Relation of conjugated bilirubin concentrations to the presence of coronary artery calcium

Predictive value of lipoprotein(a) in coronary artery calcification among asymptomatic cardiovascular disease subjects: A systematic review and meta-analysis

AIMS

Studies have indicated inconsistent results regarding the association between plasma levels of Lipoprotein(a) [Lp(a)] and coronary artery calcification (CAC). We performed a systematic review and meta-analysis to investigate the association between elevated levels of Lp(a) and risk of CAC in populations free of cardiovascular disease (CVD) symptoms.

DATA SYNTHESIS

PubMed, Web of Science, Embase, and Scopus were searched up to July 2022 and the methodological quality was assessed using Newcastle-Ottawa Scale (NOS) scale. Random-effects meta-analysis was used to estimate pooled odds ratio (OR) and 95% confidence interval. Out of 298 studies, data from 8 cross-sectional (n = 18,668) and 4 cohort (n = 15,355) studies were used in meta-analysis. Cohort studies demonstrated a positive significant association between Lp(a) and CAC, so that individuals with Lp(a)≥30-50 exposed to about 60% risk of CAC incidence compared to those with lower Lp(a) concentrations in asymptomatic CVD subjects (OR, 1.58; 95% CI, 1.38-1.80; l2, 0.0%; P, 0.483); Subgroup analysis showed that a cut-off level for Lp(a) measurement could not statistically affect the association, but race significantly affected the relationship between Lp(a) and CAC (OR,1.60; 95% CI, 1.41-1.81). Analyses also revealed that both men and women with higher Lp(a) concentrations are at the same risk for increased CAC.

CONCLUSIONS

Blood Lp(a) level was significantly associated with CAC incidence in asymptomatic populations with CVD, indicating that measuring Lp(a) may be a useful biomarker for diagnosing subclinical atherosclerosis in individuals at higher risk of CAC score.

PROSPERO REGISTRATION NUMBER

CRD42022350297.

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.

The relationship between UGT1A1 gene & various diseases and prevention strategies

UDP-glucuronyltransferase 1A1 (UGT1A1) is a member of the Phase II metabolic enzyme family and the only enzyme that can metabolize detoxified bilirubin. Inactivation and very low activity of UGT1A1 in the liver can be fatal or lead to lifelong Gilbert's syndrome (GS) and Crigler-Najjar syndrome (CN). To date, more than one hundred UGT1A1 polymorphisms have been discovered. Although most UGT1A1 polymorphisms are not fatal, which diseases might be associated with low activity UGT1A1 or UGT1A1 polymorphisms? This scientific topic has been studied for more than a hundred years, there are still many uncertainties. Herein, this article will summarize all the possibilities of UGT1A1 gene-related diseases, including GS and CN, neurological disease, hepatobiliary disease, metabolic difficulties, gallstone, cardiovascular disease, Crohn's disease (CD) obesity, diabetes, myelosuppression, leukemia, tumorigenesis, etc., and provide guidance for researchers to conduct in-depth study on UGT1A1 gene-related diseases. In addition, this article not only summarizes the prevention strategies of UGT1A1 gene-related diseases, but also puts forward some insights for sharing.

Direct Bilirubin Levels Predict Long-Term Outcomes in Patients With Acute Coronary Syndrome Under Different Glucose Metabolism Status: A 6.5-Year Cohort Study of Three-Vessel Disease

Background: There is controversy over the relationship between bilirubin and coronary artery disease. This study aimed to evaluate the predictive value of direct bilirubin (DB) in patients with complex acute coronary syndrome (ACS).

Methods: From April 2004 to February 2011, 5,322 ACS patients presenting with three-vessel disease were consecutively enrolled. Disease severity and complexity were determined by SYNTAX score (SS) and SS II. The primary endpoint was all-cause death, and the secondary endpoints were major adverse cardiovascular and cerebrovascular events (MACCE). Stratification of normal glucose regulation, prediabetes, and diabetes was based on a previous diagnosis, hypoglycemic medications, fasting blood glucose, and hemoglobin A1c.

Results: Subjects were divided into quartiles according to baseline DB (μmol/L): Q1 (0–1.6), Q2 (1.61–2.20), Q3 (2.21–2.80), and Q4 (>2.80). Multivariable logistic regression analysis showed that DB was an independent predictor of intermediate–high SS. During a median follow-up time of 6.5 years, elevated DB was associated with more all-cause death (p < 0.001) but not MACCE. DB remained to be predictive of all-cause death in the multivariable Cox regression model (Q2 vs. Q1: HR 1.043, 95% CI 0.829–1.312, p = 0.719; Q3 vs. Q1: HR 1.248, 95% CI 1.001–1.155, p = 0.048; Q4 vs. Q1: HR 1.312, 95% CI 1.063–1.620, p = 0.011). When subjects are stratified according to glucose metabolism regulation and treatment strategies, the predictivity of DB was only profound in patients with diabetes or with conservative treatment. Additionally, incorporating DB further improved the discrimination and reclassification abilities of SS II for risk prediction.

Conclusion: DB is a potential biomarker for predicting lesion severity and long-term outcomes in ACS patients.

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.

Bilirubin in metabolic syndrome and associated inflammatory diseases: New perspectives

Diabetes mellitus is one of the major global health issues, which is closely related to metabolic dysfunction and the chronic inflammatory diseases. Multiple studies have demonstrated that serum bilirubin is negatively correlated with metabolic syndrome and associated inflammatory diseases, including atherosclerosis, hypertension, etc. However, the roles of bilirubin in metabolic syndrome and associated inflammatory diseases still remain unclear. Here, we explain the role of bilirubin in metabolic syndrome and chronic inflammatory diseases and its therapeutic potential. Understanding the role of bilirubin activities in diabetes may serve as a therapeutic target for the treatment of chronic inflammatory diseases in diabetic patients.

Associations between different bilirubin subtypes and diabetic microvascular complications in middle-aged and elderly individuals

AIMS

Some studies have reported associations between bilirubin and diabetic microvascular complications. However, these studies focused only on total bilirubin (TBIL) without distinguishing different bilirubin subtypes. In this study, we aimed to investigate the associations of TBIL, direct bilirubin (DBIL) and indirect bilirubin (IBIL) levels with albuminuria/creatinine ratio (ACR) and the prevalence of diabetic retinopathy (DR) among diabetic adults.

METHODS

We analyzed 4368 individuals out of 4813 diabetic participants enrolled from seven communities in 2018 in a cross-sectional study. Participants underwent several checkups, including the measurement of anthropometric parameters, blood pressure, glucose, lipid profile, TBIL, DBIL, IBIL and ACR. DR was detected by high-quality fundus photographs and was remotely read by ophthalmologists.

RESULTS

Compared with the first quartile of DBIL, participants in the fourth quartile had a lower prevalence of high ACR (odds ratio (OR) 0.76; 95% confidence interval (CI) 0.59, 0.99) (p for trend < 0.05). Neither TBIL nor IBIL was associated with the prevalence of high ACR. In DR, higher DBIL and TBIL by one standard deviation was associated with a 19% (OR 0.81; 95% CI 0.69, 0.94) and a 12% (OR 0.88; 95% CI 0.78, 0.99) lower frequency of DR, respectively (both p for trend < 0.05). However, IBIL was not associated with the prevalence of DR. These associations were adjusted for potential confounding factors.

CONCLUSION

DBIL had a stronger association with high ACR and DR than TBIL or IBIL did in diabetic adults. The effect of DBIL on diabetic complications should be noted and investigated in further studies.

Direct bilirubin is associated with low-density lipoprotein subfractions and particle size in overweight and centrally obese women

BACKGROUND AND AIMS

Bilirubin has antioxidant and anti-inflammatory properties; serum bilirubin levels have been known to be inversely associated with cardiovascular disease. However, the effects of different bilirubin subtypes on cardiometabolic traits are unknown. In this study, we aimed to determine whether direct bilirubin is more strongly correlated with small, dense low-density lipoprotein (sdLDL) compared to other bilirubin subtypes. We also investigated which LDL subfractions exhibited the highest correlation with direct bilirubin.

METHODS AND RESULTS

A total of 288 overweight and centrally obese women were included in this study. The Pearson correlation and Steiger's Z test were used to compare the correlation coefficients between bilirubin subtypes and lipoproteins. Multiple linear regression analyses were used to evaluate the independent association between direct bilirubin and mean LDL particle size. Only direct bilirubin levels were significantly associated with the sdLDL subfraction and mean LDL particle size. Mean LDL particle size exhibited a significantly stronger correlation with direct bilirubin than sdLDL, percent sdLDL, and the sdLDL:large LDL ratio. Regression analysis showed that direct bilirubin was significantly associated with mean LDL particle size, according to both the stepwise method (β = 11.445, P value = 0.002) and the enter method (β = 11.655, P value = 0.002).

CONCLUSIONS

Direct bilirubin is more strongly correlated with the sdLDL subfraction compared with total and indirect bilirubin, and is independently associated with mean LDL particle size in overweight and centrally obese women.

Relation of High Serum Bilirubin to Short-Term Mortality Following a Myocardial Infarction Complicated by Left Ventricular Systolic Dysfunction (from the High-Risk Myocardial Infarction Database Initiative)

Higher serum bilirubin has been associated with poorer prognosis in patients with heart failure (HF). We examined the association between serum bilirubin and clinical outcomes in patients with clinical signs of HF and/or left ventricular systolic dysfunction after acute myocardial infarction (MI). A total of 7,467 patients from the High-Risk Myocardial Infarction Database Initiative with an available baseline total bilirubin concentration were studied. The association between baseline bilirubin concentrations and the composite outcome of cardiovascular mortality (CVM), nonfatal stroke, nonfatal MI or hospitalization for HF, CVM, and all-cause mortality were assessed using Cox proportional hazards models. An interaction with time was observed with associations present only in the first 90 days after randomization. The median (percentile_25-75) baseline total bilirubin concentration was 11 (8 to 14) µmol/L and was above the "normal" range (>17.1 µmol/L) in 1,053 (14.1%) patients. In multivariable analysis, with adjustment for baseline characteristics (demographic, co-morbidities, Killip score, left ventricular ejection fraction, and laboratory variables), patients with a bilirubin concentration of >17.1 µmol/L had a significantly higher risk of all the studied outcomes at 90 days (e.g., CVM: adjusted hazard ratio 1.45, 95% confidence interval 1.14 to 1.86, p = 0.003). The addition of bilirubin to a validated survival model modestly improved the risk reclassification to predict 90-day events (continuous net reclassification improvement for CVM 6.4%, 95% confidence interval 0.7% to 9.6%, p = 0.04). In patients with MI complicated with HF and/or systolic dysfunction, bilirubin concentration is an independent predictor of mortality and may improve risk stratification.

Direct, indirect and total bilirubin and risk of incident coronary heart disease in the Dongfeng-Tongji cohort

BACKGROUND

Total bilirubin (TBIL) is known to be inversely associated with coronary heart disease (CHD) risk, however, whether this association is dose-response remains inconsistent and it is unclear which subtype of bilirubin is responsible for the potential protective effect.

METHODS

We included 12,097 participants who were free of CHD, stroke, cancer and potential liver, biliary and renal diseases at baseline from September 2008 to June 2010 and were followed-up until October 2013. Cox proportional hazards models were used to assess the hazard ratios (HR) and 95% confidence interval (95% CI) of bilirubin with incident CHD risk.

RESULTS

The adjusted HRs for incident CHD increased with increasing direct bilirubin (DBIL) (p for trend = .013). Participants within the highest quintile of DBIL had 30% higher risk of incident CHD compared to those in the lowest quintile (95% CI: 1.07, 1.58). In contrast, compared with subjects in the lowest quintile of TBIL, those in the third quintile had the lowest of 24% risk for CHD incidence (95% CI: 0.63, 0.92), which showed a U-shaped association (p for quadratic trend = .040).

CONCLUSIONS

DBIL was associated with a dose-response increased risk for CHD incidence. However, a U-shaped association existed between TBIL, indirect bilirubin and incident CHD risk. Key messages Direct bilirubin is independently associated with incident coronary heart disease (CHD) in a dose-response manner. A similarly consistent U-shaped association was found between total bilirubin, indirect bilirubin and incident CHD. The potential protective effect of total bilirubin within the normal range on incident CHD should be mainly attributed to mild-to moderate elevated levels of indirect bilirubin.

The associations between serum biomarkers and stenosis of the coronary arteries

Serum biochemical indices reflect dynamic physiological and pathophysiological processes within the body, the associations between these markers and the number of stenotic coronary arteries have been rarely studied. 627 healthy controls and 1,049 coronary heart disease (CHD) patients were sequentially recruited in our hospital. The association patterns between serum biochemical markers and the numbers of stenotic coronary arteries were evaluated in a cross-sectional manner. Upon binary multiple logistic regression analysis, the risk factor patterns differed by gender. Age, high-density lipoprotein cholesterol (HDL) and homocysteine (HCY) were common risk factors for CHD in both males and females. Upon ordinal multiple logistic regression analysis, age, low-density lipoprotein cholesterol (LDL) and lipoprotein (Lp) (a) increased, and HDL decreased, as the number of stenotic coronary arteries increased in male patients. Age and Lp(a) were positively associated with the number of stenotic coronary arteries and total bilirubin (TBil) was negatively associated with the number of stenotic coronary arteries in female patients. Age and Lp(a) were common risk factors positively associated with the number of stenotic coronary arteries in both male and female patients. HDL and LDL were male-specific risk factors and TBil was a female-specific risk factor for an increasing number of stenotic coronary arteries. In conclusion, serum biomarker levels correlated with the number of stenotic coronary arteries and showed gender different patterns.

The Relationship between Serum Bilirubin and Elevated Fibrotic Indices among HBV Carriers: A Cross-Sectional Study of a Chinese Population

The study probed the association between bilirubin and hepatitis B virus (HBV) infection and progression. A cross-sectional analysis of 28,500 middle aged and elderly Chinese participants was performed to analyze the differences of bilirubin in terms of hepatitis B surface antigen (HBsAg) positive or negative and the correlation between bilirubin and severity of hepatic fibrosis estimated by non-invasive indices. Bilirubin was significantly higher in the HBsAg (+) group than the HBsAg (−) group. Higher bilirubin levels were consistently associated with elevated liver fibrosis indices among HBsAg carriers. Compared with quartile 1 of total bilirubin (TBil), the multivariable-adjusted ORs (95% CIs) for elevated fibrosis indices of quartile 4 were 2.24 (95% CIs, 1.57–3.21) estimated by fibrosis 4 score (FIB-4) and 2.22 (95% CIs, 1.60–3.08) estimated by aspartate transaminase to platelet ratio index (APRI). In addition, direct bilirubin (DBil) had a stronger association with elevated liver fibrosis indices than did indirect bilirubin (IBil). Furthermore, the relationship between DBil and elevated fibrosis indices was more robust among participants who were female, overweight or had central fat distribution. These findings suggested that bilirubin levels, especially DBil, were independently associated with an increased risk of increased fibrosis indices.

Association of Serum Bilirubin with SYNTAX Score and Future Cardiovascular Events in Patients Undergoing Coronary Intervention

BACKGROUND

Bilirubin has emerged as an important endogenous antioxidant molecule, and increasing evidence shows that bilirubin may protect against atherosclerosis. The SYNTAX score has been developed to assess the severity and complexity of coronary artery disease. The aim of this study was to evaluate whether serum bilirubin levels are associated with SYNTAX scores and whether they could be used to predict future cardiovascular events in patients undergoing coronary intervention.

METHODS

Serum bilirubin levels and other blood parameters in patients with at least 12-h fasting states were determined. The primary endpoint was any composite cardiovascular event within 1 year, including death, nonfatal myocardial infarction, and target-vessel revascularization.

RESULTS

In total, 250 consecutive patients with stable coronary artery disease (mean age 70 ± 13) who had received coronary intervention were enrolled. All study subjects were divided into two groups: group 1 was defined as high SYNTAX score (> 22), and group 2 was defined as low SYNTAX score (≤ 22). Total bilirubin levels were significantly lower in the high SYNTAX score group than in the low SYNTAX score group (0.51 ± 0.22 vs. 0.72 ± 0.29 mg/dl, p < 0.001). By multivariate analysis, serum total bilirubin levels were identified as an independent predictor for high SYNTAX score (adjusted odds ratio: 0.28, 95% confidence interval 0.04-0.42; p = 0.004). Use of the Kaplan-Meier analysis demonstrated a significant difference in 1-year cardiovascular events between high (> 0.8 mg/dl), medium (> 0.5, ≤ 0.8 mg/dl), and low (≤ 0.5 mg/dl) bilirubin levels (log-rank test p = 0.011).

CONCLUSIONS

Serum bilirubin level is associated with SYNTAX score and predicts future cardiovascular events in patients undergoing coronary intervention.

Relationship between plasma bilirubin level and oxidative stress markers in HIV-infected patients on atazanavir- vs. efavirenz-based antiretroviral therapy

OBJECTIVES

Chronic oxidative stress (OS) may play a role in cardiovascular disease in HIV-infected patients, and increased bilirubin levels may have a beneficial role in counteracting OS. Atazanavir (ATV) inhibits UDP-glucuronosyl-transferase 1A1 (UGT1A1), thus increasing unconjugated bilirubin levels. We aimed to compare changes in OS markers in patients on ATV/ritonavir (ATV/r)- vs. efavirenz (EFV)-based first-line antiretroviral therapy (ART).

METHODS

A multicentre, prospective cohort study of HIV-infected patients who started first-line ART with either ATV/r or EFV was conducted. Lipoprotein-associated phospholipase A2 (Lp-PLA2), myeloperoxidase (MPO) and oxidized low-density lipoprotein (oxLDL) were measured for 145 patients in samples obtained at baseline and after at least 9 months of ART during which the initial regimen was maintained and the patient was virologically suppressed. The change in OS markers was modelled using multiple linear regressions adjusting for baseline values and confounders.

RESULTS

After adjustment for baseline variables, patients on ATV/r had a significantly greater decrease in Lp-PLA2 [estimated difference -16.3; 95% confidence interval (CI) -31.4, -1.25; P = 0.03] and a significantly smaller increase in OxLDL (estimated difference -21.8; 95% CI -38.0, -5.6; P < 0.01) relative to those on EFV, whereas changes in MPO were not significantly different (estimated difference 1.2; 95% CI -14.3, 16.7; P = 0.88). Adjusted changes in bilirubin were significantly greater for the ATV/r group than for the EFV group (estimated difference 1.33 mg/dL; 95% CI 1.03, 1.52 mg/dL; P < 0.01). Changes in bilirubin and changes in OS markers were significantly correlated.

CONCLUSIONS

When compared with EFV, ATV/r-based therapy was associated with lower levels of oxidative stress biomarkers, which was in part attributable to increased bilirubin levels.

Risk Factors Associated with Left-Sided Cardiac Valve Calcification: A Case Control Study

OBJECTIVES

To identify risk factors associated with cardiac valve calcification that is easily detectable through routine blood tests in patients who received valve replacement therapy.

METHODS

Four hundred patients with valvular heart disease who underwent valve replacement surgery between December 2009 and January 2013 were enrolled in this study. Of these, 77 had valve calcification; the other 323 did not. Multivariate logistic regression analysis was used to assess for risk factors associated with valve calcification.

RESULTS

In our study population, rheumatic valve lesions were the most common reason for valve replacement. Degenerative nonstenotic valve lesion was a protective factor and degenerative stenotic valve lesion was a strong risk factor for valve calcification. Serum levels of gamma-glutamyl transferase (GGT) of between 30 and 46 IU/l and >90 IU/l and total bilirubin (TBIL) of between 15 and 20 μmol/l were positively correlated with valve calcification. Meanwhile, serum calcium (Ca2+) levels of between 2.3 and 2.4 mmol/l were negatively correlated with rheumatic valve calcification.

CONCLUSIONS

Degenerative stenotic lesion is a risk factor and degenerative nonstenotic lesion a protective factor for cardiac valve calcification. Serum GGT and TBIL levels are positively correlated and serum Ca2+ levels negatively correlated with rheumatic cardiac valve calcification.

Serum bilirubin levels are inversely associated with PAI-1 and fibrinogen in Korean subjects

OBJECTIVES

Oxidative stress may contribute to atherosclerosis and increased activation of the coagulation pathway. Bilirubin may reduce activation of the hemostatic system to inhibit oxidative stress, which would explain its cardioprotective properties shown in many epidemiological studies. This study investigated the association of serum bilirubin with fibrinogen and plasminogen activator inhibitor-1 (PAI-1), respectively.

METHODS

A cross-sectional analysis was performed on 968 subjects (mean age, 56.0 ± 11.2 years; 61.1% men) undergoing a general health checkup. Serum biochemistry was analyzed including bilirubin subtypes, insulin resistance (using homeostasis model of assessment [HOMA]), C-reactive protein (CRP), fibrinogen, and PAI-1.

RESULTS

Compared with subjects with a total bilirubin (TB) concentration of <10.0 μmol/L, those with a TB concentration of >17.1 μmol/L had a smaller waist circumference, a lower triglyceride level, a lower prevalence of metabolic syndrome, and decreased HOMA-IR and CRP levels. Correlation analysis revealed linear relationships of fibrinogen with TB and direct bilirubin (DB), whereas PAI-1 was correlated with DB. After adjustment for confounding factors, bilirubin levels were inversely associated with fibrinogen and PAI-1 levels, respectively. Multivariate regression models showed a negative linear relationship between all types of bilirubin and fibrinogen, whereas there was a significant linear relationship between PAI-1 and DB.

CONCLUSIONS

High bilirubin concentrations were independently associated with low levels of fibrinogen and PAI-1, respectively. The association between TB and PAI-1 was confined to the highest TB concentration category whereas DB showed a linear association with PAI-1. Bilirubin may protect against the development of atherothrombosis by reducing the hemostatic response.

Mildly elevated serum total bilirubin levels are negatively associated with carotid atherosclerosis among elderly persons with type 2 diabetes

Diabetes is strongly associated with several mechanisms of tissue damage such as oxidative stress. Serum bilirubin may have a beneficial role in preventing oxidative changes in cardiovascular disease (CVD). Limited information is available on whether serum bilirubin is an independent confounding factor for carotid atherosclerosis among elderly persons with type 2 diabetes. The study subjects were 169 men aged 79 ± 8 (mean ± SD) years and 205 women aged 81 ± 8 years that were enrolled consecutively from patients in the medical department. Carotid intima-media thickness (IMT) and plaque were derived via B-mode ultrasonography. Multiple linear regression analysis showed that serum total bilirubin (β = -0.160) was significantly associated with carotid IMT. Compared to subjects with a serum total bilirubin of tertile-1 (0.13-0.58 mg/dL), the multivariate-adjusted odds ratio (95% confidence interval) of carotid IMT ≥1.0 mm including plaque and carotid plaque was 0.46 (0.23-0.93) and 0.32 (0.17-0.60) in the Tertile-3 group (0.87-1.93 mg/dL), respectively. Next, data were further stratified by gender, age, smoking status, medication and prevalence of CVD. There were no significant differences in serum total bilirubin levels between selected subgroups. Our data demonstrated a negative association between serum total bilirubin and carotid atherosclerosis among elderly persons with type 2 diabetes.

Clinical significance of serum bilirubin and gamma-glutamyltransferase levels on coronary atherosclerosis assessed by multidetector computed tomography

BACKGROUND AND AIMS

Low bilirubin and high gamma-glutamyltransferase (GGT), which are endogenous markers of oxidative stress, confer a higher risk of cardiovascular disease (CVD). We investigated associations between serum concentrations of bilirubin, GGT and coronary atherosclerosis.

METHODS AND RESULTS

A cross-sectional analysis was performed on 1520 subjects who underwent multidetector computed tomography scans. Coronary atherosclerosis was assessed by coronary artery calcium score (CACS) and obstructive coronary artery disease (OCAD), was defined as the presence of coronary artery stenosis of ≥50%. Total bilirubin (TB) level was negatively correlated with CACS and coronary stenosis whereas GGT level was positively correlated with CACS in men. However, there was no correlation between TB, GGT levels and either CACS or coronary artery stenosis in women. In a multivariate-adjusted model, TB level was inversely associated with a CACS > 100 [odds ratio (OR) per log standard deviation (SD), 0.67; 95% confidence interval (CI), 0.52-0.87], and OCAD (OR per log SD, 0.77; 95% CI, 0.62-0.95) in men. By contrast, GGT level was positively associated with a CACS > 100 (OR per log SD, 1.35; 95% CI, 1.05-1.73) but not with OCAD. Adding TB and GGT to the conventional risk factors increased predictive accuracy for CACS > 100 (net reclassification improvement index [NRI] = 13.1%, P = 0.026; integrated discrimination index [IDI] = 0.024, P = 0.001) and for OCAD (NRI = 12.6%, P = 0.026; IDI = 0.010, P = 0.013).

CONCLUSIONS

Low TB and high GGT levels were concomitantly associated with coronary atherosclerosis in Korean men. Future studies are needed to elucidate the causal associations of TB and GGT with CVD.

Circulating Markers of Liver Function and Cardiovascular Disease Risk

Measurement of serum concentrations of various liver enzymes and other nonenzymatic proteins and metabolites of heme metabolism (eg, bilirubin) is often undertaken in clinical practice. Measurement of these liver function tests is simple, quick, and relatively inexpensive. However, interpreting the liver function test results in patients without evidence of liver disease is often challenging. Concentrations of some of liver enzymes, such as γ-glutamyltransferase or alkaline phosphatase, and concentrations of liver-derived metabolites, such as bilirubin, may be influenced by metabolic processes beyond the liver, sometimes making interpretation of the test results difficult. This scenario frequently occurs both in individuals at risk of cardiovascular disease and in patients with known cardiovascular disease, often resulting in the clinicians ignoring the test results. In this brief review, we discuss the evidence for associations between key serum liver function tests and cardiovascular disease risk and where associations are robust; we provide an interpretation for possible mechanistic links between the liver function test and cardiovascular disease.

Association of serum total bilirubin level with severity of coronary atherosclerosis is linked to systemic inflammation

OBJECTIVE

Although cardiovascular protective action of bilirubin has been attributed to its antioxidant effect, there was scarce data regarding the anti-inflammatory properties. Herein, we aimed to assess the relationship between serum total bilirubin level and severity of coronary artery disease (CAD) in association with the direct inflammatory marker such as C-reactive protein (CRP), the other indirect markers included in inflammation process such as neutrophil to lymphocyte ratio (NLR) and red cell distribution width (RDW) in patients with stable CAD.

METHODS

Angiographic data of 1501 patients were analyzed in this retrospective cross-sectional study. Patients were categorized according to Gensini scores as control, mild CAD and severe CAD groups. The association of clinical and laboratory parameters with the severity of CAD were determined by multivariable linear regression analysis.

RESULTS

Total bilirubin level in the control group was significantly higher than those of the other groups. After multivariable linear regression analysis total bilirubin [β=-3.131 (-4.481, -1.782), p<0.001] was significantly associated with the severity of CAD. Futhermore, there was a moderate and significant inverse correlation between serum total bilirubin level and the severity of CAD (r=-0.173, p<0.001), CRP (r=-0.112, p<0.001), NLR (r=-0.070, p=0.026) and RDW (r=-0.074, p=0.027).

CONCLUSION

Serum total bilirubin level was independently and inversely associated with the severity of coronary atherosclerosis in patients with stable CAD. In addition, total bilirubin level was inversely correlated with CRP, NLR and RDW. These results suggest that besides its already known effect on the oxidative stress, higher serum total bilirubin level may exhibit an anti-inflammatory effect in the coronary atherosclerotic process.

Circulating bilirubin and defense against kidney disease and cardiovascular mortality: mechanisms contributing to protection in clinical investigations

Unconjugated bilirubin is an endogenous circulating antioxidant, bound to albumin, and therefore is retained in the vascular compartment. Bilirubin has well-documented neurotoxic effects in infants; however, current evidence indicates mildly elevated bilirubin is associated with protection from cardiovascular disease and all-cause mortality in adults. Recent clinical studies show mildly elevated bilirubin is associated with protection from kidney damage and dysfunction, in addition to cardiovascular events and all-cause mortality in patients undergoing hemodialysis. This is the first review to examine the clinical evidence and summarize the potential mechanisms of action that link bilirubin to protection from kidney damage, subsequent kidney failure, and dialysis-related mortality. With this understanding, it is hoped that new therapies will be developed to prevent renal dysfunction and mortality from cardiovascular disease in at-risk individuals.

Ammonia-induced energy disorders interfere with bilirubin metabolism in hepatocytes

Hyperammonemia and jaundice are the most common clinical symptoms of hepatic failure. Decreasing the level of ammonia in the blood is often accompanied by a reduction in bilirubin in patients with hepatic failure. Previous studies have shown that hyperammonemia can cause bilirubin metabolism disorders, however it is unclear exactly how hyperammonemia interferes with bilirubin metabolism in hepatocytes. The purpose of the current study was to determine the mechanism or mechanisms by which hyperammonemia interferes with bilirubin metabolism in hepatocytes. Cell viability and apoptosis were analyzed in primary hepatocytes that had been exposed to ammonium chloride. Mitochondrial morphology and permeability were observed and analyzed, intermediates of the tricarboxylic acid (TCA) cycle were determined and changes in the expression of enzymes related to bilirubin metabolism were analyzed after ammonia exposure. Hyperammonemia inhibited cell growth, induced apoptosis, damaged the mitochondria and hindered the TCA cycle in hepatocytes. This led to a reduction in energy synthesis, eventually affecting the expression of enzymes related to bilirubin metabolism, which then caused further problems with bilirubin metabolism. These effects were significant, but could be reversed with the addition of adenosine triphosphate (ATP). This study demonstrates that ammonia can cause problems with bilirubin metabolism by interfering with energy synthesis.

Association of bilirubin with coronary artery calcification and cardiovascular events in the general population without known liver disease: the Heinz Nixdorf Recall study

BACKGROUND

Bilirubin is a product of heme oxygenase and an antioxidant per se. In selected cohorts and patient studies, bilirubin was associated with decreased risk for cardiovascular events. We aimed to determine the association of serum bilirubin with coronary artery calcification (CAC) and incident cardiovascular disease in the unselected general population.

METHODS

Participants without prior coronary heart or liver disease were drawn from the population-based Heinz Nixdorf Recall study. CAC was measured from electron beam computed tomography and quantified using the Agatston method. Incident major cardiovascular events (coronary events, stroke, cardiovascular death) were assessed during follow-up. The association of bilirubin with CAC score and incident events was calculated using regression analysis.

RESULTS

A total of 3,553 subjects (mean age 59.4 years, 44 % male) were included. Bilirubin was inversely correlated with CAC in men [estimated % change in (CAC + 1) per each gender-specific standard deviation of bilirubin [95 % confidence interval (CI): -6.1 (-11.6; -1.7) %, p = 0.032] but less so in women [-3.6 (-7.7; 0.2) %, p = 0.065], when adjusting for age only. With adjustment for traditional cardiovascular risk factors, the association was less pronounced [men: -2.5 (-7.5; 2.6) %, p = 0.35, women: -0.2 (-4.1; 3.5) %, p = 0.9]. Likewise, higher bilirubin by one standard deviation was associated with 19 % lower frequency of incident cardiovascular events in age- and gender-adjusted Cox regression analysis [hazard ratio (95 % CI): 0.81 (0.68; 0.96), p = 0.014]; this effect was slightly attenuated after adjustment for traditional cardiovascular risk factors [0.87 (0.73; 1.04), p = 0.13].

CONCLUSION

Our data from a general population suggest that a potential protective role of bilirubin in the atherosclerosis process is largely secondary to a more beneficial risk factor profile.