Single bolus injection of bilirubin improves the clinical outcome in a mouse model of endotoxemia

Cardiovascular Research Center and Department of Pharmacology, University of Virginia, Charlottesville, Virginia, USA.
Shock (Impact Factor: 2.73). 12/2007; 28(5):582-8. DOI: 10.1097/shk.0b013e31804d41dd
Source: PubMed

ABSTRACT Increasing serum levels of biliverdin and bilirubin was shown to be beneficial in settings of inflammation. Bilirubin was shown to be protective in LPS-induced lung injury in rats; however, the exact mechanism remains elusive. Here, we investigated whether a single bolus injection of bilirubin would exert anti-inflammatory effects in a mouse model of endotoxemia. Mice were challenged with sublethal doses (2 mg/kg body weight) of LPS, and the effects of intravenously administered bilirubin (40 mg/kg body weight) were assessed. In contrast to control animals, bilirubin-treated animals fully recovered from endotoxin shock within 24 h. Bilirubin treatment improved the clinical score significantly at all time points assessed, attenuated weight loss, and improved LPS-induced anorexia. Furthermore, bilirubin treatment inhibited LPS-induced leukocyte-endothelial interactions and leukocyte accumulation in various tissues. Expression of inflammatory genes, including endothelial adhesion molecules, but also IL-1beta and TNF-alpha, was significantly reduced in bilirubin-treated animals. Moreover, bilirubin inhibited LPS-induced expression of inflammatory genes in isolated cultured aortic endothelial cells and in bone marrow-derived macrophages. These data show that single-dose administration of bilirubin attenuates tissue injury induced by endotoxin, and that bilirubin, in addition to its antioxidant effects, also exerts potent anti-inflammatory activity.

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    ABSTRACT: Sepsis is associated with abnormal host immune function in response to pathogen exposure, including endotoxin (lipopolysaccharide; LPS). Cytokines play crucial roles in the induction and resolution of inflammation in sepsis. Therefore, the primary aim of this study was to investigate the effects of endogenous tetrapyrroles, including biliverdin (BV) and unconjugated bilirubin (UCB) on LPS-induced cytokines in human blood. Biliverdin and UCB are by products of haem catabolism and have strong cytoprotective, antioxidant and anti-inflammatory effects. In the present study, whole human blood supplemented with BV and without was incubated in the presence or absence of LPS for 4 and 8 hours. Thereafter, whole blood was analysed for gene and protein expression of cytokines, including IL-1β, IL-6, TNF, IFN-γ, IL-1Ra and IL-8. Biliverdin (50 μM) significantly decreased the LPS-mediated gene expression of IL-1β, IL-6, IFN-γ, IL-1Ra and IL-8 (P<0.05). Furthermore, BV significantly decreased LPS-induced secretion of IL-1β and IL-8 (P<0.05). Serum samples from human subjects and, wild type and hyperbilirubinaemic Gunn rats were also used to assess the relationship between circulating bilirubin and cytokine expression/production. Significant positive correlations between baseline UCB concentrations in human blood and LPS-mediated gene expression of IL-1β (R=0.929), IFN-γ (R=0.809), IL-1Ra (R=0.786) and IL-8 (R=0.857) were observed in blood samples (all P<0.05). These data were supported by increased baseline IL-1β concentrations in hyperbilirubinaemic Gunn rats (P<0.05). Blood samples were also investigated for complement receptor-5 (C5aR) expression. Stimulation of blood with LPS decreased gene expression of C5aR (P<0.05). Treatment of blood with BV alone and in the presence of LPS tended to decrease C5aR expression (P=0.08). These data indicate that supplemented BV inhibits the ex vivo response of human blood to LPS. Surprisingly, however, baseline UCB was associated with heighted inflammatory response to LPS. This is the first study to explore the effects of BV in a preclinical human model of inflammation and suggests that BV could represent an anti-inflammatory target for the prevention of LPS mediated inflammation in vivo.
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    ABSTRACT: Nuclear factor erythroid derived 2-related factor-2 (Nrf2) is a master transcription regulator of antioxidant and cytoprotective proteins that mediate cellular defense against oxidative and inflammatory stresses. Disruption of cellular stress response by Nrf2 deficiency causes enhanced susceptibility to infection and related inflammatory diseases as a consequence of exacerbated immune-mediated hypersensitivity and autoimmunity. The cellular defense capacity potentiated by Nrf2 activation appears to balance the population of and of lymph node cells for proper innate immune responses. Nrf2 can negatively regulate the activation of pro-inflammatory signaling molecules such as p38 MAPK, NF-, and AP-1. Nrf2 subsequently functions to inhibit the production of pro-inflammatory mediators including cytokines, chemokines, cell adhesion molecules, matrix metalloproteinases, COX-2 and iNOS. Although not clearly elucidated, the antioxidative function of genes targeted by Nrf2 may cooperatively regulate the innate immune response and also repress the expression of pro-inflammatory mediators.
    12/2009; 25(4). DOI:10.5487/TR.2009.25.4.159
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