Neuroprotective effect of GK-2, a dipeptide mimetic of nerve growth factor, during experimental focal ischemia in middle cerebral artery basin

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.

Low-Molecular-Weight Perorally Active Nerve Growth Factor Mimetic Reduces Manifestations of Diabetic Neuropathy in Wistar Rats

A low-molecular-weight nerve growth factor mimetic, compound GK-2 (bis-(N-monosuccinyl- L-glutamyl-L-lysine)hexamethylenediamide) that previously demonstrated antidiabetic activity in rats with streptozotocin-induced type 2 diabetes mellitus was studied on the model of diabetic neuropathy. It was found that in 8 weeks after diabetes mellitus development, untreated diabetic rats demonstrated impaired tactile sensitivity in von Frey test, while GK-2 therapy (7.5 mg/kg orally for 28 days) restored this parameter. The decrease of tactile sensitivity in diabetic neuropathy closely correlated with the severity of hyperglycemia (r=0.76). Our findings are consistent with the concept on the role of glucose toxicity and nerve growth factor deficiency in the pathogenesis of diabetic neuropathy and attest to feasibility of further studies of nerve growth factor mimetic GK-2 as a potential treatment for diabetes and diabetic neuropathy.

Brain-Derived Neurotrophic Factor (BDNF) As a Regulator of Apoptosis under Conditions of Focal Experimental Stroke

The immunolocalization of apoptotic factors in rat neocortex was studied on the model of permanent occlusion of the middle cerebral artery with administration of exogenous BDNF. We revealed heterogeneous distribution of pro- and anti-apoptotic factors in the stroke area and in the surrounding penumbra, where caspase-3⁺ and p53⁺ cells were found. Their number was maximum on day 3 of ischemia. The number of neurons containing anti-apoptotic factors was relatively decreased. Injection of BDNF changed the distribution of apoptotic factors. In the penumbra area, BDNF enhanced the expression of Mdm2 primarily in the pyramid cells of layers V/VI and Bcl-2 in interneurons of layers II and III. Localization of p53 and caspase-3 varied at different terms of the ischemic period and showed an inverse dependence. Considering the selective neuroprotective effect of BDNF, various mechanisms of the formation of ischemic tolerance in neurons are proposed.

GK-2 Reduces Death of Cultured Granule Neurons in Cerebellum Induced by the Toxic Effects of Zinc Ions

Peptide mimetic of nerve growth factor GK-2 in a dose of 1-2 mg/liter improves survival of cultured rat cerebellar granule neurons exposed to the cytotoxic effect of zinc ions, but has no protective effect against copper ion cytotoxicity. Experiments on cultured rat hippocampal slices demonstrated that GK-2 did not affect reactivity of pyramidal neurons and long-term potentiation in the hippocampal field CA1 and the probability of glutamate release from presynaptic terminals in the synapses of the CA3-CA1 fields. The results suggest that GK-2 does not affect the functional properties of synaptic transmission under normal conditions, but protects neurons from the toxic effects of zinc, which creates prerequisites for GK-12 use in the treatment of neurodegenerative diseases.

[An experimental evaluation of the therapeutic window of the neuroprotective activity of a low-molecular nerve growth factor mimetic GK-2]

AIM

To identify the time interval for the preservation of the effect of GK-2 depending on the start of administration after modeling ischemic stroke by the transient occlusion of the middle cerebral artery in rats.

MATERIAL AND METHODS

The experiments were performed on 33 wild-type male rats and 81 male Wistar rats. Animals were kept in standard conditions. Ischemic stroke was modelled by thread occlusion of the middle cerebral artery.

RESULTS AND CONCLUSION

It was found that GK-2 at a daily dose of 1 mg/kg, intraperitoneally, during 7 days statistically significantly reduces brain infarct volume by 20-60% at the first injection from 4 to 24h, with the highest effect 6-8 hours after surgery. Thus, the 'therapeutic window' of GK-2 detected in the experiment is no less than 24 hours, which exceeds the existing neuroprotective agents.

Innovative Therapy for Alzheimer's Disease-With Focus on Biodelivery of NGF

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder associated with abnormal protein modification, inflammation and memory impairment. Aggregated amyloid beta (Aβ) and phosphorylated tau proteins are medical diagnostic features. Loss of memory in AD has been associated with central cholinergic dysfunction in basal forebrain, from where the cholinergic circuitry projects to cerebral cortex and hippocampus. Various reports link AD progression with declining activity of cholinergic neurons in basal forebrain. The neurotrophic molecule, nerve growth factor (NGF), plays a major role in the maintenance of cholinergic neurons integrity and function, both during development and adulthood. Numerous studies have also shown that NGF contributes to the survival and regeneration of neurons during aging and in age-related diseases such as AD. Changes in neurotrophic signaling pathways are involved in the aging process and contribute to cholinergic and cognitive decline as observed in AD. Further, gradual dysregulation of neurotrophic factors like NGF and brain derived neurotrophic factor (BDNF) have been reported during AD development thus intensifying further research in targeting these factors as disease modifying therapies against AD. Today, there is no cure available for AD and the effects of the symptomatic treatment like cholinesterase inhibitors (ChEIs) and memantine are transient and moderate. Although many AD treatment studies are being carried out, there has not been any breakthrough and new therapies are thus highly needed. Long-term effective therapy for alleviating cognitive impairment is a major unmet need. Discussion and summarizing the new advancements of using NGF as a potential therapeutic implication in AD are important. In summary, the intent of this review is describing available experimental and clinical data related to AD therapy, priming to gain additional facts associated with the importance of NGF for AD treatment, and encapsulated cell biodelivery (ECB) as an efficient tool for NGF delivery.

The delayed protective effect of GK-2, а dipeptide mimetic of Nerve Growth Factor, in a model of rat traumatic brain injury

The delayed protective effect of GK-2, a dipeptide mimetic of Nerve Growth Factor, was investigated on the model of focal one-sided traumatic brain injury (TBI) of the sensorimotor cortex region on the 180th day after the injury. TBI caused a reliably disruption of the functions of the limbs contralateral to injury focus. The intraperitoneal administration of GK-2 (1 mg/kg) from 1st to 4th and from 7th to 10th days after TBI reduced the impairment of the motor functions of the limbs. This therapeutic effect significant manifested itself from the 7th day and continued until the end of the experiment - on the 180th day after TBI. Morphological studies of the animal brains on the 180th day after TBI demonstrated a decrease in the number of neurons in the V layer of the cerebral cortex and a decrease in the thickness of the corpus callosum. The treatment of animals with GK-2 after TBI statistically significant prevented a decrease in the density of neurons in the ipsilateral hemisphere and a decrease in the thickness of the corpus callosum in the contralateral hemisphere in comparison with untreated animals. Additionally, we showed in vitro that GK-2 exhibits neuroprotective properties under oxidative stress in primary hippocampal cultures. Our results demonstrate that the use of GK-2 at the early stages of development of traumatic brain damage can prevent such delayed damage as neuronal and axonal degeneration as well as reduce TBI-related disruptions of brain functions.

[The experimental strategies in the study of ischemic stroke]

Literature data and own experience in the studies of experimental stroke methodology are reviewed. Advantages and disadvantages of the common models of focal ischemia used in the laboratory practice are discussed in details. The advantages of the filament occlusion of the middle cerebral artery in rats as the most adequate model of human stroke are substantiated. The authors suggest a modification of this variant using an additional coagulation of the pterygopalatine artery that allows the exclusion of the retrograde and collateral blood flow into the inner carotid artery after ligation of the common and external carotid arteries.

Novel Technologies for Dipeptide Drugs Design and their Implantation

The article is an overview of author's data obtained in the framework of the project "The Creation of dipeptide preparations" at the V.V. Zakusov Institute of Pharmacology, Moscow, Russia. Advantages of dipeptides over longer peptides consist in that they are orally active owing to higher stability and ability to penetrate biological barriers due to the presence of specific ATP-dependent transporters in enterocytes and blood-brain barrier. Two original approaches for dipeptide drugs design have been developed. Both of them are based on the idea of a leading role of central dipeptide fragment of the peptide chain beta-turn in the peptide-receptor interaction. The first approach, named "peptide drug-based design" represents the transformation of known nonpeptide drug into its dipeptide topological analog. The latter usually corresponds to a beta-turn of some regulatory peptide. The second approach represents the design of tripeptoide mimetic of the beta-turn of regulatory peptide or protein. The results of the studies, which led to the discovery of endogenous prototypes of the known non-peptide drugs piracetam and sulpiride, are presented herein. The paper discusses the process, based on the abovementioned principles, that was used in designing of nontoxic, orally available, highly effective dipeptide drugs: nootropic noopept, dipeptide analog of piracetam; antipsychotic dilept, neurotensin tripeptoid analog; selective anxiolytic GB-115, tripeptoid analog of CCK-4, and potential neuroprotector GK-2, homodimeric dipeptide analog of NGF.

Role of Nerve Growth Factor in Plasticity of Forebrain Cholinergic Neurons

Neuronal plastic rearrangements during the development and functioning of neurons are largely regulated by trophic factors, including nerve growth factor (NGF). NGF is also involved in the pathogenesis of Alzheimer's disease. In the brain, NGF is produced in structures innervated by basal forebrain cholinergic neurons and retrogradely transported along the axons to the bodies of cholinergic neurons. NGF is essential for normal development and functioning of the basal forebrain; it affects formation of the dendritic tree and modulates the activities of choline acetyltransferase and acetylcholinesterase in basal forebrain neurons. The trophic effect of NGF is mediated through its interactions with TrkA and p75 receptors. Experimental and clinical studies have shown that brain levels of NGF are altered in various pathologies. However, the therapeutic use of NGF is limited by its poor ability to penetrate the blood-brain barrier, adverse side effects that are due to the pleiotropic action of this factor, and the possibility of immune response to NGF. For this reason, the development of gene therapy methods for treating NGF deficit-associated pathologies is of particular interest. Another approach is creation of low molecular weight NGF mimetics that would interact with the corresponding receptors and display high biological activity but be free of the unfavorable effects of NGF.

Mimetics of brain-derived neurotrophic factor loops 1 and 4 are active in a model of ischemic stroke in rats

BACKGROUND

Two dimeric dipeptides, bis-(N-monosuccinyl-l-seryl-l-lysine)hexamethylenediamide (GSB-106) and bis-(N-monosuccinyl-l-methionyl-l-serine) heptamethylenediamide (GSB-214), were designed based on the brain-derived neurotrophic factor (BDNF) loop 4 and loop 1 β-turn sequences, respectively. Earlier, both of these dipeptides were shown to exhibit neuroprotective activity in vitro (10-5-10-8 M). The present study aimed to investigate the mechanisms of action of these peptides and their neuroprotective activity in an experimental stroke model.

METHODS

We used western blot and HT-22 hippocampal neuronal cell line to investigate whether these peptides induced phosphorylation of the TrkB receptor and the AKT and ERK kinases. Rat middle cerebral artery occlusion (MCAO) was used as a stroke model. GSB-106 and GSB-214 were administered intraperitoneally (0.1 mg (1.3×10-7 mol)/kg) 4 hours after MCAO and daily for 7 days. The cerebral infarct volumes were measured with 2,3,5-triphenyltetrazolium chloride staining 21 days after MCAO.

RESULTS

Both compounds were shown to elevate the TrkB phosphorylation level while having different post-receptor signaling patterns. GSB-106 activated the PI3K/AKT and MAPK/ERK pathways simultaneously, whereas GSB-214 activated the PI3K/AKT only. In experimental stroke, the reduction of cerebral infarct volume by GSB-106 (∼66%) was significantly greater than that of GSB-214 (∼28% reduction), which could be explained by the fundamental role of the MAPK/ERK pathway in neurogenesis and neuroplasticity. Notably, between these two dipeptides, only GSB-106 exhibited antidepressant activity, as was found previously.

CONCLUSION

The results provided support for the beneficial pharmacological properties of BDNF loop 4 mimetic GSB-106, thereby suggesting a potential role for this dipeptide as a therapeutic agent.

Dimeric dipeptide mimetics of the nerve growth factor Loop 4 and Loop 1 activate TRKA with different patterns of intracellular signal transduction

Background

This study aimed at developing nerve growth factor (NGF) mimetics that selectively activate specific biological signals and, as a result, lack the side effects of the full-length protein. Two dimeric dipeptides, bis-(N-aminocaproyl-glycyl-L-lysine) hexamethylenediamide (GK-6) and bis(N-succinyl-L-glutamyl-L-lysine) hexamethylenediamide (GK-2), were designed based on the most exposed outside fragments of NGF, namely, the loop 1 and loop 4 β-turn sequences, respectively. These dipeptides exhibited neuroprotective activity in vitro at micro-nanomolar concentrations.

Results

Studies on the mechanism of action revealed that both compounds elevate the level of tyrosine kinase A (TrkA) receptor phosphorylation and that they each have different postreceptor signaling patterns. GK-6 increases the levels of extracellular signal-regulated kinase (ERK) and AKT kinase phosphorylation, whereas GK-2 only increases the level of AKT phosphorylation. Apart from the neuroprotective activity, GK-6 promoted differentiation in PC12 cells, whereas GK-2 did not. Furthermore, it was established that the neuroprotective activity of GK-2 was completely abolished by a selective inhibitor of phosphatidylinositol 3-kinase (LY294002) but not by a specific inhibitor of mitogen-activated protein kinases MEK1 and MEK2 (PD98059). In vivo experiments demonstrated that GK-2 did not induce hyperalgesia, which is one of the primary adverse effects of NGF. By contrast, GK-6 produced a significant decrease in the pain threshold of rats as determined by the tail flick test.

Conclusion

The data obtained suggest that dimeric dipeptide NGF mimetics are promising candidates in the development of pharmacological agents with NGF-like activity that are free of the main side effect of NGF.

[The development of a pharmacologically active low-molecular mimetic of the nerve growth factor]

Authors present an overview of theirs author's works on the design of low-molecular mimetic of the nerve growth factor and studies of mechanisms of action and pharmacological properties of the compound. The original working hypothesis, underlying the design of the compound, posited that different neurotrophin hairpin loops could activate different signaling cascades by interaction with the receptor and so be responsible for different effects. The mimetic bis(N-succinyl-L-glutamyl-L-lysine)hexametylendiamide (GK-2), that was designed on the basis of NGF loop 4 β-turn sequence, activated TrkA and PI3K/Akt, but not MAPK/Erk. GK-2 showed neuroprotective activity in concentrations up to 10-9М against H(2)O(2) or glutamate or MPTP-induced neurotoxicity in РС12, НТ22 cells and primary rat hippocampal neurons. At that, GK-2 has no differentiating activity. In in vivo experiments, GK-2 exhibited significant anti-ischemic, anti-parkinsonic effect, reversed impaired cognitive functions in models of Alzheimer's disease in doses 0.01 - 5 mg/kg intraperitoneally and 5-10 mg/kg orally, but does not induce side effects accompanying the full-length neurotrophin treatment, which are hyperalgesia and weight loss. It was shown that GK-2 was a low-toxicity compound (LD50=700 mg/kg, intraperitoneally, mice) and capable of crossing the blood-brain barrier. The agent GK-2 is promising for development as a neuroprotective agent and is currently in preclinical studies.

Behavioral effect of dipeptide NGF mimetic GK-2 in an in vivo model of rat traumatic brain injury and its neuroprotective and regenerative properties in vitro

A protective behavioral effect of a nerve growth factor dipeptide mimetic GK-2 in the model of open focal trauma of rat brain sensorimotor cortex and its antioxidative and regenerative properties in cultures of rat cerebellar granule cells and mouse embryonal spinal ganglion, respectively, were studied. Intraperitoneal injections of GK-2 (1 mg/kg) for 5 days daily after traumatic brain injury improved significantly motor function of limbs. Moreover, supplementation the incubation medium with GK-2 (0.5-1.5 mg/l) decreased neuronal death induced by H2O2 in cerebellar granule cell cultures and stimulated neurite outgrowth from cultured mouse embryonal spinal ganglia. Our results suggest that GK-2 exhibits pronounced positive behavioral effect in vivo as well as neuroprotective and regenerative effects in vitro, and that these neuroprotective properties probably associated with cell survival but not with cell differentiation pathway.

Original nerve growth factor mimetic dipeptide GK-2 limits the manifestations of hemorrhagic stroke in rats

The protective effects of a new low-molecular-weight mimetic of nerve growth factor hexamethylene diamide bis-(N-monosuccinyl-L-glutamine-L-lysine; GK-2) were studied on the experimental model of hemorrhagic stroke (intracerebral posttraumatic hematoma) in rats. Intraperitoneal injections of GK-2 in a dose of 1 mg/kg 4 and 24 h after surgery and 24 h before testing the CNS function on days 3, 7, and 14 prevent death of experimental animals, reduce the neurological deficit, and normalized behavior.