Low-Molecular Weight BDNF Mimetic, Dimeric Dipeptide GSB-106, Reverses Depressive Symptoms in Mouse Chronic Social Defeat Stress

Novel treatments for anorexia nervosa: Insights from neuroplasticity research

OBJECTIVE

Treatment for anorexia nervosa (AN) remains challenging; there are no approved psychopharmacological interventions and psychotherapeutic strategies have variable efficacy. The investigation of evidence-based treatments has so far been compounded by an underdeveloped understanding into the neurobiological changes associated with the acute stages of AN. There is converging evidence of deficiencies in neuroplasticity in AN.

METHOD

This paper provides an overview of neuroimaging, neuropsychological, molecular and qualitative findings relating to neuroplasticity in AN, translating these findings to the identification of novel biological and psychotherapeutic strategies.

RESULTS

Novel psychopharmacological approaches that may ameliorate deficiencies in neuroplasticity include medications such as ketamine, psilocybin and human recombinant leptin. Anti-inflammatory medications and brain-derived neurotrophic factor mimetics may emerge as potential treatments following further research. Psychotherapeutic strategies that may target neuroplastic deficiencies, as well as having wider effects on identity, include imagery rescripting, memory specificity training, cognitive remediation therapy, exposure therapies, narrative therapies, cultural interventions (e.g. music and arts therapies) and yoga/mindfulness-based interventions.

CONCLUSIONS

Treatments specifically targeted towards mitigating the neurobiological sequalae of AN are warranted, and emerging neurobiological and neuropsychological research utilising longitudinal designs and large sample sizes, as well as initial feasibility studies, are necessitated to bolster translational efforts.

Neurotrophin peptidomimetics for the treatment of neurodegenerative diseases

Neurotrophins, such as nerve growth factor and brain-derived neurotrophic factor, play an essential role in the survival of neurons. However, incorporating better features can increase their therapeutic efficacy in neurodegenerative diseases (NDs). Peptidomimetics, which mimic these neurotrophins, show potential for treating NDs. This study emphasizes the use of peptidomimetics from neurotrophins for treating NDs and their benefits. By improving bioavailability and stability, these molecules can completely transform the therapy for NDs. This in-depth review guides researchers and pharmaceutical developers, providing insight into the changing field of neurodegenerative medicine.

Electroacupuncture ameliorates chronic unpredictable mild stress-induced depression-like behavior and cognitive impairment through suppressing oxidative stress and neuroinflammation in rats

BACKGROUND

Depression is associated with lowered mood, anxiety, anhedonia, cognitive impairments, and even suicidal tendencies in severe cases. Yet few studies have directed acupuncture's mechanism toward enhancing axonal repair correlated with synaptic plasticity and anti-inflammatory effects related to oxidative stress in the hippocampus.

METHODS

Male Sprague-Dawley (SD) rats were randomly divided into control group (CON), chronic unpredictable mild stress (CUMS) group, CUMS + electroacupuncture group (EA), and CUMS + fluoxetine group (FLX) (n = 10/group). Rats were given a 28-day treatment at the Shangxing (GV23) and Fengfu (GV16) acupoints with electroacupuncture or fluoxetine (2.1 mg/kg).

RESULTS

Rats exposed to CUMS induced depression-like behaviors and spatial learning-memory impairment, changed the ionized calcium binding adaptor molecule 1 (IBA-1), Vglut1, myelin basic protein (MBP), and postsynaptic density protein 95 (PSD95) level of hippocampal, increased the Nod-like receptor protein 3 (NLRP3), atypical squamous cell (ASC), Caspase level and hippocampal reactive oxygen species (ROS), and prompted the activation of Epha4-mediated signaling and an inflammatory response. Conversely, electroacupuncture administration reduced these changes and prevented depression-like behaviors and cognitive impairment. Electroacupuncture also promoted hippocampal expression of Sirtuin1(SIRT1), Nuclear factor erythroid 2-like (Nrf2), Heme oxygenase-1 (HO-1); reduced the expression of interleukin-1β (IL-1β), interleukin-18 (IL-18), and tumor necrosis factor-alpha (TNF-α); and prevented neural damage, particularly the synaptic myelin sheath, and neuroinflammation by regulating Eph receptor A4 (EphA4) in the hippocampal.

CONCLUSION

These results indicate that electroacupuncture prevents depression-like behaviors with cognitive impairment and synaptic and neuronal damage, probably by reducing EphA4, which mediates ROS hyperfunction and the inflammatory response.

Pharmacogenetic Analysis of the Interaction of the Low-Molecular-Weight BDNF Mimetic Dipeptide GSB-106 with TRK Receptors

Using TrkA or TrkB receptor gene knockout HT-22 cells, the selectivity of the interaction of the low-molecular-weight dipeptide BDNF mimetic GSB-106 (hexamethylenediamide bis(N-monosuccinyl-L-seryl-L-lysine)) with TrkB receptors was shown.

Growth factors and their peptide mimetics for treatment of traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of disability in adults, caused by a physical insult damaging the brain. Growth factor-based therapies have the potential to reduce the effects of secondary injury and improve outcomes by providing neuroprotection against glutamate excitotoxicity, oxidative damage, hypoxia, and ischemia, as well as promoting neurite outgrowth and the formation of new blood vessels. Despite promising evidence in preclinical studies, few neurotrophic factors have been tested in clinical trials for TBI. Translation to the clinic is not trivial and is limited by the short in vivo half-life of the protein, the inability to cross the blood-brain barrier and human delivery systems. Synthetic peptide mimetics have the potential to be used in place of recombinant growth factors, activating the same downstream signalling pathways, with a decrease in size and more favourable pharmacokinetic properties. In this review, we will discuss growth factors with the potential to modulate damage caused by secondary injury mechanisms following a traumatic brain injury that have been trialled in other indications including spinal cord injury, stroke and neurodegenerative diseases. Peptide mimetics of nerve growth factor (NGF), hepatocyte growth factor (HGF), glial cell line-derived growth factor (GDNF), brain-derived neurotrophic factor (BDNF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) will be highlighted, most of which have not yet been tested in preclinical or clinical models of TBI.

Neurotrophic Activity and Its Modulation by Zinc Ion of a Dimeric Peptide Mimicking the Brain-Derived Neurotrophic Factor N-Terminal Region

Brain-derived neurotrophic factor (BDNF) is a neurotrophin (NT) essential for neuronal development and synaptic plasticity. Dysregulation of BDNF signaling is implicated in different neurological disorders. The direct NT administration as therapeutics has revealed to be challenging. This has prompted the design of peptides mimicking different regions of the BDNF structure. Although loops 2 and 4 have been thoroughly investigated, less is known regarding the BDNF N-terminal region, which is involved in the selective recognition of the TrkB receptor. Herein, a dimeric form of the linear peptide encompassing the 1-12 residues of the BDNF N-terminal (d-bdnf) was synthesized. It demonstrated to act as an agonist promoting specific phosphorylation of TrkB and downstream ERK and AKT effectors. The ability to promote TrkB dimerization was investigated by advanced fluorescence microscopy and molecular dynamics (MD) simulations, finding activation modes shared with BDNF. Furthermore, d-bdnf was able to sustain neurite outgrowth and increase the expression of differentiation (NEFM, LAMC1) and polarization markers (MAP2, MAPT) demonstrating its neurotrophic activity. As TrkB activity is affected by zinc ions in the synaptic cleft, we first verified the ability of d-bdnf to coordinate zinc and then the effect of such complexation on its activity. The d-bdnf neurotrophic activity was reduced by zinc complexation, demonstrating the role of the latter in tuning the activity of the new peptido-mimetic. Taken together our data uncover the neurotrophic properties of a novel BDNF mimetic peptide and pave the way for future studies to understand the pharmacological basis of d-bdnf action and develop novel BDNF-based therapeutic strategies.

New Frontiers in Neurodegeneration and Regeneration Associated with Brain-Derived Neurotrophic Factor and the rs6265 Single Nucleotide Polymorphism

Brain-derived neurotrophic factor is an extensively studied neurotrophin implicated in the pathology of multiple neurodegenerative and psychiatric disorders including, but not limited to, Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, traumatic brain injury, major de-pressive disorder, and schizophrenia. Here we provide a brief summary of current knowledge on the role of BDNF and the common human single nucleotide polymorphism, rs6265, in driving the pathogenesis and rehabilitation in these disorders, as well as the status of BDNF-targeted therapies. A common trend has emerged correlating low BDNF levels, either detected within the central nervous system or peripherally, to disease states, suggesting that BDNF replacement therapies may hold clinical promise. In addition, we introduce evidence for a distinct role of the BDNF pro-peptide as a biologically active ligand and the need for continuing studies on its neurological function outside of that as a molecular chaperone. Finally, we highlight the latest research describing the role of rs6265 expression in mechanisms of neurodegeneration as well as paradoxical advances in the understanding of this genetic variant in neuroregeneration. All of this is discussed in the context of personalized medicine, acknowledging there is no “one size fits all” therapy for neurodegenerative or psychiatric disorders and that continued study of the multiple BDNF isoforms and genetic variants represents an avenue for discovery ripe with therapeutic potential.

Antidepressant-like Effects of BDNF and NGF Individual Loop Dipeptide Mimetics Depend on the Signal Transmission Patterns Associated with Trk

Neurotrophins are considered as an attractive target for the development of antidepressants with a novel mechanism of action. Previously, the dimeric dipeptide mimetics of individual loops of nerve growth factor, NGF (GK-6, loop 1; GK-2, loop 4) and brain-derived neurotrophic factor, BDNF (GSB-214, loop 1; GTS-201, loop 2; GSB-106, loop 4) were designed and synthesized. All the mimetics of NGF and BDNF in vitro after a 5–180 min incubation in a HT-22 cell culture were able to phosphorylate the tropomyosin-related kinase A (TrkA) or B (TrkB) receptors, respectively, but had different post-receptor signaling patterns. In the present study, we conduct comparative research of the antidepressant-like activity of these mimetics at acute and subchronic administration in the forced swim test in mice. Only the dipeptide GSB-106 that in vitro activates mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK), phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) and phospholipase C-gamma (PLC_γ) post-receptor pathways exhibited antidepressant-like activity (0.1 and 1.0 mg/kg, ip) at acute administration. At the same time, the inhibition of any one of these signaling pathways completely prevented the antidepressant-like effects of GSB-106 in the forced swim test. All the NGF mimetics were inactive after a single injection regardless of post-receptor in vitro signaling patterns. All the investigated dipeptides, except GTS-201, not activating PI3K/AKT in vitro unlike the other compounds, were active at subchronic administration. The data obtained demonstrate that the low-molecular weight BDNF mimetic GSB-106 that activates all three main post-receptor TrkB signaling pathways is the most promising for the development as an antidepressant.

Analysis of Antidepressant-like Effects and Action Mechanisms of GSB-106, a Small Molecule, Affecting the TrkB Signaling

Induction of BDNF-TrkB signaling is associated with the action mechanisms of conventional and fast-acting antidepressants. GSB-106, developed as a small dimeric dipeptide mimetic of BDNF, was previously shown to produce antidepressant-like effects in the mouse Porsolt test, tail suspension test, Nomura water wheel test, in the chronic social defeat stress model and in the inflammation-induced model of depression. In the present study, we evaluated the effect of chronic per os administration of GSB-106 to Balb/c mice under unpredictable chronic mild stress (UCMS). It was observed for the first time that long term GSB-106 treatment (1 mg/kg, 26 days) during ongoing UCMS procedure ameliorated the depressive-like behaviors in mice as indicated by the Porsolt test. In addition, chronic per os administration of GSB-106 resulted in an increase in BDNF levels, which were found to be decreased in the prefrontal cortex and hippocampus of mice after UCMS. Furthermore, prolonged GSB-106 treatment was accompanied by an increase in the content of pTrkB^706/707 in the prefrontal cortex and by a pronounced increase in the level of pTrkB⁸¹⁶ in both studied brain structures of mice subjected to UCMS procedure. In summary, the present data show that chronic GSB-106 treatment produces an antidepressant-like effect in the unpredictable chronic mild stress model, which is likely to be associated with the regulation of the BDNF-TrkB signaling.

919 Syrup Alleviates Postpartum Depression by Modulating the Structure and Metabolism of Gut Microbes and Affecting the Function of the Hippocampal GABA/Glutamate System

Postpartum depression (PPD) is a mental disorder that affects pregnant women around the world, with serious consequences for mothers, families, and children. Its pathogenesis remains unclear, and medications for treating PPD that can be used during lactation remain to be identified. 919 syrup (919 TJ) is a Chinese herbal medicine that has been shown to be beneficial in the treatment of postpartum depression in both clinical and experimental studies. The mechanism of action of 919 TJ is unclear. 919 syrup is ingested orally, making the potential interaction between the drug and the gut microbiome impossible to ignore. We therefore hypothesized that 919 syrup could improve the symptoms of postpartum depression by affecting the structure and function of the intestinal flora, thereby altering hippocampal metabolism. We compared changes in hippocampal metabolism, fecal metabolism, and intestinal microflora of control BALB/c mice, mice with induced untreated PPD, and mice with induced PPD treated with 919 TJ, and found that 4-aminobutyric acid (GABA) in the hippocampus corresponded with PPD behaviors. Based on changes in GABA levels, multiple key gut bacterial species (Mucispirillum schaedleri, Bifidobacterium pseudolongum, Desulfovibrio piger, Alloprevotella tannerae, Bacteroides sp.2.1.33B and Prevotella sp. CAG:755) were associated with PPD. Metabolic markers that may represent the function of the intestinal microbiota in mice with PPD were identified (Met-Arg, urocanic acid, thioetheramide-PC, L-pipecolic acid, and linoleoyl ethanolamide). The relationship between these factors is not a simple one-to-one correspondence, but more likely a network of staggered functions. We therefore believe that the composition and function of the entire intestinal flora should be emphasized in research studying the gut and PPD, rather than changes in the abundance of individual bacterial species. The introduction of this concept of “GutBalance” may help clarify the relationship between gut bacteria and systemic disease.

Peptides Derived from Growth Factors to Treat Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by progressive neuron losses in memory-related brain structures. The classical features of AD are a dysregulation of the cholinergic system, the accumulation of amyloid plaques, and neurofibrillary tangles. Unfortunately, current treatments are unable to cure or even delay the progression of the disease. Therefore, new therapeutic strategies have emerged, such as the exogenous administration of neurotrophic factors (e.g., NGF and BDNF) that are deficient or dysregulated in AD. However, their low capacity to cross the blood-brain barrier and their exorbitant cost currently limit their use. To overcome these limitations, short peptides mimicking the binding receptor sites of these growth factors have been developed. Such peptides can target selective signaling pathways involved in neuron survival, differentiation, and/or maintenance. This review focuses on growth factors and their derived peptides as potential treatment for AD. It describes (1) the physiological functions of growth factors in the brain, their neuronal signaling pathways, and alteration in AD; (2) the strategies to develop peptides derived from growth factor and their capacity to mimic the role of native proteins; and (3) new advancements and potential in using these molecules as therapeutic treatments for AD, as well as their limitations.