The pH-sensitive dye acridine orange as a tool to monitor exocytosis/endocytosis in synaptosomes

Synergistic neurological threat from Сu and wood smoke particulate matter

Trace metal Cu and carbonaceous airborn particulate matter (PM) are dangerous neuropollutants. Here, the ability of Cu2+ to modulate the neurotoxicity caused by water-suspended wood smoke PM preparations (SPs) and vice versa was examined using presynaptic rat cortex nerve terminals. Interaction of Cu2+ and SPs, changes of particle size and surface properties were shown in the presence of Cu2+ using microscopy, DLS, and IR spectroscopy. In nerve terminals, Cu2+ and SPs per se elevated the ambient levels of excitatory and inhibitory neurotransmitters L-[14C]glutamate and [3H]GABA, respectively. During combined application, Cu2+ significantly enhanced a SPs-induced increase in the ambient levels of both neurotransmitters, thereby demonstrating a cumulative synergistic effect and significant interference in the neurotoxic threat associated with Cu2+and SPs. In fluorimetric measurements, Cu2+ and SPs also demonstrated cumulative synergistic effects on the membrane potential, mitochondrial potential, synaptic vesicle acidification and ROS generation. Therefore, synergistic effects of Cu2+ and SPs on the most crucial presynaptic characteristics and neurohazard of multiple pollutants through excitatory/inhibitory imbalance, disruption of the membrane and mitochondrial potential, vesicle acidification and ROS generation were revealed. Increased expansion and burden of neuropathology may result from underestimation of synergistic interference of the neurotoxic effects of Cu2+ and carbonaceous smoke PM.

Increased vesicular dynamics and nanoscale clustering of IL-2 after T cell activation

T cells coordinate intercellular communication through the meticulous regulation of cytokine secretion. Direct visualization of vesicular transport and intracellular distribution of cytokines provides valuable insights into the temporal and spatial mechanisms involved in regulation. Employing Jurkat E6-1 T cells and interleukin-2 (IL-2) as a model system, we investigated vesicular dynamics using single-particle tracking and the nanoscale distribution of intracellular IL-2 in fixed T cells using superresolution microscopy. Live-cell imaging revealed that in vitro activation resulted in increased vesicular dynamics. Direct stochastic optical reconstruction microscopy and 3D structured illumination microscopy revealed nanoscale clustering of IL-2. In vitro activation correlated with spatial accumulation of IL-2 nanoclusters into more pronounced and elongated clusters. These observations provide visual evidence that accelerated vesicular transport and spatial concatenation of IL-2 clusters at the nanoscale may constitute a potential mechanism for modulating cytokine release by Jurkat T cells.

Amphiphilic anti-SARS-CoV-2 drug remdesivir incorporates into the lipid bilayer and nerve terminal membranes influencing excitatory and inhibitory neurotransmission

Remdesivir is a novel antiviral drug, which is active against the SARS-CoV-2 virus. Remdesivir is known to accumulate in the brain but it is not clear whether it influences the neurotransmission. Here we report diverse and pronounced effects of remdesivir on transportation and release of excitatory and inhibitory neurotransmitters in rat cortex nerve terminals (synaptosomes) in vitro. Direct incorporation of remdesivir molecules into the cellular membranes was shown by FTIR spectroscopy, planar phospholipid bilayer membranes and computational techniques. Remdesivir decreases depolarization-induced exocytotic release of L-[14C] glutamate and [3H] GABA, and also [3H] GABA uptake and extracellular level in synaptosomes in a dose-dependent manner. Fluorimetric studies confirmed remdesivir-induced impairment of exocytosis in nerve terminals and revealed a decrease in synaptic vesicle acidification. Our data suggest that remdesivir dosing during antiviral therapy should be precisely controlled to prevent possible neuromodulatory action at the presynaptic level. Further studies of neurotropic and membranotropic effects of remdesivir are necessary.

The ability of carbon nanoparticles to increase transmembrane current of cations coincides with impaired synaptic neurotransmission

Here, carbon nanodots synthesized from β-alanine (Ala-CDs) and detonation nanodiamonds (NDs) were assessed using (1) radiolabeled excitatory neurotransmitters L-[¹⁴C]glutamate, D-[2,3³H]aspartate, and inhibitory ones [³H]GABA, [³H]glycine for registration of their extracellular concentrations in rat cortex nerve terminals; (2) the fluorescent ratiometric probe NR12S and pH-sensitive probe acridine orange for registration of the membrane lipid order and synaptic vesicle acidification, respectively; (3) suspended bilayer lipid membrane (BLM) to monitor changes in transmembrane current. In nerve terminals, Ala-CDs and NDs increased the extracellular concentrations of neurotransmitters and decreased acidification of synaptic vesicles, whereas have not changed sufficiently the lipid order of membrane. Both nanoparticles, Ala-CDs and NDs, were capable of increasing the conductance of the BLM by inducing stable potential-dependent cation-selective pores. Introduction of divalent cations, Zn²⁺ or Cd²⁺ on the particles` application side (cis-side) increased the rate of Ala-CDs pore-formation in the BLM. The application of positive potential (+100 mV) to the cis-chamber with Ala-CDs or NDs also activated the insertion as compared with the negative potential (-100 mV). The Ala-CD pores exhibited a wide-range distribution of conductances between 10 and 60 pS and consecutive increase in conductance of each major peak by ~10 pS, which suggest the clustering of the same basic ion-conductive structure. NDs also formed ion-conductive pores ranging from 6 pS to 60 pS with the major peak of conductance at ~12 pS in cholesterol-containing membrane. Observed Ala-CDs and NDs-induced increase in transmembrane current coincides with disturbance of excitatory and inhibitory neurotransmitter transport in nerve terminals.

Fluorescence Approaches for Characterizing Ion Channels in Synthetic Bilayers

Ion channels are membrane proteins that play important roles in a wide range of fundamental cellular processes. Studying membrane proteins at a molecular level becomes challenging in complex cellular environments. Instead, many studies focus on the isolation and reconstitution of the membrane proteins into model lipid membranes. Such simpler, in vitro, systems offer the advantage of control over the membrane and protein composition and the lipid environment. Rhodopsin and rhodopsin-like ion channels are widely studied due to their light-interacting properties and are a natural candidate for investigation with fluorescence methods. Here we review techniques for synthesizing liposomes and for reconstituting membrane proteins into lipid bilayers. We then summarize fluorescence assays which can be used to verify the functionality of reconstituted membrane proteins in synthetic liposomes.

A new insight into mechanisms of interferon alpha neurotoxicity: Expression of GRIN3A subunit of NMDA receptors and NMDA-evoked exocytosis

Neurological and psychiatric side effects accompany the high-dose interferon-alpha (IFNA) therapy. The primary genes responsible for these complications are mostly unknown. Our genome-wide search in mouse and rat genomes for the conservative genes containing IFN-stimulated response elements (ISRE) in their promoters revealed a new potential target gene of IFNA, Grin3α, which encodes the 3A subunit of NMDA receptor. This study aimed to explore the impact of IFNA on the expression of Grin3α and Ifnα genes and neurotransmitters endo/exocytosis in the mouse brain. We administered recombinant human IFN-alpha 2b (rhIFN-α2b) intracranially, and 24 h later, we isolated six brain regions and used the samples for RT-qPCR and western blot analysis. Synaptosomes were isolated from the cortex to analyze endo/exocytosis with acridine orange and L-[14C]glutamate. IFNA induced an increase in Grin3α mRNA and GRIN3A protein, but a decrease in Ifnα mRNA and protein. IFNA did not affect the accumulation and distribution of L-[14C]glutamate and acridine orange between synaptosomes and the extra-synaptosomal space. It caused the more significant acridine orange release activated by NMDA or glutamate than from control mice's synaptosomes. In response to IFNA, the newly discovered association between elevated Grin3α expression and NMDA- and glutamate-evoked neurotransmitters release from synaptosomes implies a new molecular mechanism of IFNA neurotoxicity.

Bedbug salivation patterns during hematophagy in the skin of a mammalian host

Cimex lectularius (Hemiptera:Cimicidae) infestations have increased over the past decades in several parts of the world, constituting a major urban pest with no reversion signs. The impact on human health caused by these insects, commonly known as bedbugs, is associated with their obligatory hematophagous habit. Allergies induced by hematophagous arthropod bites are related to the deposition of salivary molecules in the host tissues. Many reports of humans developing severe allergic reactions due to bedbug bites have been recorded, however, there is limited information on the salivation of bedbugs on the host, which was the objective of this study. C. lectularius females were fed on blood containing acridine orange fluorochrome, which labeled the principal salivary glands content. The salivation pattern of bedbugs was investigated using intravital microscopy during its blood meal on the ear skin of hairless mice. Saliva deposition occurred during all insect blood-feeding phases, beginning as soon as the mouthpart touched the host skin. During the probing phase, saliva was deposited in large quantities in the host dermis. In contrast, during the engorgement phase (which represents the largest blood meal of the insects), saliva was released at a much slower rate. The apparent release of saliva into the cannulated vessel and/or adjacent tissue occurs only sporadically during insect blood ingestion. However, a small area (spot) of fluorescence was detected around the proboscis tip during this feeding phase. An interesting feature of bedbugs is that they release saliva inside and outside the vessels without removing their mouthparts from the vessel lumen. This is an effective feeding strategy because it does not interrupt blood ingestion and decreases the mouthparts movements on the host's skin, minimizing the damage to tissues and contact time with the host (feeding time).

Multifunctional peptide-assembled micelles for simultaneously reducing amyloid-β and reactive oxygen species

The excessive production and deposition of amyloid-β (Aβ) is one of the most important etiologies of Alzheimer's disease (AD). The interaction between Aβ and metal ions produces aberrant reactive oxygen species (ROS), which induce oxidative stress and accelerate the progression of AD. To reduce Aβ plaques and ROS to maintain their homeostasis is an emerging and ingenious strategy for effective treatment of AD. Herein, we report the rational design of multifunctional micelles (MPGLT) based on a polymer-grafted peptide to simultaneously clear Aβ and ROS for AD therapy. The MPGLT integrating three functional peptides as a ROS scavenger (tk-GSH), β-sheet breaker (LP) and an autophagy activator (TK) respectively, could capture and degrade Aβ. Meanwhile, the tk-GSH on the surface of MPGLT effectively scavenges the intracellular ROS. Consequently, MPGLT reduced the cytotoxicity of Aβ and ROS. In vivo animal studies using an AD mouse model further showed that MPGLT could transport across the blood-brain barrier for decreasing the Aβ plaque and eliminating ROS in vivo. This peptide micelle-based synergistic strategy may provide novel insight for AD therapy.

Inhibitors of synaptic vesicle exocytosis reduce surface expression of postsynaptic glutamate receptors

Bafilomycin A1, a vacuolar H⁺-ATPase inhibitor, and botulinum toxin B and tetanus toxin, both vesicle fusion inhibitors, are widely known exocytosis blockers that have been used to inhibit the presynaptic release of neurotransmitters. However, protein trafficking mechanisms, such as the insertion of postsynaptic receptors and astrocytic glutamate-releasing channels into the plasma membrane, also require exocytosis. In our previous study, exocytosis inhibitors reduced the surface expression of astrocytic glutamate-releasing channels. Here, we further investigated whether exocytosis inhibitors influence the surface expression of postsynaptic receptors. Using pH-sensitive superecliptic pHluorin (SEP)-tagged postsynaptic glutamate receptors, including GluA1, GluA2, GluN1, and GluN2A, we found that bafilomycin A1, botulinum toxin B, and/or tetanus toxin reduce the SEP fluorescence of SEP-GluA1, SEP-GluA2, SEP-GluN1, and SEP-GluN2A. These findings indicate that presynaptic vesicle exocytosis inhibitors also affect the postsynaptic trafficking machinery for surface expression. Finally, this study provides profound insights assembling presynaptic, postsynaptic and astrocytic viewpoints into the interpretation of the data obtained using these synaptic vesicle exocytosis inhibitors.

Inhibition of sigma-1 receptors substantially modulates GABA and glutamate transport in presynaptic nerve terminals

Sigma-1 receptors (Sig-1Rs) have been implicated in many neurological and psychiatric disorders and are a novel target for the treatment of such disorders. Sig-1R expression/activity deficits are linked to neurodegeneration, whereas the mechanisms mediated by Sig-1R are still unclear. Here, presynaptic [3H]GABA and L-[14C]glutamate transport was analysed in rat brain nerve terminals (synaptosomes) in the presence of the Sig-1R antagonist NE-100. NE-100 at doses of 1 and 10 μM increased the initial rate of synaptosomal [3H]GABA uptake, whereas 50 and 100 μM NE-100 decreased this rate, exerting a biphasic mode of action.Antagonists of GABAA and GABAB receptors, flumazenil and saclofen, respectively, prevented an increase in [3H]GABA uptake caused by 10 μM NE-100. L-[14C]glutamate uptake was decreased by 10-100 μM NE-100. A decrease in the uptake of both neurotransmitters mediated by NE-100 (50-100 μM) may have resulted from simultaneous antagonist-induced membrane depolarization, which was measured using the potential-sensitive fluorescent dye rhodamine 6G. The extracellular level of [3H]GABA was decreased by 1-10 μM NE-100, but that of L-[14C]glutamate remained unchanged. The tonic release of [3H]GABA measured in the presence of NO-711 was not changed by the antagonist, suggesting that NE-100 did not disrupt membrane integrity. The KCl- and FCCP-induced transporter-mediated release of L-[14C]glutamate was decreased by the antagonist; this may underlie the neuroprotective action of the antagonist in hypoxia/ischaemia. NE-100 (10-100 μM) decreased the KCl-evoked exocytotic release of [3H]GABA and L-[14C]glutamate, whereas the induction of the release of both neurotransmitters by the Ca2+ ionophore ionomycin was not affected by the antagonist; therefore, the mitigation of KCl-evoked exocytosis was associated with the NE-100-induced dysfunction of potential-dependent Ca2+ channels. Therefore, the Sig-1R antagonist can specifically act in an acute manner at the presynaptic level through the modulation of GABA and glutamate uptake, transporter-mediated release and exocytosis.

Fitness of Outer Membrane Vesicles From Komagataeibacter intermedius Is Altered Under the Impact of Simulated Mars-like Stressors Outside the International Space Station

Outer membrane vesicles (OMVs), produced by nonpathogenic Gram-negative bacteria, have potentially useful biotechnological applications in extraterrestrial extreme environments. However, their biological effects under the impact of various stressors have to be elucidated for safety reasons. In the spaceflight experiment, model biofilm kombucha microbial community (KMC) samples, in which Komagataeibacter intermedius was a dominant community-member, were exposed under simulated Martian factors (i.e., pressure, atmosphere, and UV-illumination) outside the International Space Station (ISS) for 1.5 years. In this study, we have determined that OMVs from post-flight K. intermedius displayed changes in membrane composition, depending on the location of the samples and some other factors. Membrane lipids such as sterols, fatty acids (FAs), and phospholipids (PLs) were modulated under the Mars-like stressors, and saturated FAs, as well as both short-chain saturated and trans FAs, appeared in the membranes of OMVs shed by both post-UV-illuminated and “dark” bacteria. The relative content of zwitterionic and anionic PLs changed, producing a change in surface properties of outer membranes, thereby resulting in a loss of interaction capability with polynucleotides. The changed composition of membranes promoted a bigger OMV size, which correlated with changes of OMV fitness. Biochemical characterization of the membrane-associated enzymes revealed an increase in their activity (DNAse, dehydrogenase) compared to wild type. Other functional membrane-associated capabilities of OMVs (e.g., proton accumulation, interaction with linear DNA, or synaptosomes) were also altered after exposure to the spaceflight stressors. Despite alterations in membranes, vesicles did not acquire endotoxicity, cytotoxicity, and neurotoxicity. Altogether, our results show that OMVs, originating from rationally selected nonpathogenic Gram-negative bacteria, can be considered as candidates in the design of postbiotics or edible mucosal vaccines for in situ production in extreme environment. Furthermore, these OMVs could also be used as promising delivery vectors for applications in Astromedicine.

Acridine Orange Encapsulated Mesoporous Manganese Dioxide Nanoparticles to Enhance Radiotherapy

Manganese dioxide (MnO₂) nanoparticles are a promising type of radiosensitizer for they can catalyze H₂O₂ decomposition to produce O₂. Combining MnO₂ nanoparticles with conventional, small molecule radiosensitizers would further enhance radiotherapy (RT) efficacy due to complementary mechanisms of action. However, solid MnO₂ nanoparticles are suboptimal at drug loading, limiting the related progress. Herein we report a facile method to synthesize mesoporous MnO₂ (mMnO₂) nanoparticles, which can efficiently encapsulate small molecule therapeutics. In particular, we found that acridine orange (AO), a small molecule radiosensitizer, can be loaded onto mMnO₂ nanoparticles at very high efficiency and released to the surroundings in a controlled fashion. We show that mMnO₂ nanoparticles can efficiently produce O₂ inside cells. This, together with AO-induced DNA damage, significantly enhances RT outcomes, which was validated both in vitro and in vivo. Meanwhile, mMnO₂ nanoparticles slowly degrade in acidic environments to release Mn²⁺, providing a facile way to keep track of the nanoparticles through magnetic resonance imaging (MRI). Overall, our studies suggest mMnO₂ as a promising nanoplatform that can be exploited to produce composite radiosensitizers for RT.

High Concentration of Ketone Body β-Hydroxybutyrate Modifies Synaptic Vesicle Cycle and Depolarizes Plasma Membrane of Rat Brain Synaptosomes

Ketoacidosis is a dangerous complication of diabetes mellitus in which plasma levels of ketone bodies can reach 20-25 mM. This condition is life-threatening. In contrast, a ketogenic diet, achieving plasma levels of ketone bodies of about 4-5 mM, can be used for treating different brain diseases. However, the factors leading to the conversion of the neuroprotective ketone bodies' action to the neurotoxic action during ketoacidosis are still unknown. We investigated the influence of high concentration (25 mM) of the main ketone body, β-hydroxybutyrate (BHB), on intrasynaptosomal pH (pHi), synaptic vesicle cycle, plasma membrane, and mitochondrial potentials. Using the fluorescent dye BCECF-AM, it was shown that BHB at concentrations of 8 and 25 mM did not influence pHi in synaptosomes. By means of the fluorescent dye acridine orange, it was demonstrated that 25 mM of BHB had no effect on exocytosis but inhibited compensatory endocytosis by 5-fold. Increasing buffer capacity with 25 mM HEPES did not affect endocytosis. Glucose abolished BHB-induced endocytosis inhibition. Using the fluorescent dye DiSC3(5), it was shown that 25 mM of BHB induced a significant plasma membrane depolarization. This effect was not impacted by glucose. Using the fluorescent dye rhodamine-123, it was shown that BHB alone (25 mМ) did not alter the potential of intrasynaptosomal mitochondria.Importantly, the high concentration of BHB (25 mМ) causes the depolarization of the plasma membrane and stronger inhibition of endocytosis compared with the intermediate concentration (8 mM).

In vitro fusion of single synaptic and dense core vesicles reproduces key physiological properties

Regulated exocytosis of synaptic vesicles is substantially faster than of endocrine dense core vesicles despite similar molecular machineries. The reasons for this difference are unknown and could be due to different regulatory proteins, different spatial arrangements, different vesicle sizes, or other factors. To address these questions, we take a reconstitution approach and compare regulated SNARE-mediated fusion of purified synaptic and dense core chromaffin and insulin vesicles using a single vesicle-supported membrane fusion assay. In all cases, Munc18 and complexin are required to restrict fusion in the absence of calcium. Calcium triggers fusion of all docked vesicles. Munc13 (C1C2MUN domain) is required for synaptic and enhanced insulin vesicle fusion, but not for chromaffin vesicles, correlating inversely with the presence of CAPS protein on purified vesicles. Striking disparities in calcium-triggered fusion rates are observed, increasing with curvature with time constants 0.23 s (synaptic vesicles), 3.3 s (chromaffin vesicles), and 9.1 s (insulin vesicles) and correlating with rate differences in cells.

Age-Dependency of Levetiracetam Effects on Exocytotic GABA Release from Nerve Terminals in the Hippocampus and Cortex in Norm and After Perinatal Hypoxia

Perinatal hypoxia can lead to multiple chronic neurological deficits, e.g., mental retardation, behavioral abnormalities, and epilepsy. Levetiracetam (LEV), 2S-(2-oxo-1-pyrrolidiny1) butanamide, is an anticonvulsant drug with proven efficiency in treating patients with focal and generalized seizures. Rats were underwent hypoxia and seizures at the age of 10-12 postnatal days (pd). The ambient level and depolarization-induced exocytotic release of [³H]GABA (γ-aminobutyric acid) were analyzed in nerve terminals in the hippocampus and cortex during development at the age of pd 17-19 and pd 24-26 (infantile stage), pd 38-40 (puberty) and pd 66-73 (young adults) in norm and after perinatal hypoxia. LEV had no effects on the ambient [³H]GABA level. The latter increased during development and was further elevated after perinatal hypoxia in nerve terminals in the hippocampus during the whole period and in the cortex in young adults. Exocytotic [³H]GABA release from nerve terminals increased after perinatal hypoxia during development in the hippocampus and cortex, however this effect was preserved at all ages during blockage of GABA transporters by NO-711 in the hippocampus only. LEV realized its anticonvulsant effects at the presynaptic site through an increase in exocytotic release of GABA. LEV exerted more significant effect after perinatal hypoxia than in norm. Action of LEV was strongly age-dependent and can be registered in puberty and young adults, but the drug was inert at the infantile stage.

Modulation of neurosecretion and approaches for its multistep analysis

BACKGROUND

Neurosecretion is the multistep process occurring in separate spatial and temporal cellular boundaries which complicates its comprehensive analysis. Most of the research are focused on one distinct stage of synaptic vesicle recycling. Here, we describe approaches for complex analysis of synaptic vesicle (SV) endocytosis and separate steps of exocytosis at the level of presynaptic bouton and highly purified SVs.

METHODS

Proposed fluorescence-based strategies and analysis of neurotransmitter transport provided the advantages in studies of exocytosis steps. We evaluated SV docking/tethering, their Ca²⁺-dependent fusion and release of neurotransmitters gamma-aminobutyric acid (GABA) and glutamate in two animal models.

RESULTS

Approaches enabled us to study: 1) endocytosis/Ca²⁺-dependent release of fluorescent carbon nanodots (CNDs) during stimulation of nerve terminals; 2) the action of levetiracetam, modulator of SV glycoprotein SV2, on fusion competence of SVs and stimulated release of GABA and glutamate; 3) impairments of several steps of neurosecretion under vitamin D₃ deficiency.

CONCLUSIONS

Our algorithm enabled us to verify the method validity for multidimensional analysis of SV turnover. By increasing SV docking and the size of readily releasable pool (RRP), levetiracetam is able to selectively enhance the stimulated GABA secretion in hippocampal neurons. Findings suggest that SV2 regulates RRP through impact on the number of docked/primed SVs.

GENERAL SIGNIFICANCE

Methodology can be widely applied to study the stimulated neurosecretion in presynapse, regulation of SV docking, their Ca²⁺-dependent fusion with target membranes, quantitative analysis of expression of neuron-specific proteins, as well as for testing the efficiency of pre-selected designed neuroactive substances.

Imaging FITC-dextran as a Reporter for Regulated Exocytosis

Regulated exocytosis is a process by which cargo, which is stored in secretory granules (SGs), is released in response to a secretory trigger. Regulated exocytosis is fundamental for intercellular communication and is a key mechanism for the secretion of neurotransmitters, hormones, inflammatory mediators, and other compounds, by a variety of cells. At least three distinct mechanisms are known for regulated exocytosis: full exocytosis, where a single SG fully fuses with the plasma membrane, kiss-and-run exocytosis, where a single SG transiently fuses with the plasma membrane, and compound exocytosis, where several SGs fuse with each other, prior to or after SG fusion with the plasma membrane. The type of regulated exocytosis undertaken by a cell is often dictated by the type of secretory trigger. However, in many cells, a single secretory trigger can activate multiple modes of regulated exocytosis simultaneously. Despite their abundance and importance across cell types and species, the mechanisms that determine the different modes of secretion are largely unresolved. One of the main challenges in investigating the different modes of regulated exocytosis, is the difficulty in distinguishing between them as well as exploring them separately. Here we describe the use of fluorescein isothiocyanate (FITC)-dextran as an exocytosis reporter, and live cell imaging, to differentiate between the different pathways of regulated exocytosis, focusing on compound exocytosis, based on the robustness and duration of the exocytic events.

A self-destructive nanosweeper that captures and clears amyloid β-peptides

Cerebral amyloid β-peptide (Aβ) accumulation resulting from an imbalance between Aβ production and clearance is one of the most important causes in the formation of Alzheimer's disease (AD). In order to preserve the maintenance of Aβ homeostasis and have a notable AD therapy, achieving a method to clear up Aβ plaques becomes an emerging task. Herein, we describe a self-destructive nanosweeper based on multifunctional peptide-polymers that is capable of capturing and clearing Aβ for the effective treatment of AD. The nanosweeper recognize and bind Aβ via co-assembly through hydrogen bonding interactions. The Aβ-loaded nanosweeper enters cells and upregulates autophagy thus promoting the degradation of Aβ. As a result, the nanosweeper decreases the cytotoxicity of Aβ and rescues memory deficits of AD transgenic mice. We believe that this resourceful and synergistic approach has valuable potential as an AD treatment strategy.

Effects of surface functionalization of hydrophilic NaYF4 nanocrystals doped with Eu3+ on glutamate and GABA transport in brain synaptosomes

Specific rare earth doped nanocrystals (NCs), a recent class of nanoparticles with fluorescent features, have great bioanalytical potential. Neuroactive properties of NaYF4 nanocrystals doped with Eu3+ were assessed based on the analysis of their effects on glutamate- and γ-aminobutyric acid (GABA) transport process in nerve terminals isolated from rat brain (synaptosomes). Two types of hydrophilic NCs were examined in this work: (i) coated by polyethylene glycol (PEG) and (ii) with OH groups at the surface. It was found that NaYF4:Eu3+-PEG and NaYF4:Eu3+-OH within the concentration range of 0.5-3.5 and 0.5-1.5 mg/ml, respectively, did not influence Na+-dependent transporter-dependent l-[14C]glutamate and [3H]GABA uptake and the ambient level of the neurotransmitters in the synaptosomes. An increase in NaYF4:Eu3+-PEG and NaYF4:Eu3+-OH concentrations up to 7.5 and 3.5 mg/ml, respectively, led to the (1) attenuation of the initial velocity of uptake of l-[14C]glutamate and [3H]GABA and (2) elevation of ambient neurotransmitters in the suspension of nerve terminals. In the mentioned concentrations, nanocrystals did not influence acidification of synaptic vesicles that was shown with pH-sensitive fluorescent dye acridine orange, however, decreased the potential of the plasma membrane of synaptosomes. In comparison with other nanoparticles studied with similar methodological approach, NCs start to exhibit their effects on neurotransmitter transport at concentrations several times higher than those shown for carbon dots, detonation nanodiamonds and an iron storage protein ferritin, whose activity can be registered at 0.08, 0.5 and 0.08 mg/ml, respectively. Therefore, NCs can be considered lesser neurotoxic as compared to above nanoparticles.

Harmful impact on presynaptic glutamate and GABA transport by carbon dots synthesized from sulfur-containing carbohydrate precursor

Carbon nanoparticles that may be potent air pollutants with adverse effects on human health often contain heteroatoms including sulfur. In order to study in detail their effects on different physiological and biochemical processes, artificially produced carbon dots (CDs) with well-controlled composition that allows fluorescence detection may be of great use. Having been prepared from different types of organic precursors, CDs expose different atoms at their surface suggesting a broad variation of functional groups. Recently, we demonstrated neurotoxic properties of CDs synthesized from the amino acid β-alanine, and it is of importance to analyze whether CDs obtained from different precursors and particularly those exposing sulfur atoms induce similar neurotoxic effects. This study focused on synthesis of CDs from the sulfur-containing precursor thiourea-CDs (TU-CDs) with a size less than 10 nm, their characterization, and neuroactivity assessment. Neuroactive properties of TU-CDs were analyzed based on their effects on the key characteristics of glutamatergic and γ-aminobutyric acid (GABA) neurotransmission in isolated rat brain nerve terminals. It was observed that TU-CDs (0.5-1.0 mg/ml) attenuated the initial velocity of Na⁺-dependent transporter-mediated uptake and accumulation of L-[¹⁴C]glutamate and [³H]GABA by nerve terminals in a dose-dependent manner and increased the ambient level of the neurotransmitters. Starting from the concentration of 0.2 mg/ml, TU-CDs evoked a gradual dose-dependent depolarization of the plasma membrane of nerve terminals measured with the cationic potentiometric dye rhodamine 6G. Within the concentration range of 0.1-0.5 mg/ml, TU-CDs caused an "unphysiological" step-like increase in fluorescence intensity of the рН-sensitive fluorescent dye acridine orange accumulated by synaptic vesicles. Therefore, despite different surface properties and fluorescent features of CDs prepared from different starting materials (thiourea and β-alanine), their principal neurotoxic effects are analogous but displayed at a different level of efficiency. Sulfur-containing TU-CDs exhibit lower effects (by ~30%) on glutamate and GABA transport in the nerve terminals in comparison with sulfur-free β-alanine CDs. Our results suggest considering that an uncontrolled presence of carbon-containing particulate matter in the human environment may pose a toxicity risk for the central nervous system.

pH-Sensitive Polymeric Nanoparticles Modulate Autophagic Effect via Lysosome Impairment

In drug delivery systems, pH-sensitive polymers are commonly used as drug carriers, and significant efforts have been devoted to the aspects of controlled delivery and release of drugs. However, few studies address the possible autophagic effects on cells. Here, for the first time, using a fluorescent autophagy-reporting cell line, this study evaluates the autophagy-induced capabilities of four types of pH-sensitive polymeric nanoparticles (NPs) with different physical properties, including size, surface modification, and pH-sensitivity. Based on experimental results, this study concludes that pH-sensitivity is one of the most important factors in autophagy induction. In addition, this study finds that variation of concentration of NPs could cause different autophagic effect, i.e., low concentration of NPs induces autophagy in an mTOR-dependent manner, but high dose of NPs leads to autophagic cell death. Identification of this tunable autophagic effect offers a novel strategy for enhancing therapeutic effect in cancer therapy through modulation of autophagy.

THE EFFECT OF NITRIC OXIDE ON SYNAPTIC VESICLE PROTON GRADIENT AND MITOCHONDRIAL POTENTIAL OF BRAIN NERVE TERMINALS

The effect of nitric oxide on synaptic vesicle proton gradient and membrane potential of rat brain nerve terminals was studied. It has been shown that nitric oxide in the form of S-nitrosothiols at nanomolar concentrations had no effect on the studied parameters, but caused a rapid dissipation of synaptic vesicle proton gradient and depolarization of mitochondrial membrane in the presence of a SH-reducing compound such as dithiothreitol. Both processes were reversible and the rate of H(+)-gradient restoration depended on the redox potential of nerve terminals, namely the molar ratio of reductant/oxidant. This facts, as well as insensitivity of the studied processes to the inhibitor of NO-sensitive guanylate cyclase such as ODQ, allow suggesting that post-translational modification of thiol residues of the mitochondrial and synaptic vesicle proteins underlies the effect of nitric oxide on the key functional parameters ofpresynaptic nerve terminals.

A naphthalimide derived fluorescent sensor for solid-phase screening of cucurbit[7]uril-guest interactions

A naphthalimide based fluorescent sensor displaying a significant increase in emission upon binding CB[7] with notable pH stability was developed and utilized in a surface-bound displacement assay for the rapid detection of CB[7] encapsulation of therapeutically relevant drug classes. Previously unknown binders with moderate to strong affinities were discovered.

β-Hydroxybutyrate supports synaptic vesicle cycling but reduces endocytosis and exocytosis in rat brain synaptosomes

The ketogenic diet is used as a prophylactic treatment for different types of brain diseases, such as epilepsy or Alzheimer's disease. In such a diet, carbohydrates are replaced by fats in everyday food, resulting in an elevation of blood-borne ketone bodies levels. Despite clinical applications of this treatment, the molecular mechanisms by which the ketogenic diet exerts its beneficial effects are still uncertain. In this study, we investigated the effect of replacing glucose by the ketone body β-hydroxybutyrate as the main energy substrate on synaptic vesicle recycling in rat brain synaptosomes. First, we observed that exposing presynaptic terminals to nonglycolytic energy substrates instead of glucose did not alter the plasma membrane potential. Next, we found that synaptosomes were able to maintain the synaptic vesicle cycle monitored with the fluorescent dye acridine orange when glucose was replaced by β-hydroxybutyrate. However, in presence of β-hydroxybutyrate, synaptic vesicle recycling was modified with reduced endocytosis. Replacing glucose by pyruvate also led to a reduced endocytosis. Addition of β-hydroxybutyrate to glucose-containing incubation medium was without effect. Reduced endocytosis in presence of β-hydroxybutyrate as sole energy substrate was confirmed using the fluorescent dye FM2-10. Also we found that replacement of glucose by ketone bodies leads to inhibition of exocytosis, monitored by FM2-10. However this reduction was smaller than the effect on endocytosis under the same conditions. Using both acridine orange in synaptosomes and the genetically encoded sensor synaptopHluorin in cortical neurons, we observed that replacing glucose by β-hydroxybutyrate did not modify the pH gradient of synaptic vesicles. In conclusion, the nonglycolytic energy substrates β-hydroxybutyrate and pyruvate are able to support synaptic vesicle recycling. However, they both reduce endocytosis. Reduction of both endocytosis and exocytosis together with misbalance between endocytosis and exocytosis could be involved in the anticonvulsant activity of the ketogenic diet.

Electrochemical push-pull probe: from scanning electrochemical microscopy to multimodal altering of cell microenvironment

To understand biological processes at the cellular level, a general approach is to alter the cells' environment and to study their chemical responses. Herein, we present the implementation of an electrochemical push-pull probe, which combines a microfluidic system with a microelectrode, as a tool for locally altering the microenvironment of few adherent living cells by working in two different perturbation modes, namely electrochemical (i.e., electrochemical generation of a chemical effector compound) and microfluidic (i.e., infusion of a chemical effector compound from the pushing microchannel, while simultaneously aspirating it through the pulling channel, thereby focusing the flow between the channels). The effect of several parameters such as flow rate, working distance, and probe inclination angle on the affected area of adherently growing cells was investigated both theoretically and experimentally. As a proof of concept, localized fluorescent labeling and pH changes were purposely introduced to validate the probe as a tool for studying adherent cancer cells through the control over the chemical composition of the extracellular space with high spatiotemporal resolution. A very good agreement between experimental and simulated results showed that the electrochemical perturbation mode enables to affect precisely only a few living cells localized in a high-density cell culture.

Manipulation of isolated brain nerve terminals by an external magnetic field using D-mannose-coated γ-Fe2O3 nano-sized particles and assessment of their effects on glutamate transport

The manipulation of brain nerve terminals by an external magnetic field promises breakthroughs in nano-neurotechnology. D-Mannose-coated superparamagnetic nanoparticles were synthesized by coprecipitation of Fe(II) and Fe(III) salts followed by oxidation with sodium hypochlorite and addition of D-mannose. Effects of D-mannose-coated superparamagnetic maghemite (γ-Fe2O3) nanoparticles on key characteristics of the glutamatergic neurotransmission were analysed. Using radiolabeled L-[(14)C]glutamate, it was shown that D-mannose-coated γ-Fe2O3 nanoparticles did not affect high-affinity Na(+)-dependent uptake, tonic release and the extracellular level of L-[(14)C]glutamate in isolated rat brain nerve terminals (synaptosomes). Also, the membrane potential of synaptosomes and acidification of synaptic vesicles was not changed as a result of the application of D-mannose-coated γ-Fe2O3 nanoparticles. This was demonstrated with the potential-sensitive fluorescent dye rhodamine 6G and the pH-sensitive dye acridine orange. The study also focused on the analysis of the potential use of these nanoparticles for manipulation of nerve terminals by an external magnetic field. It was shown that more than 84.3 ± 5.0% of L-[(14)C]glutamate-loaded synaptosomes (1 mg of protein/mL) incubated for 5 min with D-mannose-coated γ-Fe2O3 nanoparticles (250 µg/mL) moved to an area, in which the magnet (250 mT, gradient 5.5 Т/m) was applied compared to 33.5 ± 3.0% of the control and 48.6 ± 3.0% of samples that were treated with uncoated nanoparticles. Therefore, isolated brain nerve terminals can be easily manipulated by an external magnetic field using D-mannose-coated γ-Fe2O3 nanoparticles, while the key characteristics of glutamatergic neurotransmission are not affected. In other words, functionally active synaptosomes labeled with D-mannose-coated γ-Fe2O3 nanoparticles were obtained.

A comparative study of neurotoxic potential of synthesized polysaccharide-coated and native ferritin-based magnetic nanoparticles

AIM

To analyze the neurotoxic potential of synthesized magnetite nanoparticles coated by dextran, hydroxyethyl starch, oxidized hydroxyethyl starch, and chitosan, and magnetic nanoparticles combined with ferritin as a native protein.

METHODS

The size of nanoparticles was analyzed using photon correlation spectroscopy, their effects on the conductance of planar lipid membrane by planar lipid bilayer technique, membrane potential and acidification of synaptic vesicles by spectrofluorimetry, and glutamate uptake and ambient level of glutamate in isolated rat brain nerve terminals (synaptosomes) by radiolabeled assay.

RESULTS

Uncoated synthesized magnetite nanoparticles and nanoparticles coated by different polysaccharides had no significant effect on synaptic vesicle acidification, the initial velocity of L-[(14)C]glutamate uptake, ambient level of L-[(14)C]glutamate and the potential of the plasma membrane of synaptosomes, and conductance of planar lipid membrane. Native ferritin-based magnetic nanoparticles had no effect on the membrane potential but significantly reduced L-[(14)C]glutamate transport in synaptosomes and acidification of synaptic vesicles.

CONCLUSIONS

Our study indicates that synthesized magnetite nanoparticles in contrast to ferritin have no effects on the functional state and glutamate transport of nerve terminals, and so ferritin cannot be used as a prototype, analogue, or model of polysaccharide-coated magnetic nanoparticle in toxicity risk assessment and manipulation of nerve terminals by external magnetic fields. Still, the ability of ferritin to change the functional state of nerve terminals in combination with its magnetic properties suggests its biotechnological potential.

New insights into molecular mechanism(s) underlying the presynaptic action of nitric oxide on GABA release

BACKGROUND

Nitric oxide (NO) is an important presynaptic modulator of synaptic transmission. Here, we aimed to correlate the release of the major inhibitory neurotransmitter GABA with intracellular events occurring in rat brain axon terminals during their exposure to NO in the range of nanomolar-low micromolar concentrations.

METHODS

Using [(3)H]GABA and fluorescent dyes (Fluo 4-AM, acridine orange and rhodamine 6G), the following parameters were evaluated: vesicular and cytosolic GABA pools, intracellular calcium concentration, synaptic vesicle acidification, and mitochondrial membrane potential. Diethylamine NONOate (DEA/NO) and S-nitroso-N-acetylpenicillamine (SNAP) were used as NO donors.

RESULTS

DEA/NO and SNAP (in the presence of dithiothreitol (DTT)) stimulated external Ca(2+)-independent [(3)H]GABA release, which was not attributed to a rise in intracellular calcium concentration. [(3)H]GABA release coincided with increasing GABA level in cytosol and decreasing the vesicular GABA content available for exocytotic release. There was a strong temporal correlation between NO-induced increase in cytosolic [GABA] and dissipation of both synaptic vesicle proton gradient and mitochondrial membrane potential. Dissipation was reversible, and recovery of both parameters correlated in time with re-accumulation of [(3)H]GABA into synaptic vesicles. The molar ratio of DTT to SNAP determined the rate and duration of the recovery processes.

CONCLUSIONS

We suggest that NO can stimulate GABA release via GABA transporter reversal resulting from increased GABA levels in cytosol. The latter is reversible and appears to be due to S-nitrosylation of key proteins, which affect the energy status of the pre-synapse.

GENERAL SIGNIFICANCE

Our findings provide new insight into molecular mechanism(s) underlying the presynaptic action of nitric oxide on inhibitory neurotransmission.

Chloride transport in functionally active phagosomes isolated from Human neutrophils

Chloride anion is critical for hypochlorous acid (HOCl) production and microbial killing in neutrophil phagosomes. However, the molecular mechanism by which this anion is transported to the organelle is poorly understood. In this report, membrane-enclosed and functionally active phagosomes were isolated from human neutrophils by using opsonized paramagnetic latex microspheres and a rapid magnetic separation method. The phagosomes recovered were highly enriched for specific protein markers associated with this organelle such as lysosomal-associated membrane protein-1, myeloperoxidase (MPO), lactoferrin, and NADPH oxidase. When FITC-dextran was included in the phagocytosis medium, the majority of the isolated phagosomes retained the fluorescent label after isolation, indicative of intact membrane structure. Flow cytometric measurement of acridine orange, a fluorescent pH indicator, in the purified phagosomes demonstrated that the organelle in its isolated state was capable of transporting protons to the phagosomal lumen via the vacuolar-type ATPase proton pump (V-ATPase). When NADPH was supplied, the isolated phagosomes constitutively oxidized dihydrorhodamine 123, indicating their ability to produce hydrogen peroxide. The preparations also showed a robust production of HOCl within the phagosomal lumen when assayed with the HOCl-specific fluorescent probe R19-S by flow cytometry. MPO-mediated iodination of the proteins covalently conjugated to the phagocytosed beads was quantitatively measured. Phagosomal uptake of iodide and protein iodination were significantly blocked by chloride channel inhibitors, including CFTRinh-172 and NPPB. Further experiments determined that the V-ATPase-driving proton flux into the isolated phagosomes required chloride cotransport, and the cAMP-activated CFTR chloride channel was a major contributor to the chloride transport. Taken together, the data suggest that the phagosomal preparation described herein retains ion transport properties, and multiple chloride channels including CFTR are responsible for chloride supply to neutrophil phagosomes.

Vesicular zinc regulates the Ca2+ sensitivity of a subpopulation of presynaptic vesicles at hippocampal mossy fiber terminals

Synaptic vesicles segregate into functionally diverse subpopulations within presynaptic terminals, yet there is no information about how this may occur. Here we demonstrate that a distinct subgroup of vesicles within individual glutamatergic, mossy fiber terminals contain vesicular zinc that is critical for the rapid release of a subgroup of synaptic vesicles during increased activity in mice. In particular, vesicular zinc dictates the Ca(2+) sensitivity of release during high-frequency firing. Intense synaptic activity alters the subcellular distribution of zinc in presynaptic terminals and decreases the number of zinc-containing vesicles. Zinc staining also appears in endosomes, an observation that is consistent with the preferential replenishment of zinc-enriched vesicles by bulk endocytosis. We propose that functionally diverse vesicle pools with unique membrane protein composition support different modes of transmission and are generated via distinct recycling pathways.

Probing the interior of synaptic vesicles with internalized nanoparticles

Synaptic vesicles are subcellular organelles that are found in the synaptic bouton and are responsible for the propagation of signals between neurons. Synaptic vesicles undergo endo- and exocytosis with the neuronal membrane to load and release neurotransmitters. Here we discuss how we utilize this property to load nanoparticles as a means of probing the interior of synaptic vesicles. To probe the intravesicular region of synaptic vesicles, we have developed a highly sensitive pH-sensing polymer dot. We feel the robust nature of the pH-sensing polymer dot will provide insight into the dynamics of proton loading into synaptic vesicles.

Presynaptic malfunction: the neurotoxic effects of cadmium and lead on the proton gradient of synaptic vesicles and glutamate transport

Exposure to Cd(2+) and Pb(2+) has neurotoxic consequences for human health and may cause neurodegeneration. The study focused on the analysis of the presynaptic mechanisms underlying the neurotoxic effects of non-essential heavy metals Cd(2+) and Pb(2+). It was shown that the preincubation of rat brain nerve terminals with Cd(2+) (200 μM) or Pb(2+) (200 μM) resulted in the attenuation of synaptic vesicles acidification, which was assessed by the steady state level of the fluorescence of pH-sensitive dye acridine orange. A decrease in L-[(14)C]glutamate accumulation in digitonin-permeabilized synaptosomes after the addition of the metals, which reflected lowered L-[(14)C]glutamate accumulation by synaptic vesicles inside of synaptosomes, may be considered in the support of the above data. Using isolated rat brain synaptic vesicles, it was found that 50 μM Cd(2+) or Pb(2+) caused dissipation of their proton gradient, whereas the application of essential heavy metal Mn(2+) did not do it within the range of the concentration of 50-500 μM. Thus, synaptic malfunction associated with the influence of Cd(2+) and Pb(2+) may result from partial dissipation of the synaptic vesicle proton gradient that leads to: (1) a decrease in stimulated exocytosis, which is associated not only with the blockage of voltage-gated Ca(2+) channels, but also with incomplete filling of synaptic vesicles; (2) an attenuation of Na(+)-dependent glutamate uptake.

Synaptosomes as a platform for loading nanoparticles into synaptic vesicles

Synaptosomes are intact, isolated nerve terminals that contain the necessary machinery to recycle synaptic vesicles via endocytosis and exocytosis upon stimulation. Here we use this property of synaptosomes to load quantum dots into synaptic vesicles. Vesicles are then isolated from the synaptosomes, providing a method to probe isolated, individual synaptic vesicles where each vesicle contains a single, encapsulated nanoparticle. This technique provided an encapsulation efficiency of ~16%, that is, ~16% of the vesicles contained a single quantum dot while the remaining vesicles were empty. The ability to load single nanoparticles into synaptic vesicles opens new opportunity for employing various nanoparticle-based sensors to study the dynamics of vesicular transporters.

Bioanalytical tools for single-cell study of exocytosis

Regulated exocytosis is a fundamental biological process used to deliver chemical messengers for cell-cell communication via membrane fusion and content secretion. A plethora of cell types employ this chemical-based communication to achieve crucial functions in many biological systems. Neurons in the brain and platelets in the circulatory system are representative examples utilizing exocytosis for neurotransmission and blood clotting. Single-cell studies of regulated exocytosis in the past several decades have greatly expanded our knowledge of this critical process, from vesicle/granule transport and docking at the early stages of exocytosis to membrane fusion and to eventual chemical messenger secretion. Herein, four main approaches that have been widely used to study single-cell exocytosis will be highlighted, including total internal reflection fluorescence microscopy, capillary electrophoresis, single-cell mass spectrometry, and microelectrochemistry. These techniques are arranged in the order following the route of a vesicle/granule destined for secretion. Within each section, the basic principles and experimental strategies are reviewed and representative examples are given revealing critical spatial, temporal, and chemical information of a secretory vesicle/granule at different stages of its lifetime. Lastly, an analytical chemist's perspective on potential future developments in this exciting field is discussed.

Ultra-fast versus sustained cholinergic transmission: a variety of different mechanisms

Although synaptic transmission was assumed to use the same mechanisms in the case of different synapses of the central and peripheral nervous system, recent research revealed a great variety of different processes. Time might be a crucial factor to be considered in this diversity. It is recalled that the speed of a chemical reaction is inversely related to affinity. "Time is gained at the expense of sensitivity" as noticed by Bernard Katz (1989). Therefore, synaptic transmission will occur at a high speed only if it is supported by low affinity reactions. In the present work, we compare two examples of ultra-rapid transmission (the Torpedo nerve electroplaque synapse and the rat hippocampus mossy fiber/CA3 synapses), with a cholinergic process operating with high affinity but at a low speed: the release of glutamate elicited by nicotine from mossy fibers of the rat hippocampus.