Association of smoking and low serum bilirubin antioxidant concentrations

Characterization of the effect of serum bilirubin concentrations on coronary endothelial function via measurement of high-sensitivity C-reactive protein and high-density lipoprotein cholesterol

Bilirubin can prevent oxidation of low-density lipoprotein (LDL) and may protect against atherosclerosis and coronary heart disease (CHD). The goal of this study was to characterize the relationship between bilirubin and CHD through measurements of bilirubin concentration, coronary endothelial function, and markers of oxidative stress, inflammation, and lipid/glucose metabolism. The study population consisted of 141 patients without CHD who underwent Doppler flow study. Vascular reactivity was examined by intracoronary administration of papaverine, acetylcholine (ACh) and nitroglycerin using a Doppler guide wire. Serum bilirubin, high-sensitivity C-reactive protein (hsCRP), malondialdehyde-modified LDL, LDL cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), fasting plasma glucose (FPG), and immunoreactive insulin were also measured. Homeostasis model assessment insulin resistance index and estimated glomerular filtration rate (eGFR) were calculated. Univariate analysis revealed that both percent change in coronary blood flow (CBF) and coronary artery diameter induced by ACh correlated positively with log-transformed bilirubin (r = 0.22, P < 0.05; r = 0.20, P < 0.05, respectively). Percent change in CBF in response to ACh correlated positively with eGFR (r = 0.24, P < 0.05) and correlated inversely with age, LDL-C, and log-transformed FPG (r = -0.24, P < 0.05; r = -0.17, P < 0.05, r = -0.22, P < 0.05, respectively). Multivariate analysis revealed that log-transformed bilirubin was the only independent predictor of percent change in CBF in response to ACh. Multivariate analysis revealed that log-transformed hsCRP and HDL-C were independent predictors of log-transformed bilirubin. These results suggest that a high level of bilirubin is associated with favorable coronary endothelial function, which may be mediated via the effect of bilirubin on inflammation and HDL-C.

Association between bilirubin and cardiovascular disease risk factors: using Mendelian randomization to assess causal inference

BACKGROUND

Elevated serum bilirubin has been associated with reduced risk of cardiovascular disease (CVD). However, serum bilirubin is also related with several potential confounders related to CVD, such as obesity. Mendelian randomization has been proposed as a method to address challenges to validity from confounding and reverse causality. It utilizes genotype to estimate causal relationships between a gene product and physiological outcomes. In this report, we demonstrate its use in assessing direct causal relations between serum bilirubin levels and CVD risk factors, including obesity, cholesterol, measures of vascular function and blood pressure.

METHODS

Study subjects included 868 asymptomatic individuals. Study subjects were genotyped at the UGT1A1*28 locus, which is strongly associated with bilirubin levels.

RESULTS

Serum bilirubin levels were inversely associated with levels of several cardiovascular disease risk factors, including body mass index (p=0.003), LDL (p=0.0005) and total cholesterol (p=0.0002). In contrast, UGT1A1*28 genotype, a known cause of elevated bilirubin levels, was not significantly associated with any of these traditional CVD risk factors. We did observe an association between genotype and brachial artery diameter (p=0.003) and cold pressor reactivity (p=0.01).

CONCLUSIONS

Our findings imply that the observed association of serum bilirubin levels with body mass index and cholesterol are likely due to confounding and suggest that previously established CVD benefits of increased bilirubin may in part be mediated by the early regulation of vascular structure and reactivity.

Inverse relation of total serum bilirubin to coronary artery calcification score detected by multidetector computed tomography in males

BACKGROUND

Serum total bilirubin has been suggested to have potential anti-inflammatory and antioxidant effects on the vasculature, acting against plaque formation and subsequent atherosclerosis. This study was designed to assess the association of serum total bilirubin with coronary artery calcification (CAC).

HYPOTHESIS

Individuals with higher bilirubin level would be less likely to develop CAC.

METHODS

Male subjects (N = 3408) underwent evaluation of CAC by cardiac computed tomography. Correlation and logistic regression analysis were performed to assess the relationships between CAC score and other variables.

RESULTS

Subjects with a higher CAC score had significantly lower total bilirubin level (P = 0.001). Total bilirubin level was negatively correlated with CAC score (r = -0.052, P = 0.002). A 0.1-mg/dL increase in bilirubin was associated with a reduced odds ratio (OR) of the risk by 29.2% for a CAC score above 100 (OR: 0.708, 95% confidence interval: 0.542-0.927, P = 0.012) after adjustment for several variables. Bilirubin was inversely correlated with high-sensitivity C-reactive protein (hsCRP) (r = -0.117, P < 0.001).

CONCLUSIONS

This study demonstrated an independent inverse association between serum total bilirubin and CAC score in males. Low serum bilirubin concentration would be useful as a potential risk factor for CAC in males. Additionally, reduced hsCRP may be 1 of the mechanisms for how bilirubin reduces CAC.

Usefulness of serum bilirubin and cardiorespiratory fitness as predictors of mortality in men

Elevated serum bilirubin has been suggested to reduce the risk for mortality. Cardiorespiratory fitness (CRF) has also been reported to have inverse association with all-cause and cardiovascular disease (CVD) mortality. The association between serum bilirubin, all-cause and CVD mortality, and the effect of CRF on the observed association was investigated. A total of 1,279 men aged 30 to 82 years underwent baseline medical examinations from 1974 to 1997 at the Cooper Clinic in Dallas, Texas. During an average of 17 years of follow-up, 698 men died, with 253 deaths due to CVD (36%). Men in the highest bilirubin quartiles had significantly lower risk for all-cause mortality compared to men in the lowest quartiles (p for trend = 0.0043), after adjusting for age and examination year. This inverse association remained significant after further adjustment for known confounders (p for trend = 0.0018). Additional adjustment for treadmill time attenuated the association (p for trend = 0.0090). Similar patterns of association were observed between serum bilirubin quartiles and CVD mortality. CRF was inversely associated with all-cause mortality (p for trend <0.0001) after adjusting for age and examination year. This inverse association also was observed after further adjusting for known confounders (p for trend = 0.0004). After additional adjustment for serum bilirubin, the association between CRF and all-cause mortality remained significant (p for trend = 0.0012). All-cause mortality and CVD mortality were significantly lower in men in the moderate- to high-fitness quartiles in the low- and high-bilirubin groups. In conclusion, serum bilirubin level and CRF level were strongly and independently associated with all-cause and CVD mortality.

Serum bilirubin links UGT1A1*28 polymorphism and predicts long-term cardiovascular events and mortality in chronic hemodialysis patients

BACKGROUND AND OBJECTIVES

Bilirubin is a protective factor with antioxidant and anti-inflammatory properties, but its association with clinical outcomes of hemodialysis patients is unknown. Bilirubin degradation is mainly determined by the activity of hepatic bilirubin uridine diphosphate-glucuronosyltransferase (UGT1A1), which is significantly influenced by a TA-repeat polymorphism in the gene's promoter, an allele designated UGT1A1*28. The study aimed to clarify the association between serum bilirubin and UGT1A1*28 polymorphism and their respective effect on outcomes of chronic hemodialysis patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The cohort study comprised 661 chronic hemodialysis patients who were prospectively followed for 12 years. The endpoints were cardiovascular events (CVEs) and all-cause mortality.

RESULTS

After adjustment for traditional and dialysis-related risk factors, individuals with bilirubin in the upper tertile had an adjusted hazard ratio of 0.32 for CVEs and 0.48 for all-cause mortality compared with those in the lower tertile. Individuals homozygous for UGT1A1*28 (genotype 7/7) had significantly higher bilirubin levels than those with 6/6 and 7/6 genotypes. In the same multivariable-adjusted model, individuals with 7/7 had approximately one tenth the risk for CVEs and one fourth the risk for all-cause mortality as compared with carriers of the 6 allele.

CONCLUSIONS

A graded, reverse association was noted between serum bilirubin and adverse outcomes among chronic hemodialysis patients. Moreover, the UGT1A1*28 polymorphism had strong effects on bilirubin levels and the 7/7 genotype might have an important effect on reducing CVEs and death.

Serum bilirubin levels in familial hypercholesterolemia: a new risk marker for cardiovascular disease?

Low concentrations of bilirubin are associated with an increased risk for cardiovascular disease (CVD). Possibly, bilirubin exerts its effect through the protection of LDL from oxidation. Therefore, we examined whether low bilirubin might also be a risk marker for CVD in patients with familial hypercholesterolemia (FH) and whether statins influence serum bilirubin levels. Patients with FH were recruited from 37 lipid clinics. After a washout period of 6 weeks, all patients were started on monotherapy with simvastatin 80 mg for a period of two years. A total of 514 patients were enrolled. Bilirubin at baseline was inversely associated with the presence of CVD, also after adjustment for age, gender, presence of hypertension, and HDL cholesterol levels. Moreover, bilirubin levels were significantly raised, by 7%, from 10.0 to 10.8 μmol/L after treatment with simvastatin 80 mg. We hypothesize first that high bilirubin levels might protect patients with FH from CVD. Furthermore, bilirubin levels were significantly increased after treatment with simvastatin 80 mg, independent of changes in liver enzymes, which might confer additional protection against CVD. Whether this is also true for lower doses of simvastatin or for other statins remains to be investigated.

Genetic influences on serum bilirubin in American Indians: The Strong Heart Family Study

OBJECTIVE

To identify genetic variation influencing serum bilirubin levels in American Indians, we performed genome-wide screening and association analyses in the Strong Heart Family Study. Bilirubin is an endogenous antioxidant that has demonstrated an inverse relationship with cardiovascular disease. Genetic variation within the promoter region of uridine diphosphate glucuronosyltransferase (UGT1A1) on chromosome 2q has been associated with elevated serum bilirubin levels in European populations. However, no study has investigated the UGT1A1 promoter in American Indians.

METHODS

Statistical analyses were carried out with 3,484 participants aged 14 to 93 years recruited from three geographic areas in the United States; Arizona, Oklahoma, and North and South Dakota.

RESULTS

Variance components linkage analysis detected a quantitative trait locus (QTL) for bilirubin on chromosome 2q in the combined centers (LOD = 6.61, P = 4.24 × 10⁻⁶) and in Oklahoma (LOD = 5.65, P = 4.57 24 × 10⁻⁵). Genetic association of the UGT1A1 promoter polymorphism was significant for all geographic locations. After adjustment using conditional linkage for UGT1A1 promoter variance, the linkage signal dropped to 1.10 in the combined sample and to 3.32 (P = 0.02) in Oklahoma, indicating this polymorphism is not completely responsible for the linkage signal in American Indians. We also detected suggestive linkage signals in the Dakotas on chromosome 10p12 (LOD = 2.18) and in the combined centers (LOD = 2.24) on chromosome 10q21.

CONCLUSIONS

Replication of a serum bilirubin QTL on chromosome 2q in American Indians implicates UGT1A1 but further genotyping is warranted to identify additional causative polymorphisms. Evidence also supports a potential novel locus for bilirubin on chromosome 10.

Relationship between bilirubin concentration, coronary endothelial function, and inflammatory stress in overweight patients

AIM

Bilirubin has antioxidant properties and may protect against atherosclerosis and coronary heart disease (CHD). Further, in patients with metabolic syndrome, hyperbilirubinemia is associated with attenuation of insulin resistance. The aim of the present study was to determine the relationship between serum bilirubin concentration and coronary endothelial function in overweight patients.

METHODS

The study population consisted of 107 patients without CHD who underwent coronary flow studies. Vascular reactivity was examined by intra-coronary administration of papaverine and nitroglycerin. Coronary endothelial function was evaluated by assessing the change in coronary artery diameter to papaverine [percent change in flow-mediated dilatation (%FMD)] and nitroglycerin (%NTG). Serum total bilirubin, high-sensitivity C-reactive protein (hs-CRP), high density lipoprotein-cholesterol (HDL-C), fasting plasma glucose and immunoreactive insulin levels were also measured, and the homeostasis model assessment insulin resistance (HOMA-IR) index was calculated. Patients were divided into two groups according to body mass index (BMI): an overweight group (BMI ≥ 25; n = 36) and a normal weight group (BMI < 25; n = 71).

RESULTS

In the overweight group, univariate analysis revealed that log-transformed total bilirubin was positively correlated with %FMD and HDL-C (r = 0.38, p< 0.05; r = 0.30, p < 0.05, respectively) and was inversely correlated with log-transformed hs-CRP and HOMA-IR (r = -0.45, p < 0.01; r = -0.45, p< 0.05, respectively). Multivariate analysis revealed that log-transformed hs-CRP was the only independent predictor of log-transformed total bilirubin (p< 0.05).

CONCLUSIONS

These results suggest that a high bilirubin level was associated with favorable coronary endothelial function in overweight patients. Further, the anti-inflammatory effects of bilirubin may mediate this effect.

Bilirubin, cardiovascular diseases and cancer: epidemiological perspectives

Owing to a potent antioxidant property of bilirubin, a growing interest has been drawn to the potential protective effects of bilirubin against oxidative stress-related diseases. This article evaluates associations of bilirubin with atherosclerotic diseases and cancer. Serum bilirubin has consistently been shown to be inversely associated with diverse atherosclerotic diseases, mostly among men in different populations. A limited number of prospective studies have shown a U-shaped or reversed J-shaped relationship between bilirubin and coronary heart disease in men and no evident association in women. Few studies have provided evidence supportive of a protective association between bilirubin and cancer risk. The findings on bilirubin-related genetic polymorphisms are inconsistent in relation to coronary heart disease and cancer.

Alteration of serum bilirubin level in schizophrenia

Abstract Objective. Alteration of serum bilirubin level in acute episodes of psychosis in patients with schizophrenia has been reported but the pattern of this alteration is controversial. Methods. Patients diagnosed as schizophrenia (162, group S) or bipolar disorder (155, group B) entered the study. The control group consisted of 95 patients admitted to cardiac care unit who had no personal or family history of major psychiatric disorders. Pre- and post-admission levels of bilirubin were measured and compared within and between the groups. Patients were examined to exclude all other causes of hyperbilirubinemia. Group S and B participants were also evaluated using positive and negative syndrome subscale (PANSS) both at admission and discharge. Results. The mean admission bilirubin levels of all the groups were in the normal range (significantly higher in group S than groups B and C) and were affected by the score of general psychopathology subscale rather than the scores of positive symptoms subscale. Conclusions. Although bilirubin decreased in all three groups at discharge, the rate of decrease was significantly higher in group S. The reason for this is not clear and needs further study.

Serum bilirubin and genes controlling bilirubin concentrations as biomarkers for cardiovascular disease

BACKGROUND

Serum bilirubin has been consistently shown to be inversely related to cardiovascular disease (CVD). Recent studies showed serum bilirubin to be associated with CVD-related factors such as diabetes, metabolic syndrome, and body mass index. Although the association of serum bilirubin with CVD has been found in both retrospective and prospective studies, less information is available on the role of genes that control bilirubin concentrations and their association with CVD.

CONTENT

In this review, we provide detailed information on the identity of the major genes that control bilirubin concentrations and their association with serum bilirubin concentrations and CVD risk. We also update the results of the major studies that have been performed on the association between serum bilirubin, CVD, and CVD-related diseases such as diabetes or metabolic syndrome. Studies consistently indicate that bilirubin concentrations are inversely associated with different types of CVD and CVD-related diseases. A conditional linkage study indicates that UGT1A1 is the major gene controlling serum bilirubin concentrations, and this finding has been confirmed in recent genomewide association studies. Studies also indicate that individuals homozygous for UGT1A1*28 have a significantly lower risk of developing CVD than carriers of the wild-type alleles.

SUMMARY

Serum bilirubin has a protective effect on CVD and CVD-related diseases, and UGT1A1 is the major gene controlling serum bilirubin concentrations. Pharmacologic, nonpharmacologic, or genetic interventions that increase serum bilirubin concentrations could provide more direct evidence on the role of bilirubin in CVD prevention.

Smoking and atherosclerotic cardiovascular disease: part II: role of cigarette smoking in cardiovascular disease development

Potential mechanisms and biomarkers of atherosclerosis related to cigarette smoking - a modifiable risk factor for that disease - are discussed in this article. These include smoking-associated inflammatory markers, such as leukocytes, high-sensitivity C-reactive protein, serum amyloid A, ICAM-1 and IL-6. Other reviewed markers are indicative for smoking-related impairment of arterial endothelial function (transcapillary leakage of albumin, inhibition of endogenous nitric oxide synthase activity and reduced endothelium-dependent vasodilation) or point to oxidative stress caused by various chemicals (cholesterol oxidation, autoantibodies to oxidized low-density lipoprotein, plasma levels of malondialdehyde and F(2)-isoprostanes and reduced antioxidant capacity). Smoking enhances platelet aggregability, increases blood viscosity and shifts the pro- and antithrombotic balance towards increased coagulability (e.g., fibrinogen, von Willebrand factor, ICAM-1 and P-selectin). Insulin resistance is higher in smokers compared with nonsmokers, and hemoglobin A1c is dose-dependently elevated, as is homocysteine. Smoke exposure may influence the kinetics of markers with different response to transient or chronic changes in cigarette smoking behavior.

Association of serum bilirubin with pulsatile arterial function in asymptomatic young adults: the Bogalusa Heart Study

The inverse association between serum bilirubin, a potent antioxidant, and oxidative stress-mediated diseases like cardiovascular disease is known. However, information is scant regarding the influence of bilirubin in relation to traditional cardiovascular risk factors on pulsatile arterial function in asymptomatic younger adults. The present study examines this aspect in 777 black and white subjects (71% white, 42% male) aged 18 to 44 years. Pulsatile arterial function was assessed in terms of large-artery (capacitive) and small-artery (oscillatory) compliances by radial artery pressure pulse contour analysis. In bivariate analysis adjusted for race and sex, bilirubin related significantly and positively to large- and small-artery compliances and high-density lipoprotein cholesterol, and inversely to age, body mass index, blood pressure variables, non-high-density lipoprotein cholesterol, triglycerides, and insulin resistance index. In multivariable analysis including race, sex, body surface area, and risk factor variables mentioned above, bilirubin did not relate to large-artery compliance, without or with smoking status in the model, whereas bilirubin associated beneficially with small-artery compliance (P=.01) in a model that excluded smoking status. When smoking status was included in the model, this association became less strong (P=.04); and smoking entered the model as an adverse predictor (P=.003). The observed beneficial association of serum bilirubin on pulsatile arterial function, albeit the attenuating effect of smoking on this relationship, in asymptomatic younger adults supports the antioxidant function of bilirubin in providing protection against oxidative stress-mediated vascular dysfunction.

Association between the UGT1A1 TA-repeat polymorphism and bilirubin concentration in patients with intermittent claudication: results from the CAVASIC study

BACKGROUND

Bilirubin has antioxidative and cytoprotective properties. Low plasma concentrations of bilirubin are reportedly associated with the development of coronary and cerebrovascular disease, and bilirubin concentrations are strongly correlated with the enzyme activity of the hepatic uridine diphosphate glucuronosyltransferase (UGT1A1). The activity of UGT1A1 is influenced by a TA-repeat polymorphism in the promoter of the UGT1A1 gene (UDP glucuronosyltransferase 1 family, polypeptide A1). In a case-control study, we investigated the association between the UGT1A1 polymorphism, bilirubin concentration, and intermittent claudication.

METHODS

We included 255 consecutive male patients presenting with intermittent claudication in the investigation and matched the patients by age and diabetes mellitus with 255 control individuals.

RESULTS

Plasma bilirubin concentrations were significantly lower in patients than in controls [mean (SD), 12.5 (5.3) micromol/L vs 15.4 (7.9) micromol/L; P < 0.001]. We found a clear association between the number of TA repeats and plasma bilirubin concentration. Considering the 6/6 TA-repeat genotype as the wild type, we observed a slight increase in bilirubin concentration individuals with the heterozygous 6/7 genotype and pronounced increases for those with the homozygous 7/7 genotype. This association occurred in both controls and patients; however, patients and controls were not significantly different with respect to UGT1A1 TA-repeat genotype frequencies.

CONCLUSIONS

Our study of a well-phenotyped group of patients with intermittent claudication and control individuals revealed a clear association between low bilirubin concentrations and peripheral arterial disease but no association between the UGT1A1 polymorphism and the disease.

Gilbert syndrome, UGT1A1*28 allele, and cardiovascular disease risk: possible protective effects and therapeutic applications of bilirubin

Serum bilirubin has been shown to be inversely related to cardiovascular disease (CVD) in both retrospective and prospective studies. Meta-analysis of existing studies has also confirmed that serum bilirubin concentrations are inversely related to CVD. Less information is known about the protective effects of slightly elevated serum bilirubin concentrations. In this review, we will focus primarily on the association of serum bilirubin and CVD and the possible protective roles of bilirubin, heme oxygenase (HO), and bilirubin UDP-glucuronosyltransferase (UGT1A1). HO and biliverdin reductase control the formation of bilirubin, whereas UGT1A1 controls bilirubin conjugation and clearance. Because of the health and therapeutic implications of slightly elevated serum bilirubin concentrations, we will discuss the recent prospective studies on cardiovascular risk in individuals with Gilbert syndrome (GS) as well as those with the UGT1A1*28 allele. Such individuals have decreased hepatic bilirubin UDP-glucuronosyltransferase activity, decreased bilirubin clearance, and increased serum bilirubin concentrations. Lastly, we will discuss some of the therapeutic approaches that could be used to increase serum bilirubin concentrations to prevent CVD and other oxidative and inflammatory diseases.

Serum Total Bilirubin Level and Prevalent Lower-Extremity Peripheral Arterial Disease

Background— Bilirubin, with recently recognized antioxidant and antiinflammatory activity, has emerged as a candidate for atheroprotection. We hypothesized that higher levels of bilirubin would reduce susceptibility to peripheral arterial disease (PAD).

Methods and Results— We analyzed 7075 adults with data available on the ankle brachial index, serum total bilirubin level, and PAD risk factors in the National Health and Nutrition Examination Survey (1999 to 2004), a nationally representative cross-sectional examination of the United States population. A 0.1 mg/dL increase in bilirubin level was associated with a 6% reduction in the odds of PAD (OR 0.94 [95% CI 0.90 to 0.98]) after adjustment for age, gender, race/ethnicity, smoking status, diabetes, hypertension, hypercholesterolemia, chronic kidney disease, CRP, and homocysteine. This result was not dependent on bilirubin levels above the reference range, liver disease, or alcohol intake. The inverse association of bilirubin with PAD tended to be stronger among men (OR 0.90 [95% CI 0.85 to 0.96]) compared with women (OR 0.97 [95% CI 0.91 to 1.04]; P interaction =0.05), and was stronger among active smokers (OR 0.81 [95% CI 0.73 to 0.90]) compared with nonsmokers (OR 0.97 [95% CI 0.93 to 1.02]; P interaction <0.01).

Conclusions— Increased serum total bilirubin level is associated with reduced PAD prevalence. This result is consistent with the hypothesis that bilirubin is protective from PAD.

Maternal active or passive smoking causes oxidative stress in cord blood

The aim of this study was to assess the influence of active and passive maternal smoking on cord blood total oxidant/antioxidant status at term. The levels of cord blood catalase (CAT), paraoxonase 1 (PON1), ceruloplasmin, total thiol and lipid hydroperoxide (LOOH), total antioxidant capacity (TAC), total oxidant status (TOS) and the oxidative stress index (OSI) were measured in samples of fetal cord blood serum from 29 nonsmokers who were not exposed to active or passive smoke, 30 passive smokers and 21 active smokers. The gestation period of all pregnancies was between 37 and 40 weeks, the pregnancies were uncomplicated and the infants were delivered vaginally. The weights of infants borne to the active smokers were significantly (P < 0.01) lower than those borne to the controls. Significantly lower concentrations of CAT, PON1 and TAC were found in the cord blood of the smokers than in that of the nonsmokers (P < 0.018). The cord blood levels of LOOH and TOS and OSI were significantly higher in the active and passive smokers than in the controls (P < 0.01). A significant positive correlation was found between maternal tobacco exposure and cord blood OSI (P < 0.001). Active or passive maternal smoking is associated with important alterations in the balance of oxidants and antioxidants in fetal cord blood and causes potent oxidative stress.

Effect of coronary angiography on oxidative DNA damage observed in circulating lymphocytes

Endogenous oxidative DNA damage is caused by multiple endogenous and exogenous factors. It is not completely known whether coronary angiography has an effect on DNA damage. The aim of this study was to investigate whether coronary angiography causes oxidative DNA damage. Fifty-four patients who underwent elective coronary angiography for diagnostic purpose were enrolled to the study. For each subject, the frequency of oxidative DNA damage was analyzed by using the comet assay, which is a sensitive biomarker of DNA damage, before and after diagnostic procedures. A highly significant increase of DNA damage mean score was observed in all patients after the coronary angiography procedure (p < 0.001). No significant associations were found between the change in oxidative DNA damage and dose of contrast media and radiation exposure time. A significant correlation was observed between the change of DNA damage and age, hyperlipidemia, hypertension, smoking, Gensini score index, and vitamin B(12) (r = 0.496, p< 0.001 ; r = 0.416, p = 0.002; r = 0.284, p = 0.038; r = 0.275, p = 0.044; r = 0.742, p < 0.001; r = -0.347, p = 0.048, respectively). The change of oxidative DNA damage was higher in patients with 3-vessel disease compared with 2-vessel disease, 1-vessel disease, and normal coronary arteries (99.6 +/-8.4, 62.0 +/-2.0, 43.2 +/-8.4, 21.6 +/-11.6 respectively; ANOVA p < 0.001). Multiple linear regression analysis showed that age and Gensini score index were independent predictors of the change of DNA damage (beta = 0.425, p = 0.003, beta = 0.684, p = 0.001 respectively). Our findings demonstrate that increased oxidative DNA damage in undergoing coronary angiography might be dependent on the severity of coronary artery disease and age, rather than on contrast media and radiation exposure time.

Cigarette smoking and irinotecan treatment: pharmacokinetic interaction and effects on neutropenia

PURPOSE

Several constituents of cigarette smoke are known to interact with drug metabolizing enzymes and potentially affect treatment outcome with substrate drugs. The purpose of this study was to determine the effects of cigarette smoking on the pharmacokinetics and adverse effects of irinotecan.

PATIENTS AND METHODS

A total of 190 patients (49 smokers, 141 nonsmokers) treated with irinotecan (90-minute intravenous administration on a 3-week schedule) were evaluated for pharmacokinetics. Complete toxicity data were available in a subset of 134 patients receiving 350 mg/m2 or 600 mg flat-fixed dose irinotecan.

RESULTS

In smokers, the dose-normalized area under the plasma concentration-time curve of irinotecan was significantly lower (median, 28.7 v 33.9 ng x h/mL/mg; P = .001) compared with nonsmokers. In addition, smokers showed an almost 40% lower exposure to SN-38 (median, 0.54 v 0.87 ng x h/mL/mg; P < .001) and a higher relative extent of glucuronidation of SN-38 into SN-38G (median, 6.6 v 4.5; P = .006). Smokers experienced considerably less hematologic toxicity. In particular, the incidence of grade 3 to 4 neutropenia was 6% in smokers versus 38% in nonsmokers (odds ratio [OR], 0.10; 95% CI, 0.02 to 0.43; P < .001). There was no significant difference in incidence of delayed-onset diarrhea (6% v 15%; OR, 0.34; 95% CI, 0.07 to 1.57; P = .149).

CONCLUSION

This study indicates that smoking significantly lowers both the exposure to irinotecan and treatment-induced neutropenia, indicating a potential risk of treatment failure. Although the underlying mechanism is not entirely clear, modulation of CYP3A and uridine diphosphate glucuronosyltransferase isoform 1A1 may be part of the explanation. The data suggest that additional investigation is warranted to determine whether smokers are at increased risk for treatment failure.

The Heme Catabolic Pathway and its Protective Effects on Oxidative Stress‐Mediated Diseases

Bilirubin, the principal bile pigment, is the end product of heme catabolism. For many years, bilirubin was thought to have no physiological function other than that of a waste product of heme catabolism--useless at best and toxic at worst. Although hyperbilirubinemia in neonates has been shown to be neurotoxic, studies performed during the past decade have found that bilirubin has a number of new and interesting biochemical and biological properties. In addition, there is now a strong body of evidence suggesting that bilirubin may have a beneficial role in preventing oxidative changes in a number of diseases including atherosclerosis and cancer, as well as a number of inflammatory, autoimmune, and degenerative diseases. The results also suggest that activation of the heme oxygenase and heme catabolic pathway may have beneficiary effects on disease prevention either through the action of bilirubin or in conjunction with bilirubin. If so, it may be possible to therapeutically induce heme oxygenase, increase bilirubin concentrations, and lower the risk of oxidative stress-related diseases.

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

BACKGROUND

Bilirubin is an antioxidant that suppresses lipid oxidation and retards atherosclerosis formation. An inverse association between serum bilirubin and coronary heart disease has been reported. Linkage studies have identified a major locus at the chromosome 2q telomere that affects bilirubin concentrations. A candidate gene in the linkage region encodes hepatic bilirubin uridine diphosphate-glucuronosyltransferase (UGT1A1). The insertion of a TA in the TATAA box of the gene, an allele designated UGT1A1*28, decreases gene transcription. Individuals homozygous for UGT1A1*28 (genotype 7/7) have increased serum bilirubin levels compared with carriers of the 6 allele. To date, no significant association between UGT1A1*28 and cardiovascular disease (CVD) events has been reported. We performed an association study in the Framingham Heart Study population to investigate whether UGT1A1*28 is associated with the risk of CVD events.

METHODS AND RESULTS

The study population included 1780 unrelated individuals from the Offspring cohort (49% males, mean age 36 years at entry) who had been followed up for 24 years. Individuals with genotype 7/7 had significantly higher bilirubin levels (mean+/-SD 1.14+/-0.44 mg/dL) than those with genotypes 6/6 and 6/7 (mean+/-SD 0.69+/-0.27 mg/dL, P<0.01). Using the Cox proportional hazards model, we found significant associations between the UGT1A1*28 allele and decreased risk of CVD. Individuals with genotype 7/7 (population frequency of 11%) had approximately one third the risk for CVD and coronary heart disease as carriers of the 6 allele, which resulted in a hazard ratio (95% confidence interval) of 0.36 (0.18 to 0.74) and 0.30 (0.12 to 0.74), respectively.

CONCLUSIONS

Homozygote UGT1A1*28 allele carriers with higher serum bilirubin concentrations exhibit a strong association with lower risk of CVD.

Low serum bilirubin levels are independently and inversely related to impaired flow-mediated vasodilation and increased carotid intima-media thickness in both men and women

BACKGROUND

Elevated levels of low-density lipoprotein (LDL) cholesterol and its oxidative modification have been described to be involved in the process of atherogenesis. Bilirubin, an antioxidant, prevents oxidative modification of LDL and therefore may protect from atherosclerosis and coronary heart disease (CHD). Impaired brachial artery flow-mediated dilatation (FMD), which means endothelial dysfunction (ED) and carotid intima-media thickness (IMT) are predictors for the development and progression of atherosclerosis. In the present study, FMD and IMT were studied in healthy subjects with lower and higher serum bilirubin concentrations in physiological ranges.

METHODS

Ninety-one healthy subjects between 25 and 45 years of age (47 with lower and 44 with higher serum bilirubin concentrations) were included in this study. Carotid IMT and brachial artery flow-mediated dilatation was measured by means of high-resolution vascular ultrasound. FMD was assessed by establishing reactive hyperemia and endothelium-independent dilatation (EID) was determined by using sublingual isosorbide dinitrate.

RESULTS

EDD in subjects with lower serum bilirubin concentrations was significantly worse than in those with higher serum bilirubin concentrations (11.6+/-4.4% versus 7.2+/-4.7%, respectively, p<0.0001). EID measurements were not significantly different between the groups (16+/-5.1% versus 16.8+/-7%, respectively). In addition, carotid IMT was significantly greater in subjects with lower serum bilirubin concentrations (0.5+/-0.13 mm versus 0.42+/-0.07 mm, p<0.0001). Furthermore, FMD in women with lower serum bilirubin concentrations was significantly lower than in women with higher serum bilirubin concentrations (11.5+/-4.9% and 17.5+/-4.7%, respectively, p<0.001). Accordingly, men with lower serum bilirubin concentrations had significantly lower FMD as compared to hyperbilirubinemic ones (11.7+/-3.6% versus 16.7+/-4.8%, respectively, p=0.009). Conversely, carotid IMT was significantly greater in both women and men with lower serum bilirubin concentrations compared to the subjects with elevated serum bilirubin concentrations (0.51+/-0.08 versus 0.41+/-0.08, p<0.001; 0.55+/-0.12 versus 0.40+/-0.07, p=0.002, in women and men, respectively).

CONCLUSION

The healthy subjects with lower serum bilirubin concentrations show significant ED and increased carotid IMT, which are predictors for atherosclerosis.

Increased oxidative stress in infants exposed to passive smoking

The purpose of this study was to assess the effect of passive cigarette smoking on the oxidative and anti-oxidative status of plasma in infants. Eighty-four infants aged 6-28 weeks were divided into two groups: the study group included infants who had been exposed to passive smoking via at least five cigarettes per day for at least the past 6 weeks at home, while the control group included infants who had never been exposed to passive smoking. The antioxidative status of plasma was assessed by the measurement of individual antioxidant components: vitamin C, albumin, bilirubin, uric acid, thiol contents and total antioxidant capacity (TAC 1 and TAC 2). Oxidative status was assessed by the determination of total peroxide levels and the oxidative stress index (OSI 1 and OSI 2). Plasma vitamin C, thiol concentration and TAC 1 and TAC 2 levels were significantly lower, whereas plasma total peroxide levels and OSI 1 and OSI 2 were significantly higher, in passive smoking infants than in the controls (P<0.01). We conclude that passive smoking has a negative impact on numerous parts of the antioxidant defence system in infants, and exposes them to potent oxidative stress.

High Serum Bilirubin Concentrations Preserve Coronary Flow Reserve and Coronary Microvascular Functions

BACKGROUND

Elevated serum bilirubin concentrations protect against atherosclerotic diseases; however, it is not clear whether higher serum bilirubin concentrations in physiological ranges work in favor of the cardiovascular system in younger persons with no cardiovascular risk factors. Accordingly, we investigated the effects of high, intermediate, and low serum bilirubin concentrations on coronary flow reserve (CFR).

METHODS AND RESULTS

Fifty-two healthy subjects with hyperbilirubinemia (total bilirubin 1.43+/-0.33 mg/dL; mean age 35.9+/-7.3), 55 subjects with intermediate bilirubin level (total bilirubin: 0.69+/-0.11 mg/dL; mean age: 36.4+/-6.8), and 53 healthy subjects with hypobilirubinemia (total bilirubin 0.37+/-0.08 mg/dL; mean age, 37.6+/-6.6) were studied. Transthoracic second harmonic Doppler echocardiography examination was performed using an Acuson Sequoia C256 Echocardiography System. Coronary diastolic peak flow velocities were measured at baseline and after dipyridamole infusion (0.84 mg/kg over 6 minutes). CFR was calculated as the ratio of hyperemic to baseline diastolic peak velocities. Demographic features, coronary risk factors, echocardiographic measurements, and biochemical measurements were similar among the 3 groups, except high-sensitivity C-reactive protein (hsCRP). CFR values were significantly higher in subjects with high bilirubin concentrations than those were in the intermediate and the low bilirubin groups (3.19+/-0.73; 2.75+/-0.42; 2.56+/-0.52, respectively; P<0.0001), and hsCRP levels were significantly lower in subjects with high bilirubin concentrations than those in both intermediate and low bilirubin groups (1.4+/-1.0, 2.0+/-1.7, 3.0+/-1.9 mg/L, respectively; P<0.001). hsCRP levels correlated with total bilirubin concentration and with CFR.

CONCLUSIONS

Elevated serum bilirubin concentrations protect from CFR impairment, coronary microvascular dysfunction, and possibly coronary atherosclerosis.

Bilirubin and the risk of common non-hepatic diseases

Bilirubin is a potent antioxidant but can be toxic at high concentrations. This article critically reviews the reported relationships of plasma bilirubin levels to the severity and/or incidence of various common non-hepatic diseases. Plasma bilirubin levels are reportedly negatively related to the risk of atherosclerotic diseases, cancers, demyelinating neuropathies and seasonal affective disorder. By contrast, the incidence and severity of schizophrenia are increased by elevated bilirubin levels. The data strongly suggest that the level of plasma bilirubin should be considered as a risk factor for several common non-hepatic diseases. Additional studies are needed to clarify the mechanisms of this influence, which are thought to be related to unconjugated bilirubin counteracting the oxidative stress underlying these disorders.

Relationship between DNA damage, total antioxidant capacity and coronary artery disease

OBJECTIVE

It has been known that there was a relation between the levels of DNA damage and the severity of the coronary artery disease (CAD). However, little is known about association of DNA damage with total antioxidant capacity (TAC) and CAD. The aim of this study is to evaluate the relationship between DNA damage, TAC and CAD.

METHODS

We used the comet assay to measure DNA damage from 53 patients with angiographically documented CAD and 42 patients with angiographically documented normal coronary vessel. The extent and severity of CAD was calculated to Gensini score index. TAC of plasma was determined using a novel automated measurement method.

RESULTS

Mean values of DNA damage were significantly higher in CAD patients than in the control group (p<0.001). There was a positive correlation between Gensini score index and DNA damage (r=0.590, p<0.001). Additionally, significantly positive correlations between score of DNA damage, and diabetes, smoking, obesity and hyperlipidemia were found (p<0.05). There was also a negative correlation between TAC and DNA damage (r=-0.711, p<0.001). The DNA damage was significantly higher in diabetic, smoker, hyperlipidemic and obese individuals than those without these conditions (p=0.001, p=0.006, p=0.001, p=0.004, respectively).

CONCLUSIONS

These data indicate that the level of DNA damage is increased and TAC level is decreased in CAD. DNA damage is correlated with the severity of the CAD, and levels of TAC.

Plasma triglycerides and type III hyperlipidemia are independently associated with premature familial coronary artery disease

OBJECTIVES

This study was designed to explore contributions of plasma total triglycerides (TGs) and type III hyperlipidemia to the risk of premature familial coronary artery disease (CAD).

BACKGROUND

Although plasma TGs are recognized as a risk factor for CAD, the independence of this association from related risk factors remains controversial. Also, the degree of CAD risk conferred by excess remnants of TG-rich lipoproteins in type III hyperlipidemia remains unclear.

METHODS

We analyzed lipids by ultracentrifugation in a series of 653 cases with premature familial CAD (myocardial infarction or revascularization by age 55 years in men or age 65 years in women, with similar onset in at least one other first-degree relative) and in 1,029 control subjects. The relationship of CAD risk to various strata of plasma TGs, high-density lipoprotein (HDL) cholesterol, and type III hyperlipidemia, and interactions among these variables were examined by multiple logistic regression, adjusting for other CAD risk factors.

RESULTS

The odds ratio for CAD with elevated plasma TG rose progressively to 11.4 in those with TGs 500 to 799 mg/dl (95% confidence interval 3.4 to 38.0, p < 0.0001) compared with <100 mg/dl, even after correction for HDL cholesterol, other elements of the metabolic syndrome, and other CAD risk factors. Risk of CAD associated with type III hyperlipidemia (found in 3.4% of cases) was also markedly increased independent of other risk factors (odds ratios of 5 to 10 depending on the model, all with p < 0.002).

CONCLUSIONS

The association between the plasma TG level and premature familial CAD is strong, graded, and independent. Risk of CAD is also strikingly elevated with type III hyperlipidemia.

Serum bilirubin levels in the U.S. population: gender effect and inverse correlation with colorectal cancer

Bilirubin, the primary end product of heme catabolism, is a key marker of liver and hematological disorders, and important cytoprotective properties have been ascribed to this bile pigment. The Third National Health and Nutrition Examination Survey, a comprehensive assessment of health and nutrition in the United States, was analyzed to determine the demographics and correlates of serum bilirubin levels in the general population. Men and women aged 17 and older were included in the weighted analysis, representing a total of 176,748,462 subjects. The mean serum total bilirubin in the adult population is 0.62 +/- 0.003 mg/dL (SEM), with a 97.5% cut-off of 1.4 mg/dL. Serum bilirubin levels are significantly higher in men (0.72 +/- 0.004) than in women (0.52 +/- 0.003 mg/dL) and are lower in non-Hispanic blacks (0.55 +/- 0.005 mg/dL) compared with non-Hispanic whites (0.63 +/- 0.004 mg/dL) and Mexican Americans (0.61 +/- 0.005 mg/dL). Bilirubin concentrations are unrelated to body weight but are reduced in active smokers. Individuals with a history of nondermatological malignancy exhibit significantly lower serum bilirubin concentrations compared with those who do not have a history of nondermatological cancer. In particular, each 1-mg/dL increase in serum bilirubin is associated with a markedly decreased prevalence of colorectal cancer (OR = 0.257; 95% CI 0.254-0.260). In conclusion, serum bilirubin levels vary significantly with gender, race, and smoking status. The observed inverse correlation between serum bilirubin concentrations and a history of nondermatological malignancy, particularly colorectal cancer, warrants further investigation of a potentially important chemopreventive function of bilirubin.

Bilirubin UDP-glucuronosyltransferase 1A1 (UGT1A1) gene promoter polymorphisms and HPRT, glycophorin A, and micronuclei mutant frequencies in human blood

A dinucleotide repeat polymorphism (5-, 6-, 7-, or 8-TA units) has been identified within the promoter region of UDP-glucuronosyltransferase 1A1 (UGT1A1) gene. The 7-TA repeat allele has been associated with elevated serum bilirubin levels that cause a mild hyperbilirubinemia (Gilbert's syndrome). Studies suggest that promoter transcriptional activity of UGT1A1 is inversely related to the number of TA repeats, and that unconjugated bilirubin concentration increases directly with the number of TA repeat elements. Because bilirubin is a known antioxidant, we hypothesized that UGT1A1 repeats associated with higher bilirubin may be protective against oxidative damage. We examined the effect of UGT1A1 genotype on somatic mutant frequency in the hypoxanthine-guanine phosphoribosyl-transferase (HPRT) gene in human lymphocytes and the glycophorin A (GPA) gene of red blood cells (both N0, NN mutants), and the frequency of lymphocyte micronuclei (both kinetochore (K)-positive or micronuclei K-negative) in 101 healthy smoking and nonsmoking individuals. As hypothesized, genotypes containing 7- and 8-TA displayed marginally lower GPA_NN mutant frequency relative to 5/5, 5/6, 6/6 genotypes ( [Formula: see text] ). In contrast, our analysis showed that lower expressing UGT1A1 alleles (7- and 8-TA) were associated with modestly increased HPRT mutation frequency ( [Formula: see text] ), while the same low-expression genotypes were not significantly associated with micronuclei frequencies (K-positive or K-negative) when compared to high-expression genotypes (5- and 6-TA). We found weak evidence that UGT1A1 genotypes containing 7- and 8-TA were associated with increased GPA_NØ mutant frequency relative to 5/5, 5/6, 6/6 genotypes ( [Formula: see text] ). These data suggest that UGT1A1 genotype may modulate somatic mutation of some types, in some cell lineages, by a mechanism not involving bilirubin antioxidant activity. More detailed studies examining UGT1A1 promoter variation, oxidant/antioxidant balance and genetic damage will be needed.

Effects of bilirubin on alveolar macrophages in rats with emphysema and expression of iNOS and NO in them

To explore the effects of bilirubin on alveolar macrophages (AM) and expression of iNOS and NO in them in emphysema model, the rats were pretreated with bilirubin before exposed to smoke. AM were isolated from bronchoalveolar lavage fluid (BALF) and cultured. Pathological microscopic examination of AM and immunohistochemical analysis of iNOS were performed. Nitric oxide (NO) content in the samples was determined by nitrate reductase technique. The results showed both alveoli and alveolar septum appeared normal in size and shape in normal group. AM showed kidney-shaped nucleus and were rich in Golgi complexes and primary lysosomes in the cytoplasm. The inner membrane of mitochondrion was continuous. Most cristae of the mitochondria were intact. In model group, the alveoli were expanded, ruptured and bullaes were formed. Both the population and sizes of AM increased significantly. Secondary lysosomes were rich in the cytoplasm. Deformation and pyknosis of the nucleus, swelling of the mitochondrions and rupture of the inner mitochondrial membrane could also be seen. At high magnification, most of the mitochondrial cristae were broken, or completely lost at certain points. In bilirubin group, alveoli partly expanded and the population of AM also increased, with morphological changes being slighter than that in model group. Both NO contents and expression of iNOS in model group were higher than those in normal group (P<0.05). In bilirubin group the two indice were lower than those in model group (P<0.05). Our findings suggested that high expression of iNOS and high NO content in AM accelerate the development of emphysema associated with smoking in rats. Bilirubin may exert protective effects on AM and retards the development of emphysema in rats.

Environmental factors and membrane polyunsaturated fatty acids in schizophrenia

There is accumulating evidence of reductions in red blood cell membrane essential fatty acids in patients with schizophrenia. The mechanisms that may underlie these reductions have yet to be determined. It is possible that the observed membrane fatty acid deficits are associated with the development of schizophrenia. Alternatively, the membrane fatty acid deficits may be due to environmental factors, such as smoking and variations in diet, which may not be associated specifically with the pathophysiology of schizophrenia. Patients with schizophrenia smoke cigarettes at very high rates. Cigarette smoke contains many pro-oxidants that contribute directly to oxidative stress. Polyunsaturated fatty acids (PUFAs) are very susceptible to oxidative effects of free radicals. Thus, smoke-induced oxidative stress could plausibly account for reductions in membrane fatty acid in schizophrenia. Recent studies provide conflicting evidence for smoking effects on membrane fatty acid deficits. Likewise, the effects of diet on membrane PUFAs in schizophrenia are not entirely clear. Essential PUFAs need to be consumed in diet. Thus, differences in membrane PUFAs observed between patients and control subjects may be due to dietary variation. Few studies that have examined dietary effects differ in their interpretation of the effects of diet on membrane PUFAs. Thus, the jury is still out whether smoking or dietary effects are the primary causes of membrane PUFA deficits in patients with schizophrenia. Future studies will need to systematically examine the potential effects of smoking and diet, as well as other environmental factors such exercise, to definitively establish whether or not PUFA abnormalities are inherent to schizophrenia.

Evidence for a gene influencing serum bilirubin on chromosome 2q telomere: a genomewide scan in the Framingham study

There is an inverse relationship between serum bilirubin concentrations and risk of coronary artery disease. The strength of the association is similar to that of smoking, systolic blood pressure, and HDL cholesterol. We carried out a genomewide scan in a Framingham Heart Study. Our study sample consisted of 330 families with 1,394 sibling pairs, 681 cousin pairs, and 89 avuncular pairs. Using variance-component methods, the heritability was estimated to be 49%+/-6%, and the genome scan demonstrated significant evidence of linkage of serum bilirubin to chromosome 2q, with a LOD score of 3.8 at location 243 cM. The peak multipoint LOD score is located 1 cM away from the uridine diphosphate glycosyltransferase 1 (UGT1A1) gene. UGT1A1 catalyzes the conjugation of bilirubin with glucuronic acid and thus enhances bilirubin elimination; therefore, it is an important candidate gene for serum bilirubin. Gilbert syndrome, a hyperbilirubinemic syndrome, has a population frequency of 2%-19% and is mainly due to a TA insertion at the promoter region of UGT1A1. Only one other region in the genome produced a multipoint LOD score >1 (LOD = 1.3). Our findings suggest that UGT1A1 may be a major gene controlling serum bilirubin levels in the population.

A genome scan for loci influencing anti-atherogenic serum bilirubin levels

Epidemiological studies have shown an association of decreased serum bilirubin levels with coronary artery disease. Two segregation analyses in large pedigrees have suggested a major gene responsible for high bilirubin levels occurring in about 12% of the population. Based on a recessive model from a previous segregation analysis, we performed a genome scan using 587 markers genotyped in 862 individuals from 48 Utah pedigrees to detect loci linked to high bilirubin levels. As a complementary approach, non-parametric linkage (NPL) analysis was performed. These two methods identified four regions showing evidence for linkage. The first region is on chromosome 2q34-37 with multipoint LOD and NPL scores of 3.01 and 3.22, respectively, for marker D2S1363. This region contains a previously described gene, uridine diphosphate glycosyltransferase 1, which has been associated with high bilirubin levels. A polymorphism in the promoter of this gene was recently shown to be responsible for Gilbert syndrome which is associated with mild hyperbilirubinemia. The other regions were found on chromosomes 9q21, 10q25-26, and 18q12 with maximum NPL scores of 2.39, 1.55, and 2.79, respectively. Furthermore, we investigated in these pedigrees the association between bilirubin levels and coronary artery disease. One-hundred and sixty-one male and 41 female subjects had already suffered a coronary artery disease event. Male patients showed significantly lower bilirubin concentrations than age-matched controls. This association, however, was not observed in females. These results provide evidence that loci influencing bilirubin variation exist on chromosomes 2q34-37, 9q21, 10q25-26, and 18q12 and confirms the association of low bilirubin levels with coronary artery disease in males.

Bilirubin ameliorates bleomycin-induced pulmonary fibrosis in rats

Many possible treatments for pulmonary fibrosis have been investigated, but except for some current clinical trials, none have succeeded in clinical trials. On the basis of the antioxidant action of bilirubin (BIL), we examined the effects of hyperbilirubinemia on the development of bleomycin (BLM)-induced pulmonary fibrosis in rats. The animals' plasma BIL level was kept within 3 and 10 mg/dl by repeated intravenous infusion of a high dose of BIL. We studied the inhibitory effects of hyperbilirubinemia on BLM-induced pulmonary fibrosis through histopathologic and biochemical analyses. Mortality of rats with BLM-induced pulmonary fibrosis was significantly lower in the three groups with hyperbilirubinemia. The ameliorating effect of hyperbilirubinemia on pulmonary fibrosis was shown by lung histology, as well as by a decreased lung content of hydroxyproline and reduced bronchoalveolar lavage fluid (BALF) concentration of transforming growth factor (TGF)-beta(1). The number of polymorphonuclear leukocytes and lymphocytes in BALF was also decreased in the groups with hyperbilirubinemia. Furthermore, oxidative metabolites of BIL in urine were present at significantly higher levels in BLM-treated rats with hyperbilirubinemia than in those without hyperbilirubinemia. These data suggest that the antioxidative action of BIL can attenuate BLM-induced pulmonary fibrosis, partly by inhibiting lung inflammation and production of TGF-beta1.

Serum bilirubin concentration in a Belgian population: the association with smoking status and type of cigarettes

BACKGROUND

The endogenous antioxidant serum bilirubin may scavenge free radical species from cigarette smoke. Smokers are expected to have lower serum bilirubin levels than never smokers, but this has never been evaluated in a random population sample of women and men. In addition, in vitro studies indicate that filter cigarette smoke might enhance bilirubin oxidation more than non-filter cigarette smoke.

METHODS

In this paper, data were analysed from the Belgian Interuniversity Research on Nutrition and Health (BIRNH) study. We investigated the association of smoking and type of cigarettes with serum bilirubin concentrations in men and women using multiple regression models taking into account differences in baseline and smoking characteristics.

RESULTS

In men, current smokers had lower crude and adjusted serum bilirubin concentrations compared with never smokers (P = 0.0001). For women, the association between smoking and serum bilirubin concentrations adjusted for age was in the same direction as for men, but did not reach statistical significance. Male former smokers had serum bilirubin concentrations in between those of current smokers and never smokers, while female former smokers had even higher (+ 0.50 micromol/l) serum bilirubin concentrations than never smokers. Male subjects smoking filter cigarettes showed a higher serum bilirubin concentration than those smoking cigarettes without a filter (adjusted difference: 0.49 micromol/l; P = 0.03). The duration of smoking was inversely and significantly related to serum bilirubin concentrations (P = 0.0003).

CONCLUSION

Smoking may lower serum bilirubin concentrations in men, especially in those smoking non-filter cigarettes. The duration of smoking is a more important determinant for serum bilirubin concentrations than the number of cigarettes smoked per day, which may indicate the cumulative negative effects of smoking on the endogenous antioxidant system. Results for females pointed in the same direction, but were less clear, possibly due to low numbers of smoking women, who were largely young and smoked mainly filter cigarettes for a shorter period of time.

Association of Serum Bilirubin Concentration with Risk of Coronary Artery Disease

Background: Lipid oxidation and formation of oxygen radicals are important elements of arterial plaque formation and atherosclerosis, and are involved in the pathophysiology of coronary artery disease (CAD). Because bilirubin has antioxidant properties, it has been suggested that it may have a protective role in the atherosclerotic process.

Approach: This review examines in vitro and in vivo studies indicating that bilirubin inhibits lipid oxidation and oxygen radical formation. Experimental and epidemiological evidence is presented that suggests that bilirubin may serve as a physiological antioxidant providing protection against atherosclerosis and CAD. Special attention is focused on studies that noted an inverse relationship between plasma bilirubin concentration and cardiovascular morbidity.

Content: Serum bilirubin concentrations in the upper portion of the reference interval reportedly reduce atherogenic risk and provide protection against CAD. In contrast, serum bilirubin concentrations in the lower portion of the reference interval may be associated with increased risk of ischemic heart disease.

Summary: Taken together, the evidence presented in this review supports the concept that bilirubin, via its antioxidant potential, has antiatherogenic properties and that an inverse relationship exists between circulating bilirubin concentrations and risk of CAD.

Comparison of various lipid, lipoprotein, and bilirubin combinations as risk factors for predicting coronary artery disease

Studies were performed to determine if serum bilirubin, when combined with various lipid and lipoprotein risk factors, enhances our ability to predict coronary artery disease (CAD). This hypothesis was tested in a retrospective study of 644 middle-aged males who had undergone coronary angiography. The traditional risk factors of cholesterol, high density lipoprotein cholesterol (HDL-C), cholesterol/HDL-C ratios, triglycerides, age, cigarette smoking, and systolic blood pressure were tested by discriminant analysis, as were various cholesterol/bilirubin, cholesterol/(HDL-C+bilirubin), and low-density lipoprotein cholesterol (LDL-C)/(HDL-C+bilirubin) ratios. Each of these bilirubin-containing ratios was found to be an independent risk predictor when tested with the traditional risk factors. When the LDL-C/(HDL-C+bilirubin) ratio was included with the traditional risk predictors, it improved the prediction of severe CAD from 28.4 to 35.3% and the overall correct classification of CAD from 68.3 to 71.1%. When the 75th percentile was used as a cut-point, the diagnostic sensitivities obtained with cholesterol/(HDL-C+bilirubin) ratios (52.1%) and LDL-C/(HDL-C+bilirubin) ratios (51.7%) were better than those obtained with cholesterol/HDL-C ratios (40.4%) (P=0.033 and 0.048, respectively). LDL-C/(HDL-C+bilirubin) ratios also improved the prediction of severe CAD over those obtained with LDL-C/HDL-C ratios (43.4%); however, the changes were not statistically significant (P=0.096). If confirmed in other populations, serum bilirubin may be combined with LDL-C/HDL-C ratios, cholesterol/HDL-C ratios, cholesterol, or with various apolipoproteins to improve the prediction of CAD.

Comparison of laboratory parameters as risk factors for the presence and the extent of coronary or carotid atherosclerosis: the significance of apolipoprotein B to apolipoprotein all ratio

We compared several "new" risk factors (autoantibodies to oxidatively modified low density lipoprotein (LDL), sialic acid content of LDL, bilirubin and C-reactive protein) with "conventional" risk factors (apolipoprotein (apo) AI, AII and B, lipoprotein(a), triglycerides, and total, LDL and high density lipoprotein (HDL) cholesterol) for the presence and the extent of coronary or carotid atherosclerosis. Forty male patients with angiographically proven coronary atherosclerosis and 31 male patients with ultrasound-proven extracranial carotid atherosclerosis were compared to 40 age matched (53+/-5 years) healthy males as control subjects, with negative parental history of atherosclerosis, no clinical signs of systemic or organ-related ischemic disease and normal extracranial carotid arteries. The apo B/apo All ratio most powerfully indicated the presence and the extent of coronary or carotid atherosclerosis. Elevated lipoprotein(a) contributed significant additional information in the assessment of the atherosclerotic risk. Increase in C-reactive protein indicated the presence (but not the extent) of coronary or carotid atherosclerosis with a similar power as lipoprotein(a). Decreased values of total bilirubin indicated the presence of atherosclerosis only in smokers. Autoantibodies to oxidatively modified LDL additionally described the atherosclerotic process, but were less important than apolipoproteins, lipoprotein(a), C-reactive protein or bilirubin. Sialic acid content of LDL added no information to the parameters discussed above. We demonstrated that in male patients apolipoproteins, especially the apo B/apo All ratio, were better indicators of the presence and the extent of coronary or carotid atherosclerosis than C-reactive protein, bilirubin, autoantibodies to oxidatively modified LDL or sialic acid content of LDL.