Mitochondrial respiratory chain deficiency leads to overexpression of antioxidant enzymes

U937 cell growth in the presence of either chloramphenicol or ethidium bromide rapidly leads to respiratory deficiency. The novel finding of this report is that this response is paralleled by a specific increase in Se-dependent and independent glutathione peroxidase activities as well as of glutathione peroxidase and heme oxygenase mRNAs. Under the same experimental conditions, catalase activity and catalase mRNA do not show appreciable changes. These results can be explained by an increased formation of H2O2 at the early times of development of respiratory deficiency followed by induction of antioxidant enzymes.