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.