Unbound Bilirubin and Acute Bilirubin Encephalopathy in Infants Born Late Preterm and Term with Significant Hyperbilirubinemia.

OBJECTIVE: To compare the association of unbound bilirubin (UB), total serum bilirubin (TSB), and bilirubin:albumin molar ratio (BAMR) with acute bilirubin encephalopathy (ABE), as assessed by bilirubin-induced neurologic dysfunction (BIND) score, in infants with significant hyperbilirubinemia (TSB ≥20 mg/dL or underwent exchange transfusion). STUDY DESIGN: In this prospective cohort study, infants ≥34 weeks of gestational age with significant hyperbilirubinemia during the first 2 postnatal weeks were eligible, unless they had craniofacial malformations, chromosomal disorders, TORCH (toxoplasmosis, other infections, rubella, cytomegalovirus and herpes simplex) infections, surgery, or a family history of congenital deafness. TSB, serum albumin, and UB were measured at hospital admission using the colorimetric, bromocresol green, and modified peroxidase method, respectively. Infants were evaluated on admission for ABE using a standardized neurologic examination and assigned a BIND score by trained physicians. Infants with a total BIND score of 0 were deemed to not have ABE, whereas those with a score ≥1 were deemed to have ABE. RESULTS: A total of 151 infants were studied, among whom 37 (24.5%) had ABE. Of these, 19 had mild ABE (BIND score 1-3) and 18 had moderate-to-severe ABE (BIND score 4-9). On logistic regression, UB, but not TSB or BAMR, was associated with ABE (aOR 1.64; 95% CI 1.17-2.3). On ordered logistic regression, UB, but not TSB or BAMR, was associated with severity of ABE (aOR 1.76; 95% CI 1.28-2.4). CONCLUSIONS: Our findings of the association between UB and ABE indicate that BIND scoring may be useful for evaluation of ABE in infants ≥34 weeks of gestational age.

Bilirubin impacts microglial autophagy via the Akt-mTOR signaling pathway.

Bilirubin encephalopathy is a severe complication of neonatal hyperbilirubinemia. With elevation of serum unconjugated bilirubin (UCB) levels, UCB crosses the blood-brain barrier and possibly leads to neurological dysfunction. Neuroinflammation is recognized as a prominent pathological feature in bilirubin encephalopathy. Recent studies have suggested that autophagy plays a crucial role in the inflammatory response. However, the potential effect of microglial autophagy in the pathogenesis of bilirubin encephalopathy remains uncertain. The in vitro findings verified that in primary cultured microglia, UCB significantly reduced the ratio of LC3B-II to LC3B-I and downregulated the expression of ATG5, Beclin-1, and ATG7, while increasing the expression of p62/SQSTM1. The results showed that UCB could decrease the number of mCherry-EGFP-LC3 positive puncta, even when chloroquine (CQ) was applied to block the microglial autophagy flux. Mechanistically, UCB was found to upregulate the expression of TLR4 and increase the phosphorylation levels of Akt and mammalian target of rapamycin (mTOR). Promoting microglial autophagy by treatment with Rapamycin (RAPA), an mTOR inhibitor, decreased the levels of NOD-like receptor protein 3 (NLRP3) inflammasome components and IL-1ß, rescued microglial overactivation, and improved neurological functions. These data indicated that UCB could impact microglial autophagy via the Akt-mTOR signaling pathway and synergistically promote neuroinflammatory responses. Enhancing autophagy might disrupt the assembly of NLRP3 inflammasome, attenuate UCB-induced neuroinflammation, and improve the prognosis of model rats with bilirubin encephalopathy. In conclusion, this study implies that regulating microglial autophagy might be a promising therapeutic strategy for bilirubin encephalopathy.

Susceptibility weighted imaging can be a sensitive sequence to detect brain damage in neonates with kernicterus: a case report.

BACKGROUND: Kernicterus in the acute phase is difficult to diagnose. It depends on a high signal on T1 at the globus pallidum and subthalamic nucleus level. Unfortunately, these areas also show a relatively high signal on T1 in neonates as an expression of early myelination. Therefore, a less myelin-dependent sequence, like SWI, may be more sensitive to detecting damage in the globus pallidum area. CASE PRESENTATION: A term baby developed jaundice on day three following an uncomplicated pregnancy and delivery. Total bilirubin peaked at 542 µmol/L on day four. Phototherapy was started, and an exchange transfusion was performed. ABR showed absent responses on day 10. MRI on day eight demonstrated abnormal high signal globus pallidus on T1w, isointense on T2w, without diffusion restriction, and high signal on SWI at globus pallidal and subthalamus level and phase image at globus pallidal level. These findings were consistent with the challenging diagnosis of kernicterus. On follow-up, the infant presented with sensorineural hearing loss and had a work-up for cochlear implant surgery. At 3 months of age, the follow-up MR shows normalization of the T1 and SWI signals and a high signal on T2. CONCLUSIONS: SWI seems more sensitive to injury than the T1w and lacks the disadvantage of the T1w sequence, where early myelin confers a high signal.

Chemoprevention of bilirubin encephalopathy with a nanoceutical agent.

BACKGROUND: Targeted rapid degradation of bilirubin has the potential to thwart incipient bilirubin encephalopathy. We investigated a novel spinel-structured citrate-functionalized trimanganese tetroxide nanoparticle (C-Mn3O4 NP, the nanodrug) to degrade both systemic and neural bilirubin loads. METHOD: Severe neonatal unconjugated hyperbilirubinemia (SNH) was induced in neonatal C57BL/6j mice model with phenylhydrazine (PHz) intoxication. Efficiency of the nanodrug on both in vivo bilirubin degradation and amelioration of bilirubin encephalopathy and associated neurobehavioral sequelae were evaluated. RESULTS: Single oral dose (0.25 mg kg-1 bodyweight) of the nanodrug reduced both total serum bilirubin (TSB) and unconjugated bilirubin (UCB) in SNH rodents. Significant (p < 0.0001) UCB and TSB-degradation rates were reported within 4-8 h at 1.84 ± 0.26 and 2.19 ± 0.31 mg dL-1 h-1, respectively. Neural bilirubin load was decreased by 5.6 nmol g-1 (p = 0.0002) along with improved measures of neurobehavior, neuromotor movements, learning, and memory. Histopathological studies confirm that the nanodrug prevented neural cell reduction in Purkinje and substantia nigra regions, eosinophilic neurons, spongiosis, and cell shrinkage in SNH brain parenchyma. Brain oxidative status was maintained in nanodrug-treated SNH cohort. Pharmacokinetic data corroborated the bilirubin degradation rate with plasma nanodrug concentrations. CONCLUSION: This study demonstrates the in vivo capacity of this novel nanodrug to reduce systemic and neural bilirubin load and reverse bilirubin-induced neurotoxicity. Further compilation of a drug-safety-dossier is warranted to translate this novel therapeutic chemopreventive approach to clinical settings. IMPACT: None of the current pharmacotherapeutics treat severe neonatal hyperbilirubinemia (SNH) to prevent risks of neurotoxicity. In this preclinical study, a newly investigated nano-formulation, citrate-functionalized Mn3O4 nanoparticles (C-Mn3O4 NPs), exhibits bilirubin reduction properties in rodents. Chemopreventive properties of this nano-formulation demonstrate an efficacious, efficient agent that appears to be safe in these early studies. Translation of C-Mn3O4 NPs to prospective preclinical and clinical trials in appropriate in vivo models should be explored as a potential novel pharmacotherapy for SNH.

Metabolic patterns in brain 18F-fluorodeoxyglucose PET relate to aetiology in paediatric dystonia.

There is a lack of imaging markers revealing the functional characteristics of different brain regions in paediatric dystonia. In this observational study, we assessed the utility of [18F]2-fluoro-2-deoxy-D-glucose (FDG)-PET in understanding dystonia pathophysiology by revealing specific resting awake brain glucose metabolism patterns in different childhood dystonia subgroups. PET scans from 267 children with dystonia being evaluated for possible deep brain stimulation surgery between September 2007 and February 2018 at Evelina London Children's Hospital (ELCH), UK, were examined. Scans without gross anatomical abnormality (e.g. large cysts, significant ventriculomegaly; n = 240) were analysed with Statistical Parametric Mapping (SPM12). Glucose metabolism patterns were examined in the 144/240 (60%) cases with the 10 commonest childhood-onset dystonias, focusing on nine anatomical regions. A group of 39 adult controls was used for comparisons. The genetic dystonias were associated with the following genes: TOR1A, THAP1, SGCE, KMT2B, HPRT1 (Lesch Nyhan disease), PANK2 and GCDH (Glutaric Aciduria type 1). The acquired cerebral palsy (CP) cases were divided into those related to prematurity (CP-Preterm), neonatal jaundice/kernicterus (CP-Kernicterus) and hypoxic-ischaemic encephalopathy (CP-Term). Each dystonia subgroup had distinct patterns of altered FDG-PET uptake. Focal glucose hypometabolism of the pallidi, putamina or both, was the commonest finding, except in PANK2, where basal ganglia metabolism appeared normal. HPRT1 uniquely showed glucose hypometabolism across all nine cerebral regions. Temporal lobe glucose hypometabolism was found in KMT2B, HPRT1 and CP-Kernicterus. Frontal lobe hypometabolism was found in SGCE, HPRT1 and PANK2. Thalamic and brainstem hypometabolism were seen only in HPRT1, CP-Preterm and CP-term dystonia cases. The combination of frontal and parietal lobe hypermetabolism was uniquely found in CP-term cases. PANK2 cases showed a distinct combination of parietal hypermetabolism with cerebellar hypometabolism but intact putaminal-pallidal glucose metabolism. HPRT1, PANK2, CP-kernicterus and CP-preterm cases had cerebellar and insula glucose hypometabolism as well as parietal glucose hypermetabolism. The study findings offer insights into the pathophysiology of dystonia and support the network theory for dystonia pathogenesis. 'Signature' patterns for each dystonia subgroup could be a useful biomarker to guide differential diagnosis and inform personalized management strategies.

Technical Report: Diagnosis and Management of Hyperbilirubinemia in the Newborn Infant 35 or More Weeks of Gestation.

CONTEXT: Severe hyperbilirubinemia is associated with kernicterus. Informed guidance on hyperbilirubinemia management, including preventive treatment thresholds, is essential to safely minimize neurodevelopmental risk. OBJECTIVE: To update the evidence base necessary to develop the 2022 American Academy of Pediatrics clinical practice guideline for management of hyperbilirubinemia in the newborn infant ≥35 weeks' gestation. DATA SOURCE: PubMed. STUDY SELECTION: English language randomized controlled trials and observational studies. Excluded: case reports or series, nonsystematic reviews, and investigations focused on <35-weeks' gestation infants. DATA EXTRACTION: Topics addressed in the previous clinical practice guideline (2004) and follow-up commentary (2009) were updated with new evidence published through March 2022. Evidence reviews were conducted for previously unaddressed topics (phototherapy-associated adverse effects and effectiveness of intravenous immune globulin [IVIG] to prevent exchange transfusion). RESULTS: New evidence indicates that neurotoxicity does not occur until bilirubin concentrations are well above the 2004 exchange transfusion thresholds. Systematic review of phototherapy-associated adverse effects found limited and/or inconsistent evidence of late adverse effects, including cancer and epilepsy. IVIG has unclear benefit for preventing exchange transfusion in infants with isoimmune hemolytic disease, with a possible risk of harm due to necrotizing enterocolitis. LIMITATIONS: The search was limited to 1 database and English language studies. CONCLUSIONS: Accumulated evidence justified narrowly raising phototherapy treatment thresholds in the updated clinical practice guideline. Limited evidence for effectiveness with some evidence of risk of harm support the revised recommendations to limit IVIG use.

MGE-Like Neural Progenitor Cell Survival and Expression of Parvalbumin and Proenkephalin in a Jaundiced Rat Model of Kernicterus.

Kernicterus is a permanent condition caused by brain damage from bilirubin toxicity. Dystonia is one of the most debilitating symptoms of kernicterus and results from damage to the globus pallidus (GP). One potential therapeutic strategy to treat dystonia in kernicterus is to replace lost GP neurons and restore basal ganglia circuits through stem cell transplantation. Toward this end, we differentiated human embryonic stem cells (hESCs) into medial ganglion eminence (MGE; the embryological origin of most of the GP neurons)-like neural precursor cells (NPCs). We determined neurochemical phenotype in cell culture and after transplanting into the GP of jaundiced Gunn rats. We also determined grafted cell survival as well as migration, distribution, and morphology after transplantation. As in the GP, most cultured MGE-like NPCs expressed γ-aminobutyric acid (GABA), with some co-expressing markers for parvalbumin (PV) and others expressing markers for pro-enkephalin (PENK). MGE-like NPCs survived in brains at least 7 weeks after transplantation, with most aggregating near the injection site. Grafted cells expressed GABA and PV or PENK as in the normal GP. Although survival was low and the maturity of grafted cells varied, many cells produced neurite outgrowth. While promising, our results suggest the need to further optimize the differentiation protocol for MGE-like NPC for potential use in treating dystonia in kernicterus.

Bilirubin Encephalopathy.

PURPOSE OF REVIEW: Hyperbilirubinemia is commonly seen in neonates. Though hyperbilirubinemia is typically asymptomatic, severe elevation of bilirubin levels can lead to acute bilirubin encephalopathy and progress to kernicterus spectrum disorder, a chronic condition characterized by hearing loss, extrapyramidal dysfunction, ophthalmoplegia, and enamel hypoplasia. Epidemiological data show that the implementation of universal pre-discharge bilirubin screening programs has reduced the rates of hyperbilirubinemia-associated complications. However, acute bilirubin encephalopathy and kernicterus spectrum disorder are still particularly common in low- and middle-income countries. RECENT FINDINGS: The understanding of the genetic and biochemical processes that increase the susceptibility of defined anatomical areas of the central nervous system to the deleterious effects of bilirubin may facilitate the development of effective treatments for acute bilirubin encephalopathy and kernicterus spectrum disorder. Scoring systems are available for the diagnosis and severity grading of these conditions. The treatment of hyperbilirubinemia in newborns relies on the use of phototherapy and exchange transfusion. However, novel therapeutic options including deep brain stimulation, brain-computer interface, and stem cell transplantation may alleviate the heavy disease burden associated with kernicterus spectrum disorder. Despite improved screening and treatment options, the prevalence of acute bilirubin encephalopathy and kernicterus spectrum disorder remains elevated in low- and middle-income countries. The continued presence and associated long-term disability of these conditions warrant further research to improve their prevention and management.

Intensive phototherapy vs. exchange transfusion for the treatment of neonatal hyperbilirubinemia: a multicenter retrospective cohort study.

BACKGROUND: Intensive phototherapy (IPT) and exchange transfusion (ET) are the main treatments for extreme hyperbilirubinemia. However, there is no reliable evidence on determining the thresholds for these treatments. This multicenter study compared the effectiveness and complications of IPT and ET in the treatment of extreme hyperbilirubinemia. METHODS: This retrospective cohort study was conducted in seven centers from January 2015 to January 2018. Patients with extreme hyperbilirubinemia that met the criteria of ET were included. Patients were divided into three subgroups (low-, medium-, and high- risk) according to gestational week and risk factors. Propensity score matching (PSM) was performed to balance the data before treatment. Study outcomes included the development of bilirubin encephalopathy, duration of hospitalization, expenses, and complications. Mortality, auditory complications, seizures, enamel dysplasia, ocular motility disorders, athetosis, motor, and language development were evaluated during follow-up at age of 3 years. RESULTS: A total of 1164 patients were included in this study. After PSM, 296 patients in the IPT only group and 296 patients in the IPT plus ET group were further divided into the low-, medium-, and high-risk subgroups with 188, 364, and 40 matched patients, respectively. No significant differences were found between the IPT only and IPT plus ET groups in terms of morbidity, complications, and sequelae. Hospitalization duration and expenses were lower in the low- and medium-risk subgroups in the IPT only group. CONCLUSIONS: In this study, our results suggest that IPT is a safe and effective treatment for extreme hyperbilirubinemia. The indication of ET for patients with hyperbilirubinemia could be stricter. However, it is necessary to have a contingency plan for emergency ET as soon as IPT is commenced especially for infants with risk factors. If IPT can be guaranteed and proved to be therapeutic, ET should be avoided as much as possible.

Neonatal acute liver failure with pulmonary yellow hyaline membrane and kernicterus

Background Neonatal acute liver failure (NALF) is a rare and life-threatening condition. It causes bilirubin to accumulate to a dangerous level in the body, causing permanent damage to vital organs such as the brain and lungs. In many cases, the etiology of NALF remains unknown. Case presentation We described a case of an 8-day-old baby girl who presented with poor oral intake, lethargy, and jaundice. Her clinical condition rapidly deteriorated with progression to multi-organ failure, and despite intensive resuscitation efforts, she expired. At autopsy, the most significant findings were liver necrosis, yellow hyaline membrane deposition in the lungs, and bilirubin deposition in the brain (kernicterus). Conclusions NALF is a rare and potentially fatal condition necessitating prompt recognition and disease-specific treatment approaches. Toxic accumulation of bilirubin in the lungs can lead to hypoxia and precipitate further ischemic injury to the liver.

Increased Serum Expression of Inflammatory Cytokines may Serve as Potential Diagnostic Biomarker for Bilirubin Encephalopathy.

OBJECTIVES: The present study was designed to explore the roles of inflammatory cytokines interleukin-1ß (IL-1ß) and Tumor growth factor-ß (TGF-ß) in the diagnosis and treatment of neonate bilirubin encephalopathy (BE). METHODS: A total of 128 BE neonates and 128 normal neonates were included. The serum samples of the BE children and controls were collected, and the levels of IL-1ß and TGF-ß were examined. Moreover, the correlation between the level of bilirubin and serum expression of IL-1ß or TGF-ß in BE patients was analyzed. Finally, receiver operating characteristic (ROC) curves were generated to determine the diagnostic value of the cytokines. RESULTS: IL-1ß and TGF-ß levels were higher in the serum of BE patients than those in non-BE patients, and the expression of either IL-1ß or TGF-ß showed a strong positive correlation with the serum expression of bilirubin in BE patients. Moreover, the results of ROC analysis showed that either IL-1ß or TGF-ß could distinguish BE patients from healthy controls. CONCLUSION: IL-1ß and TGF-ß levels were upregulated in BE and might function as potential biomarkers or therapeutic targets for BE patients.

Quantitative proteomic characterization of microvesicles/exosomes from the cerebrospinal fluid of patients with acute bilirubin encephalopathy.

Severe hyperbilirubinemia causes neurotoxicity and may lead to acute bilirubin encephalopathy (ABE) during the critical period of central nervous system development. The aim of the present study was to identify differentially expressed proteins (DEPs) in microvesicles/exosomes (MV/E) isolated from the cerebrospinal fluid (CSF) of patients with ABE. Co­precipitation was used to isolate the MV/E from the CSF of patients with ABE and age­matched controls. Isobaric tagging for relative and absolute quantification­based proteomic technology combined with liquid chromatography/tandem mass spectrometry was used to identify DEPs in the MV/E. Bioinformatics analysis was subsequently performed to investigate Gene Ontology functional annotation and Kyoto Encyclopedia of Genes and Genomes enriched signaling pathways of these DEPs. A total of four proteins were selected for further validation via western blotting. A total of 291 dysregulated proteins were identified by comparing the patients with ABE with the controls. Bioinformatics analysis indicated the involvement of immune­inflammation­associated cellular processes and signaling pathways in the pathophysiology of ABE. In conclusion, the present study identified the proteomic profile of MV/E isolated from the CSF of patients with ABE. These results may provide an improved understanding of the pathogenesis of ABE and may help to identify early diagnostic biomarkers and therapeutic targets.

A questionnaire survey on the efficacy of various treatments for dyskinetic cerebral palsy due to preterm bilirubin encephalopathy.

OBJECTIVES: Preterm children with severe dyskinetic cerebral palsy due to bilirubin encephalopathy often suffer from marked generalised hypertonus as they age. We performed a questionnaire survey to investigate patient-reported outcomes of treatments for improving their activities of daily life. METHODS: A mail questionnaire was administered to the caregivers of 67 children with preterm bilirubin encephalopathy aged >4 years. We asked about the type of treatments they received and their efficacy using a five-point subjective scale for the following five domains: motor function, postural stability, sleep, pain, and care burden. The names of oral drugs and their efficacies were also explored. RESULTS: The response rate of the questionnaires was 62.7% (42/67), and we analysed the results from 41 validated cases. All children underwent rehabilitation. A total of 30 children received oral drugs, 22 botulinum toxin, 12 orthopaedic surgery, and 3 intrathecal baclofen. Each of these treatments was subjectively reported to be effective in more than half of the recipients for each of the five domains, whereas 23 (56%) required more than two types of treatments other than rehabilitation. Chlordiazepoxide was the most commonly used oral drug, by 28 children (68%), and was discontinued in 7 patients (25%) only. In the sleep domain, the rate of a positive effect was significantly higher for oral drugs (92.7%) than the other treatments (p < 0.01). CONCLUSION: All treatments were partially effective, but their appropriate combination based on a multidisciplinary approach is essential for muscle tone management in children with preterm bilirubin encephalopathy.

IIncreased serum expression of inflammatory cytokines may serve as potential diagnostic biomarker for bilirubin encephalopathy

OBJECTIVES: The present study was designed to explore the roles of inflammatory cytokines interleukin-1β (IL-1β) and Tumor growth factor-β (TGF-β) in the diagnosis and treatment of neonate bilirubin encephalopathy (BE). METHODS: A total of 128 BE neonates and 128 normal neonates were included. The serum samples of the BE children and controls were collected, and the levels of IL-1β and TGF-β were examined. Moreover, the correlation between the level of bilirubin and serum expression of IL-1β or TGF-β in BE patients was analyzed. Finally, receiver operating characteristic (ROC) curves were generated to determine the diagnostic value of the cytokines. RESULTS: IL-1β and TGF-β levels were higher in the serum of BE patients than those in non-BE patients, and the expression of either IL-1β or TGF-β showed a strong positive correlation with the serum expression of bilirubin in BE patients. Moreover, the results of ROC analysis showed that either IL-1β or TGF-β could distinguish BE patients from healthy controls. CONCLUSION: IL-1β and TGF-β levels were upregulated in BE and might function as potential biomarkers or therapeutic targets for BE patients.

[Clinical characteristics and treatment options of hearing impairment caused by hyperbilirubinemia].

SummaryNeonatal hyperbilirubinemia is the most common clinical symptom in neonates. When the concentration of free bilirubin in blood is too high, it crosses through the blood-brain barrier and selectively deposits in specific brain nuclei to cause neurotoxicity and bilirubin neurological dysfunction. The auditory nervous system is highly sensitive to bilirubin. Therefore, auditory neuropathy is the most important or even the only clinical symptom of bilirubin neurological dysfunction. Chronic bilirubin encephalopathy can be classified to three types as mild, moderate and severe，according to the audiological manifestations and other neurological sequelae. Early recognition and intervention of bilirubin-induced hearing impairment is of great significance to improve the speech recognition rate of the referred children. This article reviews the most important studies about the clinical characteristics, pathogenesis and treatment of bilirubin-induced hearing impairment.

Histone acetylation as a new mechanism for bilirubin-induced encephalopathy in the Gunn rat.

Bilirubin neurotoxicity has been studied for decades and has been shown to affect various mechanisms via significant modulation of gene expression. This suggests that vital regulatory mechanisms of gene expression, such as epigenetic mechanisms, could play a role in bilirubin neurotoxicity. Histone acetylation has recently received attention in the CNS due to its role in gene modulation for numerous biological processes, such as synaptic plasticity, learning, memory, development and differentiation. Aberrant epigenetic regulation of gene expression in psychiatric and neurodegenerative disorders has also been described. In this work, we followed the levels of histone 3 lysine 14 acetylation (H3K14Ac) in the cerebellum (Cll) of the developing (2, 9, 17 days after the birth) and adult Gunn rat, the natural model for neonatal hyperbilirubinemia and kernicterus. We observed an age-specific alteration of the H3K14Ac in the hyperbilirubinemic animals. The GeneOntology analysis of the H3K14Ac linked chromatin revealed that almost 45% of H3K14Ac ChiP-Seq TSS-promoter genes were involved in CNS development including maturation and differentiation, morphogenesis, dendritogenesis, and migration. These data suggest that the hallmark Cll hypoplasia in the Gunn rat occurs also via epigenetically controlled mechanisms during the maturation of this brain structure, unraveling a novel aspect of the bilirubin-induced neurotoxicity.

Neuroinflammation and ER-stress are key mechanisms of acute bilirubin toxicity and hearing loss in a mouse model.

Hyperbilirubinemia (jaundice) is caused by raised levels of unconjugated bilirubin in the blood. When severe, susceptible brain regions including the cerebellum and auditory brainstem are damaged causing neurological sequelae such as ataxia, hearing loss and kernicterus. The mechanism(s) by which bilirubin exerts its toxic effect have not been completely understood to date. In this study we investigated the acute mechanisms by which bilirubin causes the neurotoxicity that contributes to hearing loss. We developed a novel mouse model that exhibits the neurological features seen in human Bilirubin-Induced Neurological Dysfunction (BIND) syndrome that we assessed with a behavioural score and auditory brainstem responses (ABR). Guided by initial experiments applying bilirubin to cultured cells in vitro, we performed whole genome gene expression measurements on mouse brain tissue (cerebellum and auditory brainstem) following bilirubin exposure to gain mechanistic insights into biochemical processes affected, and investigated further using immunoblotting. We then compared the gene changes induced by bilirubin to bacterial lipopolysaccharide (LPS), a well characterized inducer of neuroinflammation, to assess the degree of similarity between them. Finally, we examined the extent to which genetic perturbation of inflammation and both known and novel anti-inflammatory drugs could protect hearing from bilirubin-induced toxicity. The in vitro results indicated that bilirubin induces changes in gene expression consistent with endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). These gene changes were similar to the gene expression signature of thapsigargin-a known ER stress inducer. It also induced gene expression changes associated with inflammation and NF-κB activation. The in vivo model showed behavioural impairment and a raised auditory threshold. Whole genome gene expression analysis confirmed inflammation as a key mechanism of bilirubin neurotoxicity in the auditory pathway and shared gene expression hallmarks induced by exposure to bacterial lipopolysaccharide (LPS) a well-characterized inducer of neuroinflammation. Interestingly, bilirubin caused more severe damage to the auditory system than LPS in this model, but consistent with our hypothesis of neuroinflammation being a primary part of bilirubin toxicity, the hearing loss was protected by perturbing the inflammatory response. This was carried out genetically using lipocalin-2 (LCN2)-null mice, which is an inflammatory cytokine highly upregulated in response to bilirubin. Finally, we tested known and novel anti-inflammatory compounds (interfering with NF-κB and TNFα signalling), and also demonstrated protection of the auditory system from bilirubin toxicity. We have developed a novel, reversible, model for jaundice that shows movement impairment and auditory loss consistent with human symptoms. We used this model to establish ER-stress and inflammation as major contributors to bilirubin toxicity. Because of the rapid and reversible onset of toxicity in this novel model it represents a system to screen therapeutic compounds. We have demonstrated this by targeting inflammation genetically and with anti-inflammatory small molecules that offered protection against bilirubin toxicity. This also suggests that anti-inflammatory drugs could be of therapeutic use in hyperbilirubinemia.

The Preterm Infant: A High-Risk Situation for Neonatal Hyperbilirubinemia Due to Glucose-6-Phosphate Dehydrogenase Deficiency.

Prematurity and glucose-6-phosphate dehydrogenase (G6PD) deficiency are risk factors for neonatal hyperbilirubinemia. The 2 conditions may interact additively or synergistically, contributing to extreme hyperbilirubinemia, with the potential for bilirubin neurotoxicity. This hyperbilirubinemia is the result of sudden, unpredictable, and acute episodes of hemolysis in combination with immaturity of bilirubin elimination, primarily of conjugation. Avoidance of contact with known triggers of hemolysis in G6PD-deficient individuals will prevent some, but not all, episodes of hemolysis. All preterm infants with G6PD deficiency should be vigilantly observed for the development of jaundice both in hospital and after discharge home.

Efficacy of Human Adipose Tissue-Derived Stem Cells on Neonatal Bilirubin Encephalopathy in Rats.

Kernicterus is a neurological syndrome associated with indirect bilirubin accumulation and damages to the basal ganglia, cerebellum and brain stem nuclei particularly the cochlear nucleus. To mimic haemolysis in a rat model such that it was similar to what is observed in a preterm human, we injected phenylhydrazine in 7-day-old rats to induce haemolysis and then infused sulfisoxazole into the same rats at day 9 to block bilirubin binding sites in the albumin. We have investigated the effectiveness of human adiposity-derived stem cells as a therapeutic paradigm for perinatal neuronal repair in a kernicterus animal model. The level of total bilirubin, indirect bilirubin, brain bilirubin and brain iron was significantly increased in the modelling group. There was a significant decreased in all severity levels of the auditory brainstem response test in the two modelling group. Akinesia, bradykinesia and slip were significantly declined in the experience group. Apoptosis in basal ganglia and cerebellum were significantly decreased in the stem cell-treated group in comparison to the vehicle group. All severity levels of the auditory brainstem response tests were significantly decreased in 2-month-old rats. Transplantation results in the substantial alleviation of walking impairment, apoptosis and auditory dysfunction. This study provides important information for the development of therapeutic strategies using human adiposity-derived stem cells in prenatal brain damage to reduce potential sensori motor deficit.