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

The correlation of serum bilirubin levels with disease activity in patients with rheumatoid arthritis

BACKGROUND

We investigated the relationship between serum bilirubin and disease activity in patients with rheumatoid arthritis (RA).

METHODS

We included a total of 173 consecutive RA patients without steroid treatment and 346 healthy subjects; the disease activity score in 28 joints (DAS28) was used to assess disease activity in patients with RA.

RESULTS

Serum bilirubin concentrations were significantly lower in RA patients than in controls. Serum bilirubin was found to be negatively correlated with C-reactive protein (CRP) concentration and erythrocyte sedimentation rate (ESR) (r=-0.165, P=0.030; r=-192, P=0.012) in patients with RA. There was a negative correlation between the serum bilirubin and DAS28 score (r=-0.331, P<0.001). Serum bilirubin was independently associated with the DAS28 score (b=-0.225, P=0.001) in the multiple linear regression analysis.

CONCLUSIONS

Serum bilirubin concentrations are lower in patients with RA compared to controls and correlate with disease activity in patients with RA.

Characteristics of the heme catabolic pathway in mild unconjugated hyperbilirubinemia and their associations with inflammation and disease prevention

Heme catabolism exerts physiological functions that impact health through depressing inflammation. Upon reactive pathway progression, as in Gilbert’s Syndrome (GS; UGT1A1*28 polymorphism), aggravated health effects have been determined. Based on lower inflammation and improved metabolic health reported for GS, inter-group differences in heme catabolism were explored. Therefore, a case-control study including 120 fasted, healthy, age- and gender matched subjects with/without GS, was conducted. Genetic expressions of HMOX-1 and BLVRA were measured. Additionally participants were genotyped for those polymorphisms that are known (UGT1A1*28) or likely (HMOX-1 microsatellites) to impact bilirubinemia. Intracellular interleukins (IL-6, IL-1β, TNFα), circulatory C-reactive protein (CRP), serum amyloid A (SAA) and haptoglobin (Hpt) were analysed as inflammatory markers. To assess intracellular heme oxygenase 1 (HO-1) isolated PBMCs were used. In GS vs. C, inflammation markers were significantly decreased. This was supported by an altered heme catabolism, indirectly reflecting in elevated unconjugated bilirubin (UCB; main phenotypic feature of GS) and iron, decreased hemopexin (Hpx) and Hpt and in up-regulated biliverdin reductase (BLVRA) gene expressions. Moreover, HMOX (GT)_n short alleles were non-significantly more prominent in female GS individuals. Herewith, we propose a concept to elucidate why GS individuals encounter lower inflammation, and are thus less prone to oxidative-stress mediated diseases.

Inverse Association between Serum Bilirubin Levels and Retinopathy in Patients with Type 2 Diabetes Mellitus

INTRODUCTION

Oxidative stress plays a central role in the pathogenesis of Diabetic Retinopathy (DR) and serum bilirubin has been shown to have antioxidant properties.

AIM

To investigate the association between serum bilirubin concentration and DR in patients with Type 2 Diabetes Mellitus (DM).

MATERIALS AND METHODS

This was a hospital based, cross- sectional study where in 86 patients with Type 2 DM and 30 controls were recruited. The study was conducted at a tertiary care centre in Southern India between January 2014 and December 2014. The presence and the severity of DR were determined by fundus examination and grading of colour fundus photographs using the international clinical disease severity scale for DR. Serum total, direct and indirect bilirubin levels were determined in all subjects and the association between bilirubin levels and severity of DR was studied.

RESULTS

Among the 86 diabetics, 24 had no retinopathy and 62 had DR of varying grades. The mean total bilirubin level among diabetic subjects (0.52±0.17) and controls (0.51±0.19) were found to be similar. The mean total as well as direct bilirubin levels were found to be lower in patients with retinopathy as compared to no retinopathy group (p<0.001). The severity of DR was inversely proportional to the serum bilirubin levels (p=0.010). Serum total bilirubin was found to have a negative association with glycosylated haemoglobin and served as an independent determinant of DR even after adjusting for risk factors known to be associated with DR (p=0.001).

CONCLUSION

Low serum bilirubin levels are significantly associated with increased risk of DR independent of classic risk factors. Serum bilirubin can serve as a useful biomarker in identifying patients at risk for developing proliferative DR.

Effect of bilirubin concentration on the risk of diabetic complications: A meta-analysis of epidemiologic studies

Diabetes can affect many parts of the body and is associated with serious complications. Oxidative stress is a major contributor in the pathogenesis of diabetic complications and bilirubin has been shown to have antioxidant effects. The number of studies on the effect of bilirubin on the risk of diabetic complications has increased, but the results are inconsistent. Thus, we performed a meta-analysis to determine the relationship between bilirubin concentration and the risk of diabetic complications, and to investigate if there was a dose-response relationship. We carried out an extensive search in multiple databases. A fixed or random-effects model was used to calculate the pooled estimates. We conducted a dose-response meta-analysis to analyze the association between these estimates. A total of 132,240 subjects from 27 included studies were analyzed in our meta-analysis. A negative nonlinear association between bilirubin concentration and the risk of diabetic complications was identified (OR: 0.77, 95% CI: 0.73-0.81), with a nonlinear association. We also found that there was a negative association between bilirubin concentration and the risk of diabetic nephropathy, diabetic retinopathy and diabetic neuropathy. The results of our meta-analysis indicate that bilirubin may play a protective role in the occurrence of diabetic complications.

Iron Supplementation Effects on Redox Status following Aseptic Skeletal Muscle Trauma in Adults and Children

Exercise-induced skeletal muscle microtrauma is characterized by loss of muscle cell integrity, marked aseptic inflammatory response, and oxidative stress. We examined if iron supplementation would alter redox status after eccentric exercise. In a randomized, double blind crossover study, that was conducted in two cycles, healthy adults (n = 14) and children (n = 11) received daily either 37 mg of elemental iron or placebo for 3 weeks prior to and up to 72 h after an acute eccentric exercise bout. Blood was drawn at baseline, before exercise, and 72 h after exercise for the assessment of iron status, creatine kinase activity (CK), and redox status. Iron supplementation at rest increased iron concentration and transferrin saturation (p < 0.01). In adults, CK activity increased at 72 h after exercise, while no changes occurred in children. Iron supplementation increased TBARS at 72 h after exercise in both adults and children; no changes occurred under placebo condition. Eccentric exercise decreased bilirubin concentration at 72 h in all groups. Iron supplementation can alter redox responses after muscle-damaging exercise in both adults and children. This could be of great importance not only for healthy exercising individuals, but also in clinical conditions which are characterized by skeletal muscle injury and inflammation, yet iron supplementation is crucial for maintaining iron homeostasis. This study was registered at Clinicaltrials.gov Identifier: NCT02374619.

Total bilirubin level may be a biomarker of nephropathy in type 2 diabetes mellitus: A meta-analysis of observational studies based on MOOSE compliant

Recently, the number of the studies on the relationship between the total bilirubin level (TBL) and diabetic nephropathy (DN) is increasing, but their results were not consistent. Therefore, we performed a meta-analysis to analyze the relationship between TBL and the risk of DN.We searched 5 databases before October 31, 2016, and reviewed the reference list of relevant articles. The fixed or random-effects model was used to pool risk estimates. We conducted the dose-response meta-analysis to evaluate the relationship between TBL and the risk of DN.Our meta-analysis showed that TBL in the DN group was lower than that in diabetes without the kidney disease (NDN) group (standard mean difference [SMD]: -0.63, 95% CI: -0.80, -0.46). The result of each subgroup also showed that TBL in the DN group was lower than that in the NDN group. The result of meta-regression indicated that duration of diabetes mellitus might be the source of heterogeneity. Our meta-analysis also showed that there was a significant negative relationship between TBL and the risk of DN (OR: 0.86, 95%CI: 0.82, 0.90). The results of subgroup analysis were similar to those of SMD; no sources of heterogeneity were detected by meta-regression. Sensitivity analysis indicated that the results were robust. We observed a linear association between TBL and the risk of DN, and there was a negative dose-response association between TBL and the risk of DN.In conclusion, bilirubin may be used as a biomarker of DN. It helps early diagnosis and effective therapeutic strategies on DN.

Mildly elevated serum total bilirubin is negatively associated with hemoglobin A1c independently of confounding factors among community-dwelling middle-aged and elderly persons

Abnormally high glycated hemoglobin (Hb) (HbA1c) is significantly associated with oxidative stress and an increased risk of cardiovascular disease (CVD). Serum total bilirubin (T-B) may have a beneficial role in preventing oxidative changes and be a negative risk factor of CVD. Limited information is available on whether serum T-B is an independent confounding factor of HbA1c. The study subjects were 633 men aged 70 ± 9 (mean ± standard deviation (SD)) years and 878 women aged 70 ± 8 years who were enrolled consecutively from among patients aged ≥40 years through a community-based annual check-up process. We evaluated the relationship between various confounding factors including serum T-B and HbA1c in each gender. Multiple linear regression analysis pertaining to HbA1c showed that in men, serum T-B (β = -0.139) as well as waist circumference (β = 0.099), exercise habit (β = 0.137), systolic blood pressure (SBP) (β = 0.076), triglycerides (β = 0.087), and uric acid (β = -0.123) were significantly and independently associated with HbA1c, and in women, serum T-B (β = -0.084) as well as body mass index (β = 0.090), smoking status (β = -0.077), SBP (β = 0.117), diastolic blood pressure (DBP) (β = -0.155), low-density lipoprotein cholesterol (β = 0.074), prevalence of antidyslipidemic medication (β = 0.174), and uric acid (β = 0.090) were also significantly and independently associated with HbA1c. Multivariate-adjusted serum HbA1c levels were significantly high in subjects with the lowest serum T-B levels in both genders. Serum T-B is an independent confounding factor for HbA1c among community-dwelling middle-aged and elderly persons.

Association of circulating total bilirubin with the metabolic syndrome and type 2 diabetes: A systematic review and meta-analysis of observational evidence

OBJECTIVE

Emerging evidence suggests that bilirubin levels might be associated with the metabolic syndrome (MetS) and type 2 diabetes (T2D), although the nature of the association remains unclear.

DESIGN

This systematic review and meta-analysis investigated the relationship between total plasma bilirubin and the risk of MetS and T2D.

DATA SOURCES

Relevant studies were identified using five databases (Embase, Medline [Ovid], Web of Science, PubMed, Cochrane Central and Google Scholar), with the last search done on 21 October 2015. Study references were checked and authors contacted to identify additional studies.

STUDY SELECTION

Randomized controlled trials, and cohort, case-control and cross-sectional studies of adults examining the association between blood bilirubin levels and MetS and T2D were included, irrespective of language and date of publication. Abstract and full-text selection was done by two independent reviewers, with a third reviewer available in case of disagreement.

DATA EXTRACTION

Data were extracted by two independent reviewers using a predesigned data collection form.

MAIN OUTCOMES AND MEASURES

MetS and T2D.

METHODS

Summary estimates were obtained by random-effects meta-analysis.

RESULTS

Of the 2313 searched references, 16 observational studies (11 cross-sectional, two prospective, one that was both cross-sectional and prospective, two retrospective and one national survey) met our inclusion criteria. Overall, data were available for 175,911 non-overlapping participants, including 7414 MetS cases and 9406 T2D cases. In the meta-analysis of seven cross-sectional studies, the pooled odds ratio (95% confidence interval) for MetS in a comparison of extreme tertiles of serum bilirubin levels was 0.70 (95% CI: 0.62, 0.78), whereas no significant association was found for the pooled estimated relative risk between two prospective studies (0.57, 95% CI: 0.11, 2.94). The corresponding estimate was 0.77 (95% CI: 0.67, 0.87) for T2D from four cross-sectional studies.

CONCLUSION

The available evidence, mainly from cross-sectional studies, supports an inverse association of bilirubin levels with adverse metabolic outcomes. Large-scale prospective studies are now needed to establish whether bilirubin levels may be useful in the prevention of MetS and T2D.

Effect of road transportation on the serum biochemical parameters of cynomolgus monkeys and beagle dogs

To determine the effect of long-distance (approximately 600 km) road transportation on the blood biochemistry of laboratory animals, we investigated the changes in serum biochemical parameters in healthy cynomolgus monkeys and beagle dogs transported by truck from Osaka to Tsukuba, Japan. The concentrations of serum cortisol, total bilirubin and aspartate aminotransferase in monkeys increased during transportation. Serum cortisol and total bilirubin levels in dogs also increased during transportation, but serum triglyceride decreased. Serum parameter values in truck-transported monkeys and dogs returned to baseline levels within two weeks following arrival. Taken together, these results suggest that a two-week acclimation period is the minimum duration required for adaptation following road transportation.

Does bilirubin protect against developing diabetes mellitus?

After 25 years of evaluating bilirubin as a possible protective agent in neonatal and cardiovascular disease, interest has moved on to a exploring a possible protective role in diabetes mellitus (DM). This review finds conflicting prospective data for a protective relationship though there are retrospective, case-controlled data, that can only show association, which is not causality. Only prospective studies can show causality. Also, it would appear that the underlying biochemical assumptions do not readily translate from the animal to the human setting. Given that many factors impact on circulating bilirubin levels, it is not surprising that a clear-cut answer is not available; the jury is still out. Any relationship between DM and bilirubin might relate to intermediates in bilirubin metabolism, including relationships involving the genes for the enzymes participating in those steps. Nevertheless, the pursuit of bilirubin in disease causation is opening new avenues for research and if it is established that serum bilirubin can predict risks, much will have been achieved. The answer may have to come from molecular genetic analyses.

Initial Total Bilirubin and Clinical Outcome in Patients With ST-Segment Elevation Myocardial Infarction Undergoing Primary Percutaneous Coronary Intervention With Drug-Eluting Stents

BACKGROUND

Total bilirubin (TB) concentration is inversely associated with stable coronary artery disease, but there have been few studies on initial TB in patients with ST-segment elevation myocardial infarction (STEMI).

METHODS AND RESULTS

A total of 1,111 consecutive patients with STEMI undergoing primary percutaneous coronary intervention (PCI) with drug-eluting stents (DES) were divided into a high TB group (n=295) and a low TB group (n=816) according to the optimal cut-off 0.79 mg/dl. The high TB group had a higher rate of in-hospital major adverse cardiac events (MACE), a composite of cardiac death, non-fatal MI, and definite/probable stent thrombosis (14.2% vs. 4.2%, P<0.001) and cardiac death (13.9% vs. 3.9%, P<0.001) compared with the low TB group. The 30-day MACE-free survival rate was also significantly different between the groups (P<0.001, log-rank test). On multivariate Cox regression, initial high TB was a significant predictor of in-hospital MACE (HR, 2.69; 95% CI: 1.67-4.34, P=0.010) and of cardiac death (HR 2.72, 95% CI: 1.67-4.44, P=0.012). Adding initial TB to TIMI risk score significantly improved prediction for in-hospital MACE according to net reclassification improvement (NRI=5.2%, P=0.040) and integrated discrimination improvement (IDI=0.027, P=0.006).

CONCLUSIONS

Initial TB is a powerful prognostic marker, and inclusion of this can improve prediction of in-hospital MACE in patients with STEMI undergoing primary PCI with DES. (Circ J 2016; 80: 1437-1444).

Innovative biomarkers for predicting type 2 diabetes mellitus: relevance to dietary management of frailty in older adults

Type 2 diabetes mellitus (T2DM) increases in prevalence in the elderly. There is evidence for significant muscle loss and accelerated cognitive impairment in older adults with T2DM; these comorbidities are critical features of frailty. In the early stages of T2DM, insulin sensitivity can be improved by a "healthy" diet. Management of insulin resistance by diet in people over 65 years of age should be carefully re-evaluated because of the risk for falling due to hypoglycaemia. To date, an optimal dietary programme for older adults with insulin resistance and T2DM has not been described. The use of biomarkers to identify those at risk for T2DM will enable clinicians to offer early dietary advice that will delay onset of disease and of frailty. Here we have used an in silico literature search for putative novel biomarkers of T2DM risk and frailty. We suggest that plasma bilirubin, plasma, urinary DPP4-positive microparticles and plasma pigment epithelium-derived factor merit further investigation as predictive biomarkers for T2DM and frailty risk in older adults. Bilirubin is screened routinely in clinical practice. Measurement of specific microparticle frequency in urine is less invasive than a blood sample so is a good choice for biomonitoring. Future studies should investigate whether early dietary changes, such as increased intake of whey protein and micronutrients that improve muscle function and insulin sensitivity, affect biomarkers and can reduce the longer term complication of frailty in people at risk for T2DM.

The Biological Effects of Bilirubin Photoisomers

Although phototherapy was introduced as early as 1950’s, the potential biological effects of bilirubin photoisomers (PI) generated during phototherapy remain unclear. The aim of our study was to isolate bilirubin PI in their pure forms and to assess their biological effects in vitro. The three major bilirubin PI (ZE- and EZ-bilirubin and Z-lumirubin) were prepared by photo-irradiation of unconjugated bilirubin. The individual photoproducts were chromatographically separated (TLC, HPLC), and their identities verified by mass spectrometry. The role of Z-lumirubin (the principle bilirubin PI) on the dissociation of bilirubin from albumin was tested by several methods: peroxidase, fluorescence quenching, and circular dichroism. The biological effects of major bilirubin PI (cell viability, expression of selected genes, cell cycle progression) were tested on the SH-SY5Y human neuroblastoma cell line. Lumirubin was found to have a binding site on human serum albumin, in the subdomain IB (or at a close distance to it); and thus, different from that of bilirubin. Its binding constant to albumin was much lower when compared with bilirubin, and lumirubin did not affect the level of unbound bilirubin (Bf). Compared to unconjugated bilirubin, bilirubin PI did not have any effect on either SH-SY5Y cell viability, the expression of genes involved in bilirubin metabolism or cell cycle progression, nor in modulation of the cell cycle phase. The principle bilirubin PI do not interfere with bilirubin albumin binding, and do not exert any toxic effect on human neuroblastoma cells.

Recent insights into the biological functions of liver fatty acid binding protein 1

Over four decades have passed since liver fatty acid binding protein (FABP)1 was first isolated. There are few protein families for which most of the complete tertiary structures, binding properties, and tissue occurrences are described in such detail and yet new functions are being uncovered for this protein. FABP1 is known to be critical for fatty acid uptake and intracellular transport and also has an important role in regulating lipid metabolism and cellular signaling pathways. FABP1 is an important endogenous cytoprotectant, minimizing hepatocyte oxidative damage and interfering with ischemia-reperfusion and other hepatic injuries. The protein may be targeted for metabolic activation through the cross-talk among many transcriptional factors and their activating ligands. Deficiency or malfunction of FABP1 has been reported in several diseases. FABP1 also influences cell proliferation during liver regeneration and may be considered as a prognostic factor for hepatic surgery. FABP1 binds and modulates the action of many molecules such as fatty acids, heme, and other metalloporphyrins. The ability to bind heme is another cytoprotective property and one that deserves closer investigation. The role of FABP1 in substrate availability and in protection from oxidative stress suggests that FABP1 plays a pivotal role during intracellular bacterial/viral infections by reducing inflammation and the adverse effects of starvation (energy deficiency).

Evidences of Biological Functions of Biliverdin Reductase A in the Bovine Epididymis

Epididymal sperm binding protein 1 (ELSPBP1) is secreted by the epididymal epithelium via epididymosomes and is specifically transferred to dead spermatozoa during epididymal transit. We identified biliverdin reductase A (BLVRA) as a partner of ELSPBP1 by immunoprecipitation followed by tandem mass spectrometry. Pull down assays showed that these two proteins interact in the presence of zinc ions. The BLVRA enzyme is known to convert biliverdin to bilirubin, both of which possess antioxidant activity. Assessment by real-time RT-PCR showed that BLVRA is highly expressed in the caput and the corpus epididymis, but is expressed at lower levels in the testis and the cauda epididymis. It is primarily found in the soluble fraction of the caput epididymal fluid, is barely detectable in the cauda fluid, and is detectable to a lesser extent in the epididymosome fraction of both caput and cauda fluids. Immunocytometry on epididymal sperm showed that BLVRA is found on all sperm recovered from the caput region, whereas it is undetectable on cauda sperm. Biliverdin and bilirubin are found in higher concentrations in the caput epididymal fluid, as measured by mass spectrometry. Lipid peroxidation was limited by 1 μM of biliverdin, but not bilirubin when caput spermatozoa were challenged with 500 μM H2O2. Since immature spermatozoa are a source of reactive oxygen species, BLVRA may be involved in the protection of maturing spermatozoa. It is also plausible that BLVRA is implicated in haemic protein catabolism in the epididymal luminal environment.

Age-related responses in circulating markers of redox status in healthy adolescents and adults during the course of a training macrocycle

Redox status changes during an annual training cycle in young and adult track and field athletes and possible differences between the two age groups were assessed. Forty-six individuals (24 children and 22 adults) were assigned to four groups: trained adolescents, (TAD, N = 13), untrained adolescents (UAD, N = 11), trained adults (TA, N = 12), and untrained adults (UA, N = 10). Aerobic capacity and redox status related variables [total antioxidant capacity (TAC), glutathione (GSH), catalase activity, TBARS, protein carbonyls (PC), uric acid, and bilirubin] were assessed at rest and in response to a time-trial bout before training, at mid- and posttraining. TAC, catalase activity, TBARS, PC, uric acid, and bilirubin increased and GSH declined in all groups in response to acute exercise independent of training status and age. Training improved aerobic capacity, TAC, and GSH at rest and in response to exercise. Age affected basal and exercise-induced responses since adults demonstrated a greater TAC and GSH levels at rest and a greater rise of TBARS, protein carbonyls, and TAC and decline of GSH in response to exercise. Catalase activity, uric acid, and bilirubin responses were comparable among groups. These results suggest that acute exercise, age, and training modulate the antioxidant reserves of the body.

Looking to the horizon: the role of bilirubin in the development and prevention of age-related chronic diseases

Bilirubin, the principal tetrapyrrole, bile pigment and catabolite of haem, is an emerging biomarker of disease resistance, which may be related to several recently documented biological functions. Initially believed to be toxic in infants, the perception of bilirubin has undergone a transformation: it is now considered to be a molecule that may promote health in adults. Data from the last decade demonstrate that mildly elevated serum bilirubin levels are strongly associated with reduced prevalence of chronic diseases, particularly cardiovascular diseases (CVDs), as well as CVD-related mortality and risk factors. Recent data also link bilirubin to other chronic diseases, including cancer and Type 2 diabetes mellitus, and to all-cause mortality. Therefore, there is evidence to suggest that bilirubin is a biomarker for reduced chronic disease prevalence and a predictor of all-cause mortality, which is of important clinical significance. In the present review, detailed information on the association between bilirubin and all-cause mortality, as well as the pathological conditions of CVD, cancer, diabetes and neurodegenerative diseases, is provided. The mechanistic background concerning how bilirubin and its metabolism may influence disease prevention and its clinical relevance is also discussed. Given that the search for novel biomarkers of these diseases, as well as for novel therapeutic modalities, is a key research objective for the near future, bilirubin represents a promising candidate, meeting the criteria of a biomarker, and should be considered more carefully in clinical practice as a molecule that might provide insights into disease resistance. Clearly, however, greater molecular insight is warranted to support and strengthen the conclusion that bilirubin can prevent disease, with future research directions also proposed.

Circulating Total Bilirubin and Risk of Incident Cardiovascular Disease in the General Population

Objective—

To assess the association of circulating total bilirubin and cardiovascular disease (CVD) risk in a new prospective study and to determine whether adding information on total bilirubin values to established cardiovascular risk factors is associated with improvement in prediction of CVD risk.

Approach and Results—

Circulating total bilirubin levels were measured at baseline in the PREVEND (Prevention of Renal and Vascular End-stage Disease) prospective study of 7222 participants and 773 incident CVD events. Total bilirubin was log-linearly associated with CVD risk. Age- and sex-adjusted hazard ratio (95% confidence interval) for CVD per 1-SD increase in log e total bilirubin was 0.82 (0.76 to 0.88; P <0.001), which was minimally attenuated to 0.89 (0.82 to 0.96; P =0.003) after further adjustment for established risk factors. In a meta-analysis of 12 population-based prospective studies involving 9378 incident CVD cases, the pooled multivariate-adjusted relative risk (95% confidence interval) for CVD was 0.93 (0.90 to 0.97; P <0.001) per 1-SD increase in total bilirubin levels. The corresponding pooled risks for coronary heart disease and stroke were 0.95 (0.92 to 0.99; P =0.018) and 0.93 (0.88 to 0.98; P =0.006), respectively. Addition of information on total bilirubin to a CVD risk prediction model containing established risk factors was associated with a C-index change of 0.0013 (−0.0004 to 0.0029; P =0.13).

Conclusions—

There is a log-linear inverse association between circulating total bilirubin level and CVD risk, which is independent of established risk factors. Nonetheless, inclusion of total bilirubin in the standard established risk factors panel provides no significant improvement in CVD risk prediction.

Oregonin reduces lipid accumulation and proinflammatory responses in primary human macrophages

Inflammation in the vascular wall is important for the development of atherosclerosis. We have previously shown that inflammatory macrophages are more abundant in human atherosclerotic lesions than in healthy arteries. Activated macrophages produce reactive oxygen species (ROS) that promote local inflammation in atherosclerotic lesions. Here, we investigated the role of oregonin, a diarylheptanoid, on proinflammatory responses in primary human macrophages and found that oregonin decreased cellular lipid accumulation and proinflammatory cytokine secretion. We also found that oregonin decreased ROS production in macrophages. Additionally, we observed that treatment of lipopolysaccharide-exposed macrophages with oregonin significantly induced the expression of antioxidant-related genes, including Heme oxygenase-1 and NADPH dehydrogenase quinone 1. In summary, we have shown that oregonin reduces lipid accumulation, inflammation and ROS production in primary human macrophages, indicating that oregonin has anti-inflammatory bioactivities.

Serum bilirubin and the risk of hypertension

BACKGROUND

Experimental studies suggest oxidative stress could lead to the development of hypertension. Serum bilirubin is a major contributor to the antioxidant capacity in blood plasma and has been identified as an independent cardiovascular risk factor in cohort studies. However, data on the relationship between bilirubin and blood pressure are scarce and inconclusive.

METHODS

We analysed data from the National Health and Nutrition Examination Surveys (NHANES) 1999-2012 (N=31069). Fifty multiple imputed data sets were generated and analysed to avoid selection/confounding bias due to excluding individuals/variables with missing values. A minimal sufficient adjustment set of variables (MSAS) needed to estimate the unconfounded effect of bilirubin on blood pressure and hypertension (systolic/diastolic blood pressure ≥ 140/90 mmHg or using antihypertensive medication) was identified using the back-door criterion and included in all regression models.

RESULTS

After adjustment for the MSAS variables, systolic blood pressure decreased progressively up to -2.5 mmHg (p<0.001) and the prevalence of hypertension was up to 25% lower (P<0.001) in those with bilirubin ≥ 1.0 mg/dl-the highest two deciles-compared with those with 0.1-0.4 mg/dl-the lowest decile. Sensitivity analyses showed these results were unlikely to be explained by residual confounding or selection bias.

CONCLUSIONS

High serum bilirubin may decrease the risk of hypertension by inactivating and inhibiting the synthesis of reactive oxygen species in vascular cells. Strategies to boost the bioavailability of circulating and tissue bilirubin or to mimic bilirubin's antioxidant properties could have a significant impact on prevention and control of hypertension as well as coronary heart disease.

Cross-sectional and longitudinal associations between serum bilirubin and dyslipidemia in a health screening population

OBJECTIVE

To investigate cross-sectional and longitudinal associations between serum total bilirubin (TB) and dyslipidemia.

METHODS

Odds ratios (ORs) of prevalent dyslipidemia for TB were calculated in 2113 men and 1265 women. Correlation coefficients between baseline TB as well as the change in TB over 5 years and baseline log triglycerides, baseline HDL cholesterol and the changes in log triglycerides and HDL cholesterol over 5 years were calculated. Hazard ratios (HRs) of incident hypertriglyceridemia and hypo-HDL cholesterolemia for TB over 5 years were calculated in 1324 men and 915 women and 1583 men and 884 women, respectively.

RESULTS

The ORs of prevalent hypertriglyceridemia and hypo-HDL cholesterolemia for each one SD increase in TB were 0.83 (p < 0.001) in men and 0.71 (p = 0.074) in women and 0.64 (p < 0.001) in men and 0.78 (p = 0.089) in women, respectively adjusted for age, smoking, and other confounders. The baseline TB was significantly correlated with baseline log triglycerides and HDL cholesterol both in men and women while the change in TB was significantly correlated with the changes in log triglycerides and HDL cholesterol in men and the change in HDL cholesterol in women. The HRs of incident hypertriglyceridemia and hypo-HDL cholesterolemia for each one SD increase in TB were 0.99 (p = 0.848) in men and 0.74 (p = 0.033) in women and 1.08 (p = 0.345) in men and 0.85 (p = 0.220) in women, respectively adjusted for age, smoking, and other confounders.

CONCLUSION

Baseline TB was significantly associated with both prevalent hypertriglyceridemia and hypo-HDL cholesterolemia in men and with incident hypertriglyceridemia in women.

UGT1A1*28 polymorphism and acute lymphoblastic leukemia in children: a Danish case-control study

BACKGROUND

Oxidative stress is a possible risk factor in the development of acute lymphoblastic leukemia (ALL) in children. Bilirubin is a potent endogenous antioxidant, and the UGT1A1*28 polymorphism is the main genetic cause of variation in plasma bilirubin in Western Europe.

METHODS

In a case-control study of 665 incident cases of ALL in childhood in Denmark 1982-2010 and 1,379 controls, associations between UGT1A1*28 genotypes and ALL in childhood were estimated as odds ratios by logistic regression with adjustment for sex and birth decade. Subgroup analyses were carried out by age at onset in three groups, and on the ALL subtypes precursor B-cell, T-cell, and t(12;21) positive status. Cases were identified in The Danish Registry of Childhood Cancer, and genotypes were estimated from dried blood spots stored in The Danish Neonatal Screening Biobank. Controls were newborns with blood spots taken right before and after a case.

RESULTS

We found no association between ALL in childhood and UGT1A1*28 genotypes. The odds ratio was 1.01 (0.88-1.17) for heterozygotes and 1.03 (0.78-1.36) for homozygotes. Also, no associations were found in the subgroup analyses.

CONCLUSION

We found no association between the UGT1A1*28 genotypes and ALL in children.

Quantitative assessment of the multiple processes responsible for bilirubin homeostasis in health and disease

Serum bilirubin measurements are commonly obtained for the evaluation of ill patients and to screen for liver disease in routine physical exams. An enormous research effort has identified the multiple mechanisms involved in the production and metabolism of conjugated (CB) and unconjugated bilirubin (UB). While the qualitative effects of these mechanisms are well understood, their expected quantitative influence on serum bilirubin homeostasis has received less attention. In this review, each of the steps involved in bilirubin production, metabolism, hepatic cell uptake, and excretion is quantitatively examined. We then attempt to predict the expected effect of normal and defective function on serum UB and CB levels in health and disease states including hemolysis, extra- and intrahepatic cholestasis, hepatocellular diseases (eg, cirrhosis, hepatitis), and various congenital defects in bilirubin conjugation and secretion (eg, Gilbert's, Dubin-Johnson, Crigler-Najjar, Rotor syndromes). Novel aspects of this review include: 1) quantitative estimates of the free and total UB and CB in the plasma, hepatocyte, and bile; 2) detailed discussion of the important implications of the recently recognized role of the hepatic OATP transporters in the maintenance of CB homeostasis; 3) discussion of the differences between the standard diazo assay versus chromatographic measurement of CB and UB; 4) pharmacokinetic implications of the extremely high-affinity albumin binding of UB; 5) role of the enterohepatic circulation in physiologic jaundice of newborn and fasting hyperbilirubinemia; and 6) insights concerning the clinical interpretation of bilirubin measurements.

Inherited disorders of bilirubin transport and conjugation: new insights into molecular mechanisms and consequences

Inherited disorders of bilirubin metabolism might reduce bilirubin uptake by hepatocytes, bilirubin conjugation, or secretion of bilirubin into bile. Reductions in uptake could increase levels of unconjugated or conjugated bilirubin (Rotor syndrome). Defects in bilirubin conjugation could increase levels of unconjugated bilirubin; the effects can be benign and frequent (Gilbert syndrome) or rare but severe, increasing the risk of bilirubin encephalopathy (Crigler-Najjar syndrome). Impairment of bilirubin secretion leads to accumulation of conjugated bilirubin (Dubin-Johnson syndrome). We review the genetic causes and pathophysiology of disorders of bilirubin transport and conjugation as well as clinical and therapeutic aspects. We also discuss the possible mechanisms by which hyperbilirubinemia protects against cardiovascular disease and the metabolic syndrome and the effects of specific genetic variants on drug metabolism and cancer development.

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.

Using exhaled carbon monoxide and carboxyhemoglobin to evaluate the effectiveness of a chimney stove model in Peru

BACKGROUND

Measurement of biological indicators of physiological change may be useful in evaluating the effectiveness of stove models, which are intended to reduce indoor smoke exposure and potential health effects.

OBJECTIVES

We examined changes in exhaled carbon monoxide (CO), percentage carboxy-hemoglobin, and total hemoglobin in response to the installation of a chimney stove model by the Juntos National Program in Huayatan, Peru in 2008.

METHODS

Biomarkers were measured in a convenience sample comprising 35 women who met requirements for participation, and were measured before and three weeks after installation of a chimney stove. The relationships between exposure to indoor smoke and biomarker measurements were also analyzed using simple linear regression models.

RESULTS

Exhaled CO reduced from 6.71 ppm (95% CI 5.84-7.71) to 3.14 ppm (95% CI 2.77-3.66) three weeks after stove installation (P < 0.001) while % COHb reduced from 1.76% (95% CI 1.62-1.91) to 1.18% (95% CI 1.12-1.25; P < 0.001). Changes in exhaled CO and % COHb from pre- to post-chimney stove installation were not correlated with corresponding changes in exposure to CO and PM2.5 even though the exposures also reduced after stove installation.

CONCLUSION

Exhaled CO and % COHb both showed improvement with reduction in concentration after the installation of the chimney cook stoves, indicating a positive physiological response subsequent to the intervention.

The relationship of the anti-oxidant bilirubin with free thyroxine is modified by insulin resistance in euthyroid subjects

Background

The strong anti-oxidative properties of bilirubin largely explain its cardioprotective effects. Insulin resistance is featured by low circulating bilirubin. Thyroid hormone affects both bilirubin generation and its biliary transport, but it is unknown whether circulating bilirubin is associated with thyroid function in euthyroid subjects. Aim is to determine relationships of bilirubin with TSH, free T₄ and free T₃ in euthyroid subjects without type 2 diabetes mellitus (T2DM), and to assess whether such a relationship would be modified by the degree of insulin resistance.

Methods

Total bilirubin, TSH, free T₄, free T₃, glucose, insulin, lipids and transaminases were measured in 1854 fasting euthyroid subjects without T2DM, recruited from the general population (PREVEND cohort). Insulin resistance was assessed by homeostasis model assessment.

Results

Bilirubin was positively related to free T₄ (β = 0.116, P<0.001) and free T₃ (β = 0.078, P = 0.001), but bilirubin was unrelated to TSH. The relationship of bilirubin with free T₄ was modified by insulin resistance with a larger effect in more insulin resistant individuals (adjusted for age and sex: β = 0.043, P = 0.056 for interaction; additionally adjusted for smoking, alcohol intake, transaminases and total cholesterol (β = 0.044, P = 0.044 for interaction). The association of bilirubin with free T₄ was also modified by high density lipoprotein cholesterol (age- and sex-adjusted: β = 0.040, P = 0.072).

Conclusions

Low bilirubin relates to low free T₄ in euthyroid non-diabetic subjects. Low normal free T₄ may particularly confer low bilirubin in more insulin resistant individuals.

The relationship between serum bilirubin and Crohn's disease

BACKGROUND

The oxidative stress is thought to play an important role in Crohn's disease (CD). As serum bilirubin represents the major endogenous antioxidant, this article aimed to evaluate in a clinical study, whether serum bilirubin levels and genes affecting its systemic concentrations are associated with CD.

METHODS

This exploratory case-control study was based on pediatric (n = 119) and adult (n = 504) patients with CD and 370 appropriate healthy control subjects. The (GT)n and (TA)n dinucleotide variations in heme oxygenase 1 (HMOX1) and bilirubin UDP-glucuronosyl transferase (UGT1A1) gene promoters were determined by fragment analysis. Serum bilirubin levels were compared in a subset of 90 cases and 229 controls, for whom biochemical data were available.

RESULTS

Substantially lower serum bilirubin levels were detected in patients with CD compared with controls (7.4 versus 12.1 μmol/L, P < 10). Serum bilirubin levels were significantly lower in patients with CD within all UGT1A1*28 genotypes (P < 0.05). UGT1A1*28 homozygotes with wild-type NOD2 gene variant exhibited significant delay in CD manifestation (P = 0.004), while the protective effect of UGT1A1*28 homozygosity was lost in those patients with mutated NOD2 gene. No associations between CD risk and individual HMOX1 gene variants were observed.

CONCLUSIONS

CD is associated with significantly low serum bilirubin levels, most likely as a result of increased oxidative stress accompanying this inflammatory disease. UGT1A1*28 allele homozygosity, responsible for higher bilirubin levels, seems to be an important modifier of CD manifestation.

The effect of heme oxygenase on ganglioside redistribution within hepatocytes in experimental estrogen-induced cholestasis

Cholestasis is characterized by the elevation of serum total bile acids (TBA), which leads to the production of both free radicals and oxidative stress. Although they do not share the same mechanisms, membrane glycosphingolipids (GSL) and the antioxidant enzyme heme oxygenase-1 (HMOX1) both act against the pro-oxidative effect of TBA. The aim of the study was to assess the role of HMOX on GSL redistribution and composition within hepatocytes in the rat model of estrogen-induced cholestasis. Compared to the controls, an increase of total gangliosides in the liver homogenates of the cholestatic group (P=0.001) was detected; further, it paralleled along with the activation of their biosynthetic b-branch pathway (P<0.01). These effects were partially prevented by HMOX activation. Cholestasis was accompanied by a redistribution of GM1 ganglioside from the cytoplasm to the sinusoids; while HMOX activation led to the retention of GM1 in the cytoplasm (P=0.014). Our study shows that estrogen-induced cholestasis is followed by changes in the synthesis and/or distribution of GSL. These changes are not only triggered by the detergent power of accumulated TBA, but also by their pro-oxidant action. Increases in the antioxidant defenses might represent an important supportive therapeutic measure for patients with cholestatic liver disease.

Higher serum bilirubin level as a protective factor for the development of diabetes in healthy Korean men: a 4 year retrospective longitudinal study

OBJECTIVE

Bilirubin, a natural product of heme catabolism by heme oxygenase, one of key antioxidant enzymes, has been recognized as a substance with potent antioxidant and cytoprotective properties. Several studies have shown a significant negative relationship between serum bilirubin levels and the risk of metabolic disorders, including type 2 diabetes. However, longitudinal studies investigating the association of elevated serum bilirubin levels and type 2 diabetes are lacking. In the present study, we aimed to investigate the longitudinal effects of baseline serum bilirubin concentrations on the development of type 2 diabetes in healthy Korean men.

MATERIALS AND METHODS

This 4 year retrospective longitudinal observational study was conducted at the Asan Medical Center, Seoul, Republic of Korea. The study population consisted of 5960 men without type 2 diabetes who underwent routine health examinations in 2007 (baseline) and 2011 (follow-up). Baseline serum bilirubin concentrations were determined by the vanadate oxidation method.

RESULTS

During a 4 year period, 409 incident cases of diabetes (6.9 %) were identified. Incident type 2 diabetes decreased across the baseline bilirubin quartile categories (P for trend <0.001). In multivariable-adjusted model, the relative risk (RR) for the development of type 2 diabetes was significantly lower in the highest (i.e., 1.30-2.00 mg/dl) than in the lowest bilirubin quartile category (i.e., ≤ 0.90 mg/dl), even after adjustment for confounding variables (RR=0.69, 95% confidence interval 0.48-0.99, P for trend = 0.041).

CONCLUSIONS

The results indicate that serum total bilirubin level may provide additional information for predicting future development of type 2 diabetes in healthy subjects.

Interaction between TNFone and tetrapyrroles may account for their anti-genotoxic effects — a novel mechanism for DNA-protection

Bilirubin, the principal and biologically most relevant bile pigment was, until recently, considered a waste product of haem catabolism. However, current data suggest that bile pigments possess biological potential, related to their antioxidant and anti-mutagenic effects. In this context, it is now assumed that bile pigments and their derivatives exert these effects via multiple mechanisms, including discrete anti-oxidative and physico-chemical interactive effects. The major scientific focus so far has concentrated on the compounds' antioxidant action, and mechanistic investigations of possible mutagen-tetrapyrrole interaction are lacking. Therefore we tested structurally related bile pigments/derivatives (bilirubin/-ditaurate/-dimethyl ester, biliverdin/-dimethyl ester, urobilin, stercobilin and protoporphyrin) for anti-genotoxicity in the Salmonella reverse mutation assay (strains TA98, TA102), together with the synthetic mutagen 2,4,7-trinitro-9H-fluoren-9-one (TNFone). To explore possible structural interactions, molecular systems of chlorin e6 porphyrin/bilirubin/biliverdin with TNFone were assayed using circular dichroism. These data consistently revealed, at suprastoichiometric concentrations, that tetrapyrroles interact with TNFone. Addition of TNFone to chlorin e6 porphyrin, bilirubin-albumin and biliverdin-albumin led to a marked change in pigment spectra, providing evidence for tight tetrapyrrole-mutagen interaction. This conclusion was also supported by substantial, TNFone-induced decrease of bilirubin oxidation in the bilirubin-albumin system. This outcome was reflected in a bacterial model, in which most tetrapyrroles and especially protoporphyrin, significantly attenuated TNFone-induced mutagenesis. These data indicate that aromatic, tetrapyrrolic molecules interact with TNFone, providing a novel mechanism to suggest the anti-mutagenic effects of bile pigments in vivo are related to their physico-chemical interaction with genotoxins.

High sensitive C-reactive protein and serum amyloid A are inversely related to serum bilirubin: effect-modification by metabolic syndrome

BACKGROUND

Bilirubin has been implicated in cardiovascular protection by virtue of its anti-inflammatory and anti-oxidative properties. The metabolic syndrome is featured by enhanced low-grade systemic inflammation and oxidative stress. Serum amyloid A (SAA) impairs anti-oxidative properties of high-density lipoprotein (HDL). We determined relationships of high sensitive C-reactive protein (hs-CRP) and SAA with bilirubin in subjects with and without metabolic syndrome (MetS).

METHODS

Serum total bilirubin, hs-CRP, SAA and homeostasis model assessment- insulin resistance (HOMA-IR) were documented in 94 subjects with and in 73 subjects without MetS (26 and 54 subjects with type 2 diabetes mellitus (T2DM), respectively).

RESULTS

Bilirubin was lower in MetS (P = 0.013), coinciding with higher hs-CRP (P < 0.001) and SAA levels (P = 0.002). In all subjects combined, hs-CRP was inversely related to bilirubin (r = -0.203, P = 0.008), irrespective of the presence of MetS or T2DM (interaction terms: P ≥ 0.75). The inverse relationship of bilirubin with SAA was confined to subjects without MetS (r = -0.267, P = 0.009). Furthermore, the presence of either MetS or T2DM modified the relationship of bilirubin with SAA (interaction terms: β = 0.366, P = 0.003 and β = 0.289, P = 0.025, respectively) in age- and sex-adjusted analyses. Effect modification was also found for HOMA-IR (β = 0.790, P = 0.020). Of the individual MetS components, the strongest interaction of bilirubin on SAA was observed with low HDL cholesterol (β = 0.435, P < 0.001).

CONCLUSIONS

hs-CRP is inversely related to bilirubin, suggesting that low bilirubin is implicated in enhanced low-grade systemic inflammation. The inverse relationship of SAA with bilirubin was found to be absent in MetS, which could be attributable to MetS-associated abnormalities in HDL characteristics.

Behavioral and clinical correlates of serum bilirubin concentrations in Japanese men and women

BACKGROUND

A considerable interest has been drawn to potential protective effects of bilirubin against oxidative stress-related diseases. Smoking is known to be associated with lower concentrations of serum bilirubin, but other behavioral correlates of serum bilirubin have not been well studied. In this cross-sectional study, we examined the associations of behavioral and clinical factors with serum total bilirubin in Japanese men and women.

METHOD

The study subjects comprised of 4802 men and 6414 women aged 49-76 years who participated in the baseline survey of an ongoing cohort study on lifestyle-related diseases in Fukuoka, Japan. With consideration to time of the day of blood sampling and fasting hours, the associations with smoking, alcohol intake, body mass index, physical activity, coffee, tea, blood pressure, glycated hemoglobin (HbA1c), HDL cholesterol and non-HDL cholesterol with serum bilirubin were evaluated by analysis of covariance and multiple linear regression analysis.

RESULTS

While smoking was negatively associated with serum bilirubin, alcohol consumption was positively associated with serum bilirubin in both men and women. Coffee consumption was associated with lower bilirubin concentrations in both sexes. In the multiple linear regression analysis, HDL cholesterol was positively and HbA1c was negatively associated with bilirubin in both men and women, and the associations were more evident in women.

CONCLUSION

Smoking, alcohol use and coffee consumption were important behavioral correlates of serum bilirubin in Japanese men and women. Serum HDL cholesterol was a measurable clinical correlate of bilirubin in women.

Elevated bilirubin after acute ischemic stroke linked to the stroke severity

BACKGROUND

Our previous study demonstrated that the level of serum bilirubin after acute ischemic stroke (AIS) was correlated to the severity of stroke, also there has the evidence of hyperbilirubinemia prevalent in AIS. We aimed to identify the exact change of bilirubin in the early phase of AIS, and study if this kind of change linked to the severity of stroke.

METHODS

Bilirubin and other biochemical indexes were measured in 608 AIS patients and 188 transient ischemic attack (TIA) patients which set as the control group. National Institutes of Health Stroke Scale (NIHSS) scores were assessed simultaneously with blood collection. First, the level of bilirubin and its distribution were compared between the AIS and control group. According to a cut-off point, we next analyzed the impacted factors of elevated bilirubin including the direct bilirubin (Dbil) and total bilirubin (Tbil), especially the correlation between elevated bilirubin and the severity of stroke. Finally, we compared the difference of concentration and percent of elevated bilirubin among the Oxford Community Stroke Project (OCSP) subtypes.

RESULTS

The level of serum Dbil and Tbil was significantly higher in the AIS group than that in the TIA group. Different distribution was observed between the two groups, which manifested as the percent of low bilirubin level group was lower while high level group was higher in AIS than that in TIA, the p value were 0.043 and 0.078 in Dbil and Tbil, respectively. When the cut-off point of elevated bilirubin was selected as Dbil≥6.84 μmol/L and Tbil≥22.2 μmol/L, we found that both NIHSS score and relative severity of AIS were significantly associated with elevated bilirubin whenever in Dbil or Tbil, so did the OCSP subtypes. This trend was still maintained by multivariable logistic regression analysis adjust for relative influence factors. In regard of OCSP subtypes, the highest level of bilirubin was found in TACI, so did the highest rate of elevated bilirubin.

CONCLUSION

The serum levels of Dbil and Tbil were increased after AIS, which linked to the severity of stroke.

Associations between serum total bilirubin levels and functional dependence in the elderly

BACKGROUND

Many studies support the role of bilirubin as a cytoprotector in chronic inflammatory diseases, such as stroke and atherosclerosis.

AIM

To investigate the relationship between serum total bilirubin levels and functional dependence in older adults.

METHODS

Data from the National Health and Nutrition Examination Survey (1999-2002) pertaining to 2235 old adults were analysed. All participants had given a household interview, providing information of five major domains on self-reported functional status (activities of daily living, instrumental activities of daily living, leisure and social activities, lower extremity mobility and general physical activities), had completed serum total bilirubin measurement, and a questionnaire regarding personal health. Poor performance was defined as experiencing difficulty with one or more items in a given domain. Functional dependence was defined as having three or more poor performances in the five major domains. Multiple logistic regression was performed together with quartile-based stratified odds ratio (OR) comparison and trend tests.

RESULTS

The OR of functional dependence for each standard deviation increment in the serum total bilirubin level was 0.56 (P = 0.002). After additional adjustment, the inverse association remained essentially unchanged. In quartile-based analysis, participants with higher quartiles of serum total bilirubin tended to have lower ORs of functional dependence. The trends of lower likelihood of functional dependence across increasing quartiles of the serum total bilirubin level were statistically significant (P < 0.05 for all trends).

CONCLUSIONS

Higher serum total bilirubin levels were associated with lower likelihood of functional dependence in older adults.

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.