Perinatal brain injury - markers and mediators. Non-protein-bound iron and pro-inflammatory cytokines in newborn infants and neonatal pigs
Abstract: Two groups of newborn infants have an increased risk for perinatal brain injury; preterm infants and term infants subjected to birth asphyxia. Experimental studies indicate that hypoxic-ischemic insults in the perinatal period initiate a secondary neurotoxic cascade including formation of toxic reactive oxygen species as well as an inflammatory response with elevated levels of potentially neurotoxic cytokines. In the preterm infant a fetal inflammatory response to maternal infection is also directly implied in the development of brain injury and immature white matter exhibits an intrinsic vulnerability to oxidative injury. Non-protein-bound iron (NPBI), measured by a new spectrophotometric method, is a potent pro-oxidant through its capacity to catalyze the formation of the highly toxic hydroxyl radical.The aims of the study were to evaluate: (a) inflammatory activation expressed as pro-inflammatory cytokines in CSF from infants with birth asphyxia as well as preterm infants with posthemorrhagic ventricular dilatation (PHVD) and subsequent high risk for white matter injury. (b) extracellular levels of NPBI in different areas of the brain under normal conditions as well as during hypoxia and reoxygenation in newborn piglets. (d) the content of NPBI in CSF from preterm infants with PHVD.CSF was obtained from asphyxiated term infants and term control infants within 72 h from birth and from preterm infants with PHVD and preterm control infants approximately two weeks after birth. Newborn piglets were subjected to hypoxia-reoxygenation according to a model that produces clinical encephalopathy and neuropathological changes similar to those seen in term asphyxiated infants. Samples for NPBI analysis were obtained by microdialysis probes inserted into vulnerable parts of the piglet brain.There was a significant increase of the pro-inflammatory cytokines IL-6 and IL-8 in CSF after birth asphyxia. IL-6 and IL-8 levels correlated with the degree of encephalopathy and IL-6 correlated with outcome. The CSF levels of IL-1b, IL-6, IL-8, and TNF-a were elevated in infants with PHVD. NPBI was detected in all examined areas of the piglet brain under normal conditions and increased during early reoxygenation after hypoxia. NPBI was detected frequently and at high levels in CSF from infants with PHVD. Conclusions: Birth asphyxia elicits an inflammatory response with elevated pro-inflammatory cytokines in CSF and elevated cytokine levels are associated with severe clinical course and abnormal outcome. Preterm infants with PHVD exhibit an intense inflammatory response in CSF weeks after the original insult, but at this late time-point no correlation with morphological brain injury or outcome is found. NPBI is present in brain extracellular space under normal conditions and increases during reoxygenation after hypoxia. NPBI is also elevated in CSF from infants with PHVD. Elevated levels of NPBI imply impaired iron-regulation and an increased risk for oxidative injury
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