Mechanism of Neuroprotectin D1 Action after Hypoxic‐Ischemic Injury in Neonatal Mice

Abstract

Neonatal hypoxic‐ischemic (HI) brain injury remains a major contributor to neurological disorders in children. We recently reported that acute administration of triglyceride emulsions of docosahexaenoic acid (tri‐DHA) after HI injury, showed marked neuroprotection in neonatal mice decreasing infarct volume by 50%. Post‐HI tri‐DHA injection preserved Ca2+ buffering capacity and markedly decreased reactive oxygen species (ROS) production by mitochondria. We questioned whether DHA‐derived specialized pro‐resolving mediator (SPM) profiles change in ischemic brains of tri‐DHA treated mice relative to untreated mice, and if SPMs directly activate the same mechanisms of neuroprotection as tri‐DHA. After 2h reperfusion we detected a 50% increase in neuroprotectin D1 (NPD1) levels in brains of tri‐DHA treated mice compared to the control group. Tri‐DHA administration also increased brain levels of total D‐ and E‐series resolvins, and LXB4, by 5.8 and 2.5‐fold respectively. Based on these observations, we examined whether NPD1, a potent bioactive mediator derived from DHA, could lead to neuroprotection immediately after HI brain injury. We found that acute intraperitoneal administration of 20ng NPD1 after HI injury reduced infarct volume by 55% compared to saline treated mice (control group). Short‐term neurofunctional outcomes were assessed at 24h after HI. Treatment with NPD1 significantly improved righting and negative geotaxis reflex performances compared to control littermates. Mitochondria from ischemic brains of NPD1 treated mice had similar Ca2+ buffering capacity compared to naïve mice, while mitochondria from the ischemic brains of control treated mice significantly reduced Ca2+ buffering capacity by 40% compared to naïve mice (p<0.05).A number of studies by other groups have reported that dietary n‐3 fatty acids may prevent or reverse impairments in mitochondria content or function. Our findings show that acute injection of a DHA derived mediator, namely NPD1, directly provides neuroprotection after HI and this is associated, in part, by preserving mitochondrial functions.