Impact of polymer-modified gold nanoparticles on brain endothelial cells: exclusion of endoplasmic reticulum stress as a potential risk factor

Assessing cytotoxicity and endoplasmic reticulum stress in human blood-brain barrier cells due to silver and copper oxide nanoparticles

In recent years, it has been generally accepted that metal-based nanoparticles (NPs) may induce stress in the endoplasmic reticulum (ER), a key organelle where protein folding occurs. We examined ER stress in immortalized human cerebral microvascular cells (hCMEC/D3) after exposure to silver-NPs (Ag-NPs)- and copper oxide-NPs (CuO-NPs) induced toxicity at < 10 nm and < 40 nm or < 50 nm diameters, respectively. In cytotoxicity assessments, cells were exposed to different CuO-NPs (5-400 µg/mL) or Ag-NPs (1-10 µg/mL) concentration ranges for 24 h and 72 h, and tetrazole salt reduction assays (EZ4U) were performed. Also, Ag-NP or CuO-NP effects on cell proliferation, apoptosis (caspase 3/7 assays), and ER stress and cell morphology were evaluated. In ER stress assessments, RNA-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6), inositol-requiring enzyme 1 (IRE1a), and others stress factor mRNA levels were determined after 24 h treatment using Real-Time PCR. Increased stress sensors (IRE1a, PERK, and ATF6) mRNA levels were observed after exposure to Ag-NPs (< 10 and < 40 nm) or CuO-NPs (< 50 nm). We investigated the expression of tight junction (TJ) proteins (barrier junctions) and showed that both types of NP reduced of OCLN gene expression. Morphological changes were observed after Ag-NP or CuO-NP exposure using holotomographic microscopy. Our data suggest that Ag- and CuO-NPs should undergo future in vitro and in vivo toxicology studies, especially for downstream biomedical application and occupational risk assessments.

Toxicity mechanism of nanomaterials: Focus on endoplasmic reticulum stress

Over the years, although the broad application of nanomaterials has not brought convenience to people's life, growing concern surrounds their safety. Recently, much emphasis has been placed on exploring the toxicity mechanism of nanoparticles. Currently established toxic mechanisms include oxidative stress, inflammatory response, autophagy, and DNA damage. In recent years, endoplasmic reticulum stress (ERS) has gained widespread attention as another toxic mechanism of nanomaterials. It is widely acknowledged that the endoplasmic reticulum (ER) is an important site for protein synthesis, and lipids and Ca⁺ storage, playing an esseential role in the normal operation of the body functions. When the body's internal environment is damaged, the structure and function of the endoplasmic reticulum are destroyed, leading to a series of biological reactions called endoplasmic reticulum stress (ERS.) This paper reviews the mechanism of ERS in nanomaterial-associated toxicity. The process of ERS and its related unfolded protein response were briefly introduced, summarizing the factors affecting the nanoparticle ability to induce ERS and expounding on the changes of ER morphology after exposure to nanoparticles. Finally, the specific role and molecular mechanism of ERS under the action of different nanoparticles were comprehensively analyzed, including the relationship between ERS and inflammation, oxidative stress, lipid metabolism and apoptosis. This review provides a foothold for future studies on the toxic mechanism of nanoparticles, and provides novel insights into the safe application of nanoparticles and the treatment of diseases.

Gold nanostructures: synthesis, properties, and neurological applications

Recent advances in technology are expected to increase our current understanding of neuroscience. Nanotechnology and nanomaterials can alter and control neural functionality in both in vitro and in vivo experimental setups. The intersection between neuroscience and nanoscience may generate long-term neural interfaces adapted at the molecular level. Owing to their intrinsic physicochemical characteristics, gold nanostructures (GNSs) have received much attention in neuroscience, especially for combined diagnostic and therapeutic (theragnostic) purposes. GNSs have been successfully employed to stimulate and monitor neurophysiological signals. Hence, GNSs could provide a promising solution for the regeneration and recovery of neural tissue, novel neuroprotective strategies, and integrated implantable materials. This review covers the broad range of neurological applications of GNS-based materials to improve clinical diagnosis and therapy. Sub-topics include neurotoxicity, targeted delivery of therapeutics to the central nervous system (CNS), neurochemical sensing, neuromodulation, neuroimaging, neurotherapy, tissue engineering, and neural regeneration. It focuses on core concepts of GNSs in neurology, to circumvent the limitations and significant obstacles of innovative approaches in neurobiology and neurochemistry, including theragnostics. We will discuss recent advances in the use of GNSs to overcome current bottlenecks and tackle technical and conceptual challenges.

Time-Dependent Internalization of Polymer-Coated Silica Nanoparticles in Brain Endothelial Cells and Morphological and Functional Effects on the Blood-Brain Barrier

Nanoparticle (NP)-assisted procedures including laser tissue soldering (LTS) offer advantages compared to conventional microsuturing, especially in the brain. In this study, effects of polymer-coated silica NPs used in LTS were investigated in human brain endothelial cells (ECs) and blood-brain barrier models. In the co-culture setting with ECs and pericytes, only the cell type directly exposed to NPs displayed a time-dependent internalization. No transfer of NPs between the two cell types was observed. Cell viability was decreased relatively to NP exposure duration and concentration. Protein expression of the nuclear factor ĸ-light-chain-enhancer of activated B cells and various endothelial adhesion molecules indicated no initiation of inflammation or activation of ECs after NP exposure. Differentiation of CD34+ ECs into brain-like ECs co-cultured with pericytes, blood-brain barrier (BBB) characteristics were obtained. The established endothelial layer reduced the passage of integrity tracer molecules. NP exposure did not result in alterations of junctional proteins, BBB formation or its integrity. In a 3-dimensional setup with an endothelial tube formation and tight junctions, barrier formation was not disrupted by the NPs and NPs do not seem to cross the blood-brain barrier. Our findings suggest that these polymer-coated silica NPs do not damage the BBB.

Carbon nanoparticles induce endoplasmic reticulum stress around blood vessels with accumulation of misfolded proteins in the developing brain of offspring

Nano-particulate air pollution threatens developing brains and is epidemiologically related to neurodegenerative diseases involving deposition of misfolded proteins. However, the mechanism underlying developmental neurotoxicity by nanoparticles remains unknown. Here, we report that maternal exposure to low doses of carbon black nanoparticle (CB-NP) induces endoplasmic reticulum (ER) stress associated with accumulation of misfolded proteins. Notably, offspring specifically showed high induction of ER stress in perivascular macrophages and reactive astrocytes only around brain blood vessels, along with accumulation of β-sheet-rich proteins regarded as misfolded proteins. Our results suggest that maternal CB-NP exposure induced ER stress in PVMs and reactive astrocytes around blood vessels in the brain of offspring in mice. The induction of ER stress accompanied by the perivascular accumulation of misfolded proteins is likely to be associated with perivascular abnormalities and neurodegeneration, and development of neurodegenerative diseases related to particulate air pollution.

Gold nanourchins induce cellular stress, impair proteostasis and damage RNA

Gold nanoparticles have excellent potential for theranostic applications, but their impact on living cells is only partially understood. Many gold nanoparticles enter cells through endosomes/lysosomes which are linked to different cell organelles and compartments. Our study focuses on the unfolded protein response (UPR) in the endoplasmic reticulum (ER), cytoplasmic RNA-granules and proteostasis, because they are established indicators of cell stress and key regulators of cellular homeostasis. Using HeLa and renal proximal tubule cells as model systems, we show that gold nanourchins reduce cell proliferation, cause ER stress and impair proteostasis. Specifically, gold nanourchins activate the PERK-branch of the UPR, promote RNA oxidation, enhance P-body formation, and accumulate the oxidative stress marker Nrf2 and NFκB in nuclei. Taken together, our study demonstrates that gold nanourchins compromise ER, redox, protein, and RNA homeostasis. These insights provide new information on the cellular responses and molecular changes that gold nanourchins elicit in mammalian cells.

Toxic effects and involved molecular pathways of nanoparticles on cells and subcellular organelles

Owing to the increasing application of engineered nanoparticles (NPs), besides the workplace, human beings are also exposed to NPs from nanoproducts through the skin, respiratory tract, digestive tract and vein injection. This review states pathways of cellular uptake, subcellular distribution and excretion of NPs. The uptake pathways commonly include phagocytosis, micropinocytosis, clathrin- and caveolae-mediated endocytosis, scavenger receptor-related pathway, clathrin- or caveolae-independent pathway, and direct penetration or insertion. Then the ability of NPs to decrease cell viability and metabolic activity, change cell morphology, and destroy cell membrane, cytoskeleton and cell function was presented. In addition, the lowest dose decreasing cell metabolic viability compared with the control or IC₅₀ of silver, titanium dioxide, zinc oxide, carbon black, carbon nanotubes, silica, silicon NPs and cadmium telluride quantum dots to some cell lines was gathered. Next, this review attempts to increase our understanding of NP-caused adverse effects on organelles, which have implications in mitochondrial dysfunction, endoplasmic reticulum stress and lysosomal rupture. In particular, the disturbance of mitochondrial biogenesis and mitochondrial dynamic fusion-fission, mitophagy and cytochrome c-dependent apoptosis are involved. In addition, prolonged endoplasmic reticulum stress will result in apoptosis. Rupture of the lysosomal membrane was associated with inflammation, and both induction of autophagy and blockade of autophagic flow can result in cytotoxicity. Finally, the network mechanism of the combined action of multiple organelle dysfunction, apoptosis, autophagy and oxidative stress was discussed.

A multiparametric study of gold nanoparticles cytotoxicity, internalization and permeability using an in vitro model of blood-brain barrier. Influence of size, shape and capping agent

Gold nanoparticles (AuNPs) have biomedical application on imaging and due to increased optical performance, star-shaped AuNPs are of special interest. Because shape, size and capping greatly influence their toxicokinetics and toxicodynamics, a systematic multiparametric comparative study of the influence of these parameters on the cytotoxicity, internalization, and in vitro permeability was conducted in human Cerebral Microvascular Endothelial Cell line (hCMEC/D3), an in vitro model of the human blood-brain barrier (BBB). AuNPs of different size (14 nm and ∼50 nm), shape (spheres and stars), and coating (11-mercaptoundecanoic acid or MUA and sodium citrate) were synthesized and fully characterized. The time- and concentration-dependent cytotoxic profile of the tested AuNPs differed for the different AuNPs. Generally, toxicity was greater for stars relative to sphere-shaped AuNPs, and citrate coating was more toxic than MUA. Regarding the influence of size, smaller-sized AuNPs were more cytotoxic when compared at the same Au concentration. However, when the concentration of AuNPs was expressed as the number of AuNPs/mL, a higher degree of cytotoxicity was noted for the larger ̴50 nm AuNPs. To understand the influence of size, shape and capping, a systematic study design, in which only one of the variables changes, is determinant for correct data interpretation. Considering the results herein presented, for the sake of comparison of differently-sized AuNPs, it is preferable to design the study based upon the number of nanoparticles, since at a fixed Au concentration the number of particles available to promote effect is higher for smaller-sized AuNPs. Cellular internalization also differed among the tested AuNPs; although all were unable to cross the in vitro BBB, the intracellularly accumulated AuNPs can induce cell damage and later compromise BBB integrity and permeability.

Surface modification of gold nanoparticles with neuron-targeted exosome for enhanced blood-brain barrier penetration

Gold nanoparticles (AuNPs) have been extensively used as nanomaterials for theranostic applications due to their multifunctional characteristics in therapeutics, imaging, and surface modification. In this study, the unique functionalities of exosome-derived membranes were combined with synthetic AuNPs for targeted delivery to brain cells. Here, we report the surface modification of AuNPs with brain-targeted exosomes derived from genetically engineered mammalian cells by using the mechanical method or extrusion to create these novel nanomaterials. The unique targeting properties of the AuNPs after fabrication with the brain-targeted exosomes was demonstrated by their binding to brain cells under laminar flow conditions as well as their enhanced transport across the blood brain barrier. In a further demonstration of their ability to target brain cells, in vivo bioluminescence imaging revealed that targeted-exosome coated AuNPs accumulated in the mouse brain after intravenous injection. The surface modification of synthetic AuNPs with the brain-targeted exosome demonstrated in this work represents a highly novel and effective strategy to provide efficient brain targeting and shows promise for the future in using modified AuNPs to penetrate the brain.

Silica nanoparticles promote oxLDL-induced macrophage lipid accumulation and apoptosis via endoplasmic reticulum stress signaling

Oxidized low-density lipoprotein (oxLDL), a marker of hyperlipidemia, plays a pivotal role in the development of atherosclerosis through the induction of macrophage-derived foam cell formation and thereafter apoptosis. Previous studies have indicated that silica nanoparticle (SiNPs) may exert a proatherogenic role, which could induce endothelial dysfunction, and monocytes infiltration. However, little is known about SiNPs' effects on macrophage-derived foam cell formation and apoptosis in the pathogenesis of atherosclerosis. In this study, we investigated the effects of SiNPs and oxLDL coexposure on macrophage-derived lipid metabolism, foam cell and apoptosis by using Raw264.7 cells. As a result, SiNPs enhanced cytotoxicity, apoptosis, and lipid accumulation upon oxLDL stimulation. Furthermore, quantitative determination of the expression levels of genes involved in cholesterol influx or efflux showed significantly up-regulated expressions of CD36 and SRA, whereas down-regulated expressions of ATP-binding cassette A1 (ABCA1), ABCG1, and SRB1 in oxLDL-treated macrophages, especially upon the co-exposure with SiNPs. It indicated that SiNPs promoted lipid accumulation in macrophage cells through not only facilitating cholesterol influx but also inhibiting cholesterol efflux. Endoplasmic reticulum (ER) is specialized for the production, modification, even trafficking of lipids. Interestingly, ER response was triggered upon oxLDL treatment, while SiNPs coexposure augmented the ER stress. Taken together, our results revealed that SiNPs promoted oxLDL-induced macrophage foam cell formation and apoptosis, which may be mediated by ER stress signaling. Thus we propose future researches needed for a better understanding of NPs' toxicity and their interactions with various pathophysiological conditions.

Gold nanoparticle interactions with endothelial cells cultured under physiological conditions

PEGylated gold nanoparticles (AuNPs) have an extended circulation time after intravenous injection in vivo and exhibit favorable properties for biosensing, diagnostic imaging, and cancer treatment. No impact of PEGylated AuNPs on the barrier forming properties of endothelial cells (ECs) has been reported, but recent studies demonstrated that unexpected effects on erythrocytes are observed. Almost all studies to date have been with static-cultured ECs. Herein, ECs maintained under physiological cyclic stretch and flow conditions and used to generate a blood-brain barrier model were exposed to 20 nm PEGylated AuNPs. An evaluation of toxic effects, cell stress, the release profile of pro-inflammatory cytokines, and blood-brain barrier properties showed that even under physiological conditions no obvious effects of PEGylated AuNPs on ECs were observed. These findings suggest that 20 nm-sized, PEGylated AuNPs may be a useful tool for biomedical applications, as they do not affect the normal function of healthy ECs after entering the blood stream.

A review of endoplasmic reticulum (ER) stress and nanoparticle (NP) exposure

Understanding the mechanism of nanoparticle (NP) induced toxicity is important for nanotoxicological and nanomedicinal studies. Endoplasmic reticulum (ER) is a crucial organelle involved in proper protein folding. High levels of misfolded proteins in the ER could lead to a condition termed as ER stress, which may ultimately influence the fate of cells and development of human diseases. In this review, we summarized studies about effects of NP exposure on ER stress. A variety of NPs, especially metal-based NPs, could induce morphological changes of ER and activate ER stress pathway both in vivo and in vitro. In addition, modulation of ER stress by chemicals has been shown to alter the toxicity of NPs. These studies in combination suggested that ER stress could be the mechanism responsible for NP induced toxicity. Meanwhile, nanomedicinal studies also used ER stress inducing NPs or NPs loaded with ER stress inducer to selectively induce ER stress mediated apoptosis in cancer cells for cancer therapy. In contrast, alleviation of ER stress by NPs has also been shown as a strategy to cure metabolic diseases. In conclusion, exposure to NPs may modulate ER stress, which could be a target for future nanotoxicological and nanomedicinal studies.