Effects of bilirubin on neutrophil responses in newborn infants

Neonatal asphyxia as an inflammatory disease: Reactive oxygen species and cytokines

Neonatologists resuscitate asphyxiated neonates by every available means, including positive ventilation, oxygen therapy, and drugs. Asphyxiated neonates sometimes present symptoms that mimic those of inflammation, such as fever and edema. The main pathophysiology of the asphyxia is inflammation caused by hypoxic-ischemic reperfusion. At birth or in the perinatal period, neonates may suffer several, hypoxic insults, which can activate inflammatory cells and inflammatory mediator production leading to the release of larger quantities of reactive oxygen species (ROS). This in turn triggers the production of oxygen stress-induced high mobility group box-1 (HMGB-1), an endogenous damage-associated molecular patterns (DAMPs) protein bound to toll-like receptor (TLR) -4, which activates nuclear factor-kappa B (NF-κB), resulting in the production of excess inflammatory mediators. ROS and inflammatory mediators are produced not only in activated inflammatory cells but also in non-immune cells, such as endothelial cells. Hypothermia inhibits pro-inflammatory mediators. A combination therapy of hypothermia and medications, such as erythropoietin and melatonin, is attracting attention now. These medications have both anti-oxidant and anti-inflammatory effects. As the inflammatory response and oxidative stress play a critical role in the pathophysiology of neonatal asphyxia, these drugs may contribute to improving patient outcomes.

Electrochemical Sensor for Bilirubin Detection Using Paper-Based Screen-Printed Electrodes Functionalized with Silver Nanoparticles

A notable diagnostic for the detection of hemolytic diseases is bilirubin, a by-product of haemoglobin breakdown. The concentration of bilirubin ranges from 0.3 to 1.9 mg in 100 mL of blood. Low blood bilirubin levels are associated with a greater risk of coronary heart disease and anaemia. Hyperbilirubinemia results from a serum bilirubin level of more than 2.5 mg/100 mL. Therefore, it is very crucial to check the serum bilirubin level. Analytical equipment for point-of-care testing must be portable, small, and affordable. A unique method is used to detect bilirubin selectively using paper-based screen-printed carbon electrodes that were covalently linked with nanoparticles, that serves as a key biomarker for jaundice. In order to create an electrochemical biosensor, bilirubin oxidase was immobilised on electrodes modified with AgNPs. The morphology of Ag nanoparticles in terms of size and shape was determined using both UV- Vis Spectroscopy and transmission electron microscopy (TEM). The biosensor's analytical response was assessed using potentiostat (Cyclic voltammetry (CV) and linear sweep voltammetry (LSV)). The developed paper-based sensor provided optimum feedback and a broad linear range of 1 to 9 µg/mL for bilirubin, with a lower LOD of 1 µg/mL. Through tests of bilirubin in artificial blood serum, the viability is confirmed. The method that is being used makes it possible to create and use an inexpensive, miniature electrochemical sensor.

Network Pharmacology-Based Analysis on the Potential Biological Mechanisms of Yinzhihuang Oral Liquid in Treating Neonatal Hyperbilirubinemia

Objective

Neonatal hyperbilirubinemia is caused by the excessive production of bilirubin and decreased excretion ability in the neonatal period. It leads to a concentration of blood bilirubin that exceeds a certain threshold. Yinzhihuang oral liquid (YZH) is a traditional Chinese medicine mixture used in the treatment of neonatal hyperbilirubinemia in China. This article systematically explores the pharmacological mechanisms by which YZH acts in the treatment of neonatal hyperbilirubinemia through network pharmacology at the molecular level.

Methods

We adopted the method of network pharmacology, which includes active component prescreening, target gene prediction, gene enrichment analysis, and network analysis.

Results

According to the network pharmacological analysis, 8 genes (STAT3, AKT1, MAPK14, JUN, TP53, MAPK3, ESR1, and RELA) may be targets of YZH in the treatment of neonatal hyperbilirubinemia. In addition, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that YZH may regulate antioxidation, modulate lipid metabolism, and have anti-infective properties.

Conclusion

In this study, the pharmacological action and molecular mechanisms of YZH were predicted as a whole. It was found that YZH is a promising drug for treating oxidative stress due to bilirubin, as it reduces immunosuppression and helps to eliminate virus infection.

The mildly decreased preoperative bilirubin level is a risk factor for periprosthetic joint infection after total hip and knee arthroplasty

BACKGROUND

Many serologic markers are routinely tested prior to joint arthroplasty, but only few are commonly used to guide surgeons in determining patients most at risk of periprosthetic joint infection (PJI). The objective of this study was to investigate the association between preoperative bilirubin level and PJI after primary hip and knee arthroplasty.

METHODS

A retrospective analysis was performed on patients undergoing revision hip and knee arthroplasty at our hospital from January 2016 to December 2019. Laboratory biomarkers were collected before the primary arthroplasty, as well as general patient information. The association between the above serologic markers and postoperative PJI was analyzed.

RESULTS

A total of 72 patients (30 hips/42 knees) were analyzed, including 39 patients with PJI and 33 patients without PJI. Except for total bilirubin (TB) and direct bilirubin (DB), there was no significant difference between the remaining laboratory biomarkers. The preoperative TB and DB in the PJI group were 10.84 ± 0.61 μmol/L and 3.07 ± 0.19 μmol/L, respectively, which were lower than those in the non-PJI group (14.68 ± 0.75 μmol/L and 4.70 ± 0.39 μmol/L, P < 0.001). The area under the curve (AUC) of preoperative TB to predict PJI was 0.755 (P < 0.001, cutoff = 11.55 μmol/L, sensitivity = 66.67%, specificity = 75.76%). Meanwhile, the AUC of preoperative DB was 0.760 (P < 0.001, cutoff = 4.00 μmol/L, sensitivity = 84.62%, specificity = 54.45%).

CONCLUSIONS

The serum levels of TB and DB before the primary arthroplasty were lower in PJI patients than in non-PJI patients, and the preoperative values lower than 11.55 μmol/L and 4.00 μmol/L could be considered as a risk factor for postoperative PJI.

Bilirubin as a Therapeutic Molecule: Challenges and Opportunities

There is strong evidence that serum free bilirubin concentration has significant effects on morbidity and mortality in the most significant health conditions of our times, including cardiovascular disease, diabetes, and obesity/metabolic syndrome. Supplementation of bilirubin in animal and experimental models has reproduced these protective effects, but several factors have slowed the application bilirubin as a therapeutic agent in human patients. Bilirubin is poorly soluble in water, and is a complex molecule that is difficult to synthesize. Current sources of this molecule are animal-derived, creating concerns regarding the risk of virus or prion transmission. However, recent developments in nanoparticle drug delivery, biosynthetic strategies, and drug synthesis have opened new avenues for applying bilirubin as a pharmaceutical agent. This article reviews the chemistry and physiology of bilirubin, potential clinical applications and summarizes current strategies for safe and efficient drug delivery.

Bilirubin as a metabolic hormone: the physiological relevance of low levels

Recent research on bilirubin, a historically well-known waste product of heme catabolism, suggests an entirely new function as a metabolic hormone that drives gene transcription by nuclear receptors. Studies are now revealing that low plasma bilirubin levels, defined as "hypobilirubinemia," are a possible new pathology analogous to the other end of the spectrum of extreme hyperbilirubinemia seen in patients with jaundice and liver dysfunction. Hypobilirubinemia is most commonly seen in patients with metabolic dysfunction, which may lead to cardiovascular complications and possibly stroke. We address the clinical significance of low bilirubin levels. A better understanding of bilirubin's hormonal function may explain why hypobilirubinemia might be deleterious. We present mechanisms by which bilirubin may be protective at mildly elevated levels and research directions that could generate treatment possibilities for patients with hypobilirubinemia, such as targeting of pathways that regulate its production or turnover or the newly designed bilirubin nanoparticles. Our review here calls for a shift in the perspective of an old molecule that could benefit millions of patients with hypobilirubinemia.

The Anti-Inflammatory Role of Bilirubin on "Two-Hit" Sepsis Animal Model

Introduction: Bilirubin is a product of the heme catabolism pathway, and it is excreted in bile and removed from the body through the urine. Bilirubin has potent antioxidant properties but also plays a role in anti-inflammation by protecting the body against endotoxin-induced lung inflammation, down-regulating the expression of adhesion molecules, and inhibiting the infiltration of inflammatory cells. Thus, bilirubin is a promising agent that could use in inflammation disease treatment. The application of bilirubin on the “two-hit” sepsis animal model has been, to date, unknown. Methods: we used lipopolysaccharide to induce initial insults in C57BL/6 mice. After 24 h, mice underwent cecal ligation and puncture to induce the “two-hit” sepsis model. Next, mice were administered 30 mg/kg bilirubin and we observed an improvement. Results: We observed that bilirubin inhibited the expression of pro-inflammatory cytokines, while the levels of anti-inflammatory cytokines were significantly augmented in the lung. Bilirubin improved the survival rate in the sepsis model. Furthermore, we suggest that bilirubin can modulate the accumulation of T-regulatory cells and myeloid-derived suppressor cells. Notably, bilirubin suppressed the activation and functions of T-cells. Conclusions: These results clarified that bilirubin might improve tissue injury in sepsis through anti-inflammatory mechanisms.

Mildly decreased preoperative bilirubin levels are associated with infections after shoulder and knee arthroplasty

Increasing numbers of arthroplasties are also accompanied by postoperative infections. The main purpose was to evaluate preoperative serum bilirubin levels between patients with and without infections after shoulder and knee arthroplasties. For this retrospective case-control single-center study, a total of 108 patients were extracted from a prospectively collected database. Eighteen patients with infections after shoulder (n = 8) and knee (n = 10) arthroplasty were matched by age, gender, and implant type in a 1:5-scenario to 90 patients (40 shoulders and 50 knees) without postoperative infection. Demographic data, preoperative blood parameters, and postoperative infection-related outcomes were evaluated. Total bilirubin was the only preoperative parameter significantly different between the infection (8.21 ± 3.25 μmol/L or 0.48 ± 0.19 mg/dL) and noninfection (10.78 ± 4.62 μmol/L or 0.63 ± 0.27 mg/dL; P = .014) group, while C-reactive protein and other liver parameters were similar between the groups. Significantly more controls (92.1%) had preoperative bilirubin levels above 8.72 μmol/L or 0.51 mg/dL than cases (7.9%; P = .007). The 5-year infection survival-rate was 65.6% for patients with preoperative bilirubin levels < 8.72 μmol/L or < 0.51 mg/dL and 91.2% with ≥ 8.72 μmol/L or ≥ 0.51 mg/dL. Mildly decreased preoperative bilirubin levels with a cutoff at 8.72 μmol/L or 0.51 mg/dL were significantly associated to patients with infections after shoulder and knee arthroplasty. There were no differences in other blood parameters or comorbidities between patients with infections and their matched-controls.

Associations between Neonatal Serum Bilirubin and Childhood Obesity in Term Infants

Inverse correlations between serum bilirubin level and obesity had been reported in adults. We aimed to investigate the associations between neonatal hyperbilirubinemia and childhood obesity. Data was obtained from the U.S. Collaborative Perinatal Project (CPP), a multicenter study from 1959 to 1976. Data of serum bilirubin in term newborns were used to observe the association with obesity at age of 7 years. Logistic regression models were performed to calculate adjusted odds ratios (aORs) for obesity. For children from the same mother sharing similar factors, Generalized Estimating Equation (GEE) model was used to correct for intracluster correlation. Relative to newborns with total serum bilirubin (TSB) < 3 mg/dl, there are lower risks for obesity in those with 3 mg/dl ≤ TSB < 6 mg/dl (aOR 0.91; 95%CI 0.81, 1.02), 6 mg/dl ≤ TSB < 9 mg/dl (aOR 0.88; 95%CI 0.78, 0.99), 9 mg/dl ≤ TSB<13 mg/dl (aOR 0.83; 95%CI 0.71, 0.98). By stratifying for subtypes of bilirubin, the inverse correlations only existed in exposure to unconjugated bilirubin. By using the GEE model correcting for intracluster correlations, the results are consistent. In summary, exposure to bilirubin up to 13 mg/dl is inversely associated with obesity at the age of 7 years in term infants.

Brief Report: Hyperbilirubinemia Is Associated With a Decreased Risk of Carotid Atherosclerosis in HIV-Infected Patients on Virological Suppression

OBJECTIVE

To investigate the association between total, direct, and indirect bilirubin and the presence of carotid lesions in a large sample of HIV-1-infected patients on virological suppression.

DESIGN

Retrospective study on adult HIV-1-infected patients, with a carotid ultrasound (CUS) examination performed between January 2008 and August 2016, with HIV-RNA <50 copies per milliliter at CUS and without previous cardiovascular events.

METHODS

Intima media thickness was measured in 4 segments: carotid common artery and bifurcation on the left and right sides. Carotid lesion was defined as an intima media thickness ≥1.5 mm in ≥1 region at CUS. Patients were classified as: normal if all bilirubin values before CUS were below the upper normal limit and with hyperbilirubinemia if ≥1 bilirubin value above upper normal limit before CUS was recorded. Multivariate logistic regression was used to determine whether hyperbilirubinemia showed association with the presence of ≥1 carotid lesion, after adjusting for confounding factors.

RESULTS

Overall, 903 patients were evaluated, 511 with ≥1 and 392 without carotid lesions. At multivariate analysis, total [adjusted odds ratio (95% confidence interval) 0.57 (0.36 to 0.90), P = 0.016] and indirect hyperbilirubinemia before CUS [adjusted odds ratio (95% confidence interval) 0.62 (0.40 to 0.97), P = 0.036] were associated with a lower risk of carotid lesions in addition to younger age, negative hepatitis C virus antibodies, higher nadir CD4, lower low-density lipoprotein cholesterol, higher high-density lipoprotein cholesterol, lower triglycerides, and no use of statin; no effect of atazanavir treatment on carotid lesions was detected.

CONCLUSIONS

In HIV-1-treated patients, total or indirect hyperbilirubinemia was likely associated with the absence of carotid lesions.

Heme Catabolic Pathway in Inflammation and Immune Disorders

In recent years, the heme catabolic pathway is considered to play an important regulatory role in cell protection, apoptosis, inflammation, and other physiological and pathological processes. An appropriate amount of heme forms the basic elements of various life activities, while when released in large quantities, it can induce toxicity by mediating oxidative stress and inflammation. Heme oxygenase (HO) -1 can catabolize free heme into carbon monoxide (CO), ferrous iron, and biliverdin (BV)/bilirubin (BR). The diverse functions of these metabolites in immune systems are fascinating. Decades work shows that administration of degradation products of heme such as CO and BV/BR exerts protective activities in systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), multiple sclerosis (MS) and other immune disorders. This review elaborates the molecular and biochemical characterization of heme catabolic pathway, discusses the signal transduction and immunomodulatory mechanism in inflammation and summarizes the promising therapeutic strategies based on this pathway in inflammatory and immune disorders.

Effects of Soybean Lipid Infusion on Unbound Free Fatty Acids and Unbound Bilirubin in Preterm Infants

OBJECTIVE

To assess the effects of a soybean lipid emulsion infusions on levels of unbound (free) bilirubin (Bf) and unbound free fatty acids (FFAu) as well as changes in Bf and total serum bilirubin (TSB) during phototherapy in infants born preterm.

STUDY DESIGN

Ninety-seven infants born preterm (birth weight: 500-2000 g; gestational age: 23-34 weeks) were enrolled to investigate the effect of 0, 1, 2, and 3 g/kg/d of intralipid infusion on Bf and FFAu. Pre- and postphototherapy TSB, FFAu, and Bf also were analyzed in 91 infants to assess the effects of phototherapy. FFAu levels were measured with the fluorescent probe ADIFAB2 and Bf by the fluorescent Bf sensor BL22P1B11-Rh during intralipid infusion and at start and end of phototherapy. TSB and plasma albumin were measured by the diazo and bromcresol green techniques, respectively. Bilirubin-albumin dissociation constants were calculated based on Bf and plasma albumin.

RESULTS

Bf and FFAu increased with increasing intralipid dosage across all gestational ages. TSB and Bf were correlated significantly when infants received 0 or 1 g/kg/d of intralipid but not at greater doses of intralipid (2 and 3 g/kg/d). Although phototherapy effectively reduced both TSB and Bf in the total phototherapy group (by 32% and 12%, respectively), it reduced TSB, but not Bf, in infants less than 28 weeks of gestation.

CONCLUSIONS

Increasing intralipid doses result in increasing FFAu levels, which are associated with increased Bf independent of TSB. In infants born extremely preterm (<28 weeks of gestation), phototherapy effectively reduces TSB but not Bf.

Bilirubin exposure is associated with neonatal sepsis in the eight days preceding symptoms: a retrospective study

OBJECTIVE

To compare levels of bilirubin (using the area under the curve, AUC) in preterm infants before the onset of sepsis with healthy matched-controls.

METHODS

Preterm infants born between January 2011 and December 2015 with late-onset sepsis were enrolled in our retrospective study and were matched with healthy controls (sex, birth weight and gestational age). Levels of bilirubin were registered in the eight days preceding the onset of sepsis and the AUC was calculated for both groups.

RESULTS

Eighty-eight neonates (44 cases) were studied. GA and BW did not differ between cases and controls. In cases, we found a higher value of AUC (30.7 versus 22.5; p = 0.021).

CONCLUSION

In our retrospective cohort, we found that the levels of bilirubin and the AUC in the first eight days before the onset of sepsis in preterm infants were significantly higher than the healthy controls. These data suggest that the prolonged exposition to high levels of bilirubin could increase the infection susceptibility in preterm infants.

Conjugated Bilirubin Differentially Regulates CD4+ T Effector Cells and T Regulatory Cell Function through Outside-In and Inside-Out Mechanisms: The Effects of HAV Cell Surface Receptor and Intracellular Signaling

We recently reported an immune-modulatory role of conjugated bilirubin (CB) in hepatitis A virus (HAV) infection. During this infection the immune response relies on CD4+ T lymphocytes (TLs) and it may be affected by the interaction of HAV with its cellular receptor (HAVCR1/TIM-1) on T cell surface. How CB might affect T cell function during HAV infection remains to be elucidated. Herein, in vitro stimulation of CD4+ TLs from healthy donors with CB resulted in a decrease in the degree of intracellular tyrosine phosphorylation and an increase in the activity of T regulatory cells (Tregs) expressing HAVCR1/TIM-1. A comparison between CD4+ TLs from healthy donors and HAV-infected patients revealed changes in the TCR signaling pathway relative to changes in CB levels. The proportion of CD4+CD25+ TLs increased in patients with low CB serum levels and an increase in the percentage of Tregs expressing HAVCR1/TIM-1 was found in HAV-infected patients relative to controls. A low frequency of 157insMTTTVP insertion in the viral receptor gene HAVCR1/TIM-1 was found in patients and controls. Our data revealed that, during HAV infection, CB differentially regulates CD4+ TLs and Tregs functions by modulating intracellular pathways and by inducing changes in the proportion of Tregs expressing HAVCR1/TIM-1.

Rethinking the immune properties of bilirubin in viral hepatitis: from bench to bedside

Communication between the immune system and metabolic components can be exemplified by the process of heme catabolism. The immunomodulatory functions of the enzymes, substrates and active products related to catabolism of the heme group have been extensively studied. Bilirubin (BR), the final breakdown product of heme, is primarily considered to be a toxic waste product but has recently been considered to be an immunomodulatory metabolite. Through mechanisms that include intracellular signaling and transcriptional control, BR affects those immune cell functions that regulate cell proliferation, differentiation and apoptosis. During the pathogenesis of viral hepatitis, the heme degradation pathway is disrupted, resulting in changes to normal BR concentrations. These alterations have been previously studied mainly as a consequence of the infection. However, little is known about the potential immunomodulatory role played by BR in the development of infectious hepatocellular diseases. Differences in BR levels in the context of viral hepatitis are likely to provide important insights into the metabolite-mediated mechanisms controlling the immune responses underlying both the long-term persistence of hepatitis C virus (HCV) infection and the resolution of hepatitis A virus (HAV) infection during the acute phase. In this review, the cross-talk between heme catabolism and immune function is described in detail. Special emphasis is given to discoveries that hold promise for identifying immunologic features of metabolic products in the resolution of viral diseases.

Heme oxygenase and the immune system in normal and pathological pregnancies

Normal pregnancy is an immunotolerant state. Many factors, including environmental, socioeconomic, genetic, and immunologic changes by infection and/or other causes of inflammation, may contribute to inter-individual differences resulting in a normal or pathologic pregnancy. In particular, imbalances in the immune system can cause many pregnancy-related diseases, such as infertility, abortions, pre-eclampsia, and preterm labor, which result in maternal/fetal death, prematurity, or small-for-gestational age newborns. New findings imply that myeloid regulatory cells and regulatory T cells (Tregs) may mediate immunotolerance during normal pregnancy. Effector T cells (Teffs) have, in contrast, been implicated to cause adverse pregnancy outcomes. Furthermore, feto-maternal tolerance affects the developing fetus. It has been shown that the Treg/Teff balance affects litter size and adoptive transfer of pregnancy-induced Tregs can prevent fetal rejection in the mouse. Heme oxygenase-1 (HO-1) has a protective role in many conditions through its anti-inflammatory, anti-apoptotic, antioxidative, and anti-proliferative actions. HO-1 is highly expressed in the placenta and plays a role in angiogenesis and placental vascular development and in regulating vascular tone in pregnancy. In addition, HO-1 is a major regulator of immune homeostasis by mediating crosstalk between innate and adaptive immune systems. Moreover, HO-1 can inhibit inflammation-induced phenotypic maturation of immune effector cells and pro-inflammatory cytokine secretion and promote anti-inflammatory cytokine production. HO-1 may also be associated with T-cell activation and can limit immune-based tissue injury by promoting Treg suppression of effector responses. Thus, HO-1 and its byproducts may protect against pregnancy complications by its immunomodulatory effects, and the regulation of HO-1 or its downstream effects has the potential to prevent or treat pregnancy complications and prematurity.

Conjugated bilirubin affects cytokine profiles in hepatitis A virus infection by modulating function of signal transducer and activator of transcription factors

Hepatitis A virus (HAV) infection is the major cause of acute liver failure in paediatric patients. The clinical spectrum of infection is variable, and liver injury is determined by altered hepatic enzyme function and bilirubin concentration. We recently reported differences in cytokine profiles between distinct HAV-induced clinical courses, and bilirubin has been recognized as a potential immune-modulator. However, how bilirubin may affect cytokine profiles underlying the variability in the course of infection has not been determined. Herein, we used a transcription factor (TF) binding site identification approach to retrospectively analyse cytokine expression in HAV-infected children and to predict the entire set of TFs associated with the expression of specific cytokine profiles. The results suggested that modulation of the activity of signal transducers and activators of transcription proteins (STATs) may play a central role during HAV infection. This led us to compare the degree of STAT phosphorylation in peripheral blood lymphoid cells (PBLCs) from paediatric patients with distinct levels of conjugated bilirubin (CB). Low CB levels in sera were associated with increased STAT-1 and STAT-5 phosphorylation. A positive correlation was observed between the serum interleukin-6 (IL-6) content and CB values, whereas higher levels of CB correlated with reduced serum IL-8 values and with a reduction in the proportion of PBLCs positive for STAT-5 phosphorylation. When CB was used to stimulate patients' PBLCs in vitro, the levels of IL-6 and tumour necrosis factor-α were increased. The data showed that bilirubin plays a role in STAT function and affects cytokine profile expression during HAV infection.

Body fat percentage is a major determinant of total bilirubin independently of UGT1A1*28 polymorphism in young obese

Objectives

Bilirubin has potential antioxidant and anti-inflammatory properties. The UGT1A1*28 polymorphism (TA repeats in the promoter region) is a major determinant of bilirubin levels and recent evidence suggests that raised adiposity may also be a contributing factor. We aimed to study the interaction between UGT1A1 polymorphism, hematological and anthropometric variables with total bilirubin levels in young individuals.

Methods

350 obese (mean age of 11.6 years; 52% females) and 79 controls (mean age of 10.5 years; 59% females) were included. Total bilirubin and C-reactive protein (CRP) plasma levels, hemogram, anthropometric data and UGT1A1 polymorphism were determined. In a subgroup of 74 obese and 40 controls body composition was analyzed by dual-energy X-ray absorptiometry.

Results

The UGT1A1 genotype frequencies were 49.9%, 42.7% and 7.5% for 6/6, 6/7 and 7/7 genotypes, respectively. Patients with 7/7 genotype presented the highest total bilirubin levels, followed by 6/7 and 6/6 genotypes. Compared to controls, obese patients presented higher erythrocyte count, hematocrit, hemoglobin and CRP levels, but no differences in bilirubin or in UGT1A1 genotype distribution. Body fat percentage was inversely correlated with bilirubin in obese patients but not in controls. This inverse association was observed either in 6/7 or 6/6 genotype obese patients. UGT1A1 polymorphism and body fat percentage were the main factors affecting bilirubin levels within obese patients (linear regression analysis).

Conclusion

In obese children and adolescents, body fat composition and UGT1A1 polymorphism are independent determinants of total bilirubin levels. Obese individuals with 6/6 UGT1A1 genotype and higher body fat mass may benefit from a closer clinical follow-up.

Biliverdin modulates the expression of C5aR in response to endotoxin in part via mTOR signaling

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Biliverdin mitigates LPS-dependent C5aR expression in macrophages in part via mTOR.

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Biliverdin promotes phosphorylation of Akt and PS6.

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Biliverdin decreases LPS-mediated induction of C5aR-associated cytokines.

Macrophages play a crucial role in the maintenance and resolution of inflammation and express a number of pro- and anti-inflammatory molecules in response to stressors. Among them, the complement receptor 5a (C5aR) plays an integral role in the development of inflammatory disorders. Biliverdin and bilirubin, products of heme catabolism, exert anti-inflammatory effects and inhibit complement activation. Here, we define the effects of biliverdin on C5aR expression in macrophages and the roles of Akt and mammalian target of rapamycin (mTOR) in these responses. Biliverdin administration inhibited lipopolysaccharide (LPS)-induced C5aR expression (without altering basal expression), an effect partially blocked by rapamycin, an inhibitor of mTOR signaling. Biliverdin also reduced LPS-dependent expression of the pro-inflammatory cytokines TNF-α and IL-6. Collectively, these data indicate that biliverdin regulates LPS-mediated expression of C5aR via the mTOR pathway, revealing an additional mechanism underlying biliverdin’s anti-inflammatory effects.

Heme oxygenase-1: a metabolic nike

SIGNIFICANCE

Heme degradation, which was described more than 30 years ago, is still very actively explored with many novel discoveries on its role in various disease models every year.

RECENT ADVANCES

The heme oxygenases (HO) are metabolic enzymes that utilize NADPH and oxygen to break apart the heme moiety liberating biliverdin (BV), carbon monoxide (CO), and iron. Heme that is derived from hemoproteins can be toxic to the cells and if not removed immediately, it causes cell apoptosis and local inflammation. Elimination of heme from the milieu enables generation of three products that influences numerous metabolic changes in the cell.

CRITICAL ISSUES

CO has profound effects on mitochondria and cellular respiration and other hemoproteins to which it can bind and affect their function, while BV and bilirubin (BR), the substrate and product of BV, reductase, respectively, are potent antioxidants. Sequestration of iron into ferritin and its recycling in the tissues is a part of the homeodynamic processes that control oxidation-reduction in cellular metabolism. Further, heme is an important component of a number of metabolic enzymes, and, therefore, HO-1 plays an important role in the modulation of cellular bioenergetics.

FUTURE DIRECTIONS

In this review, we describe the cross-talk between heme oxygenase-1 (HO-1) and its products with other metabolic pathways. HO-1, which we have labeled Nike, the goddess who personified victory, dictates triumph over pathophysiologic conditions, including diabetes, ischemia, and cancer.

Endogenous Tetrapyrroles Influence Leukocyte Responses to Lipopolysaccharide in Human Blood: Pre-Clinical Evidence Demonstrating the Anti-Inflammatory Potential of Biliverdin

Sepsis is associated with abnormal host immune function in response to pathogen exposure, including endotoxin (lipopolysaccharide; LPS). Cytokines play crucial roles in the induction and resolution of inflammation in sepsis. Therefore, the primary aim of this study was to investigate the effects of endogenous tetrapyrroles, including biliverdin (BV) and unconjugated bilirubin (UCB) on LPS-induced cytokines in human blood. Biliverdin and UCB are by products of haem catabolism and have strong cytoprotective, antioxidant and anti-inflammatory effects. In the present study, whole human blood supplemented with BV and without was incubated in the presence or absence of LPS for 4 and 8 hours. Thereafter, whole blood was analysed for gene and protein expression of cytokines, including IL-1β, IL-6, TNF, IFN-γ, IL-1Ra and IL-8. Biliverdin (50 μM) significantly decreased the LPS-mediated gene expression of IL-1β, IL-6, IFN-γ, IL-1Ra and IL-8 (P<0.05). Furthermore, BV significantly decreased LPS-induced secretion of IL-1β and IL-8 (P<0.05). Serum samples from human subjects and, wild type and hyperbilirubinaemic Gunn rats were also used to assess the relationship between circulating bilirubin and cytokine expression/production. Significant positive correlations between baseline UCB concentrations in human blood and LPS-mediated gene expression of IL-1β (R=0.929), IFN-γ (R=0.809), IL-1Ra (R=0.786) and IL-8 (R=0.857) were observed in blood samples (all P<0.05). These data were supported by increased baseline IL-1β concentrations in hyperbilirubinaemic Gunn rats (P<0.05). Blood samples were also investigated for complement receptor-5 (C5aR) expression. Stimulation of blood with LPS decreased gene expression of C5aR (P<0.05). Treatment of blood with BV alone and in the presence of LPS tended to decrease C5aR expression (P=0.08). These data indicate that supplemented BV inhibits the ex vivo response of human blood to LPS. Surprisingly, however, baseline UCB was associated with heighted inflammatory response to LPS. This is the first study to explore the effects of BV in a preclinical human model of inflammation and suggests that BV could represent an anti-inflammatory target for the prevention of LPS mediated inflammation in vivo.

Haem catabolism: a novel modulator of inflammation in Gilbert's syndrome

BACKGROUND

Moderately elevated unconjugated bilirubin concentrations protect against inflammatory diseases and are present in individuals with Gilbert's syndrome. This study examined the relationship between circulating haem oxygenase catabolites, unconjugated bilirubin, carboxy haemoglobin, iron and inflammatory parameters.

MATERIALS AND METHODS

Seventy-six matched individuals were allocated to Gilbert's syndrome (GS) or control group (unconjugated bilirubin ≥ or < 17.1 μM). Iron, carboxy haemoglobin and high-sensitivity C-reactive protein were analysed using routine diagnostic tests. Unconjugated bilirubin and haem were analysed using high-performance liquid chromatography. The cytokines IL-1β, TNF-α and IL-6 were assessed using high-sensitivity enzyme-linked immunosorbent assays.

RESULTS

Gilbert's syndrome subjects had significantly greater levels of unconjugated bilirubin (P < 0.05), carboxy haemoglobin (P < 0.05), iron (P < 0.05), IL-1β (P < 0.05), a significantly lower body mass index (P < 0.05) and IL-6 concentrations (P < 0.05) vs. controls. Regression analysis revealed that unconjugated bilirubin mainly explained IL-1β results (16%), and body mass index+IL-6 predicted 26% of the variance in C-reactive protein concentrations.

CONCLUSIONS

A positive relationship between unconjugated bilirubin and free plasma haem, iron and carboxy haemoglobin indicated a positive feedback loop of haem oxygenase induction possibly mediated by unconjugated bilirubin. Furthermore, reduced body mass index in Gilbert's syndrome individuals was linked to reduced inflammation status, which could be influenced by circulating haem oxygenase catabolites and contribute to reduced risk of noncommunicable diseases in this population.

Unbound free fatty acids from preterm infants treated with intralipid decouples unbound from total bilirubin potentially making phototherapy ineffective

Extremely low birth weight (ELBW; <1,000 g) infants have poor outcomes, often compromised by bilirubin neurotoxicity. We measured unbound bilirubin (Bf) and unbound free fatty acid (FFAu) levels in 5 ELBW infants in a trial examining the effects of pharmacologic ductal closure on infants treated with Intralipid infusion (3 g/kg/day). The levels for all infants (mean ± SD) were: total serum bilirubin (TSB) 4.6 ± 1.7 mg/dl, FFAu 376 ± 496 nM, and Bf 42 ± 30 nM. Of the 3 infants who died, 2 had TSB <5.9 mg/dl but FFAu >580 nM and Bf >75 nM. Multiple regression revealed a major effect on Bf levels due to FFAu, indicating that Intralipid elevated levels of FFAu and Bf. Indomethacin or ibuprofen reduced Bf levels, most likely by reducing FFAu levels through lipase inhibition. Because displacement of Bf by FFAu decouples Bf from TSB, phototherapy may not reduce the risk of bilirubin or FFAu toxicity in Intralipid-treated ELBW infants.