Cerebellar axon/myelin loss, angiogenic sprouting, and neuronal increase of vascular endothelial growth factor in a preterm infant with kernicterus.
ABSTRACT We performed histologic and immunohistochemical analysis of cerebellar sections from a preterm infant (32 weeks 5 days) dead on the 4th day of life with the diagnosis of kernicterus and compared the results with 1 age-matched nonicteric patient. Poorer Luxol fast blue-periodic acid Schiff and Bodian-Luxol fast blue stainings as well as neurofilament expression were observed in the kernicterus case, indicating loss of axon neurites and myelin fibers. Elevated claudin-5 and cluster of differentiation 34 expression associated with increased blood vessel density suggests bilirubin-induced angiogenic sprouting. Upregulation of vascular endothelial growth factor and its receptor 2 was observed in nucleus dentatus and Purkinje neurons. Although upregulation of multidrug resistance-associated protein 1 was increased in cerebellar neurons, it was not able to prevent bilirubin-induced neurotoxicity. These data add new insights into the pathophysiology of kernicterus, revealing vascular endothelial growth factor and its receptor 2, as well as angiogenic sprouting, as new players in neurologic damage by unconjugated bilirubin.
Article: Time-dependent dual effects of high levels of unconjugated bilirubin on the human blood-brain barrier lining.[show abstract] [hide abstract]
ABSTRACT: In neonatal jaundice, high levels of unconjugated bilirubin (UCB) may induce neurological dysfunction (BIND). Recently, it was observed that UCB induces alterations on brain microvasculature, which may facilitate its entrance into the brain, but little is known about the steps involved. To evaluate if UCB damages the integrity of human brain microvascular endothelial cells (HBMECs), we used 50 or 100 μM UCB plus human serum albumin, to mimic the neuropathological conditions where levels of UCB free species correspond to moderate and severe neonatal jaundice, respectively. Our results point to a biphasic response of HBMEC to UCB depending on time of exposure. The early response includes increased number of caveolae and caveolin-1 expression, as well as upregulation of vascular endothelial growth factor (VEGF) and its receptor 2 (VEGFR-2) with no alterations of the paracellular permeability. In contrast, effects by sustained hyperbilirubinemia are the reduction in zonula occludens (ZO)-1 and β-catenin levels and thus of tight junctions (TJ) strands and cell-to-cell contacts. In addition, reduction of the transendothelial electrical resistance (TEER) and increased paracellular permeability are observed, revealing loss of the barrier properties. The 72 h of HBMEC exposure to UCB triggers a cell response to the stressful stimulus evidenced by increased autophagy. In this later condition, the UCB intracellular content and the detachment of both viable and non-viable cells are increased. These findings contribute to understand why the duration of hyperbilirubinemia is considered one of the risk factors of BIND. Indeed, facilitated brain entrance of the free UCB species will favor its parenchymal accumulation and neurological dysfunction.Frontiers in Cellular Neuroscience 01/2012; 6:22. · 4.17 Impact Factor
Article: Transport and metabolism at blood-brain interfaces and in neural cells: relevance to bilirubin-induced encephalopathy.[show abstract] [hide abstract]
ABSTRACT: Bilirubin, the end-product of heme catabolism, circulates in non-pathological plasma mostly as a protein-bound species. When bilirubin concentration builds up, the free fraction of the molecule increases. Unbound bilirubin then diffuses across blood-brain interfaces (BBIs) into the brain, where it accumulates and exerts neurotoxic effects. In this classical view of bilirubin neurotoxicity, BBIs act merely as structural barriers impeding the penetration of the pigment-bound carrier protein, and neural cells are considered as passive targets of its toxicity. Yet, the role of BBIs in the occurrence of bilirubin encephalopathy appears more complex than being simple barriers to the diffusion of bilirubin, and neural cells such as astrocytes and neurons can play an active role in controlling the balance between the neuroprotective and neurotoxic effects of bilirubin. This article reviews the emerging in vivo and in vitro data showing that transport and metabolic detoxification mechanisms at the blood-brain and blood-cerebrospinal fluid barriers may modulate bilirubin flux across both cellular interfaces, and that these protective functions can be affected in chronic unconjugated hyperbilirubinemia. Then the in vivo and in vitro arguments in favor of the physiological antioxidant function of intracerebral bilirubin are presented, as well as the potential role of transporters such as ABCC1 and metabolizing enzymes such as cytochromes P-450 in setting the cerebral cell- and structure-specific toxicity of bilirubin following hyperbilirubinemia. The relevance of these data to the pathophysiology of bilirubin-induced neurological diseases is discussed.Frontiers in pharmacology. 01/2012; 3:89.
Article: The evolving landscape of neurotoxicity by unconjugated bilirubin: role of glial cells and inflammation.[show abstract] [hide abstract]
ABSTRACT: Unconjugated hyperbilirubinemia is a common condition in the first week of postnatal life. Although generally harmless, some neonates may develop very high levels of unconjugated bilirubin (UCB), which may surpass the protective mechanisms of the brain in preventing UCB accumulation. In this case, both short-term and long-term neurodevelopmental disabilities, such as acute and chronic UCB encephalopathy, known as kernicterus, or more subtle alterations defined as bilirubin-induced neurological dysfunction (BIND) may be produced. There is a tremendous variability in babies' vulnerability toward UCB for reasons not yet explained, but preterm birth, sepsis, hypoxia, and hemolytic disease are comprised as risk factors. Therefore, UCB levels and neurological abnormalities are not strictly correlated. Even nowadays, the mechanisms of UCB neurotoxicity are still unclear, as are specific biomarkers, and little is known about lasting sequelae attributable to hyperbilirubinemia. On autopsy, UCB was shown to be within neurons, neuronal processes, and microglia, and to produce loss of neurons, demyelination, and gliosis. In isolated cell cultures, UCB was shown to impair neuronal arborization and to induce the release of pro-inflammatory cytokines from microglia and astrocytes. However, cell dependent sensitivity to UCB toxicity and the role of each nerve cell type remains not fully understood. This review provides a comprehensive insight into cell susceptibilities and molecular targets of UCB in neurons, astrocytes, and oligodendrocytes, and on phenotypic and functional responses of microglia to UCB. Interplay among glia elements and cross-talk with neurons, with a special emphasis in the UCB-induced immunostimulation, and the role of sepsis in BIND pathogenesis are highlighted. New and interesting data on the anti-inflammatory and antioxidant activities of different pharmacological agents are also presented, as novel and promising additional therapeutic approaches to BIND.Frontiers in pharmacology. 01/2012; 3:88.