Relationship between Cerebral Interstitial Levels of Amino Acids and Phosphorylation Potential during Secondary Energy Failure in Hypoxic-Ischemic Newborn Piglets

Abstract

The aim of this study was to determine the validity of the hypothesis that excitatory amino acids are related to phosphorylation potential during primary and secondary cerebral energy failure observed in asphyxiated infants. We report here the results of experiments using newborn piglets subjected to severe transient cerebral hypoxia-ischemia followed by resuscitation. We examined cerebral energy metabolism by phosphorus nuclear magnetic resonance spectroscopy and changes in levels of amino acid neurotransmitters in the cortex by microdialysis before, during, and up to 24 h after the hypoxic-ischemic insult. The concentrations of aspartate, glutamate, taurine, and ␥-aminobutyric acid were significantly elevated during the hypoxicischemic insult compared with prebaseline values. Shortly after resuscitation, glutamate, taurine, and ␥-aminobutyric acid concentrations decreased but then began to increase again. These secondary elevations were greater than the primary elevations. A negative linear correlation was found between primary interstitial levels of glutamate and taurine and minimum values of phosphocreatine/inorganic phosphate during the secondary energy failure. The cerebral energy state depended on the time course of changes in excitatory amino acids, suggesting that amino acids play distinct roles during the early and delayed phases of injury. Abbreviations FIO 2 , fraction of inspired oxygen GABA, ␥-aminobutyric acid PCr, phosphocreatine Pi, inorganic phosphate 31 P-MRS, phosphorus nuclear magnetic resonance spectroscopy Perinatal hypoxic-ischemic encephalopathy remains a major cause of permanent neurodevelopmental disability and infant mortality (1-4). High-energy phosphate metabolites in the brains of asphyxiated infants studied by phosphorus nuclear magnetic resonance spectroscopy ( 31 P-MRS) on the first day of life showed no differences from that in normal infants. However, inverse changes in the concentrations of phosphocreatine (PCr) and inorganic phosphate (Pi) cause a significant reduction in the [PCr]/[Pi] ratio over the next several days despite optimal medical management. Low values of [PCr]/[Pi] were founded to be associated with a very poor prognosis for survival and early neurodevelopmental outcome (5, 6). The late metabolic deterioration that characterizes such infants indicates that there is chronic metabolic stress and suggests that there may be a therapeutic window in which appropriate therapy could markedly improve outcome. The origin of this secondary energy failure is probably multifactorial and related to a combination of prolonged exposure to excitatory amino acids (which initiates cellular damage mediated by Ca 2ϩ and nitric oxide), damage caused by free radicals, immunocytotoxic reactions, impairment of protein synthesis, lack of growth factors, and decreased cerebral blood flow and oxygen delivery as a result of progressive cerebral edema (7-9). Several methods for preventing secondary brain damage have been proposed (10 -15).Some animal studies using 31 P-MRS and proton magnet...

Relationship Between Cerebral Oxygenation and Phosphorylation Potential During Secondary Energy Failure in Hypoxic-Ischemic Newborn Piglets

“…Physiologic variables were monitored and full intensive care was provided throughout the duration of the experiment. Previously, we showed that there were no changes in the phosphorylation potential of the brains of eight piglets over a period of 27 h under the same conditions of anesthesia as were used in the present study (18). Therefore, we assumed that any secondary energy failure observed in the test animals in this study was caused by HI injury and not by long-term effects of anesthesia.…”

“…Eight newborn piglets obtained within 24 h of birth and weighing 1.70 -1.90 kg were used in this study. The animal preparation method for the HI model has been reported in detail (18). Briefly, after sedation with an intramuscular injection of sodium pentobarbital (2 mg/kg), the umbilical artery and vein of each piglet were cannulated.…”

“…After baseline observations, piglets underwent cerebral HI insult for 55-75 min (mean ϭ 65 min) using a previously reported procedure (18). Cerebral HI insult was induced by inflating a blood pressure cuff positioned around the piglet's neck to 300 mm Hg and reducing the inspired oxygen fraction to 0.10 -0.06.…”

Altered Astrocyte–Neuronal Interactions After Hypoxia-Ischemia in the Neonatal Brain in Female and Male Rats

“…34,35 In the contralateral hemisphere, glutamate transfer seemed to be increased after hypoxia, indicating that the astrocytes were able to increase their uptake of glutamate in this phase and thus counteracted excitotoxicity. However, in the ipsilateral hemisphere, no such increase occurred.…”

Accumulation of Triosephosphate Isomerase, with Sequence Homology to β Amyloid Peptides, in Vessel Walls of the Newborn Piglet Hippocampus

“…Animal Preparation The protocols for animal care were in compliance with institutional guidelines (Kusaka et al, 2004). Six newborn piglets within 48 h after birth were used.…”