Impact of serum bilirubin on human diseases

A Coumarin-Porphyrin FRET Break-Apart Probe for Heme Oxygenase-1

Heme oxygenase-1 (HO-1) is a vital enzyme in humans that primarily regulates free heme concentrations. The overexpression of HO-1 is commonly associated with cardiovascular and neurodegenerative diseases including atherosclerosis and ischemic stroke. Currently, there are no known chemical probes to detect HO-1 activity, limiting its potential as an early diagnostic/prognostic marker in these serious diseases. Reported here are the design, synthesis, and photophysical and biological characterization of a coumarin-porphyrin FRET break-apart probe to detect HO-1 activity, Fe-L1. We designed Fe-L1 to "break-apart" upon HO-1-catalyzed porphyrin degradation, perturbing the efficient FRET mechanism from a coumarin donor to a porphyrin acceptor fluorophore. Analysis of HO-1 activity using Escherichia coli lysates overexpressing hHO-1 found that a 6-fold increase in emission intensity at 383 nm was observed following incubation with NADPH. The identities of the degradation products following catabolism were confirmed by MALDI-MS and LC-MS, showing that porphyrin catabolism was regioselective at the α-position. Finally, through the analysis of Fe-L2, we have shown that close structural analogues of heme are required to maintain HO-1 activity. It is anticipated that this work will act as a foundation to design and develop new probes for HO-1 activity in the future, moving toward applications of live fluorescent imaging.

Elevated Preoperative Serum Bilirubin Improves Reperfusion Injury and Survival Postliver Transplantation

Background

The cytoprotective effects of hemeoxygenase-1 and its product biliverdin/bilirubin are widely acknowledged in experimental transplant medicine. However, its potentially beneficial effect during organ reperfusion is not established.

Methods

In a matched study, we compared markers of reperfusion injury (alanine aminotransferase/aspartate aminotransferase) and transplantation outcome (complication rates, liver function, and survival) between recipient groups with “normal” versus “increased” preoperative bilirubin values. Groups were matched for donor and recipient age, liver disease, year of transplantation, and recipient’s preoperative condition (modified model for end-stage liver disease score excluding bilirubin).

Results

The postoperative transaminase peak was significantly higher when comparing the “normal” to the “increased” bilirubin group (maximum aspartate aminotransferase “normal” 2013 [325-13 210] U/L vs “increased” 1360 [221-15 460] U/L, P = 0.006; maximum alanine aminotransferase “normal” 1151 [82-6595] U/L vs “increased” 820 [66-5382] U/L, P = 0.01). Grafts in the “increased” bilirubin group had faster recovery of graft function with faster decrease in international normalized ratio at days 3 and 7 posttransplantation in the “increased” vs “normal” bilirubin group. Although long-term functional parameters (international normalized ratio and bilirubin posttransplantation) as well as surgical and biliary complication rates were similar in both groups, 1-year survival rates were significantly higher in the group with increased preoperative bilirubin (graft survival, “normal” 86% vs “increased” 97%; P = 0.006).

Conclusions

Increased bilirubin levels of liver graft recipients before transplantation are associated with reduced reperfusion injury and improved survival after transplantation.

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

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

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.

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

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

Hyperbilirubinemia decreases physiological markers in adjuvant-induced arthritis

There is evidence that a higher serum level of bilirubin (BIL) may be a protective factor for autoimmune diseases. We examined the effect of BIL supplementation in adjuvant-induced arthritis (AIA) where oxidative stress, inflammation and inadequate immune response are present. Male Lewis rats were randomized into groups: CO - control, AIA - untreated adjuvant-induced arthritis, AIA-BIL - adjuvant-induced arthritis administrated BIL (200 mg/kg b.w. daily i.p. during 14 days). Change of hind paw volume in the AIA-BIL group in comparison to the AIA group was significantly decreased after BIL administration. In CO and AIA groups we found almost untraceable levels of BIL. In the AIA-BIL group hyperbilirubinemia was observed. BIL administration significantly decreased plasma levels of C-reactive protein and ceruloplasmin in the AIA-BIL group in comparison to the AIA group. The values of white and red blood cells, hemoglobin and hematocrit were significantly decreased in AIA-BIL after BIL supplementation. Organs like spleen and thymus had a lower weight in AIA-BIL than in AIA. Histological findings showed decreased or even absent damage in hind paw joint of AIA-BIL animals. We observed an immunomodulatory effect of BIL on AIA development, which may also have a novel pharmacological impact.

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

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

Association of Serum Bilirubin with Stroke Severity and Clinical Outcomes

Objective:

The aim of the study is to explore the association of serum bilirubin levels with admission severity and short term clinical outcomes among acute ischemic stroke patients.

Methods:

Data were collected from 2361 acute ischemic stroke patients in four hospitals of Shangdong Province during January 2006 and December 2008. National Institutes of Health Stroke Scale (NIHSS) was used to assess admission and discharge severity. NIHSS≥10 at discharge or in-hospital death was defined as short-term clinical outcomes. Logistic regression and trend test were used to examine the association of serum bilirubin levels with admission severity and short term clinical outcomes.

Results:

Serum bilirubin levels were significantly and positively associated with admission severity (P for trend <0.05). The age-sex adjusted odds ratios (95% confidential intervals) of NIHSS≥10 associated with the second, third and fourth quartile of total bilirubin/direct bilirubin were 1.245 (0.873, 1.777)/1.276 (0.895, 1.818), 1.484 (1.048, 2.102)/1.628 (1.158, 2.289) and 2.869 (2.076, 3.966)/2.765 (1.996, 3.828), respectively, compared with the lowest quartile; the multivariate adjusted odds ratios of NIHSS≥10 associated with the second, third and fourth quartile of total bilirubin/direct bilirubin were 1.088(0.711, 1.665)/1.436(0.94, 2.193), 1.328(0.877, 2.011)/1.647(1.092, 2.485) and 2.336(1.579, 3.458)/3.079 (2.049, 4.623), respectively, compared with the lowest quartile. However, no association between serum bilirubin levels and short-term clinical outcomes was observed in our study.

Conclusion:

Serum bilirubin levels were associated with initial stroke severity closely. Nevertheless, there is no significant relationship between serum bilirubin levels and short-term clinical outcomes among acute ischemic stroke patients.

In vitro DNA-damaging effects of intestinal and related tetrapyrroles in human cancer cells

Epidemiological studies report a negative association between circulating bilirubin concentrations and the risk for cancer and cardiovascular disease. Structurally related tetrapyrroles also possess in vitro anti-genotoxic activity and may prevent mutation prior to malignancy. Furthermore, few data suggest that tetrapyrroles exert anti-carcinogenic effects via induction of cell cycle arrest and apoptosis. To further investigate whether tetrapyrroles provoke DNA-damage in human cancer cells, they were tested in the single cell gel electrophoresis assay (SCGE). Eight tetrapyrroles (unconjugated bilirubin, bilirubin ditaurate, biliverdin, biliverdin-/bilirubin dimethyl ester, urobilin, stercobilin and protoporphyrin) were added to cultured Caco2 and HepG2 cells and their effects on comet formation (% tail DNA) were assessed. Flow cytometric assessment (apoptosis/necrosis, cell cycle, intracellular radical species generation) assisted in revealing underlying mechanisms of intracellular action. Cells were incubated with tetrapyrroles at concentrations of 0.5, 5 and 17μM for 24h. Addition of 300μM tertiary-butyl hydroperoxide to cells served as a positive control. Tetrapyrrole incubation mostly resulted in increased DNA-damage (comet formation) in Caco2 and HepG2 cells. Tetrapyrroles that are concentrated within the intestine, including protoporphyrin, urobilin and stercobilin, led to significant comet formation in both cell lines, implicating the compounds in inducing DNA-damage and apoptosis in cancer cells found within organs of the digestive system.

Transport and metabolism at blood-brain interfaces and in neural cells: relevance to bilirubin-induced encephalopathy

Bilirubin, the end-product of heme catabolism, circulates in non-pathological plasma mostly as a protein-bound species. When bilirubin concentration builds up, the free fraction of the molecule increases. Unbound bilirubin then diffuses across blood-brain interfaces (BBIs) into the brain, where it accumulates and exerts neurotoxic effects. In this classical view of bilirubin neurotoxicity, BBIs act merely as structural barriers impeding the penetration of the pigment-bound carrier protein, and neural cells are considered as passive targets of its toxicity. Yet, the role of BBIs in the occurrence of bilirubin encephalopathy appears more complex than being simple barriers to the diffusion of bilirubin, and neural cells such as astrocytes and neurons can play an active role in controlling the balance between the neuroprotective and neurotoxic effects of bilirubin. This article reviews the emerging in vivo and in vitro data showing that transport and metabolic detoxification mechanisms at the blood-brain and blood-cerebrospinal fluid barriers may modulate bilirubin flux across both cellular interfaces, and that these protective functions can be affected in chronic unconjugated hyperbilirubinemia. Then the in vivo and in vitro arguments in favor of the physiological antioxidant function of intracerebral bilirubin are presented, as well as the potential role of transporters such as ABCC1 and metabolizing enzymes such as cytochromes P-450 in setting the cerebral cell- and structure-specific toxicity of bilirubin following hyperbilirubinemia. The relevance of these data to the pathophysiology of bilirubin-induced neurological diseases is discussed.

A cohort study of serum bilirubin levels and incident non-alcoholic fatty liver disease in middle aged Korean workers

Background

Serum bilirubin may have potent antioxidant and cytoprotective effects. Serum bilirubin levels are inversely associated with several cardiovascular and metabolic endpoints, but their association with nonalcoholic fatty liver disease (NAFLD) has not been investigated except for a single cross-sectional study in a pediatric population. We assessed the prospective association between serum bilirubin concentrations (total, direct, and indirect) and the risk for NAFLD.

Methods and Findings

We performed a cohort study in 5,900 Korean men, 30 to 59 years of age, with no evidence of liver disease and no major risk factors for liver disease at baseline. Study participants were followed in annual or biennial health examinations between 2002 and 2009. The presence of fatty liver was determined at each visit by ultrasonography. We observed 1,938 incident cases of NAFLD during 28,101.8 person-years of follow-up. Increasing levels of serum direct bilirubin were progressively associated with a decreasing incidence of NAFLD. In age-adjusted models, the hazard ratio for NAFLD comparing the highest to the lowest quartile of serum direct bilirubin levels was 0.61 (95% CI 0.54–0.68). The association persisted after adjusting for multiple metabolic parameters (hazard ratio comparing the highest to the lowest quartile 0.86, 95% CI 0.76–0.98; P trend = 0.039). Neither serum total nor indirect bilirubin levels were significantly associated with the incidence of NAFLD.

Conclusions

In this large prospective study, higher serum direct bilirubin levels were significantly associated with a lower risk of developing NAFLD, even adjusting for a variety of metabolic parameters. Further research is needed to elucidate the mechanisms underlying this association and to establish the role of serum direct bilirubin as a marker for NAFLD risk.

Hyperbilirubinemia in infants with Gram-negative sepsis does not affect mortality

BACKGROUND

Sepsis is associated with an increased production of oxidant species and a decrease in endogenous antioxidant defenses. Mortality is high, especially when endotoxins are involved, e.g., in infants with Gram-negative sepsis. Yet, chronic as well as acute unconjugated hyperbilirubinemia has been shown to protect against endotoxin-induced shock in vivo in rats and in mice. We hypothesized that hyperbilirubinemia in infants with Gram-negative sepsis improves survival and/or mitigates the inflammatory response.

OBJECTIVE

To assess the relationships between serum bilirubin concentrations on the one hand, and leukocyte count, C-reactive protein and survival on the other hand, in infants with Gram-negative sepsis.

METHODS

Retrospectively, we retrieved clinical and biochemical data from infants less than 90 days of age with a blood culture-proven Gram-negative sepsis between January 1998 and December 2005.

RESULTS

We identified 92 infants with Gram-negative sepsis in the indicated period. Median gestational age was 29 (24-42) weeks. 22 Patients died. Preceding sepsis, median total serum bilirubin concentrations were below 150 μmol/L. Median concentrations of conjugated bilirubin concentrations increased (+63%, p<0.05), and median concentrations of unconjugated bilirubin decreased (-36%, p<0.05) in infants with Gram-negative sepsis. Median total bilirubin concentrations before and during sepsis were not significantly different between survivors and non-survivors. Changes in bilirubin concentrations were not significantly correlated with changes in either white blood cell count or C-reactive protein.

CONCLUSION

Present data do not support the concept that bilirubin positively affects survival or the inflammatory response in infants with Gram-negative sepsis.

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

Background

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

Methods

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

Results

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

Conclusions

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

Keywords

Bilirubin; Diabetes; Antioxidant; Protective

Polyamine oxidase activity in peripheral blood of newborn infants with neonatal hyperbilirubinemia: is bilirubin an antioxidant?

BACKGROUND

Neonatal hyperbilirubinemia can be physiological and pathological and most frequently is a consequence of faster erythrocytes (RBC) hemolysis. Free unconjugated bilirubin is a highly toxic compound, especially for the central nervous system. The most abundant polyamines circulating in blood are spermidine (Spd) and spermine (Sp), which are mainly localized in RBC, where they control membrane permeability. Polyamine oxidase (PAO) exerts an important activity in the plasma and erythrocytes of newborn infants with hyperbilirubinemia, catalyzing the oxidative deamination of Sp and Spd, producing potentially toxic agents that induce apoptosis of mammalian cells. The present study investigated polyamine metabolism by measuring PAO activity in the blood of newborn infants with hyperbilirubinemia and explored the possible antioxidant function of bilirubin through monitoring malondialdehyde (MDA) levels.

METHODS

The study included 43 newborns, 10 in the control and 33 in the diseased group. Blood PAO activity and bilirubin and MDA levels were measured using spectrophotometric methods.

RESULTS/DISCUSSION

Our results indicate that bilirubin, at physiologic concentrations, protects neonatal erythrocytes against oxidative stress. The positive correlation between PAO activity and MDA levels with high bilirubin concentrations (> 200 micromol/L) in newborn infants indicates that in pathological conditions, bilirubin cannot exert its antioxidant function.

CONCLUSION

Investigating the function of polyamines in erythrocytes and the importance of PAO related to hemolysis and bilirubin synthesis is necessary to shed light on the functions of PAO and its metabolites on the permeability of the erythrocyte membrane.

Therapeutic applications of bilirubin and biliverdin in transplantation

Bilirubin is the end product of heme catabolism by heme oxygenases. The inducible form of these enzymes is heme oxygenase-1 (HO-1), which is the rate-limiting enzyme that can degrade heme into equimolar quantities of carbon monoxide (CO), biliverdin, and free iron. Biliverdin is very rapidly converted to bilirubin by the enzyme biliverdin reductase, and free iron upregulates the expression of ferritin. HO-1 is a ubiquitous stress protein and is induced in many cell types by various stimuli. Induced HO-1 exerts antiinflammatory effects and modulates apoptosis. Expression of HO-1 in vivo suppresses the inflammatory responses in endotoxic shock, hyperoxia, acute pleurisy, and organ transplantation, as well as ischemia-reperfusion injury, and thereby provides salutary effects in these conditions. Accumulating evidence indicates that biliverdin/bilirubin can mediate the protective effects of HO-1 in many disease models, such as IRI and organ transplantation, via its antiinflammatory, antiapoptotic, antiproliferative, and antioxidant properties, as well as its effects on the immune response. This review attempts to summarize these protective roles as well as the molecular mechanisms by which biliverdin/bilirubin benefit IRI and solid-organ transplantation, including chronic rejection, and islet transplantation.

Diurnal variation of biopyrrin excretion in random urine specimens is not corrected by creatinine

Circulating bilirubin is thought to function as a physiological antioxidant. One of the decomposition products of this process is the biopyrrins, which include two regioisomers: biotripyrrin-a (1,14,15,17-tetrahydro-2,7,13-trimethyl-1,14-deoxy-3-vinyl-16H-tripyrrin-8,12-dipropionic acid) and biotripyrrin-b (1,14,15,17-tetrahydro-3,7,13-trimethyl-1,14-deoxy-3-vinyl-16H-tripyrrin-8,12-dipropionic acid). We measured biopyrrins in random urine specimens and investigated whether the biopyrrin values obtained were valid when expressed as a ratio of the creatinine (Cr) concentrations. All of the random urine specimens collected over 48 hr were from presumably healthy adults. We measured the biopyrrins by means of an enzyme-linked immunosorbent assay (ELISA) using an anti-bilirubin monoclonal antibody. When the values were expressed in terms of the ratio to Cr, the within-day coefficient of variation (%CV) of the excretion of biopyrrins was reduced to 27%+/-10% (P<0.05) from 59%+/-27%. However, assay values on random or spot urine specimens were unreliable because of the large %CV. The biopyrrin concentrations only in the first-morning-urine specimens in terms of both absolute amounts and ratios to Cr significantly reflected those in a 24-hr urine specimen (P<0.001). Concentrations in a random urine specimen voided at the second collection or later did not correlate with the concentration in a 24-hr urine specimen (P>0.05), even if their values were corrected by Cr. The amounts of biopyrrins excreted in 24-hr urine specimens were significantly correlated with the 24-hr cortisol excretion (P<0.001) but not to uropepsin (P>0.05).