Hydrogen peroxide production by alveolar type II cells, alveolar macrophages, and endothelial cells

Extracellular H2O2 release and intracellular H2O2 production were determined in rat lung alveolar macrophages, rat alveolar type II cells, and cultured bovine aortic endothelial cells. Isolated macrophages (5 h ex vivo) released 3.1 +/- 0.09 nmol H2O2.min-1.mg cell protein-1, freshly isolated (5 h ex vivo) type II cells released 0.7 +/- 0.07 nmol H2O2.min-1.mg protein-1, and cultured endothelial cells released 0.06 +/- 0.005 nmol H2O2.min-1.mg protein-1. The rate of extracellular H2O2 release decreased rapidly over time in both fresh macrophages and freshly isolated type II cells. When the measurements were repeated at different times ex vivo, the decrease was greater than 20%/h, and H2O2 release was almost undetectable 12 h ex vivo. The decrease occurred while lactate dehydrogenase release, catalase activity, and intracellular H2O2 production remained unchanged. Catalase activity was 59.3 +/- 4.9 nmol O2 produced.min-1.mg protein-1 in type II cells, 13.2 +/- 1.8 in macrophages, and 11.4 +/- 2.7 in endothelial cells. Aminotriazole is a compound that inhibits catalase in the presence of H2O2 at a rate that is proportional to the rate of intracellular H2O2 production in or near peroxisomes. Incubation of the cells with aminotriazole led to a rapid inhibition of catalase. In 15 min the reduction of catalase activity was 69% in type II cells, 53% in macrophages, and 37% in endothelial cells. When freshly isolated type II cells were exposed to hyperoxia (95% O2) for 30 min, no changes in the rate of either intracellular H2O2 production or extracellular H2O2 release were seen.