Blood–Brain Barrier Permeability and Brain Uptake Mechanism of Kainic Acid and Dihydrokainic Acid

RGS14 limits seizure-induced mitochondrial oxidative stress and pathology in hippocampus

RGS14 is a complex multifunctional scaffolding protein that is highly enriched within pyramidal cells (PCs) of hippocampal area CA2. In these neurons, RGS14 suppresses glutamate-induced calcium influx and related G protein and ERK signaling in dendritic spines to restrain postsynaptic signaling and plasticity. Previous findings show that, unlike PCs of hippocampal areas CA1 and CA3, CA2 PCs are resistant to a number of neurological insults, including degeneration caused by temporal lobe epilepsy (TLE). While RGS14 is protective against peripheral injury, similar roles for RGS14 during pathological injury in hippocampus remain unexplored. Recent studies showed that area CA2 modulates hippocampal excitability, generates epileptiform activity and promotes hippocampal pathology in animal models and patients with TLE. Because RGS14 suppresses CA2 excitability and signaling, we hypothesized that RGS14 would moderate seizure behavior and early hippocampal pathology following seizure activity, possibly affording protection to CA2 PCs. Using kainic acid (KA) to induce status epilepticus (KA-SE) in mice, we show that the loss of RGS14 (RGS14 KO) accelerated onset of limbic motor seizures and mortality compared to wild type (WT) mice, and that KA-SE upregulated RGS14 protein expression in CA2 and CA1 PCs of WT. Our proteomics data show that the loss of RGS14 impacted the expression of a number of proteins at baseline and after KA-SE, many of which associated unexpectedly with mitochondrial function and oxidative stress. RGS14 was shown to localize to the mitochondria in CA2 PCs of mice and reduce mitochondrial respiration in vitro. As a readout of oxidative stress, we found that RGS14 KO dramatically increased 3- nitrotyrosine levels in CA2 PCs, which was greatly exacerbated following KA-SE and correlated with a lack of superoxide dismutase 2 (SOD2) induction. Assessing for hallmarks of seizure pathology in RGS14 KO, we unexpectedly found no differences in neuronal injury in CA2 PCs. However, we observed a striking and surprising lack of microgliosis in CA1 and CA2 of RGS14 KO compared to WT. Together, our data demonstrate a newly appreciated role for RGS14 in limiting intense seizure activity and pathology in hippocampus. Our findings are consistent with a model where RGS14 limits seizure onset and mortality and, after seizure, is upregulated to support mitochondrial function, prevent oxidative stress in CA2 PCs, and promote microglial activation in hippocampus.

Vanillin Benzothiazole Derivative Reduces Cellular Reactive Oxygen Species and Detects Amyloid Fibrillar Aggregates in Alzheimer's Disease Brain

The misfolding of amyloid beta (Aβ) peptides into Aβ fibrillary aggregates is a major hallmark of Alzheimer's disease (AD), which responsible for the excess production of hydrogen peroxide (H₂O₂), a prominent reactive oxygen species (ROS) from the molecular oxygen (O₂) by the reduction of the Aβ-Cu(I) complex. The excessive production of H₂O₂ causes oxidative stress and inflammation in the AD brain. Here, we have designed and developed a dual functionalized molecule VBD by using π-conjugation (C═C) in the backbone structure. In the presence of H₂O₂, the VBD can turn into fluorescent probe VBD-1 by cleaving of the selective boronate ester group. The fluorescent probe VBD-1 can undergo intramolecular charge transfer transition (ICT) by a π-conjugative system, and as a result, its emission increases from the yellow (532 nm) to red (590 nm) region. The fluorescence intensity of VBD-1 increases by 3.5-fold upon binding with Aβ fibrillary aggregates with a high affinity (K_d = 143 ± 12 nM). Finally, the VBD reduces the cellular toxic H₂O₂ as proven by the CCA assay and DCFDA assay and the binding affinity of VBD-1 was confirmed by using in vitro histological staining in 8- and 18-month-old triple transgenic AD (3xTg-AD) mice brain slices.

Chrysin-Loaded Chitosan Nanoparticle-Mediated Neuroprotection in Aβ1-42-Induced Neurodegenerative Conditions in Zebrafish

Amyloid β plaques and neurofibrillary tangles are the characteristic features of Alzheimer's disease (AD). Plaques of amyloid β play a pivotal role in affecting cognitive functions and memory. Alzheimer's disease is a progressive neurodegenerative disease and is one of the leading causes of dementia worldwide. Several treatment strategies focusing on the amyloid cascade have been implemented to treat AD. The blood-brain barrier (BBB) poses the main obstructive barrier by refraining drugs from penetrating the brain. Nanotechnology is a promising research field for brain drug delivery using nanosized particles. Zebrafish is emerging as a model of interest to elaborate on brain targeting and nanotechnology-based therapeutics for neurodegenerative diseases. In the current study, we have synthesized and characterized chrysin-loaded chitosan nanoparticles (Chr-Chi NPs) and evaluated them for neuroprotection against amyloid-β-induced toxicity. We find that treatment with Chr-Chi NPs helps to retain memory, cognition, and synaptic connections, which are otherwise compromised due to Aβ_1-42 toxicity. The NPs further help in reducing aggregates of amyloid β, thus decreasing neuronal death and generation of reactive oxygen species (ROS). Taken together, our study brings to light a novel strategy for treating AD by a combined action on the neurons and amyloid aggregates mediated by chrysin and chitosan, respectively. Chr-Chi NPs, therefore, have the potential to provide a beneficial combinatorial treatment strategy for AD.

Modulation of α-Synuclein Fibrillation by Ultrasmall and Biocompatible Gold Nanoclusters

Parkinson's disease (PD) is the second most common neurodegenerative disorder, the pathogenesis of which is closely linked to the misfolding and aggregation of the neuronal protein α-Synuclein (A-Syn). Numerous molecules that inhibit/modulate the pathogenic aggregation of A-Syn in an effort to tackle PD pathogenesis have been reported, but none so far have been successful in treating the disease at the clinic. One major reason for this is the poor blood-brain barrier (BBB) permeability of most of the molecules being used. Therefore, using BBB-permeable (and biocompatible) nanomaterials as fibrillation modulators is gaining importance. In the present work, we show how nontoxic and ultrasmall gold nanoclusters (AuNCs) can systematically modulate the pathogenic fibrillation of A-Syn in vitro, based on the chemical nature of their capping agents, using two reported easily synthesizable AuNCs as models. In addition, we detect the BBB permeability in mice of one of these AuNCs solely by making use of its intrinsic fluorescence. Thus, our work exemplifies how AuNCs can be potential therapeutics against PD; while also acting as fluorescent probes for their own BBB permeability.

Immunohistochemical Evidence for Glutamatergic Regulation of Nesfatin-1 Neurons in the Rat Hypothalamus

Nesfatin-1, identified as an anorexigenic peptide, regulates the energy metabolism by suppressing food intake. The majority of nesfatin-1-synthesizing neurons are concentrated in various hypothalamic nuclei, especially in the supraoptic (SON), arcuate (ARC) and paraventricular nuclei (PVN). We tested the hypothesis that the glutamatergic system regulates nesfatin-1 neurons through glutamate receptors. Therefore, the first aim of the proposed studies was to examine effects of different glutamate agonists in the activation of nesfatin-1 neurons using c-Fos double immunohistochemical labeling. Experimental groups were formed containing male and female rats which received intraperitoneal injections of glutamate agonists kainic acid, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) while the control rats received vehicle. The significant increase in the number of c-Fos-expressing nesfatin-1 neurons after agonist injections were observed both in female and male subjects and some of these effects were found to be sexually dimorphic. In addition, treatment with specific glutamate antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or dizocilpine (MK-801) before each of the three agonist injections caused a statistically significant reduction in the number of activated nesfatin-1 neurons in the hypothalamic nuclei including supraoptic, paraventricular and arcuate nuclei. The second aim of the study was to determine the expression of glutamate receptor subunit proteins in the nesfatin-1 neurons by using a double immunofluorescence technique. The results showed that the glutamate receptor subunits, which may form homomeric or heteromeric functional receptor channels, were expressed in the nesfatin-1 neurons. In conclusion, the results of this study suggest that nesfatin-1 neurons respond to glutamatergic signals in the form of neuronal activation and that the glutamate receptors that are synthesized by nesfatin-1 neurons may participate in the glutamatergic regulation of these neurons.

Glutamatergic Activation of Neuronostatin Neurons in the Periventricular Nucleus of the Hypothalamus

Neuronostatin, a newly identified anorexigenic peptide, is present in the central nervous system. We tested the hypothesis that neuronostatin neurons are activated by feeding as a peripheral factor and that the glutamatergic system has regulatory influences on neuronostatin neurons. The first set of experiments analyzed the activation of neuronostatin neurons by refeeding as a physiological stimulus and the effectiveness of the glutamatergic system on this physiological stimulation. The subjects were randomly divided into three groups: the fasting group, refeeding group, and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)+refeeding group. We found that refeeding increased the phosphorylated signal transducers and transcription activator-5 (pSTAT5) expression in neuronostatin-positive neurons and that the CNQX injection significantly suppressed the number of pSTAT5-expressing neuronostatin neurons. The second set of experiments analyzed the activation pathways of neuronostatin neurons and the regulating effects of the glutamatergic system on neuronostatin neurons. The animals received intraperitoneal injections of glutamate receptor agonists (kainic acid, α-amino-3-hydroxy-5methyl-4-isoazepropionic acid (AMPA), and N-methyl-D-aspartate (NMDA)) or 0.9% NaCl. The number of c-Fos-expressing neuronostatin neurons significantly increased following the AMPA and NMDA injections. In conclusion, we found that the neuronostatin neurons were activated by peripheral or central signals, including food intake and/or glutamatergic innervation, and that the glutamate receptors played an important role in this activation.

Ceftriaxone Improves Cognitive Function and Upregulates GLT-1-Related Glutamate-Glutamine Cycle in APP/PS1 Mice

Alzheimer's disease (AD) is characterized by progressive impairment of learning, memory, and cognitive deficits. Glutamate is the major excitatory neurotransmitter in the central nervous system and plays an important role in learning, memory, and cognition. The homeostasis and reutilization of glutamate are dependent on astrocytic uptake by glutamate transporter-1 (GLT-1) and the subsequent glutamate-glutamine cycle. Increasing evidence showed impairments in GLT-1 expression and uptake activity and glutamate-glutamine cycle in AD. Ceftriaxone (Cef) has been reported to upregulate the expression and uptake of GLT-1. Therefore, the present study was undertaken to explore whether Cef can improve cognitive deficits of APP/PS1 mice in early stage of AD by upregulating GLT-1 expression, and then promoting the glutamate-glutamine cycle. It was shown that Cef treatment significantly alleviated the cognitive deficits measured by Morris water maze test and upregulated GLT-1 protein expression in the hippocampus of APP/PS1 mice. Particularly, the activity of glutamine synthetase (GS) and the protein expression of system N glutamine transporter 1 (SN1), which are the key factors involved in the glutamate-glutamine cycle, were significantly upregulated as well after the Cef treatment. Furthermore, inhibition of GLT-1 uptake activity by dihydrokainic acid, an inhibitor of GLT-1, blocked the Cef-induced improvement on the cognitive deficits, GS activity, and SN1 expression. The above results suggested that Cef could improve cognitive deficits of APP/PS1 mice in early stage of AD by upregulating the GLT-1 expression, GS activity, and SN1 expression, which would lead to stimulating the glutamate-glutamine cycle.

Neurochemical investigation of multiple locally induced seizures using microdialysis sampling: Epilepsy effects on glutamate release

The objective of this study was to develop an in vivo model for locally induced epilepsy. Epilepsy is a prominent neurological disorder that affects millions of people worldwide. Patients may experience either global seizures, affecting the entire brain, or focal seizures, affecting only one brain region. The majority of epileptic patients experience focal seizures but they go undiagnosed because such seizures can be difficult to detect. To better understand the effects of focal epilepsy on the neurochemistry of a brain region with high seizure diathesis, an animal model for locally induced seizures in the hippocampus was developed. In this model, two seizure events were chemically induced by administering the epileptogenic agent, 3-mercaptopropionic acid (3-MPA), to the hippocampus to disturb the balance between excitatory and inhibitory neurotransmitters in the brain. Microdialysis was used for local delivery of 3-MPA as well as for collection of dialysate for neurochemical analyses. Two periods of seizures separated by varying inter-seizure recovery times were employed, and changes in the release of the excitatory transmitter, glutamate, were measured. Significant differences in glutamate release were observed between the first and second seizure episodes. Diminished glutamate biosynthesis, enhanced glutamate re-uptake, and/or neuronal death were considered possible causes of the attenuated glutamate release during the second seizure episode. Biochemical measurements were indicative that a combination of these factors led to the attenuation in glutamate release.

Power of Tyrosine Assembly in Microtubule Stabilization and Neuroprotection Fueled by Phenol Appendages

Microtubules play a crucial role in maintenance of structure, function, axonal extensions, cargo transport, and polarity of neurons. During neurodegenerative diseases, microtubule structure and function get severely damaged due to destabilization of its major structural proteins. Therefore, design and development of molecules that stabilize these microtubule networks have always been an important strategy for development of potential neurotherapeutic candidates. Toward this venture, we designed and developed a tyrosine rich trisubstituted triazine molecule (TY3) that stabilizes microtubules through close interaction with the taxol binding site. Detailed structural investigations revealed that the phenolic protons are the key interacting partners of tubulin. Interestingly, we found that this molecule is noncytotoxic in PC12 derived neurons, stabilizes microtubules against nocodazole induced depolymerization, and increases expression of acetylated tubulin (Ac-K40), an important marker of tubulin stability. Further, results show that TY3 significantly induces neurite sprouting as compared to the untreated control as well as the two other analogues (TS3 and TF3). It also possesses anti-Aβ fibrillation properties as confirmed by ThT assay, which leads to its neuroprotective effect against amyloidogenic induced toxicity caused through nerve growth factor (NGF) deprivation in PC12 derived neurons. Remarkably, our results reveal that it reduces the expression of TrkA (pY490) associated with NGF deprived amyloidogenesis, which further proves that it is a potent amyloid β inhibitor. Moreover, it promoted the health of the rat primary cortical neurons through higher expression of key neuronal markers such as MAP2 and Tuj1. Finally, we observed that it has good serum stability and has the ability to cross the blood-brain barrier (BBB). Overall, our work indicates the importance of phenolic -OH in promoting neuroprotection and its importance could be implemented in the development of future neurotherapeutics.

Nanodelivery systems for overcoming limited transportation of therapeutic molecules through the blood-brain barrier

Due to the impermeable structure and barrier function of the blood-brain barrier (BBB), the delivery of therapeutic molecules into the CNS is extremely limited. Nanodelivery systems are regarded as the most effective and versatile carriers for the CNS, as they can transport cargo molecules across the BBB via various mechanisms. This review emphasizes the multi-functionalization strategies of nanodelivery systems and combinatorial approaches for the delivery of therapeutic drugs and genes into the CNS. The characteristics and functions of the BBB and underlying mechanisms of molecular translocation across the BBB are also described.

Ca2+ Signals in Astrocytes Facilitate Spread of Epileptiform Activity

Epileptic seizures are associated with increased astrocytic Ca2+ signaling, but the fine spatiotemporal kinetics of the ictal astrocyte-neuron interplay remains elusive. By using 2-photon imaging of awake head-fixed mice with chronic hippocampal windows we demonstrate that astrocytic Ca2+ signals precede neuronal Ca2+ elevations during the initial bout of kainate-induced seizures. On average, astrocytic Ca2+ elevations preceded neuronal activity in CA1 by about 8 s. In subsequent bouts of epileptic seizures, astrocytes and neurons were activated simultaneously. The initial astrocytic Ca2+ elevation was abolished in mice lacking the type 2 inositol-1,4,5-trisphosphate-receptor (Itpr2-/-). Furthermore, we found that Itpr2-/- mice exhibited 60% less epileptiform activity compared with wild-type mice when assessed by telemetric EEG monitoring. In both genotypes we also demonstrate that spreading depression waves may play a part in seizure termination. Our findings imply a role for astrocytic Ca2+ signals in ictogenesis.

( S)-2-Amino-3-(5-methyl-3-hydroxyisoxazol-4-yl)propanoic Acid (AMPA) and Kainate Receptor Ligands: Further Exploration of Bioisosteric Replacements and Structural and Biological Investigation

Starting from 1-4 and 7 structural templates, analogues based on bioisosteric replacements (5a-c vs 1, 2 and 6 vs 7) were synthesized for completing the SAR analysis. Interesting binding properties at GluA2, GluK1, and GluK3 receptors were discovered. The requirements for GluK3 interaction were elucidated by determining the X-ray structures of the GluK3-LBD with 2 and 5c and by computational studies. Antinociceptive potential was demonstrated for GluK1 partial agonist 3 and antagonist 7 (2 mg/kg ip).

Toxicokinetics and Physiologically Based Pharmacokinetic Modeling of the Shellfish Toxin Domoic Acid in Nonhuman Primates

Domoic acid (DA), a neurotoxin, is produced by marine algae and has caused toxications worldwide in animals and humans. However, the toxicokinetics of DA have not been fully evaluated, and information is missing on the disposition of DA following oral exposures at doses that are considered safe for human consumption. In this study, toxicokinetics of DA were investigated in cynomolgus monkeys following single doses of 5 µg/kg DA intravenously, 0.075 mg/kg DA orally, and 0.15 mg/kg DA orally. After intravenous dosing, DA had a systemic clearance of 124 ± 71 (ml/h)/kg, volume of distribution at steady state of 131 ± 71 ml/kg and elimination half-life of 1.2 ± 1.1 hours. However, following oral dosing, the average terminal half-life of DA was 11.3 ± 2.4 hours, indicating that DA disposition follows flip-flop kinetics with slow, rate-limiting absorption. The absorption of DA was low after oral dosing with absolute bioavailability of 6% ± 4%. The renal clearance of DA was variable [21-152 (ml/h)/kg] with 42% ± 11% of the intravenous DA dose recovered in urine. A physiologically based pharmacokinetic model was developed for DA in monkeys and humans that replicated the flip-flop kinetics observed after oral administration and allowed simulation of urinary excretion and brain and kidney distribution of DA following intravenous and oral dosing. This study is the first to characterize DA disposition at exposure levels close to the current estimated tolerable daily intake and to mechanistically model DA disposition in a model species, providing important information of the toxicokinetics of DA for human safety assessment.

Strategies for transporting nanoparticles across the blood-brain barrier

The existence of blood-brain barrier (BBB) hampers the effective treatment of central nervous system (CNS) diseases. Almost all macromolecular drugs and more than 98% of small molecule drugs cannot pass the BBB. Therefore, the BBB remains a big challenge for delivery of therapeutics to the central nervous system. With the structural and mechanistic elucidation of the BBB under both physiological and pathological conditions, it is now possible to design delivery systems that could cross the BBB effectively. Because of their advantageous properties, nanoparticles have been widely deployed for brain-targeted delivery. This review paper presents the current understanding of the BBB under physiological and pathological conditions, and summarizes strategies and systems for BBB crossing with a focus on nanoparticle-based drug delivery systems. In summary, with wider applications and broader prospection the treatment of brain targeted therapy, nano-medicines have proved to be more potent, more specific and less toxic than traditional drug therapy.