Additive Neuroprotection of a 20-HETE Inhibitor with Delayed Therapeutic Hypothermia after Hypoxia-Ischemia in Neonatal Piglets

Abstract

The severity of perinatal hypoxia-ischemia and the delay in initiating therapeutic hypothermia limit the efficacy of hypothermia. After hypoxia-ischemia in neonatal piglets, the arachidonic acid metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) has been found to contribute to oxidative stress at 3 h of reoxygenation and to eventual neurodegeneration. We tested whether early administration of a 20-HETE synthesis inhibitor after reoxygenation augments neuroprotection with 3-hour delayed hypothermia. In two hypothermic groups, whole body cooling from 38.5 to 34°C was initiated 3 h after hypoxia-ischemia. Rewarming occurred from 20 to 24 h; then anesthesia was discontinued. One hypothermic group received a 20-HETE inhibitor at 5 min after reoxygenation. A sham-operated group and another hypoxia-ischemia group remained normothermic. At 10 days of recovery, resuscitated piglets with delayed hypothermia alone had significantly greater viable neuronal density in the putamen, caudate nucleus, sensorimotor cortex, CA3 hippocampus, and thalamus than did piglets with normothermic recovery, but the values remained less than those in the sham-operated group. In piglets administered the 20-HETE inhibitor before hypothermia, the density of viable neurons in the putamen, cortex and thalamus was significantly greater than in the group with hypothermia alone. Cytochrome P450 4A, which can synthesize 20-HETE, was expressed in piglet neurons in these regions. We conclude that early treatment with a 20-HETE inhibitor enhances the therapeutic benefit of delayed hypothermia in protecting neurons in brain regions known to be particularly vulnerable to hypoxia-ischemia in term newborns.

Upregulation of 20-HETE Synthetic Cytochrome P450 Isoforms by Oxygen–Glucose Deprivation in Cortical Neurons

“…In addition, the induction of the Cyp4a12a isoform, which is the primary enzyme responsible for formation of 20-HETE in the mouse, may contribute to the increase in 20-HETE production at this time. Previous studies have indicated that 20-HETE promotes increases in oxidative stress in ischemic brains (Zhu et al 2015; Yang et al 2012). Thus, the large increase in 20-HETE production at 3 h likely contributes to the ongoing neuronal cell death from that point forward.…”

Hypothermia and Rewarming Activate a Macroglial Unfolded Protein Response Independent of Hypoxic-Ischemic Brain Injury in Neonatal Piglets

“…Hypothermia confers neuroprotection in our piglet HI model by preserving viable neurons and reducing NMDA receptor activation, nitric oxide synthase relocalization, oxidative stress, and cellular necrosis. [32-35] However, hypothermia may promote apoptosis in cortex after HI [4] and in white matter with or without HI [5], which may reflect an off-target effect of hypothermia and rewarming.…”

“…[49] Rewarming reinitiates protein translation through dephosphorylation of eIF2-α in mammalian cells recovering from cold shock. [36] Upregulated protein translation with the accumulation of misfolded proteins in addition to cellular stressors from hypothermia with rewarming, such as inflammation [50] and oxidative stress, [35, 51, 52] may activate the UPR. [53, 54]…”

Cytochrome P450 eicosanoids in cerebrovascular function and disease

“…All of these cells types therefore have the necessary machinery to produce 19- and 20-HETE (Alonso-Galicia et al, 1999; Bylund et al, 2002; Al-Anizy et al, 2006; Gebremedhin et al, 1998; 2000; 2016; Carver et al, 2014, Dunn et al, 2008; Zhu et al, 2015; Zhang et al, 2017c). 20-HETE, but not 19-HETE have been detected in vascular smooth muscle cells, and more recently astrocytes and neurons (Gebremedhin et al, 1998; 2008; 2016; Zhang et al, 2017c).…”