The GABAA agonist muscimol attenuates induced airway constriction in guinea pigs in vivo

High frequency repetitive Transcranial Magnetic Stimulation promotes long lasting phrenic motoneuron excitability via GABAergic networks

Repetitive transcranial magnetic stimulation (rTMS) is a promising, innovative, and non-invasive therapy used clinically. Efficacy of rTMS has been demonstrated to ameliorate psychiatric disorders and neuropathic pain through neuromodulation of affected neural circuits. However, little is known about the mechanisms and the specific neural circuits via which rTMS facilitates these functional effects. The aim of this study was to begin revealing the mechanisms by which rTMS may tap into existing neural circuits, by using a well characterized spinal motor circuit - the phrenic circuit. Here we hypothesized that rTMS can be used to enhance phrenic motoneuron excitability in anesthetized Sprague Dawley rats. Multiple acute rTMS protocols were used revealing 10 Hz rTMS protocol induced a robust, long-lasting increase in phrenic motoneuron excitability, functionally evaluated by diaphragm motor evoked potentials (59.1 ± 21.1 % of increase compared to baseline 60 min after 10 Hz protocol against 6.0 ± 5.8 % (p = 0.007) for Time Control, -5.8 ± 7.4 % (p < 0.001) for 3 Hz, and 5.2 ± 12.5 % (p = 0.008) for 30 Hz protocols). A deeper analyze allowed to discriminate "responder" and "non-responder" subgroups among 10 Hz rTMS treated animals. Intravenous injections of GABA_A and GABA_B receptor agonists prior to 10 Hz rTMS treatment, abolished the enhanced phrenic motoneuron excitability, suggesting GABAergic input plays a mechanistic role in rTMS-induced phrenic excitability. These data demonstrate that a single high frequency rTMS protocol at 10 Hz increases phrenic motoneuron excitability, mediated by a local GABAergic "disinhibition". By understanding how rTMS can be used to affect neural circuits non-invasively we can begin to harness the therapeutic potential of this neuromodulatory strategy to promote recovery after disease or injury to the central nervous system.

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.

Novel Expression of GABAA Receptors on Resistance Arteries That Modulate Myogenic Tone

The clinical administration of GABAergic medications leads to hypotension which has classically been attributed to the modulation of neuronal activity in the central and peripheral nervous systems. However, certain types of peripheral smooth muscle cells have been shown to express GABAA receptors, which modulate smooth muscle tone, by the activation of these chloride channels on smooth muscle cell plasma membranes. Limited prior studies demonstrate that non-human large-caliber capacitance blood vessels mounted on a wire myograph are responsive to GABAA ligands. We questioned whether GABAA receptors are expressed in human resistance arteries and whether they modulate myogenic tone. We demonstrate the novel expression of GABAA subunits on vascular smooth muscle from small-caliber human omental and mouse tail resistance arteries. We show that GABAA receptors modulate both plasma membrane potential and calcium responses in primary cultured cells from human resistance arteries. Lastly, we demonstrate functional physiologic modulation of myogenic tone via GABAA receptor activation in human and mouse arteries. Together, these studies demonstrate a previously unrecognized role for GABAA receptors in the modulation of myogenic tone in mouse and human resistance arteries.

Regulation of Airway Smooth Muscle Contraction in Health and Disease

Airway smooth muscle (ASM) extends from the trachea throughout the bronchial tree to the terminal bronchioles. In utero, spontaneous phasic contraction of fetal ASM is critical for normal lung development by regulating intraluminal fluid movement, ASM differentiation, and release of key growth factors. In contrast, phasic contraction appears to be absent in the adult lung, and regulation of tonic contraction and airflow is under neuronal and humoral control. Accumulating evidence suggests that changes in ASM responsiveness contribute to the pathophysiology of lung diseases with lifelong health impacts.Functional assessments of fetal and adult ASM and airways have defined pharmacological responses and signaling pathways that drive airway contraction and relaxation. Studies using precision-cut lung slices, in which contraction of intrapulmonary airways and ASM calcium signaling can be assessed simultaneously in situ, have been particularly informative. These combined approaches have defined the relative importance of calcium entry into ASM and calcium release from intracellular stores as drivers of spontaneous phasic contraction in utero and excitation-contraction coupling.Increased contractility of ASM in asthma contributes to airway hyperresponsiveness. Studies using animal models and human ASM and airways have characterized inflammatory and other mechanisms underlying increased reactivity to contractile agonists and reduced bronchodilator efficacy of β₂-adrenoceptor agonists in severe diseases. Novel bronchodilators and the application of bronchial thermoplasty to ablate increased ASM within asthmatic airways have the potential to overcome limitations of current therapies. These approaches may directly limit excessive airway contraction to improve outcomes for difficult-to-control asthma and other chronic lung diseases.

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.

Bronchoprotection and bronchorelaxation in asthma: New targets, and new ways to target the old ones

Despite over 50years of inhaled beta-agonists and corticosteroids as the default management or rescue drugs for asthma, recent research suggests that new therapeutic options are likely to emerge. This belief stems from both an improved understanding of what causes and regulates airway smooth muscle (ASM) contraction, and the identification of new targets whose inhibition or activation can relax ASM. In this review we discuss the recent findings that provide new insight into ASM contractile regulation, a revolution in pharmacology that identifies new ways to "tune" G protein-coupled receptors to improve therapeutic efficacy, and the discovery of several novel targets/approaches capable of effecting bronchoprotection or bronchodilation.

A new approach for the study of lung smooth muscle phenotypes and its application in a murine model of allergic airway inflammation

Phenotypes of lung smooth muscle cells in health and disease are poorly characterized. This is due, in part, to a lack of methodologies that allow for the independent and direct isolation of bronchial smooth muscle cells (BSMCs) and vascular smooth muscle cells (VSMCs) from the lung. In this paper, we describe the development of a bi-fluorescent mouse that permits purification of these two cell populations by cell sorting. By subjecting this mouse to an acute allergen based-model of airway inflammation that exhibits many features of asthma, we utilized this tool to characterize the phenotype of so-called asthmatic BSMCs. First, we examined the biophysical properties of single BSMCs from allergen sensitized mice and found increases in basal tone and cell size that were sustained ex vivo. We then generated for the first time, a comprehensive characterization of the global gene expression changes in BSMCs isolated from the bi-fluorescent mice with allergic airway inflammation. Using statistical methods and pathway analysis, we identified a number of differentially expressed mRNAs in BSMCs from allergen sensitized mice that code for key candidate proteins underlying changes in matrix formation, contractility, and immune responses. Ultimately, this tool will provide direction and guidance for the logical development of new markers and approaches for studying human lung smooth muscle.

GABA receptor ameliorates ventilator-induced lung injury in rats by improving alveolar fluid clearance

Introduction

Mechanical ventilators are increasingly used in critical care units. However, they can cause lung injury, including pulmonary edema. Our previous studies indicated that γ-aminobutyric acid (GABA) receptors are involved in alveolar-fluid homeostasis. The present study investigated the role of GABA receptors in ventilator-induced lung injury.

Methods

Adult female Sprague-Dawley rats were subjected to high-tidal-volume ventilation of 40 ml/kg body weight for 1 hour, and lung injuries were assessed.

Results

High-tidal-volume ventilation resulted in lung injury, as indicated by an increase in total protein in bronchoalveolar fluid, wet-to-dry ratio (indication of pulmonary edema), and Evans Blue dye extravasation (indication of vascular damage). Intratracheal administration of GABA before ventilation significantly reduced the wet-to-dry ratio. Further, histopathologic analysis indicated that GABA reduced ventilator-induced lung injury and apoptosis. GABA-mediated reduction was effectively blocked by the GABA_A-receptor antagonist, bicuculline. The GABA-mediated effect was not due to the vascular damage, because no differences in Evans Blue dye extravasation were noted. However, the decrease in alveolar fluid clearance by high-tidal-volume ventilation was partly prevented by GABA, which was blocked by bicuculline.

Conclusions

These results suggest that GABA reduces pulmonary edema induced by high-tidal-volume ventilation via its effects on alveolar fluid clearance and apoptosis.

Airway epithelium is a predominant source of endogenous airway GABA and contributes to relaxation of airway smooth muscle tone

Chronic obstructive pulmonary disease and asthma are characterized by hyperreactive airway responses that predispose patients to episodes of acute airway constriction. Recent studies suggest a complex paradigm of GABAergic signaling in airways that involves GABA-mediated relaxation of airway smooth muscle. However, the cellular source of airway GABA and mechanisms regulating its release remain unknown. We questioned whether epithelium is a major source of GABA in the airway and whether the absence of epithelium-derived GABA contributes to greater airway smooth muscle force. Messenger RNA encoding glutamic acid decarboxylase (GAD) 65/67 was quantitatively measured in human airway epithelium and smooth muscle. HPLC quantified GABA levels in guinea pig tracheal ring segments under basal or stimulated conditions with or without epithelium. The role of endogenous GABA in the maintenance of an acetylcholine contraction in human airway and guinea pig airway smooth muscle was assessed in organ baths. A 37.5-fold greater amount of mRNA encoding GAD 67 was detected in human epithelium vs. airway smooth muscle cells. HPLC confirmed that guinea pig airways with intact epithelium have a higher constitutive elution of GABA under basal or KCl-depolarized conditions compared with epithelium-denuded airway rings. Inhibition of GABA transporters significantly suppressed KCl-mediated release of GABA from epithelium-intact airways, but tetrodotoxin was without effect. The presence of intact epithelium had a significant GABAergic-mediated prorelaxant effect on the maintenance of contractile tone. Airway epithelium is a predominant cellular source of endogenous GABA in the airway and contributes significant prorelaxant GABA effects on airway smooth muscle force.

Can we find better bronchodilators to relieve asthma symptoms?

Bronchodilators are the first line therapy during acute asthmatic exacerbations to reverse airway obstruction primarily by relaxing airway smooth muscle. Only three categories of bronchodilators exist in clinical practice: β-adrenergic agonists, anticholinergics, and methylxanthines. Each of these categories have specific drugs dating back to the early 20th century, raising the question of whether or not we can find better bronchodilators. While caffeine, theophylline, atropine, and epinephrine were the first generations of therapeutics in each of these drug classes, there is no question that improvements have been made in the bronchodilators in each of these classes. In the following editorial, we will briefly describe new classes of potential bronchodilators including: novel PDE inhibitors, natural phytotherapeutics, bitter taste receptor ligands, and chloride channel modulators, which have the potential to be used alone or in combination with existing bronchodilators to reverse acute airway obstruction in the future.

A synthetic chloride channel relaxes airway smooth muscle of the rat

Synthetic ion channels may have potential therapeutic applications, provided they possess appropriate biological activities. The present study was designed to examine the ability of small molecule-based synthetic Cl^– channels to modulate airway smooth muscle responsiveness. Changes in isometric tension were measured in rat tracheal rings. Relaxations to the synthetic chloride channel SCC-1 were obtained during sustained contractions to KCl. The anion dependency of the effect of SCC-1 was evaluated by ion substitution experiments. The sensitivity to conventional Cl^– transport inhibitors was also tested. SCC-1 caused concentration-dependent relaxations during sustained contractions to potassium chloride. This relaxing effect was dependent on the presence of extracellular Cl^– and HCO₃⁻. It was insensitive to conventional Cl^– channels/transport inhibitors that blocked the cystic fibrosis transmembrane conductance regulator and calcium-activated Cl^– channels. SCC-1 did not inhibit contractions induced by carbachol, endothelin-1, 5-hydroxytryptamine or the calcium ionophore A23187. SCC-1 relaxes airway smooth muscle during contractions evoked by depolarizing solutions. The Cl^– conductance conferred by this synthetic compound is distinct from the endogenous transport systems for chloride anions.

Estrogen effects on human airway smooth muscle involve cAMP and protein kinase A

Clinically observed differences in airway reactivity and asthma exacerbations in women at different life stages suggest a role for sex steroids in modulating airway function although their targets and mechanisms of action are still being explored. We have previously shown that clinically relevant concentrations of exogenous estrogen acutely decrease intracellular calcium ([Ca(2+)](i)) in human airway smooth muscle (ASM), thereby facilitating bronchodilation. In this study, we hypothesized that estrogens modulate cyclic nucleotide regulation, resulting in decreased [Ca(2+)](i) in human ASM. In Fura-2-loaded human ASM cells, 1 nM 17β-estradiol (E(2)) potentiated the inhibitory effect of the β-adrenoceptor (β-AR) agonist isoproterenol (ISO; 100 nM) on histamine-mediated Ca(2+) entry. Inhibition of protein kinase A (PKA) activity (KT5720; 100 nM) attenuated E(2) effects on [Ca(2+)](i). Acute treatment with E(2) increased cAMP levels in ASM cells comparable to that of ISO (100 pM). In acetylcholine-contracted airways from female guinea pigs or female humans, E(2) potentiated ISO-induced relaxation. These novel data suggest that, in human ASM, physiologically relevant concentrations of estrogens act via estrogen receptors (ERs) and the cAMP pathway to nongenomically reduce [Ca(2+)](i), thus promoting bronchodilation. Activation of ERs may be a novel adjunct therapeutic avenue in reactive airway diseases in combination with established cAMP-activating therapies such as β(2)-agonists.

Unexpected extra-renal effects of loop diuretics in the preterm neonate

The loop diuretics furosemide and bumetanide are commonly used in neonatal intensive care units (NICUs). Furosemide, because of its actions on the ubiquitous Na(+) -K(+) -2Cl(-) isoform cotransporter and its promotion of prostanoid production and release, also has non-diuretic effects on vascular smooth muscle, airways, the ductus arteriosus and theoretically the gastrointestinal tract. Loop diuretics also affect the central nervous system through modulation of the GABA-A chloride channel.

CONCLUSION

  The loop diuretics have a variety of biological effects that are potentially harmful as well as beneficial. Care should be taken with the use of these agents because the range of their effects may be broader than the single action sought by the prescribing physician.

Comparison of cell expression formats for the characterization of GABA(A) channels using a microfluidic patch clamp system

Ensemble recording and microfluidic perfusion are recently introduced techniques aimed at removing the laborious nature and low recording success rates of manual patch clamp. Here, we present assay characteristics for these features integrated into one automated electrophysiology platform as applied to the study of GABA(A) channels. A variety of cell types and methods of GABA(A) channel expression were successfully studied (defined as I(GABA)>500 pA), including stably transfected human embryonic kidney (HEK) cells expressing α(1)β(3)γ(2) GABA(A) channels, frozen ready-to-assay (RTA) HEK cells expressing α(1)β(3)γ(2) or α(3)β(3)γ(2) GABA(A) channels, transiently transfected HEK293T cells expressing α(1)β(3)γ(2) GABA(A) channels, and immortalized cultures of human airway smooth muscle cells endogenously expressing GABA(A) channels. Current measurements were successfully studied in multiple cell types with multiple modes of channel expression in response to several classic GABA(A) channel agonists, antagonists, and allosteric modulators. We obtained success rates above 95% for transiently or stably transfected HEK cells and frozen RTA HEK cells expressing GABA(A) channels. Tissue-derived immortalized cultures of airway smooth muscle cells exhibited a slightly lower recording success rate of 75% using automated patch, which was much higher than the 5% success rate using manual patch clamp technique by the same research group. Responses to agonists, antagonists, and allosteric modulators compared well to previously reported manual patch results. The data demonstrate that both the biophysics and pharmacologic characterization of GABA(A) channels in a wide variety of cell formats can be performed using this automated patch clamp system.

Low voltage vagal nerve stimulation reduces bronchoconstriction in guinea pigs through catecholamine release

OBJECTIVE

  Electrical stimulation of the vagus nerve at relatively high voltages (e.g., >10 V) can induce bronchoconstriction. However, low voltage (≤2 V) vagus nerve stimulation (VNS) can attenuate histamine-invoked bronchoconstriction. Here, we identify the mechanism for this inhibition.

METHODS

  In urethanea-nesthetized guinea pigs, bipolar electrodes were attached to both vagus nerves and changes in pulmonary inflation pressure were recorded in response to i.v. histamine and during VNS. The attenuation of the histamine response by low-voltage VNS was then examined in the presence of pharmacologic inhibitors or nerve ligation.

RESULTS

  Low-voltage VNS attenuated histamine-induced bronchoconstriction (4.4 ± 0.3 vs. 3.2 ± 0.2 cm H(2) O, p < 0.01) and remained effective following administration of a nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester, and after sympathetic nerve depletion with guanethidine, but not after the β-adrenoceptor antagonist propranolol. Nerve ligation caudal to the electrodes did not block the inhibition but cephalic nerve ligation did. Low-voltage VNS increased circulating epinephrine and norepinephrine without but not with cephalic nerve ligation.

CONCLUSION

  These results indicate that low-voltage VNS attenuates histamine-induced bronchoconstriction via activation of afferent nerves, resulting in a systemic increase in catecholamines likely arising from the adrenal medulla.

Targeting the restricted α-subunit repertoire of airway smooth muscle GABAA receptors augments airway smooth muscle relaxation

The prevalence of asthma has taken on pandemic proportions. Since this disease predisposes patients to severe acute airway constriction, novel mechanisms capable of promoting airway smooth muscle relaxation would be clinically valuable. We have recently demonstrated that activation of endogenous airway smooth muscle GABA(A) receptors potentiates β-adrenoceptor-mediated relaxation, and molecular analysis of airway smooth muscle reveals that the α-subunit component of these GABA(A) receptors is limited to the α(4)- and α(5)-subunits. We questioned whether ligands with selective affinity for these GABA(A) receptors could promote relaxation of airway smooth muscle. RT-PCR analysis of GABA(A) receptor subunits was performed on RNA isolated by laser capture microdissection from human and guinea pig airway smooth muscle. Membrane potential and chloride-mediated current were measured in response to GABA(A) subunit-selective agonists in cultured human airway smooth muscle cells. Functional relaxation of precontracted guinea pig tracheal rings was assessed in the absence and presence of the α(4)-subunit-selective GABA(A) receptor agonists: gaboxadol, taurine, and a novel 8-methoxy imidazobenzodiazepine (CM-D-45). Only messenger RNA encoding the α(4)- and α(5)-GABA(A) receptor subunits was identified in RNA isolated by laser capture dissection from guinea pig and human airway smooth muscle tissues. Activation of airway smooth muscle GABA(A) receptors with agonists selective for these subunits resulted in appropriate membrane potential changes and chloride currents and promoted relaxation of airway smooth muscle. In conclusion, selective subunit targeting of endogenous airway smooth muscle-specific GABA(A) receptors may represent a novel therapeutic option for patients in severe bronchospasm.

Functional expression of γ-amino butyric acid transporter 2 in human and guinea pig airway epithelium and smooth muscle

γ-Amino butyric acid (GABA) is a primary inhibitory neurotransmitter in the central nervous system, and is classically released by fusion of synaptic vesicles with the plasma membrane or by egress via GABA transporters (GATs). Recently, a GABAergic system comprised of GABA(A) and GABA(B) receptors has been identified on airway epithelial and smooth muscle cells that regulate mucus secretion and contractile tone of airway smooth muscle (ASM). In addition, the enzyme that synthesizes GABA, glutamic acid decarboxylase, has been identified in airway epithelial cells; however, the mechanism(s) by which this synthesized GABA is released from epithelial intracellular stores is unknown. We questioned whether any of the four known isoforms of GATs are functionally expressed in ASM or epithelial cells. We detected mRNA and protein expression of GAT2 and -4, and isoforms of glutamic acid decarboxylase in native and cultured human ASM and epithelial cells. In contrast, mRNA encoding vesicular GAT (VGAT), the neuronal GABA transporter, was not detected. Functional inhibition of (3)H-GABA uptake was demonstrated using GAT2 and GAT4/betaine-GABA transporter 1 (BGT1) inhibitors in both human ASM and epithelial cells. These results demonstrate that two isoforms of GATs, but not VGAT, are expressed in both airway epithelial and smooth muscle cells. They also provide a mechanism by which locally synthesized GABA can be released from these cells into the airway to activate GABA(A) channels and GABA(B) receptors, with subsequent autocrine and/or paracrine signaling effects on airway epithelium and ASM.

Smoking-mediated up-regulation of GAD67 expression in the human airway epithelium

Background

The production of gamma-amino butyric acid (GABA) is dependent on glutamate decarboxylases (GAD65 and GAD67), the enzymes that catalyze the decarboxylation of glutamate to GABA. Based on studies suggesting a role of the airway epithelial GABAergic system in asthma-related mucus overproduction, we hypothesized that cigarette smoking, another disorder associated with increased mucus production, may modulate GABAergic system-related gene expression levels in the airway epithelium.

Methods

We assessed expression of the GABAergic system in human airway epithelium obtained using bronchoscopy to sample the epithelium and microarrays to evaluate gene expression. RT-PCR was used to confirm gene expression of GABAergic system gene in large and small airway epithelium from heathy nonsmokers and healthy smokers. The differences in the GABAergic system gene was further confirmed by TaqMan, immunohistochemistry and Western analysis.

Results

The data demonstrate there is a complete GABAergic system expressed in the large and small human airway epithelium, including glutamate decarboxylase, GABA receptors, transporters and catabolism enzymes. Interestingly, of the entire GABAergic system, smoking modified only the expression of GAD67, with marked up-regulation of GAD67 gene expression in both large (4.1-fold increase, p < 0.01) and small airway epithelium of healthy smokers (6.3-fold increase, p < 0.01). At the protein level, Western analysis confirmed the increased expression of GAD67 in airway epithelium of healthy smokers compared to healthy nonsmokers (p < 0.05). There was a significant positive correlation between GAD67 and MUC5AC gene expression in both large and small airway epithelium (p < 0.01), implying a link between GAD67 and mucin overproduction in association with smoking.

Conclusions

In the context that GAD67 is the rate limiting enzyme in GABA synthesis, the correlation of GAD67 gene expression with MUC5AC expressions suggests that the up-regulation of airway epithelium expression of GAD67 may contribute to the increase in mucus production observed in association with cigarette smoking.

Trial registration

NCT00224198; NCT00224185

Anti-inflammatory effects of the neurotransmitter agonist Honokiol in a mouse model of allergic asthma

Chronic airway inflammation is a hallmark of asthma, an immune-based disease with great societal impact. Honokiol (HNK), a phenolic neurotransmitter receptor (γ-aminobutyric acid type A) agonist purified from magnolia, has anti-inflammatory properties, including stabilization of inflammation in experimentally induced arthritis. The present study tested the prediction that HNK could inhibit the chronic inflammatory component of allergic asthma. C57BL/6 mice sensitized to and challenged with OVA had increased airway hyperresponsiveness to methacholine challenge and eosinophilia compared with naive controls. HNK-treated mice showed a reduction in airway hyperresponsiveness as well as a significant decrease in lung eosinophilia. Histopathology studies revealed a marked drop in lung inflammation, goblet cell hyperplasia, and collagen deposition with HNK treatment. Ag recall responses from HNK-treated mice showed decreased proinflammatory cytokines in response to OVA, including TNF-α-, IL-6-, Th1-, and Th17-type cytokines, despite an increase in Th2-type cytokines. Regulatory cytokines IL-10 and TGF-β were also increased. Assessment of lung homogenates revealed a similar pattern of cytokines, with a noted increase in the number of FoxP3(+) cells in the lung. HNK was able to alter B and T lymphocyte cytokine secretion in a γ-aminobutyric acid type A-dependent manner. These results indicate that symptoms and pathology of asthma can be alleviated even in the presence of increased Th2 cytokines and that neurotransmitter agonists such as HNK have promise as a novel class of anti-inflammatory agents in the treatment of chronic asthma.