S 38093, a histamine H3 antagonist/inverse agonist, promotes hippocampal neurogenesis and improves context discrimination task in aged mice

The major biogenic amine metabolites in mood disorders

Mood disorders, including major depressive disorder and bipolar disorder, have a profound impact on more than 300 million people worldwide. It has been demonstrated mood disorders were closely associated with deviations in biogenic amine metabolites, which are involved in numerous critical physiological processes. The peripheral and central alteration of biogenic amine metabolites in patients may be one of the potential pathogeneses of mood disorders. This review provides a concise overview of the latest research on biogenic amine metabolites in mood disorders, such as histamine, kynurenine, and creatine. Further studies need larger sample sizes and multi-center collaboration. Investigating the changes of biogenic amine metabolites in mood disorders can provide biological foundation for diagnosis, offer guidance for more potent treatments, and aid in elucidating the biological mechanisms underlying mood disorders.

Targeting Microglia in Neuroinflammation: H3 Receptor Antagonists as a Novel Therapeutic Approach for Alzheimer's Disease, Parkinson's Disease, and Autism Spectrum Disorder

Histamine performs dual roles as an immune regulator and a neurotransmitter in the mammalian brain. The histaminergic system plays a vital role in the regulation of wakefulness, cognition, neuroinflammation, and neurogenesis that are substantially disrupted in various neurodegenerative and neurodevelopmental disorders. Histamine H3 receptor (H3R) antagonists and inverse agonists potentiate the endogenous release of brain histamine and have been shown to enhance cognitive abilities in animal models of several brain disorders. Microglial activation and subsequent neuroinflammation are implicated in impacting embryonic and adult neurogenesis, contributing to the development of Alzheimer's disease (AD), Parkinson's disease (PD), and autism spectrum disorder (ASD). Acknowledging the importance of microglia in both neuroinflammation and neurodevelopment, as well as their regulation by histamine, offers an intriguing therapeutic target for these disorders. The inhibition of brain H3Rs has been found to facilitate a shift from a proinflammatory M1 state to an anti-inflammatory M2 state, leading to a reduction in the activity of microglial cells. Also, pharmacological studies have demonstrated that H3R antagonists showed positive effects by reducing the proinflammatory biomarkers, suggesting their potential role in simultaneously modulating crucial brain neurotransmissions and signaling cascades such as the PI3K/AKT/GSK-3β pathway. In this review, we highlight the potential therapeutic role of the H3R antagonists in addressing the pathology and cognitive decline in brain disorders, e.g., AD, PD, and ASD, with an inflammatory component.

Histaminergic neurotransmission in aging and Alzheimer's disease: A review of therapeutic opportunities and gaps

Introduction

Alzheimer's disease (AD) is a progressive neurodegenerative disorderfeaturing a brain accumulation of extracellular β-amyloidplaques (Aβ) and intracellular neurofibrillary tautangles (NFTs). Although cognitive decline is a disease-defining symptom of AD, sleep dysfunction, a common symptom often preceding cognitive decline, hasrecently gained more attention as a core AD symptom. Polysomnography and othersleep measures show sleep fragmentation with shortening of N3 sleep togetherwith excessive daytime sleepiness (EDS) and sundowning as the main findings in AD patients. The latter reflects dysfunction of the wake-promoting neurons (WPNs), including histaminergic neurons (HAN) located in thetuberomammillary nucleus (TMN) of the posterior hypothalamus, which projectunmyelinated axons to various parts of the brain. Histamine's role in cognitionand arousal is broadly recognized. Selective targeting of histaminergic subtype-3 and 4 receptors show therapeutic potential in rodent models of AD andaging.

Method

Based on PubMed, Scopus, and google scholar databases search, this review summarizes the current knowledge on the histaminergic system in AD and aging, its therapeutic potential in AD, and highlight areas where moreresearch is needed.

Results

Animal studies have demonstrated that pharmacological manipulation of histaminergic receptors or histamine supplementation improves cognition in AD models. However, measurements of HA or HA metabolite levels in the human brainand CSF present contradictory reports due to either lack of power or controls for known confounders.

Discussion

Systemic studies including broad age, sex, neuropathological diagnosis, and disease stage are warranted to fill the gap in our current understanding of the histaminergic neurotransmitter/neuromodulator system in humans, especially age-related changes, and therapeuticpotential of histamine in AD-related dysfunction.

Revisiting Preclinical Observations of Several Histamine H3 Receptor Antagonists/Inverse Agonists in Cognitive Impairment, Anxiety, Depression, and Sleep-Wake Cycle Disorder

A relationship appears to exist between dysfunction of brain histamine (HA) and various neuropsychiatric brain disorders. The possible involvement of brain HA in neuropathology has gained attention recently, and its role in many (patho)physiological brain functions including memory, cognition, and sleep-wake cycle paved the way for further research on the etiology of several brain disorders. Histamine H3 receptor (H3R) evidenced in the brains of rodents and humans remains of special interest, given its unique position as a pre- and postsynaptic receptor, controlling the synthesis and release of HA as well as different other neurotransmitters in different brain regions, respectively. Despite several disappointing outcomes for several H3R antagonists/inverse agonists in clinical studies addressing their effectiveness in Alzheimer's disease (AD), Parkinson's disease (PD), and schizophrenia (SCH), numerous H3R antagonists/inverse agonists showed great potentials in modulating memory and cognition, mood, and sleep-wake cycle, thus suggesting its potential role in neurocognitive and neurodegenerative diseases such as AD, PD, SCH, narcolepsy, and major depression in preclinical rodent models. In this review, we present preclinical applications of selected H3R antagonists/inverse agonists and their pharmacological effects on cognitive impairment, anxiety, depression, and sleep-wake cycle disorders. Collectively, the current review highlights the behavioral impact of developments of H3R antagonists/inverse agonists, aiming to further encourage researchers in the preclinical drug development field to profile the potential therapeutic role of novel antagonists/inverse agonists targeting histamine H3Rs.

Betahistine Attenuates Seizures, Neurodegeneration, Apoptosis, and Gliosis in the Cerebral Cortex and Hippocampus in a Mouse Model of Epilepsy: A Histological, Immunohistochemical, and Biochemical Study

Epilepsy is a prevalent and chronic neurological disorder marked by recurring, uncontrollable seizures of the brain. Chronic or repeated seizures produce memory problems and induce damage to different brain regions. Histamine has been reported to have neuroprotective effects. Betahistine is a histamine analogue. The current research investigated the effects of convulsions on the cerebral cortex and hippocampus of adult male albino mice and assessed the possible protective effect of betahistine. Four groups of 40 adult male mice were organized: control, betahistine (10 mg/kg/day), pentylenetetrazole (PTZ) (40 mg/kg/ on alternate days), and Betahistine-PTZ group received betahistine 1 h before PTZ. PTZ induced a substantial rise in glutamate level and a considerable decrease in histamine level. Structural changes in the cerebral cortex and cornu ammonis (CA1) of the hippocampus were detected in the pattern of neuron degeneration. Some neurons were shrunken with dark nuclei, and others had faintly stained ones. Focal accumulation of neuroglial cells and ballooned nerve cells of the cerebral cortex were also detected. Cleaved caspase-3, glial fibrillary acidic protein, and ionized calcium-binding adaptor molecule 1 showed substantial increases, while synaptophysin expression was significantly reduced. Interestingly, these changes were less prominent in mice pretreated with betahistine. In conclusion, betahistine had shown neuroprotective properties against brain damage induced by convulsions.

Tilapia Skin Peptides Ameliorate Cyclophosphamide-Induced Anxiety- and Depression-Like Behavior via Improving Oxidative Stress, Neuroinflammation, Neuron Apoptosis, and Neurogenesis in Mice

Anxiety- and depression-like behavior following chemotherapy treatment occurs in cancer patients with high probability and no specific therapeutics are available for treatment and prevention of this complication. Here, tilapia skin peptides (TSP), a novel enzymatically hydrolyzed bioactive peptide mixture, obtained from tilapia (Oreochromis mossambicus) scraps, were studied on cyclophosphamide (CP)-induced anxiety- and depression-like behavior in mice. Mice were received intraperitoneal injection of CP for 2 weeks, while TSP was administered for 4 weeks. After the end of the animal experiment, behavioral, biochemical, and molecular tests were carried out. The mice decreased preference for sugar water, increased immobility time in the forced swimming and tail suspension test, and decreased travel distance in the open field test in the Model group, compared with the Control group. Abnormal changes in behavioral tests were significantly improved after the TSP treatment. Additionally, abnormalities on superoxide dismutase, malondialdehyde, glutathione peroxidase were rescued by administration of 1000 mg/kg/d TSP in mice than that of the Model group. TSP has normalized the expression of Iba-1 and the levels of TNF-α and IL-1β in the hippocampus of mice, which indicated that TSP could observably ameliorate neuroinflammatory response in the hippocampus of mice. TSP ameliorated the apoptosis of hippocampal neurons of CA1 and CA3 regions in the TSP group vs. the Model group. The number of doublecortin positive cells was drastically increased by administering 1000 mg/kg/d TSP in mice vs. the Model group. Furthermore, TSP reversed the Nrf2/HO-1 signaling pathway, BDNF/TrkB/CREB signaling pathway, and reduced the Bcl-2/Bax/caspase-3 apoptosis pathway. In conclusion, TSP could restore CP-induced anxiety- and depression-like behavior via improving oxidative stress, neuroinflammation, neuron apoptosis, and neurogenesis in mice hippocampus.

A Potential Strategy for Treatment of Neurodegenerative Disorders by Regulation of Adult Hippocampal Neurogenesis in Human Brain

Abstract:

Adult hippocampal neurogenesis is a multistage mechanism that continues throughout the lifespan of human and non-human mammals. These adult-born neurons in the central nervous system (CNS) play a significant role in various hippocampus-dependent processes, including learning, mood regulation, pattern recognition, etc. Reduction of adult hippocampal neurogenesis, caused by multiple factors such as neurological disorders and aging, would impair neuronal proliferation and differentiation and result in memory loss. Accumulating studies have indicated that functional neuron impairment could be restored by promoting adult hippocampal neurogenesis. In this review, we summarized the small molecules that could efficiently promote the process of adult neurogenesis, particularly the agents that have the capacity of crossing the blood-brain barrier (BBB), and showed in vivo efficacy in mammalian brains. This may pave the way for the rational design of drugs to treat humnan neurodegenerative disorders in the future.

All roads lead to Rome - a review of the potential mechanisms by which exerkines exhibit neuroprotective effects in Alzheimer's disease

Age-related neurodegenerative disorders such as Alzheimer’s disease (AD) have become a critical public health issue due to the significantly extended human lifespan, leading to considerable economic and social burdens. Traditional therapies for AD such as medicine and surgery remain ineffective, impractical, and expensive. Many studies have shown that a variety of bioactive substances released by physical exercise (called “exerkines”) help to maintain and improve the normal functions of the brain in terms of cognition, emotion, and psychomotor coordination. Increasing evidence suggests that exerkines may exert beneficial effects in AD as well. This review summarizes the neuroprotective effects of exerkines in AD, focusing on the underlying molecular mechanism and the dynamic expression of exerkines after physical exercise. The findings described in this review will help direct research into novel targets for the treatment of AD and develop customized exercise therapy for individuals of different ages, genders, and health conditions.

Histamine in the Crosstalk Between Innate Immune Cells and Neurons: Relevance for Brain Homeostasis and Disease

Histamine is a biogenic amine playing a central role in allergy and peripheral inflammatory reactions and acts as a neurotransmitter and neuromodulator in the brain. In the adult, histamine is produced mainly by mast cells and hypothalamic neurons, which project their axons throughout the brain. Thus, histamine exerts a range of functions, including wakefulness control, learning and memory, neurogenesis, and regulation of glial activity. Histamine is also known to modulate innate immune responses induced by brain-resident microglia cells and peripheral circulating monocytes, and monocyte-derived cells (macrophages and dendritic cells). In physiological conditions, histamine per se causes mainly a pro-inflammatory phenotype while counteracting lipopolysaccharide-induced inflammation both in microglia, monocytes, and monocyte-derived cells. In turn, the activation of the innate immune system can profoundly affect neuronal survival and function, which plays a critical role in the onset and development of brain disorders. Therefore, the dual role of histamine/antihistamines in microglia and monocytes/macrophages is relevant for identifying novel putative therapeutic strategies for brain diseases. This review focuses on the effects of histamine in innate immune responses and the impact on neuronal survival, function, and differentiation/maturation, both in physiological and acute (ischemic stroke) and chronic neurodegenerative conditions (Parkinson's disease).

Chronic Corticosterone Elevation Suppresses Adult Hippocampal Neurogenesis by Hyperphosphorylating Huntingtin

Chronic exposure to stress is a major risk factor for neuropsychiatric disease, and elevated plasma corticosterone (CORT) correlates with reduced levels of both brain-derived neurotrophic factor (BDNF) and hippocampal neurogenesis. Precisely how these phenomena are linked, however, remains unclear. Using a cortico-hippocampal network-on-a-chip, we find that the glucocorticoid receptor agonist dexamethasone (DXM) stimulates the cyclin-dependent kinase 5 (CDK5) to phosphorylate huntingtin (HTT) at serines 1181 and 1201 (S1181/1201), which retards BDNF vesicular transport in cortical axons. Parallel studies in mice show that CORT induces phosphorylation of these same residues, reduces BDNF levels, and suppresses neurogenesis. The adverse effects of CORT are reduced in mice bearing an unphosphorylatable mutant HTT (Hdh^{S1181A/S1201A}). The protective effect of unphosphorylatable HTT, however, disappears if neurogenesis is blocked. The CDK5-HTT pathway, which regulates BDNF transport in the cortico-hippocampal network, thus provides a missing link between elevated CORT levels and suppressed neurogenesis.

[The adult brain produces new neurons to restore balance after vestibular loss]

Following partial or total loss of peripheral vestibular inputs, a phenomenon called central vestibular compensation takes place in the hours and days following the injury. This neuroplasticity process involves a mosaic of profound rearrangements within the brain stem vestibular nuclei. Among them, the setting of a new neuronal network is maybe the most original and unexpected, as it involves an adult reactive neurogenesis in a brain area not reported as neurogenic so far. Both the survival and functionality of this newly generated neuronal network will depend on its integration to pre-existing networks in the deafferented structure. Far from being aberrant, this new structural organization allows the use of inputs from other sensory modalities (vision and proprioception) to promote the restoration of the posture and equilibrium. We choose here to detail this model, which does not belong to the traditional niches of adult neurogenesis, but it is the best example so far of the reparative role of the adult neurogenesis. Not only it represents an original neuroplasticity mechanism, interesting for basic neuroscience, but it also opens new medical perspectives for the development of therapeutic approaches to alleviate vestibular disorders.

Histamine H3 Receptor Antagonist Enhances Neurogenesis and Improves Chronic Cerebral Hypoperfusion-Induced Cognitive Impairments

Chronic cerebral hypoperfusion (CCH) is a neurodegenerative disease, which induces cognitive impairments in the central nervous system (CNS). Histamine H3 receptor (H3R) is an autoreceptor involved in the modulation of neurogenesis and synaptic plasticity in the CNS. However, the role of H3R in CCH-induced injury and the related mechanisms remain to be clarified. Here, we found that thioperamide (THIO), a H3R antagonist, promotes the proliferation of NE-4C stem cells under either normal or oxygen-glucose deprivation (OGD) condition in vitro. Thioperamide promotes the phosphorylation of cAMP-response element binding (CREB), and thereby upregulates the expression and release of brain-derived neurotrophic factor (BDNF). However, H89, an inhibitor of protein kinase A (PKA)/CREB, reverses the effects of thioperamide on either BDNF expression and release or cell proliferation in NE-4C stem cells. Moreover, thioperamide has protective effects on OGD-induced impairment of cell viability and neuronal morphology in primary neurons in vitro. Furthermore, thioperamide enhanced neurogenesis in the dentate gyrus (DG) and subventricular zone (SVZ) regions in vivo, and ameliorated CCH-induced cognitive impairments. Taken together, these findings showed that thioperamide protects primary neurons against OGD-induced injury and promotes the proliferation of neural stem cells in DG and SVZ regions through CREB/BDNF pathways, thereby improving cognitive deficit.

Histamine modulates hippocampal inflammation and neurogenesis in adult mice

Evidence points to a dual role of histamine in microglia-mediated neuroinflammation, a key pathological feature of several neurodegenerative pathologies. Moreover, histamine has been suggested as a modulator of adult neurogenesis. Herein, we evaluated the effect of histamine in hippocampal neuroinflammation and neurogenesis under physiological and inflammatory contexts. For that purpose, mice were intraperitoneally challenged with lipopolysaccharide (LPS) followed by an intrahippocampal injection of histamine. We showed that histamine per se triggered glial reactivity and induced mild long-term impairments in neurogenesis, reducing immature neurons dendritic volume and complexity. Nevertheless, in mice exposed to LPS (2 mg/Kg), histamine was able to counteract LPS-induced glial activation and release of pro-inflammatory molecules as well as neurogenesis impairment. Moreover, histamine prevented LPS-induced loss of immature neurons complexity as well as LPS-induced loss of both CREB and PSD-95 proteins (essential for proper neuronal activity). Altogether, our results highlight histamine as a potential therapeutic agent to treat neurological conditions associated with hippocampal neuroinflammation and neurodegeneration.

Histamine H3 receptor antagonists/inverse agonists: Where do they go?

Since the discovery of the histamine H₃ receptor in 1983, tremendous advances in the pharmacological aspects of H₃ receptor antagonists/inverse agonists have been accomplished in preclinical studies. At present, there are several drug candidates that reached clinical trial studies for various indications. However, entrance of these candidates to the pharmaceutical market is not free from challenges, and a variety of difficulties is engaged with their developmental process. In this review, the potential role of H₃ receptors in the pathophysiology of various central nervous system, metabolic and allergic diseases is discussed. Thereafter, the current status for H₃ receptor antagonists/inverse agonists in ongoing clinical trial studies is reviewed and obstacles in developing these agents are emphasized.

Drug-receptor kinetics and sigma-1 receptor affinity differentiate clinically evaluated histamine H3 receptor antagonists

The histamine H3 receptor is a G protein-coupled receptor (GPCR) drug target that is highly expressed in the CNS, where it acts as both an auto- and hetero-receptor to regulate neurotransmission. As such, it has been considered as a relevant target in disorders as varied as Alzheimer's disease, schizophrenia, neuropathic pain and attention deficit hyperactivity disorder. A range of competitive antagonists/inverse agonists have progressed into clinical development, with pitolisant approved for the treatment of narcolepsy. Given the breadth of compounds developed and potential therapeutic indications, we assessed the comparative pharmacology of six investigational histamine H3 agents, including pitolisant, using native tissue and recombinant cells. Whilst all of the compounds tested displayed robust histamine H3 receptor inverse agonism and did not differentiate between the main H3 receptor splice variants, they displayed a wide range of affinities and kinetic properties, and included rapidly dissociating (pitolisant, S 38093-2, ABT-239) and slowly dissociating (GSK189254, JNJ-5207852, PF-3654746) agents. S 38093-2 had the lowest histamine H3 receptor affinity (pKB values 5.7-6.2), seemingly at odds with previously reported, potent in vivo activity in models of cognition. We show here that at pro-cognitive and anti-hyperalgesic/anti-allodynic doses, S 38093-2 preferentially occupies the mouse sigma-1 receptor in vivo, only engaging the histamine H3 receptor at doses associated with wakefulness promotion and neurotransmitter (histamine, ACh) release. Furthermore, pitolisant, ABT-239 and PF-3654746 also displayed appreciable sigma-1 receptor affinity, suggesting that this property differentiates clinically evaluated histamine H3 receptor antagonists and may play a role in their efficacy.

Vortioxetine Improves Context Discrimination in Mice Through a Neurogenesis Independent Mechanism

Major Depressive Disorders (MDD) patients may exhibit cognitive deficits and it is currently unclear to which degree treatment with antidepressants may affect cognitive function. Preclinical and clinical observations showed that vortioxetine (VORT, an antidepressant with multimodal activity), presents beneficial effects on aspects of cognitive function. In addition, VORT treatment increases adult hippocampal neurogenesis (AHN) in rodents, a candidate mechanism for antidepressant activity. Pattern separation (PS) is the ability to discriminate between two similar contexts/events generating two distinct and non-overlapping representations. Impaired PS may lead to overgeneralization and anxiety disorders. If PS impairments were described in depressed patients, the consequences of antidepressant treatment on context discrimination (CD) are still in its infancy. We hypothesized that VORT-increased AHN may improve CD. Thus, in an attempt to elucidate the molecular mechanism underpinning VORT treatment effects on CD, a rodent model of PS, the role of AHN and stress-induced c-Fos activation was evaluated in the adult mouse hippocampus. Chronic treatment with VORT (1.8 g/kg of food weight; corresponding to a daily dose of 10 mg/kg, 3 weeks) improved CD in mice. Interestingly, chronic treatment with VORT reversed ablation of AHN-induced delay in CD and freezing behavior. VORT treatment decreased stress-induced c-Fos activation in the dorsal but not ventral dentate gyrus. VORT treatment did not affect c-Fos activity in the hippocampus of mice with ablated neurogenesis. This study highlights a role of VORT in CD, which may be independent from AHN and hippocampal c-Fos activation. Further studies elucidating the mechanisms underlying VORT’s effects in CD could contribute to future strategies for alleviating the disease burden for individuals suffering from depression and/or anxiety disorders.

Progress in the development of histamine H3 receptor antagonists/inverse agonists: a patent review (2013-2017)

INTRODUCTION

Since years, ligands blocking histamine H₃ receptor (H₃R) activity (antagonists/inverse agonists) are interesting targets in the search for new cures for CNS disorders. Intensive works done by academic and pharmaceutical company researchers have led to many potent and selective H₃R antagonists/inverse agonists. Some of them have reached to clinical trials.

AREAS COVERED

Patent applications from January 2013 to September 2017 and the most important topics connected with H₃R field are analysed. Espacenet, Patentscope, Pubmed, GoogleScholar or Cochrane Library online databases were principially used to collect all the materials.

EXPERT OPINION

The research interest in histamine H₃R field is still high although the number of patent applications has decreased during the past 4 years (around 20 publications). Complexity of histamine H₃R biology e.g. many isoforms, constitutive activity, heteromerization with other receptors (dopamine D₂, D₁, adenosine A_2A) and pharmacology make not easy realization and evaluation of therapeutic potential of anti-H₃R ligands. First results from clinical trials have verified potential utility of histamine H₃R antagonist/inverse agonists in some diseases. However, more studies are necessary for better understanding of an involvement of the histaminergic system in CNS-related disorders and helping more ligands approach to clinical trials and the market. Lists of abbreviations: hAChEI - human acetylcholinesterase inhibitor; hBuChEI - human butyrylcholinesterase inhibitor; hMAO - human monoamine oxidase; MAO - monoamine oxidase.

Mast cells increase adult neural precursor proliferation and differentiation but this potential is not realized in vivo under physiological conditions

There is growing evidence that both peripheral and resident immune cells play an important part in regulating adult neural stem cell proliferation and neurogenesis, although the contribution of the various immune cell types is still unclear. Mast cells, a population of immune cells known for their role in the allergic response, have been implicated in the regulation of adult hippocampal neurogenesis. Mast cell-deficient c-kit^W-sh/W-sh mice have previously been shown to exhibit significantly decreased adult hippocampal neurogenesis and associated learning and memory deficits. However, given that numerous other cell types also express high levels of c-kit, the utility of these mice as a reliable model of mast cell-specific depletion is questionable. We show here, using a different model of mast cell deficiency (Mcpt5CreR26^DTA/DTA), that precursor proliferation and adult neurogenesis are not influenced by mast cells in vivo. Interestingly, when applied at supraphysiological doses, mast cells can activate latent hippocampal precursor cells and increase subventricular zone precursor proliferation in vitro, an effect that can be blocked with specific histamine-receptor antagonists. Thus, we conclude that while both mast cells and their major chemical mediator histamine have the potential to affect neural precursor proliferation and neurogenesis, this is unlikely to occur under physiological conditions.