Review of bilirubin neurotoxicity I: molecular biology and neuropathology of disease.

Despite the availability of successful prevention strategies to prevent excessive hyperbilirubinemia, the neurological sequelae of bilirubin neurotoxicity (BNTx) still occur throughout the world. Kernicterus, encephalopathy due to BNTx, is now understood to be a spectrum of severity and phenotypes known as kernicterus spectrum disorder (KSD). A better understanding of the selective neuropathology and molecular biology of BNTx and using consistent clinical definitions of KSDs as outcome measure can lead to more accurately predicting the risk and causes of BNTx and KSDs. In Part I of our two-part review, we will summarize current and recent advances in the understanding of the selective neuropathology and molecular biology of the disease. Herein we emphasize the role of unbound, free unconjugated bilirubin as well as genetic contributions to the susceptibility BNTx and the development of KSDs. In Part II, we focus on current and possible novel methods to prevent BNTx and ABE and treat ABE and KSDs.

Review of bilirubin neurotoxicity II: preventing and treating acute bilirubin encephalopathy and kernicterus spectrum disorders.

Previously in Part I of this two-part review, we discussed the current and recent advances in the understanding of the molecular biology and neuropathology of bilirubin neurotoxicity (BNTx). Here in Part II, we summarize current treatment options available to treat the severely jaundiced infants to prevent significant brain damage and improve clinical outcomes. In addition, we review potential novel therapies that are in various stages of research and development. We will emphasize treatments for both prevention and treatment of both acute bilirubin encephalopathy (ABE) and kernicterus spectrum disorders (KSDs), highlighting the treatment of the most disabling neurological sequelae of children with mild-to-severe KSDs whose "rare disease" status often means they are overlooked by the clinical research community at large. As with other secondary dystonias, treatment of the dystonic motor symptoms in kernicterus is the greatest clinical challenge.

Early Amplitude-Integrated Electroencephalography Predicts Long-Term Outcomes in Term and Near-Term Newborns With Severe Hyperbilirubinemia.

BACKGROUND: We aimed to determine the predictive neurological prognostic value of early amplitude-integrated electroencephalography (aEEG) in term and near-term neonates with severe hyperbilirubinemia compared with cranial magnetic resonance imaging (MRI) and auditory brainstem response (ABR). METHODS: Infants of ≥35 weeks of gestation with severe hyperbilirubinemia (total serum bilirubin [TSB] ≥340 µmol/L) or with hyperbilirubinemia (TSB ≥257 µmol/L) in association with bilirubin-induced neurological dysfunction were recruited. All the subjects had an aEEG after being admitted to the neonatal intensive care unit, whereas cranial MRI and ABR were performed when TSB had come down to the normal range. All the infants were followed up to 12 months. RESULTS: During the study period, 77 of 83 infants were eligible, of which 71 had severe hyperbilirubinemia and six had hyperbilirubinemia in association with bilirubin-induced neurological dysfunction. Thirty-three infants were diagnosed with acute bilirubin encephalopathy (ABE), two of whom died of ABE, and 62 completed the follow-up, of which 12 infants had adverse outcomes. Sixty-four infants underwent aEEG, 40 infants had cranial MRI, and 39 infants had ABR. Logistic regression and the receiver-operator characteristic curve analysis showed that the ability of severely abnormal aEEG to predict adverse neurological outcomes in severe hyperbilirubinemia was no better than abnormal ABR, with a sensitivity of 35.7% versus 83.3%, a specificity of 92.0% versus 74.1%, a positive predictive value of 55.6% versus 58.8%, and a negative predictive value of 83.6% versus 90.9%. CONCLUSIONS: Early aEEG could predict adverse neurodevelopmental outcomes in neonates with severe hyperbilirubinemia, although the sensitivity was lower than ABR.

Patterns of acute bilirubin encephalopathy in Nigeria: a multicenter pre-intervention study.

BACKGROUND: Acute bilirubin encephalopathy (ABE) is an important cause of neonatal morbidity in Nigeria, accounting for 5-14% of neonatal deaths. Most newborns with severe ABE have irreversible damage before receiving treatment emphasizing the need for timely pre-admission monitoring and referral. There is limited evidence that educational interventions targeting mothers and health care providers will reduce delayed care. OBJECTIVE: To provide baseline data on the incidence of ABE and associated pre-admission risk factors in five centers of Nigeria in order to evaluate the effect of subsequent educational interventions on outcome. STUDY DESIGN: The incidence of ABE among newborns treated for hyperbilirubinemia was documented prospectively. Bivariate analysis and multivariate logistic regression were used to evaluate risk factors for acute bilirubin encephalopathy and reasons for regional differences in its occurrence. RESULTS: Of 1040 infants, 159 treated for hyperbilirubinemia (15.3%) had mild to severe bilirubin encephalopathy (including 35 deaths), but the incidence ranged from 7 to 22% between centers. Logistic regression identified four common predictors: total serum bilirubin (odds ratio 1.007 per mg/dl rise), out-of-hospital births (OR 2.6), non-alloimmune hemolytic anemia (OR 2.8), and delayed care seeking (OR 4.3). CONCLUSION: The high occurrence of bilirubin encephalopathy in Nigeria is due in large part to a delay in seeking care. A planned intervention strategy will target conditions leading to severe hyperbilirubinemia and delay.

Attenuation of neuro-inflammation improves survival and neurodegeneration in a mouse model of severe neonatal hyperbilirubinemia.

All pre-term newborns and a high proportion of term newborns develop neonatal jaundice. Neonatal jaundice is usually a benign condition and self-resolves within few days after birth. However, a combination of unfavorable complications may lead to acute hyperbilirubinemia. Excessive hyperbilirubinemia may be toxic for the developing nervous system leading to severe neurological damage and death by kernicterus. Survivors show irreversible neurological deficits such as motor, sensitive and cognitive abnormalities. Current therapies rely on the use of phototherapy and, in unresponsive cases, exchange transfusion, which is performed only in specialized centers. During bilirubin-induced neurotoxicity different molecular pathways are activated, ranging from oxidative stress to endoplasmic reticulum (ER) stress response and inflammation, but the contribution of each pathway in the development of the disease still requires further investigation. Thus, to increase our understanding of the pathophysiology of bilirubin neurotoxicity, encephalopathy and kernicterus, we pharmacologically modulated neurodegeneration and neuroinflammation in a lethal mouse model of neonatal hyperbilirubinemia. Treatment of mutant mice with minocycline, a second-generation tetracycline with anti-inflammatory and neuroprotective properties, resulted in a dose-dependent rescue of lethality, due to reduction of neurodegeneration and neuroinflammation, without affecting plasma bilirubin levels. In particular, rescued mice showed normal motor-coordination capabilities and behavior, as determined by the accelerating rotarod and open field tests, respectively. From the molecular point of view, rescued mice showed a dose-dependent reduction in apoptosis of cerebellar neurons and improvement of dendritic arborization of Purkinje cells. Moreover, we observed a decrease of bilirubin-induced M1 microglia activation at the sites of damage with a reduction in oxidative and ER stress markers in these cells. Collectively, these data indicate that neurodegeneration and neuro-inflammation are key factors of bilirubin-induced neonatal lethality and neuro-behavioral abnormalities. We propose that the application of pharmacological treatments having anti-inflammatory and neuroprotective effects, to be used in combination with the current treatments, may significantly improve the management of acute neonatal hyperbilirubinemia, protecting from bilirubin-induced neurological damage and death.

The clinical outcomes of deep gray matter injury in children with cerebral palsy in relation with brain magnetic resonance imaging.

UNLABELLED: In the present study we investigated the nature and extent of clinical outcomes using various classifications and analyzed the relationship between brain magnetic resonance imaging (MRI) findings and the extent of clinical outcomes in children with cerebral palsy (CP) with deep gray matter injury. The deep gray matter injuries of 69 children were classified into hypoxic ischemic encephalopathy (HIE) and kernicterus patterns. HIE patterns were divided into four groups (I-IV) based on severity. Functional classification was investigated using the gross motor function classification system-expanded and revised, manual ability classification system, communication function classification system, and tests of cognitive function, and other associated problems. The severity of HIE pattern on brain MRI was strongly correlated with the severity of clinical outcomes in these various domains. Children with a kernicterus pattern showed a wide range of clinical outcomes in these areas. Children with severe HIE are at high risk of intellectual disability (ID) or epilepsy and children with a kernicterus pattern are at risk of hearing impairment and/or ID. Grading severity of HIE pattern on brain MRI is useful for predicting overall outcomes. The clinical outcomes of children with a kernicterus pattern range widely from mild to severe. WHAT THIS PAPER ADDS: Delineation of the clinical outcomes of children with deep gray matter injury, which are a common abnormal brain MRI finding in children with CP, is necessary. The present study provides clinical outcomes for various domains in children with deep gray matter injury on brain MRI. The deep gray matter injuries were divided into two major groups; HIE and kernicterus patterns. Our study showed that severity of HIE pattern on brain MRI was strongly associated with the severity of impairments in gross motor function, manual ability, communication function, and cognition. These findings suggest that severity of HIE pattern can be useful for predicting the severity of impairments. Conversely, children with a kernicterus pattern showed a wide range of clinical outcomes in various domains. Children with severe HIE pattern are at high risk of ID or epilepsy and children with kernicterus pattern are at risk of hearing impairment or ID. The strength of our study was the assessment of clinical outcomes after 3 years of age using standardized classification systems in various domains in children with deep gray matter injury.

Bilirubin-Induced Audiologic Injury in Preterm Infants.

Although hyperbilirubinemia is extremely common among neonates and is usually mild and transient, it sometimes leads to bilirubin-induced neurologic damage (BIND). The auditory pathway is highly sensitive to the effects of elevated total serum/plasma bilirubin (TB) levels, with damage manifesting clinically as auditory neuropathy spectrum disorder. Compared to full-term neonates, preterm neonates are more susceptible to BIND and suffer adverse effects at lower TB levels with worse long-term outcomes. Furthermore, although standardized guidelines for management of hyperbilirubinemia exist for term and late preterm neonates, similar guidelines for neonates less than 35 weeks gestational age are limited.

Bilirubin-Induced Neurotoxicity in the Preterm Neonate.

Bilirubin-induced neurotoxicity in preterm neonates remains a clinical concern. Multiple cellular and molecular cascades likely underlie bilirubin-induced neuronal injury, including plasma membrane perturbations, excitotoxicity, neuroinflammation, oxidative stress, and cell cycle arrest. Preterm newborns are particularly vulnerable secondary to central nervous system immaturity and concurrent adverse clinical conditions that may potentiate bilirubin toxicity. Acute bilirubin encephalopathy in preterm neonates may be subtle and manifest primarily as recurrent symptomatic apneic events. Low-bilirubin kernicterus continues to be reported in preterm neonates, and although multifactorial in nature, is often associated with marked hypoalbuminemia.

The Blockade of NF-κB Activation by a Specific Inhibitory Peptide Has a Strong Neuroprotective Role in a Sprague-Dawley Rat Kernicterus Model.

Kernicterus, the permanent nerve damage occurring as a result of bilirubin precipitation, still occurs worldwide and may lead to death or permanent neurological impairments. However, the underlying mechanisms remain unclear, and effective therapeutic strategies are lacking. The present study aims to investigate the activation of NF-κB and to identify the effect of NF-κB inhibition on the newborn rat kernicterus model. The NF-κB essential modifier-binding domain peptide (NBD), coupled with the HIV trans-activator of transcription peptide (TAT) was used to inhibit NF-κB. NF-κB was significantly activated in the cerebrum at 1 and 3 h (p < 0.05) after the model was established, as measured by EMSA. NF-κB activation was inhibited by intraperitoneal administration of TAT-NBD. The general conditions of the TAT-NBD-treated rats were improved; meanwhile, these rats performed much better on the neurological evaluation, the rotarod test, and the Morris water maze test (p < 0.05) than the vehicle-treated rats at 28 days. Furthermore, the morphology of the nerve cells was better preserved in the TAT-NBD group, and these cells displayed less neurodegeneration and astrocytosis. Simultaneously, apoptosis in the brain was attenuated, and the levels of the TNF-α and IL-1ß proteins were decreased (p < 0.01). These results suggested that NF-κB was activated, and inhibition of NF-κB activation by TAT-NBD not only attenuated the acute neurotoxicity, apoptosis, and inflammation, but also improved the long term neurobehavioral impairments in the kernicterus model rats in vivo. Thus, inhibiting NF-κB activation might be a potential therapeutic approach for kernicterus.

Audiologic impairment associated with bilirubin-induced neurologic damage.

Hyperbilirubinemia occurs commonly in neonates and is usually mild and transient, with no long-lasting sequelae. However, bilirubin-induced neurologic damage may occur in some infants. The auditory pathway is the most sensitive part of the central nervous system to bilirubin-induced toxicity, and permanent sequelae may result from only moderately elevated total serum/plasma bilirubin levels. The damage to the auditory system occurs primarily within the brainstem and cranial nerve VIII, and manifests clinically as auditory neuropathy spectrum disorder.

Are the neuromotor disabilities of bilirubin-induced neurologic dysfunction disorders related to the cerebellum and its connections?

Investigators have hypothesized a range of subcortical neuropathology in the genesis of bilirubin-induced neurologic dysfunction (BIND). The current review builds on this speculation with a specific focus on the cerebellum and its connections in the development of the subtle neuromotor disabilities of BIND. The focus on the cerebellum derives from the following observations: (i) the cerebellum is vulnerable to bilirubin-induced injury; perhaps the most vulnerable region within the central nervous system; (ii) infants with cerebellar injury exhibit a neuromotor phenotype similar to BIND; and (iii) the cerebellum has extensive bidirectional circuitry projections to motor and non-motor regions of the brainstem and cerebral cortex that impact a variety of neurobehaviors. Future study using advanced magnetic resonance neuroimaging techniques have the potential to shed new insights into bilirubin's effect on neural network topology via both structural and functional brain connectivity measurements.

Subtle bilirubin-induced neurodevelopmental dysfunction (BIND) in the term and late preterm infant: does it exist?

Subtle bilirubin-induced neurological dysfunction (BIND) is defined as disturbances in sensory and sensorimotor integration, central auditory processing, coordination, and muscle tone in the absence of the classical findings of kernicterus. This review is restricted to the (sensori)motor signs of BIND associated with unconjugated hyperbilirubinemia in term and late preterm neonates. The diagnosis of BIND at follow-up requires validated, age-specific techniques that are designed to identify these disturbances in infancy and later childhood. The (sensori)motor signs of BIND are compatible with the pathological substrate of unconjugated hyperbilirubinemia and its known effects on the brain.

Cotrimoxazole and neonatal kernicterus: a review.

Sulfamethoxazole (SMX) and trimethoprim (TMP) individually and a combination known as cotrimoxazole (SMX-TMP) are widely used for the treatment of protozoan and bacterial infections. SMX-TMP is also one of the widely used antibiotics administered orally in neonates, along with gentamicin injection, for treating pneumonia and sepsis by home-based healthcare providers in Asian countries. Although the use of this drug has successfully reduced neonate mortality, there is a concern for it causing neurotoxicity. Previous clinical studies with sulfisoxazole have demonstrated occurrence of kernicterus in neonates. This sulfonamide is thought to displace bilirubin from its albumin-binding sites in plasma leading to an elevation of plasma bilirubin, which crosses the blood-brain barrier, reaches central neurons to cause kernicterus. We performed an extensive review of clinical and animal studies with cotrimoxazole, which showed no reported incidences of kernicterus with SMX-TMP use in neonates. EndNote, BasicBiosis, Embase, PubMed and Toxline database searches were conducted using specific keywords yielding 74 full-length articles relevant to the review. This review has taken into account various factors, including the disease itself, direct effects of the drug and its metabolism through conjugation and acetylation through a thorough review of the literature to examine the potentials of SMX-TMP to cause kernicterus in neonates. SMX-TMP in oral doses administered to neonates for 7-10 days is unlikely to cause kernicterus. Also, this review recommends warranting the need of future studies using animal models and clinical studies in humans to address SMX-TMP toxicity.

[Diagnostic value of amplitude-integrated electroencephalography in predicting outcome of newborn patients in neonatal intensive care unit].

OBJECTIVE: To assess the diagnostic value of amplitude-integrated electroencephalography (aEEG) in predicting outcome of newborns who were at high risk for central nervous system without severe hypoxic-ischemic encephalopathy. METHODS: Forty-two consecutive patients at risks for neurological disorders referred to our level-III NICU were prospectively enrolled in the study over a period of 3 years. They were classified on the basis of their primary diagnoses including hypoglycemic brain damage, meningoencephalitis, bilirubin encephalopathy, and metabolic disease. Clinical data were collected. Amplitude-integrated and raw EEG tracings were assessed for background pattern, sleep-wake cycling, and epileptiform activity. The neuromotor development of survivors was assessed by using the Infant Neurological International Battery (INFANIB). RESULT: The characteristic of aEEG tracings in 42 infants showed continuous normal voltage (CNV)(n = 15), discontinuous voltage (DC)(n = 9), burst-suppression (BS) BS(+) (n = 6), BS(-)(n = 7), flat (FT, n = 5); mature sleep-wake cycling (SWC, n = 4), immature SWC (n = 14), no SWC (n = 24); 30 infants (71.4%) had electrical seizures: single seizure (n = 6); repetitive seizures (n = 7), and status epilepticus (SE) (n = 17).aEEG of 20 infants who had poor outcome showed FT (n = 5), BS(-)/SE (n = 6), BS(-)/ repetitive seizures (n = 1) , BS(+)/SE (n = 1), BS(+)/repetitive seizures (n = 1), DC/SE(n = 6). Chi-square analysis and Spearman rank correlation analysis showed the classification of aEEG background pattern, SWC and comprehensive score (score system was developed by evaluation of the above 3 variables) were correlated with the outcome of these infants at high neurological risks. CONCLUSION: Amplitude-integrated electroencephalography can provide important information of the status of cerebral function in neonates at high neurological risk and help to predict their outcome.

[Amplitude-integrated electroencephalographic changes in neonates with acute bilirubin encephalopathy].

OBJECTIVE: To characterize amplitude-integrated electroencephalo graphic (aEEG) traces in neonates with acute bilirubin encephalopathy (ABE), explore the value of aEEG in early diagnosis and prediction of neurological outcome of ABE. METHOD: aEEG records of 10 cases with ABE (Oct 2009-Nov 2011) were reviewed to identify neonates with a diagnosis of ABE. Clinical data were collected. The aEEG traces were classified according to background activity (normal, moderate, or severely abnormal), presence of seizures and sleep-wake cycling (SWC). Brainstem auditory evoked potential (BAEP) and magnetic resonance imaging (MRI) were studied. The neuromotor development of survivors with ABE was assessed by using the Infant Neurological International Battery (INFANIB). RESULT: The characteristics of aEEG tracings in these infants with ABE were shown continuous normal voltage (CNV, n = 5), discontinuous voltage (DNV, n = 4), discontinuous voltage with burst-suppression (BS)BS+ (n = 1); mature SWC (n = 2), immature SWC (n = 5), no SWC (n = 3); 8 infants (80%) had electrical seizures: single seizure (n = 2); repetitive seizures (n = 2), and status epilepticus (SE) (n = 4). Among the 10 infants with ABE, no infants had normal aEEG, 3 had mildly abnormal aEEG, and 7 had severely abnormal aEEG. Eight infants accepted BAEP test, 2 were mildly abnormal and 6 were severely abnormal. Six infants accepted MRI, 1 was normal and 5 were abnormal. By chi-square analysis and Spearman rank correlation analysis, the results of aEEG classification were correlated with the phase of ABE and the severity of BAEP. These infants were followed up for more than 6 months (range 6 months to 1 year). In 3 infants with mildly abnormal aEEG, 2 were normal and 1 was transit in infanib score at 6 months of age. Of 7 infants with severely abnormal aEEG, 1 died, 3 were abnormal (2 Spastic dyskinesia and 1 hypotonia), 2 were transit in infanib score at 6 months old. 1 lost to follow-up. CONCLUSION: Amplitude-integrated electroencephalography can provide important information of the status of cerebral function in neonates with ABE and help to predict its neurological outcome.

Use of the extended parallel processing model to evaluate culturally relevant kernicterus messages.

INTRODUCTION: Kernicterus is a serious but easily preventable disease in newborns that is not well-known even by some health care professionals. This study evaluated a parent guide and poster on kernicterus awareness and prevention generated by the Centers for Disease Control and Prevention. The extended parallel processing model was used as a framework for creating the interview protocol and analyzing the results. METHOD: In-depth interviews were conducted with four parents and six health care personnel of different ethnicities to evaluate the materials. Content for the parent guide and poster was held constant, but photos were varied according to the ethnicity of the baby (white, African American, or Hispanic) and the language in which the interviews were conducted (English and Spanish). RESULTS: The parent guide was evaluated positively, but reactions to the poster were varied. The consensus was that the poster drew more attention than the pocket guide but lacked sufficient information about what jaundice is or how to treat it, while the pocket guide provided information, especially with regard to efficacy. The extended parallel processing model claims that when efficacy is equal to or higher than perceived threat, respondents should engage in recommended responses, which was the general finding from these interviews. DISCUSSION: Recommendations for improvements of the materials are presented. The focus on different ethnicities in the materials was perceived as unnecessary and potentially counter-productive. Both parents and health care professionals mentioned the lack of information regarding treatment. Providing information on the length and effectiveness of treatment for jaundice and kernicterus might increase efficacy in averting the threat in both conditions.

Moderate unconjugated hyperbilirubinemia causes a transient but delayed suppression of amplitude-integrated electroencephalographic activity in preterm infants.

BACKGROUND: Unconjugated hyperbilirubinemia occurs frequently in preterm infants and may result in bilirubin encephalopathy. Amplitude-integrated electroencephalography (aEEG) is used to evaluate brain function in newborns. OBJECTIVES: To investigate the influence of total serum bilirubin (TSB) on the aEEG amplitude of preterm infants and to evaluate aEEG as a noninvasive method to identify acute bilirubin encephalopathy. METHODS: We performed a prospective observational study of 34 infants with a gestational age (GA) of 26-31 6/7 weeks. Infants had aEEG recordings on the 1st-5th, 8th and 15th day after birth. Infants with asphyxia, intraventricular hemorrhage >grade I or circulatory insufficiency were excluded. aEEG was evaluated by calculating the mean 5th, 50th and 95th centiles of the aEEG amplitudes. RESULTS: TSB peaked on the 4th day after birth. There was no synchronous relationship between TSB and aEEG amplitudes. The 5th, 50th, and 95th aEEG amplitude centiles on the 8th day correlated negatively with the TSB peak value (r = -0.37, p = 0.048; r = -0.60, p = 0.001; r = -0.44, p = 0.017, respectively), irrespective of GA. The 5th and 50th aEEG amplitude centiles increased with increasing GA (r = 0.45, p < 0.001, and r = 0.26, p < 0.001, respectively) and postnatal age (r = 0.25, p < 0.001, and r = 0.16, p = 0.023, respectively). CONCLUSIONS: TSB had no direct effect on aEEG amplitudes in preterm infants. There is, however, a delayed effect on electrocerebral activity in the 2nd week after birth.

[Neurological dysfunction induced by bilirrubin]. / Disfunción neurológica inducida por bilirrubina.

INTRODUCTION: "Kernicterus" is a term currently used to describe bilirrubin induced brain injury in the neuro-pathological studies. This is a confusing term and nowadays we prefer bilirrubin encephalopathy or bilirrubin induced neurological dysfunction. The clinical signs vary and it is clearly decreasing in prevalence in developed countries. MATERIAL AND METHODS: We review a series of 7 patients with bilirrubin encephalopathy and variable neurological manifestations, who were seen in the Neuropaediatric Department in the last 10 years. Only one patient died in the neonatal period with hyperbilirubinaemia, sepsis and multi-organ failure. RESULTS: Diverse aetiological factors were related to hyperbilirubinaemia. All patients had clinical symptoms due to hyperbilirubinaemia. Neuroimaging during the neonatal period showed involvement of the nucleus pallidus, with hyperintensity in T1 in the brain MR scan as the most consistent finding. All the patients who survived developed neurological signs and we try to correlate them with biochemical, clinical, neuroimaging and neurophysiological parameters. CONCLUSIONS: An increase in the number of patients with bilirrubin encephalopathy has been observed over the last few years, and we attempt to find out the causes. The increased survival of the low birth weight newborns, the increase in the immigration population and the use of diagnostic neuroimaging contribute to this increase. It is a great challenge for the neonatologist and for neuropaediatricians to prevent its occurrence and to minimise the effects of bilirrubin encephalopathy.