DHA but not EPA emulsions preserve neurological and mitochondrial function after brain hypoxia-ischemia in neonatal mice

Background and Purpose: Treatment with triglyceride emulsions of docosahexaenoic acid (tri-DHA) protected neonatal mice against hypoxia-ischemia (HI) brain injury. The mechanism of this neuroprotection remains unclear. We hypothesized that administration of tri-DHA enriches HI-brains with DHA/DHA metabolites. This reduces Ca²⁺-induced mitochondrial membrane permeabilization and attenuates brain injury. Methods: 10-day-old C57BL/6J mice following HI-brain injury received tri-DHA, tri-EPA or vehicle. At 4-5 hours of reperfusion, mitochondrial fatty acid composition and Ca²⁺ buffering capacity were analyzed. At 24 hours and at 8-9 weeks of recovery, oxidative injury, neurofunctional and neuropathological outcomes were evaluated. In vitro, hyperoxia-induced mitochondrial generation of reactive oxygen species (ROS) and Ca²⁺ buffering capacity were measured in the presence or absence of DHA or EPA. Results: Only post-treatment with tri-DHA reduced oxidative damage and improved short- and longterm neurological outcomes. This was associated with increased content of DHA in brain mitochondria and DHA-derived bioactive metabolites in cerebral tissue. After tri-DHA administration HI mitochondria were resistant to Ca²⁺-induced membrane permeabilization. In vitro, hyperoxia increased mitochondrial ROS production and reduced Ca²⁺ buffering capacity; DHA, but not EPA, significantly attenuated these effects of hyperoxia. Conclusions: Post-treatment with tri-DHA resulted in significant accumulation of DHA and DHA derived bioactive metabolites in the HI-brain. This was associated with improved mitochondrial tolerance to Ca²⁺-induced permeabilization, reduced oxidative brain injury and permanent neuroprotection. Interaction of DHA with mitochondria alters ROS release and improves Ca²⁺ buffering capacity. Thismay account for neuroprotective action of post-HI administration of tri-DHA.