Alleviation of Multiple Asthmatic Pathologic Features with Orally Available and Subtype Selective GABAA Receptor Modulators

Gut health benefits and associated systemic effects provided by functional components from the fermentation of natural matrices

Recently, the role of the gut microbiota in metabolic health, immunity, behavioral balance, longevity, and intestine comfort has been the object of several studies from scientific communities. They were encouraged by a growing interest from food industries and consumers toward novel fermented ingredients and formulations with powerful biological effects, such as pre, pro, and postbiotic products. Depending on the selected strains, the operating conditions, the addition of suitable reagents or enzymes, the equipment, and the reactor configurations, functional compounds with high bioactivity, such as short-chain fatty acids, gamma-aminobutyric acid, bioactive peptides, and serotonin, can be enhanced and/or produced through fermentation of several vegetable matrices. Otherwise, their formation can also be promoted directly in the gut after the dietary intake of fermented foods: In this case, fermentation will aim to increase the content of precursor substances, such as indigestible fibers, polyphenols, some amino acids, and resistant starch, which can be potentially metabolized by endogenous gut microorganisms and converted in healthy molecules. This review provides an overview of the main functional components currently investigated in literature and the associated gut health benefits. The current state of the art about fermentation technology as a promising functionalization tool to promote the direct or indirect formation of gut-health-enhancing components was deepened, highlighting the importance of optimizing microorganism selection, system setups, and process conditions according to the target compound of interest. The collected data suggested the possibility of gaining novel functional food ingredients or products rich in functional molecules through fermentation without performing additional extraction and purification stages, which are needed when conventional culture broths are used.

Design, Synthesis, and Biological Evaluation of Novel Spiro Imidazobenzodiazepines to Identify Improved Inhaled Bronchodilators

Novel gamma-aminobutyric acid receptor (GABAAR) ligands structurally related to imidazobenzodiazepine MIDD0301 were synthesized using spiro-amino acid N-carboxyanhydrides (NCAs). These compounds demonstrated increased resistance to phase 2 metabolism and avoided the formation of a 6H isomer. Compound design was guided by molecular docking using the available crystal structure of the α1β3γ2 GABAAR and correlated with in vitro binding data. The carboxylic acid containing GABAAR ligands have high aqueous solubility, low permeability, and low cell toxicity. The inability of GABAAR ligands to cross the blood-brain barrier was confirmed in vivo by the absence of sensorimotor inhibition. Pharmacological activities at lung GABAARs were demonstrated by ex vivo relaxation of guinea pig airway smooth muscle and reduction of methacholine-induced airway hyperresponsiveness (AHR) in conscious mice. We identified bronchodilator 5c with an affinity of 9 nM for GABAARs that was metabolically stable in the presence of human and mouse microsomes.

Comparative pharmacodynamic and pharmacokinetic study of MIDD0301 and its (S) enantiomer

MIDD0301 is being developed as an oral drug to relax airway smooth muscle (ASM) and reduce lung inflammation in asthma. We report a comparative study of MIDD0301 and its S isomer (MIDD0301S), and found that the compounds have equivalent affinity for γ-aminobutyric acid type A receptor (GABA_A R) expressed in rat brain, with half maximal inhibitory concentration values of 25.1 and 26.3 nM for the S and R enantiomers, respectively. Both compounds relaxed substance P contracted ASM within 30 min and neither enantiomer revealed affinity to 48 receptors in an off-target screen. Both enantiomers reduced airway hyperresponsiveness (AHR) with nebulized and oral dosing in two mouse models of bronchoconstriction. In A/J mice, which are very sensitive to methacholine-induced bronchoconstriction, we observed reduction of AHR at 10.8 mg/kg MIDD0301 and 15 mg/kg MIDD0301S. Using oral administration, 100 mg/kg/day for 3 days of either enantiomer was sufficient to reduce AHR. In a model of severe airway inflammation induced by interferon-γ and lipopolysaccharide (LPS), we observed reduction of AHR at 7.2 mg/kg for both enantiomers using nebulized administration, and at 100 mg/kg for oral administration. MIDD0301 and MIDD0301S did not undergo Phase I metabolism. Glucuronidation was observed for both compounds, whereas only MIDD0301 formed the corresponding glucoside in the presence of kidney microsomes. Pharmacokinetic analysis identified glucuronides as the major metabolite with concentrations up to 20-fold more than the parent compound. MIDD0301 glucuronide and MIDD0301 taurine bind GABA_A Rs, although 10-fold weaker than MIDD0301. In mouse blood, the taurine adduct was only observed for MIDD0301. Overall, both compounds exhibited similar receptor binding and pharmacodynamic properties with subtle differences in metabolism and greater oral availability and blood concentrations of MIDD0301S.

Development of Inhaled GABAA Receptor Modulators to Improve Airway Function in Bronchoconstrictive Disorders

We report the modification of MIDD0301, an imidazodiazepine GABA_A receptor (GABA_AR) ligand, using two alkyl substituents. We developed PI310 with a 6-(4-phenylbutoxy)hexyl chain as used in the long-acting β2-agonist salmeterol and PI320 with a poly(ethylene glycol) chain as used to improve the brain:plasma ratio of naloxegol, a naloxone analogue. Both imidazodiazepines showed affinity toward the GABA_AR binding site of clonazepam, with IC₅₀ values of 576 and 242 nM, respectively. Molecular docking analysis, using the available α₁β₃γ₂ GABA_AR structural data, suggests binding of the diazepine core between the α1+/γ2- interface, whereas alkyl substituents are located outside the binding site and thus interact with the protein surface and solvent molecules. The physicochemical properties of these compounds are very different. The solubility of PI310 is low in water. PEGylation of PI320 significantly improves aqueous solubility and cell permeability. Neither compound is toxic in HEK293 cells following exposure at >300 μM for 18 h. Ex vivo studies using guinea pig tracheal rings showed that PI310 was unable to relax the constricted airway smooth muscle. In contrast, PI320 induced muscle relaxation at organ bath concentrations as low as 5 μM, with rapid onset (15 min) at 25 μM. PI320 also reduced airway hyper-responsiveness in vivo in a mouse model of steroid-resistant lung inflammation induced by intratracheal challenge with INFγ and lipopolysaccharide (LPS). At nebulized doses of 7.2 mg/kg, PI320 and albuterol were equally effective in reducing airway hyper-responsiveness. Ten minutes after nebulization, the lung concentration of PI320 was 50-fold that of PI310, indicating superior availability of PI320 when nebulized as an aqueous solution. Overall, PI320 is a promising inhaled drug candidate to quickly relax airway smooth muscle in bronchoconstrictive disorders, such as asthma. Future studies will evaluate the pharmacokinetic/pharmacodynamic properties of PI320 when administered orally.

GABAergic signaling by cells of the immune system: more the rule than the exception

Gamma-aminobutyric acid (GABA) is best known as an essential neurotransmitter in the evolved central nervous system (CNS) of vertebrates. However, GABA antedates the development of the CNS as a bioactive molecule in metabolism and stress-coupled responses of prokaryotes, invertebrates and plants. Here, we focus on the emerging findings of GABA signaling in the mammalian immune system. Recent reports show that mononuclear phagocytes and lymphocytes, for instance dendritic cells, microglia, T cells and NK cells, express a GABAergic signaling machinery. Mounting evidence shows that GABA receptor signaling impacts central immune functions, such as cell migration, cytokine secretion, immune cell activation and cytotoxic responses. Furthermore, the GABAergic signaling machinery of leukocytes is implicated in responses to microbial infection and is co-opted by protozoan parasites for colonization of the host. Peripheral GABA signaling is also implicated in inflammatory conditions and diseases, such as type 1 diabetes, rheumatoid arthritis and cancer cell metastasis. Adding to its role in neurotransmission, growing evidence shows that the non-proteinogenic amino acid GABA acts as an intercellular signaling molecule in the immune system and, as an interspecies signaling molecule in host–microbe interactions. Altogether, the data raise the assumption of conserved GABA signaling in a broad range of mammalian cells and diversification of function in the immune system.

Vasodilatory effects of a variety of positive allosteric modulators of GABAA receptors on rat thoracic aorta

Different subtypes of GABAA (gamma-aminobutyric acid A) receptors, through their specific regional and cellular localization, are involved in the manifestation of various functions, both at the central and peripheral levels. We hypothesized that various non-neuronal GABAA receptors are expressed on blood vessels, through which positive allosteric modulators of GABAA receptors exhibit vasodilatory effects. This study involved two parts: one to determine the presence of α1-6 subunit GABAA receptor mRNAs in the rat thoracic aorta, and the other to determine the vasoactivity of the various selective and non-selective positive GABAA receptor modulators: zolpidem (α1-selective), XHe-III-074 (α4-selective), MP-III-022 (α5-selective), DK-I-56-1 (α6-selective), SH-I-048A and diazepam (non-selective). Reverse transcription-polymerase chain reaction (RT-PCR) analysis data demonstrated for the first time the expression of α1, α2, α3, α4 and α5 subunits in the rat thoracic aorta tissue. Tissue bath assays on isolated rat aortic rings revealed significant vasodilatory effects of diazepam, SH-I-048A, XHe-III-074, MP-III-022 and DK-I-56-1, all in terms of achieved relaxations (over 50% of relative tension decrease), as well as in terms of preventive effects on phenylephrine (PE) contraction. Diazepam was the most efficient ligand in the present study, while zolpidem showed the weakest vascular effects. In addition, diazepam-induced relaxations in the presence of antagonists PK11195 or bicuculline were significantly reduced (P < 0.001 and P < 0.05, respectively) at lower concentrations of diazepam (10-7 M and 3 × 10-7 M). The present work suggests that the observed vasoactivity is due to modulation of "vascular" GABAA receptors, which after further detailed research may provide a therapeutic target.

Neuroimmune Pathophysiology in Asthma

Asthma is a chronic inflammation of lower airway disease, characterized by bronchial hyperresponsiveness. Type I hypersensitivity underlies all atopic diseases including allergic asthma. However, the role of neurotransmitters (NT) and neuropeptides (NP) in this disease has been less explored in comparison with inflammatory mechanisms. Indeed, the airway epithelium contains pulmonary neuroendocrine cells filled with neurotransmitters (serotonin and GABA) and neuropeptides (substance P[SP], neurokinin A [NKA], vasoactive intestinal peptide [VIP], Calcitonin-gene related peptide [CGRP], and orphanins-[N/OFQ]), which are released after allergen exposure. Likewise, the autonomic airway fibers produce acetylcholine (ACh) and the neuropeptide Y(NPY). These NT/NP differ in their effects; SP, NKA, and serotonin exert pro-inflammatory effects, whereas VIP, N/OFQ, and GABA show anti-inflammatory activity. However, CGPR and ACh have dual effects. For example, the ACh-M3 axis induces goblet cell metaplasia, extracellular matrix deposition, and bronchoconstriction; the CGRP-RAMP1 axis enhances Th2 and Th9 responses; and the SP-NK1R axis promotes the synthesis of chemokines in eosinophils, mast cells, and neutrophils. In contrast, the ACh-α7nAChR axis in ILC2 diminishes the synthesis of TNF-α, IL-1, and IL-6, attenuating lung inflammation whereas, VIP-VPAC1, N/OFQ-NOP axes cause bronchodilation and anti-inflammatory effects. Some NT/NP as 5-HT and NKA could be used as biomarkers to monitor asthma patients. In fact, the asthma treatment based on inhaled corticosteroids and anticholinergics blocks M3 and TRPV1 receptors. Moreover, the administration of experimental agents such as NK1R/NK2R antagonists and exogenous VIP decrease inflammatory mediators, suggesting that regulating the effects of NT/NP represents a potential novel approach for the treatment of asthma.

Nebulized MIDD0301 Reduces Airway Hyperresponsiveness in Moderate and Severe Murine Asthma Models

We report the relaxation of methacholine-constricted airways with nebulized MIDD0301, a positive allosteric γ-aminobutyric acid type A receptor (GABA_AR) modulator. The therapeutic efficacy of nebulized MIDD0301 in reducing airway resistance was investigated in spontaneous breathing mice using a whole-body plethysmograph and in unconscious mice using a forced oscillation technique. Prophylactic nebulized MIDD0301 reduced subsequent methacholine-induced bronchoconstriction in ovalbumin and house dust mite allergic asthma models and in normal mice. Nebulized MIDD0301 exhibited comparable or better therapeutic potency compared to nebulized albuterol and oral montelukast. Prophylactic nebulized MIDD0301 was also effective in reducing bronchoconstriction, comparable to nebulized albuterol or fluticasone, in a steroid resistant asthma mouse model induced by intratracheal installation of lipopolysaccharide and interferon-gamma. Oral dexamethasone was ineffective in this model. Nebulized MIDD0301 was also effective in reversing bronchospasm when dosed after methacholine challenge comparable to albuterol. Pharmacokinetic studies showed that about 0.06% of nebulized MIDD0301 entered the mouse lung when using a whole body plethysmograph and therapeutic levels were sustained in the lung for at least 25 min. Consistent with previous reports on orally dosed MIDD0301, high doses of nebulized MIDD0301 resulted in minimal brain exposure and thus no observable adverse sensorimotor or respiratory depression effects occurred. In addition, no adverse cardiovascular effects were observed following 100 mg/kg i.p. dosing. These results further demonstrate that charged imidazodiazepine MIDD0301 can selectively target lung GABA_AR without adverse motor, cardiovascular, or respiratory effects and inhaled dosing is effective in reducing bronchoconstriction in allergen and infectious lung inflammation.

A Benzodiazepine Ligand with Improved GABAA Receptor α5-Subunit Selectivity Driven by Interactions with Loop C

The family of GABA_A receptors is an important drug target group in the treatment of sleep disorders, anxiety, epileptic seizures, and many others. The most frequent GABA_A receptor subtype is composed of two α-, two β-, and one γ2-subunit, whereas the nature of the α-subunit critically determines the properties of the benzodiazepine binding site of those receptors. Nearly all of the clinically relevant drugs target all GABA_A receptor subtypes equally. In the past years, however, drug development research has focused on studying α5-containing GABA_A receptors. Beyond the central nervous system, α5-containing GABA_A receptors in airway smooth muscles are considered as an emerging target for bronchial asthma. Here, we investigated a novel compound derived from the previously described imidazobenzodiazepine SH-053-2'F-R-CH3 (SH53d-ester). Although SH53d-ester is only moderately selective for α5-subunit-containing GABA_A receptors, the derivative SH53d-acid shows superior (>40-fold) affinity selectivity and is a positive modulator. Using two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes and radioligand displacement assays with human embryonic kidney 293 cells, we demonstrated that an acid group as substituent on the imidazobenzodiazepine scaffold leads to large improvements of functional and binding selectivity for α5β3γ2 over other αxβ3γ2 GABA_A receptors. Atom level structural studies provide hypotheses for the improved affinity to this receptor subtype. Mutational analysis confirmed the hypotheses, indicating that loop C of the GABA_A receptor α-subunit is the dominant molecular determinant of drug selectivity. Thus, we characterize a promising novel α5-subunit-selective drug candidate. SIGNIFICANCE STATEMENT: In the current study we present the detailed pharmacological characterization of a novel compound derived from the previously described imidazobenzodiazepine SH-053-2'F-R-CH3. We describe its superior (>40-fold) affinity selectivity for α5-containing GABA_A receptors and show atom-level structure predictions to provide hypotheses for the improved affinity to this receptor subtype. Mutational analysis confirmed the hypotheses, indicating that loop C of the GABA_A receptor α-subunit is the dominant molecular determinant of drug selectivity.

Monocyte chemotactic protein-inducing protein 1 negatively regulating asthmatic airway inflammation and mucus hypersecretion involving γ-aminobutyric acid type A receptor signaling pathway in vivo and in vitro

BACKGROUND

Mounting evidence, consistent with our previous study, showed that γ-aminobutyric acid type A receptor (GABAAR) played an indispensable role in airway inflammation and mucus hypersecretion in asthma. Monocyte chemotactic protein-inducing protein 1 (MCPIP1) was a key negative regulator of inflammation. Recent studies showed that inflammation was largely suppressed by enhanced MCPIP1 expression in many inflammatory diseases. However, the role and potential mechanism of MCPIP1 in airway inflammation and mucus hypersecretion in asthma were still not well studied. This study was to explore the role of MCPIP1 in asthmatic airway inflammation and mucus hypersecretion in both mice and BEAS-2B cells, and its potential mechanism.

METHODS

In vivo, mice were sensitized and challenged by ovalbumin (OVA) to induce asthma. Airway inflammation and mucus secretion were analyzed. In vitro, BEAS-2B cells were chosen. Interleukin (IL)-13 was used to stimulate inflammation and mucus hypersecretion in cells. MCPIP1 Lentiviral vector (LA-MCPIP1) and plasmid-MCPIP1 were used to up-regulate MCPIP1 in lung and cells, respectively. MCP-1, thymic stromal lymphopoietin (TSLP), mucin 5AC (MUC5AC), MCPIP1, and GABAARβ2 expressions were measured in both lung and BEAS-2B cells. Immunofluorescence staining was performed to observe the expression of GABAARβ2 in cells.

RESULTS

MCPIP1 was up-regulated by LA-MCPIP1 (P < 0.001) and plasmid-MCPIP1 (P < 0.001) in lung and cells, respectively. OVA-induced airway inflammation and mucus hypersecretion, OVA-enhanced MCP-1, TSLP, MUC5AC, and GABAARβ2 expressions, and OVA-reduced MCPIP1 were significantly blunted by LA-MCPIP1 in mice (all P < 0.001). IL-13-enhanced MCP-1, TSLP, MUC5AC, and GABAARβ2 expressions, and IL-13-reduced MCPIP1 were markedly abrogated by plasmid-MCPIP1 in BEAS-2B cells (all P < 0.001).

CONCLUSION

The results of this study suggested that OVA and IL-13-induced airway inflammation and mucus hypersecretion were negatively regulated by MCPIP1 in both lung and BEAS-2B cells, involving GABAAR signaling pathway.

A Structure-Activity Relationship Comparison of Imidazodiazepines Binding at Kappa, Mu, and Delta Opioid Receptors and the GABAA Receptor

Analgesic and anti-inflammatory properties mediated by the κ opioid receptor (KOR) have been reported for oxadiazole imidazodiazepines. Affinities determined by radioligand competition assays of more than seventy imidazodiazepines using cell homogenates from HEK293 cells that overexpress KOR, µ opioid receptor (MOR), and δ opioid receptor (DOR) are presented. Affinities to synaptic, benzodiazepine-sensitive receptors (BZR) were determined with rat brain extract. The highest affinity for KOR was recorded for GL-I-30 (Ki of 27 nM) and G-protein recruitment was observed with an EC₅₀ of 32 nM. Affinities for MOR and DOR were weak for all compounds. Ester and amide imidazodiazepines were among the most active KOR ligands but also competed with ³H-flunitrazepam for brain extract binding, which is mediated predominately by gamma aminobutyric acid type A receptors (GABA_AR) of the α_1-3β_2-3γ_1-2 subtypes. Imidazodiazepines with carboxylic acid and primary amide groups did not bind KOR but interacted strongly with GABA_ARs. Pyridine substitution reduced KOR affinity. Oxadiazole imidazodiazepines exhibited good KOR binding and interacted weakly with BZR, whereas oxazole imidazodiazepines were more selective towards BZR. Compounds that lack the imidazole moiety, the pendent phenyl, or pyridine substitutions exhibited insignificant KOR affinities. It can be concluded that a subset of imidazodiazepines represents novel KOR ligands with high selectivity among opioid receptors.

Targeting Nitric Oxide Production in Microglia with Novel Imidazodiazepines for Nonsedative Pain Treatment

The goal of this research is the identification of new treatments for neuropathic pain. We characterized the GABAergic system of immortalized mouse and human microglia using electrophysiology and qRT-PCR. Cells from both species exhibited membrane current changes in response to γ-aminobutyric acid, with an EC50 of 260 and 1940 nM, respectively. Human microglia expressed high levels of the γ-aminobutyric acid type A receptor (GABAAR) α3 subunit, which can assemble with β1 and γ2/δ subunits to form functional GABAARs. Mouse microglia contained α2, α3, and α5, in addition to β1-3, γ1-2, and δ, mRNA, enabling a more diverse array of GABAARs than human microglia. Benzodiazepines are well-established modulators of GABAAR activity, prompting a screen of a library of diverse benzodiazepines in microglia for cellular effects. Several active compounds were identified by reduction of nitric oxide (NO) in interferon gamma and lipopolysaccharide activated microglia. However, further investigation with GABAAR antagonists flumazenil, picrotoxin, and bicuculline demonstrated that GABAARs were not linked to the NO response. A screen of 48 receptors identified the κ-opioid receptor and to a lesser extent the μ-opioid receptor as molecular targets, with opioid receptor antagonist norbinaltorphimine reversing benzodiazepine induced reduction of microglial NO. Functional assays identified the downregulation of inducible NO synthase as the mode of action of imidazodiazepines MP-IV-010 and GL-IV-03. Like other κ-opioid receptor agonists, GL-IV-03 reduced the agitation response in both phases of the formalin nociception test. However, unlike other κ-opioid receptor agonists, MP-IV-010 and GL-IV-03 did not impair sensorimotor coordination in mice. Thus, MP-IV-010 and GL-IV-03 represent a new class of nonsedative drug candidates for inflammatory pain.

GABAA receptor subtype modulators in medicinal chemistry: an updated patent review (2014-present)

Introduction: Ligands at the benzodiazepine binding site of the GABA_A receptor (GABA_AR) act by modulating the effect of GABA (γ-aminobutyric acid). The benzodiazepine drugs are conventionally categorized as positive allosteric modulators enhancing the chloride ion current GABA-induced. In literature there are also reported ligands that act as negative allosteric modulators, reducing chloride ion current, and silent allosteric modulators not influencing the chloride ion flux.Areas covered: This review covers patents published from 2014 to present on ligands for the benzodiazepine binding site of the GABA_ARs. Patents filed from different companies and research groups report many compounds that may be used in the treatment/prevention of a large variety of diseases.Expert opinion: Since the discovery of the first benzodiazepine about 60 years have passed and about 50 years since the identification of their target, GABA_A receptor. Even if benzodiazepines are the most popular anxiolytic drugs, the research in this field is still very active. From patents/application analysis arises that most of them claim methods for alleviating specific symptoms in different neurodegenerative diseases and their related memory deficits. Noteworthy is the presence of the α4- and α5-GABA_A receptor subtype ligands as new pharmacological tools for airway hyperresponsiveness, inflammation diseases, and asthma.

MIDD0301 - A first-in-class anti-inflammatory asthma drug targets GABAA receptors without causing systemic immune suppression

We report a 28-day repeat dose immunotoxicity evaluation of investigational drug MIDD0301, a novel oral asthma drug candidate that targets gamma amino butyric acid type A receptors (GABA_A R) in the lung. The study design employed oral administration of mice twice daily throughout the study period with 100 mg/kg MIDD0301 mixed in peanut butter. Compound dosing did not reveal signs of general toxicity as determined by animal weight, organ weight or haematology. Peanut butter plus test drug (in addition to ad libitum standard rodent chow) did not affect weight gain in the adult mice, in contrast to weight loss in 5 mg/kg prednisone-treated mice. Spleen and thymus weights were unchanged in MIDD0301-treated mice, but prednisone significantly reduced the weight of those organs over the 28-day dosing. Similarly, no differences in spleen or thymus histology were observed following MIDD0301 treatment, but prednisone treatment induced morphological changes in the spleen. The number of small intestine Peyer's patches was not affected by MIDD0301 treatment, an important factor for orally administered drugs. Circulating lymphocyte, monocyte and granulocyte numbers were unchanged in the MIDD0301-treated animals, whereas differential lymphocyte numbers were reduced in prednisone-treated animals. MIDD0301 treatment did not alter IgG antibody responses to dinitrophenyl following dinitrophenyl-keyhole limpet haemocyanin immunization, indicating that systemic humoral immune function was not affected. Taken together, these studies show that repeated daily administration of MIDD0301 is safe and not associated with adverse immunotoxicological effects in mice.

A novel GABAA receptor ligand MIDD0301 with limited blood-brain barrier penetration relaxes airway smooth muscle ex vivo and in vivo

Airway smooth muscle (ASM) cells express GABA A receptors (GABA_ARs), and previous reports have demonstrated that GABA_AR activators relax ASM. However, given the activity of GABA_ARs in central nervous system inhibitory neurotransmission, concern exists that these activators may lead to undesirable sedation. MIDD0301 is a novel imidazobenzodiazepine and positive allosteric modulator of the GABA_AR with limited brain distribution, thus eliminating the potential for sedation. Here, we demonstrate that MIDD0301 relaxes histamine-contracted guinea pig ( P < 0.05, n = 6-9) and human ( P < 0.05, n = 6-10) tracheal smooth muscle ex vivo in organ bath experiments, dilates mouse peripheral airways ex vivo in precision-cut lung-slice experiments ( P < 0.001, n = 16 airways from three mice), and alleviates bronchoconstriction in vivo in mice, as assessed by the forced-oscillation technique ( P < 0.05, n = 6 mice). Only trace concentrations of the compound were detected in the brains of mice after inhalation of nebulized 5 mM MIDD0301. Given its favorable pharmacokinetic properties and demonstrated ability to relax ASM in a number of clinically relevant experimental paradigms, MIDD0301 is a promising drug candidate for bronchoconstrictive diseases, such as asthma.

GABAA Receptor Subtypes Regulate Stress-Induced Colon Inflammation in Mice

BACKGROUND & AIMS

Psychological stress, in early life or adulthood, is a significant risk factor for inflammatory disorders, including inflammatory bowel diseases. However, little is known about the mechanisms by which emotional factors affect the immune system. γ-Aminobutyric acid type A receptors (GABA_ARs) regulate stress and inflammation, but it is not clear whether specific subtypes of GABA_ARs mediate stress-induced gastrointestinal inflammation. We investigated the roles of different GABA_AR subtypes in mouse colon inflammation induced by 2 different forms of psychological stress.

METHODS

C57BL/6J mice were exposed to early-life stress, and adult mice were exposed to acute-restraint stress; control mice were not exposed to either form of stress. We collected colon tissues and measured contractility using isometric tension recordings; colon inflammation, based on levels of cluster of differentiation 163 and tumor necrosis factor messenger RNA (mRNA) and protein and myeloperoxidase activity; and permeability, based on levels of tight junction protein 1 and occludin mRNA and protein. Mice were given fluorescently labeled dextran orally and systemic absorption was measured. We also performed studies of mice with disruption of the GABA_AR subunit α3 gene (Gabra3^-/- mice).

RESULTS

Mice exposed to early-life stress had significantly altered GABA_AR-mediated colonic contractility and impaired barrier function, and their colon tissue had increased levels of Gabra3 mRNA compared with control mice. Restraint stress led to colon inflammation in C57/BL6J mice but not Gabra3^-/- mice. Colonic inflammation was induced in vitro by an α3-GABA_AR agonist, showing a proinflammatory role for this receptor subtype. In contrast, α1/4/5-GABA_AR ligands decreased the expression of colonic inflammatory markers.

CONCLUSIONS

We found stress to increase expression of Gabra3 and induce inflammation in mouse colon, together with impaired barrier function. The in vitro pharmacologic activation of α3-GABA_ARs recapitulated colonic inflammation, whereas α1/4/5-GABA_AR ligands were anti-inflammatory. These proteins might serve as therapeutic targets for treatment of colon inflammation or inflammatory bowel diseases.

A Novel Orally Available Asthma Drug Candidate That Reduces Smooth Muscle Constriction and Inflammation by Targeting GABAA Receptors in the Lung

We describe lead compound MIDD0301 for the oral treatment of asthma based on previously developed positive allosteric α5β3γ2 selective GABAA receptor (GABAAR) ligands. MIDD0301 relaxed airway smooth muscle at single micromolar concentrations as demonstrated with ex vivo guinea pig tracheal rings. MIDD0301 also attenuated airway hyperresponsiveness (AHR) in an ovalbumin murine model of asthma by oral administration. Reduced numbers of eosinophils and macrophages were observed in mouse bronchoalveolar lavage fluid without changing mucous metaplasia. Importantly, lung cytokine expression of IL-17A, IL-4, and TNF-α were reduced for MIDD0301-treated mice without changing antiinflammatory cytokine IL-10 levels. Automated patch clamp confirmed amplification of GABA induced current mediated by α1-3,5β3γ2 GABAARs in the presence of MIDD0301. Pharmacodynamically, transmembrane currents of ex vivo CD4+ T cells from asthmatic mice were potentiated by MIDD0301 in the presence of GABA. The number of CD4+ T cells observed in the lung of MIDD0301-treated mice were reduced by an oral treatment of 20 mg/kg b.i.d. for 5 days. A half-life of almost 14 h was demonstrated by pharmacokinetic studies (PK) with no adverse CNS effects when treated mice were subjected to sensorimotor studies using the rotarod. PK studies also confirmed very low brain distribution. In conclusion, MIDD0301 represents a safe and improved oral asthma drug candidate that relaxes airway smooth muscle and attenuates inflammation in the lung leading to a reduction of AHR at a dosage lower than earlier reported GABAAR ligands.

Synthesis of chiral GABAA receptor subtype selective ligands as potential agents to treat schizophrenia as well as depression

A series of novel imidazobenzodiazepine analogs of the lead chiral ligand SH-053-2'F-S-CH3 (2), an α2/α3/α5 (Bz)GABA (A)ergic receptor subtype selective ligand, which reversed PCP-induced prepulse inhibition (PPI) of acoustic startle, were synthesized. These chiral (S)-CH3 ligands are targeted for the treatment of schizophrenia and depression. These new ligands were designed by modifying the liable ester functionality in 2 to improve the metabolic stability, cytotoxicity, and activity as compared to 2. Based on the data to date, the most promising ligands are the N-cyclopropyl amide GL-I-55 (8c) and the methyl bioisostere GL-I-65 (9a). The in vitro metabolic stability, cytotoxicity and in vivo locomotor effects are described in this report. Based on these results, 8c and 9a are the most promising for further in vivo pharmacology.

Design and Synthesis of Novel Deuterated Ligands Functionally Selective for the γ-Aminobutyric Acid Type A Receptor (GABAAR) α6 Subtype with Improved Metabolic Stability and Enhanced Bioavailability

Recent reports indicate that α6β2/3γ2 GABA_AR selective ligands may be important for the treatment of trigeminal activation-related pain and neuropsychiatric disorders with sensori-motor gating deficits. Based on 3 functionally α6β2/3γ2 GABA_AR selective pyrazoloquinolinones, 42 novel analogs were synthesized, and their in vitro metabolic stability and cytotoxicity as well as their in vivo pharmacokinetics, basic behavioral pharmacology, and effects on locomotion were investigated. Incorporation of deuterium into the methoxy substituents of the ligands increased their duration of action via improved metabolic stability and bioavailability, while their selectivity for the GABA_AR α6 subtype was retained. 8b was identified as the lead compound with a substantially improved pharmacokinetic profile. The ligands allosterically modulated diazepam insensitive α6β2/3γ2 GABA_ARs and were functionally silent at diazepam sensitive α1β2/3γ2 GABA_ARs, thus no sedation was detected. In addition, these analogs were not cytotoxic, which render them interesting candidates for treatment of CNS disorders mediated by GABA_AR α6β2/3γ2 subtypes.

Molecular Characterization of GABA-A Receptor Subunit Diversity within Major Peripheral Organs and Their Plasticity in Response to Early Life Psychosocial Stress

Gamma aminobutyric acid (GABA) subtype A receptors (GABA_ARs) are integral membrane ion channels composed of five individual proteins or subunits. Up to 19 different GABA_AR subunits (α1–6, β1–3, γ1–3, δ, ε, θ, π, and ρ1–3) have been identified, resulting in anatomically, physiologically, and pharmacologically distinct multiple receptor subtypes, and therefore GABA-mediated inhibition, across the central nervous system (CNS). Additionally, GABA_AR-modulating drugs are important tools in clinical medicine, although their use is limited by adverse effects. While significant advances have been made in terms of characterizing the GABA_AR system within the brain, relatively less is known about the molecular phenotypes within the peripheral nervous system of major organ systems. This represents a potentially missed therapeutic opportunity in terms of utilizing or repurposing clinically available GABA_AR drugs, as well as promising research compounds discarded due to their poor CNS penetrance, for the treatment of peripheral disorders. In addition, a broader understanding of the peripheral GABA_AR subtype repertoires will contribute to the design of therapies which minimize peripheral side-effects when treating CNS disorders. We have recently provided a high resolution molecular and function characterization of the GABA_ARs within the enteric nervous system of the mouse colon. In this study, the aim was to determine the constituent GABA_AR subunit expression profiles of the mouse bladder, heart, liver, kidney, lung, and stomach, using reverse transcription polymerase chain reaction and western blotting with brain as control. The data indicate that while some subunits are expressed widely across various organs (α3–5), others are restricted to individual organs (γ2, only stomach). Furthermore, we demonstrate complex organ-specific developmental expression plasticity of the transporters which determine the chloride gradient within cells, and therefore whether GABA_AR activation has a depolarizing or hyperpolarizing effect. Finally, we demonstrate that prior exposure to early life psychosocial stress induces significant changes in peripheral GABA_AR subunit expression and chloride transporters, in an organ- and subunit-specific manner. Collectively, the data demonstrate the molecular diversity of the peripheral GABA_AR system and how this changes dynamically in response to life experience. This provides a molecular platform for functional analyses of the GABA–GABA_AR system in health, and in diseases affecting various peripheral organs.