Toward understanding kernicterus: a challenge to improve the management of jaundiced newborns

Displacement of bilirubin from albumin by ibuprofen in vitro

Ibuprofen binds to plasma albumin and could interfere with the binding of bilirubin in jaundiced newborn infants. Most clinical studies have not shown increased concentrations of unbound bilirubin (UB) in plasma from infants treated with ibuprofen for a patent ductus arteriosus. However, studies in vitro have not been equally conclusive. Plasma were obtained from routine samples from jaundiced newborn infants and pooled. Total and UB were measured with the peroxidase method after addition of ibuprofen or sulfisoxazole as a known bilirubin displacer. Final ibuprofen concentrations varied from 0.43 to 2.6 mM. Bilirubin concentrations were varied from 176 to 708 microM by adding bilirubin to plasma samples. Ibuprofen caused a linear increase in UB up to +54% at a concentration of 1.8 mM, compared with an increase of 87% by sulfisoxazole (1.32 mM). A double reciprocal plot of molar concentrations of bound versus UB at bilirubin concentrations ranging from 176 to 708 microM showed a competitive displacement of bilirubin by ibuprofen. The data indicate that ibuprofen is a competitive displacer of bilirubin in vitro. Ibuprofen should be used with caution in premature infants with a significant hyperbilirubinemia.

Predicting bilirubin neurotoxicity in jaundiced newborns

PURPOSE OF REVIEW

The management of jaundice in the newborn infant is an area of clinical practice sorely lacking an evidence-based foundation, and neonatal bilirubin neurotoxicity (kernicterus) continues to occur worldwide.

RECENT FINDINGS

Studies suggest that measuring serum or plasma bilirubin binding, in particular the nonalbumin-bound or unbound bilirubin concentration (Bf), would improve jaundice management as it better predicts bilirubin neurotoxicity than the conventionally used total bilirubin concentration (BT). However, many misconceptions persist regarding the relationships between BT, Bf, the magnitude and distribution of the neonatal bilirubin load, and the risk of bilirubin neurotoxicity.

SUMMARY

Overcoming these misconceptions and integrating Bf and BT into the management of neonatal jaundice may help move clinical practice from its tradition-based approach centered primarily on BT toward an evidence-based approach that will substantially improve our ability to predict bilirubin neurotoxicity and improve the clinical management of this generally benign, but potentially catastrophic, newborn condition.

Developmental hyperbilirubinemia and CNS toxicity in mice humanized with the UDP glucuronosyltransferase 1 (UGT1) locus

High levels of unconjugated bilirubin (UCB) in newborn children is associated with a reduction in hepatic UDP glucuronosyltransferase (UGT) 1A1 activity that can lead to CNS toxicity, brain damage, and even death. Little is known regarding those events that lead to UCB accumulation in brain tissue, and therefore, we sought to duplicate this condition in mice. The human UGT1 locus, encoding all 9-UGT1A genes including UGT1A1, was expressed in Ugt1(-/-) mice. Because the most common clinical condition associated with jaundice in adults is Gilbert's syndrome, which is characterized by an allelic polymorphism in the UGT1A1 promoter, hyperbilirubinemia was monitored in humanized UGT1 mice that expressed either the Gilbert's UGT1A1*28 allele [Tg(UGT1(A1*28))Ugt1(-/-) mice] or the normal UGT1A1*1 allele [Tg(UGT1(A1*1))Ugt1(-/-) mice]. Adult Tg(UGT1(A1*28))Ugt1(-/-) mice expressed elevated levels of total bilirubin (TB) compared with Tg(UGT1(A1*1))Ugt1(-/-) mice, confirming that the promoter polymorphism associated with the UGT1A1*28 allele contributes to hyperbilirubinemia in mice. However, TB accumulated to near toxic levels during neonatal development, a finding that is independent of the Gilbert's UGT1A1*28 promoter polymorphism. Whereas serum TB levels eventually returned to adult levels, TB clearance in neonatal mice was not associated with hepatic UGT1A1 expression. In approximately 10% of the humanized UGT1 mice, peak TB levels culminated in seizures followed by death. UCB deposition in brain tissue and the ensuing seizures were associated with developmental milestones and can be prevented by enhancing regulation of the UGT1A1 gene in neonatal mice.

Reversibility of acute intermediate phase bilirubin encephalopathy

AIM

To show the potential for reversing acute intermediate to advanced phase bilirubin encephalopathy.

METHODS

Case studies.

RESULTS

Six extremely jaundiced infants had symptoms of intermediate to advanced phase acute bilirubin encephalopathy. The infants were treated aggressively. Two patients had brain magnetic resonance imaging showing increased signals in the globus pallidus. On follow-up, all infants are neurologically normal.

CONCLUSIONS

Intermediate-to-advanced stage acute bilirubin encephalopathy may occasionally be reversible. These cases provide a strong argument in favour of rapid and aggressive intervention in infants presenting with extreme jaundice and neurological symptoms.

Does Ibuprofen increase neonatal hyperbilirubinemia?

OBJECTIVE

The aim of this study was to investigate whether ibuprofen exposure was associated with increased hyperbilirubinemia in preterm infants.

METHODS

Since 2000, ibuprofen has been administered to all infants at <30 weeks of gestation who are admitted to our unit, to prevent patent ductus arteriosus. We retrospectively compared data for 418 infants subjected to ibuprofen prophylaxis (2000-2007) and 288 infants not exposed to ibuprofen (1993-1999).

RESULTS

The ibuprofen group had a significantly higher peak total serum bilirubin level (9.0 +/- 2.5 mg/dL vs 7.3 +/- 3.3 mg/dL), more need for phototherapy (398 infants [95%] vs 254 infants [87.6%]), and a longer phototherapy duration (94.3 +/- 43.6 hours vs 87.2 +/- 38.6 hours). Groups did not differ with respect to gestational age, birth weight, gender ratio, glucose-6-phosphate dehydrogenase deficiency incidence, or hypoalbuminemia (<2.5 g/dL) incidence. Hemolytic isoimmunization was diagnosed with similar incidences (no-ibuprofen group: 7 of 288 infants; ibuprofen group: 8 of 418 infants). The rates of exchange-transfusion also were similar between the groups (no-ibuprofen group: 14 infants [4.8%]; ibuprofen group: 19 infants [4.5%]).

CONCLUSIONS

Ibuprofen administration was associated with higher peak total serum bilirubin levels, and the more-pronounced hyperbilirubinemia led to longer phototherapy. The potential role of competition between ibuprofen and bilirubin in the hepatic glucuronidation pathway is discussed.

Screening for severe neonatal hyperbilirubinemia

Screening for severe neonatal hyperbilirubinemia is integral to newborn care. Predischarge risk assessment relies on documentation of visual jaundice: age at onset and progression; identification of clinical risk such as late prematurity and bruising; with determination of total bilirubin (blood or transcutaneous assay) adjusted for age in hours. Along with promotion of breastfeeding, coordination between birthing hospital and medically supervised outpatient follow-up, a systems approach allows for a safer and effective means to prevent adverse effects of extreme hyperbilirubinemia.

Intravenous lipid and bilirubin-albumin binding variables in premature infants

BACKGROUND

The lipid intake at which a significant bilirubin-displacing effect occurs as a function of gestational age (GA) is unclear.

OBJECTIVE

To determine the effect of gradual increase in IL intake from 1.5 to 3 g/kg per day on bilirubin-albumin binding variables as a function of GA in premature infants with indirect hyperbilirubinemia.

METHODS

Infants of 24 to 33 weeks' gestation at birth who received IL (20% Intralipid [Fresenius Kabi, Uppsala, Sweden]) doses of 1.5, 2, 2.5, and 3 g/kg per day over 4 consecutive days were prospectively evaluated. The blood samples were drawn twice at least 8 hours apart on each IL intake to measure total serum bilirubin and free bilirubin by the peroxidase test. The highest free bilirubin on each IL intake, the corresponding total serum bilirubin, and serum albumin were used to calculate the bilirubin/albumin binding constant or binding affinity.

RESULTS

Sixty-two infants (median GA: 28 weeks) were studied during the first 10 days of life. None of the subjects had culture-proven sepsis, had triglyceride levels of >2.05 mmol/L, or were receiving steroids. Infants were grouped in 2-week GA intervals. The cumulative frequency of elevated free bilirubin concentration (>or=90th percentile or B(f) >or= 32 nmol/L) as a function of IL intake was inversely related to GA and was significantly different among 2-week GA groups. There was significant decrease in binding affinity and increase in free bilirubin concentration with higher IL intake for <or=28 week but not for >28 week GA groups.

CONCLUSIONS

The IL intake may be associated with a significant fall in the binding affinity of bilirubin for plasma protein and a concomitant increase in free bilirubin concentration in premature infants. The lipid intake at which this occurs depends on GA.

Kernicterus in preterm infants

OBJECTIVE

We sought to clarify the features of kernicterus in preterm infants.

METHODS

The subjects of this study were 8 preterm infants with athetoid cerebral palsy whose gestational ages were < or =34 weeks. We retrospectively investigated clinical, laboratory, MRI, and brainstem auditory evoked potential (BAEP) findings.

RESULTS

Gestational age was < or =26 weeks in 6 of the 8 infants, and birth weight was <1000 g in 5 infants. Serious postnatal complications with systemic deterioration were observed in 3 infants. Total bilirubin levels were measured frequently in the majority of infants; peak values of >15 mg/dL were observed in 3 infants. No infant showed neurologic symptoms characteristic of classical acute bilirubin encephalopathy during the neonatal period. Dystonic posture and abnormal muscle tone were first recognized within 6 months' corrected age in all patients. During infancy, MRI was performed in 7 infants. Abnormal high-intensity areas were observed in the bilateral globi pallidi in all 7 infants. However, MRI during the neonatal period or after 1 year's corrected age showed no abnormal findings. BAEP measurements were abnormal in 7 of the 8 infants.

CONCLUSIONS

Preterm infants with athetotic cerebral palsy showed rather homogeneous features, similar to term infants with kernicterus, with marked hyperbilirubinemia. This combination of clinical, laboratory, neuroimaging, and neurophysiological data will contribute to the increased recognition of preterm infants with kernicterus.

Unbound (free) bilirubin: improving the paradigm for evaluating neonatal jaundice

BACKGROUND

The serum or plasma total bilirubin concentration (B(T)) has long been the standard clinical laboratory test for evaluating neonatal jaundice, despite studies showing that B(T) correlates poorly with acute bilirubin encephalopathy (ABE) and its sequelae including death, classical kernicterus, or bilirubin-induced neurological dysfunction (BIND). The poor correlation between B(T) and ABE is commonly attributed to the confounding effects of comorbidities such as hemolytic diseases, prematurity, asphyxia, or infection. Mounting evidence suggests, however, that B(T) inherently performs poorly because it is the plasma non-protein-bound (unbound or free) bilirubin concentration (B(f)), rather than B(T), that is more closely associated with central nervous system bilirubin concentrations and therefore ABE and its sequelae.

CONTENT

This article reviews (a) the complex relationship between serum or plasma bilirubin measurements and ABE, (b) the history underlying the limited use of B(f) in the clinical setting, (c) the peroxidase method for measuring B(f) and technical and other issues involved in adapting the measurement to routine clinical use, (d) clinical experience using B(f) in the management of newborn jaundice, and (e) the value of B(f) measurements in research investigating bilirubin pathochemistry.

SUMMARY

Increasing evidence from clinical studies, clinical experience, and basic research investigating bilirubin neurotoxicity supports efforts to incorporate B(f) expeditiously into the routine evaluation of newborn jaundice.

Normal neurological outcome in two infants treated with exchange transfusions born to mothers with Crigler-Najjar Type 1 disorder

Patients with Crigler-Najjar Type 1 (CN-1) disorder have an unconjugated hyperbilirubinaemia due to the complete absence in activity of uridinediphosphate glucuronosyltransferase, a bilirubin-conjugating enzyme. In pregnant women with CN-1, the foetus is at high risk of being adversely affected by the bilirubin, as unconjugated bilirubin can cross the placenta and is potentially neurotoxic. We report the long-term outcomes of two infants born to women with CN-1. These infants had exchange transfusions soon after birth and have normal neurodevelopmental outcomes at 18 months and four years of age, respectively. We propose that this intervention might have improved the neurological outcome of these infants.

Kernicterus in the 21st century: frequently asked questions

Acute kernicterus remains a clinical emergency and its delayed management represents an easily preventable neonatal brain injury. Yet, practitioners encounter recurrent questions regarding the risk and timing of bilirubin-related neurotoxicity. These include the following: does bilirubin damage the brain of healthy infants? Is there a re-emergence of kernicterus in the United States? Was kernicterus previously prevented in the United States? What was the public health impact of 1994 American Academy of Pediatrics Guidelines? What is the current incidence of kernicterus and severe neonatal hyperbilirubinemia? What is the estimated risk of kernicterus in infants with excessive hyperbilirubinemia? Is there a specific bilirubin threshold total serum bilirubin (TSB) value for neurotoxicity? Are there sequelae of severe or prolonged moderate hyperbilirubinemia in the absence of recognized acute bilirubin encephalopathy? Can we define a bilirubin level that is safe in newborns? We address these questions in the context of available data and evidence, and estimate the current risk of chronic kernicterus is about one in seven in infants with TSB >30 mg per 100 ml (513 micromol l(-1)).

Calculated free bilirubin levels and neurotoxicity

Although most bilirubin in the circulation is bound to albumin, a relatively small fraction remains unbound. The concentration of this 'free' bilirubin (B(F)) is believed to dictate the biologic effects of bilirubin in jaundiced newborns, including its neurotoxicity. The threshold at which B(F) produces changes in cellular function culminating in permanent cell injury and cell death has been the subject of considerable debate. The objective of this study was to compare calculated central nervous system (CNS) B(F) levels in Gunn rat pups during (i) peak postnatal hyperbilirubinemia and (ii) sulfadimethoxine-induced acute bilirubin encephalopathy (ABE) previously reported from our laboratory with those predicted in human neonates with peak total serum bilirubin (TSB) levels of 35 mg per 100 ml (599 micromol l(-1)), a clinical cohort that often evidence moderate-to-severe adverse post-icteric neurodevelopmental sequelae. Homozygous j/j Gunn rat pups with neonatal hyperbilirubinemia due to a deficiency of the bilirubin conjugating enzyme uridine-diphosphate-glucuronosyl transferase 1A1 were studied along with non-jaundiced littermate heterozygous J/j controls. Sulfadimethoxine was used to displace bilirubin from albumin in hyperbilirubinemic j/j Gunn rat pups to increase their brain bilirubin content and induce ABE. Calculated Gunn rat CNS B(F) levels were determined as a function of genotype, sulfadimethoxine exposure and albumin-bilirubin binding constant. These data were compared with the human CNS B(F) predicted from the calculated serum B(F) in human neonates with a TSB of 35 mg per 100 ml as a function of albumin-bilirubin binding constant, albumin concentration and the assumption that at this hazardous bilirubin level there may be rapid equilibration of B(F) between serum and brain. There was a large gap between the upper limit of the calculated CNS B(F) 95% confidence interval (CI) range in non-jaundiced J/j pups (for example, 112 nM at k=9.2 l micromol(-1)) and the lower limit seen in the saline-treated hyperbilirubinemic j/j pups (556 nM at k=9.2 l micromol(-1)) as well as between the upper limit in saline-treated hyperbilirubinemic j/j pups (1110 nM at k=9.2 l micromol(-1)) and the lower limit seen in sulfadimethoxine-treated jaundiced j/j littermates (3461 nM at k=9.2 l micromol(-1)). There was considerable overlap and remarkable similarity between the predicted human CNS B(F) values at a TSB of 35 mg per 100 ml for a range of reported human serum bilirubin-albumin binding constants and albumin concentrations, and those calculated for saline-treated hyperbilirubinemic j/j Gunn rat pups. This exercise yielded strikingly similar apparent calculated neurotoxic B(F) levels for Gunn rat pups and human neonates rather than orders of magnitude differences that might have been predicted at the outset and add to a growing literature aimed at defining clinically germane neurotoxic B(F) thresholds.Journal of Perinatology (2009) 29, S14-S19; doi:10.1038/jp.2008.218.

Clinical report from the pilot USA Kernicterus Registry (1992 to 2004)

To identify antecedent clinical and health services events in infants (>/=35 weeks gestational age (GA)) who were discharged as healthy from their place of birth and subsequently sustained kernicterus. We conducted a root-cause analysis of a convenience sample of 125 infants >/=35 weeks GA cared for in US healthcare facilities (including off-shore US military bases). These cases were voluntarily reported to the Pilot USA Kernicterus Registry (1992 to 2004) and met the eligibility criteria of acute bilirubin encephalopathy (ABE) and/or post-icteric sequelae. Multiple providers at multiple sites managed this cohort of infants for their newborn jaundice and progressive hyperbilirubinemia. Clinical signs of ABE, verbalized by parents, were often inadequately elicited or recorded and often not recognized as an emergency. Clinical signs of ABE were reported in 7 of 125 infants with a subsequent diagnosis of kernicterus who were not re-evaluated or treated for hyperbilirubinemia, although jaundice was noted at outpatient visits. The remaining infants (n=118) had total serum bilirubin (TSB) levels >20 mg per 100 ml (342 micromol l(-1); range: 20.7 to 59.9 mg per 100 ml). No specific TSB threshold coincided with onset of ABE. Of infants <37 weeks GA with kernicterus, 34.9% were LGA (large for gestational age) as compared with 24.7% of term infants (>37 weeks GA). Although >90% mothers initiated breast-feeding, assessment of milk transfer and lactation support was suboptimal in most. Mortality was 4% (5 of 125) in infants readmitted at age </=1 week. Along with a rapid rise of TSB (>0.2 mg per 100 ml per hour), contributing factors, alone or in combination, included undiagnosed hemolytic disease, excessive bilirubin production related to extra-vascular hemolysis and delayed bilirubin elimination (including increased enterohepatic circulation, diagnosed and undiagnosed genetic disorders) in the context of known late prematurity (<37 weeks), glucose 6-phosphate-dehydrogenase deficiency, infection and dehydration. Readmission was at age </=5 days in 81 of 118 (69%) infants and <10 days in 101 of 118 (86%) infants. TSB levels were </=35 mg per 100 ml (598 micromol l(-1)) in 46 (39%) infants, of whom one died before exchange transfusion, one was untreated and one was lost to follow-up. Timely and efficacious bilirubin reduction interventions defined by 'crash-cart' initiation of immediate intensive phototherapy and urgent exchange transfusion were accomplished in 11 of 43 infants, which were compared with 12 of 43 infants in whom a timely exchange sometimes could not be accomplished. No overt sequelae were found in 8 of 11 infants (73%) treated with a 'crash-cart' approach compared with none without sequelae when exchange was delayed by pre-admission delays, technical factors or need to transfer to a tertiary facility. None of the remaining 20 of 43 infants treated only with phototherapy escaped sequelae. Regardless of age at readmission and intervention, infants with peak measured TSB >35 mg per 100 ml had post-icteric sequelae (n=73). There was a narrow margin of safety between birthing hospital discharge or home birth and readmission to a tertiary neonatal/pediatric facility. Progression of hyperbilirubinemia to hazardous levels and onset of neurological signs were often not identified as infant's care and medical supervision transitioned during the first week after birth. The major underlying root cause for kernicterus was systems failure of services by multiple providers at multiple sites and inability to identify the at-risk infant and manage severe hyperbilirubinemia in a timely manner.

Photoisomers: obfuscating factors in clinical peroxidase measurements of unbound bilirubin?

OBJECTIVES

The objectives of the study were to measure the effect of 4Z,15E-bilirubin on peroxidase free bilirubin measurements and to review the literature on this topic.

METHODS

4Z,15E-Bilirubin was generated in situ in serum or serum albumin solution through controlled irradiation of isomerically pure 4Z,15Z-bilirubin IXalpha, under conditions in which the total amount of bilirubin remained constant. Reactions were monitored by difference spectroscopy, to ensure that solutions were not irradiated beyond the initial photostationary state and that concentrations of other isomers were kept to a minimum. Prepared in this way, 10% to 25% of the total bilirubin in the final solutions was in the form of the 4Z,15E-isomer. Free bilirubin in the solutions was measured with a peroxidase method, before and after irradiation. The use of bovine serum albumin as a surrogate for human albumin in in vitro studies also was investigated.

RESULTS

The findings of previous studies are not altogether consistent, with a common flaw in several being the failure to measure photoisomer concentrations. For bilirubin in serum albumin solution, conversion of approximately 25% of the 4Z,15Z-isomer to 4Z,15E-bilirubin led to a much smaller decrease (<20%) in the apparent free bilirubin concentration; for bilirubin in serum, conversion of approximately 15% of the 4Z,15Z-isomer to photoisomers resulted in a much larger increase ( approximately 40%). Irradiation of bilirubin in bovine serum albumin solution generated a very different array of photoisomers than that observed in human albumin solutions.

CONCLUSIONS

The effect of photoisomers on the accuracy and specificity of free 4Z,15Z-bilirubin measurements remains uncertain. In a clinical setting, free bilirubin measurements need to be interpreted with caution when samples contain photoisomers. Irradiated bovine albumin solutions of isomerically impure bilirubin used in previous studies are poor models for investigating the effects of phototherapy in humans and the albumin binding of photoisomers.

The cytotoxic effect of unconjugated bilirubin in human neuroblastoma SH-SY5Y cells is modulated by the expression level of MRP1 but not MDR1

In vitro and in vivo studies have demonstrated that UCB (unconjugated bilirubin) is neurotoxic. Although previous studies suggested that both MRP1 (multidrug resistance-associated protein 1) and MDR1 (multidrug resistance protein 1) may protect cells against accumulation of UCB, direct comparison of their role in UCB transport was never performed. To this end, we used an inducible siRNA (small interfering RNA) expression system to silence the expression of MRP1 and MDR1 in human neuroblastoma SH-SY5Y cells. The effects of in vitro exposure to clinically-relevant levels of unbound UCB were compared between unsilenced (control) cells and cells with similar reductions in the expression of MRP1 or MDR1, documented by RT–PCR (reverse transcription–PCR) (mRNA), immunoblotting (protein), and for MDR1, the enhanced net uptake of a specific fluorescent substrate. Cytotoxicity was assessed by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] test. MRP1-deficient cells accumulated significantly more UCB and suffered greater cytotoxicity than controls. By contrast, MDR1-deficient cells exhibited UCB uptake and cytotoxicity comparable with controls. At intermediate levels of silencing, the increased susceptibility to UCB toxicity closely correlated with the decrease in the expression of MRP1, but not of MDR1. These data support the concept that limitation of cellular UCB accumulation, due to UCB export mediated by MRP1, but not MDR1, plays an important role in preventing bilirubin encephalopathy in the newborn.

Toward understanding the connections between infant jaundice and infant feeding

Parents face a paradox when they are told: Breast is best; bottle-feeding is hazardous to health. But breast-fed babies are more likely to become severely jaundiced than bottle-fed babies, and severe jaundice can lead to brain damage. This article will explore the natural physiology of jaundice with a focus on breast-feeding-associated jaundice, primary prevention of hyperbilirubinemia, and current evidence-based recommendations about feeding jaundice breast-fed infants.

Bilirubin as an endogenous modulator of neurotrophin redox signaling

Bilirubin is neurotoxic upon excess accumulation in the brain, but it also plays important physiological roles related to its antioxidant properties. Here we report that exposure of PC12 and primary rat cerebellar granule neurons to bilirubin (0.5-10 microM) drastically decreases nerve growth factor (NGF)/brain-derived neurotrophic factor signaling to Akt and extracellular signal-regulated kinases (ERKs), indicating a direct interference of the molecule with crucial prosurvival signaling pathways. This effect likely involves the scavenging capacity of bilirubin, the latter being able to inhibit, in PC12 cells, accumulation of intracellular reactive oxygen species and phosphorylation of Akt and ERKs in response to extracellular hydrogen peroxide. Interestingly, in the absence of exogenous growth factor, bilirubin elicited the phosphorylation of ERKs and of the cAMP responsive element binding (CREB) transcription factor, a signature of NGF-dependent survival signaling. These growth factor-like signaling effects were paralleled by the induction of the neuronal nitric oxide synthase (nNOS) and generation of nitric oxide (NO). Pharmacological dissection of the signaling cascade triggered by bilirubin revealed that phosphorylation of ERKs requires NO signaling through soluble guanylyl cyclase, and, further upstream, influx of extracellular calcium is necessary for nNOS induction and NO release, likely through calcium-dependent phosphorylation of CREB. Importantly, the cascade elicited by bilirubin through NO and ERK is cytoprotective, as revealed by exacerbated bilirubin toxicity in cultures treated by either NOS or MEK inhibitors. Taken together, these observations indicate an important action of bilirubin on redox signaling by neurotrophins, with either inhibitory or agonistic effects based on growth factor availability.

Effect of storage and freezing on unbound bilirubin measurement

BACKGROUND

Unbound bilirubin (Bf) is a better predictor of bilirubin toxicity than total serum bilirubin (TSB) in the postnatal period. The Food and Drug Administration approved peroxidase test for Bf analysis is not currently available in clinical laboratories. The samples are often stored at varying temperature and for varying duration before Bf analysis.

METHODS

We evaluated the effect of storing blood samples up to 1 month at -20 degrees C and -80 degrees C on Bf measurement. In a subset of samples collected for neonates enrolled in a prospective Bf study, TSB (micromol/l) and Bf (micromol/l) were measured by the peroxidase test and then the samples were immediately frozen at -20 degrees C (n=10) or -80 degrees C (n=10) for either 2 weeks or at -20 degrees C (n=16) or -80 degrees C (n=10) for 1 month. After the designated freezing period, the samples were thawed and TSB and Bf measured again.

RESULTS

There was no effect of storage for 2 weeks at either -20 degrees C or -80 degrees C on Bf measurement. There appears to be no effect on Bf after storage at -80 degrees C for a month. However, there was significant decrease in Bf after storage at -20 degrees C for a month.

CONCLUSIONS

The results of this study suggest that blood samples for Bf measurement should be analyzed within 2 weeks after collection and storage at -20 degrees C.

Israel guidelines for the management of neonatal hyperbilirubinemia and prevention of kernicterus

Despite publication of guidelines for the prevention and management of hyperbilirubinemia in term and late-preterm newborn infants, kernicterus, although rare, continues to occur. Guidelines written for use in one country may not always be universally appropriate. Bearing this in mind, a committee appointed by the Israel Neonatal Society has formulated a set of guidelines, based on those of the American Academy of Pediatrics (2004), but adapted to the realities of the Israeli scene. The guidelines include methods of surveillance of jaundice, prediction of jaundice, assessment of risk factors, discharge planning and post-discharge follow-up, in addition to therapeutic guidelines including indications for phototherapy, exchange transfusion and the use of intravenous immune globulin. Availability of these guidelines to the international community may offer direction to physicians of other countries who may be setting up guidelines for use in their own communities.

Management of jaundice and prevention of severe neonatal hyperbilirubinemia in infants >or=35 weeks gestation

Kernicterus is still occurring but should be largely preventable if health care personnel follow the recommendations listed in this guideline. These recommendations emphasize the importance of universal, systematic assessment of the risk of severe hyperbilirubinemia, lactation support, close follow-up, and prompt intervention when necessary. A systems-based approach to prevent severe neonatal hyperbilirubinemia should be implemented at all birthing facilities and coordinated with continuing ambulatory care. Translational research is needed to better understand the mechanisms of bilirubin neurotoxicity and potential therapeutic interventions.

Ontogeny of bilirubin-binding capacity and the effect of clinical status in premature infants born at less than 1300 grams

BACKGROUND

Bilirubin is toxic to the brain and enters the brain in unbound form. Serum unconjugated, unbound bilirubin may be a good predictor of bilirubin encephalopathy. Unbound bilirubin levels may depend on the bilirubin-binding capacity of albumin, which has not been described for neonates of <28 weeks' gestation.

OBJECTIVE

The purpose of this work was to determine the ontogeny of bilirubin-binding capacity and the effect of clinical status in very preterm neonates.

METHODS

A total of 152 neonates (23-31 weeks' gestational age; 440-1300 g) were enrolled prospectively. At 5 days of age, total serum bilirubin and unbound bilirubin were measured with the unbound bilirubin-A1 analyzer (Arrows Co, Osaka, Japan) and albumin with the Bromocresol-purple method. Scatchard plots were used to estimate bilirubin-binding affinity and capacity. Clinical status for each infant was rated as high, moderate, or low risk by using a modified Score for Neonatal Acute Physiology model. Low risk was considered clinically stable.

RESULTS

Unbound bilirubin has a significant, direct correlation to total bilirubin and is greater in unstable than in stable neonates. For the entire cohort, bilirubin-binding capacity had a direct relationship to gestational age. The bilirubin-binding capacities of infants in the low- and high-risk groups also had a direct relationship to gestational age. Bilirubin-binding capacity was greater in the low-risk group (20.8 +/- 4.6 mg/dL; 356 +/- 79 micromol/L) than in the moderate- (17.8 +/- 3.5 mg/dL; 304 +/- 60 micromol/L) or high- (17.3 +/- 3.4 mg/dL; 296 +/- 58 micromol/L) risk groups. Bilirubin-binding affinity did not differ by clinical risk status or gestational age.

CONCLUSIONS

In very preterm, very low birth weight infants, bilirubin-binding capacity is directly proportional to gestational age. Bilirubin-binding capacity is lower and unbound bilirubin higher in unstable than in stable neonates. These data may be useful in guiding the management of hyperbilirubinemia in very low birth weight infants.

Cytotoxicity is predicted by unbound and not total bilirubin concentration

Although it has been suggested that the unbound, free, (B(f)) rather than total (B(T)) bilirubin level correlates with cell toxicity, direct experimental evidence supporting this conclusion is limited. In addition, previous studies never included a direct measurement of B(f), using newer, accurate methods. To test "the free bilirubin hypothesis", in vitro cytotoxicity was assessed in four cell lines exposed to different B(f) concentrations obtained by varying B(T)/Albumin ratio, using serum albumins with different binding affinities, and/or displacing unconjugated bilirubin (UCB) from albumin with a sulphonamide. B(f) was assessed by the modified, minimally diluted peroxidase method. Cytotoxicity varied among cell lines but was invariably related to B(f) and not B(T). Light exposure decreased toxicity parallel to a decrease in B(f). In the absence of albumin, no cytotoxicity was found at a B(f) of 150 nM whereas in the presence of albumin a similar B(f) resulted in a 40% reduction of viability indicating the importance of total cellular uptake of UCB in eliciting toxic effect. In the presence of albumin-bound UCB, bilirubin-induced cytotoxicity in a given cell line is accurately predicted by B(f) irrespective of the source and concentration of albumin, or total bilirubin level.

Immunizations, neonatal hyperbilirubinemia and animal-induced injuries

PURPOSE OF REVIEW

To report recent research findings and new recommendations on immunizations, neonatal hyperbilirubinemia, and animal-induced injuries.

RECENT FINDINGS

Vaccines against rotavirus and human papilloma virus have entered clinical use. Varicella outbreaks among previously vaccinated children have prompted the recommendation for a two-dose varicella vaccine series. Broader coverage for influenza vaccination is now recommended in the US and Canada. Diagnosis and treatment of neonatal hyperbilirubinemia uses population and hour-based norms for total serum bilirubin and assessment of risk factors. Delayed cord clamping is not apparently a risk factor for jaundice but warrants more study. Universal predischarge screening shows promise but is not yet officially recommended. New treatments for hyperbilirubinemia are being evaluated. Dogs are the chief cause of animal bites in children and the largest reservoir for rabies worldwide. In North America and Europe, cats and wild animals cause most human rabies. Postexposure prophylaxis should follow region-appropriate guidelines.

SUMMARY

New vaccines are available against rotavirus and human papilloma virus. Changes have been made to official immunization recommendations. Appropriate vaccine use can reduce the pediatric disease burden further. Hyperbilirubinemia is the subject of ongoing study, which may lead to improved diagnosis and treatment protocols and reduce the incidence of acute bilirubin encephalopathy. The best tool for rabies prevention after an animal bite is prompt postexposure prophylaxis.

Clinical considerations for the pharmacologic management of patent ductus arteriosus with cyclooxygenase inhibitors in premature infants

When medical management is warranted for closure of a persistent patent ductus arteriosus (PDA) in premature infants, treatment with a cyclooxygenase (COX) inhibitor is indicated. Indomethacin, available since 1976, has been the conventional pharmacologic treatment for PDA, but its use is associated with vasoconstrictive effects that impair renal, mesenteric and cerebral blood flow. Intravenous (IV) ibuprofen lysine, approved in the United States in 2006, has less severe vasoconstrictive effects on these vital organs than IV indomethacin. Clinical trials have shown both of these COX inhibitors to be equally effective in closing the PDA in approximately 70%-80% of treated infants, with less vasoconstrictive and adverse renal effects occurring with IV ibuprofen lysine.1,2 Several clinical considerations are important in the process of medical decision-making when faced with the need for PDA treatment with one of these pharmacologic agents in the premature infant. This paper focuses on these clinical considerations, including cerebral, renal and mesenteric blood flow, renal function, pulmonary effects, protein-binding capacity as it relates to hyperbilirubinemia, and platelet aggregation. No differences in chronic lung disease, pulmonary hypertension, hyperbilirubinemia and coagulopathy were observed in clinical trials when comparing these 2 COX inhibitors; however, significant differences have been observed in arterial blood flow to the cerebral, renal and mesenteric organs, suggesting that IV ibuprofen lysine may be the more favorable agent.

Increased hemolysis from saline pre-washing RBCs or centrifugal pumps in neonatal ECMO

OBJECTIVES

Hemolysis is a significant complication of extracorporeal membrane oxygenation (ECMO), with a reported incidence of 12.2%. The aims of this study were (1) to investigate hemolysis caused by saline-washed versus unwashed RBCs, (2) to determine in vitro the effects of saline washing on erythrocyte hemolytic markers and (3) to investigate hemolysis by centrifugal versus roller pumps.

STUDY DESIGN

(1) To evaluate the effect of pre-transfusion saline-washing versus non-washing, the peak plasma-free hemoglobin (FHb) and total bilirubin in the first 3 days versus the next 4 days of ECMO were compared (2) Pre- and postsaline-washed RBCs were analyzed for K+ hemoglobin, mean corpuscular volume, FHb and hemolysis at baseline and after 4 h of storage at 4 degrees C. (3) Over 10 000 neonatal ECMO cases were retrospectively reviewed to study the effect of pump type on hemolysis.

RESULTS

(1) The washed blood group had significantly more hemolysis within the first 3 days of ECMO. (2) Immediately after saline washing, the K+ and Hb concentrations were significantly decreased compared with unwashed blood, and these differences were maintained after 4 h. The osmotic fragility of washed RBCs after 4 h of storage at 4 degrees C was significantly higher than at baseline. (3) Hemolysis was reported more often in the centrifugal than in the roller pump group.

CONCLUSIONS

(1) Using unwashed RBCs decreased hemolysis within the first 3 days of ECMO. (2) Saline washing, while decreasing the concentration of K+ in the plasma, significantly increases RBC membrane osmotic fragility. (3) Hemolysis is linked to the use of centrifugal pumps.

Bilirubin-induced cell toxicity involves PTEN activation through an APE1/Ref-1-dependent pathway

Unconjugated bilirubin (UCB) is the major degradation product of the heme catabolism. A growing body of evidences suggests that UCB plays major biological effects by inhibiting cell proliferation in cancer cell lines and eliciting cell toxicity particularly in neurons and glial cells. Early molecular events responsible for bilirubin-induced cytotoxicity remain poorly understood. Using HeLa cells and mouse embryonic fibroblasts, we found that UCB at a concentration of free pigment (Bf) of 80 nM induced oxidative stress, promoting a significant increase in intracellular reactive oxygen species (ROS) and a decreased cell survival (by the MTT test). The ROS increase activated the antioxidant cell response through APE1/Ref-1, a master redox regulator in eukaryotic cells. Activation of APE1/Ref-1 was followed by a concomitant activation of Egr-1 transcription factor and by an upregulation of PTEN tumor suppressor, an Egr-1 target gene, leading to inhibition of cell growth. Blocking ROS generation with N-acetylcysteine pretreatment, restored cell survival, limited the upregulation of PTEN in response to UCB, and prevented the inhibition of cell proliferation. HeLa cells transfected with mutants of the PTEN promoter or silenced with APE1/Ref-1 small interference RNA confirmed that UCB modulates a signaling pathway involving APE1/Ref-1, Egr-1, and PTEN. These findings describe a new molecular pathway involved in the cytotoxic effects of UCB.

Successful plasmapheresis for extreme hyperbilirubinemia caused by acute Epstein-Barr virus

Epstein-Barr virus (EBV) infection can be complicated by cholestatic jaundice and hemolytic anemia, although both complications rarely occur simultaneously. An 18-year-old female developed acute EBV infection complicated by cold agglutinin hemolysis and cholestasis. Corticosteroid and ursodeoxycholic acid were initiated but bilirubin peaked at 1297.47 micromol/L (75.7 mg/dL). Plasmapheresis was initiated and with the corticosteroids, resulted in resolution of extreme hyperbilirubinemia. The patient recovered rapidly, is healthy 2 years later and is neurologically intact. The early use of plasmapheresis with corticosteroids and ursodeoxycholic should be considered in EBV infections complicated by extreme hyperbilirubinemia to prevent the rare complication of adult-onset kernicterus.

Role of multidrug resistance-associated protein 1 expression in the in vitro susceptibility of rat nerve cell to unconjugated bilirubin

Nerve cell injury by unconjugated bilirubin (UCB) has been implicated in brain damage during neonatal hyperbilirubinemia, particularly in the preterm newborn. Recently, it was shown that UCB is a substrate for the multidrug resistance-associated protein 1 (Mrp1), an ATP-dependent efflux pump, which may decrease UCB intracellular levels. To obtain a further insight into the role of Mrp1 in the increased vulnerability of immature cells to UCB, we evaluated the mRNA and the protein levels of Mrp1 throughout differentiation in primary cultures of rat neurons and astrocytes. Furthermore, in order to provide supportive evidence for the role of Mrp1 in the protection of nerve cells from UCB-induced effects, we evaluated cell susceptibility to UCB when Mrp1 was inhibited with MK571 ((E)-3-[[[3-[2-(7-chloro-2-quinolinyl) ethenyl]phenyl]-[[3-dimethylamino)-3-oxopropyl]thio]methyl]thio]-propanoic acid). The results are the first to demonstrate that Mrp1 is expressed in neurons and that both mRNA and protein levels of Mrp1 increase with cell differentiation. Additionally, inhibition of Mrp1 was associated with an increase in UCB toxic effects, namely cell death, cell dysfunction, and secretion of interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, as well as of glutamate. These results point to a novel role of Mrp1 in the susceptibility of premature babies to UCB encephalopathy, and provide a startup point for the development of a new therapeutic strategy.

Effects of sample dilution, peroxidase concentration, and chloride ion on the measurement of unbound bilirubin in premature newborns

OBJECTIVES

To assess the effects of sample dilution, peroxidase concentration, and chloride ion (Cl(-)) on plasma unbound bilirubin (B(f)) measurements made using a commercial peroxidase methodology (UB Analyzer) in a study population of ill, premature newborns.

DESIGN AND METHODS

B(f) was measured with a UB Analyzer in 74 samples at the standard 42-fold sample dilution and compared with B(f) measured at a 2-fold sample dilution using a FloPro Analyzer. B(f) was measured at two peroxidase concentrations to determine whether the peroxidase steady state B(f) (B(fss)) measurements were significantly less than the equilibrium B(f) (B(feq)), in which case it was necessary to calculate B(feq) from the two B(fss) measurements. B(f) was also measured before and after adding 100 mmol/L Cl(-) to the UB Analyzer assay buffer.

RESULTS

B(feq) at the 42-fold dilution was nearly 10-fold less than but it correlated significantly with B(feq) at the 2-fold dilution (mean 8.2+/-5.2 nmol/L versus 73.5+/-70 nmol/L, respectively, p<0.0001; correlation r=0.6). The two UB Analyzer B(fss) measurements were significantly less than B(feq) in 42 of 74 (57%) samples, and Cl(-) increased B(feq) in 66 of 74 (89%) samples by a mean of 82+/-67%.

CONCLUSIONS

B(fss) measured by the UB Analyzer at the standard 42-fold sample dilution using assay buffer without Cl(-) and a single peroxidase concentration is significantly less than the B(feq) in undiluted plasma. Accurate B(f) measurements can be made only in minimally diluted serum or plasma.

Neurodevelopmental outcome of the late preterm infant

There is very limited information about the developmental outcome of the late preterm infant. The developing brain is vulnerable to injury during this very active and important stage of fetal brain development; therefore, it is important to carefully monitor the neurologic outcome of these infants. This article discusses gestational brain development and complications of late preterm birth that contribute to the overall risk of brain injury.

Factors affecting the binding of bilirubin to serum albumins: validation and application of the peroxidase method

The unbound "free" bilirubin concentration (Bf), not the total bilirubin concentration, is the critical determinant of cellular uptake and toxicity of bilirubin. We compared Bf measured by a modified peroxidase method with published data obtained with ultrafiltration and examined conditions that affect the affinity (KF) of human (HSA) and bovine (BSA) serum albumin for bilirubin. The peroxidase and ultrafiltration methods yielded similar KF values that decreased with increasing HSA concentration and the presence of 50 mM chloride. When related to ionic strength, inhibition of BSA-bilirubin binding by chloride, bromide, and sulfate were similar, whereas phosphate buffer had a smaller effect. KF was lower at 37 degrees C than at 25 degrees C for HSA but not for BSA. KF for BSA was similar at pH 7.4 and 8.0. BSA and FCS had similar binding properties. The close agreement of Bf and KF values determined by the peroxidase method with published results obtained by ultrafiltration validates both methods and supports the use of the peroxidase method as a practical technique for measuring Bf under steady state conditions in minimally diluted serum or culture medium.

Ex uno plures: the concealed complexity of bilirubin species in neonatal blood samples

Blood from jaundiced neonates often contains several isomers of bilirubin in addition to the biosynthetic isomer that causes kernicterus. These isomers are generated during phototherapy or during normal exposure of infants to ambient light. Their presence is generally overlooked or ignored in clinical measurements of circulating bilirubin concentrations and the interpretation of these values. Whether this is justified or clinically important is presently uncertain. However, the presence of isomers may complicate the accurate measurement of free bilirubin concentrations in blood and the use of such values for identifying jaundiced infants at most risk of kernicterus.

Biliverdin-induced brainstem auditory evoked potential abnormalities in the jaundiced Gunn rat

Brainstem auditory evoked potential (BAEP) abnormalities occur in jaundiced Gunn rats given sulfadimethoxine to displace bilirubin bound to serum albumin, releasing it into the tissues. One problem with the model is that after displacement, plasma bilirubin levels drop and do not correlate with neurological dysfunction. In this report, we administered biliverdin, the immediate precursor of bilirubin, in 15- to 17-day-old Gunn rat pups to create an improved model of bilirubin-induced neurological dysfunction. Total plasma bilirubin (TB) levels were measured with a Leica bilirubinometer. Biliverdin (40 mg/kg) or phosphate-buffered saline (PBS) was administered either once and BAEPs recorded 8 h later or twice, 12 h apart, and BAEPs recorded 24 h after the initial injection. A single biliverdin injection produced a significantly decreased amplitude of BAEP wave III, 1.21+/-0.25 vs. 0.49+/-0.27 microV (control vs. biliverdin). The two-injection paradigm resulted in a significantly elevated TB (9.9+/-1.2 vs. 14.9+/-3.1 mg/dl; control vs. biliverdin), significant increases in I-II (1.15+/-0.08 vs. 1.42+/-0.09 ms) and I-III (2.17+/-0.08 vs. 2.5+/-0.13 ms) interwave intervals and a decrease in the amplitude of wave III (1.36+/-0.30 vs. 0.38+/-0.26 microV). Additionally, there were significant correlations between TB and the amplitude of wave III (r2=0.74) and TB and the I-III interwave interval (r2=0.51). In summary, biliverdin administration in jaundiced Gunn rat pups produces BAEP abnormalities consistent with those observed in the sulfadimethoxine model and human newborn hyperbilirubinemia and resulted in increased plasma bilirubin levels that correlate with the degree of neurological dysfunction.

Immunizations, neonatal jaundice and animal-induced injuries

PURPOSE OF REVIEW

To review the literature published within the last year on three topics essential to clinical pediatrics: immunizations, neonatal jaundice, and animal-induced injuries.

RECENT FINDINGS

New vaccines that protect against meningococcus, pertussis and rotavirus are safe, effective and recommended for routine immunization. Young children remain a high priority for influenza vaccination while the world awaits further developments of avian influenza. Pneumococcal and varicella vaccinations have benefited many. Debate exists on how to screen for hyperbilirubinemia in neonates and new strategies are emerging to prevent it. There seems to be no link between hyperbilirubinemia and autism spectrum disorders. We have learned that rabies can be transmitted by transplantation; it remains a global public health problem and its incidence is frequently underestimated in developing nations. Lastly, brown recluse spider bites are often misdiagnosed.

SUMMARY

The face of pediatric infectious disease is changing as we incorporate new vaccines into our routine practice. Rotavirus vaccine has significant implications for the health of children across the globe. The management strategy for neonatal jaundice continues to focus on screening and prevention. We need to devote more energy to combating rabies in countries where it is endemic.

Hyperbilirubinemia and kernicterus

This article describes new findings concerning the basic science of bilirubin neurotoxicity, new considerations of the definition of clinical kernicterus, and new and useful tools to diagnose kernicterus in older children, and discusses treatments for kernicterus beyond the newborn period and why proper diagnosis is important.

Kernicterus in late preterm infants cared for as term healthy infants

OBJECTIVE

To compare the clinical profile and health care experiences related to management of newborn jaundice and hyperbilirubinemia in preterm infants (<37(0/7) weeks gestation) who are cared for as term infants (> or =37(0/7) weeks) and develop acute and/or chronic posticteric sequelae.

METHODS

Retrospective study of a convenient sample of term and near term infants voluntarily reported to the Pilot Kernicterus Registry (1992-2003). Study infants were required to meet the clinical definitions for acute bilirubin encephalopathy (moderate or advanced severity) and/or the classical signs of kernicterus. Main outcome measures were the comparison of etiology, severity and duration of extreme hyperbilirubinemia (TSB levels >20 mg/dL), response to interventions of intensive phototherapy and exchange transfusion, and health care delivery experiences in preterm as compared with term infants.

RESULTS

No targeted attention was accorded to preterm infants during their neonatal health care experiences as related to predischarge risk assessment, feeding, discharge follow-up instructions, or breastfeeding, regardless of the known vulnerability of preterm infants to safely transition during the first week after birth. The TSB levels, age at re-hospitalization, and birth weight distribution were similar for late preterm and term infants. Large for gestational age and late preterm infants disproportionately developed kernicterus as compared with those who were appropriate for gestational age and term. Clinical management of extreme of hyperbilirubinemia, by the attending clinical providers, was not impacted or influenced by the gestational age, clinical signs, or risk assessment. This resulted in severe posticteric sequelae which was more severe and frequent in late preterm infants.

CONCLUSIONS

Late prematurity (34(0/7) to 36(6/7) weeks) of healthy infants was not recognized as a risk factor for hazardous hyperbilirubinemia by clinical practitioners. Unsuccessful lactation experience was the most frequent experience; being large for gestational age as well as the other known biologic risk factors for hyperbilirubinemia and bilirubin neurotoxicity were not identified by the clinical care providers either before discharge or at immediate postdischarge follow up.

Measurement of unbound bilirubin by the peroxidase test using Zone Fluidics

BACKGROUND

Measuring plasma unbound bilirubin concentration by the peroxidase test is useful in the management of jaundiced newborns. However, the commercially available peroxidase technology is manual, and the unbound bilirubin may be seriously underestimated at the 42-fold sample dilution and single peroxidase concentration used. We investigated improving the test by adapting it to Zone Fluidics, which is a system for automating reactant handling that requires small sample volumes and dilution.

METHODS

A computer-directed Zone Fluidics system was constructed using small diameter tubing to connect in series a water-surfactant reservoir, a bi-directional pump, a multiport selection valve to which peroxidase test reactants (45 mul of sample) are attached with one port open to air, and a spectrophotometer flow cell. Test reactants and air are sequentially aspirated through the valve into the tubing connecting the pump and valve to form a reactant "zone" surrounded by air. The zone is advanced to the spectrophotometer flow cell where total and unbound bilirubin are determined (37 degrees C) from the absorbance at 460 nm at a 2-fold sample dilution and 4 peroxidase concentrations. Imprecision was assessed in artificial controls and newborn plasma. Plasma results were compared with those obtained using the commercial method.

RESULTS

The CV for unbound bilirubin in the various controls ranged from 11% to 38% (within day) and 12% to 27% (between days). Triplicate CV measurements for newborn plasma measurements ranged from 0.6% to 31% (mean 11%, n=47). Mean unbound bilirubin by Zone Fluidics was 5-fold higher than that by the commercial method.

CONCLUSION

Zone Fluidics can be used to automate the peroxidase test and overcome many of the limitations of the commercially available peroxidase technology.