³¹P NMR spectroscopy of perinatal hypoxic‐ischemic brain damage: A model to evaluate neuroprotective drugs in immature rats

Abstract

Cerebral energy metabolism can be measured non-invasively in unanesthetized neonatal rats with 31P NMR spectroscopy. Using this technique, serial changes in high energy phosphates were determined from the right cerebral hemispheres of 7 day postnatal rat pups during a hypoxic-ischemic insult known to produce focal brain injury. During 3 h of hypoxia-ischemia the concentration of ATP dropped to 33 +/- 8% of prehypoxic (baseline) levels, phosphocreatine (PCr)/Pi decreased from 1.5 +/- 0.51 to 0.16 +/- 0.06, while pH decreased nominally by 0.2 units. After 2.5 h of recovery in air, ATP returned to 75 +/- 10% of baseline levels, PCr/Pi rose to 1.1 +/- 0.28, and pH returned to its normal value of 7.16 +/- 0.06. This model was used to test the efficacy of the adenosine deaminase inhibitor, 2-deoxycoformycin (DCF) as a potential neuroprotective drug. The data for the drug- and saline-treated populations were analyzed by integrating ATP and Pi/PCr levels over specific time intervals, expressing it relative to baseline levels, and modeling it with cubic splines. Pretreatment with 500 micrograms/kg DCF shows a small, but statistically significant, preservation of both ATP and phosphorylation potential during hypoxia and initial recovery. Brain water content (edema) at 42 h recovery was apparently associated with both mean ATP and mean Pi/PCr in the last 2 h of hypoxia-ischemia. When ATP fell below 70% of baseline, brain edema was evident at 42 h of recovery. This methodology is suitable for extension to human infants.

Increased Plasma Beta-Hydroxybutyrate, Preserved Cerebral Energy Metabolism, and Amelioration of Brain Damage During Neonatal Hypoxia Ischemia with Dexamethasone Pretreatment

“…6). There is a strong correlation between the P i /PCr ratio and the neuropathologic score, which agrees with previous reports (7,9,10). Animals with larger integrated P i /PCr values tend to have severe damage at 24 h post HI, whereas animals pretreated with DEX show no neuronal loss with P i /PCr ratios under 3.…”

NMR studies on energy metabolism of immobilized primary neurons and astrocytes during hypoxia, ischemia and hypoglycemia

“…5,30,[39][40][41][42][43] Although the duration of the insult is variable (2 min to several hours), all studies found a sharper drop in PCr than in ATP, in agreement with our observations not only for hypoxia but also for ischemia and hypoglycemia. This behaviour reflects the buffering of the ATP level at the expense of PCr.…”

Delayed (“Secondary”) Cerebral Energy Failure after Acute Hypoxia-Ischemia in the Newborn Piglet: Continuous 48-Hour Studies by Phosphorus Magnetic Resonance Spectroscopy

“…2, Table 4) resembled those reported in previous studies, including those of newborn animals (8,9,(23)(24)(25). The profound decrease in pH, was attributable in part to production of lactic acid.…”

“…Most studies of cerebroprotection have involved very small animals, such as the newborn rat, which are particularly useful for screening for suitable pharmacologic agents (23,28). Before cerebroprotective strategies are applied to human infants who have suffered a severe acute hypoxic-ischemic insult to the brain, it will bc important to prove their worth in a suitable animal model that is large enough for a wide range of systemic as well as cerebral observations to be made.…”