Bilirubin, cardiovascular diseases and cancer: epidemiological perspectives

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.

Serum Total Bilirubin and Risk of Cancer: A Swedish Cohort Study and Meta-Analysis

Simple Summary

Several studies published to date have shown inconclusive results in the association between serum bilirubin and risk of site-specific cancer types and overall cancer. Therefore, there is a need to further investigate this association. Data from the large Swedish Apolipoprotein Mortality Risk (AMORIS) cohort study was used. We found that overall high levels of bilirubin had no association with overall cancer risk. However, a positive association was found between melanoma and breast cancer risk. On the other hand, an inverse association was found between high levels of bilirubin and risk of gynecological and lung cancers. Further studies are required to establish if bilirubin can be used as a biomarker for risk assessment and/or as a novel therapeutic target.

Abstract

Bilirubin has strong antioxidant properties that have been hypothesized to be preventive against the development of cancer. Thus, we aimed to investigate the association between serum total bilirubin (STB) and risk of overall and site-specific cancers in the large Swedish Apolipoprotein Mortality Risk (AMORIS) cohort. We also performed a systematic review and meta-analysis for specific cancer types (colorectal, breast and lung). We found no association between high levels of STB and risk of overall cancer. Regarding site-specific cancer, there was an inverse association between increased STB and lung cancer (Hazard Ratio (HR) for the 4th quartile (Q4) vs. Q1: 0.50; 95%CI: 0.44–0.59) and gynecological cancer (HR for Q4 vs. Q1: 0.86; 95%CI: 0.76–0.99). A positive association was found with melanoma (HR for Q4 vs. Q1: 1.25; 95%CI: 1.06–1.47) and breast cancer (HR for Q4 vs. Q1: 1.13; 95%CI: 1.01–1.25) risk. The meta-analysis showed an inverse association between high levels of STB and risk of lung cancer (Relative risk (RR): 0.69; 95%CI: 0.55–0.86). No associations were seen for colorectal and breast cancer risk. Further studies are required to establish if bilirubin can be used as a biomarker for risk assessment and/or as a novel therapeutic target.

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

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

Association between serum bilirubin and migraine in children and adolescents

Background

Migraine in children and adolescents is very common and can be associated with equivalents, psychiatric disorders, or abnormal electroencephalogram findings. Neurogenic inflammation is involved in migraine pathogenesis where pro-inflammatory cytokines play a significant role. Recent studies have demonstrated that serum bilirubin can be considered as an antioxidant and cytoprotective agent and that its concentration may be influenced in migraine by neurogenic inflammation. Various studies have observed reduced serum bilirubin in migrainous adults, and few studies investigated the association between serum bilirubin and migraine in children and adolescents.

Objectives

To study the association between serum bilirubin and migraine in children and adolescents.

Patients and method

Serum samples were collected from 40 migrainous children and adolescents and from 40 controls. Total, direct, and indirect bilirubin concentrations were measured. Headache features, migraine equivalents, psychiatric comorbidity, and electroencephalogram findings were documented in migraineurs.

Results

Serum total, direct, and indirect bilirubin concentrations were significantly lower in migraineurs than controls. This was statistically significant associated with abnormal electroencephalogram findings during headache-free periods and not statistically significant associated with any headache feature, abnormal electroencephalogram findings during headache attacks, or psychiatric comorbidity.

Conclusion

Serum bilirubin concentration is lower in migrainous children and adolescents compared to control, with no association with specific migraine type or features, and thus may be considered a useful marker for neurogenic inflammation in migraine.

Prognostic model of patients with liver cancer based on tumor stem cell content and immune process

Globally, liver hepatocellular carcinoma (LIHC) has a high mortality and recurrence rate, leading to poor prognosis. The recurrence of LIHC is closely related to two aspects: degree of immune infiltration and content of tumor stem cells. Hence, this study aimed to used RNA-seq and clinical data of LIHC from The Cancer Genome Atlas, Estimation of Stromal and Immune cells in Malignant Tumours, mRNA stemness index score, and weighted gene correlation network analysis methods to find genes significantly linked to the aforementioned two aspects. Key genes and clinical factors were used as input. Lasso regression and multivariate Cox regression were conducted to build an effective prognostic model for patients with liver cancer. Finally, four key genes (KLHL30, PLN, LYVE1, and TIMD4) and four clinical factors (Asian, age, grade, and bilirubin) were included in the prognostic model, namely Immunity and Cancer-stem-cell Related Prognosis (ICRP) score. The ICRP score achieved a great performance in test set. The area under the curve value of the ICRP score in test set for 1, 3, and 5 years was 0.708, 0.723, and 0.765, respectively, which was better than that of other prognostic prediction methods for LIHC. The C-index evaluation method also reached the same conclusion.

Serum Bilirubin Level as a Potential Marker for the Hearing Outcome in Severe-Profound Bilateral Sudden Deafness

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Objective:

To investigate the association of serum bilirubin level with hearing outcomes in bilateral sudden sensorineural hearing loss (BSSHL) patients.

Participants:

One hundred thirteen in-patient BSSHL patients were consecutively enrolled between July 2008 and December 2015 in a tertiary center.

Main Outcome Measures:

Multivariable linear regression, generalized estimating equations (GEE), and stratified analyses were applied to examine the association between serum bilirubin level and hearing outcome measures such as final hearing threshold and absolute and relative hearing gains in BSSHL.

Results:

After full adjustment for potential confounders, total bilirubin levels (TBIL) were observed to be positively and independently associated with hearing outcomes as measured by final hearing (β [95% confidence interval {CI}]: −1.5 [−2.7, −0.2] dB HL per 1 μmol/L increase in TBIL) and absolute and relative hearing gains (β [95% CI]: 1.4 [0.2, 2.7] dB and 1.6 [0.2, 3.1] dB, respectively) in the severe to profound hearing loss subpopulation.

Conclusions:

Higher TBIL levels, within the normal or mildly elevated ranges, were independently and significantly associated with better hearing outcome in BSSHL patients with severe to profound hearing loss. Given bilirubin elevation treatments exist, our finding suggests a novel pharmacological strategy for this specific subpopulation.

Circulating Total Bilirubin and Future Risk of Hypertension in the General Population: The Prevention of Renal and Vascular End-Stage Disease (PREVEND) Prospective Study and a Mendelian Randomization Approach

BACKGROUND

Circulating total bilirubin is known to be inversely and independently associated with future risk of cardiovascular disease. However, the relationship of circulating total bilirubin with incident hypertension is uncertain. We aimed to assess the association of total bilirubin with future hypertension risk and supplemented this with a Mendelian randomization approach to investigate any causal relevance to the association.

METHODS AND RESULTS

Plasma total bilirubin levels were measured at baseline in the PREVEND (Prevention of Renal and Vascular End-Stage Disease) prospective study of 3989 men and women without hypertension. Hazard ratios (95% confidence intervals) of total bilirubin with incident hypertension were assessed. New-onset hypertension was recorded in 1206 participants during a median follow-up of 10.7 years. Baseline total bilirubin was approximately log-linearly associated with hypertension risk. Age- and sex-adjusted hazard ratio for hypertension per 1-SD increase in loge total bilirubin was 0.86 (0.81-0.92; P<0.001), which was attenuated to 0.94 (0.88-0.99; P=0.040) after further adjustment for established risk factors and other potential confounders. The association was marginally significant on further adjustment for high-sensitivity C-reactive protein (0.94; 0.88-1.00; P=0.067). A genetic variant at the UGT1A1*28 locus consistently shown to be strongly associated with circulating bilirubin levels-rs6742078-was not significantly associated with blood pressure or hypertension (P>0.05 for all), arguing against a strong causal association of circulating bilirubin with blood pressure.

CONCLUSIONS

The weak and inverse association of circulating total bilirubin with future hypertension risk may be driven by biases such as unmeasured confounding and/or reverse causation. Further evaluation is warranted.

Does bilirubin protect against developing diabetes mellitus?

After 25 years of evaluating bilirubin as a possible protective agent in neonatal and cardiovascular disease, interest has moved on to a exploring a possible protective role in diabetes mellitus (DM). This review finds conflicting prospective data for a protective relationship though there are retrospective, case-controlled data, that can only show association, which is not causality. Only prospective studies can show causality. Also, it would appear that the underlying biochemical assumptions do not readily translate from the animal to the human setting. Given that many factors impact on circulating bilirubin levels, it is not surprising that a clear-cut answer is not available; the jury is still out. Any relationship between DM and bilirubin might relate to intermediates in bilirubin metabolism, including relationships involving the genes for the enzymes participating in those steps. Nevertheless, the pursuit of bilirubin in disease causation is opening new avenues for research and if it is established that serum bilirubin can predict risks, much will have been achieved. The answer may have to come from molecular genetic analyses.

Serum Bilirubin and Their Association With C-Reactive Protein in Patients With Migraine

BACKGROUND

Increased levels of C-reactive protein (CRP) have been considered as a marker in assessing neurogenic inflammation of migraine patients. An inverse relationship between serum bilirubin and CRP has been observed in various diseases. Therefore, we analyzed serum bilirubin levels in migraine patients, and investigated the relationship between serum bilirubin and CRP in migraineurs.

METHODS

A total of 86 newly diagnosed migraine patients were consecutively recruited to this study.

RESULTS

Significantly lower median serum total bilirubin, conjugated bilirubin (CB) and unconjugated bilirubin were found in patients with migraine than healthy controls, and the levels of CRP were significantly higher in migraine patients than healthy controls. A negative correlation between CRP and CB was observed in patients with migraine (r = -0.255, P = 0.018). In a multiple linear regression model, the concentrations of CRP remained negatively correlated with CB.

CONCLUSIONS

Our study demonstrates that serum bilirubin concentrations are decreased in migraineurs, and CB levels were found to be positively correlated with CRP in migraine patents. However, larger cross-sectional and prospective studies are needed to establish whether serum bilirubin may be a useful biomarker for assessing neurogenic inflammation in migraine patients and eventually guiding the therapy.

Serum bilirubin and the risk of hypertension

BACKGROUND

Experimental studies suggest oxidative stress could lead to the development of hypertension. Serum bilirubin is a major contributor to the antioxidant capacity in blood plasma and has been identified as an independent cardiovascular risk factor in cohort studies. However, data on the relationship between bilirubin and blood pressure are scarce and inconclusive.

METHODS

We analysed data from the National Health and Nutrition Examination Surveys (NHANES) 1999-2012 (N=31069). Fifty multiple imputed data sets were generated and analysed to avoid selection/confounding bias due to excluding individuals/variables with missing values. A minimal sufficient adjustment set of variables (MSAS) needed to estimate the unconfounded effect of bilirubin on blood pressure and hypertension (systolic/diastolic blood pressure ≥ 140/90 mmHg or using antihypertensive medication) was identified using the back-door criterion and included in all regression models.

RESULTS

After adjustment for the MSAS variables, systolic blood pressure decreased progressively up to -2.5 mmHg (p<0.001) and the prevalence of hypertension was up to 25% lower (P<0.001) in those with bilirubin ≥ 1.0 mg/dl-the highest two deciles-compared with those with 0.1-0.4 mg/dl-the lowest decile. Sensitivity analyses showed these results were unlikely to be explained by residual confounding or selection bias.

CONCLUSIONS

High serum bilirubin may decrease the risk of hypertension by inactivating and inhibiting the synthesis of reactive oxygen species in vascular cells. Strategies to boost the bioavailability of circulating and tissue bilirubin or to mimic bilirubin's antioxidant properties could have a significant impact on prevention and control of hypertension as well as coronary heart disease.

Association between Serum Bilirubin and Estimated Glomerular Filtration Rate among Diabetic Patients

The subjects comprised 230 men aged 77 ± 10 (range: 50-100) years and 279 women aged 81 ± 10 (50-101) years that visited the medical department. We examined the relationship between increased serum bilirubin and renal function evaluated by estimated glomerular filtration rate (eGFR) using CKD-EPI equations modified by a Japanese coefficient. Compared with the fourth quartile in serum bilirubin (1.01-1.97 mg/dL), the nonadjusted, age and gender-adjusted, and multivariate-adjusted odds ratios {95% confidence interval (CI)} of eGFR <60 mL/min/1.73 m(2) for the first quartile in serum bilirubin (0.13-0.50 mg/dL) were 2.08 (1.25-3.44), 1.82 (1.07-3.09), and 1.53 (0.83-2.81), respectively. Moreover, compared with the fourth quartile, nonadjusted, age and gender-adjusted, and multivariate-adjusted odds ratios (95% CI) of eGFR <45 mL/min/1.73 m(2) for the first quartile were 3.50 (1.95-6.23), 3.12 (1.72-5.65), and 3.53 (1.71-7.26), respectively. The data were further stratified by gender, age, medication (antihypertensive, antidyslipidemic, and antidiabetic agents), and prevalence of cardiovascular disease (CVD). The standardized coefficients for eGFR were significant in all the subgroups other than the prevalence of CVD, and there were significant interactions between the two groups regarding CVD. Our data demonstrated an independent positive association between serum bilirubin and eGFR among diabetic patients.

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

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

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

BACKGROUND

A considerable interest has been drawn to potential protective effects of bilirubin against oxidative stress-related diseases. Smoking is known to be associated with lower concentrations of serum bilirubin, but other behavioral correlates of serum bilirubin have not been well studied. In this cross-sectional study, we examined the associations of behavioral and clinical factors with serum total bilirubin in Japanese men and women.

METHOD

The study subjects comprised of 4802 men and 6414 women aged 49-76 years who participated in the baseline survey of an ongoing cohort study on lifestyle-related diseases in Fukuoka, Japan. With consideration to time of the day of blood sampling and fasting hours, the associations with smoking, alcohol intake, body mass index, physical activity, coffee, tea, blood pressure, glycated hemoglobin (HbA1c), HDL cholesterol and non-HDL cholesterol with serum bilirubin were evaluated by analysis of covariance and multiple linear regression analysis.

RESULTS

While smoking was negatively associated with serum bilirubin, alcohol consumption was positively associated with serum bilirubin in both men and women. Coffee consumption was associated with lower bilirubin concentrations in both sexes. In the multiple linear regression analysis, HDL cholesterol was positively and HbA1c was negatively associated with bilirubin in both men and women, and the associations were more evident in women.

CONCLUSION

Smoking, alcohol use and coffee consumption were important behavioral correlates of serum bilirubin in Japanese men and women. Serum HDL cholesterol was a measurable clinical correlate of bilirubin in women.

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

AIMS/HYPOTHESIS

Bilirubin has antioxidant and anti-inflammatory activities. Previous studies demonstrated that higher bilirubin levels were associated with reduced prevalence of peripheral arterial disease (PAD). However, the relationship between bilirubin and lower-limb amputation, a consequence of PAD, is currently unknown. We hypothesised that, in patients with type 2 diabetes, bilirubin concentrations may inversely associate with lower-limb amputation.

METHODS

The relationship between baseline plasma total bilirubin levels and amputation events was analysed in 9,795 type 2 diabetic patients from the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study. The analysis plan was pre-specified. Lower-limb amputation was adjudicated blinded to treatment allocation. Relevant clinical and biochemical data were available for analyses. Amputation was a pre-specified tertiary endpoint.

RESULTS

Bilirubin concentrations were significantly inversely associated with lower-limb amputation, with a greater than threefold risk gradient across levels. Individuals with lower bilirubin concentrations had a higher risk for first amputation (HR 1.38 per 5 μmol/l decrease in bilirubin concentration, 95% CI 1.07, 1.79, p = 0.013). The same association persisted after adjustment for baseline variables, including age, height, smoking status, γ-glutamyltransferase level, HbA1c, trial treatment allocation (placebo vs fenofibrate), as well as previous PAD, non-PAD cardiovascular disease, amputation or diabetic skin ulcer, neuropathy, nephropathy and diabetic retinopathy (HR 1.38 per 5 μmol/l decrease in bilirubin concentration, 95% CI 1.05, 1.81, p = 0.019).

CONCLUSIONS/INTERPRETATION

Our results identify a significant inverse relationship between bilirubin levels and total lower-limb amputation, driven by major amputation. Our data raise the hypothesis that bilirubin may protect against amputation in type 2 diabetes.

No effect modification of serum bilirubin or coffee consumption on the association of gamma-glutamyltransferase with glycated hemoglobin in a cross-sectional study of Japanese men and women

BACKGROUND

Oxidative stress has been implicated in the development of type 2 diabetes mellitus. Bilirubin is a potent endogenous antioxidant, and coffee is a major source of exogenous antioxidants. Serum gamma-glutamyltransferase (GGT), a marker of oxidative stress, is a strong predictor of the risk of type 2 diabetes mellitus. This study evaluated the effect modification of bilirubin and coffee consumption on the association of serum GGT with glycated hemoglobin (HbA1c) and the combined effect of bilirubin and coffee on HbA1c concentrations.

METHODS

The subjects were 4492 men and 6242 women aged 49-76 years who participated in the baseline survey of an on-going cohort study on lifestyle-related diseases in Fukuoka, Japan. Geometric means of HbA1c were examined according to quartile categories of GGT, with stratification by serum total bilirubin (≥ 0.6 mg/dL versus less in men and ≥ 0.5 mg/dL versus less in women) and coffee consumption (< 1, 1-3 and ≥ 4 cups of per day). Statistical adjustment was made for age, smoking, alcohol use and body mass index by using analysis of covariance.

RESULTS

HbA1 concentrations increased progressively with increasing levels of GGT in both men and women. The increasing trend of HbA1c concentrations associated with GGT did not differ by either bilirubin status or coffee consumption. Both men and women with high bilirubin had consistently lower concentrations of HbA1c across the GGT quartiles. Higher coffee consumption was associated with lower concentrations of HbA1c in women with low bilirubin (trend P = 0.04), but not with high bilirubin (trend P = 0.37). There was no such association between coffee and HbA1c in men with either low or high bilirubin levels.

CONCLUSIONS

Bilirubin is possibly protective against deterioration of glucose metabolism. Further studies are needed regarding the combined effect of bilirubin and coffee on glucose metabolism.