Genetic variation underlying common hereditary hyperbilirubinaemia (Gilbert's syndrome) and respiratory health in the 1946 British birth cohort

Bilirubin regulates cell death type by alleviating macrophage mitochondrial dysfunction caused by cigarette smoke extract

OBJECTIVES

To explore the effects and mechanisms of bilirubin on mitochondrial function and type of macrophage cell death after exposure to cigarette smoke extract (CSE).

METHODS

RAW264.7 macrophages were treated with different concentrations of CSE and bilirubin solutions and divided into four groups: control, CSE, bilirubin, and bilirubin + CSE groups. The necrotic and apoptotic states of the macrophages were determined using an Annexin V-fluorescein 5-isothiocyanate/propidium iodide (FITC/PI) staining kit. Cytoplasmic NOD-like receptor family, pyrin domain containing 3 (NLRP3) expression in macrophages was detected by immunofluorescence and the levels of IL-1β and IL-18 in the supernatants of culture medium were detected by enzyme linked immunosorbent assay (ELISA) test. A JC-1 mitochondrial membrane potential detection kit was used to assess mitochondrial membrane damage and the adenosine triphosphate (ATP) assay kit was used to determine intracellular ATP levels. After the macrophages were stained with reactive oxygen species (ROS) specific dye, 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA), the fluorescence intensity and proportion of ROS-positive macrophages were measured using flow cytometry.

RESULTS

We observed that compared with those of 0 μM (control group), concentrations of 5, 10, or 20 μΜ bilirubin significantly decreased cell viability, which was increased by bilirubin exposure below 1 μM. The effect of CSE on macrophage viability was concentration- and time-dependent. Bilirubin of 0.2 μM could alleviate the inhibition of macrophage viability caused by 5% CSE. In addition, bilirubin intervention could reduce the occurrence of necrosis and pyroptosis to a certain extent.

CONCLUSIONS

CSE could cause mitochondrial dysfunction in macrophages, as demonstrated by a decrease in mitochondrial membrane potential and intracellular ATP levels and an increase in ROS production, while bilirubin could relieve mitochondrial dysfunction caused by CSE.

Genetic variations underlying Gilbert syndrome and HBV infection outcomes: a cross-sectional study

Background: Constant cellular damage causes a poor prognosis of hepatitis B virus (HBV) infection. Accumulating evidence indicates the cytoprotective properties of bilirubin. Here, we investigated the association of UDP glucuronosyltransferase family 1 member A1 (UGT1A1), the genetic cause of Gilbert syndrome (GS), a common condition of mild unconjugated bilirubinemia, with HBV infection outcomes. Methods: Patients (n = 2,792) with unconjugated hyperbilirubinemia were screened for HBV infection and host UGT1A1 variations in Ruijin Hospital from January 2015 to May 2023, and those with confirmed HBV exposure were included. The promoter/exons/adjacent intronic regions of UGT1A1 were sequenced. HBV infection outcomes were compared between hosts with wild-type and variant-type UGT1A1. The effect magnitudes of UGT1A1 variations were evaluated using three classification approaches. Results: In total, 175 patients with confirmed HBV exposure were recruited for final analysis. Age, gender, level of HBV serological markers, and antiviral treatment were comparable between UGT1A1 wild-type and disease-causing variation groups. Five known disease-causing mutations (UGT1A1*28, UGT1A1*6, UGT1A1*27, UGT1A1*63, and UGT1A1*7) were detected. The incidence of cirrhosis or hepatocellular carcinoma (LC/HCC) was significantly lower in UGT1A1 variant hosts than in UGT1A1 wild-type hosts (13.14% vs. 78.95%, p < 0.0001). The rarer the UGT1A1 variation a patient possessed, the higher the age at which LC/HCC was diagnosed (R = 0.34, p < 0.05). In contrast, patients without cirrhosis achieving HBsAg clearance were identified only in the UGT1A1 variant group (12.32% vs. 0%). Conclusion: The findings of this study provide insights into the association between preexisting genetically mild bilirubin elevation and viral infection outcome. We showed that the accumulation of UGT1A1 variants or the rarity of the variation is associated with a better prognosis, and the effect magnitude correlates with UGT1A1 deficiency. This study demonstrates the therapeutic potential of host UGT1A1 variations underlying GS against HBV infection outcomes.

Toward nanotechnology-enabled application of bilirubin in the treatment and diagnosis of various civilization diseases

Bilirubin, an open chain tetrapyrrole, has powerful antioxidant, anti-inflammatory, immuno-suppressive, metabolic-modulating and anti-proliferative activities. Bilirubin is a natural molecule that is produced and metabolized within the human body, making it highly biocompatible and well suited for clinical use. However, the use of bilirubin has been hampered by its poor water solubility and instability. With advanced construction strategies, bilirubin-derived nanoparticles (BRNPs) have not only overcome the disadvantages of bilirubin but also enhanced its therapeutic effects by targeting damaged tissues, passing through physiological barriers, and ensuring controlled sustained release. We review the mechanisms underlying the biological activities of bilirubin, BRNP preparation strategies and BRNP applications in various disease models. Based on their superior performance, BRNPs require further exploration of their efficacy, biodistribution and long-term biosafety in nonhuman primate models that recapitulate human disease to promote their clinical translation.

The continuing evolution of birth cohort studies: achievements and challenges

Well-designed birth cohorts are able to estimate prevalence/distribution of various health events/outcomes, and to link early-life origins with adult health and function. The past two decades have seen a surge in the establishment of new birth cohorts and their accompanying research. We discussed distinct designs of current birth cohort studies, reviewed their achievements, and highlighted insights obtained from birth cohort studies, as well as challenges we are facing. Birth cohort studies are providing increasing opportunities to identify determining factors for short- and long-term health, yielding substantial evidence to uncover biological mechanisms of diseases and phenotypes, and providing further insights for public health. Dynamic monitoring, accurate measurements, long-term follow-ups and collaborative efforts are warranted in new birth cohorts to elucidate the nature of life course relationships in contemporary generation.

Reactive Oxygen Species-Responsive Celastrol-Loaded : Bilirubin Nanoparticles for the Treatment of Rheumatoid Arthritis

Celastrol (CLT) has shown anti-rheumatic activity against rheumatoid arthritis, while its poor water solubility and high organ toxicity restrict its further therapeutic applications. To mitigate these challenges, a reactive oxygen species (ROS)-responsive nanoparticle was developed for celastrol delivery based on the excessive ROS at the pathologic sites, which was synthesized by conjugating bilirubin to a polyethylene glycol (PEG) chain. The PEGylated bilirubin self-assembled into nanoparticle (BRNP) in aqueous solution had a hydrodynamic diameter of around 68.6 nm, and celastrol was loaded into BRNP (CLT/BRNP) with a drug encapsulation efficiency of 72.6% and a loading capacity of 6.6%. In vitro study revealed that CLT/BRNP exhibited the capacity of scavenging intracellular ROS and down-regulating the level of nitric oxide after it was effectively internalized by activated macrophages. Furthermore, in adjuvant-induced arthritis rats, BRNP was accumulated preferentially at inflamed joints, alleviating the joint swelling and bone erosion, which significantly decreased the secretion of pro-inflammatory cytokines to suppress the RA progression. Importantly, CLT/BRNP markedly enhanced its anti-arthritic effect and attenuated the toxic effect compared with free celastrol. Taken together, our results suggested that CLT/BRNP could be used for targeted drug delivery in rheumatoid arthritis.

Candidate gene prioritization for chronic obstructive pulmonary disease using expression information in protein-protein interaction networks

Background

Identifying or prioritizing genes for chronic obstructive pulmonary disease (COPD), one type of complex disease, is particularly important for its prevention and treatment.

Methods

In this paper, a novel method was proposed to Prioritize genes using Expression information in Protein–protein interaction networks with disease risks transferred between genes (abbreviated as PEP). A weighted COPD PPI network was constructed using expression information and then COPD candidate genes were prioritized based on their corresponding disease risk scores in descending order.

Results

Further analysis demonstrated that the PEP method was robust in prioritizing disease candidate genes, and superior to other existing prioritization methods exploiting either topological or functional information. Top-ranked COPD candidate genes and their significantly enriched functions were verified to be related to COPD. The top 200 candidate genes might be potential disease genes in the diagnosis and treatment of COPD.

Conclusions

The proposed method could provide new insights to the research of prioritizing candidate genes of COPD or other complex diseases with expression information from sequencing or microarray data.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-021-01646-9.

Compound heterozygous UGT1A1*28 and UGT1A1*6 or single homozygous UGT1A1*28 are major genotypes associated with Gilbert's syndrome in Chinese Han people

Gilbert's syndrome (GS) is a mild condition characterized by periods of hyperbilirubinemia, which results in variations in the UDP-glucuronosyltransferase 1 (UGT1A1) gene. Variant genotypes of UGT1A1 vary in different populations in the world. The present study aimed to determine the genotype of the UGT1A1 promoter and exon that are related to the serum total bilirubin (STB) level in the Chinese Han population. A total of 120 individuals diagnosed with GS (GS group) and 120 healthy individuals (non-GS group) were enrolled. Routine blood, liver function tests, and antibodies associated with autoimmune liver diseases were assessed. Blood samples were collected for DNA purification. Sequencing of the UGT1A1 promoter and exons was conducted for post segment amplification by PCR. Compound heterozygous UGT1A1*28 and UGT1A1*6 (25/120, 20.83%), single homozygous UGT1A1*28 (24/120, 20.00%) and single heterozygous UGT1A1*6 (18/120, 15.00%) were the most frequent genotypes in the GS group. However, single heterozygous UGT1A1*6 (30/120, 25.00%) and single heterozygous UGT1A1*28 (19/120, 15.83%) were the most frequent genotypes in the non-GS group. Further, the frequencies of single homozygous UGT1A1*28, compound heterozygous UGT1A1*28 and UGT1A1*6, and compound heterozygous UGT1A1*28, UGT1A1*6 and UGT1A1*27 were significantly higher in the GS group than those in the non-GS group. The STB levels of GS patients with the homozygous UGT1A1*28 genotype were remarkably higher than those of patients with other genotypes. Homozygous UGT1A1*28 and heterozygous UGT1A1*6 variants were associated with the highest and lowest risks of hyperbilirubinemia, respectively. Our study revealed that compound heterozygous UGT1A1*28 and UGT1A1*6, or single homozygous UGT1A1*28 are major genotypes associated with GS in Chinese Han people. These findings might facilitate the precise genomic diagnosis of Gilbert's syndrome.

Serum bilirubin and chronic obstructive pulmonary disease (COPD): a systematic review

BACKGROUND

Bilirubin is a potent antioxidant and higher serum bilirubin levels have been associated with improved COPD outcomes. We performed a systematic review to evaluate the association between serum bilirubin levels and lung function (FEV1), prevalence/incidence of COPD, acute exacerbations of COPD, respiratory health status, and mortality.

METHODS

MEDLINE® and Embase were searched using Ovid® (search updated October 1st, 2019). We included studies that measured serum bilirubin levels and outcomes of interest in adults with or without underlying lung disease. We excluded studies of those with liver disease or drug-induced elevations in bilirubin. We used the Newcastle-Ottawa scale to assess individual study risk of bias (ROB) and the US Agency for Healthcare Research and Quality-Evidence Based Practice tool to assess overall strength of evidence (SOE). Two authors independently determined eligibility, performed data abstraction, assessed ROB, and determined SOE.

RESULTS

Thirteen studies (5 low risk of bias, 3 moderate and 5 high risk) were included. We found low strength of evidence for the association between higher bilirubin levels and lower risk of acute exacerbations of COPD (2 studies), mortality (3 studies), COPD diagnosis (4 studies), and lung function (FEV1) (8 studies). We found insufficient evidence on the relationship between serum bilirubin and respiratory health status/exercise capacity (1 study) and airflow obstruction (FEV1/FVC ratio) (4 studies).

CONCLUSION

Higher bilirubin levels may be associated with lower mortality and improved COPD outcomes. Randomized trials are needed to evaluate the effect of medications that raise serum bilirubin on COPD outcomes. PROSPERO registration: CRD42019145747.

Genetically raised serum bilirubin levels and lung cancer: a cohort study and Mendelian randomisation using UK Biobank

BACKGROUND

Moderately raised serum bilirubin levels are associated with lower rates of lung cancer, particularly among smokers. It is not known whether these relationships reflect antioxidant properties or residual confounding.

OBJECTIVE

This study aimed to investigate potential causal relationships between serum total bilirubin and lung cancer incidence using one-sample Mendelian randomisation (MR) and UK Biobank.

METHODS

We instrumented serum total bilirubin level using two variants (rs887829 and rs4149056) that together explain ~40% of population-level variability and are linked to mild hereditary hyperbilirubinaemia. Lung cancer events occurring after recruitment were identified from national cancer registries. Observational and genetically instrumented incidence rate ratios (IRRs) and rate differences per 10 000 person-years (PYs) by smoking status were estimated.

RESULTS

We included 377 294 participants (median bilirubin 8.1 μmol/L (IQR 6.4-10.4)) and 2002 lung cancer events in the MR analysis. Each 5 μmol/L increase in observed bilirubin levels was associated with 1.2/10 000 PY decrease (95% CI 0.7 to 1.8) in lung cancer incidence. The corresponding MR estimate was a decrease of 0.8/10 000 PY (95% CI 0.1 to 1.4). The strongest associations were in current smokers where a 5 μmol/L increase in observed bilirubin levels was associated with a decrease in lung cancer incidence of 10.2/10 000 PY (95% CI 5.5 to 15.0) and an MR estimate of 6.4/10 000 PY (95% CI 1.4 to 11.5). For heavy smokers (≥20/day), the MR estimate was an incidence decrease of 23.1/10 000 PY (95% CI 7.3 to 38.9). There was no association in never smokers and no mediation by respiratory function.

CONCLUSION

Genetically raised serum bilirubin, common across human populations, may protect people exposed to high levels of smoke oxidants against lung cancers.

Association Between Atazanavir-Induced Hyperbilirubinemia and Cardiovascular Disease in Patients Infected with HIV

BACKGROUND:

Serum bilirubin is inversely associated with cardiovascular risk. Atazanavir, an HIV protease inhibitor that competitively inhibits bilirubin conjugation, provides a unique opportunity to examine whether selectively increasing bilirubin is cardioprotective. We sought to determine whether patients receiving atazanavir manifest a reduced risk of cardiovascular disease compared with those receiving darunavir, an HIV protease inhibitor that does not increase serum bilirubin.

METHODS AND RESULTS:

This was a retrospective cohort study of 1020 patients with HIV. The main outcome was time to myocardial infarction or ischemic stroke. Mean follow‐up was 6.6±3.4 years, with 516 receiving atazanavir and 504 darunavir. Atazanavir patients exhibited significantly higher serum total bilirubin (1.7 versus 0.4 mg/dL; P<0.001) and longer mean time to ischemic event (10.2 versus 9.4 years; P<0.001). On Cox regression, atazanavir treatment (hazard ratio [HR], 0.38; 95% CI, 0.21–0.71; P=0.002) and serum bilirubin (HR, 0.60; 95% CI, 0.41–0.89; P=0.011) were independently associated with a lower risk of an ischemic event. Notably, when atazanavir and bilirubin were included together in the Cox regression model, atazanavir lost significance (HR, 0.55; 95% CI, 0.24–1.29; P=0.169) consistent with bilirubin being an intermediate variable on the causal pathway between atazanavir and its effect on cardiovascular disease. Patients on atazanavir also had a significantly lower risk of developing new cardiovascular disease (HR, 0.53; 95% CI, 0.33–0.86; P=0.010) and longer mean time to death (12.2 versus 10.8 years; P<0.001).

CONCLUSIONS:

Patients with HIV on atazanavir manifest a decreased risk of cardiovascular disease when compared with those on darunavir, an effect that appears to be mediated by serum bilirubin.

Mortality outcomes after busulfan-containing conditioning treatment and haemopoietic cell transplantation in patients with Gilbert's syndrome: a retrospective cohort study

BACKGROUND

Gilbert's syndrome is a common inherited disorder of bilirubin metabolism, characterised by mild, unconjugated hyperbilirubinaemia. However, the effect of Gilbert's syndrome on the disposition of some drugs can lead to unexpected toxicity. We tested the hypothesis that patients undergoing myeloablative conditioning and haemopoietic cell transplantation would have different mortality outcomes depending on whether or not they had laboratory evidence of Gilbert's syndrome.

METHODS

In this retrospective cohort study, we used clinical and laboratory data of patients who had haemopoietic cell transplantation from Jan 1, 1991, to Dec 31, 2011. Patients were included if they had received high-dose conditioning regimens of cyclophosphamide plus total body irradiation (CY/TBI), busulfan plus cyclophosphamide (BU/CY), busulfan plus melphalan plus thioTEPA (BUMELTT), or melphalan before transplant. Patients were excluded if their original consent forms to report transplant outcomes were not signed, if consent was withdrawn, or if they were a prisoner. Patients with Gilbert's syndrome were defined as having laboratory values before the start of conditioning therapy for unconjugated serum bilirubin concentrations of at least 17·1 μmol/L (≥1 mg/dL), normal conjugated serum bilirubin, and no evidence of hepatitis, cholestasis, or haemolysis. We assessed the association of Gilbert's syndrome with overall mortality and non-relapse mortality using adjusted Cox regression models at day 200 after transplantation.

FINDINGS

Our study cohort was 3379 patients-1855 (55%) allograft and 1524 (45%) autograft recipients. 211 (6%) patients had Gilbert's syndrome and 3168 (94%) did not have this condition. Most patients were adults (median age 45·8 years [IQR 33·2-55·5]) with haematological malignancies. For overall mortality 664 (20%) patients had died by day 200 after transplant (47 [22%] of 211 who had Gilbert's syndrome vs 617 [19%] of 3168 who did not have Gilbert's syndrome), and for non-relapse mortality 499 (92%) patients had died before relapse was recorded (38 [18%] who had Gilbert's syndrome vs 461 [15%] who did not have Gilbert's syndrome). The effect of Gilbert's syndrome on the risk of overall mortality and non-relapse mortality by transplant day 200 varied between the conditioning regimens and donor groups. In patients conditioned with a myeloablative regimen that contained busulfan (n=1131), those with Gilbert's syndrome (n=60) were at a significantly increased risk of death and non-relapse mortality by day 200 compared with those without Gilbert's syndrome (n=1071; hazard ratio [HR] 2·30, 95% CI 1·47-3·61, p=0·00030; and 2·77, 1·71-4·49, p<0·0001). In patients who received CY/TBI or melphalan conditioning regimens, those with Gilbert's syndrome had similar outcomes to those without Gilbert's syndrome (overall mortality at day 200 HR 0·90, 95% CI 0·60-1·34, p=0·60; non-relapse mortality at day 200: 0·90, 0·56-1·45, p=0·65). Analyses of causes of death and busulfan disposition provided no mechanistic explanation for the differences in mortality.

INTERPRETATION

Overall mortality and non-relapse mortality at day 200 after transplant were significantly worse in patients with Gilbert's syndrome who received busulfan-containing myeloablative conditioning regimens, compared with non-Gilbert's syndrome patients. Patients with Gilbert's syndrome should receive busulfan-containing myeloablative conditioning regimens with caution.

FUNDING

US National Institutes of Health.

Impact of higher-order heme degradation products on hepatic function and hemodynamics

BACKGROUND & AIMS

Biliverdin and bilirubin were previously considered end products of heme catabolism; now, however, there is evidence for further degradation to diverse bioactive products. Z-BOX A and Z-BOX B arise upon oxidation with unknown implications for hepatocellular function and integrity. We studied the impact of Z-BOX A and B on hepatic functions and explored their alterations in health and cholestatic conditions.

METHODS

Functional implications and mechanisms were investigated in rats, hepatocytic HepG2 and HepaRG cells, human immortalized hepatocytes, and isolated perfused livers. Z-BOX A and B were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in acute and acute-on-chronic liver failure and hereditary unconjugated hyperbilirubinemia.

RESULTS

Z-BOX A and B are found in similar amounts in humans and rodents under physiological conditions. Serum concentrations increased ∼20-fold during cholestatic liver failure in humans (p<0.001) and in hereditary deficiency of bilirubin glucuronidation in rats (p<0.001). Pharmacokinetic studies revealed shorter serum half-life of Z-BOX A compared to its regio-isomer Z-BOX B (p=0.035). While both compounds were taken up by hepatocytes, Z-BOX A was enriched ∼100-fold and excreted in bile. Despite their reported vasoconstrictive properties in the brain vasculature, BOXes did not affect portal hemodynamics. Both Z-BOX A and B showed dose-dependent cytotoxicity, affected the glutathione redox state, and differentially modulated activity of Rev-erbα and Rev-erbβ. Moreover, BOXes-triggered remodeling of the hepatocellular cytoskeleton.

CONCLUSIONS

Our data provide evidence that higher-order heme degradation products, namely Z-BOX A and B, impair hepatocellular integrity and might mediate intra- and extrahepatic cytotoxic effects previously attributed to hyperbilirubinemia.

LAY SUMMARY

Degradation of the blood pigment heme yields the bile pigment bilirubin and the oxidation products Z-BOX A and Z-BOX B. Serum concentrations of these bioactive molecules increase in jaundice and can impair liver function and integrity. Amounts of Z-BOX A and Z-BOX B that are observed during liver failure in humans have profound effects on hepatic function when added to cultured liver cells or infused into healthy rats.

Bilirubin coating attenuates the inflammatory response to everolimus-coated stents

The aim of this study was to evaluate the effects of bilirubin- and/or everolimus (EVL)-coated stents to prevent arterial neointimal hyperplasia and inflammation in vitro and in vivo. The stents were prepared by spray coating bare metal stents (BMS) with bilirubin and/or EVL. Study groups were divided into (1) BMS, (2) bilirubin-coated stents (BES), (3) commercialized stents (Synergy™; EES), and (4) bilirubin/EVL-coated stents (B-EES). The coating thickness and drug release rates were comparable to previous reports (i.e., <4 µm thickness and 50% drug release in 7 days). Smooth muscle cell migration was inhibited in both EVL-containing groups (20.5 ± 3.80% in EES and 18.4 ± 2.55% in B-EES) compared to the non-EVL-containing groups (78.0 ± 6.41% in BMS and 76.1 ± 4.88% in BES) (n = 10, p < 0.05). Stents were randomly implanted to 40 coronary arteries in 20 pigs and subjected to various analyses after 4 weeks of implantation. As results, the inflammation score was dramatically increased in the EES group (2.1 ± 0.42) compared to that of the other groups (1.5 ± 0.55, 1.3 ± 0.23, and 1.5 ± 0.27 for BMS, BES, and B-EES, respectively, n = 10, p < 0.05). Immunofluorescence analysis revealed that inflammation was prevented in the bilirubin-containing groups (BES and B-EES). However, the percent area of restenosis was decreased in the EVL-containing groups (20.5 ± 4.11% for EES and 18.4 ± 3.61% for B-EES) compared to the non-EVL-containing groups (32.3 ± 6.41% for BMS and 29.6 ± 5.95% for BES, n = 10, p < 0.05). The percent areas of restenosis determined by histopathology, optical coherence tomography, and micro-computed tomography were consistent. In addition, the stent was barely covered in the EES and B-EES groups at 4 weeks postimplantation. These dual drug-coated stents may be especially beneficial to patients who have an increased risk of inflammation. These stents have great potential for use in cardiovascular applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1486-1495, 2018.

Bilirubin acts as an endogenous regulator of inflammation by disrupting adhesion molecule-mediated leukocyte migration

There is a growing body of evidence that bilirubin, which is generated during the physiological breakdown of heme, exerts potent anti-inflammatory effects. Previous work by our group suggests that bilirubin is able to suppress inflammatory responses by preventing the migration of leukocytes into target tissues through disruption of vascular cell adhesion molecule-1 (VCAM-1)-dependent cell signaling. As VCAM-1 is an important mediator of tissue injury in the dextran sodium sulfate (DSS) murine model of inflammatory colitis, we examined whether bilirubin prevents colonic injury in DSS-treated mice. As anticipated, bilirubin-treated animals manifested significantly less colonic injury and reduced infiltration of inflammatory cells into colon tissues. We further observed that bilirubin administration was associated with a reduced number of eosinophils and monocytes in the small intestine, with a corresponding increase in peripheral blood eosinophilia, regardless of whether mice received DSS. These findings suggest that bilirubin impairs the normal migration of eosinophils into intestinal tissues, as supported by in vitro experiments showing that bilirubin blocks the VCAM-1-dependent movement of Jurkat cells across human endothelial cell monolayers. Taken together, our findings support that bilirubin ameliorates DSS-induced colitis and disrupts the physiological trafficking of leukocytes to the intestine by preventing transmigration across the vascular endothelium, potentially through the inhibition VCAM-1-mediated signaling. Our findings raise the possibility that bilirubin functions as an endogenous regulator of inflammatory responses.

Bilirubin treatment suppresses pulmonary inflammation in a rat model of smoke-induced emphysema

BACKGROUND

Cigarette smoking is a significant risk factor for emphysema, which is characterized by airway inflammation and oxidative damage.

OBJECTIVES

To assess the capacity of bilirubin to protect against smoke-induced emphysema.

METHODS

Smoking status and bilirubin levels were recorded in 58 patients with chronic obstructive pulmonary diseases (COPD) and 71 non-COPD participants. The impact of smoking on serum bilirubin levels and exogenous bilirubin (20 mg/kg/day) on pulmonary injury was assessed in a rat model of smoking-induced emphysema. At sacrifice lung histology, airway leukocyte accumulation and cytokine and chemokine levels in serum, bronchoalveolar lavage fluid (BALF) and lung were analyzed. Oxidative lipid damage and anti-oxidative components was assessed by measuring malondialdehyde, superoxide dismutase (SOD) activity and glutathione.

RESULTS

Total serum bilirubin levels were lower in smokers with or without COPD than non-smoking patients without COPD (P < 0.05). Indirect serum bilirubin levels were lower in COPD patients than patients without COPD (P < 0.05). In rats, cigarette smoke reduced serum total and indirect bilirubin levels. Administration of bilirubin reduced mean linear intercept and mean alveoli area, increased mean alveoli number, reduced macrophage, neutrophil and TNF-α content of BALF, and increased BALF and serum IL-10 level, but lowered local and systemic CCL2, CXCL2, CXCL8 and IL-17 levels. Bilirubin suppressed the smoke-induced systemic and regional oxidative lipid damage associated with increased SOD activity.

CONCLUSION

Bilirubin attenuated smoking-induced pulmonary injury by suppressing inflammatory cell recruitment and pro-inflammatory cytokine secretion, increasing anti-inflammatory cytokine levels, and anti-oxidant SOD activity in a rat model of smoke-induced emphysema.