Association of serum total bilirubin levels with the severity, extent and subtypes of coronary atherosclerotic plaques detected by coronary CT angiography

Role of bilirubin in the prognosis of coronary artery disease and its relationship with cardiovascular risk factors: a meta-analysis

Background

Bilirubin is a heme catabolism product with antioxidant, anti-inflammatory, and anti-apoptotic properties and is implicated in the prognosis of several diseases. This study evaluates the prognostic role of bilirubin in coronary artery disease (CAD) patients.

Methods

After identifying studies from the literature, meta-analyses were performed to achieve a) overall estimates of serum total bilirubin levels in patients with myocardial infarction (MI), non-MI CAD and healthy individuals; b) odds ratios (OR) of adverse outcomes between higher and lower total bilirubin levels; c) standardized mean difference (SMD) in total bilirubin levels in patients with high vs low CAD severity; and d) correlation between disease severity and total bilirubin. Metaregression analyses were performed to examine the relationship between cardiovascular risk factors and increasing quantiles of total bilirubin levels.

Results

Forty-three studies were identified. Pooled serum total bilirubin levels were 0.72 mg/dl [95% confidence interval (CI): 0.60, 0.83] in MI patients; 0.65 mg/dl [95% CI: 0.60, 0.69] in non-MI CAD patients; and 0.66 mg/dl [95% CI: 0.56, 0.75] in healthy individuals. Higher total bilirubin levels were associated with greater odds of adverse outcomes in MI patients (OR: 1.08 [95% CI: 0.99, 1.18]) but lower odds in non-MI CAD patients (OR: 0.80 [95%CI: 0.73, 0.88]). Compared to non-severe cases, total bilirubin levels were higher in patients with severe MI (SMD 0.96 [95% CI: − 0.10, 2.01]; p = 0.074) but were lower in severe non-MI CAD patients (SMD − 0.30 [95%CI: − 0.56, − 0.03]; p = 0.02). Total bilirubin levels correlated positively with MI severity (r = 0.41 [95% CI: 0.24, 0.59]; p < 0.01) but correlated negatively with non-MI CAD severity (r =  − 0.17 [95% CI: − 0.48, 0.14]; p = 0.28). Female sex was inversely associated with increasing quantiles of bilirubin (meta-regression coefficient: − 8.164 [− 14.531, − 1.769]; p = 0.016) in MI patients.

Conclusion

Prognostic role of bilirubin for CAD appears complicated, as different odds are observed for MI and non-MI CAD patients which weakens the case of causal involvement of bilirubin in CAD etiology or prognosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02899-w.

Bilirubin Nanoparticles Protect Against Cardiac Ischemia/Reperfusion Injury in Mice

Background

Ischemia/reperfusion (I/R) injury causes overproduction of reactive oxygen species, which are the major culprits of oxidative stress that leads to inflammation, apoptosis, myocardial damage, and dysfunction. Bilirubin acts as a potent endogenous antioxidant that is capable of scavenging various reactive oxygen species. We have previously generated bilirubin nanoparticles (BRNPs) consisting of polyethylene glycol–conjugated bilirubin. In this study, we examined the therapeutic effects of BRNPs on myocardial I/R injury in mice.

Methods and Results

In vivo imaging using fluorophore encapsulated BRNPs showed BRNPs preferentially targeted to the site of I/R injury in the heart. Cardiac I/R surgery was performed by first ligating the left anterior descending coronary artery. After 45 minutes, reperfusion was achieved by releasing the ligation. BRNPs were administered intraperitoneally at 5 minutes before and 24 hours after reperfusion. Mice that received BRNPs showed significant improvements in their cardiac output, assessed by echocardiogram and pressure volume loop measurements, compared with the ones that received vehicle treatment. BRNPs treatment also significantly reduced the myocardial infarct size in mice that underwent cardiac I/R, compared with the vehicle‐treatment group. In addition, BRNPs effectively suppressed reactive oxygen species and proinflammatory factor levels, as well as the amount of cardiac apoptosis.

Conclusions

Taken together, BRNPs could exert their therapeutic effects on cardiac I/R injury through attenuation of oxidative stress, apoptosis, and inflammation, providing a novel therapeutic modality for myocardial I/R injury.

Relationship between serum bilirubin levels and presence of fragmented QRS in patients with acute coronary syndrome

Aim: To assess the relationship between serum bilirubin levels and fragmented QRS (fQRS), and their association with adverse events in patients with acute coronary syndrome. Methods: This study included a total of 736 patients. Laboratory results such as bilirubin levels, renal and liver function tests were obtained from the first available blood sample. Results: Left ventricular ejection fraction, end-diastolic diameter and total bilirubin level were significantly lower in fQRS (+) group than in the control group (45.0 [40.0-55.0] vs 50.0 [45.0-60.0]%; p < 0.001; 4.7 [4.6-5.1] vs 4.7 [4.5-4.9] cm; p < 0.001; 0.66 [0.49-5.1] vs 0.72 [0.53-0.97] md/dl; p = 0.017); respectively. Occurrence of adverse events was significantly higher in fQRS (+) group (32.5 vs 20.5 %; p = 0.013) during mean 1-year follow-up period. Conclusion: Total bilirubin level is an independent predictor of fQRS formation, which is associated with the presence of adverse events in patients with acute coronary syndrome.

The role of serum bilirubin levels in determining venous thromboembolism

OBJECTIVE

Venous thromboembolism (VTE) is a disease that includes both deep venous thrombosis (DVT) and pulmonary embolism (PE). Bilirubin is an endogenous anti-inflammatory marker associated with atherothrombosis. The purpose of our study was to investigate the association of serum bilirubin levels with the presence of VTE.

METHODS

A total of 103 patients with VTE (distal DVT, n = 34; proximal DVT, n = 30; PE, n = 39) and 50 control patients were cross-sectionally enrolled. Peripheral venous duplex ultrasound and computed tomography were used for the diagnosis of VTE. Fasting blood samples were drawn for biochemical analyses.

RESULTS

Baseline characteristics were not different between groups. The VTE group had lower bilirubin level (9.0 ± 2.6 μmol/L vs 7.3 ± 3 μmol/L; P = .001) and higher high-sensitivity C-reactive protein (hs-CRP) concentration (0.8 [0.3-2] mg/L vs 1.1 [0.2-3] mg/L; P = .008) and white blood cell count (7.4 ± 1.5 × 10⁹/L vs 8.2 ± 2.7 × 10⁹/L; P = .02) compared with control patients. In the analysis of variance, the levels of total direct bilirubin and hs-CRP were clearly different between the control group and VTE subgroups (distal and proximal DVT and PE). The receiver operating characteristic curve analysis showed a cutoff value of 8.9 μmol/L for total bilirubin (sensitivity, 74%; specificity, 55%) and an area under the curve of 0.659 (P < .001).

CONCLUSIONS

Bilirubin level, hs-CRP concentration, and white blood cell count were independently associated with VTE.

Evidence of association of circulating epigenetic-sensitive biomarkers with suspected coronary heart disease evaluated by Cardiac Computed Tomography

Circulating biomarkers available in clinical practice do not allow to stratify patients with coronary heart disease (CHD) prior the onset of a clinically relevant event. We evaluated the methylation status of specific genomic segments and gene expression in peripheral blood of patients undergoing Cardiac Computed Tomography (CCT) for CHD (n = 95).

We choose to investigate cholesterol metabolism. Methylation and gene expression of low density lipoprotein receptor (LDLR), sterol regulatory element-binding factor 2 (SREBF2) and ATP-binding cassette transporter 1 (ABCA1) were evaluated by qRT-PCR. Calcium score (CACS), stenosis degree, total plaque volume (TPV), calcified plaque volume (CPV), non-calcified plaque volume (NCPV) and plaque burden (PB) were assessed in all CHD patients (n = 65). The percentage of methylation at the specific analyzed segment of LDLR promoter was higher in CHD patients vs healthy subjects (HS) (n = 30) (p = 0.001). LDLR, SREBF2 and ABCA1 mRNAs were up-regulated in CHD patients vs HS (p = 0.02; p = 0.019; p = 0.008). SREBF2 was overexpressed in patients with coronary stenosis ≥50% vs subjects with stenosis <50% (p = 0.036). After adjustment for risk factors and clinical features, ABCA1 (p = 0.005) and SREBF2 (p = 0.010) gene expression were identified as independent predictors of CHD and severity. ROC curve analysis revealed a good performance of ABCA1 on predicting CHD (AUC = 0.768; p<0.001) and of SREBF2 for the prediction of disease severity (AUC = 0.815; p<0.001). Moreover, adjusted multivariate analysis demonstrated SREBF2 as independent predictor of CPV, NCPV and TPV (p = 0.022; p = 0.002 and p = 0.006) and ABCA1 as independent predictor of NCPV and TPV (p = 0.002 and p = 0.013).

CHD presence and characteristics are related to selected circulating transcriptional and epigenetic-sensitive biomarkers linked to cholesterol pathway. More extensive analysis of CHD phenotypes and circulating biomarkers might improve and personalize cardiovascular risk stratification in the clinical settings.

Bilirubin acts as a multipotent guardian of cardiovascular integrity: more than just a radical idea

Bilirubin, a potentially toxic catabolite of heme and indicator of hepatobiliary insufficiency, exhibits potent cardiac and vascular protective properties. Individuals with Gilbert's syndrome (GS) may experience hyperbilirubinemia in response to stressors including reduced hepatic bilirubin excretion/increased red blood cell breakdown, with individuals usually informed by their clinician that their condition is of little consequence. However, GS appears to protect from all-cause mortality, with progressively elevated total bilirubin associated with protection from ischemic heart and chronic obstructive pulmonary diseases. Bilirubin may protect against these diseases and associated mortality by reducing circulating cholesterol, oxidative lipid/protein modifications, and blood pressure. In addition, bilirubin inhibits platelet activation and protects the heart from ischemia-reperfusion injury. These effects attenuate multiple stages of the atherosclerotic process in addition to protecting the heart during resultant ischemic stress, likely underpinning the profound reduction in cardiovascular mortality in hyperbilirubinemic GS. This review outlines our current knowledge of and uses for bilirubin in clinical medicine and summarizes recent progress in revealing the physiological importance of this poorly understood molecule. We believe that this review will be of significant interest to clinicians, medical researchers, and individuals who have GS.

Bilirubin in coronary artery disease: Cytotoxic or protective?

Bilirubin has traditionally been considered a cytotoxic waste product. However, recent studies have shown bilirubin to have anti-oxidant, anti-inflammatory, vasodilatory, anti-apoptotic and anti-proliferative functions. These properties potentially confer bilirubin a new role of protection especially in coronary artery disease (CAD), which is a low grade inflammatory process exacerbated by oxidative stress. In fact, recent literature reports an inverse relationship between serum concentration of bilirubin and the presence of CAD. In this article, we review the current literature exploring the association between levels of bilirubin and risk of CAD. We conclude that current evidence is inconclusive regarding the protective effect of bilirubin on CAD. A causal relationship between low serum bilirubin level and increased risk of CAD is not currently established.

Serum Total Bilirubin Levels Provide Additive Risk Information over the Framingham Risk Score for Identifying Asymptomatic Diabetic Patients at Higher Risk for Coronary Artery Stenosis

BACKGROUND

The diagnosis of coronary artery disease (CAD) is often delayed in patients with type 2 diabetes. Serum total bilirubin levels are inversely associated with CAD. However, no studies have examined whether this can be used as a biochemical marker for identifying asymptomatic diabetic patients at higher risk for having obstructive CAD.

METHODS

We performed a cross-sectional study of 460 consecutive asymptomatic patients with type 2 diabetes. All patients underwent coronary computed tomographic angiography, and their serum total bilirubin levels were measured. Obstructive CAD was defined as ≥50% diameter stenosis in at least one coronary artery.

RESULTS

Serum total bilirubin tertiles showed an inverse association with the prevalence of obstructive CAD. In multivariate logistic regression analysis, the odds ratio for the highest versus the lowest tertile of total bilirubin was 0.227 (95% confidence interval [CI], 0.130 to 0.398), and an increment of 1 µmol/L in serum total bilirubin level was associated with a 14.6% decrease in obstructive CAD after adjustment for confounding variables. Receiver operating characteristic curve analysis showed that the area under the curve for the Framingham Risk Score (FRS) plus serum total bilirubin level was 0.712 (95% CI, 0.668 to 0.753), which is significantly greater than that of the FRS alone (P=0.0028).

CONCLUSION

Serum total bilirubin level is inversely associated with obstructive CAD and provides additive risk information over the FRS. Serum total bilirubin may be helpful for identifying asymptomatic patients with type 2 diabetes who are at higher risk for obstructive CAD.

Arterial stiffness and central arterial wave reflection are associated with serum uric acid, total bilirubin, and neutrophil-to-lymphocyte ratio in patients with coronary artery disease

OBJECTIVE

Total bilirubin (TB) was recently recognized as an endogenous anti-inflammatory and anti-oxidant molecule. Uric acid (UA) takes part in cardiovascular diseases by inducing oxidative stress, inflammation, and endothelial dysfunction. We assessed the relationship between serum TB levels, serum UA levels, and inflammatory status assessed by neutrophil-to-lymphocyte ratio (N/L) and arterial stiffness and arterial wave reflection in patients with a clinical diagnosis of coronary artery disease (CAD).

METHODS

We included 145 consecutive patients admitted with stable angina pectoris (SAP) or acute coronary syndrome (ACS). Blood samples were drawn at admission for complete blood count and biochemistry. Non-invasive pulse waveform analysis for the determination of augmentation index (AIx) and carotid-femoral pulse wave velocity (PWV) measurements were performed with the commercially available SphygmoCor system.

RESULTS

When patients were divided into tertiles of PWV and AIx, median N/L and median serum UA levels were the highest and mean TB levels were the lowest in the third tertile (p<0.001 for all). AIx and PWV were positively associated with serum UA and N/L and negatively associated with serum TB levels (p<0.001 for all). After adjustments for age, gender, heart rate, systolic blood pressure, and presence of diabetes, significant correlations persisted for N/L, UA, and TB in ACS patients (p<0.05). In the SAP group, TB was significantly negatively correlated with AIx and PWV, and UA was significantly positively correlated with PWV (p<0.05).

CONCLUSION

N/L ratio and serum UA and TB levels might be used to risk-stratify patients with respect to arterial stiffness in CAD patients, especially in the presence of ACS.