The double edge of reactive oxygen species as damaging and signaling molecules in HL60 cell culture.

Aims: Our aim was to establish the conditions in which reactive oxygen species produce pathological or hormetic effects on HL60 cells.

Methods: HL60 cells were treated with either single bouts (1, 10 and 100 microM) or a sustained production (0.1, 1.0 and 10.0 nM/s) of H(2)O(2).

Results: Exposure to 10 and 100 microM H(2)O(2) activated catalase, glutathione peroxidase and glutathione reductase through post-transcriptional mechanisms and induced oxidative modification of proteins. When cells where exposed to sustained H(2)O(2) production, a clear dose-response effect was detected in the activity of the antioxidant enzymes catalase, glutathione peroxidase and Mn-SOD, with higher concentrations of H(2)O(2) inducing greater enzyme activities. Catalase, HO-1, UCP-3, iNOS and PGC-1alpha expressions were activated after sustained exposure to 1 and 10 nM H(2)O(2)/s. Although the antioxidant defenses were activated, oxidative damage appeared in DNA and proteins in cells treated with 1 and 10 nM/s.

Conclusions: HL60 cells respond to exposure to sustained levels of H(2)O(2) in a dose-response manner to H(2)O(2) concentration by activating the expression and activity of the antioxidant machinery, although the activation of the antioxidant defenses is not enough to avoid the appearance of oxidative damage. Of the two designs proposed, continuous exposure seems to be more appropriate to study the antioxidant response of HL60 cells to H(2)O(2).