Reduced expression of DNA glycosylases in post-hypoxic newborn pigs undergoing therapeutic hypothermia

Supplementary oxygen during resuscitation of the asphyxiated newborn is associated with increased generation of reactive oxygen species and oxidative stress. It is suspected that hyperoxic reoxygenation may cause increased damage to DNA, resulting in replication errors, and cell death or potential fixation of mutations if unrepaired. Therapeutic hypothermia may attenuate the development of brain damage after asphyxia, but it is not known how post-hypoxic hyperoxia and hypothermia affect accumulation of DNA-damage and DNA repair. Anaesthetised newborn pigs were randomised to control (n = 6) or severe global hypoxia (n = 46). After 20 min of reoxygenation with either room air or 100% O2, followed by 6.5 h of normothermia (deep rectal temperature 39 °C) or total body cooling (35 °C), oxidative DNA damage (8-hydroxy-2′-deoxyguanosine) in brain, liver and urine, and transcription of DNA repair glycosylases (NEIL1, NEIL3, and OGG1) in brain and liver were measured. Hypoxic pigs displayed increased urinary 8-oxodG levels: mean (SD) 8-oxodG/creatinine was 3.55 (1.46) vs. control 2.02 (0.53), p < 0.05, but levels were not affected by hyperoxia or hypothermia. Accumulation of 8-oxodG in the brain and liver did not differ across groups. Post-hypoxic transcription of DNA glycosylases was down-regulated by hypothermia: OGG1 in hippocampus and liver (p < 0.01); NEIL1 in hippocampus (p < 0.01), cortex and striatum (p < 0.05) and liver (p < 0.001); and NEIL3 in hippocampus (p < 0.01) and cerebellum (p < 0.001). Hyperoxia did not affect transcription of glycosylases in the brain. We confirm increased oxidative stress after hypoxia. DNA repair glycosylases were down-regulated by hypothermia but with no effect on accumulation of oxidative damage in genomic DNA.

Research highlights
► Hypoxia–reoxygenation caused increased oxidative stress.
► There was no accumulation of oxidative DNA damage 6.5 h after hypoxia–reoxygenation.
► Expression of DNA repair glycosylases was down-regulated in hypothermic animals.