Structure of the human histamine H1 receptor complex with doxepin

Cryo-EM Structures and AlphaFold3 Models of Histamine Receptors Reveal Diverse Ligand Binding and G Protein Bias

Background: The four subtypes of G protein-coupled receptors (GPCRs) regulated by histamine play critical roles in various physiological and pathological processes, such as allergy, gastric acid secretion, cognitive and sleep disorders, and inflammation. Previous experimental structures of histamine receptors (HRs) with agonists and antagonists exhibited multiple conformations for the ligands and G protein binding. However, the structural basis for HR regulation and signaling remains elusive. Methods: We determined the cryo-electron microscopy (cryo-EM) structure of the H4R-histamine-Gi complex at 2.9 Å resolution, and predicted the models for all four HRs in the ligand-free apo and G protein subtype binding states using AlphaFold3 (AF3). Results: By comparing our H4R structure with the experimental HR structures and the computational AF3 models, we elucidated the distinct histamine binding modes and G protein interfaces, and proposed the essential roles of Y6.51 and Q7.42 in receptor activation and the intracellular loop 2 (ICL2) in G protein bias. Conclusions: Our findings deciphered the molecular mechanisms underlying the regulation of different HRs, from the extracellular ligand-binding pockets and transmembrane motifs to the intracellular G protein coupling interfaces. These insights are expected to facilitate selective drug discovery targeting HRs for diverse therapeutic purposes.

Repeated-Dose Toxicity of Lauric Acid and Its Preventive Effect Against Tracheal Hyper-Responsiveness in Wistar Rats with Possible In Silico Molecular Targets

BACKGROUND/OBJECTIVES

Lauric acid (LA), a medium-chain fatty acid, is a promising drug for asthma treatment. This study evaluated the toxicity of repeated doses and the effect of LA on pulmonary ventilation and tracheal reactivity in asthmatic Wistar rats and identified possible molecular targets of LA action in silico.

METHODS

The rats were divided into control (CG) and LA-treated groups at 100 mg/kg (AL100G) for toxicity analysis. Pulmonary ventilation and tracheal reactivity were assessed in the control (CG), asthmatic (AG), asthmatic treated with LA at 25, 50, or 100 mg/kg (AAL25G, AAL50G, and AAL100G), and dexamethasone-treated groups (ADEXAG).

RESULTS

The results showed that LA at a dose of 100 mg/kg did not cause death or toxicity. A pulmonary ventilation analysis indicated that AG had reduced minute volume, which was prevented in AAL25G. LA at all doses prevented carbachol-induced tracheal hyper-responsiveness and reduced the relaxing effect of aminophylline, as observed in AG. An in silico analysis revealed that LA had a good affinity for nine proteins (β2-adrenergic receptor, CaV, BKCa, KATP, adenylyl cyclase, PKG, eNOS, iNOS, and COX-2).

CONCLUSIONS

LA at 100 mg/kg has low toxicity, prevents hyper-responsiveness in an asthma model in rats, and acts as a multitarget compound with a good affinity for proteins related to airway hyper-responsiveness.

Using Zebrafish G Protein-Coupled Receptors to Obtain a Better Appreciation of the Impact of Pharmaceuticals in Wastewater to Fish

Pharmaceutical discharge to the environment is of concern due to its potential adverse effects on aquatic species. It is estimated that around 40% of pharmaceuticals target G protein-coupled receptors (GPCRs). The in vitro transforming growth factor-α (TGFα) shedding assay was applied to measure the antagonistic activities of pharmaceuticals against human GPCRs. However, their ability to stimulate fish GPCRs remains unclear. Here, antagonistic activities of 30 pharmaceuticals against zebrafish dopamine (zD2a and zD2c), adrenergic family member (zβ1), and histamine (zH1 and zH3) receptors were measured by the TGFα shedding assay. The study found an interspecies difference in binding affinities between human and zebrafish: pharmaceuticals more strongly inhibited the zD2c and zH1 receptors than human D2 (hD2) and hH1 receptors, while zD2a and zβ1 receptors were less inhibited than hD2 and hβ1 receptors. The potential molecular explanations for the observed interspecies differences in binding affinity for hydroxyzine and bisoprolol were investigated using molecular docking. Pharmaceutical potency against zebrafish GPCRs and predicted effluent concentrations were used to predict equivalent quantities (EQs), and these EQs were used to prioritize pharmaceuticals of concern in wastewater in England and Japan. This study highlights the use of the TGFα shedding assay adopting zebrafish GPCRs to better understand the ecological effects of pharmaceuticals on fish.

Probing the Histamine H1 Receptor Binding Site to Explore Ligand Binding Kinetics

Analysis of structure-kinetic relationships (SKR) can contribute to an improved understanding of receptor-ligand interactions. Here, fragment 1 (4-(2-benzylphenoxy)-1-methylpiperidine) was used in different fragment growing approaches to mimic the putative binding mode of the long residence time (RT) ligands olopatadine, acrivastine, and levocetirizine at the histamine H1 receptor (H1R). SKR analyses reveal that introduction of a carboxylic acid moiety can increase RT at H1R up to 11-fold. Ligand efficiency (LE) decreases upon the introduction of the negatively charged group, whereas kinetic efficiency (KE) increases up to 8.5-fold. The olopatadine/acrivastine mimics give up to 15-fold differences in the RT, while the levocetirizine mimics afford similar RTs with only a 3-fold difference. Therefore, the levocetirizine mimics are less sensitive to structural changes. This study illustrates that for H1R, there are several ways to increase RT but the different strategies differ significantly in SKR.

Comparison of new secondgeneration H1 receptor blockers with some molecules; a study involving DFT, molecular docking, ADMET, biological target and activity

Although the antiallergic properties of compounds such as CAPE, Melatonin, Curcumin, and Vitamin C have been poorly discussed by experimental studies, the antiallergic properties of these famous molecules have never been discussed with calculations. The histamine-1 receptor (H1R) belongs to the family of rhodopsin-like G-protein-coupled receptors expressed in cells that mediate allergies and other pathophysiological diseases. In this study, pharmacological activities of FDA-approved second generation H1 antihistamines (Levocetirizine, desloratadine and fexofenadine) and molecules such as CAPE, Melatonin, Curcumin, Vitamin C, ADMET (Absorption, Distribution, Metabolism, Excretion, Toxicity) profiles, density functional theory (DFT), molecular docking, biological targets and activities were compared by calculating. Since drug development is an extremely risky, costly and time-consuming process, the data obtained in this study will facilitate and guide future studies. It will also enable researchers to focus on the most promising compounds, providing an effective design strategy. Their pharmacological activity was carried out using computer-based computational techniques including DFT, molecular docking, ADMET analysis, biological targeting, and activity methods. The best binding sites of Desloratadine, Levocetirizine, Fexofenadine, CAPE, Quercetin, Melatonin, curcumin, Vitamin C ligands to Desmoglein 1, Human Histamine H1 receptor, IgE and IL13 protons were determined by molecular docking method and binding energy and interaction states were analyzed. Fexofenadine and Quercetin ligand showed the most effective binding affinity. Melatonin had the best Caco-2 permeability PPB values of Quercetin, CAPE and Curcumin were at optimal levels. On the OATP1B1 and OATP1B3 of curcumin and CAPE, Quercetin was found to have strong inhibition effects on BCRP. Melatonin and CAPE were found to have the highest inhibition values on CYP1A2, while CAPE had the highest inhibition values on CYP2C19 and CYP2C9. Vitamin C and Quercetin were found to be safer in terms of cardiac toxicity and mutagenic risks, while Desloratadine and Levocetirizine carried high risks of neurotoxicity and hematotoxicity, while CAPE was noted for its high enzyme inhibitory activities and low toxicity profiles, while the hERG blockade, DILI, and cytotoxicity values of other compounds pointed to various safety concerns. This study demonstrated the potential of machine learning methods in understanding and discovering H1 receptor blockers. The results obtained provide important clues in the development of important strategies in the clinical use of H1 receptor blockers. In the light of these data, CAPE and Quercetin are remarkable molecules.

Ni(0)-Catalyzed Efficient, Regioselective Synthesis of Dibenzo[b,e]oxepines and Dibenzo[c,f][1,2]oxathiepine 6,6-Dioxides: Mechanistic Study by DFT Calculation and Docking Interactions

Herein, a nickel-catalyzed divergent reductive-Heck reaction of 1-bromo-2-((2-(aryl/alkyl ethynyl)phenoxy)methyl)benzene and 2-(aryl/alkyl ethynyl)phenyl 2-bromobenzenesulfonate derivatives has been demonstrated through the regulation of reducing agents and solvent systems. This scalable protocol offers regio- and stereoselective access to functionalized dibenzo[b,e]oxepine and dibenzo[c,f][1,2]oxathiepine 6,6-dioxide scaffolds in high to excellent yields under a mild set of reaction conditions. This methodology offers a predictable route for the synthesis of medium ring oxygen heterocycles and demonstrates wide substrate scope and outstanding tolerance to various functional groups like hydroxyl and, of course, practical instance via the synthesis of doxepin and nordoxepin molecules. We validate the experimentally proposed reaction mechanism using the density functional theory method. Further, molecular docking interactions were investigated accommodating some of our synthesized molecules.

Classics in Chemical Neuroscience: Deliriant Antihistaminic Drugs

Antihistaminic drugs are widely used clinically and have long been primarily known for their use to treat severe allergic conditions caused by histamine release. Antihistaminic drugs also exert central nervous system (CNS) effects, acting as anxiolytics, hypnotics, and neuroleptics. However, these drugs also have multiple serious neuropharmacological side-effects, inducing delirium, hyperarousal, disorganized behavior, and hallucinations. Due to their robust CNS effects, antihistamines are also increasingly abused, with occasional overdoses and life-threatening toxicity. Here, we discuss chemical and neuropharmacological aspects of antihistaminic drugs in both human and animal (experimental) models and outline their current societal and mental health importance as neuroactive substances.

Protein - carbohydrate interaction studies using domestic animals as role models support the search of new glycomimetic molecules

The structural dynamics of the interactions between defensins or lysozymes and various saccharide chains that are covalently linked to lipids or proteins were analyzed in relation to the sub-molecular architecture of the carbohydrate binding sites of lectins. Using tissue materials from rare and endangered domestic animals as well as from dogs it was possible to compare these results with data obtained from a human glioblastoma tissue. The binding mechanisms were analyzed on a cellular and a sub-molecular size level using biophysical techniques (e.g. NMR, AFM, MS) which are supported by molecular modeling tools. This leads to characteristic structural patterns being helpful to understand glyco-biochemical pathways in which galectins, defensins or lysozymes are involved. Carbohydrate chains have a distinct impact on cell differentiation, cell migration and immunological processes. The absence or the presence of sialic acids and the conformational dynamics in glycans are often correlated with zoonoses such as influenza- and coronavirus-infections. Receptor-sensitive glycomimetics could be a solution. The new findings concerning the function of galectin-3 in the nucleus in relation to differentiation processes can be understood when the binding specificity of neuroleptic molecules as well as the interactions between proteins and nucleic acids are describable on a sub-molecular size level.

Advanced applications of Nanodiscs-based platforms for antibodies discovery

Due to their fundamental biological importance, membrane proteins (MPs) are attractive targets for drug discovery, with cell surface receptors, transporters, ion channels, and membrane-bound enzymes being of particular interest. However, due to numerous challenges, these proteins present underutilized opportunities for discovering biotherapeutics. Antibodies hold the promise of exquisite specificity and adaptability, making them the ideal candidates for targeting complex membrane proteins. They can target specific conformations of a particular membrane protein and can be engineered into various formats. Generating specific and effective antibodies targeting these proteins is no easy task due to several factors. The antigen's design, antibody-generation strategies, lead optimization technologies, and antibody modalities can be modified to tackle these challenges. The rational employment of cutting-edge lipid nanoparticle systems for retrieving the membrane antigen has been successfully implemented to simplify the mechanism-based therapeutic antibody discovery approach. Despite the highlighted MP production challenges, this review unequivocally underscores the advantages of targeting complex membrane proteins with antibodies and designing membrane protein antigens. Selected examples of lipid nanoparticle success have been illustrated, emphasizing the potential of therapeutic antibody discovery in this regard. With further research and development, we can overcome these challenges and unlock the full potential of therapeutic antibodies directed to target complex MPs.

Alleviation of Autophagic Deficits and Neuroinflammation by Histamine H3 Receptor Antagonist E159 Ameliorates Autism-Related Behaviors in BTBR Mice

BACKGROUND/OBJECTIVES

Autism spectrum disorder (ASD) is a neurodevelopmental condition marked by social interaction difficulties, repetitive behaviors, and immune dysregulation with elevated pro-inflammatory markers. Autophagic deficiency also contributes to social behavior deficits in ASD. Histamine H3 receptor (H3R) antagonism is a potential treatment strategy for brain disorders with features overlapping ASD, such as schizophrenia and Alzheimer's disease.

METHODS

This study investigated the effects of sub-chronic systemic treatment with the H3R antagonist E159 on social deficits, repetitive behaviors, neuroinflammation, and autophagic disruption in male BTBR mice.

RESULTS

E159 (2.5, 5, and 10 mg/kg, i.p.) improved stereotypic repetitive behavior by reducing self-grooming time and enhancing spontaneous alternation in addition to attenuating social deficits. It also decreased pro-inflammatory cytokines in the cerebellum and hippocampus of treated BTBR mice. In BTBR mice, reduced expression of autophagy-related proteins LC3A/B and Beclin 1 was observed, which was elevated following treatment with E159, attenuating the disruption in autophagy. The co-administration with the H3R agonist MHA (10 mg/kg, i.p.) reversed these effects, highlighting the role of histaminergic neurotransmission in observed behavioral improvements.

CONCLUSIONS

These preliminary findings suggest the therapeutic potential of H3R antagonists in targeting neuroinflammation and autophagic disruption to improve ASD-like behaviors.

Structural basis of ligand recognition and activation of the histamine receptor family

Histamine is a biogenic amine that is critical in various physiological and pathophysiological processes, including but not limited to allergic reactions, wakefulness, gastric acid secretion and neurotransmission. Here, we determine 9 cryo-electron microscopy (cryo-EM) structures of the 4 histamine receptors in complex with four different G protein subtypes, with endogenous or synthetic agonists bound. Inside the ligand pocket, we identify key motifs for the recognition of histamine, the distinct binding orientations of histamine and three subpockets that facilitate the design of specific ligands. In addition, we also identify key residues responsible for the selectivity of immethridine. Moreover, we reveal distinct structural features as determinants of Gq vs. Gs or Gs vs. Gi coupling differences among the histamine receptors. Our study provides a structural framework for understanding the ligand recognition and G protein coupling of all 4 histamine receptors, which may facilitate the rational design of ligands targeting these receptors.

A Machine Learning Algorithm Suggests Repurposing Opportunities for Targeting Selected GPCRs

Repurposing utilizes existing drugs with known safety profiles and discovers new uses by combining experimental and computational approaches. The integration of computational methods has greatly advanced drug repurposing, offering a rational approach and reducing the risk of failure in these efforts. Recognizing the potential for drug repurposing, we employed our Iterative Stochastic Elimination (ISE) algorithm to screen known drugs from the DrugBank database. Repurposing in our hands is based on computer models of the actions of ligands: the ISE algorithm is a machine learning tool that creates ligand-based models by distinguishing between the physicochemical properties of known drugs and those of decoys. The models are large sets of "filters" made out, each, of molecular properties. We screen and score external sets of molecules (in our case- the DrugBank molecules) by our agonism and antagonism models based on published data (i.e., IC50, Ki, or EC50) and pick the top-scoring molecules as candidates for experiments. Such agonist and antagonist models for six G-protein coupled receptors (GPCRs) families facilitated the identification of repurposing opportunities. Our screening revealed 5982 new potential molecular actions (agonists, antagonists), which suggest repurposing candidates for the cannabinoid 2 (CB2), histamine (H1, H3, and H4), and dopamine 3 (D3) receptors, which may be useful to treat conditions such as neuroinflammation, obesity, allergic dermatitis, and drug abuse. These sets of best candidates should now be examined by experimentalists: based on previous such experiments, there is a very high chance of discovering novel highly bioactive molecules.

Rhodium(III)-Catalyzed C-H Activation/[5 + 2] Cascade Annulation of Aroyl Hydrazides with Iodonium Ylides for the Synthesis of Seven-Membered Dibenzodiazepinediones

A novel Rh(III)-catalyzed C-H activation/[5 + 2] cascade annulation of aroyl hydrazides with iodonium ylides is accomplished, in which diverse seven-membered dibenzodiazepinediones were afforded in moderate to excellent yields. This annulation reaction features an ideal functional group tolerance and a wide substrate scope. Large-scale and derivatization reactions were conducted to demonstrate the potential utility of this transformation.

Brønsted Acid Triggers [6/7 + 1] Cascade Cyclization by N-Alkyl Amine C(sp3)-N Cleavage: Mild Synthesis of Benzo[1,4]oxazepane and Dihydrobenzo[1,5]oxazocine

A catalyst-free mild synthesis was reported to produce medium-ring oxazepane and oxazocine derivatives from aminomaleimides and N-alkyl amines. The substrate and acidic additives were employed to cleave the C(sp3)-N bond as a one-carbon synthon for C-C and C-O coupling, thus facilitating the [n + 1] cascade cyclization reaction, which enabled the construction of seven- and eight-membered N,O-heterocycles at room temperature. The method exhibits abroad substrate scope and remarkable tolerance toward various functional groups (seven-membered 28 examples, eight-membered 8 examples, and activated N-alkyl amine 12 examples) and utilization of natural products (2 examples).

AR71, Histamine H3 Receptor Ligand-In Vitro and In Vivo Evaluation (Anti-Inflammatory Activity, Metabolic Stability, Toxicity, and Analgesic Action)

The future of therapy for neurodegenerative diseases (NDs) relies on new strategies targeting multiple pharmacological pathways. Our research led to obtaining the compound AR71 [(E)-3-(3,4,5-trimethoxyphenyl)-1-(4-(3-(piperidin-1-yl)propoxy)phenyl)prop-2-en-1-one], which has high affinity for human H3R (Ki = 24 nM) and selectivity towards histamine H1 and H4 receptors (Ki > 2500 nM), and showed anti-inflammatory activity in a model of lipopolysaccharide-induced inflammation in BV-2 cells. The presented tests confirmed its antagonist/inverse agonist activity profile and good metabolic stability while docking studies showed the binding mode to histamine H1, H3, and H4 receptors. In in vitro tests, cytotoxicity was evaluated at three cell lines (neuroblastoma, astrocytes, and human peripheral blood mononuclear cells), and a neuroprotective effect was observed in rotenone-induced toxicity. In vivo experiments in a mouse neuropathic pain model demonstrated the highest analgesic effects of AR71 at the dose of 20 mg/kg body weight. Additionally, AR71 showed antiproliferative activity in higher concentrations. These findings suggest the need for further evaluation of AR71's therapeutic potential in treating ND and CNS cancer using animal experimental models.

Binding characteristics of the doxepin E/Z-isomers to the histamine H1 receptor revealed by receptor-bound ligand analysis and molecular dynamics study

Doxepin is an antihistamine and tricyclic antidepressant that binds to the histamine H1 receptor (H1R) with high affinity. Doxepin is an 85:15 mixture of the E- and Z-isomers. The Z-isomer is well known to be more effective than the E-isomer, whereas based on the crystal structure of the H1R/doxepin complex, the hydroxyl group of Thr1123.37 is close enough to form a hydrogen bond with the oxygen atom of the E-isomer. The detailed binding characteristics and reasons for the differences remain unclear. In this study, we analyzed doxepin isomers bound to the receptor following extraction from a purified H1R protein complexed with doxepin. The ratio of the E- and Z-isomers bound to wild-type (WT) H1R was 55:45, indicating that the Z-isomer was bound to WT H1R with an approximately 5.2-fold higher affinity than the E-isomer. For the T1123.37V mutant, the E/Z ratio was 89:11, indicating that both isomers have similar affinities. Free energy calculations using molecular dynamics (MD) simulations also reproduced the experimental results of the relative binding free energy differences between the isomers for WT and T1123.37V. Furthermore, MD simulations revealed that the hydroxyl group of T1123.37 did not form hydrogen bonds with the E-isomer, but with the adjacent residues in the binding pocket. Analysis of the receptor-bound doxepin and MD simulations suggested that the hydroxyl group of T1123.37 contributes to the formation of a chemical environment in the binding pocket, which is slightly more favorable for the Z-isomer without hydrogen bonding with doxepin.

G Protein-Coupled Receptor-Ligand Pose and Functional Class Prediction

G protein-coupled receptor (GPCR) transmembrane protein family members play essential roles in physiology. Numerous pharmaceuticals target GPCRs, and many drug discovery programs utilize virtual screening (VS) against GPCR targets. Improvements in the accuracy of predicting new molecules that bind to and either activate or inhibit GPCR function would accelerate such drug discovery programs. This work addresses two significant research questions. First, do ligand interaction fingerprints provide a substantial advantage over automated methods of binding site selection for classical docking? Second, can the functional status of prospective screening candidates be predicted from ligand interaction fingerprints using a random forest classifier? Ligand interaction fingerprints were found to offer modest advantages in sampling accurate poses, but no substantial advantage in the final set of top-ranked poses after scoring, and, thus, were not used in the generation of the ligand-receptor complexes used to train and test the random forest classifier. A binary classifier which treated agonists, antagonists, and inverse agonists as active and all other ligands as inactive proved highly effective in ligand function prediction in an external test set of GPR31 and TAAR2 candidate ligands with a hit rate of 82.6% actual actives within the set of predicted actives.

Molecular Determinant Underlying Selective Coupling of Primary G-Protein by Class A GPCRs

G-protein-coupled receptors (GPCRs) transmit downstream signals predominantly via G-protein pathways. However, the conformational basis of selective coupling of primary G-protein remains elusive. Histamine receptors H2R and H3R couple with Gs- or Gi-proteins respectively. Here, three cryo-EM structures of H2R-Gs and H3R-Gi complexes are presented at a global resolution of 2.6-2.7 Å. These structures reveal the unique binding pose for endogenous histamine in H3R, wherein the amino group interacts with E2065.46 of H3R instead of the conserved D1143.32 of other aminergic receptors. Furthermore, comparative analysis of the H2R-Gs and H3R-Gi complexes reveals that the structural geometry of TM5/TM6 determines the primary G-protein selectivity in histamine receptors. Machine learning (ML)-based structuromic profiling and functional analysis of class A GPCR-G-protein complexes illustrate that TM5 length, TM5 tilt, and TM6 outward movement are key determinants of the Gs and Gi/o selectivity among the whole Class A family. Collectively, the findings uncover the common structural geometry within class A GPCRs that determines the primary Gs- and Gi/o-coupling selectivity.

Exploring GPCR conformational dynamics using single-molecule fluorescence

G protein-coupled receptors (GPCRs) are membrane proteins that transmit specific external stimuli into cells by changing their conformation. This conformational change allows them to couple and activate G-proteins to initiate signal transduction. A critical challenge in studying and inferring these structural dynamics arises from the complexity of the cellular environment, including the presence of various endogenous factors. Due to the recent advances in cell-expression systems, membrane-protein purification techniques, and labeling approaches, it is now possible to study the structural dynamics of GPCRs at a single-molecule level both in vitro and in live cells. In this review, we discuss state-of-the-art techniques and strategies for expressing, purifying, and labeling GPCRs in the context of single-molecule research. We also highlight four recent studies that demonstrate the applications of single-molecule microscopy in revealing the dynamics of GPCRs. These techniques are also useful as complementary methods to verify the results obtained from other structural biology tools like cryo-electron microscopy and x-ray crystallography.

Evaluation of Urtica dioica Phytochemicals against Therapeutic Targets of Allergic Rhinitis Using Computational Studies

Allergic rhinitis (AR) is a prevalent inflammatory condition affecting millions globally, with current treatments often associated with significant side effects. To seek safer and more effective alternatives, natural sources like Urtica dioica (UD) are being explored. However, UD's mechanism of action remains unknown. Therefore, to elucidate it, we conducted an in silico evaluation of UD phytochemicals' effects on known therapeutic targets of allergic rhinitis: histamine receptor 1 (HR1), neurokinin 1 receptor (NK1R), cysteinyl leukotriene receptor 1 (CLR1), chemoattractant receptor-homologous molecule expressed on type 2 helper T cells (CRTH2), and bradykinin receptor type 2 (BK2R). The docking analysis identified amentoflavone, alpha-tocotrienol, neoxanthin, and isorhamnetin 3-O-rutinoside as possessing a high affinity for all the receptors. Subsequently, molecular dynamics (MD) simulations were used to analyze the key interactions; the free energy of binding was calculated through Generalized Born and Surface Area Solvation (MMGBSA), and the conformational changes were evaluated. Alpha-tocotrienol exhibited a high affinity while also inducing positive conformational changes across all targets. Amentoflavone primarily affected CRTH2, neoxanthin targeted NK1R, CRTH2, and BK2R, and isorhamnetin-3-O-rutinoside acted on NK1R. These findings suggest UD's potential to treat AR symptoms by inhibiting these targets. Notably, alpha-tocotrienol emerges as a promising multi-target inhibitor. Further in vivo and in vitro studies are needed for validation.

Structural basis of ligand recognition and design of antihistamines targeting histamine H4 receptor

The histamine H4 receptor (H4R) plays key role in immune cell function and is a highly valued target for treating allergic and inflammatory diseases. However, structural information of H4R remains elusive. Here, we report four cryo-EM structures of H4R/Gi complexes, with either histamine or synthetic agonists clobenpropit, VUF6884 and clozapine bound. Combined with mutagenesis, ligand binding and functional assays, the structural data reveal a distinct ligand binding mode where D943.32 and a π-π network determine the orientation of the positively charged group of ligands, while E1825.46, located at the opposite end of the ligand binding pocket, plays a key role in regulating receptor activity. The structural insight into H4R ligand binding allows us to identify mutants at E1825.46 for which the agonist clobenpropit acts as an inverse agonist and to correctly predict inverse agonism of a closely related analog with nanomolar potency. Together with the findings regarding receptor activation and Gi engagement, we establish a framework for understanding H4R signaling and provide a rational basis for designing novel antihistamines targeting H4R.

Discovery of the novel and potent histamine H1 receptor antagonists for treatment of allergic diseases

Desloratadine, a second-generation histamine H1 receptor antagonist, has established itself as a first-line drug for the treatment of allergic diseases. Despite its effectiveness, desloratadine exhibits an antagonistic effect on muscarinic M3 receptor, which can cause side effects such as dry mouth and urinary retention, ultimately limiting its clinical application. Herein, we describe the discovery of compound Ⅲ-4, a novel H1 receptor antagonist with significant H1 receptor antagonistic activity (IC50 = 24.12 nM) and enhanced selectivity towards peripheral H1 receptor. In particular, Ⅲ-4 exhibits reduced M3 receptor inhibitory potency (IC50 > 10,000 nM) and acceptable hERG inhibitory activity (17.6 ± 2.1 μM) compare with desloratadine. Additionally, Ⅲ-4 exhibits favorable pharmacokinetic properties, as well as in vivo efficacy and safety profiles. All of these reveal that Ⅲ-4 has potential to emerge as a novel H1 receptor antagonist for the treatment of allergic diseases. More importantly, the compound Ⅲ-4 (HY-078020) has recently been granted clinical approval.

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, NFϰB, 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.

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.

Effects of Antidepressants on Sleep in Post-traumatic Stress Disorder: An Overview of Reviews

Antidepressants are a commonly used, easily accessible, and overall safe treatment option for post-traumatic stress disorder (PTSD). The present review aims to evaluate the efficacy and safety of antidepressants in treating sleep disturbances in patients with PTSD. PubMed and the Cochrane Library were searched (July 2022) for systematic reviews and meta-analyses on the treatment of PTSD. Moreover, PubMed and ClinicalTrials.gov were searched for individual trials investigating the antidepressant treatment of PTSD (up to September 2022), and reference lists of all possibly relevant identified studies were screened. Sleep-related outcomes, i.e., total sleep time, sleep quality, dreams/ nightmares, insomnia, and somnolence, were extracted independently by at least two reviewers. Metaanalytic evaluations were performed wherever possible. 39 randomised controlled trials (RCTs) were identified; data from pooled analyses, reviews, and observational studies were used for antidepressants with a weak evidence base or when their findings were deemed important. Overall, scarce data exist on the effects of antidepressants on sleep outcomes among patients with PTSD. Some evidence may support the use of amitriptyline, nefazodone, paroxetine, and sertraline for improving sleep in patients with PTSD. Τhere was a meta-analytical trend indicating improvement of nightmares with fluoxetine, less insomnia with amitriptyline and more with brofaromine, as well as more somnolence with paroxetine vs. placebo, respectively. However, data from more than 1 RCT with a considerable number of patients were only available for paroxetine. Evidence is insufficient to draw safe conclusions. More and better-designed RCTs, with consistent reporting of sleep-related outcomes, are needed.

Novel benzothiazole derivatives as multitargeted-directed ligands for the treatment of Alzheimer's disease

Neurodegenerative diseases such as Alzheimer's disease (AD) are multifactorial with several different pathologic mechanisms. Therefore, it is assumed that multitargeted-directed ligands (MTDLs) which interact with different biological targets relevant to the diseases, might offer an improved therapeutic alternative than using the traditional "one-target, one-molecule" approach. Herein, we describe new benzothiazole-based derivatives as a privileged scaffold for histamine H₃ receptor ligands (H₃R). The most affine compound, the 3-(azepan-1-yl)propyloxy-linked benzothiazole derivative 4b, displayed a K_i value of 0.012 μM. The multitargeting potential of these H₃R ligands towards AChE, BuChE and MAO-B enzymes was evaluated to yield compound 3s (pyrrolidin-1-yl-(6-((5-(pyrrolidin-1-yl)pentyl)oxy)benzo[d]thiazol-2-yl)methanone) as the most promising MTDL with a K_i value of 0.036 μM at H₃R and IC₅₀ values of 6.7 µM, 2.35 µM, and 1.6 µM towards AChE, BuChE, and MAO-B, respectively. These findings suggest that compound 3s can be a lead structure for developing new multi-targeting anti-AD agents.

Functional GPCR Expression in Eukaryotic LEXSY System

G protein-coupled receptors (GPCRs) form the largest superfamily of membrane proteins in the human genome, and represent one of the most important classes of drug targets. Their structural studies facilitate rational drug discovery. However, atomic structures of only about 20% of human GPCRs have been solved to date. Recombinant production of GPCRs for structural studies at a large scale is challenging due to their low expression levels and stability. Therefore, in this study, we explored the efficacy of the eukaryotic system LEXSY (Leishmania tarentolae) for GPCR production. We selected the human A2A adenosine receptor (A2AAR), as a model protein, expressed it in LEXSY, purified it, and compared with the same receptor produced in insect cells, which is the most popular expression system for structural studies of GPCRs. The A2AAR purified from both expression systems showed similar purity, stability, ligand-induced conformational changes and structural dynamics, with a remarkably higher protein yield in the case of LEXSY expression. Overall, our results suggest that LEXSY is a promising platform for large-scale production of GPCRs for structural studies.

Antiedematogenic and Analgesic Activities of Abietic Acid in Mice

Exacerbated inflammatory responses to harmful stimuli can lead to significant pain, edema, and other complications that require pharmacological intervention. Abietic acid (AA) is a diterpene found as a significant constituent in pine species, and evidence has identified its biological potential. The present study aimed to evaluate abietic acid's antiedematogenic and anti-inflammatory activity in mice. Swiss mice (Mus musculus) weighing 20-30 g were treated with AA at 50, 100, and 200 mg/kg. The central nervous system (CNS) effects were evaluated using open-field and rotarod assays. The antinociceptive and anti-inflammatory screening was assessed by the acetic acid and formalin tests. The antiedematogenic activity was investigated by measuring paw edema induced by carrageenan, dextran, histamine, arachidonic acid, and prostaglandin, in addition to using a granuloma model. The oral administration of abietic acid (200 mg/Kg) showed no evidence of CNS effects. The compound also exhibited significant antiedematogenic and anti-inflammatory activities in the carrageenan and dextran models, mostly related to the inhibition of myeloperoxidase (MOP) activity and histamine action and, to a lesser extent, the inhibition of eicosanoid-dependent pathways. In the granuloma model, abietic acid's effect was less expressive than in the acute models investigated in this study. In conclusion, abietic acid has analgesic and antiedematogenic activities related to anti-inflammatory mechanisms.

Molecular dynamics and free energy calculations of clozapine bound to D2 and H1 receptors reveal a cardiometabolic mitigated derivative

Most atypical antipsychotics derive from a high dropout of drug treatments due to adverse cardiometabolic side effects. These side effects are caused, in part, by the H1 receptor blockade. The current work sought a clozapine derivative with a reduced affinity for the H1 receptor while maintaining its therapeutic effect linked to D2 receptor binding. Explicit molecular dynamics simulations and end-point free energy calculations of clozapine in complex with the D2 and H1 receptors embedded in cholesterol-rich lipid bilayers were performed to analyze the intermolecular interactions and address the relevance of clozapine-functional groups. Based on that, free energy perturbation calculations were performed to measure the change in free energy of clozapine structural modifications. Our results indicate the best clozapine derivative is the iodine atom substitution for chlorine. The latter is mainly due to electrostatic interaction loss for the H1 receptor, while the halogen orientation out of the D2 active site reduces the impact on the affinity.Communicated by Ramaswamy H. Sarma.

Structural insights into the agonists binding and receptor selectivity of human histamine H4 receptor

Histamine is a biogenic amine that participates in allergic and inflammatory processes by stimulating histamine receptors. The histamine H4 receptor (H4R) is a potential therapeutic target for chronic inflammatory diseases such as asthma and atopic dermatitis. Here, we show the cryo-electron microscopy structures of the H4R-Gq complex bound with an endogenous agonist histamine or the selective agonist imetit bound in the orthosteric binding pocket. The structures demonstrate binding mode of histamine agonists and that the subtype-selective agonist binding causes conformational changes in Phe3447.39, which, in turn, form the "aromatic slot". The results provide insights into the molecular underpinnings of the agonism of H4R and subtype selectivity of histamine receptors, and show that the H4R structures may be valuable in rational drug design of drugs targeting the H4R.

Structural diversity of leukotriene G-protein coupled receptors

Dihydroxy acid leukotriene (LTB4) and cysteinyl leukotrienes (LTC4, LTD4, and LTE4) are inflammatory mediators derived from arachidonic acid via the 5-lipoxygenase pathway. While structurally similar, these two types of leukotrienes (LTs) exert their functions through interactions with two distinct G protein-coupled receptor (GPCR) families, BLT and CysLT receptors, which share low sequence similarity and belong to phylogenetically divergent GPCR groups. Selective antagonism of LT receptors has been proposed as a promising strategy for the treatment of many inflammation-related diseases including asthma and chronic obstructive pulmonary disease, rheumatoid arthritis, cystic fibrosis, diabetes, and several types of cancer. Selective CysLT1R antagonists are currently used as antiasthmatic drugs, however, there are no approved drugs targeting CysLT2 and BLT receptors. In this review, we highlight recently published structures of BLT1R and CysLTRs revealing unique structural features of the two receptor families. X-ray and cryo-EM data shed light on their overall conformations, differences in functional motifs involved in receptor activation, and details of the ligand-binding pockets. An unexpected binding mode of the selective antagonist BIIL260 in the BLT1R structure makes it the first example of a compound targeting the sodium-binding site of GPCRs and suggests a novel strategy for the receptor activity modulation. Taken together, these recent structural data reveal dramatic differences in the molecular architecture of the two LT receptor families and pave the way to new therapeutic strategies of selective targeting individual receptors with novel tool compounds obtained by the structure-based drug design approach.

Recovery of the histamine H3 receptor activity lost in yeast cells through error-prone PCR and in vivo selection

G protein-coupled receptors (GPCRs) are the largest protein family in humans and are important drug targets. Yeast, especially Saccharomyces cerevisiae, is a useful host for modifying the function and stability of GPCRs through protein engineering, which is advantageous for mammalian cells. When GPCRs are expressed in yeast, their function is often impaired. In this study, we performed random mutagenesis using error-prone PCR and then an in vivo screening to obtain mutants that recovered the activity of the human histamine H3 receptor (H3R), which loses its signaling function when expressed in yeast. Four mutations with recovered activity were identified after screening. Three of the mutations were identified near the DRY and NPxxY motifs of H3R, which are important for activation and are commonly found in class A GPCRs. The mutants responded exclusively to the yeast YB1 strain harboring Gi-chimera proteins, showing retention of G protein specificity. Analysis of one of the mutants with recovered activity, C415R, revealed that it maintained its ligand-binding characteristics. The strategy used in this study may enable the recovery of the activity of other GPCRs that do not function in S. cerevisiae and may be useful in creating GPCRs mutants stabilized in their active conformations.

Tandem Oxidative Dearomatizations of Diphenylanthracene Atropisomers

The first examples of tandem oxidative dearomatizations of 9,10-diphenylanthracene atropisomers with ortho,ortho'- formyl substituents are presented. In the presence of KMnO4, their stereoselective tandem double oxidation and spirocyclization mainly afford the syn or anti dearomatized 9,10-diphthalide anthracenes. Using Pinnick's reagent and depending on the conditions, the oxidation can mainly lead to the corresponding syn or anti diacids in good yields or to three oxidation products. An unprecedented further oxidative ring expansion toward dibenzo[b,e]oxepines is also reported.

A Novel "Activation Switch" Motif Common to All Aminergic Receptors

Aminergic receptors are G protein-coupled receptors (GPCRs) that transduce signals from small endogenous biogenic amines to regulate intracellular signaling pathways. Agonist binding in the ligand binding pocket on the extracellular side opens and prepares a cavity on the intracellular face of the receptors to interact with and activate G proteins and β-arrestins. Here, by reviewing and analyzing all available aminergic receptor structures, we seek to identify activation-related conformational changes that are independent of the specific scaffold of the bound agonist, which we define as "activation conformational changes" (ACCs). While some common intracellular ACCs have been well-documented, identifying common extracellular ACCs, including those in the ligand binding pocket, is complicated by local adjustments to different ligand scaffolds. Our analysis shows no common ACCs at the extracellular ends of the transmembrane helices. Furthermore, the restricted access to the ligand binding pocket identified previously in some receptors is not universal. Notably, the Trp6.48 toggle switch and the Pro5.50-Ile3.40-Phe6.44 (PIF) motif at the bottom of the ligand binding pocket have previously been proposed to mediate the conformational consequences of ligand binding to the intracellular side of the receptors. Our analysis shows that common ACCs in the ligand binding pocket are associated with the PIF motif and nearby residues, including Trp6.48, but fails to support a shared rotamer toggle associated with activation. However, we identify two common rearrangements between the extracellular and middle subsegments, and propose a novel "activation switch" motif common to all aminergic receptors. This motif includes the middle subsegments of transmembrane helices 3, 5, and 6 and integrates both the PIF motif and Trp6.48.

Effects of the immunoglobulin/histamine complex on panic disorder concurrent with chronic spontaneous urticaria: a case report

BACKGROUND

Panic disorder and panic attacks are two of the most common problems in psychiatry. A psychoimmunological correlation between allergic diseases and panic disorder has been strongly suggested. Histamine H1 receptor antagonists have been suggested as alternative drugs for the treatment of panic disorder. Chronic spontaneous urticaria (CSU) and panic disorder improved simultaneously with selective serotonin reuptake inhibitor antidepressants. Panic disorder has also been treated with the antihistamine chlorpheniramine. The immunoglobulin/histamine complex is a histamine-fixed immunoglobulin preparation that was reported to be effective in treating CSU. This case report describes the successful treatment of a patient with concomitant panic disorder and CSU for 23 years using immunoglobulin/histamine complex therapy.

CASE PRESENTATION

This report describes a 52-year-old female Korean patient who suffered from CSU with panic disorder for 23 years. Basic allergy tests (blood tests and skin prick tests) were conducted before and after treatment for the evaluation of allergic conditions. A multiple allergosorbent test (MAST) for the detection of allergen-specific IgE levels was also performed. The clinical severity of CSU was evaluated using the urticaria severity score system. Diagnostic interviews systematically assessed the diagnostic criteria outlined by the DSM-V, and the patient was evaluated before, during and after treatment using the Beck Depression Inventory (BDI-2) for depression, the State-Trait Anxiety Inventory (STAI) for anxiety and the Beck Hopelessness Score (BHS) for hopelessness. The patient received 2 ml of Histobulin™ (12 mg human immunoglobulin/0.15 µg histamine complex) once a week by subcutaneous injection for the treatment of CSU. Initial improvement of CSU was achieved after the third injection. After the twenty-seventh injection of Histobulin™, she showed no symptoms or signs and ceased allergic medication use. With the remission of CSU, allergic rhinitis was also completely resolved. The frequency of the common cold was significantly decreased during and after treatment. The medication frequency and development of clinical manifestations of panic disorder changed in parallel with the clinical severity of CSU. Moreover, the patient exhibited no clinical manifestations and ceased medication for panic disorder and sleeping pills for insomnia simultaneously with the remission of CSU. In the psychological evaluation, the BDI, STAI and BHS scores improved accordingly.

CONCLUSIONS

The immunoglobulin/histamine complex was effective in treating CSU and concomitant panic disorder in this patient and could be effective in treating some types of panic disorder. Considering the mechanisms of action of histamine and the immunoglobulin/histamine complex together with the patient's clinical progress, histamine seemed to be related to panic disorder in this case. The concept of histamine-mediated syndromes, including allergies and psychiatric disorders, shows that a wider disease identity may be needed. Further studies on the immunopathogenesis of panic disorder and the mechanisms of action of the immunoglobulin/histamine complex are necessary.

pH Dependence of a GPR4 Selective Antagonist Hampers Its Therapeutic Potential

Inflammatory bowel disease (IBD) is characterized by chronic mucosal inflammation of the gastrointestinal tract and is associated with extracellular acidification of mucosal tissue. Several extracellular pH-sensing receptors, including G protein-coupled receptor 4 (GPR4), play an important role in the regulation of inflammatory and immune responses, and GPR4 deficiency has been shown to be protective in IBD animal models. To confirm the therapeutic potential of GPR4 antagonism in IBD, we tested Compound 13, a selective GPR4 antagonist, in the interleukin 10-/- mouse model of colitis. Despite good exposures and albeit there was a trend toward improvement for a few readouts, Compound 13 treatment did not improve colitis in this model, and there were no signs of target engagement. Interestingly, Compound 13 behaved as an "orthosteric" antagonist, i.e., its potency was pH dependent and mostly inactive at pH levels lower than 6.8 with preferential binding to the inactive conformation of GPR4. Mutagenesis studies confirmed Compound 13 likely binds to the conserved orthosteric binding site in G protein-coupled receptors, where a histidine sits in GPR4 likely preventing Compound 13 binding when protonated in acidic conditions. While the exact mucosal pH in the human disease and relevant IBD mice models is unknown, it is well established that the degree of acidosis is positively correlated with the degree of inflammation, suggesting Compound 13 is not an ideal tool to study the role of GPR4 in moderate to severe inflammatory conditions. SIGNIFICANCE STATEMENT: Compound 13, a reported selective GPR4 antagonist, has been widely used to assess the therapeutic potential of GPR4, a pH-sensing receptor, for numerous indications. Its pH dependence and mechanism of inhibition identified in this study clearly highlights the limitations of this chemotype for target validation.

Molecular Biophysics of Class A G Protein Coupled Receptors-Lipids Interactome at a Glance-Highlights from the A2A Adenosine Receptor

G protein-coupled receptors (GPCRs) are embedded in phospholipid membrane bilayers with cholesterol representing 34% of the total lipid content in mammalian plasma membranes. Membrane lipids interact with GPCRs structures and modulate their function and drug-stimulated signaling through conformational selection. It has been shown that anionic phospholipids form strong interactions between positively charged residues in the G protein and the TM5-TM6-TM 7 cytoplasmic interface of class A GPCRs stabilizing the signaling GPCR-G complex. Cholesterol with a high content in plasma membranes can be identified in more specific sites in the transmembrane region of GPCRs, such as the Cholesterol Consensus Motif (CCM) and Cholesterol Recognition Amino Acid Consensus (CRAC) motifs and other receptor dependent and receptor state dependent sites. Experimental biophysical methods, atomistic (AA) MD simulations and coarse-grained (CG) molecular dynamics simulations have been applied to investigate these interactions. We emphasized here the impact of phosphatidyl inositol-4,5-bisphosphate (PtdIns(4,5)P₂ or PIP₂), a minor phospholipid component and of cholesterol on the function-related conformational equilibria of the human A_2A adenosine receptor (A_2AR), a representative receptor in class A GPCR. Several GPCRs of class A interacted with PIP₂ and cholesterol and in many cases the mechanism of the modulation of their function remains unknown. This review provides a helpful comprehensive overview for biophysics that enter the field of GPCRs-lipid systems.

Insight into the Mode of Action of 8-Hydroxyquinoline-Based Blockers on the Histamine Receptor 2

Histamine receptor 2 (HR_H2) blockers are used to treat peptic ulcers and gastric reflux. Chlorquinaldol and chloroxine, which contain an 8-hydroxyquinoline (8HQ) core, have recently been identified as blocking HR_H2. To gain insight into the mode of action of 8HQ-based blockers, here, we leverage an HR_H2-based sensor in yeast to evaluate the role of key residues in the HR_H2 active site on histamine and 8HQ-based blocker binding. We find that the HR_H2 mutations D98A, F254A, Y182A, and Y250A render the receptor inactive in the presence of histamine, while HR_H2:D186A and HR_H2:T190A retain residual activity. Based on molecular docking studies, this outcome correlates with the ability of the pharmacologically relevant histamine tautomers to interact with D98 via the charged amine. Docking studies also suggest that, unlike established HR_H2 blockers that interact with both ends of the HR_H2 binding site, 8HQ-based blockers interact with only one end, either the end framed by D98/Y250 or T190/D186. Experimentally, we find that chlorquinaldol and chloroxine still inactivate HR_H2:D186A by shifting their engagement from D98 to Y250 in the case of chlorquinaldol and D186 to Y182 in the case of chloroxine. Importantly, the tyrosine interactions are supported by the intramolecular hydrogen bonding of the 8HQ-based blockers. The insight gained in this work will aid in the development of improved HR_H2 therapeutics. More generally, this work demonstrates that Gprotein-coupled receptor (GPCR)-based sensors in yeast can help elucidate the mode of action of novel ligands for GPCRs, a family of receptors that bind 30% of FDA therapeutics.

Function and Role of Histamine H1 Receptor in the Mammalian Heart

Histamine can change the force of cardiac contraction and alter the beating rate in mammals, including humans. However, striking species and regional differences have been observed. Depending on the species and the cardiac region (atrium versus ventricle) studied, the contractile, chronotropic, dromotropic, and bathmotropic effects of histamine vary. Histamine is present and is produced in the mammalian heart. Thus, histamine may exert autocrine or paracrine effects in the mammalian heart. Histamine uses at least four heptahelical receptors: H1, H2, H3 and H4. Depending on the species and region studied, cardiomyocytes express only histamine H1 or only histamine H2 receptors or both. These receptors are not necessarily functional concerning contractility. We have considerable knowledge of the cardiac expression and function of histamine H2 receptors. In contrast, we have a poor understanding of the cardiac role of the histamine H1 receptor. Therefore, we address the structure, signal transduction, and expressional regulation of the histamine H1 receptor with an eye on its cardiac role. We point out signal transduction and the role of the histamine H1 receptor in various animal species. This review aims to identify gaps in our knowledge of cardiac histamine H1 receptors. We highlight where the published research shows disagreements and requires a new approach. Moreover, we show that diseases alter the expression and functional effects of histamine H1 receptors in the heart. We found that antidepressive drugs and neuroleptic drugs might act as antagonists of cardiac histamine H1 receptors, and believe that histamine H1 receptors in the heart might be attractive targets for drug therapy. The authors believe that a better understanding of the role of histamine H1 receptors in the human heart might be clinically relevant for improving drug therapy.

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-G_q 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-G_q 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-G_q complex and rather induces an inactive conformation in the absence of the G_q 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.

Improving the Modeling of Extracellular Ligand Binding Pockets in RosettaGPCR for Conformational Selection

G protein-coupled receptors (GPCRs) are the largest class of drug targets and undergo substantial conformational changes in response to ligand binding. Despite recent progress in GPCR structure determination, static snapshots fail to reflect the conformational space of putative binding pocket geometries to which small molecule ligands can bind. In comparative modeling of GPCRs in the absence of a ligand, often a shrinking of the orthosteric binding pocket is observed. However, the exact prediction of the flexible orthosteric binding site is crucial for adequate structure-based drug discovery. In order to improve ligand docking and guide virtual screening experiments in computer-aided drug discovery, we developed RosettaGPCRPocketSize. The algorithm creates a conformational ensemble of biophysically realistic conformations of the GPCR binding pocket between the TM bundle, which is consistent with a knowledge base of expected pocket geometries. Specifically, tetrahedral volume restraints are defined based on information about critical residues in the orthosteric binding site and their experimentally observed range of Cα-Cα-distances. The output of RosettaGPCRPocketSize is an ensemble of binding pocket geometries that are filtered by energy to ensure biophysically probable arrangements, which can be used for docking simulations. In a benchmark set, pocket shrinkage observed in the default RosettaGPCR was reduced by up to 80% and the binding pocket volume range and geometric diversity were increased. Compared to models from four different GPCR homology model databases (RosettaGPCR, GPCR-Tasser, GPCR-SSFE, and GPCRdb), the here-created models showed more accurate volumes of the orthosteric pocket when evaluated with respect to the crystallographic reference structure. Furthermore, RosettaGPCRPocketSize was able to generate an improved realistic pocket distribution. However, while being superior to other homology models, the accuracy of generated model pockets was comparable to AlphaFold2 models. Furthermore, in a docking benchmark using small-molecule ligands with a higher molecular weight between 400 and 700 Da, a higher success rate in creating native-like binding poses was observed. In summary, RosettaGPCRPocketSize can generate GPCR models with realistic orthosteric pocket volumes, which are useful for structure-based drug discovery applications.

Structure-based pharmacophore modeling 2. Developing a novel framework for structure-based pharmacophore model generation and selection

Pharmacophore models are three-dimensional arrangements of molecular features required for biological activity that are used in ligand identification efforts for many biological targets, including G protein-coupled receptors (GPCR). Though GPCR are integral membrane proteins of considerable interest as targets for drug development, many of these receptors lack known ligands or experimentally determined structures necessary for ligand- or structure-based pharmacophore model generation, respectively. Thus, we here present a structure-based pharmacophore modeling approach that uses fragments placed with Multiple Copy Simultaneous Search (MCSS) to generate high-performing pharmacophore models in the context of experimentally determined, as well as modeled GPCR structures. Moreover, we have addressed the oft-neglected topic of pharmacophore model selection via development of a cluster-then-predict machine learning workflow. Herein score-based pharmacophore models were generated in experimentally determined and modeled structures of 13 class A GPCR and resulted in pharmacophore models exhibiting high enrichment factors when used to search a database containing 569 class A GPCR ligands. In addition, classification of pharmacophore models with the best performing cluster-then-predict logistic regression classifier resulted in positive predictive values (PPV) of 0.88 and 0.76 for selecting high enrichment pharmacophore models from among those generated in experimentally determined and modeled structures, respectively.

Antiseizure Properties of Histamine H3 Receptor Antagonists Belonging 3,4-Dihydroquinolin-2(1H)-Ones

H₃R is becoming an attractive and promising target for epilepsy treatment as well as the discovery of antiepileptics. In this work, a series of 6-aminoalkoxy-3,4-dihydroquinolin-2(1H)-ones was prepared to screen their H₃R antagonistic activities and antiseizure effects. The majority of the target compounds displayed a potent H₃R antagonistic activity. Among them, compounds 2a, 2c, 2h, and 4a showed submicromolar H₃R antagonistic activity with an IC₅₀ of 0.52, 0.47, 0.12, and 0.37 μM, respectively. The maximal electroshock seizure (MES) model screened out three compounds (2h, 4a, and 4b) with antiseizure activity. Meanwhile, the pentylenetetrazole (PTZ)-induced seizure test gave a result that no compound can resist the seizures induced by PTZ. Additionally, the anti-MES action of compound 4a fully vanished when it was administrated combined with an H₃R agonist (RAMH). These results showed that the antiseizure role of compound 4a might be achieved by antagonizing the H₃R receptor. The molecular docking of 2h, 4a, and PIT with the H₃R protein predicted their possible binding patterns and gave a presentation that 2h, 4a, and PIT had a similar binding model with H₃R.

Treatment of allergy: Overview of synthetic anti-allergy small molecules in medicinal chemistry

The prevalence of allergic diseases has been continuously increasing over the past few decades, affecting approximately 20-30% of the global population. Allergic reactions to infection of respiratory tract, digestive tract, and skin system involve multiple different targets. The main difficulty of anti-allergy research is how to develop drugs with good curative effect and less side effects by adopting new multi-targets and mechanisms according to the clinical characteristics of different allergic populations and different allergens. This review focuses on information concerning potential therapeutic targets as well as the synthetic anti-allergy small molecules with respect to their medicinal chemistry. The structure-activity relationship and the mechanism of compound-target interaction were highlighted with perspective to histamine-1/4 receptor antagonists, leukotriene biosynthesis, Th2 cytokines inhibitors, and calcium channel blockers. We hope that the study of chemical scaffold modification and optimization for different lead compounds summarized in this review not only lays the foundation for improvement of success rate and efficiency of virtual screening of antiallergic drugs, but also can provide valuable reference for the drug design of related promising research such as allergy, inflammation, and cancer.

Function and structure of bradykinin receptor 2 for drug discovery

Type 2 bradykinin receptor (B2R) is an essential G protein-coupled receptor (GPCR) that regulates the cardiovascular system as a vasodepressor. Dysfunction of B2R is also closely related to cancers and hereditary angioedema (HAE). Although several B2R agonists and antagonists have been developed, icatibant is the only B2R antagonist clinically used for treating HAE. The recently determined structures of B2R have provided molecular insights into the functions and regulation of B2R, which shed light on structure-based drug design for the treatment of B2R-related diseases. In this review, we summarize the structure and function of B2R in relation to drug discovery and discuss future research directions to elucidate the remaining unknown functions of B2R dimerization.

Structures and Anti-Allergic Activities of Natural Products from Marine Organisms

In recent years, allergic diseases have occurred frequently, affecting more than 20% of the global population. The current first-line treatment of anti-allergic drugs mainly includes topical corticosteroids, as well as adjuvant treatment of antihistamine drugs, which have adverse side effects and drug resistance after long-term use. Therefore, it is essential to find alternative anti-allergic agents from natural products. High pressure, low temperature, and low/lack of light lead to highly functionalized and diverse functional natural products in the marine environment. This review summarizes the information on anti-allergic secondary metabolites with a variety of chemical structures such as polyphenols, alkaloids, terpenoids, steroids, and peptides, obtained mainly from fungi, bacteria, macroalgae, sponges, mollusks, and fish. Molecular docking simulation is applied by MOE to further reveal the potential mechanism for some representative marine anti-allergic natural products to target the H1 receptor. This review may not only provide insight into information about the structures and anti-allergic activities of natural products from marine organisms but also provides a valuable reference for marine natural products with immunomodulatory activities.

Design, synthesis and evaluation of 1-(1,5-bis(4-substituted phenyl)-2-methyl-1H-pyrrol-3-yl)-N-methylmethanamines as SERT inhibitors with potential antidepressant action

BM212 is a potent anti-TB agent with pharmacophoric features similar to the antidepressant drug sertraline. The shape-based virtual screening of the DrugBank database on BM212 resulted in the identification of several CNS drugs with appreciable Tanimoto scores. The docking simulations also ascertained the selectivity of BM212 towards the serotonin reuptake transporter protein (SERT) with a docking score of -6.51 kcal mol-1. Based on the SAR data available for sertraline and other antidepressant drugs, we designed, synthesized and screened twelve 1-(1,5-bis(4-substituted phenyl)-2-methyl-1H-pyrrol-3-yl)-N-methylmethanamines (SA-1 to SA-12) for in vitro SERT inhibition and in vivo antidepressant activity. The compounds were screened for in vitro 5HT reuptake inhibition using the platelet model. Among the screened compounds, (1-(1,5-bis(4-chlorophenyl)-2-methyl-1H-pyrrol-3-yl)-N-methylmethanamine) showed the same serotonin uptake inhibition (absorbance 0.22) as that of the standard drug sertraline (absorbance 0.22). BM212 had an effect on 5-HT uptake, albeit a weaker one compared to the standard (absorbance 0.671). Further, SA-5 was screened for in vivo antidepressant activity using the unpredictable chronic mild stress (UCMS) protocol to induce depression in mice. The effect of BM212 and SA-5 on the behaviour of the animals was assessed and compared against the standard drug sertraline. SA-5 at 20 mg per kg body weight was found to have a statistically significant impact on the behaviour of depressed animals.

Computational Chemistry for the Identification of Lead Compounds for Radiotracer Development

The use of computer-aided drug design (CADD) for the identification of lead compounds in radiotracer development is steadily increasing. Traditional CADD methods, such as structure-based and ligand-based virtual screening and optimization, have been successfully utilized in many drug discovery programs and are highlighted throughout this review. First, we discuss the use of virtual screening for hit identification at the beginning of drug discovery programs. This is followed by an analysis of how the hits derived from virtual screening can be filtered and culled to highly probable candidates to test in in vitro assays. We then illustrate how CADD can be used to optimize the potency of experimentally validated hit compounds from virtual screening for use in positron emission tomography (PET). Finally, we conclude with a survey of the newest techniques in CADD employing machine learning (ML).

Structure-based pharmacophore modeling 1. Automated random pharmacophore model generation

Pharmacophores are three-dimensional arrangements of molecular features required for biological activity that are often used in virtual screening efforts to prioritize ligands for experimental testing. G protein-coupled receptors (GPCR) are integral membrane proteins of considerable interest as targets for ligand discovery and drug development. Ligand-based pharmacophore models can be constructed to identify structural commonalities between known bioactive ligands for targets including GPCR. However, structure-based pharmacophores (which only require an experimentally determined or modeled structure for a protein target) have gained more attention to aid in virtual screening efforts as the number of publicly available experimentally determined GPCR structures have increased (140 unique GPCR represented as of October 24, 2022). Thus, the goal of this study was to develop a method of structure-based pharmacophore model generation applicable to ligand discovery for GPCR that have few known ligands. Pharmacophore models were generated within the active sites of 8 class A GPCR crystal structures via automated annotation of 5 randomly selected functional group fragments to sample diverse combinations of pharmacophore features. Each of the 5000 generated pharmacophores was then used to search a database containing active and decoy/inactive compounds for 30 class A GPCR and scored using enrichment factor and goodness-of-hit metrics to assess performance. Application of this method to the set of 8 class A GPCR produced pharmacophore models possessing the theoretical maximum enrichment factor value in both resolved structures (8 of 8 cases) and homology models (7 of 8 cases), indicating that generated pharmacophore models can prove useful in the context of virtual screening.

Supplementation of syringic acid-rich Phrynium pubinerve leaves imparts protection against allergic inflammatory responses by downregulating iNOS, COX-2, and NF-κB expressions

Background

The present study was designed to characterize the role of ethanolic leaf extract of Phrynium pubinerve Blume (EPP) supplement in attenuating allergic inflammation, encouraged by the presence of syringic acid in it, as this phenolic acid is reportedly promising in suppressing serum immunoglobulin E (IgE) and inflammatory cytokine levels.

Materials and methods

HPLC-DAD dereplication analysis was performed to determine the presence of the vital polyphenolic metabolites. The efficacy of EPP against lipopolysaccharide (LPS)-induced inflammation in RAW 264.7 cells was evaluated by measuring its inhibitory effects on NO and ROS/RNS production. The expressions of major inflammation-associated molecules (iNOS, COX-2, NF-κB, IL-6, and TNF-α) in RAW 264.7 cells were assessed through Western blot. Physiological and behavioral changes, BMI, and different biochemical parameters in mice blood serum were investigated in the toxicological assays. Formaldehyde-induced paw edema test in mice was conducted using established animal model. TDI-induced allergic model in mice was carried out to determine different allergy-like symptoms, and differential white blood cell (WBC) counts in blood and bronchoalveolar lavage (BAL) fluid. The intermolecular interaction analysis of the identified major metabolite of EPP with H1R and iNOS was studied by molecular docking.

Results

HPLC-DAD analysis showed the presence of syringic acid (89.19 mg/100 g EPP) and a few other compounds. LPS-induced NO generation was reduced by EPP in a concentration-dependent manner, showing IC50 of 28.20 ± 0.27 μg/mL. EPP exhibited a similar inhibitory effect on ROS/RNS production with IC50 of 29.47 ± 2.19 μg/mL. Western blotting revealed that EPP significantly downregulated the expressions of iNOS, COX-2, NF-κB, IL-6, and TNF-α in RAW 264.7 cells when challenged with LPS. The toxicological assays confirmed the dosage and organ-specific safety of EPP. In the formaldehyde-induced paw edema test, EPP caused a 66.41% reduction in mice paw volume at 500 mg/kg dose. It ameliorated TDI-induced allergy-like symptoms and decreased different inflammatory WBCs in mice's blood and BAL fluid in a dose-dependent manner. Finally, syringic acid demonstrated mentionable intermolecular binding affinity towards H1R (-6.6 Kcal/moL) and iNOS (-6.7 Kcal/moL).

Conclusions

Collectively, considerable scientific reasoning was obtained in favor of the suppressive potential of EPP against allergic inflammatory responses that are proposed to be exerted via the downregulation of iNOS, COX-2, and NF-κB expressions, H1R antagonism and suppression of cytokines, such as IL-6, and TNF-α.