Inhibition of Na⁺/H⁺ Exchanger Isoform 1 Is Neuroprotective in Neonatal Hypoxic Ischemic Brain Injury

Abstract

We investigated the role of Na(+)/H(+) exchanger isoform 1 (NHE-1) in neonatal hypoxia/ischemia (HI). HI was induced by unilateral ligation of the left common carotid artery in postnatal day 9 (P9) mice, and subsequent exposure of animals to 8% O(2) for 55 min. A pre/posttreatment group received a selective and potent NHE-1 inhibitor HOE 642 (0.5 mg/kg, intraperitoneally) 5 min before HI, then at 24 and 48 h after HI. A posttreatment group received HOE 642 (0.5 mg/kg) at 10 min, 24 h, and 48 h after HI. Saline injections were used as vehicle controls. The vehicle-control brains at 72 h after HI exhibited neuronal degeneration in the ipsilateral hippocampus, striatum, and thalamus, as identified with Fluoro-Jade C positive staining and loss of microtubule-associated protein 2 (MAP2) expression. NHE-1 protein was upregulated in glial fibrillary acidic protein-positive reactive astrocytes. In HOE 642-treated brains, the morphologic hippocampal structures were better preserved and displayed less neurodegeneration and a higher level of MAP2 expression. Motor-learning deficit was detected at 4 weeks of age after HI in the vehicle control group. Inhibition of NHE-1 in P9 mice not only reduced neurodegeneration during the acute stage of HI but also improved the striatum-dependent motor learning and spatial learning at 8 weeks of age after HI. These findings suggest that NHE-1-mediated disruption of ionic homeostasis contributes to striatal and CA1 pyramidal neuronal injury after neonatal HI.

Chronic Neurological Deficits in Mice after Perinatal Hypoxia and Ischemia Correlate with Hemispheric Tissue Loss and White Matter Injury Detected by MRI

“…The body temperature of the animals was maintained at 37°C with a heating pad. Under a surgical microscope, a midline skin incision was made, and the left common carotid artery electrically cauterized as described before [12]. The incision was rinsed with 1% lidocaine and sutured with a 6-0 Prolene suture.…”

“…We have recently reported that pharmacological inhibition of Na + /H + exchanger isoform 1 (NHE1) activity in postnatal day (P)9 mice protected hippocampal neurons at 3 days after HI [12]. Neonatal mice that were treated with HOE 642 (a potent and selective inhibitor of NHE1) showed improved motor and spatial learning at P60.…”

The Na+/H+ Exchanger-1 as a New Molecular Target in Stroke Interventions

“…The Na + /H + Exchanger-1 as a New Molecular Target in Stroke Interventions and hippocampus and improved performance on tests of motor learning and memory (Cengiz et al, 2010). These findings suggest that NHE-1 mediated disruption of ionic homeostasis can contribute to CA1 pyramidal neuronal injury after neonatal HI.…”

“…NHE-1 activity in astrocytes (Cengiz et al, 2010), neurons (Manhas et al, 2010), and microglia ) is stimulated following cerebral ischemia. Excessive stimulation of NHE-1 leads to intracellular Na + overload, and in turn causes a rise in intracellular Ca 2+ due to increased Ca 2+ influx via reversal of the Na/Ca exchanger.…”

“…In these studies, post-natal day 9 mice (P9) underwent unilateral carotid artery ligation and subsequent exposure to 55 minutes of 8% O 2 . Following carotid ligation, mice were treated with HOE 642 either immediately before or 10 minutes following exposure to hypoxia (Cengiz et al, 2010). Following HI, vehicle-treated control brains exhibited astrogliosis in the ipsilateral hippocampus, and reactive astrocytes expressed an abundant level of NHE-1.…”