Delayed 2-h post-stroke administration of R18 and NA-1 (TAT-NR2B9c) peptides after permanent and/or transient middle cerebral artery occlusion in the rat

TAT-Modified Martentoxin Displays Intravenous Antiseizure Activities

Epilepsy is a chronic disease of brain dysfunction, which arises from imbalance between excitatory and inhibitory activities in neural circuits. Previously, we reported that peptide Martentoxin (MarTX), from scorpion Buthus martensii Karsch, displayed antiseizure activities by specifically inhibiting BK(α + β4) channel currents. Injection of MarTX into the hippocampal region of mice significantly alleviated convulsive seizures. However, intravenous injection of MarTX had no antiepileptic efficacy due to the blood-brain barrier (BBB). To address this, here, we designed cell-penetrating peptide TAT-modified MarTX, in which the linker containing three glycines was put between TAT and the N-terminus of MarTX (forming MTX-N-TAT) or between TAT and the C-terminus of MarTX (forming MTX-C-TAT), respectively. We prepared them in a large amount through Escherichia coli overexpression system and then probed their antiseizure activities. Our results indicated that intravenous injection of MTX-C-TAT showed significant therapeutic efficacy of antiseizure. It increased seizure latency, reduced the total seizure duration and the number of seizures at stages 3, 4, and 5, inhibited hippocampal neuronal hyperexcitability, and exhibited neuroprotective effects on hippocampal neurons. These studies implied that MTX-C-TAT displayed intravenous antiseizure activities properly through crossing BBB and would be a potential antiepileptic drug in the future.

Efficacy of polyarginine peptides in the treatment of stroke: A systematic review and meta-analysis

BACKGROUND

Disparities exist regarding an efficient treatment for stroke. Polyarginines have shown promising neuroprotective properties based on available published studies. Thus, the present study aims to systemically review and analyze existing evidence regarding polyarginine's administration efficacy in animal stroke models.

METHOD

Medline, Scopus, Embase, and Web of Science were systematically searched, in addition to manual search. Inclusion criteria were administrating polyarginine peptides in stroke animal models. Exclusion criteria were previous polyarginine administration, lacking a control group, review articles, and case reports. Data were collected and analyzed using STATA 17.0; a pooled standardized mean difference (SMD) with a 95% confidence interval (CI), meta-regression, and subgroup analyses were presented. Risk of bias, publication bias, and level of evidence were assessed using SYRCLE's tool, Egger's analysis, and Grading of Recommendations Assessment, Development and Evaluation framework, respectively.

RESULTS

From the 468 searched articles, 11 articles were included. Analyses showed that R18 significantly decreases infarct size (SMD = -0.65; 95% CI: -1.01, -0.29) and brain edema (SMD = -1.90; 95% CI: -3.28, -0.51) and improves neurological outcome (SMD = 0.67; 95% CI: 0.44, 0.91) and functional status (SMD = 0.55; 95% CI: 0.26, 0.85) in stroke animal models. Moreover, R18D significantly decreases infarct size (SMD = -0.75; 95% CI: -1.17, -0.33) and improves neurological outcome (SMD = 0.46; 95% CI: 0.06, 0.86) and functional status (SMD = 0.35; 95% CI: 0.16, 0.54) in stroke models.

CONCLUSION

Moderate level of evidence demonstrated that both R18 and R18D administration can significantly improve stroke outcomes in animal stroke models. However, considering the limitations, further pre-clinical and clinical studies are warranted to substantiate the neuroprotective efficacy of polyarginines for stroke.

Whether short peptides are good candidates for future neuroprotective therapeutics?

Neurodegenerative diseases are a broad group of largely debilitating, and ultimately terminal conditions resulting in progressive degeneration of different brain regions. The observed damages are associated with cell death, structural and functional deficits of neurons, or demyelination. The concept of neuroprotection concerns the administration of the agent, which should reverse some of the damage or prevent further adverse changes. A growing body of evidence suggested that among many classes of compounds considered as neuroprotective agents, peptides derived from natural materials or their synthetic analogs are good candidates. They presented a broad spectrum of activities and abilities to act through diverse mechanisms of action. Biologically active peptides have many properties, including antioxidant, antimicrobial, antiinflammatory, and immunomodulatory effects. Peptides with pro-survival and neuroprotective activities, associated with inhibition of oxidative stress, apoptosis, inflammation and are able to improve cell viability or mitochondrial functions, are also promising molecules of particular interest to the pharmaceutical industries. Peptide multiple activities open the way for broad application potential as therapeutic agents or ingredients of health-promoting functional foods. Significantly, synthetic peptides can be remodeled in numerous ways to have desired features, such as increased solubility or biological stability, as well as selectivity towards a specific receptor, and finally better membrane penetration. This review summarized the most common features of major neurodegenerative disorders, their causes, consequences, and reported new neuroprotective drug development approaches. The author focused on the unique perspectives in neuroprotection and provided a concise survey of short peptides proposed as novel therapeutic agents against various neurodegenerative diseases.

Poly-arginine-18 (R18) Confers Neuroprotection through Glutamate Receptor Modulation, Intracellular Calcium Reduction, and Preservation of Mitochondrial Function

Recent studies have highlighted that a novel class of neuroprotective peptide, known as cationic arginine-rich peptides (CARPs), have intrinsic neuroprotective properties and are particularly effective anti-excitotoxic agents. As such, the present study investigated the mechanisms underlying the anti-excitotoxic properties of CARPs, using poly-arginine-18 (R18; 18-mer of arginine) as a representative peptide. Cortical neuronal cultures subjected to glutamic acid excitotoxicity were used to assess the effects of R18 on ionotropic glutamate receptor (iGluR)-mediated intracellular calcium influx, and its ability to reduce neuronal injury from raised intracellular calcium levels after inhibition of endoplasmic reticulum calcium uptake by thapsigargin. The results indicate that R18 significantly reduces calcium influx by suppressing iGluR overactivation, and results in preservation of mitochondrial membrane potential (ΔΨm) and ATP production, and reduced ROS generation. R18 also protected cortical neurons against thapsigargin-induced neurotoxicity, which indicates that the peptide helps maintain neuronal survival when intracellular calcium levels are elevated. Taken together, these findings provide important insight into the mechanisms of action of R18, supporting its potential application as a neuroprotective therapeutic for acute and chronic neurological disorders.

NMDA receptor C-terminal signaling in development, plasticity, and disease

The NMDA subtype of ionotropic glutamate receptor is a sophisticated integrator and transducer of information. NMDAR-mediated signals control diverse processes across the life course, including synaptogenesis and synaptic plasticity, as well as contribute to excitotoxic processes in neurological disorders. At the basic biophysical level, the NMDAR is a coincidence detector, requiring the co-presence of agonist, co-agonist, and membrane depolarization in order to open. However, the NMDAR is not merely a conduit for ions to flow through; it is linked on the cytoplasmic side to a large network of signaling and scaffolding proteins, primarily via the C-terminal domain of NMDAR GluN2 subunits. These physical interactions help to organize the signaling cascades downstream of NMDAR activation. Notably, the NMDAR does not come in a single form: the subunit composition of the NMDAR, particularly the GluN2 subunit subtype (GluN2A-D), influences the biophysical properties of the channel. Moreover, a growing number of studies have illuminated the extent to which GluN2 C-terminal interactions vary according to GluN2 subtype and how this impacts on the processes that NMDAR activity controls. We will review recent advances, controversies, and outstanding questions in this active area of research.

Effect of Polyarginine Peptide R18D Following a Traumatic Brain Injury in Sprague-Dawley Rats

•

Cationic arginine-rich peptides (CARPs) have previously demonstrated neuroprotective efficacy in a rat model of traumatic brain injury (TBI).

•

The CARP R18D significantly reduced the extent of axonal injury at a high dose of 1000 nmol/kg.

•

Both high (1000 nmol/kg) and low (100 nmol/kg) doses only showed a trend in functional improvement.

Background

Despite extensive studies, there are still no clinically available neuroprotective treatments for traumatic brain injury.

Objectives

In previous studies we demonstrated beneficial treatment effects of polyarginine peptides R18 (18-mer of arginine; 300 nmol/kg) and R18D (18-mer of D-arginine; 1000 nmol/kg) in a rat model of impact-acceleration closed-head injury.

Methods

We examined the efficacy of R18D when intravenously administered at a low (100 nmol/kg) and high (1000 nmol/kg) dose, 30 minutes after a closed-head injury in male Sprague-Dawley rats.

Results

At postinjury day 3, treatment with R18D at the high dose significantly reduced axonal injury (P = 0.044), whereas the low-dose treatment of R18D showed a trend for reduced axonal injury. Following assessment in the Barnes maze, both doses of R18D treatment appeared to improve learning and memory recovery compared with vehicle treatment at postinjury days 1 and 3, albeit not to a statistically significant level. Rotarod assessment of vestibulomotor recovery did not differ between R18D and the vehicle treatment groups.

Conclusions

R18D modestly decreased axonal injury only at the highest dose used but had no significant effect on functional recovery. These findings warrant further studies with additional doses to better understand peptide pharmacodynamics and provide information to guide optimal dosing.

Tissue distribution of intravenously administrated poly-arginine peptide R18D in healthy male Sprague–Dawley rats

Aim: R18D is a poly-arginine peptide that has demonstrated neuroprotection in preclinical models of excitotoxicity, stroke, hypoxic-ischemic encephalopathy and traumatic brain injury. Here, we examined the peptide’s uptake in serum. Materials & methods: Healthy, male Sprague–Dawley rats were intravenously administered either 1000 nmol/kg R18D (D-enantiomer of R18) or approximately 2.5 nmol/kg (36 ± 9 MBq) [18F]R18D, for serum and organ tissue uptake, respectively. Serum samples underwent mass spectrometric analysis to detect unbound R18D peptide. Animals administered [18F]R18D were subjected to positron emission tomography imaging. Results & conclusion: Free R18D was detected at 5 min post-infusion in serum samples. [18F]R18D was rapidly distributed to the kidney (6–7%ID/g), and a small fraction localized to the brain (0.115–0.123%ID/g) over a 60-min acquisition period.

NMDA receptor C-terminal signaling in development, plasticity, and disease

The NMDA subtype of ionotropic glutamate receptor is a sophisticated integrator and transducer of information. NMDAR-mediated signals control diverse processes across the life course, including synaptogenesis and synaptic plasticity, as well as contribute to excitotoxic processes in neurological disorders. At the basic biophysical level, the NMDAR is a coincidence detector, requiring the co-presence of agonist, co-agonist, and membrane depolarization in order to open. However, the NMDAR is not merely a conduit for ions to flow through; it is linked on the cytoplasmic side to a large network of signaling and scaffolding proteins, primarily via the C-terminal domain of NMDAR GluN2 subunits. These physical interactions help to organize the signaling cascades downstream of NMDAR activation. Notably, the NMDAR does not come in a single form: the subunit composition of the NMDAR, particularly the GluN2 subunit subtype (GluN2A–D), influences the biophysical properties of the channel. Moreover, a growing number of studies have illuminated the extent to which GluN2 C-terminal interactions vary according to GluN2 subtype and how this impacts on the processes that NMDAR activity controls. We will review recent advances, controversies, and outstanding questions in this active area of research.

Proteomic analysis of cortical neuronal cultures treated with poly-arginine peptide-18 (R18) and exposed to glutamic acid excitotoxicity

Poly-arginine peptide-18 (R18) has recently emerged as a highly effective neuroprotective agent in experimental stroke models, and is particularly efficacious in protecting cortical neurons against glutamic acid excitotoxicity. While we have previously demonstrated that R18 can reduce excitotoxicity-induced neuronal calcium influx, other molecular events associated with R18 neuroprotection are yet to investigated. Therefore, in this study we were particularly interested in protein expression changes in R18 treated neurons subjected to excitotoxicity. Proteomic analysis was used to compare protein expression patterns in primary cortical neuronal cultures subjected to: (i) R18-treatment alone (R18); (ii) glutamic acid excitotoxic injury (Glut); (iii) R18-treatment and glutamic acid injury (R18 + Glut); (iv) no treatment (Cont). Whole cell lysates were harvested 24 h post-injury and subjected to quantitative proteomic analysis (iTRAQ), coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and subsequent bioinformatic analysis of differentially expressed proteins (DEPs). Relative to control cultures, R18, Glut, and R18 + Glut treatment resulted in the detection of 5, 95 and 14 DEPs respectively. Compared to Glut alone, R18 + Glut revealed 98 DEPs, including 73 proteins whose expression was also altered by treatment with Glut and/or R18 alone, as well as 25 other uniquely regulated proteins. R18 treatment reversed the up- or down-regulation of all 73 Glut-associated DEPs, which included proteins involved in mitochondrial integrity, ATP generation, mRNA processing and protein translation. Analysis of protein-protein interactions of the 73 DEPs showed they were primarily associated with mitochondrial respiration, proteasome activity and protein synthesis, transmembrane trafficking, axonal growth and neuronal differentiation, and carbohydrate metabolism. Identified protein pathways associated with proteostasis and energy metabolism, and with pathways involved in neurodegeneration. Collectively, the findings indicate that R18 neuroprotection following excitotoxicity is associated with preservation of neuronal protein profiles, and differential protein expression that assists in maintaining mitochondrial function and energy production, protein homeostasis, and membrane trafficking.

Mitochondria and neuroprotection in stroke: Cationic arginine-rich peptides (CARPs) as a novel class of mitochondria-targeted neuroprotective therapeutics

Stroke is the second leading cause of death globally and represents a major cause of devastating long-term disability. Despite sustained efforts to develop clinically effective neuroprotective therapies, presently there is no clinically available neuroprotective agent for stroke. As a central mediator of neurodamaging events in stroke, mitochondria are recognised as a critical neuroprotective target, and as such, provide a focus for developing mitochondrial-targeted therapeutics. In recent years, cationic arginine-rich peptides (CARPs) have been identified as a novel class of neuroprotective agent with several demonstrated mechanisms of action, including their ability to target mitochondria and exert positive effects on the organelle. This review provides an overview on neuronal mitochondrial dysfunction in ischaemic stroke pathophysiology and highlights the potential beneficial effects of CARPs on mitochondria in the ischaemic brain following stroke.