Non-Protein-Bound Iron in Brain Interstitium of Newborn Pigs after Hypoxia

Abstract

Oxidative damage is implied in perinatal hypoxic-ischemic brain injury, most importantly in white matter. Nonprotein-bound iron (NPBI) catalyzes the formation of toxic hydroxyl radicals. We measured the extracellular level of NPBI through microdialysis in the cortex, striatum, and periventricular white matter before, during and after severe hypoxia in newborn pigs. NPBI was analyzed by a new spectrophotometric method in which ferrous iron is chelated by bathophenanthroline. NPBI was present in all brain areas under baseline conditions and increased in white matter from 0.97 (0.69) to 2.75 (1.85) µmol/l (not corrected for recovery rate) during early reoxygenation. NPBI may contribute to oxidative injury after perinatal hypoxic insults.

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“…Our findings of a significant rise of NPBI from baseline to the end of hypoxia in cortex, and not in periventricular white matter, are not consistent with the findings of Sävman et al [8] . An explanation for this might be the difference in models.…”

“…Increase in intracellular iron can lead to irreversible cell damage due to production of highly reactive compounds, and this combined with proteolytic activity in injured tissue can increase extracellular NPBI. Thus increase in extracellular NPBI in hypoxia-ischemia is likely to be a result of neuronal cell membrane dam age -and also subsequently a contributor to the damage through further activation of the Fenton reaction [8,50] .…”

“…One probe was inserted in striatum and one in cortex as previously described by Munkeby et al [31] . The third probe was inserted into periventricular white matter as described by Sävman et al [8] . Rectal temperature was maintained between 38.5 and 40 ° C with a heating blanket and a radiant heating lamp.…”

“…The samples from cortex and periventricular white matter were frozen immediately after sampling, and kept at -70 ° C until analyzed. They were analyzed using the method described by Sävman et al [8] and Nilsson et al [32] for detection of free iron in microdialysate. Our standard curves and detection limit were as stated in the referred articles (0.25 mol/l of NPBI).…”

“…Non-protein-bound iron (NPBI) is known to be liable to catalyze the formation of reactive oxygen species through the Fenton reaction [6] , and extracellular antioxidant defenses greatly depend on mechanisms that remove or inactivate iron [7] . Sävman et al [8] have shown that NPBI increases in the brain interstitium after hypoxia in newborn piglets. Ogihara et al [9] have previously shown that NPBI can be found in cerebrospinal fluid in asphyxiated infants, and that the levels correlate with the degree of encephalopathy.…”