The inhibitory effects of nano-Ag on voltage-gated potassium currents of hippocampal CA1 neurons

Multifaceted Regulation of Potassium-Ion Channels by Graphene Quantum Dots

Graphene quantum dots (GQDs) are emerging as a versatile nanomaterial with numerous proposed biomedical applications. Despite the explosion in potential applications, the molecular interactions between GQDs and complex biomolecular systems, including potassium-ion (K+) channels, remain largely unknown. Here, we use molecular dynamics (MD) simulations and electrophysiology to study the interactions between GQDs and three representative K+ channels, which participate in a variety of physiological processes and are closely related to many disease states. Using MD simulations, we observed that GQDs adopt distinct contact poses with each of the three structurally distinct K+ channels. Our electrophysiological characterization of the effects of GQDs on channel currents revealed that GQDs interact with the extracellular voltage-sensing domain (VSD) of a Kv1.2 channel, augmenting current by left-shifting the voltage dependence of channel activation. In contrast, GQDs form a "lid" cluster over the extracellular mouth of inward rectifier Kir3.2, blocking the channel pore and decreasing the current in a concentration-dependent manner. Meanwhile, GQDs accumulate on the extracellular "cap domain" of K2P2 channels and have no apparent impact on the K+ flux through the channel. These results reveal a surprising multifaceted regulation of K+ channels by GQDs, which might help de novo design of nanomaterial-based channel probe openers/inhibitors that can be used to further discern channel function.

Real-time fluorescence measurement of spontaneous activity in a high-density hippocampal network cultivated on a plasmonic dish

High-density cultured neuronal networks have been used to evaluate synchronized features of neuronal populations. Voltage-sensitive dye (VSD) imaging of a dissociated cultured neuronal network is a critical method for studying synchronized neuronal activity in single cells. However, the signals of VSD are generally too faint-that is, the signal-to-noise ratio (S/N) is too low-to detect neuronal activity. In our previous research, a silver (Ag) plasmonic chip enhanced the fluorescence intensity of VSD to detect spontaneous neural spikes on VSD imaging. However, no high-density network was cultivated on the Ag plasmonic chip, perhaps because of the chemical instability of the Ag surface. In this study, to overcome the instability of the chip, we used a chemically stable gold (Au) plasmonic dish, which was a plastic dish with a plasmonic chip pasted to the bottom, to observe neuronal activity in a high-density neuronal network. We expected that the S/N in real-time VSD imaging of the Au plasmonic chip would be improved compared to that of a conventional glass-bottomed dish, and we also expected to detect frequent neural spikes. The increase in the number of spikes when inhibitory neurotransmitter receptors were inhibited suggests that the spikes corresponded to neural activity. Therefore, real-time VSD imaging of an Au plasmonic dish was effective for measuring spontaneous network activity in a high-density neuronal network at the spatial resolution of a single cell.

Effect of Titanium Particles on the Voltage-Gated Potassium Channel Currents in Trigeminal Root Ganglion Neurons

PURPOSE

Titanium (Ti) is the key material used in dental implants because of its excellent biocompatibility. But wear and corrosion Ti particles had been widely reported to induce inflammation and promote bone absorption. However, little information is known about the damage of Ti particles on neurons.

MATERIALS AND METHODS

Trigeminal root ganglion (TRG) neurons were exposed to Ti particles (<5 μm). The electrophysiological properties of 2 main subtypes of voltage-gated potassium channels (VGPCs) (KA and KV) were examined by whole-cell patch-clamp techniques.

RESULT

With the presence of 0.25 mg/mL Ti particles, amplitudes of IK, A and IK, V were both obviously inhibited. For IK, A, the activation V1/2 shifted to the depolarizing direction with an increased k value, whereas the inactivation V1/2 showed obvious hyperdepolarizing shifts. For IK, V, 0.5 mg/mL Ti particles produced a depolarizing shift of activation V1/2 with a slower activation rate. No significant changes of its inactivation kinetics were found.

CONCLUSION

Titanium (Ti) particles might alter the electrophysiological properties of VGPCs on TRG neurons, which are likely to further influence the excitability of neurons.

Gold nanoparticles potentiate CaV channel currents in rat tail artery myocytes

This study was designed to unveil effects of 5-nm sized, polyvinylpyrrolidone-coated gold nanoparticles (AuNPs) on vascular Ca_V1.2 and Ca_V3.1 channels. Ba²⁺ currents through both channels (I_Ba1.2 and I_Ba3.1) were recorded in single myocytes isolated from the rat tail main artery by means of the whole-cell patch-clamp method. AuNPs increased I_Ba1.2 and I_Ba3.1 amplitude in a concentration- and V_h-dependent manner. Neither the voltage dependence of inactivation and activation curves nor inactivation and activation kinetics were affected by AuNPs. In conclusion, these findings warrant further investigation to clarify whether different types of NPs possess the same stimulatory activity and may represent a toxic hazard to humans.

The acute toxic effects of silver nanoparticles on myocardial transmembrane potential, INa and IK1 channels and heart rhythm in mice

This study focused on the potential toxicity of silver nanoparticles (AgNPs) on cardiac electrophysiology which is rarely investigated. We found that AgNPs (10^-9-10^-6g/ml) concentration-dependently depolarized the resting potential, diminished the action potential, and finally led to loss of excitability in mice cardiac papillary muscle cells in vitro. In cultured neonatal mice cardiomyocytes, AgNPs (10^-9-10^-7g/ml) concentration-dependently decreased the Na⁺ currents (I_Na), accelerated the activation, and delayed the inactivation and recovery of Na⁺ channels from inactivation within 5 min. AgNPs at 10^-8g/ml also rapidly decreased the inwardly rectifying K⁺ currents (I_K1) and delayed the activation of I_K1 channels. Intravenous injection of AgNPs at 3 mg/kg only decreased the heart rate, while at ≥4 mg/kg sequentially induced sinus bradycardia, complete atrio-ventricular conduction block, and cardiac asystole. AgNPs at 10^-10-10^-6g/ml did not increase reactive oxygen species (ROS) generation and only at 10^-6g/ml mildly induced lactate dehydrogenase (LDH) release in the cardiomyocytes within 5 min. Endocytosis of AgNPs by cardiomyocytes was not observed within 5 min, but was observed 1 h after exposing to AgNPs. Comparative Ag⁺ (≤0.02% of the AgNPs) could not induce above toxicities. We conclude that AgNPs exert rapid toxic effects on myocardial electrophysiology and induce lethal bradyarrhythmias. These acute toxicities are likely due to direct effects of AgNPs on ion channels at the nano-scale level, but not caused by Ag⁺, ROS, and membrane injury. These findings provide warning to the nanomedical practice using AgNPs.

Characterisation of the Chemical Composition and Structural Features of Novel Antimicrobial Nanoparticles

Three antimicrobial nanoparticle types (AMNP0, AMNP1, and AMNP2) produced using the Tesima^TM thermal plasma technology were investigated and their compositions were determined using a combination of analytical methods. Scanning electron micrographs provided the morphology of these particles with observed sizes ranging from 10 to 50 nm, whilst FTIR spectra confirmed the absence of polar bonds and organic impurities, and strong Raman active vibrational bands at ca. 1604 and 1311 cm^-1 ascribed to C-C vibrational motions were observed. Carbon signals that resonated at δ_C 126 ppm in the solid state NMR spectra confirmed that sp² hybridised carbons were present in high concentration in two of the nanoparticle types (AMNP1 and AMNP2). X-ray powder diffraction suggested that AMNP0 contains single phase Tungsten carbide (WC) in a high state of purity and multiple phases of WC/WC_1-x were identified in both AMNP1 and AMNP2. Finally, X-ray photoelectron spectral (XPS) analyses revealed and quantified the elemental ratios in these composite formulations.

Effects of silver nanoparticles on the interactions of neuron- and glia-like cells: Toxicity, uptake mechanisms, and lysosomal tracking

Silver nanoparticles (AgNPs) are commonly used nanomaterials in consumer products. Previous studies focused on its effects on neurons; however, little is known about their effects and uptake mechanisms on glial cells under normal or activated states. Here, ALT astrocyte-like, BV-2 microglia and differentiated N2a neuroblastoma cells were directly or indirectly exposed to 10 nm AgNPs using mono- and co-culture system. A lipopolysaccharide (LPS) was pretreated to activate glial cells before AgNP treatment for mimicking NP exposure under brain inflammation. From mono-culture, ALT took up the most AgNPs and had the lowest cell viability within three cells. Moreover, AgNPs induced H₂ O₂ and NO from ALT/activated ALT and BV-2, respectively. However, AgNPs did not induce cytokines release (IL-6, TNF-α, MCP-1). LPS-activated BV-2 took up more AgNPs than normal BV-2, while the induction of ROS and cytokines from activated cells were diminished. Ca²⁺ -regulated clathrin- and caveolae-independent endocytosis and phagocytosis were involved in the AgNP uptake in ALT, which caused more rapid NP translocation to lysosome than in macropinocytosis and clathrin-dependent endocytosis-involved BV-2. AgNPs directly caused apoptosis and necrosis in N2a cells, while by indirect NP exposure to bottom chamber ALT or BV-2 in Transwell, more apoptotic upper chamber N2a cells were observed. Cell viability of BV-2 also decreased in an ALT-BV-2 co-culturing study. The damaged cells correlated to NP-mediated H₂ O₂ release from ALT or NO from BV-2, which indicates that toxic response of AgNPs to neurons is not direct, but indirectly arises from AgNP-induced soluble factors from other glial cells.

Resveratrol Attenuates Aβ-Induced Early Hippocampal Neuron Excitability Impairment via Recovery of Function of Potassium Channels

Alzheimer's disease (AD) is an age-related neurodegenerative disease. Amyloid-β (Aβ) is not only the morphological hallmark but also the initiator of the pathology process of AD. As a natural compound found in grapes, resveratrol shows a protective effect on the pathophysiology of AD, but the underlying mechanism is not very clear. This study was to investigate whether resveratrol could attenuate Aβ-induced early impairment in hippocampal neuron excitability and the underlying mechanism. The excitability and voltage-gated potassium currents were examined in rat hippocampal CA1 pyramidal neurons by using whole-cell patch-clamp technique. It was found that Aβ_25-35 increased the excitability of neurons. Resveratrol could reverse the Aβ_25-35-induced increase in the frequency of repetitive firing and the spike half-width of action potential (AP). Moreover, resveratrol can attenuate Aβ_25-35-induced decreases in transient potassium channel (I _A ) and delay rectifier potassium channel (I _K(DR)) of neurons. It was also found that resveratrol could decline the increase of protein kinase A (PKA) and inhibit the activation of PI3K/Akt signaling pathway induced by Aβ_25-35. The results suggest that resveratrol alleviates Aβ_25-35-induced dysfunction in hippocampal CA1 pyramidal neurons via recovery of the function of I _A and I _K(DR) by inhibiting the increase of PKA and the activation of PI3K/Akt signaling pathway.

Silver nanoparticles exhibit coating and dose-dependent neurotoxicity in glutamatergic neurons derived from human embryonic stem cells

Silver nanoparticles (AgNPs) are used extensively as anti-microbial agents in various products, but little is known about their potential neurotoxic effects. In this study, we used glutamatergic neurons derived from human embryonic stem cells as a cellular model to study 20nm citrate-coated AgNPs (AgSCs) and Polyvinylpyrrolidone-coated AgNPs (AgSPs) induced neurotoxicity. AgSCs significantly damaged neurite outgrowths; increased the production of reactive oxygen species and Ca²⁺ influxes; reduced the expression of MAP2, PSD95, vGlut1 and NMDA receptor proteins at concentrations as low as 0.1μg/ml. In contrast, AgSPs exhibited neurotoxicity only at higher concentration. Furthermore, our results showed that AgSCs induced glutamate excitotoxicity by the activation of calmodulin and the induction of nitric oxide synthase; increased the phosphorylation of glycogen synthase kinase-3 α/β at Tyr²¹⁶ and Tau at Ser³⁹⁶ and reduced the expression of Tau46, which are typically observed in Alzheimer's disease. This study indicated that stem cells can provide an excellent platform for studying nanoparticle induced neurotoxicity.

Prenatal Exposure to Silver Nanoparticles Causes Depression Like Responses in Mice

Despite increasing studies on silver nanoparticles, their mechanism of action is not so clear, especially their probable toxicity on reproduction procedure, developmental process and offspring behavior. Therefore in the present study the effect of silver nanoparticles exposure during gestational period on offspring's depression behavior was assessed. Thirty virgin female mice were divided into three groups (n=10 for each group) including: one control and two experimental groups, which received an equal volume (0.2 ml) of suspension containing 0, 0.2 and 2 mg/kg of silver nanoparticles, respectively. After mating, the suspension was injected and repeated every 3 days till accouchement. Depression behaviors were assessed by tail suspension test and forced swimming test, in 45-day-old male and female progenies (6 groups, n=10). In males, both dose of silver nanoparticles (0.2 and 2 mg/kg) decreased mobility and increased immobility time in forced swimming test (P<0.05), but in female no effects were observed in mobility and immobility time. In tail suspension test, 2 mg/kg of silver nanoparticles lead to decrease of mobility time (P<0.05) and increase of immobility time (P<0.05) in female offspring but in males no significant effect was observed on mobility and immobility time. We may concluded that the prenatal exposure to silver nanoparticles probably cause gender-specific depression like behaviors in offspring, possibly through neurotoxic effect during neuronal development.

Silver and gold nanoparticles exposure to in vitro cultured retina--studies on nanoparticle internalization, apoptosis, oxidative stress, glial- and microglial activity

The complex network of neuronal cells in the retina makes it a potential target of neuronal toxicity – a risk factor for visual loss. With growing use of nanoparticles (NPs) in commercial and medical applications, including ophthalmology, there is a need for reliable models for early prediction of NP toxicity in the eye and retina. Metal NPs, such as gold and silver, gain much of attention in the ophthalmology community due to their potential to cross the barriers of the eye. Here, NP uptake and signs of toxicity were investigated after exposure to 20 and 80 nm Ag- and AuNPs, using an in vitro tissue culture model of the mouse retina. The model offers long-term preservation of retinal cell types, numbers and morphology and is a controlled system for delivery of NPs, using serum-free defined culture medium. AgNO₃-treatment was used as control for toxicity caused by silver ions. These end-points were studied; gross morphological organization, glial activity, microglial activity, level of apoptosis and oxidative stress, which are all well described as signs of insult to neural tissue. TEM analysis demonstrated cellular- and nuclear uptake of all NP types in all neuronal layers of the retina. Htx-eosin staining showed morphological disruption of the normal complex layered retinal structure, vacuole formation and pyknotic cells after exposure to all Ag- and AuNPs. Significantly higher numbers of apoptotic cells as well as an increased number of oxidative stressed cells demonstrated NP-related neuronal toxicity. NPs also caused increased glial staining and microglial cell activation, typical hallmarks of neural tissue insult. This study demonstrates that low concentrations of 20 and 80 nm sized Ag- and AuNPs have adverse effects on the retina, using an organotypic retina culture model. Our results motivate careful assessment of candidate NP, metallic or-non-metallic, to be used in neural systems for therapeutic approaches.

Multi-walled carbon nanotube inhibits CA1 glutamatergic synaptic transmission in rat's hippocampal slices

The purpose of the study was to investigate the neurotoxic effect of multi-walled carbon nanotubes (MWCNTs) on the properties of glutamatergic synaptic transmission in rat's hippocampal slices using whole-cell patch clamp technique. The amplitude and frequency of excitatory postsynaptic current (EPSC) were accessed on the hippocampal pyramidal neurons. The alterations of glutamatergic synaptic transmission in CA3-CA1 were examined by measuring both the amplitude of evoked excitatory postsynaptic current (eEPSC) and paired-pulse ratio (PPR). The data showed that the amplitude of either spontaneous excitatory postsynaptic current (sEPSC) or miniature excitatory postsynaptic current (mEPSC) was significantly inhibited by 1 μg/mL MWCNTs. However, it was found that there was a trend of different change on the frequency index. When 1 μg/mL MWCNTs was applied, there were a decreased frequency of mEPSC and an increased frequency of sEPSC, which might be due to the effect of action potential. Furthermore, the amplitudes of eEPSC at CA3-CA1 synapses were remarkably decreased. And the mean amplitude of AMPAR-mediated eEPSC was significantly reduced as well. Meanwhile, a majority of PPRs data were greater than one. There were no significant differences of PPRs between control and MWCNTs states, but an increased trend of paired-pulse facilitation was found. These results suggested that MWCNT markedly inhibited hippocampal CA1 glutamatergic synaptic transmission in vitro, which provided new insights into the MWCNT toxicology on CNS at cellular level.

Assessment of cellular responses after short- and long-term exposure to silver nanoparticles in human neuroblastoma (SH-SY5Y) and astrocytoma (D384) cells

Silver nanoparticle (AgNP, 20 nm) neurotoxicity was evaluated by an integrated in vitro testing protocol employing human cerebral (SH-SY5Y and D384) cell lines. Cellular response after short-term (4-48 h, 1-100 μ g/ml) and prolonged exposure (up to 10 days, 0.5-50 μ g/ml) to AgNP was assessed by MTT, calcein-AM/PI, clonogenic tests. Pulmonary A549 cells were employed for data comparison along with silver nitrate as metal ionic form. Short-term data: (i) AgNP produced dose- and time-dependent mitochondrial metabolism changes and cell membrane damage (effects starting at 25 μ g/ml after 4 h: EC50s were 40.7 ± 2.0 and 49.5 ± 2.1 μ g/ml for SH-SY5Y and D384, respectively). A549 were less vulnerable; (ii) AgNP doses of ≤ 18 μ g/ml were noncytotoxic; (iii) AgNO3 induced more pronounced effects compared to AgNP on cerebral cells. Long-term data: (i) low AgNP doses (≤ 1 μ g/ml) compromised proliferative capacity of all cell types (cell sensibility: SHSY5Y > A549 > D384). Colony number decrease in SH-SY5Y and D384 was 50% and 25%, respectively, at 1 μ g/ml, and lower dose (0.5 μ g/ml) was significantly effective towards SH-SY5Y and pulmonary cells; (ii) cell proliferation activity was more affected by AgNO3 than AgNPs. In summary, AgNP-induced cytotoxic effects after short-term and prolonged exposure (even at low doses) were evidenced regardless of cell model types.

Estimating the modulatory effects of nanoparticles on neuronal circuits using computational upscaling

BACKGROUND

Beside the promising application potential of nanotechnologies in engineering, the use of nanomaterials in medicine is growing. New therapies employing innovative nanocarrier systems to increase specificity and efficacy of drug delivery schemes are already in clinical trials. However the influence of the nanoparticles themselves is still unknown in medical applications, especially for complex interactions in neural systems. The aim of this study was to investigate in vitro effects of coated silver nanoparticles (cAgNP) on the excitability of single neuronal cells and to integrate those findings into an in silico model to predict possible effects on neuronal circuits.

METHODS

We first performed patch clamp measurements to investigate the effects of nanosized silver particles, surrounded by an organic coating, on excitability of single cells. We then determined which parameters were altered by exposure to those nanoparticles using the Hodgkin-Huxley model of the sodium current. As a third step, we integrated those findings into a well-defined neuronal circuit of thalamocortical interactions to predict possible changes in network signaling due to the applied cAgNP, in silico.

RESULTS

We observed rapid suppression of sodium currents after exposure to cAgNP in our in vitro recordings. In numerical simulations of sodium currents we identified the parameters likely affected by cAgNP. We then examined the effects of such changes on the activity of networks. In silico network modeling indicated effects of local cAgNP application on firing patterns in all neurons in the circuit.

CONCLUSION

Our sodium current simulation shows that suppression of sodium currents by cAgNP results primarily by a reduction in the amplitude of the current. The network simulation shows that locally cAgNP-induced changes result in changes in network activity in the entire network, indicating that local application of cAgNP may influence the activity throughout the network.

Silver nanoparticles (AgNPs) cause degeneration of cytoskeleton and disrupt synaptic machinery of cultured cortical neurons

BACKGROUND

Silver nanoparticles (AgNPs), owing to their effective antimicrobial properties, are being widely used in a broad range of applications. These include, but are not limited to, antibacterial materials, the textile industry, cosmetics, coatings of various household appliances and medical devices. Despite their extensive use, little is known about AgNP safety and toxicity vis-à-vis human and animal health. Recent studies have drawn attention towards potential neurotoxic effects of AgNPs, however, the primary cellular and molecular targets of AgNP action/s remain to be defined.

RESULTS

Here we examine the effects of ultra fine scales (20 nm) of AgNPs at various concentrations (1, 5, 10 and 50 μg/ml) on primary rat cortical cell cultures. We found that AgNPs (at 1-50 μg/ml) not only inhibited neurite outgrowth and reduced cell viability of premature neurons and glial cells, but also induced degeneration of neuronal processes of mature neurons. Our immunocytochemistry and confocal microscopy studies further demonstrated that AgNPs induced the loss of cytoskeleton components such as the β-tubulin and filamentous actin (F-actin). AgNPs also dramatically reduced the number of synaptic clusters of the presynaptic vesicle protein synaptophysin, and the postsynaptic receptor density protein PSD-95. Finally, AgNP exposure also resulted in mitochondria dysfunction in rat cortical cells.

CONCLUSIONS

Taken together, our data show that AgNPs induce toxicity in neurons, which involves degradation of cytoskeleton components, perturbations of pre- and postsynaptic proteins, and mitochondrial dysfunction leading to cell death. Our study clearly demonstrates the potential detrimental effects of AgNPs on neuronal development and physiological functions and warns against its prolific usage.

Gold- and silver nanoparticles affect the growth characteristics of human embryonic neural precursor cells

Rapid development of nanotechnologies and their applications in clinical research have raised concerns about the adverse effects of nanoparticles (NPs) on human health and environment. NPs can be directly taken up by organs exposed, but also translocated to secondary organs, such as the central nervous system (CNS) after systemic- or subcutaneous administration, or via the olfactory system. The CNS is particularly vulnerable during development and recent reports describe transport of NPs across the placenta and even into brain tissue using in vitro and in vivo experimental systems. Here, we investigated whether well-characterized commercial 20 and 80 nm Au- and AgNPs have an effect on human embryonic neural precursor cell (HNPC) growth. After two weeks of NP exposure, uptake of NPs, morphological features and the amount of viable and dead cells, proliferative cells (Ki67 immunostaining) and apoptotic cells (TUNEL assay), respectively, were studied. We demonstrate uptake of both 20 and 80 nm Au- and AgNPs respectively, by HNPCs during proliferation. A significant effect on the sphere size- and morphology was found for all cultures exposed to Au- and AgNPs. AgNPs of both sizes caused a significant increase in numbers of proliferating and apoptotic HNPCs. In contrast, only the highest dose of 20 nm AuNPs significantly affected proliferation, whereas no effect was seen on apoptotic cell death. Our data demonstrates that both Au- and AgNPs interfere with the growth profile of HNPCs, indicating the need of further detailed studies on the adverse effects of NPs on the developing CNS.

Effects of silver nanoparticles on primary mixed neural cell cultures: uptake, oxidative stress and acute calcium responses

In the body, nanoparticles can be systemically distributed and then may affect secondary target organs, such as the central nervous system (CNS). Putative adverse effects on the CNS are rarely investigated to date. Here, we used a mixed primary cell model consisting mainly of neurons and astrocytes and a minor proportion of oligodendrocytes to analyze the effects of well-characterized 20 and 40 nm silver nanoparticles (SNP). Similar gold nanoparticles served as control and proved inert for all endpoints tested. SNP induced a strong size-dependent cytotoxicity. Additionally, in the low concentration range (up to 10 μg/ml of SNP), the further differentiated cultures were more sensitive to SNP treatment. For detailed studies, we used low/medium dose concentrations (up to 20 μg/ml) and found strong oxidative stress responses. Reactive oxygen species (ROS) were detected along with the formation of protein carbonyls and the induction of heme oxygenase-1. We observed an acute calcium response, which clearly preceded oxidative stress responses. ROS formation was reduced by antioxidants, whereas the calcium response could not be alleviated by antioxidants. Finally, we looked into the responses of neurons and astrocytes separately. Astrocytes were much more vulnerable to SNP treatment compared with neurons. Consistently, SNP were mainly taken up by astrocytes and not by neurons. Immunofluorescence studies of mixed cell cultures indicated stronger effects on astrocyte morphology. Altogether, we can demonstrate strong effects of SNP associated with calcium dysregulation and ROS formation in primary neural cells, which were detectable already at moderate dosages.