Further Evidence That the UGT1A1*28 Allele Is Not Associated with Coronary Heart Disease: The ECTIM Study

Association between bilirubin levels and risk of stroke: a systematic review and meta-analysis

OBJECTIVE

To evaluate the association between bilirubin levels and stroke risk.

DESIGN

Systematic review and meta-analysis, reported in accordance with Meta-analysis Of Observational Studies in Epidemiology guidelines.

DATA SOURCES

The PubMed, Embase, Cochrane Central Register of Controlled Trials and China National Knowledge Infrastructure Databases were searched from inception up to 27 February 2022.

ELIGIBILITY CRITERIA

Cohort studies assessing the dose-response relationship between bilirubin levels and risk of stroke were eligible for inclusion. There were no language restrictions.

DATA EXTRACTION AND SYNTHESIS

All data from eligible studies were collected and assessed by two independent investigators. We generated pooled relative risks (RRs) with 95% CIs. We used a restricted cubic spline model for the dose-response analyses. Subsequent subgroup analyses were conducted according to stroke outcomes, follow-up duration, geographical area and size of the cohort.

RESULTS

Nine articles including results from 11 cohort studies with 7835 cases of stroke and 263 596 participants met the inclusion criteria. The summarised RR of stroke comparing the highest and lowest bilirubin level was 0.85 (95% CI 0.72 to 0.99). The dose-response analysis indicated that a 15 µmol/L increment of bilirubin level was associated with an 18% lower risk of stroke (RR=0.82, 95% CI 0.67 to 0.99). For ischaemic stroke, the RR was 0.76 (95% CI 0.58 to 0.99). Significant publication bias was not detected.

CONCLUSIONS

Elevated bilirubin levels were associated with a decreased risk of stroke among adults.

PROSPERO REGISTRATION NUMBER

CRD42017071497.

The Nonlinear Relationship Between Total Bilirubin and Coronary Heart Disease: A Dose-Response Meta-Analysis

Background: Evidence suggests that the total bilirubin has a protective effect on coronary heart disease (CHD), but the dose-response relationship remains controversial, and there is no meta-analysis to assess the relationship.

Methods: As of October 1, 2021, relevant literature was selected from four databases (PubMed, Web of Science, Cochrane Library, and Embase) by using a retrieval strategy. The dose-response curve between the total bilirubin and CHD was fitted by a restricted cubic spline. Stata 12.0 was used for statistical analysis.

Results: A total of 170,209 (6,342 cases) participants from 7 prospective studies were analyzed in our meta-analysis. We calculated the pooled relative risks (RRs) and 95% CIs for the association between serum bilirubin level and risk of CHD using random-effects models. Compared with the first quantile, the bilirubin level in the third quantile had a protective effect on the risk of CHD (RR, 0.90; 95% CI, 0.82–0.99). The restricted cubic spline functions depicted a U-type curve relationship between bilirubin (3.42–49 μmol/L) and CHD (P_linear < 0.001). When the bilirubin level was in the range of 3.42–13μmol/L, the protective effect of bilirubin on CHD was enhanced with increasing bilirubin levels. When the bilirubin level exceeded 13μmol/L, the protective effect of bilirubin weakened, and a dangerous effect gradually appeared with further increases in bilirubin levels.

Conclusions: Compared with a low bilirubin level, a high bilirubin level has a protective effect on the risk of CHD, and there was a U-shaped dose-response relationship between them.

Serum Bilirubin and Coronary Artery Disease: Intricate Relationship, Pathophysiology, and Recent Evidence

Coronary artery disease (CAD) is a major cause of morbidity, mortality, and healthcare expenditure. A number of environmental and genetic risk factors have been known to contribute to CAD. More recently, a number of studies have supported as well as opposed a possible protective benefit of bilirubin in CAD, since it has anti-inflammatory, antioxidant, and antiaggregatory properties that may reduce atherogenesis. It also shares associations with different forms of CAD, namely stable CAD, unstable angina pectoris, stable angina pectoris, and acute myocardial infarction. Lack of sufficient evidence, however, has failed to elucidate a causal relationship between serum bilirubin level and risk of CAD. Therefore, in this update, we attempted to simplify this intricate relationship between bilirubin and CAD, revisit the pathophysiology of disease, how bilirubin may be protective, and to summarize the findings of the current literature.

The UGT1A1*28 gene variant predicts long-term mortality in patients undergoing coronary angiography

Background:

Uridine diphosphate glycosyltransferases 1A1 (UGT1A1) plays an essential role in detoxification and excretion of several endogenous and exogenous compounds. A functional polymorphism in the promoter of the UGT1A1 gene (TA repeat insertion, UGT1A1*28, rs3064744) has been associated with reduced UGT1A1 enzyme activity. The purpose of the present study was to investigate the role of UGT1A1 genotypes in mortality.

Methods:

UGT1A1 genotypes as well as baseline plasma bilirubin levels were analyzed in participants of the Ludwigshafen Risk and Cardiovascular Health study (n=3316). UGT1A1*28 genotypes were determined on an ABI PRISM 3730 genetic analyzer.

Results:

As expected, UGT1A1 genotypes were associated with baseline bilirubin levels (*1/*1 genotype: 9.1±4.6 µmol/L; *1/*28 genotype: 10.8±5.3; *28/*28: 16.9±9.2; p<0.001). During a median follow-up of 10.4 years, 995 subjects (30.0%) died. In a multivariate regression analysis adjusting for age, sex, smoking, type 2 diabetes, dyslipidemia, alanine aminotransferase (ALT) levels and bilirubin levels, the UGT1A1*28 variant predicted lower overall mortality (hazard ratio [HR], 0.86; 95% confidence interval [CI], 0.78–0.95; p=0.003). Contrary to expected, higher baseline bilirubin levels predicted increased mortality (HR, 1.014; 95% CI, 1.002–1.025; p=0.019).

Conclusions:

The UGT1A1*28 gene variant is associated with lower mortality rates. The protective effect of the UGT1A1*28 variant likely includes mechanism other than bilirubin metabolism.

Bilirubin Decreases Macrophage Cholesterol Efflux and ATP-Binding Cassette Transporter A1 Protein Expression

BACKGROUND

Mild but chronically elevated circulating unconjugated bilirubin is associated with reduced total and low-density lipoprotein cholesterol concentration, which is associated with reduced cardiovascular disease risk. We aimed to investigate whether unconjugated bilirubin influences macrophage cholesterol efflux, as a potential mechanism for the altered circulating lipoprotein concentrations observed in hyperbilirubinemic individuals.

METHODS AND RESULTS

Cholesterol efflux from THP-1 macrophages was assessed using plasma obtained from normo- and hyperbilirubinemic (Gilbert syndrome) humans (n=60 per group) or (heterozygote/homozygote Gunn) rats (n=20 per group) as an acceptor. Hyperbilirubinemic plasma from patients with Gilbert syndrome and Gunn rats induced significantly reduced cholesterol efflux compared with normobilirubinemic plasma. Unconjugated bilirubin (3-17.1 μmol/L) exogenously added to plasma- or apolipoprotein A1-supplemented media also decreased macrophage cholesterol efflux in a concentration- and time-dependent manner. We also showed reduced protein expression of the ATP-binding cassette transporter A1 (ABCA1), a transmembrane cholesterol transporter involved in apolipoprotein A1-mediated cholesterol efflux, in THP-1 macrophages treated with unconjugated bilirubin and in peripheral blood mononuclear cells obtained from hyperbilirubinemic individuals. Furthermore, we demonstrated that bilirubin accelerates the degradation rate of the ABCA1 protein in THP-1 macrophages.

CONCLUSIONS

Cholesterol efflux from THP-1 macrophages is decreased in the presence of plasma obtained from humans and rats with mild hyperbilirubinemia. A direct effect of unconjugated bilirubin on cholesterol efflux was demonstrated and is associated with decreased ABCA1 protein expression. These data improve our knowledge concerning bilirubin's impact on cholesterol transport and represent an important advancement in our understanding of bilirubin's role in cardiovascular disease.

Circulating Markers of Liver Function and Cardiovascular Disease Risk

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

Effects of serum bilirubin on atherosclerotic processes

This review highlights the protective roles of bilirubin against the atherosclerotic process. Bilirubin belongs to the superfamily of tetrapyrrolic compounds formed during heme catabolism. Although for decades bilirubin was considered to be a harmful waste product, recent epidemiologic studies have shown that serum bilirubin levels have consistently been inversely associated with cardiovascular disease (CVD), as well as cardiovascular risk factors such as metabolic syndrome and diabetes. These clinical studies are supported by in vitro and in vivo experimental data and have demonstrated that bilirubin not only has an ability to scavenge overproduced reactive oxygen species and inhibit vascular smooth muscle cell proliferation but, additionally, has anti-inflammatory effects. In this review, we will discuss the inverse association of serum bilirubin and CVD and cardiovascular risk factors established in various clinical studies. We also review detailed experimental studies about the effect of bilirubin on atherosclerotic processes. In vitro, animal and human studies have proved that bilirubin inhibits oxidation of cholesterol which is an important step of atherosclerosis. Bilirubin attenuates chemotactic activity of monocytes and strongly inhibits adhesion of leukocytes to venule and production of pro-inflammatory cytokines. Bilirubin has inhibited serum-driven smooth muscle cell cycle progression at the G1 phase. Lastly, we will discuss briefly the influence of bilirubin on lipoprotein composition and endothelial dysfunction.

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

Whether conjugated bilirubin concentration, resulting from hepatic UDP-glucuronosyltransferase 1 A1 activity, is associated with cardiovascular disease is unknown. Our aim was to investigate the relation between serum conjugated bilirubin concentrations and coronary artery calcium score (CACS) as a measure of preclinical atherosclerosis. Data were analyzed from an occupational cohort of 14,583 subjects who underwent a cardiac computed tomographic estimation of CACS and measurements of risk factors. Logistic regression was used to describe associations between bilirubin concentrations and CACS. The proportion of subjects with a CACS >0 (total: men = 1,351, women = 111) decreased across increasing conjugated bilirubin quartiles (men p <0.001, women p = 0.005). After adjustment for age, gender, waist, systolic blood pressure, smoking, exercise, alcohol, homeostatic model assessment of insulin resistance, glucose, triglyceride, high- and low-density lipoprotein cholesterols, high-sensitivity C-reactive protein, lipoprotein (a), ferritin, fatty liver, cerebrovascular accident, coronary artery disease, hypertension, and diabetes, there was an inverse independent association between conjugated bilirubin and CACS >0 (odds ratio 0.76, 95% confidence interval 0.64 to 0.92, p = 0.004, for top vs bottom quartile). After further adjustment for estimated glomerular filtration rate, the odds ratio was 0.83 (95% confidence interval 0.69 to 0.99), p = 0.04. Exclusion of subjects with a high bilirubin (total >1.3 mg/dl) did not attenuate the association. In conclusion, there was a strong inverse and independent relation between conjugated bilirubin and CACS. The mechanism behind this association is not clear and may not be causal, but the effects of glucuronidation on cardiovascular disease risk should be tested.

Plasma total bilirubin levels predict amputation events in type 2 diabetes mellitus: the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study

AIMS/HYPOTHESIS

Bilirubin has antioxidant and anti-inflammatory activities. Previous studies demonstrated that higher bilirubin levels were associated with reduced prevalence of peripheral arterial disease (PAD). However, the relationship between bilirubin and lower-limb amputation, a consequence of PAD, is currently unknown. We hypothesised that, in patients with type 2 diabetes, bilirubin concentrations may inversely associate with lower-limb amputation.

METHODS

The relationship between baseline plasma total bilirubin levels and amputation events was analysed in 9,795 type 2 diabetic patients from the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study. The analysis plan was pre-specified. Lower-limb amputation was adjudicated blinded to treatment allocation. Relevant clinical and biochemical data were available for analyses. Amputation was a pre-specified tertiary endpoint.

RESULTS

Bilirubin concentrations were significantly inversely associated with lower-limb amputation, with a greater than threefold risk gradient across levels. Individuals with lower bilirubin concentrations had a higher risk for first amputation (HR 1.38 per 5 μmol/l decrease in bilirubin concentration, 95% CI 1.07, 1.79, p = 0.013). The same association persisted after adjustment for baseline variables, including age, height, smoking status, γ-glutamyltransferase level, HbA1c, trial treatment allocation (placebo vs fenofibrate), as well as previous PAD, non-PAD cardiovascular disease, amputation or diabetic skin ulcer, neuropathy, nephropathy and diabetic retinopathy (HR 1.38 per 5 μmol/l decrease in bilirubin concentration, 95% CI 1.05, 1.81, p = 0.019).

CONCLUSIONS/INTERPRETATION

Our results identify a significant inverse relationship between bilirubin levels and total lower-limb amputation, driven by major amputation. Our data raise the hypothesis that bilirubin may protect against amputation in type 2 diabetes.

Genetically elevated bilirubin and risk of ischaemic heart disease: three Mendelian randomization studies and a meta-analysis

BACKGROUND

Elevated plasma levels of bilirubin, an endogenous antioxidant, have been associated with reduced risk of ischaemic heart disease (IHD) and myocardial infarction (MI). Whether this is a causal relationship remains unclear.

OBJECTIVE

We tested the hypothesis that elevated plasma bilirubin is causally related to decreased risk of IHD and MI.

DESIGN

We used a Mendelian randomization approach and three independent studies from Copenhagen, Denmark. We measured bilirubin in 43 708 white individuals from the general population, and genotyped rs6742078 G>T in the uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene in 67 068 individuals, of whom 11 686 had IHD.

RESULTS

Third versus first tertile of baseline bilirubin levels was associated with 134% increased bilirubin levels, with sex- and age-adjusted hazard ratios (HRs) of 0.86 [95% confidence interval (CI), 0.76-0.98; P = 0.02] for IHD and 0.81 (95% CI, 0.66-0.99; P = 0.04) for MI, but with corresponding multifactorially adjusted HRs of 0.93 (95% CI, 0.82-1.06; P = 0.29) and 0.90 (95% CI, 0.73-1.12; P = 0.35). UGT1A1 rs6742078 TT versus GG genotype was associated with 95% increased bilirubin levels (P < 0.001); TT versus GG genotype was associated with odds ratios (ORs) of 1.03 (95% CI, 0.96-1.11; P = 0.73) for IHD and 1.01 (95% CI, 0.92-1.12; P = 0.68) for MI. Finally, in a meta-analysis of the present three studies and eight previous studies including a total of 14 711 cases and 60 324 controls, the random effects OR for ischaemic cardiovascular disease for genotypes with approximately 100% increased bilirubin levels versus reference genotypes was 1.01 (95% CI, 0.88-1.16).

CONCLUSION

These data suggest that plasma bilirubin is not causally associated with risk of IHD.

Inter and intra-ethnic differences in the distribution of the molecular variants of TPMT, UGT1A1 and MDR1 genes in the South Indian population

Molecular variants of polymorphic drug metabolizing enzymes and drug transporters are attributed to differences in individual's therapeutic response and drug toxicity in different populations. We sought to determine the genotype and allele frequencies of polymorphisms for major phase II drug-metabolizing enzymes (TPMT, UGT1A1) and drug transporter (MDR1) in South Indians. Allelic variants of TPMT (*2,*3A,*3B,*3C & *8), UGT1A1 (TA)6>7 and MDR1 (2677G>T/A & 3435C>T) were evaluated in 450-608 healthy South Indian subjects. Genomic DNA was extracted by phenol-chloroform method and genotype was determined by PCR-RFLP, qRT-PCR, allele specific PCR, direct sequencing and SNaPshot techniques. The frequency distributions of TPMT, UGT1A1 and MDR1 gene polymorphisms were compared between the individual 4 South Indian populations viz., Tamilian, Kannadiga, Andhrite and Keralite. The combined frequency distribution of the South Indian populations together, was also compared with that of other major populations. The allele frequencies of TPMT*3C, UGT1A1 (TA)7, MDR1 2677T, 2677A and 3435T were 1.2, 39.8, 60.3, 3.7, and 61.6% respectively. The other variant alleles such as TPMT*2, *3A, *3B and *8 were not identified in the South Indian population. Sub-population analysis showed that the distribution of UGT1A1 (TA)6>7 and MDR1 allelic variants differed between the four ethnic groups. However, the frequencies of TPMT*3C allele were similar in the four South Indian populations. The distribution of TPMT, UGT1A1 and MDR1 gene polymorphisms of the South Indian population was significantly different from other populations.

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.

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.

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.

Hyperbilirubinemia syndromes (Gilbert-Meulengracht, Crigler-Najjar, Dubin-Johnson, and Rotor syndrome)

Hyperbilirubinemia is an important clinical sign that often indicates severe hepatobiliary disease of different etiologies. Inherited non-haemolytichyperbilirubinemic conditions include Dubin-Johnson, Rotor, and Gilbert-Meulengracht syndromes, which are important differential diagnoses indicating benign disease that require no immediate treatment. Dubin-Johnson and Rotor syndromes are rare, exhibit mixed direct and indirect hyperbilirubinemia as well as typical profiles or urinary coproporphyrin excretion. Gilbert-Meulengracht disease leads to unconjugated hyperbilirubinemia because of impaired glucuronidation activity, and is part of a spectrum of genetic variants also encompassing fatal Crigler-Najjar syndrome. Gilbert-Meulengracht syndrome can be diagnosed by clinical presentation, biochemistry and genotyping, and carries significance regarding the disposition towards drug-associated toxicity. In addition, the precise diagnosis of these inherited hyperbilirubinemic syndromes avoids unnecessary invasive procedures for suspected more severe hepatobiliary disease.

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.

Plasma bilirubin and UGT1A1*28 are not protective factors against first-time myocardial infarction in a prospective, nested case-referent setting

BACKGROUND

Bilirubin, an effective antioxidant, shows a large variation in levels between individuals and has been positively associated with reduced cardiovascular disease risk. A major reason for the variability is a common promoter polymorphism, UGT1A1*28, which reduces the transcription of the enzyme that conjugates bilirubin, UDP-glucuronosyltransferase 1A1. The aim of the study was to evaluate a possible protective effect of plasma bilirubin and the UGT1A1*28 polymorphism against myocardial infarction in a prospective case-referent setting.

METHODS AND RESULTS

Subjects (n=618) with a first-ever myocardial infarction (median event age, 60.5 years; median lag time, 3.5 years) and 1184 matched referents were studied. Plasma bilirubin was lower in cases versus referents. Despite a strong gene-dosage effect on bilirubin levels in both cases and referents, the UGT1A1*28 polymorphism did not influence the risk of myocardial infarction. Among multiple other variables, serum iron showed one of the strongest associations with bilirubin levels.

CONCLUSIONS

We found no evidence for a protective effect of the UGT1A1*28 polymorphism against myocardial infarction and consequently neither for bilirubin. The lower bilirubin levels in cases might be caused by decreased production, increased degradation, or increased elimination.

Haplotypes in the UGT1A1 gene and their role as genetic determinants of bilirubin concentration in healthy German volunteers

BACKGROUND

Genetic variations of UDP-glucuronyltransferase 1A1 (UGT1A1) influence the concentration of serum bilirubin. We investigated the association of four common polymorphisms including UGT1A1-53(TA)(n), and common haplotypes of the UGT1A1 gene with bilirubin levels in 218 Caucasian volunteers.

METHODS

Total bilirubin was measured in serum of 218 healthy Caucasian volunteers. Genotyping of four genetic variants was performed: UGT1A1-53(TA)(6/7), UGT1A1c.-3279T>G, UGT1A1c.-3156G>A, and UGT1A1c.211G>A. The association between polymorphisms/haplotypes and bilirubin levels were determined.

RESULTS

Minor allele frequencies were 0.36 for UGT1A1-53(TA)(7), 0.47 for c.-3279G, 0.33 for c.-3156A and 0.006 for c.211A. The three promoter polymorphisms were in close linkage disequilibrium. Common haplotypes were: -53(TA)(6)/c.-3279T/c.211G (frequency 0.530), -53(TA)(7)/c.-3279G/c.211G (frequency 0.365), and -53(TA)(6)/c.-3279G/c.211G (frequency 0.099). Male sex, UGT1A1-53(TA)(6/7) and the c.-3279GG variant were significantly associated with higher bilirubin concentrations.

CONCLUSIONS

Two UGT1A1 promoter polymorphisms (-53(TA)(6/7) and c.-3279T>G) and a common haplotype of the UGT1A1 gene are associated with serum bilirubin concentrations in Caucasians.

Common variants of four bilirubin metabolism genes and their association with serum bilirubin and coronary artery disease in Chinese Han population

OBJECTIVES

Studies have revealed an inverse relationship between serum total bilirubin (TBIL) levels and coronary artery disease (CAD). This study investigated the genetic variants of four bilirubin metabolism genes--heme oxygenase-1 (HMOX1), biliverdin reductase A (BLVRA), solute carrier organic anion transporter family member 1B1 (SLCO1B1), and uridine diphosphate glycosyltransferase 1A1 (UGT1A1)--in relation to TBIL levels and CAD.

METHODS AND RESULTS

Thirty-five common single nucleotide polymorphisms (SNPs) were genotyped in 2380 unrelated Han participants who underwent angiocardiography at hospitals in Shanghai, China. Only three genetic variants--rs4399719 (UGT1A1 T-2473G), rs887829 (UGT1A1 G-364A), and rs4148323 (UGT1A1 G211A)--were associated with TBIL levels (each P<0.001). Four significant associations with CAD were detected after controlling age and the false discovery rate at 15%: the recessive effect of SNP rs887829 (UGT1A1 G-364A) [age-adjusted odds ratio (OR): 0.24; 95% confidence interval (CI): 0.10-0.60; P=0.0014] and dominant effect of rs4149013 (SLCO1B1 A-12099G) (age-adjusted OR: 0.70; 95% CI: 0.55-0.91; P=0.0069) on male CAD, and the additive effects of rs2877262 (BLVRA G+1238/in6C) (age-adjusted OR: 0.73; 95% CI: 0.59-0.89; P=0.0021) and rs2690381 (BLVRA G+2613/in6A) (age-adjusted OR: 0.70; 95% CI: 0.56-0.86; P=0.0008) on female CAD. SNPs rs2877262 and rs2690381 were both in a linkage disequilibrium block within BLVRA with r greater than 0.750. Correspondingly, this block was identified to be associated with female CAD.

CONCLUSION

Our study provides genetic evidences for the difference in the impact of these four bilirubin metabolism genes on TBIL levels and CAD.

Conditional linkage and genome-wide association studies identify UGT1A1 as a major gene for anti-atherogenic serum bilirubin levels--the Framingham Heart Study

OBJECTIVE AND METHODS

Low bilirubin levels are significantly associated with cardiovascular diseases (CVD). In previous genome-wide linkage studies we identified a major locus on chromosome 2q harboring the candidate gene UDP-glucuronosyltransferase (UGT1A1). The activity of this enzyme is significantly influenced by a TA-repeat polymorphism in the promoter of the gene. In a prospective study individuals with genotype (TA)7/(TA)7 had significantly higher bilirubin levels and approximately one-third the risk of CVD as carriers of the wildtype (TA)6 allele. In the present study we performed a conditional linkage study to investigate whether this polymorphism explains the observed linkage peak and extended our analysis by a genome-wide association study on bilirubin levels in 1345 individuals.

RESULTS

After adjustment for the bilirubin variance explained by this polymorphism, the LOD score on chromosome 2q dropped from 3.8 to 0.4, demonstrating that this polymorphism explains the previous linkage result. For the genome-wide association study, the closest marker to UGT1A1 was in the top ranking SNPs. The association became even stronger when we considered the TA-repeat polymorphism in the analysis (p=2.68 x 10(-53)). Five other SNPs in other regions reached genome-wide significance without obvious connection to bilirubin metabolism.

CONCLUSIONS

Our studies suggest that UGT1A1 may be the major gene with strong effects on bilirubin levels and the TA-repeat polymorphism might be the key polymorphism within the gene controlling bilirubin levels. Since this polymorphism has a high frequency and a substantial impact on the development of CVD, the gene might be an important drug target.

Serum bilirubin levels, UGT1A1 polymorphisms and risk for coronary artery disease

Low levels of the antioxidative serum bilirubin are associated with vascular aging and an increased risk for coronary artery disease (CAD). UGT1A1 is the major gene influencing bilirubin concentrations. Therefore, we investigated an association of bilirubin levels and two polymorphisms in the promoter of UGT1A1 (-53(TA-repeat) polymorphism and T-3279G) in 477 patients with premature, familial CAD and 619 age- and sex-matched controls. Bilirubin concentrations were significantly lower in cases than in controls (0.62+/-0.36 vs. 0.76+/-0.41 mg/dl for men, p=1.2 x 10(-10); and 0.42+/-0.29 vs. 0.55+/-0.23 mg/dl, p=1.9 x 10(-9) for women). Both polymorphisms showed a strong association with bilirubin levels with higher levels for homozygote carriers of the minor allele. These associations were most pronounced in male controls and patients (p=5.9 x 10(-26) and p=3.4 x 10(-16), respectively, for the -53(TA-repeat) polymorphism). Logistic regression analysis revealed low bilirubin levels but not the UGT1A1 polymorphisms to be significantly associated with CAD: OR (95% CI) 0.90 (0.86-0.94), p=2.6 x 10(-6) for men and 0.77 (0.68-0.87), p=3.2 x 10(-5) for women, respectively for each 0.1mg/dl increase of bilirubin. These results indicate that it is rather decreased bilirubin levels in general than the changes in the genetic variation of this gene that increase the risk for CAD.

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.

The Tunisian population history through the Crigler-Najjar type I syndrome

Crigler-Najjar syndrome type I (CN-I) is a rare and severe metabolic disorder. A recurrent mutation - c.1070A>G in exon 3 - was identified in the Tunisian population, suggesting a founder effect. In 2004, the detection of this mutation in two Kuwaiti Bedouin families has called the Tunisian founder effect in question again. To determine the origin of this mutation, 21 Tunisian and 2 Kuwaiti Bedouin CN-I patients were screened using nine genetic markers. Haplotype analysis confirmed the founder effect hypothesis and dated the appearance of this mutation some 32 generations ago in the Tunisian population. Using the same genetic analysis, the ancestor haplotype was identified in these two families. This result genetically confirms the blending of the Bedouin nomads within today's Tunisian population. After population migration from east to west, this mutation was introduced into the Tunisian population, and then perpetuated, probably because of marriages in isolated communities.