Alcohol use disorder (AUD) affects over 28 million people in the United States1. People with AUD are 2-4 times more likely to develop respiratory infections2,3, increasing risk for premature morbidity and mortality3,4,5. Alcohol misuse increases susceptibility to respiratory infections, in part through suppressing lung immune function. Alveolar macrophages (AMs) are the first line of cellular defense against pathogens in the lower lung, where they phagocytize and clear inhaled microbes. However, chronic alcohol consumption impairs the capacity of AMs to engulf and kill pathogens6,7.
The immune functions of AMs, such as phagocytosis, are energy-demanding processes that require metabolically active pathways necessary for high adenosine triphosphate (ATP) generation. Mitochondrial oxidative phosphorylation is the most efficient cellular process for producing ATP, but chronic ethanol (EtOH) exposure increases mitochondrial-derived oxidative stress, which can result in mitochondrial dysfunction in AMs8,9,10. Mitochondrial respiration measured using cellular oxygen consumption rate (OCR) can be quantified using an extracellular flux bioanalyzer in real-time. Mitochondrial respiration profiles assessed in response to oligomycin (ATP synthase inhibitor), carbonyl cyanide- p-trifluoromethoxyphenylhydrazone (FCCP, proton uncoupler), and rotenone/antimycin A (R/A, mitochondrial complex I and III inhibitors, respectively) are used to determine mitochondrial bioenergetics. Chronic EtOH decreases mitochondrial bioenergetics in AMs, as evidenced by diminished mitochondrial basal respiration, ATP-linked respiration, maximal respiration, and spare respiratory capacity10.
Cells have various levels of dependency on sources of fuels, such as pyruvate, glutamine, or fatty acids, for ATP production. They also have a level of flexibility whereby they can switch fuel usage to regulate cellular bioenergetics. Glutaminolysis is a key pathway for mitochondrial respiration, particularly when pyruvate is shunted towards lactic acid production or when fatty acids are insufficient. Our recent study showed that chronic EtOH exposure increases AM dependency on glutamine and decreases AM flexibility to use glutamine and other fuel sources for mitochondrial respiration11. These results, along with data demonstrating that treatment of EtOH-exposed MH-S cells with the pyruvate oxidation inhibitor UK5099 did not alter mitochondrial bioenergetics compared to media control-exposed MH-S cells treated with UK5099, suggested a shift away from pyruvate-dependent respiration and towards glutamine-dependent respiration in EtOH MH-S cells. However, this shift is insufficient to meet AM bioenergetic demands11. Herein, we describe the methods to assess glutamine as a fuel source for mitochondrial respiration in chronic EtOH-exposed AMs using an extracellular flux bioanalyzer. This protocol was created and optimized for a 96-well (11.04 mm2 area) format and should be adjusted for larger cell culture well sizes. Glutamine dependency for mitochondrial bioenergetics is determined using bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl) ethyl sulfide (BPTES, inhibitor of glutaminase 1) to selectively inhibit the enzymatic conversion of glutamine to glutamate. The data presented in this study are additional biological replicates for the media control- and BPTES-treated experimental groups of untreated control- and chronic EtOH-exposed mouse AM cell line, MH-S cells, that are published in Crotty et al.11.