Antioxidant vitamin and nucleotide effects on homeostasis human small airway epithelial cells in normoxia and hyperoxia

Homeostasis of the small airway epithelial (SAE) cell monolayer likely is pivotal to maintain defenses against lung insults. We examined the effects of antioxidant vitamins (vitamins C and E) and mononucleotides (AMP and UMP) on homeostasis of human SAE cells (Clonetics); nucleotides may protect against oxidant DNA damage or stress-induced apoptosis. Subconfluent and near-confluent SAE cells were cultured for 2 days in normoxia or hyperoxia (95% O₂). Total cell number and viability, thymidme incorporation, LDH release, and apoptotic changes were measured. In normoxic subconfluence, there was minimal apoptosis but significant thymidine incorporation. Normoxic near-confluent cells had more significant apoptosis and loner thymidine incorporation than subconfluent cells along with more detached non-viable cells. Hyperoxia suppressed thymidine incorporation and augmented apoptosis in both sub- and near-confluent cells, but the effects were greater in subconfluence. Necrosis, as indicated by LDH release, was minimal m all conditions. Vitamin E (10^-7 mol/L) prevented the hyperoxic decline of thymidine incorporation in subconfluence and protected against hyperoxia-induced apoptosis in both subconfluence and near-confluence (p<0.02). Vitamin C (10^-7 mol/L) prevented apoptosis in hyperoxia only in near-confluence (p<0.05). UMP and AMP (10-100 μmol/L) prevented hyperoxia-induced apoptosis in near-confluence (p<0.05) but not in subconfluence. Confluence determines the homeostasis of SAE cells and the effects of hyperoxia and protection by vitamins and nucleotides.