Low serum total bilirubin concentrations are associated with increased prevalence of metabolic syndrome in Chinese

Exploring the inverse relationship between serum total bilirubin and systemic immune-inflammation index: insights from NHANES data (2009-2018)

BACKGROUND

Bilirubin is known for its multifaceted attributes, including antioxidant, anti-inflammatory, immunomodulatory, and antiapoptotic properties. The systemic immune-inflammation index (SII) is a recent marker that reflects the balance between inflammation and immune response. Despite the wealth of information available on bilirubin's diverse functionalities, the potential correlation between the total bilirubin (TB) levels and SII has not been investigated so far.

METHODS

Leveraging data from the National Health and Nutrition Examination Survey spanning 2009-2018, the TB levels were categorized using tertiles. Employing the chi-squared test with Rao and Scott's second-order correction and Spearman's rank correlation analysis, the association between TB and SII was examined. The potential nonlinearities between TB and SII were evaluated using restricted cubic spline (RCS) analysis. Weighted linear regression, adjusted for covariates, was used to explore the correlation between TB and SII, with further subgroup analyses.

RESULTS

A total of 16,858 participants were included, and the findings revealed significant SII variations across TB tertiles (p < 0.001). The third tertile (Q3) exhibited the lowest SII level at 495.73 (295.00) 1000 cells/µL. Spearman rank correlation disclosed the negative association between TB and SII. RCS analysis exposed the lack of statistically significant variations in the nonlinear relationship (p > 0.05), thereby providing support for a linear relationship. Weighted linear regression analysis underscored the negative correlation between TB and SII (β 95% CI - 3.9 [- 5.0 to  - 2.9], p < 0.001). The increase in the TB levels is associated with a significant linear trend toward decreasing SII. After controlling for relative covariates, this negative correlation increased (p < 0.001). Subgroup analysis confirmed the significant negative TB-SII association.

CONCLUSION

A notable negative correlation between TB and SII implies the potential protective effects of bilirubin in inflammation-related diseases.

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.

Mildly elevated serum bilirubin and its correlations with lipid levels among male patients undergoing health checkups

BACKGROUND

Bilirubin's ability to lower lipid levels was confirmed by several studies, but those studies mainly focused on total bilirubin (TBil). The present study aimed to elucidate the correlations of the two subtypes of bilirubin with lipid levels.

METHODS

A total of 1732 male patients undergoing health checkups were categorized into three groups according to the levels of direct bilirubin (DBil) and indirect bilirubin (IBil). The differences in medical characteristics among the three groups were analysed.

RESULTS

Subjects in the elevated DBil group had the lowest serum alanine aminotransferase (ALT), total cholesterol (TC), blood urea nitrogen (BUN), γ-glutamyl transpeptidase (γ-GT), fasting blood glucose (FBG), haemoglobin (HGB), and triglyceride (TG) levels in contrast to the other groups (P < 0.01), while subjects in the elevated IBil group had the highest ALT, γ-GT, BUN, serum creatinine (SCR), HGB, TC, and TG levels among the three groups (P < 0.01). DBil levels exhibited a significant negative correlation with TC (r = -0.777, P < 0.01) and TG (r = -0.397, P < 0.01) levels, while IBil levels exhibited a significant positive correlation with TC (r = 0.790, P < 0.01) and TG (r = 0.302, P < 0.01) levels. The frequencies of abnormal TC, TG, HGB and BUN levels were the lowest in the elevated DBil group, while the levels of these four variables were the highest in the elevated IBil group. Mildly elevated DBil levels were related to lower TG (OR = 0.112, 95% CI = 0.027-0.458) and TC (OR = 0.097, 95% CI = 0.013-0.700), and mildly elevated IBil levels were connected with increased TC (OR = 3.436, 95% CI = 2.398-4.924) and TG (OR = 1.636, 95% CI = 1.163-2.303). DBil was an independent protective factor against increased TC (OR = 0.702, 95% CI = 0.602-0.817, P < 0.01) and TG (OR = 0.632, 95% CI = 0.541-0.739, P < 0.01) levels, and IBil was an independent risk factors for increased TC (OR = 1.251, 95% CI = 1.176-1.331, P < 0.01).

CONCLUSIONS

DBil was an independent protective factor against high TC and TG levels. IBil was an independent risk factors for elevated TC levels. The prognostic value of IBil levels warrants further attention.

The association between serum ferritin and bilirubin with glycemic control among patients with type 2 diabetes mellitus

Previous evidence has shown an association between serum ferritin and bilirubin levels in the development of type 2 diabetes mellitus (T2DM) and glycemic control. However, the evidence is scarce in Saudi Arabia. In this study, we aimed to evaluate the association between serum ferritin and bilirubin levels with glycemic control in patients with T2DM. This was a cross-sectional study that involved 153 patients with T2DM recruited from outpatient diabetes clinics. Participants were categorized into two groups: well-controlled and uncontrolled T2DM, based on their glycemic status. We focused on comparing the iron profile and bilirubin levels between these two groups and examining the influence of antidiabetic medications on these parameters. A total of 153 patients with T2DM were included (58.2% women and 41.8% men). In both univariate and multivariate analyses, ferritin levels did not have a statistically significant association with glycemic control. However, patients with well-controlled T2DM had a significantly higher median level of total bilirubin and direct bilirubin than those with uncontrolled T2DM. Only direct bilirubin showed a statistically significant association with FBG less than 130 mg/dl and HbA1c level less than 7.0%. Ferritin level was not associated with glycemic control in patients with T2DM. On the other hand, direct bilirubin level was an independent predictor of better glycemic control. Monitoring direct bilirubin levels could aid in predicting glycemic control in T2DM and could be a potential target for developing antidiabetic medications.

Serum total bilirubin and one-year prognosis of patients with coronary artery disease and psoriasis

To evaluate the potential predictive value of total bilirubin (TBIL) for one-year prognosis in patients with coronary artery disease (CAD) and psoriasis. 278 psoriasis patients who underwent coronary angiography and were diagnosed as CAD were recruited. Baseline TBIL was measured at admission. Patients were divided into three groups according to the third tertiles of TBIL. The coronary angiography showed that lower TBIL was associated with the severity of lesion calcification. After a mean follow-up of 315 days, major adverse cardiac and cerebrovascular events (MACCEs) were reported in 61 patients. Compared with patients with higher TBIL tertiles, the incidence of MACCEs increased significantly in patients with middle and lower TBIL tertiles. The incidence of MACCEs in one-year follow-up was significantly different between higher and lower tertiles. The findings indicate that decreased TBIL is a potential predictor of poor prognosis in patients with psoriasis and CAD.

Association of Low Serum Bilirubin Concentrations and Promoter Variations in the UGT1A1 and HMOX1 Genes with Type 2 Diabetes Mellitus in the Czech Population

Bilirubin has potent biological beneficial effects, protecting against atherosclerosis, obesity, and metabolic syndrome. The aim of this study was to assess serum bilirubin concentrations and (TA)n and (GT)n microsatellite variations in the promoter regions of the UGT1A1 and HMOX1 genes, respectively, in patients with type 2 diabetes mellitus (T2DM). The study was carried out in 220 patients with T2DM and 231 healthy control subjects, in whom standard biochemical tests were performed. The (TA)n and (GT)n dinucleotide variations were determined by means of fragment (size-based) analysis using an automated capillary DNA sequencer. Compared to controls, both male and female patients with T2DM had lower serum bilirubin concentrations (9.9 vs. 12.9 μmol/L, and 9.0 vs. 10.6 μmol/L, in men and women, respectively, p < 0.001). Phenotypic Gilbert syndrome was much less prevalent in T2DM patients, as was the frequency of the (TA)7/7UGT1A1 genotype in male T2DM patients. (GT)nHMOX1 genetic variations did not differ between diabetic patients and controls. Our results demonstrate that the manifestation of T2DM is associated with lower serum bilirubin concentrations. Consumption of bilirubin due to increased oxidative stress associated with T2DM seems to be the main explanation, although (TA)n repeat variations in UGT1A1 partially contribute to this phenomenon.

Suppressing Hepatic UGT1A1 Increases Plasma Bilirubin, Lowers Plasma Urobilin, Reorganizes Kinase Signaling Pathways and Lipid Species and Improves Fatty Liver Disease

Several population studies have observed lower serum bilirubin levels in patients with non-alcoholic fatty liver disease (NAFLD). Yet, treatments to target this metabolic phenotype have not been explored. Therefore, we designed an N-Acetylgalactosamine (GalNAc) labeled RNAi to target the enzyme that clears bilirubin from the blood, the UGT1A1 glucuronyl enzyme (GNUR). In this study, male C57BL/6J mice were fed a high-fat diet (HFD, 60%) for 30 weeks to induce NAFLD and were treated subcutaneously with GNUR or sham (CTRL) once weekly for six weeks while continuing the HFD. The results show that GNUR treatments significantly raised plasma bilirubin levels and reduced plasma levels of the bilirubin catabolized product, urobilin. We show that GNUR decreased liver fat content and ceramide production via lipidomics and lowered fasting blood glucose and insulin levels. We performed extensive kinase activity analyses using our PamGene PamStation kinome technology and found a reorganization of the kinase pathways and a significant decrease in inflammatory mediators with GNUR versus CTRL treatments. These results demonstrate that GNUR increases plasma bilirubin and reduces plasma urobilin, reducing NAFLD and inflammation and improving overall liver health. These data indicate that UGT1A1 antagonism might serve as a treatment for NAFLD and may improve obesity-associated comorbidities.

Bilirubin Levels Are Negatively Correlated with Adiposity in Obese Men and Women, and Its Catabolized Product, Urobilin, Is Positively Associated with Insulin Resistance

Bilirubin levels in obese humans and rodents have been shown to be lower than in their lean counterparts. Some studies have proposed that the glucuronyl UGT1A1 enzyme that clears bilirubin from the blood increases in the liver with obesity. UGT1A1 clearance of bilirubin allows more conjugated bilirubin to enter the intestine, where it is catabolized into urobilin, which can be then absorbed via the hepatic portal vein. We hypothesized that when bilirubin levels are decreased, the urobilin increases in the plasma of obese humans, as compared to lean humans. To test this, we measured plasma levels of bilirubin and urobilin, body mass index (BMI), adiposity, blood glucose and insulin, and HOMA IR in a small cohort of obese and lean men and women. We found that bilirubin levels negatively correlated with BMI and adiposity in obese men and women, as compared to their lean counterparts. Contrarily, urobilin levels were positively associated with adiposity and BMI. Only obese women were found to be insulin resistant based on significantly higher HOMA IR, as compared to lean women. The urobilin levels were positively associated with HOMA IR in both groups, but women had a stronger linear correlation. These studies indicate that plasma urobilin levels are associated with obesity and its comorbidities, such as insulin resistance.

Molecular mechanisms of metabolic associated fatty liver disease (MAFLD): functional analysis of lipid metabolism pathways

The metabolic-associated fatty liver disease (MAFLD) is a condition of fat accumulation in the liver in combination with metabolic dysfunction in the form of overweight or obesity and insulin resistance. It is also associated with an increased cardiovascular disease risk, including hypertension and atherosclerosis. Hepatic lipid metabolism is regulated by a combination of the uptake and export of fatty acids, de novo lipogenesis, and fat utilization by β-oxidation. When the balance between these pathways is altered, hepatic lipid accumulation commences, and long-term activation of inflammatory and fibrotic pathways can progress to worsen the liver disease. This review discusses the details of the molecular mechanisms regulating hepatic lipids and the emerging therapies targeting these pathways as potential future treatments for MAFLD.

Blood and Urinary Biomarkers of Antipsychotic-Induced Metabolic Syndrome

Metabolic syndrome (MetS) is a clustering of at least three of the following five medical conditions: abdominal obesity, high blood pressure, high blood sugar, high serum triglycerides, and low serum high-density lipoprotein (HDL). Antipsychotic (AP)-induced MetS (AIMetS) is the most common adverse drug reaction (ADR) of psychiatric pharmacotherapy. Herein, we review the results of studies of blood (serum and plasma) and urinary biomarkers as predictors of AIMetS in patients with schizophrenia (Sch). We reviewed 1440 studies examining 38 blood and 19 urinary metabolic biomarkers, including urinary indicators involved in the development of AIMetS. Among the results, only positive associations were revealed. However, at present, it should be recognized that there is no consensus on the role of any particular urinary biomarker of AIMetS. Evaluation of urinary biomarkers of the development of MetS and AIMetS, as one of the most common concomitant pathological conditions in the treatment of patients with psychiatric disorders, may provide a key to the development of strategies for personalized prevention and treatment of the condition, which is considered a complication of AP therapy for Sch in clinical practice.

Bilirubin as an indicator of cardiometabolic health: a cross-sectional analysis in the UK Biobank

BACKGROUND

Mildly elevated bilirubin, a by-product of hemoglobin breakdown, might mitigate cardiometabolic risk factors including adiposity, dyslipidemia, and high blood pressure (BP). We investigated the cross-sectional relationship between (total) bilirubin and baseline cardiometabolic risk factors in 467,519 UK Biobank study participants.

METHODS

We used multivariable-adjusted linear regression to estimate associations between bilirubin levels and risk factors of cardiometabolic diseases including body mass index (BMI), waist and hip circumferences (WC, HC), waist-to-hip ratio (WHR), fat mass (FM), and trunk FM, and the blood lipids: apolipoprotein A-I (apoA-I), apolipoprotein B (apoB), apoB/apoA-I, lipoprotein (a), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), LDL/HDL, TC/HDL, triglycerides (TG). Log-transformed bilirubin was modelled with restricted cubic splines and predicted mean values with 99% confidence intervals (CI) for each risk marker were estimated, separately. Second, we applied principal component analysis (PCA) for dimension reduction to in turn six anthropometric traits (height, weight, BMI, WC, HC, and WHR) and all above lipids. Last, we estimated associations (99%CI) between bilirubin and three components of the metabolic syndrome, i.e. WC, TG, and BP using logistic regression.

RESULTS

After multivariable adjustments, higher levels of bilirubin were inversely associated with indicators of general adiposity (BMI and FM) and of body fat distribution (WC, HC, WHR, and trunk FM) in both men and women. For example, women with mildly elevated bilirubin (95th percentile equal to 15.0 µmol/L), compared to women with low bilirubin (5th percentile equal to 4.5 µmol/L), had on average a 2.0 kg/m2 (99% CI 1.9-2.1) lower BMI. Inverse associations were also observed with dyslipidemia among men and women. For example, mildly elevated bilirubin among men (95th percentile equal to 19.4 µmol/L) compared to low levels of bilirubin (5th percentile equal to 5.5 µmol/L) were associated with approx. 0.55 mmol/L (99% CI 0.53-0.56) lower TG levels, with similar inverse associations among women. Multiple-trait analyses using PCA confirmed single-trait analyses. Men and women with mildly elevated bilirubin levels ≥ 17.1 µmol/L, compared to low-normal bilirubin < 10 µmol/L had 13% (99% CI 8%-18%) and 11% (99% CI 4%-17%) lower odds of exceeding systolic BP levels of ≥ 130 mm Hg, respectively.

CONCLUSIONS

Higher levels of bilirubin were inversely associated with cardiometabolic risk factors including adiposity, dyslipidemia, and hypertension.

Novel Function for Bilirubin as a Metabolic Signaling Molecule: Implications for Kidney Diseases

Bilirubin is the end product of the catabolism of heme via the heme oxygenase pathway. Heme oxygenase generates carbon monoxide (CO) and biliverdin from the breakdown of heme, and biliverdin is rapidly reduced to bilirubin by the enzyme biliverdin reductase (BVR). Bilirubin has long been thought of as a toxic product that is only relevant to health when blood levels are severely elevated, such as in clinical jaundice. The physiologic functions of bilirubin correlate with the growing body of evidence demonstrating the protective effects of serum bilirubin against cardiovascular and metabolic diseases. Although the correlative evidence suggests a protective effect of serum bilirubin against many diseases, the mechanism by which bilirubin offers protection against cardiovascular and metabolic diseases remains unanswered. We recently discovered a novel function for bilirubin as a signaling molecule capable of activating the peroxisome proliferator-activated receptor α (PPARα) transcription factor. This review summarizes the new finding of bilirubin as a signaling molecule and proposes several mechanisms by which this novel action of bilirubin may protect against cardiovascular and kidney diseases.

The association between bilirubin and hypertension among a Chinese ageing cohort: a prospective follow-up study

BACKGROUND

Hypertension is highly prevalent and associated with the elevated risks of cardiovascular diseases, dementia, and physical disabilities among adults. Although the correlation between bilirubin and hypertension has been reported, the observation in quinquagenarian population is scarce. We aimed to examine bilirubin-hypertension association in Guankou Ageing Cohort Study.

METHODS

Participants ≥ 55 years were recruited and their questionnaires and physical examination data were collected. Kaplan-Meier survival analysis and Cox proportional hazards regression were implemented to assess the hypertension risk. The non-liner dose-response relationships of bilirubin-hypertension were determined by restricted cubic spline (RCS) models. Receiver operating characteristic (ROC) curves and multiple factors analysis (MFA) were performed to evaluate the predictive abilities.

RESULTS

1881 eligible participants (male 43.75%, female 56.25%) with the median age of 61.00 (59.00-66.00) were included. The hazard ratio (HR, 95% CI) of serum total bilirubin (STB) and unconjugated bilirubin (UCB) were 1.03 (1.01-1.05) and 1.05 (1.03-1.07), while conjugated bilirubin (CB) showed a weak protective effect with the HR of 0.96 (0.92-0.99), and the associations remained significant in all models. RCS analyses further indicated the similar bidirectional effects of STB and UCB with the cut-off of 12.17 μmol/L and 8.59 μmol/L, while CB exhibited inverse bidirectional dose-response relationship with a cut-off of 3.47 μmol/L. ROC curves and MFA showed baseline STB combined with age, BMI, and waist circumference could well discriminate the low and high of hypertension risk.

CONCLUSIONS

Our findings suggested the higher levels of total and unconjugated bilirubin were hazardous factors of hypertension, while an inverse effect presented when more bilirubin was conjugated.

Association of Serum Bilirubin With Metabolic Syndrome and Non-Alcoholic Fatty Liver Disease: A Systematic Review and Meta-Analysis

OBJECTIVE

Metabolic syndrome (MetS) and non-alcoholic fatty liver disease (NAFLD) are the leading chronic diseases worldwide. There are still many controversies about the association between serum bilirubin and MetS or NAFLD. This study aims to evaluate the association of serum total bilirubin (TBIL), direct bilirubin (DBIL), indirect bilirubin (IBIL) with MetS and NAFLD.

METHODS

Multiple databases were searched for relevant studies until November 2021. Randomized controlled trials, cross-sectional and cohort studies evaluating the association between serum bilirubin levels and MetS or NAFLD were included.

RESULTS

Twenty-four cross-sectional and cohort studies with 101, 517 participants were finally analyzed. Fifteen studies and 6 studies evaluated the association between bilirubin and MetS or NAFLD in health screening population, respectively, while 3 studies evaluated the association between bilirubin and non-alcoholic steatohepatitis (NASH) in NAFLD patients. Random effect model analysis showed the inverse association between TBIL and MetS in male (95%CI=0.71-0.96) and gender-neutral (95%CI=0.61-0.91) group. However, no significant association was found in females. Notably, the inverse association between DBIL and MetS was noticed in male (95%CI=0.36-0.75), female (95%CI=0.16-0.58) and gender-neutral population (95%CI=0.67-0.92). IBIL level was inversely associated with MetS in females (95%CI=0.52-0.96), whereas no statistical correlation presented in males. TBIL was not statistically correlated with NAFLD in gender-neutral or male subgroup. Similarly, there were no association between DBIL or IBIL and NAFLD in gender-neutral subgroup. However, the negative correlation between DBIL and NAFLD existed in males (95%CI=0.76-0.96). In NAFLD patients, IBIL analysis showed an inverse association with NASH (95%CI=0.01-0.12).

CONCLUSION

Serum TBIL and DBIL levels, especially DBIL levels, assume an inverse correlation with MetS in healthy population. Serum IBIL is inversely associated with the onset and degree of NASH in NAFLD patients. Exogenous bilirubin supplement may be a potential strategy to assist in lowering the risk of developing MetS and NAFLD.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/, identifier CRD42021293349.

Associations between serum total bilirubin, obesity and type 2 diabetes

BACKGROUND

This study aims to examine the cross-sectional association between serum total bilirubin (STB) and type 2 diabetes (T2D) risk in the general population, and whether obesity could moderate this association.

METHODS

We used data from the 1999-2018 National Health and Nutrition Examination Surveys (NHANES), including a total of 38,641 US adult participants who were 18 years or older. The STB was classified as the low, moderate, and high groups according to tertiles.

RESULTS

We found that participants with lower STB had a significantly higher risk of T2D than those with moderate (OR = 0.81; 95% CI 0.74, 0.89; P < 0.001) and high (OR = 0.65; 95% CI 0.59, 0.73; P < 0.001) STB. Also, a significant interaction between body mass index (BMI) and STB on T2D was observed (P < 0.001). Stratified analysis showed that low STB was associated with a 20% and 27% decrease of T2D risk for moderate and high STB groups in obese patients, however, these effect estimates were smaller in the population with lower BMI (< 30 kg/m²). Similar associations of STB with glycohemoglobin and insulin resistance were observed.

CONCLUSION

This study suggests that STB is associated with an elevated risk of T2D. More importantly, we reported for the first time that BMI may moderate the association between bilirubin and T2D.

Bilirubin deficiency renders mice susceptible to hepatic steatosis in the absence of insulin resistance

Background & aims

Plasma concentrations of bilirubin, a product of heme catabolism formed by biliverdin reductase A (BVRA), inversely associate with the risk of metabolic diseases including hepatic steatosis and diabetes mellitus in humans. Bilirubin has antioxidant and anti-inflammatory activities and may also regulate insulin signaling and peroxisome proliferator-activated receptor alpha (PPARα) activity. However, a causal link between bilirubin and metabolic diseases remains to be established. Here, we used the global Bvra gene knockout (Bvra^–/–) mouse as a model of deficiency in bilirubin to assess its role in metabolic diseases.

Approach & results

We fed mice fat-rich diets to induce hepatic steatosis and insulin resistance. Bile pigments were measured by LC-MS/MS, and hepatic lipids by LC-MS/MS (non-targeted lipidomics), HPLC-UV and Oil-Red-O staining. Oxidative stress was evaluated measuring F₂-isoprostanes by GC-MS. Glucose metabolism and insulin sensitivity were verified by glucose and insulin tolerance tests, ex vivo and in vivo glucose uptake, and Western blotting for insulin signaling. Compared with wild type littermates, Bvra^–/– mice contained negligible bilirubin in plasma and liver, and they had comparable glucose metabolism and insulin sensitivity. However, Bvra^–/– mice exhibited an inflamed and fatty liver phenotype, accompanied by hepatic accumulation of oxidized triacylglycerols and F₂-isoprostanes, in association with depletion of α-tocopherol. α-Tocopherol supplementation reversed the hepatic phenotype and observed biochemical changes in Bvra^–/– mice.

Conclusions

Our data suggests that BVRA deficiency renders mice susceptible to oxidative stress-induced hepatic steatosis in the absence of insulin resistance.

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Low plasma levels of bilirubin associate with increased metabolic disease risk.

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A direct link between bilirubin and metabolic disease remains to be established.

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Global BVRA deficiency causes global bilirubin deficiency and a fatty, inflamed liver.

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This hepatic phenotype is linked to decreased vitamin E and increased lipid oxidation.

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Vitamin E supplements restore normal liver phenotype in BVRA deficiency.

Heme-oxygenase and lipid mediators in obesity and associated cardiometabolic diseases: Therapeutic implications

Obesity-mediated metabolic syndrome remains the leading cause of death worldwide. Among many potential targets for pharmacological intervention, a promising strategy involves the heme oxygenase (HO) system, specifically its inducible form, HO-1. This review collects and updates much of the current knowledge relevant to pharmacology and clinical medicine concerning HO-1 in metabolic diseases and its effect on lipid metabolism. HO-1 has pleotropic effects that collectively reduce inflammation, while increasing vasodilation and insulin and leptin sensitivity. Recent reports indicate that HO-1 with its antioxidants via the effect of bilirubin increases formation of biologically active lipid metabolites such as epoxyeicosatrienoic acid (EET), omega-3 and other polyunsaturated fatty acids (PUFAs). Similarly, HO-1and bilirubin are potential therapeutic targets in the treatment of fat-induced liver diseases. HO-1-mediated upregulation of EET is capable not only of reversing endothelial dysfunction and hypertension, but also of reversing cardiac remodeling, a hallmark of the metabolic syndrome. This process involves browning of white fat tissue (i.e. formation of healthy adipocytes) and reduced lipotoxicity, which otherwise will be toxic to the heart. More importantly, this review examines the activity of EET in biological systems and a series of pathways that explain its mechanism of action and discusses how these might be exploited for potential therapeutic use. We also discuss the link between cardiac ectopic fat deposition and cardiac function in humans, which is similar to that described in obese mice and is regulated by HO-1-EET-PGC1α signaling, a potent negative regulator of the inflammatory adipokine NOV.

Association of Serum Bilirubin Level with Metabolic Syndrome and Non-Alcoholic Fatty Liver Disease: A Cross-Sectional Study of 1672 Obese Children

As in adults, obesity also plays a central role in the development of metabolic syndrome (MS) in children. Non-alcoholic fatty liver disease (NAFLD) is considered a manifestation of MS. Not only MS but also NAFLD seem to be inversely associated with serum bilirubin concentrations, an important endogenous tissue protector when only mild elevated. The aim of the study was to evaluate the association between serum bilirubin levels and the prevalence of MS and NAFLD in Italian obese children and adolescents. A retrospective cross-sectional study was performed in 1672 patients aged from 5 to 18 years. Clinical and laboratory parameters were assessed. NAFLD was measured by liver ultrasonography. The study was approved by the Ethical Committee of the Istituto Auxologico Italiano (research project code 1C021_2020, acronym BILOB). MS was present in 24% and fatty liver (FL) in 38% of this population. Bilirubin was not associated with FL and MS as a whole, but it was inversely associated only with selected components of MS, i.e., large WC, high blood pressure and high triglycerides. Our data suggest that bilirubin is not protective against MS and NAFLD in the presence of severe obesity.

Relationship between serum bilirubin concentration and sarcopenia in patients with type 2 diabetes: a cross-sectional study

OBJECTIVE

The prevalence of sarcopenia is high in patients with type 2 diabetes mellitus (T2DM). Oxidative stress and inflammation play important roles in the pathogenesis of sarcopenia in diabetes. Bilirubin has been shown to possess anti-oxidative activity. We aimed to explore the relationship between bilirubin and sarcopenia in patients with T2DM.

METHODS

A total of 251 patients (124 men and 127 postmenopausal women) with T2DM, aged ≥50 years, participated in a cross-sectional study. The serum concentrations of bilirubin (TBIL), direct bilirubin (DBIL) and indirect bilirubin (IBIL) were measured. Muscle mass was measured using dual-energy X-ray absorptiometry.

RESULTS

TBIL and IBIL were positively associated with appendicular skeletal muscle mass index (SMI) in men, but not in women. After adjustment for multiple factors in multiple linear regression analysis, TBIL and IBIL were also significantly associated with SMI in men. In multiple logistic regression analysis, participants in the highest quartile of IBIL demonstrated a lower odds ratio for sarcopenia in men.

CONCLUSIONS

Both TBIL and IBIL are positively associated with muscle mass in men with T2DM. Furthermore, IBIL may protect against sarcopenia in men with T2DM.

Effects of 6-Month Military Deployment on Physical Fitness, Body Composition, and Selected Health-Related Biomarkers

ABSTRACT

Sedliak, M, Sedliak, P, and Vaara, JP. Effects of 6-month military deployment on physical fitness, body composition, and selected health-related biomarkers. J Strength Cond Res 35(4): 1074-1081, 2021-The purpose was to study the effects of 6-month deployment to Afghanistan on physical performance, anthropometrical, and health-related biochemical parameters in soldiers with sedentary to light physical workload shifts. Twenty-five male soldiers (30 ± 4 years) volunteered and were measured before and after the 6-month deployment. Another 25 home-land-based male soldiers (30 ± 6 years) served as controls. Total body fat percentage decreased in deployed soldiers (Pre: 23.2 ± 5.3 vs. Post: 20.8 ± 5.5%, p < 0.05), whereas no change was observed in control (20.2 ± 6.9 vs. 20.5 ± 7.0%). Physical performance improved in deployed soldiers in 4 × 10-m shuttle run (10.86 ± 0.90 vs. 10.49 ± 0.63 seconds) and pull-up test to failure (4.7 ± 3.7 vs. 7.5 ± 6.7 rep.) (p < 0.05) but not in the controls for the respective tests (10.28 ± 0.74 vs. 10.40 ± 0.76 seconds and 10.2 ± 7.8 vs. 10.2 ± 7.5 rep.). Deployed soldiers also improved 5-km run with a simulated combat gear time (29.2 ± 3.1 vs. 27.4 ± 3.0 minutes), whereas in control the time increased (26.4 ± 2.9 vs. 27.8 ± 2.6 minutes, p < 0.05). Load at maximum power output in bench press was improved in deployed soldiers (51.6 ± 11.3 vs. 56.2 ± 12.6 kg, p < 0.05). Serum glucose and creatinine decreased (5.46 ± 0.53 vs. 4.87 ± 0.74 mmol·L-1 and 87.4 ± 10.7 vs. 80.9 ± 10.2 μmmol·L-1, respectively), and hemoglobin and hematocrite increased (15.13 ± 0.82 vs. 16.75 ± 0.85 g·dl-1 and 45.3 ± 1.5 vs. 48.1 ± 2.4%, respectively, p < 0.05) in the deployment group. In conclusion, after 6-month deployment consisting of sedentary and low physical occupational load, soldiers were able to increase their physical fitness and decrease their body fat content and improve selected health-related biochemical parameters. Therefore, the adoption and promotion of leisure-time physical activity in soldiers during deployments is essential to maintain combat readiness.

Bilirubin as a metabolic hormone: the physiological relevance of low levels

Recent research on bilirubin, a historically well-known waste product of heme catabolism, suggests an entirely new function as a metabolic hormone that drives gene transcription by nuclear receptors. Studies are now revealing that low plasma bilirubin levels, defined as "hypobilirubinemia," are a possible new pathology analogous to the other end of the spectrum of extreme hyperbilirubinemia seen in patients with jaundice and liver dysfunction. Hypobilirubinemia is most commonly seen in patients with metabolic dysfunction, which may lead to cardiovascular complications and possibly stroke. We address the clinical significance of low bilirubin levels. A better understanding of bilirubin's hormonal function may explain why hypobilirubinemia might be deleterious. We present mechanisms by which bilirubin may be protective at mildly elevated levels and research directions that could generate treatment possibilities for patients with hypobilirubinemia, such as targeting of pathways that regulate its production or turnover or the newly designed bilirubin nanoparticles. Our review here calls for a shift in the perspective of an old molecule that could benefit millions of patients with hypobilirubinemia.

Gut Microbiota: The Missing Link Between Helicobacter pylori Infection and Metabolic Disorders?

Helicobacter pylori (H. pylori) is a gram-negative bacterium that infects approximately 4.4 billion individuals worldwide. Although the majority of infected individuals remain asymptomatic, this bacterium colonizes the gastric mucosa causing the development of various clinical conditions as peptic ulcers, chronic gastritis and gastric adenocarcinomas and mucosa-associated lymphoid tissue lymphomas, but complications are not limited to gastric ones. Extradigestive pathologies, including metabolic disturbances such as diabetes, obesity and nonalcoholic fatty liver disease, have also been associated with H. pylori infection. However, the underlying mechanisms connecting H. pylori with extragastric metabolic diseases needs to be clarified. Notably, the latest studies on the topic have confirmed that H. pylori infection modulates gut microbiota in humans. Damage in the gut bacterial community (dysbiosis) has been widely related to metabolic dysregulation by affecting adiposity, host energy balance, carbohydrate metabolism, and hormonal modulation, among others. Taking into account that Type 2 diabetic patients are more prone to be H. pylori positive, gut microbiota emerges as putative key factor responsible for this interaction. In this regard, the therapy of choice for H. pylori eradication, based on proton pump inhibitor combined with two or more antibiotics, also alters gut microbiota composition, but consequences on metabolic health of the patients has been scarcely explored. Recent studies from our group showed that, despite decreasing gut bacterial diversity, conventional H. pylori eradication therapy is related to positive changes in glucose and lipid profiles. The mechanistic insights explaining these effects should also be addressed in future research. This review will deal with the role of gut microbiota as the linking factor between H. pylori infection and metabolic diseases, and discussed the impact that gut bacterial modulation by H. pylori eradication treatment can also have in host's metabolism. For this purpose, new evidence from the latest human studies published in more recent years will be analyzed.

Rats Genetically Selected for High Aerobic Exercise Capacity Have Elevated Plasma Bilirubin by Upregulation of Hepatic Biliverdin Reductase-A (BVRA) and Suppression of UGT1A1

Exercise in humans and animals increases plasma bilirubin levels, but the mechanism by which this occurs is unknown. In the present study, we utilized rats genetically selected for high capacity running (HCR) and low capacity running (LCR) to determine pathways in the liver that aerobic exercise modifies to control plasma bilirubin. The HCR rats, compared to the LCR, exhibited significantly higher levels of plasma bilirubin and the hepatic enzyme that produces it, biliverdin reductase-A (BVRA). The HCR also had reduced expression of the glucuronyl hepatic enzyme UGT1A1, which lowers plasma bilirubin. Recently, bilirubin has been shown to activate the peroxisome proliferator-activated receptor-α (PPARα), a ligand-induced transcription factor, and the higher bilirubin HCR rats had significantly increased PPARα-target genes Fgf21, Abcd3, and Gys2. These are known to promote liver function and glycogen storage, which we found by Periodic acid–Schiff (PAS) staining that hepatic glycogen content was higher in the HCR versus the LCR. Our results demonstrate that exercise stimulates pathways that raise plasma bilirubin through alterations in hepatic enzymes involved in bilirubin synthesis and metabolism, improving liver function, and glycogen content. These mechanisms may explain the beneficial effects of exercise on plasma bilirubin levels and health in humans.

Rapid and simultaneous analysis of direct and indirect bilirubin indicators in serum through reagent-free visible-near-infrared spectroscopy combined with chemometrics

Indirect (IBil), direct (DBil) and total (TBil) bilirubin are important clinical indicators of hepatobiliary diseases, which require rapid detection in diagnosis and treatment. IBil and DBil have a structural relationship with several macromolecules in hepatobiliary metabolism. Here, the rapid analysis models for bilirubin indicators using serum visible-near-infrared (Vis-NIR) spectroscopy were established. Norris derivative filter with optimisation was used for spectral pretreatment; the optimal parameters (derivative order, number of smoothing points, number of differential gaps) were (2, 15, 9) for IBil; (2, 13, 9) for DBil, respectively. Equidistant combination-partial least squares (EC-PLS) was used for large-scale wavelength screening. Wavelength step-by-step phase-out PLS (WSP-PLS) was used for secondary wavelength optimisation. The wavelength models of the optimal EC-WSP-PLS for IBil and DBil included 11 and 18 wavelengths, respectively. In independent validation, the root-mean-square errors and correlation coefficient for prediction (SEP, R_P), and ratio of performance-to-deviation (RPD) were 0.90 μmol L^-1, 0.975, and 4.4 for IBil; 0.71 μmol L^-1, 0.955, and 3.3 for DBil, respectively. TBil was subjected to spectral analysis, and the summation of the prediction values of IBil and DBil was compared. The latter was obviously better, and SEP, R_P, RPD were 0.82 μmol L^-1, 0.990, 7.1, respectively. The results for IBil, DBil and TBil indicated high correlation, low error and good overall prediction ability and confirmed the feasibility of the simultaneous analysis of bilirubin indicators through reagent-free serum Vis-NIR spectroscopy. The proposed method is crucial for the rapid screening of large populations and the treatment of hepatobiliary diseases.

Serum Bilirubin Level as a Potential Marker for the Hearing Outcome in Severe-Profound Bilateral Sudden Deafness

Supplemental Digital Content is available in the text

Objective:

To investigate the association of serum bilirubin level with hearing outcomes in bilateral sudden sensorineural hearing loss (BSSHL) patients.

Participants:

One hundred thirteen in-patient BSSHL patients were consecutively enrolled between July 2008 and December 2015 in a tertiary center.

Main Outcome Measures:

Multivariable linear regression, generalized estimating equations (GEE), and stratified analyses were applied to examine the association between serum bilirubin level and hearing outcome measures such as final hearing threshold and absolute and relative hearing gains in BSSHL.

Results:

After full adjustment for potential confounders, total bilirubin levels (TBIL) were observed to be positively and independently associated with hearing outcomes as measured by final hearing (β [95% confidence interval {CI}]: −1.5 [−2.7, −0.2] dB HL per 1 μmol/L increase in TBIL) and absolute and relative hearing gains (β [95% CI]: 1.4 [0.2, 2.7] dB and 1.6 [0.2, 3.1] dB, respectively) in the severe to profound hearing loss subpopulation.

Conclusions:

Higher TBIL levels, within the normal or mildly elevated ranges, were independently and significantly associated with better hearing outcome in BSSHL patients with severe to profound hearing loss. Given bilirubin elevation treatments exist, our finding suggests a novel pharmacological strategy for this specific subpopulation.

Bilirubin remodels murine white adipose tissue by reshaping mitochondrial activity and the coregulator profile of peroxisome proliferator-activated receptor α

Activation of lipid-burning pathways in the fat-storing white adipose tissue (WAT) is a promising strategy to improve metabolic health and reduce obesity, insulin resistance, and type II diabetes. For unknown reasons, bilirubin levels are negatively associated with obesity and diabetes. Here, using mice and an array of approaches, including MRI to assess body composition, biochemical assays to measure bilirubin and fatty acids, MitoTracker-based mitochondrial analysis, immunofluorescence, and high-throughput coregulator analysis, we show that bilirubin functions as a molecular switch for the nuclear receptor transcription factor peroxisome proliferator-activated receptor α (PPARα). Bilirubin exerted its effects by recruiting and dissociating specific coregulators in WAT, driving the expression of PPARα target genes such as uncoupling protein 1 (Ucp1) and adrenoreceptor β 3 (Adrb3). We also found that bilirubin is a selective ligand for PPARα and does not affect the activities of the related proteins PPARγ and PPARδ. We further found that diet-induced obese mice with mild hyperbilirubinemia have reduced WAT size and an increased number of mitochondria, associated with a restructuring of PPARα-binding coregulators. We conclude that bilirubin strongly affects organismal body weight by reshaping the PPARα coregulator profile, remodeling WAT to improve metabolic function, and reducing fat accumulation.

Antiobesity Effect of Biochanin-A: Effect on Trace Element Metabolism in High Fat Diet-Induced Obesity in Rats

BACKGROUND

Imbalanced diets have contributed to the increased prevalence of obesity and other metabolic disorders in the modern world including trace element metabolism. However, the underlying mechanisms are not fully understood.

AIM AND OBJECTIVES

The present study investigated the effects of Biochanin A (BCA) on the changes in element metabolism induced by HFD-induced obese rats.

METHODS

BCA was administered orally for 30 days to experimental obese rats. Changes in body weight, glucose, insulin resistance and lipid profiles of plasma, as well as the level of trace elements (Fe, Zn, Mg and Cu) in various tissues (liver, kidney, heart and pancreas) and hepsidine and heme oxygenase, were observed in experimental rats.

RESULTS

The administration of BCA elicited a significant (p<0.05) reduction in, glucose, insulin, ferritin, total cholesterol, phospholipids, free fatty acids, VLDL-C, LDL-C, triglycerides and hepsidin. Significant alterations were observed in trace elements level, HDL-C, transferrin, bilirubin and HO - 1 level.

CONCLUSION

These findings suggested that HFD results in derangement of trace elements in the tissues of rats fed with HFD. BCA may alleviate the derangement of HFD induced trace elements metabolism by modulating hyperglycemic and insulin resistance status and altering hepcidin and HO-1.

Associations between Neonatal Serum Bilirubin and Childhood Obesity in Term Infants

Inverse correlations between serum bilirubin level and obesity had been reported in adults. We aimed to investigate the associations between neonatal hyperbilirubinemia and childhood obesity. Data was obtained from the U.S. Collaborative Perinatal Project (CPP), a multicenter study from 1959 to 1976. Data of serum bilirubin in term newborns were used to observe the association with obesity at age of 7 years. Logistic regression models were performed to calculate adjusted odds ratios (aORs) for obesity. For children from the same mother sharing similar factors, Generalized Estimating Equation (GEE) model was used to correct for intracluster correlation. Relative to newborns with total serum bilirubin (TSB) < 3 mg/dl, there are lower risks for obesity in those with 3 mg/dl ≤ TSB < 6 mg/dl (aOR 0.91; 95%CI 0.81, 1.02), 6 mg/dl ≤ TSB < 9 mg/dl (aOR 0.88; 95%CI 0.78, 0.99), 9 mg/dl ≤ TSB<13 mg/dl (aOR 0.83; 95%CI 0.71, 0.98). By stratifying for subtypes of bilirubin, the inverse correlations only existed in exposure to unconjugated bilirubin. By using the GEE model correcting for intracluster correlations, the results are consistent. In summary, exposure to bilirubin up to 13 mg/dl is inversely associated with obesity at the age of 7 years in term infants.

Bilirubin Safeguards Cardiorenal and Metabolic Diseases: a Protective Role in Health

PURPOSE OF REVIEW

To discuss recent advances indicating that bilirubin safeguards against cardiorenal and metabolic diseases.

RECENT FINDINGS

Several investigations from human patient populations and experimental animal models have shown that bilirubin improves cardiorenal and metabolic dysfunction. The latest studies found an entirely new function of bilirubin suggesting that it acts as a hormone signaling molecule capable of activating nuclear receptors for burning fat, which may explain several of its protective actions. This review highlights the current findings (within the last 3 years) regarding cardiorenal and metabolic protective effects of bilirubin and the latest mechanism(s) that may be mediating these effects.

Total bilirubin is negatively related to diabetes mellitus in Chinese elderly: a community study

Background

Serum total bilirubin (TB) was used as a predictor of diabetes mellitus (DM) and this study was undertaken to investigate the relationship between serum TB and DM.

Methods

In this cross-sectional study, a total of 3,867 subjects older than 65 years were recruited from East China. The anthropometric data, lifestyle and past history were collected. The fasting blood glucose, total cholesterol (TC), triglycerides (TGs), TB and alanine aminotransferase (ALT) were detected. The prevalence of DM was calculated for every serum TB quartile. Logistic regression analysis was employed to evaluate the relationship between serum TB and DM.

Results

Serum TB was significantly higher in non-DM than DM patients (P=0.001). Serum TB was negatively related to the prevalence of DM (P=0.004). Logistic regression analysis revealed that serum TB was an independent prognostic factor of DM [odds ratio (OR): 0.876, 95% confidence interval (CI): 0.807-0.951].

Conclusions

Our results showed serum TB in physiological range is an independent risk factor of DM in old people; the prevalence of DM in old people has a linear relationship with serum TB quartiles; the prevalence of DM reduces with the increasing of serum TB within physiological range.

HO-1 and CD39: It Takes Two to Protect the Realm

Cellular protective mechanisms exist to ensure survival of the cells and are a fundamental feature of all cells that is necessary for adapting to changes in the environment. Indeed, evolution has ensured that each cell is equipped with multiple overlapping families of genes that safeguard against pathogens, injury, stress, and dysfunctional metabolic processes. Two of the better-known enzymatic systems, conserved through all species, include the heme oxygenases (HO-1/HO-2), and the ectonucleotidases (CD39/73). Each of these systems generates critical bioactive products that regulate the cellular response to a stressor. Absence of these molecules results in the cell being extremely predisposed to collapse and, in most cases, results in the death of the cell. Recent reports have begun to link these two metabolic pathways, and what were once exclusively stand-alone are now being found to be intimately interrelated and do so through their innate ability to generate bioactive products including adenosine, carbon monoxide, and bilirubin. These simple small molecules elicit profound cellular physiologic responses that impact a number of innate immune responses, and participate in the regulation of inflammation and tissue repair. Collectively these enzymes are linked not only because of the mitochondria being the source of their substrates, but perhaps more importantly, because of the impact of their products on specific cellular responses. This review will provide a synopsis of the current state of the field regarding how these systems are linked and how they are now being leveraged as therapeutic modalities in the clinic.

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.

Bilirubin alleviates alum-induced peritonitis through inactivation of NLRP3 inflammasome

Bilirubin is an endogenous substance derived from heme catabolism. In this study, we aimed to assess the anti-inflammatory activity of bilirubin, and to determine the mechanism thereof. The anti-inflammatory activity of bilirubin was evaluated using lipopolysaccharide (LPS)-treated peritoneal macrophages (PMs) and Raw264.7 cells, and mice with alum-induced peritonitis. The mRNA and proteins of NOD-like receptor family pyrin domain containing 3 (Nlrp3) and inflammatory cytokines were determined using qPCR and Western blotting, respectively. Distribution of phosphorylated (p) p65 [a NF-κB (nuclear factor-κB) subunit] in the cytoplasm and nucleus were evaluated by immunofluorescence analysis and electrophoretic mobility shift assay. Bilirubin prior to LPS treatment decreased protein expressions of Nlrp3, pro-interleukin (IL)-1β and mature IL-1β in PMs, whereas bilirubin post LPS treatment showed no effects. Bilirubin prior to LPS treatment dose-dependently repressed expressions of Nlrp3 and IL-1β, and inhibited translocation of p-p65 to nucleus in Raw264.7 cells. Bilirubin treatment decreased myeloperoxidase activity and reduced the levels of inflammatory cytokines (i.e., IL-1β, TNFα and IL-6) in lavage fluid in mice with alum-induced peritonitis. This was accompanied by a lower mortality rate. In addition, the mRNAs of Nlrp3 and IL-1β in peritoneal exudates cells were decreased, and the levels of p-p65 and mature IL-1β proteins were reduced. In conclusion, bilirubin acted on inflammation and alleviated alum-induced peritonitis through inactivation of Nlrp3 inflammasome.

Immune challenge-induced oxidative damage may be mitigated by biliverdin

An effective immune response results in the elimination of pathogens, but this immunological benefit may be accompanied by increased levels of oxidative damage. However, organisms have evolved mechanisms to mitigate the extent of such oxidative damage, including the production and mobilization of antioxidants. One potential mechanism of mitigating immune challenge-induced changes in oxidative physiology is increasing biliverdin production. Biliverdin is chemically an antioxidant, but within-tissue correlations between biliverdin concentration and oxidative damage have never been directly examined. To test how biliverdin tissue concentrations are associated with physiological responses to an immune challenge, we exposed northern bobwhite quail (Colinus virginianus) to one of four treatments: injection of a non-pathogenic antigen - either lipopolysaccharide or phytohemagglutinin, control injection of phosphate-buffered saline or a sham procedure with no injection. Twenty-four hours later, we quantified oxidative damage and triglyceride concentration in the plasma, and biliverdin concentration in the plasma, liver and spleen. We found that both types of immune challenge increased oxidative damage relative to both non-injected and vehicle-injected controls, but treatment had no effects on any other metric. However, across all birds, oxidative damage and biliverdin concentration in the plasma were negatively correlated, which is consistent with a localized antioxidant function of biliverdin. Additionally, we uncovered multiple links between biliverdin concentration, change in mass during the immune challenges and triglyceride levels, suggesting that pathways associated with biliverdin production may also be associated with aspects of nutrient mobilization. Future experiments that manipulate biliverdin levels or oxidative damage directly could establish a systemic antioxidant function or elucidate important physiological impacts on body mass maintenance and triglyceride storage, mobilization or transport.

Helicobacter pylori infection as a risk factor for serum bilirubin change and less favourable lipid profiles: a hospital-based health examination survey

Background

Helicobacter pylori infection is associated with several extragastric conditions including dyslipidemia and metabolic syndrome. This study aimed to investigate additional metabolic parameters associated with H. pylori infection in a Chinese population.

Methods

Using a case-control approach we studied 617 subjects with ¹³C-urea breath test (¹³C-UBT) values ≥10‰ who were defined as being positive for H. pylori (cases), while 617 sex and age- matched subjects with ¹³C-UBT values ≤1‰ were defined as H. pylori negative (controls) in Beijing Tongren Hospital from March 2016 to May 2017. Biochemical parameters including serum bilirubin and lipids were tested.

Results

A total of 1982 subjects participated in this study. The H. pylori infected subjects had significantly lower serum direct bilirubin concentrations (2.34 ± 0.38 vs. 2.47 ± 0.90 μmol/L, P = 0.008). H. pylori infection was independently associated with lower direct bilirubin levels (OR = 1.497, 95% CI =1.121–1.999, P = 0.006) or total bilirubin levels (OR = 1.322, 95% CI =1.005–1.738, P = 0.046) after adjustment for age, sex, body mass index (BMI), alanine aminotransferase (ALT), aspartate aminotransferase (AST), high-density lipoprotein cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), total cholesterol (TC) and triglycerides(TG). In addition, the H. pylori infected subjects had higher LDL-C levels (2.98 ± 0.76 vs. 2.89 ± 0.75 mmol/L, P = 0.033) and lower HDL-C levels (1.39 ± 0.37 vs. 1.44 ± 0.41 mmol/L, P = 0.044). LDL-C was negatively correlated with direct bilirubin concentration (R = − 0.260, P < 0.0001).

Conclusions

Bilirubin has been found to be a potent endogenous antioxidant and negatively associated with metabolic syndrome. Our results suggest that H. pylori infection is an independent risk factor for serum bilirubin reduction and less favorable lipid profiles.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-3787-8) contains supplementary material, which is available to authorized users.

Lower serum total bilirubin concentration is associated with higher prevalence of gestational diabetes mellitus in Japanese pregnant women

We aimed to clarify the pathophysiological significance of total bilirubin (TB) in gestational diabetes mellitus (GDM). This was a cross-sectional study that included 616 pregnant Japanese women (368 normal glucose tolerance [NGT] and 248 GDM). Serum TB concentration, homeostasis model assessment of insulin resistance (HOMA-IR), and other clinical parameters were compared in NGT and GDM women. TB concentration was also compared according to the number of abnormal OGTT values. Logistic regression analysis was used to evaluate the association between TB and GDM prevalence. A multiple linear regression model was used to evaluate the association between TB and HOMA-IR. TB concentrations were significantly lower in GDM women than in NGT women. This result did not change after adjustments for TB sampling timing were made. Out of 248 GDM women, the prevalences of 1- and 2/3- abnormal OGTT values (1- and 2/3-AV) GDM were 72.2% (n = 179) and 27.8% (n = 69), respectively. In the multiple comparisons, TB concentrations were significantly lower in women with 2/3-AV GDM than in women with NGT and 1-AV GDM. Multiple logistic regression analysis showed that TB was a significantly associated factor for 2/3-AV, but not for total GDM. HOMA-IR was significantly higher in GDM women than in NGT women. The univariate, but not multivariate, analysis showed that TB was a significantly associated factor for HOMA-IR. Our findings suggest that hypobilirubinemia may be involved in the pathogenesis of GDM.

Bilirubin, a new therapeutic for kidney transplant?

In patients with end-stage renal disease, kidney transplantation has been associated with numerous benefits, including increased daily activity, and better survival rates. However, over 20% of kidney transplants result in rejection within five years. Rejection is primarily due to a hypersensitive immune system and ischemia/reperfusion injury. Bilirubin has been shown to be a potent antioxidant that is capable of potentially reversing or preventing damage from reactive oxygen species generated from ischemia and reperfusion. Additionally, bilirubin has several immunomodulatory effects that can dampen the immune system to promote organ acceptance. Increased bilirubin has also been shown to have a positive impact on renal hemodynamics, which is critical post-transplantation. Lastly, bilirubin levels have been correlated with biomarkers of successful transplantation. In this review, we discuss a multitude of potentially beneficial effects that bilirubin has on kidney acceptance of transplantation based on numerous clinical trials and animal models. Exogenous bilirubin delivery or increasing endogenous levels pre- or post-transplantation may have therapeutic benefits.

Alanine Aminotransferase and Total Bilirubin Are Synergistically Associated with Metabolic Syndrome Among Middle-Aged and Elderly Japanese Women

BACKGROUND

Metabolic syndrome (MetS) is associated with an increased risk of major cardiovascular events. Alanine aminotransferase (ALT) at high levels and total bilirubin (T-BiL) at low levels were oxidative potentials, but it was uncertain whether ALT and T-BiL had an additive interaction for the risk of MetS.

METHODS

From a single community, we recruited 864 women (70 ± 8 years) during their annual health examination. We cross-sectionally investigated whether ALT and T-BiL are associated with MetS and its components based on the modified criteria of the National Cholesterol Education Program's Adult Treatment Panel (NCEP-ATP) III report.

RESULTS

Of these subjects, 415 women (48.0%) had MetS. Participants with MetS had a higher ALT and lower T-BiL level than those without MetS. The adjusted-odds ratios (OR) (95% confidence interval [CI]) for MetS across tertiles of ALT and T-BiL were 1.00, 1.19 (0.78-1.81), and 1.86 (1.24-2.80) and 1.00, 0.96 (0.65-1.43), and 0.54 (0.36-0.81), respectively. When ALT and T-BiL were categorized into three binary characteristics by tertiles of ALT and T-BiL, high T-BiL was associated with decreased risk for MetS in a multivariable model (OR: 0.55, 95% CI: 0.37-0.82), especially among those with 1st tertile ALT. Similarly, high ALT was also associated with increased risk for MetS in a multivariate model (OR: 1.81, 95% CI: 1.20-2.71), especially among those with 2nd & 3rd tertiles of T-BiL. In the formal testing of addictive interaction between ALT and T-BiL for MetS, presence of T-BiL <0.72 mg/dL (1st and 2nd tertile) alone was not associated with increased risk of MetS in a multivariate analysis, and presence of ALT ≥16 IU/L (2nd and 3rd tertile) alone was not associated with increased risk of MetS.

CONCLUSIONS

These results suggested that higher ALT and lower T-BiL levels were synergistically associated with MetS, independent of other confounding factors among Japanese women.

Untangling the relationship between diet and visceral fat mass through blood metabolomics and gut microbiome profiling

BACKGROUND/OBJECTIVES

Higher visceral fat mass (VFM) is associated with an increased risk for developing cardio-metabolic diseases. The mechanisms by which an unhealthy diet pattern may influence visceral fat (VF) development has yet to be examined through cutting-edge multi-omic methods. Therefore, our objective was to examine the dietary influences on VFM and identify gut microbiome and metabolite profiles that link food intakes to VFM.

SUBJECTS/METHODS

In 2218 twins with VFM, food intake and metabolomics data available we identified food intakes most strongly associated with VFM in 50% of the sample, then constructed and tested the 'VFM diet score' in the remainder of the sample. Using linear regression (adjusted for covariates, including body mass index and total fat mass), we investigated associations between the VFM diet score, the blood metabolomics profile and the fecal microbiome (n=889), and confirmed these associations with VFM. We replicated top findings in monozygotic (MZ) twins discordant (⩾1 s.d. apart) for VFM, matched for age, sex and the baseline genetic sequence.

RESULTS

Four metabolites were associated with the VFM diet score and VFM: hippurate, alpha-hydroxyisovalerate, bilirubin (Z,Z) and butyrylcarnitine. We replicated associations between VFM and the diet score (beta (s.e.): 0.281 (0.091); P=0.002), butyrylcarnitine (0.199 (0.087); P=0.023) and hippurate (-0.297 (0.095); P=0.002) in VFM-discordant MZ twins. We identified a single species, Eubacterium dolichum to be associated with the VFM diet score (0.042 (0.011), P=8.47 × 10-5), VFM (0.057 (0.019), P=2.73 × 10-3) and hippurate (-0.075 (0.032), P=0.021). Moreover, higher blood hippurate was associated with elevated adipose tissue expression neuroglobin, with roles in cellular oxygen homeostasis (0.016 (0.004), P=9.82x10-6).

CONCLUSIONS

We linked a dietary VFM score and VFM to E. dolichum and four metabolites in the blood. In particular, the relationship between hippurate, a metabolite derived from microbial metabolism of dietary polyphenols, and reduced VFM, the microbiome and increased adipose tissue expression of neuroglobin provides potential mechanistic insight into the influence of diet on VFM.

Relationship between Serum Bilirubin Levels and Metabolic Syndrome in Patients with Schizophrenia Spectrum Disorders

Objective

We investigated the relationship between serum bilirubin levels and metabolic syndrome (MetS), and the longitudinal effects of baseline serum bilirubin concentrations on MetS in patients with schizophrenia spectrum disorders undergoing atypical antipsychotics.

Methods

The sample of this study consisted of 131 patients with schizophrenia spectrum disorders. Waist circumference, blood pressure, and levels of triglycerides, high-density lipoprotein cholesterol, fasting glucose, and insulin were evaluated at baseline and at month six. Serum bilirubin levels were measured at baseline. Serum bilirubin levels of the patients with and without MetS criteria were compared. We also compared patients with high and low bilirubin levels (upper and lower 50th percentiles of serum bilirubin levels) in terms of MetS criteria, MetS frequency, and course of MetS.

Results

Serum direct bilirubin levels were more consistently related to MetS and MetS-related variables. The waist circumference and triglyceride criteria for MetS were significantly related to low serum direct bilirubin at baseline; waist circumference and fasting glucose criteria, and insulin resistance were associated with low serum direct bilirubin at follow-up. MetS diagnosis and the presence of the waist circumference criterion were more frequent at the baseline and the follow-up in low bilirubin group. At the end of the follow-up period, the rate of reverse MetS was significantly higher in the high bilirubin group.

Conclusion

Our results have suggested that serum direct bilirubin levels showed a more reliable and stable relationship with abdominal obesity for MetS components.in patients with schizophrenia spectrum disorders using antipsychotics. Further studies are required.

Handgrip Strength Is Positively Associated with Mildly Elevated Serum Bilirubin Levels among Community-Dwelling Adults

Handgrip strength (HGS) is a useful measure of health-related quality of life and general muscle strength. Serum total bilirubin (T-B) may present potential beneficial effects in preventing oxidative changes which are associated with a risk of metabolic syndrome and the development of cardiovascular disease. Limited information is available regarding whether HGS is an independent confounding factor for serum T-B. The study participants were 214 men aged 71 ± 8 (mean ± standard deviation) years and 302 women aged 71 ± 7 years that were enrolled consecutively from among paticipants aged ≥ 50 years through an annual check-up process. We evaluated the relationship between serum T-B and confounding factors within each sex. HGS related significantly with serum T-B in both men (r = 0.156, p = 0.023) and women (r = 0.173, p = 0.003). Multiple linear regression analysis showed that in men, HGS (β = 0.173) as well as smoking status (β = -0.147), exercise habit (β = 0.138), low-density lipoprotein cholesterol (β = 0.146), and hemoglobin A1c (HbA1c) (β = -0.198) were significantly and independently associated with serum T-B. In women, HGS (β = 0.159) as well as smoking status (β = -0.116), high-density lipoprotein cholesterol (β = 0.159), and HbA1c (β = -0.161) were significantly and independently associated with serum T-B. Multivariate-adjusted serum T-B levels were significantly lower in subjects with the lowest HGS level in both sexes. Increased HGS is strongly associated with increased serum T-B, independent of confounding factors in both sexes.

Mice with hyperbilirubinemia due to Gilbert's syndrome polymorphism are resistant to hepatic steatosis by decreased serine 73 phosphorylation of PPARα

Gilbert's syndrome in humans is derived from a polymorphism (TA repeat) in the hepatic UGT1A1 gene that results in decreased conjugation and increased levels of unconjugated bilirubin. Recently, we have shown that bilirubin binds directly to the fat-burning nuclear peroxisome proliferator-activated receptor-α (PPARα). Additionally, we have shown that serine 73 phosphorylation [Ser(P)⁷³] of PPARα decreases activity by reducing its protein levels and transcriptional activity. The aim of this study was to determine whether humanized mice with the Gilbert's polymorphism (HuUGT*28) have increased PPARα activation and reduced hepatic fat accumulation. To determine whether humanized mice with Gilbert's mutation (HuUGT*28) have reduced hepatic lipids, we placed them and C57BL/6J control mice on a high-fat (60%) diet for 36 wk. Body weights, fat and lean mass, and fasting blood glucose and insulin levels were measured every 6 wk throughout the investigation. At the end of the study, hepatic lipid content was measured and PPARα regulated genes as well as immunostaining of Ser(P)⁷³ PPARα from liver sections. The HuUGT*28 mice had increased serum bilirubin, lean body mass, decreased fat mass, and hepatic lipid content as well as lower serum glucose and insulin levels. Also, the HuUGT*28 mice had reduced Ser(P)⁷³ PPARα immunostaining in livers and increased PPARα transcriptional activity compared with controls. A chronic but mild endogenous increase in unconjugated hyperbiliubinemia protects against hepatic steatosis through a reduction in Ser(P)⁷³ PPARα, causing an increase in PPARα transcriptional activity.

Association between liver function and metabolic syndrome in Chinese men and women

Metabolic syndrome (MS) could be associated with liver function. Our study aimed to investigate the association between liver function and MS in a large cohort of Chinese men and women. We enrolled 32,768 ostensibly healthy participants. The associations between liver function and MS of both genders were analyzed separately after dividing total bilirubin (TBIL), gamma glutamyltransferase (GGT), alanine aminotransferase (ALT) into quartiles. Young males had significantly higher MS prevalence than females, yet after menopause, females had higher MS prevalence. We used TBIL, GGT and ALT quartiles as categorical variables in binary logistic regression models. Significantly decreased MS risks were demonstrated in TBIL quartiles 2 to 4 for males, and quartiles 3 to 4 for females. As to GGT and ALT, significantly increased MS risks were shown in high quartiles for both genders. Aging also resulted in significantly higher MS risks in both genders except for young females. This study displayed close associations between liver function and MS, which were influenced by gender and age. A high TBIL level had protective effect against MS, while high GGT and ALT levels were risk factors for MS. It is meaningful that liver function is used as clinical risk predictors for MS.

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.

Serum bilirubin levels and risk of type 2 diabetes: results from two independent cohorts in middle-aged and elderly Chinese

Serum bilirubin is a potent endogenous antioxidant and has been identified as cardiovascular risk in cohort studies, while the relation to type 2 diabetes (T2D) in the elderly remains unclear. We investigated both cross-sectional and prospective associations between serum bilirubin levels and T2D risk in the Dongfeng-Tongji (DFTJ) cohort, and replicated the prospective findings in a nested case-control study (509 cases and 509 controls) within the Singapore Chinese Health Study (SCHS). In the cross-sectional analysis of DFTJ cohort (15,575 participants with 2,532 diabetes cases), serum bilirubin levels (total, direct and indirect) increased in new on-set diabetes and decreased with the diabetic duration. In the longitudinal analysis of DFTJ cohort (772 incident diabetes cases during 4.5 years of follow-up among 12,530 diabetes-free participants at baseline), positive association was found between direct bilirubin and T2D risk comparing extreme quartiles, similar results were observed in the nested case-control study within SCHS. Total and indirect bilirubin levels were not significantly associated with T2D in either cohort. In conclusion, our findings do not support the protective association between serum bilirubin levels and incident T2D in the middle-aged and elderly adults; instead, direct bilirubin levels were associated with increased risk of T2D.