health concern. As plastic particles are present in water, soil, air and food, human exposure via intestine and lung is unavoidable, but possible health effects are still to be elucidated. To better understand the Mode of Action of plastic particles, it is key to use experimental models that best reflect human physiology. Novel assessment methods like advanced cell models and several alternative approaches are currently used and developed in the scientific community. So far, the use of cancer cell line-based models is the standard approach regarding in vitro nanotoxicology. However, among the many advantages of the use of cancer cell lines, there are also disadvantages that might favor other approaches. In this review, we compare cell line-based models with stem cell-based in vitro models of the human intestine and lung. In the context of nanoplastics research, we highlight the advantages that come with the use of stem cells. Further, the specific challenges of testing nanoplastics in vitro are discussed. Although the use of stem cell-based models can be demanding, we conclude that, depending on the research question, stem cells in combination with advanced exposure strategies might be a more suitable approach than cancer cell lines when it comes to toxicological investigation of nanoplastics.

Comparison of In Vitro Approaches to Assess the Antibacterial Effects of Nanomaterials

The antibacterial properties of nanomaterials (NMs) can be exploited in a range of consumer products (e.g., wound dressings, food packaging, textiles, medicines). There is also interest in the exploitation of NMs as treatments for infectious diseases to help combat antibiotic resistance. Whilst the antibacterial activity of NMs has been assessed in vitro and in vivo in numerous studies, the methodology used is very varied. Indeed, while numerous approaches are available to assess the antibacterial effect of NMs in vitro, they have not yet been systematically assessed for their suitability and sensitivity for testing NMs. It is therefore timely to consider what assays should be prioritised to screen the antibacterial properties of NMs. The majority of existing in vitro studies have focused on investigating the antibacterial effects exhibited by silver (Ag) NMs and have employed a limited range of assays. We therefore compared the antibacterial effects of copper oxide (CuO) NMs to Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis at various concentrations (12.5-200 µg/mL) using a battery of tests (well and disc diffusion, plate counts-time-kill method, optical density measurement-OD, Alamar Blue and live/dead viability assays, and quantitative polymerase chain reaction). CuO NMs were most toxic to B. subtilis and E. coli, while P. aeruginosa was the least sensitive strain. All assays employed detected the antibacterial activity of CuO NMs; however, they varied in their sensitivity, time, cost, technical difficulty and requirement for specialized equipment. In the future, we suggest that a combination of approaches is used to provide a robust assessment of the antibacterial activity of NMs. In particular, we recommend that the time-kill and OD assays are prioritised due to their greater sensitivity. We also suggest that standard operating protocols are developed so that the antibacterial activity of NMs can be assessed using a harmonised approach.

In Vitro High-Throughput Toxicological Assessment of Nanoplastics

Sub-micrometer particles derived from the fragmentation of plastics in the environment can enter the food chain and reach humans, posing significant health risks. To date, there is a lack of adequate toxicological assessment of the effects of nanoplastics (NPs) in mammalian systems, particularly in humans. In this work, we evaluated the potential toxic effects of three different NPs in vitro: two NPs obtained by laser ablation (polycarbonate (PC) and polyethylene terephthalate (PET1)) and one (PET2) produced by nanoprecipitation. The physicochemical characterization of the NPs showed a smaller size, a larger size distribution, and a higher degree of surface oxidation for the particles produced by laser ablation. Toxicological evaluation performed on human cell line models (HePG2 and Caco-2) showed a higher toxic effect for the particles synthesized by laser ablation, with PC more toxic than PET. Interestingly, on differentiated Caco-2 cells, a conventional intestinal barrier model, none of the NPs produced toxic effects. This work wants to contribute to increase knowledge on the potential risks posed by NPs.

Lipoic Acid-Coated Silver Nanoparticles: Biosafety Potential on the Vascular Microenvironment and Antibacterial Properties

Purpose: To study and compare the antibacterial properties and the potential cytotoxic effects of commercially available uncoated silver nanoparticles (AgNPs) with lipoic acid coated silver nanoparticles (AgNPsLA) developed by our group. The antibacterial, cytotoxic, and hemolytic properties of those NPs were assessed with the main objective of investigating if AgNPsLA could maintain their antibacterial properties while improving their biosafety profile over uncoated AgNPs within the blood vessel's microenvironment. Methods: Comercially available uncoated 2.6 nm AgNPs and 2.5 nm AgNPsLA synthesized and characterized as previously described by our group, were used in this study. Antimicrobial activity was assessed on a wide range of pathogens and expressed by minimal inhibitory concentrations (MIC). Assessment of cytotoxicity was carried out on human umbilical vein endothelial cells (HUVEC) using an MTT test. Detection of reactive oxygen species, cell apoptosis/necrosis in HUVEC, and measurement of mitochondrial destabilization in HUVEC and platelets were performed by flow cytometry. The potential harmful effect of nanoparticles on red blood cells (RBCs) was investigated measuring hemoglobin and LDH released after exposure to NPs. Transmission electron microscopy was also used to determine if AgNPs and AgNPsLA could induce any ultrastructural changes on HUVEC cells and Staphylococcus aureus bacteria. Results: AgNPs and AgNPsLA had antimicrobial properties against pathogens associated with catheter-related bloodstream infections. AgNPs, in contrast to AgNPsLA, induced ROS production and apoptosis in HUVEC, ultrastructural changes in HUVEC and S. aureus, depolarization of mitochondrial membrane in HUVEC and platelets, and also hemolysis. Conclusion: AgNPsLA synthesized by our group have antimicrobial activity and a better biosafety profile than uncoated AgNPs of similar size. Those observations are of critical importance for the future in vivo investigations and the potential application of AgNPsLA in medical devices for human use.

Use of an in silico knowledge discovery approach to determine mechanistic studies of silver nanoparticles-induced toxicity from in vitro to in vivo

BACKGROUND

Silver nanoparticles (AgNPs) are considered a double-edged sword that demonstrates beneficial and harmful effects depending on their dimensions and surface coating types. However, mechanistic understanding of the size- and coating-dependent effects of AgNPs in vitro and in vivo remains elusive. We adopted an in silico decision tree-based knowledge-discovery-in-databases process to prioritize the factors affecting the toxic potential of AgNPs, which included exposure dose, cell type and AgNP type (i.e., size and surface coating), and exposure time. This approach also contributed to effective knowledge integration between cell-based phenomenological observations and in vitro/in vivo mechanistic explorations.

RESULTS

The consolidated cell viability assessment results were used to create a tree model for generalizing cytotoxic behavior of the four AgNP types: SCS, LCS, SAS, and LAS. The model ranked the toxicity-related parameters in the following order of importance: exposure dose > cell type > particle size > exposure time ≥ surface coating. Mechanistically, larger AgNPs appeared to provoke greater levels of autophagy in vitro, which occurred during the earlier phase of both subcytotoxic and cytotoxic exposures. Furthermore, apoptosis rather than necrosis majorly accounted for compromised cell survival over the above dosage range. Intriguingly, exposure to non-cytotoxic doses of AgNPs induced G2/M cell cycle arrest and senescence instead. At the organismal level, SCS following a single intraperitoneal injection was found more toxic to BALB/c mice as compared to SAS. Both particles could be deposited in various target organs (e.g., spleen, liver, and kidneys). Morphological observation, along with serum biochemical and histological analyses, indicated that AgNPs could produce pancreatic toxicity, apart from leading to hepatic inflammation.

CONCLUSIONS

Our integrated in vitro, in silico, and in vivo study revealed that AgNPs exerted toxicity in dose-, cell/organ type- and particle type-dependent manners. More importantly, a single injection of lethal-dose AgNPs (i.e., SCS and SAS) could incur severe damage to pancreas and raise blood glucose levels at the early phase of exposure.

Advanced Nanoparticle-Based Drug Delivery Systems and Their Cellular Evaluation for Non-Small Cell Lung Cancer Treatment

Lung cancers, the number one cancer killer, can be broadly divided into small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC), with NSCLC being the most commonly diagnosed type. Anticancer agents for NSCLC suffer from various limitations that can be partly overcome by the application of nanomedicines. Nanoparticles is a branch within nanomedicine that can improve the delivery of anticancer drugs, whilst ensuring the stability and sufficient bioavailability following administration. There are many publications available in the literature exploring different types of nanoparticles from different materials. The effectiveness of a treatment option needs to be validated in suitable in vitro and/or in vivo models. This includes the developed nanoparticles, to prove their safety and efficacy. Many researchers have turned towards in vitro models that use normal cells or specific cells from diseased tissues. However, in cellular works, the physiological dynamics that is available in the body could not be mimicked entirely, and hence, there is still possible development of false positive or false negative results from the in vitro models. This article provides an overview of NSCLC, the different nanoparticles available to date, and in vitro evaluation of the nanoparticles. Different types of cells suitable for in vitro study and the important precautions to limit the development of false results are also extensively discussed.

Moderating cellular inflammation using 2-dimensional titanium carbide MXene and graphene variants

The effective control of microbial and metabolically derived biological toxins which negatively impact physical health remains a key challenge for the 21st century. 2-Dimensional graphene and MXene nanomaterials are relatively new additions to the field of biomedical materials with superior external surface areas suited to adsorptive remediation of biological toxins. However, relatively little is known about their physiological interactions with biological systems and, to date, no comparative biological studies have been done. This study compares titanium carbide MXene (Ti3C2Tx) in multilayered and delaminated forms with graphene variants to assess the impact of variable physical properties on cellular inflammatory response to endotoxin stimulus. No significant impact on cell metabolism or induction of inflammatory pathways leading to cell death was observed. No significant increase in markers of blood cell activation and haemolysis occurred. Whilst graphene nanoplatelets (GNP), graphene oxide (GO) and Ti3C2Tx showed insignificant antibacterial activity towards Escherichia coli, silver nanoparticle-modified GO (GO-Ag) induced bacterial cell death and at a lower dose than silver nanoparticles. All nanomaterials significantly reduced bacterial endotoxin induced THP-1 monocyte IL-8, IL-6 and TNF-α cytokine production by >99%, >99% and >80% respectively, compared to control groups. This study suggests the utility of these nanomaterials as adsorbents in blood contacting medical device applications for removal of inflammatory cytokines linked to poor outcome in patients with life-threatening infection.

Survival Mechanisms and Xenobiotic Susceptibility of Keratinocytes Exposed to Metal-Derived Nanoparticles

Metal-derived nanoparticles (Mt-NPs) are increasingly used in cosmetology due to their ultraviolet shielding (titanium dioxide [TiO₂]), antioxidant (cerium dioxide [CeO₂]), and biocidal (silver [Ag]) properties. In the absence of overt toxicity (i.e., cell death), Mt-NPs are considered safe for cosmetic applications. However, there is little understanding about the mechanisms involved in the survival of keratinocytes exposed to subtoxic levels of Mt-NPs. Human keratinocytes (HaCaT) were exposed subacutely to subtoxic concentrations (≤30 μg/mL, 48-72 h) of rutile (r) TiO₂ (cylindrical), CeO₂ (cubic) and Ag (spherical) with a core/hydrodynamic size of <50/<100 nm and >98% purity. Mt-NP uptake was indirectly quantified by changes in the light side scatter, where the kinetics (time/dose-response) suggested that the three types of Mt-NPs were similarly uptaken by keratinocytes. rTiO₂ and CeO₂, but not Ag-NPs, increased autophagy, whose inhibition prompted cell death. No increase in the steady-state levels of reactive oxygen species (ROS) was induced by exposure to any of the Mt-NPs tested. Interestingly, intracellular Ag-NP aggregates observed an increased far-red autofluorescence (≥740 nm em), which has been ascribed to their binding to thiol molecules such as glutathione (GSH). Accordingly, inhibition of GSH synthesis, but not the impairment of oxidized GSH recycling, sensitized keratinocytes to Ag-NPs suggesting that GSH homeostasis, and its direct scavenging of Ag-NPs, but not ROS, is essential for keratinocyte survival upon exposure to Ag-NP. rTiO₂ and Ag, but not CeO₂-NPs, compromised metabolic flux (glycolysis and respiration), but ATP levels were unaltered. Finally, we also observed that exposure to Mt-NPs sensitized keratinocytes to non-UV xenobiotic exposure (arsenite and paraquat). Our results demonstrate the differential contribution of autophagy and GSH homeostasis to the survival of human keratinocytes exposed to subtoxic concentrations of Mt-NPs and highlight the increased susceptibility of keratinocytes exposed to Mt-NPs to a second xenobiotic insult.

Investigation of Twenty Metal, Metal Oxide, and Metal Sulfide Nanoparticles' Impact on Differentiated Caco-2 Monolayer Integrity

The use of engineered nanomaterials (ENMs) in foods and consumer products is rising, increasing the potential for unintentional ingestion. While the cytotoxicity of many ENMs has been investigated, less attention has been given to adverse impact on the intestinal barrier integrity. Chronical disruption of gastrointestinal integrity can have far reaching health implications. Using fully differentiated Caco-2 cells, the perturbation of intestinal barrier function and cytotoxicity were investigated for 20 metal, metal oxide, and metal sulfide ENMs. Caco-2 cells were exposed to 50 μg/mL ENMs for 24 hours. ENM formulations were characterized at 0 and 24 hours, and In Vitro Sedimentation, Diffusion and Dosimetry Modeling was applied to calculate the effective dose of exposure during 24 hours. The apparent permeability coefficient (P_app) was determined for fluorescent labeled dextran (3,000 Da) and tight junction integrity was evaluated by immunofluorescence microscopy. Cytotoxicity was investigated by determining lactate dehydrogenase release (LDH) and cell metabolic activity (tetrazolium based MTS) assays. Four ENMs led to significantly increased P_app, (15.8% w/w% Ag-SiO₂ nanoparticle (NP), 60 nm CdS NP, 100 nm V₂O₅ flakes, and 50 nm ZnO NP), while one ENM (20 nm MgO NP) decreased P_app. With the exception of CdS NP, significantly increased P_app was not connected with cell cytotoxicity. The calculated effective dose concentration was not correlated with increased P_app. Our results illustrate that while many metal, metal oxide, and metal sulfide ENMs do not adversely affect monolayer integrity or induce cytotoxicity in differentiated Caco-2 cells, a subset of ENMs may compromise the intestinal integrity. This study demonstrated the use of differentiated Caco-2 monolayer and P_app as an endpoint to identify and prioritize ENMs that should be investigated further. The interaction between ENMs and the intestinal epithelium needs to be evaluated to understand potential intestinal barrier dysfunction and resulting health implications.

Silver Nanoparticles and Metallic Silver Interfere with the Griess Reaction: Reduction of Azo Dye Formation via a Competing Sandmeyer-Like Reaction

Silver (Ag) is the most common nanomaterial (NM) in consumer products. Much research has been focused on elucidating the potential impact of Ag-containing NMs on human health, e.g., cytotoxicity, genotoxicity, or proinflammatory responses. In the case of proinflammatory responses, a frequently used end point is the induction of nitric oxide (NO), which is indirectly quantified as nitrite (NO₂^-) with the Griess reaction. After preliminary studies in a macrophage-like cell culture system showed anomalous false negative results in the presence of silver nanoparticles (Ag NPs), we studied the influence of Ag on the detection of NO₂^- in a cell-free environment. Solutions containing a known concentration of NaNO₂ were prepared in H₂O, PBS, or complete cell culture medium (CCM) and analyzed using the Griess reaction in the presence of Ag in its metallic or ionic state. In Milli-Q H₂O, the impact of salts on the detection was investigated using NaCl and KBr. After completion of the Griess reaction, the samples were analyzed spectrophotometrically or chromatographically. It was found that the presence of metallic but not ionic Ag interfered with the quantification of NO₂^-. The effect was more pronounced in PBS and H₂O containing NaCl or KBr. The chromatographical analysis provided evidence of a competing reaction consuming the intermediate diazonium salt, which is critical to the Griess reaction. These findings demonstrate yet another substantial interference of NMs with a frequently used in vitro assay. If gone unnoticed, this interference might cause false negative results and an impaired hazard assessment of Ag NMs.