The fate of silver nanoparticles in authentic human saliva

Understanding the role of biomolecular coronas in human exposure to nanomaterials

Nanomaterials (NMs) are increasingly used in medical treatments, electronics, and food additives. However, nanosafety-the possible adverse effects of NMs on human health-is an area of active research. This review provides an overview of the influence of biomolecular coronas on NM transformation following various exposure routes. We discuss potential exposure pathways, including inhalation and ingestion, describing the physiology of exposure routes and emphasising the relevance of coronas in these environments. Additionally, we review other routes to NM exposure, such as synovial fluid, blood (translocation and injection), dermal and ocular exposure, as well as the dose and medium impact on NM interactions. We emphasize the need for an in-depth characterisation of coronas in different biological media, highlighting the need and opportunity to study lung and gastric fluids to understand NM behaviour and potential toxicity. Future research aims to predict better in vivo outcomes and address the complexities of NM interactions with biological systems.

Transformation, Absorption and Toxicological Mechanisms of Silver Nanoparticles in the Gastrointestinal Tract Following Oral Exposure

Oral exposure is known as the primary way for silver nanoparticles (AgNPs), which are commonly used as food additives or antibacterial agents in commercial products, to enter the human body. Although the health risk of AgNPs has been a concern and extensively researched over the past few decades, there are still numerous knowledge gaps that need to be filled to disclose what AgNPs experience in the gastrointestinal tract (GIT) and how they cause oral toxicity. In order to gain more insight into the fate of AgNPs in the GIT, the main gastrointestinal transformation of AgNPs, including aggregation/disaggregation, oxidative dissolution, chlorination, sulfuration, and corona formation, is first described. Second, the intestinal absorption of AgNPs is presented to show how AgNPs interact with epithelial cells and cross the intestinal barrier. Then, more importantly, we make an overview of the mechanisms underlying the oral toxicity of AgNPs in light of recent advances as well as the factors affecting the nano-bio interactions in the GIT, which have rarely been thoroughly elaborated in published literature. At last, we emphatically discuss the issues that need to be addressed in the future to answer the question "How does oral exposure to AgNPs cause detrimental effects on the human body?".

Oral exposure to Ag or TiO2 nanoparticles perturbed gut transcriptome and microbiota in a mouse model of ulcerative colitis

Silver (nAg) and titanium dioxide (nTiO₂) nanoparticles improve texture, flavour or anti-microbial properties of various food products and packaging materials. Despite their increased oral exposure, their potential toxicities in the dysfunctional intestine are unclear. Here, the effects of ingested nAg or nTiO₂ on inflamed colon were revealed in a mouse model of chemical-induced acute ulcerative colitis. Mice (eight/group) were exposed to nAg or nTiO₂ by oral gavage for 10 consecutive days. We characterized disease phenotypes, histology, and alterations in colonic transcriptome (RNA sequencing) and gut microbiome (16S sequencing). Oral exposure to nAg caused only minor changes in phenotypic hallmarks of colitic mice but induced extensive responses in gene expression enriching processes of apoptotic cell death and RNA metabolism. Instead, ingested nTiO₂ yielded shorter colon, aggravated epithelial hyperplasia and deeper infiltration of inflammatory cells. Both nanoparticles significantly changed the gut microbiota composition, resulting in loss of diversity and increase of potential pathobionts. They also increased colonic mucus and abundance of Akkermansia muciniphila. Overall, nAg and nTiO₂ induce dissimilar immunotoxicological changes at the molecular and microbiome level in the context of colon inflammation. The results provide valuable information for evaluation of utilizing metallic nanoparticles in food products for the vulnerable population.

Fate and transformation of silver nanoparticles in different biological conditions

The exploitation of silver nanoparticles (AgNPs) in biomedicine represents more than one third of their overall application. Despite their wide use and significant amount of scientific data on their effects on biological systems, detailed insight into their in vivo fate is still lacking. This study aimed to elucidate the biotransformation patterns of AgNPs following oral administration. Colloidal stability, biochemical transformation, dissolution, and degradation behaviour of different types of AgNPs were evaluated in systems modelled to represent biological environments relevant for oral administration, as well as in cell culture media and tissue compartments obtained from animal models. A multimethod approach was employed by implementing light scattering (dynamic and electrophoretic) techniques, spectroscopy (UV-vis, atomic absorption, nuclear magnetic resonance) and transmission electron microscopy. The obtained results demonstrated that AgNPs may transform very quickly during their journey through different biological conditions. They are able to degrade to an ionic form and again reconstruct to a nanoparticulate form, depending on the biological environment determined by specific body compartments. As suggested for other inorganic nanoparticles by other research groups, AgNPs fail to preserve their specific integrity in in vivo settings.

RNA-extraction-free nano-amplified colorimetric test for point-of-care clinical diagnosis of COVID-19

The global pandemic of coronavirus disease 2019 (COVID-19) highlights the shortcomings of the current testing paradigm for viral disease diagnostics. Here, we report a stepwise protocol for an RNA-extraction-free nano-amplified colorimetric test for rapid and naked-eye molecular diagnosis of COVID-19. The test employs a unique dual-prong approach that integrates nucleic acid (NA) amplification and plasmonic sensing for point-of-care detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with a sample-to-assay response time of <1 h. The RNA-extraction-free nano-amplified colorimetric test utilizes plasmonic gold nanoparticles capped with antisense oligonucleotides (ASOs) as a colorimetric reporter to detect the amplified nucleic acid from the COVID-19 causative virus, SARS-CoV-2. The ASOs are specific for the SARS-CoV-2 N-gene, and binding of the ASOs to their target sequence results in the aggregation of the plasmonic gold nanoparticles. This highly specific agglomeration step leads to a change in the plasmonic response of the nanoparticles. Furthermore, when tested using clinical samples, the accuracy, sensitivity and specificity of the test were found to be >98.4%, >96.6% and 100%, respectively, with a detection limit of 10 copies/μL. The test can easily be adapted to diagnose other viral infections with a simple modification of the ASOs and primer sequences. It also provides a low-cost, rapid approach requiring minimal instrumentation that can be used as a screening tool for the diagnosis of COVID-19 at point-of-care settings in resource-poor situations. The colorimetric readout of the test can even be monitored using a handheld optical reader to obtain a quantitative response. Therefore, we anticipate that this protocol will be widely useful for the development of biosensors for the molecular diagnostics of COVID-19 and other infectious diseases.

Transformation of silver nanoparticles released from skin cream and mouth spray in artificial sweat and saliva solutions: particle size, dissolution, and surface area

The use of silver nanoparticles (Ag NPs) in consumer products can result in diffuse environmental dispersion of both NPs and ionic silver. This study investigated the transformation of Ag NPs present in two consumer products (skin cream, mouth spray) in terms of release of Ag NPs and ionic silver and changes in particle size in artificial sweat and saliva solutions. Large differences in silver release were observed with the smaller sized Ag NPs in mouth spray releasing more silver compared with the Ag NPs of the skin cream. Substantial particle agglomeration took place in both artificial sweat and saliva, forming large-sized agglomerates (> 100 nm). The amount of dissolved silver in solution after 24 h was less than 10% of the total amount of Ag NPs for both products. The results show that the Ag NPs of these consumer products will largely remain as NPs even after 24 h of skin or saliva contact. The use of normalization by geometric surface area of the particles was tested as a way to compare dissolution for Ag NPs of different characteristics, including pristine, bare, as well as PVP-capped Ag NPs. Normalization of silver dissolution with the geometric surface area was shown promising, but more extensive studies are required to unambiguously conclude whether it is a way forward to enable grouping of the dissolution behavior of Ag NPs released from consumer products.

Interaction of Differently Coated Silver Nanoparticles With Skin and Oral Mucosal Cells

Silver nanoparticles (AgNP) can be found in different consumer products and various medical devices due to their excellent biocidal properties. Despite extensive scientific literature reporting biological effects of AgNP, there is still a lack of scientific evidence on how different surface functionalization affects AgNP interaction with the human skin and the oral epithelium. This study aimed to investigate biological consequences following the treatment of HaCaT and TR146 cells with AgNP stabilized with negatively charged sodium bis(2-ethylhexyl)-sulfosuccinate (AOT), neutral polyvinylpyrrolidone (PVP), and positively charged poly-l-lysine (PLL). All AgNP were characterized by means of size, shape and surface charge. Interactions with biological barriers were investigated in vitro by determining cell viability, particle uptake, oxidative stress response and DNA damages following AgNP treatment. Results showed a significant difference in cytotoxicity depending on the surface coating used for AgNP stabilization. All three types of AgNP induced apoptosis, oxidative stress response and DNA damages in cells, but AOT- and PVP-coated AgNP exhibited lower toxicity than positively charged PLL-AgNP. Considering the number of data gaps related to the safe use of nanomaterials in biomedicine, this study highlights the importance of particle surface functionalization that should be considered during design and development of future AgNP-based medical products.

The oxygen reduction reaction at silver electrodes in high chloride media and the implications for silver nanoparticle toxicity

The oxygen reduction reaction (ORR) at neutral pH in various aqueous chloride-containing solutions was investigated voltammetrically. In particular, the ORR was performed in high chloride containing aqueous media including authentic and synthetic seawater under oxygen saturated conditions and compared with that in aqueous nitrate and perchlorate media. The experimental voltammograms revealed a two-electron process forming hydrogen peroxide in low chloride media. In contrast, high concentration chloride solutions, including both synthetic and authentic seawater showed an increase of overpotential, accompanied by a splitting of the voltammetric peak into two one-electron features indicating the formation of superoxide in the first step and its release from the silver-solution interface. The implications for silver nanoparticle toxicology are discussed given the markedly greater toxicity of superoxide over peroxide and the high levels of chloride in biological media as well as in seawater.

Salivary Excretion of Renal-Clearable Silver Nanoparticles

Salivary elimination is an important pathway for the body to excrete small molecules with digestive enzymes. However, very few engineered nanoparticles can be excreted through salivary glands, which often host bacteria or viruses during infection and involve in disease transmission. Herein, we report that renal clearable glutathione coated AgNPs (GS-AgNPs) can selectively accumulate in the submandibular salivary gland, followed by being excreted in its excretory duct. By conducting head-to-head comparison on in vivo transport and interactions of both GS-AgNPs and glutathione coated gold nanoparticles (GS-AuNPs) with the same sizes, we found that low-density GS-AgNPs showed much higher vascular permeability than GS-AuNPs and can rapidly penetrate into submandibular salivary glands, be efficiently taken up by striated and excretory duct cells, and eventually secreted into saliva.

Does Hypertension affect Saliva Properties?

Statement of the Problem:

Systemic conditions can affect the salivary glands and oral health. Hypertension induces xerostomia. Because the function of saliva is related to its quality and quantity, therefore, any changes in saliva can lead to diminished quality of patient’s life.

Purpose:

The aim of this study was to determine the relationship between pH and viscosity of cumulative unstimulated saliva and hypertension in adults with sustained hypertension.

Materials and Method:

This cross sectional study took place on patients referred to oral medicine faculty of Shahid Sadoughi University of Medical Science. The patients’ blood pressure was measured and the 135 patients fitting the inclusion criteria participated in the study. Their unstimulated cumulative saliva was collected by spitting method and pH of the samples was measured by digital pH-meter set. The viscosity of the samples was measured by comparing the amount of saliva displacement in the thistle tube with control fluids at mm/10 seconds. The data was analyzed by SPSS version 20 software and ANOVA tests and Tukey multiple comparison and their nonparametric equivalent (p≤ 0.005).

Results:

The results of this study showed that there was a significant relationship between pH and viscosity of unstimulated saliva of normotensive and borderline hypertensive patients (p<.0001and p< .005, respectively) and between normotensive and stage I hypertensive patients (p<.0001, p<0.000). Therefore, hypertension had a direct and significant relationship with saliva viscosity but a reverse relationship with saliva pH.

Conclusion:

Hypertension can reduce the pH and increase the salivary viscosity in hypertensive patients, which subsequently lead to changes in quality and quantity of secreted saliva and influence the oral health and quality of the patient’s life.

Transformation of Nanomaterials and Its Implications in Gut Nanotoxicology

Ingestion of engineered nanomaterials (ENMs) is inevitable due to their widespread utilization in the agrifood industry. Safety evaluation has become pivotal to identify the consequences on human health of exposure to these ingested ENMs. Much of the current understanding of nanotoxicology in the gastrointestinal tract (GIT) is derived from studies utilizing pristine ENMs. In reality, agrifood ENMs interact with their microenvironment, and undergo multiple physicochemical transformations, such as aggregation/agglomeration, dissolution, speciation change, and surface characteristics alteration, across their life cycle from synthesis to consumption. This work sieves out the implications of ENM transformations on their behavior, stability, and reactivity in food and product matrices and through the GIT, in relation to measured toxicological profiles. In particular, a strong emphasis is given to understand the mechanisms through which these transformations can affect ENM induced gut nanotoxicity.

The Food Matrix and the Gastrointestinal Fluids Alter the Features of Silver Nanoparticles

Silver nanoparticles (AgNPs) are used in the agri-food sector, which can lead to their ingestion. Their interaction with food and their passage through the gastrointestinal tract can alter their properties and influence their fate upon ingestion. Therefore, this study aims at developing an in vitro method to follow the fate of AgNPs in the gastrointestinal tract. After incorporation of AgNPs into a standardized food matrix, a precolonic digestion is simulated and AgNPs are characterized by different techniques. The presence of food influences the AgNPs properties by forming a corona around nanoparticles. Even if the salivary step does not impact significantly the AgNPs, the pH decrease and the digestive enzymes induce the agglomeration of AgNPs during the gastric phase, while the addition of intestinal fluids disintegrates these clusters. AgNPs can thus reach the intestinal cells under nanometric form, although the presence of food and gastrointestinal fluids modifies their properties compared to pristine AgNPs. They can form a corona around the nanoparticles and act as colloidal stabilizer, which can impact the interaction of AgNPs with intestinal epithelium. This study demonstrates the importance of taking the fate of AgNPs in the gastrointestinal tract into account to perform an accurate risk assessment of nanomaterials.

Hazard characterization of silver nanoparticles for human exposure routes

Silver nanoparticles (AgNPs) have been widely used for a multitude of applications without full comprehensive knowledge regarding their safety. In particular, lack of data on hazard characterization may lead to uncertainties regarding potential human health risk. To provide the foundation for human health risk assessment of AgNPs, this study evaluates existing hazard characterization data, including reported pharmacokinetics, symptoms, and their corresponding dose-response relationships. Human equivalent relationships are also provided by extrapolation from animal dose-response relationships. From the data analyzed, it appears that AgNPs may persist for long periods (from days to years) in the human body. It was found that AgNP toxicity on traditional major targets of exogenous substances were generally underestimated. Some omissions of toxicity on sensitive systems in the AgNP toxicity assessment require attention, such as reprotoxicity and neurotoxicity. The necessity of the establishment of toxicity tests specifically for nanomaterials is highlighted. The scientific basis of a toxicity testing strategy is advised by this study, which paves the way for the monitoring and regulation of the ENP utilization in various industries.

The complex puzzle of dietary silver nanoparticles, mucus and microbiota in the gut

Hundreds of consumer and commercial products containing silver nanoparticles (AgNPs) are currently used in food, personal-care products, pharmaceutical, and many other applications. Human exposure to AgNPs includes oral intake, inhalation, and dermal contact. The aim of this review was to focus on oral intake, intentional and incidental of AgNPs where well-known antimicrobial characteristics that might affect the microbiome and mucus in the gastrointestinal tract (GIT). This critical review summarizes what is known regarding the impacts of AgNPs on gut homeostasis. It is fundamental to understand the forms of AgNPs and their physicochemical characterization before and during digestion. For example, lab-synthesized AgNPs differ from "real" ingestable AgNPs used as food additives and dietary supplements. Similarly, the gut environment alters the chemical and physical state of Ag that is ingested as AgNPs. Emerging research on in vitro and in vivo rodent and human indicated complex multi-directional relationships among AgNPs, the intestinal microbiota, and the epithelial mucus. It may be necessary to go beyond today's descriptive approach to a modeling-based ecosystem approach that might quantitatively integrate spatio-temporal interactions among microbial groups, host factors (e.g., mucus), and environmental factors, including lifestyle-based stressors. It is suggested that future research (1) utilize more representative AgNPs, focus on microbe/mucus interactions, (2) assess the effects of environmental stressors for longer and longitudinal conditions, and (3) be integrated using quantitative modeling.

Lipoic acid capped silver nanoparticles: a facile route to covalent protein capping and oxidative stability within biological systems

Covalent attachment of human serum albumin protein to the surface of spherical lipoic acid capped silver nanoparticles results in the generation of stable nanoparticle–protein hybrids with well defined surface composition. Enhanced stability towards oxidation and in the presence of complex media with high ionic strength, holds promise towards the use of these conjugates as therapeutics in biomedical applications and sensing.

Covalent attachment of human serum albumin protein to the surface of spherical lipoic acid capped silver nanoparticles results in the generation of stable nanoparticle–protein hybrids with well defined surface composition.

Translocation of transition metal oxide nanoparticles to breast milk and offspring: The necessity of bridging mother-offspring-integration toxicological assessments

Although infant nanomaterial exposure is a worldwide concern, breastfeeding transfer of transition metal-oxide nanoparticles to as well as their toxicity to offspring are still unclear. Breastfeeding transmits nutrition and immunity from mothers to their offspring; it also provides a portal for maternal toxins to enter offspring. Thus, a toxicology assessment of both mothers and their offspring should be established to monitor nanomaterial exposure during lactation. Here, we determined the effects of the exposure route on the biodistribution, biopersistence, and toxicology of nanoparticles (titanium dioxide, zinc oxide, and zirconium dioxide) in both mouse dams and their offspring. Oral and airway exposure routes were tested using gavage and intranasal administration, respectively. Biodistribution in the main organs (breast, liver, spleen, lung, kidney, intestine, and brain) and biopersistence in the blood and milk were determined using inductively coupled plasma mass spectrometry. Hematology and histomorphology analyses were performed to determine the toxicology of the nanoparticles. A reduced offspring body weight was found with the reduced nanoparticle size. Furthermore, both oral and airway exposure increased the nanoparticle concentrations in the main tissues and milk. More nanoparticles were transferred into maternal tissues and milk via airway exposure than via oral exposure. During the transfer of the metal from the exposed nanoparticles to milk, the immune cell pathway played a more important role in the airway route than in the oral exposure route. Finally, maternal exposure via both the oral and airway routes reduced the body weight and survival rate of their breastfeeding offspring, which could possibly be attributed to the toxicity of nanoparticles to blood cells and organs. In conclusion, maternal exposure to nanoparticles led to a reduced body weight and survival rate in breastfed offspring, and nanoparticle exposure via the airway route led to a higher immune response and tissue injury than that via the oral exposure route. This study suggests that the use of products containing metal nanoparticles in breastfeeding mothers and their offspring should be reconsidered to maintain a safe breastfeeding system.

Electrochemical Detection and Quantification of Lithium Ions in Authentic Human Saliva Using LiMn2O4-Modified Electrodes

We report an electrochemical sensor for the detection of lithium ions (Li⁺) in authentic human saliva at lithium manganese oxide (LiMn₂O₄)-modified glassy carbon electrodes (LMO-GCEs) and screen-printed electrodes (LMO-SPEs). The sensing strategy is based on an initial galvanostatic delithiation of LMO followed by linear stripping voltammetry (LSV) to detect the reinsertion of Li⁺ in the analyte. The process was investigated using powder X-ray diffraction and voltammetry. LSV measurements reveal a measurable lower limit of 50.0 μM in both LiClO₄ aqueous solutions and synthetic saliva samples, demonstrating the applicability of the proposed analytical method down to low Li⁺ concentrations. Four different samples of authentic human saliva were then analyzed with the established sensing strategy using LMO-SPEs, showing good linearity over a concentration range up to 5.0 mM Li⁺ with high reproducibility (RSD < 7%) and applicability for routine monitoring purposes. The total time needed to analyze a sample is less than 3 min.

Ultrafine Silver Nanoparticles Embedded in Cyclodextrin Metal-Organic Frameworks with GRGDS Functionalization to Promote Antibacterial and Wound Healing Application

The challenge of bacterial infection increases the risk of mortality and morbidity in acute and chronic wound healing. Silver nanoparticles (Ag NPs) are a promising new version of conventional antibacterial nanosystem to fight against the bacterial resistance in concern of the drug discovery void. However, there are several challenges in controlling the size and colloidal stability of Ag NPs, which readily aggregate or coalesce in both solid and aqueous state. In this study, a template-guided synthesis of ultrafine Ag NPs of around 2 nm using water-soluble and biocompatible γ-cyclodextrin metal-organic frameworks (CD-MOFs) is reported. The CD-MOF based synthetic strategy integrates AgNO₃ reduction and Ag NPs immobilization in one pot achieving dual functions of reduced particle size and enhanced stability. Meanwhile, the synthesized Ag NPs are easily dispersible in aqueous media and exhibit effective bacterial inhibition. The surface modification of cross-linked CD-MOF particles with GRGDS peptide boosts the hemostatic effect that further enhances wound healing in synergy with the antibacterial effect. Hence, the strategy of ultrafine Ag NPs synthesis and immobilization in CD-MOFs together with GRGDS modification holds promising potential for the rational design of effective wound healing devices.

Dissolution and Phosphate-Induced Transformation of ZnO Nanoparticles in Synthetic Saliva Probed by AGNES without Previous Solid-Liquid Separation. Comparison with UF-ICP-MS

The variation over time of free Zn²⁺ ion concentration in stirred dispersions of ZnO nanoparticles (ZnO NPs) prepared in synthetic saliva at pH 6.80 and 37 °C was followed in situ (without solid-liquid separation step) with the electroanalytical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). Under these conditions, ZnO NPs are chemically unstable due to their reaction with phosphates. The initial stage of transformation (around 5-10 h) involves the formation of a metastable solid (presumably ZnHPO₄), which later evolves into the more stable hopeite phase. The overall decay rate of ZnO NPs is significantly reduced in comparison with phosphate-free background solutions of the same ionic strength and pH. The effective equilibrium solubilities of ZnO (0.29-0.47 mg·L^-1), as well as conditional excess-ligand stability constants and fractional distributions of soluble Zn species, were determined in the absence and presence of organic components. The results were compared with the conventional ultrafiltration and inductively coupled plasma-mass spectrometry (UF-ICP-MS) methodology. AGNES proves to be advantageous in terms of speed, reproducibility, and access to speciation information.

Dissolution Behavior and Biodurability of Ingested Engineered Nanomaterials in the Gastrointestinal Environment

Engineered nanomaterials (ENM) are extensively used as food additives in numerous food products, and at present, little is known about the fate of ingested ENM (iENM) in the gastrointestinal (GI) environment. Here, we investigated the dissolution behavior, biodurability, and persistence of four major iENM (TiO₂, SiO₂, ZnO, and two Fe₂O₃) in individual simulated GI fluids (saliva, gastric, and intestinal) and a physiologically relevant digestion cascade (saliva → gastric → intestinal) in the fasted state over physiologically relevant time frames. TiO₂ was found to be the most biodurable and persistent iENM in simulated GI fluids with a maximum of only 0.42% (4 μM Ti⁴⁺ ion release) dissolution in cascade digestion, followed by iron oxides, of which the rod-like morphology was more biodurable and persistent (0.7% maximum dissolution, 8.7 μM Fe³⁺) than the acicular one (2.27% maximum dissolution, 16.7 μM Fe³⁺) in the cascade digestion, respectively. SiO₂ and ZnO were less biodurable than Fe₂O₃, with 65.5% (416 μM Si⁴⁺) and 100% (1718.1 μM Zn²⁺) dissolution in the gastric phase, respectively. In the intestinal phase, however, Si⁴⁺ ions reprecipitated, possibly due to sudden pH changes, while ZnO remained completely dissolved. These observations were also confirmed using high-resolution particle size and concentration, and electron microscopy, time-dependent analysis. In terms of decreasing biodurability and persistence in the simulated GI environment, the tested nanomaterials can be ranked as follows: TiO₂ ≫ rod-like Fe₂O₃ > acicular Fe₂O₃ ≫ SiO₂ > ZnO, which is in agreement with limited animal biokinetics data. Chronic uptake of these iENM as particles or ions by the GI tract, especially in the presence of a food matrix and authentic digestive media, and associated implications for human health warrants further investigation.