Preterm intraventricular cerebral hemorrhage: role of cell-free hemoglobin

Sammanfattning: Cerebral intraventricular hemorrhage in preterm infants continues to be a major clinical problem associated with neurodevelopmental abnormalities manifested by cognitive, behavioral, attentional, social and motor deficits. Hypothesis and aims: The central thesis is that the cytotoxicity of extravasated blood and of consequently released cell-free hemoglobin(Hb) is pivotal for the pathophysiological events causally involved in brain injury. The general aim focuses on the development and implementation of novel neuroprotective strategies with the aim of promoting brain development in preterm infants with high risk for neurodevelopmental impairment.Methods: Paper I. The presence and distribution of cell-free Hb in the periventricular white matter was evaluated in preterm rabbit pups with intraventricular hemorrhage(IVH). Paper II. The distribution, deposition and effect of cell-free Hb on cerebellar development was investigated following IVH in preterm rabbit pups. The protective effect of the cell-free Hb scavenger haptoglobin (Hp) was evaluated. Paper III. The relative cytotoxicity of the different cell-free Hb metabolites was evaluated in mixed glial cell culture. Paper IV. The biodistribution and functional protection of intraventricularly administered recombinant ( alpha 1 microglobulin (rA1M), a heme and radical scavenger was investigated following IVH in preterm rabbit pups.Results: Paper I. IVH was associated with extensive amounts of cell-free Hb in the periventricular white matter, with a wide distribution throughout the brain. Paper II. IVH was followed by a decreased proliferation in the external granular layer (EGL), delayed Purkinje cell maturation and activated microglia in the cerebellum. Cell-free Hb was present in all cerebellar layers, with a gradient towards the molecular and white matter layers. Intraventricular administration of Hp resulted in a partial reversion of the damaging effects following IVH. Paper III. Met/oxidized Hb and not oxyHb was found to initiate a proinflammatory and oxidative response with cytoskeletal disintegration in mixed glial cell cultures. Paper IV. Administered rA1M following IVH was widely distributed in periventricular white matter tissue and present throughout the fore- and mid brain extending to the cerebellum,with a high coexistence of cell-free Hb. Administration of r A1M resulted in an attenuation of proinflammatory and oxidative damage.Conclusions: IVH is characterized by the penetration of cell-free Hb into periventricular brain tissue and cerebellum resulting in a proinflammatory and oxidative damage to the brain. Hp and A1M, scavengers of cell-free Hb and Hbmetabolites respectively, attenuate the damage sustained by the periventricular white matter and cerebellum, affirming cell-free Hb to be causally involved in the brain damage resulting from IVH. Hp and A1M hence appear potential candidates for neuroprotective strategies against brain damage following IVH