LC-MS/MS determination of GTS-201, a dipeptide mimetic of the brain-derived neurotrophic factor, and neurotransmitter metabolites with application to a pharmacokinetic study in rats.

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family with diverse psychopharmacological effects including antidepressant and anxiolytic actions. However, the clinical use of BDNF is limited due to its poor pharmacokinetic properties. The development of low-molecular-weight BDNF mimetics passing through the blood-brain barrier is an emerging strategy for improved managing psychiatric diseases. The present study characterizes a novel dipeptide mimetic of the 2nd BDNF loop named GTS-201, which exhibits psychotropic properties in experimental animal models of anxiety and alcohol dependence. The aim of this work was to study the pharmacokinetics of GTS-201 in rats at a saturating dosage of 5 mg/kg applied by the intraperitoneal route and to characterize the effects on neurotransmitter levels in the blood and brain. The maximum concentration (Cmax) of GTS-201 in the plasma (867 ± 69 ng/ml) was recorded at 35 ± 7.7 min after administration (Tmax) with a half-elimination period (T1/2) of 19.5 ± 1.8 min, while in the brain tissue Cmax was 14.92 ± 3.11 ng/ml, Tmax was 40.0 ± 7.7 min and T1/2 were 87.5 ± 12.7 min. The relative tissue availability of the GTS-201 for the brain reached 2.9%. At the dose applied, GTS-201 induced a significant increase of serotonin (5-fold) and dopamine levels in the brain tissue (8-fold) along with a decrease in cortisol content in blood plasma 45 min after acute administration. In summary, GTS-201 crosses the blood-brain barrier after acute administration and affects the activity of serotonergic and dopaminergic systems, which may underlie its neuropsychotropic effects described previously.

Effect of nootropic dipeptide noopept on CA1 pyramidal neurons involves α7AChRs on interneurons in hippocampal slices from rat.

Noopept (NP) is a proline-containing dipeptide with nootropic and neuroprotective properties. We have previously shown that NP significantly increased the frequency of spontaneous IPSCs in hippocampal CA1 pyramidal cells mediated by the activation of inhibitory interneurons in stratum radiatum. The cholinergic system plays an important role in the performance of cognitive functions, furthermore multiple behavioral and clinical facts link NP with the cholinergic system. The present study was undertaken to reveal the possible interaction of NP with neuronal nicotinic acetylcholine receptors (nAChRs). Currents were recorded from rat hippocampal neurons using the whole-cell, patch-clamp technique. NP (5 µM) increased the action potential firing frequency recorded from GABAergic interneurons in the stratum radiatum (SR) of CA1 region. This effect was almost completely abolished by the application of the α7 nAChR-selective antagonists α-bungarotoxin (α-BGT; 6 nM) and methyllycaconitine (MLA; 20 nM). The increase in the frequency of spontaneous IPSCs in CA1 pyramidal cells induced by NP was also eliminated by α7 nAChRs antagonists. These results imply the involvement of α7 nAChRs in the modulation of hippocampal neuronal activity caused by NP and indicate that a7 nAChRs are an important site of action of NP.

The neuropeptide cycloprolylglycine produces antidepressant-like effect and enhances BDNF gene expression in the mice cortex.

BACKGROUND: Cycloprolylglycine (CPG) is an endogenous dipeptide with a wide range of psychotropic activity and putative therapeutic potential for depression. A small but growing body of data suggests that antidepressant-like effect of CPG is associated with neuroplastic changes in the brain or 5-HT system modulation. However, the mechanisms of the dipeptide action remain elusive. AIMS: Here, we characterize the effects of chronic CPG administration on behavior and genes expression of antidepressants sensitive catalepsy (ASC) mice strain, characterized by depressive-like behavior. METHODS: ASC mice were injected with saline, fluoxetine (10 mg/kg/day), or CPG (1 and 2 mg/kg/day) during 2 weeks. Behavior was studied using the open field test, novel object test, elevated plus maze test, forced swim test, and tail suspension test (TST). The expressions of genes coding BDNF, CREB, 5-HT1A and 5-HT2A receptors, TPH2, and SERT in the brain were measured with quantitative real-time reverse transcription polymerase chain reaction (RT-PCR). RESULTS: Chronic intraperitoneal administration of 1 and 2 mg/kg of CPG revealed the significant antidepressant-like effect by decreasing immobility time in the TST. At the same time, CPG did not negatively affect locomotor activity, cognition, or anxiety. In the real-time quantitative polymerase chain reaction (PCR) assay, chronic CPG treatment (2 mg/kg for 14 days) increased Bdnf mRNA level in the frontal cortex. CONCLUSIONS: Our findings extend the evidence for the effectiveness of CPG to reduce depressive-like behaviors. The antidepressant-like effect of CPG is mediated, as least in part, by BDNF-dependent mechanism. The exact mechanism remains to be elucidated, and further studies are warranted.

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.

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 ß-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 ß-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.

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.

The nootropic and neuroprotective proline-containing dipeptide noopept restores spatial memory and increases immunoreactivity to amyloid in an Alzheimer's disease model.

The effects of the novel proline-containing nootropic and neuroprotective dipeptide, noopept (GVS-111, N-phenylacetyl-L-prolylglycine ethyl ester) were investigated in NMRI mice following olfactory bulbectomy. We have shown previously that these animals developed Alzheimer's disease (AD)-like behaviour, morphology and biochemistry including impairment of spatial memory, regional neuronal degeneration and elevated Abeta peptide brain levels. In the current investigation, spatial memory was assessed using the Morris water maze and serum antibodies to in vitro morphologically characterized amyloid structures of both Abeta((25-35)) peptide and equine lysozyme, as well as to neurotrophic glial factor S100b, were analyzed by enzyme-linked immunosorbent assay (ELISA). Noopept (administered at a dose of 0.01 mg/kg for a period of 21 days and during a further 5 days training) restored spatial memory and increased serum antibody levels to oligomers of Abeta((25-35)) peptide but not to equine lysozyme amyloid or S100b protein in bulbectomized animals. The positive immunotropic effect of noopept to Abeta((25-35)) peptide prefibrillar aggregates was more marked in sham-operated compared to the bulbectomized subjects which were characterized by an overall suppression of immunoreactivity. Enhancement of the immune response to Abeta((25-35)) peptide prefibrils caused by noopept may attenuate the neurotoxic consequences of amyloid fibrillization and also be associated with an improvement in spatial memory in bulbectomized mice. These actions of noopept, combined with its previously reported neuroprotective and cholinomimetic properties, suggests that this dipeptide may well be useful for improving cognitive deficits induced by neurodegenerative diseases.