The inhibition of apoptosis in swine brain by hyperbaric oxygen therapy following cardiopulmonary arrest

Study objectives: It has been demonstrated that 4 atmospheres of hyperbaric oxygen therapy delivered after a 25-minute cardiopulmonary arrest in swine has produced immediate and sustained (2 hours) spontaneous return of circulation. Recent studies have shown that hyperbaric oxygen can improve neurologic recovery in cerebral ischemia models, but the mechanism remains controversial. This study tested the hypothesis that hyperbaric oxygen therapy delivered during cardiopulmonary resuscitation after a 25-minute cardiac arrest in swine would result in an attenuation of cerebral cortical apoptosis compared with animals resuscitated at surface pressure. Methods: Eighteen adolescent swine were anesthetized and underwent induced cardiac arrest for 25 minutes, producing a model of complete global ischemia. The animals were randomized to 3 groups, representing 3 pressures of oxygen ventilation provided during the cardiopulmonary resuscitation of the swine. Six animals per group received oxygen ventilation at surface pressure, 2 atmospheres, or 4 atmospheres. After 2 hours of resuscitation, the animals' brains were harvested and flash frozen in liquid nitrogen. The degree of apoptosis in each sample of cerebral cortex was determined through the measurement of DNA laddering, caspase-3 activity, poly(adenosine diphosphate ribose) polymerase (PARP) expression, and nucleosome cleavage. The average degree of apoptosis of the 3 groups was compared. Results: The relative density of PARP (caspase-3 substrate) was smaller in the group treated at surface depth (5.71) than in the 2-atmosphere group or the 4-atmosphere group (8.39 and 8.63, respectively; P =.04). There was no evidence of DNA laddering in any animals in group 3 (4 ATA), whereas 2 animals in group 1 (surface pressure) and 1 animal in group 2 (2 ATA) showed evidence of DNA laddering. Relative caspase-3 activity in the 4-ATA, 2-ATA, and surface-treated animals was 0.0327, 0.0402, and 0.0407 units/μg protein, respectively, whereas the relative quantity of nucleosome cleavage in the same groups was 0.108, 0.137, and 0.140 Abs[ 405 492 ], respectively (no statistical significance). Conclusion: The groups receiving hyperbaric oxygen therapy showed less apoptosis than the group treated at surface pressure, as measured by PARP cleavage. A similar trend exists as measured by the other tests (DNA laddering, caspase-3 assay, nucleosome enzyme-linked immunosorbent assay).