Allopregnanolone restores hippocampal-dependent learning and memory and neural progenitor survival in aging 3xTgAD and nonTg mice

Neurosteroids: A potential target for neuropsychiatric disorders

Neurosteroids are steroids produced by endocrine glands and subsequently entering the brain, and also include steroids synthesis in the brain. It has been widely known that neurosteroids influence many neurological functions, including neuronal signaling, synaptic adaptations, and neuroprotective effects. In addition, abnormality in the synthesis and function of neurosteroids has been closely linked to neuropsychiatric disorders, such as Alzheimer's disease (AD), schizophrenia (SZ), and epilepsy. Given their important role in brain pathophysiology and disorders, neurosteroids offer potential therapeutic targets for a variety of neuropsychiatric diseases, and that therapeutic strategies targeting neurosteroids probably exert beneficial effects. We therefore summarized the role of neurosteroids in brain physiology and neuropsychiatric disorders, and introduced the recent findings of synthetic neurosteroid analogues for potential treatment of neuropsychiatric disorders, thereby providing insights for further research in the future.

Neuroactive Steroids, Toll-like Receptors, and Neuroimmune Regulation: Insights into Their Impact on Neuropsychiatric Disorders

Pregnane neuroactive steroids, notably allopregnanolone and pregnenolone, exhibit efficacy in mitigating inflammatory signals triggered by toll-like receptor (TLR) activation, thus attenuating the production of inflammatory factors. Clinical studies highlight their therapeutic potential, particularly in conditions like postpartum depression (PPD), where the FDA-approved compound brexanolone, an intravenous formulation of allopregnanolone, effectively suppresses TLR-mediated inflammatory pathways, predicting symptom improvement. Additionally, pregnane neurosteroids exhibit trophic and anti-inflammatory properties, stimulating the production of vital trophic proteins and anti-inflammatory factors. Androstane neuroactive steroids, including estrogens and androgens, along with dehydroepiandrosterone (DHEA), display diverse effects on TLR expression and activation. Notably, androstenediol (ADIOL), an androstane neurosteroid, emerges as a potent anti-inflammatory agent, promising for therapeutic interventions. The dysregulation of immune responses via TLR signaling alongside reduced levels of endogenous neurosteroids significantly contributes to symptom severity across various neuropsychiatric disorders. Neuroactive steroids, such as allopregnanolone, demonstrate efficacy in alleviating symptoms of various neuropsychiatric disorders and modulating neuroimmune responses, offering potential intervention avenues. This review emphasizes the significant therapeutic potential of neuroactive steroids in modulating TLR signaling pathways, particularly in addressing inflammatory processes associated with neuropsychiatric disorders. It advances our understanding of the complex interplay between neuroactive steroids and immune responses, paving the way for personalized treatment strategies tailored to individual needs and providing insights for future research aimed at unraveling the intricacies of neuropsychiatric disorders.

Alfaxalone does not have long-term effects on goldfish pyramidal neuron action potential properties or GABAA receptor currents

Anesthetics have varying physiological effects, but most notably alter ion channel kinetics. Alfaxalone is a rapid induction and washout neuroactive anesthetic, which potentiates γ-aminobutyric acid (GABA)-activated GABAA receptor (GABAA-R) currents. This study aims to identify any long-term effects of alfaxalone sedation on pyramidal neuron action potential and GABAA-R properties, to determine if its impact on neuronal function can be reversed in a sufficiently short timeframe to allow for same-day electrophysiological studies in goldfish brain. The goldfish (Carassius auratus) is an anoxia-tolerant vertebrate and is a useful model to study anoxia tolerance mechanisms. The results show that alfaxalone sedation did not significantly impact action potential properties. Additionally, the acute application of alfaxalone onto naive brain slices caused the potentiation of whole-cell GABAA-R current decay time and area under the curve. Following whole-animal sedation with alfaxalone, a 3-h wash of brain slices in alfaxalone-free saline, with saline exchanged every 30 min, was required to remove any potentiating impact of alfaxalone on GABAA-R whole-cell currents. These results demonstrate that alfaxalone is an effective anesthetic for same-day electrophysiological experiments with goldfish brain slices.

Allopregnanolone pleiotropic action in neurons and astrocytes: calcium signaling as a unifying mechanism

Objective

Allopregnanolone (Allo) is a neurosteroid with pleiotropic action in the brain that includes neurogenesis, oligogenesis, human and rodent neural stem cell regeneration, increased glucose metabolism, mitochondrial respiration and biogenesis, improved cognitive function, and reduction of both inflammation and Alzheimer's disease (AD) pathology. Because the breadth of Allo-induced responses requires activation of multiple systems of biology in the absence of an Allo-specific nuclear receptor, analyses were conducted in both neurons and astrocytes to identify unifying systems and signaling pathways.

Methods

Mechanisms of Allo action were investigated in embryonic hippocampal neurons and astrocytes cultured in an Aging Model (AM) media. Cellular morphology, mitochondrial function, and transcriptomics were investigated followed by mechanistic pathway analyses.

Results

In hippocampal neurons, Allo significantly increased neurite outgrowth and synaptic protein expression, which were paralleled by upregulated synaptogenesis and long-term potentiation gene expression profiles. Mechanistically, Allo induced Ca2+/CREB signaling cascades. In parallel, Allo significantly increased maximal mitochondrial respiration, mitochondrial membrane potential, and Complex IV activity while reducing oxidative stress, which required both the GABAA and L-type Ca2+ channels. In astrocytes, Allo increased ATP generation, mitochondrial function and dynamics while reducing oxidative stress, inflammasome indicators, and apoptotic signaling. Mechanistically, Allo regulation of astrocytic mitochondrial function required both the GABAA and L-type Ca2+ channels. Furthermore, Allo activated NRF1-TFAM signaling and increased the DRP1/OPA1 protein ratio, which led to increased mitochondrial biogenesis and dynamics.

Conclusion

Collectively, the cellular, mitochondrial, transcriptional, and pharmacological profiles provide evidence in support of calcium signaling as a unifying mechanism for Allo pleiotropic actions in the brain.

The Interaction Between NF-κB and Estrogen in Alzheimer's Disease

Post-menopausal women are at a higher risk of developing Alzheimer's disease (AD) than males. The higher rates of AD in women are associated with the sharp decline in the estrogen levels after menopause. Estrogen has been shown to downregulate inflammatory cytokines in the central nervous system (CNS), which has a neuroprotective role against neurodegenerative diseases including AD. Sustained neuroinflammation is associated with neurodegeneration and contributes to AD. Nuclear factor kappa-B (NF-κB) is a transcription factor involved with the modulation of inflammation and interacts with estrogen to influence the progression of AD. Application of 17β-estradiol (E2) has been shown to inhibit NF-κB, thereby reducing transcription of NF-κB target genes. Despite accumulating evidence showing that estrogens have beneficial effects in pre-clinical AD studies, there are mixed results with hormone replacement therapy in clinical trials. Furthering our understanding of how NF-κB interacts with estrogen and alters the progression of neurodegenerative disorders including AD, should be beneficial and result in the development of novel therapeutics.

Alfaxalone anaesthesia increases brain derived neurotrophic factor levels and preserves postoperative cognition by activating pregnane-X receptors: an in vitro study and a double blind randomised controlled trial

BACKGROUND

Alfaxalone is a fast acting intravenous anaesthetic with high therapeutic index. It is an analogue of the naturally-occurring neurosteroid allopregnanolone responsible for maintenance of cognition and neuroprotection by activation of brain pregnane X receptors and consequent increased production of mature brain-derived neurotrophic factor (m-BDNF). Two studies are reported here: an in vitro study investigated whether alfaxalone activates human pregnane X receptors (h-PXR) as effectively as allopregnanolone; and a clinical study that measured postoperative changes in serum m-BDNF and cognition in patients after alfaxalone anaesthesia compared with propofol and sevoflurane.

METHODS

In vitro Activation of h-PXR by allopregnanolone and alfaxalone solutions (206 - 50,000 nM) was measured using human embryonic kidney cells expressing h-PXR hybridised and linked to the firefly luciferase gene. Light emission by luciferase stimulated by each ligand binding with h-PXR was measured. Clinical A double blind prospective randomised study of patients undergoing hip arthroplasty anaesthetised with alfaxalone TIVA (n = 8) or propofol TIVA (n = 3) or propofol plus sevoflurane inhalational anaesthesia (n = 4). The doses of anaesthetics were titrated to the same depth of anaesthesia (BIS 40-60). Subjects' cognitive performance was assessed using the Grooved Pegboard Test, Digit Symbol Substitution Test (DSST) and Mini Mental State examination (MMSE) for 7 days postoperatively. Serum m-BDNF concentrations were measured for 7 postoperative days.

RESULTS

In vitro Allopregnanolone and alfaxalone both activated h-PXR, alfaxalone being more efficacious than allopregnanolone: 50,000 nM, p = 0.0019; 16,700 nM, p = 0.0472; 5600 nM, p = 0.0031. Clinical Alfaxalone treated subjects scored better than propofol and sevoflurane anaesthetised patients in the cognition tests: (MMSE p = 0.0251; Grooved Pegboard test dominant hand pre v post anaesthesia scores p = 0.8438 for alfaxalone and p = 0.0156 for propofol and propofol/sevoflurane combined). The higher cognition scores were accompanied by higher serum m-BDNF levels in the alfaxalone anaesthetised patients (p < 0.0001).

CONCLUSIONS

These results suggest that sedation and anaesthesia induced by the synthetic neuroactive steroid alfaxalone may be accompanied by effects normally caused by physiological actions of allopregnanolone at PXR, namely, increased secretion of m-BDNF and consequent neuroprotection and preservation of cognition.

TRIAL REGISTRATION

The clinical trial was registered on 17/01/2018 with the Australian New Zealand Clinical Trials Registry: registration number ACTRN12618000064202 [Universal Trial Number U1111-1198-0412].

Low serum allopregnanolone levels in children with attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) has increasing evidence for the role of neurohormones in its etiopathogenesis. It has been suggested that the effects of neurosteroids on the brain in the early developmental period may predispose to neurodevelopmental pathologies. In our study, we examined serum dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEA-S), and allopregnanolone levels in children with ADHD and whether these neurosteroids differ in the presence of specific learning disorder (SLD) and oppositional defiant disorder (ODD) comorbidities (ADHD+SLD and ADHD+ODD). We also investigated the relationship between neurosteroid levels and the severity of ADHD symptoms. Thirty-five prepubertal children with ADHD and 33 prepubertal healthy children, all aged 6-10 years, were included in this study. The severity of ADHD symptoms was assessed with the parent-rated and teacher-rated Turgay DSM-IV Disruptive Behavior Disorders Rating Scale (T-DSM-IV-S). Serum allopregnanolone levels were significantly lower in the ADHD group compared to healthy controls. When analyzed according to comorbidity status, serum allopregnanolone levels were lower in ADHD+SLD and ADHD+ODD groups compared to healthy controls. However, when compared to healthy children, serum DHEA and DHEA-S levels in children with ADHD were not significantly different. Serum allopregnanolone levels were negatively associated with teacher-rated T-DSM-IV-S hyperactivity/impulsivity scores for all participants only. These findings suggest that allopregnanolone may play a role in the pathophysiology of ADHD, especially in the presence of ODD and SLD comorbidities.

Allopregnanolone: Regenerative therapeutic to restore neurological health

Chronic stress has been proposed as a driver of altered brain structure and function, including the pathogenesis of neurodegenerative diseases and a driver of disease progression. A key outcome of stress in the brain is structural remodeling of neural architecture, which may be a sign of successful adaptation, whereas persistence of these changes when stress ends indicate failed resilience. Neuroendocrine homeostasis and stress response are mainly dependent upon the functioning of the hypothalamic-pituitary-adrenal axis. Neurosteroids will fluctuate depending on whether the stress is acute or chronic. Advancements in neurosteroid research have led to the identification of multiple targets for drug development, but the most promising innovative target may be neurogenesis, given its potential impact in neurodegenerative disorders like Alzheimer's disease. Allopregnanolone is an endogenous pregnane neurosteroid and a reduced metabolite of progesterone, which acts as a potent allosteric modulator and direct activator of the GABA-chloride channel complex. Perhaps the most intriguing finding related to the potential therapeutic effects of allopregnanolone is its potential to promote neuroregeneration.

Lack of placental neurosteroid alters cortical development and female somatosensory function

Placental endocrine function is essential to fetal brain development. Placental hormones include neurosteroids such as allopregnanolone (ALLO), a regulator of neurodevelopmental processes via positive allosteric modulation of the GABAA receptor (GABAA-R). Using a mouse model (plKO) in which the gene encoding the ALLO synthesis enzyme is specifically deleted in trophoblasts, we previously showed that placental ALLO insufficiency alters cerebellar white matter development and leads to male-specific autistic-like behavior. We now demonstrate that the lack of placental ALLO causes female-predominant alterations of cortical development and function. Placental ALLO insufficiency disrupts cell proliferation in the primary somatosensory cortex (S1) in a sex-linked manner. Early changes are seen in plKO embryos of both sexes, but persist primarily in female offspring after birth. Adolescent plKO females show significant reduction in pyramidal neuron density, as well as somatosensory behavioral deficits as compared with plKO males and control littermates. Assessment of layer-specific markers in human postmortem cortices suggests that preterm infants may also have female-biased abnormalities in cortical layer specification as compared with term infants. This study establishes a novel and fundamental link between placental function and sex-linked long-term neurological outcomes, emphasizing the importance of the growing field of neuroplacentology.

Relationship between adult subventricular neurogenesis and Alzheimer’s disease: Pathologic roles and therapeutic implications

Alzheimer’s disease (AD) is a neurodegenerative disease that is characterized by irreversible cognitive declines. Senile plaques formed by amyloid-β (Aβ) peptides and neurofibrillary tangles, consisting of hyperphosphorylated tau protein accumulation, are prominent neuropathological features of AD. Impairment of adult neurogenesis is also a well-known pathology in AD. Adult neurogenesis is the process by which neurons are generated from adult neural stem cells. It is closely related to various functions, including cognition, as it occurs throughout life for continuous repair and development of specific neural pathways. Notably, subventricular zone (SVZ) neurogenesis, which occurs in the lateral ventricles, transports neurons to several brain regions such as the olfactory bulb, cerebral cortex, striatum, and hippocampus. These migrating neurons can affect cognitive function and behavior in different neurodegenerative diseases. Despite several studies indicating the importance of adult SVZ neurogenesis in neurodegenerative disorders, the pathological alterations and therapeutic implications of impaired adult neurogenesis in the SVZ in AD have not yet been fully explained. In this review, we summarize recent progress in understanding the alterations in adult SVZ neurogenesis in AD animal models and patients. Moreover, we discuss the potential therapeutic approaches for restoring impaired adult SVZ neurogenesis. Our goal is to impart to readers the importance of adult SVZ neurogenesis in AD and to provide new insights through the discussion of possible therapeutic approaches.

Golexanolone, a GABAA receptor modulating steroid antagonist, restores motor coordination and cognitive function in hyperammonemic rats by dual effects on peripheral inflammation and neuroinflammation

Aims

Hyperammonemic rats show peripheral inflammation, increased GABAergic neurotransmission and neuroinflammation in cerebellum and hippocampus which induce motor incoordination and cognitive impairment. Neuroinflammation enhances GABAergic neurotransmission in cerebellum by enhancing the TNFR1‐glutaminase‐GAT3 and TNFR1‐CCL2‐TrkB‐KCC2 pathways. Golexanolone reduces GABA_A receptors potentiation by allopregnanolone. This work aimed to assess if treatment of hyperammonemic rats with golexanolone reduces peripheral inflammation and neuroinflammation and restores cognitive and motor function and to analyze underlying mechanisms.

Methods

Rats were treated with golexanolone and effects on peripheral inflammation, neuroinflammation, TNFR1‐glutaminase‐GAT3 and TNFR1‐CCL2‐TrkB‐KCC2 pathways, and cognitive and motor function were analyzed.

Results

Hyperammonemic rats show increased TNFα and reduced IL‐10 in plasma, microglia and astrocytes activation in cerebellum and hippocampus, and impaired motor coordination and spatial and short‐term memories. Treating hyperammonemic rats with golexanolone reversed changes in peripheral inflammation, microglia and astrocytes activation and restored motor coordination and spatial and short‐term memory. This was associated with reversal of the hyperammonemia‐enhanced activation in cerebellum of the TNFR1‐glutaminase‐GAT3 and TNFR1‐CCL2‐TrkB‐KCC2 pathways.

Conclusion

Reducing GABA_A receptors activation with golexanolone reduces peripheral inflammation and neuroinflammation and improves cognitive and motor function in hyperammonemic rats. The effects identified would also occur in patients with hepatic encephalopathy and, likely, in other pathologies associated with neuroinflammation.

Age-related neuroendocrine, cognitive, and behavioral co-morbidities are promoted by HIV-1 Tat expression in male mice

In the U.S. about half of the HIV-infected individuals are aged 50 and older. In men living with HIV, secondary hypogonadism is common and occurs earlier than in seronegative men, and its prevalence increases with age. While the mechanisms(s) are unknown, the HIV-1 trans-activator of transcription (Tat) protein disrupts neuroendocrine function in mice partly by dysregulating mitochondria and neurosteroidogenesis. We hypothesized that conditional Tat expression in middle-aged male transgenic mice [Tat(+)] would promote age-related comorbidities compared to age-matched controls [Tat(−)]. We expected Tat to alter steroid hormone milieu consistent with behavioral deficits. Middle-aged Tat(+) mice had lower circulating testosterone and progesterone than age-matched controls and greater circulating corticosterone and central allopregnanolone than other groups. Young Tat(+) mice had greater circulating progesterone and estradiol-to-testosterone ratios. Older age or Tat exposure increased anxiety-like behavior (open field; elevated plus-maze), increased cognitive errors (radial arm water maze), and reduced grip strength. Young Tat(+), or middle-aged Tat(−), males had higher mechanical nociceptive thresholds than age-matched counterparts. Steroid levels correlated with behaviors. Thus, Tat may contribute to HIV-accelerated aging.

Medroxyprogesterone acetate positively modulates specific GABAA-receptor subtypes - affecting memory and cognition

Medroxyprogesterone acetate (MPA) is a progestin widely used in humans as hormone replacement therapy and at other indications. Many progestin metabolites, as the progesterone metabolite allopregnanolone, have GABA_A-receptor modulatory effects and are known to affect memory, learning, appetite, and mood. In women, 4 years chronic treatment with MPA doubles the frequency of dementia and in rats, MPA causes cognitive impairment related to the GABAergic system. Activation of the membrane bound GABA_A receptor results in a chloride ion flux that can be studied by whole-cell patch-clamp electrophysiological recordings. The purpose of this study was to clarify the modulatory effects of MPA and specific MPA metabolites, with structures like known GABA_A-receptor modulators, on different GABA_A-receptor subtypes. An additional aim was to verify the results as steroid effects on GABA response in single cells taken from rat hypothalamus. HEK-293 cell-lines permanently expressing the recombinant human GABA_A-receptor subtype α1β2γ2L or α5β3γ2L or α2β3γ2S were created. The MPA metabolites 3α5α-MPA,3β5α-MPA and 3β5β-MPA were synthesised and purified for electrophysiological patch-clamp measurements with a Dynaflow system. The effects of MPA and tetrahydrodeoxycorticosterone were also studied. None of the studied MPA metabolites affected the responses mediated by α1β2γ2L or α5β3γ2L GABA_A receptors. Contrary, MPA clearly acted both as a positive modulator and as a direct activator of the α5β3γ2L and α2β3γ2S GABA_A receptors. However, in concentrations up to 10 μM, MPA was inactive at the α1β2γ2L GABA_A receptor. In the patch-clamp recordings from dissociated cells of the preoptic area in rats, MPA increased the amplitude of responses to GABA. In addition, MPA alone without added GABA, evoked a current response. In conclusion, MPA acts as a positive modulator of specific GABA_A receptor subtypes expressed in HEK cells and at native GABA receptors in single cells from the hypothalamic preoptic area.

The effects of neurosteroid allopregnanolone on synaptic dysfunction in the hippocampus in experimental parkinsonism rats: An electrophysiological and molecular study

The dopaminergic system is a powerful candidate targeted for changes of synaptic plasticity in the hippocampus. Higher incidence of Parkinson's disease (PD) in men than women indicates the influence of sex hormones on the PD development. Previous studies have shown that neurodegenerative diseases such as PD are related to the decline of Allopregnanolon (Allo), a metabolite of progesterone; it is also well known that learning and memory are influenced by oscillations in steroidal hormones. Although abnormalities in hippocampal plasticity have been observed in the toxic models of PD, effects of Allo on hippocampal LTP and hippocampal synaptic protein levels, which play an important role in maintaining the integrity of neural connections, have never been analyzed thus far. Experimental groups subjected to the long-term potentiation (LTP) were studied in the CA1 area of the hippocampus. In addition, the levels of hippocampal postsynaptic density protein 95 (PSD-95), neurexin-1 (Nrxn1) and neuroligin (Nlgn) as synaptic molecular components were determined by immunoblotting. Although dopamine denervation did not alter basal synaptic transmission and pair-pulse facilitation of field excitatory postsynaptic potentials (fEPSPs), the induction and maintenance of LTP were impaired in the CA1 region. In addition, the levels of PSD-95, Nrxn1 and Nlgn were significantly decreased in the hippocampus of 6-OHDA-treated animals. Such abnormalities in synaptic electrophysiological aspects and protein levels were abolished by the treatment with Allo. These findings showed that partial dopamine depletion led to unusual synaptic plasticity in the CA1 as well as the decrease in synaptic proteins in the hippocampus. Our results demonstrated that Allo ameliorated these deficits and preserved pre- and post-synaptic proteins. Therefore, Allo may be an effective factor in maintaining synaptic integrity in the mesolimbic pathway.

Exploratory imaging outcomes of a phase 1b/2a clinical trial of allopregnanolone as a regenerative therapeutic for Alzheimer's disease: Structural effects and functional connectivity outcomes

Introduction

Allopregnanolone (ALLO), an endogenous neurosteroid, promoted neurogenesis and oligogenesis and restored cognitive function in animal models of Alzheimer's disease (AD). Based on these discovery research findings, we conducted a randomized-controlled phase 1b/2a multiple ascending dose trial of ALLO in persons with early AD (NCT02221622) to assess safety, tolerability, and pharmacokinetics. Exploratory imaging outcomes to determine whether ALLO impacted hippocampal structure, white matter integrity, and functional connectivity are reported.

Methods

Twenty-four individuals participated in the trial (n = 6 placebo; n = 18 ALLO) and underwent brain magnetic resonance imaging (MRI) before and after 12 weeks of treatment. Hippocampal atrophy rate was determined from volumetric MRI, computed as rate of change, and qualitatively assessed between ALLO and placebo sex, apolipoprotein E (APOE) ε4 allele, and ALLO dose subgroups. White matter microstructural integrity was compared between placebo and ALLO using fractional and quantitative anisotropy (QA). Changes in local, inter-regional, and network-level functional connectivity were also compared between groups using resting-state functional MRI.

Results

Rate of decline in hippocampal volume was slowed, and in some cases reversed, in the ALLO group compared to placebo. Gain of hippocampal volume was evident in APOE ε4 carriers (range: 0.6% to 7.8% increased hippocampal volume). Multiple measures of white matter integrity indicated evidence of preserved or improved integrity. ALLO significantly increased fractional anisotropy (FA) in 690 of 690 and QA in 1416 of 1888 fiber tracts, located primarily in the corpus callosum, bilateral thalamic radiations, and bilateral corticospinal tracts. Consistent with structural changes, ALLO strengthened local, inter-regional, and network level functional connectivity in AD-vulnerable regions, including the precuneus and posterior cingulate, and network connections between the default mode network and limbic system.

Discussion

Indicators of regeneration from previous preclinical studies and these exploratory MRI-based outcomes from this phase 1b/2a clinical cohort support advancement to a phase 2 proof-of-concept efficacy clinical trial of ALLO as a regenerative therapeutic for mild AD (REGEN-BRAIN study; NCT04838301).

Positive GABAA receptor modulating steroids and their antagonists: Implications for clinical treatments

GABA is the main inhibitory neurotransmitter in the brain and GABAergic transmission has been shown to be of importance for regulation of mood, memory and food intake. The progesterone metabolite allopregnanolone (Allo) is a positive GABA_A receptor modulating steroid with potent effects. In humans, disorders such as premenstrual dysphoric disorder (PMDD), hepatic encephalopathy and polycystic ovarian syndrome are associated with elevated Allo levels and increased negative mood, disturbed memory and increased food intake in some individuals. This is surprising because Allo shares many properties with benzodiazepines and is mainly considered to be anxiolytic and anti-depressant. However, it is well established that, in certain individuals, GABA_A receptor activating compounds could have paradoxical effects and thus be anxiogenic in low physiological plasma concentrations but anxiolytic at high levels. We have demonstrated that isoallopregnanolone (Isoallo), the 3β-OH sibling of Allo, functions as a GABA_A receptor modulating steroid antagonist (GAMSA) but without any effects of its own on GABA_A receptors. The antagonistic effect is noted in most GABA_A subtypes investigated in vitro to date. In vivo, Isoallo can inhibit Allo-induced anaesthesia in rats, as well as sedation or saccadic eye velocity in humans. Isoallo treatment has been studied in women with PMDD. In a first phase II study, Isoallo (Sepranolone; Asarina Pharma) injections significantly ameliorated negative mood in women with PMDD compared with placebo. Several GAMSAs for oral administration have also been developed. The GAMSA, UC1011, can inhibit Allo induced memory disturbances in rats and an oral GAMSA, GR3027, has been shown to restore learning and motor coordination in rats with hepatic encephalopathy. In humans, vigilance, cognition and pathological electroencephalogram were improved in patients with hepatic encephalopathy on treatment with GR3027. In conclusion GAMSAs are a new possible treatment for disorders and symptoms caused by hyperactivity in the GABA_A system.

Progress and Pitfalls in Developing Agents to Treat Neurocognitive Deficits Associated with Schizophrenia

Cognitive impairments associated with schizophrenia (CIAS) represent a central element of the symptomatology of this severe mental disorder. CIAS substantially determine the disease prognosis and hardly, if at all, respond to treatment with currently available antipsychotics. Remarkably, all drugs presently approved for the treatment of schizophrenia are, to varying degrees, dopamine D₂/D₃ receptor blockers. In turn, rapidly growing evidence suggests the immense significance of systems other than the dopaminergic system in the genesis of CIAS. Accordingly, current efforts addressing the unmet needs of patients with schizophrenia are primarily based on interventions in other non-dopaminergic systems. In this review article, we provide a brief overview of the available evidence on the importance of specific systems in the development of CIAS. In addition, we describe the promising targets for the development of new drugs that have been used so far. In doing so, we present the most important candidates that have been investigated in the field of the specific systems in recent years and present a summary of the results available at the time of drafting this review (May 2022), as well as the currently ongoing studies.

Allopregnanolone Improves Locomotor Activity and Arousal in the Aged CGG Knock-in Mouse Model of Fragile X-Associated Tremor/Ataxia Syndrome

Carriers of the fragile X premutation (PM) can develop a variety of early neurological symptoms, including depression, anxiety and cognitive impairment as well as being at risk for developing the late-onset fragile X-associated tremor/ataxia syndrome (FXTAS). The absence of effective treatments for FXTAS underscores the importance of developing efficacious therapies to reduce the neurological symptoms in elderly PM carriers and FXTAS patients. A recent preliminary study reported that weekly infusions of Allopregnanolone (Allop) may improve deficits in executive function, learning and memory in FXTAS patients. Based on this study we examined whether Allop would improve neurological function in the aged CGG knock-in (CGG KI) dutch mouse, B6.129P2(Cg)-Fmr1^tm2Cgr/Cgr, that models much of the symptomatology in PM carriers and FXTAS patients. Wild type and CGG KI mice received 10 weekly injections of Allop (10 mg/kg, s.c.), followed by a battery of behavioral tests of motor function, anxiety, and repetitive behavior, and 5-bromo-2'-deoxyuridine (BrdU) labeling to examine adult neurogenesis. The results provided evidence that Allop in CGG KI mice normalized motor performance and reduced thigmotaxis in the open field, normalized repetitive digging behavior in the marble burying test, but did not appear to increase adult neurogenesis in the hippocampus. Considered together, these results support further examination of Allop as a therapeutic strategy in patients with FXTAS.

Glutamate and GABA in Microglia-Neuron Cross-Talk in Alzheimer's Disease

The physiological balance between excitation and inhibition in the brain is significantly affected in Alzheimer’s disease (AD). Several neuroactive compounds and their signaling pathways through various types of receptors are crucial in brain homeostasis, among them glutamate and γ-aminobutyric acid (GABA). Activation of microglial receptors regulates the immunological response of these cells, which in AD could be neuroprotective or neurotoxic. The novel research approaches revealed the complexity of microglial function, including the interplay with other cells during neuroinflammation and in the AD brain. The purpose of this review is to describe the role of several proteins and multiple receptors on microglia and neurons, and their involvement in a communication network between cells that could lead to different metabolic loops and cell death/survival. Our review is focused on the role of glutamatergic, GABAergic signaling in microglia–neuronal cross-talk in AD and neuroinflammation. Moreover, the significance of AD-related neurotoxic proteins in glutamate/GABA-mediated dialogue between microglia and neurons was analyzed in search of novel targets in neuroprotection, and advanced pharmacological approaches.

Neurosteroids: A novel promise for the treatment of stroke and post-stroke complications

Stroke is the primary reason for death and disability worldwide, with few treatment strategies to date. Neurosteroids, which are natural molecules in the brain, have aroused great interest in the field of stroke. Neurosteroids are a kind of steroid that acts on the nervous system, and are synthesized in the mitochondria of neurons or glial cells using cholesterol or other steroidal precursors. Neurosteroids mainly include estrogen, progesterone (PROG), allopregnanolone, dehydroepiandrosterone (DHEA), and vitamin D (VD). Most of the preclinical studies have confirmed that neurosteroids can decrease the risk of stroke, and improve stroke outcomes. In the meantime, neurosteroids have been shown to have a positive therapeutic significance in some post-stroke complications, such as epilepsy, depression, anxiety, cardiac complications, movement disorders, and post-stroke pain. In this review, we report the historical background, modulatory mechanisms of neurosteroids in stroke and post-stroke complications, and emphasize on the application prospect of neurosteroids in stroke therapy.

Ligustrazine Attenuates Hyperhomocysteinemia-induced Alzheimer-like Pathologies in Rats

Ligustrazine, an alkaloid extracted from the traditional Chinese herbal medicine Ligusticum Chuanxiong Hort, has been clinically applied to treat the cerebrovascular diseases. Hyperhomocysteinemia (Hhcy) is an independent risk factor for Alzheimer's disease (AD). Memory deficits can be caused by Hhcy via pathologies of AD-like tau and amyloid-β (Aβ) in the hippocampus. Here, we investigated whether homocysteine (Hcy) can induce AD-like pathologies and the effects of ligustrazine on these pathologies. The Hcy rat model was constructed by 14-day Hcy injection via vena caudalis, and rats were treated with daily intragastric administration of ligustrazine at the same time. We found that the pathologies of tau and Aβ were induced by Hcy in the hippocampus, while the Hcy-induced tau hyperphosphorylation and Aβ accumulation could be markedly attenuated by simultaneous ligustrazine treatment. Our data demonstrate that ligustrazine may be used as a promising neuroprotective agent to treat the Hcy-induced AD-like pathologies.

Effect of Allopregnanolone on Spatial Memory and Synaptic Proteins in Animal Model of Metabolic Syndrome

Metabolic Syndrome (MetS) is considered a common disorder, especially with a sedentary lifestyle and unhealthy food consumption. Cognitive impairment is one of the MetS consequences that worsens the quality of life of the patients. The study aimed to assess the therapeutic effect of the neurosteroid Allopregnalonone on spatial memory and, therefore, the expression of two synaptic plasticity markers in the hippocampus. Thirty-two male rats were divided into four groups: control groups, MetS, and MetS + Allopregnalone. Spatial memory has been evaluated by the Y-maze task and blood pressure measured by the rat tail method. Biochemical evaluation of serum glucose, insulin, lipid profile, and hippocampal expression of Synaptophysin and Associated Protein 43 (GAP-43) were performed for assessing Allopregnanolone on serum and hippocampal markers. Allopregnanolone therapy improved working spatial memory, hypertension, and biochemical markers measured in the serum and hippocampus.

The potential involvement of cholinergic system in finasteride induced cognitive dysfunction

OBJECTIVE

Neurosteroids are known to exert diverse functions in the brain. 5α-reductase (5α-R), a rate-limiting enzyme involved in the biosynthesis of neurosteroids is inhibited by finasteride. Clinical studies suggest that administration of finasteride causes the emergence of affective symptoms and cognitive dysfunction. Modeling this in rats would provide an opportunity to understand the mechanisms. Accordingly, in the present study, we evaluated the effects of repeated finasteride administration on spatial learning and memory in the partially baited radial arm maze task (RAM) and social cognitive behavior in the social interaction test. Further, to initiate the quest to understand the mechanisms underlying the effects of finasteride, in a separate group of animals, acetylcholinesterase (AChE) activity in the frontal cortex, hippocampus, septum and striatum was estimated.

METHODS

2 months old male Wistar rats were trained to learn a partially baited radial arm maze task (four trials per day till they reach a choice accuracy of 80 %). Following this, rats were administered with either vehicle (HPβCD) or finasteride (30 or 100 mg/Kg, s.c.) for 7 days and then subjected to retention test on the eighth day. To evaluate the social cognition, finasteride was administered for 7 days, followed by social interaction test on the eighth day. All the sessions were video-recorded and analyzed using Noldus Ethovision XT™ software. Following finasteride administration, on the eighth day, rats were euthanized, and AChE activity was estimated by modified Ellman's method.

RESULTS

Finasteride (100 mg/Kg, s.c.) administration decreased the percent correct choice during the retention trial of the RAM task. This was paralleled by an increase in the number of total number of errors and reference memory errors. In the social interaction test, finasteride (100 mg/Kg, s.c.) administration decreased the time spent with the rat compared to the object, implying decreased sociability and diminished social preference evidenced by similar time spent with the novel and familiar rat. Reduced AChE activity was observed in the frontal cortex, hippocampus and septum.

CONCLUSION

Our study provides evidence that repeated administration of finasteride decreases social interaction and results in cognitive deficits, potentially through a cholinergic mechanism. Further studies are required to understand the exact link between the cognitive effects and the cholinergic system. A deeper probe of the current findings holds promise for the development of novel neurosteroid-based therapeutics to treat affective and cognitive disorders.

The mechanistic link between selective vulnerability of the locus coeruleus and neurodegeneration in Alzheimer's disease

Alzheimer's disease (AD) is neuropathologically characterized by the intracellular accumulation of hyperphosphorylated tau and the extracellular deposition of amyloid-β plaques, which affect certain brain regions in a progressive manner. The locus coeruleus (LC), a small nucleus in the pons of the brainstem, is widely recognized as one of the earliest sites of neurofibrillary tangle formation in AD. Patients with AD exhibit significant neuronal loss in the LC, resulting in a marked reduction of its size and function. The LC, which vastly innervates several regions of the brain, is the primary source of the neurotransmitter norepinephrine (NE) in the central nervous system. Considering that NE is a major modulator of behavior, contributing to neuroprotection and suppression of neuroinflammation, degeneration of the LC in AD and the ultimate dysregulation of the LC-NE system has detrimental effects in the brain. In this review, we detail the neuroanatomy and function of the LC, its essential role in neuroprotection, and how this is dysregulated in AD. We discuss AD-related neuropathologic changes in the LC and mechanisms by which LC neurons are selectively vulnerable to insult. Further, we elucidate the neurotoxic effects of LC de-innervation both locally and at projection sites, and how this augments disease pathology, progression and severity. We summarize how preservation of the LC-NE system could be used in the treatment of AD and other neurodegenerative diseases affected by LC degeneration.

Safety, tolerability, and pharmacokinetics of allopregnanolone as a regenerative therapeutic for Alzheimer's disease: A single and multiple ascending dose phase 1b/2a clinical trial

INTRODUCTION

Allopregnanolone is an endogenous neurosteroid with the potential to be a novel regenerative therapeutic for Alzheimer's disease (AD). Foundations of mechanistic understanding and well-established preclinical safety efficacy make it a viable candidate.

METHODS

A randomized, double-blinded, placebo-controlled, single and multiple ascending dose trial was conducted. Intravenous allopregnanolone or placebo was administered once-per-week for 12 weeks with a 1-month follow-up. Participants with early AD (mild cognitive impairment due to AD or mild AD), a Mini-Mental State Examination score of 20-26 inclusive, and age ≥55 years were randomized (6:2 to three allopregnanolone dosing cohorts or one placebo cohort). Primary endpoint was safety and tolerability. Secondary endpoints included pharmacokinetic (PK) parameters and maximally tolerated dose (MTD). Exploratory endpoints included cognitive and imaging biomarkers.

RESULTS

A total of 24 participants completed the trial. Allopregnanolone was safe and well tolerated in all study participants. No differences were observed between treatment arms in the occurrence and severity of adverse events (AE). Most common AE were mild to moderate in severity and included rash (n = 4 [22%]) and fatigue (n = 3 [17%]). A single non-serious AE, dizziness, was attributable to treatment. There was one serious AE not related to treatment. Pharmacokinetics indicated a predictable linear dose-response in plasma concentration of allopregnanolone after intravenous administration over 30 minutes. The maximum plasma concentrations for the 2 mg, 4 mg, 6 mg, and 10 mg dosages were 14.53 ng/mL (+/-7.31), 42.05 ng/mL (+/-14.55), 60.07 ng/mL (+/-12.8), and 137.48 ng/mL (+/-38.69), respectively. The MTD was established based on evidence of allopregnanolone-induced mild sedation at the highest doses; a sex difference in the threshold for sedation was observed (males 10 mg; females 14 mg). No adverse outcomes on cognition or magnetic resonance imaging-based imaging outcomes were evident.

CONCLUSIONS

Allopregnanolone was well tolerated and safe across all doses in persons with early AD. Safety, MTD, and PK profiles support advancement of allopregnanolone as a regenerative therapeutic for AD to a phase 2 efficacy trial.

TRIAL REGISTRATION

ClinicalTrials.gov-NCT02221622.

Allopregnanolone Promotes Neuronal and Oligodendrocyte Differentiation In Vitro and In Vivo: Therapeutic Implication for Alzheimer's Disease

Previous studies demonstrated that the endogenous neurosteroid allopregnanolone (Allo) promotes regeneration of rodent and human neural progenitor/neural stem cells (NSCs) in vitro and in vivo, and restores neurogenesis and cognitive function in the male triple transgenic mouse model of Alzheimer's disease (3xTgAD). In this study, we investigated Allo regulation of neuronal differentiation of adult mouse neural stem cells from both sexes. Outcomes indicated that the age-dependent shift from neuronal to glial differentiation was accelerated and magnified in 3xTgAD adult NSCs compared to that in age-matched non-Tg NSCs. Coincident with the decline in neuronal differentiation, the number of immature neurons declined earlier in 3xTgAD mice, which was consistent with observations in the aged Alzheimer's human brain. Allo treatment restored the neuron/astrocyte ratio derived from adult 3xTgAD NSCs and increased both NSC proliferation and differentiation in the 3xTgAD brain. Allo treatment also significantly increased expression of Olig2, an oligodendrocyte precursor cell marker, as well as Olig2-positive cells in the corpus callosum of 3xTgAD mice. Increased neuronal and oligodendrocyte differentiation was paralleled by an increase in the expression levels of insulin-like growth factor-1 (IGF-1) and IGF-1 receptor (IGF-1R). Collectively, these findings are consistent with Allo acting as a pleiotropic therapeutic to promote regeneration of gray and white matter in the Alzheimer's brain.

24 hour patterning in gene expression of pineal neurosteroid biosynthesis in young chickens (Gallus gallus domesticus L.)

The pineal gland, one of the three equivalent avian biological clock structures, is also the site of intensive neurosteroid synthesis (7α-hydroxypregnenolone and allopregnanolone). Pineal neurosteroid biosynthesis involves six enzymes: cytochrome P450 side-chain cleavage - Cyp11a1 encoded, cytochrome P450_7α - Cyp7b1, 3β-hydroxysteroid dehydrogenase - Hsd3b2, 5α-reductase - Srd5a1, 3α-hydroxysteroid dehydrogenase - Akr1d1, and 5β-reductase - Srd5a3. Regulation of neurosteroid biosynthesis is not fully understood; although it is known that the E4BP4 transcription factor induces activation of biosynthetic cholesterol genes, which are the targets for SREBP (element-binding protein transcription factor). SREBP principal activity in the pineal gland is suppression and inhibition of the Period2 canonical clock gene, suggesting our hypothesis that genes encoding enzymes involved in neurosteroidogenesis are under circadian clock control and are the Clock Control Genes (CCGs). Therefore, through investigation of daily changes in Cyp11a1, Cyp7b1, Hsd3b2, Akr1d1, Srd5a1, and Srd5a3, pineal genes were tested in vivo and in vitro, in cultured pinealocytes. Experiments were carried out on pineal glands taken from 16-day-old chickens in vivo or using in vitro cultures of pinealocytes collected from 16-day-old animals. Both the birds in the in vivo experiments and the pinealocytes were kept under controlled light conditions (LD 12:12) or in constant darkness (DD). Subsequently, materials were prepared for RT-qPCR analysis. Results revealed that three of the six tested genes: Cyp11a1, Cyp7b1, and Srd5a3 demonstrated significant 24-hour variation in in vivo and in vitro. Findings of this study confirm that these genes could be under clock control and satisfy many of the requirements to be identified as CCGs.

Interleukin 6 reduces allopregnanolone synthesis in the brain and contributes to age-related cognitive decline in mice

Cognitive decline with age is a harmful process that can reduce quality of life. Multiple factors have been established to contribute to cognitive decline, but the overall etiology remains unknown. Here, we hypothesized that cognitive dysfunction is mediated, in part, by increased levels of inflammatory cytokines that alter allopregnanolone (AlloP) levels, an important neurosteroid in the brain. We assessed the levels and regulation of AlloP and the effects of AlloP supplementation on cognitive function in 4-month-old and 24-month-old male C57BL/6 mice. With age, the expression of enzymes involved in the AlloP synthetic pathway was decreased and corticosterone (CORT) synthesis increased. Supplementation of AlloP improved cognitive function. Interestingly, interleukin 6 (IL-6) infusion in young animals significantly reduced the production of AlloP compared with controls. It is notable that inhibition of IL-6 with its natural inhibitor, soluble membrane glycoprotein 130, significantly improved spatial memory in aged mice. These findings were supported by in vitro experiments in primary murine astrocyte cultures, indicating that IL-6 decreases production of AlloP and increases CORT levels. Our results indicate that age-related increases in IL-6 levels reduce progesterone substrate availability, resulting in a decline in AlloP levels and an increase in CORT. Furthermore, our results indicate that AlloP is a critical link between inflammatory cytokines and the age-related decline in cognitive function.

Codonopsis pilosula polysaccharide attenuates Aβ toxicity and cognitive defects in APP/PS1 mice

Codonopsis pilosula Polysaccharides (CPPs), a traditional Chinese medicine used for thousands of years, is a potential neuroprotective polysaccharide via a relatively poorly understood mechanism. We previously reported that CPPs attenuated tau pathology in hTau transfected mice and therefore in the current work investigated the effect of CPPs on Aβ toxicity and cognitive defects in APP/PS1 mice model. It was found that one-month intragastric administration of CPPs significantly ameliorated cognitive defects in APP/PS1 mice. In addition, CPPs treatment mitigated the loss of the synaptic plasticity and increased the synaptic proteins including synaptotagmin and PSD95. The expression of Aβ42 and Aβ40 was remarkably decreased in the hippocampus of APP/PS1 mice after CPPs treatment. We also found that CPPs coincubation significantly reduced the amount of APPβ and Aβ42 expression in cells. Intriguingly, the activity of BACE1 was decreased following CPPs treatment in both the hippocampus of APP/PS1 mice and in vitro experiments. Collectively, these results indicated that CPPs attenuated Aβ pathology in APP/PS1 mice, and down-regulating BACE1 might be the underlaying mechanism which could be a therapeutic target for alleviating cognitive defects in AD pathology.

Steroids and Alzheimer's Disease: Changes Associated with Pathology and Therapeutic Potential

Alzheimer's disease (AD) is a multifactorial age-related neurodegenerative disease that today has no effective treatment to prevent or slow its progression. Neuroactive steroids, including neurosteroids and sex steroids, have attracted attention as potential suitable candidates to alleviate AD pathology. Accumulating evidence shows that they exhibit pleiotropic neuroprotective properties that are relevant for AD. This review focuses on the relationship between selected neuroactive steroids and the main aspects of AD disease, pointing out contributions and gaps with reference to sex differences. We take into account the regulation of brain steroid concentrations associated with human AD pathology. Consideration is given to preclinical studies in AD models providing current knowledge on the neuroprotection offered by neuroactive (neuro)steroids on major AD pathogenic factors, such as amyloid-β (Aβ) and tau pathology, mitochondrial impairment, neuroinflammation, neurogenesis and memory loss. Stimulating endogenous steroid production opens a new steroid-based strategy to potentially overcome AD pathology. This article is part of a Special Issue entitled Steroids and the Nervous System.

Allopregnanolone restores the tyrosine hydroxylase-positive neurons and motor performance in a 6-OHDA-injected mouse model

AIMS

It has been reported that allopregnanolone (APα) promotes the neurogenesis of the neural progenitor cells (NPCs) in the subventricular zone (SVZ) and prevents the decrease of dopaminergic neurons in 6-hydroxydopamine (6-OHDA)-treated mice by binding to γ-aminobutyric acid A receptor (GABAAR) and then opening voltage-gated L-type Ca²⁺ channel, but the underlying mechanisms remain elusive. The aim of this study was to explore the possible involvement of GABAAR and calcium/calmodulin-dependent protein kinase II delta 3 (CaMKIIδ3) in this process.

METHODS

6-OHDA-treated mice and primary cultured midbrain cells were administrated with APα and GABAAR antagonist bicuculline (Bic), and the proliferation and differentiation of NPCs, the tyrosine hydroxylase (TH)-positive neurons and their fibers, the expression levels of CaMKIIδ3 and brain-derived neurotrophic factor (BDNF), and motor functions were measured using ELISA, immunohistochemical staining, real-time RT-PCR, Western blot, and behavioral test.

RESULTS

Allopregnanolone significantly promoted the phosphorylation of cytoplasmic CaMKIIδ3 and its nuclear translocation by binding to GABAAR, which, in turn, increased the expression levels of BDNF. This may account for the findings that the exogenous APα enhanced the proliferation and differentiation of NPCs, and ameliorated the nigrostriatal system and behavioral performance in 6-OHDA-treated mice.

CONCLUSIONS

Allopregnanolone may directly activate GABAAR, which, in turn, enhance the proliferation and differentiation of NPCs via upregulating the expression levels of CaMKIIδ3, and finally contribute to the restoration of dopaminergic neurons in 6-OHDA-treated mice.

Agrochemicals and neurogenesis

Agrochemicals or pesticides are compounds widely used to prevent, destroy or mitigate pests such as insects, rodents, herbs and weeds. However, most of them also act as environmental estrogens, anti-estrogens and/or antiandrogenic chemicals. In addition, both herbicides (such as glyphosate and paraquat) and insecticides (such as pyrethroids, organophosphates, neonicotinoids and rotenone) have been shown to exert significant adverse effects on hippocampal neurogenesis. These effects are particularly important because neurogenesis dysregulation could be associated with cognitive decline and neuropathologies such as Alzheimer's disease. This review focuses on the most commonly used agrochemicals in Argentina and their effects on the hippocampal neurogenesis of mammals. It also discusses the disruption of hormone synthesis and action as a possible mechanism through which these chemical compounds could alter the brain functions. Finally, we propose some lines of research to study the potential endocrine mechanisms involved in the effects of agrochemicals on human health and biodiversity.

Alternatives to amyloid for Alzheimer's disease therapies-a symposium report

For decades, Alzheimer's disease research has focused on amyloid as the primary pathogenic agent. This focus has driven the development of numerous amyloid-targeting therapies; however, with one possible exception, none of these therapies have been effective in preventing or delaying cognitive decline in patients, and there are no approved disease-modifying agents. It is becoming more apparent that alternative drug targets are needed to address this complex disease. An increased understanding of Alzheimer's disease pathology has highlighted the need to target the appropriate disease pathology at the appropriate time in the disease course. Preclinical and early clinical studies have focused on targets, including inflammation, tau, vascular health, and the microbiome. This report summarizes the presentations from a New York Academy of Sciences' one-day symposium entitled "Alzheimer's Disease Therapeutics: Alternatives to Amyloid," held on November 20, 2019.

PPAR and functional foods: Rationale for natural neurosteroid-based interventions for postpartum depression

Allopregnanolone, a GABAergic neurosteroid and progesterone derivative, was recently approved by the Food and Drug Administration for the treatment of postpartum depression (PPD). Several mechanisms appear to be involved in the pathogenesis of PPD, including neuroendocrine dysfunction, neuroinflammation, neurotransmitter alterations, genetic and epigenetic modifications. Recent evidence highlights the higher risk for incidence of PPD in mothers exposed to unhealthy diets that negatively impact the microbiome composition and increase inflammation, all effects that are strongly correlated with mood disorders. Conversely, healthy diets have consistently been reported to decrease the risk of peripartum depression and to protect the body and brain against low-grade systemic chronic inflammation. Several bioactive micronutrients found in the so-called functional foods have been shown to play a relevant role in preventing neuroinflammation and depression, such as vitamins, minerals, omega-3 fatty acids and flavonoids. An intriguing molecular substrate linking functional foods with improvement of mood disorders may be represented by the peroxisome-proliferator activated receptor (PPAR) pathway, which can regulate allopregnanolone biosynthesis and brain-derived neurotropic factor (BDNF) and thereby may reduce inflammation and elevate mood. Herein, we discuss the potential connection between functional foods and PPAR and their role in preventing neuroinflammation and symptoms of PPD through neurosteroid regulation. We suggest that healthy diets by targeting the PPAR-neurosteroid axis and thereby decreasing inflammation may offer a suitable functional strategy to prevent and safely alleviate mood symptoms during the perinatal period.

Yokukansankachimpihange Improves the Social Isolation-Induced Sleep Disruption and Allopregnanolone Reduction in Mice

Yokukansankachimpihange (YKSCH), a traditional Japanese medicine composed of 9 crude drugs, is designed to improve neurosis, insomnia in adults, and night crying in children. YKSCH has been reported to improve diurnal rhythm in patients with Alzheimer's disease and prolong the total sleeping time in healthy subjects. However, little is known about how YKSCH alleviates sleep disorders. Here, we investigated whether and how YKSCH treatment affected sleep latency and duration in group-housed and socially isolated mice. Male ddy mice were treated with YKSCH [1,500 mg/kg, per os (p.o.)] in group-housed or socially isolated conditions for 3–4 weeks. After the last injection, mice were intraperitoneally (i.p.) administered with pentobarbital (60 mg/kg) and the sleep latency and duration was evaluated. The results show that pretreatment with YKSCH had no effect on sleep latency or duration in group-housed mice. However, YKSCH treatment significantly improved the reduced sleep duration in socially isolated mice. This effect of YKSCH was inhibited by the administration of bicuculline (3 mg/kg, i.p.), a GABA_A receptor antagonist. Furthermore, we showed that YKSCH treatment improved the decrease in allopregnanolone content and its synthase expression levels in the olfactory bulb. These results suggest that YKSCH treatment improved social isolation stress-induced insomnia via the GABAergic pathway and that the mechanism of action of YKSCH is partly due to improvement of allopregnanolone levels of expression.

Inhibition of 5α Reductase Impairs Cognitive Performance, Alters Dendritic Morphology and Increases Tau Phosphorylation in the Hippocampus of Male 3xTg-AD Mice

Recent work has suggested that 5α-reduced metabolites of testosterone may contribute to the neuroprotection conferred by their parent androgen, as well as to sex differences in the incidence and progression of Alzheimer's disease (AD). This study investigated the effects of inhibiting 5α-reductase on object recognition memory (ORM), hippocampal dendritic morphology and proteins involved in AD pathology, in male 3xTg-AD mice. Male 6-month old wild-type or 3xTg-AD mice received daily injections of finasteride (50 mg/kg i.p.) or vehicle (18% β-cyclodextrin, 1% v/b.w.) for 20 days. Female wild-type and 3xTg-AD mice received only the vehicle. Finasteride treatment differentially impaired ORM in males after short-term (3xTg-AD only) or long-term (3xTg-AD and wild-type) retention delays. Dendritic spine density and dendritic branching of pyramidal neurons in the CA3 hippocampal subfield were significantly lower in 3xTg-AD females than in males. Finasteride reduced CA3 dendritic branching and spine density in 3xTg-AD males, to within the range observed in vehicle-treated females. In the CA1 hippocampal subfield, dendritic branching and spine density were reduced in both male and female 3xTg-AD mice, compared to wild type controls. Hippocampal amyloid β levels were substantially higher in 3xTg-AD females compared to both vehicle and finasteride-treated 3xTg-AD males. Site-specific Tau phosphorylation was higher in 3xTg-AD mice compared to sex-matched wild-type controls, increasing slightly after finasteride treatment. These results suggest that 5α-reduced neurosteroids may play a role in testosterone-mediated neuroprotection and may contribute to sex differences in the development and severity of AD.

Allopregnanolone Modulates GABAAR-Dependent CaMKIIδ3 and BDNF to Protect SH-SY5Y Cells Against 6-OHDA-Induced Damage

Allopregnanolone (APα), as a functional neurosteroid, exhibits the neuroprotective effect on neurodegenerative diseases such as Parkinson’s disease (PD) through γ-aminobutyric acid A receptor (GABAAR), but it has not been completely understood about its molecular mechanisms. In order to investigate the neuroprotective effect of APα, as well as to clarify its possible molecular mechanisms, SH-SY5Y neuronal cell lines were incubated with 6-hydroxydopamine (6-OHDA), which has been widely used as an in vitro model for PD, along with APα alone or in combination with GABAAR antagonist (bicuculline, Bic), intracellular Ca²⁺ chelator (EGTA) and voltage-gated L-type Ca²⁺ channel blocker (Nifedipine). The viability, proliferation, and differentiation of SH-SY5Y cells, the expression levels of calmodulin (CaM), Ca²⁺/calmodulin-dependent protein kinase II δ3 (CaMKIIδ3), cyclin-dependent kinase-1 (CDK1) and brain-derived neurotrophic factor (BDNF), as well as the interaction between CaMKIIδ3 and CDK1 or BDNF, were detected by morphological and molecular biological methodology. Our results found that the cell viability and the number of tyrosine hydroxylase (TH), bromodeoxyuridine (BrdU) and TH/BrdU-positive cells in 6-OHDA-treated SH-SY5Y cells were significantly decreased with the concomitant reduction in the expression levels of aforementioned proteins, which were ameliorated following APα administration. In addition, Bic could further increase the number of TH or BrdU-positive cells as well as the expression levels of aforementioned proteins except for TH/BrdU-double positive cells, while EGTA and Nifedipine could attenuate the expression levels of CaM, CaMKIIδ3 and BDNF. Moreover, there existed a direct interaction between CaMKIIδ3 and CDK1 or BDNF. As a result, APα-induced an increase in the number of TH-positive SH-SY5Y cells might be mediated through GABAAR via Ca²⁺/CaM/CaMKIIδ3/BDNF (CDK1) signaling pathway, which would ultimately facilitate to elucidate PD pathogenesis and hold a promise as an alternative therapeutic target for PD.

Allopregnanolone Reverses Bioenergetic Deficits in Female Triple Transgenic Alzheimer's Mouse Model

Previously, we reported that the neurosteroid allopregnanolone (Allo) promoted neural stem cell regeneration, restored cognitive function, and reduced Alzheimer's Disease (AD) pathology in the triple transgenic Alzheimer's mouse model (3xTgAD). To investigate the underlying systems biology of Allo action in AD models in vivo, we assessed the regulation of Allo on the bioenergetic system of the brain. Outcomes of these analysis indicated that Allo significantly reversed deficits in mitochondrial respiration and biogenesis and key mitochondrial enzyme activity and reduced lipid peroxidation in the 3xTgAD mice in vivo. To explore the mechanisms by which Allo regulates the brain metabolism, we conducted targeted transcriptome analysis. These data further confirmed that Allo upregulated genes involved in glucose metabolism, mitochondrial bioenergetics, and signaling pathways while simultaneously downregulating genes involved in Alzheimer's pathology, fatty acid metabolism, and mitochondrial uncoupling and dynamics. Upstream regulatory pathway analysis predicted that Allo induced peroxisome proliferator-activated receptor gamma (PPARG) and coactivator 1-alpha (PPARGC1A) pathways while simultaneously inhibiting the presenilin 1 (PSEN 1), phosphatase and tensin homolog (PTEN), and tumor necrosis factor (TNF) pathways to reduce AD pathology. Collectively, these data indicate that Allo functions as a systems biology regulator of bioenergetics, cholesterol homeostasis, and β-amyloid reduction in the brain. These systems are critical to neurological health, thus providing a plausible mechanistic rationale for Allo as a therapeutic to promote neural cell function and reduce the burden of AD pathology.

Current status and future prospects of stem cell therapy in Alzheimer's disease

Alzheimer’s disease is a common progressive neurodegenerative disorder, pathologically characterized by the presence of β-amyloid plaques and neurofibrillary tangles. Current treatment approaches using drugs only alleviate the symptoms without curing the disease, which is a serious issue and influences the quality of life of the patients and their caregivers. In recent years, stem cell technology has provided new insights into the treatment of neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. Currently, the main sources of stem cells include neural stem cells, embryonic stem cells, mesenchymal stem cells, and induced pluripotent stem cells. In this review, we discuss the pathophysiology and general treatment of Alzheimer’s disease, and the current state of stem cell transplantation in the treatment of Alzheimer’s disease. We also assess future challenges in the clinical application and drug development of stem cell transplantation as a treatment for Alzheimer’s disease.

GABA-A receptor modulating steroids in acute and chronic stress; relevance for cognition and dementia?

Cognitive dysfunction, dementia and Alzheimer's disease (AD) are increasing as the population worldwide ages. Therapeutics for these conditions is an unmet need. This review focuses on the role of the positive GABA-A receptor modulating steroid allopregnanolone (APα), it's role in underlying mechanisms for impaired cognition and of AD, and to determine options for therapy of AD. On one hand, APα given intermittently promotes neurogenesis, decreases AD-related pathology and improves cognition. On the other, continuous exposure of APα impairs cognition and deteriorates AD pathology. The disparity between these two outcomes led our groups to analyze the mechanisms underlying the difference. We conclude that the effects of APα depend on administration pattern and that chronic slightly increased APα exposure is harmful to cognitive function and worsens AD pathology whereas single administrations with longer intervals improve cognition and decrease AD pathology. These collaborative assessments provide insights for the therapeutic development of APα and APα antagonists for AD and provide a model for cross laboratory collaborations aimed at generating translatable data for human clinical trials.

Widespread Cortical Thickness Is Associated With Neuroactive Steroid Levels

Background

Neuroactive steroids are endogenous molecules with regenerative and neuroprotective actions. Both cortical thickness and many neuroactive steroid levels decline with age and are decreased in several neuropsychiatric disorders. However, a systematic examination of the relationship between serum neuroactive steroid levels and in vivo measures of cortical thickness in humans is lacking.

Methods

Peripheral serum levels of seven neuroactive steroids were assayed in United States military veterans. All (n = 143) subsequently underwent high-resolution structural MRI, followed by parcellelation of the cortical surface into 148 anatomically defined regions. Regression modeling was applied to test the association between neuroactive steroid levels and hemispheric total gray matter volume as well as region-specific cortical thickness. False discovery rate (FDR) correction was used to control for Type 1 error from multiple testing.

Results

Neuroactive steroid levels of allopregnanolone and pregnenolone were positively correlated with gray matter thickness in multiple regions of cingulate, parietal, and occipital association cortices (r = 0.20–0.47; p < 0.05; FDR-corrected).

Conclusion

Positive associations between serum neuroactive steroid levels and gray matter cortical thickness are found in multiple brain regions. If these results are confirmed, neuroactive steroid levels and cortical thickness may help in monitoring the clinical response in future intervention studies of neuroregenerative therapies.

Cyclic changes and actions of progesterone and allopregnanolone on cognition and hippocampal basal (stratum oriens) dendritic spines of female rats

Ovarian steroids modulate the neuronal structure and function during the estrous cycle, contrasting peak effects during the proestrus cycle and low effects during the metestrus cycle. An ovariectomy (OVX) decreases gonadal hormones and tests the effects of substitutive therapies. We studied female rats with a normal estrous cycle and we also studied the effects of systemic progesterone (P4, 4.0 mg/kg) or its reduced metabolite allopregnanolone (ALLO, 4.0 mg/kg, both for 10 days) in females who had had an OVX 16.5 weeks prior to the study (long-term OVX) with the novel object recognition test (NORT) for associative memory. The dendritic shape and spine density in Golgi-impregnated basal dendrites (stratum oriens) of hippocampal pyramidal neurons was also studied. Proestrus females had a better performance than metestrus or OVX females in short-term memory (tested 1 h after the acquisition phase). Proestrus and metestrus females showed better results than OVX females for long-term memory (24 h after the initial phase). Both P4 and ALLO recovered the cognitive impairment induced by long-term OVX. Also, proestrus females had a higher density of dendritic spines than metestrus females, OVX reduced the density of spines when compared to intact females, whereas both P4 and ALLO treatments increased the dendritic spine density, number of dendritic branches along the dendritic length, and branching order compared to vehicle. These data add the dendrites of the stratum oriens as an additional site for naturally occurring changes in spine density during the estrous cycle and evidence the actions of progestins in both behavioral recovery and the structural dendritic rearrangement of hippocampal pyramidal neurons in long-term OVX female rats.

From Cannabinoids and Neurosteroids to Statins and the Ketogenic Diet: New Therapeutic Avenues in Rett Syndrome?

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused mainly by mutations in the MECP2 gene, being one of the leading causes of mental disability in females. Mutations in the MECP2 gene are responsible for 95% of the diagnosed RTT cases and the mechanisms through which these mutations relate with symptomatology are still elusive. Children with RTT present a period of apparent normal development followed by a rapid regression in speech and behavior and a progressive deterioration of motor abilities. Epilepsy is one of the most common symptoms in RTT, occurring in 60 to 80% of RTT cases, being associated with worsening of other symptoms. At this point, no cure for RTT is available and there is a pressing need for the discovery of new drug candidates to treat its severe symptoms. However, despite being a rare disease, in the last decade research in RTT has grown exponentially. New and exciting evidence has been gathered and the etiopathogenesis of this complex, severe and untreatable disease is slowly being unfolded. Advances in gene editing techniques have prompted cure-oriented research in RTT. Nonetheless, at this point, finding a cure is a distant reality, highlighting the importance of further investigating the basic pathological mechanisms of this disease. In this review, we focus our attention in some of the newest evidence on RTT clinical and preclinical research, evaluating their impact in RTT symptomatology control, and pinpointing possible directions for future research.

Influence of Nanomolar Deltamethrin on the Hallmarks of Primary Cultured Cortical Neuronal Network and the Role of Ryanodine Receptors

BACKGROUND

The pyrethroid deltamethrin (DM) is broadly used for insect control. Although DM hyperexcites neuronal networks by delaying inactivation of axonal voltage-dependent [Formula: see text] channels, this mechanism is unlikely to mediate neurotoxicity at lower exposure levels during critical perinatal periods in mammals.

OBJECTIVES

We aimed to identify mechanisms by which acute and subchronic DM altered axonal and dendritic growth, patterns of synchronous [Formula: see text] oscillations (SCOs), and electrical spike activity (ESA) functions critical to neuronal network formation.

METHODS

Measurements of SCOs using [Formula: see text] imaging, ESA using microelectrode array (MEA) technology, and dendritic complexity using Sholl analysis were performed in primary murine cortical neurons from wild-type (WT) and/or ryanodine receptor 1 ([Formula: see text]) mice between 5 and 14 d in vitro (DIV). [Formula: see text] binding analysis and a single-channel voltage clamp were utilized to measure engagement of RyRs as a direct target of DM.

RESULTS

Neuronal networks responded to DM ([Formula: see text]) as early as 5 DIV, reducing SCO amplitude and depressing ESA and burst frequencies by 60-70%. DM ([Formula: see text]) enhanced axonal growth in a nonmonotonic manner. [Formula: see text] enhanced dendritic complexity. DM stabilized channel open states of RyR1, RyR2, and cortical preparations expressing all three isoforms. DM ([Formula: see text]) altered gating kinetics of RyR1 channels, increasing mean open time, decreasing mean closed time, and thereby enhancing overall open probability. SCO patterns from cortical networks expressing [Formula: see text] were more responsive to DM than WT. [Formula: see text] neurons showed inherently longer axonal lengths than WT neurons and maintained less length-promoting responses to nanomolar DM.

CONCLUSIONS

Our findings suggested that RyRs were sensitive molecular targets of DM with functional consequences likely relevant for mediating abnormal neuronal network connectivity in vitro. https://doi.org/10.1289/EHP4583.

Brexanolone, a neurosteroid antidepressant, vindicates the GABAergic deficit hypothesis of depression and may foster resilience

The GABAergic deficit hypothesis of depression states that a deficit of GABAergic transmission in defined neural circuits is causal for depression. Conversely, an enhancement of GABA transmission, including that triggered by selective serotonin reuptake inhibitors or ketamine, has antidepressant effects. Brexanolone, an intravenous formulation of the endogenous neurosteroid allopregnanolone, showed clinically significant antidepressant activity in postpartum depression. By allosterically enhancing GABA _A receptor function, the antidepressant activity of allopregnanolone is attributed to an increase in GABAergic inhibition. In addition, allopregnanolone may stabilize normal mood by decreasing the activity of stress-responsive dentate granule cells and thereby sustain resilience behavior. Therefore, allopregnanolone may augment and extend its antidepressant activity by fostering resilience. The recent structural resolution of the neurosteroid binding domain of GABA _A receptors will expedite the development of more selective ligands as a potential new class of central nervous system drugs.

Mitochondria- and Oxidative Stress-Targeting Substances in Cognitive Decline-Related Disorders: From Molecular Mechanisms to Clinical Evidence

Alzheimer's disease (AD) is the most common form of dementia affecting people mainly in their sixth decade of life and at a higher age. It is an extensively studied neurodegenerative disorder yet incurable to date. While its main postmortem brain hallmarks are the presence of amyloid-β plaques and hyperphosphorylated tau tangles, the onset of the disease seems to be largely correlated to mitochondrial dysfunction, an early event in the disease pathogenesis. AD is characterized by flawed energy metabolism in the brain and excessive oxidative stress, processes that involve less adenosine triphosphate (ATP) and more reactive oxygen species (ROS) production respectively. Mitochondria are at the center of both these processes as they are responsible for energy and ROS generation through mainly oxidative phosphorylation. Standardized Ginkgo biloba extract (GBE), resveratrol, and phytoestrogens as well as the neurosteroid allopregnanolone have shown not only some mitochondria-modulating properties but also significant antioxidant potential in in vitro and in vivo studies. According to our review of the literature, GBE, resveratrol, allopregnanolone, and phytoestrogens showed promising effects on mitochondria in a descending evidence order and, notably, this order pattern is in line with the existing clinical evidence level for each entity. In this review, the effects of these four entities are discussed with special focus on their mitochondria-modulating effects and their mitochondria-improving and antioxidant properties across the spectrum of cognitive decline-related disorders. Evidence from preclinical and clinical studies on their mechanisms of action are summarized and highlighted.

Allopregnanolone Treatment Improves Plasma Metabolomic Profile Associated with GABA Metabolism in Fragile X-Associated Tremor/Ataxia Syndrome: a Pilot Study

Currently, there is no effective treatment for the fragile X-associated tremor/ataxia syndrome (FXTAS), a late-onset neurodegenerative disorder. In this pilot study, we evaluated whether allopregnanolone, a natural neurosteroid that exerts beneficial effects in neurodegenerative diseases, nervous system injury, and peripheral neuropathies, could improve lymphocytic bioenergetics and plasma pharmacometabolomics in six males with FXTAS (68 ± 3 years old; FMR1 CGG repeats 94 ± 4; FXTAS stages ranging from 3 to 5) enrolled in a 12-week open-label intervention study conducted at the University of California Davis from December 2015 through July 2016. Plasma pharmacometabolomics and lymphocytic mitochondria function were assessed at baseline (on the day of the first infusion) and at follow-up (within 48 h from the last infusion). In parallel, quantitative measurements of tremor and ataxia and neuropsychological evaluations of mental state, executive function, learning, memory, and psychological symptoms were assessed at the same time points. Allopregnanolone treatment impacted significantly GABA metabolism, oxidative stress, and some of the mitochondria-related outcomes. Notably, the magnitude of the individual metabolic response, as well as the correlation with some of the behavioral tests, was overwhelmingly carrier-specific. Based on this pilot study, allopregnanolone treatment has the potential for improving cognitive and GABA metabolism in FXTAS aligned with the concept of precision medicine.

The impact of sensory and motor enrichment on the epigenetic control of steroidogenic-related genes in rat hippocampus

In the present study, we analyzed the effects of a short-term environmental enrichment on the mRNA expression and DNA methylation of steroidogenic enzymes in the hippocampus. Thus, young adult (80-day-old) and middle-aged (350-day-old) Wistar female rats were exposed to sensory (SE) or motor (ME) enrichment during 10 days and compared to animals housed under standard conditions. SE was provided by an assortment of objects that included plastic tubes and toys; for ME, rodent wheels were provided. In young adult animals, SE and ME increased the mRNA expression of cytochrome P450 17α-hydroxylase/c17,20-lyase, steroid 5α-reductase type 1 (5αR-1) and 3α-hydroxysteroid dehydrogenase and decreased the methylation levels of 5αR-1 gene. In middle-aged rats, ME and SE upregulated the gene expression of aldosterone synthase and decreased the methylation state of its promoter. These results propose that SE and ME differentially regulate the transcription of neurosteroidogenic enzymes through epigenetic mechanisms in young and aged rats.

Neurosteroid Actions in Memory and Neurologic/Neuropsychiatric Disorders

Memory dysfunction is a symptomatic feature of many neurologic and neuropsychiatric disorders; however, the basic underlying mechanisms of memory and altered states of circuitry function associated with disorders of memory remain a vast unexplored territory. The initial discovery of endogenous neurosteroids triggered a quest to elucidate their role as neuromodulators in normal and diseased brain function. In this review, based on the perspective of our own research, the advances leading to the discovery of positive and negative neurosteroid allosteric modulators of GABA type-A (GABA_A), NMDA, and non-NMDA type glutamate receptors are brought together in a historical and conceptual framework. We extend the analysis toward a state-of-the art view of how neurosteroid modulation of neural circuitry function may affect memory and memory deficits. By aggregating the results from multiple laboratories using both animal models for disease and human clinical research on neuropsychiatric and age-related neurodegenerative disorders, elements of a circuitry level view begins to emerge. Lastly, the effects of both endogenously active and exogenously administered neurosteroids on neural networks across the life span of women and men point to a possible underlying pharmacological connectome by which these neuromodulators might act to modulate memory across diverse altered states of mind.