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

Association between bilirubin and biomarkers of metabolic health and oxidative stress in the MARK-AGE cohort

Recent studies have shown that elevated concentrations of unconjugated bilirubin (UCB) may be a protective host factor against the development of noncommunicable diseases (NCDs), whereas low levels of UCB are associated with the opposite effect. The results of this European study, in which 2,489 samples were tested for their UCB concentration using high-performance liquid chromatography (HPLC) and additional data from the MARK-AGE database were used for analysis, provide further evidence that elevated UCB concentrations are linked to a lower risk of developing NCDs and may act as a predictive marker of biological aging as individuals with elevated UCB concentrations showed favorable outcomes in metabolic health and oxidative-stress-related biomarkers. These findings underline the significance of studying individuals with moderate hyperbilirubinemia and investigate UCB routinely, also in the setting of aging, since this condition affects millions of people worldwide but has been underrepresented in clinical research and practice until now.

The Evaluation of the Genetic Variation Types of the Uridine Diphosphate Glucuronosyl Transferase 1A1 Gene by Next-Generation Sequencing and Their Effects on Bilirubin Levels in Obese Children

Background and Objectives: Obesity is a major nutritional problem with an increasing prevalence among children and adolescents. The uridine-diphosphate-glucuronosyl-transferase1A1 (UGT1A1) gene encodes the UDP-glucuronosyl transferase enzyme, converting the toxic form of bilirubin to a soluble, nontoxic form. There are yet to be studies on the evaluation of the UGT1A1 variant types detected by next-generation sequencing (NGS) and their effects on bilirubin levels in nonsyndromic obese children. Methods: Forty-five children with body mass index (BMI) >95 percentile (p) constituted the obesity group and fourteen healthy children with BMI <85p constituted the control group. Anthropometric, clinical features, and biochemical parameters were evaluated. Furthermore, the UGT1A1 gene was sequenced by NGS. Results: The obese patients had lower total, direct, and indirect bilirubin levels (p = 0.422, 0.026, and 0.568, respectively). In addition, obese patients had more genetic variations in the UGT1A1 gene compared with the control group (62.2% and 50%, respectively). We found that children with variations had higher total direct and indirect bilirubin levels compared with those without variation (p = 0.016, 0.028, and 0.015, respectively). Children diagnosed with obesity in the first two years of their life had fewer genetic variations and lower total bilirubin levels (p = 0.000 and 0.013, respectively). Conclusions: It is assumed that bilirubin can be protective against many chronic diseases. Although bilirubin levels are found to be lower in obese children compared with the control group, some variations in the UGT1A1 gene may be supported by raising bilirubin. We suggest that high bilirubin levels caused by those UGT1A1 variations may be protective against obesity and its many negative effects.

Inverse association between total bilirubin and type 2 diabetes in U.S. South Asian males but not females

AIMS

United States South Asians constitute a fast-growing ethnic group with high prevalence of type 2 diabetes (T2D) despite lower mean BMI and other traditional risk factors compared to other races/ethnicities. Bilirubin has gained attention as a potential antioxidant, cardio-protective marker. Hence we sought to determine whether total bilirubin was associated with prevalent and incident T2D in U.S. South Asians.

METHODS

We conducted a cross-sectional and prospective analysis of the Mediators of Atherosclerosis in South Asians Living in America (MASALA) study. Total bilirubin was categorized into gender-specific quartiles (Men: <0.6, 0.6, 0.7-0.8, >0.8; Women: <0.5, 0.5, 0.6, >0.6 mg/dl). We estimated odds of type 2 diabetes as well as other cardiovascular (CV) risk factors using multivariable logistic regression.

RESULTS

Among a total 1,149 participants (48% female, mean [SD] age of 57 [9] years), 38% had metabolic syndrome and 24% had T2D. Men and women in the lowest bilirubin quartile had 0.55% and 0.17% higher HbA1c than the highest quartile. Men, but not women, in the lowest bilirubin quartile had higher odds of T2D compared to the highest quartile (aOR [95% CI]; Men: 3.00 [1.72,5.23], Women: 1.15 [0.57,2.31]). There was no association between bilirubin and other CV risk factors.

CONCLUSION

Total bilirubin was inversely associated with T2D in SA men but not women. Longitudinal studies are needed to understand temporality of association.

Total bilirubin and bilirubin-to-triglycerides ratio predict changes in glycated hemoglobin in healthy children

Objective

Bilirubin and triglycerides can regulate insulin secretion and glucose uptake. The aim of our study is to analyze associations between total bilirubin (TB) and the bilirubin-to-triglycerides ratio (BTR) with metabolic markers in healthy prepubertal children.

Methods

Subjects were 246 healthy children (mean age 8), of whom 142 (58%) were reevaluated 4 years later (mean age 12). The subjects were stratified according to age into three groups (<7.8 years; 7.8-9.6 years; and >9.6 years; n=82 each) at baseline and into two groups (<12.9 years and ≥12.9 years; n=71 each) at follow-up. Anthropometrics and laboratory parameters [TB and its fractions (direct and indirect bilirubin), triglycerides, HDL-cholesterol, glucose, insulin, HOMA-IR, HOMA-B and glycated hemoglobin (HbA1c)] were assessed at both baseline and follow-up.

Results

TB and BTR showed independent and negative association with baseline and follow-up HbA1c. These associations were stronger for BTR and in the highest age group. No independent associations were observed with HOMA-IR or HOMA-B.

Conclusion

TB and BTR are independently associated with HbA1c and predict its changes over time in healthy children. Our results indicate that TB and BTR may be useful parameters in studies of glucose tolerance in healthy children.

Genetics of Plasma Bilirubin and Associations between Bilirubin and Cardiometabolic Risk Profiles in Danish Children and Adolescents

Bilirubin is the end product of heme catabolism, mainly produced by the breakdown of mature red blood cells. Due to its anti-inflammatory, antioxidant, antidiabetic, and antilipemic properties, circulating bilirubin concentrations are inversely associated with the risk of cardiovascular disease, type 2 diabetes, and all-cause mortality in adults. Some genetic loci associated with circulating bilirubin concentrations have been identified by genome-wide association studies in adults. We aimed to examine the relationship between circulating bilirubin, cardiometabolic risk factors, and inflammation in children and adolescents and the genetic architecture of plasma bilirubin concentrations. We measured fasting plasma bilirubin, cardiometabolic risk factors, and inflammatory markers in a sample of Danish children and adolescents with overweight or obesity (n = 1530) and in a population-based sample (n = 1820) of Danish children and adolescents. Linear and logistic regression analyses were performed to analyze the associations between bilirubin, cardiometabolic risk factors, and inflammatory markers. A genome-wide association study (GWAS) of fasting plasma concentrations of bilirubin was performed in children and adolescents with overweight or obesity and in a population-based sample. Bilirubin is associated inversely and significantly with a number of cardiometabolic risk factors, including body mass index (BMI) standard deviation scores (SDS), waist circumference, high-sensitivity C-reactive protein (hs-CRP), homeostatic model assessment for insulin resistance (HOMA-IR), hemoglobin A1c (HbA1c), low-density lipoprotein cholesterol (LDL-C), triglycerides, and the majority of measured inflammatory markers. In contrast, bilirubin was positively associated with fasting plasma concentrations of alanine transaminase (ALT), high-density lipoprotein cholesterol (HDL-C), systolic blood pressure (SDS), and the inflammatory markers GH, PTX3, THBS2, TNFRSF9, PGF, PAPPA, GT, CCL23, CX3CL1, SCF, and TRANCE. The GWAS showed that two loci were positively associated with plasma bilirubin concentrations at a p-value threshold of <5 × 10-8 (rs76999922: β = -0.65 SD; p = 4.3 × 10-8, and rs887829: β = 0.78 SD; p = 2.9 × 10-247). Approximately 25% of the variance in plasma bilirubin concentration was explained by rs887829. The rs887829 was not significantly associated with any of the mentioned cardiometabolic risk factors except for hs-CRP. Our findings suggest that plasma concentrations of bilirubin non-causally associates with cardiometabolic risk factors in children and adolescents.

Optimal glycated hemoglobin A1c value for prediabetes and diabetes in patients with pancreatic diseases

Background

Some articles suggest that using HbA1c alone for diabetes diagnosis is inappropriate. It requires considerable researches to explore the efficacy of HbA1c for diagnosing hyperglycemia in patients with pancreatic disease.

Methods

This study analyzed 732 patients, comprising of 331 without pancreatic disease and 401 patients diagnosed with pancreatic diseases. All participants underwent the HbA1c assay and oral glucose tolerance test. Kappa coefficients were calculated to assess agreement between the HbA1c and glucose criteria. The receiver operating characteristic curve (ROC) was used to calculate the optimal HbA1c value. DeLong test was analyzed to compared the aera under curves (AUCs).

Results

There were 203 (61.3%) patients with NGT, 78 (23.6%) with prediabetes, and 50 (15.1%) with diabetes in patients without pancreatic diseases. In patients with pancreatic disease, 106 participants were diagnosed with NGT (36.4%), 125 with prediabetes (31.2%), and 130 with diabetes (32.4%). Patients with pancreatic disease exhibited elevated levels of bilirubin, transaminase enzymes, aspartate transaminase, high density lipoprotein cholesterol and total bile acid. The sensitivity and specificity of the HbA1c (6.5%) for diagnosing pancreatic diabetes were 60.8% (95% CI 52.3, 69.3) and 92.6% (95% CI 89.5, 95.7). In prediabetes, the sensitivity and specificity of HbA1c (5.7%) is 53.2% (44.3, 62.0) and 59.6 (51.5, 67.6). The optimal HbA1c value for diagnosing diabetes was 6.0% (AUC = 0.876, 95% CI 0.839, 0.906), with the sensitivity of 83.8% and the specificity of 76.8%. The optimal HbA1c value for the diagnosis of prediabetes was 5.8% (AUC = 0.617, 95% CI: 0.556, 0.675), with the corresponding sensitivity and specificity of 48.0% and 72.6% respectively. The combined tests (HbA1c, 6.0% or FPG, 7.0mmol/L) presented the sensitivity of 85.7% (95% CI 79.1, 91.3)and the specificity of 92.6% (95% CI 87.6, 97.3) in pancreatic diabetes.

Conclusion

From our results, the recommended HbA1c by ADA criterion may not be sufficiently sensitive to diagnose hyperglycemia in pancreatic disease. The optimal value of 5.8% and 6.0% improved the accuracy for diagnosing prediabetes and diabetes and should be considered to be applied. Besides, we advocate the combination of HbA1c and FPG test for the diagnosis of diabetes in patients with pancreatic diseases.

Association Between Serum Bilirubin and Atrial Fibrillation: A Mendelian Randomization Study

BACKGROUND AND OBJECTIVES

The association between bilirubin and atrial fibrillation (AF) has been evaluated previously in observational studies but with contradictory results. This study evaluated the causal association between serum bilirubin level and AF using Mendelian randomization (MR) analysis.

METHODS

This cross-sectional study includes 8,977 participants from the Dong-gu Study. In the observational analysis, multivariate logistic regression was performed to evaluate the association between bilirubin and prevalent AF. To evaluate the causal association between bilirubin and AF, MR analysis was conducted by using the UGT1A1 rs11891311 and rs4148323 polymorphisms as instrumental variables.

RESULTS

Elevated serum bilirubin levels were associated with an increased risk for AF in observational analysis (total bilirubin: odds ratio [OR], 1.31; 95% confidence interval [95% CI], 1.15-1.48 per 1 standard deviation [SD]; direct bilirubin: OR, 1.31; 95% CI, 1.18-1.46 per 1 SD), whereas the genetically predicted serum bilirubin levels in MR analysis did not show this association (total bilirubin: OR, 1.02; 95% CI, 0.67-1.53 per 1 SD; direct bilirubin: OR, 1.03; 95% CI, 0.61-1.73 per 1 SD).

CONCLUSIONS

Genetically predicted bilirubin levels were not associated with prevalent AF. Thus, the observational association between serum bilirubin levels and AF may be non-causal and affected by reverse causality or unmeasured confounding.

Bilirubin in metabolic syndrome and associated inflammatory diseases: New perspectives

Diabetes mellitus is one of the major global health issues, which is closely related to metabolic dysfunction and the chronic inflammatory diseases. Multiple studies have demonstrated that serum bilirubin is negatively correlated with metabolic syndrome and associated inflammatory diseases, including atherosclerosis, hypertension, etc. However, the roles of bilirubin in metabolic syndrome and associated inflammatory diseases still remain unclear. Here, we explain the role of bilirubin in metabolic syndrome and chronic inflammatory diseases and its therapeutic potential. Understanding the role of bilirubin activities in diabetes may serve as a therapeutic target for the treatment of chronic inflammatory diseases in diabetic patients.

Association between serum total bilirubin levels and the risk of type 2 diabetes mellitus

AIM

To confirm whether serum bilirubin is an independent risk factor of type 2 diabetes mellitus (T2DM) onset in patients with impaired fasting glycemia (IFG) and impaired glucose tolerance (IGT).

METHODS

This was a prospective cohort study carried out at the Diabetic Identification Center of Tianjin Metabolic Diseases Hospital. Serum total bilirubin (TBIL) was measured at baseline and the patients were grouped according to baseline bilirubin quartiles. The outcome was the confirmation of T2DM by oral glucose tolerance test (OGTT) during the 3-year follow-up. Logistic regression was used to determine the risk factors for T2DM development and whether bilirubin levels are independently associated with T2DM development.

RESULTS

Finally, 523 patients were analyzed. After 3 years, 310 participants were diagnosed with diabetes based on OGTT. Baseline quartiles of total bilirubin were inversely associated with diabetes risk, even after multivariable adjustment. The adjusted ORs for diabetes were 1.0 (reference), 0.83 (95% CI 0.74-0.96), 0.78 (95% CI 0.68-0.90), 0.74 (95% CI 0.64-0.87) for the 1st, 2nd, 3rd, and 4th quartiles of baseline serum total bilirubin, respectively (P < 0.001).

CONCLUSION

In patients with IFG or IGT, low levels of serum total bilirubin were associated with a significantly increased risk of T2DM.

Systemic regulation of bilirubin homeostasis: Potential benefits of hyperbilirubinemia

Neurotoxic bilirubin is the end product of heme catabolism in mammals. Bilirubin is solely conjugated by uridine diphospho-glucuronosyltransferase 1A1, which is a membrane-bound enzyme that catalyzes the transfer of glucuronic acid. Due to low function of hepatic and intestinal uridine diphospho-glucuronosyltransferase 1A1 during the neonatal period, human neonates develop mild to severe physiological hyperbilirubinemia. Accumulation of bilirubin in the brain leads to the onset of irreversible brain damage, termed kernicterus. Breastfeeding is one of the most significant factors that increase the risk of developing kernicterus in infants. Why does this most natural way of feeding increase the risk of brain damage or even death? This question leads to the hypothesis that breast milk-induced hyperbilirubinemia might bring certain benefits that outweigh those risks. While bilirubin is neurotoxic and cytotoxic, this compound is also a potent antioxidant. There are studies showing improved clinical conditions in patients with hyperbilirubinemia. Accumulating evidence also shows that genetic polymorphisms linked to hyperbilirubinemia are beneficial against various diseases. In this review article, we first introduce the production, metabolism, and transport of bilirubin. We then discuss the potential benefits of neonatal and adult hyperbilirubinemia. Finally, epigenetic factors as well as metabolomic information associated with hyperbilirubinemia are described. This review article advances the understanding of the physiological importance of the paradoxical compound bilirubin. (Hepatology 2018;67:1609-1619).

Relationship between serum bilirubin concentrations and diabetic nephropathy in Shanghai Han's patients with type 1 diabetes mellitus

Background

Recent studies highlight a negative association between total bilirubin concentrations and albuminuria in patients with type 2 diabetes mellitus. Our study evaluated the relationship between bilirubin concentrations and the prevalence of diabetic nephropathy (DN) in Chinese patients with type 1 diabetes mellitus (T1DM).

Methods

A total of 258 patients with T1DM were recruited and bilirubin concentrations were compared between patients with or without diabetic nephropathy. Multiple stepwise regression analysis was used to examine the relationship between bilirubin concentrations and 24 h urinary microalbumin. Binary logistic regression analysis was performed to assess independent risk factors for diabetic nephropathy. Participants were divided into four groups according to the quartile of total bilirubin concentrations (Q1, 0.20–0.60; Q2, 0.60–0.80; Q3, 0.80–1.00; Q4, 1.00–1.90 mg/dL) and the chi-square test was used to compare the prevalence of DN in patients with T1DM.

Results

The median bilirubin level was 0.56 (interquartile: 0.43–0.68 mg/dL) in the DN group, significantly lower than in the non-DN group (0.70 [interquartile: 0.58–0.89 mg/dL], P < 0.001). Spearman’s correlational analysis showed bilirubin concentrations were inversely correlated with 24 h urinary microalbumin (r = -0.13, P < 0.05) and multiple stepwise regression analysis showed bilirubin concentrations were independently associated with 24 h urinary microalbumin. In logistic regression analysis, bilirubin concentrations were significantly inversely associated with nephropathy. In addition, in stratified analysis, from the first to the fourth quartile group, increased bilirubin concentrations were associated with decreased prevalence of DN from 21.90% to 2.00%.

Conclusion

High bilirubin concentrations are independently and negatively associated with albuminuria and the prevalence of DN in patients with T1DM.

Supplementation with Phycocyanobilin, Citrulline, Taurine, and Supranutritional Doses of Folic Acid and Biotin-Potential for Preventing or Slowing the Progression of Diabetic Complications

Oxidative stress, the resulting uncoupling of endothelial nitric oxide synthase (eNOS), and loss of nitric oxide (NO) bioactivity, are key mediators of the vascular and microvascular complications of diabetes. Much of this oxidative stress arises from up-regulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. Phycocyanobilin (PhyCB), the light-harvesting chromophore in edible cyanobacteria such as spirulina, is a biliverdin derivative that shares the ability of free bilirubin to inhibit certain isoforms of NADPH oxidase. Epidemiological studies reveal that diabetics with relatively elevated serum bilirubin are less likely to develop coronary disease or microvascular complications; this may reflect the ability of bilirubin to ward off these complications via inhibition of NADPH oxidase. Oral PhyCB may likewise have potential in this regard, and has been shown to protect diabetic mice from glomerulosclerosis. With respect to oxidant-mediated uncoupling of eNOS, high-dose folate can help to reverse this by modulating the oxidation status of the eNOS cofactor tetrahydrobiopterin (BH4). Oxidation of BH4 yields dihydrobiopterin (BH2), which competes with BH4 for binding to eNOS and promotes its uncoupling. The reduced intracellular metabolites of folate have versatile oxidant-scavenging activity that can prevent oxidation of BH4; concurrently, these metabolites promote induction of dihydrofolate reductase, which functions to reconvert BH2 to BH4, and hence alleviate the uncoupling of eNOS. The arginine metabolite asymmetric dimethylarginine (ADMA), typically elevated in diabetics, also uncouples eNOS by competitively inhibiting binding of arginine to eNOS; this effect is exacerbated by the increased expression of arginase that accompanies diabetes. These effects can be countered via supplementation with citrulline, which efficiently enhances tissue levels of arginine. With respect to the loss of NO bioactivity that contributes to diabetic complications, high dose biotin has the potential to "pinch hit" for diminished NO by direct activation of soluble guanylate cyclase (sGC). High-dose biotin also may aid glycemic control via modulatory effects on enzyme induction in hepatocytes and pancreatic beta cells. Taurine, which suppresses diabetic complications in rodents, has the potential to reverse the inactivating impact of oxidative stress on sGC by boosting synthesis of hydrogen sulfide. Hence, it is proposed that concurrent administration of PhyCB, citrulline, taurine, and supranutritional doses of folate and biotin may have considerable potential for prevention and control of diabetic complications. Such a regimen could also be complemented with antioxidants such as lipoic acid, N-acetylcysteine, and melatonin-that boost cellular expression of antioxidant enzymes and glutathione-as well as astaxanthin, zinc, and glycine. The development of appropriate functional foods might make it feasible for patients to use complex nutraceutical regimens of the sort suggested here.

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.

Comparative Effectiveness of Diabetic Oral Medications Among HIV-Infected and HIV-Uninfected Veterans

OBJECTIVE

Type 2 diabetes is increasingly common in HIV-infected individuals. The objective of this study was to compare the glycemic effectiveness of oral diabetic medications among patients with and without HIV infection.

RESEARCH DESIGN AND METHODS

A longitudinal cohort study was conducted among HIV-infected and uninfected veterans with type 2 diabetes initiating diabetic medications between 1999 and 2010. Generalized estimating equations were used to compare changes in hemoglobin A_1c (HbA_1c) through the year after medication initiation, adjusting for baseline HbA_1c level and clinical covariates. A subanalysis using propensity scores was conducted to account for confounding by indication.

RESULTS

A total of 2,454 HIV-infected patients and 8,892 HIV-uninfected patients initiated diabetic medications during the study period. The most commonly prescribed medication was metformin (n = 5,647, 50%), followed by a sulfonylurea (n = 5,554, 49%) and a thiazolidinedione (n = 145, 1%). After adjustment for potential confounders, there was no significant difference in the change in HbA_1c level among the three groups of new users. HIV infection was not significantly associated with glycemic response (P = 0.24). Black and Hispanic patients had a poorer response to therapy compared with white patients, with a relative increase in HbA_1c level of 0.16% (95% CI 0.08, 0.24) [1.7 mmol/mol (0.9, 2.6)] (P < 0.001) and 0.25% (0.11, 0.39) [2.7 mmol/mol (1.2, 4.3)] (P = 0.001), respectively.

CONCLUSIONS

We found that glycemic response was independent of the initial class of diabetic medication prescribed among HIV-uninfected and HIV-infected adults with type 2 diabetes. The mechanisms leading to poorer response among black and Hispanic patients, who make up a substantial proportion of those with HIV infection and type 2 diabetes, require further investigation.

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.

Higher direct bilirubin levels during mid-pregnancy are associated with lower risk of gestational diabetes mellitus

Bilirubin concentrations have been recently reported to be negatively associated with type 2 diabetes mellitus. We examined the association between bilirubin concentrations and gestational diabetes mellitus. In a prospective cohort study, 2969 pregnant women were recruited prior to 16 weeks of gestation and were followed up until delivery. The value of bilirubin was tested and oral glucose tolerance test was conducted to screen gestational diabetes mellitus. The relationship between serum bilirubin concentration and gestational weeks was studied by two-piecewise linear regression. A subsample of 1135 participants with serum bilirubin test during 16-18 weeks gestation was conducted to research the association between serum bilirubin levels and risk of gestational diabetes mellitus by logistic regression. Gestational diabetes mellitus developed in 8.5 % of the participants (223 of 2969). Two-piecewise linear regression analyses demonstrated that the levels of bilirubin decreased with gestational week up to the turning point 23 and after that point, levels of bilirubin were increased slightly. In multiple logistic regression analysis, the relative risk of developing gestational diabetes mellitus was lower in the highest tertile of direct bilirubin than that in the lowest tertile (RR 0.60; 95 % CI, 0.35-0.89). The results suggested that women with higher serum direct bilirubin levels during the second trimester of pregnancy have lower risk for development of gestational diabetes mellitus.

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.

Haeme oxygenase signalling pathway: implications for cardiovascular disease

Evidence now points to the haeme oxygenase (HO) pathway as a possible actor in modulating risk for cardiovascular disease (CVD). In particular, the HO pathway may represent a key endogenous modulator of oxidative, inflammatory, and cytotoxic stress while also exhibiting vasoregulatory properties. In this review, we summarize the accumulating experimental and emerging clinical data indicating how activity of the HO pathway and its products may play a role in mechanisms underlying the development of CVD. We also identify gaps in the literature to date and suggest future directions for investigation. Because HO pathway activity can be influenced not only by genetic traits and environmental stimuli but also by a variety of existing pharmacologic interventions, the pathway could serve as a prime target for reducing the overall burden of CVD. Further work is needed to determine the role of HO pathway products as possible prognostic markers of risk for clinical CVD events and the extent to which therapeutic augmentation or inhibition of HO pathway activity could serve to modify CVD risk.

Serum bilirubin concentrations are positively associated with serum C-peptide levels in patients with Type 2 diabetes

AIMS

To investigate the relationship between physiological serum total bilirubin concentrations and serum C-peptide levels in Korean patients with Type 2 diabetes.

METHODS

A total of 588 patients with Type 2 diabetes were investigated in this cross-sectional study. Fasting C-peptide level, 2-h postprandial C-peptide level and ΔC-peptide (postprandial C-peptide minus fasting C-peptide) level were measured in all patients.

RESULTS

Fasting C-peptide level, postprandial C-peptide level and ΔC-peptide level tended to be higher in patients with higher bilirubin concentrations. Partial correlation analysis showed that serum bilirubin levels were significantly correlated with fasting C-peptide level (r = 0.159, P < 0.001), postprandial C-peptide level (r = 0.209, P < 0.001) and ΔC-peptide level (r = 0.186, P < 0.001) after adjustment for other covariates. In the multivariate model, the association between serum bilirubin concentrations and serum C-peptide levels remained significant after adjustment for confounding factors including age, gender, familial diabetes, hypertension, hyperlipidaemia, BMI, HbA1c , duration of diabetes and associated liver function tests (fasting C-peptide level: β = 0.083, P = 0.041; postprandial C-peptide level: β = 0.106, P = 0.005; ΔC-peptide level: β = 0.096, P = 0.015, respectively).

CONCLUSIONS

Serum bilirubin concentrations within the physiological range were positively associated with serum C-peptide levels in patients with Type 2 diabetes.

Physiological serum bilirubin concentrations are inversely associated with the prevalence of cardiovascular autonomic neuropathy in patients with Type 2 diabetes

AIMS

Although severe hyperbilirubinaemia causes kernicterus in neonates, normal to modestly elevated bilirubin concentrations have been reported to be neuroprotective. However, the relationship between serum bilirubin concentrations and cardiovascular autonomic neuropathy in patients with Type 2 diabetes is currently unknown. This study assessed the relationships between physiological serum total bilirubin concentrations and cardiovascular autonomic neuropathy in patients with Type 2 diabetes.

METHODS

A total of 2991 patients with Type 2 diabetes were investigated in this cross-sectional study. Cardiovascular autonomic neuropathy was diagnosed by a cardiovascular reflex test. According to the American Diabetes Association criteria, the degree of cardiovascular autonomic dysfunction was graded into normal, early, definite and severe. Cardiovascular autonomic neuropathy was either definite or severe in the present study. An analysis of covariance after adjustment for other covariates was performed. A logistic regression model was used to assess an association of cardiovascular autonomic neuropathy with serum total bilirubin tertiles.

RESULTS

Serum total bilirubin concentrations were significantly lower in subjects with cardiovascular autonomic neuropathy. The mean total bilirubin values differed significantly according to the severity of cardiovascular autonomic dysfunction (normal 13.0 μmol/l; early 12.3 μmol/l; definite 11.8 μmol/l; severe 10.1 μmol/l; P for trend < 0.001) after adjustment for other covariates. In multivariate analysis, serum total bilirubin levels were significantly associated with cardiovascular autonomic neuropathy (odds ratio 0.36; 95% CI 0.21-0.63 for the highest vs. the lowest bilirubin tertile, P < 0.001).

CONCLUSIONS

Serum total bilirubin concentrations within the physiologic range are inversely associated with the prevalence of cardiovascular autonomic neuropathy in patients with Type 2 diabetes.

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.

Diabetes, bilirubin and amputations: is there a link?

A study by Chan et al in this issue of Diabetologia (DOI: 10.1007/s00125-012-2818-4 ) reports that low plasma bilirubin levels are associated with an increased risk of amputation in patients with type 2 diabetes mellitus participating in the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study. These findings raise the interesting and clinically relevant hypothesis that bilirubin protects against risk of amputation in patients with type 2 diabetes. This commentary considers some of the limitations associated with research aiming to define any link between circulating bilirubin levels and vascular disease. Numerous confounding factors (several of which may be present in patients with type 2 diabetes) may explain why the literature regarding this potentially protective role of bilirubin remains controversial.