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

In vitro hepatic trans-differentiation of human mesenchymal stem cells using sera from congestive/ischemic liver during cardiac failure

Cellular therapy for end-stage liver failures using human mesenchymal stem cells (hMSCs)-derived hepatocytes is a potential alternative to liver transplantation. Hepatic trans-differentiation of hMSCs is routinely accomplished by induction with commercially available recombinant growth factors, which is of limited clinical applications. In the present study, we have evaluated the potential of sera from cardiac-failure-associated congestive/ischemic liver patients for hepatic trans-differentiation of hMSCs. Results from such experiments were confirmed through morphological changes and expression of hepatocyte-specific markers at molecular and cellular level. Furthermore, the process of mesenchymal-to-epithelial transition during hepatic trans-differentiation of hMSCs was confirmed by elevated expression of E-Cadherin and down-regulation of Snail. The functionality of hMSCs-derived hepatocytes was validated by various liver function tests such as albumin synthesis, urea release, glycogen accumulation and presence of a drug inducible cytochrome P450 system. Based on these findings, we conclude that sera from congestive/ischemic liver during cardiac failure support a liver specific microenvironment for effective hepatic trans-differentiation of hMSCs in vitro.

Bilirubin increases insulin sensitivity in leptin-receptor deficient and diet-induced obese mice through suppression of ER stress and chronic inflammation

Obesity-induced endoplasmic reticulum (ER) stress causes chronic inflammation in adipose tissue and steatosis in the liver, and eventually leads to insulin resistance and type 2 diabetes (T2D). The goal of this study was to understand the mechanisms by which administration of bilirubin, a powerful antioxidant, reduces hyperglycemia and ameliorates obesity in leptin-receptor-deficient (db/db) and diet-induced obese (DIO) mouse models. db/db or DIO mice were injected with bilirubin or vehicle ip. Blood glucose and body weight were measured. Activation of insulin-signaling pathways, expression of inflammatory cytokines, and ER stress markers were measured in skeletal muscle, adipose tissue, and liver of mice. Bilirubin administration significantly reduced hyperglycemia and increased insulin sensitivity in db/db mice. Bilirubin treatment increased protein kinase B (PKB/Akt) phosphorylation in skeletal muscle and suppressed expression of ER stress markers, including the 78-kDa glucose-regulated protein (GRP78), CCAAT/enhancer-binding protein (C/EBP) homologous protein, X box binding protein (XBP-1), and activating transcription factor 4 in db/db mice. In DIO mice, bilirubin treatment significantly reduced body weight and increased insulin sensitivity. Moreover, bilirubin suppressed macrophage infiltration and proinflammatory cytokine expression, including TNF-α, IL-1β, and monocyte chemoattractant protein-1, in adipose tissue. In liver and adipose tissue of DIO mice, bilirubin ameliorated hepatic steatosis and reduced expression of GRP78 and C/EBP homologous protein. These results demonstrate that bilirubin administration improves hyperglycemia and obesity by increasing insulin sensitivity in both genetically engineered and DIO mice models. Bilirubin or bilirubin-increasing drugs might be useful as an insulin sensitizer for the treatment of obesity-induced insulin resistance and type 2 diabetes based on its profound anti-ER stress and antiinflammatory properties.

Association between inherited monogenic liver disorders and chronic hepatitis C

AIM: To determine the frequencies of mutations that cause inherited monogenic liver disorders in patients with chronic hepatitis C.

METHODS: This study included 86 patients with chronic hepatitis C (55 men, 31 women; mean age at diagnosis, 38.36 ± 14.52 years) who had undergone antiviral therapy comprising pegylated interferon and ribavirin. Viral load, biochemical parameter changes, and liver biopsy morphological data were evaluated in all patients. The control group comprised 271 unrelated individuals representing the general population of Latvia for mutation frequency calculations. The most frequent mutations that cause inherited liver disorders [gene (mutation): ATP7B (H1069Q), HFE (C282Y, H63D), UGT1A1 (TA)7, and SERPINA1 (PiZ)] were detected by polymerase chain reaction (PCR), bidirectional PCR allele-specific amplification, restriction fragment length polymorphism analysis, and sequencing.

RESULTS: The viral genotype was detected in 80 of the 86 patients. Viral genotypes 1, 2, and 3 were present in 61 (76%), 7 (9%), and 12 (15%) patients, respectively. Among all 86 patients, 50 (58%) reached an early viral response and 70 (81%) reached a sustained viral response. All 16 patients who did not reach a sustained viral response had viral genotype 1. Case-control analysis revealed a statistically significant difference in only the H1069Q mutation between patients and controls (patients, 0.057; controls, 0.012; odds ratio, 5.514; 95%CI: 1.119-29.827, P = 0.022). However, the H1069Q mutation was not associated with antiviral treatment outcomes or biochemical indices. The (TA) 7 mutation of the UGT1A1 gene was associated with decreased ferritin levels (beta regression coefficient = -295.7, P = 0.0087).

CONCLUSION: Genetic mutations that cause inherited liver diseases in patients with hepatitis C should be studied in detail.

High prevalence of the UGT1A1*28 variant in HIV-infected individuals in Greece

Hyperbilirubinaemia with or without jaundice is one of the side effects of atazanavir boosted with low-dose ritonavir (ATV/rit) related to the drug plasma levels, as a result of its metabolism by UGT1A1 – uridine diphosphate-glucuronosyl transferase. Genotyping for UGT1A1*28 before initiation of antiretroviral therapy containing atazanavir may aid in identifying individuals at risk of hyperbilirubinaemia. Our objective was to estimate the prevalence of the UGTA1A1*28 polymorphism in HIV-infected individuals in Greece and to determine its potential association with hyperbilirubinaemia in patients receiving ATV/rit. The prevalence of the UGTA1A1*28 variant was estimated in 79 HIV-infected patients prior to the administration of the first-line treatment. The UGTA1A1*28 variant was detected in 46 out of 79 individuals (58.2%). Antiretroviral therapy was administered to 64/79 patients (81%). Among them, 26/64 (40.6%) received ATV/rit. Of the ATV/rit-treated patients, 14 were found to be carriers of the UGT1A1*28 variant (54%), and maximum serum bilirubin levels were significantly higher in the carrier population (4.71 vs. 2.69 mg/dL, p = 0.026). In 50% of the population, maximum levels were recorded in the first month of follow-up. Although carriage of UGT1A1 is linked with the development of hyperbilirubinaemia, the implementation of a pharmacogenomic approach in clinical practice cannot yet be recommended as a standard of care.

Impact of the genes UGT1A1, GSTT1, GSTM1, GSTA1, GSTP1 and NAT2 on acute alcohol-toxic hepatitis

Alcohol metabolism causes cellular damage by changing the redox status of cells. In this study, we investigated the relationship between genetic markers in genes coding for enzymes involved in cellular redox stabilization and their potential role in the clinical outcome of acute alcohol-induced hepatitis. Study subjects comprised 60 patients with acute alcohol-induced hepatitis. The control group consisted of 122 healthy non-related individuals. Eight genetic markers of the genes UGT1A1, GSTA1, GSTP1, NAT2, GSTT1 and GSTM1 were genotyped. GSTT1 null genotype was identified as a risk allele for alcohol-toxic hepatitis progression (OR 2.146, P=0.013). It was also found to correlate negatively with the level of prothrombin (β= −11.05, P=0.037) and positively with hyaluronic acid (β=170.4, P=0.014). NAT2 gene alleles rs1799929 and rs1799930 showed opposing associations with the activity of the biochemical markers γ-glutamyltransferase and alkaline phosphatase; rs1799929 was negatively correlated with γ-glutamyltransferase (β=−261.3, P=0.018) and alkaline phosphatase (β= −270.5, P=0.032), whereas rs1799930 was positively correlated with Γ-glutamyltransferase (β=325.8, P=0.011) and alkaline phosphatase (β=374.8, P=0.011). Enzymes of the glutathione S-transferase family and NAT2 enzyme play an important role in the detoxification process in the liver and demonstrate an impact on the clinical outcome of acute alcohol-induced hepatitis.

Endogenous Tetrapyrroles Influence Leukocyte Responses to Lipopolysaccharide in Human Blood: Pre-Clinical Evidence Demonstrating the Anti-Inflammatory Potential of Biliverdin

Sepsis is associated with abnormal host immune function in response to pathogen exposure, including endotoxin (lipopolysaccharide; LPS). Cytokines play crucial roles in the induction and resolution of inflammation in sepsis. Therefore, the primary aim of this study was to investigate the effects of endogenous tetrapyrroles, including biliverdin (BV) and unconjugated bilirubin (UCB) on LPS-induced cytokines in human blood. Biliverdin and UCB are by products of haem catabolism and have strong cytoprotective, antioxidant and anti-inflammatory effects. In the present study, whole human blood supplemented with BV and without was incubated in the presence or absence of LPS for 4 and 8 hours. Thereafter, whole blood was analysed for gene and protein expression of cytokines, including IL-1β, IL-6, TNF, IFN-γ, IL-1Ra and IL-8. Biliverdin (50 μM) significantly decreased the LPS-mediated gene expression of IL-1β, IL-6, IFN-γ, IL-1Ra and IL-8 (P<0.05). Furthermore, BV significantly decreased LPS-induced secretion of IL-1β and IL-8 (P<0.05). Serum samples from human subjects and, wild type and hyperbilirubinaemic Gunn rats were also used to assess the relationship between circulating bilirubin and cytokine expression/production. Significant positive correlations between baseline UCB concentrations in human blood and LPS-mediated gene expression of IL-1β (R=0.929), IFN-γ (R=0.809), IL-1Ra (R=0.786) and IL-8 (R=0.857) were observed in blood samples (all P<0.05). These data were supported by increased baseline IL-1β concentrations in hyperbilirubinaemic Gunn rats (P<0.05). Blood samples were also investigated for complement receptor-5 (C5aR) expression. Stimulation of blood with LPS decreased gene expression of C5aR (P<0.05). Treatment of blood with BV alone and in the presence of LPS tended to decrease C5aR expression (P=0.08). These data indicate that supplemented BV inhibits the ex vivo response of human blood to LPS. Surprisingly, however, baseline UCB was associated with heighted inflammatory response to LPS. This is the first study to explore the effects of BV in a preclinical human model of inflammation and suggests that BV could represent an anti-inflammatory target for the prevention of LPS mediated inflammation in vivo.

Correlations between serum bilirubin levels and diabetic nephropathy progression among Japanese type 2 diabetic patients: a prospective cohort study (Diabetes Distress and Care Registry at Tenri [DDCRT 5])

OBJECTIVE To assess the correlations between serum bilirubin levels and diabetic nephropathy development and progression in type 2 diabetic patients. RESEARCH DESIGN AND METHODS Longitudinal data were obtained from 2,511 type 2 diabetic patients registered in a Japanese diabetes registry. To assess the independent correlations between serum bilirubin levels and either the development or progression of diabetic nephropathy, we used logistic regression analysis adjusted for potential confounders. RESULTS The median follow-up period was 503.4 days (range 238-777). The mean patient age, BMI, and HbA1c level was 65.2 years, 24.7 kg/m(2), and 7.5% (58.5 mmol/mol), respectively. Baseline serum bilirubin levels were significantly associated with the urinary albumin-creatinine ratio at baseline (P < 0.001) and 1 year after registration (P < 0.001). Multivariable adjusted odds ratios for progression from microalbuminuria to macroalbuminuria for the second, third, and fourth quartile of serum bilirubin levels were 0.89 (95% CI 0.49-1.58), 0.93 (0.47-1.83), and 0.33 (0.13-0.84), respectively, showing a statistically significant linear trend across categories (P = 0.032). However, this trend disappeared after adjustment for hemoglobin levels. CONCLUSIONS Serum bilirubin levels were associated with diabetic nephropathy progression in type 2 diabetic patients independent of possible confounders. Serum bilirubin levels might be the link in the correlation between hemoglobin levels and nephropathy progression.

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.

Oxidative stress and endothelial dysfunction: clinical evidence and therapeutic implications

An imbalance of nitric oxide (NO) and reactive oxygen species (ROS), so-called "oxidative stress," may promote endothelial dysfunction, leading to cardiovascular complications. Activation of nicotinamide-adenine dinucleotide phosphate oxidase, xanthine oxidase, cyclooxygenase, and mitochondrial electron transport, inactivation of the antioxidant system, and uncoupling of endothelial NO synthase lead to oxidative stress along with an increase in ROS production and decrease in ROS degradation. Although experimental studies, both in vitro and in vivo, have shown a critical role of oxidative stress in endothelial dysfunction under the condition of excessive oxidative stress, there is little information on whether oxidative stress is really involved in endothelial function in humans. In a clinical setting, we showed an association between oxidative stress and endothelial function, especially in patients with renovascular hypertension as a model of increased oxidative stress and in patients with Gilbert syndrome as a model of decreased oxidative stress, through an increase in the antioxidant property of unconjugated bilirubin.

Gilbert's syndrome and the risk of death: a population-based cohort study

BACKGROUND AND AIMS

Gilbert's syndrome is a common familial hyperbilirubinemia that may reduce the risk of various age-related diseases because of the antioxidant properties of bilirubin. We conducted a large cohort study using The Health Improvement Network primary care database and compared all-cause mortality rates in those with and without Gilbert's syndrome.

METHODS

Mortality rates in patients with a diagnosis of Gilbert's syndrome and raised bilirubin level (n = 4266) were compared with those of patients with similar characteristics but with normal bilirubin levels (n = 21 968). Multivariate Poisson regression was also used to estimate adjusted mortality rate ratios.

RESULTS

During the 350 000 PYs of follow up across the Gilbert's and comparison cohorts, there were 1174 deaths. Mortality rates were 24/10 000 PYs in the Gilbert's cohort versus 50/10 000 PYs in the comparison cohort. Mortality rates were around half in patients with Gilbert's syndrome after accounting for sociodemographics and general health indicators (adjusted mortality rate ratio: 0.5 [95% confidence interval; 0.4-0.7; P < 0.001]).

CONCLUSIONS

Mortality rates observed for people with Gilbert's syndrome in the general population are almost half those of people without evidence of Gilbert's syndrome.

Elevated serum bilirubin levels are inversely associated with coronary artery atherosclerosis

BACKGROUND

Inverse correlations of high serum bilirubin with metabolic and cardiovascular disease have been suggested. However, anti-atherogenic effects of bilirubin have not been well-established in terms of the presence of plaques and stenosis identified in coronary computed tomography (CT).

METHODS

A cross-sectional study was conducted on 2862 men who were free of cardiovascular disease and underwent coronary CT as part of a routine medical screening examination. Coronary stenotic lesions were considered to be incidences of coronary atherosclerosis, and stenosis was classified as stenosis <50% or ≥50%, according to degree of stenosis.

RESULTS

The prevalences of coronary atherosclerosis and stenosis ≥50% in subjects with elevated bilirubin levels (>1.2 mg/dL) were lower than those in subjects with normal bilirubin levels (≤1.2 mg/dL) (19.9% vs. 27.9%, p < 0.001, 8.5% vs. 10.3%, p = 0.044). Bilirubin was inversely associated with total plaques (odds ratio [OR] 0.59, 95% confidence interval [CI] 0.48-0.73 in the 4th quartile vs. 1st quartile) and calcified plaques (OR 0.60, 95% CI 0.49-0.75) in univariate analysis. After adjusting for traditional risk factors, it was found that coronary atherosclerosis (OR 0.73, 95% CI 0.56-0.94 in the 4th quartile vs. 1st quartile) and calcified plaque (OR 0.66, 95% CI 0.53-0.84) were inversely associated with the bilirubin grade in a dose-dependent manner.

CONCLUSIONS

The serum bilirubin level was inversely associated with coronary atherosclerosis and calcified plaques in a dose-dependent manner. These results suggested that serum bilirubin could be used as a protective biomarker of coronary artery disease.

The role of bilirubin and its protective function against coronary heart disease

BACKGROUND

Atherosclerotic cardiovascular disease is the leading cause of morbidity and mortality both in industrialized and developing countries. Atherosclerosis is a chronic inflammatory disease of the arterial wall, which also involves deposition and peroxidation of lipids. Bilirubin, an important endogenous antioxidant, may limit lipid peroxidation and retard the progression of atherosclerosis. Previous studies have reported an inverse relationship between serum bilirubin levels and the risk of coronary artery disease (CAD). Taking into account that atherosclerosis is a complex process that is initiated and accelerated by diverse risk factors, we aimed to test the antiatherosclerotic effects of bilirubin in a population with multiple risk factors for CAD.

METHODS

The study included 221 patients who underwent coronary angiography owing to symptoms suggestive of ischemia and/or positive noninvasive stress test results. Of the patients, 76 had normal coronary angiograms and served as the control group. The remaining 145 patients with documented CAD and two or more cardiovascular risk factors constituted the study group. The study group (n=145) was further classified according to the Gensini score as follows: group 1 if Gensini score was 1-19 (minimal CAD, n=82), and group 2 if Gensini score was 20 or higher (significant CAD, n=63). Biochemical assessments including total and direct serum bilirubin levels were carried out using standard methods in automated systems.

RESULTS

All of the cardiovascular risk factors were found significantly more frequently in the study group (groups 1 and 2) than in the control group. Total and direct serum bilirubin levels did not differ significantly between the control group, group 1, and group 2. There was a moderate and significant positive correlation between direct bilirubin levels and the Gensini score (r = 0.158, p = 0.019). There was no significant correlation between total bilirubin levels and the Gensini score.

CONCLUSION

In conclusion, our findings suggest that in the presence of multiple risk factors, similar concentrations of serum bilirubin may not confer the same level of protection against CAD as in an individual with a more favorable risk profile. The relationship between direct bilirubin levels and the Gensini score is unlikely to be causative, given the established antiatherosclerotic effects of bilirubin.

Antihypertensive actions of moderate hyperbilirubinemia: role of superoxide inhibition

BACKGROUND

Moderate (approximately 2-fold) increases in plasma unconjugated bilirubin levels are able to attenuate the development of angiotensin II (Ang II)-dependent hypertension. To determine the specific role of decreases in superoxide production to the blood pressure-lowering effects of moderate hyperbilirubinemia (MHyB), we performed this study, in which the Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin was given to Ang II-infused mice in the presence and absence of moderate hyperbilirubinemia.

METHODS

Apocynin (14mM) was administered in the drinking water prior to treatment with UDP-glucuronosyltransferase 1A1 antisense morpholino (16 μg/kg), which was administered by intravenous injection every third day. Treatments were started before the implantation of Ang II-containing minipumps (1μg/kg/min) and continued throughout the protocol.

RESULTS

Ang II infusion increased blood pressure to 145±2mm Hg. Apocynin treatment alone reduced blood pressure to 135±5mm Hg, whereas MHyB alone decreased blood pressure to 118±5mm Hg in Ang II-infused mice. Prior inhibition of NADPH oxidase with apocynin did not result in a further decrease in blood pressure in MHyB mice, which averaged 117±3mm Hg (n = 6 mice per group). In aortic preparations, apocynin treatment decreased Ang II-mediated superoxide production from 2433±120 relative light units (RLU)/min/mg to 1851±126 RLU/min/mg (n = 4 mice per group), which was similar to levels observed in MHyB mice alone (1473±132 RLU/min/mg) or in combination with apocynin (1503±115 RLU/min/mg).

CONCLUSIONS

Our results indicate that MHyB lowers blood pressure by a mechanism that is partially dependent on the inhibition of superoxide production.

Association of SNPs in the UGT1A gene cluster with total bilirubin and mortality in the Diabetes Heart Study

OBJECTIVE

A negative relationship between total bilirubin concentration (TBili) and CVD risk has been documented in a series of epidemiological studies. In addition, TBili is thought to be under strong genetic regulation via the UGT1A gene family, suggesting it may be a heritable CVD risk factor. However, few studies directly relate TBili-associated UGT1A variants to CVD severity or outcome. This study replicated the genetic association for TBili in the Diabetes Heart Study (DHS), and examined the relationships of TBili-associated SNPs with measures of subclinical CVD and mortality.

METHODS

This investigation included 1220 self-described European American (EA) individuals from the DHS, a family-based study examining risk for macrovascular complications in type 2 diabetes (T2D). Genetic associations with TBili were examined using the Affymetrix Genome-wide Human SNP Array 5.0 and the Illumina Infinium Human Exome beadchip v1.0. Subsequent analyses assessed the relationships of the top TBili-associated SNPs with measures of vascular calcified plaque and mortality.

RESULTS

A genome-wide association study detected 18 SNPs within the UGT1A gene family associated with TBili at p < 5 × 10(-8). The top hit was rs887829 (p = 8.67 × 10(-20)). There was no compelling evidence of association between the top TBili-associated SNPs and vascular calcified plaque (p = 0.05-0.88). There was, however, evidence of association with all-cause mortality (p = 0.0004-0.06), the top hit being rs2741034.

CONCLUSION

These findings support a potential role for UGT1A genetic variants in risk for mortality in T2D. Further quantification of the extent of CVD risk conferred by UGT1A gene family variants in a high risk cohort with T2D is still required.

Unconjugated bilirubin, a potent endogenous antioxidant, is decreased in patients with non-alcoholic steatohepatitis and advanced fibrosis

BACKGROUND AND AIM

Oxidative stress is considered a key element in the progression of non-alcoholic fatty liver to non-alcoholic steatohepatitis (NASH). Unconjugated bilirubin is the main endogenous lipid antioxidant and is cytoprotective in different tissues and organs. In this study, it was evaluated if unconjugated bilirubin levels are associated with the degree of liver injury in patients with non-alcoholic fatty liver disease.

METHODS

Two hundred and eighty-five patients were retrospectively evaluated with biopsy-confirmed non-alcoholic fatty liver disease. Multiple logistic regression models were used to assess the relationship of steatosis, inflammation, and fibrosis levels to the features of patients.

RESULTS

Unconjugated bilirubin levels differed significantly according to inflammation and fibrosis scores. Unconjugated bilirubin was lower in patients with moderate-severe inflammation compared with those with absent-mild (P = 0.001) and in patients with moderate-severe fibrosis compared with those with absent-mild (P < 0.001), whereas no difference was observed for steatosis grades. At logistic regression analysis, low unconjugated bilirubin levels were associated with moderate-severe inflammation (odds ratio, 0.11; 95% confidence interval 0.02-0.76; P = 0.025) and moderate-severe fibrosis (odds ratio, 0.013; 95% confidence interval 0.001-0.253; P = 0.004).

CONCLUSIONS

Low unconjugated bilirubin levels are independent predictors of advanced inflammation and fibrosis in patients with steatohepatitis, indicating the lack of antioxidant protection as a possible molecular determinant for the progression of liver injury.

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.

Carotid Intima Media Thickness and Its Association With Total Bilirubin Levels in Patients With Coronary Artery Ectasia

Atherosclerosis plays an important role in the etiopathogenesis of coronary artery ectasia (CAE). The relationship between total bilirubin (TBil) and carotid intima media thickness (cIMT) in patients with CAE has not been fully investigated. Hence, we evaluated the relationship between TBil levels and cIMT in 142 consecutive eligible patients with CAE, newly diagnosed coronary artery disease (CAD), and normal coronary arteries. There were no significant differences in TBil ( P = .772) and cIMT ( P = .791) between the CAE and CAD groups. Bilirubin levels were significantly lower in both CAE and CAD groups compared to the controls ( P < .01). The cIMT was significantly higher in both CAE and CAD groups compared to control participants ( P < .01). A negative correlation between cIMT and TBil was found in all the groups ( P < .01, r = .354). We show for the first time that patients with CAE and CAD have lower TBil and greater cIMT compared to controls with normal coronary angiograms.

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.

Serum bilirubin levels are inversely associated with nonalcoholic fatty liver disease

BACKGROUND/AIMS

Serum bilirubin exerts antioxidant and cytoprotective effects. In addition, elevated serum bilirubin levels are associated with a decreased risk of metabolic and cardiovascular diseases. However, few studies have evaluated whether serum bilirubin is associated with non-alcoholic fatty liver disease (NAFLD), which is closely associated with other metabolic diseases. The aim of this study was thus to elucidate the association between serum total bilirubin levels and NAFLD.

METHODS

A cross-sectional study of 17,348 subjects undergoing a routine health check-up was conducted. Subjects positive for hepatitis B or hepatitis C virus, or with other hepatitis history were excluded. NAFLD was diagnosed on the basis of typical ultrasonographic findings and an alcohol consumption of less than 20 g/day.

RESULTS

The mean age of the subjects was 49 years and 9,076 (52.3%) were men. The prevalence of NAFLD decreased steadily as the serum bilirubin level increased in both men and women (P<0.001 for both). Multivariate regression analysis adjusted for other metabolic risk factors showed that serum bilirubin level was inversely associated with the prevalence of NAFLD [odds ratio (OR)=0.88, 95% confidence interval (CI)=0.80-0.97]. Furthermore, there was an inverse, dose-dependent association between NAFLD and serum total bilirubin levels (OR=0.83, 95% CI=0.75-0.93 in the third quartile; OR=0.80, 95% CI=0.71-0.90 in the fourth quartile vs. lowest quartile, P for trend <0.001).

CONCLUSIONS

Serum bilirubin levels were found to be inversely associated with the prevalence of NAFLD independent of known metabolic risk factors. Serum bilirubin might be a protective marker for NAFLD.

Bilirubin and beyond: a review of lipid status in Gilbert's syndrome and its relevance to cardiovascular disease protection

Gilbert's syndrome (GS) is characterized by a benign, mildly elevated bilirubin concentration in the blood. Recent reports show clear protection from cardiovascular disease in this population. Protection of lipids, proteins and other macromolecules from oxidation by bilirubin represents the most commonly accepted mechanism contributing to protection in this group. However, a recent meta-analysis estimated that bilirubin only accounts for ~34% of the cardioprotective effects within analysed studies. To reveal the additional contributing variables we have explored circulating cholesterol and triacylglycerol concentrations, which appear to be decreased in hyperbilirubinemic individuals/animals, and are accompanied by lower body mass index in highly powered studies. These results suggest that bilirubin could be responsible for the development of a lean and hypolipidemic state in GS. Here we also discuss the possible contributing mechanisms that might reduce circulating cholesterol and triacylglycerol concentrations in individuals with syndromes affecting bilirubin metabolism/excretion, which we hope will stimulate future research in the area. In summary, this article is the first review of lipid status in animal and human studies of hyperbilirubinemia and explores possible mechanisms that could contribute to lowering circulating lipid parameters and further explain cardiovascular protection in Gilbert's syndrome.

Phycocyanin and phycocyanobilin from Spirulina platensis protect against diabetic nephropathy by inhibiting oxidative stress

We and other investigators have reported that bilirubin and its precursor biliverdin may have beneficial effects on diabetic vascular complications, including nephropathy, via its antioxidant effects. Here, we investigated whether phycocyanin derived from Spirulina platensis, a blue-green algae, and its chromophore phycocyanobilin, which has a chemical structure similar to that of biliverdin, protect against oxidative stress and renal dysfunction in db/db mice, a rodent model for Type 2 diabetes. Oral administration of phycocyanin (300 mg/kg) for 10 wk protected against albuminuria and renal mesangial expansion in db/db mice, and normalized tumor growth factor-β and fibronectin expression. Phycocyanin also normalized urinary and renal oxidative stress markers and the expression of NAD(P)H oxidase components. Similar antioxidant effects were observed following oral administration of phycocyanobilin (15 mg/kg) for 2 wk. Phycocyanobilin, bilirubin, and biliverdin also inhibited NADPH dependent superoxide production in cultured renal mesangial cells. In conclusion, oral administration of phycocyanin and phycocyanobilin may offer a novel and feasible therapeutic approach for preventing diabetic nephropathy.

Cardiovascular events as a function of serum bilirubin levels in a large, statin-treated cohort

BACKGROUND

Serum bilirubin is an endogenous antioxidant that is routinely measured before a statin is prescribed primarily to assess liver function, but the association with cardiovascular disease (CVD) in this population has not been explored.

METHOD AND RESULTS

We identified patients from a United Kingdom primary care database (The Health Improvement Network) with measurements of serum total bilirubin levels recorded 3 months before the first statin treatment between January 1, 2000, and December 31, 2010, and no history of liver disease or CVD. In total, 130 052 patients met the inclusion criteria, and after a median follow-up of 43 months, there were 7850 CVD events. In men, the incidence of CVD in the lowest decile category of bilirubin (1-6 μmol/L [0.06-0.35 mg/dL]) was 215 per 10 000 person-years compared with 163 per 10 000 person-years in the highest decile (19-40 μmol/L [1.1-2.3 mg/dL]). Similar differences were seen for women. After conventional CVD risk factors were accounted for, the associations with bilirubin were nonlinear (L shaped), and the models predicted that, compared with patients with a bilirubin level of 10 μmol/L (0.6 mg/dL), those with a similar CVD risk profile but a bilirubin level of 5 μmol/L (0.3 mg/dL) had an 18% (95% confidence interval, 9-27) higher risk of any CVD event, a 34% (95% confidence interval, 13-56) higher risk of myocardial infarction, and a 33% (95% confidence interval, 21-46) higher risk of death resulting from any cause.

CONCLUSIONS

Serum bilirubin level measured before a statin prescription to assess liver function is an independent risk factor for CVD and death in both men and women.

CYP2C19 genotype has a major influence on labetalol pharmacokinetics in healthy male Chinese subjects

PURPOSE

The pharmacokinetics (PK) of labetalol show wide inter-subject variability, but the genetic causes for this are largely undetermined. This study was performed to examine whether common polymorphisms in UGT1A1, UGT2B7, CYP2C19 and ABCB1 affect the PK of labetalol.

METHODS

The PK of labetalol were determined in 37 Chinese healthy male subjects who took a single oral dose of 200 mg labetalol. Plasma concentrations of labetalol were determined by a high-performance liquid chromatographic method. Subjects were genotyped for the CYP2C19 2 and 3, UGT1A1 6, 28 and 60, UGT2B7 2 and ABCB1 1236C>T, 2677G>T/A and 3435C>T polymorphisms.

RESULTS

Subjects with the CYP2C19 2/ 2 genotype had a higher peak concentration (255.5 ± 80.1 vs. 156.0  ±  66.3 ng/mL; P < 0.05) and area under the concentration-time curve (AUC0-∞; 1,473.7 ± 493.6 vs. 502.8 ± 176.1 ng[Symbol: see text]h/mL; P < 0.001) than subjects with 60 or 28, and UGT2B7 2 did not result in a significant effect. Subjects with ABCB1 2677TA or TT or ABCB1 3435TT genotypes had higher AUC0-∞ and lower total clearance than the wild-types (P < 0.05), but this appeared to be related to the distribution of CYP2C19 genotypes. The CYP2C19 genotype appeared to be the only predictor of labetalol concentrations, accounting for approximately 60 % of the total variance in the AUC0-∞.

CONCLUSION

Our results suggest that the PK of labetalol are significantly affected by the common CYP2C19 polymorphisms in individuals of Chinese ethnicity. Future larger studies are needed to evaluate the effect of CYP2C19 and UGT1A1 polymorphisms on the PK of labetalol stereoisomers and the pharmacodynamic effects.

Association between total bilirubin and hemoglobin A1c in Korean type 2 diabetic patients

Recent studies have shown that bilirubin is negatively associated with hemoglobin A1c (HbA1c) in the general population. The association between bilirubin and HbA1c in serum of diabetes patients has not yet been studied. The aim of the present study was to evaluate the association between total bilirubin and HbA1c in Korean patients with type 2 diabetes. A total of 690 of the 1,275 type 2 diabetes patients registered with the public health centers in Seo-gu, Gwangju and Gokseong-gun, Jeollanam-do participated in this study. Following an overnight fast, venous blood and urine samples were collected and analyzed. The mean HbA1c values differed significantly according to total bilirubin (≤ 0.4 mg/dL, 7.6%; 0.5 mg/dL, 7.3%; 0.6-0.7 mg/dL, 7.2%; and ≥ 0.8 mg/dL, 7.1%; P for trend = 0.016) after we adjusted for other confounding factors. When the odds ratio (OR) was adjusted for other confounding factors, there was a significant association between total bilirubin and HbA1c (OR, 0.4 [95% confidence interval, 0.2-0.8] for total bilirubin ≥ 0.8 mg/dL versus ≤ 0.4 mg/dL. In conclusion, total bilirubin concentrations in serum are negatively associated with HbA1c levels after adjustment for sex, age, and other confounding factors in type 2 diabetes patients.

Gilbert syndrome: the UGT1A1*28 promoter polymorphism as a biomarker of multifactorial diseases and drug metabolism

Gilbert syndrome belongs to the group of the most common human metabolic disorders and is characterized by an elevated level of bilirubin in blood serum. A polymorphism of the 5´ end of the UGT1A1 gene promoter, a homozygous insertion of TA pairs (genotype UGT1A1*28/*28), results in a decrease in bilirubin glucuronidation activity and therefore leads to an increase in the level of unconjugated bilirubin (hyperbilirubinemia). Genotyping the UGT1A1 promoter is an important step in the determination of the etiology of free hyperbilirubinemia of unknown origin. Molecular diagnosis enables avoiding invasive diagnostic procedures, such as liver biopsy, in establishing the appropriate diagnosis and prognosis, as well as in establishing the correct therapeutic procedures in a variety of diseases (e.g., chemotherapy or bone marrow transplantation). Moreover, the UGT1A1*28/*28 genotype has emerged as an important element in drug tolerance, as well as in multifactorial diseases, such as cancer. However, the role of this polymorphism is still not completely understood. In this review we have summarized current knowledge and attempted to propose directions for further research.

Human UDP-glucuronosyltransferases: feedback loops between substrates and ligands of their transcription factors

Expression profiles of human adult and fetal hepatic and intestinal UDP-glucuronosyltransferases (UGTs), information about their endo- and xenobiotic substrates, and their transcriptional regulation suggests regulatory circuits between some UGT substrates and ligands of their transcription factors. For examples: (i) bilirubin is solely conjugated by UGT1A1 and activates its transcription factors Ah receptor, PXR and CAR. (ii) Hepatotoxic lithocholic acid (LCA) is oxidized to hyodeoxycholic acid, the latter conjugated by UGT2B4 and UGT2B7. LCA is also an agonist of FXR and PPARα, which are controlling these UGTs. (iii) Similar feedback loops possibly exist between some eicosanoids, PPARα and UGTs. (iv) Regulatory circuits may also have evolved between dietary polyphenols, which are efficient substrates of UGTs and activators of the Ah receptor. Although many newly developed drugs are conjugated by promiscuous UGTs, the discussed regulatory circuits may provide hints to evolutionary important UGT substrates.

Hyperbilirubinemia, augmentation of endothelial function, and decrease in oxidative stress in Gilbert syndrome

BACKGROUND

Patients with Gilbert syndrome have mild unconjugated hyperbilirubinemia. It has been shown that bilirubin is an endogenous antioxidant. We evaluated the role of oxidative stress in endothelial function in patients with Gilbert syndrome under normal conditions without cardiovascular risk factors.

METHODS AND RESULTS

A total of 108 young men with Gilbert syndrome without cardiovascular risk factors and 108 age-matched healthy men (normal controls) were enrolled in this study. Serum concentrations of bilirubin were higher in patients with Gilbert syndrome than in control subjects (29.2±11.6 versus 9.4±2.7 μmol/L; P<0.001). Serum concentrations of malondialdehyde-modified low-density lipoprotein and urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG), as indices of oxidative stress, were lower in patients with Gilbert syndrome than in control subjects (61.8±24.5 versus 72.5±21.8 U/L, P=0.034; 7.8±2.4 versus 10.4±3.2 ng/mg creatinine, P=0.001, respectively). Flow-mediated vasodilation was greater in patients with Gilbert syndrome than in normal control subjects (7.2±2.2% versus 5.9±1.7%; P<0.001). Vascular responses to nitroglycerine were not significantly different between the 2 groups. Flow-mediated vasodilation correlated with serum concentration of bilirubin (r=0.44, P<0.001), malondialdehyde-modified low-density lipoprotein (r=-0.25, P=0.01), and urinary excretion of 8-OHdG (r=-0.27, P=0.004) in patients with Gilbert syndrome but not in control subjects. In addition, serum concentration of bilirubin correlated with malondialdehyde-modified low-density lipoprotein (r=-0.20, P=0.04) and 8-OHdG (r=-0.21, P=0.02) in patients with Gilbert syndrome but not in control subjects.

CONCLUSIONS

Patients with Gilbert syndrome had low levels of oxidative stress associated with hyperbilirubinemia and enhancement of endothelium-dependent vasodilation.

CLINICAL TRIAL REGISTRATION

URL: http://www.umin.ac.jp. Unique identifier: UMIN000003409.

Relationship between total bilirubin and endothelial function, inflammation and oxidative stress in HIV-infected adults on stable antiretroviral therapy

OBJECTIVES

Enhanced inflammation is evident in HIV infection, even with virological suppression. Outside HIV infection, studies show an independent association between higher total bilirubin and better endothelial function as well as a lower prevalence of coronary heart disease, possibly as a consequence of the anti-inflammatory and antioxidant effect of bilirubin. The aim of this study was to determine whether such an association exists in HIV-infected individuals.

METHODS

A cross-sectional study was performed in HIV-1-infected adults on stable antiretroviral therapy (ART) to determine if a relationship exists between total bilirubin and endothelial function [flow-mediated dilation (FMD) of the brachial artery], inflammation [interleukin-6 (IL-6), soluble tumour necrosis factor receptors, C-reactive protein, and adhesion molecules], coagulation markers (fibrinogen and D-dimer) and oxidative stress (F (2) -isoprostanes). Endpoints were compared based on total bilirubin levels and atazanavir status using distributionally appropriate, two-sample tests. Correlation coefficients were determined between total bilirubin and endpoints. Linear regression was used to model the relationship between total bilirubin (and atazanavir status) and FMD.

RESULTS

A total of 98 adults were included in the study. Total bilirubin was higher in the atazanavir group when compared to the non-atazanavir group [median (interquartile range) 1.8 (1.1-2.6) vs. 0.6 (0.4-1.4) mg/dL; P < 0.01] as were insulin, the homeostasis model assessment of insulin resistance (HOMA-IR) and fibrinogen. Total bilirubin was positively correlated with fibrinogen and was not correlated with other outcomes. After adjustment, neither total bilirubin nor atazanavir status was associated with FMD.

CONCLUSIONS

In virologically suppressed, HIV-infected adults on stable ART, neither total bilirubin nor atazanavir use was associated with improved endothelial function as measured using FMD, inflammation or oxidative stress as measured using biomarkers.

A genome-wide association study of total bilirubin and cholelithiasis risk in sickle cell anemia

Serum bilirubin levels have been associated with polymorphisms in the UGT1A1 promoter in normal populations and in patients with hemolytic anemias, including sickle cell anemia. When hemolysis occurs circulating heme increases, leading to elevated bilirubin levels and an increased incidence of cholelithiasis. We performed the first genome-wide association study (GWAS) of bilirubin levels and cholelithiasis risk in a discovery cohort of 1,117 sickle cell anemia patients. We found 15 single nucleotide polymorphisms (SNPs) associated with total bilirubin levels at the genome-wide significance level (p value <5 × 10(-8)). SNPs in UGT1A1, UGT1A3, UGT1A6, UGT1A8 and UGT1A10, different isoforms within the UGT1A locus, were identified (most significant rs887829, p = 9.08 × 10(-25)). All of these associations were validated in 4 independent sets of sickle cell anemia patients. We tested the association of the 15 SNPs with cholelithiasis in the discovery cohort and found a significant association (most significant p value 1.15 × 10(-4)). These results confirm that the UGT1A region is the major regulator of bilirubin metabolism in African Americans with sickle cell anemia, similar to what is observed in other ethnicities.

Serum γ-glutamyltransferase: independent predictor of risk of diabetes, hypertension, metabolic syndrome, and coronary disease

Serum γ-glutamyltransferase (GGT) is associated with oxidative stress and hepatic steatosis. The extent to which its value in determining incident cardiometabolic risk (coronary heart disease (CHD), metabolic syndrome (MetS), hypertension and type 2 diabetes) is independent of obesity needs to be further explored in ethnicities. After appropriate exclusions, a cohort of 1,667 adults of a general population (age 52 ±11 years) was evaluated prospectively at 4 year's follow-up using partly Cox proportional hazard regressions. GGT activity was measured kinetically, and values were log-transformed for analyses. MetS was identified by Adult Treatment Panel-III criteria modified for male abdominal obesity. Median (interquartile range) GGT activity was 24.9 (17.0; 35.05) U/l in men, 17.0 (12.3; 24.0) U/l in women. In linear regression analysis, while smoking status was not associated, (male) sex, sex-dependent age, alcohol usage, BMI, fasting triglycerides and C-reactive protein (CRP) were significant independent determinants of circulating GGT. Each 1-s.d. increment in (= 0.53 ln GGT) GGT activity significantly predicted in each sex incident hypertension (hazard ratio (HR) 1.20 (95% confidence interval (CI) 1.10; 1.31)), and similarly MetS, after adjustment for age, alcohol usage, smoking status, BMI and menopause. Strongest independent association existed with diabetes (HR 1.3 (95% CI 1.1; 1.5)) whereas GGT activity tended to marginally predict CHD independent of total bilirubin but not of BMI. Higher serum total bilirubin levels were protective against CHD risk in women. We conclude that elevated serum GGT confers, additively to BMI, risk of hypertension, MetS, and type 2 diabetes but only mediates adiposity against CHD risk.

Bilirubin inhibits neointima formation and vascular smooth muscle cell proliferation and migration

Bilirubin is a heme metabolite generated by the concerted action of the enzymes heme oxygenase and biliverdin reductase. Although long considered a toxic byproduct of heme catabolism, recent preclinical, and clinical studies indicate the bilirubin exerts beneficial effects in the circulation. In the present study, we determined whether local administration of bilirubin attenuates neointima formation following injury of rat carotid arteries. In addition, the ability of bilirubin to regulate the proliferation and migration of human arterial smooth muscle cells (SMCs) was investigated. Local perivascular administration of bilirubin immediately following balloon injury of rat carotid arteries significantly attenuated neointima formation. Bilirubin-mediated inhibition of neointimal thickening was associated with a significant decrease in ERK activity and cyclin D1 and A protein expression, and an increase in p21 and p53 protein expression in injured blood vessels. Treatment of human aortic SMCs with bilirubin inhibited proliferation and migration in a concentration-dependent manner without affecting cell viability. In addition, bilirubin resulted in a concentration-dependent increase in the percentage of cells in the G₀/G₁ phase of the cell cycle and this was paralleled by a decrease in the fraction of cells in the S and G₂M phases of the cell cycle. Finally, bilirubin had no effect on mitochondrial function and ATP content of vascular SMCs. In conclusion, these studies demonstrate that bilirubin inhibits neointima formation after arterial injury and this is associated with alterations in the expression of cell cycle regulatory proteins. Furthermore, bilirubin blocks proliferation and migration of human arterial SMCs and arrests SMCs in the G₀/G₁ phase of the cell cycle. Bilirubin represents an attractive therapeutic agent in treating occlusive vascular disease.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Bile pigments in pulmonary and vascular disease

The bile pigments, biliverdin, and bilirubin, are endogenously derived substances generated during enzymatic heme degradation. These compounds have been shown to act as chemical antioxidants in vitro. Bilirubin formed in tissues circulates in the serum, prior to undergoing hepatic conjugation and biliary excretion. The excess production of bilirubin has been associated with neurotoxicity, in particular to the newborn. Nevertheless, clinical evidence suggests that mild states of hyperbilirubinemia may be beneficial in protecting against cardiovascular disease in adults. Pharmacological application of either bilirubin and/or its biological precursor biliverdin, can provide therapeutic benefit in several animal models of cardiovascular and pulmonary disease. Furthermore, biliverdin and bilirubin can confer protection against ischemia/reperfusion injury and graft rejection secondary to organ transplantation in animal models. Several possible mechanisms for these effects have been proposed, including direct antioxidant and scavenging effects, and modulation of signaling pathways regulating inflammation, apoptosis, cell proliferation, and immune responses. The practicality and therapeutic-effectiveness of bile pigment application to humans remains unclear.

Bilirubin, renal hemodynamics, and blood pressure

Bilirubin is generated from the breakdown of heme by heme oxygenase and the reduction of biliverdin by the enzyme biliverdin reductase. Several large population studies have reported a significant inverse correlation between plasma bilirubin levels and the incidence of cardiovascular disease. Protection from cardiovascular disease is also observed in patients with Gilbert’s syndrome which is a disease characterized by mutations in hepatic UGT1A1, the enzyme responsible for the conjugation of bilirubin into the bile. Despite the strong correlation between plasma bilirubin levels and the protection from cardiovascular disease, the mechanism by which increases in plasma bilirubin acts to protect against cardiovascular disease is unknown. Since the chronic antihypertensive actions of bilirubin are likely due to its renal actions, the effects of moderate increases in plasma bilirubin on renal hemodynamics as well as bilirubin’s potential effects on renal tubule function will be discussed in this review. Mechanisms of action as well as the potential for antihypertensive therapies targeting moderate increases in plasma bilirubin levels will also be highlighted.

Unconjugated hyperbilirubinemia in patients with non-alcoholic fatty liver disease: a favorable endogenous response

The clinical significance of increased frequency of unconjugated hyperbilirubinemia in patients with non-alcoholic fatty liver disease (NAFLD) is unknown. Serum bilirubin is an endogenous anti-oxidant, and oxidative stress plays an important role in the pathogenesis of NAFLD. In this study, we have documented 25.4% prevalence of unconjugated hyperbilirubinemia in 204 consecutive NAFLD patients. These patients had a significantly less severe liver disease on histopathology and/or fibroScan which may be attributed to anti-oxidant effect of bilirubin.

Liver dysfunction in chronic heart failure: prevalence, characteristics and prognostic significance

BACKGROUND

Although abnormal liver morphology and function have long been recognized, characterization and importance of liver dysfunction in heart failure are poorly defined. This study sought to investigate the relevance of circulating liver function tests (LFTs) in an unselected chronic heart failure (CHF) cohort.

MATERIALS AND METHODS

A total of 1032 consecutive ambulatory patients with CHF were enrolled from 2000 to 2008. Clinical and laboratory variables including LFTs were collected at study entry. Follow-up (median 36 months) was available in 1002 (97·1%) patients. The endpoint was defined as death from any cause or heart transplantation. Hazard ratios (HR) for transplant-free survival were estimated per log unit using Cox proportional hazard regression models for sex-stratified data.

RESULTS

Sex-specific prevalence of cholestatic enzyme elevation was 19·2% as opposed to elevated transaminases in 8·3%. Cholestatic enzymes, but not transaminases, were significantly associated with severity of heart failure syndrome and backward failure. The endpoint was recorded in 339 patients (33·8%). T-Bil, γ-glutamyltransferase (GGT) and alkaline phosphatase (ALP) were associated with adverse outcome in bivariate models. Of these, GGT [HR 1·22 (1·06, 1·41); P = 0·006] and ALP [HR 1·52 (1·09, 2·12); P = 0·014] were independently associated with the endpoint after adjustment for a wide array of clinical and laboratory predictors.

CONCLUSIONS

Liver dysfunction is frequent in CHF and characterized by a predominantly cholestatic enzyme profile that is associated with disease severity and prognosis. Thus, we propose a cardio-hepatic syndrome in CHF. Future studies are needed to clarify the exact mechanisms of organ interaction.

A genome-wide search for non-UGT1A1 markers associated with unconjugated bilirubin level reveals significant association with a polymorphic marker near a gene of the nucleoporin family

Variants in the UGT1A1 gene and its promoter are known to determine levels of unconjugated bilirubin (UCB), but do not explain all cases of unconjugated hyperbilirubinemia. To discover associations with variants in genes other than UGT1A1, we undertook a genome-wide association study. We recruited 200 participants to cover the entire range of quantitative variation in UCB level. The data set -- after data curation, including analyses for population stratification and cryptic relatedness -- comprised genotypes at 512,349 SNP loci on 182 individuals. Quantitative trait locus (QTL) association analyses were performed, after adjusting the UCB level for effects of age, gender, and genotype at the dinucleotide (TA) insertion locus in UGT1A1 that is known to significantly modulate UCB level. A significant association of a polymorphic marker (rs2328136) near the NUP153 gene (which produces a 153 kDa nucleoporin) was obtained (p = 0.002, after multiple-testing correction). The frequency of the variant allele (A) at the rs2328136 locus in our study population is 40%, higher than most global populations. NUP153, whose product is a major regulatory factor in bidirectional transport of biomolecules across nucleus to cytosol, is associated with the transport of biliverdin reductase, which is important for bilirubin conjugation.

Metabolic syndrome: nature, therapeutic solutions and options

INTRODUCTION

Metabolic syndrome (MetS) defines the clustering in an individual of multiple metabolic abnormalities, based on central obesity and insulin resistance. In addition to its five components, prothrombotic and proinflammatory states are essential features. The significance of MetS lies in its close association with the risk of type 2 diabetes and cardiovascular disease (CVD). This field being an evolving one necessitated the current review.

AREAS COVERED

The areas covered in this review include the so far unproven concept that enhanced low-grade inflammation often leads to dysfunction of the anti-inflammatory and atheroprotective properties of apolipoprotein A-I (apoA-I) and HDL particles, which further increases the risk of diabetes and CVD. It was emphasized that lifestyle modification is essential in the prevention and management of MetS, which includes maintenance of optimal weight by caloric restriction, adherence to a diet that minimizes postprandial glucose and triglyceride fluctuations, restricting alcohol consumption, smoking cessation and engaging in regular exercise. Drug therapy should target the dyslipoproteinemia and the often associated hypertension or dysglycemia.Statins are the drugs of first choice, to be initiated in patients with MetS at high 10-year cardiovascular risk. Such treatment is inadequate if fasting serum triglycerides remain at > 150 mg/dl, when niacin should be combined. Fibrates, omega 3 fatty acids, metformin, angiotensin-converting enzyme inhibitors and pioglitazone are additional options in drug therapy.

EXPERT OPINION

Research on MetS in subpopulations prone to impaired glucose tolerance and insulin resistance has indicated that proinflammatory state and oxidative stress are often prominently involved in MetS, to the extent that evidence of impaired function of HDL and apo A-I particles is discernible by biological evidence of functional defectiveness via outcomes studies and/or correlations with inflammatory and anti-inflammatory biomarkers. A sex difference has been clear in this development.

High Total Bilirubin as a Protective Factor for Diabetes Mellitus: An Analysis of NHANES Data From 1999 - 2006

Background

Diabetes Mellitus (DM) is a rampantly growing epidemic in the United States, affecting nearly 10% of the adult population. Studies have shown that higher levels of Total Bilirubin (TBili) convey a protective effect with regard to cardiovascular risk. In this study, we will examine the relationship between TBili level and prevalence of DM to discern whether a similar relationship exists.

Methods

The National Health and Nutrition Examination Survey (NHANES) is a comprehensive survey performed regularly to evaluate the overall health and nutrition status of the United States population. For the purpose of this study, we combined NHANES data collected between 1999 and 2006. Totally 15,876 eligible participants were selected after excluding all patients younger than twenty years, those with a history of abnormal liver function tests, or those who disclosed a history of liver disease. The data collected on these individuals was adjusted for demographic characteristics, as well as risk factors for DM, and was analyzed via multivariate logistic regression, using SAS proc survey methodology.

Results

After age adjustment, increased TBili was associated with 26% reduction in diabetes risk (OR 0.74, 95% CI 0.64 - 0.88). Multivariate analysis, adjusting for all diabetes risk factors assessed, confirmed this association (OR 0.80, 95% CI 0.67 - 0.95).

Conclusions

Our results show that a higher level of serum TBili is associated with odds of having a lower incidence of DM. This finding supports the hypothesis that the antioxidant nature of TBili, demonstrating a protective effect with regard to the risk of stroke, atherosclerosis, and vasculitis in prior research, also extends to DM risk. Furthermore, research has shown that higher levels of TBili increase glucose mobilization into the cells, leading to more efficient, biologic glucose utilization. There is no doubt that the beneficial effect of TBili is multifactorial; thus further investigation is warranted.

Keywords

Bilirubin; Diabetes; Antioxidant; Protective

Mayo Genome Consortia: a genotype-phenotype resource for genome-wide association studies with an application to the analysis of circulating bilirubin levels

OBJECTIVE

To create a cohort for cost-effective genetic research, the Mayo Genome Consortia (MayoGC) has been assembled with participants from research studies across Mayo Clinic with high-throughput genetic data and electronic medical record (EMR) data for phenotype extraction.

PARTICIPANTS AND METHODS

Eligible participants include those who gave general research consent in the contributing studies to share high-throughput genotyping data with other investigators. Herein, we describe the design of the MayoGC, including the current participating cohorts, expansion efforts, data processing, and study management and organization. A genome-wide association study to identify genetic variants associated with total bilirubin levels was conducted to test the genetic research capability of the MayoGC.

RESULTS

Genome-wide significant results were observed on 2q37 (top single nucleotide polymorphism, rs4148325; P=5.0 × 10(-62)) and 12p12 (top single nucleotide polymorphism, rs4363657; P=5.1 × 10(-8)) corresponding to a gene cluster of uridine 5'-diphospho-glucuronosyltransferases (the UGT1A cluster) and solute carrier organic anion transporter family, member 1B1 (SLCO1B1), respectively.

CONCLUSION

Genome-wide association studies have identified genetic variants associated with numerous phenotypes but have been historically limited by inadequate sample size due to costly genotyping and phenotyping. Large consortia with harmonized genotype data have been assembled to attain sufficient statistical power, but phenotyping remains a rate-limiting factor in gene discovery research efforts. The EMR consists of an abundance of phenotype data that can be extracted in a relatively quick and systematic manner. The MayoGC provides a model of a unique collaborative effort in the environment of a common EMR for the investigation of genetic determinants of diseases.

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.

γ-Glutamyltransferase rather than total bilirubin predicts outcome in chronic heart failure

BACKGROUND

Gamma-glutamyltransferase (GGT) and total bilirubin (T-Bil) are elevated and of prognostic significance in chronic heart failure (CHF). This study sought to compare these novel cardiovascular risk markers in CHF.

METHODS AND RESULTS

We evaluated 1,087 ambulatory patients from our heart failure program. Long-term follow-up was available in 1,056 patients. The combined end point was defined as death of any cause or heart transplantation. Prevalence of elevated GGT was 43% in men and 48% in women, that of T-Bil 17% and 8%, respectively. Both variables were significantly correlated with severity of heart failure. GGT and T-Bil were associated with transplant-free survival in bivariate analysis (P values <.001 and .006, respectively). However, GGT (hazard ratio [HR] 1.28, 95% confidence interval [CI] 1.13-1.44; P < .001), but not T-Bil, remained an independent predictor of prognosis in the multivariate model. Also, categorized GGT levels beyond the gender-specific normal ranges were predictive of the combined end point (HR 1.55, 95% CI 1.23-1.95). Elevation of both GGT and T-Bil further increased the risk of reaching the end point (HR 2.57, 95% CI 1.74-3.18).

CONCLUSIONS

GGT and T-Bil are associated with disease severity in CHF. However, only GGT is independently associated with adverse outcome. Our findings further highlight the clinical importance of GGT in cardiovascular disease.