Sulforaphane Suppresses Hepatitis C Virus Replication by Up-Regulating Heme Oxygenase-1 Expression through PI3K/Nrf2 Pathway

Hepatitis C virus (HCV) infection-induced oxidative stress is a major risk factor for the development of HCV-associated liver disease. Sulforaphane (SFN) is an antioxidant phytocompound that acts against cellular oxidative stress and tumorigenesis. However, there is little known about its anti-viral activity. In this study, we demonstrated that SFN significantly suppressed HCV protein and RNA levels in HCV replicon cells and infectious system, with an IC50 value of 5.7 ± 0.2 μM. Moreover, combination of SFN with anti-viral drugs displayed synergistic effects in the suppression of HCV replication. In addition, we found nuclear factor erythroid 2-related factor 2 (Nrf2)/HO-1 induction in response to SFN and determined the signaling pathways involved in this process, including inhibition of NS3 protease activity and induction of IFN response. In contrast, the anti-viral activities were attenuated by knockdown of HO-1 with specific inhibitor (SnPP) and shRNA, suggesting that anti-HCV activity of SFN is dependent on HO-1 expression. Otherwise, SFN stimulated the phosphorylation of phosphoinositide 3-kinase (PI3K) leading Nrf2-mediated HO-1 expression against HCV replication. Overall, our results indicated that HO-1 is essential in SFN-mediated anti-HCV activity and provide new insights in the molecular mechanism of SFN in HCV replication.

Reduced circulating oxidized LDL is associated with hypocholesterolemia and enhanced thiol status in Gilbert syndrome

A protective association between bilirubin and atherosclerosis/ischemic heart disease clearly exists in vivo. However, the relationship between bilirubin and in vivo oxidative stress parameters in a clinical population remains poorly described. The aim of this study was to assess whether persons expressing Gilbert syndrome (GS; i.e., unconjugated hyperbilirubinemia) are protected from thiol oxidation and to determine if this, in addition to their improved lipoprotein profile, could explain reduced oxidized low-density lipoprotein (oxLDL) status in them. Forty-four matched GS and control subjects were recruited and blood was prepared for the analysis of lipid profile and multiple plasma antioxidants and measures of oxidative stress. GS subjects possessed elevated plasma reduced thiol (8.03±1.09 versus 6.75±1.39 nmol/mg protein; P<0.01) and glutathione concentrations (12.7±2.39 versus 9.44±2.45 μM; P<0.001). Oxidative stress status (reduced:oxidized glutathione; GSH:GSSG) was significantly improved in GS (0.49±0.16 versus 0.32±0.12; P<0.001). Protein carbonyl concentrations were negatively associated with bilirubin concentrations and were significantly lower in persons with >40 μM bilirubin versus controls (<17.1 μmol/L; P<0.05). Furthermore, absolute oxLDL concentrations were significantly lower in GS subjects (P<0.05). Forward stepwise regression analysis revealed that bilirubin was associated with increased GSH:GSSG ratio and reduced thiol concentrations, which, in addition to reduced circulating LDL, probably decreased oxLDL concentrations within the cohort. In addition, a marked reduction in total cholesterol concentrations in hyperbilirubinemic Gunn rats is presented (Gunn 0.57±0.09 versus control 1.69±0.40 mmol/L; P<0.001), arguing for a novel role for bilirubin in modulating lipid status in vivo. These findings implicate the physiological importance of bilirubin in protecting from atherosclerosis by reducing thiol and subsequent lipoprotein oxidation, in addition to reducing circulating LDL concentrations.

Alanine aminotransferase decreases with age: the Rancho Bernardo Study

Background

Serum alanine aminotransferase (ALT) is a marker of liver injury. The 2005 American Gastroenterology Association Future Trends Committee report states that serum ALT levels remain constant with age. This study examines the association between serum ALT and age in a community-dwelling cohort in the United States.

Methods

A cross-sectional study of 2,364 (54% female) participants aged 30–93 years from the Rancho Bernardo Study cohort who attended a research clinic visit in 1984–87. Demographic, metabolic co-variates, ALT, bilirubin, gamma glutamyl transferase (GGT), albumin, and adiposity signaling biomarkers (leptin, IL-6, adiponectin, ghrelin) were measured. Participants were divided into four-groups based upon age quartile, and multivariable-adjusted least squares of means (LSM) were examined (p for trend <0.05).

Results

ALT decreased with increasing age, with mean ALT levels (IU/L) of 23, 21, 20, and 17 for those between quartile ages 30–62, 63–71, 72–77, and 78–93 years (p<0.0001). Trends of decreasing LSM ALT with age and the decreasing prevalence of categorically defined elevated serum ALT with age remained robust after adjusting for sex, alcohol use, metabolic syndrome components, and biomarkers of adiposity (p-value <0.0001), and was not materially changed after adjusting for bilirubin, GGT, and albumin.

Conclusions

ALT levels decrease with age in both men and women independent of metabolic syndrome components, adiposity signaling biomarkers, and other commonly used liver function tests. Further studies are needed to understand the mechanisms responsible for a decline in ALT with age, and to establish the optimal cut-point of normal ALT in the elderly.

Heme oxygenase-1 mediates the inhibitory actions of brazilin in RAW264.7 macrophages stimulated with lipopolysaccharide

Brazilin, the main constituent of Caesalpinia sappan L., is a natural red pigment that has been reported to possess anti-inflammatory properties. This study aimed to identify a novel anti-inflammatory mechanism of brazilin. We found that brazilin did not cause cytotoxicity below 300 microM, and activated heme oxygenase-1 (HO-1) protein synthesis in a concentration-dependent manner at 10-300 microM in RAW264.7 macrophages without affecting mRNA transcription of HO-1. Additionally, brazilin increased bilirubin production and HO-1 activity in RAW264.7 macrophages. In lipopolysaccharide (LPS)-stimulated macrophages, brazilin suppressed the release of nitric oxide (NO), prostaglandin E(2) (PGE(2)), interleukin (IL)-1beta and tumor necrosis factor-alpha (TNF-alpha), and reduced the expression of inducible nitric oxide synthase (iNOS). A specific inhibitor of HO-1, Zn(II) protoporphyrin IX, blocked the suppression of NO production, cytokines release and iNOS expression by brazilin. These results suggest that brazilin possesses anti-inflammatory actions in macrophages and works through a novel mechanism involving the action of HO-1.

Statin treatment increases formation of carbon monoxide and bilirubin in mice: a novel mechanism of in vivo antioxidant protection

Heme oxygenase (HO) has a central role in cellular antioxidant defences and vascular protection, and it may mediate pleiotropic actions of drugs used in cardiovascular therapy. We investigated whether long-term use of statins upregulates HO activity and increases carbon monoxide (CO) and bilirubin levels in vivo. Adult FvB mice were given atorvastatin or rosuvastatin (5 mg/kg) daily by i.p. injections for 1, 2, or 3 weeks. HO activity, tissue CO, bilirubin, and antioxidant levels, total plasma bilirubin, and carboxyhemoglobin (COHb) were measured. Fold changes in heart HO activity significantly increased after 1, 2, and 3 weeks of atorvastatin (1.24 ± 0.06 (p ≤ 0.05); 1.29 ± 0.26 (p ≤ 0.03); 1.33 ± 0.08 (p < 0.01), respectively) and 2 and 3 weeks of rosuvastatin (1.23 ± 0.20 (p ≤ 0.03); 1.63 ± 0.42 (p < 0.01), respectively). Heart tissue CO and COHb levels also increased after 3 weeks with atorvastatin (1.30 ± 0.24 (p ≤ 0.05); 1.92 ± 0.17 (p ≤ 0.001), respectively) and rosuvastatin (1.47 ± 0.13 (p ≤ 0.004); 1.63 ± 0.12 (p ≤ 0.001), respectively). Significant increases in heart antioxidant levels were observed after statin treatment and corroborated by heart bilirubin content elevations. Antioxidant level increases were abolished by treatment with an HO inhibitor. These findings suggest that the induction of HO and the production of its products, CO and bilirubin, may be a mechanism by which statins exert antioxidant actions and confer cardioprotection in vivo.

In vitro production of bilirubin photoisomers by light irradiation using neoBLUE

BACKGROUND

The light-emitting diode is used as one of the new light sources for phototherapy. NeoBLUE (Atom Medical, Tokyo, Japan) incorporates blue light-emitting diodes for the treatment of neonatal hyperbilirubinemia. The authors compared the in vitro efficacy of neoBLUE with conventional phototherapy devices.

METHODS

The three light devices used included neoBLUE and two conventional phototherapy devices with six blue-white (BW) or six green (GR) fluorescent tubes. A bilirubin/human serum albumin solution (15 mg/dL) in 200 x 300 mm elliptical bag was irradiated with each three light device. The average light intensity of neoBLUE, BW and GR was 22.5, 10.2 and 2.6 microW/cm(2) per nm, respectively, for the irradiated area. Bilirubin photoisomers and native bilirubin were measured by high-performance liquid chromatography.

RESULTS

In neoBLUE, BW and GR, the respective production rate of cyclobilirubin was 6.0, 3.7 and 3.9 x 10(-2) mg/dL/min, and the respective (4Z, 15E)-bilirubin/(4Z, 15Z)-bilirubin ratio after irradiation was 0.44, 0.33 and 0.12; the (4Z, 15Z)-bilirubin reduction rate at 20 min after irradiation was 60, 68 and 82%, respectively. The reduction rate of (4Z, 15Z)-bilirubin correlated with the (4Z, 15E)-bilirubin/(4Z, 15Z)-bilirubin ratio.

CONCLUSION

Phototherapy using the neoBLUE under high level may be clinically more effective than therapy using the conventional light source from the results of the production rate of cyclobilirubin.

Energy change in the formation of conjugated bilirubin: a possible responsive mechanism for liver cell pathology

Bilirubin is formed when red blood cells die and their hemoglobin is broken down within the macrophages into heme and globins. In the liver, bilirubin is conjugated with UDP-glucuronate, making it water-soluble diglucuronide. Concerning this conjugation, a molecule of bilirubin reacts with two molecules of glucoronic acid. However, the nature of this energy-consuming reaction in the formation of conjugated bilirubin has never been reported, and this can be important for its potential implication in hyperbilirubinemia. In this work, the author calculated the energy required by conjugated-bilirubin formation per molecule. The energy required for complex formation is -22 kCal/mol. The nature of this energy-producing reaction can be a good explanation. Increased energy delivery in conjugated hyperbilirubinemia in liver disease might be a responsive mechanism to hepatic damage.

Elevated serum BAFF levels in patients with autoimmune hepatitis

Serum cytokines are thought to be involved in autoimmune hepatitis (AIH) pathogenesis via immune dysregulation. B-cell activating factor belonging to the tumor necrosis factor family (BAFF) is a member of the tumor necrosis factor (TNF) superfamily and is known for its role in the survival and maturation of B cells. The aim of the study was to evaluate the serum levels of BAFF in patients with AIH and determine its relation to the clinical features of AIH. We examined serum BAFF levels in 55 patients with AIH, 14 patients with acute hepatitis (AH), 33 patients with chronic hepatitis C, and 33 healthy subjects by enzyme-linked immunosorbent assay. Liver function tests, quantitative immunoglobulin, and antinuclear antibody levels were also assayed in AIH patients. Serum BAFF levels were elevated in AIH patients compared with healthy subjects (AIH: 2.07+/-1.21 pg/ml, control: 0.77+/-0.22 pg/ml). Similarly, serum BAFF levels were significantly higher in AIH patients compared with AH or chronic hepatitis C patients. There was a positive correlation between BAFF and aspartate aminotransferase (r=0.513, p<0.0001), alanine aminotransferase (r=0.435, p<0.0001), total bilirubin (r=0.419, p<0.01), and soluble CD30 (r=0.579, p<0.0001) in AIH patients. However, there was no correlation between BAFF and levels of gammaglobulins or titer of antinuclear antibodies. Corticosteroid treatment resulted in marked reduction in serum BAFF levels in AIH patients. These results suggest that BAFF contributes to liver injury and disease development in AIH patients.

Modulation by heme and zinc protoporphyrin of colonic heme oxygenase-1 and experimental inflammatory bowel disease in the rat

Reactive oxygen species, suggested to be involved in inflammatory bowel disease, may be modulated by endogenous anti-oxidant products of heme oxygenase-1 (HO-1). In the present work, HO-1 expression in trinitrobenzene sulphonic acid (TNBS)-induced colitis in the rat and the effects of HO-1 modulation, particularly by the HO-1 inducer, heme, were further evaluated. Colitis was induced by intracolonic challenge with TNBS and assessed macroscopically and by myeloperoxidase (MPO) assay. Heme oxygenase activity was determined by measurement of bilirubin formation and HO-1 protein expression was determined by Western blotting. TNBS challenge led to an early and substantial induction of HO-1 protein expression and heme oxygenase activity in the colon that peaked after 48-72 h and declined over 10 days. Heme (30 micromol/kg/day, s.c) increased colonic HO-1 protein expression and enzyme activity and decreased colonic damage and myeloperoxidase activity. Short-term administration of cadmium chloride (2 mg/kg, s.c.), another known HO-1 inducer, also reduced the colonic injury and myeloperoxidase levels. In contrast, the HO-1 inhibitor, zinc protoporphyrin (50 micromol/kg/day, s.c) significantly increased the colonic damage and myeloperoxidase activity over 10 days, as did tin protoporphyrin (30 micromol/kg/day, s.c). These results support the proposal that induction of HO-1 provides a protective mechanism in this model under both acute and more-chronic conditions, and that its selective up-regulation could thus be of therapeutic potential in colitis.

Evidence for the expression and enzymatic activity of haem oxygenase-1 in the lungs of horses

The aim of this study was to characterise the expression of haem oxygenase-1 (HO-1) in healthy lung tissue from horses and to measure its activity. Samples of lung tissue were collected from six horses euthanased for reasons other than respiratory disease. HO-1 expression and activity were detected in type II alveolar epithelial cells, macrophages and neutrophils in all the samples examined. The activity was dependent on the presence of NADPH and inhibited quantitatively by the addition of increasing concentrations of a competitive inhibitor of HO-1, tin mesoporphyrin IX.

Systemic effects of orally-administered zinc and tin (IV) metalloporphyrins on heme oxygenase expression in mice

Some metalloporphyrins (Mps) inhibit heme oxygenase (HO), the rate-limiting enzyme in the production of bilirubin, and are potential compounds for the treatment of neonatal jaundice. We studied the safety and efficacy of Mps following oral administration. Adult HO-1-luc reporter mice were administered 30 micromol/kg body weight of tin mesoporphyrin (SnMP), zinc bis glycol deuteroporphyrin (ZnBG), or zinc protoporphyrin (ZnPP), or vehicle by oral gavage. Bilirubin production was measured as total body carbon monoxide (CO) excretion (VeCO). HO activity was quantitated via CO measurements by gas chromatography. HO-1 protein was determined by Western blot. HO-1 transcription levels were assessed by in vivo bioluminescence imaging. A significant 28% decrease in bilirubin production occurred within 3 h of SnMP treatment and persisted beyond 48 h. Bilirubin production decreased 15% and 9% by 3 h after administration of ZnBG and ZnPP, respectively, but returned to baseline within 48 h. Maximal inhibition of liver, spleen, and intestine HO activity was seen at 3 h with inhibitory effects decreasing in the order: SnMP > or = ZnBG > or = ZnPP. After SnMP treatment, HO-1 transcription increased 5.7-fold after 24 h. Furthermore, liver and spleen HO-1 protein significantly increased 3.7- and 2.0-fold, respectively, after 24 h. HO-1 transcription and protein were not affected in ZnBG- or ZnPP-treated mice. We conclude that the three Mps are absorbed at different rates in the mouse and affect bilirubin production and HO-1 expression in a tissue- and time-dependent manner.

Early expression of heme oxygenase-1 in leukocytes correlates negatively with oxidative stress and predicts hepatic and renal dysfunction at late stage of sepsis

Oxidative stress triggered by septic insult may be the major cause of multiple organ dysfunction syndrome (MODS) in intensive unit care patients. The inducible form of heme oxygenase-1 (HO-1) can be induced by cytokines, lipopolysaccharide, and reactive oxygen species during sepsis. These facts raise the question of whether the expression of HO-1 in leukocytes can indicate the level of oxidative stress of multiple organs in sepsis. Clinical peritonitis was simulated in an animal model by cecal ligation and puncture (CLP). The level of oxidative stress was examined by plasma lipid peroxidation (LPO). Liver function was analyzed by plasma aspartate aminotransferase, alanine aminotransferase, total bilirubin, and direct bilirubin. Lung function was evaluated by severity of edema. Renal function was measured by blood urea nitrogen and creatinine. The correlation between early HO-1 induction and LPO level or organ functional indicators of the same rat at late sepsis was analyzed by linear regression. The results showed that the protein content of HO-1 increased at 9 h after CLP, whereas expression of HO-1 mRNA in leukocytes was significantly increased (P < 0.01) at 6 h after CLP. Plasma level of LPO and the indices of hepatic, pulmonary, and renal function were significantly increased at 18 h after CLP. Moreover, highly negative correlations were observed between HO-1 mRNA expression at 6 h after CLP and level of LPO or severity of hepatic/renal dysfunction at 18 h after CLP. These results suggest that early HO-1 mRNA expression in leukocytes may represent oxidative stress and may predict the severity of liver and renal dysfunction during sepsis.

The effectiveness of oral tin mesoporphyrin prophylaxis in reducing bilirubin production after an oral heme load in a transgenic mouse model

BACKGROUND

Neonatal jaundice is commonly encountered and rarely associated with morbidity and mortality. Nonetheless, infants with glucose-6-phosphate dehydrogenase deficiency often have hemolysis (a heme load) caused by an environmental oxidant trigger, thus increasing their risk for serious morbidity. The use of tin mesoporphyrin (SnMP) has been proposed for interdicting the development of severe hyperbilirubinemia in a variety of conditions.

OBJECTIVES

We studied the in vivo effects of prophylactic oral SnMP on heme oxygenase (HO) activity and bilirubin production, as indexed by the excretion rate of carbon monoxide (VeCO), following a subsequent oral heme load.

METHODS

Adult mice were exposed serially to heme and assessed for in vivo bilirubin production rates, HO-1 transcription and protein, and HO activity. The effect of prophylaxis with a single oral dose of SnMP prior to an oral heme load was assessed by measuring VeCOand tissue HO activities.

RESULTS

After serial heme exposures, VeCO, HO-1 transcription and protein, and liver and spleen HO activities increased incrementally. After pretreatment with oral SnMP, bilirubin production decreased in response to an oral heme load. Also, heme-mediated increases in liver, spleen, and intestine HO activities were significantly dampened.

CONCLUSIONS

A single oral dose of SnMP results in durable inhibition of bilirubin production and HO activity for at least 24 h in a mouse model of oral heme loading. Further studies are needed to fully elucidate the duration of this protection against hyperbilirubinemia due to a delayed heme load and any long-term consequences of prophylaxis with SnMP on HO-1 transcription and HO-1 protein.

Bile reflux in the constellation of gastroesophageal reflux disease

Gastric acid and bile acids are a particularly noxious combination when they interact with the mucosa of the upper intestinal tract. There is a critical pH range, between 3 and 6, in which bile acids exist in their soluble, un-ionized form, can penetrate cell membranes, and accumulate within mucosal cells. At a lower pH, bile acids are precipitated, and at a higher pH, bile acids exist in their noninjurious ionized form. Experimental, clinical, and immunohistochemical studies show that acid and bile reflux are increased in patients who suffer from GERD, are the key factor in the pathogenesis of Barrett's esophagus, and possibly are related to the development of esophageal adenocarcinoma.

Bilirubin production and oxidation in CSF of patients with cerebral vasospasm after subarachnoid hemorrhage

Delayed cerebral vasospasm after subarachnoid hemorrhage (SAH) remains a significant cause of mortality and morbidity; however, the etiology is, as yet, unknown, despite intensive research efforts. Research in this laboratory indicates that bilirubin and oxidative stress may be responsible by leading to formation of bilirubin oxidation products (BOXes), so we investigated changes in bilirubin concentration and oxidative stress in vitro, and in cerebral spinal fluid (CSF) from SAH patients. Non-SAH CSF, a source of heme oxygenase I (HO-1), and blood were incubated, and in vitro bilirubin production measured. Cerebrospinal fluid from SAH patients was collected, categorized using stimulation of vascular smooth muscle metabolism in vitro, and information obtained regarding occurrence of vasospasm in the patients. Cerebral spinal fluid was analyzed for hemoglobin, total protein and bilirubin, BOXes, malonyldialdehyde and peroxidized lipids (indicators of an oxidizing environment), and HO-1 concentration. The formation of bilirubin in vitro requires that CSF is present, as well as whole, non-anti-coagulated blood. Bilirubin, BOXes, HO-1, and peroxidized lipid content were significantly higher in CSF from SAH patients with vasospasm, compared with nonvasospasm SAH CSF, and correlated with occurrence of vasospasm. We conclude that vasospasm may be more likely in patients with elevated BOXes. The conditions necessary for the formation of BOXes are indeed present in CSF from SAH patients with vasospasm, but not CSF from SAH patients without vasospasm.

Heme oxygenase and the cardiovascular-renal system

Heme oxygenase (HO) has been shown to be important for attenuating the overall production of reactive oxygen species (ROS) through its ability to degrade heme and to produce carbon monoxide (CO), biliverdin/bilirubin, and the release of free iron. Excess free heme catalyzes the formation of ROS, which may lead to endothelial cell (EC) dysfunction as seen in numerous pathological conditions including hypertension and diabetes, as well as ischemia/reperfusion injury. The upregulation of HO-1 can be achieved through the use of pharmaceutical agents, such as metalloporphyrins and some HMG-CoA reductase inhibitors. Among other agents, atrial natriretic peptide and donors of nitric oxide (NO) are important modulators of the heme-HO system, either through induction of HO-1 or the biological activity of its products. Gene therapy and gene transfer, including site- and organ-specific targeted gene transfer, have become powerful tools for studying the potential role of HO-1/HO-2 in the treatment of various cardiovascular diseases as well as diabetes. HO-1 induction by pharmacological agents or gene transfer of human HO-1 into endothelial cells (ECs) in vitro increases cell-cycle progression and attenuates Ang II, TNF-, and heme-mediated DNA damage; administration in vivo acts to correct blood pressure elevation following Ang II exposure. Moreover, site-specific delivery of HO-1 to renal structures in spontaneously hypertensive rats (SHR), specifically to the medullary thick ascending limb of the loop of Henle (mTALH), has been shown to normalize blood pressure and provide protection to the mTAL against oxidative injury. In other cardiovascular situations, delivery of human HO-1 to hyperglycemic rats significantly lowers superoxide (O(2)(-)) levels and prevents EC damage and sloughing of vascular EC into the circulation. In addition, administration of human HO-1 to rats in advance of ischemia/reperfusion injury considerably reduces tissue damage. The ability to upregulate HO-1 through pharmacological means or through the use of gene therapy may offer therapeutic strategies for cardiovascular disease in the future. This review discusses the implications of HO-1 delivery during the early stages of cardiovascular system injury or in early vascular pathology and suggests that pharmacological agents that regulate HO activity or HO-1 gene delivery itself may become powerful tools for preventing the onset or progression of certain cardiovascular pathologies.

Heme oxygenase-1 activity after excitotoxic injury: immunohistochemical localization of bilirubin in neurons and astrocytes and deleterious effects of heme oxygenase inhibition on neuronal survival after kainate treatment

An increased expression of the inducible form of heme oxygenase (HO), HO-1, is found in the hippocampus after kainate injection, but thus far it is unclear whether the HO-1 is enzymatically active. The present study was carried out, using monoclonal antibodies to bilirubin and HO-1 and histochemical staining for iron, to compare the products of HO enzymatic activity, bilirubin and iron, with HO-1 expression in the kainate-lesioned hippocampus. There was a close correlation between bilirubin and HO-1 expression, and both bilirubin and HO-1 were observed in damaged neurons at early times, and astrocytes at later times (weeks), after kainate injection. These results indicate that the increased HO-1 in the hippocampus is enzymatically active. Too determine whether HO-1 activity after kainate could have a protective or, perhaps, destructive effect, kainate-injected rats were injected intraperitoneally with a blood-brain barrier-permeable inhibitor of HO, tin protoporphyrin (SnPP), and the effects of such treatment were compared with effects in rats that received kainate and saline injection. It was found that SnPP treatment did not improve neuronal survival. Instead, increased mortality was observed in rats treated with SnPP. Four SnPP-injected rats vs. one saline-injected rats died after kainate treatment. The surviving SnPP-treated rats showed significantly less hippocampal field that containing Nissl or MAP2 staining (an indicator of surviving neurons) compared with the saline-injected rats. These results indicate that HO-1 induction had a net protective effect on neurons in the kainate model of excitotoxic injury.

Recent advances in the pharmacotherapy for hyperbilirubinaemia in the neonate

Jaundice is a common cause for diagnostic works-up and therapeutic intervention in neonates. This is motivated by the risk for severe neurological sequelae (kernicterus). The mainstays of treatment for the past decades have been exchange transfusion and phototherapy. Exchange transfusion is now becoming rare due to immune prophylaxis in Rhesus-negative women, and treatment of sensitised infants with intravenous immunoglobulin. Several different pharmacological approaches have been studied as far as the treatment of neonatal jaundice. Of these, the focus of attention in recent years has been on the haem oxygenase inhibitors (metal meso- and protoporphyrins). These are effective inhibitors of bilirubin production and have been shown to significantly reduce peak serum bilirubin levels in several clinical trials, both when used prophylactically and therapeutically. However, questions remain regarding long-term safety, as well as the advisability of whole-scale inhibition of bilirubin production. Nevertheless, in selected infants with a high risk of severe jaundice, the use of haem oxygenase inhibitors may be acceptable. Pharmacotherapy in jaundiced infants is fraught with risks, as many drugs may increase the entry of bilirubin into the brain and presumably, the risk for neurotoxicity. Both the displacement of bilirubin from its albumin binding and interference with the function of phosphoglycoprotein in the blood-brain barrier are documented mechanisms in this respect.

Neonatal bilirubin production-conjugation imbalance: effect of glucose-6-phosphate dehydrogenase deficiency and borderline prematurity

OBJECTIVE

To evaluate relations between production and conjugation of bilirubin in the pathophysiology of jaundice in glucose-6-phosophate dehydrogenase (G6PD) deficient neonates.

METHODS

Term and borderline premature (35-37 weeks gestational age), healthy, male, G6PD deficient neonates were studied close to the beginning of the 3rd day. Blood carboxyhaemogobin corrected for inspired CO (COHbc; an index of bilirubin production) and serum total conjugated bilirubin (TCB; a reflection of bilirubin conjugation) were measured in simultaneously drawn blood samples by gas chromatography and reverse phase high performance liquid chromatography respectively. A bilirubin production-conjugation index comprising COHbc/TCB was determined; a high index reflects imbalance between the bilirubin production and conjugation processes. COHbc and TCB individually and the production-conjugation index were studied in relation to serum total bilirubin (STB) concentration.

RESULTS

Fifty one G6PD deficient neonates were sampled at 51 (8) hours. COHbc values did not correlate with STB (r=0.22, p=0.15). TCB did correlate inversely with STB (r=-0.42, p=0.004), and there was a positive correlation between the production-conjugation index and STB (r=0.45, p=0.002). The production-conjugation index (median (interquartile range)) was higher in the premature (n=8) than term neonates (2.31 (2.12-3.08) v 1.05 (0.53-1.81), p=0.003). This difference was the result of changes in TCB.

CONCLUSIONS

The data show that jaundice in G6PD deficient neonates is the result of an imbalance between production and conjugation of bilirubin with a tendency for inefficient bilirubin conjugation over increased haemolysis in its pathogenesis. Borderline premature infants are at special risk of bilirubin production-conjugation imbalance.

Heme oxygenase-1 messenger RNA expression is induced in peripheral blood mononuclear cells of pediatric cancer patients with systemic inflammatory response syndrome

OBJECTIVE

To determine whether heme oxygenase-1 messenger RNA expression in peripheral blood mononuclear cells is induced in pediatric cancer patients with the systemic inflammatory response syndrome (SIRS) and whether this expression correlates with the heme oxygenase-1 products, bilirubin and carboxyhemoglobin.

DESIGN

Prospective, controlled study.

SETTING

A tertiary care pediatric oncology hospital.

PATIENTS

Fourteen patients admitted to the intensive care unit with a diagnosis of SIRS by American College of Chest Physicians/Society for Critical Care Medicine consensus criteria and 17 control patients (off therapy, no acute illness).

INTERVENTIONS

Blood for bilirubin, carboxyhemoglobin, and heme oxygenase-1 messenger RNA expression was collected at study entry. SIRS patients continued to have samples collected every 12 hrs for 1 wk or until intensive care unit discharge. Heme oxygenase-1, bilirubin, and carboxyhemoglobin levels of SIRS patients were compared with controls, and correlation between heme oxygenase-1 and products was assessed.

MEASUREMENTS AND MAIN RESULTS

Within 48 hrs of study entry, maximum heme oxygenase-1 expression for all SIRS patients compared with controls was 5.5 +/- 1.0 vs. 1.1 +/- 0.1 (p < .0006). Maximum expression was > or =2.3-fold in 13 of 14 SIRS patients. Maximum heme oxygenase-1 expression also differed from minimum (5.5 +/- 1.0 vs. 1.6 +/- 0.3, p < .003). Maximum bilirubin and carboxyhemoglobin levels within 48 hrs of study entry differed between SIRS patients and controls (3.0 +/- 0.8 vs. 0.3 +/- 0.1, p = .006; and 1.2 +/- 0.2 vs. 0.6 +/- 0.1, p = .001, respectively). Bilirubin, but not carboxyhemoglobin, correlated with heme oxygenase-1 expression (p = .0013).

CONCLUSIONS

Heme oxygenase-1 messenger RNA, bilirubin, and carboxyhemoglobin levels were increased within 48 hrs of admission in pediatric cancer patients with SIRS. Heme oxygenase-1 expression correlated with serum bilirubin levels. The increase in heme oxygenase-1 expression may add to the understanding of the increase in serum bilirubin observed in patients with SIRS/sepsis. These findings support a role for heme oxygenase-1 in the physiologic response to inflammatory stress.

A major role for carbon monoxide as an endogenous hyperpolarizing factor in the gastrointestinal tract

Carbon monoxide (CO) is proposed as a physiological messenger. CO activates cGMP and has a direct effect on potassium channels. Both actions of CO lead to hyperpolarization of a cell's resting membrane potential, suggesting that CO may function as a hyperpolarizing factor, although direct evidence is still lacking. Here we take advantage of the known membrane potential gradient that exists in the muscle layers of the gastrointestinal tract to determine whether CO is an endogenous hyperpolarizing factor. We find that heme oxygenase-2-null mice have depolarized smooth muscle cells and that the membrane potential gradient in the gut is abolished. Exogenous CO hyperpolarizes the membrane potential. Regions of the canine gastrointestinal tract that are more hyperpolarized generate more CO and have higher heme oxygenase activity than more depolarized regions. Our results suggest that CO is a critical hyperpolarizing factor required for the maintenance of intestinal smooth muscle membrane potential and gradient.

New approach for the establishment of an hepatocyte cell line derived from rat early embryonic stem cells

A cell line with the characteristics of hepatocytes was established from rat early embryonic stem cells (REES). This cell line was established using a new novel method of Ishiwata et al. from two cell embryos taken from the spontaneous dwarf rat (SDR). The hepatocyte cell line (REES-hep) was instituted from dark red colored tissue in embryos during embryogenesis using REES cell line cultured in the presence of embryotrophic factors. These cell lines were cultured with DMEM/F12 medium supplemented 10% FBS and 1 ng/ml of LIF. They were found to maintain their diploid state, were characterized with 42 normal chromosomes and proliferated to confluence; contact inhibition was also present. These cells produced albumin when cultured using a collagen sponge gel system and reconstructed in a funicular form resembling the cell cords of liver. The cells also produced albumin and bilirubin when transplanted into the spleen of SDR Reconstruction of a REES-hep cell line from early embryonic stem cells should help in treating hepatic insufficient patients. It will be valuable for further research, as an introduction to cell transplantation and application for use in a bio-hybrid typed liver apparatus.

Biliverdin reductase: a major physiologic cytoprotectant

Bilirubin, an abundant pigment that causes jaundice, has long lacked any clear physiologic role. It arises from enzymatic reduction by biliverdin reductase of biliverdin, a product of heme oxygenase activity. Bilirubin is a potent antioxidant that we show can protect cells from a 10,000-fold excess of H2O2. We report that bilirubin is a major physiologic antioxidant cytoprotectant. Thus, cellular depletion of bilirubin by RNA interference markedly augments tissue levels of reactive oxygen species and causes apoptotic cell death. Depletion of glutathione, generally regarded as a physiologic antioxidant cytoprotectant, elicits lesser increases in reactive oxygen species and cell death. The potent physiologic antioxidant actions of bilirubin reflect an amplification cycle whereby bilirubin, acting as an antioxidant, is itself oxidized to biliverdin and then recycled by biliverdin reductase back to bilirubin. This redox cycle may constitute the principal physiologic function of bilirubin.

Imbalance between production and conjugation of bilirubin: a fundamental concept in the mechanism of neonatal jaundice

OBJECTIVE

The objective of this study was to evaluate the roles of production and conjugation of bilirubin, individually and in combination, in the mechanism of neonatal jaundice.

METHODS

A cohort of healthy, term male newborns was sampled on the third day of life, coincident with routine metabolic screening, for blood carboxyhemoglobin determination, a reflection of heme catabolism, and for serum unconjugated and conjugated bilirubin fractions, reflecting bilirubin conjugation. The former was determined by gas chromatography, corrected for inspired CO (COHbc), and expressed as percentage of total hemoglobin. Serum bilirubin fractions were quantified by alkaline methanolysis and reverse phase high performance liquid chromatography. The sum of all bilirubin fractions comprised serum total bilirubin (STB). Total conjugated bilirubin (TCB) was comprised of the sum of the conjugated fractions and was expressed as percentage of STB (TCB[%]). A "bilirubin production/conjugation index" (COHbc/[TCB(%)] represented the combined roles of these modalities in the mechanism of bilirubinemia. Relationships between STB concentrations on the one hand, and COHbc values, TCB(%) proportions, and the production/conjugation index on the other, were determined by applying a best-fit regression analysis methodology.

RESULTS

Mean (+/- standard deviation) STB concentration at the time of sampling was 114 +/- 48 micro mol/L (range: 8-263 micro mol/L). Mean COHbc value was 0.77 +/- 0.19%, and median (interquartile range) TCB(%) was 0.737 (0.465-1.260)%. COHbc values correlated directly with STB concentrations (r = 0.38; s = 46.1), and TCB(%) correlated inversely with STB (r = 0.40; s = 45.8). The production/conjugation index correlated positively with STB values (r = 0.61; s = 45.8), the r value for the index being higher than that of either COHbc or TCB(%), individually. The bilirubin production/conjugation index seemed to have a biphasic relationship to STB: STB values rose steeply in concert with increasing index values in the lower range of the index, and subsequently plateaued in the higher range of the index.

CONCLUSIONS

Within the range of STB concentrations encountered, both increasing bilirubin production and diminishing bilirubin conjugation contributed to STB. The production/conjugation index confirmed that imbalance between production and conjugation of bilirubin plays an important role in the mechanism of neonatal bilirubinemia. alkaline methanolysis, bilirubin, bilirubin conjugation, carbon monoxide, carboxyhemoglobin, gas chromatography, hemolysis, high performance liquid chromatography, physiologic jaundice.

The jaundiced newborn. Understanding and managing transitional hyperbilirubinemia

Neonatal jaundice is one of the most common conditions diagnosed by the pediatrician. This normally benign transitional phenomenon is a dynamic balance between the production and elimination of bilirubin. These processes can be exacerbated by a number of pathophysiologic conditions, which cause either an increase in bilirubin production rates, such as hemolysis, or a decrease in bilirubin elimination rates, such as bilirubin conjugation defects. The most dangerous circumstance for an infant is the combination of increased bilirubin production with impaired elimination. These infants are at considerable risk for developing excessive and potentially dangerous hyperbilirubinemia and subsequent kernicterus. Therefore, the importance of early recognition of the imbalance is paramount. In this review, we will discuss the various risk factors associated with hyperbilirubinemia and describe strategies for the diagnosis and management of transitional hyperbilirubinemia.

Haem degradation in animals and plants

Two enzyme systems have evolved for the reduction of linear tetrapyrroles: one family, found in plants, algae and cyanobacteria, uses ferredoxin and catalyses the reduction of the terminal pyrrole rings (A and D) and one of the vinyl side chains to form various light-harvesting and light-sensing chromophores. The other group (biliverdin reductases A and B) utilize NAD(P)H and catalyse reduction at C10 (hydride addition) to form the 'bile' pigments bilirubin-IX alpha and bilirubin-IX.

Isoimmunization is unlikely to be the cause of hemolysis in ABO-incompatible but direct antiglobulin test-negative neonates

OBJECTIVE

It is stated that the direct antiglobulin (Coombs') test (DAT) may be negative in ABO hemolytic disease of the newborn. Thus, significant jaundice in neonates who are A-B incompatible with their mothers but DAT test negative is often attributed to isoimmunization and another diagnosis is not sought. We wished to determine the rate of bilirubin production, as an objective measure of hemolysis, in 2 groups of DAT-negative neonates--ABO-compatible and ABO-incompatible--and in DAT-positive ABO-incompatible neonates.

METHODS

In consecutive, term, healthy newborns who were admitted to the general care nursery, we measured the level in parts per million (ppm) of end-tidal breath carbon monoxide (CO), corrected for inspired CO (ETCOc), an index of the rate of bilirubin production. We compared the levels in DAT-negative ABO-incompatible neonates with those in ABO-compatible neonates and with the levels in DAT-positive ABO-incompatible neonates. Statistical analysis was performed using 2-sample t and chi(2) tests.

RESULTS

There was no significant difference between the mean 12-hour ETCOc levels in DAT-negative ABO-incompatible neonates (n = 60, 2.2 +/- 0.6 ppm) versus DAT-negative ABO-compatible neonates (n = 171, 2.1 +/- 0.6 ppm), although there was a difference between the mean levels in DAT-positive ABO-incompatible neonates (n = 14, 3.4 +/- 1.8 ppm) and the DAT-negative groups. Four DAT-negative ABO-incompatible neonates had elevated ETCOc levels; in 2, we diagnosed a specific hematologic abnormality, namely, glucose-6-phosphate dehydrogenase deficiency in 1 and elliptocytosis in the other.

CONCLUSION

In DAT-negative newborns with significant jaundice or increased bilirubin production, even if ABO-incompatible, a cause other than isoimmunization should be sought.

Modification of hepatic genomic DNA using RNA/DNA oligonucleotides

The ideal gene therapy is one that repairs the precise genetic defect without additional modification of the genome. Such a strategy has been developed for correcting single nucleotide mutations by using RNA/DNA oligonucleotides, or chimeraplasts. This approach for in situ repair is based on the delivery of exogenous DNA designed to mediate genomic base conversion, insertion, or deletion, thereby, correcting the genetic mutation. Using in vivo delivery systems to hepatocytes via the asialoglycoprotein receptor, we targeted rat liver DNA and successfully modified the genomic sequence by chimeraplasty. The changes in both the hepatic genes, and their associated phenotypes remained stable for 2 years. In addition, we also examined the potential to alter sequence defects in mitochondrial DNA. Therefore, we determined whether mitochondria possess the enzymatic machinery for chimeraplast-mediated DNA changes. Using an in vitro DNA repair assay of mutagenized plasmids and an Escherichia coli readout system, we showed that extracts from highly purified rat liver mitochondria have the essential enzymatic activity to mediate precise single-nucleotide changes at a frequency similar to liver nuclear extracts. Moreover, single-stranded oligonucleotides carrying a single nucleotide mismatch with the target sequence were capable of promoting gene conversion using either mitochondrial or nuclear extracts. Several approaches now exist for the precise repair of genetic mutations using either single-stranded or RNA/DNA chimeric oligonucleotides.

Heme oxygenase-1 induction may explain the antioxidant profile of pentaerythrityl trinitrate

The organic nitrate pentaerythrityl tetranitrate (PETN) is known to exert long-term antioxidant and antiatherogenic effects by as yet unidentified mechanisms. In cultured endothelial cells derived from human umbilical vein, the active PETN metabolite PETriN (0.01-1 mM) increased heme oxygenase (HO)-1 mRNA and protein levels in a concentration-dependent fashion. HO-1 induction was accompanied by a marked increase in catalytic activity of the enzyme as reflected by enhanced formation of carbon monoxide and bilirubin. Pretreatment with PETriN or bilirubin at low micromolar concentrations protected endothelial cells from hydrogen peroxide-mediated toxicity. HO-1 induction and endothelial protection by PETriN were not mimicked by isosorbide dinitrate, another long-acting nitrate. The present study demonstrates that PETriN stimulates mRNA and protein expression as well as enzymatic activity of the antioxidant defense protein HO-1 in endothelial cells. Increased HO-1 expression and ensuing formation of cytoprotective bilirubin may contribute to and explain the specific antioxidant and antiatherogenic actions of PETN.

Atrial natriuretic peptide reduces cyclosporin toxicity in renal cells: role of cGMP and heme oxygenase-1

Using cultured proximal renal tubular epithelial cells (LLC-PK1), the present study investigates the effect of atrial natriuretic peptide (ANP) on cytotoxicity induced by cyclosporin A (CsA). Preincubation with ANP (1-100 nM) protected LLC-PK1 cells from CsA-induced toxicity in a concentration-dependent manner. A cytoprotective effect comparable to ANP was observed when preincubating the cells with 8-bromo cGMP (1-100 microM) or the antioxidant heme oxygenase (HO) metabolite bilirubin (0.1-10 microM). ANP or cGMP produced increases in HO-1 protein levels at concentrations that were also effective in cellular protection. Moreover, incubation with ANP or 8-bromo cGMP led to increased HO activity, i.e., formation of bilirubin in the cell lysate (up to 3-fold over basal). Tin protoporphyrin-IX (SnPP; 19 microM), an inhibitor of HO activity, completely abolished ANP-induced cytoprotection. Our results demonstrate that HO-1 is a cellular target of ANP and cGMP in renal cells. HO-1 induction and ensuing formation of antioxidant metabolites may be a novel pathway by which ANP protects from CsA-dependent nephrotoxicity and preserves renal function.

The biology of bilirubin production

Heme oxygenase (HO), the rate-limiting enzyme in bilirubin production, has been identified from the late 1960s. This enzyme has been shown to have many other roles in recent years. The inducible form is regulated by oxidative stress, inflammation, and heavy metals, among others, and is cytoprotective in many instance. Nonetheless, there are instances when HO-1 can be deleterious due to the release of iron from the reaction. Another important by-product, carbon monoxide, is a vasodilator and a neurotransmitter and has been implicated in signal transduction pathways. More recently, nonenzymatic, signaling roles of HO have been suggested. This may serve to regulate the endogenous activity of this enzyme when cellular heme levels are low.

Pitfalls in preparation of (3)H-unconjugated bilirubin by biosynthetic labeling from precursor (3)H-5-aminolevulinic acid in the dog

We report problems encountered during preparation of tritium-labeled unconjugated bilirubin ((3)H-UCB) from precursor (3)H-5-aminolevulinic acid ((3)H-ALA) in 2 dogs with external biliary drainage installed into the animals under general anesthesia. Under prolonged sedation, 12.9 or 14.0 mCi of (3)H-ALA was administered intravenously in two divided doses, and bile was collected for 9 hours. In one animal, taurocholate (TC) infusion was needed to maintain bile flow. (3)H-UCB was isolated from the bile and recrystallized with the improved method of Webster et al (Webster CC, Tiribelli C, Ostrow JD. J Lab Clin Med 2001;137:370-3). Based on radioactivity and pigment content, hourly bile collections were pooled to optimize specific activities. Surprisingly, in the first dog, only 2.9% of injected radioactivity was recovered in bile and only 14.1% in urine, and the specific activities of the crystalline (3)H-UCB from the two pools were only 39.5 and 30.0 x 10(3) dpm/microg. High-performance liquid chromatography analysis revealed that only 4% of ALA degraded during 5 minutes in injection solution at pH 6.8. The low incorporation of (3)H-ALA and low specific activity of (3)H-UCB was apparently caused mainly by prior degradation and exchange of labile tritium of the (3)H-ALA and probably by enhanced endogenous ALA synthesis caused by the anesthetic/sedative agents. Revised procedures in the second dog improved the incorporation of (3)H-ALA to 11.9% excreted in bile and the specific activity of the crystalline (3)H-UCB to 122.0 and 50.8 x 10(3) dpm/microg, while urinary excretion of tritium increased to 28.5%. These experiences emphasize possible pitfalls in preparing (3)H-UCB by biosynthetic labeling from (3)H-ALA administered to dogs.

Role of heme oxygenase-1 in hypoxia-reoxygenation: requirement of substrate heme to promote cardioprotection

Heme oxygenase-1 (HO-1) catalyzes the enzymatic degradation of heme to carbon monoxide, bilirubin, and iron. All three products possess biological functions; bilirubin, in particular, is a potent free radical scavenger of which its antioxidant property is enhanced at low oxygen tension. Here, we investigated the effect of severe hypoxia and reoxygenation on HO-1 expression in cardiomyocytes and determined whether HO-1 and its product, bilirubin, have a protective role against reoxygenation damage. Hypoxia caused a time-dependent increase in both HO-1 expression and heme oxygenase activity, which gradually declined during reoxygenation. Reoxygenation of hypoxic cardiomyocytes produced marked injury; however, incubation with hemin or bilirubin during hypoxia considerably reduced the damage at reoxygenation. The protective effect of hemin is attributable to increased availability of substrate for heme oxygenase activity, because hypoxic cardiomyocytes generated very little bilirubin when incubated with medium alone but produced substantial bile pigment in the presence of hemin. Interestingly, incubation with hemin also maintained high heme oxygenase activity levels during the reoxygenation period. Reactive oxygen species generation was enhanced after hypoxia, and hemin and bilirubin were capable once again to attenuate this effect. These results indicate that the HO-1-bilirubin pathway can effectively defend hypoxic cardiomyocytes against reoxygenation injury and highlight the issue of heme availability in the cytoprotective action afforded by HO-1.

Increased expression of heme oxygenase-1 and bilirubin accumulation in foam cells of rabbit atherosclerotic lesions

Heme oxygenase-1 (HO-1) catalyzes the regiospecific oxidative degradation of heme to biliverdin IXalpha, iron, and carbon monoxide. Biliverdin IXalpha is subsequently reduced to bilirubin IXalpha by biliverdin reductase. HO-1 expression is induced under various disease conditions, including atherosclerosis, but it is unknown whether HO-1 catalyzes heme breakdown in the regions at risk. Using hypercholesterolemic rabbits fed a cholesterol-enriched diet, we attempted to demonstrate the involvement of HO-1 induction and bilirubin IXalpha production in atherosclerotic regions. Expression levels of HO-1 mRNA were elevated in the aortas of hypercholesterolemic rabbits. In situ hybridization and immunohistochemistry revealed that mRNA and protein of HO-1 are induced in endothelial cells and foam cells (lipid-filled macrophages) in atherosclerotic lesions. Furthermore, immunohistochemistry with the use of an anti-bilirubin-IXalpha monoclonal antibody, 24G7, demonstrated accumulation of bilirubin IXalpha in foam cells, indicating that heme is actually degraded in atherosclerotic lesions. Remarkably, bilirubin IXalpha, like HO-1 protein, is predominantly accumulated in the perinuclear regions of foam cells. These results provide the first in vivo evidence of the colocalization of HO-1 and bilirubin IXalpha in foam cells, suggesting a role of HO-1 induction in the modulation of macrophage activation in atherosclerosis.

Cyclobilirubin formation by in vitro photoirradiation with neonatal phototherapy light

BACKGROUND

The main mechanism of phototherapy for neonatal hyperbilirubinemia is the production and excretion of (EZ)- and (EE)-cyclobilirubin (4E,15Z- and 4E,15E-cyclobilirubin). Thus, the clinical efficacy of the light source for phototherapy must be evaluated by cyclobilirubin formation from (ZZ)-bilirubin in in vitro photoirradiation.

METHODS

In the present study, we investigated the in vitro production pattern of bilirubin photoisomers by phototherapy light from the bilirubin-human serum albumin complex.

RESULTS

No clear difference was found in the curves relative to (ZZ)-bilirubin and its photoisomers under aerobic and anaerobic conditions. The ratio of (EZ)-cyclobilirubin to (ZZ)-bilirubin increased proportionately to the dose of irradiating light and no photoequilibrium state was observed analogous to that found in configurational photoisomerization. The concentration of (EZ)- and (EE)-cyclobilirubin increased proportionately with the grade of the percentage decrease in A(460 nm) from 0 to 23%. With a percentage decrease in A(460 nm) of 23% or more, the cyclobilirubin concentrations reached a steady state. The reason for this appears to be that the concentration of (ZZ)-bilirubin, a substrate for photoisomers, dropped below 1 mg/100 mL. Biliverdin was produced only in trace amounts. However, the absorption at 520--700 nm increased after a percentage decrease in A(460 nm) of more than 23%.

CONCLUSIONS

The results of the present study show that little bilirubin photooxidation occurred with in vitro aerobic photoirradiation. Before the concentration of cyclobilirubin reaches a steady state, it is theoretically valid to use the percentage decrease in A(460 nm) for the evaluation of the clinical efficacy of the light source.

Role of heme oxygenase-1 and Kupffer cells in the production of bilirubin in the rat liver

Heme oxygenase (HO)-1, the heme-degrading enzyme in macrophages, plays a key role in bilirubin metabolism. HO-1 is expressed in various tissue macrophages, especially Kupffer cells. This study aimed to examine the roles of macrophages and HO-1 in the modulation of heme catabolism in rat livers. Rats treated with or without liposome-encapsulated dichloromethylene diphosphonate, a macrophage-depleting reagent, were administered with heat-denatured red blood cells (h-RBC), and the time course of the biliary output of bilirubin and the expressions of HO-1 mRNA and protein were monitored. Immunohistochemistry in the control rat liver revealed that Kupffer cells constitute a major cellular component expressing HO-1, while hepatocytes exhibited little expression. The levels of HO-1 expression in Kupffer cells were elevated immediately after injection of h-RBC. In Kupffer cell-depleted livers, however, HO-1-expressing cells were not detected even after h-RBC administration. HO-1 mRNA levels were elevated at 2 h after administration of h-RBC in control rat livers, while they were very low in Kupffer cell-depleted rat livers. The control and Kupffer cell-depleted groups exhibited distinct time courses of biliary bilirubin excretion. In the untreated control rats, total bilirubin excretion increased about two-fold at 5 h after h-RBC administration. In contrast, the Kupffer cell-depleting treatment decreased the level of bilirubin production; administration of h-RBC to Kupffer cell-depleted rats did not accelerate the generation of bilirubin. These results suggest that Kupffer cells serve both as a sensor for scenesent RBC clearance and an effector that upregulates heme-degrading capacity and bilirubin production.

Carbon monoxide and bilirubin production in neonates

Neonatal hyperbilirubinemia is a normal postnatal phenomenon resulting from a transitional imbalance between the production and elimination of bilirubin in the neonate. Bilirubin has been shown to be not only a potent antioxidant, but also toxic at excessive concentrations. As a result, the biology of bilirubin, its production, regulation, and measurements have been the focus of extensive studies. Bilirubin, carbon monoxide, and iron are derived from the degradation of heme, a ubiquitous two-step pathway catalyzed by the enzyme, heme oxygenase. It has been shown that these metabolically active products from the heme catabolic pathway may, in turn, influence many other biologic processes. This report provides a brief overview of these interrelationships in the hope that it may provide insight into the central role this pathway plays in the existence of most organisms.

Hepatic uptake of bilirubin and its conjugates by the human organic anion transporter SLC21A6

Bilirubin, the end product of heme catabolism, is taken up from the blood circulation into the liver. This work identifies a high-affinity transport protein mediating the uptake of bilirubin and its conjugates into human hepatocytes. Human embryonic kidney cells (HEK293) permanently expressing the recombinant organic anion-transporting polypeptide 2 (human OATP2, also known as LST-1 or OATP-C; symbol SLC21A6) showed uptake of [(3)H]monoglucuronosyl bilirubin, [(3)H]bisglucuronosyl bilirubin, and [(3)H]sulfobromophthalein with K(m) values of 0.10, 0.28, and 0.14 microm, respectively. High-affinity uptake of unconjugated [(3)H]bilirubin by OATP2 occurred in the presence of albumin and was not mediated by another basolateral hepatic uptake transporter, human OATP8 (symbol SLC21A8). OATP2 and OATP8 differed by their capacity to extract substrates from albumin before transport. In comparison to the high-affinity transport by OATP2, OATP8 transported [(3)H]sulfobromophthalein and [(3)H]monoglucuronosyl bilirubin with lower affinity, with K(m) values of 3.3 and 0.5 microm, respectively. The organic anion indocyanine green potently inhibited transport mediated by OATP2, with a K(i) value of 112 nm, but did not inhibit transport mediated by OATP8. Human OATP2 may play a key role in the prevention of hyperbilirubinemia by facilitating the selective entry of unconjugated bilirubin and its glucuronate conjugates into human hepatocytes.

Structure of human biliverdin IXbeta reductase, an early fetal bilirubin IXbeta producing enzyme

Biliverdin IXbeta reductase (BVR-B) catalyzes the pyridine nucleotide-dependent production of bilirubin-IXbeta, the major heme catabolite during early fetal development. BVR-B displays a preference for biliverdin isomers without propionates straddling the C10 position, in contrast to biliverdin IXalpha reductase (BVR-A), the major form of BVR in adult human liver. In addition to its tetrapyrrole clearance role in the fetus, BVR-B has flavin and ferric reductase activities in the adult. We have solved the structure of human BVR-B in complex with NADP+ at 1.15 A resolution. Human BVR-B is a monomer displaying an alpha/beta dinucleotide binding fold. The structures of ternary complexes with mesobiliverdin IValpha, biliverdin IXalpha, FMN and lumichrome show that human BVR-B has a single substrate binding site, to which substrates and inhibitors bind primarily through hydrophobic interactions, explaining its broad specificity. The reducible atom of both biliverdin and flavin substrates lies above the reactive C4 of the cofactor, an appropriate position for direct hydride transfer. BVR-B discriminates against the biliverdin IXalpha isomer through steric hindrance at the bilatriene side chain binding pockets. The structure also explains the enzyme's preference for NADP(H) and its B-face stereospecificity.

Administration of bacterial lipopolysaccharide to rats induces heme oxygenase-1 and formation of antioxidant bilirubin in the intestinal mucosa

Heme oxygenase (HO)-1, the rate-limiting enzyme in heme degradation, is induced by oxidative stress and its major end product, bilirubin, is a potent physiological antioxidant. We studied the induction of HO-1 and bilirubin production in intestinal mucosa using a rat model of sepsis. E. coli lipopolysaccharide was administered intraperitonealy to male Wistar rats and intestinal mucosa was harvested. Intestinal lipid peroxides increased significantly at 1 hr and peaked at 170% of the control value at 5 hr. GSH significantly decreased at 3 hr, reaching the nadir of 50% of the control value at 5 hr. HO-1 mRNA was maximally induced fivefold at 3 hr and HO-1 protein maximally increased to 10 times the control value at 7.5 hr. Both bilirubin and bilirubin oxidative metabolites were maximally increased at 10 hr, to 4.3 and 3.7 times the control value, respectively. These data suggest that oxidative stress in sepsis quickly induces HO-1 in intestinal mucosa and that subsequent production of bilirubin works as an antioxidant. The small intestinal mucosa is an active participant in the general response to sepsis.

Ontogenic profile of some antioxidants and lipid peroxidation in human placental and fetal tissues

Reactive oxygen species (ROS) pose a serious threat to maternal and fetal health during pregnancy. However, there is little information on the oxidative damage caused by ROS and its protection during prenatal life. The present study highlights the status of various antioxidants in human placental and fetal tissues at different phases of gestation. The activity profile of scavenging enzymes, superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase as well as the concentrations of non-enzymatic antioxidants, ascorbic acid, alpha-tocopherol, bilirubin and glutathione have been determined in human placental whole homogenate, placental brush border membrane and fetal liver over gestational periods ranging from 6 weeks of pregnancy till birth. The ontogenic profile of lipid peroxidation, a marker of oxidative damage has also been investigated in the feto-placental system. Catalase, superoxide dismutase and glutathione reductase activities increased significantly, but glutathione peroxidase activity remained almost the same throughout development. Except alpha-tocopherol and bilirubin, the concentrations of other non-enzymic scavengers followed a significant increasing trend with advancement of pregnancy. Results indicate that there is gradual suppression of lipoperoxide formation with the progress of gestation to protect the fetus against oxygen toxicity.

Association of serum bilirubin concentration with risk of coronary artery disease

BACKGROUND

Lipid oxidation and formation of oxygen radicals are important elements of arterial plaque formation and atherosclerosis, and are involved in the pathophysiology of coronary artery disease (CAD). Because bilirubin has antioxidant properties, it has been suggested that it may have a protective role in the atherosclerotic process.

APPROACH

This review examines in vitro and in vivo studies indicating that bilirubin inhibits lipid oxidation and oxygen radical formation. Experimental and epidemiological evidence is presented that suggests that bilirubin may serve as a physiological antioxidant providing protection against atherosclerosis and CAD. Special attention is focused on studies that noted an inverse relationship between plasma bilirubin concentration and cardiovascular morbidity.

CONTENT

Serum bilirubin concentrations in the upper portion of the reference interval reportedly reduce atherogenic risk and provide protection against CAD. In contrast, serum bilirubin concentrations in the lower portion of the reference interval may be associated with increased risk of ischemic heart disease.

SUMMARY

Taken together, the evidence presented in this review supports the concept that bilirubin, via its antioxidant potential, has antiatherogenic properties and that an inverse relationship exists between circulating bilirubin concentrations and risk of CAD.

Dynamics of haem oxygenase-1 expression and bilirubin production in cellular protection against oxidative stress

The inducible isoform of haem oxygenase (HO-1) has been proposed as an effective system to counteract oxidant-induced cell injury. In several circumstances, this cytoprotective effect has been attributed to increased generation of the antioxidant bilirubin during haem degradation by HO-1. However, a direct implication for HO-1-derived bilirubin in protection against oxidative stress remains to be established. In the present study, we examined the dynamics of HO-1 expression and bilirubin production after stimulation of vascular smooth-muscle cells with hemin, a potent inducer of the HO-1 gene. We found that hemin-mediated increase in HO-1 protein expression and haem oxygenase activity is associated with augmented bilirubin levels. The majority of bilirubin production occurred early after exposure of cells to hemin. Hemin pre-treatment also resulted in high resistance to cell injury caused by an oxidant-generating system. Interestingly, this protective effect was manifest only when cells were actively producing bilirubin as a consequence of increased haem availability and utilization by HO-1. Tin protoporphyrin IX, an inhibitor of haem oxygenase activity, significantly reduced bilirubin generation and reversed cellular protection afforded by hemin treatment. Furthermore, addition of bilirubin to the culture medium markedly reduced the cytotoxicity produced by oxidants. Our findings provide direct evidence that bilirubin generated after up-regulation of the HO-1 pathway is cytoprotective against oxidative stress.

Heme oxygenase-1-derived bilirubin ameliorates postischemic myocardial dysfunction

Bilirubin is a potent antioxidant generated intracellularly during the degradation of heme by the enzyme heme oxygenase. The purpose of this study was to determine the role of increased cardiac bilirubin in protection against postischemic myocardial dysfunction. Rat hearts were isolated and perfused according to the Langendorff technique to evaluate the recovery of myocardial function after 30 min of global ischemia and 60 min of reperfusion. We found that upregulation of the inducible isoform of heme oxygenase (HO-1) by treatment of animals with hemin 24 h before ischemia ameliorated myocardial function and reduced infarct size (tetrazolium staining) on reperfusion of isolated hearts. Tin protoporphyrin IX, an inhibitor of heme oxygenase activity, completely abolished the improved postischemic myocardial performance observed after hemin-mediated HO-1 induction. Likewise, cardiac tissue injury was exacerbated by treatment with tin protoporphyrin IX. Increased cardiac HO-1 expression and heme oxygenase activity were associated with enhanced tissue bilirubin content and an increased rate of bilirubin release into the perfusion buffer. Furthermore, exogenously administered bilirubin at concentrations as low as 100 nanomolar significantly restored myocardial function and minimized both infarct size and mitochondrial damage on reperfusion. Our data provide strong evidence for a primary role of HO-1-derived bilirubin in cardioprotection against reperfusion injury.