Changes in Intracellular pH Play a Secondary Role in Hydrogen Sulfide-Induced Nasal Cytotoxicity

Abstract

Hydrogen sulfide (H₂S) is a naturally occurring gas that is also associated with several industries. The potential for widespread human inhalation exposure to this toxic gas is recognized as a public health concern. The nasal epithelium is particularly susceptible to H₂S-induced pathology. Cytochrome oxidase inhibition is postulated as one mechanism of H₂S toxicity. Another mechanism by which the weak acid H₂S could cause nasal injury is intracellular acidification and cytotoxicity. To further understand the mechanism by which H₂S damages the nasal epithelium, nasal respiratory and olfactory epithelial cell isolates and explants from naive rats were loaded with the pH-sensitive intracellular chromophore SNARF-1 and exposed to air or 10, 80, 200, or 400 ppm H₂S for 90 min. Intracellular pH was measured using flow cytometry or confocal microscopy. Cell lysates were used to quantify total protein and cytochrome oxidase activity. A modest but statistically significant decrease in intracellular pH occurred following exposure of respiratory and olfactory epithelium to 400 ppm H₂S. Decreased cytochrome oxidase activity was observed following exposure to >10 ppm H₂S in both respiratory and olfactory epithelia. None of the treatments resulted in cytotoxicity. The intracellular acidification of nasal epithelial cells by high-dose H₂S exposure and the inhibition of cytochrome oxidase at much lower H₂S concentrations suggest that changes in intracellular pH play a secondary role in H₂S-induced nasal injury.