Histamine H3 receptor and cholinesterases as synergistic targets for cognitive decline: Strategies to the rational design of multitarget ligands

Antihistamines H1 as Potential Anthelmintic Agents against the Zoonotic Parasite Angiostrongylus cantonensis

Infections caused by parasitic helminths pose significant health concerns for both humans and animals. The limited efficacy of existing drugs underscores the urgent need for novel anthelmintic agents. Given the reported potential of antihistamines against various parasites, including worms, this study conducted a screening of clinically available antihistamines against Angiostrongylus cantonensis-a nematode with widespread implications for vertebrate hosts, including humans. Twenty-one anti-H1 antihistamines were screened against first-stage larvae (L1) of A. cantonensis obtained from the feces of infected rats. Standard anthelmintic drugs ivermectin and albendazole were employed for comparative analysis. The findings revealed four active compounds (promethazine, cinnarizine, desloratadine, and rupatadine), with promethazine demonstrating the highest potency (EC50 = 31.6 μM). Additionally, morphological analysis showed that antihistamines induced significant changes in larvae. To understand the mechanism of action, antimuscarinic activities were reported based on average pK i values for human muscarinic receptor (mAChR) subtypes of the evaluated compounds. Furthermore, an analysis of the physicochemical and pharmacodynamic properties of antihistamines revealed that their anthelmintic activity does not correlate with their activity at H1 receptors. This study marks the first documentation of antihistamines' activity against A. cantonensis, offering a valuable contribution to the quest for novel agents effective against zoonotic helminths.

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

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

4-Oxypiperidine Ethers as Multiple Targeting Ligands at Histamine H3 Receptors and Cholinesterases

This study examines the properties of a novel series of 4-oxypiperidines designed and synthesized as histamine H3R antagonists/inverse agonists based on the structural modification of two lead compounds, viz., ADS003 and ADS009. The products are intended to maintain a high affinity for H3R while simultaneously inhibiting AChE or/and BuChE enzymes. Selected compounds were subjected to hH3R radioligand displacement and gpH3R functional assays. Some of the compounds showed nanomolar affinity. The most promising compound in the naphthalene series was ADS031, which contained a benzyl moiety at position 1 of the piperidine ring and displayed 12.5 nM affinity at the hH3R and the highest inhibitory activity against AChE (IC50 = 1.537 μM). Eight compounds showed over 60% eqBuChE inhibition and hence were qualified for the determination of the IC50 value at eqBuChE; their values ranged from 0.559 to 2.655 μM. Therapy based on a multitarget-directed ligand combining H3R antagonism with additional AChE/BuChE inhibitory properties might improve cognitive functions in multifactorial Alzheimer's disease.

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.

Multitargeting Histamine H3 Receptor Ligands among Acetyl- and Propionyl-Phenoxyalkyl Derivatives

Alzheimer's disease (AD) is a neurodegenerative disorder, for which there is no effective cure. Current drugs only slow down the course of the disease, and, therefore, there is an urgent need to find effective therapies that not only treat, but also prevent it. Acetylcholinesterase inhibitors (AChEIs), among others, have been used for years to treat AD. Histamine H₃ receptors (H₃Rs) antagonists/inverse agonists are indicated for CNS diseases. Combining AChEIs with H₃R antagonism in one structure could bring a beneficial therapeutic effect. The aim of this study was to find new multitargetting ligands. Thus, continuing our previous research, acetyl- and propionyl-phenoxy-pentyl(-hexyl) derivatives were designed. These compounds were tested for their affinity to human H₃Rs, as well as their ability to inhibit cholinesterases (acetyl- and butyrylcholinesterases) and, additionally, human monoamine oxidase B (MAO B). Furthermore, for the selected active compounds, their toxicity towards HepG2 or SH-SY5Y cells was evaluated. The results showed that compounds 16 (1-(4-((5-(azepan-1-yl)pentyl)oxy)phenyl)propan-1-one) and 17 (1-(4-((6-(azepan-1-yl)hexyl)oxy)phenyl)propan-1-one) are the most promising, with a high affinity for human H₃Rs (K_i: 30 nM and 42 nM, respectively), a good ability to inhibit cholinesterases (16: AChE IC₅₀ = 3.60 µM, BuChE IC₅₀ = 0.55 µM; 17: AChE IC₅₀ = 1.06 µM, BuChE IC₅₀ = 2.86 µM), and lack of cell toxicity up to 50 µM.

Beyond monoamines: I. Novel targets and radiotracers for Positron emission tomography imaging in psychiatric disorders

With the emergence of positron emission tomography (PET) in the late 1970s, psychiatry had access to a tool capable of non-invasive assessment of human brain function. Early applications in psychiatry focused on identifying characteristic brain blood flow and metabolic derangements using radiotracers such as [¹⁵ O]H₂ O and [¹⁸ F]FDG. Despite the success of these techniques, it became apparent that more specific probes were needed to understand the neurochemical bases of psychiatric disorders. The first neurochemical PET imaging probes targeted sites of action of neuroleptic (dopamine D₂ receptors) and psychoactive (serotonin receptors) drugs. Based on the centrality of monoamine dysfunction in psychiatric disorders and the measured success of monoamine-enhancing drugs in treating them, the next 30 years witnessed the development of an armamentarium of PET radiopharmaceuticals and imaging methodologies for studying monoamines. Continued development of monoamine-enhancing drugs over this time however was less successful, realizing only modest gains in efficacy and tolerability. As patent protection for many widely prescribed and profitable psychiatric drugs lapsed, drug development pipelines shifted away from monoamines in search of novel targets with the promises of improved efficacy, or abandoned altogether. Over this period, PET radiopharmaceutical development activities closely paralleled drug development priorities resulting in the development of new PET imaging agents for non-monoamine targets. Part one of this review will briefly survey novel PET imaging targets with relevance to the field of psychiatry, which include the metabotropic glutamate receptor type 5 (mGluR5), purinergic P₂ X₇ receptor, type 1 cannabinoid receptor (CB₁ ), phosphodiesterase 10A (PDE10A), and describe radiotracers developed for these and other targets that have matured to human subject investigations. Current limitations of the targets and techniques will also be discussed.

Multitargeting approaches to cognitive impairment: Synthesis of aryl-alkylpiperazines and assessment at cholinesterases, histamine H3 and dopamine D3 receptors

Multitargeting ligands on enzymes and receptors may generate a profile for a potential treatment of cognitive impairment. Considering this, a set of 21 substituted aryl-alkyl-piperazines were designed, prepared and tested for their binding affinities at histamine H₃ and dopamine D₃ receptors (H₃R and D₃R, respectively) as well as acetyl- and butyrylcholinesterases (AChE/BChE) as potentially synergistic profile. Initial screening of the compounds at H₃R and D₃R was done at 1 or 10 µM and 100 µM at AChE and BChE assays. The most promising compounds were then evaluated in full concentration-response curves to estimate the K_i and IC₅₀ values. Results showed that several compounds were ligands at H₃R (n = 10), D₃R (n = 6), AChE (n = 3), and BChE (n = 9). Compounds LINS05006 (K_i H₃R 2.8 µM; D₃R 0.7 µM; IC₅₀ BChE 26.3 µM) and LINS05015 (K_i H₃R 1.1 µM; D₃R 3.1 µM; IC₅₀ AChE 97.8 µM; BChE 43.7 µM) are highlighted since presented affinity in three different. These results suggest that methylpiperazine moiety led to balanced activity at all three classes of targets, and longer linker provided the best affinities. These compounds presented high ligand efficiency values (LE > 0.3) and may have adequate pharmacokinetic profile as suggested by calculated physicochemical properties.

Ring-fused 3β-acetoxyandrost-5-enes as novel neuroprotective agents with cholinesterase inhibitory properties

Alzheimer´s disease (AD) is an intellectual disorder caused by organic brain damage and cerebral atrophy, characterized by the loss of memory, judgment, and abstract thinking followed by declining cognitive functions, language, and the ability to perform daily living activities. Many efforts have been made to decrease the effects of the disease but also to block the neurodegenerative process. Cholinesterase inhibitors (ChEIs) are a group of medicines that act at the neurotransmission of acetylcholine, preventing its excessive breakdown and helping to improve cognitive functions in patients with AD. In this work, 16 chiral steroids, namely ring-fused 3β-acetoxyandrost-5-ene derivatives, their precursor and two 16-dehydroprogesterone-derived dioximes, were assessed as cholinesterase inhibitors and neuroprotective agents. The results demonstrated that some of the tested steroids are cholinesterase inhibitors and the majority selective for acetylcholinesterase inhibition. Albeit, one ring-fused 3β-acetoxyandrost-5-ene containing N-methylpiperidine ring (compound 2g) demonstrated to be a selective and potent inhibitor of the butyrylcholinesterase enzyme. (S)- 4,4a,5,6,7,8-(hexahydronaphthalen-2-one)-fused 3β-acetoxyandrost-5-ene (compound 6) showed high neuroprotective effect, high ability to restore the mitochondrial membrane potential from glutamate intoxication, and dramatic improvement in cell morphology. The described results provided relevant structure-activity relationship data.

Anti-inflammatory effects of new human histamine H3 receptor ligands with flavonoid structure on BV-2 neuroinflammation

OBJECTIVE

Microglia play an important role in the neuroinflammation developed in response to various pathologies. In this study, we examined the anti-inflammatory effect of the new human histamine H₃ receptor (H₃R) ligands with flavonoid structure in murine microglial BV-2 cells.

MATERIAL AND METHODS

The affinity of flavonoids (E243 -flavone and IIIa-IIIc-chalcones) for human H₃R was evaluated in the radioligand binding assay. The cytotoxicity on BV-2 cell viability was investigated with the MTS assay. Preliminary evaluation of anti-inflammatory properties was screened by the Griess assay in an in vitro neuroinflammation model of LPS-treated BV-2 cells. The expression and secretion of pro-inflammatory cytokines were evaluated by real-time qPCR and ELISA, respectively. The expression of microglial cell markers were determined by immunocytochemistry.

RESULTS

Chalcone derivatives showed high affinity at human H₃R with K_i values < 25 nM. At the highest nontoxic concentration (6.25 μM) compound IIIc was the most active in reducing the level of nitrite in Griess assay. Additionally, IIIc treatment attenuated inflammatory process in murine microglia cells by down-regulating pro-inflammatory cytokines (IL-1β, IL-6, TNF-α) at both the level of mRNA and protein level. Our immunocytochemistry studies revealed expression of microglial markers (Iba1, CD68, CD206) in BV-2 cell line.

CONCLUSIONS

These results emphasize the importance of further research to accurately identify the anti-inflammatory mechanism of action of chalcones.

Benzophenone Derivatives with Histamine H3 Receptor Affinity and Cholinesterase Inhibitory Potency as Multitarget-Directed Ligands for Possible Therapy of Alzheimer's Disease

The multitarget-directed ligands demonstrating affinity to histamine H₃ receptor and additional cholinesterase inhibitory potency represent a promising strategy for research into the effective treatment of Alzheimer's disease. In this study, a novel series of benzophenone derivatives was designed and synthesized. Among these derivatives, we identified compound 6 with a high affinity for H₃R (K_i = 8 nM) and significant inhibitory activity toward BuChE (IC₅₀ = 172 nM and 1.16 µM for eqBuChE and hBuChE, respectively). Further in vitro studies revealed that compound 6 (4-fluorophenyl) (4-((5-(piperidin-1-yl)pentyl)oxy)phenyl)methanone) displays moderate metabolic stability in mouse liver microsomes, good permeability with a permeability coefficient value (P_e) of 6.3 × 10^-6 cm/s, and its safety was confirmed in terms of hepatotoxicity in the HepG2 cell line. Therefore, we investigated the in vivo activity of compound 6 in the Passive Avoidance Test and the Formalin Test. While compound 6 did not show a statistically significant influence on memory and learning, it showed analgesic properties in both acute (ED₅₀ = 20.9 mg/kg) and inflammatory (ED₅₀ = 17.5 mg/kg) pain.

Neurotoxicity Assessment of 1-[(2,3-Dihydro-1-Benzofuran-2-yl)Methyl]Piperazine (LINS01 Series) Derivatives and their Protective Effect on Cocaine-Induced Neurotoxicity Model in SH-SY5Y Cell Culture

Excessive levels of dopamine in the synaptic cleft, induced by cocaine for example, activates dopaminergic receptors, mainly D₁R, D₂R, and D₃R subtypes, contributing to neurotoxic effects. New synthetic 1-[(2,3-dihydro-1-benzofuran-2-yl)methyl]piperazine derivatives (the LINS01 compounds), designed as histaminergic receptor (H₃R) ligands, are also dopaminergic receptor ligands, mainly D₂R and D₃R. This study aims to evaluate the neurotoxicity of these new synthetic LINS01 compounds (LINS01003, LINS01004, LINS01011, and LINS01018), as well as to investigate their protective potential on a cocaine model of dopamine-induced neurotoxicity using SH-SY5Y cell line culture. Neurotoxicity was assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH), and automated cell counting with fluorescent dyes (acridyl orange and propidium iodide) assays. Concentration-response curves (CRCs) were performed for all LINS compounds and cocaine using MTT assay. The results show that LINS series did not decrease cell viability after 48h of exposure-except for 100 µM LINS01018, which was discontinued from the study. Likewise, MTT, LDH, and fluorescent dyes staining showed no difference is cell viability for LINS compounds at 10 µM. When incubated with 2.5 mM cocaine (lethal concentration 50) for 48h, 10 µM of each LINS compound, metoclopramide (D₂R antagonist) and haloperidol (D₂R/D₃R antagonist), ameliorated cocaine-induced neurotoxicity. However, only metoclopramide, haloperidol, and LINS01011 compound significantly decreased LDH released in the culture medium, suggesting that this new synthetic compound presents a more robust effect. This preliminary in vitro neurotoxicity study suggests that LINS01 compounds are not neurotoxic, and that they play a promising role in preventing cocaine-induced neurotoxicity.

Evaluation of the Histamine H3 Receptor Antagonists from LINS01 Series as Cholinesterases Inhibitors - Enzymatic and Modeling Studies

Histamine is involved in several CNS processes including cognition. In the last years, H₃ receptor (H₃ R) antagonists have been widely explored for their potential on dementias and other cognitive dysfunctions, and the cooperative role between histamine and acetylcholine neurotransmissions on cognitive processes is widely known in literature. This motivated us to assess the potential of 1-[(2,3-dihydrobenzofuran-1-yl)methyl]piperazines (LINS01 compounds) as inhibitors of cholinesterases, and thus this work presents the inhibitory effect of such compounds against acetyl (AChE) and butyrylcholinesterase (BChE). A set of 16 selected compounds were evaluated, being compounds 2d and 2e the most potent inhibitors of both cholinesterases (IC₅₀ 13.2 - 33.9 μM) by competitive mechanism, as indicated by the kinetic assays. Molecular docking simulations suggested that the allylpiperazine and dihydrobenzofuran motifs present in these compounds are important to perform π-interactions with key tryptophan residues from the enzymes, increasing their affinity for both H₃ R and cholinesterases. Metric analysis support that compound 2d (LINS01022) should be highlighted due to its balanced lipophilicity (ClogP 2.35) and efficiency (LE 0.32) as AChE inhibitor. The results add important information to future design of dual H₃ R-cholinesterases ligands.