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The relationship between serum levels of total bilirubin and coronary plaque vulnerability

Zhu, Ke-Fua,*; Wang, Yu-Mingb,*; Wang, Yu-Qiand; Wang, Ning-Fuc

doi: 10.1097/MCA.0000000000000309
Original Research
Free

Objectives Previous studies have reported that serum total bilirubin provides some protection against coronary artery disease (CAD); however, the relationship between serum levels of total bilirubin and culprit/target plaque vulnerability in patients with CAD remains unclear. In this study, we investigated the association between total bilirubin and tissue characterization of coronary plaque in patients with CAD.

Methods We enrolled 85 consecutive patients with CAD who underwent coronary angiography and intravascular ultrasound analyses [45 with acute coronary syndrome (ACS); 40 with stable angina pectoris (SAP)], and 45 age-matched participants served as the control group. Serum levels of total bilirubin in all participants were measured. The stability of the coronary plaque was compared between the ACS group and the SAP group, and the relationship between serum levels of total bilirubin and the features of coronary plaque was analyzed.

Results Serum levels of total bilirubin in the ACS group were significantly lower than those in the SAP and control groups (P<0.01). Serum levels of total bilirubin were positively associated with fibrous plaques (r=0.386, P<0.001), whereas they were negatively associated with plaque burden (r=−0.413, P<0.001), lipid plaque (r=−0.419, P<0.001), and remodeling index (r=−0.275, P<0.05). Furthermore, an independent association between serum levels of total bilirubin and lipid-rich plaques (odds ratio, 0.78; 95% confidence interval, 0.64–0.95) was observed.

Conclusion Serum total bilirubin levels were found to be inversely associated with coronary plaque vulnerability, and decreased serum levels of total bilirubin may be an important factor for coronary lipid plaque formation, which contributes to the pathogenesis of CAD.

aDepartment of Cardiology, Hangzhou First People’s Hospital, Zhejiang Chinese Medical University

bZhejiang University

cDepartment of Cardiology, Hangzhou First People’s Hospital, Hangzhou, China

dCésar Ritz Colleges Switzerland, Brig, Switzerland

* Ke-Fu Zhu and Yu-Ming Wang contributed equally to the writing of this article.

Correspondence to Ning-Fu Wang, MD, Department of Cardiology, Hangzhou First People’s Hospital, No. 261, Huansha Road, Hangzhou 310006, Zhejiang Province, China Tel: +86 571 8791 4773; fax: +86 571 8791 4773; e-mail: ningfuwang.zcmu@hotmail.com

Received August 14, 2015

Received in revised form September 5, 2015

Accepted September 9, 2015

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Introduction

Coronary artery disease (CAD), one of the major forms of cardiovascular disease, is the most common cause of human death worldwide 1. Previous studies have evidenced that vulnerable plaques play a critical role in the development of acute coronary syndrome (ACS), which may possibly cause sudden cardiac death 2–4. The pathophysiological mechanism of vulnerable plaques is sudden rupture, swiftly forming a clot that blocks the flow of blood through a coronary artery. Therefore, it is necessary and helpful to seek biomarkers associated with plaque vulnerability in CAD.

Bilirubin, an effective endogenous antioxidant, is considered as the scavenger of reactive oxygen radicals, and it alleviates the amplification of oxidized low-density lipoprotein, which is a major step in the atherosclerotic process 5–7. Several studies have reported that low serum total bilirubin levels were correlated with an increased risk for CAD 8,9. However, the relationship between serum levels of bilirubin and plaque vulnerability has not been investigated yet. The purpose of this study was to examine whether serum bilirubin levels are associated with coronary plaque characteristics in patients with CAD using intravascular ultrasound (IVUS).

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Methods

Participants and definitions

From January 2014 to June 2015, 85 consecutive patients [45 with ACS and 40 with stable angina pectoris (SAP)] from Hangzhou First People’s Hospital (Zhejiang, China) were enrolled into this study. The patients were divided into SAP and ACS groups according to symptoms and clinical examinations. The ACS group included 19 patients with unstable angina pectoris (UAP) and 26 patients with acute myocardial infarction (AMI). Patients with typical invariable chest pain over 3 months (with typical invariable meaning the same degree of exertion and excitation provocation and the same location, quality, and 3–5-min duration) were categorized into the SAP group 10. Patients with ACS were identified according to the guidelines of the European Society of Cardiology and the American College of Cardiology/American Heart Association 11. The diagnosis of UAP was based on thoracic discomfort of typical character, depressed ST of 0.1 mV or higher, and/or T-wave inversion on ECG, but normal troponin levels (in at least two blood samples 0 and 6 h after admission). UAP symptoms were defined as new onset of severe, progressive, or resting angina. AMI was diagnosed as chest pain, elevation of troponin I (0.10 ng/ml), and new ST-segment change or new left-bundle branch block on ECG. Another 45 participants who were age-matched and had no evidence of cardiovascular disease – defined as no typical chest pain on exertion, no myocardial infarction or UAP, a negative exercise test, and normal coronary artery findings on coronary angiography – were selected as the control group.

Exclusion criteria were as follows: (i) congenital heart disease, cardiomyopathy, primary valvular disease, infectious endocarditis, and secondary cardiac muscle disease; (ii) symptomatic peripheral vascular disease (transient ischemic attack, stroke, intermittent claudication, peripheral revascularization, or amputation); (iii) thyroid disease, autoimmune disease, hematologic disease, malignant tumor, history of any liver disease, digestive system disorders, end-stage renal disease with maintenance hemodialysis, and evidence of ongoing infection or inflammation; (iv) severe stenotic left main coronary artery lesions. The study protocol was approved by the ethics committee of Hangzhou First People’s Hospital, and written informed consent was obtained from each participant.

The age, sex, BMI, clinical presentations, medical history, and medications used were recorded for each participant upon admission to the hospital. BMI was calculated as weight (kg) divided by the square of height (m2).

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Laboratory examination

In AMI patients, blood samples were obtained from the patients upon arrival at the emergency unit. Fasting blood samples were collected the morning after admission for the remaining participants. The levels of total bilirubin and direct bilirubin were determined by the vanadate oxidase method using a clinical automated biochemistry analyzer (Hitachi 7600; Hitachi High-Technologies, Tokyo, Japan). Indirect bilirubin level was calculated as total bilirubin minus direct bilirubin. All of the samples were measured in duplicate.

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Coronary angiography

The standard Judkins technique was used for coronary angiography. Each angiogram was read jointly by two experienced interventional cardiologists who were blinded to the participants’ clinical information. Coronary artery lesions were evaluated using calipers to determine the extent of artery narrowing. CAD was defined as the presence of more than 50% diameter stenosis in at least one major coronary artery. The reference segment diameter was averaged from 5-mm-long angiographically normal segments proximal to the lesion; if a normal proximal segment could not be identified, a distal angiographically normal segment was analyzed as described previously 12. Characteristics of coronary arterial plaques were assessed using a grayscale IVUS combined with an integrated backscatter (IB)-IVUS.

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Grayscale intravascular ultrasound

IVUS examination was performed before any intervention and after the intracoronary administration of 200 μg nitroglycerine. The conventional IVUS images and IB signals were acquired using an IVUS system (Clear View; Boston Scientific, Natick, Massachusetts, USA) and a 40 MHz 2.5 Fr intravascular catheter. The imaging catheter was advanced more than 10 mm beyond the lesion, and an automated pullback system was applied to a point greater than 10 mm proximal to the lesion, at a standard pullback speed of 0.5 mm/s. All IVUS data were analyzed by two independent observers.

Images were quantified for external elastic membrane (EEM) cross-sectional area (CSA), lumen area, and plaque+media CSA (P+M CSA) using the software included in the IVUS system. P+M CSA was defined as EEM CSA−lumen area. The percent plaque burden was calculated as follows: [(EEM CSA–lumen area)/EEM CSA]×100. The remodeling index was calculated as the ratio of the EEM CSA at the measured lesion (minimum luminal site) to the reference EEM CSA (the average of the proximal and distal reference segments).

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Integrated backscatter-intravascular ultrasound

IB values for three histological categories (calcification, fibrosis, and lipid pool) were calculated as the average power of the ultrasound backscattered signal from a small volume of tissue using a fast Fourier transform, measured in decibels. The calcified volume, fibrous volume, and lipid volume were calculated from three-dimensional IVUS images as the sum of the calcified, fibrous, and lipid areas in each CSA at 1-mm axis intervals, respectively. The percentages of calcified, fibrous, and lipid plaques [calcified, fibrous, and lipid (volume)/plaque area (volume)×100] were calculated automatically.

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Statistical analysis

Numerical data were presented as mean±SD or median (interquartile range), and analyzed using Student’s t-test, one-way analysis of variance, the Mann–Whitney U-test, or the Kruskal–Wallis test, as appropriate. The normality assumption was evaluated using the Shapiro–Wilk test. Categorical data were expressed as number (%) and compared among study groups using the χ2-test or Fisher’s exact test. Pearson’s correlation coefficient was calculated to assess the association between serum concentrations of total bilirubin and characteristics of the coronary plaque. The relationship between the presence of a coronary lipid-rich plaque and serum levels of total bilirubin and other clinical parameters was evaluated using univariate and multivariate logistic regression analyses. Statistical analyses were carried out on SPSS version 20 (IBM-SPSS Inc., Armonk, New York, USA), and the associated results were plotted using GraphPad Prism 6 (GraphPad, San Diego, California, USA). A P-value of less than 0.05 was accepted as statistically significant.

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Results

Anthropometric, clinical, and laboratory data of the study population

The anthropometric, clinical, and laboratory data of the patients with ACS (n=45) and SAP (n=40), and of controls (n=40) are summarized in Table 1. The mean age of the ACS group was 63.1±9.6 years and of the SAP group was 63.0±9.7 years, with the control group sharing a similar mean age (61.7±10.1 years). The majority of patients in the ACS and SAP groups were male and in the overweight to obesity range, with mean BMI values of 26.1±4.1 kg/m2 and 25.6±3.4 kg/m2, respectively. No significant differences were observed between these three groups in terms of medical history, such as hypertension, type 2 diabetes mellitus, and family history of CAD, and the current smoking or drinking status. In terms of biochemical characteristics, patients of the ACS group had significantly higher levels of low-density lipoprotein cholesterol compared with the SAP and control groups (P<0.05). Furthermore, the frequencies of patients with ACS and SAP under treatment with aspirin were higher compared with controls (P<0.01 and 0.001).

Table 1

Table 1

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Serum bilirubin levels

Comparisons of serum levels of total bilirubin, direct bilirubin, and indirect bilirubin are shown in Fig. 1. Serum total bilirubin levels in the ACS group were significantly lower than those in the SAP and control groups (10.42±3.12 vs. 12.31±3.30 μmol, P<0.01; 10.42±3.12 vs. 13.74±2.69 μmol, P<0.001); however, the serum total bilirubin levels were in the normal range among these three groups. The ACS group also had the lowest level of serum direct bilirubin when compared with the SAP and control groups (2.68±0.92 vs. 3.41±1.10 μmol, P<0.01; 2.68±0.92 vs. 3.77±0.89 μmol, P<0.001). Nevertheless, no significant differences were observed in the distribution of serum indirect bilirubin levels between the ACS and SAP groups (7.74±2.79 vs. 8.90±3.29 μmol, P>0.05).

Fig. 1

Fig. 1

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Coronary angiographic and IVUS findings

Table 2 summarizes the angiographic and IVUS findings in patients with CAD. There were no significant differences in target vessel and lesion location between the ACS and SAP groups on angiographic analysis. On analyzing the data from grayscale IVUS images, the results demonstrated that the ratio of the plaque area to the minimum luminal area and the remodeling index were significantly higher among ACS patients than among SAP patients (10.97±4.29 vs. 8.74±4.61 mm2, P<0.05; 1.09±0.19 vs. 1.01±0.14, P<0.05). Furthermore, the IB-IVUS results showed that the ACS group had a significantly higher ratio of percent lipid plaque (51.07±12.38 vs. 43.37±14.13%, P<0.01) and a lower ratio of percent fibrous plaque (43.10±11.13 vs. 50.21±12.89%, P<0.01) than SAP patients.

Table 2

Table 2

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Relationship between serum total bilirubin concentrations and characteristics of coronary plaque

In all CAD patients, Pearson’s correlation analyses evidenced that serum levels of total bilirubin were negatively correlated with the remodeling index (ρ=−0.275, P<0.05), plaque burden (ρ=−0.413, P<0.001), and lipid plaque (ρ=−0.419, P<0.001), whereas they were found to be positively correlated with fibrous plaque (ρ=0.386, P<0.001) on IVUS (Fig. 2). Multivariate regression analysis showed that serum total bilirubin concentrations were independently associated with plaque burden (β=−7.403, P<0.01), percentage of lipid plaque (β=−0.084, P<0.01), and percentage of fibrous plaque (β=0.061, P<0.05; Table 3).

Fig. 2

Fig. 2

Table 3

Table 3

In addition, over 33% of lipid area was defined as lipid-rich plaque in a lesion on the basis of a previous study 13. Univariate logistic regression analysis identified that total bilirubin levels were negatively correlated with lipid-rich plaques. Multivariate logistic regression analysis indicated estimated glomerular filtration rate [odds ratio, 1.06; 95% confidence interval (CI), 1.01–1.12] and total bilirubin level (odds ratio, 0.78; 95% CI, 0.64–0.95) as independent factors correlated with lipid-rich plaques (Table 4).

Table 4

Table 4

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Discussion

To the best of our knowledge, this is the first study to evaluate the relationship between serum levels of total bilirubin and coronary arterial plaque characteristics in patients with CAD using IVUS. Our research showed that serum total bilirubin levels in the ACS group were significantly lower than those in the SAP and control groups, although both groups had serum total bilirubin levels in the normal range. Further IVUS data demonstrated that serum total bilirubin levels were inversely correlated with the percentage of lipid plaques and plaque burden, as well as with the remodeling index, in CAD patients. In addition, the association between serum total bilirubin levels and coronary lipid-rich plaques was found to be statistically significant in both univariate analyses and multivariate analyses after adjusting for recognized risk factors. Collectively, these findings suggested that serum levels of total bilirubin might serve as a biomarker for monitoring CAD, especially for coronary atherosclerotic plaque vulnerability in the pathogenesis of CAD.

It is well known that coronary plaque composition is an important determinant of clinical progression and outcomes of CAD. Large lipid-rich plaques are considered to be histologic markers of plaque vulnerability 14,15. Those vulnerable plaques that do not produce severe stenosis can undergo sudden rupture with acute occlusive thrombosis, leading to ACS and other relevant acute clinical events 16,17. In previous pathologic studies, vulnerable plaque of the culprit lesions was found in approximately 70% of patients with CAD who had sudden cardiac death 18–20. Previous IVUS studies have found the incidence rates of vulnerable plaques to be 16–66% in the culprit lesions of ACS patients 21–23 and 22–32% in the target lesions of SAP patients 21,22,24, respectively. Therefore, more attention must be paid to vulnerable plaques, especially the lipid-rich plaques other than coronary stenosis, in clinical practice.

Several studies have found that serum total bilirubin concentrations are inversely associated with the risk for cardiovascular disease 8,25. Early in 1994, Schwertner et al.8 reported that low serum levels of total bilirubin exhibited a strong association with higher risk for CAD. Subsequently, a meta-analysis of 11 relevant studies showed an inverse relation between serum bilirubin levels and the severity of CAD 26. Interestingly, Gilbert’s syndrome, known as a common idiopathic hyperbilirubinemia caused by a mutation, was also associated with a lower risk for CAD 27. Moreover, a study from Turkey reported that serum bilirubin levels were significantly associated with the presence, severity, and the noncalcified morphology of atherosclerotic plaques detected by computed tomography angiography 28. Gullu et al.29 reported that greater serum bilirubin levels had a protective effect against impaired coronary flow reserve and coronary microvascular dysfunction. Erdogan et al.30 found that greater bilirubin concentrations were related to favorable coronary collateral flow in patients with chronic total occlusion when undergoing coronary angiography. Through our research, we found an inverse correlation between serum total bilirubin levels and coronary plaque vulnerability in CAD patients using IVUS, which was consistent with the findings of previous studies.

Unfortunately, the exact pathophysiological mechanisms underlying this association have not been completely elucidated. It is commonly acknowledged by both in-vitro and in-vivo studies that serum bilirubin has potent antioxidant properties, besides its role in assessing liver function 5,7. This natural product of heme metabolism makes up to 10% of the total antioxidant capacity in normobilirubinemic adults 31,32 and has the ability to scavenge peroxyl radicals and to inhibit peroxidation of LDL-derived lipids, which is known to prevent plaque formation and atherosclerosis 7. Bilirubin can also prolong the survival of human ventricular myocytes against in-situ generated oxyradicals in response to MI 33, and direct application of bilirubin to vascular endothelial tissue appears to improve markers of oxidative stress and cellular dysfunction 34. Further, bilirubin also has anticomplement properties, providing defense against inflammatory processes 35. Overall, the anti-inflammatory and anticomplement effects of bilirubin make it an important protection factor or enable it to slow the progression of atherosclerosis in CAD 36.

Several limitations of the present study should be taken into consideration. First, the relatively small number of participants with and without CAD in this single-center trial limited the power to prove an inverse relationship between total bilirubin level and plaque vulnerability. Second, because racial differences existed in the prevalence of CAD, as well as in the extent and morphology of coronary atherosclerosis, our findings could not be generalized to all populations. Thus, a large-scale multicenter clinical study is required to confirm our results. Finally, repeat intracoronary IVUS imaging was not performed, which might decrease the diagnostic accuracy and affect the investigation of the dynamic nature of coronary artery lesions.

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Conclusion

The present study showed that serum total bilirubin levels in the ACS group were lower than those in SAP and control groups. IVUS data indicated that serum total bilirubin levels were inversely associated with coronary atherosclerotic plaque vulnerability. Decreased serum total bilirubin levels may play a role in the development of lipid plaques, which contributes to the pathogenesis of CAD. Thus, serum total bilirubin levels will serve as a sensitive biomarker for the evaluation of coronary atherosclerotic plaque vulnerability.

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Acknowledgements

This study was funded by the Project of Science Technology Department of Zhejiang Province, China (No. 2012C33127).

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Conflicts of interest

There are no conflicts of interest.

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References

1. Gaziano TA, Bitton A, Anand S, Abrahams-Gessel S, Murphy A. Growing epidemic of coronary heart disease in low- and middle-income countries. Curr Probl Cardiol 2010; 35:72–115.
2. Fuster V, Badimon L, Badimon JJ, Chesebro JH. The pathogenesis of coronary artery disease and the acute coronary syndromes (1). N Engl J Med 1992; 326:242–250.
3. de Feyter PJ, Ozaki Y, Baptista J, Escaned J, Di Mario C, de Jaegere PP, et al.. Ischemia-related lesion characteristics in patients with stable or unstable angina. A study with intracoronary angioscopy and ultrasound. Circulation 1995; 92:1408–1413.
4. Sano K, Kawasaki M, Ishihara Y, Okubo M, Tsuchiya K, Nishigaki K, et al.. Assessment of vulnerable plaques causing acute coronary syndrome using integrated backscatter intravascular ultrasound. J Am Coll Cardiol 2006; 47:734–741.
5. Stocker R, Yamamoto Y, McDonagh AF, Glazer AN, Ames BN. Bilirubin is an antioxidant of possible physiological importance. Science 1987; 235:1043–1046.
6. Dennery PA, McDonagh AF, Spitz DR, Rodgers PA, Stevenson DK. Hyperbilirubinemia results in reduced oxidative injury in neonatal Gunn rats exposed to hyperoxia. Free Radic Biol Med 1995; 19:395–404.
7. Wu TW, Fung KP, Wu J, Yang CC, Weisel RD. Antioxidation of human low density lipoprotein by unconjugated and conjugated bilirubins. Biochem Pharmacol 1996; 51:859–862.
8. Schwertner HA, Jackson WG, Tolan G. Association of low serum concentration of bilirubin with increased risk of coronary artery disease. Clin Chem 1994; 40:18–23.
9. Breimer LH, Wannamethee G, Ebrahim S, Shaper AG. Serum bilirubin and risk of ischemic heart disease in middle-aged British men. Clin Chem 1995; 41:1504–1508.
10. Kaul P, Naylor CD, Armstrong PW, Mark DB, Theroux P, Dagenais GR. Assessment of activity status and survival according to the Canadian Cardiovascular Society angina classification. Can J Cardiol 2009; 25:e225–e231.
11. Pundziute G, Schuijf JD, Jukema JW, Decramer I, Sarno G, Vanhoenacker PK, et al.. Evaluation of plaque characteristics in acute coronary syndromes: non-invasive assessment with multi-slice computed tomography and invasive evaluation with intravascular ultrasound radiofrequency data analysis. Eur Heart J 2008; 29:2373–2381.
12. Mintz GS, Nissen SE, Anderson WD, Bailey SR, Erbel R, Fitzgerald PJ, et al.. American College of Cardiology Clinical Expert Consensus Document on Standards for Acquisition, Measurement and Reporting of Intravascular Ultrasound Studies (IVUS). A report of the American College of Cardiology Task Force on Clinical Expert Consensus Documents. J Am Coll Cardiol 2001; 37:1478–1492.
13. Takahashi K, Kakuta T, Yonetsu T, Lee T, Koura K, Hishikari K, et al.. In vivo detection of lipid-rich plaque by using a 40-MHz intravascular ultrasound: a comparison with optical coherence tomography findings. Cardiovasc Interv Ther 2013; 28:333–343.
14. Davies MJ, Richardson PD, Woolf N, Katz DR, Mann J. Risk of thrombosis in human atherosclerotic plaques: role of extracellular lipid, macrophage, and smooth muscle cell content. Br Heart J 1993; 69:377–381.
15. Fernandez-Ortiz A, Badimon JJ, Falk E, Fuster V, Meyer B, Mailhac A, et al.. Characterization of the relative thrombogenicity of atherosclerotic plaque components: implications for consequences of plaque rupture. J Am Coll Cardiol 1994; 23:1562–1569.
16. Little WC, Constantinescu M, Applegate RJ, Kutcher MA, Burrows MT, Kahl FR, et al.. Can coronary angiography predict the site of a subsequent myocardial infarction in patients with mild-to-moderate coronary artery disease? Circulation 1988; 78:1157–1166.
17. Fishbein MC, Siegel RJ. How big are coronary atherosclerotic plaques that rupture? Circulation 1996; 94:2662–2666.
18. Naghavi M, Libby P, Falk E, Casscells SW, Litovsky S, Rumberger J, et al.. From vulnerable plaque to vulnerable patient: a call for new definitions and risk assessment strategies: Part I. Circulation 2003; 108:1664–1672.
19. Virmani R, Kolodgie FD, Burke AP, Farb A, Schwartz SM. Lessons from sudden coronary death: a comprehensive morphological classification scheme for atherosclerotic lesions. Arterioscler Thromb Vasc Biol 2000; 20:1262–1275.
20. Falk E, Shah PK, Fuster V. Coronary plaque disruption. Circulation 1995; 92:657–671.
21. Hong MK, Mintz GS, Lee CW, Kim YH, Lee SW, Song JM, et al.. Comparison of coronary plaque rupture between stable angina and acute myocardial infarction: a three-vessel intravascular ultrasound study in 235 patients. Circulation 2004; 110:928–933.
22. Fujii K, Kobayashi Y, Mintz GS, Takebayashi H, Dangas G, Moussa I, et al.. Intravascular ultrasound assessment of ulcerated ruptured plaques: a comparison of culprit and nonculprit lesions of patients with acute coronary syndromes and lesions in patients without acute coronary syndromes. Circulation 2003; 108:2473–2478.
23. Kotani J, Mintz GS, Castagna MT, Pinnow E, Berzingi CO, Bui AB, et al.. Intravascular ultrasound analysis of infarct-related and non-infarct-related arteries in patients who presented with an acute myocardial infarction. Circulation 2003; 107:2889–2893.
24. Maehara A, Mintz GS, Bui AB, Walter OR, Castagna MT, Canos D, et al.. Morphologic and angiographic features of coronary plaque rupture detected by intravascular ultrasound. J Am Coll Cardiol 2002; 40:904–910.
25. Djousse L, Levy D, Cupples LA, Evans JC, D’Agostino RB, Ellison RC. Total serum bilirubin and risk of cardiovascular disease in the Framingham offspring study. Am J Cardiol 2001; 87:1196–1200.
26. Novotny L, Vitek L. Inverse relationship between serum bilirubin and atherosclerosis in men: a meta-analysis of published studies. Exp Biol Med 2003; 228:568–571.
27. Lin JP, O’Donnell CJ, Schwaiger JP, Cupples LA, Lingenhel A, Hunt SC, et al.. Association between the UGT1A1*28 allele, bilirubin levels, and coronary heart disease in the Framingham Heart Study. Circulation 2006; 114:1476–1481.
28. Canpolat U, Aytemir K, Yorgun H, Hazirolan T, Kaya EB, Sahiner L, et al.. Association of serum total bilirubin levels with the severity, extent and subtypes of coronary atherosclerotic plaques detected by coronary CT angiography. Int J Cardiovasc Imaging 2013; 29:1371–1379.
29. Gullu H, Erdogan D, Tok D, Topcu S, Caliskan M, Ulus T, et al.. High serum bilirubin concentrations preserve coronary flow reserve and coronary microvascular functions. Arterioscler Thromb Vasc Biol 2005; 25:2289–2294.
30. Erdogan T, Cicek Y, Kocaman SA, Canga A, Cetin M, Durakoglugil E, et al.. Increased serum bilirubin level is related to good collateral development in patients with chronic total coronary occlusion. Intern Med 2012; 51:249–255.
31. Kalousova M, Novotny L, Zima T, Braun M, Vitek L. Decreased levels of advanced glycation end-products in patients with Gilbert syndrome. Cell Mol Biol 2005; 51:387–392.
32. Kumar A, Pant P, Basu S, Rao GR, Khanna HD. Oxidative stress in neonatal hyperbilirubinemia. J Trop Pediatr 2007; 53:69–71.
33. Wu TW, Wu J, Li RK, Mickle D, Carey D. Albumin-bound bilirubins protect human ventricular myocytes against oxyradical damage. Biochem Cell Biol 1991; 69:683–688.
34. Kawamura K, Ishikawa K, Wada Y, Kimura S, Matsumoto H, Kohro T, et al.. Bilirubin from heme oxygenase-1 attenuates vascular endothelial activation and dysfunction. Arterioscler Thromb Vasc Biol 2005; 25:155–160.
35. Basiglio CL, Arriaga SM, Pelusa F, Almara AM, Kapitulnik J, Mottino AD. Complement activation and disease: protective effects of hyperbilirubinaemia. Clin Sci 2010; 118:99–113.
36. Nakagami T, Toyomura K, Kinoshita T, Morisawa S. A beneficial role of bile pigments as an endogenous tissue protector: anti-complement effects of biliverdin and conjugated bilirubin. Biochim Biophys Acta 1993; 1158:189–193.
Keywords:

acute coronary syndrome; bilirubin; coronary plaque; intravascular ultrasound; stable angina pectoris

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