Bilirubin unbound: déjà vu all over again?

Effect of Synbiotic on the Treatment of Jaundice in Full Term Neonates: A Randomized Clinical Trial

PURPOSE

Jaundice accounts for most hospital admissions in the neonatal period. Nowadays, in addition to phototherapy, other auxiliary methods are used to reduce jaundice and the length of hospitalization. This study aimed to investigate the effect of probiotics on the treatment of hyper-bilirubinemia in full-term neonates.

METHODS

In this randomized clinical trial, 83 full-term neonates, who were admitted to the hospital to receive phototherapy in the first 6 months of 2015, were randomly divided into two groups: synbiotic (SG, n=40) and control (CG, n=43). Both groups received phototherapy but the SG also received 5 drops/day of synbiotics. Serum bilirubin, urine, stool, feeding frequency, and weight were measured daily until hospital discharge. A p-value<0.05 was considered statistically significant.

RESULTS

The mean total serum bilirubin in the SG was lower than that in the CG (9.38±2.37 and 11.17±2.60 mg/dL, respectively). The urine and stool frequency in the SG was significantly higher than that in the CG (p<0.05). The duration of hospitalization in the SG was shorter than that in the CG.

CONCLUSION

Use of synbiotics as an adjuvant therapy had a significant treatment effect on jaundice in full-term neonates. Further studies including larger samples with long follow-up periods are essential to confirm the benefits of routine use of synbiotics in neonatal patients with jaundice.

Bilirubin binding in jaundiced newborns: from bench to bedside?

BACKGROUND

Bilirubin-induced neurologic dysfunction (BIND) is a spectrum of preventable neurological sequelae in jaundiced newborns. Current total plasma bilirubin (B_T) concentration thresholds for phototherapy and/or exchange transfusion poorly predict BIND.

METHODS

The unbound (free) bilirubin (B_f) measured at these B_T thresholds provides additional information about the risk for BIND. B_f can be readily adapted to clinical use by determining B_f population parameters at current B_T thresholds. These parameters can be established using a plasma bilirubin binding panel (BBP) consisting of B_T, B_f, and two empiric constants, the maximum B_T (B_Tmax) and the corresponding equilibrium association bilirubin constant (K).

RESULTS

B_Tmax and K provide the variables needed to accurately estimate B_f at B_T < B_Tmax to obtain B_f at threshold B_T in patient samples. Once B_f population parameters are known, the BBP in a newborn can be used to identify poor bilirubin binding (higher B_f at the threshold B_T compared with the population) and increased risk of BIND.

CONCLUSION

The BBP can also be used in jaundice screening to better identify the actual B_T at which intervention would be prudent. The BBP is used with current B_T thresholds to better identify the risk of BIND and whether and when to intervene.

Jack Aviv and brains of children

Both lead intoxication in early childhood and deficient bilirubin-binding capacity (BBC) of blood in jaundiced neonates indicate risk for brain damage. Zinc protoporphyrin (ZPP) is a biomarker for lead intoxication (PbI) as well as well as for iron deficiency. Under the leadership of Jack Aviv, Aviv Biomedical, Inc. developed robust hematofluorometers for point-of-care assays of ZPP in blood and for the high-affinity BBC of blood. These assays use just drops of whole blood and are simple, fast and inexpensive. ZPP by hematofluorometry has been used world-wide as a primary screen for lead intoxication since 1979. Recent clinical studies enabled by an Aviv Biomedical, Inc. bilirubin hematofluorometer have renewed interest in BBC-based assessment of neurotoxicity for improved management of neonatal jaundice. This article sketches Jack Aviv's contribution to the development and application of hematofluorometry.

The Bilirubin Binding Panel: A Henderson-Hasselbalch Approach to Neonatal Hyperbilirubinemia

Poor plasma bilirubin binding increases the risk of bilirubin neurotoxicity in newborns with hyperbilirubinemia. New laboratory tests may soon make it possible to obtain a complete bilirubin binding panel when evaluating these babies. The 3 measured components of the panel are the plasma total bilirubin concentration (B_Total), which is currently used to guide clinical care; the bilirubin binding capacity (BBC); and the concentration of non-albumin bound or free bilirubin (B_Free). The fourth component is the bilirubin-albumin equilibrium dissociation constant, K_D, which is calculated from B_Total, BBC, and B_Free The bilirubin binding panel is comparable to the panel of components used in the Henderson-Hasselbalch approach to acid-base assessment. Bilirubin binding population parameters (not prospective studies to determine whether the new bilirubin binding panel components are better predictors of bilirubin neurotoxicity than B_Total) are needed to expedite the clinical use of bilirubin binding. At any B_Total, the B_Free and the relative risk of bilirubin neurotoxicity increase as the K_D/BBC ratio increases (ie, bilirubin binding worsens). Comparing the K_D/BBC ratio of newborns with B_Total of concern with that typical for the population helps determine whether the risk of bilirubin neurotoxicity varies significantly from the inherent risk at that B_Total Furthermore, the bilirubin binding panel individualizes care because it helps to determine how aggressive intervention should be at any B_Total, irrespective of whether it is above or below established B_Total guidelines. The bilirubin binding panel may reduce anxiety, costs, unnecessary treatment, and the likelihood of undetected bilirubin neurotoxicity.

A Hypothesis for Using Pathway Genetic Load Analysis for Understanding Complex Outcomes in Bilirubin Encephalopathy

Genetic-based susceptibility to bilirubin neurotoxicity and chronic bilirubin encephalopathy (kernicterus) is still poorly understood. Neonatal jaundice affects 60–80% of newborns, and considerable effort goes into preventing this relatively benign condition from escalating into the development of kernicterus making the incidence of this potentially devastating condition very rare in more developed countries. The current understanding of the genetic background of kernicterus is largely comprised of mutations related to alterations of bilirubin production, elimination, or both. Less is known about mutations that may predispose or protect against CNS bilirubin neurotoxicity. The lack of a monogenetic source for this risk of bilirubin neurotoxicity suggests that disease progression is dependent upon an overall decrease in the functionality of one or more essential genetically controlled metabolic pathways. In other words, a “load” is placed on key pathways in the form of multiple genetic variants that combine to create a vulnerable phenotype. The idea of epistatic interactions creating a pathway genetic load (PGL) that affects the response to a specific insult has been previously reported as a PGL score. We hypothesize that the PGL score can be used to investigate whether increased susceptibility to bilirubin-induced CNS damage in neonates is due to a mutational load being placed on key genetic pathways important to the central nervous system's response to bilirubin neurotoxicity. We propose a modification of the PGL score method that replaces the use of a canonical pathway with custom gene lists organized into three tiers with descending levels of evidence combined with the utilization of single nucleotide polymorphism (SNP) causality prediction methods. The PGL score has the potential to explain the genetic background of complex bilirubin induced neurological disorders (BIND) such as kernicterus and could be the key to understanding ranges of outcome severity in complex diseases. We anticipate that this method could be useful for improving the care of jaundiced newborns through its use as an at-risk screen. Importantly, this method would also be useful in uncovering basic knowledge about this and other polygenetic diseases whose genetic source is difficult to discern through traditional means such as a genome-wide association study.

Neonatal bilirubin binding capacity discerns risk of neurological dysfunction

BACKGROUND

Bilirubin binding capacity (BBC) defines the dynamic relationship between an infant's level of unbound or "free" bilirubin and his/her ability to "tolerate" increasing bilirubin loads. BBC is not synonymous with albumin (Alb) levels because Alb binding of bilirubin is confounded by a variety of molecular, biologic, and metabolic factors.

METHODS

We utilized a novel modification of a previously developed hematofluorometric method to directly assay BBC in whole blood from preterm and term neonates and then combined these data with an archived database. Total bilirubin (TB) was also measured, and multiple regression modeling was used to determine whether BBC in combination with TB measurements can assess an infant's risk for developing bilirubin-induced neurotoxicity.

RESULTS

TB and BBC levels ranged from 0.7-22.8 to 6.3-47.5 mg/dl, respectively. Gestational age (GA) correlated with BBC (r = 0.54; P < 0.0002) with a slope of 0.93 mg/dl/wk by logistic regression. Our calculations demonstrate that recently recommended GA-modulated TB thresholds for phototherapy and exchange transfusion correspond to 45 and 67% saturation of our observed regression line, respectively.

CONCLUSION

We speculate that the spread of BBC levels around the regression line (± 5.8 mg/dl) suggests that individualized BBC assays would provide a robust approach to gauge risk of bilirubin neurotoxicity compared with TB and GA.

The enigma of low bilirubin kernicterus in premature infants: why does it still occur, and is it preventable?

Low bilirubin kernicterus in preterm neonates, though rare, remains an unpredictable and refractory form of brain injury. Hypoalbuminemia, co-morbid CNS insult(s), infection, and inflammation are contributing causes that, in many cases, appear to interact in potentiating bilirubin neurotoxicity. Despite compulsive attention to serum bilirubin levels, and clinical and laboratory indices of neurotoxicity risk, low bilirubin kernicterus continues to be seen in contemporary NICUs. While efforts to refine and improve current treatment guidelines are certainly needed, such revision(s) will also have to take into account the risks and benefits of any intervention, including phototherapy.

Bilirubin-albumin binding, bilirubin/albumin ratios, and free bilirubin levels: where do we stand?

Treatment for unconjugated hyperbilirubinemia is predominantly based on one parameter, i.e., total serum bilirubin (TSB) levels. Yet, overt kernicterus has been reported in preterm infants at relatively low TSB levels, and it has been repeatedly shown that free unconjugated bilirubin (freeUCB) levels, or bilirubin/albumin (B/A) ratios for that matter, are more closely associated with bilirubin neurotoxicity. In this article, we review bilirubin-albumin binding, UCBfree levels, and B/A ratios in addition to TSB levels to individualize and optimize treatment especially in preterm infants. Methods to measure bilirubin-albumin binding or UCBfree are neither routinely performed in Western clinical laboratories nor incorporated in current management guidelines on unconjugated hyperbilirubinemia. For bilirubin-albumin binding, this seems justified because several of these methods have been challenged, and sufficiently powered prospective trials on the clinical benefits are lacking. Technological advances in the measurement of UCBfree may provide a convenient means for integrating UCBfree measurements into routine clinical management of jaundiced infants. A point-of-care method, as well as determination of UCBfree levels in various newborn populations, is desirable to learn more about variations in time and how various clinical pathophysiological conditions affect UCBfree levels. This will improve the estimation of approximate UCBfree levels associated with neurotoxicity. To delineate the role of UCBfree in the management of jaundiced (preterm) infants, trials are needed using UCBfree as treatment parameter. The additional use of the B/A ratio in jaundiced preterms has been evaluated in the Bilirubin Albumin Ratio Trial (BARTrial; Clinical Trials: ISRCTN74465643) but failed to demonstrate better neurodevelopmental outcome in preterm infants <32 weeks assigned to the study group. Awaiting a study in which infants are assigned to be managed solely on the basis of their B/A ratio (with TSB excluded ) versus TSB levels alone-and determining which group does better-the additional use of the B/A ratio in the management of hyperbilirubinemia in preterms is not advised. In conjunction with TSB levels, other parameters possibly allow for more accurate prediction of bilirubin toxicity. Yet, different methodologies for estimating these parameters exist, and sufficiently powered, prospective clinical trials supporting their clinical benefit, i.e., reduced bilirubin neurotoxicity when using these parameters, are lacking. Their use in addition to TSB needs to be prospectively evaluated, especially in preterm neonates, and preferentially in randomized clinical trials, which include specific risk factors and assessment of clinical relevant outcome measures for detecting those infants at risk of bilirubin toxicity.

The bilirubin albumin ratio in the management of hyperbilirubinemia in preterm infants to improve neurodevelopmental outcome: a randomized controlled trial--BARTrial

Background and Objective

High bilirubin/albumin (B/A) ratios increase the risk of bilirubin neurotoxicity. The B/A ratio may be a valuable measure, in addition to the total serum bilirubin (TSB), in the management of hyperbilirubinemia. We aimed to assess whether the additional use of B/A ratios in the management of hyperbilirubinemia in preterm infants improved neurodevelopmental outcome.

Methods

In a prospective, randomized controlled trial, 615 preterm infants of 32 weeks' gestation or less were randomly assigned to treatment based on either B/A ratio and TSB thresholds (consensus-based), whichever threshold was crossed first, or on the TSB thresholds only. The primary outcome was neurodevelopment at 18 to 24 months' corrected age as assessed with the Bayley Scales of Infant Development III by investigators unaware of treatment allocation. Secondary outcomes included complications of preterm birth and death.

Results

Composite motor (100±13 vs. 101±12) and cognitive (101±12 vs. 101±11) scores did not differ between the B/A ratio and TSB groups. Demographic characteristics, maximal TSB levels, B/A ratios, and other secondary outcomes were similar. The rates of death and/or severe neurodevelopmental impairment for the B/A ratio versus TSB groups were 15.4% versus 15.5% (P = 1.0) and 2.8% versus 1.4% (P = 0.62) for birth weights ≤1000 g and 1.8% versus 5.8% (P = 0.03) and 4.1% versus 2.0% (P = 0.26) for birth weights of >1000 g.

Conclusions

The additional use of B/A ratio in the management of hyperbilirubinemia in preterm infants did not improve their neurodevelopmental outcome.

Trial Registration

Controlled-Trials.com ISRCTN74465643

Jaundice and kernicterus in the moderately preterm infant

Moderate preterm infants remain at increased risk for adverse outcomes, including acute bilirubin encephalopathy (ABE). Evidence-based guidelines for management of hyperbilirubinemia in preterm infants less than 35 weeks' gestational age are not yet optimized. High concentrations of unconjugated bilirubin can cause permanent posticteric neurologic sequelae (kernicterus). Clinical manifestations of ABE in preterm infants are similar to, but often more subtle than, those of term infants. This review outlines clinical strategies to operationalize management of hyperbilirubinemia in moderately preterm infants to meet recently published consensus-based recommendations.

An approach to the management of hyperbilirubinemia in the preterm infant less than 35 weeks of gestation

We provide an approach to the use of phototherapy and exchange transfusion in the management of hyperbilirubinemia in preterm infants of <35 weeks of gestation. Because there are limited data for evidence-based recommendations, these recommendations are, of necessity, consensus-based. The recommended treatment levels are based on operational thresholds for bilirubin levels and represent those levels beyond which it is assumed that treatment will likely do more good than harm. Long-term follow-up of a large population will be needed to evaluate whether or not these recommendations should be modified.

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.

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.

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.

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.

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.