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Models of bilirubin neurological damage: lessons learned and new challenges. Pediatr Res 2022:10.1038/s41390-022-02351-x. [PMID: 36302856 DOI: 10.1038/s41390-022-02351-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Revised: 09/26/2022] [Accepted: 10/03/2022] [Indexed: 11/09/2022]
Abstract
OBJECTIVE Jaundice (icterus) is the visible manifestation of the accumulation of bilirubin in the tissue and is indicative of potential toxicity to the brain. Since its very first description more than 2000 years ago, many efforts have been undertaken to understand the molecular determinants of bilirubin toxicity to neuronal cells to reduce the risk of neurological sequelae through the use of available chemicals and in vitro, ex vivo, in vivo, and clinical models. Although several studies have been performed, important questions remain unanswered, such as the reasons for regional sensitivity and the interplay with brain development. The number of new molecular effects identified has increased further, which has added even more complexity to the understanding of the condition. As new research challenges emerged, so does the need to establish solid models of prematurity. METHODS This review critically summarizes the key mechanisms of severe neonatal hyperbilirubinemia and the use of the available models and technologies for translational research. IMPACT We critically review the conceptual dogmas and models used for studying bilirubin-induced neurotoxicity. We point out the pitfalls and translational gaps, and suggest new clinical research challenges. We hope to inform researchers on the pro and cons of the models used, and to help direct their experimental focus in a most translational research.
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Bianco A, Dvořák A, Capková N, Gironde C, Tiribelli C, Furger C, Vitek L, Bellarosa C. The Extent of Intracellular Accumulation of Bilirubin Determines Its Anti- or Pro-Oxidant Effect. Int J Mol Sci 2020; 21:ijms21218101. [PMID: 33143041 PMCID: PMC7663266 DOI: 10.3390/ijms21218101] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Revised: 10/26/2020] [Accepted: 10/28/2020] [Indexed: 12/14/2022] Open
Abstract
Background: Severe hyperbilirubinemia can cause permanent neurological damage in particular in neonates, whereas mildly elevated serum bilirubin protects from various oxidative stress-mediated diseases. The present work aimed to establish the intracellular unconjugated bilirubin concentrations (iUCB) thresholds differentiating between anti- and pro-oxidant effects. Methods: Hepatic (HepG2), heart endothelial (H5V), kidney tubular (HK2) and neuronal (SH-SY5Y) cell lines were exposed to increasing concentration of bilirubin. iUCB, cytotoxicity, intracellular reactive oxygen species (ROS) concentrations, and antioxidant capacity (50% efficacy concentration (EC50)) were determined. Results: Exposure of SH-SY5Y to UCB concentration > 3.6 µM (iUCB of 25 ng/mg) and >15 µM in H5V and HK2 cells (iUCB of 40 ng/mg) increased intracellular ROS production (p < 0.05). EC50 of the antioxidant activity was 21 µM (iUCB between 5.4 and 21 ng/mg) in HepG2 cells, 0.68 µM (iUCB between 3.3 and 7.5 ng/mg) in SH-SY5Y cells, 2.4 µM (iUCB between 3 and 6.7 ng/mg) in HK2 cells, and 4 µM (iUCB between 4.7 and 7.5 ng/mg) in H5V cells. Conclusions: In all the cell lines studied, iUCB of around 7 ng/mg protein had antioxidant activities, while iUCB > 25 ng/mg protein resulted in a prooxidant and cytotoxic effects. UCB metabolism was found to be cell-specific resulting in different iUCB.
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Affiliation(s)
- Annalisa Bianco
- Italian Liver Foundation (FIF), Bldg Q—AREA Science Park Basovizza, SS14 Km 163,5, 34149 Trieste, Italy; (A.B.); (C.T.)
- Department of Life Sciences, University of Trieste, 34127 Trieste, Italy
| | - Aleš Dvořák
- Institute of Medical Biochemistry and Laboratory Diagnostics, Faculty General Hospital and 1st Faculty of Medicine, Charles University, 121 08 Prague 2, Czech Republic; (A.D.); (N.C.); (L.V.)
| | - Nikola Capková
- Institute of Medical Biochemistry and Laboratory Diagnostics, Faculty General Hospital and 1st Faculty of Medicine, Charles University, 121 08 Prague 2, Czech Republic; (A.D.); (N.C.); (L.V.)
| | - Camille Gironde
- AOP/MH2F Team, LAAS-CNRS, 7 avenue de l’Europe, 31400 Toulouse, France; (C.G.); (C.F.)
| | - Claudio Tiribelli
- Italian Liver Foundation (FIF), Bldg Q—AREA Science Park Basovizza, SS14 Km 163,5, 34149 Trieste, Italy; (A.B.); (C.T.)
| | - Christophe Furger
- AOP/MH2F Team, LAAS-CNRS, 7 avenue de l’Europe, 31400 Toulouse, France; (C.G.); (C.F.)
| | - Libor Vitek
- Institute of Medical Biochemistry and Laboratory Diagnostics, Faculty General Hospital and 1st Faculty of Medicine, Charles University, 121 08 Prague 2, Czech Republic; (A.D.); (N.C.); (L.V.)
- 4 Department of Internal Medicine, Faculty General Hospital and 1 Faculty of Medicine, Charles University, 121 08 Prague 2, Czech Republic
| | - Cristina Bellarosa
- Italian Liver Foundation (FIF), Bldg Q—AREA Science Park Basovizza, SS14 Km 163,5, 34149 Trieste, Italy; (A.B.); (C.T.)
- Correspondence:
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Hansen TWR, Wong RJ, Stevenson DK. Molecular Physiology and Pathophysiology of Bilirubin Handling by the Blood, Liver, Intestine, and Brain in the Newborn. Physiol Rev 2020; 100:1291-1346. [PMID: 32401177 DOI: 10.1152/physrev.00004.2019] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Bilirubin is the end product of heme catabolism formed during a process that involves oxidation-reduction reactions and conserves iron body stores. Unconjugated hyperbilirubinemia is common in newborn infants, but rare later in life. The basic physiology of bilirubin metabolism, such as production, transport, and excretion, has been well described. However, in the neonate, numerous variables related to nutrition, ethnicity, and genetic variants at several metabolic steps may be superimposed on the normal physiological hyperbilirubinemia that occurs in the first week of life and results in bilirubin levels that may be toxic to the brain. Bilirubin exists in several isomeric forms that differ in their polarities and is considered a physiologically important antioxidant. Here we review the chemistry of the bilirubin molecule and its metabolism in the body with a particular focus on the processes that impact the newborn infant, and how differences relative to older children and adults contribute to the risk of developing both acute and long-term neurological sequelae in the newborn infant. The final section deals with the interplay between the brain and bilirubin and its entry, clearance, and accumulation. We conclude with a discussion of the current state of knowledge regarding the mechanism(s) of bilirubin neurotoxicity.
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Affiliation(s)
- Thor W R Hansen
- Division of Paediatric and Adolescent Medicine, Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway; and Department of Pediatrics, Stanford University School of Medicine, Stanford, California
| | - Ronald J Wong
- Division of Paediatric and Adolescent Medicine, Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway; and Department of Pediatrics, Stanford University School of Medicine, Stanford, California
| | - David K Stevenson
- Division of Paediatric and Adolescent Medicine, Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway; and Department of Pediatrics, Stanford University School of Medicine, Stanford, California
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Dennery PA. Evaluating the beneficial and detrimental effects of bile pigments in early and later life. Front Pharmacol 2012; 3:115. [PMID: 22737125 PMCID: PMC3381237 DOI: 10.3389/fphar.2012.00115] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 05/29/2012] [Indexed: 12/28/2022] Open
Abstract
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.
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Affiliation(s)
- Phyllis A Dennery
- Division of Neonatology, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine Philadelphia, PA, USA
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Calligaris SD, Bellarosa C, Giraudi P, Wennberg RP, Ostrow JD, Tiribelli C. Cytotoxicity is predicted by unbound and not total bilirubin concentration. Pediatr Res 2007; 62:576-80. [PMID: 18049372 DOI: 10.1203/pdr.0b013e3181568c94] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Although it has been suggested that the unbound, free, (B(f)) rather than total (B(T)) bilirubin level correlates with cell toxicity, direct experimental evidence supporting this conclusion is limited. In addition, previous studies never included a direct measurement of B(f), using newer, accurate methods. To test "the free bilirubin hypothesis", in vitro cytotoxicity was assessed in four cell lines exposed to different B(f) concentrations obtained by varying B(T)/Albumin ratio, using serum albumins with different binding affinities, and/or displacing unconjugated bilirubin (UCB) from albumin with a sulphonamide. B(f) was assessed by the modified, minimally diluted peroxidase method. Cytotoxicity varied among cell lines but was invariably related to B(f) and not B(T). Light exposure decreased toxicity parallel to a decrease in B(f). In the absence of albumin, no cytotoxicity was found at a B(f) of 150 nM whereas in the presence of albumin a similar B(f) resulted in a 40% reduction of viability indicating the importance of total cellular uptake of UCB in eliciting toxic effect. In the presence of albumin-bound UCB, bilirubin-induced cytotoxicity in a given cell line is accurately predicted by B(f) irrespective of the source and concentration of albumin, or total bilirubin level.
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Sequeira D, Watchko JF, Daood MJ, O'Day TL, Mahmood B. Unconjugated bilirubin efflux by bovine brain microvascular endothelial cells in vitro. Pediatr Crit Care Med 2007; 8:570-5. [PMID: 17906594 DOI: 10.1097/01.pcc.0000288716.63685.1b] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES The passage of unconjugated bilirubin (UCB) across the blood-brain barrier into the central nervous system is a crucial first step in the development of kernicterus. The objective of the current study was to characterize the passage of UCB across primary bovine brain microvascular endothelial cell (BBMVEC) monolayers in vitro. DESIGN Experimental study. SETTING Research institute. SUBJECTS BBMVECs. INTERVENTIONS Tritiated UCB (H-UCB) transport at 60, 80, 100, 200, 300, and 400 nM concentrations was tested in both the apical to basolateral (A--> B) and basolateral to apical (B-->A) directions in BBMVEC monolayers in vitro with or without preincubation with pharmacologic active transport inhibitors cyclosporine A, indomethacin, or MK571. MEASUREMENTS AND MAIN RESULTS The rate of H-UCB transport in the B-->A direction was 6.2- to 7.3-fold higher than in the A-->B direction, suggesting active efflux of UCB. Cyclosporine A (5 microM), a model inhibitor of P-glycoprotein, enhanced A-->B while decreasing B-->A UCB transport, resulting in an overall decrease in BBMVEC UCB efflux of between 46% and 54%. Indomethacin (10 microM) and MK-571 (50 microM), respectively a substrate and potent inhibitor of multidrug resistance-associated protein-1, had no effect. CONCLUSIONS We conclude that 1) UCB is transported by BBMVEC monolayers in vitro in a net B-->A direction (i.e., active efflux); and 2) cyclosporine A partially inhibits such transport. We speculate that the blood-brain barrier limits the passage and central nervous system retention of UCB by active transport and that this may be accounted in part by P-glycoprotein.
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Affiliation(s)
- Deryk Sequeira
- Department of Pediatrics, University of Pittsburgh School of Medicine, Magee-Womens Research Institute, Pittsburgh, PA, USA
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Seubert JM, Darmon AJ, El-Kadi AOS, D'Souza SJA, Bend JR. Apoptosis in murine hepatoma hepa 1c1c7 wild-type, C12, and C4 cells mediated by bilirubin. Mol Pharmacol 2002; 62:257-64. [PMID: 12130676 DOI: 10.1124/mol.62.2.257] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Elevated serum and tissue bilirubin concentrations that occur in pathological conditions such as cholestasis, jaundice, and other liver diseases are known to stimulate cytotoxic responses. In preliminary studies, we noted that bilirubin seemed to cause apoptosis in murine hepatoma Hepa 1c1c7 wild-type (WT) cells. Consequently, we investigated apoptosis caused by bilirubin in WT, mutant C12 [aryl hydrocarbon receptor (AHR)-deficient], and C4 (AHR nuclear translocator-deficient) Hepa 1c1c7 cells. Three independent measures of apoptosis were used to quantify the effects of exogenous bilirubin (0, 1, 10, 25, 50, or 100 microM). Caspase-3 activity and cytochrome c release from mitochondria increased at 3 h post-treatment, before increased caspase-8 activity at 6 h, and nuclear condensation by 24 h after treatment with bilirubin. No differences in whole-cell lipid peroxidation were observed between the cell types; however, intracellular reactive oxygen species (ROS) production was greater in WT cells than C12 or C4 cells 3 h after bilirubin exposure. Pretreatment of cells for 1 h with 1 or 10 microM alpha-naphthoflavone, an AHR antagonist, before bilirubin exposure resulted in decreased caspase-3 activity at 6 h and nuclear condensation at 24 h in WT cells. These results indicate that bilirubin, a potential AHR ligand, causes apoptosis in murine Hepa 1c1c7 WT cells by a mechanism(s) partially involving the AHR, disruption of membrane integrity, and increased intracellular ROS production.
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Affiliation(s)
- John M Seubert
- Department of Pharmacology and Toxicology, University of Western Ontario, London, Canada
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Abstract
AIM To determine the effects of endotoxin and cytokines on the cytotoxic effects of bilirubin. METHODS A cell-culture model was developed to simulate the effect of an infection by adding endotoxin from E. coli (LPS) and pro-inflammatory cytokines (TNF-alpha, IL-Ialpha, IL-1beta, and IL-6) to the medium. The cytotoxic effects were measured by a modified MTT method. Four cell lines were tested; they were neuroblastoma, glioblastoma, liver, and endothelial cells. RESULTS Both endotoxin and pro-inflammatory cytokines were demonstrated to enhance bilirubin cytotoxicity on all the cell lines tested, as illustrated by endothelial cell from umbilical vein. Endotoxin and TNF-alpha also showed an additive effect. TNF-alpha concentrations at much lower than clinical sepsis levels have been shown to produce significant cytotoxic effects. CONCLUSION We speculate that in the jaundiced neonate, infection may increase the risk of tissue damage or kernicterus.
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Affiliation(s)
- C Y Yeung
- Department of Paediatrics, The University of Hong Kong, Queen Mary Hospital, Pokfulam Road, Hong Kong, China
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