Construction and application of H1R ligand screening materials based on SMA stabilization and his-tag covalent immobilization of membrane proteins.

The histamine H1 receptor (H1R) plays a pivotal role in allergy initiation and undergoes the necessity of devising a high-throughput screening approach centered on H1R to screen novel ligands effectively. This study suggests a method employing styrene maleic acid (SMA) extraction and His-tag covalent bonding to immobilize H1R membrane proteins, minimizing the interference of nonspecific proteins interference while preserving native protein structure and maximizing target exposure. This approach was utilized to develop a novel material for high-throughput ligand screening and implemented in cell membrane chromatography (CMC). An H1R-His-SMALPs/CMC model was established and its chromatographic performance (selectivity, specificity and lifespan) validated, demonstrating a significant enhancement in lifespan compared to previous CMC models. Subsequently, this model facilitated high-throughput screening of H1R ligands in the compound library and preliminary activity verification of potential H1R antagonists. Identification of a novel H1R antagonist laid the foundation for further development in this area.

Blocking H1R signal aggravates atherosclerosis by promoting inflammation and foam cell formation.

Atherosclerosis (AS) is a chronic inflammatory arterial disease, in which abnormal lipid metabolism and foam cell formation play key roles. Histamine is a vital biogenic amine catalyzed by histidine decarboxylase (HDC) from L-histidine. Histamine H1 receptor (H1R) antagonist is a commonly encountered anti-allergic agent in the clinic. However, the role and mechanism of H1R in atherosclerosis have not been fully elucidated. Here, we explored the effect of H1R on atherosclerosis using Apolipoprotein E-knockout (ApoE-/-) mice with astemizole (AST, a long-acting H1R antagonist) treatment. The results showed that AST increased atherosclerotic plaque area and hepatic lipid accumulation in mice. The result of microarray study identified a significant change of endothelial lipase (LIPG) in CD11b+ myeloid cells derived from HDC-knockout (HDC-/-) mice compared to WT mice. Blocking H1R promoted the formation of foam cells from bone marrow-derived macrophages (BMDMs) of mice by up-regulating p38 mitogen-activated protein kinase (p38 MAPK) and LIPG signaling pathway. Taken together, these findings demonstrate that blocking H1R signal aggravates atherosclerosis by promoting abnormal lipid metabolism and macrophage-derived foam cell formation via p38 MAPK-LIPG signaling pathway. KEY MESSAGES: Blocking H1R signal with AST aggravated atherosclerosis and increased hepatic lipid accumulation in high-fat diet (HFD)-fed ApoE-/- mice. Blocking H1R signal promoted macrophage-derived foam cell formation via p38 MAPK-LIPG signaling pathway.

Blockade of histamine receptor H1 augments immune checkpoint therapy by enhancing MHC-I expression in pancreatic cancer cells.

BACKGROUND: Although immune checkpoint blockade (ICB) therapy has proven to be extremely effective at managing certain cancers, its efficacy in treating pancreatic ductal adenocarcinoma (PDAC) has been limited. Therefore, enhancing the effect of ICB could improve the prognosis of PDAC. In this study, we focused on the histamine receptor H1 (HRH1) and investigated its impact on ICB therapy for PDAC. METHODS: We assessed HRH1 expression in pancreatic cancer cell (PCC) specimens from PDAC patients through public data analysis and immunohistochemical (IHC) staining. The impact of HRH1 in PCCs was evaluated using HRH1 antagonists and small hairpin RNA (shRNA). Techniques including Western blot, flow cytometry, quantitative reverse transcription polymerase chain reaction (RT-PCR), and microarray analyses were performed to identify the relationships between HRH1 and major histocompatibility complex class I (MHC-I) expression in cancer cells. We combined HRH1 antagonism or knockdown with anti-programmed death receptor 1 (αPD-1) therapy in orthotopic models, employing IHC, immunofluorescence, and hematoxylin and eosin staining for assessment. RESULTS: HRH1 expression in cancer cells was negatively correlated with HLA-ABC expression, CD8+ T cells, and cytotoxic CD8+ T cells. Our findings indicate that HRH1 blockade upregulates MHC-I expression in PCCs via cholesterol biosynthesis signaling. In the orthotopic model, the combined inhibition of HRH1 and αPD-1 blockade enhanced cytotoxic CD8+ T cell penetration and efficacy, overcoming resistance to ICB therapy. CONCLUSIONS: HRH1 plays an immunosuppressive role in cancer cells. Consequently, HRH1 intervention may be a promising method to amplify the responsiveness of PDAC to immunotherapy.

Development of simultaneous determination of dopamine 2, histamine 1, and muscarinic acetylcholine receptor occupancies by antipsychotics using liquid chromatography with tandem mass spectrometry.

Receptor occupancy is an indicator of antipsychotic efficacy and safety. It is desirable to simultaneously determine the occupancy of multiple brain receptors as an indicator of the efficacy and central side effects of antipsychotics because many of these drugs have binding affinities for various receptors, such as dopamine 2 (D2), histamine 1 (H1), and muscarinic acetylcholine (mACh) receptors. The purpose of this study was to develop a method for the simultaneous measurement of multiple receptor occupancies in the brain by the simultaneous quantification of unlabeled tracer levels using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Rats were pre-administered with a vehicle, displacer, or olanzapine, and mixed solutions of raclopride, doxepin, and 3-quinuclidinyl benzilate (3-QNB) were administered (3, 10, and 30 µg/kg). The brain tissue and plasma tracer concentrations were quantified 45 min later using LC-MS/MS, and the binding potential was calculated. The highest binding potential was observed at 3 µg/kg raclopride, 10 µg/kg doxepin, and 30 µg/kg 3-QNB. Tracer-specific binding at these optimal tracer doses in the cerebral cortex was markedly reduced by pre-administration of displacers. D2, H1, and mACh receptor occupancy by olanzapine increased in a dose-dependent manner, reaching 70-95%, 19-43%, and 12-45%, respectively, at an olanzapine dose range of 3-10 mg/kg. These results suggest that simultaneous determination of in vivo D2, H1, and mACh receptor occupancy is possible using LC-MS/MS.

Comprehensive mapping of histamine H1 receptor mRNA in the mouse brain.

Histamine H1 receptor (H1R) in the central nervous system plays an important role in various functions, including learning and memory, aggression, feeding behaviors, and wakefulness, as evidenced by studies utilizing H1R knockout mice and pharmacological interventions. Although previous studies have reported the widespread distribution of H1R in the brains of rats, guinea pigs, monkeys, and humans, the detailed distribution in the mouse brain remains unclear. This study provides a comprehensive description of the distribution of H1R mRNA in the mouse brain using two recently developed techniques: RNAscope and in situ hybridization chain reaction, both of which offer enhanced sensitivity and resolution compared to traditional methodologies such as radioisotope labeling, which were used in previous studies. The H1R mRNA expression was observed throughout the entire brain, including key regions implicated in sleep-wake regulatory functions, such as the pedunculopontine tegmental nucleus and dorsal raphe. Additionally, strong H1R mRNA signals were identified in the paraventricular hypothalamus and ventromedial hypothalamus, which may explain the potential mechanisms underlying histamine-mediated feeding regulation. Notably, we identified strong H1R mRNA expression in previously unreported cerebral regions, such as the dorsal endopiriform nucleus, bed nucleus of the accessory olfactory tract, and postsubiculum. These findings significantly contribute to our understanding of the multifaceted roles of H1R in diverse brain functions.

The antiglycation potential of H1 receptor antagonists - in vitro studies in bovine serum albumin model and in silico molecular docking analyses.

The H1 receptor belongs to the family of rhodopsin-like G-protein-coupled receptors activated by the biogenic amine histamine. H1 receptor antagonists are widely used in the treatment of allergies. However, these drugs could have a much broader spectrum of activity, including hypoglycemic effects, which can broaden the spectrum of their use. The aim of the study was to evaluate the antiglycation potential of twelve H1 receptor antagonists (diphenhydramine, antazoline, promethazine, ketotifen, clemastine, pheniramine, cetirizine, levocetirizine, bilastine, fexofenadine, desloratadine, and loratadine). Bovine serum albumin (BSA) was glycated with sugars (glucose, fructose, galactose, and ribose) and aldehydes (glyoxal and methylglyoxal) in the presence of H1 blockers. The tested substances did not induce a significant decrease in the content of albumin glycation end-products, and the inhibition rate of glycoxidation was not influenced by the chemical structure or generation of H1 blockers. None of the tested H1 receptor antagonists exhibited strong antiglycation activity. Antiglycemic potential of H1 blockers could be attributed to their antioxidant and anti-inflammatory activity, as well as their effects on carbohydrate metabolism/metabolic balance at the systemic level.

The role of histamine H1 receptor in the anterior cingulate cortex on nociception level following acute restraint stress in male rats.

Considering the importance of pain and stress, we decided to investigate the intra-anterior cingulate cortex (ACC) microinjection of histamine and mepyramine alone and concurrently on acute pain induced by hot plate following restraint stress in male rats. 24-gauge, 10 mm stainless steel guide cannula was implanted over the ACC in the incised scalp of 4 groups. Restraint stress in healthy rats produced a significant increase (p < .05) in the pain threshold. The simultaneous microinjection of 4 µg/side histamine and 8 µg/side mepyramine as a histaminergic system inverse agonist in healthy nonrestraint animals did not affect the pain threshold. Although Histamine decreased the threshold of pain meaningfully, mepyramine elevated it in a significant manner (p < .05). In the restrained animals, intra-ACC microinjection of histamine produced no significant impact on the pain threshold. However, intra-ACC microinjection of mepyramine before histamine, significantly (p < .01) altered the result and enhanced the threshold of pain. The results of our study demonstrated that histaminergic neurons have an important role in the processing of pain in the ACC following restraint stress.

Histamine H1 Receptor-Mediated JNK Phosphorylation Is Regulated by Gq Protein-Dependent but Arrestin-Independent Pathways.

Arrestins are known to be involved not only in the desensitization and internalization of G protein-coupled receptors but also in the G protein-independent activation of mitogen-activated protein (MAP) kinases, such as extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), to regulate cell proliferation and inflammation. Our previous study revealed that the histamine H1 receptor-mediated activation of ERK is dually regulated by Gq proteins and arrestins. In this study, we investigated the roles of Gq proteins and arrestins in the H1 receptor-mediated activation of JNK in Chinese hamster ovary (CHO) cells expressing wild-type (WT) human H1 receptors, the Gq protein-biased mutant S487TR, and the arrestin-biased mutant S487A. In these mutants, the Ser487 residue in the C-terminus region of the WT was truncated (S487TR) or mutated to alanine (S487A). Histamine significantly stimulated JNK phosphorylation in CHO cells expressing WT and S487TR but not S487A. Histamine-induced JNK phosphorylation in CHO cells expressing WT and S487TR was suppressed by inhibitors against H1 receptors (ketotifen and diphenhydramine), Gq proteins (YM-254890), and protein kinase C (PKC) (GF109203X) as well as an intracellular Ca2+ chelator (BAPTA-AM) but not by inhibitors against G protein-coupled receptor kinases (GRK2/3) (cmpd101), ß-arrestin2 (ß-arrestin2 siRNA), and clathrin (hypertonic sucrose). These results suggest that the H1 receptor-mediated phosphorylation of JNK is regulated by Gq-protein/Ca2+/PKC-dependent but GRK/arrestin/clathrin-independent pathways.

Molecular mechanism of antihistamines recognition and regulation of the histamine H1 receptor.

Histamine receptors are a group of G protein-coupled receptors (GPCRs) that play important roles in various physiological and pathophysiological conditions. Antihistamines that target the histamine H1 receptor (H1R) have been widely used to relieve the symptoms of allergy and inflammation. Here, to uncover the details of the regulation of H1R by the known second-generation antihistamines, thereby providing clues for the rational design of newer antihistamines, we determine the cryo-EM structure of H1R in the apo form and bound to different antihistamines. In addition to the deep hydrophobic cavity, we identify a secondary ligand-binding site in H1R, which potentially may support the introduction of new derivative groups to generate newer antihistamines. Furthermore, these structures show that antihistamines exert inverse regulation by utilizing a shared phenyl group that inserts into the deep cavity and block the movement of the toggle switch residue W4286.48. Together, these results enrich our understanding of GPCR modulation and facilitate the structure-based design of novel antihistamines.

Pharmacological Characterization of the Zebrafish (Danio Rerio) Histamine H1 Receptor Reveals the Involvement of the Second Extracellular Loop in the Binding of Histamine.

The zebrafish (Danio rerio) histamine H1 receptor gene (zfH1R) was cloned in 2007 and reported to be involved in fish locomotion. Yet, no detailed characterization of its pharmacology and signaling properties have so far been reported. In this study, we pharmacologically characterized the zfH1R expressed in HEK-293T cells by means of [3H]-mepyramine binding and G protein-signaling assays. The zfH1R [dissociation constant (KD), 0.7 nM] displayed similar affinity for the antagonist [3H]-mepyramine as the human histamine H1 receptor (hH1R) (KD, 1.5 nM), whereas the affinity for histamine is 100-fold higher than for the human H1R. The zfH1R couples to Gαq/11 proteins and activates several reporter genes, i.e., NFAT, NFÏ°B, CRE, VEGF, COX-2, SRE, and AP-1, and zfH1R-mediated signaling is prevented by the Gαq/11 inhibitor YM-254890 and the antagonist mepyramine. Molecular modeling of the zfH1R and human H1R shows that the binding pockets are identical, implying that variations along the ligand binding pathway could underly the differences in histamine affinity instead. Targeting differentially charged residues in extracellular loop 2 (ECL2) using site-directed mutagenesis revealed that Arg21045x55 is most likely involved in the binding process of histamine in zfH1R. This study aids the understanding of the pharmacological differences between H1R orthologs and the role of ECL2 in histamine binding and provides fundamental information for the understanding of the histaminergic system in the zebrafish. SIGNIFICANCE STATEMENT: The use of the zebrafish as in vivo models in neuroscience is growing exponentially, which asks for detailed characterization of the aminergic neurotransmitter systems in this model. This study is the first to pharmacologically characterize the zebrafish histamine H1 receptor after expression in HEK-293T cells. The results show a high pharmacological and functional resemblance with the human ortholog but also reveal interesting structural differences and unveils an important role of the second extracellular loop in histamine binding.

Disruption of Histamine-H1R signaling exacerbates cardiac microthrombosis after periodontal disease via TLR4/NFκB-p65 pathway.

Periodontal disease is a chronic inflammatory disease that is highly correlated with cardiovascular disease(CVD). Histamine has been proven to participate in the pathophysiological processes of cardiovascular disease and oral inflammation. However, the role of histamine in the development of cardiac microthrombosis caused by periodontal disease has not been fully elucidated. We established a murine periodontal inflammation model by injecting lipopolysaccharide (LPS) or Porphyromonas gingivalis (P. gingivalis). In order to examine the effect of histamine/H1R signaling on cardiac injury after periodontal disease, we used histidine decarboxylase- knockout (HDC-/-) mice and histamine 1 receptor (H1R) antagonist. Our results demonstrated that LPS-induced periodontal inflammation significantly increased CD11b+Gr-1+ neutrophils in the peripheral blood and myocardial interstitium. Histamine deficiency resulted in further increases in P. gingivalis, neutrophils, inflammatory cytokines, and cardiac microthrombosis in the myocardium of HDC-/- mice compared to wild-type (WT) mice. Mechanistic analysis showed that blocking H1R could synergistically interact with LPS, further increasing the phosphorylation of p65, exacerbating the inflammatory response of neutrophils and endothelial cell damage. Conclusively, the disruption of histamine-H1R signaling exacerbates cardiac microthrombosis after periodontal disease via TLR4/NFκB-p65 pathway. Our findings not only reveal a link between periodontal inflammation and myocardial injury but also provided some thoughts for the use of H1R antagonist in clinical practice.

The Roles of Histamine Receptor 1 (hrh1) in Neurotransmitter System Regulation, Behavior, and Neurogenesis in Zebrafish.

Histamine receptors mediate important physiological processes and take part in the pathophysiology of different brain disorders. Histamine receptor 1 (HRH1) is involved in the development of neurotransmitter systems, and its role in neurogenesis has been proposed. Altered HRH1 binding and expression have been detected in the brains of patients with schizophrenia, depression, and autism. Our goal was to assess the role of hrh1 in zebrafish development and neurotransmitter system regulation through the characterization of hrh1-/- fish generated by the CRISPR/Cas9 system. Quantitative PCR, in situ hybridization, and immunocytochemistry were used to study neurotransmitter systems and genes essential for brain development. Additionally, we wanted to reveal the role of this histamine receptor in larval and adult fish behavior using several quantitative behavioral methods including locomotion, thigmotaxis, dark flash and startle response, novel tank diving, and shoaling behavior. Hrh1-/- larvae displayed normal behavior in comparison with hrh1+/+ siblings. Interestingly, a transient abnormal expression of important neurodevelopmental markers was evident in these larvae, as well as a reduction in the number of tyrosine hydroxylase 1 (Th1)-positive cells, th1 mRNA, and hypocretin (hcrt)-positive cells. These abnormalities were not detected in adulthood. In summary, we verified that zebrafish lacking hrh1 present deficits in the dopaminergic and hypocretin systems during early development, but those are compensated by the time fish reach adulthood. However, impaired sociability and anxious-like behavior, along with downregulation of choline O-acetyltransferase a and LIM homeodomain transcription factor Islet1, were displayed by adult fish.

Histamine H1- and H4-receptor expression in human colon-derived cell lines.

In previous studies, we demonstrated the involvement of H4R in inflammatory bowel disease (IBD) and IBD-associated colon cancer in mice and could ascribe H4R-mediated histamine function to colon epithelial cells. The transferability of obtained data to humans is however lacking. Functional expression of H4R on colon epithelial cells is a prerequisite to pursue the hypothesis of involvement of H4R in carcinogenesis. Thus, we here compared the expression of histamine receptor subtypes in a series of cell lines. Out of these, three colon-derived cell lines displaying different combinations of H1R and H4R expression were submitted to functional analyses. Human hematopoietic HMC-1, HL-60, and U937, lung-derived A549 and Calu-3, and colorectal LoVo, SW 480, Caco-2, HT-29, and HCT116 cells were included in the study. mRNA expression was quantified by RT-qPCR. For functional analyses, Caco-2, HT-29, and HCT116 cells were treated by incubation with 1 - 10 µM histamine in the presence or absence of selective histamine receptor antagonists. Calcium mobilization, cAMP accumulation, and cell proliferation were measured by fluorimetry, mass spectrometry, and real-time bioimpedance measurements, respectively. Histamine receptor expression was heterogeneous in the cell lines tested. In most cell lines, we detected H1R mRNA while H4R mRNAs were found only occasionally. The colon-derived epithelial cell lines LoVo, SW480, and HT-29 expressed H1R mRNA exclusively, while in HCT116 cells H1R and H4R mRNAs and in CaCo-2 H2R mRNA were detectable. Subsequent functional analyses in HT29, Caco-2, and HCT116 cells, however, indicated that only HT-29 responded to histamine stimulation, by means of H1R. For a detailed analysis of histamine receptor function, esp. that of H1R and H4R, in human colon-derived cell lines, the cell lines tested here are not fully convenient unless genetically modified.

Computational Analysis of Histamine Protonation Effects on H1R Binding.

Despite numerous studies investigating histamine and its receptors, the impact of histamine protonation states on binding to the histamine H1-receptor (H1R) has remained elusive. Therefore, we assessed the influence of different histamine tautomers (τ-tautomer, π-tautomer) and charge states (mono- vs. dicationic) on the interaction with the ternary histamine-H1R-Gq complex. In atomistic molecular dynamics simulations, the τ-tautomer formed stable interactions with the receptor, while the π-tautomer induced a rotation of the histamine ring by 180° and formed only weaker hydrogen bonding interactions. This suggests that the τ-tautomer is more relevant for stabilization of the active ternary histamine-H1R-Gq complex. In addition to the two monocationic tautomers, the binding of dicationic histamine was investigated, whose interaction with the H1R had been observed in a previous experimental study. Our simulations showed that the dication is less compatible with the ternary histamine-H1R-Gq complex and rather induces an inactive conformation in the absence of the Gq protein. Our data thus indicate that the charge state of histamine critically affects its interactions with the H1R. Ultimately these findings might have implications for the future development of new ligands that stabilize distinct H1R activation states.

Anti-chlamydial effects of azelastine hydrochloride and the impact of the histamine H1 receptor on chlamydial development.

Introduction. Azelastine hydrochloride, a second-generation histamine H1 receptor (H1R) antagonist, exhibits anti-chlamydial effects against Chlamydia trachomatis (CT) in HeLa cells (genital infection model).Hypothesis/Gap Statement. Non-antibiotic pharmaceutical interactions with CT are an understudied field and the anti-chlamydial effects of azelastine are a potential interaction requiring further elucidation.Aim. To explore the underlying anti-chlamydial mechanisms of azelastine.Methodology. We assessed the specificity of azelastine for the chlamydial species and host cell type, the timing of azelastine application and whether the anti-chlamydial effects could be reproduced with different H1R-modulating compounds.Results. We observed similar anti-chlamydial azelastine effects for Chlamydia muridarum as well as for an ocular CT strain in human conjunctival epithelial cells (ocular infection model). Pre-incubating host cells with azelastine before infection mildly reduced chlamydial inclusion numbers and infectivity. Incubation of cells with azelastine initiated concomitantly with the chlamydial infection, or initiated several hours post-infection, reduced inclusion size, number and infectivity, and altered chlamydial morphology. These effects were strongest when azelastine was added shortly after or with the infection. Azelastine effects were not alleviated by increased concentrations of culture medium nutrients. Additionally, we did not observe anti-chlamydial effects when incubating cultures either with a different H1R antagonist or agonist, indicating that azelastine effects are probably H1R-independent.Conclusion. Accordingly, we conclude that azelastine anti-chlamydial effects are not restricted to a specific chlamydial species, strain or culture model, and are probably not mediated by H1R antagonism. Thus, it appears likely that off-target mechanisms of azelastine may explain our observations.

Histamine promotes angiogenesis through a histamine H1 receptor-PKC-VEGF-mediated pathway in human endothelial cells.

Histamine is a well-known inflammatory mediator, but how histamine induces angiogenesis remains poorly understood. In the present study, we demonstrated a dose-dependent dynamic tube formation in the human endothelial cell line EA.hy926 in the presence of histamine that was completely blocked by histamine H1 receptor (H1R) and protein kinase C (PKC) inhibitors. However, histamine H2, H3, and H4 receptor inhibitors did not inhibit tube formation, suggesting that H1R-PKC signaling is involved in histamine-induced tube formation. Moreover, we found an H1-specific induction of vascular endothelial growth factor (VEGF) expression. Inhibition of VEGF receptor 2 (VEGFR2) suppressed the histamine-induced tube formation, indicating that VEGF is downstream of histamine signaling. Additionally, we demonstrated that histamine stimulation induces the expression of critical regulators of angiogenesis such as matrix metalloproteinase (MMP)-9 and MMP-14 metalloproteases, as histamine-induced tube formation is blocked by MMP inhibitors. In summary, our study indicates that histamine can activate the H1R in human endothelial cells and thereby promote tube formation through the PKC, MMP, and VEGF signaling pathways.

Simultaneous activation of CXC chemokine receptor 4 and histamine receptor H1 enhances calcium signaling and cancer cell migration.

C-X-C chemokine receptor 4 (CXCR4) is widely overexpressed in various types of cancer and is involved in several cancer phenotypes including tumor growth, survival, and metastasis. The roles of histamine and histamine receptor H1 (HRH1) in cancer pathogenesis remain controversial. Here, we show that HRH1 is widely expressed in various cancer cell lines and cancer tissues and that coexpression of CXCR4 and HRH1 is associated with poor prognosis in breast cancer. Using bimolecular fluorescence complementation and bioluminescence resonance energy transfer donor saturation assays, we demonstrate that CXCR4 and HRH1 can assemble into a heteromeric complex. Simultaneous activation of CXCR4 and HRH1 synergistically increases calcium flux in MDA-MB-231 cells that endogenously express CXCR4 and HRH1 but not in cells deficient in CXCR4 or HRH1. Costimulation of CXCR4 and HRH1 also significantly enhances CXCL12-induced MDA-MB-231 cell migration, while histamine alone does not induce cell migration. Synergistic effects on calcium flux and cell migration are inhibited by the Gαi inhibitor pertussis toxin and the Gαq inhibitor YM254890, suggesting that the Gαi and Gαq pathways are involved in the synergy. Enhanced calcium signaling and cell migration are also observed in NCI-H23 and HeLa cells, which coexpress CXCR4 and HRH1. Taken together, our findings demonstrate an interplay between CXCR4 and HRH1, and suggest the possibility of the CXCR4-HRH1 heteromer as a potential therapeutic target for anticancer therapy.

Receptor and Ionic Mechanism of Histamine on Mouse Dorsolateral Striatal Neurons.

The dorsolateral striatum (DLS) is the critical neural substrate that plays a role in motor control and motor learning. Our past study revealed a direct histaminergic projection from the tuberomammillary nucleus (TMN) of the hypothalamus to the rat striatum. However, the afferent of histaminergic fibers in the mouse DLS, the effect of histamine on DLS neurons, and the underlying receptor and ionic mechanisms remain unclear. Here, we demonstrated a direct histaminergic innervation from the TMN in the mouse DLS, and histamine excited both the direct-pathway spiny projection neurons (d-SPNs) and the indirect-pathway spiny projection neurons (i-SPNs) of DLS via activation of postsynaptic H1R and H2R, albeit activation of presynaptic H3R suppressed neuronal activity by inhibiting glutamatergic synaptic transmission on d-SPNs and i-SPNs in DLS. Moreover, sodium-calcium exchanger 3 (NCX3), potassium-leak channels linked to H1R, and hyperpolarization-activated cyclic nucleotide-gated channel 2 (HCN2) coupled to H2R co-mediated the excitatory effect induced by histamine on d-SPNs and i-SPNs in DLS. These results demonstrated the pre- and postsynaptic receptors and their downstream multiple ionic mechanisms underlying the inhibitory and excitatory effects of histamine on d-SPNs and i-SPNs in DLS, suggesting a potential modulatory effect of the central histaminergic system on the DLS as well as its related motor control and motor learning.

Curcuminoids, a major turmeric component, have a sleep-enhancing effect by targeting the histamine H1 receptor.

Turmeric (Curcuma longa) had been considered as a universal panacea in functional foods and traditional medicines. In recent, the sedative-hypnotic effect of turmeric extract (TE) was reported. However, sleep-promoting compounds in TE have been not yet demonstrated. Curcuminoids (curcumin, demethoxycurcumin, and bisdemethoxycurcumin) are the major constituents of turmeric being responsible for its various biological activities. Therefore, they can be first assumed to be sedative-hypnotic compounds of TE. In the present study, we aimed to investigate the effects and underlying mechanisms of curcuminoids and each constituent on the sleep-wake cycle of mice. Molecular docking studies, histamine H1 receptor (H1R) binding assays, and H1R knockout animal studies were used to investigate the molecular mechanisms underlying the sleep-promoting effects. Curcuminoids and their constituents reduced sleep latency and increased sleep duration in the pentobarbital-induced sleep test in mice. In addition, curcuminoids significantly increased the duration of NREMS and reduced sleep latency without altering the REMS and delta activity. Curcumin, demethoxycurcumin, and bisdemethoxycurcumin were predicted to interact with H1R in the molecular model. In the binding affinity assay, we found that curcuminoids, as well as their constituents, significantly bind to H1R with the Ki value of 1.49 µg mL-1. Furthermore, sleep latency was reduced and NREMS frequency was increased following curcuminoid administration in wild-type mice but not in H1R knockout mice. Therefore, we conclude that curcuminoids reduce sleep latency and enhance the quantity of NREMS by acting as modulators of H1R, indicating their usefulness in treating insomnia.