Association between the UGT1A1*28 allele, bilirubin levels, and coronary heart disease in the Framingham Heart Study

A Novel Kidney Failure Prediction Model in Individuals With CKD: Impact of Serum Bilirubin Levels

CONTEXT

Predicting the progression of chronic kidney disease (CKD) to end-stage kidney disease (ESKD) is crucial for improving patient outcomes.

OBJECTIVE

To reveal the highly predictive activity of serum bilirubin levels for the progression of CKD to ESKD, and to develop and validate a novel ESKD prediction model incorporating serum bilirubin levels.

METHODS

We assessed the relative importance of 20 candidate predictors for ESKD, including serum bilirubin levels, in a CKD cohort (15 ≤ estimated glomerular filtration rate [eGFR] < 60 mL/min/1.73 m2), and subsequently developed a prediction model using the selected variables. The development cohort comprised 4103 individuals with CKD who underwent follow-up at Kyushu University Hospital, Japan, from 2008 to 2018. The primary outcome was incident ESKD, defined as an eGFR < 15 mL/min/1.73 m2, chronic dialysis, or renal transplantation.

RESULTS

The mean follow-up time was 7.0 ± 4.2 years, during which 489 individuals (11.9%) progressed to ESKD. The Cox proportional hazard model selected eGFR, serum bilirubin, proteinuria, age, diabetes, gender, hypertension, serum albumin, and hemoglobin in order of their importance. The predictive performance of the model was optimized by incorporating these 9 variables in discrimination evaluated by time-dependent area under the curve (AUC). This model also demonstrated excellent calibration. Additionally, this model exhibited excellent predictive performance in both discrimination (2-year AUC: 0.943, 5-year AUC: 0.935) and calibration in a validation cohort (n = 2799).

CONCLUSION

Serum bilirubin levels were strong predictors for the progression of CKD to ESKD. Our novel model that incorporates serum bilirubin levels could accurately predict ESKD in individuals with CKD.

The Role of Renal Medullary Bilirubin and Biliverdin Reductase in Angiotensin II-Dependent Hypertension

BACKGROUND

Increased circulating bilirubin attenuates angiotensin (Ang) II-induced hypertension and improves renal hemodynamics. However, the intrarenal mechanisms that mediate these effects are not known. The goal of the present study was to test the hypothesis that bilirubin generation in the renal medulla plays a protective role against Ang II-induced hypertension.

METHODS

Twenty-week-old male C57Bl/6J mice were implanted with intrarenal medullary interstitial (IRMI) catheters following unilateral nephrectomy. After this time, biliverdin IXα was specifically infused into the kidney (3.6 mg/day) for 3 days before implantation with an osmotic minipump delivering Ang II (1,000 ng/kg/min). BP was recorded for 3 days, 1 week after minipump infusion, in conscious mice. To further explore the antihypertensive role of renal medullary bilirubin generation, mice with specific deletion of biliverdin reductase-A (Blvra) in the thick ascending loop of Henle were generated. At 20 weeks, BlvraTALHKO and control mice (Blvrafl/fl) were infused with Ang II for 2 weeks.

RESULTS

IRMI infusion of biliverdin significantly decreased blood pressure compared with mice infused with vehicle (118 ± 4 vs. 158 ± 2 mmHg, p < 0.05). Angiotensin-II infusion resulted in significantly higher blood pressure measured in conscious mice 7 days after implantation in BlvraTALHKO as compared to Blvrafl/fl mice (152 ± 2 vs. 140 ± 3 mmHg, P < 0.05).

CONCLUSIONS

Altogether, these findings show that medullary bilirubin and biliverdin reductase can improve hypertension and that mechanisms that increase bilirubin and biliverdin reductase in the renal medulla could be an effective approach to treat hypertension.

Assessing Association Between Circulating Bilirubin Levels and the Risk of Frailty: An Observational and Mendelian Randomization Study

BACKGROUND

Bilirubin is a by-product of haemoglobin breakdown and has been reported to be a potent antioxidant recently. While elevated levels of bilirubin have been linked to a reduced risk of various diseases, their role remains unknown in frailty. This study aims to explore the relationship between serum bilirubin levels and the risk of frailty.

METHODS

This cohort study included 442 223 White British participants (aged 39 to 73 years) with an available frailty index at baseline (2006 to 2010) from the UK Biobank. The associations of total/direct bilirubin levels with the continuous frailty index were analysed by multivariable linear regression, and multivariable logistic regression was used after classifying frailty outcomes into non-frailty, pre-frailty and frailty. A Mendelian randomization (MR) analysis was applied to evaluate the association of genetically predicted bilirubin levels with frailty risk.

RESULTS

The prevalence rates of both pre-frailty and frailty were 46.17% and 12.49%, respectively, with higher rates observed in women than in men (pre-frailty: 47.33% vs. 44.79%, frailty: 13.64% vs. 11.13%, respectively). There was a non-linear negative association between total bilirubin levels and frailty indexes (p < 0.0001). Mildly elevated total bilirubin levels had protective effects against pre-frailty (OR = 0.863, 95% CI: 0.849 to 0.879, p < 0.001) and frailty (OR = 0.660, 95% CI: 0.641 to 0.679, p < 0.001). Increased total bilirubin levels were more beneficial for women with frailty risk (percent changes per SD μmol/L = -0.37%, 95% CI: -0.40% to -0.34%). The MR analysis revealed a negative association between genetically predicted total/direct bilirubin levels and frailty risk (both p < 0.0001).

CONCLUSIONS

Circulating total/direct bilirubin levels were negatively associated with frailty risk in White British individuals. Mildly elevated total bilirubin levels were more beneficial for women subpopulation.

Bilirubin bioconversion to urobilin in the gut-liver-kidney axis: A biomarker for insulin resistance in the Cardiovascular-Kidney-Metabolic (CKM) Syndrome

The rising rates of obesity worldwide have increased the incidence of cardiovascular disease (CVD), making it the number one cause of death. Higher plasma bilirubin levels have been shown to prevent metabolic dysfunction and CVD. However, reducing levels leads to deleterious outcomes, possibly due to reduced bilirubin half-life that escalates the production of its catabolized product, urobilinogen, produced by gut bacteria and naturally oxidized to urobilin. Recent findings suggest that the involvement of the microbiome catabolism of bilirubin to urobilin and its absorption via the hepatic portal vein contributes to CVD, suggesting a liver-gut axis involvement. We discuss the studies that demonstrate that urobilin is frequently raised in the urine of persons with CVD and its probable role in acquiring the disease. Urobilin is excreted from the kidneys into the urine and may serve as a biomarker for Cardiovascular-Kidney-Metabolic (CKM) Syndrome. We deliberate on the newly discovered bilirubin reductase (BilR) bacterial enzyme that produces urobilin. We discuss the bacterial species expressing BilR, how they impact CVD, and whether suppressing urobilin production and increasing bilirubin may provide new therapeutic strategies for CKM. Possible therapeutic mechanisms for achieving this goal are discussed.

Bilirubin, a hepatoprotective agent that activates SIRT1, PGC-1α, and PPAR-α, while inhibiting NF-κB in rats with metabolic-associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) is a chronic liver disorder characterized by fatty liver disease alongside overweight or obesity and/or type 2 diabetes mellitus (T2DM). Timely intervention is crucial for a potential cure. This study aimed to investigate the effects of bilirubin, an endogenous antioxidant, on lipid metabolism and inflammation in MAFLD. Specifically, it examined bilirubin's impact on SIRT1, PPAR-α, and NF-κB in the livers of rats with MAFLD induced by a high-fat diet (HFD) and streptozotocin (STZ) administration. Forty eight-week adult male Sprague Dawley rats were divided into five groups (n = 8): Control, HFD-STZ, HFD-S-BR6, HFD-S-BR14, and C-BR14. In the last three groups, bilirubin administration was performed intraperitoneally for 6 and 14 weeks (10 mg/kg/day). We selected the key genes associated with MAFLD and subsequently performed GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses to explore the enriched biological processes and signaling pathways. Hence, the gene expression of SIRT1, PGC-1α, PPAR-α, and inflammatory genes (NF-κB, TNF-α, IL-6, and IL-1β) was measured using Real-time quantitative PCR. Stereological and histopathological alterations of liver structure as well as lipid profile, biochemical indices, and liver indices, were also assessed among different groups. The enrichment analysis identified that several signaling pathways and biological processes might be related to MAFLD. Bilirubin-treated rats contained higher PPAR-α, PGC-1α, and SIRT1 expression levels by approximately 5.7-, 2.1-, and 2.2-fold, respectively, compared to the HFD-receiving rats (p < 0.0001, p < 0.05, and p < 0.05). Whereas, the genes involved in the inflammatory cascades, including NF-κB, TNF-α, and IL-6, were downregulated by 0.6-fold (p < 0.05) following 14-week treatment of bilirubin, while only significantly decreased expression of NF-κB and IL-6 (approximately 0.6-fold, p < 0.05) were observed after 6-week treatment of bilirubin. Remarkably, bilirubin administration favorably reversed the effects of HFD on the liver's volume and cell numbers and ameliorated the related structural changes. It also improved lipid profile, biochemical parameters, and liver indices of HFD-STZ rats. This study indicated that bilirubin acts as a protective/ameliorative compound against MAFLD, particularly through regulating the key genes involved in lipid metabolism and inflammation in HFD-STZ rats.

The Clinical Value of Serum Creatinine-to-Bilirubin Ratio in Predicting the Severity and Prognosis of Acute Pancreatitis

INTRODUCTION

Bilirubin (BIL) and creatinine (Cr) have long been recognized as potential early indicators of disease severity. A recent study found that the Cr-to-BIL ratio (CTR) was more sensitive and specific than either serum Cr or BIL alone. Our research focused on the clinical significance of CTR in evaluating the severity and prognosticating outcomes of acute pancreatitis (AP) in patients.

METHODS

Patients diagnosed with AP at the First Affiliated Hospital of Guangdong Pharmaceutical University between July 1, 2016, and December 31, 2020 were included. The analysis then focused on examining the relationship between CTR levels and the severity of the illness, the occurrence of complications, and the prognosticating outcomes for individuals diagnosed with AP. A total of 286 AP patients were enrolled.

RESULTS

Multivariate regression analyses indicated that AP patients with elevated CTR levels were more likely to develop severe AP. They exhibited higher MODS, Ranson, and APACHE-II scores, an increased incidence of organ failures (acute heart failure [AHF], acute kidney injury [AKI], and acute myocardial infarction), higher 30-day all-cause mortality rates, and a worse prognosis, often requiring more frequent use of vasoactive and diuretic agents compared to those with lower CTR levels. When CTR >14.05, AP patients had increased occurrence of AHF and AKI, higher 30-day all-cause mortality rates, more frequently using vasoactive agent and diuretic agent. Besides, the disease severity scores (MODS, Ranson, and APACHE-II) and hospital stays were markedly increased.

CONCLUSION

AP patients with elevated CTR levels are prone to more severe disease progression, increased complications, and poorer outcomes compared to those with lower CTR levels.

Bilirubin, once a toxin but now an antioxidant alleviating non-alcoholic fatty liver disease in an autophagy-dependent manner in high-fat diet-induced rats: a molecular and histopathological analysis

Background and purpose

As an endogenous antioxidant, bilirubin has surprisingly been inversely correlated with the risk of non-alcoholic fatty liver disease (NAFLD). Thereupon, the current evaluation was designed to assess the positive effects of bilirubin on the autophagy flux, as well as the other pathogenic processes and parameters involved in the expansion of NAFLD.

Experimental approach

Thirty adult male rats weighing 150-200 g with free access to sucrose solution (18%) were randomly subdivided into 5 groups (n = 6). Subsequently, the animals were euthanized, and their blood specimens and liver tissue samples were collected to measure serum biochemical indices, liver histopathological changes, intrahepatic triglycerides content, and tissue stereological alterations. Furthermore, the expression levels of autophagy-related genes (Atgs) were measured to assess the state of the autophagy flux.

Findings/Results

Fasting blood glucose, body weight, as well as liver weight, liver-specific enzyme activity, and serum lipid profile indices markedly decreased in rats that underwent a six-week bilirubin treatment compared to the control group. In addition, histopathological studies showed that hepatic steatosis, fibrosis, inflammation, and necrosis significantly decreased in the groups that received bilirubin compared to the control animals. Bilirubin also caused significant alterations in the expression levels of the Atgs, as well as the Beclin- 1 protein.

Conclusion and implication

Bilirubin may have potential ameliorative effects on NAFLD-associated liver damage. Moreover, the beneficial effects of bilirubin on intrahepatic lipid accumulation and steatosis were comparable with the group that did not ever receive bilirubin.

Protective and curative effects of unconjugated bilirubin on gene expression of LOX-1 and iNOS in the heart of rats receiving high-fat diet and low dose streptozotocin: a histomorphometric approach

BACKGROUND

Atherosclerosis is a chronic inflammatory condition affecting the large arteries and is a major cause of cardiovascular diseases (CVDs) globally. Increased levels of adhesion molecules in cardiac tissue serve as prognostic markers for coronary artery occlusion risk. Given the antioxidant properties of bilirubin and its inverse correlation with atherosclerosis, this study aimed to assess the beneficial effects of bilirubin on atherosclerotic indices and heart structure in high-fat diet-fed diabetic rats with atherosclerosis.

METHODS

Atherosclerosis was induced in three out of five groups of adult male Sprague Dawley rats through a 14-week period of high-fat diet (HFD) consumption and a single low dose of streptozotocin (STZ) (35 mg/kg). The atherosclerotic rats were then treated with intraperitoneal administration of 10 mg/kg/day bilirubin for either 6 or 14 weeks (treated and protected groups, respectively), or the vehicle. Two additional groups served as the control and bilirubin-treated rats. Subsequently, the mRNA expression levels of vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), lectin-like LDL receptor 1 (LOX-1), and the inducible nitric oxide synthase (iNOS) were analyzed using quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). Histopathological and stereological analyses were performed to assess changes in the heart structure.

RESULTS

Bilirubin significantly decreased the expression of VCAM-1, ICAM-1, LOX-1, and iNOS genes in the treated group. Moreover, bilirubin mitigated pathological damage in the left ventricle of the heart. Stereological analysis revealed a decrease in the left ventricle and myocardium volume, accompanied by an increase in vessel volume in rats treated with bilirubin.

CONCLUSION

These findings demonstrate that mild hyperbilirubinemia can protect against the progression of atherosclerosis and heart failure by improving lipid profile, modulating adhesion molecules, LOX-1, and iNOS gene expression levels.

UCP1 expression in human brown adipose tissue is inversely associated with cardiometabolic risk factors

OBJECTIVE

Brown adipose tissue (BAT) is a therapeutic target for obesity. 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) is commonly used to quantify human BAT mass and activity. Detectable 18F-FDG uptake by BAT is associated with reduced prevalence of cardiometabolic disease. However, 18F-FDG uptake may not always be a reliable marker of BAT thermogenesis, for example, insulin resistance may reduce glucose uptake. Uncoupling protein 1 (UCP1) is the key thermogenic protein in BAT. Therefore, we hypothesised that UCP1 expression may be altered in individuals with cardiometabolic risk factors.

METHODS

We quantified UCP1 expression as an alternative marker of thermogenic capacity in BAT and white adipose tissue (WAT) samples (n = 53) and in differentiated brown and white pre-adipocytes (n = 85).

RESULTS

UCP1 expression in BAT, but not in WAT or brown/white differentiated pre-adipocytes, was reduced with increasing age, obesity, and adverse cardiometabolic risk factors such as fasting glucose, insulin, and blood pressure. However, UCP1 expression in BAT was preserved in obese subjects of <40 years of age. To determine if BAT activity was also preserved in vivo, we undertook a case-control study, performing 18F-FDG scanning during mild cold exposure in young (mean age ∼22 years) normal weight and obese volunteers. 18F-FDG uptake by BAT and BAT volume were similar between groups, despite increased insulin resistance.

CONCLUSION

18F-FDG uptake by BAT and UCP1 expression are preserved in young obese adults. Older subjects retain precursor cells with the capacity to form new thermogenic adipocytes. These data highlight the therapeutic potential of BAT mass expansion and activation in obesity.

Genetic variation in UGT1A1 is not associated with altered liver biochemical parameters in healthy volunteers participating in bioequivalence trials

Introduction: Bioequivalence clinical trials are conducted in healthy volunteers whose blood tests should be within normal limits; individuals with Gilbert syndrome (GS) are excluded from these studies on suspicion of any liver disease, even if the change is clinically insignificant. GS is a benign genetic disorder characterized by elevated bilirubin levels, the primary cause of which is the presence of polymorphisms in UGT1A1 gene. In this work, subjects with UGT1A1 intermediate (IM) or poor (PM) metabolizer genotype-informed phenotypes were investigated to determine whether they have a higher incidence of liver disease or other biochemical parameters. Methods: The study population comprised 773 healthy volunteers who underwent biochemical analysis at baseline and at the end of the study which were genotyped for UGT1A1*80 (rs887829), as an indicator of UGT1A1*80+*28 (rs887829 and rs3064744), and UGT1A1*6 (rs4148323). Results: Bilirubin levels were higher in subjects IMs and PMs compared to normal metabolizers (NMs). Decreased uric acid levels was observed in PMs compared to NMs. No associations were observed in liver enzyme levels according to UGT1A1 phenotype. Discussion: Considering that there is no hepatic toxicity in subjects with UGT1A1 IM or PM phenotype, who are more likely to develop GS, this study suggests that they could be included in bioequivalence clinical trials as their biochemical parameters are not affected outside normal ranges.

Higher baseline serum bilirubin levels are associated with increased risk of early neurological deterioration in women with acute ischemic stroke

Background and objectives

Early neurological deterioration (END) occurs in up to one-third of patients with acute ischemic stroke (AIS) and associated with poor outcome. The role of serum bilirubin in END remains controversial. This study aims to investigate the association of total bilirubin (TBIL), direct bilirubin (DBIL) and indirect bilirubin (IBIL) with END.

Methods

This study was a cross-sectional retrospective study with 344 AIS patients enrolled. We retrospectively reviewed consecutive AIS patients with END through a medical record retrieval system and enrolled patients as control randomly from the AIS patients without END at the same period. The bilirubin levels were compared between the END group and No END group. The correlations of bilirubin with END were assessed according to the bilirubin tertiles on the cohort of different genders.

Results

In women, as the bilirubin level increased, the occurrence of END showed an increasing trend. The linear association was significant based on the tertiles of all bilirubin types (TBIL p = 0.003; DBIL p = 0.025; IBIL p = 0.025), while in men no similar trend was observed. After adjustment for confounders, higher TBIL (p for trend 0.009) and DBIL (p for trend 0.033) levels were associated with increased risk of END in women. The adjusted OR for T3 relative to T1 was 5.240 (95% CI 1.496-18.347) in TBIL and 3.549 (95% CI 1.089-11.566) in DBIL. Multivariate logistic regression showed that DBIL was independently associated with END in women (OR 1.717, 95% CI 1.106-2.666). The study also found that DBIL was superior to TBIL and IBIL in prediction of END occurrence in women, with greater predictive value.

Discussion

There were gender differences in the relationship between bilirubin and END, and DBIL level was positively associated with END occurrence in women, not in men. DBIL had greater incremental predictive value for END than TBIL and IBIL.

Sex differences in the relationship between serum total bilirubin and risk of incident metabolic syndrome in community-dwelling adults: Propensity score analysis using longitudinal cohort data over 16 years

BACKGROUND

Research on identifiable risks for metabolic syndrome (MetS) is ongoing, and growing evidence suggests that bilirubin is a potent antioxidant and cytoprotective agent against MetS. However, there have been conflicting results on the association between bilirubin and MetS. Our study aimed to validate the association by separately stratifying data for men and women in a longitudinal prospective study.

METHODS

Data were derived from the Korean Genome Epidemiology Study provided by the Korea Centers for Disease Control and Prevention. Data from 5,185 adults aged 40-69 years (3,089 men and 2,096 women) without MetS were analyzed. The participants were divided according to sex-specific quartiles of serum total bilirubin levels and followed up biennially for 16 years (until 2018). The log-rank test was used for obtaining the Kaplan-Meier curves of cumulative incidence of MetS according to sex-specific serum total bilirubin quartiles, and the hazard ratios (HRs) with 95% confidence intervals (CIs) for incident metabolic syndrome were analyzed with a multiple Cox proportional hazard regression analysis model, after propensity score matching for removing differences at baseline.

RESULTS

With increasing serum total bilirubin quartiles, the incidence rate per 1000 person-years proportionally decreased in both men and women. After propensity score matching and adjusting for confounding variables, the HRs (95% CIs) for MetS of the highest quartile in reference to the lowest quartile were 1.00 (0.80-1.24) for men and 0.80 (0.65-0.99) for women. Higher quartiles of serum total bilirubin showed significantly lower cumulative incidence of MetS in women (log-rank test p = 0.009), but not in men (log-rank test p = 0.285).

CONCLUSION

Serum total bilirubin levels were significantly inversely associated with MetS in women, but there was no significant association observed in men. Sex differences in the effects of serum total bilirubin should be noted when predicting incident MetS by sex in clinical settings.

Time-resolved map of serum metabolome profiling in D-galactose-induced aging rats with exercise intervention

Exercise, an intervention with wide-ranging effects on the whole body, has been shown to delay aging. Due to aging and exercise as modulator of metabolism, a picture of how exercise delayed D-galactose (D-gal)-induced aging in a time-resolved manner was presented in this paper. The mapping of molecular changes in response to exercise has become increasingly accessible with the development of omics techniques. To explore the dynamic changes during exercise, the serum of rats and D-gal-induced aging rats before, during, and after exercise was analyzed by untargeted metabolomics. The variation of metabolites was monitored to reveal the specific response to D-gal-induced senescence and exercise in multiple pathways, especially the basal amino acid metabolism, including glycine serine and threonine metabolism, cysteine and methionine metabolism, and tryptophan metabolism. The homeostasis was disturbed by D-gal and maintained by exercise. The paper was expected to provide a theoretical basis for the study of anti-aging exercise.

Predictive values of bilirubin for in-hospital adverse events in patients with ST-segment elevation myocardial infarction after primary percutaneous coronary intervention

PURPOSE

To investigate the association between serum bilirubin levels and in-hospital Major Adverse Cardiac Events (MACE) in patients with ST-segment Elevation Myocardial Infarction (STEMI) undergoing primary Percutaneous Coronary Intervention (PCI).

METHODS

A total of 418 patients with STEMI who underwent primary PCI were enrolled from October 1st, 2021 to October 31st 2022. The average age of enrolled participants was 59.23 years, and 328 patients (78.50%) were male patients. Patients were divided into MACE (patients with angina pectoris after infarction, recurrent myocardial infarction, acute heart failure, cardiogenic shock, malignant arrhythmias, or death after primary PCI) (n = 98) and non-MACE (n = 320) groups. Univariate and multivariate logistic regression analyses were performed to estimate the association between different bilirubin levels including Total Bilirubin (TB), Direct Bilirubin (DB), Indirect Bilirubin (IDB), and risk of in-hospital MACE. The area under the Receiver Operating Characteristic (ROC) curve was used to determine the accuracy of bilirubin levels in predicting in-hospital MACE.

RESULTS

The incidence of MACE in STEMI patients increased from the lowest to the highest bilirubin tertiles. Multivariate logistic regression analysis showed that increased total bilirubin level was an independent predictor of in-hospital MACE in patients with STEMI (p for trend = 0.02). Compared to the first TB group, the ORs for risk of MACE were 1.58 (95% CI 0.77‒3.26) and 2.28 (95% CI 1.13‒4.59) in the second and third TB groups, respectively. The ROC curve analysis showed that the areas under the curve for TB, DB and IDB in predicting in-hospital MACE were 0.642 (95% CI 0.578‒0.705, p < 0.001), 0.676 (95% CI 0.614‒0.738, p < 0.001), and 0.619 (95% CI 0.554‒0.683, p < 0.001), respectively.

CONCLUSIONS

The current study showed that elevated TB, DB, and IDB levels are independent predictors of in-hospital MACE in patients with STEMI after primary PCI, and that DB has a better predictive value than TB and IDB.

Genetics of Plasma Bilirubin and Associations between Bilirubin and Cardiometabolic Risk Profiles in Danish Children and Adolescents

Bilirubin is the end product of heme catabolism, mainly produced by the breakdown of mature red blood cells. Due to its anti-inflammatory, antioxidant, antidiabetic, and antilipemic properties, circulating bilirubin concentrations are inversely associated with the risk of cardiovascular disease, type 2 diabetes, and all-cause mortality in adults. Some genetic loci associated with circulating bilirubin concentrations have been identified by genome-wide association studies in adults. We aimed to examine the relationship between circulating bilirubin, cardiometabolic risk factors, and inflammation in children and adolescents and the genetic architecture of plasma bilirubin concentrations. We measured fasting plasma bilirubin, cardiometabolic risk factors, and inflammatory markers in a sample of Danish children and adolescents with overweight or obesity (n = 1530) and in a population-based sample (n = 1820) of Danish children and adolescents. Linear and logistic regression analyses were performed to analyze the associations between bilirubin, cardiometabolic risk factors, and inflammatory markers. A genome-wide association study (GWAS) of fasting plasma concentrations of bilirubin was performed in children and adolescents with overweight or obesity and in a population-based sample. Bilirubin is associated inversely and significantly with a number of cardiometabolic risk factors, including body mass index (BMI) standard deviation scores (SDS), waist circumference, high-sensitivity C-reactive protein (hs-CRP), homeostatic model assessment for insulin resistance (HOMA-IR), hemoglobin A1c (HbA1c), low-density lipoprotein cholesterol (LDL-C), triglycerides, and the majority of measured inflammatory markers. In contrast, bilirubin was positively associated with fasting plasma concentrations of alanine transaminase (ALT), high-density lipoprotein cholesterol (HDL-C), systolic blood pressure (SDS), and the inflammatory markers GH, PTX3, THBS2, TNFRSF9, PGF, PAPPA, GT, CCL23, CX3CL1, SCF, and TRANCE. The GWAS showed that two loci were positively associated with plasma bilirubin concentrations at a p-value threshold of <5 × 10-8 (rs76999922: β = -0.65 SD; p = 4.3 × 10-8, and rs887829: β = 0.78 SD; p = 2.9 × 10-247). Approximately 25% of the variance in plasma bilirubin concentration was explained by rs887829. The rs887829 was not significantly associated with any of the mentioned cardiometabolic risk factors except for hs-CRP. Our findings suggest that plasma concentrations of bilirubin non-causally associates with cardiometabolic risk factors in children and adolescents.

Atazanavir-induced unconjugated hyperbilirubinemia prevents vascular hyporeactivity during experimental human endotoxemia

Objective

Inflammation-induced free radical release is important in the pathogenesis of several diseases, including atherosclerosis and sepsis. Heme oxygenase (HO) breaks down heme into carbon monoxide, iron, and biliverdin. Biliverdin IXα is directly converted to bilirubin by biliverdin reductase. Unconjugated bilirubin is a powerful antioxidant, and elevated levels have beneficial effects in preclinical models and human cardiovascular disease. However, its impact during acute inflammation in humans is unknown. In the present study, we investigated the impact of atazanavir-induced (unconjugated) hyperbilirubinemia on antioxidant capacity, inflammation, and vascular dysfunction in human experimental endotoxemia.

Approach and results

Following double-blinded four-day treatment with atazanavir 2dd300 mg (or placebo), twenty healthy male volunteers received 2 ng/kg Escherichia coli lipopolysaccharide intravenously. Blood was drawn to determine the bilirubin levels, antioxidant capacity, and cytokine response. It was demonstrated that following atazanavir treatment, total bilirubin concentrations increased to maximum values of 4.67 (95%CI 3.91-5.59) compared to 0.82 (95%CI 0.64-1.07) mg/dL in the control group (p<0.01). Furthermore, the anti-oxidant capacity, as measured by the ferric-reducing ability of plasma (FRAP), was significantly increased with 36% in hyperbilirubinemia subjects (p<0.0001), and FRAP concentrations correlated strongly to bilirubin concentrations (R2 = 0.77, p<0.001). Hyperbilirubinemia attenuated the release of interleukin-10 from 377 (95%CI 233-609) to 219 (95%CI 152-318) pg/mL (p=0.01), whereas the release of pro-inflammatory cytokines remained unaltered. In vitro, in the absence of hyperbilirubinemia, atazanavir did not influence lipopolysaccharide-induced cytokine release in a whole blood assay. Vascular function was assessed using forearm venous occlusion plethysmography after intra-arterial infusion of acetylcholine and nitroglycerin. Hyperbilirubinemia completely prevented the LPS-associated blunted vascular response to acetylcholine and nitroglycerin.

Conclusions

Atazanavir-induced hyperbilirubinemia increases antioxidant capacity, attenuates interleukin-10 release, and prevents vascular hyporesponsiveness during human systemic inflammation elicited by experimental endotoxemia.

Clinical trial registration

http://clinicaltrials.gov, identifier NCT00916448.

Association between bilirubin levels and risk of stroke: a systematic review and meta-analysis

OBJECTIVE

To evaluate the association between bilirubin levels and stroke risk.

DESIGN

Systematic review and meta-analysis, reported in accordance with Meta-analysis Of Observational Studies in Epidemiology guidelines.

DATA SOURCES

The PubMed, Embase, Cochrane Central Register of Controlled Trials and China National Knowledge Infrastructure Databases were searched from inception up to 27 February 2022.

ELIGIBILITY CRITERIA

Cohort studies assessing the dose-response relationship between bilirubin levels and risk of stroke were eligible for inclusion. There were no language restrictions.

DATA EXTRACTION AND SYNTHESIS

All data from eligible studies were collected and assessed by two independent investigators. We generated pooled relative risks (RRs) with 95% CIs. We used a restricted cubic spline model for the dose-response analyses. Subsequent subgroup analyses were conducted according to stroke outcomes, follow-up duration, geographical area and size of the cohort.

RESULTS

Nine articles including results from 11 cohort studies with 7835 cases of stroke and 263 596 participants met the inclusion criteria. The summarised RR of stroke comparing the highest and lowest bilirubin level was 0.85 (95% CI 0.72 to 0.99). The dose-response analysis indicated that a 15 µmol/L increment of bilirubin level was associated with an 18% lower risk of stroke (RR=0.82, 95% CI 0.67 to 0.99). For ischaemic stroke, the RR was 0.76 (95% CI 0.58 to 0.99). Significant publication bias was not detected.

CONCLUSIONS

Elevated bilirubin levels were associated with a decreased risk of stroke among adults.

PROSPERO REGISTRATION NUMBER

CRD42017071497.

Associations of genome-wide and regional autozygosity with 96 complex traits in old order Amish

BACKGROUND

Autozygosity, the proportion of the genome that is homozygous by descent, has been associated with variation in multiple health-related traits impacting evolutionary fitness. Autozygosity (FROH) is typically measured from runs of homozygosity (ROHs) that arise when identical-by-descent (IBD) haplotypes are inherited from each parent. Population isolates with a small set of common founders have elevated autozygosity relative to outbred populations.

METHODS

In this study, we examined whether degree of autozygosity was associated with variation in 96 cardiometabolic traits among 7221 Old Order Amish individuals residing in Lancaster County, PA. We estimated the average length of an ROH segment to be 6350 KB, with each individual having on average 17.2 segments 1.5 KB or larger. Measurements of genome-wide and regional FROH were used as the primary predictors of trait variation in association analysis.

RESULTS

In genome-wide FROH analysis, we did not identify any associations that withstood Bonferroni-correction (p = 0.0005). However, on regional FROH analysis, we identified associations exceeding genome-wide thresholds for two traits: serum bilirubin levels, which were significantly associated with a region on chromosome 2 localized to a region surrounding UGT1A10 (p = 1 × 10- 43), and HbA1c levels, which were significantly associated with a region on chromosome 8 localized near CHRNB3 (p = 8 × 10- 10).

CONCLUSIONS

These analyses highlight the potential value of autozygosity mapping in founder populations.

Genetically determined serum bilirubin level and the risk of heart failure: A mendelian randomization study

Background: The association between serum bilirubin level and heart failure (HF) was controversial in previous observational studies and the causal effects of bilirubin on HF have not been investigated. Here, we conducted a Mendelian randomization (MR) study to investigate the associations between genetically determined bilirubin level and HF. Methods: Summary data on the association of single nucleotide polymorphisms (SNPs) with serum bilirubin levels were obtained from genome-wide association study (GWAS) for individuals of European descent and East Asian descent separately. Statistical data for gene-HF associations were extracted from three databases: the HERMES Consortium (47,309 cases and 930,014 controls), FinnGen study (30,098 cases and 229,612 controls) for European population and Biobank Japan (2,820 HF cases and 192,383 controls) for East Asian population. We applied a two-sample Mendelian randomization framework to investigate the causal association between serum bilirubin and HF. Results: Findings from our MR analyses showed that genetically determined serum bilirubin levels were not causally associated with HF risk in either European or East Asian population (odds ratio [OR] = 1.01 and 95% confidence interval [CI] = .97-1.05 for HERMES Consortium; OR = 1.01 and 95% CI = .98-1.04 for FinnGen Study; OR = .82, 95% CI: .61-1.10 for Biobank Japan). These results remained unchanged using different Mendelian randomization methods and in sensitivity analyses. Conclusion: Our study did not find any evidence to support a causal association between serum bilirubin and HF.

Establishment of a Predictive Model for Poor Prognosis of Incomplete Revascularization in Patients with Coronary Heart Disease and Multivessel Disease

OBJECTIVE

To establish a predictive model for poor prognosis after incomplete revascularization (ICR) in patients with multivessel coronary artery disease (MVD).

METHODS

Clinical data of 757 patients with MVD and ICR after percutaneous coronary intervention (PCI) in the Affiliated Hospital of Chengde Medical University from January 2020 to August 2021 were retrospectively collected. The least absolute shrinkage and selection operator regression method was used to screen variables, and multivariate logistic regression was used to establish a predictive model. An independent cohort was used to validate the model. The C-statistic was used to verify and evaluate the discriminative ability of the model; the calibration curve was drawn, and the decision curve analysis (DCA) was performed to evaluate the calibration degree, the clinical net benefit, and the practicability of the model.

RESULTS

The predictive factors included female, age, unconjugated bilirubin, uric acid, low-density lipoprotein, hyperglycemia, total occlusion, and severe tortuosity lesion on coronary angiography. The C-statistic of the training and validation sets were 0.628 and 0.745, respectively. The statistical value of the Hosmer-Lemeshow test for the calibration curve of the training and validation sets were 5.27(P = 0.873) and 6.27 (P = 0.792), respectively. DCA showed that the model was clinically applicable when the predicted probability value of major adverse cardiovascular events(MACEs) ranged from 0.07 to 0.68.

CONCLUSIONS

We established a predictive model for poor prognosis after ICR in patients with MVD. The predictive and calibration ability and the clinical net benefit of the predictive model were good, indicating that it can be used as an effective tool for the early prediction of poor prognosis after ICR in patients with MVD.

Pharmaceutical strategies for preventing toxicity and promoting antioxidant and anti-inflammatory actions of bilirubin

Bilirubin (BR) is the final product of haem catabolism. Disruptions along BR metabolic/transport pathways resulting from inherited disorders can increase plasma BR concentration (hyperbilirubinaemia). Unconjugated hyperbilirubinemia may induce BR accumulation in brain, potentially causing irreversible neurological damage, a condition known as BR encephalopathy or kernicterus, to which newborns are especially vulnerable. Numerous pharmaceutical strategies, mostly based on hemoperfusion, have been proposed over the last decades to identify new valid, low-risk alternatives for BR removal from plasma. On the other hand, accumulating evidence indicates that BR produces health benefits due to its potent antioxidant, anti-inflammatory and immunomodulatory action with a significant potential for the treatment of a multitude of diseases. The present manuscript reviews both such aspects of BR pharmacology, gathering literature data on applied pharmaceutical strategies adopted to: (i) reduce the plasma BR concentration for preventing neurotoxicity; (ii) produce a therapeutic effect based on BR efficacy in the treatment of many disorders.

Genetically personalised organ-specific metabolic models in health and disease

Understanding how genetic variants influence disease risk and complex traits (variant-to-function) is one of the major challenges in human genetics. Here we present a model-driven framework to leverage human genome-scale metabolic networks to define how genetic variants affect biochemical reaction fluxes across major human tissues, including skeletal muscle, adipose, liver, brain and heart. As proof of concept, we build personalised organ-specific metabolic flux models for 524,615 individuals of the INTERVAL and UK Biobank cohorts and perform a fluxome-wide association study (FWAS) to identify 4312 associations between personalised flux values and the concentration of metabolites in blood. Furthermore, we apply FWAS to identify 92 metabolic fluxes associated with the risk of developing coronary artery disease, many of which are linked to processes previously described to play in role in the disease. Our work demonstrates that genetically personalised metabolic models can elucidate the downstream effects of genetic variants on biochemical reactions involved in common human diseases.

Relationship between serum indirect bilirubin levels and skeletal muscle mass in older male and female patients with type 2 diabetes

Objective

We previously showed that low serum bilirubin levels are associated with disability in quality of daily living in older patients with diabetes. However, the underlying mechanism is not fully understood. The aim of this study is to assess the relationship between serum bilirubin levels and skeletal muscle mass in older patients with type2 diabetes.

Methods

A total of 272 older patients with type2 diabetes (152 male and 120 female) aged 60 years and over were continuously recruited from April 2020 to July 2020. Body composition was evaluated by bioelectrical impedance analysis. The skeletal muscle mass index (SMI) was calculated as appendicular muscle mass divided by height squared (m²).

Results

The SMI was markedly lower in old-old patients (aged 75 years and over) than in young-old patients (aged 60–74 years) in both male and female (7.1 ± 0.8 kg/m² vs 7.6 ± 0.9 kg/m², P<0.001; 5.5 ± 0.9 kg/m² vs 6.3 ± 0.8 kg/m², P<0.001, respectively). Multivariate regression analysis showed that the SMI was associated with body mass index (BMI) (p<0.001) and age (p = 0.048) in male young-old patients, while it was associated with BMI (p<0.001), age (p = 0.008), and serum indirect bilirubin levels (p = 0.038) in male old-old patients. In female, the SMI was associated with BMI (p<0.001) and age (p = 0.042) in young-old patients and associated with BMI alone (p<0.001) in old-old patients.

Conclusion

Serum indirect bilirubin levels may be associated with the decreased skeletal muscle mass in male older patients (aged 75 years and over) with type 2 diabetes.

Use of high-resolution metabolomics to assess the biological perturbations associated with maternal exposure to Bisphenol A and Bisphenol F among pregnant African American women

BACKGROUND

Human and animal exposure to bisphenol A (BPA) has been associated with adverse developmental and reproductive effects. The molecular mechanisms by which BPA exposure exerts its effects are not well-understood, even less known about its analogues bisphenol F (BPF). To address these knowledge gaps, we conducted an untargeted metabolome-wide association study (MWAS) to identify metabolic perturbations associated with BPA/BPF exposures in a pregnant African American cohort.

METHODS

From a subset of study participants enrolled in the Atlanta African American Maternal-Child cohort, we collected both urine samples, for targeted exposure assessment of BPA (N = 230) and BPF (N = 48), and serum samples, for high-resolution metabolomics (HRM) profiling (N = 230), during early pregnancy (8-14 weeks' gestation). Using an established untargeted HRM workflow consisting of MWAS modeling, pathway enrichment analysis, and chemical annotation and confirmation, we investigated the potential metabolic pathways and features associated with BPA/BPF exposures.

RESULTS

The geometric mean creatinine-adjusted concentrations of urinary BPA and BPF were 0.85 ± 2.58 and 0.70 ± 4.71 µg/g creatinine, respectively. After false positive discovery rate correction at 20 % level, 264 and 733 unique metabolic features were significantly associated with urinary BPA and BPF concentrations, representing 10 and 12 metabolic pathways, respectively. Three metabolic pathways, including steroid hormones biosynthesis, lysine and lipoate metabolism, were significantly associated with both BPA and BPF exposure. Using chemical standards, we have confirmed the chemical identity of 16 metabolites significantly associated with BPA or BPF exposure.

CONCLUSIONS

Our findings support that exposure to BPA and BPF in pregnant women is associated with the perturbation of aromatic amino acid metabolism, xenobiotics metabolism, steroid biosynthesis, and other amino acid metabolism closely linked to stress responses, inflammation, neural development, reproduction, and weight regulation.

Association of serum total bilirubin levels with progressive renal decline and end-stage kidney disease: 10-year observational cohort study in Japanese patients with diabetes

Objective

Previous reports have demonstrated the association of serum bilirubin levels with the progression of diabetic nephropathy. The objective of this study is to assess the association of basal bilirubin levels with progressive renal decline (PRD) and end-stage kidney disease (ESKD).

Methods

A total of 298 patients with diabetes who visited Kyushu University Hospital (Japan) were recruited and followed up for 10 years. PRD was defined as a negative change in estimated glomerular filtration ratio (eGFR) >3.7%/year, 2.5th percentile. Logistic regression analysis was performed to evaluate the association of total bilirubin levels with PRD and its cut-off point was determined by receiver operating characteristic (ROC) analysis. Kaplan-Meier method and Cox hazard regression analysis were used to evaluate the predictive ability of its cut-off point for ESKD.

Results

Logistic regression model showed that total bilirubin levels were significantly associated with PRD, and ROC analysis showed that its cut-off point was 0.5 mg/dL. Kaplan-Meier method showed that the percent of patients who reached two endpoints, composite endpoint (ESKD or doubling of creatinine level) or 30% eGFR decline, was significantly higher in the low bilirubin group than in the high bilirubin group (18.5% vs 11.0%, P = 0.045; 49.1% vs 42.1%, P = 0.045, respectively, log-rank test). Cox hazard regression models confirmed the independence of the predictive ability of its cut-off point.

Conclusions

Serum total bilirubin levels were negatively associated with PRD in diabetic nephropathy and its cut-off point was 0.5 mg/dL. It may be clinically useful for identifying patients at high risk of ESKD.

Crosstalk between Host Genome and Metabolome among People with HIV in South Africa

Genome-wide association studies (GWAS) of circulating metabolites have revealed the role of genetic regulation on the human metabolome. Most previous investigations focused on European ancestry, and few studies have been conducted among populations of African descent living in Africa, where the infectious disease burden is high (e.g., human immunodeficiency virus (HIV)). It is important to understand the genetic associations of the metabolome in diverse at-risk populations including people with HIV (PWH) living in Africa. After a thorough literature review, the reported significant gene−metabolite associations were tested among 490 PWH in South Africa. Linear regression was used to test associations between the candidate metabolites and genetic variants. GWAS of 154 plasma metabolites were performed to identify novel genetic associations. Among the 29 gene−metabolite associations identified in the literature, we replicated 10 in South Africans with HIV. The UGT1A cluster was associated with plasma levels of biliverdin and bilirubin; SLC16A9 and CPS1 were associated with carnitine and creatine, respectively. We also identified 22 genetic associations with metabolites using a genome-wide significance threshold (p-value < 5 × 10−8). In a GWAS of plasma metabolites in South African PWH, we replicated reported genetic associations across ancestries, and identified novel genetic associations using a metabolomics approach.

Associations between UGT1A1 and SLCO1B1 polymorphisms and susceptibility to neonatal hyperbilirubinemia in Thai population

Hyperbilirubinemia is the main mechanism that causes neonatal jaundice, and genetics is one of the risk factors of hyperbilirubinemia. Therefore, this study aims to explore the correlation between two genes, UGT1A1 and SLCO1B1, and hyperbilirubinemia in Thai neonates. One hundred thirty seven neonates were recruited from Division of Clinical Chemistry, Ramathibodi Hospital. UGT1A1*28 and *6 were determined by pyrosequencing whereas, SLCO1B1 388A > G and 521 T > C genetic variants were determined by TaqMan® real-time polymerase chain reaction. Neonates carrying with homozygous (AA) and heterozygous (GA) variants in UGT1A1*6 were significantly related to hyperbilirubinemia development compared with wild type (GG; P < 0.001). To the combined of UGT1A1, total bilirubin levels in homozygous variant were higher significantly than heterozygous variant and wild type (P = 0.002, P = 0.003, respectively). Moreover, SLCO1B1 combination was significant differences between the hyperbilirubinemia and the control group (P = 0.041). SLCO1B1 521 T > C variant provide protection for Thai neonatal hyperbilirubinemia (P = 0.041). There are no significant differences in UGT1A1*28 and SLCO1B1 388A > G for the different severity of hyperbilirubinemia. The combined UGT1A1*28 and *6 polymorphism is a strong risk factor for the development of severe hyperbilirubinemia in Thai neonates. Therefore, we suggest neonates with this gene should be closely observed to avoid higher severities of bilirubin.

Association of Plasma Bilirubin Levels With Peripheral Arterial Disease in Chinese Hypertensive Patients: New Insight on Sex Differences

Background and aims: Previous studies have indicated that Plasma total bilirubin (TBiL) might play an essential role in peripheral arterial disease (PAD). However, the effects of different levels of TBiL on PAD development remain uncertain. We aimed to examine the TBiL and the prevalence of PAD among Chinese adults with hypertension, with particular attention paid to sex differences.

Methods: A total of 10,900 hypertensive subjects were included in the current study. The mean age of our study participants was 63.86 ± 9.25 years, and there were 5,129 males and 5,771 females. The outcome was peripheral arterial disease (PAD), defined as present when the ankle-brachial index (ABI) of either side was ≤0.90. The association between TBiL and PAD was examined using multivariate logistic regression analysis and the restricted cubic spline.

Results: Of 10,900 hypertensive participants, 350 (3.21%) had PAD, and the mean plasma total bilirubin was 14.66 (6.86) μmol/L. The mean TBiL was 15.67 μmol/L in men and 13.76 μmol/L in women. The smoothing curve showed that a U-shaped curve association existed between TBiL and the prevalence of PAD in Chinese adults with hypertension. When stratified by sex, TBiL was significantly U-shaped associated with PAD among men but not women. Among males, the inflection point was 11.48 μmol/L; to the left inflection point, the effect size and 95% CI were 0.08, 0.01, 0.66, respectively; to the right inflection point, OR, 5.16; 95% CI,1.64, 16.25.

Conclusions: We found an independent U-shaped association between TBiL and the prevalence of PAD among hypertensive subjects and a differential association between men and women. We further revealed a turning point by threshold effect analysis.

Elevated serum bilirubin may significantly reduce coronary heart disease risk in females: A prospective cohort study

BACKGROUND AND AIMS

There is still inconsistent evidence over the protective effect of total bilirubin on the development of coronary heart disease (CHD). Therefore, we aimed to investigate the association between bilirubin in population subtypes and the risks of CHD between different gender and menstruation subgroups.

METHODS AND RESULTS

In this prospective cohort study, 29,750 participants free of CHD with an average age of 47 ± 14 years were recruited at baseline; of these, 720 CHD first-attack cases were collected after 7-years of follow up. The covariate-adjusted Cox proportional hazards models were used to estimate hazard ratios (HRs) of CHD with 95% confidence intervals (CIs). The serum bilirubin concentration was quarterly stratified based on the distribution of healthy population without CHD onset. The HRs of incident CHD decreased with elevated bilirubin in females (ρ trend<0.05), but not males. In postmenopausal females, compared with the lowest quartile of total bilirubin, the adjusted HRs for the third and fourth quartiles were 0.64 (95% CI: 0.45, 0.93) and 0.59 (95% CI: 0.42, 0.86), the adjusted HRs in the third and fourth quartiles of direct bilirubin were 0.56 (0.39, 0.82) and 0.56 (0.38, 0.81), and for indirect bilirubin, corresponding HR in the highest quartile was 0.56 (0.38, 0.83).

CONCLUSION

Elevated serum bilirubin was inversely associated with adjusted HRs of CHD in females, especially postmenopausal females. The relationship between elevated direct bilirubin and reduced HRs of CHD may be closer than indirect bilirubin in postmenopausal females.

Dependence of blood biochemical parameters on various genotypes of the UGT1A1 gene associated with gilbert's syndrome

Diagnosis of Gilbert's syndrome is based on the detection of homozygous carriage of an additional TA-repeat in the promoter of the UGT1A1 gene, leading to a decrease in the activity of the UGT enzyme. No large studies have been done in the Russian Federation on the prevalence of carriage of Gilbert's syndrome, as well as the biochemical and molecular profile of such patients. The aim of the study is to evaluate biochemical and molecular genetic parameters in patients with Gilbert's syndrome in Russia. The study included 124 healthy volunteers (group 1) and 5650 patients with suspected Gilbert's syndrome (group 2). The number of TA-repeats of the promoter region of the UGT1A1 gene was determined by the method of fragment analysis for all participants. The following biochemical parameters were analyzed for 299 patients from group 2: the level of bilirubin and its fractions, AST, ALT, cholesterol and LDL. In group 1 the prevalence of genotype (TA)6/(TA)6 was 39,52%, (TA)6/(TA)7 - 53,23%, (TA)7/(TA)7 - 7,26%, no rare forms were found. In group 2 the prevalence of genotype (TA)6/(TA)6 was 6,04%, (TA)6/(TA)7 - 20,05%, (TA)7/(TA)7 - 73,7%, rare alleles - 0,2%. Rare alleles included (TA)5/(TA)6, (TA)5/(TA)7, (TA)6/(TA)8 and (TA)7/(TA)8, as well as a new genotype not described in the literature previously - (TA)7/(TA)9. When assessing the level of total bilirubin and its fractions, a difference was revealed between the genotype of Gilbert's syndrome (TA)7/(TA)7 and the reference genotype (TA)6/(TA)6, and between genotypes (TA)7/(TA)7 and (TA)6/(TA)7. A significant increase in total bilirubin was demonstrated in carriers of a larger number of TA-repeats. There was no significant difference in the concentration of ALT, AST, cholesterol or LDL between different genotypes.The number of TA-repeats of the UGT1A1 gene affects the increase of total bilirubin and its indirect fraction, including the cases of rare allelic variants (TA≤5, TA≥8), but not the activity of ALT and AST and the lipid profile.

Sexual Dimorphism: increased sterol excretion leads to hypocholesterolaemia in female hyperbilirubinaemic Gunn rats

Abstract

Circulating bilirubin is associated with reduced serum cholesterol concentrations in humans and in hyperbilirubinaemic Gunn rats. However, mechanisms contributing to hypocholesterolaemia remain unknown. Therefore, this study aimed to investigate cholesterol synthesis, transport and excretion in mutant Gunn rats. Adult Gunn and control rats were assessed for daily faecal sterol excretion using metabolic cages, and water was supplemented with [1‐¹³C]‐acetate to determine cholesterol synthesis. Bile was collected to measure biliary lipid secretion. Serum and liver were collected for biochemical analysis and for gene/protein expression using RT‐qPCR and western blot, respectively. Additionally, serum was collected and analysed from juvenile rats. A significant interaction of sex, age and phenotype on circulating lipids was found with adult female Gunn rats reporting significantly lower cholesterol and phospholipids. Female Gunn rats also demonstrated elevated cholesterol synthesis, greater biliary lipid secretion and increased total faecal cholesterol and bile acid excretion. Furthermore, they possessed increased hepatic low‐density lipoprotein (LDL) receptor and SREBP2 expression. In contrast, there were no changes to sterol metabolism in adult male Gunn rats. This is the first study to demonstrate elevated faecal sterol excretion in female hyperbilirubinaemic Gunn rats. Increased sterol excretion creates a negative intestinal sterol balance that is compensated for by increased cholesterol synthesis and LDL receptor expression. Therefore, reduced circulating cholesterol is potentially caused by increased hepatic uptake via the LDL receptor. Future studies are required to further evaluate the sexual dimorphism of this response and whether similar findings occur in females with benign unconjugated hyperbilirubinaemia (Gilbert's syndrome).

Key points

Female adult hyperbilirubinaemic (Gunn) rats demonstrated lower circulating cholesterol, corroborating human studies that report a negative association between bilirubin and cholesterol concentrations.

Furthermore, female Gunn rats had elevated sterol excretion creating a negative intestinal sterol balance that was compensated for by elevated cholesterol synthesis and increased hepatic low‐density lipoprotein (LDL) receptor expression.

Therefore, elevated LDL receptor expression potentially leads to reduced circulating cholesterol levels in female Gunn rats providing an explanation for the hypocholesterolaemia observed in humans with elevated bilirubin levels.

This study also reports a novel interaction of sex with the hyperbilirubinaemic phenotype on sterol metabolism because changes were only reported in females and not in male Gunn rats.

Future studies are required to further evaluate the sexual dimorphism of this response and whether similar findings occur in females with benign unconjugated hyperbilirubinaemia (Gilbert's syndrome).

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.

Hepatic Interactions in Atherosclerotic Heart Disease

Atherosclerotic heart disease remains a major cause of morbidity and mortality worldwide. The past few decades have seen the emergence of chronic inflammation as a mediator of atherosclerosis. Although the heart and vascular system remain the organ systems most affected in the atherosclerotic process, chronic inflammation and ischemia trigger a systemic multi-organ response. The liver is a critical organ for systemic hemostasis and recent developments have established an important role of the liver in response to atherosclerosis and myocardial ischemia. In addition, the rapid emergence of systemic liver diseases has unraveled a pathophysiological link with heart disease with therapeutic implications. In this review, we explore the relationship between the liver and the heart in myocardial ischemia, describe epidemiological associations between various liver pathologies and coronary heart disease, and elucidate practical challenges in the clinical management of patients with concomitant coronary heart disease and hepatic abnormalities.

Oxidative Stress and Related Biomarkers in Gilbert's Syndrome: A Secondary Analysis of Two Case-Control Studies

Bilirubin is an important antioxidant and a modulator of biological functions. However, most of the protection against oxidative stress was shown in vitro or ex vivo. The aim of this case-control study was to investigate whether subjects with Gilbert's syndrome (GS) experience different levels of lipid and protein oxidation (as well as differences in oxidative stress related markers) compared to healthy controls. GS subjects (n =119) demonstrated higher serum levels of unconjugated bilirubin (p < 0.001), a lower BMI (p < 0.001), 37% higher antioxidant potential assessed as ferric reducing ability potential (p < 0.001), higher advanced oxidation protein products (p < 0.01) andlower apolipoprotein B (p < 0.05), hs-C-reactive protein (p < 0.05), interleukin 6 (p < 0.001) and interleukin 1 beta (p < 0.05) values compared to healthy controls (n =119). Furthermore, the resting heart rate was significantly lower in the GS group (p < 0.05). Stronger protective effects for GS subjects were demonstrated in the older subgroup (n =104, average age 50 years) compared to those of the younger group (n =134, average age 27 years). Although not all markers related to oxidative stress were different between the groups (e.g., malondialdehyde, homocysteine, oxLDL, and myeloperoxidase; p >0.05), the observed differences contribute to the explanation of why GS serves as an important protector in the pathogenesis of metabolic, oxidative stress related diseases.

Bilirubin Links HO-1 and UGT1A1*28 Gene Polymorphisms to Predict Cardiovascular Outcome in Patients Receiving Maintenance Hemodialysis

Serum bilirubin levels, which are determined by a complex interplay of various enzymes, including heme oxygenase-1 (HO-1) and uridine diphosphate–glucuronosyl transferase (UGT1A1), may be protective against progression of cardiovascular disease (CVD) in hemodialysis patients. However, the combined effect of HO-1 and UGT1A1*28 gene polymorphisms on CVD outcomes among hemodialysis patients is still unknown. This retrospective study enrolled 1080 prevalent hemodialysis patients and the combined genetic polymorphisms of HO-1 and UGT1A1 on serum bilirubin were analyzed. Endpoints were CVD events and all-cause mortality. Mean serum bilirubin was highest in patients with S/S + S/L of the HO-1 promoter and UGT1A1 7/7 genotypes (Group 1), intermediate in those with S/S + S/L of the HO-1 promoter and UGT1A1 7/6 + 6/6 genotypes (Group 2), and lowest in the carriers with the L/L HO-1 promoter and UGT1A1 7/6 + 6/6 genotypes (Group 3) (p < 0.001). During a median follow-up of 50 months, 433 patients developed CVD. Compared with patients in Group 3, individuals among Groups 1 and 2 had significantly lower risks for CVD events (adjusted hazard ratios (aHRs) of 0.35 for Group 1 and 0.63 for Group 2), respectively. Compared with the lower bilirubin tertile, the aHRs were 0.72 for the middle tertile and 0.40 for the upper tertile for CVD events. We summarized that serum bilirubin as well as HO-1 and UGT1A1 gene polymorphisms were associated with CVD among patients receiving chronic hemodialysis.

Bilirrubina: Medición y utilidad clínica en la enfermedad hepática

Un aumento en los niveles plasmáticos de bilirrubina es una alteración frecuente. Puede deberse a cualquier causa que altere alguna de las fases de su metabolismo: a) producción excesiva de bilirrubina (ej. hemólisis patológica); b) defecto en la captación hepática, con aumento de bilirrubina indirecta); c) defecto de conjugación, por alteración del enzima encargada (UDP-glucuronosiltransferasa); y d) defecto de excreción biliar, con aumento de bilirrubina directa, por defectos en las proteínas encargadas de la excreción, o bien por la imposibilidad del paso de la bilis a través de los conductos biliares hasta el intestino. Una lesión hepática de cualquier causa, al disminuir el número de hepatocitos, puede producir una disminución de la captación de bilirrubina indirecta desde el plasma y una disminución del transporte y excreción de la bilirrubina directa hacia los conductillos biliares. Se pueden usar diferentes técnicas analíticas para medir la bilirrubina y sus metabolitos en el suero, la orina y las heces. La bilirrubina sérica se mide mediante (1) la "reacción diazo", actualmente el método de referencia; (2) cromatografía líquida de alta resolución (HPLC); (3) métodos oxidativos, enzimáticos y químicos; (4) espectrofotometría directa; y (5) métodos transcutáneos. Aunque la bilirrubina es un marcador clásico de disfunción hepática, no siempre indica una lesión de este órgano. Por tanto, para obtener un diagnóstico preciso, el significado de las alteraciones de este parámetro biológico ha de valorarse en conjunción con la anamnesis del paciente, la magnitud de la alteración, y el patrón de las alteraciones bioquímicas. acompañantes.

Measurement and clinical usefulness of bilirubin in liver disease

Elevated plasma bilirubin levels are a frequent clinical finding. It can be secondary to alterations in any stage of its metabolism: (a) excess bilirubin production (i.e., pathologic hemolysis); (b) impaired liver uptake, with elevation of indirect bilirubin; (c) impaired conjugation, prompted by a defect in the UDP-glucuronosyltransferase; and (d) bile clearance defect, with elevation of direct bilirubin secondary to defects in clearance proteins, or inability of the bile to reach the small bowel through bile ducts. A liver lesion of any cause reduces hepatocyte cell number and may impair the uptake of indirect bilirubin from plasma and diminish direct bilirubin transport and clearance through the bile ducts. Various analytical methods are currently available for measuring bilirubin and its metabolites in serum, urine and feces. Serum bilirubin is determined by (1) diazo transfer reaction, currently, the gold-standard; (2) high-performance liquid chromatography (HPLC); (3) oxidative, enzymatic, and chemical methods; (4) direct spectrophotometry; and (5) transcutaneous methods. Although bilirubin is a well-established marker of liver function, it does not always identify a lesion in this organ. Therefore, for accurate diagnosis, alterations in bilirubin concentrations should be assessed in relation to patient anamnesis, the degree of the alteration, and the pattern of concurrent biochemical alterations.

Effect of Silymarin Treatment on Circulating Bilirubin and Cardiovascular Disease Risk Factors in Healthy Men: A Single-Blind, Randomized Crossover Trial

This clinical trial (ACTRN12619001296123) investigated the impact of silymarin (Legalon®) on circulating bilirubin concentration, lipid status, systemic inflammation, and antioxidant status. The study design was a randomized, placebo-controlled, single-blind crossover trial of healthy men (18-65 years), conducted at Griffith University, Gold Coast, Australia. Participants were recruited from Griffith University and were randomized to silymarin (140 mg silymarin capsules thrice daily) or placebo (3 capsules containing mannitol taken daily) for 14 days followed by a ≥4-week washout and crossover to the other arm. The main outcomes were whether silymarin treatment would increase serum bilirubin concentration by >0.29 mg/dL, change serum lipid status (cholesterol and triglycerides), inflammation (c-reactive protein), and antioxidant capacity (ferric reducing ability of plasma) compared with baseline. Silymarin consumption (n = 17) did not affect serum concentrations of unconjugated bilirubin (0.73 versus 0.67 mg/dL, P = .79), cholesterol (185 versus 189 mg/dL, P = .19), triglycerides (94.2 versus 92.3 mg/dL, P = .79), c-reactive protein (0.17 versus 0.09 mg/dL, P = .23), or antioxidant status (6.61 versus 6.67 mg Fe²⁺ /dL, P = .40). These findings challenge previous reports and manufacturer claims of hyperbilirubinemia following silymarin treatment and are critical to guiding researchers toward an effective means to mildly elevate bilirubin, which evidence suggests could protect from cardiovascular disease.

Significance of Heme and Heme Degradation in the Pathogenesis of Acute Lung and Inflammatory Disorders

The heme molecule serves as an essential prosthetic group for oxygen transport and storage proteins, as well for cellular metabolic enzyme activities, including those involved in mitochondrial respiration, xenobiotic metabolism, and antioxidant responses. Dysfunction in both heme synthesis and degradation pathways can promote human disease. Heme is a pro-oxidant via iron catalysis that can induce cytotoxicity and injury to the vascular endothelium. Additionally, heme can modulate inflammatory and immune system functions. Thus, the synthesis, utilization and turnover of heme are by necessity tightly regulated. The microsomal heme oxygenase (HO) system degrades heme to carbon monoxide (CO), iron, and biliverdin-IXα, that latter which is converted to bilirubin-IXα by biliverdin reductase. Heme degradation by heme oxygenase-1 (HO-1) is linked to cytoprotection via heme removal, as well as by activity-dependent end-product generation (i.e., bile pigments and CO), and other potential mechanisms. Therapeutic strategies targeting the heme/HO-1 pathway, including therapeutic modulation of heme levels, elevation (or inhibition) of HO-1 protein and activity, and application of CO donor compounds or gas show potential in inflammatory conditions including sepsis and pulmonary diseases.

Clinical impact of serum bilirubin levels on kidney transplant outcomes

Serum bilirubin, a potent endogenous antioxidant, has been associated with decreased risks of cardiovascular disease, diabetes, and kidney disease. However, the effects of serum bilirubin on kidney transplant outcomes remain undetermined. We analyzed 1628 patients who underwent kidney transplantations between 2003 and 2017. Patients were grouped into sex-specific quartiles according to mean serum bilirubin levels, 3–12 months post-transplantation. Median bilirubin levels were 0.66 mg/dL in males and 0.60 mg/dL in females. The intra-individual variability of serum bilirubin levels was low (9%). Serum bilirubin levels were inversely associated with graft loss, death-censored graft failure, and all-cause mortality, independent of renal function, donor status, and transplant characteristics. Multivariable analysis revealed that the lowest serum bilirubin quartile was associated with increased risk of graft loss (HR 2.64, 95% CI 1.67–4.18, P < 0.001), death-censored graft failure (HR 2.97, 95% CI 1.63–5.42, P < 0.001), and all-cause mortality (HR 2.07, 95% CI 1.01–4.22, P = 0.046). Patients with lower serum bilirubin were also at greater risk of rejection and exhibited consistently lower glomerular filtration rates than those with higher serum bilirubin. Serum bilirubin levels were significantly associated with transplantation outcomes, suggesting that bilirubin could represent a therapeutic target for improving long-term transplant outcomes.

Serum Bilirubin and Coronary Artery Disease: Intricate Relationship, Pathophysiology, and Recent Evidence

Coronary artery disease (CAD) is a major cause of morbidity, mortality, and healthcare expenditure. A number of environmental and genetic risk factors have been known to contribute to CAD. More recently, a number of studies have supported as well as opposed a possible protective benefit of bilirubin in CAD, since it has anti-inflammatory, antioxidant, and antiaggregatory properties that may reduce atherogenesis. It also shares associations with different forms of CAD, namely stable CAD, unstable angina pectoris, stable angina pectoris, and acute myocardial infarction. Lack of sufficient evidence, however, has failed to elucidate a causal relationship between serum bilirubin level and risk of CAD. Therefore, in this update, we attempted to simplify this intricate relationship between bilirubin and CAD, revisit the pathophysiology of disease, how bilirubin may be protective, and to summarize the findings of the current literature.

Relationship between serum bilirubin levels, urinary biopyrrin levels, and retinopathy in patients with diabetes

Objective

Previous reports have indicated that serum bilirubin levels may be associated with diabetic retinopathy. However, the detailed mechanism is not fully understood. In this study, we evaluated the relationship between the severity of diabetic retinopathy and various factors including bilirubin levels and factors influencing bilirubin metabolism.

Methods

The study participants consisted of 94 consecutive patients with diabetes mellitus admitted to Kyushu University Hospital from April 2011 to July 2012. The patients were classified into three groups: no retinopathy (NDR), simple retinopathy (SDR), and pre-proliferative or proliferative retinopathy (PDR). The relationship between the severity of retinopathy and various factors was evaluated using univariate and logistic regression analyses. In addition, multivariate regression analysis was performed to evaluate the significant determinants for bilirubin levels.

Results

In univariate analysis, a significant difference was found among NDR, SDR and PDR in bilirubin levels, duration of diabetes, systolic blood pressure, and macroalbuminuria. Logistic regression analysis showed that PDR was significantly associated with bilirubin levels, duration of diabetes, and systolic blood pressure (OR 0.737, 95% CI 0.570–0.952, P = 0.012; OR 1.085, 95% CI 1.024–1.149, P = 0.006; OR 1.036, 95% CI 1.011–1.062, P = 0.005, respectively). In turn, multivariate regression analysis showed that bilirubin levels were negatively associated with high-sensitivity C-reactive protein levels and PDR, but positively correlated with urinary biopyrrin levels, oxidized metabolites of bilirubin.

Conclusion

PDR was negatively associated with bilirubin levels. This negative association may be due to a decreased production of bilirubin rather than its increased consumption considering the positive association between bilirubin and biopyrrin levels.

Association between serum bilirubin and mucosal healing among Japanese patients with ulcerative colitis: a cross-sectional study

PURPOSE

Bilirubin is known to have antioxidant effects. Several pieces of evidence regarding association between serum bilirubin and UC exist. Three studies found that serum bilirubin was inversely associated with severity of ulcerative colitis (UC), but no evidence regarding an association between serum bilirubin and mucosal healing (MH) has yet been shown. Thus, we evaluated this issue among Japanese patients with UC.

METHODS

The study subjects consisted of 304 Japanese patients with UC. Serum total bilirubin and indirect bilirubin were divided into quartiles on the basis of the distribution of all study subjects (low, moderate, high, and very high). Several endoscope specialists were responsible for evaluating MH, which was defined as a Mayo endoscopic subscore of 0. The information on clinical remission was collected using medical records.

RESULTS

The mean age was 49.9 years, the percentage of male patients was 59.2%, and the percentage of MH was 29.3%. High serum total bilirubin was independently positively associated with MH (OR 2.26 [95%CI 1.13-4.61]. However, after adjustment for confounding factors, the association between total bilirubin and MH disappeared. Very high serum indirect bilirubin was independently positively associated with MH (OR 2.31 [95%CI 1.10-5.00], p for trend = 0.026). No association between bilirubin and clinical remission was found.

CONCLUSIONS

Among Japanese patients with UC, serum indirect bilirubin, but not total bilirubin, was significantly positively associated with MH but not clinical remission.

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.

Exploring the causal pathway from bilirubin to CVD and diabetes in the UK biobank cohort study: Observational findings and Mendelian randomization studies

BACKGROUND AND AIMS

Some studies reported that mildly elevated serum bilirubin levels were associated with decreased risk of cardiovascular disease (CVD) and diabetes. Whether these are causal relationships remains unclear. This study aims to examine the causal effects of bilirubin on CVD, diabetes and their subtypes.

METHODS

The data we used in this study includes individual data from the UK Biobank cohort with 331,002 white British participants, and summary data from published genome wide associations studies (GWAS) findings. We used individual data to perform logistic regression for the observational study and two-stage least squares method for the Mendelian randomization (MR) study. We also performed several traditional MR methods and MR-TRYX by summary data.

RESULTS

The observational study supported the association relationships between bilirubin and CVD and diabetes and their subtypes. Results of MR showed strong evidence for negative causal associations of log_e total bilirubin with CVD [OR 0.92, 95%CI 0.88-0.95, p-value 2.15 × 10^-6], coronary heart disease [OR 0.90, 95%CI 0.85-0.96, p-value 1.54 × 10^-3] and hypertensive diseases [OR 0.91, 95%CI 0.88-0.95, p-value 5.89 × 10^-6], but no evidence for diabetes [OR 0.94, 95%CI 0.86-1.02, p-value 0.14] and its subtypes. We also obtained similar results for direct bilirubin. We found that blood pressure, cholesterol, C-reactive protein, alcohol and white blood cell count played important roles in the causal pathway from bilirubin to CVD. Two sample MR and sensitivity analyses showed consistent results with one sample MR.

CONCLUSIONS

Genetically determined bilirubin was negatively associated with the risk of CVD but had no evident causal association with diabetes in the UK Biobank cohort of white British.

Plasma Metabolomic Signatures of Chronic Obstructive Pulmonary Disease and the Impact of Genetic Variants on Phenotype-Driven Modules

Background: Small studies have recently suggested that there are specific plasma metabolic signatures in chronic obstructive pulmonary disease (COPD), but there have been no large comprehensive study of metabolomic signatures in COPD that also integrate genetic variants. Materials and Methods: Fresh frozen plasma from 957 non-Hispanic white subjects in COPDGene was used to quantify 995 metabolites with Metabolon's global metabolomics platform. Metabolite associations with five COPD phenotypes (chronic bronchitis, exacerbation frequency, percent emphysema, post-bronchodilator forced expiratory volume at one second [FEV1]/forced vital capacity [FVC], and FEV1 percent predicted) were assessed. A metabolome-wide association study was performed to find genetic associations with metabolite levels. Significantly associated single-nucleotide polymorphisms were tested for replication with independent metabolomic platforms and independent cohorts. COPD phenotype-driven modules were identified in network analysis integrated with genetic associations to assess gene-metabolite-phenotype interactions. Results: Of metabolites tested, 147 (14.8%) were significantly associated with at least 1 COPD phenotype. Associations with airflow obstruction were enriched for diacylglycerols and branched chain amino acids. Genetic associations were observed with 109 (11%) metabolites, 72 (66%) of which replicated in an independent cohort. For 20 metabolites, more than 20% of variance was explained by genetics. A sparse network of COPD phenotype-driven modules was identified, often containing metabolites missed in previous testing. Of the 26 COPD phenotype-driven modules, 6 contained metabolites with significant met-QTLs, although little module variance was explained by genetics. Conclusion: A dysregulation of systemic metabolism was predominantly found in COPD phenotypes characterized by airflow obstruction, where we identified robust heritable effects on individual metabolite abundances. However, network analysis, which increased the statistical power to detect associations missed previously in classic regression analyses, revealed that the genetic influence on COPD phenotype-driven metabolomic modules was modest when compared with clinical and environmental factors.

Rats Genetically Selected for High Aerobic Exercise Capacity Have Elevated Plasma Bilirubin by Upregulation of Hepatic Biliverdin Reductase-A (BVRA) and Suppression of UGT1A1

Exercise in humans and animals increases plasma bilirubin levels, but the mechanism by which this occurs is unknown. In the present study, we utilized rats genetically selected for high capacity running (HCR) and low capacity running (LCR) to determine pathways in the liver that aerobic exercise modifies to control plasma bilirubin. The HCR rats, compared to the LCR, exhibited significantly higher levels of plasma bilirubin and the hepatic enzyme that produces it, biliverdin reductase-A (BVRA). The HCR also had reduced expression of the glucuronyl hepatic enzyme UGT1A1, which lowers plasma bilirubin. Recently, bilirubin has been shown to activate the peroxisome proliferator-activated receptor-α (PPARα), a ligand-induced transcription factor, and the higher bilirubin HCR rats had significantly increased PPARα-target genes Fgf21, Abcd3, and Gys2. These are known to promote liver function and glycogen storage, which we found by Periodic acid–Schiff (PAS) staining that hepatic glycogen content was higher in the HCR versus the LCR. Our results demonstrate that exercise stimulates pathways that raise plasma bilirubin through alterations in hepatic enzymes involved in bilirubin synthesis and metabolism, improving liver function, and glycogen content. These mechanisms may explain the beneficial effects of exercise on plasma bilirubin levels and health in humans.

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.