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1.
Mol Med ; 26(1): 98, 2020 10 30.
Article in English | MEDLINE | ID: covidwho-894987

ABSTRACT

BACKGROUND: Mechanical ventilation, in combination with supraphysiological concentrations of oxygen (i.e., hyperoxia), is routinely used to treat patients with respiratory distress, such as COVID-19. However, prolonged exposure to hyperoxia compromises the clearance of invading pathogens by impairing macrophage phagocytosis. Previously, we have shown that the exposure of mice to hyperoxia induces the release of the nuclear protein high mobility group box-1 (HMGB1) into the pulmonary airways. Furthermore, extracellular HMGB1 impairs macrophage phagocytosis and increases the mortality of mice infected with Pseudomonas aeruginosa (PA). The aim of this study was to determine whether GTS-21 (3-(2,4-dimethoxybenzylidene) anabaseine), an α7 nicotinic acetylcholine receptor (α7nAChR) agonist, could (1) inhibit hyperoxia-induced HMGB1 release into the airways; (2) enhance macrophage phagocytosis and (3) increase bacterial clearance from the lungs in a mouse model of ventilator-associated pneumonia. METHOD: GTS-21 (0.04, 0.4, and 4 mg/kg) or saline were administered by intraperitoneal injection to mice that were exposed to hyperoxia (≥ 99% O2) and subsequently challenged with PA. RESULTS: The systemic administration of 4 mg/kg i.p. of GTS-21 significantly increased bacterial clearance, decreased acute lung injury and decreased accumulation of airway HMGB1 compared to the saline control. To determine the mechanism of action of GTS-21, RAW 264.7 cells, a macrophage-like cell line, were incubated with different concentrations of GTS-21 in the presence of 95% O2. The phagocytic activity of macrophages was significantly increased by GTS-21 in a dose-dependent manner. In addition, GTS-21 significantly inhibited the cytoplasmic translocation and release of HMGB1 from RAW 264.7 cells and attenuated hyperoxia-induced NF-κB activation in macrophages and mouse lungs exposed to hyperoxia and infected with PA. CONCLUSIONS: Our results indicate that GTS-21 is efficacious in improving bacterial clearance and reducing acute lung injury via enhancing macrophage function by inhibiting the release of nuclear HMGB1. Therefore, the α7nAChR represents a possible pharmacological target to improve the clinical outcome of patients on ventilators by augmenting host defense against bacterial infections.


Subject(s)
Benzylidene Compounds/pharmacology , Hyperoxia/immunology , Macrophages, Alveolar/drug effects , Pseudomonas Infections/drug therapy , Pyridines/pharmacology , Ventilator-Induced Lung Injury/drug therapy , alpha7 Nicotinic Acetylcholine Receptor/antagonists & inhibitors , Animals , Disease Models, Animal , HMGB1 Protein/metabolism , Hyperoxia/diet therapy , Macrophages, Alveolar/immunology , Macrophages, Alveolar/metabolism , Male , Mice , Mice, Inbred C57BL , Phagocytosis/drug effects , Pseudomonas aeruginosa , RAW 264.7 Cells
2.
Neurochem Int ; 138: 104779, 2020 09.
Article in English | MEDLINE | ID: covidwho-436706

ABSTRACT

The brain nicotinic acetylcholine receptors (nAChRs) expressed in pre-synaptic nerve terminals regulate neurotransmitter release. However, there is no evidence for the expression of nAChRs in synaptic vesicles, which deliver neurotransmitter to synaptic cleft. The aim of this paper was to investigate the presence of nAChRs in synaptic vesicles purified from the rat brain and to study their possible involvement in vesicles life cycle. According to dynamic light scattering analysis, the antibody against extracellular domain (1-208) of α7 nAChR subunit inhibited synaptic vesicles clustering. Sandwich ELISA with nAChR subunit-specific antibodies demonstrated the presence of α4ß2, α7 and α7ß2nAChR subtypes in synaptic vesicles and showed that α7 and ß2 nAChR subunits are co-localized with synaptic vesicle glycoprotein 2A (SV2A). Pre-incubation with either α7-selective agonist PNU282987 or nicotine did not affect synaptic vesicles clustering but delayed their Ca2+-dependent fusion with the plasma membranes. In contrast, nicotine but not PNU282987 stimulated acidification of isolated synaptic vesicles, indicating that α4ß2 but not α7-containing nAChRs are involved in regulation of proton influx and neurotransmitter refilling. Treatment of rats with levetiracetam, a specific modulator of SV2A, increased the content of α7 nAChRs in synaptic vesicles accompanied by increased clustering but decreased Ca2+-dependent fusion. These data for the first time demonstrate the presence of nAChRs in synaptic vesicles and suggest an active involvement of cholinergic regulation in neurotransmitter release. Synaptic vesicles may be an additional target of nicotine inhaled upon smoking and of α7-specific drugs widely discussed as anti-inflammatory and pro-cognitive tools.


Subject(s)
Brain/metabolism , Cell Membrane/metabolism , Membrane Fusion/physiology , Synaptic Vesicles/metabolism , alpha7 Nicotinic Acetylcholine Receptor/metabolism , Animals , Brain/drug effects , Cell Membrane/drug effects , Female , Hydrogen-Ion Concentration , Male , Membrane Fusion/drug effects , Mice , Mice, Inbred C57BL , Mice, Knockout , Nicotinic Agonists/pharmacology , Nicotinic Antagonists/pharmacology , Rats , Rats, Wistar , Synaptic Vesicles/drug effects , alpha7 Nicotinic Acetylcholine Receptor/agonists , alpha7 Nicotinic Acetylcholine Receptor/antagonists & inhibitors
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