Assessment of Mitochondrial Function and Vascular Permeability in Lungs of Rats Susceptible to Hyperoxia-induced Acute Respiratory Distress Syndrome (ARDS)
Authors: Taheri Pardis , Dash Ranjan , Dave Devanshi , Clough Anne , Jacobs Elizabeth , Audi Said 
Published: May 2023

Objective: ARDS carries a mortality rate >30% due to lack of early detection tools, inability to identify patients at risk for progression, and limited therapies. Exposure of adult rats to hyperoxia (100% O2) is a well-established model of human ARDS, with the first clinical evidence of lung injury after >40 hours and death by 72 hours. Yet, adult rats exposed to 60% O2 for 7 days (H-S) show no clinical signs of injury. However, when pre-exposed to H-S, rats become more susceptible to lung injury as evidenced by a decrease in their subsequent survival time in 100% O2. The objective of this study was to assess mitochondrial function and vascular permeability in lungs of H-S rats to elucidate their role in hyperoxia susceptibility. Methods: Adult Sprague-Dawley rats were exposed to 60% O2 (H-S) or room air (normoxia) for 7 days. Lungs were isolated and the pulmonary vascular endothelial filtration coefficient ( Kf ) was determined as a measure of pulmonary vascular permeability, and lung tissue mitochondrial membrane potential (Δψm) was determined using the cationic dye rhodamine 6G. Expression of the electron transport chain complexes was measured in lung tissue homogenate using western blotting. Finally, mitochondria were isolated from lung tissue and Δψm was probed using the cationic dye rhodamine 123. Results: H-S rats gained body weight at the same rate as normoxic rats, with no difference in lung wet weight or wet/dry weight ratio. Kf was 178% larger in H-S lungs compared to normoxics. Lung tissue homogenate studies showed decreased complex I (-81%) and II (-23%) expression, but increased complex IV (+31%) expression, with no change in complex III or V expression. Isolated mitochondria studies showed that H-S resulted in an increase in the time needed for Δψm repolarization following ADP-stimulated depolarization in the presence of complex I (+64%) or complex II (+23%) substrates, consistent with decreased complex I and II activity. In contrast, Δψm in isolated perfused lungs was relatively unchanged in lungs of H-S rats. Discussion: Increase in complex IV expression along with an excess of complex I, which is the case in health, might be sufficient to overcome the effect of a decrease in complex I expression and maintain Δψm in lungs of H-S rats. However, after sensitization, complex I expression is low enough that additional stress (e.g., exposure to 100% O2) which further decreases complex I expression and deteriorates lung tissue mitochondrial bioenergetics, may have significant effect on lung tissue cellular functions. These observations suggest a potential role for mitochondrial dysfunction and vascular permeability in the susceptibility of H-S rats to hyperoxia-induced ARDS, which is clinically relevant since ventilation with 60% O2 is often required for prolonged periods of time, particularly with COVID-19. We thank Sushma Kaul for her help with the experiments. This work was supported by NIH 2R15HL129209-02 (Audi, Clough, Jacobs), NSF DMS 2153387 (Dash), and VA Merit Review Award BX001681 (Jacobs, Audi, Clough). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.