Molecular Physiology and Pathophysiology of Bilirubin Handling by the Blood, Liver, Intestine, and Brain in the Newborn.

Bilirubin is the end product of heme catabolism formed during a process that involves oxidation-reduction reactions and conserves iron body stores. Unconjugated hyperbilirubinemia is common in newborn infants, but rare later in life. The basic physiology of bilirubin metabolism, such as production, transport, and excretion, has been well described. However, in the neonate, numerous variables related to nutrition, ethnicity, and genetic variants at several metabolic steps may be superimposed on the normal physiological hyperbilirubinemia that occurs in the first week of life and results in bilirubin levels that may be toxic to the brain. Bilirubin exists in several isomeric forms that differ in their polarities and is considered a physiologically important antioxidant. Here we review the chemistry of the bilirubin molecule and its metabolism in the body with a particular focus on the processes that impact the newborn infant, and how differences relative to older children and adults contribute to the risk of developing both acute and long-term neurological sequelae in the newborn infant. The final section deals with the interplay between the brain and bilirubin and its entry, clearance, and accumulation. We conclude with a discussion of the current state of knowledge regarding the mechanism(s) of bilirubin neurotoxicity.

Neonatal hyperbilirubinaemia: a global perspective.

Hyperbilirubinaemia, presenting as jaundice, is a ubiquitous and frequently benign condition in newborn babies but is a leading cause of hospitalisation in the first week of life. In some infants jaundice can become severe, progressing to acute bilirubin encephalopathy and kernicterus with a substantial risk of neonatal mortality and long-term neurodevelopmental impairments. Severe hyperbilirubinaemia and its sequelae continue to occur in industrialised countries with functioning medical systems and a disproportionately high burden also persists in low-income and middle-income countries due primarily to delays in delivering effective treatments that are routinely available in high-income countries. In this Review we summarise up-to-date evidence on the epidemiology of neonatal jaundice including its global burden based on estimates of its prevalence, and both fatal and non-fatal health outcomes. We also discuss the management of severe hyperbilirubinaemia including the prevention of kernicterus, and highlight future directions for research.

Guidelines for the Management of Extremely Premature Deliveries: A Systematic Review.

BACKGROUND AND OBJECTIVES: Available data on survival rates and outcomes of extremely low gestational age (GA) infants (22-25 weeks' gestation) display wide variation by country. Whether similar variation is found in statements by national professional bodies is unknown. The objectives were to perform a systematic review of management from scientific and professional organizations for delivery room care of extremely low GA infants. METHODS: We searched Embase, PubMed, and Google Scholar for management guidelines on perinatal care. Countries were included if rated by the United Nations Development Programme's Human Development Index as "very highly developed." The primary outcome was rating of recommendations from "comfort care" to "active care." Secondary outcomes were specifying country-specific survival and considering potential for 3 biases: limitations of GA assessment; bias from different definitions of stillbirths and live births; and bias from the use of different denominators to calculate survival. RESULTS: Of 47 highly developed countries, 34 guidelines from 23 countries and 4 international groups were identified. Of these, 3 did not state management recommendations. Of the remaining 31 guidelines, 21 (68%) supported comfort care at 22 weeks' gestation, and 20 (65%) supported active care at 25 weeks' gestation. Between 23 and 24 weeks' gestation, much greater variation was seen. Seventeen guidelines cited national survival rates. Few guidelines discussed potential biases: limitations in GA (n = 17); definition bias (n = 3); and denominator bias (n = 7). CONCLUSIONS: Although there is a wide variation in recommendations (especially between 23 and 24 weeks' GA), there is general agreement for comfort care at 22 weeks' GA and active care at 25 weeks' GA.

Metyrapone, an inhibitor of cytochrome oxidases, does not affect viability in a neuroblastoma cell model of bilirubin toxicity.

BACKGROUND: Unconjugated hyperbilirubinemia may cause brain damage in infants, and globally remains a source of neonatal morbidity and mortality. A significant inter-individual variability in vulnerability to bilirubin toxicity remains largely unexplained. An enzyme located in mitochondria oxidizes bilirubin. We hypothesized that inhibiting bilirubin oxidation in human neuronal cell cultures exposed to bilirubin would increase cell death. METHODS: The ability of mitochondrial membranes from CHP-212 human neuroblastoma cells to oxidize bilirubin was verified by spectrophotometry. Intact cells in culture were exposed to bilirubin (75 µM) with or without metyrapone (250 µM) for 24 h, stained with Annexin-V and Propidium iodide and analyzed for apoptosis and necrosis by flow cytometry. RESULTS: Bilirubin caused a significant reduction of viability, from 84 ± 2.0% (mean ± SEM) vs 67 ± 2.7% (p < 0.05), but adding metyrapone to the bilirubin-exposed cells did not further impact cell viability. Metyrapone alone did not influence cell viability. CONCLUSION: Herein we have shown that metyrapone does not increase cell death in neuroblastoma cells in culture exposed to bilirubin. Our results question the relationship between the oxidative mechanism evaluated by spectrophotometry and cell viability. Our findings add to the discussion on whether bilirubin oxidation represents a potentially important protective mechanism in neurons challenged by hyperbilirubinemia.

Ethics, choices, and decisions in acute medicine: a national survey of Norwegian physicians' attitudes.

OBJECTIVE: To study the attitudes of Norwegian physicians to resuscitation of hypothetical patients all at risk of neurological sequelae. DESIGN: Mail-based survey. SETTING: A cohort of Norwegian physicians who are representative of the national physician corps. INTERVENTIONS: A total of 1650 Norwegian physicians (7% of practicing physicians in Norway) received a written questionnaire describing six scenarios of patients all in need of emergency life-saving intervention. Respondents were asked whether they would resuscitate; whether such resuscitation was in the patient's best interest; whether a surrogate's refusal of intervention would be accepted; and whether they would have wanted resuscitation if the patient were their own child, their spouse, or themselves. Positive or negative responses on a four-point Likert scale were recorded. MEASUREMENTS AND MAIN RESULTS: A total of 1,069 respondents (response rate, 65%). Physicians responding to these scenarios were a) more inclined to resuscitate an anonymous patient than if the patient were themselves or their kin; b) willing to resuscitate although they do not consider this intervention to be in the patient's best interest; c) willing to refrain from resuscitation on surrogate request in spite of a reasonably good prognosis; d) willing to accept surrogate's refusal of resuscitation in spite of a stated opinion that such intervention would be in the patient's best interest; and e) less willing to resuscitate newborn infants compared with older children and adults (except the aged) with similar prognoses. CONCLUSION: There appear to be differences in medical thinking about best interest, surrogate decision making, and the relative value of lives as far as these are applied to acute, life-saving treatment.

Prevention of neurodevelopmental sequelae of jaundice in the newborn.

Although its cause, jaundice in the newborn, is extremely common, the disabling neurological disorder kernicterus is very rare. Kernicterus may be prevented by selecting those infants who are at risk of extreme jaundice or who may be particularly vulnerable to bilirubin neurotoxicity. Because the tools for achieving that goal are inadequate, a secondary strategy is needed. This involves a plan for emergency treatment of severely jaundiced infants, in particular those who present with neurological symptoms. In this paper I review the strategies for preventing extreme jaundice, and for reversing neurotoxicity in those infants for whom the principal strategies fail. Briefly, the tools for prevention include measurement of bilirubin while the infant is staying in the maternity unit, plotting the value on an hour-specific chart, assessing other risk factors for jaundice, and educating the parents. Emergency treatment should include immediate, high-irradiance phototherapy, consideration of intravenous immune globulin, and preparation for an exchange transfusion.

Nursing assessment during oxygen administration in ventilated preterm infants.

AIM: To document nurses' opinions about their assessments of oxygen requirements in ventilated preterm infants receiving oxygen supplementation. METHODS: Survey design with descriptive statistics. The sample consisted of 111 nurses employed in clinical positions in neonatal intensive care units within Norway's five regional hospitals. The questionnaire included questions about physiological and clinical observations used when assessing oxygen administration in ventilated preterm infants. RESULTS: A major finding was the gap between the criteria laid down in professional and research literature, vs the criteria nurses perceived they were using when they assessed the oxygen requirements of preterm infants. The respondents stated that they used oxygen saturation to assess the infants' oxygen requirements when adjusting oxygen supplementation. Only 17% of the nurses used the oxygen-haemoglobin dissociation curve in their assessments. Those who responded that they used the curve did not use it correctly. CONCLUSION: Assessment of O2 requirement is based on insufficient information and calls for evaluation of local, national as well as international education. Close collaboration between doctors and nurses is essential in planning care for individual patients.

Administration of drugs known to inhibit P-glycoprotein increases brain bilirubin and alters the regional distribution of bilirubin in rat brain.

P-glycoprotein (P-gp) is an ATP-dependent integral plasma membrane efflux pump, expressed in abundance in brain capillary endothelial cells and astrocytes. P-gp contributes to the blood-brain barrier in limiting the influx and retention of a variety of lipophilic compounds, including unconjugated bilirubin. Several drugs block P-gp function and thereby enhance intracellular accumulation of P-gp substrates. In this study we proposed that pretreatment with drugs known to inhibit P-gp function in clinically relevant doses would alter the uptake of bilirubin in the brain of 32- to 36-d-old rats. In the first arm of the study, the animals received pretreatment with an i.v. infusion of either propanolol, erythromycin, verapamil, ceftriaxone, rifampin, or saline, 10 min before an i.v. bolus of 50 mg/kg bilirubin was given. Except for the erythromycin-treated rats, all treatment groups had significantly higher brain-to-serum bilirubin ratios than control animals (p < 0.05, Welch's t test). In the second arm of the study, treatment with either ceftriaxone or rifampin or saline i.v. preceded a 50 mg/kg i.v. bolus of radioactive bilirubin. Analysis of seven different brain regions by scintillation counting showed that the distribution patterns differed significantly between the study groups (p < 0.001, ANOVA), however, not in accordance with a kernicteric staining pattern. Because of limited knowledge of expression and function of P-gp and other membrane transport proteins in the newborn, the implications of this study remain to be seen. We speculate that drugs known to inhibit P-gp function may increase the risk of bilirubin encephalopathy in the hyperbilirubinemic infant.

P-glycoprotein expression in mouse brain increases with maturation.

The mdr1a isoform of P-glycoprotein (Pgp) is an integral plasma membrane efflux pump expressed in adult brain capillary endothelial cells and astrocytes of the blood-brain barrier. We determined the developmental pattern of Pgp expression in brain tissue at embryonic day 16 (E16), day of life 0 (D0), day of life 7 (D7), day of life 21 (D21), and adults (Ad). The relative expression of Pgp mRNA and protein was indexed as a percent (mean +/- SEM) of D0 levels. Pgp mRNA levels increased significantly (p < 0.01) with maturation (E16: 75 +/- 8%; D21: 303 +/- 37%, and Ad: 1,160 +/- 120%). Similarly, Pgp protein expression was observed at E16 and increased significantly (p < 0.01) during development (E16: 52 +/- 8%; D7: 187 +/- 23%; D21: 440 +/- 48%, and Ad: 441 +/- 56%). This developmental pattern of enhanced blood-brain barrier Pgp expression with maturation was confirmed by immunohistochemistry. We conclude that (i) Pgp expression in mouse brain is limited during late embryogenesis and the newborn period; (ii) Pgp expression increases markedly with postnatal maturation, and (iii) by D21 brain Pgp protein expression approximates adult levels.