Dose-time dependency of hyperbaric hyperoxia-induced DNA strand breaks in human immune cells visualized with the comet assay.

Undersea & hyperbaric medicine : journal of the Undersea and Hyperbaric Medical Society, Inc

PubMedID: 24984312

Witte J, Kähler W, Wunderlich T, Radermacher P, Wohlrab C, Koch A. Dose-time dependency of hyperbaric hyperoxia-induced DNA strand breaks in human immune cells visualized with the comet assay. Undersea Hyperb Med. 2014;41(3):171-81.
PURPOSE
Hyperbaric oxygen exposure may induce dose-dependent DNA damage in peripheral blood mononuclear cells (PBMCs), and repetitive exposures of man may have protective cellular effects.

METHOD
PBMCs, freshly isolated from non-divers and pure oxygen divers, were exposed to ambient air (21kPa) and hyperoxia at different levels: 100kPa, 240kPa, 400kPa and 600kPa) for up to 6.5 hours in an experimental pressure chamber. DNA double-strand breaks were studied in the comet assay by calculating the "tail moment" and an alternative "Yes or No" method for damaged nuclei. Previously, the experimental procedure had been optimized for human cell experiments: Pre-tests assured that DNA damage could be considered to be oxygen-induced; and cell viability remained over 95% during exposure time.

RESULTS
Visible DNA damage increased with the partial pressure of oxygen (pO2) and exposure time dose-dependently. Linear regressions revealed r2 between 0.61 and 0.98 with the Yes/No method, and significant differences in slopes from control. Tail moment showed similar results, but with less accuracy. The PBMCs of oxygen divers exposed to 400kPa pO2 (up to six hours) showed a significant lower slope in the linear regression.

CONCLUSION
Oxygen induces dose-dependent DNA double-strand breaks, and the Yes/No discrimination is superior to the tail moment in linearity and accuracy. Oxygen diver PBMCs seem to be more resistant to hyperbaric oxygen.