Unbound bilirubin levels in phototherapy-treated preterm infants receiving soy-based lipid emulsion

Factors Affecting the Relationship Between Total and Unbound Bilirubin in Preterm and Term Infants

AIM

Newborn infants universally experience jaundice, most of which is physiologic, but in some high-risk situations, it may lead to neurological dysfunction or death. Unbound bilirubin (Bf) may be the best predictor of bilirubin toxicity in this population. The goal of the study is to examine the relationship between total serum bilirubin (TSB) and Bf and the influencing factors.

METHODS

To calculate the relationship of Bf to TSB, we created a ratio (R) Bf/TSB × 106 to allow the comparison of products with varied concentrations. We then applied it to simultaneously obtain TSB and Bf measurements in infants to examine the influence of prematurity, haemolysis, feeding (breast or bottle feedings) and phototherapy. We also examined R at potential toxic Bf levels in the preterm group.

RESULTS

The population consisted of 170 term and 130 preterm infants. The R was 3.64 ± 1.08 (SD) in term and 15.18 ± 9.8 in preterm infants. Prematurity and high TSB that required phototherapy significantly increased R. Higher R-values were seen at higher Bf toxic threshold levels.

CONCLUSION

An R-value can reflect the relationship between Bf and TSB. The values are greater in prematurity and in infants with high TSB, which requires phototherapy.

Unbound bilirubin and risk of severe neurodevelopmental impairment in extremely low birthweight newborns

BACKGROUND

Unbound bilirubin (UB) was measured on day 5 ± 1 in 1101 ELBW newborns in the Aggressive vs Conservative Phototherapy randomized controlled trial. We accessed this dataset to quantify the UB-mediated risk of severe neurodevelopmental impairment (sNDI) in extremely low birthweight (ELBW) newborns.

METHODS

UB levels were standardized within laboratories as z-score percentiles. A dichotomous UB exposure variable was based on sharply increased risk of sNDI at the 85th percentile (UBz>85th). Targeted maximum likelihood estimation with ensemble machine learning (TMLE + ML) and logistic regression (LR) were used to estimate sNDI risk attributable to UBz>85th.

RESULTS

UB - total bilirubin correlation was poor: R2 0.24, 95% CI: 0.19, 0.30. The UB level corresponding to the UBz>85th cut-point in this cohort was estimated to be between 0.56 and 0.79 µg/dL. In 825 survivors with known sNDI status the crude risk difference (RD) associated with UBz>85th was 19.5%. With TMLE + ML, the RD was 14.4% (95% CI: 5.7%, 23.1%) corresponding to a number need to harm (NNH) of 7 (95% CI: 4, 18). LR results were similar: RD 12.4% (95% CI: 4.7%, 20.1%), NNH 8 (95% CI: 5, 21).

CONCLUSIONS

Exposure to UBz>85th was associated with a large increase in risk of sNDI in ELBW newborns.

IMPACT

Accessing the only large dataset with measures of unbound bilirubin (UB) and neurodevelopmental outcomes in extremely low birthweight (ELBW) newborns we found poor correlation between UB and total bilirubin (TB). The risk of severe neurodevelopmental impairment (sNDI) associated with UB rose non-linearly with an inflection point at UB z-score 85th percentile (UBz>85th), increasing the risk of sNDI by an estimated 14% (number need to harm: 7). The current incidence of exposure to harmful UB levels in very premature newborns is unlikely to be rare. TB levels provide a false sense of security to clinicians caring for very premature newborns.

Impact of Protein Binding Capacity and Daily Dosage of a Drug on Total Serum Bilirubin Levels in Susceptible Infants

Hyperbilirubinemia is a common pathological condition in neonates. Free bilirubin can penetrate the blood-brain barrier (BBB), which can lead to bilirubin neurotoxicity. In the context of predicting the risk of bilirubin neurotoxicity, although the specificity and sensitivity of free bilirubin levels are higher than those of total serum bilirubin (TSB), free bilirubin is not widely monitored in clinical practice. The threshold TSB levels at which phototherapy must be administered have been established previously. However, TSB levels are not well correlated with neurodevelopmental outcomes. Currently, TSB levels are commonly used to guide phototherapy for neonatal hyperbilirubinemia. Some clinical drugs can displace bilirubin from its albumin-binding sites, and consequently upregulate plasma bilirubin. Daily dosages play a vital role in regulating bilirubin levels. A drug with both a high protein binding capacity and high daily dosage significantly increases bilirubin levels in infants. Premature or very low birth weight (VLBW) infants are vulnerable to the upregulation of bilirubin levels as they exhibit the lowest reserve albumin levels and consequently the highest bilirubin toxicity index. Because bilirubin is involved in maintaining the balance between pro-oxidant and antioxidant agents, the downregulation of bilirubin levels is not always desirable. This review provides insights into the impact of protein binding capacity and daily dosage of drugs on the bilirubin levels in susceptible infants.

Effects of lipid emulsions on unbound bilirubin and response to phototherapy in preterm infants

OBJECTIVE

Bilirubin-induced neurotoxicity is mediated by the fraction of total serum bilirubin (TSB) not bound to albumin (Bf). Unbound free fatty acids (FFAu) generated from lipid emulsions compete with bilirubin for albumin binding, increasing Bf. Soy-based (IL) and soy-MCT-olive-fish oil-based (SMOF) lipid emulsions contain different fatty acids with distinct albumin binding affinities. IL increases Bf in preterm infants, but the effects of SMOF on Bf are not known. Our objective was to compare changes in TSB, Bf, FFAu, and response to phototherapy in preterm infants receiving SMOF and IL. We hypothesized that SMOF would be associated with lower Bf and better response to phototherapy than IL.

METHODS

Very preterm and low birth weight infants (<1500 g, <32 weeks) were infused with IL (n = 20) or SMOF (n = 20) as prescribed by providers. Phototherapy was prescribed using the standard care practice. FFAu profiles and levels, TSB, and Bf were measured on 0, 1, 2, and 3 g/kg/day of lipid infusion and at the initiation and termination of phototherapy. TSB was analyzed in the clinical laboratory using the diazo technique. FFAu and Bf were measured using fluorescent probes.

RESULTS

Escalating doses of IL and SMOF increased FFAu levels and Bf, but not TSB. Phototherapy did not significantly decrease Bf for infants receiving either lipid. IL-treated infants had higher levels of unbound linoleic acid, and SMOF-treated infants had higher unbound arachidonic, oleic, and docosahexaenoic acids.

CONCLUSIONS

IL and SMOF both increase Bf similarly, and phototherapy does not significantly affect Bf for infants receiving them.

Neonatal hyperbilirubinemia and the role of unbound bilirubin

BACKGROUND

Neonatal jaundice occurs in more than 80% of newborn infants. Although mild jaundice is physiologic and possibly neuroprotective, severe hyperbilirubinemia can lead to neurologic dysfunction and death. Hyperbilirubinemia is due to an imbalance between bilirubin production and the developing excretory capacity in the first days of life. Management utilizes total serum bilirubin (TSB) levels, although recent advances suggest a role for unbound bilirubin.

GOALS

The goal of this review is to examine bilirubin biology, toxicology, and clinical effects, discuss preventive and therapeutic measures, describe neurodevelopmental consequences, and propose that, with the advent of new technology, unbound bilirubin is the optimal measurement for the management.

METHODS

Comprehensive review on neonatal hyperbilirubinemia.

RESULTS

Neonatal hyperbilirubinemia can be prevented by tin mesoporphyrin to limit heme oxygenase activity, a key enzyme in bilirubin production, or restricting bilirubin's absorption from the gastrointestinal tract. Treatment modalities include removing bilirubin from the body by exchange transfusion, binding to immunoglobulin, or converting it to a water-soluble isomer with phototherapy. While these approaches have evolved during the past decades, the diagnosis, intervention indications, and prognosis have consistently relied on TSB concentration despite its poor ability to predict an outcome.

CONCLUSIONS

Total serum bilirubin is inadequate to optimize care of the term and preterm infant with hyperbilirubinemia. A rapid, accurate, and more effective indicator of bilirubin neurotoxicity is needed to manage jaundiced infants and for the universal screening of newborn infants. Future measurements of free bilirubin unattached to albumin will improve the management of neonatal hyperbilirubinemia.

Bilirubin/albumin (B/A) ratios correlate with unbound bilirubin levels in preterm infants

BACKGROUND

A strong correlation between the bilirubin/albumin (B/A) ratio and unbound bilirubin (UB) levels in newborns ≥35 weeks of gestation has been reported. However, in preterm infants, the usefulness of B/A ratios remains unclear.

METHODS

We obtained serum from 381 newborns <35 weeks of gestation. UB levels were measured using the glucose oxidase-peroxidase method. Total serum bilirubin (TB) and albumin (Alb) concentrations were measured spectrophotometrically. Samples were then stratified into two groups based on the infant's phototherapy use. B/A ratios were calculated and correlated with UB levels. Samples taken from infants prior to or never receiving phototherapy (No PTx) were then stratified by gestational age (GA) epochs: 22-27, 28-29, 30-31, and 32-34 weeks and B/A ratios correlated with UB levels.

RESULTS

B/A ratios significantly correlated with UB levels in samples from the No PTx cohort (n = 1250; y = 1.83x - 0.15, r2 = 0.93) when compared with samples from infants post-phototherapy (Post-PTx, n = 2039; y = 1.05x + 0.09, r2 = 0.69). Even when stratified by GA, the correlation remained.

CONCLUSIONS

In preterm infants <35 weeks of gestation, B/A ratios correlated with UB levels better in infants prior to or never receiving phototherapy than in those infants receiving phototherapy.

IMPACT

The bilirubin/albumin (B/A) ratio significantly correlates with unbound bilirubin (UB) levels in preterm infants <35 weeks of gestation. The B/A ratio can be used as an index of UB levels in preterm infants <35 weeks of gestation. The B/A ratio is useful, especially when UB measurements are not available, for managing hyperbilirubinemia in preterm infants.

Curcumin Prevents Cerebellar Hypoplasia and Restores the Behavior in Hyperbilirubinemic Gunn Rat by a Pleiotropic Effect on the Molecular Effectors of Brain Damage

Bilirubin toxicity to the central nervous system (CNS) is responsible for severe and permanent neurologic damage, resulting in hearing loss, cognitive, and movement impairment. Timely and effective management of severe neonatal hyperbilirubinemia by phototherapy or exchange transfusion is crucial for avoiding permanent neurological consequences, but these therapies are not always possible, particularly in low-income countries. To explore alternative options, we investigated a pharmaceutical approach focused on protecting the CNS from pigment toxicity, independently from serum bilirubin level. To this goal, we tested the ability of curcumin, a nutraceutical already used with relevant results in animal models as well as in clinics in other diseases, in the Gunn rat, the spontaneous model of neonatal hyperbilirubinemia. Curcumin treatment fully abolished the landmark cerebellar hypoplasia of Gunn rat, restoring the histological features, and reverting the behavioral abnormalities present in the hyperbilirubinemic rat. The protection was mediated by a multi-target action on the main bilirubin-induced pathological mechanism ongoing CNS damage (inflammation, redox imbalance, and glutamate neurotoxicity). If confirmed by independent studies, the result suggests the potential of curcumin as an alternative/complementary approach to bilirubin-induced brain damage in the clinical scenario.