Selective and differential interactions of BNN27, a novel C17-spiroepoxy steroid derivative, with TrkA receptors, regulating neuronal survival and differentiation

Positive Allosteric Modulators of Trk Receptors for the Treatment of Alzheimer's Disease

Neurotrophins are important regulators of neuronal and non-neuronal functions. As such, the neurotrophins and their receptors, the tropomyosin receptor kinase (Trk) family of receptor tyrosine kinases, has attracted intense research interest and their role in multiple diseases including Alzheimer's disease has been described. Attempts to administer neurotrophins to patients have been reported, but the clinical trials have so far have been hampered by side effects or a lack of clear efficacy. Thus, much of the focus during recent years has been on identifying small molecules acting as agonists or positive allosteric modulators (PAMs) of Trk receptors. Two examples of successful discovery and development of PAMs are the TrkA-PAM E2511 and the pan-Trk PAM ACD856. E2511 has been reported to have disease-modifying effects in preclinical models, whereas ACD856 demonstrates both a symptomatic and a disease-modifying effect in preclinical models. Both molecules have reached the stage of clinical development and were reported to be safe and well tolerated in clinical phase 1 studies, albeit with different pharmacokinetic profiles. These two emerging small molecules are interesting examples of possible novel symptomatic and disease-modifying treatments that could complement the existing anti-amyloid monoclonal antibodies for the treatment of Alzheimer's disease. This review aims to present the concept of positive allosteric modulators of the Trk receptors as a novel future treatment option for Alzheimer's disease and other neurodegenerative and cognitive disorders, and the current preclinical and clinical data supporting this new concept. Preclinical data indicate dual mechanisms, not only as cognitive enhancers, but also a tentative neurorestorative function.

Effects of low doses of the novel dehydroepiandrosterone (DHEA) derivative BNN27 in rat models of anxiety

RATIONALE

Several lines of evidence indicate that the neurosteroid dehydroepiandrosterone (DHEA) is involved in anxiety. BNN27 is a new DHEA derivative lacking steroidogenic effects. The beneficial effects exerted by BNN27 in preclinical models of schizophrenia and memory disorders have been recently reported.

OBJECTIVES

The present study was designed to investigate the effects of this DHEA novel analog on anxiety-like behavior in rats.

METHODS

To this end, the light/dark box, the open field, the contextual fear conditioning, and the excessive self-grooming induced by the serotonin 5-HT2c receptor agonist mCPP tests were utilized.

RESULTS

Animals treated acutely with BNN27 (1, 3, and 6 mg/kg) dose dependently spent more time in the bright compartment of the light/dark box and in the central zone of the open field with respect to their vehicle-treated cohorts. Further, BNN27 reduced freezing behavior and weakened the mCPP-induced excessive self-grooming.

CONCLUSIONS

Our data indicate that BNN27 is a highly potent anxiolytic agent, as in all studied paradigms it showed anxiolytic-like effects in male rats.

A quest for the stereo-electronic requirements for selective agonism for the neurotrophin receptors TrkA and TrkB in 17-spirocyclic-dehydroepiandrosterone derivatives

Introduction

The neurotrophin system plays a pivotal role in the development, morphology, and survival of the nervous system, and its dysregulation has been manifested in numerous neurodegenerative and neuroinflammatory diseases. Neurotrophins NGF and BDNF are major growth factors that prevent neuronal death and synaptic loss through binding with high affinity to their specific tropomyosin-related kinase receptors namely, TrkA and TrkB, respectively. The poor pharmacokinetic properties prohibit the use of neurotrophins as therapeutic agents. Our group has previously synthesized BNN27, a prototype small molecule based on dehydroepiandrosterone, mimicking NGF through the activation of the TrkA receptor.

Methods

To obtain a better understanding of the stereo-electronic requirements for selective activation of TrkA and TrkB receptors, 27 new dehydroepiandrosterone derivatives bearing a C17-spiro-dihydropyran or cyclobutyl moiety were synthesized. The new compounds were evaluated for their ability (a) to selectively activate the TrkA receptor and its downstream signaling kinases Akt and Erk1/2 in PC12 cells, protecting these cells from serum deprivation-induced cell death, and (b) to induce phosphorylation of TrkB and to promote cell survival under serum deprivation conditions in NIH3T3 cells stable transfected with the TrkB receptor and primary cortical astrocytes. In addition the metabolic stability and CYP-mediated reaction was assessed.

Results

Among the novel derivatives, six were able to selectively protect PC12 cells through interaction with the TrkA receptor and five more to selectively protect TrkB-expressing cells via interaction with the TrkB receptor. In particular, compound ENT-A025 strongly induces TrkA and Erk1/2 phosphorylation, comparable to NGF, and can protect PC12 cells against serum deprivation-induced cell death. Furthermore, ENT-A065, ENT-A066, ENT-A068, ENT-A069, and ENT-A070 showed promising pro-survival effects in the PC12 cell line. Concerning TrkB agonists, ENT-A009 and ENT-A055 were able to induce phosphorylation of TrkB and reduce cell death levels in NIH3T3-TrkB cells. In addition, ENT-A076, ENT-A087, and ENT-A088 possessed antiapoptotic activity in NIH-3T3-TrkB cells exclusively mediated through the TrkB receptor. The metabolic stability and CYP-mediated reaction phenotyping of the potent analogs did not reveal any major liabilities.

Discussion

We have identified small molecule selective agonists of TrkA and TrkB receptors as promising lead neurotrophin mimetics for the development of potential therapeutics against neurodegenerative conditions.

Neurotrophin Analog ENT-A044 Activates the p75 Neurotrophin Receptor, Regulating Neuronal Survival in a Cell Context-Dependent Manner

Neuronal cell fate is predominantly controlled based on the effects of growth factors, such as neurotrophins, and the activation of a variety of signaling pathways acting through neurotrophin receptors, namely Trk and p75 (p75NTR). Despite their beneficial effects on brain function, their therapeutic use is compromised due to their polypeptidic nature and blood-brain-barrier impermeability. To overcome these limitations, our previous studies have proven that DHEA-derived synthetic analogs can act like neurotrophins, as they lack endocrine side effects. The present study focuses on the biological characterization of a newly synthesized analog, ENT-A044, and its role in inducing cell-specific functions of p75NTR. We show that ENT-A044 can induce cell death and phosphorylation of JNK protein by activating p75NTR. Additionally, ENT-A044 can induce the phosphorylation of TrkB receptor, indicating that our molecule can activate both neurotrophin receptors, enabling the protection of neuronal populations that express both receptors. Furthermore, the present study demonstrates, for the first time, the expression of p75NTR in human-induced Pluripotent Stem Cells-derived Neural Progenitor Cells (hiPSC-derived NPCs) and receptor-dependent cell death induced via ENT-A044 treatment. In conclusion, ENT-A044 is proposed as a lead molecule for the development of novel pharmacological agents, providing new therapeutic approaches and research tools, by controlling p75NTR actions.

Microneurotrophin BNN27 Reduces Astrogliosis and Increases Density of Neurons and Implanted Neural Stem Cell-Derived Cells after Spinal Cord Injury

Microneurotrophins, small-molecule mimetics of endogenous neurotrophins, have demonstrated significant therapeutic effects on various animal models of neurological diseases. Nevertheless, their effects on central nervous system injuries remain unknown. Herein, we evaluate the effects of microneurotrophin BNN27, an NGF analog, in the mouse dorsal column crush spinal cord injury (SCI) model. BNN27 was delivered systemically either by itself or combined with neural stem cell (NSC)-seeded collagen-based scaffold grafts, demonstrated recently to improve locomotion performance in the same SCI model. Data validate the ability of NSC-seeded grafts to enhance locomotion recovery, neuronal cell integration with surrounding tissues, axonal elongation and angiogenesis. Our findings also show that systemic administration of BNN27 significantly reduced astrogliosis and increased neuron density in mice SCI lesion sites at 12 weeks post injury. Furthermore, when BNN27 administration was combined with NSC-seeded PCS grafts, BNN27 increased the density of survived implanted NSC-derived cells, possibly addressing a major challenge of NSC-based SCI treatments. In conclusion, this study provides evidence that small-molecule mimetics of endogenous neurotrophins can contribute to effective combinatorial treatments for SCI, by simultaneously regulating key events of SCI and supporting grafted cell therapies in the lesion site.

Neurotrophin-targeted therapeutics: A gateway to cognition and more?

Neurotrophins, such as brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), are small proteins expressed in the brain and peripheral tissues, which regulate several key aspects of neuronal function, including neurogenesis, synaptic plasticity and neuroprotection, but also programmed cell death. This broad range of effects is a result of a complex downstream signaling pathway, with differential spatial and temporal activation patterns further diversifying their physiological effects. Alterations in neurotrophin levels, or known polymorphisms in neurotrophin genes, have been linked to a variety of disorders, including depression and Alzheimer's disease (AD). Historically, their therapeutic potential in these disorders has been hampered by the lack of suitable tool molecules for clinical studies. However, recent advancements have led to the development of new therapeutic candidates, which are now in clinical testing.

Getting Into the Brain: The Intranasal Approach to Enhance the Delivery of Nerve Growth Factor and Its Painless Derivative in Alzheimer’s Disease and Down Syndrome

The neurotrophin Nerve Growth Factor (NGF) holds a great potential as a therapeutic candidate for the treatment of neurological diseases. However, its safe and effective delivery to the brain is limited by the fact that NGF needs to be selectively targeted to the brain, to avoid severe side effects such as pain and to bypass the blood brain barrier. In this perspective, we will summarize the different approaches that have been used, or are currently applied, to deliver NGF to the brain, during preclinical and clinical trials to develop NGF as a therapeutic drug for Alzheimer’s disease. We will focus on the intranasal delivery of NGF, an approach that is used to deliver proteins to the brain in a non-invasive, safe, and effective manner minimizing systemic exposure. We will also describe the main experimental facts related to the effective intranasal delivery of a mutant form of NGF [painless NGF, human nerve growth factor painless (hNGFp)] in mouse models of Alzheimer’s disease and compare it to other ways to deliver NGF to the brain. We will also report new data on the application of intranasal delivery of hNGFp in Down Syndrome mouse model. These new data extend the therapeutic potential of hNGFp for the treatment of the dementia that is progressively associated to Down Syndrome. In conclusion, we will show how this approach can be a promising strategy and a potential solution for other unmet medical needs of safely and effectively delivering this neuroprotective neurotrophin to the brain.

ENT-A010, a Novel Steroid Derivative, Displays Neuroprotective Functions and Modulates Microglial Responses

Tackling neurodegeneration and neuroinflammation is particularly challenging due to the complexity of central nervous system (CNS) disorders, as well as the limited drug accessibility to the brain. The activation of tropomyosin-related kinase A (TRKA) receptor signaling by the nerve growth factor (NGF) or the neurosteroid dehydroepiandrosterone (DHEA) may combat neurodegeneration and regulate microglial function. In the present study, we synthesized a C-17-spiro-cyclopropyl DHEA derivative (ENT-A010), which was capable of activating TRKA. ENT-A010 protected PC12 cells against serum starvation-induced cell death, dorsal root ganglia (DRG) neurons against NGF deprivation-induced apoptosis and hippocampal neurons against Aβ-induced apoptosis. In addition, ENT-A010 pretreatment partially restored homeostatic features of microglia in the hippocampus of lipopolysaccharide (LPS)-treated mice, enhanced Aβ phagocytosis, and increased Ngf expression in microglia in vitro. In conclusion, the small molecule ENT-A010 elicited neuroprotective effects and modulated microglial function, thereby emerging as an interesting compound, which merits further study in the treatment of CNS disorders.

Development and Biological Characterization of a Novel Selective TrkA Agonist with Neuroprotective Properties against Amyloid Toxicity

Neurotrophins are growth factors that exert important neuroprotective effects by preventing neuronal death and synaptic loss. Nerve Growth Factor (NGF) acts through the activation of its high-affinity, pro-survival TrkA and low-affinity, pro-apoptotic p75NTR receptors. NGF has been shown to slow or prevent neurodegenerative signals in Alzheimer's Disease (AD) progression. However, its low bioavailability and its blood-brain-barrier impermeability limit the use of NGF as a potential therapeutic agent against AD. Based on our previous findings on synthetic dehydroepiandrosterone derivatives, we identified a novel NGF mimetic, named ENT-A013, which selectively activates TrkA and exerts neuroprotective, anti-amyloid-β actions. We now report the chemical synthesis, in silico modelling, metabolic stability, CYP-mediated reaction phenotyping and biological characterization of ENT-A013 under physiological and neurodegenerative conditions. We show that ENT-A013 selectively activates the TrkA receptor and its downstream kinases Akt and Erk1/2 in PC12 cells, protecting these cells from serum deprivation-induced cell death. Moreover, ENT-A013 promotes survival of primary Dorsal Root Ganglion (DRG) neurons upon NGF withdrawal and protects hippocampal neurons against Amyloid β-induced apoptosis and synaptic loss. Furthermore, this neurotrophin mimetic partially restores LTP impairment. In conclusion, ENT-A013 represents a promising new lead molecule for developing therapeutics against neurodegenerative disorders, such as Alzheimer's Disease, selectively targeting TrkA-mediated pro-survival signals.

Analgesic and Anti-Inflammatory Effects of the Synthetic Neurosteroid Analogue BNN27 during CFA-Induced Hyperalgesia

Dehydroepiandrosterone (DHEA), an adrenal and neurosteroid hormone with strong neuroprotective and immunomodulatory properties, and ligand for all high-affinity neurotrophin tyrosine kinase receptors (Trk), also exerts important effects on hyperalgesia. Its synthetic, 17-spiro-epoxy analogue, BNN27, cannot be converted to estrogen or androgen as DHEA; it is a specific agonist of TrkA, the receptor of pain regulator Nerve Growth Factor (NGF), and it conserves the immunomodulatory properties of DHEA. Our study aimed to evaluate the anti-nociceptive and anti-inflammatory properties of BNN27 during Complete Freund’s Adjuvant (CFA)-induced inflammatory hyperalgesia in mice. Hyperalgesia was evaluated using the Hargreaves test. Inflammatory markers such as cytokines, NGF and opioids were measured, additionally to corticosterone and the protein kinase B (AKT) signaling pathway. We showed for the first time that treatment with BNN27 reversed hyperalgesia produced by CFA. The effect of BNN27 involved the inhibition of NGF in the dorsal root ganglia (DRG) and the increased synthesis of opioid peptides and their receptors in the inflamed paw. We also found alterations in the cytokine levels as well as in the phosphorylation of AKT2. Our findings strongly support that BNN27 represents a lead molecule for the development of analgesic and anti-inflammatory compounds with potential therapeutic applications in inflammatory hyperalgesia.

Identification of Novel Positive Allosteric Modulators of Neurotrophin Receptors for the Treatment of Cognitive Dysfunction

Alzheimer's disease (AD) is the most common neurodegenerative disorder and results in severe neurodegeneration and progressive cognitive decline. Neurotrophins are growth factors involved in the development and survival of neurons, but also in underlying mechanisms for memory formation such as hippocampal long-term potentiation. Our aim was to identify small molecules with stimulatory effects on the signaling of two neurotrophins, the nerve growth factor (NGF) and the brain derived neurotrophic factor (BDNF). To identify molecules that could potentiate neurotrophin signaling, 25,000 molecules were screened, which led to the identification of the triazinetrione derivatives ACD855 (Ponazuril) and later on ACD856, as positive allosteric modulators of tropomyosin related kinase (Trk) receptors. ACD855 or ACD856 potentiated the cellular signaling of the neurotrophin receptors with EC50 values of 1.9 and 3.2 or 0.38 and 0.30 µM, respectively, for TrkA or TrkB. ACD855 increased acetylcholine levels in the hippocampus by 40% and facilitated long term potentiation in rat brain slices. The compounds acted as cognitive enhancers in a TrkB-dependent manner in several different behavioral models. Finally, the age-induced cognitive dysfunction in 18-month-old mice could be restored to the same level as found in 2-month-old mice after a single treatment of ACD856. We have identified a novel mechanism to modulate the activity of the Trk-receptors. The identification of the positive allosteric modulators of the Trk-receptors might have implications for the treatment of Alzheimer's diseases and other diseases characterized by cognitive impairment.

The Impact of Obesity on Microglial Function: Immune, Metabolic and Endocrine Perspectives

Increased life expectancy in combination with modern life style and high prevalence of obesity are important risk factors for development of neurodegenerative diseases. Neuroinflammation is a feature of neurodegenerative diseases, and microglia, the innate immune cells of the brain, are central players in it. The present review discusses the effects of obesity, chronic peripheral inflammation and obesity-associated metabolic and endocrine perturbations, including insulin resistance, dyslipidemia and increased glucocorticoid levels, on microglial function.

Quantification of BNN27, a novel neuroprotective 17-spiroepoxy dehydroepiandrosterone derivative in the blood and retina of rodents, after single intraperitoneal administration

BNN27 is a novel 17‐spiroepoxy derivative of the neurosteroid Dehydroepiandrosterone with neuroprotective properties. The purpose of this study was the detection and quantification of BNN27 after single intraperitoneal administration, in the serum and retina of normal rodents. Forty‐two C57BL/6 mice and 48 Sprague–Dawley rats were used for the quantification of BNN27 in the blood serum and retina, respectively. BNN27 was injected intraperitoneally (i.p.) at concentrations of 100 and 30 mg/kg of body weight (b.w.), respectively. The blood was collected with retro‐orbital bleeding and the retina was isolated after enucleation at various time points. The molecule concentrations were measured with Liquid chromatography‐mass spectrometry (LC‐MS). Non‐compartmental analysis was used to determine pharmacokinetic parameters. BNN27 was found to have an elimination constant k_el = 0.465 h⁻¹ and mean residence time (MRT) 2.154 h in the mouse serum. The maximum concentration (C_max) in the retina was detected at 2 h (tCmax) after intraperitoneal administration and was equal to 1100 ng/g. BNN27 is rapidly eliminated from both blood and retina. In the retina specifically, it is undetectable 6 h after injection. BNN27 shows a rapid systemic elimination as anticipated by its small size and lipophilicity. It is measurable in small peripheral tissues such as the rat retina, after one single i.p. injection, using a simple method such as LC‐MS. Its detection in the retina corroborates the existing biological data that the molecule crosses the blood–retinal barrier, highlighting it as a potential neuroprotective agent for retinal disease.

The beneficial role of the synthetic microneurotrophin BNN20 in a focal demyelination model

BNN20, a C17-spiroepoxy derivative of the neurosteroid dehydroepiandrosterone, has been shown to exhibit strong neuroprotective properties but its role in glial populations has not been assessed. Our aim was to investigate the effect of BNN20 on glial populations by using in vitro and in vivo approaches, taking advantage of the well-established lysophosphatidylcholine (LPC)-induced focal demyelination mouse model. Our in vivo studies, performed in male mice, showed that BNN20 treatment leads to an increased number of mature oligodendrocytes (OLs) in this model. It diminishes astrocytic accumulation during the demyelination phase leading to a faster remyelination process, while it does not affect oligodendrocyte precursor cell recruitment or microglia/macrophage accumulation. Additionally, our in vitro studies showed that BNN20 acts directly to OLs and enhances their maturation even after they were treated with LPC. This beneficial effect of BNN20 is mediated, primarily, through the neurotrophin receptor TrkA. In addition, BNN20 reduces microglial activation and their transition to their pro-inflammatory state upon lipopolysaccharides stimulation in vitro. Taken together our results suggest that BNN20 could serve as an important molecule to develop blood-brain barrier-permeable synthetic agonists of neurotrophin receptors that could reduce inflammation, protect and increase the number of functional OLs by promoting their differentiation/maturation.

The novel dehydroepiandrosterone (DHEA) derivative BNN27 counteracts cognitive deficits induced by the D1/D2 dopaminergic receptor agonist apomorphine in rats

RATIONALE

Schizophrenia is a devastating mental disease that affects nearly 1% of the population worldwide. It is well documented that the dopaminergic (DAergic) system is compromised in schizophrenia. It is of note that the mixed dopamine (DA) D₁/D₂ receptor agonist apomorphine induces schizophrenia-like symptoms in rodents, including disruption of memory abilities. Neuroactive steroids, comprising dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHEAS), were shown to affect brain DAergic system and to be involved in schizophrenia. BNN27 is a novel DHEA derivative, which is devoid of steroidogenic activity. It has recently been reported that BNN27 counteracted schizophrenia-like behavioural deficits produced by glutamate hypofunction in rats.

OBJECTIVES

The aim of the present study was to investigate the ability of BNN27 to attenuate non-spatial, spatial recognition and discrete memory deficits induced by apomorphine in rats.

METHODS

To this end, the object recognition task (ORT), the object location task (OLT) and the step-through passive avoidance test (STPAT) were used.

RESULTS

BNN27 (3 and 6 mg/kg, i.p.) attenuated apomorphine (0.5 mg/kg, i.p.)-induced non-spatial, spatial recognition and discrete memory deficits. Interestingly, the effects of compounds on memory cannot be ascribed to changes in locomotor activity.

CONCLUSIONS

Our findings suggest that BNN27 is effective to DA dysfunction caused by apomorphine, attenuating cognitive impairments induced by this D1/D2 receptor agonist in rats. Additionally, our findings illustrate a functional interaction between BNN27 and the DAergic system that may be of relevance for schizophrenia-like behavioural symptoms.

Psychoactive properties of BNN27, a novel neurosteroid derivate, in male and female rats

RATIONALE

Νeurosteroids, like dehydroepiandrosterone (DHEA), play an important role in neurodegeneration and neural protection, but they are metabolized in androgens, estrogens, or other active metabolites. A newly developed synthetic DHEA analog, BNN27 ((20R)-3β,21-dihydroxy-17R,20-epoxy-5-pregnene), exerts neurotrophic and neuroprotective actions without estrogenic or androgenic effects.

OBJECTIVES

This study aimed to investigate potential anxiolytic or antidepressant properties of BNN27.

METHODS

Male and female adult Wistar rats were treated with BNN27 (10, 30, or 90 mg/kg, i.p.) and subjected to behavioral tests measuring locomotion, exploration, and "depressive-like" behavior (open field, light/dark box, hole-board, and forced swim tests). The hippocampus and prefrontal cortex were collected for glutamate and GABA measurements, and trunk blood was collected for gonadal hormone analysis.

RESULTS

Acute high-dose BNN27 reduced locomotion and exploratory behavior in both sexes. Intermediate acute doses (30 mg/kg) of BNN27 reduced exploration and testosterone levels only in males, and enhanced progesterone levels in both sexes. Notably, with the present design, BNN27 had neither anxiolytic nor antidepressant effects and did not affect estrogen levels. Interestingly, acute administration of a low BNN27 dose (10 mg/kg) increased glutamate turnover, GABA, and glutamine levels in the hippocampus. The same dose also enhanced glutamate levels in the prefrontal cortex of males only. Sex differences were apparent in the basal levels of behavioral, hormonal, and neurochemical parameters, as expected.

CONCLUSIONS

BNN27 affects locomotion, progesterone, and testosterone levels, as well as the glutamatergic and GABAergic systems of the hippocampus and prefrontal cortex in a sex-dependent way.

3β, 6β-dichloro-5-hydroxy-5α-cholestane facilitates neuronal development through modulating TrkA signaling regulated proteins in primary hippocampal neuron

Potentiating neuritogenesis through pharmacological intervention might hold therapeutic promise in neurodegenerative disorders and acute brain injury. Here, we investigated the novel neuritogenic potentials of a steroidal chlorohydrin, 3β, 6β-dichloro-5-hydroxy-5α-cholestane (hereafter, SCH) and the change in cellular proteome to gain insight into the underlying mechanism of its neurotrophic activity in hippocampal neurons. Morphometric analysis showed that SCH promoted early neuronal differentiation, dendritic arborization and axonal maturation. Proteomic and bioinformatic analysis revealed that SCH induced upregulation of several proteins, including those associated with neuronal differentiation and development. Immunocytochemical data further indicates that SCH-treated neurons showed upregulation of Hnrnpa2b1 and Map1b, validating their proteomic profiles. In addition, a protein-protein interaction network analysis identified TrkA as a potential target connecting most of the upregulated proteins. The neurite outgrowth effect of SCH was suppressed by TrkA inhibitor, GW441756, verifying TrkA-dependent activity of SCH, which further supports the connection of TrkA with the upregulated proteins. Also, the computational analysis revealed that SCH interacts with the NGF-binding domain of TrkA through Phe327 and Asn355. Collectively, our findings provide evidence that SCH promotes neuronal development via upregulating TrkA-signaling proteins and suggest that SCH could be a promising therapeutic agent in the prevention and treatment of neurodegenerative disorders.

Effect of topical administration of the microneurotrophin BNN27 in the diabetic rat retina

PURPOSE

Diabetic retinopathy (DR) is a complex eye disease associated with diabetes mellitus. It is characterized by three pathophysiological components, namely microangiopathy, neurodegeneration, and inflammation. We recently reported that intraperitoneal administration of BNN27, a novel neurosteroidal microneurotrophin, reversed the diabetes-induced neurodegeneration and inflammation in rats treated with streptozotocin (STZ), by activating the NGF TrkA and p75 receptors. The aim of the present study was to investigate the efficacy of BNN27 to protect retinal neurons when applied topically as eye drops in the same model.

METHODS

The STZ rat model of DR was employed. BNN27 was administered as eye drops to diabetic Sprague-Dawley rats for 7 days, 4 weeks post-STZ (70 mg/kg) injection. Immunohistochemistry and western blot analyses were employed to examine the viability of retinal neurons in control, diabetic, and diabetic-treated animals and the involvement of the TrkA receptor and its downstream signaling ERK1/2 kinases, respectively.

RESULTS

BNN27 reversed the STZ-induced attenuation of the immunoreactive brain nitric oxide synthetase (bNOS)- and tyrosine hydroxylase (TH)-expressing amacrine cells and neurofilament (NFL)-expressing ganglion cell axons in a dose-dependent manner. In addition, BNN27 activated/phosphorylated the TrkA receptor and its downstream prosurvival signaling pathway, ERK1/2 kinases.

CONCLUSIONS

The results of this study provide solid evidence regarding the efficacy of BNN27 as a neuroprotectant to the diabetic retina when administered topically, and suggest that its pharmacodynamic and pharmacokinetic profiles render it a putative therapeutic for diabetic retinopathy.

Neurosteroids as regulators of neuroinflammation

Neuroinflammation is a physiological protective response in the context of infection and injury. However, neuroinflammation, especially if chronic, may also drive neurodegeneration. Neurodegenerative diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD) and traumatic brain injury (TBI), display inflammatory activation of microglia and astrocytes. Intriguingly, the central nervous system (CNS) is a highly steroidogenic environment synthesizing steroids de novo, as well as metabolizing steroids deriving from the circulation. Neurosteroid synthesis can be substantially affected by neuroinflammation, while, in turn, several steroids, such as 17β-estradiol, dehydroepiandrosterone (DHEA) and allopregnanolone, can regulate neuroinflammatory responses. Here, we review the role of neurosteroids in neuroinflammation in the context of MS, AD, PD and TBI and describe underlying molecular mechanisms. Moreover, we introduce the concept that synthetic neurosteroid analogues could be potentially utilized for the treatment of neurodegenerative diseases in the future.

Nerve Growth Factor modulates LPS - induced microglial glycolysis and inflammatory responses

Microglia, the parenchymal immune cells of the central nervous system, orchestrate neuroinflammation in response to infection or damage, and promote tissue repair. However, aberrant microglial responses are integral to neurodegenerative diseases and critically contribute to disease progression. Thus, it is important to elucidate how microglia - mediated neuroinflammation is regulated by endogenous factors. Here, we explored the effect of Nerve Growth Factor (NGF), an abundant neurotrophin, on microglial inflammatory responses. NGF, via its high affinity receptor TrkA, downregulated LPS - induced production of pro-inflammatory cytokines and NO in primary mouse microglia and inhibited TLR4 - mediated activation of the NF-κB and JNK pathways. Furthermore, NGF attenuated the LPS - enhanced glycolytic activity in microglia, as suggested by reduced glucose uptake and decreased expression of the glycolytic enzymes Pfkβ3 and Ldhα. Consistently, 2DG - mediated glycolysis inhibition strongly downregulated LPS - induced cytokine production in microglial cells. Our findings demonstrate that NGF attenuates pro-inflammatory responses in microglia and may thereby contribute to regulation of microglia - mediated neuroinflammation.

Neurosteroids in Pain Management: A New Perspective on an Old Player

Since the discovery of the nervous system’s ability to produce steroid hormones, numerous studies have demonstrated their importance in modulating neuronal excitability. These central effects are mostly mediated through different ligand-gated receptor systems such as GABA_A and NMDA, as well as voltage-dependent Ca²⁺ or K⁺ channels. Because these targets are also implicated in transmission of sensory information, it is not surprising that numerous studies have shown the analgesic properties of neurosteroids in various pain models. Physiological (nociceptive) pain has protective value for an organism by promoting survival in life-threatening conditions. However, more prolonged pain that results from dysfunction of nerves (neuropathic pain), and persists even after tissue injury has resolved, is one of the main reasons that patients seek medical attention. This review will focus mostly on the analgesic perspective of neurosteroids and their synthetic 5α and 5β analogs in nociceptive and neuropathic pain conditions.

Effects of BNN27, a novel C17-spiroepoxy steroid derivative, on experimental retinal detachment-induced photoreceptor cell death

Retinal detachment (RD) leads to photoreceptor cell death secondary to the physical separation of the retina from the underlying retinal pigment epithelium. Intensifying photoreceptor survival in the detached retina could be remarkably favorable for many retinopathies in which RD can be seen. BNN27, a blood-brain barrier (BBB)-permeable, C17-spiroepoxy derivative of dehydroepiandrosterone (DHEA) has shown promising neuroprotective activity through interaction with nerve growth factor receptors, TrkA and p75^NTR. Here, we administered BNN27 systemically in a murine model of RD. TUNEL⁺ photoreceptors were significantly decreased 24 hours post injury after a single administration of 200 mg/kg BNN27. Furthermore, BNN27 increased inflammatory cell infiltration, as well as, two markers of gliosis 24 hours post RD. However, single or multiple doses of BNN27 were not able to protect the overall survival of photoreceptors 7 days post injury. Additionally, BNN27 did not induce the activation/phosphorylation of TrkA^Y490 in the detached retina although the mRNA levels of the receptor were increased in the photoreceptors post injury. Together, these findings, do not demonstrate neuroprotective activity of BNN27 in experimentally-induced RD. Further studies are needed in order to elucidate the paradox/contradiction of these results and the mechanism of action of BNN27 in this model of photoreceptor cell damage.

Tropomyosin receptor kinase: a novel target in screened neuroendocrine tumors

Tropomyosin receptor kinase (Trk) inhibitors are investigated as a novel targeted therapy in various cancers. We investigated the in vitro effects of the pan-Trk inhibitor GNF-5837 in human neuroendocrine tumor (NET) cells. The human neuroendocrine pancreatic BON1, bronchopulmonary NCI-H727 and ileal GOT1 cell lines were treated with GNF-5837 alone and in combination with everolimus. Cell viability decreased in a time- and dose-dependent manner in GOT1 cells in response to GNF-5837 treatment, while treatment in BON1 and NCI-H727 cells showed no effect on cellular viability. Trk receptor expression determined GNF-5837 sensitivity. GNF-5837 caused downregulation of PI3K-Akt-mTOR signaling, Ras-Raf-MEK-ERK signaling, the cell cycle and increased apoptotic cell death. The combinational treatment of GNF-5837 with everolimus showed a significant enhancement in inhibition of cell viability vs single substance treatments, due to a cooperative PI3K-Akt-mTOR and Ras-Raf-MEK-ERK pathway downregulation, as well as an enhanced cell cycle component downregulation. Immunohistochemical staining for Trk receptors were performed using a tissue microarray containing 107 tumor samples of gastroenteropancreatic NETs. Immunohistochemical staining with TrkA receptor and pan-Trk receptor antibodies revealed a positive staining in pancreatic NETs in 24.2% (8/33) and 33.3% (11/33), respectively. We demonstrated that the pan-Trk inhibitor GNF-5837 has promising anti-tumoral properties in human NET cell lines expressing the TrkA receptor. Immunohistochemical or molecular screening for Trk expression particularly in pancreatic NETs might serve as predictive marker for molecular targeted therapy with Trk inhibitors.

The Synthetic Microneurotrophin BNN27 Affects Retinal Function in Rats With Streptozotocin-Induced Diabetes

BNN27, a C17-spiroepoxy derivative of DHEA, was shown to have antiapoptotic properties via mechanisms involving the nerve growth factor receptors (tropomyosin-related kinase A [TrkA]/neurotrophin receptor p75 [p75^NTR]). In this study, we examined the effects of BNN27 on neural/glial cell function, apoptosis, and inflammation in the experimental rat streptozotocin (STZ) model of diabetic retinopathy (DR). The ability of BNN27 to activate the TrkA receptor and regulate p75^NTR expression was investigated. BNN27 (2,10, and 50 mg/kg i.p. for 7 days) administration 4 weeks post-STZ injection (paradigm A) reversed the diabetes-induced glial activation and loss of function of amacrine cells (brain nitric oxide synthetase/tyrosine hydroxylase expression) and ganglion cell axons via a TrkA receptor (TrkAR)-dependent mechanism. BNN27 activated/phosphorylated the TrkA^Y490 residue in the absence but not the presence of TrkAR inhibitor and abolished the diabetes-induced increase in p75^NTR expression. However, it had no effect on retinal cell death (TUNEL⁺ cells). A similar result was observed when BNN27 (10 mg/kg i.p.) was administered at the onset of diabetes, every other day for 4 weeks (paradigm B). However, BNN27 decreased the activation of caspase-3 in both paradigms. Finally, BNN27 reduced the proinflammatory (TNFα and IL-1β) and increased the anti-inflammatory (IL-10 and IL-4) cytokine levels. These findings suggest that BNN27 has the pharmacological profile of a therapeutic for DR, since it targets both the neurodegenerative and inflammatory components of the disease.

The novel synthetic microneurotrophin BNN27 protects mature oligodendrocytes against cuprizone-induced death, through the NGF receptor TrkA

BNN27, a member of a chemical library of C17-spiroepoxy derivatives of the neurosteroid DHEA, has been shown to regulate neuronal survival through its selective interaction with NGF receptors (TrkA and p75NTR ), but its role on glial populations has not been studied. Here, we present evidence that BNN27 provides trophic action (rescue from apoptosis), in a TrkA-dependent manner, to mature oligodendrocytes when they are challenged with the cuprizone toxin in culture. BNN27 treatment also increases oligodendrocyte maturation and diminishes microglia activation in vitro. The effect of BNN27 in the cuprizone mouse model of demyelination in vivo has also been investigated. In this model, that does not directly involve the adaptive immune system, BNN27 can protect from demyelination without affecting the remyelinating process. BNN27 preserves mature oligodendrocyte during demyelination, while reducing microgliosis and astrogliosis. Our findings suggest that BNN27 may serve as a lead molecule to develop neurotrophin-like blood-brain barrier (BBB)-permeable protective agents of oligodendrocyte populations and myelin, with potential applications in the treatment of demyelinating disorders.

The novel dehydroepiandrosterone (DHEA) derivative BNN27 counteracts delay-dependent and scopolamine-induced recognition memory deficits in rats

Experimental evidence indicates that the neurosteroids dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHEAS) are involved in cognition. BNN27 is a novel 17C spiroepoxy-DHEA derivative, which devoid of steroidogenic activity. The neuroprotective effects of BNN27 have been recently reported. The present study was designed to investigate the effects of BNN27 on recognition memory in rats. For this purpose, the novel object task (NOT), a procedure assessing non-spatial recognition memory and the novel location task (NLT), a procedure evaluating spatial recognition memory were used. Intraperitoneal (i.p.) administration of BNN27 (3 and 10mg/kg) antagonized delay-dependent deficits in the NOT in the normal rat, suggesting that this DHEA derivative affected acquisition, storage and retrieval of information. In addition, BNN27 (3 and 10mg/kg, i.p.) counteracted the scopolamine [0.2mg/kg, subcutaneously (s.c.)]-induced non-spatial and spatial recognition memory deficits. These findings suggest that BNN27 may modulate different aspects of recognition memory, potentially interacting with the cholinergic system, relevant to cognition.

BNN27, a 17-Spiroepoxy Steroid Derivative, Interacts With and Activates p75 Neurotrophin Receptor, Rescuing Cerebellar Granule Neurons from Apoptosis

Neurotrophin receptors mediate a plethora of signals affecting neuronal survival. The p75 pan-neurotrophin receptor controls neuronal cell fate after its selective activation by immature and mature isoforms of all neurotrophins. It also exerts pleiotropic effects interacting with a variety of ligands in different neuronal or non-neuronal cells. In the present study, we explored the biophysical and functional interactions of a blood-brain-barrier (BBB) permeable, C17-spiroepoxy steroid derivative, BNN27, with p75^NTR receptor. BNN27 was recently shown to bind to NGF high-affinity receptor, TrkA. We now tested the p75^NTR-mediated effects of BNN27 in mouse Cerebellar Granule Neurons (CGNs), expressing p75^NTR, but not TrkA receptors. Our findings show that BNN27 physically interacts with p75^NTR receptors in specific amino-residues of its extracellular domain, inducing the recruitment of p75^NTR receptor to its effector protein RIP2 and the simultaneous release of RhoGDI in primary neuronal cells. Activation of the p75^NTR receptor by BNN27 reverses serum deprivation-induced apoptosis of CGNs resulting in the decrease of the phosphorylation of pro-apoptotic JNK kinase and of the cleavage of Caspase-3, effects completely abolished in CGNs, isolated from p75^NTR null mice. In conclusion, BNN27 represents a lead molecule for the development of novel p75^NTR ligands, controlling specific p75^NTR-mediated signaling of neuronal cell fate, with potential applications in therapeutics of neurodegenerative diseases and brain trauma.