Zeta potential is one of the most critical properties of nanomaterials (NMs) which provides an estimation of the surface charge, and therefore electrostatic stability in medium and, in practical ...terms, influences the NM's tendency to form agglomerates and to interact with cellular membranes. This paper describes a robust and accurate read‐across model to predict NM zeta potential utilizing as the input data a set of image descriptors derived from transmission electron microscopy (TEM) images of the NMs. The image descriptors are calculated using NanoXtract (http://enaloscloud.novamechanics.com/EnalosWebApps/NanoXtract/), a unique online tool that generates 18 image descriptors from the TEM images, which can then be explored by modeling to identify those most predictive of NM behavior and biological effects. NM TEM images are used to develop a model for prediction of zeta potential based on grouping of the NMs according to their nearest neighbors. The model provides interesting insights regarding the most important similarity features between NMs—in addition to core composition the main elongation emerged, which links to key drivers of NM toxicity such as aspect ratio. Both the NanoXtract image analysis tool and the validated model for zeta potential (http://enaloscloud.novamechanics.com/EnalosWebApps/ZetaPotential/) are freely available online through the Enalos Nanoinformatics platform.
Enrichment of experimental nanosafety data with computational data is the next frontier of nanosafety. Here, an automated tool for extraction of 18 image nanodescriptors, and their utilization to build a predictive model based on grouping and read‐across from nearest neighbors is presented as part of a toolbox for in silico nanosafety.
Alternate transcripts of the human ether-à-go-go-related gene (hERG1) encode two subunits, hERG 1a and 1b, which form potassium channels regulating cardiac repolarization, neuronal firing frequency, ...and neoplastic cell growth. The 1a and 1b subunits are identical except for their unique, cytoplasmic N termini, and they readily co-assemble in heterologous and native systems. We tested the hypothesis that interactions of nascent N termini promote heteromeric assembly of 1a and 1b subunits. We found that 1a and 1b N-terminal fragments bind in a direct and dose-dependent manner. hERG1 hetero-oligomerization occurs in the endoplasmic reticulum where co-expression of N-terminal fragments with hERG1 subunits disrupted oligomerization and core glycosylation. The disruption of core glycosylation, a cotranslational event, allows us to pinpoint these N-terminal interactions to the earliest steps in biogenesis. Thus, N-terminal interactions mediate hERG 1a/1b assembly, a process whose perturbation may represent a new mechanism for disease.
Engineered nanoparticles (NPs) undergo physical, chemical, and biological transformation after environmental release, resulting in different properties of the “aged” versus “pristine” forms. While ...many studies have investigated the ecotoxicological effects of silver (Ag) NPs, the majority focus on “pristine” Ag NPs in simple exposure media, rather than investigating realistic environmental exposure scenarios with transformed NPs. Here, the effects of “pristine” and “aged” Ag NPs are systematically evaluated with different surface coatings on Daphnia magna over four generations, comparing continuous exposure versus parental only exposure to assess recovery potential for three generations. Biological endpoints including survival, growth and reproduction and genetic effects associated with Ag NP exposure are investigated. Parental exposure to “pristine” Ag NPs has an inhibitory effect on reproduction, inducing expression of antioxidant stress related genes and reducing survival. Pristine Ag NPs also induce morphological changes including tail losses and lipid accumulation associated with aging phenotypes in the heart, abdomen, and abdominal claw. These effects are epigenetic remaining two generations post‐maternal exposure (F2 and F3). Exposure to identical Ag NPs (same concentrations) aged for 6 months in environmentally realistic water containing natural organic matter shows considerably reduced toxicological effects in continuously exposed generations and to the recovery generations.
Environmental aging of Ag NPs, in salt‐only or natural organic matter containing medium, reduces toxicological effects in both continuously exposed and recovery generations of Daphnia magna. Parental exposure to “pristine” Ag NPs causes morphological changes including tail losses and lipid accumulation associated with aging phenotypes as well as inhibiting reproduction, inducing expression of antioxidant stress related genes, and reducing survival.
Mutations in the KCNT1 (Slack, KNa1.1) sodium-activated potassium channel produce severe epileptic encephalopathies. Expression in heterologous systems has shown that the disease-causing mutations ...give rise to channels that have increased current amplitude. It is not known, however, whether such gain of function occurs in human neurons, nor whether such increased KNa current is expected to suppress or increase the excitability of cortical neurons. Using genetically engineered human induced pluripotent stem cell (iPSC)-derived neurons, we have now found that sodium-dependent potassium currents are increased several-fold in neurons bearing a homozygous P924L mutation. In current-clamp recordings, the increased KNa current in neurons with the P924L mutation acts to shorten the duration of action potentials and to increase the amplitude of the afterhyperpolarization that follows each action potential. Strikingly, the number of action potentials that were evoked by depolarizing currents as well as maximal firing rates were increased in neurons expressing the mutant channel. In networks of spontaneously active neurons, the mean firing rate, the occurrence of rapid bursts of action potentials, and the intensity of firing during the burst were all increased in neurons with the P924L Slack mutation. The feasibility of an increased KNa current to increase firing rates independent of any compensatory changes was validated by numerical simulations. Our findings indicate that gain-of-function in Slack KNa channels causes hyperexcitability in both isolated neurons and in neural networks and occurs by a cell-autonomous mechanism that does not require network interactions.
The wide use of titanium dioxide nanoparticles (TiO2 NPs) in industrial applications requires the investigation of their effects on human health. In this context, we investigated the effects of ...nanosized and bulk titania in two different crystalline forms (anatase and rutile) in vitro. By colony forming efficiency assay, a dose-dependent reduction of the clonogenic activity of Balb/3T3 mouse fibroblasts was detected in the presence of rutile, but not in the case of anatase NPs. Similarly, the cell transformation assay and the micronucleus test showed that rutile TiO2 NPs were able to induce type-III foci formation in Balb/3T3 cells and appeared to be slightly genotoxic, whereas anatase TiO2 NPs did not induce any significant neoplastic or genotoxic effect. Additionally, we investigated the interaction of TiO2 NPs with Balb/3T3 cells and quantified the in vitro uptake of titania using mass spectrometry. Results showed that the internalization was independent of the crystalline form of TiO2 NPs but size-dependent, as nano-titania were taken up more than their respective bulk materials.
In conclusion, we demonstrated that the cytotoxic, neoplastic and genotoxic effects triggered in Balb/3T3 cells by TiO2 NPs depend on the crystalline form of the nanomaterial, whereas the internalization is regulated by the particle size.
Summary
Whether the antibacterial properties of silver nanoparticles (AgNPs) are simply due to the release of silver ions (Ag+) or, additionally, nanoparticle‐specific effects, is not clear. We used ...experimental evolution of the model environmental bacterium Pseudomonas putida to ask whether bacteria respond differently to Ag+ or AgNP treatment. We pre‐evolved five cultures of strain KT2440 for 70 days without Ag to reduce confounding adaptations before dividing the fittest pre‐evolved culture into five cultures each, evolving in the presence of low concentrations of Ag+, well‐defined AgNPs or Ag‐free controls for a further 75 days. The mutations in the Ag+ or AgNP evolved populations displayed different patterns that were statistically significant. The non‐synonymous mutations in AgNP‐treated populations were mostly associated with cell surface proteins, including cytoskeletal membrane protein (FtsZ), membrane sensor and regulator (EnvZ and GacS) and periplasmic protein (PP_2758). In contrast, Ag+ treatment was selected for mutations linked to cytoplasmic proteins, including metal ion transporter (TauB) and those with metal‐binding domains (ThiL and PP_2397). These results suggest the existence of AgNP‐specific effects, either caused by sustained delivery of Ag+ from AgNP dissolution, more proximate delivery from cell‐surface bound AgNPs, or by direct AgNP action on the cell's outer membrane.
Mutations in the KCNT1 (Slack, K
1.1) sodium-activated potassium channel produce severe epileptic encephalopathies. Expression in heterologous systems has shown that the disease-causing mutations ...give rise to channels that have increased current amplitude. It is not known, however, whether such gain of function occurs in human neurons, nor whether such increased K
current is expected to suppress or increase the excitability of cortical neurons. Using genetically engineered human induced pluripotent stem cell (iPSC)-derived neurons, we have now found that sodium-dependent potassium currents are increased several-fold in neurons bearing a homozygous P924L mutation. In current-clamp recordings, the increased K
current in neurons with the P924L mutation acts to shorten the duration of action potentials and to increase the amplitude of the afterhyperpolarization that follows each action potential. Strikingly, the number of action potentials that were evoked by depolarizing currents as well as maximal firing rates were increased in neurons expressing the mutant channel. In networks of spontaneously active neurons, the mean firing rate, the occurrence of rapid bursts of action potentials, and the intensity of firing during the burst were all increased in neurons with the P924L Slack mutation. The feasibility of an increased K
current to increase firing rates independent of any compensatory changes was validated by numerical simulations. Our findings indicate that gain-of-function in Slack K
channels causes hyperexcitability in both isolated neurons and in neural networks and occurs by a cell-autonomous mechanism that does not require network interactions.
mutations lead to severe epileptic encephalopathies for which there are no effective treatments. This study is the first demonstration that a
mutation increases the Slack current in neurons. It also provides the first explanation for how this increased potassium current induces hyperexcitability, which could be the underlining factor causing seizures.
Chemotherapy-induced peripheral neuropathy (CIPN) is widely recognized as a potentially severe toxicity that often leads to dose reduction or discontinuation of cancer treatment. Symptoms may persist ...despite discontinuation of chemotherapy and quality of life can be severely compromised. The clinical symptoms of CIPN, and the cellular and molecular targets involved in CIPN, are just as diverse as the wide variety of anticancer agents that cause peripheral neurotoxicity. There is an urgent need for extensive molecular and functional investigations aimed at understanding the mechanisms of CIPN. Furthermore, a reliable human cell culture system that recapitulates the diversity of neuronal modalities found in vivo and the pathophysiological changes that underlie CIPN would serve to advance the understanding of the pathogenesis of CIPN. The demonstration of experimental reproducibility in a human peripheral neuronal cell system will increase confidence that such an in vitro model is clinically useful, ultimately resulting in deeper exploration for the prevention and treatment of CIPN. Herein, we review current in vitro models with a focus on key characteristics and attributes desirable for an ideal human cell culture model relevant for CIPN investigations.
There is a critical need to better define the relationship among particle size, surface area, and dissolution rate for nanoscale materials to determine their role in the environment, their toxicity, ...and their technological utility. Although some previous studies concluded that nanoparticles dissolve faster than their bulk analogs, contradictory evidence suggests that nanoparticles dissolve more slowly. Furthermore, insufficient characterization of the nanoparticulate samples and the solution chemistry in past studies obscures the relationship between particle size, surface area, and dissolution rate. Here we report amorphous SiO2 dissolution rates in aqueous solutions determined from complementary mixed-flow and closed reactor experiments at 6.9 ≥ pH ≥ 11.2 and 25 °C as a function of particle diameter from 25 to 177 nm. Experiments were performed at far-from-equilibrium conditions to isolate kinetic effects from those of changing the reaction driving force on overall dissolution rates. Measured far-from-equilibrium mass normalized dissolution rates are nearly independent of particle size, but corresponding BET surface area normalized rates decrease substantially with decreasing particle size. Combining these observations with existing established kinetic rate equations allows the prediction of nanoparticle dissolution rates as a function of both particle size and aqueous fluid saturation state.
Defects in the trafficking of subunits encoded by the human ether-à-go-go-related gene (hERG1) can lead to catastrophic arrhythmias and sudden cardiac death due to a reduction in IKr-mediated ...repolarization. Native IKr channels are composed of two α subunits, hERG 1a and 1b. In heterologous expression systems, hERG 1b subunits efficiently produce current only in heteromeric combination with hERG 1a. We used Western blot analysis and electrophysiological recordings in HEK-293 cells and Xenopus oocytes to monitor hERG 1b maturation in the secretory pathway and to determine the factors regulating surface expression of hERG 1b subunits. We found that 1b subunits expressed alone were largely retained in the endoplasmic reticulum (ER), thus accounting for the poor functional expression of homomeric 1b currents. Association with hERG 1a facilitated 1b ER export and surface expression. We show that hERG 1b subunits fail to mature because of an “RXR” ER retention signal specific to the 1b N terminus of the human sequence and not conserved in other species. Mutating the RXR facilitated maturation and functional expression of homomeric hERG 1b channels in a charge-dependent manner. Co-expression of the 1b RXR mutants with hERG 1a did not further enhance 1b maturation, suggesting that hERG 1a promotes 1b trafficking by overcoming the RXR-mediated retention. Thus, selective trafficking mechanisms regulate subunit composition of surface hERG channels.
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