Bilirubin and the risk of common non-hepatic diseases

Establishment of an assistive diagnostic model for schizophrenia with oxidative stress biomarkers

Objective: In this study, alterations in oxidative stress-related indicators were evaluated in drug-naïve, first-episode schizophrenia (SCZ) patients, and the effectiveness of blood serum glucose, superoxide dismutase (SOD), bilirubin in the objective assistive diagnosis of schizophrenia was explored. Materials and methods: We recruited 148 drug-naïve, first-episode SCZ patients and 97 healthy controls (HCs). Blood biochemical indexes including blood glucose, SOD, bilirubin and homocysteine (HCY) in participants were measured, the indexes were compared between patients with SCZ and HCs. The assistive diagnostic model for SCZ was established on the basis of the differential indexes. Results: In SCZ patients, the blood serum levels of glucose, total (TBIL), indirect bilirubin (IBIL) and homocysteine (HCY) were significantly higher than those in HCs (p < 0.05), and the serum levels of SOD were significantly lower than those in HCs (p < 0.05). There was a negative correlation between SOD with the general symptom scores and total scores of PANSS. After risperidone treatment, the levels of uric acid (UA) and SOD tended to increase in patients with SCZ (p = 0.02, 0.19), and the serum levels of TBIL and HCY tended to decrease in patients with SCZ (p = 0.78, 0.16). The diagnostic model based on blood glucose, IBIL and SOD was internally cross-validated, and the accuracy was 77%, with an area under the curve (AUC) of 0.83. Conclusion: Our study demonstrated an oxidative state imbalance in drug-naïve, first-episode SCZ patients, which might be associated with the pathogenesis of the disease. Our study proved that glucose, IBIL and SOD may be potential biological markers of schizophrenia, and the model based on these markers can assist the early objective and accurate diagnosis of schizophrenia.

Endothelial senescence in vascular diseases: current understanding and future opportunities in senotherapeutics

Senescence compromises the essential role that the endothelium plays in maintaining vascular homeostasis, so promoting endothelial dysfunction and the development of age-related vascular diseases. Their biological and clinical significance calls for strategies for identifying and therapeutically targeting senescent endothelial cells. While senescence and endothelial dysfunction have been studied extensively, distinguishing what is distinctly endothelial senescence remains a barrier to overcome for an effective approach to addressing it. Here, we review the mechanisms underlying endothelial senescence and the evidence for its clinical importance. Furthermore, we discuss the current state and the limitations in the approaches for the detection and therapeutic intervention of target cells, suggesting potential directions for future research.

Employing biochemical biomarkers for building decision tree models to predict bipolar disorder from major depressive disorder

BACKGROUND

Conventional biochemical parameters may have predictive values for use in clinical identification between bipolar disorder (BD) and major depressive disorder (MDD).

METHODS

This study enrolled 2470 hospitalized patients with BD (n = 1333) or MDD (n = 1137) at reproductive age from 2009 to 2018 in China. We extracted 8 parameters, uric acid (UA), direct bilirubin (DBIL), indirect bilirubin (IDBIL), lactic dehydrogenase (LDH), free triiodothyronine (FT3), thyroid-stimulating hormone (TSH), high-density lipoprotein (HDL) and prealbumin of male, patients and 12 parameters, UA, DBIL, IBIL, LDH, FT3, TSH, glutamic-pyruvic transaminase (GPT), white blood cell (WBC), alkaline phosphatase (ALP), fasting blood glucose (FBG), triglyceride and low-density lipoprotein (LDL) of female patients. Backward stepwise multivariate regression analysis and the Chi-Square Automatic Interaction Detection (CHAID) segmentation analysis via SPSS Decision Tree were implemented to define the discrimination of BD and MDD.

RESULTS

DBIL was extracted as the first splitting variable, with LDH and IBIL as the second, TSH and prealbumin as the third in the model of male patients (p-value < .05). For the model of female patients, DBIL was also extracted as the first splitting variable, with UA, LDH, and IBIL as the second, triglyceride and FT3 as the third (p-value < .05). The predictive accuracies of the Decision Tree and multiple logistic regression models were similar (74.9% vs 76.9% in males; 74.4% vs 79.5% in females).

CONCLUSIONS

This study suggests the value of the Decision Tree models, which employ biochemical parameters as diagnostic predictors for BD and MDD. The CHAID Decision Tree identified that patients with concomitantly increased LDH, IBIL, and decreased DBIL could be in the group that showed the highest risk of being diagnosed as BD.

MELD-XI score predict no-reflow phenomenon and short-term mortality in patient with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention

INTRODUCTION

No-reflow phenomenon (NRP) is one of the complications that mostly occur during percutaneous coronary intervention (PCI). In this study, we comprehensively examined the relationship between the model for end-stage liver disease-XI (MELD-XI) score and NRP. Moreover, we discussed whether the MELD-XI score could be considered as an accurate risk assessment score of patients with ST-segment elevation myocardial infarction (STEMI) who are candidates for PCI.

METHODS

This retrospective study involved 693 patients with acute STEMI and who underwent an emergency PCI. They were divided into a normal reflow group or a no-reflow group on the basis of the flow rate of post-interventional thrombolysis in myocardial infarction. Univariate, multivariate logistic regression, and Cox regression analyses were performed to identify the independent predictors of NRP in both groups. Receiver operator characteristic (ROC) curves and Kaplan-Meier curves were plotted to estimate the predictive values of the MELD-XI score.

RESULTS

MELD-XI score was found to be an independent indicator of NRP (odds ratio: 1.247, 95% CI: 1.144-1.360, P < 0.001). Multivariate Cox regression analysis also revealed that the MELD-XI score is an independent prognostic factor for 30-day all-cause mortality (hazard ratio: 1.155, 95% CI: 1.077-1.239, P < 0.001). Moreover, according to the ROC curves, the cutoff value of the MELD-XI score to predict NRP was 9.47 (area under ROC curve: 0.739, P < 0.001). The Kaplan-Meier curves for 30-day all-cause mortality revealed lower survival rate in the group with a MELD-XI score of > 9.78 (P < 0.001).

CONCLUSION

The MELD-XI score can be used to predict NRP and the 30-day prognosis in patients with STEMI who are candidates for primary PCI. It could be adopted as an inexpensive and a readily available tool for risk stratification.

Translational Approach to the Protective Effect of Bilirubin in Diabetic Kidney Disease

Bilirubin has been regarded as a powerful endogenous antioxidant and anti-inflammatory molecule, able to act on cellular pathways as a hormone. Diabetic kidney disease (DKD) is a common chronic complication of diabetes, and it is the leading cause of end-stage renal disease. Here, we will review the clinical and molecular features of mild hyperbilirubinemia in DKD. The pathogenesis of DKD involves oxidative stress, inflammation, fibrosis, and apoptosis. Serum bilirubin levels are positively correlated with the levels of the antioxidative enzymes as superoxide dismutase, catalase, and glutathione peroxidase, while it is inversely correlated with C-reactive protein, TNF-α, interleukin (IL)-2, IL-6, and IL-10 release in diabetic kidney disease. Bilirubin downregulates NADPH oxidase, reduces the induction of pro-fibrotic factor HIF-1α expression, cleaved caspase-3, and cleaved PARP induction showing lower DNA fragmentation. Recent experimental and clinical studies have demonstrated its effects in the development and progression of renal diseases, pointing out that only very mild elevations of bilirubin concentrations result in real clinical benefits. Future controlled studies are needed to explore the precise role of bilirubin in the pathogenesis of DKD and to understand if the use of serum bilirubin levels as a marker of progression or therapeutic target in DKD is feasible and realistic.

The LDL/HDL ratio predicts long-term risk of coronary revascularization in ST-segment elevation myocardial infarction patients undergoing percutaneous coronary intervention: a cohort study

Clinical indicators do not adequately predict the long-term prognosis of patients with ST-segment elevation myocardial infarction (STEMI) following percutaneous coronary intervention (PCI). The low-density lipoprotein (LDL)/high-density lipoprotein (HDL) ratio is expected to be a reliable predictor of the long-term prognosis of these patients. This study aimed to explore the correlation between the LDL/HDL ratio and long-term prognosis in STEMI patients undergoing PCI. Patients with confirmed STEMI who underwent PCI in 7 hospitals in China from January 2009 to December 2011 were enrolled. Information about clinical endpoints, including all-cause death and major adverse cardiovascular events, was collected. Overall, 915 patients were included for analysis, the average follow-up time was 112.2 months. According to the LDL/HDL ratio, the patients were divided into 3 groups using the three-quantile method: low (LDL/HDL≤1.963), medium (1.963<LDL/HDL<2.595), and high (LDL/HDL≥2.595) LDL/HDL groups. The rate of coronary revascularization was higher in the high LDL/HDL group (28.52%) than in the low (17.38%, P=0.001) and medium (19.34%, P=0.010) LDL/HDL groups. The hazard ratio of coronary revascularization was significantly higher in the high LDL/HDL group than in the low (P=0.007) and medium (P=0.004) LDL/HDL groups. Increased LDL/HDL ratio was an independent risk factor for long-term coronary revascularization in STEMI patients undergoing PCI (HR=1.231, 95%CI: 1.023-1.482, P=0.028). These findings suggest that an increased LDL/HDL ratio was an independent risk factor for long-term coronary revascularization in STEMI patients undergoing PCI. The risk of coronary revascularization was significantly increased in patients with LDL/HDL≥2.595.

Blood metabolic signatures of hikikomori, pathological social withdrawal

Background

A severe form of pathological social withdrawal, ‘hikikomori,’ has been acknowledged in Japan, spreading worldwide, and becoming a global health issue. The pathophysiology of hikikomori has not been clarified, and its biological traits remain unexplored.

Methods

Drug-free patients with hikikomori (n = 42) and healthy controls (n = 41) were recruited. Psychological assessments for the severity of hikikomori and depression were conducted. Blood biochemical tests and plasma metabolome analysis were performed. Based on the integrated information, machine-learning models were created to discriminate cases of hikikomori from healthy controls, predict hikikomori severity, stratify the cases, and identify metabolic signatures that contribute to each model.

Results

Long-chain acylcarnitine levels were remarkably higher in patients with hikikomori; bilirubin, arginine, ornithine, and serum arginase were significantly different in male patients with hikikomori. The discriminative random forest model was highly performant, exhibiting an area under the ROC curve of 0.854 (confidential interval = 0.648–1.000). To predict hikikomori severity, a partial least squares PLS-regression model was successfully created with high linearity and practical accuracy. In addition, blood serum uric acid and plasma cholesterol esters contributed to the stratification of cases.

Conclusions

These findings reveal the blood metabolic signatures of hikikomori, which are key to elucidating the pathophysiology of hikikomori and also useful as an index for monitoring the treatment course for rehabilitation.

The compensatory antioxidant response system with a focus on neuroprogressive disorders

Major antioxidant responses to increased levels of inflammatory, oxidative and nitrosative stress (ONS) are detailed. In response to increasing levels of nitric oxide, S-nitrosylation of cysteine thiol groups leads to post-transcriptional modification of many cellular proteins and thereby regulates their activity and allows cellular adaptation to increased levels of ONS. S-nitrosylation inhibits the function of nuclear factor kappa-light-chain-enhancer of activated B cells, toll-like receptor-mediated signalling and the activity of several mitogen-activated protein kinases, while activating nuclear translocation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2 or NFE2L2); in turn, the redox-regulated activation of Nrf2 leads to increased levels and/or activity of key enzymes and transporter systems involved in the glutathione system. The Nrf2/Kelch-like ECH-associated protein-1 axis is associated with upregulation of NAD(P)H:quinone oxidoreductase 1, which in turn has anti-inflammatory effects. Increased Nrf2 transcriptional activity also leads to activation of haem oxygenase-1, which is associated with upregulation of bilirubin, biliverdin and biliverdin reductase as well as increased carbon monoxide signalling, anti-inflammatory and antioxidant activity. Associated transcriptional responses, which may be mediated by retrograde signalling owing to elevated hydrogen peroxide, include the unfolded protein response (UPR), mitohormesis and the mitochondrial UPR; the UPR also results from increasing levels of mitochondrial and cytosolic reactive oxygen species and reactive nitrogen species leading to nitrosylation, glutathionylation, oxidation and nitration of crucial cysteine and tyrosine causing protein misfolding and the development of endoplasmic reticulum stress. It is shown how these mechanisms co-operate in forming a co-ordinated rapid and prolonged compensatory antioxidant response system.

Induction of Mild Hyperbilirubinemia: Hype or Real Therapeutic Opportunity?

Observational epidemiological studies showed that mild hyperbilirubinemia has beneficial effects on the prevention of cardiovascular disease, type 2 diabetes mellitus, and metabolic syndrome. In mammals, bilirubin plays a major role as a potent antioxidant. Uridine 5'-diphospho-glucuronosyl transferase (UGT)1A1 variants coding for bilirubin UDP-glucuronosyl transferase resulting in mild hyperbilirubinemia (as in Gilbert syndrome (GS)) may confer a strong genetic advantage. Strategies to boost bioavailability of bilirubin or to mimic GS represent an attractive approach to prevent many oxidative stress and inflammation-mediated diseases. Even a tiny, micromolar increase in serum bilirubin concentrations substantially decreases the risk of oxidative stress-mediated diseases. There are several possible ways to achieve this, including lifestyle changes, changes in dietary patterns, regular physical activities, or use of chemical drug or of specific plant products either in the form of regular food items or nutraceuticals. Further basic and experimental research is required to fully uncover this promising therapeutic field.

Diabetes escalates knee osteoarthritis in rats: Evidence of adaptive mechanism

Clinical reports on the coexistence of diabetes mellitus (DM) and osteoarthritis (OA) dated back to the 1960 s. Therefore, the study investigated the effects of induced DM and/or knee osteoarthritis (KOA) on known biomarkers in male Wistar rats. Twenty rats of five animals per group were induced with DM and/or knee OA using streptozotocin plus nicotinamide and sodium monoiodoacetate. Afterwards, they were left untreated for four weeks.The results showed that pro-inflammatory and pro-oxidative events were most significantly expressed in D + OA group and least in OA group. In contrast to the other experimental groups, there was a decreased bone formation in DM group.Unexpectedly, there were significant increases in bone and cartilage degradation markers in diabetic group, relative to D + OA group. In conclusion, diabetic-osteoarthritic state is characterised by more altered biochemical profile, relative to what is probable in either disease condition. Nevertheless, this situation remains subject to the influence of endogenous homeostatic mechanisms.

Bilirubin Is Inversely Associated With Cardiovascular Disease Among HIV-Positive and HIV-Negative Individuals in VACS (Veterans Aging Cohort Study)

Background

Bilirubin may protect against cardiovascular disease (CVD) by reducing oxidative stress. Whether elevated bilirubin reduces the risk of CVD events among HIV⁺ individuals and if this differs from uninfected individuals remain unclear. We assessed whether bilirubin independently predicted the risk of CVD events among HIV⁺ and uninfected participants in VACS (Veterans Aging Cohort Study).

Methods and Results

We conducted a prospective cohort study using VACS participants free of baseline CVD. Total bilirubin was categorized by quartiles. CVD as well as acute myocardial infarction, heart failure, and ischemic stroke events were assessed. Cox regression was used to evaluate hazard ratios of outcomes associated with quartiles of total bilirubin in HIV⁺ and uninfected people after adjusting for multiple risk factors. There were 96 381 participants (30 427 HIV⁺); mean age was 48 years, 48% were black, and 97% were men. There were 6603 total incident CVD events over a mean of 5.7 years. In adjusted models, increasing quartiles of baseline total bilirubin were associated with decreased hazards of all outcomes (hazard ratio, 0.86; 95% confidence interval, 0.80–0.91). Among HIV⁺ participants, results persisted for heart failure, ischemic stroke, and total CVD, but nonsignificant associations were observed for acute myocardial infarction.

Conclusions

VACS participants (regardless of HIV status) with elevated bilirubin levels had a lower risk of incident total CVD, acute myocardial infarction, heart failure, and ischemic stroke events after adjusting for known risk factors. Future studies should investigate how this apparently protective effect of elevated bilirubin could be harnessed to reduce CVD risk or improve risk estimation among HIV⁺ individuals.

Synergistic and non-synergistic effects of salmon calcitonin and omega - 3 fatty acids on antioxidant, anti-inflammatory, and haematological indices in diabetic rats

The optimum therapy for the management of diabetes mellitus (DM) has been a controversial issue. Therefore, the study investigated the effects of salmon calcitonin (Sct) and/or omega-3 fatty acids {eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA); EPA/DHA ratio?=?3/2} relative to metformin in diabetic male Wistar rats. Forty rats were used for this study. They were randomly divided into 8 groups of five (5) rats each, which were treated with single or combined administration of salmon calcitonin, N-3 and metformin. DM was induced by the administration of streptozotocin (65?mg/kg b.w., i.p.), 15?min after the administration of nicotinamide (110?mg/kg b.w., i.p.). Nine days afterwards, treatments started, and they lasted for 28 days. Sct was administered at 2.5 and 5.0 IU/kg b.w./day (i.m.), while, N-3 and metformin were administered at 200 and 180?mg/kg b.w./day (p.o.) respectively. The results showed that the induced DM significantly increased pro-inflammatory markers, and significantly altered antioxidant and haematological indices. The combined administration of Sct and N-3 had synergistic effects on total bilirubin and total antioxidant capacity, but, non-synergistic actions on malondialdehyde, uric acid, interleukin-6, lactate dehydrogenase, superoxide dismutase, catalase, glutathione peroxidase, and the haematological parameters. These effects were comparable to that of metformin which showed a more or less therapeutic action than N-3. The study concluded that the antioxidant, anti-inflammatory, and haematological effects of the combined administration of Sct and N-3 is comparable to that of metformin. Nevertheless, the latter showed more or less therapeutic effects relative to N-3.

Mortality outcomes after busulfan-containing conditioning treatment and haemopoietic cell transplantation in patients with Gilbert's syndrome: a retrospective cohort study

BACKGROUND

Gilbert's syndrome is a common inherited disorder of bilirubin metabolism, characterised by mild, unconjugated hyperbilirubinaemia. However, the effect of Gilbert's syndrome on the disposition of some drugs can lead to unexpected toxicity. We tested the hypothesis that patients undergoing myeloablative conditioning and haemopoietic cell transplantation would have different mortality outcomes depending on whether or not they had laboratory evidence of Gilbert's syndrome.

METHODS

In this retrospective cohort study, we used clinical and laboratory data of patients who had haemopoietic cell transplantation from Jan 1, 1991, to Dec 31, 2011. Patients were included if they had received high-dose conditioning regimens of cyclophosphamide plus total body irradiation (CY/TBI), busulfan plus cyclophosphamide (BU/CY), busulfan plus melphalan plus thioTEPA (BUMELTT), or melphalan before transplant. Patients were excluded if their original consent forms to report transplant outcomes were not signed, if consent was withdrawn, or if they were a prisoner. Patients with Gilbert's syndrome were defined as having laboratory values before the start of conditioning therapy for unconjugated serum bilirubin concentrations of at least 17·1 μmol/L (≥1 mg/dL), normal conjugated serum bilirubin, and no evidence of hepatitis, cholestasis, or haemolysis. We assessed the association of Gilbert's syndrome with overall mortality and non-relapse mortality using adjusted Cox regression models at day 200 after transplantation.

FINDINGS

Our study cohort was 3379 patients-1855 (55%) allograft and 1524 (45%) autograft recipients. 211 (6%) patients had Gilbert's syndrome and 3168 (94%) did not have this condition. Most patients were adults (median age 45·8 years [IQR 33·2-55·5]) with haematological malignancies. For overall mortality 664 (20%) patients had died by day 200 after transplant (47 [22%] of 211 who had Gilbert's syndrome vs 617 [19%] of 3168 who did not have Gilbert's syndrome), and for non-relapse mortality 499 (92%) patients had died before relapse was recorded (38 [18%] who had Gilbert's syndrome vs 461 [15%] who did not have Gilbert's syndrome). The effect of Gilbert's syndrome on the risk of overall mortality and non-relapse mortality by transplant day 200 varied between the conditioning regimens and donor groups. In patients conditioned with a myeloablative regimen that contained busulfan (n=1131), those with Gilbert's syndrome (n=60) were at a significantly increased risk of death and non-relapse mortality by day 200 compared with those without Gilbert's syndrome (n=1071; hazard ratio [HR] 2·30, 95% CI 1·47-3·61, p=0·00030; and 2·77, 1·71-4·49, p<0·0001). In patients who received CY/TBI or melphalan conditioning regimens, those with Gilbert's syndrome had similar outcomes to those without Gilbert's syndrome (overall mortality at day 200 HR 0·90, 95% CI 0·60-1·34, p=0·60; non-relapse mortality at day 200: 0·90, 0·56-1·45, p=0·65). Analyses of causes of death and busulfan disposition provided no mechanistic explanation for the differences in mortality.

INTERPRETATION

Overall mortality and non-relapse mortality at day 200 after transplant were significantly worse in patients with Gilbert's syndrome who received busulfan-containing myeloablative conditioning regimens, compared with non-Gilbert's syndrome patients. Patients with Gilbert's syndrome should receive busulfan-containing myeloablative conditioning regimens with caution.

FUNDING

US National Institutes of Health.

6,7-dimethoxy-1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid attenuates heptatocellular carcinoma in rats with NMR-based metabolic perturbations

AIM

6,7-dimethoxy-1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid (M1) was synthesized and evaluated for in-vivo antiproliferative action in diethylnitrosamine-induced hepatocarcinogenic rats.

MATERIALS & METHODS

The antiproliferative effect of M1 was assessed by various biochemical parameters, histopathology of liver and HPLC analysis. Proton nuclear magnetic resonance-based serum metabolic study was implemented on rat sera to explore the effects of M1 on hepatocellular carcinoma-induced metabolic alterations.

RESULTS

M1 showed protective action on liver and restored the arrangement of liver tissues in normal proportion. HPLC analysis displayed a good plasma drug concentration after its oral administration. Score plots of partial least squares discriminate analysis models exhibited that M1 therapy ameliorated hepatocellular carcinoma-induced metabolic alterations which signified its antiproliferative potential.

CONCLUSION

M1 manifested notable antiproliferative profile, and warrants further investigation for future anticancer therapy.

The role of antioxidants in the chemistry of oxidative stress: A review

This Review Article is focused on the action of the reactive oxygenated species in inducing oxidative injury of the lipid membrane components, as well as on the ability of antioxidants (of different structures and sources, and following different mechanisms of action) in fighting against oxidative stress. Oxidative stress is defined as an excessive production of reactive oxygenated species that cannot be counteracted by the action of antioxidants, but also as a perturbation of cell redox balance. Reactive oxygenated/nitrogenated species are represented by superoxide anion radical, hydroxyl, alkoxyl and lipid peroxyl radicals, nitric oxide and peroxynitrite. Oxidative stress determines structure modifications and function modulation in nucleic acids, lipids and proteins. Oxidative degradation of lipids yields malondialdehyde and 4-hydroxynonenal, but also isoprostanes, from unsaturated fatty acids. Protein damage may occur with thiol oxidation, carbonylation, side-chain oxidation, fragmentation, unfolding and misfolding, resulting activity loss. 8-hydroxydeoxyguanosine is an index of DNA damage. The involvement of the reactive oxygenated/nitrogenated species in disease occurrence is described. The unbalance between the oxidant species and the antioxidant defense system may trigger specific factors responsible for oxidative damage in the cell: over-expression of oncogene genes, generation of mutagen compounds, promotion of atherogenic activity, senile plaque occurrence or inflammation. This leads to cancer, neurodegeneration, cardiovascular diseases, diabetes, kidney diseases. The concept of antioxidant is defined, along with a discussion of the existent classification criteria: enzymatic and non-enzymatic, preventative or repair-systems, endogenous and exogenous, primary and secondary, hydrosoluble and liposoluble, natural or synthetic. Primary antioxidants are mainly chain breakers, able to scavenge radical species by hydrogen donation. Secondary antioxidants are singlet oxygen quenchers, peroxide decomposers, metal chelators, oxidative enzyme inhibitors or UV radiation absorbers. The specific mechanism of action of the most important representatives of each antioxidant class (endogenous and exogenous) in preventing or inhibiting particular factors leading to oxidative injury in the cell, is then reviewed. Mutual influences, including synergistic effects are presented and discussed. Prooxidative influences likely to occur, as for instance in the presence of transition metal ions, are also reminded.

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.

Acute alcohol consumption elevates serum bilirubin: an endogenous antioxidant

BACKGROUND

Moderate alcohol consumption has been associated with both negative and favorable effects on health. The mechanisms responsible for reported favorable effects remain unclear. Higher (not necessarily elevated) concentrations of serum bilirubin, an antioxidant, have also been associated with reduced risk of cardiovascular disease and all-cause mortality. This study tests the hypothesis that single dose alcohol consumption elevates bilirubin providing a potential link between these observations.

METHODS

18 healthy individuals (eight cigarette smokers) were administered alcohol, calibrated to achieve blood concentrations of 20, 80 and 120 mg/dL, in random order in three laboratory sessions separated by a week. Each session was preceded by and followed by 5-7 days of alcohol abstinence. Serum bilirubin was measured at 7:45 a.m. prior to drinking, at 2p.m., and at 7:45 the next morning. Mixed effects regression models compared baseline and 24h post-drinking bilirubin concentrations.

RESULTS

Total serum bilirubin (sum of indirect and direct) concentration increased significantly after drinking from baseline to 24h in non-smokers (from M = 0.38, SD = 0.24 to M = 0.51, SD = 0.30, F(1,32.2) = 24.24, p<.0001) but not in smokers (from M = 0.25, SD = 0.12 to M = 0.26, SD = 0.15, F(1,31.1) = 0.04, p = 0.84). In nonsmokers the indirect bilirubin concentration and the ratio of indirect (unconjugated) to direct (conjugated) bilirubin also increased significantly.

CONCLUSIONS

Alcohol consumption leads to increases in serum bilirubin in nonsmokers. Considering the antioxidant properties of bilirubin, our findings suggest one possible mechanism for the reported association between alcohol consumption and reduced risk of some disorders that could be tested in future longitudinal studies.

Conjugated bilirubin affects cytokine profiles in hepatitis A virus infection by modulating function of signal transducer and activator of transcription factors

Hepatitis A virus (HAV) infection is the major cause of acute liver failure in paediatric patients. The clinical spectrum of infection is variable, and liver injury is determined by altered hepatic enzyme function and bilirubin concentration. We recently reported differences in cytokine profiles between distinct HAV-induced clinical courses, and bilirubin has been recognized as a potential immune-modulator. However, how bilirubin may affect cytokine profiles underlying the variability in the course of infection has not been determined. Herein, we used a transcription factor (TF) binding site identification approach to retrospectively analyse cytokine expression in HAV-infected children and to predict the entire set of TFs associated with the expression of specific cytokine profiles. The results suggested that modulation of the activity of signal transducers and activators of transcription proteins (STATs) may play a central role during HAV infection. This led us to compare the degree of STAT phosphorylation in peripheral blood lymphoid cells (PBLCs) from paediatric patients with distinct levels of conjugated bilirubin (CB). Low CB levels in sera were associated with increased STAT-1 and STAT-5 phosphorylation. A positive correlation was observed between the serum interleukin-6 (IL-6) content and CB values, whereas higher levels of CB correlated with reduced serum IL-8 values and with a reduction in the proportion of PBLCs positive for STAT-5 phosphorylation. When CB was used to stimulate patients' PBLCs in vitro, the levels of IL-6 and tumour necrosis factor-α were increased. The data showed that bilirubin plays a role in STAT function and affects cytokine profile expression during HAV infection.

The pharmacological features of bilirubin: the question of the century

This review looks at the toxicity and metabolism of bilirubin in terms of its pharmacological potential. Its role has gained importance as more research has revealed the functional significance and interrelationship between the gasotransmitters nitric oxide and carbon monoxide. The biological actions of bilirubin have mostly been characterized in the high micromolar range where toxic effects occur. However, it could also prove to be an important cytoprotector for brain tissue, which is inherently less equipped for antioxidant defense. Plasma bilirubin levels negatively correlate to a number of disease states. Higher levels of bilirubin that are still within the normal range provide a protective effect to the body. The effects on various disorders could be tested using controlled pharmacological upregulation of the molecule with animal models. At nanomolar concentrations, considerable benefits have been obtained when the molecule was delivered pharmacologically under in vitro or in vivo test conditions, particularly in neurodegenerative disorders and after tissue or organ transplantation. The induction of heme oxygenase-1 (HMOX-1) via the activation of nuclear factor erythroid 2-related factor or the use of bile pigments in the harvesting of diseased tissue are novel applications, and like every new therapy, should be used with caution. HMOX-1 is tissue specific, and in exceptional states, such as schizophrenia and specific types of renal disorder, the same therapy may have disastrous effects.

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

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

Does Serum Bilirubin level on admission predict TIMI flow grade and in-hospital MACE in patients with STEMI undergoing primary PCI

We evaluated the association of total bilirubin with post-percutaneous coronary intervention (PCI) coronary blood flow and in-hospital major adverse cardiac events (MACEs) in patients with ST-segment elevation myocardial infarction (STEMI) undergoing primary PCI. A total of 536 consecutive patients with STEMI (male 79%, mean age = 59.9 ± 12.6 years) admitted within 6 hours from symptom onset were enrolled. Patients were divided into 2 groups based on the thrombolysis in myocardial infarction (MI) flow grade. In-stent thrombosis, nonfatal MI, and in-hospital mortality were significantly higher in no-reflow group (P = .007, P = .002, and P < .001, respectively). On multivariate regression, the total bilirubin levels remained independent predictors of no-reflow (odds ratio [OR] 1.586, 95% confidence interval [CI] 1.02-2.47; P = .042) and in-hospital MACE (OR 1.399, 95% CI 1.053-1.857; P = .020). Serum bilirubin levels were independently associated with no-reflow and in-hospital MACE in patients with STEMI undergoing primary PCI.

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.

Bilirubin levels and the burden of coronary atherosclerosis in patients with STEMI

We investigated whether serum bilirubin level (a marker of heme oxygenase activity) is a predictor of high levels of SYNTAX score (SXscore) in patients with acute myocardial infarction. Patients (n = 281; male 77%; mean age 60 ± 12) who were admitted with ST-elevation myocardial infarctions (STEMIs) were enrolled. Patients were divided into 2 groups. Group 1 was defined as SXscore <22 and group 2 was defined as SXscore ≥22. Total bilirubin levels were significantly higher in the high-SXscore group than in the low-SXscore group (0.86 ± 0.42 vs 1.02 ± 0.51, P = .005). A significant correlation was detected between total bilirubin and SXscore (r = .42; P = .001). At multivariate analysis, total bilirubin (odds ratio: 1.86, 95% confidence interval 1.04-3.35; P = .038) was an independent risk factor for high SXscore in patients with STEMI. In conclusion, serum bilirubin level is independently associated with SXscore in patients with STEMI.

Prognostic significance of serum antioxidant parameters in immunocompetent patients with cryptococcal meningitis

The purpose of this investigation was to determine whether endogenous antioxidants were prognostic factors in immunocompetent patients with cryptococcal meningitis (CM). The clinical features, alterations of serum albumin, bilirubin, and uric acid (UA) levels before and after six weeks of treatment in 94 immunocompetent patients with CM from January 2000 to December 2010 were retrospectively analyzed. The patients with CM had lower serum albumin and UA levels and higher bilirubin levels before treatment. After six weeks of treatment, the serum bilirubin levels decreased significantly and the serum UA levels increased significantly in 'cured/improved' patients. The serum UA level was negatively correlated with log cerebrospinal fluid (CSF) cryptococcal count and positively correlated with the CSF glucose level. A significantly lower level of serum UA was associated with high CSF open pressure, hydrocephalus, brain lesions, and consciousness disturbance. Moreover, the good outcome was 7.779 times more likely to occur in patients with an increase in the serum UA level ≥38.8% after six weeks of treatment. A logistic regression analysis also confirmed that an increase in the serum UA level ≥38.8% after six weeks of treatment was an independent good outcome predictor. Though there were abnormal conditions of serum antioxidants, the variation in the UA level could serve as a potential indicator of therapeutic efficacy in immunocompetent patients with CM.

Circular dichroism spectroscopy is a sensitive tool for investigation of bilirubin-enzyme interactions

Noncovalent complex formation of unconjugated bilirubin with various enzymes has been demonstrated by measuring induced circular dichroism (ICD) peaks associated with the pigment VIS absorption band. Preferential binding of the P- or M-helical conformer of bilirubin to dehydrogenases, catalase, alkaline phosphatase, and α-chymotrypsin is responsible for the characteristic exciton CD couplet that undergoes remarkable changes upon the addition of enzymatic cofactors (NADH, AMP) and an inhibitor (acridine). Alterations of the ICD spectra refer to a direct binding competition between bilirubin and NADH for a common binding site on alcohol dehydrogenase and catalase, suggesting a potential mechanism for the inhibitory effect of BR reported on NAD(P)H dependent enzymes. NADH and bilirubin form a ternary complex with glutamate dehydrogenase indicated by peculiar CD spectral changes that are proposed to be generated by allosteric mechanism. α-chymotrypsin binds bilirubin in its catalytic site, as indicated by CD displacement experiments performed with the competitive inhibitor acridine. Surprisingly, the closely related trypsin does not induce any CD signal with bilirubin. Taking into consideration the clinically relevant but controversial and poorly understood areas of bilirubin biochemistry, the fast and simple CD spectroscopic approach presented here may help to unfold diverse physiological and pathophysiological roles of BR on a molecular level.

Primary biliary cirrhosis is associated with oxidative stress and endothelial dysfunction but not increased cardiovascular risk

AIM

  Primary biliary cirrhosis (PBC) is a chronic cholestatic disease which is associated with hypercholesterolaemia. Further, cholestatic diseases are associated with deficiencies of anti-oxidant vitamins. Despite these associations PBC is not associated with an increase in cardiovascular mortality. The aim of this study is to assess if primary biliary cirrhosis is associated with oxidative stress, endothelial dysfunction and alteration of vascular compliance which is a surrogate marker for cardiovascular risk.

METHODS

  Fifty-one PBC patients and 34 control subjects were studied. Lipid soluble vitamins A, and E in addition to ascorbate and carotenoids were measured to assess anti-oxidant status. C-reactive protein, hydroperoxides and adhesion molecules sICAM-l/sVCAM-l were assessed as serological measures of endothelial function. Finally, measures of vascular compliance were assessed by applanation tonometer.

RESULTS

  CRP, sICAM and sVCAM were all significantly higher in PBC patients (469.14 vs 207.13, P < 0.001; 768.12 vs 308.03,P < 0.001; 708.40 vs 461.31, P < 0.001) whilst anti-oxidant vitamin levels were lower in PBC patients, with ascorbate, vitamin E and vitamin A all significantly lower in PBC patients (39.91 vs 72.68, P < 0.001; 2.63 vs 3.14, P = 0.02; 1.08 vs 1.81, P < 0.001). Despite these findings PBC patients have a lower pulse wave velocity than control subjects (8.22 m/s vs 8.78 m/s, P = 0.022).

CONCLUSION

  PBC patients appear to have reduced vascular risk as assessed by pulse wave velocity but concurrently have evidence of endothelial dysfunction, inflammation and anti-oxidant deficiency.

Alteration of serum bilirubin level in schizophrenia

Abstract Objective. Alteration of serum bilirubin level in acute episodes of psychosis in patients with schizophrenia has been reported but the pattern of this alteration is controversial. Methods. Patients diagnosed as schizophrenia (162, group S) or bipolar disorder (155, group B) entered the study. The control group consisted of 95 patients admitted to cardiac care unit who had no personal or family history of major psychiatric disorders. Pre- and post-admission levels of bilirubin were measured and compared within and between the groups. Patients were examined to exclude all other causes of hyperbilirubinemia. Group S and B participants were also evaluated using positive and negative syndrome subscale (PANSS) both at admission and discharge. Results. The mean admission bilirubin levels of all the groups were in the normal range (significantly higher in group S than groups B and C) and were affected by the score of general psychopathology subscale rather than the scores of positive symptoms subscale. Conclusions. Although bilirubin decreased in all three groups at discharge, the rate of decrease was significantly higher in group S. The reason for this is not clear and needs further study.

Hyperbilirubinemia syndromes (Gilbert-Meulengracht, Crigler-Najjar, Dubin-Johnson, and Rotor syndrome)

Hyperbilirubinemia is an important clinical sign that often indicates severe hepatobiliary disease of different etiologies. Inherited non-haemolytichyperbilirubinemic conditions include Dubin-Johnson, Rotor, and Gilbert-Meulengracht syndromes, which are important differential diagnoses indicating benign disease that require no immediate treatment. Dubin-Johnson and Rotor syndromes are rare, exhibit mixed direct and indirect hyperbilirubinemia as well as typical profiles or urinary coproporphyrin excretion. Gilbert-Meulengracht disease leads to unconjugated hyperbilirubinemia because of impaired glucuronidation activity, and is part of a spectrum of genetic variants also encompassing fatal Crigler-Najjar syndrome. Gilbert-Meulengracht syndrome can be diagnosed by clinical presentation, biochemistry and genotyping, and carries significance regarding the disposition towards drug-associated toxicity. In addition, the precise diagnosis of these inherited hyperbilirubinemic syndromes avoids unnecessary invasive procedures for suspected more severe hepatobiliary disease.

Variants in the UGT1A1 gene and the risk of pediatric nonalcoholic fatty liver disease

OBJECTIVE

Oxidative stress is increased in nonalcoholic fatty liver disease (NAFLD). Variants in the UGT1A1 gene contribute to increased bilirubin levels, and bilirubin can act as an antioxidant. We hypothesize that variant UGT1A1 genotypes reduce the risk for NAFLD development.

METHODS

Two hundred thirty-four obese children 6 to 13 years of age were recruited. NAFLD was determined through liver ultrasonography. The UGT1A1 genotypes UGT1A1*6 and UGT1A1*28 were detected. We assessed the effects of UGT1A1 genotypes on pediatric NAFLD.

RESULTS

In total, 12% of the obese children had NAFLD. The subjects with NAFLD had lower serum total bilirubin levels (0.25 +/- 0.30 mg/dL) than did those without NAFLD (0.36 +/- 0.38 mg/dL; P = .021). With conditioning on the effects of age- and gender-adjusted BMI, waist/hip ratio, and adiponectin levels, variant UGT1A1*6 genotypes were a protecting factor for NAFLD, with an estimated adjusted odds ratio of 0.31 (95% confidence interval: 0.11-0.91; P = .033), but variant UGT1A1*28 genotypes were not significantly associated with the occurrence of NAFLD.

CONCLUSIONS

Variant UGT1A1*6 genotypes are associated with a lower risk of NAFLD in obese Taiwanese children. The UGT1A1 genotype is a new risk factor for pediatric NAFLD.

Bilirubin inhibits the TNFalpha-related induction of three endothelial adhesion molecules

Since an increased serum unconjugated bilirubin (UCB) level has been proposed as an independent protective factor against atherosclerotic disease, we investigated the molecular events at the basis of this effect. HUVEC and H5V cells were treated with TNFalpha and UCB and the effects assessed on E-selectin, VCAM-1 and ICAM-1. In HUVEC cells, UCB blunted the TNFalpha-induced gene upregulation of E-selectin VCAM-1 and ICAM-1. The same pattern was observed in H5V cells except for ICAM-1. UCB also inhibited the PMN endothelial adhesion in HUVEC H5V cells. Western blot and FACS analysis confirmed that UCB prevented TNFalpha-induced over-expression of adhesion molecules proteins in H5V cells. These data contribute to further explain the protective effect of bilirubin against development of atherosclerosis.

Bile constituents in hibernating golden-mantled ground squirrels (Spermophilus lateralis)

Background

Golden-mantled ground squirrels (S. lateralis) are anorexic during the winter and survive by exploiting hibernation to reduce energetic demands. The liver normally plays a critical role in fueling and regulating metabolism and one might expect significant changes in hepatobiliary function with hibernation. We analyzed bile collected from animals in summer, animals in winter that were either torpid, active between bouts of torpor, or which failed to enter hibernation in order to characterize the effects of hibernation on hepatobiliary function per se.

Results

Surprisingly, hibernator bile did not differ from summer squirrel bile in key characteristics including [bile acids], [cholesterol], [free fatty acids], [lecithin], and osmolality. One major distinction between summer and winter squirrels was that winter squirrels experience >5 fold increases in [bilirubin]. Such an increase may have significant physiological consequences that could aid in survivorship of torpor. Animals that failed to hibernate, despite being anorexic, were very similar to summer squirrels in all measured parameters except they had lower bile acid and lecithin concentrations.

Conclusion

The data indicate that despite extended anorexia, differences in metabolic fuel privation, and bouts of reduced body temperatures, hibernators normally do not experience broad changes in hepatobiliary function.

Bilirubin and glutathione have complementary antioxidant and cytoprotective roles

Glutathione (GSH) and bilirubin are prominent endogenous antioxidant cytoprotectants. Despite tissue levels that are thousands of times lower than GSH, bilirubin is effective because of the biosynthetic cycle wherein it is generated from biliverdin by biliverdin reductase (BVR). When bilirubin acts as an antioxidant, it is oxidized to biliverdin, which is immediately reduced by BVR to bilirubin. Why does the body employ both of these 2 distinct antioxidant systems? We show that the water-soluble GSH primarily protects water soluble proteins, whereas the lipophilic bilirubin protects lipids from oxidation. Mice with deletion of heme oxygenase-2, which generates biliverdin, display greater lipid than protein oxidation, while the reverse holds for GSH depletion. RNA interference depletion of BVR increases oxidation of lipids more than protein. Depletion of BVR or GSH augments cell death in an oxidant-specific fashion.

Variability and function of family 1 uridine-5'-diphosphate glucuronosyltransferases (UGT1A)

The substrate spectrum of human UDP-glucuronosyltransferase 1A (UGT1A) proteins includes the glucuronidation of non-steroidal anti-inflammatory drugs, anticonvulsants, chemotherapeutics, steroid hormones, bile acids, and bilirubin. The unique genetic organization of the human UGT1A gene locus, and an increasing number of functionally relevant genetic variants define tissue specificity as well as a broad range of interindividual variabilities of glucuronidation. Genetic UGT1A variability has been conserved throughout the protein's evolution and shows ethnic diversity. It is the biochemical and genetic basis for clinical phenotypes such as Gilbert's syndrome and Crigler-Najjar's disease as well as for the potential for severe, unwanted drug side effects such as in irinotecan treatment. UGT1A variants influence the metabolic effects of xenobiotic exposure and therefore have been linked to cancer risk. Detailed knowledge of the organization, function, and pharmacogenetics of the human UGT1A gene locus is likely to significantly contribute to the improvement of drug safety and efficacy as well as to the provision of steps toward the goal of individualized drug therapy and disease risk prediction.

Bilirubin-induced cell toxicity involves PTEN activation through an APE1/Ref-1-dependent pathway

Unconjugated bilirubin (UCB) is the major degradation product of the heme catabolism. A growing body of evidences suggests that UCB plays major biological effects by inhibiting cell proliferation in cancer cell lines and eliciting cell toxicity particularly in neurons and glial cells. Early molecular events responsible for bilirubin-induced cytotoxicity remain poorly understood. Using HeLa cells and mouse embryonic fibroblasts, we found that UCB at a concentration of free pigment (Bf) of 80 nM induced oxidative stress, promoting a significant increase in intracellular reactive oxygen species (ROS) and a decreased cell survival (by the MTT test). The ROS increase activated the antioxidant cell response through APE1/Ref-1, a master redox regulator in eukaryotic cells. Activation of APE1/Ref-1 was followed by a concomitant activation of Egr-1 transcription factor and by an upregulation of PTEN tumor suppressor, an Egr-1 target gene, leading to inhibition of cell growth. Blocking ROS generation with N-acetylcysteine pretreatment, restored cell survival, limited the upregulation of PTEN in response to UCB, and prevented the inhibition of cell proliferation. HeLa cells transfected with mutants of the PTEN promoter or silenced with APE1/Ref-1 small interference RNA confirmed that UCB modulates a signaling pathway involving APE1/Ref-1, Egr-1, and PTEN. These findings describe a new molecular pathway involved in the cytotoxic effects of UCB.

Influence of hypoxia and ischemia preconditioning on bilirubin damage to astrocytes

Hypoxia-ischemia in the perinatal period is a common cause of neurologic disability in children and is often associated with neonatal morbidity and mortality. Another frequent condition of the newborn is hyperbilirubinemia and it is well known that deposition of unconjugated bilirubin (UCB) in the central nervous system can damage nerve cells and cause encephalopathy. Interestingly, some studies report the onset of cerebral hypoxia-ischemia as a risk factor for UCB encephalopathy, since that condition often precedes neonatal hyperbilirubinemia. However, the cellular mechanisms triggered by hypoxia-ischemia that may enforce UCB deleterious effects are not well elucidated. Therefore, we designed this study to investigate whether hypoxia (HP) or combined oxygen-glucose deprivation (OGD) followed by reoxygenation, modifies glial cell susceptibility to UCB injury. Thus, cultured astrocytes were exposed to HP or OGD for 4 h and returned to normoxic conditions for another 12 h prior to incubation with UCB for 4 h. HP and OGD effects in UCB toxicity were compared to normoxic conditions. Our results demonstrate that HP and OGD preconditioning increase the vulnerability of glial cells to UCB damage by enhancing some of the deleterious effects of UCB, namely cell death by both apoptosis and necrosis. This preconditioning also augments the UCB-induced stimulation of an inflammatory response by an effect that involves the activation of the nuclear factor kappaB activation. These findings provide a novel basis for the increased risk of brain damage in jaundiced newborns that were previously exposed to hypoxia or ischemia during the perinatal period, namely during delivery.

Apoptosis and impairment of neurite network by short exposure of immature rat cortical neurons to unconjugated bilirubin increase with cell differentiation and are additionally enhanced by an inflammatory stimulus

Nerve cell injury induced by unconjugated bilirubin (UCB) has been implicated in brain damage during severe neonatal hyperbilirubinemia, although the molecular mechanisms underlying UCB neurotoxicity are still not clarified. It has been suggested recently that there is an association between hyperbilirubinemia and long-term neurologic dysfunctions. We incubated immature neurons with UCB to evaluate the short- and long-term effects of UCB on apoptotic death and on neuritic outgrowth and ramification. We also evaluated whether mature neurons, exposed previously to UCB in an early stage of differentiation, are more sensitive to apoptosis or to neuritic breakdown when treated with inflammatory agents, such as lipopolysaccharide and tumor necrosis factor-alpha. Results show that exposure of immature neurons to UCB increased apoptosis and provoked a reduction of both neurite extension and number of nodes. These injurious effects observed in immature cells treated with UCB were increasingly perpetuated along cell differentiation, as compared to neurons incubated in the absence of UCB. In addition, neurons that were exposed to UCB when immature showed an increased susceptibility to death by apoptosis, as well as an additional decrease in neurite outgrowth when incubated with an inflammatory agent afterward. This work shows, for the first time, that UCB induces neurite changes consistent with neurodevelopment abnormalities. Furthermore, pre-exposure to UCB followed by an inflammatory stimulus leads to an enhanced susceptibility to long-term apoptosis, as well as a greater neuritic breakdown. These data support the association between neonatal hyperbilirubinemia and the later development of mental illness, such as schizophrenia.

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

Bilirubin, the principal bile pigment, is the end product of heme catabolism. For many years, bilirubin was thought to have no physiological function other than that of a waste product of heme catabolism--useless at best and toxic at worst. Although hyperbilirubinemia in neonates has been shown to be neurotoxic, studies performed during the past decade have found that bilirubin has a number of new and interesting biochemical and biological properties. In addition, there is now a strong body of evidence suggesting that bilirubin may have a beneficial role in preventing oxidative changes in a number of diseases including atherosclerosis and cancer, as well as a number of inflammatory, autoimmune, and degenerative diseases. The results also suggest that activation of the heme oxygenase and heme catabolic pathway may have beneficiary effects on disease prevention either through the action of bilirubin or in conjunction with bilirubin. If so, it may be possible to therapeutically induce heme oxygenase, increase bilirubin concentrations, and lower the risk of oxidative stress-related diseases.

Inflammatory signalling pathways involved in astroglial activation by unconjugated bilirubin

During neonatal hyperbilirubinaemia, astrocytes activated by unconjugated bilirubin (UCB) may contribute to brain toxicity through the production of cytokines. As a first step in addressing the signal transduction cascades involved in the UCB-induced astroglial immunological response, we tested whether tumour necrosis factor (TNF)-alpha receptor 1 (TNFR1), mitogen-activated protein kinase (MAPK) and nuclear factor kappaB (NF-kappaB) would be activated in astrocytes exposed to UCB, and examined the profile of cytokine production. Astrocyte cultures stimulated with UCB showed a rapid rise in TNFR1 protein levels, followed by activation of the MAPKs p38, Jun N-terminal kinase1/2 and extracellular signal-regulated kinase1/2, and NF-kappaB. Interestingly, the induction of these signal effectors preceded the early up-regulation of TNF-alpha and interleukin (IL)-1beta mRNAs, and later secretion of TNF-alpha, IL-1beta and IL-6. Treatment of astrocytes with UCB also induced cell death, with levels comparable to those obtained after exposure of astrocytes to recombinant TNF-alpha and IL-1beta. Moreover, loss of cell viability and cytokine secretion were reduced when the NF-kappaB signal transduction pathway was inhibited, suggesting a key role for NF-kappaB in the astroglial response to UCB. These results demonstrate the complexity of the molecular mechanisms involved in cell injury by UCB during hyperbilirubinaemia and provide a basis for the development of novel therapeutic strategies.