Exogenous ketone salts inhibit superoxide production in the rat caudal solitary complex during exposure to normobaric and hyperbaric hyperoxia.

The use of hyperbaric oxygen (HBO2) in hyperbaric and undersea medicine is limited by the risk of seizures [i.e., central nervous system (CNS) oxygen toxicity, CNS-OT] resulting from increased production of reactive oxygen species (ROS) in the CNS. Importantly, ketone supplementation has been shown to delay onset of CNS-OT in rats by ∼600% in comparison with control groups (D'Agostino DP, Pilla R, Held HE, Landon CS, Puchowicz M, Brunengraber H, Ari C, Arnold P, Dean JB. Am J Physiol Regu Integr Comp Physiol 304: R829-R836, 2013). We have tested the hypothesis that ketone body supplementation inhibits ROS production during exposure to hyperoxygenation in rat brainstem cells. We measured the rate of cellular superoxide ([Formula: see text]) production in the caudal solitary complex (cSC) in rat brain slices using a fluorogenic dye, dihydroethidium (DHE), during exposure to control O2 (0.4 ATA) followed by 1-2 h of normobaric oxygen (NBO2) (0.95 ATA) and HBO2 (1.95, and 4.95 ATA) hyperoxia, with and without a 50:50 mixture of ketone salts (KS) dl-β-hydroxybutyrate + acetoacetate. All levels of hyperoxia tested stimulated [Formula: see text] production similarly in cSC cells and coexposure to 5 mM KS during hyperoxia significantly blunted the rate of increase in DHE fluorescence intensity during exposure to hyperoxia. Not all cells tested produced [Formula: see text] at the same rate during exposure to control O2 and hyperoxygenation; cells that increased [Formula: see text] production by >25% during hyperoxia in comparison with baseline were inhibited by KS, whereas cells that did not reach that threshold during hyperoxia were unaffected by KS. These findings support the hypothesis that ketone supplementation decreases the steady-state concentrations of superoxide produced during exposure to NBO2 and HBO2 hyperoxia.NEW & NOTEWORTHY Exposure of rat medullary tissue slices to levels of O2 that mimic those that cause seizures in rats stimulates cellular superoxide ([Formula: see text]) production to varying degrees. Cellular [Formula: see text] generation in the caudal solitary complex is variable during exposure to control O2 and hyperoxia and significantly decreases during ketone supplementation. Our findings support the theory that ketone supplementation delays onset of central nervous system oxygen toxicity in mammals, in part, by decreasing [Formula: see text] production in O2-sensitive neurons.