Anti-inflammatory effects of the GABA(B) receptor agonist baclofen in allergic contact dermatitis

El-Gazar A, M. Ragab G, A. Essa M, M. Abdel-Haleem K, El-Dahmy RM. Transcending Traditional Treatment: The Therapeutical Potential of Nanovesicles for Transdermal Baclofen Delivery in Repeated Traumatic Brain Injury

Purpose

The repositioning of previously approved drugs is occupying the researchers' plans. Baclofen (Bac) was our candidate for its established neuroprotective capacity, with a proposal of efficient drug delivery as non-ionic surfactant-based nanovesicles (NISNV) formulae against mild repetitive traumatic brain injury (mRTBI) in rats, thus reducing the number of orally or injected medications, especially in severely comatose patients or pediatrics.

Methods

A (23) factorial design was implemented for confining Bac-loaded NISNV formulae, where a bunch of variables were inspected. An in-vivo experiment was done to test the prepared formula's efficacy transdermally. The following parameters were measured: brain expression of gamma amino butyric acid B (GABAB), protein kinase C- α (PKC-α), focal adhesion kinase (FAK), TNF-α and nuclear factor kappa B (NF-κB) p65, malondialdehyde (MDA), superoxide dismutase (SOD), and histopathology.

Results

The particle size (PS) and entrapment efficiency percent (EE%) speckled from 60.40±0.28% to 88.02±0.01% for the former and 174.64±0.93 to 1174.50±3.54 nm for the latter. In vitro release% after 8 hours ranged from 63.25±5.47% to 84.79±3.75%. The optimized formula (F4) illustrated desirability=1, with 630.09±3.53 µg/cm2 of Bac permeated over 8 hours, which equates to 100% of Bac. Bac post-trauma treatment restored brain expression of GABAB and PKC-α, while decreasing FAK. Besides enhancing the histological findings, the anti-inflammatory effect was clear by decreasing TNF-α and NF-κB p65. Consequently, significant antioxidant sequelae were revealed herein by diminishing MDA levels and restoring SOD activity.

Conclusion

Transdermal delivery of Bac-loaded niosomes confirmed neuroprotection and succeeded in surpassing skin-to-brain barriers, which makes it a promising therapeutic option for repeated traumas.

Anti-proliferative and anti-inflammatory effects of the application of baclofen cream, a GABAB receptor agonist, on skin inflammation in mice

Previous studies have demonstrated the role of γ-aminobutyric acid type B (GABAB) receptors in skin-related conditions and pain. However, most studies have focused on the main effects of GABAB on the central nervous system. Therefore, this study has aimed to determine the potential topical anti-inflammatory and anti-proliferative effects of baclofen cream in an inflammatory skin disease model. The effects of the baclofen cream were evaluated using acute and chronic models of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced skin inflammation in mouse ears. Histological and immunohistochemical evaluations were performed using an ear oedema assay. The effect of baclofen on keratinocyte proliferation was assessed in PAM212, the murine keratinocyte cell line. The results demonstrate that a single topical application of 5% baclofen, 7.5% baclofen, and 1% dexamethasone each inhibited acute TPA-induced ear oedema (58.94 ± 6.14%, 47.73 ± 11.26%, and 87.33 ± 4.59%, respectively). These results were confirmed by histological analysis. In the chronic model, baclofen (5%) and dexamethasone (1%) each inhibited ear oedema and the maximum inhibitory effect was reached at the end of the experiment (9th day of TPA application) with a percentage inhibition of 54.60 ± 6.15% for baclofen and 71.68 ± 3.45% for dexamethasone, when compared to the vehicle. These results were confirmed by histological analysis. Baclofen and dexamethasone also reduced proliferating cell nuclear antigen expression by 62.01 ± 6.65% and 70.42 ± 6.11%, respectively. However, baclofen did not inhibit keratinocyte proliferation in PAM212 cells. In conclusion, these results demonstrate that baclofen exhibits notable topical antiproliferative and anti-inflammatory properties and could be a potential therapeutic alternative for treating inflammatory and proliferative skin diseases.

GABAergic signaling beyond synapses: an emerging target for cancer therapy

Traditionally, γ-aminobutyric acid (GABA) is best known for its role as a primary inhibitory neurotransmitter reducing neuronal excitability in the mammalian central nervous system (CNS), thereby producing calming effects. However, an emerging body of data now supports a function for GABA beyond neurotransmission as a potent factor regulating cancer cell growth and metastasis, as well as the antitumor immune response, by shaping the tumor microenvironment (TME). Here, we review the current knowledge on GABA's effects on the function of tumor cells, tumor-immune interactions, and the underlying molecular mechanisms. Since altered GABAergic signaling is now recognized as a feature of certain types of solid tumors, we also discuss the potential of repurposing existing GABAergic agents as a new class of anticancer therapy.

The GABA and GABA-Receptor System in Inflammation, Anti-Tumor Immune Responses, and COVID-19

GABA and GABA_A-receptors (GABA_A-Rs) play major roles in neurodevelopment and neurotransmission in the central nervous system (CNS). There has been a growing appreciation that GABA_A-Rs are also present on most immune cells. Studies in the fields of autoimmune disease, cancer, parasitology, and virology have observed that GABA-R ligands have anti-inflammatory actions on T cells and antigen-presenting cells (APCs), while also enhancing regulatory T cell (Treg) responses and shifting APCs toward anti-inflammatory phenotypes. These actions have enabled GABA_A-R ligands to ameliorate autoimmune diseases, such as type 1 diabetes (T1D), multiple sclerosis (MS), and rheumatoid arthritis, as well as type 2 diabetes (T2D)-associated inflammation in preclinical models. Conversely, antagonism of GABA_A-R activity promotes the pro-inflammatory responses of T cells and APCs, enhancing anti-tumor responses and reducing tumor burden in models of solid tumors. Lung epithelial cells also express GABA-Rs, whose activation helps maintain fluid homeostasis and promote recovery from injury. The ability of GABA_A-R agonists to limit both excessive immune responses and lung epithelial cell injury may underlie recent findings that GABA_A-R agonists reduce the severity of disease in mice infected with highly lethal coronaviruses (SARS-CoV-2 and MHV-1). These observations suggest that GABA_A-R agonists may provide off-the-shelf therapies for COVID-19 caused by new SARS-CoV-2 variants, as well as novel beta-coronaviruses, which evade vaccine-induced immune responses and antiviral medications. We review these findings and further advance the notions that (1) immune cells possess GABA_A-Rs to limit inflammation in the CNS, and (2) this natural "braking system" on inflammatory responses may be pharmacologically engaged to slow the progression of autoimmune diseases, reduce the severity of COVID-19, and perhaps limit neuroinflammation associated with long COVID.

Gamma-amino butyric acid (GABA) supplementation alleviates dexamethasone treatment-induced oxidative stress and inflammation response in broiler chickens

This experiment was conducted to investigate the effect of Gamma-amino butyric acid (GABA) on growth performance, serum and liver antioxidant status, inflammation response and hematological changes, in male broiler chickens under experimentally induced stress via in-feed dexamethasone (DEX). A total of 300 male chicks (Ross 308) on day 7 after hatching, were randomly selected into four groups which were positive control group (PC, without any treatment), negative control (NC, with 1 mg/kg DEX), a third group received 1 mg/kg DEX and 100 mg/kg GABA (DG ⁺) and the last one was (DG ⁺⁺) which received 1 mg/kg DEX and 200 mg/kg GABA. Each group has five replicates (15 birds/replicate). Dietary GABA modulated DEX-induced adverse effects on body weight, feed intake, and feed conversion ratio. The DEX-induced effect of serum levels of IL-6 and IL-10 was reduced by dietary GABA supplementation. The activity of serum and liver superoxide dismutase, catalase, glutathione peroxidase were enhanced and malondialdehyde was reduced by GABA supplementation. The serum levels of total cholesterol & triglyceride were higher while low-density lipoprotein & high-density lipoprotein were lower in GABA groups than NC group. GABA supplementation also significantly decreased the heterophil, heterophil/lymphocyte ratio and elevated the activities of aspartate aminotransferase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP) than NC group. In conclusion, dietary GABA supplementation can alleviate DEX stress-induced oxidative stress and inflammation response.

Immunomodulation by foods and microbes: Unravelling the molecular tango

Metabolic health and immune function are intimately connected via diet and the microbiota. Nearly 90% of all immune cells in the body are associated with the gastrointestinal tract and these immune cells are continuously exposed to a wide range of microbes and microbial-derived compounds, with important systemic ramifications. Microbial dysbiosis has consistently been observed in patients with atopic dermatitis, food allergy and asthma and the molecular mechanisms linking changes in microbial populations with disease risk and disease endotypes are being intensively investigated. The discovery of novel bacterial metabolites that impact immune function is at the forefront of host-microbe research. Co-evolution of microbial communities within their hosts has resulted in intertwined metabolic pathways that affect physiological and pathological processes. However, recent dietary and lifestyle changes are thought to negatively influence interactions between microbes and their host. This review provides an overview of some of the critical metabolite-receptor interactions that have been recently described, which may underpin the immunomodulatory effects of the microbiota, and are of relevance for allergy, asthma and infectious diseases.

Trio-Drug Combination of Sodium Valproate, Baclofen and Thymoquinone Exhibits Synergistic Anticonvulsant Effects in Rats and Neuro-Protective Effects in HEK-293 Cells

Epilepsy is a chronic brain disorder, with anti-epileptic drugs (AEDs) providing relief from hyper-excitability of neurons, but largely failing to restrain neurodegeneration. We investigated a progressive preclinical trial in rats, whereby the test drugs; sodium valproate (SVP; 150 and 300 mg/kg), baclofen (BFN; 5 and 10 mg/kg), and thymoquinone (THQ; 40 and 80 mg/kg) were administered (i.p, once/day for 15 days) alone, and as low dose combinations, and subsequently tested for antiseizure and neuroprotective potential using electrical stimulation of neurons by Maximal electroshock (MES). The seizure stages were monitored, and hippocampal levels of m-TOR, IL-1β, IL-6 were measured. Hippocampal histopathology was also performed. Invitro and Insilco studies were run to counter-confirm the results from rodent studies. We report the synergistic effect of trio-drug combination; SVP (150 mg/kg), BFN (5 mg/kg) and THQ (40 mg/kg) against generalized seizures. The Insilco results revealed that trio-drug combination binds the Akt active site as a supramolecular complex, which could have served as a delivery system that affects the penetration and the binding to the new target. The potential energy of the ternary complex in the Akt active site after dynamics simulation was found to be -370.426 Kcal/mol, while the supramolecular ternary complex alone was -38.732 Kcal/mol, with a potential energy difference of -331.694 Kcal/mol, which favors the supramolecular ternary complex at Akt active site binding. In addition, the said combination increased cell viability by 267% and reduced morphological changes induced by Pentylenetetrazol (PTZ) in HEK-293 cells, which indicates the neuroprotective property of said combination. To conclude, we are the first to report the anti-convulsant and neuroprotective potential of the trio-drug combination.

Anti-inflammatory Effects of Ivermectin in the Treatment of Acetic Acid-Induced Colitis in Rats: Involvement of GABAB Receptors

BACKGROUND

Recent investigations have proposed the potential role of gamma-aminobutyric acid (GABA) in regulating motility and immunity of the gastrointestinal system.

AIMS

We aimed to investigate the anti-inflammatory effects of ivermectin (IVM) through GABA_B receptors following acetic acid-induced colitis in rats.

METHODS

In a controlled experimental study, we enrolled 78 male Wistar rats (13 groups; 6 rats/group). After colitis induction using acetic acid (4%), IVM, baclofen (a standard GABA_B agonist) or the combination of both agents was delivered to rats orally (by gavage), with the same dosage continued for 5 days. The control group received the vehicle, and prednisolone (a standard anti-inflammatory agent) was administered in a separate group as the positive control. Colon samples were collected on the sixth day for histopathological evaluations and measurement of myeloperoxidase (MPO) activity, TNF-α levels, and p-NF-ĸB p65, COX-2 and iNOS expression levels.

RESULTS

The greatest recovery was found after administering IVM 0.5, baclofen 0.5, or IVM 0.2 + baclofen 0.2 mg/kg/day (ulcer index [UI] = 1.4 ± 0.4, 1.7 ± 0.6, and 1.4 ± 0.3, respectively; p  < 0.001 vs. the control [UI = 6.5 ± 0.7]). Histopathological evaluations revealed a significant decrease in the inflammation severity in the three above-mentioned groups. P-NF-ĸB p65, COX-2, and iNOS expression, MPO activity, and TNF-α levels also decreased dramatically following treatment with IVM 0.5, baclofen 0.5, or the combination therapy (p < 0.001 vs. the control).

CONCLUSIONS

IVM exerted promising anti-inflammatory effects in treating acetic acid-induced colitis in rats. Its synergistic effect with baclofen also signified the possible involvement of GABA_B receptors in this process.

GABA Administration Ameliorates Sjogren’s Syndrome in Two Different Mouse Models

Sjögren’s syndrome (SS) is a chronic autoimmune disease characterized by lymphocytic infiltrates in the salivary and lachrymal glands resulting in oral and ocular dryness. There are no clinically approved therapies to slow the progression of SS. Immune cells possess receptors for the neurotransmitter GABA (GABA-Rs) and their activation has immunoregulatory actions. We tested whether GABA administration has potential for amelioration of SS in NOD.B10-H2^b and C57BL/6.NOD-Aec1Aec2 mice, two spontaneous SS models. Oral GABA treatment was initiated (1) after the development of sialadenitis but before the onset of overt symptoms, or (2) after the appearance of overt symptoms. When assessed weeks later, GABA-treated mice had greater saliva and tear production, as well as quicker times to salvia flow, in both SS mouse models. This was especially evident when GABA treatment was initiated after the onset of overt disease. This preservation of exocrine function was not accompanied by significant changes in the number or area of lymphocytic foci in the salivary or lachrymal glands of GABA-treated mice and we discuss the possible reasons for these observations. Given that GABA-treatment preserved saliva and tear production which are the most salient symptoms of SS and is safe for consumption, it may provide a new approach to help ameliorate SS.

The relationship between allergic diseases and tic disorders: A systematic review and meta-analysis

This systematic review aims to 1) explore the association between tic disorders (TD) and allergic diseases (AD), 2) judge whether patients with a diagnosis of TD are prone to suffer from a specific AD, by compiling the literature and analyzing the evidence. A literature search was conducted in PubMed and Embase database on February 24, 2021. The inclusion criteria for the literature were all comparative studies that reported TD patients were diagnosed with allergic illness as well. We identified that TD is positively associated with asthma, allergic rhinitis and allergic conjunctivitis, respectively. Especially, provisional tic disorder (PTD) patients might be more likely to suffer from these three AD, although it is still difficult to accurately predict which specific AD is prone to be accompanied by a specific TD. Shared genetic and etiological factors are suggested responsible for the AD-TD association. Large prospective cohort studies in future might shed light on a deep understanding of the relationship between immune disorders and tics.

GABAA-Receptor Agonists Limit Pneumonitis and Death in Murine Coronavirus-Infected Mice

There is an urgent need for new approaches to limit the severity of coronavirus infections. Many cells of the immune system express receptors for the neurotransmitter γ-aminobutyric acid (GABA), and GABA-receptor (GABA-R) agonists have anti-inflammatory effects. Lung epithelial cells also express GABA-Rs, and GABA-R modulators have been shown to limit acute lung injuries. There is currently, however, no information on whether GABA-R agonists might impact the course of a viral infection. Here, we assessed whether clinically applicable GABA-R agonists could be repurposed for the treatment of a lethal coronavirus (murine hepatitis virus 1, MHV-1) infection in mice. We found that oral GABA administration before, or after the appearance of symptoms, very effectively limited MHV-1-induced pneumonitis, severe illness, and death. GABA treatment also reduced viral load in the lungs, suggesting that GABA-Rs may provide a new druggable target to limit coronavirus replication. Treatment with the GABA_A-R-specific agonist homotaurine, but not the GABA_B-R-specific agonist baclofen, significantly reduced the severity of pneumonitis and death rates in MHV-1-infected mice, indicating that the therapeutic effects were mediated primarily through GABA_A-Rs. Since GABA and homotaurine are safe for human consumption, they are promising candidates to help treat coronavirus infections.

COR758, a negative allosteric modulator of GABAB receptors

Allosteric modulators of G protein coupled receptors (GPCRs), including GABA_BRs (GABA_BRs), are promising therapeutic candidates. While several positive allosteric modulators (PAM) of GABA_BRs have been characterized, only recently the first negative allosteric modulator (NAM) has been described. In the present study, we report the characterization of COR758, which acts as GABA_BR NAM in rat cortical membranes and CHO cells stably expressing GABA_BRs (CHO-GABA_B). COR758 failed to displace the antagonist [³H]CGP54626 from the orthosteric binding site of GABA_BRs showing that it acts through an allosteric binding site. Docking studies revealed a possible new allosteric binding site for COR758 in the intrahelical pocket of the GABA_B1 monomer. COR758 inhibited basal and GABA_BR-stimulated O-(3-[³⁵Sthio)-triphosphate ([³⁵S]GTPγS) binding in brain membranes and blocked the enhancement of GABA_BR-stimulated [³⁵S]GTPγS binding by the PAM GS39783. Bioluminescent resonance energy transfer (BRET) measurements in CHO-GABA_B cells showed that COR758 inhibited G protein activation by GABA and altered GABA_BR subunit rearrangements. Additionally, the compound altered GABA_BR-mediated signaling such as baclofen-induced inhibition of cAMP production in transfected HEK293 cells, agonist-induced Ca²⁺ mobilization as well as baclofen and the ago-PAM CGP7930 induced phosphorylation of extracellular signal-regulated kinases (ERK1/2) in CHO-GABA_B cells. COR758 also prevented baclofen-induced outward currents recorded from rat dopamine neurons, substantiating its property as a NAM for GABA_BRs. Altogether, these data indicate that COR758 inhibits G protein signaling by GABA_BRs, likely by interacting with an allosteric binding-site. Therefore, COR758 might serve as a scaffold to develop additional NAMs for therapeutic intervention.

Homotaurine limits the spreading of T cell autoreactivity within the CNS and ameliorates disease in a model of multiple sclerosis

Most multiple sclerosis (MS) patients given currently available disease-modifying drugs (DMDs) experience progressive disability. Accordingly, there is a need for new treatments that can limit the generation of new waves T cell autoreactivity that drive disease progression. Notably, immune cells express GABAA-receptors (GABAA-Rs) whose activation has anti-inflammatory effects such that GABA administration can ameliorate disease in models of type 1 diabetes, rheumatoid arthritis, and COVID-19. Here, we show that oral GABA, which cannot cross the blood-brain barrier (BBB), does not affect the course of murine experimental autoimmune encephalomyelitis (EAE). In contrast, oral administration of the BBB-permeable GABAA-R-specific agonist homotaurine ameliorates monophasic EAE, as well as advanced-stage relapsing-remitting EAE (RR-EAE). Homotaurine treatment beginning after the first peak of paralysis reduced the spreading of Th17 and Th1 responses from the priming immunogen to a new myelin T cell epitope within the CNS. Antigen-presenting cells (APC) isolated from homotaurine-treated mice displayed an attenuated ability to promote autoantigen-specific T cell proliferation. The ability of homotaurine treatment to limit epitope spreading within the CNS, along with its safety record, makes it an excellent candidate to help treat MS and other inflammatory disorders of the CNS.

Comprehensive Review of Topical Analgesics for Chronic Pain

PURPOSE OF REVIEW

Topical analgesics are a non-opioid option for the treatment of chronic pain conditions including neuropathic pain, musculoskeletal pain, and osteoarthritis. There are many topical medications available; however their efficacy is variable. This article reviews the various topical analgesics, their mechanisms of action, and their efficacy.

RECENT FINDINGS

Studies have found topical NSAIDs are useful in treating acute musculoskeletal pain syndromes (strains and sprains) and show some efficacy in treating hand and knee osteoarthritis (Derry et al. Cochrane Database Syst Rev 5:CD008609, 2017). Topical capsaicin 8% has been shown to be efficacious in the treatment of postherpetic neuralgia, painful diabetic peripheral neuropathy, and HIV-neuropathy (Derry et al. Cochrane Database Syst Rev 1:CD007393, 2017). Topical lidocaine has been widely studied and found to reduce pain in patients with postherpetic neuralgia (Knezevic et al. Pain Manag 7:537-58, 2017). Although many other topical analgesics are available, there is limited data to support the efficacy of other agents. Topical analgesics are a relatively benign treatment for chronic pain conditions including neuropathic pain, musculoskeletal, and myofascial pain. There is evidence to support the use of topical NSAIDs, high concentration topical capsaicin, and topical lidocaine for various painful conditions.

GABAB-Receptor Agonist-Based Immunotherapy for Type 1 Diabetes in NOD Mice

Some immune system cells express type A and/or type B γ-aminobutyric acid receptors (GABA_A-Rs and/or GABA_B-Rs). Treatment with GABA, which activates both GABA_A-Rs and GABA_B-Rs), and/or a GABA_A-R-specific agonist inhibits disease progression in mouse models of type 1 diabetes (T1D), multiple sclerosis, rheumatoid arthritis, and COVID-19. Little is known about the clinical potential of specifically modulating GABA_B-Rs. Here, we tested lesogaberan, a peripherally restricted GABA_B-R agonist, as an interventive therapy in diabetic NOD mice. Lesogaberan treatment temporarily restored normoglycemia in most newly diabetic NOD mice. Combined treatment with a suboptimal dose of lesogaberan and proinsulin/alum immunization in newly diabetic NOD mice or a low-dose anti-CD3 in severely hyperglycemic NOD mice greatly increased T1D remission rates relative to each monotherapy. Mice receiving combined lesogaberan and anti-CD3 displayed improved glucose tolerance and, unlike mice that received anti-CD3 alone, had some islets with many insulin⁺ cells, suggesting that lesogaberan helped to rapidly inhibit β-cell destruction. Hence, GABA_B-R-specific agonists may provide adjunct therapies for T1D. Finally, the analysis of microarray and RNA-Seq databases suggested that the expression of GABA_B-Rs and GABA_A-Rs, as well as GABA production/secretion-related genes, may be a more common feature of immune cells than currently recognized.

Effects of Daily Raspberry Consumption on Immune-Metabolic Health in Subjects at Risk of Metabolic Syndrome: A Randomized Controlled Trial

Consumption of red raspberries has been reported to exert acute beneficial effects on postprandial glycemia, insulinemia, triglyceridemia, and cytokine levels in metabolically disturbed subjects. In a two-arm parallel-group, randomized, controlled trial, 59 subjects with overweight or abdominal obesity and with slight hyperinsulinemia or hypertriglyceridemia were randomized to consume 280 g/day of frozen raspberries or to maintain their usual diet for 8 weeks. Primary analyses measured metabolic differences between the groups. Secondary analyses performed with omics tools in the intervention group assessed blood gene expression and plasma metabolomic changes following the raspberry supplementation. The intervention did not significantly affect plasma insulin, glucose, inflammatory marker concentrations, nor blood pressure. Following the supplementation, 43 genes were differentially expressed, and several functional pathways were enriched, a major portion of which were involved in the regulation of cytotoxicity, immune cell trafficking, protein signal transduction, and interleukin production. In addition, 10 serum metabolites were found significantly altered, among which β-alanine, trimethylamine N-oxide, and bioactive lipids. Although the supplementation had no meaningful metabolic effects, these results highlight the impact of a diet rich in raspberry on the immune function and phospholipid metabolism, thus providing novel insights into potential immune-metabolic pathways influenced by regular raspberry consumption.

Role of dietary gamma-aminobutyric acid in broiler chickens raised under high stocking density

The present study was conducted to evaluate the effects of dietary gamma-aminobutyric acid (GABA) in broiler chickens raised in high stocking density (HSD) on performance and physiological responses. A total of 900 male broiler chicks (Ross 308) at 1 d old were assigned in a 2 × 2 factorial arrangement to 4 treatments (10 replicates per treatment) with stocking density, 7.5 birds/m² (low stocking density; LSD) or 15 birds/m² (HSD), and dietary GABA, 0 or 100 mg/kg. Chickens raised in HSD exhibited a decrease in body weight gain in all phases (P < 0.05) and feed intake in starter and whole phases (P < 0.01), and an increase in feed conversion ratio in the finisher phase (P < 0.01) compared with LSD-raised chickens. However, dietary GABA did not affect growth performance nor interacted with stocking density on production variables. The HSD vs. LSD increased relative liver weight on d 35 whereas dietary GABA increased relative liver weight and decreased relative bursa weight on d 21. Both stocking density and dietary GABA affected yield and quality of breast and leg muscles. Dietary GABA increased (P < 0.05) width of tibia on d 35 and interacted (P = 0.054) with stocking density on breaking stocking density on d 35. The HSD vs. LSD group lowered (P < 0.05) feather coverage scores. Significant interaction between stocking density and GABA on surface temperature of shank on d 21 was noted (P = 0.024). Dietary GABA exhibited an opposite effect on the concentrations of cecal short-chain fatty acids depending on stocking density leading to a moderate to significant interaction. Stocking density decreased alpha-1-acid glycoprotein whereas dietary GABA decreased heterophil-to-lymphocyte ratio and corticosterone in blood or serum samples. Serum biochemical parameters were altered by stocking density or dietary GABA. It is concluded that dietary GABA alleviated stress indices including corticosterone and heterophil-to-lymphocyte ratio, but failed to reverse stocking density-induced growth depression.

Effect of Topical Baclofen 5% on Post-Hemorrhoidectomy Pain: Randomized Double Blind Placebo-Controlled Clinical Trial

BACKGROUND

Baclofen is an agonist for a subtype of gamma-amino butyric acid (GABA-B) receptors and traditionally been used for the systemic treatment of spasticity. Topical application of baclofen has been shown to reduce pain in patients with localized neuropathic pain.

OBJECTIVES

In this study, we investigate the efficacy of baclofen cream (5%) in reducing postoperative pain and analgesic requirement after open hemorrhoidectomy.

DESIGN

The patients were randomly assigned to either baclofen (5%) cream or placebo immediately after surgery and then every 12 h for 14 days.

PATIENTS

A total of 66 patients with third- and fourth-degree hemorrhoids undergoing open hemorrhoidectomy were randomly assigned to this trial.

SETTING

This study was conducted at a single educational hospital.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcomes were intensity of pain, measured with a visual analog scale, and the analgesic requirement, measured by the amount of the acetaminophen consumption.

RESULTS

No significant difference was found in baseline characteristics between the two groups. Postoperative pain score of the baclofen group was significantly lower on week 1 (P = 0.01) and week 2 (P = 0.02) than the placebo group. Similarly, patients in the baclofen group consumed significantly less analgesic medication on week 1 (P = 0.025) and week 2 (P = 0.024) than the control group.

CONCLUSION

Topical application of baclofen effectively relieves pain after hemorrhoidectomy with minimal side effects.

Propofol reduces acute lung injury by up-regulating gamma-aminobutyric acid type a receptors

BACKGROUND

We used a two-hit lung injury rat model that involves mechanical ventilation (MV) following lipopolysaccharide exposure to investigate the effects of propofol on the expression of GABA_A receptors (GABA_AR) and cytokine responses, and we then determined the specific effects of GABA on cytokine responses in vitro in alveolar epithelial cells (AECs).

METHODS

Forty-eight adult male Wister rats were equally and randomly divided into the following 4 groups (n = 12) using a random number table: sham group, sham+propofol group, lipopolysaccharide (LPS) + VILI group, and LPS + VILI + propofol group. All animals were anesthetized, and the animals received a 3.75 mg/kg intratracheal instillation of endotoxins or phosphate-buffered saline (PBS) as the control, as described previously. After 30 min, rats were ventilated for 5 h in a volume-controlled ventilation mode. In the LPS + VILI group, animals were ventilated with a tidal volume (Vt) of 22 ml/kg and zero positive end-expiratory pressure (PEEP) at a respiratory rate of 16-18 breaths/min, whereas control (sham) rats were ventilated with a Vt of 6 ml/kg and PEEP of 5 cmH₂O at a rate of 45-55 breaths/min. The FiO₂ remained constant as 0.4, propofol was administered intravenously in the LPS + VILI + propofol and sham + propofol groups at a rate of 10 mg·kg^-1·h^-1 while normal saline at the same rate was intravenously administered in the LPS + VILI and sham groups during the entire mechanical ventilation period. Five hours after mechanical ventilation, the rats were killed. Survival rates, histopathology, concentrations of inflammatory mediators in bronchoalveolar lavage fluid (BALF), wet weight/dry weight (W/D) ratio of the lung, myeloperoxidase (MPO) activity in lung tissues, and expression of GAD and GABA_AR by immunohistochemical detection and Western blotting were assessed. Then, human type II-like alveolar epithelial cells (A549 cells) were cultured to full confluence and incubated with GABA (100 nM) alone, picrotoxin alone, a GABA_AR antagonist (PTX, 50 nM), or GABA + PTX for 10 min, followed by stimulation with LPS (control) at 100 ng/ml for 4 h. The concentrations of IL-1β, IL-2, IL-8, and IL-10 were then measured.

RESULTS

Administration of propofol in a two-hit lung injury rat model can increase survival rates and the expression of GAD and GABA_AR (P < .05). The administration of propofol can attenuate the release of pro-inflammatory cytokines both in vivo and in vitro, and the administration of propofol can attenuate histopathological changes, the W/D ratio, and MPO activity (P < .05).

CONCLUSIONS

In this study, we found that the administration of propofol improved lung function, alleviated lung injury, and up-regulated the GAD and GABA_AR expressions in a two-hit model of acute lung injury (ALI) characterized by intratracheal instillation of an endotoxin and prolonged MV. Therefore, the protective effects of propofol may be associated with the up-regulation of GABA_A receptors in AECs.

Slc6a13 deficiency promotes Th17 responses during intestinal bacterial infection

The γ-amino butyric acid (GABA)ergic system shapes the activation and function of immune cells. The present study was conducted to explore the regulation of GABA transporter (GAT)-2 on the differentiation of Th17 cells. Here we found that Th17 cells show higher abundance of GAT-2, and have distinct cellular metabolic signatures, such as the GABA shunt pathway, as compared to naïve T cells. GAT-2 deficiency had little effect on the metabolic signature in naïve T cells, but impaired the GABA uptake and GABA shunt pathway in Th17 cells. GAT-2 deficiency had little effect on T cell development and peripheral T cell homeostasis; however, its deficiency promoted Th17 cell differentiation in vitro. Mechanistically, GAT-2 deficiency promoted differentiation of Th17 cells through activation of GABA-mTOR signaling. In a mouse model of intestinal infection and inflammation, GAT-2 deficiency promoted Th17 responses. Collectively, GAT-2 deficiency promotes Th17 cell responses through activation of GABA-mTOR signaling.

A Clinically Applicable Positive Allosteric Modulator of GABA Receptors Promotes Human β-Cell Replication and Survival as well as GABA's Ability to Inhibit Inflammatory T Cells

A major goal of T1D research is to develop new approaches to increase β-cell mass and control autoreactive T cell responses. GABAA-receptors (GABAA-Rs) are promising drug targets in both those regards due to their abilities to promote β-cell replication and survival, as well as inhibit autoreactive T cell responses. We previously showed that positive allosteric modulators (PAMs) of GABAA-Rs could promote rat β-cell line INS-1 and human islet cell replication in vitro. Here, we assessed whether treatment with alprazolam, a widely prescribed GABAA-R PAM, could promote β-cell survival and replication in human islets after implantation into NOD/scid mice. We observed that alprazolam treatment significantly reduced human islet cell apoptosis following transplantation and increased β-cell replication in the xenografts. Evidently, the GABAA-R PAM works in conjunction with GABA secreted from β-cells to increase β-cell survival and replication. Treatment with both the PAM and GABA further enhanced human β-cell replication. Alprazolam also augmented the ability of suboptimal doses of GABA to inhibit antigen-specific T cell responses in vitro. Thus, combined GABAA-R agonist and PAM treatment may help control inflammatory immune responses using reduced drug dosages. Together, these findings suggest that GABAA-R PAMs represent a promising drug class for safely modulating islet cells toward beneficial outcomes to help prevent or reverse T1D and, together with a GABAA-R agonist, may have broader applications for ameliorating other disorders in which inflammation contributes to the disease process.

Gut microbiota and inflammation in chronic kidney disease and their roles in the development of cardiovascular disease

The health and proper functioning of the cardiovascular and renal systems largely depend on crosstalk in the gut-kidney-heart/vessel triangle. Recent evidence suggests that the gut microbiota has an integral function in this crosstalk. Mounting evidence indicates that the development of chronic kidney and cardiovascular diseases follows chronic inflammatory processes that are affected by the gut microbiota via various immune, metabolic, endocrine, and neurologic pathways. Additionally, deterioration of the function of the cardiovascular and renal systems has been reported to disrupt the original gut microbiota composition, further contributing to the advancement of chronic cardiovascular and renal diseases. Considering the interaction between the gut microbiota and the renal and cardiovascular systems, we can infer that interventions for the gut microbiota through diet and possibly some medications can prevent/stop the vicious cycle between the gut microbiota and the cardiovascular/renal systems, leading to a decrease in chronic cardiovascular and renal diseases.

Functionalization-dependent effects of cellulose nanofibrils on tolerogenic mechanisms of human dendritic cells

Background

Cellulose nanofibrils (CNF) are attractive nanomaterials for various biomedical applications due to their excellent biocompatibility and biomimetic properties. However, their immunoregulatory properties are insufficiently investigated, especially in relation to their functionalization, which could cause problems during their clinical application.

Methods

Using a model of human dendritic cells (DC), which have a central role in the regulation of immune response, we investigated how differentially functionalized CNF, ie, native (n) CNF, 2,2,6,6-tetramethylpiperidine 1-oxyl radical-oxidized (c) CNF, and 3-aminopropylphosphoric acid-functionalized (APAc) CNF, affect DC properties, their viability, morphology, differentiation and maturation potential, and the capacity to regulate T cell-mediated immune response.

Results

Nontoxic doses of APAcCNF displayed the strongest inhibitory effects on DC differentiation, maturation, and T helper (Th) 1 and Th17 polarization capacity, followed by cCNF and nCNF, respectively. These results correlated with a specific pattern of regulatory cytokines production by APAcCNF-DC and their increased capacity to induce suppressive CD8⁺CD25⁺IL-10⁺ regulatory T cells in immunoglobulin-like transcript (ILT)-3- and ILT-4- dependent manner. In contrast, nCNF-DC induced predominantly suppressive CD4⁺CD25^hiFoxP3^hi regulatory T cells in indolamine 2,3-dioxygenase-1-dependent manner. Different tolerogenic properties of CNF correlated with their size and APA functionalization, as well as with different expression of CD209 and actin bundles at the place of contact with CNF.

Conclusion

The capacity to induce different types of DC-mediated tolerogenic immune responses by functionalized CNF opens new perspectives for their application as well-tolerated nanomaterials in tissue engineering and novel platforms for the therapy of inflammatory T cell-mediated pathologies.

Dysregulation of GABAergic Signalling Contributes in the Pathogenesis of Diarrhea-predominant Irritable Bowel Syndrome

Background/Aims

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a prevalent functional bowel disorder. Abdominal pain, discomfort and altered intestinal habits are the salient features of IBS-D. Low grade inflammation and altered neurotransmitters are the 2 recently identified factors contributing to the pathogenesis of IBS-D, but their role and interactions has not been elucidated in detail. Here we investigate the potential role of γ-aminobutyric acid (GABA) in regulating gut inflammation during IBS-D.

Methods

Blood samples and colonic mucosal biopsies from clinically diagnosed IBS-D patients and controls were collected. Levels of GABA were measured in serum samples through enzyme-linked immunosorbent assay (ELISA). Expression of GABAergic system and proinflammatory cytokines were analyzed in biopsy samples by reverse transcriptase polymerase chain reaction (RT-PCR). Effect of GABA and its antagonist on the expression of proinflammatory cytokines in lipopolysaccharide (LPS)-stimulated HT-29 cells was examined through RT-PCR.

Results

ELISA data revealed diminished level of GABA in IBS-D patients as compared to controls. RT-PCR analysis showed altered GABAergic signal system in IBS-D patients as compared to controls. GABA reduced the expression of proinflammatory cytokines in LPS stimulated HT-29 cells, whereas bicuculline methiodide (GABA antagonist) upregulated the expression of same cytokines in LPS stimulated HT-29 cells.

Conclusions

Our sets of data indicate that diminished level of GABA and altered GABAergic signal system contributes to pathogenesis of IBS-D by regulating inflammatory processes. These results provide novel evidence for anti-inflammatory role of GABA in IBS-D patients by altering the expression of pro-inflammatory cytokines.

Preventive and Therapeutic Role of Functional Ingredients of Barley Grass for Chronic Diseases in Human Beings

Barley grass powder is the best functional food that provides nutrition and eliminates toxins from cells in human beings; however, its functional ingredients have played an important role as health benefit. In order to better cognize the preventive and therapeutic role of barley grass for chronic diseases, we carried out the systematic strategies for functional ingredients of barley grass, based on the comprehensive databases, especially the PubMed, Baidu, ISI Web of Science, and CNKI, between 2008 and 2017. Barley grass is rich in functional ingredients, such as gamma-aminobutyric acid (GABA), flavonoids, saponarin, lutonarin, superoxide dismutase (SOD), K, Ca, Se, tryptophan, chlorophyll, vitamins (A, B1, C, and E), dietary fiber, polysaccharide, alkaloid, metallothioneins, and polyphenols. Barley grass promotes sleep; has antidiabetic effect; regulates blood pressure; enhances immunity; protects liver; has anti-acne/detoxifying and antidepressant effects; improves gastrointestinal function; has anticancer, anti-inflammatory, antioxidant, hypolipidemic, and antigout effects; reduces hyperuricemia; prevents hypoxia, cardiovascular diseases, fatigue, and constipation; alleviates atopic dermatitis; is a calcium supplement; improves cognition; and so on. These results support that barley grass may be one of the best functional foods for preventive chronic diseases and the best raw material of modern diet structure in promoting the development of large health industry and further reveal that GABA, flavonoids, SOD, K-Ca, vitamins, and tryptophan mechanism of barley grass have preventive and therapeutic role for chronic diseases. This paper can be used as a scientific evidence for developing functional foods and novel drugs for barley grass for preventive chronic diseases.

GABA Regulates Release of Inflammatory Cytokines From Peripheral Blood Mononuclear Cells and CD4+ T Cells and Is Immunosuppressive in Type 1 Diabetes

The neurotransmitter γ-aminobutyric acid (GABA) is an extracellular signaling molecule in the brain and in pancreatic islets. Here, we demonstrate that GABA regulates cytokine secretion from human peripheral blood mononuclear cells (PBMCs) and CD4⁺ T cells. In anti-CD3 stimulated PBMCs, GABA (100 nM) inhibited release of 47 cytokines in cells from patients with type 1 diabetes (T1D), but only 16 cytokines in cells from nondiabetic (ND) individuals. CD4⁺ T cells from ND individuals were grouped into responder or non-responder T cells according to effects of GABA (100 nM, 500 nM) on the cell proliferation. In the responder T cells, GABA decreased proliferation, and inhibited secretion of 37 cytokines in a concentration-dependent manner. In the non-responder T cells, GABA modulated release of 8 cytokines. GABA concentrations in plasma from T1D patients and ND individuals were correlated with 10 cytokines where 7 were increased in plasma of T1D patients. GABA inhibited secretion of 5 of these cytokines from both T1D PBMCs and ND responder T cells. The results identify GABA as a potent regulator of both Th1- and Th2-type cytokine secretion from human PBMCs and CD4⁺ T cells where GABA generally decreases the secretion.

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GABA regulates cytokine secretion in anti-CD3-stimulated peripheral blood mononuclear cells (PBMCs) and CD4⁺ T cells.

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GABA inhibits secretion of 47 cytokines in PBMCs from type 1 diabetes patients.

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GABA regulates secretion of pro- and anti-inflammatory cytokines in a concentration-dependent manner.

GABA is a signal molecule in the brain, blood and pancreatic islets where it is secreted by the insulin-producing β cells. GABA has many roles in human islets including optimizing function and survival of β cells. Bhandage et al. now show that GABA is a potent regulator of secretion of both pro- and anti-inflammatory cytokines in stimulated immune cells. In type 1 diabetes the β-cell mass is diminished and thus the protective effect of GABA in the islets although not in blood. Targeting GABA signaling in diabetes mellitus is likely to be a part of the solution when curing diabetes.

MCP-1 produced by keratinocytes is associated with leucocyte recruitment during elicitation of nickel-induced occupational allergic contact dermatitis

To investigate the expression profile of monocyte chemoattractant peptide-1 (MCP-1) by keratinocytes after nickel exposure and to identify its role for leucocyte migration during nickel-induced occupational allergic contact dermatitis (OACD), 26 workers diagnosed with nickel-induced OACD were enrolled. Skin biopsies from the positive nickel-challenged sites at different time points were assessed by immunohistochemistry (IHC) for MCP-1, CD68, CD45RO, and in situ hybridization (ISH) for MCP-1, using chronic periumbilical dermititis as controls. The expressions of MCP-1 in HaCaT cell culture after nickel treatment were quantified by enzyme-linked immunosorbent assay. The results showed that at positive nickel-challenged sites, strong expressions of MCP-1, both messenger RNA (mRNA) and protein, were detected in the basal keratinocytes during the early phase (24-48 h after nickel application), paralleled by the recruitment of CD68⁺ and CD45RO⁺ cells to the skin compartments. The expressions of MCP-1 declined gradually in the late phase (72-96 h after nickel application). Treatment with nickel sulfate at noncytotoxic concentrations (0.01-100 µM) induced a concentration-related elevation of MCP-1 expression by HaCaT cells compared to the untreated cells. The data indicated that a temporal expression pattern of MCP-1 produced by keratinocytes after nickel exposure was involved in the complex process of mononuclear cell infiltration during elicitation of nickel-induced OACD. Targeting MCP-1 might be a potential therapeutic strategy for OACD.

Very low doses of muscimol and baclofen ameliorate cognitive deficits and regulate protein expression in the brain of a rat model of streptozocin-induced Alzheimer's disease

Recent studies devoted to neuroprotection have focused on the role of the gamma-aminobutyric acid (GABA) system in regulating neuroinflammatory processes which play a key role in the neurodegenerative processes observed in Alzheimer's disease (AD) by inducing glial cell overactivation and impairing neurotransmission. Data on the efficacy of classical GABA-A and GABA-B receptor agonists (muscimol and baclofen, respectively) in animal models of AD are not available. Moreover, no published studies have examined the ability of optimal doses of these compounds to prevent neuroinflammation, the alterations in neurotransmission and cognitive deficits. In the present study, we used a non-transgenic rat model of AD obtained by intracerebroventricular streptozocin (STZ) injection and assessed the effects of muscimol and baclofen at very low doses (0.01-0.05mg/kg) on spatial memory and the expression of cortical and hippocampal proteins related to neuroinflammation, namely proteins involved in astroglial functions (glial fibrillary acidic protein, GFAP), GABA synthesis (GABA synthesizing enzyme, glutamic acid decarboxylase 67, GAD67) and acetylcholine degradation (acetylcholine esterase). The presented study demonstrated that in a rat model of STZ-induced AD both muscimol and baclofen at the tested doses exerted memory-enhancing and anti-inflammatory effects, as well as normalization of acetylcholine esterase and GABA expression. We suggested that the function of very low doses of GABA receptor agonists differs from typical GABA-related inhibition and may be mediated by the allosteric sites of GABA receptors or other non-specific cell regulatory pathways.

Attenuated GABAergic Signaling in Intestinal Epithelium Contributes to Pathogenesis of Ulcerative Colitis

BACKGROUND

Neuromediators produced by enteric nervous system regulate inflammatory processes via interacting with enteric immune system. Role of γ-aminobutyric acid (GABA), which is also a neuromediator, has been implicated in autoimmune diseases like multiple sclerosis, type 1 diabetes, and rheumatoid arthritis, where they modulate the immune responses. However, its role in ulcerative colitis (UC) has not been defined.

AIMS

This study was carried out to investigate the role of GABA and its signaling components in pathogenesis of UC.

METHODS

Peripheral blood, colon mucosal biopsy, and fecal specimens were collected from UC and control groups. Quantification of GABA was done using ELISA. Expression of GABAergic signal system components was analyzed through RT-PCR analysis. Enumeration of GABA-producing bacteria was done by qPCR analysis. Activity of p38 MAPK and expression of proinflammatory cytokines were determined by immunohistochemistry and RT-PCR analysis, respectively.

RESULTS

GABA levels were significantly reduced in patients with UC as compared to control group when measured in serum and colon biopsy. Altered expression of GABAergic signal system was observed in UC patients. Reduced abundance of selected GABA-producing bacteria was detected in stool samples of UC patients as compared to control. p38 MAPK activity and expression of its downstream effector cytokines were found to be increased in UC patients as compared to control.

CONCLUSIONS

Reduced levels of GABA were observed in patients with UC, and this leads to hyperactivation of p38 MAPK and overexpression of downstream effector cytokines suggesting a role of GABA in pathogenesis of UC.

Repurposing Lesogaberan to Promote Human Islet Cell Survival and β-Cell Replication

The activation of β-cell's A- and B-type gamma-aminobutyric acid receptors (GABAA-Rs and GABAB-Rs) can promote their survival and replication, and the activation of α-cell GABAA-Rs promotes their conversion into β-cells. However, GABA and the most clinically applicable GABA-R ligands may be suboptimal for the long-term treatment of diabetes due to their pharmacological properties or potential side-effects on the central nervous system (CNS). Lesogaberan (AZD3355) is a peripherally restricted high-affinity GABAB-R-specific agonist, originally developed for the treatment of gastroesophageal reflux disease (GERD) that appears to be safe for human use. This study tested the hypothesis that lesogaberan could be repurposed to promote human islet cell survival and β-cell replication. Treatment with lesogaberan significantly enhanced replication of human islet cells in vitro, which was abrogated by a GABAB-R antagonist. Immunohistochemical analysis of human islets that were grafted into immune-deficient mice revealed that oral treatment with lesogaberan promoted human β-cell replication and islet cell survival in vivo as effectively as GABA (which activates both GABAA-Rs and GABAB-Rs), perhaps because of its more favorable pharmacokinetics. Lesogaberan may be a promising drug candidate for clinical studies of diabetes intervention and islet transplantation.

Intestinal Microbiota-Derived GABA Mediates Interleukin-17 Expression during Enterotoxigenic Escherichia coli Infection

Intestinal microbiota has critical importance in pathogenesis of intestinal infection; however, the role of intestinal microbiota in intestinal immunity during enterotoxigenic Escherichia coli (ETEC) infection is poorly understood. The present study tested the hypothesis that the intestinal microbiota is associated with intestinal interleukin-17 (IL-17) expression in response to ETEC infection. Here, we found ETEC infection induced expression of intestinal IL-17 and dysbiosis of intestinal microbiota, increasing abundance of γ-aminobutyric acid (GABA)-producing Lactococcus lactis subsp. lactis. Antibiotics treatment in mice lowered the expression of intestinal IL-17 during ETEC infection, while GABA or L. lactis subsp. lactis administration restored the expression of intestinal IL-17. L. lactis subsp. lactis administration also promoted expression of intestinal IL-17 in germ-free mice during ETEC infection. GABA enhanced intestinal IL-17 expression in the context of ETEC infection through activating mechanistic target of rapamycin complex 1 (mTORC1)-ribosomal protein S6 kinase 1 (S6K1) signaling. GABA-mTORC1 signaling also affected intestinal IL-17 expression in response to Citrobacter rodentium infection and in drug-induced model of intestinal inflammation. These findings highlight the importance of intestinal GABA signaling in intestinal IL-17 expression during intestinal infection and indicate the potential of intestinal microbiota-GABA signaling in IL-17-associated intestinal diseases.

Radiation protective effects of baclofen predicted by a computational drug repurposing strategy

Exposure to ionizing radiation causes damage to living tissues; however, only a small number of agents have been approved for use in radiation injuries. Radioprotector is the primary countermeasure to radiation injury and none radioprotector has indeed reached the drug development stage. Repurposing the long list of approved, non-radioprotective drugs is an attractive strategy to find new radioprotective agents. Here, we applied a computational approach to discover new radioprotectors in silico by comparing publicly available gene expression data of ionizing radiation-treated samples from the Gene Expression Omnibus (GEO) database with gene expression signatures of more than 1309 small-molecule compounds from the Connectivity Map (cmap) dataset. Among the best compounds predicted to be therapeutic for ionizing radiation damage by this approach were some previously reported radioprotectors and baclofen (P<0.01), a chemical that was not previously used as radioprotector. Validation using a cell-based model and a rodent in vivo model demonstrated that treatment with baclofen reduced radiation-induced cytotoxicity in vitro (P<0.01), attenuated bone marrow damage and increased survival in vivo (P<0.05). These findings suggest that baclofen might serve as a radioprotector. The drug repurposing strategy by connecting the GEO data and cmap can be used to identify known drugs as potential radioprotective agents.

Inhibiting neuroinflammation: The role and therapeutic potential of GABA in neuro-immune interactions

The central nervous system, once thought to be a site of immunological privilege, has since been found to harbour immunocompetent cells and to communicate with the peripheral nervous system. In the central nervous system (CNS), glial cells display immunological responses to pathological and physiological stimuli through pro- and anti-inflammatory cytokine and chemokine signalling, antigen presentation and the clearing of cellular debris through phagocytosis. While this neuroinflammatory signalling can act to reduce neuronal damage and comprises a key facet of CNS homeostasis, persistent inflammation or auto-antigen-mediated immunoreactivity can induce a positive feedback cycle of neuroinflammation that ultimately results in necrosis of glia and neurons. Persistent neuroinflammation has been recognised as a major pathological component of virtually all neurodegenerative diseases and has also been a focus of research into the pathology underlying psychiatric disorders. Thus, pharmacological strategies to curb the pathological effects of persistent neuroinflammation are of interest for many disorders of the CNS. Accumulating evidence suggests that GABAergic activities are closely bound to immune processes and signals, and thus the GABAergic neurotransmitter system might represent an important therapeutic target in modulating neuroinflammation. Here, we review evidence that inflammation induces changes in the GABA neurotransmitter system in the CNS and that GABAergic signalling exerts a reciprocal influence over neuroinflammatory processes. Together, the data support the hypothesis that the GABA system is a potential therapeutic target in the modulation of central inflammation.

Modulation of TLR3/TLR4 inflammatory signaling by the GABAB receptor agonist baclofen in glia and immune cells: relevance to therapeutic effects in multiple sclerosis

The GABAB receptor agonist, baclofen, is used to treat muscle tightness and cramping caused by spasticity in a number of disorders including multiple sclerosis (MS), but its precise mechanism of action is unknown. Neuroinflammation drives the central pathology in MS and is mediated by both immunoreactive glial cells and invading lymphocytes. Furthermore, a body of data indicates that the Toll-like receptor (TLR) family of innate immune receptors is implicated in MS progression. In the present study we investigated whether modulation of GABAB receptors using baclofen can exert anti-inflammatory effects by targeting TLR3 and(or) TLR4-induced inflammatory signaling in murine glial cells and human peripheral blood mononuclear cells (PBMCs) isolated from healthy control individuals and patients with the relapse-remitting (RR) form of MS. TLR3 and TLR4 stimulation promoted the nuclear sequestration of NF-κB and pro-inflammatory cytokine expression in murine glia, while TLR4, but not TLR3, promoted pro-inflammatory cytokine expression in PBMCs isolated from both healthy donors and RR-MS patients. Importantly, this effect was exacerbated in RR-MS patient immune cells. We present further evidence that baclofen dose-dependently attenuated TLR3- and TLR4-induced inflammatory signaling in primary glial cells. Pre-exposure of PBMCs isolated from healthy donors to baclofen attenuated TLR4-induced TNF-α expression, but did not affect TLR4-induced TNF-α expression in RR-MS patient PBMCs. Interestingly, mRNA expression of the GABAB receptor was reduced in PBMCs from RR-MS donors when compared to healthy controls, an effect that might contribute to the differential sensitivity to baclofen seen in healthy and RR-MS patient cells. Overall these findings indicate that baclofen differentially regulates TLR3 and TLR4 signaling in glia and immune cells, and offers insight on the role of baclofen in the treatment of neuroinflammatory disease states including MS.

The anti-spasticity drug baclofen alleviates collagen-induced arthritis and regulates dendritic cells

Baclofen is used clinically as a drug that treats spasticity, which is a syndrome characterized by excessive contraction of the muscles and hyperflexia in the central nervous system (CNS), by activating GABA(B) receptors (GABA(B)Rs). Baclofen was recently reported to desensitize chemokine receptors and to suppress inflammation through the activation of GABA(B)Rs. GABA(B)Rs are expressed in various immune cells, but the functions of these receptors in autoimmune diseases remain largely unknown. In this study, we investigated the effects of baclofen in murine collagen-induced arthritis (CIA). Oral administration of baclofen alleviated the clinical development of CIA, with a reduced number of IL-17-producing T helper 17 (T(H)17) cells. In addition, baclofen treatment suppressed dendritic cell (DC)-primed T(H)17 cell differentiation by reducing the production of IL-6 by DCs in vitro. Furthermore, the pharmacological and genetic blockade of GABA(B)Rs in DCs weakened the effects of baclofen, indicating that GABA(B)Rs are the molecular targets of baclofen on DCs. Thus, our findings revealed a potential role for baclofen in the treatment of CIA, as well as a previously unknown signaling pathway that regulates DC function.

Baclofen, a GABABR agonist, ameliorates immune-complex mediated acute lung injury by modulating pro-inflammatory mediators

Immune-complexes play an important role in the inflammatory diseases of the lung. Neutrophil activation mediates immune-complex (IC) deposition-induced acute lung injury (ALI). Components of gamma amino butyric acid (GABA) signaling, including GABA B receptor 2 (GABA_BR2), GAD65/67 and the GABA transporter, are present in the lungs and in the neutrophils. However, the role of pulmonary GABA_BR activation in the context of neutrophil-mediated ALI has not been determined. Thus, the objective of the current study was to determine whether administration of a GABA_BR agonist, baclofen would ameliorate or exacerbate ALI. We hypothesized that baclofen would regulate IC-induced ALI by preserving pulmonary GABA_BR expression. Rats were subjected to sham injury or IC-induced ALI and two hours later rats were treated intratracheally with saline or 1 mg/kg baclofen for 2 additional hours and sacrificed. ALI was assessed by vascular leakage, histology, TUNEL, and lung caspase-3 cleavage. ALI increased total protein, tumor necrosis factor α (TNF-α and interleukin-1 receptor associated protein (IL-1R AcP), in the bronchoalveolar lavage fluid (BALF). Moreover, ALI decreased lung GABA_BR2 expression, increased phospho-p38 MAPK, promoted IκB degradation and increased neutrophil influx in the lung. Administration of baclofen, after initiation of ALI, restored GABA_BR expression, which was inhibited in the presence of a GABA_BR antagonist, CGP52432. Baclofen administration activated pulmonary phospho-ERK and inhibited p38 MAPK phosphorylation and IκB degradation. Additionally, baclofen significantly inhibited pro-inflammatory TNF-α and IL-1βAcP release and promoted BAL neutrophil apoptosis. Protective effects of baclofen treatment on ALI were possibly mediated by inhibition of TNF-α- and IL-1β-mediated inflammatory signaling. Interestingly, GABA_BR2 expression was regulated in the type II pneumocytes in lung tissue sections from lung injured patients, further suggesting a physiological role for GABA_BR2 in the repair process of lung damage. GABA_BR2 agonists may play a potential therapeutic role in ALI.

GABA and GABA receptors in the gastrointestinal tract: from motility to inflammation

Although an extensive body of literature confirmed γ-aminobutyric acid (GABA) as mediator within the enteric nervous system (ENS) controlling gastrointestinal (GI) function, the true significance of GABAergic signalling in the gut is still a matter of debate. GABAergic cells in the bowel include neuronal and endocrine-like cells, suggesting GABA as modulator of both motor and secretory GI activity. GABA effects in the GI tract depend on the activation of ionotropic GABAA and GABAC receptors and metabotropic GABAB receptors, resulting in a potential noteworthy regulation of both the excitatory and inhibitory signalling in the ENS. However, the preservation of GABAergic signalling in the gut could not be limited to the maintenance of physiologic intestinal activity. Indeed, a series of interesting studies have suggested a potential key role of GABA in the promising field of neuroimmune interaction, being involved in the modulation of immune cell activity associated with different systemic and enteric inflammatory conditions. Given the urgency of novel therapeutic strategies against chronic immunity-related pathologies, i.e. multiple sclerosis and Inflammatory Bowel Disease, an in-depth comprehension of the enteric GABAergic system in health and disease could provide the basis for new clinical application of nerve-driven immunity. Hence, in the attempt to drive novel researches addressing both the physiological and pathological importance of the GABAergic signalling in the gut, we summarized current evidence on GABA and GABA receptor function in the different parts of the GI tract, with particular focus on the potential involvement in the modulation of GI motility and inflammation.

CXCL12 chemokine and GABA neurotransmitter systems crosstalk and their putative roles

Since CXCL12 and its receptors, CXCR4 and CXCR7, have been found in the brain, the role of this chemokine has been expanded from chemoattractant in the immune system to neuromodulatory in the brain. Several pieces of evidence suggest that this chemokine system could crosstalk with the GABAergic system, known to be the main inhibitory neurotransmitter system in the brain. Indeed, GABA and CXCL12 as well as their receptors are colocalized in many cell types including neurons and there are several examples in which these two systems interact. Several mechanisms can be proposed to explain how these systems interact, including receptor–receptor interactions, crosstalk at the level of second messenger cascades, or direct pharmacological interactions, as GABA and GABA_B receptor agonists/antagonists have been shown to be allosteric modulators of CXCR4. The interplay between CXCL12/CXCR4-CXCR7 and GABA/GABA_A-GABA_B receptors systems could have many physiological implications in neurotransmission, cancer and inflammation. In addition, the GABA_B agonist baclofen is currently used in medicine to treat spasticity in patients with spinal cord injury, cerebral palsy, traumatic brain injury, multiple sclerosis, and other disorders. More recently it has also been used in the treatment of alcohol dependence and withdrawal. The allosteric effects of this agent on CXCR4 could contribute to these beneficial effects or at the opposite, to its side effects.

Opposite role played by GABAA and GABAB receptors in the modulation of peristaltic activity in mouse distal colon

We investigated the role of GABA on intestinal motility using as model the murine distal colon. Effects induced by GABA receptors recruitment were examined in whole colonic segments and isolated circular muscle preparations to analyze their influence on peristaltic reflex and on spontaneous and neurally-evoked contractions. Using a modified Trendelenburg set-up, rhythmic peristaltic contractions were evoked by gradual distension of the colonic segments. Spontaneous and neurally-evoked mechanical activity of circular muscle strips were recorded in vitro as changes in isometric tension. GABA, at low concentrations (10-50 µM), potentiated peristaltic activity and the neural cholinergic contractions, whilst it, at higher concentrations (500 µM-1mM), had inhibitory effects. GABA excitatory effects were mimicked by muscimol, GABAA-receptor agonist, and prevented by bicuculline, GABAA-receptor antagonist, which per se reduced peristaltic activity and the cholinergic contractile responses. Inhibitory effects were mimicked by baclofen, GABAB-receptor agonist, and antagonized by phaclofen, GABAB-receptor antagonist and by hexamethonium, neural nicotinic receptor antagonist. Guanethidine was ineffective on GABA effects. Non-cholinergic responses were not affected by GABA agents. All drugs failed to affect the response to carbachol. Lastly, GABAC receptor agonist/antagonist had any effect on colonic motility. In conclusion, GABA in mouse distal colon is a modulator of peristaltic activity via the regulation of acetylcholine release from cholinergic neurons through interaction with GABAA or GABAB receptors. GABAA receptors are recruited at low GABA concentrations, increasing acetylcholine release and propulsive activity. At high GABA concentrations the activation of GABAB receptors overrides GABAA receptor effects, decreasing acetylcholine release and peristaltic activity.

CXCL12 chemokine and its receptors as major players in the interactions between immune and nervous systems

The chemokine CXCL12/stromal cell-derived factor 1 alpha has first been described in the immune system where it functions include chemotaxis for lymphocytes and macrophages, migration of hematopoietic cells from fetal liver to bone marrow and the formation of large blood vessels. Among other chemokines, CXCL12 has recently attracted much attention in the brain as it has been shown that it can be produced not only by glial cells but also by neurons. In addition, its receptors CXCR4 and CXCR7, which are belonging to the G protein-coupled receptors family, are abundantly expressed in diverse brain area, CXCR4 being a major co-receptor for human immunodeficiency virus 1 entry. This chemokine system has been shown to play important roles in brain plasticity processes occurring during development but also in the physiology of the brain in normal and pathological conditions. For example, in neurons, CXCR4 stimulation has been shown regulate the synaptic release of glutamate and γ-aminobutyric acid (GABA). It can also act post-synaptically by activating a G protein activated inward rectifier K⁺ (GIRK), a voltage-gated K channel Kv2.1 associated to neuronal survival, and by increasing high voltage activated Ca²⁺ currents. In addition, it has been recently evidenced that there are several cross-talks between the CXCL12/CXCR4–7 system and other neurotransmitter systems in the brain (such as GABA, glutamate, opioids, and cannabinoids). Overall, this chemokine system could be one of the key players of the neuro-immune interface that participates in shaping the brain in response to changes in the environment.

Identification of novel autoantibodies to GABA(B) receptors in patients with neuropsychiatric systemic lupus erythematosus

OBJECTIVE

The gamma-aminobutyric acid type B receptors (GABAR(B)) are G-protein coupled receptors for GABA, the main inhibitory neurotransmitter in the brain. We identified GABAR(B) subunits as candidate antigens in patients with SLE using a random peptide display library. The aim of this study was to investigate the possible link between anti-GABAR(B) antibodies and disease activity and NPSLE.

METHODS

ELISA was performed with recombinant proteins of GABAR(B1b) and GABAR(B2) on serum samples from patients with SLE (n = 88), scleroderma (n = 20), myositis (n = 20) or vasculitis (n = 20) as well as healthy subjects (n = 20). Cerebrospinal fluid (CSF) from 23 patients with SLE was also examined.

RESULTS

Autoantibodies to GABAR(Bs) were exclusive to patients with SLE (P < 0.001) and positively associated with SLEDAI (anti-GABAR(B1b), P = 0.001; anti-GABAR(B2), P < 0.001). Of note, autoantibodies were positively linked with NPSLE (anti-GABAR(B1b), P = 0.02; anti-GABAR(B2), P = 0.03). Moreover, anti-GABAR(Bs) was detected in 61.5% of CSF samples from patients with active NPSLE, a frequency that was significantly higher than that for patients with non-SLE syndromes.

CONCLUSION

Anti-GABAR(B) antibodies could represent novel candidate markers for disease activity and NPSLE.

Role of chemokines in proteinuric kidney disorders

Experimental and human studies have shown that proteinuria contributes to the progression of renal disease. Overexposure to filtered proteins promotes the expression and release of chemokines by tubular epithelial cells, thus leading to inflammatory cell recruitment and renal impairment. This review focuses on recent progress in cellular and molecular understanding of the role of chemokines in the pathogenesis of proteinuria-induced renal injury, as well as their clinical implications and therapeutic potential.

Baclofen and other GABAB receptor agents are allosteric modulators of the CXCL12 chemokine receptor CXCR4

CXCR4, a receptor for the chemokine CXCL12 (stromal-cell derived factor-1α), is a G-protein-coupled receptor (GPCR), expressed in the immune and CNS and integrally involved in various neurological disorders. The GABAB receptor is also a GPCR that mediates metabotropic action of the inhibitory neurotransmitter GABA and is located on neurons and immune cells as well. Using diverse approaches, we report novel interaction between GABAB receptor agents and CXCR4 and demonstrate allosteric binding of these agents to CXCR4. First, both GABAB antagonists and agonists block CXCL12-elicited chemotaxis in human breast cancer cells. Second, a GABAB antagonist blocks the potentiation by CXCL12 of high-threshold Ca(2+) channels in rat neurons. Third, electrophysiology in Xenopus oocytes and human embryonic kidney cell line 293 cells in which we coexpressed rat CXCR4 and the G-protein inward rectifier K(+) (GIRK) channel showed that GABAB antagonist and agonist modified CXCL12-evoked activation of GIRK channels. To investigate whether GABAB ligands bind to CXCR4, we expressed this receptor in heterologous systems lacking GABAB receptors and performed competition binding experiments. Our fluorescent resonance energy transfer experiments suggest that GABAB ligands do not bind CXCR4 at the CXCL12 binding pocket suggesting allosteric modulation, in accordance with our electrophysiology experiments. Finally, using backscattering interferometry and lipoparticles containing only the CXCR4 receptor, we quantified the binding affinity for the GABAB ligands, confirming a direct interaction with the CXCR4 receptor. The effect of GABAergic agents on CXCR4 suggests new therapeutic potentials for neurological and immune diseases.

Inhibitory role for GABA in atherosclerosis

γ-Aminobutyric acid (GABA), the classical inhibitory neurotransmitter in the nervous system, has a parallel inhibitory role in the immune system. It affects a variety of functional properties of the immune cells like monocyte migration, macrophage cholesterol efflux, regulatory T cell proliferation and inflammatory cytokine secretion. All of these are the main pathologic processes of atherosclerosis, a chronic inflammatory disease involving both innate and adaptive immune responses in the artery wall. Moreover, GABA has neuroprotective effects in brain ischemic injury, which is one of the serious complications of atherosclerosis. Therefore, we hypothesize GABA may be a prospect immune cell targeting therapy in atherosclerosis.

Targeting chemokines in proteinuria-induced renal disease

INTRODUCTION

Proteinuria is a common finding in glomerular diseases that contributes to the progression of chronic kidney injury. Tubular cells reabsorb the excess of albumin and other plasma proteins from the tubular lumen, triggering several pathophysiologic responses, such as overexpression of fibrogenic mediators and inflammatory chemokines. Chemokines are implicated both in the recruitment of inflammatory infiltrate and in a number of physiological and pathological processes related to protein overload.

AREAS COVERED

In recent years, the specific chemokines and their receptors and the intracellular signaling pathways involved in proteinuria-induced renal damage have been identified. This review provides an overview of the role of chemokines and their receptors in proteinuria-related renal disease and summarizes novel therapeutic approaches to restrain the progression of renal damage.

EXPERT OPINION

Inhibition of chemokine-induced biological activities is a promising therapeutic strategy in proteinuric disorders. Neutralizing antibodies and small organic molecules targeting chemokines and chemokine receptors have been proven to prevent inflammation and renal damage in experimental models of protein overload. Some of these compounds are currently being tested in human clinical trials.

Systemic treatment with the inhibitory neurotransmitter γ-aminobutyric acid aggravates experimental autoimmune encephalomyelitis by affecting proinflammatory immune responses

Transcriptomic and proteomic analyses of multiple sclerosis (MS) lesions indicate alterations in the gamma-aminobutyric acid (GABA) inhibitory system, suggesting its involvement in the disease process. To further elucidate the role of GABA in central nervous system (CNS) inflammation in vivo, the chronic myelin oligodendrocyte glycoprotein (MOG)(35-55) experimental autoimmune encephalomyelitis (EAE) model was used. Daily GABA injections (200mg/kg) from day 3 onwards significantly augmented disease severity, which was associated with increased CNS mRNA expression levels of tumor necrosis factor alpha (TNF-α) and interleukin (IL)-6. GABA-treated mice showed enhanced MOG-dependent proliferation and were skewed towards a T helper 1 phenotype. Moreover, in vitro, the lipopolysaccharide (LPS)-induced increase in interleukin (IL)-6 production by macrophages was enhanced at low GABA concentrations (0.03-0.3mM). In sharp contrast to exogenous GABA administration, endogenous GABA increment by systemic treatment with the GABA-transaminase inhibitor vigabatrin (250mg/kg) had prophylactic as well as therapeutic potential in EAE. Together, these results indicate an immune amplifying role of GABA in neuroinflammatory diseases like MS.

Effects of anesthetic regimes on inflammatory responses in a rat model of acute lung injury

PURPOSE

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter through activation of GABA receptors. Volatile anesthetics activate type-A (GABA(A)) receptors resulting in inhibition of synaptic transmission. Lung epithelial cells have been recently found to express GABA(A) receptors that exert anti-inflammatory properties. We hypothesized that the volatile anesthetic sevoflurane (SEVO) attenuates lung inflammation through activation of lung epithelial GABA(A) receptors.

METHODS

Sprague-Dawley rats were anesthetized with SEVO or ketamine/xylazine (KX). Acute lung inflammation was induced by intratracheal instillation of endotoxin, followed by mechanical ventilation for 4 h at a tidal volume of 15 mL/kg without positive end-expiratory pressure (two-hit lung injury model). To examine the specific effects of GABA, healthy human lung epithelial cells (BEAS-2B) were challenged with endotoxin in the presence and absence of GABA with and without addition of the GABA(A) receptor antagonist picrotoxin.

RESULTS

Anesthesia with SEVO improved oxygenation and reduced pulmonary cytokine responses compared to KX. This phenomenon was associated with increased expression of the π subunit of GABA(A) receptors and glutamic acid decarboxylase (GAD). The endotoxin-induced cytokine release from BEAS-2B cells was attenuated by the treatment with GABA, which was reversed by the administration of picrotoxin.

CONCLUSION

Anesthesia with SEVO suppresses pulmonary inflammation and thus protects the lung from the two-hit injury. The anti-inflammatory effect of SEVO is likely due to activation of pulmonary GABA(A) signaling pathways.