Date of Award

2020

Document Type

Dissertation

Degree Name

Philosophy (Ph.D)

Department

Pharmaceutical Sciences

First Advisor

Lin L Mantell

Second Advisor

Joanne M Carroll

Third Advisor

Francis X Schanne

Abstract

Prolonged exposure to hyperoxia can compromise macrophage bacterial clearance functions, contributing to the increased susceptibility to pulmonary infections observed in hospital and ventilator-associated pneumonia (HAP/VAP). Previously studies in our lab demonstrate that activation of the α7 nicotinic acetylcholine receptor (α7nAChR) has protective effects against proinflammatory lung injury in animals subjected to prolonged hyperoxic exposure and bacterial infections. In this study, we demonstrated that administration of GAT107, an α7nAChR agonistic positive allosteric modulator (ago-PAM), improved survival by attenuating hyperoxia-compromised bacterial clearing functions of mice with Pseudomonas aeruginosa (PA) lung infection. GAT107 decreased the bacterial burden in mice lungs by attenuating the hyperoxia-compromised phagocytic functions of both cultured macrophages, RAW 264.7 cells, and those isolated from mice. In hyperoxia-exposed RAW macrophages, GAT107 treatment attenuated oxidation of F-actin, a critical cytoskeletal component involved in phagocytosis. In hyperoxia-compromised mice with PA lung infection, GAT107 ameliorated hyperoxia-induced oxidative stress levels and increased the antioxidant oxidant potential in lung tissues and also in cultured macrophages. GAT107 induced the activation of the master antioxidant transcription factor, Nrf2, and significantly increased the levels of its down-stream antioxidant heme oxygenase-1 (HO-1) protein in macrophages. In macrophages, hyperoxia induced mitochondrial membrane perturbation and also elevated mitochondrial superoxide (mitoSOX) levels, which was attenuated with GAT107 treatment. GAT107 decreased mitoSOX via attenuating hyperoxia-compromised manganese superoxide dismutase (MnSOD) activity and had no effect on its total protein levels. MnSOD activity was found to be strongly correlated with the extent of cysteine glutathionylation, which was attenuated in GAT107-treated macrophages. Thus, these data suggest that GAT107 provides protective effects against PA infection-induced inflammatory lung injury via attenuating hyperoxia-impaired macrophage function via restoring redox balance. GAT107-elicited efficacy in macrophage functions under hyperoxic conditions is through restoring the redox imbalance mediated partly by mitochondrial stress and MnSOD functions. Thus, GAT107 may be a potential therapeutic agent acting to improve host defense functions in the subjects exposed to prolonged periods of hyperoxia, such as VAP, HAP, and COVID-19.

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