102 - GAT107, a Novel Agonistic Positive Allosteric Modulator of α7 Nicotinic Acetylcholine Receptor Restores Hyperoxia-Compromised Macrophage Function

Abstract

Macrophages are the first line of defense against invading pathogens. However, exposure to prolonged hyperoxia compromises their ability to phagocytose and kill bacteria. Exposure to prolonged hyperoxia (≥95% O2) leads to the release of nuclear HMGB1 into the extracellular milieu, where HMGB1 acts as a potent proinflammatory cytokine and suppresses macrophage’s functions (2). The vagus nerve of the autonomous nervous system regulates the secretion of proinflammatory cytokines, thus may modulate HMGB1-mediated damage. Agonists bind to the orthosteric site of α7nAchR and at high concentrations may cause desensitization and can disrupt the endogeous tone of the receptor. Use of ago-PAM (positive allosteric modulator) of the α7nAchR can synergize and enhance orthosteric site mediated signaling without disrupting the endogenous signaling. We tested whether GAT107 (a novel ago-PAM) can (1) decrease hyperoxia-induced HMGB1 release from macrophages and (2) improve hyperoxia-compromised macrophage phagocytosis. RAW 264.7 cells, a macrophage like cell line, were exposed to different concentrations of GAT107 prior to exposure to 95% O2. The results show that GAT107 at trace concentrations (1.1 and 3.3μM) improved hyperoxia-compromised phagocytic ability of macrophages. In addition, at the same concentrations it effectively inhibits oxidative stress-induced release of nuclear HMGB1 to the extracellular milieu at concentrations that are non-toxic to the cells. These data indicate that GAT107 can improve hyperoxia-compromised phagocytosis via inhibiting nuclear HMGB1 release into the extracellular milieu. Therefore, targeting α7nAchR using GAT107 may be a possible novel pharmacological agent that can be used to mediate proinflammatory reflex in macrophages.