MicroNeurotrophins Improve Survival in Motor Neuron-Astrocyte Co-Cultures but Do Not Improve Disease Phenotypes in a Mutant SOD1 Mouse Model of Amyotrophic Lateral Sclerosis

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.

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.

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.

Botulinum Toxin Type A Possibly Affects Cav3.2 Calcium Channel Subunit in Rats with Spinal Cord Injury-Induced Muscle Spasticity

INTRODUCTION

Spinal cord injury (SCI) often causes muscle spasticity, which can be inhibited by using calcium channel blocker. Botulinum toxin type A (BoT-A) shows therapeutic efficacy on spasticity and may exert inhibitory effects on the calcium channel.

METHODS

A rat model with muscle spasticity was established after SCI via contusion and compression. Different concentrations (0, 1, 3 and 6 U/kg) of BoT-A Botox were injected in the extensor digitorum longus (EDL) muscles of the right hindlimb in the muscle spasticity model. The changes of muscle spasticity and calcium level in EDL muscles were measured after the establishment of SCI-induced spasticity. Cav3.2 calcium channel subunit and its mutant (M1560V) were analyzed using Western blot before (input) or after immunoprecipitation with anti-FLAG antibody, and their currents were measured in motoneurons by using whole-cell voltage clamp recordings.

RESULTS

SCI induced muscle spasticity, whereas calcium level in EDL muscles and expression of Cav3.2 was increased in the SCI model when compared with the sham group (p < 0.05). BoT-A Botox treatment significantly reduced muscle spasticity and calcium level in EDL muscles and Cav3.2 expression in a dose-dependent way (p < 0.05). The ratio of biotinylated to total Cav3.2 was reduced in the mutant (M1560V) of Cav3.2 and lower than that in the wild Cav3.2. BoT-A Botox intervention also reduced the current values of calcium channel and the ratio in a dose-dependent way (p < 0.05).

DISCUSSION

BoT-A Botox possibly attenuates SCI-induced muscle spasticity by affecting the expression of Cav3.2 calcium channel subunit in the rat models. There may be multiple mechanisms for the function of BoT-A Botox. Further work is needed to be done to address these issues.

Cromolyn sodium delays disease onset and is neuroprotective in the SOD1G93A Mouse Model of amyotrophic lateral sclerosis

Accumulating evidence suggests that neuroinflammatory processes are implicated in the initiation and progression of amyotrophic lateral sclerosis (ALS). Previous reports have demonstrated an increase in microgliosis and astrogliosis in the lumbar spinal cord of SOD1^G93A transgenic mice before the onset of symptoms, a neuroinflammatory response which correlated with disease progression. Importantly, early stage homeostatic microglia enhanced motor neuron survival, while pro-inflammatory microglia were toxic to motor neurons in the SOD1^G93A mice. Recent studies from our group have demonstrated that cromolyn sodium, an FDA approved compound, exerts neuroprotective effects in mouse models of Alzheimer's disease by altering microglial cell activation. Here, we tested the neuroprotective and anti-inflammatory effects of cromolyn sodium in the SOD1^G93A mouse model of ALS. Our results indicate that cromolyn sodium treatment significantly delayed the onset of neurological symptoms, and improved deficits in PaGE performance in both male and female mice, however, there was only an effect on survival in female mice. Furthermore, there was a significant increase in motor neuron survival in the lumbar spinal cord as well as a significant decrease in the denervation of the neuromuscular junction of the tibialis anterior muscle in cromolyn treated transgenic SOD1^G93A mice. Lastly, cromolyn treatment decreased the expression of pro-inflammatory cytokines/chemokines in the lumbar spinal cord and plasma and decreased mast cell degranulation in the tibialis anterior muscle of transgenic SOD1^G93A mice. Together, these findings suggest that cromolyn sodium provides neuroprotection in the SOD1^G93A mice by decreasing the inflammatory response.

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.

Amphiphilic Nanocarrier Systems for Curcumin Delivery in Neurodegenerative Disorders

Neurodegenerative diseases have become a major challenge for public health because of their incurable status. Soft nanotechnology provides potential for slowing down the progression of neurodegenerative disorders by using innovative formulations of neuroprotective antioxidants like curcumin, resveratrol, vitamin E, rosmarinic acid, 7,8-dihydroxyflavone, coenzyme Q10, and fish oil. Curcumin is a natural, liposoluble compound, which is of considerable interest for nanomedicine development in combination therapies. The neuroprotective effects of combination treatments can involve restorative mechanisms against oxidative stress, mitochondrial dysfunction, inflammation, and protein aggregation. Despite the anti-amyloid and anti-tau potential of curcumin and its neurogenesis-stimulating properties, the utilization of this antioxidant as a drug in neuroregenerative therapies has huge limitations due to its poor water solubility, physico-chemical instability, and low oral bioavailability. We highlight the developments of soft lipid- and polymer-based delivery carriers of curcumin, which help improve the drug solubility and stability. We specifically focus on amphiphilic liquid crystalline nanocarriers (cubosome, hexosome, spongosome, and liposome particles) for the encapsulation of curcumin with the purpose of halting the progressive neuronal loss in Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis (ALS).

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.

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.

Role and Therapeutic Potential of Astrocytes in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive degeneration of motor neurons in the spinal cord, brain stem, and motor cortex. The molecular mechanism underlying the progressive degeneration of motor neuron remains uncertain but involves a non-cell autonomous process. In acute injury or degenerative diseases astrocytes adopt a reactive phenotype known as astrogliosis. Astrogliosis is a complex remodeling of astrocyte biology and most likely represents a continuum of potential phenotypes that affect neuronal function and survival in an injury-specific manner. In ALS patients, reactive astrocytes surround both upper and lower degenerating motor neurons and play a key role in the pathology. It has become clear that astrocytes play a major role in ALS pathology. Through loss of normal function or acquired new characteristics, astrocytes are able to influence motor neuron fate and the progression of the disease. The use of different cell culture models indicates that ALS-astrocytes are able to induce motor neuron death by secreting a soluble factor(s). Here, we discuss several pathogenic mechanisms that have been proposed to explain astrocyte-mediated motor neuron death in ALS. In addition, examples of strategies that revert astrocyte-mediated motor neuron toxicity are reviewed to illustrate the therapeutic potential of astrocytes in ALS. Due to the central role played by astrocytes in ALS pathology, therapies aimed at modulating astrocyte biology may contribute to the development of integral therapeutic approaches to halt ALS progression.