
==== Front
Sci Rep
Sci Rep
Scientific Reports
2045-2322
Nature Publishing Group UK London

39227723
71497
10.1038/s41598-024-71497-x
Article
Association of elevated baseline bilirubin caused by preadmission statin use with cardiovascular prognosis in patients undergoing elective percutaneous coronary intervention
Zhu Yunhui 1
Li Duanbin 1
Li Jing 2
Wang Yao 1
Chen Zhebin 1
Lv Qingbo 1
Fu Guosheng fugs@zju.edu.cn

1
Zhang Wenbin 3313011@zju.edu.cn

1
1 grid.13402.34 0000 0004 1759 700X Department of Cardiology, Key Laboratory of Cardiovascular Intervention and Regenerative Medicine of Zhejiang Province, Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, 3 East Qingchun Road, Hangzhou, 310016 Zhejiang People’s Republic of China
2 Jinhua Wenrong Hospital, Jinhua, People’s Republic of China
3 9 2024
3 9 2024
2024
14 2045125 2 2024
28 8 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
Bilirubin is widely recognized to possess antioxidant and anti-inflammatory characteristics. However, the relationship between bilirubin and coronary artery disease (CAD) remains controversial, particularly in individuals receiving Percutaneous Coronary Intervention (PCI). Given that statins may enhance the production of heme oxygenase-1 (HO-1) and bilirubin, we investigated the long-term cardiovascular prognostic role of bilirubin levels elevated by statin use in patients undergoing PCI. Data of 6945 subjects undergoing PCI were enrolled in this study. We divided the patients into two groups based on serum total bilirubin (TB) levels detected prior to PCI. The high TB group consisted of patients with serum TB values > 8.4 μmmol/L, while the low TB group consisted of patients with serum TB values ≤ 8.4 μmmol/L. The median follow-up time was 836 days. Cox proportional hazards models were performed to evaluate the hazard ratios (HRs) and 95% confidence interval (CI) for the incidence of major adverse cardiovascular event (MACE) associated with bilirubin levels. The association between TB levels and risk of MACE was significant [adjusted HR = 0.557, 95% CI (0.59–0.96), p = 0.020). Linear analysis was performed to determine the association between preadmission usage of statin and bilirubin level. The preadmission usage of statin independently linearly increases TB [adjusted-β = 0.371, 95% CI (0.134–0.608), p = 0.002] and direct bilirubin (DB) [adjusted-β = 0.411, 95% CI (0.300–0.522), p < 0.001). Mediation analysis demonstrated a direct protective role of preadmission statins treatment (β = − 0.024, p < 0.01), TB (β = − 0.003, p < 0.05) and DB (β = − 0.009, p < 0.05). Furthermore, it was found that TB (4.0%) and DB (12.0%) mediated the relationship between preadmission statins therapy and MACE. Bilirubin has a protective effect against MACE. In patients with normal bilirubin level undergoing elective PCI, preadmission statin use elevated bilirubin levels, which were independently associated with a lower incidence of MACE over the long-term follow-up period.

Keywords

Percutaneous coronary intervention
Bilirubin
Preadmission statin
Major adverse cardiovascular events
Coronary artery disease
Subject terms

Cardiology
Biomarkers
National Natural Science Foundation of China82070408 Zhang Wenbin issue-copyright-statement© Springer Nature Limited 2024
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pmcIntroduction

Coronary artery disease (CAD) is one of the leading causes of mortality and morbidity worldwide1. Early management and prevention of adverse events in CAD patients shortly after onset of symptoms are crucial2. This includes medication and revascularization3. As a primary method of revascularization, percutaneous coronary intervention (PCI) is a definitive treatment for a wide range of CAD patients4.

Bilirubin is thought as a metabolic end product of hemoglobin5. Recently, more research has demonstrated that serum total bilirubin (TB) is a effective anti-oxidant at physiological circumstances of oxygen level6. Many studies on animals have shown the protective effect of bilirubin using ischemia/reperfusion (I/R) model7,8. Several studies have revealed the protective effect of bilirubin on incidence of CAD9,10 as well as post-PCI outcomes, including studies conducted in acute coronary syndrome (ACS) populations11,12. However, several studies have reported opposite findings. They showed that elevated serum total bilirubin has been related with a higher mortality in ACS patients13 and in-hospital MACE in patients with NSTEMI14 and STEMI15. Therefore, in patients undergoing PCI, prognosis protective effect of bilirubin within normal range for post- PCI remains unclear.

As a prevention medication for cardiovascular events, statins are thought to potentially affect liver function and elevate bilirubin level16. Recent studies demonstrate that the anti-atherogenic effects of statins are not solely due to lowering LDL-C, but also include cholesterol-independent effects17. These pleiotropic effects encompass immunosuppressive and anti-inflammatory properties18. One of the underlying mechanisms of statins is activating heme oxygenase-1 (HO-1)19,20, a key step in breaking down heme into biliverdin, which is then converted into bilirubin by biliverdin reductase21. However, there is also evidence to the contrary. Kwok Leung Ong et al.22 showed that statins were anomalously linked with a reduced concentration of total bilirubin, possibly due to their effects on metabolism of LDL-C and glucose.

Therefore, the association between bilirubin and the prognosis of CAD patients remains controversial. Previous studies have not focused on the long-term prognostic role of bilirubin in the PCI population with normal liver function. Thus, this study aims to explore this issue. Additionally, we investigated whether the long-term benefits of statins on cardiovascular events are mediated by their effects on serum bilirubin levels23.

Methods

Subjects

This retrospective cohort study of single center collected data from Sir Run Run Shaw Hospital in Hangzhou, China, from November 2014 to June 2020. A total of 6945 subjects who had been diagnosed with CAD were enrolled. The flow chart is presented in Supplement Fig. 1. The patients who underwent elective PCI were included into the cohort. The following subjects were excluded: (1) individuals with severe heart failure (NYHA ≥ III), hepatic or renal insufficiency, malignancy, acute or chronic infections, or other serious illnesses; (2) subjects with elevated bilirubin (TB > 17.1 μmuol/L, DB > 6.8 μmuol/L, IDB > 10.2 μmuol/L) due to liver and gallbladder diseases such as hepatitis and gallstones; (3) Preoperative use of lipid-lowering strategies other than statins therapy, including combination with fibrates, ezetimibe, and other lipid-lowing treatments; (4) Prehospital intensive statin therapy. Statin use prior admission, bilirubin and liver function of patients were measured at the time of admission. After screening, 2445 patients were enrolled in this study. The study was conducted under the criteria set by the Declaration of Helsinki, and authorized by the Institutional Ethics Committee in Sir Run Run Shaw Hospital. Informed consent had been acquired for all participants.

Serum bilirubin

The serum bilirubin levels before PCI were measured and recorded for analysis. Supplement Fig. 2 showed the ROC curve of bilirubin to MACE. According to optimal cutoff value of TB (8.35 μmmol/L) based on the Youden index, the participants were divided to two groups. The high TB group (n = 1715) consisted of patients with serum TB > 8.4 μmmol/L, while the low TB group (n = 730) consisted of patients with serum TB ≤ 8.4 μmmol/L. The optimal cutoff values of DB (3.35 μmmol/L) and IDB (5.50 μmmol/L) were also calculated.

Preadmission statin use

Pre-admission treatment with lipid-lowering drugs was obtained using questionnaires. Of the 2445 participants, 880 patients were receiving statin therapy prior to hospital admission, including atorvastatin, rosuvastatin, pravastatin, simvastatin, and pitavastatin. Depending on the number of subjects using different statin types, the study population was divided into three groups including atorvastatin (n = 566), rosuvastatin (n = 259) and others (n = 55).

Endpoints

The primary endpoint in this study is major adverse cardiovascular event (MACE), which was the combination of all-cause death, cardiac death, recurrent not-fatal myocardial infarction, and ischemic stroke events. The secondary endpoints contained all-cause death, cardiac death, recurrent MI, ischemic stroke and revascularization, including target lesion revascularization (TLR) and target vessels revascularization (TVR).

Causal assumption

Statins are thought to have a protective effect against MACE16. Meanwhile, recent studies reported that statins cause a potential increase of serum bilirubin19. However, the relationship between bilirubin and prognosis after PCI remains controversial. To clarify the causality of bilirubin and clinical outcomes, we assumed bilirubin plays a protective role against MACE in population with normal liver function and statins can improve prognosis indirectly through the pathway of bilirubin.

Definitions

Intensive statin therapies were defined as atorvastatin > 20 mg, rosuvastatin > 10 mg, simvastatin > 40 mg or pitavastatin > 2 mg.

Statistical analysis

Continuous variables were presented as mean ± SD or median/interquartile range. In the analysis of continuous variables, comparisons between two groups were performed by using t-test or Kruskal–Wallis test. Comparisons between more than two groups ware made by ANOVA. Categorical variables were presented as frequency/percentage and group comparisons were made by chi-square test. The Kaplan–Meier method was applied to compare the time-to-event curves of different bilirubin levels. Multivariable Cox regression analysis was performed to assess the correlation between bilirubin level and incidence of MACE adjusted for age > 60 years, male, BMI > 25, current smoking, hypertension, diabetes and history of any CVD, WBC > 10 × 109/L, LDL > 3.12 mmol/L, CTO, statin and aspirin/clopidogrel. Multivariable linear analysis was used to determine the association between preadmission statin use and bilirubin level on admission adjusted for age, sex, BMI, diabetes, hypertension, smoking, WBC, ALT, GGT, statin, aspirin/clopidogrel and β-blocker. Hazard ratios (HRs) were presented with 95% CIs. Statistical analysis was conducted using SPSS 22.0 and Amos. p values < 0.05 was considered as statistically significant. Mediation analysis from pre-hospital statins use to incidence of MACE via bilirubin was performed by Amos.

Results

Population demographics

A total of 2445 subjects were included in this study, with 730 patients in the low TB group and 1715 patients in the high TB group.The baseline clinical and procedural characteristics of the two groups are presented in Table 1. Compared to the high TB group, subjects in the low TB group were older (67.19 vs. 66.08 years, p = 0.015), had a lower proportion of males (58.4% vs. 65.3%, p < 0.001), had a lower BMI (23.90 vs. 24.56 kg/m2, p = 0.009) and had a higher incidence of diabetes (30.7% vs. 26.2%, p = 0.022). Additionally, the low TB group had less frequent statin use prior to admission (29.4% vs. 37.9%, p < 0.001). Patients with lower TB also had higher WBC (6.91 vs. 6.52 × 109/L, p < 0.001), higher CRP (2.20 vs. 1.52 mg/L, p < 0.001) and a higher incidence of hyperlipidemia (27.7% vs. 18.4%, p < 0.001). The low TB group exhibited a lower percentage of ACEI use (12.4% vs. 16.8%, p = 0.008). No significant differences were detected between the two groups regarding blood pressure, hypertension, current smoking status, LDL-C, angiographic finding, PCI procedure, and other discharge medication use (ARB, statin, aspirin, clopidogrel, ticagrelor, and β-blocker).Table 1 Baseline characteristics.

	Overall (n = 2445)	Low TB (n = 730) (≤ 8.4 μmmol/L)	High TB (n = 1715) (> 8.4 μmmol/L)	p value	
Demographic characteristics	
 Age, years	66.41 ± 9.92	67.19 ± 10.14	66.08 ± 9.81	0.015*	
 Male, n (%)	1549 (63.4)	427 (58.4)	1122 (65.3)	< 0.001*	
 BMI, kg/m2	24.36 ± 5.46	23.90 ± 3.21	24.56 ± 6.15	0.009*	
 SBP, mmHg	133.13 ± 19.67	133.71 ± 20.61	132.88 ± 19.26	0.340	
 DBP, mmHg	73.44 ± 12.00	72.87 ± 12.82	73.69 ± 11.63	0.142	
 Hypertension, n (%)	1567 (64.09)	475 (65.1)	1092 (63.7)	0.621	
 Hyperlipidemia, n (%)	503 (20.8)	192 (27.7)	311 (18.4)	< 0.001*	
 Diabetes, n (%)	673 (27.53)	224 (30.7)	449 (26.2)	0.022*	
 Current smoking, n (%)	558 (23.3)	168 (23.6)	390 (23.1)	0.825	
 PCI history, n (%)	18 (0.73)	6 (0.82)	12 (0.70)	0.773	
 CBAG history, n (%)	9 (0.37)	2 (0.27)	7 (0.41)	0.624	
Laboratory examination	
 WBC, 109/L	6.65 ± 2.04	6.91 ± 2.20	6.52 ± 2.00	< 0.001*	
 CRP, mg/L	1.70 (0.80–4.10)	2.20 (0.93–5.51)	1.52 (0.73–3.70)	< 0.001*	
 TG, mmol/L	1.36 (0.99–1.93)	1.47 (1.04–2.15)	1.32 (0.96–1.84)	< 0.001*	
 LDL-C, mmol/L	2.29 ± 0.93	2.35 ± 1.01	2.26 ± 0.90	0.053	
 HDL-C, mmol/L	1.04 ± 0.27	1.00 ± 0.26	1.05 ± 0.27	< 0.001*	
 CKMB, U/L	16 (12–20)	16 (12–20)	16 (12–20)	0.456	
 DDi, mg/L	0.37 (0.25–0.63)	0.42 (0.27–0.74)	0.35 (0.24–0.57)	0.001*	
Angiographic findings and procedural data	
 CTO, n (%)	256 (10.7)	78 (10.9)	178 (10.6)	0.884	
 LM, n (%)	142 (5.9)	47 (6.5)	95 (5.6)	0.442	
 LAD, n (%)	1474 (61.3)	431 (60.0)	1043 (61.9)	0.414	
 LCX, n (%)	489 (20.3)	143 (19.9)	346 (20.5)	0.773	
 RCA, n (%)	669 (27.8)	213 (29.7)	456 (27.1)	0.21	
 Number of stent, n	1.51 ± 0.819	1.56 ± 0.84	1.49 ± 0.81	0.08	
 Thrombus, n (%)	52 (2.2)	13 (1.8)	39 (2.3)	0.533	
 Calcification, n (%)	384 (16.0)	106 (14.8)	278 (16.5)	0.316	
Medication	
 Prehospital statin, n (%)	865 (35.4)	215 (29.4)	650 (37.9)	< 0.001*	
 ACEI, n (%)	376 (15.5)	90 (12.4)	286 (16.8)	0.008*	
 ARB, n (%)	908 (37.4)	269 (37.1)	639 (37.5)	0.906	
 Statin, n (%)	2420 (99.5)	720 (99.3)	1700 (99.6)	0.421	
 Aspirin, n (%)	2330 (95.8)	699 (96.4)	1631 (95.6)	0.421	
 Clopidogrel, n (%)	2006 (82.5)	594 (81.9)	1412 (82.8)	0.661	
 Ticagrelor, n (%)	402 (16.5)	129 (17.8)	273 (16.0)	0.304	
 β-Blocker, n (%)	1261 (51.9)	368 (50.8)	893 (52.3)	0.502	
Data are expressed as mean ± SD (standard deviation) for normally distributed data, median [IQR] for abnormal distributed data and n (%) for categorical variables.

TB total bilirubin, DB direct bilirubin, IDB indirect bilirubin, BMI body mass index, SBP systolic blood pressure, DBP diastolic blood pressure, PCI percutaneous coronary intervention, CABG coronary artery bypass grafting, WBC white blood cell, CRP C-reactive protein, TG triglyceride, LDL-C low-density lipoprotein cholesterol, HDL-C high-density lipoprotein cholesterol, CK-MB creatine kinase-MB, DDi D-dimer, CTO chronic total occlusion, LM left main coronary artery, LAD left anterior descending artery, LCX left circumflex artery, RCA right coronary artery, ACEI angiotensin-converting enzyme inhibitor, ARB angiotensin receptor blockers. *p < 0.05.

Clinical outcomes

All 2445 patients undergoing PCI were followed up for a median of 836 days. During the follow-up period, 131 (5.4%) cases of MACE were recorded, including 76 (3.11%) all caused deaths, 34 (1.51%) cardiac deaths, 28 (1.15%) non-fatal MIs and 31 (1.27%) strokes. Table 2 showed the differences in endpoints between the low and high bilirubin groups. Patients in the high TB group had a lower incidence of MACE (p = 0.003), all caused death (p < 0.001), cardiac death (p = 0.003) and TLR (p = 0.029). Additionally, Kaplan–Meier curves in Fig. 1 demonstrate that higher levels of TB (LogRank p = 0.002), DB (LogRank p = 0.012) and IDB (LogRank p = 0.033) were associated with a decreased cumulative incidence of MACE.Table 2 Association between serum total bilirubin and clinical outcomes.

	Overall (n = 2445)	Low TB (n = 730) (≤ 8.4 μmmol/L)	High TB (n = 1715) (> 8.4 μmmol/L)	p value	
MACE	131 (5.4%)	55 (7.5%)	76 (4.4%)	0.003*	
 All death	76 (3.11%)	43 (5.89%)	33 (1.92%)	< 0.001*	
 CV death	34 (1.51%)	18 (2.47%)	16 (0.93%)	0.003*	
 MI	28 (1.15%)	2 (0.27%)	26 (1.52%)	0.015*	
 Stroke	31 (1.27%)	12 (1.64%)	19 (1.11%)	0.278	
Revascularize	206 (8.43%)	65 (8.90%)	141 (8.22%)	0.578	
 TLR	101 (4.13%)	40 (5.48%)	61 (3.55%)	0.029*	
 TVR	126 (5.15%)	47 (6.44%)	79 (4.61%)	0.061	
 Non TVR	92 (3.76%)	20 (2.74%)	72 (4.20%)	0.083	
TB total bilirubin, DB direct bilirubin, IDB indirect bilirubin. MACE (Major cardiovascular adverse event) was defined as a composite of all caused death, CV (cardiovascular) death, MI (myocardial infarction) and stroke. Revascularize includes target lesion revascularization (TLR) and target vessels revascularization (TVR). *p < 0.05.

Fig. 1 Kaplan–Meier curve analysis between bilirubin categories and MACE. Kaplan–Meier curve between (A) total bilirubin and MACE, LogRank p = 0.002; (B) direct bilirubin and MACE, LogRank p = 0.012; (C) indirect bilirubin and MACE, LogRank p = 0.033.

Association between bilirubin and MACE

In Table 3, Cox proportional hazards models adjusted for multiple variables demonstrated that higher levels of TB were independently protective against the incidence of MACE [adjusted HR = 0.557, 95% CI (0.197–0.573), p = 0.020] and all caused death [adjusted HR = 0.269, 95% CI (0.136–0.531), p < 0.001]. Consistently, DB also exhibited an independent protective effect against MACE [adjusted HR = 0.385, 95% CI (0.181–0.819), p = 0.013] and all caused death [adjusted HR = 0.331, 95% CI (0.115–0.952), p = 0.040]. IDB was found to be an independent factor for all caused death [adjusted HR = 0.314, 95% CI (0.159–0.622), p = 0.001] and cardiac death [adjusted HR = 0.356, 95% CI (0.135–0.936), p = 0.036] but not for MACE [adjusted HR = 0.590, 95% CI (0.343–1.015), p = 0.057].Table 3 Cox proportional-hazards model of factors associated with endpoints.

	Model 1 (unadjusted)	Model 2 (adjusted)	Model 3 (adjusted)	
Unadjusted HR (95% CI)	p value	Adjusted HR (95% CI)	p value	Adjusted HR (95% CI)	p value	
MACE	
 TB > 8.4 μmol/L	0.584 (0.413–0.827)	0.002*	0.517 (0.309–0.863)	0.012*	0.557 (0.197–0.573)	0.020*	
 DB > 3.3 μmol/L	0.589 (0.387–0.895)	0.013*	0.370 (0.182–0.752)	0.006*	0.385 (0.181–0.819)	0.013*	
 IDB > 5.5 μmol/L	0.676 (0.479–0.971)	0.034*	0.547 (0.319–0.937)	0.028*	0.590 (0.343–1.015)	0.057	
All death	
 TB > 8.4 μmol/L	0.321 (0.204–0.505)	< 0.001*	0.251 (0.128–0.494)	< 0.001*	0.269 (0.136–0.531)	< 0.001*	
 DB > 3.3 μmol/L	0.406 (0.219–0.752)	0.004*	0.266 (0.094–0.756)	0.013*	0.331 (0.115–0.952)	0.040*	
 IDB > 5.5 μmol/L	0.395 (0.252–0.621)	< 0.001*	0.292 (0.149–0.573)	< 0.001*	0.314 (0.159–0.622)	0.001*	
Cardiac death	
 TB > 8.4 μmol/L	0.370 (0.189–0.727)	0.004*	0.403 (0.160–1.013)	0.053	0.478 (0.186–1.227)	0.125	
 DB > 3.3 μmol/L	0.376 (0.145–0.973)	0.044*	0.564 (0.186–1.716)	0.313	0.820 (0.263–2.560)	0.732	
 IDB > 5.5 μmol/L	0.377 (0.192–0.741)	0.005*	0.300 (0.118–0.762)	0.011*	0.356 (0.135–0.936)	0.036*	
MI	
 TB > 8.4 μmol/L	5.501 (1.306–23.176)	0.020*	4.487 (0.587–34.857)	0.151	4.381 (0.551–34.832)	0.163	
 DB > 3.3 μmol/L	1.821 (0.865–3.836)	0.115	1.432 (0.464–4.420)	0.532	0.989 (0.291–3.362)	0.986	
 IDB > 5.5 μmol/L	9.368 (1.273–68.949)	0.028*	3.251 (0.417–25.361)	0.261	3.464 (0.436–27.543)	0.240	
Stroke	
 TB > 8.4 μmol/L	0.659 (0.320–1.358)	0.259	1.098 (0.345–3.490)	0.874	1.150 (0.362–3.652)	0.812	
 DB > 3.3 μmol/L	0.245 (0.074–0.907)	0.021*	NA	0.954	NA	0.956	
 IDB > 5.5 μmol/L	0.804 (0.370–1.748)	0.582	1.221 (0.339–4.400)	0.760	1.234 (0.342–4.454)	0.748	
Revascularize	
 TB > 8.4 μmol/L	1.007 (0.758–1.337)	0.962	0.925 (0.608–1.408)	0.717	0.963 (0.631–1.470)	0.862	
 DB > 3.3 μmol/L	0.868 (0.654–1.153)	0.330	1.151 (0.760–1.742)	0.507	1.178 (0.772–1.797)	0.447	
 IDB > 5.5 μmol/L	1.205 (0.882–1.645)	0.242	0.934 (0.596–1.463)	0.765	0.982 (0.624–1.544)	0.937	
TLR	
 TB > 8.4 μmol/L	0.649 (0.436–0.968)	0.034*	0.773 (0.427–1.399)	0.395	0.788 (0.434–1.434)	0.436	
 DB > 3.3 μmol/L	0.950 (0.624–1.446)	0.811	1.111 (0.603–2.047)	0.735	1.164 (0.625–2.169)	0.632	
 IDB > 5.5 μmol/L	0.903 (0.584–1.397)	0.648	0.792 (0.423–1.483)	0.466	0.820 (0.436–1.544)	0.539	
TVR	
 TB > 8.4 μmol/L	0.714 (0.498–1.025)	0.068	0.749 (0.438–1.279)	0.289	0.772 (0.450–1.324)	0.347	
 DB > 3.3 μmol/L	0.855 (0.583–1.256)	0.426	0.994 (0.565–1.747)	0.982	1.060 (0.595–1.888)	0.842	
 IDB > 5.5 μmol/L	0.972 (0.654–1.447)	0.891	0.782 (0.443–1.381)	0.397	0.805 (0.453–1.431)	0.460	
Model 1: adjusted for none.

Model 2: adjusted for age > 60 years, male, BMI > 25, current smoking, hypertension, diabetes and history of any CVD.

Model 3: further adjusted for WBC > 10 × 109/L, LDL > 3.12 mmol/L, CTO, statin and aspirin/clopidogrel.

MACE major cardiovascular adverse event, MI myocardial infarction, TLR target lesion revascularization, TVR target vessels revascularization, TB total bilirubin, DB direct bilirubin, IDB indirect bilirubin. *p < 0.05.

Association between preadmission statin and bilirubin level

As shown in Supplement Table 1, patients with statins prior to hospital admission had higher TB (10.20 vs. 9.77, p < 0.001) and DB levels (3.32 vs. 2.89, p < 0.001) than those not taking statins. Furthermore, the association between statin and bilirubin is irrelevant to the type of statin (Supplement Table 2). Additionally, the multiple-adjusted linear regression models were shown in Table 4. The results demonstrated that patients taking statins prior admission independently linearly increase TB [adjusted-β = 0.371, 95% CI (0.134–0.608), p = 0.002] and DB [adjusted-β = 0.411, 95% CI (0.300–0.522), p < 0.001). Furthermore, Supplement Table 3 showed that in the population using preoperative statins, the effect of different statin types (atorvastatin, rosuvastatin, and others) on bilirubin elevation was no significant difference. Overall, preadmission use of statins, regardless of the type, is significantly associated with elevated baseline levels of total bilirubin and direct bilirubin in CAD patients.Table 4 Multiple linear regression of bilirubin level with the preadmission use of statins.

	Model 1 (unadjusted)	Model 2 (adjusted)	Model 3 (adjusted)	
Unadjusted-β (95% CI)	p value	Adjusted-β (95% CI)	p value	Adjusted-β (95% CI)	p value	
Total bilirubin	
 Preadmission statin	0.392 (0.172–0.612)	< 0.001*	0.421 (0.184–0.659)	0.001*	0.371 (0.134–0.608)	0.002*	
Direct bilirubin	
 Preadmission statin	0.402 (0.297–0.507)	< 0.001*	0.445 (0.332–0.557)	< 0.001 *	0.411 (0.300–0.522)	< 0.001*	
Indirect bilirubin	
 Preadmission statin	− 0.010 (− 0.174 to 0.154)	0.906	− 0.023 (− 0.202 to 0.155)	0.798	− 0.041 (− 0.220 to 0.138)	0.654	
Model 1: adjusted for none.

Model 2: adjusted for age, sex, BMI, current smoking, hypertension, and diabetes.

Model 3: further adjusted for WBC, ALT, GGT, statin, aspirin/clopidogrel and β-blocker. *p < 0.05.

Mediation analysis

Structural equation model with additional observational variables was conducted by Amos to assess the mediating effect of preadmission statins treatment and the incidence of MACE (Fig. 2). Mediation analysis indicated a significant positive causal relationship between preadmission statin treatment and TB (β = 0.392, p < 0.05) and DB (β = 0.402, p < 0.05) levels. The results indicated both preadmission statin treatment (β = − 0.024, p < 0.01) and TB (β = − 0.003, p < 0.05) were significantly and negatively associated with MACE via direct pathway. The indirect effect account for 4.0% of the total prehospital effect on MACE. Furthermore, both prehospital statins therapy (β = − 0.022, p < 0.05) and DB (β = − 0.009, p < 0.05) were also directly significantly negatively associated with MACE. The indirect effect account for 12.0% of the total prehospital effect on MACE. This indicated that bilirubin, in particular direct bilirubin was a mediating factor in the association between prehospital statin treatment and MACE.Fig. 2 Mediation analysis from pre-hospital statin use to MACE via (A) total bilirubin and (B) direct bilirubin or indirect bilirubin. *p < 0.05, **p < 0.01, ***p < 0.001.

Discussion

This retrospective observational study enrolled 2445 patients with normal liver function and bilirubin levels undergoing elective PCI. The data revealed an independent correlation between baseline serum TB and DB levels and the cumulative survival rates for MACE and all caused mortality after PCI. Moreover, elevated levels of direct bilirubin were strongly associated with preadmission statin use. This suggested that preadmission statin use may improve the long-term prognosis of patients after PCI by increasing bilirubin levels within the normal range, beyond its cholesterol-lowering effect16.

Despite being a metabolic byproduct of hemoglobin breakdown, bilirubin has been reported to possess antioxidant properties at physiological concentrations24. These protective mechanisms include safeguarding mitochondrial function8 and reducing ox-LDL levels25. Stocker et al. demonstrated bilirubin’s ability to scavenge peroxyl radicals effectively in vitro6, and indirect bilirubin, as known as unconjugated bilirubin, binds to human albumin, thereby preventing the oxidation caused by peroxyl radicals of fatty acids which bound to albumin in vitro26. Moreover, bilirubin has been shown to suppress NADPH oxidase activity both and in vivo and in vitro, thereby reducing ROS production in vessels27,28. Additionally, bilirubin interacts with other antioxidants, resulting in enhanced inhibition of lipid and lipoprotein peroxidation29,30. This reduction in oxidative stress by bilirubin improves microvascular dysfunction and is believed to help maintain endothelial function by mitigating oxidative stress and restoring the physiological effects of nitric oxide (NO).

Clinical investigations into the relationship between bilirubin and coronary artery endothelial function have been conducted. Peyton et al.31 demonstrated that bilirubin could inhibit the migration and proliferation of smooth muscle cells in coronary artery, potentially reducing the risk of restenosis after PCI. Factors that enhance endothelial function may decelerate the progression of atherosclerosis and reduce cardiovascular complications. Several clinical studies have shown a negative association between bilirubin levels and the risk of cardiovascular diseases, including CAD10, stroke32, and peripheral artery disease33. In addition to the antioxidant effect, Zhu et al.34 also found that bilirubin could inhibit the production of TNF-α, MCP-1 and IL-1β. In addition to bilirubin, many inflammation-related markers such as CRP/albumin ratio35 and HALP (hemoglobin, albumin, lymphocyte, and platelet) score36, have also shown prognostic predictive capabilities in CAD patients.

However, there are also some contradictory reports about the effect of bilirubin. Higher serum bilirubin concentration has been shown to be positively associated with the severity of CAD in NSTEMI14 and increased in-hospital adverse events in STEMI patients15,37. This is consistent with the result about the association of TB with MI in the present study. On the other hand, the contrary results might be associated with the minor events per variable (EVP) of MIs.

Heme oxygenase-1 is one of the rate-limiting enzymes in the process of heme catabolism, which could be triggered by cellular stress following AMI, leading to elevated bilirubin levels38. Therefore, increased activity of HO-1 and elevated of bilirubin level in a cellular stress state appear to be a protective manner for the myocardium through antioxidant effect. Clark et al. demonstrated that an increase in exogenous bilirubin concentration could reduce the area of infarction after ischemia and enhance left ventricular systolic function in rat heart25. In addition to being activated under stress, HO-1 can also be stimulated by various drugs such as aspirin and simvastatin20,39, which at least partly explain the fact that statin use elevates the baseline bilirubin levels. Furthermore, statin elevated serum bilirubin levels through other potential mechanisms as well, including inhibition of bilirubin UDP-glucuronosyl transferase40 and prevention of bilirubin oxidation41. All of these mechanisms could be potential causes of statin elevated bilirubin in this study. Therefore, the usage of statins could be associated with its anti-inflammatory and antioxidant effects partially through elevated bilirubin.

Clinical implications and limitations

This study provides evidence about the association between baseline bilirubin levels and long-time outcomes in patients undergoing PCI and the relationship among prehospital statin, elevated direct bilirubin levels and MACE. These results demonstrated that bilirubin level was an inverse predictor of incidence of MACE after PCI and had a protective effect. Thus, in patients using statin prior to hospital admission, better outcomes were correlated with statin-induced direct bilirubin elevation, not just LDL-C lowering effects. Due to the adverse effect of statins on the liver, the elevation of liver enzyme and bilirubin may be caused by the hepatotoxicity of statins16. Therefore, this study screened population with normal liver function and bilirubin levels, demonstrating that statin-induced elevations of bilirubin within the normal range still have positive implications for postoperative outcomes after PCI. Muchova et al.19 indicated this result in mice, showing that the serum TB level was elevated following statin therapy (rosuvastatin and atorvastatin) for 3 weeks, but did not affect liver function indicators including ALT, AST, ALP and GGT.

The potential limitations of our present study should be clarified. First, because of the characteristics of retrospective studies, it was not convenient to collect information on symptoms and electrocardiograms, which prevented us from classifying the included patients who underwent PCI. Moreover, the bilirubin level of patients are baseline data. Due to the limitations in data collection, we did not conduct a study on bilirubin levels during the follow-up period after PCI, preventing us from further validating the association between bilirubin levels and cardiovascular outcomes. In subsequent research, we will aim to further collect bilirubin levels at different follow-up times and analyze how these changes impact cardiovascular outcomes. Second, our findings show that both direct bilirubin and indirect bilirubin have a protective effect on MACE. However, the use of statin only increased direct bilirubin levels but not indirect bilirubin. The mechanism between statin and the two forms remains unconfirmed. As the activity of HO-1 was not assayed, the relationship among statin, HO-1, and bilirubin could not be assessed, and the pathway of how statin raises direct bilirubin is unclear. Lastly, in this study, the time span of participants enrolment was up to 5 years. Therefore, confounding influences resulting from the advances and refinements in pharmacotherapy or intervention might lead to conclusions that are not sufficiently accurate.

Conclusion

Bilirubin has a protective effect against MACE. In patients undergoing elective PCI with normal range of bilirubin level, preadmission statin usage raised bilirubin levels, which were related to lower incidence of MACEs over the long-term follow up period independently.

Supplementary Information

Supplementary Information.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-024-71497-x.

Acknowledgements

This work was supported by grants from the National Natural Science Foundation of China (82070408), the Medical Health Science and Technology Project of Zhejiang Provincial Health Commission (2021RC014), and the Traditional Chinese Medicine Science and Technology Project of Zhejiang Province (2021ZB172).

Author contributions

WBZ and GSF conceived and designed the study. YHZ organized these data and drafted the manuscript with the help of DBL, JL, YW, and ZBC. YHZ and DBL analyzed the data and drew the pictures. JL, and QBL reviewed and edited the manuscript, WBZ, and GSF detected any errors in the whole process. All authors have read and approved the manuscript for submission.

Funding

This work was supported by grants from the National Natural Science Foundation of China (82070408), the Medical Health Science and Technology Project of Zhejiang Provincial Health Commission (2021RC014), and the Traditional Chinese Medicine Science and Technology Project of Zhejiang Province (2021ZB172).

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests

The authors declare no competing interests.

Ethics approval and consent to participate

The study was approved by the Ethics Committee of Sir Run Run Shaw Hospital of Zhejiang University. (20201217-36).

Publisher's note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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