Hyperoxia Decreases Glycolytic Capacity, Glycolytic Reserve and Oxidative Phosphorylation in MLE-12 Cells and Inhibits Complex I and II Function, but Not Complex IV in Isolated Mouse Lung Mitochondria

Kumuda C Das,Mika Jekabsons

doi:10.1371/journal.pone.0073358

Kumuda C Das, Mika Jekabsons

Open Access

https://doi.org/10.1371/journal.pone.0073358

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Abstract

High levels of oxygen (hyperoxia) are frequently used in critical care units and in conditions of respiratory insufficiencies in adults, as well as in infants. However, hyperoxia has been implicated in a number of pulmonary disorders including bronchopulmonary dysplasia (BPD) and adult respiratory distress syndrome (ARDS). Hyperoxia increases the generation of reactive oxygen species (ROS) in the mitochondria that could impair the function of the mitochondrial electron transport chain. We analyzed lung mitochondrial function in hyperoxia using the XF24 analyzer (extracellular flux) and optimized the assay for lung epithelial cells and mitochondria isolated from lungs of mice. Our data show that hyperoxia decreases basal oxygen consumption rate (OCR), spare respiratory capacity, maximal respiration and ATP turnover in MLE-12 cells. There was significant decrease in glycolytic capacity and glycolytic reserve in MLE-12 cells exposed to hyperoxia. Using mitochondria isolated from lungs of mice exposed to hyperoxia or normoxia we have shown that hyperoxia decreased the basal, state 3 and state3 μ (respiration in an uncoupled state) respirations. Further, using substrate or inhibitor of a specific complex we show that the OCR via complex I and II, but not complex IV was decreased, demonstrating that complexes I and II are specific targets of hyperoxia. Further, the activities of complex I (NADH dehydrogenase, NADH-DH) and complex II (succinate dehydrogenase, SDH) were decreased in hyperoxia, but the activity of complex IV (cytochrome oxidase, COX) remains unchanged. Taken together, our study show that hyperoxia impairs glycolytic and mitochondrial energy metabolism in in tact cells, as well as in lungs of mice by selectively inactivating components of electron transport system.

Highlights

Supplemental oxygen therapy is a frequent modality in critical care units and is required for patients with compromised oxygen availability
In the present report we have shown that exposure of type II mouse lung epithelial cells (MLE-12) to 24-hours of hyperoxia decreases basal oxygen consumption rate (OCR), ATP turnover, maximal respiration and spare respiratory capacity (SRC)
We have shown that, whereas there was no significant change in the rate of glycolysis in normoxia or hyperoxia, glycolytic capacity and glycolytic reserve were significantly decreased in cells exposed to hyperoxia

Summary

Introduction

Supplemental oxygen therapy is a frequent modality in critical care units and is required for patients with compromised oxygen availability. High levels of oxygen (hyperoxia) are used in conjunction with anesthetics for protection against hypoxemia [1]. Hyperoxia is administered to premature newborn infants, which is believed to be a factor in the development of BPD [2]. Supplemental oxygen therapy is clinically important, significant oxygen toxicity in the lung resulting from hyperoxia is a major impediment in the use of oxygen therapy [3]. Perturbed energy metabolism in hyperoxia is believed to cause impaired lung growth and repair during and following hyperoxia. Mitochondrial dysfunction in hyperoxia has been shown to cause alveolar developmental arrest in a mouse BPD model [4]. Understanding the molecular mechanisms of lung energy metabolism in hyperoxia is important to developing an appropriate intervention strategy for supplemental oxygen therapy

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