In-vivo histamine H3 receptor antagonism activates cellular signaling suggestive of symptomatic and disease modifying efficacy in Alzheimer’s disease

Scutellarein derivatives with histamine H3 receptor antagonism and cholinesterase inhibitory potency as multi target-directed ligands for possible Alzheimer's disease therapy

A series of scutellarein 7-l-amino acid carbamate-4'-cycloalkylamine propyl ether conjugates were designed and synthesized for the first time as multifunctional agents for Alzheimer's disease (AD) therapy. The designed compounds exhibited more balanced and effective multi-target potency. Among them, compound 11l, l-Valine carbamate derivative of scutellarein cycloheptylamine ether, exhibited the most potent inhibition of electric eel AChE enzymes and human AChE enzymes, with an IC50 values of 7.04 μM and 9.73 μM, respectively. Moreover, 11l exhibited more potent H3R antagonistic activities than clobenpropit, with an IC50 value of 1.09 nM. Compound 11l not only displayed excellent inhibition of self- and Cu2+-induced Aβ1-42 aggregation (95.48 % and 88.63 % inhibition, respectively) but also induced the disassembly of self- and Cu2+-induced Aβ fibrils (80.16 % and 89.30 % disaggregation, respectively). Moreover, 11l significantly reduced tau protein hyperphosphorylation induced by Aβ25-35. It exhibited effective antioxidant activity and neuroprotective potency, and inhibited RSL3-induced PC12 cell ferroptosis. Assays of hCMEC/D3 and hPepT1-MDCK cell line permeability indicated that 11l would have optimal blood-brain barrier permeability and intestinal absorption characteristics. In addition, in vivo studies revealed that compound 11l significantly attenuated learning and memory impairment in an AD mouse model. Finally, a pharmacokinetic characterization of 11l indicated favorable druggability and pharmacokinetic properties. Taken together, our results suggest that 11l is a potential candidate for AD treatment and merits further investigation.

GSK3: A potential target and pending issues for treatment of Alzheimer's disease

Glycogen synthase kinase-3 (GSK3), consisting of GSK3α and GSK3β subtypes, is a complex protein kinase that regulates numerous substrates. Research has observed increased GSK3 expression in the brains of Alzheimer's disease (AD) patients and models. AD is a neurodegenerative disorder with diverse pathogenesis and notable cognitive impairments, characterized by Aβ aggregation and excessive tau phosphorylation. This article provides an overview of GSK3's structure and regulation, extensively analyzing its relationship with AD factors. GSK3 overactivation disrupts neural growth, development, and function. It directly promotes tau phosphorylation, regulates amyloid precursor protein (APP) cleavage, leading to Aβ formation, and directly or indirectly triggers neuroinflammation and oxidative damage. We also summarize preclinical research highlighting the inhibition of GSK3 activity as a primary therapeutic approach for AD. Finally, pending issues like the lack of highly specific and affinity-driven GSK3 inhibitors, are raised and expected to be addressed in future research. In conclusion, GSK3 represents a target in AD treatment, filled with hope, challenges, opportunities, and obstacles.

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.

Inflammatory signaling pathways in the treatment of Alzheimer's disease with inhibitors, natural products and metabolites (Review)

The intricate nature of Alzheimer's disease (AD) pathogenesis poses a persistent obstacle to drug development. In recent times, neuroinflammation has emerged as a crucial pathogenic mechanism of AD, and the targeting of inflammation has become a viable approach for the prevention and management of AD. The present study conducted a comprehensive review of the literature between October 2012 and October 2022, identifying a total of 96 references, encompassing 91 distinct pharmaceuticals that have been investigated for their potential impact on AD by inhibiting neuroinflammation. Research has shown that pharmaceuticals have the potential to ameliorate AD by reducing neuroinflammation mainly through regulating inflammatory signaling pathways such as NF‑κB, MAPK, NLRP3, PPARs, STAT3, CREB, PI3K/Akt, Nrf2 and their respective signaling pathways. Among them, tanshinone IIA has been extensively studied for its anti‑inflammatory effects, which have shown significant pharmacological properties and can be applied clinically. Thus, it may hold promise as an effective drug for the treatment of AD. The present review elucidated the inflammatory signaling pathways of pharmaceuticals that have been investigated for their therapeutic efficacy in AD and elucidates their underlying mechanisms. This underscores the auspicious potential of pharmaceuticals in ameliorating AD by impeding neuroinflammation.

The Potent and Selective Histamine H3 Receptor Antagonist E169 Counteracts Cognitive Deficits and Mitigates Disturbances in the PI3K/AKT/GSK-3β Signaling Pathway in MK801-Induced Amnesia in Mice

The role of histamine H3 receptors (H3Rs) in memory and the prospective of H3R antagonists in pharmacological control of neurodegenerative disorders, e.g., Alzheimer's disease (AD), is well-accepted. Therefore, the procognitive effects of acute systemic administration of H3R antagonist E169 (2.5-10 mg/kg, i.p.) on MK801-induced amnesia in C57BL/6J mice using the novel object recognition test (NORT) were evaluated. E169 (5 mg) provided a significant memory-improving effect on MK801-induced short- and long-term memory impairments in NORT. The E169 (5 mg)-provided effects were comparable to those observed with the reference phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and were abrogated with the H3R agonist (R)-α-methylhistamine (RAMH). Additionally, our results demonstrate that E169 ameliorated MK801-induced memory deficits by antagonism of H3Rs and by modulation of the level of disturbance in the expression of PI3K, Akt, and GSK-3β proteins, signifying that E169 mitigated the Akt-mTOR signaling pathway in the hippocampus of tested mice. Moreover, the results observed revealed that E169 (2.5-10 mg/kg, i.p.) did not alter anxiety levels and locomotor activity of animals in open field tests, demonstrating that performances improved following acute systemic administration with E169 in NORT are unrelated to changes in emotional response or in spontaneous locomotor activity. In summary, these obtained results suggest the potential of H3R antagonists such as E169, with good in silico physicochemical properties and stable retained key interactions in docking studies at H3R, in simultaneously modulating disturbed brain neurotransmitters and the imbalanced Akt-mTOR signaling pathway related to neurodegenerative disorders, e.g., AD.

Current Drug Targets in Alzheimer's Associated Memory Impairment: A Comprehensive Review

Alzheimer's disease (AD) is the most prevalent form of dementia among geriatrics. It is a progressive, degenerative neurologic disorder that causes memory and cognition loss. The accumulation of amyloid fibrils and neurofibrillary tangles in the brain of AD patients is a distinguishing feature of the disease. Therefore, most of the current therapeutic goals are targeting inhibition of beta-amyloid synthesis and aggregation as well as tau phosphorylation and aggregation. There is also a loss of the cholinergic neurons in the basal forebrain, and first-generation therapeutic agents were primarily focused on compensating for this loss of neurons. However, cholinesterase inhibitors can only alleviate cognitive symptoms of AD and cannot reduce the progression of the disease. Understanding the molecular and cellular changes associated with AD pathology has advanced significantly in recent decades. The etiology of AD is complex, with a substantial portion of sporadic AD emerging from unknown reasons and a lesser proportion of early-onset familial AD (FAD) caused by a mutation in several genes, such as the amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2) genes. Hence, efforts are being made to discover novel strategies for these targets for AD therapy. A new generation of AChE and BChE inhibitors is currently being explored and evaluated in human clinical trials for AD symptomatic treatment. Other approaches for slowing the progression of AD include serotonergic modulation, H3 receptor antagonism, phosphodiesterase, COX-2, and MAO-B inhibition. The present review provides an insight into the possible therapeutic strategies and their molecular mechanisms, enlightening the perception of classical and future treatment approaches.

Chemical Probes for Histamine Receptor Subtypes

Ligands with different properties and different selectivity are highly needed for in vitro and in vivo studies on the (patho)physiological influence of the chemical mediator histamine and its receptor subtypes. A selection of well-described ligands for the different receptor subtypes and different studies is shown with a particular focus on affinity and selectivity. In addition, compounds with radioactive or fluorescence elements will be presented with their beneficial use for other species or different investigations.

Thioperamide attenuates neuroinflammation and cognitive impairments in Alzheimer's disease via inhibiting gliosis

Alzheimer's disease (AD) is an age-related neurodegenerative disease, which characterized by deposition of amyloid-β (Aβ) plaques, neurofibrillary tangles, neuronal loss, and accompanied by neuroinflammation. Neuroinflammatory processes are well acknowledged to contribute to the progression of AD pathology. Histamine H3 receptor (H3R) is a presynaptic autoreceptor regulating histamine release via negative feedback way. Recently, studies show that H3R are highly expressed not only in neurons but also in microglia and astrocytes. H3R antagonist has been reported to have anti-inflammatory efficacy. However, whether inhibition of H3R is responsible for the anti-neuroinflammation in glial cells and neuroprotection on APPswe, PSEN1dE9 (APP/PS1 Tg) mice remain unclear. In this study, we found that inhibition of H3R by thioperamide reduced the gliosis and induced a phenotypical switch from A1 to A2 in astrocytes, and ultimately attenuated neuroinflammation in APP/PS1 Tg mice. Additionally, thioperamide rescued the decrease of cyclic AMP response element-binding protein (CREB) phosphorylation and suppressed the phosphorylated P65 nuclear factor kappa B (p-P65 NF-κB) in APP/PS1 Tg mice. H89, an inhibitor of CREB signaling, abolished these effects of thioperamide to suppress gliosis and proinflammatory cytokine release. Lastly, thioperamide alleviated the deposition of amyloid-β (Aβ) and cognitive dysfunction in APP/PS1 mice, which were both reversed by administration of H89. Taken together, these results suggested the H3R antagonist thioperamide improved cognitive impairment in APP/PS1 Tg mice via modulation of the CREB-mediated gliosis and inflammation inhibiting, which contributed to Aβ clearance. This study uncovered a novel mechanism involving inflammatory regulating behind the therapeutic effect of thioperamide in AD.

Activation of CREB-mediated autophagy by thioperamide ameliorates β-amyloid pathology and cognition in Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease, and the imbalance between production and clearance of β-amyloid (Aβ) is involved in its pathogenesis. Autophagy is an intracellular degradation pathway whereby leads to removal of aggregated proteins, up-regulation of which may be a plausible therapeutic strategy for the treatment of AD. Histamine H3 receptor (H3R) is a presynaptic autoreceptor regulating histamine release via negative feedback way. Our previous study showed that thioperamide, as an antagonist of H3R, enhances autophagy and protects against ischemic injury. However, the effect of thioperamide on autophagic function and Aβ pathology in AD remains unknown. In this study, we found that thioperamide promoted cognitive function, ameliorated neuronal loss, and Aβ pathology in APP/PS1 transgenic (Tg) mice. Interestingly, thioperamide up-regulated autophagic level and lysosomal function both in APP/PS1 Tg mice and in primary neurons under Aβ-induced injury. The neuroprotection by thioperamide against AD was reversed by 3-MA, inhibitor of autophagy, and siRNA of Atg7, key autophagic-related gene. Furthermore, inhibition of activity of CREB, H3R downstream signaling, by H89 reversed the effect of thioperamide on promoted cell viability, activated autophagic flux, and increased autophagic-lysosomal proteins expression, including Atg7, TFEB, and LAMP1, suggesting a CREB-dependent autophagic activation by thioperamide in AD. Taken together, these results suggested that H3R antagonist thioperamide improved cognitive impairment in APP/PS1 Tg mice via modulation of the CREB-mediated autophagy and lysosomal pathway, which contributed to Aβ clearance. This study uncovered a novel mechanism involving autophagic regulating behind the therapeutic effect of thioperamide in AD.

Influence of ketotifen and conventional antiepileptic drugs on the exploratory and spontaneous locomotor activity in mice

Drug interactions are major problems in polytherapy, especially in epilepsy, and inappropriate drug selection may result in increased frequency of seizures.

In this study, the influence of histamine type 1 (H1) receptor antagonist ketotifen and four chosen antiepileptic drugs (AEDs) on mice activity was examined. We evaluated three parameters of locomotor activity in mice: horizontal total activity with total distance and vertical activity, as well as animal spontaneous activity. Experiments were divided into two 15-minutes studies. During the first 15 minutes, we examined exploratory activity in mice; in the second period, spontaneous activity was tested. In the experiment, Ketotifen or vehicle were administered once or for 7 days daily, whereas AEDs were given only once before test performance.

Our results show that ketotifen given alone once or for 7 days significantly increased exploratory locomotor activity in mice without affecting their spontaneous activity. However, in combination with AEDs, ketotifen given once or for 7 days differently affected spontaneous and locomotor activity in mice. Our study indicates that the combination of ketotifen with AEDs needs special attention in pharmacotherapy of epilepsy.

Histamine beyond its effects on allergy: Potential therapeutic benefits for the treatment of Amyotrophic Lateral Sclerosis (ALS)

ALS currently remains a challenge despite many efforts in performing successful clinical trials and formulating therapeutic solutions. By learning from current failures and striving for success, scientists and clinicians are checking every possibility to search for missing hints and efficacious treatments. Because the disease is very complex and heterogeneous and, moreover, targeting not only motor neurons but also several different cell types including muscle, glial, and immune cells, the right answer to ALS is conceivably a multidrug strategy or the use of broad-spectrum molecules. The aim of the present work is to gather evidence about novel perspectives on ALS pathogenesis and to present recent and innovative paradigms for therapy. In particular, we describe how an old molecule possessing immunomodulatory and neuroprotective functions beyond its recognized effects on allergy, histamine, might have a renewed and far-reaching momentum in ALS.

Brain Histamine Modulates the Antidepressant-Like Effect of the 3-Iodothyroacetic Acid (TA1)

3-iodothyroacetic acid (TA1), an end metabolite of thyroid hormone, has been shown to produce behavioral effects in mice that are dependent on brain histamine. We now aim to verify whether pharmacologically administered TA1 has brain bioavailability and is able to induce histamine-dependent antidepressant-like behaviors. TA1 brain, liver and plasma levels were measured by LC/MS-MS in male CD1 mice, sacrificed 15 min after receiving a high TA1 dose (330 μgkg^-1). The hypothalamic mTOR/AKT/GSK-β cascade activation was evaluated in mice treated with 0.4, 1.32, 4 μgkg^-1 TA1 by Western-blot. Mast cells were visualized by immuno-histochemistry in brain slices obtained from mice treated with 4 μgkg^-1 TA1. Histamine release triggered by TA1 (20-1000 nM) was also evaluated in mouse peritoneal mast cells. After receiving TA1 (1.32, 4 or 11 μgkg^-1; i.p.) CD1 male mice were subjected to the forced swim (FST) and the tail suspension tests (TST). Spontaneous locomotor and exploratory activities, motor incoordination, and anxiolytic or anxiogenic effects, were evaluated. Parallel behavioral tests were also carried out in mice that, prior to receiving TA1, were pre-treated with pyrilamine (10 mgkg^-1; PYR) or zolantidine (5 mgkg^-1; ZOL), histamine type 1 and type 2 receptor antagonists, respectively, or with p-chloro-phenylalanine (100 mgkg^-1; PCPA), an inhibitor of serotonin synthesis. TA1 given i.p. to mice rapidly distributes in the brain, activates the hypothalamic mTOR/AKT and GSK-3β cascade and triggers mast cells degranulation. Furthermore, TA1 induces antidepressant effects and stimulates locomotion with a mechanism that appears to depend on the histaminergic system. TA1 antidepressant effect depends on brain histamine, thus highlighting a relationship between the immune system, brain inflammation and the thyroid.

7-Pyrrolidinethoxy-4'-Methoxyisoflavone Prevents Amyloid β-Induced Injury by Regulating Histamine H3 Receptor-Mediated cAMP/CREB and AKT/GSK3β Pathways

In studies on the treatment of Alzheimer’s disease (AD), in which cognition is enhanced even modestly or selectively, it has been considered that the histamine H3 receptor (H3R) may be a potential target. In this study, we aimed at evaluating the ability of 7-pyrrolidinethoxy-4′-methoxyisoflavone (indicated as LC1405), a novel potential H3R antagonist identified from our H3R antagonist screening system, to ameliorate amyloid β (Aβ)-induced cognitive deficits, and to explore the underlying mechanisms that are related to H3R-modulated signaling. Our results demonstrated that LC1405 effectively reduced the progression of Aβ-associated disorders, such as improved learning and memory capabilities, preserved tissues from suffering neurodegeneration and ultrastructural abnormalities, and ameliorated cholinergic dysfunction in an APP/PS1 double transgenic mouse model of AD. In an in vitro model, LC1405 protected neuronal cells against copper-induced Aβ toxicity, as demonstrated by the improvement in cell viability and decrease in neuronal apoptotic ratio. In addition, treatment with LC1405 resulted in the up-regulation of acetylcholine (ACh) or histamine release and provided neuroprotection through cellular signaling cascades involving H3R-mediated cAMP/CREB and AKT/GSK3β pathways. Furthermore, the beneficial effects of LC1405 on Aβ-mediated toxicity and H3R-mediated cAMP/CREB and AKT/GSK3β axes were reversed after pharmacological activation of H3R. In conclusion, our results demonstrated that LC1405 blocked Aβ-induced toxicity through H3R-modulated signaling transduction both in vitro and in vivo. The results also suggested that LC1405 might have translational potential as a complementary therapy to control disease progression in AD patients who developed cognitive deficits with H3R-related ACh neurotransmission abnormality.

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.

Monoamines and their Derivatives on GPCRs: Potential Therapy for Alzheimer's Disease

Albeit cholinergic depletion remains the key event in Alzheimer's Disease (AD), recent information describes stronger links between monoamines (trace amines, catecholamines, histamine, serotonin, and melatonin) and AD than those known in the past century. Therefore, new drug design strategies focus efforts to translate the scope on these topics and to offer new drugs which can be applied as therapeutic tools in AD. In the present work, we reviewed the state-of-art regarding genetic, neuropathology and neurochemistry of AD involving monoamine systems. Then, we compiled the effects of monoamines found in the brain of mammals as well as the reported effects of their derivatives and some structure-activity relationships. Recent derivatives have triggered exciting effects and pharmacokinetic properties in both murine models and humans. In some cases, the mechanism of action is clear, essentially through the interaction on G-protein-coupled receptors as revised in this manuscript. Additional mechanisms are inhibition of enzymes for their biotransformation, regulation of free-radicals in the central nervous system and others for the effects on Tau phosphorylation or amyloid-beta accumulation. All these data make the monoamines and their derivatives attractive potential elements for AD therapy.

Brain histamine modulates recognition memory: possible implications in major cognitive disorders

Several behavioural tests have been developed to study and measure emotionally charged or emotionally neutral memories and how these may be affected by pharmacological, dietary or environmental manipulations. In this review, we describe the experimental paradigms used in preclinical studies to unravel the brain circuits involved in the recognition and memorization of environmentally salient stimuli devoid of strong emotional value. In particular, we focus on the modulatory role of the brain histaminergic system in the elaboration of recognition memory that is based on the judgement of the prior occurrence of an event, and it is believed to be a critical component of human declarative memory. The review also addresses questions that may help improve the treatment of impaired declarative memory described in several affective and neuropsychiatric disorders such as ADHD, Alzheimer's disease and major neurocognitive disorder. LINKED ARTICLES: This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc.

Current progress, challenges and future prospects of diagnostic and therapeutic interventions in Alzheimer's disease

The diverse pathological mechanisms and their implications for the development of effective diagnostic and therapeutic interventions in Alzheimer's disease are presented with current progress, challenges and future prospects.

Hybrid approach to structure modeling of the histamine H3 receptor: Multi-level assessment as a tool for model verification

The crucial role of G-protein coupled receptors and the significant achievements associated with a better understanding of the spatial structure of known receptors in this family encouraged us to undertake a study on the histamine H3 receptor, whose crystal structure is still unresolved. The latest literature data and availability of different software enabled us to build homology models of higher accuracy than previously published ones. The new models are expected to be closer to crystal structures; and therefore, they are much more helpful in the design of potential ligands. In this article, we describe the generation of homology models with the use of diverse tools and a hybrid assessment. Our study incorporates a hybrid assessment connecting knowledge-based scoring algorithms with a two-step ligand-based docking procedure. Knowledge-based scoring employs probability theory for global energy minimum determination based on information about native amino acid conformation from a dataset of experimentally determined protein structures. For a two-step docking procedure two programs were applied: GOLD was used in the first step and Glide in the second. Hybrid approaches offer advantages by combining various theoretical methods in one modeling algorithm. The biggest advantage of hybrid methods is their intrinsic ability to self-update and self-refine when additional structural data are acquired. Moreover, the diversity of computational methods and structural data used in hybrid approaches for structure prediction limit inaccuracies resulting from theoretical approximations or fuzziness of experimental data. The results of docking to the new H3 receptor model allowed us to analyze ligand-receptor interactions for reference compounds.

Therapeutics of Neurotransmitters in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease, characterized by the loss of memory, multiple cognitive impairments and changes in the personality and behavior. Several decades of intense research have revealed that multiple cellular changes are involved in disease process, including synaptic damage, mitochondrial abnormalities and inflammatory responses, in addition to formation and accumulation of amyloid-β (Aβ) and phosphorylated tau. Although tremendous progress has been made in understanding the impact of neurotransmitters in the progression and pathogenesis of AD, we still do not have a drug molecule associated with neurotransmitter(s) that can delay disease process in elderly individuals and/or restore cognitive functions in AD patients. The purpose of our article is to assess the latest developments in neurotransmitters research using cell and mouse models of AD. We also updated the current status of clinical trials using neurotransmitters' agonists/antagonists in AD.

Isoform-Specific Biased Agonism of Histamine H3 Receptor Agonists

The human histamine H₃ receptor (hH₃R) is subject to extensive gene splicing that gives rise to a large number of functional and nonfunctional isoforms. Despite the general acceptance that G protein-coupled receptors can adopt different ligand-induced conformations that give rise to biased signaling, this has not been studied for the H₃R; further, it is unknown whether splice variants of the same receptor engender the same or differential biased signaling. Herein, we profiled the pharmacology of histamine receptor agonists at the two most abundant hH₃R splice variants (hH₃R₄₄₅ and hH₃R₃₆₅) across seven signaling endpoints. Both isoforms engender biased signaling, notably for 4-[3-(benzyloxy)propyl]-1H-imidazole (proxyfan) [e.g., strong bias toward phosphorylation of glycogen synthase kinase 3β (GSK3β) via the full-length receptor] and its congener 3-(1H-imidazol-4-yl)propyl-(4-iodophenyl)-methyl ether (iodoproxyfan), which are strongly consistent with the former's designation as a "protean" agonist. The 80 amino acid IL3 deleted isoform hH₃R₃₆₅ is more permissive in its signaling than hH₃R₄₄₅: 2-(1H-imidazol-5-yl)ethyl imidothiocarbamate (imetit), proxyfan, and iodoproxyfan were all markedly biased away from calcium signaling, and principal component analysis of the full data set revealed divergent profiles for all five agonists. However, most interesting was the identification of differential biased signaling between the two isoforms. Strikingly, hH₃R₃₆₅ was completely unable to stimulate GSK3β phosphorylation, an endpoint robustly activated by the full-length receptor. To the best of our knowledge, this is the first quantitative example of differential biased signaling via isoforms of the same G protein-coupled receptor that are simultaneously expressed in vivo and gives rise to the possibility of selective pharmacological targeting of individual receptor splice variants.

SAR110894, a potent histamine H3-receptor antagonist, displays disease-modifying activity in a transgenic mouse model of tauopathy

Introduction

Tau hyperphosphorylation and neurofibrillary tangles are histopathologic hallmarks of tauopathies. Histamine H3-receptor antagonists have been proposed to reduce tau hyperphosphorylation in preclinical models.

Methods

We evaluated the ability of SAR110894, a selective histamine H3-receptor antagonist, to inhibit tau pathology and prevent cognitive deficits in a tau transgenic mouse model (THY-Tau22).

Results

SAR110894 treatment for 6 months (but not 2 weeks) in THY-Tau22 mice decreased both tau hyperphosphorylation at pSer396-pSer404 (AD2 signal) in the hippocampus and the number of AT8 (pSer199/202-Thr205) positive cells in the cortex and decreased the formation of neurofibrillary tangles in the cortex, hippocampus, and amygdala. Macrophage inflammatory protein 1-alpha messenger RNA expression was decreased in the hippocampus. SAR110894 also prevented episodic memory deficits, and this effect was still detected after treatment washout.

Discussion

Long-term SAR110894 treatment could have potential disease modifying activity in neurodegenerative tauopathies.

The Histamine H3 Receptor: Structure, Pharmacology, and Function

Among the four G protein-coupled receptors (H₁-H₄) identified as mediators of the biologic effects of histamine, the H₃ receptor (H₃R) is distinguished for its almost exclusive expression in the nervous system and the large variety of isoforms generated by alternative splicing of the corresponding mRNA. Additionally, it exhibits dual functionality as autoreceptor and heteroreceptor, and this enables H₃Rs to modulate the histaminergic and other neurotransmitter systems. The cloning of the H₃R cDNA in 1999 by Lovenberg et al. allowed for detailed studies of its molecular aspects. In this work, we review the characteristics of the H₃R, namely, its structure, constitutive activity, isoforms, signal transduction pathways, regional differences in expression and localization, selective agonists, antagonists and inverse agonists, dimerization with other neurotransmitter receptors, and the main presynaptic and postsynaptic effects resulting from its activation. The H₃R has attracted interest as a potential drug target for the treatment of several important neurologic and psychiatric disorders, such as Alzheimer and Parkinson diseases, Gilles de la Tourette syndrome, and addiction.

Old and new acetylcholinesterase inhibitors for Alzheimer's disease

INTRODUCTION

To date, pharmacological treatment of Alzheimer's disease (AD) includes Acetylcholinesterase Inhibitors (AChEIs) for mild-to-moderate AD, and memantine for moderate-to-severe AD. AChEIs reversibly inhibit acetylcholinesterase (AChE), thus increasing the availability of acetylcholine in cholinergic synapses, enhancing cholinergic transmission. These drugs provide symptomatic short-term benefits, without clearly counteracting the progression of the disease.

AREAS COVERED

On the wake of successful clinical trials which lead to the marketing of AChEIs donepezil, rivastigmine and galantamine, many compounds with AChEI properties have been developed and tested mainly in Phase I-II clinical trials in the last twenty years. Here, we review clinical trials initiated and interrupted, and those ongoing so far.

EXPERT OPINION

Despite many clinical trials with novel AChEIs have been carried out after the registration of those currently used to treat mild to moderate AD, none so far has been successful in a Phase III trial and marketed. Alzheimer's disease is a complex multifactorial disorder, therefore therapy should likely address not only the cholinergic system but also additional neurotransmitters. Moreover, such treatments should be started in very mild phases of the disease, and preventive strategies addressed in elderly people.

Heteroreceptor Complexes Formed by Dopamine D1, Histamine H3, and N-Methyl-D-Aspartate Glutamate Receptors as Targets to Prevent Neuronal Death in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder causing progressive memory loss and cognitive dysfunction. Anti-AD strategies targeting cell receptors consider them as isolated units. However, many cell surface receptors cooperate and physically contact each other forming complexes having different biochemical properties than individual receptors. We here report the discovery of dopamine D₁, histamine H₃, and N-methyl-D-aspartate (NMDA) glutamate receptor heteromers in heterologous systems and in rodent brain cortex. Heteromers were detected by co-immunoprecipitation and in situ proximity ligation assays (PLA) in the rat cortex where H₃ receptor agonists, via negative cross-talk, and H₃ receptor antagonists, via cross-antagonism, decreased D₁ receptor agonist signaling determined by ERK1/2 or Akt phosphorylation, and counteracted D₁ receptor-mediated excitotoxic cell death. Both D₁ and H₃ receptor antagonists also counteracted NMDA toxicity suggesting a complex interaction between NMDA receptors and D₁-H₃ receptor heteromer function. Likely due to heteromerization, H₃ receptors act as allosteric regulator for D₁ and NMDA receptors. By bioluminescence resonance energy transfer (BRET), we demonstrated that D₁ or H₃ receptors form heteromers with NR1A/NR2B NMDA receptor subunits. D₁-H₃-NMDA receptor complexes were confirmed by BRET combined with fluorescence complementation. The endogenous expression of complexes in mouse cortex was determined by PLA and similar expression was observed in wild-type and APP/PS1 mice. Consistent with allosteric receptor-receptor interactions within the complex, H₃ receptor antagonists reduced NMDA or D₁ receptor-mediated excitotoxic cell death in cortical organotypic cultures. Moreover, H₃ receptor antagonists reverted the toxicity induced by ß_1-42-amyloid peptide. Thus, histamine H₃ receptors in D₁-H₃-NMDA heteroreceptor complexes arise as promising targets to prevent neurodegeneration.

Donepezil, an acetylcholine esterase inhibitor, and ABT-239, a histamine H3 receptor antagonist/inverse agonist, require the integrity of brain histamine system to exert biochemical and procognitive effects in the mouse

Histaminergic H3 receptors (H3R) antagonists enhance cognition in preclinical models and modulate neurotransmission, in particular acetylcholine (ACh) release in the cortex and hippocampus, two brain areas involved in memory processing. The cognitive deficits seen in aging and Alzheimer's disease have been associated with brain cholinergic deficits. Donepezil is one of the acetylcholinesterase (AChE) inhibitor approved for use across the full spectrum of these cognitive disorders. We addressed the question if H3R antagonists and donepezil require an intact histamine neuronal system to exert their procognitive effects. The effect of the H3R antagonist ABT-239 and donepezil were evaluated in the object recognition test (ORT), and on the level of glycogen synthase kinase 3 beta (GSK-3β) phosphorylation in normal and histamine-depleted mice. Systemic administration of ABT-239 or donepezil ameliorated the cognitive performance in the ORT. However, these compounds were ineffective in either genetically (histidine decarboxylase knock-out, HDC-KO) or pharmacologically, by means of intracerebroventricular (i.c.v.) injections of the HDC irreversible inhibitor a-fluoromethylhistidine (a-FMHis), histamine-deficient mice. Western blot analysis revealed that ABT-239 or donepezil systemic treatments increased GSK-3β phosphorylation in cortical and hippocampal homogenates of normal, but not of histamine-depleted mice. Furthermore, administration of the PI3K inhibitor LY294002 that blocks GSK-3β phosphorylation, prevented the procognitive effects of both drugs in normal mice. Our results indicate that both donepezil and ABT-239 require the integrity of the brain histaminergic system to exert their procognitive effects and strongly suggest that impairments of PI3K/AKT/GSK-3β intracellular pathway activation is responsible for the inefficacy of both drugs in histamine-deficient animals.

International Union of Basic and Clinical Pharmacology. XCVIII. Histamine Receptors

Histamine is a developmentally highly conserved autacoid found in most vertebrate tissues. Its physiological functions are mediated by four 7-transmembrane G protein-coupled receptors (H1R, H2R, H3R, H4R) that are all targets of pharmacological intervention. The receptors display molecular heterogeneity and constitutive activity. H1R antagonists are long known antiallergic and sedating drugs, whereas the H2R was identified in the 1970s and led to the development of H2R-antagonists that revolutionized stomach ulcer treatment. The crystal structure of ligand-bound H1R has rendered it possible to design new ligands with novel properties. The H3R is an autoreceptor and heteroreceptor providing negative feedback on histaminergic and inhibition on other neurons. A block of these actions promotes waking. The H4R occurs on immuncompetent cells and the development of anti-inflammatory drugs is anticipated.

Chlorophenoxy aminoalkyl derivatives as histamine H(3)R ligands and antiseizure agents

A series of twenty new chlorophenoxyalkylamine derivatives (9-28) was synthesized and evaluated on their binding properties at the human histamine H3 receptor (hH3R). The spacer alkyl chain contained five to seven carbon atoms. The highest affinities have shown the 4-chloro substituted derivatives 10 and 25 (Ki=133 and 128 nM, respectively) classified as antagonists in cAMP accumulation assay (EC50=72 and 75 nM, respectively). Synthesized compounds were also evaluated for anticonvulsant activity in Antiepileptic Screening Program (ASP) at National Institute of Neurological Disorders and Stroke (USA). Two compounds (4-chloro substituted derivatives: 20 and 26) were the most promising and showed in the MES seizure model in rats (after ip administration) ED50 values of 14 mg/kg and 13.18 mg/kg, respectively. Protective indexes (PI=TD50/ED50) were 3.2 for 20 and 3.8 for 26. Moreover, molecular modeling and docking studies were undertaken to explain affinity at hH3R of target compounds, and the experimentally and in silico estimation of properties like lipophilicity and metabolism was performed. Antiproliferative effects have been also investigated in vitro for selected compounds (10 and 25). These compounds neither possessed significant antiproliferative and antitumor activity, nor modulated CYP3A4 activity up to concentration of 10 μM.

Cherry-picked ligands at histamine receptor subtypes

Histamine, a biogenic amine, is considered as a principle mediator of multiple physiological effects through binding to its H1, H2, H3, and H4 receptors (H1-H4Rs). Currently, the HRs have gained attention as important targets for the treatment of several diseases and disorders ranging from allergy to Alzheimer's disease and immune deficiency. Accordingly, medicinal chemistry studies exploring histamine-like molecules and their physicochemical properties by binding and interacting with the four HRs has led to the development of a diversity of agonists and antagonists that display selectivity for each HR subtype. An overview on H1-R4Rs and developed ligands representing some key steps in development is provided here combined with a short description of structure-activity relationships for each class. Main chemical diversities, pharmacophores, and pharmacological profiles of most innovative H1-H4R agonists and antagonists are highlighted. Therefore, this overview should support the rational choice for the optimal ligand selection based on affinity, selectivity and efficacy data in biochemical and pharmacological studies. This article is part of the Special Issue entitled 'Histamine Receptors'.

Emerging drug targets for Aβ and tau in Alzheimer's disease: a systematic review

AIMS

Currently, treatment for Alzheimer's disease (AD) focuses on the cholinergic hypothesis and provides limited symptomatic effects. Research currently focuses on other factors that are thought to contribute to AD development such as tau proteins and Aβ deposits, and how modification of the associated pathology affects outcomes in patients. This systematic review summarizes and appraises the evidence for the emerging drugs affecting Aβ and tau pathology in AD.

METHODS

A comprehensive, systematic online database search was conducted using the databases ScienceDirect and PubMed to include original research articles. A systematic review was conducted following a minimum set of standards, as outlined by The PRISMA Group . Specific inclusion and exclusion criteria were followed and studies fitting the criteria were selected. No human trials were included in this review. In vitro and in vivo AD models were used to assess efficacy to ensure studied agents were emerging targets without large bodies of evidence.

RESULTS

The majority of studies showed statistically significant improvement (P < 0.05) of Aβ and/or tau pathology, or cognitive effects. Many studies conducted in AD animal models have shown a reduction in Aβ peptide burden and a reduction in tau phosphorylation post-intervention. This has the potential to reduce plaque formation and neuronal degeneration.

CONCLUSIONS

There are many emerging targets showing promising results in the effort to modify the pathological effects associated with AD. Many of the trials also provided evidence of the clinical effects of such drugs reducing pathological outcomes, which was often demonstrated as an improvement of cognition.

The human histaminergic system in neuropsychiatric disorders

Histaminergic neurons are exclusively located in the hypothalamic tuberomamillary nucleus, from where they project to many brain areas. The histaminergic system is involved in basic physiological functions, such as the sleep-wake cycle, energy and endocrine homeostasis, sensory and motor functions, cognition, and attention, which are all severely affected in neuropsychiatric disorders. Here, we present recent postmortem findings on the alterations in this system in neuropsychiatric disorders, including Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), depression, and narcolepsy. In addition, we highlight the need to validate animal models for these diseases and also for Tourette's syndrome (TS) in relation to alterations in the histaminergic system. Moreover, we discuss the potential for, and concerns over, the use of novel histamine 3 receptor (H3R) antagonists/inverse agonists as treatment for such disorders.

Synthesis and characterization of new bivalent agents as melatonin- and histamine H3-ligands

Melatonin is an endogenous molecule involved in many pathophysiological processes. In addition to the control of circadian rhythms, its antioxidant and neuroprotective properties have been widely described. Thus far, different bivalent compounds composed by a melatonin molecule linked to another neuroprotective agent were synthesized and tested for their ability to block neurodegenerative processes in vitro and in vivo. To identify a novel class of potential neuroprotective compounds, we prepared a series of bivalent ligands, in which a prototypic melatonergic ligand is connected to an imidazole-based H₃ receptor antagonist through a flexible linker. Four imidazolyl-alkyloxy-anilinoethylamide derivatives, characterized by linkers of different length, were synthesized and their binding affinity for human MT₁, MT₂ and H₃ receptor subtypes was evaluated. Among the tested compounds, 14c and 14d, bearing a pentyl and a hexyl linker, respectively, were able to bind to all receptor subtypes at micromolar concentrations and represent the first bivalent melatonergic/histaminergic ligands reported so far. These preliminary results, based on binding affinity evaluation, pave the way for the future development of new dual-acting compounds targeting both melatonin and histamine receptors, which could represent promising therapeutic agents for the treatment of neurodegenerative pathologies.

Histamine H3 receptor antagonism by ABT-239 attenuates kainic acid induced excitotoxicity in mice

The multifaceted pathogenesis of temporal lobe epilepsy (TLE) offers a number of adjunctive therapeutic prospects. One such therapeutic strategy could be targeting H3 receptor (H3R) by selective H3R antagonists which are perceived to have antiepileptic and neuroprotective potential. Kainic acid (KA) induced seizure, a reliable model of TLE, triggers epileptogenic events resulting from initial neuronal death and ensuing recurring seizures. The present study aimed to determine whether pre-treatment with ABT-239, a novel H3R antagonist, and its combinations with sodium valproate (SVP) and TDZD-8 (glycogen synthase kinase-3β (GSK3β) inhibitor) can prevent the excitotoxic events in mice exposed to KA (10 mg/kg i.p.). ABT-239 (1 and 3 mg/kg i.p.) significantly attenuated KA-mediated behavioural and excitotoxic anomalies and restored altered expression of Bax, cleaved caspase-3, phospho-Akt (Ser473) and cAMP response element binding protein (CREB). Surprisingly, restoration of Bcl2 and phospho-GSK3β (Ser9) by ABT-239 did not reach the level of statistical significance. Co-administration of ABT-239 (1 and 3 mg/kg) with a sub-effective dose of SVP (150 mg/kg i.p.) yielded improved efficacy than when given alone. Similarly, low and high dose combinations of ABT-239 (1 and 3 mg/kg) with TDZD-8 (5 and 10 mg/kg i.p.) produced greater neuroprotection than any other treatment group. Our findings suggests a neuroprotective potential of ABT-239 and its combinations with SVP and TDZD-8 against KA-induced neurotoxicity, possibly mediated through in part each by modulating Akt/GSK3β and CREB pathways. The use of H3R antagonists as adjuvant in the treatment of human TLE might find potential utility, and can be pursued further.

Dual histamine H3R/serotonin 5-HT4R ligands with antiamnesic properties: pharmacophore-based virtual screening and polypharmacology

In recent years, preclinical and clinical studies have generated considerable interest in the development of histamine H3 receptor (H3R) antagonists as novel treatment for degenerative disorders associated with impaired cholinergic function. To identify novel scaffolds for H3R antagonism, a common feature-based pharmacophore model was developed and used to screen the 17,194 compounds of the CERMN (Centre d'Etudes et de Recherche sur le Médicament de Normandie) chemical library. Out of 268 virtual hits which have been gathered in 34 clusters, we were particularly interested in tricyclic derivatives also exhibiting a potent 5HT4R affinity. Benzo[h][1,6]naphthyridine derivatives showed the highest H3R affinity, and compound 17 (H3R Ki = 41.6 nM; 5-HT4R Ki = 208 nM) completely reversed the amnesiant effect of scopolamine at 3 mg/kg in a spatial working memory experiment. For the first time we demonstrated the feasibility to combine H3R and 5-HT4R activities in a single molecule, raising the exciting possibility that dual H3R antagonist/5HT4R agonist have potential for the treatment of neurodegenerative diseases such as Alzheimer's disease.

Procognitive properties of drugs with single and multitargeting H3 receptor antagonist activities

The histamine H3 receptor (H3 R) is an important modulator of numerous central control mechanisms. Novel lead optimizations for H3 R antagonists/inverse agonists involved studies of structure-activity relationships, cross-affinities, and pharmacokinetic properties of promising ligands. Blockade of inhibitory histamine H3 autoreceptors reinforces histaminergic transmission, while antagonism of H3 heteroreceptors accelerates the corticolimbic liberation of acetylcholine, norepinephrine, glutamate, dopamine, serotonin and gamma-aminobutyric acid (GABA). The H3 R positioned at numerous neurotransmission crossroads indicates therapeutic applications of small-molecule H3 R modulators in a number of psychiatric and neurodegenerative diseases with various clinical candidates available. Dual target drugs displaying H3 R antagonism/inverse agonism with inhibition of acetylcholine esterase (AChE), histamine N-methyltransferase (HMT), or serotonin transporter (SERT) are novel class of procognitive agents. Main chemical diversities, pharmacophores, and pharmacological profiles of procognitive agents acting as H3 R antagonists/inverse agonists and dual H3 R antagonists/inverse agonists with inhibiting activity on AChE, HMT, or SERT are highlighted here.

Xanthoceraside attenuates tau hyperphosphorylation and cognitive deficits in intracerebroventricular-streptozotocin injected rats

RATIONALE

Xanthoceraside, a novel triterpenoid saponin extracted from the fruit husks of Xanthoceras sorbifolia Bunge, reverses cognitive deficits in intracerebroventricular injection of Aβ25-35 or Aβ1-42 mice. However, whether xanthoceraside has a positive effect on hyperphosphorylated tau protein remains unclear.

OBJECTIVES

We investigated the effects of xanthoceraside on behavioural impairments induced by intracerebroventricular injection of streptozotocin (STZ) in rats and its potential mechanisms.

MATERIALS AND METHODS

The rats were administered with xanthoceraside (0.06, 0.12 or 0.24 mg/kg) or vehicle once daily after STZ intracerebroventricular injections. The Y-maze test and novel object recognition test were performed 21 and 22 days after the second STZ injection, respectively. The levels of hyperphosphorylated tau, phosphatidylinositol-3-kinase (PI3K)/serine/threonine protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3β), protein phosphatase 1 (PP-1) and protein phosphatase 2A (PP-2A) were also tested by Western blot.

RESULTS

Xanthoceraside treatment significantly attenuated learning and memory impairments and reduced the level of STZ-induced hyperphosphorylated tau protein. Xanthoceraside also enhanced PP-2A and PP-1 expressions, increased PI3K (p85) and Akt (Ser473) phosphorylation and decreased GSK-3β (tyr216) phosphorylation.

CONCLUSIONS

Xanthoceraside has protective effect against learning and memory impairments and inhibits tau hyperphosphorylation in the hippocampus, possibly through the inhibition of the PI3K/Akt-dependent GSK-3β signalling pathway and an enhancement of phosphatases activity.

Safety, tolerability and pharmacokinetics of the histamine H3 receptor antagonist, ABT-288, in healthy young adults and elderly volunteers

AIM

The objective of this work was to characterize the safety, tolerability and pharmacokinetics of ABT-288, a highly selective histamine H3 receptor antagonist, in healthy young adults and elderly subjects following single and multiple dosing in a phase 1 setting.

METHODS

Single doses (0.1, 0.3, 1, 3, 10, 20 and 40 mg ABT-288) and multiple doses (0.5, 1.5, 3 and 6 mg ABT-288 once-daily for 14 days) were evaluated in young adults and multiple doses (0.5, 1.5, 3 and 5 mg ABT-288 once-daily for 12 days) were evaluated in elderly subjects using randomized, double-blind, placebo-controlled, dose-escalating study designs. The effect of food on ABT-288 pharmacokinetics (5 mg single dose) was evaluated using an open label, randomized, crossover design.

RESULTS

ABT-288 safety, tolerability and pharmacokinetics were comparable in young and elderly subjects. Single doses up to 40 mg and multiple doses up to 3 mg once-daily were generally safe and well tolerated. The most frequently reported adverse events were hot flush, headache, abnormal dreams, insomnia, nausea and dizziness. ABT-288 exposure (AUC) was dose-proportional over the evaluated dose ranges. The mean elimination half-life ranged from 40 to 61 h across dose groups. Steady state was achieved by day 10 of once-daily dosing with 3.4- to 4.2-fold accumulation. Food did not have a clinically meaningful effect on ABT-288 exposure.

CONCLUSIONS

Based on the above results, 1 and 3 mg once-daily doses of ABT-288 were advanced to phase 2 evaluation in Alzheimer's patients.

The neglected role of histamine in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by beta-amyloid plaques accumulation and cognitive impairment. Both environmental factors and heritable predisposition have a role in AD. Histamine is a biogenic monoamine that plays a role in several physiological functions, including induction of inflammatory reactions, wound healing, and regeneration. The Histamine mediates its functions via its 4 G-protein-coupled Histamine H1 receptor (H1R) to histamine H1 receptor (H4R). The histaminergic system has a role in the treatment of brain disorders by the development of histamine receptor agonists, antagonists. The H1R and H4R are responsible for allergic inflammation. But recent studies show that histamine antagonists against H3R and regulation of H2R can be more efficient in AD therapy. In this review, we focus on the role of histamine and its receptors in the treatment of AD, and we hope that histamine could be an effective therapeutic factor in the treatment of AD.

Ascending monoaminergic systems alterations in Alzheimer's disease. translating basic science into clinical care

Extensive neuropathological studies have established a compelling link between abnormalities in structure and function of subcortical monoaminergic (MA-ergic) systems and the pathophysiology of Alzheimer's disease (AD). The main cell populations of these systems including the locus coeruleus, the raphe nuclei, and the tuberomamillary nucleus undergo significant degeneration in AD, thereby depriving the hippocampal and cortical neurons from their critical modulatory influence. These studies have been complemented by genome wide association studies linking polymorphisms in key genes involved in the MA-ergic systems and particular behavioral abnormalities in AD. Importantly, several recent studies have shown that improvement of the MA-ergic systems can both restore cognitive function and reduce AD-related pathology in animal models of neurodegeneration. This review aims to explore the link between abnormalities in the MA-ergic systems and AD symptomatology as well as the therapeutic strategies targeting these systems. Furthermore, we will examine possible mechanisms behind basic vulnerability of MA-ergic neurons in AD.

Drug pipeline in neurodegeneration based on transgenic mice models of Alzheimer's disease

Alzheimer's disease (AD) is one of the most important neurodegenerative disorders, bringing about huge medical and social burden in the elderly worldwide. Many aspects of its pathogenesis have remained unclear and no effective treatment exists for it. Within the past 20 years, various mice models harboring AD-related human mutations have been produced. These models imitate diverse AD-related pathologies and have been used for basic and therapeutic investigations in AD. In this regard, there are a wide variety of preclinical trials of potential therapeutic modalities using AD mice models which are of paramount importance for future clinical trials and applications. This review summarizes more than 140 substances and treatment modalities being used in transgenic AD mice models from 2001 to 2011. We also discuss advantages and disadvantages of each model to be used in therapeutic development for AD.

Histamine H3 receptor antagonists in relation to epilepsy and neurodegeneration: a systemic consideration of recent progress and perspectives

The central histaminergic actions are mediated by H(1) , H(2) , H(3) and H(4) receptors. The histamine H(3) receptor regulates the release of histamine and a number of other neurotransmitters and thereby plays a role in cognitive and homeostatic processes. Elevated histamine levels suppress seizure activities and appear to confer neuroprotection. The H(3) receptors have a number of enigmatic features like constitutive activity, interspecies variation, distinct ligand binding affinities and differential distribution of prototypic splice variants in the CNS. Furthermore, this Gi/Go-protein-coupled receptor modulates several intracellular signalling pathways whose involvement in epilepsy and neurotoxicity are yet to be ascertained and hence represent an attractive target in the search for new anti-epileptogenic drugs. So far, H(3) receptor antagonists/inverse agonists have garnered a great deal of interest in view of their promising therapeutic properties in various CNS disorders including epilepsy and related neurotoxicity. However, a number of experiments have yielded opposing effects. This article reviews recent works that have provided evidence for diverse mechanisms of antiepileptic and neuroprotective effects that were observed in various experimental models both in vitro and in vivo. The likely reasons for the apparent disparities arising from the literature are also discussed with the aim of establishing a more reliable basis for the future use of H(3) receptor antagonists, thus improving their utility in epilepsy and associated neurotoxicity.

Histamine H3 receptor antagonists/inverse agonists on cognitive and motor processes: relevance to Alzheimer's disease, ADHD, schizophrenia, and drug abuse

Histamine H3 receptor (H3R) antagonists/inverse agonists possess potential to treat diverse disease states of the central nervous system (CNS). Cognitive dysfunction and motor impairments are the hallmark of multifarious neurodegenerative and/or psychiatric disorders. This review presents the various neurobiological/neurochemical evidences available so far following H3R antagonists in the pathophysiology of Alzheimer's disease (AD), attention-deficit hyperactivity disorder (ADHD), schizophrenia, and drug abuse each of which is accompanied by deficits of some aspects of cognitive and/or motor functions. Whether the H3R inverse agonism modulates the neurochemical basis underlying the disease condition or affects only the cognitive/motor component of the disease process is discussed with the aim to provide a rationale for their use in diverse disease states that are interlinked and are accompanied by some common motor, cognitive and attentional deficits.