Controversies in bilirubin biochemistry and their clinical relevance

Exploring the feasibility and clinical impact of ultrasound microvascular flow imaging in detecting brain injury in hyperbilirubinemia neonates

Neonatal hyperbilirubinemia is a prevalent condition during the neonatal period, and in severe instances, it can result in brain damage accompanied by irreversible neurological consequences. Therefore, early detection and intervention are paramount. This research aimed to detect early-stage brain damage resulting from neonatal hyperbilirubinemia through the application of two-dimensional cranial ultrasound and microvascular blood flow (MV-Flow) imaging techniques. Clinical data, along with gray-scale and microvascular ultrasound images of the basal ganglia, were collected from 85 neonates (hyperbilirubinemia group vs. non-hyperbilirubinemia group: 51 vs. 34). The Globus Pallidus to Putamen (G/P) ratio and the vascular index (VIMV) were calculated. A comparative analysis of clinical and ultrasonographic data between the groups was conducted. The hyperbilirubinemia group had higher mean G/P ratios (1.39 ± 0.49 vs. 1.16 ± 0.12, P < 0.05) and lower VIMV, which was negatively correlated with TSB levels (coronal: r = -0.419, P < 0.05; parasagittal: r = -0.448, P < 0.05). Cranial gray-scale ultrasound demonstrates altered gray values in the basal ganglia region, and the MV-Flow technique reveals and quantifies the microvascular structure of this region. These methods may serve as potential biological markers for the early assessment of bilirubin-induced brain damage.

Serum Direct Bilirubin as a Biomarker for Breast Cancer

Background

The role of serum total bilirubin (TB) in cancer has been a subject of controversy, as has the role of its subtypes, particularly serum direct bilirubin (DB). The aim of the present study was to investigate the association between serum DB levels and breast cancer, as well as to assess the diagnostic utility of serum DB in breast cancer.

Methods

A total of 5299 patients diagnosed with breast cancer for the first time at Taizhou Hospital of Zhejiang Province were included in the study, and 10028 healthy physical examination subjects were included as healthy controls. Logistics regression was used to investigate the relationship between serum DB and breast cancer, and the value of serum DB in the diagnosis of breast cancer was assessed by means of receiver operator characteristic (ROC) curve analysis.

Results

The serum DB concentration in the breast cancer group was significantly higher than the healthy controls (P < 0.001). Multivariate logistic regression results show that serum DB was an independent risk factor for breast cancer (odds ratio [OR]=4.504, 95% confidence interval [CI]: 4.200-4.831). Subjects with a serum DB concentration in the fourth quartile had a higher risk of breast cancer occurrence compared to those in the first quartile after adjusting for age (OR = 7.155, 95%CI: 6.474-7.907). The optimal cut-off value of serum DB for diagnosing breast cancer was determined to be 2.75 μmol/L, with an area under the curve (AUC) of 0.712 (95% CI: 0.703-0.722). This value exhibited good specificity (77.0%) and negative predictive value (77.8%).

Conclusion

Serum DB was identified as a risk factor for breast cancer, demonstrating good diagnostic potential for the disease. These findings suggest that serum DB could serve as a promising serum molecular marker for breast cancer.

Clinical overview of phototherapy for neonatal hyperbilirubinaemia

The most efficient emission spectrum of light for phototherapy is blue-green light emission diode light with peak emission at 478 nm. In the irradiance interval of phototherapy, the relationship between efficacy and irradiance is almost linear, and it is negatively related to the haemoglobin. The action sites of phototherapy are the extravascular compartment and cutaneous blood. The most immature neonates treated aggressively had not only a lower frequency of neurodevelopmental impairment than conservatively treated, but also greater mortality. Intermittent and continuous phototherapy are assumed to be equally efficient. Home-based fibreoptic phototherapy is effective and safe. Important progress is still occurring in phototherapy.

Bilirubin isomers during LED phototherapy of hyperbilirubinemic neonates, blue-green (~478 nm) vs blue

BACKGROUND

The clinical part of this randomized controlled trial concerning phototherapy of neonates with hyperbilirubinemia showed that the recommended blue-green LED light (≈478 nm) was 31% more efficient than standard blue LED light (≈459 nm) measured by the decline in total serum bilirubin. Lumirubin has biologic effects. The aim was to compare the serum bilirubin isomers, efficacy, and biologic effects between the two phototherapy groups.

METHODS

Inclusion criteria: neonates healthy except for hyperbilirubinemia, gestational age ≥33 weeks, birth weight ≥1800 g, and postnatal age >24 h. Forty-two neonates were randomized to receive overhead blue-green light and 44 blue light. Treatment 24 h. The light irradiance was equal.

RESULTS

The percentage decrease of combined bilirubin isomers was 47.8% for blue-green light vs 33.4% for blue light, the ratio being 1.43. Corresponding values for Z,Z-bilirubin were 55.6% vs 44.2%, the ratio being 1.26. The increase in the absolute serum concentrations of the photoisomer Z,E-bilirubin and thereby combined photoisomers were greater using blue light.

CONCLUSION

Blue-green light was essentially more efficient determined by the decline of combined bilirubin isomers and Z,Z-bilirubin itself. Regarding biological effects neonates receiving blue-green light might be more affected than neonates receiving blue light.

IMPACT

Phototherapy of hyperbilirubinemic neonates using blue-green LED light with a peak emission of 478 nm was 43% more efficient than standard blue LED light with a peak emission of 459 nm was measured by the decline of serum combined bilirubin isomers, and the decline of toxic Z,Z-bilirubin was 26% greater. Apparently, there was a discrepancy between the huge drop in total serum bilirubin and the low serum concentrations of E,Z-bilirubin and E,Z-lumirubin. This was caused by the rapid excretion of E,Z-lumirubin. Lumirubin has biologic effects. Due to greater lumirubin production neonates exposed to blue-green light might be more affected than those exposed to blue light.

Activation of Nrf2/HO-1 signaling pathway exacerbates cholestatic liver injury

Nuclear factor erythroid 2-related factor-2 (Nrf2) antioxidant signaling is involved in liver protection, but this generalization overlooks conflicting studies indicating that Nrf2 effects are not necessarily hepatoprotective. The role of Nrf2/heme oxygenase-1 (HO-1) in cholestatic liver injury (CLI) remains poorly defined. Here, we report that Nrf2/HO-1 activation exacerbates liver injury rather than exerting a protective effect in CLI. Inhibiting HO-1 or ameliorating bilirubin transport alleviates liver injury in CLI models. Nrf2 knockout confers hepatoprotection in CLI mice, whereas in non-CLI mice, Nrf2 knockout aggravates liver damage. In the CLI setting, oxidative stress activates Nrf2/HO-1, leads to bilirubin accumulation, and impairs mitochondrial function. High levels of bilirubin reciprocally upregulate the activation of Nrf2 and HO-1, while antioxidant and mitochondrial-targeted SOD2 overexpression attenuate bilirubin toxicity. The expression of Nrf2 and HO-1 is elevated in serum of patients with CLI. These results reveal an unrecognized function of Nrf2 signaling in exacerbating liver injury in cholestatic disease.

Simultaneous determination of free biliverdin and free bilirubin in serum: A comprehensive LC-MS approach

BACKGROUND

Prognosis, diagnosis, and treatment of several diseases strongly rely on the sensitive, selective, and accurate determination of specific biomarkers in relevant biological samples. Free biliverdin and free bilirubin represent important new biomarkers of oxidative stress, however, the lack of suitable analytical methods for their determination has hindered progress in biomedical and clinical research.

RESULTS

Here, we introduce a first comprehensive approach for robust and simultaneous determination of these bilins in serum using liquid chromatography - mass spectrometry (LC-MS). The developed analytical method exhibits linearity for both analytes within the concentration range of 0.5-100 nM, with limits of detection and quantitation determined at 0.1 nM and 0.5 nM, respectively. Moreover, several analytical pitfalls related to the intrinsic molecular structures of free bilirubin and free biliverdin and their trace concentration levels in biological samples are discussed here in detail for the first time. We have shown that the solubility, chemical stability, and affinity of these bilins to various materials strongly depend on the solvent, pH, and addition of stabilizing and chelating agents. Finally, the validated LC-MS method was successfully applied to the analysis of both bilins in fetus bovine serums, yielding higher free bilirubin/biliverdin ratios compared with previously reported values for human serum.

SIGNIFICANCE

Failure to recognize and address the challenges presented here often leads to substantial analytical errors and consequently biased interpretation of the obtained results. This pertains not only to LC-MS, but also to many other analytical platforms due to the compound-derived sources of error.

IL-10 dependent modulatory effect of regulatory B10 cells on local scar formation following Roux-en-Y choledochojejunostomy in a novel rat model

Choledochojejunostomy has been common surgical treatment of biliary tract disease. Scar formation at anastomotic often results in postoperative complications associated with bleak post-operative recovery, in which local inflammation may be a potential target to modulate local scar formation. This study investigated the effect of regulatory B10 cells on local scar formation through interleukin-10 signal pathway following Roux-en-Y choledochojejunostomy (RCJS) in a novel rat model. Sprague-Dawley (SD) rats with RCJS were randomly divided into blank group, experimental group, IL-10 blocking group, control group, and received different interventions and duration. Injected through dorsal vein of penis, rats in different groups were treated respectively according to scheme. These interventions were performed during surgery, on 1st day, and 2nd day after surgery. Related indexes, including blood examination, specimen tissue of anastomotic detection, were recorded and compared in different interventional groups. Rats in experimental groups had more rapid recovery in liver function and inflammatory index, and higher in IL-10 level. Flow cytometry analysis showed that rats in experimental groups had highest content of B10 cells and lowest content of CD4+CD25- T cells in peripheral blood. Wider anastomotic by macroscopical observation, and slighter proliferation of collagen fiber and smooth muscle fiber, lower α-SMA and TGF-β1 levels by pathological staining were detected in experimental groups. Higher expression of the IL-10 gene and lower expression of TGF-β1 at anastomotic were detected in experimental groups. B10 cells may relieve local inflammation of anastomotic following RCJS in rats through IL-10-dependent modulatory effect, and improve local scar formation.

Study on the Common Molecular Mechanism of Metabolic Acidosis and Myocardial Damage Complicated by Neonatal Pneumonia

Pneumonia is a common clinical disease in the neonatal period and poses a serious risk to infant health. Therefore, the understanding of molecular mechanisms is of great importance for the development of methods for the rapid and accurate identification, classification and staging, and even disease diagnosis and therapy of pneumonia. In this study, a nontargeted metabonomic method was developed and applied for the analysis of serum samples collected from 20 cases in the pneumonia control group (PN) and 20 and 10 cases of pneumonia patients with metabolic acidosis (MA) and myocardial damage (MD), respectively, with the help of ultrahigh-performance liquid chromatography-high-resolution mass spectrometry (UPLC-HRMS). The results showed that compared with the pneumonia group, 23 and 21 differential metabolites were identified in pneumonia with two complications. They showed high sensitivity and specificity, with the area under the curve (ROC) of the receiver operating characteristic curve (ROC) larger than 0.7 for each differential molecule. There were 14 metabolites and three metabolic pathways of sphingolipid metabolism, porphyrin and chlorophyll metabolism, and glycerophospholipid metabolism existing in both groups of PN and MA, and PN and MD, all involving significant changes in pathways closely related to amino acid metabolism disorders, abnormal cell apoptosis, and inflammatory responses. These findings of molecular mechanisms should help a lot to fully understand and even treat the complications of pneumonia in infants.

Non-Enzymatically Colorimetric Bilirubin Sensing Based on the Catalytic Structure Disruption of Gold Nanocages

As an essential indicator of liver function, bilirubin is of great significance for clinical diagnosis. A non-enzymatic sensor has been established for sensitive bilirubin detection based on the bilirubin oxidation catalyzed by unlabeled gold nanocages (GNCs). GNCs with dual-localized surface plasmon resonance (LSPR) peaks were prepared by a one-pot method. One peak around 500 nm was ascribed to gold nanoparticles (AuNPs), and the other located in the near-infrared region was the typical peak of GNCs. The catalytic oxidation of bilirubin by GNCs was accompanied by the disruption of cage structure, releasing free AuNPs from the nanocage. This transformation changed the dual peak intensities in opposite trend, and made it possible to realize the colorimetric sensing of bilirubin in a ratiometric mode. The absorbance ratios showed good linearity to bilirubin concentrations in the range of 0.20~3.60 μmol/L with a detection limit of 39.35 nM (3σ, n = 3). The sensor exhibited excellent selectivity for bilirubin over other coexisting substances. Bilirubin in real human serum samples was detected with recoveries ranging from 94.5 to 102.6%. The method for bilirubin assay is simple, sensitive and without complex biolabeling.

Bilirubin gates the TRPM2 channel as a direct agonist to exacerbate ischemic brain damage

Stroke prognosis is negatively associated with an elevation of serum bilirubin, but how bilirubin worsens outcomes remains mysterious. We report that post-, but not pre-, stroke bilirubin levels among inpatients scale with infarct volume. In mouse models, bilirubin increases neuronal excitability and ischemic infarct, whereas ischemic insults induce the release of endogenous bilirubin, all of which are attenuated by knockout of the TRPM2 channel or its antagonist A23. Independent of canonical TRPM2 intracellular agonists, bilirubin and its metabolic derivatives gate the channel opening, whereas A23 antagonizes it by binding to the same cavity. Knocking in a loss of binding point mutation for bilirubin, TRPM2-D1066A, effectively antagonizes ischemic neurotoxicity in mice. These findings suggest a vicious cycle of stroke injury in which initial ischemic insults trigger the release of endogenous bilirubin from injured cells, which potentially acts as a volume neurotransmitter to activate TRPM2 channels, aggravating Ca²⁺-dependent brain injury.

Bilirubin Removal by Polymeric Adsorbents for Hyperbilirubinemia Therapy

Hyperbilirubinemia, presenting as jaundice, is a life-threatening critical illness in newborn babies and acute severe hepatic failure patients. Over the past few decades, extracorporeal hemoadsorption by adsorbent therapy has been widely applied in the treatment of hyperbilirubinemia. The capability of hemoadsorption depends on the adsorbents. Most of the clinically used bilirubin adsorbents are made up of styrene/divinylbenzene copolymer and quaternary ammonium salt, which usually have poor biocompatibility and weak mechanical strength. To overcome the drawbacks of commercial polymer adsorbents, advanced synthetic and natural polymers with/without nanomaterials have been designed, and novel adsorbent fabrication technologies have also been developed. In this review, the adsorption mechanism of bilirubin adsorbents has been summarized, which is the basic criterion in adsorbent development. Furthermore, the preparation method, adsorption mechanism, relative merits and practicability of the emerging bilirubin adsorbents have been evaluated. Based on the existing studies, this work highlights the future direction of the efforts on how to design and develop bilirubin adsorbents with good overall clinical performance. Perhaps this study can change traditional perspectives and propose new strategies for bilirubin clearance from the aspects of pathogenic mechanisms, metabolic pathways, and material-based innovation.

Management of severe hyperbilirubinemia in the cholestatic neonate: a review and an approach

A review of the literature demonstrates that severe total hyperbilirubinemia (total serum bilirubin ≥ 20 mg/dL [340 µmol/L]) in some cholestatic term (≥37 weeks) and late-preterm (≥34^0/7-36^6/7 weeks) gestation neonates poses a risk for bilirubin-induced brain damage. When the direct bilirubin fraction is <50% of the total serum bilirubin this risk is associated with the total serum bilirubin alone and treatment decisions should be based on the total serum bilirubin. On the other hand, there are limited data on the risk of bilirubin-induced brain damage in the neonate with severe total hyperbilirubinemia and a direct bilirubin fraction that is equal to or exceeds 50% of the total serum bilirubin. When this rare combination occurs, efforts to keep the indirect bilirubin fraction from reaching severe levels might, nevertheless, be prudent.

Effect of Direct Bilirubin Level on Clinical Outcome and Prognoses in Severely/Critically Ill Patients With COVID-19

Objectives

We aimed to investigate how changes in direct bilirubin (DBiL) levels in severely/critically ill the coronavirus disease (COVID-19) patients during their first week of hospital admission affect their subsequent prognoses and mortality.

Methods

We retrospectively enrolled 337 severely/critically ill COVID-19 patients with two consecutive blood tests at hospital admission and about 7 days after. Based on the trend of the two consecutive tests, we categorized patients into the normal direct bilirubin (DBiL) group (224), declined DBiL group (44) and elevated DBiL group (79).

Results

The elevated DBiL group had a significantly larger proportion of critically ill patients (χ²-test, p < 0.001), a higher risk of ICU admission, respiratory failure, and shock at hospital admission (χ²-test, all p < 0.001). During hospitalization, the elevated DBiL group had significantly higher risks of shock, acute respiratory distress syndrome (ARDS), and respiratory failure (χ²-test, all p < 0.001). The same findings were observed for heart damage (χ²-test, p = 0.002) and acute renal injury (χ²-test, p = 0.009). Cox regression analysis showed the risk of mortality in the elevated DBiL group was 2.27 (95% CI: 1.50–3.43, p < 0.001) times higher than that in the normal DBiL group after adjusted age, initial symptom, and laboratory markers. The Receiver Operating Characteristic curve (ROC) analysis demonstrated that the second test of DBiL was consistently a better indicator of the occurrence of complications (except shock) and mortality than the first test in severely/critically ill COVID-19 patients. The area under the ROC curve (AUC) combined with two consecutive DBiL levels for respiratory failure and death was the largest.

Conclusion

Elevated DBiL levels are an independent indicator for complication and mortality in COVID-19 patients. Compared with the DBiL levels at admission, DBiL levels on days 7 days of hospitalization are more advantageous in predicting the prognoses of COVID-19 in severely/critically ill patients.

Fluorescent sensing of free bilirubin at nanomolar level using a Langmuir-Blodgett film of glucuronic acid-functionalized gold nanoclusters

Serum bilirubin is an important indicator to assess liver function and diagnose various types of liver diseases. The level of serum bilirubin is also negatively correlated with the risk of cardiovascular disease and cancer. We had fabricated a fluorescent film sensor aiming at free bilirubin detection at the nanomolar level. Gold nanoclusters capped by human serum albumin (HSA-AuNCs) were utilized as a fluorescent platform for bilirubin biorecognition. HSA-AuNCs were functionalized with glucuronic acid to increase the binding sites for bilirubin. An ultrathin film of glucuronic acid-functionalized gold nanoclusters was obtained by the Langmuir-Blodgett (LB) technique. When exposed to bilirubin, the interaction between free bilirubin and the functionalized AuNCs resulted in fluorescent quenching of the film. Good linearity could be achieved for the quenching efficiency versus the logarithm of free bilirubin concentration over a concentration range of 1.00 nM~5.00 μM. The limit of detection (LOD) was calculated to be (2.70 ± 0.14) × 10^-1 nM (S/N = 3). The film sensor presents a good anti-interference capability towards common substances coexisting with bilirubin in serum. Satisfactory results achieved in the tests of real serum samples indicate that the LB film sensor can be used for bilirubin determination in nanomolar concentration.

Physiologically increased total bilirubin is associated with reduced risk of first myocardial infarction: A meta-analysis and dose-response analysis

AIM

Bilirubin has potential predictive and prognostic value for myocardial infarction (MI), but the clinical evidence remains controversial. We performed this meta-analysis to systematically quantify the relationships between circulating bilirubin levels and the incidence of MI and post-MI adverse events.

DATA SYNTHESIS

We searched the PubMed, Cochrane Library, Embase, and Web of Science databases for ad-hoc studies, published up to October 17, 2020, recording bilirubin before MI (predictive analyses) or adverse events (prognostic analyses). Relative risks (RR) were pooled by a random-effects model. The dose-response analysis was conducted by restricted cubic splines. In patients without previous MI, increased total bilirubin (TB) reduced the risk of long-term (>3 year) first MI by 22% (95% confidence interval [CI]: 0.69-0.88, n = 4). The dose-response analysis indicated that the RR for first MI decreased by 2.7% per each 2 μmol/L increment of TB (three studies, 95% CI: 1.3%-4.1%, P < 0.001), with a cut-off value of 12.60 μmol/L for RR > 1.00. Elevated bilirubin reduced the incidence of first and recurrent MI by 36% (95% CI: 0.42-0.98, n = 7). However, after suffering MI, higher TB concentrations could not decrease the risk of recurrent MI (RR: 1.02, 95% CI: 0.67-1.55, n = 5) and increased the incidence of short-term (<1 year) post-MI major adverse cardiovascular events, all-cause mortality, and cardiovascular mortality, but not long-term (≥1 year).

CONCLUSION

Higher TB levels within a physiological range reduced the incidence of long-term first MI, with a cut-off value of 12.60 μmol/L.

Effect of blue LED phototherapy centered at 478 nm versus 459 nm in hyperbilirubinemic neonates: a randomized study

BACKGROUND

Treatment of choice for hyperbilirubinemic neonates is blue light matching the absorption spectrum of bilirubin-albumin in vitro with maximum absorption at 459 nm. Blue LED light centered at 478 nm was hypothesized as being more efficient than that centered at 459 nm. This study compares the bilirubin-reducing effect of the two light qualities with equal irradiance in a randomized nonblinded clinical trial.

METHODS

Inclusion criteria were healthy hyperbilirubinemic neonates with gestational age ≥33 weeks. Forty-nine neonates included in each group received phototherapy from above for 24 h. Mean irradiances were 9.2 × 10¹⁵ and 9.0 × 10¹⁵ photons/cm²/s for the 478 and 459 nm groups, respectively.

RESULTS

Mean [95% CI] decreases in total serum bilirubin were 150 [141, 158] and 120 [111, 130] µmol/L for the 478 and 459 nm groups, respectively; mean difference was 29 [17, 42] µmol/L. Mean [95% CI] percentage decreases in bilirubin were 54.8% [52.5, 57.0] and 41.8% [39.3, 44.3]; mean difference was 12.9 [9.6, 16.3] percentage points. After adjustment this difference was 13.4 [10.2, 16.7] percentage points. All differences were highly statistically significant (P < 0.001).

CONCLUSION

Blue LED light centered at 478 nm had a greater bilirubin-reducing effect than that centered at 459 nm with equal irradiance quantified as photon fluence rate.

IMPACT

Blue LED light centered at 478 nm had a greater in vivo bilirubin-reducing effect than blue LED light centered at 459 nm with equal irradiance quantified as photon fluence rate in the treatment of hyperbilirubinemic late preterm or term neonates. LED light centered at 478 nm might reduce the duration of phototherapy compared to LED light centered at 459 nm as the same effect can be obtained while exposing the infants to fewer photons. Blue light matching the absorption spectrum of the bilirubin-albumin complex in vitro with peak absorption at 459 nm is used worldwide as it is considered to be the most effective light for phototherapy of jaundiced neonates. This study showed that blue LED light centered at 478 nm had a greater bilirubin-reducing effect than blue LED light centered at 459 nm. Therefore, blue LED light centered at 478 nm should be used instead of blue light centered at 459 nm. By this, the risk of potential side effects might be minimized, and the duration of phototherapy potentially reduced.

Bilirubin Levels as Potential Indicators of Disease Severity in Coronavirus Disease Patients: A Retrospective Cohort Study

Objectives: The coronavirus disease (COVID-19) pandemic has caused a large number of deaths. Some patients with severe or critical COVID-19 have been observed to have elevated bilirubin levels. Studies on the association of bilirubin level and mortality in patients with COVID-19 are limited. This study aimed to examine the role of bilirubin levels in COVID-19 severity and mortality.

Methods: A retrospective cohort study was conducted in patients hospitalized with COVID-19 in Leishenshan Hospital in Wuhan, China. Cox regression analyses and logistic regression analyses were conducted to investigate the risks for mortality and disease severity, respectively. Kaplan–Meier analyses with log-rank tests were performed to assess the association between bilirubin level and survival.

Results: In total, 1,788 patients with COVID-19 were included in the analysis. 5.8% (4/69) of patients in the elevated serum total bilirubin (STB) group died, compared to 0.6% (11/1,719) of patients in the non-elevated STB group. The median alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in the elevated STB group were 29 U/L [interquartile range (IQR): 16–45 U/L] and 22 U/L (IQR: 13–37 U /L), respectively, which were significantly higher than the median ALT (median: 23, IQR: 15–37) and AST (median: 20, IQR: 16–26) activities in the non-elevated STB group (both p < 0.05). Patients with an elevated STB level showed increased mortality [hazard ratio (HR): 9.45, P = 0.002], elevated conjugated bilirubin (CB) levels (HR: 4.38, P = 0.03), and an elevated ratio of CB to unconjugated bilirubin (UCB, CB/UCB) (HR: 2.49, P = 0.01). CB/UCB was positively correlated with disease severity (odds ratio: 2.21, P = 0.01).

Conclusions: COVID-19 patients with elevated STB and CB levels had a higher mortality, and CB/UCB was predictive of disease severity and mortality. Thus, it is necessary to pay special attention to COVID-19 patients with elevated bilirubin levels in clinical management.

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.

Is serum bilirubin level a predictor factor in parotid gland carcinoma?

Introduction

Bilirubin levels have been associated with risk of several malignancies. The association between pretreatment serum bilirubin levels and overall survival of patients with parotid gland carcinoma is unclear.

Objectives

In this study, we assessed the effect of serum bilirubin levels to overall survival in malignant parotid tumors.

Methods

This study included a total of 35 patients, 15 female and 20 male. The mean age of these patients was 60.7 ± 14.5 years. All patients who were diagnosed with parotid gland carcinoma and underwent total parotidectomy between 2008 and 2018, were retrospectively assessed. The relationship between the overall survival of patients and total bilirubin, direct bilirubin, and indirect bilirubin levels was estimated. The receiver operating characteristic (ROC) curve analysis was performed to determine the optimal cut-off points.

Results

Patients with low direct bilirubin, total bilirubin and indirect bilirubin had significantly longer overall survival than those with high levels. Cut-off values for total bilirubin, direct bilirubin and indirect bilirubin were detected as 0.545 mg/dL, 0.175 mg/dL and 0.435 mg/dL, respectively.

Conclusion

In our study, we observed that increased preoperative bilirubin levels are associated with reduced survival time in the postoperative period of patients with parotid gland carcinoma.

Serum bilirubin level predicts postoperative overall survival in oral squamous cell carcinoma

BACKGROUND

Aberrant level of serum bilirubin, marker of hepatobiliary and hematological disorders, was associated with patient prognosis in several human malignancies. In this study, we aim to evaluate the predictive value of serum bilirubin for clinicopathologic characteristics and survival of patients with oral squamous cell carcinoma (OSCC).

METHODS

This study retrospectively reviewed 129 patients with OSCC and 129 normal controls matched for age and sex. The association between levels of preoperative direct bilirubin (DBIL), indirect bilirubin (IBIL), total bilirubin (TBIL), and clinical variables was analyzed. A proportional hazards regression model was used to find out the independent predictors of survival.

RESULTS

Significantly lower TBIL (P = .009) and IBIL (P < .001) were found in OSCC patients compared with normal controls. DBIL (P = .011) and lymph-node metastasis (P = .031) were found to be independent prognostic factors. Patients with higher DBIL (≥4.0 μmol/L) had longer overall survival than those with lower DBIL (P = .002). Patients with both lymph-node metastasis and lower DBIL showed the shortest overall survival (P = .001).

CONCLUSIONS

Lower DBIL was associated with a poorer prognosis and may be regarded as an independent prognostic marker for patients with OSCC.

Diagnostic criteria and contributors to Gilbert's syndrome

Hyperbilirubinemia is a well-known condition in the clinical setting; however, the causes of elevated serum bilirubin are diverse, as are the clinical ramifications of this condition. For example, diagnoses of individuals vary depending on whether they exhibit an unconjugated or conjugated hyperbilirubinemia. Diagnoses can include conditions of disordered bilirubin metabolism (Gilbert's, Crigler-Najjar, Rotor, or Dubin-Johnson syndromes) or an acquired disease, including alcoholic/non-alcoholic fatty liver disease, hepatotropic hepatitis, cirrhosis, or hepato-biliary malignancy. Assessment of bilirubin concentrations is typically conducted as part of routine liver function testing. Mildly elevated total bilirubin with normal serum activities of liver transaminases, biliary damage markers, and red blood cell counts, however, may indicate the presence of Gilbert's syndrome (GS), a benign condition that is present in ∼5-10% of the population. In this case, mildly elevated unconjugated bilirubin in GS is strongly associated with "reduced" prevalence of chronic diseases, particularly cardiovascular diseases (CVD) and type 2 diabetes mellitus (and associated risk factors), as well as CVD-related and all-cause mortality. These reports challenge the dogma that bilirubin is simply a potentially neurotoxic by-product of heme catabolism and emphasize the importance of understanding its potential beneficial physiologic and detrimental pathophysiologic effects, in order to appropriately consider bilirubin test results within the clinical laboratory setting. With this information, we hope to improve the understanding of disorders of bilirubin metabolism, emphasize the diagnostic importance of these conditions, and outline the potential impact GS may have on resistance to disease.

Case-control study of the efficacy of retrogastric Roux-en-Y choledochojejunostomy

The traditional, retrocolic/antegastric Roux-en-Y choledochojejunostomy is technically complicated, and the incidence of postoperative complications remains high. Here we report the outcome of 59 consecutively treated patients (study group, SG) that underwent a new choledochojejunostomy method in which the jejunal loop is passed behind the antrum pyloricum (retrogastric route). A retrospective comparison was made between this group of patients and 187 patients (control group, CG) that underwent conventional Roux-en-Y choledochojejunostomy (antegastric route). Baseline clinicopathological characteristics were similar in both groups, except for the BMI, which was significantly higher in the SG. The time spent on constructing the anastomosis, as well as overall postoperative complications, did not differ between groups. Compared with the CG, the incidence of postoperative delayed gastric emptying was decreased in the SG, and the time elapsed before the patients' first postoperative liquid food consumption was shorter. We ascribe these beneficial effects to the superiority of the modified, retropyloric choledochojejunostomy approach, and propose that this surgical technique is particularly suitable for obese patients, especially those with a short ascending bowel loop.

Bilirubin isomer distribution in jaundiced neonates during phototherapy with LED light centered at 497 nm (turquoise) vs. 459 nm (blue)

BACKGROUND

Phototherapy using blue light is the treatment of choice worldwide for neonatal hyperbilirubinemia. However, treatment with turquoise light may be a desirable alternative. Therefore, the aim of this randomized, controlled study was to compare the bilirubin isomer distribution in serum of jaundiced neonates after 24 h of therapy with narrow-band (LED) light centered at 497 nm (turquoise) vs. 459 nm (blue), of essentially equal irradiance.

MATERIALS

Eighty-three neonates (≥33 wk gestational age) with uncomplicated hyperbilirubinemia were included in the study. Forty neonates were exposed to light centered at 497 nm and 43 infants with light centered at 459 nm. Irradiances were 5.2 × 10(15) and 5.1 × 10(15) photons/cm(2)/s, respectively.

RESULTS

After 24 h of treatment no significant differences in serum concentrations of total bilirubin isomers and Z,Z-bilirubin were observed between the 2 groups. Interestingly, concentrations of Z,E-bilirubin, and thus also total bilirubin isomers formed during therapy, were highest for infants receiving light centered at 459 nm, while the concentration of E,Z-bilirubin was highest for those receiving light centered at 497 nm. No significant difference was found between concentrations of E,Z-lumirubin.

CONCLUSION

Therapy with LED light centered at 497 nm vs. 459 nm, applied with equal irradiance on the infants, resulted in a different distribution of bilirubin isomers in serum.

Biology of Bilirubin Photoisomers

Phototherapy is the main treatment for neonatal hyperbilirubinemia. In acute treatment of extreme hyperbilirubinemia, intensive phototherapy may have a role in 'detoxifying' the bilirubin molecule to more polar photoisomers, which should be less prone to crossing the blood-brain barrier, providing a 'brain-sparing' effect. This article reviews the biology of bilirubin isomers. Although there is evidence supporting the lower toxicity of bilirubin photoisomers, there are studies showing the opposite. There are methodologic weaknesses in most studies and better-designed experiments are needed. In an infant acutely threatened by bilirubin-induced brain damage, intensified phototherapy should be used expediently and aggressively.

Hyperbilirubinemia exaggerates endotoxin-induced hypothermia

Systemic inflammation is accompanied by an increased production of reactive oxygen species (ROS) and by either fever or hypothermia (or both). To study aseptic systemic inflammation, it is often induced in rats by the intravenous administration of bacterial lipopolysaccharide (LPS). Knowing that bilirubin is a potent ROS scavenger, we compared responses to LPS between normobilirubinemic Gunn rats (heterozygous, asymptomatic; J/+) and hyperbilirubinemic Gunn rats (homozygous, jaundiced; J/J) to establish whether ROS mediate fever and hypothermia in aseptic systemic inflammation. These two genotypes correspond to undisturbed versus drastically suppressed (by bilirubin) tissue accumulation of ROS, respectively. A low dose of LPS (10 μg/kg) caused a typical triphasic fever in both genotypes, without any intergenotype differences. A high dose of LPS (1,000 μg/kg) caused a complex response consisting of early hypothermia followed by late fever. The hypothermic response was markedly exaggerated, whereas the subsequent fever response was strongly attenuated in J/J rats, as compared to J/+ rats. J/J rats also tended to respond to 1,000 μg/kg with blunted surges in plasma levels of all hepatic enzymes studied (alanine aminotransferase, aspartate aminotransferase, gamma-glutamyl transferase), thus suggesting an attenuation of hepatic damage. We propose that the reported exaggeration of LPS-induced hypothermia in J/J rats occurs via direct inhibition of nonshivering thermogenesis by bilirubin and possibly via a direct vasodilatatory action of bilirubin in the skin. This hypothermia-exaggerating effect might be responsible, at least in part, for the observed tendency of J/J rats to be protected from LPS-induced hepatic damage. The attenuation of the fever response to 1,000 μg/kg could be due to either direct actions of bilirubin on thermoeffectors or the ROS-scavenging action of bilirubin. However, the experiments with 10 μg/kg strongly suggest that ROS signaling is not involved in the fever response to low doses of LPS.

Early formation of bilirubin isomers during phototherapy for neonatal jaundice: effects of single vs. double fluorescent lamps vs. photodiodes

BACKGROUND

In neonatal jaundice, phototherapy converts bilirubin to more polar photoisomers which can be excreted without conjugation. We measured changes in the concentration of bilirubin Z,E-photoisomer during the first 4 h of intensive phototherapy using single fluorescent lights as a reference, compared to double fluorescent lights, and a single unit of photodiodes.

METHODS

Neonates (N = 42; birth weight: 1,200-4,690 g; gestational age: 28-42 wk) were studied during phototherapy. Infants were randomized to: (i) single, or (ii) double fluorescent phototherapy; or (iii) single unit photodiodes. Irradiance was measured. Serum bilirubin (by cooximetry) and Z,E bilirubin (by high-pressure liquid chromatography) were measured at 0,15, 30, 60, 120, and 240 min after the start of phototherapy. Data were analyzed with a linear mixed model.

RESULTS

There was a highly significant increase of Z,E-bilirubin over time (P < 0.0001), starting at 15 min. Photoisomers reached ~25% of total bilirubin concentration after 4 h. However, there were no significant differences between the three randomized groups in spite of significantly higher irradiance using double fluorescent lights vs. single fluorescent or photodiodes.

CONCLUSION

Formation of bilirubin photoisomers is rapid, and occurs early during intensive phototherapy for neonatal jaundice. The rate and level of photoisomerization was not influenced by irradiance and light source.

Impairment of enzymatic antioxidant defenses is associated with bilirubin-induced neuronal cell death in the cerebellum of Ugt1 KO mice

Severe hyperbilirubinemia is toxic during central nervous system development. Prolonged and uncontrolled high levels of unconjugated bilirubin lead to bilirubin-induced encephalopathy and eventually death by kernicterus. Despite extensive studies, the molecular and cellular mechanisms of bilirubin toxicity are still poorly defined. To fill this gap, we investigated the molecular processes underlying neuronal injury in a mouse model of severe neonatal jaundice, which develops hyperbilirubinemia as a consequence of a null mutation in the Ugt1 gene. These mutant mice show cerebellar abnormalities and hypoplasia, neuronal cell death and die shortly after birth because of bilirubin neurotoxicity. To identify protein changes associated with bilirubin-induced cell death, we performed proteomic analysis of cerebella from Ugt1 mutant and wild-type mice. Proteomic data pointed-out to oxidoreductase activities or antioxidant processes as important intracellular mechanisms altered during bilirubin-induced neurotoxicity. In particular, they revealed that down-representation of DJ-1, superoxide dismutase, peroxiredoxins 2 and 6 was associated with hyperbilirubinemia in the cerebellum of mutant mice. Interestingly, the reduction in protein levels seems to result from post-translational mechanisms because we did not detect significant quantitative differences in the corresponding mRNAs. We also observed an increase in neuro-specific enolase 2 both in the cerebellum and in the serum of mutant mice, supporting its potential use as a biomarker of bilirubin-induced neurological damage. In conclusion, our data show that different protective mechanisms fail to contrast oxidative burst in bilirubin-affected brain regions, ultimately leading to neurodegeneration.

Bilirubin, platelet activation and heart disease: a missing link to cardiovascular protection in Gilbert's syndrome?

Gilbert's syndrome (GS) is a relatively common condition, inducing a benign, non-hemolytic, unconjugated hyperbilirubinemia. Gilbert's Syndrome is associated with mutation in the Uridine Glucuronosyl Transferase 1A1 (UGT1A1) gene promoter, reducing UGT1A1 activity, which normally conjugates bilirubin allowing its elimination from the blood. Individuals with GS demonstrate mildly elevated plasma antioxidant capacity caused by elevated levels of unconjugated bilirubin (UCB), reduced thiols and glutathione. Interestingly, the development of, and risk of mortality from, cardiovascular disease is remarkably reduced in GS individuals. An explanation for this protection may be explained by bilirubin's ability to inhibit multiple processes that induce platelet hyper-reactivity and thrombosis, thus far under-appreciated in the literature. Reactive oxygen species are produced continuously via metabolic processes and have the potential to oxidatively modify proteins and lipids within cell membranes, which may encourage the development of thrombosis and CVDs. Oxidative stress induced platelet hyper-reactivity significantly increases the risk of thrombosis, which can potentially lead to tissue infarction. Here, we discuss the possible mechanisms by which increased antioxidant status might influence platelet function and link this to cardiovascular protection in GS. In summary, this is the first article to discuss the possible role of bilirubin as an anti-thrombotic agent, which inhibits platelet activation and potentially, organ infarction, which could contribute to the reduced mortality rate in mildly hyperbilirbinemic individuals.

The UDP-glucuronosyltransferases of the blood-brain barrier: their role in drug metabolism and detoxication

UDP-glucuronosyltransferases (UGTs) form a multigenic family of membrane-bound enzymes expressed in various tissues, including brain. They catalyze the formation of β-D-glucuronides from structurally unrelated substances (drugs, other xenobiotics, as well as endogenous compounds) by the linkage of glucuronic acid from the high energy donor, UDP-α-D-glucuronic acid. In brain, UGTs actively participate to the overall protection of the tissue against the intrusion of potentially harmful lipophilic substances that are metabolized as hydrophilic glucuronides. These metabolites are generally inactive, except for important pharmacologically glucuronides such as morphine-6-glucuronide. UGTs are mainly expressed in endothelial cells and astrocytes of the blood brain barrier (BBB). They are also associated to brain interfaces devoid of BBB, such as circumventricular organ, pineal gland, pituitary gland and neuro-olfactory tissues. Beside their key-role as a detoxication barrier, UGTs play a role in the steady-state of endogenous compounds, like steroids or dopamine (DA) that participate to the function of the brain. UGT isoforms of family 1A, 2A, 2B and 3A are expressed in brain tissues to various levels and are known to present distinct but overlapping substrate specificity. The importance of these enzyme species with regard to the formation of toxic, pharmacologically or physiologically relevant glucuronides in the brain will be discussed.

Quantitative assessment of the multiple processes responsible for bilirubin homeostasis in health and disease

Serum bilirubin measurements are commonly obtained for the evaluation of ill patients and to screen for liver disease in routine physical exams. An enormous research effort has identified the multiple mechanisms involved in the production and metabolism of conjugated (CB) and unconjugated bilirubin (UB). While the qualitative effects of these mechanisms are well understood, their expected quantitative influence on serum bilirubin homeostasis has received less attention. In this review, each of the steps involved in bilirubin production, metabolism, hepatic cell uptake, and excretion is quantitatively examined. We then attempt to predict the expected effect of normal and defective function on serum UB and CB levels in health and disease states including hemolysis, extra- and intrahepatic cholestasis, hepatocellular diseases (eg, cirrhosis, hepatitis), and various congenital defects in bilirubin conjugation and secretion (eg, Gilbert's, Dubin-Johnson, Crigler-Najjar, Rotor syndromes). Novel aspects of this review include: 1) quantitative estimates of the free and total UB and CB in the plasma, hepatocyte, and bile; 2) detailed discussion of the important implications of the recently recognized role of the hepatic OATP transporters in the maintenance of CB homeostasis; 3) discussion of the differences between the standard diazo assay versus chromatographic measurement of CB and UB; 4) pharmacokinetic implications of the extremely high-affinity albumin binding of UB; 5) role of the enterohepatic circulation in physiologic jaundice of newborn and fasting hyperbilirubinemia; and 6) insights concerning the clinical interpretation of bilirubin measurements.

The roles of MRP2, MRP3, OATP1B1, and OATP1B3 in conjugated hyperbilirubinemia

Increased concentrations of bilirubin glucuronides in blood plasma indicate hepatocellular dysfunction. Elucidation of the transport processes of bilirubin conjugates across the basolateral (sinusoidal) and the canalicular plasma membrane domains of hepatocytes has decisively contributed to our current understanding of the molecular basis of conjugated hyperbilirubinemia in human liver diseases. Under normal conditions, unconjugated bilirubin is taken up into hepatocytes by transporters of the organic anion-transporting polypeptide (OATP) family, followed by conjugation with glucuronic acid, and ATP-dependent transport into bile. This efflux across the canalicular membrane is mediated by multidrug resistance protein 2 (MRP2 or ABCC2), which is a 190-kDa glycoprotein transporting with high affinity and efficiency monoglucuronosyl bilirubin and bisglucuronosyl bilirubin into bile. MRP2 is hereditarily deficient in human Dubin-Johnson syndrome. Under pathophysiological conditions such as cholestatic liver injury and MRP2 inhibition, the basolateral efflux pump multidrug resistance protein 3 (MRP3 or ABCC3) is responsible for the occurrence of conjugated hyperbilirubinemia. MRP3 is a glycoprotein with a similar molecular mass as MRP2, with 48% amino acid identity, and with overlapping substrate specificity. Human MRP3 is the only basolateral efflux pump shown to transport bilirubin glucuronides. In human and rat hepatocytes, MRP3/Mrp3 is strongly upregulated under conditions of cholestasis and MRP2 deficiency. This is in line with the concept that basolateral efflux pumps of the hepatocyte compensate for impaired canalicular efflux of compounds into bile and contribute to balance the rate of uptake or synthesis of compounds in hepatocytes with the capacity for efflux into bile.

Effect of polyphenols extracted from tamarind (Tamarindus indica L.) seed coat on pathophysiological changes and red blood cell glutathione peroxidase activity in heat-stressed broilers

The purpose of this study was to determine the effect of polyphenols extracted from the tamarind seed coat (PETSC) on glutathione peroxidase (GPx) activity, red blood cell parameters and bilirubin in heat-stressed broilers. One hundred forty-seven broilers, 18-days old were divided into two groups. In group 1, broilers were maintained at an environmental temperature of 26 ± 2 °C throughout the experimental period. In group 2, the broilers were maintained at 38 ± 2 °C (cyclic temperature: 26 ± 2 °C; -38 ± 2 °C; and -26 ± 2 °C, and broilers were maintained at 38 ± 2 °C for 6 h/ day) and received PETSC at a concentration of 0, 100, 200, 300, 400 or 500 mg/kg in their diet ad libitum. Parameters were investigated on days 1, 7, 14 and 21 of the experimental period. Results showed that GPx activity of heat-stressed broilers that received 100 mg/kg of PETSC in their diet was lower (P < 0.05) than that in broilers fed the other concentrations. The mean total red blood cell count and hemoglobin concentration of heat-stressed broilers that received 100 mg/kg PETSC was higher (P < 0.05) than those in broilers in group 1 and those fed the other concentrations. The mean bilirubin level in the excreta of heat-stressed broilers that received 100 mg/kg of PETSC was lower (P < 0.05) than that in broilers that received 0, 300, 400 and 500 mg/kg of PETSC. This showed that PETSC could reduce GPx activity and bilirubin in feces, and increase red blood cell parameters in heat-stressed broilers.

Molecular modeling to provide insight into the substrate binding and catalytic mechanism of human biliverdin-IXα reductase

Human biliverdin-IXα reductase (hBVR-A) catalyzes the conversion of biliverdin-IXα to bilirubin-IXα in the last step of heme degradation and is a key enzyme in regulating a wide range of cellular responses. Though the X-ray structure of hBVR-A is available including cofactor, a crystal structure with a bound substrate would be even more useful as a starting point for protein-structure-based inhibitor design, but none have been reported. The present study employed induced fit docking (IFD) to study the substrate binding modes to hBVR-A of biliverdin-IXα and four analogues. The proposed substrate binding modes were examined further by performing molecular dynamics (MD) simulations followed by molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) calculations. The predicted binding free energies for the five biliverdin-IXα analogues match well with the relative potency of their reported experimental binding affinities, supporting that the proposed binding modes are reasonable. Furthermore, the ternary complex structure of hBVR-A binding with biliverdin-IXα and the electron donor cofactor NADPH obtained from MD simulations was exploited to investigate the catalytic mechanism, by calculating the reaction energy profile using the quantum mechanics/molecular mechanics (QM/MM) method. On the basis of our calculations, the energetically preferred pathway consists of an initial protonation of the pyrrolic nitrogen on the biliverdin substrate followed by hydride transfer to yield the reduction product. This conclusion is consistent with a previous mechanistic study on human biliverdin IXβ reductase (hBVR-B).

The evolving landscape of neurotoxicity by unconjugated bilirubin: role of glial cells and inflammation

Unconjugated hyperbilirubinemia is a common condition in the first week of postnatal life. Although generally harmless, some neonates may develop very high levels of unconjugated bilirubin (UCB), which may surpass the protective mechanisms of the brain in preventing UCB accumulation. In this case, both short-term and long-term neurodevelopmental disabilities, such as acute and chronic UCB encephalopathy, known as kernicterus, or more subtle alterations defined as bilirubin-induced neurological dysfunction (BIND) may be produced. There is a tremendous variability in babies' vulnerability toward UCB for reasons not yet explained, but preterm birth, sepsis, hypoxia, and hemolytic disease are comprised as risk factors. Therefore, UCB levels and neurological abnormalities are not strictly correlated. Even nowadays, the mechanisms of UCB neurotoxicity are still unclear, as are specific biomarkers, and little is known about lasting sequelae attributable to hyperbilirubinemia. On autopsy, UCB was shown to be within neurons, neuronal processes, and microglia, and to produce loss of neurons, demyelination, and gliosis. In isolated cell cultures, UCB was shown to impair neuronal arborization and to induce the release of pro-inflammatory cytokines from microglia and astrocytes. However, cell dependent sensitivity to UCB toxicity and the role of each nerve cell type remains not fully understood. This review provides a comprehensive insight into cell susceptibilities and molecular targets of UCB in neurons, astrocytes, and oligodendrocytes, and on phenotypic and functional responses of microglia to UCB. Interplay among glia elements and cross-talk with neurons, with a special emphasis in the UCB-induced immunostimulation, and the role of sepsis in BIND pathogenesis are highlighted. New and interesting data on the anti-inflammatory and antioxidant activities of different pharmacological agents are also presented, as novel and promising additional therapeutic approaches to BIND.

Transport and metabolism at blood-brain interfaces and in neural cells: relevance to bilirubin-induced encephalopathy

Bilirubin, the end-product of heme catabolism, circulates in non-pathological plasma mostly as a protein-bound species. When bilirubin concentration builds up, the free fraction of the molecule increases. Unbound bilirubin then diffuses across blood-brain interfaces (BBIs) into the brain, where it accumulates and exerts neurotoxic effects. In this classical view of bilirubin neurotoxicity, BBIs act merely as structural barriers impeding the penetration of the pigment-bound carrier protein, and neural cells are considered as passive targets of its toxicity. Yet, the role of BBIs in the occurrence of bilirubin encephalopathy appears more complex than being simple barriers to the diffusion of bilirubin, and neural cells such as astrocytes and neurons can play an active role in controlling the balance between the neuroprotective and neurotoxic effects of bilirubin. This article reviews the emerging in vivo and in vitro data showing that transport and metabolic detoxification mechanisms at the blood-brain and blood-cerebrospinal fluid barriers may modulate bilirubin flux across both cellular interfaces, and that these protective functions can be affected in chronic unconjugated hyperbilirubinemia. Then the in vivo and in vitro arguments in favor of the physiological antioxidant function of intracerebral bilirubin are presented, as well as the potential role of transporters such as ABCC1 and metabolizing enzymes such as cytochromes P-450 in setting the cerebral cell- and structure-specific toxicity of bilirubin following hyperbilirubinemia. The relevance of these data to the pathophysiology of bilirubin-induced neurological diseases is discussed.

A genome-wide association study of total bilirubin and cholelithiasis risk in sickle cell anemia

Serum bilirubin levels have been associated with polymorphisms in the UGT1A1 promoter in normal populations and in patients with hemolytic anemias, including sickle cell anemia. When hemolysis occurs circulating heme increases, leading to elevated bilirubin levels and an increased incidence of cholelithiasis. We performed the first genome-wide association study (GWAS) of bilirubin levels and cholelithiasis risk in a discovery cohort of 1,117 sickle cell anemia patients. We found 15 single nucleotide polymorphisms (SNPs) associated with total bilirubin levels at the genome-wide significance level (p value <5 × 10(-8)). SNPs in UGT1A1, UGT1A3, UGT1A6, UGT1A8 and UGT1A10, different isoforms within the UGT1A locus, were identified (most significant rs887829, p = 9.08 × 10(-25)). All of these associations were validated in 4 independent sets of sickle cell anemia patients. We tested the association of the 15 SNPs with cholelithiasis in the discovery cohort and found a significant association (most significant p value 1.15 × 10(-4)). These results confirm that the UGT1A region is the major regulator of bilirubin metabolism in African Americans with sickle cell anemia, similar to what is observed in other ethnicities.

Recommendations for pregnancies in patients with crigler-najjar syndrome

During pregnancy, the developing foetus in mothers with Crigler-Najjar type 1 and 2 is exposed to raised levels of unconjugated bilirubin, with the risk of neurotoxicity. We describe two pregnancies in a patient with Crigler-Najjar type 2, who was carefully monitored prior to and during pregnancy and phototherapy adjusted to maintain serum bilirubin levels below 200 μmol/l and the bilirubin/albumin molar ratio below 50%. Both pregnancies resulted in normal delivery of healthy infants who had normal neurological development. A review of all reported pregnancies in Crigler-Najjar patients and a set of recommendations are presented.

Association between unconjugated bilirubin and schizophrenia

The evidence regarding the association between schizophrenia and the fractions of bilirubin is mixed. In a retrospective case-control design we examined the association between total bilirubin, conjugated bilirubin, unconjugated bilirubin and schizophrenia. The relevance of our findings and that of the association of unconjugated bilirubin to schizophrenia is discussed.