Cigarette smoking and serum bilirubin subtypes in healthy Korean men: the Korea Medical Institute study

Differential effects of environmental exposures on clinically relevant endophenotypes between sexes

Sex and gender differences play a crucial role in health and disease outcomes. This study used data from the National Health and Nutrition Examination Survey to explore how environmental exposures affect health-related traits differently in males and females. We utilized a sex-stratified phenomic environment-wide association study (PheEWAS), which allowed the identification of associations across a wide range of phenotypes and environmental exposures. We examined associations between 272 environmental exposures, including smoking-related exposures such as cotinine levels and smoking habits, and 58 clinically relevant blood phenotypes, such as serum albumin and homocysteine levels. Our analysis identified 119 sex-specific associations. For example, smoking-related exposures had a stronger impact on increasing homocysteine, hemoglobin, and hematocrit levels in females while reducing serum albumin and bilirubin levels and increasing c-reactive protein levels more significantly in males. These findings suggest mechanisms by which smoking exposure may pose higher cardiovascular risks and greater induced hypoxia for women, and greater inflammatory and immune responses in men. The results highlight the importance of considering sex differences in biomedical research. Understanding these differences can help develop more personalized and effective health interventions and improve clinical outcomes for both men and women.

Interplay Of Serum Bilirubin and Tobacco Smoking with Lung and Head and Neck Cancers in a Diverse, EHR-linked Los Angeles Biobank

Background

Bilirubin is a potent antioxidant with a protective role in many diseases. We examined the relationships between serum bilirubin (SB) levels, tobacco smoking (a known cause of low SB), and aerodigestive cancers, grouped as lung cancers (LC) and head and neck cancers (HNC).

Methods

We examined the associations between SB, LC, and HNC using data from 393,210 participants from a real-world, diverse, de-identified data repository and biobank linked to the UCLA Health system. We employed regression models, propensity score matching, and polygenic scores to investigate the associations and interactions between SB, tobacco smoking, LC, and HNC.

Results

Current tobacco smokers showed lower SB (-0.04mg/dL, 95% CI: [-0.04, -0.03]), compared to never-smokers. Lower SB levels were observed in HNC and LC cases (-0.10 mg/dL, [-0.13, -0.09] and - 0.09 mg/dL, CI [-0.1, -0.07] respectively) compared to cancer-free controls with the effect persisting after adjusting for smoking. SB levels were inversely associated with HNC and LC risk (ORs per SD change in SB: 0.64, CI [0.59,0.69] and 0.57, CI [0.43,0.75], respectively). Lastly, a polygenic score (PGS) for SB was associated with LC (OR per SD change of SB-PGS: 0.71, CI [0.67, 0.76]).

Conclusions

Low SB levels are associated with an increased risk of both HNC and LC, independent of the effect of tobacco smoking. Additionally, tobacco smoking demonstrated a strong interaction with SB on LC risk. Lastly, genetically predicted low SB (using a polygenic score) is negatively associated with LC. These findings suggest that SB could serve as a potential early and low-cost biomarker for LC and HNC. The interaction with tobacco smoking suggests that smokers with lower bilirubin could likely be at higher risk for LC compared to never smokers, suggesting the utility of SB in risk stratification for patients at risk for LC. Lastly, the results of the polygenic score analyses suggest potential shared biological pathways between the genetic control of SB and the risk of LC development.

Interplay Of Serum Bilirubin and Tobacco Smoking with Lung and Head and Neck Cancers in a Diverse, EHR-linked Los Angeles Biobank

Background

Bilirubin is a potent antioxidant with a protective role in many diseases. We examined the relationships between serum bilirubin (SB) levels, tobacco smoking (a known cause of low SB), and aerodigestive cancers, grouped as lung (LC) and head and neck (HNC).

Methods

We examined the associations between SB, LC and HNC using data from 393,210 participants from UCLA Health, employing regression models, propensity score matching, and polygenic scores.

Results

Current tobacco smokers showed lower SB (-0.04mg/dL, 95% CI: [-0.04, -0.03]), compared to never-smokers. Lower SB levels were observed in HNC and LC cases (-0.10 mg/dL, [-0.13, -0.09] and -0.09 mg/dL, CI [-0.1, -0.07] respectively) compared to cancer-free controls with the effect persisting after adjusting for smoking. SB levels were inversely associated with HNC and LC risk (ORs per SD change in SB: 0.64, CI [0.59,0.69] and 0.57, CI [0.43,0.75], respectively). Lastly, a polygenic score (PGS) for SB was associated with LC (OR per SD change of SB-PGS: 0.71, CI [0.67, 0.76]).

Conclusions

Low SB levels are associated with an increased risk of both HNC and LC, independent of the effect of tobacco smoking with tobacco smoking demonstrating a strong interaction with SB on LC risk. Additionally, genetically predicted low SB (from polygenic scores) is negatively associated with LC.

Impact

These findings suggest that SB could serve as a potential early biomarker for LC and HNC.

Association between elevated serum bilirubin levels with preserved lung function under conditions of exposure to air pollution

BACKGROUND

High serum bilirubin levels have been shown to be associated with an improved pulmonary function test results. Their potential ability to similarly benefit pulmonary function in an environment of polluted air has not been tested. We retrospectively analyzed data of 15,605 apparently healthy individuals in order to evaluate the effect of serum bilirubin levels on forced expiratory volume in 1 s (FEV1).

METHODS

Individuals attended the Tel-Aviv Medical Center Inflammatory Survey for a routine annual health check between February, 2002 and June, 2009 and were divided into low, medium and high serum bilirubin levels. Their FEV1 results were compared under various levels of air pollution. Air pollution and weather data were obtained from air pollution monitoring stations of the Israeli Ministry of Environmental Protection.

RESULTS

The elevated serum bilirubin concentrations on FEV1 were evaluated under moderate and high pollution levels FEV1 and were significantly higher in participants with high blood bilirubin levels compared to medium or low levels (p < 0.001 and p = 0.018, respectively). Participants with high levels of bilirubin had preserved FEV1 under exposure to high and medium pollution levels of both Nitrogen Oxide (NOx) and Carbon Monoxide (CO) pollutants (p = 0.003 and p = 0.022, respectively). The multivariate regression analysis revealed that the influence of bilirubin under conditions of air pollution remained significant even after adjustment for FEV1 confounders, but the interaction was not significant.

CONCLUSIONS

Elevated serum bilirubin concentrations are associated with preserved lung function in healthy individuals in Israel exposed to high levels of air pollution.

Direct Bilirubin Levels and Risk of Metabolic Syndrome in Healthy Chinese Men

Background

Serum bilirubin is a potent endogenous antioxidant with anti-inflammatory properties. Several cross-sectional studies have reported that bilirubin was negatively associated with metabolic syndrome. However, in recent longitudinal studies, the relations between bilirubin and metabolic syndrome are inconsistent. Moreover, previous studies mainly focused on serum total bilirubin which is the sum of direct bilirubin and indirect bilirubin. For these reasons, the longitudinal effect of bilirubin subtypes on incident metabolic syndrome was evaluated in Chinese men.

Methods

The study cohort involved 1339 Chinese men without metabolic syndrome. Metabolic syndrome was defined by the American Heart Association/National Heart, Lung and Blood Institute (AHA/NHLBI) criteria, using BMI for the replacement of waist circumference.

Results

There are 117 incident metabolic syndrome cases (8.7%) during 5 years of follow-up among 1339 metabolic syndrome-free participants at baseline. After adjusting for age, drinking, smoking, physical activity, TG, and LDL-C, the odd ratios (ORs) and 95% confidence intervals (CIs) for MetS incidence in the second, third, and fourth quartiles versus the first quartile of DBil concentration were 1.00 (0.61-1.63), 0.57 (0.32-1.02), and 0.51 (0.28-0.92) (P_trend = 0.031), respectively.

Conclusions

Our findings support the negative association between direct bilirubin and incident metabolic syndrome in healthy Chinese men over 5-year period.

Cigarette smoking behaviour and blood metabolomics

BACKGROUND

Identifying circulating metabolites related to cigarette smoking may provide insight into the biological mechanisms of smoking-related diseases and the nature of addiction. However, previous studies are limited, generally small, and have largely targeted a priori metabolites.

METHODS

We examined associations between cigarette smoking and metabolites using an untargeted metabolomics approach in 892 men and women from four studies including participants from Italy, USA, China and Finland. We examined associations between individual log-transformed metabolites and two key smoking phenotypes (current smoking status and cigarettes per day [cig/day]) using linear regression. Fixed-effect meta-analysis was used to combine results across studies. Strict Bonferroni thresholds were used as our significance criteria. We further examined associated metabolites with other metrics of smoking behaviuor (current versus former, former versus never, smoking duration and years since quitting) in the US study.

RESULTS

We identified a total of 25 metabolites associated with smoking behaviours; 24 were associated with current smoking status and eight with cig/day. In addition to three well-established nicotine metabolites (cotinine, hydroxycotinine, cotinine N-oxide), we found an additional 12 xenobiotic metabolites involved in benzoatic (e.g. 3-ethylphenylsulphate) or xanthine metabolism (e.g. 1-methylurate), three amino acids (o-cresol sulphate, serotonin, indolepropionate), two lipids (scyllo-inositol, pregnenolone sulphate), four vitamins or cofactors [e.g. bilirubin (Z,Z)], and one carbohydrate (oxalate).

CONCLUSIONS

We identified associations between cigarette smoking and a diverse range of metabolites. Our findings, with further validation in future studies, have implications regarding aetiology and study design of smoking-related diseases.

Serum bilirubin concentration is modified by UGT1A1 haplotypes and influences risk of type-2 diabetes in the Norfolk Island genetic isolate

Background

Located in the Pacific Ocean between Australia and New Zealand, the unique population isolate of Norfolk Island has been shown to exhibit increased prevalence of metabolic disorders (type-2 diabetes, cardiovascular disease) compared to mainland Australia. We investigated this well-established genetic isolate, utilising its unique genomic structure to increase the ability to detect related genetic markers. A pedigree-based genome-wide association study of 16 routinely collected blood-based clinical traits in 382 Norfolk Island individuals was performed.

Results

A striking association peak was located at chromosome 2q37.1 for both total bilirubin and direct bilirubin, with 29 SNPs reaching statistical significance (P < 1.84 × 10⁻⁷). Strong linkage disequilibrium was observed across a 200 kb region spanning the UDP-glucuronosyltransferase family, including UGT1A1, an enzyme known to metabolise bilirubin. Given the epidemiological literature suggesting negative association between CVD-risk and serum bilirubin we further explored potential associations using stepwise multivariate regression, revealing significant association between direct bilirubin concentration and type-2 diabetes risk. In the Norfolk Island cohort increased direct bilirubin was associated with a 28 % reduction in type-2 diabetes risk (OR: 0.72, 95 % CI: 0.57-0.91, P = 0.005). When adjusted for genotypic effects the overall model was validated, with the adjusted model predicting a 30 % reduction in type-2 diabetes risk with increasing direct bilirubin concentrations (OR: 0.70, 95 % CI: 0.53-0.89, P = 0.0001).

Conclusions

In summary, a pedigree-based GWAS of blood-based clinical traits in the Norfolk Island population has identified variants within the UDPGT family directly associated with serum bilirubin levels, which is in turn implicated with reduced risk of developing type-2 diabetes within this population.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0291-z) contains supplementary material, which is available to authorized users.

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.

Active and Passive Smoking and Serum Total Bilirubin in a Rural Korean Population

INTRODUCTION

Serum bilirubin is an endogenous antioxidant biomarker and its low level is a potential risk factor for smoking related health disorders. This study investigated the association of cigarette smoke with serum total bilirubin among Koreans.

METHODS

Between 2006 and 2011, we examined 4899 Korean adults living in a rural community. After excluding 38 participants with serum bilirubin more than 2mg/dL, 75 participants who did not report their smoking status or who had liver or bile duct disorders, and 711 participants with liver enzymes exceeding the upper reference values, we performed a cross-sectional analysis on 4075 participants. Participants were classified into four groups: never-smokers without secondhand smoke exposure (SHSE), never-smokers with SHSE, former smokers, and active smokers. Serum total bilirubin concentration was measured using the enzyme method.

RESULTS

Compared to never-smokers without SHSE, never-smokers with SHSE (β = -0.025 mg/dL), former smokers (β = -0.049 mg/dL), and active smokers (β = -0.149 mg/dL) had significantly lower serum bilirubin even after adjusting for demographic factors, study year, alanine aminotransferase, gamma-glutamyl transferase, hemoglobin, lifestyle factors, and chronic diseases. A sex-stratified analysis indicated that for men, former smokers and active smokers were significantly associated with having lower bilirubin when compared to never-smokers without SHSE. However, for women, never-smokers with SHSE and active smokers were significantly associated with having lower bilirubin when compared to never-smokers without SHSE.

CONCLUSION

Our findings suggest that both active and passive cigarette smoking are associated with low serum bilirubin among Korean adults.

IMPLICATIONS

Our results suggest that not only active smoking but also passive smoking including SHSE can have an influence on decreasing serum bilirubin levels. With this different point of view, our study supports efforts to create smoke-free environments in order to foster more favorable serum bilirubin profiles, which may improve endothelial function and reduce the risk of cardiovascular disease.

Serum bilirubin levels predict future development of metabolic syndrome in healthy middle-aged nonsmoking men

BACKGROUND

Despite epidemiologic research demonstrating an inverse relationship between serum bilirubin levels and the prevalence of metabolic syndrome, prospective data on serum bilirubin as a predictor of incident metabolic syndrome are limited.

METHODS

Serum bilirubin was examined as a risk marker for incident metabolic syndrome in a prospective study of 468 Taiwanese middle-aged men who were free of metabolic syndrome and other systemic diseases at baseline. These subjects were followed up in annual health examinations between 2001 and 2009 for the development of metabolic syndrome, which was defined according to unified criteria set by several major organizations.

RESULTS

Among the study subjects, 377 were nonsmokers and 91 were current smokers. All individuals were then stratified into 3 groups according to their baseline serum bilirubin levels (low, normal, and high). During a mean follow-up period of 7.58 years, 66 subjects developed metabolic syndrome. The incidence of metabolic syndrome was significantly reduced in the high-bilirubin group compared with the low-bilirubin group (6.4% vs 22.4%, P < .001). Multivariate Cox regression analysis revealed that the hazard ratio for incident metabolic syndrome between the highest and lowest tertiles of serum bilirubin levels was 0.246 (95% confidence interval 0.120-0.503). However, although it remained clearly evident in nonsmokers, the inverse correlation was attenuated in current smokers.

CONCLUSIONS

Increased serum bilirubin was associated with a reduced future risk of metabolic syndrome in apparently healthy middle-aged, nonsmoking men. Our findings support the predictive role of serum total bilirubin for future development of metabolic syndrome.

Serum Bilirubin and Disease Progression in Mild COPD

BACKGROUND

COPD is a chronic inflammatory disorder associated with oxidative stress. Serum bilirubin has potent antioxidant actions, and higher concentrations have been shown to protect against oxidative stress. The relation between serum bilirubin and COPD progression is unknown.

METHODS

Serum bilirubin was measured in 4,680 smokers aged 35 to 60 years old with mild to moderate airflow limitation. The relationship of serum bilirubin to postbronchodilator FEV₁ and rate of FEV1 decline over 3 to 9 years was determined using regression modeling. Total and disease-specific mortality were also ascertained.

RESULTS

Serum bilirubin was positively related to FEV₁ (P < .001). Serum bilirubin was also negatively related to the annual decline in FEV₁ when adjusted for baseline demographics, pack-years smoked, and baseline measures of lung function (P = .01). Additionally, serum bilirubin was negatively associated with risk of death from coronary heart disease (P = .03); however, the relationships between bilirubin and other mortality end points were not statistically significant (P > .05).

CONCLUSIONS

Bilirubin is inversely related to COPD disease severity and progression. Higher serum bilirubin concentration was associated with a higher FEV₁ and less annual decline in FEV₁. Bilirubin was also associated with less coronary heart disease mortality. These data support the hypothesis that bilirubin has a protective effect on COPD disease progression, possibly through its antioxidant actions. Bilirubin may prove useful as an easily accessible and readily available blood-based COPD biomarker.

Combined effects of smoking and bilirubin levels on the risk of lung cancer in Korea: the severance cohort study

BACKGROUND

Smoking is a major risk factor for lung cancer. Bilirubin, an antioxidant, is inversely associated with the risk of diseases related to oxidative stress. This study was conducted to determine the influence of smoking and bilirubin levels on the risk of lung cancer in the Severance cohort study.

METHODS

This study included 68,676 Korean who received a health examination at Severance Health Promotion Center from 1994 to 2004. Serum bilirubin measurements within normal range were divided into tertiles whereas smoking states were divided as never-smokers, former smokers and current smokers. A diagnosis of lung cancer was coded as occurring based on the report from the National Cancer Registry. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) were calculated using Cox proportional hazards model.

RESULTS

At the end of the study period, 240 patients (men: 181, women: 59) developed lung cancer. Compared to those with bilirubin levels ≥ 1.0 mg/dL, HRs (95% CI) for lung cancer were 2.8 (1.8-4.2) for subjects having bilirubin levels from 0.2 to 0.7 mg/dL in men. When we stratified our analysis by smoking status, bilirubin consistently showed a protective effect on the risk of lung cancer on both never- and current smokers. Current smokers having bilirubin levels from 0.2 to 0.7 mg/dL had a risk of lung cancer by 6.0-fold higher than never-smokers with bilirubin levels ≥ 1.0 mg/dL in men.

CONCLUSION

In this large prospective study, higher baseline bilirubin level in the normal range was associated with low risk of lung cancer. Smoking and low bilirubin levels were cumulatively associated with a higher risk of lung cancer.

Smoking cessation is followed by increases in serum bilirubin, an endogenous antioxidant associated with lower risk of lung cancer and cardiovascular disease

INTRODUCTION

Lower concentrations of serum bilirubin, an endogenous antioxidant, have been associated with risk of many smoking-related diseases, including lung cancer and cardiovascular disease, and current smokers are reported to have lower bilirubin levels than nonsmokers and past smokers. This study evaluates the effects of smoking cessation on bilirubin levels.

METHODS

In a secondary analysis of a 6-week placebo-controlled trial of naltrexone for smoking cessation, indirect and total bilirubin concentrations were evaluated at baseline and following smoking cessation. Individuals who were continuously abstinent for 6 weeks (n = 155) were compared to those who were not (n = 193). Participants reported smoking ≥ 20 cigarettes daily at baseline and received smoking cessation counseling, 21 mg nicotine patch daily, and either placebo or 1 of 3 doses of naltrexone (25, 50, or 100mg) for 6 weeks. Change in indirect and total bilirubin following the quit date was measured at Weeks 1, 4, and 6 compared to baseline.

RESULTS

Individuals who were continuously abstinent from smoking, independent of naltrexone condition, showed a significantly greater mean increase in indirect (~unconjugated) bilirubin (0.06 mg/dl, SD = 0.165) compared to those who did not (mean = 0.02, SD = 0.148, p = .015). Similar results were obtained for total bilirubin (p = .037).

CONCLUSIONS

Smoking cessation is followed by increases in bilirubin concentration that have been associated with lower risk of lung cancer and cardiovascular disease.

The relationship between total bilirubin levels and total mortality in older adults: the United States National Health and Nutrition Examination Survey (NHANES) 1999-2004

Objective

Due to its anti-oxidant and anti-inflammatory properties, bilirubin has been associated with reduced cardiovascular risk. A recent study demonstrated an L-shaped association of pre-treatment total bilirubin levels with total mortality in a statin-treated cohort. We therefore investigated the association of total bilirubin levels with total mortality in a nationally representative sample of older adults from the general population.

Methods

A total of 4,303 participants aged ≥60 years from the United States National Health and Nutrition Examination Survey 1999–2004 with mortality data followed up through December 31, 2006 were included in this analysis, with a mean follow-up period of 4.5 years.

Results

Participants with total bilirubin levels of 0.1–0.4 mg/dl had the highest mortality rate (19.8%). Compared with participants with total bilirubin levels of 0.5–0.7 mg/dl and in a multivariable regression model, a lower total bilirubin level of 0.1–0.4 mg/dl was associated with higher risk of total mortality (hazard ratios, 1.36; 95% confidence interval, 1.07–1.72; P = 0.012), while higher levels (≥0.8 mg/dl) also tended to be associated with higher risk of total mortality, but this did not reach statistical significance (hazard ratios, 1.24; 95% confidence interval, 0.98–1.56; P = 0.072).

Conclusion

In this nationally representative sample of older adults, the association of total bilirubin levels with total mortality was the highest among those with a level between 0.1 and 0.4 mg/dl. Further studies are needed to investigate whether higher total bilirubin levels could be associated with a higher mortality risk, compared to a level of 0.5–0.7 mg/dl.

Serum bilirubin may serve as a marker for increased heme oxygenase activity and inducibility in tissues--a rationale for the versatile health protection associated with elevated plasma bilirubin

Unconjugated bilirubin functions intracellularly as a potent inhibitor of NADPH oxidase complexes, and albumin-bound bilirubin contributes significantly to the oxidant scavenging activity of plasma. So it is not surprising that serum levels of bilirubin have been found to correlate inversely with risk for vascular diseases and a host of other disorders. Nonetheless, recent Mendelian randomization analyses reveal that individuals who carry low expression alleles of the hepatic bilirubin conjugating enzyme UGT1A1, and hence have somewhat elevated levels of plasma bilirubin throughout life, are not at decreased risk for vascular disorders. This likely reflects the fact that, in most people, plasma levels of unconjugated, unbound bilirubin--the fraction of bilirubin capable of fluxing back into cells--are so low (near 1 nM) that they can exert only a trivial antioxidant influence on cells. In light of these findings, it is reasonable to propose that the inverse correlation of plasma bilirubin and disease risks noted in many studies often reflect the fact that elevated plasma bilirubin can serve as a marker for an increased propensity to generate bilirubin within cells. Consistent with this view, high expression alleles of the major enzymatic source of bilirubin, heme oxygenase-1 (HO-1), do associate with decreased vascular risk in the majority of studies that have addressed this issue, and increased plasma bilirubin has been reported in carriers of these alleles. Hence, the consistent reduction in vascular risk noted in people with Gilbert syndrome (traditionally defined as having serum bilirubin in excess of 20 μM) is likely attributable to an increased rate of bilirubin generation within tissues, rather than to the decreased hepatic UGT1A1 activity that characterizes this syndrome. However, there is good reason to suspect that, at some sufficiently high plasma bilirubin level--as in individuals with very intense Gilbert syndrome or in Gunn rats lacking UGT1A1 activity--the plasma bilirubin pool does indeed provide some antioxidant protection to cells. Strategies for boosting bilirubin production within cells via HO-1 induction, or for mimicking bilirubin's antioxidant activity with cyanobacterial phycobilins, may have important potential for health promotion.