Investigating mitochondrial dysfunction in human lung cells exposed to redox-active PM components.

Area of Science:

• Environmental Health
• Cellular Biology
• Toxicology

Background:

• Ambient particulate matter (PM) exposure contributes to cardiopulmonary diseases via oxidative stress.
• 1,2-naphthoquinone (1,2-NQ), a PM component, is a redox-active electrophile previously linked to mitochondrial hydrogen peroxide (H₂O₂) production.
• The precise mechanisms by which 1,2-NQ affects cellular respiration and H₂O₂ production remain unclear.

Purpose of the Study:

• To investigate the effects of 1,2-NQ on mitochondrial respiration in human airway epithelial cells.
• To elucidate the mechanisms underlying 1,2-NQ-induced H₂O₂ production.
• To characterize the impact of 1,2-NQ on cellular oxygen consumption.

Main Methods:

• Utilized extracellular flux analysis to measure oxygen consumption rate (OCR) in BEAS-2B cells and isolated mitochondria.
• Employed complex-specific assays and NADPH depletion (via glucose deprivation) to differentiate mitochondrial and non-mitochondrial oxygen utilization.
• Tested environmentally relevant quinones (1,4-naphthoquinone, 9,10-phenanthrenequinone, 1,4-benzoquinone) for comparison.

Main Results:

• 1,2-NQ exposure caused a rapid, dose-dependent increase in OCR in BEAS-2B cells, independent of mitochondrial respiration.
• This increased OCR exceeded that of mitochondrial uncoupling and was sensitive to NADPH depletion, indicating extra-mitochondrial redox cycling.
• Environmentally relevant redox-cycling quinones mimicked this effect, while non-redox-cycling quinones did not.
• In mitochondria, 1,2-NQ inhibited Complex I-linked respiration, suggesting impaired pyruvate metabolism.

Conclusions:

• 1,2-NQ primarily drives increased oxygen consumption through extra-mitochondrial redox cycling in airway cells.
• A novel mechanism of mitochondrial inhibition by 1,2-NQ involves impairment of Complex I-linked respiration.
• Extracellular flux analysis is valuable for studying redox-active electrophiles in air pollution, though methodological challenges exist.