Lower Bilirubin Concentrations Research Articles

Short-term outcomes of infants with hyperbilirubinemia-associated auditory neuropathy spectrum disorder in neonatal intensive care unit

Hyperbilirubinemia is a high-risk factor for auditory neuropathy spectrum disorder (ANSD) as well as hearing loss in general. This study described the outcomes of hyperbilirubinemia-associated ANSD infants diagnosed in hearing screening in the neonatal intensive care unit (NICU).A total of 578 children with hyperbilirubinemia admitted to the NICU between October 2020 and October 2021 were included in this study. The distortion product otoacoustic emission (DPOAE) and automatic auditory brainstem response (AABR) were combined for hearing screening, and those who failed the DPOAE or/and AABR underwent an auditory brainstem response (ABR) test. Infants with ANSD were followed up for 12 months.Forty infants (40/578, 6.9%) failed the DPOAE or/and AABR tests, of which, 13 (13/578, 2.2%) were diagnosed as ANSD, and 27 (27/578, 4.7%) were diagnosed as having sensorineural hearing loss (SNHL). Of the 13 ANSD infants followed up for 12 months, 7 recovered, 3 improved, 3 did not recover, and 1 was lost, equating to improved or recovered hearing in 75% (9/12) of ANSD infants at 12 months of age. Moreover, the maximum bilirubin in recovered or improved ANSD infants was 408.6 ± 129.0 μmol/L, while the maximum bilirubin in unrecovered ANSD infants was 749.3 ± 323.0 μmol/L. Furthermore, poorly differentiated and absent ABR waveforms were observed in 6 and 14 ears at 1 month, 2 ears were lost, 6 (6/6, 100.0%) and 6 (6/12, 50.0%) ears were recovered or improved at 12 months of age.s: The incidence of hyperbilirubinemia associated-ANSD was 2.2% of infants screened in the NICU. ANSD caused by hyperbilirubinemia may be transient, with most infants improving or recovering hearing by 12 months of age. Infants with poorly differentiated ABR waveforms and low bilirubin concentration are more likely to recover and hearing aids are not recommended in hyperbilirubinemia-associated ANSD below 12 months of age.

Effect of Serum Bilirubin Levels on Contrast-induced Acute Kidney Injury: A Systematic Evaluation and Meta-analysis.

Contrast-induced acute kidney injury (CI-AKI) is an important complication following the use of iodinated contrast media. Bilirubin has a protective effect but may also aggravate CI-AKI. The purpose of this systematic review was to assess whether bilirubin is a risk factor for CI-AKI. We searched the databases PubMed, Embase, Web of Science, Cochrane Library, Scopus, Ovid Medline, CNKI (China National Knowledge Infrastructure), VPCS (Vip Paper Check System), Wanfang, and CBM (Chinese BioMedical Literature Database) from the initial date to May 6, 2023. We summarized the results by directly combining the effect-size odds ratio (OR) and 95% confidence interval (CI) and identified sources of heterogeneity through subgroup analysis, sensitivity analysis, and meta-regression analysis. A total of 10 studies (14 data sets) were included: 7 retrospective studies (10 data sets) and 3 prospective studies (4 data sets), involving 12776 participants. The incidence of CI-AKI of 16% (95% CI: 14-19%). Total bilirubin was positively associated with the occurrence of CI-AKI (OR = 1.80; 95% CI: 1.36-2.38). Both low and high bilirubin concentrations were risk factors for CI-AKI. The incidence of CI-AKI was higher in the low bilirubin group than in the high bilirubin group.

Total Bilirubin Yields Prognostic Information Following a Myocardial Infarction in the Elderly.

Total bilirubin consists of an unconjugated form, solubilized by its binding to albumin, and a conjugated form representing a minor part of the circulating bilirubin. As total bilirubin in physiological concentrations is a powerful antioxidant, its concentration gradient may reflect the health status of an individual, and serve as a prognostic indicator of outcome in primary and secondary cardiovascular disease prevention. The aim of this study was to assess the association between total bilirubin and incident cardiovascular events following a myocardial infarction. Total bilirubin in serum was measured at baseline 2-8 weeks after hospitalization for an MI in 881 patients, aged 70 to 82 years, included in the OMEMI (Omega-3 Fatty acids in Elderly with Myocardial Infarction) study, where patients were followed-up for up to 2 years. The first major adverse clinical event (MACE) was the primary endpoint and consisted of nonfatal MI, unscheduled coronary revascularization, stroke, hospitalization for heart failure or all-cause death. As total bilirubin was non-normally distributed, log-transformed values and quartiles of bilirubin were analyzed using Cox regression models. The median (Q1, and Q3) baseline concentration of bilirubin was 11 (9, and 14) µmol/L, and higher log-transformed concentrations were associated with male sex, lower New York Heart Association (NYHA) class and non-smoking. MACE occurred in 177 (20.1%) patients during the follow-up. Higher concentrations of bilirubin were associated with a lower risk of MACE: HR 0.67 (95%CI 0.47-0.97) per log-unit increase, p = 0.032. Patients in the lowest quartile of bilirubin (<9 µmol/L) had the highest risk with HR 1.61 (95%CI 1.19-2.18), p = 0.002, compared to quartiles 2-4. This association remained significant even after adjusting for age, sex, body mass index (BMI), smoking status, NYHA class and treatment allocation: HR 1.52 (1.21-2.09), p = 0.009. Low concentrations of bilirubin (<9 µmol/L) are associated with increased nonfatal cardiovascular events or death in elderly patients with a recent myocardial infarction.

Outer Membrane Integrity-Dependent Fluorescence of the Japanese Eel UnaG Protein in Live Escherichia coli Cells.

Reporter genes are important tools in many biological disciplines. The discovery of novel reporter genes is relatively rare. However, known reporter genes are constantly applied to novel applications. This study reports the performance of the bilirubin-dependent fluorescent protein UnaG from the Japanese eel Anguilla japonicas in live Escherichia coli cells in response to the disruption of outer membrane (OM) integrity at low bilirubin (BR) concentrations. Using the E. coli wild-type strain MC4100, its isogenic OM-deficient mutant strain NR698, and different OM-active compounds, we show that BR uptake and UnaG fluorescence depend on a leaky OM at concentrations of 10 µM BR and below, while fluorescence is mostly OM integrity-independent at concentrations above 50 µM BR. We suggest that these properties of the UnaG-BR couple might be applied as a biosensor as an alternative to the OM integrity assays currently in use.

Changes in plasma electrolytes, minerals, and hepatic markers of health across the transition period in dairy cows divergent in genetic merit for fertility traits and postpartum anovulatory intervals

Peripartum metabolism and subsequent reproductive performance of dairy cows are linked, with maladaptation over the transition period associated with poor reproductive success. A herd of seasonal calving, grazing dairy cows was established that differed in their genetic merit for fertility traits. The heifers were produced by a customized mating program to achieve a 10-percentage point divergence in the New Zealand fertility breeding value (FertBV) as follows: +5 FertBV (POS) versus -5% FertBV (NEG), while also limiting divergence in other breeding values, including body weight, body condition score, and milk production. In this study, we aimed to characterize differences in metabolic, mineral, and metabolic stress marker profiles during their first postpartum transition period as primiparous heifers and to examine if animals with longer postpartum anestrous intervals (PPAI; more than 66 d compared with less than 35 d) had greater metabolic dysfunction. Blood was sampled at -21, -14, -7, 0, 4, 7, 10, 14, 17, 21, 28, and 35 d relative to calving in 455 primiparous cows and plasma analyzed. The NEG cows had lower concentrations of both plasma nonesterified fatty acids and β-hydroxybutyrate at d 7 compared with POS cows. Detailed temporal profiling of various metabolic, mineral, and metabolic stress markers was undertaken in a subset of cows (n = 70). Cows were selected retrospectively to create 4 groups in a 2 × 2 factorial design with either a POS or NEG FertBV and either a short (19-35 d) or long (66-131 d) PPAI. The NEG cows tended, on average, to have lower nonesterified fatty acids and β-hydroxybutyrate concentrations compared with POS cows across the transition period. Mean body weight and body condition score was greatest in NEG cows when compared with the POS cows and an interaction with day demonstrated this only occurred precalving. They also had indications of improved liver health precalving, with higher albumin-to-globulin ratios and lower bilirubin concentrations. Concentrations of aspartate aminotransferase were lower, and the Na-to-Cl ratio was greater in cows with a long versus a short PPAI at d 28 and d 35 after calving, potentially because of cows with a short PPAI (19-35 d) returning to estrous during this time. Magnesium concentrations were lower in NEG cows with a short PPAI from d 21 onwards, indicating NEG cows may metabolically respond to estrous differently than POS cows. The NEG-long PPAI cows had greater gamma-glutamyl transferase concentrations from calving until d 28 and lower bilirubin concentrations throughout the transition period. Together, the results demonstrate significant effects of FertBV on peripartum metabolic status. However, most of the markers tested returned to reference intervals within 4 d after calving or remained within those intervals for the whole transition period, indicating relatively minor biological effects of FertBV on transition period adaptation. The profound differences in reproductive performance among the groups was not explained by underlying differences in metabolic responses during the transition period.

Bilirubin reduces visceral obesity and insulin resistance by suppression of inflammatory cytokines.

ObjectiveAlthough previous studies have reported a negative relationship between serum bilirubin concentration and the development of diabetes mellitus (DM), the relationship between bilirubin and insulin resistance has not been thoroughly assessed. This study was designed to determine the relationships between bilirubin, body fat distribution, and adipose tissue inflammation in patients with type 2 DM and the effect of bilirubin in an obese animal model.MethodBody fat distribution was measured using an abdominal dual bioelectrical impedance analyzer in patients with type 2 DM. We also measured glycemic control, lipid profile, serum bilirubin concentration and other clinical characteristics, and determined their relationships with body fat distribution. In the animal study, biliverdin (20 mg/kg daily) was orally administered to high-fat diet (HFD)-induced obese (DIO) mice for 2 weeks, after which intraperitoneal insulin tolerance testing was performed. Then, adipocyte area, adipocytokine expression, and macrophage polarization were evaluated in epididymal adipose tissues.ResultsIn the clinical study, univariate analysis showed that a lower bilirubin concentration was significantly correlated with higher body mass index, waist circumference, triglyceride, uric acid, creatinine, visceral fat area and lower HDL-C. In multivariate analyses, bilirubin concentration significantly correlated with diastolic blood pressure, creatinine, and visceral fat area. However, there was no association between bilirubin concentration and subcutaneous fat area. In the animal study, DIO mice treated with biliverdin had smaller adipocytes than untreated DIO mice and biliverdin improved HFD-induced insulin resistance. Biliverdin treatment reversed the higher gene expression of Cd11c, encoding an M1 macrophage marker, and Tnfa, encoding the proinflammatory cytokine tumor necrosis factor-α, in the adipose tissues of DIO mice. These data suggest biliverdin administration alleviates insulin resistance by ameliorating inflammation and the dysregulation of adipocytokine expression in adipose tissues of DIO mice.ConclusionsBilirubin may protect against insulin resistance by ameliorating visceral obesity and adipose tissue inflammation.

Pamidronate decreases bilirubin-impaired cell death and improves dentinogenic dysfunction of stem cells from human deciduous teeth

BackgroundHyperbilirubinemia that occurs in pediatric liver diseases such as biliary atresia can result in the development of not only jaundice in the brain, eyes, and skin, but also tooth abnormalities including green pigmentation and dentin hypoplasia in the developing teeth. However, hyperbilirubinemia-induced tooth impairments remain after liver transplantation. No effective dental management to prevent hyperbilirubinemia-induced tooth impairments has been established.MethodsIn this study, we focused on pamidronate, which is used to treat pediatric osteopenia, and investigated its effects on hyperbilirubinemia-induced tooth impairments. We cultured stem cells from human exfoliated deciduous teeth (SHED) under high and low concentrations of unconjugated bilirubin in the presence or absence of pamidronate. We then analyzed the effects of pamidronate on the cell death, associated signal pathways, and dentinogenic function in SHED.ResultsWe demonstrated that a high concentration of unconjugated bilirubin induced cell death in SHED via the mitochondrial pathway, and this was associated with the suppression of AKT and extracellular signal-related kinase 1 and 2 (ERK1/2) signal pathways and activation of the nuclear factor kappa B (NF-κB) signal pathway. The high concentration of unconjugated bilirubin impaired the in vitro and in vivo dentinogenic capacity of SHED, but not the low concentration. We then demonstrated that pamidronate decreased the bilirubin-induced cell death in SHED via the altered AKT, ERK1/2, and NF-κB signal pathways and recovered the bilirubin-impaired dentinogenic function of SHED.ConclusionsOur findings suggest that pamidronate may prevent tooth abnormalities in pediatric patients with hyperbilirubinemia.

Limitations and opportunities of whole blood bilirubin measurements by GEM premier 4000\xae

BackgroundNeonatal hyperbilirubinemia has traditionally been screened by either total serum bilirubin or transcutaneous bilirubin. Whole blood bilirubin (TwB) by the GEM Premier 4000® blood gas analyzer (GEM) is a relatively new technology and it provides fast bilirubin results with a small sample volume and can measure co-oximetry and other analytes. Our clinical study was to evaluate the reliability of TwB measured by the GEM and identify analytical and clinical factors that may contribute to possible bias.Methods440 consecutive healthy newborn samples that had plasma bilirubin ordered for neonatal hyperbilirubinemia screening were included. TwB was first measured using the GEM, after which the remainder of the blood was spun and plasma neonatal bilirubin was measured using the VITROS 5600® (VITROS).Results62 samples (14%) were excluded from analysis due to failure in obtaining GEM results. Passing-Bablok regression suggested that the GEM results were negatively biased at low concentrations of bilirubin and positively biased at higher concentrations relative to the VITROS results (y = 1.43x-61.13). Bland-Altman plots showed an overall negative bias of the GEM bilirubin with a wide range of differences compared to VITROS. Both hemoglobin concentration and hemolysis affected the accuracy of the GEM results. Clinically, male infants had higher mean bilirubin levels, and infants delivered by caesarean section had lower hemoglobin levels. When comparing the number of results below the 40th percentile and above the 95th percentile cut-offs in the Bhutani nomogram which would trigger discharge or treatment, GEM bilirubin exhibited poor sensitivity and poor specificity in contrast to VITROS bilirubin.ConclusionsAn imperfect correlation was observed between whole blood bilirubin measured on the GEM4000® and plasma bilirubin on the VITROS 5600®. The contributors to the observed differences between the two instruments were specimen hemolysis and the accuracy of hemoglobin measurements, the latter of which affects the calculation of plasma-equivalent bilirubin. Additionally, the lack of standardization of total bilirubin calibration particularly in newborn specimens, may also account for some of the disagreement in results.

Low concentrations of bilirubin inhibit activation of hepatic stellate cells in vitro

Hepatic stellate cell (HSC) activation serves a key role in liver fibrosis, and is associated with chronic liver diseases. Bilirubin, a product of heme degradation, has been demonstrated to have antioxidant properties. The present study investigated the effects of physiological concentrations of bilirubin on rat HSC activation. Rat HSCs were isolated and cultured for several generations to induce activation. The activated HSCs were subsequently treated with 0, 1, 10 or 20 mg/l bilirubin and assayed for parameters of cell activation. As the bilirubin concentration increased, HSCs demonstrated reduced production of reactive oxygen species, reduced protein expression levels of α-smooth muscle actin, a decreased mRNA expression ratio of tissue inhibitor of matrix metalloproteinase-1/matrix metalloproteinase-2, decreased proliferation and increased apoptosis. In conclusion, elevated bilirubin levels, within its physiological concentration range, appeared to inhibit HSC activation. These findings suggested a potential role for bilirubin in the treatment of fibrosis that requires further investigation.

Increased mortality in critically ill patients with mild or moderate hyperbilirubinemia

PurposeIncreased bilirubin concentrations may be related to outcome, but this has not been well studied. We evaluated the relationship between total serum bilirubin levels and outcome in critically ill patients. Materials and methodsData were analyzed from adult critically ill patients included in a 1-day international prevalence study after excluding those with an obvious underlying cause of hyperbilirubinemia. ResultsSerum bilirubin concentrations were >1 mg/dL in 2803 (31%) of 8973 patients, and these patients had higher mortality rates than patients with lower bilirubin concentrations (30% vs 21%, P<.01). For serum bilirubin values of 1.1-6 mg/dL, there was a linear increase in crude mortality (R2=0.96), with the highest hospital mortality (42%) in patients with bilirubin concentrations between 3.7 and 6.0 mg/dL. There was no further increase in the mortality rates for patients with bilirubin concentrations >6 mg/dL. A serum bilirubin concentration >1 mg/dL was an independent risk factor for mortality in multilevel analysis. ConclusionsHyperbilirubinemia without a recognized cause was common and independently associated with increased mortality. There was a linear correlation of mortality with bilirubin concentration for values between 1 and 6 mg/dL but not for higher values.

Determination of Structural and Morphological Parameters of Human Bulbar Conjunctiva from Optical Diffuse Reflectance Spectra

We have developed a method for on-the-fl y retrieval of the volume concentration of blood vessels, the average diameter of the blood vessels, the blood oxygenation level, and the molar concentrations of chromophores in the bulbar conjunctiva from its diffuse reflectance spectra, measured when the radiation delivery and detection channels are spatially separated. The relationship between the diffuse reflectance spectrum of the conjunctiva and its unknown parameters is described in terms of an analytical model, constructed on the basis of a highly accurate approximation analog of the Monte Carlo method. We have studied the effect of localization of hemoglobin in erythrocytes and localization of erythrocytes in the blood vessels on the power of the retrieval of structural and morphological parameters for the conjunctiva. We developed a device for obtaining video images of the conjunctiva and contactless measurements of its diffuse reflectance spectrum. By comparing simulated diffuse reflectance spectra of the conjunctiva with the experimental measurements, we established a set of chromophores which must be taken into account in the model for reproducing the experimental data within the measurement error. We observed absorption bands for neuroglobin in the experimental spectra, and provided a theoretical basis for the possibility of determining its absolute concentrations in the conjunctiva. We have shown that our method can detect low bilirubin concentrations in blood.

Life-long correction of hyperbilirubinemia with a neonatal liver-specific AAV-mediated gene transfer in a lethal mouse model of Crigler-Najjar Syndrome.

Null mutations in the UGT1A1 gene result in Crigler-Najjar syndrome type I (CNSI), characterized by severe hyperbilirubinemia and constant risk of developing neurological damage. Phototherapy treatment lowers plasma bilirubin levels, but its efficacy is limited and liver transplantation is required. To find alternative therapies, we applied AAV liver-specific gene therapy to a lethal mouse model of CNSI. We demonstrated that a single neonatal hUGT1A1 gene transfer was successful and the therapeutic effect lasted up to 17 months postinjection. The therapeutic effect was mediated by the presence of transcriptionally active double-stranded episomes. We also compared the efficacy of two different gene therapy approaches: liver versus skeletal muscle transgene expression. We observed that 5-8% of normal liver expression and activity levels were sufficient to significantly reduce bilirubin levels and maintain lifelong low plasma bilirubin concentration (3.1±1.5 mg/dl). In contrast, skeletal muscle was not able to efficiently lower bilirubin (6.4±2.0 mg/dl), despite 20-30% of hUgt1a1 expression levels, compared with normal liver. We propose that this remarkable difference in gene therapy efficacy could be related to the absence of the Mrp2 and Mrp3 transporters of conjugated bilirubin in muscle. Taken together, our data support the concept that liver is the best organ for efficient and long-term CNSI gene therapy, and suggest that the use of extra-hepatic tissues should be coupled to the presence of bilirubin transporters.

Transcutaneous screening for hyperbilirubinemia in neonates

Description of the condition Hyperbilirubinemia is a term used to describe elevated levels of bilirubin in the blood. In newborns, hyperbilirubinemia becomes clinically apparent as jaundice, a yellow coloration of the skin and the sclera, at serum bilirubin levels > 5 mg/dL (Porter 2002). Hyperbilirubinemia is very common in both term and preterm newborn infants (occurring in around 60% of newborns) and results from a predisposition to produce bilirubin and the newborn’s limited ability to excrete it (Lauer 2011). Jaundice or hyperbilirubinemia is the most common cause of hospital readmission in the neonatal period (Soskolne 1996; Maisels 1998; Escobar 2005). Most cases of newborn jaundice are mild and self limited. However, in rare cases, infants can have very high levels of bilirubin that can lead to bilirubin encephalopathy and kernicterus (Newman 2006). The threshold concentration of bilirubin and/or the duration of hyperbilirubinemia responsible for causing kernicterus injury in newborn infants is not known (Dennery 2004). Low concentrations of bilirubin may have some antioxidant benefits, suggesting that bilirubin should not be completely eliminated. Studies from developed countries estimate the incidence of kernicterus to range from about 0.4 to 2 per 100,000 (Sgro 2006; Manning 2007; Burke 2009). However, studies from developing countries suggest that the incidence may be much higher (Nair 2003; Owa 2009). The acute phase signs of kernicterus are poor feeding, lethargy, high-pitched cry, hypertonia or hypotonia, opisthotonos and seizures. The chronic manifestations include athetoid cerebral palsy, motor delay, gaze palsy, dental dysplasia, mental retardation and sensorineural hearing loss (AAP 2004). Current treatments for hyperbilirubinemia include phototherapy and exchange transfusion (usually reserved for severe cases of hyperbilirubinemia) (NICE 2010).

Behavioral and clinical correlates of serum bilirubin concentrations in Japanese men and women.

BackgroundA considerable interest has been drawn to potential protective effects of bilirubin against oxidative stress-related diseases. Smoking is known to be associated with lower concentrations of serum bilirubin, but other behavioral correlates of serum bilirubin have not been well studied. In this cross-sectional study, we examined the associations of behavioral and clinical factors with serum total bilirubin in Japanese men and women.MethodThe study subjects comprised of 4802 men and 6414 women aged 49–76 years who participated in the baseline survey of an ongoing cohort study on lifestyle-related diseases in Fukuoka, Japan. With consideration to time of the day of blood sampling and fasting hours, the associations with smoking, alcohol intake, body mass index, physical activity, coffee, tea, blood pressure, glycated hemoglobin (HbA1c), HDL cholesterol and non-HDL cholesterol with serum bilirubin were evaluated by analysis of covariance and multiple linear regression analysis.ResultsWhile smoking was negatively associated with serum bilirubin, alcohol consumption was positively associated with serum bilirubin in both men and women. Coffee consumption was associated with lower bilirubin concentrations in both sexes. In the multiple linear regression analysis, HDL cholesterol was positively and HbA1c was negatively associated with bilirubin in both men and women, and the associations were more evident in women.ConclusionSmoking, alcohol use and coffee consumption were important behavioral correlates of serum bilirubin in Japanese men and women. Serum HDL cholesterol was a measurable clinical correlate of bilirubin in women.

Plasma total bilirubin levels predict amputation events in type 2 diabetes mellitus: the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study

Bilirubin has antioxidant and anti-inflammatory activities. Previous studies demonstrated that higher bilirubin levels were associated with reduced prevalence of peripheral arterial disease (PAD). However, the relationship between bilirubin and lower-limb amputation, a consequence of PAD, is currently unknown. We hypothesised that, in patients with type 2 diabetes, bilirubin concentrations may inversely associate with lower-limb amputation. The relationship between baseline plasma total bilirubin levels and amputation events was analysed in 9,795 type 2 diabetic patients from the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study. The analysis plan was pre-specified. Lower-limb amputation was adjudicated blinded to treatment allocation. Relevant clinical and biochemical data were available for analyses. Amputation was a pre-specified tertiary endpoint. Bilirubin concentrations were significantly inversely associated with lower-limb amputation, with a greater than threefold risk gradient across levels. Individuals with lower bilirubin concentrations had a higher risk for first amputation (HR 1.38 per 5μmol/l decrease in bilirubin concentration, 95% CI 1.07, 1.79, p = 0.013). The same association persisted after adjustment for baseline variables, including age, height, smoking status, γ-glutamyltransferase level, HbA1c, trial treatment allocation (placebo vs fenofibrate), as well as previous PAD, non-PAD cardiovascular disease, amputation or diabetic skin ulcer, neuropathy, nephropathy and diabetic retinopathy (HR 1.38 per 5μmol/l decrease in bilirubin concentration, 95% CI 1.05, 1.81, p = 0.019). Our results identify a significant inverse relationship between bilirubin levels and total lower-limb amputation, driven by major amputation. Our data raise the hypothesis that bilirubin may protect against amputation in type 2 diabetes.

Measuring Free Bilirubin: The Clinical Perspective

In 1959, Gerald Odell first proposed that albumin and tissue compete for binding bilirubin and that this competition is mediated by a very low concentration of free bilirubin (Bf)2 (bilirubin not bound to plasma proteins). He argued that displacement of albumin-bound bilirubin by binding competitors could explain the reported high incidence of kernicterus in premature infants receiving sulfonamide prophylaxis (1). This sentinel publication led to a flurry of proposed binding tests, most of which were nonspecific competitive-binding assays, until 1974, when Jacobsen and Wennberg presented a method for measuring Bf in infant plasma that was based on the observation that only unbound bilirubin serves as a substrate for enzymatic oxidation by horseradish peroxidase (2). Several studies from Japan, where the peroxidase assay had been adapted to a semiautomated instrument, identified a clear relationship of Bf with acute neurotoxicity in premature infants (3) and with acute auditory impairment in term infants (4). Enthusiasm was tempered in the US by a perceived difficulty in performing the assay and by confusion regarding the poor correlation between Bf and outcome in premature babies who died with kernicterus at very low total bilirubin (Bt) concentrations (5). The reported high incidence of death of infants with kernicterus was isolated to specific care centers: Very high Bf/Bt ratios in affected infants indicated very poor binding, and the phenomenon of lethal kernicterus at low Bt concentrations largely disappeared after cessation of benzyl alcohol use as a preservative in multiple-dose vials or solutions for parenteral therapy (6). Kernicterus is still occasionally observed at low Bt concentrations in babies with sepsis or …

Cigarette Smoking and Serum Bilirubin Subtypes in Healthy Korean Men: The Korea Medical Institute Study

ObjectivesCigarette smoking is a modifiable risk factor for cardiovascular disease. Bilirubin is a potent antioxidant and its concentration decreases in smokers. However, studies about the association between cigarette smoking and bilirubin are scarce and most are limited to total bilirubin. Additionally, bilirubin is highly related to hemoglobin. Therefore, this study evaluates the association between bilirubin subtypes and cigarette smoking in healthy Korean men independently of hemoglobin.MethodsThis study included 48 040 Korean men aged 30 to 87 years who visited the Korea Medical Institute for routine health examinations from January to December, 2007. The association of smoking with total, direct, and indirect bilirubin was assessed by logistic regression analysis taking into consideration differences in subjects and smoking characteristics.ResultsCurrent smokers had lower bilirubin concentrations than never-smokers and ex-smokers. Smoking amount and duration were inversely significantly associated with total, direct, and indirect bilirubin. In a multivariable adjusted model, compared to never-smokers, the odds ratios (ORs) and 95% confidence intervals (CIs) of current smokers with the highest number of pack-years were 1.7 (1.6 to 1.9) for total, 1.5 (1.4 to 1.6) for direct, and 1.7 (1.6 to 1.9) for indirect bilirubin. After further adjustment for hemoglobin, this association became stronger (OR [95% CI], 2.1 [1.9 to 2.2] for total; 1.9 [1.8 to 2.0] for direct; 2.0 [1.9 to 2.2] for indirect bilirubin).ConclusionsIn this study, bilirubin subtypes are inversely associated with smoking status, smoking amount, and smoking duration in healthy Korean men independently of hemoglobin. Further studies are needed to investigate this association in healthy Korean women.

Serum bilirubin levels in familial hypercholesterolemia: a new risk marker for cardiovascular disease?

Low concentrations of bilirubin are associated with an increased risk for cardiovascular disease (CVD). Possibly, bilirubin exerts its effect through the protection of LDL from oxidation. Therefore, we examined whether low bilirubin might also be a risk marker for CVD in patients with familial hypercholesterolemia (FH) and whether statins influence serum bilirubin levels. Patients with FH were recruited from 37 lipid clinics. After a washout period of 6 weeks, all patients were started on monotherapy with simvastatin 80 mg for a period of two years. A total of 514 patients were enrolled. Bilirubin at baseline was inversely associated with the presence of CVD, also after adjustment for age, gender, presence of hypertension, and HDL cholesterol levels. Moreover, bilirubin levels were significantly raised, by 7%, from 10.0 to 10.8 μmol/L after treatment with simvastatin 80 mg. We hypothesize first that high bilirubin levels might protect patients with FH from CVD. Furthermore, bilirubin levels were significantly increased after treatment with simvastatin 80 mg, independent of changes in liver enzymes, which might confer additional protection against CVD. Whether this is also true for lower doses of simvastatin or for other statins remains to be investigated.

Cellular antioxidant activity of bilirubin in the human endothelial cell line EA.hy 926 is mediated by bilitranslocase

. The latter can be ascribed to an efficientamplification cycle whereby bilirubin, acting as antioxi-dant, is itself oxidized to biliverdin and then recycled backto bilirubin by NADPH-dependent biliverdin reductase.Bilitranslocase, a bilirubin-specific membrane carrier thatmediates cellular uptake of bilirubin, has recently beenfound in the vascular endothelium. However, the levels ofalbumin-free bilirubin in plasma and tissues are only 10to 50 nM. Therefore, the objective of this study was to elu-cidate the antioxidant activity of low concentrations ofbilirubin and the involvement of bilitranslocase-medi-ated plasma membrane transport in human endothelialcells.

Cruciferous Vegetable Feeding Alters UGT1A1 Activity: Diet- and Genotype-Dependent Changes in Serum Bilirubin in a Controlled Feeding Trial

Chemoprevention by isothiocyanates from cruciferous vegetables occurs partly through up-regulation of phase II conjugating enzymes, such as UDP-glucuronosyltransferases (UGT). UGT1A1 glucuronidates bilirubin, estrogens, and several dietary carcinogens. The UGT1A1*28 polymorphism reduces transcription compared with the wild-type, resulting in decreased enzyme activity. Isothiocyanates are metabolized by glutathione S-transferases (GST); variants may alter isothiocyanate clearance such that response to crucifers may vary by genotype. We evaluated, in a randomized, controlled, crossover feeding trial in humans (n = 70), three test diets (single- and double-"dose" cruciferous and cruciferous plus apiaceous) compared with a fruit and vegetable-free basal diet. We measured serum bilirubin concentrations on days 0, 7, 11, and 14 of each 2-week feeding period to monitor UGT1A1 activity and determined effects of UGT1A1*28 and GSTM1/GSTT1-null variants on response. Aggregate bilirubin response to all vegetable-containing diets was statistically significantly lower compared with the basal diet (P < 0.03 for all). Within each UGT1A1 genotype, lower bilirubin concentrations were seen in *1/*1 in both single- and double-dose cruciferous diets compared with basal (P < 0.03 for both); *1/*28 in double-dose cruciferous and cruciferous plus apiaceous compared with basal, and cruciferous plus apiaceous compared with single-dose cruciferous (P < 0.02 for all); and *28/*28 in all vegetable-containing diets compared with basal (P < 0.02 for all). Evaluation of the effects of diet stratified by GST genotype revealed some statistically significant genotypic differences; however, the magnitude was similar and not statistically significant between genotypes. These results may have implications for altering carcinogen metabolism through dietary intervention, particularly among UGT1A1*28/*28 individuals.