Hyperbilirubinemia results in reduced oxidative injury in neonatal Gunn rats exposed to hyperoxia

Bilirubin Exerts Protective Effects on Alveolar Type II Pneumocytes in an In Vitro Model of Oxidative Stress

Newborn infants face a rapid surge of oxygen and a more protracted rise of unconjugated bilirubin after birth. Bilirubin has a strong antioxidant capacity by scavenging free radicals, but it also exerts direct toxicity. This study investigates whether cultured rat alveolar epithelial cells type II (AEC II) react differently to bilirubin under different oxygen concentrations. The toxic threshold concentration of bilirubin was narrowed down by means of a cell viability test. Subsequent analyses of bilirubin effects under 5% oxygen and 80% oxygen compared to 21% oxygen, as well as pretreatment with bilirubin after 4 h and 24 h of incubation, were performed to determine the induction of apoptosis and the gene expression of associated transcripts of cell death, proliferation, and redox-sensitive transcription factors. Oxidative stress led to an increased rate of cell death and induced transcripts of redox-sensitive signaling pathways. At a non-cytotoxic concentration of 400 nm, bilirubin attenuated oxidative stress-induced responses and possibly mediated cellular antioxidant defense by influencing Nrf2/Hif1α- and NFκB-mediated signaling pathways. In conclusion, the study demonstrates that rat AEC II cells are protected from oxidative stress-induced impairment by low-dose bilirubin.

Hyperbilirubinemia Among Infants Born Preterm: Peak Levels and Association with Neurodevelopmental Outcomes

OBJECTIVE

To describe the distribution of peak bilirubin levels among infants born before 29 weeks of gestation in the first 14 days of life and to study the association between quartiles of peak bilirubin levels at different gestational ages and neurodevelopmental outcomes.

STUDY DESIGN

Multicenter, retrospective, nationwide cohort study of neonatal intensive care units in the Canadian Neonatal Network and Canadian Neonatal Follow-Up Network, including neonates born preterm at 220/7 to 286/7 weeks of gestation born between 2010 and 2018. Peak bilirubin levels were recorded during the first 14 days of age. Main outcome was significant neurodevelopmental impairment, defined as cerebral palsy with Gross Motor Function Classification System ≥3, or Bayley III-IV scores of <70 in any domain, or visual impairment, or bilateral hearing loss requiring hearing aids.

RESULTS

Among 12 554 included newborns, median gestational age was 26 weeks (IQR 25-28) and birth weight was 920 g (IQR 750-1105 g). The median peak bilirubin values increased as gestational age increased (112 mmol/L [6.5 mg/dL] at 22 weeks and 156 mmol/L [9.1 mg/dL] at 28 weeks). Significant neurodevelopmental impairment was identified in 1116 of 6638 (16.8%) of children. Multivariable analyses identified an association between peak bilirubin in the highest quartile and neurodevelopmental impairment (aOR 1.27, 95% CI 1.01-1.60) and receipt of hearing aid/cochlear implant (aOR 3.97, 95%CI: 2.01-7.82) compared with the lowest quartile.

CONCLUSION

In this multicenter cohort study, peak bilirubin levels in neonates of <29 weeks of gestation increased with gestational age. Peak bilirubin values in the highest gestational age-specific quartile were associated with significant neurodevelopmental and hearing impairments.

The value of blood-based measures of liver function and urate in lung cancer risk prediction: A cohort study and health economic analysis

BACKGROUND

Several studies have reported associations between low-cost blood-based measurements and lung cancer but their role in risk prediction is unclear. We examined the value of expanding lung cancer risk models for targeting low-dose computed tomography (LDCT), including blood measurements of liver function and urate.

METHODS

We analysed a cohort of 388,199 UK Biobank participants with 1873 events and calculated the c-index and fraction of new information (FNI) for models expanded to include combinations of blood measurements, lung function (forced expiratory volume in 1 s - FEV1), alcohol status and waist circumference. We calculated the hypothetical cost per lung cancer case detected by LDCT for different scenarios using a threshold of ≥ 1.51 % risk at 6 years.

RESULTS

The c-index was 0.805 (95 %CI:0.794-0.816) for the model containing conventional predictors. Expanding to include blood measurements increased the c-index to 0.815 (95 %CI: 0.804-0.826;p < 0.0001;FNI:0.06). Expanding to include FEV1, alcohol status, and waist circumference increased the c-index to 0.811 (95 %CI: 0.800-0.822;p < 0.0001;FNI: 0.04). The c-index for the fully expanded model containing all variables was 0.819 (95 %CI:0.808-0.830;p < 0.0001;FNI:0.09). Model expansion had a greater impact on the c-index and FNI for people with a history of smoking cigarettes relative to the full cohort. Compared with the conventional risk model, the expanded models reduced the number of participants meeting the criteria for LDCT screening by 15-21 %, and lung cancer cases detected by 7-8 %. The additional cost per lung cancer case detected relative to the conventional model was £ 1018 for adding blood tests and £ 9775 for the fully expanded model.

CONCLUSION

Blood measurements of liver function and urate made a modest improvement to lung cancer risk prediction compared with a model containing conventional risk factors. There was no evidence that model expansion would improve the cost per lung cancer case detected in UK healthcare settings.

Serum metabolic profiling of coal worker's pneumoconiosis using untargeted lipidomics

In this work, untargeted lipidomics was employed to analyze the effects of coal dust exposure on serum metabolite profiles. Furthermore, the potential of differential metabolites as novel biomarkers for diagnosis was investigated by binary logistic classification model. Nineteen differential metabolites were found among the three groups. The compounds were enriched in pathways associated with linoleic acid metabolism and pyrimidine metabolism. Fifty-three differential metabolites were found in coal dust-exposed people and CWP patients, and they were mainly enriched in glycerophospholipid metabolism. Three differential metabolites were correlated with lung function values. The diagnostic model, composed of lysoPI (16:0/0:0), bilirubin, and lysoPC (24:1/0:0), showed strong discrimination ability between dust-exposed people and CWP patients. The sensitivity, specificity, and AUC values of the model were 0.869, 0.600, and 0.750, respectively. The results suggest that coal worker's pneumoconiosis causes abnormal lipid metabolism in the body. A diagnostic model may aid current CWP diagnostic methods, and lysoPI (16:0/0:0), bilirubin, and lysoPC (24:1/0:0) can be used as potential CWP biomarkers. Further study is warranted to validate the findings in larger populations.

Mechanisms exploration of Terrestrosin D on pulmonary fibrosis based on plasma metabolomics and network pharmacology

Terrestrosin D (TED) is the active ingredient of Tribulus terrestris L., which is used in traditional Chinese medicine (TCM) formulations and has a wide range of pharmacological activities. A previous study showed that TED alleviated bleomycin (BLM)-induced pulmonary fibrosis (PF) in mice. However, the mechanisms underlying the therapeutic effect of TED are still unclear and need further investigation. In this study, we evaluated the effect of TED in a mice of BLM-induced PF in terms of histopathological and biochemical indices. UHPLC-MS-based plasma metabolomics combined with network pharmacology was used to explore the pathological basis of PF and the mechanism of action of TED. Histological and biochemical analyses showed that TED mitigated inflammatory injury in the lungs, especially at the dosage of 20 mg/kg. Furthermore, BLM changed the plasma metabolite profile in the mice, which was reversed by TED via regulation of amino acid and lipid metabolism. Subsequently, a biomarkers-targets-disease network was constructed, tumor necrosis factor (TNF)-α and transforming growth factor (TGF)-β1 were identified as the putative therapeutic targets of TED. Both factors were quantitatively analyzed by enzyme-linked immunosorbent assay (ELISA). Taken together, the combination of UHPLC-MS-based metabolomics and network pharmacology can unveil the mechanisms of diseases and drug action.

Hyperbilirubinemia in the Term Infant: Re-evaluating What We Think We Know

This article attempts to highlight contemporary issues relating to term neonatal hyperbilirubinemia and to focus attention on controversial issues and concepts with the potential to effect change in clinical approach. On the one hand, the focus is bilirubin neurotoxicity, which is now known to encompass a wide, diverse spectrum of features. The various aspects of this spectrum are outlined and defined. On the other hand, bilirubin also possesses antioxidant properties. As such, mild hyperbilirubinemia is suggested as actually offering the neonate some protective advantage.

Neurotoxicity of Unconjugated Bilirubin in Neonatal Hypoxic-Ischemic Brain Injury in vitro

Background: The pathophysiology of bilirubin neurotoxicity in course of hypoxic-ischemic encephalopathy (HIE) in term and preterm infants is still poorly understood. We hypothesized that oxidative stress may be a common mechanism that link hyperbilirubinemia and HIE. Objectives: The objective of the present study was to evaluate whether unconjugated bilirubin (UCB) may enhance the HI brain injury by increasing oxidative stress and to test pioglitazone and allopurinol as new antioxidant therapeutic drugs in vitro. Methods: The effects of UCB were tested on organotypic hippocampal slices subjected to 30 min oxygen-glucose deprivation (OGD), used as in vitro model of HIE. The experiments were performed on mature (14 days in culture) and immature (7 days in culture) slices, to mimic the brains of term and preterm infants, respectively. Mature and immature slices were exposed to UCB, human serum albumin (HSA), pioglitazone, and/or allopurinol for 24 h, immediately after 30 min OGD. Neuronal injury was assessed using propidium iodide (PI) fluorescence. ROS formation was quantified by using the 2',7'-dichlorodihydrofluorescein diacetate (DCF-DA) method. Results: In mature slices, we found that the neurotoxicity, as well as oxidative stress, induced by OGD were enhanced by UCB. HSA significantly prevented UCB-increased neurotoxicity, but had a slight reduction on ROS production. Allopurinol, but not pioglitazone, significantly reduced UCB-increased neurotoxicity induced by OGD. In immature slices exposed to OGD, no increase of neuronal death was observed, whereas oxidative stress was detected after UCB exposure. HSA, pioglitazone and allopurinol have no protective effects on both OGD-induced neuronal death and on UCB-induced oxidative stress. For this reason, UCB, pioglitazone and allopurinol was also tested on ischemic preconditioning protocol. We found that UCB abolished the neuroprotection induced by preconditioning and increased oxidative stress. These effects were restored by allopurinol but not pioglitazone. Conclusions: UCB characterized a different path of neuronal damage and oxidative stress in mature and immature hippocampal slice model of HIE. Management of hyperbilirubinemia in a complex pathological condition, such as HIE and hyperbilirubinemia, should be very careful. Allopurinol could deserve attention as a novel pharmacological intervention for hyperbilirubinemia and HIE.

New insights into the role of heme oxygenase-1 in acute kidney injury

Acute kidney injury (AKI) is attended by injury-related biomarkers appearing in the urine and serum, decreased urine output, and impaired glomerular filtration rate. AKI causes increased morbidity and mortality and can progress to chronic kidney disease and end-stage kidney failure. AKI is without specific therapies and is managed by supported care. Heme oxygenase-1 (HO-1) is a cytoprotective, inducible enzyme that degrades toxic free heme released from destabilized heme proteins and, during this process, releases beneficial by-products such as carbon monoxide and biliverdin/bilirubin and promotes ferritin synthesis. HO-1 induction protects against assorted renal insults as demonstrated by in vitro and preclinical models. This review summarizes the advances in understanding of the protection conferred by HO-1 in AKI, how HO-1 can be induced including via its transcription factor Nrf2, and HO-1 induction as a therapeutic strategy.

Genetically raised serum bilirubin levels and lung cancer: a cohort study and Mendelian randomisation using UK Biobank

BACKGROUND

Moderately raised serum bilirubin levels are associated with lower rates of lung cancer, particularly among smokers. It is not known whether these relationships reflect antioxidant properties or residual confounding.

OBJECTIVE

This study aimed to investigate potential causal relationships between serum total bilirubin and lung cancer incidence using one-sample Mendelian randomisation (MR) and UK Biobank.

METHODS

We instrumented serum total bilirubin level using two variants (rs887829 and rs4149056) that together explain ~40% of population-level variability and are linked to mild hereditary hyperbilirubinaemia. Lung cancer events occurring after recruitment were identified from national cancer registries. Observational and genetically instrumented incidence rate ratios (IRRs) and rate differences per 10 000 person-years (PYs) by smoking status were estimated.

RESULTS

We included 377 294 participants (median bilirubin 8.1 μmol/L (IQR 6.4-10.4)) and 2002 lung cancer events in the MR analysis. Each 5 μmol/L increase in observed bilirubin levels was associated with 1.2/10 000 PY decrease (95% CI 0.7 to 1.8) in lung cancer incidence. The corresponding MR estimate was a decrease of 0.8/10 000 PY (95% CI 0.1 to 1.4). The strongest associations were in current smokers where a 5 μmol/L increase in observed bilirubin levels was associated with a decrease in lung cancer incidence of 10.2/10 000 PY (95% CI 5.5 to 15.0) and an MR estimate of 6.4/10 000 PY (95% CI 1.4 to 11.5). For heavy smokers (≥20/day), the MR estimate was an incidence decrease of 23.1/10 000 PY (95% CI 7.3 to 38.9). There was no association in never smokers and no mediation by respiratory function.

CONCLUSION

Genetically raised serum bilirubin, common across human populations, may protect people exposed to high levels of smoke oxidants against lung cancers.

Association Between Serum Bilirubin and the Progression of Carotid Atherosclerosis in Type 2 Diabetes

Objective

This study investigated whether serum bilirubin levels can predict the progression of carotid atherosclerosis in individuals with type 2 diabetes mellitus (T2DM).

Methods

This observational study included 1,381 subjects with T2DM in whom serial measurements of carotid intima-media thickness (CIMT) were made at 1- to 2-year intervals for 6–8 years. The progression of carotid atherosclerosis was defined as newly detected plaque lesions on repeat ultrasonography. After dividing total serum bilirubin levels into tertiles, the association between total serum bilirubin at baseline and plaque progression status was analyzed.

Results

Among 1,381 T2DM patients, 599 (43.4%) were categorized as having plaque progression in their carotid arteries. Those with plaque progression were significantly older; showed a higher prevalence of hypertension, abdominal obesity, and chronic kidney disease; and had a longer duration of T2DM, higher levels of total cholesterol (TC), triglycerides, and insulin resistance, and lower total bilirubin concentrations than those with no plaque progression. When total serum bilirubin levels were divided into tertiles, the highest tertile group was younger than the lowest tertile group, with higher levels of TC and high-density lipoprotein cholesterol. Multiple logistic regression analysis demonstrated that higher serum bilirubin levels were associated with a significantly lower risk of CIMT progression (odds ratio, 0.584; 95% confidence interval, 0.392–0.870; p=0.008). Age (p<0.001), body mass index (p=0.023), and TC (p=0.019) were also associated with the progression of carotid atherosclerosis in T2DM patients.

Conclusion

Total serum bilirubin is independently associated with progression of atherosclerosis in the carotid arteries in T2DM patients.

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 of Lower Serum Bilirubin With Loss of Residual Kidney Function in Peritoneal Dialysis Patients

Bilirubin is recognized as an endogenous antioxidant, and low serum bilirubin is reported to be associated with the progression of kidney disease. However, it is unclear whether serum bilirubin levels are associated with the loss of residual kidney function (RKF) in peritoneal dialysis (PD) patients. This study investigated the relationship between serum total bilirubin and loss of RKF. We prospectively followed 94 PD patients who started PD in our hospital between June 2006 and May 2016. Ten patients who had chronic liver disease or cirrhosis were excluded. Patients were divided into three groups based on serum total bilirubin concentration tertiles: tertile 1 (T1) < 0.3, T2 = 0.3, and T3 ≥ 0.4 mg/dL. We estimated the relationship between serum bilirubin and loss of RKF, defined as daily urine volume (<100 mL) within 3 years after starting PD, using a Cox proportional hazards model. During the 3-year observation period, 22 patients lost RKF. The incidence rate of loss of RKF increased linearly with the decrease in serum total bilirubin levels (P for trend < 0.05). After adjusting for confounding factors, low serum total bilirubin level was shown to be an independent predictor of loss of RKF (hazard ratio [HR] for every 0.1 mg/dL decrease, 1.50; 95% confidence interval [CI], 1.01-2.51; HR [95%CI] for T2 and T1 [vs. T3] 2.03 [0.65-7.88] and 3.70 [1.00-15.9]). This study suggests that low serum total bilirubin levels are associated with the loss of RKF in PD patients.

Bilirubin Links Heme Metabolism to Neuroprotection by Scavenging Superoxide

Bilirubin is one of the most frequently measured metabolites in medicine, yet its physiologic roles remain unclear. Bilirubin can act as an antioxidant in vitro, but whether its redox activity is physiologically relevant is unclear because many other antioxidants are far more abundant in vivo. Here, we report that depleting endogenous bilirubin renders mice hypersensitive to oxidative stress. We find that mice lacking bilirubin are particularly vulnerable to superoxide (O₂^⋅-) over other tested reactive oxidants and electrophiles. Whereas major antioxidants such as glutathione and cysteine exhibit little to no reactivity toward O₂^⋅-, bilirubin readily scavenges O₂^⋅-. We find that bilirubin's redox activity is particularly important in the brain, where it prevents excitotoxicity and neuronal death by scavenging O₂^⋅- during NMDA neurotransmission. Bilirubin's unique redox activity toward O₂^⋅- may underlie a prominent physiologic role despite being significantly less abundant than other endogenous and exogenous antioxidants.

Potential protective effects of bilirubin following the treatment of neonatal hypoxic-ischemic encephalopathy with hypothermia therapy

Background: Therapeutic hypothermia (TH) is the standard therapy for hypoxic-ischemic encephalopathy (HIE) and is associated with a wide range of physiological changes. Objective: We re-evaluated the effects of HIE and TH on bilirubin measurements following HIE in a center involved in the China cooling randomized controlled trial (RCT). Methods: Serial serum bilirubin concentrations measured during the first week of life were compared among the HIE + NT (normothermia) group, HIE + TH treatment group and control group (without HIE). Survivors of HIE were followed and assessed at approximately 2 years of age, and the results were correlated with peak bilirubin levels during the first week of life. Results: One hundred and thirty-eight infants were available for analysis. Significantly lower bilirubin levels were recorded in the HIE + NT group than in the controls (P<0.05). Significant differences were not observed among the patients in the HIE + NT group (mild to severe) or between the HIE + TH group and the HIE + NT group at any time point (P>0.05). The peak serum bilirubin concentrations recorded at 96 h of age showed a good correlation with the results of the Bayley Scales of Infant and Toddler Development, third edition (BSID-III) (P=0.02). Conclusion: Bilirubin potentially exerts a neuroprotective effect during the first week of life, and low temperature does not affect the possible antioxidant function of bilirubin during TH following HIE.

Changes in bilirubin in infants with hypoxic-ischemic encephalopathy

Antioxidant properties of bilirubin have been reported in many studies. We hypothesized that bilirubin might be involved in neuroprotection mechanisms against oxidative stress in infants with hypoxic-ischemic encephalopathy (HIE) and that total serum bilirubin (TSB) might increase in these patients. We retrospectively studied infants with gestational age ≥ 35 weeks and birth weight ≥ 1800 g who were admitted to the neonatal intensive care unit (NICU) with a diagnosis of moderate-to-severe HIE and received or did not receive therapeutic hypothermia. We evaluated peak TSB and changes of mean TSB in these patients in comparison with a control group of infants admitted to the NICU with diagnoses other than HIE. Peak and mean TSB values were lower in the no hypothermia and hypothermia groups in comparison with the control group, while differences were not noted between infants who received hypothermia or did not. Regression analysis showed that HIE and hypothermia significantly reduced the risk of developing TSB values higher than median value (> 8.4 mg/dL) in our population.Conclusion: Peak and mean TSB values were lower in infants with moderate-to-severe HIE than in control infants. HIE and hypothermia independently decreased TSB. These results exclude a TSB increase as a neuroprotective mechanism in infants with HIE. We speculated that low TSB values in infants with HIE could be due to hypoxic repression of HO expression and represent a defensive strategy for limiting brain injuries in these patients. What is Known: • The role of oxidative stress in the pathophysiology of hypoxic-ischemic encephalopathy (HIE) has been elucidated in many studies, and other studies have demonstrated the antioxidant properties of bilirubin. • The potential neuroprotective role of bilirubin as antioxidant agent has never been evaluated in infants with HIE. What is New: • Mean total serum bilirubin (TSB) values are lower in infants with moderate-to-severe HIE than in control infants, since HIE and hypothermia independently decreased TSB. • An increase in bilirubin was not a neuroprotective mechanism in infants with HIE possibly because of hypoxic repression of HO expression as defensive strategy for limiting brain injuries.

Bilirubin and oxidative stress in term and preterm infants

Hyperbilirubinemia is the most frequent clinical problem neonatologists must deal with during the newborn period. It has been suggested that bilirubin is involved in the balance between antioxidant and pro-oxidant agents due to its antioxidant properties. However, the relevance of these effects in vivo in term and preterm infants is still debated. We performed a literature review of studies that investigated the association between total serum bilirubin (TSB) and oxidative stress in newborn infants. We found that studies in term infants give contradictory results, while studies in preterm infants suggest that the TSB increase is associated with an oxidative stress increase due to concurrent factors other than bilirubin level, such as heme oxygenase (HO) activity. Moreover, it could be speculated that low physiologic TSB values are associated with antioxidant effects, while high pathologic TSB values are associated with pro-oxidant effects. Literature data do not allow the establishment of whether if the antioxidant properties of bilirubin are important from a clinical point of view and can affect the outcome in ill infants.

Absence of the biliverdin reductase-a gene is associated with increased endogenous oxidative stress

Bilirubin, a byproduct of heme catabolism, has been shown to be an effective lipid-soluble antioxidant in vitro. Bilirubin is able to inhibit free radical chain reactions and protects against oxidant-induced damage in vitro and ex vivo. However, direct evidence for bilirubin's antioxidant effects in vivo remains limited. As bilirubin is formed from biliverdin by biliverdin reductase, we generated global biliverdin reductase-a gene knockout (Bvra^-/-) mice to assess the contribution of bilirubin as an endogenous antioxidant. Bvra^-/- mice appear normal and are born at the expected Mendelian ratio from Bvra^+/- x Bvra^+/- matings. Compared with corresponding littermate Bvra^+/+ and Bvra^+/- animals, Bvra^-/- mice have green gall bladders and their plasma concentrations of biliverdin and bilirubin are approximately 25-fold higher and 100-fold lower, respectively. Naïve Bvra^-/- and Bvra^+/+ mice have comparable plasma lipid profiles and low-molecular weight antioxidants, i.e., ascorbic acid, α-tocopherol and ubiquinol-9. Compared with wild-type littermates, however, plasma from Bvra^-/- mice contains higher concentrations of cholesteryl ester hydroperoxides (CE-OOH), and their peroxiredoxin 2 (Prx2) in erythrocytes is more oxidized as assessed by the extent of Prx2 dimerization. These data show that Bvra^-/- mice experience higher oxidative stress in blood, implying that plasma bilirubin attenuates endogenous oxidative stress.

Bilirubin Decreases Macrophage Cholesterol Efflux and ATP-Binding Cassette Transporter A1 Protein Expression

BACKGROUND

Mild but chronically elevated circulating unconjugated bilirubin is associated with reduced total and low-density lipoprotein cholesterol concentration, which is associated with reduced cardiovascular disease risk. We aimed to investigate whether unconjugated bilirubin influences macrophage cholesterol efflux, as a potential mechanism for the altered circulating lipoprotein concentrations observed in hyperbilirubinemic individuals.

METHODS AND RESULTS

Cholesterol efflux from THP-1 macrophages was assessed using plasma obtained from normo- and hyperbilirubinemic (Gilbert syndrome) humans (n=60 per group) or (heterozygote/homozygote Gunn) rats (n=20 per group) as an acceptor. Hyperbilirubinemic plasma from patients with Gilbert syndrome and Gunn rats induced significantly reduced cholesterol efflux compared with normobilirubinemic plasma. Unconjugated bilirubin (3-17.1 μmol/L) exogenously added to plasma- or apolipoprotein A1-supplemented media also decreased macrophage cholesterol efflux in a concentration- and time-dependent manner. We also showed reduced protein expression of the ATP-binding cassette transporter A1 (ABCA1), a transmembrane cholesterol transporter involved in apolipoprotein A1-mediated cholesterol efflux, in THP-1 macrophages treated with unconjugated bilirubin and in peripheral blood mononuclear cells obtained from hyperbilirubinemic individuals. Furthermore, we demonstrated that bilirubin accelerates the degradation rate of the ABCA1 protein in THP-1 macrophages.

CONCLUSIONS

Cholesterol efflux from THP-1 macrophages is decreased in the presence of plasma obtained from humans and rats with mild hyperbilirubinemia. A direct effect of unconjugated bilirubin on cholesterol efflux was demonstrated and is associated with decreased ABCA1 protein expression. These data improve our knowledge concerning bilirubin's impact on cholesterol transport and represent an important advancement in our understanding of bilirubin's role in cardiovascular disease.

Serum bilirubin concentrations and incident coronary heart disease risk among patients with type 2 diabetes: the Dongfeng-Tongji cohort

AIMS

Elevated serum bilirubin levels are associated with decreased coronary heart disease (CHD) risk in cross-sectional studies among diabetic patients, but prospective evidence is limited. We investigated the relationship of serum bilirubin levels with incident CHD risk among type 2 diabetes patients.

METHODS

In a prospective study of 2918 type 2 diabetes embedded in the Dongfeng-Tongji cohort, serum total bilirubin (TBil), direct bilirubin (DBil), and indirect bilirubin (IBil) were measured at baseline. Cox proportional hazards models were used to examine the association between serum bilirubin levels and CHD risk.

RESULTS

A total of 440 CHD cases were identified during 12,017 person-years of follow-up. Compared with extreme quartiles, the adjusted hazard ratio and 95% confidence interval of incident CHD were 0.74 (0.56-0.99) with P trend = 0.08 in IBil, while in TBil and DBil, the bilirubin-CHD associations were not significant. Moreover, serum TBil and IBil levels were interacted with drinking status on the risk of incident CHD (P interaction = 0.021 and 0.037, respectively), and the associations were evident in ever drinkers. In drinkers, when serum TBil or IBil concentrations increased 1 μmol/L, the CHD risk both decreased 6% (95% CIs 0.89-0.99 and 0.87-1.00, respectively).

CONCLUSIONS

Serum IBil levels were marginally related to decreased incident CHD risk among type 2 diabetes. Drinking could potentially enhance the associations of serum TBil and DBil levels with incident CHD risk.

Heme Oxygenase 1 as a Therapeutic Target in Acute Kidney Injury

A common clinical condition, acute kidney injury (AKI) significantly influences morbidity and mortality, particularly in critically ill patients. The pathophysiology of AKI is complex and involves multiple pathways, including inflammation, autophagy, cell-cycle progression, and oxidative stress. Recent evidence suggests that a single insult to the kidney significantly enhances the propensity to develop chronic kidney disease. Therefore, the generation of effective therapies against AKI is timely. In this context, the cytoprotective effects of heme oxygenase 1 (HO-1) in animal models of AKI are well documented. HO-1 modulates oxidative stress, autophagy, and inflammation and regulates the progression of cell cycle via direct and indirect mechanisms. These beneficial effects of HO-1 induction during AKI are mediated in part by the by-products of the HO reaction (iron, carbon monoxide, and bile pigments). This review highlights recent advances in the molecular mechanisms of HO-1-mediated cytoprotection and discusses the translational potential of HO-1 induction in AKI.

Jaundice, phototherapy and DNA damage in full-term neonates

OBJECTIVE

Phototherapy is the standard therapeutic approach for neonatal hyperbilirubinemia. Oxidative effects of phototherapy may have potential harms, including DNA damage. Unconjugated bilirubin (UCB) might also possess antigenotoxic potential. Intensive phototherapy is more efficacious than conventional phototherapy in treating hyperbilirubinemia. This study aimed to assess the impact of hyperbilirubinemia and the two different types of phototherapy on DNA damage in peripheral blood mononuclear cells of neonates.

STUDY DESIGN

The study was conducted on term neonates with non-hemolytic hyperbilirubinemia and control healthy neonates. Genotoxicity was assessed using single-cell gel electrophoresis (Comet assay) in peripheral mononuclear cells. Blood samples were obtained at enrollment in all infants and after intensive or conventional phototherapy in jaundiced infants.

RESULT

DNA damage did not significantly differ between jaundiced and non-jaundiced neonates (11.4±8.7 and 10.9±8.3 arbitrary units (AU), respectively, P=0.58). It increased significantly after exposure to phototherapy compared with prephototherapy values (45.6±14.7 vs 11.4±8.7 AU, respectively, P<0.001). The duration of phototherapy correlated positively with markers of DNA damage (r=0.86, P<0.001); however, the intensity of used light did not significantly impact genotoxicity.

CONCLUSION

Hyperbilirubinemia does not influence DNA damage, whereas both conventional and intensive phototherapy are associated with DNA damage in term infants with hyperbilirubinemia.

Hyperbilirubinemia exaggerates endotoxin-induced hypothermia

Systemic inflammation is accompanied by an increased production of reactive oxygen species (ROS) and by either fever or hypothermia (or both). To study aseptic systemic inflammation, it is often induced in rats by the intravenous administration of bacterial lipopolysaccharide (LPS). Knowing that bilirubin is a potent ROS scavenger, we compared responses to LPS between normobilirubinemic Gunn rats (heterozygous, asymptomatic; J/+) and hyperbilirubinemic Gunn rats (homozygous, jaundiced; J/J) to establish whether ROS mediate fever and hypothermia in aseptic systemic inflammation. These two genotypes correspond to undisturbed versus drastically suppressed (by bilirubin) tissue accumulation of ROS, respectively. A low dose of LPS (10 μg/kg) caused a typical triphasic fever in both genotypes, without any intergenotype differences. A high dose of LPS (1,000 μg/kg) caused a complex response consisting of early hypothermia followed by late fever. The hypothermic response was markedly exaggerated, whereas the subsequent fever response was strongly attenuated in J/J rats, as compared to J/+ rats. J/J rats also tended to respond to 1,000 μg/kg with blunted surges in plasma levels of all hepatic enzymes studied (alanine aminotransferase, aspartate aminotransferase, gamma-glutamyl transferase), thus suggesting an attenuation of hepatic damage. We propose that the reported exaggeration of LPS-induced hypothermia in J/J rats occurs via direct inhibition of nonshivering thermogenesis by bilirubin and possibly via a direct vasodilatatory action of bilirubin in the skin. This hypothermia-exaggerating effect might be responsible, at least in part, for the observed tendency of J/J rats to be protected from LPS-induced hepatic damage. The attenuation of the fever response to 1,000 μg/kg could be due to either direct actions of bilirubin on thermoeffectors or the ROS-scavenging action of bilirubin. However, the experiments with 10 μg/kg strongly suggest that ROS signaling is not involved in the fever response to low doses of LPS.

Targeting heme oxygenase-1 and carbon monoxide for therapeutic modulation of inflammation

The heme oxygenase-1 (HO-1) enzyme system remains an attractive therapeutic target for the treatment of inflammatory conditions. HO-1, a cellular stress protein, serves a vital metabolic function as the rate-limiting step in the degradation of heme to generate carbon monoxide (CO), iron, and biliverdin-IXα (BV), the latter which is converted to bilirubin-IXα (BR). HO-1 may function as a pleiotropic regulator of inflammatory signaling programs through the generation of its biologically active end products, namely CO, BV and BR. CO, when applied exogenously, can affect apoptotic, proliferative, and inflammatory cellular programs. Specifically, CO can modulate the production of proinflammatory or anti-inflammatory cytokines and mediators. HO-1 and CO may also have immunomodulatory effects with respect to regulating the functions of antigen-presenting cells, dendritic cells, and regulatory T cells. Therapeutic strategies to modulate HO-1 in disease include the application of natural-inducing compounds and gene therapy approaches for the targeted genetic overexpression or knockdown of HO-1. Several compounds have been used therapeutically to inhibit HO activity, including competitive inhibitors of the metalloporphyrin series or noncompetitive isoform-selective derivatives of imidazole-dioxolanes. The end products of HO activity, CO, BV and BR may be used therapeutically as pharmacologic treatments. CO may be applied by inhalation or through the use of CO-releasing molecules. This review will discuss HO-1 as a therapeutic target in diseases involving inflammation, including lung and vascular injury, sepsis, ischemia-reperfusion injury, and transplant rejection.

Analysis of oxidative stress expressed by urinary level of biopyrrins and 8-hydroxydeoxyguanosine in patients with chronic schizophrenia

AIMS

Previous studies have supported the claim that psychological stress induces the production of reactive oxygen species. Several authors have suggested that patients with psychiatric disorders show high levels of oxidative stress markers. We examined different oxidative stress markers in patients with chronic schizophrenia.

METHODS

This study included 29 patients with chronic schizophrenia and 30 healthy volunteers. The concentration of urinary biopyrrins and 8-hydroxydeoxyguanosine (8-OHdG), as measured by enzyme-linked immunosorbent assay, were normalized to the urinary concentration of creatinine. Psychiatric symptoms were assessed by the administration of the Brief Psychiatric Rating Scale (BPRS).

RESULTS

The concentration of biopyrrins in patients with chronic schizophrenia was significantly higher when compared with healthy volunteers. The correlation between biopyrrin level and the duration of illness was highly significant. There were no significant differences in the levels of urinary 8-OHdG between the two groups. In schizophrenic patients, the level of urinary biopyrrins showed correlations with BPRS scores, while the level of urinary 8-OHdG did not show correlations with BPRS.

CONCLUSIONS

Urinary biopyrrins are increased in patients with chronic schizophrenia while urinary 8-OHdG is not increased. These findings suggest that patients with chronic schizophrenia are under the condition of certain oxidative stresses.

Endogenously elevated bilirubin modulates kidney function and protects from circulating oxidative stress in a rat model of adenine-induced kidney failure

Mildly elevated bilirubin is associated with a reduction in the presence and progression of chronic kidney disease and related mortality, which may be attributed to bilirubin's antioxidant properties. This study investigated whether endogenously elevated bilirubin would protect against adenine-induced kidney damage in male hyperbilirubinaemic Gunn rats and littermate controls. Animals were orally administered adenine or methylcellulose solvent (vehicle) daily for 10 days and were then monitored for 28 days. Serum and urine were assessed throughout the protocol for parameters of kidney function and antioxidant/oxidative stress status and kidneys were harvested for histological examination upon completion of the study. Adenine-treated animals experienced weight-loss, polyuria and polydipsia; however, these effects were significantly attenuated in adenine-treated Gunn rats. No difference in the presence of dihydroadenine crystals, lymphocytic infiltration and fibrosis were noted in Gunn rat kidneys versus controls. However, plasma protein carbonyl and F2-isoprostane concentrations were significantly decreased in Gunn rats versus controls, with no change in urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine or kidney tissue F2-isoprostane concentrations. These data indicated that endogenously elevated bilirubin specifically protects from systemic oxidative stress in the vascular compartment. These data may help to clarify the protective relationship between bilirubin, kidney function and cardiovascular mortality in clinical investigations.

Bilirubin treatment suppresses pulmonary inflammation in a rat model of smoke-induced emphysema

BACKGROUND

Cigarette smoking is a significant risk factor for emphysema, which is characterized by airway inflammation and oxidative damage.

OBJECTIVES

To assess the capacity of bilirubin to protect against smoke-induced emphysema.

METHODS

Smoking status and bilirubin levels were recorded in 58 patients with chronic obstructive pulmonary diseases (COPD) and 71 non-COPD participants. The impact of smoking on serum bilirubin levels and exogenous bilirubin (20 mg/kg/day) on pulmonary injury was assessed in a rat model of smoking-induced emphysema. At sacrifice lung histology, airway leukocyte accumulation and cytokine and chemokine levels in serum, bronchoalveolar lavage fluid (BALF) and lung were analyzed. Oxidative lipid damage and anti-oxidative components was assessed by measuring malondialdehyde, superoxide dismutase (SOD) activity and glutathione.

RESULTS

Total serum bilirubin levels were lower in smokers with or without COPD than non-smoking patients without COPD (P < 0.05). Indirect serum bilirubin levels were lower in COPD patients than patients without COPD (P < 0.05). In rats, cigarette smoke reduced serum total and indirect bilirubin levels. Administration of bilirubin reduced mean linear intercept and mean alveoli area, increased mean alveoli number, reduced macrophage, neutrophil and TNF-α content of BALF, and increased BALF and serum IL-10 level, but lowered local and systemic CCL2, CXCL2, CXCL8 and IL-17 levels. Bilirubin suppressed the smoke-induced systemic and regional oxidative lipid damage associated with increased SOD activity.

CONCLUSION

Bilirubin attenuated smoking-induced pulmonary injury by suppressing inflammatory cell recruitment and pro-inflammatory cytokine secretion, increasing anti-inflammatory cytokine levels, and anti-oxidant SOD activity in a rat model of smoke-induced emphysema.

Association of serum total bilirubin level with severity of coronary atherosclerosis is linked to systemic inflammation

OBJECTIVE

Although cardiovascular protective action of bilirubin has been attributed to its antioxidant effect, there was scarce data regarding the anti-inflammatory properties. Herein, we aimed to assess the relationship between serum total bilirubin level and severity of coronary artery disease (CAD) in association with the direct inflammatory marker such as C-reactive protein (CRP), the other indirect markers included in inflammation process such as neutrophil to lymphocyte ratio (NLR) and red cell distribution width (RDW) in patients with stable CAD.

METHODS

Angiographic data of 1501 patients were analyzed in this retrospective cross-sectional study. Patients were categorized according to Gensini scores as control, mild CAD and severe CAD groups. The association of clinical and laboratory parameters with the severity of CAD were determined by multivariable linear regression analysis.

RESULTS

Total bilirubin level in the control group was significantly higher than those of the other groups. After multivariable linear regression analysis total bilirubin [β=-3.131 (-4.481, -1.782), p<0.001] was significantly associated with the severity of CAD. Futhermore, there was a moderate and significant inverse correlation between serum total bilirubin level and the severity of CAD (r=-0.173, p<0.001), CRP (r=-0.112, p<0.001), NLR (r=-0.070, p=0.026) and RDW (r=-0.074, p=0.027).

CONCLUSION

Serum total bilirubin level was independently and inversely associated with the severity of coronary atherosclerosis in patients with stable CAD. In addition, total bilirubin level was inversely correlated with CRP, NLR and RDW. These results suggest that besides its already known effect on the oxidative stress, higher serum total bilirubin level may exhibit an anti-inflammatory effect in the coronary atherosclerotic process.

Hemolysis in neonatal rats results in auditory impairment

CONCLUSION

This study suggests that hyperbilirubinemia in the neonatal rat can impair auditory function and induce peripheral nerve pathology by reducing neurofilament-positive cells in spiral ganglion neurons (SGNs). This finding indicates a potential connection between hyperbilirubinemia and auditory impairment.

OBJECTIVE

To establish a neonatal rat hyperbilirubinemia induced by hemolysis and assess the possible link between hyperbilirubinemia and auditory impairment.

METHODS

Wistar rats were divided into two groups - a bilirubin exposure group injected with phenylhydrazine hydrochloride at 7 and 28 days of age to induce hyperbilirubinemia, and a control group given saline. Auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAEs) were determined to assess auditory function. Cochlea basilar membrane stretch preparations and cochlear frozen sections were examined for morphological changes in hair cells and SGNs.

RESULTS

At day 7, ABR wave I, III, and V latencies, and I-III, I-V interwave intervals (IWIs) in the experimental group were significantly prolonged compared with those in the control group. ABR thresholds were also elevated in the experimental group. We found no significant difference in DPOAEs in the bilirubin exposure group compared to the control group. The ABRs and DPOAEs in the experimental group were restored at age 28 days. Cochlear hair cells showed no signs of loss in either group; however, the total number of neurofilament-positive cells in SGNs was significantly reduced in the phenylhydrazine-treated animals.

Effect of bilirubin on triglyceride synthesis in streptozotocin-induced diabetic nephropathy

We aimed to elucidate the effect of bilirubin on dyslipidemia and nephropathy in a diabetes mellitus (DM) type I animal model. Sprague-Dawley rats were separated into control, DM, and bilirubin-treated DM (Bil) groups. The Bil group was injected intraperitoneally with 60 mg/kg bilirubin 3 times per week and hepatoma cells were cultured with bilirubin at a concentration of 0.3 mg/dL. The Bil group showed lower serum creatinine levels 5 weeks after diabetes onset. Bilirubin treatment also decreased the amount of mesangial matrix, lowered the expression of renal collagen IV and transforming growth factor (TGF)-β1, and reduced the level of apoptosis in the kidney, compared to the DM group. These changes were accompanied by decreased tissue levels of hydrogen superoxide and NADPH oxidase subunit proteins. Bilirubin decreased serum total cholesterol, high-density lipoprotein cholesterol (HDL-C), free fatty acids, and triglycerides (TGs), as well as the TG content in the liver tissues. Bilirubin suppressed protein expression of LXRα, SREBP-1, SCD-1, and FAS, factors involved in TG synthesis that were elevated in the livers of DM rats and hepatoma cells under high-glucose conditions. In conclusion, bilirubin attenuates renal dysfunction and dyslipidemia in diabetes by suppressing LXRα and SREBP-1 expression and oxidative stress.

Circulating bilirubin and defense against kidney disease and cardiovascular mortality: mechanisms contributing to protection in clinical investigations

Unconjugated bilirubin is an endogenous circulating antioxidant, bound to albumin, and therefore is retained in the vascular compartment. Bilirubin has well-documented neurotoxic effects in infants; however, current evidence indicates mildly elevated bilirubin is associated with protection from cardiovascular disease and all-cause mortality in adults. Recent clinical studies show mildly elevated bilirubin is associated with protection from kidney damage and dysfunction, in addition to cardiovascular events and all-cause mortality in patients undergoing hemodialysis. This is the first review to examine the clinical evidence and summarize the potential mechanisms of action that link bilirubin to protection from kidney damage, subsequent kidney failure, and dialysis-related mortality. With this understanding, it is hoped that new therapies will be developed to prevent renal dysfunction and mortality from cardiovascular disease in at-risk individuals.

Withholding parenteral nutrition during critical illness increases plasma bilirubin but lowers the incidence of biliary sludge

Cholestatic liver dysfunction (CLD) and biliary sludge often occur during critical illness and are allegedly aggravated by parenteral nutrition (PN). Delaying initiation of PN beyond day 7 in the intensive care unit (ICU) (late PN) accelerated recovery as compared with early initiation of PN (early PN). However, the impact of nutritional strategy on biliary sludge and CLD has not been fully characterized. This was a preplanned subanalysis of a large randomized controlled trial of early PN versus late PN (n = 4,640). In all patients plasma bilirubin (daily) and liver enzymes (alanine aminotransferase [ALT], aspartate aminotransferase [AST], gamma-glutamyl transpeptidase [GGT], alkaline phosphatase [ALP], twice weekly; n = 3,216) were quantified. In a random predefined subset of patients, plasma bile acids (BAs) were also quantified at baseline and on days 3, 5, and last ICU-day (n = 280). Biliary sludge was ultrasonographically evaluated on ICU-day 5 (n = 776). From day 1 after randomization until the end of the 7-day intervention window, bilirubin was higher in the late PN than in the early PN group (P < 0.001). In the late PN group, as soon as PN was started on day 8 bilirubin fell and the two groups became comparable. Maximum levels of GGT, ALP, and ALT were lower in the late PN group (P < 0.01). Glycine/taurine-conjugated primary BAs increased over time in ICU (P < 0.01), similarly for the two groups. Fewer patients in the late PN than in the early PN group developed biliary sludge on day 5 (37% versus 45%; P = 0.04).

CONCLUSION

Tolerating substantial caloric deficit by withholding PN until day 8 of critical illness increased plasma bilirubin but reduced the occurrence of biliary sludge and lowered GGT, ALP, and ALT. These results suggest that hyperbilirubinemia during critical illness does not necessarily reflect cholestasis and instead may be an adaptive response that is suppressed by early PN.

Effects of serum bilirubin on atherosclerotic processes

This review highlights the protective roles of bilirubin against the atherosclerotic process. Bilirubin belongs to the superfamily of tetrapyrrolic compounds formed during heme catabolism. Although for decades bilirubin was considered to be a harmful waste product, recent epidemiologic studies have shown that serum bilirubin levels have consistently been inversely associated with cardiovascular disease (CVD), as well as cardiovascular risk factors such as metabolic syndrome and diabetes. These clinical studies are supported by in vitro and in vivo experimental data and have demonstrated that bilirubin not only has an ability to scavenge overproduced reactive oxygen species and inhibit vascular smooth muscle cell proliferation but, additionally, has anti-inflammatory effects. In this review, we will discuss the inverse association of serum bilirubin and CVD and cardiovascular risk factors established in various clinical studies. We also review detailed experimental studies about the effect of bilirubin on atherosclerotic processes. In vitro, animal and human studies have proved that bilirubin inhibits oxidation of cholesterol which is an important step of atherosclerosis. Bilirubin attenuates chemotactic activity of monocytes and strongly inhibits adhesion of leukocytes to venule and production of pro-inflammatory cytokines. Bilirubin has inhibited serum-driven smooth muscle cell cycle progression at the G1 phase. Lastly, we will discuss briefly the influence of bilirubin on lipoprotein composition and endothelial dysfunction.

Signaling function of heme oxygenase proteins

SIGNIFICANCE

Many reports have underscored the importance of the heme degradation pathway that is regulated by heme oxygenase (HO). This reaction releases bile pigments and carbon monoxide (CO), which are important antioxidant and signaling molecules. Thus, the reaction of HO-1 would have significant cytoprotective effects. Nevertheless, the importance of this protein goes beyond its enzymatic action. New evidence outlines significant effects of inactive forms of the HO-1 protein.

RECENT ADVANCES

In fact, the role of the HO protein in cellular signaling, including transcription factor activation, binding to proteins, phosphorylation, and modulation of protein function, among others, has started being elucidated. The mechanism by which the inducible form of HO-1, in particular, can migrate to various cellular compartments to mediate important signaling or how and why it binds to key transcription factors and other proteins that are important in DNA repair is also described in several physiologic systems.

CRITICAL ISSUES

The signaling functions of HO-1 may have particular relevance in clinical circumstances, including cancer, as redistribution of HO-1 into the nuclear compartment is observed with cancer progression and metastasis. In addition, along with oxidative stress, the pleiotropic functions of HO-1 modulate antioxidant defense. In organ transplantation, HO and its byproducts suppress rejection at multiple levels and in sepsis-induced pulmonary dysfunction, inhaled CO or modulation of HO activity can change the course of the disease in animals.

FUTURE DIRECTIONS

It is hoped that a more detailed understanding of the various signaling functions of HO will guide therapeutic approaches for complex diseases.

Heme oxygenase-1: a metabolic nike

SIGNIFICANCE

Heme degradation, which was described more than 30 years ago, is still very actively explored with many novel discoveries on its role in various disease models every year.

RECENT ADVANCES

The heme oxygenases (HO) are metabolic enzymes that utilize NADPH and oxygen to break apart the heme moiety liberating biliverdin (BV), carbon monoxide (CO), and iron. Heme that is derived from hemoproteins can be toxic to the cells and if not removed immediately, it causes cell apoptosis and local inflammation. Elimination of heme from the milieu enables generation of three products that influences numerous metabolic changes in the cell.

CRITICAL ISSUES

CO has profound effects on mitochondria and cellular respiration and other hemoproteins to which it can bind and affect their function, while BV and bilirubin (BR), the substrate and product of BV, reductase, respectively, are potent antioxidants. Sequestration of iron into ferritin and its recycling in the tissues is a part of the homeodynamic processes that control oxidation-reduction in cellular metabolism. Further, heme is an important component of a number of metabolic enzymes, and, therefore, HO-1 plays an important role in the modulation of cellular bioenergetics.

FUTURE DIRECTIONS

In this review, we describe the cross-talk between heme oxygenase-1 (HO-1) and its products with other metabolic pathways. HO-1, which we have labeled Nike, the goddess who personified victory, dictates triumph over pathophysiologic conditions, including diabetes, ischemia, and cancer.

Effects of phototherapy using different light sources on oxidant and antioxidant status of neonates with jaundice

BACKGROUND/AIM

Neonates have limited antioxidant protective capacity. It has recently been demonstrated that phototherapy used for treatment of neonatal jaundice produces oxidative stress. Various phototherapy devices using different light sources are available for phototherapy. We aimed to investigate the effects of phototherapy applied with different light sources on the global oxidant/antioxidant status in neonates.

METHODS

Term and late-preterm (≥35 weeks) newborn infants hospitalized to receive phototherapy for non-hemolytic jaundice in the 2-9 days of life were enrolled. Infants who received conventional phototherapy with fluorescent lamps were defined as group 1, intensive light emitting diode (LED) phototherapy as group 2, and fiberoptic phototherapy as group 3. The serum total antioxidant capacity (TAC) and total oxidant status (TOS) were measured before and 24 h after phototherapy. Oxidative stress index (OSI) was calculated.

RESULTS

Twenty nine patients were included in each group. At the beginning of phototherapy serum TAC, TOS and OSI levels were similar in all groups. After phototherapy serum TAC decreased significantly in all three groups (p < 0.001). Total oxidant status increased significantly in group 1 (p < 0.001) and group 2 (p = 0.001) whereas a statistically insignificant increase was observed in group 3 (p = 0.057). After phototherapy OSI increased significantly in group 1 (p < 0.001), group 2 (p = 0.001), and group 3 (p = 0.038).

CONCLUSION

As indicated by increased OSI, oxidant/antioxidant balance is disturbed in favor of oxidants after blue fluorescent light, LED and fiberoptic phototherapy.

New insights in bilirubin metabolism and their clinical implications

Bilirubin, a major end product of heme breakdown, is an important constituent of bile, responsible for its characteristic colour. Over recent decades, our understanding of bilirubin metabolism has expanded along with the processes of elimination of other endogenous and exogenous anionic substrates, mediated by the action of multiple transport systems at the sinusoidal and canalicular membrane of hepatocytes. Several inherited disorders characterised by impaired bilirubin conjugation (Crigler-Najjar syndrome type I and type II, Gilbert syndrome) or transport (Dubin-Johnson and Rotor syndrome) result in various degrees of hyperbilirubinemia of either the predominantly unconjugated or predominantly conjugated type. Moreover, disrupted regulation of hepatobiliary transport systems can explain jaundice in many acquired liver disorders. In this review, we discuss the recent data on liver bilirubin handling based on the discovery of the molecular basis of Rotor syndrome. The data show that a substantial fraction of bilirubin conjugates is primarily secreted by MRP3 at the sinusoidal membrane into the blood, from where they are subsequently reuptaken by sinusoidal membrane-bound organic anion transporting polypeptides OATP1B1 and OATP1B3. OATP1B proteins are also responsible for liver clearance of bilirubin conjugated in splanchnic organs, such as the intestine and kidney, and for a number of endogenous compounds, xenobiotics and drugs. Absence of one or both OATP1B proteins thus may have serious impact on toxicity of commonly used drugs cleared by this system such as statins, sartans, methotrexate or rifampicin. The liver-blood cycling of conjugated bilirubin is impaired in cholestatic and parenchymal liver diseases and this impairment most likely contributes to jaundice accompanying these disorders.

Gilbert's syndrome and the risk of death: a population-based cohort study

BACKGROUND AND AIMS

Gilbert's syndrome is a common familial hyperbilirubinemia that may reduce the risk of various age-related diseases because of the antioxidant properties of bilirubin. We conducted a large cohort study using The Health Improvement Network primary care database and compared all-cause mortality rates in those with and without Gilbert's syndrome.

METHODS

Mortality rates in patients with a diagnosis of Gilbert's syndrome and raised bilirubin level (n = 4266) were compared with those of patients with similar characteristics but with normal bilirubin levels (n = 21 968). Multivariate Poisson regression was also used to estimate adjusted mortality rate ratios.

RESULTS

During the 350 000 PYs of follow up across the Gilbert's and comparison cohorts, there were 1174 deaths. Mortality rates were 24/10 000 PYs in the Gilbert's cohort versus 50/10 000 PYs in the comparison cohort. Mortality rates were around half in patients with Gilbert's syndrome after accounting for sociodemographics and general health indicators (adjusted mortality rate ratio: 0.5 [95% confidence interval; 0.4-0.7; P < 0.001]).

CONCLUSIONS

Mortality rates observed for people with Gilbert's syndrome in the general population are almost half those of people without evidence of Gilbert's syndrome.

Hyperbilirubinemia and urinary tract infection: the effect of indirect hyperbilirubinemia on the in vitro growth of uropathogen Escherichia coli in newborn urine

High serum bilirubin is antioxidant and cytoprotective. We evaluated if urine samples of hyperbilirubinemic newborns impede uropathogenic Escherichia coli growth. Bag-urine samples of hyperbilirubinemic newborns (study group) were cultured at presentation and during remission. Urine sample were obtained only once from healthy newborns (control group). Escherichia coli [2 × 104 colony-forming unit (cfu)/mL] was inoculated into the sterile urine samples and colony counts were determined after 24 h. Bilirubin levels at presentation and remission were also recorded. Escherichia coli colony counts of the control versus study groups and of the presentation versus remission samples in the study group were compared. There were 13 study and 17 control cases. Escherichia coli colony counts were not different in the study group at presentation versus remission (5.4 ± 0.7 vs. 5.5 ± 0.8 log10, respectively; p = 0.659). Escherichia coli colony count of the control group (5.2 ± 0.6 log10) was also not different from the study group. In conclusion, the urine of hyperbilirubinemic newborns did not affect the growth rate of uropathogenic E. coli.

A product of heme catabolism modulates bacterial function and survival

Bilirubin is the terminal metabolite in heme catabolism in mammals. After deposition into bile, bilirubin is released in large quantities into the mammalian gastrointestinal (GI) tract. We hypothesized that intestinal bilirubin may modulate the function of enteric bacteria. To test this hypothesis, we investigated the effect of bilirubin on two enteric pathogens; enterohemorrhagic E. coli (EHEC), a Gram-negative that causes life-threatening intestinal infections, and E. faecalis, a Gram-positive human commensal bacterium known to be an opportunistic pathogen with broad-spectrum antibiotic resistance. We demonstrate that bilirubin can protect EHEC from exogenous and host-generated reactive oxygen species (ROS) through the absorption of free radicals. In contrast, E. faecalis was highly susceptible to bilirubin, which causes significant membrane disruption and uncoupling of respiratory metabolism in this bacterium. Interestingly, similar results were observed for other Gram-positive bacteria, including B. cereus and S. aureus. A model is proposed whereby bilirubin places distinct selective pressure on enteric bacteria, with Gram-negative bacteria being protected from ROS (positive outcome) and Gram-positive bacteria being susceptible to membrane disruption (negative outcome). This work suggests bilirubin has differential but biologically relevant effects on bacteria and justifies additional efforts to determine the role of this neglected waste catabolite in disease processes, including animal models.

Bilirubin is the terminal breakdown product of heme, which is deposited at high concentrations in the human intestine, where it can come into contact with host cells, the gastrointestinal (GI) microflora, and invading pathogens. Here, we report that bilirubin can act as a protectant for the Gram-negative bacterial pathogen E. coli O157:H7, which causes severe hemorrhagic diarrhea and life-threatening kidney damage. Paradoxically, bilirubin is highly toxic towards another enteric opportunistic pathogen, the Gram-positive bacterium E. faecalis. Whereas the protection of E. coli stems from the neutralization of host reactive oxygen species, bilirubin's toxicity toward E. faecalis is rooted in its lipophilic properties, which drives the rapid association of bilirubin with bacteria, leading to disrupted cell membranes and concomitant death. These results suggest small molecule metabolites can modulate bacterial communities in the intestine, a finding that may have important implications for diseases caused by enteric bacteria and disrupted flora.

Protection from age-related increase in lipid biomarkers and inflammation contributes to cardiovascular protection in Gilbert's syndrome

Recent epidemiological and clinical data show protection from CVD (cardiovascular disease), all-cause mortality and cancer in subjects with GS (Gilbert's syndrome), which is characterized by a mildly elevated blood bilirubin concentration. The established antioxidant effect of bilirubin, however, contributes only in part to this protection. Therefore we investigated whether mildly elevated circulating UCB (unconjugated bilirubin) is associated with altered lipid metabolism. The study was performed on GS and age- and gender-matched healthy subjects (n=59 per group). Full lipoprotein profile, TAG (triacylglycerols), Apo (apolipoprotein)-A1, Apo-B, lipoprotein(a), the subfractions of LDL (low-density lipoprotein) and selected pro-inflammatory mediators were analysed. A hyperbilirubinaemic rodent model (Gunn rats, n=40) was investigated to further support the presented human data. GS subjects had significantly (P<0.05) improved lipid profile with reduced total cholesterol, LDL-C (LDL-cholesterol), TAG, low- and pro-atherogenic LDL subfractions (LDL-1+LDL-2), Apo-B, Apo-B/Apo-A1 ratio and lower IL-6 (interleukin 6) and SAA (serum amyloid A) concentrations (P=0.094). When the control and GS groups were subdivided into younger and older cohorts, older GS subjects demonstrated reduced lipid variables (total cholesterol and LDL-C, TAG and LDL-C subfractions, Apo-B/Apo-A1 ratio; P<0.05; Apo-B: P<0.1) compared with controls. These data were supported by lipid analyses in the rodent model showing that Gunn rat serum had lower total cholesterol (2.29±0.38 compared with 1.27±0.72 mM; P<0.001) and TAG (1.66±0.67 compared with 0.99±0.52 mM; P<0.001) concentrations compared with controls. These findings indicate that the altered lipid profile and the reduced pro-inflammatory status in hyperbilirubinaemic subjects, particularly in the older individuals, probably contribute additionally to the commonly accepted beneficial antioxidant effects of bilirubin in humans.

Association of serum total bilirubin levels with the severity, extent and subtypes of coronary atherosclerotic plaques detected by coronary CT angiography

In this study, we aimed to evaluate whether serum total bilirubin was associated with the severity and morphology of coronary atherosclerotic plaques detected by computed tomography angiography (CTA). The study population consisted of 1,115 patients (55.2 % men) who underwent dual-source 64-slice CTA for the assessment of coronary artery disease (CAD). Coronary arteries were evaluated on 16 segment basis and critical coronary plaque was described as luminal narrowing >50 %, whereas plaque morphology was assessed on per segment basis. Serum bilirubin levels were determined using commercially available assay kits. The critical atherosclerotic lesions were detected in 431/1,115 (38.6 %) subjects by CTA. Serum total bilirubin levels were found to be lower in patients with any coronary plaque (0.62 ± 0.21 vs. 0.70 ± 0.25 mg/dL, p = 0.002). Also bilirubin level was lower in patients with critical stenosis compared to non-critical stenosis (0.57 ± 0.18 vs. 0.70 ± 0.24 mg/dL, p < 0.001). Subjects having primarily noncalcified plaque (NCP) and mixed plaque (MP) have lower bilirubin levels compared to calcified plaque (CP) and normal subjects (0.62 ± 0.20 for NCP and 0.60 ± 0.19 for MP, 0.65 ± 0.26 for CP and 0.71 ± 0.25 for normal subjects, p < 0.001). This independent association was remained for NCP after multinominal regression analysis (OR: 0.76; 95 % CI 0.58-0.88; p < 0.001). Our study demonstrated that serum bilirubin level was significantly associated with the presence, severity and the noncalcified morphology of atherosclerotic plaques detected by CTA. Further prospective clinical studies are needed to clarify the exact physiopathologic and prognostic role of bilirubin in CAD.

Usefulness of serum lipid peroxide as a diagnostic test for hypoxic ischemic encephalopathy in the full-term neonate

OBJECTIVE

To evaluate the usefulness of serum lipid peroxide (LPO) for hypoxic ischemic encephalopathy (HIE) in full-term neonates.

STUDY DESIGN

Diagnostic test evaluation forming three groups: (1) healthy full-term neonates (n=59), (2) at-risk full-term neonates without HIE (n=57) and (3) at-risk full-term neonates with HIE (n=57). HIE diagnosis was made using the Finer clinical classification at 48 h after birth. Serum LPO was taken at 4 h after birth and determined by spectrophotometry.

RESULT

One hundred seventy-three full-term neonates were studied. Fifty-one of the at-risk full-term neonates with HIE (51/57) had high serum LPO and two of the at-risk full-term neonates without HIE (2/57) (P<0.001). Serum LPO level had 89% sensitivity, 96% specificity, 96% positive predictive value, 90% negative predictive value, 24 positive probability ratio, 0.11 negative probability ratio and 92% diagnostic usefulness.

CONCLUSION

Serum LPO level could be a useful test for early diagnosis of HIE in full-term neonates.

Bilirubin and beyond: a review of lipid status in Gilbert's syndrome and its relevance to cardiovascular disease protection

Gilbert's syndrome (GS) is characterized by a benign, mildly elevated bilirubin concentration in the blood. Recent reports show clear protection from cardiovascular disease in this population. Protection of lipids, proteins and other macromolecules from oxidation by bilirubin represents the most commonly accepted mechanism contributing to protection in this group. However, a recent meta-analysis estimated that bilirubin only accounts for ~34% of the cardioprotective effects within analysed studies. To reveal the additional contributing variables we have explored circulating cholesterol and triacylglycerol concentrations, which appear to be decreased in hyperbilirubinemic individuals/animals, and are accompanied by lower body mass index in highly powered studies. These results suggest that bilirubin could be responsible for the development of a lean and hypolipidemic state in GS. Here we also discuss the possible contributing mechanisms that might reduce circulating cholesterol and triacylglycerol concentrations in individuals with syndromes affecting bilirubin metabolism/excretion, which we hope will stimulate future research in the area. In summary, this article is the first review of lipid status in animal and human studies of hyperbilirubinemia and explores possible mechanisms that could contribute to lowering circulating lipid parameters and further explain cardiovascular protection in Gilbert's syndrome.

Evaluating the beneficial and detrimental effects of bile pigments in early and later life

The heme degradation pathway has been conserved throughout phylogeny and allows for the removal of a pro-oxidant and the generation of unique molecules including bile pigments with important cellular functions. The impact of bile pigments on health and disease are reviewed, as is the special circumstance of neonatal hyperbilirubinemia. In addition, the importance of promoter polymorphisms in the UDP-glucuronosyl transferase gene (UGTA1), which is key to the elimination of excess bilirubin and to the prevention of its toxicity, are discussed. Overall, the duality of bile pigments as either cytoprotective or toxic molecules is highlighted.

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.